microsoft word 16-2597_s engineering, technology & applied science research vol. 9, no. 2, 2019, 3955-3958 3955 www.etasr.com subhani: mechanical performance of honeycomb sandwich structures using three-point bend test mechanical performance of honeycomb sandwich structures using three-point bend test tayyab subhani department of mechanical engineering, college of engineering, university of hail hail, saudi arabia ta.subhani@uoh.edu.sa abstract—in this study, honeycomb sandwich structures were prepared and tested. facesheets of sandwich structures were manufactured by carbon fiber epoxy matrix composites while nomex® honeycomb was used as core material. an epoxy-based adhesive film was used to bond the composite facesheets with honeycomb core. four different curing temperatures ranging from 100 o c to 130 o c were applied with curing times of 2h and 3h. three-point bend test was performed to investigate the mechanical performance of honeycomb sandwich structures and thus optimize the curing parameters. it was revealed that the combination of a temperature of 110 o c along with a curing time of 2h offered the optimum mechanical performance together with low damage in honeycomb core and facesheets. keywords-honeycomb sandwich; mechanical; three-point bend test; epoxy; carbon fiber i. introduction honeycomb sandwich structures are widely used for aerospace structural applications. a honeycomb sandwich structure comprises of two stiff and strong skins or facesheets joined together with a honeycomb core. such a structural configuration offers light weight with high stiffness. good fatigue strength and thermal insulation are additional attributes of honeycomb sandwich structures [1]. in sandwich structures, facesheets carry the bending stress applied to the structure while the honeycomb core bears the shear loads and increases the stiffness of the sandwich structure while holding the two facesheets. moreover, increase in the thickness of honeycomb core increases stiffness and flexural strength of sandwich structures. in addition to honeycomb, foam and wood are also used as core materials in sandwich structures. however, due to its stiffness, crushing strength and fatigue properties, the honeycomb core enjoys a special edge over other core structures [2]. honeycomb cores are made of polymeric, metallic and ceramic materials such as aluminum, carbon, fiberglass, alumina and kevlar. facesheets are made of steels, aluminum and composite materials. for the bonding of facesheets with the honeycomb core, adhesives, fasteners and adhesive films are used. the properties of adhesive materials play a vital role in the overall mechanical performance of honeycomb structures [3]. the adhesive material firmly attaches the facesheets to the honeycomb core in order to effectively transfer the load from one facesheet to another through the core [4]. therefore, good bonding between the facesheets and the honeycomb core defines the load-bearing capacity of a sandwich structure. upon the application of a bending load, shear stresses are developed at the interface, which is actually the adhesive joint between the core and the facesheet. the shear stress may debond the two components of the sandwich structure thus paving the way to a structural disaster. therefore, the adhesive joint formed at the interface by an adhesive material influences significantly the mechanical performance of a honeycomb sandwich structure [3]. evaluation of mechanical properties is the prime requisite before taking a sandwich structure into actual implementation [3]. three-point bend test is usually carried out to investigate the shear and flexural rigidities of sandwich structures. in particular, properties such as facing bending strength, core shear strength, core shear modulus and transverse shear rigidity can be obtained using the three-point bend test. in [4], numerical investigation of the three-point bend test was performed on sandwich honeycomb structures containing aluminum facesheets. numerical and experimental study on the bending behavior of honeycomb sandwich panel with ceramic facesheet is shown in [5, 6]. air-blast loading of sandwich structures is another way of mechanical characterization [7]. in addition to the mechanical performance evaluation, the failure mechanism of sandwich structures is also critical to assess the way in which the damage will result [8]. the absorption of crushing energy of sandwich structures has been evaluated during damage in [9]. the understanding of interfacial fracture in sandwich structures is yet another prime requirement [10]. as a result, a variety of tests have been devised to investigate the core-facesheet adhesion [1, 2]. in the current study, honeycomb structures were tested under three-point bend test to explore their mechanical properties after bonding the facesheets and the honeycomb core with an epoxy-based adhesive. facesheets were made of carbon fiber epoxy matrix composite while nomex® honeycomb was used as core. compression bonding method was used to cure the adhesive film using 4 different temperatures and 2 curing times. based upon the acquired data, the curing parameters of the adhesive films were optimized. corresponding author: tayyab subhani engineering, technology & applied science research vol. 9, no. 2, 2019, 3955-3958 3956 www.etasr.com subhani: mechanical performance of honeycomb sandwich structures using three-point bend test ii. experiment description the honeycomb sandwich structures were prepared by employing carbon fiber epoxy matrix composite facesheets of 1mm thickness, nomex® honeycomb core of 20mm thickness and 5.5mm cell size, and epoxy-based adhesive film. the adhesive film was procured from cnme international, china with the trade name of cnmehp-272d and 0.34-0.38mm thickness. the hexagonal phenolic impregnated nomex® honeycomb core was purchased from armicore composite company, china. the composite facesheets were prepared indigenously, for details see [11]. for the manufacturing of sandwich structures, the adhesive film was applied on the rough surface of the two composite facesheets and was bonded with the honeycomb core. the sandwich panel was gripped between the metallic plates and loaded under compression. in total, 8 sandwich panels were prepared for curing at 4 different temperatures of 100 o c, 110 o c, 120 o c and 130 o c and 2 curing times of 2h and 3h. the specimens cut from the 8 sandwich panels were tested under three-point bend test according to astm standard c393/c393m. rectangular shaped specimens with 203.2mm length, 76.2mm width and ~22mm thickness were used. four mechanical properties, namely (a) core ultimate shear stress, (b) facing bending stress, (c) core shear rigidity, and (d) core shear modulus were evaluated by the three-point bend test in order to evaluate the mechanical performance of honeycomb sandwich structures. iii. results and discussion the load-displacement curves are shown in figures 1 and 3, respectively. the values of the mechanical properties including facing bending strength, core shear strength, core shear modulus and transverse shear rigidity are shown in figures 2 and 4. a. two hour curing time figure 1 displays the load-displacement curves of the honeycomb structures cured from 100 o c to 130 o c for 2h under three-point bending load. increase in peak load values was observed when the curing temperature increased from 100 o c to 110 o c. this increase in peak load value resulted in enhancing the facing bending strength from 48.6±2.4mpa to 57.2±3.1mpa, core shear strength from 0.62±0.03mpa to 0.73±0.05mpa, core shear modulus from 37.0±5.3mpa to 39.1±4.1mpa and transvers shear rigidity from 60.1±3.5kn to 63.1±2.4kn respectively, as shown in figure 2. however, further increase in temperature, to 120 o c and 130 o c, lowered peak load values, 1.89kn and 1.80kn respectively, while simultaneously it lowered the mechanical properties: facing bending strength from 46.2±1.8mpa to 43.9±0.8mpa, core shear strength from 0.59±0.01mpa to 0.56±0.02mpa, core shear modulus from 23.3±2.1mpa to 19.4±2.7mpa and transverse shear rigidity from 38.5±1.4kn to 32.9±1.7kn respectively. the decrease in mechanical properties may be caused by the distortion in the fillet leading to unsymmetrical shape and porosity created because of the evaporation of volatile contents in the adhesive film [12, 13]. fig. 1. load-displacement curves of honeycomb sandwich structures cured at 100 o c, 110 o c, 120 o c and 130 o c for 2h. fig. 2. (a) facing bending strength, (b) core shear strength, (c) core shear modulus, and (d) transverse shear rigidity of honeycomb sandwich structures cured at 100 o c, 110 o c, 120 o c and 130 o c for 2h. engineering, technology & applied science research vol. 9, no. 2, 2019, 3955-3958 3957 www.etasr.com subhani: mechanical performance of honeycomb sandwich structures using three-point bend test b. three hour curing time three-point bend test results of honeycomb sandwich structures cured at 100 o c, 110 o c, 120 o c and 130 o c for 3h, shown in figures 3 and 4 followed the same trend with the honeycomb sandwich structures cured for 2h. peak load values were observed at 100 o c and 110 o c, respectively, thus producing facing bending strength of 48.8±2.3mpa and 54.7±3.5mpa, cores shear strength of 0.62±0.03mpa and 0.69±0.07mpa, core shear modulus of 33.2±4.3mpa and 38.1±5.6mpa and transverse shear rigidity of 56.2±2.6kn and 64.0±4.2kn respectively. further increase in curing temperature to 120 o c and 130 o c reduced peak load values and thus the mechanical properties of composite honeycomb sandwich panels. facing bending strength reduced from 51.0±2.6mpa to 33.2±1.1mpa, core shear strength from 0.65±0.04mpa to 0.42±0.01mpa, core shear modulus from 29.4±2.7mpa to 17.3±0.8mpa and transverse shear rigidity from 49.4±2.0kn to 29.8±1.1kn respectively, as shown in figure 4. fig. 3. load-displacement curves of honeycomb sandwich structures cured at 100 o c, 110 o c, 120 o c and 130 o c for 3h. c. cross-sectional photographs the cross-sectional views of sandwich structures, which showed maximum and minimum mechanical properties after three-point bend test, are shown in figures 5 and 6. the sandwich structure cured at 130 o c for 3h (figure 5(b)) showed minimum mechanical properties, which may be caused by to the presence of unsymmetrical fillets or poor interfacial adhesion [11]. the cross-sectional magnified view of this specimen after the three-point bend test is shown in figure 6(b), which shows local indentation as well as shear deformation failure of the honeycomb core spread over a vast area. in contrast, the sandwich structure processed at 110 o c for 2h offered maximum mechanical properties (figure 5(a)), with the magnified view of this specimen (figure 6(a)) indicating a localized damage zone. these two sandwich structures were intentionally selected because one of these showed maximum values while the other displayed minimum values. the crosssectional photographs are presented to reveal the effect of variations of curing parameters of adhesive films upon the failure modes of honeycomb cores. the upper facesheet failures are clearly visible in the middle of the sandwich structures, which are due to the loading span. the upper facesheets in the sandwich structures were under compressive load. upon reaching the peak load, the load drops continuously along with the crushing of the honeycomb core (figures 1 and 3). the process continues until the failure of the upper facesheet. the load decreases due to the fact that the load exceeds the compression strength of the structures, which is a combination of honeycomb core strength, adhesive film strength and the stiffness of the facesheets [12]. fig. 4. (a) facing bending strength, (b) core shear strength, (c) core shear modulus, and (d) transverse shear rigidity of honeycomb sandwich structures cured at 100 o c, 110 o c, 120 o c and 130 o c for 3h. the local indentations on the upper facesheets are also clearly visible, which may be due to localized core compression (figure 5). as discussed above, the magnified images of the same specimens (figure 6) show that the structure with maximum mechanical properties exhibited a localized damage in the honeycomb core while the structure engineering, technology & applied science research vol. 9, no. 2, 2019, 3955-3958 3958 www.etasr.com subhani: mechanical performance of honeycomb sandwich structures using three-point bend test with minimum mechanical properties exhibited damage in honeycomb core at a large scale. this indicates that the good quality bonding of the facesheet with honeycomb core promotes the mechanical properties despite the fact that the compressive strength of honeycomb core shows the same value. fig. 5. cross-sectional views of sandwich structures cured at (a) 110 o c for 2h and (b) 130 o c for 3h. fig. 6. cross-sectional magnified views of sandwich structures cured at (a) 110 o c for 2h and (b) 130 o c for 3h. d. effect of curing temperature and time experimental data and photographic observations indicate that both curing temperature and curing time of adhesive film affect the mechanical performance of honeycomb sandwich structures. optimized curing parameters for composite honeycomb structures were found to be 110 o c for 2h, at which the sandwich panels showed maximum mechanical properties which may be caused by the formation of symmetrical fillets [13]. at the specified curing parameters, the honeycomb structures showed maximum peak loads prior to the deformation of the core and failure of upper facesheet. the related mechanical properties of the sandwich structures at these parameters were also higher than the other structures’. at optimized curing parameters, the adhesive film forms a suitable fillet between the honeycomb core and the facesheets, which in turn transfers the load effectively from one facesheet to another through the core. it should be noted that increase in temperature helps the flow of adhesive film toward the walls of the core and thus making the film less viscous. however, at the same time the increased temperature promotes the curing of the adhesive film. as a result, the mechanical properties of honeycomb sandwich structures increased by increase in the temperature from 100 o c to 110 o c after preparing a symmetrical fillet while further rise in temperature resulted in premature curing of the film without the formation of a uniform fillet. iv. conclusion honeycomb sandwich structures were prepared by using carbon fiber epoxy matrix composite facesheets, nomex® honeycomb core and epoxy-based adhesive film. compression technique was utilized to prepare sandwich structures by optimizing the curing parameters of the adhesive film. temperature of 110 o c and curing time of 2h exhibited optimum mechanical performance, i.e. maximum load bearing capability and associated mechanical properties. the ability of the flow of adhesive film and the formation of adequate adhesive fillets are the possible reasons behind the increased mechanical properties at optimized parameters of adhesive film. localized damage area in optimized honeycomb structure was also found to be lower than the one observed in structures showing poor mechanical performance. references [1] j. avery, b. v. sankar, “compressive failure of sandwich beams with debonded face-sheets”, journal of composite materials, vol. 34, no. 14, pp. 1176-1199, 2000 [2] w. j. cantwell, p. davies, “a test technique for assessing core-skin adhesion in composite sandwich structures”, journal of materials science letters, vol. 13, no. 3, pp. 203-205, 1994 [3] a. johnson, g. d. sims, “mechanical properties and design of sandwich materials”, composites, vol. 17, no. 4, pp. 321-328, 1986 [4] m. giglio, a. gilioli, a. manes, “numerical investigation of a three point bending test on sandwich panels with aluminum skins and nomex ™ honeycomb core”, computational materials science, vol. 56, pp. 6978, 2012 [5] z. wang, z. li, w. xiong “numerical study on three-point bending behavior of honeycomb sandwich with ceramic tile”, composites part b: engineering, vol. 167, pp. 63-70, 2019 [6] z. wang, z. li, w. xiong “experimental investigation on bending behavior of honeycomb sandwich panel with ceramic tile face-sheet”, composites part b: engineering, vol. 164, pp. 280-286, 2019 [7] g. s. langdon, c. j. von klemperer, b. k, rowland, g. n. nurick, “the response of sandwich structures with composite face sheets and polymer foam cores to air-blast loading: preliminary experiments”, engineering structures, vol. 36, pp. 104-112, 2012 [8] h. fan, q. zhou, w. yang, z. jingjing, “an experimental study on the failure mechanims of woven textile sandwich panels under quasi-static loading”, composites part b: engineering, vol. 41, no. 8, pp. 686-692, 2010 [9] o. velecela, m. s. found, c. soutis, “crushing energy absorption of gfrp sandwich panels and corresponding monolithic laminates”, composites part a: applied science and manufcaturing, vol. 38, no. 4, pp. 1149-1158, 2007 [10] w. j. cantwell, r. scudamore, j. ratcliffe, p. davies, “interfacial fracture in sandwich laminates”, composites science and technology, vol. 59, no.14, pp. 2079-2085, 1999 [11] u. farooq, m. s. ahmad, s. a. rakha, n. ali, a. a. khurram, t. subhani, “interfacial mechanical performance of composite honeycomb sandwich panels for aerospace applications”, arabian journal for science and engineering, vol. 42, no. 5, pp. 1775-1782, 2017 [12] r. okada, m. t. kortschot, “the role of the resin fillet in the delimination of honeycomb sandwich structures”, composites science and technology, vol. 62, no. 14, pp. 1811-1819, 2002 [13] j. rion, y. leterrier, j. a. e. manson, “prediction of the adhesive fillet size for skin to honeycomb core bonding in ultra-light sandwich structures”, composites part a: applied science and manufacturing, vol. 39, no. 9, pp. 1547-1555, 2008 microsoft word 21-25-2982_s engineering, technology & applied science research vol. 9, no. 5, 2019, 4689-4694 4689 www.etasr.com elgharbi et al.: intelligent control of a photovoltaic pumping system intelligent control of a photovoltaic pumping system abdessamia elgharbi physics department, university of tunis el manar, tunis, tunisia abdogharbi@yahoo.fr dhafer mezghani physics department, university of tunis el manar, tunis, tunisia dhafer.mezghanni@gmail.com abdelkader mami physics department, university of tunis el manar, tunis, tunisia abdelkader.mami@fst.utm.tn abstract—this paper presents the application of the adaptive neuro fuzzy inference system (anfis) to track the maximum power of a photovoltaic generator that feeds a motor-pump group unit through a pulse width modulation (pwm) inverter powered by a single ended primary inductance converter (sepic) installed in the laboratory. the anfis control is trained in different temperatures and irradiances and the maximum power point tracking system varies automatically the duty cycle of the sepic converter. the performance of the mppt controller is tested in simulations in matlab/simulink. keywords-pv pumping system; mppt; sepic; anfis i. introduction in photovoltaic (pv) systems, sunlight is converted into dc electricity. from the pv module we get low voltage, so we have to increase this voltage using an sepic converter. the mppt of the pv system using sepic converter is controlled by intelligent controllers, in our case the developed adaptive neuro fuzzy inference system (anfis) model. this paper addresses the above problem and presents the anfis method used as the mppt algorithm from which are many presented in previous papers [1]. many papers focused on the comparison of the anfis with some other artificial intelligence (ai) methods such as neural networks (nns), fuzzy logic (fl) and proved that anfis is the most suitable for use in uncertain systems [2] and without a doubt presented anfis as the most suitable algorithm for mpp tracking. ii. photovoltaic pumping system photovoltaic conversion is produced by exposing the solar cell to sunlight. the received energy causes disordered movement of the electrons within the material. the current collection is done by the metal contacts (electrodes). if these electrodes are connected to an external circuit, a direct current flows. in a pv generator a number of solar cells are assembled to form a pv module. in our case we combined four kaneka gsa 60 (60watt) pv panels connected in series delivering enough power for the system, a single ended primary inductance converter (sepic) and a motor pump ebara as shown in figure 1. the induction motor pump is supplied from the pv generator whose volt/ampere characteristics depend nonlinearly on solar insulation, temperature variations and on the current drawn by the motor-pump [3]. the pv generator behavior is equivalent to a current source shunted by a junction diode, if we neglect the physical phenomena of pv cell such as contact resistance, current lost by photocell sides and the age of cells [4-6]. the pv panel operation can be described using a complete physical mathematical model as shown in figure 2 and described by (1)-(3) [7-10]. fig. 1. synoptic diagram of the pumping structure fig. 2. electrical scheme of pv module i�� � i�� � �� ��� ��������������� ����� � �v�� � r i���r � (1) i�� � !�""����"#���$%&'(" ("$%& (2) t � #*+,��-.'(" /.. � t0 (3) where ec is the solar illumination (w/m 2 ), ecref is the reference illumination (1000w/m 2 ), ta is the ambient temperature (°c), tref is the reference ambient temperature (25°c), t is the surface temperature of the pv generator (°c or °k), icc is the total short-circuit current for the state reference (a), kisc is the short-circuit -temperature current coefficient (0.0017a/°c), is is the opposite total current of the pv generator (a), k is the boltzmann constant (1.38.10 -23 j/°k), q is the electron charge (1.6.10 -19 c) and noct the nominal operating temperature 45°. iii. sepic the sepic exchanges energy between the capacitors and inductors in order to convert the voltage from input to the output. the amount of energy exchanged is controlled by a switch, which is typically a transistor such as a mosfet. the corresponding author: abdessamia elgharbi engineering, technology & applied science research vol. 9, no. 5, 2019, 4689-4694 4690 www.etasr.com elgharbi et al.: intelligent control of a photovoltaic pumping system output voltage depends on the duty cycle applied to the switch [3]. it can be higher or lower than the input voltage. fig. 3. sepic converter topology if we apply the kirchhoff's voltage law in continuous conduction mode, the duty cycle will be given by [15]: d � #�234 � �6 ' #�234 ���7 � �6 ' (4) where vin is the input voltage, vout is the output voltage and vd is the threshold voltage of the diode. for the desired output, the variation of the duty cycle will depend on the input voltage. the parameters of the sepic converter used in this work were developed in a previous study [12]. table i. sepic parameters parameter value input voltage, vin 300v output voltage, vout 310v outut current, io 1.19a switching frequency, fsw 5khz duty cycle, d 0.508 l1 60mh l2 60mh cs 100µf cin 2000µf cout 2000µf inductor selection δi9 0.491a iv. mppt control using anfis algorithm in this part, a robust control of mppt using anfis will be presented which have been developed in matlab/simulink. it consists of the pv generator with mppt control, an sepic converter, a voltage source inverter controlled by pulse width modulation strategy [13] and a motor pump unit as shown in the simulink model in figure 4. fig. 4. simulink model of the proposed pv pumping system. the explanation for creating and the levels comprising the anfis cognitive method are described in [12, 13]. in this proposed method the photovoltaic system uses a mppt control using anfis algorithm which automatically varies the duty cycle of the sepic in order to generate the required voltage to extract maximum power. the data input for the anfis is irradiance and temperature and the output is the optimal voltage of the pv generator vpopt. two voltages are compared and the error is given to a proportional integral (pi) controller, to generate control signals. the control signal generated by the pi controller is given to the pwm generator. the generated pwm signal that controls the duty cycle of the sepic converter in order to adjust the operating point of the pv module is shown in figure 5. fig. 5. the generated pwm signal of the sepic engineering, technology & applied science research vol. 9, no. 5, 2019, 4689-4694 4691 www.etasr.com elgharbi et al.: intelligent control of a photovoltaic pumping system by training the anfis with a sufficient number of epochs, and adjusting the values of membership function, it generates a set of fuzzy rules in order to produce the appropriate output for different input values. the simulink model of pv module generates the training data set for anfis by varying the operating temperature from 25°c to 45°c in steps of 10°c and the solar irradiance level from 200w/m 2 to 1000w/m 2 in steps of 100w/m 2 . for each pair of operating temperature and solar irradiance, the optimal voltage of pv module is recorded. thus, in total 45 training data sets and 100 epochs were used to train the anfis model. anfis constructs a fuzzy inference system (fis) by using input/output data sets and the membership function parameters of fis are tuned using the hybrid optimization method which is a combination of least-squares and back propagation algorithm. anfis is a takagi sugeno network within the adaptive systems facilitating learning and training. figure 7 presents the anfis structure developed by the matlab code. anfis controller works according to the input values of temperature (°c) and sun illumination (w/m 2 ) based on the trained .fis file. as we can see in figure7, this is a five-layer network with two inputs and one output. each input parameter has five membership functions which are learned by the anfis method. according to input-output mapping of data sets, twenty-five fuzzy rules are derived. a 3-dimentional plot between temperature, irradiance and optimal voltage presenting the surface generated by the anfis is shown in figure 8. fig. 6. neuro fuzzy designer fig. 7. anfis controller structure the anfis surface depicts that the maximum available power point of solar pv module increases with increase in irradiance and moderate temperature which verifies the nonlinear behavior of the pv module. having obtained the right value vopt output of the anfis, the error between vopt and vpv will be entered into the pi block to generate the control signal of the pwm block and thus the pwm duty cycle of the sepic converter is created. fig. 8. surface between the inputs and the output v. simulation results the results were obtained using matlab/simulink to perform simulation. figures 9-10 present the p-v and i-v characteristics with different values of irradiance and temperature. fig. 9. p-v characteristics in different temperatures fig. 10. i-v characteristics in different temperatures engineering, technology & applied science research vol. 9, no. 5, 2019, 4689-4694 4692 www.etasr.com elgharbi et al.: intelligent control of a photovoltaic pumping system fig. 11. panel voltage (vp) characteristic for different values of irradiance fig. 12. panel voltage (vp) characteristic for different values of temperature note that the voltage vp of the pv generator shown in figures 11-12 follows a linear curve over time, and any increase in illumination is accompanied by an increase in the optimal voltage vpopt.figures 13-14 present the output optimal voltage (vpopt) of the anfis maximum power point tracking at 25°c for different illumination values. fig. 13. vpopt of the anfis maximum power point tracking in 600w/m 2 in figures 15-16 we see the vpopt of the anfis maximum power point tracking at 1000w/m 2 for different temperature values. a fast continuation of the evolution of the pv voltage is observed, as well as for current and electrical power with respect to their optimal values related to the variation of climatic conditions. fig. 14. vpopt of the anfis maximum power point tracking in 800w/m 2 fig. 15. vpopt of the anfis maximum power point tracking in 25°c fig. 16. vpopt of the anfis maximum power point tracking in 45°c the application of the sepic converter allows the generator to follow its mppt and to provide the required operation voltage of the voltage source inverter for maximum efficiency. the output voltage of the anfis controller engineering, technology & applied science research vol. 9, no. 5, 2019, 4689-4694 4693 www.etasr.com elgharbi et al.: intelligent control of a photovoltaic pumping system produces very high efficiency and stability for different irradiance and temperature scenarios. the results in figures 1719 illustrate the output voltage of the sepic for 1000w/m 2 of illumination for different values of temperature. fig. 17. output voltage (vout) of the sepic converter in 45°c fig. 18. vout of the sepic in 30°c fig. 19. vout of the sepic in 20°c the time evolution of the composed voltages in the output voltage inverter is presented in figure 20, the average model of the wave generated by the pwm voltage inverter subsequently allows obtaining a constant motor torque. the simulation speed of motor-pump and the water flow at 45°c for different illumination levels (600, 800, 1000w/m 2 ) is shown consecutively in figures 21 and 22. we note that using the anfis command, the speed of rotation of the motor-pump set has increased with the illumination to reach 2834rpm, which affects the water flow, which in turn evolved from 27.45l/min to 34l/min. by examining the temporal evolutions of the voltage of the photovoltaic panel vp and the speed of rotation of the motor pump shaft, we observe that in steady state these variables are constant over time for varying input parameters. fig. 20. output phase voltage (vs1) of the dc-ac inverter fig. 21. speed of the motor-pump for different illuminations fig. 22. time variation of the water flow (l/min) engineering, technology & applied science research vol. 9, no. 5, 2019, 4689-4694 4694 www.etasr.com elgharbi et al.: intelligent control of a photovoltaic pumping system in figures 23-24 we present the electromagnetic couple (cem) in temperature of 45°c and different values of illumination which varies from 600w/m 2 to 1000w/m 2 . fig. 23. the electromagnetic couple (cem) in 800w/m 2 fig. 24. the cem in 1000w/m 2 fig. 25. the statoric currents of the motor-pump vi. conclusion and outlook based on the simulation results we conclude that the predefined control objectives were achieved. the maximum power point tracking control of the pv pumping system using anfis based sepic was presented in this paper. for each considered illumination and temperature the optimal voltage was reached using anfis maximum power point tracking method. the robustness of this intelligent control system was tested in load changes, and the influence of fluctuating solar radiation on the dynamics was investigated. as future research, it is possible to implement an artificial intelligence technique to control the hybrid sources (photovoltaic and wind). references [1] s. selvan, p. nair, u. umayal, “a review on photo voltaic mppt algorithms”, international journal of electrical and comuter engineering, vol. 6, no. 2, pp. 567-582, 2016 [2] f. d. murdianto, o. penangsang, a. priyadi, “modeling and simulation of mppt-bidirectional using adaptive neuro fuzzy inference system (anfis) in distributed energy generation system”, 2015 international seminar 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(in french) [6] y. oueslati, study of performance of a photovoltaic generator coupled to the network draft, msc thesis, high school of sciences and techniques of tunis, 2007 (in french) [7] a. nouaiti, a. saad, a. mesbahi, m. khalfallah, m. reddak, “design and test of a new three-phase multilevel inverter for pv system applications”, engineering technology & applied science research, vol. 9, no. 1, pp. 3846-3851, 2019 [8] a. s. saidi, m. ben slimene, m. a. khlifi, “transient stability analysis of photovoltaic system with experimental shading effects”, engineering technology & applied science research, vol. 8, no. 6, pp. 3592-3597, 2018 [9] s. javadpoor, d. nazarpour, “modeling of pv-fc-hydrogen hybrid power generation system”, engineering technology & applied science research, vol. 7, no. 2, pp. 1455-1457, 2017 [10] z. r. labidi, h. schulte, a. mami, “a systematic controller design for a photovoltaic generator with boost converter using integral state feedback control”, engineering technology & applied science research, vol. 9, no. 2, pp. 4030-4036, 2019 [11] d. zhang, designing a sepic converter, application report 1484, texas instruments, 2013 [12] h. othmani, h. chaouali, d. mezghani, a. mami, “design and building of sepie dc-dc converter devoted to kaneka gsa-60 pv panels”, 7th international conference on modelling, identification and control, monastir, tunisia, may 8-10, 2015 [13] d. mezghani, h. othmani, a. mami, “bond graph modeling and robust control of a photovoltaic generator that powered an induction motor pump via sepic converter”, electrical energy systems, vol. 29, no. 3, article id e2746, 2019 [14] a. arora, p. gaur, “comparison of ann and anfis based mppt controller for grid connected pv systems”, annual ieee india conference, new delhi, india, december 17-20, 2015 [15] f. bendary, e. m. elsaied, w. a. mohamed, z. e. afifi, “geneticanfis hybrid algorithm for optimal maximum power point tracking of pv systems”, 17th international middle east power systems conference, mansoura, egypt, december 15-17, 2015 microsoft word 33-3036_s_etasr_v9_n5_pp4755-4758 engineering, technology & applied science research vol. 9, no. 5, 2019, 4755-4758 4755 www.etasr.com adil et al.: performance analysis of duplicate record detection techniques performance analysis of duplicate record detection techniques syed hasan adil department of computer science, iqra university, karachi, pakistan hasan.adil@iqra.edu.pk syed saad azhar ali department of electrical and electronic engineering, universiti teknologi petronas, seri iskandar, malaysia saad.azhar@utp.edu.my mansoor ebrahim department of computer science, iqra university, karachi, pakistan mebrahim@iqra.edu.pk kamran raza department of computer science, iqra university, karachi, pakistan kraza@iqra.edu.pk abstract—in this paper, a comprehensive performance analysis of duplicate data detection techniques for relational databases has been performed. the research focuses on traditional sql based and modern bloom filter techniques to find and eliminate records which already exist in the database while performing bulk insertion operation (i.e. bulk insertion involved in the loading phase of the extract, transform, and load (etl) process and data synchronization in multisite database synchronization). the comprehensive performance analysis was performed on several data sizes using sql, bloom filter, and parallel bloom filter. the results show that the parallel bloom filter is highly suitable for duplicate detection in the database. keywords-duplicate detection; bloom filter; sql; database i. introduction duplicate record detection [1, 2] is a process of identifying pairs of records that belong to the same entity in one or more databases. despite the development of many indexing techniques like isam, b-tree, bitmap, and hash indexing, still the process of matching two records that belong to the same entity requires time which is proportional to the number of existing records. therefore, an alternative technique is required to perform duplicate record detection. duplicate data detection has very important applications in many critical areas including databases, distributed databases, and data warehouses. data synchronization is a task demanded in a centralized database in case of standby after a database failure, or in a distributed database when we have to synchronize multiple remotely distributed database instances, or even in the load part of the extraction, transform, and load (etl) process where new data have to be loaded into the database in a continuous process. data streams like video, audio, etc. are some of the sources of big data which we want to process in real-time. in-stream processing, duplicate data detection is one of the most important tasks but at the same time it is very challenging due to the amount of data that continuously arrive at high speed. we can deal with these challenging requirements through a more robust technique like bloom filters which have the potential to perform better than the traditional duplicate detection techniques used in relational databases. therefore, in this paper, we will deeply investigate the application of bloom filters in order to identify duplicate records in databases, distributed databases, and data warehouses. the main objective of the paper is to implement in sql, bloom filter, and parallel bloom filter duplication detection techniques and to decide which one is the most appropriate for duplication detection. ii. related work bloom filter [3] is a probabilistic data structure developed in 1970. bloom filters are primarily based on hash functions. bloom filters are a space-efficient data structure based on the computation of several hash functions. a bloom filter has zero probability of false negative, but it can have more than zero probability of false positive (though it is possible to minimize the false-positive probability to zero depending on parameter selection). false-positive means that the filter may identify a new entry as already existing, even though this is not true. in addition to highly space-efficient, operations like insert and search are very fast in bloom filters. deletion is generally not allowed in the bloom filters due to the additional required amount of work. while deciding about the bloom filter, one must consider a tradeoff between the space and false positive. so, if space is more important, then the bloom filter is an ideal choice (with a very little chance of false-positive). however, if even a little chance of false positives cannot be tolerated, then, in that case, one cannot use the bloom filter. many different variants of the original bloom filters have been proposed which include but are not limited to counting bloom filter [4], d-left counting bloom filter [5], compressed bloom filter [6], bloomier filter [7], space-code bloom filter [8], dynamic bloom corresponding author: syed hasan adil engineering, technology & applied science research vol. 9, no. 5, 2019, 4755-4758 4756 www.etasr.com adil et al.: performance analysis of duplicate record detection techniques filter [9], etc. the applications of bloom filters [10, 11] include but are not limited to spell checking, collaboration in p2p networks, resource and packet routing, cache optimization, url shortening, video recommendation, string matching, spam filtering, dos and ddos detection, anomaly detection, etc. in this research, we applied sql, bloom filter, and parallel bloom filter to perform duplicate detection while performing bulk insertion operation in database, distributed database, and data warehouse using different numbers of tuples (i.e. from thousand to one million tuples in the tables as well as for the bulk operation) in the table. iii. proposed methodology the discussion in the previous section acknowledged the importance of duplication detection in databases, distributed databases, and data warehouses while importing bulk data. duplication detection in large databases is a very computational hungry task because each inserting record needs to be compared with all the exiting records in the database. it is important to note that we cannot perform a comparison based on primary keys because data are coming from various sources. in this research work, we have implemented three different approaches (i.e. sql, bloom filter, and parallel bloom filter) to compare their performance on duplicate detection using different number of records (i.e. existing records in the table/new records to insert in the table ratio equal to 1000/1000, 10000/10000, 100000/100000, and 1000000/1000000). the overall process flow of each approach is described in figure 3 for sql based approach, figure 4 for bloom filter, and figure 5 for the parallel bloom filter. the table used to perform duplicate detection is shown in figure 1, while the script used to generate data is shown in figure 2. the different steps of each approach are described below: create table students ( stud_id int identity primary key, stud_name nvarchar(25), stud_address nvarchar(100), stud_country nvarchar(25) ) fig. 1. schema of the table used for analysis declare @id int declare @totalrecords int set @id = 1 set @totalrecords = 1000 while @id <= @totalrecords begin insert into students values ('student ' + cast(floor(rand() * 100) as nvarchar(25)), 'address ' + cast(floor(rand() * 100) as nvarchar(100)), 'country ' + cast(floor(rand() * 100) as nvarchar(25))) set @id = @id + 1 end fig. 2. script used to generate random data fig. 3. the workflow of duplication detection using sql based approach fig. 4. the workflow of duplication detection using bloom filter-based approach engineering, technology & applied science research vol. 9, no. 5, 2019, 4755-4758 4757 www.etasr.com adil et al.: performance analysis of duplicate record detection techniques fig. 5. the workflow of duplication detection using parallel bloom filter-based approach a. sql based approach the different steps involved in finding duplicate records using sql based approach are described below: • step 1: in this step, data from the import file are loaded by the application. • step 2: in this step, the next record is fetched from the file. if a record exists, then move to step 3 otherwise end the process. • step 3: in this step, all columns of the record are concatenated without key column. • step 4: in this step the record (i.e. concatenated columns) has been matched with all existing records (i.e. each record with concatenated columns) in the table for a duplicate check using the where clause in the select statement. figure 6 shows the concatenated column query. • step 5: in this step, if the record does not exist, then insert it into the actual table. otherwise, insert into the duplicate database. go back to step 2. select * from students where concat(stud_name, stud_address, stud_country) = ‘name,address,country’ fig. 6. the select statement b. bloom filter-based approach the steps involved in finding duplicate records using the bloom filter-based approach are described below: • steps 1-3, 5 are the same as in the sql based approach. • step 4: in this step the records (i.e. concatenated columns) are matched with all existing records (i.e. each record with concatenated columns) in the bloom filter without involving the source table in the search process. the bloom filter must be updated for each record inserted into the source table. so, the bloom filter always reflects the current state of the table in the database. c. parallel bloom filter-based approach the steps involved in finding duplicate records using parallel bloom filter-based approach are described below: • steps 1-3, 5 are the same as in the sql and bloom filterbased approaches. step 4: this step is like step 4 of bloom filter, but the only difference is that the records (i.e. concatenated columns) are matched in parallel with all existing records (i.e. each record with concatenated columns) in the bloom filter. this helps in utilizing multiple cores of the host machine and reduces the time required to match all the records. iv. results and discussion the workflow of the three approaches used in this paper is presented in figures 3-5. all three approaches were used to detect duplicates in four different cases. in case i, the table contains 1000 records and the bulk insert file also contains 1000 records (950 unique and 50 duplicate records). in case ii, the table contains 10000 records and the bulk insert file also contains 10000 records (9800 unique and 200 duplicate records). in case iii, the table contains 100000 records and the bulk insert also contains 100000 records (95000 unique and 5000 duplicate records). in case iv, the table contains 1000000 records and the bulk insert file also contains 1000000 records (850000 unique and 150000 duplicate records). the obtained results (i.e. process time, and time) after the execution of all combination of analysis are presented in table i. table i. experimental results for duplication detection number of records technique time (h:min:s.ms) time (ms) existing: 1000 new: 1000 unique new: 950 duplicate new: 50 bf 00:00:00.010 10 parallel bf 00:00:00.010 10 query 00:00:09.320 9320 existing: 10000 new: 10000 unique new: 9800 duplicate new: 200 bf 00:00:00.050 50 parallel bf 00:00:00.030 30 query 00:02:26.880 146880 existing: 100000 new: 100000 unique new: 95000 duplicate new: 5000 bf 00:00:00.450 450 parallel bf 00:00:00.210 210 query 01:14:43.170 4483170 existing: 1000000 new: 1000000 unique new: 850000 duplicate new: 150000 bf 00:00:04.850 4850 parallel bf 00:00:01.930 1930 query 14:01:23.190 50483190 bf: bloom filter engineering, technology & applied science research vol. 9, no. 5, 2019, 4755-4758 4758 www.etasr.com adil et al.: performance analysis of duplicate record detection techniques figure 7 compares visually the performance of sql, bloom filter, and parallel bloom filter approaches. the graph in figure 7 is plotted using log10 of time in ms instead of time in ms and the number of records to process (the reason this is the rapidly growing difference between the process execution time of sql and the other approaches with increase in the number of rows to compare) between the processing time of sql and bloom filter/parallel bloom filter approach. figure 8 compares the performance of bloom-filter and parallel bloom-filter. tabular and visual analyses clearly show the high suitability of parallel bloom filter for duplicate detection. it becomes the only viable solution when the number of rows in the table or the rows that need to insert becomes very large. fig. 7. execution time for duplicate detection comparison fig. 8. execution time for duplicate detection comparison v. conclusion this study presented a comprehensive performance analysis of three database duplicate detection techniques. performance analysis was conducted using different numbers of existing records in the database with bulk data insertion of different sizes. the relative time difference between sql and bloom filter-based for duplicate detection and insertion rapidly increases with the increase in the record number. the relative time difference between the bloom filter and the parallel bloom filter also substantially increases with the increase of records, although not that rapidly. the research concludes that parallel bloom filter is the most scalable and the optimum solution for duplicate detection in databases, distributed databases, data warehouses, and in general for any application which requires duplicate detection. due to the advent of modern highly parallel computing architecture, it is highly advisable to implement a parallel version of the algorithm which can scale on multicore and multiple processors to efficiently utilize the aggregate computing power. references [1] a. k. elmagarmid, p. g. ipeirotis, v. s. verykios, “duplicate record detection: a survey”, ieee transactions on knowledge and data engineering, vol. 19, no. 1, pp. 1-16, 2007 [2] o. h. akel, a comparative study of duplicate record detection techniques, msc thesis, middle east university, 2012 [3] b. h. bloom, “space/time trade-offs in hash coding with allowable errors”, communications of the acm, vol. 13, no. 7, pp. 422-426, 1970 [4] l. fan, p. cao, j. almeida, a. z. broder, “summary cache: a scalable wide-area web cache sharing protocol”, ieee/acm transactions on networking, vol. 8, no. 3, pp. 281-293, 2000 [5] f. bonomi, m. mitzenmacher, r. panigrahy, s. singh, g. varghese, “an improved construction for counting bloom filters”, in: european symposium on algorithms, springer, pp. 684-695, 2006 [6] m. mitzenmacher, “compressed bloom filters”, ieee/acm transactions on networking, vol. 10, no. 5, pp. 604-612, 2002 [7] b. chazelle, j. kilian, r. rubinfeld, a. tal, “the bloomier filter: an efficient data structure for static support lookup tables”, fifteenth annual acm-siam symposium on discrete algorithms, new orleans, usa, january 11-14, 2004 [8] a. kumar, j. xu, j. wang, “space-code bloom filter for efficient perflow traffic measurement”, ieee journal on selected areas in communications, vol. 24, no. 12, pp. 2327-2339, 2006 [9] d. guo, j. wu, h. chen, x. luo, “theory and network applications of dynamic bloom filters”, 25th ieee international conference on computer communications, barcelona, spain, april, 23-29, 2006 [10] s. geravand, m. ahmadi, “bloom filter applications in network security: a state-of-the-art survey”, computer networks, vol. 57, no. 18, pp. 4047-4064, 2013 [11] y. emami, r. javidan, “an energy-efficient data transmission scheme in underwater wireless sensor networks”, engineering, technology & applied science research, vol. 6, no. 2, pp. 931-936, 2016 execution time execution time microsoft word 11-3502_s_etasr_v10_n3_pp5643-5647 engineering, technology & applied science research vol. 10, no. 3, 2020, 5643-5647 5643 www.etasr.com masmoum & alama: use of tying devices to mitigate pounding of adjacent building blocks tying devices to mitigate pounding of adjacent building blocks mohammed s. masmoum civil engineering department king abdulaziz university jeddah, saudi arabia ms.masmoum@gmail.com mohammed-sohaib a. alama civil engineering department king abdulaziz university jeddah, saudi arabia sohaib.alama@hotmail.com abstract—adjacent building blocks separated by thermal expansion joints are vulnerable to pounding during earthquakes. the specified saudi building code minimum separation may be very large and does not necessarily eliminate pounding forces. this research discusses the feasibility of tying the adjacent building blocks with simple devices to mitigate structural pounding when separated by thermal joints. six and twelve-story moment resistance frames of intermediate ductility were designed for seismic loads of moderate risk. the seismic response was studied for frames with variable separation distances in three cases related to thermal joint, code minimum separation, required separation to eliminate pounding force, and in a fourth case in which the tying device was used along with thermal separation. a linear elastic model was used to model the assigned gap links between the adjacent building blocks. the tying device was modeled with a tension-only hook element. four normalized earthquake records were used with inelastic-time history analysis to assess the seismic response of the adjacent building blocks. the proposed tying devices reduced successfully the pounding forces by 40% to 60% for adjacent building blocks with installed thermal separations. building damage as observed from damage index and the hysteretic response was not influenced by the pounding force, indicating that the tying may be used on existing buildings with thermal separation as a partial mitigation technique to reduce the pounding hazard in such cases. further improvement on the tying device will increase the mitigation of the pounding hazard. keywords-pounding; expansion joint; minimum separation; tying devices i. introduction saudi arabian cities exhibited a major development in the recent years and the demand for residential housing and highrise buildings is high. high-rise buildings require sophisticated designs since those flexible structures might include expansion joints that separate them from adjacent rigid structures. this scenario can be idealized by a high-rise tower surrounded by a podium or adjacent to a parking structure. the difference in mass and stiffness between flexible and rigid structures might make them move out-of-phase during strong ground motion events. this movement makes adjacent building blocks prone to pounding hazards. it is thought that tying of adjacent buildings together with a simple tying device allowing thermal movement and preventing out-of-plane movement of the blocks during earthquakes is ought to reduce pounding forces and mitigate seismic hazards. saudi building code [1] requires a minimum separation distance to reduce or eliminate pounding. the minimum separation distance calculation is based on the square root sum of squares (srss) of maximum inelastic drifts of adjacent building blocks. such separation distance might be wide and requires special architectural treatment to cover the gaps between the adjacent building blocks. so, if the tying device proves feasible in mitigating seismic hazards, it will allow buildings to be placed with narrower separation gaps. the feasibility of tying building blocks with a simple tying device as a means of mitigating pounding and reducing the required separation was validated through the study of the seismic response of adjacent building blocks designed according to sbc requirements. during the 1985 mexico city earthquake, over 40% of the buildings were severely damaged or collapsed and 15% of them collapsed due to pounding [2]. in 1989 loma prieta earthquake, more than 200 buildings were damaged due to pounding in a radius of 90km from the epicenter which indicates that pounding could be catastrophic for cities near or far from active faults [3]. the proposed methods to account for minimum required separation include 1) absolute sum of displacement (abs), 2) srss, and 3) spectral difference method using double difference combination (ddc) rule [48]. sbc 301-2007 did adopt the concept of srss rather than dcc, abs, due to its simplicity, high accuracy, and small differences in the minimum required separation [9-10]. a comparison between these methods concluded that srss can be practical and provide the required separation distance [1112]. the need of providing mitigation methods between buildings that do not have enough gap were discussed in [13] by providing a numerical study with different ground motion records to simulate the pounding between light-mass and heavy-mass three-story buildings. the research objective was to measure the efficiency of the available mitigation methods in reducing the required seismic gaps based on time historyanalysis with nonlinear viscoelastic model. it was observed that linking the buildings with springs with stiffness more than 2×10 4 kn/m or dampers with damping ratio more than 1×10 6 kg/s reduced the required seismic gap by 85%. this reduction happened because the adjacent buildings were fully connected and vibrated in-phase due to the link installation corresponding author: mohammed s. masmoum engineering, technology & applied science research vol. 10, no. 3, 2020, 5643-5647 5644 www.etasr.com masmoum & alama: use of tying devices to mitigate pounding of adjacent building blocks knowing that adjacent buildings are different in dynamical properties and equal in heights. structural tying of the adjacent building blocks in one complex can make them response as a single structure [14]. the additional relative stiffness due to tying should not create a deficiency on the interacted portions. the originality of this study is that it proposes tying the adjacent building blocks with simply manufactured steel plates that can be anchored to adjacent buildings blocks and accommodated within the floor finishes using thermal gaps only. ii. methodology the necessary details for building design and ground motion scaling are explained in [15]. inelastic time history analysis was used to compute the response of the adjacent building blocks for which the beams were modeled using a single component model with takeda hysteric behavior selected for the nonlinear rotational hinges at beam ends. in the other-hand, bi-axial interacting hinges were assumed on at the end of the columns. the hinges were defined using automatic hinge generator of sap2000 [16]. four cases were considered: • case 1: buildings are separated with thermal expansion joints and without tying devices. • case 2: buildings are separated with code required separation distances and without tying devices. • case 3: buildings are separated with enough distance to totally avoid pounding forces and without tying devices. • case 4: buildings are separated with thermal expansion joints and tied with the proposed tying devices. two main response parameters were used to compare the cases in-order to evaluate the feasibility of tying devices in mitigating pounding hazards. the first was the maximum pounding force and the second was the damage state of the buildings. the damage state will be assessed based on inelastic hinge rotations and will be compared with the damage limits as prescribed in [14]. in order to get an overall damage state, a damage index is proposed as per table i and figures 1 and 2. table i. damage weight criteria hinge plastic rotation θ index a to b 0 b to io 1 io to ls 2 ls to cp 3 more than cp 4 damage index (building) ∑�no. plastic hinges � weighted index� no. plastic hinges in the building members � 4 fig. 1. beams positive and negative backbone curves for m3 hinges fig. 2. column backbone curves for interacting p-m2-m3 hinges iii. modeling contact and tying of frames nonlinear contact elements were used at the joint interface between adjacent frames to account for contact force utilizing the gap element in sap2000. details are given in [15]. the tying device was modeled using a hook link element in sap2000. the link connects two joints located around the expansion joint as shown in figures 3-4. the hook link will simulate tying of adjacent building blocks if the relative displacement exceeds the specified thermal gap opening, in this case 10mm for the studied frames. fig. 3. hook link assignment in sap2000 fig. 4. representation for the hook link in sap2000 if the total value of the relative displacement of connected joints exceeds 10mm, the link will hook the adjacent building blocks. if the total value of the relative displacement lies between 0 and 10mm, the hook link will not connect the joints as shown in (1). the stiffness of the hook link will be equal to the axial stiffness of the tying devices shown in figure 5. ! " �0� $ �% & '()*� + 0,-../� % & '()*� $ �% & '()*� 0 0 (1) engineering, technology & applied science research vol. 10, no. 3, 2020, 5643-5647 5645 www.etasr.com masmoum & alama: use of tying devices to mitigate pounding of adjacent building blocks figure 5 shows a concept drawing for the proposed tie. the axial stiffness is computed for the rod plates that are expected to be flexible in resisting the tying force as determined in (2). k2334 ! 5 �67 (2) where e is the steel modulus of elasticity (200,000n/mm 2 ), a and l are the effective cross-sectional area and the length of the rod plates respectively. ,-../ is the axial stiffness of the tying device assumed to remain elastic throughout the response. fig. 5. conceptual drawing for proposed tying device iv. results and discussion for record rsn0020, building blocks damage states showed acceptable performance as they indicate light damages with plastic hinge rotation less than the life safety limit [14] as shown in figure 6. the pounding force of case 1 was 1330kn while for case 4 it was 614kn showing a 54% reduction when tying devices were used. also, hysteretic relation for the 6th floor hinges with separations for cases 2-4 are shown in figure 7. the maximum plastic hinge rotation indicates a satisfactory performance less than the life safety limit for all cases. pounding forces did not cause a significant effect on the plastic hinge maximum rotation. fig. 6. rsn0020 weighted damage indices for adjacent building blocks with installation of tying devices for record rsn0169, building blocks damage state showed acceptable performance as the building blocks exhibited light damages with plastic hinge rotation less than the life safety limit [14] as shown in figure 8. the pounding force of case 1 was 753kn, but the pounding force of case 4 was 584kn showing a 23% reduction when tying devices were used. the hysteretic relation for the 6th floor hinges with separations for cases 2-4 are shown in figure 9. fig. 7. rsn0020 hysteretic plot for hinges at 6th floor from a 12-story and a 6-story building block with tying devices installation fig. 8. rsn0020 weighted damage indices for adjacent building blocks with installation of tying devices the maximum plastic hinge rotation indicates a satisfactory performance less than the life safety limit for all cases. pounding forces did not cause a significant effect on the plastic hinge maximum rotation. figure 10 compares the maximum pounding forces in the 6th floor for adjacent building blocks for the four studied cases. the bar chart demonstrates the computed forces in the gap and hook link with 10mm separation distance (case 4). minimum required separation distance is highlighted by a straight line. there are two records requiring 300mm to avoid pounding and this value is more than the minimum required separations of 225mm by the code (case 2). for full details for the analysis results refer to [17]. engineering, technology & applied science research vol. 10, no. 3, 2020, 5643-5647 5646 www.etasr.com masmoum & alama: use of tying devices to mitigate pounding of adjacent building blocks fig. 9. rsn0169 hysteretic plot for hinges at 6th floor from a 12-story and a 6-story building block with tying devices installation fig. 10. comparison between maximum pounding force with tying devices and without tying devices for all the records v. conclusion based on the results obtained during the course of the work reported in this paper and earlier works [15, 17], the following points can be concluded: • the proposed tying devices successfully reduced pounding forces from 40% to 60% for adjacent building blocks with 10mm separation comparing to adjacent building blocks without tying devices. building damage as observed from damage index and hysteretic response was not influenced by pounding force in either case. this indicates that tying can be used on existing buildings with thermal separation as a partial mitigation technique to reduce pounding hazards. further improvement on the tying device will increase the mitigation of the pounding hazard. • tying devices can be used on buildings with normal expansion joints and mitigate the pounding effect on similar or better level than seismic joints with code minimum required separations. this was clearly shown as the maximum pounding force reduced from 1330kn for code separation to 614kn using the tying device with thermal separation only. the observed building damage from the damage index and hysteretic response was not influenced by the pounding force in either case. • the effect of pounding on the hysteretic damage of the building blocks can be better assessed by comparing the enclosed hysteretic area of the plastic hinges of the structure in addition to the maximum plastic rotation before and after the installation of tying devices. • tying devices could be designed based on nonlinear analysis using the methodology used in this work. • it was observed that the pounding force will not be more than 20% of the adjacent building blocks base shear summation. this approximation with the results from further parametric studies can be used to estimate the maximum tying force for design purposes. • the equivalent spring stiffness based on floor lateral displacement can be assumed as gap link stiffness to give a converged solution. if the integration did not converge, the stiffness value might need a further multiplicand to reach a converged solution. • it was observed that pounding forces could not be eliminated by applying the code minimum separation distance of 225mm. this was especially observed when using nonlinear response history analysis for sites that are characterized with liquefiable soils. references [1] sbc committee 301, structural loading and forces, saudi building code national committee, 2007 [2] e. rosenblueth, r. meli, “the 19875 earthquake: causes and effects in mexico city”, concrete international, vol. 8, pp. 23–34, 1986 [3] k. kasai, b. f. maison, “building the 1989 pounding damage during loma prieta earthquake”, engineering structures, vol. 19, no. 3, pp. 195–207, 1997 [4] v. jeng, k. kasai, b. f. maison, “a spectral difference method to estimate building separations to avoid pounding”, earthquake spectra, vol. 8, no. 2, pp. 201–223, 1992 [5] j. penzien, “evaluation of building separation distance required to prevent pounding during strong earthquakes”, earthquake engineering & structural dynamics, vol. 26, no. 8, pp. 849–858, 1997 [6] j. h. lin, “separation distance to avoid sesmic pounding of adjacent buildings”, earthquake engineering and structural dynamics, vol. 26, pp. 395–403, 1997 [7] r. e. valles, a. m. reinhorn, evaluation, prevention and mitigation of pounding effects in building structures, national center for earthquake engineering research, 1997 [8] h. p. hong, s. s. wang, p. hong, “critical building separation distance in reducing pounding risk under earthquake excitation”, structural safety, vol. 25, no. 3, pp. 287–303, 2003 [9] d. lopez-garcia, t. t. soong, “evaluation of current criteria in predicting the separation necessary to prevent seismic pounding between nonlinear hysteretic structural systems”, engineering structures, vol. 31, no. 5, pp. 1217–1229, 2009 [10] r. jankowski, s. mahmoud, earthquake-induced structural pounding, springer international publishing, 2015 engineering, technology & applied science research vol. 10, no. 3, 2020, 5643-5647 5647 www.etasr.com masmoum & alama: use of tying devices to mitigate pounding of adjacent building blocks [11] m. j. favvata, “minimum required separation gap for adjacent rc frames with potential inter-story seismic pounding”, engineering structures, vol. 152, pp. 643–659, 2017 [12] m. isteita, k. porter, “safe distance between adjacent buildings to avoid pounding in earthquakes”, 16th world conference on earthquake engineering, santiago chile, january 9-13, 2017 [13] r. jankowski, s. mahmoud, “mitigation of pounding effects”, in: earthquake-induced structural pounding, springer international publishing, pp. 103–132, 2015 [14] asce/sei committee 7, minimum design loads for buildings and other structures”, american society of civil engineers, 2010 [15] m. masmoum, s. alama, “required seperation to mitigate pounding of adjacent building blocks”, engineering, technology & applied science research, vol. 8, no. 6, pp. 3565-3569, 2018 [16] computers and structures inc., csi analysis reference manual for sap2000, etabs, safe, and csi bridge. computers and structures inc., 2016 [17] m. masmoum, buildings pounding mitigation using tying device, msc thesis, king abdulaziz university, 2019 microsoft word 14-2335_s1 engineering, technology & applied science research vol. 8, no. 6, 2018, 3561-3564 3561 www.etasr.com khahro & memon: non excusable delays in construction industry: a causal study non excusable delays in construction industry: a causal study shabir hussain khahro department of engineering management, college of engineering, prince sultan university, riyadh, saudi arabia shkhahro@psu.edu.sa zubair ahmed memon department of engineering management, college of engineering, prince sultan university, riyadh, saudi arabia zamemon@psu.edu.sa abstract—delays are one of the major problems construction industry faces. delays can lead to many negative effects such as arbitration between owners and contractors, increased cost, loss of productivity and revenue, and contract termination. various studies have been carried out to highlight the general causes of delays and suggest possible remedial measures to minimize the effect of delays on a project. this study aims to highlight the critical factors with specific reference to non-excusable delays (neds) only. it also suggests possible remedial measures to minimize the effects of contractor-oriented neds which is a significant type of delays in the construction industry. a qualitative study has been conducted for this research. data have been collected by the use of a set of questionnaires on numerous construction project stakeholders. relative importance index (rii) has been used for prioritizing the factors. results show that slow material mobilization, subcontractor unreliability and shortage of labor and materials are the most critical ned causes. this paper aims to provide a prerequisite knowledge to practitioners to make a more informed decision in managing ned. keywords-delays; non-excusable delay; construction projects; project failure; mitigation i. introduction construction industry plays an essential role in a country’s socio-economic development [1, 2]. however, it faces a wide range of challenges, one of which is the frequent occurrences of construction delays. delay is one of the most common problems in the construction industry [3]. to achieve the dismal profit margins, it requires massive all-around efforts to develop a schedule and control it efficiently. with low-profit margins and the involvement of many parties, these projects have an inherent risk of schedule slippages and subsequent monetary losses [4]. it is not uncommon for a construction project to experience a delay. while contractors never want delays to happen, they do occur. delays may occur at any time on a project. a delay means loss of profit and/or risk of facing hefty liquidated damages [5]. at 2016, the global average value of a construction delay dispute was reported to be a staggering us$46million, a trend that has been climbing upwards from 2010. claims and disputes are the inevitable results of delays to a project [6]. authors in [7] evaluated the records of more than 4000 projects and concluded that delays and cost overruns are common in the construction projects and the success rate of completing a project on time is poor. authors in [8] concluded that 50% of construction delays are neds, delays for which the contractor is responsible. authors in [9-11] observed the detrimental effect on a contractor’s performance, particularly on a contractor’s schedule. there are a number of studies in the literature that classify delays according to their nature and define various types of delays. authors in [12-16] classify the delays into three categories, as shown in figure 1. fig. 1. delay classification in compensable, excusable delays, generally the owner remains responsible and a contractor may be granted the extension of time and the extra cost. non-compensable excusable delays are earthquakes, snowfalls, heavy rains, tsunamis, wars, etc. in such cases, delays cannot be controlled either by client or contractor and normally the contractor will be granted the extension of time and money to complete the task. the third type of delays, neds, is purely contractor’s fault: material related delays, labor-related delays, equipment related delays, financial issues etc. in this case, contractors normally have to face a financial penalty. construction industry is one of the leading development sectors of any country. in pakistan, it contributes 2.74% to development, 2.65% to gdp and the 7.31% of labor force in 2017 [17]. in pakistan, it has been observed that delay is a key reason for project failure. very little evidence is available from previous studies regarding pakistani construction industry on issues related to the causes of neds which influence contractor’s performance. hence, this research attempts to engineering, technology & applied science research vol. 8, no. 6, 2018, 3561-3564 3562 www.etasr.com khahro & memon: non excusable delays in construction industry: a causal study investigate and evaluate the issues related to the causes of neds during the construction stage of projects, with an emphasis on critical factors. ii. research methodology qualitative research methodology has been employed. the research has been undertaken in three phases. in the first phase the candidate factors were selected from the existing literature. in the second phase, field data were collected about these factors causing neds in constructions in pakistan and analysis was done using the rii method: 5 1rii i i i w x a n = = × ∑ (1) where wi=the weight given to the i th response: i=1, 2, 3, 4, 5, xi=frequency of the i th response, a=the highest weight (5 in this study), and n=the number of respondents. authors in [5, 11, 18] successfully used this method for the analysis of construction delays. in the third phase, a list of corrective actions for critical factors was generated. iii. results and discussion the questionnaire was divided into two segments: the first segment was for collection of general information from the respondents and the second segment regarded ned matrix which contains information about neds and causes leading to neds. the respondents have to rank the different factors of neds that influence a contractor’s performance in construction projects. in the ned matrix, a total number of 42 different factors which cause neds in the construction industry of pakistan were placed and these factors were grouped in 14 different ned causal areas (table i). a second questionnaire set was categorized into four major segments. segment 1 contained general information and company profile. segments 2 and 3 contained technical questions, related to the respondent, regarding contractor’s performance and evaluation of critical factors. in the last segment, evaluation of possible remedial measures to deal with ned was done. table ii shows the rank of the causal area with causes of ned based on the respondents' opinion. it is observed that material related delays, improper construction methods and inadequate supervision are the most significant ned causal areas. whereas, shortage of equipment/labor/material, improper equipment, poor planning and shortage of labor are the significant causes for ned with the highest rii score. critical delays are those which cause delay to the entire project completion date while non-critical delays do not necessarily affect the project completion date but affect progress. in every project, delays are determined regarding their effect at the project completion date. delays can be a combination of small and big delays that occurred during the whole project. therefore, critical delays are taken more into consideration than noncritical delays. table ii shows the core critical factors for neds. the last objective of this study is to point appropriate corrective actions for the critical factors which affect the schedule performance of contractor. table iii shows the suggested remedial measures. table i. critical factors for each group of ned causes causal area cause of delays rii rank avg. score 1 material related delays poor planning 4.467 1 4.4 unavailability of resources 4.322 2 shortage of materials 4.29 3 2 labor related delays shortage of labor 4.419 1 3.9 strikes 3.935 2 low productivity 3.37 3 3 equipment related delays improper equipment 4.338 1 4.2 unskilled equipment operator 4.225 2 poor planning 4.064 3 4 financial related delays improper equipment 4.5 1 4.3 unskilled equipment operator 4.209 2 poor planning 4.177 3 5 improper planning related delays poor planning 4.29 1 4.3 slow mobilization/late delivery 4.258 2 defective work/rework 4.225 3 6 lack of control related delays defective work/rework 4.354 1 4.3 poor quality 4.354 2 poor planning 4.209 3 7 subcontractor related delays poor planning 4.274 1 4.1 subcontractor bankruptcy 4.08 2 shortage of labor 4 3 8 technical personnel shortages poor planning 4.387 1 3.9 poor qualification 4.161 2 shortage of personnel 3.032 3 9 poor coordination shortage of equipment/labor/material 4.516 1 4.3 poor planning 4.145 2 slow mobilization/late delivery 4.129 3 10 inadequate supervision defective work/rework 4.354 1 4.3 poor quality 4.354 2 poor monitoring and control 4.322 3 11 improper construction method wrong method statement 4.387 1 4.3 inappropriate practices/procedures 4.338 2 defective work/rework 4.322 3 12 poor communication poor planning 4.37 1 4.3 shortage of materials 3.967 2 damaged materials 3.322 3 13 improper scheduling poor planning 4.161 1 4.0 inappropriate practices/procedures 4.096 2 shortage equipment 3.79 3 14 slow decision making lack of experience 4.096 1 4.0 poor planning 4.032 2 shortage equipment 3.79 3 iv. conclusions and suggestions the objectives of this study were to identify the most important causes of ned and to suggest corrective measures for ned critical factors that affect the performance of a construction contractor in pakistan. intensive government involvement is needed to prevent and mitigate an issue that may delay projects. results showed that financial problems, followed by equipment problems, lack of equipment, engineering, technology & applied science research vol. 8, no. 6, 2018, 3561-3564 3563 www.etasr.com khahro & memon: non excusable delays in construction industry: a causal study manpower and insufficient communication between the main actors are the main causes of neds. table ii. ned critical factors rank critical factors 1 slow mobilization/late delivery 2 unreliable supplier/subcontractor 3 shortage of equipment/labor/materials 4 delay in manufacturing 5 delay in material selection 6 delay in importing materials/equipment 7 poor planning 8 low productivity 9 lack of experience 10 inappropriate practices/procedures 11 poor monitoring and control 12 low morale/motivation 13 shortage of personnel 14 too many responsibilities 15 defective work/rework 16 working in remote areas table iii. selected remedial measures ned critical factor selected corrective action slow mobilization/late delivery a penalty clause for delay in material selection and delivery would minimize the occurrence of late delivery. unreliable supplier/subcontractor a fine clause would govern the reliability and performance of sub-contractor. shortage of equipment/labor/ materials a penalty clause stipulated by the contractor for shortage of materials/labor/equipment. delay in manufacturing engaging additional personnel will influence cost. delay in material selection engaging an appropriate resource will influence time and cost. delay in imported material/equipment ideally a contract clause for delivery may influence the delivery program poor planning engaging additional experienced personnel would minimize the impact but may influence the cost. low productivity using work sampling data, managers will be able to make accurate decisions to control the factors that positively and adversely affect job productivity. lack of experience engaging an experienced planning engineer would influence the cost. inappropriate practices/procedures benchmarking and constantly improving the practices/procedure will minimize the impact. poor monitoring and control systematic monitoring and control taking into consideration accuracy, short regular intervals, effective feedback and standard procedures will minimize poor monitoring and control. low morale/motivation ideally, improving job satisfaction would influence morale/motivation. shortage of personnel proper personnel planning and provision will reduce shortage too many responsibilities sharing with different companies and checking manufacturing details from all industries. defective work/rework where works are defective the contractor is entitled to provide for corrective actions and improvements. working in remote areas barring late workers and morning inspection would minimize late arrival. all respondents agreed that the contractors' performance can be easily judged and verified by the scheduled performance. usually the contractors have planned the works before their start and, daily or weekly, the real performance of a site is updated to check the work progress. it is suggested that remedial and project managers can save the cost for the contractor and bring successful project completion and positive impact on the construction industry. the success or failure of a commercial construction project depends largely on the construction schedule and whether it is met or not. delays in the construction schedule impact negatively both owners and contractors. construction industry is flooded with fast track projects nowadays and there is always a pressure on the contractor to bid as low as possible, resulting in low profit margins. to achieve these dismal profit margins, requires massive all-round efforts of developing a schedule and efficiently controlling it. in addition to “you may delay, but time will not”, benjamin franklin also said that “time is money”. while it is doubtful that he was thinking about construction delays when he coined these phrases, his words are spot-on. delays incurred during a construction project can have severe negative impacts on owners and contractors alike. care must therefore be taken during the drafting and negotiation of construction contracts to ensure that the parties' financial interests are adequately protected in the event delays result in late project completion. references [1] y. c. kog, “project management and delay factors of public housing construction”, practice periodical on structural design and construction, vol. 23, no. 1, p. 04017028, 2018 [2] t. h. ali, s. h. khahro, f. a. memon, “occupational accidents: a perspective of pakistan construction industry”, mehran university research journal of engineering and technology, vol. 33, no. 3, pp. 341-345, 2014 [3] d. arditi, s. nayak, a. damci, “effect of organizational culture on delay in construction”, international journal of project management, vol. 35, no. 2, pp. 136-147, 2017 [4] pco, importance of schedule delay analysis on construction projects – a contractor’s perspective, available at: https://projectcontrolsonline .com/blogs/13-category1/715-importance-of-schedule-delay-analysison-construction-projects--a-contractors-perspective, 2017 [5] z. a. memon, “remedial measure for delays at construction stage”, mehran university research journal of engineering and technology, vol. 23, no. 1, pp. 9-20, 2004 [6] m. lepage, “types of schedule delays in construction projects”, available at: https://www.planacademy.com/types-of-schedule-delays-inconstruction, 2017 [7] p. w. g. morris, g. h. hough, the anatomy of major projects, wiley, 1987 [8] m. z. a. majid, r. mccaffer, “factors of non-excusable delays that influence contractors’ performance”, journal of management in engineering, vol. 14, no. 3, pp. 42-49, 1998 [9] s. a. h. tumi, “causes of delays in construction industry in libya”, international conference on economics and administration, bucharest, romania, november 14-15, 2009 [10] m. e. a. el-razek, h. a. bassioni, m. a. mobarak, “causes of delay in building construction projects in egypt”, journal of construction engineering and management, vol. 134, no. 11, pp. 831-840, 2008 [11] s. a. assaf, m. al-khalil, m. al-hazmi, “causes of delay in large building construction projects”, international journal of project management, vol. 24, no. 4, pp. 349-257, 2006 [12] m. sambasivan, y. k. soon, “causes and effects of delays in malaysian construction industry”, international journal of project management, vol. 25, no. 5, pp. 517-526, 2007 [13] n. hamzah, m. a. khoiry, i. arshad, n. m. tawil, a. i. che ani, “cause of construction delay theoretical framework”, procedia engineering, vol. 20, pp. 490-495, 2011 engineering, technology & applied science research vol. 8, no. 6, 2018, 3561-3564 3564 www.etasr.com khahro & memon: non excusable delays in construction industry: a causal study [14] g. agyekum-mensah, a. d. knight, “the professionals’ perspective on the causes of project delay in the construction industry”, engineering, construction and architectural management, vol. 24, no. 5, pp. 828841, 2017 [15] r. h. ansah, s. sorooshian, s. bin mustafa, “the 4ps: a framework for evaluating construction projects delays”, journal of engineering and applied sciences, vol. 13, no. 5, pp. 1222-1227, 2018 [16] a. adam, p. e. b. josephson, g. lindahl, “aggregation of factors causing cost overruns and time delays in large public construction projects: trends and implications”, engineering, construction and architectural management, vol. 24, no. 3, pp. 393-406, 2017 [17] a. yusufzai, “pakistan’s gdp growth highest in decade: economic survey”, propakistani, available at: https://propakistani.pk/2017/05/25/ pakistans-gdp-growth-highest-decade-economic-survey, 2017 [18] o. t. ibironke, t. o. oladinrin, o. adeniyi, i. v. eboreime, “analysis of non-excusable delay factors influencing contractors’ performance in lagos state, nigeria”, journal of construction in developing countries, vol. 18, no. 1, pp. 53-72, 2013 microsoft word 06-849-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1241-1244 1241 www.etasr.com faridi masouleh et al.: optimization of etl process in data warehouse through a combination of … optimization of etl process in data warehouse through a combination of parallelization and shared cache memory m. faridi masouleh m. a. afshar kazemi m. alborzi a. toloie eshlaghy information technology management department science and research branch, islamic azad university tehran, iran m.faridi@srbiau.ac.ir information technology management department science and research branch, islamic azad university tehran, iran m.afsharkazemi@ yahoo.com information technology management department science and research branch, islamic azad university tehran, iran mahmood_alborzi@ yahoo.com information technology management department science and research branch, islamic azad university tehran, iran toloie@gmail.com abstract—extraction, transformation and loading (etl) is introduced as one of the notable subjects in optimization, management, improvement and acceleration of processes and operations in data bases and data warehouses. the creation of etl processes is potentially one of the greatest tasks of data warehouses and so its production is a time-consuming and complicated procedure. without optimization of these processes, the implementation of projects in data warehouses area is costly, complicated and time-consuming. the present paper used the combination of parallelization methods and shared cache memory in systems distributed on the basis of data warehouse. according to the conducted assessment, the proposed method exhibited 7.1% speed improvement to kattle optimization instrument and 7.9% to talend instrument in terms of implementation time of the etl process. therefore, parallelization could notably improve the etl process. it eventually caused the management and integration processes of big data to be implemented in a simple way and with acceptable speed. keywords-shared cache memory; etl process; parallelization; etl optimization i. introduction data warehouse applications have utilized extraction, transformation and loading (etl) processes through tools that extract data from data resources, transform them to an acceptable format and load them in a data provider [1]. such processes include a collection of instruments used for extracting, cleaning, customization, remolding, merging and data loading from different far away databases to a data warehouse [2]. during etl, the data of required data providers (databases, text files, old systems and widespread pages) is extracted and transformed into compatible data within a definite framework and placed into a data reservoir. different specialties such as commercial analysis, database design and programming are essential for implementation of etl process. prior to etl implementation data providers, their destination and the transformation needed should be recognized and determined. this requires an initial data gathering and modeling stage followed by a more detailed one in the etl design and implementation stage [3]. a variety of approaches have been discussed to optimize etl. in [7], authors determined a etl process path for optimization of implementation time. they improved the operations and tasks related to a process without using the parallelization process. in [1, 4-5], authors proposed a theoretical framework which formally defined the scenario of etl processes in the form of an undirected acyclic graph. in [6], authors used a law-based optimization method which was a complicated method demanding abundant coding. in [7], authors presented a new solution to discover a standard conceptual model in order to implement the extraction, transformation and loading operations. they categorized their method into three phases: the first is the mapping of terms and instructions, the second phase was based on conceptual structure and the last phase of modeling was based on uml concepts. in [8], authors presented a new method based on stream control in etl to optimize process speed. they accomplished to commercialize their method and provide a new idea for other researches. in [4], authors used an intelligent method based on grid in physical and cyber environments to manage and improve the etl process. they generally developed their study on big data for the emergence of the fields related to cyber and physical systems which were based on text. they finally achieved to integrate the spatial and nonspatial data in cyber environment. engineering, technology & applied science research vol. 6, no. 6, 2016, 1241-1244 1242 www.etasr.com faridi masouleh et al.: optimization of etl process in data warehouse through a combination of … with regard to the examination of weak and strong points of former researches, the present paper has presented a new combined method by usage of parallelization techniques and simultaneous use of multiple cores to process and manage different databases in scattered locations as well as the application of cache memory shared between cores which conduct the operations of implementation, transformation and loading of data from distributed data bases in different locations and main data warehouse located in a definite place. ii. concepts of etl etl is considered a process which should be continually performed in system. this process is also conducted in return for operative data which come to existence in organization during time. what matters in the establishment of an intelligent business organization is the creation of a proper architecture and structure so that etl process should be conducted compatible with different operations in which it occurs. so the structure applied for prior etl has great importance. the etl process should be conducted in different stages since it is applied in large volume of data and is usually accompanying with data integration. the noteworthy issue is that when etl process initiates during these stages, the high volume of network traffic and processing of database servers may cause disorder in other intelligent business processes. an etl system has four main sections: • extraction • transformation • loading • meta data a. extraction phase the data should be initially extracted from respective data providers. in this phase, the data may be deleted from initial data providers or copied in data warehouse without being omitted. the old data are often not applicable in organization's daily affairs whose maintenance is merely for keeping the system history would be deleted from preliminary data providers and transferred to data reservoir. so the efficiency and performance of aforesaid data resources would be kept at a desirable level. data extracted from initial data providers are usually placed in staging space of data warehouse and processed in other etl phases. this space is a relational data base emerged as temporary memory space for data processing. the phase of data extraction is usually conducted at the level of data resources especially when the respective data resource is a data base. the prevalent method in old systems for data extraction is the production of text files on the basis of data. the new systems apply odbc, oledb and api for this purpose. b. transformation phase after extraction of data, certain processes should be done so that they reach a proper and integrated format. this phase is performed as follows: • data validation: compatibility and absence of contradiction between new data extracted from data providers and information present in data warehouse is examined. • data verification: do the fields have correct values? for example, in a field with on and off values, do all the data possess one of the two values? • data transformation: data originates from diverse data providers and so similar fields may have diverse values. for example, a two value field may be on and off in a data provider and 0 and 1 in other data providers. the entire data entering the warehouse should be modified in this respect. • applying business regulations: in this phase we should consider if present data is compatible with organizational needs. for example does the customer information includes their first and family name? • data integration: is it possible for one system to keep customer information and the other system keep the sales information. the data present in both systems should be integrated. this is actually the most complicated phase in etl process. a part of this process could be implemented in data extraction phase such as old information systems in which information is gathered from entire data files and a text file is created base on them [7]. c. loading phase data transformed to respective standard form are placed into data warehouse in this phase. the data are loaded periodically and not continually due to their high volume. in other words, when data are transformed in a data provider or new information is added, the changes are not instantaneously transferred to data warehouse. but they are updated periodically and in a regular time span [7]. d. meta data meta data includes information on transmission and conversion of data, data warehouse performance, contradiction in data providers, determined data base diagrams and the data warehouse places in which initial data resources are mapped. the data present in meta data could be applied in cases such as automatic supervision, prediction of organizational trends and reapplication of information [7]. iii. architecture and analysis of the recommended scheme figure 1 demonstrates the architecture of the recommended scheme. it is observed that all data that belong to distributed databases in diverse locations enters the target operative space and each takes a responsibility in present processor system. the cores also simultaneously receive and process the data and transfer them to data warehouse in a parallel form. the present paper generally used two combined strategies of engineering, technology & applied science research vol. 6, no. 6, 2016, 1241-1244 1243 www.etasr.com faridi masouleh et al.: optimization of etl process in data warehouse through a combination of … parallelization and shared cache memory in order to optimize the etl operations and manage the data in data bases. fig. 1. the recommended scheme a. shared cache memory one of the notable and remarkable issues in etl process is the challenge of separate utilization of cache memory. in case that in a distributed operative system, separate cache memories were used in input and output, the processor and main memory are obliged to transfer the caches in each specific operation. it is itself an important issue in great and sensitive matters which demand high speed operation. figure 2a demonstrates the manner of using cache memory in different instruments. it is seen that this type of systems require transition and duplication in each time of implementation. figure 2b demonstrates another condition of dependent cache memory. the present paper averts the challenge of transition of cache memory by different providers through application of cache memory shared between diverse providers. so it is not essential to transfer cache memory in each performance by different providers in each system which finally leads to the improvement of speed, etl process and system operation. figure3 shows an aspect of common cache memory. the manner of parallelization of processes in system in present study is based on the processing cores existing in operative environments. so the procedure is that by entering a process to etl process, in case of the inactivity of each processor and its cores, the mentioned operation is selected and processed by inactive core. after the completion of processing, the core is placed in queue and is ready to receive the process. it is to be mentioned that the processors and related active cores are implemented in queues and controls and processes the operation. fig. 2. utilization of dependent cache memory (a) in diverse instruments (b) in different instruments fig. 3. utilization of common cache memory shared in different instrument iv. results evaluation c# language is used for the optimization of etl operation in distributed data bases in this paper (table i). the comparisons conducted in terms of speed, optimization level of etl process by this instrument or others including kettle [9] and talend [10] will be described in following section. it is to be mentioned that the following jquery is used to assess the results and extract records: select d_year, c_nation, sum (lo_revenue lo_supplycost) as profit from date, customer, supplier, part, lineorder where lo_custkey = c_custkey and lo_suppkey = s_suppkey and lo_partkey = p_partkey and lo_orderdate = d_datekey and c_region = ’america’ and s_region = ’america’ and (p_mfgr = ’mfgr#1’ or p_mfgr = ’mfgr#2’) group by d_year, c_nation order by d_year, c_nation five different data bases and different numbers of samples were employed. further, shared cache memory, different number of cores and serial and parallel implementation were also investigated. results are depicted in figures 4-5. it is shown that the level of difference between parallel implementation of etl process with parallel and shared cache memory is very significant, however it functions 263 times better than average condition (figure 6). table ii demonstrates a brief account of different implementation times in m/s compared to recommended method. figure 7 demonstrates the comparison between the recommended scheme and other etl optimization instruments. as shown, the proposed method exhibits about 7.1% speed improvement compared to kattle optimization instrument and 7.9% to talend instrument. table i. output and results volume(mbyte) samples number serial running time parallel running time 0.143051 100 5133 14 0.715255 500 28,111 27 1.430511 1,000 54,834 39 2.861022 2,000 106,960 52 7.152557 5,000 208,638 65 14.30511 10,000 406,974 77 28.61022 20,000 793,853 90 42.91534 30,000 1,548,508 103 (a) (b) engineering, technology & applied science research vol. 6, no. 6, 2016, 1241-1244 1244 www.etasr.com faridi masouleh et al.: optimization of etl process in data warehouse through a combination of … fig. 4. implementation time fig. 5. serial implementation time fig. 6. comparison between parallel implementation time and shared memory with serial implementation (m/s) fig. 7. comparison between recommended methods with other etl optimization instruments table ii. comparison between implementation time of recommended method and etl optimization instruments volume(gig) recomme nded method kattle tool talend tool 1 927 2500 2500 2 1900 5100 5000 3 3150 7000 6700 4 6300 12500 12000 5 12200 15000 13200 6 13000 16000 14000 7 15500 20000 17000 8 20200 24000 22000 v. conclusion a variety of methods have been proposed for etl optimization in distributed and big data banks that integrate various instruments. with regard to the importance of the issue and the challenges in this area, including confidence and speed, the present paper introduced a new method that includes both methods of parallelization and shared cache memory. the proposed scheme shows almost 7.1% speed improvement compared to kattle optimization instrument and 7.9% compared to talend instrument. future work may focus in the utilization of real parallelization hardware instead of virtual hardware and optimization of etl process in a cloud environment. references [1] a. simitsis, p. vassiliadis, t. sellis, “optimizing etl processes in data warehouses”, ieee 21st international conference on data engineering (icde'05), pp. 2-4, 2005 [2] j. a. sharp, data flow computing: theory and practice, intellect books, 1992. [3] m. bala, o. boussaid, z. alimazighi, “big-etl: extractingtransforming-loading approach for big data”, international conference on parallel and distributed processing techniques and applications (pdpta), pp. 1-4, 2015 [4] a. v. simitsis, p. vassiliadis, t. sellis “optimizing etl processes in data warehouses”, 21st international conference on data engineering (icde 2005), pp. 564–575, 2005 [5] a. w. simitsis, , k. wilkinson, u. dayal, m. castellanos, “optimizing etl workflows for fault-tolerance”, 26st international conference on data engineering, pp. 385–396, 2010 [6] a. behrend, “optimized incremental etl jobs for maintaining data warehouses”, 14th international database engineering & applications symposium, pp. 216-224, montreal, quebec, canada — august 16 18, 2010 [7] s. h. a. el-sappagh, a. m. a. hendawi, a. h. el bastawissy, “a proposed model for data warehouse etl processes”, journal of king saud university computer and information sciences, vol. 23, no. 2, pp. 91-104, 2011 [8] a. longo, s. giacovelli, m. bochicchio, "fact – centered etl: a proposal for speeding business analytics up", procedia technology, vol. 16, pp. 471-480, 2014 [9] p. kettle, "pentaho kettle project", kettle project, 2014 [10] x. liu, optimizing etl dataflow using shared caching and parallelization methods. arxiv, corr abs/1409.1639, 2014 microsoft word 9-3021_s_etasr_v9_n5_pp4623-4626 engineering, technology & applied science research vol. 9, no. 5, 2019, 4623-4626 4623 www.etasr.com buller et al.: influence of coarse aggregate gradation on the mechnical properties of concrete, part ii … influence of coarse aggregate gradation on the mechnical properties of concrete, part ii: no-fines vs. ordinary concrete abdul salam buller department of civil engineering, quaid-e-awam university of engineering, science & technology, larkana campus, sindh, pakistan buller.salam@quest.edu.pk zaheer ahmed tunio department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, sindh, pakistan zaheerahmedtunio@gmail.com fahad-ul-rehman abro department of civil engineering, mehran university of engineering and technology, jamshoro, sindh, pakistan fahad.abro@gmail.com tariq ali department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, sindh, pakistan tariqdehraj@gmail.com karam ali jamali department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, sindh, pakistan tespublic@yahoo.com abstract—this study aims to investigate the effect of different gradations of coarse aggregates on mechanical properties of nofines concrete (nfc). nfc reduces a structure’s self-weight, thus minimizing cost. the effects of coarse aggregate gradation on mechanical properties such as compressive strength, split tensile strength, and flexural strength were studied and compared at the end of 28-day water curing. a fixed cementto-aggregate proportion 1:6 with 0.5 water/cement (w/c) ratio was adopted. four gradations of coarse aggregates ranging between specific maximum and minimum size were used, namely 5mm-4mm, 10mm-4mm, 20mm-4mm and 20mm-15mm. the results of this study reveal the substantial effect of the gradation of coarse aggregates on strength properties compressive and tensile strength of nfc. keywords-no-fines;aggregate graddation;cement to agggregate proportion;compressive strength;texture i. introduction concrete without fines is a type of lightweight porous concrete acquired by removing the sand from the ordinary concrete mix. it is a material of two phases, rough aggregates, surrounded by a thin layer of cement paste without fine aggregates. nfc is a type of lightweight concrete produced from only cement water and coarse aggregates. the coarse aggregates are covered with cement paste and linked point-topoint with thin cement paste holding aggregates in a matrix, augmenting concrete strength. it is recognized that self-weight constitutes a very big percentage of the complete structure load in concrete buildings. there are significant benefits in decreasing the concrete unit weight. appropriate resistance of structural light weight aggregate concrete (lwac) is now prevalent in use. in frame structures, the petition walls are free of charge where the construction of these non-structural elements with low-strength lightweight concrete would result in a subsequent reduction in the overall weight of the structure. nfc has many applications, [1-13], described in part i [14]. civil engineers have been challenged to transform waste into helpful building materials [13, 15] and large quantities of raw materials and waste, in particular demolition waste, are used as recycled aggregates for the construction and use of nonfinished concrete waste, making it more economical compared to standard concrete [16, 17]. nfc is an environmentally friendly paving material because it has much higher voids in its body than those of normal concrete resulting in rainwater runoff from it [11]. nfc’s cement/aggregate ratio usually varies from 1:6 to 1:10 and aggregate is usually used from 20mm to 10mm [14, 16] and the proportion of water to cement ranges from 0.28 to 0.40 [18]. no concrete fines normally used are single sized coarse aggregates. this resulted to the concept of carrying out an experimental study to explore the impact of various gradations of coarse aggregates used in concrete nofines in the first part [14]. in this part, the impact of coarse aggregates’ size have been researched regarding mechanical characteristics. compressive and tensile strength tests were performed in samples cast from four distinct lots of coarse aggregates. the results of nfc were compared with that of conventional concrete. ii. experimental procedure the main aim of this study is to investigate unit weight, compressive strength, splitting tensile strength, and flexural strength of no-fines and ordinary concrete. cement-aggregate (c-a) proportions 1:6 of nfc and 1:2:4 of ordinary concrete were adopted. four different coarse aggregate gradations, corresponding author: abdul salam buller engineering, technology & applied science research vol. 9, no. 5, 2019, 4623-4626 4624 www.etasr.com buller et al.: influence of coarse aggregate gradation on the mechnical properties of concrete, part ii … namely 5mm-4mm, 10mm-4mm, 20mm-4mm, and 20mm15mm, were used. nfc and ordinary concrete were cast with 0.5 w/c ratio. ordinary portland cement (opc) as per standard of astm c150 was used to manufacture the specimens of both concretes. crushed stones obtained from the local market were used as coarse aggregates. they were washed, air dried to ssd, and sieved accordingly to achieve each specified aggregate gradation. potable water was used for casting and curing of all specimens. all the ingredients of each respective mix were batched accordingly following the proper mixing procedure in an electric operated mixer and were cast accordingly. a total number of 20 cube specimens for nfc and 20 for ordinary concrete (nc) of standard size of 150mm×150mm×150mm, 20 cylinders for nfc and nc of standard size of 150mm×300mm and 20 prisms for nfc and nc of standard size of 100mm×100mmx500mm were cast. the specimens were demoulded after 24 hours of casting and were kept in a curing tank up for 28 days. before testing the specimens for compressive, splitting tensile, and flexural strength, all the specimens were weighed to determine their unit weight. to determine compressive, splitting tensile, and flexural strength, the cubes, cylinders, and prisms were tested in a universal testing machine (utm) (see part i [14] for more utm testing pictures). the ultimate loads at the failure of specimens were recorded. five cubes, cylinders, and prisms for nfc and nc were cast from each batch. the ultimate compressive, splitting tensile and flexural strength, and the unit weight of each of the five specimens was measured and the average was used as the final value. fig. 1. specimens under curing iii. results and discussion a. compressive strength of nfc the results of average compressive strength are presented in table i. table i. average compressive strength and unit weight of nfc s.no. aggregate gradation (mm) c-a proportion w/c ratio compressive strength (mpa) unit weight (kg/m 3 ) 1 5-4 1:6 0.5 4.9 1687 2 10-4 1:6 0.5 8.2 1843 3 20-4 1:6 0.5 9.8 1891 4 20-15 1:6 0.5 6.4 1735 b. splitting tensile strength of nfc the results of average splitting tensile strength are presented in table ii. table ii. average splitting tensile strength and unit weight of nfc s.no. aggregate gradation (mm) c-a proportion w/c ratio splitting tensile strength (mpa) unit weight (kg/m 3 ) 1 5-4 1:6 0.5 0.6 1687 2 10-4 1:6 0.5 1.3 1843 3 20-4 1:6 0.5 1.7 1891 4 20-15 1:6 0.5 1.1 1735 c. flexural strength of nfc the results of average flexural strength are presented in table iii. table iii. average flexural strength and unit weight of nfc s.no. aggregate gradation (mm) c-a proportion w/c ratio flexural strength (mpa) unit weight (kg/m 3 ) 1 (5-4) 1:6 0.5 1.2 1687 2 (10-4) 1:6 0.5 2.4 1843 3 (20-4) 1:6 0.5 3.8 1891 4 (20-15) 1:6 0.5 2.1 1735 fig. 2. view of a prism sample before and after testing in utm d. compressive strength of nc the results of average compressive strength are presented in table iv. table iv. average compressive strength and unit weight of ordinary concrete s.no. aggregate gradation (mm) mix proportion w/c ratio compressive strength (mpa) unit weight (kg/m 3 ) 1 5-4 1:2:4 0.5 21.2 2339 2 10-4 1:2:5 0.5 29 2366 3 (20-4) 1:2:4 0.5 30.4 2445z engineering, technology & applied science research vol. 9, no. 5, 2019, 4623-4626 4625 www.etasr.com buller et al.: influence of coarse aggregate gradation on the mechnical properties of concrete, part ii … e. splitting tensile strength of nc the results of average splitting tensile strength are presented in table v. table v. average splitting tensile strength and unit weight of ordinary concrete s.no. aggregate gradation (mm) c-a proportion w/c ratio splitting tensile strength (mpa) unit weight (kg/m 3 ) 1 5-4 1:2:4 0.5 2.2 2339 2 10-4 1:2:4 0.5 2.7 2366 3 20-4 1:2:4 0.5 3.4 2445 f. flexural strength of nc the results of average compressive strength are presented in table vi. table vi. average flexural strength and unit weight of ordinary concrete s.no. aggregate gradation (mm) c-a proportion w/c ratio flexural strength (mpa) unit weight (kg/m 3 ) 1 5-4 1:2:4 0.5 3.4 2339 2 10-4 1:2:4 0.5 3.5 2366 3 20-4 1:2:4 0.5 3.8 2445 fig. 3. compressive, spilitting tensile, and flexural strength of nfc vs. aggregate gradation and c-a proportion at 0.5 w/c ratio fig. 4. compressive, spilitting tensile, and flexural strength of nc vs. aggregate gradation and c-a proportion at 0.5 w/c ratio the results reveal the pronounced effect of aggregate gradation and c-a proportion on the compressive strength. figures 3-4 depict the effect of various course aggregate gradations on the compressive, splitting tensile, and flexural strength of nfc and nc. the significant effect of aggregate gradation is self-evident from the tables’ values and figures. nfc manufactured with 20mm-4mm gradation exhibited the and the nfc with 5mm-4mm gradation yielded the lowest compressive, splitting tensile, and flexural strength of the respective group of nfc having the same c-a 1:6 proportion and 0.5 w/c ratio. on the other hand, 20mm-4mm had high compressive, splitting tensile, and flexural strength at 1:2:4 mix proportion and 0.5 w/c ratio. this infers the significance of aggregate gradation, c-a proportion on the compressive strength, splitting tensile strength, and flexural strength of both nfc and nc. fig. 5. comparision between unit weight of nfc and nc g. unit weight table i also shows the values of average unit weight of nfc produced with different aggregate gradation, 1:6 c-a proportion and 0.5 w/c ratio. the 20mm-4mm coarse aggregate gradation had 1891kg/m 3 and the 5mm-4mm coarse aggregate gradation had 1687kg/m 3 unit weight respectively. the difference between the maximum and minimum values of unit weight is calculated to be only 12.1% while the difference percentage of nfc and nc is 33%.the unit weight of nfc is slightly affected due to variation in aggregate gradation, c-a proportion and w/c ratio but without any significant trend regarding those parameters. this may be observed in figure 5 where the unit weight values are compared graphically. iv. conclusion • aggregate gradation significantly affects compressive, splitting tensile, and flexural strength of nfc. • a difference of 50%, 64% and 68% was observed between the maximum and minimum compressive, splitting tensile, and flexural strength respectively of nfc due to variation in aggregate gradation and c-a proportion. • nfc produced with 20mm-4mm gradation 1:6 c-a proportion and 0.5 w/c ratio exhibited the highest compressive strength of 9.8mpa. engineering, technology & applied science research vol. 9, no. 5, 2019, 4623-4626 4626 www.etasr.com buller et al.: influence of coarse aggregate gradation on the mechnical properties of concrete, part ii … • the minimum compressive, splitting tensile, and flexural strength was found to be 4.9mpa, 0.6mpa, and 1.2 mpa in the case of nfc with 5mm-4mm aggregate gradation, 1:6 c-a proportion at 0.5 w/c ratio. • a difference of 30%, 35% and 10% was observed between the maximum and minimum compressive, splitting tensile, and flexural strength respectively of nc due to variation in aggregate gradations. • nc produced with 20mm-4mm gradation mix proportion 1:2:4 at 0.5 w/c ratio exhibited the highest compressive, splitting tensile, and flexural strength of 30.4mpa, 3.4mpa, and 3.8mpa, respectively. • the minimum compressive, splitting tensile, and flexural strength of nc was found to be 4.9mpa, 0.6mpa, and 1.2mpa when using 5-4mm aggregate gradation, 1:2:4 mix proportion at 0.5 w/c ratio. • the unit weight of nfc was found to be marginally affected by the variation in aggregate gradation, c-a proportion and w/c ratio. • the maximum difference between the minimum and maximum unit weight (1687kg/m 3 and 1891kg/m 3 ) was found to be only about 10%. • the unit weight of nc was found not to be marginally affected by the variation in aggregate gradation, c-a proportion and w/c ratio. • in nc the maximum difference between the minimum and maximum unit weight (2339kg/m 3 and 2445kg/m 3 ) was found to be only about 4%. based on the results of the experimental study conducted and the discussions and conclusions made above it may be concluded that while producing nfc, the aggregate gradation, c-a proportion, and w/c ratio may be chosen appropriately particularly when the compressive strength is the major parameter of consideration. however, to a limited extent, unit weight and apparent texture also depend upon these factors. acknowledgment the authors are grateful to the quaid-e-awam university of engineering, science and technology, nawabshah for providing the research facilities. references [1] m. r. lomte, “a review on study and analysis of strength, permeability and void ratio of pervious concrete”, international journal for research in applied science & engineering technology, vol. 6, no. 1, pp. 1717-1720, 2018 [2] s. ali, s. kacha, “correlation among properties of no fines concrete – a review”, national conference on applications of nano technology in civil engineering, vadodara, india, february, 2017 [3] g. yuvaraj, k. sundaravadivelu, p. vembuli, r. shankaranarayanan, e. ramya, “a study on compressive strength of pervious concrete by varying the size of aggregate”, international journal of engineering science and computing, vol. 7, no. 4, pp. 10149-10152, 2017 [4] g. divya, l. reena, “an experimental stduies on behaviour of pervious concrete by using addition of admixtures”, international research journal of engineering and technology, vol. 4, no. 4, pp. 2366-2370, 2017 [5] u. m. muthaiyan, “studies on the properties of pervious fly ash–cement concrete as a pavement material”, cogent engineering, vol. 4, no. 1, article id, 1318802, pp. 1-17, 2017 [6] k. b. thombre, a. b. more, s. r. bhagat, “investigation of strength and workability in no-fines concrete”, international journal of engineering research & technology, vol. 5, no. 9, pp. 390-393, 2016 [7] k. r. balsaraf, d. r. kurhade, k. a. varpe, n. s. lohote, d. s. mehetre, “a review paper on no fines concrete”, international journal of engineering sciences & management”, vol. 7, no. 1, pp. 293-303, 2017 [8] p. p. pragnya, k. b. parikh, a. r. darji, “a review on experimental investigation of pervious concrete using alternate materials”, journal of emerging technologies and innovative research, vol. 4, no. 3, pp. 68-70, 2017 [9] c. h. s. priyanka, “experimental analysis on high strength pervious concrete”, international journal of advances in mechanical and civil engineering, vol. 4, no. 2, pp. 9-13, 2017 [10] w. t. kuo, c. c. liu, d. s. su, “use of washed municipal solid waste incinerator bottom ash in pervious concrete”, cement and concrete composites, vol. 37, pp. 328-335, 2013 [11] b. alam, m. javed, q. ali, n. ahmad, m. ibrahim., “mechanical properties of no-fines bloated slate aggregate concrete for construction application, experimental study”, international journal of civil and structural engineering, vol. 3, no. 2, 2012 [12] a. cheng, h. m. hsu, s. j. chao, k. l. lin, “experimental study on properties of pervious concrete made with recycled aggregate”, international journal of pavement research and technology, vol. 4, no. 2, pp. 104-110, 2011 [13] a. k. jain, j. s. chouhan, “effect of shape of aggregate on compressive strength and permeability properties of pervious concrete”, international journal of advanced engineering research and studies, vol. 1, no. 1, pp. 120-126, 2011 [14] z. a. tunio, t. ali, a. s. buller, f. u. r. abro, m. a. abbasi, “influence of coarse aggregate gradation on the mechnical properties of concrete, part i: no-fines concrete”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4612-4615, 2019 [15] m. kovac, a. sicakova, “pervious concrete as a sustainable solution for pavements in urban areas”, environmental engineering 10th international conference, vilnius, lithuania, april 27-28, 2017 [16] m. a. memon, m. a. bhutto, n. a. lakho, i. a. halepoto , a. n. memon, “effects of uncrushed aggregate on the mechanical properties of no-fines concrete”, engineering, technology & applied science research, vol. 8, no. 3, pp. 2882-2886, 2018 [17] i. barisic, m. galic, i. n. grubesa, “pervious concrete mix optimization for sustainable pavement solution”, iop conference series: earth and environmental science, vol. 90, article id 012091, 2017 [18] a. alam, s. naz, “experimental study on properties of no-fine concrete”, international journal of informative & futuristic research, vol. 2, no. 10, pp. 3687-3694, 2015 microsoft word 19-3378_s_etasr_v10_n2_pp5448-5451 engineering, technology & applied science research vol. 10, no. 2, 2020, 5448-5451 5448 www.etasr.com bheel et al.: use of marble powder and tile powder as cementitious materials in concrete use of marble powder and tile powder as cementitious materials in concrete naraindas bheel department of civil technology h.c.s.t. hyderabad, sindh, pakistan naraindas04@gmail.com karam ali kalhoro department of civil technology h.c.s.t. hyderabad, sindh, pakistan kalhorokaramali@gmail.com tarique aziz memon department of civil technology h.c.s.t. hyderabad, sindh, pakistan memon1972@gmail.com zain-ul-zaheer lashari department of civil technology h.c.s.t. hyderabad, sindh, pakistan zain.lashari@yahoo.com mushtaq ahmed soomro department of civil technology h.c.s.t. hyderabad, sindh, pakistan soomromushtaque0@gmail.com uzair ahmed memon department of civil technology h.c.s.t. hyderabad, sindh, pakistan uzairsahib60@gmail.com abstract—the use of agricultural and industrial waste products as raw materials in the construction industry is investigated extensively. these products are inexpensive and help in environmental sustainability, as environmental pollution is thus reduced. this study focused in investigating the properties of fresh, physical and hardened concrete blended with marble (mp) and tile powder (tp) of several proportions, such as 0%, 5% (2.5%mp + 2.5%tp), 10% (5%mp + 5%tp), 15% (7.5%mp + 7.5%tp), and 20% (10%mp + 10%tp) by weight. a total of 60 concrete cylinders were cast with 0.45 water/cement ratio, 1:1.96:2.14 mix ratio, and were cured for 7 and 28 days. these cylinders were used for checking the compressive and splitting tensile strength of concrete. the experimental results showed that compressive and splitting tensile strengths were increased by 8.90% and 8.30% respectively for the 2.5%mp + 2.5%tp sample after 28 days. keywords-marble powder; tile powder; utilizing waste products; reducing environmental pollution; increasing strength of concrete i. introduction cement concrete is a widely used material in constructions [1]. concrete consists of paste and aggregates. the paste consists of water and cement, while the aggregates consist of sand and coarse aggregates, with cement being the most important component, which in contact with water forms a paste, binding the aggregates together into a solid mass [2, 3]. cement production emits large amounts of co2, which has adverse effects on the environment [4]. the production of 1 ton of cement emits 1-1.25 tons of co2, contributing significantly to global warming. thus, for environmental protection, immediate action is required to minimize the production and use of cement [5-9]. many methods have been proposed on the use of industrial or agricultural waste as partial cement substitutes [10]. industrial waste includes waste from marble powder, blast furnace slag, tile powder [11], fly ash and silica fume, while agricultural waste includes rice husk ash [12, 13], corn cob ash [14], wheat straw ash, ground coal bottom ash [15, 16], coconut waste, and bagasse ash, which are used to replace partially the cement in concrete [17, 18]. the use of these wastes as substitutes for cement not only reduces the cost of concrete, but it also minimizes the negative environmental impacts associated to their disposal, and the release of co2 during cement production [19, 20]. marble powder is a by-product of the marble industry. sludge or wet powder is formed during polishing, finishing and cutting marble stone. fine marble powder, left after processing, polishing, and cutting of marble, is poured into landfills, catchment areas, rivers, dead wells and seasonal rivers, affecting negatively the soil, reducing soil fertility, and subsequently annual crop yield [21-24]. marble waste mainly consists of boulders, which are used as aggregates, and fine powder which is dumped. waste marble powder utilization could reduce environmental degradation and co2 emissions from cement production [25, 26]. about 100 million tons of tiles are produced annually. the 15-30% of the total tile production is converted into waste, without processing. tile powder utilization has many advantages, such as energy saving, cost and environmental risk reduction [29]. tile waste could be utilized in concrete to enhance some of its properties, such as strength. the construction industry could consume waste tile powder, helping to solve this environmental problem [27, 28]. many studies have been conducted on the use of tile by-products in concrete to increase its effectiveness [30, 31]. the current study investigated the properties of fresh, physical and hardened concrete, blended with several percentages of marble powder (mp) and tile powder (tp) as partial substitutes of cement in concrete. ii. research methodology this study’s purpose was to investigate and evaluate the properties of fresh, physical and hardened concrete, by using 0%mp + 0%tp, 2.5%mp + 2.5%tp, 5%mp + 5%tp, 7.5%mp + 7.5% tp, and 10%mp + 10%tp as partial substitutes of cement in concrete. sixty concrete cylinders were cast, with mix ratio of 1:1.96:2.14, at 0.45 water/cement ratio (w/c). after casting, all specimens were kept in a curing tank, corresponding author: naraindas bheel engineering, technology & applied science research vol. 10, no. 2, 2020, 5448-5451 5449 www.etasr.com bheel et al.: use of marble powder and tile powder as cementitious materials in concrete and they were tested after 7 and 28 days in a universal testing machine (utm). standard cylinders, with 4in diameter and 8in height, were used for casting the specimens, under the astm c 192 code procedure. these concrete cylinders were used to obtain compressive and indirect tensile strengths. moreover, concrete samples were tested for density and water absorption after 28 days. three concrete samples were cast for each ratio, and the final result was considered as their mean. this study was conducted in the laboratory of concrete technology, in h.c.s.t. hyderabad, sindh, pakistan. table i. concrete mixes iii. materials used a. cement the cement used was ordinary portland, cement locally available in the market of hyderabad, sindh, pakistan. the experimental results of cement are shown in table ii. table ii. physical properties of cement b. fine and coarse aggregates the aggregates used are locally available in the region of hyderabad. hill sand was used as fine aggregate (fa). it was passed through #4 sieves, and 20mm crushed stone was used as coarse aggregates (ca). the properties of the laboratory test results of the aggregates are shown in table iii. table iii. properties of aggregates s.no properties fa ca 01 fineness modulus 2.80 -- 02 water absorption 1.10% 0.75% 03 specific gravity 2.61 2.65 04 bulk density 128lb/ft 3 106lb/ft 3 c. marble powder (mp) mp was collected from the region of hyderabad. after its collection, it was sieved through #300 sieves and could be utilized as partial substitute of cement in the mix concrete. d. tile powder (tp) tile powder was collected from the region of hyderabad, it was sieved through #300 sieves in order to be used as partial cement replacement in concrete mixes [11]. iv. results and discussions a. workability of fresh concrete fresh concrete was measured for workability in terms of slump losses. as shown in figure 1, slump value improves as marble powder and tile powder increases, as in [11]. it was observed that the demand of water in the concrete mix declined as the amount of mp and tp increased. the slump value was increased at 3in on the 10%mp + 10tp, while the minimum recorded value was 1.6in on the control sample. fig. 1. slump test b. density of concrete the concrete specimens were used to analyze the density of the hardened concrete. figure 2 indicates that the density of the conventional concrete is greater than of the mixes produced with various proportions of mp and tp. the density value of the control mix was 144.90lb/ft 3 , while a minimum density value of 140lb/ft 3 was noticed on the 10%mp + 10%tp sample. density reduced as mp and tp increased. fig. 2. density of concrete c. water absorption of conctrete water absorption of the hardened concrete specimens was measured. figure 3 shows that the water absorption is greater mix id rha + fa (%) f.a & ca (%) cement (%) mix ratio w/c ratio 01 0%mp+0%tp 100 100 1.1.96:2.14 0.45 02 2.5%mp+2.5%tp 100 95 1.1.96:2.14 0.45 03 5%mp+5%tp 100 90 1.1.96:2.14 0.45 04 7.5%mp+7.5%tp 100 85 1.1.96:2.14 0.45 05 10%mp+10%tp 100 80 1.1.96:2.14 0.45 s. n. tests results 01 normal consistency 30% 02 initial setting time 48min 03 final setting time 240min 04 specific gravity 3.15 engineering, technology & applied science research vol. 10, no. 2, 2020, 5448-5451 5450 www.etasr.com bheel et al.: use of marble powder and tile powder as cementitious materials in concrete on the conventional concrete than the mixes prepared with various proportions of mp and tp. the water absorption of the control mix was 3.41%, while the lowest (2.87%) was measured on the 10%mp + 10%tp sample. water absorption value reduced as the content of mp and tp increased. fig. 3. water absorption of concrete d. compressive strength of concrete the cylindrical samples were used for investigating the compressive strength of the concrete blended with several ratios of mp and tp. figure 4 shows that maximum compressive strength was improved by 0.6% and 8.9% on the 2.5%mp + 2.5%tp sample, while it reduced about 17.9% and 8.95% on the 10%mp + 10%tp sample, after 7 and 28 days respectively. this trend was also noted in [32]. fig. 4. compressive strength of concrete e. indirect tensile strength of concrete the cylinder specimens were tested on a utm for discovering their tensile strength, following the astm code. figure 5 shows that maximum splitting tensile strength improved by 6.80% and 8.30% on the 2.5%mp + 2.5%tp, while it reduced by 23.40% and 19.60% on the 10%mp + 10%tp sample, after 7 and 28 days respectively. this trend was also noted in [11, 33]. fig. 5. split tensile strength of concrete v. conclusions on the basis of the experimental results obtained, it is concluded that: • the slump value was enhanced for the 10%mp + 10tp, while the minimum slump value was recorded on the control mix. • the water absorption value of the control mix was 3.41%, while the lowest water absorption was 2.87% on the 10%mp + 10%tp mix. • the density value of the control mix was 144.90lb/ft 3 , while the minimum density value was 140lb/ft 3 on the 10%mp + 10%tp mix. • maximum compressive strength increased by 0.6% and 8.9% on the 2.5%mp + 2.5%tp mix, while it reduced by 17.9% and 8.95% on the 10%mp + 10%tp mix, after 7 and 28 days respectively. • maximum splitting tensile strength increased by 6.80% and 8.30% on the 2.5%mp + 2.5%tp mix, while it reduced by 23.40% and 19.60% on the 10%mp + 10%tp mix, after 7 and 28 days respectively. vi. future work the use of chemical admixtures along with marble and tile powder may give better results and reduce cost in construction works, so in the future this prospect should be investigated. references [1] n. gautam, v. krishna, a. srivastava, “sustainability in the concrete construction”, international journal of environmental research and development, vol. 4, no. 1, pp. 81-90, 2014 [2] a. manimaran, m. somasundaram, p. t. ravichandran, “experimental study on partial replacement of coarse aggregate by bamboo and fine aggregate by quarry dust in concrete”, international journal of civil engineering and technology, vol. 8, no. 8, pp. 1019-1027, 2017 [3] k. krizova, p. novosad, t. jarolím, “production of self compacting concrete scc with portland and blended cement cem i, cem ii with fly ash and limestone admixtures”, advanced materials research, vol. 1124, pp. 45-50, 2015 [4] s. a. mangi, m. h. w. ibrahim, n. jamaluddin, m. f. arshad, f. a. memon, r. p. jaya, s. shahidan, “a review on potential use of coal engineering, technology & applied science research vol. 10, no. 2, 2020, 5448-5451 5451 www.etasr.com bheel et al.: use of marble powder and tile powder as cementitious materials in concrete bottom ash as a supplementary cementing material in sustainable concrete construction”, international journal of integrated engineering, vol. 10, no. 9, pp. 28-36, 2018 [5] s. a. abdullah anwar, s. mohd, a. husain, s. a. ahmad, “replacement of cement by marble dust and ceramic waste in concrete for sustainable development”, international journal of innovative science, engineering and technology, vol. 2, no. 6, pp. 496-503, 2015 [6] a. d. sakalkale, g. d. dhawale, r. s. kedar, “experimental study on use of waste marble dust in concrete”, international journal of engineering research and applications, vol. 4, no. 10, pp. 44-50, 2014 [7] r. siddique, “performance characteristics of high-volume class f fly ash concrete”, cement and concrete research, vol. 34, no. 3, pp. 487-493, 2004 [8] v. m. 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research in applied science and engineering technology, vol. 5, no. 3, pp. 473-479, 2017 [31] s. aswin, v. mohanalakshmi, a. a. rajesh, “effects of ceramic tile powder on properties of concrete and paver block”, global research and development journal for engineering, vol. 3, no. 4, pp. 84–87, 2018 [32] h. s. arel, “re-use of waste marble in producing green concrete”, international journal of civil and environmental engineering, vol. 10, no. 11, pp. 1377-1386, 2016 [33] b. p. r. v. s. priyatham, d. v. s. k. chaitanya, b. dash, “experimental study on partial replacement of cement with marble powder and fine aggregate with quarry dust”, international journal of civil engineering and technology, vol. 8, no. 6, pp.774-781, 2017 microsoft word 28-3674l_s_etasr_v10_n4_pp6047-6051 engineering, technology & applied science research vol. 10, no. 4, 2020, 6047-6051 6047 www.etasr.com samo et al.: determination of potential tidal power sites at east malaysia determination of potential tidal power sites at east malaysia kamran ahmed samo department of electrical engineering quaid-e-awam engineering, science and technology larkana, pakistan kamransamo2@gmail.com zafar ali siyal department of energy and environment engineering quaid-e-awam engineering, science and technology nawabshah, pakistan zafarsiyal@quest.edu.pk imran ahmed samo chemical resource engineering department beijing university of chemical technology beijing, china imran.samo@yahoo.com andrew ragai henry rigit mechanical engineering department universiti malaysia sarawak kota samarahan, malaysia arigit@unimas.my abstract—tidal range energy is one of the most predictable and reliable sources of renewable energy. this study’s main aim is to determine potential sites for tidal range power in east malaysia, by analyzing tidal range distributions and resources and the feasibility of constructing barrages. investigation was conducted in 34 sites, estimating their potential energy outputs and studying their areas for constructing barrages. only 18 sites were marked as appropriate for constructing a tidal range energy extraction barrage. the highest potential power was found in tanjung manis, and its maximum capacity was calculated as 50.7kw. the second highest potential of tidal power extraction was found in kuching barrage at pending, where an energy harvester could produce electric power up to 33.1kw. keywords-tidal range; renewable energy; potential site; power; east malaysia i. introduction oceans possess a huge potential to generate electric power [1]. generating electricity from ocean power can offer many advantages compared to other renewable energy sources [2]. ocean power is a vast and comparatively reliable source. thermal power can be harvested from oceans by the temperature difference of warm shallow and deeper cold waters, and kinetic power can be harvested from tides, waves, and streams. salinity gradient power is the energy extracted by the difference in the salt concentration between sea and river water. although malaysia is located in the equatorial zone surrounded by sea, this ocean power has not attracted much attention by the local government [3]. the country’s total coastline is 4,675km, west and east malaysia have 2,068km and 2,607km of coastline respectively [4]. the long length of malaysia’s coastline is a huge advantage in utilizing tidal range energy as a reliable alternative energy source [5]. ii. literature review α potential site can be determined by the maximum available tidal energy. the east coast of malaysia, was studied in [6] where four areas with high exploitable tidal water energy were determined. data for potential energy production at the east coast of peninsular malaysia, covering kelantan and terengganu regions, were obtained from malaysia meteorology department (mmd), department of mapping and survey, and national hydrographic centre, while potential regions were determined through gis. tidal power derives from the tidal range, as the water is confined in a basin during a high tide, and it runs out through a turbine at low tide [7-9]. the energy extracted from a tidal barrage can be calculated by considering the tidal range of water, as: � = ℎ × � × � (1) where e is the potential energy (j), h is the tidal range (m), ρ is the water density (1025kg/m3), and g is the gravitational force (9.81m/s2). generated power can be calculated, concerning the space of barrage and tidal ocean as: � = ( ×( ×�)× ) � (2) where, e is the potential energy (j), a is the barrage area (m2), h is the tidal range (m), and t is the duration in one day (s). the width of the river site was assumed to be about 200m and the area of the tidal barrage was about 200×200m [6]. the barrage area was considered using data from the department of irrigation and the department of drainage in malaysia [6]. a graph of the optimum upper limit of power generated per month, created at tanjung berhala, terengganu, is shown in figure 1. data were analyzed by month, and the maximum daily power was considered. corresponding author: kamran ahmed samo engineering, technology & applied science research vol. 10, no. 4, 2020, 6047-6051 6048 www.etasr.com samo et al.: determination of potential tidal power sites at east malaysia according to figure 1 the produced power’s upper limit was between 90kw and 203kw. fig. 1. optimum upper limit of power generated per month of 2006 – © tanjung berhala, terengganu [6] the method presented in [6] was utilized with minor differences in this study, in order to calculate the power of the tidal range sites. water mass was replaced by water density in (1), and as this research deals with one-way instead of two-way generation, 2 is used instead of 4 in (2). potential energy based on tidal range can be calculated by (1), while the power output can be calculated by (2). this study considered four different areas in east coast of malaysia, and the resources of tidal range power at 34 sites of sabah and sarawak coastline were examined, as suggested in [6, 10]. those chosen 34 areas were measured using google maps, in order to determine the feasibility of a barrage construction. iii. methodology figure 2 shows a data flow diagram of this research method, including determination of sites, data analysis, power output calculation, and map production using google maps. in [6], power output was calculated for four sites using data from 2006 and 2007. this study calculated the power output of 34 sites using data from 2015. previous researchers [6, 11] assumed the barrage area of their studied sites at 200×200m, while this research uses their actual area, except the already constructed kuching barrage at pending. fig. 2. flow chart of the proposed methodology. a. available resources tidal range data of 2015 were acquired from sarawak marine department (smd). these data included tables, namely sarawak hourly high and low tide tables, and nautical charts. google maps were used to measure the area and produce maps to show the position of tidal range sites. sigma software was used for data analysis. matlab was used for producing graphs of tidal range potential sites. equations (1) and (2) were used for calculating maximum power. some preferable sites are in the sea while others are located inland. b. navigational charts navigational charts detail the physical features of the sites, depth of sea water in meters, and nearby land information. coordinates acquired from satellite navigation systems, such as global positioning system (gps) using world geodetic system (wgs) 1984 datum can be plotted directly on these charts [12]. c. calculating available energy resources the determination of possible tidal range sites was performed after analyzing tidal range energy resources. low and high tide data were acquired from [13]. the barrage areas were assumed measuring area’s width on google maps. equations (1) and (2) were used to calculate the power output of each site. d. calculation of power output for tidal range sites calculations were performed after examining each site’s hourly tide tables. water’s tidal range influences the potential power output from the barrage, as noted in (1) and (2). figure 3 shows the calculation procedure flow chart. fig. 3. flow chart of calculated power output for 34 tidal range sites. power can be generated through a barrage. a barrage exists already at pending, named kuching barrage. therefore, the actual area was used for calculating the power engineering, technology & applied science research vol. 10, no. 4, 2020, 6047-6051 6049 www.etasr.com samo et al.: determination of potential tidal power sites at east malaysia output of kuching barrage, and the estimated area using google maps was used for calculating the potential power output of the other 33 sites. in [6, 14], two-way power generation was utilized. however, this research deals with only one-way generation, like the kuching barrage, as some sites are also on a river mouth without any prominent basin. table i depicts the 34 tidal range sites with their coordinates. table i. research sites no sites latitude (n) longitude (e) 1 sematan 01 47 109 47 2 pasarlundo 01 40 109 51 3 kuala santubong 01 43 110 19 4 pending 01 33 110 23 5 muaratebas 01 38 110 28 6 pulaulakei 01 45 110 30 7 sri aman 01 14 111 27 8 kuala rajang 02 09 111 15 9 tanjung manis 02 09 111 22 10 sarikei 02 08 111 37 11 bintangor 02 10 112 38 12 lebaan (tanjungensurai) 02 19 111 40 13 sibu 02 17 111 49 14 kanowit 02 06 112 09 15 kuala paloh 02 25 111 15 16 kuala igan 02 48 111 43 17 kuala mukah 02 54 112 05 18 kuala balingian 03 00 112 35 19 kuala tatau 03 04 112 48 20 kuala kemena 03 10 113 02 21 bintulu port 03 16 113 04 22 miri 02 24 113 59 23 kuala baram 04 35 113 59 24 miri port 04 34 114 02 25 kuala limbang 04 51 115 01 26 bandar limbang 04 44 115 00 27 kuala lawas 04 57 115 25 28 bandar lawas 04 15 115 23 29 labuan faderal territory 05 17 115 15 30 kota kinabalu 05 59 116 04 31 kudat 06 52 116 50 32 sandakan 05 48 118 04 33 lahaddatu 05 01 118 20 34 tawau 04 14 117 53 e. calculation of areas the areas of 33 tidal range sites and the river were measured using google maps. the width of barrage gates, piers and service structure was assumed by taking the fixed width of each gate of the barrage as 25m, the pier as 4m, and the barrage length as 37m, similarly to the ones already constructed on kuching barrage. measurement techniques are shown in figure 4 which shows the typical cross-section of the proposed barrage. given the preliminary width, the number of gates was decided. the width of the ship lock was also defined as 25m. after deciding the effective width, which is the sum of all gates, piers and ship lock, the remaining space was used for service structures or abutments. f. potential sites the selection of appropriate potential sites should take into account the maximum available energy and an environmental impact assessment (eia) study [15]. a thorough eia study is required on these potential sites, something that is beyond the scope of this study. the potential sites should be free from security (navigational police) and should not obstruct the commercial shipping line. fig. 4. measurement techniques calculating proposed barrage’s width. iv. results and discussion a. calculated areas of tidal range sites the width of a river or stream varies across different locations. so after selecting the best possible width of gates and piers, the remaining width was considered for constructing abutment and service buildings. it was also observed that some locations are not appropriate for constructing a barrage for power generation. the proposed barrages were based on the constructed kuching barrage at pending. table ii shows the calculations for the january power output of the kuching barrage. the first three columns show the data variables of (1), column 4 shows the potential energy, power output is shown in column 5 by using (2), and column 6 shows power in kilowatts. power output was calculated in a daily basis for all tidal range sites. in table ii, a represents the barrage area, and h is the tidal range calculated from high and low tide data [13]. b. extractable energy at tidal range sites the potential extractable energy of the 34 tidal range sites in sabah and sarawak coastline was calculated. it was concluded that only 18 of them are appropriate for power generation. figure 5 shows the potential power output of the 18 main potential sites. the highest potential power was noted in tanjung manis in the sarawak region, measured between 50.7kw and 39.2kw. results showed that maximum power was observed in january and october, while minimum was observed in june. the second highest power was calculated at pending, being between 33.1kw and 25.1kw. the maximum power was observed in october, while the minimum was observed in june. the kuala kemena in sarawak region was identified as the least potential site, as its potential power was calculated between 1.9kw to 0.9kw. the maximum potential energy of kuala kemena was calculated during july and december, while the engineering, technology & applied science research vol. 10, no. 4, 2020, 6047-6051 6050 www.etasr.com samo et al.: determination of potential tidal power sites at east malaysia minimum was found in january and september. the greater power values in [6] are explained by the two-way power generation, the areas defined as 200×200m, and the variations in yearly tidal ranges. table ii. calculation of power output of pending site h p g e p kw 3.6 1025 9.81 36198.9 11161.3275 11.2 3.9 1025 9.81 39215.475 13099.05797 13.1 4.3 1025 9.81 43237.575 15923.83839 15.9 4.7 1025 9.81 47259.675 19024.20714 19.0 4.9 1025 9.81 49270.725 20677.73714 20.7 4.9 1025 9.81 49270.725 20677.73714 20.7 4.9 1025 9.81 49270.725 20677.73714 20.7 4.7 1025 9.81 47259.675 19024.20714 19.0 4.4 1025 9.81 44243.1 16673.09417 16.7 4.1 1025 9.81 41226.525 14476.99964 14.5 3.6 1025 9.81 36198.9 11161.3275 11.2 3.2 1025 9.81 32176.8 8818.826667 8.8 2.7 1025 9.81 27149.175 6278.246719 6.3 2.6 1025 9.81 26143.65 5821.803542 5.8 2.7 1025 9.81 27149.175 6278.246719 6.3 2.6 1025 9.81 26143.65 5821.803542 5.8 3.2 1025 9.81 32176.8 8818.826667 8.8 3.9 1025 9.81 39215.475 13099.05797 13.1 4.7 1025 9.81 47259.675 19024.20714 19.0 5.3 1025 9.81 53292.825 24191.48839 24.2 5.8 1025 9.81 58320.45 28971.22354 29.0 6.0 1025 9.81 60331.5 31003.6875 31.0 6.0 1025 9.81 60331.5 31003.6875 31.0 5.9 1025 9.81 56309.4 27007.65667 27.0 5.0 1025 9.81 50276.25 21530.33854 21.5 4.2 1025 9.81 42232.05 15191.80688 15.2 3.8 1025 9.81 38209.95 12435.92354 12.4 3.4 1025 9.81 34187.85 9955.628542 10.0 3.0 1025 9.81 30165.75 7750.921875 7.8 3.2 1025 9.81 32176.8 8818.826667 8.8 3.5 1025 9.81 35193.375 10549.86589 10.5 fig. 5. potential power of 18 main sites of sarawak coastline malaysia. figure 6 shows the location of 18 tidal range potential sites in a map generated by google maps. the locations of the maximum potential power sites (i.e. tanjung manis site and pending site) are shown in figure 6 as numbers 4 and 7. figure 7 shows the maximum and minimum of potential energy for the 18 sites, while table iii shows their mean tidal range and maximum and minimum potential power. fig. 6. position of 18 potential sites, © google maps, terrametrics . fig. 7. max/min potential power in convenient tidal range sites. table iii. tidal range mean and max/min power per site no sites tidal range mean (m) pmax (kw) pmin (kw) 1 sematan 3.0 12.5 9.8 2 pasarlundo 2.9 10.3 8.4 3 kuala santubong 3.3 21.5 15.9 4 pending 4.2 33.1 25.1 5 sri aman 2.9 15.9 10.0 6 kuala rajang 3.8 27.5 20.7 7 tanjung manis 4.0 50.7 39.2 8 sarikei 3.9 19.5 15.5 9 bintangor 3.8 17.4 14.5 10 lebaan (tanjungensurai) 3.0 27.9 6.6 11 sibu 2.0 5.4 4.2 12 kuala paloh 3.0 21.8 3.9 13 kuala igan 1.6 6.8 4.2 14 kuala mukah 1.4 2.8 1.7 15 kuala kemena 1.0 1.9 0.9 16 kuala limbang 1.4 2.3 1.1 17 bandar limbang 1.3 1.9 0.8 18 kuala lawas 1.3 1.9 1.0 c. selection of suitable site a total of 18 tidal range sites seem to be suitable for power generation. as ranges differ in all these tidal range sites, sites with larger tides generate more power compared to sites with lower. these sites were assumed preliminary, engineering, technology & applied science research vol. 10, no. 4, 2020, 6047-6051 6051 www.etasr.com samo et al.: determination of potential tidal power sites at east malaysia the final sites should be selected after a thorough feasibility study. however, as kuching barrage constructed at pending has a strong potential for power generation, an energy harvester could be installed for extracting energy [16]. v. conclusion this research studied the potential energy generation in 34 sites in east malaysia, pinpointing 18 locations as suitable for the construction of a energy generation barrage. however, these sites were assumed as preliminary, as the final sites should be selected after a thorough feasibility study. two sites were considered as having the highest potential. the maximum calculated power sites are the tanjung manis and the pending site. the highest energy potential was calculated to come from tanjung manis and was measured between 50.7kw and 39.2kw, while the second highest power was calculated for pending, between 33.1kw and 25.1kw. however, there is already an existing barrage at pending site, and this is the only site where power could be generated by just installing turbines. references [1] a. s. bahaj, “generating electricity from the oceans,” renewable and sustainable energy reviews, vol. 15, no. 7, pp. 3399–3416, sep. 2011, doi: 10.1016/j.rser.2011.04.032. 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[15] a. a. mahessar, a. n. laghari, s. qureshi, i. a. siming, a. l. qureshi, and f. a. shaikh, “environmental impact assessment of the tidal link failure and sea intrusion on ramsar site no. 1069,” engineering, technology & applied science research, vol. 9, no. 3, pp. 4148–4153, jun. 2019. [16] m. l. tuballa and m. l. s. abundo, “operational impact of res penetration on a remote diesel-powered system in west papua, indonesia,” engineering, technology & applied science research, vol. 8, no. 3, pp. 2963–2968, jun. 2018. microsoft word 30-2720_s_etasr_v9_n3_pp4230-4234 engineering, technology & applied science research vol. 9, no. 3, 2019, 4230-4234 4230 www.etasr.com winanri et al : comparison analysis between traditional contracts and long segment contracts ... comparison analysis between traditional and long segment contracts on national road preservation activities in indonesia riliane prima winanri department of civil engineering, sriwijaya university, palembang, indonesia riliane.pw@gmail.com betty susanti department of civil engineering, sriwijaya university, palembang, indonesia b_susanti@yahoo.com ika juliantina department of civil engineering, sriwijaya university, palembang, indonesia ikawig@yahoo.com abstract—national road preservation activities in indonesia are usually carried out using a traditional approach system, namely in-house system and contract system with a design-bid-build (dbb) approach. an alternative contract method to improve the quality of roads is the long segment contract. its definition is carrying out road preservation activities in one continuous segment with the aim to obtain good road conditions for all segments. this study aims to compare the performance under traditional approaches and long segment contracts. road performance is expressed in functional performance terminology and uses the international roughness index (iri) indicator. the research was conducted on the outer urban road of palembang indralaya intersection meranjat which is part of the national road section in the province of south sumatra, indonesia. results showed that the road performance contracted with traditional approaches was better than that of long segment ones. this was not expected and was probably due to the lack of understanding of the parties involved in the long segment contract to the principles of fulfilling road service performance. the contractors are not interested in carrying out routine road maintenance projects because the value of the work is small and there is a lack of experience regarding routine maintenance. keywords-traditional contracts; long segment contracts; iri values i. introduction road preservation is generally carried out in traditional approach systems, namely in-house and contract system with dbb delivery approach [1]. the contract is an integral part of the project delivery. in order to improve road quality, an alternative contract method is required which will include considerations of performance aspects, such as guaranteed contracts, performance-based contracts (pbc), and long road maintenance contracts (long segment maintenance contracts) or long segment contracts. there are difficulties in implementing pbc pilot projects in indonesia. the challenges of implementing pbc start from the procurement stage to implementation [2, 3]. the supreme audit agency (bpk) recommended that pbc implementation should be reviewed, because bpk cannot measure the effectiveness of using public funds based on performance measures as required in pbc. bpk always applies a volume-based measurement system for all uses of these public funds. consequently, applying long segment contracts is an alternative way to overcome these difficulties. traditional approaches with both in-house and contract-based systems in the implementation of road construction have not been oriented to better cost, time and project quality [4]. authors in [5] stated that contracts with traditional approaches have some difficulties in effectively managing quality, time and costs. meanwhile, poor work quality will have an impact on the road service life which will become shorter and will result in high road maintenance costs [6]. the weakness of traditional contracts is that they are not oriented towards the aspects of road performance and cost, concerning their lack of efficiency on road maintenance costs. this condition favors the implementation of long segment contracts since they are oriented towards those two aspects. in 2016, long segment contracts started to be implemented for road preservation on several national roads in indonesia. the aim was to obtain good road conditions for all segments. based on the background, a problem was formulated on comparing the performance of roads on preservation activities between traditional approaches and long segment contracts. the scope of the analysis was based on the assessment of the functional conditions of the road using the iri. the results of preservation activities under traditional approaches and long segment contracts were compared. as a final outcome, challenges and opportunities for the implementation of long segment contracts occurred as a consideration for road managers in road preservation programs. ii. literature review a. road maintenance contract road maintenance contract is one of the contract forms in the implementation of construction work. based on the government regulation of the republic of indonesia number 29 of 2000 on the implementation of construction services, the construction work contract is divided into three forms, namely compensation types, duration of construction work, and method of payment. the contract is inseparable from its project delivery. project delivery method is a project implementation corresponding author: b. susanti engineering, technology & applied science research vol. 9, no. 3, 2019, 4230-4234 4231 www.etasr.com winanri et al : comparison analysis between traditional contracts and long segment contracts ... method approach designed to define relationships, roles and responsibilities of the parties involved in each stage of the project to achieve the objectives. 1) traditional road maintenance contracts in road maintenance, there are two traditional approaches, namely in-house system and contract system with a dbb delivery approach [1]. in-house is applied for routine maintenance work, while the input-based contract system with dbb delivery approach or traditional contract system is applied for periodic maintenance work and road improvement. authors in [7] state that traditional contract is a form of construction work contract based on the division of tasks aspects. the contract agency assigns the contractor to carry out one of these jobs: planning, supervision, or implementation. in-house is a form of construction work contract based on the aspect of job division. however in-house is not a form of contract since it is the implementation of work planned, carried out, and selfmonitored without buying it up to contractor [7]. the weakness of traditional approach systems is that they have some difficulties in effectively managing quality, time and costs. poor work quality will have an impact on the road service life which will become shorter and results in high road maintenance costs. 2) long segment contract one way to overcome the problem of low road quality is the application of alternative contracting methods, ones that consider the performance aspects of the work results. the alternative contract methods include guaranteed contracts, pbc, and long segment contracts. based on the circular of the directorate general of bina marga number 09/se/db/2015 on the implementation of procurement process and work on road preservation in long segment, the definition of long segment is road preservation activities in one continuous segment (can be more than one roads) which is carried out with the aim of obtaining the same road conditions, namely a good road condition and meeting standards throughout the segments (the standard is in accordance with [8]. meanwhile, the scope of activities (output) of long segment work includes widening, reconstruction, rehabilitation, and maintenance of roads. based on the delivery approach, long segment contracts are also dbb contracts like traditional contracts, yet have performance as the main aspect and maintenance as the scope of activities. b. road pavement performance pavement performance is a function of the relative ability of pavement to serve traffic in a certain period. the performance of pavement is determined on the requirements of road functional conditions and structural conditions. the structural conditions of the road begin with the condition of the road structural layer and continue to the lower layer, consisting of the road surface layer, upper foundation layer, bottom foundation layer and subgrade. structural pavement performance shows pavement carrying capacity. the measurements use benkelman beam or falling weight deflectometer (fwd) test equipment. the functional condition of the road is the service condition of the road pavement surface for road users in the form of roughness, road surface unevenness that provides comfort, and security for traffic. functional pavement performance is expressed in surface index (si) or present serviceability index (psi), surface distress index (sdi), road condition index (rci), and iri. this study compared the pavement performance based on the assessment of the functional conditions of the road in the form of iri values. iri value is an international index that shows the size describing the value of surface inequality indicated as the cumulative length of surface fluctuation per unit length. iri is expressed in meters per kilometer of the length of the road (m/km). the method for measuring road surface roughness used the national association of australian state road authorities (naasra). the relationship between the iri values and the criteria for road conditions on asphalt roads, panmac roads and land /gravel roads is given in table i. table i. criteria for road conditions based on pavement type condition criteria iri value based on pavement type asphalt road penmac road land /gravel road good iri≤4 iri≤8 iri≤10 medium iri>4 and iri≤8 iri>8 and iri≤10 iri>10 and iri≤12 minor damaged iri>8 and iri≤12 iri>10 and iri≤12 iri>12 and iri≤16 heavy damaged iri>12 iri>12 iri>16 iii. research methodology a. research location this research was conducted in south sumatra province, one of the largest provinces in indonesia and the largest in sumatra. in ogan ilir district, it focused on national road preservation activities conducted by the balai besar pelaksanaan jalan nasional v palembang, covering the outer urban road of palembang-indralaya intersection-meranjat with the segment numbers of 005 and 007. the total length of the sections is 29.05km consisting of the outer urban road of palembang-indralaya intersection of 16.45km and indralaya intersection-meranjat which is of 12.60km long . b. data collection the method of secondary data collection was utilized in this study. the secondary data in this study were the road functional performance data, namely the iri value on the outer urban road of palembang-indralaya intersection-meranjat from 2011 to 2017 derived from the national road planning and monitoring unit (p2jn) of south sumatra province. the data were the iri results at the end of the year of road preservation. the iri values of the traditional approaches were the result of preservation activities under these approaches from 2011 to 2015, while the iri values that showed the functional performance of the road in the long segment contract studied were the results of preservation activities under long segment contracts from 2016 to 2017. the recapitulation of iri values are provided in table ii. regarding data processing and analysis, the performance of road pavements on the outer urban road of palembang-indralaya intersection-meranjat is: • collecting the iri data of 2011 to 2017, namely the iri values per segment of 100 meters on the functional outer engineering, technology & applied science research vol. 9, no. 3, 2019, 4230-4234 4232 www.etasr.com winanri et al : comparison analysis between traditional contracts and long segment contracts ... urban road of palembang-indralaya intersection (16.45km) and indralaya intersection-meranjat (12.60km). • determine the iri values representing the iri values of the road by averaging the iri value per segment: ��� ��� �� ����� � ��.�� ��� ������ ��� ������ ��.�� ������ � !��� "##�$ (1) • comparing the average iri values per year. comparing the iri values of the results of road preservation activities using traditional contracts (from 2011 to 2015) with the iri values resulting from road preservation activities using long segment contracts (from 2016 to 2017). • conducting semi-structured interviews with relevant stakeholders, the owner and the contractor, to strengthen the analysis of the comparison of road pavement performance between traditional contracts and long-segment contracts so that potential benefits could be obtained in implementing long segment contracts. table ii. iri value from 2011 until 2017 road segments iri value year 2011 2012 2013 2014 2015 2016 2017 outer urban road of palembang-indralaya intersection 6.39 4.51 5.01 4.84 3.35 5.05 4.74 indralaya intersectionmeranjat 5.27 4.66 4.23 4.87 2.98 4.81 4.58 c. data analysis iri value data processing was carried out on the outer urban road of palembang-indralaya intersection and the road segments of indralaya intersection–meranjat from 2011 to 2017. iri value data processing on the outer urban road of palembang-indralaya intersection was carried out per road segment. the results were then grouped based on the road conditions along the road given in figure 1. the calculation of the average iri value on a road of 16.45km with 165 segments is as follows: ��� %�� ��� &%'(� � )*+,-# "./ � 5.05 iv. discussion based on the results of data analysis, the comparison outputs of the performance of road pavement between traditional contracts and long segment contracts on outer urban road of palembang-indralaya intersection and road segments of indralaya intersection–meranjat are provided in figures 2 and 3. the iri values of the traditional contracts tended to decrease. in 2016, as the initial year of applying the long segment contract, the iri values on both segments re-increased. in 2017, both iri values decreased again. 2016 was the first year of implementing a long segment scheme and at the same year iri values tended to increase. this is because of the lack of optimal implementation of preservation activities on the scope of long segment contract activities, especially the routine road maintenance activities. fig. 1. strip map of road condition based on the iri values on the outer urban road of palembang-indralaya intersection in 2016 fig. 2. iri value comparison on outer urban road of palembang-indralaya intersection road segments fig. 3. iri calue comparison on indralaya–meranjat road segments 02+000 03+000 # # # # # # # # # # # # # # 03+000 04+000 05+000 06+000 # # # # # # # # # # # # # # # # # # 06+000 07+000 08+000 09+000 # # # # 09+000 10+000 11+000 12+000 # # # # # # # # # 12+000 13+000 14+000 15+000 # # # # # # # # # # # # # # # # # 15+000 # # # good = km = medium = km = minor damaged = km = heavy damaged = km = the total length = km = 38.91% 00+000 0.61% 100.00% 0.100 16.450 information : 53.2% 7.29% 16+000 16+450 01+000 6.400 8.750 1.200 engineering, technology & applied science research vol. 9, no. 3, 2019, 4230-4234 4233 www.etasr.com winanri et al : comparison analysis between traditional contracts and long segment contracts ... there was a lack of understanding regarding to routine maintenance activities by the contractors. they prioritized works such as widening, reconstruction, rehabilitation, and reactive road activities, although fixed penalty is applied for the delay in repairing damage in the scope of routine maintenance. routine road maintenance is that the road components (road pavement, road shoulders, drainage systems, road additions, and road equipment) are maintained at all times and are in good service conditions based on the required performance. as for routine maintenance activities such as closing sealing, patching, spot leveling, pavement edge repair, asphalt surfacing, crack repair, corrugated surface repair, and deep rutting to maintain a standard transverse slope. according to the palembang p2jn, 2016 was the initial year for implementing long segment contract on the outer urban road of palembang-indralaya-meranjat, along with the other long segment scheme applications in indonesia. the ministry of public works of the directorate general of bina marga conducted modifications to the long segment contract in 2017, namely changes in payment terms for the scope of routine road maintenance activities. in 2016 the payment for the scope of routine road maintenance activities was lump sum, but in 2017 it changed to volume based for all the scopes of activities on long segment contracts. it is expected that the contractor can prioritize road maintenance activities. this change of payment intended contractors’ bid prices for routine road maintenance to be more measurable and not too low. in implementing the contracts, the payment was in accordance with the volume based to make it easy to optimize the program. if there was an addendum to the contract (work added/reduced) in the scope of routine maintenance activities, it became more flexible to shift funds. from the previous discussion, the potential benefits for implementing long segment contracts are: 1) road conditions are better maintained and the cost of road maintenance is more efficient. the application of kbk has the opportunity to improve the quality and service of national roads through sustainable road management and maintenance, as well as saving on road maintenance costs with the value of the npv of kbk of 70% of npv traditional contracts [9]. the implementation of kbk in the procurement of goods and services in developing countries can reduce costs and time constraints and improve procurement quality [10]. kbk generates cost reduction in a contract and improves the quality of a product or service [11]. pbc is an alternative and cost-effective solution, both reducing direct costss and indirect costs compared to traditional contracting approaches [5]. this is in line with the long segment contract, in which road damage can be quickly handled, road components can be maintained at all times, and in good service conditions to prevent continuous damage. by preventing greater road damage, the cost of road preservation activities becomes more efficient. in addition, with long contracts, the road maintenance cost segment becomes smaller because of the optimization of the cost of road management, including the cost of procurement of goods/construction services, road supervision costs, and overhead (general) road construction. 2) national road work outcomes are in accordance with the applied performance indicators meeting the road service levels in long segment contracts is regulated in the special specifications skh.1.10.a regarding the maintenance of road performance and special specifications skh.1.10.2 on the maintenance of bridge performance. if the providers cannot meet the level of road and bridge services on the specified response time, they will be sanctioned financially in the form of payment deductions in accordance with the special specifications for maintenance of road performance of section skh-1.10.a.4.3 and special specifications for maintenance of bridge performance skh-1.10.b.4.5. therefore, road organizers have an extra motive to get steady road conditions throughout the segment. 3) program optimization in implementing long segment contracts the long segment contract has the advantage that one contract covers four road preservation activities, namely widening, reconstruction, rehabilitation, and maintenance. therefore, the long segment contracts are flexible and the programs can be optimized with available funds. furthermore, after a payment is modified for the scope of routine maintenance activities to be volume based, it becomes easier to shift funds. program optimization on long segment contracts can be carried out as follows: • adjustment of location of activities is effective against field conditions or field engineering results. • delay (holding) for damaged segments which cannot be handled. • decrease in time of plans for rehabilitation and or reconstruction activities. • transfer of funds between the scope of activities. given the program optimization, the road preservation activities meet the needs and the road along the segment can be maintained. the challenges in the application of the long segment contract are: 1) lack of experience in long segment contract the directorate general of bina marga has developed a long segment contract since 2016 with 256 packages of national road preservation, 25 of those are managed by balai besar pelaksanaan jalan nasional v palembang (bbpjn v palembang). according to satker p2jn palembang, the long segment contracts are more accountable in terms of financial administration. they can also improve maintenance standards and overcome poor in-house (direct labor-based) performance in national road maintenance. the application of long segment contracts is better than the traditional contract approach, but it has not been widely disseminated. to get a steady and uniform road condition along the integrated segment, it is expected that long segment contracts are not only applied to national roads, but also to provincial and district/city road maintenance. 2) lack of contractor’s understanding in implementing long segment contracts engineering, technology & applied science research vol. 9, no. 3, 2019, 4230-4234 4234 www.etasr.com winanri et al : comparison analysis between traditional contracts and long segment contracts ... the number of contractors having experience in kbk is limited [9, 12, 13]. it is a challenge in implementing kbk. the lack of knowledge of kbk still needs to be dealt with in order to prepare for its application. similarly, for the implementation of long segment contracts, the lack of understanding of contractor in carrying out road maintenance activities needs to be dealt with because these activities are the main scope of long segment contracts. it is necessary to improve the contractors’ quality in meeting the level of road services, and to maximize performance inspections. v. conclusion the results of data analysis show that the functional performance of the road, namely the iri value as a result of road preservation activities on traditional contracts is better than the iri value on long segment contracts, which is not in accordance with the expected target. due to the lack of understanding of the scope of routine maintenance activities, the directorate general of bina marga modified its payment from lump sum to volume based in 2017. as a result in 2017 the iri value decreased. there is a potential benefit for implementing long segment contracts, as road conditions get better maintained and the cost of road maintenance becomes more efficient because the work results are held in accordance with the applied performance indicators and program optimization can be achieved. but, there are challenges that are still to be faced, namely the contractors’ lack of experience knowledge, and understanding of implementing long segment contracts. references [1] b. susanti, model penilaian kelayakan penerapan kontrak berbasis kinerja untuk proyek pemeliharaan jalan nasional, institusi teknologi bandung, 2017 (in indonesian) [2] e. james, “meningkatkan hasil pemeliharaan aset jalan nasional indonesia”, jurnal prakarsa infrastruktur indonesia, vol. 24, pp. 19-23, 2016 (in indonesian) [3] r. wirahadikusumah, m. abduh, “metoda kontrak inovatif untuk peningkatan kualitas jalan: peluang dan tantangan”, pola manajemen proyek untuk kondisi berjalan dan masa depan, jakarta, indonesia, 2003 (in indonesian) [4] p. pakkala, “performance-based contracts—international experiences”, trb executive workshop, finnish road administration, washington, usa, 2005 [5] a. straub, “cost saving from performance-based maintenance contracting”, internasional journal of strategic property management, vol. 13, no. 3, pp. 205-217, 2009 [6] puslitbang jalan dan jembatan, kajian penerapan kontrak berbasis kinerja untuk konstruksi jalan di atas tanah lunak, laporan akhir, departemen pekerjaan umum, 2006 (in indonesian) [7] n. yasin, kontrak kontruksi di indonesia, penerbit gramedia, 2013 (in indonesian) [8] persyaratan teknis jalan dan kriteria perencanaan teknis jalan, peraturan menteri pekerjaan umum, 2011 (in indonesian) [9] r. z. tamin, a. z. tamin, p. f. marzuki, “performance based contract application opportunity and challanges in indonesian national road management”, procedia engineering, vol. 14, pp. 851-858, 2011 [10] b. a. ambaw, j. telgen, “pbc as a solution for public procurement problems: some ethiopian evidence”, european journal of business and management, vol. 9, no. 34, pp. 97-108, 2017 [11] m. sultana, a. rahman, s. chowdhury, “a review of performancebased maintenance of road infrastructure by contracting”, international journal of productivity and performance management, vol. 62, no. 3, pp. 276-292, 2013 [12] m. sultana, a. rahman, s. chowdhury, “an overview of issues to consider before introducing performance-based road maintenance contracting”, world academy of science, engineering and technology, vol. 62, pp. 350-355, 2012 [13] n. malahayati, s. husin, a. mursalin, “kajian sistem kontrak konvensional dan sistem performance based contract (pbc) pada proyek pemeliharaan jalan”, prosiding seminar reguler seri 1 jts unsyiah-eltees-mts, 2010 (in indonesian) microsoft word 2-2904_s_etasr_v9_n5_pp4586-4590 engineering, technology & applied science research vol. 9, no. 5, 2019, 4586-4590 4586 www.etasr.com torchani et al.: dynamic economic/environmental dispatch problem considering prohibited … dynamic economic/environmental dispatch problem considering prohibited operating zones ahmed torchani college of engineering, university of hail, hail, saudi arabia and university of tunis, ensit, lisier laboratory, tunisia tochahm@yahoo.fr attia boudjemline college of engineering, university of hail, hail, saudi arabia a_boudjemline@hotmail.com hatem gasmi college of engineering, university of hail, hail, saudi arabia and university of tunis el-manar, enit, tunisia gasmi_hatem@yahoo.fr yassine bouazzi college of engineering, university of hail hail, saudi arabia and university of tunis el manar, enit, photovoltaic and semiconductor materials laboratory, tunis, tunisia yassine.bouazzi@gmail.com tawfik guesmi college of engineering, university of hail, hail, saudi arabia and university of sfax, enis, tunisia tawfiq.guesmi@gmail.com abstract—along with economic dispatch, emission dispatch has become a key problem under market conditions. thus, the combination of the above problems in one problem called economic emission dispatch (eed) problem became inevitable. however, due to the dynamic nature of today’s network loads, it is required to schedule the thermal unit outputs in real-time according to the variation of power demands during a certain time period. within this context, this paper presents an elitist technique, the second version of the non-dominated sorting genetic algorithm (nsagii) for solving the dynamic economic emission dispatch (deed) problem. several equality and inequality constraints, such as valve point loading effects, ramp rate limits and prohibited operating zones (poz), are taken into account. therefore, the deed problem is considered as a nonconvex optimization problem with multiple local minima with higher-order non-linearities and discontinuities. a fuzzy-based membership function value assignment method is suggested to provide the best compromise solution from the pareto front. the effectiveness of the proposed approach is verified on the standard power system with ten thermal units. keywords-dynamic environmental/economic dispatch; prohibited operating zones; multi-objective optimization; nondominated sorting genetic algorithm i. introduction in electric power systems, improvement of operation and planning has become more important under the current market conditions and several tools have been developed in this context [1, 2]. economic load dispatch (ed) is one of them. it aims to schedule the outputs of the committed generating units so as to minimize the total fuel cost under specific system equality and inequality constraints. this objective can no longer be considered alone due to severe environmental standards imposed by legislations. in this respect, the clean air act amendments have been applied in the usa to reduce pollution and atmospheric emissions such as sulfur oxides, sox, and nitrogen oxides, nox, caused by fossil-fueled thermal units [3, 4]. hence, improvements in dispatching electric power must consider both monetary profits and reduced emissions of gaseous pollution. thus, we are facing a bi-objective minimization problem, which has been frequently known as the static environmental/economic dispatch (seed) problem. seed can only handle a single loading condition at a particular time instant [3-8]. due to the large variation of the load demand and dynamic nature of the power systems in recent years, it is mandatory to schedule the generator outputs in real time according to the variation of power demands over a certain time period. there are several formulations of this problem, known as the dynamic environmental/economic dispatch (deed) problem [9-12]. generally, deed is a dynamic optimization problem having the same objectives as seed over a time period subdivided into smaller time intervals with respect to the constraints imposed on system operation by generator ramp-rate limits. time period and time intervals can be one day and one hour, respectively. therefore, the operational decision at an hour may affect the operational decision at a later hour. authors in [11-16] summarize several techniques for solving dispatch problems. conventional methods, such as dynamic programming, nonlinear programming, network flow method, and interior point method [16] have been criticized as they are iterative, sensitive to initial solution and converge into local optimum solution. to overcome these difficulties, more recent works centered around artificial intelligence (ai), such as genetic algorithm [17], tabu search [18], particle swarm optimization [19-20], simulated annealing [12], differential evolution [13] and bacterial corresponding author: ahmed torchani engineering, technology & applied science research vol. 9, no. 5, 2019, 4586-4590 4587 www.etasr.com torchani et al.: dynamic economic/environmental dispatch problem considering prohibited … foraging [14]. these techniques proved to have a clear edge over traditional methods in solving deed problems without any or less restrictions on the shape of the objective functions curves where multiple pareto-optimal solutions can be obtained in a single run. most of the past studies have only focused on the seed problem except for a few where the multi-objective deed problem is considered [14]. in [14], prohibited operating zones, ramp rate limit constraints and valve point loading effects (vple) have been considered. therefore, the deed becomes highly nonlinear and with discontinuous and non-convex cost functions. within this context, this paper presents an elitist multiobjective approach for solving the deed problem including poz, valve point loading effects, and ramp rate limit constraints. this proposed method, called second version of the non-dominated sorting genetic algorithm (nsagii), incorporates a crowding distance comparison at the end of each iteration in order to facilitate the convergence of the optimization algorithm to the real pareto optimal front. in general terms, the contribution of this study is to show that the nsga approach used frequently for solving continuous problems can be efficient for non-smooth and non-convex deed problems if a non-domination sorting technique is incorporated in the optimization algorithm. in addition, the ramp rate limit constraints have been considered during transition from the last hour of a day to the first hour of the next. a fuzzy set theory [5] is used to extract the best compromise solution from the pareto optimal front for the decision makers. the proposed approach was tested on a tenunit test system incorporating all above constraints. this approach showed a very competitive performance when compared with the original nsga algorithm. ii. problem formulation the deed problem is considered as a multi-objective problem (mop). it aims to minimize simultaneously the total fuel cost and total emission of thermal units over a certain period of time subdivided into smaller time intervals. several equality and inequality constraints are considered in the problem formulation. considering a power system with n generators, the total fuel cost function tc in ($/h) including vple and emission in (ton/h) are, respectively described by (1) and (2) [20]: ( ) ( ) 2 min sin 1 1 t n t t t c a b p c p d e p pt i i i i ii i i i t i    = + + + −∑ ∑     = =   (1) ( ) ( ) 2 2 10 exp 1 1 t n t t t e p p pt i i i i ii i i t i α β γ η λ   −  = + + +∑ ∑   = =    (2) where, t ip is real power output of the i-th unit at time t. t is the number of hours. ia , ib , ic , id and ie are the cost coefficients of the i-th unit. iα , iβ , iγ , iη and iλ are the emission coefficients of the i-th unit. objective functions ct and et are optimized subject to the constraints described below. a. generation limits min max , 1,..., t p p p i ni i i≤ ≤ = (3) b. power balance constraints total demand power t dp and total losses t lp must be covered at each interval of time t. 0, 1,..., 1 n t t t p p p t t i d l i − − = =∑ = (4) in this study, total losses are expressed as follows [20]: 1 1 1 n n n t t t t p p b p b p b l i ij j oi i oo i j i = + +∑ ∑ ∑ = = = (5) where ijb , oib , oob are called b coefficients. c. ramp rate limits 1t t down p p r i i i − − ≤ (6) 1 upt t p p r i i i −− ≤ (7) where down ir and up ir are the down and up rate limits of the ith unit, respectively. d. constraints due to prohibited operating zones min 1 1 , 2,..., max t p p pii i kt t k p p p p k zi ii i i z tip p p i ii  ≤ ≤   − ∈ ≤ ≤ =   ≤ ≤ (8) where iz is the number of prohibited operating zones for the ith unit, and k ip and k ip are upper and lower bounds of the prohibited zone number k. iii. implementation of the proposed method multi-objective evolutionary algorithms using nondominated sorting and sharing, such as nsga and npga, have been criticized for the absence of elitism. therefore, the second version of nsga, called nsgaii [21] is utilized in this study for solving the deed problem. in this approach, the sharing function approach is replaced with a crowded comparison. initially, an offspring population qt is created from the parent population pt at the t-th generation. then, a combined population rt is formed: r p q t t t = ∪ (9) rt is sorted into different no-domination levels fj. so, we can write: 1 rr f jt j  =  =   ∪ (10) engineering, technology & applied science research vol. 9, no. 5, 2019, 4586-4590 4588 www.etasr.com torchani et al.: dynamic economic/environmental dispatch problem considering prohibited … where, r is the number of fronts. to offer a higher precision with reduced cpu time, this algorithm has been implemented using real-coded genetic algorithm in [5, 19]. iv. results and simulation the effectiveness of the proposed optimization algorithm for solving the deed problem is assessed on the 10-unit system. all system data are taken from [14, 20]. the b-loss coefficients are given below. 0.49 0.14 0.15 0.15 0.16 0.17 0.17 0.18 0.19 0.20 0.14 0.45 0.16 0.16 0.17 0.15 0.15 0.16 0.18 0.18 0.15 0.16 0.39 0.10 0.12 0.12 0.14 0.14 0.16 0.16 0.15 0.16 0.10 0.40 0.14 0.10 0.11 0.12 0.14 0.15 0.16 0.17 0.12 0.14 0.35 0.11 0.13 0.13 0.4 10b −= 15 0.16 0.17 0.15 0.12 0.10 0.11 0.36 0.12 0.12 0.14 0.15 0.17 0.15 0.14 0.11 0.13 0.12 0.38 0.16 0.16 0.18 0.18 0.16 0.14 0.12 0.13 0.12 0.16 0.40 0.15 0.16 0.19 0.18 0.16 0.14 0.15 0.14 0.16 0.15 0.42 0.19 0.20 0.18 0.16 0.15 0.16 0.15 0.18 0.16 0.19 0.44                                  (11) the nsgaii algorithm is implemented in matlab r2009a on a 64-bit operating system on a pc with an intel i32370m cpu at 2.40ghz. the best compromise solution is generated from the pareto front using a fuzzy based membership function value assignment method [5]. the nsgaii parameters to find the best pareto set for the seed problem have been chosen by trial and error and they were used for the deed problem. in this study, the maximum number of generations and the population size were both chosen to be 200. • test case 1: the seed problem for the ten-unit system with pd=1036mw was considered in this case. optimal outputs of thermal units for best cost, best emission and best compromise solution have been computed using the proposed optimization algorithm. results have been compared with those obtained using nsga. • test case 2: the deed for the test system over a 24-hour time horizon was solved under all previous constraints. poz limits in mw shown in table i are taken from [22]. therefore the problem will be more complicated with discontinuities. the hourly variation of the load is depicted in figure 1. table i. unit operating limits in mw unit min ip max ip down ir up i r prohibited zone 1 150 470 80 80 [150 165], [448 453] 2 135 470 80 80 [90 110], [240 250] 3 73 340 80 80 4 60 300 50 50 5 73 243 50 50 6 57 160 50 50 7 20 130 30 30 8 47 120 30 30 [20 30], [40 45] 9 20 80 30 30 10 10 55 30 30 [12 17], [35 45] a. seed problem: test case 1 for the validation of the proposed algorithm, a comparison with the first version of nsga is suggested in this case. from figure 1, it is clear that nsgaii provides the best results and it has better diversity characteristics of non-dominated solutions. from table ii, the minimum fuel cost and emission provided by nsgaii are $61,775.44 and 3,785.47lb respectively. moreover, the highest value of the fuel cost is found for minimum emission and the highest value of the emission corresponds to the minimum fuel cost since they are conflicting objective functions. fig. 1. hourly load variation fig. 2. pareto solutions with nsgaii and nsga (case 1) b. deed problem considering all constraints: test case 2 in this case, the generation output of unit at each hour has been adjusted considering poz. consequently, discontinuities are introduced in cost and emission curves corresponding to the poz. the hourly evolution of the optimum generations using the proposed algorithm for minimum cost is shown in figure 3. it is clear that the outputs of all units are maximum at hour 12 which corresponds to the maximum load (2150mw). in this sub-section, optimum solution for minimum emission is not displayed due to the space limitation. table iii shows the compromise solution extracted from the pareto solutions. it is clear that the proposed scheduling of generations satisfies all previous constraints. engineering, technology & applied science research vol. 9, no. 5, 2019, 4586-4590 4589 www.etasr.com torchani et al.: dynamic economic/environmental dispatch problem considering prohibited … fig. 3. hourly evolution of the optimum solution for minimum cost v. conclusion the deed problem is one of the most crucial issues to be solved in the power system field. it has a great importance in reducing emission of harmful gases and saving energy. in this study, the deed problem has been formulated as a biobjective optimization problem with nonlinear constraints including vple, ramp rate limits and prohibited operating zones. the second version of the non-dominated sorting genetic algorithm (nsgaii) has been suggested for solving the deed problem for 24-hour dispatch intervals. to demonstrate the effectiveness of the proposed approach, the standard power system with ten thermal units was used. various cases with different levels of complexity and discontinuity have been considered. the results of the proposed approach are significantly improved when compared with nsga. in addition, this approach has the capacity to optimize any number of objective functions simultaneously and generate the pareto front in a single run. therefore, other objectives can be included in the main problem such as voltage drop and real power losses. table ii. optimum solutions for case 1 minimum fuel cost minimum emission best compromise solution method nsagii nsga nsgaii nsga nsgaii nsga p1 165.657 165.304 165.465 165.277 165.092 165.400 p2 135.000 135.000 136.471 138.754 135.000 135.073 p3 73.0000 73.0000 85.943 89.8068 78.3817 73.0000 p4 60.0000 60.0000 87.8645 88.9776 85.9374 77.8433 p5 221.551 224.103 135.325 124.263 123.237 131.320 p6 120.835 118.647 126.733 126.764 128.576 124.444 p7 130.000 130.000 91.4739 97.8403 129.019 130.000 p8 120.000 120.000 91.9147 89.3054 84.4827 120.000 p9 20.0000 20.0000 79.6906 79.8941 79.5035 51.7425 p10 10.0000 10.0000 55 55.0000 46.6442 47.0783 cost ($/h) 61775.4 61802.6 63914.4 63905.5 62974.5 62486.2 emission (lb/h) 4781.79 4800.55 3785.47 3785.51 3880.30 3998.43 acknowledgment the present work was undertaken within the research project (no: 160803), funded by the deanship of scientific research, at the university of hail, which is gratefully acknowledged. table iii. best compromise solution of deed for test case 2 hour p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 1 165.0185 136.1190 73.0000 88.1843 125.1063 121.1142 130.0000 119.4657 52.5923 45.2700 2 165.1026 135.1579 81.5542 108.405 173.2150 122.5238 100.0000 120.0000 80.0000 46.7179 3 165.0594 135.7696 130.6567 127.3521 183.7788 159.8147 129.6961 120.0000 80.0000 54.5710 4 165.5635 182.8389 164.0515 160.2915 225.3338 159.3824 130.0000 119.8330 79.8469 54.9029 5 165.4107 202.1567 185.8223 182.477 240.2090 159.8194 129.8451 119.7818 79.8544 54.6686 6 205.1453 218.9835 245.006 228.7587 243.0000 160.0000 121.126 120.0000 80.0000 55.0000 7 200.0936 220.9863 294.5041 278.7587 243.0000 160.0000 106.1606 120.0000 77.1945 55.0000 8 232.4056 297.4300 259.7886 263.0712 243.0000 157.1222 127.8133 120.0000 80.0000 55.0000 9 295.7609 309.5763 339.7886 263.2257 241.7996 160.0000 130.0000 120.0000 80.0000 55.0000 10 317.6374 355.8988 340.0000 300.0000 243.0000 160.0000 130.0000 120.0000 80.0000 55.0000 11 358.3159 412.7551 340.0000 300.0000 243.0000 160.0000 130.0000 120.0000 74.8769 55.0000 12 379.7618 434.7244 339.9887 299.9990 242.9959 160.0000 129.9935 119.9976 80.0000 54.9757 13 346.8023 381.7131 340.0000 299.9520 242.9962 159.9909 130.0000 119.977 79.9899 55.0000 14 302.4077 308.1888 300.5633 295.9688 243.0000 160.0000 130.0000 119.9821 80.0000 55.0000 15 228.2163 264.2944 285.2806 270.8877 243.0000 159.4424 129.6214 119.887 79.9751 54.5439 16 165.3236 222.6713 209.3282 239.4035 243.0000 159.4886 129.903 120.0000 54.6538 54.5022 17 165.1747 216.9418 186.1643 189.4035 242.8615 159.9508 129.8344 119.8230 55.0000 55.0000 18 226.6097 223.5607 229.9497 234.5908 242.8186 160.0000 130.0000 119.9758 55.0000 54.7545 19 239.3959 299.4056 276.9271 258.0446 242.9016 159.8063 129.7669 119.8321 54.7896 54.8522 20 276.0364 342.8300 340.0000 300.0000 243.0000 160.0000 130.0000 120.0000 80.0000 55.0000 21 302.8172 308.8301 298.5865 298.2182 242.3453 159.9713 129.7167 119.7893 80.0000 54.8529 22 224.9485 228.8301 218.5865 258.7530 209.6452 160.0000 130.0000 120.0000 80.0000 46.5327 23 165.4124 149.0684 141.616 209.7076 166.2512 157.8307 128.9253 119.6998 79.8154 45.7563 24 165.5672 135.0000 73.0000 138.1843 175.1063 145.5599 123.5542 120.0000 80.0000 53.6633 total cost ($) 2526555.7207 total emission (lb) 302900.8703 total losses (mw) 1301.8534 engineering, technology & applied science research vol. 9, no. 5, 2019, 4586-4590 4590 www.etasr.com torchani et al.: dynamic economic/environmental dispatch problem considering prohibited … references [1] f. milano, “an open source power system analysis toolbox”, ieee transactions on power systems, vol. 20, no. 3, pp. 1199-1206, 2005 [2] r. d. zimmerman, c. e. m. sanchez, r. j. thomas, “matpower steadystate operations, planning and analysis tools for power systems research and education”, ieee transactions on power systems, vol. 26, no. 1, pp. 12-19, 2011 [3] s. boudab, n. golea, “combined economic-emission dispatch problem: dynamic neural networks solution approach”, journal of renewable and sustainable energy, vol. 9, no. 3, article id 035503, 2017 [4] m. basu, “economic environmental dispatch using multi-objective differential evolution”, applied soft computing, vol. 11, no. 2, pp. 2845-2853, 2011 [5] m. a. 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enhancement using sfcl and smes sfcl-smes control for power system transient stability enhancement including scig-based wind generators abdelkrim zebar electrical engineering department university ferhat abbas setif 1 setif, algeria zebarkarim@yahoo.fr lakhdar madani electrical engineering department university ferhat abbas setif 1 setif, algeria zebarkarim@yahoo.fr abstract—the resolution of the environment pollution depends on renewable energy sources, such as wind energy systems. these systems face transient and voltage stability issues with wind energy employing fixed-speed induction generators to be augmented with resistive type superconducting fault current limiter (sfcl) and superconducting magnetic energy storage (smes) devices. the use of a combined model based on sfcl and smes for promoting transient and voltage stability of a multi-machine power system considering the fixed-speed induction generators is the primary focus of this study. our contribution is the development of a new model that combines the advantages of sfcl and smes. the proposed model functions assure flexible control of reactive power using smes controller while reducing fault current using superconducting technologybased sfcl. the effectiveness of the proposed combined model is tested on the ieee11-bus test system applied to the case of a three-phase short circuit fault in one transmission line. keywords-distributed wind generation(dwg); superconducting fault current limiter (sfcl); superconducting magnetic energy storage (smes); transient stability i. introduction with the increased penetration of the distributed generations (dgs), the mostly used induction machines are wind generators. induction machines face stability problems, similar to the transient stability of synchronous machines [1-2]. so, it is important to analyze the transient stability of power systems including wind power stations. in power system stability studies, the term transient stability usually refers to the ability of the synchronous machines to remain in synchronism during brief periods that follow large disturbances, such as severe lightning strikes, loss of heavily loaded transmission lines, loss of generation stations, or short circuits on buses [34]. on the other hand, the braking resistor (br) has been recognized and used as a cost-effective measure for transient stability control of synchronous generators for a long time. according to some recent reports, brs can be used for wind generator stabilization as well [5-6]. the selection of a suitable device for the stabilization of fixed-speed wind generators is a matter of interest. the static synchronous compensator (statcom) and static var compensator (svc) are reported of being able to stabilize the fixed speed wind generator [7-8]. the research on the application of superconducting devices in power systems, such as the smes as a tool for the stabilization of grid-connected wind generator systems [9-11], is recently developed. an smes is a large superconducting coil capable of storing electric energy in the magnetic field generated by the direct current (dc) current flowing through it, and the real and reactive power can be absorbed (charging) by or released (discharging) from the coil according to the system power requirements. sfcls can suppress short-circuit currents using the unique quench characteristics of superconductors. in the event of a fault, the superconductor undergoes a transition into its normal state (quenching). after quenching, the current is commutated to a shunt resistance and is then limited rapidly [12–14]. in this paper, the potential influence of the combined application of sfcls and shunt controller smes is proposed and investigated for improving both transient stability and voltage regulation of the power system containing a distributed wind generation based on conventional fixed speed induction generator. moreover, the optimal location of the proposed coordinated controller (sfcl–smes) is also analyzed. the effectiveness of the proposed combined model is tested on the ieee 11-bus test system applied to the case of three-phase short circuit fault in one transmission line. simulation results for the system under study are presented and discussed. they show that the optimal location selected by the proposed method improves the transient stability of the power system when a fault occurs. ii. mathematical model this section gives a mathematical model for the power system network which includes modelling of synchronous generator, dwg, sfcl, and smes. a. synchronous generator for transient stability analysis, a synchronous machine model is considered as a classic fourth-degree model (figure 1) and is simulated in matlab/simulink [15]. the systems basic elements are: � is the power angle of the generator, �� is the rotor speed with respect to synchronous reference, � is the inertia constant of the generator, �� is the mechanical input torque to the generator which is assumed to be constant, �� is corresponding author: abdelkrim zebar engineering, technology & applied science research vol. 10, no. 2, 2020, 5477-5482 5478 www.etasr.com zebar & madani: power system transient stability enhancement using sfcl and smes the electromagnetic torque to the generator, d is the damping constant of the generator, � ′ is the quadrature-axis transient voltage, ��� is the reference voltage, � � ′ is the direct-axis open-circuit transient time constant of the generator, � � ′ is the quadrature axis open-circuit transient time constant of the generator, � is the direct-axis synchronous reactance, � ′ is the direct axis transient reactance, � ′ is the quadrature axis transient reactance, � is the terminal voltage of the generator, and � and i� are the direct and quadrature axis currents of the generator respectively. fig. 1. the synchronous generator model b. dwg dwgs contain many wind turbines and their detailed modeling may be unaffordable due to computational burden. in order to reduce dimensionality, aggregation techniques are used to obtain equivalent models. a proper equivalent model can be easily obtained for fixed-speed wind turbines where a one-toone correspondence between wind speed and active power output exists. in this case, aggregation is performed by adding the mechanical power of each wind turbine and by using an equivalent squirrel cage induction generator (scig) which receives the total mechanical power [16-18]. a simplified transient model of a scig is given in [19]. the dwg penetration level in the system is defined as [20]: ) cg p dwg p (100 dwg p dwg % +∗= (1) where pdwg and pcg are the amount of total active power generated by dwg and centralized generation respectively. c. smes figure 2 shows the basic configuration of a thyristor-based smes unit which consists of a y-delta transformer, an ac/dc thyristor controlled bridge converter, and a superconducting coil or inductor [21]. the converter impresses positive or negative voltage on the superconducting coil. charge and discharge are easily controlled by simply changing the delay angle that controls the sequential firing of the thyristors. • if α is less than 90, the converter operates in the rectifier mode (charging). • if α is greater than 90, the converter operates in the inverter mode (discharging). as a result power can be absorbed from or released to the power system according to the requirements. at the steady state smes should not consume any real or reactive power. the voltage �� of the dc side of the converter is expressed by: �� � ��� cos � (2) where ��� is the ideal no-load maximum dc voltage of the bridge. fig. 2. typical schematic diagram of an smes unit the current and voltage of superconducting inductor are related as: ��� � � ��� � ��� ! ���� � �" (3) where ���� is the initial current of the inductor. the real power #�� absorbed or delivered by the smes is given by: #�� � �� ��� (4) the energy stored in the superconducting inductor is: $�� � $��� ! � #��� � �" (5) where $�� � 1 2 '�� ���� (⁄ is the initial energy in the inductor. this is applicable for the twelve pulse converter also [21]. since the bridge current ��� is not reversible, the bridge output power #�� can be positive or negative depending on ��. if �� is positive, power is transferred from the power system to the smes, while if it is negative, power is released from the smes unit. the thyristor-based smes using a six pulse converter is simulated in matlab/simulink as shown in figure 3. fig. 3. circuit of smes engineering, technology & applied science research vol. 10, no. 2, 2020, 5477-5482 5479 www.etasr.com zebar & madani: power system transient stability enhancement using sfcl and smes d. sfcl depending on the superconducting materials and operation principles, the superconducting fault current limiters can be classified into different types [22]. in the resistive type the superconductor is directly connected in series to the line to be protected while in the inductive concept the superconductor is magnetically coupled into the line [23]. fig. 4. modified transmission line with sfcl the sfcl is a device that limits the fault current by generating impedance when a fault occurs. in addition, the limiting impedance generated to limit fault currents is helpful in increasing the generator output degraded by a fault, thus providing stabilization. sfcls installed in series with transmission lines can be operated during the period from the fault occurrence to fault clearing [24]. the equivalent circuit of the transmission line with sfcl is illustrated in figure 4. the associated equation for rsfcl can be described by: ( ) (1 exp( ))sfcl m scr t r t t= − − (6) where rm is the expected maximum value of sfcl resistance in the normal state (rm≈20ω) and tsc is the time constant of transition from the superconducting state to the normal state, which is assumed to be 1ms. the three phase of the resistance sfcl model is simulated in matlab/simulink as shown in figure 5. fig. 5. the three phase resistance sfcl model iii. simulation results to investigate the efficiency and the robustness of the proposed sfcl and smes based controller on the power system transient stability in the presence of distributed wind generation, the model is integrated in the ieee benchmark four-machine two-area test system in the case of a three phase short circuit fault in the transmission line. the test system consists of eleven buses, four synchronous generators connected to buses 1, 2, 3, and 4 respectively through transformers which contribute to the supply of two loads through transmission lines, and two fully symmetrical areas linked together by two 230kv lines of 220km length [25, 26]. dwg is connected to each of the load buses. the configuration is shown in figure 6. fig. 6. on-line diagram of the electrical test system considering the combined controller sfcl and smes technical data such as voltage regulator, governor turbine, buses and branches information are given in [23]. the transient stability is assessed by the criterion of relative rotor angles, using the time domain simulation method. the sim power systems toolbox of matlab/simulink was used to carry out simulations. iv. optimal location of sfcl-smes for secure operation of power systems, it is required to maintain an adequate voltage stability margin, not only under normal conditions, but also in contingency cases. in this study, the voltage stability index using continuation power flow is proposed for the optimal location of smes and sfcl. from the continuation power flow (cpf) results shown in figure 7 [18], the buses 5, 6, 7, 8, 9, 10, and 11 are the critical buses. among these buses, bus 8 has the weakest voltage profile. figure 8 shows the pv curves for the ieee four-machine twoarea test system without considering sfcl and smes. fig. 7. curves for the ieee four-machine two-area test system at first, the buses are classified according to three procedures: engineering, technology & applied science research vol. 10, no. 2, 2020, 5477-5482 5480 www.etasr.com zebar & madani: power system transient stability enhancement using sfcl and smes procedure1: all buses are classified according to voltage stability index. in this study, bus 8 is considered as a candidate bus, the main role of the statom is to control voltage at this bus by exchanging reactive (capacitive or inductive) power with the network. procedure 2: buses are classified according to the value of fault currents (three phase fault). procedure 3: buses are classified according to the reactive power compensation consumed by the dwg. the dwg will generate an active power, equal to the amount of power consumed by the load. however, in order to generate this necessary active power, the dwg needs to consume reactive power from the network. bus 9 is considered as the point of common coupling (pcc) where the wg is connected and the main role of the smes is to compensate for this reactive power. fig. 8. critical buses based on continuation power flow v. impact of the sfcl-smes controller on power system transient stability enhancement three logic cases are considered: in the base case, which indicates the original system, there is no sfcl and smes, in the system. in the second case, with smes at the weak bus (low voltage stability index) and sfcl at a bus which has high fault current. in the third case, with smes at the pcc and sfcl at another bus with a high fault current. a. case 1 a 3-phase fault occurs at t=1s on line 7–8 near bus 8 and it is cleared by opening the line at both ends. a wg at bus 9 is considered with a penetration level of 20%. generator 2 is the nearest generator to the fault location and therefore it has the most rotor speed deviation for this fault. the fault clearing time is fct=0.266s at first and then fct=0.300s. simulation results on the rotor angle differences and rotor speed deviation of the four generators without considering sfcl and smes controller are shown in figures 9–10 respectively. it can be seen that the relative rotor angles are damped and consequently the system maintains its stability, but when the ftc increased to 0.300s, the relative angles (δ14, δ24 and δ34) increase indefinitely, so at this critical situation the system loses its stability. fig. 9. relative rotor angles without sfcl–smes fig. 10. rotor speed deviation without sfcl–smes b. case 2 in order to maximize voltage stability index and to improve power system transient stability, smes is located at the weak bus (low voltage stability index) and the sfcl is placed in line 7–8 which has a high fault current. the smes will try to support the voltage by injecting reactive power on the line when the voltage is lower than the reference voltage. the first mentioned fault in the previous sub-section is applied again. time domain simulation was performed at cleared time 0.333s. fig. 11. relative rotor angles considering sfcl–smes 1 2 3 4 5 6 7 8 9 10 11 0 0.2 0.4 0.6 0.8 1 1.2 1.4 v o lt a g e m a g n it u d e ( p .u ) bus engineering, technology & applied science research vol. 10, no. 2, 2020, 5477-5482 5481 www.etasr.com zebar & madani: power system transient stability enhancement using sfcl and smes we can see from figure 11 that the maximum relative rotor angles are δ14=13°, δ24=28°, and δ34=14°, the relative rotor angles δ14, δ24, and δ34 are damped and therefore the system becomes more stable in comparison with the first case. the critical clearing time is enhanced to a new value (0.483s). c. case 3 in case 2 the sfcl was placed in the line 7–8 which had a high fault current and the smes was located at the weak bus. in this case the smes is placed at the pcc. the purpose becomes to reduce the current in line 7–8 (high fault current) and maximize dynamically voltage stability index. in this case the smes compensates the reactive power consumed by the dwg and the fault current is reduced by the sfcl in order to enhance the performance of the smes dynamically during fault and alternatively the required size of smes will be reduced (economic aspect). as a result, the reactive powers delivered by generating units reduce. compared to the two other cases, the critical clearing time is improved. the sfcl is placed in line 7–8. the first mentioned fault in the sub-section (case 1) is applied again. the fault is cleared after 0.427s. in figure 13, we can see that the maximum relative rotor angles are δ14=15.61°, δ24=14.54°, and δ34=1.68°, the relative rotor angles are damped and therefore the system becomes more stable than the first two cases. it can be also seen that the system response with the smes at the pcc is better than that with the smes at the weak bus in the sense of reduced settling time. the critical clearing time is enhanced to a new value 0.511s. fig. 12. relative rotor angles considering sfcl–smes table i. margin stability (cct) controller cct (s) case 1 without sfcl and smes 0.271 case 2 with smes and sfcl: smes at the weak bus (high voltage stability index) sfcl at a bus (high fault current) 0.483 case 3 with smes and sfcl: smes at the pcc sfcl at a bus (high fault current) 0.511 it is important to note that the integration of smes in coordination with sfcl in suitable locations may help the system improve transient stability. table i shows the values of margin stability (cct) obtained corresponding to different cases. vi. conclusion power systems are facing new challenges such as the utilization of renewable energy sources and distributed generation, the increased demand, the limited resources, the environmental regulations, and competitive electricity markets. this poses potential problems to power systems from the perspective of management. in addition, decentralized production, in particular wind generation does not attend system services. that is why the recent penetration of this resource is limited and conditioned on the participation in systems services such as voltage regulation, control of power flow, damping of power oscillations, reactive power compensation, load balancing and transient stability. superconducting fault current limiters (sfcl) and superconducting magnetic energy storages (smes) can be a solution to these problems. in this study, the multi-machine power system transient stability improvement contains a large dwg via sfcl and smes. coordinated application was studied. the results of the simulations performed on the ieee benchmarked four-machine two-area test system in the presence of distributed wind generation and considering a three phase short circuit, clearly indicate that the proposed combined controller, when placed at suitable locations, can be used as an effective means capable of enhancing the margin stability and extend the critical clearing time in a multi-machine power system. references [1] m. h. ali, b. wu, “comparison of stabilization methods for fixed-speed wind generator systems”, ieee transactions on power delivery, vol. 25, no. 1, pp. 323–331, 2010 [2] n. e. akpeke, c. m. muriithi, c. mwaniki, “contribution of facts devices to the transient stability improvement of a power system integrated with a pmsg-based wind turbine”, engineering, technology & applied science research, vol. 9, no. 6, pp. 4893-4900, 2019 [3] a. karami, s. z. esmaili, “transient stability assessment of power systems described with detailed models using neural networks”, international journal of electrical power and energy systems, vol. 45, no. 1, pp. 279–292, 2013 [4] a. s. saidi, m. b. slimene, m. a. khlifi, “transient stability analysis of photovoltaic system with experimental shading effects”, engineering, technology & applied science research, vol. 8, no. 6, pp. 3592–3597, 2018 [5] m. aten, j. martinez, p. j. cartwright, “fault recovery of a wind farm with fixed speed induction generators using a statcom”, wind engineering, vol. 29, no. 4, pp. 365–375, 2005 [6] h. gaztanaga, i. e. otadui, d. ocnasu, s. bacha, “real-time analysis of the transient response improvement of fixed-speed wind farms by using a reduced-scale statcom prototype”, ieee transactions on power systems, vol. 22, no. 2, pp. 658–666, 2007 [7] m. h. ali, t. murata, j. tamura, “effect of coordination of optimal reclosing and fuzzy controlled braking resistor on transient stability during unsuccessful reclosing”, ieee transactions on power systems, vol. 21, no. 3, pp. 1321–1330, 2006 [8] a. causebrook, d. j. atkinson, a. g. jack, “fault ride-through of large wind farms using series dynamic braking resistors (march 2007)”, ieee transactions on power systems, vol. 22, no. 3, pp. 966–975, 2007 [9] s. nomura, y. ohata, t. hagita, h. tsutsui, s. t. iio, r. shimada, “wind farms linked by smes systems”, ieee transactions on applied superconductivity, vol. 15, no. 2, pp. 1951–1954, 2005 engineering, technology & applied science research vol. 10, no. 2, 2020, 5477-5482 5482 www.etasr.com zebar & madani: power system transient stability enhancement using sfcl and smes [10] m. h. ali, t. murata, j. tamura, “minimization of fluctuations of line power and terminal voltage of wind generator by fuzzy logic-controlled smes”, international review of electrical engineering, vol. 1, no. 4, pp. 559–566, 2006 [11] m. h. ali, t. murata, j. tamura, “wind generator stabilization by pwm voltage source converter and chopper controlled smes”, record of icem (international conference on electrical machines) 2006, 2006 [12] b. w. lee, j. sim, k. b. park, i. s. oh, “practical application issues of superconducting fault current limiters for electric power systems”, ieee transactions on applied superconductivity, vol. 18, no. 2, pp. 620– 623, 2008 [13] b. c. sung, d. k. park, j. w. park, t. k. ko, “study on optimal location of a resistive sfcl applied to an electric power grid”, ieee transactions on applied superconductivity, vol. 19, no. 3, pp. 2048– 2052, 2009 [14] b. c. sung, d. k. park, j. w. park, t. k. ko, “study on a series resistive sfcl to improve power system transient stability: modeling, simulation, and experimental verification”, ieee transactions on industrial electronics, vol. 56, no. 7, pp. 2412–2419, 2009 [15] n. a. tabak, stabilite dynamique des systemes electriques multimachines: modelisation, commande, observation et simulation, phd thesis, university of lyon, 2008 (in french) [16] h. a. p. painemal, wind farm model for power system stability analysis, phd thesis, university of illinois at urbana-champaign, 2010 [17] a. zebar, a. hamouda, k. zehar, “impact of the location of fuzzy controlled static var compensator on the power system transient stability improvement in presence of distributed wind generation”, revue roumaine des sciences techniques-serie electrotechnique et energetique, vol. 60, no. 4, pp. 426–436, 2015 [18] s. h. e. osman, g. k. irungu, d. k. murage, “application of fvsi, lmn and cpf techniques for proper positioning of facts devices and scig wind turbine integrated to a distributed network for voltage stability enhancement”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4824-4829, 2019 [19] n. k. roy, m. j. hossain, h. r. pota, “voltage profile improvement for distributed wind generation using d-statcom”, ieee power and energy society general meeting, detroit, usa, july 24-28, 2011 [20] m. reza, p. h. schavemaker, j. g. slootweg, w. l. kling, l. v. d. sluis, “impacts of distributed generation penetration levels on power systems transient stability”, ieee power engineering society general meeting, denver, usa, june 6-10, 2004 [21] m. h. ali, b. wu, r. a. dougal, “an overview of smes applications in power and energy systems”, ieee transactions on sustainable energy, vol. 1, no. 1, pp. 38-47, 2010 [22] m. noe, m. steurer, “high-temperature superconductor fault current limiters: concepts, applications, and development status”, superconductor science and technology, vol. 20, no. 3, pp. r15-r29, 2007 [23] s. nemdili, s. belkhiat, “electrothermal modeling of coated conductor for a resistive superconducting fault-current limiter”, journal of superconductivity and novel magnetism, vol. 26, pp. 2713-2720, 2013 [24] m. sjostrom, r. cherkaoui, b. dutoit, “enhancement of power system transient stability using superconducting fault current limiters”, ieee transactions on applied superconductivity, vol. 9, no. 2, pp. 13281330, 1999 [25] m. klein, g. j. rogers, s. moorty, p. kundur, “analytical investigation of factors influencing power system stabilizers performance”, ieee transactions on energy conversion, vol. 7, no. 3, pp. 382-390, 1992 [26] p. kundur, power system stability and control, mcgraw-hill, 1994 microsoft word 4-mevaa.doc etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 43-48 43 www.etasr.com meva’a et al: model and reduction of inactive times in a maintenance workshop… model and reduction of inactive times in a maintenance workshop following a diagnostic error l. meva’a r. danwé t. beda department of mechanical engineering department of mechanical engineering department of mechanical engineering national advanced school of engineering national advanced school of engineering national advanced school of engineering yaoundé, cameroon yaoundé, cameroon yaoundé, cameroon lucien_mevaa@hotmail.com rdanwe@yahoo.fr abstract — the majority of maintenance workshops in manufacturing factories are hierarchical. this arrangement permits quick response in advent of a breakdown. reaction of the maintenance workshop is done by evaluating the characteristics of the breakdown. in effect, a diagnostic error at a given level of the process of decision making delays the restoration of normal operating state. the consequences are not just financial loses, but loss in customers’ satisfaction as well. the goal of this paper is to model the inactive time of a maintenance workshop in case that an unpredicted catalectic breakdown has occurred and a diagnostic error has also occurred at a certain level of decisionmaking, during the treatment process of the breakdown. we show that the expression for the inactive times obtained, is depended only on the characteristics of the workshop. %ext, we propose a method to reduce the inactive times. keyword: hierachical system; catalectic breakdown; diagnostic error; model, inactive time. i. introduction competing environment put companies under a lot of pressure. they have to meet up with production goals and also gain a portion of the market. in this context, error are reduced and unforeseen breakdowns [1, 2] that may occur in production tools can prove disruptive. it is the responsibility of the maintenance workshop to resolve such events in the shortest time possible. restoration to the normal state can be considered as an indicator of the workshop’s performance. various works have been dedicated to systems’ performance (e.g. [3, 4]), having the same objective: the amelioration of system performance. regnier first approached the topic of the reactivity of systems that faced a disruptive event [5]. he was followed by humez [6]. both proposed a model of systems based on a multi-leveled structure, the decision making model grai [7, 8]. recently, a model was developed by the authors, in order to express the reaction of a medical unit in relation to different parameters, notably the reference periods of the different levels at which the decision were made [9]. the same model is employed in this paper. we have considered the multi-leveled structure for the organization of maintenance workshops. regarding the return to normal state, the general objective is divided into sub objectives having acceptable dimensions and complexity. the difficulties in aggregating heterogeneous information and the loss of communication between decision levels can be removed. in the case of a diagnostic error, the error can have repercussions right up to the peak of the structure. in the first part of the paper, we present the hypotheses of our work, and then, in the second part, we propose a model of the inactive time following a diagnostic error. next, we propose a method to reduce the inactive times. we end with a numerical application of the approach. ii. hypotheses of the study we consider that the maintenance workshop is hierarchical and multi-leveled. therefore, several levels of decision making exists, some of which are shown in figure 1. the treatment of a catalectic breakdown, which makes production tools unavailable, follows a precise process which is based on the following hypotheses: • we consider the arrival of an unexpected breakdown at a post to be a disruptive event for the maintenance workshop. • we consider the most unfavorable case of the disruption, to be that it appears at level 0, is not treated and has repercussions right up to the nth level where it’s finally treated. • regarding the propagation of the event, we consider that the disturbance appears at a level, where it’s not treated and has repercussions at higher levels. this repercussion moves from one level to the next until it gets to the level where it’s treated. • we consider the functioning to be periodic: repercussion from one level to the next has two phases, an upstream phase which is the ascending phase (from lower levels to higher levels), and a downstream phase, which corresponds to repercussions from a level that elaborates it to a lower level, which applies it. in both phases, the repercussion from one level to the next is etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 43-48 44 www.etasr.com meva’a et al: model and reduction of inactive times in a maintenance workshop… done at the end of the period. this conduct is said to be periodic. • transmission of the event or response from one level to next is not instantaneous. there is a non-zero transmission delay upstream and downstream between two consecutive levels. • at each level, there is a shift (which could be zero) between the reference date, time origin t(0) and the start date of the reference period of level k considered as xk(0). this shift is not necessarily the same for all levels. • a diagnostic error occurs only at level 0 of the upstream phase and it is only noticed at higher levels right up to the level n (the last level). • once a diagnostic error is discovered at a given level, the management is no longer periodic, from the level where it’s discovered to the level 0 until it returns to this same level. iii. model of the inactive time a. model of the delay in reaction. the objective presented in figure 2 is to express the reaction delay of the system as a function of the occurrence date of an unwanted even and the system parameters, notably the start date of the reference period of the different levels involved in the treatment. fig. 1. example of the proccess on two levels fig. 2. . objective of the model where x k (0) :initialization date of the reference period. u 0 : occurrence date of the event. t : reaction time of the maintenance workshop. ( ){ }[ ] n0,1,...,k k0 0x,uft == we designate a sub process to every passage of an event in a level. therefore, every level k, except for the highest level (k=n), has two sub processes spk and sp2n-k which treats the upstream and downstream events respectively as shown in figure 3. the level n which treats the event has only a single sub process: spn therefore, the process has in total 2n+1 sub processes (0,1,……,2n). in every sub process spi , except for the last one, the event in the upstream phase passes through four successive states and the reaction in the downstream phase also passes through four successive states as presented in table 1. the last sub process sp2n, has just the three first stages. table i. differents states of treatment designation state upstream phase downstream phase duration e1 evaluation of the gravity verification for coherence ti,1 e2 preliminary treatment elaboration of the decision framework ti,2 e3 waiting for the end of the period waiting for the end of the period ti,3 e4 transfer to a higher level transfer to a lower level ti,4 the appreciation of the gravity of the event in the state e1 in the upstream phase determines the mode of periodic or factual treatment. we define below the parameters of the model: t0 : reference date k : level considered i : index of the sub process considered l : index of the state of the event j : number of the period order n : level at which the event is treated spi : sub process i of the system el : state l of the treatment of the event pk : duration of a period of the level k ji :synchronization period for which the event is treated in spi; x k (0) : start date of the reference period for the level k x i 0 : arrival date of the event in the sub process spi t level 1 t level 2 t t sp0 sp1 sp2 sp3 sp4 stage e1 stage e2 stage e3 stage e4 key level 0 reaction process (n+1) levels input output x k (0)k=0,1,…, n u 0 t etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 43-48 45 www.etasr.com meva’a et al: model and reduction of inactive times in a maintenance workshop… ti,l : duration of the state l of spi s : execution date of the reaction; t : reaction delay of the system to the event u i : entrance date into spi, of the event x k (j) : finish date of the period j of the level k x i l : finish date of the state el for the event spi ; s i : exit date of the event (end of the last stage) of spi ; for any sub process, the treatment sequence is the same. figure 3 presents the dates for which the perturbation in the sub process changes state. fig. 3. duration and change of state in a sub process spi there exists two distinct dynamics in the treatment process. one part is the dynamic of the event (its change of states) which is made at irregular instances and is a function of the duration of the different states which are intrinsic characteristics of the system in relation to a given event. the other is the dynamic of decision making which is regular, since it is periodic at each level. however, the two dynamics have to be synchronized so that the event can pass from the state e3 to the state e4, as shown in figure 3, before a decision relative to its treatment is finally taken. one of the two dynamics has to adapt itself to the other. this is what makes the difference between the periodic conduct and factual conduct. in factual conduct, it is the dynamic of decision making that adapts itself to that of the event, and given that it’s irregular, the factual conduct is therefore forced to be irregular. on the contrary, in periodic conduct, it’s the dynamic of the event which adapts to that of decision making. this is what will involve the wait times before the treatment of the event. in reality, the two modes coexist in the designation of mixed conduct, which means that it operates on a periodic conduct, but for critical events, decision is taken without waiting for the end of the period. the passage from a period j to the next j+1, on a given level k, effects itself at finish date of the period k, x k (j), which is given by: x k (j)=pk+x k (j-1) or : x k (j)=jpk+x k (0) in periodic conduct, the event is treated in a sub process spi, at a period ji,, of the level k (where the sub process appears), which we determine as follows: ( ) ( )      +        −++ = =−++∈∃= not if1 p 0xttu ej λp0xttusuch thatinλifλj k k i,2i,1 i i k k i,2i,1 i i where e represents the real part of x. the dates for change of states of the event (passage from the state el to the state el+1), for each of the four states in the sub process spi, x1 i , are given by: { } ( )    == ∈∀+= 3ljxx 1,2,4ltxx i ki 3 li, i 1-l i l for l=3, the equation which we have, shows clearly the synchronization between the two dynamics. it permits us to determine the date for which transfer decision for the event is taken. this date coincide with the end of the synchronization period ji,, of the sub process spi. the entrance u i and the exit s i of spi in the upstream phase of the process are such that:    = = i 4 i i 0 i xs xu we thus obtain:        += += += += i,4 i 3 i 4 ki ki 3 i,2 i 1 i 2 li, i 0 i 1 txx p.j)0(xx txx txx what proceeds the exit date is therefore: s i =x k (0)+jipk+ti,4 this result is true for all the sub processes i, except for the last one, i=2n, for which reason the state e4 does not exist, (consequently t2n,4=0). for i =2n we have to consider a diagnostic error at level 0 in the upstream phase only, which is noticed only at higher levels until it gets to the highest level n. in the case where an error is noticed at level 0, correction is done immediately and does not affect the maintenance process. on the contrary, if the error is only noticed at higher levels, the diagnostic error causes a delay ∆t which increases the treatment time of the breakdown as shown in figure 4. we then have: s 2n =x 2n (0)+j2np0+∆t the entrance date of an event in a sub process is equal to its exit date from the proceeding sub process. 0 j x k (j) ji u i ti,4 ti,2 pk 1 x k (0) ti,3 s i x i 0 t0 sub process i=k sub process i=2n-k ti,1 x i 3 etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 43-48 46 www.etasr.com meva’a et al: model and reduction of inactive times in a maintenance workshop… fig. 4. delay in a diagnostic error detected at level 2 parameters at entrance:    =∀ n,...,1,0k)0(x u k 0 parameters: { }   =∈∀ =∀ 0,1,...2niet1,2,4lt n0,1,...,kp li, k , except t2n,4 which does not exit. calculation: for i=0,1,…,2n-1    = ++= + i1i i,4ki ki su tpj)0(xs s 2n =x 0 (0)+j2np0+∆t the expression of ∆t is given by: ( )∑ ∑ = = →→ +++++=∆ n 2i n 1i i,41-i1,4-ii1,2-i1,1-i0,20,1 tttt2ttt where: 1,4-iit → : transition time from sub process i to sub process i-1. i,41-it → : transition time from sub process i-1 to sub process i. we apply a realistic hypothesis that: i,4i,41-i1,4-ii ttt == →→ consequently: ( ) ∑∑ == ++++=∆ n 1i i,4 n 2i 1,2-ii1,-i0,20,1 t2tt2ttt reaction delay represents the time that elapses between the occurrence and execution of the response. in reference to our model, difference has to be made between the exit date of the process event (exit date of the last sub process sp2n ) and the occurrence date of the event at the first level 0. this is written as: 02n ust −= or: ( ) 002n0 utpj(0)xt −∆++= we therefore have an expression for the reaction delay as a function of the system parameters. b. calculating inactive time at each level k of decision making, the state e3 in the upstream phase and downstream phase represents the wait for the end of the period. for this reason we are going to establish another expression for the delay in the previous reaction. it’s gotten by uniquely expressing as a sum, on the entire process, the duration of the events in all the different states of every sub process. equally at this stage, effects of diagnostic errors detected at a level other than level 0 in the upstream phase should be integrated: ttttt 2n 0i 1-2n 0i i,4 2 1l li, 2n 0i i,3 ∆+        ++         = ∑ ∑∑∑ = === which is of the form: (1)+(2) with:       ∑ = 2n 0i i,3 t (1) and ttt 1-2n 0l i,4 2n 0i 2 1l li, ∆+      +∑∑∑ == = (2) this expression illustrates that reaction delay is made of part (1) which constitutes the inactive time, and part (2) which constitutes the actual time for the process, therefore has an incompressible priority. approaching this expression for the reaction time using that which has been obtained previously, the inactive time (1) is written:         ∆+         += ∑ ∑∑∑ = === ttt-tt 2n 0i 1-2n 0i i,4 2 1l li, 2n 0i i,3 or: ( )         ++−= ∑ ∑∑∑ = === 2n 0i 1-2n 0i i,4 2 1l li, 00 02n 2n 0i i,3 tt(0)xu-pjt upstream phase ∆t level 0 level 1 level 2 level 3 e4 e1e2e3 e1e2e3 e4 e1e2e3 e4 e1e2 e4 e1e2 e4 e1e2 e4 e1e2e3 e4 e1e2e3 etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 43-48 47 www.etasr.com meva’a et al: model and reduction of inactive times in a maintenance workshop… we realize that delay in diagnostic error does not influence the calculation of inactive times; this is explained by the factual treatment of error before moving to the periodic treatment. in this equation, for a given system and event, only j2n varies as a function of the start dates of the reference period for the levels. all the other terms are constants. in order to reduce the reactivity delay, it is imperative to reduce the inactive times, tk,3 and t2n-k,3 (duration of the stage e3), of the two sub processes upstream and downstream, appearing at the level k by adjusting the start date x k (0), of the reference period of the level, in a manner to cancel one of the two inactive times. the adjustment on a level is carried out in the following manner: if min(tk,3 , t2n-k,3) ≤ x k (0), then x k (0)=x k (0) – min(tk,3 , t2n-k,3) if not x k (0)=pk + [x k (0) min(tk,3 , t2n-k,3)] the result is the elimination of the shorter of the two wait times. we obtain a new start date for the reference period and a new wait time which is smaller. for the entire treatment process, we successively apply the same principle to all levels of the process starting with the lowest preference. the algorithm below permits us to effect this calculation: x k (0)=0 ∀ k=0,1 ;…,n for k ranging from 0 to n, do : if min(tk,3 , t2n-k,3)=0, then k=k+1 if not, if min(tk,3 , t2n-k,3) ≤ x k (0) x k (0)= x k (0) min(tk,3 , t2n-k,3) if not x k (0)=pk + [x k (0) min(tk,3, t2n-k,3)] end if k=k+1 end if end iv. application the data for the example are as follows: • time unit is the minute. • the reference date is any minute considered to be the time origin. • the occurrence date of the event after the reference minute is u 0 =3min. • the periods of the levels are: p0=6 min, p1=4 min and p2=2 min. • we initialize the reference period of all the levels to the reference date t0=0. that’s to say: x 1 (0)=x 2 (0)=x 3 (0)=0. the duration of the dates of the different stages of each sub process are given in table 2 below: table ii. duration of the stages sub process i duration ti,1 duration ti,2 duration ti,4 0 2 2 5 1 3 3 5 2 2 3 4 3 2 2 2 4 3 2 we also consider that there is an error of diagnostic made in level zero that we realize at level 1. we obtained the following results which we’ve regrouped in table 3: table iii. simulation results calculated data u i ti,3 ji s i 3 5 2 17 17 1 6 29 29 0 17 38 38 2 11 46 46 11 9 70 the exit date of the event is s 4 =70 min. the reaction delay is t=67 min. the total wait time is 19 min. next we apply the algorithm to reduce the wait times at the different levels. we obtain the following results per level: a. for the level 0, sub processes sp0 and sp4 none of the wait times is zero, we proceed to the adjustment. the smallest wait time is t0,3=5 min in sp0. it is superior to x 0 (0)=0. the new value of x 0 (0) is: x 0 (0)=p0+[x 0 (0)-min(t0,3,t4,3)]=6+(0-5)=1 we obtain the following results: parameters results x 0 (0) x 1 (0) x 2 (0) t0,3 t1,3 t2,3 t3,3 t4,3 s t 1 0 0 0 2 0 2 10 65 62 the new wait times are 14min b. for the level 1, sub process sp1 and sp3 we have the same value of inactive time t1,3= t4,3 =2 min. the new value of x 1 (0) is: x 1 (0)=p1+[x 1 (0)-min(t1,3,t3,3)]=4+(0-2)=2 the wait times are 14 min and we obtain the following results parameters results x 0 (0) x 1 (0) x 2 (0) t0,3 t1,3 t2,3 t3,3 t4,3 s t 1 2 0 0 0 0 2 12 65 62 etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 43-48 48 www.etasr.com meva’a et al: model and reduction of inactive times in a maintenance workshop… c. for the level 2, sub process sp2 the wait times t2,3 is zero. we do not adjust the start date of the reference period for this level. we conserve x 2 (0)=0. the results are the same to those previously obtained. parameters results x 0 (0) x 1 (0) x 2 (0) t0,3 t1,3 t2,3 t3,3 t4,3 s t 1 2 0 0 0 0 2 12 65 62 at the exit of level 2, we obtain a total inactive time of 14 min instead of the initial 19 min. bringing back the time unit of the previous example which was the minute, the reduction of 5 min obtained on the reaction delay which brings it back to 62 min is important for the maintenance workshop. we think on the other part that the inactive time of 14min to the end of the process are incompressible in the measure or, after the principle of the method, one of the two inactive times at a level is zero. v. conclusion and perspectives in this article we modeled the inactive times in a maintenance workshop following an unforeseen breakdown. we have established that this breakdown depends on system characteristics. after characterizing a diagnostic error at level 0 which is only noticed in higher levels in the upstream phase, we’ve showed that this error does not influence the inactive times of a maintenance workshop faced with a breakdown. we have realized an application which models and reduces inactive times. the data that we used as input come from a maintenance workshop and a study is currently performed in order to compare the results with what we have on the field. the first results are globally satisfactory. a study is also conducted for the analysis of error estimation compared with the inactive time accuracy as well as for an analysis of model limitations. as an added perspective, we will extend our model of inactive times, using a mix conduct which gives a better representation of systems functioning. references [1] g. illya, reliability theory with application and risk, berlin, springer 2000. [2] d. smith, reliability, maintainability and risk, kidlington, elsevier, 2005. [3] f. chan, h. qi, “feasibility of performance measurement system for process based approach and measures”, integrated manufacturing systems, vol. 14, pp. 179-190, 2007. [4] f.a. gruat la forme, référentiel d’évaluation de la performance d’une chaîne logistique. application à une entreprise d’ameublement. thèse de doctorat, lyon, france 2007. [5] p. regnier, conduite réactive des systèmes de production: intégration des régimes périodique et évènement. thèse de doctorat en sciences. université de bordeaux i, 1998. [6] j.b. menye, etude de la promptitude d’un système de pilotage de production travaillant en régime périodique. dea de productique. université de bordeaux i, 2003. [7] v. humez, proposition d’un outil d’aide à la décision pour la gestion des commandes en cas de pénuries : une approche par la performance. thèse de doctorat inp, toulouse, france, 2008. [8] g. doumeingt, s. kleinhans, and n. malhene, “a proposal for an evolution management methodology”, apms’96 gem time, kyoto, 1996. [9] l. meva’a, r. danwe, j. nganhou, “modeling the wait time of a hierarchical system: case study of an internal medicine unit” international journal of engineering and technology, vol. 3, issue 1, pp 6-12, 2011 microsoft word 35-3462_s_etasr_v10_n4_pp6087-6091 engineering, technology & applied science research vol. 10, no. 4, 2020, 6987-6091 6087 www.etasr.com alfraidi et al.: impact of endogenous risk factors on risk cost in ppp projects in saudi arabia impact of endogenous risk factors on risk cost in ppp projects in saudi arabia yahya alfraidi architecture engineering department university of hail hail, saudi arabia y.alfraidi@uoh.edu.sa saleh mohammed alzahrani civil engineering department university of business & technology jeddah, saudi arabia s.alzahrani@ubt.edu.sa mohamed hssan hassan abdelhafez architecture engineering department, university of hail, hail, saudi arabia and architecture engineering department, university of aswan, aswan, egypt mo.abdelhafez@uoh.edu.sa halim boussabaine faculty of business and law the british university in dubai dubai, united arab emirates halim@buid.ac.ae abstract-the formation of the public-private partnership (ppp) contracts is based on the grounds that the construction, progress, operation, and investment of a project must be allocated to a private organization under a contract. the risks associated with ppp projects are usually associated with resource improvement and development as well as the long-term operation of the project. it is known that cost and time overruns are among the obvious risks faced by a project during the development phase. cost and time overruns are major sources of monetary risk. the risk and its impact may vary at different phases during the life cycle of a ppp project. in traditional procurement, all of the monetary risks are covered by the public sector. most of the projects delivered under traditional procurement involve a price confirmation to indicate standard cost risks. this paper aims to investigate the impact of endogenous factors on budget overrun in ppp projects in saudi arabia. the paper briefly illustrates the content regarding the ppp risk evaluating systems and explains the association between risk occurrences and cost overrun in the kingdom of saudi arabia (ksa). the paper concludes with recommendations for future research. keywords-public private partnership (ppp); risk; risk pricing; system dynamics (sd) i. introduction developing countries usually prioritize investing in construction development. mega construction projects need huge financial and human resources. building complex engineering projects requires a prominent level of expertise, and well-managed teams with sufficient monetary resources, which are often beyond the capability of a single contractor [1]. the public and the private sector are concerned about the pricing risks associated with ppp projects. many projects depicted cost and time overruns and project failure leading to unexpected results. risk management's cost may affect risk allocation. the main challenges faced by organization managers involve dealing with the uncertainty and the intricacy of ppp projects and inaccurate cost incorporation during the decision-making phase. only a few organizations incorporate the risk probability in their strategy [2]. the shortcomings of the management in terms of their processes and functionality are evident from the complexity associated with projects which indicate the failure of managers to handle the vital characteristics of major projects. the understanding of managers concerning the emergent characteristics is determined by their perceptions leading to loss of insight [3]. cost overrun usually results from inappropriate management of risks and may be prevented if each party to the contract displays proper understanding of risk responsibilities, conditions of risk, risk preferences, and risk management expertise. the party that displays the best potential and expertise of risk management must be allocated with the management responsibility [4, 5]. as per [6], this allocation of risk to the competent party is imperative for the execution of construction projects within the specified cost where the owner is responsible for the quality, progress, and the costs of the project [7]. all the risks are not allocated to the contractor in case of traditional procurement. conversely, ppp projects are known to exhibit more certainty in terms of cost and time. however, it is not necessary to allocate all risks to the private sector in order to accomplish value for money, the risks are rather allocated to the party that is most efficient in risk management [8]. the involvement of the private sector in public sector projects has been done in the past, however, the scope and extent of the concept witnessed drastic development and progress in the past three decades. the private-public cooperation existed in various forms in various parts of the world depending upon the regions’ law systems and economic conditions. however, the main motive behind the cooperation of private and public sectors was the allocation of long-term public project risks to the private sector which is usually more capable of handling these risks. the interconnection between the value for money and risk allocation is one of the most corresponding author: yahya alfraidi engineering, technology & applied science research vol. 10, no. 4, 2020, 6987-6091 6088 www.etasr.com alfraidi et al.: impact of endogenous risk factors on risk cost in ppp projects in saudi arabia significant features of ppp projects [9]. the risk allocation determines the real worth of ppps whereas the prices used for compensating the contract costs are too high in project life cycle techniques [10]. the precise measurement and assessment of risk cost require a reasonable level of expertise and competency on the part of the risk analyst. in the case of the absence of comprehension and information regarding the consequences of unexpected events and the magnitude of these consequences, analysts require theoretical models to predict the outcome prices in case of unexpected events. therefore, the risk analyst must have a comprehension of the appropriate methods for obtaining precise information to enable them to allocate risk in an appropriate manner and make the project successful [11]. the concept of project risk analysis exists for years, however, concerning the construction sector, the theory of risk pricing under uncertainty is not yet fully developed. the significance of this concept is evident from the fact that data obtained from qualitative and quantitative studies serve as the basis of a majority of risk pricing decisions in ppp projects [12]. not much verification was found in support of the government’s claim that the allocation of risk is the cause of additional ppp cost [13]. practically, there is no research on investigating the association between risk allocation and construction cost. this study fills this gap and investigates the association between risk allocation and risk cost involved in a ppp project executed in ksa. ii. research methodology various phases are involved in the research method as shown in figure 1. the first phase presents the literature reviews of the concept in order to comprehend the risk factors that are likely to have an impact on the construction cost unit associated with a ppp project. this technique corresponds to the existing research regarding this concept. consequently, a list of risk factors has been generated and more risk factors were incorporated into the existing list. this was followed by the recognition of suitable risk descriptions based on project management viewpoints regarding the ppp projects. a survey questionnaire was distributed among ppp experts to obtain their views regarding the detection of risks, assessment of risk impact, and risk pricing associated with ppp projects. the experts participating in the survey were requested to suggest the most appropriate risk allocation for the risk factors based on the extent of risk cost. the data obtained from the answered questionnaires were analyzed and converted into microsoft excel and statistical package for social science (spss) format to obtain numerical data for the research. experimental analysis was conducted to determine the grading of the extent of the impact of the risk associated with ppp projects on risk cost by survey respondents. the outcomes obtained from the analysis were stated in terms of risk occurrence. the impact of risk is estimated by making use of the data regarding the probability of risk occurrence and the intensity of its impact [2]. in other words, if the probability of risk occurrence is represented by p and the intensity of the impact of this risk on the project is represented by i [4], then the expected risk effect value or ev would be given as follows: ev = p.i (1) fig. 1. research methodology. the anticipated impacts of risks were represented in a 1 to 25 scale. the data collection is stabilized between 0 and 1. this was followed by the development of multiple regression equations based on these values. iii. endogenous risk factors even though the field of risk management aims to the mitigation of risk impact in construction projects, there is still a need of a systematic approach in the modeling of the impact of the risk factors into the construction cost. moreover, this needs to be expanded in the modeling of the interactions and the interdependency of the endogenous risk factors into the construction cost of certain types of projects such as ppp projects, which are tackled in this research paper. the risk factors of ppp projects have been investigated in [14-16], especially the factors that are influencing cost overrun, project termination, and time delay. these three factors are the drivers of increased cost in construction projects. as described above, a questionnaire survey was conducted to provide a general review of the current pricing risk practice in ksa. the main aim of this survey was to investigate the impact of risk on cost unit and the best risk allocation in ppp projects. the impact of risk factors will be assessed based on the respondent perspectives and experience. descriptive analysis for endogenous risk category is mapped into 4 sub-categories: project selection risks, project finance risks, construction risks, and related risks. every sub-category consists of some factors, the top-ranked factors are chosen to be studied in the present research, which include: public resistance towards projects, uncompetitive tender, financial resources, elevated financial cost, elevated bidding cost, impediment in allowance payment, impediment in financial closure, construction time impediment, intricacy of design & construction, flaws in design, construction technology risks, quality risks, inadequate dedication from the public/private sector, inadequate distribution of accountability and risk, inconsistency between project parties, and strikes. on the other hand, low ranked factors such as: level of demand for the project, land acquisition, competition risk, inaccurate estimates, financial attraction of project to investors, lack of creditworthiness, inability to service debt, lack of government guarantees, material availability, labor availability, poor quality of workmanship, the default of sub-contractors or suppliers, contractual risk, contractor failure, different working methods between partners, inadequate experience in ppp, organization and coordination risks, inadequate negotiation period before engineering, technology & applied science research vol. 10, no. 4, 2020, 6987-6091 6089 www.etasr.com alfraidi et al.: impact of endogenous risk factors on risk cost in ppp projects in saudi arabia initiation, and cultural differences between main stakeholders, were neglected. iv. modeling endogenous risks impact the efficiency of construction, management and engineering projects can be assessed with the help of regression modeling [17, 18]. the basic principle behind the regression modeling technique is that the dependent variable y is changed as a result of the change in the independent variable x. multiple regression models were used for the forecast of the dependent variable (construction cost overrun) and the independent variables (endogenous risk factors associated with the construction cost overrun): � = �� + ∑ �� � �� + � (2) in (2), y represents the value of a dependent variable, β0 represents the constant or regression coefficient, rpi represents the value of independent variables, and εi represents a constant term or noise. various combinations of independent variables (the endogenous risk factors associated with the construction cost overrun) were analyzed. the multi-linear models aim to allocate the extent of risk cost by outlining risk into the alternating variable. the model explained the association between various risk factors. the regression models help experts in conducting risk price analysis using theoretical methods. this implies that every independent variable will be considered as a theoretical variable integrated with a probability distribution practically obtained from the study data. in order to practically outline the risk impact of independent variables, the multiple regression equation was devised as: � ���� ��� = a+ ������� + ������� + ������� + ������� + ������� + ������� + ������� + ������� + ������� + ������� + ������� + ������� + ������� + ������� + ������� + ������� + α (3) in the above equation, a represents the constant or regression coefficient and α represents the constant term or noise, y represents the endogenous risk impact, and rp represents the factors shown in table i. table i. endogenous risk factors model factor endogenous risk factor rp28 public resistance towards projects rp29 uncompetitive tender rp33 financial resources rp35 elevated financial cost rp36 elevated bidding costs rp37 impediment in allowance payment rp40 impediment in financial closure rp45 construction time impediment rp50 intricacy of design and construction rp51 flaws in design rp53 construction technology risks rp56 quality risks rp59 inadequate dedication from public/private sector rp61 inadequate distribution of accountability and risk rp63 inconsistency between project parties rp64 strikes the measurement of project risks was carried out using construction cost overruns. there are several exogenous risk independent variables and the construction cost overrun is the dependent variable. if the y value increases, it is assumed that the risk price has increased along with construction risks. hence, there is a price that a stakeholder would charge to bear all risks. furthermore, it may also be suggested that if the y value increases, the exogenous risks are proved to be significant. the risk bearer can bear all risks if the suitable price has been identified. v. results with the help of multiple regression, the proxy variable (dependent variable) value can be predicted. the value used is that of the endogenous risk factors (independent variables). tables ii and iii show the multiple regression analysis outputs extracted from the spss software. these results indicate that there is an effect of almost all endogenous risk factors since their p-values are below 0.05. on the other hand, the common alpha level is 0.05 and the p-value for rp28 (0.054) and rp29 (0.052) are a little higher, which is why it can be stated that they are not statistically significant. these p values do not fit the range which is relevant for the current research assumption part of the equation. for each of the risk impact events, the coefficient magnitude can be observed in table i. the highest level of positive effect upon cost overrun is observed in table ii for rp45. it can also be observed that there are mostly negative endogenous risk event impact coefficients. hence, it is stated that low-cost overruns would occur if there is a high influence of risk events. the generated model statistics are presented in table iii. it is observed that the endogenous multiple regression model includes 16 risk impact events with r 2 = 0.902 and p<0.05. therefore, the results indicate that in both models, significant variations are present within the data set of the risk impact events. table ii. endogenous model regression result factor unstandardized coefficients standardized coefficients t sig. b std. error beta (constant) 0.161 0.036 4.463 0.000 rp28 -0.145 0.074 -0.123 -1.969 0.054 rp29 0.218 0.110 0.135 1.993 0.052 rp33 -0.169 0.063 -0.170 -2.679 0.010 rp35 -0.433 0.069 -0.385 -6.293 0.000 rp36 0.378 0.078 0.290 4.863 0.000 rp37 0.192 0.063 0.147 3.028 0.004 rp40 -0.311 0.104 -0.183 -2.994 0.004 rp45 0.746 0.067 0.693 11.151 0.000 rp50 0.414 0.083 0.381 4.968 0.000 rp51 -0.173 0.074 -0.175 -2.347 0.023 rp53 -0.302 0.088 -0.220 -3.440 0.001 rp56 0.640 0.125 0.440 5.140 0.000 rp59 -0.317 0.098 -0.218 -3.242 0.002 rp61 -0.224 0.077 -0.193 -2.907 0.005 rp63 0.339 0.086 0.242 3.933 0.000 rp64 -0.337 0.125 -0.206 -2.698 0.009 dependent variable y: rp44 = construction cost overrun table iii indicates that the p-value is lower than 5%, and the model explains quite a strong supposition against the null hypothesis since p≤1%. engineering, technology & applied science research vol. 10, no. 4, 2020, 6987-6091 6090 www.etasr.com alfraidi et al.: impact of endogenous risk factors on risk cost in ppp projects in saudi arabia table iii. integrated model regression r r 2 std. error of the estimate change statistics r 2 change f change df1 df2 sig. f change 0.962 0.902 0.0621433 2.653 39.741 16 51 0.000 predictors: (constant), rp28, rp29, rp33, rp35, rp36, rp37, rp40, rp45, rp50, rp51, rp53, rp56, rp59, rp61, rp63, rp64 the central alterations of the dependent variable with the independent variable for each unit of change are represented by its regression coefficient. the rest of the model predictors have been kept constant. within a flawless environment, the predictors can be measured using the same reliability levels. hence, using the unstandardized coefficients, the predictor variable weights present in table ii were applied upon (3): � ���� ��� = 0.161−0.145∗ ���� +0.218∗ ���� −0.169∗ ����−0.433∗����+0.378∗����+0.192∗����−0.311∗����+0.7 46∗���� +0.414∗���� −0.173∗���� −0.302∗ ���� +0.640∗ ���� −0.317∗���� −0.224∗���� +0.339∗���� −0.337∗����+ 0.036 0 ≥ y ≥1 (4) the approximations for the theoretical and observed data and the reference line can both be seen in the exogenous risk impact event p-p plot. the reference line and the observed data are quite close which indicates that the observed data and the derived equations are extracted from the same population and similar distributions (figure 2). fig. 2. endogenous risks p-p plot. fig. 3. endogenous model risk cost output probability density/ cumulative overlay. fig. 4. endogenous model risk impact output probability density / cumulative overlay vi. discussion with the help of the literature review, we have been able to extract the risk influence upon the ppp projects in a systematic manner. using a theoretical base, the classification has been carried out in terms of risk type, risk source, and project environment (internal or external). several variables influence the project-specific risk events, including project company effectiveness, project stakeholder relationships, and many more. however, construction risk parameters like inaccurate estimates and others are responsible for the development of internal risk events. after a thorough analysis of the literature, a risk impact event list was created, even though the literature did not shed light on cost overrun and risk event relationship which was investigated through models. the risk event relationship models can be efficiently presented through multiple regression procedures. this regression analysis technique is adequate and able to state the relationship between the independent and dependent variables using the observed behavior that is stated by the statistically measured relationships. hence, regression models were developed using multiple regression analysis. these models helped to identify the classified risk event influence where the independent variable is cost overrun. the f-statistic (sig.<0.01) “significance” value was presented using the anova tests which indicate that the significance of the developed regression models is at a 99% confidence level. hence, the results indicate that the developed models are acceptable. even though the anova tests proved to be useful for testing the developed model and its ability to analyze the variations present in risk event data, it is still not able to indicate the level of relationship among the proxy variable and risk events. therefore, the coefficient of determination (r 2 ) is used to measure the relationship strength. it should be noted that the current research does not include several risk events that might influence the final results in other circumstances. vii. conclusion cost overrun is mostly caused by uncertainties within the environment of a construction project. in the current research, analysis has been carried out upon the interdependency and association among risk constructs, exogenous risk constructs, and risk outcomes. the acquired multiple-regression equations state the relationship among risk constructs. the monte carlo simulation helps model the risk construct while keeping in mind its stochastic nature. according to the results, (figures 3engineering, technology & applied science research vol. 10, no. 4, 2020, 6987-6091 6091 www.etasr.com alfraidi et al.: impact of endogenous risk factors on risk cost in ppp projects in saudi arabia 4), 17 sr is the cost with the minimum risk impact of 0.025 and 892 sr is the cost with maximum risk impact of 0.776. further analysis must be carried out upon the relationship among exogenous and endogenous risk variables to help enhance the extraction of the risk impact amplification because of the active interdependency among system factors along with the output results and system input factors. many construction projects are completed over budget and over time. the presence of uncertainties, inherent in construction projects’ environment, plays an essential role in construction cost overrun. this research has addressed the vital issue of interdependency between risk constructs and risk consequences. the interaction between the risk constructs is captured using multiple regression equations. the stochastic nature of the risk constructs was modeled. there is a need to further investigate the interaction between risk factors in order to increase the detection of any amplification of risk impacts due to the dynamic interdependency within system variables and between the system input variables and output 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[11] m. p. abednego and s. o. ogunlana, “good project governance for proper risk allocation in public–private partnerships in indonesia,” international journal of project management, vol. 24, no. 7, pp. 622– 634, oct. 2006, doi: 10.1016/j.ijproman.2006.07.010. [12] a. boussabaine, risk pricing strategies for public-private partnership projects. hoboken, nj, usa: wiley-blackwell, 2013. [13] d. j. price, a. m. pollock, and s. player, “public risk for private gain? the public audit implications of risk transfer and private finance.” public health policy unit, school of public policy, ucl, london, 2004. [14] a. d. ibrahim, a. d. f. price, and a. r. j. dainty, “the analysis and allocation of risks in public private partnerships in infrastructure projects in nigeria,” journal of financial management of property and construction, vol. 11, no. 3, pp. 149–164, jan. 2006, doi: 10.1108/13664380680001086. [15] a. dziadosz, a. tomczyk, and o. kapliński, “financial risk estimation in construction contracts,” procedia engineering, vol. 122, pp. 120– 128, jan. 2015, doi: 10.1016/j.proeng.2015.10.015. [16] a. alfraidi, s. m. alzahrani, f. binsarra, m. h. h. abdelhafez, e. m. noaime, and m. a. s. mohamed, “impact of political risk on construction cost in ppp project in ksa,” international journal of advanced and applied sciences, vol. 7, no. 5, pp. 6–11, may 2020, doi: 10.21833/ijaas.2020.05.002. [17] f.-m. liou and c.-p. huang, “automated approach to negotiations of bot contracts with the consideration of project risk,” journal of construction engineering and management, vol. 134, no. 1, pp. 18–24, jan. 2008, doi: 10.1061/(asce)0733-9364(2008)134:1(18). [18] j. s. russel, “decision models for analysis and evaluation of construction contractors,” construction management and economics, vol. 10, no. 3, pp. 185–202, jul. 2006, doi: 10.1080/01446199200000018. microsoft word 25-2743_s__etasr_v9_n3_pp4203-4208 engineering, technology & applied science research vol. 9, no. 3, 2019, 4203-4208 4203 www.etasr.com al-omari: lightweight dynamic crypto algorithm for next internet generation lightweight dynamic crypto algorithm for next internet generation ahmad h. al-omari computer science department, faculty of science northern border university, arar, saudi arabia ahmed.alomari@nbu.edu.sa, kefia@yahoo.com abstract—modern applications, especially real time applications, are hungry for high-speed end-to-end transmission which usually conflicts with the necessary requirements of confidential and secure transmission. in this work, a relatively fast, lightweight and attack-resistant crypto algorithm is proposed. the algorithm is a symmetric block cipher that uses a secure pre-shared secret as the first step. then, a dynamic length key is generated and inserted inside the cipher text. upon receiving the cipher text, the receiver extracts the key from the received cipher text to decrypt the message. in this algorithm, ciphering and deciphering are mainly based on simple xor operations followed by substitutions and transpositions in order to add more confusion and diffusion to the algorithm. experimental results show faster encryption/decryption time when compared to known encryption standards. keywords-dynamic crypto algorithm; lightweight crypto algorithm; dynamic cryptography; shared secrets; next internet generation security i. introduction several emerging areas of information and communication technology (ict) require interconnected devices like internet of things (iot) and sensor networks. iot and smart applications are growing rapidly and are commonly accessed through smartphones. currently, more and more smart devices are daily connected to the internet, such as smartphones, smart tvs, video game consoles and even most of the home devices like refrigerators and air-conditioners [1]. all these devices suffer from being resource-constrained regarding their low processing power, limited battery power life, small display size, small memory, and limited storing capacity. as iot and other smart applications are growing rapidly, they encounter many risks and challenges such as dealing with huge amounts of data, processing power, energy consumption, address security and privacy threats [2]. security and privacy are fundamental requirements for any application, especially smart applications. the current modern standard cryptographic algorithms were originally designed for traditional desktop/server implementations and many of them consume an unacceptable amount of system resources (computation power, ram, storage, etc.) and are not suitable for resourceconstrained devices.[2]. therefore, there is a need for lightweight cryptography (lwc) algorithms that suit such resource-constrained devices [3-4]. lwc is one of the most promising research areas in cryptography since it is considered fast in encryption processing, resistant to attacks and low in resource requirements. there are no strict properties needed in order to classify an encryption algorithm as an lwc [5]. according to the national institute of standards and technology (nist), the main reasons for adopting lwc for smart power constrained devices are the need for efficient end-to-end communication and adoptability in resource-constrained smart devices [3, 6]. generally, any cryptographic design should take into considerations the tradeoff between security, cost and performance. the performance measurements include power, energy consumption, latency and throughput. security requirements, on the other hand, aim to maintain an acceptable level of secrecy and privacy of the system. cryptography, which is part of security, is divided into symmetric and asymmetric cryptography. the symmetric cryptography algorithms use a single private key for encryption and decryption and are originally designed for a wide range of applications that use hardware devices with high processing power and large resources. on the other hand, the asymmetric cryptography algorithms use a pair of keys, a public and a private one. one key is used for encryption and the other for decryption. traditional symmetric and asymmetric algorithms are not suitable for constrained devices while lightweight cryptographic algorithms are the best choice [7]. some of the candidate applications for the lwc algorithms include wireless sensor network (wsn), radio-frequency identification, wireless body area network (wban), iot, smart cards, embedded systems, smart systems, etc. [8-9]. these applications support dissimilar devices in heterogeneous environments with minimum human intervention. for example, iot devices communicate with minimum or no human intervention, a fact that represents a new challenge to the iot system by both exposing many security attacks as well as gaining unauthorized device access by the attacker device. this may essentially result in severe system damages. moreover, some iot implementations are cloud-based applications which have many security issues and challenges [3, 10]. this work focuses on introducing a new model of symmetric block cipher encryption. it is classified as lwc since it requires only a small amount of resources like memory, computing, storage, time and space. corresponding author: ahmad h. al-omari engineering, technology & applied science research vol. 9, no. 3, 2019, 4203-4208 4204 www.etasr.com al-omari: lightweight dynamic crypto algorithm for next internet generation ii. related work lightweight encryption is a recent scientific field. many lightweight block ciphers (lwbcs) have been proposed. some of these were modifications and simplifications of traditional block ciphers while others were new like the data encryption standard lightweight (desl) which is basically based on the original design principles of des with a variant of using a single s-box instead of eight s-boxes. desl is claimed to be resistant against most common known attacks like differential, linear, and davis-murphy attacks, and it is used in low resource devices like rfid, wsnr, wbn and iot [11]. over the last decade, variations of lwc with different properties have been proposed [12]. a word-oriented stream cipher [13] that takes 128-bit as an initial vector and an initial key as inputs while the generated output is a 32-bit key-stream. afterwards, the keystream is used to encrypt the plain text. the word-oriented stream cipher algorithm was developed to deal with 8-bit characters in the encryption/decryption process. in each step, the algorithm output is an 8-bit key character, which is bitwise added to the plain-text characters to produce the cipher-text character. the same operation is performed for the decryption process. theoretically, the proposed algorithm shows high performance through high nonlinear complexity. an extensive literature survey of more than 100 algorithms was performed in order to systemize the concept of lwc in [12]. the survey identified two categories of lwc algorithms. the first is the ultra-lwc, which deals with highly specialized algorithms providing one function with high performance on one platform and the second is the ubiquitous cryptography which deals with multilateral algorithms in terms of functionality and implementation. a new dynamic crypto symmetric algorithm [14-16] that uses a pre-shared secret was proposed to regenerate a predefined table. the regenerated table is again rearranged and shifted many times before the shared-key insertion. the encryption/decryption operations used in this algorithm are simple bitwise xor operations between the plaintext and the scrambled text. results show a faster algorithm that achieves better performance than the traditional aes and des. moreover, plenty encryption algorithms especially designed for hardware restricted resources can be easily found. for example, mcryption and crypton are two proposed block ciphers that have the option of using a key size of the length 64-bit, 96-bit or 128-bit. the architecture and the function of each component are simplified in order to run to power-constrained devices [17-18]. hummingbird-2 is a primitive authentication encryption algorithm especially designed for resource-constrained devices such as rfid tags, wsn and very small hardware or software and it is also suitable for resource-restricted devices. this algorithm uses a 128-bit key and a 64-bit initialization vector [19]. authors in [21] improved the original work of [20] by enhancing the transformation table composition. it was proved that swapping rows with columns gives better results. authors in [20] recommended performing the key insertion inside the plain text from both sides simultaneously. moreover, an enhancement was added to adopt a key size of 128 bytes and plaintext size of 190 bytes. in [21], more enhancements and contributions were added. these enhancements act as adding extra features. the final improvement was using cryptographically secure pseudorandom number generators (csprng) to generate and share the shared value. iii. the proposed solution a. background this study represents a symmetric encryption algorithm called lightweight dynamic crypto (lwdc) for the next internet generation. the original work of this study first appeared on 2008 [15]. different researchers added their contributions and enhancements on the original algorithm [1416, 20-21]. the main architecture of the original algorithm has slightly changed since its first release. the enhancements were added on detailed processes in order to achieve a more stable and attack resistant algorithm. the original algorithm consists of three main processes, the index generation process (igp), the encryption process (ep) and the decryption process (dp) [16]. the general architecture of the original algorithm is briefly described as: • the igp is common between the ep and the dp. first, an initial table and a shared-secret are generated and shared. the shared-secret is used to generate the transformation table (tt) and the table of indexes (ti). • the ep is performed by xor-ing the plaintext with the cipher-key to generate the scrambled text. then the cipherkey is inserted inside the scrambled text according to the values from the ti and the result is the ciphertext (c). • the dp is performed exactly as the ep process but in the reverse order. in the dp process, the cipher-key is extracted back from the c. b. the solution architecture in this work, additional cryptographic enhancement properties were added to the original algorithm. these enhancements include: • using the csprng to generate a random shared secret in order to be difficult, but not impossible, for an adversary to predict. • using the csprng to generate a random shared secret key, which should also be difficult, yet not impossible to predict. • using the ipsec based on the internet key exchange protocol (ikev2) to establish a secure connection to exchange data. ipsec is a standard protocol aiming to provide end-to-end security for the internet protocol (ip). the exchanged messages are protected by ipsec and the ipsec session is authenticated using ikev2 [22]. • adding the concept of confusion and diffusion (cd) property to the algorithm by implementing substitution and permutation boxes (s-p-(box)). the cd concept was firstly proposed in [22] as basic building blocks for any cryptographic system. according to [22], the cd concept aims to thwart cryptographic attacks of the statistical cryptanalysis type. confusion strives to make the relationship between the statistics of the ciphertext and the value of the encryption key as complex as possible while engineering, technology & applied science research vol. 9, no. 3, 2019, 4203-4208 4205 www.etasr.com al-omari: lightweight dynamic crypto algorithm for next internet generation the diffusion strives to make the statistical relationship between the plaintext and the ciphertext as complex as possible in order to thwart attempts to deduce the key [2, 23]. the three main processes of the algorithm are described briefly below [16]: 1) index generation process • the shared-value (shrdv) is randomly generated by using the blum blum shub cryptographically secure pseudorandom number generator (bbs-csprng) and is shared by the ipsec-ikev2 tunneling protocol. • the initial table, init, is a 16*16 (hex) table, which is fixed and shared between the sender and the receiver. • the transformation table, trant, is a table that is generated by performing permutation on the init based on the value of shrdv. • the indexing table, indt, is the result of performing another permutation on the transt based on the value deduced from the transt. 2) encryption process • the plaintext (p) is the original text that is going to be encrypted. • the key t is the system key which represents the heart of the encryption process. after generating the key k, it is used to bitwise xored p⊕k and is inserted inside the resulted scrambled table scrt. • scrt is the result of performing the xor operation between the p and the key. • the key insertion keyi is the result of inserting the key k inside the scrt. • the s-box is added to the algorithm to enhance the confusion and diffusion properties of the algorithm. • the ciper text c is the encrypted text. 3) decryption process • the s-box is used to recover back the original form of the c before the key recovery (kr) process is performed. • the kr is the first step in decrypting the c. in the kr process, k is extracted back from the c whereas the scrt is regenerated back. • p is recovered back by performing xor operation between the scrt and the k, p⊕k. the lwdc architecture shown on figure 1 and the pseudo code on figure 2 represent the general design process architecture of the algorithm. the most important component of any encryption algorithm is the encryption key. the key selection process and the key value should be carefully chosen. the encryption key properties include a key secrecy, a key length and an initial value (seed) [24]. the basic principle in choosing any encryption key (shared value) is to be obtained from one of the known cryptographically secure pseudorandom number generators (csprng) like lavarand, simon cooper or landon curt noll. the strength of csprngs depends on their properties. these properties are represented in the difficulty of finding the next bit to be generated from the previous given sequence of bits without having any clue of the seed in polynomial time. in addition to these properties, the algorithm should satisfy forward and backward unpredictability. all of these properties are found in the blum blum shub (bbs) pseudo random number generator. the bbs is considered as the most preferable algorithm for cryptographic purpose like key generation since it is based on quadratic residue npcomplete problem [25]. based on that, the bbs-csprng technique was added to generate the shared value shrdv=f(bbs-csprng) assuming that the ikev2 protocol is used to share the secret value between the communicating parties. fig. 1. the lightweight encryption architecture fig. 2. the pseudocode the other enhancement to the algorithm is adding the sbox before generating c, the s-box will add more cd which is an important property of any block cipher algorithm. cd is performed by applying a constant number of (cd) rounds to the index generation process igp ipsec establishment shrdv = f(bbs-csprng) transt = (init, shrdv) indxt = f(transt) the encryption process ep scrt = (plaintxt ⊕ key) keyi = f(scrt, key, indxt) c= s-box(f(keyi)) the decryption process de kr= f((s-box(c), indxt)) scrt = f(kr) key = f(kr) p= (scrt ⊕ key) engineering, technology & applied science research vol. 9, no. 3, 2019, 4203-4208 4206 www.etasr.com al-omari: lightweight dynamic crypto algorithm for next internet generation extend the domain of a public random permutation [22]. in the decryption process, the same procedures are performed as in the encryption process but in reverse order. the algorithm could be implemented either in hardware or software. in case of hardware limited resources implementation, it is recommended to burn the algorithm on the hardware chipset while in the software implementation it will be easy to use as a portable and fast encryption-decryption algorithm. c. implementation and analysis the algorithm was tested by using java jdk 1.7.0_171 and the java cryptography extension (jce) on a fujitsu laptop i74702mq cpu (8-gb ram, windows-7). the same files that were used to test the svscs algorithm in [21] were used in the experiments and the testing was performed on 10 different file sizes and the results were finally compared with the lwdc results. ep and dp processes were performed on different p sizes. it is worth mentioning that the comparison was performed on the encryption-decryption time which includes the sub-processes of both algorithms (table i). the key generation process, (s-p)-box, table scrambling, key insertion, and the encryption time for the different plaintext size are listed on table i. table i. encryption time comparison plaintext size in mb time alg. 0.35 0.99 1.65 3.30 6.60 11.80 key gen. svscs 0.0117 0.0118 0.0112 0.0116 0.0116 0.0118 lwdc 0.0116 0.0117 0.0110 0.0113 0.0116 0.0118 (s-p)-box svscs 0.0058 0.0589 0.1011 0.0502 0.1178 0.3583 lwdc 0.0059 0.0590 0.1022 0.0502 0.1189 0.3594 scrambling svscs 0.0286 0.0967 0.1346 0.1987 0.5871 0.7220 lwdc 0.0272 0.0990 0.1364 0.2004 0.6201 0.7579 key insert svscs 0.0132 0.0523 0.0686 0.2590 0.2770 0.6021 lwdc 0.0145 0.0564 0.0788 0.2675 0.2872 0.6245 encryption svscs 0.0593 0.2197 0.3165 0.5194 0.9936 1.6942 lwdc 0.0594 0.2214 0.3180 0.5207 0.9969 1.6994 the encryption time comparison between the svscs and our algorithm is shown in figure 3, in which the encryption time looks equal for both algorithms. in fact, the svscs is a little bit faster than our algorithm because the svcs performs the (s-p)-box operation before the key insertion process, whereas in our algorithm the (s-p)-box is performed after the key insertion which expands table size. the rest of the figures (figures 4-7) show the time variation between the sub encryption operations for both algorithms. the key generation time is shown on figure 4 where it is clear that our algorithm is a little bit faster than the svscs regardless of data size due to the bbs-csprng being used. the (s-p)-box time which represents the cd properties is shown on figure 5 where it is clear that our algorithm consumes more time than the svscs, due to the (s-p)-box operations that are performed on a larger table size than the one of the svscs. the table scrambling time is shown in figure 6 in which no significant time difference is noticed between the algorithms. the key insertion process shown in figure 7 indicates that there is no significant time difference between the algorithms. decryption time comparison between svscs and our algorithm is listed on table ii. the key generation process is not calculated here since it is generated in the encryption phase. fig. 3. encryption time fig. 4. key generation time fig. 5. confusion and diffusion time fig. 6. table scrambling time fig. 7. key insertion time engineering, technology & applied science research vol. 9, no. 3, 2019, 4203-4208 4207 www.etasr.com al-omari: lightweight dynamic crypto algorithm for next internet generation decryption time comparison between the svscs and our algorithm is shown in figure 8. the decryption time looks equal for both algorithms. in some cases our algorithm performs faster than the svscs and in other cases the svscs performs faster. the time difference is not significant. the algorithm was improved by adding the ipsec-ikev2 to exchange the secret shared value, by adding the bbs-csprng to generate the secure shared value, and by changing the location of the (s-p)-box operations in the algorithm. these enhancements give extra randomness (confusion and diffusion) to the cipher text and make it more attack-resistant. however, the added enhancements did not affect the encryption speed negatively, the detailed analysis on [16, 20] is still valid in this enhanced version of the algorithm. on this work, the cipher text becomes more resistant to brute force attacks since the algorithm uses a plaintext size of 190 bytes (1520 bits), key size of 128 bytes (1024 bits) and the (s-p)-box. moreover, using the cd properties in addition to the key insertion process produces a well-mixed and shuffled ciphertext. thus, it will be hard to solve a plaintext size of (2(1520))×(2(1024)). in this case, the only possibility to attack the algorithm is to use cryptanalysis attacks. from the previous studies, it is proven that the algorithm outperforms the speed of the advanced encryption standard (aes). it is 15 times faster in encryption and 9 times faster in decryption [14-16, 20-21]. table ii. decryption time comparison ciphertext size in mb time alg. 0.35 0.99 1.65 3.30 6.60 11.80 s-box svscs 0.0230 0.0212 0.1455 0.0878 0.1321 0.6987 lwdc 0.0228 0.0251 0.1634 0.0943 0.1567 0.7012 scrambling svscs 0.0306 0.1001 0.1532 0.3175 0.6078 0.9874 lwdc 0.0304 0.1098 0.1612 0.3220 0.6231 0.9913 recovery svscs 0.0147 0.1182 0.0608 0.1836 0.4827 0.4050 lwdc 0.0132 0.1163 0.0610 0.1926 0.4931 0.4069 decryption svscs 0.1215 0.3745 0.6841 1.0050 2.0025 3.7836 lwdc 0.1117 0.4695 0.5996 1.1099 2.3634 3.4918 fig. 8. decryption time iv. conclusion the proposed algorithm shows faster encryption-decryption time than the conventional standard algorithm (aes). the algorithm has the property of hardware and software implementation and hence the uploading of the code on the hardware chipset for faster processing is recommended. the algorithm is simple in nature but very hard to break. adding the ipsec-ikev2, the bbs-csprng and the (s-p)-box puts the algorithm in the levels of the modern lightweight symmetric encryptions in the market. acknowledgment the authors gratefully acknowledge the approval and the support of this research from the deanship of scientific research study by the grant no. 7189-sci-2017-1-8-f7, northern border university, arar, saudi arabia. references [1] m. talbi, f. maddouri, a. jemai, m. s. bouhlel, “application of a lightweight encryption algorithm to a quantized speech image for secure iot”, sixth international conference on advances in computing, electronics and communication, rome, italy, 2017 [2] s. singh, p. k. sharma, s. y. moon, j. h. park, “advanced lightweight encryption algorithms for iot devices: survey, challenges and solutions”, journal of ambient intelligence and humanized computing, 2017 [3] k. a. mckay, 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“indifferentiability of confusion-diffusion networks”, in: advances in cryptology–eurocrypt 2016, lecture notes in computer science, vol. 9666, pp. 679-704, springer, 2016 [24] h. feistel, cryptographic coding for data-bank privacy, ibm thomas j. watson research center, 1970 [25] g. singh, supriya, “a study of encryption algorithms (rsa, des, 3des and aes) for information security”, international journal of computer applications, vol. 67, no. 19, pp. 33–38, 2013 [26] divyanjali, ankur, v. pareek, “an overview of cryptographically secure pseudorandom number generators and bbs”, international conference on advances in computer engineering & applications, ghaziabad, india, february 15, 2015 microsoft word 38-3330_s_etasr_v10_n1_pp5307-5313 engineering, technology & applied science research vol. 10, no. 1, 2020, 5307-5313 5307 www.etasr.com alshammari: evaluation of power system reliability and quality levels for (n-2) outage contingency evaluation of power system reliability and quality levels for (n-2) outage contingency badr m. alshammari department of electrical engineering college of engineering university of hail hail, saudi arabia bms.alshammari@uoh.edu.sa abstract—one of the main objectives of electric power utilities keeping up a continuous and adequate power supply to the customers at a sensible cost. this paper contributes to the solution of the reliability and quality assessment problems in power systems, using the (n-2) outage contingency scenario to evaluate power system’s reliability and quality levels. therefore, the methodology presented in this paper is based on the integration of reliability measures, quality indices, and contingency analysis. while reliability formulas have traditionally been applied to small and illustrative power systems, large-scale reliability and quality assessment go far beyond direct implementation of formulas. systems with hundreds of buses and tens of complex stations can only be analyzed using advanced and numerically effective large-scale algorithms for reliability and quality assessment as demonstrated in this paper. keywords-reliability; evaluation; contingency; large-scale power systems i. introduction power system reliability is defined as the probability of an electric power system to perform a required function under given conditions for a given time interval. a generalized form of the reliability definition, takes into consideration the effect of repair or replacement after a failure [1-3]. in general, a component in a power system may exist in one of two states, namely “operation” or “failure”. in some cases, extra states may be considered to indicate partial operation, derated functioning or repair and maintenance. in other words, an electric power network containing generation and transmission facilities could be divided into several states in terms of the degree to which adequacy and security constraints are satisfied in a reliability evaluation of the composite system [4-5]. power system reliability evaluations have been concentrated on the analysis of system adequacy, the ability to supply all loads within performance requirements [6-8]. power system components, in this regard, are divided into two main parts, namely the generating equipment and the transmission equipment. in general, a component is a piece of equipment or a group of items which is viewed as an entity and is not subdivided during reliability analysis. main generating components are the boiler installation (single or multiple), common header system, turbine, generator, and boiler. transmission lines and transformers are considered as main transmission components [8-11]. a secure system is able to tolerate the outage of components without interrupting the demand supply. given an electric power system on n components, the n−k criterion is used to evaluate the outage of k components [12-14]. reliability indices for a power system are calculable from either its performance history or from component data utilizing mathematical models which express the system reliability indices in terms of the component indices included in the ieee committee reports [15-18]. most of the traditional contingency assessment methods do exclude the probability of contingency in the analysis. they rather define a so-called set of credible contingencies, which are equally considered in the evaluation. however, it is known that some contingencies, which have critical effects on the system performance, may have a much lower probability of occurrence than those having less impact on the system. therefore, an accurate assessment of the impact of contingencies on the system performance should not overlook the probability of contingency occurrence. the nature of the large-scale power systems causes a major problem in computational resources when numerous contingency and system operating scenarios have to be examined and analyzed [19]. the investigated reliability indices are not only useful for the design of flexible power supply reliability for customers but also beneficial to the long-term system capacity expansion planning of electric power systems [20-21]. this study contributes to the solution of the reliability indices and system quality performance problem in real power systems. the computational scheme presented in this paper can effectively assess a composite system’s reliability and power quality, analyzes the network structure, generation and load balance, evaluates various composite system performance reliability indices applied to the system subject to (n-2) contingency with certain or random occurrences. a practical application to a portion of the saudi power grid is also presented in this paper for demonstration purposes. ii. problem formulation the novel methodology applied in this paper is based on the original work of [20]. the reliability of a power system depends on the reliability of its individual components as well as the size and structure of the system. various factors should be taken into account when evaluating the reliability of the system. examples of these factors are the operation and failure time distributions, failure modes, operation practices and load priorities. corresponding author: badr m alshammari engineering, technology & applied science research vol. 10, no. 1, 2020, 5307-5313 5308 www.etasr.com alshammari: evaluation of power system reliability and quality levels for (n-2) outage contingency a. reliability evaluation processes the reliability evolution of a power system can be described by a six-step procedure as shown in figure 1 [22]. step i represents the component constants and capabilities. steps ii and iii represent the possible component outages and the definition of possible system failure modes resulting from single or multiple component outages. step iv represents the possible realizations of the component performance which may be actual or simulated. step v describes the system model, where the system performance is obtained. the techniques used for such analysis are selected based on their accuracy and speed to suit either planning or operation studies. at step vi the system model results are analyzed to evaluate the system reliability. fig. 1. reliability evaluation processes b. conditional probabilities of system failure in almost all probability applications in reliability evaluation, component failures within a fixed environment are assumed to be independent events. it is entirely possible that component failure can result in system failure in a conditional sense. this can occur in parallel facilities that are not completely redundant. if the load can be considered as a random variable and described by a probability distribution, the failure at any point due to component outage is conditional upon the load exceeding some value at which a satisfactory voltage level at the load point can be maintained. if two events a and b are considered to be independent, then: � �� ∩ � � � ���� ∙ ���� (1) if the occurrence of a is dependent upon n number of events bi, which are mutually exclusive, then: � �� � � ∑ ����|�� ∙ ������ ��� (2) if the occurrence of a is dependent upon only two mutually exclusive events for component b, success and failure, designated as bx and by respectively, then: � �� � � ���|��� ∙ ����� � ������� ∙ ����� (3) with respect to reliability, this can be expressed in a simpler form: p(system failure) = p(system failure if b is good) p(bx)+ p(system failure if b is bad) p(by) the complementary form is similar as: p(system success) = p(system success if b is good) p(bx)+ p(system success if b is bad) p(by) iii. large-scale reliability modeling the practical power system is large-scale in nature. it consists of numerous elements, which are characterized by forced outage rates representing their tendency to be off-service due to malfunctions. a suitable technique would implement an efficient sectioning scheme in order to keep possession of only the parts of the system affected by a contingency, while the rest of the system is modeled by network equivalents. the use of the partitioning scheme permits a faster contingency analysis for large systems. in order to accurately simulate practical operator's response to power network outages, a maximum load-supply optimization scheme should be employed prior to the evaluation of various system reliability measures. the optimization algorithm evaluates the post-outage generationload pattern based on real-time emergency dispatch procedures, which try to maximize the amount of system load supplied during the system outage. the generation and transmission reserve capacities of the retained network represent the optimization variables which are manipulated to maximize the load supplied during the outage situation. in this work, the system reliability indices and power quality performance are determined based on the optimized post-outage generation-load pattern. these reliability and quality indices can then be evaluated and displayed for real life networks of loads of interest associated with various system outages and according to their probability of occurrence. iv. power system reliability indices in general, a set of system-wide outage-based reliability indices can be defined. these reliability indices, which can easily be coded into computer programs, are sufficient to describe a range of practical reliability measures in large-scale power systems. this section summarizes the most widely-used indices for measuring the levels of power system reliability under outage conditions. for a contingency m, the values of the network variables will be the solution of the maximum loadsupply optimization problem. also, let fm be the probability of contingency scenario m (the sum of fm for all m, including basecase contingency-free scenario is 2). then the following three system-wide contingency-based reliability indices may be defined. a. system-wide loss of load probability loss of load probability (lolp) indicates the probability (chance) that a system load would be fully or partially lost due to randomly occurring single or multiple contingencies (outages) in the system. the random nature of the outages is simulated using the actual historical outage data of various system elements. the loss of load probability can be expressed in (4): engineering, technology & applied science research vol. 10, no. 1, 2020, 5307-5313 5309 www.etasr.com alshammari: evaluation of power system reliability and quality levels for (n-2) outage contingency ���� � ∑ ������������ (4) where: ������� � ����{ ������ ���} (5) represents the system loss of load probability for any assumed contingency m (loss of generation and/or transmission) in the power grid, ����� ��� � "��#� (6) represents the loss of load probability at bus � for contingency m, and: "� ��� �     ≤ p > pif1 p pif0 o(m) o(m) �� �� (7) where op� denotes the scheduled demand at load bus �. in (4), mc denotes the number of contingencies considered and y� is a 0 or l factor to indicate subsystems (if desired). b. system-wide expected value of demand not served the expected value of demand not served (edns) reliability index can be shown with the following equations: ) ln =1 (dns ( )dnsyε ε=∑ � � � (8) where nl is the number of load buses in the system, ε�%&'�� � )dns( (m) m 1=m c � ε∑ (9) represents the expected value of demand not served at bus �, ( ) ) ( ) m m l m l (dns f dnsε = (10) represents the expected value of demand not served at bus � for the contingency m and: demand not served at bus for contingency (m) l m dns =� (11) c. system-wide expected value of energy not served expected energy not served (eens) indicates the amount of twh of energy per year that is likely not to be supplied to a system load center due to randomly occurring single or multiple contingencies (outages) in the system. therefore the eens can be expressed in (12)-(15) as: ε�(&'� � )ens( y n =1 l �� � ε∑ (12) where: ε�(&'�� � )ens( (m) m 1=m c � ε∑ (13) represents the expected value of energy not served at a bus �, ε�(&'��� � ens f (m)m � (14) represents the expected value of energy not served at bus � for contingency m, and (&'�� � dns t (m)(m) � (15) represents the energy not served at bus � for contingency m and t (m) denotes the time duration of contingency m. v. quality assessment in power systems a. general both issues of reliability and quality represent considerable challenges. the first issue could be resolved with the use of advanced large-scale network analysis with efficient sparsematrix algorithms as simulated in this paper. the second issue has to be dealt with in a more careful manner. the main difficulty, in this regard, was the formulation of the overall composite quality problem in terms of the trio-interactions between generation, transmission and demand in a global manner. a fact also demonstrated in this paper is the harmony relationship between available generation capacities, transmission capabilities and required demand levels. more importantly, the methodology used and the choice for technical system quality expressions had to be in full harmony with what is being used inside the utilities by operators, technicians, engineers and managers. the term integrated (or composite) system quality has quietly evolved over the years, although less formally, to address the ever challenging dilemma of economy versus security/reliability. a power system with low reliability standing is no less desirable than a costly system with generous reserves and stand-by facilities. a “quality” system is one in which electric energy flows, as un-interrupted as possible, from generation through transmission to load with neither bottling nor redundancy in any portion of the system. in any real system, the composite quality index is undermined, e.g. by generation bottling where available generation cannot be provided through a deficient transmission portion. indeed, from the cost effectiveness point of view, the integrated system quality index would also suffer if transmission redundancy occurs (i.e. more transmission capacity than actually needed). it is clear that the problem under consideration is of a global nature and deals mainly with the generation-transmission-load connectivity and capacity aspects. therefore, at least in the first phase, an integrated system quality study should address important issues like the “need for” and “level of utilization” of various generation and transmission facilities in the power grid and assess whether such facilities are indeed in the “right place” and with the “right amount”. b. station and system quality indices figure 2 demonstrates the basic model structure for evaluating various quality indices. the following reliability and quality indices are defined: minimum load lost = mld_lost � max2 0 � − 5 (16) engineering, technology & applied science research vol. 10, no. 1, 2020, 5307-5313 5310 www.etasr.com alshammari: evaluation of power system reliability and quality levels for (n-2) outage contingency maximum load lost = xld_lost � max2 0 � � � 4 5 (17) minimum generation bottled = mgn_btld � max2 0 � 45 (18) maximum generation bottled = xgn_btld � max2 0 : � ; 4 5 (19) minimum capacity un-utilized= mcp_nutz � max2 0 5 4 : 4 ; (20) maximum capacity un-utilized= xcp_nutz � max2 0 5 4 : (21� minimum capacity surplus = mcp_spls � max2 0 5 4 � 4 � (22) maximum capacity surplus = xcp_spls � max2 0 5 4 � (23) fig. 2. basic model for quality evaluation system-wide quality indices are evaluated using similar formulas as (16)-(23), which in this case are applied to system areas and zones of interest. the system connectivity structure is used in rather complex algorithms to interconnect various stations among a given area (or zone) and between different areas (or zones) in the system. vi. large-system reliability and quality indices the overall program structure which is used in this paper revolves around three major tasks during normal program execution. the first major task is the preparation of several database blocks, which contain system nodes and element data, area and zone definitions, outage history data, station element data, station configuration data, and flow pattern data. the second includes validation of all database entries using a comprehensive 3-level data checking routine. in the third major task, various station and system reliability and quality indices are evaluated (including loss-of-load probability, bottled generation, surplus capacity, and unutilized transmission). a block diagram of the overall program organization is shown in figure 3. vii. application of reliability performance and quality evaluation the system reliability performance has been applied to a practical power system comprising of a portion of the interconnected saudi power grid, where overall system reliability indices are evaluated and assessed. the power system consists of two main regions, namely the central and the eastern region. the two systems are interconnected through two 380kv and one 230kv double-circuit lines. the system model used in the current application comprises of 119 buses (19 generators, 100 loads), 334 lines and 122 transformers, as shown in figure 4. fig. 3. overall program organization engineering, technology & applied science research vol. 10, no. 1, 2020, 5307-5313 5311 www.etasr.com alshammari: evaluation of power system reliability and quality levels for (n-2) outage contingency fig. 4. single-line diagram of the power system model used the power system will be studied in depth in regard to its reliability and quality measures. the reliability and quality study criteria include, (n-2) outage scenarios for the 380kv transmission grid as well as for the individual 132kv substations. the detailed station results show the impact of individual station component outages on various station capability and reliability measures. if exactly one prior outage in another station element had occurred prior to a particular outage, the result is said to be associated with an (n-2) contingency scenario. in this, regard, the (n-2) results include the same outage-set except for breakers (major station nonprotection equipment). a. loss of load in stations for (n-2) contingencies figure 5 shows 3-dimensional graphs depicting the variation of loss of load in stations of the worst double contingency (excluding breaker outages) on station load loss for some examples on the analyzed stations. fig. 5. 3-dimensional graph showing variation of loss of load in stations of (n-2) contingency for (n-2) contingencies in station #8001, the combined outage of transformer #grid-t3 and any of the other elements (one at-a-time) would cause about 64.2mva or 32% of load loss, although this element has no reported historical outages. a maximum load loss of 80.3mva in station #8008 is caused by outage of transformer. for (n-2) contingencies in station #8009, the combined outage of transformer and any of the other elements (one at-a-time) would cause about 55.8mva of load loss. in station #8014, on the other hand, the combined outage of transformer would result in a maximum load loss of 145.7mva. for (n-2) contingencies in station #8076, the outage of the transmission or transformer combined with and any of the other elements (one at-a-time), would decrease the maximum station flow from 14.2mva to 4.8mva and would cause about 9.4mva of load loss. b. maximum station flow for (n-2) contingeny table i summarizes the impact of the worst double contingency (excluding breaker outages) on maximum station flow for some examples of the analyzed sec-c stations. for easy reference and comparison, the stations are ordered in accordance with the percentage drop in maximum flow. although different outages in station #8004 would not influence the station flow capability, which stays constant at 20.4mva. on the other hand, in station #8077, a heavy drop of 2.5mva (88%) in the maximum station flow would occur subjected to outages in the breaker or the transformer. c. quality results for (n-2) contingency scenarios figure 6 shows the value of some quality indices. the expected demand not served (edns_indx) for the entire system is 387.9mw, almost 69% of this occurs in riyadh city (c1) alone. maximum expected load not served (elns_indx) engineering, technology & applied science research vol. 10, no. 1, 2020, 5307-5313 5312 www.etasr.com alshammari: evaluation of power system reliability and quality levels for (n-2) outage contingency of 434.6mva and the expected energy not served (eens_indx) of 8.4gwh occur in the same area. the worst values of the expected generator power bottled (e_gp_btld) of 76%, expected generator energy bottled (e_ge_btld) of 77% and expected non-utilized capacity (e_cp_nutz) of 72% also occur in c1. on the other hand, the dawadmi area (c5) and riyadh rural (c4) would not cause any e_gp_btld or e_ge_btld. the maximum of the priority-based excess at no outage element (a_b_excs0) of 9874mva and the maximum of priority-based excess at one outage element (a_b_excs1) of 9596.2mva occur at qassim area. the overall system would not experience any priority-based deficit at no outage element (a_b_dfct0) or priority-based deficit at one outage element (a_b_dfct1). table i. impact of worst case single contingency on station maximum flow for n-2 contigensy station no. station maximum flow percentage change (%) nominal (mva) minimum (mva) 8004 20.4 20.4 0 8813 102.9 88.7 14 8079 428.4 276.7 35 9006 700 320.5 54 8007 147.8 58.2 60 8077 21.7 2.5 88 fig. 6. output system quality chart viii. conclusion lower service reliability levels jeopardize energy supply continuity and increase the likelihood of additional maintenance and the restoration costs due to the resulting higher rate of system outages. on the other hand, system performance quality indicates the desired harmony balance between generation facilities, transmission capabilities, and consumer demand levels in various zones of the electric power system. poor system quality levels often imply either deficiency or excess in the designed overall system capabilities. symptoms of poor system quality include generation bottling (available generation that cannot be used because of transmission limitations), unutilized transmission, capacity deficiency, and energy surplus. the costs associated with low service reliability or poor system quality are enormous, and can be largely avoided if enhancing system planning simulation models and appropriate computer-sided solution tools are developed and used to detect and correct potential problems. in this regards, this paper contributes to the solution of these problems using (n-2) outage contingency scenarios to evaluate power system reliability and quality levels. while reliability formulas have traditionally been applied to small and illustrative power systems, large-scale reliability and quality assessment goes far beyond direct formula implementation. systems with hundreds of buses and tens of complex stations can only be analyzed using advanced and numerically effective large-scale algorithms for reliability and quality assessment, as has been demonstrated in this paper. the reliability and performance quality indices, when evaluated at a given load level and a certain scenario ((n-2) outage contingency scenario) of available generation and transmission capacities, would provide indications. acknowledgment this work was supported by the university of hail. references [1] r. billinton, power system reliability evaluation, gordon and brach, 1970 [2] j. endrenyi, reliability modeling in electric power system, john wiley and sons, 1978 [3] h. f. lester, “power system: functional reliability more than component reliability is key in serving customers”, ieee spectrum, vol. 18, pp. 5859, 1981 [4] r. billinton, e. khan, “a security based approach to composite power system 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billinton, d. huang, “effects of load forecast uncertainty on bulk electric system reliability evaluation”, ieee transactions on power systems, vol. 23, no. 2, pp. 418-425, 2008 [10] m. a. el-kady, b. m. alshammari, “a practical framework for reliability and quality assessment of power systems”, journal of energy and power engineering, vol. 3, no. 4, pp. 499-507, 2011 [11] b. m. alshammari, m. a. el-kady, y. a. al-turki, “power system performance quality indices”, european transactions on electrical power, vol. 21, no. 5, pp. 1704–1710, 2011 [12] b. m. alshammari, m. a. el-kady, “probabilistic assessment of power system performance quality”, journal of energy and power engineering, vol. 4, no. 5, pp. 372-379, 2012 [13] s. gope, a. k. goswami, p. k. tiwari, “transmission congestion management using a wind integrated compressed air energy storage system”, engineering, technology & applied science research, vol. 7, no. 4, pp. 1746-1752, 2017 [14] o. kahouli, b. ashammari, k. sebaa, m. 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pes summer meeting, san francisco, usa, july 20-25, 1975 [18] m. a. el-kady, b. a. alaskar, a. m. shaalan, b. m. al-shammri, “composite reliability and quality assessment of interconnected power systems”, international journal for computation and mathematic in electrical and electronic engineering, vol. 26, no. 1, pp. 7-21, 2007 [19] s. t. lee, “estimating the probability of cascading outages in a power grid”, 16th pscc, glasgow, scotland, july 14-18, 2008 [20] b. m. alshammari. “evaluation of power system reliability levels for (n-1) outage contingency”, international journal of advanced and applied sciences, vol. 6, no. 11, pp. 68-74, 2019 [21] b. m. alshammari, “assessment of reliability and quality performance using impact of shortfall generation capacity index on power systems”, engineering, technology & applied science research, vol. 9, no. 6, pp. 4937-4941, 2019 [22] j. van casteren, m. bollen, m. schrnieg, “reliability assessment of electrical power systems: the weibull-markov stochastic model”, ieee transactions on industry applications, vol. 36, no. 3, pp. 911-915, 2000 microsoft word 34-3714_setasr_v10_n4_pp6080-6086 engineering, technology & applied science research vol. 10, no. 4, 2020, 6080-6086 6080 www.etasr.com lemita et al.: gradient descent optimization control of an activated sludge process based on radial … gradient descent optimization control of an activated sludge process based on radial basis function neural network abdallah lemita department of electronics, faculty of engineering ferhat abbas university setif i setif, algeria abdallahlemita@yahoo.fr sebti boulahbel department of electronics, faculty of engineering ferhat abbas university setif i setif, algeria boulahbel_s@yahoo.fr sami kahla research center in industrial technologies cheraga, algiers, algeria samikahla40@yahoo.com abstract-most systems in science and engineering can be described in the form of ordinary differential equations, but only a limited number of these equations can be solved analytically. for that reason, numerical methods have been used to get the approximate solutions of differential equations. among these methods, the most famous is the euler method. in this paper, a new proposed control strategy utilizing the euler and the gradient method based on radial basis function neural network (rbfnn) model have been used to control the activated sludge process of wastewater treatment. the aim was to maintain the dissolved oxygen (do) level in the aerated tank and have the substrate concentration chemical oxygen demand (cod5) within the standard limits. the simulation results of do show the robustness of the proposed control method compared to the classical method. the proposed method can be applied in wastewater treatment systems. keywords-activated sludge process; euler method; gradient method; nonlinear system; rbf neural network; wastewater treatment i. introduction various industrial processes often generate large quantities of wastewater that must be treated in the safest and least expensive way, according to the discharge regulations. this water, prior to its discharge, is treated through a primary and a secondary process, which increase production cost. therefore, modern industries seek ways to reduce the use of water during the production process and/or means for a more efficient and low-cost secondary treatment. the primary treatment consists of an operation that separates solid particulate materials and coarse contaminants, by previous decanting. the secondary treatment is after the decanting and consists in the biological removal of dissolved contaminant material by the use of active sludge consisting of microorganisms that metabolize the dissolved organic matter in aerobic conditions [1, 2]. dissolved oxygen (do) level has a direct influence on the activity of the microorganisms. insufficient supply of do worsens the quality of the treated wastewater, and for that reason the control of the do concentration became the most studied control in activated sludge process [3]. many control strategies have been proposed for activated sludge process of wastewater treatment, starting from classical controllers such as the proportionalintegral derivative (pid) controller to keep the process at a set-point [4, 5] and fuzzy logic control to improve the operational performance of the system [6, 7]. some modern controllers based on the process model have been also used for the activated sludge process. model predictive control (mpc) methods have been applied on the distinct activated sludge process [8-10]. an adaptive fuzzy control strategy for do concentration was used to control the activated sludge process in [11]. the controller manipulates the flow control valves supplying air to the bioreactor. in [12], takagi-sugeno fuzzy pi control has been applied for managing do concentration. authors considered the dilution rate, influent do and influent substrate concentration as the disturbance. two control strategies which as a gain scheduling pi control and a model predictive control (mpc) were used to maintain substrate concentration in the effluent within the standard limits by controlling the do concentration in [13]. authors in [14], employed a fuzzy model-based predictive controller for activated sludge process. the objective was to maintain the do concentration. authors in [15] used a takagi sugeno (ts) fuzzy inference system (fis) to approximate the feedback linearization law for controlling the do concentration in the bioreactor. the purpose was to obtain the chemical oxygen demand (cod5) limited in the effluent. piotrowski proposed nonlinear fuzzy control for tracking the do reference trajectory in activated sludge process via the aeration system [16]. sequencing batch reactor and aeration system are modeled as plant control performed by the cascade nonlinear adaptive corresponding author: sami kahla engineering, technology & applied science research vol. 10, no. 4, 2020, 6080-6086 6081 www.etasr.com lemita et al.: gradient descent optimization control of an activated sludge process based on radial … control system extended by an anti-windup filter in [17]. authors in [18] developed an adaptive neural technique using a disturbance observer to solve the do concentration control problem. in this paper, a nonlinear control strategy based on euler and gradient method to control the do in wastewater treatment process via aeration rate is proposed. the performance of the proposed control strategy laws is illustrated with numerical simulations and their results are compared with a conventional pi controller’s. ii. euler method let us consider the following differential equation: ( ) ( ) ( )( )tutytf t ty u u ,,= ∂ ∂ (1) ( ) 00, yyu u =ℜ∈∀ is the initial condition, t : time, u: input control, uy : output system. considering both control inputs ( ) 0utu = , and ( ) 1utu = , then (1) yields: ( ) ( )( )0,, 00 utytft ty u u = ∂ ∂ (2) ( ) ( )( )1 1 1 , , u u y t f t y t u t ∂ = ∂ (3) figure 1 shows the curves of (2) and (3). fig. 1. curve of equations (2) and (3). the numerical solution of the differential equation (2) is defined to be a set of points ( )kk yt , and each point is an approximation to the corresponding points ( )( )kk tyt , . we begin by discretizing the variable t into n equal subintervals such as htttttt nn =−==−=− −11201 ... , the parameter h is the step size. the principal of euler's method is to approximate the solutions of (2). we begin by integrating the two parts of (2) between 0t and 1t (we begin by choosing a step size htt =− 01 ). the system equation can be written as follows: ( ) ( ) ( )( )∫+= 1 0 000 001 ,, t t uuu dtutytftyty (4) by using the euler method, (4) can be written as: ( ) ( ) ( )( )001 ,, 000 utythftyty uuu +≈ (5) for 0≥k : ( ) ( ) ( )( ) ,,. 01 000 utytfhtyty kukkuku +=+ (6) the objective of the proposed algorithm is to control the system output ( )10 +ku ty in order to track a desired reference ( )1+ktr via the input controlu . for that reason, we have to find at every instant kt the value of ku that makes the system output 0u y track the referencer . iii. gradient descent algorithm for controlling of nonlinear system gradient descent is an iterative minimization method. in this paper, the gradient descent method is employed to control a nonlinear system. from (6), we have: ( ) ( ) ( )( ) 0 0 01 0 0 0 0 . , , u u u y t y t h f t y t u= + (7) firstly, at time 1t , we have to find 1u where ( ) ( )110 trtyu = . ( ) ( ) ( )( )10001 ,,. 001 utytfhtyty uuu += (8) the input control ku is adjusted by using the gradient descent algorithm by minimizing the objective function with respect to 0u . the objective function in this case is the squared error ( )1te between ( )11 tyu and ( )10 tyu . ( ) ( )( ) ( ) ( )( ) ( ) ( )( )211 2 11 2 11 0 01 2 1 2 1 2 1 tytr tytytete u uu − =−== (9) the input control 1u is updated by using the gradient descent algorithm: ( ) 0 1 01 . u te uu ∂ ∂ −= λ (10) whereλ is the learning rate parameter. ( ) ( ) ( ) 0 1 1 1 01 0 0 .. u ty ty te uu u u ∂ ∂ ∂ ∂ −= λ (11) ( ) ( ) 0 1 1 0 1 0 . . u y t u u e t u λ ∂ = + ∂ (12) the rbf neural network will be used to determine ( ) 0 1 0 u y t u ∂ ∂ . engineering, technology & applied science research vol. 10, no. 4, 2020, 6080-6086 6082 www.etasr.com lemita et al.: gradient descent optimization control of an activated sludge process based on radial … iv. rbfnn algorithm the radial basis function neural network (rbfnn) is introduced in [19]. the rbfnn has three layers: an input layer, a nonlinear hidden layer that uses gaussian function as activation function, and a linear output layer [20-22]. rbfnns have many uses, including function approximation, classification, and system control. they have the advantage of fast learning speed and are able to avoid the problem of local minimum. the structure of the rbf neural network is illustrated in figure 2. fig. 2. rbf neural network structure. the output of the jth hidden neuron with center ci,j and width parameter bj is:           − −= 2 2 , 2 exp j ji j b cx h (13) where [ ]tnxxxx ,...,, 21= is the input vector of the rbf network. the rbfnn output can be described in the following equation:           − −== ∑∑ == 2 2 , 1 ,1 , 2 exp j jim j jl m j jjlnn b cx whwy (14) where wl,j is the weight between the hidden layer and the output layer. the center ci,j, the basis width parameter bj and the weights wl,j of the rbfnn are adjusted by using the gradient descent algorithm to minimize the sum of square error rbfe (the error between the system output 0uy and the rbfnn output ym (figure 3)) by using the following equations: ( ) ( ) ( ) ( )( )211 ,,,,, −−−+∆+−= kckcckckc jijijijiji α (15) ( ) ( ) ( ) ( )( )211 −−−+∆+−= kbkbbkbkb jjjjj α (16) ( ) ( ) ( ) ( )( )211 ,,,,, −−−+∆+−= kwkwwkwkw jljljljljl α (17) the expression of erbf is given as: ( )( ) ( ) ( )( ) 2 1 2 2 1 2 1 ∑∑ = −== r k nnurbfrbf kykykee k (18) the corresponding modifier formulas are:         − =∆ 2 , ,, .. j ji jjlrbfji b cx hwec η (19) 3 2 , , .. j ji jjlrbfj b cx hweb − =∆ η (20) jrbfjl hew ., η=∆ (21) where a is momentum factor, and η is the learning rate. generally, it is difficult or impossible to find ( ) 0 10 u tyu ∂ ∂ , therefore the rbfnn is used to approximate it. if the rbfnn output nny is equal to the system output 0uy , we can use the rbfnn output to find ( ) 0 10 u tyu ∂ ∂ . the rbfnn output nny will approach the system output [23], then 0u y could be written as: ( )           − − ∂ ∂ = ∂ ∂ = ∂ ∂ = ∂ ∂ ≈ ∂ ∂ ∑ ∑ = = 2 2 , 1 1 ,1 1 ,1 1100 1 2 exp 0 j jir j j j r j j nnnnu b cx x w hw xx y u y u ty (22) so: ( ) j r j j j j u h b xc w u ty . 1 2 1,1 ,1 0 10 ∑ =         − = ∂ ∂ (23) with [ ] 01 2 0 tt u x x x u y = =   and 1,1 1,2 1, , 2,1 2,2 2, ... ... m i j m c c c c c c c   =     . fig. 3. schema of rbfnn. substituting in (16), we get the control law in (24): engineering, technology & applied science research vol. 10, no. 4, 2020, 6080-6086 6083 www.etasr.com lemita et al.: gradient descent optimization control of an activated sludge process based on radial … ( ) j r j j j j h b xc wteuu ... 1 2 1,1 ,1101 ∑ =         − += λ (24) for k≥0: ( ) j r j j kj jkkk h b uc wteuu ... 1 2 ,1 ,111 ∑ =++         − += λ (25) we replace the found value of 1+ku in (6): ( ) ( ) ( )( )11 ,,. 000 ++ += kkukkuku utytfhtyty (26) according to this, we can obtain: ( ) ( )110 ++ = kku trty . the structure of the proposed method is illustrated in figure 4. fig. 4. schema of the proposed control strategy. v. mathematical model of the wastewater treatment process the activated sludge process is a biological treatment that uses microorganisms (biomass) to remove organic matter, nitrogen, and phosphorus. the organic and nitrogen removal are the most used in wastewater treatment. the schema of the wastewater treatment process is illustrated in figure 5. fig. 5. schema of activated sludge process. the process consists of a biological reactor (aeration tank) where the microorganism (biomass) population is developed aiming to remove the substrate from the reactor, and a settler. in the settler tank, the solids are separated from the wastewater. a part of the removed sludge is recycled back to the aeration tank. the mathematical model considered in this paper contains four differential equations: the biomass concentration x, the substrate concentration s, the do concentration do and the recycled biomass concentration xr. the model is given by the following equations [24, 25]: ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) 1 , , , , . . 1 . . . r r x t f t x t s t do t x t t t x t d r x t r d x tµ ∂ = = ∂ − + + (27) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) 2 , , , , 1 . . 1 . . r in s t f t x t s t do t x t t t x t d r s t d s y µ ∂ = = ∂ − − + + (28) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( )( ) 3 0 max , , , , . . 1 . . . r in do t f t x t s t do t x t t k t x t d r do t y kla do do t ddo µ ∂ = = ∂ − − + + − + (29) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) 4 , , , , . 1 . . . r r r x t f t x t s t do t x t t d r x t d r x tβ ∂ = = ∂ + − + (30) with: ( ) ( ) ( ) ( ) ( )max . . s do s t do t t s t k do t k µ µ= + + (31) ( )kwkla .α= . where w is the air flow rate, which will be considered as the input control to maintain the oxygen concentration level in the aeration tank. the used step size is h=0.5. more details about the model parameters can be found in the appendix. vi. results and discussion the proposed method has been used to control the organic cod5 in the aeration tank through concentration control. figures 6 and 7 show the do and substrate concentration in open loop (without control). we can see clearly that the substrate concentration is above the standard limit of 20mg/l the control of substrate became a necessity. in order to test the effectiveness and the performance of the proposed method, the used set-point of the dissolved oxygen concentration changes immediately from 5mg/l to 5.5mg/l and from 5.5mg/l to 6.5mg/l and from 6mg/l to 7mg/l. for comparison, two controllers have been used: the pi controller with parameters: kp=3, ki=0.9 and the pso-pi with the optimized parameters: kp=7.3618 and ki=8.8304. at the beginning the dilution rate and the influent substrate concentration are considered constants (d=0.04h-1 and sin=200mg/l). engineering, technology & applied science research vol. 10, no. 4, 2020, 6080-6086 6084 www.etasr.com lemita et al.: gradient descent optimization control of an activated sludge process based on radial … fig. 6. dissolved oxygen concentration. fig. 7. chemical oxygen demand cod5. (a) (b) fig. 8. a) dissolved oxygen concentration with constant dilution rate d=0.04h-1, b) zoomed view. fig. 9. aeration rate (control variable). do concentration with constant dilution rate is depicted in figure 8. from the simulations results it can be seen that the proposed controllers are able to control the do level to track the desired set-point doref, contrary of the pi controller that doesn't track the desired reference doref. initially the set-point for do level doref is 5mg/l and the control variable or aeration rate w is at 40m3/l (figure 9). after a while, when the do level doref suddenly changed to 5.5mg/l the aeration rate w increased to 45m3/l to satisfy the augmented demand for oxygen (the do level changes to track the set-point level doref). so, w depends on the demand of oxygen (when w increases the do level increases, and vice versa). the dilution rate and the influent substrate concentration are considered variables (in real wastewater treatment systems). in figure 10, different values of dilution rate were considered to cover the work domain (the water flow entering the reactor is not constant throughout the operation). figure 11 shows the influent substrate concentration sin with different values to assure a real study of the wastewater system. fig. 10. dilution rate. when the influent substrate concentration increases from 200mg/l to 300mg/l, the pi controller from figure 12 is strongly affected by this change and it is not able to track the set-point reference, in contrast with the proposed method that rejects the disturbance generated by the influent substrate concentration while the do concentration has a good tracking of the set-point reference. the evolution of the aeration rate obtained by the control methods under different values of dilution rate and influent substrate concentration are depicted in d o ( m g /l ) s ( m g /l ) w d ilu ti o n r a te ( 1 /h ) engineering, technology & applied science research vol. 10, no. 4, 2020, 6080-6086 6085 www.etasr.com lemita et al.: gradient descent optimization control of an activated sludge process based on radial … figure 13. it can be seen that the power signal (control variable) of the proposed method is higher compared with the pi controller and pso-pi controller respectively. fig. 11. influent substrate concentration. (a) (b) fig. 12. a) dissolved oxygen concentration with modified dilution rate and influent substrate, b) zoomed view. in figure 14 we can see that the chemical oxygen demand cod5 is biologically degraded below 20mg/l (the legislation limit on wastewater treatment) and the wanted objective is established in the case of variable set-point of the dissolved oxygen concentration. in order to compare the different control strategies, their performance should be assessed by the integral of absolute error (iae) and the integral of square error (ise). these criteria are computed as: ( )dtteiae ∫ ∞ = 0 (32) ( ) dtteise ∫ ∞ = 0 2 (33) fig. 13. aeration rate (control variable). fig. 14. chemical oxygen demand cod5. table i. simulated iae and ise of the controllers used control methods iae ise pi controller 0.0498 0.0259 pso-pi controller 0.0309 0.0135 gradient method based on rbfnn 0.0048 0.0010 vii. conclusion wastewater treatment processes are very marked nonlinear systems because of the limited measurement data available on biological processes, a fact that complicates the control task when using the classical methods. in this paper, the proposed control method based on euler and gradient has been established to control the chemical oxygen demand cod5 via the control of the do concentration in an activated sludge process of wastewater treatment (no measurements of the substrate concentration are needed). the effectiveness of the proposed method was evaluated through a comparison with the classic pi controller. a variable set-point reference for the do concentration has been designed. based on the above results, it s in ( m g /l ) w 0 50 100 150 200 250 0 10 20 30 40 50 60 70 80 90 time h s ( m g /l ) substrate concentration limit of substrate concentration: 20 mg/l engineering, technology & applied science research vol. 10, no. 4, 2020, 6080-6086 6086 www.etasr.com lemita et al.: gradient descent optimization control of an activated sludge process based on radial … can be seen that the proposed controller is proven to be the better choice in terms of performance, required time for establishment, and process overshoot. appendix model parameters description parameters units values biomass yield factor hy 0.65 maximum specific growth rate maxµ 1−h 0.15 half-saturation coefficient for micro-organisms s k 1. −lmg 100 oxygen half-saturation coefficient for micro-organisms do k 1. −lmg 2 maximum do concentration maxdo 1. −lmg 10 model constant 0k 0.5 oxygen transfer rate α 0.018 ratio of recycled r 0.6 ratio of waste flow β 0.2 influent substrate concentration ins 1. −lmg 200 influent do concentration indo 1. −lmg 0.5 oxygen mass transfer coefficient kla 1−h aeration rate w 13. −hm dilution rate d 1−h initial values variable concentration symbols units values substrate concentration ss 1. −lmg 88 biomass concentration x 1. −lmg 20 dissolved oxygen concentration do 1. −lmg 2 recycle biomass concentration rx 1. −lmg 320 references [1] j. boer and p. blaga, “optimizing production costs by redesigning the treatment process of the industrial waste water,” procedia technology, vol. 22, pp. 419–424, jan. 2016, doi: 10.1016/j.protcy.2016.01.071. 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[25] h. zhou, “dissolved oxygen control of wastewater treatment process using self-organizing fuzzy neural network,” ciesc j. vol. 68, pp.1516–1524, 2017. microsoft word 03-3290_s_etasr_v10_n2_pp5361-5366 engineering, technology & applied science research vol. 10, no. 2, 2020, 5361-5366 5361 www.etasr.com mangi et al.: parametric study of pile response to side-by-side twin tunneling in stiff clay parametric study of pile response to side-by-side twin tunneling in stiff clay naeem mangi department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan naeem08ce30@gmail.com daddan khan bangwar department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan daddan@quest.edu.pk hemu karira department of civil engineering mehran university of engineering & technology khairpur mir’s, sindh, pakistan engr.hemu07civil@gmail.com samiullah kalhoro department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan samiullahkalhoro63@gmail.com ghulam rasool siddiqui department of civil engineering mehran university of engineering & technology khairpur mir’s, sindh, pakistan ghulamrasoolsiddiqui@gmail.com abstract—a three dimensional coupled-consolidation numerical parametric study was carried out in order to gain new insight of single pile response to side-by-side twin tunneling in saturated stiff clay. an advanced hypo plasticity (clay) constitutive model with small-strain stiffness was adopted. the effects of relative to the pile tunnel depths were investigated by simulating the twin tunnels near the pile at various depths of tunnels, namely near the pile shaft, adjacent to the pile toe, and below the pile toe. it was found that the second tunneling in each case resulted in a larger settlement than the one due to the first tunneling with a maximum percentage difference of 175% in the case of twin tunneling near the mid-depth of the shaft. this occurred due to the degradation of clay stiffness around the pile during the first tunneling. conversely, the first tunneling-induced bending moment was reduced substantially during the second tunneling. the most critical location of twin tunnels relative to the pile was found to be below the pile toe. keywords-twin tunneling; pile foundation; parameteric study i. introduction tunnel excavation-induced stress relief and ground movements inevitably cause additional deformation and stress on adjacent pile foundations. it is a major concern for designers and engineers to evaluate the adverse effects on the existing piles. to understand the pile–soil–tunnel interaction mechanism, many field monitoring studies and centrifuge model tests [1-3] and analytical solutions and numerical modeling studies [4-7] have been conducted. they all concluded that tunneling adjacent to existing pile foundations caused pile settlement, additional axial load on piles, and induced bending moments along the piles, which is unfavourable for piled foundations. their magnitudes are likely depended on the relative locations of tunnels and piles. however, most previous studies have focused on the effects of a single tunnel on single piles and pile groups. in fact, twin tunneling is particularly favoured when developing underground transportation systems [8]. to obtain a satisfactory numerical model of the single pile response to sideby-side twin-tunneling, the analysis needs to take account of the soil’s small strain non-linearity. in view of the aforementioned issues, this study aims to systematically investigate the settlement and load transfer mechanism of an existing single pile due to side-by-side twin tunnels in saturated stiff clay. to achieve these objectives, a three-dimensional coupled-consolidation numerical parametric study was carried out by varying the twin tunnel depths relative to the pile. ii. three dimensional coupled consolidation analysis to investigate single pile response to side-by-side twin tunneling in stiff saturated clay, a three-dimensional coupled consolidation numerical parametric study was conducted. to facilitate validation of the numerical model, the tunnel diameter, pile diameter, embedded length, and clear distance between the pile and the tunnel were identical (in prototype scale) to those in the centrifuge test [9]. figure 1 shows the elevation view of the configuration of a typical numerical simulation in which twin tunnels were excavated adjacent to the pile toe. the diameter of each tunnel (d) was 6m. the embedded length (lp) and diameter (dp) of the pile were 18m and 0.8m respectively. the modeled pile represents a cylindrical reinforced concrete (grade 40, reinforcement ratio=1) with a bending moment capacity of 800knm. the center-to-center distance between each tunnel and the pile was 5.5m (0.92d). it is worth noting that, in reality, high-rise buildings are unlikely to be built on a single pile. this hypothesized study is a more virtual case [3]. this simplification was made to understand the settlement and load transfer mechanism more clearly. the length of each model tunnel (along its longitudinal direction) is 72m, which is corresponding author: naeem mangi engineering, technology & applied science research vol. 10, no. 2, 2020, 5361-5366 5362 www.etasr.com mangi et al.: parametric study of pile response to side-by-side twin tunneling in stiff clay equivalent to 12d. each tunnel excavation was simulated in 28 steps. at each step, the tunnel advanced a distance of 2.5m (0.42d) [2]. the time increment of one day for each step was adopted in the finite element analysis. a monitoring section was selected at the transverse centreline of the pile (i.e. y/d=0) as a reference for the tunnel advancements. the parametric study consisted of nine different numerical simulations (in total) in which the existing single pile was located between the twin tunnels, which were excavated one after the other on either side of the pile at various depths of tunnels (zt) relative to the pile length (lp), namely near the pile shaft (zt/lp=0.67 and 0.83), adjacent to the pile toe (zt/lp=1.00) and below the pile toe (zt/lp=1.17, 1.33, 1.50, 1.67, 1.83 and 2.00). in addition to these simulations, a pile load test (l) was conducted numerically in “greenfield” conditions (i.e. with no tunnels present) to obtain the ultimate capacity of the pile in stiff clay. based on this, the working load was then calculated with a factor of safety of 3.0. the obtained working load was applied to the pile in the parametric analysis simulating twin tunneling. table i summarises the conducted numerical simulations. fig. 1. configuration of a typical numerical run representing case of zt/lp=1.00 table i. numerical simulations summary description of numerical run zt/lp c/d twin tunneling near the pile shaft 0.67 1.5, 1.5 0.83 2.0, 2.0 twin tunneling next to the pile toe 1.00 2.5, 2.5 twin tunneling below the pile toe 1.17 3.0, 3.0 1.33 3.5, 3.5 1.50 4.0, 4.0 1.67 4.5, 4.5 1.83 5.0, 5.0 2.00 5.5, 5.5 zt=tunnel depth, lp=pile length, c/d=cover to diameter of tunnel ratio iii. finite element mesh and boundary condtions figure 2 shows an isometric view of a typical finite element mesh (for the case of zt/lp=1.0).the size of the mesh for each numerical simulation is 72m×72m×60m. these dimensions were sufficiently large to minimize the boundary effects in the numerical simulation because a further increase in the dimensions of the finite element mesh did not lead to any change in the computed results. regarding the element size in the mesh, it is found that further halving the adopted mesh size leads to a change in the computed results of no more than only 0.2%, suggesting that the mesh is sufficiently fine. eight-noded hexahedral brick elements were used to model the soil and the pile. four-noded shell elements were adopted to model each tunnel lining. roller and pin supports were applied to the vertical sides and the base of the mesh, respectively. therefore, movements normal to the vertical boundaries and in all directions of the base were restrained. the water table was assumed to be at the ground surface. initially, the pore water pressure distribution was assumed to be hydrostatic. free drainage was allowed at the top boundary of the mesh. the tunnel lining was assumed to be continuous and impervious. fig. 2. finite element mesh and boundary conditions of a typical numerical analysis (zt/lp=1.00) interaction between the piles and surrounding soil was modeled by the surface-to-surface contact provided in abaqus software package [10]. the surface-to-surface contact considers the shape of both the master and slave surface in the contacting region and allows pile-soil friction. the penalty approach was used for tangential contact and the normal behavior was modeled as hard contact with no normal relative displacement between the pile and the surrounding soil. the interface was modelled by the coulomb’s friction law, in which the interface friction coefficient (µ) and limiting displacement (γlim) are required as input parameters. a limiting shear displacement of 5mm was assumed to achieve full mobilization of the interface friction equal to µ×p', where p' is the normal effective stress between two contact surfaces, and a typical value of µ for a bored pile of 0.35 was used [11]. the tunneling stress release process was modelled by the “element death” technique which is widely used in finite element analysis. in this technique, elements and nodes can be deactivated and activated. in this study, the volume loss is predefined before tunneling by specifying the area of the annulus gap between the tunnel lining and the excavated soil. pattern of the non-uniform displacement boundaries was determined according to the displacement controlled model (dcm) in [5]. the soil inside the segment is excavated by deactivating soil elements inside it ground water table working load (1.93 mn) existing single pile (lp=18 m) stiff clay note:lp is embedded length of pile zt is depth of tunnel axis from the ground surface zt=18 m 11 m first tunnel second tunnel 2.5 m 2.5 m engineering, technology & applied science research vol. 10, no. 2, 2020, 5361-5366 5363 www.etasr.com mangi et al.: parametric study of pile response to side-by-side twin tunneling in stiff clay and by specifying zero horizontal displacement at the tunnel face of the tunnel segment to be excavated. in the meantime, the shell elements representing the tunnel lining are activated. iv. constitutive model and model parameters used in finite element analysis a basic hypoplastic model was developed to capture the nonlinear behavior (upon monotonic loading at medium-to large-strain levels) of granular materials [12]. the basic model consists of five parameters (table ii). to account for the strain dependency and path dependency of the soil stiffness (at small strains), authors in [12] further improved the basic hypoplastic model by incorporating the concept of intergranular strain, which requires five additional parameters. the hypoplastic clay model with small strain stiffness has been implemented in the finite element software package abaqus through a user-defined subroutine. the coefficient of lateral earth pressure at rest, ko was estimated by the relevant equation in [14]. the concrete pile and tunnel lining were assumed to be linear elastic with young's modulus of 35gpa and poisson's ratio of 0.25. the thickness of the lining was taken as 0.25m. the unit weight of concrete was taken as 24kn/m 3 . the parameters for the piles and the tunnel lining are summarized in table iii. table ii. adopted model parameters of kaolin clay description value effective angle of shearing resistance at critical state, φ’ 22 o parameter controlling the slope of the isotropic normal compression line in the ln(1+e) versus lnp plane, λ* [13] 0.11 parameter controlling the slope of the isotropic normal compression line in the ln(1+e) versus lnp plane, κ* [13] 0.026 parameter controlling the position of the isotropic normal compression line in the ln(1+e)–lnp plane, n 1.36 parameter controlling the shear stiffness at mediumto largestrain levels, r 0.65 parameter controlling the initial shear modulus upon 180° strain path reversal, mr 14 parameter controlling the initial shear modulus upon 90° strain path reversal, mt 11 size of elastic range, r 1×10 -5 parameter controlling the rate of degradation of the stiffness with strain, βr 0.1 parameter controlling the degradation rate of stiffness with strain, χ 0.7 initial void ratio, e 1.05 dry density (kg/m 3 ) 1136 coefficient of permeability, k (m/s) 1×10 -9 table iii. adopted concrete parameters in fem description value young's modulus, e 35gpa poisson's ratio, νννν 0.3 density, ρρρρ 2400kg/m 3 v. interpretation of computed results a. induced pile settlement due to twin tunnels figure 3 illustrates the pile settlement induced after the first and th second tunnel at different depths relative to the pile (zt/lp). the long-term pile settlement (i.e. 15 years after twin tunneling completion) is included in the figure. the measured induced pile settlement tunneling at different depths in centrifuge modeling reported by [9, 15] is also shown in the figure for comparison. a linear increase in twin tunnelinginduced settlement was observed as the tunnel depth increased from zt/lp=0.67 to 1.33. however, as the depth increased further (1.50≤zt/lp≤2.0), the induced settlement decreased with a similar trend. this computed result is consistent with the one measured in centrifuge tests simulating tunneling at different depths relative to piles in stiff clay [9] and in sand [8]. this tunneling-induced settlement mechanism with zt/lp can be attributed to the influence zone of tunneling-induced ground movement and stress-release-affected regions. in the case of zt/lp=1.33, the entire pile stood within the influence zone of tunneling-induced ground movement, and the stress release region was developed directly underneath the pile toe. when zt/lp=0.67, 0.83 and 1.00, the pile was located only partially within the influence zones. therefore, the pile experienced larger settlement in the case of zt/lp=1.33 than in these cases. although the entire pile in the cases of zt/lp=1.50, 1.67, 1.83 and 2.00 was located inside the tunneling-induced ground movement, the tunneling-induced pile settlement was less than that of zt/lp=1.33. this is because the location of the pile toe was beyond the tunneling-induced stress-release-affected region in these cases. fig. 3. computed load settlement curve from the pile load test without tunneling qualitatively, the second tunneling-induced settlement trend with respect to zt/lp was similar to the first tunnelinginduced settlement. however, the magnitude of the pile settlement induced by the second tunnel was higher than that induced by the first tunnel in each case. this can be attributed to the degradation of clay stiffness around the pile due to stress release and the development of shear strains as a result of the first tunnel excavation. the largest settlement (175% of sp due to the first tunnel) was induced by the second tunnel when zt/lp=0.67. it can be seen that the settlement of the pile reduced in the long term (i.e. 15 years after completion of the twin tunnels) in all cases. this pile heave is attributed to the dissipation of excessive negative pore pressure generated 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00 0.50 0.67 0.83 1.00 1.17 1.34 1.50 1.67 1.84 2.00 n o rm a li se d p il e h e a d s e tt le m e n t (s p /d p ): % tunnel depth relative to pile (zt/lp) loganathan et al., 2000 after first tunnel ng et al., 2013 after twin tunnels series6 slong term settlement (15 years after twin tunnelling) (cummulative) computed (this study)measured (centrifuge) 1.33 1.83 engineering, technology & applied science research vol. 10, no. 2, 2020, 5361-5366 5364 www.etasr.com mangi et al.: parametric study of pile response to side-by-side twin tunneling in stiff clay around the pile due to the twin tunnels. the maximum reduction of the pile settlement (17.2% of the settlement after twin tunnels) was observed in the case zt/lp=1.33. b. changes in axial load distribution figure 4 illustrates the axial force distribution along the pile with normalized depth (i.e., z/lp) below the ground surface after twin tunneling when zt/lp=0.67, 1.00 and 1.33. the axial load distribution before tunneling (after applying the working load) is also included in the figure as a reference. before tunneling, the pile carried approximately 75% of the working load (i.e. 1010kn) with its shaft resistance and the remainder with its end-bearing resistance. because tunneling was carried out near the mid-depth of the pile shaft in the case zt/lp=0.67, tunnel-induced reduction in normal stresses to the pile shaft and downward soil movement caused an increase in axial load along the entire length of the pile after the first and second tunnel excavations. at the end of the first tunneling, the maximum increment in the axial force (63% of that at working load) was computed at z/lp=0.7, which is above the tunnel spring line. by inspecting the axial load distribution after the first tunnel excavation, it is observed that along the upper half of the pile (0≤z/lp≤0.6), the shaft resistance decreases to zero. consequently, the load was transferred to the lower half of the pile. to maintain equilibrium, the pile had to settle to further mobilize the end-bearing and shaft resistance along the lower portion (z/lp>0.6). this led to increases of 73% and 24% in the mobilized end-bearing and shaft resistance at the lower portion (z/lp>0.5) respectively upon completion of the first tunnel. the second tunneling in the case zt/lp=0.67 caused a further reduction of the normal stresses to the pile shaft. consequently, soil settled more than the pile, resulting in negative skin friction (nsf) along the upper half of the pile (0≤z/lp≤0.6). this suggests that this portion of the pile is subjected to dragload by the surrounding soil. this caused the pile to settle more than that due to the first tunnel. to maintain vertical equilibrium of the pile, the soil surrounding the lower part of the pile (z/lp>0.6) resisted its settlement by mobilizing positive skin friction (psf) at the pile–soil interface and endbearing resistance at the toe of the pile. owing to the second tunneling, the end-bearing and mobilized shaft resistance increased to 190% and 18%, respectively. owing to twin tunneling adjacent to the pile toe (zt/lp=1.00), the axial load increased along the pile at depths ranging from 0.42 to 1.0lp. the increase in axial load resulted from reduced shaft resistance, which was caused by stress release from twin tunneling adjacent to the pile toe. the reduction percentages in shaft resistance were 22% and 43% after the first and twin tunneling (cumulative) respectively. consequently, the axial load borne by the shaft resistance along the pile at depths ranging from 0.42 to 1.0lp was transferred downward to the pile toe, leading to a 75% and 156% increase in mobilized end-bearing resistance after the first and twin (cumulative) tunneling, respectively. in contrast to the tunneling near the mid-depth of the pile shaft (zt/lp=0.67) and adjacent to the pile toe (zt/lp=1.00), the axial load decreased along the entire length of the pile when twin tunnels were excavated below the pile toe (zt/lp=1.33). the advancement of the twin tunnels led to reductions in the end-bearing of the pile as a result of stress release from 2% volume loss. to compensate for the decrease in end-bearing resistance, the pile had to settle substantially to mobilize the shaft resistance along the entire pile length. this result is similar to those measured in the field [16]. the end-bearing decreased by 12% and 28% owing to the first and twin tunnels, respectively. fig. 4. axial load distribution along the pile length c. twin-tunneling induced bending moment along the pile figure 5 illustrates the induced bending moment along the pile after the first and second tunneling in the cases of zt/lp=0.67, 1.00 and 1.33. a positive bending moment means that tensile stress was induced along the pile shaft facing the first tunnel. the measured bending moment of a single pile subjected to single tunneling in centrifuge model test [9] was also included for comparison. since there was no rigid constraint at the pile head (pile head was free to move and rotate), no bending moment was induced at/near the head of the pile in all the cases. it can be observed that in the case of zt/lp=0.67, the maximum positive bending moment was induced in the pile at z/lp=0.6 near spring line of the first tunnel. authors in [17] have also reported a measured maximum bending moment occurring at the spring line of the tunnel near the shaft of the pile group. this happened because the pile was subjected to lateral soil movement towards the tunnel resulting from significant stress release. the magnitude of the maximum positive bending moment was 400knm (which is 50% of the pile bm capacity). on the other hand negligible bending moment was induced near the pile toe (below the tunnel spring line), because the tunneling induced soil movement below the tunnel spring line was insignificant [2]. subsequently, the pile was subjected to stress release on the opposite side of the pile as a result of the second tunnel’s excavation near the mid-depth of the pile shaft. consequently, the induced-bending moment decreased along the pile after the second tunneling. the induced-bending moment along the pile was not returned to zero after the second tunneling as the soil does not behave elastically. finally, a positive bending moment 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 n o r m a li z e d d e p th ( z /l p ) axial force: kn before tunnelling c/d=1.5 1st tunnel 2nd tunnel c/d=1.5 c/d=1.5 c/d=1.5 c/d=1.5 c/d=1.5 c/d=1.5 after 1st tunnelling after 2nd tunnelling zt/lp = 0.67 zt/lp = 0.67 zt/lp = 1.00 zt/lp = 1.33 zt/lp = 1.33 zt/lp = 1.00 engineering, technology & applied science research vol. 10, no. 2, 2020, 5361-5366 5365 www.etasr.com mangi et al.: parametric study of pile response to side-by-side twin tunneling in stiff clay with magnitude of 50knm was induced. owing to the soil inward movement towards the first tunnel when zt/lp=1.00, positive bending moment was induced at the lower part of the pile (0.7≤z/lp≤1.0). to counter-balance this induced positive bending moment, negative bending moment was developed along the upper part of the pile (0≤z/lp≤0.7). the magnitudes of maximum induced positive and negative bending moment were 130knm. the measured induced bending moment along the pile due to single tunneling in centrifuge reported by [9] was positive and smaller than the one computed in magnitude. this may be caused by the tunneling-induced volume loss which was modeled as 1% in the centrifuge test. the subsequent tunneling at zt/lp=1.00 on the opposite side of the pile reduced the induced bending moment significantly. the maximum induced bending moment was 37knm at z/lp=0.6 after the twin tunnel excavation. fig. 5. induced bending moment along the pile length in contrast to the induced bending moment in the case zt/lp=0.67, negative bending moment was induced along the entire pile length due to the first tunnel advancement in the case of zt/lp=1.33. however, the magnitude of maximum bending (100kpa at z/lp=0.7) was less than the one in the case zt/lp=0.67. also, no bending was induced at the pile toe and head. it can be seen that the induced bending moment during the first tunnel advancement in the case of tunneling near the mid-depth of the pile (zt/lp=0.67) and adjacent the pile toe (zt/lp=1.00) was less than that in the case of tunneling below the pile toe (zt/lp=1.33). therefore, in the case of zt/lp=1.33, the most critical issue to be considered is the relatively large settlement. vi. discussion it is well recognized that the stress-strain relationship of soils is highly nonlinear even at very small strains. the stiffness of most soils decreases as strain increases and depends on the recent stress or strain history of the soil. owing to nonlinear soil behavior, a tunnel excavation can cause reduction in the stiffness of the soil. therefore, it is vital to investigate the pile responses not only to the first tunnel but also to the subsequent tunnel in clay in a twin-tunneling transportation system. keeping these issues into consideration, effects of twin side by side tunneling on a single pile in stiff clay were investigated in this study. it was revealed that the second tunneling caused larger settlement and smaller bending moment in the pile. this finding is the major contribution of this parametric study. vii. conclusions based on the modeled ground conditions, geometry, and tunneling method, the following conclusions can be drawn: • due to the degradation of the stiffness of the clay surrounding the pile as a result of tunneling-induced stress release and shear strain, the second tunneling caused larger settlement than the first in each case. when zt/lp=0.67 the second tunneling-induced settlement was the largest (i.e. 175% of sp from the first tunnel) of all cases. the cumulative settlements of the pile resulting from the working load and twin tunneling in the cases zt/lp=0.67, 1.00 and 1.33 were 25, 39, and 47mm (i.e. 3.1, 4.9, and 5.9 of the pile diameter) respectively. • the first tunneling in the case zt/lp=0.67 induced the largest bending moment (50% of the pile bm capacity) at the spring line of the tunnel. however, the induced bending moment along the pile decreased significantly due to the excavation of the second tunnel in each case because of the side-by-side twin tunneling configuration in which the second tunnel caused a stress release on the opposite side of the pile. • when of zt/lp=0.67, the second tunneling-induced soil movement due to stress release mobilized negative shaft friction at the upper part of the pile. consequently, a downward load transfer was observed along the pile, further mobilizing the pile end-bearing. similarly, in the case zt/lp=1.00, the load borne by the pile shaft was transferred to the pile toe as a result of the twin tunneling reduction in the shaft resistance at the lower part of the pile (0.3≤z/lp≤0.9). acknowledgement the authors would like to acknowledge the financial support provided by the quaid-e-awam university of engineering, science & technology, sindh and pakistan. references [1] g. gudehus, “a comprehensive constitutive equation for granular materials”, soils and foundations, vol. 36, no. 1, pp. 1-12, 1996 [2] k. ishihara, “liquefaction and flow failure during earthquakes”, geotechnique, vol. 43, no. 3, pp. 351-451, 1993 [3] c. w. w. ng, “the state-of-the-art centrifuge modelling of geotechnical problems at hkust”, journal of zhejiang university science a, vol. 15, pp. 1-21, 2014 [4] j. jaky, “the coefficient of earth pressure at rest”, journal of the society of hungarian architects and engineers, pp. 355-358, 1944 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -150 -100 -50 0 50 100 150 200 250 300 350 400 450 n o r m a li z e d d e p th ( z /l p ) induced bending moment: knm measured series3 series11 series12 1st tunnel 2nd tunnel c/d=1.5 c/d=1.5 c/d=2.5 c/d=2.5 c/d=3.5 c/d=3.5 after 1st tunnelling after 2nd tunnelling meaured (loganathan et al., 2000) computed (this study) zt/lp = 0.67 zt/lp = 0.67 zt/lp = 1.00 zt/lp = 1.33 zt/lp = 1.33 zt/lp = 1.00 engineering, technology & applied science research vol. 10, no. 2, 2020, 5361-5366 5366 www.etasr.com mangi et al.: parametric study of pile response to side-by-side twin tunneling in stiff clay [5] k. h. chiang, c. j. lee, “responses of single piles to tunneling-induced soil movements in sandy ground”, canadian geotechnical journal, vol. 44, no. 10, pp. 1224-1241, 2007 [6] a. niemunis, i. herle, “hypoplasic model for cohesionless soils with elastic strain range”, mechanics of cohesive-frictional materials, vol. 2, no. 4, pp. 279-299, 1997 [7] c. w. w. ng, m. a. soomro, y. hong, “three-dimensional centrifuge modelling of pile group responses to side-by-side twin tunnelling”, tunelling and underground space technology, vol. 43, pp. 350-361, 2014 [8] c. w. w. ng, h. lu, s. y. peng, “three-dimensional centrifuge modelling of the effects of twin tunnelling on an existiong pile”, tunneling and underground space technology, vol. 35, pp. 189-199, 2013 [9] n. loganathan, h. g. poulos, d. p. stewart, “centrifuge model testing of tunnelling-induced ground and pile deformations”, geotechnique, vol. 50, no. 3, pp. 283-294, 2000 [10] abaqus user’s manual, version 6.8.2, dassault systemes, 2008 [11] d. masin, “hypoplastic cam-clay model”, geotechnique, vol. 62, no. 6, pp. 549-553, 2012 [12] a. m. marshall, r. j. mair, “tunneling beneath driven or jacked endbearing piles in sand”, canadian geotechnical journal, vol. 48, no. 12, pp. 1757-1771, 2011 [13] s. w. jacobsz, j. r. standing, r. j. mair, t. hagiwara, t. sugiyama, “centrifuge modelling of tunnelling near driven piles”, soils and foundations, vol. 44, no. 1, pp. 49-56, 2004 [14] p. w. mayne, f. h. kulhawy, “k0-ocr relationships in soils”, journal of the geotechnical engineering-asce, vol. 108, no. 6, pp. 851-872, 1982 [15] d. a. mangejo, m. a. soomro, n. mangi, i. a. halepoto, i. a. dahri, “a parametric study of effect on single pile integrity due to an adjacent excavation induced stress release in soft clay”, engineering, technology & applied science research, vol. 8, no. 4, pp. 3189-3193, 2018 [16] m. a. soomro, a. s. brohi, d. k. bangwar, s. a. bhatti, “3d numerical modelling of pile group responses to excavation-induced stress release in silty clay”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2577-2584, 2018 [17] d. r. coutts, j. wang, “monitoring of reinforced concrete piles under horizontal and vertical loads due to tunnelling”, international conference on tunnels and underground structures, singapore, november 26-29, 2000 microsoft word 26-3091_s_etasr_v9_n5_pp4718-4723 engineering, technology & applied science research vol. 9, no. 5, 2019, 4718-4723 4718 www.etasr.com khattara et al.: an efficient metaheuristic approach for the multi-period technician routing and … an efficient metaheuristic approach for the multiperiod technician routing and scheduling problem abouliakdane khattara electrical engineering department, ferhat abbas setif 1 university, setif, algeria yekdane87@univ-setif.dz wahiba ramdane cherif-khettaf loria, umr 7503, university of lorraine, nancy, france ramdanec@loria.fr mohammed mostefai electrical engineering department, ferhat abbes setif 1 university, setif, algeria mostefai@univ-setif.dz abstract—in this paper, we address a new variant of the multiperiod technician routing and scheduling problem. this problem is motivated by a real-life industrial application in a telecommunication company. it is defined by a set of technicians having distinct skills that could perform a set of geographically scattered tasks over a multi-period horizon. each task is subject to time constraints and must be done at most once over the horizon by one compatible technician. the objective is to minimize the total working time (composed by routing time, service time, and waiting time), the total cost engendered by the rejected tasks, and the total delay. two variants of variable neighborhood descent are proposed, and three variants of variable neighborhood search to solve this problem. computational experiments are conducted on benchmark instances from the literature. an analysis of the performance of the proposed local search procedures is given. the results show that our methods outperform the results of a mimetic method published in the literature. keywords-technician routing and scheduling problem (trsp); variable neighborhood search (vns); variable neighborhood descent (vnd) i. introduction technician routing and scheduling problem (trsp) is a new challenge in logistics for the service sector and especially for utility companies in energy (gas, electricity), telecommunications, and water distribution areas [1]. the trsp consists of planning tasks assigned to commercial or technical personnel, over a set of periods (days) in order to visit industrial facilities or customers for different types of activities: installation, inspection, repair, and maintenance. until recently, the trsps, both static and dynamic cases, have received a limited attention. thus, the number of publications and scientific reports is limited, although several variants of the trsp have been studied in the literature. these variants can be divided into two classes: (i) one period trsp, and (ii) multiperiod trsp. the one period trsp has been studied by authors who consider constraints as skills, time windows, tools, spare parts, stochastic service and stochastic travel times, multiple depots, and customer priority [1-6]. for the multiperiod trsp, we can mention [7], which introduces the multiperiod technician scheduling problem with experience based on service times and stochastic customers. the aim is to minimize the expected sum of each day’s total service times over a finite horizon. another multi-period trsp was proposed in 2007 [8]. this problem consists in computing a schedule for technicians to perform a set of tasks on a five day horizon. the routing aspect is not considered, and tasks have different proficiency skill level constraints, that require a team of technicians. authors in [10] studied the one-periodic variant of this problem, namely, the service technician routing and scheduling problem by taking on consideration the routing aspect. authors in [9] presented a multi-period technician routing problem faced by a water distribution and treatment company. in [9], requests were divided into two categories (users requested interventions and company scheduled visits), and the skill constraints were not included. in this paper, we propose the study of a new multi-period trsp variant where skill constraints and routing aspects are considered simultaneously, inspired by a realistic application in the telecommunication field. from the above survey, it appears that most papers on trsp considered several realistic constraints, but to the best of our knowledge, the multi-periodic variant of trsp with skill constraints and routing aspects has not been considered in the literature. the papers that consider a multi-periodic trsp with skill constraints, and routing aspects, included other specific constraints as the technician team constraint [10]. our study is also an extension of the problem studied in [9, 11 ,12] in which the skill constraints are ignored. as the considered problem is np-hard and since it results from the combination of complex constraints, large instances can hardly be solved by exact methods. so, the best way to tackle this problem is by using the metaheuristic approaches. we choose a variable neighborhood search (vns) to solve our problem, because its effectiveness has been proven on a number of variants of vehicle routing problems (vrp) as the vehicle routing problem with time windows [13], the vehicle routing problem with multiple depots and time windows [14, 15], the periodic vehicle routing problem [16], and the workforce scheduling and routing problem [17]. in this paper, we propose two variants of variable neighborhood descent, as well as three variants of variable neighborhood search to solve the trsp with skill constraints and routing aspects. corresponding author: abouliakdane khattara re tr ac te d engineering, technology & applied science research vol. 9, no. 5, 2019, 4718-4723 4719 www.etasr.com khattara et al.: an efficient metaheuristic approach for the multi-period technician routing and … ii. problem description we consider a multi-period horizon h of several days (typically one week). for each day h∈h, a set of technicians k with different skills are available (a technician has one skill or more). each technician k∈k has a known starting and ending location d∈d, which corresponds to the technician’s home or office (the starting location is the same with the ending location). each technician has a working time limit per day maxtimek,h. requests belong to two categories: non-urgent tasks (nt) generated by the company, and urgent requests (ut) formulated by customers through a call center, for emergency reasons. note that ut∪nt=t, with t the set of all tasks known in advance. let si be the service time of the task i. the urgent tasks i∈ut are planned on a fixed day hi and are subjected to customer appointments within a given time window (bi, ei), where bi is the beginning of the time window, and ei the end of the time window. the task i could be affected to a technician k if the arriving time at task i (denoted aik) is before the end of the time windows (aik<ei). if ∀ k∈k, aik≥ei, then the task i is considered as a rejected task. if aik≤bi, a waiting time wik occurs, with wik=bi-aik. if aik≤ei, and aik+si>ei, a delay lik occurs, with lik=(aik+si)-ei. non-urgent tasks are characterized by a validity period composed of one or several days [hbi, hei]∈h, where hbi is the early day and hei is the deadline for the execution of i. a request i requires certain skills (qualifications), and must be executed by only one compatible technician. the goal is to build a set of routes per day and per technician (at most |kh| routes per day). each route rhk is a sequence of tasks assigned to only one technician k and one-day h. the following constraints must be satisfied: 1) each task must be executed at most once within the validity period or within the time window, 2) the total time of each route rhk should not exceed maxtimek,h, 3) the competence requirements must be respected, 4) each route must start and end at the same location d ∈ d. the objective function, measured in monetary units denoted f(x), consists in minimizing three costs: (i) the total working time composed by routing time that depends on the number of kilometers travelled by each technician, the service time and the waiting time, (ii) the total cost engendered by the ejected tasks, and (iii) the total delay. iii. solution methodology in this section, we describe the general framework of the variable neighborhood search (vns), and then we present the basic components of the vns that we have developed to solve our problem. a. variable neighborhood search vns is a metaheuristic, or a framework created 1997 [18, 19] for approximately solving optimization problems, including combinatorial and non-linear continuous optimization problems [20, 21]. vns is based on the systematic changes of neighborhood structures during the search for a (near) optimal solution of a considered problem. these changes occur in both descent phase, to improve the solution, and shaking and perturbation phase that aims to escape local optima traps. the main structure of the vns (algorithm 1) is shown in figure 1. fig. 1. algorithm 1:variable neighborhood search vns the inputs of vns heuristic are x, kmax and tmax, and they present the initial solution, the number of neighborhoods to be explored and the maximum allowed cpu time. the main ingredients of variable neighborhood search include an improvement procedure to improve the current solution and a shaking procedure to perturb the search and escape from the corresponding valley, see lines 3 and 4. the improvement procedure in line 5 could be a single local search or an ordered list of set of neighborhoods. b. initial solution we propose to use as an initial solution the best insertion method with sorting list. this method is performed by two steps. in the first step, a list of unserved tasks (l, l=t), is sorted in increasing order according to validity day (vd), that represents the length of the period (number of days) in which the tasks can be done, vdi=hei–hbi. in the second step, the algorithm select a task i from the head of l, and scan all feasible insertions in all routes rhk. the insertion cost of i in a route rhk between two tasks x and y, named δ(i,rhk,x,y) will be calculated as in (1). the algorithm performs the best insertion. ( ) ( ) ( ) , , , – xi iy xy jk jk i rhk x y c c c j rhk i w j rhk i l δ = + + σ ∈ ∪ +σ ∈ ∪ (1) c. local search procedures we propose five local search operators to be used either individually or together to focus the search in the inner loop of vns. we consider three intra-route and two inter-route local search methods. the best improvement strategy is used for each method. the local search methods are: • one intra-route relocate: one node (task) from the route is removed and reinserted in other positions in the same route. • one intra-route exchange: two nodes (tasks) are exchanged in the same route. • 2 opt: two arcs are removed and reinserted in the same route • one inter-route relocate: one node (task) from the route is removed and reinserted in one other route in the solution. • one inter-route exchange: two nodes (tasks) are exchanged between two different routes. d. variable neighborhood descent procedures the variable neighborhood descent (vnd) procedures explore several neighborhood structures either in a sequential or nested (or composite) fashion to possibly improve a given solution [21] because the solution which is a local optimum with respect to several neighborhood structures is more likely re tr ac te d engineering, technology & applied science research vol. 9, no. 5, 2019, 4718-4723 4720 www.etasr.com khattara et al.: an efficient metaheuristic approach for the multi-period technician routing and … to be a global optimum than the solution generated as a local optimum for just one neighborhood structure. the order of neighborhoods may play an important role in the quality of the final solution [22]. two variants of vnd are discussed in this paper regarding the decision made in neighborhood change procedure. if an improvement has been detected in some neighborhood: (1) basic vnd (b-vnd): we return to the first neighborhood on the list, (2) union vnd (u-vnd): at each iteration all the neighborhoods in the list are used to explore the search, and the next incumbent solution is the best one found by the best neighborhood. the outline of basic vnd is presented in algorithm 2 (figure 2). the steps of the sequential neighborhood change which is presented in line 5 (algorithm 1) and line 7 (algorithm 2) are given in algorithm 3 (figure 3). if an improvement of the incumbent solution in some neighborhood structure occurs, the search is resumed in the first neighborhood structure (according to the defined order) of the new incumbent solution, otherwise the search is continued in the next neighborhood (according to the defined order). fig. 2. algorithm 2: variable neighborhood descent vnd fig. 3. algorithm 3: neighborhood change procedure e. shaking procedure the shaking procedure is used in vns as mentioned in line 3 of algorithm 1 in order to hopefully resolve local minima traps. our shaking procedure consists in selecting a random solution from the k th neighborhood structure, nk(x). iv. computational results all developed algorithms were implemented in matlab and all tests were carried out on a macbook pro intel core™ i73520m with 2.90ghz cpus, sharing a memory of 8gb (the algorithms use only one cpu). our problem is an extension of the problem studied in [9, 11, 12], in which the skill constraints are ignored. for this, we use the data instance used in [9, 11, 12], and evaluate the performance of our methods with their mimetic algorithm. we first compare the performance of different local search procedures with the initial solution. different vnd procedures are then tested and compared. finally, we compare and evaluate the vns procedures proposed in this paper. a. description of experimental data sets in order to evaluate and assess the performance of the proposed approaches, we compare them with the methods proposed by tricoire in [9, 11, 12]. the instances of [9, 11, 12] are used for tests. for this, the skill constraints in our problem are relaxed, and lunch break constraints are added. they are inspired by a real life case, and they are available with detailed experimental results in [9] as well as on the web site: http://www. emn.fr/z-auto/routing-pbs/. all instances have a five-day planning horizon and three technicians available every day. the demands are randomly distributed over a 40km 2 map, and euclidean distances are used. the technicians drive at a constant average speed of 35km/h. two sizes of instances are tested c1 with 100 customers and c2 with 180 customers, each one with 5 variants according to the distribution and the percentage of time windows and the percentage of urgent and non-urgent tasks. b. evaluation of the performance of the local search procedures we study the impact of the locale search procedures. the results are shown in table i. the first column indicates the name of each instance. column 2 presents the result found by the initial solution, which is based on the best insertion strategy. the remained columns provide both the gap and the computing time for each local search operator. the gap is calculated by (2). row 13 mentions the average results of all instances. the ranks of the local search operators according to their performances and computing time are provided in the last two rows. the best results are in bold. ( )–( )gap% /( ) ( )heuristic heuristic ls heuristic lsf x f x f x+ += (2) from table i, we note that the 2 opt operator is the best one in almost all instances but it is the third one in terms of computing time. it is also worth noting that all the operators perform well and they all improve on average at least 7.14% and at most 9.66% the results found by the heuristic. c. variable neighborhood descent procedures the aim of this section is to evaluate and to compare different variants of vnd procedures according to the manner in which the neighborhood is changed after each improvement occurs. namely, it is obvious that the order of neighborhoods on the list affect the performance of vnd procedures [22]. thus, we take into account two possible orders of ls procedures according to their performance: 1) the value of f(x), and 2) the computing time. the used orders are mentioned in table ii. the results of vnd procedures on tricoire instances are summarized in table iii. the settings of the vnd variant are provided in column and row headings as described above. for example, in table iii, the values in the two cells, at the intersection of the row c100_1 and 4 th column, correspond to value achieved by b-vnd that explores neighborhoods using the 1st order, as well as its execution time in second. the next column reports the percentage deviation of the obtained solution compared to best solution of the mimetic algorithm r et ra ct ed engineering, technology & applied science research vol. 9, no. 5, 2019, 4718-4723 4721 www.etasr.com khattara et al.: an efficient metaheuristic approach for the multi-period technician routing and … proposed by tricoire [9, 11,12]. the deviations are calculated by: ( )dev% – / ( ) ( ) ( )vnd memetic memeticf x f x f x= (3) the next column reports the percentage deviation of the obtained solution compared to the result found by the initial solution, which is calculated by (2). in table iii, we report the results obtained by b-vnd and u-vnd using the two proposed orders. the average results are mentioned in the two last rows. in table iii, values in bold followed by a star represent new best solutions obtained by our method. table i. comparison between local search procedures 2 opt one intra route relocate one intra route exchange one inter route exchange one inter route relocate instances f(x)heuristic gap time (s) gap time (s) gap time (s) gap time (s) gap time (s) c1_1 21024.64 14.04% 0.40 12.74% 0.47 12.79% 0.47 0.00% 0.29 3.74% 5.79 c1_2 19347.33 6.15% 0.40 4.63% 0.45 4.65% 0.41 3.11% 5.49 5.30% 4.31 c1_3 19658.79 8.68% 0.39 6.55% 0.43 5.74% 0.36 0.72% 1.53 4.29% 3.45 c1_4 22232.21 9.86% 0.40 7.29% 0.29 7.32% 0.35 7.13% 5.26 6.10% 2.96 c1_5 18219.65 -2.63% 0.19 -2.75% 0.28 -1.84% 0.24 -2.46% 2.58 8.58% 7.05 c2_1 39085.88 10.03% 1.76 7.04% 1.45 7.07% 1.96 15.04% 44.40 8.27% 30.95 c2_2 34873.74 12.22% 1.76 6.69% 1.62 5.89% 1.34 4.29% 22.04 6.47% 20.96 c2_3 36349.52 13.70% 1.70 13.22% 1.75 11.36% 1.52 13.09% 39.18 15.12% 24.57 c2_4 36679.56 8.59% 1.46 7.32% 1.95 6.00% 1.64 7.72% 29.95 7.97% 25.62 c2_5 33700.93 11.00% 1.74 8.42% 1.27 9.58% 1.46 12.25% 28.76 6.23% 19.96 avg 28117.23 9.66% 1.02 7.47% 0.99 7.14% 0.98 7.17% 17.95 7.58% 14.56 rank (f(x)) 1 3 5 4 2 rank (time) 3 2 1 5 4 table ii. orders of local search procedures 5 local search operators 1st 2nd order of local search 2 opt 1 3 one intra route relocate 3 2 one intra route exchange 5 1 one inter route exchange 4 5 one inter route relocate 2 4 from the results presented in table iii, we may conclude the following: the vnd variants that explore neighborhoods in 1 st order offer the best results in both objective function and cpu time compared to the other order type. if we consider the average results over all test instances, it appears that the best average results are obtained by u-vnd even when we change the order of neighborhoods. so we can say that the u-vnd is more effective than b-vnd in terms of the objective function and cpu time. from the average results over all test instances we show that all our vnd procedures implemented and discussed in this paper are competitive and perform better than the mimetic algorithm when solving the same problem. for 6 instances among 10, a new best solution is found by our method. table iii. evaluation of different variants of vnd b-vnd u-vnd orders 1st 2nd 1st 2nd instances mimetic of tricoire value % dev mimetic %dev heuristic value % dev mimetic % dev heuristic value % dev mimetic % dev heuristic value % dev mimetic % dev heuristic c100_1 f(x) 17893.91 17578.37* -1.76% 19.61% 17594.18 -1.68% 19.50% 17578.37* -1.76% 19.61% 17594.03 -1.68% 19.50% time (s) 9.92 11.42 8.97 13.28 c100_2 f(x) 15977.12 17202.92 7.67% 12.47% 17136.03 7.25% 12.90% 17153.67 7.36% 12.79% 17164.61 7.43% 12.72% time (s) 9.52 9.58 8.06 8.73 c100_3 f(x) 16714.03 17493.5 4.66% 12.38% 17529.38 4.88% 12.15% 17491.94 4.65% 12.39% 17538.11 4.93% 12.09% time (s) 7.32 5.93 5.03 6.74 c100_4 f(x) 17489.36 18285.77 4.55% 21.58% 18265.73 4.44% 21.72% 18229.85 4.23% 21.95% 18031.33 3.10% 23.30% time (s) 11.37 12.68 9.5 14.03 c100_5 f(x) 16025.91 16535.47 3.18% 10.19% 16611.1 3.65% 9.68% 16535.47 3.18% 10.19% 16364.41 2.11% 11.34% time (s) 9.83 9.78 9.91 15.47 c180_1 f(x) 28945.36 28607.43 -1.17% 36.63% 29299.56 1.22% 33.40% 28405.93* -1.86% 37.60% 28579.51 -1.26% 36.76% time (s) 113.28 107.17 84.19 96.87 c180_2 f(x) 31191.12 28156.24 -9.73% 23.86% 27780.88 -10.93% 25.53% 27748.3 -11.04% 25.68% 27729.19* -11.10% 25.77% time (s) 66.39 72.82 58.22 46.09 c180_3 f(x) 27728,44 26464,43 -4,56% 37,35% 27472,29 -0,92% 32,31% 26034,96* -6,11% 39,62% 26886,39 -3,04% 35,20% time (s) 85,99 89,47 78,46 77,85 c180_4 f(x) 30245,61 29348,92 -2,96% 24,98% 29522,29 -2,39% 24,24% 30124,57 -0,40% 21,76% 29238,94* -3,33% 25,45% time (s) 57,23 76,22 52,22 61,71 c180_5 f(x) 28158,57 26880,26 -4,54% 25,37% 26566,25 -5,65% 26,86% 26395,74* -6,26% 27,68% 26625 -5,45% 26,58% time (s) 78,74 93,93 70,71 60,92 average f(x) 23036,94 22655,33 -1,66% 24,11% 22777,77 -1,13% 23,44% 22569,88 -2,03% 24,58% 22575,15 -2,00% 24,55% time (s) 44,96 48.9 38.53 40.17 re tr ac te d engineering, technology & applied science research vol. 9, no. 5, 2019, 4718-4723 4722 www.etasr.com khattara et al.: an efficient metaheuristic approach for the multi-period technician routing and … it is worth noting that all vnd procedures also perform better and they all improve on average at least 23.44% and at most 24.58% the results found by the heuristic. that means that vnd procedures improve the solution in average 15% more than the single local search operators (table i). d. variable neighborhood search procedures in this section we evaluate and compare three variants of vns procedures regarding to the improvement procedures in the inner loop: (1) b-vns that uses a simple local search in the inner loop at each iteration and move to the other one as in algorithms 1 and 3, (2) vns_b-vnd that uses a b-vnd procedure, and (3) vns_u-vnd that uses a u-vnd in the improvement phase. the neighborhoods in the vnd procedures are ordered in the 1 st order. the performances of vns procedures have been tested on class c1 of the instances described above. we tested our vns procedures by using 4 different time limits, ranging from 360s to 1140s. for each instance and each vns we ran the algorithm 5 times. the results are summarized in table iv and figure 4. table iv. evaluation of different variants of vns bvns vns_b-vnd vns_u-vnd time limit (s) instances mimetic of tricoire % dev_best % dev_avg % dev_best % dev_avg % dev_best % dev_avg 360 average c1 16820.07 -0.27% 1.56% -1.04% 0.18% -1.25% 0.14% 720 -0.56% 1.06% -1.59% -0.37% -1.87% -0.27% 1080 -0.56% 0.99% -1.69% -0.53% -2.11% -0.47% 1440 -0.57% 0.89% -1.96% -0.66% -2.19% -0.60% average -0.49% 1.12% -1.57% -0.34% -1.85% -0.30% for each time limit and each vns variant, we report the deviation from the best solution found over all variants of instance of class c1 in 5 runs compared to the best solution found by the mimetic algorithm of [9, 11, 12] (named % dev_best in table iv). we also compute the deviation from the average value of the solutions found in 5 runs for all instances of c1 compared to the best solution found by the mimetic algorithm (named % dev_avg in table iv). the deviations are calculated by (3). fig. 4. comparison between vns procedures from the results presented in table iv and figure 4 we may draw the following conclusions: firstly, we remark that the performance of vns procedures in this paper depends on the time limit. as we have a long time we achieve the best results. all vns variants outperform the results of the mimetic algorithm even if our vns methods are stopped at 360s. the collaboration of all local search procedures is more beneficial than only the use of one local search in the inner loop in the vns procedure. if we consider the average results over all variants of instance c1, it appears that the best average results are obtunded by vns_u-vnd, and that confirms what we found in the last section. v. conclusion and perspectives in this paper, we considered a new variant of the multiperiod technician routing and scheduling problem motivated by a real-life industrial application in a telecommunication company. to solve the problem, two variants of variable neighborhood descent b-vnd and u-vnd, as well as three variants of variable neighborhood search bvns, vns_b-vnd and vns_u-vnd are proposed. all heuristic methods were tested and compared with the methods proposed by tricoire [9, 11,12]. the results confirm the effectiveness of our methods. regarding future work, we will generate other instances to intensify the experimentations. also, we will consider the dynamic aspect, where the demands appear dynamically over the planning horizon. references [1] v. pillac, c. gueret, a. l. medaglia, “a parallel matheuristic for the technician routing and scheduling problem”, optimization letters, vol. 7, no. 7, 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neighborhood search: basics and variants”, euro journal on computational optimization, vol. 5, no. 3, pp. 1-32, 2016 [22] a. mjirda, r. todosijevic, s. hanafi, p. hansen, n. mladenovic, “sequential variable neighborhood descent variants: an empirical study on the traveling salesman problem”, international transactions in operational research, vol. 24, no. 3, pp. 615-633, 2016 re tr ac te d engineering, technology & applied science research vol. 8, no. 5, 2018, 3360-3365 3360 www.etasr.com pekin alakoc & apaydin: a fuzzy control chart approach for attributes and variables a fuzzy control chart approach for attributes and variables nilufer pekin alakoc college of engineering and technology american university of the middle east kuwait nilufer.alakoc@aum.edu.kw aysen apaydin department of insurance and actuary sciences ankara university ankara, turkey aapaydin@ankara.edu.tr abstract—the purpose of this study is to present a new approach for fuzzy control charts. the procedure is based on the fundamentals of shewhart control charts and the fuzzy theory. the proposed approach is developed in such a way that the approach can be applied in a wide variety of processes. the main characteristics of the proposed approach are: the type of the fuzzy control charts are not restricted for variables or attributes, and the approach can be easily modified for different processes and types of fuzzy numbers with the evaluation or judgment of decision maker(s). with the aim of presenting the approach procedure in details, the approach is designed for fuzzy c quality control chart and an example of the chart is explained. moreover, the performance of the fuzzy c chart is investigated and compared with the shewhart c chart. the results of simulations show that the proposed approach has better performance and can detect the process shifts efficiently. keywords-component; fuzzy set theory; statistical process control; fuzzy control charts; average run length i. introduction recently, quality improvement has become the main interest of firms all over the world. there are several benefits of achieving better standards: increase in revenue, productivity, customer satisfaction and market share. statistical methods such as design of experiments, hypotheses testing and statistical process control play an important role in quality improvement. the primary tool of statistical process control is quality control charts which were first introduced by walter a. shewhart [1]. a control chart provides information on changes of process mean and variance so that corrective actions can be undertaken as early as possible which leads to reduce variability, improve productivity and quality. on the other hand, statistical process control problems include uncertainty as most of the real world systems. if there is uncertainty in the process or if quality characteristics are described by human subjectivity, then the process cannot be defined accurately by shewhart control charts. therefore, fuzzy set theory is used to explain and model problems. the idea of fuzzy set theory was first introduced in [2], afterwards the theory was used in development of many procedures, approaches and fields to define and model systems. applications of fuzzy theory on statistical process control have taken attention and been investigated widely which resulted in a new perspective in quality improvement. many studies [3-10] were mainly focused on the adaptation of linguistic terms such as perfect, good, medium etc. to control charts. in [3, 4], authors proposed two fuzzy control chart approaches: probabilistic approach and membership approach. as an extension of these studies, a new approach for considering linguistic terms to express the process outcomes was introduced [5, 6]. in another study on linguistic data [7], fuzzy control chart generation procedures were compared. in [8], authors studied on linguistic terms and suggested fuzzy approaches for attributes. recently, an approach called transition probability approach based on markov chain theory was developed [9]. attribute control charts were discussed in [10, 11] and reviewed in [12]. a fuzzy approach for the determination of variable sampling interval was developed by a composition function [13]. in [14], authors suggested a fuzzy control chart based on fuzzy regression analysis with neural network and degree of fuzziness, and generated the fuzzy data by combining experts’ opinion and measurements. in another study, direct fuzzy approach (dfa) was introduced for c control charts without using any defuzzification method [15]. studies on fuzzy statistical quality control were reviewed in [16, 17] and the open fields and challenges for future work were discussed briefly. in [18-21], authors studied on fuzzy approaches for attributes control charts and emphasized the critical role of fuzzy data. a fuzzy c chart monitored with weighted possibilistic mean and weighted interval valued possibilistic mean of fuzzy numbers was introduced in [22]. there are many studies on monitoring variable control charts for uncertain observations. the former fuzzy control charting approach for variables is based on plotting control charts by considering uncertain process parameters for both variables and attributes [23]. in [24], authors developed a fuzzy chart with pearson goodness of fit statistic which includes a warning line besides its upper control limit. different procedures for variable control charts in which the shewhart control limits are modified with uncertainty and randomness were proposed in [25-27]. contributions to fuzzy process control works from a different point of view were also proposed, e.g. fuzzy ewma, cusum control charts [28], adaptation of the run rules and recognition of the unnatural patterns of fuzzy control charts [29-31]. engineering, technology & applied science research vol. 8, no. 5, 2018, 3360-3365 3361 www.etasr.com pekin alakoc & apaydin: a fuzzy control chart approach for attributes and variables authors in [32] investigated fuzzy multivariate control charts, in [33], nonparametric shewhart control chart for fuzzy data, and control charts autocorrelated fuzzy observations in [34]. this paper introduces a new approach for constructing fuzzy control charts. the approach is proposed as an extension of shewhart control charts and differs from the previous studies in flexible assumptions which do not restrict the type of the chart and application area. the charting procedure is based on membership degrees of fuzzy numbers, the pattern of -cut fuzzy numbers and fuzzy limits on the chart. the out of control condition is determined by a decision function which is developed by considering the distribution of membership degrees, the probability of type i error and 3 control limits. a simulation study is performed to demonstrate the performance of the approach. ii. design of fuzzy control chart a. the procedure the approach is flexible and not restricted to a specified type of control chart, because any assumptions about the type of quality characteristic or the distribution of quality characteristic are not required. for this reason, the approach can be modified easily for control charts with different purposes. during the development process several different fuzzy control charts are plotted and different applications are examined. a sensitivity analysis is performed based on the applications and then effects of fuzzy numbers and parameters of membership function are investigated. if measurements and control limits of an approach are fuzzy numbers then the most essential part of constructing a fuzzy control chart is to define the intersection situations of fuzzy limits and numbers. if all the fuzzy numbers are between the fuzzy limits, then the process is in control and the membership degree of being in control is 1. similarly, if any fuzzy number is completely out of the fuzzy control limits then the process is out of control and the membership degree is 0. however, it is not easy to define the process if any fuzzy number intersects with the fuzzy control limits. the approach classifies these situations by a formula and assigns a membership degree to each fuzzy number in such a way that the importance of having a fuzzy number between the fuzzy limits, and the importance of intersecting with fuzzy limits are differentiated with the perspective of the decision maker. the proposed fuzzy control chart plots measurements of a quality characteristic in the form of -cut fuzzy numbers. the fuzzy control chart represents the fuzzy control limits and center line by two parallel lines which show upper and lower values of -cut fuzzy limits. -cut fuzzy numbers are illustrated with lines perpendicular to the limits. let is a trapezoidal fuzzy number, such that =( , , , ), then -cut trapezoidal fuzzy number is an interval in the form of = + ( − ), − ( − ), = , . if measurements are denoted by trapezoidal fuzzy numbers, then fuzzy control limits, and , and the fuzzy center line, of fuzzy ̅ and r charts are defined as: ̅ = − , − , ̅ − , ̅ − ̅ = , , ,̅ ̅  ̅ = − , + , ̅ + , ̅ +  = ( , , , ) = ( , , , )= ( , , , ) where = ∑ ⁄ , = max − and = , , , , = 1,…, . similarly, fuzzy control limits and the center line of fuzzy c control chart are calculated by: = − 3 ̅, − 3√ ,̅ ̅ − 3 , ̅ − 3√ = , , ̅, ̅ = + 3√ , + 3 , ̅ + 3√ ,̅ ̅ + 3 ̅  triangular fuzzy numbers are special cases of trapezoidal fuzzy numbers. trapezoidal fuzzy numbers are reduced to triangular fuzzy numbers when = ,. let is a triangular fuzzy number, denoted by = ( , , ), then -cut triangular fuzzy number is an interval such that = , . so that the fuzzy control limits of c chart, and , are triangular fuzzy numbers: = − 3√ ,̅ − 3 , ̅ − 3√ = , , ̅ = + 3√ , + 3 , ̅ + 3√ ̅  the approach is not limited to any specified type of fuzzy numbers, but for the simplicity, the procedure is explained by triangular fuzzy numbers. if is the -cut range of ith fuzzy number, then this range is defined as: = , + , + ,   where, , is the part of the range of -cut fuzzy number that intersects with any of the -cut fuzzy control limits, and , , , are the parts of the range of -cut fuzzy number that are between and out of the -cut control limits, respectively. figure 1 represents an example of the definitions on triangular fuzzy numbers. for the first fuzzy number, (fn1), , > 0, , = 0 and , > 0 and for the second one, (fn2), , = 0 , , > 0 and , > 0 . the membership function, which is the weighted sum of ranges, , , , and , is stated as follows: = , ( ) ,( )   where = − , and = min − , and are defined to standardize the membership function, and  engineering, technology & applied science research vol. 8, no. 5, 2018, 3360-3365 3362 www.etasr.com pekin alakoc & apaydin: a fuzzy control chart approach for attributes and variables is the weight of -cut fuzzy number that intersects with any one of the -cut control limits. even though, the value of  is based on the production processes and expert's experiences, the value is expected to be in [0, 0.5], and so that 0 < (1 − ) <⁄ 1. fig. 1. examples of on triangular fuzzy numbers. is a random variable and has a probability distribution based on the process. this yields to have multiple values for membership degree of a fuzzy number which means fuzzy of fuzziness. hence, the proposed fuzzy membership function necessitates the use of type-2 fuzzy set theory. type-2 fuzzy sets, first introduced in [35] are the higher order of type-1 fuzzy sets. in type-1 fuzzy sets the membership degree for each element is a crisp number in [0, 1], whereas the membership degree of type-2 fuzzy sets for each element is a fuzzy set in [0, 1]. for the simplicity of the approach and to increase the applicability, it is assumed that , which is determined by the decision maker(s), is a single constant value. this assumption reduces the procedure to type-1 fuzzy theory. after the calculation of membership degrees for each fuzzy number, the next step of the procedure is to describe the state of the process by the decision function given in (7) and monitoring the process. process = in control, if < 1out of control, if 0 <  where, is a parameter such that 0 1. b. estimation of decision function parameter the determination of the decision function parameter,  is an important part of the approach because if a value assigned is greater than it should be then the probability of type i error increases. this situation has the same effect with moving the control limits closer to the center line on shewhart control charts. on the other hand, when the estimate is less than it should be, the probability of type i error decreases, and the probability of type ii error increases. in this section, the estimation of the parameter is explained with the studies on membership degrees and their probability distributions. in the development process of the approach a detailed study is performed to estimate . different data sets are experimented and fuzzy control charts are plotted under various process scenarios. data sets from binomial, poisson and normal distributions with a variety of parameter values are generated randomly for constructing fuzzy p, np, c, u, ̅, r and s control charts. membership degrees of fuzzy numbers are calculated and the distribution of these membership degrees is investigated individually. sixty one different continuous probability distributions are fitted to all data sets by easyfit 5.5. as a consequence of the applications, it is statistically proved that for all shewart control charts, the distribution of membership degrees is beta distribution with two shape parameters which is left skewed with one peak. in order to standardize the estimates, all the data sets are considered together and the parameters are estimated by the maximum likelihood method which provides = 3.6974 and =1.1807. figure 2 illustrates the histogram of a random sample of membership degrees of 1000 triangular fuzzy numbers which are randomly generated from different distributions. the membership degrees are calculated by the corresponding control charts. fig. 2. histogram of membership degrees and b (3.6974, 1.1807) (=0.33 and =0.60). the next step is to determine the value of the decision function parameter . it is estimated by the probability of observing a point outside the control limits when the process is in control, which is 0.0027 type i error probability of shewhart control chart. the decision function for a fuzzy control chart is: process = in control, if 0.1856 < 1out of control, if 0 < 0.1856 iii. an application of fuzzy c control chart in this section, an application of the approach is presented by fuzzy c control chart. the number of defective products in each package is assumed to be expressed by fuzzy numbers. the defects or nonconformities occur according to poisson distribution, which forms the basis of the c control chart. in order to plot a fuzzy control chart, a set of fuzzy data is generated randomly from the poisson distribution. it is assumed that the process is in control when c=25 and triangular fuzzy numbers are formed by subtracting and adding 1.5 times of standard deviation of the data. a random sample of 30 -cut triangular fuzzy numbers and membership degrees are given in table i. fuzzy control limits and fuzzy central line are illustrated in figure 3 and obtained as follows: =(0.114,11.815,23.977) , = (18.317,27.567,36.817) , =(31.156,43.318,55.020) and . = 7.135,16.680 , . =23.867,31.267 , . = 38.453,47.999 . in this application, the membership degrees of fuzzy numbers are computed by the assumption that the importance of having a number between the fuzzy limits is twice the importance of intersecting with engineering, technology & applied science research vol. 8, no. 5, 2018, 3360-3365 3363 www.etasr.com pekin alakoc & apaydin: a fuzzy control chart approach for attributes and variables fuzzy limits, which means = 1 3⁄ . fuzzy c control chart is given in figure 4. the membership degrees of 12 fuzzy numbers are 1 which means these numbers are completely between the -cut fuzzy control limits. the rest of the values are smaller than 1, but not . consequently, the fuzzy c control chart shows a pattern in which -cut fuzzy numbers are randomly distributed and the process is in control. table i. sample 1: -cut triangular fuzzy numbers and membership degrees () no no 1 14.30 18.00 21.70 0.8392 16 18.30 22.00 25.70 1.0000 2 32.30 36.00 39.70 0.9158 17 39.30 43.00 46.70 0.5000 3 14.30 18.00 21.70 0.8392 18 38.30 42.00 45.70 0.5104 4 16.30 20.00 23.70 0.9743 19 27.30 31.00 34.70 1.0000 5 10.30 14.00 17.70 0.5689 20 19.30 23.00 26.70 1.0000 6 27.30 31.00 34.70 1.0000 21 16.30 20.00 23.70 0.9743 7 32.30 36.00 39.70 0.9158 22 21.30 25.00 28.70 1.0000 8 25.30 29.00 32.70 1.0000 23 10.30 14.00 17.70 0.5689 9 32.30 36.00 39.70 0.9158 24 33.30 37.00 40.70 0.8482 10 17.30 21.00 24.70 1.0000 25 38.30 42.00 45.70 0.5104 11 21.30 25.00 28.70 1.0000 26 12.30 16.00 19.70 0.7040 12 36.30 40.00 43.70 0.6455 27 18.30 22.00 25.70 1.0000 13 19.30 23.00 26.70 1.0000 28 19.30 23.00 26.70 1.0000 14 15.30 19.00 22.70 0.9068 29 33.30 37.00 40.70 0.8482 15 19.30 23.00 26.70 1.0000 30 37.30 41.00 44.70 0.5779 fig. 3. fuzzy control limits and central line. fig. 4. fuzzy c control chart for the data in table i. the application is repeated for the second data set generated from poisson distribution with c=27. thirty triangular fuzzy numbers are generated randomly for the second set and the membership degrees of these numbers are calculated. table ii presents -cut triangular fuzzy numbers and membership degrees of the second sample. fuzzy c control chart in figure 5 shows the -cut fuzzy control limits and the central line which are calculated by the first data set. the membership degrees of the corresponding fuzzy numbers that are smaller than are also presented on the chart. figure 5 indicates that “the process is out of control”. this result is due to the 48th and 58th fuzzy numbers which have membership values smaller than . the 48th number is completely out of cut fuzzy upper control limit with = 0.000. on the other hand, the -cut of the 58th fuzzy number intersects with the cut fuzzy lower control limit with a membership degree of 0.1253. moreover, the pattern of the chart provides information about the randomness of the process. in figure 5 there is a shift in the process mean up to 43th fuzzy number and then, a clear increasing trend. after the 48th number a descending trend can be observed. consequently, all these symptoms and the membership degrees point toward the nonrandomness and out of control state in the process output. table ii. sample 2: -cut triangular fuzzy numbers and membership degrees () no no 31 18.84 23.00 27.16 1.0000 46 33.84 38.00 42.16 0.7812 32 10.84 15.00 19.16 0.6540 47 31.84 36.00 40.16 0.9004 33 24.84 29.00 33.16 1.0000 48 49.84 54.00 58.16 0.0000 34 23.84 28.00 32.16 1.0000 49 44.84 49.00 53.16 0.1929 35 7.84 12.00 16.16 0.5000 50 23.84 28.00 32.16 1.0000 36 22.84 27.00 31.16 1.0000 51 24.84 29.00 33.16 1.0000 37 14.84 19.00 23.16 0.8925 52 27.84 32.00 36.16 1.0000 38 18.84 23.00 27.16 1.0000 53 28.84 33.00 37.16 1.0000 39 21.84 26.00 30.16 1.0000 54 23.84 28.00 32.16 1.0000 40 19.84 24.00 28.16 1.0000 55 24.84 29.00 33.16 1.0000 41 20.84 25.00 29.16 1.0000 56 21.84 26.00 30.16 1.0000 42 6.84 11.00 15.16 0.4830 57 15.84 20.00 24.16 0.9521 43 27.84 32.00 36.16 1.0000 58 0.84 5.000 9.16 0.1253 44 32.84 37.00 41.16 0.8408 59 5.84 10.00 14.16 0.4234 45 23.84 28.00 32.16 1.0000 60 18.84 23.00 27.16 1.0000 fig. 5. fuzzy c control chart for the data in table ii. iv. fuzzy control chart performance the most effective and commonly used performance measure is the average run length (arl), which is the average number of points plotted on a control chart before an out of control condition is observed. if the process observations are uncorrelated, then arl is calculated as given below arl = = (one point plots out of control) if the process is in control, arl is denoted by arl where arl0 = 1 (type i error probability)⁄ . it is desired to have a large value for arl0 which gives fewer false alarm rates. on the other hand, if an assignable variable occurs, then the probability of being in the out of control state increases and more numbers give out of control signals. when the process is out of control, the arl is denoted by arl and defined by arl = 1 (1 − type ii error probability)⁄ . in order to reduce the time to detect out of control situation, small values for arl engineering, technology & applied science research vol. 8, no. 5, 2018, 3360-3365 3364 www.etasr.com pekin alakoc & apaydin: a fuzzy control chart approach for attributes and variables are required. in this section, the performance of fuzzy c control chart is calculated and the fuzzy control chart is compared with shewhart c control chart. all the computations are carried out by c++ programming language and one million simulation runs are performed for each arl. the fuzzy numbers are generated randomly, and it is assumed that the process is in control when the mean number of nonconformities is = =14 and the process is out of control when = + where = 1,2,…,9. firstly, reference quantities of the fuzzy chart are determined to have the same arl with shewart control chart. these are = 0.6, = 0.1856 and = 1 3⁄ . then, the process parameter is shifted and run lengths are averaged to get arl . table iii presents the summary of the results. the second column gives shewart c control chart arl values which are calculated by (12) and (13): = p < lcl/ + p > ucl/ = p lcl < < ucl/  table iii. performance of shewart and fuzzy c control charts shift ( ) arl shewhart c control chart arl fuzzy c control chart 0 370.1580 374.6512 1 160.6629 139.1889 2 76.1332 69.5200 3 39.6020 36.0776 4 22.4160 21.4669 5 13.6749 14.0383 6 8.9138 9.4132 7 6.1615 6.7849 8 4.4863 5.2133 9 3.4206 4.3388 it can be concluded that for small shifts of the parameter, the fuzzy control chart arl is significantly less than shewart control chart arl , which means fuzzy control chart performance is better than shewart control chart. as the shift increases the arl values approach shewart control chart and both of the charts result to almost the same performance. v. conclusions and discussion many real life problems cannot be modeled or defined by classical methods. for this reason, fuzzy logic has been applied to real life applications and science. fuzzy control charts that are constructed with fuzzy set theory reflect the uncertainty better than shewhart control charts. this paper presents a fuzzy approach that integrates fuzzy set theory and the basics of shewhart control charts. the approach is developed by a decision function and a membership function based on -cut fuzzy numbers, fuzzy 3 control limits, and intersection situations of fuzzy numbers and fuzzy control limits. an example is included to demonstrate the applicability and efficiency of the proposed fuzzy control charts. moreover, the performance of fuzzy control charts is investigated and the fuzzy c control chart is compared with the shewhart c control chart. the approach is investigated with various applications in the development stage. the functions, parameters and decisions are tested for verification and validation of the approach. as a result of these studies, some advantages of the proposed approach are derived. at first, the type of fuzzy numbers is not specified. the choice of fuzzy numbers depends on the decision maker. second, process is defined without using any transformation techniques, which minimizes the loss of information and biased decisions. the membership function is calculated by weighted mean of ratios. third, with respect to the process the weights can be changed. the approach is easy to understand and calculate. it is flexible and does not require any important assumptions that restrict the application area. therefore, the approach can be modified easily for different processes and applied to both variables and attributes control charts with small modifications. another advantage of the approach is that the decision function has two linguistic decisions, “the process is in control” and “the process is out of control”. depending on the process, the number of decisions can be increased or a warning decision can be added. finally, the process is defined by the membership function which provides more flexibility compared to shewhart control charts and previous studies. references [1] d. c. montgomery, introduction to statistical quality control, 7th edition, john wiley & sons inc., ny, usa, 2013 [2] l. a. zadeh, “fuzzy sets”, information and control, vol. 8, no. 3, pp. 338-353, 1965 [3] 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“fuzzy control chart a better alternative for shewhart average chart”, quality & quantity, vol. 41, no. 3, pp. 375385, 2007 [25] a. faraz, r.b. kazemzadeh, m. b. moghadam, a. bazdar, “constructing a fuzzy shewhart control chart for variables when uncertainty and randomness are combined”, quality & quantity, vol. 44, no. 5, pp. 905-914, 2009 [26] a. faraz, a. f. shapiro, “an application of fuzzy random variables to control charts”, fuzzy sets and systems, vol. 161, pp. 2684-2694, 2010 [27] m. h. shu, h. c. wu, “fuzzy x and r control charts: fuzzy dominance approach”, computers & industrial engineering, vol. 61, no. 3, pp. 676-686, 2011 [28] s. b. akhundjanov, f. pascual, “moving range ewma control charts for monitoring the weibull shape parameter”, journal of statistical computation and simulation, vol. 85, no. 9, pp. 1864-1882, 2015 [29] j. d. t. tannock, “a fuzzy control charting method for individuals”, international journal of production research, vol. 41. no. 5, pp. 10171032, 2003 [30] m. gulbay, c. kahraman, “development of fuzzy process control charts and fuzzy unnatural pattern analyses”, computational statistics & data analysis, vol. 51, no. 1, pp. 434-451, 2006 [31] n. pekin alakoc, a. apaydin, “sensitizing rules for fuzzy control charts”, world academy of science, engineering and technology, international journal of mechanical, aerospace, industrial, mechatronic and manufacturing engineering, vol. 7, no. 5, pp.931-935, 2013 [32] m. n. pastuizaca fernandez, a. carrion garcia, o. ruiz barzola, “multivariate multinomial t2 control chart using fuzzy approach”, international journal of production research, vol. 53, no. 7, pp. 2225– 2238, 2015 [33] d. wang, o. hryniewicz, “a fuzzy nonparametric shewhart chart based on the bootstrap approach”, international journal of applied mathematics and computer science, vol. 25, no. 2, pp. 389-401, 2015 [34] b. sadeghpour gildeh, n. shafiee, “x-mr control chart for autocorrelated fuzzy data using dp,q-distance”, the international journal of advanced manufacturing technology, vol. 81, no. 5-8, pp. 1047-1054, 2015 [35] l. a. zadeh, “the concept of a linguistic variable and its application to approximate reasoning 1”, information sciences, vol. 8, no. 3, pp. 199-249, 1975 authors profile nilufer pekin alakoc, graduated from the department of statistics at middle east technical university in turkey and received her msc degree from industrial engineering department at the same university. she obtained her phd degree in statistics. her research interests are mainly in the area of statistical quality control, statistical applications in industrial engineering and operations research. she is currently working as assistant professor at the american university of the middle east in kuwait. aysen apaydin, is professor at the department of insurance and actuary sciences at ankara university in turkey. she has more than 35 years of experience in statistics and statistical applications. she has published 4 textbooks and more than 115 scientific publications and conference papers. she has worked in several administrative positions and served as organizer and council member of more than 20 congresses, symposiums and colloquiums. dr. apaydin is currently working as student and information coordinator at ankara university. engineering, technology & applied science research vol. 7, no. 3, 2017, 1699-1707 1699 www.etasr.com rezaei and babaei: designing a model for knowledge socialization using sociability processes of human… designing a model for knowledge socialization using sociability processes of human resource management: a case study kiana rezaei department of information technology management college of management and economics science and research branch islamic azad university tehran, iran. mohammadreza babaei department of industrial management college of management and accounting yadegar-e-imam khomeini (rah) shahrerey branch islamic azad university tehran, iran abstract—this study develops a model for knowledge socialization using sociability processes of human resources through an applied research approach. two types of participants participated in this study. the first type included academic and industrial experts; the second type included employees and managers of ansar bank. ten experts were asked to identify criteria and weigh the identified criteria. using simple random sampling, the sample size was estimated at 207. field and archival studies were used to collect data. validity and reliability of the distributed questionnaire were confirmed by organizational experts. using theoretical literature and surveying experts, 18 criteria were identified of which 12 criteria (desirable and joyful workplace, management and leadership support in sociability process, training courses, transparency in working relations, team work, organizational trustful climate, job description and job knowledge, tangible incentives, participatory system, informal technique, defined career path, individual values aligned with organizational value) were selected by screening for prioritization and analysis. fuzzy ahp and structural equation modelling based on partial least squares were used for prioritization and weighting. fuzzy ahp model showed that desirable workplace (0.163), participatory systems and brainstorming (0.149), transparency in working relations (0.114), and informal techniques (0.111) gained the highest weights; finally, pls model showed that all 12 identified criteria were effective on socialization of knowledge management. keywords-sociability of human resources; organizational knowledge; knowledge socialization i. introduction currently, the world is increasingly changing around organizations; as scientists assert, the only thing that will not change in this period is the change itself [1]. due to the complexity of environment and growing competition in any industry, suitable strategies cannot merely lead to competitive advantage and good competitive position [2]. knowledge is the first strategic resource for organizations and acts as a key competitive factor in the global economy. nevertheless, research has shown that half of human information is completely outdated every five years and is replaced by new knowledge and information [3]. therefore, organizations need to adopt processes and strategies to share knowledge among members and allow them to gain experiences of others. however, evidence suggests that this is seriously challenged in iranian organizations. in iranian organizations, members do not share knowledge with each other; knowledge sharing as one of the most fundamental pillars of knowledge-based organization is the missing link in these organizations [4]. a plan cannot be successful merely by determining plans and adopting strategic decisions. in other words, even a well-developed strategy will be useless if it is not implemented [5, 6]. however, evidence suggests that literature and practical activities and efforts made in organizations mostly focus on development of strategy rather than implementation of strategies; implementation and its aspects have been neglected [5-7]. nevertheless, it can be claimed that although socialization of organizational knowledge as a basic approach has been adopted by various organizations, its successful implementation depends on suitable conditions and requirements such as financial, material, technical and human resources. this study focuses on human resources. experience shows that success and failure of organizations directly depend on quality and effectiveness of employees. modern successful organizations have realized that they need global hr managers to compete in global markets. more importantly, technological revolution that has occurred in recent decades highlighted the role of human resources as an important organizational resource. the current study tends to address this by focusing on ansar bank and using the feldman model [17]. therefore, this study examines the extent to which socialization of organizational knowledge can be expected by using socialization process of human resource management and the extent to which each socialization process of hr management can predict development and socialization of knowledge. ii. literature review organizational sociability is a process in which a new employee is converted from an outsider to an effective insider engineering, technology & applied science research vol. 7, no. 3, 2017, 1699-1707 1700 www.etasr.com rezaei and babaei: designing a model for knowledge socialization using sociability processes of human… for the organization; this happens when an employee enters an organizational domain [8]. sociability of hr management is the process whereby new people acquire necessary and sufficient information about the organization, adapt to the conditions by adopting its values, norms and culture, and learn their tasks and expectations [9]. to measure this dimension, a researcher-made questionnaire is used with following aspects: 1) pre-entry practices involving all thoughts and attitudes delivered to employees; 2) starting practices or encounter with the organization involving all knowledge, lessons and experiences which are gained at the first encounters with the organization; 3) evolutionary practices involving changes which occur after several years of work and experience and help harmonizing with governing conditions of the organization. knowledge is a competitive advantage and one of the most important factors of production which must be directed and managed. knowledge is one of the most important intangible components of organizations employed in organizational mechanisms and processes and allows innovation in the organization. accordingly, measurement of knowledge and other intangible assets is very important in business processes [10]. numerous definitions have been presented for knowledge management. one of these definitions which have standardized and integrated various definitions is the australian standard definition in 2003 which knowledge management is a disciplined approach to achieve organizational goals by optimum use of organizational knowledge. another definition considers knowledge management in terms of business. in [11], it was asserted that knowledge management encompasses all systemic activities associated with knowledge creation and knowledge sharing within the organization in relation with customers, partners and owners of knowledge. in knowledge environment, knowledge management is defined as any systemic activity which is compatible with usage, dissemination and encoding of organizational goals. knowledge socialization refers to quantitative and qualitative development of the knowledge needed for the organization, knowledge sharing between members and its proper management [12, 13]. in [2], authors examined the role of knowledge-based leadership on practices of knowledge management and innovation. they evaluated effect of knowledge-based leadership on knowledge management practices for innovation and competitive advantage using several hypotheses. they found that knowledge management practices mediated the relationship between knowledge-based leadership and innovative performance. moreover, knowledge management practices were effective on innovative performance. in [14], authors evaluated the effect of implicit sociability practices on job satisfaction and use of newcomers. they developed a new self-evaluation model for newcomers to evaluate sociability practices of employees on organizational commitment and engagement in work. proper sociability improved implementation and commitment and ultimately job satisfaction of chinese hotel employees. in [15], authors addressed interactive leadership and innovation focusing on mediating role of knowledge absorption capacity. they asserted that proper strategies alone are not enough for organizations; organizations need to adapt to their surrounding environment. analysis of questionnaires distributed among 28 top managers showed a positive and significant relationship between interactive leadership and knowledge absorption capacity and between knowledge management capacity and organizational innovation. this supported the mediating role of knowledge absorption capacity. in [16], authors examined the relationship between leadership styles and knowledge management and increased commitment of employees of khuzestan bus company. findings indicated that the increased knowledge management and leadership styles promoted organizational commitment among employees. moreover, both leadership styles and knowledge management predicted organizational commitment of employees. iii. conceptual model based on literature review, the conceptual model is developed and shown in figure 1. fig. 1. knowledge socialization model engineering, technology & applied science research vol. 7, no. 3, 2017, 1699-1707 1701 www.etasr.com rezaei and babaei: designing a model for knowledge socialization using sociability processes of human… iv. hypotheses  hypothesis 1: desirable workplace is effective on socialization of knowledge management in sociability process.  hypothesis 2: top management support is effective on socialization of knowledge management in sociability process.  hypothesis 3: transparency in working relations is effective on socialization of knowledge management in sociability process.  hypothesis 4: training course is effective on socialization of knowledge management in sociability process.  hypothesis 5: teamwork is effective on socialization of knowledge management in sociability process.  hypothesis 6: organizational trustful climate is effective on socialization of knowledge management in sociability process.  hypothesis 7: job description is effective on socialization of knowledge management in sociability process.  hypothesis 8: organizational incentive is effective on socialization of knowledge management in sociability process.  hypothesis 9: participatory system is effective on socialization of knowledge management in sociability process.  hypothesis 10: defined career path is effective on socialization of knowledge management in sociability process.  hypothesis 11: informal technique is effective on socialization of knowledge management in sociability process.  hypothesis 12: alignment of individual values with organizational values is effective on socialization of knowledge management in sociability process. v. research methodology this was an extensive research using descriptive and survey methodologies. experts were surveyed to identify criteria. to test the model, the developed questionnaires were distributed among target population selected by sampling methods. the criteria identified through interviews and archival studies were classified and compiled. the developed model was tested by using structural equation modeling. statistical tests were used to prioritize effective factors on knowledge socialization. two types of participants enrolled in this study because of being two questionnaires. the first type included academic and industrial experts; the second type included 450 employees and managers of ansar bank. ten experts were asked to identify criteria and weight the identified criteria (first questionnaire). using simple random sampling, the sample size was estimated at 207 for testing hypothesis (second questionnaire). archival and field studies were used to collect data. archival studies included literature review. field studies included interviews and questionnaires. validity and reliability of the distributed questionnaire was confirmed by organizational experts. by reviewing literature and surveying experts, 18 criteria were identified of which 12 criteria (desirable and joyful workplace, management and leadership support in sociability process, training courses, transparency in working relations, team work, organizational trustful climate, job description and job knowledge, tangible incentives, participatory system, informal technique, defined career path, individual values aligned with organizational value) were selected by screening for prioritization and analysis. fuzzy analytic hierarchy process (ahp) and structural equation modelling based on partial least squares were used for prioritization and weighting. vi. results and finding a. prioritization using fuzzy ahp as shown in review of literature regarding effective factors of knowledge socialization in sociability process of human resources, following criteria were extracted for evaluating knowledge socialization (table i). these criteria were confirmed by experts and supervisors for their effect on knowledge socialization in sociability process. table i. effective factors on knowledge socialization in sociability symbol criterion c1 desirable and joyful workplace c2 management and leadership support in sociability process c3 training courses c4 transparency in working relations c5 team work c6 organizational trustful climate c7 job description and job knowledge c8 tangible incentives c9 participatory system c10 informal technique c11 defined career path c12 individual values aligned with organizational value since 10 experts were surveyed, 10 different matrices were formed for comparison of criteria. first, these matrices were converted to a single matrix. table ii lists the fuzzy numbers used. the best method to integrate pairwise comparisons tables of all respondents is to use geometric mean, because pairwise comparisons provides data in the form of ratios; moreover, the inverse property of pairwise comparisons matrix explains the use of this method, because geometric mean maintains this property of the matrix. let ãkij be the element related to the k-th respondent for comparison of the criterion i relative to the criterian j; geometric mean was calculated for corresponding elements by: nn k k ijij aa 1 1 ~~          engineering, technology & applied science research vol. 7, no. 3, 2017, 1699-1707 1702 www.etasr.com rezaei and babaei: designing a model for knowledge socialization using sociability processes of human…  10 1 1021 ~....~~~ ijijij aaaija  12 1 10 ((1, 2, 3) (1,1,1) (2, 3, 4) (1, 2, 3) (2, 3, 4) (0.25, 0.33, 0.5) (1,1,1) (2, 3, 4) (1, 2, 3) (2, 3, 4)) (0.9,1.22,1.53) a             using the above formula, criteria were compared as follows (table iii) : table ii. fuzzy numbers used lowest moderate value highest preference 11 1equally preferred 12 3intermediate 23 4moderately preferred 34 5intermediate 45 6strongly preferred 56 7intermediate 67 8very strongly preferred 78 9intermediate 99 9extremely preferred table iii. primary pairwise comparison matrix by integrating expert judgements (first class) criterion c1 c2 c3 c4 c5 c6 c1 1.00 1.00 1.00 0.90 1.22 1.53 1.53 1.83 2.13 1.15 1.57 2.02 1.41 1.89 2.35 1.89 2.51 3.12 c2 0.65 0.82 1.12 1.00 1.00 1.00 1.28 1.68 2.17 1.10 1.57 2.11 1.26 1.61 1.97 1.74 2.45 3.16 c3 0.47 0.55 0.65 0.46 0.60 0.78 1.00 1.00 1.00 0.55 0.75 1.07 0.92 1.16 1.47 0.88 1.12 1.45 c4 0.49 0.64 0.87 0.47 0.64 0.91 0.93 1.34 1.81 1.00 1.00 1.00 1.00 1.23 1.46 1.41 1.86 2.29 c5 0.43 0.53 0.71 0.51 0.62 0.79 0.68 0.92 1.21 0.68 0.81 1.00 1.00 1.00 1.00 0.93 1.13 1.41 c6 0.32 0.40 0.53 0.32 0.41 0.57 0.69 0.90 1.14 0.44 0.58 0.79 0.71 0.88 1.07 1.00 1.00 1.00 c7 0.23 0.29 0.39 0.28 0.32 0.38 0.40 0.48 0.63 0.34 0.41 0.52 0.43 0.49 0.61 0.42 0.55 0.78 c8 0.38 0.50 0.65 0.42 0.52 0.68 0.67 0.90 1.20 0.44 0.57 0.78 0.45 0.59 0.85 0.65 0.81 1.07 c9 0.21 0.26 0.33 0.26 0.31 0.38 0.31 0.40 0.54 0.36 0.49 0.67 0.29 0.36 0.47 0.34 0.44 0.58 c10 0.50 0.67 0.93 0.61 0.71 0.85 1.01 1.27 1.56 0.76 1.06 1.37 0.88 1.14 1.47 1.01 1.40 1.91 c11 0.20 0.23 0.27 0.20 0.23 0.28 0.26 0.32 0.43 0.21 0.25 0.31 0.22 0.27 0.35 0.31 0.38 0.47 c12 0.16 0.18 0.20 0.17 0.20 0.24 0.21 0.25 0.31 0.18 0.22 0.28 0.18 0.22 0.29 0.21 0.25 0.31 criterion c7 c8 c9 c10 c11 c12 c1 2.59 3.41 4.26 1.53 2.01 2.60 3.02 3.85 4.68 1.07 1.49 1.99 3.76 4.39 5.02 4.89 5.55 6.18 c2 2.63 3.12 3.57 1.47 1.94 2.38 2.60 3.19 3.87 1.22 1.46 1.71 3.41 4.15 4.82 4.20 5.00 5.86 c3 1.58 2.22 2.81 0.84 1.11 1.49 1.87 2.52 3.19 0.64 0.79 0.99 2.32 3.11 3.89 3.23 4.05 4.81 c4 1.91 2.43 2.94 1.28 1.76 2.27 1.49 2.06 2.74 0.73 0.94 1.31 3.19 3.99 4.93 3.57 4.62 5.69 c5 1.64 2.02 2.35 1.18 1.71 2.23 2.14 2.79 3.46 0.66 0.85 1.10 2.86 3.72 4.49 3.42 4.52 5.53 c6 1.28 1.81 2.39 0.93 1.24 1.55 1.71 2.29 2.94 0.52 0.72 0.99 2.13 2.61 3.19 3.23 4.03 4.80 c7 1.00 1.00 1.00 0.57 0.73 0.90 1.15 1.40 1.68 0.37 0.45 0.56 1.52 1.92 2.32 1.94 2.60 3.29 c8 1.12 1.37 1.76 1.00 1.00 1.00 1.69 2.21 2.75 0.70 0.81 0.95 1.83 2.50 3.23 2.49 3.33 4.21 c9 0.59 0.72 0.87 0.36 0.45 0.59 1.00 1.00 1.00 0.33 0.37 0.42 1.23 1.68 2.11 1.62 2.18 2.67 c10 1.78 2.23 2.73 1.14 1.37 1.67 2.39 2.73 3.02 1.00 1.00 1.00 2.81 3.43 4.09 4.09 5.14 6.10 c11 0.43 0.52 0.66 0.31 0.40 0.55 0.47 0.59 0.81 0.24 0.29 0.36 1.00 1.00 1.00 1.22 1.60 2.11 c12 0.30 0.38 0.51 0.23 0.28 0.37 0.37 0.46 0.62 0.16 0.19 0.24 0.47 0.62 0.82 1.00 1.00 1.00 b. consistency rate of the integrated matrix fuzzy numbers of above table were defuzzified by: 4 j = 1 , 2 , . . . , m 6 j j j j a b c s    then, weighted sum vectors (wsv) was calculated by multiplying primary values of group comparisons (table 4) by total prioritization vectors (final weight of criterion) and calculating the sum of each row: table iv. wsv values wsv criterion 1.96 c1 1.8 c2 1.138 c3 1.39 c4 1.196 c5 0.97 c6 0.62 c7 0.92 c8 0.5 c9 1.34 c10 0.371 c11 0.273 c12 consistency vector (c.v) was calculated by dividing elements of above vector by prioritization vector of criteria shows in table v. table v. c.v values c.v criterion 12.02 c1 12.17 c2 12.09 c3 12.2 c4 12.04 c5 12.16 c6 12.18 c7 12.23 c8 12.11 c9 12.14 c10 12.15 c11 12.13 c12 12.135 mean then, consistency index was calculated by: 1 2 .1 3 5 1 2 c i 0 .0 1 2 1 1    where, n denotes the number of alternatives and λmax denotes the mean c.v. finally, consistency rate (c.r) was calculated by: c.i c.r= r.i engineering, technology & applied science research vol. 7, no. 3, 2017, 1699-1707 1703 www.etasr.com rezaei and babaei: designing a model for knowledge socialization using sociability processes of human… as shown in the table, r.i=1.56; thus: c.i 0.012 c.r= 0.008 r.i 1.56   the calculated c.i<0.1 indicates that pairwise comparisons is well consistent and the model is completely significant. c. fuzzy weights of criteria considering fuzzy ahp, data available in the integrated matrix of criteria was analyzed as follows. using geometric mean, value of the j-th criterion was determined relative to other criteria by: 1 12 1 11 12 13 14 15 16 17 18 19 110 111 112( )r a a a a a a a a a a a a                        for example, value of the first criterion was calculated as: 1 1 12 ((1,1,1) (0.9,1.22,1.53) (1.53,1.83, 2.13) (1.15,1.57, 2.02) (1.41,1.89, 2.35)... (1.07,1.49,1.99) (3.76, 4.39, 5.02) (4.89, 5.55, 6.18)) (1.778, 2.24, 2.707) r           where, triangular fuzzy number (0.9, 1.21, 1.53) was the fuzzy value of the first criterion versus the second criterion and the triangular fuzzy number (1.778, 2.24, 2.707) was fuzzy value of the first criterion versus nine other criteria (table vi). table vi. fuzzy value of pairwise comparisons ir ilr imr iur 1r 1.778 2.240 2.707 2r 1.632 2.033 2.465 3r 1.012 1.281 1.604 4r 1.204 1.549 1.961 5r 1.080 1.355 1.672 6r 0.858 1.092 1.382 7r 0.567 0.690 0.853 8r 0.813 1.020 1.301 9r 0.460 0.566 0.705 10r 1.227 1.517 1.852 11r 0.344 0.414 0.517 12r 0.256 0.305 0.380 fuzzy weights of criteria were determined as follows: 1 1 2 3 4 5 6 7 8 9 10 11 12( )i iw r r r r r r r r r r r r r                           value of each criterion was multiplied by the inverse fuzzy sum of values. for example, fuzzy weight of the first criterion was calculated by: 1 1 1 1 2 3 4 5 6 7 8 9 10 11 12( )w r r r r r r r r r r r r r                           1 (1.778, 2.24, 2.707) (1 / (2.707 2.465 1.6 1.96 1.67 1.38 0.85 1.3 0.705 1.85 0.52 0.38), w               1 / (2.24 2.03 1.28 1.55 1.35 1.09 0.69 1.02 0.566 1.52 0.414 0.305),           1/ (1.77 1.63 1.012 1.2 1.08 0.858 0.567 0.813 0.46 1.22 0.344 0.256)            (1 .1 0 2 , 0 .1 5 9 , 0 .2 4 1) fuzzy weight of the first criterion was (0.102, 0.159, 0.241). fuzzy weights are listed in table vii. table vii. fuzzy weights of criteria jw ~ jlw jmw juw defuzzified weight 1w 0.102 0.159 0.241 0.163 1 2w 0.094 0.145 0.220 0.149 2 3w 0.058 0.091 0.143 0.094 6 4w 0.069 0.110 0.175 0.114 3 5w 0.062 0.096 0.149 0.099 5 6w 0.049 0.078 0.123 0.080 7 7w 0.033 0.049 0.076 0.051 9 8w 0.047 0.073 0.116 0.075 8 9w 0.026 0.040 0.063 0.042 10 10w 0.071 0.108 0.165 0.111 4 11w 0.020 0.029 0.046 0.031 11 12w 0.015 0.022 0.034 0.023 12 as shown in table 7 as the last step of fuzzy ahp, desirable workplace (0.163), participatory systems and brainstorming (0.149), transparency in working relations (0.114), and informal techniques (0.111) gained the highest weights; in other words, these criteria are expected to influence socialization of knowledge management in sociability process. vii. model testing structural equation modeling was used for analysis of the conceptual model by smartpls software. structural model is reported below. coefficients of significance (t-value) were used for analyzing significance of the relationships, as shown in the figures 2 and 3. in these figures, blue circles show variables and rectangles show measurement indexes of variables or questions of the questionnaire. these figures show pls model for estimates of significance (t-values) (figure 2) and the standardized estimate (β-value) (figure 3). the hypothesis is confirmed for t-values>|1.96| and t-values<|1.96|; otherwise, the hypothesis is rejected. in this regard, β-value ranges from zero to one; β-values close to one indicate higher effect of independent variable on the dependent variable. viii. measurement model evaluation to measure reliability of the measurement model, convergent validity and discriminant validity were tested by confirmatory factor analysis (cfa) and average variance extracted (ave). as shown in table viii, all factor loadings were at least 0.5. therefore, convergent validity of data is completely confirmed. ix. hypothesis testing hypotheses were tested by using β-values and t-values. for any path, t-values>1.96 indicate significance of the path and the hypothesis is confirmed (α=0.05). table ix shows the results of t-test. a β-value=0.158 indicates direct and positive effect of desirable workplace on knowledge socialization. the results indicate that top management support is effective on engineering, technology & applied science research vol. 7, no. 3, 2017, 1699-1707 1704 www.etasr.com rezaei and babaei: designing a model for knowledge socialization using sociability processes of human… socialization of knowledge management at 99% confidence interval (t-value=3.202); moreover, β-value=0.218 indicates direct and positive effect of top management support on knowledge socialization. the results indicate that transparency of working relations is effective on socialization of knowledge management (t-value=3.905); moreover, β-value=0.454 indicates direct and positive effect of transparency of working relations on knowledge socialization. the results indicate that training course is effective on socialization of knowledge management at 99% confidence interval (t-value=5.197); moreover, β-value=0.311 indicates direct and positive effect of training courses on knowledge socialization. the results indicate that team work is effective on socialization of knowledge management at 99% confidence interval (tvalue=3.761); moreover, β-value=0.349 indicates direct and positive effect of team work on knowledge socialization. the results indicate that trustful climate is effective on socialization of knowledge management (t-value=4.075); moreover, βvalue=0.193 confirms this hypothesis. the results indicate that job description is effective on socialization of knowledge management (t-value=3.045); moreover, β-value=0.178 indicates effectiveness of job description on knowledge socialization. the results indicate that organizational incentive is effective on socialization of knowledge management (tvalue=2.721); moreover, β-value=0.156 indicates direct and positive effect of organizational incentives on knowledge socialization. the results indicate that participatory system is effective on socialization of knowledge management at 95% confidence interval (t-value=1.996); moreover, β-value=0.048 indicates slight, but positive effect of participatory systems on knowledge socialization. the results indicate that career path is effective on socialization of knowledge management (tvalue=3.125); moreover, β-value=0.206 confirms this hypothesis. the results indicate that formal technique is effective on socialization of knowledge management (tvalue=5.011); moreover, β-value=0.210 confirms this hypothesis. the results indicate that alignment of individual values with organizational values is effective on socialization of knowledge management (t-value=4.463); moreover, βvalue=0.188 indicates direct and positive effect of this criterion on knowledge socialization. table viii. factor loadings of the observed variables constructs question factor loading t-value ave cr cronbach’s desirable and joyful workplace 2 0.871 48.972 0.667 0.856 0.747 3 0.839 30.503 1 0.734 15.479 management and leadership support in sociability process 4 0.905 56.300 0.813 0.929 0.885 6 0.905 49.244 5 0.896 58.745 transparency in working relations 7 0.902 48.226 0.776 0.912 0.856 8 0.872 42.100 9 0.869 46.201 training courses 10 0.877 50.171 0.755 0.902 0.838 11 0.873 36.717 12 0.857 33.684 team work 13 0.931 95.993 0.773 0.910 0.851 15 0.887 50.892 14 0.817 24.659 organizational trustful climate 18 0.928 88.707 0.822 0.932 0.892 17 0.907 77.356 16 0.886 46.635 job description and job knowledge 20 0.897 65.738 0.729 0.889 0.813 21 0.859 41.596 19 0.804 17.737 tangible incentives 23 0.947 126.782 0.820 0.932 0.890 24 0.890 47.000 22 0.879 42.789 participatory system 27 0.885 28.224 0.639 0.840 0.714 26 0.812 17.165 25 0.69 18.751 defined career path 28 0.892 42.595 0.741 0.895 0.825 30 0.867 52.105 29 0.822 28.737 informal technique 32 0.900 41.677 0.770 0.909 0.851 31 0.873 51.942 33 0.860 30.460 alignment of individual values with organizational values 34 0.875 35.547 0.738 0.894 0.824 36 0.855 50.204 35 0.848 37.128 39 0.901 52.242 41 0.881 48.142 38 0.846 49.881 42 0.846 47.248 37 0.817 48.111 engineering, technology & applied science research vol. 7, no. 3, 2017, 1699-1707 1705 www.etasr.com rezaei and babaei: designing a model for knowledge socialization using sociability processes of human… table ix. t-test results for hypothesis testing hypothesis variable -value t-value result independent dependent 1 desirable and joyful workplace knowledge socialization 0.158 4.702 confirmed 2 management and leadership support in sociability process knowledge socialization 0.218 3.202 confirmed 3 transparency in working relations knowledge socialization 0.454 3.905 confirmed 4 training courses knowledge socialization 0.311 5.197 confirmed 5 team work knowledge socialization 0.349 3.716 confirmed 6 organizational trustful climate knowledge socialization 0.193 4.075 confirmed 7 job description and job knowledge knowledge socialization 0.178 3.045 confirmed 8 tangible incentives knowledge socialization 0.156 2.721 confirmed 9 participatory system knowledge socialization 0.048 1.996 confirmed 10 defined career path knowledge socialization 0.206 3.125 confirmed 11 informal technique knowledge socialization 0.210 5.011 confirmed 12 alignment of individual values with organizational values knowledge socialization 0.188 4.463 confirmed fig. 2. pls model for estimates of significance fig. 3. pls model for standardized estimates engineering, technology & applied science research vol. 7, no. 3, 2017, 1699-1707 1706 www.etasr.com rezaei and babaei: designing a model for knowledge socialization using sociability processes of human… sociability is a process performed by an organization to introduce values, cultures and organizational goals to newcomers. this process is transformed because it enables the organization to provide an optimal level of learning in the organization. for, it is believed that the main reason for transformation of an organization to a learning organization results from knowledge socialization. many organizations always tend to use dialogue in sociability process to enable learning and consequently learning organization. in this study, the first important factor which was identified in sociability process and considered important in prioritization is desirable and joyful workplace. different studies have been conducted on desirable and joyful workplace; these studies individually emphasized that a desirable and joyful workplace is effective in increasing commitment, work ethics, performance and personal productivity. another important factor of sociability process which can improve socialization and explicit-implicit knowledge exchange is related to top management support. however, managers and leaders of an organization will prevent a culture in relation to socialization of organizational knowledge if they are indifferent to these actions in sociability process and do not provide the opportunity for creating and disseminating explicit and implicit knowledge of people. therefore, managers will be able to provide the opportunity for improving socialization of knowledge management by increasing organizational incentives. transparency in working conditions as well as knowledge flow can establish trust and security in the organization. in other words, employees will trust the organization and share their implicit knowledge socially with other departments by increasing trust in work relations and organizational relations by increasing transparency in relations and meritocracy existing in the organization or increasing observation of knowledge flow required. trust is an old discussion in all the studies conducted. for human resources, the most important factor is job security and trust in work relations. finally, informal tactics can be considered as a major factor in increasing and improving socialization of organizational knowledge. using experiences of experts, managers provide newcomers with the required organizational knowledge correctly. this can provide the opportunity for improving the required organizational knowledge. by increasing socialization of knowledge, managers and organizations tend to provide more innovative services which fit to market demands; otherwise (unrealized knowledge socialization), organizations will not be able to use their intangible capitals for gaining competitive advantage. x. conclusion in this paper, the ahp method was used for prioritization. ten experts were asked to rank the criteria and perform pairwise comparisons. results showed that desirable workplace (0.163), participatory systems and brainstorming (0.149), transparency in working relations (0.114), and informal techniques (0.111) gained the highest weights; in other words, these criteria are expected to influence socialization of knowledge management in sociability process. experts believed that a desirable and joyful environment, participatory systems and brainstorming promote knowledge socialization in the organization. transparency of working relations and knowledge flow as well as informal techniques used for knowledge socialization increase by experienced elites used in sociability process. this study evaluated the effect of the identified criteria on socialization of knowledge management from perspective of ansar bank using pls model. the results indicate that all 12 criteria had a positive and significant effect on socialization of knowledge management. in fact, the results of statistical analysis indicate that desirable workplace is effective on socialization of knowledge management. informal techniques can be considered as the main criterion in increasing and improving socialization of organizational knowledge. using informal techniques, managers use experiences of experts to provide newcomers with the organizational knowledge required. this can provide the opportunity for improving organizational knowledge. by promoting knowledge socialization, managers tend to deliver more innovative services which are fitted to market demand. otherwise, organizations will not be able to use their intangible assets for achieving competitive advantage. references [1] k. choi, “a structural relationship analysis of hotel employees turnover inten-tion”,asia 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administrative science quarterly, vol. 21, no. 3, pp. 433-452, 1976 microsoft word 48-2966_s_etasr_v9_n4_pp4574-4580 engineering, technology & applied science research vol. 9, no. 4, 2019, 4574-4580 4574 www.etasr.com arhin et al.: acceptable wait time models at transit bus stops acceptable wait time models at transit bus stops stephen a. arhin howard university transportation research center, washington dc, usa adam gatiba howard university transportation research center, washington dc, usa melissa anderson howard university transportation research center, washington dc, usa babin manandhar howard university transportation research center, washington dc, usa melkamsew ribbisso howard university transportation research center, washington dc, usa abstract—this study aimed at determining patrons’ acceptable wait times beyond the bus scheduled arrival time at bus stops in washington, dc and to develop accompanying prediction models to provide decision-makers with additional tools to improve patronage. the research primarily relied on a combination of manual and video-based data collection efforts. manual field data collection was used for surveying patrons to obtain their suggested acceptable wait times at bus stops, while video-based data collection was used to obtain bus stop characteristics and operations. in all, 3,388 bus patrons at 71 selected bus stops were surveyed. also, operational data for 2,070 bus arrival events on 226 routes were extracted via video playback. data were collected for am peak, pm peak and mid-day periods of nine-month duration from may 2018 through january 2019. the results of the survey showed that the minimum acceptable wait time beyond the scheduled arrival time was reported to be 1 minute, while the maximum acceptable wait time was reported to be 20 minutes. regression analyses were conducted to develop models to predict the maximum acceptable wait time based on factors including temperature, presence of shelter at the bus stops, average headway of buses, and patrons’ knowledge of bus arrival times. the models were developed for a.m., p.m. and mid-day periods. the f-statistics for the models were determined to be statistically significant with p values<0.001 at 5% level of significance. also, the variance explained by the models (r 2 ) ranged from 64% to 82%. further, a test of hypothesis revealed that though female patrons generally had lesser maximum acceptable wait times than male patrons, the mean difference was determined not to be statistically significant. however, the mean differences in the maximum acceptable wait time of patrons based on ethnicity were determined to be statistically significant at 5% percent level of significance. the study revealed that caucasian patrons have significantly lower maximum acceptable wait times compared to patrons of other ethnic groups. keywords-crashes; unsignalized intersection; artificial neural network; injury severity i. introduction the wait time at bus stops is one of the primary measures for assessing reliability of transit services, especially in urban areas. the uncertainty associated with waiting affects bus patrons’ perception of quality of the service provided. if transit buses arrive at scheduled times, passengers are less likely to have the need to find alternative mode(s) of transportation. however, if buses are chronically late at bus stops, patrons may feel that the bus system is unreliable and may most likely seek alternative modes of transportation. studies in this subject area have therefore been of interest to transit service agencies and officials in a bid to gain more insight into improving quality of service. ii. literature review a. wait time as a measure of transit service reliability in assessing the reliability of transit services, transit agencies and officials have, among other indicators, used passenger wait times as a performance measure. passengers’ perception of transit service quality is affected by wait times. wait time is considered an appropriate measure of service reliability for high frequency routes where the arrival of passengers is random and the average wait time approximates half the headway [1]. for low frequency services, passengers usually synchronize their arrival time at bus stops with the arrival of buses, thus minimizing wait times [2]. authors in [3] considered waiting cost functions to account for headway and service reliability. the study contends that by analyzing the behavior of passengers, the cost of waiting can be broken down into two components: the actual mean time spent waiting and the potential waiting time. the potential waiting time is the additional time passengers have to budget for waiting and is determined as the 95% of the waiting time. this has been found to be very sensitive to service reliability. hence, by minimizing the waiting cost function, service reliability can be improved. a similar conclusion was made in [4] which analyzed the service reliability of a high frequency bus line in helsinki using avl and apc data. the study found that passengers accessed the reliability of bus services mainly in terms of additional waiting and travel time. it was recommended that reduction in wait and travel time increases passenger satisfaction which leads to increase in patronage. b. relationship between waiting time and headway headway is the time between two vehicles passing the same point traveling in the same direction on a given route. several studies have sought to establish the relationship between headway and waiting times of passengers. one of the corresponding author: stephen a. arhin (saarhin@howard.edu) engineering, technology & applied science research vol. 9, no. 4, 2019, 4574-4580 4575 www.etasr.com arhin et al.: acceptable wait time models at transit bus stops earliest studies focused (among other issues) on passengers wait time for bus services with short headways was conducted in 1957 [2]. it concluded that the average waiting time of passengers who randomly arrive at a boarding point is minimum when the service is perfectly regular. the following model to estimate average wait time was suggested: ���� ���� = ∑ ��∑ (1) where h is the headway (in seconds). it was showed that the behavior of passengers of a bus network in stuttgart (germany) showed that passengers’ arrival at a bus stop is schedule-dependent when headways exceed 8 minutes. thus, most passengers synchronize their arrivals with those of the buses, reducing the time spent waiting [5]. another model was developed in [6] which took into consideration the random arrival of passengers during peak periods. the random waiting time, wr, was related to the headway h by (2): � = ℎ/2[1 + (�/ℎ)�] (2) where σ is the standard deviation of bus headway h. an analysis of passenger wait times and headways of buses data in manchester (england) showed a linear relationship between wait time and headway [7]. the findings of the study corroborated previous study and concluded that the arrival behavior of passengers is schedule-dependent when headways exceed 8 minutes. a higher headway threshold of 12 minutes was however established in a study that utilized passenger arrival data in london [8]. further, a comprehensive review of key elements of service reliability in boston, massachusetts revealed that irregular headways lead to variability in expected waiting times [9]. the average wait times of passengers has been estimated to be one-half of the headway. this simple model is valid when the arrival of passengers at the bus stop is random and the headways are regular. however, realistically, these conditions are never satisfied, leading to model inadequacy. c. passenger wait time distribution and modeling a number of studies have examined the distribution of passenger wait times and developed models to estimate wait time. authors in [10] developed arrival distribution curves based on data collected at 28 bus, tram and commuter rail stations in zurich (switzerland). the stations were served by scheduled public transits with headways ranging from 2.33 to 30 minutes. the observations were made on weekdays during the morning, evening and mid-day periods. the analysis of the results showed both passenger arrivals and wait times have a logarithmic relationship with headway. it further concluded that passengers begin to arrive at stations near the scheduled departure times, even for very short headways. the arrival rate of passengers transferring from rail to buses was fitted to normal, exponential, lognormal and gamma distributions [11]. it was concluded that the lognormal and gamma distributions had the most appropriate fit for passengers transferring directly and non-directly. similar conclusions were made in a study conducted in beijing (china) [12]. in that study, passenger arrival times were fitted to extreme value, exponential, lognormal, gamma and normal distributions. the results showed that the arrival time of passengers at bus stops connected to rail stations were best fitted with the lognormal distribution, while arrival time of passengers at bus stops not connected to rail stations were best fitted with the gamma distribution. the distribution of actual passenger wait times and perceived wait times based on data collected from bus stops in london (uk) was investigated in [13]. the results showed that the actual wait time of passengers followed the gamma distribution while the perceived wait time of passengers followed the lognormal distribution. also, a study was conducted to develop a multiple linear regression model to predict perceived wait time of passengers based on data collected at three bus stops in harbin (china). in all, 234 passengers were surveyed. factors considered in the development of the model included gender, level of education, having a time device, presence of a companion, travel purpose, riding frequency, walking time, reserved waiting, waiting mood, waiting behavior, waiting time interval (morning or evening peak). the significance of the factors in the model was tested at 5% significant level. anova results showed that gender, level of education, and walking time were not statistically significant predictors of perceived waiting time. beyond the generalized linear models, other studies have used machine learning techniques to develop passenger wait time models. artificial neural networks (anns) were used to develop passenger wait time models based on data collected on passengers using a high-speed train service in beijing in [14]. the predictors used in the model were trip distance, transport mode, travel time, familiarity of the service facility, and level of education. the architecture of the developed ann model consists of one input layer with 5 neurons, two hidden layers with 8 and 3 neurons respectively, and an output layer with a single neuron. sigmoid and purelin transfer functions were used as activation functions in the hidden and output layers respectively. also, the conjugate gradient method was used as learning algorithm. the model was trained with a data set of 720 samples, and validated with a data set of 336 samples. the model developed predicted passenger wait time with an average error of 9.2%. iii. methodology a. study area description this research is based on data obtained in the district of columbia (dc). dc is divided into four (unequal) quadrants: northwest (nw), northeast (ne), southeast (se), and southwest (sw) which are further divided into eight (8) wards. as of 2017, the population of dc was approximately 694,000 with an annual growth rate of approximately 1.41%. the city is highly urbanized and it is ranked as the sixth most congested city in the united states with each driver spending an average of 63 hours per year in traffic. washington metropolitan area transit authority (wmata) is the agency that oversees the operations of metrobus service in the area. wmata has a bus fleet of 1,595 buses that make more than 400,000 trips each day. these buses serve about 11,500 bus stops and operate on 325 routes in dc, portions of maryland, and virginia, covering a total land area of about 1,500 square engineering, technology & applied science research vol. 9, no. 4, 2019, 4574-4580 4576 www.etasr.com arhin et al.: acceptable wait time models at transit bus stops miles. of the total number of bus stops, 2,556 (22.2%) have shelters, while the remaining do not. b. data collection 1) selection of bus stops the study considered 71 bus stops in the dc at which bus operational and survey data were collected. two main types of bus stops were considered: bus stops with and without shelter. the bus stops were selected based on criteria of being on routes with longer headways, having high patronage, and proximity to metro rail station. data collection at the selected bus stops was conducted over a nine-month duration from may 2018 through january 2019. data were collected during the am peak (7:00 am -9:30 am), pm peak (4:00 pm6:30 pm) and mid-day periods (10:00 am – 2:30 pm). two forms of data collection were performed: bus passengers’ survey and bus operational data collection. the data collection schedule was organized to achieve a robust sample size. 2) survey data collection passengers waiting for the arrival of the next bus at the selected bus stops were randomly selected and interviewed during morning, evening and mid-day periods from monday to friday. the field researchers conducted the survey by the use of electronic forms on computer tablets and paper questionnaires. the following information were obtained during the survey: temperature at the bus stop, presence of shelter at bus stop, arrival time and gender of passengers, knowledge of bus arrival time, and the maximum and minimum acceptable wait time beyond the bus scheduled arrival time for which the passenger is willing to wait. a total of 3,388 passengers were surveyed over the period of the study. when the minimum number of responses was not obtained during a particular peak period due to weather or low passenger turnout, additional passenger were surveyed on the same day and peak period the following week. 3) bus operational data bus operational data were collected at each of the 78 selected bus stops. the data were collected by installing video recording cameras at the bus stops. the video recordings took place on weekdays (monday to friday) over a 12-hour duration (6:30 am to 6:30 pm). the following data were obtained of each bus arrival event during the morning, evening and midday periods via video playback: • bus arrival time: a bus was determined to have arrived at a bus stop when it came to a complete stop allowing onboarding and alighting. • bus departure time: a bus had departed the bus stop when the last passenger had either boarded or alighted and the doors were shut. from the collected data, bus arrival and departure times were used to compute headway by finding the difference between the arrival time of a bus and that of the preceding bus on the same route. therefore, the headway was computed as: a b ah at at= − (3) where ha is the actual bus headway, ata is the arrival time of bus a, and atb is the arrival time of bus b. in all, a total of 2,070 bus arrival events on 226 routes were extracted, computed and compiled in an excel spreadsheet for further analysis. c. data analysis 1) descriptive statistics descriptive statistics such as frequencies, mean, median, and standard deviation were computed for the bus stop, passenger and bus operational characteristics data. 2) model development to investigate the relationship between the maximum acceptable waiting time and variables such as average headway, knowledge of bus arrival time, presence of shelter, and temperature at the bus stops, linear regression analyses were conducted. regression models were developed for a.m., p.m. and mid-day period. the general regression model for maximum acceptable wait time took the following form: ����� = ��� + �(�)� � + �(�!)��� +�("#��)�$� + �(%&)�'� + ( (4) where, ���� is the maximum acceptable wait time, ahthe average headway, t the temperature, kbat the knowledge of bus arrival time, and ps the presence of shelter. mawt is the dependent variable while t, ah, kbat, and ps are independent variables. the constants, βki are the regression coefficients with an associated error of ε~n (0, σ 2 ) with k=0,1…4 for the first, second, third, fourth and fifth regression coefficients respectively. also, i=1, 2 and 3 for the a.m., mid, and p.m. peak periods, respectively. in order to develop a robust model, the variables were tested to ensure they satisfied the assumptions of normality of errors, multicollinearity, and homoscedasticity. 3) hypothesis testing the test statistic primarily used in this study for the comparison is that of the mean. the hypothesis that there is a significant difference in the average mawt of passengers based on their gender and ethnicity was tested at 5% level of significance. 4) difference in mawt based on gender it is hypothesized that there is a statistically significant difference in the average mawt based on the passenger’s gender. this is mathematically expressed as: !): + = +� (5) !,:+ ≠ +� (6) where, x1 is the mean mawt of female passengers and x2 the mean mawt of male passengers. 5) difference in mawt based on ethnicity it is hypothesized that the there is significant difference in the average mawt based on ethnicity. this mathematically is expressed as: !): . = .� = .$ = .' = ./ (7) engineering, technology & applied science research vol. 9, no. 4, 2019, 4574-4580 4577 www.etasr.com arhin et al.: acceptable wait time models at transit bus stops !,:. ≠ .� ≠ .$ ≠ .' ≠ ./ (8) where, y1-y5 are the mean mawts of african american, caucasian, hispanic, asian and other passengers respectively. a preliminary analysis of the data to test for the parametric assumptions of normality and equality of variance indicated a statistically significant violation of these assumptions. the preliminary analysis showed a log-normal distribution of mawt across gender and ethnicity confirming the findings of previous studies. in order to test for statistically significant differences in mawt of passengers based on gender and ethnicity, the non-parametric wilcoxon rank-sum test and kruskal-wallis test were used respectively. wilcoxon ranksum test is a statistical analysis used to determine if there is any significant difference between the means of two groups of independent variables. this method tests the null hypothesis by comparing the ranks of the observations of the two groups of variables to decide whether or not the mean ranks are statistically significant. the statistical significance of the wilcoxon rank-sum test statistic ws is determined as follows: �01 = 23 (234 2�4 )� (9) &56788888 = 9232� (234 2�4 ) � (10) : = 6;< 6788888=>?788888 (11) where �1 is the wilcoxon rank-sum test statistic, �01 the mean of the test statistics, &56788888 the standard error of the test statistic, @ the sample size of the male passengers, @� the sample size of female passengers, and z the z score of the test statistic. for a significance level set at 5%, z-score values greater than 1.96 are deemed as statistically significant kruskal-wallis test is used to determine if there is any significant difference between the means of the groups of independent variables. this method tests the null hypothesis by comparing the ranks of the observations of three or more groups of a variable to decide whether or not the mean ranks are statistically significant. the statistical significance of the kruskal-wallis test statistic h, is determined as: ! = �a(a4 ) ∑ bc� 2c d�e − 3(h + 1) (12) where n is the total sample size, i� is the sum of ranks for each group, and @j is the sample size of each group. the h is then compared to a critical value hc, which approximates to the chisquare distribution. if h is higher than hc, then we do not accept the null hypothesis. iv. results a. descriptive statistics the mean acceptable passenger wait time is presented in table i. the descriptive statistics of the headways of buses are presented in table ii. the mean headway was measured to be 1,119.5s (18.65 minutes). the minimum headway was measured to be 290.75s (4.83 minutes), while the minimum headway was measured to be 3,500s (58.33 minutes). table i. mean acceptable wait times category avg. max. acceptable wait time (minutes) avg. min. acceptable wait time (minutes) time of day am 7.0 2.5 mid 10.5 4.0 pm 7.5 3.0 shelter without shelter 7.5 3.0 with shelter 9.0 3.0 gender male 8.5 3.0 female 8.0 3.0 ethnicity white 7.0 2.0 black 8.5 3.0 hispanic 8.3 3.0 asian 8.4 3.5 other 8.5 3.0 kbat no 10.5 4.0 yes 7.0 2.5 quadrant ne 8.0 3.0 nw 7.0 3.0 se 10.0 3.0 sw 9.0 3.5 table ii. descriptive statistics for bus head way statistic value (s) mean 1,195.23 median 1,097.28 minimum 290.75 maximum 3,500.00 b. regression analysis this section presents the results of the regression analyses to develop to predict the mawts of bus passengers. models were developed for a.m., p.m., and mid-day periods. thus, three models were developed. the adequacy and significance of the regression models were tested at 5% level of significance. the overall performance of the models was evaluated using the p-values of the models’ f-statistics, the r 2 , and adjusted r 2 values. also, the statistical significance of the models’ predictors was evaluated using the p-values of the predictors’ f-statistics. in order to achieve the optimal relationship between the dependent variable, mawt, and the independent variables temperature t, average headway, ah, time of day, ps and knowledge of bus arrival time, kbat, several curve estimations between the dependent variable and each independent variable were performed. the transformations were necessary to obtain the best relationship between the dependent and independent variables. the expressions used to transform each independent variable are shown in table iii. logistic and cubic transformations of ah and t respectively, resulted in the most favorable relationships with the mawt while ps and kbat remained untransformed. the summaries of the results of the regression analyses are presented in table iv. c. model testing 1) kolmogorov-smirnov (k-s) test the results of the k-s tests for mawt show that the maximum difference d between the cumulative distribution of the predicted and observed mawts for all the models were less engineering, technology & applied science research vol. 9, no. 4, 2019, 4574-4580 4578 www.etasr.com arhin et al.: acceptable wait time models at transit bus stops than the critical value of 1.36 at 5% level of significance. this implies that the models sufficiently predict the observed values. table iii. data transformation variable transformed variable selected relationship with dependent variable transformation formula ah ahtr logistic 1 ( ) ln(1 / )f x x= t ttr cubic 3 2 ( )f x x= kbat kbat linear 3 ( )f x x= ps ps linear 4 ( )f x x= 2) normality of errors normality of errors assumption was tested for using the normal probability plot. the observed cumulative probabilities of the standardized residuals are plotted against the expected cumulative probabilities of the standardized residuals. the plots showed that the data follow the diagonal lines for all the models, indicating that the errors are normally distributed. 3) multicollinearity the test for multicollinearity showed that the vif of all the variables in the models were less than the maximum value of 10. thus, multicollinearity between the independent variables is absent. table iv. summary of results # peak period model r 2 adj. r 2 f-statistic sig. 1 am ����,k = −0.40 + (1.07p10</)�$ − 0.642r@ s 1�!t− 2.22"#�� + 3.265%& 0.645 0.640 489.652 0.000 2 mid ����kvw = −2.678 + (1.37p10</)�$ − 0.904r@ s 1�!t − 1.048"#�� + 2.705%& 0.822 0.821 1,258.751 0.000 3 pm ����zk = 1.372 + (1.37p10</)�$ − 0.326r@ s 1�!t− 1.171"#�� + 2.074%& 0.798 0.793 1,117.277 0.000 4) homoscedacity the residual plots of the three models showed an even distribution about the zero line which confirms that the models fit the dataset well. d. hypotheses test 1) test results for significance difference in mean mawt based on gender tables v and vi present the results of the test of hypothesis for significance difference in mawt based on gender. the mean rank of female passengers was estimated to be 1,683.63 while the mean rank of male passengers was 1,705.11, as shown in table v. the wilcoxon w statistic was computed to be 2,949,722.00 as shown in table vi. this statistic had a zscore of -0.660, which is statistically non-significant at 5% level of significance (p=0.509). thus, the analysis showed that there is no significant difference in the mawt of passengers based on gender. table v. rank s-gender gender n mean rank sum of ranks female 1752 1,683.63 2,949,722.00 male 1635 1,705.11 2,787,856.00 total 3387 table vi. test of hypothesis statistics gender test statistic value wilcoxon w 2,949,722.00 z -0.660 asymp. sig. (2-tailed) 0.509 2) test results for significance difference in mean mawt based on ethnicity the results of the test of hypothesis for significance difference in mawt based on ethnicity are presented in tables vii and viii. white passengers had the least mean rank of 1,365.61, while passengers of other ethnicity than the specified ones had the highest mean rank of 1,895.57 as exhibited in table vii. the kruskal-wallis h-statistic was estimated to be 131.91 as shown in table viii. this statistic was determined to be statistically significant at 5% level of significance (p<0.001). thus, the analysis showed there are significant differences in the mawt based on ethnicity. table vii. ranks-ethnicity ethnicity n mean rank white 778 1,365.61 black 771 1,729.34 hispanic 747 1,801.01 asian 545 1,764.19 other 546 1,895.57 total 3,387 table viii. test of hypothesis statistics – ethnicity test statistic value kruskal-wallis h 131.91 df 4 asymp. sig. 0.000 a post-hoc analysis was used to investigate the between ethnicity differences in passengers’ mawt. since the data did not meet the parametric assumptions of normality and homogeneity of variance, the games howell post hoc test was used for the analysis. the results of the analysis are shown in engineering, technology & applied science research vol. 9, no. 4, 2019, 4574-4580 4579 www.etasr.com arhin et al.: acceptable wait time models at transit bus stops table ix. the table compares the mean difference in mawt of passengers of each ethnicity group to all the others. the statistical significances of these differences are also presented. the results show that, the statistically significant differences in mawt were between caucasian (white) and african, hispanic, asian as well as passengers specified as belonging to “other” ethnic groups. white patrons’ mawt statistical significantly was lower than all other ethnic groups (p-value<0.001). table ix. results of post hoc test (i) ethnicity (j) ethnicity mean difference (i-j) sig. white black -0.950* 0.000 hispanic -1.190* 0.000 asian -1.044* 0.000 other -1.430* 0.000 black white 0.950* 0.000 hispanic -0.240 0.535 asian -0.094 0.980 other -0.480* 0.030 hispanic white 1.190* 0.000 black 0.240 0.535 asian 0.145 0.911 other -0.240 0.602 asian white 1.044* 0.000 black 0.094 0.980 hispanic -0.145 0.911 other -0.386 0.193 other white 1.430* 0.000 black 0.480* 0.030 hispanic 0.240 0.602 other 0.386 0.193 *the mean difference is significant at the 0.05 level. v. discussion the current research aimed at developing regression models to predict the maximum acceptable wait time of bus passengers based on weather conditions, average headway of buses, patrons knowledge of bus arrival time and the presence of shelter at the bus stops. the results of the analysis of the obtained survey data confirmed some of the findings in previous studies and also provided new insight about the acceptable wait time of bus passengers. most patrons’ acceptable wait times ranged from 5 to 15 minutes. the mean maximum acceptable wait time of patrons during the mid-day period was found to be higher than during the a.m. and p.m. peak periods which corroborates the findings in [13]. the least mean wait time recorded occurred during the a.m. peak period. this can be explained by the fact that most patrons during the a.m. commute to work and need to arrive on time. the mean acceptable wait times of patrons waiting at bus stops with shelter was approximately 20% higher than mean acceptable wait times of patrons at bus stops without shelter (authors in [14] reported a 30% difference). regarding gender, the mean maximum acceptable wait times of male and female passengers was approximately equal. this gives an indication that the gender of a passenger does not determine his/her waiting tolerance level. in terms of race, white patrons reported the lowest mean maximum acceptable wait time, while black and “other” passengers recorded the highest of that variable. hispanic and asian passengers had approximately the same average maximum acceptable wait times. also, bus passengers who had knowledge of the arrival time of the bus were observed to have lower acceptable wait times compared to those who had no knowledge of the arrival time. patrons with knowledge of the arrival time of buses, tend to be less tolerant when buses do not arrival as scheduled. statistical analysis of the data was conducted to develop predictive models for acceptable wait times based on weather condition (temperature), average headway of buses, and passengers’ knowledge of bus arrival time and presence of shelter. statistical significant differences in the average maximum acceptable wait times of patrons based on gender and ethnicity were investigated. the analysis was conducted at a 5% level of significance. regression models were developed for the a.m., p.m., and mid-day peak periods. all the models were found to fit the data with statistically significant fstatistics (p<0.001). in addition, temperature, average headways, presence of shelter, and knowledge of bus arrival time of all the models were determined to be statistically significant predictors (p<0.001). in general, the maximum acceptable wait time of passengers tends to increase as temperature increased. thus, lesser acceptable wait times are expected when temperatures are comparatively lower. also, the acceptable wait times increase with increasing bus headway. moreover, patrons who are aware of the arrival times of buses had shorter maximum acceptable wait times. in addition, at bus stops with shelter, patrons are more likely to wait longer. the kolmogorov-smirnov tests showed that all the models significantly predict acceptable wait time at 95% confidence interval. the variances explained by the models range from 64% to 82%. the results of the wilcoxon sign-ranked tests showed that the difference in the acceptable wait times of patrons based on the gender was not statistically significant (p=0.509). however, the kruskal-wallis test showed a statistically significant difference in the mean acceptable wait times based on ethnicity. the test reported a statistically significant h-statistic of 15.544 (p=0.001). a post-hoc analysis revealed that there is a statistically significant difference of the acceptable wait times between white patrons and the other ethnicities. vi. conclusion and recommendations the models developed in this research are potentially useful tools that transit agencies could use to improve bus scheduling and operations to ultimately retain and improve ridership. it is recommended that research in the future should explore the use of machine learning and artificial intelligence techniques to predict the wait time of patrons and also incorporate other factors such as average dwell time of buses. acknowledgment the authors extend their appreciation to the u.s. department of transportation’s university transportation centers program and the mineta transportation institute for the funding of this study. references [1] t. reed, “reduction in the burden of waiting for public transit due to real time schedule information: a conjoint analysis study”, pacific rim transtech conference. 1995 vehicle navigation and information engineering, technology & applied science research vol. 9, no. 4, 2019, 4574-4580 4580 www.etasr.com arhin et al.: acceptable wait time models at transit bus stops systems conference proceedings. 6th international vnis. a ride into the future, seattle, usa, july30-august 2, 1995 [2] p. i. welding, “the instability of a close-interval service”, journal of the operational research society, vol. 8, pp. 133–142, 1957 [3] p. g. furth, t. h. j. muller, “service reliability and optimal running time schedules”, transportation research record, vol. 2034, no. 1, pp. 55-61, 2007 [4] t. firew, analysis of service reliability of public transportation in the helsinki capital region: the case of bus line 550, msc thesis, aalto university, 2016 [5] w. weber, the travel time of the passengers of public transport depending on railway type and location, traffic science institute at the technical university stuttgart, 1966 [6] e. osuna, f. newell, “control strategies for an idealized bus system”, transportation science, vol. 6, no. 1, pp. 52-71, 1972 [7] p. seddon, m. day, “bus passenger waiting times in greater manchester”, traffic engineering and control, vol. 15, no. 9, pp. 442445, 1974 [8] k. joliffe, t. hutchinson, “a behavioral explanation of the association between bus and passenger arrivals at a bus stop”, transportation science, vol. 9, pp. 248-282, 1975 [9] l. c. cham, understanding bus service reliability: a practical framework using avl/apc data, msc thesis, massachusetts institute of technology, 2006 [10] m. luethi, a. weidmann, a. nash, “passenger arrival rates at public transport stations”, trb 86th annual meeting compendium of papers. transportation research board, washington, usa, january 21-25, 2007 [11] s. guo, l. yu, x. chen, y. zhang, “modeling waiting time for passengers transferring from rail to buses”, transportation planning and technology, vol. 34, no. 8, 29, pp. 795-809, 2007 [12] h. gong, x. chen, “an application-oriented model of passenger waiting time based on bus departure time intervals”, transportation planning and technology, vol. 39, no. 4, pp. 424-437, 2016 [13] i. kaparias, c. l. rossetti, v. trozzi, “analyzing passenger arrivals rates and waiting time at bus stops”, 94th annual meeting of the transportation research board, washington, dc, usa, january 11-15, 2015 [14] z. k. gurmu, w. fan, “artificial neural network travel time prediction model for buses using only gps data”, journal of public transportation, vol. 17, no. 2, pp. 45-65. 2014 microsoft word 31-2787_s_etasr_v9_n3_pp4235-4242 engineering, technology & applied science research vol. 9, no. 3, 2019, 4235-4242 4235 www.etasr.com belkadi et al.: energy design and optimization of a greenhouse: a heating, cooling and lighting study energy design and optimization of a greenhouse a heating, cooling and lighting study anouar belkadi ur-laper, faculty of sciences of tunis, university of tunis el manar tunis, tunisia dhafer mezghani ur-laper, faculty of sciences of tunis, university of tunis el manar tunis, tunisia abdelkader mami ur-laper, faculty of sciences of tunis, university of tunis el manar tunis, tunisia abstract—this paper presents a new approach to properly optimize the energy consumption in a greenhouse. an improved intermediate modeling to establish the energy balance in a greenhouse within a higher precision was adopted. while the classical model focuses on the efficient cooling and heating demands and neglects the profound impact of lighting parameters, it was shown that these three necessary components are interdependent, and they should be taken into account all together to comfortably reach optimal crop production and energy consumption. this study’s contribution is the classical model’s improvement and the demonstration of the fact that the heat released by the luminaries and the energy used by this equipment has fundamental consequences on the energy balance as well as the preferred choice of the possible shape of the greenhouse and its adequate cover. keywords-cooling; energy; greenhouse design; heating; lighting i. introduction facing a constant increase of world population, an efficient food production system is ought to aim accurately for cost minimization, to allow a sufficient supply and adequately meet the consumers’ demand. being one of the most energy demanding sectors in modern agriculture, the greenhouse industry is in definite need of energy consumption reduction, while maintaining an adequate microclimate for cultivating crops, thus guaranteeing minimal production expenses and an optimal crop quality. because of the considerable importance of thermal modeling of a greenhouse typically used for energy simulation, to optimize energy-efficient designs and to verify the economic feasibility of greenhouse production, studies have been conducted to develop the greenhouse thermal models and try to correctly describe the specific process of heat and mass transfer in greenhouses [1-3]. greenhouse thermal models are generally classified into three specific groups: static, dynamic and intermediate. static models [4-6] determine the productive capacities of heating and cooling equipment and are based on approximate heat gains and losses, depending on periodic collected meteorological data. on the other hand, intermediate models [7-14] consider the factor of sunlight, while complex dynamic models [9, 15-18] are principally based on the integration of numerous greenhouse components. despite the relative accuracy of these models, the estimation of heating energy requirements over long periods or for a greenhouse with different configurations requires very complex modifications and does not mention the effect of evapotranspiration of plants and control systems of the environment on the greenhouse’s energy balance. in order to obtain higher yield and better production quality in the greenhouse, this study will start from the equations used in the energy balance of previous models as references. our contribution is to develop an updated version of these models. ii. methodology a. greenhouses studied shapes four forms of greenhouses studied (elliptic, even span, uneven span and rectangular), as shown in figure 1. fig. 1. analyzed greenhouse forms. the analysis of these greenhouses is carried out for the same greenhouse volume of 4420m 3 and the same dimension of the base surface (w=34m, l=40 m). b. covering materials of studied greenhouses five different covering materials of greenhouses were studied. the characteristics of these materials are shown in table i [9, 16, 20, 21]. c. heat balance inside the greenhouse to fix the climatic problem inside the greenhouse, several factors must be inevitably retained during the establishment of corresponding author: anouar belkadi (belkadi.anouar@gmail.com) engineering, technology & applied science research vol. 9, no. 3, 2019, 4235-4242 4236 www.etasr.com belkadi et al.: energy design and optimization of a greenhouse: a heating, cooling and lighting study the energy balance. the energy balance of the greenhouse is precisely the heat transfer and the mass exchange between the greenhouse and the external environment. this multidimensional quantity can be expressed according to (1): = l gs q q q (1) in this energy equation, positive qs means that the heat loss is greater than the heat gain, which would imply a need for warming up the greenhouse, whereas in case this value is negative, it would indicate the heat gain is greater than the heat loss so there is necessarily a need, to cool it. we could classify the various parameters intervening in the development of the energy balance equation in two categories: • first category defines the structure of the greenhouse by its geometric shape, the diverse materials which constitute its shell, mainly in terms of materials selected for its cover, and the temperature, light and moisture to retain inside the greenhouse. • second category: it is, essentially, related to the external environmental conditions of the greenhouse like solar radiation level, wind speed, external temperature, humidity degree, altitude, latitude and the orientation of the greenhouse. table i. covering materials characteristics pf gl leg pc acr index m1 m2 m3 m4 m5 lc 0.000152 0,003 0,0032 0,01 0,006 solar transmission 0,87 0,905 0,78 0,9 0,9 long-wave transmission 50 3 <3 <3 <5 kc 0,33 0,76 0,76 0,17 0,2 ach 0,85 1,1 1,1 1,1 1,1 d. traditional model design our approach is essentially based on the results of previous intermediate models that took into account the different components that act on the energy balance. these theoretical models have paved the way for our contribution. in the traditional model the heat gain qg calculation depends only on the solar radiation as shown in (2): τ= sg r f iq a (2) while the precise determination of the heat loss was generally based on the calculation of two fundamental parameters, the heat transfer caused by the phenomenon of conduction and convection qcd-cv and the heat transfer due to the infiltration qinf. the convection and conduction heat transfer is calculated by (3): ( ) g in outcd cv q u a t t− = − (3) where u is the overall heat transfer coefficient and which was taken as general constant [1]. the heat transfer due to the infiltration qinf is estimated by (4): ( ) ch a a g in outinf a c vq t tρ= − (4) figure 2 represents the energy demand of heating and cooling for the elliptic form equipped by polyethylene covering material applied in the climatic and geographical conditions of the tunisian latitude, and by keeping the desired indoor temperature of the cultivated invariably to 20°c, according to the previous equations. fig. 2. energy demand of the heating and cooling using traditional approaches note that despite the same temperature of some months (april and november, 17°c), (may and october, 21°c), we do not have the same behavior in terms of heating-cooling and this is expected since a sunny day with a low temperature does not mean we will have a need for heating and vice versa (a hot day with low sun does not mean that we will need ventilation). in order to represent the energy demand of all shapes and all covering materials studied in this paper, we replicated the same process for all the chosen shapes and covering materials, the results are presented in table ii. table ii. traditional model avg daily heating and cooling applied to tunisia [kwhm -2 ] even span uneven span elliptic rectangular m1 4,472 4,483 4,799 4,549 m2 3,334 3,339 3,513 3,369 m3 4,940 4,956 5,387 5,055 m4 3,666 3,673 3,658 3,711 m5 4,102 4,112 4,396 4,179 we can deduct through table ii that if using the traditional model without any changes in the energy balance, the most appropriate shape is the even span equipped with m2, while the worst is the elliptic form equipped with m3. according to our analysis of the different computation models of the energy balance, the traditional model remains an ineffective one, despite it took into consideration the majority of the parameters intervening in the equation of the energy balance, since it ignored the impact of other parameters that must be included such as: • the global heat transfer coefficient u has been defined as a constant whereas it should be dynamic since it depends on the internal and external engineering, technology & applied science research vol. 9, no. 3, 2019, 4235-4242 4237 www.etasr.com belkadi et al.: energy design and optimization of a greenhouse: a heating, cooling and lighting study conditions of the greenhouse such as the properties of the covering material, the air velocity outside and inside the greenhouse, and the ambient and desired temperature. therefore, the variable u cannot be considered as a constant when establishing the energy equilibrium equation of a greenhouse. • heat loss due to long-wave radiation qlw in general, thermal radiation emitted from inside the greenhouse can be partly absorbed by the cover, reflected in the greenhouse or transmitted to the outside of the greenhouse. depending on the degree of transparency of the greenhouse cover, the exchange of long-wave radiation by the transparent surface will cause a significant effect on the heat loss so a considerable amount of heat will be transmitted to the outside. • soil heat loss qf and the heat due to the perimeter qp the heat loss engendered from the greenhouse's floor is principally due to the conduction of the soil and the heat transfer of the perimeter. this quantity exerts an effect on the estimate of the equation of the energy balance that we should not neglect in order to increase the accuracy of the results of the energy balance equation. • heat loss due to evaporation qevap the evapotranspiration remains a crucially essential component that we should not neglect while establishing the equation of the energy balance because it represents a significant amount of heat loss. this quantity is produced from the plant leaves and the ground surface. • the absence of the lighting effect qli qli is the sufficient amount of specific heat typically emitted by the lighting system. previous studies and researches have overlooked the energy weight of lighting in the choice of the shape and cover of the greenhouse and its impact on the energy balance equation, while our model in its analysis considers the predicted effects of lighting on the model. e. presentation of bghm model our developed model, named bghm, is typically based on the cultivation of tomatoes inside greenhouses in the climatic and geographical conditions of the tunisian latitude band. we took into account the neglected parameters of the traditional model: qlw, qf, qp, qevap, and the heat gains from lighting qli. we have also recalculated the overall heat loss coefficient u which was taken static during the study of the traditional model [1], and which is in fact dynamic. we claim by our approach to highlight the direct impact of the specific shape of the greenhouse and its adequate coverage of the energy needed by acting on various components that have been severely neglected in the successful establishment of the energy balance equation: mainly cooling, heating and lighting. to perform this, we will update the traditional model by injecting the neglected parameters qlw, qf, qp, qevap with and without the heat gain from lighting qli, as this factor has been neglected in the majority of studies who worked on the energy balance equation, in order to emphasize on the importance of the effect of the lighting component to retain an efficient system in terms of energy. 1) bghm program design in order to develop our model, we have created the program presented in figure 3. fig. 3. flowchart of the program 2) study of bghm model without lighting impact we will therefore resume the traditional model and remodel it while injecting in the energy balance equation the neglected parameters qlw, qf, qp, qevap and the improvement of the qcd-cv by adopting a dynamic heat transfer ud. the equation qcd-cv then becomes as follows: ( ) d g in ov tc ud c u a t tq − = − (5) where: 1 1 1 1 0 [ ]idu h lc kc h − − − −= + + (6) and h0 and hi can be estimated as shown in (7)-(8): 0 2.8 1.2 v h w= + (7) 1/3 1/2 1.52[ ] 5.2 ( ) i in out ch g h t t a s l= − + (8) the heat transfer through the greenhouse floor qf is: 1 ( ) s f if n s k d a tq t −= − (9) the heat transfer through the greenhouse perimeter qp, is estimated by (10): ( ) p g n oup i t f p t tq = − (10) the long wave radiation heat loss qlw is calculated as: 0 (1 ) ( ) l g in s yw k q h a t tτ= − − (11) engineering, technology & applied science research vol. 9, no. 3, 2019, 4235-4242 4238 www.etasr.com belkadi et al.: energy design and optimization of a greenhouse: a heating, cooling and lighting study where, tsky, is calculated by: 1.5 0.552( 273.15) -273,15 sky out t t= + (12) finally, the heat transfer engendered by the process of evapotranspiration qevap, is calculated as shown in (13)-(14): evap t v q m l= (13) 1 ( ) ( ) t p m a wps wi ra rsρ −= − + (14) where ap could be determined from the plant’s leaf area index, while wps and wi could be calculated as: 1 100.6219 1. )5( 32 ps ws ws w p p −= − (15) 1 1010 ..6 322 519 ( ) i w w w p p −= − (16) by assuming a negligible temperature difference between tin and tplant, we could deduce the actual vapor pressure from the relative humidity and the saturated vapor pressure as shown in (17)-(18): 33 1 6 2 1.10 . 2 3.10 4 .10 . 9 3 5. 10 . 6 . ln( ) 1 exp 1000 −− − + − + − − +    =        −  c a c c a c a c a c a p ws (17) where a=tin +273.15, c1=-5.80002, c2=1.3915, c3=48.64024, c4=41.764768, c5=14.45209310, and c6=6.5459673. w ws h p p r= (18) in order to calculate ra and rs we could apply (19) and (20): 0.2 0.8 220 a f i r l v −= (19) 1 200 (1 (exp(0.05( 50))) ) sr rs iτ −= + − (20) we can apply the above theoretical development on the various shapes and covers of the greenhouse. figure 4 accurately represents the need for heating and cooling of the elliptic form equipped by polyethylene covering material during the different months of the year. to conclude, we will precisely calculate the energy demand in specific terms of heating and cooling using the bghm model without lighting potential effect to correctly determine the most efficient form and greenhouse cover (table iii). based on the results of table iii, it is clear that the most efficient form is the elliptic if the greenhouse is adequately covered by the polyethylene film m3, while if we utilized the traditional models we would have shown that this form was the worst energy-efficient and therefore the most economically expensive. table iii. average daily heating and cooling of our model without lighting impact [kwh m-²] even span uneven span elliptic rectangular m1 3,677 3,683 3,669 3,723 m2 3,996 4,005 3,983 4,210 m3 3,462 3,469 3,452 3,514 m4 3,651 3,657 3,643 3,696 m5 3,554 3,562 3,543 3,612 fig. 4. estimated heating and cooling load of the elliptic shape 3) study of bghm model with lighting impact we will calculate the artificial lighting requirements to determine the hourly lighting energy demand [w] which will allow us to deduce the heating effect of the lighting system. starting from the fact that any lighting device emits heat as well as light, from our model we will check the impact of these two parameters on the choice of the form and the covering material which must be used. to do this we will, at first, present the need of illumination of a tomato plant (table iv). then we will determine the daily light to calculate the additional energy effort that meets the optimal need of the cultivation of our plant. table iv. tomato plant needs [23-27]. parameters value daily photoperiod 16 hours required illumination(1) 8475 lux 1lux=0.0177µmol×m -2 s -1 a) lighting system design • daylight calculation to design the daylight system, we started with the 3d modeling of each shape of the selected greenhouse, then, we defined the covering material properties, the type of the reference sky (clear sky, overall sky, and covered sky), the hours and the days considered for the simulation to create the daylight scenes. daylight from 07:00 am to 10:00 pm was simulated, for the 1st, 8th, 15th and 22th of each month. this process has been applied for all types and covering materials of the greenhouse. an example of the daylight simulation of the elliptic form equipped with m3 has been shown in figure 5 (a) and (b) for august and december respectively. in order to compare the daylight of a different shape, we calculated the average daylight illumination of each greenhouse’s type applied for m3 covering material. the results are shown in figure 6. by referring to figure 6 we could deduce that the rectangular shape of the greenhouse is apparently the best in terms of daylight and that the elliptic shape remains the least efficient. in order to study the impact of coating materials on daytime lighting, we have simulated, through dialux evo, all types of coating materials for a reference date and time 15/06/2018 at 1:00 pm), because the lighting depends not only engineering, technology & applied science research vol. 9, no. 3, 2019, 4235-4242 4239 www.etasr.com belkadi et al.: energy design and optimization of a greenhouse: a heating, cooling and lighting study on the transparency but also on light reflection and absorption, and the height, size and shape of the greenhouse. the results are shown in table v. the gain/loss illumination factor to all greenhouse types with combined effects of covering material and applied greenhouse types, is shown in figure 7. (a) (b) fig. 5. daylight simulation results in (a) august, (b) december. fig. 6. daylight illumination of all greenhouse types. table v. effect of the covering materials covering material illumination simulated on (15-06-2018 at 1 pm) [klux] gain/loss compared to reference m3 [%] m1 13.185 4.5% m2 11.705 -7.6% m3 12.596 taken as reference m4 13.182 4.4% m5 13182 4.4% fig. 7. average annual daylight illumination of all greenhouse types. figure 7 shows the daylight illumination of all greenhouse types. it is clearly noticed that the rectangular greenhouse has the best value in terms of lux level, while m3 and m4 have the lower lighting values. there is not a big difference in the rest of the material. • lighting energy demand in order to design the required artificial lighting, we have applied the process described in figure 8 to meet the target lux level for the tomato plant which is 8475lux [22]. fig. 8. lighting design process engineering, technology & applied science research vol. 9, no. 3, 2019, 4235-4242 4240 www.etasr.com belkadi et al.: energy design and optimization of a greenhouse: a heating, cooling and lighting study after all calculations were done, we used 1400 luminaries of 60w suspended at 1.8m from the working plan (floor) and within an efficiency of 160lm·w -1 and a cct of 4000k. according to the simulation, our target was achieved within an illumination of 8478 vs 8475 (target) and a consumption of about 61w·m -2 . an example of false color rendering of the simulation is shown in figure 9, which proves that illumination is around our target light level and that the light distribution remains uniform throughout the entire greenhouse area. fig. 9. a sample false color rendering of a lighting configuration, and light distribution map of the greenhouse to reduce the lighting energy, we have implemented a daylight system control consisting of a light sensor connected to a raspberry pi3 in order to transmit the value of the light in real time to calculate the difference between the target value and the sensor value in the pwm signal, to dim the luminaries in order to obtain a uniform illumination equal to the desired value at any time t from 7:00 am to 10:00 pm when the daily ppfd is lower than the target value of the tomato plant. once the daily ppfd is reached, the lighting system will be automatically switched off. to estimate the average of the compensated illumination of all greenhouse types equipped with m3 we have to subtract the illumination of the total installed luminaries (when all luminaries are on) from the daylight. finally, we calculated the compensated need of illumination, to deduct the annual power consumption of lighting for all greenhouse types and covering as shown in figure 10. we note that in figure 10 the need for energy compensation in lighting remains high compared to the other greenhouse forms, especially in the case of the rectangular form. despite the satisfactory results so far, in terms of the choice of shape and coverage and their impact on the efficiency of the lighting system, we will look further into our analysis to see if there is an impact of the heat emitted by the luminaries and, if applicable, its effect on the energy equilibrium equation and on the response of the equation to the variation of heating and cooling components. this amount of energy allowed us not only to estimate the energy requirement of the lighting, but also to estimate heat loss from the lighting equipment as mentioned in (21): ' " li l q w k k= (21) fig. 10. lighting energy demand after all calculations are done, the estimated heat gains and losses are represented in figures 11-12. figure 11 shows the monthly evolution of energy captured by solar radiation qsr , the evolution of the global greenhouse gain system which encompasses qsr, and the heat effect gained from the lighting system. we also note that the difference between the heat gains due to the solar energy and the global heat gains are approximately identical during the hot period which is expected since the need of additional lighting in these months decreases because they have more daylight. fig. 11. monthly evolution of heat gain fig. 12. monthly evolution of heat loss engineering, technology & applied science research vol. 9, no. 3, 2019, 4235-4242 4241 www.etasr.com belkadi et al.: energy design and optimization of a greenhouse: a heating, cooling and lighting study figure 12 represents the evolution of the heat loss caused by conduction convection qcd-cv, infiltration qinf, perimeter heat transfer qp and soil qf, heat transfer due to long wave radiation qlw, and the evapotranspiration qevap. it can be seen from figure 12 that the quantities of heat qp, qinf, qcd-cv follow a double sign, which is expected since these quantities depend on both internal and external temperatures of the greenhouse. they are positive when the external temperature is lower than the internal temperature and vice versa. in order to compare the state of the different models in terms of energy demand (heating and cooling), the models are presented in figure 13. fig. 13. monthly evolution of energy demand according to figure 13 the energy demand estimate by the traditional model remains inaccurate, whereas with the improvement of this model by the injection of the neglected parameters, there is a clear improvement. we also note that the energy gap in cooling and heating is around 49.87% compared to the traditional model. our developed model, even if the direct results at this elevated level are satisfactory, shows better results and allows demonstrating the considerable weight of the heat effect of the lighting on sufficient accuracy of the energy demand level in heating and cooling. the potential impact of lighting equipment’s electrical consumption for the various possible shapes and coverage materials is shown in table vi. table vi. total energy demand* [kwh m-²] even span uneven span elliptic rectangular m1 4,022 4,010 4,084 4,028 m2 4,205 4,196 4,262 4,237 m3 3,763 3,751 3,824 3,775 m4 3,996 3,984 4,058 4,001 m5 3,829 3,819 3,888 3,848 * heating, cooling, and lighting according to table vi, our developed model points that the uneven span is the most efficient form. our model adequately supported the model parameters conveniently overlooked by the traditional model and the impact of the lighting system and its effects. iii. conclusion this research showed that the energy balance can exclusively reveal the optimal values of energy consumption if all the principal determinants that cause a direct effect on the fundamental process of greenhouse cultivation, are taken into account. from this study, the following conclusions are derived: • the need for energy consumption has been optimized by adopting the uneven span form. • in our energy equation, it is possible to confirm that the uneven span form could improve the efficiency of our energy balance more significantly by using appropriately polyethylene m3 as greenhouse cover. • the development of the heat release effect of the lighting system enabled a considerable gain in electric energy, especially during the cold period, since it enabled a residual heat to be amply provided. therefore, a tangible net cost reduction efficient energy ordinarily required by the greenhouse tomato cultivation was observed. • the proposed model exhibited a substantial gain, reaching 49.87%, of the energy consumption of cooling and heating compared to the reference “traditional” model. nomenclature ag greenhouse area [m²] af greenhouse floor area [m²] ap plant area [m²] acr acrylic ach number of air changes per hour [m 3 s -1 ] cct correlated color temperature, [ k] ca specific heat of air [j. kg-1 k -1 ] d depth of constant soil temperature [m] fp perimeter heat loss factor, [w.m -1 . k -1 ] g glass h height of the greenhouse [m] h0 outside convective heat transfer coefficients hi ohe inside convective heat transfer coefficients isr solar radiation on the horizontal surface [w.m -2 ] k’ lighting allowance factor k” heat conversion factor ks thermal conductivity of soil [w m -1 k -1 ] kc thermal conductivity [w m -1 k -1 ] l length of the greenhouse [m] lf characteristic length plant leaves [m] lv latent heat of water vaporization, [j kg -1 ] lmax maximum illumination inside the greenhouse [lux] leg low e glass lc covering material thickness [m] mt moisture transfer rate, [kg s -1 ] pf polyethylene film pc polycarbonate pg perimeter of the greenhouse [m] pw partial pressure of the water vapor, [kpa] pws partial pressure at saturation, [kpa] qcd-cv conduction and convection heat transfer [w] qinf infiltration heat transfer [w] qf floor heat transfer [w] qp perimeter heat transfer [w] qlw long-wave radiation heat transfer [w] qevap evapotranspiration heat transfer [w] qs total required heating and cooling power [w] qsr solar radiation heat gain [w] qli lighting heat gain [w] qg total heat gain inside the greenhouse [w] engineering, technology & applied science research vol. 9, no. 3, 2019, 4235-4242 4242 www.etasr.com belkadi et al.: energy design and optimization of a greenhouse: a heating, cooling and lighting study ql total heat losses from the greenhouse [w] ra aerodynamic resistance [s m -1 ] rs stomatal resistance, [s m -1 ] rh relative humidity sg section of the greenhouse [m] t in inside air temperature [°c] tout average outdoor air temperature [°c] ts greenhouse soil temperature [°c] tsky sky temperature [°c] tplant plant temperature [°c] u static overall heat transfer coefficient ud dynamic overall heat transfer coefficient vi indoor airspeed airspeed, m s -1 vg volume of the greenhouse [m] w width of the greenhouse [m] wl lighting energy consumption [w] wv wind velocity [m s -1 ] wi humidity ratio of air at indoor temperature wps saturated humidity ratio of air at the plant temperature ρα density of internal air [kg m -3 ] τ transmissivity of the greenhouse cover references [1] s. d’arpa, 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journal of cleaner production, vol. 131, pp. 145-154, 2016 [27] d. a. damers, m. dorais, c. h. wien, a. gosselin, “effects of supplemental light duration on greenhouse tomato (lycopersicon esculentum mill.) plants and fruit yields”, scientia horticulturae, vol. 74, no. 4, pp. 295-306, 1998 microsoft word 5-424-ed2.doc engineering, technology & applied science research vol. 4, no. 2, 2014, 618-624 618 www.etasr.com sellaf et al.: geotechnical properties of rubber tires and sediments mixtures geotechnical properties of rubber tires and sediments mixtures hamid sellaf civil engineering department, djillali liabes university of sidi bel abbes, algeria hamidsellaf@yahoo.com habib trouzine civil engineering department, djillali liabes university of sidi bel abbes, algeria h_trouzine@yahoo.fr mouloud hamhami civil engineering department, djillali liabes university of sidi bel abbes, algeria mouloudhm@yahoo.fr aissa asroun civil engineering department, djillali liabes university of sidi bel abbes, algeria a_asroun@yahoo.fr abstract— an experimental work was undertaken to study the effect of rubber tires on the geotechnical properties of a dredged sediment, using a mixing ratio of large size. for comparison, two types of soil were studied (dredged sediment from fergoug dam and tizi tuff from the north west of algeria). taking into account the high compressibility and the low water absorption of the rubber tires, grain size analysis, density, atterberg limits analysis, chemical composition, direct shear tests, loadingunloading tests, modified proctor and cbr tests are performed on the two soils and their mixtures with different scrap tire rubber (10, 20, 25 and 50%). the results show that liquid limits and plastic indexes decrease with the scrap tire rubber content and that the decrease is more significant for soil with high plasticity. cohesion also decreases with scrap tire rubber content when the internal friction angle is vacillating. compression and recompression indexes increase gradually with the scrap tire rubber content and the variation for compression index is more significant for the two soils. compaction characteristics and cbr values decrease with scrap tire rubber content. the cbr values for w=3% are important compared to those with w=5% excepted for mixture with (75% tuff and 25% scrap tire rubber). the results show that the scrap tire rubber can be used as a reinforcement material for dredged soil, but with a content that should not highly affect the compressibility. keywords—sediments; waste tires; rubber; valorizing; tests; geotechnical i. introduction the world’s reservoirs are currently filling up with sediments at a rate of approximately 1% per year [1, 2]. this implies that within about 50 years, the world’s water storage in reservoirs will be half of the current storage, which will have large economical and environmental consequences, especially in semi-arid environments where many reservoirs have been built for water supply, irrigation, flood control and production of electricity [3]. fergoug dam is one of many others that have such problems. it is located in the north-west of algeria, at the bottom of the atlas buttresses, approximately 20 km in the south of the town of el-mohammadia (province of mascara) (figure 1). the total catchment area of fergoug is estimated to be 8340 km2. the average altitude is about 790 m with a maximum altitude of 1454 m [4]. in its actual position the fergoug dam is an earthfill dam with an initial capacity of 17 million m3 in 1970. in 1977, its capacity fell to 9.67 million m3, with an annual rate of silting exceeding one million of m3 [4]. several methods of valorization are available such as the sediments dredging reuse. these methods understand valorization with physics, chemical, biological, immobilization, thermal additives [5-13]. pneumatic waste is polluting and cumbersome. it constitutes a varied population by size, degrees of ageing, wear, shapes of ears. the worn tires are composed primarily of synthetic rubber, carbon dioxide, silicon and steel. algeria generates over than 26000 tons of waste tires per year [14]. waste tires can be disposed in landfills or tire stockpiles. there are several methods of recycling tires in the field of civil engineering e.g. as a retaining wall and as a decorative element [15-16]. fig. 1. localisation of sites engineering, technology & applied science research vol. 4, no. 2, 2014, 618-624 619 www.etasr.com sellaf et al.: geotechnical properties of rubber tires and sediments mixtures currently several researchers directed their studies on the valorization of the sediments, with the aim of using them in the field of civil engineering, which portrays the greatest need for materials. this work is interested particularly in the valorization of the sediments, with an aim of studying the mechanical behavior of the scrap rubber mixtures compared to other results of tizi tuff which is primarily used in the area of mascara with the same percentage of scrap rubber. ii. experimental study. a. materials and methods 1) investigated soils two soils of different origins and physical properties were selected. the first sample was obtained from a site located in fergoug in mascara in the north-west of algeria. the second sample was a tuff from the region of tizi, mascara in the north-west of algeria. these two soils were subject to several laboratory identification tests using standard procedures adopted by afnor and iso standards [17-21]. the results are shown in table i. the specific weight of the fergoug sample was 24.6 kn/m3 while that of the tuff was 25.9 kn/m3. the particle size distribution for the soils is shown in table i. the chemical analysis of the soils was carried out in accordance with [22], and the results are presented in table ii. 2) tires rubber fibres scrap tire rubber fibres can be obtained from tires through two principal processes: (i) ambient, which is a method of processing where scrap tire rubber is processed at or above ordinary room temperature; (ii) cryogenic, a process that uses liquid nitrogen to freeze the rubber until it becomes brittle and then uses a hammer mill to shatter the frozen rubber into smooth particles [23]. tire rubber fibre consists of a complex mixture of elastomers, polyisoprene, polybutadiene and styrene-butadiene. stearic acid (1.2%), zinc oxide (1.9%), extender oil (1.9%) and carbon black (31.0%), are also important components of tires [24-25]. table i. some properties of the investigated soils the used rubber fibre, the same used in [16], is produced from used automobile tires by shredding them mechanically in ambient temperature. steel was removed by magnetic separation and textile by density. it was not possible to determine the gradation curve for the tire chips as for normal aggregates since they were elongated particles between 5 and 30 mm with an average value of 7 mm: the sample contains scrap tire rubber fibre (approximately 59% of weight) and scrap tire rubber powder (approximately 41% of weight) with the latter tending to lump together. scrap tire rubber was characterized by a specific weight of 0.83 and insignificant water absorption. some behavior parameters of the rubber are given in table iii. table ii. chemical compositions of soils used in the study property fergoug sediment tizi tuff sio2 (%) 62.68 24.42 al2o3 (%) 7.39 2.65 fe2o3 (%) 0.71 0.58 cao (%) 12.51 31.48 mgo (%) 0.37 2.61 naoh (%) 4.90 cl (%) p.f2 (%) 16.27 33.39 table iii. some properties of scrap tire rubber fibre properties tire rubber fiber references density (mg/m3) 1.153-1.198 akbulut et al. 2007 tensile strength (mpa) 16-20 khorami et al. 2010 elongation (%) 400-500 khorami et al. 2010 b. mixtures design 1) preparation of soil-rubber mixtures because the temperature can alter the rubber, the water content of samples was determined by drying at 35°c±5°c. samples were considered as completely dry when the difference between two weighings does not exceed 0.2% for an interval of 24 hours. according to some pertinent studies on fibre reinforced soils, the studied percentages of polypropylene are generally 0.05, 0.015 and 0.025% of the weight of the parent soil [26-27] or 0.1, 0.2, 0.3, 0.4 and 0.5% of the weight of the parent soil [28]. for tire rubber fibre, the studied percentages are 1, 2, 3, 4 and 5% of the total weight of the reinforced samples [28]. fibres and lime or cement with soils were mixed in all of cited studies. cetin et al. [29] studied mixtures prepared by cohesive soil with 10, 20, 25 and 50% of pure fine and coarse grained tire-chips. for this study, soils were mixed with scrap tire rubber fibre and the contents of fibre were chosen as 10, 20, 25 and 50% by total weight of composite samples. as the fibre tended to lump together, considerable care and time were spent to get a homogeneous distribution of the fibre in the mixtures. the used materials were called s, t and c for fergoug sediment, tizi tuff and scrap tire rubber fibre respectively. 2) preparation of composite soil samples in many researches, specimens are prepared at optimum proctor or at water content corresponding to the liquid limit. in our study, since the specific weight of rubber is less than half that of soils and used mix ratios are larger (till 50% of scrap tire rubber), the sediment mixtures were prepared with 20% of water content and then specimens were statically compacted in the standard proctor mould in five layers to ensure uniform dry density. samples heave were allowed under a seating surcharge of 1 kpa, the choice of this seating surcharge is a result of the great difference of specific gravities of components. after the compaction of the soils and their mixtures, the cylindrical properties fergoug sediment tizi tuff liquid limit (%) 38.28 28 plastic limit (%) 15.09 13 plasticity index (%) 23.19 15 specific weight γs ( kn/m 3) 24.6 25.9 grains sizes analysis gravel (%) sand (%) 16 40 silt (%) 28.6 50 clay (%) 55.4 10 methylene blue values volume of blue vb (cm3) 5.5 4.5 specific surface sst (m²/g) 115.5 94.5 engineering, technology & applied science research vol. 4, no. 2, 2014, 618-624 620 www.etasr.com sellaf et al.: geotechnical properties of rubber tires and sediments mixtures unreinforced and composite samples were extruded from the mould using a hydraulic jack. the samples were wrapped in plastic to prevent water loss. since it is impossible to determine the specific gravities of scrap tire rubber and composite samples with the method described in [18] (because rubber floats on the surface of the liquid), the specific weight of scrap tire rubber is measured by helium pycnometer while those of composite samples are calculated theoretically using each components’ dry mass and specific gravities values as follow:    s d1 d2 d1 s1 d2 s2g = (m +m ) m g + m g     where: gs: specific density (dimensionless) md: dry mass of specimen (kg) table iv presents the different specific gravities of the soils and their mixtures. it can be observed that the value of the specific weight of composite samples decreases with rubber content and reaches its half for the sample with 50% of scrap tire rubber content. table iv. specific weight of soils, scrap tire rubber and their mixtures. rubber content 0% 10% 20% 25% 50% 100% specific weight γs (kn/m 3) sediment 24.6a 23.0b 21.3b 20.5b 1.6.4b tuff 25.9a 24.1b 22.4b 21.5b 17.1b 8.3a a experimental value, b calculated value iii. experimental results and discussion a. consistency limits atterberg limit tests were performed to determine the consistency limits values of the soils and their mixtures according to the methods described in the french standard [17]. 1) effects of scrap tire rubber on the liquid limit figures 2 and 3 show the effects of fibre on the consistency limits for s and t soils and their mixtures. the liquid limits are expected to decrease gradually when the scrap tire rubber fibre content increases for the two soils. however, the reduction of the liquid limit for the s soil was considerable. 2) effects of scrap tire rubber on the plastic limit for the s soil, the plastic limit decreases gradually for the sample of increased fibre. for the t soil, the plastic limit decreases gradually for the sample of increased fibre. the results of atterberg limit test indicate that the s soil has a higher value of plasticity index than the tizi tuff. the low plasticity of the t soil makes the mixtures less susceptible to fibre compared to the s soil. the change in consistency limits of mixtures may be due to the mixture type [30], the cation exchange capacity [31-32], and the relative amount of clay mineral in the mixtures [33]. interestingly, the plastic limits studied for tire-cohesive clayey soil mixtures by [29] stay at first about the same then show some amount of decrease and then stay about the same. these results are similar to those of typical fine grained cohesive soils with medium plasticity [29]. 0 10 20 30 40 50 0 10 20 30 40 0 10 20 30 40 l iq u id a n d p la st ic l im its a n d p la st ic ity i n d e x (% ) scrap tire rubber (%) liquid limit plastic limit plasticity index fig. 2. effect of rubber tires on the consistency limits of the soil s 0 10 20 30 40 50 0 10 20 30 40 0 10 20 30 40 l iq u id a n d p la s tic l im its a n d p la s tic ity in d e x ( % ) scrap tire rubber (%) liquid limit plastic limit plasticity index fig. 3. effect of rubber tires on the consistency limits of the soil t ab-malek and stevenson [34] studied the effect of 42 year immersion in sea water on natural rubber; they concluded that absorbed water of rubber has been less than 5% of its dry mass. the literature contains a considerable number of empirical techniques for assessing the swelling potential of soils, which correlated with consistency limits, moisture content, dry density, and depth of the soil samples [35]. b. direct shear tests (dst) laboratory dsts were conducted to measure the shear properties of a soil, including the yield point, the cohesion c and the soil internal friction angle ø, as affected by different soil moisture contents and dry bulk densities. this test is carried out according to french standard [36]. direct shear tests were conducted using an apparatus consisted of a soil shear box, a loading head, a weight hanger, and weights to generate engineering, technology & applied science research vol. 4, no. 2, 2014, 618-624 621 www.etasr.com sellaf et al.: geotechnical properties of rubber tires and sediments mixtures normal loads. the shear box had two square rings for holding the soil sample. the cross-section of the box was 60 to 60 mm and the height was 50.8 mm. the horizontal displacement of the movable ring was achieved with a motor. the tests are carried out in a damp and pressed state. the line of rupture is obtained following the application of three normal stresses (1, 2 and 3 bar) to obtain more precision for the statistical study. figure 4 and 5 show the curves of shearing tests. it is noted that there is a decrease in cohesion with the increase of scrap rubber. on the other hand, the line of variation of internal friction angle is almost vacillating depending on the scrap tire rubber content. 0 10 20 30 40 50 22 24 26 28 30 32 34 internal friction angle cohesion scrap tire rubber content (%) in te rn a l fr ic ti o n a n g le ( d e g re e s) 80 100 120 140 160 180 c o h e s io n (k p a ) fig. 4. effect of rubber tires on cohesion and angle of internal friction of the soil s 0 10 20 30 40 50 22 24 26 28 30 32 internal friction angle cohesion scrape tire rubber content(%) in te rn a l fr ic tio n a n g le ( d e g re e s ) 80 100 120 140 160 180 c o h e sio n (k p a ) fig. 5. effect of rubber tires on cohesion and angle of internal friction of the soil t c. odometer tests : loading–unloading tests because tire rubber is highly compressible and its specific weight is less than half that of the soils, a complementary test program under odometer conditions was also performed to obtain additional information on the mechanical behaviour of the soils and the mixtures although the compressibility of rubber particles is considered negligible compared to the compressibility of the composite skeleton in computation. the compression index cc and the recompression index cr were determined for soils and composite samples according to [37]. 1) effect of scrap tire rubber on compression index. figures 6 and 7 show the compression indices for the studied soils and mixtures. it is well known that the compression index cc is the slope of the linear portion of the pressure void ratio curve on a semi-log plot. the values of cc are relatively small because the remoulded cc is always smaller than the undisturbed cc. the values vary from 0.126 to 0.423 for the tizi tuff and its mixtures and from 0.112 to 0.571 for fergoug sediment and its mixtures. for the two soils, cc increases gradually with rubber content. 2) effect of scrap tire rubber on recompression index the recompression (swell) index (i.e., slope of the e-log p plot during unloading or decompression) is presented in this study as the decompression index, cr (figures 6 and 7). the values of the recompression index cr of undisturbed soil are generally about 5 times smaller than cc [38]. for all tested samples, cr is smaller than cc and it increases with scrap rubber content. the values of cr range from 0.114 to 0.261 for the tizi tuff and its mixtures and from 0.109 to 0.211 for fergoug sediment and its mixtures. d. modified proctor tests this test is carried out according to the french standard [39]. the optimal water content wopt and the maximum dry density gdmax are determined. the proctor curves are drawn taking into account the added scrap rubber. the results will be then compared with those obtained on tizi tuff. the values of optimum moisture content are 12.1% and 7.94% for respectively s and t soils, whereas the maximum dry density is about 1.97 for t soil which is 17% greater for s soil. fig. 6. effect of tires rubber content on compression and recompression indices of soil s with the addition of scrap tire rubber contents (figure 8), the optimum moisture content and the maximum dry unit weights of s and t soils decrease. this can be due to change of the particle size distribution, organic content (especially for sediment) or surface area of the composite samples which can change the soil state from buoyant to semibuoyant. engineering, technology & applied science research vol. 4, no. 2, 2014, 618-624 622 www.etasr.com sellaf et al.: geotechnical properties of rubber tires and sediments mixtures e. cbr tests cbr (california bearing ratio) values are commonly used in mechanistic design as an indicator of strength and bearing capacity of a sub grade soil, sub base, and base course material used in road and airfield pavements. the cbr of a soil is the ratio obtained by dividing the stress required to cause a standard piston to penetrate 2.5 mm, 5.00 mm, 7.50 mm and 10.00 mm into the soil by a standard penetration stress at each depth of penetration [40]. the cbr may be thought of as an index value comparing the strength of the soil to that of crushed rock. cbr loading values according to different penetration for s and t soils and their mixtures for respectively w=3 and 5% are shown in figures 9 and 10. cbr tests in this study were performed in accordance with [41]. cbr values for s and t soils and their mixtures are given in table v. table v. cbr values of soils and mixtures. soil mixtures cbr values (w=3%) cbr values (w=5%) 100% s 16.56 11.54 90% s+10%c 14.55 8.53 80% s+20%c 7.53 4.52 75% s+25%c 6.52 5.02 50% s+50%c 4.01 3.01 100% t 15.55 12.04 90% t+10%c 14.55 9.03 80% t+20%c 8.03 8.03 75% t+25%c 7.02 7.53 50% t+50%c 4.52 2.51 results indicate that cbr values for the two soils decrease with scrap tire rubber content. the maximal value of cbr is given for w=3% for all mixtures except for the mixture of t soil with 25% of scrap tire rubber where the maximal cbr value was obtained for w=5%. the fergoug sediment needs greater pressure to make power for the penetration than the tizi tuff. thus, the pressure of 3% is more than the pressure of 5%, which proves that water impacts negatively on the compaction characteristics of mixtures. also the scrap rubber affects negatively on cbr values of soils. the results highlight an appreciable increase in load compaction when the additions of 20% of scrap tire rubber are proceeded. fig. 7. effect of tires rubber content on compression and recompression indices of soil t 0 10 20 30 40 50 4 6 8 10 12 w opt for s soil g dmax for s soil w opt for t soil g dmax for t soil scrap tire rubber content (%) o p ti m u m w a te r c o n te n t (% ) 0,8 0,9 1,0 1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 1,9 2,0 m a x im u n d ry u n it w e ig h t fig. 8. evolution of features proctor for s and t soils and theirs mixtures. fig. 9. cbr loading according to different penetration for s and t soils and their mixtures for w=3%. fig. 10. cbr loading according to different penetration for s and t soils and their mixtures for w=5%. engineering, technology & applied science research vol. 4, no. 2, 2014, 618-624 623 www.etasr.com sellaf et al.: geotechnical properties of rubber tires and sediments mixtures iv. conclusion in this study, the effect of scrap rubber content on the geotechnical characteristics of fergoug sediment and tizi tuff were investigated and the following conclusions were drawn:  geotechnical’s characteristics vary depending on the scrap rubber content: the liquid limit, the plasticity index rundown with the increase of scrap tire rubber content. this decrease is more significant for plastic soil.  the scrap tire rubber content changed the compaction parameters of fergoug sediment and tizi tuff. the optimum moisture content and specific weight values decreased with the scrap tire rubber contents.  for shearing tests, a decrease in cohesion with the increase of scrap tire rubber is observed when the variation of internal friction angle is vacillating.  compression and recompression indexes increase gradually with the scrap tire rubber content for the two soils. the increase is more significant for the compression index.  the cbr values for w=3% are larger than those for w=5% except for the mixture (75% tuff + 25% scrap tire rubber). thus, the pressure needed for a water content w=3% is greater than for 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chi minh city, vietnam my.dth@ou.edu.vn diep van nguyen ho chi minh city open university ho chi minh city, vietnam diep.nv@ou.edu.vn phong thanh nguyen ho chi minh city open university ho chi minh city, vietnam phong.nt@ou.edu.vn abstract—human resources development is one of the main issues in the socio-economic development strategy and the transform of any region in the context of industry 4.0. however, vietnamese human resources have been poorly evaluated in the areas of quality, lack of dynamism, and creativity. therefore, this paper presents a fuzzy logic approach to ranking seven skills shortage in vietnam’s labor market, namely lifelong learning, adaptive capacity, information technology capacity, creativity and innovation capacity, problem-solving capacity, foreign language competency, and organizing and managing competency. the results showed that the problem-solving skill has the largest gap between an enterprise’s requirements and the actual response of employees. keywords-fuzzy logic; industry 4.0; human resources; skill shortage; vietnam i. introduction theories of economic growth, especially the endogenous growth model, have recognized the role of human factors in economic growth. author in [1] has shown with empirical evidence that human resources are a key factor in determining economic growth and reducing poverty. thus, human resource development is one of the core issues in the socio-economic development strategy and the transformation of growth models of countries or regions, especially in the context of the industry 4.0 [2-6]. many studies have emphasized that higher education decides the quality of a country's human resources [7-12]. in vietnam, the 11 th central committee's meeting, 8 th session issued a resolution for fundamental innovation in comprehensive education and training, aiming to this goal. authors in [13] suggested that a high level of education leads to high labor productivity and the higher the total education level of a country, the faster its economy will develop. however, globalization and technological progress have led to structural changes in the organization of businesses and the manner of work and, at the same time, changes in the demand for qualified employees and the professional profile of candidates [14, 15]. cedefop in [16] confirmed the difficulty encountered by the employers in finding the candidates with the right skills when recruiting. the labor market in vietnam is no exception. the world economic forum's 2017 [17] global human resource assessment showed that vietnam's overall human resource index ranked only 64/130. in particular, the “competencies”, “development”, and “creativity” components in the rankings were 85/130, 67/130, and 120/130, respectively. similarly, the assessment of the world economic forum's readiness to participate in the 4.0 revolution shows that the ranking of highly skilled human resources and labor in vietnam was quite low, 70/100 and 81/100 [18]. this was also the reason for overall low labor productivity. in three decades (1991-2022), vietnam's labor productivity increased, but not significantly [19]. vietnam's labor productivity is only higher than the ones of the group of lowincome countries and is at the threshold of 50% of the lowmiddle income countries. from 2017 to 2022, vietnam's labor productivity is double the average labor productivity of lowincome countries, equal to more than 50% of low-income countries and 18.3% of middle-countries. in general, vietnamese human resources have been poorly evaluated in the areas of quality, lack of dynamism, and creativity. the world bank report on the labor force in vietnam also pointed the weakness of the vietnamese workforce that lacks the necessary skills [20]. the survey results of the report show that 40% of skilled workers lacked the necessary skills. for technicians, this number was up to 80%. skill shortages were also drivers of increased training expenditures and average labor costs [21]. skills can be approached as a multi-dimensional concept, comprised of the quality of education, major areas of study, and previous working experience, otherwise serious bias in human capital evaluation may arise [22]. besides, various types of skills can be noted, such as technical skills, cognitive skills, soft skills, etc. also, the required labor market skills have dynamically changed to adapt to the technological innovations of industry 4.0 [23-26]. for institutions of higher education, the optimal training for the labor market is strategically prioritized [27]. therefore, it is essential that skill shortage criteria should be identified and ranked for efficient and effective remedy measures and vietnamese higher education is not an exception. in recent years, the application of artificial intelligence in understanding the human thought process and its application in real environment has become a prominent theme. fuzzy logic has paved the way for modeling human behavior and mathematically obscure concepts. this is the method preferred by researchers to solve evaluation issues and decision making, given its two advantages: i) objectiveness and ii) fuzzy corresponding author: phong thanh nguyen engineering, technology & applied science research vol. 10, no. 3, 2020, 5864-5868 5865 www.etasr.com duong et al.: using fuzzy approach to model skill shortage in vietnam’s labor market in the context … evaluation for dynamic reflection of the research’s object. therefore, this paper is applying a fuzzy approach to the model skills shortage in vietnam’s labor market. ii. research background skill shortages occur when employers fail to find candidates with the right skills [28-32]. in designing a new training program or redesigning an existing training program, determining the capabilities and competencies that university graduates must acquire during the educational process is one of the most important aspects of the process. authors in [14] suggested that having a clear career orientation is expected to create educational needs at universities that integrate common core competencies so students can ensure full participation in the labor market upon graduation. to achieve this goal, universities need to know what business requires from university graduates, including their level of preparation, and what business believe that can be improved. however, answering the question of what is required for business is not simple. oecd conducted a survey of adult skills (piaac) [33] which included questions about skills and designed an assessment exercise. the skill measure was derived from a combination of self-reported information and skill proficiency. authors in [34] explored the piaac data and proposed a new measure of skill mismatching, categorizing laborers into three groups: matched, under-skilled and over-skilled. however, the piaac only included information on literacy and numeracy skills, which does cover very well the competencies required by the labor market. previous studies have also focused on evaluating the capacity of the undergraduate laborers. authors in [14] surveyed 872 enterprises in spain and performed indepth interviews with 40 business directors or individuals in charge of personnel. they pointed out that students needed to improve their interpersonal skills, teamwork, attitude and motivation toward work, lifelong learning, computer skills, and time management skills. research showed that differences between the expectations of enterprises and the practical capacity of newly graduated university employees were substantial. new employees often needed up to a year to undertake the assigned jobs. authors in [35] interviewed enterprises in new zealand to discover whether a gap between the expectations of businesses and the proficiency of new accountants existed. the findings showed that employers appreciated some of the characteristics of newly graduated accountants, such as basic knowledge about the field of work, communication ability, teamwork skills, and lifelong learning capacity. however, they lacked other important competencies such as skills to apply knowledge in practice and the ability to grasp and handle jobs [36, 37]. authors in [38] further clarified that employers required graduates to have qualifications such as research skills, teamwork, communication skills, flexibility, and time management skills. nevertheless, there were still differences between employers’ expectations and the selfevaluated ability of students. moreover, the perception of such differences also varied. for instance, many new graduates were satisfied with their time management, while employers were dissatisfied with this aspect of the work of the new employees. in the 21 st century, employees have had to meet new challenges in the skill requirements. authors in [39] insisted that nowadays businesses required workers to be able to work effectively in a volatile economy. they also suggested that the characteristics of a new graduate were more important than the subjects they studied. therefore, workers to work on soft skills such as their learning ability, adaptability, communication skills, problem-solving and decision-making, teamwork, and creative capacity. furthermore, 309,000 vacancies in 169 professions of various professional levels in the united kingdom (uk) was analyzed [40]. the research indicated that employers found it difficult to recruit suitable workers in 106,000 of these positions. the industries that encountered the labor shortages included nursing, computer programming, and human resources. the survey also found that the labor supply shortage at smalland medium-sized businesses was much more serious than at the larger ones. one of the main reasons for this deficiency was the “low number of applicants with the required skills”. future employment trends in [16] implied that current job supply was structured around the records or functions that, in addition to the scientific and technical knowledge provided by the university, required the development of a wide range of skill demands such as customer interaction, product innovation, planning/organization, learning to learn, problem-solving, customer service, team working, communication, technical or job-specific, advanced ict, foreign languages, and advanced literacy. in general, most workforce studies have agreed that the practical capacity of the laborers has not met the requirements of the enterprises. therefore, many businesses believe that university graduates need to improve their skills in the areas of creativity, problem-solving, foreign-language competence and information technology. authors in [41] used a fuzzy analytic hierarchy process to rank the applicants’ profiles to determine the fittest applicant. this approach has proven to be helpful in complicated contexts in a fast-changing world. a similar approach was used in [42] in developing a competency model of undergraduate employees in the vietnamese labor market. the findings confirmed the importance of the priority of critical thinking and problem solving, followed by organizing and managing ability, lifelong learning, adaptability, creativity and innovation, expertise and digitalization, and foreign language knowledge. further exploration of the gaps between the actual and expected skills was made in the paper to guide educators as well as individuals in meeting the labor market demand iii. research methodology a two-part questionnaire was prepared to collect data: part 1 consisted of information of the people and enterprises that participated in the survey. these included: (i) personal information (gender, title, year of birth) and (ii) information about the enterprises (headquarters, field of activity). part 2 consisted of the evaluation criteria of enterprises on the ability to meet the job requirements of university-trained labor. until recently in vietnam, no unified set of criteria existed for assessing the quality of such labor. the criteria used to determine labor capacity in vietnam were drawn from [42] and were used to create the enterprises’ survey questionnaire on the ability to meet job requirements of university graduates. these engineering, technology & applied science research vol. 10, no. 3, 2020, 5864-5868 5866 www.etasr.com duong et al.: using fuzzy approach to model skill shortage in vietnam’s labor market in the context … criteria include: (i) lifelong learning, (ii) creativity and innovation, (iii) it, (iv) adaptability, (v) critical thinking and problem-solving, (vi) foreign languages, and (vii) organizing and managing ability. these criteria were assessed on an 11level scale (level 0 corresponding to completely disagree and level 10 to completely agree). in the questionnaire our commitment to use the information only for research purposes was expressed, along with the commitment to keep the information confidential to respondents. the questionnaire was sent to enterprises to determine their assessment on the actual capacity of workers. the research team used the following three criteria to select businesses: (i) development orientation of ho chi minh city (hcmc), vietnam, (ii) the importance of industry groups in socio-economic fields, and (iii) the location of the enterprises in ho chi minh city. based on these criteria, the study focused on businesses in the fields of it, economics or commerce, transportation, finance or banking and insurance, health services, and tourism (see table i). table i. research sample description firm information industry number of firms percentage information technology 9 15.00% economics and commerce 7 11.67% transportation 9 15.00% finance, banking, insurance 9 15.00% health service 6 10.00% tourism 9 15.00% others 11 18.33% total 60 100% location number of firms percentage district 1 18 30.00% district 2 2 3.33% district 3 6 10.00% district 5 2 3.33% district 7 1 1.67% district 8 2 3.33% district10 3 5.00% binh tan district 2 3.33% binh thanh district 3 5.00% go vap district 1 1.67% phu nhuan district 6 10.00% tan binh district 7 11.67% tan phu district 7 11.67% total 60 100% respondent information gender number of people percentage male 29 48.33% female 31 51.67% total 60 100% position number of people percentage chief executive officer ceo 1 1.67% director/deputy director 15 25.00% head/deputy head of department 44 73.33% total 60 100% there were 60 survey questionnaire responses from businesses. table i provides the information of the enterprises in the sample. specifically, most of these enterprises were located in district 1 (30%). district 1 is considered the economic hub of hcmc with the highest number of domestic and foreign enterprise offices. this is also the district with the largest shopping centers in hcmc. these enterprises mainly operate in the field of commerce and services, such as it, transportation. finance, banking, insurance, and tourism (accounting for 15% for each sector). this is also a still developing area, and it made the biggest contribution to the economic growth of the city in 2019. specifically, the three service sectors with the higher proportion of growth than the average included: wholesale and retail, transportation and warehousing, and finance and banking. meanwhile, the it sector contributed 4.44% to the city's domestic products in 2019, and ho chi minh city wants to have at least 1,000 more businesses in this field in the future. notably, the percentage of females was slightly higher than that of males. also, the respondents were mainly heads or deputy heads of departments of human resources and administration. finally, to calculate the weights of critical skills shortage in vietnam’s labor market, the fuzzy set theory based on analytic hierarchy process was adopted due to its advantage to deal with uncertainty, inaccuracy, and ambiguity of data input by experts [43-47]. for defuzzified the fuzzy weights, in this research, we applied the following coa method [48]: [( ) ( )] / 3 i i i i i i w w w w w w bnp u l m l l= − + − + (1) where i w bnp is the best nonfuzzy performance (bnp) value of the fuzzy weights of the i th criterion [49]. iv. results and discussion the research results are presented in table ii. seven main criteria composed the hierarchical model. among these skills, the ability to analyze, detect, and solve problems created the largest gap between an enterprise’s requirements and the actual response of employees. this reflects the common trend of industry 4.0 in the skills demand of labor forces [50]. overall, enterprises required workers to meet at 8.1 points on average on the scale of labor capacity. however, enterprises assessed that the actual capacity of employees was only 6.0 points. table ii. results skills shortage rank lifelong learning 6 innovation 4 information technology 7 adaptability 3 problem solving 1 foreign language 5 organization 2 ranked second on the difference between the requirements of businesses and the employees’ ability in practice was the organizing and managing capacity. specifically, enterprises sought, on average, for university graduates to reach 7.7 points, employees achieved only an average of 5.9 points. therefore, the gap between the requirements of enterprises and the practical capacity of workers was about 1.8 points. in addition, the panel discussion also confirmed the higher decentralisation in managing capacity. this complies with higher process integration and cross-functional perspectives. other indicators that also showed that the practical capacities of labor had not kept up with the requirements of businesses were adaptive capacity and creativity and innovation capacity. the average engineering, technology & applied science research vol. 10, no. 3, 2020, 5864-5868 5867 www.etasr.com duong et al.: using fuzzy approach to model skill shortage in vietnam’s labor market in the context … requirement level of enterprises for these two indicators were 8.1 and 8.0 points respectively. however, businesses reported that employees only had 6.5 points for adaptive capacity and 6.6 points for creative capacity. the differences between the requirements of enterprises and the practical capacity of workers for foreign language and lifelong learning were quite small. on average, enterprises required employees to achieve 7.8 points for their ability to use foreign languages, and the actual capacity of workers was 6.6 points. similarly, the indicators for lifelong learning ability were 7.4 points and 6.3 points respectively. the capacity with the smallest gap was the it ability. this finding implies that the importance of continuous learning has been projected by higher education institutions in vietnam to adapt to future qualification requirements derived from industry 4.0 [51, 52]. according to the assessment of enterprises, employees were well equipped for this skill (reaching 7.2 points). therefore, although the requirement for this indicator was quite high (8.2 points), the difference between the requirements of enterprises and the practical capacity of employees was only about 1 point. v. conclusion this paper explored enterprise assessment of university graduates in ho chi minh city to meet the job requirements. the results showed that some industries have surplus labor, some lack labor, while others have too many managers and not enough people to do the work. furthermore, the quality of trained workers has not yet satisfied the requirements of employers. specifically, the authors surveyed seven indicators, namely lifelong learning, adaptive capacity, information technology capacity, creativity and innovation capacity, problem-solving capacity, foreign language competency, and organizing and managing competency. it was shown that the practical capacity of employees is much lower than the requirements of enterprises. the difference was statistically significant. a skill shortage creates unemployment and 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of social economics, vol. 45, no. 2, pp. 316-339, 2018 [54] n. m. ha, “the effect of firm's growth on firm survival in vietnam”, international business research, vol. 6, no. 5, pp. 142-156, 2013 microsoft word 2-2682_s1_etasr_v9_n3_pp4085-4091 engineering, technology & applied science research vol. 9, no. 3, 2019, 4085-4091 4085 www.etasr.com villareal & tongco: multi-sensor fusion workflow for accurate classification and mapping of … multi-sensor fusion workflow for accurate classification and mapping of sugarcane crops marife kung villareal school of engineering, university of san carlos talamban campus, cebu city, philippines and college of engineering and design, silliman university, dumaguete city, philippines mkvillareal27@gmail.com alejandro fernandez tongco school of engineering, university of san carlos, cebu city, philippines aftongco@usc.edu.ph abstract—this study aims to assess the classification accuracy of a novel mapping workflow for sugarcane crops identification that combines light detection and ranging (lidar) point clouds and remotely-sensed orthoimages. the combined input data of plant height lidar point clouds and multispectral orthoimages were processed using a technique called object-based image analysis (obia). the use of multi-source inputs makes the mapping workflow unique and is expected to yield higher accuracy compared to the existing techniques. the multi-source inputs are passed through five phases: data collection, data fusion, image segmentation, accuracy validation, and mapping. data regarding sugarcane crops were randomly collected in ten sampling sites in the study area. five out of the ten sampling sites were designated as training sites and the remaining five as validation sites. normalized digital surface model (ndsm) was created using the lidar data. the ndsm was paired with orthophoto and segmented for feature extraction in obia by developing a ruleset in ecognition software. a rule-set was created to classify and to segment sugarcane using ndsm and orthophoto from the training and validation area sites. a machine learning algorithm called support vector machine (svm) was used to classify entities in the image. the svm was constructed using the ndsm. the height parameter ndsm was applied, and the overall accuracy assessment was 98.74% with kappa index agreement (kia) 97.47%, while the overall accuracy assessment of sugarcane in the five validation sites were 94.23%, 80.28%, 94.50%, 93.59%, and 93.22%. the results suggest that the mapping workflow of sugarcane crops employing obia, lidar data, and orthoimages is attainable. the techniques and process used in this study are potentially useful for the classification and mapping of sugarcane crops. keywordsimage analysis; sugarcane mapping; remote sensing i. introduction global sugar production is approximately 180 million tons. world production is dominated by brazil, followed by india, european union, and thailand. sugarcane occupies about 80% of the world sugar production and is cultivation is concentrated in asia and south/central america [1]. historically, there are recurring supply and demand imbalances reflected in extremely volatile prices on the world market. for the past several decades, world production of sugar has been more than the consumption, leading to low prices and stock overhangs. due to the result of crop failures in one or more of the main producing countries, there have been shorter periods of deficit. because of the crop failures short term price spikes, followed by equally sharp declines occur [1]. increasing attention has been paid to sugarcane plantation in recent years not only for strained sugar supply due to rapid global population increase but also for a growing demand for biomass energy. considering the global environment, sugarcane is an important resource of alcohol which can be processed into biofuels for motor vehicles and generation of electricity. regarding economic and environmental aspects, there is a strong demand for effective methods of providing timely and accurate information on sugarcane growing areas and growth conditions at regional and global scale [2]. despite the contribution of the production of sugarcane to the economic growth in the philippines, there are insufficient records that can help growers make accurate decisions or proper planning to improve production. according to the sugar regulatory administration (sra), the sugar industry contributes about php 87 billion (1.68 billion dollars) to the national economy, with more than 700,000 workers. the productivity contribution of 80% comes from landholdings with size less than 5 hectares and the 1% comes from farms greater than 100 hectares [3]. expanding the production of sugarcane is important to increase yield and maximize profit. the use of remote sensing technology and techniques for detailed mapping and effective data management has facilitated the expansion of small-scale growers and increased agronomic crop yield [4]. object-based image analysis (obia) is gaining much attention in the remote sensing community. it is a subdiscipline of giscience devoted to partitioning remote sensing (rs) imagery into meaningful image objects. the characteristics of obia are assessed through spatial, spectral, and temporal scales [5]. the obia workflows are highly customizable, allowing the presence of human semantics and hierarchical networks [6, 7]. generally, there are two main processes in obia: segmentation and classification. segmentation is the process of grouping adjacent pixels together based on their homogeneity to create meaningful “objects” and these objects are subjected to classification. the segmentation and classification can be processed easily by the different algorithms in ecognition (trimble ecognition version corresponding author: alejandro fernandez tongco engineering, technology & applied science research vol. 9, no. 3, 2019, 4085-4091 4086 www.etasr.com villareal & tongco: multi-sensor fusion workflow for accurate classification and mapping of … 9) because much of the work referred to as obia is originated from ecognition software [8–10]. object-based classification can be done through user-defined rule-sets. studies have been conducted using obia with other remote sensing techniques. authors in [11–13] combined obia with data mining. authors in [14, 15] used obia and images from the landsat/tm/oli and irs/liss-3 satellites. authors in [16] also used landsat/tm/oli for sugarcane mapping, but with modis ev12 time series. authors in [17] used obia procedure for uav images to map and extract information for sugarcane skips in planting row. the use of obia with the ndsm feature from lidar data and orthoimages can provide detailed mapping and aid in the precise inventory of agricultural crops. lidar is one remote sensing tool used in resource mapping, and it has emerged as a powerful active remote sensing method for direct measurement of 3d plant structure in precision agriculture [18, 19]. the lidar-derived digital elevation information makes it invaluable in improving identification and delineation of remotely-sensed data. lidar technology has been applied in several studies concerning crops and geographic features. authors in [20] used the lidar technology to measure sugarcane height. author in [21] applied lidar as a groundbased scanning system for measurements in sugarcane burning operations, whereas authors in [22, 23] used it in mangrove extraction in different coastal areas and as one of the layers during data processing. authors in [24, 25] found that height features derived from lidar data can significantly differentiate between high and low vegetation. in [26], highresolution digital elevation models (dem) derived from remotely sensed lidar data for contrast mapping used the dissimilarity between artificial and natural slopes to identify and to map discrete features. in [27], lidar intensity and height information, contributed to the normalized digital surface model for land-use classification in shady areas. lidar-derived agricultural land-cover map and field surveyvalidated data was used for a theoretical biomass resource assessment, as well as an available potential of sugarcane millbased residue in [28]. multispectral satellite imagery and lidar-derived digital elevation information was used for classifying estuarine vegetation types in [29]. obia, lidar, and orthoimages have been used with several other remote sensing techniques: obia can turn remote sensing into a meaningful image object, lidar has been used to generate a detailed resource mapping, and rgb with orthoimages visually observe the texture information to produce a combination of the three – a promising technological advancement for resource mapping. considering the usefulness of this technique, it is widely studied in agriculture, coastal, and resource mappings, risk management, etc. with the integration of lidar data and high spatial resolution orthoimages, more input data layers are available for object-based svm classification [30, 31]. however, different classes of objects are not separable by direct thresholding. hence, samples from different classes of objects need to be classified using machine learning algorithms [32]. among the machine learning algorithms, the svm is used to classify objects in the image [33]. the svm represents a group of theoretically superior non-parametric machine learning algorithms where there is no assumption made on the distribution of underlying data [34–36]. the basic concept behind svm is to search for a balance between the standardized term and the training errors [37]. svms are not particular with training sample size. it is possible to successfully work with limited quantity and quality of training samples. in fact, only a quarter of the original training samples in an image are required to produce an equally high accuracy for the classification of two crops [38]. the most important characteristic is svm’s ability to generalize from a limited amount and from the quality of training data [39, 40]. the ruleset developed in ecognition and the validation using svm for the classification of sugarcane crops is potentially useful to the crop yield estimation of the sugar industry in the philippines. multi-sensor fusion of lidar data and orthoimages were employed in the sugarcane plantation in philippines. the sugar industry requires spatially explicit tools to provide reliable and precise information on sugarcane areas and on the location of sugarcane fields to improve accuracy in monitoring sugarcane production and yield estimates [41–43]. the study aims to assess the classification accuracy of a novel mapping workflow for sugarcane crops identification that combines lidar point clouds and remotely-sensed orthoimages. this paper demonstrates the rule-set developed in ecognition using lidar data and orthoimages to test and assess accuracy by applying them in the testing and validation sites. svm is used in the validation sites to obtain accuracy results, which would be beneficial to the philippines sugar monitoring agency. ii. materials and methods a. study area medellin is a municipality in the northern part of cebu, philippines. the study area for this mapping is barangay poblacion (11°08'07.0"n 123°57'43” e), which is one of the villages of medellin as shown in figure 1. the main source of income is agriculture, particularly sugarcane crops. fig. 1. map of study area with sugarcane at barangay poblacion, medellin, cebu philippines b. process workflow this study used obia for classification. the process workflow is shown in figure 2. the five phases in the process engineering, technology & applied science research vol. 9, no. 3, 2019, 4085-4091 4087 www.etasr.com villareal & tongco: multi-sensor fusion workflow for accurate classification and mapping of … workflow is data collection, data fusion, image segmentation, accuracy validation, and mapping. fig. 2. process workflow c. data collection lidar data and orthoimages used in this study have been pre-processed by phil-lidar research center at the university of san carlos, talamban-campus. the lidar sensor used was a pegasus at an altitude of 800m and scanning angle of 50 o . the resolution was 1m. data were collected from the sampling sites via visual interpretation from the orthoimages in the study area. according to [22, 44, 45] samples can be collected after segmentation and checked visually in orthoimages. the ndsm provides the height information of the objects that must be classified. the ndsm was produced by subtracting digital terrain model (dtm) from the canopy surface model or digital surface model (dsm). the orthoimage is an aerial rgb photo. using the rgb alone, one can perform obia (segmentation and classification). the best feature to be used in rgb is texture information which can be observed by visual inspection. according to [46] the classification accuracy and reliability are estimated visually using rgb orthomosaic. d. data fusion the ndsm were integrated with orthoimages for image segmentation and rule-set development in ecognition to produce the classified image. the ndsm provided the real heights of the objects above the ground and was segmented according to a certain height threshold. thresholding was done on grayscale images. thresholding an image is classifying these pixels into groups setting an upper and lower bound to each group. the segmentation was done to differentiate highrise objects among others. the ndsm was used from the lidar data by applying plant height thresholds. lidar data provide accurate measurements of land cover structures in the vertical plane but have limited coverage in the horizontal plane. rgb data provided extensive coverage of land cover classes in the horizontal plane but were relatively insensitive to variation in their height. therefore, the integration of lidar and multispectral greatly improved the measurement and mapping of landcover classes [47, 48]. this paper gives emphasis on the classification of a certain class of vegetation which was medium elevation objects with a mean threshold condition of less than or equal to 2.0m in the lidar ndsm. with rgb alone some object classes like trees can be misclassified as grass or something else. this was where lidar data become very useful. the ndsm was the lidar height data normalized with respect to the ground surface. all ground points in ndsm were normalized to zero. e. image segmentation segmentation started with classifying pixels to produce a land cover or land classification result, classification was done on the “segments” or groups of pixels (“object” based classification). there were four image layers used in the objectbased image analysis. these layers were ndsm from lidar and orthophoto consisting of three bands, red, green, blue for pre-segmentation process. image layers were assigned to synchronize the segmentation process. the segmentation process was based on ndsm and orthophoto images. the features used in rgb were texture information which was observed by visual inspection (figures 3-4). the rule-set (figure 5), was developed in ecognition, was used in the five training and the five validation sites in the study area. site no orthophoto ndsm 1 2 3 4 5 fig. 3. training site orthophotos and ndsm of the study area engineering, technology & applied science research vol. 9, no. 3, 2019, 4085-4091 4088 www.etasr.com villareal & tongco: multi-sensor fusion workflow for accurate classification and mapping of … site no orthophoto ndsm 1 2 3 4 5 fig. 4. validation site orthophotos and ndsm of the study area. fig. 5. rule-set applied to the training and validation sites training and validation sites were identified through visual interpretation of the orthoimages. according to [49], the training sites can be interpreted from high resolution imagery. in the segmentation process (figure 6), the high, medium and low elevation objects were classified. the quad tree-based was the first segmentation process using ndsm and having a scale parameter of 2.0m. quadtree segmentation was used to create image objects by cutting and creating squares of different sizes to easily separate images with significant proportion of background. scale parameters values were based on a trial and error principle and a suitable value was found through a series of tests [50]. spectral difference segmentation was conducted with maximum spectral difference of 2.0m. the spectral difference was to merge neighboring image objects if the difference between their layer mean intensities was below the value given by the maximum spectral difference. spectral difference was designed to refine existing segmentation results, by merging spectrally similar image objects produced by previous segmentations. the multiresolution segmentation algorithm consecutively merged pixels or existing image objects. multi-resolution was an optimization procedure which, for a given number of image objects, minimizes the average heterogeneity and maximizes their respective homogeneity. in the pre-classification process, high elevation objects were assigned to a mean ndsm greater than 2.0 (ndsm>2.0). medium elevation was assigned to mean ndsm such as 0.25≤ndsm≤2.0. the objects identified for medium elevation were sugarcane and shrub. the “shrub” class consisted of vegetation or crops that were within the height range of 0.25 and 2 meters. a method needs to be developed on this kind of vegetation. the remaining objects, less than or equal to 0.25m were considered as low elevation objects. after assigning objects, another segmentation process follows, the multi-resolution segmentation. in figure 7, examples of quadtree, spectral difference and multi-resolution segmentation are shown. fig. 6. segmentation process of high and medium elevation objects. fig. 7. examples of (a) quadtree, (b) spectral difference, and (c) multiresolution segmentations. segmentation algorithms were used to subdivide entire images at pixel level, or specific image objects from other domains into smaller image objects. to discriminate other objects, ndsm was used as a discriminating factor to group the objects according to their heights. the orthoimages (rgb) for the texture information of the image were done by visual inspection. f. accuracy validation using svm svm is a supervised learning algorithm used to classify entities in an image. it was used to classify land features in the images. the classified objects were obtained from the (a) (b) (c) engineering, technology & applied science research vol. 9, no. 3, 2019, 4085-4091 4089 www.etasr.com villareal & tongco: multi-sensor fusion workflow for accurate classification and mapping of … segmentation procedure. ndsm was used as a feature to develop the svm model. the process was done by sample collection through manual classification. sugarcane was extracted from the segmented images. the samples collected for sugarcane were 5846. only a quarter of the original training samples in an image were required to produce equally high classification accuracy. the ability of svm to generalize well from a limited amount and/or quality of training data is its most important characteristic [39, 40]. svm was applied to the validation sites to test the accuracy of the samples. g. classification map the final classification map was generated using the qgis software (qgis ver. 2.18 las palmas de g.c.). segmented images from ecognition were exported to qgis as raster files and converted to polygons to generate the classified map for barangay poblacion. sugarcane, shrub, high, and low elevation objects were identified. iii. results and discussion a. classified images sugarcane crops were extracted and classified using ndsm to discriminate and group objects according to their height. multi-resolution segmentation in ecognition was used to delineate medium elevation objects using the setting (scale parameter = 40, shape = 0.2 and compactness = 0.5). sugarcane was identified as a medium elevation object based on ndsm. validation no classified image training site classified image validation site 1 2 3 4 5 fig. 8. classification results on training and validation sites then, samples were collected for sugarcane. orthoimages were used for texture and visual inspection to verify sugarcane crops in the study area. as a result, in the classification process using the svms applied to the training and validation sites, sugarcane was identified as shown in figure 8. a final classified map with sugarcane crops of barangay poblacion is shown in figure 9. fig. 9. land cover classification map of barangay poblacion. b. accuracy assessment overall accuracy and kia for sugarcane are 98.74% and 97.47% respectively. accuracy results were obtained after svm using ecognition. table i is an example of the confusion matrix. accuracy assessment and kia for each validation site are shown in table ii. table i. accuracy assessment after svm. confusion matrix user class/sample sugarcane shrub sum sugarcane 5846 109 5955 shrub 30 5043 5073 sum 5876 5152 accuracy producer 0.9948945 0.978843 user 0.9816961 0.994 hellden 0.9882512 0.986406 short 0.9767753 0.973176 kia per class 0.989 0.96082 totals overall accuracy 0.9873957 kia 0.9746584 accuracy and kia results in validation site 2 were low compared to the other sites due to the area coverage and misclassifications of sugarcane class as shrub class. the similarities in spectral characteristics of sugarcane crops with other vegetation such as shrub, result to low accuracy [29]. experimenting on other lidar derivatives was needed to improve classification and segmentation [22]. the overall accuracy assessment for each validation site shows that sugarcane is correctly classified. according to [51], the kappa statistic or kia indicates the extent to which the classification result is better than pure chance: the higher the kia value, the greater the classification accuracy. with the overall accuracy results, this study will be able to address the existing problem engineering, technology & applied science research vol. 9, no. 3, 2019, 4085-4091 4090 www.etasr.com villareal & tongco: multi-sensor fusion workflow for accurate classification and mapping of … of sra and provide accurate information for policy makers in the sugar industry. table ii. accuracy assessment after svm for each validation site. validation site accuracy assessment (%) kia (%) 1 94.23 78.91 2 82.76 58.63 3 94.50 71.90 4 93.59 85.46 5 93.22 67.67 c. assessment of the system workflow the graph of the different overall accuracy assessment, kia and accuracy for sugarcane in the five validation sites is shown in figure 10. fig. 10. graph of sugarcane accuracy assessment and kia. the high accuracy of the results indicates that the process workflow developed in this study is applicable and useful in the classification of sugarcane crops in other areas. the overall high accuracy is comparable with using traditional data and techniques [22]. this study extracts sugarcane crops in barangay poblacion medellin cebu. the high accuracy results of the developed process can be used for mapping and monitoring of sugarcane crops in philippines and in other sugar producing countries. iv. conclusion this study developed a mapping workflow to assess classification accuracy for sugarcane crop identification using obia, lidar data and orthoimages. the accuracy results in the validation sites were 94.23%, 80.28%, 94.50%, 93.59% and 93.22%, and the overall accuracy result was 98.74% (kia was 97.47%). therefore, using this workflow in identifying sugarcane in other areas with acceptable accuracy assessment is possible. this can contribute to regional and global scale of providing information on sugarcane growing areas and growth conditions. further research with additional samples is necessary in order to improve the workflow. the data used in the process are essential because the workflow is dependent on the images provided by lidar or any other remote sensing technology. acknowledgement authors wish to thank phil-lidar research center at the university of san carlos, talamban campus for the provided data, and silliman university for the financial support. references [1] canadian sugar institute, global sugar trade (wto), available at: https://sugar.ca/international-trade/global-sugar-trade-(wto).aspx [2] l. hui, j. chen, z. pei, s. zhang, x. hu, “monitoring sugarcane growth using envisat asar data”, ieee transactions on geoscience and remote sensing, vol. 47, no. 8, pp. 2572–2580, 2009 [3] bureau of agricultural statistics, 23rd annual publication, 2012 [4] e. m. abdel-rahman, f. b. ahmed, “the application of remote sensing techniques to sugarcan (saccharum spp. hybrid) production: a review of the literature”, international journal of remote sensing, vol. 29, no. 13, pp. 3753-3767, 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pp. 227-242, 2013 [51] t. m. lillesand, r. w. kiefer, j. chipman, remote sensing and image interpretation, john wiley & sons, 2004 ab cap and eff mi we cur the we ele loa a n pro ele aut oft stru adv and use dim las th lig sim is we mo 2]. me and inv joi cur we sur we engineerin www.etasr the prope departm bstract—in this pacity of the re d the tensile sh fects of differ crohardness a eld processes rrents and 2-6 e welded mate ere determined ectrode pressur ad bearing capa negative effect keywords-dp operties; expuls resistance s ectrical weldin tomotive indu ten preferred ructure is ofte vantages of sp d economical er requiremen mensions. for ser welding or his will allow ghter and have mple manufact accepted tha eldability, and orphology and . after spot echanical and d heat affec vestigate these ints. the prim rrent, electrod elding parame rface appearan eld internal dis ng, technology r.com effect erties o muhamm faculty of ment of manu karabuk u karabuk melitas@ka s study, the ma esistance spot w hear propertie rent welding and tensile sh were perform 6bar electrode erials was eva d. experiment re and weld c acity. it was al on the tensile s p1000 steel; wel sion i. in spot welding ng processes. ustry especiall as the joinin en joined wi pot welding ar . however, to nts, the part r this reason, i combination o the engine ind improved rigi turing process at the availa d this depend d the mechanic weld, consi metallurgical cted zone (h e changes for mary welding de pressure) eters also affe nce, weld nu scontinuities [5 y & applied sci elitas & ts of th of rsw med elitas technology ufacturing eng university k, turkey arabuk.edu.tr aximum tensile welded dp1000 s of the joints parameters ear properties med by using pressures. th aluated and th al results show urrent increas lso observed th shear load bear lding; microha troduction (rsw) is rsw is a p ly for sheet m ng technique. ith the spot re that it is rela o apply spot ts must have it is expected of joined techn dustry to build idity and stren s. for automo able material ds on the sh cal properties o iderable chan l properties of haz). it is the safety stre parameters (w affect the h fect welding q ugget size, we 5]. ience research & demir: the ef he we w jun gineering e shear load be 0 steel was mea were evaluated on microstru s were investi 5ka and 7ka he microstruct he hardness p wed that incr sed the tensile hat the expulsio ring capacity. ardness; tensile one of the process used i materials, wh automobile welds [1, 2] atively fast, du welds and to e somewhat to be replaced niques in the f d structures th ngth [1-4]. rsw otive applicatio has a good heet thickness of the base me nges occur in f the rsw re very importa ength of the w weld time, we eat input. pr quality factor eld penetration h v effects of the w elding nctions earing asured d. the ucture, igated. a weld ure of rofiles easing shear on had e shear oldest in the hich is body . the urable meet large d by a future. hat are w is a ons, it d spot s, the etal [1, n the egions ant to welded elding rimary rs like n and she 24% is o are rap valu stee stee abb and thin firs cur esti uni dp rela pro aca stee opt des diff dp 500 dp the dp tab vol. 8, no. 4, 20 welding paramet param s of d dep it is reported eet metal used %. the produc of significant i widely prefe idly in the au ues per unit els were used els is becomin breviation expr d it is seen th nner section a st generation rrently, it is he imated that it w que economic 1000 steel wa ated to the eff operties of the ademic workin el was studied timum levels o sired quality [7 ferent welding 1000 steel wa ii the commer 0x500mm and 1000 steel ma e microstructu 1000 automo ble i, respectiv fig 018, 3116-3120 ters on tensile meters p1000 bilg faculty o partment of me karabuk karabu bdemir@k d that the effe d in automobi ction of these importance. e erred. the us utomotive indu weight. whil initially, today ng more wide ress the tensile hat materials w are more prefe of the adv eavily used in will continue t c and techno as used. there fect of the rs e dp1000 ste ng and industr d in detail. it is of the welding 7]. in the exp g current and s aimed. i. experime rcial dp1000 d had 1.2mm t ainly consists ure and chemi tive sheet ste vely. g. 1. microstru 0 properties of r s on te 0 shee ge demir f engineering echanical eng k university uk, turkey karabuk.edu.tr ect of reducin iles on vehicl parts with new especially dual e of these st ustry due to th le dp350, d y the use of d espread. the e strength of th with higher te erred [6]. dual anced autom the automotiv to be used in th ologic properti are very few sw process o eel. due to th rial area, rsw s very importa g parameters t perimental stud d electrode pr ental proced 0 automotive thickness. the of ferrite and ical composit eel are shown ucture of dp1000 3116 rsw junctions ensile et stee g gineering r ng the thickne le weight is a w generation s l phase (dp) s teels has incre heir higher stre dp500, and d dp760 and dp numbers afte he material in ensile strength l phase steel i motive sheet ve industry and he future, due ies. in this s studies in liter on the tensile heir importan w of the dual p ant to determin to obtain a we dy, optimizatio essure in rsw dure sheet steel e microstructu martensite ph ion of comme n in figure 1 0 steel s of … el ess of about steels steels eased ength dp600 p1000 er dp mpa h and is the steel. d it is to its study, rature shear ce in phase ne the eld of on of w of was ure of hases. ercial 1 and m 14 spe ele [8] pre sam thi par sho (1c fig ste we po nit usi use me qn hv ma dis reg me the spo 1.2 cro [8] a. th engineerin www.etasr table i. material c dp1000 0.136 al 0.044 the specime 273 standard ecimen is show fig. specimens w ectrodes with ]. the applied essures were mples for each is study was c rameters used own in tab cycle=0.02s). a gure 3. transv eel and specim elded pieces w lished specim tric acid + 98% ing a nikon e ed in the micro easurements. m nees type v v0.2 (1.961n apping using stribution and gions of we easurements w e nugget. ten ot welded spec 2mm thickness osshead speed ]. fig i microstructu in this study hese samples’ ng, technology r.com chemical c si mn 6 0.203 1.57 ti v 4 0.001 0.00 ens were prepa ds for rsw. wn in figure 2 2. the techn were subjecte flat conical tip d currents were 2-6bar. rsw h electrode pre carried out con d in the liter ble ii [9, 1 a resistance s verse metallog mens passing were prepared mens were etch % methanol). epiphot 200 l ostructure ana microhardness vickers microh ) load and 1 0.2mm grid d the individu elded joints were made in o nsile shear tes cimens. resis s, 30mm widt d used for the g. 3. resistanc iii. result ure y, ten differen structures w y & applied sci elitas & composition of d n p s 7 0.021 0.0 nb c 09 0.021 0.0 ared in accord the technica 2. nical drawing of sp ed to rsw u p at different e 5ka and 7ka w was applie essure. the rs nsidering som rature and the 0]. time un spot welded sp graphic specim through the d by the stan hed with a 2% the microstru light microsco alyses were als s testing was hardness testin 5s holding ti spacing reve ual hardness [8, 10]. o one direction, ts were perfo tance spot we th and 110mm tensile shear ce spot welded sp ts and discus nt rsw samp were examine ience research & demir: the ef dp1000 steel (%) s cr 003 0.022 0 u fe 01 97.897 0 dance with en al drawing o pecimen using 8mm c welding param a and the elec ed by taking sw process u me of the ideal ese parameter nit is cyclepecimen is sho mens of the dp central part o ndard method % nital solution ucture was ana ope. the spec so used for har conducted us ng machine w me. microhar ealed the har values in se on each sa along the rad ormed on resis lded specimen m gauge length test was 2mm pecimen sion ples were obt d visually an h v effects of the w ni 0.039 co 0.021 n iso of the copper meters ctrode three used in rsw rs are -based own in p1000 of the d. the n (2% alyzed cimens rdness sing a with a rdness rdness elected ample, dius of stance ns had h. the m/min tained. nd by ster that an e sam ima sho mic men esti hig ther fig fig. pres fig. pres ha mar it w ferr 12] mic dp stre rise the thin not mic vol. 8, no. 4, 20 welding paramet reo and optic t welding sam example of we mple welded ages of haz own at figur crostructures o ntioned in th imated for gen her alloying c refore higher h g. 4. macro s (a) 5. haz and ssures and 5ka we (a) 6. haz and ssures and 7ka we contrast to th azs of the r rtensite althou was observed rite and marte . indeed, the crostructures 1000 compris ength as 1000 es essentially w weld metal i nness and the t enough tim crostructure in 018, 3116-3120 ters on tensile microscopy. v mples were obt eld profile as m with 7ka-2 and weld me res 5 and 6 of the weld me he related lite neral grade of ontent of the c hardenability. tructure of dp100 (b) d weld metal m elding current a) (b) d weld metal m elding current a) he related lite rsw sample ugh little lowe that, dual pha ensite phases main differen is the marten ses higher mv mpa because with the hard m is quite high e water-cooled me for carb n the weld m 0 properties of r visual inspect tained normal macro structur 2bar. moreov etal of the all 6. as seen etal are formed erature, these f dual phase st commercial du 00 rsw sample w (c) (d) microstructures 2bar, b) 3bar, c) 4 (c) (d) microstructures 2bar, b) 3bar, c) 4 erature, it cou es are showin ering througho ase microstruc for all electr nce between d nsite volume vf than dp60 e the strength martensite pha because sheet d electrodes. t bon diffusion metal and ha 3117 rsw junctions tion results sh lly. figure 4 s re of dp1000 r ver, microstru rsw sample in these fig d as martensite e results coul eels because o ual phase steel welded with 7ka(e) at different ele 4bar, d) 5bar, e) 6 (e) at different ele 4bar, d) 5bar, e) 6 uld be said tha ng nearly w out transition ctures consist rode pressures dp600 and dp fractions (m 00 to ensure h of dual phase ase. cooling ra t metal specim therefore, the n. as a r az predomin s of … owed shows rsw ucture es are gures, es. as ld be of the ls and -2bar ectrode 6bar ectrode 6bar at the wholly zone. ed of s [11, p1000 mvf). higher steel ate in mens’ ere is result, nantly con thr ele dis me and b. sho the rs the ho ma un ste str ma con den tra go mo ma ma res ver tra ph zon be usa dep au the ind du we flo sol aus fas all for int sam als the engineerin www.etasr nsists of marte roughout the ectrode pressu ssolved in the etal increases b d therefore thi table ii. e microhardne microhardne own in figure e weld metal sw process. t e base metal. a owever, as har ay decrease. derstand the eels [13, 14]. rengthening m artensite is st nsists of high nsity. this is ansformation t od resistance ovements in artensite and artensite and spectively in ry fast heating ansformation. ase, even som nes have high evaluated th able range for pendence on uthors in [11] r e generation duction which al phase steel elding, melting owing and sq lidification, a stenite decom st. because of oy elements’ r dp1000, hi teresting result mples showed so may be abl e effects of the ng, technology r.com ensite phase [1 base metal, ures. this is e e austenite fro because of rap is may increas welding pa electrode press welding curre electrode tip diam down time (c squeeze time welding time hold time (c separation tim ess ess results obt es 7 and 8. it in dp steels the hardness c as hardness i rdness increas therefore, it hardness and martensitic tr mechanism for trong phase d carbon conten due to the vo to martensite. barrier again dual phase ferrite phases ferrite volum dp1000 steel g and cooling c in welding, w me haz also co her hardness th hat hardness v r all welding p martensite is reported that, of higher am h causes highe ls essentially g and then so queezing stag austenitization mposition occu f these fast c content, weld igher compar t about hazs d higher hard le to explain w e hardenability y & applied sci elitas & 1, 11]. genera haz and w explained as om base meta pid cooling af e the mvf” [1 arameters for r sure(bar) ent (ka) meter(mm) cycle) (cycle) (cycle) cycle) e (cycle) tained in the r can be seen t increases con can become ab increases, stren ses, embrittlem t is importan d metallurgica ransformation r steels. it is due to its mi nt and high un olume expansi hard and stro nst dislocatio structure. d s at the begin me fractions a l. during weld cycle leads aus weld metal co ools from aust han the base m values of the parameters. t s a good wa increasing of mount of mart er hardness [1 contain two p olidification oc ges. through n and then ur. here, cool cooling rates d metal has h ed to dp600 s from dp600 dness than dp what was disc y and cooling ience research & demir: the ef ally, mvf incr weld metal fo “the rate of al towards the fter welding pr 10]. rsw processing 2-6 5-7 8 15 35 20 10 15 rsw process that the hardn nsiderably aft bout 2 times t ngth also incr ment and toug nt to analyze al structure o is a hardenin s well known icrostructure w nmobile dislo ion during aus ong martensit n slip action dp steels co nning of the are 70% and ding processe stenite to mart ools from aus tenite and thus metal [15]. it e specimens a to explain hard ay [9, 10, 12 heat input incr tensite deform 1]. in other w phases. during ccurs at the c hout weld co transformatio ling rates are and higher am higher hardena 0. there is a . haz of the p600. these r cussed above rates on prop h v effects of the w reased for all ferrite e weld rocess es are ness of er the that of reases. ghness e and of dp ng and n that which cation stenite te is a ns and ontain rsw. d 30% es, the tensite stenite s these could are in dness, , 15]. reases mation words, g spot current ooling on or quite mount ability a very rsw results about erties. as har rela mat har con carb rule par seen 7ka fig. weld fig. weld c. cap mea eva tens wer she hav sam tens vol. 8, no. 4, 20 welding paramet seen in figu rdness. sever ationships bet terial’s hardne rdness, in cas ntent, is expec bon content o e. all weld m rameters have n in figures 7 a and 5ka sam 7. hardness d pressures 8. hardness d pressures tensile prope in this study pacity of the asured and t aluated [10]. t sile shear pro re performed t ear load bearin ving effect on t mples are give sile-shear load 018, 3116-3120 ters on tensile ures 7 and 8, ral researche tween marten ess. author in se of exceedi cted to be mo f the used stee metal specimen shown hardne 7 and 8 whic mples hardness values of the 5k values of the 7k erties y, the maxim specimens du the strength the effects of operties were to the joined s ng capacity w the joint quali en in figure d bearing capa 0 properties of r higher marten ers have giv nsite mass ca n [16] reporte ing 0.05% o ore than 350h el sheet mater ns’ hardness o ess values high h show the d s results. ka weld current ka weld current mum tensile s uring the tens properties of different weld investigated. samples to dete which is one ity. tensile she 9. as can be acity pertains t 3118 rsw junctions nsite means h ven some u arbon content ed that, marte f mass of ca hv. in this s rials confirmed f different we her than 350h differences bet samples with di samples with di shear load be sile shear test f the joints ding paramete tensile shear ermine their te of the param ear forces of a e seen, the hi to the sample o s of … higher useful t and ensite arbon study, d this elding hv as tween fferent fferent earing t was were ers on tests ensile meters all the ighest of the joi co see we fig par has the exp res q= r= ele cur the we cap ele ob inc the she det ele alw she occ we pre we liq del tou ene 7k exp she litt spo wh see engineerin www.etasr ined at 3bar onversely, the en for the sa elding current. g. 9. maximum rameters when the ef s been observ e tensile shea planation can sistance spot w =i2rt equation =total resistan ectrode pressu rrent increase e heat input of elding. this, in pacity of weld ectrode pressur served from creases heat in ey all stated th ear load bearin expulsion fo termined by m ectrical, metall ways occurs at eets or the curring at the elding time, essure. as the eld metal exce quid nugget a lineates the w ughness agains ergies of the ka-6bar) are pulsion. comp ear load beari tle smaller. c ot welded join hen the tensil en that incre ng, technology r.com electrode p lowest tensile mple joined m tensile shear fo ffects of electr ved that increa ar load beari n be that hea welding which n where i=cur nce and t=w ure, total res s. this increa f the sample d n turn, increas ded joints [17 re in rsw has figure 9 th nput. authors hat increasing ng capacity of ormation durin many complica lurgical, and m t the faying su electrode/wo faying surface welding cur e total useful w eds a critical v and expulsion weld energy ab st loads. as ca welds with smaller than mpared to weld ing capacity o consequently, nts is usually d le shear curve easing electro y & applied sci elitas & pressure, 7ka e shear load be at 4bar electr orce values obtain rode pressures asing electrode ing capacity at input in th h is calculated rrent passing t welding time sistance r de ase in the wel during current ses the tensile 7]. author in s affected the j hat increasing in [19-22] inv welding curre f the samples. ng the weldin ated paramete mechanical pr urface of the up orkpiece inte es is often a re rrent or ins welding heat value, the molt n happens [2 bsorption cap an be seen in f expulsion (5k the ones of ds without ex of the welds w quality contro determined by es in figure 9 ode pressure ience research & demir: the ef a welding cu earing capaciti rode pressure, ned at different w s were evalua e pressure incr of the joints e welding zo d by the use through the sa . with incre ecreases whe ld current incr passing time e shear load be [18] indicate joint’s strength g welding c vestigated rsw ent increased t ng process is ers, such as the rocesses [23, 2 pper and lowe erfaces. expu esult from exc sufficient elec implemented ten metal crac 25]. failure e ability and fr figure 9, the f ka-4bar, 7ka the welds w xpulsion, the t with expulsion ol of the resis y tensile shear 9 are analyzed and weld c h v effects of the w urrent. ies are , 5ka welding ated, it reases s. an one in of the ample, easing en the reases of the earing d that h. it is current w and tensile often ermal, 24]. it r steel ulsion essive ctrode to the cks the energy acture failure a-4bar, without tensile n is a stance r tests. d, it is current incr that cap mea eva mic inv 1. 2. 3. 4. 5. 6. 7. pro tur [1] [2] [3] [4] [5] [6] vol. 8, no. 4, 20 welding paramet reases the tens t this in turn in in this study pacity of the asured and t aluated. the crostructure, m estigated. the it could be sa formed as ma showing near generally, m welding param the hardness increases afte about 2 times that, haz an metal. all rsw sa different para 350hv. thes this study. it was observ shear load be joined at 7ka it is seen th current increa compared to load bearing 4bar, 7ka-4b this work w ojects coordin rkey). project n m. elitas, b. d tensile strength sheet steel”, 2 technology in c b. demir, “an aisi 4140 an fractions”, met 1159-1166, 200 y. cho, s. rhe spot welding”, w c. a. campos, of galvannealed pp. 876-881, 20 f. hayat, b. de current on the m en 10130–199 2009 b. aydemir, e. properties of d resistance spot 687, pp. 17-28, 018, 3116-3120 ters on tensile sile shear load ncreases the to iv. co y, the maxim specimens d the strength effects of di microhardness e conclusions r aid that micros artensite and h rly wholly mar martensite volu meters. s of the weld er the rsw s compared to nd weld metal amples, whic ameters, show se were explai ved that, the earing capaciti a-3bar and 5ka hat increasing ased the tensil o welds witho capacity of t ar, 7ka-6bar) acknow was supporte nation unit of number: kbu refer emir, o. yazici, “ h and fracture m 2nd international cappadocia, nev investigation on nd its impact str tallofizika i nove 07 ee, “experimental welding journal, m. p. guerrerod interstitial free s 002 emir, m. acarer, mechanical prope 99) steel”, metalli aydemir, e. kal dp1000 steel shee welded (rsw)”, 2017 0 properties of r d bearing capa oughness of the onclusions mum tensile s during tensile properties of ifferent weldi and tensile sh resulting from structures of th hazs of the r rtensite. ume fractions metal in dp s process. hard the base meta l had higher h h had been wed hardness v ined with carb highest and t ies pertain to a-4bar respect g electrode pr e shear load b out expulsion, the welds with was a little sm wledgment ed by the s f karabuk un ubap-17-kprences “the effects of th modes of the rsw conference on sehir, turkey, oc the production o rength at differe eishie tekhnolog l study of nugget vol. 82, no. 8, p -mata, r. colas, steel”, isij intern s. aslanlar, “effe erties of resistanc ic materials, vol luc, “investigatio ets joints with re , engineer and m 3119 rsw junctions acity. it can be e joints. shear load be e shear tests f the joints ing parameter hear properties this study are he weld metal rsw samples s increased fo steels conside dness can inc al. it was obse hardness than welded by u values higher bon content rul the lowest ten the samples o tively. ressure, and bearing capacit , the tensile h expulsion ( maller. cientific res niversity (kara -463. he electrode press w junctions of d material scienc ctober 11-13, 2017 of dual-phase stee ent martensite v ii , vol. 29, no. formation in resi pp. 195-201, 2003 r. garza, “weld national, vol. 42, fect of welding tim ce spot welded if l. 47, no. 1, pp. on of tensile and f emote laser (rlw machinery, vol. 5 s of … e said earing was were rs on were : were were or all erably crease erved base using r than les in nsileof the weld ty. shear (5kaearch abuk, sure on dp600 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conditions in matlab/simulink environment and also with real time digital simulator (rtds) hardware. when the supply voltages are balanced and sinusoidal, the two control strategies are converging to the same compensation characteristics but when the supply voltages are distorted and/or un-balanced sinusoidal, these control strategies result in different degrees of compensation in harmonics. the p-q control strategy is unable to yield an adequate solution when source voltages are not ideal. extensive simulations are carried out with pi controller for both p-q and id-iq control strategies for different voltage conditions and adequate results were presented. the 3-ph 4-wire shaf system is also implemented on rtds hardware to further verify its effectiveness. the detailed simulation and rtds hardware results are included. keywordsharmonic compensation, shaf, p-q control strategy, id-iq control strategy, pi controller, rtds hardware. i. introduction harmonics surfaced as a buzz word from 1980’s which always threaten the normal operation of power system and user equipment. highly automatic electric equipments, in particular, cause enormous economic loss every year. owing both power suppliers and power consumers are concerned about the power quality problems and compensation techniques. sinusoidal voltage is a conceptual quantity produced by an ideal ac generator built with finely distributed stator and field windings that operate in a uniform magnetic field. since neither the winding distribution nor the magnetic field are uniform in a working ac machine, voltage waveform distortions are created, and the voltage-time relationship deviates from the pure sine function. the distortion at the point of generation is very small (about 1% to 2%), but nonetheless it exists. since this is a deviation from a pure sine wave, the deviation is in the form of an episodic function, and by definition, the voltage distortion contains harmonics [1]. it is noted that non-sinusoidal current results in many problems for the utility power supply company, such as: low power factor, low energy efficiency, electromagnetic interference (emi), distortion of line voltage etc. and it is noted that, in three-phase four-wire system, zero line may be overheated or causes fire disaster as a result of excessive harmonic current going through the zero line three times or times that of three. thus a perfect compensator is necessary to avoid the consequences due to harmonics [2]. though several control strategies have been developed but still two control theories, instantaneous active and reactive currents (id–iq) method and instantaneous active and reactive power (p-q) methods [3-4] are always dominant. the present paper is mainly focused on two control strategies (p-q and id-iq) with pi controller. to validate current observations, extensive simulations are carried out with pi controller for both p-q and id-iq methods for different voltage conditions like sinusoidal, non-sinusoidal, and un-balanced conditions and adequate results were presented. the 3-ph 4-wire shaf system is also implemented on a real time digital simulator (rtds hardware) [5] to further verify its effectiveness. ii. control strategy in this section two control strategies are discussed in detail. ideal analysis has done in steady state conditions of the active power filter. steady state analysis, using fast fourier transform (fft) for the two control methods that are presented, is briefly enlightened below. figure 1 shows a basic architecture of three-phase four wire shunt active filter. l a i l b i l c i cv * c a i * c b i * c c i 1dc v 2dc v fa i fb i fc i av bv cv av bv lossp 1 c 2 c sc i sb i sa i 0s i la i lb i lc i 0l i ca i cb i cc i c b a ε c r fig. 1. three-phase four wire shunt active filter. etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 54-62 55 www.etasr.com suresh and panda: simulation and rtds hardware implementation of shaf… a. instantaneous real and reactive power method k ε v△ ε * i + ∆(1 ε)ca * i ∆(1 ε)ca ∼   ∼  ∼  ∼ ≈ ∼  α β ο transf. & power calcul. α β ο transf. & power calcul. α β volt re fer. pll & sine gener i la i lb i lc 50hz 50hz p' q′ p' q′ α β current re fer. * icα * i cβ α β ο inverse transf. * ica * i cb * icc va v b vc i β ′ iα′ v dc1 v dc2 dc voltage regulator v ref 50hz v *α v * β p q i 0 20hz 20hz ploss �p v△ 5%v ref 1 i fa s1 s2 s3 s4 s5 s6 + + − − − i fa i fc i fb i fa fig. 2. control block diagram of shunt active power filter. transformation of the phase voltages va, vb, and vc and the load currents ila, ilb, and ilc into the α β orthogonal coordinates are given in equation (1-2). the compensation objectives of active power filters are the harmonics present in the input currents. present architecture represents three phase four wire and it is realized with constant power controls strategy [6]. figure 2 illustrates control block diagram and inputs to the system are phase voltages and line currents of the load. it was recognized that resonance at relatively high frequency might appear between the source impedance. so a small high pass filter is incorporated in the system. the power calculation is given in detail form in equation (3). v v v v v 1 1 1 2 2 2 0 a 2 1 1 = 1 vα b3 2 2 β c3 3 0 2 2                              (1) 1 1 1 2 2 2i i 0 l a 2 1 1 i = 1 iα l b3 2 2 i iβ 3 3 l c 0 2 2                                   (2) p v 0 0 i 0 0 0 p = 0 v v iα αβ q i 0 v -v βαβ                              (3) from figure 2 we can observe a high pass filter with cut off frequency 50 hz separates the powers p~− from p and a low-pass filter separates 0 p from 0 p . the powers p~ and 0 p of the load, together with q, should be compensated to provide optimal power flow to the source. it is important to note that system used is three phase four wire, so additional neutral currents has to be supplied by the shunt active power filter thus ploss is incorporated to correct compensation error due to feed forward network unable to suppress the zero sequence power. since active filter compensates the whole neutral current of the load in the presence of zero-sequence voltages, the shunt active filter eventually supplies po. consequently if active filter supplies po to the load, this make changes in dc voltage regulator, hence additional amount of active power is added automatically to ploss which mainly provide energy to cover all the losses in the power circuit in the active filter [7]. thus, with this control strategy shunt active filter gains additional capability to reduce neutral currents and there-by supply necessary compensation when it is most required in the system. thus the αβ reference currents can be found with following equation.       +−       −+ =         qp∆p~1 22* * αβ βα βαβ νν νν ννc ca i i (4) ∆ p = 0 loss p p+ where p~ is the ac component / oscillating value of p, 0 p is the dc component of p0, etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 54-62 56 www.etasr.com suresh and panda: simulation and rtds hardware implementation of shaf… loss p is the losses in the active filter, loss p is the average value of loss p , ∆ p provides energy balance inside the active power filter and using equation (5) inverse transformation can be done. * * 1 1 0 2 -ii * 0ca 2 1 1 3 i * = icαcb 3 2 22 ii * cβcc 1 1 3 2 22                                   (5) where ica*, icb*, icc* are the instantaneous three phase current references in addition pll (phase locked loop) employed in shunt filter tracks automatically, the system frequency and fundamental positive–sequence component of three phase generic input signal. appropriate design of pll allows proper operation under distorted and unbalanced voltage conditions. controller includes small changes in positive sequence detector as harmonic compensation is mainly concentrated on three phase four wire [8]. as we know in threephase three wire, va′, vb′, vc′ are used in transformations which resemble absence of zero sequence component and it is given in equation (6). thus in three phase four wire it was modified as vα′, vβ′ and it is given in equation (7). 1 0 v 'a v 'α2 1 3 v ' = v 'b 3 2 2 β v 'c 1 3 2 2                             (6) i ' -i 'v ' α βα p'1 = v ' 2 2 i ' i ' q'i ' + i 'β αβα β                   (7) the dc capacitor voltages vdc1 and vdc2 may be controlled by a dc voltage regulator. a low-pass filter with cut-off frequency 20hz is used to render it insensitive to the fundamental frequency (50hz) voltage variations. the filtered voltage difference =v= vdc2-vdc1 produces voltage regulation ε according to the following limit function generator: ref ref ref ref ref 1; v 0.05v v ; 0.05v v 0.05v 0.05v 1; v 0.05v ε ε ε = − ∆ < − ∆ = − ≤ ∆ ≤ − = ∆ > where vref is a pre-defined dc voltage reference and 0.05vref was arbitrarily chosen as an acceptable tolerance margin for voltage variations. if (vdc1 + vdc2) < vref, the pwm inverter should absorb energy from the ac network to charge the dc capacitor. the inverse occur if (vdc1 + vdc2) > vref. the signal loss p generated in the dc voltage regulator is useful for correcting voltage variations due to compensation errors that may occur during the transient response of shunt active filter. b. instantaneous active and reactive current method (id – iq) in this method reference currents are obtained through instantaneous active and reactive currents id and iq of the non linear load [9-10]. calculations follows similar to the instantaneous power theory, however dq load currents can be obtained from equation (8). two stage transformations give away relation between the stationary and rotating reference frame with active and reactive current method. figure 4 shows voltage and current vectors in stationary and rotating reference frames. the transformation angle ‘θ’ is sensible to all voltage harmonics and unbalanced voltages; as a result dθ/dt may not be constant. arithmetical relations are given in equation (8) and (9); finally reference currents can be obtained from equation (10). − + fig. 3. active powers filter control circuit. d α β α 2 2 q β α β α β i v v i1 = i -v v iv + v                (8) where iα , iβ are the instantaneous α-β axis current references d α q β i icosθ sinθ = i i-sinθ cosθ                (9) d 2 2 q icic v v1 icic v vv v α α β β β αα β −      =      +     (10) where icd ,icq are compensation currents . etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 54-62 57 www.etasr.com suresh and panda: simulation and rtds hardware implementation of shaf… one of the advantages of this method is that angle θ is calculated directly from main voltages and thus makes this method frequency independent by avoiding the pll in the control circuit. consequently synchronizing problems with unbalanced and distorted conditions of main voltages are also evaded. thus id – iq achieves large frequency operating limit essentially by the cut-off frequency of voltage source inverter (vsi) [11]. figures 3 and 5 show the control diagram for shunt active filter and harmonic injection circuit. on owing load currents id and iq are obtained from park transformation then they are allowed to pass through the high pass filter to eliminate dc components in the nonlinear load currents. filters used in the circuit are butterworth type and to reduce the influence of high pass filter an alternative high pass filter (ahpf) can be used in the circuit. it can be obtained through the low pass filter (lpf) of same order and cut-off frequency simply difference between the input signal and the filtered one, which is clearly shown in figure 5. butterworth filters used in harmonic injecting circuit have cut-off frequency equal to one half of the main frequency (fc=f/2), with this a small phase shift in harmonics and sufficiently high transient response can be obtained. fig. 4. instantaneous voltage and current vectors. fig. 5. park transformation and harmonic current injection circuit. the function of voltage regulator on dc side is performed by proportional – integral (pi) controller, inputs to the pi controller are, change in dc link voltage (vdc) and reference voltage (vdc*), on regulation of first harmonic active current of positive sequence id1h + it is possible to control the active power flow in the vsi and thus the capacitor voltage vdc. in similar fashion reactive power flow is controlled by first harmonic reactive current of positive sequence iq1h + . on the contrary the primary end of the active power filters is just the exclusion of the harmonics caused by nonlinear loads hence the current iq1h + is always set to zero. iii. construction of pi controller figure 6 shows the internal structure of the control circuit. the control scheme consists of pi controller [12], limiter, and three phase sine wave generator for reference current generation and generation of switching signals. fig. 6. conventional pi controller the peak value of reference currents is estimated by regulating the dc link voltage. the actual capacitor voltage is compared with a set reference value. the error signal is then processed through a pi controller, which contributes to zero steady error in tracking the reference current signal. the output of the pi controller is considered as peak value of the supply current (imax), which is composed of two components: (a) fundamental active power component of load current, and (b) loss component of apf; to maintain the average capacitor voltage to a constant value. peak value of the current (imax) so obtained, is multiplied by the unit sine vectors in phase with the respective source voltages to obtain the reference compensating currents. these estimated reference currents (isa*, isb*, isc*) and sensed actual currents ( isa, isb, isc ) are compared at a hysteresis band, which gives the error signal for the modulation technique. this error signal decides the operation of the converter switches. in this current control circuit configuration, the source/supply currents isabc are made to follow the sinusoidal reference current iabc, within a fixed hysteretic band. the width of hysteresis window determines the source current pattern, its harmonic spectrum and the switching frequency of the devices. the dc link capacitor voltage is kept constant throughout the operating range of the converter. in this scheme, each phase of the converter is controlled independently. to increase the current of a particular phase, the lower switch of the converter associated with that particular phase is turned on while to decrease the current the upper switch of the respective converter phase is turned on. with this one can realize, potential and feasibility of pi controller. the actual source currents are monitored instantaneously, and then compared to the reference currents [13] generated by the proposed algorithm. in order to get accurate instantaneously control, switching of igbt device should be such that the error signal should approaches to zero, thus provides quick response. for this reason, hysteresis current controller with fixed band which derives the switching signals of three phase igbt based vsi bridge is used. the upper device and the lower device in one phase leg of vsi are switched in complementary manner else a dead short circuit will be take place. the apf reference currents isa, isb, isc compared with sensed source currents isa, isb, isc and the etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 54-62 58 www.etasr.com suresh and panda: simulation and rtds hardware implementation of shaf… error signals are operated by the hysteresis current controller to generate the firing pulses which activate the inverter power switches in a manner that reduces the current error. iv. rtds hardware the real time digital simulator (rtds) allows developers to accurately and efficiently simulate electrical power systems and their ideas to improve them the rtds simulator operates in real time, therefore not only allowing the simulation of the power system, but also making it possible to test physical protection and control equipment. this gives developers the means to prove their ideas, prototypes and final products in a realistic environment. the rtds is a fully digital power system simulator capable of continuous real time operation. it performs electromagnetic transient power system simulations with a typical time step of 50 microseconds utilizing a combination of custom software and hardware. the proprietary operating system used by the rtds guarantees “hard real time” during all simulations. it is an ideal tool for the design, development and testing of power system protection and control schemes. with a large capacity for both digital and analogue signal exchange (through numerous dedicated, high speed i/o ports) physical protection and control devices are connected to the simulator to interact with the simulated power system. v. simulator hardware the real time digital simulation hardware used in the implementation of the rtds is modular, hence making it possible to size the processing power to the simulation tasks at hand. figure 7 illustrates typical hardware configurations for real time digital simulation equipment. as can be seen, the simulator can take on several forms including a new portable version which can easily be transported to a powerplant or substation for on-site pre-commissioning tests. each rack of simulation hardware contains both processing and communication modules. the mathematical computations for individual power system components and for network equations are performed using one of two different processor modules. an important aspect in the design and implementation of any real time simulation [14] tool is its ability to adapt to future developments. since the power system industry itself continues to advance with the introduction new innovative devices, both the hardware and software of the simulator must be able to follow such changes. great care has been taken to ensure such upward compatibility in all aspects of the real time simulator. adhering to this approach provides significant benefit to all simulator users since they are able to introduce new features to already existing simulator installations. vi. system performance in this section 3 phase 4 wire shunt active power filter responses are presented in transient and steady state conditions. in the present simulation ahpf (alternative high pass filter) were used in butterworth filter with cut-off frequency fc=f/2. simulation shown here are for different voltage conditions like sinusoidal, non-sinusoidal, and unbalanced conditions. simulation is carried out with pi controller for both instantaneous real active and reactive power control strategy (p-q) and active and reactive current control strategy (id-iq). figure 8, figure 9 and figure 10 illustrates the performance of shunt active power filter under different main voltages, as load is highly inductive, current draw by load is integrated with rich harmonics. figure 8 illustrates the performance of shunt active power filter under balanced sinusoidal voltage condition, thd for p-q method with pi controller using matlab simulation is 2.15% and using rtds hard ware is 2.21; thd for id-iq method with pi controller using matlab simulation is 1.97% and using rtds hard ware is 2.04% . figure 9 illustrates the performance of shunt active power filter under un-balanced sinusoidal voltage condition, thd for p-q method with pi controller using matlab simulation is 4.16% and using rtds hard ware is 4.23; thd for id-iq method with pi controller using matlab simulation is 3.11% and using rtds hard ware is 3.26%. fig. 7. rtds hardware etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 54-62 59 www.etasr.com suresh and panda: simulation and rtds hardware implementation of shaf… figure 10 illustrates the performance of shunt active power filter under balanced non-sinusoidal voltage condition, thd for p-q method with pi controller using matlab simulation is 5.32% and using rtds hard ware is 5.41; thd for id-iq method with pi controller using matlab simulation is 4.92% and using rtds hard ware is 5.05%. fig 11 gives the comparison between p-q and id-iq control strategies with pi controller using matlab/simulink and rtds hardware. it is shown that total harmonic distortion (thd) of id-iq control strategy with pi controller is better than thd of p-q control strategy with pi controller in both matlab/simulink environment and also when using rtds hardware. 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -400 -300 -200 -100 0 100 200 300 400 time (sec) s o u rc e v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) s o u rc e c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (amps) f il te r c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 0 200 400 600 800 1000 time (sec) d c l in k v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -40 -30 -20 -10 0 10 20 30 40 time (sec) l o a d c u rr e n t ( a m p s) 0 10 20 30 40 50 0 0.2 0.4 0.6 0.8 1 harmonic order thd= 2.15% m a g ( % o f f u n d a m e n ta l) 3ph 4w bal sin p-q with pi controller ( matlab simulation) 3ph 4w bal sin p-q with pi controller ( rt ds hardware) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -400 -300 -200 -100 0 100 200 300 400 time (sec) s o u rc e v o lt a g e (v o lt s ) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) s o u rc e c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -40 -30 -20 -10 0 10 20 30 40 time (sec) l o a d c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) f il te r c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 0 200 400 600 800 1000 time (sec) d c l in k v o lt a g e (v o lt s) 0 10 20 30 40 50 0 0.2 0.4 0.6 0.8 1 harmonic order thd= 1.97% m a g ( % o f f u n d a m e n ta l) 3ph 4w bal sin id-iq with pi controller ( matlab simulation) 3ph 4w bal sin id-iq with pi controller ( rt ds hardware) (a) (b) (c) (d) fig. 8. 3ph 4wire shunt ative filter response with pi controller under balanced sinusoidal using (a) p-q with matlab (b) p-q with rtds hardware (c) id-iq with matlab (d) id-iq with rtds hardware etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 54-62 60 www.etasr.com suresh and panda: simulation and rtds hardware implementation of shaf… 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -400 -300 -200 -100 0 100 200 300 400 time (sec) s o u rc e v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) s o u rc e c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) f il te r c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 0 200 400 600 800 1000 time (sec) d c l in k v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -40 -30 -20 -10 0 10 20 30 40 time (sec) l o a d c u rr e n t ( a m p s) 0 10 20 30 40 50 0 1 2 3 4 5 harmonic order thd= 4.16% m a g ( % o f f u n d a m e n ta l) 3ph 4w un-bal sin p-q with pi controller ( matlab simulation) 3ph 4w un-bal sin p-q with pi controller ( rt ds hardware) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -400 -300 -200 -100 0 100 200 300 400 time (sec) s o u rc e v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) s o u rc e c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -40 -30 -20 -10 0 10 20 30 40 time (sec) l o a d c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) f il te r c u rr e n t ( a m p s ) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 0 200 400 600 800 1000 time (sec) d c l in k v o lt a g e (v o lt s ) 0 10 20 30 40 50 0 1 2 3 4 5 harmonic order thd= 3.11% m a g ( % o f f u n d a m e n ta l) 3ph 4w un-bal sin id-iq with pi controller ( matlab simulation) 3ph 4w un-bal sin id-iq with pi controller ( rt ds hardware) (a) (b) (c) (d) fig. 9. 3ph 4wire shunt ative filter response with pi controller under un-balanced sinusoidal using (a) p-q with matlab (b) p-q with rtds hardware (c) id-iq with matlab (d) id-iq with rtds hardware vii. conclusion in the present paper two control strategies are developed and verified with three phase four wire system. though the two strategies are capable to compensate current harmonics in the 3 phase 4-wire system, but it is observed that instantaneous active and reactive current (id-iq) control strategy with pi controller leads to better result under unbalanced and non-sinusoidal voltage conditions compared to the instantaneous active and reactive power (p-q) control strategy. further, p-q theory needs additional pll circuit for synchronization, since it is a frequency variant method, whereas in id-iq method angle ‘θ’ is calculated directly from main voltages. this enables the (id-iq) method to be frequency independent. thus large numbers of synchronization problems with un-balanced and nonsinusoidal voltages are avoided. over all, it is shown that the performance of id-iq control strategy with pi controller is superior to p-q control strategy with pi controller. etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 54-62 61 www.etasr.com suresh and panda: simulation and rtds hardware implementation of shaf… 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -400 -300 -200 -100 0 100 200 300 400 time (sec) s o u rc e v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) s o u rc e c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) f il te r c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 0 200 400 600 800 1000 time (sec) d c l in k v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -40 -30 -20 -10 0 10 20 30 40 time (sec) l o a d c u rr e n t ( a m p s) 0 10 20 30 40 50 0 2 4 6 8 10 harmonic order thd= 5.31% m a g ( % o f f u n d a m e n ta l) 3ph 4w non-sin p-q with pi controller ( matlab simulation) 3ph 4w non-sin p-q with pi controller ( rt ds hardware) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -400 -300 -200 -100 0 100 200 300 400 time (sec) s o u rc e v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) s o u rc e c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) f il te r c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 0 200 400 600 800 1000 time (sec) d c l in k v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -40 -30 -20 -10 0 10 20 30 40 time (sec) l o a d c u rr e n t ( a m p s) 0 10 20 30 40 50 0 1 2 3 4 5 harmonic order thd= 4.92% m a g ( % o f f u n d a m e n ta l) 3ph 4w bal non-sin id-iq with pi controller ( matlab simulation) 3ph 4w bal non-sin id-iq with pi controller ( rt ds hardware) (a) (b) (c) (d) fig. 10. 3ph 4wire shunt ative filter response with pi controller under balanced non-sinusoidal using (a) p-q with matlab (b) p-q with rtds hardware (c) id-iq with matlab (d) id-iq with rtds hardware fig. 11. thd for p-q and id-iq control strategies with pi controller using matlab and rtds hardware etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 54-62 62 www.etasr.com suresh and panda: simulation and rtds hardware implementation of shaf… references [1] h. akagi, “new trends in active filters for power conditioning”, ieee transactions on industrial applications, vol. 32, no. 6, pp. 13121322, 1996. [2] f. z. peng, g. w. ott jr, d. j. adams, “harmonic and reactive power compensation based on the generalized instantaneous reactive power theory for three-phase four-wire systems” ieee transactions on power electronics, vol. 13, no. 5, pp. 1174-1181, 1998 [3] l. gyugyi, e. c. strycula, “active ac power filters”, ieee iias annual meeting, pp. 529-535, 1976. 529p. [4] m. i. m. montero, e. r. cadaval, f. b. gonzalez, “comparison of control strategies for shunt active power filters in three-phase fourwire systems”, ieee transactions on power electronics, vol. 22, no. 1, pp. 229-236, 2007. [5] s. mikkili, a. k. panda, s. yellasiri, “rtds hardware implementation and simulation of 3-ph 4-wire shaf for mitigation of current harmonics using p-q control strategy with fuzzy controller”, journal of power electronics & power systems vol. 1, no. 1, pp. 1323, 2011. [6] h. akagi, e.h. watanabe, “instantaneous power theory and applications to power conditioning”, new jersey. ieee press/wileyinter-science 2007 isbn: 978-0-470-10761-4, 2007 [7] o. vodyakho, c. c. mi, “three-level inverter-based shunt active power filter in three-phase three-wire and four-wire systems” ieee transactions on power electronics, vol. 24, no. 5, pp. 1350–1363, 2009. [8] v. soares, p. verdelho, g. marques, “active power filter control circuit based on the instantaneous active and reactive current id –iq method”, ieee power electronics specialists conference, vol. 2, pp. 1096-1101, 1997. [9] m. aredes, j. hafner, k. heumann,. “three-phase four-wire shunt active filter control strategies” ieee transactions on power electronics, vol. 12, no. 2, pp. 311 318 , 1997. [10] p. rodriguez, j. i. candela, a. luna, l. asiminoaei, “current harmonics cancellation in three-phase four-wire systems by using a four-branch star filtering topology”, ieee transactions on power electronics, vol. 24, no. 8, pp. 1939-1950, 2009. [11] p. salmeron, r. s. herrera, “distorted and unbalanced systems compensation within instantaneous reactive power framework”, ieee transactions on power delivery, vol. 21, no. 3, pp. 1655-1662, 2006. [12] s. mikkili, a. k. panda, s. yellasiri, “fuzzy controller based 3phase 4wire shunt active filter for mitigation of current harmonics with combined p-q and id-iq control strategies”, journal of energy and power engineering, vol. 3, no. 1, pp. 43-52, 2011. [13] s. mikkili, a. k. panda, s. s. patnaik, s. yellasiri, “comparison of two compensation control strategies for shaf in 3ph 4wire system by using pi controller”, india international conference on power electronics, pp. 1-7, 2011. [14] p. forsyth, t. maguire, r. kuffel, “real time digital simulation for control and protection system testing”, in ieee proceedings power electronics specialists conference, vol. 1, pp. 329 – 335, 2004. authors profile suresh mikkili was born in bapatla, andhra pradesh, india on 5 th aug 1985. he received b.tech degree in electrical and electronics engineering from jntu university hyderabad in may 2006 and masters (m.tech) in electrical engineering from n.i.t rourkela, india in may 2008.he has worked as a asst.prof in electrical engineering, s.i.t.e, t.p.gudem from june 2008 to dec-2009 and in v.k.r & v.n.b engineering college from dec2009 to july 2010. he is currently pursuing ph.d degree in electrical engineering at n.i.t rourkela, india from july 2010. his main area of research includes power quality improvement issues, active filters, and soft computing techniques. . anup kumar panda: born in 1964. he received the b.tech in electrical engineering from sambalpur university, india in 1987. he received the m.tech in power electronics and drives from indian institute of technology, kharagpur, india in 1993 and ph.d. in 2001 from utkal university. join as a faculty in igit, sarang in 1990. served there for eleven years and then join national institute of technology, rourkela in january 2001 as an assistant professor and currently continuing as a professor in the department of electrical engineering. he has published over forty articles in journals and conferences. he has completed two mhrd projects and one nampet project. guided two ph.d. scholars and currently guiding four scholars in the area of power electronics & drives. his research interest include analysis and design of high frequency power conversion circuits, power factor correction circuits, power quality improvement in power system and electric drives. microsoft word 17-3573_s_etasr_v10_n4_pp5979-5985 engineering, technology & applied science research vol. 10, no. 4, 2020, 5979-5985 5979 www.etasr.com salemdeeb & erturk: multi-national and multi-language license plate detection using convolutional … multi-national and multi-language license plate detection using convolutional neural networks mohammed salemdeeb electronics & telecommunications engineering department kocaeli university kocaeli, turkey en_mis@hotmail.com sarp erturk electronics & telecommunications engineering department kocaeli university kocaeli, turkey sertur@kocaeli.edu.tr abstract—many real-life machine and computer vision applications are focusing on object detection and recognition. in recent years, deep learning-based approaches gained increasing interest due to their high accuracy levels. license plate (lp) detection and classification have been studied extensively over the last decades. however, more accurate and language-independent approaches are still required. this paper presents a new approach to detect lps and recognize their country, language, and layout. furthermore, a new lp dataset for both multinational and multi-language detection, with either one-line or two-line layouts is presented. the yolov2 detector with resnet feature extraction core was utilized for lp detection, and a new low complexity convolutional neural network architecture was proposed to classify lps. results show that the proposed approach achieves an average detection precision of 99.57%, whereas the country, language, and layout classification accuracy is 99.33%. keywords-license plate detection; license plate classification; lpd; yolo detector; convolutional neural network; deep learning i. introduction object detection and classification has attracted a lot of research the recent years, with the advancements in vision technology, computer technology, and deep learning algorithms [1]. object detection aims to estimate the location of objects of interest contained in an image, while object classification aims to categorize an object within a certain number of categories [2]. traditional object detection and classification approaches have three steps, namely informative region selection, feature extraction and classification. in region selection, it is possible to scan the entire image using a multiscale sliding window, as numerous objects may appear in different locations with various sizes and aspect ratios [1]. feature extraction aims to obtain visual features providing a semantic and robust representation. some popular feature extraction methods used in the literature are haar-like features [3], scale-invariant feature transform (sift) [4], histogram of oriented gradients (hog) [5], and hybrid feature selection techniques [6]. classification aims to assign a target object in one of many categories. traditional classification approaches include supported vector machine (svm) [7], adaboost [8], and deformable part-based models (dpm) [9]. recent breakthroughs in convolutional neural network (cnn)-based approaches [10] attracted researchers to use regions with cnn (r-cnn) features for object detection [11]. cnn-based methods have the capacity to learn complex features with deeper architectures and utilize training algorithms to learn informative object representations without the need to design the features manually [12]. furthermore, researchers studied extensively various cnn models such as alexnet [10], vgg [13], googlenet [14], resnet [15], and fdrenet [16] to improve the accuracy of classification and regression problems in machine learning. generic object detection refers to the detection of objects from predefined classes obtaining the spatial location (e.g. bounding box) inside an image. it can typically be categorized into two types, namely regression/classification and region-based methods [17]. region-based methods include r-cnn [11], fast r-cnn [18], faster r-cnn [19] and mask r-cnn [20]. on the other hand, regression/classification-based methods include yolo (you only look once) [21], ssd [22], yolov2 [23] and yolov3 [24]. automatic license plate recognition (alpr) is a group of techniques that use license plate detection (lpd), character segmentation, and character recognition on images to identify vehicle lp numbers. alpr is also referred as license plate detection and recognition (lpdr). alpr is used in various real-life applications such as parking systems, electronic toll collection, and traffic security and control [25]. state-of-the-art object detection algorithms based on deep learning have provided promising results for lp country and layout classification. however, the multi-orientation and multi-scale nature of lps in addition to distortion and illumination issues, make lpd a challenging task to perform [26]. lpd using deep learning has been extensively studied over the last decade. authors in [27] proposed the use of a cnn-based multidirectional (md)-yolo framework for lpd, but their method does not successfully detect small lps. in [28] a faster r-cnn approach was presented, detecting at first vehicle regions and then locating the lp in each vehicle region. its performance evaluation results showed 98.39% precision and 96.83% recall. a new approach was proposed in [29], referred as yolo-l, where the prospective number and size of lp candidate boxes are selected using “k-means++” clustering with a modified yolov2 model and pre-identification to distinguish lps from similar objects. this method achieved a precision of 98.86% corresponding author: mohammed salemdeeb engineering, technology & applied science research vol. 10, no. 4, 2020, 5979-5985 5980 www.etasr.com salemdeeb & erturk: multi-national and multi-language license plate detection using convolutional … and a recall of 98.86%. researchers in [30] introduced the largest brazilian lp dataset, referred as ufpr dataset, and proposed a four stage lpdr system comprising of vehicle detection, lpd, character segmentation, and character recognition. the lpd stage used cr-cnn core fast-yolo, obtained a recall of 98.33%. furthermore, researchers in [31] introduced a large and comprehensive chinese lp dataset called ccpd, and proposed an end-to-end lpdr system using rpnet in the lpd phase, comparing the detection of average precision (ap) results to ssd, yolov2, and faster r-cnn detection techniques by using 250k unique car lps. on the other hand, little research has been performed on multi-language and multi-national lp detection, mostly due to the lack of international lp datasets. nevertheless, a few recent studies focused on developing a global end-to-end alpr system, as reported in [32]. authors in [32] proposed an approach for multi-national license plate detection for images with complex backgrounds, in which the yuv color space was initially used for detecting the rear vehicle lights, and the lp area was detected using a histogram-based approach on the edge energy map. the utilized dataset comprised of lps from america, china, serbia, italy, pakistan, united arab emirates (uae), and hungary. the dataset had only single-line lps and obtained a detection accuracy of 90%. researchers in [33] used vgg with lstm to classify the registration country of lps from latvia, lithuania, estonia, russia, sweden, poland, germany, finland, and belarus. a recent research used tiny yolov3 to detect lps from south korea, taiwan, greece, usa, and croatia [34]. several approaches expressed interest in multi-national lps, but they tested their detectors on each country’s dataset separately, rather than accumulating them into one dataset [35-38]. moreover, multi-language lps were addressed in a few approaches. authors in [38] proposed a mask r-cnn detector for lps with english and arabic characters from usa and tunisia. in [39] korean and english lps were targeted, using the term multi-style detection to refer to different country, language and one or two-line lp styles. most of the reported researches studied the lp classification (lpc) problem inside the lpd stage. in these cases, the detector determines the bounding box, and at the same time gives the class label of an lp. however, in [32, 37] multinational lpd was presented by just detecting lps, without providing any other information for nation, language or layout. in [33] the classification of detected lps by the issuing country was studied, reporting a classification accuracy of 92.8%. on the other hand, authors in [39] proposed a module to classify the detected lps to single and double-line, without reporting its accuracy but only the entire system results. in this paper, multi-national lps from usa, europe (eu), turkey (tr), uae and kingdom of saudi arabia (ksa) are targeted, using yolov2 detector with resnet50 feature extraction for lpd. for this purpose, a new dataset, named as lpdc2020, was constructed and presented. after the segmentation of the detected lps, a cnn was used to detect the country, language and the one or two-line layout of the lp. the proposed detector and classifier were also tested on several benchmark datasets from those countries, in addition to lpdc2020. the proposed approach aims to close the gap in multi-national, multi-language and multi-layout lp detection problem, by utilizing a single unified system, and to the best of our knowledge it is the first and only study incorporating lps from north and south america, europe, and middle east (tr, uae and ksa). ii. datasets a. lp datasets available in the literature most of the frequently used lp datasets utilized in previous researches are available online, and their details are summarized in table i. any private datasets, not publicly accessible, are disregarded. table i. a summary of publicly available lp datasets dataset year # of images accuracy % country caltech [40] 1999 126 usa zemris [41] 2002 510 86.2 croatia ucsd [42] 2005 405 89.5 usa snapshots [43] 2007 97 85 croatia medialab [44] 2018 730 greece reid [45] 2017 77k 96.5 czech ufpr [30] 2018 4500 78.33 brazil b. lpdc2020 dataset this paper introduces a new lp dataset, which was collected manually using mobile cameras in turkey, named lpdc2020. it has two image sets: vehicular images to train the lpd module, and cropped lp images to train the lpc module. in addition, due the lack of publicly available arabic lp datasets, images for ksa and uae lps available in the internet were used. all images were processed and annotated manually in a labor-intensive process. table ii shows the number of lpd images collected for each country. some sample lps from different countries with one and two-line layouts included in the dataset are shown in figure 1. table iii shows the structure of lpdc2020 classification dataset. it is noted that, taking one and two-line layouts into account, the lpc dataset incorporates 11 different characteristics. the total number of cropped lp images is 29030, containing lp images from the previously mentioned countries. table ii. a summary of lpdc2020 lpd dataset country tr eu usa ksa uae total # of images 4182 2636 715 1000 488 9021 fig. 1. some sample lps from different contries with various layouts. engineering, technology & applied science research vol. 10, no. 4, 2020, 5979-5985 5981 www.etasr.com salemdeeb & erturk: multi-national and multi-language license plate detection using convolutional … table iii. structure of the lpdc2020 lpc dataset country language of characters layout number of instances br latin one-line 3714 two-line 900 uae arabic one-line 500 two-line 276 eu latin one-line 5296 two-line 4350 ksa arabic one-line 290 two-line 792 tr latin one-line 7771 two-line 3560 usa latin one-line 1401 iii. fundamentals of cnn the fundamentals of any cnn are the convolutional layers consisting of learnable filters having small spatial size and specific depth. for an input image i and kernel k the general equation of 2d convolution [46] used in computer vision and machine learning is defined as: (� ∗�)(�, �) = ∑ ∑ �(� + �,� + )�(�, ) �� (1) with i and m being the row indexes, while j and n are the column indexes. the activation layer produces an output value of the neuron using certain activation functions for a given input value. an example is the rectified linear unit (relu) [10], where the output will be zero for negative input values and same as the input in any other case. the second important part of cnn is the pooling layer, which is responsible for reducing the input’s spatial size by keeping the most important activations. this reduces the amount of computations and the number of learnable parameters. a dropout layer is used to combat overfitting, omitting randomly some neurons in each training step by setting their activation values to zero. as a result, the network can learn using a random combination of neurons. the fully connected (fc) layer, also called as dense layer [47], is the third important part of cnns. each neuron in the input layer is connected to all output neurons of this layer. the purpose of the fc layer is to learn for non-linear combinations of features. for x neurons input, learnable weight matrix w, and learnable bias vector b, the output of the fully connected layer y can be expressed as: � = �� +� (2) at the end of the architecture, i.e. after the last fully connected layer, a softmax layer is used. this layer is used for classification problems, providing a probabilistic interpretation of the input with respect to the sum of all input exponentials, declared as: �������(�)� = ���∑ ����� ! (3) this layer is also called the loss function layer, since during training a loss function is applied at the end of the cnn. in general, for n samples, the mean square error (mse) can be used in object detection as in (4) and cross-entropy function is used for classification problems as in (5) [47]: "#$% = &'∑ (�� −�)�)*'�+& (4) ",-.//01�2-.34 = −∑ {�� ln(�)�)+(1−��)ln (1− �)�)}'�+& (5) where, �� is the i-th actual output, and �)� is the i-th predicted output. iv. proposed approach this research addresses two problems; the detection of an lp in an image, and the classification of the detected lp’s country, language, and layout. a. license plate detection the proposed approach is based on using the yolov2 detector with the resnet50 [15] network as the core cnn for the lp detector. the utilized resnet50 architecture is displayed in table iv. table iv. resnet50 architecture layer size filters input 224 × 224 × 3 ------- conv1 112 ×112 ×64 7 × 7 ×64, stride 2 max pooling 56 ×56 ×64 3 ×3 max pool, stride 2 conv2 56 ×56 ×256 a 1 ×1,643 ×3,641 × 1,256b ×3 conv3 28 ×28 ×512 a1 × 1,1283 × 3,1281 × 1,512b ×4 conv4 14 ×14 × 1024 a 1 × 1,2563 × 3,2561 × 1,1024b ×6 conv5 7 ×7 ×2048 a 1 × 1,5123 × 3,5121 × 1,2048b ×3 average pooling 1 ×1 ×2048 7×7 fully connected 1 ×1 ×1000 1000 softmax 1 ×1 ×1000 ------- the input layer size of resnet50 was redesigned to be 672×672 instead of the original 224×224 pixels. the original size did not provide adequate features for lpd. for an original vehicular image with small size it will be difficult to detect the lp region after reducing its resolution. naturally, there is a restriction on the minimum lp size required inside the detector’s input image, due to the network forward propagation size of resnet50, which is 224/7=32. hence, lps sized 32×32 pixels will correspond to a single point in the output feature map and consequently, any smaller regions will vanish. the proposed detector core network was designed to have a forward propagation size of 672/42=16. the first 40 layers of resnet50 were used in the proposed yolov2 core cnn. the input size was set to 672×672 pixels, and the output feature map was 42×42 pixels. the minimum lp size was set to 16x16 pixels. it should be noted that smaller lps can still be detected but with lower precision. in addition, the proposed approach can detect lps sized up to 670×670 pixels. figure 2 shows the block diagram of the proposed approach. the proposed detector had 27992604≈28m total learnable parameters. the yolov2 detector divides the input image to an s×s grid, where s is the output feature map size of the yolov2 core resnet40 (i.e. the output of conv4 layer), and s was set to 42. anchor boxes were downsized by forward propagation size. yolov2 uses a anchor boxes to predict objects. the engineering, technology & applied science research vol. 10, no. 4, 2020, 5979-5985 5982 www.etasr.com salemdeeb & erturk: multi-national and multi-language license plate detection using convolutional … detection results are the bounding boxes and the confidence scores, so that for c class probabilities [23] the number of filters is given by: e��fg �� ��h�fg� = (i +5�< j (6) fig. 2. block diagram of the proposed approach. the lp sizes in lpdc2020 were analyzed to select their anchor boxes, using the pyramid of anchors method of faster r-cnn [19]. as shown in figure 3, lp sizes span on a range of 10 to 670 pixels. hence, in order to select anchor boxes of high intersection of union (iou), six minimum lp sizes were used. these sizes were defined as 10×10, 10×20, 10×30, 10×40, 10×50, and 30×14 pixels, with a pyramid level of 15 and anchor box pyramid scale of 1.3. as a result, 90 anchor boxes with a minimum of 0.625 and mean iou of 0.85 were obtained. according to (6), the proposed last yolov2 layer had 540 filters. fig. 3. lp sizes in lpdc2020 dataset. b. license plate classification α simple cnn was designed for lp classification, and its accuracy is compared to vgg [13]. the input image size is set to 224×224 pixels, being the same as the input size of vgg network for fair comparison. the classification cnn construction is shown in table v. the proposed classifier design has a total number of 2635773≈2.64m learnable parameters, being much less than the vgg learnable parameter amount of 138m. both a batch normalization (bn) [48] and a relu non-linear activation layer [10] follow each convolutional layer. bn normalizes the input batch mean and standard deviation, and then performs scaling and shifting based on learnable scale and shift parameters [48]. all convolution kernels have a size of 5×5 with stride 1 without padding. hence, each convolutional layer results in a dimension shrinkage of 4 rows/columns. the dimension of the output feature map was computed according to (7): �.k2 l��0lmn*o lp � 1 (7) where �.k2 is the output feature map width, ��� is the input feature map width, �q is the kernel width, r is the padding, and �/ is the kernel stride in the horizontal direction. for input/output height relation, (7) can be applied using s instead of �. the input size is 224×224×3. after 4 pooling and 8 convolutional layers, the output size is reduced to 6×6×128. after that, conv9 and conv10 layers shrink the output to 1×1×512 neurons. using this design, the input image is convolved to a single neuron with 512 channels. afterwards, these neurons are fitted to 11 classes in the fc layer by applying (2). this layer weights all input neurons and forwards them to the softmax layer, which provides a score for the 11 classes and performs the classification task as described in (3). it is safe to note that the proposed design is a simple stacked cnn with a low number of learnable parameters. table v. proposed cnn design for classification layer filters & size output size learnable parameters input 224×224×3 conv1 5×5×32 220×220×32 2496 conv2 5×5×32 216×216×32 25696 maxpooling 2×2 108×108×32 conv3 5×5×64 104×104×64 51392 conv4 5×5×64 100×100×64 102592 maxpooling 2×2 50×50×64 conv5 5×5×96 46×46×96 153888 conv6 5×5×96 42×42×96 230688 maxpooling 2×2 21×21×96 conv7 5×5×128 17×17×128 307584 conv8 5×5×128 13××13×128 409984 maxpooling 2×2 6×6×128 conv9 5×5×256 2×2×256 819968 conv10 2×2×512 1×1×512 525824 fully connected 11 1×1×11 5643 softmax 1×1×11 c. practical aspects the training process used stochastic gradient descent with momentum (sgdm) [46]. the sgdm training was carried out for 10 epochs, with an initial learning rate (lr) drop factor of 0.5 for every 2 epochs. the training set was shuffled for every epoch. in yolov2 training, the mini-batch size was only six images, due to memory constraints, and lr was set to 1×10 -5 . also, lp classification cnn mini-batch size was 120 images and lr was set to 2.5×10 -2 . after the first results, model parameter tuning was applied to continue training, using adam adaptive learning rate optimization [46]. in adam, the batch size was doubled and lr was halved every 10 epochs, as long as the final error shows improvement. engineering, technology & applied science research vol. 10, no. 4, 2020, 5979-5985 5983 www.etasr.com salemdeeb & erturk: multi-national and multi-language license plate detection using convolutional … v. results and discussion a matlab environment was used to evaluate the proposed approach. a geforce 1060 6gb ram gpu with computational capability of 6.1 was used for training and testing. the next subsections describe the evaluation criteria for both lpd and lpc. a. lpd the lp detection performance evaluation was performed using precision (p), recall (r) and average precision (ap) values. any detected lp bounding box having an overlap greater than iou=0.5 with the ground truth bounding box is considered as a correct detection. precision is the percentage of the number of correctly detected lps over the total number of detected lps. r is the percentage of the number of correctly detected lps over the total number of ground truth lps. ap is the area under the precision recall curve. p and r are calculated by (8) and (9), where tp is true positive, fp is false positive, and fn is false negative detection. rgft���� uv wonxo (8) yft�hh uv wonx' (9) table vi shows the proposed detector’s ap performance compared to previous approaches presented in [32, 33, 37]. the proposed detector outperforms the previous approaches in terms of ap performance. it should be noted that in [32] only the accuracy for detected over all lps in a private dataset is evaluated. authors in [37] evaluated only the lpd precision, without presenting any ap values. it is evident that the proposed approach provides better detection score. table vi. multi-set lpd comparison results. approach detector score processing time (s) [32] image processing 90.4% ap 0.25 [33] vgg+ lstm 98.07% ap not reported [37] image processing + alexnet + svm 99.03% p 0.16 proposed resnet40+ yolov2 99.57% ap 0.09 those approaches were selected because they evaluated performance using images from all the countries of interest together in one dataset. hence, these approaches can be considered as multi-national and multi-language lpd methods. furthermore, some researches trained and tested detectors for different datasets separately, in order to evaluate the performance on each dataset. table vii provides a comparison in terms of p, r and ap performance for these methods. in order to conduct a fair comparison, there was a need to train the proposed detector on every dataset separately. however, the proposed detector had higher r rate and ap on all datasets. this is partly due to the large number of different lps used in lpdc2020 and to its superior architecture. it is noted that one and two-line lp layout classification was studied in [34] with classification results combined in the character recognition stage for multi-national korean, taiwanese, chinese, and latin lps. table viii shows the proposed method’s ap results per country. it is apparent that the performance is similar, with slightly lower results for ksa lps. table vii. single-set lpd comparison results approach caltech dataset zemris dataset medialab dataset various datasets [34] tiny yolov3 p=100% r=100% 98% 99% 98.8% 99.7% taiwan: 100/100% korea: 98.3/99% [35] vgg+ faster rcnn ap = 98.03% ------ china: 98.33% taiwan: 98.80% [36] vgg +ssd ap = 98.4% 97.83% 99.8% --- [38] mask rcnn p=98.9% r=98.6% ------ taiwan: 99.1% china: 99.4% tunisia: 97.9% proposed resnet40+ yolov2 p=98.43% r=100% ap=99.96% 97.88% 100% 99.99% 98.4% 99.75% 99.74% snapshots: 98/100/99.99% ucsd: 99/100/99.93% table viii. lpd results for lpdc2020 dataset per country dataset tr eu usa uae ksa proposed resnet40+ yolov2 99.48% 99.91% 99.95% 99.55% 98.67% b. lpc the proposed cnn for classifying the lp’s issuing country, language and layout was evaluated in terms of overall accuracy. table ix shows the classification accuracy of the proposed cnn. the proposed cnn classification is only 0.38% less accurate than vgg16, which is regarded to be state-of-the-art, but with significantly fewer learnable parameters. the number of learnable parameters of the proposed approach is only 1.9% of the parameters used in vgg16. as a result, the proposed cnn is faster and less complex with a small penalty in classification accuracy. table ix. proposed cnn lp classification accuracy cnn architecture accuracy learnable parameters vgg16 99.71% 136 m proposed cnn 99.33% 2.635 m table x shows the misclassification rates of the proposed approach. it is noted that turkish and european union’s lps have a higher classification error, as they share the same lp style standard. in contrast, br and uae have a unique style, and usa lps can include object shapes varying from standard lp characters, making it easy to classify them with a small error. table x. misclassification of lpdc2020-lpc datasets country language of characters layout number of instances misclassified lps br latin one-line 3714 0 two-line 900 0 uae arabic one-line 500 0 two-line 276 0 eu latin one-line 5296 14 two-line 4350 0 ksa arabic one-line 290 0 two-line 792 4 tr latin one-line 7771 18 two-line 3560 0 usa latin one-line 1401 3 engineering, technology & applied science research vol. 10, no. 4, 2020, 5979-5985 5984 www.etasr.com salemdeeb & erturk: multi-national and multi-language license plate detection using convolutional … vi. conclusion detecting country and language is important to build a global alpr system, while correct layout classification is essential in order to read the detected characters in the right order. this paper focused on lp detection and classification of multi-national and multi-language lps with different layouts from br, usa, eu, tr, ksa and uae, proposing a method that can detect lps regardless of their country of origin, language or layout. furthermore, a second classification stage was used to recognize lps’ issuing country, language and layout. in addition, a new multi-national, multi-language and multi-layout 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[48] s. ioffe and c. szegedy, “batch normalization: accelerating deep network training by reducing internal covariate shift,” in proceedings of the 32 nd international conference on machine learning, jun. 2015, pp. 448–456. microsoft word 19-993-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1307-1315 1307 www.etasr.com mobarak and alshehri: perspectives of safe work practices: improving personal electrical safety of … perspectives perspectives of safe work practices: improving personal electrical safety of low-voltage systems from electrical hazards youssef mobarak electrical engineering department, faculty of engineering, king abdulaziz university, rabigh, saudi arabia ysoliman@kau.edu.sa abdullah alshehri electrical engineering department, faculty of engineering, king abdulaziz university, rabigh, saudi arabia aaashehri@gmail.com abstract—a person’s understanding of a safety hazard has a dramatic effect on his or her behavior. an in-depth understanding of a hazard usually results in a healthy respect for what can happen. people who know the most about a specific hazard tend to rely more heavily on procedures and plans to guide their actions. personal protective equipment selection and use are influenced by increased understanding of a hazard. training and training programs are influenced by the depth of knowledge held by all members of the line organization. recent work has focused attention on the thermal effects of arc flashes. however, when electrical energy is converted into thermal energy in an arcing fault, still another energy conversion is taking place. applications are on record that suggest that a considerable amount of force is created during an arcing fault. concrete block walls can be destroyed by the increased pressure that is created during an arcing fault. this study is present about preventing injuries to people. we will study about injuries and then develop some understanding about electrical hazards. also, we will present about safe work practices, responsible, and then about what makes us act as we do. keywords-personal electrical safety; injuries; electrical hazards; safe work practices; responsibility. i. introduction electricity hazards have been well documented through the years and various papers, guides and books have been published that focus on such hazards, the reasons, analysis, prevention measures etc in various applications [1-65]. an extended list is provided in the references section. historically, the obvious issue of direct contact was first reported but in the mid-80s the issue of arc flashes also started to gain attention. since most arc-flash burns are recorded just as burns, some estimates suggest that 80 percent of all injuries from an electrical hazard is the result of an arc. the plasma in an electrical arc can reach 35,000 of. in fact, it will reach that temperature unless the energy source is removed before it gets there. people have been fatally burned at distances greater than 10 feet from the arc. in one arcing-fault incident, two people who were standing about 18 feet from an electrical arc were fatally burned. more than 2000 people are admitted to burn centers annually with severe electrical burns. several standards and guides ghave been published that focus on arc flashes. arcpro is a commercially available software that will project an incident-energy calculation. many commercially available system analysis computer programs, such as edsa, also contain software that calculates incident energy. many of the calculation methods do not correlate with one another. they might provide a different result. insufficient information is available to suggest that one method provides more accurate information than another. where do these conditions exist?. the arc-flash issue can be reduced to these facts. you can calculate incident energy by one of several methods]. an employer/owner should provide enough information about the electrical circuit that enables a worker to select protective equipment. national electrical codes usually require a label on equipment where potential for an arc-flash injury exists. however, you really don’t know how much protective equipment will prevent an injury. a worker should wear clothing that provides significant flash protection as his or her normal work clothes. you should also be advised that the ppe selected by any method will not necessarily eliminate an injury. incident energy is calculated at a prescribed distance. if the ppe is 100 percent effective at that distance, some part of the worker’s body probably will be closer and subjected to greater thermal energy. the best alternative is to create an electrically safe work condition. if the source of energy is removed with assurance that it cannot reaccumulate, all exposure to an electrical hazard has been removed. this practice should always be the first option. stop, stand still, think. does something seem out of place? smell. equipment that is beginning to fail frequently gives off an unusual smell. feel. does the equipment or device feel warm or hot to the touch? engineering, technology & applied science research vol. 6, no. 6, 2016, 1307-1315 1308 www.etasr.com mobarak and alshehri: perspectives of safe work practices: improving personal electrical safety of … listen. is there an unusual sound? the first generally recognized hazard associated with electrical energy was fire. these conditions frequently result in a fire. there is much left to discuss. review your employer’s plan and procedures. minimize exposure to the hazard by doing as much work as possible before exposing the hazard. a barrier should be installed to cover any conductor that must remain energized. a rented generator be installed to permit the equipment to be completely locked out, and safety grounds help to eliminate the possibility of an unexpected backfeed. ii. injuries for an injury to occur, an unintended release of energy or an unexpected contact with some source of energy must occur. only an unintended interaction with some source of energy can cause an injury. the exposure may be intended or unintended, can only be the result of an unsafe condition, an unsafe act, or through the use of unsafe equipment. an unsafe act is when an energy release is the result of a person’s action, such as if a person cuts the ground probe from a nema 5-15 cord cap. an unsafe condition is when the working environment is influenced by a condition that results in a release of energy, such as if a person leaves a hole in the floor unguarded or uncovered. unsafe equipment might be poorly maintained equipment, or it might be an electrical circuit that has oversized fuses. if we lumped all unsafe conditions and all unsafe equipment together, they would account for about one-third of all injuries. unsafe acts are the basic cause for two-thirds of all injuries. we could also categorize all injuries by the type of energy. if we did, electrical injuries would be the largest category. a. causes of injuries: this section compares unsafe equipment and unsafe conditions with unsafe acts. as the chart suggests in figure 1a, unsafe acts is the major cause of injury. this chart also suggests that if we could somehow eliminate unsafe acts as a cause of injury, we could reduce the number of electrical injuries by a significant degree. once an incident is in progress, a person can do little to avoid being injured. the trick then, is to take some action before an incident has a chance to begin. b. heinrich’s relationship: a theory developed by h.w. heinrich states that for every 300,000 unsafe acts, there are 30,000 near misses, 300 recordable injuries, 30 lost-time injuries, and 1 fatality as shown in figure 1b. over the years, these relationships have proven to be relatively accurate. some people feel that if the energy source is electrical, then a zero can be taken from the relationship. however, that contact with an energized electrical conductor has a very significant chance of electrocution. c. injury analysis: this analysis of data suggests that an injury from electrical energy fits into these categories. the study used data that was collected over a ten-year period from 120,000 employees. the data shows that a population of this size can expect to have 125 lost time injuries each year. of these injuries, 25.7% injuries involve the eyes, 21% result in permanent disability and 2.4% are fatal. for every 25,000 workers, a fatality is experienced each year. it should be noted that these statistics don’t include burn injuries from either current flow or arc flash because they are categorized as burns fig. 1. injuries, and heinrich’s relationship iii. electrical hazards a. electric fire: a fire caused by high-resistance connections might occur when mechanical joints in an electrical conductor loosen as the conductor material heats and cools in its normal use cycle. the heating and cooling cycle causes the connector to expand and contract. the connector material stretches during this cycle, resulting in decreased contact pressure. conductor material can flow away from the point where pressure is applied, which causes the pressure to decrease. the high-resistance connection generates heat that can, in-turn, ignite any nearby flammable material. an improper welding path can cause sparks at remote locations. if any flammable material is nearby, the sparks can result in ignition. if electrical insulating material is inadequately rated, the conductor can contact a surface at a different potential. of course, hazardous flammable material can be ignited by either of the above means or by a static discharge. in either case, a fire will likely result. b. electric shock: no one really knows how many non-fatal shock accidents happen each year. however, records show that at least 30,000 do occur. now consider that perhaps 1 in 50 maybe 1 in 100 shock accidents are recorded. an electrocution is an electrical shock that is of a magnitude large enough or long enough to result in a fatality. records show that, in industry, over 600 people are electrocuted each year. electrocution is the sixth leading cause of industrial fatalities. figure 2 illustrates the number of electrocutions, by year, from 1992 to 1998. a short glossary follows: touch potential: electricity always takes the path of least resistance. if a person touches an energized point with a hand, and the other hand is in contact with ground or a grounded object (figure 3a), the current will likely flow from the one hand to the other. this type of contact is called hand to hand. step potential: a similar current path can exist from one foot to the other. this foot-to-foot contact is called step potential as in figure 3b. a potential difference exists between engineering, technology & applied science research vol. 6, no. 6, 2016, 1307-1315 1309 www.etasr.com mobarak and alshehri: perspectives of safe work practices: improving personal electrical safety of … a person’s feet. that current will flow through the trunk of the body. touch potential: still another type of touch potential can exist (figure 3c), as the path that current might take with a hand-to-foot contact. when contact is first made with an energized conductor, the surface contact between the skin and the conductor is high. as the current increases, the contact resistance is driven lower. if the skin’s surface should break, contact resistance effectively disappears. only internal impedance remains. blood and nerve tissue are very good conductors. body tissue is primarily a saline solution that conducts electricity very well. at first contact, the current probably will flow across the surface of the skin. fig. 2. electrocutions by year fig. 3. electrical shock types characteristics of the body: the body can be considered to be essentially an electrical system. a small voltage is chemically generated within the brain, and the nerves deliver the signal to the muscle. the current flow is in the microampere range. the muscle reacts to the strength of the signal. a stronger signal means to constrict more. if an external source of voltage sends a signal to a muscle, the muscle reacts as if the signal were a normal signal. if the external signal is greater than the signal generated by the brain, the muscle is told to stay clamped. the let-go threshold has been reached. automatic body functions such as heartbeat and breathing become confused at the powerful signal. they cease to operate normally. fibrillation of the heart occurs quite rapidly. figure 4 shows how much current can be expected to flow in case a person makes contact with ordinary utilization voltages. best dry conditions on this chart, the green line indicates the amount of current that will flow under the best of conditions. the worker is wearing dry gloves. the worker’s shoes are in good condition. the black vertical line at the left represents 110 volts. reading across to the current line, we can see that the worker will experience a current flow of about 14 ma. the vertical line on the right represents 480 volts. again reading to the left axis, we can see that the worker will experience a current flow of about 55 ma. the notes on the right side of the chart suggest what kind of reaction a person’s body might experience. worst but normal conditions are shown in figure 4b, this graph represents a different set of conditions. the worker has been at it for a while, and his or her gloves are damp from perspiration. the impedance introduced by the gloves is reduced. the green line still represents the dry conditions we saw in figure 4a. the red line has been added to represent the amount of current flow that is likely in event of contact with an energized conductor with the damp gloved hand. again, the vertical line on the left represents 110 volts. the vertical line on the right represents 480 volts. as you can see, the current flow at 110 volts is well into the let-go threshold. the current flow at 480 volts is well into the range that will cause fibrillation. fig. 4. expected current flow in a person exposed to shock: a person is likely to receive an electrical shock any time he or she contacts an exposed energized conductor. an inadequate ground of any type can cause a voltage to exist at points where it is unexpected. poor equipment design or installation can result in conductive components that are exposed. for instance, if a hot and neutral conductor are interchanged, an external surface can be energized. equipment must be maintained so that the installed condition is approximated for the life of the installation. the most common means of exposure to shock is by poor work practice or procedures. injuries frequently occur when the worker believes that the conductor is de-energized. should a condition exist that permits a large current to flow through earth, such as a significant fault or lightning discharge, a voltage gradient is generated in the earth path. if a person contacts two points along the path of current flow, some current is likely to be diverted through the person’s body. some informative pictures are shown in figure 5. electric shock hazard and protection: table i shows what a body’s reaction might be to various amounts of current. the differences in the two columns to the right are not really related to males and females. instead, females are generally assumed to have a smaller body frame. the issue seems to be current density. engineering, technology & applied science research vol. 6, no. 6, 2016, 1307-1315 1310 www.etasr.com mobarak and alshehri: perspectives of safe work practices: improving personal electrical safety of … protect from exposure to shock: so, you avoid exposure to electrical shock or electrocution. shut it off – lock it out. stay outside the safe approach boundary. wear protective equipment that is adequately rated for the potential exposure. keep your grounding system in good repair. this means that you have to test them from time to time. keep all doors closed and covers in place. if the door is closed, there is no exposed energized conductor. treat energized electrical conductors with respect. the insulation could be damaged. the insulation could be deteriorated with no visual indication. train people to be able to recognize when and how exposure to electrical shock can exist. train people to understand how to completely avoid or minimize their exposure to shock by selecting and wearing adequate protective equipment. train people to understand and accept their personal limitations. they should know the limit of their knowledge and their skill. train people to practice continual awareness of their exposure to electrical shock. use signs and labels to warn people that an electrical hazard exists and that their exposure is elevated. fig. 5. electric shock hazard and protection table i. effect of current on the human body effect ac in ma (males) ac in ma (females) slight sensation in hand 0.4 0.3 perception threshold 1.1 0.7 shock not painful muscular control not lost 1.8 1.2 shock painful muscular control not lost 9.0 6.0 shock painful and severe muscular control not lost 23.0 15.0 shock possible ventricular fibrillation effect from 3-second shocks `100.0 100.0 c. arc flash: when an arc-flash event happens, pressure that is created by the superheated air and vaporizing metal expels droplets of molten metal and other parts and pieces with great force. arcflash events usually happen very quickly. although many people have seen the effects of an arcing fault, most have never seen the event itself. figures 6-7 shows stills from a video taken by a camera that shoots 30,000 frames per second. in the picture are two electricians mannequins, not real people. one is near the equipment, and the other is near the right side of the photo. figure 7 are intended to illustrate the kind of pressure force that the person would feel on his or her body. arcing faults may not be in a starter unit or a circuit breaker enclosure a fault can occur at any place in the circuit. fig. 6. a photograph of a grab fig. 7. the kind of pressure force that the person would feel on his or her body electrical arc burn hazards: the plasma of an electrical arc can reach a temperature of 35,000of. the plasma temperature does not reach that temperature instantaneously. normally, the overcurrent device removes the energy source within two or three seconds. however, the rate of temperature rise is considerable. usually an overcurrent device operates within the first second and quenches the arc. sometimes the overcurrent device does not operate as intended, and the arc temperature gets quite high. in a normal situation where the overcurrent device removes the energy in less than one second, the plasma temperature can reach 15,000 to 17,000 of. ordinary street clothing can ignite if its temperature reaches 700 to 1400of. the ignition temperature varies as the construction material changes from nylon, polyester, or similar material to cotton and wool. if a person’s clothing ignites, the engineering, technology & applied science research vol. 6, no. 6, 2016, 1307-1315 1311 www.etasr.com mobarak and alshehri: perspectives of safe work practices: improving personal electrical safety of … burning material will subject the person to about 1400of. however, the person will be subjected to that high temperature for several seconds before the flame is extinguished or the clothing is removed. some materials will melt when burning and deposit the molten material onto the surface of the person’s skin. copper melts at about 1800of. the metal droplets that are expelled during the faulted condition are also at that temperature. sometimes the droplets will melt through the clothing, but sometimes the clothing will be ignited by the molten copper. table ii shows what might happen to a person’s skin if subjected to elevated temperature. table ii. skin temperature tolerance relationship skin temperature time of skin temperature damage caused 110 of 6.0 hours cell breakdown begins 158 of 1.0 second total cell destruction 176 of 0.1 second second degree burn 200 of 0.1 second third degree burn important event factors: arc-flash events happen very quickly. many people who were present when an arc flash occurred did not even see the flash. the events are very unpredictable. an arc flash might occur in one set of conditions and in similar conditions a second time might not occur. these events are normally started by a person doing something. even when equipment fails, the event is usually precipitated by a person doing something. these events are not related to the system of grounding. regardless of solid ground, resistance ground, or if the system is ungrounded, the events and their results seem to be the same. these events are not related to voltage. instead, they are related to energy: specifically, the amount of energy that is available within the system at the point of the fault. these events usually happen as a result of movement. a contactor operating, a switch handle moving, an errant movement by a worker, or similar events normally initiate arc-flash events. approach boundaries: the arc-flash protection boundary is related to arc flash only, with no relationship to electrical shock or electrocution. the limited, restricted, and prohibited approach boundaries are intended to trigger additional protective measures to prevent shock or electrocution. it is important to understand that the prohibited approach boundary represents a distance beyond which contact with an exposed energized conductor is likely. a work task that requires or enables an approach closer than this dimension should be prohibited. figure 8 illustrates the four approach boundaries. again, the limited, restricted, and prohibited approach boundaries represent increased exposure to shock. these boundaries are fixed, based on the circuit voltage. the arcflash protection boundary is not fixed. the distance moves in and out from the exposed energized conductor, based on the amount of energy that is available in the system. they are based on the system voltage and do not change from one circuit to another. the limited approach boundary may change, depending on the relative position of the worker. if the relation position can change, then the distance is moveable. moveable means that the conductor might move, such as in an overhead line construction, or if the worker is on a moveable platform such as an articulating basket. fixed means that the worker is on a stable platform, such as a floor, and the conductor is held in place, such as a buss within a piece of equipment, shock approach boundaries show in table iii. fig. 8. four approach boundaries table iii. shock approach boundaries approach boundary number system voltage range limited restricted prohibited phase to phase exposed movable conductor exposed fixed circuit part includes inadvertent movement adder includes reduced inadvertent movement adder energized part employee – distance in feet – inches 0 to 300 not specified not specified not specified not specified 51 to 300 v 10 ft. 0 in. 3 ft. 6 in. avoid contact avoid contact over 300 v not over 750 v 10 ft. 0 in. 3 ft. 6 in. 1 ft. 0 in. 0 ft. 1 in. over 750 v not over 2 kv 10 ft. 0 in. 4 ft. 0 in. 2 ft. 0 in. 0 ft. 3 in. over 2 kv not over 15 kv 10 ft. 0 in. 5 ft. 0 in. 2 ft. 2 in. 0 ft. 7 in. over 15 kv not over 36 kv 10 ft. 0 in. 6 ft. 0 in. 2 ft. 7 in. 0 ft. 10 in. protective clothing and personal protective equipment (ppe): a flash-hazard analysis is intended to determine the amount of available fault energy that the system can provide. available energy is dependent on the size of the transformer together with the impedance of the circuit. technical papers have defined incident energy as the amount of energy that might be “incident” on a material that is at a specified distance from the arc. if the incident energy is known and protective clothing is selected that has a rating equal to or greater than the engineering, technology & applied science research vol. 6, no. 6, 2016, 1307-1315 1312 www.etasr.com mobarak and alshehri: perspectives of safe work practices: improving personal electrical safety of … available energy, then an injury is unlikely. protective clothing can be selected based on the amount of incident energy. flash protection: up to 6 inches: where the transformer ahead of the equipment is 500 kva or smaller and the overcurrent protection is current limiting. up to 18 inches: where the transformer ahead of the equipment is 75 kva or smaller and without current limiting overcurrent protection. more than 18 inches: where the transformer is larger than 500 kva and without current-limiting overcurrent protection. as the size of the transformer increases above 500 kva, the amount of needed protection also increases. where the transformer is more than 750 kva, incident energy should be calculated or determined h in the electrical safety program guide. use protective clothing: always wear flame-resistant clothing. the greater protective value of the clothing, the greater the protection. cover every body part that is within the flash-protection boundary with protection. keep all fasteners closed. buttons and zippers should be buttoned or zipped. wear heavy-duty leather gloves. leather is not classified with an established rating. however, normally an arc-flash event is so fast that the leather will provide the necessary protection. sometimes the cotton stitching that holds the gloves together will burn, but the gloves will hold together long enough to afford significant protection. wear heavy-duty leather shoes. like heavy-duty leather gloves, leather shoes will afford significant protection. workers should not wear sneakers or shoes of similarly light construction. wear polycarbonate safety glasses in addition to any other face protection. the polycarbonate material protects the eyes from the ultraviolet energy. d. arc blast: the kind of injuries that are typical with an arc blast are broken bones when a body is literally thrown across a room. metal parts and pieces are propelled across a room. there is a tremendous increase in pressure during an arcing fault. when the temperature of the plasma exceeds the melting point of copper, the conductor changes state from solid to liquid. as the temperature exceeds the boiling point of the liquid copper, the copper liquid becomes copper vapor. now, when water changes state from liquid to steam, the water volume expands four times, unless constrained in an enclosure. when the copper vaporizes, it expands many thousands of times. even without a containing enclosure, the speed at which the change of state occurs is so fast that there is a very significant increase in pressure surrounding the plasma. a pressure wave is created by the leading edge of this pressure buildup. without an enclosure, the pressure wave travels outward from the arc until the volume is large enough for the atmospheric pressure to stabilize. the air surrounding the arc plasma is also heated very rapidly, increasing the pressure buildup. these results are similar to a lightning bolt. the conducting plasma is very hot, and thunder is the acoustic response to the pressure wave. pressure measured means that a force will be applied for each unit of surface area. if we make some assumptions about the surface area of an average electrician, then we can estimate the amount of force that an electrician would feel from the leading edge of the pressure wave. figure 9 is intended to help make that judgment. one axis is marked in distance from an electrical arc, and the other axis represents the amount of force that an electrician would feel for a specific arcing fault. the diagonal lines represent an electrical fault current. fig. 9. arc-blast pressure on human body arc-blast injuries: when the wave front hits the worker from the front, the pressure at his or her back is still at atmospheric pressure. a differential pressure will exist from the front to the back of the worker. a differential pressure will also exist from the external surface of the worker and all internal surfaces inside the worker. injuries that might result from these differences in pressure include broken bones, cuts, and contusions. sensitive components of the inner ear can easily be damaged. internal organs can receive significant damage. the rapid increase in pressure can destroy the electrical equipment and expel parts and pieces with tremendous force. avoid arc-blast injury: if an arcing fault is impossible, then the chance of an arc-blast injury does not exist. any person who happens to be nearby when an arcing fault occurs is exposed to an injury from arc blast. experience shows that if the equipment is not arc-resistant equipment, the chance of the enclosure being destroyed is significant. maintain equipment and systems adequately. the integrity of electrical enclosures is very important. coordinate the overcurrent devices so that minimum time is required to clear the fault. flame-retardant ppe is not intended for protection from arc blast. however, arc-flash ppe might be a blend that includes abrasion-resistant textile. it is not possible for there to be exposure to injury from arc blast without a simultaneous exposure to arc flash. e. safe work practices: the plan should identify each step in the job and consider electrical hazards at each step. the plan should identify all hazards to which a worker might be exposed. the plan should consider the type and degree of exposure to each hazard. the grounding system is a primary strategy of the nec and serves to limit potential differences between conductive components and structures. inadequate maintenance will permit dangerous potentials to exist. procedures and policies contain wisdom that has been derived in the past. workers should always implement each requirement of the procedure. engineering, technology & applied science research vol. 6, no. 6, 2016, 1307-1315 1313 www.etasr.com mobarak and alshehri: perspectives of safe work practices: improving personal electrical safety of … electrically safe work condition: identify all sources of energy from drawings. the drawings must be up to date. if the information on the drawing is inadequate, the worker is at an elevated risk of injury. it is important to ensure that disconnecting devices are rated for operation under load. as equipment ages, the failure rate increases. sometimes the mechanical linkage in a disconnecting means fails, and all phases fail to open. where it is physically possible, open the door and look at each phase contact to make sure that an opening exist in each phase conductor. install lockout devices together with tags on all lockout points identified in the first step. always test for voltage with an adequately rated voltmeter. we recommend that a single-function device be the instrument of choice to avoid the possibility of setting the meter on the wrong scale. the device should be listed by an independent testing laboratory. if there is any possibility that the equipment could become reenergized by an overhead line that falls or by induction coupling from another source or by any component failure, then a ground set should be installed. plan the work: a work plan is a sequential listing of all the steps necessary to accomplish a job assignment. begin the process by identifying each step and writing the plan on paper. if the work sequence is simple and each step easily remembered, it may not be necessary to write the plan on paper. however, a written plan is always an advantage. identify and gather necessary procedures, manufacturer’s information, or drawings. review the work plan with someone else who is qualified to execute the job. identify all hazards associated with the work. be sure to consider both electrical and nonelectrical hazards. create an electrically safe work condition. if any ppe is needed, gather it all together, then inspect it to make certain that it will function as needed. assemble all test equipment that will be needed to perform the task and inspect it to ensure that it is not cracked, broken, or otherwise damaged. seek authority to perform the work. no exposure to an electrical hazard should be accepted without questioning the necessity to do so. ensure that the line organization is willing to accept any increased exposure. plan every job: a plan is a step-by-step list of all steps necessary to complete a job. the job might be either small or large. however, no job should be started until a plan is made. every person who will participate in or be associated with the job must have the same plan. if someone does not understand the plan, it is likely that something will go wrong. to plan the job, break it down into small steps. the steps identify the sequential process that must be accomplished to execute the job. all tasks should be planned. the plan should clearly identify the scope of the job. any change in scope should be cause to stop the work process and generate a new plan with the new scope or modify the original plan. everyone must be advised of the change in the plan. the plan should identify the boundaries of the job. everyone must understand boundaries and then respect those boundaries. work that is not within the recognized boundary must not be performed. the plan should clearly point out the time frame in which the job is expected to be completed. it may not be necessary for the plan to be written. the key is whether everyone involved in the job understands the plan. it is important that the plan be reviewed by someone who was not involved in producing the plan. if the plan is in writing, the review is more reliable. when reviewing the work plan, think about what could go wrong. the job lineup should include information about emergency procedures. what device will be used in case of an emergency, where is the communication device, where is the fire extinguisher, and what is to be done if there is a technical problem. make sure that all tools that are needed to perform the task are available. when exposure to an electrical hazard already exists, it is not the right time to be looking for a tool. workers are inclined to improvise a tool and use it improperly if a tool is needed and not readily available. if a special tool is needed, then be sure to procure the tool and have it available. isolate the equipment: the term clt-3 means clear, lock, tag, try, and test. • clear – people should be cleared away from the equipment and the electrical circuit that will be involved in the work task. • lock – locks should be installed in accordance with an established procedure or plan. installation of lockout devices should be one of the steps that is executed when establishing an electrically safe work condition • tag – together with locks, tags and their attachment devices make up a lockout device that should be installed when establishing an electrically safe work condition. • try – equipment that has a push button and is capable of running should be tried. trying to run the equipment is one indication that the correct disconnecting means has been opened. • test – for our purposes, testing for the absence of voltage is a critical step to ensure that no voltage exists on the exposed conductor. where it is physically possible, visibly verify that a break in all the power conductors exists. always test every conductor before touching it. test every conductor every time. if it is necessary to leave the work site, even for a few minutes, test every conductor when you return to the work location. assess people’s abilities: consider the qualifications of the person(s) that will perform the work task. when a work task is begun, the worker’s occupation, title, or job classification has little bearing on whether they can avoid an incident or not. knowledge and skill are the only characteristics that will help prevent an incident. think about the person’s experience and his or her state of training. the person had sufficient training to execute the physical aspects of the work task. the person had sufficient training to recognize and avoid electrical hazards. the person have the knowledge about protective strategies to avoid initiating an incident. the worker have physical dexterity to perform the task. the worker in a mental condition that enables him or her to remain focused on the work task. think about whether you have the skill to evaluate the condition of the worker. you understand the hazards enough to evaluate the exposure and determine if the risk is acceptable. it necessary to review the work with engineering, technology & applied science research vol. 6, no. 6, 2016, 1307-1315 1314 www.etasr.com mobarak and alshehri: perspectives of safe work practices: improving personal electrical safety of … someone who is better qualified to determine if the risk is both necessary and acceptable. the employer, the employee, and the owner are all responsible. they are each responsible for some element of the process of keeping people from being injured. for the process to be effective, each of these parts must be involved. the employer is responsible for: • establishing an electrical safety programme for the overall organization • defining and publishing safety policies and procedures • providing safety equipment that is needed to minimize exposure to electrical hazards • providing safety training for employees that enables each worker to know what hazards the employee is responsible for implementing the procedures that are defined by the employer. however, it is not that simple. each employee should provide the feedback that is necessary to keep procedures and practices up to date. employees are responsible for ensuring that training provided by the employer is understood. employees must be an integral part of the process for preventing injury to themselves and their fellow workers. the owner is inherently responsible for contactors that are working on site. in the strictest sense, the contractor might be the employer. however, the owner must make sure that the contractor is advised of all safety hazards to which contract employees might be exposed. the owner might be the landlord for a multinational corporation, or it might be the person who operates the facility for a small company. the owner must make certain that the contractor has been informed about hazards that exist on the site and should make certain that the contractor has an electrical safety programm that addresses the hazards which exist on the site. conclusions: this study focuses on safe work practices especially in terms of electrical hazards and actually arc flash hazards. potential hazards, causes, impacts and protection measures are discussed. a point by point guide is given for the person in charge. the basic steps are: think through the work plan and consider all possible exposure to the hazards of shock, arc flash, or arc blast. determine what approach boundaries will apply to each step in the work plan. consider every electrical conductor and every electrical component to be energized until the absence of voltage is verified. ensure that all employees are properly trained and equipped and that safety procedures are updated and known to all. acknowledgment this project was funded by the deanship of scientific research (dsr), king abdulaziz university, jeddah, under grant no. 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32-39, 2008 [65] n. langerman, “laboratory safety?”, journal of chemical health and safety, vol. 6, no. 3, pp. 49–50, 2009 [66] s. mohamed, t. ali, w. tam, “national culture and safe work behavior of construction workers in pakistan”, safety science, vol. 47, pp. 29–35, 2009 [67] a. sharif, n. norazahar, “at-risk behaviour analysis and improvement study in chemical engineering laboratories”, international journal of chemical and environmental engineering, vol. 2, no. 1, pp. 51–55, 2011 microsoft word 34-2340_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3488-3491 3488 www.etasr.com maniam et al.: a comparative study of construction waste generation rate based on different … a comparative study of construction waste generation rate based on different construction methods on construction project in malaysia haritharan maniam faculty of civil and environmental engineering, universiti tun hussein onn malaysia (uthm), parit raja, malaysia sasitharan nagapan faculty of civil and environmental engineering, universiti tun hussein onn malaysia (uthm), parit raja, malaysia sasitharan@uthm.edu.my abd halid abdullah faculty of civil and environmental engineering, universiti tun hussein onn malaysia (uthm), parit raja, malaysia shivaraj subramaniam faculty of civil and environmental engineering, universiti tun hussein onn malaysia (uthm), parit raja, malaysia samiullah sohu faculty of civil and environmental engineering, universiti tun hussein onn malaysia (uthm), parit raja, malaysia abstract—high construction waste (cw) generation in malaysia has serious impacts although there are very little available data regarding the relevant issue in malaysia. this lack of data results in improper cw management and cw disposal without proper control measures. to control the implications of cw, it is very important to understand their quantity which is currently unknown. past researches in malaysia, found that cw generation was affected by construction methods (cms) practiced on site. the aim of this study is to compare the cw generation rate between different cms for on-going construction projects in malaysia. common cms practiced in malaysia are conventional construction method (ccm), mixed construction method (mcm) and industrialized building system (ibs). to obtain cw generation data, site visit (sv) method, which consists of direct measurement (dm) and indirect measurement (im) is applied to this study. ccm was recorded to have the highest amount of waste. ibs method records 77.188 tons and mcm 53.191 tons. regarding the average waste generation rate (awgr), ibs recorded a value of 0.018 tons per square meter, while mcm recorded 0.030 tons per square meter and ccm recorded the highest amount of 0.046 tons per square meter. keywords-construction waste generation; construction method i. introduction construction sector has an important role in promoting economy growth in malaysia [1]. many infrastructure projects and buildings have been built [2] and cw in landfill results in a large burden and a costly issue for solid waste management [3]. wastes have the potential to affect the human well-being and environment [4]. despite the fact that this problem has caught the attention of the media for a long time, measures taken to control the waste generation are very few [5]. attention towards cw was only given after the implications have increased regarding environmental issues [6]. there is no printed and reliable data related to cw in malaysia [1, 7]. in addition, malaysia still lacks researches on cw generation [8]. the general components in cw are inert materials (e.g. concrete, timber, metal, bricks, etc.), which cause small damage to the environment. proper cw measurement is vital to initiate an effective management at both project and regional level [9]. cw generation is affected by a few factors in the construction field, like improper management, low awareness, rules and regulations. cw generation also depends on the cm practiced and materials utilized at construction sites [10]. the limited number of cw generation data attracts the attention of local researchers to explore this field. ii. literature review a. types of cms according to researches from table i, the cms implemented in malaysia are, conventional construction method (ccm), mixed construction method (mcm) and industrialized building system (ibs) method. table i. construction methods used in malaysia reference construction method ccm ibs mcm [1] ● ● ● [8] ● [13] ● ● ● b. cw issues in malaysia the construction industry plays a significant role in malaysia’s development both in infrastructure and economic sectors. malaysian construction industry has experienced a vast development over the last 20 years. almost all projects carried out are very complex, and require higher skills with superior technologies, fast track and concurrent practices of work and engineering, technology & applied science research vol. 8, no. 5, 2018, 3488-3491 3489 www.etasr.com maniam et al.: a comparative study of construction waste generation rate based on different … higher competitive terms of price [11]. in malaysian construction industry, data availability is not satisfactory even for current projects [12]. moreover, the construction industry’s impact on nature is noteworthy as the major infrastructure projects high demands, residential and commercial constructions are generating high volumes of cw [13]. countries like malaysia tend to concentrate more in the topic of construction and demolition waste generation, including waste causes, waste generation rate, and factors affecting waste generation, because these portions have received higher attention. c. construction waste density the construction waste calculated from this study will be either in m 3 or metric tons. the waste composition density is used to convert the waste into tonnage. table ii shows the waste composition density obtained by solid waste and nonphysical waste obtained by public cleansing management corporation (swcorp) [5]. unit density is used to convert m 3 to tons. table ii. density of waste composition waste composition density, k (ton/m 3 ) concrete 1.27 soil and aggregates 1.25 brick 1.20 tiles and ceramics 0.59 metal 0.42 timber 0.34 glass 0.61 plastics 0.23 paper and cardboard 0.21 mixed waste/ demolition waste 1.40 d. study objectives this study aims to compare cw generation rates between different cms for on-going construction projects in malaysia. to achieve this aim, the objectives of this study are: 1. to identify current cms practiced at construction sites. 2. to quantify cw generation rate for each cm. 3. to compare the cm generation rate among different cms. iii. research methodology this methodology is implemented by visiting the construction site for a field survey defined in terms of field measurement (fm). this method consists of direct and indirect measurements to collect cw generation data. a. direct measurements this method measures on site the weight of the waste produced or its volume. some assumptions must be made prior to direct measurement. four assumptions were made depending on how cw was stockpiled, gathered, scattered or stacked. for stockpiled waste, a rectangular based pyramid was assumed, and the volume was calculated by: 1 3 vs l b h= × × (1) for gathered waste, the layout shape was assumed cuboid, and the volume (vg) was derived from: vg l b h= × × (2) b. indirect measurements for indirect measurements, truck load records were used to estimate the cw volume generated on site. the containers’ volume and the number of trucks for waste collecting were recorded. c. cw generation rate calculation the principle of this methodology is to obtain the waste generation rate in ton/m 2 (weight per construction area). total area of the project floor needs to be calculated from the building plan and recorded for calculation of waste generation rate. the waste generation rate can be calculated from: c w / gfa= (3) where w is the total waste generated from construction project (tons), gfa is the gross floor area and c is the waste generation rate in ton/m². iv. results and discussion obtained results were sorted according to the three cms stated previously, namely conventional construction method (ccm), industrialized building system (ibs), and mixed construction method (mcm). each building site was monitored for 3 months in order to obtain the data. all chosen sites were at the construction stage. a. total construction waste waste data are shown in table iii. table iii. total waste for each site and cm project/site total waste (tons) ccm 1 276 ccm 2 241.334 ccm 3 192.414 ccm 4 80.878 ibs 1 98.89 ibs 2 49.83 ibs 3 112 ibs 4 48.03 mcm 1 10.824 mcm 2 28.36 mcm 3 25.02 mcm 4 148.56 b. construction waste generation 1) conventional construction method (ccm) figure 1 illustrates, three months of construction waste data collected for ccm sites. these data were collected continuously by following the site progress. total waste generated by every site was calculated. we see that ccm 1 records the highest amount of waste. the least amount of wastes is recorded in ccm 4. 2) ibs method four sites were selected regarding ibs method. data were collected separately for each site. the collected data are shown engineering, technology & applied science research vol. 8, no. 5, 2018, 3488-3491 3490 www.etasr.com maniam et al.: a comparative study of construction waste generation rate based on different … in figure 2. the highest amount of total waste was produced from ibs 3. the second highest amount of waste was recorded from ibs 1. ibs 2 and 4 produced the same amount of total waste. the waste generation for each site is not the same every month. the least amount of waste production was during the first month of measurements on ibs 4. fig. 1. construction waste obtained from ccm sites fig. 2. construction waste obtained from ibs sites 3) mcm the next four sites were chosen for using mcm during construction. mcm involves combinations of ccm and ibs, therefore it is also known as partial ibs. in general terms, it is the introduction of ibs elements into conventional construction. figure 3 shows the relative collected cw data. fig. 3. construction waste obtained from mcm site the highest waste generation is from mcm 4. during the first month, mcm 4 recorded a huge amount of waste generation compared to the other four sites that used mcm. the second highest waste was produced from mcm 2. the third was mcm 3 and the least amount of waste was from mcm 1. c. waste generation rate waste data obtained for every site of the previous part are analyzed in this section. all data from the 12 sites are compared according to their construction methods. following this, the gross floor area (gfa) of all sites is considered to draw the waste generation rate (wgr). wgr is used as a tool or a reference point at the construction industry to identify the waste generation rate per square meter. thus, the more the gfa, the lesser the wgr should be. 1) ccm the relative data are shown table iv. the total average amount of waste generated for ccm sites is 197.657 tons. table iv shows that, the highest wgr was produced by ccm 1, which is 0.130ton/m 2 , and the second highest was from ccm 4 with 0.046ton/m 2 . the average wgr for the ccm sites is 0.046ton/m 2 . table iv. waste generation rate for ccm project total cw (tons) gfa (m 2 ) wgr (ton/m 2 ) ccm 1 276 2121.17 0.130 ccm 2 241.334 187000 0.001 ccm 3 192.414 38853 0.005 ccm 4 80.878 1745 0.046 average 197.657 0.046 2) ibs table v shows, the wgr for ibs method sites. ibs 1 had the the highest gfa, which was 58680m 2 . the second highest gfa was from ibs 2, at 43200m 2 . the average waste amount generated from this construction method was 77.188 tons. ibs 4 recorded the highest wgr, which was 0.012ton/m 2 , followed by ibs 3, ibs 1 and ibs 2 whith 0.003, 0.002 and 0.001ton/m 2 respectively. the average amount of wgr from ibs method sites is 0.018ton/m 2 . table v. waste generation rate for ibs project total cw (tons) gfa (m 2 ) wgr (ton/m 2 ) ibs 1 98.89 58680 0.002 ibs 2 49.83 43200 0.001 ibs 3 112 38410 0.003 ibs 4 48.03 4064 0.012 average 77.188 0.018 3) mcm the measure results are shown in table vi. the highest gfa is from mcm 4, at 7460m 2 and the second biggest area is from mcm 1 at 1856m 2 . the average waste amount for mcm sites is 53.191 tons. the highest wgr was from mcm 3 at 0.06ton/m 2 . overall the average wgr for mcm sites is 0.03ton/m 2 . table vi. waste generation rate for mcm project total cw (tons) gfa (m 2 ) wgr (ton/m 2 ) mcm 1 10.824 1856 0.006 mcm 2 28.36 1808 0.016 mcm 3 25.02 416 0.060 mcm 4 148.56 7460 0.020 average 53.191 0.030 engineering, technology & applied science research vol. 8, no. 5, 2018, 3488-3491 3491 www.etasr.com maniam et al.: a comparative study of construction waste generation rate based on different … d. average waste generation rate (awgr) figure 4 shows the average waste generated for each construction method. fig. 4. awgr for the different construction methods (ton/m 2 ). when compared with the other two methods, ccm recorded the highest waste per area which is 0.046ton/m 2 . the second highest was mcm with 0.03ton/m 2 . the least amount of waste generation per area was recorded for ibs sites, which was 0.018ton/m 2 . v. conclusion this paper introduced a study that relates construction method and construction waste generation rate. this study was conducted based on the construction methods existing in malaysia. the aim and the three objectives of our research were achieved. the relationship between construction method and construction waste generation rate was revealed. from the research, we learned that the conventional method generates higher construction waste than the modern construction method or ibs. construction waste generation study is wide and still at an early stage in malaysia. exploring on infrastructure project would be a pioneer for malaysian construction waste generation studies. by conducting research on infrastructure projects, the importance of the study enhanced. furthermore, the relationship on the type of project and construction waste generation is a suggested future topic. this relationship will reveal whether the waste generation rate is affected by the type of project or not. example of existing projects in malaysia such as residential, non-residential, social amenities and infrastructure projects are recommended to be explored. additionally, existing private and government projects in malaysia should be considered in future studies. recycle, reuse and reduce (3r) element will be an interesting part of future studies. by implementing 3r in construction waste, effective construction waste management practices would be identified. indirectly, local contractors will be exposed to the sustainable development in the construction industry. references [1] c. mach, t. fujiwara, c. s. ho, “construction and demolition waste generation rates for high-rise buildings in malaysia”, waste management & research, vol. 34, no. 12, pp. 1224-1230, 2016 [2] v. w. y. tam, “rate of reusable and recyclable waste in construction”, the open waste management journal, vol. 4, pp. 28-32, 2011 [3] p. j. dolan, r. g. lampo, j. c. dearborn, concepts for reuse and recycling of construction and demolition waste, cerl technical report 99/58, us army corps of engineers, construction engineering research laboratories, 1999 [4] h. arslan, n. cosgun, b. salg, “construction and demolition waste management in turkey”, in: waste management, an intergraded vision, intechopen, 2012 [5] s. nagapan, i. a. rahman, a. asmi, n. f. adnan, “study of site's construction waste in batu pahat, johor”, procedia engineering, vol. 53, pp. 99-103, 2013 [6] t. u. ganiron jr, “recycling concrete debris from construction and demolition waste”, international journal of advanced science and technology, vol. 77, pp. 7-24, 2015 [7] s. mahayuddin, j. pereira, w. badaruzzaman, m. mokhtar, “construction waste index for waste control in residential house project”, sb 10 new zealand, te papa, new zealand, may 26-28, 2010 [8] r. noor, a. ridzuan, i. endut, b. noordin, z. shehu, a. ghani, “the quantification of local construction waste for the current construction waste management practices: a case study in klang valley”, 2013 ieee business engineering and industrial applications colloquium, langkawi, malaysia, april 7-9, 2013 [9] h. bergsdal, r. a. bohne, h. brattebo, “projection of construction and demolition waste in norway”, journal of industrial ecology, vol. 11, no. 3, pp. 27-39, 2008 [10] u. f. a. r. mohammed, a. s. h. mohamed, “a glance on construction solid waste management in khartoum”, international journal of science, engineering and technology research, vol. 5, no. 1, pp. 101106, 2016 [11] m. a. eusuf, m. ibrahim, r. islam, “the construction and demolition wastes in klang valley, malaysia”, planning malaysia journal, vol. 10, no. 3, pp. 99-124, 2012 [12] r. a. begum, c. siwar, j. j. pereira, a. h. jaafar, “a benefit–cost analysis on the economic feasibility of construction waste minimisation: the case of malaysia”, resources, conservation and recycling, vol. 48, no. 1, pp. 86-98, 2006 [13] s. k. lachimpadi, j. j. pereira, m. r. taha, m. mokhtar, “construction waste minimisation comparing conventional and precast construction (mixed system and ibs) methods in high-rise buildings: a malaysia case study”, resources, conservation and recycling, vol. 68, pp. 96103, 2012 engineering, technology & applied science research vol. 8, no. 6, 2018, 3657-3667 3657 www.etasr.com kiamehr et al.: a multi-objective optimization model for designing business portfolio in the iranian … a multi-objective optimization model for designing business portfolio in the oil industry amir kamran kiamehr faculty of management and economics, department of industrial management, tarbiat modares university, tehran, iran adel azar faculty of management and economics, department of industrial management, tarbiat modares university, tehran, iran azara@modares.ac.ir mahmoud dehghan nayeri faculty of management and economics, department of industrial management, tarbiat modares university, tehran, iran abstract—designing a business portfolio is one of the key decisions in developing corporate strategy. most of the previous models are either non-quantitative or financial with an emphasis on optimizing a portfolio of investments or projects. this research represents a multi-objective optimization model that firstly, employs quantitative methods in strategic decisionmaking, and secondly, quantifies and considers non-financial, strategic variables in problem modeling. in this regard, links between businesses within a portfolio have been classified into four groups of market synergy, capabilities synergy, parenting costs, and sharing benefits, and have been structured as a conceptual model. although the conceptual model can be applied to various industries, it is formulated for designing the portfolio of multi-business companies in iran oil industry. the model has been solved for three cases by nsga-ii algorithm and strategic insights have been explored for different corporate types. keywords-corporate strategy; business portfolio; multi-objective optimization; oil industry i. introduction the historical trend about how business portfolios form represents the tendency of companies to engage in diverse businesses during the 50's to 80's and the emergence of large multi-purpose companies; then, the trend reversed from the 80's to now by focusing on a major and specialized business, or ultimately a portfolio of “related” businesses [1]. over the past decades, how to define a business portfolio has been one of the key issues in strategic planning for businesses. studies in this regard have been developed in areas such as diversification, vertical integration, outsourcing, m&a, partnerships, and allocation of resources among businesses [2]. the studies and models in this area can be divided into two main groups. the first group includes famous models such as ge/mckinsey matrix and boston consulting group growth/share matrix [3, 4]. they consider entering or not entering into a business with limited and conceptual criteria such as industry attractiveness and competitive status. on the contrary, the second group of financially-focused studies are seeking to maximize profit or minimize risk of investment portfolios, like numerous studies based on markowitz's famous model for portfolio optimization [5]. however, it seems that the studies and the developed models in this area are faced with weaknesses in terms of efficiency for strategic decision-making because the first group of models is conceptual and high level and they cannot provide the necessary analysis to support management decisions. meanwhile, the second group is suitable for optimizing stock and investments portfolios while the components in design of a business portfolio cannot be described only in the context of financial indicators. in order to meet this need, this research is an attempt to develop a quantitative model that can support strategic decision-making at the corporate level for designing a business portfolio. ii. literature review over the past decades, two key levels of strategy have been defined for organizations. first, “corporate strategy” that defines the territory of the corporation and shows businesses which corporates should enter into. secondly, “business strategy” that deals with how corporations compete within an industry or market [2, 6]. authors in [7] structured approaches related to corporate strategy in four groups including portfolio management, restructuring, transferring skills, and sharing activities. each approach is based on a different mechanism for value adding by the corporation. portfolio management is based on diversification, mainly through the acquisition of attractive businesses, providing capital, goal setting, and monitoring of business outcomes. in restructuring approach, the focus is on potentials of business units that are prone to change. in skills transfer approach, focus is on synergy and the transfer of skills and knowledge among the value chain of businesses. in sharing activities approach, the value is created through shared operations in value chain such as the use of a shared distribution system or creation of competitive advantage through cost reduction. in the above structure, the first two approaches are based on the creation of value through the association of the parent company with each of the independent businesses, while the other two concepts are focused on extracting value through the link between businesses and their synergy. in a general view, corporate strategy can be considered as a decision on product range and vertical range, which is discussed in the literature in terms of diversification and vertical integration, respectively. evidence suggests that in the 1950s and 1980s, companies began to design diverse and unrelated business portfolios, they set up multifunctional companies and diversified businesses that ultimately led to the formation of so-called “conglomerates”. based on the engineering, technology & applied science research vol. 8, no. 6, 2018, 3657-3667 3658 www.etasr.com kiamehr et al.: a multi-objective optimization model for designing business portfolio in the iranian … experience, the above process was reversed from 1980, and in that period unprofitable businesses were left aside. then, refocusing has once again been highlighted on major and specialized businesses or the formation of a portfolio of related businesses [2]. in some studies, it has been shown that the focus strategy has a positive impact on the corporate's value for shareholders, but some argue that corporate devaluation after diversification is due to the ownership of new businesses at lower prices during the diversification process [8]. despite decades of debate in this area, portfolio design and issues like the amount of diversification and vertical integration are still at the heart of the attention of businesses and researchers [9-11]. the persistence of these questions is because of the fact that although there are evidence of failure of many diversification strategies in the age of diversification, there are still undeniable advantages for diversity including the possibility of growth (in the sense of going beyond the current industry's boundaries), risk reduction due to its distribution in a portfolio of businesses, savings by globalization, benefit of the parent company, and reaching an internal market [2, 12, 13]. it can be concluded that the effectiveness of diversification is subject to conditions [14, 15]. moreover, importance and complexity of decision making on the business portfolio in various industries varies according to the volume of the required investment, the variety of components in the value chain, and the existing risks. in this regard, the oil industry can be ranked high. for example, in the field of exploration and production, decisions are very complex and risky due to the uncertainty and large number of factors involved. the selection of the optimal portfolio of projects in this section is influenced by diverse topics including corporate strategies and constraints, reservoir geology assessment, engineering data, economic forecasts, financial model, and regulatory aspects [16]. in this regard, mathematical optimization models have been widely developed for the oil industry by researchers. author in [17] used genetic algorithm for optimizing portfolio in the oil and gas industry. in his model, the portfolio is composed of projects, not businesses. in other words, it is the investment portfolio of the oil company. he also argues the advantages of the portfolio theory for this purpose. it enables decision makers to consider set of available opportunities beyond merely examining the independent economic indicators of each project and approving or rejecting investment in it. it also gives them the opportunity to reach a portfolio of projects with maximum returns at a certain level of risk. in general, mathematical optimization models offered for the oil industry can be classified into three strategic areas of portfolio selection, tactical planning such as production planning, and operation such as well optimization [18]. in this framework and given the complexity of decision making in the oil industry, portfolio design models have always been considered, used and developed [19, 20]. new tools such as the theory of real options have also been used for this purpose [21]. however, in previous researches on portfolio optimization, financial approaches based on markowitz's foundation have been applied. in the oil industry, the use of portfolio concept and portfolio theory has focused primarily on portfolio selection methods for projects and assets. hence, quantitative models for designing a business portfolio that consider strategic concepts have not developed in this industry. iii. designing model a. conceptual model in order to develop a model that provides the optimal business portfolio, we first need to determine the goals we are seeking for optimization. according to the existing literature and workshops organized by a focus group of experts, four main objectives were identified, namely maximum profitability, minimum investment, maximum growth and maximum profit robustness (minimum profitability risk). the first two objectives can be integrated as the economic value added (eva) concept. economic value added, one of the most widely used criteria in economic profitability models [22], is a good indicator of differentiation between portfolio with higher returns than lower returns [23]. despite fundamental similarities, eva provides better strategic and management illustration of economic returns for a company compared to npv which is basically developed to model the profitability of a project [24]: p eva wacc c c   = −     (1) in this equation, p is net operating profit after tax, c is invested capital, and wacc is weighted average cost of capital. accordingly, it can be said that each of the businesses in the portfolio at each period creates an economic value added independently and this trend of value adding during the periods leads to growth and robustness. based on existing literature, we formulate this cross-business impact as follows: 1. capability synergy: a business in a portfolio can affect the level of capability in another business by different ways, such as sharing activities or utilizing existing knowledge and expertise. 2. market share synergy: participating in a business can change the market of another business. for example, creating a market for another business or prevent its presence in a market, because of legal constraints. 3. parenting costs: having a portfolio of businesses instead of an individual business can create costs such as overheads, management costs or so-called holding costs, which are called “parenting costs” in this research. 4. sharing benefits: engaging in a business can save money in the cost structure of another business, which is called “sharing benefits”. these benefits can be realized in a variety of ways such as using shared resources or services, or increasing bargaining power with suppliers. therefore, we can present a high-level, conceptual model (figure 1) in which the value creation of any business is a function of the revenue, cost, and profitability mechanisms of the business. these factors are independently influenced by the internal variables (capabilities) and the external variables (market) of each business, while being systematically affected by the link between the businesses in the fourfold form above. engineering, technology & applied science research vol. 8, no. 6, 2018, 3657-3667 3659 www.etasr.com kiamehr et al.: a multi-objective optimization model for designing business portfolio in the iranian … fig. 1. conceptual model now, if x represents the presence or absence in a business, the above model can be formulated for business i in the period t in the form of the following mathematical relations: ( )1 , i tmax z f eva= (2) , 2 i t de max z f dt   =     (3) ) , 2 3 ( i tp min z f = (4) ( ), , ,,i t i t i teva f p i= (5) ( ), , ,,i t i t i tp f e c= (6) ( ), , ,and , , , ,i t i t i te c f i s cb pc sb= (7) ), , , (s cb pc sb f g= (8) )( jg f x= (9) b. structuring industry businesses according to existing literature [25-27], industry evidence, and expert opinions, a structure for oil industry businesses is presented at three levels in figure 2. fig. 2. three-level structure for value chain of oil industry businesses c. modeling level-1 businesses for modeling development and production business, a simplified model of iran's new oil contracts, known as ipc, is considered. in this model, the contract period for a field is 20 years, during which the development of the field will take place over a period of 5 years, after which there will be three 5-year periods equal to 15 years of production. capital expenditures related to the development period will be repaid by the national oil company during the operation period (with a delay of 5 years) including financial costs. operating costs are repaid on an annual basis, and the oil company will receive a certain amount of remuneration (reward) per barrel of production. in refining business, we consider five years as construction (or acquisition) period as well, while having 25 years (5 periods) of operation. we assume that there is no competition to obtain the license for investment in these two businesses of level-1. since this research seeks to model a business and not a project, we consider another type of costs as indirect costs of a business in the model. it includes non-project costs such as costs for administration or key personnel of the headquarters. table i. model variables for level-1 businesses variable description 𝑪𝑿𝒊,𝒕 investment in business i in period t 𝒖𝒕 increase in oil production capacity in period t 𝑼𝒕 oil production in period t 𝒒𝒕 increase in refining capacity in period t 𝑸𝒕 production of refining products in period t 𝑹𝒕 rewards of oil production (remuneration) in period t 𝑶𝑿𝒕 direct costs of refinery operation in period t 𝑬𝒊,𝒕 income from business i in period t 𝑰𝑪𝒊,𝒕 indirect business costs i 𝑷𝒊,𝒕 profit by business i in period t 𝑷𝒊 𝒇 future potential benefits from investment in business i 𝑬𝑽𝑨𝒊,𝒕 economic value added from business i in period t in development and production, if cx dollars is needed to increase production capacity for a barrel per day, with cb1 as the capabilities level of the company in this business (which is defined in the range of 0 to 1 and its average is the normal capability in the industry), we will have: 1 1, ( .5). t t cb cx u cx + = (10) the power relationship is used to estimate the amount of investment required to build a refinery. it is widely applied to estimate initial investment costs for a refinery based on investment and capacity of a reference refinery [28]. according to this equation, if c0 is regarded as the amount of investment to build a sample refinery with an annual capacity of q0 while we have company's capability (cb2), then: 2, 0.6 2 0 0 ( .5). . t t cx q cb q c = + (11) the production capacity added in each period will be achieved not in that period but in future periods. therefore, the amount of oil produced and refined product in each period is: 1 t 3 0 t t i i u u − = −  =  (12) engineering, technology & applied science research vol. 8, no. 6, 2018, 3657-3667 3660 www.etasr.com kiamehr et al.: a multi-objective optimization model for designing business portfolio in the iranian … 1 5 0 t t i i t q q − = −  =  (13) in the contracts described for development and production, the corporate's profits in each period are equivalent to f dollars reward per barrel of oil production: ( )5*365 . . t tr f u= (14) in refining business, income is equal to the sales of refined products. if p is the weighted average price of the corporate’s refined products, by assuming 330 days of operation annually, we have: 2, (5*330) . o t t t e q p= (15) in development and production, the investment and the operating costs are both reimbursed by the national iranian oil company, therefore, they are eliminated from the model calculations. in the refining business, the operating costs, which mainly include cost of feed, fuel, catalysts, etc. are directly related to the amount of refined products produced per period. therefore, if we assume that the production of a barrel of petroleum products costs ox dollars, operation cost in each period can be calculated considering the level of corporate's capability in refining business: 2, 2 (5 * 330) . ( .5) t t ox q ox cb = + (16) meanwhile, indirect costs are affected by both production/operation and development of fields or new refineries. therefore, they could be considered as a function of income or profits in each period (ai dollar per barrel), the volume of investments in development (bi dollars per investment dollar), and fixed costs of the business (ci). 1 1, 1 1 1, 1 1 ( ) ( .5) t t t x ic a r b cx c cb = + + + (17) 2 2, 2 2, 2 2, 2 2 ( ) ( .5) t t t x ic a e b cx c cb = + + + (18) in these equations, ci represents the costs involved in having an operating business, regardless of contracts and projects such as cost of key personnel, buildings, etc. now we can calculate the business profits of development and production in each period: 1 1, 1 1 1, 1 1 ( ) ( .5) t t t x ic a r b cx c cb = + + + (19) 2, 2, 2, t t t t p e ox ic= − − (20) therefore, the economic value added is: , , , . i t i t t i t eva p wacc cx= − (21) in addition, it should be noted that a part of investments in the 20-year period of the model, leads to future production in years after the problem period. hence, at the end of the 20th year, potential future profits have been generated in addition to the profits received. if the average profitability per production over the 20 years is calculated and called pi, we assume that profitability for production in future periods will continue according to such average. by discounting future profits with the rate of wacct, we will have: 4 1,1 1 4 1 tt tt p p u = = =   (22) 4 2,1 2 4 1 tt tt p p q = = =   (23) ( ) 7 1 1 5 . 1 f t t t t p u p wacc= = +  (24) ( ) 9 2 2 5 . 1 f t t t t p q p wacc= = +  (25) d. modeling level-2 and level-3 businesses while investment is a key function in level-1 businesses, in level-2 and level-3 businesses that are contracting and service businesses, investment is not essential. in these businesses, the cash flow depends on the company’s contracts and invoices. nevertheless, drilling services (k=2) and construction and installation (k=4) are “equipment-based”. therefore, investing in machines and equipment is required in mentioned businesses. the variables for each business in level-2 (j=1-3) and level-3 (k=1-5) are defined in table ii. table ii. model variables for level-2 and level-3 businesses variable description level-3 level-2 𝑲𝒌,𝒕 ′′ investment in period t 𝑬𝒌,𝒕 ′′ 𝑬𝒋,𝒕 ′ income in period t 𝑰𝑪𝒌,𝒕 ′′ 𝑰𝑪𝒋,𝒕 ′ direct costs in period t 𝑫𝑪𝒌,𝒕 ′′ 𝑫𝑪𝒋,𝒕 ′ indirect costs in period t 𝑷𝒊,𝒕 𝑷𝒊,𝒕 profit in period t 𝑬𝑽𝑨𝒊,𝒕 𝑬𝑽𝑨𝒊,𝒕 economic value added in period t if we show the total market value of business j in period t as m'j,t and the total market value of business k in period t as m''j,t , we will have: ' ' ' ' , , ( .5) j t j j t j j e y m s cb= + (26) '' '' '' '' , , ( .5) k t k k t k k e z m s cb= + (27) where s'j and s''j represent the corporate’s potential market share (percentages) in business j and k, which is affected by the market conditions, the number of competitors and the intensity of the competition. since service contracts are often awarded competitively through tenders, all this potential market share is not actualized. indeed, the corporate's capability in a business (cb'k and cb''j) is a determinant factor in this regard. therefore, in the above relation, s'j and s''k indicate the effect engineering, technology & applied science research vol. 8, no. 6, 2018, 3657-3667 3661 www.etasr.com kiamehr et al.: a multi-objective optimization model for designing business portfolio in the iranian … of external factors outside the control of the company. cb'j and cb''k represent the effects of internal factors such as bid prices on tenders, capabilities, competitive advantage, and so on. we also assume that each business has a specific profit margin (m'j and m''k), which is the remainder of the contract after deducting direct costs. thus, we have the direct costs: ( )' ' ' , ,' 1 ( .5) j j t j t j m dc e cb − = + (28) ( )'' '' '' , ,'' 1 ( .5) k k t k t k m dc e cb − = + (29) indirect costs of a business are a function of the amount of contracts in hand (a' and a'' dollars per each dollar of contract value) as an indicator of current workload of the corporate. in case of equipment-based businesses, it is also a function of inhand equipment (b'' dollars per each dollar of investment in equipment) as an indicator of business size and related maintenance costs: ' ' ' ' j, ,' ( ) ( .5) j t j t j y ic a e c cb = + + (30) '' '' '' '' '' '' k, k, k,'' ( ) ( .5) k t t t k z ic a e b k c cb = + + + (31) where c' and c'' indicate the fixed costs that occur regardless of having a contract during a period only because of the presence of that business, such as the cost of key personnel and staff. based on the above, the profit could be calculated as: ' ' ' ' , , , ,j t j t j t j t p e dc ic= − − (32) '' '' '' '' , , , ,k t k t k t k t p e dc ic= − − (33) and for economic value added: ' ' , ,j t j t eva p= (34) '' '' '' , , , . k t k t t k t eva p wacc k= − (35) e. synergy of businesses so far, the model has been developed by considering businesses independent. however, the link and synergy between them is a decisive factor in portfolio design. in other words, adopting a systematic look at the portfolio of businesses suggests that being or not being in a business can affect parameters of another business. if cbi, cb'j and cb''k are independent capability parameters in each business of level 1, 2 and 3, adopting a system approach means that being in an business can lead to an increase or decrease in the capability level of another business. if cbi, cb'j and cb''k are respectively the variables relating to the corporate's capabilities in each three level businesses, we define: [-1,1] cb m, p ,n,q   as the capability impact factor of business m from level p on business n from level q. now, the effect of all other businesses on business n of the level q could be shown by the “capability synergy function” for business n of level q which is defined as: 2 3 5 ,1, , , 2, , ,3, ,1 1 1 , 3 3 5 1 1 1 . . . cb cb cb i i n q j j n q k k n qi j kcb n q i j ki j k x y z g x y z    = = = = = = + + = + +       (36) therefore, we will have: ),1.(1 cb i i i cb cb g= + (37) )' ' ,2.(1 cb j j j cb cb g= + (38) )'' '' ,3.(1 cb k k k cb cb g= + (39) having the above mentioned function, corporate's capability level in a business that was considered as an independent parameter is now modified by considering the synergistic effect of other businesses in the portfolio. in the same way, if the parameters si, s'j and s''k are the potential market share in each business of level 1, 2 and 3, adopting a system approach and considering the presence in other businesses can lead to an increase or decrease in this share and a change in the market position. if si, s'j, and s''k are respectively the variables indicating potential market share in each of the level 1, 2 and 3 businesses, by considering the link between businesses in a portfolio, we define: [-1,1] s m, p ,n,q   as the market impact factor of business m from the level p on business n from level q. meanwhile, we can define the “market synergy function” for business n from level q as: 2 3 5 ,1, , , 2, , ,3, ,1 1 1 , 3 3 5 1 1 1 . . . s s s i i n q j j n q k k n qi j ks n q i j ki j k x y z g x y z    = = = = = = + + = + +       (40) ,1 )1.( i s i i s s g= + (41) ' ' ,2 .(1 ) s j j j s s g= + (42) '' '' ,3 .(1 ) s k k k s s g= + (43) f. parenting cost and sharing benefits by establishing a portfolio of businesses, new overhead costs, called “parenting costs”, are generated. since these costs have a direct relation to size of the corporate and its operation, we can estimate them as a percentage (h) of the total income: 2 3 5 ' '' , , , 1 1 1 . t i t j t k t i j k pc h e e e = = =   = + +       (44) moreover, given that these costs are mainly spent on strategic management, financial management, audits and controls, etc., we distribute it equally among active businesses: , 3 3 5 1 1 1 . i t i t i j ki j k x pc pc x y z = = = = + +   (45) ' , 3 3 5 1 1 1 . j t j t i j ki j k y pc pc x y z = = = = + +   (46) engineering, technology & applied science research vol. 8, no. 6, 2018, 3657-3667 3662 www.etasr.com kiamehr et al.: a multi-objective optimization model for designing business portfolio in the iranian … '' , 3 3 5 1 1 1 . k t k t i j ki j k z pc pc x y z = = = = + +   (47) conversely, by forming a business portfolio, it is possible to share costs among some businesses. for this purpose, we define [-1,1] sb m, p ,n,q   as the sharing impact factor between business m at level p with business n at level q. now, we define the “sharing benefit function” for business n from level q as: 2 3 5 ,1, , , 2, , ,3, ,1 1 1 , 3 3 5 1 1 1 . . . sb sb sb i i n q j j n q k k n qi j ksb n q i j ki j k x y z g x y z    = = = = = = + + = + +       (48) to apply the benefits of cost sharing into the model, we assume that the cost-sharing function decreases the indirect costs of each business in each period. since this cost sharing cannot be unlimited and must include a part of indirect costs, we restrict it to a θ percentage of indirect costs. therefore, we will have: , ,1 , ( , ). sb i t i i t sb min g ic= (49) ' ' , ,2 , ( , ). sb j t j j t sb min g ic= (50) '' '' , ,3 , ( , ). sb k t k i k sb min g ic= (51) by considering parenting costs and cost sharing benefits, business profits should be modified as follows: 1, 1, 1, 1, t t t t t p r ic sb pc= − + − (52) 2, 2, 2, 2, 2, 2, t t t t t t p e ox ic sb pc= − − + − (53) ' ' ' ' ' ' , , , , , ,j t j t j t j t j t j t p e dc ic sb pc= − − + − (54) '' '' '' '' '' '' , , , , , ,k t k t k t k t k t k t p e dc ic sb pc= − − + − (55) g. objective function according to the conceptual model, the objective function is: ( ) 4 2 3 5 ' '' 1 , , , 1 1 1 1 1 2 1 1 i t j t k tt t i j kt f f max z eva eva eva wacc p p = = = =    = + +  +    + +     (56) ( ) ( ) ( ) 4 2 3 5 ' ' '' '' 2 , 1 , , 1 , , 1 , 2 1 1 1 i t i t j t j t k t k t t i j k max z e e e e e e + + + = = = =   = − + − + −         (57) 2 4 2 3 5 ' '' 3 , , , 1 1 1 1 i t j t k t t i j k min z p p p p = = = =    = + + −            (58) h. constraints the first constraint is the limitation of resources for investment. if the total capital available for the period t is ct, then we have: '' '' 1, 2, 2, 4, t t t t t cx cx k k c+ + +  (59) moreover, minimum required investment for level-1 and equipment-based businesses in level-3 can be defined as: , ( ) i t i cx c min (60) '' '' , ( ) j t j k k min (61) in equipment-based businesses (k=2,4), we consider that reinvestment in each period should be at least equal to the rate of depreciation in that business (τk): '' , 1 '' , k t k k t k k  +  (62) although size, the potential contribution of the market and capabilities are still decisive for equipment-based businesses (“drilling” and “construction and installation”), available equipment is also a limiting factor because the services provided by these businesses are depended on their equipment and machinery. hence, we apply the following limitation in the model for these businesses (k=2,4): '' '' , , 1 5 t k t k k k i i e z k =   (63) where ηk is the “revenue generating ratio” which is defined for each equipment-based business (k=2,4) as the maximum amount of annual revenue that could be generated per unit of investment in equipment and machinery. meanwhile, investing in a business is subject to the presence in it. so: ( ) ,1 0i i tx cx− = (64) ( ) '' ,1 0k k tz k− = (65) finally: , 0,1 i j x y = (66) other variables 0 (67) iv. solving the model and results to solve the model, three companies in the iranian oil and gas industry were studied (cases 1-3). each of these companies represents a type of corporate that has the competitive advantage and capability mainly in level 1, 2 and 3 of the hierarchy presented in figure 2 respectively. in order to analyze the results better, the model is solved in two modes: • system inter-relationship mode (si-mode): in this case, the links among businesses in the forms of market synergy, capabilities synergy, parenting costs and sharing benefits are included in the model. • elements independency mode (ei-mode): in this case, the relationships between businesses and their impact on each other are removed from the model. hence, all variables and parameters are considered independent of other existing businesses in the portfolio. to solve in the ei approach, the values of cb m, p ,n,q  , s m, p ,n,q  , h ,and θ are considered equal to zero. engineering, technology & applied science research vol. 8, no. 6, 2018, 3657-3667 3663 www.etasr.com kiamehr et al.: a multi-objective optimization model for designing business portfolio in the iranian … fuzzy delphi method has been used to determine the parameters of synergy, sharing benefits and capability level of case studies (tables iv-vi). the linguistic variables used for this purpose are the seven-point scale presented in table iii [29]. defuzzification of values is done by center of gravity (cog) method [30]. other parameters used to solve the model are presented in tables vii and viii. table iii. linguistic variables used in the research fuzzy number linguistic variables (0.9,1, 1) very high (vh) (0.7, 0.9, 1) high (h) (0.5, 0.7, 1) medium high (mh) (0.3, 0.5, 0.7) medium (m) (0.1, 03, 05) medium low (ml) (0, 0.1, 0.3) low (l) (0, 0, 0.1) very low (vl) table iv. market impact factor ( s m ,p ,n ,q  ) q=1 q=2 q=3 total n=1 n=2 n=1 n=2 n=3 n=1 n=2 n=3 n=4 n=5 p=1 m=1 0.000 0.190 0.430 0.430 0.033 0.550 0.430 0.550 0.367 0.033 3.013 m=2 0.240 0.000 0.033 0.033 0.430 0.033 0.033 0.033 0.367 0.550 1.752 p=2 m=1 0.097 0.033 0.000 0.240 0.033 0.430 0.430 0.097 0.033 0.033 1.426 m=2 0.097 0.033 0.240 0.000 0.033 0.097 0.033 0.430 0.367 0.033 1.363 m=3 0.033 0.097 0.033 0.190 0.000 0.033 0.033 0.097 0.367 0.430 1.313 p=3 m=1 0.097 0.033 0.240 0.097 0.033 0.000 0.190 0.190 0.033 0.033 0.946 m=2 0.033 0.033 0.240 0.097 0.033 0.190 0.000 0.033 0.033 0.033 0.725 m=3 0.067 0.033 0.097 0.240 0.033 0.190 0.033 0.000 0.240 0.033 0.966 m=4 0.033 0.033 0.033 0.097 0.097 0.033 0.033 0.240 0.000 0.240 0.839 m=5 0.033 0.097 0.033 0.097 0.240 0.033 0.033 0.033 0.240 0.000 0.839 total 0.73 0.582 1.379 1.521 0.965 1.589 1.248 1.703 2.047 1.418 table v. capability impact factor ( cb m ,p ,n ,q  ) q=1 q=2 q=3 total n=1 n=2 n=1 n=2 n=3 n=1 n=2 n=3 n=4 n=5 p=1 m=1 0.000 0.217 0.190 0.083 0.033 0.083 0.083 0.083 0.067 0.033 0.872 m=2 0.217 0.000 0.033 0.083 0.217 0.033 0.033 0.033 0.083 0.083 0.815 p=2 m=1 0.217 0.033 0.000 0.067 0.033 0.083 0.190 0.067 0.033 0.033 0.756 m=2 0.190 0.033 0.067 0.000 0.217 0.033 0.033 0.083 0.190 0.083 0.929 m=3 0.033 0.217 0.033 0.217 0.000 0.033 0.033 0.083 0.190 0.083 0.922 p=3 m=1 0.430 0.033 0.273 0.190 0.033 0.000 0.217 0.190 0.033 0.033 1.432 m=2 0.067 0.033 0.217 0.033 0.033 0.067 0.000 0.033 0.033 0.033 0.549 m=3 0.217 0.083 0.083 0.273 0.067 0.190 0.033 0.000 0.190 0.190 1.326 m=4 0.033 0.067 0.033 0.258 0.258 0.033 0.033 0.067 0.000 0.067 0.849 m=5 0.033 0.430 0.033 0.083 0.273 0.033 0.033 0.217 0.190 0.000 1.325 total 1.437 1.146 0.962 1.287 1.164 0.588 0.688 0.856 1.009 0.638 table vi. sharing impact factor ( sb m ,p ,n ,q  ) q=1 q=2 q=3 total n=1 n=2 n=1 n=1 n=2 n=1 n=1 n=2 n=1 n=1 p=1 m=1 0.000 0.387 0.175 0.175 0.033 0.175 0.058 0.175 0.033 0.058 1.269 m=2 0.387 0.000 0.033 0.033 0.175 0.033 0.033 0.083 0.083 0.175 1.035 p=2 m=1 0.175 0.033 0.000 0.175 0.058 0.175 0.217 0.083 0.058 0.058 1.032 m=2 0.175 0.033 0.175 0.000 0.387 0.083 0.058 0.083 0.217 0.083 1.294 m=3 0.033 0.175 0.058 0.387 0.000 0.083 0.058 0.083 0.217 0.083 1.177 p=3 m=1 0.175 0.033 0.175 0.083 0.083 0.000 0.083 0.258 0.033 0.058 0.981 m=2 0.058 0.033 0.217 0.058 0.058 0.083 0.000 0.058 0.033 0.033 0.631 m=3 0.175 0.083 0.083 0.083 0.083 0.258 0.058 0.000 0.083 0.387 1.293 m=4 0.033 0.083 0.058 0.217 0.217 0.033 0.033 0.083 0.000 0.083 0.840 m=5 0.058 0.175 0.058 0.083 0.083 0.058 0.033 0.387 0.083 0.000 1.018 total 1.269 1.035 1.032 1.294 1.177 0.981 0.631 1.293 0.840 1.018 table vii. capability level of cases in each business 𝒄𝒃𝟓 ′′ 𝒄𝒃𝟒 ′′ 𝒄𝒃𝟑 ′′ 𝒄𝒃𝟐 ′′ 𝒄𝒃𝟏 ′′ 𝒄𝒃𝟑 ′ 𝒄𝒃𝟐 ′ 𝒄𝒃𝟏 ′ 𝒄𝒃𝟐 𝒄𝒃𝟏 parameter 0.08 0.08 0.40 0.78 0.40 0.22 0.22 0.40 0.78 0.78 case 1 0.92 0.08 0.92 0.08 0.78 0.92 0.92 0.78 0.22 0.40 case 2 0.60 0.92 0.50 0.03 0.08 0.22 0.22 0.08 0.08 0.08 case 3 engineering, technology & applied science research vol. 8, no. 6, 2018, 3657-3667 3664 www.etasr.com kiamehr et al.: a multi-objective optimization model for designing business portfolio in the iranian … table viii. model parameters value parameter value parameter value parameter value parameter 0.0002 𝒂𝟏 19,800 𝒄𝒙 0.15 𝒔𝟒 ′′ 32,000,000,000 𝑴𝟏 ′ 0.0002 𝒂𝟐 56 𝒐𝒙 0.10 𝒔𝟓 ′′ 48,000,000,000 𝑴𝟐 ′ 0.0020 𝒂′ 4.8 𝒇 0.515 𝑾𝑨𝑪𝑪 25,000,000,000 𝑴𝟑 ′ 0.0020 𝒂′′ 75,000,000 𝑪𝟏(𝒎𝒊𝒏) 2,700,000,000 𝑪𝟎 2,400,000,000 𝑴𝟏 ′′ 0.0100 𝒃𝟏 150,000,000 𝑪𝟐(𝒎𝒊𝒏) 150,000 𝑸𝟎 12,800,000,000 𝑴𝟐 ′′ 0.0100 𝒃𝟐 6,000,000 𝑲𝟐 ′′(𝒎𝒊𝒏) 65 𝒑𝒕 2,400,000,000 𝑴𝟑 ′′ 0.0500 𝒃′′ 5,500,000 𝑲𝟒 ′′(𝒎𝒊𝒏) 0.07 𝒎𝟏 ′ 25,550,000,000 𝑴𝟒 ′′ 4,950,000 𝒄𝟏 250,000,000 𝑪𝒕-case1 0.08 𝒎𝟐 ′ 1,250,000,000 𝑴𝟓 ′′ 3,700,000 𝒄𝟐 500,000,000 𝑪𝒕-case2 0.08 𝒎𝟑 ′ 0.05 𝒔𝟏 ′ 3,050,000 𝒄′ 750,000,000 𝑪𝒕-case3 0.19 𝒎𝟏 ′′ 0.05 𝒔𝟐 ′ 3,050,000 𝒄′′ 1.62 𝜼𝟐 0.41 𝒎𝟐 ′′ 0.10 𝒔𝟑 ′ 0.031 𝒉 1.12 𝜼𝟒 0.15 𝒎𝟑 ′′ 0.05 𝒔𝟏 ′′ 0.5 𝝉𝟐/𝝉𝟒 0.08 𝒎𝟒 ′′ 0.05 𝒔𝟐 ′′ 0.42 𝜽 0.15 𝒎𝟓 ′′ 0.15 𝒔𝟑 ′′ the model we developed in this research is a highly complex one with a np-hard type that requires meta-heuristic methods to be solved. therefore, we used non-dominant genetic algorithm as one of the most efficient and applicable multi-objective methods for obtaining appropriate answers [31]. studies have shown that the improved version of this algorithm (nsga-ii) has better performance and less computational complexity than the previous versions, and provides better answers than the other presented algorithms [32]. using this algorithm, the model is solved by matlab software for each of the three cases in both ei and si modes. the initial population is 200, the number of generations is 100, and the crossover rate is 0.8. the chromosome defined for solving this model is a string of length 26, 10 of which (to enter or not enter into a business) are boolean variables. the rest (investment variables) are continuous variables. the objective function values for the answers set are shown in figures 4 to 9 in the form of the pareto front. square polynomial fitting is used in order to gain a better picture of answers. in order to improve the results and reduce the impact of out-of-range answers, bi-square method has been used for robust fitting. fig. 3. pareto front of objective functions for the first case si mode fig. 4. pareto front of objective functions for the first case ei mode fig. 5. pareto front of objective functions for the second case si mode fig. 6. pareto front of objective functions for the second case ei mode fig. 7. pareto front of objective functions for the third case si mode in figures 9-11, values of each objective function for the three cases are shown in both si and ei modes. engineering, technology & applied science research vol. 8, no. 6, 2018, 3657-3667 3665 www.etasr.com kiamehr et al.: a multi-objective optimization model for designing business portfolio in the iranian … fig. 8. pareto front of objective functions for the third case ei mode fig. 9. z1 for the three cases in si and ei modes fig. 10. z2 for the three cases in si and ei modes fig. 11. z3 for the three cases in si and ei modes in order to analyze the results obtained from decision variables, which represent entering or not entering into a business, the simple mean of values in each set of answers is calculated and presented separately for ei and si modes in figures 12 and 13. fig. 12. enter/not enter decision variable for the three cases si mode fig. 13. enter/not enter decision variable for the three cases ei mode v. discussion and conclusion the main achievement of this research is the structuring and formulation of qualitative concepts of corporate strategy in form of a quantitative optimization model. it can support top management in the process of strategic decision making and designing business portfolio. analyzing synergistic impact factors shows that having engineering business in the portfolio has the greatest impact on improving the capability-level of other businesses. on the other hand, “development and production” and “refining” businesses, followed by level-2 businesses, have the most positive impact on increasing the market share of other businesses. such pattern shows that specialized and knowledge cores, which in the studied industry means engineering capabilities, have a significant role in enhancing the firm's capabilities even in upstream businesses. hence, maintaining such businesses in vertical integration structure instead of outsourcing is feasible. for example, engaging in “subsurface engineering” (k=1) that provides capabilities such as reservoir engineering and geology can affect the firm's capabilities in the “development and production” (i=1) and promote it. moreover, entering into upstream businesses of the value chain can create internal markets for downstream businesses. in other words, in addition to direct benefits, investing in an upstream-level engineering, technology & applied science research vol. 8, no. 6, 2018, 3657-3667 3666 www.etasr.com kiamehr et al.: a multi-objective optimization model for designing business portfolio in the iranian … business can indirectly lead to new sources of income for the downstream businesses of a portfolio. nevertheless, such benefits should be evaluated considering the costs incurred by entering the business, required investment and parenting costs needed for holding management. legal barriers or strategic directions for assigning work to subsidiaries should also be considered in this regard. findings also show that the portfolio of the level-2 firm (case 2) performs better from the value adding point of view compared to level-1 companies (case 1). although these results are obtained within our defined assumptions and constraints, it shows that presence in higher-level businesses does not necessarily mean more economic value added. corporate managers should choose the optimum portfolio by considering internal factors such as the level of capabilities and external factors such as market potentials, as well as the interactions among businesses and their impact on each other. besides, the optimal diversification-concentration strategies for each type of corporation could by proposed based on results: • type 1 (high level of competitive advantages and capabilities in level-1 businesses): the portfolio should be formed with a focus on level-1 capital-based businesses, including “development and production” and “refinement” along with outsourcing of level-2 e&c operations. in order to play a better role as an employer, protecting corporate investments, benefit from internal markets and reduce risk, applying a “limited and relevant diversification” can be considered by entering into some level-3 businesses, especially engineering businesses. • type 2 (high level of competitive advantages and capabilities in level-2 businesses): the best strategy for these firms is “diversification”|. these firms would be better placed in all level-2 e&c businesses, upstream and downstream. it is also better for these companies to include “engineering” in their business portfolio as it makes them more capable and with better performance in level-2 contracting tasks. • type 3 (high level of competitive advantage and capabilities in level-3 businesses): the appropriate strategy for these firms is “focus”. these firms must refrain from engaging in field development and production contracts, investment, ownership of refineries and e&c businesses of level-2. on the contrary, they should focus on those specialized engineering services in which they are more capable and competitive. the findings also confirm that portfolio business performance (as a whole) is different from the total revenueexpenditure structure of individual business. presence in a business can change the components of another business and, consequently, its revenue-expenditure structure. this effect does not necessarily mean that the values of the objective functions are improved when considering the whole portfolio, but could provide a more realistic picture of the portfolio's value-adding potential. vi. future work suggestions given the wide range of stakeholders and decision criteria, further objectives could be included in prospective models, especially non-financial and non-economic ones such as environmental impacts or sustainable development, which have considerable importance in decision making for oil industry. also, criteria such as employment creation and energy security that are of interest to national oil companies could be considered in future optimizations. moreover, the dynamics of the relationship between variables over time periods can be applied in the model. for example, a continuous presence in a business can improve the market position in an upcoming period, and it will provide the firm with a competitive advantage compared to a newcomer. in addition, many of the variables used as deterministic variables can actually be defined as probabilistic variables, thus, the model becomes a probabilistic optimization model, in which the risk concept will be closer to real situations by covering issues beyond the fluctuations of profitability as it is considered in this research. references [1] l. g. franko, “the death of diversification? the focusing of the world's industrial corporates, 1980-2000”, business horizons, vol. 47, no. 4, pp. 41-50, 2004 [2] r. m. grant, contemporary strategy 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leekwijck, e. e. kerre, “defuzzification: criteria and classification”, fuzzy sets and systems, vol. 108, no. 2, pp. 159-178, 1999 [31] konak, d. w. coit, a. e. smith, “multi-objective optimization using genetic algorithms: a tutorial”, reliability engineering & system safety, vol. 91, no. 9, pp. 992-1007, 2006 [32] k. deb, s. agrawal, a. pratap, t. meyarivan, “a fast elitist nondominated sorting genetic algorithm for multi-objective optimization: nsga-ii”, lecture notes in computer science, vol. 1917, pp. 849-858, springer, berlin, heidelberg, 2000 microsoft word 10-3153_s_etasr_v9_n6_pp4917-4924 engineering, technology & applied science research vol. 9, no. 6, 2019, 4917-4924 4917 www.etasr.com naeem et al.: a review of shaped charge variables for its optimum performance a review of shaped charge variables for its optimum performance khalid naeem school of chemical and materials engineering, national university of sciences and technology islamabad, pakistan khalid.phd@scme.nust.edu.pk arshad hussain school of chemical and materials engineering, national university of sciences and technology islamabad, pakistan principal@scme.nust.edu.pk shakeel abbas al-technique corporation of pakistan islamabad, pakistan shakeelabbas@hotmail.com abstract—shaped charge is a device for focusing the chemical energy of explosives to a particular point or line for penetration or cutting purpose respectively. they are used for the penetration or cutting of various types of targets on land, water, underground, underwater, or air. their shape is either conical or linear and consists of explosive, casing and liner. the liner is bent towards the central axis producing a thin hypervelocity jet by the energy released as a result of the explosive detonation. this jet is utilized against the target. shaped charges can perforate or penetrate targets like aircrafts, ships, submarines, armored vehicles, battle tanks, and bunkers. this paper presents a detailed review of analytical works, computer simulations, and experimental results related to the liner. among modern diagnostic techniques flash x-rays, radiography is the best and widely used in the experiments performed in the last 40 years. powder metallurgy, which started in the late twentieth century raised the efficiency of shaped charges to new altitudes. the efficiency of the shaped charge depends on numerous factors such as explosive’s type, liner’s material, geometry and metallurgy, manufacturing technique, and casing thickness. factors concerning the liner’s material, metallurgical advancements, and geometry are discussed chronologically and in detail. keywords-conical liners; hemispherical liners; sintered powder liners; rolled homogenous armor i. introduction a shaped charge is an explosive cylinder with a cavity opposite to the detonation point. the shape of the cavity may vary from conical to bow-shape. the cavity in the explosive is either empty or may contain a liner made of metal, alloy or any other material, a status known as hollow charge and shaped charge respectively. a typical shaped charge is shown in figure 1. the shaped charge is known by different names in different parts of the globe, for example, hohlladung [1] and cumulative charge [2] in germany and the soviet union respectively. liners for shaped charges are manufactured according to the requirements in the form of cone, parabola, hemisphere, vshape or any other suitable form [3]. the v-shaped liner is also known as linear cutting charge used mainly for demolition purposes [4]. detonating a hollow cylindrical charge on or near the target produces a deeper cavity in the target than a cylindrical explosive without a cavity. this is known as the neumann or munroe effect [5]. in case of the lined cavity and axial symmetric geometries, an outgoing spherical detonation wave is produced from the detonation point. the detonation wave moves toward the liner at a speed of 5000 to 8000m/s dictated by the type of explosive [6]. the detonation wave exerts a pressure in the range of twenty to two thousand gpa on the liner which behaves as an inviscid incompressible fluid [7]. this pressure causes the liner to collapse at a strain rate of 10 4 s -1 to 10 7 s -1 . the collapse of the liner starts from the apex toward the centerline to form a jet. as the detonation wave progresses on the liner towards the base a big chunk of the liner flows into a slug. typical velocities of the jet and slug are 10,000 and 1,000m/s respectively [3]. this velocity gradient produces elongation in the jet, causing necking or breakup of the jet [8]. the high-velocity jet exerts pressure on the target which exceeds the target strength resulting in penetration [9]. at these high velocities the penetration of the jet is independent of the target strength but instead depends on its density [10]. the cavity is produced by the lateral displacement of the material due to intense pressure. the cavity further deepens when the shaped charge is moved a certain optimal distance away from the target known as standoff (so). the so depends on the size, geometry and the type of the explosive used in the shaped charge [11]. shaped charges are utilized for hypervelocity impact in space-related studies [12]. fig. 1. cutview of a shaped charge with a target ii. history of shaped charges the history of shaped charges begins with the utilization of the unlined cavity charge by franz in 1792 using black powder corresponding author: khalid naeem engineering, technology & applied science research vol. 9, no. 6, 2019, 4917-4924 4918 www.etasr.com naeem et al.: a review of shaped charge variables for its optimum performance which deflagrates. at that time there was no concept of detonation or detonator. after the invention of the detonator, foerster in 1833 successfully detonated the unlined cavity charge [13]. the invention of detonating caps patented by bloem can be regarded as the first lined cavity [14]. later on, munroe also performed experiments in the united states on the unlined and lined cavity [15]. to optimize the performance of shaped charges, multiple variables like casing material, casing thickness, high explosive type, liner to explosive mass ratio, cone angle, manufacturing technique of the liner, insertion of wave-shaper, grain size control, liner material, thickness, geometry, so distance, cone angle, bimetallic liner and multimaterial liners have been studied one by one or in parallel. optimization by wave-shaper and its effect on the detonation wave-front was conducted in [16]. a detailed work on the shaped charges can be seen in [17]. the current article is particularly focused on the utilization of different materials as liner, metallurgical advancements and geometry of the liner. iii. materials for the liner of shaped charge at first, the material employed for liner fabrication was copper (cu). its selection was based on its better elongation and moderate density [18]. it was found that steel liners with thickness up to 1mm perform better against armor plates than the grey-iron casting having thickness up to 1.5mm [19]. the microstructures of cu and tantalum (ta) liners were compared in [20]. the density of the liner plays an important role in penetration because the square root of the liner’s density is directly proportional to its penetration [21]: � ∝ ������ (1) the exact form of the equation is: � = � ∗ � ∗ ����� /��� ��� (2) where p, l, λ, and ρ denote penetration, jet length, a constant having value between 1 and 2 and density respectively [22]. it was found that brass and lead’s (pb) performance is not better than cu’s, and cu with smaller gain performs better than with larger grain. an alloy of cu and tungsten (w) was used for liner in [23] and the experiments were observed using flash x-ray (fxr). improved penetration for the subject alloy was observed due to the increased density and break-up time. the effects of jet rotation and so on penetration were also studied. because of its higher density, molybdenum (mo) was tested as a liner in [24-25]. at high strain rate the jet penetration depends upon the square root of the jet density and its length as shown in (2), therefore using high density materials like mo and w gives greater penetration in comparison to low density liners. tungsten made liners were simulated and studied analytically in [26]. shaped charge with reduced slug was patented by authors in [27]. the slug was reduced by introducing a double layer liner. the layer contacting the explosive disintegrates reducing the mass of the slug and the second layer produces the jet. liner made of al was used in [28] for penetration in concrete. the development of a al jet and its penetration was modeled with the hydrodynamic tool cale. copper liners preheated to 400-600 0 c were investigated in [29]. it was found that heating increased penetration power. liner of mo was used in [30]. the material was analyzed with the analytical tool jetform, hydro-code grim and experimentally. the liner was manufactured using six different techniques. the jets captured with fxr were compared with the results obtained from analytical and hydro-code and were found in close agreement. cu liners were used in [31-32]. jet formation, elongation and its particulation for aluminium (al), nickel (ni), cu, mo, ta, uranium and w as liner materials were studied in [31] and the conclusion was that cu, mo and w have better properties for shaped charge liner. silver, zirconium, titanium and depleted uranium (du) were tested as liners in [33]. all produced a ductile jet having longer breakup time than cu. it was concluded that these four materials give better performance at longer so when compared to cu. the use of du for liner was abondoned on the basis of its toxicity and radiation hazards. a study of liner made-up of a w-cu-ni alloy was carried out in [34]. cu with 20% pb was investigated with 2-d hydro-code in [35] to create a bigger hole in well casing and a small hole in the firing gun at the same time. because of high densities and high or moderate sound velocities mo, ta, w, and their alloys were studied in [36] for liners of shaped charges and explosively formed penetrators. the jet breakup was studied experimentally and numerically in [37]. the formula for the jet break up time published in 1979 was further investigated by authors in [38] using a cu liner. the effects in the variation of constants used in the formula by changing liner material, thickness, metallurgical state, and type of explosive were also included. al, cu, and w were investigated analytically and experimentally against hard rocks and concrete in [39]. the effect of current flow in cu jet was investigated in [40]. it was found that when injecting high current in the liner, the jet tip is less affected, whereas distortion of the jet is observed where the jet particles are not aligned along the jet axis by fxr. the effect of magnetic field on a cu liner showed that increasing the field decreases the penetration [41]. cu liner was further analyzed in [42] using autodyn. changes in the shape of the jet by the detachment of explosive from the casing, air bubbles inside the explosive, eccentric initiation and dimensional inaccuracies in the liner were analyzed at different so distances. the tandem warhead consists of two warheads: the precursor fitted at the front and the main warhead fitted after the precursor at some distance. it is mostly used against armored vehicles protected by explosive reactive armor (era). the precursor of the tandem detonates on the era mounted on the armored vehicle and the main warhead then attacks the bare armored vehicle. cu, al and steel liners were tested experimentally in [43] considering their incorporation in tandem warheads against concrete. it was found that a smaller diameter deep hole is produced by cu liner when compared to the al liner. the hole diameter and depth produced by steel liner is intermediate among the ones caused by cu and al. comparative numerical and experimental study of cu and cu-w liners with the same charge to mass of the liner was carried out in [44]. the tip velocity of the jets obtained from both liners is the same in the air but when the target was submerged in water the jet tip velocity of cu-w liner decreased slowly in comparison with cu liner. zirconium was utilized as a liner material in [45]. engineering, technology & applied science research vol. 9, no. 6, 2019, 4917-4924 4919 www.etasr.com naeem et al.: a review of shaped charge variables for its optimum performance bimetallic liners were studied by authors in [46] whereas bimetallic and reactive liners were studied experimentally in [47]. it was concluded that a single metal liner is better than a bimetallic liner. multi-material liners were studied numerically in [48] and it was suggested that they can be utilized for military purposes or in well perforation. the effect of a magnetic field on the penetration of a magnetized liner was analyzed in [49]. jet penetration was reduced in the presence of an axial magnetic field in the liner just before the shot, and a transverse field in the conducting target. the decreased penetration was caused by the amplification of the magnetic field in the jet formation region. a study of the jet formation in the initial stages from al liners was conducted in [50]. the simulated results were validated by experiments. ofhc (oxygen free high conductivity) copper was used in both simulations and experiments against steel submerged in the water behind the air gap in [51]. polytetrafluoroethylene (ptfe) with added cu powder was used in [52] as a shaped charge jet. cu powder was added to improve penetration and mechanical properties of normal ptfe. improved mechanical properties were verified by static compression and split hopkinson pressure bar test. the interaction of cu-w jet with the target material was investigated in [53]. for this reason, three target materials cu, carbon steel, and ti-6al-4v alloy were selected for penetration. the penetration depth ratio was found to be 10:28:21 respectively which indicated that the same jet behaves differently when the target material is changed. ofhc cu was utilized by authors in [54] in order to study the effects of drift velocity and so distance between jet particles on penetration. addition of zinc (zn) and ni in the cu-w alloy for was studied in [55]. it was found that w–cu– zn and w–cu–ni alloys have decreased target penetration because of the transverse dissipation of jet energy. addition of zn in the alloy decreased the melting point of the matrix, making it easier to melt and squeeze out. this reduced the lubrication effect of the matrix and the interaction between the w particles and the targets was facilitated. the addition of ni in the alloy increases the melting point of the matrix phase making it harder to melt. as a result, the lubrication effect decreased. the interaction between jets and targets and the transverse dissipation of the jet energy are the consequences of reduced lubrication, leading to decreased penetration. the damage mechanism in thick concrete was investigated numerically and experimentally in [56] with al and cu liners. experiments showed that the conical al liner had higher destructive power than cu liners in concrete. al and cu were also investigated numerically in [57] using ls-dyna. less penetration but bigger hole diameter in concrete-like targets for al liner were observed. low-density materials, namely float glass, lucite, and perspex were simulated as precursor shaped charge liner for tandem warhead against era in [58]. simulation by autodyn-2d showed that the jets from lowdensity liners were better than cu liner’s in terms of jet tip velocity, ductility, and jet tip diameter. these low-density liners did not create any hindrance to the main jet, so they can be utilized as precursor liner materials against era. steel, al, and cu were utilized against spaced and layered concrete in [59]. length and diameter of shaped charges were 60mm and the target was 120mm away. it was found by experiments and simulations that regarding steel and cu liners having cone angle smaller than 120°, the spaced target provided better protection than the layered target, but this was not true for al liner. considering cost effectiveness, cu and al are the best choices for rha and concrete-like targets respecitively. for greater penetration, high density materials like mo, w and du are used but they are toxic and, above all, du is radioactive. against composite and spaced armor, reactive metal and reactive metal powder liners perform better than the earlier mentioned ones. recently, research is focused on the liners made of reactive material which produces enhanced damage to the target [60]. iv. metallurgical advancements metallic liners are mostly formed by machining, diepressing, or rolling. the liner produced by such techniques has two distinct parts, the jet and the slug. the slug is heavier and slower than the jet. the low-velocity slug pulls the jet from behind, decreases its performance and in some cases, it fills the hole created by the jet. this is undesirable in perforation of well casing. this drove researchers to powder metallurgy, where the liners are manufactured from metal powder by sintering. it is the process of compacting granules to form a solid material by heat or pressure without melting [61]. early powder metallurgy was intended for high strength materials [62]. initial experiments on liners made of a mixture of w or titanium powder with carbon were conducted in [63]. liners fabricated with metal powder were studied in [64] using fxr. the hole diameter and penetrations in rolled homogeneous armor (rha) were investigated at different stand-off distances. various theoretical aspects which come across when interpreting the penetration of jet from the un-sintered powdered metal liner were discussed in [65]. the penetration model was improved by incorporating the jet’s porous compressible nature. experimental and numerical data on the powder liners made of cu and cu-w are available in [66]. it was found that powder metallurgy technology has the potential to manufacture liners of small calibres up to several dozen millimetres and it enables designing and manufacturing liners in various shapes and chemical compositions, which is beyond the scopes of traditional manufacturing technology [66, 67]. electroformed cu liners were analyzed in [68] with backscattered kikuchi patterns and optical microscopy. to get different grain sizes, the liners were annealed at 410, 530 and 650°c. the grain growth was firstly uniform and normal, but different and abnormal at ascending temperatures. the performance of w-cu powder liner is given in [69]. the penetration depth of non-sintered and sintered powder liners and of the spinning cu plate liner were tested at sos, showing that sintered powder liner performed better. scanning electron microscope was used to study the morphology of the liners. powder liner of ni-al was investigated in [70]. fxr was used to photograph the jet whereas x-ray diffraction and optical and electron microscopy were utilized to investigate the reactive behavior of a liner. the effect of porosity on powder liners was investigated in [71]. three types of liner made up of cu, al and cu-w-pb of different cone angles and sos were tested. it was found that penetration increases linearly in metal targets whereas the diameter of the entrance hole decreases linearly with decreasing al content in the liner material. engineering, technology & applied science research vol. 9, no. 6, 2019, 4917-4924 4920 www.etasr.com naeem et al.: a review of shaped charge variables for its optimum performance a detailed study of the sintered and non-sintered cu liners with particle size below 20μm is given in [72]. examination showed that the sintered powder liner of cu is having higher purity, density, lower wall thickness, and better penetration compared to the non-sintered one. to get reactive liner, al powder was sprayed over cu [73]. reactivity was confirmed by the recovered jet. phase transformation also took place as traces of γ -alumina α -alumina were found. cu liner was sprayed with al-ni powder using a kinetic spray deposition method for enhanced reactive liner in [74]. formation and penetration of jet composed of polymeric based reactive liner were studied numerically and observed by fxr in [75]. the liners were made by cold isostatic pressing at a pressure of 250mpa. the numerical results were in good agreement with the experiments. a straight and continuous jet was formed from the reactive liner. jet formation and particulation time for polymeric reactive liners is less than cu liners due to lack of ductility. the hole produced by reactive liners had a bigger diameter and less depth compared to the one produced by cu. penetration of a jet having variable density distribution was studied in [76]. a jet having variable density was produced from an un-sintered cu-w powder liner. a new analytical model was presented to describe this variable density jet phenomenon by incorporating modifications in the earlier established virtual origin model. an analytical model was validated by numerical and experimental results. the behavior of reactive liners and its demolition power was investigated in [77]. experiments, numerical simulation, and theoretical analysis were carried out for this purpose. liners manufactured by pressing and sintering of al-ptfe in 26.5/73.5 weight per cent gave much better collateral damage to the target due to the release of chemical energy contained in reactive materials. the effect of density variation on the penetration was studied in [78]. to achieve different densities of the same material, liners were manufactured by cold isostatic and uniaxial pressing. liners produced by the former technique have no density variation whereas those produced by the later have it along the liner height. autodyn was utilized to study the effects of metal powder liner density. it was numerically found and experimentally confirmed that liners produced by uniaxial pressing are more efficient than isostatic pressed against rha targets. new manufacturing techniques and new alloys were employed with the development of metallurgy. the new techniques are robust and reproducable in comparison to previous techniques like machining, rolling etc. and the new alloys perfrom better. the grain size was controlled for better performance. currently, graphene powder is pressed to get shaped charge liners [79]. isostatic and die pressed liners were compared and it was found that higher density is achieved by the former while the latter is more suitable for liner mass production. sintered powder metal liners need to be further investigated as there is room for improvement. v. liner geometries the shape or geometry of a liner is an important factor regarding penetration [80]. the shape can be optimized according to the nature of the target, stand-off distance and required hole diameter. shape manipulation started as early as the history of the lined cavity. the liner was introduced by munroe and neumann but it could not be concluded who discovered it first. wasag (westfalische anhaltische sprengstoff actien gesellschaft) patents in 1911 are about the lined cavity [19]. british navy studied the liner for shaped charges for torpedoes in 1913. scaled conical shaped charges with an apex angle of 42 0 were studied by in 1960 [81]. work on conical liners was carried out in 1963 [82] and a new analytical method of computing penetration variables for shaped-charge jets was found. in the same year, open apex conical liners with varied cone angles were tested to get hypervelocity pellet [83]. the ways to isolate the tip of a shaped charge jet from the rest of the jet and slug were discussed. in [84], conical liners of 60 o and 42 o were utilized to find their penetration in granite. magnetic field lines could be traced out by barium (ba) ions because the sunlight is resonantly scattered by ions into several visible wavelengths and the ions move in a spiral path about magnetic field lines when travelling parallel to the field lines. to study this effect, hollow conical liners of ba were detonated at an altitude of 500km [85]. the study in [1] was conducted on 42° conically liners to find which portion of the cone contributes to the tip of the jet. experiments were performed on cones with apex filled to various heights to obtain efficient jet for penetration. the study on conical liners was pushed further by more recent researches. in [86], authors observed that the ductility of metals like al and cu increases by an order of magnitude when the strain rate is increased. the same was supported by the finding that the jet elongation at breakup is proportional to the jet velocity gradient times the breakup-time. this gave a correct size prediction of the average fragment dimension and a formula for the breakup time of jet for conical liners was deduced. a unified approach for the penetration of conical shaped charge is given in [87]. fxr was used to find the shape of the jet at specified intervals and the results were compared with the analytical predictions. small conical shaped charges were utilized to initiate explosives in [88]. an analytical model for the calculation of the dynamic penetration of inclined shaped charges at some arbitrary standoff and for various obliquities of the target plate was given in [89]. the obtained analytical model could be easily applied to get penetration estimations by changing parameters for the shaped charge and target. hemispherical shaped charges with tapered liners were introduced in [90]. numerical simulations of the hemispherical and conical liners were conducted by authors in [91] using help and epic hydro-codes. the results predicted by the hydro-codes were confirmed by the experiments. authors in [92] showed that the maximum depth of penetration for a jet can be calculated theoretically using the tip velocity of the jet, the distance of the target plate from the virtual origin of the jet, particulation time, the efficient residual velocity and the square root of the ratio of target to jet density. to prove the above-given relations, experiments were conducted with 150mm base diameter shaped charges at 6, 12, and 24 calibres stand-off against rha. conical, hemispherical and efp liners were utilized in [11] against concrete with various materials and varying so. twodimensional simulations were carried in [93] to study the penetration of conical shaped charges and long rods. the shape was further innovated to star-shaped and carried out its threedimensional simulations with trek-up [94]. it was shown engineering, technology & applied science research vol. 9, no. 6, 2019, 4917-4924 4921 www.etasr.com naeem et al.: a review of shaped charge variables for its optimum performance that the star shape can be optimized to get better efficiency. in [95], al conical and trumpet liners with different thicknesses were investigated experimentally. the liners were tested against steel and sand targets at about 15 and 3 cd (charge diameter) stand-off. fxr was utilized to find the jet characteristic. hemispherical liners of degressive thickness were investigated numerically in [96]. simulations were compared with the jets from conical liners having 10 cd penetrations. it was found that the jets produced by hemispherical liners of degressive thickness have comparable head velocity and penetration power to the jets obtained from conical liners. the effects of conical, hemispherical and spherical-segment shaped liners over water-submerged steel plates were studied numerically using smooth particle hydrodynamics model in [80]. it was found that in submerged target the shock waves which reached the target earlier than the jet produced damage. efp has better motion dynamics due to its spherical shape so it produced a high-pressure shock wave having higher damaging effects. shaped charges are meant for deep penetration in the target but they produce a smaller diameter hole. conical cu liner was utilized in [97] as a precursor for tandem warhead against concrete targets. to get a 1:1 ratio of hole diameter to depth, a w type of shaped charge was introduced in [98]. w type liners were tested numerically and experimentally observed by high-speed photography. reproducibility is highly required in the production of any manufactured goods. in [99], an optimized and reproducible linear shaped charge was presented. precision linear-shaped charges were developed in [100]. linear shaped charges were designed in [101] using the lesca code and in [102] using autodyn. it was observed that linear-shaped charges behave like conical shaped charges in the process of jet penetration. analytical steady-state equation of motion for the jet of linearshaped charges was given in [103] incorporating changes to the birkhoff theory. the equation was verified by autodyn simulations. smooth particle hydrodynamic model was applied to study the process of linear-shaped charge formation and penetration in the steel target in [104]. simulation results were in agreement with the experimental ones. linear shaped charges were investigated using ls-dyna in [105] and the simulation results were compared with the experimental ones. liner thickness and so distance were studied in [106] using abaqus and the results were validated by experiments. it was shown that jet penetration increased by choosing an optimum so distance and by decreasing liner thickness. the availability of simulation software made possible predicting minor changes in the geometry of the liner, something that is almost impossible to do otherwise. software can simulate minor changes like angle variation upto half degree and thickness upto 0.1mm depending upon grid fineness. simulations save a lot of money and time and make the process robust. geometry plays a pivoting role in penetration enhancement and must be catered seriously. vi. conclusion optimization of shaped charge is a great challenge as it involves multiple variables to be investigated. this paper is intended to update and provide guidelines for the readers in designing a shaped charge liner against numerous targets. the three variables, liner material, geometry, and liner metallurgy which play important role in the modeling of shaped charges have been discussed with references from the initial experimental and analytical studies whereas numerical simulations have also been reviewed and discussed. a design optimized for one type of target can give very less or even no penetration for another. reactive metal liners were found well suited for concrete and concrete-like targets. with the development of powder metallurgy in the 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no. 3, pp. 977-986, 2018 microsoft word 39-3426_s1_etasr_v10_n2_pp5561-5564 engineering, technology & applied science research vol. 10, no. 2, 2020, 5561-5564 5561 www.etasr.com vekteris et al.: an efficiency study of the aerodynamic sound generators suitable for acoustic particle … an efficiency study of the aerodynamic sound generators suitable for acoustic particle agglomeration vladas vekteris department of mechanics and materials engineering vilnius gediminas technical university vilnius, lithuania vladas.vekteris@vgtu.lt darius ozarovskis department of mechanics and materials engineering vilnius gediminas technical university vilnius, lithuania darius.o@vilpra.lt vadim moksin department of mechanics and materials engineering vilnius gediminas technical university vilnius, lithuania vadim.moksin@vgtu.lt vytautas turla department of mechatronics, robotics and digital manufacturing vilnius gediminas technical university vilnius, lithuania vytautas.turla@vgtu.lt eugenijus jurkonis department of mechatronics, robotics and digital manufacturing vilnius gediminas technical university vilnius, lithuania eugenijus.jurkonis@vgtu.lt abstract—the object of this study is the acoustic field generated by aerodynamic acoustic generators of various types and designs. six types of aerodynamic acoustic generators were studied experimentally and theoretically to determine the parameters of their generated acoustic field. it was established that the aerodynamic hartmann type sound generator produces the necessary for acoustic particle agglomeration acoustic field and can be used in acoustic air cleaning equipment. it was established that classical theoretical calculation methods underestimate the design features of aerodynamic acoustic generators and cannot be used to calculate their characteristics. keywords-acoustic generator; frequency; sound pressure level i. introduction studies show that the efficiency of air cleaning equipment can be significantly improved if the distributed particles in the air being cleaned are treated by an acoustic field. authors in [1, 2] established that the relative air humidity measured above an open surface tank is decreased up to 1.6 times in the presence of an acoustic field when compared with the humidity obtained from the conventional push-pull air removal system. authors in [3] increased the average cleaning efficiency of cyclone separator from 87.2 to 97.5 by placing an aerodynamic sound generator at the bottom of the conical part of the cyclone separator. authors in [4] improved significantly the fine particle removal efficiency with the combined effect of acoustic agglomeration and vapor condensation, reaching up to 80% with a sound pressure level of 150db. an acoustic agglomeration process promoting the formation of particle clusters to enhance particle capturing efficiency without adding flow resistance in the air distribution ductwork provides an energy-efficient solution [5]. however, this method requires reliable, energy-efficient sound generators that can operate in various environments including aggressive ones. such generators should be able to generate high-intensity sound fields with sound pressure level above 100db [5], which is typically required to produce efficient acoustic agglomeration in several seconds. the most efficient are sound generators which emit acoustic waves at the ultrasonic frequency range [6]. in order to design a suitable sound generator, it is necessary to ensure that the acoustic field characteristics correspond to the characteristics of dust or aerosol particles exposed to that field [7, 8]. increased radiation intensity causes increased relative speed of the particles. particle adhesion is characterized by the characteristic frequency of the acoustic field. in case of 1μm size particles the characteristic frequency equals to 7.2mhz [7]. if the particle size is increased to 10m, the characteristic frequency is decreased to 72khz [7]. however, at very high frequencies with respect to the characteristic frequency, particle amplitude becomes independent on the frequency, but only on the ratio of densities of particle and environmental medium. therefore, in order to investigate the acoustic characteristics of the designed sound generator, it is necessary to analyze the pressure of the generated sound. ii. objects of reserch and experimental setup six aerodynamic acoustic field generator prototypes (figures 1-6) were designed and manufactured. the prototypes were experimentally studied to determine the considered parameters of generated acoustic field: sound pressure and frequency. corresponding author: vadim moksin engineering, technology & applied science research vol. 10, no. 2, 2020, 5561-5564 5562 www.etasr.com vekteris et al.: an efficiency study of the aerodynamic sound generators suitable for acoustic particle … the first acoustic generator aag-1 is shown in figure 1. compressed air flow enters into the generator through coupling 1 and then is distributed to the central 5 and peripheral channels 6, which direct the air into the resonance chamber 7. after the pressure in chamber 7 reaches a certain critical pressure, compressed air flow breaks through the air flow passing the channel 5 and leaves through the nozzle 4. after the outburst air pressure in the chamber 7 is decreased, air flow starts to pass through channel 5 and comes out through the nozzle 4 until the pressure in chamber 7 reaches certain value. then the described cycle is repeated creating air flow pulsation and acoustic field as a result. (a) (b) fig. 1. acoustic generator aag-1: a) 3d model, b) longitudinal section (a) (b) fig. 2. acoustic generator aag-2: a) 3d model, b) longitudinal section the second acoustic generator aag-2 is presented in figure 2. compressed air flow is fed through coupling 1 into the primary chamber 5. then the compressed air enters into the secondary chamber 6 of the acoustic generator through the diverging hole 7. due to the hole with increasing diameter 7, air vortexes and pressure fluctuations are created in the chamber 6. two air flows (primary and secondary) are created in the chamber 6 resulting from the turbulence. these flows come out through the hole 8 of the nozzle 3. pressure fluctuations of outgoing compressed air flow generate highfrequency acoustic field. the third acoustic generator aag-3 is shown in figure 3. compressed air flow is supplied through coupling 1 into the diffuser 2. then air flow bypassing the tab 5 of the diffuser enters into the nozzle 7 through slots 4. due to the holes 6 additional air flows are ejected into the nozzle 7 which are mixed with the main flow of compressed air. tab 5 and stepped narrowing of the nozzle 7 cause the turbulent flow. mixed air flow generates acoustic field passing through the nozzle 7. (a) (b) fig. 3. acoustic generator aag-3: a) 3d model, b) longitudinal section the fourth acoustic generator aag-4 is shown in figure 4. compressed air flow through the coupling 1 enters into the central channel 4. in addition, the secondary compressed air flow is supplied through coupling 3 which flows the channel 5 and cross the main flow near the end of the nozzle 2. the intersection of two compressed air flows causes the pressure pulsations which generate high-frequency acoustic field. the fifth acoustic generator aag-5 is shown in figure 5. compressed air flow is supplied through coupling 1 into central channel 5 and is directed toward the nozzle 4. in addition, the secondary air flow is supplied through coupling 2 into the housing 3. this air flow enters the channel 5 through the inclined channels 6 that direct it opposite to the main flow. the intersecting opposed flows create pressure pulsations and generate high-frequency acoustic field leaving the nozzle 4. the sixth acoustic generator aag-6 is shown in figure 6. compressed air flow coming out of the nozzle 1 periodically fills the resonator 2. then the air bursts coming out from the resonator collide with the compressed air exiting from nozzle 1. density fluctuations are generated as a result and generate a high-pressure acoustic field. aerodynamic acoustic generators of this type are known as hartmann type generators. engineering, technology & applied science research vol. 10, no. 2, 2020, 5561-5564 5563 www.etasr.com vekteris et al.: an efficiency study of the aerodynamic sound generators suitable for acoustic particle … (a) (b) fig. 4. acoustic generator aag-4: a) 3d model, b) longitudinal section (a) (b) fig. 5. acoustic generator aag-5: a) 3d model, b) longitudinal section a bruel & kjaer compact sound level meter type 2250-s with frequency analysis software bz-7222, bz-7223 and sound recording option bz-7226 were used for the measurements of sound pressure level and frequency analysis. the experimental setup is shown in figure 7. iii. results and discussion the results of parameter calculation of the aerodynamic acoustic generators are presented in table i. the graphical representation of the results is shown in figure 8. the calculation results show that air flow rate and generator’s outlet diameter have the greatest influence on the frequency and power of acoustic field emitted by the aerodynamic acoustic generator. aag-2 and aag-4 sound generators with small diameter holes theoretically generate an acoustic field of 47.2khz frequency. this frequency is more than exceeds the human hearing threshold, being more than the double of its upper limit. calculations show that these two generators are the most powerful. aag-6 generator with large outlet theoretically should emit a low-frequency (138hz) acoustic field. its power is respectively the lowest. (a) (b) fig. 6. acoustic generator aag-6: a) 3d model, b) longitudinal section fig. 7. experimental setup. 1: sound level meter/analyzer, 2: acoustic chamber, 3: compressed air port the experimental results are presented in figure 9, which contains a comparison of the acoustic characteristics of the manufactured generators. it can be seen from figure 9 that aag-6 acoustic generator is the most powerful. it can be also noticed that the sound pressure peak generated by the acoustic generator is repeated every 8khz, i. e. at 8 and 16khz. engineering, technology & applied science research vol. 10, no. 2, 2020, 5561-5564 5564 www.etasr.com vekteris et al.: an efficiency study of the aerodynamic sound generators suitable for acoustic particle … table i. theoretical parameters of the aerodynamic acoustic generators generatorfrequency, hz sound power, w wm wd wk aag-1 1.99e+04 3.13e+014.51e+016.50e+01 aag-2 4.72e+04 1.76e+028.01e+023.65e+03 aag-3 3.71e+03 1.09e+00 1.67e-01 2.57e-02 aag-4 4.72e+04 1.76e+028.01e+023.65e+03 aag-5 2.49e+03 4.89e-01 4.40e-02 3.97e-03 aag-6 1.38e+02 1.49e-03 2.84e-06 5.38e-09 fig. 8. the theoretical results of the aerodynamic acoustic generators fig. 9. the sound pressure levels of acoustic field generated by acoustic generators iv. conclusions the results of the theoretical calculations of the prototypes of the acoustic generators differ from the experimental data as classical theoretical calculation methods underestimate the design features of aerodynamic acoustic generators. therefore, it is necessary to formulate the assumptions and determine the empirical correction factors evaluating design peculiarities of aerodynamic acoustic sources. the experimental studies have shown that the aerodynamic efficiency of the generator is influenced not only by the principle of operation and the ratio of dimensions of its structural elements, but also by the technological fulfillment of the acoustic source. the experimental studies have shown that the most powerful aerodynamic generator is aag-6. its resonant chamber was the largest compared to the other prototypes and the edges were sharpest, i.e. chamfers were not removed. the aag-6 acoustic field generator exhibits the clearest sound pressure pulsations. sound pressure peaks are repeated every 8khz, i.e. at 8 and 16khz and exceed 100db. therefore, such prototype was chosen to be used to generate sound waves in an acoustic cyclone separator. references [1] v. vekteris, i. tetsman, v. mokshin, “investigation of the efficiency of the lateral exhaust hood enhanced by aeroacoustic air flow”, process safety and environmental protection, vol. 109, pp. 224-232, 2017 [2] v. vekteris, i. tetsman, v. moksin, “experimental investigation of influence of acoustic wave on vapour precipitation process”, engineering, technology & applied science research, vol. 3, no. 2, pp. 408-412, 2013 [3] v. vekteris, v. strishka, d. ozarovskis, v. mokshin, “numerical simulation of air flow inside acoustic cyclone separator”, aerosol and air quality research, vol. 15, no. 2, pp. 625-633, 2015 [4] j. yan, l. chen, l. yang, “combined effect of acoustic agglomeration and vapor condensation on fine particles removal”, chemical engineering journal, vol. 290, pp. 319-327, 2016 [5] b. f. ng, j. w. xiong, m. p. wan, “application of acoustic agglomeration to enhance air filtration efficiency in air-conditioning and mechanical ventilation (acmv) systems”, plos one, vol. 12, no. 6, pp. 1-26, 2017 [6] k. kilikeviciene, r. kacianauskas, a. kilikevicius, a. maknickas, j. matijosius, a. rimkus, d. vainorius, “experimental investigation of acoustic agglomeration of diesel engine exhaust particles using new created acoustic chamber”, powder technology, vol. 360, pp. 421-429, 2020 [7] v. n. khmeliov, a. v. shalunov, r. v. barsukov, s. n. tsyganok, d. s. abramenko, “acoustic coagulation of aerosols”, vestnik of the i.i. polzunov altai state technical university, no. 1-2, pp. 66-74, 2008 (in russian) [8] a. v. gridchin, a. v. shalunov, k. v. shalunova, a. n. galakhov, v. n. khmeliov, s. n. tsyganok, a. n. lebedev, “multifrequency ultrasonic oscillating system with stepped disk emitter”, 10th international conference and seminar on micro/nanotechnologies and electron devices, novosibirsk, russia, july 1-6, 2009 (in russian) microsoft word etasr_v11_n3_pp7290 engineering, technology & applied science research vol. 11, no. 3, 2021, 7290 7290 www.etasr.com phan: erratum and addendum: “contractor’s attitude towards risk and risk management in … erratum and addendum: “contractor’s attitude towards risk and risk management in construction in two western provinces of vietnam” van tien phan department of construction vinh city, viet nam vantienkxd@vinhuni.edu.vn since the publication of our original paper in vol. 10, no. 6 of this journal [1], the author has detected several misprints and errors that are corrected here, in the order in which they appear in the original paper. a new reference ([2]) should be added in the reference list of the original paper as reference number 2. the last sentence of the abstract should be rewritten as follows: “the importance of applying an effective risk management has been investigated, which is shared between the planning and production phase, whereas risk identification is the most important in the risk management process.” similarly, the conclusions of [1] should be rewritten as above. in part ii: the first sentence should be modified as “the questionnaire investigation method applied in [2] to study the risk management in construction projects of swedish contractor, is also applied in this paper.” the next sentence: “therefore, this form of survey integrates two types of data and the core assumption of this approach is that a combination of qualitative and quantitative methods leads to a better understanding of the problem [10]” should be removed. the last paragraph of part ii should include a citation of [2] in the first part and update the research data as following: “an invitation email was sent to 215 contractors in two western provinces of vietnam, which received 120 responses. the response rate is about 55%.” the last part of the paragraph should be removed as redundant. the text to be removed is “about 70% of the respondents had more than 15 years of experience within the construction industry and the majority (88%) where contractors, 24% where developers and 2,38% where consultants. the size of the companies where equally represented, approximately 48% had more than 1000 employees while 52% had less than 1000 employees.” in part iii, the following part should also be removed as redundant: “contractors were the 78%, developers (clients) the 19%, and consultants the 13% of the participants. interviews were conducted only with contractors. an equal distribution among company sizes was attained in the data collection, as stated above. a difference of opinion related to the company size will merely be mentioned when a significant differentiation can be observed between them, otherwise an overall picture of the industry will be presented due to similar answers to the questions.” the following sentence in part iii should also be removed: “the overwhelming majority of the respondents in both the questionnaire and the interviews described themselves as being risk-neutral rather than risk averse or risk-seekers, which coincides with previous studies.” in the discussion of question 1) how do you perceive risk within the construction industry, the collected data should be adjusted as following: “the results indicate that most of the respondents consider risk as a combination of threats and opportunities. about 94% (113 respondents) have chosen the above option. the rest (7 respondents) perceive risk as a natural hazard.” figure 1 may be removed as redundant. in the discussion of question 2) what is your attitude in relation to risk, the collected data should be adjusted as following: “most of the respondents dislike risks (92% or 110 respondents) and some selected “risk seeking” or “risk avoiding” as their answers. this result is almost contrary to a result published in [2], in which the majority of the respondents choose a neutral approach balanced between avoiding and risks. this hints that in vietnam, contractors seem to be more prone to avoid and limit risks in construction” finally, the interview part should be perceived as a subjective view of the matter that cannot offer objectivity. references [1] v. t. phan, "contractor’s attitude towards risk and risk management in construction in two western provinces of vietnam," engineering, technology & applied science research, vol. 10, no. 6, pp. 6418-6421, 2020. https://doi.org/10.48084/etasr.3339. [2] d. petrovic, "risk management in construction projects: a knowledge management perspective from swedish contractors," m.s. thesis, department of real estate and construction management, royal institue of technology, stockholm, sweden, 2017. microsoft word 38-2606_s1 engineering, technology & applied science research vol. 9, no. 2, 2019, 4071-4074 4071 www.etasr.com al-rawashdeh: investigation of an induction wound rotor motor to work as a synchronous generator investigation of an induction wound rotor motor to work as a synchronous generator ayman y. al-rawashdeh department of electrical engineering, faculty of engineering technology, al-balqa applied university, amman, jordan dr.ayman.rawashdeh@bau.edu.jo abstract—this paper aims at investigating the use of an induction wound rotor motor to generate voltage instead of the old diesel engines that are still used in many factories, like old cement factories, in jordan. in this investigation, a simulation model of induction wound rotor motor was implemented using matlab/simulink. the excitation dc current was connected to a two-phase rotor circuit, and the voltage-current performance characteristics were investigated and evaluated under different load types. the simulation results confirmed the possibility of using the induction wound rotor motor as a synchronous generator. keywords-slip ring; induction motor; synchronous generator; model; gear box; coupling; excitation; load variation i. introduction one of the main problems of electrical supply in industry and agriculture is the interruption of the main power supply source and the need to an emergency power supply source. in most cases, the emergency power supply sources are diesel engines, e.g. the shinko diesel engine (1982) used in jordan cement factories (figure 1, table i). diesel generators are known to cause problems especially for old engine models including their regular need to operate for at least one hour per week and the high maintenance and operative coasts. moreover, the hardware is not available and long order and delivery times are needed. fig. 1. a shinko diesel engine. induction motors are classified by their rotor construction [1]. of the different types, the current study investigates the use of wound rotor motor. from the known speed torque characteristic of the induction motor, the motor can act either as a motor or a generator [2]. when the speed of the induction motor is less than the synchronous speed and its slip is positive, the induction motor operates as a motor. when its speed is more than the synchronous speed and its slip is negative, the machine works as a generator. in the current investigation, a new method that allows an induction motor to operate as a generator is suggested. a wound rotor induction motor can operate as a synchronous generator based on its construction which is similar to a synchronous generator with non-salient poles. in wound rotor induction motors, the dc excitation current can be supplied to a rotor circuit through slip rings and carbon brushes. this gives the possibility of converting an asynchronous machine into a synchronous generator operation mode which can be used as an emergency power supply, which allows the utilization of power sources more effectively and efficiently. table i. shinko diesel engine parameters synchronous generator brushless exciter type gfy45648-4 h 3 type gjg219ta output 1251kva pf 0.8 output 18kw volt 400v 50hz dc 95v curr 1804a 1500rpm dc 189a ex volt 95v, 4 poles ex volt 70v ex curr 183v ip 22s ex curr 8.5a serial. no. 82128145051 insul f ii. proposed system description and model to investigate the voltage–current characteristics of the wound rotor induction motor in the generator operation mode, matlab simulations (table ii) were performed under different load types including resistive, inductive and capacitive loads [3-5]. to supply the excitation dc current, a two phase rotor circuit of the slip ring motor can be connected [6, 7]. as shown from the model in figure 2 and figure 4(c), the rotor circuit includes just two phases. this scheme of connection induced more magnetomotive force than the three phase connection [8, 9]. corresponding author: ayman y. al-rawashdeh engineering, technology & applied science research vol. 9, no. 2, 2019, 4071-4074 4072 www.etasr.com al-rawashdeh: investigation of an induction wound rotor motor to work as a synchronous generator table ii. block description of the matlab simulation block name block description simple gear represents a fixed-ratio gear or gear box. no inertia or compliance is modeled in this block. connections b (base) and f (follower) are mechanical rotational conserving ports. the relations between base and follower rotation directions are specified with the output shaft rotates parameter. inertia the block represents an ideal mechanical rotational inertia. it has one mechanical rotational conserving port. the block positive direction is from its port to the reference point. this means that the inertia torque is positive if the inertia is accelerated in the positive direction. ideal torque source represents an ideal source of torque that generates torque at its terminals proportional to the input physical signal. ideal rotational motion sensor is a device that converts an across variable measured between two mechanical rotational nodes into a control signal proportional to the angular velocity or angle. the sensor is ideal since it does not account for inertia, friction, delays, energy consumption,etc. connections r and c are mechanical rotational conserving ports and connections w and a are physical signal output ports for velocity and angular displacement, respectively. torque sensor it is a device that converts a variable passing through the sensor into a control signal proportional to the torque with a specified coefficient of proportionality. the sensor is ideal since it does not account for inertia, friction, delays, energy consumption, etc. connections r and c are mechanical rotational conserving ports that connect the sensor to the line whose torque is being monitored. connection t is a physical signal port that outputs the measurement result. the sensor positive direction is from port r to port c. dc voltage source ideal dc voltage source. dc machine implements a (wound-field or permanent magnet) dc machine. for the wound-field dc machine, access is provided to the field connections so that the machine can be used as a separately excited, shunt-connected or a series-connected dc machine. asynchronous machine implements a three-phase asynchronous machine (wound rotor, squirrel cage or double squirrel cage) modeled in a selectable dq reference frame (rotor, stator, or synchronous). stator and rotor windings are connected in wye to an internal neutral point. fig. 2. the rotor circuit of the slip ring motor with two phases. the total magnetomotive force of this connection for each harmonics can be calculated from: f� � 2f∅�cos � � (1) the relation between the first harmonic magnetomotive force of this connection to the first magneto motive force of the one phase is: � � � �∅��� �� � �∅ ≅ 1.5 (2) where f� , f�� are the total magnetomotive force and magnetomotive force of the one phase, respectively. it could be clearly concluded that when the dc current is supplied by two phases of the rotor circuit, the total induced magnetomotive force is 1.5 times more than the induced magnetomotive force of one phase. the flowing dc excitation current by the rotor circuit (figure 2), is used to induce the total machine’s magnetomotive force in all three rotor phases [10, 11], and: i � ��i� � i�� (3) where ib=ic=0.5ia. the suggested connection method of the rotor circuit shown in figure 2, gives 1.15 times more magnetomotive force than the traditional connection in which the dc excitation current supplied by each phase separately. as a prime mover for the system a dc motor was used, coupled with a wound rotor motor by a gear box with 1:1 ratio (figure 3(a)). (a) (b) (c) fig. 3. (a) general model blocks of the system, (b) general model of the system, (c) the general model used to collect data . figure 3(b) shows the prime mover, dc motor and a wound rotor induction motor which is driven by the prime mover and is used to generate ac power. the excitation current of the induction motor is a dc current and it is supplied from an external dc source through a slip ring and carbon brushes [11]. firstly, the prime mover is run to a rated speed and then, step engineering, technology & applied science research vol. 9, no. 2, 2019, 4071-4074 4073 www.etasr.com al-rawashdeh: investigation of an induction wound rotor motor to work as a synchronous generator by step, it supplies dc excitation current to wound rotor motor to record the measurements at no load and load operation conditions. the investigation process was done at a constant speed (speed of the prime mover), power factor and excitation current. at first, the experiment was done without load, to investigate the no load operation condition e � f�i"� at i � 0 and constant speed. then the experiment was repeated with the same connection circuit but with different connecting loads, resistive, inductive and capacitive, to the terminals of the generator [8, 12, 13]. the output voltages and load currents were recorded using measurement devices. the rated parameters of the investigated motor were v& � 220v, p � 60w, p � 1500rpm , i" � 1,7a, i�0 � 0.47a. iii. results and discussion firstly, the experiment was done without load to investigate the no load operation condition e � f�i"� at i � 0 and constant speed. table iii lists the experimental outputs of the module measured without load. tables iv, v and vi, list the experimental outputs of the module as a function of the r-, l and c-loads, respectively. table iii. experimental outputs of the module measured at no-load condition. if ea 0 0 0.2108 31.46 0.2499 37.40 0.3000 44.44 0.4989 75.68 0.6001 89.98 0.9996 148.06 1.4990 205.04 table iv. experimental outputs of the module measured as a function of r-load i v p 0.00 229.90 0.00 0.0300 220.88 9.96 0.0696 211.86 19.98 0.9960 203.94 30.00 0.1297 194.92 39.69 0.1598 187.88 49.98 0.1899 179.96 60.00 0.2096 177.92 69.96 0.2298 165.88 79.98 table v. experimental outputs of the module measured as a function of l-load. i v l 0.0696 211.86 0.000 0.9960 188.98 0.416 0.1396 169.84 0.833 0.1795 154.00 1.250 0.2096 139.92 1.666 the measurements of voltage, current and power were recorded using a voltmeter, an ampere meter and a wattmeter. results for the voltage, current and power outputs with different load types (tables iii, iv, v, and vi) are plotted graphically in figure (5). the obtained simulation results were in total agreement with the experimental results and findings in [1, 3]. the results of the r and l-loads revealed that the output voltage of the generator decreased slightly as load increases. the results reveal the increase in the current of the generator with increasing load (figure 5). the obtained results showed that the voltage – current characteristics with different load types had drooping (resistive and inductive) or rising (capacitive) character which can be explained by the effect of the rotor magnetic field – armature field – on the main magnetic field, especially with an increase in the load. (a) (b) (c) fig. 4. (a) a simulation model of the prime mover, (b) a simulation model of the gear box, (c) a simulation model of the wound rotor engineering, technology & applied science research vol. 9, no. 2, 2019, 4071-4074 4074 www.etasr.com al-rawashdeh: investigation of an induction wound rotor motor to work as a synchronous generator table vi. experimental outputs of the module measured as a function of c-load. i v c 0.0696 211.86 0.000 0.0696 216.92 0.416 0.0898 224.84 0.833 0.1099 231 1.250 0.1297 236.94 1.666 fig. 5. experimental relation between generated voltage and load current of a wound rotor induction motor with different load types. iv. conclusion the obtained results from the experiments conducted in the paper, revealed similarities between the wound rotor induction motor in generating operation mode, and the known characteristics of the synchronous generators. based on the observed similarities, the current study provides a proof of the possible use of the wound rotor induction motor as an emergency power supply instead of the currently used old diesel generators. references [1] k. y. patil, d. s. chavan, “use of slip ring induction generator for wind power generation”, international journal of engineering research and applications, vol. 2, no. 4, pp.1107-1110, 2012 [2] s. djurovic, d. s. vilchis-rodriguez, a. c. smith, “investigation of wound rotor induction machine vibration signal under stator electrical fault conditions”, the journal of engineering, vol. 2014, no. 5, pp. 248258, 2014 [3] m. barakat, s. elmasry, m. e. bahgat, a. a. sayed, “effect of rotor current control for wound rotor induction generator on the wind turbine performance”, international journal of power electronics and drive system, vol. 2, no. 2, pp. 117-126, 2012 [4] f. i. bakhsh, m. m. shees, m. s. j. asghar, “performance of wound rotor induction generators with the combination of input voltage and slip power control”, russian electrical engineering, vol. 85, no. 6, pp. 403–417, 2014 [5] o. albarbarawi, a. al-rawashdeh, g. qaryouti, “simulink modelling of the transient cases of three phase induction motors”, international journal of electrical & computer sciences, vol. 17, no. 4, pp. 6-15, 2017 [6] d. aguilar, g. vazquez, a. rolan, j. rocabert, f. corcoles, p. rodriguez, “simulation of wound rotor synchronous machine under voltage sags”, 2010 ieee international symposium on industrial electronics, bari, italy, july 4-7, 2010 [7] e. tuinman, p. piers, r. de weerdt, “simulation of a direct on line start of a large induction motor connected to a salient pole synchronous generator”, international conference on simulation '98, york, uk, september 30-october 2, 1998 [8] s. devabhaktuni, s. v. jayaram kumar, “different self excitation techniques for slip ring self excited induction generator”, international journal of computer applications, vol. 38, no. 2, pp. 1926, 2012 [9] c. h. watanabe, a. n. barreto, “self-excited induction generator/forcecommutated rectifier system operating as a dc power supply”, iee proceedings b electric power applications, vol. 134, no. 5, pp. 225260, 1987 [10] s. s. murthy, o. p. malik, a. k. tandon, “analysis of self-excited induction generators”, iee proceedings c generation, transmission and distribution, vol. l29, no. 6, pp. 260-265, 1982 [11] s. devabhaktuni, s. v. jayaram kumar, “selection of capacitors for the self excited slip ring induction generator with external rotor capacitance”, journal of energy technologies and policy, vol. 2, no. 2, pp. 66-77, 2012 [12] b. s. srikanth, r. anguraja, p. r. khatei, “experimental investigation on an induction motor to work as an alternator”, international journal of scientific & engineering research, vol. 4, no. 5, pp. 129-132, 2013 [13] d. aguilar, a. luna, a. rolan, g. vazquez, g. acevedo, “modeling and simulation of synchronous machine and its behavior against voltage sags”, ieee international symposium on industrial electronics, seoul, korea, july 5-8, 2009 authors profile dr. ayman y. al-rawashdeh phd. mechatronics. eng, was born on 1970 in jordan. he obtained his diploma degree in 1995 and phd in 2008 in the field of mechatronics engineering. currently he works as an assistant professor at the electrical department, faculty of engineering technology, al-balqa applied university, jordan. his main interest is renewable energy and drive system analysis and simulations microsoft word 47-2986_s_etasr_v9_n5_pp4842-4845 engineering, technology & applied science research vol. 9, no. 5, 2019, 4842-4845 4842 www.etasr.com kupusamy et al.: construction waste estimation analysis in residential projects of malaysia construction waste estimation analysis in residential projects of malaysia kumanan kupusamy department of building & construction engineering, university tun hussein onn malaysia, batu pahat, malaysia k.kumanankupusamy@gmail.com sasitharan nagapan department of building & construction engineering, university tun hussein onn malaysia, batu pahat, malaysia sasitharan@uthm.edu.my abd halid abdullah department of building & construction engineering, university tun hussein onn malaysia, batu pahat, malaysia abdhalid@uthm.edu.my suaathi kaliannan department of building & construction engineering, university tun hussein onn malaysia, batu pahat, malaysia suaathikaliannan@gmail.com samiullah sohu department of civil engineering. quaid-e-awam university of engineering, science & technology, campus larkana, pakistan sohoosamiullah@gmail.com shivaraj subramaniam department of building & construction engineering, university tun hussein onn malaysia, batu pahat, malaysia shivaraj103@gmail.com haritharan maniam department of building & construction engineering, university tun hussein onn malaysia, batu pahat, malaysia haritharanmaniam@gmail.com abstract—construction and demolition (c&d) waste account for an oversized share of all solid waste generated worldwide. statistical data confirm that, globally, 10-30% of waste originates from construction and demolition works. the types of waste from construction activities are wood, metals, concrete waste and mixed wastes. waste generation continues to increase with the economy and population growth. a great challenge is providing more waste disposal facilities such as landfills to treat the waste. rapid urbanization and insufficient attention to c&d waste generation, particularly in developing countries like malaysia, have contributed to an urgent need for additional research on waste generation as there is a lack of information. the aim of this study is to predict the construction waste generation for the peninsular of malaysia by quantifying construction waste generation data for kuala lumpur and to estimate the construction waste generation in 2016 for the peninsular of malaysia. the estimation approach used was the proportion method with 20% of total sites in each state. indirect waste measurement method was used to estimate waste generation. total waste generation for kuala lumpur was around 6,101.46 metric tons. the predicted total amount of c&d waste generated for residential projects throughout malaysia peninsular is 63,101.93 metric tons. the initial prediction of construction waste generation for malaysia peninsular can be used as a baseline for future study. keywords-construction; waste; estimation; proportional i. introduction construction and demolition (c&d) waste is produced during construction, renovation, and demolition of buildings and structures. construction waste is anything generated as a result of construction and then abandoned, regardless of whether it has been processed or stockpiled. it comprises of surplus materials from site clearance, excavation, construction, refurbishment, renovation, demolition and road works. construction industry is a key part in the economy of any country. in malaysia, this industry has been playing a vital role in economy’s growth [1]. nowadays, construction industry is quickly developing as a result of the modernization in the way of life, demands of infrastructure projects, changes in consumption habits, and the population increment [2]. the construction industry is commonly environmentally unfavorable [3]. c&d waste account for an oversized share of total solid waste generated worldwide. this industry contributes significantly to the environmental problem in terms of natural resources exploration, irreversible transformation of the natural environment and accumulation of pollutants in the atmosphere [4]. construction waste is generated throughout the construction process, during site clearance, material damage, material use, material non-use, excess procurement and human errors. moreover, statistical data confirm that 10-30% of total waste is originated from construction and demolition works [5]. the main types of waste from construction activities are wood, metals, concrete waste, plastics, papers and cardboards, glass, hazardous wastes (such as paints and glues), etc.[6]. construction waste is produced through the project from pre-construction stage, rough construction stage and finishing stage. generation of construction waste can be caused by various factors. it is vital to recognize and comprehend those causes for controlling waste generation at its source [7]. causes of construction waste generation on-site are: lack of skills and corresponding author: sasitharan nagapan engineering, technology & applied science research vol. 9, no. 5, 2019, 4842-4845 4843 www.etasr.com kupusamy et al.: construction waste estimation analysis in residential projects of malaysia experience of construction workers, lack of skills and experience of demolition contractors, wasteful use of materials in construction activities, inappropriate methods for loading and shipment of building materials from suppliers to sites, inappropriate methods for handling building materials on-site, frequent demolitions due to reworks and change of orders, traditional methods of construction, inappropriate packaging of building materials and components, inappropriate inventory of building materials and components, and low quality of buildings materials and components. there is still a lack of data on construction waste generation for malaysia. field measurement research on construction waste generation is negligible in malaysia. questionnaire based data are less accurate because they draw conclusions from individual assumptions on waste generation without proper evidence and data. moreover, the research done by previous researchers mainly focuses on specific sites and does not include state or county wide data. field measurement data will be more accurate on construction waste compared to questionnaire survey data. ii. construction waste categories construction waste is classified by source and type. in order to quantify the construction waste adequately, it is useful to have a classification of wastes by source and type of generated waste [8]. hence, waste generated on the construction site can be classified in the following two classes: • building waste, generated during the construction process due to defects, damages, breakage or simply due to excess. • packaging waste generated from packaging of materials and products delivered to construction site. the main types of waste from construction activities are wood, metals, mineral debris (such as stone, bricks, mortar and concrete), plastics, papers and cardboards, glass, and hazardous waste (such as paints and glues). iii. the construction waste issue in other countries various minimization programs have been conducted to enhance sustainability in construction. in australia, the c&d waste accounts for 16–40% of total solid generated waste. a total of 19.0 million tons of c&d waste had been produced in australia in 2008-2009, out of which 8.5 million tons were disposed to landfills while 10.5 million tons, or 55%, was recovered and recycled [9]. in romania, the c&d waste was the 4% of the total in 2003, 10% in 2004 and 7% in 2005. in total amounts, the quantity of c&d produced waste in 2004 was 646,400 tons and dropped in 2005 to 466,893 tons [10]. in usa, 136 million tons of building-related c&d debris are generated each year [11], out of which only 20–30% is recycled [12]. in the uk, every year around 70 million tons of c&d materials and soil end up as waste [13], and the wastage rate in the uk construction industry is as high as 10–15% [14]. the waste amount from c&d activities has remained at around 100 million tons annually in recent years, while demolition accounted for around 32.7 million tons in 2007, which means demolition waste takes about 30% of all annual construction generated waste [15]. in tehran, iran about 18,250,000 tons of c&d waste is produced annually [16]. in china, according to the report by the environment protection department (epd), about 2900 tons of c&d waste were received at landfills per day in 2007. china produces 29% of the world’s municipal solid waste (msw) each year, with nearly 40% of this amount produced by construction activities [17]. in japan, the amount of construction waste dropped from 99 million tons to 77 million tons in a ten-year period (1995–2005), while the recycling rate increased from 58% to 92% in the same period [4]. iv. construction waste in malaysia malaysia has experienced a quick infrastructure development over the last decade. c&d waste constitutes around 20% to 30% of the total waste in landfills. the amount of demolition waste is double the amount of construction waste. construction waste management has become an issue that needs high concern in many developing countries because it has an adverse effect on economy, environment and social aspects [7]. illegal dumping is a common issue and also a solution for contractors who deal in malaysia [18]. construction industry development board (cidb), mainly focuses on solid waste [7]. there are poor regulations and guidelines managing the c&d waste generation in malaysia. in this manner, a satisfactory conclusion about c&d waste management must be determined. there is no reliable data and information related to construction waste in malaysia. in addition, malaysia still lacks researches on construction waste generation [19]. v. waste amount estimation waste quantification utilized site accounting, record keeping, and waste characterization to recognize the creation of construction waste. it was a mean to estimate the quantity of generated construction waste, thus, assessing the potential for waste reduction. waste quantification can also help in decision making in assessing the feasibility of recycling programs as practiced in countries like the usa, hong kong, and taiwan. nonetheless, malaysia was yet falling behind in establishing the quantified benchmark for construction waste generation rate among its contractors as compared to other countries [17]. site visiting and field measurements were used to investigate the waste generation rates. field measurement surveys, in direct or indirect approaches can be utilized to collect c&d waste generation data. direct measurements require the weighting of the waste produced or to measure on site its volume. indirect measurements are frequently used for practical estimations. vi. research methodology indirect measurements were used. authors in [20] employed truck load records to estimate the volume of c&d waste generated on site. they recorded the number of trucks for waste collecting and the containers’ volume for deriving total waste volume at a project level. for the purpose of indirect quantification at a regional level, authors in [21] obtained truck load records from landfills. mix waste data were calculated based on bin measurements and waste bin trips per day or week depending on the amount of the waste produced in site. after that, month data were calculated based on the engineering, technology & applied science research vol. 9, no. 5, 2019, 4842-4845 4844 www.etasr.com kupusamy et al.: construction waste estimation analysis in residential projects of malaysia addiction of daily and weekly data. this process was repeated for the twelve months of the year. with limited data available, cross-proportion method [21] deemed appropriate to be adopted in predicting the total construction generated waste [22]. vii. data collection and analysis according to the data from cidb in 2015, kuala lumpur is one of leading states in malaysia in construction development. construction waste in kuala lumpur is managed by the local authorities. this research focuses on construction waste generation mainly for residential type of projects. the residential sector in the city is growing rapidly in line with supply and demand of the population [23]. however, the produced waste is mixed in the majority sites and not separated according to respective types. indirect data were collected from 38 sites during 2016. the data were taken from delivery orders by construction waste truck loads. the average tonnage of the waste generation for kuala lumpur was calculated. based on the data, the estimation of waste generation for other states in malaysia peninsular was calculated. table i shows the total data collection for kuala lumpur residential projects in 2016 (1-year period). the data were taken by using indirect methods. thirty eight sites were visited for data collection in the kuala lumpur region. waste quantification was high in january of 2016 (699.7633 tons), july (857.192 tons) and september (725.1662 tons). waste generation was less than 500 tons the other months. the month with the lowest waste production was april and july had the highest production. table i. total data collection for kuala lumpur month average (tons) jan 699.7633 feb 312.0925 mac 378.054 apr 194.34 may 326.044 jun 352.5443 july 857.192 aug 363.608 sept 725.1662 oct 405.8421 nov 411.632 dec 311.7453 apparently, the total number of construction projects for each state was important in estimating the required number of samples using the cross-proportion method. cidb has published a statistic for construction projects in malaysia in 2015. using the number of project sites in kuala lumpur which were measured through the indirect measurement method, the number of required project sites to be measured in other states can be estimated. employing the cross-proportion method, the basic mathematical formula to determine the proportionate total weight of c&d waste for another state relative to the total weight of c&d waste was obtained. the basic mathematical formula used in the cross-proportion method to determine the proportionate number of estimated project sites to be measured in another state relative to the number of project sites measured in a certain state is (1) : 1 2 1 2 c c q q = (1) where c1 is the number of project sites measured in a certain state, c2 it the number of estimated project sites to be measured in another state, q1 is the total number of project sites in a certain state, and q2 is the total number of project sites in another state. using the number of project sites in kuala lumpur which were measured through indirect measurement method (i.e. 38 sites), and the total number of project sites in kuala lumpur (190) and johor (350), the number of required project sites to be measured in the state of johor can be estimated using (1) as c2=70 sites. therefore, 70 project sites in johor should be measured in order to be proportionate to the 38 project sites measured in kuala lumpur. employing the cross-proportion method, the basic mathematical formula to determine the proportionate total weight of c&d waste (i.e. based on the required number of project sites) for another state relative to the total weight of c&d waste (i.e. based on the number of project sites measured) obtained in a certain state is shown in (2) as: 1 2 1 2 t t c c = (2) where t1 is the total tonnage of c&d waste in a certain state (i.e. based on the number of project sites measured), t2 is the total tonnage of c&d waste estimated in another state (i.e. based on the number of estimated project sites to be measured), c1 is the number of project sites measured in a certain state, and c2 the number of estimated project sites to be measured in another state. therefore, the total weight of c&d waste generated (i.e. based on the number of estimated project sites to be measured) in the state of johor can be estimated using (2) as: 2 6,101.46/38 /70t= 2 11239.53t = metric tons. based on the limited data collected in kuala lumpur, the rough assumption and prediction using cross-proportion method has been made to generate the value of estimated c&d waste generated in terms of tonnage for the 12 states of the malaysia peninsular. it is worth noting that the estimated amount obtained represents only 20% of the total residential project sites in each state. table ii shows that the predicted total amount of c&d waste generated for residential projects throughout peninsular malaysia was 600,727.39 metric tons, which was based on the 20% of the total project sites considered in each state. it was shown that selangor was the highest waste generator in the residential projects with 142156.86 tons in the year 2016, followed by johor with 106999.79 tons. the least waste was generated in perlis (4585.71 tons) and kedah (30571.37 tons). malaysian industrial areas such as selangor and johor produce more waste than less developed states such as perlis. engineering, technology & applied science research vol. 9, no. 5, 2019, 4842-4845 4845 www.etasr.com kupusamy et al.: construction waste estimation analysis in residential projects of malaysia table ii. predicted annual amount of c&d waste in malaysia peninsular state predicted waste (tons) wilayah persekutuan 58085.60 johor 106999.79 kedah 30571.37 kelantan 10699.98 melaka 25985.66 negeri sembilan 48914.19 pahang 48914.19 pulau pinang 56557.03 perak 50442.76 perlis 4585.71 selangor 142156.86 terengganu 16814.25 total 600,727.39 viii. conclusion this study successfully achieved its aim of predicting the construction waste generation for the malaysian peninsular. there is a limited number of studies conducted on this field. using the proportion methodology along with indirect measurements, this research had done the estimation of waste generation for residential projects in peninsular malaysia using kuala lumpur field measurement data. however, the projection of data includes the 20% of construction waste sites in kuala lumpur and other states. the predicted total annual amount of construction waste generated for residential projects throughout peninsular malaysia was 600,727.39 metric tons. it is shown that selangor was the highest waste generator in the residential projects in 2016, followed by johor. the least waste were generated in perlis and kedah, because industrial areas produce more waste than less developed states. this study had done the initial prediction by visiting and taking measurements on the 20% of the construction sites. in the future, this percentage could be augmented. acknowledgement authors would like to thank the cidb and the solid waste and public cleansing management corporation (swcorp) for the information provided in this study. also, the universiti tun hussein onn malaysia and the ministry of education, malaysia. funds for the study were provided by the fundamental research grant scheme (frgs) no.1624, and grant no. u704. references [1] m. f. hasmori, i. said, r. deraman, n. h. abas, s. nagapan, m. h. ismail, f. s. khalid, a. f. roslan, “significant factors of construction delays among contractors in klang valley and its mitigation”, international journal of integrated engineering, vol. 10, no. 2, pp. 3236, 2018 [2] s. nagapan, i. a. rahman, a. asmi, a. h. memon, i. latif, “issues on construction waste: the need for sustainable waste management”, ieee colloquium on humanities, science and engineering, kota kinabalu, malaysia, december 3-4, 2012 [3] s. nagapan, s. kaliannan, a. h. abdullah, s. sohu, r. deraman, m. f. hasmori, n. h abas, “preliminary survey on the crucial root causes of material waste generation in malaysian construction industry”, vol. 8, no. 6, pp. 3580–3584, 2018 [4] a. p. kern, m. f. dias, m. p. kulakowski, l. p. gomes, “waste generated in high-rise buildings construction: a quantification model based on statistical multiple regression”, waste management, vol. 39, pp. 35–44, 2015 [5] m. f. b. yusof, study on construction & demolition waste management in construction site, bsc thesis, university college of engineering & technology malaysia, 2006 [6] s. jalali, “quantification of construction waste amount”, available at: https://core.ac.uk/download/pdf/55608453.pdf, 2007 [7] s. nagapan, i. a. rahman, a. asmi, a. h. memon, r. m. zin, “identifying causes of construction waste-case of central region of peninsula malaysia”, international journal of integrated engineering, vol. 4, no. 2, pp. 22-28, 2012 [8] a. f. masudi, c. r. c. hassan, n. z. mahmood, s. n. mokhtar, n. m. sulaiman, “waste quantification models for estimation of construction and demolition waste generation: a review”, international journal of global environmental issues, vol. 12, no. 2-4, pp. 269-281, 2012 [9] s. zakar, overview of demolition waste in the uk, bre, 2009 [10] o. f. kofoworola, s. h. gheewala, “estimation of construction waste generation and management in thailand”, waste management, vol. 29, no. 2, pp. 731–738, 2010 [11] k. sandler, p. swingle, oswer innovations pilot: building deconstruction and reuse, epa 2006 [12] a. a. najafpoor, a. zarei, f. j. behnam, m. v. shahroudi, a. zarei, “a study identifying causes of construction waste production and applying safety management on construction site”, iranian journal of health sciences, vol. 2, no. 3, pp. 49–54, 2014 [13] waste strategy 2000 for england and wales, crown, 2000 [14] c. mcgrath, m. anderson, “waste minimizing on a construction site”, building research establishment digest, vol. 447, pp. 441-454, 2000 [15] x. chen, w. lu, “identifying factors influencing demolition waste generation in hong kong”, journal of cleaner production, vol. 141, pp. 799–811, 2017 [16] b. r. broujeni, g. a. omrani, r. naghavi, s. s. afraseyabi, “construction and demolition waste management (tehran case study)”, engineering technology & applied science research, vol. 6, no. 6, pp. 1249-1252, 2016 [17] h. wu, h. duan, l. zheng, j. wang, y. niu, g. zhang, “demolition waste generation and recycling potentials in a rapidly developing flagship megacity of south china: prospective scenarios and implications”, construction and building materials, vol. 113, pp. 1007– 1016, 2016 [18] c. s. poon, a. t. w. yu, l. jaillon, “reducing building waste at construction sites in hong kong”, construction management and economics, vol. 22, no. 5, pp. 461–470, 2004 [19] h. maniam, s. nagapan, a. h. abdullah, s. subramaniam, s. sohu, “a comparative study of construction waste generation rate based on different construction methods on construction project in malaysia”, engineering, technology & applied science research, vol. 8, no. 5, pp 3488-3491, 2018 [20] n. kartam, n. a. mutairi, i. a. ghusain, j. a. humoud, “environmental management of construction and demolition waste in kuwait”, waste management, vol. 24, no. 10, pp. 1049–1059, 2004 [21] s. d. sawaitul, k. p. wagh, p. n. chatur, “classification and prediction of future weather by using back propagation algorithm: an approach”, international journal of emerging technology and advanced engineering, vol. 2, no. 1, pp. 110–113, 2012 [22] d. stanley, d. mcgowan, s. h. hull, “pitfalls of over-reliance on cross multiplication as a method to find missing values”, texas mathematics teacher, vol. 11, no. 1, pp. 9-11, 2003 [23] a. a. mustaffa, m. f. hasmori, a. s. sarif, n. f. ahmad, n. y. zainun, “the use of uav in housing renovation identification: a case study at taman manis 2”, iop conference series: earth and environmental science, vol. 140, article id 012003, 2018 microsoft word 26-2746_s engineering, technology & applied science research vol. 9, no. 3, 2019, 4209-4212 4209 www.etasr.com bhell et al.: use of rice husk ash as cementitious material in concrete use of rice husk ash as cementitious material in concrete naraindas bheel department of civil engineering, mehran university of engineering and technology, jamshoro, pakistan naraindas04@gmail.com abdul wahab abro department of civil engineering, mehran university of engineering and technology, jamshoro, pakistan ablwab82@gmail.com irfan ali shar department of civil engineering, mehran university of engineering and technology, jamshoro, pakistan irfanshar2000@gmail.com ali aizaz dayo department of civil engineering, mehran university of engineering and technology, jamshoro, pakistan aliaizaz890@gmail.com sultan shaikh department of civil engineering, mehran university of engineering and technology, jamshoro, pakistan sultan11civil@gmail.com zubair hussain shaikh department of civil engineering, mehran university of engineering and technology, jamshoro, pakistan azubair.shaikh56@gmail.com abstract—in this research, rice husk ash (rha) was used as a partial substitute for cement in concrete to reduce its cost, and alternative processing methods using agricultural/industrial waste were found. the main objective of this study was to determine the fresh (flowability) and hardened (splitting tensile strength and compressive strength) concrete properties using rha at 0%, 5%, 10%, 15% and 20% by weight. a total of 90 concrete samples (45 cubes and 45 cylinders) were prepared and cured on 7, 14, and 28 days to the design of target strength 28n/mm 2 , and ultimately, these concrete specimens were tested on utm. three concrete specimens were cast for each proportion and ultimately the average of the three concrete samples was taken as the final result. the flowability of fresh concrete decreases with increasing content of rha in concrete. the results showed that the compressive and tensile strength of the concrete specimens increased by 11.8% and 7.31%, respectively by using 10% rha at 28 days curing. keywords-rice husk ash; cement replacement material; improved strength; reduced construction cost; utilizing disposal waste i. introduction concrete is widely and globally used throughout the history of humankind [1]. concrete is a mixture of sand and crushed rock combined together by a hardened paste of hydraulic cement and water [2]. the increased use of concrete is going to grow the demand for its ingredients’ resources (cement, sand, and gravel). the high rate of concrete constituents is increasing rapidly and hence there is a requirement for an unconventional material that is low-cost and readily presented that will also give a similar or greater strength when used for concrete [3]. cement is one of the constituents of concrete which is costly and its production releases large amounts of co2 during its manufacturing [4-8]. manufacturing one tonne of cement releases about one tonne of co2 in the atmosphere while 1.6 tonnes of natural resources are required to produce about one tonne of cement [9-11]. in many studies the cement is partially replaced by agricultural/industrial waste such as glass powder, sugar cane bagasse ash, rice husk ash (rha), blast furnace slag, maize cob ash, millet husk ash, fly ash etc. in order to reduce cost, waste and co2 emissions while these resources are easily available [9, 12]. rha is the by-product of agricultural waste [13-15], it is considered unwanted and is mostly air burned [16, 17]. currently disposing of agro/industrial waste is a serious problem. one of these agro wastes is rice husk. rice husk annual produced quantity is about 120 million tonnes per year in the paddy field [17-19]. the husk manufactured from rice processing is either burnt or dumped. rice husk is burnt at a certain temperature under atmosphere. rha possess 85% of silica content that is known as non-crystalline silica and it could be utilized as partial cement replacement material [2024]. rha is measured as a highly pozzolanic material [25-29] and it can be used as an additional material in concrete decreasing the environmental problem. a research study of the hardening properties of concrete was carried out in [30] using 10% rha. in this study, concrete samples were cured and tested after 7, 14, 28, and 56 days, using a mixing ratio of 1:2:4 with water-cement ratio 0.45, 0.50, and 0.60. the results showed that the compressive and tensile strengths increased by 14.51% and 10.71%, respectively, at 0.45 water-cement ratio when 10% rha was used in concrete with a curing time of 56 days. authors in [31] reported that rha is beneficial to reduce the temperature of concrete as compared to plain cement concrete. authors in [32] carried out researched on the hardened properties of concrete blended with cement by 5%, 10%, 15% and 20% weight. the concrete samples were designed for target strength of 25n/mm 2 and were cured for 7 and 28 days. the result was that the crushing strength improved by 15.74% when using 10% of rha in concrete at 28 days [32]. rha plays an essential role in the characteristics of cementitious materials [33]. the size of corresponding author: naraindas bheel engineering, technology & applied science research vol. 9, no. 3, 2019, 4209-4212 4210 www.etasr.com bhell et al.: use of rice husk ash as cementitious material in concrete the rha particles is finer than opc, which augments concrete properties [34]. the size of rha particles is around 25 microns which makes rha capable of playing a vital role as filler in cement [35]. in this experimental study, rha was blended in concrete by weight in proportions up to 20%. ii. research methodology research was conducted on the fresh and hardened properties of concrete by using 0%, 5%, 10%, 15% and 20% of rha as cement substituent material in concrete. a total of 90 concrete samples (45 cubes and 45 cylinders) were prepared and cured at 7, 14, and 28 days to the design of target strength of 28n/mm 2 . to get an optimum mix, a number of trail mixes are completed using variable cement (binder), coarse aggregates, fine aggregates, and water. while getting the desirable mix, rha was used as cement substituent material to determine the characteristics strength of concrete specimens and ultimately, these concrete specimens were tested on utm while obeying the british standard (bs) code. in this study, the concrete cubes were cast for compressive strength and cylinders were cast for splitting tensile strength. three concrete specimens were cast for each proportion and finally, an average value of the three specimens was taken as the final result. this research work was completed in the concrete laboratory of the department of civil engineering, college of science and technology, hyderabad, sindh, pakistan. iii. materials used a. cement the cement that was used is available locally in the market under the brand name pak land. b. fine aggregates hilly sand was used as fine aggregates of zone-ii which passed through sieve no. 4 (4.75mm). the fineness modulus, water absorption and specific gravity of fine aggregates are 2.61, 1.8% and 2.60 respectively. c. coarse aggregates the coarse aggregates used were 20mm in size and were available in the local market. the water absorption and the specific gravity of coarse aggregates were 1.4% and 2.73 respectively. d. rice husk ash rice husk was collected from the region of sakrand and it was air-dried. rha was acquired by using uncontrolled temperature burning method. the desired ash was sieved through #30 sieves. e. water drinking water, available in the lab, was used. iv. results and discussion a. fresh concrete workability the flow of fresh concrete was conducted by slump cone having the dimensions of 10cm top diameter, 20cm bottom diameter and 30cm height. the maximum flow of fresh concrete was 65mm while using 0% rha as cement substituent material in concrete and the minimum value of workability was 25mm at 20% rha by weight. it was concluded that the flow of fresh concrete decreases with an increase in the amount of rha in concrete. the experimental results are shown in figure1. fig. 1. workability of fresh concrete b. compressive strength compressive strength test were conducted on cubes (100mm×100mm×100mm) by using different rha percentages. three specimens were cast for each proportion and ultimately, an average value of these three concrete specimens was taken as the final result. the compressive strength was maximum at 10% of rha used as cement substituent material in concrete and minimum at 20% of rha, at 7, 14, and 28 days. the results are shown in figure 2. fig. 2. compressive strength of concrete at 7, 14, and 28 days c. splitting tensile strength splitting tensile strength tests were conducted on cylinders (200mm×100mm) of various rha percentages which were cured at 7, 14, and 28 days. three concrete samples were cast for each proportion and an average was taken as the final result. the maximum splitting tensile strength of concrete was noted at 10% rha specimens and the minimum splitting strength of concrete was recorded at 20%. the cylinders were tested on utm. the experimental work results are shown in figure 3. v. conclusions • the flow of fresh concrete was noted maximum while using 0% rha as cement substituent material in concrete. the minimum value of workability was recorded at 20% rha. engineering, technology & applied science research vol. 9, no. 3, 2019, 4209-4212 4211 www.etasr.com bhell et al.: use of rice husk ash as cementitious material in concrete • it was concluded that the flow of fresh concrete decreases with an increase in the amount of rha in concrete. • the compressive strength was maximum at 10% rha concrete and minimum at 20% rha concrete at 7, 14, and 28 days. • the maximum splitting tensile strength of concrete was noted at 10% rha concrete and the minimum splitting strength was recorded at 20% rha concrete at 7, 14, and 28 days. fig. 3. split tensile strength at 7, 14, and 28 days references [1] a. manimaran, m. somasundaram, p. t. ravichandran, “experimental study on partial replacement of coarse aggregate by bamboo and fine aggregate by quarry dust in concrete”, international journal of civil engineering and technology, vol. 8, no. 8, pp. 1019-1027, 2017 [2] m. k. nemati, “chapter 5: aggregates for concrete”, in: concrete technology-fiber reinforced concrete final report, university of washington, 2013 [3] p. a. shirule, a. rahman, r. d. gupta, “partial replacement of cement with marble dust powder”, international journal of advanced engineering and studies, vol. 1, no. 3, pp. 175–177, 2012 [4] j. alex, j. dhanalakshmi, b. ambedkar, “experimental investigation on rice husk ash as cement replacement on concrete production”, construction and 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international research journal of engineering and technology, vol. 4, no. 7, pp. 1252–1254, 2017 [33] v. m. malhotra, p. k. mehta, pozzolanic and cementitious materials, taylor & francis, 2004 [34] a. m. nevile, j. j. brooks, concrete technology, longman scientific and technical, 1990 [35] s. rukzon, p. chindaprasirt, r. mahachai, “effect of grinding on chemical and physical properties of rice husk ash”, international journal of minerals, metallurgy and materials, vol. 16, no. 2, pp. 242-247, 2009 microsoft word 35-2598_s engineering, technology & applied science research vol. 9, no. 2, 2019, 4057-4061 4057 www.etasr.com iqbal: modern control laws for an articulated robotic arm: modeling and simulation modern control laws for an articulated robotic arm modeling and simulation jamshed iqbal department of electrical and electronics engineering, university of jeddah, saudi arabia department of electrical engineering, fast national university, islamabad, pakistan jmiqbal@uj.edu.sa abstract—the robotic manipulator has become an integral component of modern industrial automation. the current paper deals with the mathematical modeling and non-linear control of this manipulator. dh-parameters are used to derive kinematic model while the dynamics is based on euler-lagrange equation. two modern control strategies, h∞ and model predictive control (mpc), are investigated to develop the control laws. for an optimal performance, the controllers have been fine-tuned through a simulation conducted in matlab/simulink environment. the designed control laws are subjected to various inputs and tested for effectiveness in transient parameters like settling time and overshoot as well as steady state error. simulation results confirm the effectiveness of the developed controllers by precisely tracking the reference motion trajectories. keywords-non-linear control; robotic arm manipulator; mechatronics; dh-parameters; euler-lagrange equation i. introduction robots are considered key elements in automation, thus their application horizon is increasing [1]. autonomy and intelligence in robots is primarily caused by the advancements in technology and research in domains like modeling, design, control and artificial intelligence (ai) [2]. modeling and simulation in different scientific domains is gaining enormous interest among the scientific community in order to develop indepth understanding of real-world applications. study and modeling of an anthropomorphic system may help the better understanding of general human biomechanics and may also lead to formulating control laws of the actual biological agent. the basis of developing the control system for a robotic manipulator is the feedback loop, which plays a pivotal role to dampen the uncertainties. the control system neutralizes numerous disturbances and uncertainties in the plant. the solution to the control problem involves defining input signals like torque or actuator input voltage to achieve the desired behavior. the controller must be capable of handling the effects of nonlinearities, dynamic coupling and complexity. trivial strategies based on linear control laws are not able to handle the above mentioned issues [3]. thus, implementation of nonlinear control laws has been presented [4-7]. to meet the performance requirements to control multi-degree of freedom (dof) robotic manipulators, nonlinear control based on sliding mode control (smc) [8, 9], computed torque control (ctc), h∞ and model predictive control (mpc) [10] have been reported. mpc is an optimal control technique which predicts the future behavior of the system based on current states and responses. to ensure better tracking performance in constrained environment, an online process is utilized to compute future values. the optimized control signal is then formulated considering both prediction results and past behavior. an in-depth review of mpc based control strategies has been presented in [11]. authors in [12] used mpc for position and force control of a human arm like a seven dof robotics manipulator. in [13], a real-time computation method for mpc has been presented, which introduced a mapping of offline approximation approach in neural networks (nn). the proposed technique has been implemented on a low cost field programmable gate array (fpga) to show its less hardware and computational time requirements. a comparison of mpc with the proportional integral derivative (pid) and ctc has been presented in [14]. authors in [15] have proposed nn based mpc and pid law to control the vibration and position of 2link flexible arm. h∞ control law provides system robustness and high performance in spite of uncertainties and disturbances. in this control law, it is assumed that all the system states and disturbances can be sent as feedback to create a close loop system. authors in [16] presented feedback control of a linearized model of a selective compliance assembly robot arm (scara) based on h∞ control. in [17], authors suggested discrete time dynamical method as a solution of the h∞ control problem. a state-space h∞ solution using the riccati equation has been proposed in [18]. h∞ framework has been used in [19] to solve the control and management problem of tradeoffs in the specifications. this paper presents the design of h∞ and mpc control laws for a six dof robotic arm where links and joints are serially connected. the formulation of the control laws is based on the derived kinematics and dynamics of the robotic arm. the efficacy of both control strategies has been demonstrated through tracking results for various inputs. ii. mathematical model of the robotic arm robotic manipulator ed7220c is a commercial robot developed for academic purposes. this anthropomorphic arm is corresponding author: jamshed iqbal engineering, technology & applied science research vol. 9, no. 2, 2019, 4057-4061 4058 www.etasr.com iqbal: modern control laws for an articulated robotic arm: modeling and simulation used for modeling and control in the present work. the endeffector is a gripper. all joints have a single dof except the wrist. the wrist can move in roll and pitch planes. specifications of the robotic arm are presented in [20]. a. kinematic models kinematic modeling involves the joints and the end-effector position without considering the associated forces. it provides the position and orientation of end-effector based on robot joints’ angular position. in the present research, dh parameter based approach has been used to derive the kinematics of the manipulator. the axis assignment is shown in figure 1 and the resulting dh parameters are expressed in table i. fig. 1. kinematic representation of the arm showing assignment of frames on various joints table i. denavit-hartenberg (dh) parameters parameter symbol joint (i) 1 2 3 4 5 6 link twist ���� 0 -90° 0 0 -90° 0 link length ���� 0 0 l2 l3 0 0 joint angle �� θ1 θ2 θ3 θ4 θ5 0 joint distance �� l 1 0 0 0 0 l4 the transformation matrices, calculated through dhparameters presented in table i, for each link are given in (1), while the overall transformation is computed as given in (2): �� � �� �� 0 0�� �� 0 00 0 1 ��0 0 0 1 � �� � � �� �� 0 00 0 1 0 �� �� 0 00 0 0 1� (1)��� � �� �� 0 ���� �� 0 00 0 1 00 0 0 1 � �� � ��� �� 0 ���� �� 0 00 0 1 00 0 0 1 � ��� � �� �� 0 00 0 1 0 �� �� 0 00 0 0 1� �� � �1 0 0 00 1 0 00 0 1 ��0 0 0 1 � �� �� ��� ��� ��� ��� ��� ��������� � ���� �������� � ���� �� ���� ����������� ���� �������� ���� �� ���� ��� ������ ������ ���� �0 0 0 1 � (2) and the nomenclature used is: sab=sin(a+b), sabc=sin(a+b+c), cab=cos(a+b), and cabc=cos(a+b+c). given the required position and orientation of the tool, the transformation matrix presented in (2) is used to determine the corresponding joint angles. the computed joint angle positions are achieved through the controller which generates the appropriate signals for the dc motors but this requires the dynamic model presented below. b. dynamic model the dynamic model of the robotic arm gives information of torque and other forces resulting in the motion of the robot. the dynamic model can be formulated using various methods including recursive lagrange, recursive newton-euler and euler-lagrange. the dynamic model derived here uses the euler-lagrange equations. this is the most commonly followed approach due to its simplicity and compact description. the nomenclature for the deriving dynamics of the arm is presented in table ii. table ii. nomenclature for dynamic model symbol remarks �� mass of link i ��� position of center of mass (com) of link i ��� angular velocity of link i with reference to its frame �! linear velocity of link i w.r.t. its com "# total kinetic energy related to each link $# total potential energy related to each link $%&'� potential energy reference (�� inertia tensor of link i with reference to its frame ) acceleration of gravity the potential and kinetic energy of each link of the arm have been computed using (3-4) respectively: $� ��)# ��� � $%&'� (3) "� �� �� �!# �! � �� ��� (�� ��� (4) lagrangian has been calculated by the difference of these energies of the complete system. torque corresponding to each link is determined by the partial differentiation of lagrangian w.r.t q and *+ as given in (5): , "# $# , ../ 0102+ 0102 (5) the resulting torque is given in (6): τ m5q, q+8q9 � g5q8 � v5q, q+8 (6) where is the 4×1 torque vector applied to the robot’s joints. )5*8, <5*, *+8 and =5*, *+8 are respectively the 4×1 vector of gravitational force, the 4×1 vector of coriolis centrifugal force and the 4×4 inertia matrix. *9 , *+ and q are 4×1 vectors for angular acceleration, angular velocity and angular position. for complete derivation of system dynamics, see [20]. iii. the controller design a. mpc based controller the key concept behind the design of the mpc law is to consider a discrete-time model of a system and to formulate an engineering, technology & applied science research vol. 9, no. 2, 2019, 4057-4061 4059 www.etasr.com iqbal: modern control laws for an articulated robotic arm: modeling and simulation optimization problem which is solved based on an objective cost function. consider a plant in discrete-time representation (7)-(8) where the number of inputs is m, the number of outputs is q and the number of states is n1. >5" � 18 � >5"8 � � $5"8 (7) y5k8 c x5k8 (8) where u is the control input vector, x is the state vector, and y is the output vector. a is a square matrix termed as state matrix while b is the input matrix. a and b are properties of the system and are based on the system’s elements and structure. c is the output matrix which depends on the particular choice of output variables. the optimal control signal can be written as in (9): ∆d 5e#e � fg8��5e#fh e#i >5"�88 (9) where, e j k�k��…k�mn��� 0k�…k�mn��� 00…k�mn��� ………… 00…k�mn�mo�p np and nc represent the number of samples used for prediction and the number of samples used for control respectively. also, f j caca�…cast p rs in (9) is the set-point information and can be represented based on set-point signal rki i.e. rvw x1 1 … 1y r5k[8 r\ r5k[8 the principle of receding horizon is employed in developing incremental optimal control, which gives rise to: u5k8 ∑ ∆u5k[8 _� ∆u5k[8 kar5k[8 kbcdx5k[8 where u5k8 ∑ ∆u5k[8 _� efg� ihi�j ikl km 5e#e � fg8��5e#i8 en ihi�j o�o�opj km 5e#e � fg8��5e#fh8 in the present work, feedback linearization has been used to linearize the nonlinear system given in (6). the state feedback control law for linearization of the model is given in (10). τ m5q85ud q+ q8 � g5q8 � v5q, q+ 8 (10) where $� is given by receding horizon algorithm i.e.: ud5k8 ∑ ∆ud5k[8_� , ∆ud5k[8 kar5k[8 kbcd x5k[8 thus, a complete mpc law can be expressed as in (11): -5"8 = q *+5"8 *5"8 � ∑ reni5"�8 efg� >5"�8st� u � < � ) (11) the developed law resides on matrices ky and kmpc. their values are based on number of samples np and nc. thus, the overall computation time depends on window sizes. b. h∞ control law to design h∞ control law, a minimization problem is formulated while considering stability, robustness and performance normalization. the minimization problem is solved using the infinitive norm for the feedback-loop transfer function matrix. considering a linear plant, (12) gives the generalized state space model. >+ 5j8 � >5j8 � � $5j8 v5j8 k >5j8 � w $5j8 (12) where x(t), u(t) and y(t) represent state vectors, control input and output respectively. d is a feed forward matrix or direct transmission matrix which is determined by the selected output variables. considering a perturbed system with disturbance vector w(t) and error vector z(t), (13) represents the state space model while (14) gives the transfer function matrix. >+ 5j8 � >5j8 � ��l5j8 � ��$5j8 v5j8 k� >5j8 � w�� l5j8 � w�� $5j8 (13) x5j8 k� >5j8 � w�� l5j8 � w�� $5j8 �5�8 ≔ � �⋯k�k� ⋮⋯⋮⋮ ��⋯w��w�� ��⋯w��w��� (14) h∞ control law is designed using state feedback linearization approach based on (6). the developed control law is given in (15). =5*85$� *+ *8 � )5*8 � <5*, *+ 8 (15) where uc is the auxiliary control signal. after applying (15), appropriate values of weight coefficients wu and wp are respectively selected for the perturbation and input. the calculation of k is based on s over ks design approach and solution of the two riccati equations, ensuring the stability of the system i.e.: mink stabilizing � wc5i � tk8��w�k5i � tk8�� �� < γ (16) k serves as an auxiliary control which gives the signals $�� as output based on the input joint angles *�. $� [$�� $�� $�� $��y# can be calculated after all $�� are known. iv. simulation results and discussion matlab/simulink is used for simulation. s-functions are used for the plant and controller in simulation environment. a sampling time of 5ms is selected for controlling the modeled robotic manipulator. a. mpc simulation results the performance of mpc control law for different target trajectories is investigated. the investigation also includes the effect of the control horizon �� and the prediction horizon �g. engineering, technology & applied science research vol. 9, no. 2, 2019, 4057-4061 4060 www.etasr.com iqbal: modern control laws for an articulated robotic arm: modeling and simulation keeping �� constant while changing �g and vice versa revealed the importance of both horizons in the controller design. it is observed that the response of the system is related with the size of the control window. the performance is enhanced when the size is increased. tuning based on trial and error resulted in optimal values as �g 100 and �� 20 . figures 2 and 3 present the trajectory tracking results when the system is subjected to ramp and step inputs respectively. it can be inferred from the results that all the joints demonstrated identical response with different torques applied to the joints. shoulder joint exhibited relatively higher torque requirements in comparison with wrist, elbow and waist joints. (a) (b) fig. 2. ramp response: (a) trajectory tracking, (b) corresponding torques (a) (b) fig. 3. step response: (a) trajectory tracking, (b) corresponding torques b. h∞ simulation results the weight functions have significant effect on the performance of the designed control law. in the present research, the weight functions have been selected based on the guideline reported in [21]. the selected weight functions are given in (17): wc5s8 0.95 v���.� v��v��� v� .� and w�5s8 0.01 (17) the effect of changing �� values on the developed controller is investigated. the results reveal that the selected value is a good choice. weight functions (17) are used to plot ramp, step and sinusoidal responses of the system. figures 4 and 5 present the tracking results of ramp and sinusoidal references. it is evident from the plots that all the joints of the robotic arm showed similar behavior. a delay is also observed in the controller’s response for reference trajectories. (a) (b) fig. 4. ramp response: (a) trajectory tracking (b) corresponding torques (a) (b) fig. 5. sinusoidal response: (a) trajectory tracking, (b) corresponding torques engineering, technology & applied science research vol. 9, no. 2, 2019, 4057-4061 4061 www.etasr.com iqbal: modern control laws for an articulated robotic arm: modeling and simulation the results obtained by mpc and h∞ control laws are compared. the performance achieved by both controllers has been characterized w.r.t various parameters. table iii summarizes the comparative results based on step responses offered by both control strategies. for settling time, ±5% of the desired joint angle has been considered. it is pertinent to mention here that the given results are based on the selected gains and may vary with different gains selection. table iii. comparative performance parameter remarks control strategy h∞∞∞∞ mpc rise time tr (sec) 4.305 0.77 peak time tp (sec) 5.06 1.005 settling time ts (sec) 3.68 0.68 overshoot %os 1.9 % 4.5% v. conclusion a model of a six dof robotic arm is presented in this paper followed by the derivation of two modern control laws, mpc and h∞. simulation results confirmed that both control laws offer adequate tracking performance. comparative analysis of the performance achieved by both controllers reveals that mpc over performs h∞, on the expense of higher overshoot for controlling the robotic arm. the size of the prediction window can be increased to reduce overshoot in mpc response. in the future, it is planned to realize both control strategies on a real robotic platform. for this purpose, a custom platform named as autarep (autonomous articulated robotic educational platform) has already been designed and fabricated. also, it is planned to investigate the control performance when the robotic arm is subjected to disturbances and uncertainties. moreover, application-oriented study to explore practical avenues of the proposed research is anticipated. references [1] j. iqbal, r. u. islam, s. z. abbas, a. a. khan, s. a. ajwad, “automating industrial tasks through mechatronic systems–a review of robotics in industrial perspective”, tehnicki vjesnik, vol. 23, no. 3, pp. 917-924, 2016 [2] s. g. khan, g. herrmann, m. al grafi, t. pipe, c. melhuish, “compliance control and human–robot interaction: part 1—survey”, international journal of humanoid robotics, vol. 11, no. 3, pp. 1430001-1430028, 2014 [3] s. a. ajwad, j. iqbal, r. u. islam, a. alsheikhy, a. almeshal, a. mehmood, “optimal and robust control of multi dof robotic manipulator: design and hardware realization”, cybernetics and systems, vol. 49, no. 1, pp. 77-93, 2018 [4] i. ahmad, a. saaban, a. ibrahin, m. shahzad, “a research on the synchronization of two novel chaotic systems based on a nonlinear active control algorithm”, engineering, technology & applied science research, vol. 5, no. 1, pp. 739-747, 2014 [5] s. irfan, a. mehmood, m. t. razzaq, j. iqbal, “advanced sliding mode control techniques for inverted pendulum: modelling and simulation”, engineering science and technology, an international journal, vol. 21, pp. 753-759, 2018 [6] w. alam, a. mehmood, k. ali, u. javaid, s. alharbi, j. iqbal, “nonlinear control of a flexible joint robotic manipulator with experimental validation”, strojniski vestnik-journal of mechanical engineering, vol. 64, no. 1, pp. 47-55, 2018 [7] o. khan, m. pervaiz, e. ahmad, j. iqbal, “on the derivation of novel model and sophisticated control of flexible joint manipulator”, revue roumaine des sciences techniques-serie electrotechnique et energetique, vol. 62, no. 1, pp. 103-108, 2017 [8] a. rezoug, b. tondu, m. hamerlain, “experimental study of nonsingular terminal sliding mode controller for robot arm actuated by pneumatic artificial muscles”, ifac proceedings, vol. 47, pp. 1011310118, 2014 [9] j. iqbal, m. i. ullah, a. a. khan, m. irfan, “towards sophisticated control of robotic manipulators: an experimental study on a pseudoindustrial arm”, strojniski vestnik-journal of mechanical engineering, vol. 61, no.7-8, pp. 465-470, 2015 [10] m. i. ullah, s. a. ajwad, m. irfan, j. iqbal, “mpc and h-infinity based feedback control of non-linear robotic manipulator”, ieee international conference on frontiers of information technology, islamabad, pakistan, december 19-21, 2016 [11] a. bemporad, “model predictive control design: new trends and tools”, ieee conference on decision and control, san diego, usa, december 13-15, 2006 [12] j. de la casa cardenas, a. s. garcia, s. s. martinez, j. g. garcia, j. g. ortega, “model predictive position/force control of an anthropomorphic robotic arm”, ieee international conference on industrial technology, seville, spain, march 17-19, 2015 [13] h. ayala, r. sampaio, d. m. munoz, c. llanos, l. coelho, r. jacobi, “nonlinear model predictive control hardware implementation with custom-precision floating point operations”, 24th ieee mediterranean conference on control and automation, athens, greece, june 21-24, 2016 [14] m. makarov, m. grossard, p. rodriguez-ayerbe, d. dumur, “generalized predictive control of an anthropomorphic robot arm for trajectory tracking”, ieee/asme international conference on advanced intelligent mechatronics, budapest, hungary, july 3-7, 2011 [15] j. o. pedro, t. tshabalala, “hybrid nnmpc/pid control of a two-link flexible manipulator with actuator dynamics”, 10th ieee asian control conference, kota kinabalu, malaysia, may 31-june 3, 2015 [16] h. s. ali, l. boutat-baddas, y. becis-aubry, m. darouach, “h∞ control of a scara robot using polytopic lpv approach”, 14th ieee mediterranean conference on control and automation, ancona, italy, june 28-30, 2006 [17] b. chen, x. liu, c. lin, k. liu, “robust h∞ control of takagi–sugeno fuzzy systems with state and input time delays”, fuzzy sets and systems, vol. 160, no. 4, pp. 403-422, 2009 [18] j. c. doyle, k. glover, p. p. khargonekar, b. a. francis, “state-space solutions to standard h/sub 2/and h/sub infinity/control problems”, ieee transactions on automatic control, vol. 34, no. 8, pp. 831-847, 1989 [19] m. makarov, m. grossard, p. rodriguez-ayerbe, d. dumur, “modeling and preview h∞ control design for motion control of elastic-joint robots with uncertainties”, ieee transactions on industrial electronics, vol. 63, no. 10, pp. 6429-6438, 2016 [20] s. manzoor, r. u. islam, a. khalid, a. samad, j. iqbal, “an opensource multi-dof articulated robotic educational platform for autonomous object manipulation”, robotics and computer-integrated manufacturing, vol. 30, no. 3, pp. 351-362, 2014 [21] b. a. francis, a course in h∞ control theory, lecture notes in control and information sciences, springer-verlag, 1987 author profile j. iqbal holds a phd in robotics from the italian institute of technology (iit), italy and three master degrees in various fields of engineering from finland, sweden and pakistan. he is currently working as an associate professor in the university of jeddah, saudi arabia. with more than 15 years of multi-disciplinary experience, his research interests include robot analysis and control. he has more than 50 isi-indexed journal papers on his credit with an h-index of 24. he is a senior member of ieee, usa. microsoft word 34-2722_s1_etasr_v9_n4_pp4500-4503 engineering, technology & applied science research vol. 9, no. 4, 2019, 4500-4503 4500 www.etasr.com mohamed: effects of cold rolling and aging treatment on the properties of cu-be alloy effects of cold rolling and aging treatment on the properties of cu-be alloy masoud ibrahim mohamed chemical and materials engineering department, northern border university, arar, saudi arabia, on leave from mechanical engineering department, fayoum university, egypt ibrahim_64@yahoo.com abstract—the effects of precipitated phases during aging treatment on the properties of the cu-be alloy have been extensively studied. in this study, the effect of cold rolling on the precipitated phases of the cu-be alloy compared with nondeformed alloy during isothermal and low heating rate aging of 2 0 c/min have been investigated. hardness changes, differential scanning calorimetry (dsc), dilatation analysis, and transmission electron microscopy (tem) were used in this study. hardening and contraction were strongly increased at an early aging time for the cold rolled cu-be alloy. in addition, the dsc curves revealed an exothermic peak from the γ΄΄ phase. this peak increased and shifted to lower aging time by increasing the cold rolling reduction. in addition, the hardness remarkably increased at lower aging temperatures for the cold rolled specimens. the contraction from the dilatation curves and the exothermic peaks shifted to lower aging temperatures in cold rolled specimens. the hardening of cu-be alloy is believed to be from the γ΄ phase, and the contraction and the first exothermic peak in dsc curves from γ΄΄ phase. tem observations are in a good agreement with the above explanation and strongly revealed that γ΄΄ and γ΄ phases were highly accelerated by the effect of cold rolling. keywords-precipitation hardening; transmission electron microscopy;age hardening; solution treatment; cold rolling i. introduction cu-be alloy has been used very widely for springs, diaphragms, bearings and non-sparking tools because it has excellent mechanical properties, high electrical conductivity, and high corrosion resistance. aging after quenching from solution treatment remarkably hardens the alloy [1-4]. the precipitation sequence in this alloy has been extensively studied and can be summarized as follows [5-8]: α supersaturated solid-solution→g.p zones →γ΄΄→γ΄→γ (cube). the g.p zones are monolayer plates that form coherently on {100} matrix and revealed as streaks along 200〈 〉 α directions, γ΄΄ is a metastable phase with a monoclinic structure appearing as intensity maxima in the streaks along the 200〈 〉 α directions with aging treatment [9-13]. with farther aging the intensity maxima began to change to arrowhead-like shape, which shows the precipitation of γ ́ phase, this phase is metastable with a b.c.c. structure. the stable γ phase precipitate has an equilibrium b.c.c. structure [8, 14-19]. few studies have been done on the effect of cold rolling on the hardening behavior of cu-be alloy. in this paper the precipitation of γ΄΄ and γ ́ phases through aging of this alloy under the effect of cold rolling have been studied using hardness measurements, thermo-mechanical analysis (tma), and differential scanning calorimetry (dsc). transmission electron microscopy (tem) has been used for phase transformation studies. ii. experimεntal μethod cold-rolled plates of cu-be alloy (japanese industrial standard #c1720), which contains beryllium of 1.9mass% and 0.2mass% cobalt were used in this study. this alloy was received as a cold rolled plate of 2.5mm thickness. test pieces with size of 10mm width, 120mm length were cut out from the 2.5mm thickness plate in the rolling direction figure 1(a). (a) (b) (c) fig. 1. (a) specimen for cold rolling, (b) specimen for dilatation measurements, and (c) illustration of the heat treatments for the nd and the cr specimens: (i) solution treatment, (ii) isothermal aging at 360℃. corresponding author: masoud ibrahim mohamed (i) 80 0 c × 2h (ii) 360 0 c × time engineering, technology & applied science research vol. 9, no. 4, 2019, 4500-4503 4501 www.etasr.com mohamed: effects of cold rolling and aging treatment on the properties of cu-be alloy the cutout test pieces were first solution heat-treated at 800℃ for 2 hours followed by water quenching. the quenched specimens were cold rolled (at room temperature) with different reduction ratios (1, 2, 4, 8 and 12%). these cold rolled specimens were aged treated at 360℃ for different time intervals up to 180min. figure 1 (c) shows the heat treatment cycle. specimens of 10mm×10mm×2.5mm were cut out from the non-deformed (nd) and cold rolled (cr) plates for hardness measurements after aging at 360℃. hardness was measured by the mean value of 10 measurements using vickers hardness tester with the load of 9.8n. specimens of 2.5mm×2.5mm×40mm were cut out from the aged plates for dilatation measurements through heating of cu-be alloy (figure 1(b)). specimens of 20mg in weight were used for dsc tests. specimens of 2.5mm width, 13mm length were cut out for the tma during heating at 800℃. thin foils suitable for tem observation were prepared using double jet electro polishing technique. diffraction pattern, bright-field image were performed, the diffraction pattern was obtained on the [001] direction. the transmission electron microscope employed was hitachi h-9000nar. iii. results and discussion hardness changes for the nd and cr plates during aging at 360℃ are shown in figure 2. the cu-be alloy shows higher hardness values compared with the non-deformed. fig. 2. changes in hardness of cu-be alloy during isothermal aging at 360℃ a little cold rolling enhances the hardness remarkably at an early stage of aging and the hardness increases slightly with increasing reduction ratio of cold rolling. it is clear that the hardness of the cr specimens increases earlier than the one of the nd specimen. after 20min aging, the hardness increased from about 150hv to 220hv and 310hv at 1% and 12% for nd and cr, respectively. thus, it seems that cold rolling promotes the hardening of this alloy at early aging time. dilatation tests revealed higher shrinkage at early aging time after cold rolling as shown in figure 3. it is clear from figures 2 and 3 that the hardening and dilatation curves of the cr and nd specimens are strongly coexisting, showing remarkable increase of the hardness and shrinkage at early aging stage and are almost steady after about one hour aging. previous studies on the effect of cooling rate on aging behavior of cu-be alloy showed that the contraction was caused by the precipitation of γ΄ ́phase while the hardening was mainly related to γ ́ phase [8, 9]. therefore, it can be concluded that cold rolling enhanced the precipitation of both γ΄΄ and γ ́ phases. this will be clarified below by tem observation for cr and nd specimens after different heat treatments. fig. 3. dilatation behavior of cu-be alloy during isothermal aging at 360℃ hardness changes were measured for the nd and cr specimens (up to 30% reduction) after heating to different temperatures at a heating rate of 2℃/min, followed by water quenching. figure 4 shows that as the heating temperature increases, the hardness increases to reach a maximum at about 380℃ and then decreases. at 300℃, remarkable hardness increase was revealed for the cr specimens compared with the nd specimens. the maximum hardness slightly increases and shifts to lower temperatures as the cold rolling reduction ratio increases. generally, the hardness increases of cu-be alloy mainly due to γ ́ phase precipitation. at higher temperatures, over 380℃, the hardness decreased due to γ ́phase dissolution and/or γ stable phase formation as reported in [8, 9, 12]. fig. 4. effect of cold rolling on hardening of cu-be alloy, heating rate 2℃/min figure 5 shows the dilatation curves for the nd and cr specimens of this cu-be alloy during heating up to 600℃ at 2℃/min heating rate. the cold rolled specimens show that shrinkage increase started at about 280℃. with increasing temperature the shrinkage increased to a maximum of 0.20% at about 370℃, and then decreased. as the reduction ratio of cold rolling increased, the maximum shrinkage slightly decreased and shifted to lower temperatures. engineering, technology & applied science research vol. 9, no. 4, 2019, 4500-4503 4502 www.etasr.com mohamed: effects of cold rolling and aging treatment on the properties of cu-be alloy fig. 5. effect of cold rolling on dilatation of cu-be alloy, heating rate 2℃/min on the other hand, the nd specimens show a very slight expansion during the same heating conditions. it is interesting to note that the hardening and dilatation curves for this alloy (figures 4 and 5) have similar behavior of increasing to maximum and decreasing as the heating temperature increases. maximum contraction and maximum hardness are obtained at the same temperature of about 370~380℃ and shift to lower temperatures with increasing cold rolling reduction ratio. figure 6 shows the dsc curves for the nd and the cr specimens during heating up to 500℃. the first exothermic peak is the highest for the nd specimen and appeared around 350℃. this peak decreased and shifted to lower temperatures for the cold rolled specimens. with further heating a peak like a shoulder appeared at around 380℃. fig. 6. dsc curves of cu-be alloy, heating rate 2℃/min the first exothermic peak may be due to the γ΄ ́ phase and/or g.p zones precipitation. on the other hand, the shoulder may be due to the γ ́ phase precipitation. this assumption is based on the maximum hardness obtained at the same temperature of 380℃ as shown in figure 4. tem observation was investigated for cr and nd cu-be alloys after heat treatment at different conditions corresponds to the different exothermic heat changes, dilatation and hardness changes. if we consider the height of the peaks as an indication of the amount of the precipitated phases, it can be concluded that, cold rolling enhanced the formation of γ΄΄ phase and g.p zones and slightly decreased its amount. οn the other hand, the amount of γ΄ phase increased by cold rolling. as mentioned earlier, shrinkage mainly occurs due to the precipitation of γ΄΄ phase. from this point of view it seems that the first peak was obtained from the dsc curves of figure 6 for the nd specimen mainly due to g.p zones formation, not γ΄ ́phase precipitation. figure 7(a) and (d) shows the electron diffraction pattern of the nd and 4% cr specimens respectively. the nd specimen showed mainly weak g.p. zones, while the 4% cr specimen revealed g.p. zones with small amount of γ΄΄ phase (marked with arrows). the electron diffraction pattern of the nd specimen after aging at 360℃ for 20min revealed only g.p zones as shown in figure 7(b). it is noted, however, that 4% cr specimen precipitates γ΄ ́and γ ́phases after the same aging conditions (figure 7(e)). figure 7(c) and (f) shows the electron diffraction patterns of the nd and 4% cr specimens after heating to 348℃ and 316℃ respectively. the nd specimen showed g.p zones and small amount of γ΄΄ phase, while 4%cr specimen showed mainly γ΄΄ phase (marked with arrows) after heating to the lower temperature of 316℃. it is noted, however, that the 4% cr specimen precipitates γ΄΄ and γ΄ phases after the same aging condition (figure 7(e)). fig. 7. tem diffraction pattern, (a) as st, (b) s.t +20min aging, (c) s.t +348℃, (d) 4% cr (e), 4% cr +20min aging, and (f) 2% cr +316℃. incident beam is parallel to [001] fig. 8. tem micrograph, shows the bright field image corresponding to figure 7 figure 8 shows the bright filed image (bfi) corresponding to the electron diffraction pattern in figure 7. electron diffraction pattern of the nd and 2% cr specimens after heating to 380℃ and 360℃ respectively are shown in figure 9(a) and (d). the nd specimen revealed mainly γ ́ phase as arrowhead structure at 1/3[002]. on the other hand, 2% cr specimen showed γ ́ phase after heating to the lower temperature of 360℃. this means that cold rolling promotes engineering, technology & applied science research vol. 9, no. 4, 2019, 4500-4503 4503 www.etasr.com mohamed: effects of cold rolling and aging treatment on the properties of cu-be alloy the precipitation of γ΄ ́ and γ΄ phases coincidently with the result of the hardness change, dsc curves, tma curves and dilatation. figure 9(b) and (e) shows the electron diffraction pattern for the nd and 2% cr specimens after heating to 500℃ respectively. at this high temperature mainly γ phase was precipitated in the nd and 2% cr specimens. γ phase was revealed more clearly in 2% cr specimen. in figures 9(c) and (f) the schematics for the electron diffraction pattern are shown. thus, phase precipitation depends strongly on cold rolling, it is apparent that the precipitation of γ΄΄ and γ΄ phases was accelerated by the effect of cold rolling. fig. 9. electron diffraction pattern: (a) st +380℃, (b) st +500℃, (c) schematic illustration for the diffraction pattern, (d) 2% cr +360℃, (e) 2% cr +500℃, (f) schematic illustration for the diffraction pattern. the incident beam is parallel to [001]. iv. conclusion the influences of cold rolling and heat treatment on the age-hardening behavior of the cu-be alloy were investigated for nd and cr specimens. the obtained results are summarized as follows: • at early stage aging, the hardening and shrinkage of the cu-be alloy were strongly suppressed by the effect of cold rolling. maximum hardness and shrinkage appeared at almost the same temperature of about 370-380℃. • dsc curves showed that cold rolling promotes the first exothermic peak and shifts it to lower temperatures, thus cold rolling enhanced the precipitation of γ΄΄ phase. • the tma curves revealed that cold rolled specimens highly shrink with heating and the maximum shrinkage shifts to lower temperature with increasing of the cold rolling reduction. • dsc, dilatation changes, tma, and tem studies coexisted and revealed that the precipitation of γ΄΄ and γ΄ phases were accelerated by cold rolling. acknowledgement the author wishes to acknowledge the approval and the support of this research study by the grant no. 7593-eng2018-3-9-f from the deanship of scientific research, northern border university, arar, saudi arabia. references [1] e. rocha-rangel, j. a. rodrguez-garcia, c. a. hernandez-bocanegra, “precipitation hardening of cu-be alloys”, chemxpress vol. 5 no. 4, pp. 132-136, 2014 [2] m. mankani, s. s. sharma, “heat treatment of mill-hardened beryllium copper for space applications”, universal journal of mechanical engineering, vol. 3, no. 4, pp. 147-150, 2015 [3] z. zhu, y. cai, k. song, y. zhou, j. zou, “precipitation characteristics of the metastable γ″ phase in a cu-ni-be alloy”, materials, vol. 11, no. 8, article id 1394, 2018 [4] t. tang, y. l. kang, l. j. yue, x. l. jiao, “precipitation behavior of cu-1.9be-0.3ni-0.15co alloy during aging”, acta metallurgica sinica (english letters), vol. 28, no. 3, pp. 307-315, 2015 [5] y. tang, y. kang, l. yue, x. jiao, “mechanical properties optimization of a cu–be–co–ni alloy by precipitation design”, journal of alloys and compounds, vol. 695, pp. 613-625, 2017 [6] y. tang, y. kang, l. dejia, m. shen, y. hu, l. zhao, “tuning low cycle fatigue properties of cu-be-co-ni alloy by precipitation design”, metals-open access metallurgy journal, vol. 8, article id 444, 2018 [7] s. montecinos, s. tognana, w. salgueiro, “influence of microstructure on the young's modulus in a cu-2be (wt.%) alloy”, journal of alloys and compounds, vol. 729, pp. 43-48, 2017 [8] l. yagmur, o. duygulu, b. aydemir, “investigation of metastable γ΄ precipitate using hrtem in aged cu–be alloy”, materials science and engineering a, vol. 528, no. 12, pp. 4147-4151, 2011 [9] w. bonfield, b. c. edwards, “precipitation hardening in cu 1.81 wt % be 0.28 wt % co”, journal of materials science, vol. 9, no. 3, pp. 398408, 1974 [10] i. m. masoud, k. naito, h. era, k. kishitake, “a shape memory behavior newely reveled in cu-be alloy”, 7th cairo university international mdp conference, cairo, egypt, february 15-17, 2000 [11] l. yang, f. y. zhang, m. f. yan, m. l. zhang, “microstructure and mechanical properties of multiphase layer formed during thermodiffusing of titanium into the surface of c17200 copper-beryllium alloy”, applied surface science, vol. 292, no. 1, pp. 225-230, 2014 [12] k. esmati, h. omidvar, j. jelokhani, m. naderi, “study on the microstructure and mechanical properties of diffusion brazing joint of c17200 copper beryllium alloy“, materials & design, vol. 53, pp. 766773, 2014 [13] a. khodabakhshi, v. abouei, n. mortazavi, s. h. razavi, h. hooshyar, m. esmaily, “effects of cold working and heat treatment on microstructure and wear behaviour of cu–be alloy c1720”, tribologymaterials, surfaces & interfaces, vol. 9, no. 3, pp. 118-127, 2015 [14] r. monzen, s. okawara, c. watanable, “stress-assisted nucleation and growth of γ″ and γ′ precipitates in a cu–1.2 wt %be–0.1 wt%co alloy aged at 320°c”, philosophical magazine, vol. 92, no. 14, pp. 18261843, 2012 [15] r. j. price, a. kelly, “deformation of age hardened crystals of copper1.8 wt.% beryllium”, acta metallurgica, vol. 11, no. 8, pp. 915-922, 1963 [16] w. ozgowicz, e. kalinowska-ozgowicz, b. grzegorczyk, “thermomechanical treatment of low-alloy copper alloys of the kind cuco2be and cuco1nibe”, journal of achevements in materials and manfacturing engineering, vol. 46, no. 2, pp. 161-168, 2011 [17] r. o. galicia, c. g. garcia, m. a. alcantara, a. h. vazquez, “influence of heat treatment and composition variations on microstructure, hardness, and wear resistance of c18000 copper alloy”, isrn mechanical engineering, vol. 2012, article id 248989, 2012 [18] y. lim, k. lee, s. moon, “effects of a post-weld heat treatment on the mechanical properties and microstructure of a friction-stir-welded beryllium-copper alloy”, metals-open access metallurgy journal, vol. 9, no. 4, article id 461, 2019 [19] m. hariram, d. theerath, p. chakravarthy, r. a. kumar, “influence of cold work on aging response of c17200-beryllium copper alloy c17200”, materials today: proceedings, vol. 4, no. 10, pp. 11188– 11193, 2017 microsoft word 14-15-3022_s_etasr_v9_n5_pp4649-4653 engineering, technology & applied science research vol. 9, no. 5, 2019, 4649-4653 4649 www.etasr.com musa et al.: experimental study of the two-phase flow patterns of air-water mixture at vertical bend … experimental study of the two-phase flow patterns of air-water mixture at vertical bend inlet and outlet veyan a. musa department of mechanical engineering, university of zakho, zakho, kurdistan region, iraq veyan.musa@staff.uoz.edu.krd lokman a. abdulkareem department of petroleum engineering, university of zakho, zakho, kurdistan region, iraq lokman.abdulkareem@uoz.edu.krd omar m. ali department of mechanical engineering, university of zakho, zakho, kurdistan region, iraq omar.ali@uoz.edu.krd abstract—air-water two-phase flow in pipes introduces a noticeable challenge due to the complexity of the fluids. thus, to estimate the best design and reasonable financing cost of the transportation pipelines where the bends are presenting a part of their accessories, the investigators should have been able to estimate the flow regime occurring at different directions. an experiment was carried out by using a 90 o bend fixed with two pipes where the flow was upstream from a vertical to a horizontal pipe which were representing the bend inlet and outlet respectively. two wire-mesh sensors were used for obtaining the data of the void fractions (α) at water superficial velocities (usl) which changed from 0.052 to 0.419m/s, and air superficial velocities (usg) from 0.05 to 4.7m/s. furthermore, the characterization of flow regimes of the air-water flow at both bend inlet and outlet were competed accurately by using void fraction analysis of the time series, power spectral density (psd), tomographic images observed by the sensor program, and the probability density function (pdf) method. the flow regimes of vertical flow lines at the bend inlet were observed as bubbly, capbubble, slug, and churn flow, whereas the flow regimes of the horizontal flow line at the bend outlet were characterized as having stratified, stratified wavy, bubbly, plug, slug, wavy annular, and semi-annular flow due to the gravity and bend effects. keywords-flow pattern in vertical pipes; flow pattern in horizontal pipes; air-water flow; wire mesh sensor (wms); twophase flow at bends i. introduction generally, two-phase flow exists in a wide scope of mechanical applications and can be noticed in many scientific fields [1]. in chemical processes various two-phase flow forms occur in pipelines, reactors, plant parts, components, and bubble columns. in each case, the two-phase flow is considered as an important factor to improve the productivity and safety of the procedures. therefore, the suitable control of such flow properties is of significant importance to raise the efficiency of the operating system [2]. air-water mixture flows in transportation pipelines and bends occur in a lot of applications such as the transport heat exchange pipelines, transportation water pipelines, reactor system of thermal-hydraulic, etc. this kind of flow is unpredictable because it has a complex quality while it is passed through different behavior bends when compared with single-phase flow. in fact, the two-phase flow in bends conducts as inhomogeneous stage dispersion and flow inversion occurs under the influence of gravity, buoyancy, and centrifugal forces. the primary experimental research in such studies has been presented in [3]. authors investigated the flow distribution of air-water mixture flow through a vertical riser pipe of 7.6cm diameter directed to 90 o bend, and they studied the impact of angular position (φ) and phase velocity on the flow distribution. the authors submitted a straightforward model to foresee how each phase is acting along the bend, and they found the relationship between gravity and centrifugal forces which are communicated by the adjusted of froude number and characterized by: �� = �� (� × sin� × ����)⁄ (1) where fr is froude number, j is the phase velocity, ���� is the bend curvature radius, and φ is the angular position. at the point where fr=1, the phases are in harmony and have a tendency to stay in the original trajectory. when fr<1 the gas phase moves to the external axis side while the water phase flows in the internal axis side, and when fr>1, the gas tends to move to the internal axis side of the bend. in an experimental investigation of the air-water flow patterns [4], the authors estimated the effect of 90 o elbow with 5.03cm diameter on the bubbly flow structures in a development horizontal flow line. they used a probe conductivity dual sensor. fifteen different conditions have been tested within the regimes of bubbly flow. significantly, they are illustrated clearly, the elbow effect on the void fraction (α) distribution. in addition, the test demonstrated that the bend increases the fluctuation of the flow for both horizontal and vertical directions of the pipe cross-section area. authors in [5] obtained similar results in a 45 o shape with the same diameter and conditions. in [6], an experimental study was carried out to study the effects of fluctuating forces on a 90 o , 5.25cm diameter elbow. an aggregate of 36 tests was completed to cover the annular, bubbly, and slug flow regimes by using an impedance probe as measurement technique. the dominating corresponding author: veyan a. musa engineering, technology & applied science research vol. 9, no. 5, 2019, 4649-4653 4650 www.etasr.com musa et al.: experimental study of the two-phase flow patterns of air-water mixture at vertical bend … force frequency was observed significantly in the slug flow pattern. the root means square values of fluctuation force persistently rise with increase in the gas flow rate and greatest value is achieved at annular flow. authors in [7] studied experimentally the two-phase flow in a 90 o bend of 3.4cm internal diameter. the void fractions were tested in two situations, horizontal to vertical and vertical downstream to a horizontal flow line. the test has been performed under different values of phase superficial speeds, varied from 0.21 to 0.90m/s for water and 0.3 to 4m/s for air. the experiment utilized time series pdf analysis and visual imaging technique to portray the flow conducts and patterns. the outcome where that wavy, stratified, slug, and plug regimes were noticed in the horizontal pipe in contrast, the churn and slug flow patterns were observed at the vertical pipe. author in [8] studied the flow regime of gas-liquid flow using pdf, liquid holdup in the domain of time series, and psd to identify the flow regimes in the transparent inclined pipe. the experimental study in [9] exhibited the identification of air-water flow in a 50mm horizontal pipe by using pdf and the void fraction of time series under different water and air superficial velocities according to the analysis estimated in [10]. they observed the following flow regimes in the horizontal pipe: annular-wavy, slug, bubbly, and stratified flow under air superficial velocities from 0.23 to 10.5m/s and water superficial velocities from 0.05 to 1.7m/s by using wms to obtain the void fraction values. authors in [11] identified the flow of air-water patterns in a horizontal pipe of 5cm diameter by using wms and they improved the possibility of identification flow patterns by pdf and void fraction of time series correlation technique. many techniques have been utilized to characterize the flow patterns of the gas-liquid flow, such as x-ray tomography [2], wire-mesh sensor (wms) [12], and electrical capacitance tomography (ect). authors in [13] obtained and used an innovated wms sensor which depends on the conductivity alteration in the properties between flow fluids. the wms was exhibited in 1998 at tomographic imaging, and after it has been improved in [14] as an optimistic technique to obtain the hold-up (h) of water in oil depending on the conductivity of the liquid. finally, the comprehension of the air-water flow properties accounts on the knowledge of the flow patterns occurring inside the pipes, therefore the exact prediction of the two-phase flow pattern is the starting point for designing systems able to save energy and diminish system collapse by calculating the void fractions and estimating the bend effect on the air-water flow regimes of the vertical riser pipe to the horizontal flow line. ii. experimental design the current investigation was conducted at the research center of helmholtz centrum dresden rossendorf (hzdr) in germany. the flow consisted of air and tap water at room temperature of 22 o c with atmospheric pressure. a 90 o bend of a 15.35cm curvature radius has been joined between the riser vertical pipe and the horizontal pipe with a diameter of 6.7cm. two wire mesh sensors were fixed on the flow path before and after the bend ends with a 20cm distance from the bend ends. the flow direction was vertically upstream to the horizontal flow line. the void fractions (α) of time series information were obtained by two sensors (wms1 and wms2) as shown in figure 1. the flow patterns of the flow lines were examined for 13 different values of air superficial velocity (usg) ranging from 0.05 to 4.7m/s and constant water superficial velocity (usl) ranging from 0.052 to 0.419m/s. fig. 1. the 90 o bend frame. iii. results the following methods were utilized to classify the flow regimes occurring at the bend inlet in the vertical pipe and at the bend outlet in the horizontal pipe: the time series of void fraction, the tomographic images of the wms program, power spectral density (psd), probability density function (pdf), and mean void fraction and liquid holdup (h). a. at steady liquid superficial velocity (usl) of 0.052m/s at usl=0.052m/s and gas superficial velocity us=0.05m/s at the bend inlet, the mean void fraction fluctuates at 0.1 with a few peaks (figure 2(a)). the plot of pdf exhibits a single peak of high pdf value of 0.17 with a void fraction α=0.1 (figure 2(b)). the amplitude value of the spectrum accomplishes its maximum value at 1.5hz and declines gradually to the right (figure 2(c)). the plot features are referred to the bubbly pattern. at the bend outlet, the plot of the void fraction is shown as a straight line with some waves under the mean void fraction of about 0.5. the pdf curve shows a hill shape with α values between 0.3 to 0.6, whereas the plot of psd is characterized by a peak value of about 70 near zero frequency. regarding the amount of air and water that entered the bend, the outlet stratified wavy regime is conducted normally because the turbulent flow which occurred at the bend outlet was waving the phases. by increasing the usg value to 0.28m/s at the bend inlet, the mean void fraction fluctuated frequently under the values of 0.2 and 0.7 (figure 3(a)) the pdf plot exhibits two peaks at pdf values 0.01 and 0.05 (figure 3(b)), while the psd plot shows a single peak with a maximum of about 60 at 1.75hz (figure 3(c)). this value is declined and fluctuated with increase in frequency to the right and is characterized as slug flow. the increment in usg led to an increase in the taylor bubbles length and shrinking of the air bubbles into the water, thus, the slug flow was obtained. at the bend outlet for the horizontal flow line, the flow was observed engineering, technology & applied science research vol. 9, no. 5, 2019, 4649-4653 4651 www.etasr.com musa et al.: experimental study of the two-phase flow patterns of air-water mixture at vertical bend … as stratified wavy, which is estimated by the plot of the void fraction as a straight line at 0.7 with a few waves. the pdf plot is characterized by a single peak at 0.1, and the psd plot shows a maximum spectrum peak of about 80 near 0hz. the waves in the flow tend to increase the psd value, thus the stratified wavy plot depicts a higher value than the stratified flow plot. the stratified wavy pattern is obtained as a result of the bend effect, where the small amount of water is mixed with considerably high values of usg. when the usg value reached 1.4m/s, the flow pattern was of a churn regime at the bend inlet for the vertical flow line. the mean void fraction oscillates under a high value of about 0.8 (figure 4(a)). the pdf plot has one peak at 0.75 (figure 4(b)), while the maximum spectrum peak shows a small value of 30 at 2hz with a larger base scope (figure 4(c)). the increase of usg value raises the instability of the water slugs. when the usg achieves a critical point, the water slugs will be penetrated and this prompts the flow pattern to change its form into churn flow. at the bend outlet for the horizontal flow line, the flow regime is observed as stratified wavy because the increment of usg with a little amount of water mass flow rate make flow wavy and unstable due to the bend influence. fig. 2. flow pattern identification methods by (a) void fraction of time series, (b) pdf technique, (c) psd analysis, and (d) tomographic images at usl=0.052m/s and usg=0.05 m/s. fig. 3. flow pattern identification methods by using (a) void fraction of time series, (b) pdf technique, (c) psd analysis, and (d) tomographic images at usl=0.052m/s and usg=0.28m/s. at usg=2.36m/s, the flow regime is identified as churn flow at the bend inlet as displayed in figure 5 while the wavy annular flow at the bend outlet is characterized through the pdf chart by small peaks fluctuating around 0.15 with (α) tailing from 0.7 to 0.95 (figure 5(b)). the psd curve displays the wavy annular pattern showing 10% less power spectral than the plot of the stratified wavy regime (figure 5 (c)). the increment of usg with the differentiator of the density between the two phases, in addition to the effect of the bend forces the water phase to flow at the pipe base with waves. when increasing the usg value to 4.7m/s as illustrated in figure 6, semi-annular flow is observed at the bend outlet in comparison with the churn flow from the vertical flow line at the bend inlet. at the bend outlet, the mean void fraction conducts as a straight line with some waves at the high value of 0.9 (figure 6(a)) and the pdf plot has a single peak shifted to the right (figure 6(b)), referring to semi-annular flow. the interfaces occurring between air and water at the bend pushed the little amount of water to flow along with the pipe basement and air flew on it with high velocity. fig. 4. flow pattern identification methods by using (a) void fraction of time series, (b) pdf technique, (c) psd analysis, and (d) tomographic images at usl=0.052m/s and usg=1.4m/s. fig. 5. flow pattern identification methods by using (a) void fraction of time series, (b) pdf technique, (c) psd analysis, and (d) tomographic images at usl=0.052m/s and usg=2.36m/s. fig. 6. flow pattern identification methods by using (a) void fraction of time series, (b) pdf technique, (c) psd analysis, and (d) tomographic images at usl=0.052m/s and usg=4.7m/s. engineering, technology & applied science research vol. 9, no. 5, 2019, 4649-4653 4652 www.etasr.com musa et al.: experimental study of the two-phase flow patterns of air-water mixture at vertical bend … b. at steady liquid superficial velocity usl=0.262m/s for the horizontal flow line (the bend outlet) at usg=0.05m/s as in figure 7, the bubbly flow is estimated when the mean void fraction is fluctuated at 0.1 with a few peaks at 0.3 (figure 7(a)). the bubbly flow is also characterized through the pdf chart: the plot shows a single peak to the left with a small base from 0.1 to 0.2 (figure 7(b)), whereas the power spectrum shows a maximum value of 10 at 0.75hz (figure 7(c)). the amount of water was enough for the pipe diameter to fill the cross-section area in spite of bend impacts, thus, the bubbly flow at the vertical pipe was observed to have the same pattern of the horizontal flow line. when the usg reached 0.28m/s (figure 8), the flow pattern was similar to plug flow at the bend outlet for the horizontal flow line in contrast with the slug flow that was observed at the vertical flow line. the plug flow is characterized by the time series method when the mean void fraction fluctuates at very low values near to zero and high void fraction of 0.7 at the same time (figure 8(a)). the pdf curve shows two peaks at 0.13 and 0.05 at void fractions 0.1 and 0.6 respectively (figure 8(b)). furthermore, the power spectrum exhibits high value of about 350 near 0hz (figure 8(c)). fig. 7. flow pattern identification methods by using (a) void fraction of time series, (b) pdf technique, (c) psd analysis, and (d) tomographic images at usl=0.262m/s and usg=0.05m/s. fig. 8. flow pattern identification methods by using (a) void fraction of time series, (b) pdf technique, (c) psd analysis, and (d) tomographic images at usl =.262m/s and usg=0.28=m/s. slug flow is observed at usg values from 0.34 to 0.9m/s at the bend outlet for the horizontal flow line comparing with the slug flow that arrived from the bend inlet as showed in figure 9. for the horizontal flow line, as figure 9(a) shows, the slug pattern is identified when the void fraction fluctuates at high values (when the water height is less than the pipe radius) and has low values near zero (when the horizontal cross-sectional area is filled with water). the pdf curve shows two or more peaks around 0.08 at low and high void fraction values (figure 9(b)). moreover, the power spectrum of the slug flow exhibited a higher value of 450 at very low frequencies (figure 9(c)). the water slugs which arrived from the vertical pipe due to the higher void fraction and moderate usg values ranged from 0.34 to 0.9m/s are reverse inside the bend center flow line due to the gravity force that led the water to move at the bottom pipe base with considerable water slugs flow frequently at the top. stratified wavy flow is observed at usg increases from 1.4 to 2.36m/s as showed in figure 10, and the wavy annular regime is recognized at usg=4.7m/s as demonstrated in figure 11. when the usg increases more, to 2.83m/s, it breaks the slugs of water down due to the high velocity of the flow that produces wavy annular flow which is noticed at the bend outlet of the horizontal flow line. fig. 9. flow pattern identification methods by using (a) void fraction of time series, (b) pdf technique, (c) psd analysis, and (d) tomographic images at usl=0.262m/s and usg=0.34m/s. fig. 10. flow pattern identification methods by using (a) void fraction of time series, (b) pdf technique, (c) psd analysis, and (d) tomographic images at usl=0.262m/s and usg=1.4m/s. fig. 11. flow pattern identification methods by using (a) void fraction of time series, (b) pdf technique, (c) psd analysis, and (d) tomographic images at usl=0.262m/s and usg=2.83m/s. c. mean void fraction and liquid holdup (h) the liquid holdup (h) of the two-phase flow is characterized as a liquid volumetric rate fraction over the total mixture volumetric rates. the mean liquid holdup (h) values engineering, technology & applied science research vol. 9, no. 5, 2019, 4649-4653 4653 www.etasr.com musa et al.: experimental study of the two-phase flow patterns of air-water mixture at vertical bend … are obtained by calculating the average of all local crosssectional liquid holdup values over the time series. the mean h of the air-water flow diminishes linearly when the air superficial velocity, usg, gradually increases at steady water superficial velocity usl. this might clarify that bubbles expand steeply with increasing usg rates [15]. additionally, it is observed that the increasing or decreasing of the rate of the liquid phase is affected directly by the (h), and this influence is noticeable. figure 12 shows the plots of the mean (h) for constant usl values of 0.052, 0.157, 0.262, 0.314, and 0.419m/s regarding usg values altered from 0.05 to 4.7m/s at the vertical and undeveloped horizontal flow lines. it appears that the mean liquid holdup h diminishes steeply by the increasing of usg at all conditions in both flow lines (b) and (c). the mean liquid holdup at low usl diminishes dramatically at the bend outlet as compared with the bend inlet. the correlations between the mean liquid holdups at different usg values of this test are compared with [7-9]. fig. 12. liquid holdup (h) of the usg for vertical and horizontal flow line. iv. conclusion the increasing of water superficial velocity did not change the pattern in the vertical pipe, but it has a clear impact due to the effect of the 90-degree bend, gravitational force, and the buoyancy force on the flow patterns of the horizontal flow lines. these forces acted on the flow and forced the water to move inside the region of the bend centerline while the air flowed at the outside centerline of the bend. as a result, the large bubbles were broken up in the bend entrances during the imbalance which occurred by the surface tension and the centrifugal force. the flow patterns at the bend outlet may show a different behavior which depends on the bend curvature radius and diameter, fluid properties, temperature, etc. consequently, the bubbly flow regime in the vertical pipe changed to stratified-wavy flow at low usl values. in addition, the bubbly flow pattern in the vertical pipe altered to bubbly and plug flow regime at higher values of usl in the horizontal pipe. besides, the slug flow in the vertical pipe changed to the stratified-wavy pattern at low usl values, and to slug pattern as the value of usl increased. the churn pattern in the vertical pipe varied to the stratified-wavy, and semi-annular pattern at low usl in the horizontal flow lines and, to wavy-annular flow pattern at higher usl. finally, no stratified flow regime was observed at the horizontal flow lines under the tests, and no bubbly, plug, and slug flow was observed at the horizontal flow lines due to the low values of usl. references [1] c. t. crowe, multiphase flow handbook, crc press, 2005 [2] m. j. da silva, impedance sensors for fast multiphase flow measurement and imaging, phd thesis, technische universität dresden, 2008 [3] g. c. gardner, p. h. neller, “phase distributions in flow of an air-water mixture round bends and past obstructions at the wall of a 76‐mm bore tube”, proceedings of the institution of mechanical engineers, vol. 184, no. 33, pp. 93-101, 1969 [4] s. kim, j. h. park, g. kojasoy, j. m. kelly, “local interfacial structures in horizontal bubbly flow with 90-degree bend”, 14th international conference on nuclear engineering, july 17-20, 2006 [5] j. d. talley, s. kim, t. guo, g. kojasoy, “geometric effects of 45-deg elbow in horizontal air-water bubbly flow”, nuclear technology, vol. 167, no. 1, pp. 2–12, 2009 [6] y. liu, m. shuichiro, h. takashi, i. mamoru, m. hideyuki, k. yoshiyuki, k. koichi, “experimental study of internal two-phase flow induced fluctuating force on a 90° elbow”, chemical engineering science, vol. 76, no. 2012, pp. 173–187, 2012 [7] f. saidj, r. kibboua, a. azzi, n. ababou, b. j. azzopardi, “experimental investigation of air-water two-phase flow through vertical 90° bend”, experimental thermal and fluid science, vol. 57, pp. 226– 234, 2014 [8] l. a. abdulkareem, tomographic investigation of gas-oil flow in inclined risers, phd thesis, university of nottingham, 2011 [9] m. de salve, g. monni, b. panella, “horizontal air-water flow analysis with wire mesh sensor”, in: 6th european thermal sciences conference (eurotherm 2012), iop publishing, 2012 [10] a. e. dukler, m. g. hubbard, “a model for gas-liquid slug flow in horizontal and near horizontal tubes”, industrial & engineering chemistry fundamentals, vol. 14, no. 4, pp. 337–347, 1975 [11] w. liu, c. tan, f. dong, “local characteristic of horizontal air-water two-phase flow by wire-mesh sensor”, transactions of the institute of measurement and control, vol. 40, no. 3, pp. 746-761, 2016 [12] h. f. velasco pena, o. m. h. rodriguez, “applications of wire-mesh sensors in multiphase flows”, flow measurement and instrumentation, vol. 45, pp. 255–273, 2015 [13] h. m. prasser, a. bottger, j. zschau, “a new electrode-mesh tomography for gas-liquid flows”, flow measurement and instrumentation, vol. 9, no. 2, pp. 111–119, 1998 [14] i. d. johnson, method and apparatus for measuring water in crude oil, united states patent 4644263, 1987 [15] d. j. nicklin, j. o. wilkes, j. f. davidson, “two-phase flow in vertical tubes”, proceedings of the institution of mechanical engineers, vol. 40, no. 1, pp. 61–68, 1962 microsoft word 04-3382_s-d_etasr_v10_n2_pp5367-5370 engineering, technology & applied science research vol. 10, no. 2, 2020, 5367-5370 5367 www.etasr.com shaikh et al.: a short review on green supply chain management practices: the impact on … a short review on green supply chain management practices the impact on operational and environmental performance fazal ali shaikh department of economics university of sindh jamshoro, pakistan muhammad saeed shahbaz department of management sciences shaheed zulfikar ali bhutto institute of science and technology, pakistan nasurullah odhano department of economics university of sindh jamshoro, pakistan abstract—the aspects of sustainability and ecology have gradually become matters of significant concern within supply chain management processes. the aim of this study is to investigate the impact of the green supply chain on the environment and on operational performance. this study considers environmental management practices within firms, sustainable supply chain management practices relating to suppliers and customers, and environmentally conscious product and process design, by adopting a case-study approach and focusing on four major firms. the findings of this study reveal that the companies applying green supply chain management achieve better environmental performance but at an extra cost. meanwhile, green practices provide improved customer satisfaction and attraction for retailers, distributors, and authorities. keywords-green supply chain; environmental performance; operational performance; case study i. introduction the concepts pertaining to supply chain environmental management (scem) or green supply chain management (gscm) are usually understood by the industry as the monitoring of the environmental performance of suppliers. however, the exercise of conscious trade has been gaining escalating consideration. a growing number of companies are pondering over the amalgamation of ecological practices in their policy designs [1]. several motives are given to firms in order to become more environmental friendly. there are several motivational factors for introducing and applying the gscm concept [2], such as market probabilities, trade efficiency, regulatory fulfillment, and risk management [3]. gscm has a major role in confirming all the above elements [4]. environmental impact may occur at all levels of a products’ production chain and life time and gscm comes out as a significant novel practice for enterprises to accomplish lowering their environmental impact [5, 6]. ii. literature review an empirical inspection of american buying supervisors regarding green buying showed that the fundamental motivating element for green buying is meeting the regulations. the effectiveness of environmental regulations on buying practices is expected to become the second most significant concern in the future [4]. though the link between gscm and firms’ performance has been explored, the outcomes have not been decisive. there are two opposite theories regarding the connection between performance and environmental impact [7]. the first one proposes that environmental administration should just ensure the fulfillment of regulations and the second that environmental administration should be allowed to increase costs and investments in order to achieve better results. the impact of environmental parameters over the investment in terms of electricity use concluded that they are connected with the fall down in industrial manufacturing [8]. an optimistic connection between a firms’ performance and environment friendly practices has been documented in [9]. the suggested framework and empirical outcomes hint to a positive impact of ecological practices to market share and cost. recent research provided an understanding of the potential design of supply chain practices to improve ecoefficient performance. smaller and localized firms were found to be easier to follow more eco-friendly approaches [10]. connection with proprietors supports the acceptance and progress of creative environmental technologies [11], while dealing with clients and staff and cooperative r&d leads towards better environmental performance. it is vague however whether gscm leads to a positive or negative economical outcome. the actual long term economic impact is not easily assessed through considering a single factor such as short span profitability or sales performance [12]. firms that reduce their environmental impact face an increased production cost but are also expected to gradually gain an increased market share [5]. authors in [13] pointed out that environmental administration is in fact a creative environmental design for improving institutional performance. it has been indicated that an eco-efficient administration approach is capable to enhance a firm’s functional performance [14]. a strong connection has been found between the meetings of objectives and staff contribution to environmental administration [7]. returns on cost could be positively influenced when clients have a preference for the products/services of environment-friendly companies, while investment can be minimized via proactively handling environmental parameters that may cause hurdles. in addition, eco-friendly approaches may result to innovations that corresponding author: fazal ali shaikh (fazal_110_shaikh@hotmail.com) engineering, technology & applied science research vol. 10, no. 2, 2020, 5367-5370 5368 www.etasr.com shaikh et al.: a short review on green supply chain management practices: the impact on … may provide a head-start advantage to firms, at least through a marketing point of view [15]. a positive connection between business communal performance and profit has also been documented [16]. it should be mentioned however that empirical studies regarding gscm practices are scarce. the questions set in this study are: i) what are the effects of green supply chain over the environmental and functional performance of firms, and ii) what type of environmental administration practices are recommended to enhance the firm’s eco-efficient performance. the framework of the study is developed to explore the connection between different gscm practices [17]. there is a consensus in the literature that eco-friendly practices are a key factor in enhancing a firm’s progress [18]. previous studies highlighted several dimensions of gscm [19-21] (tables i-ii). table i. environmental management practices environmental management practices within a firm commitment to gscm from senior and middle-level managers total quality environmental management environmental compliance and auditing program iso 14000 certification gscm practices relating to suppliers and customers cooperation with suppliers for environmental objectives supplier’s iso 14000 certification company-wide environmental audits environmental management for suppliers internal management provide training to build supplier environmental management capacity cooperation with customers for eco-design and cleaner production cooperation with customers for green packaging environmentally conscious product and process design environmentally friendly raw materials design of products for reduced consumption of material and energy design of products for reuse, recycle, and recovery of materials product design aiming to avoid or reduce the use of hazardous products and/or their manufacturing process optimization of the process to reduce solid/liquid waste and emission use of reverse logistics table ii. environmental and operational performance constructs environmental performance reduction of solid/liquid waste and emissions reduction of consumption for hazardous/toxic materials reduction of frequency of environmental accidents reduction of electricity usage operational performance cost savings and increased efficiency product quality improvement increase in market share new market opportunities enhance employee motivation and performance increase in sales it has been found that encouragement from moderate scale directors, apart from manager’s guidance, is also a key factor for fruitful gscm application [22]. it has also been observed that gscm may offer several advantages from cost reduction to increased public involvement (i.e. creating a trend) in the firm’s policy and, thus an increased market share [2, 23]. thus, environmental concerns are becoming a visible ingredient of tactical patterns within firms [24]. green advertising and environmentally friendly packaging are practices that may improve the environmental impact of the delivery chain [2, 3]. to highlight the environmental influence of packaging, several countries have plans that aim to reduce the cost of wrapping [25]. it has been reported that standardized recyclable containers and fine merchandising designs minimize scarcity and recovery time making the product cost-friendly while also being eco-friendly [26]. eco-efficient alert manufacturing and procedure patterns could integrate several such ideas, from reducing the consumption of materials and energy during the first stages of the production chain and implementing cleaner practices to minimize solid and liquid wastes to the utilization of eco-friendly logistics. thus, the return on investment (roi) has been considered a crucial dimension of gscm [27]. iii. case studies the public data regarding the gscm practices of four major firms are considered as case studies. the firms were selected considering their market share, overall status, data availability and their overall environmental policy. major firms were selected so that the principles and practices described may be considered as a future trend roadmap for smaller firms and policy makers. a. eastman chemical company eastman is devoted to durable supply chain administration practices and functional presentation improvement practices such as measuring brokers contributions, evolving substitutes strategies of supply, establish broker’s solutions, enhancing packaging, utilizing recyclable packaging and encouraging supply chain networking, besides developing clients’ solutions and managing material recovery [28, 29]. eastman follows several environmental quantifiers and evolved the eco-efficient function practices by adding a greenhouse decrease objective, called tri (toxic release inventory). the design of eastman’s energy management policy has combined the demand for reasonable energy consumption with the demand to reduce production cost, e.g. by ensuring that the produced heat is used in more than one chemical processes. the firm also claims to apply efficient water administration practices and use recyclable materials in order to reduce waste [25]. b. westpac bank, australia the basic advantage of this firm is that it is working along with brokers and clients to enhance its manufacturing and products, e.g. in redesigning the packaging and in utilizing recyclable materials in several products. that process has brought enhancements in production and reduced logistic costs [30]. the company has declared a committance to comply with, or even exceed, the environmental legislation requirements in the areas it operates. the firm claims that has ensured reduced energy consumption and emissions in transportation, while it is a certified carbon neutral business [31]. c. coca cola enterprises the firm endorses the five strategic firm responsibility and sustainability crs stress dimensions [28]. coca cola invested us $34.8 million in 2008 on capital schemes concerning their three eco-efficient spotlight fields. in addition, they are evolving a cost-friendly evaluation process to focus on engineering, technology & applied science research vol. 10, no. 2, 2020, 5367-5370 5369 www.etasr.com shaikh et al.: a short review on green supply chain management practices: the impact on … common reporting standard (crs) investments. the firm has highlighted certain goals in the field of energy consumption, water management, durable wrapping manufacture assortment, wellbeing, and diverse and comprehensive culture. it has decreased its entire carbon mark to 15% in 2020 in comparison to the 2007 baseline. the firm also follows a water sustainable function in which the usage of water is reduced and water neutral effectiveness is achieved. to decrease the influence of package related waste, the utilization of recyclable resources has been set as a major goal [32, 33]. the company evaluated and claims it have reduced its carbon marks by utilizing a hybrid fleet, establishing a water durable function thus decreasing the ratio of water utilization and preserving more than 300 million liters of water, while it carried out a pilot study of entrenched stream footprint [19]. for reducing the influence of packaging materials the company stayed away from the use of around 31,000 metric tons of packaging materials, while 2.7% of the total quantity was recovered. d. ernst and young the firm has adopted the sustainability assurance methodology and is a member of the china financial institution’s green finance committee. the provided services are eco-friendly and comply with the international standards and regulations. the company is specialized in providing tailored sustainability services to its clients such as consultations and funding regarding carbon emission reduction, supply chain management, risk management, etc. [34]. iv. discussion it is sufficient to say that in the days to come, carbon emissions will be considered tantamount to currency. hence it is significant for international firms to take measures to control their supply chain and to estimate future costs and liabilities. struggling against the inflation of energy and to decrease inhouse emissions approximately 40% of the firms have invested in reusable energy generation, which provides a firm grip over the cost of energy and also improves firm credibility and may even become profitable when selling the surplus of the produced electricity [30]. a growing number of traders are contending the launch of durable production to enhance their market share. a large proportion of participants account the sustainability as a chance for revenue growth. credibility plus the name of the brand are the areas where prospects for sustainability and carbon concerned politics arise. several prominent firms have to determine the full prospective and potential of advantages and profits in the account of sustainable chain administration [20]. a firm’s reputation is harmed if its supply chain is found to be communally irresponsible [35]. environmental friendly and sustainable practices on the other hand improve the reputation of a firm and, ultimately, its market share even with increased cost products [36]. major firms devote significant resources towards improving their environmental impact, developing and establishing alternative techniques and approaches, reducing energy consumption, improving packaging, enhancing the use of reusable materials etc. besides the prominent eco-friendly practices, other minor practices such as greenhouse excretion reduction and protection of logistics effectiveness have also been documented. other frequently accomplished advantages are augmented effectiveness, reduced cost, enhanced risk administration, revenue growth, and credible reputation. it is significant for a company to have an ethical supply chain. the functional aspect that needs to amalgamate to the existing framework is enhanced risk administration and credibility [21]. the firms that include sscm practices found a prominent impact on their environmental and functional performance. the limitation of this research was the convenience of sampling, so more and detailed case studies can be carried out. v. conclusion 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chakraborty & tharini: pneumonia and eye disease detection using convolutional neural networks pneumonia and eye disease detection using convolutional neural networks parnasree chakraborty electronics & communication engineering bsa crescent institute of science & technology chennai, india c. tharini electronics & communication engineering bsa crescent institute of science & technology chennai, india abstract—automatic disease detection systems based on convolutional neural networks (cnns) are proposed in this paper for helping the medical professionals in the detection of diseases from scan and x-ray images. cnn based classification helps decision making in a prompt manner with high precision. cnns are a subset of deep learning which is a branch of artificial intelligence. the main advantage of cnns compared to other deep learning algorithms is that they require minimal preprocessing. in the proposed disease detection system, two medical image datasets consisting of optical coherence tomography (oct) and chest x-ray images of 1-5 year-old children are considered and used as inputs. the medical images are processed and classified using cnn and various performance measuring parameters such as accuracy, loss, and training time are measured. the system is then implemented in hardware, where the testing is done using the trained models. the result shows that the validation accuracy obtained in the case of the eye dataset is around 90% whereas in the case of lung dataset it is around 63%. the proposed system aims to help medical professionals to provide a diagnosis with better accuracy thus helping in reducing infant mortality due to pneumonia and allowing finding the severity of eye disease at an earlier stage. keywords-convolutional neural network; artificial intelligence; x-rays; pneumonia i. introduction a medical image based disease detection system using cnn is proposed in this paper. the suggested system has the ability of detecting pneumonia and eye disease from x-rays and scan images respectively. the novel feature of the proposed system is that it has been implemented using low cost hardware. in [1], a diagnostic system is proposed for detecting retinal diseases. the result shows that the performance of the proposed method is comparable to that of human experts. however, the implementation of the system using hardware is not suggested. a computationally efficient algorithm is introduced in [2]. adam stochastic optimization method is used to train the neural network. empirical results demonstrate that adam works well in practice and compares favourably to other stochastic optimization methods. in [3], the effect of the convolutional network depth on its accuracy is investigated and changes in architectural configuration which improve the accuracy of the algorithm are proposed. a deep-learning-based approach to detect diseases and pests in tomato plants using images is presented in [4]. the images are captured in-place by camera devices with various resolutions and are processed. the experimental results show that the proposed system can effectively recognize nine different types of diseases and pests in tomato plants. in [5], the face detection and face recognition pipeline framework (fdrenet) is proposed which involves face detection through histograms of oriented gradients and uses siamese technique and contrastive loss to train a deep learning architecture. however, disease detection is not investigated in this paper. on the other hand, a review of the applications of ai in soil management, crop management, weed management and disease management can be seen in [6], but disease management and disease detection in humans using ai are not investigated. ii. datasets used in order to test the proposed idea, two datasets were considered. the lung dataset consisted from images from [7] and the eye dataset from images from [8]. data are essential to train any neural network. the neural network, apart from other parameters, is only as good as the data it is trained on. for training the cnn, medical image data are used. two different kinds of publicly available medical image datasets are considered for training two convolutional neural networks. oct images in the iris region of the eye are considered for eye disease detection. oct is a non-invasive method of capturing biological tissues using low-coherence light. it can capture two dimensional and three dimensional images of micro meter level. the images of the oct scan are classified under 4 categories: i) choroidal neovascularization, ii) diabetic macular edema, iii) multiple drusen, and iv) normal. choroidal neovascularization is the creation of new blood vessels in the choroid region of the eye. this problem is a major cause of vision loss. macular edema is build-up of fluid in an area in the center of the retina. this build up causes the macular to thicken, distorting vision. drusen consists of multiple deposits under retina. drusen is a fatty protein made up of lipids. having drusen may increase the possibility of age-related macular degeneration. the dataset contains normal/healthy iris scan images too. the images are collected from [8] dataset which contains more than 5gb of 84438 images from [9, 10] which are classified on the above mentioned categories. chest x-ray images of children belonging to 3 classifications: i) viral pneumonia, ii) bacterial pneumonia, and iii) normal were taken from [7] and are considered in this study. pneumonia is an corresponding author: p. chakraborty (prernasree@crescent.education) engineering, technology & applied science research vol. 10, no. 3, 2020, 5769-5774 5770 www.etasr.com chakraborty & tharini: pneumonia and eye disease detection using convolutional neural networks infection that accumulates in the lung’s air sacs causing hindrance for breathing. the lung image dataset contains 1gb of 5238 images belonging to the 3 above mentioned categories. both datasets were split into three sets: train, test and validation. figure 1 describes the training of a neural network. the given data is split into training, validation and testing data with each utilizing 70%, 20% and 10% of the data respectively. after each iteration of training, the neural network is tested with the validation data to see its performance at that instant. after completing the whole training process, the performance is evaluated using the testing data. this proposed method is heavily inspired from [11] and a similar neural network with the lung data which was presented in [12]. the image datasets [7-10] are first collected and annotated or labeled in order to distinguish the normal images from images with diseases. to generate the training dataset the existing labeled data are further used to generate a new dataset using a technique called augmentation. annotated and augmented data are used for training the proposed neural network. fig. 1. block diagram of the proposed system iii. convolutional neural networks cnns [3] are a type of deep artificial neural networks, used mainly to identify and cluster images, and perform object recognition. a cnn consists of image processing layers and neural network layers namely: (a) convolutional layer, (b) pooling layer, (c) flattening layer, (d) relu layer, and (e) softmax layer. these layers are described briefly below. a. convolutional layer the convolutional layer is the main building block of a cnn. the layer's parameters consist of a set of user-defined learnable filters (or kernels), which is generally a 3×3 matrix, and iterates through each submatrix of the input. the number of input filters used is generally of the order of 2n. during a forward pass, each filter is convolved across the dimensions of the input image matrix, the mathematical function carried out being dot product and thus producing a 2-dimensional featureextracted matrix of that filter. this reveals various details like vertical or horizontal edges of the images which are extracted and fed into the next layer. the weights that are used are generated randomly using the glorot uniform distribution function. figure 2 shows the filters. figure 3(c) demonstrates the output image when an input image, shown in figure 3(a) is convolved with the one of the above displayed filters. fig. 2. the 32 filters used in the proposed cnn b. pooling layer another important concept used in cnns is pooling, which is a form of non-linear down-sampling. out of the several pooling functions analyzed in [13], max-pooling is the most effective. max-pooling partitions the input image into a set of (n×n) (generally 2×2) sub matrices and the output is the maximum value. the convolved image is first converted into arrays and then maxpooling is performed. figure 3 displays the convolution and maxpooling steps. in maxpooling the dimensions of the image are reduced from a 50×50 matrix to a 24×24 matrix. (a) (b) (c) (d) fig. 3. (a) input image, (b) filter function, (c) resultant convoluted image, and (d) the pooling layer’s output shrinking the 50×50 image to a 24×24 image engineering, technology & applied science research vol. 10, no. 3, 2020, 5769-5774 5771 www.etasr.com chakraborty & tharini: pneumonia and eye disease detection using convolutional neural networks c. flattening layer the output from the pooling layer will be in a matrix form which can’t be fed into the neural network. the flattening layer converts the n×n matrix from the pooling layer into a n2×1 matrix which is a compatible format to be fed into the neural network. d. relu layer relu is the abbreviation of rectified linear unit, which applies a non-saturating activation function. these functions remove negative values of weights by replacing them with zero. it increases the nonlinear properties of the decision function. this activation function is used in input and hidden layers of the neural network. the type of relu used is leaky relu. relu as explained in [14] is used in the neural network layers. figure 4 shows the leaky relu activation function. mathematically, the leaky relu can be defined as: y = 0.01 x when x < 0 (1) y = x when x > 0 (2) fig. 4. graphical representation of the relu e. softmax layer this layer is predominantly used when the neural network solves multiclass-classification problems. it usually consists of a number of output nodes with softmax as activation function. softmax function assigns probability to each node in the output layer. these probability values are normalized to one. the node with highest value is the prediction of the neural network. the relu layer and the softmax layer both use backpropagation [15] and forward propagation to train the cnn. figure 5 shows the softmax function. mathematically, softmax function can be defined as: σ(z)i = ��� ∑ ������ (3) where i= 1, 2,….k and z= z1, z2,…..zk. equation (3) shows the standard exponential function to each element zi of the input vector z and normalizes these values by dividing by their sum. this normalization ensures that the sum of the components of the output vector σ(z) is 1. 1) loss function loss function or cost function generally is the difference between the actual output and the predicted output. the main aim of the loss function is to reduce error. i.e. to minimize the difference between the predicted value and the actual value. the loss function predominantly used in both datasets is mean squared error. in this method, the difference between the predicted and the actual output is squared. it is better than the gradient descent methods for decreasing loss [16]. the sum of all these squares is divided by their total number. mathematically this can be represented as � ∑ �yi � ȳi���� (4) where n is the number of inputs, yi is the actual output and ŷi is the predicted output. fig. 5. graphical representation of the softmax function 2) optimizer the optimizer is a function which is guided by the loss function to update the weights so that the loss is minimized. it does so by changing the learning rate after every iteration in accordance with the calculated loss function. the weights of each node change based on the learning rate. if the learning rate is too fast, the neural network may not learn enough to generalize. if the learning rate is too low, the neural network may learn very slowly. the neural network needs to learn in an optimum speed and optimum manner and that is helped by the optimizer function. the optimizers used were the adam optimizer and the root mean square propagation optimizer. 3) adam optimizer it is one of the best optimizers available. it is computationally efficient, it augments optimized learning and has very little memory requirements. adam [2] stands for adaptive moment estimation. instead of changing the weights based on the first moment (mean) alone or based on the second moment (variance) alone, this uses both first moment and second moment to update the learning parameters: θt+1 = θt � √ṽ� � � m̂� (5) where mt and vt are first moments and second moments respectively, and η is the learning rate. iv. results and discussion neural networks with different architectures have been considered. the architecture of a neural network mainly engineering, technology & applied science research vol. 10, no. 3, 2020, 5769-5774 5772 www.etasr.com chakraborty & tharini: pneumonia and eye disease detection using convolutional neural networks depends on parameters such as the optimizer type, the number of nodes in each layers etc. the results are discussed below. a. lung dataset table i shows the results for the lung dataset [7]. the architecture comprises of an input layer, multiple hidden layers and an output layer. the training accuracy, training losses, validation accuracy and validation losses with respect to the number of iterations used for simulation are listed. the simulation is performed using python integrated development environment (ide) spyder. the maximum validation accuracy obtained in the case of the lung dataset is only around 63% with 10 epochs/iterations and 5215 steps per epoch. this result can be further improved with larger size dataset. in table ii, the complete architecture consisting of two pairs of convolution layers (named as conv2d_13 and conv2d_14), maxpooling layers (named as max_pooling2d_13 and max_pooling2d_14), and a flattening layer are shown. the optimum artificial neural network consists of an input layer consisting of 7 nodes and an output layer consisting of 3 nodes for each classification. table i. observations of the lung dataset iterations optimizer training validation accuracy loss accuracy loss 10 rmsprop 0.4848 0.2122 0.4706 0.2131 15 adam 0.7549 0.1215 0.4706 0.2901 10 adamax 0.4849 0.2108 0.4118 0.2217 15 rmsprop 0.4779 0.3009 0.4290 0.2308 12 rmsprop 0.4851 0.2108 0.5294 0.2040 15 adamax 0.7682 0.2286 0.5294 0.2286 10 adam 0.7698 0.2201 0.6309 0.2252 15 adam 0.5396 0.3547 0.3509 0.3688 table ii. summary of the nn for lung dataset which yielded the best parameters durin g training and testing layer (type) output shape param # conv2d_13 (conv2d) (none, 30, 30, 32) 896 max_pooling2d_13 maxpooling (none, 15, 15, 32) 0 conv2d_14 (conv2d) (none, 13, 13, 64) 18496 max_pooling2d_14 (maxpooling (none, 6, 6, 64) 0 flatten_7 (flatten) (none, 2304) 0 dense_13 (dense) (none, 7) 16135 dense_14 (dense) (none, 3) 24 total params: 35,551, trainable params: 35,551, non-trainable params: 0 param# in tables ii and iv indicates the number of input weights that is processed through that one given layer. total params is the sum of all the input weights in the total architecture of the neural network. the output shape denotes the number of inputs at a time (given by none) followed by the expected shape of the input. b. eye dataset table iii shows the observations for eye dataset [8-10]. the maximum validation accuracy obtained in the case of the eye dataset is around 90% which can be further improved with a larger size dataset. table iv shows the summary of the neural network model which yielded the best parameters during training and validation for eye disease detection. the maximum number of epochs used for the eye dataset ranged from 5 to 64, and the maximum validation accuracy was obtained for 15 epochs. table iii. observations of the eye dataset iterations optimizer training validation accuracy loss accuracy loss 15 adam 0.7060 0.1016 0.9062 0.039 5 adam 0.6823 0.1079 0.7812 0.078 20 adam 0.6886 0.1062 0.8438 0.072 32 adam 0.7031 0.1031 0.0982 0.718 34 rmsprop 0.4702 0.1608 0.5625 0.143 13 adam 0.6625 0.1120 0.7812 0.085 64 adam 0.7379 0.0942 0.7241 0.098 10 adam 0.7969 0.5274 0.7325 0.688 table iv. summary of the nn for eye dataset which yielded the best parameters durin g training and testing layer (type) output shape param # conv2d (conv2d) (none, 48, 48, 32) 320 max_pooling2d (maxpooling2d) (none, 24, 24, 32) 0 conv2d_1 (conv2d) (none, 22, 22, 32) 9248 max_pooling2d_1 (maxpooling2 (none, 11, 11, 32) 0 flatten (flatten) (none, 3872) 0 dense (dense) (none, 4) 15492 total params: 25,060, trainable params: 25,060, non-trainable params: 0 it can be seen from table iii that for the eye dataset the optimizer predominantly used was the adam optimizer. in the 5th trial of table iii, the rms prop optimizer was used. the loss was the mean squared error loss function with the exception of the 8th trial where categorical cross entropy loss function was used. the complete architecture consists of two pairs of convolution layers (named as conv2d and conv2d_1) and maxpooling layers (named as max_pooling2d and max_pooling2d_1) and a flattening layer named as flatten. the ann has an output layer consisting of four nodes, one for each kind of classification. the output shape consists of a 4 dimensional array for the 2 pairs of convolutional and maxpooling layer. the 1st dimension (denoted by none in all the given pairs) is the number of inputs that will be fed into that given layer at that particular given time. it is mentioned as none because these observations were taken after training, when there was not any input to be fed into at that instant of time. the rest of the 3 dimensions mention the dimensions of a single input unit. the same holds true for remaining flattening and neural network layers. v. deployment the neural networks which yielded the best parameters were saved in h5 format and were deployed in a raspberry pi which uses raspbian with features to program in python 3.5.3. a simple graphic user interface (gui) was made where the user was asked to enter the directory of the image and the neural network would make the prediction and display the result. snapsots of the results and of the gui output for both datasets can be seen in figures 6-11. the complete setup used to implement the proposed system using hardware is shown in figure 12. the hardware part includes the raspberry pi board for interface with the gui using tkinter library in python ide. further, there are two ways to connect the lcd to the raspberry pi board: 4 bit mode and 8 bit mode. in this work, 4 bit mode was used in which the byte to be sent is split into two sets that (upper bits and lower bits) of 4 bits each which are sent one by one over 4 data wires. engineering, technology & applied science research vol. 10, no. 3, 2020, 5769-5774 5773 www.etasr.com chakraborty & tharini: pneumonia and eye disease detection using convolutional neural networks fig. 6. gui output of the neural network predicting the given iris image has diabetic macular edema fig. 7. gui output of the neural network predicting the given iris image has choroidal neovascularisation fig. 8. gui output predicting the given iris image has multiple drusen fig. 9. gui output predicting the given iris image doesn’t have any disease fig. 10. gui output predicting the given x-ray image has viral pneumonia fig. 11. gui output of the neural network predicting the given x-ray image has bacterial pneumonia figures 13 and 14 show the eye disease detection system and the pneumonia detection system implemented in hardware. fig. 12. experimental setup fig. 13. result obtained for a normal human iris scan fig. 14. result obtained for human chest x-ray of bacterial pneumonia vi. conclusions and future work a medical image based disease detection system using convolutional neural networks is proposed and developed. the eye disease detection system effectively classifies the normal eye images and eye images with diseases like choroidal neovascularization, diabetic macular edema, and multiple drusen. lung image dataset [7] consisted of bacterial pneumonia, viral pneumonia, and normal lung x-ray images of children in the age group of 1-5 years. the training model was simulated using python libraries like tensorflow, keras, skimage, etc. to improve training speed. the enhanced speed engineering, technology & applied science research vol. 10, no. 3, 2020, 5769-5774 5774 www.etasr.com chakraborty & tharini: pneumonia and eye disease detection using convolutional neural networks of the training model yielded the real time implementation of the systems more suitable. the proposed system has the potential to be used in generalized high-end applications in biomedical imaging and provides a cost effective solution at a single board computer (raspberry pi). regarding future work, focus will be given in improving the current results. another promising application will be to extend the idea for identification of various diseases not only in humans but also in plants and crops. references [1] d. s. kermany, m. goldbaum, w. kai et al., “identifying medical diagnoses and treatable diseases by image-based deep learning”, cell, vol. 172, no. 5, pp. 1122-1131, 2018 [2] d. p. kingma, j. ba, “adam: a method for stochastic optimization”, international conference on learning representations, san diego, usa, may 7-9, 2015 [3] k. simonyan, a. zisserman, “very deep convolutional networks for large-scale image recognition”, international conference on learning representations, san diego, usa, may 7-9, 2015 [4] a. fuentes, s. yoon, s. cheol kim, d. sun park, “a robust deeplearning-based detector for real-time tomato plant diseases and pests recognition”, sensors, vol. 17, no. 19, article id 2022, 2017 [5] d. virmani, p. girdhar, p. jain, p. bamdev, “fdrenet: face detection and recognition pipeline”, engineering, technology & applied science research ,vol. 9, no. 2, pp. 3933-3938, 2019 [6] n. c. eli-chukwu, “applications of artificial intelligence in agriculture: a review”, engineering, technology & applied science research, vol. 9, no. 4, pp. 4377-4383, 2019 [7] d. kermany, k. zhang, m. goldbaum, “labeled optical coherence tomography (oct) and chest x-ray images for classification”, mendeley data, vol. 2, 2018 [8] k. s. mader, “eye oct datasets: retina oct datasets with accompanying fundus images from published studies”, available at: https://www.kaggle.com/kmader/eye-oct-datasets [9] t. mahmudi, r. kafieh, h. rabbani, “comparison of macular octs in right and left eyes of normal people”, in: proceedings spie 9038, medical imaging 2014: biomedical applications in molecular, structural, and functional imaging, 90381k, san diego, california, usa feb. 15-20, 2014 [10] m. k. jahromi, r. kafieh, h. rabbani, a. m. dehnavi, a. peyman, f. hajizadeh, mohammadreza ommani, “an automatic algorithm for segmentation of the boundaries of corneal layers in optical coherence tomography images using gaussian mixture model”, journal of medical signals and sensors, vol. 4, no. 3, pp. 171-180, 2014 [11] p. rajpurkar, j. irvin, r. l. ball, et. al, “deep learning for chest radiograph diagnosis: a retrospective comparison of the chexnext algorithm to practicing radiologists”, plos medicine, vol. 15, no. 11, article id e1002686, 2018 [12] x. gu, l. pan, h. y. liang, r. yan, “classification of bacterial and viral childhood pneumonia using deep learning in chest radiography”, 3rd international conference on multimedia and image processing, guiyang, china, march 16-18, 2018 [13] d. scherer, a. muller, s. behnke, “evaluation of pooling operations in convolutional architectures for object recognition”, 20th international conference on artificial neural networks, thessaloniki, greece, september 15-18, 2010 [14] k. he, x. zhang, s. ren, j. sun, “delving deep into rectifiers: surpassing human-level performance on image net classification”, in: proceedings of the ieee international conference on computer vision, pp. 1026-1034, ieee, 2015 [15] y. lecun, l. buttou, g. b. orr, k. r. muller, ”efficient backprop”, in: neural networks: tricks of the trade, 2nd edition, springer-verlag, 1998 [16] y. lecun, l. bottou, y. bengio, p. haner, “gradient-based learning applied to document recognition”, proceedings of the ieee, vol. 86, no. 11, pp. 2278-2324, 1998 authors profile parnasree chakraborty is an assistant professor (sr.grade) in the department of electronics and communication engineering at b. s. abdur rahman crescent institute of science & technology. her research interests include digital signal processing, ai & robotics, wireless sensor networks, and digital communication. she is a life member of the iste. she has published many papers in journals and conferences in the area of signal processing and wireless sensor networks. c. tharini is a professor and the head of the department of electronics and communication engineering at b. s. abdur rahman crescent institute of science & technology. she received her phd in information and communication engineering from anna university in 2011. her research interests include wireless communication, wireless sensor networks and signal processing algorithms for wireless sensor networks. she is an active member of the computer society of india. she has a teaching experience of more than 15 years. her students are presently working in wireless sensor networks, signal processing and in the wireless communication domain. she has published many papers in international journals and in conferences in the area of signal processing and wireless sensor networks. microsoft word 32-3334_s_etasr_v10_n2_pp5520-5523 engineering, technology & applied science research vol. 10, no. 2, 2020, 5520-5523 5520 www.etasr.com soomro et al.: contractor’s selection criteria in construction works in pakistan contractor’s selection criteria in construction works in pakistan noor ul islam soomro department of civil engineering mehran university of engineering and technology jamshoro sindh, pakistan noorsoomro93@gmail.com nafees ahmed memon department of civil engineering mehran university of engineering and technology jamshoro sindh, pakistan nafees.memon@faculty.muet.edu.pk aftab hameed memon department of civil engineering quaid-e-awam university of engineering, science and technology, nawabshah, sindh, pakistan aftabm78@hotmail.com kashif rafique memon department of civil engineering mehran university of engineering and technology jamshoro sindh, pakistan kashif.memon33@gmail.com abstract—the contractor is the primary stakeholder in materializing a project concept. for the successful completion of any project, it is compulsory for the contractor to have relevant experience. the selection of the appropriate contractor depends on various criteria. this study aims to study these selection criteria. based on 71 questionnaire forms received from representatives of contractor, consultant and client firms involved in execution works of construction activities it is found that quality, bid amount, technical capability, financial stability, and experience are five commonly adopted criteria for contractor selection in construction works in pakistan. on the other hand, quality, technical capability, financial stability, equipment availability, and management capability are reported as the top five effective criteria for appropriate contractor selection for any construction project. keywords-contractor selction; selection criteria; pakistan; sindh; construction works i. introduction the success of a project depends on the performance of the contractor, hence its selection is essential. the selection of the right contractor reduces cost while assuring high quality work [1]. a research carried out in hong kong identified five critical factors for project success: initiation and transmission of conflict resolution, energy, resource sharing among project participants and responsibilities have been defined clearly [2]. in traditional contracting, the contractors are mostly selected based on lowest bid criterion which often results in declination of quality, cost, and completion time of the project. thus, it is essential to select a suitable contractor for the project for achieving effective performance and successful completion. this paper focuses on studying the contractor selection criteria adopted in construction works in pakistan. this paper identified the level of adoption for selection criteria of contractors and the level of effectiveness of each criterion. the level of adoption references to the occurrence, i.e. how common each criterion is used in construction industry, while the level of effectiveness defines the importance of the criteria. ii. contractor selection criteria for the success of any construction work, contractor selection is very imperative phase. a selection criterion is involved in judging and measuring the potential of contractors. the skills of contractors are judged and calculated. some common criteria considered in contractor selection are: • technical capacity: contractors must have the capability of completing project activities successfully [3]. • experience: experience plays an important role in performing any task with ease and perfection. hence, it is essential to select the contractor based on its relevant work experience in past [3]. • management capacity: planning, organizing and handling of project express the management capability of the contractor [3]. • financial stability: overall financial position and capability must be examined based on the cash flow of the contractor [3]. • past performance: past performance should be considered for time, quality, and cost control requirements [4]. • past relationship: clients need to gather all the information regarding the contractor and evaluate its past affiliation which contributes in construction activities [4]. • reputation: project manager must have an opinion about the contractor’s past performance and reputation regarding the success in projects’ completion [4]. • occupational health and safety: contractors must apply occupational health and safety principles [3]. corresponding author: noor ul islam soomro engineering, technology & applied science research vol. 10, no. 2, 2020, 5520-5523 5521 www.etasr.com soomro et al.: contractor’s selection criteria in construction works in pakistan • quality: the contractor must be capable to maintain the desirable quality standards [3]. • organizational skills: focus on the effective utilization of the required resources with teamwork creating environment for team work while directly reduce the level of individual stress. • current workload: it refers to the present workload of the running project [3]. • equipment: it should be ensured that the contractor has the sufficient equipment required for the project [6]. • human resources: human resource management deals with employee selection, recruiting, providing orientation, training, and development, appraising employee performance, motivating employees, deciding compensation, and ensuring safety, welfare, health and incompliance with labor laws [6]. • project-specific requirements: they are some specific requirements necessary to ensure the specific project’s success. they are meant to align the project resources with the objectives of the owner. the benefits of collecting project requirements include cost reduction, higher project success rate, enhanced stakeholder communication and effective management of change [5]. • business location: the location of a business is the place where it is situated and it refers to the nearby locations where all the requirements can be achieved successfully. the owner should look at the advantages which each area has to offer [5]. • bid amount: it is colloquially known as a “bid” in markets, and is often lower than the asking price [4]. if the contractor is technically sound and has adequate experience, equipment availability, and personnel to satisfy the client, it can achieve the successful completion of the project. further, the financial soundness of the contractor may help to achieve the best quality and project success within the desired time. if the contractor management capability is high, then it is easy for the contractor to deal with technical personnel with experience, quality, and management and project management capabilities. if the contractor’s reputation is high then past performance and past relationships are considered by the clients making the contractor favorable for more awarding contracts. the selection of a suitable contractor is the key to project success by awarding the contracts to the lowest price with multi-criteria selection practices. both technical and financial criteria are considered in a multi criteria process. most changes occur by local official authorities and are useful for maintaining construction quality. a study of gaza strip showed that central bidding committee provides a fair bid evaluation process, with equal opportunities to all bidders, and suitable responsibility [4]. authors in [3] revealed that financial soundness, technical ability, management capability and health and safety are major criteria for selecting a contractor. various researchers have highlighted different criteria for selecting the appropriate contractor as shown in table i. table i. contractor selection criteria [3] [4] [5] [6] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] experience � � � � � � � � � � � � � � � technical capability � � � � � � � � � � � � financial stability � � � � � � � � � � � � � � � � � management capability � � � � � � � � � � � � � � past relationship � � � past performance � � � � � � � � � � � � occupational health and safety � � � � � � � � � � � � � � reputation � � � � � � � organizational skills � � � � quality � � � � � � � � � � environmental aspects � � current workload � � � equipment � human resources/ managerial resources � � � � project-specific requirements � � business location � bid amount � � � iii. data collection and analysis results the data for this study were gathered through a survey amongst construction practitioners. out of 120 sent survey forms, 71 were received from various professionals in relevant fields. prior to the analysis of the gathered data, the reliability of the data was assessed by cronbach's alpha computed with statistical software package spss. cronbach's alpha for the level of adoption of the criteria is 0.949 while the alpha for the level of effectiveness is 0.859. the value of alpha for adoption level and level of effectiveness are higher than 0.7 (the alpha value is considered satisfactory if it is greater than 0.7 [7]), hence, the data are considered reliable and can be considered for further analysis and drawing conclusions. the forms were analyzed statistically and the results are discussed below. a. respondents profile the respondents participating in the survey had strong technical profile and were employed in the construction sector. the characteristics of the participants are summarized in table engineering, technology & applied science research vol. 10, no. 2, 2020, 5520-5523 5522 www.etasr.com soomro et al.: contractor’s selection criteria in construction works in pakistan ii, from which it can be observed that the majority of the participants (33 out of 71) are representatives of client firms while at the second level, 24 participants are engaged in contractor companies, and 14 participants are working with consultants. among these respondents, 36 have completed civil engineering education, 26 have finished a master, 6 have a diploma, while 3 are phd holders. these respondents are working for several years in construction works with experience spanning from less than 5 years (49) to more than 20 years (5). among these participants, 13 are involved in project executions with contract sum above rs. 3000m, 14 are working in projects costing rs. 400m to 3000m and the other practitioners are working in projects costing below rs. 400m. eight participants are directors of their companies, 11 are working at a managerial level, 28 are resident and planning engineers, while 24 respondents are site supervisors and site engineers. table ii. profile of respondents frequency percent cumulative percent organization type consultant 14 19.7 19.7 contractor 24 33.8 53.5 client 33 46.5 100.0 education level diploma 6 8.5 8.5 degree 36 50.7 59.2 master 26 36.6 95.8 phd 3 4.2 100.0 experience level 0-5 years 49 69.0 69.0 06-10 years 9 12.7 81.7 11-15 years 5 7.0 88.7 16-20 years 3 4.2 93.0 21-25 years 2 2.8 95.8 more than 25 years 3 4.2 100.0 project size (rs.) less than rs. 20m 18 25.4 25.4 20m 50m 16 22.5 47.9 50m 150m 4 5.6 53.5 150m 400m 6 8.5 62.0 400m – 800m 8 11.3 73.2 800m – 1800m 5 7.0 80.3 1800m –3000 m 1 1.4 81.7 above 3000m 13 18.3 100.0 b. level of adoption of contractor’s selection criteria the participants responding in the survey process were required to rate the adoption level of various criteria of contractor’s selection considered by their respective companies. the respondents were asked to indicate the level of adoption using a 5 point scale where 1=never, 2=sometimes, 3=moderately, 4=usually and 5=always. mean value, standard deviation, and ranking obtained from statistical analysis of the data collection for these criteria are presented in table iii. it can be seen that quality with mean value of 3.90 and standard deviation 1.232 is reported as the most commonly adopted criterion and is ranked first by the participants. bid amount with mean value of 3.87 and standard deviation 1.120 is placed second and technical capability is third with a mean value of 3.87 and standard deviation 1.170. the participants were also asked to mark the level of effectiveness of all these criteria. table iii. contractor selection criteria adoption level contractor selection criteria frequency for scale m e a n s .d r a n k 1 2 3 4 5 quality 6 3 12 21 29 3.90 1.232 1 bid amount 3 6 13 24 25 3.87 1.120 2 technical capability 3 8 11 22 27 3.87 1.170 3 financial stability 4 8 14 18 27 3.78 1.229 4 experience 8 13 4 13 33 3.70 1.487 5 past performance 3 10 14 23 21 3.69 1.166 6 equipment 4 12 10 27 18 3.60 1.200 7 management capability 3 11 17 22 18 3.57 1.154 8 reputation 5 9 17 21 19 3.56 1.215 9 organizational skills 5 9 17 21 19 3.56 1.215 10 project-specific requirements 3 13 16 23 16 3.50 1.157 11 human resources/ managerial resources 6 14 14 19 18 3.40 1.293 12 current workload 7 11 19 18 16 3.35 1.266 13 environmental aspects 8 12 17 18 16 3.30 1.304 14 occupational health and safety 7 11 24 15 14 3.25 1.227 15 business location 7 15 16 22 11 3.21 1.229 16 past relationship 5 16 21 20 9 3.16 1.133 17 table iv. effectiveness level of contractor selection criteria contractor selection criteria frequency for scale m e a n s .d r a n k 1 2 3 4 5 quality 4 2 17 18 30 3.95 1.139 1 experience 6 3 11 19 32 3.95 1.247 2 technical capability 4 10 11 17 29 3.80 1.271 3 financial stability 5 8 9 24 25 3.78 1.241 4 equipment 4 7 12 26 22 3.77 1.161 5 management capability 2 8 17 23 21 3.74 1.091 6 bid amount 3 8 15 27 18 3.69 1.103 7 reputation 3 7 22 20 19 3.63 1.111 8 current workload 4 8 15 28 16 3.61 1.125 9 past performance 3 11 15 24 18 3.60 1.152 10 organizational skills 2 11 18 23 17 3.59 1.102 11 project-specific requirements 3 8 20 28 12 3.53 1.039 12 human resources/ managerial resources 5 10 16 24 16 3.50 1.193 13 past relationship 4 13 25 20 9 3.23 1.075 14 business location 4 16 20 21 10 3.23 1.127 15 occupational health and safety 4 17 18 22 10 3.23 1.139 16 environmental aspects 6 15 17 23 10 3.22 1.185 17 the respondents were asked to indicate the level of effectiveness using a 5 point scale as 1=not effective, 2=less effective, 3=moderately effective, 4=very effective and 5=extremely effective. analysis of the data was performed with mean value and standard deviation calculation and is presented in table iv. it can be seen that that quality with mean value of 3.95 and standard deviation 1.139 is reported as the most effective criterion, with technical capability and financial engineering, technology & applied science research vol. 10, no. 2, 2020, 5520-5523 5523 www.etasr.com soomro et al.: contractor’s selection criteria in construction works in pakistan stability following with mean value of 3.8 and 3.78 respectively. equipment availability and management capability were at the fourth and fifth place. iv. conclusion this paper focused on highlighting the contractor’s selection criteria adopted in construction works in pakistan. this aim was achieved through a survey of construction practitioners using a form based on 17 criteria identified in the literature. mean value and standard deviation analysis of the 71 survey forms received revealed that quality, bid amount, technical capability, financial stability and experience are common criteria adopted in construction projects of pakistan for selecting the most appropriate contractor. the study also highlighted that quality, technical capability, financial stability, equipment availability, and management capability are the most effective criteria for selecting a contractor for any construction project. the findings of this study will be very useful for consultants and clients in order to select a 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research vol. 9, no. 5, 2019, 4735-4740 4735 www.etasr.com alghamdi: suitability of quaternary sediments of wadi arar, saudi arabia as construction materials suitability of quaternary sediments of wadi arar, saudi arabia, as construction materials an environmental radioactivity approach mohammed a. m. alghamdi faculty of earth science, king abdulaziz university, jeddah, saudi arabia mmushrif@kau.edu.sa abstract—the surficial quaternary deposits of wadi arar were radioactively evaluated for construction purposes. the concentrations of 226 ra, 232 th, and 40 k were used to evaluate the radioactive suitability of wadi arar. gamma-spectrometry technique with an hpge detector was used to measure the concentrations of ra, th, and k. the average specific activities of ra, th, and k were 22.92, 16.99, and 223.66bq/kg respectively. the average value of the air absorbed dose rate (d) was 30.47ngy/h. the average values of the indoor and outdoor annual effective dose equivalent (aede) were 149.46 and 37.36µsv/y respectively. the average value of the radium equivalent activity index (raeq) was 64.44bq/kg. the maximum values of the external and internal hazard index (h) were 0.20 and 0.27 respectively. radioactivity concentration and hazard index values are within the acceptable global values and do not pose any significant radiological threat to the population. these results reflect the safety of wadi arar as a site for construction and the potential to use depositional sediments at the site as construction materials. keywords-environmental; geology; construction; radiation; hpge i. introduction wadis, coasts, and deserts are possible construction sites and sources for construction materials. radioactive hazards are one of the factors that affect the selection of construction material sites. geological, geochemical, pathological, and ecological processes along with seasonal changes are some of the main processes that influence natural radioactivity [1]. radiation level concentrations differ depending on rock-type, soil, or sediment [2]. the discharge of gamma radiation from naturally occurring radioisotopes depends on land conditions, and is globally characterized by various levels [3]. due to the presence of active faults and lineaments, some areas experience elevated concentrations of k, ra, and th in soil samples [4]. similar researches concluded in varying results. gamma-ray spectroscopy was used to assess the average effective dose of 226 ra, 232 th, and 40 k in punjab, india in [5]. assessments of the natural radionuclide contents of 238 u, 232 th, and 40 k at tushki, egypt using gamma-spectrometry analysis showed high background radiation, thankfully far from habitation and cultivated regions [6]. naturally occurring radioactivity in soil samples at akwa ibom, which were evaluated were less than the recommended safety limits [7]. all health hazard indices were well below their recommended limits for samples collected from locations at aden, south of yemen [8]. maximum and minimum activity 40 k concentrations of sediments in water samples at abuja, nigeria were ranked in [9]. soil sediments in the udi and ezeagu areas of the enugu state, nigeria have reduced concentrations of 40 k, 226 ra, and 232 th [10]. authors in [11] found that the radiological effects of soil samples from geregu were below the standard limits and posed no potential significant effects on public health. authors in [2] analyzed the radionuclide activity concentrations of 40 k, 226 ra, and 232 th in sand deposits from the bharathapuzha river, india, and found that the concentrations were higher than the international recommended values. the specific natural radionuclide activities in sediment samples collected from beni haroun dam, algeria had no hazardous indices compared with analog measurements from other locations [12]. in saudi arabia, the strategic road that connects arar and aljouf is crossing wadi arar while the urban expansion of arar extends in the southeastern direction towards wadi arar (figure 1). radon concentrations in this wadi, reflect a significant correlation between the rad7 and cr-39 techniques that were used to detect it [14], while it has a significant correlation with coarse and fine sand grain size [15]. authors in [16-19] used gamma spectroscopic analysis measuring the radioactivity of ra, th, and k, to obtain hazard indices in alkhobar, jeddah, aqabah, and ad-dahna respectively. according to them, the hazard indices at ad-dahna were below the global average value, but the values of k at jeddah and aqabah were higher than the global average. considering 226 ra, 232 th, and 40 k, this study was conducted on 22km of the surficial deposits of wadi arar (figure 1). the assessment of radiation concentrations and hazard indices at this wadi will allow us to i) evaluate the site validity for future urbanization and the potential use of sediment deposits as construction materials, ii) support interpretations of subsurface structural geology, and iii) perform comparisons and corresponding author: mohammed a. m. alghamdi engineering, technology & applied science research vol. 9, no. 5, 2019, 4735-4740 4736 www.etasr.com alghamdi: suitability of quaternary sediments of wadi arar, saudi arabia as construction materials interpretations of radiation hazards in wadi environments with the global environment. fig. 1. study area profiles in wadi arar. (screenshot from google earth [13], © 2018 google, image © 2019 maxar technologies, image © 2019 cnes/airubus) ii. study area a. geological setting the arar quadrangle underlies the late cretaceous aruma formation and paleogene and neogene sedimentary rocks [20]. sedimentary rock units of devonian, silurian, and ordovician are also representative of the subsurface formations. wadi arar cuts off these formations from the southwest to the northeast, filling this area with quaternary deposits, such as gravel, sand, and silt, which lie above the sedimentary rocks. according to the structural geology perspective, the arar arch traverses the study area, trending from southwest to northeast. flood seasons have continually transported these deposits and soil sediments on the same trend of arar arch. b. location and sampling geological and topographic maps of the northern border region [13, 20] were used to adapt to the study area. the study area of wadi arar is located between 30°50’30’’n and 30°56’30’n and 40°50’30’’e and 41°02’30’’e. seven profiles (a, b, c, d, e, f, and g) were chosen at the peak of water deposition or sediment erosion. the total distance from profile a to g was 22km, with an average distance of 3km between each profile (figure 1). five samples of 1kg from each station were sealed in plastic bags and stored for laboratory tests. iii. hazard parameters a. detector samples with an average weight of 180g were placed in sealed cylindrical 100ml plastic containers and used to measure the naturally occurring radioactive materials (norm). the containers were stored for one month to obtain secular equilibrium in each natural radioactive series, where the rate of daughter decay reaches equilibrium with that of the parents. activity concentration measurements were performed using a gamma-ray spectrometer equipped with a high-purity germanium (hpge) detector that was enclosed in a 10cm cylindrical multilayer graded shield (canberra 747e). the hpge detector has an efficiency of 60% and energy resolution of 2.4kev at 1,332.5kev from a 60 co gamma-ray. the detector was coupled with an amplifier to the computer using a multichannel analyzer. calibration of the energy, efficiency of the detector and efficiency of the sample geometry were performed using the methods described in [21–23]. 1,461 kev γ-line was used to determine 40 k activity while 226 ra and 232 th activities were determined indirectly using the most intense noninterfering gamma lines (295 and 352kev for 214 pb, 609, 1120, and 1764kev for 214 bi, 583 and 2614kev for 208 tl, 338, 911, and 968kev for 228 ac). each sample was measured for 24hr in order to obtain a sufficient amount of data [24]. b. air-absorbed dose rate (d) the measured concentrations of 226 ra, 232 th, and 40 k were converted to a total absorbed gamma dose rate in the air at one meter above the ground using the monte carlo method [3] based on the following equation: �����.�� � 0.462��� � 0.621��� � 0.0417�� (1) where d is the air-absorbed dose rate and ���,���,and ��are the activities, in bq/kg, of ra, th, and k, respectively. c. annual effective dose equivalent (aede) the annual effective dose provides a measure of the total radiation risk to an individual organism. the conversion coefficient from the absorbed dose in the air to the effective dose and the indoor occupancy factor was used to estimate the annual effective dose with a conversion factor of 0.7sv/gy [2]. assuming that people spend, on average, approximately 20% of their time outdoors and 80% indoors [3], the annual effective dose was calculated with the following equations: aede indoor �msv y� � � �ngy.h� x 8760 h x 0.8 x 0.7 sv gy� -10�. (2) aede outdoor �msv y� � � �ngy.h� x 8760 h x 0.2 x 0.7 sv gy� -10�. (3) d. γ-ray radiation hazard indexes (1234) the natural radiation in building materials is not uniform and is typically determined by the concentrations of 226 ra, 232 th, and 40 k [2]. uniformity for radiation is denoted in terms of radium equivalent activity raeq, in bq/kg, to match the specific activity of a fabric that contains a different quantity of 226 ra, 232 th, and 40 k by a single amount. it is a commonly used hazard index, which is calculated using the following equation [2]: 1234 � 5�� � 1.43 5�� � 0.0775� (4) where cra, cth, and ck are the activity concentrations of 226 ra, 232 th, and 40 k, in bq/kg respectively. it has been assumed that 370bq/kg of 226 ra, 259bq/kg of 232 th, or 4810bq/kg of 40 k produce the same gamma dose rate [2]. e. hazard index (738, 79:) in their research on sandy soil, authors in [24] obtained an external hazard index using the 1234 expression from (4) by engineering, technology & applied science research vol. 9, no. 5, 2019, 4735-4740 4737 www.etasr.com alghamdi: suitability of quaternary sediments of wadi arar, saudi arabia as construction materials suggesting that the maximum allowed value (equal to unity) corresponds to the upper limit of raeq (370bq/kg). this index value must be less than unity to maintain an insignificant level of radiation hazard, i.e. the radiation exposure due to construction material radioactivity is limited to 1.0msv/y. the external hazard index can be defined with the following equation: 738 � � ;<= >?@ � ;ab cde � ;f gh @ i 1 (5) where ���, ���, and ��� are the specific activities of ra, th, and k in bq/kg respectively, while 370, 259 and, 4810 are the activities, in bq/kg, of ra, th, and k that produce the same gamma dose rate. in addition to the external hazard index, radon and its shortlived daughter products are hazardous to respiratory organs [3]. internal exposure to radon and its daughter products can be quantified with the internal hazard index 79: [3], which is given by the following equation: 79: � j ;<= hd � ;ab cde � ;f gh @ k i 1 (6) where 185, 259 and, 4810 are the activities of ra, th, and k respectively that produce the same gamma dose rate. the value of the internal hazard index 79: must be less than unity to maintain a negligible level of radiation hazard [25]. iv. results the concentrations of the naturally radioactive elements (k, ra, and th) and the hazard indices from soil sediments in the surficial layer at different locations of the wadi arar are listed in table i and plotted in figures 2–7. table i. natural radionuclide activity levels and radiation risk indices. location indice 226 ra 232 th 40 k d aede indoors aede outdoors raeq hex hin unit bq/kg bq/kg bq/kg ngy/h µsv/y µsv/y bq/kg a 19.80 8.56 132.89 20.00 98.14 24.53 42.27 0.11 0.17 b 21.85 16.59 260.00 31.24 153.25 38.31 65.59 0.18 0.24 c 20.79 18.89 305.96 34.09 167.25 41.81 71.36 0.19 0.25 d 22.59 17.16 169.20 28.15 138.09 34.52 60.16 0.16 0.22 e 26.20 20.13 241.95 34.69 170.20 42.55 73.62 0.20 0.27 f 25.93 19.13 265.30 34.92 171.32 42.83 73.71 0.20 0.27 g 23.31 18.45 190.30 30.16 147.96 36.99 64.35 0.17 0.24 average 22.92 16.99 223.66 30.47 149.46 37.36 64.44 0.17 0.24 max. allowable value [2] 35 30 400 57 450 70 370 ≤1 ≤1 the average concentrations of ra, th, and k at wadi arar are 22.9, 17.0, and 223.7bq/kg respectively, while the value range was 19.8–26.2 for ra, 8.56–20.13 for th and 132.89– 305.96 for k. it was observed that k>ra>th which is consistent with their global order while the average concentrations of ra, th, and k were lower than the average internationally recommended concentrations of 35, 30, and 400 respectively [3]. th and k were 0.6 times lower than the average internationally recommended values, whereas ra was 0.7 times lower. depending on the similarity between the three radioactive isotopes at each location, data were plotted using a 3-d method to classify the wadi arar from a radioactivity cluster perspective (figure 3). wadi arar was classified into three clusters: the first cluster included profiles a, d, and g, the second included profiles c and b, and the third included profiles e and f. fig. 2. ra, th, and k concentrations at the wadi arar which show a generally increasing trend in k concentration (red arrows) fig. 3. a 3-d plot of the ra, th, and k concentrations (bq/kg) for the different study area profiles fig. 4. the absorbed dose in air which shows a generally increasing trend in concentration (red arrow) engineering, technology & applied science research vol. 9, no. 5, 2019, 4735-4740 4738 www.etasr.com alghamdi: suitability of quaternary sediments of wadi arar, saudi arabia as construction materials fig. 5. the annual indoor and outdoor effective dose. doses are characterized by a generally increasing trend (red arrow) fig. 6. the radium equivalent activity raeq showing a generally increasing trend (red arrow) fig. 7. internal and external hazard indices characterized by a generally increasing trend (red arrow) assuming that the naturally occurring radionuclides have a uniform distribution [3], the absorbed dose rates (d) were calcated from the gamma radiation in the air at 1m above the ground. the rates varied from 20 to 34.92ngy/hr, with an average value of 30.47ngy/hr (table i). figure 4 shows two peaks of the d values at stations c and f. the d values increase from the northeast (location a) to the southwest (location g) (red arrow). based on these results, the wadi arar can be classified into two absorbed dose zones, i.e. a–d and d–g. the calculated values for aede were between 98.14 and 171.32µsv/y, with an average of 149.46µsv/y. the annual effective outdoor dose rate ranges from 24.53 to 42.83µsv/y, with an average of 37.36µsv/y (table i). figure 5 shows the changes in both indoor and outdoor annual effective dose, which are characterized by a general trend (red arrow) that increased from location a to g with two peaks at c and f. table i also summarizes the raeq estimated values for the study area. figure 6 shows the changes that occur at each location, which are characterized by a general trend that increases from a to g with two peaks at c and f. the calculated values for the external and internal hazard index (hex and hin) ranged from 0.11 to 0.20 and 0.17 to 0.27 respectively. figure 7 illustrates those changes, which are characterized by a general hazard index trend (red arrow) that increases in the southwest direction (location d). based on the results for both isotope concentrations and hazard indices, two radioactive zones can be assessed. the values increase from the northeast to the southeast and are lower than average global values. v. discussion it was observed that, the values at profile d were less than the international average for a gamma radiation dose level from terrestrial sources [3] and less than the average value reported by numerous countries such as the united states, switzerland, spain, greece, egypt, iran, india, china, and korea in 2005 [4]. the results for the indoor and outdoor aede were within the average global limits, which are 450 and 70µsv/y, respectively. therefore the sampled sediments can be safely used for construction materials. the estimated average raeq value was lower than the maximum permissible value of 370bq/kg suggested for building materials concerning radiation hazards [2]. hex and hin values were lower than unity, so the soil samples at wadi arar are considered safe and can be used as construction materials without posing any significant radiological threat to the population, according to [26]. the concentrations of radioactive elements generally increase from the northeast to southwest. in comparison with 232 th and 226 ra, 40 k has the highest radioactive concentrations throughout wadi arar, which includes two concentration peaks at profiles c and f (figure 2), indicative of the availability of potash feldspar minerals. fluctuations in the radioactive concentrations may represent the availability of more rock and mineral resources in the study area, such as carbonate and silicate minerals that include sedimentary rocks from the badanh and zallum formations, i.e. limestone, sandstone, and shale [20, 27]. based on a similarity analysis, figure 2 shows profiles a, d, and g as one cluster, which has reduced 40 k concentrations, whereas profiles e and f represent another cluster that has increased 226 ra concentrations. profiles b and c have the highest 40 k concentrations. the availability of more sha’ibs [28] or tributaries that pass through profiles a, d, and g possibly transport new sediment to wadi deposits may reduce the isotope radiation concentration. additional sediments modify the deposit composition by adding new minerals. on the other hand, the proximity of geological structures, such as the arar arch folds or graben faults, possibly changes radioactive element concentrations (figure 8). for example, weathering and erosion can affect the fold’s hinge zone and cover it with sediments. profiles a, d, and g are located on engineering, technology & applied science research vol. 9, no. 5, 2019, 4735-4740 4739 www.etasr.com alghamdi: suitability of quaternary sediments of wadi arar, saudi arabia as construction materials identical rock types, where profile a is located on the first fold limb, d is located on the second fold limb, and g is on the third fold limb. these locations may create a situation that yields identical radioactive concentrations at a small-scale. background radiation is present everywhere so, spectrum analysis should be conducted using lead absorbers around the instruments. otherwise high temperature can create electrical noise and ruin the detector, so the detector must be cooled. from a radiation perspective, local authorities have to take the conclusions of this paper in consideration along with the construction codes in wadi arar. the results of this study on the radioactivity in wadi arar can be used for global comparison and mapping. this requires essenstial communication between the construction sector and the population regarding the radiation issues in wadi arar. fig. 8. i: a map view of the study area, ii: a virtual fold cross-section, and iii: a virtual fault cross-section vi. conclusion based on the acquired results from this study on the radioactivity of 226 ra, 232 th, and 40 k in wadi arar, the following can be concluded: • the average radioactivity concentrations of 226 ra, 232 th, and 40 k of the soil surface deposits in wadi arar are 22.92, 16.99, and 223.66bq/kg respectively, while their range is 19.8–26.2, 8.56–20.12, and 132.89–305.96bq/kg, respectively. • radioactivity tends to increase from the northeast to southwest. • based on the fluctuations in radioactivity, wadi arar deposits can be divided into two radiological zones: from locations a to d and from d to g with maximum concentrations of 365 and 265bq/kg, respectively. • from a radiological perspective and regardless of 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official publications of the european communities, 1999 [27] m. a. m. alghamdi, “grain size distribution and mineral composition of surficial quaternary sediments of wadi arar, saudi arabia”, international journal of advances in science engineering and technology, vol. 6, no. 1, pp. 40–43, 2018 [28] m. a. m. alghamdi, a. a. e. hegazy, “physical properties of soil sediment in wadi arar, kingdom of saudi arabia”, international journal of civil engineering, vol. 2, pp. 1-8, 2013 microsoft word 09-3093_s2etasr_v9_n6_pp4912-4916 engineering, technology & applied science research vol. 9, no. 6, 2019, 4912-4916 4912 www.etasr.com jamali et al: analysis of co2, co, no, no2, and pm particulates of a diesel engine exhaust analysis of co2, co, no, no2, and pm particulates of a diesel engine exhaust qadir bakhsh jamali department of mechanical engineering quest, nawabshah, pakistan qjamali@quest.edu.pk muhammad tarique bhatti department of mechanical engineering quest campus larkana, pakistan trqbhatti@quest.edu.pk qamar abbas qazi department of mechanical engineering quest, nawabshah, pakistan qaziqamarabbas@yahoo.com bakar hussain kaurejo department of mechanical engineering indus university, karachi, pakistan baqar.hussain@indus.edu.pk ishfaque ali qazi department of mechanical engineering quest campus larkana, pakistan ishfaquealiqazi@gmail.com shafquat hussain solangi department of mechanical engineering quest, nawabshah, pakistan shafquat13me31@gmail.com abdul sattar jamali department of mechanical engineering quest, nawabshah, pakistan jamali_sattar@quest.edu.pk abstract—exhaust emissions of a diesel engine are considered to be a substantial source of environmental pollution. diesel engines are mainly used in vehicles and power generation. the usage of diesel engines is unavoidable as they give more power and performance, but at the same time, higher usage of diesel engines leads to increased air pollution, sound pollution, and emissions to the environment. therefore, various attempts have been made to control the harmful emissions of engines. for this reason, different devices have been made such as catalytic convertors to overcome emission problems and purify the harmful gases. in order to meet these ends, a new system was designed that would contribute to controlling the air pollution of the engines. the system is also known as an aqua silencer, and its design is somehow different but still can be used as a silencer. the newly designed emission controller was installed in a test-bed diesel engine and a total of twenty experiments were conducted with and without the new emission controller at constant speed and at constant load. during these experiments, exhaust gases were analyzed with flue gas analyzers measuring co2, co, no2, no, and pm. the study concluded that the contaminants of diesel engine exhaust gases were) controlled by the developed emission controller. keywords-emission control; diesel engine; aqua silencer; carbon dioxide; nitrogen oxide i. introduction internal combustion (ic) engines have become highly imperative in transportation and industry. diesel engines are the most commonly preferred engines, especially in the application of heavy-duty vehicles. besides other sources, these engines are counted as one of the largest environmental pollution contributors due to their exhaust emissions (figure 1). the use of ti nano tubes in an aqua silencer along with charcoal can absorb toxin gases [1]. the performance and emissions using alcohol fumigation in the presence of hot exhaust gas recirculation (egr) were examined in [2]. the egr results to great reductions in nox emission, amounting up to 30 to 40% at higher loads [2]. in [3], the aqua silencer was used in the reduction of toxic gases and noise. this experiment gives an effective way to reduce emission gases from the engine exhaust. moreover, aqueous ammonia solution can be used as an absorber for the reduction of co2, so2, and nox from exhaust gases of ic engines. the aqueous ammonia process can simultaneously remove co2, so2, nox and also hydrocarbons that may be present in the exhaust gas. a study was conducted on a single cylinder four stroke cycle direct injection diesel engine at a constant speed with a fuel injection pressure of 200bars. tests were conducted using commercial diesel fuel and diesel fuel with 10% and 20% water by volume. it was found that the water emulsification has the potential to improve brake thermal efficiency and brake specific fuel consumption [4]. in order to check the system's performance an aqua silencer was directly integrated in the exhaust of the engine and its effects were studied in [6]. the use of a new catalyst converter to replace the noble metals platinum (pt), palladium (pd), and rhodium (rh) has been studied. materials such as zeolite, nickel oxide, and metal oxide have been found to effectively reduce emissions. beside this, ultrasonic treatment with a combination of electroplating technique, citrate method and plasma electrolytic oxidation (peo) have been carried out on producing an effective catalyst in reducing exhaust emissions [7]. aqua silencer covers the effect of black smoke, nox emissions, and sound from the exhaust gases. after implementing the aqua silencer, the engine tended to corresponding author: qadir bakhsh jamali engineering, technology & applied science research vol. 9, no. 6, 2019, 4912-4916 4913 www.etasr.com jamali et al: analysis of co2, co, no, no2, and pm particulates of a diesel engine exhaust have nox emissions and sound completely eliminated, whereas carbon monoxide (co) emission reduced up to 53%, unburned hydrocarbon (ubhc) was reduced up to 41% and co2 emission reduced up to 44% in comparison with the existing system [8]. fig. 1. composition of diesel exahust gases [5] aqua silencer is thermally effective and technically feasible for use at reducing engine noise and toxic emissions but certain improvements so as to fit in the application with the engine exhausting unit are in order [9]. in [10], the toxic contents in petrol engine exhausts at various running speeds were studied by changing the limestone content in the rtp silencer. reduction of hc and co emissions were observed by changing the limestone content from 25 to 150 grams. in [11], co emissions were reduced up to 53% with the use of an aqua silencer. ubhc can be reduced by 41% and co2 emissions by 44%. the catalytic converters are used to reduce the amounts of nitrogen oxides, co, and ubhc in automotive emissions. during vehicle use, the converter is exposed to heat, which causes the metal particles to agglomerate and their overall surface area to decrease. as a result, catalyst activity deteriorates [12]. the effect of various engine parameters on the control of these emissions is reported with different versions of the engine in [13]. authors in [14] reported that the ubhc emission in a twin spark engine is reduced up to 12% as compared to the single spark engine while the co emission in the twin spark engine is reduced to a great extent. in [15], a prototype emission control system was designed and tested on a gasoline-fueled vehicle. federal test procedure (ftp) emission results show a 35% reduction in hydrocarbons emitted during the cold transient segment due to adsorption. ii. materials and methods the design of a new emission controller was carried out based on the engine parameters and material requirements. in the first step, a cad model was designed on creo parametric 3.0 with all suitable dimensions. the section view of the emission control unit is shown in figures 2 and 3. the emission controller was installed, and the experiments were carried out on low speed of the diesel engine. the research and test bed model was the dwe-6/10-js-dv (figure 4), which is available at the thermodynamics laboratory of quaid-eawam university of engineering, science & technology. the detailed specifications of this test bed diesel engine are given in table i. the gases obtained from the diesel engine exhaust were analyzed by the flue analyzer (flue gas analyzer model no. testo 350xl), whether they were purified or not and the purification extent was estimated. to measure the total suspended particles (tsp) in the flue gases a device named aerocet 531s was used to count the pm. table i. specifications of diesel engine test unit number of cylinders 01 bore 80mm stroke (piston displacement) 95mm (477cc) compression ratio 23:1 starting method manual (cell starter upon request) output/rational speed 8.5ps/2200 rpm (max) cooling system water cooled type horizontal fig. 2. section view of emission control unit fig. 3. detailed drawing of the emission control unit (dimensions are given in inches) figure 4 shows the complete unit of aqua silencer. when the exhaust gases of the diesel engine enter the device, they pass through the perforated tube. the holes in the perforated tube are designed in a way that the large mass gases form smaller gas bubbles. it is a closed end tube and all the gases can pass through the holes. the perforated tube is completely immersed in a lime water solution where the gases chemically react and less precipitates are created. around the circumference of the perforated tube, there is double activated charcoal. the charcoal is highly porous and possesses extra free valences, so it has the ability to absorb flue gases. engineering, technology & applied science research vol. 9, no. 6, 2019, 4912-4916 4914 www.etasr.com jamali et al: analysis of co2, co, no, no2, and pm particulates of a diesel engine exhaust fig. 4. assembly of the system fig. 5. hand held pm and flue gas analyzer iii. results measurements were taken in order to compare the emissions of the test bed diesel engine with and without installation of the newly designed system at different loads and different speeds (rpm). a total of twenty experiments were performed at constant load and constant speed to observe the behavior of emissions with respect to these parameters. a. performance evaluation the performance evaluation experiment data sheets for constant load and constant speed are illustrated in tables ii and iii. table ii. engine emissions at constant speed s y s te m s s p e e d t o r q u e c o 2 ( p p m ) c o ( p p m ) n o 2 ( p p m ) n o ( p p m ) p m ( m g /l ) w it h o u t 9 5 0 0.2 990 283 9.0 52 0.09 0.4 1505 298 8.4 54 0.088 0.6 4020 240 6.4 58 0.103 0.8 7605 330 4.1 56 0.144 1.0 9700 382 4.3 50 0.212 w it h 0.2 690 325 3.0 46 0.101 0.4 1150 320 6.1 48 0.108 0.6 3410 230 5.4 55 0.105 0.8 4024 265 2.6 48 0.107 1.0 5500 308 1.2 44 0.148 b. co2 emissions carbon dioxide (co2) is a colorless and non-combustion gas released when fuels with carbon content burn fully. consequently, co2 is a significant parameter in exhaust emissions from engine. the co2 emissions at constant speed and at constant load of the diesel engine, with and without the emission control unit, are shown in figures 6 and 7 respectively. these graphs show that the co2 obtained from the newly developed emission controller is less than without it. table iii. engine emissions at constant torque s y st e m s t o r q u e s p e e d c o 2 ( p p m ) c o ( p p m ) n o 2 ( p p m ) n o ( p p m ) p m ( m g /l ) w it h o u t 0 .4 950 1508 298 8.5 53 0.088 1050 3900 200 10.2 48 0.112 1150 6690 220 13.6 60 0.086 1250 8660 290 16.5 77 0.094 1350 9800 188 17.8 80 0.142 w it h 950 1206 242 6.3 48 0.086 1050 3875 296 5.6 42 0.094 1150 4300 180 12.5 51 0.096 1250 5560 290 15 63 0.103 1350 6078 205 17.2 77 0.118 fig. 6. comparative results of co2 emissions at constant speed fig. 7. comparative results of co2 emissions at constant load c. co emissions carbon monoxide emissions are colorless, odor free and toxic gases produced as an effect of incomplete burning of carbon. the emission of co results from oxidation of fuel consisting of carbon and hydrogen with oxygen. co is produced as a result of the deterioration of the resulting yield. the co emissions at constant speed and load, with and without the emission control unit, are shown in figures 8 and 9. it can be seen that co emission is more in the absence of the emission controller. engineering, technology & applied science research vol. 9, no. 6, 2019, 4912-4916 4915 www.etasr.com jamali et al: analysis of co2, co, no, no2, and pm particulates of a diesel engine exhaust fig. 8. comparative results of co emissions at constant speed fig. 9. comparative results of co emissions at constant load d. nox emissions fig. 10. comparative results of no2 emissions at constant speed fig. 11. comparative results of no2 emissions at constant load the emissions of nitric oxides (nox) are affected by the emission controller due to the use of limewater. the hydroxides in the water absorb noxious thus noxious emissions are less than the actual emissions from the diesel engine. the no2 emissions at constant speed and at constant load of the diesel engine, with and without the emission control unit, are shown in figures 10 and 11. the no emissions at constant speed and at constant load of the diesel engine with and without the emission control unit are shown in figures 12 and 13 respectively. we can see that the nox emissions decreased when using the newly developed emission controller. fig. 12. comparative results of no emissions at constant speed fig. 13. comparative results of no emissions at constant load e. particulate matter (pm) emissions particulate matter (pm) air pollution is an air suspended combination of solid and liquid particles depending upon the size, shape, surface area, number, chemical composition, solubility, and source. it is known that diesel fuel is a major emitter of pm generation. the pm emissions at constant speed and at constant load of the diesel engine with and without the emission control unit are shown in figures 14 and 15. fig. 14. comparative results of pm emissions at constant speed engineering, technology & applied science research vol. 9, no. 6, 2019, 4912-4916 4916 www.etasr.com jamali et al: analysis of co2, co, no, no2, and pm particulates of a diesel engine exhaust fig. 15. comparative results of pm emissions at constant load iv. comparative study a comparative study was conducted between the developed system (with and without the implementation of the control unit at the exhaust of the diesel engine) and the standardized values of diesel engine exhaust. the comparison is illustrated in table iv. table iv. comparative study results standard with the system without the system co (ppm) 100 325 382 co2 (ppm) 5000 5500 9700 no (ppm) 25 55 58 no2 (ppm) 5 6.1 9 pm (mg/l) 0.02 0.148 0.212 v. conclusion in this study, experiments were conducted on a diesel engine with an emission control system (commonly known as an aqua silencer) to investigate its impact on the engine’s emission characteristics. the study concluded that this system can be used along with or instead of a catalytic converter. with this unit the emissions at the tailpipe of an exhaust system can be easily lowered below the specified levels. with the use of lime water in the silencer, the toxic levels of nox gases are decreased along with the temperature of the final exhaust gases which has also a positive effect on the environment. the water contamination is found to be negligible, because of the amount of the acidity level inside which plays the role of absorbing the noxious products of combustion. co is not highly controlled due to its negligible presence in the emissions (0.20% by volume) and does not pose any health hazard when compared to gasoline engines. the double layer of activated charcoal used helped in adsorbing several harmful constituents. by using the perforated tubing, there will not be any excessive back pressure formation as high mass bubbles get converted into low mass bubbles and the noise is slightly reduced due to tubing and water. fuel consumption remains the same after the implementation of this system. this system is also cheap to build and maintain as compared to other emission control methods. references [1] m. p. patel, s. r. gajjar, “a literature review on design and development of industrial generator silencer”, international journal for scientific research & development, vol. 3, no. 1, pp. 335-339, 2015 [2] g. s. hebbar, a. k. bhat, “diesel emission control by hot egr and ethanol fumigation; an experimental investigation”, international journal of modern engineering research, vol. 2, no. 4, pp. 1486-1491, 2012 [3] i. k. patel, s. r. gajjar, “design and development of aqua silencer for two-stroke petrol engine”, international journal of innovative research in science and technology, vol. 1, no. 1, pp. 31-37, 2014 [4] s. s. rawale, s. n. patil, a. a. nandrekar, a. s. kabule, “use of aqueous ammonia in silencer for removal of co2, so2, and nox from exhaust gases of i.c. engines”, international journal of engineering science and innovative technology, vol. 2, no. 5, pp. 157-160, 2013 [5] w. a. majewski, m. k. khair, diesel emissions and their control, sae international, 2012 [6] s. raj, a. k. aniyan, a. aji, a. raj, a. mohan, t. r. sharon, “fabrication and testing of portable twin filter aqua silencer”, international journal of mechanical and industrial technology, vol. 3, no. 2, pp. 177-186, 2015 [7] k. i. patel, r. engineer, p. k. patel, “cfd analysis of perforated tube of aqua silencer”, indian journal of research, vol. 4, no. 5, pp. 182-184, 2015 [8] p. chen, j. wang, “estimation and adaptive nonlinear model predictive control of selective catalytic reduction systems in automotive applications”, journal of process control, vol. 40, pp. 78-92, 2016 [9] g. m. p. yadav, k. nagaraju, h. raghavendra, b. m. k. reddy, g. n. reddy, j. b. kumar, k. srikanth, k. jagadesh, “modeling and experimental investigations of the sound and emissions performance for 4-stroke multi cylinder diesel engine with an aqua silencer”, international journal for research in applied science & engineering technology, vol. 3, no. 5, pp. 541-553, 2015 [10] a. a. kumar, n. anoop, a. jawed, p. p. bijoy, t. v. midhun, n. p. shiyas, r. krishna, “design and development of aqua silencer”, international journal of engineering and innovation technology, vol. 5, no. 11, pp. 35-41, 2013 [11] a. saraf, t. khese, t. shah, g. gaikwad, s. d. bhaisare, “design and analysis of aqua silencer”, international research journal of engineering and technology, vol. 4, no. 2, pp. 1432-1436, 2017 [12] a. gaikwad, p. taware, v. kannan, v. kachare, p. ghayal, “study on development of aqua silencer”, international journal for research publications in engineering and technology, vol. 3, no. 4, pp. 199-203, 2017 [13] h. tanaka, m. taniguchi, n. kajita, m. uenishi, i. tan, n. sato, k. narita, m. kimura, “design of the intelligent catalyst for japan ulev standard”, topics in catalysis, vol. 30, no. 1-4, pp. 389-396, 2004 [14] p. v. k. murthy, s. n. kumar, m. v. s. m. krishna, v. v. r. s. rao, d. n. reddy, “aldehyde emissions from two-stroke and four-stroke spark ignition engines with methanol blended gasoline with catalytic converter”, international journal of engineering research and technology, vol. 3, no. 3, pp. 793-802, 2010 [15] i. altin, i. sezer, a. bilgin, “effects of the stroke/bore ratio on the performance parameters of a dual-spark-ignition (dsi) engine”, energy & fuels, vol. 23, no. 4, pp. 1825-1831, 2008 microsoft word 30-2537_s engineering, technology & applied science research vol. 9, no. 1, 2019, 3822-3825 3822 www.etasr.com reddy & chaganti: investigating optimum sio2 nanolubrication during turning of aisi 420 ss investigating optimum sio2 nanolubrication during turning of aisi 420 ss nune madan mohan reddy department of mechanical engineering bits pilani hyderabad campus telangana, india madan008phd@gmail.com phaneendra kiran chaganti department of mechanical engineering bits pilani hyderabad campus telangana, india phaneendrakiran@yahoo.co.in abstract—aisi 420 martensitic stainless steel is used for making gas and steam turbine blades, steel balls and medical instruments, due to its anti-corrosive properties. turning of aisi 420 ss would be a worthy procedure specifically in manufacturing high surface finish parts. in this work, effort has been made to investigate the cooling and lubricating performance of sio2 (silicon dioxide) nanoparticles at different weight concentrations of 0.1g, 0.5g and 1g mixed in a novel developed base fluid (synthetic). the performance of optimum sio2 based cutting fluid is evaluated based on the turning process with output responses like surface finish and cutting temperature. taguchi technique was used with standard l9(3**4) orthogonal array. the responses, surface roughness, and cutting temperature were analyzed using s/n (signal-to-noise) and anova (analysis of variance). this analysis identifies the significant input parameter combination to obtain minimum surface roughness and temperature. keywords-taguchi; sio2 nanoparticles; anova; orthogonal array; cutting fluid i. introduction water was firstly proposed as a cutting fluid to reduce temperature and enhance surface finish and tool life in metal cutting process [1]. onwards, many cutting fluids were introduced and used by the machining industry. recently, industries realized the cost, environmental and health issues in the use of these cutting fluids [2-4]. the industry expects a cutting fluid with minimal cost, more output and best quality [5]. few attempts were made in the past to develop such a cutting fluid by including nanoparticles in it and it was named as nanolubricant, which includes a combination of metallic or non-metallic nanometer sized particle in the cutting fluid. in the past decade more attention was paid to nanolubricants due to their enhanced thermal properties like thermal conductivity and convective heat transfer coefficient [6]. most commonly used nanoparticles in the base fluid were titanium oxide, molybdenum disulphide and silicon dioxide. compared to others, sio2 nanoparticles have shown a significant improvement in machining and thermal properties and a reasonable improvement in lubrication effect [7-11]. these sio2 nanoparticles impinge between metal surfaces and create rolling action enhancing lubrication [12]. another study on sio2 nanolubricant [13] shows 62.67% and 30.86% lower forces in dry machining and application of conventional oil based cutting fluid. turbine blade materials like aisi 420, do have a high chromium percentage (i.e. 13 to 14%). turning of these high hardness materials raises high temperature at the cutting zone and more surface roughness on the machined surface. the surface finish of these materials is critical as poor surface finish leads to surface cracks and to fail at high centrifugal forces [14]. there are a few studies in the literature on the machinability of aisi 420 using nanolubricants [8-10] and some of them used doe (design of experiments) [15]. frequently used doe are response surface and taguchi methods. response surface method is expensive compared to taguchi method. taguchi method suggests a few experiments while keeping the analysis at par with other methods [16]. this work aims to minimize the surface roughness of machined aisi 420 material using sio2 nanolubricant. the control factors were speed, feed, depth of cut and the weight of sio2 nanoparticles in the base fluid. the responses considered were surface finish of the workpiece and cutting temperature in the cutting zone. the experiments were planned and conducted using l9 orthogonal array. ii. materials and methods a. workpiece, tool and nanoparticles the experiments were carried out on a cnc lathe machine (hmt praga model) as shown in figure 1. the workpiece material considered for turning was aisi 420 with 50mm diameter and 120mm length. fig. 1. cutting temperature measurement with thermocouple. a hss (high speed steel) uncoated carbide insert (cnmg 120408) with 0.8mm nose radius was used. the corresponding author: n. m. m. reddy engineering, technology & applied science research vol. 9, no. 1, 2019, 3822-3825 3823 www.etasr.com reddy & chaganti: investigating optimum sio2 nanolubrication during turning of aisi 420 ss workpiece and the cutting tool properties are given in table i. each experiment was conducted using a new cutting edge. the size of the sio2 nanoparticles used in the cutting fluid was 521.4nm (table ii). adding sio2 nanoparticles in the cutting fluid may improve the convective heat transfer coefficient and net heat carrying capacity, which is essential requirement for a cutting fluid. table i. workpiece and tool material properties material properties workpiece cutting tool type aisi420 martensitic stainlesssteel uncoated hss carbide insert conductivity (w/mk) 24.9 105 density (kg/m 3 ) 7800 15000 modulus (gpa) 200 620 poisson’s ratio 0.28 0.22 specific heat cp (j/kg o c) 460 670 table ii. sio2 nanoparticle properties properties sio2 nanoparticles physical structure amorphous crystalline powder conductivity (w/cm k) 0.015 density (g/cm3) 2.1 b. plan of experiments all the experimental procedures used taguchi l9 orthogonal array. considered control parameters were speed, feed, depth of cut and sio2 nanoparticle concentration in the base fluid. all parameters were kept at 3 levels: low, medium and high. the responses measured were surface roughness and temperature at the cutting zone. each experiment was repeated thrice to ensure repeatability and the average value of these three experiments is given below. the list of planned experiments is specified in table iii. table iii. design of experiments and control factors # orthogonal array l9 (3**4) speed-a (m/min) vc feed-b (mm/rev) f depth of cutc (mm) ap sio2 *-d (g) a b c d 1 1 1 1 1 150 0.10 0.10 0.1 2 1 2 2 2 150 0.15 0.20 0.5 3 1 3 3 3 150 0.20 0.30 1 4 2 1 2 3 175 0.10 0.20 1 5 2 2 3 1 175 0.15 0.30 0.1 6 2 3 1 2 175 0.20 0.10 0.5 7 3 1 3 2 200 0.10 0.30 0.5 8 3 2 1 3 200 0.15 0.10 1 9 3 3 2 1 200 0.20 0.20 0.1 * concentration iii. results and discussion the responses obtained were analyzed with s/n ratio and significant factors were also identified. the smaller-thebetter s/n ratio equation was chosen for the responses surface roughness and cutting temperature: ������ � ��� ��� � �10� �� � � ∑ ��� ������� (1) the responses and corresponding s/n ratios are given in iv. anova was done to find significant parameters and the optimal concentration of sio2 nanoparticle in the based fluid to get least surface roughness and cutting temperature. table iv. experimental and s/n results # vc f ap sio2 (g) surface roughness cutting temperature ra (µm) ra. s/n (db) t ( o c) t. s/n (db) 1 150 0.10 0.1 0.1 0.47 6.55 169 -44.5 2 150 0.15 0.2 0.5 0.35 9.11 162 -44.1 3 150 0.20 0.3 1 0.26 11.7 148 -43.4 4 175 0.10 0.2 1 0.49 6.19 153 -43.6 5 175 0.15 0.3 0.1 0.64 3.87 178 -45.0 6 175 0.20 0.1 0.5 0.53 5.51 167 -44.4 7 200 0.10 0.3 0.5 0.58 4.73 173 -44.7 8 200 0.15 0.1 1 0.29 10.7 164 -44.2 9 200 0.20 0.2 0.1 0.61 4.29 182 -45.2 a 5% level of significance was considered for anova. the anova results for surface roughness, cutting temperature are discussed in the following sections. a. surface roughness the s/n ratios of surface roughness varied from 3.87db to 11.7db. optimal combination of factors for minimum surface roughness can be obtained from the plot in figure 2. this shows that 150m/min cutting speed, feed 0.15mm/rev, 0.1mm depth of cut and 1g sio2 nanoparticle combination gives minimum surface roughness. among all 4 factors the concentration of sio2 nanoparticles was having an s/n ratio of 9.55db. this emphasizes the importance of sio2 nanoparticles in controlling the surface roughness of the parts produced. detailed s/n ratios of all input parameters for different levels are presented in table v. fig. 2. optimum combination of control factors for minimum surface roughness (µm). anova for surface roughness was analyzed and the results are given in table vi. these results show 50.65% contribution from concentration of sio2 nanoparticles showing its significance. regarding the other factors, speed engineering, technology & applied science research vol. 9, no. 1, 2019, 3822-3825 3824 www.etasr.com reddy & chaganti: investigating optimum sio2 nanolubrication during turning of aisi 420 ss is contributing 37.66%, feed 7.14% and depth of cut 4.55% in reducing surface roughness. the interaction plot for the control factors is shown in figure 3. in general, the parallel lines in the interaction plot show no interactions and the intersecting lines represent the presence of interactions between control factors. figure 3 shows that most of the factors were having a two way interaction in influencing the output surface roughness. table v. ratio of s/n response for surface roughness level cutting speed feed depth of cut sio2 concentration 1 9.12 5.82 7.60 4.90 2 5.19 7.91 6.53 6.45 3 6.59 7.16 6.76 9.55 ∆ 3.93 2.08 1.07 4.64 rank 2 3 4 1 table vi. anova for surface roughness sources degrees of freedom sum of squares mean of squares contribution percentage (%) cutting speed 2 0.058 0.029 37.66 feed 2 0.011 0.005 7.14 depth of cut 2 0.007 0.003 4.55 sio2 nanoparticle concentration 2 0.078 0.039 50.65 error 0 total 8 0.154 100 fig. 3. control factors interaction for surface roughness (µm). fig. 4. optimum combination of control factors for lower cutting temperature ( o c). b. cutting temperature a similar study was carried out considering cutting temperature. optimal parameter combination for minimal temperature may be interpreted from figure 4. the s/n ratio for cutting temperature ranged from -45.2db to -43.3db and is given in table iv. the s/n ratio response table at different levels of input parameters is given in table vii. the optimal parameter combination was chosen based on the s/n ratio value at the particular level. the optimal parameter condition for minimum cutting temperature is 150m/min speed (44.05db), 0.1mm/rev feed (-44.34db), 0.2mm depth of cut (44.38db) and 1gram (-43.80 db) sio2 nanoparticle concentration. as before, for the cutting temperature the nanoparticle concentration is having the highest s/n ratio, proving its significance among other factors. the ranking of the parameters obtained by the value of s/n ratio was specified in table vii. the anova results for the cutting temperature are given in table viii. the results show that concentration of sio2 nanoparticle contributed 70.53% in the temperature variance. among the other factors, cutting speed contributes 27.97% and the contribution from depth of cut and feed are negligible. table vii. s/n response for cutting temperature level cutting speed feed depth of cut sio2 concentration 1 -44.05 -44.34 -44.44 -44.94 2 -44.39 -44.50 -44.38 -44.47 3 -44.77 -44.37 -44.39 -43.80 ∆ 0.72 0.16 0.06 1.14 rank 2 3 4 1 table viii. anova for cutting temperature sources degrees of freedom sum of squares mean of squares contribution percentage (%) cutting speed 2 281 140 27.97 feed 2 14 7 1.40 depth of cut 2 1 0 0.10 sio2 nanoparticle concentration 2 708.7 354.3 70.53 error 0 total 8 1004.7 100 interaction effect for the factors is shown in figure 5. in this, most of the lines representing the factors are nonparallel showing the two way interactions. in figure 5, irrespective of other factors, the temperature at the 1-gram concentration of sio2 nanoparticle is lower. this can be attributed to the increased heat carrying capacity and thermal conductivity of nanoparticles in the base fluid. the general regression equations were obtained based on the experimental results and are given below: 130 0 273 10 0 167 24 1� � . . . . o c t c v f ap x= + × + × − × − × (2) 0 144 0 00267 0 467 0 317 0 253� � . . . . . c r m v f ap xα µ = + × − + × − × (3) where vc is speed used, f is feed, depth of cut is ap and the concentration of sio2 nanoparticles is x. the r-square values obtained for cutting temperature and surface roughness are 98% and 73.3% respectively. the given regression polynomial equations are useful for predicting the cutting temperature and surface roughness. 0.200.150.10 0.30.20.1 1.00.50.1 0.60 0.45 0.30 0.60 0.45 0.30 0.60 0.45 0.30 cutting speed (m/min) feed (mm/rev) depth of cut (mm) sio2 concentration (gram) 150 175 200 (m/min) speed c utting 150 175 200 (m/min) speed c utting 150 175 (m/min) speed c utting 0.10 0.15 0.20 (mm/rev) f eed 0.10 0.15 0.20 (mm/rev) f eed 0.1 0.2 0.3 cut (mm) depth of interaction plot for surface roughness (um) data means engineering, technology & applied science research vol. 9, no. 1, 2019, 3822-3825 3825 www.etasr.com reddy & chaganti: investigating optimum sio2 nanolubrication during turning of aisi 420 ss fig. 5. control factors interaction for cutting temperature ( o c). iv. conclusions in the present work, an optimal level of sio2 nanoparticles concentration in a base fluid for minimal cutting temperature and surface roughness was determined. the machining experiments were conducted on aisi 420. speed, feed, depth of cut and sio2 nanoparticle concentration were considered as factors and taguchi l9 orthogonal array was used to design the experiments. based on the responses measured from the experiments the following observations were made: • minimum surface roughness was observed on the machined surface of the workpiece for 1g of sio2 nanoparticles in base fluid, 150m/min cutting speed, 0.15mm/rev feed and 0.1mm depth of cut. • minimum cutting temperature was observed for 1g of sio2 nanoparticles in base fluid, 150m/min cutting speed, 0.10mm/rev feed and 0.2mm depth of cut. • based on anova it was observed that sio2 nanoparticles contribute 50.65% in reducing surface roughness and 70.53% in obtaining minimum cutting temperature. • a polynomial equation was proposed to obtain a relationship between input parameters and responses, i.e. cutting temperature and surface roughness. from these results, it can be concluded that the machining performance, in terms of cutting temperature and surface finish of workpiece, was improved by adding 1g sio2 nanoparticles in the base fluid. these results give a direction to develop new cutting fluid with sio2 nanoparticles. acknowledgment authors are thankful to bits, hyderabad campus and anurag group of institutions for providing the experimental facilities. references [1] w. f. sales, a. e. diniz, a. r. machado, “application of cutting fluids in machining processes”, journal of the brazilian society of mechanical sciences, vol. 23, no. 2, pp. 227-240, 2001 [2] f. klocke, g. eisenblatter, “dry cutting”, cirp annals, vol. 46, no. 2, pp. 519-526, 1997 [3] e. kalhofer, “dry machining principles and applications”, 2th international seminar on high technology, santa barbara d’oeste, brazil, 1997 [4] u. heisel, m. lutz, d. spath, r. wassmer, u. walter, “application of minimum quantity cooling lubrication technology”, in: production engineering vol. ii, universities of stuttgart and karlsruhe, institute for machine tools i institute for machine tools and production science processes, pp. 4954, 1998 [5] s. debnath, m. m. reddy, q. s. yi, “environmental friendly cutting fluids and cooling techniques in machining: a review”, journal of cleaner production, vol. 83, pp. 33-47, 2014 [6] n. a. c. sidik, s. samion, j. ghaderian, m. n. a. w. m. yazid, “recent progress on the application of nanofluids in minimum quantity lubrication machining: a review”, international journal of heat and mass transfer, vol. 108a, pp. 79-89, 2017 [7] m. sayuti, a. a. d. sarhan, f. salem, “novel uses of sio2 nanolubrication system in hard turning process of hardened steel aisi4140 for less tool wear, surface roughness and oil consumption”, journal of cleaner production, vol. 67, pp. 265-276, 2014 [8] r. k. singh, a. k. sharma, a. r. dixit, a. mandal, a. k. tiwari, “experimental investigation of thermal conductivity and specific heat of nanoparticles mixed cutting fluids”, materials today: proceedings, vol. 4, no. 8, pp. 8587-8596, 2017 [9] m. m. r. nune, p. k. chaganti, “experimental investigation on turning of turbine blade material aisi 410 under minimum quantity cutting fluid”, materials today: proceedings, vol. 4, no. 2, pp. 1057-1064, 2017 [10] n. m. m. reddy, c. p. kiran, “investigating the machining performance of turbineblade profile using sio2 nanoparticle based eco-friendly cutting fluid”, xiii international conference on high speed machining, montigny-les-metz, france, october 4-5, 2016 [11] a. a. minea, “hybrid nanofluids based on al2o3, tio2 and sio2: numerical evaluation of different approaches”, international journal of heat and mass transfer, vol. 104, pp. 852-860, 2017 [12] m. sayuti, o. m. erh, a. a. d. sarhan, m. hamdi, “investigation on the morphology of the machined surface in end milling of aerospace al6061-t6 for novel uses of sio2 nanolubrication system”, journal of cleaner production, vol. 66, pp. 655-663, 2014 [13] r. k. singh, a. k. sharma, a. r. dixit, a. mandal, a. k. tiwari, “experimental investigation of thermal conductivity and specific heat of nanoparticles mixed cutting fluids”, materials today: proceedings, vol. 4, no. 8, pp. 8587-8596, 2017 [14] c. p. kiran, s. clement, “surface quality investigation of turbine blade steels for turning process”, measurement, vol. 46, no. 6, pp. 1875-1895, 2013 [15] a. m. el-tamimi, t. m. el-hossainy, “investigating the machinability of aisi 420 stainless steel using factorial design”, materials and manufacturing processes, vol. 23, no. 4, pp. 419-426, 2008 [16] s. k. khare, s. agarwal, “optimization of machining parameters in turning of aisi 4340 steel under cryogenic condition using taguchi technique”, procedia cirp, vol. 63, pp. 610-614, 2017 microsoft word etasr_7-1_1345-1352.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1345-1352 1345 www.etasr.com abu bakar et al.: cumulative effect of crumb rubber and steel fiber on the flexural toughness of concrete cumulative effect of crumb rubber and steel fiber on the flexural toughness of concrete badorul hisham abu bakar school of civil engineering universiti sains malaysia, engineering campus penang, malaysia cebad@usm.my ahmed tareq noaman school of civil engineering universiti sains malaysia, engineering campus penang, malaysia atn_en@yahoo.com hazizan md. akil school of materials and mineral resources eng., universiti sains malaysia, engineering campus penang, malaysia hazizan@usm.my abstract—concrete properties, such as toughness and ductility, are enhanced to resist different impacts or blast loads. rubberized concrete, which could be considered a green material, is produced from recycled waste tires grinded into different crumb rubber particle sizes and mixed with concrete. in this study, the behavior of rubberized steel fiber-reinforced concrete is investigated. flexural performance of concrete beams (400×100×100 mm) manufactured from plain, steel fiber, crumb rubber and combination crumb rubber and steel fiber are also evaluated. similarly, concrete slabs (500×500×50 mm) are also tested under flexural loading. flexural performance of the sfrrc mixtures was significantly enhanced. the toughness and maximum deflection of specimens with rubber were considerably improved. steel fiber/crumb rubber-reinforced concrete can be used for practical application, which requires further studies. keywords-rubberized steel fiber; toughness; flexural behavior i. introduction resistance of concrete structures against the effects of impact loading, which may suddenly occur, has been the focus of considerable attention. concrete properties, such as toughness and ductility, are tuned to enhance the resistance against different impact or blast loads. various studies have enhanced these properties by utilizing natural or artificial waste products to improve the toughness of cement composite or concrete [1-3]. rubberized concrete could be considered a green material produced by recycling waste tires from different crumb rubber particles and mixed with concrete by replacing a specified portion of aggregate. public disposal of waste tires has posed serious environmental concern. the combination of these tires with concrete as partial replacement of aggregate presents a potential solution to the environmental problem, beside the other innovative techniques used to recycle them in civil engineering [4]. crumb rubber concrete exhibits reduced mechanical properties depending on their content [5, 6]. however, in [7] it was observed that concrete toughness and ductility are enhanced because of the ability of rubber aggregate to deform after failure. rubber crumbs were incorporated into concrete mixture at various volumetric replacement ratios from 5% to 20% of the coarse aggregate. the damping ratio was determined for the concrete column from free vibration test. rubberized concrete columns showed better performance than normal concrete due to enhancement in damping ratios by about 3%. this characteristic indicates that concrete containing crumb rubber aggregate is more capable to dissipate kinetic energy. rubberized concrete may be used in various civil engineering applications, such as blast walls, bollards, and road traffic barriers, in which the design strength is not a critical parameter. rubber combined with steel fiber is an innovative material with high tensile properties. in [8], authors evaluated the post-cracking performances of recycled steel fibers from waste tires concrete by testing flexural beams and slabs. the post-cracking behavior of recycled steel fiber reinforced concrete showed reduced brittle behavior, which indicates that more energy is absorbed and that toughness can be possibly increased by more than 100%. waste recycled rubber interacts with steel fibers and bonds with cement paste such that the steel fiber in the waste recycled rubber also increases concrete deformability under applied loads [9]. thus, the flexural performances of rubberized and rubberized steel fiber concrete beams were analyzed experimentally. the effect of crumb rubber inclusion as partial replacement of fine aggregate volume at three different ratios, namely, 17.5%, 20%, and 22.5%, into plain concrete (pc) was investigated. similar ratios of crumb rubber were combined with the steel fiber concrete (sfc) mixture. finally, flexural tests on rubberized concrete slabs were conducted to determine their flexural properties. ii. experimental program a. materials and mix design the mixture used in this study was prepared to achieve concrete compressive strength of 45 mpa on day 28. ordinary portland cement, crushed aggregate from local source with maximum aggregate size of 14 mm, and natural river sand as fine aggregate were used in this work. crumb rubber was produced by grinding waste tires to produce the desired size in this study (0.15–2.36 mm). the properties of fine and coarse engineering, technology & applied science research vol. 7, no. 1, 2017, 1345-1352 1346 www.etasr.com abu bakar et al.: cumulative effect of crumb rubber and steel fiber on the flexural toughness of concrete aggregate and crumb rubber aggregate are listed in table i. figure 1 shows the recycled crumb rubber particles adapted for the experiments. steel fiber (hooked-end bundled) with aspect ratio of 80, circular diameter of 0.75 mm, specific gravity of 7.85, and tensile strength of 1050 mpa is used, as shown in figure 1. a polycarboxylic (ether-based) superplasticizer (sp) was used to enhance the low workability of the sfc mixtures. table i. properties of natural aggregate and crumb rubber type of aggregate specific gravity absorption% moisture content% fineness modulus specific area mm2/g coarse 2.65 1.0 1.0 6.27 na fine 2.64 2.0 3.0 3.93 0.672 rubber 0.73 10.6 1.4 na 0.774 fig. 1. crumb rubber and steel fiber. concrete mixtures were prepared with different replacement ratios of fine river sand volume by crumb rubber particles. the replacement ratios were 17.5%, 20%, and 22.5%, and the corresponding samples were designated as cr17.5, cr20, and cr22.5. the sfc mixture was considered a reference mix without crumb rubber. the volume fraction of the steel fiber was fixed (0.5%). rubberized steel fiber reinforced concrete mixtures were prepared by adding crumb rubber at the same replacement ratios for rubberized concrete (i.e., 17.5%, 20%, and 22.5%), and the corresponding samples were denoted as sfcr17.5, sfcr20, and sfcr22.5. plain (pc), steel fiber (sfc) concrete mixtures, and mix proportions are presented in table ii. other mixtures, such as rubberized and rubberized steel fiber. compositions of concrete mixes are presented in tables iii and iv, respectively. for all mixes water/cement ratio was fixed = 0.47. iii. experimental details and procedures a. compressive strength test compressive strength tests were conducted using three cubes with 100 mm sides in accordance with the british standard bs 1881: part 116 [10] on three cubic specimens for each mixture, using an oil hydraulic machine with a capacity of 3,000 kn. the compressive strength was calculated from the measured load over the area of the cube. b. four – point bending test four-point bending tests were carried out on the rubberized steel fiber beams to investigate the effect of combination between crumb rubber and steel fiber on the flexural performance of concrete. the flexural test setup and specimen geometry are illustrated in figure 2. three beams of each type of mixture were prepared for this test. the beams were 100 mm wide, 100 mm deep, and 400 mm long, with loaded span of 300 mm.the experimental setup is in accordance with astm c1609 [11]. the test was carried out using a 100 kn ag-x series shimadzu universal testing machine. the concrete specimens were loaded to ultimate failure under constant displacement rate at a loading rate of 0.1 mm/min. the loads versus mid-span deflection data were recorded, and the modulus of rupture (mor) was calculated. three specimens from each mixture were tested for 28 days. table ii. concrete mix design for plain and steel fiber mixtures mix cement steel fiber coarse aggregate fine aggregate pc 430 0 907 814 sfc 430 39 907 814 table iii. concrete mix design for rubberized mixtures mix cement coarse aggregate fine aggregate rubber cr17.5% 430 907 670 39.5 cr20% 430 907 649 45.3 table iv. concrete mix design for steel fiber reinforced rubberized mixtures mix cement steel fiber coarse aggregate fine aggregate rubber sfrc17.5% 430 39 907 670 39.5 sfrc20% 430 39 907 649 45.3 sfrc22.5% 430 39 907 630 50.3 fig. 2. test set-up for the four-point bending test. c. flexura test of slabs square slabs with dimensions of 500×500×50 mm were prepared to investigate their behavior under static loading. the tested slabs were fixed on the built-in testing machine after 28 days of moist curing (figure 3). slab specimens were placed on steel supports consisting of four rollers supported by four-sided rigid square steel hollow tubes. the span between the steel rollers was 430 mm (figure 4). the load was applied through a circular steel ram with a diameter of 100 mm adjusted to the centerline of the slab. the loading rate was 1.5 mm/min following the method presented in [12]. the test was stopped when the measured mid-span deflection of the concrete slabs reached approximately several millimeters. this test was engineering, technology & applied science research vol. 7, no. 1, 2017, 1345-1352 1347 www.etasr.com abu bakar et al.: cumulative effect of crumb rubber and steel fiber on the flexural toughness of concrete conducted to investigate the effect of combined steel fiber and crumb rubber on the static test results of slabs with different percentages of crumb rubber as green material with enhanced energy absorption capacity, as previously reported [7]. fig. 3. flexural test of concrete slabs. fig. 4. test set-up of the concrete slabs. iv. results and discussions a. compressive strength the results of the compressive strength tests of different concrete cubes for 28 days are presented in figure 5. the compressive strength decreased with the increase of crumb rubber ratio. the combined effect of steel fiber and crumb rubber limited this reduction. however, the tendency of a small amount of hooked-end steel fiber (0.5% by volume) to improve the compressive strength could be ignored. the compressive strengths of sfcr17.5, sfcr20, and sfcr22.5 were reduced by 21%, 25%, and 27%, respectively, compared with sfc. b. flexural behavior of beams the flexural performance of the concrete mixtures was assessed in terms of the first crack load, first crack strength, ultimate flexural load, ultimate flexural strength (mor), midspan deflection at maximum loads, flexural stiffness, and flexural toughness, according to the four-point bending test. the typical load–deflection curves of the different concrete mixtures with varying percentages of crumb rubber aggregate are shown in figures 6 (a) and (b). the averages of three fourpoint bending tests of loading and stresses for each batch are presented in table v. the load–deflection curves showed that the maximum load that can be sustained by the rubberized concrete is generally lower than that of non-rubberized concrete (whether with or without steel fiber). this reduction is similar to the results from the compressive loading tests. by contrast, the reduction rate in the flexural loads is smaller than that of the compressive loads. the curves for the rubberized concrete present a load–deflection capacity with the same shape. the load capacity declined with the increased content of crumb rubber aggregate in the concrete mix, but the increase in crumb rubber led to a more ductile behavior by increasing the deflections before failure. the shape of the curves for rubberized steel fiber concrete became less sharp than that of the original mix with only steel fiber. this result was also observed in [13], where it was reported that the crumb rubber does not affect the post-peak resistance capacity offered by the steel fiber. an enhancement of the deflection measured up to failure was obtained with the increase of rubber aggregate particles in the fibrous cement composites (table vi). maximum deflection was observed at 20% content of crumb rubber for plain concrete mixes. a similar trend was observed for the rubberized steel fiber concrete mixes. the increase in the deflection capacity at ultimate load, which is defined as the strain capacity [13], indicates an increase in the deformability of rubberized concrete. the cumulative effect of steel fiber and crumb rubber was confirmed through the enhanced ductility and reduced cracking caused by steel fiber [14]. therefore, additional restrain of cracks is provided by the presence of crumb rubber particles [15]. a similar trend was observed in the interaction between recycled and industrial steel fiber and rubber granulates [16]. according to astm c1018 [17], the first crack load is defined as the point on the load–deflection curve where the tendency of the curve changes from linear to nonlinear behavior, and the first crack deflection is the deflection value that is related to this load. the first crack strength was calculated based on the load obtained at first crack for different mixtures. the effect of crumb rubber incorporation on the first cracking strength is shown in figure 7(a). first cracking strength decreased by 18% because of the partial replacement of fine aggregate sand by recycled crumb rubber particles. the combined effect of steel fiber is to minimize the reduction in the first cracking strength. crumb rubber did not enhance the first crack deflection. the partial replacement of 20% of the fine aggregate with crumb rubber resulted in the 30% enhancement of the first cracking deflection compared with pc. this tendency could be attributed to the effect of crumb rubber, which could be neglected in the presence of hooked-end steel fiber with relatively high aspect ratio. figure 7(b) also shows that the crumb rubber content had an evident effect, that is, the ultimate strength of concrete (plain or fiber) decreased with the increase in rubber ratio. the reduction rate increased from 16% to 22% by partial substitution of fine aggregate with crumb rubber in steel fiber reinforced concrete. this trend of systematic reduction was reported because of the lack of pairing between the cement paste and the rubber aggregate [4]. flexural stiffness k was also determined from the flexural behavior of the concrete beams (table vi). k is presented as the linear part of the load–deflection curve of rubberized engineering, technology & applied science research vol. 7, no. 1, 2017, 1345-1352 1348 www.etasr.com abu bakar et al.: cumulative effect of crumb rubber and steel fiber on the flexural toughness of concrete concrete between 50% and 10% of the ultimate load [18, 19]. the reduction in stiffness of concrete indicates an increase in deformability, which facilitates the enhancement of the capacity of concrete sections to absorb more energy and exhibit better ductile behavior when subjected to high loading rate. toughness, which was determined by calculating the area under the load–deflection curves up to failure, was observed to be enhanced considerably in the presence of crumb rubber (table vi). the rates of increase were 28.8%, 31.1%, and 26.4% at 17.5%, 20%, and 22.5% crumb rubber content, respectively. these values indicate that the flexural toughness of rubberized concrete beam is sensitive to rubber ratio. toughness increases by increasing rubber content. further replacement of fine aggregate by crumb rubber reduced the toughness values. thus, optimum results were obtained at 20% (50.3 kg/m3). a similar trend was observed in [20] where the highest fracture energy value was recorded at 25% replacement of coarse aggregate by chipped tire rubber. reduced fracture energy was observed beyond this ratio. however, rubber aggregate improve the concrete deformability by reducing the local stresses occurred around the microcracks [3]. thus, a weakness occurred in the rubberized cement composite under loading, causing detrimental to the energy absorbed [20]. toughness values are also presented in table vi. it is clear that all rubberized steel fiber concrete mixes exhibited the highest toughness results compared with the other samples. the enhancement was due to the increase in the peak deflection capacity due to inclusion of rubber aggregate from waste tires in concrete. higher toughness generally offers an excellent property for civil engineering materials for sound barriers and paving constructions [21]. table v. results of flexural loads and strength of beams mix first crack load (n) ultimate flexural load (n) first crack strength (mpa) ultimate flexural strength (mpa) pc 15569 15569 4.60 4.60 sfc 15856 16684 4.75 4.95 cr17.5 12491 13275 3.74 3.92 cr20 12110 12933 3.63 3.81 cr22.5 11950 12671 3.58 3.75 sfcr17.5 13694 14030 4.11 4.15 sfcr20 13557 13752 4.06 4.13 sfcr22.5 12743 12925 3.82 3.87 table vi. deflections, stiffness and toughness of concrete beams under flexure mix first crack deflection (mm) maximum mid span deflection (mm) flexural stiffness (kn/mm) toughness (kn.mm) pc 1.07 1.07 14.18 7.048 sfc 0.80 1.41 19.45 16.032 cr17.5 1.35 1.51 9.05 9.086 cr20 1.40 1.55 8.87 9.243 cr22.5 1.39 1.54 8.69 8.913 sfcr17.5 0.81 1.80 17.21 20.576 sfcr20 0.82 1.83 16.91 21.343 sfcr22.5 0.83 1.78 15.94 20.331 20 25 30 35 40 45 50 0 17.5 20 22.5 c o m p re s s iv e s tr e n g th ( m p a ) crumb rubber ratio (%) plain steel fibre fig. 5. compressive strength results. (a) 0 2 4 6 8 10 12 14 16 18 0 0.5 1 1.5 2 f le x u ra l lo a d ( k n ) deflection (mm) sfc sfcr17.5 sfcr20 sfcr22.5 (b) 0 2 4 6 8 10 12 14 16 18 0 0.5 1 1.5 2 f le x u ra l lo a d ( k n ) deflection (mm) sfc sfcr17.5 sfcr20 sfcr22.5 fig. 6. load – deflection curves of beams (a) rubberized, (b) steel fiber rubberized concrete. c. flexural behavior of slabs table vii presents the average test results for slabs of each mixture. flexural test results of slabs are also presented as load–deflection curves in figures 8(a) to 8(h). all tested rubberized steel fiber concrete specimens had similar load– deflection trends with a linear branch until the ultimate load was reached and then a descending branch with softening in strain. scattering was observed in the descending branch, engineering, technology & applied science research vol. 7, no. 1, 2017, 1345-1352 1349 www.etasr.com abu bakar et al.: cumulative effect of crumb rubber and steel fiber on the flexural toughness of concrete which can be attributed to the distribution of fiber in the cracked portions at the post-peak load [8]. the curve for the rubberized steel fiber concrete slabs showed a higher descending slope than the plain rubberized slab because of the presence of steel fiber. the rubber aggregate increased the ultimate defection capacity up to a specified replacement ratio (20%). further increase in ratio resulted in lower values for the slope in the post-cracking phase. this phenomenon could be explained by the weakness in the matrix of slabs produced by further rubber replacement. the bridging effect of crumb rubber fiber is not provided at this stage. the increase in the concrete strength could lead to an increase in the energy absorption capacity [12]. however, rubberized mixes, with or without fiber reinforcement, exhibited reduced ultimate load and increased strain capacity [13]. moreover, rubber mixes tended to exhibit reduced elastic stage compared with pc or sfc slabs. this finding was also previously reported and attributed to the lower tangential elastic modulus of the rubbercrete slabs [22]. further studies on the combined effect of steel fiber and crumb rubber aggregate with long rubber fiber should be conducted. thus, the bridging action could be duplicated and the post-cracking deflection capacity could be enhanced. the rubber aggregate has a considerable effect on the toughness of concrete slabs (figures 9 a and b). table vii shows that the energy absorption capacity (toughness) of concrete slabs increased, with rates of increase of approximately 17%, 20%, and 15% at 17.5%, 20%, and 22.5% replacement ratios, respectively. a minimum of 15% enhancement of toughness was noted, although a decrease in toughness was observed beyond 20%. a similar trend was observed when crumb rubber was combined with steel fiber. the steel fiber with 0.5% crumb rubber provided the mixtures with initial enhancement of 14 times more than that of pc. further improvements in the toughness values were achieved by inclusion of crumb rubber. the rates of increase were approximately 16%, 19%, and 14% for the 17.5%, 20% and 22.5% slabs, respectively, compared with the sfc slabs. this property indicates that utilizing crumb rubber with steel fiber results in lower weight, higher toughness, and better energy absorption capacity before failure of concrete slabs. in [23], authors presented the combination of steel fiber and crumb rubber to produce layered concrete slabs subjected to impact force by replacing a specified portion of the steel fiber concrete thickness. the results obtained showed a reduction in weight and more energy dissipation in the rubberized steel fiber concrete plates, which acts as a cushion layer to reduce the effects of impact force. figure 10 (a) and (b) show adequate residual strengths for the four different mixtures, namely, sfc, sfcr17.5, sfcr20, and sfcr22.5, after the test because of the steel fiber that improved the ultimate flexural strength, energy absorption capacity, and ductility. an increase in the mid-span deflection with the increase in the crumb rubber ratio was also observed. this finding indicates enhanced flexural performance by improved results obtained from flexure test of concrete slabs ductility and energy absorption capacity for the concrete slabs (figure 11). table vii. results obtained from flexure test of concrete slabs mix ultimate load (kn) maximum deflection at middle (mm) toughness (kn.mm) pc 35.16 18.98 42.05 sfc 37.94 22.97 588.65 cr17.5 29.17 20.75 49.15 cr20 28.39 21.40 50.40 cr22.5 27.38 20.62 48.23 sfcr17.5 31.80 25.76 682.68 sfcr20 31.18 26.65 701.17 sfcr22.5 29.82 25.61 671.95 (a) (b) fig. 7. flexural strength at (a) first crack, and (b) ultimate strength. v. conclusions in the present study, concrete beams and slabs were prepared by combining hooked-end steel fiber with crumb rubber aggregate to produce a green innovative material with some desirable properties. the concrete beams, whether plain with crumb rubber or steel fiber with crumb rubber, were subjected to four-point bending load. the slabs were subjected to centre point load to investigate their flexural performance. slump and compressive strength tests were also conducted. the following conclusions were drawn: engineering, technology & applied science research vol. 7, no. 1, 2017, 1345-1352 1350 www.etasr.com abu bakar et al.: cumulative effect of crumb rubber and steel fiber on the flexural toughness of concrete (a) pc (b) cr17.5 (c) cr20 (d) cr22.5 (e) sfc (f) sfcr17.5 (g) sfcr20 (h) sfcr22.5 fig. 8. load – mid span deflection graphs for concrete slabs. engineering, technology & applied science research vol. 7, no. 1, 2017, 1345-1352 1351 www.etasr.com abu bakar et al.: cumulative effect of crumb rubber and steel fiber on the flexural toughness of concrete (a) 36 38 40 42 44 46 48 50 52 0 17.5 20 22.5 t o u g h n e s s ( k n .m m ) crumb rubbe r content % plain concrete (b) 500 550 600 650 700 750 0 17.5 20 22.5 t o u g h n e s s ( k n .m m ) crumb rubbe r content % steel fiber concrete fig. 9. effect of crumb rubber inclusion on toughness of concrete slabs (a) plain concrete, and (b) steel fiber concrete. • the compressive strength of all rubberized mixtures decreased with the increase in the partial substitution of crumb rubber aggregate in plain or steel fiber concrete. the loss of compressive strength values was not less than 20%. • the inclusion of crumb rubber into the concrete mixtures, with or without fiber, resulted in reduced flexural strength at first crack and ultimate failure for concrete beams under four-point bending load. • by contrast, toughness, which was determined by calculating the area under the load–deflection curves up to maximum deflection, improved significantly in the presence of crumb rubber. the optimum replacement ratio of sand aggregate by recycled crumb rubber aggregate was 20%. • all rubberized steel fiber reinforced concrete mixes exhibited the highest toughness values compared with the other samples in this study. the enhancements were due to the lower reduction in load and the increase in the ultimate deflection capacity. • the ultimate deflection values increased as the crumb rubber ratio increased. in addition, better flexural performance and improved concrete slab bendability before failure were observed when steel fiber was incorporated into the concrete mixture. • the post-cracking behavior of the rubberized concrete slabs could induce more ductile behavior with the increase in the waste tire crumb rubber aggregate ratio up to 20%. a significant increase in toughness of approximately 16 times was observed for the sfcr20 mixture compared with pc. • the experimental results showed a promising application of steel fiber/crumb rubber-reinforced concrete, which requires further studies. (a) (b) fig. 10. failure of concrete steel fiber rubberized concrete slabs under flexural loading. (a) top (sfcr22.5) (b) bottom (csfr22.5) fig. 11. failure of steel fiber rubberized concrete (sfcr22.5) engineering, technology & applied science research vol. 7, no. 1, 2017, 1345-1352 1352 www.etasr.com abu bakar et al.: cumulative effect of crumb rubber and steel fiber on the flexural toughness of concrete acknowledgements the work presented herein was funded by the universiti sains malaysia grant (cluster for polymer composite: 1001/pkt/8640013). references [1] h. toutanji, “the use of rubber tire particles in concrete to replace mineral aggregates”, cem. conc. comp., vol. 18, no. 2, pp. 135-139, 1996 [2] z. ismail, e. al-hashmi, “use of waste plastic in concrete mixture as aggregate replacement”, waste management, vo. 28, no. 11, pp. 20412047, 2008 [3] c. wang, y. zhang, z. zhao, “fracture process of rubberized concrete by fictitious crack model and ae monitoring”, comp. concrete, vo. 9, no. 1, pp. 51-61, 2012 [4] e. ganjian, m. khorami, a. maghsoudi, “scrap-tyre-rubber replacement for aggregate and filler in concrete”, const. build. mats., vo. 23, no. 5, pp. 1828-1836, 2009 [5] m. bekhiti, h. trouzine, a. asroun, “properties of waste tire rubber powder”, eng. technol. appl. sci. res., vol. 4, no. 4, pp. 669-672, 2014 [6] k. najim, m. hall, “workability and mechanical properties of crumbrubber concrete”, proc. of the ice – const. mats., vol. 166, no. 1, pp. 7-17, 2013 [7] j. xue, m. shinozuka, “rubberized concrete: a green structural material with enhanced energy-dissipation capability”, const. build. mats., vo. 42, pp. 196-204, 2013 [8] g. centonze, m. leone, m. aiello, “steel fibers from waste tires as reinforcement in concrete: a mechanical characterization”, const. build. mats., vo. 36, pp. 46-57, 2012 [9] d. flores-medina, n. flores medina, f. hernández-olivares, “static mechanical properties of waste rests of recycled rubber and high quality recycled rubber from crumbed tyres used as aggregate in dry consistency concretes”, materials struct., vol. 47, no. 7, pp.1185-1193, 2013 [10] british standards institute (bs), method for determination of compressive strength of concrete cubes, bs 1881:116, london, 1983 [11] american society for testing and materials (astm), standard test method for flexural performance of fiber-reinforced concrete (using beam with third-point loading), astm c1609-12, astm international, west conshohocken, pa, 2012 [12] a. khaloo, m. afshari, “flexural behaviour of small steel fiber reinforced concrete slabs”, cem. and concrete comp., vo. 27, no. 1, pp. 141-149, 2005 [13] a. turatsinze, j. granju, s. bonnet, “positive synergy between steelfibers and rubber aggregates: effect on the resistance of cement-based mortars to shrinkage cracking”, cem. conc. resch., vol. 36, no. 9, pp. 1692-1697, 2006 [14] r. olivito, f. zuccarello, “an experimental study on the tensile strength of steel fiber reinforced concrete”, composite part b: eng., vol. 41, no. 3, pp. 246-255, 2010 [15] a. turatsinze, s. bonnet, j. granju, “mechanical characterisation of cement-based mortar incorporating rubber aggregates from recycled worn tyres”, build. envt., vol. 40, no. 2, pp. 221-226, 2005. [16] d. bjegovic, a. baricevic, s. lakusic, d. damjanovic, i. duvnjak, “positive interaction of industrial and recycled steel fibers in fiber reinforced concrete”, j. of civil eng. manag., vo. 19, (sup1), pp. 50-60, 2013 [17] american society for testing and materials (astm), standard test method for flexural toughness and first-crack strength of fiber-reinforced concrete (using beam with third-point loading), astm c1018-97, astm international, west conshohocken, pa, 1997 [18] a. turatsinze, m. garros, “on the modulus of elasticity and strain capacity of self-compacting concrete incorporating rubber aggregates”, res. conserv. recy., vol. 52, no. 10, pp. 1209-1215, 2008 [19] k. najim, m. hall, “mechanical and dynamic properties of selfcompacting crumb rubber modified concrete”, const. build. mats., vol. 27, no. 1, pp. 521-530, 2012 [20] m. reda taha, a. el-dieb, m. abd el-wahab, m. abdel-hameed, “mechanical, fracture, and microstructural investigations of rubber concrete”, j. of materials in civil eng., vol. 20, no. 10, pp. 640-649, 2008 [21] t. c. ling, “effects of compaction method and rubber content on the properties of concrete paving blocks”, const. build. mats., vol. 28, no. 1, pp. 164-175, 2012 [22] b. mohammed, “structural behavior and m–k value of composite slab utilizing concrete containing crumb rubber”, const. build. mats., vol. 24, no. 7, pp. 1214-1221, 2010 [23] p. sukontasukkul, s. jamnam, m. sappakittipakorn, n. banthia, “preliminary study on bullet resistance of double-layer concrete panel made of rubberized and steel fiber reinforced concrete”, materials struct., vol. 47, no. (1-2), pp. 117-125, 2013 microsoft word 17-3578_s_etasr_v10_n5_pp6237-6241 engineering, technology & applied science research vol. 10, no. 5, 2020, 6237-6241 6237 www.etasr.com mubarak: effect of carrier phase on gps multipath tracking error the effect of carrier phase on gps multipath tracking error omer mohsin mubarak department of electrical engineering jouf university saudi arabia ommubarak@ju.edu.sa abstract—multipath is one of the main sources of tracking error in gps receivers. this tracking error has previously been analyzed against the relative delay of the line of sight (los) and reflected signals. however, only carrier phase differences of 0 and π were used, since they give tracking error with maximum magnitude. this paper shows that tracking error does not change linearly with changing carrier phase difference. tracking error plots against relative carrier phase difference of the los and reflected signals have been used to analyze the relationship between the two in various scenarios. while maximum positive and negative errors are found at carrier phase difference of 0 and π, a sharp increase in tracking error is found around the phase difference of π. there is a zero crossing in all plots but that point is dependent on relative amplitude, delay, and carrier phase difference of the two signals. the analysis has also been extended to narrow correlators receiver. tracking error is significantly reduced in this case, however, similar characteristics have been observed when the tracking error is analyzed against the relative carrier phase difference. moreover, the tracking error was found to be less dependent on the relative delay between the two signals when correlators spacing is reduced. keywords-multipath; global navigation satellite system; global positioning system; carrier phase; tracking error i. introduction the reflection of the line of sight (los) satellite signal from nearby objects, also known as multipath, causes tracking errors in the global positioning system (gps) receivers [1-3]. tracking errors caused by multipath can be positive or negative and depend on relative amplitude, carrier phase, and code delay of the reflected signal with respect to the los signal [4]. a plot of maximum positive and maximum negative code tracking errors against relative delay of a reflected signal is called as the multipath error envelope and is generally used to represent error characteristics [5-7] and effects of mitigation techniques [8-9]. it shows the maximum deviation in tracking error that can be caused by variations of carrier phase difference between the los and the reflected signals for a given relative amplitude and code delay between the two signals. two maximums are obtained for relative carrier phase differences of 0 and π radians. however, the error envelope does not provide details of how tracking error is changed when the carrier phase difference between the two signals changes from 0 to π or vice versa. this paper analyzes the effect of carrier phase difference between the los and the reflected signals on multipath tracking error. ii. experimental setup in a gps receiver, correlators are placed on the correlation function to track the code phase of a received gps signal. typically, three correlators are used, one at the prompt or on time correlation position and other two (early and late) symmetrically placed on either side [7, 10]. early and late correlators use equally advanced and delayed versions of prompt code respectively, such that for a triangular correlation function their equal energy implies that prompt correlator tracks the peak. equal energy is ensured using a discriminator function, which in simplest form is the difference in energy of the two. tracking loops adjust local code and carrier, aiming to maintain discriminator output to zero. in the presence of a reflected signal, the correlation function shape is distorted. in this case, even with zero output of discriminator function, prompt correlator code is not aligned with received signal, resulting in tracking error [2]. in this paper, a perfect triangular function v(t) is used as an autocorrelation function for determining tracking error. the counterfeit signal is given as scaled, phased and delayed version of v(t). the received signal g(t) is then given as the sum of the los and counterfeit signal by: ���� = ���� + ����� − �� (1) where , � and � are respectively the relative amplitude, the carrier phase difference, and the delay of the counterfeit signal with respect to los. the discriminator function is given by: ��� = ������� ∗��� − ������� ∗��� (2) where dl and de are given by (3) and (4) respectively. ����� = ��� + ��+ ����� + � − �� (3) ����� = ��� − �� + ����� −� − �� (4) where � is the correlator spacing between early and prompt, or prompt and late correlators. wide correlators, i.e. with 1 chip spacing between early and late correlators (�=0.5 chips), are used in this paper, except in section v. corresponding author: omer mohsin mubarak engineering, technology & applied science research vol. 10, no. 5, 2020, 6237-6241 6238 www.etasr.com mubarak: effect of carrier phase on gps multipath tracking error iii. motivation figure 1 shows the tracking error for a multipath signal with relative amplitude of 0.5 and carrier phase offsets (φ) of 0, π/4, π/2, 3π/4, and π, with respect to the los signal. relative amplitude of 0.5 implies that reflected signal is of half amplitude than the los signal and φ=0 implies that the reflected signal is in-phase with the los signal. the tracking error is zero in all cases for reflected signal delay of over 1.5 chips. plots confirm that maximum error magnitude is obtained when the reflected signal is in-phase or completely out of phase (φ=π) with the los signal. however, it can also be noted that plots are not uniformly spaced as phase difference is increased by π/4. for example, plots for φ=0 and φ=π/4 are much closer as compared to the plots for φ=π/4 and φ=π/2, although in both cases the difference in phase is π/4. fig. 1. tracking error plot against signal’s relative delay for a multipath signal with relative amplitude of 0.5 and varying carrier phase offsets (φ) with respect to the los signal. similar patterns are observed for other relative amplitudes of multipath signal with respect to the los signal. figures 2 and 3 show the tracking errors for a multipath signal with relative amplitude of 0.3 and 0.8 respectively. it can be observed that the overall error magnitude is smaller for relative amplitude of 0.3 and higher for relative amplitude of 0.8, as compared to figure 1. however, similar to figure 1, the plots in both figures are not uniformly spaced as phase difference is increased by π/4. fig. 2. tracking error plot against signal’s relative delay for a multipath signal with relative amplitude of 0.3 and varying carrier phase offsets (φ) with respect to the los signal. non-linear change in tracking error with changing carrier phase difference provided motivation to explore the effect of phase difference between the los and reflected signals on tracking error. fig. 3. tracking error plot against signal’s relative delay for a multipath signal with relative amplitude of 0.8 and varying carrier phase offsets (φ) with respect to the los signal. iv. tracking error analysis this section analyzes the changes in tracking error with changing carrier phase difference between the los and reflected signals. figures 4-6 show the tracking error plots against relative carrier phase difference of the los and reflected signals, with relative amplitudes of 0.3, 0.5, and 0.8. respectively. fig. 4. tracking error plot against signal’s relative phase difference for a multipath signal with relative amplitude of 0.3 and varying multipath signal delay (d) with respect to the los signal. fig. 5. tracking error plot against signal’s relative phase difference for a multipath signal with relative amplitude of 0.5 and varying multipath signal delay (d) with respect to the los signal. the following can be observed from these plots: • it is confirmed that for a given relative amplitude and delay between signals, the maximum positive error is obtained for φ=0 and the maximum negative error is obtained for φ=π, in all cases. engineering, technology & applied science research vol. 10, no. 5, 2020, 6237-6241 6239 www.etasr.com mubarak: effect of carrier phase on gps multipath tracking error • the change in tracking error with increasing carrier phase difference is non-linear for all cases. • there is a sharp increase in tracking error around φ=π for all cases. • there is no single phase difference which can give zero tracking error in all cases, since zero crossing for each plot is different. zero crossing of a plot is dependent on all three parameters, i.e. relative amplitude, delay, and carrier phase difference between the los and reflected signals. • figure 4 plots have the least variation in tracking error as phase difference is changed from 0 to π radians. this implies that the dependence of the tracking error on carrier phase difference is higher for higher relative amplitudes of the reflected signal. fig. 6. tracking error plot against signal’s relative phase difference for a multipath signal with relative amplitude of 0.8 and varying multipath signal delay (d) with respect to the los signal. v. tracking error with narrow correlator the previous analysis has used wide correlators, i.e. 1 chip spacing between early and late correlator of a receiver. reduced spacing of 0.1 chip between early and late correlators, termed as the narrow correlator, has been used for mitigating the tracking error caused by multipath for various global navigation satellite signals [8, 11-13]. this can be confirmed from figure 7, which shows the tracking error with reflected signal relative amplitude of 0.5 using a narrow correlator. fig. 7. tracking error plot against signal’s relative delay for a multipath signal with relative amplitude of 0.5 and varying carrier phase offsets (φ) with respect to the los signal, using narrow correlators in receiver. comparing this with figure 1, it can be seen that the tracking error has been significantly reduced. the tracking error is zero when separation between the los and reflected signals is more than 1.05 chips, instead of 1.5 chips in figure 1. the maximum tracking error is 0.025 chips instead of 0.25 chips obtained with wide correlators. similarly, reduced error can be observed in figures 8-9, as compared with similar relative amplitude plots in figures 2-3 respectively. it can again be noted that the plots in figures 7-9 are not uniformly spaced. similar to wide correlators, plots for φ=0 and φ=π/4 are much closer than the plots for φ=π/4 and φ=π/2, although in both cases the difference in phase is π/4. therefore, the change in tracking error against carrier phase difference is analysed in this section for a narrow correlator receiver. fig. 8. tracking error plot against signal’s relative delay for a multipath signal with relative amplitude of 0.3 and varying carrier phase offsets (φ) with respect to the los signal, using narrow correlators in receiver. fig. 9. tracking error plot against signal’s relative delay for a multipath signal with relative amplitude of 0.8 and varying carrier phase offsets (φ) with respect to the los signal, using narrow correlators in receiver. figures 10-12 show tracking error plots against relative carrier phase difference of the los and reflected signals using narrow correlators in a receiver, with relative amplitudes of 0.3, 0.5, and 0.8 respectively. all the 5 observations noted in the previous section for wide correlators, are also valid for these narrow correlator based plots. moreover, out of delays of 0.25, 0.5, 0.75, 1, and 1.25 chips, the 1.25 chips plot stays at zero in all the 3 figures, as the reflected signal delay of over 1.05 chips gives zero tracking error irrespective of the relative amplitude and carrier phase difference of the reflected signal with respect to the los signal. it can also be noted that plots are much closer as compared to the plots obtained using wide correlators for the same relative amplitude. for example, the plots in figure 10 are much closely spaced as compared to the plots in figure 4, although both are obtained for relative amplitude of 0.3 and the same set of relative delays. engineering, technology & applied science research vol. 10, no. 5, 2020, 6237-6241 6240 www.etasr.com mubarak: effect of carrier phase on gps multipath tracking error fig. 10. tracking error plot against signal’s relative phase difference for a multipath signal with relative amplitude of 0.3 and varying multipath signal delay (d) with respect to the los signal, using narrow correlators in receiver. fig. 11. tracking error plot against signal’s relative phase difference for a multipath signal with relative amplitude of 0.5 and varying multipath signal delay (d) with respect to the los signal, using narrow correlators in receiver. fig. 12. tracking error plot against signal’s relative phase difference for a multipath signal with relative amplitude of 0.8 and varying multipath signal delay (d) with respect to the los signal, using narrow correlators in receiver. vi. conclusion multipath is a source of tracking error in gps receivers, which leads to positioning errors [3, 14-17]. multipath error envelopes have been used to analyze tracking error caused by multipath [5-9]. however, they only provide maximum positive and negative error for a given relative amplitude and code delay between the two signals. two maximums are obtained for relative carrier phase differences of 0 and π radians, whereas the tracking error for relative carrier phase differences between 0 and π radians has not been explored earlier. this paper has analyzed the tracking error caused by multipath and specifically the effect of carrier phase on error. tracking error plots against relative carrier phase difference of the los and reflected signals have been used instead of conventional tracking error plots against relative delay of the two signals. this novel analysis confirmed that maximum positive and negative errors are obtained for φ=0 and φ=π respectively. it has also been observed that change in tracking error with increasing carrier phase difference is non-linear and the error increases sharply around φ=π. the zero crossing of a tracking error plot is found to be dependent on relative amplitude, delay and carrier phase difference between the los and the reflected signals, i.e. there is no single carrier phase difference between the two signals which gives zero tracking error. moreover, the dependence of tracking error on carrier phase difference is found to be higher for higher relative amplitude of the reflected signal. tracking error has also been analyzed for a receiver using narrow correlators, which are generally used to reduce the tracking error caused by multipath. the spacing between early and late correlators was reduced to 0.1 chip, instead of 1 chip in wide correlators. as a result, maximum tracking error reduced to 0.025 chips instead of 0.25 chips. moreover, tracking error is zero when the separation between the los and reflected signals is more than 1.05 chips, instead of 1.5 chips for wide correlator receivers. characteristics observed for tracking error using wide correlators are also found to be valid when narrow correlators were used. moreover, the plots for different multipath signal delays are found to be much closer as compared to the plots obtained using wide correlators for the same set of signal parameters. this implies that the tracking error is less dependent on relative delay between the two signals when narrow correlators are used. these findings can be useful for finding better estimates of tracking error in a gps receiver for multipath with given relative amplitude, carrier phase difference, and delay between the two signals. references [1] x. chen and f. dovis, “enhanced cadll structure for multipath mitigation in urban scenarios,” in proceedings of the 2011 international technical meeting of the institute of navigation, san diego, ca, 2011, pp. 678–686. [2] o. m. mubarak and a. dempster, “carrier phase analysis to mitigate multipath effect,” presented at the ignss symposium 2007, the university of new south wales, sydney, australia, dec. 2007. [3] o. m. mubarak and a. g. dempster, “exclusion of multipath-affected satellites using early late phase,” journal of global positioning systems, vol. 9, no. 2, pp. 145–155, 2010. [4] k. yedukondalu, a. d. sarma, and v. s. srinivas, “estimation and mitigation of gps multipath interference using adaptive filtering,” progress in electromagnetics research m, vol. 21, pp. 133–148, 2011, doi: 10.2528/pierm11080811. [5] t. g. ferreira and f. d. nunes, “advanced multipath mitigation techniques for gnss receivers,” presented at the 1st seminar of the portuguese committee, lisbon, portugal, nov. 2007. [6] o. m. mubarak and a. g. dempster, “analysis of early late phase in single-and dual-frequency gps receivers for multipath detection,” gps solutions, vol. 14, no. 4, pp. 381–388, sep. 2010, doi: 10.1007/s10291010-0162-z. [7] a. pirsiavash, a. broumandan, and g. lachapelle, “characterization of signal quality monitoring techniques for multipath detection in gnss applications,” sensors (basel, switzerland), vol. 17, no. 7, jul. 2017, doi: 10.3390/s17071579. engineering, technology & applied science research vol. 10, no. 5, 2020, 6237-6241 6241 www.etasr.com mubarak: effect of carrier phase on gps multipath tracking error [8] a. j. v. dierendonck, p. fenton, and t. ford, “theory and performance of narrow correlator spacing in a gps receiver,” navigation, vol. 39, no. 3, pp. 265–283, 1992, doi: 10.1002/j.2161-4296.1992.tb02276.x. [9] a. pirsiavash, a. broumandan, and g. lachapelle, “performance evaluation of signal quality monitoring techniques for gnss multipath detection and mitigation,” presented at the international technical symposium on navigation and timing (itsnt), toulouse, france, nov. 2017. [10] e. d. kaplan, understanding gps: principles and applications, second edition, 2nd edition. bs: artech house, 2005. [11] m. e. cannon, g. lachapelle, w. qiu, s. l. frodge, and b. remondi, “performance analysis of a narrow correlator spacing receiver for precise static gps positioning,” in proceedings of 1994 ieee position, location and navigation symposium plans’94, apr. 1994, pp. 355–360, doi: 10.1109/plans.1994.303337. [12] z. xuefen, c. xiyuan, and c. xin, “comparison between strobe correlator and narrow correlator on mboc dll tracking loop,” in 2011 ieee international instrumentation and measurement technology conference, may 2011, pp. 1–4, doi: 10.1109/imtc.2011.5944083. [13] j. h. lee et al., “a gps multipath mitigation technique using correlators with variable chip spacing,” e3s web of conferences, vol. 94, 2019, doi: 10.1051/e3sconf/20199403006, art. no. 03006. [14] m. orabi, j. khalife, a. a. abdallah, z. m. kassas, and s. s. saab, “a machine learning approach for gps code phase estimation in multipath environments,” in 2020 ieee/ion position, location and navigation symposium (plans), apr. 2020, pp. 1224–1229, doi: 10.1109/plans46316.2020.9110155. [15] t. kos, i. markezic, and j. pokrajcic, “effects of multipath reception on gps positioning performance,” presented at the elmar-2010, zadar, croatia, sep. 2010. [16] i. rumora, n. sikirica, and r. filjar, “an experimental identification of multipath effect in gps positioning error,” transnav, international journal on marine navigation and safety od sea transportation, vol. 12, no. 1, pp. 29–32, mar. 2018, doi: 10.12716/1001.12.01.02. [17] t. l. dammalage, “the effect of multipath on single frequency c/a code based gps positioning,” engineering, technology & applied science research, vol. 8, no. 4, pp. 3270–3275, aug. 2018. author’s profile omer mohsin mubarak received the b.s. in electronics engineering from the ghulam ishaq khan institute of engineering sciences & technology, pakistan, and the m.e. and ph.d. degrees from the university of new south wales, australia in 2006 and 2010 respectively. from 2013 to 2016, he was with iqra university, pakistan and during this period he served as head of the electronics engineering department and head of computing & technology department. he is currently working as an assistant professor at jouf university, saudi arabia. his research interests include multipath mitigation, spoofing detection and other signal processing techniques for gnss receivers. he is a senior member of ieee, usa. microsoft word 27-2923_s_etasr_v9_n4_pp4463-4468 engineering, technology & applied science research vol. 9, no. 4, 2019, 4463-4468 4463 www.etasr.com manig et al.: crack pattern investigation in the structural members of a framed two-story building … crack pattern investigation in the structural members of a framed two-floor building due to excavationinduced ground movement naeem mangi department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan naeem08ce30@gmail.com dildar ali mangnejo department of civil engineering, mehran university of engineering & technology, shaheed zulfiqar ali bhutto campus, khairpur mir’s, pakistan dildarali72@gmail.com hemu karira department of civil engineering, mehran university of engineering & technology, shaheed zulfiqar ali bhutto campus, khairpur mir’s, pakistan engr.hemu07civil@gmail.com m. kumar department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan manojbhoopani475@gmail.com ashfaque ahmed jhatial department of civil engineering, mehran university of engineering & technology, shaheed zulfiqar ali bhutto campus, khairpur mir’s, pakistan ashfaqueahmed@muetkhp.edu.pk f. r. lakhair department of civil engineering, mehran university of engineering & technology, shaheed zulfiqar ali bhutto campus, khairpur mir’s, pakistan faisallakhair722@gmail.com abstract—increased urbanization causes traffic and parking issues especially in metropolitan cities like karachi, london, shanghai, etc. to accommodate parking issues for the vehicles mainly in urban areas (excavated) underground parking areas under or nearby high rise buildings are preferred. as a result of excavation, ground movements occur that have major impact on structures, buildings and utilities. the past research usually oversimplified surface structure as an equivalent elastic beam, which is unable to represent the behavior of a framed building realistically. in this study, the detrimental effects (i.e. crack pattern) on a two floor rcc framed building founded on piles due to an adjacent excavation-induced ground movement are investigated. elasto-plastic coupled-consolidation analysis was adopted. the hypoplastic constitutive model was used to capture soil behavior. it is an advanced model which is able to capture the soil unique features which are non-linear behavior, stiffness degradation (with stress, strain & path dependent), and stressstrain dependent soil dilatancy. the concrete damaged plasticity (cdp) model was used to capture the cracking behavior in the concrete beams, columns and piles. it was revealed that the induced slope and tilting are not equal. consequently, the frame was distorted. as a result, tension cracks were induced at the inner side of the column. keywords-excavation; rcc framed building; crack pattern i. introduction high rise building load is transferred to the surrounding soil through pile foundations. as a result, high stress regime is generated around the pile [1]. on the other hand, ground excavations result in ground movement due to induced-stress release [2]. with the increase in population, urbanization is also increasing, causing traffic and parking issues, especially in metropolitan cities. to accommodate parking issues, mainly in urban areas, excavations under or nearby high rise buildings are preferred. as a result, ground movements occur that have major impact on nearby structures [3]. excavations carried out near a building may cause its distortion, affect pile foundation or even cause collapse. it is important for a geotechnical engineer to assess these dangerous situations when an excavation is carried out nearby a building. to cope with parking issues on congested cities, underground transportation systems (underground parking) have been developed. these excavations are sometimes unavoidable to be constructed adjacent to existing buildings. this condition leads to the challenge of assessing and protecting the integrity of the framed building. authors in [3] investigated the damage mechanism and behavior of a framed building, on shallow foundation with separate footing and different infill configuration, due to tunnelling induced ground movements, by carrying out a series of numerical analyses. they concluded that the sensitive performance of a framed building on stiffer ground is more than that on softer ground. besides that, the infill configuration plays a significant role in the performance of a framed building. when infill walls are subjected to tunnelling caused ground movements, the structure distortion is significantly reduced. authors in [4] investigated the effects of selected geotechnical and structural parameters on the response of masonry buildings subjected to tunnelling induced settlements. a sensitivity study has been carried out to determine the influence of building cracking and soil structure interface parameters. it was concluded that the high dependency of the corresponding author: naeem mangi engineering, technology & applied science research vol. 9, no. 4, 2019, 4463-4468 4464 www.etasr.com manig et al.: crack pattern investigation in the structural members of a framed two-story building … structural response on the soil structure interface stiffness and material cracking suggests that this model could be used in extensive parametric analyses to improve the existing damage design curves. authors in [1] carried out a sensitivity study on a 2d finite element model that was validated by comparing experimental results. the study investigated the effects of building weight, openings, initial damage, material properties, applied settlement profile and normal and shear behavior of base interface. the results assessed the major role played by the normal stiffness of the soil structure and the quasi brittle masonry behavior. the results showed the high dependency of the final damage to soil–structure interaction and on material cracking. authors in [5-8, 27] reported that existing buildings affect tunnelling induced ground movement profile in a similar way as induced settlement tunnelling impacts existing adjacent buildings. authors in [9] compared the response of different types of buildings founded on shallow foundation, which are subjected to excavation induced ground settlement, and provided a better understanding of the complex soil structure interaction in the building response. authors in [10] suggested estimating the stiffness of framed building by simply adding separate bending stiffness of all the floor slabs. authors in [11] carried out three centrifuge tests which were performed to study the effects of a multi propped deep excavation on the behavior of piles in dry toyoura sand. it was concluded that lateral restraints imposed on pile head have a significant influence on the induced pile bending moment which can exceed the pile bending capacity. authors in [12] proposed an analytical method to evaluate the reduction of capacity and increase in settlement of a nearby pile during excavation. the pile settlement due to excavation depends on the shaft friction of the pile and the soil movement pattern. authors in [13] studied the lateral response of a pile group using a finite element method and concluded that pile bending moment and lateral deformation increase significantly with increase in excavation depth. authors in [29, 32] developed design charts for the computation of the lateral behaviour of a single pile existing nearby a deep excavation in soft ground. before carrying out the multi-strutted deep excavation, the numerical model and its soil parameters were calibrated by using the centrifuge test results and the triaxial tests reported in [15, 18]. the aim of this study is to give an insight into the tilting behavior and settlement of a pile group by making changes in pile length, excavation depth, supporting system stiffness, pile group distance from the excavation, permeability, initial working load, and soil state. in addition to that, the continuous changes in excess pore water pressure and long term settlement of the pile group having different positions of pile toe relative to the final exaction level are studied. authors in [17] found that the maximum apparent earth pressure for the upper 10% of height exceeded the trapezoidal boundary of the apparent earth pressure diagrams for both soft clay and stiff clay that were initially proposed. no significant difference among the apparent earth pressure values of excavation supported by wall of different stiffness was found. authors in [11] carried out field studies on a 10m deep multi-propped excavation in overconsolidated and fissured gault clay comparing measured and peck’s earth pressure. the measured values were near to the lower bound of peck’s chart. the strut load of the lowest prop was found to be smaller to some extent due to the low lateral stress in the ground following the construction of the diaphragm wall. authors in [17] studied numerically a case where the clear distance between piles and the 0.8m thick diaphragm wall was 3m. there was reasonable agreement between the measured and predicted results regarding the location of maximum deflection and bending moment. authors in [28] concluded that computed bending moments in the steptapered piles based on upper-bound finite element results were smaller than their moment capacity, indicating that the actual moments in the piles were not large enough to cause cracking. apart from field monitoring, this problem has been investigated by means of centrifuge modeling in soft kaolin clay [18]. authors concluded that the distance between pile and diaphragm wall is an important parameter which plays a major role on generated bending moment in the pile. in the presence of initial applied load, the soil surrounding the pile foundation experiences higher stress level before the starting of adjacent excavation. the excavation induced stress released in the ground induced bending moment and settlement. continuum numerical methods using finite-element computer programs offer powerful tools to model complex construction processes, including deep excavations. the ability to predict excavation-induced ground movements reliably, however, is wholly dictated by the input of representative parameters for the soil and the other structural components of the excavation [6, 8]. existing numerical codes are extremely demanding of such prior information. a practical alternative to complement numerical analysis is to discover mechanisms of behavior by means of model tests and to use them to understand the performance of buildings when subjected to excavation-induced deformations. in order to observe these mechanisms, authors in [24, 25] studied small-scale models tested in a 8m diameter geotechnical centrifuge machine at the cambridge university. the aim of these centrifuge tests was to simulate the excavation-soil-building interaction and to understand the mechanisms involved, rather than modeling a specific prototype. therefore, it was decided to use sand for all the centrifuge tests due to the significantly smaller time required in preparation before testing compared to clay. an excavation system, which adopted a new technique for simulating the excavation process in-flight, was developed to investigate the interaction between soil and model buildings. the test results provided new insight into the fundamental mechanisms involved. in this paper, a detailed description of the centrifuge models (and associated test procedures) is presented followed by presentation of results from two key centrifuge tests. most of the previous research was focused on the damaging effects to structures founded on shallow foundation due to excavation. surface structures were usually oversimplified as equivalent elastic beams, which does not represent the behavior of a framed building realistically. the damaging effects on piles due to excavation were rarely reported. structural components such as piles, beams and columns were assumed as elastic. so, the main objective of this study is to estimate the crack patterns induced in the structural members due to adjacent excavation. to achieve this, three-dimensional finite element analysis (i.e. coupled consolidation parametric study) engineering, technology & applied science research vol. 9, no. 4, 2019, 4463-4468 4465 www.etasr.com manig et al.: crack pattern investigation in the structural members of a framed two-story building … was conducted. the angular distortion and crack pattern in the framed building are reported and discussed. ii. three-d coupled consolidation analysis a. exacavation description the 12m deep exaction is carried out nearby a building at a vertical interval of 3m. a diaphragm wall having depth of 18m with 0.6m is used to support the soil mass on the excavation side. the clear distance between diaphragm and an adjacent pile is kept 3m. the wall penetration depth to excavation depth ratio is typically 0.5 to 2 [22], so a value of 0.5 is taken in this study. props are used at the vertical interval of 3m along the excavated soil mass to support the diaphragm wall. the props are modeled with axial rigidity of 81×103knm [17]. the horizontal spacing of props is 8m. figure 1 illustrates the geometry of a typical case with excavation depth of 12m. fig. 1. geometry of the problem adopted in this study b. finite element mesh and boundary conditions figure 2 describes the finite element mesh used in this case with size of 20m×25m×22m. in this three dimensional parametric study, solid elements (with 8-node trilinear continuum) were used to model soil, pile and diaphragm wall. solid continuum elements are small material blocks. they can be used to build models of nearly any shape subjected to different loading because they are connected to each other like bricks in a building or tiles in a mosaic. each node of a solid continuum element has three degrees of freedom for describing displacements in x, y and z directions and one degree of freedom for taking pore pressure into account. the props were modeled by using truss elements which are long, slender structural members that can transmit only axial force but cannot transmit moment. each truss element node has two degrees of freedom, one for displacement and one for rotation. to restrain the horizontal and vertical movement of sides, roller supports were applied. the base of the mesh was restrained in every direction by applying pin/fix supports on it. the ground water table level was taken at ground surface. at geostatic state, pore pressure distribution was taken as hydrostatic. the top of the mesh was considered drainage boundary. the frictional interface was taken between pile and soil and wall and soil. the interface was modeled by the coulomb’s friction law, in which the interface friction coefficient (µ) and limiting displacement (γlim) are the input parameters. ιnterface friction coefficient of 0.35 and limiting shear displacement of 5mm were assumed to achieve full mobilisation of the interface friction [19]. excavation was carried out by deactivating soil elements within the zone of excavation. activation of truss elements procedure was adopted for prop installation on the wall. fig. 2. finite element mesh and boundary conditions c. constitutive model and its parameters’ hypoplastic model a hypoplastic constitutive model was used to capture soil behavior. it is an advanced model which is able to capture the unique features of soil as non-linear behavior, degradation of stiffness and stress-strain dependent dilatancy of soil. basically nonlinear behavior within the range of strain level of medium to large (due to monotonic loading) of the granular material is captured by using the basic hypoplastic model [20-22]. there are five parameters ��,λ∗,κ∗,ϕ�and required for the basic model. the parameters n and λ * control the normal compression line location and its slope in ln�1 � �� vs ln� ′ diagram. similarly, the parameter κ * is used to regulate the slope of the unloading line. the value of r is responsible for controlling the large shear strain modulus. the critical state friction angle is represented by φc. authors in [31] further implemented the concept of intergranular strain to improve the basic hypoplastic model. moreover, five additional parameters (required by the intergranular strain) were included into the basic model for considering the strain and path dependency of soil stiffness: r, βγ, χ, mt and mr. βγ and χ determine the rate of stiffness degradation and r is an elastic range. ko (coefficient of lateral earth pressure at rest) was calculated by jaky’s equation: k� � �1 � sinφ �� (1) 3.0 m formation level excavation depth (he) = 12 m wall penetration ratio = 0.5 prop 1 (1.0 m) prop 2 (4.0 m) prop 3 (7.0 m) prop 4 (10.0 m) diaphragm wall thickness = 0.6 m depth = 18.0 m clay single piles length = 18.0 m diameter = 0.8 m plinth beam gf columns ff beam gf beam ff columns engineering, technology & applied science research vol. 9, no. 4, 2019, 4463-4468 4466 www.etasr.com manig et al.: crack pattern investigation in the structural members of a framed two-story building … hypoplastic clay model parameters are given in table i. table i. hypoplastic model parameters description value critical state angle, φ΄ 22 o slope of normal compression line, λ* 0.11 slope of unloading line, κ* 0.026 position of normal compression line, n 1.36 shear stiffness at medium to large strain level parameter, r 0.65 initial shear stiffness with 180°strain path, mr 14 initial shear stiffness with 90°strain path, mt 11 elastic range, r 1×10 -5 rate of degradation of stiffness with strain, βr 0.1 degradation rate of stiffness with strain, χ 0.7 void ratio at initial condition, e 1.05 density (kg/m 3 ) 1136 co-efficient of permeability, k (m/s) 1×10 -9 d. concrete damaged plasticity (cdp) model the cdp model was used to capture cracking behavior in the concrete beams, columns and piles. the cdp model provides a general capability for modeling concrete and other quasi-brittle materials in all types of structures (beams, trusses, shells, and solids). this model uses concepts of isotropic damaged elasticity in combination with isotropic tensile and compressive plasticity to represent the inelastic behavior of concrete. it can be used for plain concrete, even though it is intended primarily for the analysis of reinforced concrete structures and used with rebar to model concrete reinforcement. it is designed for applications in which concrete is subjected to monotonic, cyclic, and dynamic loading under low confining pressures. table ii. adopted concrete parameters description value young's modulus, e 35gpa poisson's ratio, ν 0.3 density, ρ 2400kg/m 3 e. numerical modeling procedure numerical analysis modeling procedure for a typical case is summarized as: step 1: set up the initial boundary and initial stress conditions (i.e. static stress conditions with varying k0=0.63). step 2: activate the brick elements representing single pile (modeled as wished-in-place). step 3: the construction of the two-floor rcc building was carried out as follows: (a) construct the plinth beam by activating its elements on the single piles. (b) erect the ground floor columns on the plinth beam followed by ground floor beams by activating their elements. (c) similarly, construct the columns and beams of the first floor of the frame. step 4: allow excess pore pressure, which generated in result of application of load of the frame on the pile, to dissipate. step 5: activate the brick elements representing the diaphragm wall. step 6: simulate staged multi-propped excavation. after excavating to 3m depth, the first level of props is installed at 1m below the ground surface. step 7: repeat step 6 to excavate the next stages and install props until the last stage of excavation (i.e. he=12m) is completed. iii. interpretation of computed results a. induced frame angular distortion due to excavation angular distortion (which is defined as shearing distortion of the frame) can be induced in the frame due to the adjacent excavation. mathematically, angular distortion is calculated as: angular distortion = slope − tilting. (2) figure 3 shows the induced angular distortion in the twofloor frame (i.e. bay 1 and bay 2) due to excavation-induced stress release. the horizontal axis represents the normalized excavation depth and the vertical axis shows the angular distortion induced in the bays. the angular distortion at any vertex is taken positive if the frame is compressed diagonally at that vertex. fig. 3. induced angular distortion in the frame due to excavation it can be observed that negative angular distortion is induced in bay 1 during excavation. this implies that the diagonals bd and ac of bay 1 were stretched and compressed during excavation, respectively. this can be attributed to differential settlement and tilting of the frame due to excavation induced stress release. consequently, the column ad of the frame (in bay 1) is subjected to tension towards its inner side. as a result, the tension crack can be induced at the inner side of the column (discussed later). unlike bay 1, bay 2 was distorted at vertex c positively during excavation. as the excavation progresses, the positive distortion at the vertex c of bay 2 increases. this implies that the diagonals ce and bf of -0.04 -0.03 -0.02 -0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 a n g u la r d is to rt io n : % normalised excavation depth (h/he) bay 1 bay 2 bay 1 bay 2 l a l cb h d e f engineering, technology & applied science research vol. 9, no. 4, 2019, 4463-4468 4467 www.etasr.com manig et al.: crack pattern investigation in the structural members of a framed two-story building … bay 2 were compressed and elongated during excavation, respectively. this reason can be attributed to the differential settlement and tilting of the frame due to excavation induced stress release. consequently, the column cf of the frame (in bay 2) is subjected to tension towards its inner side. as a result, the tension crack can be induced at the inner side of the column (discussed below). b. progressive development of tension-induced crack pattern in the frame as discussed above, angular distortion is induced in the frame. as a result, tension is developed in the columns of bay 1 and bay 2. figure 4 illustrates the development of tensioninduced cracks (i.e. crack pattern) in the plinth beam and columns on excavation completion. for reference, the tension damage before excavation is included in the figure. the tension damage is expressed in terms of dt (i.e. damaget) in the numerical modeling. the values of dt range from 0 to 1 where zero represents no damage and one complete damage in tension induced in structural member, respectively. as expected, no tension damage (damaget=0) is developed in the frame before excavation. however, as excavation progresses, damage failure is induced in the plinth beam and the lower part of the ground floor columns. on excavation completion, the magnitude of scale of damage (dtmax) became as high as 0.97 in the bottom layer of the portion of the plinth beam resting on the pile. this suggests that the induced maximum tensile stress in that portion of the plinth beam exceeded the yield stress of the pile. consequently, the stiffness and strength of the concrete degraded significantly. fig. 4. excavation-induced cracking pattern in the frame iv. conclusion induced slope and tilting are not equal. consequently, the frame was distorted. as a result, tension cracks were induced at the inner side of the column. on completion of the excavation, the magnitude of dt became as high as 0.97 in the bottom layer of the portion of the plinth beam resting on the pile. references [1] g. giardina, a. v. v. d. graaf, m. hendriks, j. g. rots, a. marini, “numerical analysis of a masonry facade subject to tunnelling-induced settlements”, engineering structures, vol. 54, pp. 234-247, 2013 [2] h. j. burd, g. t. houlsby, c. e. augarde, g. liu, “modelling tunnelling-induced settlement of masonry buildings”, proceedings of the institution of civil 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performance of the one museum park west excavation”, journal of geotechnical and geoenvironmental engineering, vol. 141, no. 1, pp. 1-11, 2014 [29] h. g. poulos, l. t. chen, “pile response due to excavation-induced lateral soil movement”, journal of geotechnical and geoenvironmental engineering, vol. 123, no. 2, pp. 94-99, 1997 [30] d. masin, j. bohac, p. tuma, “modelling of a deep excavation in a silty clay”, 15th european conference on soil mechanics and geotechnical engineering, athens, greece, 2011 [31] a. niemunis, i. herle, “hypoplastic model for cohesionless soils with elastic strain range”, mechanics of cohesive-frictional materials, vol. 2, no. 4, pp. 279-299, 1997 [32] l. z. wang, k. x. chen, y. hong, c. w. w. ng, “effect of consolidation on responses of a single pile subjected to lateral soil movement”, canadian geotechnical journal, vol. 52, no. 6, pp. 769782, 2015 [33] d. a. mangnejo, n. mangi, “the responses of an end-bearing pile to adjacent multipropped excavation: 3d numerical modelling”, civil engineering journal, vol. 5, no. 3, pp. 552-562, 2019 [34] d. a. mangnejo, m. a. soomro, n. mangi, i. a. halepoto, i. a. dahri, “a parametric study of effect on single pile integrity due to an adjacent excavation induced stress release in soft clay”, engineering, technology & applied science research, vol. 8, no. 4, pp. 3189-3193, 2018 microsoft word kunene-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 363-367 363 www.etasr.com kunene and allopi: comparison between conditions of major roads… comparison between conditions of major roads within and outside the port of durban oscar kunene durban university of technology durban, south africa mbongenik@yahoo.com dhiren allopi durban university of technology durban, south africa allopid@dut.ac.za abstract—over the past years road traffic has increased at the port of durban. due to the lack of maintenance, this has resulted in road deterioration. roads are considered as the most important transport mode at the port of durban. it is an important mean for facilitating economic growth of local, regional and national industries. for the port to maintain global competitiveness with the current trend of globalization, it has to be ensured that the roads are well maintained. the purpose of the paper is to provide an overview of road condition within and outside the port. verification and assessment of the condition of the existing eight major roads was conducted. comparisons between the condition of the eight major roads within and outside the port were highlighted. conclusions and recommendations were also drawn based on the findings. keywords-road condition; verification; assessment; pavement management system; port of durban i. introduction a. background of the study in the past, all roads within the port of durban were owned and maintained by transnet national ports authority (tnpa, formerly known as portnet). currently, not all roads within the port are owned and maintained by tnpa, e.g. public roads (ethekwini municipality) and access roads to private terminals (lessees). some roads are divided into two, with one section of the road falling within the port boundary and another section falling outside the port boundary. these roads are maintained by both tnpa and ethekwini municipality. tnpa is the landlord for the port of durban. private companies and other transnet divisions such as transnet port terminals and transnet freight rail leases land from tnpa. ethekwini municipality is the local government for the city of durban, in which the port of durban is located. in the eighty five years leading up to 1995, the south african railways and harbours held a monopoly on transport over a 50 km lead distance from the port and therefore all cargo owners, both import and export, were obliged to dispatch their products by rail. this led to large areas of the bayhead becoming the preserve of the railways and large marshalling yards and carriage and wagon workshops were established in the area. when rail was the dominant mode of transport to the port, all the marshalling yards were used and, in fact, the lack of marshalling space often proved to be the bottleneck of the port [1]. in the last fifteen years, with the deregulation of road transport, there was an immediate and extensive switch of general cargo from rail to road transport with the current split being close to 80% road and 20% rail. the result of this switch has placed tremendous pressure on the road network while railway facilities are now greatly under-utilised and the usage of this prime space needs to be incorporated into the future planning of the port [1]. based on service level agreement for ethekwini municipality, highlighting response time for road maintenance, the reasonable time for repair of potholes is within 48 hours, sink hole and traffic signals are within 24 hours, road, sidewalk repairs, reinstatements of trenches, broken kerbs and road signs are repaired within 10 days [2]. b. objectives of the study the main purpose of the study was to determine the following: • to compare the condition of roads within and outside the port which are owned by different authorities. • to identify and assess the condition of the eight major roads within and outside the port. • to determine factors that affect road condition. • to recommend measures based on the findings. c. study limitations the study focuses on comparisons between conditions of roads within and outside the port of durban. it covers the eight major roads which are main accesses to the port of durban. figure 1 shows the eight major roads within the port of durban that connect the south, west and north of ethekwini municipality. these roads are bayhead, quayside, maydon, rick turner (formerly known as francois road), wisely, south coast, bluff and iran roads. sections of these roads extend outside the port boundary. all roads highlighted in dotted lines are sections of the roads outside the port. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 363-367 364 www.etasr.com kunene and allopi: comparison between conditions of major roads… fig. 1. road network inside and outside port of durban. ii. methodology the pavement management system manual was used as a reference for physical site measurements conducted as part of the assets verification process. verification and assessment were conducted as per table i. table i. schedule of verification and assessments road name date of survey length within port (km) length outside port (km) .umber of lanes in each direction quayside 25/10/2011 3 0.3 1 maydon 27/10/2011 2.4 0 1 rick turner 01/11/2011 0.4 4 1 wisely 01/11/2011 0.6 0 2 bayhead 03/11/2011 5 0.5 2 south coast 03/11/2011 2.3 7 1 bluff 10/11/2011 2.4 6 1 iran 10/11/2011 1.6 0 1 note: the full length of roads such as maydon, wisely and iran roads falls within the port. bayhead, quayside, rick turner, south coast and bluff road are divided into two sections. the measurements recorded represent the section of roads within and outside the port. the visual inspection (eyeball method) was identified for assessing the condition of the road infrastructure. this method is a quick visual inspection of the road on a routine basis to identify problems. the visual inspections were conducted on all eight major roads within the port and section of roads outside the port. the comparison between the roads within and outside the port was also conducted. during the visual inspection of each road, an inspection report was compiled which included the following components: road markings, traffic signs, potholes, cracks, rutting, aggregate loss, riding quality, surface drainage and unpaved shoulders. each component was rated using the following rating method in table ii: table ii. rating method [3] percentage description rating detailed description 100-90% excellent a it is new and perfect. no maintenance work required at this stage 89-70% very good b it looks like new and minor maintenance work may be required at a later stage 69-50% good c it is moderate and maintenance work may be required within 12 months 49-30% fair d it is reasonable but maintenance work may be required within 6 months 29%-10% poor e it is not safe and need urgent attention 9%-0% very poor f it is very poor and reconstruction work required urgently the findings of the assessment for the eight major roads within and outside the port (where applicable) were recorded on inspection reports. table iii shows an example of an inspection report that was conducted on section of bayhead road within the port: table iii. inspection report conducted on bayhead road component weight rating weighted average road markings 10 65% 6.5 traffic signs 10 65% 6.5 potholes 20 45% 9 cracks 10 45% 4.5 rutting 10 45% 4.5 aggregate loss 10 45% 4.5 riding quality 10 50% 5.0 surface drainage 15 45% 6.75 unpaved shoulders 5 65% 3.25 total 100 50.5 the weighting of each component was identified based on the importance and damage that can be caused if that particular component was not repaired. rating score was based on the condition of the component and table ii was used during the rating process. iii. results the results from the inspection reports conducted on the eight major roads within the port are shown in figure 2. maydon and south coast roads are low rated roads which are in a poor condition. quayside road is highly rated and in a very good condition. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 363-367 365 www.etasr.com kunene and allopi: comparison between conditions of major roads… fig. 2. summary of major road condition within the port the following are results obtained during the assessment of roads within the port: • quayside road (71.5%) falls under b (very good) category. it looks like new and minor maintenance work may be required at a later stage. • rick turner (59.5%), iran road (59.5%) and bayhead road (50.5%) fall under c (good) category. it is moderate and maintenance work may be required within 12 months. • wisely road (49%) and bluff road (45%) fall under d (fair) category. it is reasonable but maintenance work may be required within 6 months. • maydon road (28.8%) and south coast road (28%) fall under e (poor) category. it is not safe and needs urgent attention. fig. 3. longitudinal and crocodile cracks on south coast road figure 3 shows the longitudinal cracks found on sections of bayhead road within the port where the asphalt layer failed at the joint. the results from the inspection reports conducted at the five major roads that have sections which fall outside the port are shown in figure 4, namely bayhead, quayside, rick turner, south coast and bluff roads. the full length of maydon, wisely and iran road falls within the port and hence cannot be assessed. south coast road is a low rated road which is in a fair condition and all other roads are rated above 70%. fig. 4. assessment of road condition outside of the port. the following are results obtained during the assessment of roads outside the port: • bayhead (94%) and quayside road (91.5%) fall under a (excellent) category. it is new and perfect. no maintenance work required at this stage. • rick turner (71%) and bluff road (75%) fall under b (very good) category. it looks like new and minor maintenance work may be required at the later stage. • south coast road (40%) falls under d (fair) category. it is reasonable but maintenance work may be required within 6 months. figure 5 shows the typical defects found on sections of rick turner road outside the port near king edward hospital. fig. 5. aggregates loss on rick turner road. the section of roads which falls outside the port are in a good condition compared to the section of roads within the port as shown in figure 6. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 363-367 366 www.etasr.com kunene and allopi: comparison between conditions of major roads… fig. 6. comparison between roads within and outside of the port. iv. factors affecting road conditions there are a number of factors that contribute to poor condition of roads within the port of durban such as: • growth of container cargo • increase in the dimension and weight of trucks • transport deregulation over the past years and overloading a brief discussion on each factor is highlighted: a. growth of container cargo the port of durban has been experiencing high growth rate in container traffic which impacts on road infrastructure condition. about 70% of south african container cargos are handled at the port of durban. the port of durban has a dedicated container terminal that handles 2,7 million twenty foot equivalent units (teu) per annum. average growth of container volumes over the past few years is between 5-7% per annum. fig. 7. container volumes at the port of durban [4] figure 7 shows the container volumes handled at the port of durban over the years where it increased from 1,9 million teu in year 2005 to 2,7 million teu in year 2011. this has put pressure on the roads within the port and resulted in deterioration of the road condition [4]. b. increase in dimension and weight of trucks there has been an increase in the dimension and weight of trucks over the years. the overall length of trucks has increased rapidly from 13m in 1960 to 22m in 1996, which is currently used these days, that is almost double. the weight, which is gross combination mass (gcm) has increased from 38000 tons to 58800 tons. these changes in dimensions and weight of trucks have resulted due to global modification of trucks capacity. these changes have major impact on road condition at the port of durban [5]. the history of the trucks dimensions and weight are as follows: • in 1970: overall length of truck increased from 13 m to 17 m. gross combination mass increased from 38000 tons to 41020 tons. • in 1980: overall length of truck increased from 17 m to 20 m. gross combination mass increased from 41020 tons to 47007 tons. • in 1990: overall length of truck increased from 20 m to 22 m. gross combination mass increased from 47007 tons to 56000 tons. • in 1996: overall length of truck remains at 22 m. gross combination mass increased from 56000 tons to 58800 tons with 5% overload allowance [6]. c. transport deregulation over the past years and overloading by the 1970's, government realized that transport deregulation was necessary and that the railway administration would have to be relieved of its former social obligations (i.e. transport of uneconomic traffic or on money-losing branches and secondary lines and passenger services in general). the form of transport deregulation was debated for another ten years. by 1989 de-facto deregulation had taken place [7]. a government white paper on transport was published in 1991. while specific issues were identified, consensus could not be reached on implementing necessary control mechanisms such as the road traffic quality system (rtqs) and how fair and equitable road-user fees could be levied to the different size motor vehicles. but the legislation was enacted, the road permit system abolished, and a transport “free-for-all” was allowed to develop [7]. government enacted further legislation, while the department of transport unilaterally changed existing statutes, which resulted in larger heavy vehicles appearing on the highways. axle loads were increased, the bridge formula relaxed, but the rtqs was not implemented. competition within the road industry and not just against rail led to price cutting, overloading, un-roadworthy vehicles and excessive pressure on truck drivers to work long and uncontrolled hours [7]. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 363-367 367 www.etasr.com kunene and allopi: comparison between conditions of major roads… enforcement is a particular issue in the area of truck overloading, where some haulers are able to improve their costs by overloading their vehicles, secure in the knowledge that enforcement will be sporadic at best. while the haulers realize a cost advantage, they create an additional cost in road maintenance and repair. truck overloading is one of the principal sources of road damage in the country: the 30% to 40% of trucks that are overloaded caused 60% of the damage to the road network [1]. v. conclusions and recommenditions maydon and sections of south coast roads which falls within the port are low rated roads and are in a poor condition. these roads are not safe and urgent attention is required. quayside road is in a better condition compared to other roads and falls under category b (very good). the section of south coast road which falls outside the port is a low rated road and is in a fair condition. all sections of roads which fall outside of the port are owned by ethekwini municipality and most of these roads are in good condition except for south coast road. the public are involved in ensuring that these roads are well maintained by informing ethekwini municipality via a 24 hour toll free number. transnet national ports authority owns all sections of roads which fall within the port and they are in a fair condition but much work needs to be done. the public are not well informed on who can assist if there are defects on the road. the major problems are experienced when there is a change of ownership. it is recommended that these eight major roads have their own budget and assessed separately to other roads because of their importance. the ownership must be clear by installation of boards or signs on each road indicating the owner’s name and contact details so that it will be easy for road users to report any defect on any road. fast track handover period of ownership will ensure that there is continuity in terms of maintenance. more attention must be paid in terms of regular inspections of roads within the port in order to improve their standard to be similar to roads outside the port. it is recommended that the area supervisor, maintenance manager and road engineer for both parties (ethekwini municipality and transnet national port authority) conduct visual inspections annually. it is further recommended that problem areas be inspected as often as required. it is recommended that on site or laboratory material testing be conducted as and when there are failures to the base, sub-base and road surface layers (asphalts). the road freight industry in south africa needs to be regulated especially on overloading and truck driving hours. weigh bridges and truck toll fees are possible solutions. incidences of motor vehicle roadworthiness non compliance have been highlighted by the large number of trucks. truck driver working hours have also become a major issue that must be addressed urgently. the establishment of a railway safety regulator has set standards for the rail industry but a similar regulator is urgently needed for the road industry. acknowledgment the author thanks supervisor professor dhiren allopi for his guidance and support throughout the study. thanks to transnet national ports authority and ethekwini municipality for allowing me to access their information. also, the financial support from durban university of technology is greatly appreciated. references [1] department of transport kwazulu-natal, national transport master plan 2005-2050, 2008 [2] city of durban, standard engineering specification, 1992 [3] transnet national ports authority, port maintenance manual, road module, 2004 [4] transnet national ports authority, summary of cargo handled at ports of south africa, 2012 [online] available at: http://www.transnetnationalportsauthority.net/doingbusinesswithus/cal endar%20years/calendar%20year%202005.pdf [accessed in october 2012] [5] h. ghoos, j. korsgaard, l. runge-schmidt, h. agerschou, “berth and terminal design in general. storage facilities and cargo handling systems” in planning and design of port marine terminal, thomas telford, ltd, 2004 [6] b. sheat, “truck dimensions and weight”, railways africa, issue 5, pp 13-20, 1997 [7] road and rail association of south africa, modal issues, 2007 [online] available at: http://www.rra.co.za/?page_id=15738 [accessed in october 2012] engineering, technology & applied science research vol. 8, no. 4, 2018, 3168-3171 3168 www.etasr.com mavromatakis et al.: photovoltaic systems and net metering in greece photovoltaic systems and net metering in greece fotis mavromatakis department of electrical engineering technological educational institute of crete heraklion, crete, greece fotis@staff.teicrete.gr george viskadouros department of electrical engineering technological educational institute of crete heraklion, crete, greece viskadouros@staff.teicrete.gr hara haritaki department of accounting and finance technological educational institute of crete heraklion, crete, greece haritaki@staff.teicrete.gr george xanthos department of business administration technological educational institute of crete heraklion, crete, greece xanthos@staff.teicrete.gr abstract—the latest measure for the development of photovoltaics in greece utilizes the net-metering scheme. under this scheme the energy produced by a pv system may be either consumed by the local loads or be injected to the grid. the final cost reported in an electricity bill depends upon the energy produced by the pv system, the energy absorbed from the grid and the energy injected to the grid. consequently, the actual electricity consumption profile is important to estimate the benefit from the use of this renewable energy source. the state latest statistics in greece for households reveal that the typical electrical consumption is 3750 kwh while 10244 kwh are consumed in the form of thermal energy. we adopt in our calculations the above amount of electrical energy but assume four different scenarios. these different hourly profiles are examined to study the effects of synchronization upon the final cost of energy. the above scenarios are applied to areas in different climate zones in greece (heraklion, athens and thessaloniki) to examine the dependence of the hourly profiles and the solar potential upon the financial data with respect to internal rate of return, payback times, net present value and the levelized cost of energy. these parameters are affected by the initial system cost and the financial parameters. keywords-photovoltaic; net metering; modeling; financial i. introduction one of the support mechanisms to promote photovoltaic (pv) technology and reduce the energy costs for residential and commercial customers is related to the local production of renewable energy (self-production). the net metering scheme involves grid connected systems and is available in many countries worldwide. utilities can better manage peak loads since pv systems generate most of their power around noon time. local power production allows reducing the strain in the electrical distribution system and the transmission and distribution losses. part of the energy generated by the pv system may be consumed by the loads (self-consumption) of the owner of the pv system, e.g. lights, refrigerators, pumps, etc, while any surplus energy will be exported to the grid. the owner of the pv system will be billed for the net energy which is basically equal to the energy retrieved from the grid minus the energy injected to the grid. in greece the relevant law was introduced in 2014. recently, in 2017, the greek state setup the details of net metering and introduced the concept of virtual net metering. under this scheme the points of energy production and consumption may well differ electrically or spatially. in addition, it is foreseen that a customer may incorporate more points of consumption into the energy balance agreement. in this work we focus on the net metering scheme for residential customers. the total billing of energy in households involves basically two parts. the first part refers to the cost of the actual energy consumed by the customer (“energy supply charges”). the second part refers to a few regulated costs like those related to transmission, distribution, services of common wealth, reduction of gas pollution, special fees and other charges (“regulated costs”). the “energy supply charges” depend upon the specific energy supplier company, which may be other than the greek public power corporation (ppc), whereas the “regulated costs” are common to all energy suppliers. both categories of costs are calculated in a specific way and in this work those defined by the ppc are adopted. we explore the implications of net metering at three different geographical areas in greece. for each area, we assume a number of hourly profiles for the loads resulting to the same annual energy consumption. adopting typical values for the financial data the payback times, net present value and the levelized cost of energy are calculated and compared. ii. model data the input model data may be distinguished to two categories. the first involves the data related to the photovoltaic system while the second involves the data related to the consumer load. the pv*sol software was utilized for the hourly pv calculations [1]. this software makes use of the meteonorm database to retrieve solar irradiance and meteorological data for the selected sites: heraklion – crete, ath pea con typ kw ran sum ave 37 am kw (84 mo fol fol on wi “re fro syn loa a. rat pv dif sys to com loa the dep am tha res the sce the ath ado ava ado con ado pro be engineerin www.etasr thens attica ak power of e nsumed energ pical commerc w while the m nge of 250-3 mmarizes the b site heraklio athens thessalon according to erage annual e 50 kwh, whi mounts to 139 wh refers to th 4.9%), water ostly used to g llowed by wo llow with muc the electrical ll be conside egulated costs om the grid, nchronization ads. the hourly e formally, the tio of self-cons v system. th fference betwe stem minus th formally, the 100%. the mi mpletely out o ads) while the e produced p pend upon the mount of energ at is adopted a sulting in the e consumer u enario (s2) uti e centre of re thens and the opted in the c ailable as a opted in this s nsumption in opts a load c ofile to increas a real profile ng, technology r.com and thessalo each pv system gy. in all case cial inverter w modules are ch 300w at st basic data for table i. ghi (kwh/m on 1870 s 1710 niki 1580 o the greek s electrical energ le the corresp 94 kwh [3]. hermal energy heating (4.4% generate therm ood burning (2 ch smaller per l energy and it ered in the n s” depend ma it is importan between the energy profiles e degree of syn sumed energy e self-consum een the ac e e ac energy i e degree of sy inimum degre of phase with e maximum re pv energy. c e degree of sy gy consumed f assumes that worst-case sc under the net ilizes results f enewable ener average hourl current work [ built-in profi study. the spe a block of fla curve centered se the degree e, but it is imp y & applied sci niki norther m was chosen s, the pv sys with a nomina haracterized by tc conditions all three sites. basic data gt m2) (kwh/m 1960 1800 1670 statistical aut gy consumptio ponding total the additiona y which is use %) and cookin mal energy is 23.8%). other rcentages. in t is the energy net metering ainly upon the nt to understa generation of s nchronization, y over the ener med energy is energy (eac) p injected to the ynchronization ee refers to loa the solar ener efers to loads consequently, ynchronization from the grid. all loads are o cenario (s1), i t metering sc from a short su rgy sources (c ly profile of a [4]. the third ile in the sof ecific profile r ats. finally, th d close to noo of synchroniz plemented to ience research rn greece [2]. n to fully matc tem comprise al power aroun y peak power s. table i b pp m2) (kw) 2.43 2.65 2.80 thority in 201 on of a househ energy requir al energy of ed for space h ng (9.7%). th diesel oil (60 r sources of e this work we y of 3750 kw scheme. sinc e energy cons and the conce f pv power an , s, is defined rgy produced b s calculated a roduced by th grid (einj). n may vary fro ads that are bas rgy (e.g. only that exactly m , the billing n since it affec the first load on during the i.e. highest co cheme. the s urvey perform cres) in the a all measureme load profile ( ftware and is refers to the e he last scenario on time with zation. this ma study the effe h v mavro . the ch the s of a nd 2.5 in the below 13 the hold is ement 10244 eating he fuel 0.3%), energy focus wh that ce the sumed ept of nd the as the by the as the he pv m 0% sically y night match costs cts the curve night ost for second med by area of ents is s3) is s also energy o (s4) a flat ay not ects of incr arb the 3,7 b. cus calc are in stat per eur the acc met cor scen arou scen scen pur pro than con of z eve calc und fina inv of s and of s the cos resi still ene c h vol. 8, no. 4, 20 omatakis et al.: reased synchr itrary units. t total annual 50 kwh. fi financial dat as already m stomers and i culated with d issued every one calendar ted by the pp riod in herak ros. this value ppc and ar cording to the tering (s1), w rresponding co nario s1, the und noon tim nario, concern nario (s4) is a rposes. it is u ofile. during n the energy r ntribution to th zero net energy ery site and ev culated to dete der the net me ancial calcul estment. anot synchronizatio d scenarios. th synchronizatio other two citi st of energy w idence. it is c l worth cons ergy. tabl heraklion athens thessaloniki cost of energy eraklion (1 yr) 018, 3168-3171 photovoltaic sy ronization. all the software n energy consu ig. 1. the dif ta mentioned, th in this case, data provided b four months, i year. accord pc, the cost o klion, without e does not incl re, then, attrib greek law. in where all loads ost drops to best scenario me. the total c ning the same an ideal scena unlikely to co summer time equired by the he total cost. t y, there is a m very scenario, ermine the ann etering scheme lations conce ther interesting on which is sho he dependence on is evident. ies and are no without net m clear that even idering net m le ii. degre s1 0.0% 3 0.0% 3 0.0% 3 285 € 2 1 systems and net l profiles are normalizes the umed by the h fferent hourly prof his work focu the typical by the ppc [5 i.e. there are th ding to the r of a typical fo net metering ude charges th buted to the n the worst-ca s are active du around 92 e is s4 where t cost rises to 2 four-month su ario and is sho onsider a resid the pv energ e loads but stil this is becaus minimum cost s the four-mon nual electricity e. these costs erning the g parameter is own in table e of the saving similar costs ot repeated her metering rises t n in the worstmetering to r ee of synchron s2 s 7.8% 44 7.3% 43 6.7% 42 204 € 20 3169 t metering in g shown figure ese profiles, so household loa files uses on reside cost of energ 5]. the energy hree clearance esidential tari our-month sum g, amounts to hat are collecte local municip ase scenario o uring the nigh euros. contrar the loads are a 28 euros under ummer period. wn for compa dence with su gy is usually h ll there is a non se even in the set by the ppc nth billing cost y and savings are adopted i viability of s the annual d ii for all three gs upon the d s are calculate re. the total an to 664 euros -case scenario educe the co ization s3 s4 4.5% 71.3 .4% 70.1 2.4% 68.2 00 € 132 greece e 1 in o that ads is ential gy is y bills e bills iff as mmer o 220 ed by pality of net ht, the ry to active r this . this arison uch a higher nzero e case c. for ts are costs in the f the egree e sites egree ed for nnual for a o it is ost of 4 3% 1% 2% 2 € engineering, technology & applied science research vol. 8, no. 4, 2018, 3168-3171 3170 www.etasr.com mavromatakis et al.: photovoltaic systems and net metering in greece iii. discussion the use of net metering by residential customers in three different areas and climate zones in greece is considered in this work. the cost of energy for each scenario is practically the same for all sites explored, while the annual degree of synchronization shows minor variations (table ii). the financial metrics used to evaluate the viability of the investment of such domestic pv systems involve the levelized cost of electricity (lcoe), the simple payback time (pbt), the net present value (npv) and the internal rate of return (irr). these are calculated following the formulation provided by the national renewable energy laboratory (nrel) [6]. the lcoe represents the cost of energy per kwh produced by the pv system over the investment horizon, while the simple pbt represents the time it takes for the net revenues to equal the initial investment cost. the npv represents the savings over the same period taking in terms of the current value of the money. the irr represents the deflated cost of capital at which the npv becomes zero during the life time of the project. the basic financial parameters used in the calculations are summarized in table iii. in this work the investment time interval is set to 25 years and basically, reflects the duration of the contract signed with the hellenic electricity distribution network operator s.a. under the net metering scheme. however, it must be made clear that this doesn’t represent the actual life time of a pv module. it formally represents the time interval, at the end of which, a module may not produce less than 80% of its initial power rating (guaranteed by the manufacturers). a module will keep producing energy although degraded by about 0.4%/yr [7, 8]. table iii. financial data initial cost (€/kw)1 system degradation2 inverter replacement (€/kw)3 waccnom4 & inflation5 scenarios 1,000.0 0.4% 350 7% & 4% s1, s2, s3, s4 1,250.0 0.4% 350 7% & 4% s1, s2, s3, s4 1,500.0 0.4% 350 7% & 4% s1, s2, s3, s4 1initial cost of pv system 2system degradation per year 3inverter replacement per ten years 4waccnom: nominal weighted average cost of capital 5inflation: the annual inflation rate a replacement time of string inverters of 10 years, considering a good quality inverter, is adopted. in such small pv systems the owner of the system may carry out the operation and maintenance costs (o&m) and thus, do not pay any costs for the cleaning of the modules and the inverter, the inspection of cable connections, etc. finally, a fixed cost of 300 euros is incorporated in year 0 costs as a grid connection fee foreseen by the state law. a single-phase grid connection is assumed since the examined pv peak power is small. to examine the viability of the investment it is crucial to integrate local economy parameters such as the inflation and the nominal weighted average cost of capital (wacc). inflation is an increase in the cost of goods and services per unit time. for convenience, inflation is customary to refer to a year. based on the performance of economic indicators, an average annual inflation rate of 4% was selected [9]. on the other hand, wacc is associated with the amount of profit that obtained from saving capital. net metering is nothing more than an agreement with a power company, enabling the consumer to install a solar power system to meet part or all of the energy consumption. the power company compensates the energy generated by the solar modules with the power consumed by the owner of the photovoltaic system. when there is excess energy because the consumption is low it will be supplied to the grid. on the other hand, when the pv system does not produce enough energy (e.g. clouds or night time) then energy will be consumed from the grid. when the demand for electricity is consistent with production, the compensation price increases and thus, depreciation of capital spent for the installation of the system becomes faster. it should be noted that the excess energy does not lead to income growth due to lack of agreement in tariff for net metering systems. the analysis of a household in heraklion shows that, in the worst-case scenario s1 (just night loads), the breakeven point is 13 years for a pv system price of 1,250 €/kwp. this parameter ranges from 9 to 16 years considering system prices of 1,000 and 1,500 €/kwp and all possible scenarios. the cash flow analysis for this household meets the agreement mentioned earlier for the electrical energy demand and shows that in the consumption profile s2 (mixed daily and nights loads) the breakeven point is 8 years for a pv system price of 1,250 €/kw. generally, in the case of scenarios s2 and s3 which better represent everyday profiles, the breakeven points drop to 7, 8 and 12 years for the corresponding initial system costs reported in table iii. the financial savings for these consumption profiles in heraklion are very close to 3,600 euros (npv) while the internal rate of return is close to 11-12% for the price of 1,250 €/kw which is quite satisfactory since the real average cost of capital in the calculations is 2.9%. if the real cost of capital is below the irr value of 11-12%, then the investment is viable (table iv). the analysis for the cities of athens and thessaloniki also confirms that the worst-case scenario is s1 while scenario s4 is the best one as expected. however, both are unlikely to occur under typical conditions. scenarios 2 and 3 are more realistic and provide very similar results for all cities despite the different origins of the hourly profile data. the financial savings range from around 2,300 € (1,500 €/kwp) to 3,700 € (1,000 €/kwp) which are, of course, lower than the corresponding values in heraklion due to the increased cost of the pv system (2.43 kwp vs 2.80 kwp). it was necessary to increase the installed pv power since the solar irradiance in northern greece is reduced by around 17% with respect to the solar irradiance in heraklion, crete while the household electrical loads remain the same among all cities. the internal rates of return for the typical scenarios s2 and s3 are around 12% for heraklion, 10% for athens and 9% for thessaloniki adopting the unit cost of 1,250 €/kwp. since the real cost of capital of 2.9% (7% nominal and 4% inflation) is less than these irrs, the investment is viable with a net present value ranging from around 3,000 to 3,600 €. the breakeven times are nine (9) years for heraklion and twelve (12) years for the other two cities for the same scenarios suggesting that a residential customer will benefit from the net engineering, technology & applied science research vol. 8, no. 4, 2018, 3168-3171 3171 www.etasr.com mavromatakis et al.: photovoltaic systems and net metering in greece metering scheme. furthermore, depending on the size of the pv system the savings in co2 emissions range from 53,000 to 62,000 kg [10]. finally, the levelized cost of energy (lcoe) is also calculated, although it is not directly related to the net metering measure. the high solar potential in greece offers the opportunity to establish low lcoe values with respect to other european countries. under the data given, it is calculated that the lcoe ranges from the minimum of 0.052 €/kwh in heraklion and for a system cost of 1,000 €/kwp to a maximum of 0.081 €/kwh in thessaloniki and for a system cost of 1,500 €/kwp. table iv. economic metrics for a household in heraklion investment area heraklion consumption profile s1 s2 s3 s4 synchronization (%) 0.0% 37.8% 44.5% 71.3% lcoe (€) 0.0613 breakeven (year) 13 9 9 8 irr 8.4% 11.5% 11.6% 14.0% npv (€) 2,164 3,593 3,625 4,776 simple payback (year) 8.8 7.3 7.2 6.3 pp=2.43 kwp, cost 1,250 €/kwp these results agree with studies of the lcoe [11]. it is estimated that the final savings will increase since the formal clearance time interval for the energy consumed and produced is three years while the simulations are conducted on an annual timeline. future work involves the simulation of solar data with 1-minute resolution to explore the effect upon the degree of synchronization since hourly data smooth out any shorter time variations. furthermore, it is interesting to examine the case where the energy required to supply all kind of residential loads may be in the form of electrical energy excluding the use of wood, natural gas, lp gas or diesel oil for e.g. heating, cooking. heat pumps with a high coefficient of performance can account for the heating loads (space heating, hot water). iv. conclusions in this paper we present the results from the economic analysis of pv systems under the net metering scheme in different cities and climate zones in greece (heraklion, athens and thessaloniki). several input parameters like the initial system cost, inflation, cost of capital and other parameters are used to examine different scenarios for potential investors of small residential pv systems. residential customers may adopt the net metering scheme to reduce the cost of energy bills. the lifetime earnings (npv) for a residence in heraklion amounts to around 3,600 € while the breakeven time occurs at the ninth (9th) year of operation for a system cost of 1,250€/kwp. an irr of 12% is calculated for the same site. the degree of synchronization is around 40% for typical household hourly profiles and it affects the final energy cost. under the specific scenarios the breakeven point is 12 years, the irr is around 9% and the npv is a bit less than 3,000 € for a site in northern greece. references [1] valentin energy software, pv*sol simulation program for photovoltaic systems, berlin, 2018 [2] meteonorm global meteorological database for engineers, planners and education, version 4.0.95, switzerland [3] greek statistical authority, yearly report, 2013, http://www.statistics.gr [4] center for rewenable energy sources, http://www.cres.gr [5] ppc, residential tariffs, https://www.dei.gr/en [6] e. drury, p. denholm, r. margolis, the impact of different economic performance metrics on the perceived value of solar photovoltaics, nrel technical report/tp-6a20-52197, 2011 [7] r. m. smith, d. c. jordan, s. r. kurtz, outdoor pv module degradation of current-voltage parameters, nrel, world renewable energy forum denver, colorado, may 13–17, 2012 [8] f. vignola, j. peterson, r. kessler, f. lin, b. marion, a. anderberg, f. mavromatakis, pv module performance after 30 year without washing, 43rd conference of the american solar energy society (solar 2014), san francisco, california, july 06-10, 2014 [9] interest rates of deposits and loans, bank of greece, https://www.bankofgreece.gr/ [10] european co2 emission data, https://www.eea.europa.eu/data-andmaps/indicators/overview-of-the-electricity-production-2/assessment [11] c. kost, s. shammugam, v. juelch, h. t. nguyen, t. schegl, fraunhofer institute for solar energy systems ise, levelized cost of electricity, renewable energy technologies, 2018 . microsoft word 26-3464_s_etasr_v10_n5_pp6294-6300 engineering, technology & applied science research vol. 10, no. 5, 2020, 6294-6300 6294 www.etasr.com khan & hoque: highly stable photonic local carriers for phased array receiver system highly stable photonic local carriers for phased array receiver system md. rezaul hoque khan islamic university of technology, dhaka, bangladesh and university of twente, netherlands rhkhan@iut-dhaka.edu md. ashraful hoque islamic university of technology dhaka, bangladesh mahoque@iut-dhaka.edu abstract—in this paper, a complete system analysis of photonic local carrier generation technique has been investigated. the generated carrier is potentially suitable to replace the existing microwave/rf local carrier (lc) used in commercial low noise blocks (lnbs) for the phased array (pa) receiver system. the optical lc generated from heterodyning of two commercialized lasers is being stabilized with an optical frequency lock loop (ofll). this approach resulted in a generated carrier at the kuband (10.7ghz to 12.75ghz) signal received from a pa receiver. various loop parameters of the ofll have been investigated to comply with the requirements of the commercial lnbs the proposed ofll shows a 2400 fold improvement in the frequency stability at 1000s averaging time compared to its free running condition. it is also demonstrated that with an optimized loop gain of 30db, the loop response time of the proposed ofll becomes 11�s. keywords-optical frequency lock loop (ofll); microwave carrier generation; locking range; frequency stability i. introduction stabilization of laser frequency differences is essential in many modern experimental schemes. applications extend from advanced optical fiber telecommunications in atomic clocks or in high resolution atomic and molecular spectroscopy [1-4] to precision spectroscopy and sensing [5, 6]. phase coherence of the two laser fields locked at a frequency offset is not required in many applications and a mere frequency lock is an adequate solution. in any case, the optical phase lock loop (opll) is a standout amongst the most commonly utilized locking techniques. when the opll is designed to ensure only the stabilization of the frequency drift and not the consistency of the phase, it is called optical frequency locked loop (ofll). in all these applications, a precisely defined optical frequency is needed and long-term stability must be ensured for correct system operation, with a required degree of stability and accuracy that depends on the application. practically speaking, a beat signal is produced between the laser to be frequencystabilized (slave) and a second laser with known frequency (master) [7]. to stabilize the optically generated carrier, the beat signal is often mixed down to a lower frequency which is far better to be taken care of electronically [8, 9]. the main difference among the various frequency locking schemes which have been developed in the last decade, is the method used to generate and process the error signal employed for locking the slave laser [10]. a very simple locking scheme was demonstrated in [11] using an electronic delay line in conjunction with a phase detector as a frequency dependent phase shifter. this scheme has the advantage of large capture range, but as a drawback the beat frequency must be tuned by a manual adjustment of the delay line length. as a consequence, real-time, rapid tuning of the beat frequency is impossible. other methods used to generate beat frequency use frequency multiplier. a different approach converts the beat frequency to a proportional voltage by a frequency-to-voltage converter (fvc). the voltage is then compared to a reference voltage, which sets the beat frequency [12]. this approach is limited to the maximum operating frequency of the commercial fvc and can be improved by using a hybrid analog-digital locking scheme using high performance fvcs [13]. nevertheless the scheme suffers from the limited bandwidth of the fvc. recently, a highly stable and wide tunable frequency locking scheme has been presented, where a high-speed frequency divider (prescaler) is used on the beat signal before processing the error signal [14]. the main disadvantage of the use of the prescaler is that it degrades the loop response time and limits the loop bandwidth. generating the error signal from the amplitude response of an rf filter to realize a sensitive analog fvc is also proposed [8, 15]. an alternative of these modulation-free error conversion techniques is the use of electrical filters [16] or frequency multipliers [17]. however, to the best of our knowledge, none of the above schemes reported any investigation on the long term frequency stability of the beat spectrum of the ofll. a simple ofll technique based on the concept presented in [11] is proposed in this paper and its performance is improved with the use of a variable delay line in the frequency discriminator to facilitate beat frequency tuning. ii. proposed optical frequency locked loop scheme the frequency of a diode laser depends on the injection current and the temperature and is very sensitive to fluctuations of those parameters. for example, the dfb laser (avanex inc., a1905lmi) used in our experiment has a frequency sensitivity to injection current and temperature of 325mhz/ma and 10ghz/ 0 c respectively [18]. several studies and experiments show that the beat signal generated by a free-running heterodyning system suffers a substantial frequency drift [19]. laser frequency drifts by hundreds of mhz in an ordinary corresponding author: m. r. h. khan engineering, technology & applied science research vol. 10, no. 5, 2020, 6294-6300 6295 www.etasr.com khan & hoque: highly stable photonic local carriers for phased array receiver system environment [20]. the maximum permissible frequency drift of the generated carrier is 5mhz [21], according to the dvb-s specification [22]. the carrier signal, generated by heterodyning of two lasers, is used for the downconversion of the 10.7ghz to 12.75ghz k �-band signal received from a phased array antenna (paa). the block diagram of the proposed ofll is presented in figure 1. the proposed scheme is able to generate an adjustable carrier as specified in [22]. (a) (b) fig. 1. proposed ofll: (a) block diagram, (b) experimental setup. the two lasers used for the experiments are a dfb laser avanex a1905lmi and a tunable laser diode (tld) santec tsl-210. in the experiment, the tunable laser and the dfb laser are employed as a master laser and slave laser having optical frequencies ��� and ��� , respectively, to produce the beat frequency, δ�� ��� � ���. the beat signal is provided by a 20ghz bandwidth photodetector (discovery semiconductor dsc30s) and is amplified by 20db by a commercial rf amplifier (minicircuit zx60-183). a power splitter (minicircuit zfrsc-123-s) is used to tap the beat signal for monitoring. the output signal from the power splitter is mixed with a reference signal, �� �, at ∼10ghz frequency provided by a signal generator (agilent psg e8267d). an error frequency, � δ�� � �� �, is produced at the output of the rf mixer (minicircuit zx05-153lh-s). the error signal, � cos�2π� �� , is then passed through a variable frequency discriminator, where � is the amplitude of the error signal. in the frequency discriminator, the signal is divided into two equal parts by an rf splitter and recombined at a mixer (minicircuits sbl 48) after a variable delay line (narda 3752) has deferred one part. hence, we can write: ( )e1 ec t 2 v v os ω =   (1) ( )( )e2 e 1c 2 v v os tω τ = −  (2) where �� and �� are the signals combined in the mixer, � 2π�δ�� � �� ��, and �� is the time delay. the resultant signal of the frequency discriminator at the output of the mixer, �� is [23]: ( ) ( )( )if0 if 1 if 1cos 2 cos 2 2 ... v v f f tπ τ π τ π  = + − +  (3) the high-frequency term (the 2 nd term in the bracket) is eliminated by a low pass filter (lpf) (minicircuit slp-50), called the loop filter. as a result, the lpf output produces a series of nulls when � �� �2� � 1�π/2 , where � "0,"1,"2 ... the feedback system acts on the slave laser injection current and allows to actively control the emission frequency of the slave laser, so that a constant frequency difference between the slave and the master laser is maintained. the frequency of the slave laser is tuned by applying an external voltage to its injection current controller (ilx lightwave ldc-3724). the conversion factor of this external voltage and the change of emission frequency of the slave laser, %��, is measured to be 31.25&10 '�mhz/mv. a. characterization of the rf discriminator utilizing a passive rf component and realizing a delay of ��=3ns, the discriminator output at the lpf as a function of the beat frequency is shown in figure 2. the offset frequency between the first null from the reference frequency is given by δ� 1/2��, where 1/�� denotes the spacing of the nulls that the ofll lockes on. the point a and b in figure 2 is the nearest null to the reference frequency where the frequency to voltage conversion factor, %(, is maximum and amounts to be 300mv/ghz. a higher �� will reduce the δ� and will increase the slope at the nulls which ultimately will give a higher conversion of %(. the various parameters and their values used in our analysis are summarized in table i. fig. 2. beat frequency as a function of error voltage for a delay of ��=3ns. table i. various loop parameters parameter value dimension total gain of the rf amplifiers 30db %) external voltage-to-frequency 31.25&10 '� %�� conversion factor of the slave laser mhz/mv frequency-to-voltage conversion 300 mv/ghz %( factor of the discriminator time constant of the current 300 μs �� controller of the slave laser time constant of the lpf 1.58μs �� engineering, technology & applied science research vol. 10, no. 5, 2020, 6294-6300 6296 www.etasr.com khan & hoque: highly stable photonic local carriers for phased array receiver system iii. optical frequency lock loop analysis the proposed ofll in figure 1 can be represented as a generic model for the feedback system and its s-domain representation is presented in figure 3. in this model of the ofll, the optical and the electrical connections are represented by doted and solid lines respectively. the optical field from the master and the slave laser are represented by +�� and +�� respectively. the fields are combined and put to a pd. the beat frequency is mixed with the reference frequency, �� �. the downconverted signal is then amplified by an rf amplifier having a gain of %). an rf frequency discriminator having a frequency-to-voltage conversion factor %( converts the downconverted frequency into proportional error voltage. the error signal is passed through a lpf having a laplace transform of the frequency response, ,�-�, to filter out the high frequency component from the error signal. the error signal is applied to the current controller of the slave laser. the external voltage-to-frequency conversion factor and the time constant of the slave laser controller are denoted by %�� and �� respectively. fig. 3. linearized s-domain representation of the ofll. from the linearized s-domain representation of the ofll the open-loop transfer function of the ofll is defined as the product of the transfer functions of all the elements in the loop: ( ) ( ) ( )pd mix a fvc sl fm fmg s k k k k k f s kf s= = (4) where % %.(%/01%)%234%�� is the total gain. the closedloop transfer function of the ofll is [24]: ( ) ( ) 2 2 2 2 2 2 2 n 2 2 2 n n 4 2 4 1 4π f 1 s sζ2πf 4π f 1 k r c r k f h s s s f f k π π π = + + + =   + + +    (5) where �5 and 6 represent the natural frequency and the damping factor of the loop and are expressed by: c n f f ζ = (6) n rf f k= (7) iv. experimental results in this section we will the stability of the ofll will be investigated and analyzed. moreover, some other functionalities of a carrier, namely the maximum tuning range and the maximum tuning rate (the speed at which the generated carrier can be tuned to a certain frequency) need to be investigated. like any feedback system, the dynamics of these functionalities is determined by various parameters like loop gain and loop response. also, the effect of various loop parameters (i.e. loop natural frequency and damping factor) on these functionalities of the ofll will be investigated. a. locking offset range and capture range the discriminator signal at the output of the lpf as a function of the beat frequency is shown in figure 3. the error voltage is applied to the external tuning port of the current controller of the slave laser. this will ultimately change the emission frequency of the slave laser until the error voltage becomes zero. hence, the generated carrier signal is eventually locked to the reference signal with a fixed offset frequency. the relation of the delay in the frequency discriminator and the offset frequency, as given in (4) is plotted in figure 4. the measured values are also plotted and found to be close to the calculated values. fig. 4. the relation of the delay in the frequency discriminator and the offset frequency voltage for a delay of ��=3ns. from figure 3, with ��=3.3ns, the locking 150mhz offset frequency from the reference signal and the nulls are spaced by 300mhz. figure 4 shows the relation of the delay in the frequency discriminator and the offset frequency. this offset frequency range also gives the range of frequencies from the reference signal at which the free-running carrier signal becomes locked, also called the capture range of the ofll. in figure 3, the error signal provides a capture range given by "1/2�� "150mhz. b. beat frequency tuning once the optically generated carrier signal is locked with the reference signal, the generated carrier signal can be tuned by simply varying the delay. the beat frequency is locked at 125, 135, 142, 151 and 166.6mhz offset frequency from the reference frequency. as given in (4), for delays of 3, 3.3, 3.5, 3.7, and 4ns the beat frequency will be locked at 166.6, 151, 142, 135, and 125mhz respectively. the beat frequency tuning for various delays is shown in figure 5. engineering, technology & applied science research vol. 10, no. 5, 2020, 6294-6300 6297 www.etasr.com khan & hoque: highly stable photonic local carriers for phased array receiver system fig. 5. beat frequency tuning by varying delay. c. frequency resolution the frequency resolution is determined by the slope of the error signal at the locking point. as indicated by (4), a longer delay line �� reduces the capture range but enhances resolution. in order to demonstrate the effect of delay on the sensitivity, for a fixed delay, the reference frequency was tuned from 9.66ghz to 9.54ghz, as shown in figure 6. depending on the delay, for example 3, 3.5, and 4ns, the beat frequency is also tuned with an offset frequency of 166.6, 142, and 125mhz respectively from the reference frequency. figure 6 shows the frequency resolution of the locked signal for various delays. in the measurement the reference frequency was changed to demonstrate the frequency resolution. moreover, the inset in figure 6 shows the change of resolution due to the change of delay. fig. 6. frequency resolution of the locked signal for various delays. the inset shows a highlighted portion of the measurement. d. loop response time the step response provides an insight in loop response time and loop settling time. note that the time taken for a feedback system to stay within 10% of its final value is called settling time. one widely used measure of the response speed of a feedback system is the time it requires to reach the 90% of its final value, which is called loop response time. with the help of (6) and (7), for a given loop bandwidth (1mhz in our experiment), the calculated loop response time values are plotted in figure 7 for various loop natural frequencies and damping factors. from figure 7 we can see that for a 1mhz loop bandwidth, the loop response becomes faster for a lower damping factor with higher settling time. the optimum value of the damping factor should be chosen by carefully considering both loop response time and settling time. from figure 7 we can observe that there is a trade-off between the loop response time and settling time. with higher damping factor, the loop response time increases with decreasing settling time. the optimum value of the damping factor can be indicated as 6 1 where both loop response time and settling time are optimum. the optimized loop natural frequency �5 is 1mhz. fig. 7. loop response time for various natural frequencies and damping factors. the step response measurement procedure is shown in figure 8. the step signal from a vector signal generator (agilent psg e8267d) will introduce an external disturbance in the current controller of the slave laser (dfb laser) of the ofll and due to this aggravation, the signal will suffer a temporary deviation from the desired frequency. the ofll will recover the system into the former stable condition soon after the disturbance and this duration of the generated carrier signal from its unstable condition is measured by an oscilloscope (agilent infinium 54854a) by synchronizing with the vector signal generator through an external trigger. employing the values of the parameters in table i, for a given value of gain, %) 14db, the natural frequency, �5, and the damping factor, 6, can be calculated using (7) and (8) as 1mhz and 1, respectively. for %) 10db the calculated values of the natural frequency and the damping factor become �5=0.62mhz and 6=1.7 respectively. fig. 8. loop response time measurement setup. engineering, technology & applied science research vol. 10, no. 5, 2020, 6294-6300 6298 www.etasr.com khan & hoque: highly stable photonic local carriers for phased array receiver system from figure 9, for 6=1 and 6=1.7 the speed of the response of the loop is found to be 0.35 and 0.85μs respectively. from figure 9(a) it is evident that for a value of 6=1 the calculated loop settling time is found to be 0.78μs which is slower than the 0.58μs (figure 9(b)) for 6=1.7 (called critical damping). the experimental results are in good agreement with the calculated values. from figure 9 we can observe that there is a trade-off between loop response time and settling time. with higher damping factor, the loop response time increases with decrease of settling time. the optimum value of damping factor can be indicated as 6=1 where both loop response time and settling time are also optimum. the optimized loop natural frequency, �5 is 1mhz. (a) (b) fig. 9. loop settling time comparison, using step response, on calculated and measured values for damping factor of (a) 1 and (b) 1.7. e. frequency response the frequency response of the ofll is plotted in figure 10. the x-axis has been normalized by dividing the frequency by loop natural frequency �5. the plot shows how the loop behaves in the frequency domain. figure 10 shows the result of the frequency response of the ofll for various damping factors. the frequency response of the loop in figure 10 looks very similar to that of the frequency response of a low pass filter. this is what an ofll acts in practice. if the frequency is equal to the natural frequency (i.e. when f/fn=1) the oscillation becomes very large. this phenomenon is reflected in figure 10(a) for 6=1. larger damping factors have lower overshoot, i.e. better response, but also have long response time [29], as can be observed in figure 10(b) for 6=1.7. note that the higher frequency term in (3) needs to be filtered out, the response does it by keeping the loop bandwidth narrow. for the same values of natural frequency and damping factor, the calculated result of the frequency response is presented in figure 10. the experimental results are in good agreement with the calculated values. the step/impulse response of the system, a time domain response, can be converted into a frequency domain response by simply performing fourier transformation. the calculated frequency response of the loop in figure 10 is actually a time domain response (step response/impulse) of figure 7. the time and frequency domain measurement values from figure 7 and figure 10 are in a good agreement. (a) (b) fig. 10. experimental and calculated results of the frequency response of the ofll, the x-axis is the normalized frequency and the y-axis is the response in db. f. long term frequency stability analysis typically, a free-running microwave frequency, �8 )9 , deviates from the required frequency, �0( ): , with variable direction and rate of change. in order to express the long term frequency stability of a carrier, the allan deviation ;< is often used. to evaluate this frequency stability, ;< is proven to be a valuable tool to quantify the stability of an optically generated microwave carrier [26]: ( ) ( ) 1 2 2 1 1 1 [ ] 2 1 m y i i i y y m σ τ − + = = − − ∑ (8) where =0 is the i th of the m fractional frequency values averaged over the measurement (sampling) interval � . the measured frequency stability of the generated carrier is expressed in allan deviation in figure 11 for both locked and free running conditions. for the free-running condition, for an increased averaging time of � =1s to � =1000s, the allan deviation increases from 2.5×10 -10 to 6×10 -9 . however, by implementing the ofll the corresponding improved long-term frequency stability could be 3×10 -10 and 2.5×10 -12 . the ofll shows a 2400-fold improvement in the frequency stability at 1000s averaging time. a typical quartz oscillator (wenzel 501engineering, technology & applied science research vol. 10, no. 5, 2020, 6294-6300 6299 www.etasr.com khan & hoque: highly stable photonic local carriers for phased array receiver system 04623e) has an allan deviation frequency stability of 4×10 -7 [27]. a typical atomic oscillator used as a clock source may provide a frequency stability of allan deviation of 1×10 -10 for 1s averaging time [28]. a radio frequency (rf) clock signal transmission over 100m via fiber link results in an allan deviation of 1.3×10 -10 for 1s averaging time [29]. the long term frequency stability of the presented work shows the superior performance of allan deviation of 1×10 -10 for an averaging time of 10 3 s compared to opll setups involving integrated phase-frequency detectors (pfd) [30]. fig. 11. allan deviation of the frequency stability of the ofll under freerunning and locked conditions. v. conclusion system analysis and experimental demonstration of an optically generated lc designed to comply with the requirements of the standard lc signal used in commercial lnbs have been investigated in this paper. the lc signal was used for the downconversion of the 10.7ghz to 12.75ghz signal received from a pa receiver. an ofll was also implemented to stabilize the generated lc signal. detailed analysis of the ofll scheme has been presented. the loop filter and the loop gain of the ofll should be chosen properly to make the feedback system stable and fast. it was also demonstrated that with an optimized gain of 14db, the loop response time becomes 0.35μs with a settling time of 11.5μs. the presented results emphasize the effectiveness of the use of the ofll in improving the long-term stability of the freerunning microwave carrier by a 2400-fold improvement in the frequency stability at 1000s averaging time. previous research merely presents straightforward time domain measurements and lacks complete frequency domain measurements of the loop response. the presented research focused on this highly interesting topic. both time and frequency domain measurement values are in a good agreement with each other. moreover, the presented implementation shows batter performance in terms of the capture range of 150mhz compared to the very recent investigation of a few hundred khz in [31]. acknowledgments the authors acknowledge the support of the smart mix program of the dutch ministry of economic affairs and the dutch ministry of education, culture and science. references [1] s. h. yim, s.-b. lee, t. y. kwon, and s. e. park, “optical phase locking of two extended-cavity diode lasers with ultra-low phase noise for atom interferometry,” applied physics b, vol. 115, no. 4, pp. 491– 495, jun. 2014, doi: 10.1007/s00340-013-5629-5. 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[29] b. sprenger, j. zhang, z. h. lu, and l. j. wang, “atmospheric transfer of optical and radio frequency clock signals,” optics letters, vol. 34, no. 7, pp. 965–967, apr. 2009, doi: 10.1364/ol.34.000965. [30] m. lipka, m. parniak, and w. wasilewski, “optical frequency locked loop for long-term stabilization of broad-line dfb laser frequency difference,” applied physics b, vol. 123, no. 9, p. 238, aug. 2017, doi: 10.1007/s00340-017-6808-6. [31] b. chen, k. wu, l. yan, j. xie, and e. zhang, “stabilization of synthetic wavelength using offset-frequency locking for the measurement accuracy improvement of the laser synthetic wavelength interferometer,” optical engineering, vol. 57, no. 3, p. 034106, mar. 2018, doi: 10.1117/1.oe.57.3.034106. microsoft word 04-3155_s_etasr_v9_n6_pp4883-4885 engineering, technology & applied science research vol. 9, no. 6, 2019, 4883-4885 4883 www.etasr.com chakravorty & saraswat: improving power flow capacity of transmission lines using dpfc with … improving power flow capacity of transmission lines using dpfc with a pem fuel cell jaydeep chakravorty electrical engineering department indus university ahmedabad, india jyoti saraswat alpla india, pvt. ltd. dadra & nagar havali gujarat, india abstract—the electrical power system is one complex architecture integrating generation, transmission, distribution, and utilization sections. the exponential increase in power requirements made this system more complex and dynamic. providing good quality and uninterrupted power has become a challenge. in this respect, facts devices are playing a vital role in improving power quality and also in increasing the transmission capacity of lines. in this paper. distributed power flow controller (dpfc), with a pem fuel cell, has been used in an ieee-14 bus system to improve system power flow capacity. the proposed ieee-14 bus with dpfc has been simulated in matlab/simulink. the effects are exhibited and analyzed. keywords-dpfc; pem; power quality i. introduction uninterrupted electrical power supply is a major requirement for the development of a country. to meet the increasing need of uninterrupted good quality power is a big challenge. due to the increasing demand of power, power system networks are becoming very complex. with very fast increase in non-linear loads in the power system, the supply of good quality power has become a major problem. to cater these needs, facts devices are playing a very vital role in increasing the efficiency of the transmission system [1-2]. studies conducted in improving power quality by incorporating facts devices can be seen in [3-11]. various algorithms have also been developed with the help of which it is feasible now to efficiently place facts devices in the power system, something that has drastically reduced the cost of operation and also has improved the quality of power transfer [12-13]. this paper proposes a method to improve power transfer capability of the system with the proposed dpfc with a pem fuel cell [14]. the optimal location of the proposed dpfc has been decided with the help of artificial algae algorithm [15]. the complete proposed system has been simulated in matlab/simulink and the result has been compared with the system without dpfc in it. ii. transmission line representation a simple representation of transmission line is show in figure.1 between bus-i and bus-j, the line admittance is ��� � ���� � � ��� � , and the bus voltages are ��∠��and ��∠�� respectively. the real ����� and reactive ����� power flowing from bus-i to bus-j can be written as: ��� � ������ � �������� cos��� � ��� sin���� (1) ��� � ���� ���� � !" � #��������� sin��� ���� cos���� (2) where, ��� � �� � ��. real power pji and reactive power qji flowing from bus j to bus i are given by: ��� � ������ � �������� cos��� � ��� sin���� (3) ��� � ���� ���� � !" � #��������� sin��� ���� cos���� (4) fig. 1. transmission line representation iii. dpfc model in this model, dpfc with a pem fuel cell has been used. the complete representation dpfc with a pem fuel cell has been discussed in [14]. the complete matlab model of is shown in figure 2. iv. ieee-14 bus system the ieee-14 bus system simulink model is shown in figure 3. the location of dpfc has been decided by the application of artificial algae algorithm [15]. the numerical data and the parameters are taken from [16]. the proposed ieee-14 bus system has 19 lines, 11 load buses, 1 slack bus and 2 generator buses. v. artificial algae algorithm the optimal location of dpfc has been has been determined by the application of artificial algae algorithm [15], which gives very good results for nonlinear optimization [17]. corresponding author: jaydeep chakravorty (jaydeepchak@yahoo.co.in ) engineering, technology & applied science research vol. 9, no. 6, 2019, 4883-4885 4884 www.etasr.com chakravorty & saraswat: improving power flow capacity of transmission lines using dpfc with … in this algorithm an artificial algae colony represents each individual. the process of this technique has three steps, helical movementt, reproduction and adaptation. after each cycle of operation, the population in the colonies is modified in the helical movement phase. it is assumed that the colony swims in all three dimensions in order to reach the light. colony’s energy will increase and its movement will slow down as it reaches the light. to increase the local search ability of the algorithm as the colonies approach the light, the algorithm starts searching the space with smaller and smaller steps. on the other hand, the colonies which are far away from the light will search the space with bigger steps, which in turn increases global search ability. artificial algae algorithm has a strong balance between exploration and exploitation. the pseudo code is given in figure 4. fig. 2. dpfc with a pem fuel cell [14] fig. 3. ieee-14 bus system vi. results and discussion the voltage profile of the system with and without the application of dpfc when applied to the ieee 14 bus system is shown in figure 5. the optimal location of dpfc was obtained by the application of artificial algae algorithm. the ieee 14 bus system was tested first without the dpfc in the system and then with the dpfc embedded in the system. engineering, technology & applied science research vol. 9, no. 6, 2019, 4883-4885 4885 www.etasr.com chakravorty & saraswat: improving power flow capacity of transmission lines using dpfc with … 1. to generate initial population with random solution of n algal colonies. 2. evaluate f(xi) for i = 1,2,3, ……, d 3. while the stopping condition is not reached 4. for i = 1 to n 5. while the energy of the i-th colony is not finished 6. modify the colony 7. end while 8. end for 9. apply evolution strategy 10. apply adaptation strategy 11. end of while fig. 4. artificial algae algorithm pseudo code fig. 5. voltage profile the real and reactive power loss values for normal load condition, 125% load and 150% load are shown in table i and ii respectively. table i. real power loss normal load 125% load 150% load without dpfc with dpfc without dpfc with dpfc without dpfc with dpfc real power loss (mw) 14.5 13.2 26.01 24.99 38.32 35.57 table ii. reactive power loss normal load 125% load 150% load without dpfc with dpfc without dpfc with dpfc without dpfc with dpfc reactive power loss (mw) 29.3 28.5 69.45 67.3 98.23 96.6 from the above results it can be concluded that by the proper application of dpfc in the system, its voltage profile can be improved. the application of the proposed dpfc with a pem fuel cell has reduced the real and reactive power loss in the system at different load conditions. vii. conclusion in this paper, a 14 bus ieee system with dpfc has been simulated in matlab/simulink. it was observed that the power flow capacity of the system with dpfc is more than the one of the same system without dpfc. the simulation of the proposed system took a very long time to give the output. in the future, some modifications in the design of the system may be applied in order to reduce simulation time. references [1] n. g. hingorani, l. gyugyi, understanding facts: concepts and technology of flexible ac transmission systems, ieee press, 2000 [2] abb, technologies that changed the world: facts, available at: https://new.abb.com/facts/about-facts/technologies-that-changed-theworld-facts [3] l. gyugyi, c. d. schauder, s. l. williams, t. r. rietman, d. r. torgerson, a. edris, “the unified power flow controller: a new approach to power transmission control”, ieee transactions on power delivery, vol. 10, no. 2, pp. 1085-1092, 1995 [4] c. chengaiah, r. v. s. satyanarayana, “power flow assesment in transmission lines using simulink model with upfc”, international conference on computing, electronics and electrical technologies, kumaracoil, india, march 21-22, 2012 [5] z. huang, y. ni, c. m. shen, f. f. wu, s. chen, b. zhang, “application of unified power flow controller in interconnected power systems: modeling, interface, control strategy, and case study”, ieee transactions on power systems, vol. 15, no. 2, pp. 817-823, 2000 [6] c. chengaiah, r. v. s. satyanarayana, g. v. marutheswar, “study on effect of upfc device in electrical transmission system: power flow assessment”, international journal of electrical and electronics engineering, vol. 1, no. 4, pp. 66-70, 2012 [7] p. kannan, s. chenthur pandian, “case study on power quality improvement of thirty bus system with upfc”, international journal of computer and electrical engineering, vol. 3, no. 3, pp. 417-420, 2011 [8] a. r. bhowmik, c. nandi, “implementation of unified power flow controller (upfc) for power quality improvement in ieee 14-bus system”, international journal of circuit theory and applications, vol. 2, no. 6, pp. 1889-1896, 2011 [9] e. gholipour, s. saadate, “improving of transient stability of power systems using upfc”, ieee transactions on power delivery, vol. 20, no. 2, pp. 1677-1682, 2005 [10] a. k. sahoo, s. s. dash, t. thyagarajan, “an improved upfc control to enhance power system stability”, modern applied science, vol. 4, no. 6, pp. 37-48, 2010 [11] a. j. f. keri, a. s. mehraban, x. lombard, a. eiriachy, a. a. edris, “unified power flow controller (upfc): modeling and analysis”, ieee transactions on power delivery, vol. 14, no. 2, pp. 648-654, 1999 [12] a. m. vural, m. tumay, “steady state analysis of unified power flow controller; mathematical modelling and simulation studies”, ieee bologna power tech conference, bologna, italy, june 23-26, 2003 [13] s. n. singh, i. erlich, “locating unified power flow controller for enhancing power system loadability”, international conference on future power systems, amsterdam, netherlands, november 18, 2005 [14] j. chakravorty, j. saraswat, v. bhatia, “modeling a distributed power flow controller with a pem fuel cell for power quality improvement”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2585-2589, 2018 [15] j. charavorty, j. saraswat, “deciding optimal location of dpfc in transmission line using artificial algae algorithm”, engineering, technology & applied science research, vol. 9, no. 2, pp. 39783980, 2019 [16] m. p. aghababa, m. e. akbari, a. m. shotorbani, “an efficient modified shuffled frog leaping optimization algorithm”, international journal of computer applications, vol. 32, no. 1, pp. 26-30, 2011 [17] s. a. uymaz, g. tezel, e. yel, “artificial algae algorithm (aaa) for nonlinear global optimization”, applied soft computing, vol. 31, pp. 153-171, 2015 microsoft word etasr_7-1_1398-1404.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1398-1404 1398 www.etasr.com mollamotalebi et al.: a weight-based query forwarding technique for super-peer-based grid resource… a weight-based query forwarding technique for super-peer-based grid resource discovery mahdi mollamotalebi department of computer engineering buinzahra branch islamic azad university buinzahra, iran mmahdi2@live.utm.my raheleh maghami department of computer engineering buinzahra branch islamic azad university buinzahra, iran maghamy@qiau.ac.ir abdul samad ismail faculty of computing universiti teknologi malaysia skudai, malaysia abdsamad@utm.my abstract—grid computing environments include heterogeneous resources shared by a large number of computers to handle data and process intensive applications. the required resources must be accessible for the grid applications on demand, which makes resource discovery a critical service. in recent years, different techniques are provided to index and discover grid resources. response time and message load during the search process highly affect the efficiency of resource discovery. this paper proposes a technique to forward the queries based on the resource types accessible through each neighbor in super-peer-based grid resource discovery approaches. the proposed technique is simulated in gridsim and the experimental results indicated that it is able to reduce the response time and message load during the search process especially when the grid environment contains a large number of nodes. keywords-grid computing; resource discovery; super-peer; weight-table; query forwarding i. introduction grid computing aims to handle data and process intensive applications. grid environments typically include a large number of nodes each of which owns one or more resources to be shared and used by the applications [1, 2]. with regard to the continuous increasing of networks’ bandwidth and resource varieties, grid computing is emerging as the next-generation computing platform in government, science, and business [3]. resource discovery is the process that takes the execution requirements of grid applications, searches the network for required resources and returns a set of grid nodes including resources matched to the application requests [4]. grid environments are inherently large-scale and dynamic. as a result, grid resource discovery is a time and message consuming process which affects the efficiency of the entire grid [5]. the response time and message load are two important factors for evaluating the efficiency of resource discovery approaches. the response time refers to the time between issuing a resource request and returning the resource owner addresses, and message load indicates the number of messages transferred between the grid nodes per second during the search process [6, 7]. the super-peer is a prevalent resource discovery approach in grid environments. in super-peer-based approach, the large-scale grid environment is divided into several smallscale environments in order to increase the scalability of resource discovery. some other approaches are based on hierarchical [8-12], peer-to-peer [13, 14], agent-based [15], and centralized [16] structures. this paper proposes a weight-based technique to improve the super-peer-based resource discovery approaches in terms of the response time and message load. in the super-peer structure, each node has the role of either regular-peer or super-peer. the super-peer nodes are connected to each other as peer-to-peer. in addition, each super-peer node acts as a central server for a set of regular-peers. a regular-peer sends the resource information and resource queries to its related super-peer node [17, 18]. when a regular-peer needs to explore the grid for some required resources, it sends a query message to its local super-peer. if the local super-peer finds the desired resources in its local index, it returns the resource reference to the requesting regular node. otherwise, it forwards the query to its neighboring super-peer nodes. some recent proposed super-peer-based resource discovery techniques for grid environments are described in the following paragraphs. in [19], the authors proposed a resource discovery system which uses the super-peer nodes in a framework based on chord [13]. the chord has a single ring to index the resources, but this technique uses multiple rings. each node of a ring can keep the addresses of some resources matching the queries. one node in a ring does not necessarily own the real resources but it may maintain their ip addresses. a super-ring is used to keep the nodes pointing to other rings. this technique decreases the message load however it highly depends on the information existed in the cache. it also benefits from the inherent load balancing of chord. on the other hand, it cannot control the traffic of different rings. it uses some monitoring considerations but in dynamic conditions, the monitoring potentially needs to transfer more messages. in [12], the authors proposed a technique in which the super-peer nodes make relation between different physical organizations and maintain the local domain’s resource information. some contact peers are defined in each domain to handle the grid registrations. different domains can have their own grid frameworks and they are communicated only through the super-peers. in this technique, the query is not forwarded to engineering, technology & applied science research vol. 7, no. 1, 2017, 1398-1404 1399 www.etasr.com mollamotalebi et al.: a weight-based query forwarding technique for super-peer-based grid resource… all the neighboring nodes to traverse the network. instead, the receiving super-peer node forwards the query to a selected number of neighbors. to this end, the super-peer nodes record the number of query-hits obtained by each neighbor in previous search attempts. in the next search processes, the super-peer node forwards the received query to the neighbors who had the highest number of query-hits in the past and by this way, it decreases the message loads. in [20], the authors proposed a resource discovery technique for superpeer-based structure using semantic and fuzzy theory. it considered delay as a major parameter of fuzzy system. the amount of semantic similarity between node services is the other parameter of the fuzzy system. thus, it used delay, bandwidth and semantic similarity as the input parameters of fuzzy system to create semantic overlay network. the scheme consists of node grouping and resource discovery, and fuzzy theory is used in both phases. it uses a hybrid p2p structure where the nodes are divided into groups. this technique could increase the number of adequate discovered resources and reduce the response time. on the other hand, the precision of resource discovery is decreased because it emphasizes on the geographical factors to group and search the resources. in [21], the authors presented a super-peer based technique for the discovery of resources in grid environment which supports multi-attribute and range queries. the technique summarizes resource information to improve its scalability. it also exploits routing indices (ris) to handle the priority of tasks and resolves the problem of access to all domains’ summaries. it uses clustering to perform the summarization and builds a tree of gathered information. then it creates a summary of the database by applying two steps, pruning and leafing. in the first step, branches are pruned at a given depth such that no branch is deeper than the chosen depth. although its scalability, this technique is not as efficient in terms of message load and response time due to the processing overheads related to the summarization steps. ii. description of weighted-sp the weight-based super-peer (weighted-sp) technique aims to reduce the message load and response time of the super-peer resource discovery by limiting the neighbor nodes receiving the forwarded queries. it is performed by adding a weight table to indexing nodes indicating the weight of their neighbors to be chosen. in each indexing node, the weight table indicates the number of resource types that are accessible through each path. by this way, when a query is received by an indexing node, it forwards the query to the limited number of neighbors with the highest weights for the requested resource type. it is not possible in super-peer structure to be aware of the resource information comprehensively during the join or update processes. this is because the super-peer nodes are related to each other as p2p without any hierarchical organizations. also publishing all the resource join and update messages to other super-peer nodes will impose a dramatic message load on the system. thus, weighted-sp updates the number of resource types in the weight tables during the search process instead of the join or update processes. for this purpose, whenever a query reached the resource owner, the resource discovery process returns the found resource owner address to the requester node and then, the weight table of the super-peer nodes in the backward path of the successful query is updated. the weighted-sp scheme is illustrated in figure 1. each super-peer node keeps the resource information of its local regular nodes and the weight table. the weight table includes a row for each neighbor of current super-peer. in each row, there are columns corresponding to the resource types existing in the grid. the weight tables of super-peer nodes are empty in the initial state of grid environment establishment. in this situation, super-peer nodes which have no information about the resource types in their weight table, forward the queries to all of their neighbors. but after each query forwarding, the weight tables are updated for the requested resource type. fig. 1. the schema of weighted-sp resource discovery the search process is initiated by regular nodes in the grid. the regular node issues its resource query and sends it to the local super-peer node. the super-peer node first investigates the local regular nodes to find the required resource. if the resource is found, the address of found resource owner will be returned to the requester node and the search process will be terminated. otherwise, the super-peer node sorts its weight table information related to the requested resource type and sends the query to a specified percent of neighboring nodes which highest number of resource types are accessible through them. this process is continued until the required resource is found or all the super-peer nodes are investigated. by this manner, the query is forwarded to the neighbors with the highest probability of success at each step of the search process. weighted-sp uses the backward messages to be informed about the successful search results and updates the weight tables of the super-peer nodes located in the path of successful search processes. the weight tables of super-peer nodes are empty during the initial state of grid environment establishment. in this situation, super-peer nodes which have no information about the resource types in their weight table, forward the queries to all of their neighbors. after each query forwarding, the weight tables are updated for the requested resource type. the implementation design for weighted-sp is presented in figure 2. engineering, technology & applied science research vol. 7, no. 1, 2017, 1398-1404 1400 www.etasr.com mollamotalebi et al.: a weight-based query forwarding technique for super-peer-based grid resource… fig. 2. implementation design of weighted-sp the request manager module generates the resource requests and nodes’ join/leave events. the generated resource requests are assigned to users randomly and sent to the module broker. the module broker is responsible to schedule the resource requests and responses. it acts as a medium between the resource discovery system and grid environment. it analyzes the received resource requests according to the receive time, separates multiple attribute requests to make different independent queries, schedules all queries and forwards them in turn to the gis. then it waits for the resource owner address to be returned from the gis module. when the matched resource owner address is discovered by the gis and returned, module broker sends the allocation request to the found resource owner. the indexing nodes and resource information are handled by the gis. almost all modules are related to the gis to transfer the resource information or get the search results. when a resource is allocated to an application, its value will be updated and the new resource information is sent to the gis. the resource handler module is responsible to send any resource information changes caused by the resource allocation, join, and leave events to the gis and subsequently the gis updates all indices related to the changed resource information. the resource handler also manages the allocation requests sent by the broker. if a resource is available, then it will be allocated to the requesting application for specified period of time which is determined by the initial resource requester. the gis is responsible to index resource information and locate the resource owners according to the received requests. after finding the resource owner addresses, the gis returns them back to broker to handle the allocation process. the report writer module receives statistical information of requested resources, transferred messages, and successful results of the search processes to analyze and make the appropriate reports according to the comparison and analysis requirements. for each experiment, r resource requests are issued. the resources join and leave the network and these events cause to transfer more messages. moreover, after finding a required resource, the found resource is allocated to the requester node. the resource information changes caused by the allocation events also should be considered. the update messages that are related to the allocation events are estimated by the (1) such that s is the success rate of queries, r is the number of issued resource requests, and k is the rate of multi-attribute query issues that request two resources. 1 n =2(k+1) s r (1)⋅ ⋅ 2 1 n n =h (2) n ⋅ the messages related to join and leave events are estimated by (2) where n represents the number of regular nodes and n is the number of super-peer nodes. assuming h1 as the rate of join and leave events, the equation specifies the messages that are issued for the regular nodes’ join and leave events. in addition to the above mentioned update messages, some messages are transferred for random change events that are applied by the system on the resources. each grid node shares one to three resources. equation (3) calculates these messages as well the allocation and join/leave events such that r is the maximum number of resources in each grid node and h2 is the rate of change events on the resources. r c 1 2 i=1 n m =n +n + (h2 i) (3) n ⋅ ⋅å considering the number of issued resource requests as r, and k as the rate of multi-attribute queries, the number of resource requests reached to an super-peer node is estimated by (4). rm = 2 (k+1) r (4) n ⋅ ⋅ n c r i=1 i p m= (m +m (1)) (5) n ⋅ ⋅å considering the update and request messages at each superpeer node, and with regard to p percent of neighbors chosen to forward the queries by super-peer nodes, the overall transferred engineering, technology & applied science research vol. 7, no. 1, 2017, 1398-1404 1401 www.etasr.com mollamotalebi et al.: a weight-based query forwarding technique for super-peer-based grid resource… messages can be estimated by (5). the implementation methods for weighted-sp including the join/leave, request issue, and search processes are presented and described in the following paragraphs. figure 3 presents the algorithm of the join events for grid resources in weighted-sp. fig. 3. the algorithm of grid nodes’ join events in weighted-sp once the request manager issues a join event, the method joinrequest() will be performed. this method chooses one of the free nodes to join the grid environment. with regard to the random event issues of join and leave events, usually there are some free nodes available to be chosen. after choosing a free node, its status will be changed to active and its resource is added to the existing resources of grid environment. then a super-peer node that has free capacity to index the new received node will be found and assigned to the joint grid node. moreover, the new node is added to the regular nodes of the found super-peer. figure 4 presents the pseudo code of the leave events for grid resources in weighted-sp. the method leaverequest() first chooses a random node to be left. the leave event can be issued for the grid node or a resource of grid node. it is specified by the request manager through the parameter ’type’ that is set to ’complete leave’ if the grid node should be left from the grid. if the leave event issued for a resource of an existing grid node, a random number between one to three is chosen and then the resource will be removed from the chosen grid node. moreover, the request manager issues events to leave the super-peer nodes. in this cases, the method leaverequestsp() is performed that substitutes a free superpeer for the leaving one. for this purpose, the process copies the neighbors and related nodes of the leaving super-peer node to the new one. the method requestissue() in fig. 5 chooses a regular node as random to issue a resource request. with regard to possibility of issuing multi-attribute queries in weighted-sp, and existence of one to three resources in each grid node, this process adds a random number of resources in the query. considering that weighted-sp uses the successful query messages to update the weight table of super-peers in the backward path, the super-peer of current regular node is kept in the global variable originsp. this variable is used subsequently in the method wtableupdate. then the query is forwarded to the local super-peer of current regular node. fig. 4. the algorithm of grid nodes’ leave events in weighted-sp fig. 5. the algorithm of resource request issue in weighted-sp the receivedrequest()method that is shown in figure 6 is responsible to handle the search process of requested resources. the super-peer node investigates its related regular nodes to satisfy the received query. if one of its regular nodes could satisfy the query, the super-peer performs the wtableupdate process in order to update the weight table of super-peers in backward path and search process is terminated. if the superpeer node did not found any matched resource in its related regular nodes, it sets the number of neighbors to forward the query considering the specified percentage by the user. the weight table of current super-peer node is copied in tempwtable to prevent information changes in the original weight table during the search process. engineering, technology & applied science research vol. 7, no. 1, 2017, 1398-1404 1402 www.etasr.com mollamotalebi et al.: a weight-based query forwarding technique for super-peer-based grid resource… the number of branches to forward the query is set considering the percentage of forwarding branches specified by the user. then the weight table of current indexing node is copied to tempwtable in order to find the branches that highest number of requested resource type is accessible through them. this copy of the weight table is needed to prevent changes in the original weight table of the indexing node during the forward steps. at each step of query forwards, the neighbor with highest number of accessible resource type is found and the query is forwarded to it. the index of appropriate neighbor to forward the query is kept by the variable hindex. in order to remove the highest value form the next forward steps, its value is set to zero in the tempwtable fig. 6. the algorithm of resource discovery in weighted-sp the wtableupdate process shown in figure 7 is responsible to update the weight table of superpeer nodes in backward path upon finding the required resource. its first parameter is the address of super-peer node that should update its weight table. the query is send as the second parameter to inform the receiving super-peer that this update is related to which resource type. the third parameter is the address of current super-peer. the receiving super-peer adds the value of resource type that is accessible through its neighbor. then it fetches the previous super-peer in order to perform the update process. the update process is repeated until reaching the original super-peer node related to the initial requester regular node. fig. 7. the algorithm of weight table update in weighted-sp iii. simulation results and evaluation in order to perform the simulation experiments for the proposed technique, it is implemented in java under the simulation toolkit gridsim version 5.2. the hardware platform includes cpu intel core 2 duo 2.93 ghz and 4 gb of ram. the experiments are performed by different number of grid nodes i.e. 1000, 5000, 10000, and 20000. also, to investigate the impacts of the forwarded neighbors, three values i.e. 25, 50, and 75 of the forward percentages are considered for the indexing nodes. in addition, to have the reliable results, 1000 resource requests are issued per experiment and the average results of the message load and response times are calculated. in order to compare and evaluate the results, an existing superpeer-based technique [21] is simulated in the same hardware and software platform. this technique is referred as sp in the rest of this paper. the message load in the performed experiments is measured by dividing the number of messages transferred during the search process to the time spent for issuing all the requests. also, the response time is taken by calculating the average value of all the requests’ response time. the response time of each request is the duration between issuing the request and finding the result. the experimental results of weightedsp are presented in the following paragraphs. table iσφάλμα! το αρχείο προέλευσης της αναφοράς δεν βρέθηκε. presents the message load of weighted-sp for different number of grid nodes and forwarding percentage values. also, the reduction rates of the message load for weighted-sp relative to sp are presented in table ii. table i. the message load of weighted-sp for different number of grid nodes and forwarding percentage values number of grid nodes 1000 5000 10000 20000 pr =25% 4.6 13.6 30.6 61.1 pr =50% 6.1 17.58 40.52 80.1 pr =75% 7.39 22.34 51.4 104.73 sp 8.41 25.74 60.49 124.97 the reduction rates of message load indicate that choosing the lower percentages of neighbors to forward the queries results to the higher rates of reductions in the message load. the reduction rate of message load is not equal to the excluded neighbors since the weight tables are used only to limit the query forwards. the update messages between super-peer nodes and their related regular nodes are transferred regardless to the weight tables. σφάλμα! το αρχείο προέλευσης της αναφοράς δεν βρέθηκε. presents the average response time of engineering, technology & applied science research vol. 7, no. 1, 2017, 1398-1404 1403 www.etasr.com mollamotalebi et al.: a weight-based query forwarding technique for super-peer-based grid resource… sp and weighted-sp for different number of grid nodes. the response time of resource discovery is affected by the weightbased forwards of the queries because the neighbors with lower accessibility of required resource types are excluded from the search process. therefore, the average response time for the issued queries is reduced. table ii. the message load reduction rates of weighted-sp for different forwarding percentages number of grid nodes 1000 5000 10000 20000 overall reduction rate pr =25% 45.2% 47% 49.3% 51.1% 48.15% pr =50% 27.4% 31.7% 33% 35.9% 32% pr =75% 12% 13.2% 15% 16.1% 14% table iii. the average response time of sp and weighted-sp for different number of grid nodes number of grid nodes 1000 5000 10000 20000 weighted-sp 0.19 0.32 0.45 0.59 sp 0.2 0.35 0.51 0.67 reduction rate 5% 8.5% 11.5% 11.9% in order to identify the appropriate values of the forwards percentage, the success rates of the search processes are measured. because the weight-based query forwarding excludes some neighbors form the search domain, it affects negatively the success rate of the search process. table iv presents the success rate of weighted-sp for different number of grid nodes and query forwarding percentages. the success rate of weighted-sp is less than sp in all cases. it is because weighted-sp excludes some neighbors from the investigation during the search process. but the success rate does not increase significantly when the queries are forwarded to more neighbors. it is because the success rate of weighted-sp depends to the information of weight tables more than the forwarding percentage. if the weight tables do not contain useful information about the resource types, this technique cannot forward the queries to the appropriate grid nodes. in weighted-sp, the super-peer nodes are not informed about the resource information of other ones, and the weight tables are updated by using the results of resource queries. thus more number of requests enriches the information of weight tables. in order to investigate the impacts of number of issued queries on the success rate of weighted-sp, the experiments are repeated with three more values i.e. 5000, 10000, and 20000 of the issued resource queries. table v presents the success rate of weighted-sp for 1000 grid nodes and different number of issued queries. the results indicate that issuing more number of queries increases the success rate of weighted-sp. it is because the weight table’s information of super-peer nodes in weighted-sp depends on the search results of issued queries. the higher number of issued queries enriches the information of weight tables, and subsequently the queries can be forwarded more efficiently toward the appropriate neighbors. as a result, weighted-sp could reduce the message load and response time of the search process by excluding some neighbors form the search domain based on the specified percentage of query forwards. because the results of the search processes are used to update the weight table of super-peer nodes, more number of issued queries enriches the weight tables of weighted-sp and subsequently it increases the success rate of this technique. table iv. the success rate of weighted-sp for different number of grid nodes and query forwarding percentages number of grid nodes 1000 5000 10000 20000 pr =25% 44.8% 45% 45.2% 45.5% pr =50% 47.2% 47.6% 47.9% 48.1% pr =75% 49.7% 51% 51.7% 52.3% table v. the impact of number of issued queries on the success rate of weighted-sp number of requests 1000 5000 10000 20000 pr =25% 44.8% 47.1% 51.7% 57.8% pr =50% 47.2% 58.8% 64.1% 74.9% pr =75% 49.7% 69.1% 75.3% 79.6% average of success rates 47% 58% 63% 71% iv. conclusion the resource discovery service responsible to find the resources required by grid applications has an important role in grid computing systems. this paper proposes a weight-based technique to improve the super-peer-based grid resource discovery solutions in terms of message load and response time. in the proposed technique, each indexing node keeps a weight table consisting of its neighbors and the number of different resource types that are accessible through each neighbor. in super-peer structure, the resource information of other super-peer nodes cannot be collected during the join or update processes, and such information is collected by using the successful search results. the experimental results of the proposed technique indicated that it reduces the message load and response time during the search process. with regard to the contents of the weight tables, choosing higher percentage of neighbors to forward the queries causes the system to act similarly to conventional super-peer-based systems. on the other hand, choosing a very low percent of neighbors excludes many resource owners from the search domain. the results showed that choosing more than 75% of neighbors could result to suitable values of the message load and response time while keeping the success rates high. in addition, higher number of resource requests enriches the weight tables of the proposed technique in the super-peer-based structure and causes it to act more efficiently. engineering, technology & applied science research vol. 7, no. 1, 2017, 1398-1404 1404 www.etasr.com mollamotalebi et al.: a weight-based query forwarding technique for super-peer-based grid resource… references [1] d. puppin, s. moncelli, r. baraglia, n. tonellotto, f. silvestri, “a grid information service based on peer-to-peer”, 11th international euro-par conference, lisbon, portugal, august 30-september 2, 2005 [2] m. a. arafah, h. s. al-harbi, s. h. bakry, “grid computing: a stope view”, international journal of network management, vol. 17, pp. 295305, 2007 [3] m. r. islam, m. t. hasan, g. ashaduzzaman, “an architecture and a dynamic scheduling algorithm of grid for providing security for real‐ time data‐ intensive applications”, international journal of network management, vol. 21, pp. 402-413, 2011 [4] m. hauswirth, r. schmidt, “an overlay network for resource discovery in grids”, sixteenth international workshop on database and expert systems applications, pp. 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robles-gomez, s. ros, r. hernandez, l. tobarra, "p2p-based resource discovery in dynamic grids allowing multi-attribute and range queries”, parallel computing, vol. 39, pp. 615-637, 2013 microsoft word 40-3097_s_etasr_v9_n5_pp4801-4807 engineering, technology & applied science research vol. 9, no. 5, 2019, 4801-4807 4801 www.etasr.com jake et al.: spectral re-growth suppression in the fbmc-oqam signal under the non-linear … spectral re-growth suppression in the fbmcoqam signal under the non-linear behavior of a power amplifier jimmy jake department of electrical engineering, pan african university, institute for basic sciences, technology and innovation, nairobi, kenya jakeloponi@gmail.com elijah mwangi school of engineering, university of nairobi, nairobi, kenya mwangiel2010@gmail.com kibet langat dpt of telecommunication and information engineering, jomo kenyatta university of agriculture and technology, nairobi, kenya kibetlp@jkuat.ac.ke abstract—typically, the filter bank multicarrier with offset quadrature amplitude modulation (fbmc-oqam) bears some impressive properties that make it popular as one of the substitutes to orthogonal frequency division multiplexing (ofdm) for the upcoming technology of broadband wireless communication systems. although fbmc-oqam preserves the multicarrier modulation (mcm) features, its spectrum usually suffers from impairments when subjected to the nonlinear behavior of a power amplifier (pa) which results in spectral regrowth. due to the spectrum limitation and low energy efficiency foreseen in the forthcoming 5g networks, it is vital to confine the spectrum of the fbmc-oqam signal within the allocated band of interest. in this paper, the suppression of the spectral regrowth experienced on the fbmc-oqam signal due to the nonlinear distortion effects introduced by the pa is investigated. the crest factor reduction (cfr) method in combination with an adaptive digital pre-distortion (dpd) are used. the peak windowing technique based on sequential asymmetric superposition windowing (sasw) algorithm is used in the cfr part while the least square estimation with qr-decomposition (lse/qr) has been used as the coefficient’s estimator and adaptation algorithm in the dpd part. the performance of the two combined techniques has been evaluated on systemvue2018 simulation platform. the adjacent channel leakage ratio (aclr) and the error vector magnitude (evm) have been considered as the performance merits. the simulation results show that the proposed techniques significantly improve the spectrum, first by reducing the papr of the fbmc-oqam signal by about 1.5db. secondly, the spectral re-growth has been reduced by about -45.74db adjacent channel leakage suppression and the error vector magnitude measure has been obtained to be about 7.12%. (-22.95db). these values lead to better average input power of the fbmc-oqam signal and improvement in the spectral efficiency and they are in accordance with the 3gpp standard for wideband signals in nonlinear systems. keywords-fbmc-oqam; spectral re-growth; nonlinear pa; cfr; sasw; adaptive dpd; lse with qr decomposition i. introduction the dynamic growth in the number of users that have different demands for accessing information under wireless communication is leading to spectrum scarcity. this has prompted a concern for the investigation of new techniques to address the issues of spectrum and energy efficiency improvement. orthogonal frequency division multiplexing (ofdm) modulation scheme had been widely used in the existing wireless domain due to its ability to effectively minimize the issues of delay spread in the broadband wireless channels in the long-term evolution (lte) 4g cellular networks [1-3]. however, the ofdm signal is time-limited because it is centered on the use of rectangular pulses in the time domain which leads to slowly decaying behavior in the frequency domain. these features make ofdm inappropriate, especially in situations where users need to be asynchronized and strict limits on the out-of-band radiation levels are highly required. to overcome these limitations, the fbmc-oqam scheme has been studied as an alternative waveform candidate to ofdm and is becoming the leading contender among the multicarrier modulation schemes proposed for the upcoming wireless communication systems, because of its ability of minimizing the out-of-band emission (oobe), cyclic prefix (cp) free transmission, and robustness to the asynchronous situation [4-6]. unfortunately, the fbmc-oqam signal still suffers from high peak-to-average power ratio (papr) which is susceptive to the nonlinear behavior of the pa, and as a result, it suffers from spectral re-growth. high peak signals require amplification with power amplifiers that have high linearity. however, such power amplifiers come with high cost and they compromise energy efficiency [7, 8] which may not be suitable to many telecommunication network providers, that is why nonlinear power amplifiers are still common in many wireless transmitters, due to the high cost and low energy efficiency of the linear power amplifiers, the use of nonlinear power amplifiers is preferred. however, they cause signal distortion which requires compensation techniques for signals with high peak values. among these techniques are clipping and filtering, peak cancellation, and peak windowing for crest factor reduction [9, 10] while feedforward, feedback, and predistortion [10, 11] were used for nonlinearity compensation. corresponding author: jimmy jake engineering, technology & applied science research vol. 9, no. 5, 2019, 4801-4807 4802 www.etasr.com jake et al.: spectral re-growth suppression in the fbmc-oqam signal under the non-linear … these techniques allow the nonlinear pa to operate at higher output power while maintaining linearity and increase in energy efficiency. reducing the crest factor enhances energy efficiency and linearization approaches required to compensate the nonlinearities introduced by the pas. however, in practice, the crest factor reduction (cfr) technique slightly degrades the signal quality which results in reduced data throughput. in regard to multicarrier signals such as fbmc-oqam, degradation within the required bandwidth has less significance than degradation that results from the broadening of signal bandwidth [10]. in this work, the peak windowing approach [9, 10] based on the kaiser window together with sequential asymmetric superposition widowing (sasw) algorithm [12] is used to reduce the high peak values experienced on the fbmc-oqam signal. the reasons for this are that this algorithm is applicable to both single and multicarrier signals. also, it can handle the over-attenuation issues that arise as a result of unnecessary window superpositioning. the concurrent application of crest factor reduction and digital pre-distortion techniques can provide an amicable solution to meet the requirements of linearity and energy efficiency benefits [13]. digital predistortion (dpd) techniques are currently popular in the cellular communication domain as nonlinearity compensating techniques [14]. due to the high flexibility and excellent linearization performance, dpd has been mostly used in linearizing pas and it tends to be an essential linearization technique in the current and next-generation wireless communication systems. owing to the dynamic nature of the pa nonlinearity, adaptive digital pre-distortion will be used here as a nonlinearity compensating technique to deal with the issues of the spectral re-growth experienced on the fbmcoqam signal in order to maintain the characteristics of the signal under the nonlinear behavior of the pa. although adaptive digital pre-distortion can be modeled as a nonlinear technique using volterra series, look-up table (lut) and memory polynomial (mp) [15, 16], the main focus here is on the memory polynomial model which is a truncated version of volterra series due to its elegance and simplicity in implementation. the least square estimation (lse) algorithm has been used on many occasions to estimate the coefficients of nonlinear systems [10, 17]. here, the lse with qr decomposition is used to estimate and adapt the model’s coefficients. this is because of its ability in dealing with the over-determined problems which may arise because of the large number of samples used and also the ill-conditioned and rank-deficient scenarios that may be encountered during the inversion of the transfer function of the nonlinear power amplifier. to the best of our knowledge, no published study has used the combination of the two algorithms to concurrently minimize both the papr and the spectral re-growth of the fbmc-oqam under the nonlinear effects of the pa. ii. related work in [15], the impact of hpa nonlinearity on the performance of ofdm and fbmc-oqam systems was investigated, where saleh’s model for the nonlinear hpa was considered. in this study, two pre-distortion schemes which were based on the indirect learning architecture were presented. the first scheme aimed to compensate simultaneously the amplitude and phase distortions induced by the nonlinear hpa, while the second aimed to compensate these distortions separately. it was shown that the first pre-distortion scheme performs worse in the fbmc-oqam system than in the ofdm. with the second pre-distortion scheme, the phase and amplitude pre-distortions were made separately. the ofdm and fbmc-oqam systems reached the same performance showing that a higher attention must be paid in phase correction in fbmc-oqam. authors in [18] presented an innovative algorithm for scalar feedback digital pre-distortion, known as orthogonal scalar feedback linearization to compensate the nonlinear distortion and reduce the spectral re-growth in nonlinear power amplifiers. the adaptation of the discrete model coefficients becomes orthogonal in the intermodulation domain. this scheme presented a lower intermodulation at the power amplifier output and was compared with existing scalar feedback digital pre-distortion algorithms in achieving faster convergence time and lower output power variation. the problem of this method is that the coefficients are adjusted independently while the lower order coefficients are affected by the higher order ones. also, the adjustment on the current coefficient affects the adjustments made on the previous coefficients, which causes non-orthogonality of coefficients in the intermodulation domain. the distortion caused by nonlinear power amplifiers brought up the desire for correction. in [19], the performance of 5g candidate waveforms such as fbmc and ufmc with nonlinear power amplifiers was evaluated using digital pre-distortion and an iterative correction algorithm with hard detection and was compared to the ofdm waveform. it was observed that, in regards to power amplifier without memory effects, the ufmc presents the most robust behavior while the fbmc suffers more impact in terms of ber. it was also noted that the iterative correction with hard detection algorithm is effective on the three waveforms and that no many iterations are needed to reach a result close to linear performance. the scenario with memory power amplifier changes this result a bit. in this case, the fbmc is the one that overcomes the others in terms of ber performance. the 5g waveforms had showed more robustness when compared to the 4g waveform (ofdm). iii. system model a. overview of the fbmc-oqam system the overall concept of the fbmc-oqam is the transmission of complex symbols, where the in-phase and quadrature components are interleaved by a half symbol duration, �/2. in the oqam pre-processing, the complex input symbol vectors ��,� are converted into real symbols, where the in-phase and the quadrature components are time staggered by half a symbol period in order to maintain the orthogonality between carriers. for 0≤m≤2m-1 and 0≤n≤n-1, where m and n are the symbols and subcarriers indices respectively, the oqam processing mathematical formulation is given as in [20]. the procedure of the oqam pre-processing in the fbmc transmitter is illustrated as in figure 1. after the oqam preprocessing, the real symbols undergo poly-phase filtering that engineering, technology & applied science research vol. 9, no. 5, 2019, 4801-4807 4803 www.etasr.com jake et al.: spectral re-growth suppression in the fbmc-oqam signal under the non-linear … involves ifft transformations along with filtering by a synthesis filter bank (sfb) with an impulse response �� as illustrated in figure 2. fig. 1. oqam pre-processing in the fbmc transmitter fig. 2. sfb implementation in the fbmc transmitter a discrete-time baseband fbmc-oqam signal ���� upsampled by a factor �/2 is then obtained [21]: ��� � � � s��,�,s��,�,………………. ,s����,�� (1) ��� � ∑ ∑ ��, !�� "�#$���"� %� & ' (! # )* +,-./ 0*+12,3 (2) where � 4.5 is the fbmc-oqam modulation function, ��, are oqam processed from ��,� vectors and 6�, is the phase term equal to 7 # ' 8 9� & :'. the physical layer for dynamic spectrum access and cognitive radio (phydyas) prototype filter introduced in [22, 23] with overlapping factor k=4 is considered here as the pulse shaping filter in the fbmc-oqam system because of its optimal localization characteristics of the signal in both time and frequency domains. b. cfr-based sequential asymmetric superposition windowing algorithm a major challenge of dealing with multicarrier systems such as fbmc-oqam is the resulting high peak values. this mainly occurs because each subcarrier is usually modulated and filtered individually which results in more instantaneous power than the average power. the peak-to-average power ratio (papr) of the discrete-time fbmc-oqam signal is [24]: ;<;= ���� � >?@abcbdef |h 0�| ,� i4|h 0�|,5 (3) where j4.5 is the expectation value. here, the advantage of the sequential asymmetric superposition windowing (sasw) algorithm is explored because of its application in both single and multicarrier signals. at first, a window length is specified and when the peaks are detected in the window, they are grouped into blocks, and their locations are then indexed. in order to minimize the over-attenuation introduced by the unnecessary window superpositioning, an overall windowing function for each block is constructed in an iterative manner to deal with the dynamic fluctuation of the peaks. the window segment for the grouped peaks is then smoothened by the addition of all the asymmetric peak windows in the block. the sequential asymmetric superposition windowing (sasw) algorithm is applied to the peaks in each block, where only the peaks with large values take part in the decision making of the scaling function. the crest factor reduction (cfr) based on sequential asymmetric superposition windowing is given by [12]: klm��� � 1 & ∑ op�q�4rsp�� & �q� 8 rtp�� & �q�5 u v"�u (4) where rsp��� and rtp��� are the left and right side of the window functions respectively with different window lengths, op�q� is the new weighting index factor for those concealed peaks indexed by q as op�q� � 0. c. digital pre-distortion in wireless systems fundamentals the basic concept of the dpd technique is illustrated in figure 3. a transfer function of a nonlinear pa is shown with xyx ��� as the input and z �� as the output. if the dpd model manipulates the signal with a proper inverse transfer function such as shown on the transfer function with ��� as input and xyx ��� as output, the final output z �� of the pa will be a linear signal with respect to the original input ���. unlike circuit-level nonlinearity compensation, digital pre-distortion uses the black-box-based behavioral modeling procedures to describe and invert the input signal before the pa [25]. under this concept, only the pa input and output relationship are considered in the nonlinearity compensation process. this significantly relieves the burden of analogue circuit design and debugging. fig. 3. basic concept of digital pre-distortion d. digital pre-distortion model description the power amplifier is an essential component of the transmitter. however, its operation near the saturation zone creates nonlinear distortion to the input signals which result in spectrum re-growth. therefore, there is a need to compensate these nonlinearities in order to maintain the spectrum of the input signal within the specified band of interest. the engineering, technology & applied science research vol. 9, no. 5, 2019, 4801-4807 4804 www.etasr.com jake et al.: spectral re-growth suppression in the fbmc-oqam signal under the non-linear … nonlinearity of the pa is usually dynamic due to its build-up components, aging, and other environmental factors. therefore, an adaptive identification of the dynamic nonlinear behavior of the pa is essential. to compensate for this nonlinear and the dynamic distortion in the pas, adaptive dpd models based on indirect learning architecture (ila) with memory polynomial (mp) are used because of their simplicity [10]. this concept is illustrated in figure 4, where the adaptive dpd model is applied to adjust the signal sample ��� in the digital domain to compensate for the nonlinear behavior of the pa output z �� in the analogue domain. the pa output is monitored by an observation path and converted to the digital domain where the input signal xyx ��� to the pa and the feedback signal [��� from the pa output are compared and an adaptive algorithm is implemented where the dpd coefficients in the pre-distorter block are updated accordingly. the overall idea of using the adaptive dpd is to adjust the fbmc-oqam signal ��� in such a way as to minimize the distortion introduced by the nonlinear pa in a dynamic manner. fig. 4. ila for an adaptive digital pre-distortion model extraction e. digital pre-distortion authentication procedures the dpd can be carried out in multi-step procedures where the adjacent-channel-power (acp) assessment of the transmitter is verified. due to the dynamic nonlinear distortion and memory effects of the nonlinear pa, the dpd parameters are trained for several iterations. however, this requires a robust testing platform in order to evaluate the dpd performance properly. this work only considers the simulation-based platform. dpd algorithms are intrinsically mathematical and need to be performed on a processor with high computational ability, therefore, a simulation-based environment, known as systemvue2018 has been used as the modeling and verification platform. the modeling procedures are: step 1 baseband source: generating a digital baseband data sequence with required sampling rate such as fbmcoqam signal ����. step 2 crest factor reduction: reducing the peak of the fbmc-oqam baseband signal in order to minimize clipping during amplification. step 3 signal pre-distortion: the original digital baseband signal is pre-distorted using an inverse transfer function model of the pa. this compensates the nonlinearity distortion effects of the pa. step 4 signal up-conversion: up-converting the digital baseband signal to the required analogue frequency, with appropriate signal power in order to drive the pa. step 5 signal amplification: a power amplifier is employed to amplify the signal before transmission to compensate for the attenuations that may be encountered by the signal in the free space propagation. step 6 feedback signal attainment: the output of the nonlinear pa is down-converted to the baseband signal, and then the baseband analogue signal is captured with an adc. step 7 dpd parameter extraction and updating: the dpd parameters are calculated and then the coefficients are updated in the digital pre-distorter. step 8 time alignment: to obtain matched pa input and output, the original input and output signals of the pa are captured and aligned in the time domain so that the sample delay introduced by the feedback path can be characterized and compensated with no system deadlock. step 9 performance assessment: a spectrum analyzer is used to assess the frequency-domain nonlinearity compensation performance such as the aclr or capturing the signal gain to assess the time-domain performance such as the evm. these procedures are modeled in systemvue2018-based platform as illustrated in figure 5. fig. 5. a simulation-based dpd procedure iv. behavior modeling of the digital pre-distortion system a. memory polynomial model the mp model has been considered as a special case of the volterra model due to its elegancy and simple structure for incorporating memory effects into the static nonlinear polynomial model and has been extensively used in a variety of applications, especially in the linearization of power amplifiers with memory [10]. the nonlinearities with memory effects can be generally described as the sum of the outputs from the polynomial functions and can be written as [11]: xyx��� � ∑ ∑ \],� �� & ^�| �� & ^�|]��_�"�y]"� (5) where ; and ` are the nonlinearity order and memory depth of the mp-based model respectively and \],� are the coefficients of the model. engineering, technology & applied science research vol. 9, no. 5, 2019, 4801-4807 4805 www.etasr.com jake et al.: spectral re-growth suppression in the fbmc-oqam signal under the non-linear … the output of the nonlinear pa z �� is a function of the dpd signal xyx��� and is given by: z �� � ∑ ∑ \],� xyx � & ^�| xyx � & ^�| ]��_ �"� y ]"� (6) in the indirect learning architecture dpd (post-dpd – figure 4), the nonlinear function of the pa is inverted in order to identify the nonlinearity behavior of the pa which acts as a feedback signal, essentially acting as a post-distorter on the pa output signals. since the nonlinearity behavior of the pa is modeled by dpd using mp, the pre-distortion of the nonlinear pa is functionally the same as the post-distortion. the input to the post-dpd block is the direct inversion of the nonlinear pa transfer function and is given as: [��� � ∑ ∑ \],�z � & ^�|z � & ^�| ]��_ �"� y ]"� (7) where the parameters ;,`, and \],� are the same as in the predistortion model. b. coefficients estimation and adaptation algorithm fbmc-oqam is the most demanding modulation scheme for the next generations of wireless communication industry. a relatively large number of samples have to be allocated to it to identify the small number of coefficients for the dpd algorithm. therefore, the lse with qr decomposition (lse/qr) algorithm is used to estimate the coefficients of the model due to the over-determined problem experienced on the signal because of the large number of the samples used. the lse is more commonly used because of its easy implementation and satisfactory performance [17]. 1) coefficients estimation the coefficients \],� in (7) can be solved by using the lse by defining a new signal variable as in [17]. the output of the pre-distorter training block (post-dpd) of figure 4 with the gain of the amplifier a set to unit can be solve using the lse solution as given in [17] where the coefficients of the predistorter training block (post-dpd) become: \b � rcr���rcd̂ (8) the matrix r is ill-conditioned even if the signal is scaled and normalized at the range of the values of the polynomial orders. using the `= decomposition method, the matrix r can be factorized into: r � `= (9) where the matrix ` is ' × 9 with orthonormal columns and = is an invertible 9 × 9 upper triangular matrix. the orthonormal matrix ` preserves the norm or distance in any transformation. the `= decomposition rotates the matrix r until the point where the set of linear equations can be solved by backsubstitution in the matrix =, since ` is orthonormal, i.e.: `c` � g (10) then: `cd̂ � `c`=\b � =\b (11) since = is invertible, the estimate for the coefficients becomes: \b � =��`cd̂ (12) where [•] h stands for complex conjugate transpose. equation (12) is relatively straightforward to solve, and since = is triangular, the coefficients can be found by backsubstitution in the vector `cd̂. this procedure avoids the inversion of the rcr in the normal equation (8) and the associated numerical instabilities. this algorithm is in-built in the systemvue2018 software and it is generally robust in dealing with ill-conditioned and rank-deficient matrices. the coefficients of the pre-distorter obtained off-line through (12) are copied to the pre-distorter on the feed-forward path as the initial coefficients. because of the dynamic nature of the pa nonlinearity stated above, the coefficients can be updated adaptively as demonstrated in figure 4. 2) coefficients adaptation the pre-distortion coefficients adaptation is quite straightforward for indirect learning architecture. considering the nonlinear memory polynomial model of the dpd as in (5), the pre-distorted input signal to the pa ( xyx���) is compared to the post-distorted output signal [���� from the pa. the absolute error signal h� at any sample instant � is then obtained by the equation given in [10]. then, the estimate of the coefficients error (∆a ̂) can be minimized by taking the difference between the error term and the post-distortion update in the least square manner as given in [10]. the coefficient update relation can be expressed starting from the lse expression by describing the coefficient estimation from the output of the post-distorted signal [���� and the pre-distorted signal ( xyx���) as: xyx v� � [.\ (13) in block matrix form: \ij = ([v c [v) ��[v c . xyxv (14) then the error term for the estimation block uses the previously-calculated coefficients and is written as: h = [vk�.\ij − xyxvk� (15) expanding (15) and upon simplification, we get: \ij − \bvk� = −∆\ (16) therefore, the error expression for the pre-distorter coefficients becomes: h = −[vk�.∆\ (17) this coefficient error is used to update the pre-distorter coefficients through: \bvk� = \ij − m.∆\ (18) where the parameter m is used to speed up or stabilize the convergences of the pre-distorted signal and it depends on the number of the coefficients used. v. simulation results and performance analysis this section presents the simulation results of the performance of the fbmc-oqam signal in terms of the error engineering, technology & applied science research vol. 9, no. 5, 2019, 4801-4807 4806 www.etasr.com jake et al.: spectral re-growth suppression in the fbmc-oqam signal under the non-linear … vector magnitude (evm) and adjacent channel leakage ratio (aclr) when subjected to the nonlinear power amplifier. these performances are evaluated when the nonlinearities are compensated with concurrent application of cfr and dpd. the 16qam mapping method has been used for the fbmcoqam system because it is less susceptive to noise and data errors. an fbmc-oqam signal with phydyas prototype filter with overlapping factor n=4 is employed. the simulation parameters for the fbmc-oqam signal are based on the 3gpp release 13 to 15 and beyond [26] and the nonlinear power amplifier parameters settings are shown in table i and ii respectively. table i. fbmc-oqam simulation parameters parameters values carrier frequency 6ghz sampling rate with oversampling 320mhz sampling rate without oversampling 20mhz oversampling ratio 4 modulation type 16qam number of subcarriers 512 subcarriers ifft length 2048 filter overlapping factor 4 filter bank structure polyphase network ifft table ii. nonlinear power amplified parameter settings parameters settings amplifier gain 1db output 1db gain compression power 0.01w output third order intercept power 0.1w saturation power 0.032w gain compression at saturation 3db reference impedance 50ω in the crest factor reduction (cfr), a peak windowing based on sequential asymmetric superposition windowing (sasw) with maximum kaiser window length of 500 to enable the smooth transition on the window edge is used. a kaiser window adjustment parameter (6) equal to 15 to determine the rolling-off window’s edge and maximum iteration time equal to 20 was considered due to its steady convergence level. a block size for each cfr operation of 1000 and a target papr value of 6db were considered. the cfr technique performance results are shown in figure 6 where the peak value of the original fbmc-oqam signal has been reduced by about 1.5db. for the dpd technique, the memory polynomial model was used with nonlinear order p=7 and a memory depth of q=3, which only consider odd-order polynomials due to the odd-order intermodulation product characteristics of the nonlinear pa transfer function. figure 7(a) shows the power spectrum density (psd) plot of the original fbmc-oqam signal. the amplified version of the fbmc-oqam signal without dpd is labeled as (b), and (c) is the dpd response. although the dpd responded by suppressing a significant amount of the spectral re-growth, less gain is experienced after the nonlinearity compensation with the dpd. this is because of the high peak characteristics of the fbmc-oqam signal and the nonlinearity behavior of the pa which exhibited high spectral re-growth after the amplification of the fbmc-oqam signal. fig. 6. ccdf plot of the performance of the cfr technique fig. 7. psd of (a) original fbmc-oqam signal, (b) pa output without dpd, (c) pa output with dpd fig. 8. psd of (a) reduced crest factor of the fbmc-oqqam signal, (b) pa output, (c) pa output with combined cfr and dpd it can be observed in figure 8 that using cfr simultaneously with dpd can significantly reduce the spectral re-growth by about -45.74db adjacent channel leakage suppression. the error vector magnitude (evm) measure is found to be about 7.12% (-22.95db) which is clearly reaching the target of the standard evm value for wideband signals which was standardized to be 8% (-22db) by 3gpp. vi. conclusion spectral re-growth suppression of the fbmc-oqam signal under the nonlinear behavior of a power amplifier has been studied in this paper. regarding the cfr of the fbmc-oqam signal, a peak windowing technique with sequential asymmetric superposition windowing (sasw) algorithm has been proposed, which showed consistency in reducing the large engineering, technology & applied science research vol. 9, no. 5, 2019, 4801-4807 4807 www.etasr.com jake et al.: spectral re-growth suppression in the fbmc-oqam signal under the non-linear … peak values of the fbmc-oqam signal by about 1.5db. this leads to an increase in the average input power of the fbmcoqam signal. regarding nonlinearity compensation, memory polynomial based dpd with lse along with qr decomposition (lse/qr) which utilized the indirect learning architecture (ila-dpd) have been employed. the cfr and dpd techniques have been jointly applied to mitigate the issues of both high peak and nonlinearities experienced on the fbmc-oqam signals. the application of both cfr and dpd significantly reduced the spectral re-growth which resulted from the nonlinear behavior of the pa by about -45.74db adjacent channel leakage ratio (aclr) suppression. the error vector magnitude (evm) measure was found to be about 7.12% (-22.95db) which is less than the evm value for wideband signals standardized by 3gpp to be 8% (-22db). in this paper, much emphasis has been given to the fbmcoqam waveform. nevertheless, it would be of equal interest to study other waveforms and compare them with fbmcoqam under the same proposed techniques, in the 5g context. references [1] w. jiang, t. kaiser, “from ofdm to fbmc: principles and comparisons”, in: signal processing for 5g: algorithms and implementations, john wiley & sons, 2016 [2] s. patil, s. patil, u. kolekar, “implementation of 5g using ofdm and fbmc (filter bank multicarrier) /oqam (offset quadrature amplitude modulation)”, international 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a. shabbir, “5g networks : challenges and techniques for energy efficiency”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2864–2868, 2018 [8] a. shabbir, h. r. khan, s. a. ali, s. rizvi, “design and performance analysis of multi-tier heterogeneous network through coverage, throughput and energy efficiency”, engineering, technology & applied science research, vol. 7, no. 6, pp. 2345–2350, 2017 [9] y. rahmatallah, s. mohan, “peak-to-average power ratio reduction in ofdm systems : a survey and taxonomy”, ieee communications surveys and tutorials, vol. 15, no. 4, pp. 1567–1592, 2013 [10] j. wood, behavioral modeling and linearization of rf power amplifiers, first edition, artech house, 2014 [11] z. he, w. ye, s. feng, “digital predistortion of power amplifiers based on compound memory”, ieice electronic express, vol. 10, no. 21, pp. 1–5, 2013 [12] m. v. d. nair, r. giofre, p. colantonio, f. giannini, “sequential asymmetric superposition windowing for crest factor reduction and its effects on doherty power amplifier”, integrated nonlinear microwave and millimetre-wave circuits workshop, taormina, italy, october 1-2, 2015 [13] m. v. d. nair, r. giofre, p. colantonio, f. giannini, “effects of digital predistortion and crest factor reduction techniques on efficiency and linearity trade-off in class ab gan-pa”, 10th european microwave integrated circuits conference, paris, france, september 7-8, 2015 [14] f. m. ghannouchi, o. hammi, m. helaoui, behavioral modeling and predistortion of wideband wireless transmitters, first edition, john wiley & sons, 2015 [15] r. zayani, y. medjahdi, h. bouhadda, h. shaiek, d. roviras, r. bouallegue, “adaptive predistortion techniques for non-linearly amplified fbmc-oqam signals”, ieee 79th vehicular technology conference, seoul, south korea, may 18-19, 2014 [16] m. sajedin, a. ghorbani, h. r. a. dava, “nonlinearity compensation for high power amplifiers based on look-up table method for ofdm transmitters”, international journal of advanced computer science and information technolog, vol. 3, no. 4, pp. 354–367, 2014 [17] w. gao, linearization techniques for rf power amplifiers, springer, 2017 [18] h. d. rodrigues, t. c. pimenta, r. a. a. d. souza, l. l. mendes, “orthogonal scalar feedback digital pre-distortion linearization”, ieee transactions on broadcasting, vol. 64, no. 2, pp. 319–330, 2018 [19] v. vasconcellos, g. c. ornelas, a. n. barreto, “performance of 5g candidate waveforms with non-linear power amplifiers”, ieee 9th latin-american conference on communications, guatemala city, guatemala, november 8-10, 2017 [20] s. s. k. c. bulusu, h. shaiek, d. roviras, “pa linearization of fbmcoqam signals with overlapped recursive error correcting predistortion”, international symposium on wireless communication systems, poznan, poland, september 20-23, 2016 [21] t. jiang, d. chen, c. ni, d. qu, oqam/fbmc for future wireless communications principles technologies and applications, first edition, academic press, 2018 [22] m. bellanger, “fbmc physical layer: a primer”, european project, vol. 1, no. 1, pp. 1–31, 2010 [23] a. sahin, i. guvenc, h. arslan, “a survey on multicarrier communications: prototype filters, lattice structures, and implementation aspects”, ieee communications surveys and tutorials, vol. 16, no. 3, pp. 1312–1338, 2014 [24] h. wang, “a hybrid papr reduction method based on slm and multi-data block pts for fbmc/oqam systems”, information, vol. 9, article id 246, 2018 [25] l. guan, a. zhu, “green communications : digital predistortion for wideband rf power amplifier”, ieee microwave magazine, vol. 15, no. 7, pp. 84-99, 2014 [26] 5g americas, wireless technology evolution towards 5g: 3gpp release 13 to release 15 and beyond, 5g americas, 2017 microsoft word khelil-ce_r3.doc etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 488-496 488 www.etasr.com khelil et al.: modeling of fatigue crack propagation in aluminum alloys using an energy… modeling of fatigue crack propagation in aluminum alloys using an energy based approach f. khelil laboratoire de mécanique de lille (lml), university of lille1, france foudil.khelil@univ-lille1.fr b. aour laboratory of environmental technology research, enset d’oran, algeria ben_aour@yahoo.fr m. belhouari department of mechanical engineering, university of sidi bel abbes, algeria m_belhouari@yahoo.com n. benseddiq lml, university of lille1, france noureddine.benseddiq@ univ-lille1.fr abstract—materials fatigue is a particularly serious and unsafe kind of material destruction. investigations of the fatigue crack growth rate and fatigue life constitute very important and complex problems in mechanics. the understanding of the cracking mechanisms, taking into account various factors such as the load pattern, the strain rate, the stress ratio, etc., is of a first need. in this work an energy approach of the fatigue crack growth (fcg) was proposed. this approach is based on the numerical determination of the plastic zone by introducing a novel form of plastic radius. the experimental results conducted on two aluminum alloys of types 2024-t351 and 7075-t7351 were exploited to validate the developed numerical model. a good agreement has been found between the two types of results. keywordsfatigue crack growth; energetic approach; plastic zone; aluminum alloys. i. introduction in these last years, the concepts of fracture mechanics allowed a better definition of the stresses and strains fields at the vicinity of crack tips under static and dynamic loadings. cracking laws, empirical or formal, were developed in order to explore with an acceptable approximation the fatigue crack growth. indeed, cracks’ growth is related to the existence of a plastic zone (pz) at the crack tip, the formation and the intensification of which is accompanied by energy dissipation. thus, the amount of the cyclic plastic strain energy may represent with precision the rate of damage at the crack tip. the use of a cyclic plastic dissipation criterion for fatigue crack growth was first proposed by rice [1]. from this date, plastic energy approaches to fatigue crack extension prediction have been the subject of several experimental, analytical and numerical investigations [2-10]. weertman [11] proposed that the crack advances when the accumulated plastic energy at the crack tip reaches a critical value. then, shozo et al [2] measured the cyclic work to produce a unit area of fatigue crack for a steel of low carbon content and for high resistance aluminum alloys, using micro strain gages stuck in the plastic zone associated with a fatigue crack. subsequently, different techniques have been developed to evaluate the plastic energy, such as sub-grain size measurements [3], infrared thermography [4], micro-calorimetry [6] and by direct measurement of hysteresis energy under the loading line of a compact tensile (ct) specimen [12, 20]. following the work of bodner et al [5], klingbeil [7] has proposed a crack growth law, in which the fatigue crack growth rate was related to the total plastic energy dissipated ahead of a crack tip under cyclic loading. this model has been further extended to mixed mode fatigue delamination of layered materials across the interface [10, 14]. recently, mazari et al [15] proposed an empirical correction factor which takes into account the over evaluations obtained by hysteresis loops and shows the different effects of plasticity, crack closure and opening mode. in this paper, a new approach, for the evaluation of the cyclic plastic strain energy at the crack tip in mode i, has been proposed. this approach is based on the numerical determination of the plastic zone by introducing a novel form of plastic radius. the theoretical basis related to the surface energy creation and the evolution of the energy parameters will be discussed in section 2. section 3 is devoted to the presentation of the experimental data exploited for the validation. then, section 4 describes the development of the numerical algorithm used for the evaluation of the cyclic plastic strain energy. the obtained results are presented and discussed in the last section. ii. theoretical background a. energetic description of fatigue crack growth the description of kinetics of fatigue failure is very important for estimating fatigue lifetime of a component. the knowledge of crack propagation direction and crack growth rate makes it possible to predict the lifetime by means of kinetics fatigue failure diagrams (kffd). however, for an estimation of the cyclic plastic strain energy wp, the area of the hysteresis loop (figure 1), which characterizes the energy corresponding to one loading cycle, can be used. to this end, a power law relationship between stress and strain has been proposed by morrow [13] as follows: 1 1 n " w . n "       (1) where "n is the exponent linking the stress amplitude  and the plastic strain amplitude p . etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 488-496 489 www.etasr.com khelil et al.: modeling of fatigue crack propagation in aluminum alloys using an energy… on the other hand, a specific energy, u, is defined as, 2 pw u b da / dn    (2) where b is the specimen thickness and /da dn is the fatigue crack growth rate. fig. 1. schematic drawing showing hysteresis loop. the evolution of u as a function of /da dn can be subdivided according to three stages of the kffd. it should be noted that this diagram can be easily obtained experimentally by measuring crack propagation as a function of the stress intensity factor (see figure 2). the obtained curve is characterized by three stages which are commonly referred to as stage i, ii and iii respectively [16, 17]. fig. 2. a typical fatigue crack growth rate curve (kinetic fatigue failure diagram: kffd). the relation between r and log k is linear [11, 18, 19], whereas that between /da dn and u can be written as: 4 2 c da a k dn g u   (3) b. the cyclic plastic strain enery– proposed model assuming that the energy is primarily dissipated in the plastic zone, a comparison can be made between the measured values and those predicted theoretically by assuming propagation in mode i. rice [1] and tracey [21] gave an expression for the equivalent shear strain 3  near the crack tip defined in terms of the amplitude function  nr  as follows: 1 1 ' 0 / ( ( ) / ) n ng r r    (4) where r and  are the polar coordinates at the crack tip, g the shear modulus, 0 0 / 3  the yield stress under pure shear and  nr  can be considered the dominant singular term approximation to the elastic-plastic boundary which depends upon the hardening exponent n’ and is given as a function of  in the normalized form [21]:      20/ /n nf r k   (5) where  nf  is a dimensionless function which defines the profile of iso-deformation as a function of polar coordinates at the crack tip. according to rice [1], the singularity of equivalent cyclic strain can be described by applying the tensile form of (4-5) by simply replacing k by δk and σ0 by δσ0 related to the cyclic stress-strain law. 3p / g    (6) where p and  are the plastic strain and stress amplitude. consequently the cyclic stress strain curve gives the hardening law for the material at the crack tip [22]: 0 0 n'              (7) where  and  are the equivalent strain and stress amplitude, 0 and 0 0 / 3g    represent the cyclic yield strength of the material. using the expressions 3    and 0 0 / 3  , equation (4) can be rewritten as follows :   1/1 0 3 n nr g r                  (8) therefore within the hypothesis given by rice [1], the equivalent strain amplitude near the crack tip is given by:   1/1 2 0 0 . n nf k r                   (9)   =2a   = 2 a ap ae a wp etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 488-496 490 www.etasr.com khelil et al.: modeling of fatigue crack propagation in aluminum alloys using an energy… where k is the stress intensity range which can be given as a function of the maximum and minimum stresses and the crack length a as follows:  max mink a     . in order to evaluate the amplitude of the equivalent average strain  chalant [23] considered an element with a rectangular or circular form located at the crack tip so that: 0 1 s ds s     (10) where s is the surface of the element at the crack tip. in the case of a rectangular element with dimensions d1 and d2 (see figure 3a), we get [16, 23]: 2 1 1 1 1 1 0 1 1 2 2 0 1 1 2 n ' n ' n 'n ' k d i d i n '                          (1) the terms 1i and 2i are given by:         0 0 1 1 1 1 20 1 1 2 2 1 2 2 n ' n n ' n ' / n n ' f i .d co s f i .d sin                                (12) with 1 2 0 12 d tan d   (13)  (a) (b) fig. 3. elements at crack tip: (a) rectangular, (b) circular. the drawing shows the hysteresis loop. in the case of a circular crack tip element with a radius r1 (figure 3b), the expression of the amplitude of the equivalent average strain is given by [12]: 2 1 1 1 0 1 0 2n ' n ' k r i                       (14) with   12 1 0 / n 'ni f d         (15) the plastic energy throughout the plastic zone is obtained by integrating the plastic energy per surface element given by (1), i.e. 0 1 " ( ) 4 . . 1 " ps p n w pz ds n       (16) where ps is the surface of a quarter of the plastic zone. hence 2 0 0 1 4 1 p/ r p n " w ( pz ) . .r dr d n "          (17) with pr indicates the limit of cyclic plastic zone. if we assume that pr is defined by the distance for which the total equivalent strain is equal to 0 , we have, from (9): 2 0 p n k r f ( )     (18) the integral (17) can be evaluated by substituting the expressions (5-8) for  and p , which gives after simplification [12] :       4 22 0 0 0 0 1 " 2 1 ' . 1 " i n kn w pz n f d n                   (19) this expression can be rewritten as follows:     0 011 1 pz n" w pz n ' . .s n"      (20) with   4 22 0 0 2 ipz n k s f d                (21) indicating simply the surface of the plastic zone. on the other hand, engerand [24] proosed the tresca or von mises criteria to compute the limit of the plastic zone. it is interesting to note that (19) enables us to express the energy dissipated throughout the plastic zone per unit thickness as a function of 4k , which conforms to the theoretical models given by klingbeil [7], mazari et al [15]. and ranganathan et al [8]. hence, in order to obtain a similar variation as a function of 4k , we propose to compute the plastic zone surface using the following expressions for the plastic rays:   4 2 2 2 0 1 1 2 3 2 2 2p k r ( pd ) cos sin b                       (22) for plane strain, and: 4 2 2 0 1 ( ) cos 1 3sin 2 2 2p k r ps b                      (23) etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 488-496 491 www.etasr.com khelil et al.: modeling of fatigue crack propagation in aluminum alloys using an energy… for plane stress. by using (22) and (23), the new model proposed for the calculation of plastic energy per unit thickness can be written as follows:   0 0. . .m pzmmw pz s      (24) where m is a constant which depends on the material and the criterion used and ms indicates the surface of the plastic zone determined by expressions (22) or (23). hence, the total dissipated energy q in the specimen is given by:  q w pz b   (25) iii. experimental details a. material and specimen configurations the tests were conducted on two aluminum alloys, the 2024 alloy in the t351 condition and the 7075 alloy in the t7351 condition. the nominal composition and mechanical properties of these alloys are given in tables i and ii respectively. in table ii, the parameters k and n are computed from the relationship of ludwik [25]: .( )npk  (26) table i. nominal composition (in %) of the studied alloys. alloy si fe cu mn mg cr zn ti al 2024 0.10 0.22 4.46 0.66 1.50 0.01 0.04 0.02 remain 7075 0.07 0.16 1.52 0.04 2.55 0.20 6.00 0.04 remain table ii. nominal mechanical properties of the studied alloys material 2024-t351 7075-t7351 conventional yield stress at 0.2% of plastic strain 0.2  (mpa) 318 470 stress at fracture r  (mpa) 524 539 elongation a% 12.8 11.7 strength coefficient k(mpa) 652 960.5 hardening coefficient n 0.104 0.051 the tests were carried out using compact tension specimens (ct) with thicknesses of 10 mm for 2024 and 6 mm for 7075 (figure 4). the direction of cracking has been taken in the rolling direction. all mechanical tests were conducted using an instron servohydraulic machine at a typical test frequency of 20 hz in temperature room with a stress ratio of r=0.5. maxmin /r p p (27) where pmin and pmax are the minimum and maximum load in the cycle. fig. 4. cyclic test configuration on a compact tension specimen. the crack propagation rate was measured by optical techniques on the polished side of the specimen using a travelling microscope with a precision of 0.01 mm. the total dissipated energy was evaluated by the area locked up inside the recorded hysteresis cycles. the stress intensity range for this geometry is given by newman [26]:   with . p a k f z z wb w     (28) where w and b are respectively the width and the thickness of the specimen, a, is the crack length, and max minp p p   , is the amplitude applied load. in order to obtain more precision, two functions of compliance  f z were used:  for 0.2 0.3z  [26]:   2 3 4 5 6 4.55 40.32 414.7 1698 3781 4287 2017 f z z z z z z z        (29)  for 0.3 0.7z  [27]:   0 5 1 5 2 5 3 5 4 5 29 6 185 5 655 7 1017 638 9 . . . . . f z . z . z . z z . z      (30) b. identification of the cyclic plastic strain energy parameters the results obtained after the dentification of the cyclic plastic strain energy parameters are summarized in table iii. table iii. cyclic plastic strain energy parameters for 2024-t351 0 0 m 'n "n integral 4w k  914 0.0111 6.67e-4 0.148 0.078 0.0138 2.92e-13 for 7075-t7351 0 0 m 'n "n integral 4w k  705 0.00849 1.26e-5 0.166 0.0765 0.0140 4.85e-13 for the particular materials under study, we finally obtain:  for 2024-t351: 13 42 92 10 joule mw , . k /  (31)  for 7075-t7351: p pmax pmin p time p p b a w etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 488-496 492 www.etasr.com khelil et al.: modeling of fatigue crack propagation in aluminum alloys using an energy… 13 44 85 10 joule mw , . k /   (32) c. identification of paris law fatigue crack growth in the ct specimens was modeled according to the paris law, where the fcg rate, da/dn, is described in terms of the stress intensity range k according to the following relationship [28]:   mda c k dn  (33) where c and m are the fatigue crack growth coefficient and exponent, respectively.   y = 6e-09x4.5849 y = 3e-08x3.1987 1.0e-07 1.0e-06 1.0e-05 1.0e-04 1.0e-03 1.0e-02 1 10 100 k (mp a.m^1) d a/ d n ( m m /c y cl e) 2024t351 7075t7351 fig. 5. fitting of experimental data with a paris law figure 5 shows typical results of the experiments used in constructing plots of log(da/dn) in terms of log(k) for each aluminum alloy. a power law model was fit to the steady state region (stage ii) of fatigue crack growth and the paris law coefficient (c) and exponent (m) were determined for each specimen that underwent stable fatigue crack growth. a logarithmic scale was used to represent the curve as a straight line. thus, a linear regression returns the material parameters c and m. by identifying the paris law parameters according to experimental data's of the two alloys, we found that c=6.0e-9 and m=4.5849 with a slope of 4.58 for 2024-t351. however, for 7075-t7351: c=3.0e-8 and m=3.1987 with a slope of 3.20. it is worth noting that the 2024 aluminum alloy remains as an important aircraft structural material due to its extremely good damage tolerance and high resistance to fatigue crack propagation [29]. however, the 7075-t7351 offers good stresscorrosion cracking resistance [30]. iv. implementation of the proposed approach a computer program has been written in matlab language. the program was developed to calculate the stress intensity factor, the size of the plastic zone, the crack growth rate, the number of cycles and the cyclic plastic strain energy. conditions of plane strain and von mises criterion were considered. first, we specify ct specimen dimensions (b: thickness, w: width, a0: initial crack length, aend: crack length for forced termination), quantities relevant to material properties (e: young’s modulus, ν: poisson’s ratio, y: yield stress, c and m: material constants of paris law and the amplitude of the applied load). then, the program computes the stress intensity factor range k, the plastic radius rp, the fatigue crack growth rate ,da dn and the energetic parameters as shown by the flaw-chart in figure 6. fig. 6. flow chart of the numerical process. etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 488-496 493 www.etasr.com khelil et al.: modeling of fatigue crack propagation in aluminum alloys using an energy… v. results and discussion it is worth noting that the evolution of the cyclic plastic strain energy is directly related to the change of the plastic zone size at the crack tip as described in section (ii.b). in what follows, we will first deal with the evolution of the plastic zone. then, we will analyze in detail the evolution of the cyclic plastic strain energy and the speed of crack propagation. a. evolution of the plastic zone the purpose of this section is to study in detail the evolution of the plastic zone at the crack tip during the crack growth on the two aluminum alloys. it should be noted that, at the crack tip of a ductile material, the strain fields are significant and leading to a considerable extent of the plastic zone. in this case, the mechanical energy at the crack tip is absorbed by the material in the form of linear defects (dislocations) [20,31].on the other hand, the size of the plastic zone depends not only on the nature of the materials, but also on the intensity of the mechanical energy at the crack tip, the geometry and the size of the crack. noting that the hardening (maximum consolidation of material) characterized by its rate, can significantly slow the extension of the plastic zone. figure 7 shows the evolution of the plastic zone for both aluminum alloys (2024 and 7075) using tracey model (figure 7a) and the proposed model (figure 7b). it is found that the size of the plastic zone calculated by the proposed model is about 16 times (for 2024) and 18 times (for 7075) greater than that calculated by the tracey model. furthermore, we observe that the 2024 alloy, whose mechanical properties of ductility are higher than 7075, presents the largest size of the plastic zone. we have obtained for:  tracey model: s(pz) of 2024 = 2,37  s(pz) of 7075.  proposed model: s(pz) of 2024 = 2,12  s(pz) of 7075. b. evolution of the total dissipated energy in the specimen it should be noted that the crack extension which leads to the fracture occurs when the provided energy is sufficient to overcome the material strength. assuming that this energy is mainly dissipated in the plastic zone, a comparison can be made between the measured values and those predicted theoretically as shown in figure 8 by assuming propagation in mode i. c. evolution of the total dissipated energy in the specimen it should be noted that the crack extension which leads to the fracture occurs when the provided energy is sufficient to overcome the material strength. assuming that this energy is mainly dissipated in the plastic zone, a comparison can be made between the measured values and those predicted theoretically as shown in figure 8 by assuming propagation in mode i. (a) ‐3,00 ‐2,00 ‐1,00 0,00 1,00 2,00 3,00 ‐1,50 ‐0,50 0,50 1,50 y / ( k /   0 )^ 4 x/(k/0)̂ 4 2024t351 7075t7351 crack (b) ‐0,30 ‐0,20 ‐0,10 0,00 0,10 0,20 0,30 ‐0,30 ‐0,20 ‐0,10 0,00 0,10 y / ( k /   0 )^ 4 x/(k/0)^4 2024t351 7075t7351 crack fig. 7. evolution of the normalized plastic zone in the case of : (a) the tracey model and (b) the proposed model for both aluminum alloys. figure 8 illustrates the evolution of the total dissipated energy according to the amplitude of the stress intensity factor k for both types of aluminum alloys in the case of a constant stress ratio of r=0.5. it can be seen that the theoretical estimates given by the tracey model are much lower than the experimental measurements. however, a good prediction has been obtained by the proposed model. noting that for 2024 etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 488-496 494 www.etasr.com khelil et al.: modeling of fatigue crack propagation in aluminum alloys using an energy… (figure 8a), q calculated by the tracey model is about 11 to 76 times weaker than the measured q; the difference is less for high values of ∆k. the same trends have been also found for 7075 (figure 8b). the gap between the theoretical estimates of tracey and the measured values ranges from 3, for high values of ∆k, to 10 for the low values of ∆k. this difference can be allotted in a great part to the size of the estimated plastic zone which is much lower than that measured especially for materials that exhibit a high ductility as that of 2024-t351 in comparison with that of 7075-t7531. on the other hand, it may be noted from figure 8, that the results obtained by the proposed model are in good agreement with experimental data for both types of aluminum alloys. it is also observed that for the same value of ∆k, the total dissipated energy of 2024-t351 is higher than that of 7075-t7531. (a)   1,0e-07 1,0e-06 1,0e-05 1,0e-04 1,0e-03 1,0e-02 1 10 100 k (mp a.m^1/2) q ( j/ cy cl e) exp. result s t racey model p roposed model (b)   1,0e-06 1,0e-05 1,0e-04 1,0e-03 1,0e-02 1,0e-01 1 10 100 k (mpa.m^1/2) q ( j/ cy cl e) exp. res ults tracey mo del p ro po s ed mo del fig. 8. comparison of measured and estimated dissipated energy per cycle for (a) 2024-t351 and (b) 7075-t7351. vi. relationship between q and da dn the evolution of the crack growth rate is studied as a function of energetic parameters in order to interpret the crack behavior in various elucidated regimes. figure 9 shows the evolution of da/dn in terms of the total dissipated energy q for r=0.5. for both aluminum alloys, the experimental results can be subdivided into two distinct stages as shown in figure 9. in the case of 2024, the stage i is defined by da/dn210-5 mm/cycle. in this stage we note a strong decrease in crack propagation speed with the total dissipated energy. a logarithmic approximation can be used in this stage. the relationship obtained is given by: y = 0.7346x 1.272 y = 2e-05ln(x) + 0.0001 1.0e-07 1.0e-06 1.0e-05 1.0e-04 1.0e-03 1.0e-02 0.00001 0.0001 0.001 0.01 0.1 q (j/cycle) d a/ d n ( m m /c y cl e) exp . results prop osed m odel fig. 9. comparison of measured evolution of da/dn with q for 2024t351 y = 0.1123x 0.8382 y = 0.0001ln(x) + 0.0011 1.0e-05 1.0e-04 1.0e-03 1.0e-02 0.0001 0.001 0.01 0.1 q (j/cy cle) d a/ d n ( m m /c y cl e) exp . results prop osed m odel fig. 10. evolution of da/dn with q for 7075-t7351. the black lines represent the regression curves of experimental results using power and logarithmic functions etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 488-496 495 www.etasr.com khelil et al.: modeling of fatigue crack propagation in aluminum alloys using an energy… stage ii is defined by da/dn10-5 mm/cycle. this region exhibits a stable evolution of the crack growth and a power law can be used as an approximation in this stage: 1 2720 7346 . da . q dn  (35) in the case of 7075, stage i is defined by da/dn2.10-4 mm/cycle. the evolution of the crack growth in this regime is unstable. if we use a logarithmic function, we can determine a relationship of the form: 0 0001 0 0011 da . ln( q ) . dn   (36) stage ii is defined by da/dn 2.10-4 mm/cycle. the obtained law has the following form: 0 83820 1123 . da . q dn  (37) one can observe that there is a good agreement in the stage ii between experimental data and the results obtained by the proposed model for both types of aluminum alloys. furthermore, the straight lines of slope 0.316 for 2024 and 0.086 for 7075 can be deduced from the proposed model. indeed, we obtain the following expressions: 1 14620 316 . da . q dn  for 2024t351 (38) 0.79970.086 da q dn  for 7075t7531 (39) however a significant difference was found in stage i between experimental data and the results of the proposed model. this limits, therefore, the application of the proposed model in the stage where the crack propagation is stable. vii. conclusions in this study an energy based approach of fatigue crack growth has been proposed. this approach provides a direct link between the cyclic plastic strain energy and the plastic zone at the crack tip. in order to validate the model, experimental data conducted on ct specimens of aluminum alloys (2024-t351 and 7075-t7351), under constant amplitude with a stress ratio of r=0.5 and mode i loading, have been exploited. the following conclusions have been drawn:  the measured values of the cyclic plastic strain energy for both types of aluminum alloys are substantially higher than those calculated by the tracey model. however, a relatively good agreement has been found between the experimental data and the results obtained by the proposed model.  a correct modeling of the plastic zone is necessary to accurately determine the total cyclic plastic dissipation at the crack tip. the size of the plastic zone calculated by the proposed model is about 16 to 18 times greater than that calculated by the tracey model. finally, it should be noted that the simplicity of the current modeling approach limits its ability to account for the crack closure, the environment and the variable amplitude loadings effects, which are topics of ongoing research. acknowledgements it should be noted that the experimental tests were carried out and provided within the framework of a cooperation project "cmep 389 mdu 97" between the laboratory of mechanics and energetic (university djillali liabes of sidi bel abbes (algeria)) and the laboratory of mechanics and rheology (university françois rabelais of tours (france)). the authors especially thank professor n. ranganathan and his team for their support and assistance. references [1] j. r. rice, “the mechanics of crack tip deformation and extension by fatigue”, fatigue crack propagation special technical publication 415, astm, pp. 247-311, philadelphia, 1967 [2] i. 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profile of a modern metal: aluminum from within, 6th edition, wiley, 2010 [30] p. s. pao, s. j. gill , c. r. feng, “on fatigue crack initiation from corrosion pits in 7075-t7351 aluminum alloy”, scripta materialia, vol. 43, no. 5, pp. 391-396, 2000 [31] j. w. kysar, “energy dissipation mechanisms in ductile fracture”, journal of the mechanics and physics of solids, vol. 51, no. 5, pp. 795824, 2003 microsoft word 6-2969_setasr_v9_n5_pp4605-4611 engineering, technology & applied science research vol. 9, no. 5, 2019, 4605-4611 4605 www.etasr.com kumar & singh: environmental economic dispatch with the use of particle swarm optimization … environmental economic dispatch with the use of particle swarm optimization technique based on space reduction strategy t. manoj κumar department of electrical and electronics engineering, saveetha school of engineering, simats, chennai, india manojkumart99@gmail.com n. albert singh bharat sanchar nigam limited chennai, india basisngc@gmail.com abstract—this paper introduces a professional edition of particle swarm optimization (pso) technique, intending to address the environmental economic dispatch problem of thermal electric power units. space reduction (sr) strategy based pso is proposed, in order to obtain the pareto optimal solution in the prescribed search space, by enhancing the speed of the optimization process. pso is a natural algorithm, which can be used in a wide area of engineering issues. many papers have illustrated different techniques that solve various types of dispatch problems, with numerous pollutants as constraints. search sr strategy is applied to pso algorithm in order to increase the particles’ moving behavior, by using effectively the search space, and thus increasing the convergence rate, so as to attain the pareto optimal solution. the validation of sr-pso algorithm is demonstrated, through its application on an indian system with 6 generators and three ieee systems with 30, 57 and 118 buses respectively, for variable load demands. the minimum fuel cost and least emission solutions are achieved by examining various load conditions. keywords-search space reduction; particle swarm optimization (pso); environmental/economic dispatch (eed) problem; pareto optimal solution i. introduction the process of satisfying energy demands raises concerns regarding to energy durability and environmental protection, in conjunction with the market and regulatory demands. environmental/economic electricity dispatch (eed) is a technique to plan the energy generator unit’s output with load demand. eed is essential to create sufficient capacity in order to meet consistently variable client load demands at minimal cost under various difficulties. the eed problem is nonlinear, discontinuous and multimodal. it is essential to deliver power, generated by several units on an optimum current economic climate basis in order to attain the best results in the generating system. many methods have been used to solve the dispatch. in [1] the modulated particle swarm optimization (mpso) technique was presented to solve the eed problem of thermal units, modulating particles’ velocity for better exploration and exploitation of search space. this modulation of velocity is controlled by introducing a sinusoidal constraint function in the control equation. a fuzzified multi-objective particle swarm optimization (fmopso) algorithm was proposed in [2] where, in order to validate the effectiveness of the proposed method, a comparative study was conducted with other techniques, like weighted aggregation (wa) and multi-objective evolutionary algorithm (moea). many further issues are to be considered, such as the nonlinear characteristics of ramp rate limits and the prohibited operating zones of power system operations. in [3] a new strength pareto evolutionary algorithm (spea) was proposed in order to compete with nonlinear objectives. diversity preserving mechanism has been developed to resolve the pareto optimal issue. an artificial bee colony, improved with dynamic population size (abcdp), has been introduced in [4], to prove the efficiency and effectiveness in handling the nonlinear multi-objective function. in [5], a modified bacterial foraging algorithm (mbfa) was developed for the solution of the eed problem, using the global optimum bacterium having successful foraging strategy. this method shows the capability of obtaining quality compromise solution and the operator has to decide different objectives according to system constraints. another method of the hybrid multi-objective algorithm based on particle swarm optimization (pso) and differential evolution (de) was proposed in [6], where the search space is completely explored by the pso, while de takes the initiative in exploiting the subspace with sparse solutions. in this approach, the exploration and exploitation capability has been improved by the effective usage of crowding distance and time variant acceleration coefficients. a new multi-objective particle swarm optimization (mopso) that resolves the eed issue is explained in [7]. this technique is the multi-objective version of pso, offering the redefinition of global and local best individuals in search space. the potential and efficiency of this method is proved by obtaining multiple optimal solutions in one simulation run and validating the diversity and well-distributed characteristics of the non-dominated solutions. a flower pollination technique, used to resolve the economic load dispatch (eld) and combined economic and emission dispatch (ceed) problems is suggested in [8]. simulation results were compared to other swarm based techniques to show its effectiveness. its main advantage is that it can be used for large-scale power systems corresponding author: manoj κumar engineering, technology & applied science research vol. 9, no. 5, 2019, 4605-4611 4606 www.etasr.com kumar & singh: environmental economic dispatch with the use of particle swarm optimization … with valve-point effects. many parameters were checked such as converging property, computational efficiency, and economic effect. spiral optimization algorithm (soa) is used in [9], to resolve the economic and emission dispatch problem, in order to obtain minimum fuel cost and emanation level, while satisfying the required load demand and operational constraints. this is a metaheuristic optimization algorithm having several advantages, including its few control variables, local searching capability, fast results, easy using process and simple structure. the multi-objective differential evolution (mode) algorithm is described in [10] to resolve the eed problem. crowding entropy diversity tactic is used in order to preserve the diversity of pareto optimal solution. also, fuzzy set theory is employed to extract the best compromise between fuel cost and emission. a stochastic pso method was used in [11], by formulating both deterministic and stochastic models to deal with the economic load dispatch problem, considering the environmental impacts as constraints. in [12] a niched pareto genetic algorithm (npga) approach is presented, considering the whole eed problem as a multi-objective issue, with total fuel cost and emissions as competing objective functions. the main advantage of this method is that there is no restriction on the number of objectives to optimize. fpa is explained in [13], where only fuel cost is considered as the objective function to resolve the eld problem, while both fuel cost and emissions are considered for ceed. the superiority of fpa to other algorithms is discussed, even for a large power system with valve-point effects. a nonlinear fractional approach for resolving the eed is elaborated in [14], presenting two simultaneous models of objective functions with nonlinear constraints. the first model minimizes the quotient of fuel cost and emission function, while the latter minimizes the total fuel cost expressed as a quadratic objective function. the non-dominated sorting genetic algorithm (nsga-ii) faces many drawbacks, such as lack of uniform diversity and absence of lateral diversity. these can be eliminated by introducing dynamic crowding distance (dcd), using a modified nsga-ii algorithm [15]. differential evolution (de) algorithm is developed with emission constrained economic dispatch problem in [16], to minimize the fuel cost. but due to the heavy environmental impact created by the thermal power plants, it has to be considered as an additional objective function. the innovative tribe-modified differentia evolution (tribe-mde) is presented in [17] to solve the multi-objective eed problem. this multi-objective problem can be altered into a min-max problem, in order to be resolved with the tribemde algorithm. a bare-bones multi-objective pso algorithm to resolve the eed issue is presented in [18]. several advantages are reported here, such as particle updating strategy without tuning procedures and mutation operation, with expanded search capability. the time-varying acceleration based pso (pso-tvac) technique is proposed in [22] to resolve the eed problem. the standard pso algorithm can be improved by adjusting the acceleration constant in order to get a balanced exploration and exploitation capability. in [24], the exact method to resolve the eed problem and pso to get the pareto optimal solution is elaborated. in [25], different evolutionary algorithms are applied to solve eed problems in various electrical power systems, comparing their performance. resolving the economic dispatch problem by an improved version of the random drift pso algorithm is explained in [26]. in [27], an improved pso, called biogeography-based learning particle swarm optimization (blpso), is presented for solving the ed problems involving different constraints. the chaotic bat algorithm is deployed in [28] for solving the ed problem, involving equality and inequality constraints such as power balance, prohibited operating zones, and ramp rate limits. an improved differential evolution algorithm for the eld problem, with or without valve-point effects, is explained in [29]. an adaptive pso with heterogeneous multicore parallelism and gpu acceleration is deployed in [30], while new swarm intelligence is applied in [32]. in [31], the resolution of multi-objective eed problem by utilizing the grey wolf optimization algorithm is explained, analyzing various operating constraints. a new optimization technique named elephant herd optimization (eho) was proposed in [33], for global optimization. like most different metaheuristic algorithms, eho is not using the preceding individuals inside the later updating process. in [34], a combined heat and power economic dispatch problem is resolved, utilizing an advanced modified pso technique on different systems. in [35], a tlabc algorithm is proposed, which employs three hybrid search stages, in its search for the optimization parameters. the primary purpose of this study is to present the utilization of space reduction particle swarm optimization (sr-pso) optimization technique in power systems. sr-pso is a versatile and well-balanced mechanism that improves exploration and exploitation. the sr-pso method is proposed to resolve environmental/economic dispatch (eed) problems for different power systems, such as an indian utility system having 6 units, and three ieee systems with 30, 57 and 118 buses respectively. results are studied comparatively with other researches from the relevant literature. ii. problem formulation in order to resolve the eed problem, we should examine the best mixture of power generation that diminishes the aggregate cost, by considering fuel and emission expenditure, under numerous working conditions. the multi-objective advancement technique is commonly used to get the ideal solution for real-world challenges. the main objectives are: • minimization of fuel cost: in a power system with n number of generators, the total fuel price can be determined by: iii n i iii n i ig cpbpapfpf ++== ∑∑ == 1 2 0 )()( (1) where �(��) denotes the total generation fuel cost, �� represents the electrical output of � generator, ��, � and �� signify the cost coefficients of � generator and �denotes the quantity of generators assigned to the operating system • minimization of emissions: total emissions with fossil gas based heat generation are given by: 2 0 1 ( ) ( ) n n g i i i i i i i i i e p e p p pα β γ = = = = + +∑ ∑ (2) engineering, technology & applied science research vol. 9, no. 5, 2019, 4605-4611 4607 www.etasr.com kumar & singh: environmental economic dispatch with the use of particle swarm optimization … where �(��) denotes total emissions and ��, �� and �� are the emission coefficients of the i th unit. the multi-objective search engine optimization problem offers two goals, economy and emissions. it is transformed into a solitary objective search engine optimization problem as: ( ) ( ) (1 ) ( ) g g g t p u f p u e p= ∗ + − (3) where � is total cost and 0 < � < 1 is a compromising factor. when � is zero, the aim function is only emission dispatch problem which limits the emissions of the plant. when � is 1, the objective function becomes entirely a conventional economical load dispatch problem, which restricts the availability expenses of this scheme. eed problem has two constraints. firstly, there are the generator’s constraints, as the real power productivity of every generator will be in the middle of its base, while optimum limits and the inequality constraints for every generator must be assured: min max , 1,..... gi gi gi p p p i n≤ ≤ = (4) where ��� ��� and ��� ��� are the lower and upper limits of power of the i th unit. secondly, there are the power balance constraints, where the aggregate power loss has the real power reduction in transmission line pl and total demand pd. then: 1 0 g i d l i p p p = − − =∑ (5) in which the system loss function l p is given by: mwpbpp jij n i n j il )( 1 1 ∑ ∑ = = = (6) iii. sr-pso implementation in the eed problem inspired by the social behavior of animals like bird flocking, fish schooling and swarm basic principle, pso is broadly utilized for the resolution of the heavily limited eed problem. the particles move throughout the multi-dimensional search space till they discover the optimal solution. by their own knowledge (���� ) and the knowledge achieved by nearest particles ( ��� ), every particle updates its situation throughout the flight. velocity and position of the i th particle, for fitness evaluation at (! + 1) iteration in m-dimensional search space, are given by: 1 1 1 2 2 . . .( ) . .( ) k k k k best best i i i i g i v wv c r p x c r g x + = + − + − (7) 11 ++ += k i k i k i vpp , 0 0 = =k i v (8) where, i is particle's index, k represents the discrete time index, n denotes the number of particles in a group, m signify the dimensions of a particle, w is the inertia weight factor, �� ��� represents the best position found by th i particle , � ��� symbolizes the best position create by swarm, c1, c2 symbolize the acceleration coefficients, r1, r2 represent the uniform random values in the array [0, 1], �� # and $� # indicate the position and velocity of the i th particle at k th iteration. a new strategy of the pso algorithm is introduced for solving eed problems. indicators will be addressed about how to handle the inequality and equality constraints of the eed complications, when adjusting every search point in pso. a new method of pso with sr strategy based optimization technique is used in order to improve the convergence rate of the process. this approach is activated, when the performance is not increased throughout a pre-specified time. in this method, the search space can be regulated with the proper usage of constant %. the distance between the global best and maximum or minimum values of position values are added or subtracted with that constant, giving: 1 m ax m ax m ax ( ) k k k k i i i i p p p g b e s t + = − − ∆ (9) 1 min min m in ( ) k k k k i i i i p p p g b e s t + = + − ∆ (10) a. updating the inertia weight the update of inertia weight is essential for resolving optimization problems. for high level optimization problems, a local optimum exists which is close to global optimum solutions. consequently, the utilization capability of the search algorithm should be adequate to acquire the best solutions. hence, the update of inertia weight is essential during the iteration process. this has to be done according to cycles. the up gradation of inertia weight is given below: maxmin max ));(logexp( itr itr w w w e =−= ηη (11) b. updating the position and velocity of particles the perceptive manners are taken into consideration, regarding the best and worst experience of particles in the given search space. consequently, the idea of preceding knowledge of position and velocity of each particle is recommended, if the present fitness of every particle is weighted against its fitness value. if this value is small, then it can be treated as its experience. this particle’s occurrence generates significantly less variety compared to worst experience and affords enhanced exploration and exploitation of space without utilizing supplementary regional random exploration. c. formulating the objective function numerous objectives are certainly converted into one, by simply pre-multiplying the excess weight supplied by the customer, with all targets, by utilizing weighted sum approach. the weights are usually picked in such a method that each one provides comparable importance for the problem. usually weights happen to be preferred in such a way that their arithmetical sum is normally equal to one. the eed problem is represented as: iit teutfuf cos)1(cos ∗−+∗= (12) every single objective function takes any kind of value within the array and u is the weighting factor which decides the change of pressure over every objective function. the weighting factor u can take distinct values between 0 and 1. equal chances to reduce both objective functions can be engineering, technology & applied science research vol. 9, no. 5, 2019, 4605-4611 4608 www.etasr.com kumar & singh: environmental economic dispatch with the use of particle swarm optimization … acquired when w is located to 0.5, where equal weight is set to both objective functions. an array of several solutions is usually obtained, known as pareto optimal alternatives. d. algorithm of the proposed method the implementation of sr-pso in eed problem consists of the following steps: i) initialization, setting the initial velocity to zero and randomizing particles’ position. ii) position upgrade, where every particle’s position and velocity are updated, by considering the corresponding constraints. iii) fitness value calculation, for all particles. iv) obtain ���� , ��� and thereafter save the corresponding positions. v) use the proposed strategy based on space reduction. vi) go to step (ii) until the required criterion is obtained. here the optimization problem has the equality and inequality constraints explained before. equality constraints indicate a problem to random optimization algorithms, though it is tough to meet up with the optimization procedure. here constraints are managed as follows: 1) equality constraints a new system is suggested to tackle this constraint in the eed issue. at all iterations, (3) is contented above. i) initially disregard the network losses and then randomly generate almost all units’ power levels 121 ........... −+++ nppp ii) determine the end unit's power level using (10) iii) determine the transmission losses by utilizing (6) iv) include losses into power by regulating the last unit's power level as: ).......( 121 − +++−= ndn ppppp (13) 2) inequality constraints lower and upper power limits are checked after each iteration to make sure they concur with (4). if a particle flies out of limits, the current position shall be upgraded to the prior best position (���� ). figure 1 demonstrates the flowchart of the suggested sr-pso technique. the cognitive and the social element in this algorithm have no constants. the position and velocity of the i th particle can be calculated using the following equations: 1 2 ( 1) ( ) ( 1 ( ( )) ( 2 ( ( )) i b v k w v k c r a n d p x k c r a n d p x k + = ∗ + ∗ ∗ − + ∗ ∗ − (14) )1()()1( ++=+ kvkxkx (15) 1 1 1 1 max (( ) ) f i i iterc c c c iter = − ∗ + (16) ))(( 2 max 222 iif c iter iterccc +∗−= (17) where �&'(��� is the maximum iteration number and the inertia weight limits are between 0.4 and 0.9. )*�, )+�, )*,, and )+, denote the initial and the final values for cognitive and social factors, while )* and )+ represent the cognitive and social factors respectively. fig. 1. flowchart for the proposed sr-pso eed problem resolution iv. simulation results and analysis a. test system 1: indian utility system the suggested technique is analyzed using an indian utility system with six generators. fuel rate and emission constants, lower and upper limitation,s and transmission loss coefficient matrix are extracted from [20]. for the simplification of the multi-objective problem, only �-� emission is considered. also, the valve-point effects aren’t considered for the problem. simulation results are extracted using the power demand of 900mw. the algorithms were applied utilizing matlab programming language. during the simulation process, the compromise factor alpha takes values from 0 to 1. the optimization results with different alpha values are specified in table i. these simulation results are compared with [23] in table ii. the variation of total fuel cost with total emission is shown in figure 2. the best compromise solution can be obtained from the resultant graph. table i. optimization results on an indian utility system test system control variables sr-pso pl (mw) total fuel cost ($/hr) total emissions (kg/hr) ieee 30 bus system pd=200mw, α=0 2.8283 545.2791 210.6876 pd=200mw, α=0.5 3.5697 526.7653 217.5804 pd=200mw, α=1 4.4955 518.5650 235.4381 engineering, technology & applied science research vol. 9, no. 5, 2019, 4605-4611 4609 www.etasr.com kumar & singh: environmental economic dispatch with the use of particle swarm optimization … table ii. eed results with of 900mw demand parameters sr-pso ig p economic dispatch (mw) emission dispatch (mw) 1 120.5966 86.9897 2 35.2975 30.5767 3 16.6013 22.9873 4 10.0000 20.6892 5 10.0000 20.4620 6 12.0000 21.1235 pl (mw) 4.4955 2.8283 cost ($/hr) 518.5650 545.2791 emissions (kg/hr) 235.4381 210.6876 fig. 2. variation of generation cost with emission for different values of α b. test system 2: ieee 30-bus system this system has 6 generators and transmission losses are taken into consideration. the valve-point effects are not considered. fuel and emission rate constants along with various inequality power constraints are taken from [19]. the simulation results are described using 200mw power demand. table iii shows the ideal solution of sr-pso. the economic and emission dispatch results are shown in table iv using compromise factor α as 1 and 0 respectively. the variation of total fuel rate with the total pollutant is definitely calculated with different values of compromise factors. the variation is plotted in figure 3 and the best solution with the least value of fuel rate and pollutant can be found out from the graph. table iii. optimization results of the ieee 30 bus system test system control variables sr-pso pl (mw) total fuel cost ($/hr) total emissions (kg/hr) ieee 30 bus system pd=200mw, α=0 2.8283 545.2791 210.6876 pd=200mw, α=0.5 3.5697 526.7653 217.5804 pd=200mw, α=1 4.4955 518.5650 235.4381 c. test system 3: ieee 57-bus system this system has 7 generators and 42 loads connected in various buses. the entire load demand is 1250.8mw and 336.4mvar, without line limitations. analysis has been conducted without considering transmission losses. fuel and emission rate constants alongside various inequality power constraints are taken from [21]. table v shows the optimization results for 3 different values of α. the eed result is shown in table vi. the variation of total fuel cost with total emissions is shown in figure 4 for various values of α. the best compromise solution can be obtained with the best execution time from the resultant graph. the simulation results of srpso are described using the power demand of 900mw. table iv. eed results with 200mw demand parameters sr-pso ig p economic dispatch (mw) emission dispatch (mw) 1 120.5966 86.9897 2 35.2975 30.5767 3 16.6013 22.9873 4 10.0000 20.6892 5 10.0000 20.4620 6 12.0000 21.1235 pl (mw) 4.4955 2.8283 cost ($/hr) 518.5650 545.2791 emission(kg/hr) 235.4381 210.6876 fig. 3. variation of generation cost with emission for different values of α table v. optimization results of the ieee 57 bus system test system control variables sr-pso total fuel cost ($/hr) total emission (kg/hr) ieee 57 bus system pd=900mw, α=0 5086.2578 1667.0086 pd=900mw, α=0.5 2717.3640 2595.5687 pd=900 mw, α=1 2534.5068 3114.8429 table vi. eed results with 900mw demand parameters sr-pso ig p economic dispatch (mw) emission dispatch (mw) 1 384.5697 188.4421 2 10.0000 93.8984 3 20.0000 104.1802 4 10.0000 94.1156 5 341.1844 173.7787 6 10.0000 93.9535 7 124.2458 151.6316 cost ($/hr) 2534.5068 5086.2578 emission (kg/hr) 3114.8429 1667.0086 engineering, technology & applied science research vol. 9, no. 5, 2019, 4605-4611 4610 www.etasr.com kumar & singh: environmental economic dispatch with the use of particle swarm optimization … fig. 4. variation of generation cost with emission for different values of α d. test system 4: ieee 118-bus system simulations were run on a typical 118-bus system. this is one of the largest power systems with 14 generating units. the fuel and emission rate constants, alongside various inequality power constraints were taken from [19]. the optimization results are listed in table vii. economic and emission dispatch results are demonstrated in table viiι. the system load demand is 950mw. total fuel cost variation and total emissions are given in figure 5. table vii. optimization results of the ieee 118 bus system test system control variables sr-pso pl (mw) total fuel cost ($/hr) total emissions (kg/hr) ieee 118 bus system pd=950mw, α=0 7.6657 4594.7261 23.4037 pd=950mw, α=0.5 7.3835 4441.8930 91.2697 pd=950mw, α=1 10.0603 4347.8062 398.2422 table viii. eed results with 950mw demand parameters sr-pso ig p economic dispatch (mw) emission dispatch (mw) 1 102.6883 70.5071 2 90.7391 50.0000 3 50.0000 77.7310 4 50.0000 88.6522 5 50.0000 67.6157 6 50.0020 50.0007 7 50.0000 73.4310 8 50.0002 72.3253 9 63.2259 73.2658 10 63.1861 89.5837 11 62.8433 50.0000 12 177.3753 72.4813 13 50.0000 72.0719 14 50.0000 50.0000 pl (mw) 10.0603 7.6657 cost ($/hr) 4347.8062 4594.7261 emission (kg/hr) 398.2422 23.4037 v. conclusion sr-pso analysis was conducted in order to resolve the eed problem for the above mentioned power systems. power dispatch is planned into two objective functions, diminishing concurrently total operating cost and pollutant emissions. two objectives converge into one function, by utilizing a mathematic modeling method. optimum values of required variables are obtained for several loading conditions for ieee systems having 30, 57 and 118 buses and an indian utility system with six generators. the result satisfies all the chosen constraints. the comparison shows that the proposed approach has competitive performance in resolution conditions and computation time. the proposed sr-pso is robust, efficient and simple. this paper does not impose any constraints on the number of objectives and may be extended to incorporate more objectives, by utilizing various algorithms. fig. 5. variation of generation cost with emission for different values of α references [1] v. k. jadoun, n. gupta, k. r. niazi, a. 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sdavid@teiath.gr m. georgiou department of medical instruments technology technological educational institute of athens mary_georgiou@yahoo.gr e. fysikopoulos department of electrical and computer engineering national technical university of athens lefteris.fysikopoulos@gmail.com g. loudos department of medical instruments technology technological educational institute of athens gloudos@teiath.gr abstract—�uclear medicine (spect and pet) provides functional information, which is complementary to the structural. in cancer imaging radiopharmaceuticals allow visualization of cancer cells functionality, thus small cell population can be imaged. this allows early diagnosis, as well as fast assessment of response to therapy. our system is a single head gamma camera based on an r3292 position sensitive photomultiplier tube (pspmt), coupled to a 10cm in diameter csi:tl crystal. we have assessed two csi:tl crystals with pixel size of 2x2mm 2 and 3x3mm 2 respectively. three collimators were tested: a) a hexagonal, 1.1mm in diameter, general purpose parallel hole collimator b) a 1mm pinhole and c) a 2mm pinhole. systems were tested using capillary phantoms. all measurements were carried out in photon counting mode with gamma radiation produced by 99m tc. using the 2x2mm 2 crystal and the 1mm pinhole collimator a resolution better than 1mm was achieved. this allows very detailed imaging of small animals. using the 3x3mm 2 and the 2mm pinhole collimator a resolution of 1.3mm was possible with suitable sensitivity for breast imaging. those results indicate that this system is suitable for animal and breast studies. the next step will be clinical evaluation of the camera. keywordsdedicated gamma camera; pspmt; small animal imaging; scintimammography; pinhole i. introduction recently there has been a growing interest in compact and high resolution small gamma cameras, which are used for applications ranging from small animal imaging to scintimammography [1]-[3]. several groups have been working on the development of the small gamma cameras using position sensitive photomultiplier tubes (pspmt) and pixellated scintillator crystals [2]-[6]. the spatial resolution of these systems is mainly determined by the degree of pixellation; thus the use of discrete crystals allows the selection of intrinsic spatial resolution of the system independently of scintillator’s light yield. this technique assigns an event to a specific crystal location and improves the spatial linearity of the fov at the edges, compared with a continuous scintillator plate [7], [8]. image quality in single photon emission computed tomography (spect) is strongly influenced by the gamma detector capability to estimate energy and positioning of the γevent. traditionally gamma rays are detected by scintillator crystals that produce a scintillated light pulse, which is amplified, commonly by a position-sensitive photomultiplier tube (pspmt), and readout via charge division techniques [8, 9]. detectors based on pspmts have the advantages of a continuous photodetector surface (i.e. no gaps between pmts in anger camera). cameras based on pspmts are increasingly used for in vivo small animal studies [10], [11]. the benefits of small field of view systems have been explored in clinical environment and mainly in scintimammography [13], [14]. scintimmamography is a breast imaging technique based on nuclear medicine a technique that involves injection of a radioactive tracer (dye) into the patient. since the tracer accumulates differently in cancerous and non-cancerous tissues, scintimammography allows physicians to determine whether cancer is present or not. scintimammography is a supplemental breast exam that is used in specific patient’s population, to investigate a breast abnormality, following conventional x-ray mammography and before biopsy. the past fifteen years there has been increased interest in dedicated breast imagers using single photon emission mammography (spem) or positron emission mammography (pem) methods; thus a number of such dedicated systems have been developed and some are commercially available. although x-ray mammography remains the best screening method, it is characterized by low sensitivity, especially in the case of dense breasts. this leads to a large number of negative biopsies, part of which could be avoided. since, needle biopsy has obvious financial and psychological effects; there is need for a more sensitive second examination. scintimammography using conventional gamma cameras or pet systems is not sensitive due to the large size of those systems and the limited performance. typical cases where scintimammography with dedicated breast imagers is clinically useful, is in the case of etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 17-22 18 www.etasr.com david et al: experimental evaluation of a dedicated pinhole spect system … dense breasts or in order to follow up therapy, so that metabolic changes in breast tumors can be depicted a few days following treatment. in this work, a dedicated single-head round gamma camera based on an r3292 pspmt, coupled to an 10cm in diameter csi:tl crystal were tested. two crystals with pixel size of 2x2mm 2 for small animal imaging and 3x3mm 2 for breast examinations were have assessed, respectively. performance metrics include a 1mm and a 2mm pinhole collimator and crystal combinations are compared both for spatial resolution and sensitivity. images resulting from flooding of the two round csi:tl crystals with 99m tc gamma rays are shown. moreover profiles of line images from a 1mm capillary tube having 50 µci to 100 µci 99m tc were used in order to determine the better full width at half-maximum (fwhm) of the system with respect to the magnification factor of the pinhole apparatus. ii. materials and methods a. dedicated gamma ray imager description the dedicated small gamma camera consists of a discrete array of 2 x 2 x 3mm 3 or a 3 x 3 x 5mm 3 csi:tl crystals with 0.22mm spacing coupled to a 12.7cm round cross-wire anode pspmt (hamamatsu r3292) with simple resistive charge division readout of the 28x and 28y cross-wire anodes [15]. the general purpose collimator used has 1.5mm diameter and 2.2cm long hexagonal holes with 0.2mm septa. a resistive current divider network reduced the number of signals from 56 to 4. the four charges arriving at the resistive divider ends (qxa , qxb , qyc and qyd) [16] were preamplified and finally amplified by two 519 of mech-tronics nuclear dual amplifiers (4 channels). the acquisition system is based on a fast 7070 analog to digital converter (adc) module connected to a fast multiparameter acquisition system operating in the windows environment (mpa/win). the multiparameter system controls the four adcs (dependent mode) and acquires data in list mode through a 1 mbyte first in first out register (fifo) inside the mpa card. the centroid position (x, y) of the incident light pulse distribution on the photocathode is obtained by anger’s equations. the sum of the four charges provides the total energy deposited by the incident gamma ray. raw data processing and visualisation was carried out using custom software written in c++. the camera is shielded by 1cm lead and by 5mm tungsten on the side facing the radiation. a high applied voltage of 950 v was used; this voltage takes advantage of the full adcs dynamic range, without noise amplification. b. pinhole imaging characteristics and collimator designs. the imaging geometry of the pinhole collimator as compared to that of the parallel-hole collimator is shown in fig.1. the object is positioned close to the pinhole aperture, and a reversed and magnified image is projected onto the detector. comprehensive discussions of the principle of pinhole imaging in nuclear medicine can be found in [17]. the unique feature of pinhole imaging is that the image is magnified as compared to the image of the parallel-hole collimator. due to this magnification, the limits imposed by the intrinsic resolution of the camera system can be overcome. in addition, the pinhole collimator also provides a better trade-off between image resolution and photon detection efficiency than the parallel-hole collimator. however, sensitivity is not stable uniform in the entire field of view, thus corrections have to be taken into account. figure 1. schematic view of pinhole imaging as compared with parallel-hole collimator. reproduced by [18] from the basic pinhole geometry shown in figure 1, z is the object-to-collimator distance, l is the collimator length, and a, is the effective hole diameter of the pinhole aperture. the magnification factor m is given by the equation 1. /m l z= (1) the resolution of pinhole imaging is determined by the size of the pinhole aperture, the gamma photon energy, and the material used to fabricate the pinhole aperture [18]. c. flood correction for parallel collimator. flood correction is a necessary step in pixellized scintillators and is performed following the procedure reported in [19]. the uniformity correction was based on a flood source, consisting of a plastic container filled with radioactive solution of (2 mci 99mtc). the source was sufficiently large to cover the entire detector and was placed in direct contact with the collimated detector. a large number of counts (`4,000,000) were collected to minimize the statistical noise. using the raw flood image figure 2(a) a grid that maps each crystal pixel is determined figure 2(b) and the values in each crystal pixel are summed leading to the flood matrix figure 2(c) that is used to correct raw images. figure 3 demonstrates an example of uncorrected image raw image (a), summed image (b) and the flood corrected image (c) for a thin capillary filled with a 99m tc solution. figure 2. the raw flood image (a); the grid that maps each crystal pixel (b) and the summed flood matrix (c) that is used for flood correction. a flood 99m tc source has been used. (a) (b) (c) etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 17-22 19 www.etasr.com david et al: experimental evaluation of a dedicated pinhole spect system … figure 3. an example of the uncorrected raw image (a), summed image (b) and the flood corrected image (c) of a thin capillary filled with a 99m tc solution. d. experimental method 1) system sensitivity the sensitivity was defined as the fraction of events emitted by the line source over those actually detected by the system. we used a 1 mm capillary tube source filled with a 3.7mbq (100µci) 99mtc solution, placed perpendicular to the x-direction across the gamma camera fov at 0mm distance source from collimator. measurements were carried out for 300sec. radioactivity decay and corrections in background counts were corrected in sensitivity calculations. 2) system spatial resolution spatial resolution was measured as a function of the distance from source to the detector surface, by using a capillary filled with 99mtc. measurements were repeated as capillary stepped (vertically and horizontally) at several positions across the detector fov. the fwhm of the capillary tubes profiles were calculated using gaussian fit. fwhm values (in mm) were extracted by multiplying by 2.35 times the variance of the distribution σ. for the evaluation of pinhole apparatus the line source images were obtained. two different keel edge pinhole collimators with 2 and 3 mm hole were evaluated. the distance from each pinhole to line source varied horizontally from 1mm to 90mm. the images were acquired using a 100% energy window. the full width at half-maximum (fwhm) was calculated by the average of three profiles of the line images. 3) system linearity linearity was measured with a flood source phantom consisting of a plastic container filled with 99m tc radioactive solution with radioactivity varied from µci to 22 mci with increasing activity (in the same volume). the source was placed in direct contact with the collimated detector. a maximum activity in order to have linear response of events was determined. 4) system energy resolution system energy resolution is expressed as a percentage and is equal to the photopeak fwhm divided by the photopeak center energy, measured with the collimator in place. system’s energy resolution is always larger than the intrinsic. energy spectra were obtained by placing a 99m tc point source at the center of the fov above the detector surface. all measurements were carried out after the optimization of adjusting parameters (hv, amplifier gain, settings of the discriminators, adcs coincidence time and conversion gain) that provided maximum rating combined with the best imaging performance. iii. results and discussion table i shows the results of the measurements regarding, system spatial resolution and system sensitivity of the dedicated gamma camera equipped with 2 x 2 x 3mm 3 and 3 x 3 x 5mm 3 discrete csi:tl pixellated crystals at zero source to parallel collimator distance. table i. gamma camera characteristics detector characteristics 3 x 3 x 5mm 3 csi:tl 2 x 2 x 3mm 3 csi:tl coating thickness (g/cm 2 ) 0.85* 0.68* crystal array pitch 0.22 0.22 fwhm spatial resolution (mm) 4.5 3.7 fwhm energy resolution @ 140 kev (%) 22 23 sensitivity (cps / mbq) 198 156 quantum detection efficiency @ 140 kev (%) 85.7 68.9 * assuming 100% packing density the crystal array with 2x2 mm 2 crystal size shows improved detector spatial resolution as compared to the 3x3 mm 2 crystal (3.7 mm fwhm and 4.5 mm fwhm respectively). figure 4, shows the spatial resolution variation with increased source to parallel collimator distance. 0 5 10 15 20 25 0 5 10 15 20 csi:tl crystal 3x3x5mm 3 csi:tl crystal 2x2x3mm 3 source to collimator distance (cm) s p a ti a l r e s o lu ti o n ( f w h m ) figure 4. variation of spatial resolution with source to collimator distance. the csi:tl pixellated scintillator of 2 x 2 x 2mm 3 has better resolution properties at distance smaller than 15 cm. up to this point, spatial resolution properties of pixellated csi:tl scintillators is almost the same. the sensitivity of the system remains the same with the variation of source to parallel collimator distance as we expected. (a) (b) (c) etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 17-22 20 www.etasr.com david et al: experimental evaluation of a dedicated pinhole spect system … the imaging geometry of the pinhole collimator as compared to that of the parallel-hole collimator is shown in figure 3. the unique feature of pinhole imaging is that the image is magnified as compared to the image of the parallelhole collimator. due to this magnification, the limits imposed by the intrinsic resolution of the camera system can be overcome. however, sensitivity doesn’t stable uniform in the entire field of view, thus corrections have to be taken into account. the pinhole to absorption plane distance of 8 cm secure lower than 50% efficiency reduction at the edges of fov. that distance was experimentally determined after positioning a point source at the center of fov and at the critical angle, varying the pinhole to absorption plane distance. the critical angle is the tapered angle that ‘sees’ the edge of the detector. 0 2 4 6 8 10 0 1 2 3 4 5 pinhole 1mm pinhole 2mm source to pinhole distance (cm) s p a ti a l r e so lu ti o n ( f w h m ) in m m figure 5. spatial resolution for the 2x2mm 2 csi:tl crystal using the 1mm and 2mm pinhole collimator. 0 2 4 6 8 10 0 50 100 150 200 pinhole 1mm pinhole 2mm source to collimator distance (cm) c o u n ts p e r s e c o n d figure 6: system sensitivity for the 2x2mm2 csi:tl crystal with 1 and 2 mm aperture pinhole recorded with increasing source to pinhole distance. a line source with ~50µci 99mtc radioactivity was imaged; the distance between the crystal surface and the collimator was 8 cm. the source to pinhole distance varied from 1 to 9. the spatial resolution as well as the sensitivity recorded by the detector equipped with pinhole collimators is shown in figures 5 and 6. the pixellated csi:ti scintillators were set 8 cm away from the center of 1 and 2mm keel edge pinhole collimators. metrics were carried out changing the distance of the line source from the collimator. that distance was increased by a step of 1 cm. the measurements were finished when the magnification factor became little down to 1. in figure 7 and 8, the variation of spatial resolution as well as the sensitivity performance achieved by 3x3mm 2 csi:ti scintillator combined with 1 and 2mm keel edge pinhole collimators were shown. 0 2 4 6 8 10 0 1 2 3 4 5 pinhole 1mm pinhole 2mm source to pinhole distance (cm) s p a ti a l r e so lu ti o n ( f w h m ) in m m figure 7: spatial resolution for the 3x3mm 2 csi:tl crystal using the 1mm and 2mm pinhole collimator. 0 2 4 6 8 10 0 50 100 150 200 pinhole 2mm pinhole 1mm source to collimator distance (cm) c o u n ts p e r s e c o n d figure 8: system sensitivity for the 3x3mm2 csi:tl crystal with 1 and 2 mm aperture pinhole recorded with increasing source to pinhole distance. a line source with 50µci 99m tc radioactivity was imaged; the distance between the crystal surface and the collimator was 8 cm. the source to pinhole distance varied from 1 to 9. for all cases spatial resolution was found best (i.e. 0.79) for: (a) a magnification factor equal to eight (at 1 cm source to collimator distance), (b) a 1 mm pinhole aperture, which overcomes the physical limitation of crystal pixel size. the best spatial resolution achieved with the 2 mm pinhole aperture was etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 17-22 21 www.etasr.com david et al: experimental evaluation of a dedicated pinhole spect system … 1.2 1.3 mm depending on crystal pixel size. this result is significantly better than that found for the parallel collimator. in all cases, the sensitivity recorded by the system with the pinhole collimator drops exponentially, when source to collimator distance increases. this is in agreement with what is theoretically expected. for distances higher than 8 cm, the sensitivity increases again due to image dimensions decrease. point sensitivity and counting rate linearity were evaluated for a range of activities from ~37 mbq to 0.814 gbq (~1 22 mci) with a 99m tc source in air. 0 5 10 15 20 25 0 10000 20000 30000 2x2 csi:tl 3x3 csi:tl radioactivity (mci) c o u n ts p e r s e c o n d figure 9: counting rate linearity for 3x3mm 2 and 2x2mm 2 csi:tl pixellated scintillator plates. a good linearity is evident up to 10 mci (figure 9), which is adequate for the activity ranges of small animal imaging and scintimammography. for activity values higher than 10 mci, non-linearities and saturation effects begin to appear. at 20mci, only a noise signal was imaged. at high count rates, both counts and spatial resolution are lost. the former is due to dead time (the time during which the system cannot process another event), and the latter is primarily due to pulse summation (pile up) of low energy pulses which produce mispositioned signals. after 22mci radioactivity, a paralyzing effect drops the counts recorded by the system [20]. iv. concusions and future work a dedicated system suitable to perform in vivo imaging of small animals and scintimmamography has been built and tested. using the 2x2mm 2 crystal and the 1mm pinhole collimator a resolution better than 1mm was achieved. using the 3x3mm 2 and the 2mm pinhole collimator a resolution of 1.3mm was possible with suitable sensitivity for breast imaging. those results indicate that this system is suitable for animal and breast studies. future work includes energy spectra correction for each crystal in the array. for each individual crystal spectrum, the location of the photopeak will be identified. improvement of readout using a subtractive resistive technique will improve raw image quality. small animal studies are carried out, in order to assess systems performance in dynamic animal studies. the next step is object’s rotation, to acquire projection data for pinhole spect imaging. finally breast phantoms are being imaged as an initial step before the clinical evaluation of the camera. references [1] r.pani, m.n. cinti, r.pellegrini et al., “compact large fov gamma camera for breast molecular imaging”, 'ucl. instr. and meth. a, vol. 569, pp. 255–259, 2006 [2] carrie b. hruska, michael k. o’connor and douglas a. collins, “comparison of small field of view gamma camera systems for scintimammography”, 'ucl. med. commun., vol. 26, pp. 441–445, 2005 [3] s.vecchio, n. belcari, p. bennati, “a single photon emission computer tomograph for breast cancer imaging”, 'ucl. instr. and meth. a, vol. 581, pp. 84-87, 2007 [4] r.wojcik, s. majewski, d. steinbach and a.g. weisenberger, “high spatial resolution gamma imaging detector based on 5” diameter r3292 hamamatsu pspmt,” ieee trans. 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'ucl. sci., vol. 44, no. 3, pp. 494-498, 2002, june 1997 [17] barrett h , swindell w, (1981) radiological imaging: the theory of imaging formation, detection, and processing, vol. 1 & 2, new york: academic press. [18] qi yu-jin., “high-resolution spect for small-animal imaging” 'uclear science and techniques“. vol.17. no.3, pp. 164-169, 2006 [19] steinbach d, majewski s, williams m, kross b,weisenberger a g and wojcik r, “development of a small field of view scintimammography camera based on a yap crystal array and a position sensitive pmt, ” ieee med. imag. conf. conf. rec. pp. 1251–1256, 1997 [20] g. f. knoll, radiation detection and measurement, (singarore: john wiley & sons), 2 nd edition, 1989 etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 17-22 22 www.etasr.com david et al: experimental evaluation of a dedicated pinhole spect system … authors profile stratos david received his diploma from the department of medical instruments technology, technological educational institute of athens, greece, in 2004. he received his master degree in medical physics from the medical school of university of patras in 2006. he received his phd from medical school of university of patras in 2010. he is now working in the field of small field of view detectors for spect and pet and detector components evaluation. maria georgiou received her diploma in electrical and computer engineering from the national technical university of athens (ntua), greece, in 2007. since 2009 she is a phd student in the medical school of thessaly. her work is mainly focused on the development of electronics for field of view spect and pet systems and scintimammography. eleytherios fysikopoulos received his diploma in electrical and computer engineering from the national technical university of athens (ntua), greece, in 2007. since 2009 he is a phd student in national technical university of athens. he is working in the field of data acquisition using compact adcs and fpgas for application in small spect and pet systems. george loudos is an assistant professor in the department of medical instruments technology, technological educational institute of athens, since 2008. he received his diploma in electrical engineering from the national technical university of athens (ntua), greece, in 1998 and his phd in biomedical engineering in 2003 (ntua). his research interests are focused on molecular imaging using nuclear medicine techniques and medical instrumentation. more specifically he is interested in the development of dedicated systems for small animal imaging and scintimammography, software for spect and pet, monte carlo simulations of pet/spect systems and radionuclide dosimetry. on application level, he is interested in in vivo imaging of radiopharmaceuticals, radiolebelled nanoparticles and application of spect/pet in the study of biological processes. microsoft word 35-2342_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3492-3495 3492 www.etasr.com alzahougi et al.: rsw junctions of advanced automotive sheet steel by using different … rsw junctions of advanced automotive sheet steel by using different electrode pressures abdulkarim alzahougi faculty of technology karabuk university karabuk, turkey aalzahougi@yahoo.com muhammed elitas faculty of technology karabuk university karabuk, turkey melitas@karabuk.edu.tr bilge demir faculty of engineering karabuk university karabuk, turkey bdemir@karabuk.edu.tr abstract—the effects of different types of welding current and electrode pressure on tensile shear properties of resistance spot welding (rsw) of commercial dp600 steel have been investigated in this study. in tensile shear tests of the welded joints, tensile shear force and maximum displacement were utilized to characterize the performance of the welding process. nugget diameter has been measured to create a clear definition of rsw physical properties. experimental results show that tensile shear load bearing capacity increases as the electrode pressure increases. low current value occurs at low and at high electrode pressures. during high current value, the material can exhibit superior mechanical properties. the effect of electrode pressure on tensile shear load bearing capacity increases as welding current increases. keywords-dp600; rsw; electrode pressure; tensile shear force; mechanical properties i. introduction global demand for energy saving and increasing concern for environmental pollution and global warming affect the scientific community and relevant studies are on the rise. the improvement of strength, capacity and properties of materials, most importantly metals, reduces material cross section, the reduction of part weight and the resultant decrease in fuel consumption, has made possible to reduce greenhouse gas emissions. for various functional requirements of current vehicles, advanced high strength steel is the ideal solution [1]. one of the most important and most valuable properties of advanced strength steels is the excellent strength-ductility relationship. dp and the trip steels have been developed for this purpose. dp steels usually have tensile strength of 6001200mpa and elongation of 15-25% [2]. dp steels are absorptive and are endowed with high tensile strength, low yield strength or tensile strength ratio, perfect formability, and high tensile energy. these advantages make dp steels attractive for automotive applications [3]. rsw is the major joining technique utilized for automobile production and manufacturing. a common automotive body consists of a broad number of rsw, between 3000 and 5000 spots [4]. during rsw, broad changes in the mechanical and metallurgical properties of the weld metal and the heat affected zone (haz) are taking place. the investigation of these changes is important and relevant for the safety, protection and strength of the welded joints [5]. some studies examined the mechanical properties of rsw junctions of dp steels. authors in [6] laid emphasis on the carbon equivalence which increases the hardness of the weld zone which in turn forms a very strong correlation between chemical composition and mechanical properties. advanced high strength steel (ahss), reached much higher tensile strength than the conventional high strength steel (hss). authors in [7] studied and examined the welding process design and optimization of rsw parameters. they observed the tensile strength values which revealed weaker correlation with higher current. authors in [8] studied the microstructure of rsw and the friction stir welded (fsw) with dp600 samples. the results of the rsw hss showed that the high strength-weight ratio and its mechanical properties are ideal for automotive applications. however, it has been noticed that microstructure changes alongside with rsw affect mechanical properties with transformations occurring in the base metal microstructure. authors in [9] noted that the effect of welding currents on the capacity of the welding strength lasts longer than welding time. authors in [10] observed the effect of the weld nugget size on the overload fracture mode of the rsw samples. in [11], a discovery was found about optimal welding parameters which were selected through the utilization of taguchi experimental design method. authors in [12] examined, evaluated and studied the transition of the rsw dp780 steel from the interface-fracture mode to the pullouttype of the fracture mode in tension and in transverse stress loading situations. authors in [13] investigated the effect of holding time on microstructure, hardness and mechanical properties for the welded joints with different levels of thickness. authors in [14] investigated the effects of multistage tempering process on nugget size, microstructure, microhardness and tensile fracture behavior of the dp590 steel with rsw while utilizing finite element models. authors in [15] investigated the welded joints of the dp980 steel sheets and the effects on stiffness properties of the pulsed current. there are many studies on welding, however they are typically and usually about welding parameters like weld current, weld time etc. in relation with the electrode pressure or force. to the best of our knowledge there hasn’t been any engineering, technology & applied science research vol. 8, no. 5, 2018, 3492-3495 3493 www.etasr.com alzahougi et al.: rsw junctions of advanced automotive sheet steel by using different … research conducted on rsw junctions of the ahss particularly in relation to the dp600 sheet steel through the utilization of different electrode pressures. regarding advanced automotive sheet steels, dp600 has a proper place and relevance based on its properties and low cost when compared to other ahss. in this study, rsw process was applied to dp600 at different welding currents and electrode/weld pressures. tensile shear tests were applied to the base material (bm) and the rsw samples at electrode pressures of 2-6bar at 5ka and 7ka welding currents. the effects of the different electrode/weld pressures and welding currents on tensile shear properties of the dp600 steel were investigated. ii. experimental procedure commercial dp600 steel is available in sheet metal layers of 250mm*250mm*1mm. 230vac heat input, 50hz frequency and 2500va power capacity from the spectrolab model lavfa18a were utilized to determine the chemical composition of the dp600 steel material. steel’s chemical composition is shown in table i while its microstructure is shown in figure 1. fig. 1. microstructure view of dp600 steel table i. chemical composition of dp600 steel (%) material c si mn s cr ni dp600 0.077 0.253 1.86 0.006 0.177 0.012 al ti v sn fe 0.127 0.002 0.004 0.006 97.472 the samples were designed according to en iso 14273 standard for the rsw operation. the rsw samples were cut to dimensions of 100mm*30mm*1mm through the shearing process from the 250mm*250mm sheets. the samples were overlapped for 35mm. with the consequent size of rsw, overlapped samples were 165mm. rsw was carried out through the utilization of two different welding currents, 5ka and 7ka, and 5 different electrode pressures of 2-6bar. the ac machine for the spot welding was equipped with a device for the pneumatic control of the phase shift of the ac current. before their joining, the surface of the test pieces was cleaned and thereafter the welded utilized conical water-cooled cu–cr alloy electrodes. the diameter of the contact surface of the electrode was 8mm [16]. the woodworking mould was utilized to readjust the samples during the welding, to avoid axis misalignment and to protect and readjust the sparks from spattering. three-resistance spot welded samples were created singularly for each experiment parameter. the water-cooling system of the electrodes was kept under specific constant water control because of the excess of the heat input. rsw parameters utilized in this study are presented in table ii [17, 18]. the time unit is cycle-based (1cycle=0.02s). the rsw process steps and a sample photograph are shown in figures 2 and 3 respectively. table ii. welding parameters for rsw processing electrode pressure (bar) 2-6 welding current (ka) 5, 7 electrode tip diameter (mm) 8 down time (cycle) 15 squeeze time (cycle) 35 welding time (cycle) 20 hold time (cycle) 10 separation time (cycle) 15 fig. 2. rsw process steps fig. 3. rsw sample image tensile shear test parameters are the 5ka and 7ka welding currents, and 2bar to 6bar electrode pressures. the samples were tested for each of the experimental parameters and the arithmetic means of these values were calculated. in addition, tensile test was applied to the base material for comparison. in addition to the tensile shear data which has been generally utilized in the literature, there is now a reference to the parts of the joining made on the nugget welding profile shown in figure 3. in this way, shear data are also considered as stress data. rsw samples had 1mm thickness, 30mm width and 110mm gauge length. the crosshead speed value utilized for the tensile shear test was 2mm/min [16]. iii. results and discussion during tensile shear tests, maximum tensile shear force value which allows the fracture to occur was evaluated and examined to assess the tensile shear load bearing capacity characteristics of the joint [18]. base material was also subjected to tensile test. the effects of electrode pressure and welding current on tensile shear load bearing capacity were studied. authors in [17] reported that micro voids of large size were formed in the low electrode forces of the rsw process. it was observed that nugget solidifies before electrodes were moved away from the weld region. since the weld nugget was not sufficiently suppressed at relatively lower electrode forces, shrinkage voids were formed because of the low stress during this time [17]. in addition to other approaches, and because of increased electrode progression and cramping as the electrode force increases, the significant parts of the voids are closed, and fewer shrinkage voids occur in the welded area. any increment engineering, technology & applied science research vol. 8, no. 5, 2018, 3492-3495 3494 www.etasr.com alzahougi et al.: rsw junctions of advanced automotive sheet steel by using different … of the welding current provides a capable level of current efficiency. hence, the effectiveness of the welding processes increases [3, 17]. through this discovery, variations of the nugget diameter were investigated in the rsw joints which depended on the welding parameters. the strong relationship between the increment of maximum tensile shear load bearing capability and the increment of the area been subjected to upcoming stress level was caused by the nugget diameter [5]. obtained results of the tensile shear test are presented in tables iii and iv for samples joined with 7ka and 5ka respectively. table iii. tensile shear test results with 7ka welding current electrode pressure (bar) nugget diameter (mm) tensile shear force (kn) maximum displacement (mm) 2 7.49 13.1687 5.382 3 7.62 13.8750 6.877 4 7.89 13.9156 6.818 5 7.22 13.4875 7.434 6 7.06 12.2219 4.430 base material 19.2125* 13.665 *this is the ultimate tensile force for base material’s condition of unwelded or before welding. differentiating from others, it wasn’t spot-welded. it had size of 100*30 and it is one of the overloaded parts. it was tested in order to evaluate maximum load bearing-capacity. table iv. tensile shear test results with 5ka welding current electrode pressure (bar) nugget diameter (mm) tensile shear force (kn) maximum displacement (mm) 2 7.41 13.5594 7.979 3 7.63 13.6938 7.968 4 7.71 13.7605 7.136 5 7.91 13.8359 7.953 6 7.15 13.5609 8.097 the maximum tensile shear load bearing capacity of the samples increased along with electrode pressure until 4bar. after this pressure level, it showed a high tendency to decrease. this shows that 4bar pressure is the optimum value for 7ka rsw. at welding current of 5ka, the maximum tensile shear load bearing capacity was reached at 5bar, indicating a higher tendency to decrease afterwards (table iv). sensitive values were taken from the graph (figure 4), as the event in which the melt-pressure exceeded 7ka-4bar and 5ka-5bar respectively. in that stage, electrodes undergo a much deeper level of sinking with excessive pressure and thus nugget thickness is reduced [17, 19]. the thickness of the rsw nugget-base material had passed the lateral area, which was also falling at a time. the lateral area forms a core basis for tensile approach. the decrease in the lateral area and the decrease in the nugget thickness coexist [5]. the indentation depth ought not to be beyond 30% of the sheet thickness [2, 9]. the electrode depth indentation experimental values were within standard levels. nugget formation was strongly examined as dependent on the material type and welding parameters. the excessive sinking of the electrodes to the rsw samples causes an increment in the welding heat input because of the excessive increase of the indentation-contact. excessive heat input, strong electrode contact, and electrode retention could disrupt the nugget geometry and weld profile. moreover, the pressure can cause cracks on the nugget surface and lateral surface areas. in addition, excessive heat input causes grain growth in the haz and weld metal and causes the strength to decrease [3, 5]. studies on advanced strength steels show a strong relationship between nugget size and tensile shear strength [3, 20]. the mean diameter of the nugget had been measured as been up to approximately 7mm in [21-24] and it can be used for dp600 steel [4]. these results can be explained by 5 t rule (t: material thickness), which was recommended to be the most appropriate rule according to japanese [25] and german [26] standards. after examination of the results in tables iii and iv, it was seen that the strength of the dp600 steel increased in direct proportion to the nugget diameter until an optimum value and it decreased thereafter [18]. maximum tensile shear force values obtained at these different welding currents depended on the electrode pressure (figure 4). the 7ka-4bar values of the rsw were near to ideal. the maximum tensile shear load bearing capacity value occurred at 5bar electrode pressure in 5ka samples. the effect of the electrode pressure on the tensile shear force is greater in the 7ka samples. the graph of the 5ka samples is almost horizontal. this shows that the effect and the sensitivity of the electrode pressure were lower at lower current values. because of this, it was asserted that as the current increases, the effect of the pressure increases. as the electrode pressure increases, the welding current will have the potential to decrease. fig. 4. maximum tensile shear force values obtained the highest reported tensile shear force values were from 12.5kn to 16.67kn [17], 13.69kn [21], 11.67kn [18], 3.1259.75kn [2], and 10-14.7kn[27]. the greatest value of the tensile shear load bearing capacity was, reported in [17] and the lowest in [2]. some of the differences observed between maximum tensile shear force values can be attributed to differences in the chemical composition of the steels used, rsw parameters, and sheet thickness. the tensile shear load bearing capacity obtained in our study resulted in a category that could be classified as been close to high values. iv. conclusions rsw process was applied to the commercial automotive sheet steel dp600 at different welding currents and electrode/weld pressures. these tensile shear tests were applied to the base material and to the rsw samples at electrode pressures of 2bar to 6bar at 5ka and 7ka welding currents. the effects on the tensile shear properties of the dp600 steel were studied and the following results were obtained: • at lower current values, effect and sensitivity of the electrode pressure were observed to be less. as the current engineering, technology & applied science research vol. 8, no. 5, 2018, 3492-3495 3495 www.etasr.com alzahougi et al.: rsw junctions of advanced automotive sheet steel by using different … increased, the effect of the pressure increased. as the electrode pressure increased, the welding current could also reduce. • welding parameters and nugget diameter are important factors that determine the load-bearing capacity of the overloaded rsw junction samples. • the welding current efficiency had increased up to 4bar at 7ka welding current and up to 5bar at 5 ka welding current. as the welding current increased, heat input, nugget diameter, tensile shear force value, and maximum tensile shear load bearing capacity increased. • the tensile shear load bearing capacity was directly proportional to the nugget diameter. • tensile strength of the base material decreased after rsw. acknowledgment this work was supported by the scientific research projects coordination unit of karabuk university (karabuk, turkey). project number: kbübap-17-kp-463. references [1] m. a. erden, “the effect of the sintering temperature and 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“effects of electrode tip morphology on resistance spot welding quality of dp590 dual phase steel”, the international journal of advanced manufacturing technology, vol. 83, no. 9-12, pp. 1917-1926, 2016 [15] c. sawanishi, t. ogura, k. taniguchi, r. ikeda, k. oi, k. yasuda, a. hirose, “mechanical properties and microstructures of resistance spot welded dp980 steel joints using pulsed current pattern”, science and technology of welding and joining, vol. 19, no. 1, pp. 52-59, 2014 [16] f. hayat, i. sevim, “the effect of welding parameters on fracture toughness of resistance spot-welded galvanized dp600 automotive steel sheets”, the international journal of advanced manufacturing technology, vol. 58, no. 9-12, pp. 1043-1050, 2012 [17] c. ma, d. l. chen, s. d. bhole, g. boudreau, a. lee, e. biro, “microstructure and fracture characteristics of spot-welded dp600 steel”, materials science and engineering: a, vol. 485, no. 1-2, pp. 334-346, 2008 [18] m. i. khan, m. l. kuntz, e. biro, y. zhou, 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pp. 443-449, 2014 [23] s. daneshpour, m. kocak, s. riekehr, c. h. j. gerritsen, “mechanical characterization and fatigue performance of laser and resistance spot welds”, welding in the world, vol. 53, no. 9-10, pp. 221-228, 2009 [24] m. elitas, b. demir, “the effects of the welding parameters on tensile properties of rsw junctions of dp1000 sheet steel”, engineering, technology & applied science research, vol. 8, no. 4, pp. 3116-3120, 2018 [25] jis z3140. method of inspection for spot welds, japanese industrial standard 1989 [26] dvs 2923. resistance spot welding, german standard [27] d. zhao, y. wang, d. liang, p. zhang, “an investigation into weld defects of spot-welded dual-phase steel”, the international journal of advanced manufacturing technology, vol. 92, no. 5-8, pp. 3043-3050, 2017 microsoft word 10-2991_s_etasr_v9_n5_pp4627-4630_protasi engineering, technology & applied science research vol. 9, no. 5, 2019, 4627-4630 4627 www.etasr.com duc: experimental water quality analysis from the use of high sulfuric fly ash as base course … experimental water quality analysis from the use of high sulfuric fly ash as base course material for road building nguyen viet duc faculty of civil engineering thuyloi university hanoi, vietnam ducnv@tlu.edu.vn abstract—water quality directly influences human life. drinking water contamination can result in severe health problems. this paper deals with the analysis of water specimens from submergence of material containing high sulfuric fly ash as base course material for road building. the specimens were obtained from real road testing. results showed that for the material that used fly ash and chemical admixture, water quality was suitable for drinking in accordance with the standard parameters prescribed by the vietnam ministry of health, while for the material that used the same fly ash without chemical admixture, the total arsenic content was eight times higher than that of the former. thus, if one desires to utilize fly ash with high sulfur as base course material for road building, it needs to be used in combination with appropriate chemical admixture, so that it would not affect ground water quality. keywords-fly ash with high sulfur; base course material; real road testing; water quality analysis; chemical admixture i. introduction electricity consumption is growing nowadays especially in developing countries like vietnam along with economy transformation [1]. according to the recent forecasting consumption, vietnam electricity system will need more than 500gwh by the year 2030 [2-5]. the latest master plan for the power system of the country revealed that a half of that figure will be supplied by coal-fired thermal power plants [6]. along with that, there will be million tons of fly ash from these plants dumped to the environment. apart from the ordinary fly ash, there will be also a vast amount of fly ash with high sulfuric content, which can be used for concrete or cement if it is properly treated [7-10]. in order to improve the environmental acceptability and reduce the construction cost of the deep mixing method, the replacement of ordinary portland cement by supplementary cementing materials such as ordinary fly ash has been recently involved into road building [11-16]. when mixed with lime and water, fly ash forms a compound similar to cement. when used with cement, fly ash improves strength and durability, particularly where the locally available soil is poor [17, 18]. fly ash with high sulfur has been attempted to be used as base course material for road building [19-21]. this type of fly ash improved the physical and mechanical properties of soil similarly to the ordinary fly ash. however, when it rains, water falling on the road diffuses into soil along with other materials used for road building, which might be detrimental to ground water quality, and ultimately would affect public health [22-24]. the aim of this paper is to evaluate water, which was used for submerging the specimens up to saturated condition. the specimens were obtained from a road which was built by using fly ash with high sulfur as base coarse material. water quality was evaluated in accordance with the standards prescribed by the vietnam ministry of health [25]. ii. water sample collection in this study, a real road building test was performed. onekilometer rural road in ward huu lung, lang son province, vietnam was taken into consideration. the road was divided into four segments of 250 meters each, which served for testing four different materials, as shown in table i. the first material was local soil with 5% cement and 5% fine crushed stone. the second and third ones were mixes with 9% and 5% high sulfur fly ash and 5% cement. in the third mix, chemical admixture was also used with the amount of 5% cement weight. fly ash with high sulfur was not added into the fourth mix, which used only 5% cement and admixture. table i. materials used for the road building test material 1 material 2 material 3 material 4 local soil 1 1 1 1 cement pc40 0.05 0.05 0.05 0.05 fine crushed stone 0.05 fly ash with high sulfur 0.09 0.05 chemical admixture 0.0025 0.0025 all road building tests were carried out by equipment provided from the vietraco jsc such as sakai® stabilizer machine, rollers, rammers, etc. at first, the optimum moisture content of the local soil was determined, depending upon the water content that might be added to the soil. for the first road segment (material 1), after the placement of fine corresponding author: nguyen viet duc, thuyloi university, 175 tay son, dong da, hanoi, vietnam engineering, technology & applied science research vol. 9, no. 5, 2019, 4627-4630 4628 www.etasr.com duc: experimental water quality analysis from the use of high sulfuric fly ash as base course … crushed stone, cement was dispersed with a thin layer, as it can be seen in figure 1. for the rest road segments (material 2, material 4) cement and/or fly ash with high sulfur were placed above the local soil. after the placing of raw materials (fine crushed stone, cement, and/or fly ash), the stabilizer machine came in and blended local soil and raw materials together. chemical admixture and water were added during the mixing process (figure 2). finally, a rammer and a roller came in to press and vibrate the composite material until its surface became plane and dense. fig. 1. cement and/or fly ash placement on the road before mixing with local soil underneath at 28 days, specimen extraction was carried out from all the road segments by a hand-held coring machine. the specimens from those segments are shown in figure 3. after extraction from the field, all specimens were moved to the laboratory for further study. the specimens were submerged into distilled water for 72 hours until reaching a saturated condition, as it can be seen in figure 4. after that, water sample collection was conducted, as shown in figure 5. water quality was estimated following the directives of [25] (table ii). fig. 2. picture of on site equipment during the test (a) (b) (c) (d) fig. 3. sample extraction from the four road segments: a) material 1, b) material 2, c) material 3, d) material 4 fig. 4. specimen submergence into distilled water fig. 5. water sample collection used for analysis engineering, technology & applied science research vol. 9, no. 5, 2019, 4627-4630 4629 www.etasr.com duc: experimental water quality analysis from the use of high sulfuric fly ash as base course … table ii. standard values of potable water [8] parameters units standard value ph indicator 6.5-8.5 ammonium content mg/l ≤ 3 total arsenic content mg/l ≤ 0.01 chloride content mg/l ≤ 300 total iron content mg/l ≤ 0.3 lead content mg/l ≤ 0.01 total mercury content mg/l ≤ 0.001 total manganese content mg/l ≤ 0.3 nitrite content mg/l ≤ 3 e coli and/or coliform bacteria no bacteria / 100 ml iii. results and discussion the results of water quality analysis are presented in table iii. it can be seen that the ph indicator of all samples, including the ones with fly ash (materials 2-3), complies with the standard potable water values in table ii. regarding ammonium content, the similar outcome is also observed. total arsenic content from all samples is within the standard values except the one of material 2. chloride content from the water of material 2 is the highest, however all of them are within standard values. the other parameters such as total iron content, lead content, total mercury content, total manganese content and nitrite content from the water of all samples are in compliance with the standard values. eventually, no e coli and/or coliform bacteria were found in the water of all materials. table iii. water quality analysis results parameters units material 1 2 3 4 ph indicator 7.93 7.88 7.94 8.27 ammonium content mg/l 2.99 2.79 2.59 2.47 total arsenic content mg/l 0.006 0.08 0.009 0.009 chloride content mg/l 5.68 6.75 5.68 6.04 total iron content mg/l 0.262 0.21 0.08 0.08 lead content mg/l 0.009 0.009 0.008 0.001 total mercury content mg/l 0.001 0.001 0.001 0.001 total manganese content mg/l 0.16 0.074 0.0016 0.0043 nitrite content mg/l 0.545 0.593 0.591 0.583 e coli and/or coliform bacteria no no no no it is noteworthy that due to the total arsenic content from the water of material 2, which is about eight times higher than that of the rest, only this material that used fly ash with high sulfur would not be applied for road building, because arsenic is very harmful [22]. on the other hand, material 3 also involves fly ash with high sulfur, but the difference here is the use of proper chemical admixture. according to the supplier, this admixture is able to be dispersed around heavy metals in the specimen and prevent them from being emitted to water. iv. conclusion although fly ash with high sulfur can improve physical and mechanical properties of road building soil, the environmental issue related to the use of this industrial waste must be examined. water from specimen submergence of the material that used fly ash with high sulfur for road building was analyzed in this study. the main conclusions of this study are: • water derived from specimen submergence of all materials in this study complies with the quality parameters prescribed by the vietnam ministry of health, except for water sampled from the material that used fly ash with high sulfur. • for the material that used the same fly ash and chemical admixture, the water quality was suitable for drinking. the admixture seemed to prevent metallic substances, which are very harmful for human health, from being emitted to water during submergence. • thus, if one desires to utilize high sulfur fly ash for road building, it is recommended to be used in combination with the appropriate chemical admixture, so that it would not affect ground water quality. acknowledgment the author would like to express his gratitude to mr. dao minh, ceo of vietraco jsc for his help and contribution to the present paper. references [1] http://data.worldbank.org/country/vietnam [2] general statistics office of vietnam, master investigation on population and households, general statistics office of vietnam, 2009 [3] general statistics office of vietnam, master investigation on population and households, general statistics office of vietnam, 2014 [4] general statistics office of vietnam, united nations fund for population activities, vietnam population projection 2014-2049, vietnam news agency publishing house, 2016 [5] v. h. m. nguyen, c. v. vo, k. t. p. nguyen, b. t. t phan, “forecast on 2030 vietnam elecitricity consumption”, engineering, technology & applied science research, vol. 8, no. 3, pp. 2869-2874, 2018 [6] institute of energy, evn, revised power master plan no. vii, ministry of industry and trade, 2015 [7] l. d. luong, d. v. nguyen, h. t. luu, h. v. le, t. m. nguyen, “study on fluidized bed combusion fly ash with high sulfur from cao ngan coal-fired thermal power plant for production of construction materials”, vietnamese journal of science and technology, vol. 1-2, no. 6, pp. 816, 2010 [8] c. s. shon, d. saylak, s. mishra, “evaluation of manufactured fluidized bed combustion ash aggregate as road base coarse materials”, world of coal ash conference, denver, usa, may 9-12, 2011 [9] d. gazdic, m. fridrichova, k. kulisek, l. vehovska, “the potential use of the fbc ash for the preparation of blended cements”, procedia engineering, vol. 180, pp. 1298-1305, 2017 [10] x. m. xie, l. guo, “study on preparation and properties of fly ash concrete with high sulfur and high-calcium fly”, 2nd ieee international conference on information management and engineering, chengdu, china, april 16-18, 2010 [11] h. afrin, “a review on different types soil stabilization techniques”, international journal of transportation engineering and technology, vol. 3, no. 2, pp. 19-24, 2017 [12] b. r. phanikumar, s. s. radhey, “effect of fly ash on engineering properties of expansive soil” journal of geotechnical and geoenvironmental engineering, vol. 130, no 7, pp. 764-767, 2004 [13] a. hilmi, m. aysen, “analyses and design of a stabilized fly ash as pavement base material”, fuel, vol. 85, no. 16, pp. 2359-2370, 2006 [14] s. karthik, e. k. ashok, p. gowtham, g. elango, d. gokul, s. thangaraj, “soil stabilization by using fly ash”, journal of mechanical and civil engineering, vol. 10, no. 6, pp. 20-26, 2014 engineering, technology & applied science research vol. 9, no. 5, 2019, 4627-4630 4630 www.etasr.com duc: experimental water quality analysis from the use of high sulfuric fly ash as base course … [15] j. vestin, m. arm, d. nordmark, a. lagerkvist, p. hallgren, b. lind, “fly ash as a road construction materials”, wascon 2012 conference proceedings, iscowa and sgi, 2012 [16] a. μouratidis, “stabilization of pavements with fly-ash”, conference on use of industrial byproducts in road construction, thessaloniki, greece, 2004 [17] n. s. pandian, k. c. krishna, b. leelavathamma, “effect of fly ash on the cbr behavior of soils”, indian geotechnical conference, allahabad, india, 2002 [18] m. r. hall, k. b. najim, p. keikhaei dehdezi, “soil stabilization and earth construction: materials, properties and techniques”, in: modern earth buildings, pp. 222-255, woodhead publishing limited, 2012 [19] v. d. nguyen, “cementitious materials for stabilizing clayey soils in road building”, international journal of engineering and technology, vol. 7, no. 4, pp. 6105-6108, 2018 [20] american coal ash association, fly ash facts for fighway engineers, federal highway administration, 2003 [21] s. κolias, a. κarahalios, “analytical design of pavements incorporating a capping layer of stabilized soil with high calcium fly ash and or cement”, 1 st conference for the utilization of industrial by products in building construction, thessaloniki , greece, 2005 [22] a. n. laghari, z. a. siyal, d. k. bangwar, m. a. soomro, g. walasai, f. a. shaikh, “grounwater quality analysis for human consumption: a case study of sukkur city, pakistan”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2616-2620, 2018 [23] s. v. s. prasanth, n. s. magesh, k. v. jitheshlal, “evaluation of groundwater quality and its suitability for drinking and agricultutal use in the coastal stretch of alappuzha distrist, kerala, india”, applied water science, vol. 2, no. 3, pp. 165-175, 2012 [24] a. olusola, o. adeyeye, o. durowoju, “groundwater: quality levels and human exposure, sw nigeria”, journal of environmental geography, vol. 10, no. 1-2, pp. 23-29, 2017 [25] vietnam ministry of health, national technical regulation on domestic water quality, 2009 engineering, technology & applied science research vol. 8, no. 3, 2018, 3054-3059 3054 www.etasr.com duranay et al.: fuzzy sliding mode control of dc-dc boost converter fuzzy sliding mode control of dc-dc boost converter zeynep bala duranay eee department firat university, technology faculty elazig, turkey zbduranay@firat.edu.tr hanifi guldemir eee department firat university, technology faculty elazig, turkey hguldemir@firat.edu.tr servet tuncer eee department firat university, technology faculty elazig, turkey stuncer@firat.edu.tr abstract—a sliding mode fuzzy control method which combines sliding mode and fuzzy logic control for dc-dc boost converter is designed to achieve robustness and better performance. a fuzzy sliding mode controller in which sliding surface whose reference is obtained from the output of the outer voltage loop is used to control the inductor current. a linear pi controller is used for the outer voltage loop. the control system is simulated using matlab/simulink. the simulation results are presented for input voltage and load variations. simulated results are given to show the effectiveness of the control system. keywords-boost converter; dc-dc converter; flc; fuzzy logic; sliding mode i. introduction voltage-mode control and current-mode control are two methods used to control dc-dc converters [1]. the voltagemode control is robust to disturbances, but slow. current-mode control has a fast transient response but is more complex than voltage mode control. classical pi and hysteretic controllers are the most used controllers for dc-dc converters. the linearized converter model around an operating point obtained from the state space average model [2] is used for conventional linear controllers. the classical controllers are simple to implement but the effect of variation of system parameters cannot be avoided, due to the dependence of linearized model parameters on the converter’s operating point [3]. the controller for dc-dc converters must account the nonlinearity and parameter variations. it should maintain stability and provide fast response in any operating condition. classical control methods for dc-dc converters are not much efficient in achieving the desired performance [4-5]. a nonlinear control technique developed in [6] derived from variable structure control theory is called sliding mode control (smc) has advantages of simple implementation, robustness and fast transient response [7]. smc is used to maintain the output voltage of the converter to be independent of parameters, input and load variations [8]. it provides invariant system dynamics to uncertainties when controlled in the sliding mode [9]. smc has a problem of chattering. chattering is undesirable oscillations having finite amplitude and frequency due to the presence of unmodeled dynamics or discrete time implementation [10]. some methods such as equivalent control and boundary layer approach are used to reduce the chattering. equivalent control based methods cannot be used to reduce chattering because of their finite number of output values. the boundary layer approach has a problem of reaching sliding mode due to the replacement of the discontinuous control action with a continuous saturation function [10]. fuzzy sliding mode control (fsmc) is another method used to avoid the chattering problem [11]. fuzzy logic control is a nonconventional and robust control technique which is suitable for nonlinear systems characterized by parametric fluctuation or uncertainties [12-13]. fsmc has the advantage of not being directly related to the mathematical model of the controlled systems as the smc. fsmc combines fuzzy logic and smc to control the dc-dc converter to achieve better performance. in fsmc, the fuzzy system is used to estimate the upper bound of the uncertain disturbances to reduce the chattering. fuzzy logic controller (flc) has an increased level of efficiency regarding nonlinear converters. in this method, the control action is generated by linguistic rules which do not require an accurate mathematical model of the system, hence the complexity of the nonlinear model is decreased [14-15]. flc overcomes the deficiency resulting from using linearized small signal models and improves the dynamic behavior. ii. dc-dc boost converter mathematical model the output voltage of a boost type dc-dc converter is higher than the input source voltage. this is achieved by periodically opening and closing the switching element in the converter circuit. the dc-dc boost converter is shown in figure 1. the switching period is t. the switch is kept open for time (1-d)t and is kept closed for time dt. the analysis is done by examining voltage across and current through the capacitor for both times, when the switch is open and when the switch is closed. continuous conduction mode (ccm) will be assumed in which the inductor current will have a nonzero value due to load variations. when the switch is closed, the diode in the circuit is reverse biased and becomes open circuit as shown in figure 2(a). then the voltage across the inductor is: = = (1) and the current through the capacitor is: 2(b bec th the equ cur (1) val clo engineerin www.etasr = if the switch b), the inducto comes forwar hen the voltage= e current throu= fig. 2. boost rearranging uations by tak rrent through ), (3) and (2), lues 0 and 1 osed when u=1= 1= 1 u taking x1=i ng, technology r.com h changes to or current cann rd biased prov e across the ind= ugh the inducto= fig. 1. b t converter operat (1)-(4) and king the volta the inductor (4) with u wh 1 representing 1 and switch isu u and x2=v , th y & applied sci off position a not change sud viding path fo ductor become or is: boost converter. (a) (b) tion (a) switch clo d representin age across the as state varia hich is the cont g the switch s open when u hen the state eq ience research (2) as shown in f ddenly and the or inductor cu es: (3) (4) osed (b) switch o ng them as e capacitor an able and comb trol input takin position (swit u=0) then we h (5) (6) quations becom h v durana figure diode urrent. pen. state nd the bining ng the tch is have: me, forc slid reac reg slid inse we whe fun surf vec eve requ slid sho fulf whe traj equ in [ also mai reac the stea tha def vol. 8, no. 3, 20 ay et al.: fuzzy x = 1 ux = 1 u the smc the ce the system ding surface in ching the slid ime of contro ding mode. in ensitive to par have the state= , ere x is the s nction vector. face s(x)=0 th, , = the aim is t ctor x tracks a = en with the quired control i= 1 0 since the aim ding surface an ould ensure the filled [16]: | | ere  is a p ectories hit the iv. sliding mode uations govern [18-19]. the p o presented ag in objective in ch the switchin state equation ady state outp at is, = ∗= ∗ = 0 the sliding f fined as, = ∗ 018, 3054-3059 sliding mode u xx x iii. sliding eory uses a h trajectory to n the state spa ding surface is ol system on n sliding mod rameter variati e equation in st, state vector, u if the function hen, , , , , to find a cont desired traject∗ model uncer input is given 00 m is to force nd slide toward e stability and positive consta e sliding surfa sliding mod e controller des ning the contro performance of gainst input v n sliding mod ng surface and ns for boost co put voltage sh function is for = 0 9 control of dc g mode contr high speed sw move and sta ace. the system s called reach the sliding su de, the system ions and distu tate space form u is the contro n vector f is d 0 0 trol action u s tory x* that is, rtainties and by (12): the system s ds the origin, t the following ant that guar ace in finite tim e controller sign procedure oller were der f the sliding m voltage and lo de control is to d stay on that s onverter given hould be the d rmed by the s 3055 -dc boost con (7) (8) rol witching strateg ay on a path c m trajectory b hing mode an urface is know m response rem urbances. assu m, (9) ol input and f discontinuous (10) such that the , (11) disturbances. (12) states to reach the control str inequality mu (13) rantees the sy me [17]. r design e and the nece rived and pres mode controller oad variations. o force the err surface [20]. u n in (3) and (4 desired voltage (14) (15) state variable (16) verter gy to called before nd the wn as mains uming f is a on a ) state ) the ) h the rategy ust be ) ystem essary ented r was . the ror to using 4), the e v*. ) ) error, ) lin the and sho and val so the vo lin of as con con the aut pro tec con sho vre me and and use e(k me th∆ engineerin www.etasr the referenc near voltage co ∗ = in order to f e control signa= 1 to guarantee d slides over it0 ould be satisfie= ∗ d state variabl lues at the stea olving the ineq e existing cond thus the out ltage for slidin the most im nguistic variabl linguistic vari big and less ntrol is closer nsists of a set e linguistic co tomatic contro ocesses are chniques [21]. nsists of fuz own in figure + d/dt v* ef e c fig. 3 input data ar embership fun d the linguistic d then control ed to convert k) which is easured curren he output of th , which is ng, technology r.com ce value ∗ is ontroller as force the syste al is e the state tra t, the reaching ed. since, les are constan ady state, ∗ = quality given dition of slidin tput voltage s ng mode to exi v. fuzzy mportant featu les rather than iables are sent , and represen r to human th t of linguistic ontrol rules ba ol strategy. f too complex a fuzzy logic zzification, in 3. ru d m fuzzifier d ek cek . fuzzy logic re converted in nctions in the c variables de ller action is o the fuzzy res the differenc nt values is use he fuzzy contr used to obtai y & applied sci obtained from em states to th ajectory to rea g law condition nt and coincide= 0 in (19) by rep ng mode, should be high ist. y logic contr ure of fuzzy l n numerical va tences in a nat nted by fuzzy hinking and n control rules. ased on expert lc is used w for analysis c controller fo nference and ule base decision making defu ata base controlled boost nto linguistic v fuzzifier. us finition, fuzzy obtained. defu sults to contro ce between ed as input to t roller is the ch in the pwm s ience research m the output o (17 he sliding line (18 ach the slidin n, (19 (20 e with the refe placing (17) w (21 her than the s rol logic is that it ariables [14]. v tural language y sets. fuzzy natural langua . the flc con t knowledge in with systems w s by conven or a boost con defuzzificatio uzzifier boost converte converter. values by the u sing the know y rules are eva uzzification st ol action. the the reference the fuzzy cont hange in duty ignal for the s h v durana of the 7) e s=0, 8) ng line 9) 0) erence we get ) source t uses values e, such logic age. it nverts nto an whose ntional nverter on as er v0 use of wledge luated tage is e error e and troller. cycle switch in arch met min an pro qua the obt star inpu num due deg fuz con beh fig dete indu dete betw s is con 1. 2. 3. pre vol. 8, no. 3, 20 ay et al.: fuzzy the converte hitecture is the thods are used nimum and m nd and or op oduct composi alitative action centroids of tain the crisp o rts with the uts. the inpu mber of fuzzy e to its simpl gree of memb zifier interfac ntroller are de havior. input a gures 4 and 5. ermined from ductor. the va ermined by c ween 0 and 1. s the error (e) ntrol rules are o if the error b big meaning t reference poin the reference if the output a small chang if the desire steady, there fi fig surface view sented in fi 018, 3054-3059 sliding mode er. a mamd e one in which d in the infere maximum fun perators respec ition method n to a quantitat all output m output. the de definition of ut resolution y levels. the licity is chose ership for a g ce. the contro etermined from and output me values of the m the maximu alues of the o considering th the fuzzy rul ) and is the obtained based between the re that the outpu nt, then ∆ sh value quickly of the conver ge in duty cycl ed reference should be no c ig. 4. input m g. 5. output m w of the rules igure 6. the 9 control of dcdani type fuz h max–min an ence engine a ctions are use ctively in the c has been us tive action. w membership fu esign of a fuz membership increases w triangular me en for the con given input is ol rules for th m the dc–d embership fun e input membe um current flo utput member he duty ratio les are given i change of err d on the follow eference and m ut of the conve hould be big to . rter is near the le is needed. is achieved a change in the membership functi membership funct s of the fuzz e rules are 3056 -dc boost con zzy logic co nd center of gr and defuzzifica ed to describ control rules. s sed to change weighted avera unctions is use zzy logic contr functions fo with the incre embership fun ntroller input. determined i he designed f dc boost conv nctions are giv ership function owing through rship function interval whi in table i, in w ror (ce). the f wing criteria: measured curre erter is far from o take the outp e desired refer and the outp duty cycle. ions. tions. zy logic contr derived from verter ontrol ravity ation. e the sum– e the age of ed to troller r the easing nction . the in the fuzzy verter ven in ns are h the ns are ch is which fuzzy ent is m the put to rence, put is rol is m the com err des bo the and hig ext suc des fre app non con con exp mo con per cri fu by enh by cur con vo con a f as the per con red engineerin www.etasr mbinations of ror for a func sign procedur ost [23] and b e fuzzy contro d load variatio ghly reliable a ternal disturba fig vi. fuzzy logic ccessfully app sign for uncer ee technique b proach for co nlinearities or ntrol of uncert nventional tec pert knowled odel. sliding m ntrol the d rformance an iteria ensure uzzy system is estimating t hances the sys the differenc rrent which i nnected to the ltages is used ntrol input is d form of the con the controller e scaled outp riod’s duty cyc= this represe ntroller outpu duces steady-s ng, technology r.com f the inputs w ction of outpu re is presente buck-boost con oller was also ons. it is foun and robust to ances [16]. table i. ce e n n n z nm p z g. 6. surface fuzzy slidin is a robust plied to stabil rtain nonlinea based on heu ollecting hum r uncertaintie tain systems th chniques. fuz dge of the sy mode and fuzz dc-dc boost nd to improve the stability s used to reduc the bound of stem robustne ce of measure is obtained by e error betwee as the input t determined by nditional state r output. the put ∆ by cle d[k − 1]. s1 ∆ ents a discrete ut. integrating state error. the y & applied sci which are the e ut. fuzzy log ed for dc-dc nverters [24]. t o presented ag nd that fuzzy c change in circ smf rule tabl n z p nb nm z m z pm z pm pb e: e ce: change of view of the fuzzy ng mode con technique th lity analysis a ar systems [25 uristics metho an knowledge es. it is used hat cannot be zy controller ystem besides zy logic contr converter e robustness. of the fsm ce the chatteri f the uncerta ess [21]. slidin d current and y the output en reference an to the fuzzy co y a set of fuzzy ments. the du duty cycle is h and the so, the fuzzy co e time integr g the fuzzy e block diagra ience research error and chan gic based cont c [22], buck the performan gainst input v controlled syst cuit parameter le p z m b error, error y rules. ntroller hat has been and control s 5-28]. it is a m ods. it provid e and dealing for modeling easily controll design is bas s the mathem rol are combin to achieve lyapunov sta controlled sy ing of the con ain disturbanc ng surface, obt d reference ind of a pi cont nd measured o ontroller. the y rules expres uty cycle is obt obtained by a previous sam ontroller outpu (22 ration of the controller’s o am of the duty h v durana nge in troller [16], nce of oltage tem is rs and n very system model des an g with g and led by sed on matical ned to better ability ystem. nverter ces. it tained ductor troller output fuzzy sed as tained adding mpling ut is: 2) fuzzy output y cycle calc con tria des dyn load per con bot outp sin outp inn is con outp con con refe var tab firs vol. 8, no. 3, 20 ay et al.: fuzzy culation is giv ntrol signal u angular carrier signed overall the aim is to namic perform d changes. th rformance und ntrol and fsm th the disturba tput voltage lo nce the dynami tput voltage, a er current loop controlled by nverter circuit. tput voltage. f ntrolled boost ntrolled dc-d erence voltage riations. a bo ble ii is used fo fig. 9. sim table vs 2 the performa st tested for the 018, 3054-3059 sliding mode ven in figure is obtained by r signal. the fsm controlle fig. 7. duty fig. 8. f vii. sim o implement mance even w hat system sh der different op m control appro ance rejection oop controller ics of the curre a fuzzy sliding p. the output y the duty ra . fsm control figure 9 show t converter. t dc boost conv es, under inp oost converter for the simulati mulink block of th ii. parame (v) l (mh) 20 4 ance of the fs e reference vo 9 control of dce 7. the pulse y comparing t simulink rep er is given in f y cycle calculation fsm controller. mulations a robust cont with input volt ould have an perating condit oach is implem and tracking r is a linear ent is much fa g mode contro voltage of dc atio of the sw ller is used to s the block di the performa erter is monit put voltage va r with the pa ions. he fsm controlled ters of boost c c (f) r 1200 sm controlled oltage change. 3057 -dc boost con e width modu the signal d w presentation o figure 8. n. troller with a tage variations invariant dyn tions. a casca mented to imp performance pi type contr ster than that o oller is used i c-d boost conv witch used in obtain the de iagram of the ance of the ored with diff ariations, and arameters give d boost converter. converter r () 200 d boost conver the output vo verter ulated with a of the good s and namic ade pi prove . the roller. of the in the verter n the esired fsm fsm ferent load en in . rter is oltage engineering, technology & applied science research vol. 8, no. 3, 2018, 3054-3059 3058 www.etasr.com duranay et al.: fuzzy sliding mode control of dc-dc boost converter and current waveforms are shown in figure 10 for a step change in the desired reference voltage from 30v to 40v at time t=0.5s. load variation is applied to the fsm controlled boost converter to test its robustness under load variation. figure 11 shows the voltage and current waveforms when the load resistance is changed from r=200 to r=100 at time t=0.5s. 30 v output voltage is maintained during the load change. test for the input voltage change is also made to see the effects of the input voltage variations on the output voltage. a step change in input voltage is made when the converter is at steady state with a 30v output voltage. the performance of the controlled system is shown in figure 12 and figure 13 when a change in input voltage from 20v to 15v and 20v to 25v occurs at the time t=5s. in figure 12, a decrease in input voltage occurs and in figure 13, an increase in input voltage occurs at t=0.5s. figures 10-13 prove the robustness of the fsm control against changes in the load and input voltage. the recovering feature of the fsm controlled boost converter can be clearly seen. fig. 10. output voltage and output and input current waveforms for step change in reference voltage. fig. 11. output voltage and output and input current waveforms for step load variations. fig. 12. output voltage and output and input current waveforms when input voltage decreased from 20v to 15v. fig. 13. output voltage and output and input current waveforms when input voltage increased from 20v to 25v. viii. conclusions a sliding mode fuzzy controller designed and simulated for a dc-dc boost converter to improve the performance and achieve robustness. the error obtained from the load current and the reference current which is the sliding surface and its derivative are used as inputs to the fuzzy controller which controls the duty ratio of the signal driving the switch in the converter circuit. matlab/simulink programming environment is used for the simulations. the obtained results show that the controlled system is robust against load and input voltage variations. a good dynamic performance is also achieved. references [1] l. h. dixon, average current-mode control of switching power supplies, unitrode power supply design seminar handbook, unitrode corporation, 1990 [2] a. j. forsyth, s. v. mollov, “modeling and control of dc-dc converters”, power engineering journal, vol. 12, no. 5, pp. 229-236, 1998 [3] p. mattavelli, l. rosetto, g. spiazzi, “small-signal analysis of dc-dc converters with sliding mode control”, ieee transactions on power electronics, vol. 12, no. 1, pp. 96-102, 1997 [4] c. k. tse, k. m. adams, “quasi-linear analysis and control of dc-dc converters”, ieee transactions on power electronics, vol. 7, no. 2, pp. 315-323, 1992 [5] m. ahmed, m. kuisma, k. tolsa, p. silventoinen, “standard procedure 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14, no. 5, pp. 676–697, 2006 [28] t. gupta, r. r. boudreaux, r. m. nelms, j. y. hung, “implementation of a fuzzy controller for dc-dc converters using an inexpensive 8-b microcontroller”, ieee transactions on industrial electronics, vol. 44, no. 5, pp. 661-669, 1997 microsoft word 39-3676_s1etasr_v10_n4_pp6116-6125 engineering, technology & applied science research vol. 10, no. 4, 2020, 6116-6125 6116 www.etasr.com alamer & soh: feather: a proposed lightweight protocol for mobile cloud computing security feather: a proposed lightweight protocol for mobile cloud computing security ahmed alamer department of computer science and information technology, school of engineering and mathematical sciences, la trobe university, australia and department of mathematics, tabuk university, saudi arabia a.alamer@latrobe.edu.au ben soh department of computer science and information technology, school of engineering and mathematical sciences, la trobe university, victoria, australia b.soh@latrobe.edu.au abstract-ensuring security for lightweight cryptosystems in mobile cloud computing is challenging. encryption speed and battery consumption must be maintained while securing mobile devices, the server, and the communication channel. this study proposes a lightweight security protocol called feather which implements mickey 2.0 to generate keystream in the cloud server and to perform mobile device decryption and encryption. feather can be used to implement secure parameters and lightweight mechanisms for communication among mobile devices and between them and a cloud server. feather is faster than the existing cloak protocol and consumes less battery power. feather also allows more mobile devices to communicate at the same time during very short time periods, maintain security for more applications with minimum computation ability. feather meets mobile cloud computing requirements of speed, identity, and confidentiality assurances, compatibility with mobile devices, and effective communication between cloud servers and mobile devices using an unsafe communication channel. keywords-mobile cloud computing; lightweight encryption; battery consumption; offloading tasks; mickey 2.0 i. introduction data transfer between two mobile devices and from a mobile device to the cloud should be done securely, through multiple different communication channels, such as wi-fi, 4g and 5g. a secure protocol for data transfer through unsecure communication methods is required. as mobile devices have limited computation power, it can be difficult to address all security cryptosystem tasks. authors in [1] proposed a mobile cloud computing enterprise that consists of mobile devices, a wireless core, wi-fi access points, and regional information centres. in addition to the limited computational capabilities of mobile devices, battery consumption due to heavy computations adds another challenge. authors in [2] showed that mobile computing could save energy, such as battery life and wireless energy, by offloading some tasks to a cloud server, which is used to transfer the data in some applications, however some applications are not energy efficient. to meet security challenges, as well as the demand for a lighter security protocol to save time and address computation power, device hardware limitations, and battery consumption, the research questions to answer are: • how can mickey 2.0 be implemented efficiently to secure communication between mobile devices in mobile cloud computing? • how can the performance of a new security protocol be evaluated against the existing protocols? • how can the claim that the proposed protocol is immune from attack be justified? the aims of this research are: • to implement mickey 2.0 efficiently to secure communication between mobile devices in mobile cloud computing. • to evaluate the performance of the new security protocol against the existing protocols. • to provide a clear justification that the new security protocol is immune from possible attacks. this paper proposes a new protocol, feather, to better meet the security and energy needs of mobile cloud computing and mobile devices than existing protocols. ii. background a. mobile computing mobile cloud computing serves important applications, such as mobile learning, mobile commerce, mobile gaming, ehealth applications, and web searching, [3] and is growing at a fast rate, with 4.78 billion mobile devices globally predicted by the end of 2020 [4]. with many devices connected to each other via large networks, there is a vulnerability to attacks that requires the use of reliable security protocols. encryption systems suitable for these devices on insecure communication channels are needed. a secure communication protocol must meet the following requirements: speed, identity protection, confidentiality, compatibility with mobile devices, and effective communication between cloud servers and mobile devices through a communication channel that is not safe. many cryptosystems meet the demand for private and secure corresponding author: ahmed alamer engineering, technology & applied science research vol. 10, no. 4, 2020, 6116-6125 6117 www.etasr.com alamer & soh: feather: a proposed lightweight protocol for mobile cloud computing security transfer of confidential information. however, some require a large computation capability. the advanced encryption system (aes) is widely used because it is a very strong and secure cryptosystem [5]. however, it is a “heavy” system that requires large computational resources, has high power consumption, and is therefore not suitable for mobile devices with limited computation capacity. some researchers have introduced lightweight versions of aes for small devices, such as ale [6], to reduce the demand on resources, such as central processing units (cpus) and memory, used to generate the keystream. some components in cloud computing such as embedded systems on cloud computing with 32-bit, 16-bit, and 8-bit microcontrollers cannot meet real time demands for conventional methods of cryptography [7]. therefore, aes is a poor solution for many embedded devices in cloud computing that have low computation ability. b. cloud computing for a lighter encryption method in cloud computing, lightweight stream ciphers can be implemented to provide the required security. lightweight stream ciphers include a decryption function and an encryption function to handle messages of arbitrary length. thus, they are better than block ciphers, such as aes, that only handle inputs of a fixed length. due to their functionalities, they are well adapted to low bandwidth or noisy communications and thus are appropriate for cloud computing. speed, memory, number of cpus, and cost efficiency are also important factors [8]. in [9], a mickey 2.0 variant, mickey 2.0.85, was proposed as the preferred choice over other lightweight stream ciphers. it is lighter and has lower energy consumption, which means it is more cost efficient [10]. however, the protocol can be adapted to implement other lightweight ciphers, such as trivium or grain. al-omari [11] proposed a lightweight block cipherbased encryption mechanism and tested a faster algorithm by comparing it to an aes cipher in terms of speed. ali et al. [12] focused on a cloud-based file distribution and management model, and showed that the ability of cloud computing to adapt is important for users, and not only in terms of data storage. the study also addressed the problem of offloading tasks to the server by using multiple servers and demonstrated how this method provides more security when sharing data. hassan et al. [13] discussed cloud computing applications using machine learning approaches as a useful direction for predicting loading using statistical analysis, as well as for ensuring service level agreements. iii. literature review bahrami and singhal [14] studied the adequacy of using aes in mobile cloud computing and explained that, due to cost, cryptosystems such as aes are not suitable for mobile devices, because mobile devices have limited resources, such as limited power energy, low speed processors, and tiny ram capacity. aes is not the appropriate encryption technique, since offload and download is done for every single transferred file. they introduced lightweight methods, such as pseudorandom permutation, based on chaos systems. another solution is using lightweight security methods that provide a balance between energy efficiency and security. a lightweight security technique can be considered an easy operation (i.e. a permutation) instead of using complicated and expensive operations when using secret key or public key encryptions [15-17]. a. the advantage of using stream ciphers in small devices a stream cipher is a symmetric cryptosystem that uses the same key for encryption and decryption. stream ciphers can transform data faster than other ciphers, such as block ciphers, and also faster than ciphers in an asymmetric cryptosystem [18, 19]. stream ciphers are less secure than other, symmetric and block cipher, types of cryptosystems, such as aes which is one of the most secure ciphers. the encryption process in aes involves permutations and a substitution process and requires a number of rounds, which increases the power and storage requirements. on the other hand, lightweight stream ciphers such as mickey 2.0, trivium, and grain [20] need much less power and memory. widely used lightweight stream ciphers for small applications include e0 (bluetooth), rc4 (web), and the a5 family (gms) [21]. stream ciphers have advantages due to their high throughput property and low computational complexity. lightweight stream ciphers [22] are a better choice than block ciphers because they need less memory and less hardware complexity b. using lightweight stream ciphers in cloud computing and mobile cloud computing lightweight stream ciphers have several advantages for cloud computing. they provide fast encryption by generating a secure keystream faster than other popular ciphers, such as aes. they need fewer computation facilities, such as cpus and memory from the cloud, which reduces cost and power consumption significantly. additionally, they include faster encryption, the consumption of less battery power, and lower bandwidth requirements. c. aes and cloak protocols cloak is a lightweight protocol based on the aes cipher that enables two mobile devices to communicate, while leaving the keystream generation on an external server [23]. as cloak can get the keystream from either trusted or untrusted external servers, the main security concern is to protect the keystream. security can be compromised by fetching the keystream from an external server and from communication media. lightweight stream ciphers that can be used in mobiles include trivium [24], grain [25], and mickey 2.0 [26]. mickey 2.0 cipher is more resistant to statistical attacks [2729] and it can produce large throughput. the lightweight protocol developed in this study does not rely on the server to be secure and will not be compromised as in the cloak protocol, which assumes the security of the server relies on the server provider [23]. using mickey 2.0 in this lightweight protocol to provide a secure keystream is significantly faster than using aes. for example, the time needed by the server to generate the keystream is reduced, which in turn reduces the time to transfer the data between the server and the mobile. adithya et al. [30] introduced another enhancement for the cloak security, which is compared to the proposed feather protocol in this study in figure 3, and discussed in section viii. engineering, technology & applied science research vol. 10, no. 4, 2020, 6116-6125 6118 www.etasr.com alamer & soh: feather: a proposed lightweight protocol for mobile cloud computing security iv. the lightweight protocol feather a. overview the study designed a mickey 2.0 cipher based protocol called feather to strengthen confidentiality and protection during messaging between mobile devices, as well as communication between devices and the cloud server (see figure 1). the mickey 2.0 cipher produced a secure keystream in the external server to reduce reliance on mobile devices that have limited computing power and memory. the role of mobile devices is only encryption and decryption, which allows mobile devices to compute and reduce the amount of energy consumed by the device battery. fig. 1. mobile cloud basic communication. a lightweight secure protocol is introduced for communication between devices and the external server over the cloud, as well as design applications on mobile devices for the process of verification and encryption and decryption. the proposed protocol is faster and can move larger files than the cloak cipher [23]. the protocol also maintains a high level of security. the protocol was designed to achieve security through the application of the mickey 2.0 cipher with additional protection systems for identity verification, such as hash functions, time stamps, and out-of-band passwords. a lightweight stream cipher is needed to generate the keystream faster and use fewer resources, so more secure applications can take advantage of advances in mobile cloud computing. if the keystream generated in the server is faster, it will allow more mobiles to get it from the cloud compared to a heavy encryption system like aes. thus, it will be more efficient and will reduce cost. using mickey 2.0 meets most of these needs. b. design principles there are ten design principles for a lightweight protocol: 1) avoid implementing a heavy encryption method as some popular encryption algorithms, such as aes, require considerable resources in terms of cpu time and/or memory usage, the protocol should offload the more computing-intensive steps to a server in the cloud while simplifying the steps carried out on the mobile device. therefore, a lightweight protocol can offload generation and storage of the keystream to a server using the mickey 2.0 algorithm. 2) avoid relying entirely on the server it is important to avoid relying entirely on the server to ensure communication security. then, even if an adversary compromises the server, it cannot easily use the captured keystream data to decrypt messages directly. although the client receives a keystream from the server, the client does not use it directly. instead, the client selects a few random values using primitive polynomials to apply the keystream to the plaintext to compute the encrypted data. 3) send messages between client and server over the internet the protocol must assume an adversary may intercept messages or an impostor may try to insert invalid messages in the client–server communication. one popular approach is to use a key-exchange algorithm, such as diffie–hellman (which is vulnerable to a man-in-the-middle attack), or a more sophisticated station-to-station protocol [31], which avoids this vulnerability. the significant computation of these approaches may not be appropriate for simple mobile or microcontroller devices. the protocol needs to assume the ability to send brief out-of-band messages using a different communication medium. for example, if the protocol is implemented on top of the http protocol, a secret out-of-band message may be sent by email or sms. in this protocol, an outof-band message is sent from the server to the client to convey a one-time-pad, and from one client to another to convey a file token and the secret values (using primitive polynomials) used to step through the keystream. 4) focus on authentication on unique security parameters for authentication, this protocol uses a “bring something, know something” technique. the protocol assumes that each mobile device (or microcontroller device) has a universally unique identifier (uuid). it also allows each user to select a username that is not necessarily unique. these are combined using a hash function to generate a unique identifier (uid) for each user. at the initiation of the protocol, each user registers its uid and then communicates an encrypted copy of its secret password to the server. for subsequent communication, all messages between the client and the server are validated using a digital signature based on hashing the message and the secret password. in this case, the “bring something” refers to the device and its uuid and the “know something” refers to the user’s secret password. since an adversary does not know the secret password, it cannot generate a valid signature, so the client and server can reject messages with invalid signatures. 5) secure the communication between the client and the cloud server client-server communication security relies on a shared keystream. this shared keystream is first generated by the server when the client sends a message to register the user. in its response to the client, the server sends the shared keystream, encrypted with the one-time-pad, to prevent an adversary from capturing the keystream. engineering, technology & applied science research vol. 10, no. 4, 2020, 6116-6125 6119 www.etasr.com alamer & soh: feather: a proposed lightweight protocol for mobile cloud computing security 6) offload the keystream generation to the cloud server the server implementation may use any reasonable technique for keystream generation. in practice, a method is needed that is computationally efficient and still provides a reasonable level of security. to generate a new keystream for each user, the server must first create an initial key (or key+iv pair). 7) ensure client request for the keystream from the cloud authentications when the client submits a request to generate a new keystream, it includes a token and expiry time. there are two possible implementations. the server may simply generate and store a key, and then generate the actual keystream “on the fly” whenever requested. alternatively, the server may generate the keystream right away and store it as a file to be retrieved later when the client submits the corresponding token. the expiry time allows the client to limit the time the keystream is stored on the server. this reduces the availability of the keystream if an adversary tries to compromise the server. 8) ensure there are possible and flexible variations for secure data transfer to enhance the security of the protocol, the server never has access to the unencrypted data. the data are encrypted by the client, using a modified version of the keystream, and this modification is unknown to the server. when transferring encrypted data from one client to another, there are three main options available. • in one variation, since the data are securely encrypted, the file can be uploaded to any simple file server. this may provide an increased level of security since it introduces a separation from the keystream server and the file server. in fact, clients would be free to use a variety of different file servers to transfer encrypted data files, as long as these are communicated between the sender and receiver. • in a simpler implementation, the clients can upload or download the encrypted data to the server and are being identified by a unique token which can be pseudo-randomly generated. any other client can download the encrypted file, asynchronously, once it receives the appropriate token from the first client. some efficiency can be gained if the file upload and download is implemented on the keystream server, since the same protocol mechanism can be used to download a keystream (given a token) or to download encrypted data (given a token). in fact, once a keystream is generated and stored as a file, the keys used to generate the keystream could be deleted, reducing the vulnerability of the protocol. • in the third option, the encrypted data could also be transferred directly and synchronously from one client to another. this approach could make sense when a pair of clients wants to send and receive a number of smaller messages, as in a secure chat session. this can be accomplished first by generating and downloading a keystream and then sending encrypted messages back and forth without requiring an intermediate file server. 9) modify the keystream to further enhance security for efficiency, the client uses a keystream generated by the remote server, but for security, the keystream is modified in a way unknown to the server. in particular, the client randomly selects a few parameters that describe a particular pseudorandom permutation of keystream values. by sharing these secret permutation parameters with the other client through an out-of-band communication, the other client will be able to decrypt the encrypted file. 10) ensure data in the cloud server are tied to expiry time the security of the protocol is enhanced by reducing how long information is retained before being deleted. the keystream and the encrypted files have an associated expiry time, after which the server deletes them. this reduces the information that is exposed if the server is compromised. c. algorithmic demonstration of the feather protocol 1) channels 1. insecure channel e.g internet http 2. out-of-band channel e.g sms 2) algorithm 1: mobile device step 1: register mobile with server i. pick a unique username ii. create uid: hash (username, device id) iv. get the timestamp t v. send register action (via channel 1) with payload [mobile phone number, uid, t] vi. wait for response vii. if ok status received, go to step 2. otherwise, error status received, go to step 1 (ii). step 2: update password with server i. wait for one-time-pad, otp ii. provide a password iii. create hashed password, pass: hash (password, uid) iii. create an encryption d: xor (pass, otp) iv. get the timestamp t v. create the payload, x: hash (uid, d, t) vi. send update action with payload vii. wait for response viii. if ok status received, go to step 3. otherwise, error status received, go to step 2 (ii). step 3: validate password with server, if the first time i. send validate action with payload x ii. go to step 4. step 4: generate keystream from server i. provide a unique 32-byte token ii. send generate action with no payload iii. wait for keystream response, with bytes size n iv. go to step 5. step 5: share keystream with another mobile i. specify expiry time, e ii. get the timestamp t engineering, technology & applied science research vol. 10, no. 4, 2020, 6116-6125 6120 www.etasr.com alamer & soh: feather: a proposed lightweight protocol for mobile cloud computing security iii. create a unique token: hash (uid, e, t) iv. create an encryption f: xor (token, keystream) v. create the payload, x: hash (message, pass, uid, e, t, f, n) vi. send payload x (via channel 2) vii. go to step 6. step 6: upload to server i. provide a 32-byte file-id ii. create a file: hash (uid, file-id, e, t) iii. create an encryption f: xor (file, keystream) iv. create an encryption d: xor (file-contents, token, keystream) v. send upload action with payload [uid, f, d]. step 7: request from server i. if token + keystream, create an encryption f: xor (token, keystream). otherwise: an encryption f: xor (file-id, keystream) ii. get the timestamp t iii. create the payload x: hash (pass, uid, f, t) iv. send request action with payload x. 3) algorithm 2: server step 1: wait for registration request from mobile i. receive registration action with uid: ii. get the timestamp t iii. if no account with the uid exists: a. create a new account b. respond with [ok status, t] c. send one-time-pad (via channel 2) d. go to step 2 otherwise, account with uid exists: a. respond with [error status, error code, t] b. go to step 1. step 2: wait for update request from mobile i. receive update action with encrypted payload, d, and signature ii. recompute the signature iii. decrypt the hashed password, pass iv. validate the message v. if message is valid: a. respond with [ok status] b. go to step 3. otherwise: a. respond with [error status] b. go to step 2 step 3: if process validate request received (only first time) i. go to step 2 (ii). otherwise, go to step 4. step 4: wait for generate request from mobile i. if no payload, generate keystream: a. generate random mickey 2.0 keystream b. respond with the key c. go to step 4. otherwise, payload received: a. create hashed payload: hash (payload, keystream) b. store hashed payload c. go to step 5. step 5: wait for upload request from mobile i. receive upload action with encrypted file payload ii. store the file iii. respond with [ok status]. otherwise something goes wrong, respond with [error status]. step 6: wait for ‘request’ request from mobile: i. receive request action with encrypted token or file-id ii. lookup the token and create the requested data d: xor (token + keystream). otherwise d: xor (file-contents, keystream) iii. get the timestamp t iv. create the payload x: hash (pass, d, t, ok status) v. respond with payload x v. protocol implementation the feather communication protocol enables mobile devices with limited computational resources to share encrypted files with the help of an external server that has greater computing, storage, and bandwidth resources. the protocol uses two communication channels. the first channel is assumed to be insecure, such as the internet using http to transport messages between the mobile devices and the external server. the second channel carrying “out-of-band” messages is assumed to be secure and could be implemented using sms messages to mobile devices, or possibly email. the first channel allows mobile devices to initiate six actions by sending a message to the external server and receiving a response. the second out-of-band channel is used to send and receive three kinds of secret information: • a one-time-pad, which could use a more secure parameter instead of justification. • a file id. • a token id (and some additional parameters). the protocol also uses a cryptographic hash function, such as sha-256, which outputs a 32-byte hash value. for distinct pairs of strings, s and t, h(s)≠h(t) (with very high probability). messages in the protocol are simply concatenated key = value pairs of parameters. each of the 11 possible parameters is identified by a unique character: a = action s = status c = code (error code) u = uid p = phone f = token or file d = data n = number e = expire t = timestamp x = signature the timestamp is unix time in seconds, and can help prevent “replay attacks”. the cryptographic signature is a hash of the entire message string (before the signature is added) and is used to authenticate messages. the six actions and messages are: register, update, validate, generate, engineering, technology & applied science research vol. 10, no. 4, 2020, 6116-6125 6121 www.etasr.com alamer & soh: feather: a proposed lightweight protocol for mobile cloud computing security upload, and request. figure 2 illustrates the secure communication between the basic components, server, mobile devices and communication channel. fig. 2. feather protocol message communications between the mobile devices and the cloud server. a. register the person using the mobile device app provides a username (e.g. “jason”). the device hardware is also assumed to have a unique hardware identifier (e.g. device id). the mobile app combines these strings using a hash function to get a unique id that can be sent to the external server without revealing any private information. uid = h(device id, username); 32-byte value. the mobile device also has a telephone number at which it can receive an out-of-band message via sms. the person registers an account on the external server by sending a message: a = register u = uid p = phone t = timestamp when the external server receives this message, if no account exists for that uid, a new account is created, and this message is sent back: s = ok t = timestamp if an account already exists for that uid the server responds: s = error c = code (indicating type or error) t = timestamp if an account already exists for the given uid, the person needs to pick a new username to create a different uid: one-time-pad via sms following a successful register message, the external server sends a one-time-pad to the mobile device via an out-ofband channel using sms to the phone number provided. the person would need to cut-and-paste this string into the mobile device app to be stored. b. update in the mobile device app, the person also provides a password (e.g. “mysecret”), which provides a type of “bring something, know something” security (bring something = mobile device, know something = username, password). the user’s simple password is combined with the uid to create a “hashed password”, which will be sent to the external server. pass = h(uid, password) the hashed password is encrypted using xor with the secret one-time-pad. the entire message (before the signature) is hashed to create a cryptographic signature for authentication. a = update u = uid d = xor(pass, otp(one-time-pad)) t = time x = h(message) the external server confirms the validity of the message by recomputing the signature, and then decrypts and stores the hashed password in the account. the response is either ok or error. c. validate this message is optional but useful for debugging purposes when implementing this protocol for the first time. the mobile device sends the following message asking the external server to confirm that the hashed password and signature are valid. a = validate u = uid d = xor(pass, otp) t = time x = h(message, pass) the external server decodes the hashed password, recomputes the signature, and responds with either ok or error. d. generate the mobile device provides a unique 32-byte token and asks the external server to generate a new encryption key that will be used to generate a keystream of “number” bytes that will be stored until a given “expire” time. the unique token is created by hashing the uid, expire, and timestamp: token = h(uid, expire, timestamp) the token is xor-encrypted with the shared-keystream. the message sent to the server has these parameters: a = generate u = uid f = xor(token, shared-keystream) n = number (of bytes in the keystream) e = expire t = timestamp x = h(message, pass) engineering, technology & applied science research vol. 10, no. 4, 2020, 6116-6125 6122 www.etasr.com alamer & soh: feather: a proposed lightweight protocol for mobile cloud computing security the external server generates a random mickey 2.0 key (20 bytes of key+iv). there are two implementation-dependent choices: • the server can simply store the 20-byte in association with the token and generate the keystream on-the-fly when requested, or • the server can generate and store the keystream and then discard the 20-byte key. with this option, the token becomes equivalent to a file-id, and the keystream becomes equivalent to the file contents. e. upload the mobile device asks the external server to store a file by providing a 32-byte file-id, the encrypted contents of the file, and an expiration time, after which the file will be deleted. the unique file-id is created by hashing the uid, filename, expire, and timestamp: file = h(uid, filename, expire, timestamp) the file-id is xor-encrypted with the shared-keystream. the mobile device sends a message with these parameters: a = upload u = uid f = xor(file, shared-keystream) d = xor(file-contents, token-keystream) the external server stores the file and responds with ok or else error if something goes wrong. f. request a mobile device can request a token-keystream or encrypted file contents by providing the appropriate 32-byte token or file-id. the message has these parameters: a = request u = uid f = xor(token, shared-keystream) or f = xor(file, shared-keystream) t = timestamp x = h(message, pass) the external server uses the token (or file-id) to look up the requested data and sends it back to the mobile device. s = ok d = xor(token-keystream, shared-keystream) or d = xor(file-contents, shared-keystream) t = timestamp x = h(message, pass) the protocol assumes the first mobile device (the sender) is able to communicate the “token” and “file” to the second mobile device (the receiver) through a secure out-of-band channel, here assumed to be via an sms message. it is important that the communication remains secure even if the external server is compromised by an adversary. therefore, the token-keystream is not used directly to encrypt the file contents, since someone with access to the server could easily decrypt the file. instead, the first mobile device must pick several random numbers r1, r2, r3, ... that are used to walk through the bytes of the token-keystream in a deterministic but difficult to predict order. these sets of random numbers must also be communicated to the second mobile device through a secure out-of-band channel. for example, for a tokenkeystream with length n=2 k -1, which is a prime number, the index of the next byte to be used could be calculated as: index(i) = r1 mod n index(i+1) = (r2 * index(i) + r1) mod n the mobile app was designed in android studio and then the app was transferred as a file to be converted into a mobile local app. the code was written in java on the android studio platform, which works on all major operating systems (i.e. windows, macos and linux). vi. results and analysis the performance of feather protocol is measured on two items: the overall speed and battery consumption. a. speed performance five different mobile devices with android-based operating systems, shown in table i, were used to test the protocol performance. the total time from downloading the keystream, encryption, and writing to storage was measured. tables ii–v show the computations in five different android-based devices. table i. specifications of the used mobile devices d-1 d-2 d-3 d-4 d-5 model name lg v20 huawei nova 3e samsung galaxy s9+ samsung galaxy a6+ lenovo m10 tablet os android 7.0 nougat android 8.1 with emui 8.0 android 9.0 p android 8.0 oreo android 8.0 oreo api level 24 26 28 26 27 cpu quad-core 2.15ghz + 1.6ghz quad-core 2.36ghz octa-core (4×2.7ghz & 4×1.7ghz) octa-core 1.8ghz octa-core 1.8ghz chipset qualcomm snapdragon 820 hisilicon kirin 659 qualcomm snapdragon 845 qualcomm snapdragon 450 qualcomm snapdragon 450 ram 4gb 4gb 6gb 4gb 3gb gpu adreno 530 mali-t830 mp2 adreno 630 adreno 506 adreno 506 battery 3200mah, li-ion 3000mah, li-polymer 3500mah, li-ion 3500mah, li-ion 4,850mah, li-ion polymer table ii shows the total time average for the five different devices. the lg v20 device was the slowest at 18.44169s. however, it was very fast for 8mb file size. the samsung galaxy s9+ device had the fastest total time average (for download, decode and write) at 10.3438s. the total time for all five devices was 71.6456s and the average was 14.3291s. in the experiments, 15 different file sizes from 1kb to 16mb were used to measure the overall performance, as shown in tables iii-v. it is clear that feather can handle large files, and 16mb file size is sufficient to transfer documents and photos. these calculations use the samsung galaxy s9+, and a 16mb file only needs about 19.0s overall time which includes downloading the encrypted file from the external server, decryption time and storing it to the device (write). engineering, technology & applied science research vol. 10, no. 4, 2020, 6116-6125 6123 www.etasr.com alamer & soh: feather: a proposed lightweight protocol for mobile cloud computing security table ii. running 8mb file 60 times and average time (s) d-1 d-2 d-3 d-4 d-5 down load 18.0833 11.594383 10.162450 17.28501 13.083 decode 0.13299 0.090583 0.0872030 0.151201 0.1143 write 0.22536 0.12371666 0.0941666 0.2327666 0.1841 total time 18.44169 11.80868266 10.3438196 17.668978 13.382 table iii. running 3 to 512kb files and calculating time (s) file size 32kb 64kb 128kb 256kb 512kb download 0.324 0.38 0.424 0.743 1.001 decode 0.00102 0.0015886 0.0023127 0.0085227 0.01105 write 0.085 0.066 0.068 0.057 0.052 total time 0.41002 0.4475886 0.4943127 0.8085227 1.0640 table iv. running 1 to 16mb files and calculating time (s) file size 1mb 2mb 4mb 8mb 16mb download 1.684 2.957 5.439 9.625 18.664 decode 0.036893 0.02132 0.0324316 0.0836791 0.1598017 write 0.057 0.085 0.092 0.106 0.19 total time 1.777893 3.06332 5.5634316 9.8146791 19.013801 b. power consumption an android-based application, gsam battery monitor [32] was used to measure the overall battery power consumption of feather using a samsung galaxy s9+ with a 3500mah liion battery. after running gsam and the mobile app for feather, the results showed that performing the operations on 10 files varying in size from 2 to 16mb consumed less than 1% of all apps running in the background, which consumed 1% of battery power, so feather consumes only 0.0001% of battery power. c. . feather vs. cloak the proposed feather protocol is lighter than cloak and is much faster. comparing the performance for file sizes of 1, 2, 4, and 8mb shows that feather is faster. for example, in table vi, the total time for 8mb file size is 110s for cloak and about 9.8s for feather. therefore, feather is even more practical if multiple devices need to communicate at the same time. in addition, feather consumes 80% less battery power than cloak. adithya et al. [30] presented another secure application of cloak protocol in apache server, using a graphical user interface to provide more security, however it takes 1 to 2s for users to enter the digits. feather, cloak and [30] are compared in figure 3. table v. cloak and feather protocols: total speed time for different file sizes file size (mb) total time (s) cloak feather 1 20 1.77789342 2 30 3.06332185 4 60 5.56343165 8 110 9.81467915 vii. attack analysis this section provides an analysis of common attacks and shows how feather is resistant to these types of attacks. a. man in the middle attacks the attacker can interrupt data, inject information, and redirect the traffic. this can be between the two devices or between the devices and the external server, thus it works on the communication channel. this can be prevented by providing strong mutual authentication and end point authentication, as the feather protocol does, and by using hashing for messages, so as all messages are wrapped in hash functions. thus, feather is immune from man in the middle attacks. fig. 3. cloak, feather and adithya et al. [30] speed performance comparison. b. insider attacks on the server side, if an insider can gain access to the information they only gain access to the keystream. however, the message will be included in a hash function, as well as the one-time-pad, and another secure parameter such as the timestamp or a random number only known by the mobile device users. on the mobile side, the mobile will validate the messages received from the server and other mobiles. c. denial of service attacks the feather protocol has steps in the external server to authenticate users before accessing the service by: 1) authentication of users’ credentials, 2) updating the accessing parameters, and 3) validating the users’ messages and hash functions. as verification by the server and devices is mutual, a denial of service attack is not applicable. d. chosen iv-attacks the keystream is generated by using mickey 2.0 and (key, iv) as the initial input. in feather, the iv is not used more than once with the same key, thus feather eliminates this threat by preventing the reuse of the iv, as well as by including the iv in the hash function, so an attacker choosing the iv will not result in the key being revealed. e. two-time pad attacks assuming there are two messages m1 and m2, if the same key (k) is used (called two-time pad), and there are two ciphertexts (c1, c2) then: engineering, technology & applied science research vol. 10, no. 4, 2020, 6116-6125 6124 www.etasr.com alamer & soh: feather: a proposed lightweight protocol for mobile cloud computing security m1⊕ k that results in c1 and m2⊕ k that results in c2. therefore, it is easy for the attacker to perform the xor operation for ciphertexts in order to reveal the plaintext as: c1 ⊕ c2 that is, using statistical frequency analysis leads to m1 ⊕ m2. in the feather protocol, each file is encrypted by a different keystream as well as a different one-time-pad for every session and time timestamp. thus, this attack is not applicable. f. impersonation attacks this kind of attack occurs when the attacker gains access to a mobile device and requests a response from the server. the server will validate and authenticate the request. as mobile users will be using a hash function, including a one-time-pad (as discussed in the protocol implementation), the server also will hash the keystream with a one-time-pad among other user credentials, meaning this attack is not feasible with feather. g. brute force attacks as the complexity of a brute force attack in key=80bit in general is 2 80 , the feather protocol used a hash function. for example, using d-3 (a user may choose other stronger hash functions, and that will not affect the speed performance as the slower part is the downloading time), the computation power relies on the implementation, and adding other secure parameters such as using otp, that is similar to the one-timepad cipher, which substantially raises the computation power needed to break the protocol. viii. discussion in feather, downloading is the most time-consuming task compared to the cloak protocol. if it is required for more than two mobile devices to communicate at the same time, the external server generating the keystream in the feather protocol is much faster than cloak. this will reduce the overall time as the decoding time is just performing xor on messages with the keystream, which is fast. the mobile battery lifetime is also longer. the proposed lightweight security protocol feather provides confidentiality, authorisation, and security for users in mobile cloud computing technology and iot technology. it also helps reducing power consumption, which will improve the overall performance of mobile applications. the proposed protocol was analyzed against possible known attacks, which showed that it is secure for implementation. the mickey 2.0 cipher was used as a pseudo-random number generator. however, the feather protocol can be adapted to use other iv-based lightweight synchronous stream ciphers. the proposed mickey 2.0.85 [9] which is 23% faster in generating pseudo-random numbers, can also be used, however, even using mickey 2.0 in feather is fast enough. mickey 2.0.85 is useful for other smaller applications. the feather protocol offers a secure contribution to mobile cloud computation. the comparison in figure 3 shows that feather is much faster than the recent cloak and [30] protocols, and it also provides more security. the limitations of this study include the testing on five devices, although the cloak protocol [23] was also tested on five devices. future work could involve further testing of the performance of feather on a wider range of devices, and compare it to a wider range of existing protocols. another important direction for future research is adapting other lightweight ciphers such as trivium, grain, and other lightweight block ciphers to generate the keystream in the server, and then implementing feather and calculating the overall execution time. ix. conclusion ensuring security in mobile cloud computing is critical but challenging. the proposed lightweight security protocol, feather, will reduce cost and time used in the external server. therefore, it can increase the number of devices communicating at the same time and enhance mobile cloud computing applications. the feather protocol has better performance than existing protocols and can help meet the requirements for secure mobile cloud computing with internet connectivity. acknowledgment the authors would like to thank dr david jones for his advices on the mobile cloud computing settings. references [1] p. bahl, r. y. han, l. e. li, and m. satyanarayanan, “advancing the state of mobile cloud computing,” in proceedings of the third acm workshop on mobile cloud computing and services, low wood bay, lake district, uk, jun. 2012, pp. 21–28, doi: 10.1145/2307849.2307856. 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[32] “gsam battery monitor – apps on google play.” https://play.google.com/store/apps/details?id=com.gsamlabs.bbm&hl=en _au (accessed jul. 23, 2020). microsoft word final-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 413-415 413 www.etasr.com caccetta et al: an improved clarke and wright algorithm to solve the capacitated vehicle… an improved clarke and wright algorithm to solve the capacitated vehicle routing problem louis caccetta dpt of mathematics and statistics curtin university of technology australia l.caccetta@curtin.edu.au mamoon alameen dpt of engineering the australian college of kuwait kuwait m.radiy@ack.edu.kw mohammed abdul-niby dpt of engineering the australian college of kuwait kuwait m.nibi@ack.edu.kw abstract— this paper proposes an effective hybrid approach that combines domain reduction with the clarke and wright algorithm to solve the capacitated vehicle routing problem. the hybrid approach is applied to solve 10 benchmark capacitated vehicle routing problem instances. the dimension of the instances was between 21 to 200 customers. the results show that domain reduction can improve the classical clarke and wright algorithm by about 18%. the hybrid approach improves the large instances significantly in comparison with the smaller size instances. this paper will not show the time taken to solve each instance, as the clarke and wright algorithm and the hybrid approach took almost the same cpu time. keywordsclarke and wright; capacitated vehicle routing problem; domain reduction i. introduction the vehicle routing problem (vrp) is an important problem in the distribution network and has a significant role in cost reduction and service improvement. the problem is one of visiting a set of customers using a fleet of vehicles, respecting constraints on the vehicles, customers, drivers etc [1]. the goal is to produce a minimum cost routing plan specified for each vehicle. the problem of vehicle scheduling was first formulated in 1959 [2] and may be stated as a set of customers, each with a known location and a known requirement for some commodity, that is to be supplied from a single depot by delivery vehicles, subject to the following conditions and constraints: • the demands of all customers must be met. • each customer is served by only one vehicle. • the capacity of the vehicles may not be violated (for each route the total demands must not exceed the capacity). the objective of a solution may be stated, in general terms, as that of minimizing the total cost of delivery, namely the costs associated with the fleet size and the cost of completing the delivery routes [3]. the problem frequently arises in many diverse physical distribution situations. for example bus routing, preventive maintenance inspection tours, salesmen routing and the delivery of any commodity such as mail, food or newspapers [4]. the vehicle routing problem is an integer programming problem that falls into the category of np-hard problems. as the problems become larger, there will be no guarantee that optimal tours will be found within reasonable computing time [5]. ii. problem formulation the capacitated vehicle routing problem (cvrp) is to satisfy the demand of a set of customers using a fleet of vehicles with minimum cost. the problem is described as follows [4]: let: • c= {1, 2,…, n}: the set of customer location. • 0: depot location. • g=(�,e): the graph representing the vehicle routing network with �={0,1,…,n} and e={(i,j):i,j∈�, i<j}. • jq : demand of customer j. • q: common vehicle capacity. • m: number of delivery vehicles. • ij c : distance or associated cost between locations i and j. • l: maximum distance a vehicle can travel. • j p : a lower bound on the cost of travelling from the depot to customer j. • ( )sℓ : lower bound on the number of vehicles required to visit all locations of s in an optimal solution. note that s ⊆ c and ( ) 1s ≥ℓ . • s : the complement of s in c • ij x : 1,2, or 0 etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 413-415 414 www.etasr.com caccetta et al: an improved clarke and wright algorithm to solve the capacitated vehicle… the problem is to: • minimize z= ij ij i � i j c x ∈ < ∑∑ i∈�, i<j (1) subject to: • 0 2 i i c x m ∈ =∑ , i∈c (2) • 2ij ji j i i j x x < < + =∑ ∑ , i∈c (3) • , , ,3 -2( ), ij i j s s c s nx s s ∈ ⊆ ≤ ≤≤∑ ℓ (4) • ij x =1, 2, or 0 (5) iii. the clarke and wright algorithm the clarke and wright algorithm [6] is the most popular heuristic algorithm for the vrp. the algorithm calculates all the savings sij between customers i and j. assuming that ci0 is the cost of travelling from the depot to customer i and cij is the cost of travelling from customer i to j. the following is a description of the clarke and wright algorithm to solve the cvrp: • step 1: compute the savings 0 0 ij i j ij s c c c= + for i,j =1,…, n and i ≠ j. rank the savings sij and list them in descending order. • step 2: create the "savings list." process the savings list beginning with the topmost entry in the list (the largest sij). for the savings under consideration (sij), include link (i, j) in a route if no route constraints will be violated through the inclusion of (i, j). the following three cases need to be considered. • case 1: if neither i nor j have already been assigned to a route, then a new route is initiated including both i and j. • case 2: if exactly one of the two points (i or j) has already been included in an existing route and that point is not interior to that route (a point is interior to a route if it is not adjacent to the depot in the order of traversal of points), then the link (i, j) is added to that same route. if the point is interior and not violating the capacity then add (i, j) to the same route. if it’s violating the capacity make a new route with the point (customer) i. • case 3: if both i and j have already been included in two different existing routes and neither point is interior to its route, then the two routes are merged by connecting i and j. if they are interior then the merge cannot be done. • step 3: if the savings list sij has not been exhausted, return to step 2, processing the next entry in the list; otherwise, stop. iv. domain reduction observing the work of [7-11], one can see that some significant work has been done to improve the accuracy of the classical algorithms. however, one of the weaknesses in classical algorithms lays in accuracy, especially when dealing with large instances. this paper shows that domain reduction can solve the problem of the accuracy for large instances. domain reduction is a method that deletes some unneeded values from the domain using a logical based approach [12]. in this paper the domain reduction will be applied by adding a new constraint that deletes some large numbers from the distance matrix and thus forbids the use of certain links. the new restriction is: ij c r≤ i,j=1,2,…,n where cij represent the cost between i and j, and r is a threshold that depends on the maximum number in the distance matrix. the domain reduction procedure starts by dividing the distance matrix into four parts based on the distance. in the other hand the demand matrix will be divided into four parts starting from the lowest to the greatest. customers with lowest demands and high (or very high) costs will be highlighted as critical customers. in the other hand, customers with high (or very high) demands and with lowest (or average) costs will be referred to as leading customers. the domain reduction will delete all the high and very high costs from the cost matrix. for the critical customers we delete the highest 50% of the edges. taking the obtained solution in consideration, the same procedure should be repeated by applying the domain reduction on the remaining values. the domain reduction procedure will delete some unneeded values from the distance matrix. this will improve the solution especially when combined with the clarke and wright algorithm. table i illustrates how the domain reduction procedure divides the cost and demand matrices. table i. domain reduction logic very high cost path very high demands high cost path high demands average cost path average demands lowest cost path lowest demands v. computations this section combines the domain reduction with the clarke and wright algorithm. the algorithm is employed to solve 10 benchmark vrp instances [13-16]. a look up table for the instances used can be seen in table ii. the details of each instance can also be found in [17]. table iii shows the obtained results. table ii. look-up table for the 10 benchamrk vrp instances instance reference 1-3 13 4 14 5-6 15 7-10 16 etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 413-415 415 www.etasr.com caccetta et al: an improved clarke and wright algorithm to solve the capacitated vehicle… table iii. the c&w saving algorithm and domain reduction table iii shows that domain reduction improved the classical clarke and wright rapidly. it’s clear that as the instances become larger, the solution improves better and get closer to simulating annealing results. surveying the results for the last five instances one can see that the improved clarke and wright provides better results on large instances. the 48 customers problem improved by about 1% but other large instances show better improvements. the 101 customers problem improved by 16%. the 121 customers problem improved by 38%. the problem 151 customers problem improved by 49.8%. for the 200 customers problem, the improvement was 46%. vi. conclusion in general, the saving approach used by the clarke and wright algorithm can provide good solutions for small size instances. however, for large instances calculating the savings may consider large values which affect the solution. hence, combining domain reduction with the clarke and wright algorithm is far better approach than using the clarke and wright algorithm alone to solve large instances. in addition, classical heuristics are easy to understand and implement compared to meta-heuristics. however, meta-heuristics can provide better results in most of the cases. this paper showed that classical algorithms can also provide accurate results. references [1] c. groër, parallel and serial algorithms for vehicle routing problems, phd thesis, university of maryland, proquest, 2008 [2] g. b. dantzig, j. h. ramser, “the truck dispatching problem”, management science, vol. 6, no. 1, pp. 80-91, 1959 [3] n. christofides, s. eilon, “an algorithm for the vehicle dispatching problem”, operational research, vol. 20, no. 3, pp. 309-318, 1969 [4] n. r. achuthan, l. caccetta, s. p. hill, “a new subtour elimination constraint for the vehicle routing problem”, european journal of operational research, vol. 91, no. 3, pp. 573-586, 1996 [5] n. r. achuthan, l. caccetta, “integer linear programming formulation for a vehicle routing problem”, european journal of operational research, vol. 52, no. 1, pp. 86-89, 1991 [6] g. clarke, j. wright, “scheduling of vehicles from a central depot to a number of delivery points”, operations research, vol. 12, no. 4, pp. 568-581, 1964 [7] a. a. juan, j. faulin, r. ruiz, b. barrios, s. caballé, “the sr-gcws hybrid algorithm for solving the capacitated vehicle routing problem”, applied soft computing, vol. 10, no. 1, pp. 215-224, 2010 [8] a. a. juan, j. faulin, j. jorba, d. riera, d. masip, b. barrios, “on the use of monte carlo simulation, cache and splitting techniques to improve the clarke and wright savings heuristics”, journal of the operational research society, vol. 62, no. 6, pp. 1085-1097, 2011 [9] t. pichpibul, r. kawtummachai, “new enhancement for clarke-wright savings algorithm to optimize the capacitated vehicle routing problem”, european journal of scientific research, vol. 78, no. 1, pp. 119-134, 2012 [10] k. kanthavel, p. prasad, “optimization of capacitated vehicle routing problem by nested particle swarm optimization”, american journal of applied sciences, vol. 8, no. 2, pp. 107-112, 2011 [11] l. xiaodong, “a summarization of algorithms for vehicle routing problem with time windows”, european journal of scientific research, vol. 73, no. 3, pp. 296-309, 2012 [12] a. caprara, m. locatelli, “global optimization problems and domain reduction strategies”, mathematical programming, vol. 125, no. 1, pp. 123-137, 2010 [13] m. groetschel, c. l. monma, m. stoer, “computational results with a cutting plane algorithm for designing communication networks with low connectivity constraints”, operations research, vol. 40, no. 2, pp. 309330, 1992 [14] s. eilon, c. d. t. watson-gandy, n. christofides, distribution management: mathematical modelling and practical analysis, griffin, london, 1971 [15] m. held, r. m. karp, “the traveling salesman problem and minimum spanning trees”, operations research, vol. 18, no. 6, pp. 1138-1162, 1970 [16] n. christofides, a. mingozzi, p. toth, “the vehicle routing problem”, in combinatorial optimization. wiley, chichester, pp 315-338,1979 [17] branch cut and price resource web, vehicle routing data sets usa, http://www.coin-or.org/symphony/branchandcut/vrp/data customer number classical c&w modified c&w domain reduced improvement percentage simulating annealing 21 3754 3658 62% 2.7% 3314 24 1659 1404 70% 15.3% 1473 26 1891 1888 50% 0.15 1779 31 1336 1278 5% 4.3 1269 42 2391 1747 55% 26.9 1528 48 19342 19181 65% 0.83 17888 101 803 672 25% 16% 409.918 121 934 574 30% 38% 336.485 151 958 480 45% 49.8 368.996 200 1291 697 45% 46% 652.158 microsoft word vekteris-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 408-412 408 www.etasr.com vekteris et al.: experimental investigation of influence of acoustic wave on vapour precipitation process experimental investigation of influence of acoustic wave on vapour precipitation process vladas vekteris department of machine engineering vilnius gediminas technical university vilnius, lithuania vekteris@vgtu.lt ina tetsman department of machine engineering vilnius gediminas technical university vilnius, lithuania ina.tetsman@vgtu.lt vadim mokšin department of machine engineering vilnius gediminas technical university vilnius, lithuania vadim@vgtu.lt abstract—the measurement results of acoustic field parameters above electroplating bath, in presence of water vapour, are analyzed in this work. suction was created by means of side exhausters. it is obtained that the sound field generator generated a sound level of 130–140 db at frequency interval between 1 and 10 khz. it is shown that aerosol coagulation and precipitation processes are intensified under the mentioned conditions. the concentration of vapour and other aerosols in removal air decreases as a result, therefore air cleaning equipment costs can be reduced and cleaning efficiency increased. keywords: aerosol; water vapour; exhauster; acoustic coagulation; sound frequency; sound level i. introduction electroplating processes are widely used in a variety of industries; the number of such technologies constantly increases. these processes are performed in electroplating bathes by means of electrolysis. small hydrogen, oxygen and other gas bubbles are formed at the electrodes during such processes as a result of electrochemical and chemical reactions. these bubbles then get released from the electroplating solution. electroplating solutions contain hazardous substances concentration of which at the workplace can‘t exceed permissible according hygiene norm. to reduce the concentration of these substances electroplating lines are equipped with powerful local ventilation systems. according to their position in respect to the pollution source, exhausters can be divided to the following groups: open, side and close. their purpose is to collect and remove pollutants from the vaporized surface of electroplating bath and to control the concentration of pollutants at the workplace [1, 2]. the additional air flow (from blowers) which directs polluted air towards the exhauster can be used to improve air cleaning efficiency. such exhausters are called side activated. the amount of evaporated substance depends on the chemical composition of the solution, the temperature of the solution, the vaporized surface area, time and characteristics of the motion of the environmental air [3, 4]. if some amount of pollutants was successfully returned back into the steaming liquid, thus reducing the concentration of the pollutants, it would be possible to reduce the energy consumptions of the air cleaning equipment. therefore it is proposed to generate an acoustic field above the bath solution surface, thus causing acoustic coagulation of aerosol particles. this would allow a reduction of the concentration of pollutants (aerosols) in the polluted air flow; i. e. air will be cleaned before being removed. the hartmann generator [5, 6] can be used to generate high-pressure acoustic waves. gravitational coagulation follows acoustic coagulation. the scheme of this phenomenon is presented in figure 1. a particle which radius r is bigger than the radii of the neighbor particles comes into the gravitational field, its falling velocity increases and the particle collides with some of the smaller particles (which radii are r) as the result [3]. the coagulation rate or air cleaning efficiency depends on the following parameters of the acoustic field [7, 8]: intensity, frequency and exposure time. it is established [9] that 4–5 s are enough for aerosol precipitation. increasing time to 30 s and more doesn‘t lead to improved coagulation efficiency. in accordance with parker and brandt [10] experiments concentration depends exponentially on time and a parameter called coagulation coefficient. fig. 1. aerosol particles coagulation process etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 408-412 409 www.etasr.com vekteris et al.: experimental investigation of influence of acoustic wave on vapour precipitation process the first experimental data dealing with the impact of acoustic fields on coagulation process [7, 10] was obtained at low sound frequencies. for example, stokes in experiments with smoke soot obtained optimal frequency interval between 3 and 4 khz [7]. for zinc oxide smoke (particle size about 5 µm) and sulphuric acid mist (particle size was varied from 5 to 100 µm) optimal frequency was about 1 khz. in case of smaller particles which size is less than 10 µm sound pressure level should not exceed 137 db and reynolds number should be less than 0.4. specific velocity can be taken as 0.32 m/s. in the present work, the indirect parameter –air humidity at different temperatures-was proposed to evaluate the coagulation efficiency. ii. analysis the dependence of particle and flow amplitudes ratio on frequency and particle size is presented in figure 2. this dependence is described by the following formula: 1 9 4 1 2 2 +         = m p f p fr x x µ πρ (1) where xp is the amplitude of the particle, xf is the amplitude of the medium (gas mix), r is the radius of the particle, ρp is the density of the particle, f is the frequency of the acoustic field, µm is the dynamic viscosity of the flow. fig. 2. amplitude ratio as a function of the frequency of the acoustic field and the diameter of particles in accordance with figure 2, oscillations of particles which diameter is bigger than 10 µm are hardly observed when frequency varied from 1 to 100 khz. oscillations of smaller particles are observed in whole range of frequencies. optimum value of the ratio is about 0.8. it can be stated that not only aerosol properties (for example initial concentration in the air) influence the coagulation process, but also the parameters of the acoustic field. when particle size increases, frequency must be reduced to excite oscillations of the particles in the flow. fig. 3. experimental stand: 1 – bath, 2 – liquid, 3 – heater, 4 – thermometer, 5 – side exhauster, 6 – fan, 7 – variable-frequency drive, 8 – blower and acoustic wave generator, 9 – valve, 10 – pressure gauge, 11 – hydrophone, 12 – data storage, 13, 15 – computer, 14 – temperature and humidity meter etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 408-412 410 www.etasr.com vekteris et al.: experimental investigation of influence of acoustic wave on vapour precipitation process iii. experimental stand a special experimental stand was designed and built. this stand is shown in figure 3. liquid 2 was heated in electroplating bath 1 by means of heater 3. temperature was monitored by thermometer 4. vaporized liquid was removed by means of side exhauster 5 which was attached to the edge of the bath and connected to fan 6. air flow rate was controlled by variable-frequency drive 7. special construction blower – acoustic wave generator 8 was mounted above the liquid surface as shown in figure 3. acoustic wave was generated due to the compressed air flow pulsations. air flow was directed at the liquid surface near the edge of the bath as it can be seen in figure 3. compressed air was supplied through valve 9, and its pressure was controlled by pressure gauge 10. acoustic field parameters were measured by hydrophone 11, measured data was stored in data storage 12 and then processed by means of computer 13. air humidity was measured by temperature and humidity meter fht 70 datalog 14, measurement results were processed by means of computer 15. aerosol concentration in the air was reduced due to precipitation above the formation zone. a specially designed blower – acoustic wave generator was used to intensify the mentioned process. its scheme is presented in figure 4. it consists of hollow collector 1 which has nozzles 2 connected to collector‘s holes. spherical resonators 3 were placed against nozzles 2 to direct the flow to the outlet. the air flow leaving the nozzle 2 collides with the air from the resonator, thus sound (standing acoustic wave) was generated. fig. 4. scheme of the acoustic wave generator: 1 – collector, 2 – nozzle, 3 – resonator iv. experimental technique and results the primarily parameters of the acoustic field generated by the acoustic wave generator were measured. when air compressed to 4–5 bar pressure was supplied to the generator, the sound pressure amplitude reached 154 pa. sound pressure level at frequency interval between 1 and 21 khz didn’t drop less than 120 db, i.e. minimal value required for dispersed droplets coagulation [11]. in order to ensure the optimal parameters of acoustic field the ratio of the nozzle diameter d and resonator diameter d was varied. results of measurements are presented in figure 5. it can be seen from figure 5, that if diameters ratio equal to 1:2, 130–140 db sound pressure level is achieved at 1–4 khz frequency interval. if the ratio is equal to 1:5, sound pressure level above 130 db is achieved at 6–9 frequency interval (figure 5 b). the shift toward the limit of audibility is evident. 4k 8k 12k 16k 20k 24k [hz] 100 110 120 130 140 [db/1u pa] autospectrum(signal 1) mark 1 (real) \ fft analyzer 4k 8k 12k 16k 20k 24k [hz] 100 110 120 130 140 [db/1u pa] autospectrum(signal 1) mark 3 (real) \ fft analyzer a) b) fig. 5. sound pressure level spectrum of acoustic wave generator when nozzle and resonator diameters ratio was equal to: a) – 1:2, b) – 1:5 etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 408-412 411 www.etasr.com vekteris et al.: experimental investigation of influence of acoustic wave on vapour precipitation process next, the air humidity above the vaporized liquid was measured. it was tried to establish its dependence on the temperature of the liquid and the distance from liquid surface. in order to compare results four cases were analyzed: • when vapour from the liquid surface raised freely and removal equipment was turned off. • when vapour was removed from the liquid surface by means of the side exhauster. • when vapour was removed from the liquid surface by means of the activated side exhauster (with additional air flow which directs polluted air towards the exhauster, acoustic wave generator was used as conventional blower). • when vapour was removed from the liquid surface by means of the side exhauster with the use of the acoustic wave generator. temperature of the liquid was varied from 50 to 85°c. results of humidity measurements are presented in fig. 6. these results were obtained when distance from liquid surface was varied from 0 (bath edge) to 300 mm. a) b) c) d) fig. 6. humidity of air measured at different distances from liquid surface as function of the liquid temperature and air removal method: a) – 0 mm distance (edge of the bath; b) – 100 mm distance above the bath; c) – 200 mm distance above the bath; d) – 300 mm distance above the bath etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 408-412 412 www.etasr.com vekteris et al.: experimental investigation of influence of acoustic wave on vapour precipitation process it is evident from figure 6 that the precipitation process is intensified in the presence of the acoustic field. when the temperature increases humidity increases also. as it can be seen from figure 6, air humidity doesn‘t depend on the distance from the liquid surface when temperature reaches 80 °c value. at such temperatures, the impact of the acoustic field on the coagulation process becomes most apparent. in other words, acoustic coagulation equipment becomes more effective with the increase of the initial concentration of the aerosol particles. v. conclusions 1. it is obtained that lower acoustic field frequencies between 1 and 4 khz are more effective for small particles with diameter less than 10 µm. 2. acoustic field positively impacts the coagulation process of dispersed in air drops and mist (aerosol) particles. 3. it is obtained that acoustic field frequency and sound pressure level are the main parameters of the acoustic field that influence the aerosol coagulation process. 4. obtained experimental data shows that acoustic coagulation efficiency increases with the increase of the initial concentration of the aerosol particles in air. references [1] v. vekteris, i. tetsman, v. striška, “experimental research of suction velocity of side exhausters”, proceedings of the 15th international conference “mechanika-2010”, kaunas, lithuania, pp. 477-481, 2010 [2] i. tetsman, v. striška, “research on the efficiency of side exhausters (šoninių siurbtuvų efektyvumo tyrimas)” science–future of lithuania, vol. 2, no. 4, pp. 42-45, 2010 (in lithuanian) [3] k. r. spurny, aerosol chemical processes in the environment, crc press, 2000 [4] p. baltrenas, dust removal from air at building material factories, stroyizdat, 1990 (in russian). [5] w. strauss, air pollution control, wiley interscience, 1978 [6] a. g. vetoshkin, environment protection technology, publishing house of penza technology institute, 2004 (in russian) [7] o. s. balabekov, air cleaning in chemical industry: processes and equipment, chemistry, 1991 (in russian) [8] l. bergman, ultrasound and its application in science and technique, publishing house of foreign literature, 1957 (in russian) [9] v. a. gudemchuk, v.f. podoshevnikov, b.d. tartakovskii, “role of the turbulence in the phenomenon of acoustic coagulation of aerosols”, akusticheskii zhurnal, vol. 5, no. 2, pp. 246-258, 1959 (in russian) [10] l. d. rozenberg, physical basics of ultrasound technology, science, 1969 (in russian) [11] v. n. khmeliov, o. v. popova, multifunctional ultrasound devices and their use in individual production, farming and household, 1997 (in russian) engineering, technology & applied science research vol. 8, no. 4, 2018, 3141-3148 3141 www.etasr.com samadi et al.: achieving optimal degrees of freedom for an interference network with general … achieving optimal degrees of freedom for an interference network with general message demand zainalabedin samadi school of electrical engineering iran university of science & technology tehran, iran z.samadi@gmail.com vahid tabataba vakili school of electrical engineering iran university of science & technology tehran, iran vakily@iust.ac.ir farzan haddadi school of electrical engineering iran university of science & technology tehran, iran haddadi@iust.ac.ir abstract—the concept of degrees of freedom (dof) has been adopted to resolve the difficulty of studying the multi-user wireless network capacity regions. interference alignment (ia) is an important technique developed recently for quantifying the dof of such networks. in the present study, a single-hop interference network with k transmitters and n receivers is taken into account. each transmitter emits an independent message and each receiver requests an arbitrary subset of the messages. using the linear ia techniques, the optimal dof assignment has been analyzed. assuming generic channel coefficients, it has been shown that the perfect ia cannot be achieved for a broad class of interference networks. analytical evaluation of dof feasibility for general interference channels (ifcs) is complicated and not available yet. iterative algorithm designed to minimize the leakage interference at each receiver is extended to work with general ifcs. this algorithm provides numerical insights into the feasibility of ia, which is not yet available in theory. keywords-interference channel; interference alignment; degrees of freedom; channel state information i. introduction despite the intensive research on multi‐user wireless communication networks over the past three decades, the subject is still not well understood from information‐theoretic perspective. capacity limits of many multi‐user networks are still unknown (even for a small number of users). for example, the capacity region of a two‐user single‐antenna interference channel (ifc) is still unknown, though the region can be bounded up to a constant value [1]. researchers have derived various approximations of the capacity region of the ifcs. for example, the maximum total degrees of freedom (dof) correspond to the first order approximation of the sum‐rate capacity in high snr regime. dof is not a new concept, it is widely known as the multiplexing gain in point‐to‐point communication scenarios. it was termed as spatial dof in [2], referring to the maximum multiplexing gain. in the present study, the maximum multiplexing gain is presumed to be the total dof. the study of dof of interference networks was pioneered in [3]. in [2], the total dof of two‐user multiple‐ input multiple‐output ifc is provided. interference alignment (ia) is a powerful scheme developed recently for quantifying the dof region of multi‐user networks. ia refers to the construction of signals in such a way that their mutual interference aligns at the receivers, facilitating simple interference cancellation techniques. the remaining dimensions are designated for communicating the desired signal, keeping it free from interference. ia was first introduced in [4], and clarified in [5]. the analysis of dof is shown to be very useful in revealing the capacity potential of the ifcs. the channel capacity of ifc is limited with large number of users. authors in [3, 6], showed that the total number of η=κμ/2 dof can be achieved asymptotically via infinite time (frequency) expansion under block fading channel for a k-user m antenna ifc. this result indicates that the capacity of each user is unbounded regardless of the user number k. the achieving method is based on ia. the principal assumption enabling this surprising result is that the channel extensions are exponentially long in k and are generic (e.g., drawn from a continuous probability distribution). however, there is an important distinction between perfect ia schemes and partial ia schemes. perfect ia schemes are able to exactly achieve the outer bound of the dof with a finite symbol extension of the channel. in contrast, partial ia schemes pay a penalty in the form of the overflow room required to “almost” align interference. study of the design and feasibility of linear beamforming for ia without symbol extensions has received significant attention [7-10]. in general, linear ia can be described by a set of bilinear equations which correspond to the zero‐forcing conditions at each receiver. one can count the number of “independent unknowns” and the number of scalar equations in this quadratic system defining ia to verify if the total number of variables exceeds the total number of constraints in the system of equations. if a system has more variables than constraints, it is called a proper system. otherwise, it is called an improper system [7]. while it is known that almost all improper systems are infeasible [8-9], the feasibility of the proper systems is still an area of active research. in [8-10], a set of sufficient conditions for feasibility are established. in this paper, we consider the case of interference networks with general message demands. in this setup, there are k transmitters and n receivers, each equipped with m antennas. each transmitter em arb gen [6] sub net opt to alg ma lea per eff int obt con ext cas sce mo wh ach cha pro me v, k tra the on req le req and con tra gre and a r tim rel wh sig fad th ass dis rec engineerin www.etasr mits a unique bitrary subset neralization o ], to the case w bset of the twork is evalu timally alloca achieve the to as an alter gorithmic appr any of those akage at each rfectly be a fectiveness is terference leak tain the optim ncerned with tended the ite se of general enarios. the rest of t odel is introdu hy linear ia hieve the tota annel extensio oposed to ach essage demand and concludin consider a k transmitters ansmitters and e system mod e and only o quest an arbitr et sj, j ϵ[n] be quested by rec d is the s ntributing to is ansmitters are eater than zero d want to achi reliable commu me slot , t  lationship: here 1≤j≤n is gnal of transm ding factors o he channel fa sumed to be stribution. z[j] ceiver j. the ng, technology r.com message and t of the me of the multiple where each rec transmitted m uated in [11]. ate dofs to th otal dof of suc rnative to the roaches have methods aim receiver so t attained. the s that when kage will be mal solutions the feasibilit erative ia algo l ifc to eva the paper is o uced in sectio scheme, over al number of ons. in section hieve optimal ds. simulation ng remarks are ii. sy k×n user sing and n recei receivers hav del is shown in one independe rary set of mes the set of indi ceiver j, where set of indices the interfere s the set of all defined as the o. all transmi ieve the maxim unication. cha  is characteriz the user inde mitter k, h[jk](t) f the channel ading factors e independen ](t) is the ad noise terms y & applied sci sama each receiver ssages. this e unicasts scen ceiver is intere messages. do in this work, e transmitters ch a network. e closed form been propose m to minimiz that ‐at the be e suggested n perfect ia zero and suc . in this pap ty of the per orithm develo luate ia feas organized as fo on ii. in secti r a single an dof with a n iv, an iterat l dof of an n results are p e presented in ystem model gle‐hop interfe ivers. we as ve m antennas n figure 1. e ent message. ssages from m ces of those tr e [n] is defined s of those tra ence at rece l active transm e transmitters itters share a c mum possible annel output at zed by the foll ex, x[k](t) is th t), 1≤k≤k is t from transmi at different ntly drawn fr dditive white are all assu ience research adi et al.: achiev r is interested construction nario consider ested in an arb of region for we evaluate h of this archit m designs, s ed in the liter ze the interfe est case‐the ia insight for a is possible ch algorithms per, we are m rfect ia. we oped in [12], sibility of dif follows. the s ion iii, it is a ntenna ifc, c limited numb tive ia algorit ifc with g provided in s section vi. erence network ssume that a s. an illustrati each transmitte each receive multiple transm ransmitted mes d as [n]={1,… ansmitted mes eiver j. obvi mitters, where with assigned common band sum rate along t receiver j and lowing input‐o (1) he m×1 transm the m×m mat itter k to recei time instant from a conti gaussian no umed to be d h v ving optimal d in an is a red in bitrary r this how to ecture everal rature. erence a can their e, the s may mostly have to the fferent system argued cannot ber of thm is eneral ection k with ll the ion of er has er can mitters. ssages …..,n} ssages ously, active d dof dwidth g with d over output mitted trix of iver j. ts are inuous ise at drawn ind dist assu p: whe ind the belo exp diag tran be d whe sign bea ind is a rece info glob as a hav reg cor vol. 8, no. 4, 20 degrees of free dependently f tribution with umed that all ere e is the dex is omitted time expansio ow, we use panded signals h[jk]=diag(h[ gonal matrix. nsmitted mess described as fo ere y[j]=[y[j](1 nal vector ov amforming ma dependent sign a d[k]×1 vector eived noise ormation (csi bal csi at tran authors in [1 an interference ve derived do ion of such a rresponding do the total dof 018, 3141-3148 edom for an int from a gau h zero mean transmitters a expectation ta for convenien on in number uppercase bo s. [jk](1), h[jk](2), . denoting th age k as v[k], ollows, 1)t, y[j](2)t,… ver the extend atrix of transm nal symbols tra r of the transm vector at rec i) is assumed nsmitters. fig. 1. 11], have refer e network wit of region of a system with of region is de f number is de 8 terference netw ussian indepe and unit va are subject to aken over tim nce. let den of symbols. f old fonts to , , … h[jk](τ)), he beamformi the extended ., y[j](τ)t]τ is ded channel, v mitter k, and d[ ansmitted from mitted symbols ceiver j. perf to be availab user ifc mode rred to the afo th general mes this setup. d h power cons efined as efined as: 3142 work with gener endent identi ariance. it is a power cons (1) me. hereafter, note the durati from this poin denote the is a μτ×μτ b ing matrix o channel mode (2) the μτ×1 rec v[k] is the μτ [k] is the numb m transmitter k and is a μ fect channel ble at receivers el. orementioned ssage demand enote the cap straint p as (3) . ral … ically also straint time on of nt and time‐ block f the el can eived τ×d[k] ber of k. x[k] μτ×1 state s and setup ds and pacity , engineering, technology & applied science research vol. 8, no. 4, 2018, 3141-3148 3143 www.etasr.com samadi et al.: achieving optimal degrees of freedom for an interference network with general … iii. linear vector ia limitation dof region for the setup described in section ii has been derived by [11], as follows, (5) where is the set of message indices requested by receiver . optimal dof assignment in an ifc with general message demands is obtained by solving the following linear programming problem; (6) where z is defined as a g×1 vector consisted of scalar elements . implies that all elements of z should be smaller than m. the solution to the feasibility problem is not known in general. in other words, given a set of randomly generated channel matrices and a degree‐of‐freedom allocation , it is not known if one can almost surely find the transmit and receive filters that will satisfy the feasibility conditions. if we look at the problem of finding the precoding and zero‐forcing matrices when the channel coefficients are arbitrary and given, the problem is computationally intractable. in particular, [8] established that for an arbitrary k‐user mimo ifc, checking the achievability of a certain dof tuple is np‐hard when each user and transmitter has more than 2 antennas. the notion of regular ifc will be introduced below and it will be shown that perfect ia is not feasible for single antenna regular ifc. the distributed ia developed in this paper will be useful in numerically evaluating the feasibility problem for general ifc. regular networks are defined as ifcs for which the only optimal dof assignment is equal dof assignment for all active transmitters. theorem 1 implies that an ifc in which all prime receivers request the same number of transmitted messages and each transmitter sends message to an equal number of prime receivers is a regular network.  theorem 1. the only dof point that achieves total number of dof of an ifc where all receivers request the same number of transmitted messages and each transmitter sends message to equal number of receivers is , ,..., 1 1 1 m m m β β β         d (4) proof. maximum total number of dof for this network is obtained to be 1 km β  , where β is the number of requested messages for each prime receiver [11]. obviously, total dof is achieved by [ ] 1 k md β   . it is now intended to show that this is the only dof point that achieves total number of dof. it is worth noting that as prime receivers are addressed those receivers whose requested message sets are not a subset of any other requested message set. if theorem 1 is not true, there is at least one which is strictly greater than . we would also have the following lemma: in the specified channel structure, we should have (8) where g is the number of prime receivers. assume that there is a where , which implies that . thus, using (5), we will have (4) the first equality, a , is derived from the fact that , is derived from dof region inequalities in (5) and c is implied from the assumption that . equation (9) contradicts the assumption that this dof assignment achieves total dof number. therefore, the lemma is valid. based on (5), in order to characterize dof region, we should consider g inequalities of the form (5) since each message is requested by receivers, summing all g inequalities, we have (11) where is defined as . using the fact that there is at least one strictly greater than , along with lemma 1, it is obtained that (12) substituting (12) in (11), we will have the following inequality: wh ach do net  mo bro is n sat net ele con do net me can a s the eac ach ext con me eve thi tot at usi me engineerin www.etasr hich contradic hieves total d of point that twork. theorem 2. generic, the regular inter finite extensi proof. it sho ore than 1 do oadcast or mu not unique in t tisfies twork. for ex ements, receiv nsidered as a of gain, and twork is 1. th ethods like tim n achieve the special case o e channel stru ch receiver is s fig. 2. the proof fo hieve the oute tensions of nsider a hypot essages achiev ery transmitte is is the only tal number of d let message transmitter k ing zero‐forci essages ng, technology r.com cts the assum of number. t achieves the assuming th total number rference netwo ion of the chan ould be noted of, otherwise ultiple access c this case. in fa ac xample, if a s ver and its c a multiple acc therefore the here is no nee me division b total number o of 6×3 user if ucture along w shown in figu 6 3 user ifc or the general er bound of 6/ this channel. thetical achiev ves 1 dof if er and zero‐for dof point in dof of this ne be bea k. receiver j ing. at receiv , the y & applied sci sama mption that thi herefore, e total numbe hat the chann of the dof o ork cannot be nnel. that the regul , the network channel. optim act, every k×1 chieves optim et, say si, wo orresponding cess channel e total numb ed for ia in th based multiple of dof of this fc with gener with requested ure 2. with general mes case is simila /3 dof for thi over this vable scheme w possible, usin rcing at every n achievable r etwork, accord mformed alon intends to d ver j, to dec e vectors cor ience research adi et al.: achiev (6) is dof assign is the er of dof o nel coefficient of a single an e achieved us ar ifc should k is equivalen mal dof assign 1 vector mal dof of ould have k o transmitters c without losin er of dof o his case and s e access techn structure. con ralized messag set of messa sage demands. ar. it is intend is setup. cons extended ch where each of ng beamformi y receiver. not egion that ach ding to theorem ng 3×1 vector ecode ode 2 indepe rresponding t h v ving optimal d nment e only of this ts are ntenna sing a d have nt to a nment that f this or k-1 can be g any of this simple niques nsider ge set, ges at ded to sider 3 hannel, f the 6 ing at te that hieves m 1. endent to the des dire the dim rece abo line rece wh cor resp the unk que not are sho bili exp var mo infe vec con ind whe nυ as whe at r ante netw requ the acc whe usin eve vol. 8, no. 4, 20 degrees of free sired message ections. since 4 interferin mension. ia req thus, the to eiver j can de ove criteria, th early indepen eiver. this req here d(s) is rresponding to pectively, and receivers. fo observe that known precod estion is raised t. authors in [ selected rand ould have almo inear equations pected to be riables is less oreover, [8] p easible when ctor. it can be nstitutes an i dependent varia ere l is is less than th ere receiver j. the ennas at each work. in the f quirements is s channel. consider a 3n cording to the ere each of th ng beamform ery receiver. t 018, 3141-3148 edom for an int es should oc signals come ng vectors m quirements ca otal dimension ecode all its de he desired sig dent of the quirement imp defined as th are the se o the desired d 3 is the total or example, a . t (14) is a se ding and zer d as to whethe [7] argued tha domly and ind ost surely a per s is called pro feasible almo than or equ proved that im each transmit observed that mproper set ables in this sy the numb is the num he number of is th erefore, using h node, we c following, it i still infeasible n symbol exten orem 1, the on he 6 transmitt ming at every the 3n×n vec 8 terference netw ccupy 2 lin e from a space must occupy an be written as n of the inte esired messag gnal vectors a interference d plies that, he dimension ets of the recei d and undesir subspace dim at user 1, et of bilinear ro‐forcing filt er a system ad at when the ch dependently, t rfect alignmen per, in other w ost surely wh al to the num mproper syste tter uses only the set of ia of equations ystem can be o ber of cha mber desired st equations, νe, he number of 3 extensions o cannot achiev is proved that e using every nsion of the ch nly achievable ters achieves transmitter an ctors 3144 work with gener early indepen e of 3 dimens the remainin s follows. (7) erference is 1 ges. along wit are required t dimension at (8) of a subspac ived signal ve red signal vec mension availab is obtaine r equations in ters. a feasi dmits perfect i hannel coeffic the proper sys nt solution. a words, perfect hen the numb mber of equat em of equatio one beamfor requirements, s. the numbe obtained as (16) annel extens treams at recei , which is obt (17) interfering str of the channel ve 6 dof for t this system o finite extensio hannel over w e scheme is the n dof if pos nd zero‐forcin sh ral … ndent sions, ng 1 1 and th the to be each ce s, ectors ctors, ble at ed as n the ibility ia or cients stems set of ia is er of tions. ons is rming (14), er of ) sions. iver j. ained reams l or 3 r this of ia on of which, e case sible, ng at hould engineering, technology & applied science research vol. 8, no. 4, 2018, 3141-3148 3145 www.etasr.com samadi et al.: achieving optimal degrees of freedom for an interference network with general … satisfy ia conditions along with the linear independence condition. ia requirements at 3 receivers can be summarized as follows, (9) since diagonal channel matrices are almost surely full rank, after some algebraic manipulations, (18) becomes (10) where matrices are obtained as follows, (11) and cm is defined as (12) assuming is of rank n, [13] has shown that (20) implies n eigenvectors of lie in . since all channel matrices are diagonal, the set of eigenvectors of channel matrices, their inverse and product are column vectors of the identity matrix. define and note that ei exists in , therefore, the set of equations in (19) implies that (13) thus, at receiver 1, the desired signal is not linearly independent of the interference signal, , and hence, receiver 1 cannot fully decode w[1] and w[4] solely by zero‐forcing the interference signal. therefore, if the channel coefficients are completely random and generic, we cannot obtain 6/3 dof for the 6×3 user single antenna ifc through linear ia schemes. regular ifcs are mostly encountered in networks with few users. we have evaluated optimal dof assignment for random configurations of a 10×10 ifc. roughly, 25% of the evaluated networks were regular ifcs. it is implied that there are many cases where perfect ia for a single antenna ifc is not feasible. iv. distributed ia algorithm for general ifc in general, the optimal dof solution for each specific configuration can be obtained by solving the linear programming problem (6), using methods like simplex algorithm. the closed form solution for each arbitrary requested message set structure is not straightforward. moreover, analytical evaluation of dof feasibility is not straightforward. interference can be aligned in networks with single antenna nodes through the channel extension in frequency or time as long as the channel is varying across frequency or time. however, this approach requires long symbol extensions. for example, the achievable scheme presented in [11] uses at least 1536 extensions of the single 6×3 antenna introduced in figure 2 to achieve d={1/3, 1/12, 1/24, 1/192, 1/1536} number of dofs for the transmitters. total dof number of 0.47 is achieved for this scheme which is still far less than the optimal dof of 2 for this channel. due to these difficulties, it is preferred if ia can be accomplished without or with limited symbol extensions. actually, ia schemes are most likely to be used in mimo networks. feasibility of perfect ia is not yet available in theory for most mimo networks. iterative algorithms provide numerical insights into the feasibility of ia in these cases. in this section, distributed ia algorithm presented in [12] is extended to be utilized for the case of general ifc with multiple antenna nodes and with no symbol extensions. based on the system model presented in section ii, ia feasibility conditions are derived as follows, (23) while the rank condition is typically assumed to be automatically satisfied, this is not true in the case of symbol extensions because channel matrices cannot be assumed to be generic. when no symbol extensions is applied and the mimo channels are generic, the rank condition is satisfied with probability one. in other words, with generic channels there is no need to explicitly introduce the rank constraint into the optimization problem. equation (23) requires that at each receiver, all interferences must be suppressed, leaving as many interference‐free dimensions as the dof allocated to that receiver. the intention is to use alternating optimization procedure similar to [12], to find the transmit precoding and receive zero‐ forcing matrices. we start with arbitrary transmit and receive filters and iteratively update these filters to approach ia. alternating optimization procedure is realized by switching the direction of communication. the total interference leakage at receiver j due to all undesired transmitters is given by: (24) engineering, technology & applied science research vol. 8, no. 4, 2018, 3141-3148 3146 www.etasr.com samadi et al.: achieving optimal degrees of freedom for an interference network with general … where (14) let us define as the set of receivers that request message from transmitter k, i.e., . in the reciprocal network, the total interference leakage at receiver k due to all undesired transmitters is given by (26): (15) where (16) is the interference covariance matrix at receiver k. the iterative algorithm alternates between the original and reciprocal networks. in the original network, each receiver solves the following optimization problem. (17) in other words, receiver j chooses its interference suppression filter to minimize the leakage interference due to all undesired transmitters. the dimensional received signal subspace that contains the least interference is the space spanned by the eigenvectors corresponding to the smallest eigenvalues of the interference covariance matrix . thus, the columns of are given by: (29) where is the eigenvector corresponding to the smallest eigenvalue of . for the second step, consider the reciprocal network obtained by reversing the roles of the transmitters and the receivers. the transmit precoding matrices in the reciprocal network, , are the receive interference suppression matrices from the original network. each receiver in the reciprocal network solves the following optimization problem. (30) similarly, the columns of are given by: (31) the receive zero‐forcing filters in the reciprocal network are then used as the transmit precoding matrices in the original network, and the algorithm iterates again. the iterations continue in this manner until the algorithm converges. the proof of convergence for this algorithm is similar to the one presented in [12]. it can be observed that each step in the algorithm reduces the value of the total leakage interference. the total leakage interference for general ifc is defines as follows, (32) where is defined in (24). the algorithm presented in this section seeks perfect ia. in particular it seeks to create an interference free subspace of the required number of dimensions that is designated as the desired signal subspace. however, note that perfect ia may not always be feasible. in such scenarios, the network structure should be reconfigured. simulation results indicate that residual interference due to the imperfect ia significantly degrades the achievable sum rate performance in high signal to noise ratios. we can either reduce the number of transmitted streams, increase the number of receive antennas, use relays in the network to accommodate ia, or use channel extension to make ia feasible. in the following, we will consider the case of reduced number of transmitted streams (rns) and increased number of receive antennas (ina) along with the case of optimal dof assignment (oda). v. simulation ρesults in this section we run simulations to illustrate practical feasibility of the optimal dof assignment. consider the 6×3 user regular ifc shown in figure 2. it is proved that perfect ia is not feasible for this network, assuming single antenna nodes. we consider a mimo interference channel where each transmitter/receiver is equipped with 3 antennas. optimal dof assignments for this structure is obtained as d[k]=1, k=[6]. the system of bilinear equations for ia requirements of this network constitutes an improper system because the number of the independent variables is 18 which is less than the number of equations which is 24. therefore, we expect the perfect ia to be still infeasible. this fact is confirmed with simulation results. we allocate power 1/d to each column of the precoding matrices, and set the noise power level to σ2=10-p/10, where p=[0:10:60]db. final results are obtained by averaging over 200 channel realizations, where each channel element is i.i.d. zero mean unit variance circularly symmetric complex gaussian. we run 104 iterations of the extended minimum leakage algorithm for each simulation. we plot the sum rate of each system. the sum rate is computed as , where is defined as the covariance matrix of desired signal for receiver j. it is observed in figure 3 that the sum rate of oda case is limited with residual interference at high signal to noise ratios. sum rate performance is also plotted for two cases of rns (d[1]=0, d[k]=1, k=2) and ina (4 receive antennas). we compare the performance of the iterative ia algorithms for this channel with orthogonal schemes and isotropic transmission. th equ th tra reg fig reg hig the eac ent hig (d[ rec lea it i tha the sch fea use req s3= ass d[3] rec equ lik rec wit sol int ful sho fea sig des in engineerin www.etasr he sum rate for ual time shari he isotropic tra ansmitter send gardless of the g. 3. performa gular ifc. it is observed gh signal to n e upperbound ch receiver n tail channel e gh signal to n [1]=…=d[6]=1) ceiver nodes akage interfere is realized tha at, the system ese cases nυ=n heme. iterative algo asibility of ia er. we evalua quested messa ={3,4,5}. solv signment for 3]=d[4]=d[5]=0 ceiver node f uations is prop kely to be feas ceived dofs is th an idea of w lution or not. h terference is p ll‐rank, the slo ould be close asible. the slo gnal to noise sired signal sp this scenario ng, technology r.com r the orthogon ing for the use ansmission ca ds d[k]=1, k e channel infor ance of the itera d that orthogo noise ratios in on the dof fo node is 6, ap extensions. th noise ratios sug ) can be achie without chan ence for each o at ia is feasibl of the bilinea ne=16 for rn orithm can al a strategy for ate the iterativ age sets defi ving the linear this network .2. we have for the simul per in this cas sible for this s s 3 1 /j j n n   whether the alg hence, if perfe perfectly suppr ope of the sum to 10/3. figu ope of the sum e ratios. eva pace confirms and there is y & applied sci sama nal scheme is c ers, and with p ase refers to th k=[6] stream rmation. ative ia algorith onal schemes o this specific or this network pproaching the he slope of th ggests that 6 eved by using nnel extension of three receiv le in case of r ar equations is s scheme and lso be used to a given num ve algorithm f ned as s1={1 r programmin k is obtained e assumed 5 lations. the se, nυ=40, ne= scenario. the 10 / 3 . this m gorithms conv ect alignment ressed and the m rate at high s ure 4 suggests m rate is appro aluating leaka the fact that p no need for ience research adi et al.: achiev calculated assu power 6p per he case where m of equal p hm for the 6 outperform od structure. alth k with 3 anten e upperbound he ina sum r degrees of fre g 4 antennas n. for feasibl vers should be rns and ina. s proper for bo nυ=ne=24 fo o check theor mber of stream for a 5×3 ifc 1,5}, s2={1,2} ng (6), optima d as d[1]=d[2] antennas at system of bi =36, hence, o average numb measure provid verge to a perfe is achieved, i. direct channe signal to noise s that perfect oximately 3 a age interferen perfect ia is fe the rns and h v ving optimal d uming node. e each power 3 user da at hough nnas at d may rate at eedom at the le ia, e zero. . note oth of or ina retical ms per c with } and l dof ]=0.4, each ilinear da is ber of des us fect ia e., the els are ratios ia is at high nce in easible d ina stra od opt fig. ifc as a equ enc that regu of netw min thi resu gen real this and ben [1] [2] [3] [4] [5] [6] vol. 8, no. 4, 20 degrees of free ategies in this da in this ca timal dof assi 4. performan . the concept an interference ual number o countered in ne t perfect ia ular ifcs with the optimal d works is not nimum leakag is algorithm is ults suggest th neral ifc, iter lization of ia s network. nu d simultaneous nefits of using r. h. etkin, d capacity to with vol. 54, no. 12 s. jafar, m. interference cha 53, no. 7, pp. 2 a. host-madse networks”, iee adelaide, austr m. a. maddah over mimo x performance an 54, no. 8, pp. 3 s. a. jafar, s. channel”, ieee 151-170, 2008 v. r. cadamb freedom of the information th 018, 3141-3148 edom for an int network. in f ase, which em ignment. nce of the iterati vi. co of regular int e network in w of optimal d etworks with f cannot be ac h generic chan dof assignme easily mathe ge ia is exten s based on the hat, despite th rative ia algo and evaluation umerical comp s isotropic tran distributed ia refer d. n. c. tse, h. hin one bit”, iee 2, pp. 5534-5562, fakhereddin, “d annel,”, ieee tr 2637-2642, 2007 en, a. nosratinia ee international ralia, pp. 2065-20 -ali, a. s. mota x channels: interf nalysis”, ieee tr 457-3470, 2008 shamai, “degree e transactions on e, s. a. jafar, “ e k -user interfe eory,vol. 54, no. 8 terference netw fact, rns has mphasizes the ive ia algorithm onclusion terference netw which all activ dof. regular few number of chieved for t nnel coefficie ent for the ge ematically tra nded to work e network recip he non‐symm orithm is still n of the perfec parisons to or nsmission sche a algorithms ar rences wang, “gaussia ee transactions o 2008 degrees of free ransactions on inf a, “the multiple symposium on 069, september 4ahari, a. k. khan ference alignmen ransactions on in es of freedom re information the “interference alig erence channel”, . 8, pp. 3425-344 3147 work with gener less sum rate benefits of u for the 5 3 g work is introd ve transmitters ifcs are m f users. it is pr the single an nts. the feasi eneral interfer actable. distrib with general procity. simul metric nature o useful in pra ct ia feasibilit rthogonal sch emes show tha re significant. an interference ch on information t edom for the m formation theory exing gain of w n information t -9, 2005 ndani, “communi nt, decompositio nformation theory egion for the mim ory, vol. 54, no. gnment and degr ieee transactio 1, 2007 ral … e than using general duced have mostly roved tenna ibility rence buted ifc. lation of the ctical ty for hemes at the hannel theory, mimo y, vol. wireless theory, ication on, and y, vol. mo x . 1, pp. rees of ons on engineering, technology & applied science research vol. 8, no. 4, 2018, 3141-3148 3148 www.etasr.com samadi et al.: achieving optimal degrees of freedom for an interference network with general … [7] c. m. yetis, t. gou, s. jafar, a. h. kayran, “on feasibility of interference alignment in mimo interference networks”, ieee transactions on signal processing, vol. 58, no. 9, pp. 4771-4782, 2010 [8] m. razaviyayn, g. lyubeznik, l. zhi-quan, “on the degrees of freedom achievable through interference alignment in a mimo interference channel”, ieee transactions on signal processing, vol. 60, no. 2, pp. 812-821, 2011 [9] t. liu, c. yang, “on the feasibility of linear interference alignment for mimo interference broadcast channels with constant coefficients”, ieee transactions on signal processing, vol. 60, no. 9, pp. 2178-2191, 2013 [10] l. ruan, v. n. lau, m. z. win, “the feasibility conditions for interference alignment in mimo networks”, ieee transactions on signal processing, vol. 61, no. 8, pp. 2066-2077, 2013 [11] l. ke, a. ramamoorthy, z. wang, h. yin, “degrees of freedom region for an interference network with general message demands”, ieee transactions on information theory, vol. 58, no. 6, pp. 3787-3797, 2012 [12] k. gomadam, v. cadambe, s. jafar, “a distributed numerical approach to interference alignment and applications to wireless interference networks”, ieee transactions on information theory, vol. 57, no. 6, pp. 3309-3322, 2011 [13] z. samadi, v. t. vakili, f. haddadi, “channel aided interference alignment”, iet signal processing, vol. 11, no. 7, pp. 854-860, 2017 authors profile zainalabedin samadi was born in hashtroud, iran, on april 26, 1985. he received the b.s. degree from the ferdowsi university of mashhad, mashhad, iran, in 2008, the m.s. degree from iran university of science and technology, tehran, iran, in 2011. he is currently working toward the ph.d. in the department of electrical engineering, iran university of science and technology. his research interests include multiuser information theory, joint source-channel coding, spread-spectrum systems and emerging interference alignment techniques. vahid tabataba vakili received the b.s. degree from sharif university of technology, tehran, iran, in 1970, the m.s. degree from the university of manchester, manchester, u.k., in 1973, and ph.d. from the university of bradford, bradford, u.k., in 1977, all in electrical engineering. in 1985, he joined the department of electrical engineering, iran university of science and technology, tehran. in 1997, he was promoted to associate professor. he has served as the head of the communications engineering department and as the head of postgraduate studies. his research interests are in the areas of mobile cellular systems, interference cancellation for cdma systems, and space–time processing and coding. farzan haddadi was born in 1979. he received b.sc., m.sc., and ph.d. degrees in communication systems from sharif university of technology, tehran, iran, in 2001, 2003, and 2010, respectively. in 2011, he joined iran university of science and technology faculty, tehran, iran. his research interests include array signal processing, statistical signal processing, nondestructive testing, sonar systems, and detection theory. microsoft word 26-2611_s engineering, technology & applied science research vol. 9, no. 2, 2019, 4007-4011 4007 www.etasr.com abdullah & saada: free convection mhd couette flow with application of periodic temperature and … free convection mhd couette flow with application of periodic temperature and constant heat flux on walls mustafa rashied abdullah faculty of engineering al-ahliyya amman university amman, jordan mrashied@ammanu.edu.jo nidhal saada faculty of engineering al-ahliyya amman university amman, jordan n.saada@ammanu.edu.jo abstract—numerical analysis and analytical solution were performed to study the free convection in transient couette flow of an electrically conducting fluid confined between two vertical parallel plates. constant heat flux on the wall with uniform vertical motion in its own plane and periodic temperature on the stationary wall were applied. the dimensionless governing momentum and energy equations are solved numerically using a fully implicit finite difference method. an analytical solution using eigenfunction expansion method is carried out for temperature profile in case of constant plate temperature. analytical and numerical results converge at a satisfactory degree. the effect of different physical parameters on the transient velocity and temperature, such as grashof’s number (gr), magnetic parameter (m), prandtl number (pr) and temperature frequency are also studied. it is found that the velocity increases with an increase in gr and time, while it decreases with an increase in pr and m. keywords-magnetohydrodynamics (mhd); couette flow; free convection i. introduction magnetohydrodynamic (mhd) flow of a viscous incompressible electrically conducting fluid has many industrial and engineering applications. one of the main mhd fluid dynamics problems is the couette flow, in which one of the two parallel plates is moving relatively to the other. some important applications of the couette flow are mhd power generators and pumps, aerodynamic heating, electrostatic precipitation, polymer technology and petroleum industry. the effect of the magnetic field on the natural convection flow between two vertical plates under various conditions has been studied extensively. for instance, the laplace transform technique was used to obtain expressions for velocity and temperature fields and their related quantities for the unsteady free convective flow of an incompressible viscous fluid between two vertical parallel plates for impulsive start of one of the plates [1]. the combined effect of natural convection and uniform transverse magnetic field on the couette flow of an electronically conducting fluid between two parallel plates for impulsive motion of one of the plates was studied in [2], in which expressions for velocity and temperature fields were presented for two different cases, under the assumption of negligible induced magnetic field. the effects of magnetic interaction number, slip factor and relative temperature difference on velocity and temperature profiles, and entropy generation in mhd flow of a fluid with variable properties over a rotating disk was studied in [3], where velocities, temperature profiles, and average entropy generation rate were obtained for different parameter values [3]. the effect of the magnetic field and of the internal heat generation on the free convection flow in a rectangular cavity filled with a porous medium was investigated in [4]. results indicated that there is an inverse relationship between the nusselt number and the hartmann number. the reverse occurs with an increase in magnetic field inclination angle. the impact of a varying magnetic field on forced convective heat transfer was investigated in [5]. results indicated an increase in the kelvin forces associated with a thermal boundary layer thickness decrease (higher reynolds number). the couette flow of an electrically conducting fluid between two parallel plates in the presence of a transverse magnetic field in case of constant heat flux has been studied extensively. a closed form solution for the transient free convection flow of a viscous fluid between two infinite vertical parallel plates in the presence of radiation was presented in [6]. the flow is set up due to the free convective currents occurring as a result of the application of constant heat flux at one wall and constant temperature on the other wall. an exact solution to the problem of natural convection in unsteady couette flow between two long vertical parallel plates in the presence of constant heat flux and thermal radiation was presented in [7]. it was found that the configuration of the flow field is significantly effected significantly by the interaction between radiation, buoyancy forces and the applied shear force induced by a uniform vertical motion of the hot wall. authors in [8] studied the unsteady oscillatory couette flow between vertical parallel plates with constant radiative heat flux for an optically thick fluid. the perturbation method was used to find an analytical solution for the velocity and temperature functions and it was found that the increasing of the thermal radiation parameter increases the fluid flow of thick fluids such as blood. corresponding author: mustafa rashied abdullah engineering, technology & applied science research vol. 9, no. 2, 2019, 4007-4011 4008 www.etasr.com abdullah & saada: free convection mhd couette flow with application of periodic temperature and … other studies were carried out in order to investigate the effect of varying plate temperature on the behavior of couette flow [9-13]. the effect of free convection on heat transfer and flow through a highly porous medium bounded by two vertical parallel porous plates assuming periodic temperature at the moving plate was investigated in [9]. authors in [10] investigated the problem of mhd free convection and oscillatory flow of an optically thin fluid bounded by two horizontal porous parallel walls under the influence of an external imposed transverse magnetic field in a porous medium with periodic wall temperature. an exact solution to the problem of unsteady free convection flow and heat transfer in a viscous incompressible fluid between two long vertical parallel plates was presented in [11]. the temperature at one of the plates increases linearly with time while that at the other plate remains constant at the initial fluid temperature. authors in [12] studied the effect of free convection on the heat transfer and the flow through a highly porous medium bounded by two vertical parallel porous plates in presence of a transverse magnetic field. the approximate solutions for velocity and temperature were obtained by assuming periodic temperature at the moving plate. authors in [13] studied the magnetic field effect on an unsteady free convection flow of a viscous incompressible electrically conducting fluid with dissipative heat between two long vertical parallel plates where the temperature of one of the plates oscillates about a constant nonzero mean temperature. radiation effects on free convection mhd couette flow with variable wall temperature in the presence of heat generation have been studied in [14]. authors in [15] analyzed the effects of thermal radiation and constant mass diffusion on the transient laminar free convective flow in a vertical channel with variable temperature. authors in [16] studied the mhd effect on unsteady free convection between a pair of infinite vertical couette plates. the temperature of the plates was assumed to vary with time. the objective of this study is to investigate the transient free convection mhd couette flow with the presence of both periodic temperature and constant heat flux on walls. a numerical analysis of the dimensionless equations is performed and verified by an analytical solution in case of constant plate temperature. ii. mathematical formulation consider a two-dimensional mhd flow of an incompressible electrically conducting viscous fluid between two long vertical parallel plates separated by a distance h as shown in figure 1. a conductive liquid with density ρ, dynamic viscosity µ , and electrical conductivity σ fills the region between the plates. the coordinates x, y are aligned, respectively, along the plate axis, and width. the plate is placed in a uniform transverse magnetic field of flux density bo in the y direction. at time t≤0, the two walls and the fluid are assumed to have the same stationary temperature t0. at time t>0, the plate at y=0 starts moving with a constant velocity and a constant heat flux, while the plate at y=h is heated with periodic temperature and maintained stationary. to setup the mathematical model of the problem, the following assumptions are made: • the fluid physical properties are constant. • the fluid flow is unsteady, laminar, incompressible, viscous, electrically conducting and fully developed. • the magnetic reynolds numbers are small, hence the induced magnetic field is negligible. fig. 1. schematic diagram of the system based on the above assumptions and applying the magnetic field with a presence of periodic plate temperature, the transient governing equations of the mhd flow that present the fluid motion and temperature are: �� �� � ���� � � � ��� ��� ���� � � (1) ��� �� �� � � ��� ��� (2) where u is the axial velocity, t is the fluid temperature, υ is the kinematic viscosity, k is the thermal conductivity, and cp is the speicific heat, with initial and boundary conditions: � � 0: � � 0 � � � for all y � � 0: � � � �� �� � ! "� # � 0 (3) � � 0 � � �$ � %��$ � ��&'()� "� # � * to write the governing equations in dimensionless form, the following dimensionless variables are introduced: + � �, , . � /� ,� , ( � ,�0) / , 1 � � �� ,2 � �3���43��, 5 � �, ���� 6 , 78 � 9:,���43��� /�� , ;8 � 6<=! (4) the dimensionless equations become: �> �? � 782 � ��> �@� 51 (5) �a �? � b cd ��a �@� (6) the corresponding boundary conditions can be specified as: 0 0 0 for all y 0 1 1 at 0 : , : , u u y y τ θ θ τ ≤ = = ∂ > = = − = ∂ (7) 0 1 at 1, cos� �u yθ ε ωτ= = + = engineering, technology & applied science research vol. 9, no. 2, 2019, 4007-4011 4009 www.etasr.com abdullah & saada: free convection mhd couette flow with application of periodic temperature and … iii. numerical analysis finite difference technique is applied to solve the dimensionless momentum and energy equations to determine the velocity and temperature distributions for different parameter values. a uniform grid consisting of a large number of nodes in the y direction is used. crank-nicolson method is used to solve the equations with a large amount of time steps. crank-nicolson method is fully implicit and numerically stable. it has a higher order of accuracy when the solutions are directly obtained from the thomas algorithm. iv. analytical solution the numerical solution can be verified by its comparison with the analytical solution for the case of constant wall temperature (ε=0). the analytical eigenfunction expansion method is used to solve the energy equation. the dimensionless time dependent energy equation can be written as: �a �? � b cd ��a �@� (8) the boundary conditions for constant wall temperature can be written as follows: 0 0 for all y 0 1 at 0 : : yy τ θ θ τ ≤ = ∂ > = − = ∂ (9) 1 at 1yθ = = since the boundary conditions are non homogeneous, we can convert them to homogeneous by introducing: j�+,.� � 2�+,.� �2 +� (10) then the energy equation becomes: �l �? � b cd ��l �@� (11) and the boundary conditions can be specified as: 0 2 for all y 0 0 at 0 : � � : f y f yy τ τ ≤ = − ∂ > = = ∂ (12) f 0 at 1, y= = let j�+,.� � ∅�+�o�.� . taking the derivatives and substituting into (11) yields the eigenvalue problem as: p�∅ p@� � q∅ � 0 �r �@ �0� � ∅�1� � 0 (13) where λ is the separation constant. the solution of the above equation will be: ∅t�+� � �&'u√q+w (14) with eigenvalues: qt � x yt3b y z[ y (15) for each n, the solution for δ(τ) is ot�.� � \ 3]^_=` . hence the series solution for f(y,τ) is: j�+,.� � ∑ btctdb �&'u√q+w\ e] =`? (16) which satisfies the non-homogeneous initial condition j�+,0� � �+ 2� . hence bt � 3y f x1 � √q sin u√qw[ , where i � 1,2,……,∞. then the final form of solution is: 2�+,.� � l∑ 3yf x1 � √q sin u√qw[ ctdb �&'u√q+w\ e] =`?m ��2 +� (17) the coefficient of heat transfer (nusselt number), is given by: n� � ,� op oq� ��3��� (18) using the dimensionless temperature expression, the nusselt number at moving and stationary plates can be written as: n� � 3ba� ,?� x �a �@[@d � b a� ,?� (19) n�b � x�a�@[@db � l∑ l y√f 'riu√qw � 2 'ri y u√qwm ctdb \ e] =`?m 1 (20) v. results and discussion in this section, the effect of different dimensionless parameters on the velocity and temperature profiles is discussed. the numerical solution using crank-niclson technique for velocity and temperature profiles is computed for different values of magnetic parameter, prandtl number, grashof number, and temperature frequency. the following parameter values are used to get the results: gr=5, pr=7, m=1, ω=10, ε=0.2, τ=1. figure 2 illustrates the effect of grashof number on the dimensionless velocity profile. it is seen that the effect of increasing gr would be to increase the velocity u when all other parameters are held constant. figure 3 shows the effect of magnetic field on the velocity profile which clearly indicates that the increase in the applied magnetic intensity would result in a decrease in velocity. fig. 2. velocity profile for different grashof numbers (gr) the effect of the prandtl number pr on the velocity profile is shown in figure 4. it shows that increasing pr would decrease the velocity. the effect of pr on the temperature field is illustrated in figure 5. it is observed that as pr increases, the temperature in the fluid decreases. also, it is seen that pr has a engineering, technology & applied science research vol. 9, no. 2, 2019, 4007-4011 4010 www.etasr.com abdullah & saada: free convection mhd couette flow with application of periodic temperature and … significant influence on the temperature of the plate with constant heat flux for higher values of pr as shown in figure 5. fig. 3. velocity profile for different magnetic parameter (m) fig. 4. velocity profile for different prandtl numbers (pr) fig. 5. temperature profile for different prandtl number (pr) the transient velocity and temperature profiles are shown in figures 6 and 7 for different locations on the fluid. it is noticed that the effect of increasing time is to increase the velocity and temperature until they reach a steady state, and the required time is reduced as we move towards the stasionary plate which has a periodic temperature. it is noticed also that both velocity and temperature have oscillatory behavior with higher amplitude nearby the stationary plate which decays as we move away from the plate. fig. 6. transient velocity at different points on the y coordinate fig. 7. transient temperature at different points on the y coordinate to study the effect of plate temperature frequency on the transient temperature profile, the pulsed volume must be cleared. as shown in figure 8, as the frequency increases, the temperature difference appears to fade away with time. hence, it seems that the temperature at high frequency is continuous rather than oscilating. fig. 8. transient temperature for different values of temparature frequency a comparison of the transient temperature results of the crank-niclson solution (fully implicit method) with analytical solution in the case of ε=0 for temperature profile is shown in figure 9. it is seen that the results are in good agreement with each other. fig. 9. comparison of temperature numerical and analytical results vi. conclusions a fully implicit numerical solution to the problem of transient free convective couette flow of a viscous incompressible fluid confined between two vertical parallel plates in the presence of constant heat flux and periodic temperature on the walls has been prersented. the dimensionless governing partial differential equations are solved by the crank-niclson technique and verified by an eigen function expansion method. the effect of different parameters such as magnetic parameter, grashof number, prandtl number and time are studied. the conclusions of the study are: engineering, technology & applied science research vol. 9, no. 2, 2019, 4007-4011 4011 www.etasr.com abdullah & saada: free convection mhd couette flow with application of periodic temperature and … • the effect of mhd on the fluid flow appears through the magnetic parameter effect. magnetic field exerts a retarding influence on the fluid velocity, which means that a slightly conductive fluid is not affected by the presence of the magnetic field. that could mean that control of the flow can be obtained by controlling the magnetic flux and by a good choice of electrical conductivity. • increasing the grashof number will cause an increase on velocity. • increasing the prandtl number will decrease velocity and temperature. • the periodic behavior of the plate temperature is reflected on transient velocity and temperature profiles. nomenclature bo magnetic flux density (t) cp specific heat, (j. kg -1 . k -1 ) gr grashof number k thermal conductivity, (w.m -1 . k -1 ) m magnetic parameter pr prandtl number t time, (s) t temperature, (k) tw wall temperature, (k) t0 initial fluid temperature, (k) u velocity component in the x direction, (m.s -1 ) u dimensionless velocity x, y cartesian coordinates y dimensionless coordinate ε small reference parameter ω frequency of oscillation, (rad.s -1 ) ω dimensionless frequency φ, δ separation variables ɵ dimensionless temperature τ dimensionless time λ separation constant ν kinematic viscosity, (m 2 .s -1 ) σ electrical conductivity, (siemens.m -1 ) ρ density, (kg. m -3 ) µ dynamic viscosity, (kg. m -1 .s -1 ) references [1] a. singh, “natural convection in unsteady couette motion”, defence science journal, vol. 38, no. 1, pp. 35-41, 1988 [2] b. jha, “natural convection in unsteady mhd couette flow”, heat and mass transfer, vol. 37, no. 4, pp. 329-331, 2001 [3] m. m. rashidi, n. kavyani, s. abelman, “investigation of entropy generation in mhd and slip over a rotating porous disk with variable properties”, international journal of heat and mass transfer, vol. 70, pp. 892-917, 2014 [4] a. m. rashad, m. m. rashidi, g. lorenzini, s. e. ahmed, a. m. aly, “magnetic field and internal heat generation effects on the free convection in a rectangular cavity filled with a porous medium saturated with cu–water nanofluid”, international journal of heat and mass transfer, vol. 104, pp. 878–89, 2017 [5] m. sheikholeslami, k. vajravelu, m. m. rashidi, “forced convection heat transfer in a semi annulus under the influence of a variable magnetic field”, international journal of heat and mass transfer, vol. 92, pp. 339–348, 2016 [6] r. chaudhary, p. jain, “exact solutions of incompressible couette flow with constant temperature and constant heat flux on walls in the presence of radiation”, turkish journal of engineering and environmental sciences, vol. 31, no. 5, pp. 297–304, 2007 [7] m. narahari, “effects of thermal radiation and free convection currents on the unsteady couette flow between two vertical parallel plates with constant heat flux at one boundary”, wseas transactions on heat and mass transfer, vol. 5, no. 1, pp. 21-30, 2010 [8] k. bunonyo, e. amos, i. c. eli, “unsteady oscillatory couette flow between vertical parallel plates with constant radiative heat flux”, asian research journal of mathematics, vol. 11, no. 2, pp. 1-11, 2018 [9] p. sharma, b. sharma, r. c. tamkang, “unsteady free covection oscillatory couette flow through a porous medium with periodic wall temperature”, journal of mathematics, vol. 38, no. 1, pp. 93-102, 2007 [10] c. israel-cookey, e. amos, c. nwaigwe, “mhd oscillatory couette flow of a radiating viscous fluid in a porous medium with periodic wall temperature”, american journal of scientific and industrial research, vol. 1, no. 2, pp. 326-331, 2010 [11] m. narahari, b. dutta, “free convection flow and heat transfer between two vertical parallel plates with variable temperature at one boundary”, acta technica, vol. 56, pp. 103–113, 2011 [12] m. raju, s. varma, “unsteady mhd free convection oscillatory couette flow through a porous medium with periodic wall temperature”, imanager’s journal on future engineering & technology, vol. 6, no. 4, pp. 7-12, 2011 [13] n. ahmed, k. sarma, d. p. barua, “magnetic field effect on free convective oscillatory flow between two vertical parallel plates with periodic plate temperature and dissipative heat”, applied mathematical sciences, vol. 6, no. 39, pp. 1913-1924, 2012 [14] s. das, b. sarkar, r. n. jana, “radiation effects on free convection mhd couette flow started exponentially with variable wall temperature in presence of heat generation”, open journal of fluid dynamics, vol. 2, no. 1, pp. 14-27, 2012 [15] h. k. mandal, s. das, r. n. jana, “transient free convection in a vertical channel with variable temperature and mass diffusion”, chemical and process engineering research, vol. 23, pp. 38-54, 2014 [16] b. zigta, p. koya, “the effect of mhd on free convection with periodic temperature and concentration in the presence of thermal radiation and chemical reaction”, international journal of applied mechanics and engineering, vol. 22, no.4, pp. 1059-1073, 2017 engineering, technology & applied science research vol. 8, no. 3, 2018, 2963-2968 2963 www.etasr.com tuballa and abundo: operational impacts of renewable energy systems on a remote diesel-powered … operational impact of res penetration on a remote diesel-powered system in west papua, indonesia maria lorena l.tuballa school of engineering, university of san carlos cebu city, philippines and college of engineering and design, silliman university, dumaguete city, philippines mlt_kin@yahoo.com michael lochinvar s. abundo nanyang technopreneurship centre, nanyang technological university, singapore and school of engineering, university of san carlos, cebu city, philippines michael.abundo@ntu.edu.sg abstract—when a new power source connects to the distribution or transmission grid, an assessment of its impact is necessary. technical studies must assess the possible effects of a proposed expansion, reinforcement or modification to evaluate the possible incidents that may occur. typically, the calculations or analyses done are load flow, short-circuit, and transient stability. the possible renewable energy (re) sources are determined first. the details of the existing electrical system, including the specifications for the elements used, are obtained and logical assumptions are utilized for those that are not known. the load flow analysis in the considered case revealed that the re presence reduces diesel generation. the 119 kw pv array and the 54 kw tidal turbine displace most diesel generation: 22% of gen 4 and 21.8% of gen 5. the diesel-solar system brought the diesel generation down by 20.05% of gen 4 and 20% of gen 5. the diesel-tidal combination lessened the diesel generation by 1.92% of gen 4 and 1.83% of gen 5. short-circuit analysis alerts indicating the operating percentages of the circuit breakers that are beyond their interrupting ratings are presented. the transient stability analysis depicts that re sources affect the existing system and appear to be putting in more stress. the studied systems are not transient-stable based on the results. while it is relatively simple to plan to put up renewables in remote island systems, there are many factors to consider such as the possible impacts of the re sources. keywords-electrical grid; renewable energy; transient stability; diesel generation; tidal turbine i. introduction in a typical distribution system, where a traditional electric grid that interconnects smaller grids is available, whenever a new significant power generation source connects to the distribution or transmission grid, whether it is conventional or a renewable energy (re) resource, a grid impact assessment or grid impact study is necessary. these are sets of technical studies used to assess the possible effects of the proposed expansion, reinforcement, or modifications to evaluate the possible incidents that may occur. power system issues are mostly dependent on system size, geographical distribution, planned capacities of variable renewable resources, system operation scheme, market structure, size of the balancing area and interconnection capacity. typically, the calculations or analyses done on a grid impact study are load flow, shortcircuit and transient stability studies. for remote islands that are not connected to the usual grid system, it is also rather important to see the impact of a new generation. the objective of the current study is to assess the impacts of solar energy, wind energy and tidal energy system on the operational characteristics of an electrical system powered only by diesel generators. the specific location in indonesia is pt bintuni utama murni wood industries (pt bumwi), a mangrove processing and woodchip plant. the company specializes in mangrove utilization and forest management. it started as a primary supplier of mangrove logs to the japanese paper industry. the concession area is in pulao amutu besar, bintuni bay, west papua, with a total area of 82,120 hectares. the site activities include harvesting mangrove logs and processing them to make woodchips. the wood chip factory is located in the southern part of the island, with no available conventional electricity grid, thus the energy demand is met by off-grid diesel generators. the diesel fuel supply comes from sorong, approximately 500 km away from the island. the reported high fuel cost is around 13,000 idr ($0.89 usd) per liter and base consumption for power generation is around 220,600 liters per year. the company aims to lessen its dependence on diesel fuel and achieve a sustainable power system by integrating re. it plans to include tidal energy in its supply as the site is surrounded by a large bay. ii. west papua woodchip factory site indonesia is an archipelago and the indonesian transmission network is segregated into many power grids—eight interconnected networks and isolated grids that are all operated by pln, a government-owned monopoly on electricity distribution in indonesia. pln prioritizes the development of renewable resources to supply local grids where available and interconnects grids where feasible [1]. pln operates a total of 4600 diesel systems outside java-bali and approximately, there are 30.000 small diesel generator sets in the rural areas [2]. indonesia’s latest electricity ratio is approximately 86% and at present, its total plant capacity is 54 gw, 17% of which come from new and renewable energy (nre) sources. by 2025 total plant capacity is expected to grow to 115 gw and nre contribution to increase to 37% [3]. as of 2014, the electricity engineering, technology & applied science research vol. 8, no. 3, 2018, 2963-2968 2964 www.etasr.com tuballa and abundo: operational impacts of renewable energy systems on a remote diesel-powered … ratio targets reflect papua as needing most of the capacity additions [4]. a. the existing electrical system the pt bumwi electrical plant houses five generator sets which supply power to the camp. the main loads are three 220kw three-phase wood chipper machines. other loads include residential, workshop, bulldozer rooms, conveyor belts, and ship loading. b. solar resource indonesia, like any tropical country and being located in the equatorial line has abundant solar energy potential. the indonesian energy potential for solar averages at 4.8 kwh/m2/day [5]. the pt bumwi site is located at 02° 31' 11" s and 133° 35' 48" e. homer, a microgrid optimization software, provides average horizontal global solar radiation, expressed in kwh/m2, for each hour of the year by specifying the coordinates of the site. table i shows the representative clearness indices and daily radiation for the different months of the year while figure 1 illustrates the global solar radiation table i. site clearness indices and daily radiation month clearness index daily radiation (kwh/m2/d) january 0.489 5.04 february 0.493 5.2 march 0.482 5.07 april 0.508 5.12 may 0.531 5.01 june 0.511 4.62 july 0.488 4.48 august 0.479 4.67 september 0.479 4.93 october 0.497 5.2 november 0.514 5.3 december 0.491 5 c. wind resource in general, a 2 m/s minimum is required to start rotating most small wind turbines and the typical cut-in speed (when a small turbine starts generating power) is 3.5 m/s, with 10–15 m/s speeds producing maximum generation power [6]. the average recorded wind speed here is 2.32 m/s. although this meets the minimum speed required to start rotating most small wind turbines, the typical cut-in speed of 3.5m/s, occurs only around 7% of the time [7]. figure 2 shows the wind rose. this limitation makes wind turbine generation at pt bumwi impractical. d. tidal resource tidal stream energy is a form of energy arising from the movement of masses of water or tides. certain types of tidal stream generators or tidal turbines function similarly to wind turbines, with the only difference that they are underwater. the pt bumwi site is situated near a strait, pointing to some good tidal in-stream resource in the area. the assessment of the tidal resource potential in the pt bumwi factory was made by oceanpixel, a spin-off of nanyang technological university dedicated to increasing the ocean renewable energy uptake in south east asia. the technical report [8] data are taken into account in the current study. bathymetrical data is collected using an echo sounder. the bathymetry is computed by interpolating the combined data sets of the indonesian nautical maps and the collected depth data. tidal flows and velocities are determined using an acoustic doppler current profiler (adcp). the recorded maximum current speed is 1.6 m/s while the average current speed flowing through the center of the narrow strait in pt bumwi is 0.7625 m/s. from the assessment, the monthly available resource is roughly 1.733 gwh. table ii shows the monthly speed averages of the projected tidal resource. fig. 1. plot of pt bumwi solar radiation fig. 2. wind rose e. modeling parameters the diesel generators are modeled based on their specifications. details that are not known or specified are left as default values. wood chippers are modeled as induction motors, corresponding to nameplate ratings. other loads are modeled as lumped loads. ratings for the lumped loads require real and reactive power components and these are taken from energy loggers deployed on their respective panels on site. the capacitor banks in pt bumwi consists of six parallel threephase capacitors, each rated 23.2 kvar. the inputs are taken from phmkp440.3.28, 10-84 lvac power capacitors data sheet, the capacitors installed in the site. whenever solar panels are involved in etap, there is an option to calculate the irradiance for a specified location. in this case, it is 1.3361° s, 133.1747° e. figure 3 shows the irradiance calculator and the pv array editor configurations used. the tidal turbine is not an engineering, technology & applied science research vol. 8, no. 3, 2018, 2963-2968 2965 www.etasr.com tuballa and abundo: operational impacts of renewable energy systems on a remote diesel-powered … available element in etap, hence the tidal turbine is modeled as a wind turbine generator. the characteristics of the schottel in-stream turbine are used for the wind turbine inputs and specified according to the actual type that would be running with the diesel generators in pt bumwi. in a separate microgrid simulation, the suggested optimal size for the tidal turbine is 54 kw. figure 4 shows the info and turbine specifications tabs. table ii. monthly tidal current speed averages month tidal speed (m/s) january 1.042 february 0.909 march 0.956 april 1.019 may 1.03 june 0.96 july 0.894 august 0.933 september 0.891 october 0.969 november 1.031 december 1.044 fig. 3. irradiance calculator and pv array editor fig. 4. tidal turbine info and ratings tabs (modeled as wind turbine) iii. results and discussion in figure 5 the simplified single-line diagram of the pt bumwi electrical system implemented in etap is shown. it consists of 7 buses, 15 branches, 5 diesel generators (two running diesel generators at a time, usually gen 4 and gen 5), 9 different connected loads and 6 capacitors each rated 23.2 kvar. a. load flow study load flow studies aim to determine whether an existing or reinforced system can satisfy the voltage and current limits, under steady-state conditions. it must be seen that the loading levels of all transmission lines and substation equipment are below 90% of the maximum continuous ratings of phase conductors and transformers. deviations may only be acceptable on the contingency that depends on the condition of the facility. voltage variations in the system for all voltage levels shall remain within ±5% of the nominal value during normal conditions and during single outage contingency events. the load flow results are obtained for different configurations: existing diesel system, diesel-solar system and diesel-tidal system and diesel-solar-tidal system. there are no significant issues found in the load flow. the presence of the re reduces the percent generation of the diesel generators, with the diesel-solar-tidal displacing the most diesel generation: 22% of gen 4 and 21.8% of gen 5. the diesel-solar system brought the diesel generation down to 20.05% of gen 4 and 20% of gen 5. the diesel-tidal combination lessened the diesel generation by 1.92% of gen 4 and 1.83% of gen 5. the dieselsolar-tidal would have displaced only roughly 6% of gen 4’s generation and 6.1% of gen 5’s generation if the solar pv were sized to match the tidal turbine. the load flow studies for the other configurations do not reflect any voltage issue. table iii displays the load flow analyzer results. table iii. load flow analyzer results system id % pf % generation diesel gen 4 83.48% 36.4% gen 5 83.48% 65.5% diesel-solar gen 4 77.14% 29.1% gen 5 77.14% 52.4% diesel-tidal gen 4 85.51% 35.7% gen 5 85.51% 64.3% wtg1 77.14% 16.9% diesel-solar-tidal gen 4 79.55% 28.4% gen 5 79.55% 51.2% wtg1 77.14% 16.9% b. short circuit study short circuit studies determine the magnitude of currents that flow through electrical faults and compare these against the ratings of the equipment to ensure that proper protection is present. short-circuit levels through all circuit breakers have to be within acceptable limits not just to prevent costly replacement projects but to ensure safety to equipment and personnel. in addition to the short-circuit study, a protectioncoordination can be done to determine the trip settings of the protective devices in the system in order to achieve maximum protection with minimum interruption for all faults that can possibly occur. in this study, protection coordination is not covered. the majority of fault studies include only three-phase and single line-to-ground faults. three-phase faults, though they rarely occur (around 5% of initial faults) are usually the most severe. on the other hand, single line-to-ground faults are engineering, technology & applied science research vol. 8, no. 3, 2018, 2963-2968 2966 www.etasr.com tuballa and abundo: operational impacts of renewable energy systems on a remote diesel-powered … the most common (80%). the rest are either line-to-line or lineto-line-to-ground faults. the short-circuit analysis program in etap enables the analysis of the effect of different types of faults such as 3-phase, line-to-ground, line-to-line, and line-toline-to-ground faults on distribution systems. the program calculates total short-circuit currents and the contributions of individual motors, generators, and utility ties in the system. fault duties are in compliance with the latest editions of the ansi/ieee standards and iec standards. table iv gives the short circuit analysis results. fig. 5. the pt bumwi single-line diagram in etap table iv. short circuit abalysis results faulted bus system (no re) system (solar) system (td) system (solar and td) bus 17 3-phase faults – device duty cbg1-4 operating 217.5% cbg1-4 operating 160.2% cbg1-4 operating 220.4% cbg1-4 operating 162.6% bus 18 3-phase faults – device duty cbg5 operating 217.5% cb pva oparating 192.2% cbg5 operating 160.2% cbg5 operating 220.4% cb pva oparating 195.1% cbg5 operating 162.6% main bus 3-phase faults – device duty cbg1-5 operating 217.5% cbg1-5 operating 160.2% cbg1-5 operating 220.4% cbg1-5 operating 162.6% bus 46 no alert no alert no alert no alert bus 36 3-phase faults – device duty cb wc1-2 operating 280.4% cb wc1-2 operating 173.9% cb wc1-2 operating 175.7% cb wc1-2 operating 175% bus 33 3-phase faults – device duty cb cap16 operating 132.6% cb cap1-6 operating 132.2% cb cap1-6 operating 133.2% cb cap1-6 operating 132.8% c. transient stability transient stability is the ability of the system to maintain synchronism when subjected to a severe fault or disturbance. generators and large machines connected to the system should remain in synchronism and maintain stable operation during normal and during contingency events. the fault clearing times must be adequate and breakers need to trip or be manually tripped before any catastrophic event occurs. the clearing time used was 0.08 seconds, (4 cycles) [9]. a threephase fault was assumed to have occurred in bus 18 at 1.000 sec and cleared at 1.080 sec, with a 20-second simulation time. figure 6 shows the details of the transient stability study case. some of the transient stability plots for the two diesel generators, the loads and the buses are shown below. in figure 7, the generator reactive power has hugely defined peaks and dips and highly frequent changes in amplitudes in the presence of the re sources. the case looks worse in the diesel-solar system. figure 8 shows the load reactive power plot in the diesel-generator system. when the system is run by diesel alone, these parameters show some degree of stability, but not totally as load reactive power is not the same as the reactive power after fault clearing. the generator electrical power plots are shown in figure 9. they display similar behavior with that observed in figure 7. these almost noise-like plots need the more attention. engineering, technology & applied science research vol. 8, no. 3, 2018, 2963-2968 2967 www.etasr.com tuballa and abundo: operational impacts of renewable energy systems on a remote diesel-powered … fig. 6. transient stability study case details fig. 7. generator reactive power fig. 8. load reactive power (diesel only) fluctuations in the load reactive power and load electrical power are also observed in the presence of the re sources. figure 10 exhibits the behavior of the bus frequency in the diesel, solar and tidal configuration. it shows the worst among the three simulated systems. as to the generator speed, variation is most unfavorable in the diesel-solar configuration. figure 11 shows the generator speed variations after the fault clearing–when the system is powered by diesel, by diesel and solar and by the diesel, solar and tidal combination. the plots illustrate that after fault clearing, the generators, buses and load parameters do not return to their original state. fig. 9. generator electrical power fig. 10. bus frequency engineering, technology & applied science research vol. 8, no. 3, 2018, 2963-2968 2968 www.etasr.com tuballa and abundo: operational impacts of renewable energy systems on a remote diesel-powered … fig. 11. generator speed iv. conclusion this study gives an insight on the operational impacts of re on an island grid. the load flow analysis revealed that the re presence reduces the diesel generation. the 119 kw pv array and the 54 kw tidal turbine (here simulated as a wind turbine generator) displace the most diesel generation: 22% of gen 4 and 21.8% of gen 5. the diesel-solar system diesel generation brought the diesel generation down by 20.05% of gen 4 and 20% of gen 5. the diesel-tidal combination lessened the diesel generation by 1.92% of gen 4 and 1.83% of gen 5. the short-circuit analysis alerts indicate the operating percentages of the circuit breakers that are beyond their interrupting ratings. since the circuit breaker ratings are assumed, before actual replacements and/or modifications are done, the models of these protective devices need to be identified and data inputs changed accordingly. the transient stability analysis depicts that the intermittency of the re sources affects the existing system and appears to be putting in more stresses. the systems in the study are not transient-stable acknowledgment authors would like to thank engineering research for development and technology (erdt), oceanpixel pte. ltd. and green forest product & tech. pte. ltd. references [1] p. tharakan, summary of indonesia’s energy sector assessment, adb, 2015 [2] s. blocks, “business assessment for diesel hybrid systems in indonesia, german-indonesian chamber of industry and commerce, 2013 [3] ministry of energy and mineral resources republic of indonesia, indonesia’s renewable energy and energy conservation development, 2015 [4] pwc, power in indonesiainvestment and taxation guide, 2017 [5] unep dtu partnership, indonesian solar pv rooftop program (isprp)facilitating implementation and readiness for mitigation (firm), 2016 [6] branz ltd., “wind turbine systems”, available at: http://www.level.org.nz/energy/renewable-electricity-generation/windturbine-systems/ , 2017 [7] j. valleser, “a techo-economic feasibility study of implementing a hybrid renewable energy microgrid at pt bumwi camp, amutu besar, bintuni bay, indonesia”, university of san carlos, 2016 [8] ocean pixel, tidal in-stream energy resource assessment in bintuni bay, west papua, indonesia, 2015 [9] d. k. neitzel, “protective devices maintenance as it applies to the arc/flash hazard”, conference record of the 2004 annual pulp and paper industry technical conference, ieee, pp. 209-215, 2004 engineering, technology & applied science research vol. 8, no. 3, 2018, 3018-3022 3018 www.etasr.com kanona et al.: a review of ground target detection and classification techniques in forward … a review of ground target detection and classification techniques in forward scattering radars mohammed e. a. kanona school of telecommunication future university khartoum, sudan mohammedkanona@gmail.com mohamed ghazli hamza school of telecommunication future university khartoum, sudan mohghazli@gmail.com ashraf g. abdalla school of telecommunication future university khartoum, sudan agea33@yahoo.com m. k. hassan faculty of electrical engineering universiti teknologi malaysia, johor, malaysia memo1023@gmail.com abstract—this paper presents a review of target detection and classification in forward scattering radar (fsr) which is a special state of bistatic radars, designed to detect and track moving targets in the narrow region along the transmitter-receiver base line. fsr has advantages and incredible features over other types of radar configurations. all previous studies proved that fsr can be used as an alternative system for ground target detection and classification. the radar and fsr fundamentals were addressed and classification algorithms and techniques were debated. on the other hand, the current and future applications and the limitations of fsr were discussed. keywords-neural network; pca; z-score; target classification; recognition; forward scattering radar i. introduction radar systems and stations are used for detecting various objects in space and establishing their current position, as well as determining velocities and trajectories for moving objects [1]. from the basic point of view, this is achieved by transmitting an electromagnetic (em) wave from the transmitting antenna. if the target is located within the radar coverage area, the wave will be reflected back to the receiving antenna [2]. there are different types of radar systems, based on the transmitter-receiver topology: (a) the monostatic radar, where the transmitter and the receiver are spatially combined, and (b) the bistatic radar which consists of a single transmitter and a single receiver which are separated by a distance, comparable to the maximum range [1]. a forward scattering radar (fsr) is a special state of bistatic radar [3], designed to detect and track targets moving in the narrow region along the transmitter-receiver base line. its most attractive feature is radar cross section (rcs) which considers the target’s physical cross section, the wavelength, the shape of the target’s surface. a basic comparison to the traditional monostatic radar can be found in [4], whereas probably its most important feature is its robustness against stealth technology [5]. moreover, the fsr receiver can utilize radiation from non-cooperative transmitters without revealing its location. in a hostile environment this is highly desirable as the receiver may be used covertly. all these advantage features created a ‘come back’ interest to fsr. in addition, fsr can be used for target classification, requires relatively simple hardware and has a long coherent interval of the received signal. this is the consequence of the loss in range resolution [6-7]. on the other hand, the fsr presents a conservative class of systems which have a number of fundamental limitations, that include the absence of the range resolution and operation within the narrow angles. this therefore requires the target to be very close to the transmitterreceiver baseline and the radar loses its ability to measure the range when the target crosses the base line. ii. previous and related works some of the main literature devoted to the fsr is given in [8, 9]. generally, there is a lack of recent publications on fsr. earlier publications, pertaining to the forward scattering, were devoted to estimating the rcs of an object at the forward scattering. among others, [5] provides a theoretical analysis and various experimental results to prove that the ram coatings did not impose any effect on forward scattering when applied on highly conducting objects which were larger than the wavelength of the carrier. nevertheless, the advantages of the fsr became known much later. these included the increase in the rcs of the object at the forward scattering. in [4], author presented a fast and simple approach for estimating the effective forward scattering rcs for the different targets at various operating frequencies. this was followed by [10], in which authors experimentally confirmed that the rcs, at forward scattering, was bigger than the one in the monostatic case by 30-40 db, depending on the frequency of the carrier. authors in [11] discussed target detection and estimated the detection zones at forward scattering. they showed that the detection zone of a fsr was dependent on the type of the object and its flight trajectory. they calculated the bistatic rcs of the objects, related to the xy cartesian co-ordinates to estimate the detection zones. authors in [12] on the other hand, suggested that the detection is always lost at zero doppler. this area is known as the ‘dead zone’. authors in [1] suggested that the areas worthy of investigation are the system issues of the engineering, technology & applied science research vol. 8, no. 3, 2018, 3018-3022 3019 www.etasr.com kanona et al.: a review of ground target detection and classification techniques in forward … fsr. these include system configurations and system parameters, such as the operating frequencies, power levels, and baseline distance. all that delayed the deployment of fsr in practical applications. a. target detection in fsr authors in [13] discussed the fsr technology, the current and possible applications and the limitations of fsr in a feasibility study to the automatic ground target detection and classification. also, the extraction of features from the radar measurements was introduced. authors proved that the fsr system has a huge potential to be used as an alternative for ground target detection and classification based on pca as feature extraction and the classification algorithm (k-nearest neighbor classifier) by a real experiment of three vehicles carried out on a public road. authors in [14, 15] touched the problem of extracting the doppler signature in different interference environments by using hilbert transform and wavelet technique in order to predict the existence of target. two experimentations have been done to collect the fsr signal under high clutter. the proposed method gave a good result with some reservations of wavelet issues. soon after, authors in [16, 17] studied the effect of clutter on the automatic target classification (atc) accuracy in fsr. it was shown that using conventional clutter-uncompensated atc system can achieve high target classification accuracy at high scr only, but the accuracy drops significantly with decreasing scr. the employment of clutter-compensated atc system is shown to improve significantly the classification accuracy at low scr. authors in [18] continued in the same field with new improvements in the existing method proposed in [14, 15] by considering a rough environment (receiver and surrounding noises). results showed that target detection using a hilbert transform is applicable only for certain conditions but target detection employing the wavelet technique is more robust against clutter and noise. an inclusive comparison of various wavelet threshold selection rules for different types of wavelet filters and levels of decomposition is conducted to study the effect on target detection with fsr. two sets of field experiments were carried out to validate the proposed method, and target signals under the influence of large clutter were successfully detected using the proposed method with a confidence level exceeding 75%. then authors in [19] implemented the haar and meyer wavelet technique in fsr which gives more detailed scales and variation information from the measured signals. the results from the wavelet technique showed that they could find the similarity between signals of each target and dissimilarity between different targets. authors in [21] investigated accurate signal modeling for detecting moving targets in fsr by modifying the existing model algorithm by using numerous simulations. they claim that all the existing signal models and algorithms are built based on the assumptions that the baseline is long, diffraction angle is small and velocity direction of the target is approximately perpendicular to the baseline, the ground-based fsr system is characterized by short baseline and large diffraction angle and the velocity direction of the target is not always perpendicular to the baseline. therefore in many cases, the above assumptions introduce significant errors to the results in the ground-based fsr. in the light of the ground-based fsr system, the signal model and imaging algorithm in traditional sisar imaging technology are modified and gave good results. authors in [22] state that, the received signal in fsr depends on the target’s electrical size and trajectory, which are unknown a priori. as a result, in practical situations, it is impossible to obtain the accurate reference function at the reception side. that’s why they proposed a signal processing algorithm which includes the construction of the adaptive reference functions and the identification of target velocity and observation time by the adaptation of an optimal filter (quasioptimal). they tested the algorithm performance under practical motion trajectories such as different motion directions and baseline crossing points, which indicates the effectiveness of the proposed algorithm in a practical case for fsr. as result they found that the proposed methods are suitable for the identification of target parameters, and in particular when observing target’s time and speed. by knowing those parameters the possibility to obtain accurate target recognition rises. authors in [23] discussed fsr cross section of different target specification by conducting a simulation for analysis of a multi-car model. the study showed the effects of different target specifications on rcs radiation pattern at different angle for each frequency. novel studies were in [24, 25]. authors used gps radio shadow instead of previous fsr models in order to build a passive fsr system. investigation on different moving objects was introduced. the results showed that from fs-gps radio shadows of different objects, information about the parameters of the object (size, speed and direction of movement, distance to the receiver) can be extracted from the width, shape and length of the received fs shadow. the occurrence of fs shadow is essential physical phenomena, which can be used to extract some useful information about the objects that create it. in [26], authors proved the forward scattering gps radio shadows system can be used for detecting road vehicles in urban environment. authors in [27] followed the previous study of target shadow with the practical aspects of the target profile reconstruction in a single node groundbased fsr system and discussed the target return signal for three different cars measured in real outdoors environment. the study proved that modeling approach can be successfully used for simulation of the doppler phase history, which is required in the procedure of complex envelope extraction. the similarity of the reconstructed and original profiles demonstrates that tspr delivers results suitable for both visual interpretations of target profile and atc. b. classification techniques in fsr in [2, 28-30], it was shown that fsr can be effectively used for ground target detection, and in particular automatic vehicle recognition and classification using different techniques and scenarios. researchers classified four different types of vehicles into categories based on their sizes and types at frequency 1 ghz in ideal case scenario where the vehicles are crossing the baseline perpendicularly. in order to perform the classification, the combination of principal component analysis (pca) and k-nearest neighbor (knn) was proposed. obtained engineering, technology & applied science research vol. 8, no. 3, 2018, 3018-3022 3020 www.etasr.com kanona et al.: a review of ground target detection and classification techniques in forward … results showed that good vehicle classification performance can be achieved. authors in [31] worked on the evaluation of a network of forward scattering (fs) radar micro sensors for the detection and classification of ground targets based on the findings of [8]. the system power budget was operating in line of sight (los) conditions. it was evaluated at both theoretical and experimental level in terms of power budget analysis and resolution. authors demonstrated that an excellent resolution is achievable. the potential resolution of the system is equal to the target’s horizontal dimension. the dynamic range of the system is also shown to be very high. in addition, a number of practical targets were considered as simulation examples over a wide range of radar carrier frequencies. in [29], authors proved that fsr system has a huge potential to be used as an alternative system for ground target detection and classification. authors in [32] proposed another solution based on using vehicle height and length and height profiles obtained by a microwave (mw) radar sensor. a precise feature vector can be extracted, and simple deterministic algorithms can be applied to determine the vehicle class. field trials using a spread-spectrum mw radar sensor system operating on these principles have been carried out. they confirmed that accurate classification of a large number of vehicle classes can be reached. authors in [33] used image technique formulation to obtain the electric field integral equations (efies) in order to classify cylindrical targets from their ultra wide-band radar returns. then, the efies were solved numerically by the method of moment (mom). because of the wide frequency range of the ultrawide-band radar signal, the database to be used for target classification becomes very large. to deal with this problem and to provide robustness, wavelet transform was utilized. application of wavelet transform significantly reduces the size of the database. the coefficients obtained by wavelet transform are used as the inputs of artificial neural networks (anns). then, the actual performances of the anns were investigated by receiver operating characteristic (roc) analysis. therefore, the compressed inputs of the anns were determined and a dataset was formed. rbf, grnn and mlp were investigated in this work. according to the testing and training rates, the best classifier is the mlp. to support this result, sensitivity and specificity values and the roc curves were obtained and it was observed that mlp was better. authors in dealt with a new system that uses neural network(nn)-based methodology with various types of training algorithms. it reiterates the uniqueness and the ability of the neural network implementation to accurately classify unknown vehicle signature on the available training data, the input of nn is defined as the vehicle length and back-propagation nn (bpnn) was used as a nn model. the paper proves that nn is suitable to be used as a classifier since the classification accuracy exceeds more than 90%. authors in [35] on the other hand, proved the potential and utilization of nns by comparing the knn classifier and the conventional method (pca) with the proposed. results showed that nns can be effectively employed in fsr as an automatic classifier. after implementing multi-layer perceptron (mlp), a bpnn trained with three back-propagation algorithms gave very promising results in vehicle recognition and vehicle categorization. 10% of overall data was misclassified in vehicle recognition and only 2% of overall data was misclassified in vehicle categorization. the same classification method was applied in [14, 36], but with different trajectory known as angle of detection. theoretically, target’s trajectory is one of the factors affecting the target’s signature which contributes towards the poor performance of the classification system. hence, by using multiple sensors, the discrepancies in classification performance could be reduced. later, the same classification system has been tested at low frequencies: ultra high frequency (uhf) and very high frequency (vhf) bands [37]. the paper proved that a good classification performance can be obtained even at low frequency. authors in [38] proposed a novel ground vehicle classification approach using unmodulated cw radar. the radar was set up to look forward down to the road. vehicles were modeled as body targets composed of multiple scattering centers. analysis showed that the spatial distribution of scattering centers can be derived from the doppler signature of radar echo. hough transform was performed to estimate the distribution which was then used for classification. in experiments, vehicles were classified into three types at an average accuracy of 94.8%. authors in [39, 40] designed and developed three novel, distinct automatic target recognition (atr) methods. for the classification they divided the observed targets into predefined classes (extremely randomized trees or subspace methods). a key feature of the approach was the breaking of the recognition problem into a set of subproblems by decomposing the parameter space, which consist of the frequency, the polarization, the aspect angle and the bistatic angle, into regions and build one recognizer for each region. authors in [41] claimed that all previous studies did not consider a rough environment analysis in ground target classification systems and all experiments have been on ideal environment which significantly effects the classifier output. after adding simulation noises to the fsr signal output nn was used as classifier. as result it was found that classification using an ann is robust against noise to a certain extent of noise. they developed an enhanced classification process in [42]. however the performance of the classification system was still below satisfactory level especially under the influence of external factors such as clutter [16], target trajectory uncertainties [43] and features used as the input to the classifier. authors in [44] addressed the importance of feature extraction process in the fsr system by evaluating manual and automatic reduction techniques (pca and z-score). the main objective of this study was to analyze the most suitable feature extraction algorithm to classify ground vehicles based on their physical size. they continued in [45, 46] by improving the classification accuracy by the combination of z-score and nn. it was shown that as the number of features increases, the classification accuracy increases. the highest percentage of classification accuracy can be achieved when using a nn5 system. authors in [47] used lte signal as a source for passive bistatic radar (pbr) for detection and location of ground moving targets depending on bistatic rcs. conventional processing was used as classification approach. they performed simulations using computer simulation technology (cst) microwave studio. the simulation results showed that engineering, technology & applied science research vol. 8, no. 3, 2018, 3018-3022 3021 www.etasr.com kanona et al.: a review of ground target detection and classification techniques in forward … the large area of ground moving target, had better outcome compared to other ground moving targets which is compatible with babinet’s principle, which declares a target of physical cross-sectional area is proportionate to rcs. in [48], same authors rolled in their previous study but this time detected humans instead of vehicles. real experiments were done by testing and evaluating different human sizes. it was discovered that the psd of the individuals are inversely proportional to their heights. in pca, data of the individuals show a good convergence in terms of their respective groups. authors in [49, 50] proposed a passive fsr system that can exploit the peculiar advantages of the enhancement in forward scatter radar cross section (fsrcs) for target detection and recognition using lte signals. this paper illustrates the first classification result in the passive fsr system. the great potential in the passive fsr system provides a new research area in passive radar that can be used for diverse remote monitoring applications. in [51], authors presented the latest feasibility studies and experimental results from using lte signals in pbr applications. details are provided about aspects such as signal characteristics, experimental configurations, and snr studies. six experimental scenarios were carried out to investigate the detection performance of the proposed system on ground-moving targets. the detection ability was demonstrated through the use of a cross-ambiguity function. the detection results suggested that lte signals are suitable as a source signal for pbr. iii. conclusion this paper presents a review of target detection and classification in fsr and its advantages over other types of radar configuration. it is generally accepted that fsr can be used as an alternative system for ground target detection and classification. further, recent research focused on the application of different classifiers to accurately classify unknown vehicle signatures. moreover, feature extraction was addressed, especially pca and z-score to improve classification accuracy. the area of ground vehicle classification is very interesting, that’s why intensive studies have been conducted in the last few years looking for alternatives to old systems, using fsr theory to reduce the cost and to make use of the existing transmitted signals. therefore, gsm, lte, gps and fm were tested for detection and recognition of vehicles and humans as well using the same classification techniques. however, a number of problems are still unsolved, including the choice of optimum frequency, a more precise and intelligent speed estimation algorithm plus the absence of the range resolution and operation within the narrow angles. another set of problems is the choice of the feature extraction before injecting the signature into the classifier. future research will focus on using artificial intelligence, especially nns with 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detection and recognition system using passive forward scattering radar”, science international, vol. 29, no. 1, pp. 69-73, 2017 [49] r. s. a. r. abdullah, n. h. a. aziz, n. e. abdul rashid, a. a. salah, f. hashmin, “analysis on target detection and classification in lte based passive forward scattering radar”, sensors, vol. 16, no. 10, p. 1607, 2016 [50] r. s. a. r. abdullah, a. a. salah, n. h. a. aziz, n. e. abdul rashid, “vehicle recognition analysis in lte based forward scattering radar”, in ieee radar conference, philadelphia, pa, usa, ieee, 2016 [51] r. s. a. r. abdullah, a. a. salah, a. ismail, f. hashim, n. e. abdul rashid, n. h. a. aziz, “lte-based passive bistatic radar system for detection of ground-moving targets”, etri journal, vol. 38, no. 2, pp. 302-313, 2016 microsoft word 20-2725_s1_etasr_v9_n3_pp4176-4181 engineering, technology & applied science research vol. 9, no. 3, 2019, 4176-4181 4176 www.etasr.com kote & wadkar: modeling of chlorine and coagulant dose in a water treatment plant by artificial … modeling of chlorine and coagulant dose in a water treatment plant by artificial neural networks alka s. kote department of civil engineering, dr. d. y. patil institute of technology, pune, india alkakote26@gmail.com dnyaneshwar v. wadkar dr. d. y. patil institute of technology, and aissms college of engineering, pune, india dvwadkar_civil@yahoo.co.in abstract—coagulation and chlorination are complex processes of a water treatment plant (wtp). determination of coagulant and chlorine dose is time-consuming. many times wtp operators in india determine the coagulant and chlorine dose approximately using their experience, which may lead to the use of excess or insufficient dose. hence, there is a need to develop prediction models to determine optimum chlorine and coagulant doses. in this paper, artificial neural networks (ann) are used for prediction due to their ability to learn and model non-linear and complex relationships. separate ann models for chlorine and coagulant doses are explored with radial basis neural network (rbfnn), feed-forward neural network (ffnn), cascade feed forward neural network (cfnn) and generalized regression neural network (grnn). for modeling, daily water quality data of the last four years are collected from the plant laboratory of wtp in maharashtra (india). in order to improve performance, these models are established by varying input variables, hidden nodes, training functions, spread factor, and epochs. the best models are selected based on the comparison of performance measures. it is observed that the best performing chlorine dose model using defined statistics is found to be rbfnn with r=0.999. similarly, the cfnn coagulant dose model with bayesian regularization (br) training function provided excellent estimates with network architecture (2-40-1) and r=0.947. based on the above models, two graphical user interfaces (guis) were developed for real-time prediction of chlorine and coagulant dose, which will be useful for plant operators and decision makers. keywords-artifical neural networks; chlorine dose; coagulant dose; water treatment, modelling i. introduction water treatment consists of many complex physical and chemical processes. the efficiency of these processes is accomplished by examining the quality of outlet water. generally, in india, wtp operators take necessary remedial measures for water quality improvement using only their experience. this practice is inefficient and time-consuming in monitoring real-time responses [1, 2]. in a wtp, coagulation and disinfection are essential treatment processes as they assure the supply of safe and clear water. conventionally, chlorine is the most widely used disinfectant, and aluminum sulphate (alum) used as a coagulant due to its high efficiency and low cost. mainly, two common vital factors, turbidity and applied dosages, decide the effectiveness of chlorination and coagulation [3]. turbidity provides a shield to microbes, which reduces the efficiency of chlorination. it raises chlorine demand, which results in less availability of residual chlorine in water distribution networks (wdns) [4, 5]. in india, wdns are old, have leakage issues responsible for microbial contamination, and there is a tendency of plant operators to apply higher chlorine dose for maintaining the desired residual chlorine in the wdn. the high chlorine dose increases the probability of trihalomethane (thm) formation. consumption of thm containing water creates adverse effects on human health such as high blood pressure, reproductive system disorders, and cancer inception [6]. a chlorine predictive model will help monitoring the process and avoid complex laboratory analysis, which requires more time and money. coagulation and chlorination processes show non-linear nature that is hard to express using linear mathematical models [7]. it is difficult to model water treatment processes due to complex interactions among many chemical and physical reactions. thus, the application of anns is considered for the prediction of optimum coagulant and chlorine dose. an ann is a biologically inspired system consisting of a number of interconnected elements called neurons. these neurons are arranged in input, hidden and output layers. all the layers are well connected like human brain synapses where weights are optimized by using input and output variables [8]. an ann has the ability to learn and model non-linear and complex relationships. several studies have been carried out on the prediction of the coagulant dose for particular wtp [9-15]. rbfnns and grnns have shown good performance capabilities for predicting residual chlorine in wtp [16]. thus, two ann models are explored for prediction of coagulant and chlorine dose for a major wtp of pimpri-chinchwad municipal corporation (pcmc), maharashtra, india. ii. materials and methods a. study area the wtp under study is located in pcmc, maharashtra, india, 18°37'33.87'' n and 73°48'43.76''e. this wtp supplies 428mld of water to an area of 177km 2 with 117,936 water connections and 59 elevated service reservoirs. corresponding author: alka s. kote engineering, technology & applied science research vol. 9, no. 3, 2019, 4176-4181 4177 www.etasr.com kote & wadkar: modeling of chlorine and coagulant dose in a water treatment plant by artificial … b. methodology this study presents an ann-based methodology for the prediction of chlorine and coagulant dose in a wtp. chlorine dose models were developed with input variables the coagulant dose, outlet water turbidity, and residual chlorine and the chlorine dose as the output variable. similarly, coagulant dose models are developed with input variables the inlet and outlet water turbidity, and coagulant dose as the output variable. daily data of inlet and outlet water quality were collected from the plant laboratory over a period of four years (2012-2016). ann models were developed using matlab version 16. four ann models are developed: rbfnn, feed-forward neural network (ffnn), cascade feed forward neural network (cfnn) and grnn by trial and error method with modifying input variables, hidden nodes, training functions, spread factor (sf), and epochs for improving the models’ performance. the establishment of an optimum number of hidden nodes in ann applications is always a challenging task. there is no precise and easy way to achieve the optimum number of nodes in each layer [17-20]. to build hidden neurons in a hidden layer in this study, information of nodes in both input and output layers is used. during the development of the ann models, training and testing data are split into 75:30 and 80:20 respectively. diversified training functions such as bayesian regularization (br), levenberg-marquardt (lm), resilient back propagation (rp), bfgs quasi-newton (bfg), one step secant (oss), conjugate gradient back propagation (cgb), conjugate gradient back propagation with fletcher-powell (cgf), variable learning rate gradient descent (vlrgd), gradient descent (gd), gradient descent with momentum (gdm) are used for the development of ffnn and cfnn models. it has been reported that the sf of 1 and 0.1 provided the best testing performance of the rbfnn and grnn models respectively [10]. therefore, in this study, both rbfnn and grnn models are tried for sf ranging from 0.1 to 15. the performance of these ann models is quantified by using standard statistics which means (х̅), standard deviation (σ), skewness (ɣ1), kurtosis (ɣ2) and error statistics such as the coefficient of regression (r), mean square error (mse), and mean absolute error (mae). the best performing ann model is selected for its highest r and lowest mse and mae values. also, the mapping of predicted series with observed series is checked for standard statistics, time series plots and scatter plots. two guis for prediction of chlorine and coagulant dose were developed for the best model in each category. iii. results and discussion based on the above explained methodology, 48 ann models for prediction of chlorine dose and 44 ann models for prediction of coagulant dose were developed. the networks were rigorously trained and the performances of the training functions are shown in table i. it is found that training functions lm and br are highly effective (r=0.943 and r=0.947 respectively) for ffnn and cfnn. the other training functions showed very poor correlation between the observed and the predicted values. therefore, lm and br training functions are used for further development of the best models. table i. training function performance training stage training function r lm 0.943 br 0.947 bfg -0.866 rp 0.142 cgb -0.729 cgf -0.882 oss 0.016 vlrgd -0.591 gd -0.321 gdm 0.187 a. chorine dose ann model chlorine dose ann models were developed using 1849 data samples of input variables, namely coagulant dose, outlet water turbidity, and residual chlorine and chlorine dose as the output variable. these variables are closely associated with chlorination process. ann models namely model i, ii and iii were developed by varying input variables. 1) chorine dose ann model i for the development of the ann model i, one input variable, viz coagulant dose is adopted. sixteen ffnn, cfnn, rbfnn, and grnn models were developed. these models were compared using performance measures and it was observed that all the models resulted in poor performance (r<0.72). figure 1 shows the plot of the observed and predicted series of ffnn, cfnn, rbfnn, and grnn chlorine dose models during the testing. fig. 1. comparison of best chlorine dose ann model i (testing stage) 2) chorine dose ann model ii for the development of ann model ii, two input variables, coagulant dose and residual chlorine were adopted. several ffnn, cfnn, rbfnn, and grnn models were developed and tested to get an appropriate network that provided satisfactory performance. standard statistics were observed engineering, technology & applied science research vol. 9, no. 3, 2019, 4176-4181 4178 www.etasr.com kote & wadkar: modeling of chlorine and coagulant dose in a water treatment plant by artificial … during the testing stage. σ varied from 0.036 to 0.128, ɣ1 varied from -1.713 to -8.717 and ɣ2 from 17.667 to 89.15. similarly, error statistics such as mse varied from 0.001 to 0.020, mae from 0.015 to 0.120 and r from 0.695 to 0.97. however, there is prominent supremacy in prediction by rbfnn 2 model with an sf of 0.1. the comparison of the best chlorine dose ann model ii among ffnn, cfnn, rbfnn, and grnn models is shown in figure 2. fig. 2. comparison of best chlorine dose ann model ii (testing stage) 3) chorine dose ann model iii for the development of the ann model iii, three input variables, coagulant dose, outlet water turbidity and residual chlorine were adopted. for rbfnn and grnn models, the values of sf varied from 0.1 to 15 whereas training functions varied for ffnn and cfnn models and minimum/maximum values of performance parameters were noted. the developed models were tested in order to get an appropriate network that provided satisfactory performance. a comparison of the best chlorine dose ann model iii among ffnn, cfnn, rbfnn, and grnn models is shown in figure 3 where the nature of plot of predicted chlorine dose by rbfnn3 model is closely associated with the observed chlorine dose. the performance of all ann models is displayed in table ii, indicating minimum and maximum values of standard statistics and error statistics. standard statistics variation was as follows: σ varied from 0.026 to 1.005, ɣ1 from -10.24 to 1.032 and ɣ2 from 5.309 to 110.45. similarly, the error statistics variation was: mse varied from 0.001 to 1.069, mae varied from 0.009 to 0.98 and r from -0.237 to 0.99. the rbfnn model with sf 0.1 produced the highest r compared to all other ann models. in rbfnn and grnn models, it was found that the prediction efficiency increased, with decrease in sf value. further, ffnn and cfnn models with br training function produced good prediction when compared to all other training functions. however, these models are less efficient. fig. 3. comparison of best chlorine dose ann model iii (testing stage) table ii. minimum and maximum values of standard and error statistics of chorine dose ann model iii model min/max values standard statistics error statistics х̅ σ ɣ1 ɣ2 r mse mae rbfnn min 1.771 0.026 -10.24 7.813 -.237 1.069 0.009 max 1.949 1.005 1.032 110.45 0.999 0.001 0.391 grnn min 1.851 0.138 -3.786 11.231 0.053 0.023 0.099 max 1.91 0.166 -2.324 28.395 0.477 0.051 0.199 ffnn min 1.867 0.166 -3.107 5.309 0.239 0.025 0.1 max 1.918 0.192 -1.035 20.4 0.444 1.028 0.982 cfnn min 1.882 0.164 -2.263 4.76 0.277 0.035 0.124 max 1.898 0.234 -0.51 12.078 0.433 0.143 0.344 there is a prominent supremacy in the prediction with sf ranging from 0.1 to 1 in rbfnn models. therefore, the performance parameters of the best rbfnn models during the training and testing stages are shown in tables iii and iv. also, it is observed that rbfnn3 model gave better performance than rbfnn2 and rbfnn1. table iii. standard statistics of the best rbfnn models ann model training testing х̅ σ ɣ1 ɣ2 х̅ σ ɣ1 ɣ2 observed values 1.909 0.208 2.097 12.31 1.954 0.171 2.53 12.39 rbfnn1 1.910 0.137 -1.967 15.71 1.962 0.120 -2.43 12.28 rbfnn2 1.910 0.044 -4.286 62.15 1.954 0.036 -1.71 17.66 rbfnn3 1.910 0.026 -3.027 98.89 1.953 0.026 1.032 21.04 table iv. parameters of the best rbfnn models ann model training testing r mse mae r mse mae rbfnn1 0.715 0.014 0.068 0.753 0.018 0.077 rbfnn2 0.978 0.002 0.013 0.977 0.001 0.015 rbfnn3 0.989 0.001 0.006 0.999 0.001 0.009 table iii provides the standard statistics х̅, σ, ɣ1 and ɣ2 of the best ann models during training and testing. it was found that the rbfnn 3 model showed the lowest σ and higher engineering, technology & applied science research vol. 9, no. 3, 2019, 4176-4181 4179 www.etasr.com kote & wadkar: modeling of chlorine and coagulant dose in a water treatment plant by artificial … positive ɣ2. this lowest σ implies that the data points are near the mean of the database while the higher ɣ2 indicates the set of the database had a heavier tail as compared to a normal distribution. furthermore, in table iv the rbfnn3 model delivered excellent performance with r=0.999, mse=0.001 and mae=0.009 during testing stage. time series plot and scatter plots of rbfnn3 model during the testing stage are shown in figures 4 and 5. it is seen that the observed and predicted series of chlorine dose are close thereby indicating the best model. overall, the rbfnn model showed excellent prediction results. fig. 4. times series plot of rbfnn 3 during testing stage fig. 5. scatter plot of rbfnn models during testing stage b. coagulant dose ann model regarding coagulant dose ann models, 44 models were tried using ffnn and cfnn networks considering inlet and outlet water turbidity as input variables. the database of input and output variables required for the ann modeling consisted of 11688 data points. the training and testing data were divided as 75:30 and 80:20 during model building. the development of ann models was carried out through several steps of training and testing with various training functions as depicted in section ii (b). it was observed that br and lm training functions gave good r-values 0.947 and 0.944 respectively whereas rp, oss and gdm showed poor performance and bfg, cgf, cgb, vlrgd, and gd showed negative correlation, indicating their incapability. therefore, lm and br training functions were used for development of ffnn and cfnn models namely ffnn1, ffnn2, cfnn1, and cfnn2. during the development of these models, hidden nodes varied from 15 to 60, and corresponding r was found to range between 0.936 to 0.947. it wass observed that the best performance was produced by a cfnn model using br training function with hidden node number=40, with r=0.952 for training, r=0.922 for testing, and overall r=0.947. the cfnn model, due to the weighted connections of input layer with the hidden and output layers, mapped the input-output relationship very well. also, br training function delivers a decisive benchmark for finishing the training step and counters overtraining of the network. table v shows the performance of the best models during the testing stage. it is seen that both ffnn and cfnn models perform equally good, however cfnn model showed a slightly better prediction. in the testing stage, the cfnn model showed a reduction in mse (46.85%). the error statistics of the cfnn model are very near to the observed values. the prediction of coagulant dose by the developed best cfnn2 model during testing stage was carried out with 248 data points. the observed coagulant dose at the wtp is constant for a specific period, which is indicated by the straight line, whereas predicted coagulant dose by cfnn2 model shows variation as shown in figure 6 table v. performance comparison of the best ann models ann models training function epochs hidden nodes r mse ffnn1 model lm 26 60 0.944 185.09 ffnn2 model br 500 50 0.945 113.13 cfnn1 model lm 36 60 0.943 59.22 cfnn2 model br 500 40 0.947 99.28 fig. 6. prediction of coagulant dose by the best cfnn2 model during the testing stage it is seen that the predicted values of the coagulant dose do not follow the pattern of the actual coagulant dose from 60 to 90 data points. this could be due to a wide range of data points of inlet water turbidity as well as coagulant dose during the ann training. despite the significant variations, the average actual coagulant dose and predicted coagulant dose show a similar trend. among all the models, the cfnn2 model gave the best performance with r=0.947 and mse=99.28. therefore, the cfnn model is more capable and precise in the modeling of the coagulation process. iv. model implementation the presence of residual chlorine in the wdn is a major concern in india due to water leakage and distribution issues. engineering, technology & applied science research vol. 9, no. 3, 2019, 4176-4181 4180 www.etasr.com kote & wadkar: modeling of chlorine and coagulant dose in a water treatment plant by artificial … hence, the required residual chlorine at the outlet of wtp is an important aspect for the distribution network. two guis were developed to determine chlorine and coagulant dose using the best performed rbfnn3, and cfnn2 models respectively (figures 7-8). in the gui of chlorine dose, the chlorine dose is predicted by using coagulant dose, outlet water turbidity, and residual chlorine. the plant operator can decide the chlorine dose as per desired residual chlorine (0.2mg/l) at the end of wdn. similarly, in the gui of coagulant dose, the plant operator can decide the coagulant dose by using inlet water turbidity and outlet water turbidity (less than 5ntu). fig. 7. snap shot of the chlorine dose ann model gui fig. 8. snap shot of coagulant dose ann model gui v. conclusion the chlorine and coagulant dose in a wtp are typically determined through laboratory analysis that requires a long experimental time. thus, guis were developed for chlorine and coagulant dose using anns. during the ann development, it was observed that br training function had better prediction capability than lm, rp, bfg, oss, cgb, cgf, vlrgd, gd and gdm. among all chlorine dose ann models, the rbfnn3 model (r=0.999) delivered the most excellent performance. one of the most important findings of the study is that the decreasing order of sf increases the performance of rbfnn and grnn models. for the development of coagulant dose models, it was found that the number of input variables increased the performance of ann models. all ffnn and cfnn models with lm and br training functions performed well especially for lower values of coagulant dose. however, higher values showed under prediction. cfnn2 model (r=0.947) with br training function provided the best prediction for the coagulant dose. the guis of the best ann models will be very useful tools to plant operators and managers for deciding the required chlorine and coagulant dose. references [1] d. wu, l. shang-lien, “predicting real-time coagulant dosage in water treatment by artificial neural networks and adaptive-network-based fuzzy inference system”, engineering applications of artificial intelligence, vol. 21, pp. 1189–1195, 2011 [2] o. bello, y. hamam, k. djouani, “coagulation process control in water treatment plants using multiple model predictive control”, alexandria engineering journal, vol. 53, no 4, pp. 420-435, 2014 [3] m. s. gibbs, n. morgan, h. r. maier, g. c. dandy, j. b. nixon, m. holmes, “investigation into the relationship between chlorine decay and water distribution parameters using data-driven methods”, mathematical and computer modelling ,vol. 44, no. 5-6, pp.485–498, 2006 [4] m. w. lechevallier, k. k. au, water treatment and pathogen control: process efficiency in achieving safe drinking water, iwa publishing, 2004 [5] j. a. crump, g. o. okoth, l. slutsker, d. o. ogaja, b. h. keswick, s. p. luby, “effect of point-of-use disinfection, flocculation and combined flocculation disinfection on drinking water quality in western kenya”, journal of applied microbiology, vol. 97, no. 1, pp. 225–231, 2004 [6] e. hood, “tap water and trihalomethanes: flow of concerns continues”, environmental health perspectives, vol. 113, no. 7, pp. 472-474, 2005 [7] m. m. hamed, m. g. khalafallah, e. a. hassanien, “prediction of wastewater treatment plant performance using artificial neural networks”, environmental modelling, vol. 19, no. 10, pp. 919-928, 2004 [8] p. hajela, l. berke, “neurobiological computational modes in structural analysis and design”, computers & structures, vol. 41, no. 4, pp. 657– 667, 1991 [9] a. robenson, s. r. a. shukor, n. araiz, “development of process inverse neural network model to determine the required alum dosage at segama wtp, sabah, malaysia”, 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neural networks for predicting optimal alum doses and treated water quality parameters”, environmental modelling & software, vol. 19, no. 5, pp. 485–494, 2004 [15] b. larmrini, a. benhammou, m. v. le lann, a. karama, “a neural software sensor for online prediction of coagulant dosage in a drinking wtp ”, transactions of the institute of measurements and control, vol. 27, no. 3, pp. 195-213, 2005 [16] d. wadkar, a. kote, “prediction of residual chlorine in a water treatment plant using generalized regression neural network”, international journal of civil engineering and technology, vol. 8, no. 8, pp. 1264–1270, 2017 engineering, technology & applied science research vol. 9, no. 3, 2019, 4176-4181 4181 www.etasr.com kote & wadkar: modeling of chlorine and coagulant dose in a water treatment plant by artificial … [17] f. khayatian, l. satro, g. dallo, “application of neural networks for evaluating energy performance certificates of residential buildings”, energy and buildings, vol. 125,pp. 45-54, 2016 [18] hecht-nielsen, “theory of the back-propagation neural network”, international joint conference on neural networks, washington, usa, august 6, 1989 [19] y. najjar, i. basheer, m. hajmeer, “computational neural networks for predictive microbiology methodology”, international journal of food microbiology, vol. 34, no. 1, pp. 27–49,1997 [20] l. m. salchenberger, m. cinar, n. a. lash, “neural networks: a new tool for predicting thrift failures”, decision sciences, vol. 23, no. 4, pp. 899–916, 1992 microsoft word 38-2749_s_etasr_v9_n3_pp4276-4280 engineering, technology & applied science research vol. 9, no. 3, 2019, 4276-4280 4276 www.etasr.com sohu et al.: controlling measures for causes of cost overrun in highway projects of sindh province controlling measures for cost overrun causes in highway projects of sindh province samiullah sohu department of civil engineering, quaide-awam university of engineering, science and technology, sindh, pakistan engr.samiullah@quest.edu.pk abd halid abdullah faculty of civil and environmental engineering, universiti tun hussein onn malaysia, johor, malaysia abdhalid@uthm.edu.my sasitharan nagapan faculty of civil and environmental engineering, universiti tun hussein onn malaysia, johor, malaysia sasitharan@uthm.edu.my touqeer ali rind department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan touqeerali@muetkhp.edu.pk ashfaque ahmed jhatial department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan ashfaqueahmed@muetkhp.edu.pk abstract—cost overrun is a serious issue in the construction industry worldwide, including pakistan. cost overrun is a critical and serious issue found in highway projects among all construction projects in pakistan. cost overrun occurs when the final cost of the projects exceeds the actual cost of the project. the main objective of this research is to identify the main causes of cost overrun and to determine possible mitigation measures of the identified main causes of cost overrun from contractors of highway/road projects of pakistan. in this study, a mixed mode (quantitative and qualitative) approach was used. a deep literature review helped to identify the 30 most common causes of cost overrun in the construction industry. in the first stage, a questionnaire was developed, and a survey was carried out among professional and experts who were working with contractors in highway projects. in the second stage, a semistructured questionnaire was developed, and a survey was carried out to determine the possible mitigation measures of the identified main causes of cost overrun. collected data for the first stage from experts were inserted in spss and were analyzed by using the average index method and the data of the second stage were analyzed by content analysis. it is expected that the findings of this research will be useful and helpful for the construction stakeholders to control and mitigate the major causes of cost overrun. keywords-cost overrun; highway projects; contractors; controlling measures i. introduction the construction industry is known as a major source of economic growth of any country [1]. the construction industry advances the quality standard of living by the construction of infrastructures such as schools, roads, hospitals, etc. [2]. the construction industry is known as a complex in nature and fragmented industry, therefore it is facing critical problems of cost overrun, low quality, time overrun, construction waste, low productivity, etc. out of these problems, cost overrun is one of the major ones as money is always of high importance [3, 4]. cost overrun is a serious issue for developing and developed countries [5]. the basic definition of cost overrun is that the final cost is higher than the one that was budgeted in an earlier stage [6]. in qatar construction industry more than 50% of construction projects faced serious issues of cost overrun [7, 8]. as reported in [9], 60% of construction projects in singapore were badly affected by cost overrun. according to [10] most construction projects have an experience of an average increase in cost of more than 33%. cost overrun or budget overrun in the construction projects is known as a universal and regular phenomenon whereas only a few projects are rarely completed within the approved and estimated budget [11]. according to [12], cost overrun is more than 100% of the total cost of a project in both developed and developing countries. pakistan construction industry is also facing this serious issue [13, 14], but the issue occurs mostly in highway projects. construction projects of pakistan have faced the issue of cost overrun and most projects have crossed 50% from the actual cost of the project [15]. although various studies have been conducted on cost overrun in construction projects, only a few have found mitigation measures of the major causes of cost overrun, probable because the causes vary from country to country [16]. pakistan is a developing country, facing the issue of cost overrun in all types of construction projects especially in highway projects. therefore, there is a need to explore the major causes of cost overrun in highway projects and determine ways to cope with the problem. hence, the research objectives of this research are: • to find the major causes of cost overrun in highways/road projects in pakistan. • to determine possible mitigation measures from experienced respondents for the identified causes. corresponding author: samiullah sohu engineering, technology & applied science research vol. 9, no. 3, 2019, 4276-4280 4277 www.etasr.com sohu et al.: controlling measures for causes of cost overrun in highway projects of sindh province ii. literature ρeview many researches have studied the causes of cost overrun in different types of construction projects and as a result a number of causes of cost overrun in construction have been found. authors in [17] identified the most critical causes of cost overrun in construction projects in afghanistan by conducting a questionnaire survey of 75 respondents from different organizations. the results of the survey concluded that the major causes which affect the total cost of the construction project were delay in process of payments by the client to the contractor, corruption in tendering and billing, financial difficulties, problems faced by the contractor/builder, security issues at the construction site, market inflations, and sudden changes from the client. authors in [18] carried a quantitative survey which aimed to identify the major causes of cost overrun in cambodia construction projects. the results of the survey showed that mistakes in the estimation of project cost, lack of communication, and unsuitable construction methods were the main causes of cost overrun. authors in [19] carried a survey regarding construction projects of india to find the major causes of cost overrun. a questionnaire was distributed among 190 professional experts in the construction industry. the results identified that escalation in raw materials, lack of communication between parties, frequent and sudden design changes, wastage and misuse of materials at the construction site, labor disputes, lack of on-site financial control, owner interference, mistakes during construction, relationship issues, and labor and management issues were the major reasons. a research was conducted in palestine construction industry by conducting a survey through the distribution of 151 questionnaires to contractors, clients and consultants [20]. through analysis of the collected data, it was revealed that material, design and documentation, professional management, contractual relationships, external factors, owner’s responsibilities, government relations, contractor’s responsibilities, consultant’s responsibilities, labor and equipment were the major causes of cost overrun. authors in [21] carried a questionnaire survey and interviewed professionals and experts of the construction industry in south africa. the outcome of the survey was that incomplete information at the time of tendering, changes in the scope of the project, contractual claims, improper planning for funds, additional works and improper fund monitoring were found as the main causes of cost overrun. authors in [22] investigated the main causes of cost overrun in uganda's construction projects by conducting a questionnaire survey. the results of the survey showed that the main causes of cost overrun were high-interest and inflation rates, changes in the scope of the project, poor control and poor monitoring, deficiencies in contract documents, and delay in the process of payments. authors in [16] recognized the causes of cost overrun by using quantitative method. the main causes were contactor poor site management, additional work, poor supervision, poor project management assistance, rapid design changes, delayed payments of completed works, material cost, unforeseen site conditions, shortages and delay of material arrival at the site, and inaccurate estimates. based on [23-36], thirty common causes of cost overrun were identified: inadequate planning, delay in payment process by client, owner interference, poor contract management, delay in decision making, shortage of material, fluctuation in price of materials, financial difficulties by contractor, poor site management, natural disasters, change in material specifications and type, poor financial control at site, mistakes and errors in design, lack of experience of the technical consultant, additional works, mistakes and discrepancies in contract document, accidents, poor design, severe overtime, fraudulent practices and kickboards, the relationship between management and labor, delay in approval, problems with neighbours, complicated design, incompetent subcontractor, inadequate monitoring, inaccurate site investigation, schedule delay, and high labor cost. author in [37] conducted research by using the structured questionnaire approach to identify the major factors of cost overrun in transport/highway projects in canada. results of the research were that external factors, problems in the estimated cost, changes in design and other conditions were the major factors. authors in [38] conducted research to find the main causes of cost overrun in highway projects in the uk. the main causes of cost overrun turned out to be changes in design, inflation, changes in the price of materials, complex nature of the project, changes in the scope of the project, contract procedure and inadequate procurement in transport projects of united kingdom. iii. research methodology to achieve the objectives of this research, a mixed mode (questionnaire survey and semi-structured questionnaire survey) approach was used. the process of the research method is given below. an extended literature review was conducted on cost overrun in construction projects, which helped to identify 30 causes of cost overrun in construction projects. a questionnaire was developed consisting of two parts, namely part a and part b. part a was designed to obtain the personal information of the respondents. part b comprised of the common cost overrun causes. a five-point likert scale was used. its numeric values ranged from 1 for “extremely significant to 5 for “not significant”. a pilot a study was carried out to check the relevancy of cost overrun causes given in the questionnaire to highway project contractors. the participants were 40 contractors. a total of 39 complete answered questionnaires were received from the respondents and all were valid and considered for further analysis. the response rate for this research was 96%. mean value (mv) was used to rank the cost overrun causes in highway projects of pakistan. the cut-off scale was adapted from [39] for the relevancy of cost overrun causes to highway projects, as shown in table i. table i. test specifications and conditions mean score level of relevancy below 4 non-relevant above 4 relevant pilot b: a semi-structured questionnaire survey was carried out among 30 professionals and experts working with contractors in handling highway projects, in order to engineering, technology & applied science research vol. 9, no. 3, 2019, 4276-4280 4278 www.etasr.com sohu et al.: controlling measures for causes of cost overrun in highway projects of sindh province determine possible mitigation measures for the major nine cost overrun causes which were identified by an actual questionnaire survey. the collected data were analyzed by content analysis. the educational level and occupation of the respondents are shown in figures 1 and 2. fig. 1. academic qualification of respondents fig. 2. occupation of respondents a quantitative questionnaire was designed and distributed among 100 selected respondents from contractors of highway projects to identify the most significant mitigation measures of major causes of cost overrun. the occupation and the educational level of the selected respondents (contractors) for the actual questionnaire are presented in figures 3 and 4. the collected data from the actual questionnaire survey were evaluated using spss with mv. fig. 3. occupation of respondents iv. data analysis, results and discussion the statistical package for the social sciences (spss) version 22 was used to check the data off stage one questionnaire. cronbach’s alpha (α) was used to check the reliability of the collected data from the questionnaire survey. the result of the reliability test was 0.894. according to [40] if the value of cronbach’s alpha is more than 0.7, then the data are valid and reliable and if the value of cronbach’s alpha is below 0.7, then the data are not valid and reliable. thus, since the value of α was above 0.7, the collected data are valid. table ii shows the major causes of cost overrun which were calculated by using the average index method and having mean value more than 4.0. table ii shows that “inadequate planning” scored the highest mean value of 4.624 and ranked as the first cause of cost overrun in highway projects. it was followed by “frequent design changes” and “financial difficulties faced by the client”. fig. 4. academic qualification of respondents table ii. major causes of cost overrun major causes mean value rank inadequate planning 4.624 1st frequent design changes 4.468 2nd financial difficulties faced by the client 4.468 3rd owner interference 4.309 4th delays in decision making 4.298 5th fluctuation of the process in the material 4.213 6th poor contract management 4.188 7th mistakes in design 4.115 8th shortage of labor 4.027 9th a. mitigation measures for the major causes of cost overrun table iii shows the results of the semi-structured questionnaire survey. the possible mitigation measures for major cost overrun causes regarding construction were investigated. these mitigation measures were analyzed by content analysis technique. the results of the semi-structured questionnaire helped get the possible mitigation measures of the 9 main causes of cost overrun. each cause has a minimum of four possible mitigation measures. b. significant mitigation measures of major causes of cost overrun table iv represents the results of the structured questionnaire survey. the most significant mitigation measures for major cost overrun causes were identified by using mean value (mv). the most significant mitigation measures of the major causes of cost overrun had the highest mv. from the at least four possible mitigation measures, the measure having the highest mv was selected as the most significant one. a total of nine significant mitigation measures were identified, one for each of the respective main causes of cost overrun in highway projects. engineering, technology & applied science research vol. 9, no. 3, 2019, 4276-4280 4279 www.etasr.com sohu et al.: controlling measures for causes of cost overrun in highway projects of sindh province table iii. semi-structured questionnaire for mitigation measures of major causes of cost overrun results causes mitigation measures frequency inadequate planning the client should plan each activity before starting the project 27 the planning committee should visit the site before tendering project 24 competent staff should be appointed in the planning section 20 the project should be planned as per its scope/need 18 frequent design changes the complexity of contract/wrong concept/formulation should be avoided 27 violation of environmental and human safety should be avoided 24 competent and well-experienced engineers should be posted/appointed 20 details should be provided 18 financial difficulties faced by the client sufficient funds should be kept for each project 27 donor/investor should start a project on the availability of funds 25 funds of the project should not be transferred to other projects 24 government should allocate funds on time 21 owner interference appointment of favoured contractors should be avoided 26 approval and procedural delays should be avoided 23 changes in key posts should be avoided 20 political appointments should be avoided 17 delay in decision making sufficient data & details should be provided to take decisions 27 a competent and qualified team should be appointed to take decisions 25 favoritism and nepotism should be avoided 24 communication between parties should be adopted to expedite activities at project 22 the client should arrange frequent meetings with all involved engineers 19 fluctuation of material prices proper planning and scheduling should be adopted 28 proper policies should be adopted by the government 26 sufficient material should be stored 25 inordinate delay in project implementation should be avoided 23 poor contract management a qualified team should be appointed until the completion of the project 26 planning and scheduling should be done for every activity 23 coordination between parties should be adopted 22 daily routine matters should be recorded at the site 20 mistakes in design favoritism should be avoided 29 experienced consultant in highway construction should be appointed 27 experienced staff under consultant should be appointed 25 consultants profile should be evaluated before awarding of the project 23 shortage of labor sufficient facilities should be given to skilled labor 28 high wages should be paid to skilled labor 26 training should be given to unskilled labor 25 government should adopt policies so that maximize skilled labor 22 table iv. μajor causes and mitigation measures major causes mitigation measures mv inadequate planning the client should plan each activity before starting the project 4.592 frequent design changes details should be provided 4.297 financial difficulties faced by the client donor/investor should start a project on the availability of funds 4.319 owner interference approval and procedural delays should be avoided 4.571 delay in decision making a competent and qualified team should be appointed to take decisions 4.329 fluctuation of material prices proper policies should be adopted by the government 4.571 poor contract management a qualified team should be appointed until the completion of the project 4.331 mistakes in design experienced consultant in highway construction should be appointed 4.297 shortage of labor sufficient facilities should be given to skilled labor 4.235 v. conclusion cost overrun is one of the major and serious issues the construction industry is facing, especially in highway projects. a thorough literature review was conducted, and a questionnaire was designed consisting of 30 main causes identified from previous studies. out of these 30 causes, 9 major causes of cost overrun were identified from professionals working with contractors in highway projects of pakistan. a semi-structured questionnaire survey offered a source of information based on the participants’ experience in relation to controlling major causes of cost overrun. a structured questionnaire was designed on the findings of the semistructured questionnaire and was distributed among 100 randomly selected respondents working with contractors, which helped to identify the most significant controlling measures for the major causes of cost overrun in highway/road projects. the findings of this research are going to be useful to the stakeholders of the construction of highway projects. references [1] a. a. jhatial, s. sohu, n. k. bhatti, m. t. lakhiar, r. oad, “effect of steel fibres on the compressive and flexural strength of concrete”, international journal of advanced and applied sciences, vol. 5, no. 10, pp. 16–21, 2018 [2] y. al-emad, n. hamid, structural relationships model of delay factors in makkah construction industry, universiti tun 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chamuriho, n. m. lema, “an investigation into materials wastes on building construction projects in kampala-uganda”, scholarly journal of engineering research, vol. 1, no. 1, pp. 11–18, 2012 [40] l. xin, w. rong, “survey research on relationship among service failures, service recovery and customer satisfaction”, international conference on management science and engineering, harbin, china, august 20-22, 2007 microsoft word 36-2538_s engineering, technology & applied science research vol. 9, no. 1, 2019, 3859-3862 3859 www.etasr.com iqbal et al.: an experimental study on the performance of calcium carbonate extracted from … an experimental study on the performance of calcium carbonate extracted from eggshells as weighting agent in drilling fluid raheel iqbal institute of petroleum & natural gas engineering, mehran university of engineering & technology, jamshoro, pakistan 15pg46@students.muet.edu.pk muhammad zubair institute of petroleum & natural gas engineering, mehran university of engineering & technology, jamshoro, pakistan 13pet04@students.muet.edu.pk fawad pirzada institute of petroleum & natural gas engineering, mehran university of engineering & technology, jamshoro, pakistan fawadpirzada8@gmail.com faisal abro institute of petroleum & natural gas engineering, mehran university of engineering & technology, jamshoro, pakistan faisal.abro@hotmail.com muhammad ali institute of petroleum & natural gas engineering, mehran university of engineering & technology, jamshoro, pakistan muhamadali5014@gmail.com avinash valasai department of mining engineering, mehran university of engineering & technology, jamshoro, pakistan amvalasai@gmail.com abstract—drilling mud density is an important factor in drilling operations. the cost of the drilling mud used for oil and gas well drilling can be 10%-15% of the total drilling cost, and the deeper the well, the more the needed drilling mud. this research aims to prepare a mud that provides performance similar to the conventional mud and to lower down the dependency of primordial caco3 technology by exploring it from trash/polluted and naturally occurring materials. for that purpose, a mud was prepared by replacing primordial caco3 with caco3 derived from eggshells, as eggshells contain caco3 in high amounts ranging from 70% to 95%. the success of this project will provide an affordable solution and an alternative way to explore new methodologies of obtaining caco3. the obtained results of this research are quite satisfactory. caco3 obtained from eggshells is used in high amounts, 275–410g to achieve density ranges from 9.5 to 11.0 pounds per gallon whereas, the needed quantity of pure caco3 is 150g to obtain density of 10.5 pounds per gallon. apart from this, it is also observed that eggshell based caco3 samples are more efficient in rheological properties compared to the market samples of caco3. the ph of pure caco3 sample of 10.5 pounds per gallon density is almost the same with the sample of eggshell caco3 of 10.5 pounds per gallon density. keywords-drilling fluid; weighting agent; mud balance; calcium carbonate; rheological properties i. introduction drilling fluid has obligatory properties like carrying out rock cutting towards the surface, cleaning and cooling the pit, decreasing resistive forces, stabilizing wellbore, and preventing fluids to flow from pores into the borehole. various methods for designing suitable drilling muds are developed for avoiding problems encountered during drilling. the drilling mud should be user friendly, cost effective and economically viable. therefore drilling muds are basically formulated to decrease the effect of damage and to ensure the possibility and economically viability of rotary drilling in hydrocarbon containing formations. the filter cakes which are formed after the intrusion of drilling mud in the pore space of pay zone are compressible and contain varying porosity and permeability characteristics, with low void spaces at the filter channel surface and maximum void spaces on cake surface. in order to reduce filtrate invasion, fluid loss additives such as organic polymers which prohibit water invasion are used. during the formulation of the mud, the microscopic structure and composition of the filter cake related to it and the information of the characteristics of filtration are of main importance [1]. during drilling and completion varying drilling muds in the borehole are used. the most significant factor is the physical and chemical compatibility of the mud with the reservoir rock. by formation damage these muds can reduce the productivity of the well by invasion. consequently additives are used i.e. caco3,which can reduce the chance of these damages in the formations by forming a filter cake of low permeability (optimum thickness) that reduces further invasion of solids and filtrate the pore spaces of rock. after drilling these cakes are washed by for maximizing the flow in the wellbore. fluid loss and viscosity of mud are important factors which must be investigated throughout the drilling of a well [2]. for that reason, mud is treated with several types of additives i.e. different polymers and chemicals, to achieve requirements important for the particular well such as rheology, control of corresponding author: r. iqbal engineering, technology & applied science research vol. 9, no. 1, 2019, 3859-3862 3860 www.etasr.com iqbal et al.: an experimental study on the performance of calcium carbonate extracted from … fluid loss, weight of mud etc. starch and calcite are the most important materials used to control fluid loss and to increase the weight of mud by forming mud cake respectively [3]. ii. experimental work a. caco3 analysis in eggshells by titration technique calcite is a major component of eggshells ranging from 70% to 95%. the technique of titration named as back titration is used for the reaction of acids with calcium present in the blended powder of eggshells. calcium dissolves in acids rather than pure water: caco3(s) + 2hcl(aq) → cacl2(aq) + h2o(l) + co2(g) this reaction is slow mostly when it reaches completion hence this technique cannot be directly used. sufficient amount of acid must be added to dissolve all the calcium carbonate. then, sodium hydroxide will be added that will react with the remaining hcl. the unreacted amount is calculated by determining the difference between the amount of hcl that was added initially and the amount of hcl that remained after the titration. the caco3 amount present in the sample is calculated as discussed. given equation is used to determine the amount of caco3 in the sample: naoh(aq) + hcl(aq) → h2o(l) + nacl(aq) b. drilling fluid preparation and properties a few additives along with barite baso4, calcite caco3 are commonly used in water-based drilling mud. the three main factors which affect drilling fluid performance are density, viscosity and ph. fluid samples preparation at laboratory scale is obtained by adding chemicals taken in grams into 350ml barrels (standard laboratory barrel). this research involves the preparation of five water-based drilling fluid samples which contain bentonite as a filtration controller and viscosifier, caustic soda for ph control, and starch for filtration control. along with them, soda ash and xanthan gum are also used as hardness and rheology control materials respectively. the composition of all these additives is constant for all prepared samples except calcite. the most important part of these samples is the concentration of caco3 as a weighting agent. it is used to increase densities of samples from 9.0 to 11 pounds per gallon (ppg). the required amount of caco3 as a weighting agent is determined by: 945 2 1 weighting agent sacks/100 barrels) 22 5 2 ( ( ) . w w w − = − (1) and the formula to determine the required amount of barite as a weighting agent can be written as: ( ) 2 weighting agent sacks/100 ba 1470 2 1 5 rrels 3 ( )w w w − = − (2) where, w1 is indicating the initial weight of mud (ppg) and w2 is indicating the required weight of mud (ppg). c. density of mud mud density is the main parameter to consider during study as it directly affects the formation of filter cake. the most common additive to increase the mud weight in production zones is mostly calcite (caco3) which is widely used during drilling of zone of interest. five drilling mud samples by formulating both calcites (pure calcium carbonate, eggshell calcium carbonate) are prepared in this study to achieve densities ranging from 9.5 to 11.0 ppg. the amount used for the formulation of pure calcite base sample is 150g as shown in table i, and the amount for the formulation of eggshells based samples ranges from 275g to 410g as shown in figure 1 to achieve mud density from 9.5 to 11.0 ppg. fig. 1. amount of calcium carbonate vs densities d. drilling fluid rheological properties rheological properties are categorized in gel strength, yield point and apparent viscosity. rheology is the basis of all investigations ranging from hydraulics of wellbore to the evaluation of mud system functionality. mud rheological properties are continuously tested throughout the drilling operation. mud rheological properties are very critical to maintain control while tackling the wellbore problems, because inappropriate rheological properties may result in loss of time and money. besides rheological properties, filtration, ph, chemical analysis (alkalinity and lime content, chloride content, calcium content, etc.), and resistivity are also tested throughout the drilling. in the laboratory (as in the drilling site), a rotational viscometer is frequently used to measure the rheological properties of mud. readings are taken on 600, 300, 200, 100, 60, 30 and 6rpm (rotations per minute). later these readings are plotted on a chart of shear stress and shear rate which are used to determine viscosity and appropriate viscosity model. rotational viscometer also provides the information about other rheological properties, including effective viscosities (µa, µp, and µe), gel strength (gel) and yield point (yp) as shown in table ii. given equations are utilized for these purposes: apparent viscosity µa, (cp) = ∅��� � (3) plastic viscosity µp, (cp)= ∅600 � ∅300 (4) effective viscosity µe,(cp) = �� �∅ � (5) yield point yp, (lb/100ft 2 )=∅300 � µ� (6) shear stress τ, (lb/100ft 2 ) = 1.065 * ø (7) shear rate ɣ, sec -1 = 1.7023 * ω (8) engineering, technology & applied science research vol. 9, no. 1, 2019, 3859-3862 3861 www.etasr.com iqbal et al.: an experimental study on the performance of calcium carbonate extracted from … where, ø indicates the reading of dial, lb/100ft 2 and ω indicates rotation of rotor speed (rpm). bingham plastic model is a basic two-parameter model used in drilling industry widely to identify the properties related to flow for the different mud types. it is known as the most common fluid model to estimate non-newtonian fluids’ rheology. shear stress is a straight line function of shear rate which is the basic supposition of this model. yield point is also named as threshold stress, it is the point where shear rate is zero. by the reduction in colloidal solids, the optimum plastic viscosity (pv) is achieved. table i. drilling mud samples and its composition product per lab barrel (350 ml) sample number 1 2 3 4 5 water (ml) 325.50 325.50 325.50 325.50 325.50 bentonite (g) 24.50 24.50 24.50 24.50 24.50 barite pure caco3 (g) 150 eggshell caco3 (g) 275 320 365 410 starch (g) 0.40 0.40 0.40 0.40 0.40 caustic soda (g) 0.20 0.20 0.20 0.20 0.20 soda ash (g) 0.25 0.25 0.25 0.25 0.25 xanthanum (g) 1.00 1.00 1.00 1.00 1.00 table ii. rheological properties of mud samples sample number 1 2 3 4 5 plastic viscosity (cp) 22 10.5 17.1 23 32 apparent viscosity (cp) 38 20.5 33 39.25 50 yield point (lb/100 ft 2 ) 32 20 31.8 32.5 36 gel strength@10 min (lb/100 ft 2 ) 16.5 12.8 19.5 20 20.6 θ600 76 41 66 78.5 100 θ300 54 30.5 48.9 55.5 68 θ200 45 26.5 42 46 56 θ100 35 21.5 33 35.5 42 θ60 29 19 29 31 36 θ30 19.5 17 25 26 29 θ6 15 13 19 19.5 21 to carry cuttings out of the hole, yield point should be high enough, but not very much because pump pressure would become incompatible with drilling operation. for both low and high shear rates ranges, bingham plastic model has its own limitations. the physical/solid reason behind this behavior is that the liquid generally contains particles (clay) or large molecules (polymers) which generally have some kind of interaction, while creating a weak solid structure, known as a false body, and at that point a certain amount of stress is required to break it. under viscous forces the particles tend to move as the structure breaks. the results which are acceptable for a drilling mud diagnosis are produced by bingham plastic model. but, for hydraulic calculations its accuracy is not very high. a bingham body doesn’t begin to flow until a shearing stress, corresponding to the yield value, is exceeded. the results for the bingham plastic model are obtained by the graph between shear stress and shear rate in figure 2, plotted with the use of (6) and (7). e. drilling fluid ph determination it is important to know mud ph because it affects the solubility of the organic thinners, contaminant removal, corrosion mitigation, and the dispersion of clays present in the mud. ph is mostly used to express drilling fluid’s, especially water-based mud, acidity or alkalinity. generally, its value ranges from 0 to 14. ph is expressed by (9): ph=-log[h] (9) where, [h] is the hydrogen ion concentration in mol. ph value decreases as the acidity of the fluid increases by the addition of more hydrogen atoms. generally, ph of the neutral fluid is 7. values above 7 indicate alkaline ph below 7 indicate acidic ph. in drilling mud there are three main chemical components involved which are hydroxyl ions (oh ), carbonate ions (co3 -2 ) and alkalinity of drilling mud including (hco3 ) bicarbonates ions. for better ph measurement, ph meter is mostly used rather than the litmus paper, because ph meter provides quantitative information where litmus paper provides qualitative information about the acidity of the drilling mud. fig. 2. bingham plastic model of samples iii. results and discussion a. caco3 determination by back titration the outcomes from the back titration method for the caco3 amount can be determined by washing, boiling, peeling off the membranes, and heating of the eggshells at 120°c, and the resulting value is showing 74% presence of caco3 in the eggshells blended powder. b. characteristics of drilling fluids the densities of 5drilling fluid samples of both ordinary caco3 and eggshell caco3, ranging from 9.0 to 11.0 ppg are shown in figure 1. table ii provides comprehensive information about the rheological properties of the prepared sample. variations in rheological properties were observed with the increase of amount of caco3 of eggshells. besides this, the purpose of increased density was achieved by increasing the amount of caco3 obtained from eggshells. in general, the increment in sample density causes increment in rheological properties’ values. meanwhile, the drilling fluid sample no. 4 (based on 10.5 ppg eggshell caco3) exhibits engineering, technology & applied science research vol. 9, no. 1, 2019, 3859-3862 3862 www.etasr.com iqbal et al.: an experimental study on the performance of calcium carbonate extracted from … similar rheological property values with sample no. 1 (based on 10.5 ppg pure caco3). c. bingham plastic model it is discussed that non-newtonian fluids exhibit a relationship between shear rate and shear stress measured for the formulated samples as shown in figure 2. according to the graphs which are plotted for 5 water-based drilling fluid samples, shear stress increases with increasing amount of eggshell caco3, while pure caco3 sample no. 1 is showing almost the same trend with the sample no. 4 of eggshell caco3. a general trend line is drawn for the bingham plastic fluid and it is observed that the yield point of 36ib/100ft 2 is obtained for eggshell caco3 sample no. 5, and it is also measured by viscometer and discussed in table ii. d. ph determination the ph of the prepared sample is determined by using ph meter and the obtained results are shown in figure 3. if a comparison is generated between the calcite based samples of same densities then it is observed that the sample no. 1 of pure caco3 has almost the same ph value with the sample no. 4 of eggshell caco3 with 10.5 ppg density, which indicates that there is no impact of the amount of caco3 on the ph of both samples. the required amounts for both samples are varying but as density reached 10.5 ppg for both samples, they show almost the same ph. fig. 3. ph of samples iv. conclusion on the basis of laboratory measurements analysis and interpretation, the main concluded points are: • mud density of 10.5lb/gal is optimum for the x well. it was selected among 5 prepared mud densities, considering that it can sustain formation pressure. by using another mud density the formation starts to create fractures in the well. • caco3 obtained from eggshells is used in higher amounts from 275g to 410g to achieve densities ranging from 9.5 to 11.0lb/gal. pure caco3 took only 150g to obtain density of 10.5lb/gal. apart from this, it is also observed that eggshell caco3 samples are more efficient in rheological properties than the samples from market caco3. • it is observed that the ph of pure caco3 sample of 10.5lb/gal has almost the same value with the sample of eggshell caco3 of 10.5lb/gal density. • it was observed that the prepared samples of eggshells caco3 are producing unpleasant smell after 1-2 days of preparation. • however, by heating the eggshells at a temperature ranging from 300°c to 500°c, better results for the amount of caco3 will be obtained. by doing this the efficiency of the caco3 is improved as the acids which are present in the shells are removed and the smell dissipates. references [1] k. a. fattah, a. lashin, “investigation of mud density and weighting materials effect on drilling fluid filter cake properties and formation damage”, journal of african earth sciences, vol. 117, pp. 345-357, 2016 [2] s. gogoi, p. talukdar, “use of calcium carbonate as bridging and weighting agent in the non damaging drilling fluid for some oilfields of upper assam basin”, international journal of current research, vol. 7, no. 8, pp. 18964-18981, 2015 [3] t. hudson, m. coffey, “fluid loss control through the use of a liquid thickened completion and work over brine”, journal of petroleum technology, vol. 35, no. 10, pp. 1776-1782, 1983 [4] m. sajjadian, e. e. motlagh, a. a. daya, “laboratory investigation to use lost circulation material in water base drilling fluid as lost circulation pills”, international journal of mining science, vol. 2, no. 1, pp. 33-38, 2016 [5] n. gaurina-medimurec, “laboratory evaluation of calcium carbonate particle size selection for drill-in fluids”, rudarsko-gcolofkonaftnizbomik, vol. 14, pp. 4753, 2002 [6] a. odabasi, an experimental study of particle size and concentration effects of calcium carbonate on rheological and filtration properties of drill-in fluids, msc thesis, middle east technical university, 2015 [7] r. samavati, n. abdullah, t. k. nowtarki, s. a. hussain, d. r. a. biak, “rheological and fluid loss properties of water based drilling mud containing hcl-modified fufu as a fluid loss control agent”, international journal of chemical engineering and applications, vol. 5, no. 6, pp. 446-450, 2014 [8] m. amani, j. k. hassiba, “the effect of salinity on the rheological properties of water based mud under high pressures and high temperatures for drilling offshore and deep wells”, spe kuwait international petroleum conference and exhibition, kuwait city, kuwait, 10-12 december, 2012 [9] p. k. jha, v. mahto, v. k. saxena, “emulsion based drilling fluids: an overview”, international journal of chem tech research, vol. 6, no. 4, pp. 2306-2315, 2014 [10] p. talalay, z. hu, h. xu, d. yu, l. han, j. han, l. wang, “environmental considerations of low-temperature drilling fluids”, annals of glaciology, vol. 55, no. 65, pp. 31-40, 2014 [11] p. o. ogbeide, s. a. igbinere, “the effect of additives on rheological properties of drilling fluid in highly deviated wells”, futo journal series, vol. 2, no. 2, pp. 68–82, 2016 [12] n. al-malki, p. pourafshary, h. al-hadrami, j. abdo, “controlling bentonite-based drilling mud properties using sepiolite nanoparticles”, petroleum exploration and development, vol. 3, no. 4, pp. 717-723, 2016 [13] c. kelessidis, “drilling fluid challenges for oil-well deep drilling”, nternational multidisciplinary scientific geoconference sgem 2009, albena, bulgaria, june 14-19, 2009 microsoft word 43-3338_s_etasr_v10_n1_pp5340-5345 engineering, technology & applied science research vol. 10, no. 1, 2020, 5340-5345 5340 www.etasr.com duong et al.: available transfer capability determination for the electricity market using cuckoo … available transfer capability determination for the electricity market using cuckoo search algorithm thanh long duong faculty of electrical engineering technology industrial university of ho chi minh city ho chi minh city, vietnam duongthanhlong@iuh.edu.vn thuan thanh nguyen faculty of electrical engineering technology industrial university of ho chi minh city ho chi minh city, vietnam nguyenthanhthuan@iuh.edu.vn ngoc anh nguyen faculty of electrical engineering technology industrial university of ho chi minh city ho chi minh city, vietnam nguyenngocanh@iuh.edu.vn tong kang college of electrical and information engineering hunan university, china kangtong126@126.com abstract—in the electricity market, power producers and customers share a common transmission network for wheeling power from generation to consumption points. all parties in this open access environment may try to produce energy from cheaper sources for greater profit margin, which may lead to transmission congestion, which could lead to violation of voltage and thermal limits, threatening the system security. to solve this, available transfer capability (atc) must be accurately estimated and optimally utilized. thus, accurate determination of atc to ensure system security while serving power transactions is an open and trending research topic. many optimization approaches to deal with the problem have been proposed. in this paper, cuckoo search algorithm (csa) is applied for determining atc problem between the buses in deregulated power systems without violating system constraints such as thermal, voltage constraints. the suggested methodology is tested on ieee 14 and ieee 24bus for normal and contingency cases. the simulation results are compared with the corresponding results of ep, pso, and gwo and show that the csa is an effective method for determining atc. keywords-csa; atc; congestion; electricity market i. introduction one of the key features of the competitive electricity market is fair and open transmission access of the network to all users which may result to the frequent overloading of transmission system facilities. assessment of available transfer capability for the economic utilization of the available system components with regard to system security plays a vital role in operational planning and real time operation of a system. with the development of renewable energy power generation technology and the increase of power load demand, renewable energy power generation can not only service specific users outside the power grid, but also can be massively incorporated into the power grid. renewable energy power generation has many advantages, but its intermittent and stochastic output may influence the power system. renewable energy power generation could increase the uncertainties of the power system which has significant effects on the transfer capability of the transmission system. hence, transmission congestion management problem and analysis of the impacts of renewable energy has become an important challenge [1-4]. secure and reliable operation of transmission network requires the independent system operators (iso) to determine and update atc at regular intervals for its optimal commercial use [5]. the atc of a transmission network is the unutilized transfer capability of the network for the transfer of power for further commercial activity, over and above the already committed usage [6]. essentially, atc is a measure of the extra transmission capability above the base case power transfer for the purpose of power marketing. atc value can be derived by considering various parameters relating to transfer capabilities such as total transfer capability (ttc), transmission reliability margin (trm), and capacity benefit margin (cbm). ttc is the summation of all the network transfers (base case and commercial transfers) including the margins for system security and reliability, and existing transmission commitments (etc). trm is the network margin reserved for system uncertainties whereas cbm is the network margin reserved for external generation in case of emergency generation outages. it is measured by the loss of load expectation. adequate atc is needed to ensure all economic transactions, while sufficient atc is needed to facilitate electricity market liquidity. it is necessary to maintain economical and secure operation over a wide range of system operating conditions and constraints. an accurate value of atc can be used in forecasting future upgrading of the transmission network. the precise calculation of atc should include system constraints such as voltage limit, thermal limit, real and reactive power generation limit, and system uncertainties. corresponding author: thanh long duong engineering, technology & applied science research vol. 10, no. 1, 2020, 5340-5345 5341 www.etasr.com duong et al.: available transfer capability determination for the electricity market using cuckoo … several approaches have been proposed for atc computation including linear approximation methods (lams) [7], repetitive power flow (rpf) [8], continuation power flow (cpf) [9], optimal power flow (opf) [10], and artificial intelligence (ai) techniques [11]. different ai techniques have been used to solve various optimization problems [12-14]. applying meta-heuristic algorithms for determining the atc have been proposed recently: genetic algorithm (ga) [15], bee algorithm (ba) [16], particle swarm optimization (pso) [17], and evolutionary programming (ep) [18-19]. ai approaches are employed to avoid local optimal solutions associated with conventional optimization techniques, especially for highly nonlinear systems. authors in [20] have developed a new meta-heuristic algorithm called cuckoo search algorithm (csa) which is inspired from the obligate brood parasitic behavior of some cuckoo species. a cuckoo bird will choose a random nest of other species and lay and dump its egg in it. an egg is either hatched and carried over to the next generation or abandoned by the host bird. it is an efficient meta-heuristic algorithm that balances between the local search strategy (exploitation) and the whole space (exploration) [21]. in each generation, there are two new populations created using the levy flight and discovering alien egg mechanisms. the first mechanism helps csa to explore the search space while the second mechanism supports csa to exploit the search space, ensuring that the obtained results from csa have better quality compared to others. in addition, there is only one control parameter for csa in the search process, which makes it more reliable for applying to the optimal problem. the csa algorithm has been proposed for solving power system security in [22]. in this paper, csa is applied for determining the atc of power transactions between sources and sink areas in a deregulated power system considering thermal and voltage limits. the proposed approach is demonstrated on the ieee 14-bus and the ieee 24-bus test systems. ii. objective function the main objective of this work is to determine the available power that can be transferred from a specific set of generators of a source area to loads in a sink area, subject to real and reactive power generation limits, voltage limits, and line thermal limits. the atc is determined by starting from an initial point and then increasing the load by a factor λ until a system limit is reached [15]. the details of atc computation are given below: )()( 0 1 0 max 1 λλ ∑∑ == −= load i di load i di atc obj ppf (1) subject to: • the real and reactive power balance equations: gigio j diocij pppp +=++∑ ∀ )1( , λ (2) gigio j diocij qqqq +=++∑ ∀ )1( , λ (3) • the power generation limits: max 0 gigigio ppp ≤+≤ (4) max 0 gigigio qqq ≤+≤ (5) • the voltage limits: maxmin iii vvv ≤≤ (6) • the apparent power flow limit: max2 , 2 , ijcijcijij sqps ≤+= (7) to effect the generation and load changes, the active power generation and the active and reactive loads in the source and sink areas, respectively, need to be modified using the scalar parameter λ. 0 ( ) . (1 ) gi gi p pλ λ= + (8) 0 ( ) . (1 ) di di p pλ λ= + (9) 0 ( ) . (1 ) di di q q= +λ λ (10) where pgio, pdio and qgio, qdio are the active and reactive power respectively of bus i in the base case. λ=0 corresponds to no transfer (base case) and λ=λmax corresponds to the largest value of transfer power that causes no limit violations. pdi(λmax) is the sum of load in sink area when λ=λmax while pdio refers to the sum of load when λ=0. iii. application of csa on atc problem determination the steps of determining the atc problem using the proposed csa are presented below. step 1: read the power system data and set associated parameters such as the host nests size n, the probability of an alien egg in a nest of a host bird to be discovered pa∈ [0, 1], the number of variables to be optimized d, the maximum number of iterations itmax. step 2: initialize n host nests {xi (i=1, 2, …, n)}. each of these nests is concatenated of two strings and represents a feasible solution to the optimization problem. step 3: evaluate the fitness function of the initial n host nests based on the results of power flow analysis, choose the best value of each nest xbesti (i=1, 2, … , n) and the global best nest among all nests gbest which is corresponding to the best fitness function, store the fitness values and the best fitness value. lim 2 lim 2 1 1 lim 2 max 2 1 1 nb nb f obj p gi gi q gi gi i i nb nl v i i s li li i i f f k (p p ) k (q q ) k (v v ) k (s s ) = = = = = − − − − − − − − ∑ ∑ ∑ ∑ (11) step 4: get cuckoos (new solutions) randomly based on the previous best nest via lévy flights. the new solution for each nest is calculated using (12) and (13): 1 new new i i i x xbest rand xα= + × ×∆ (12) engineering, technology & applied science research vol. 10, no. 1, 2020, 5340-5345 5342 www.etasr.com duong et al.: available transfer capability determination for the electricity market using cuckoo … where α>0 is the updated step size, rand1 is a normally distributed stochastic number, and the increased value new ix∆ is determined by: ( ) 1 new u u i i vv rand x xbest gbest rand β σ σ ∆ = × × − (13) where randu and randv are two normally distributed stochastic variables with standard deviation σu and σv given in (14). 1 ( 1) 2 (1 )sin( 2) [(1 ) 2] 2 1 u v β β β πβ σ β β σ −   γ + =   γ +    = (14) where β is the distribution factor (0.3≤β≤1.99). step 5: evaluate the new solutions’ fitness function based on the results of power flow analysis, determine the newly best value of each nest xbesti and the global best nest gbest by comparing the stored fitness values in step 3 with the newly calculated ones, update the best value of each nest xbesti and the global best nest gbest, store the fitness values and the best fitness value. fig. 1. the flowchart of the proposed process of applying the csa to determine atc step 6: discovering an alien egg in a nest of a host bird with the probability of pa creates a new solution for the problem similar to the lévy flights. the new solution because of this action is calculated by (15), (16) and (17): disc disc i i i x xbest c x= + ×∆ (15) 2 1 0 a if rand p c otherwise < =   (16) 3 1 2 [ ( ) ( )] disc i i i x rand randp xbest randp xbest∆ = × − (17) where rand2 and rand3 are the distributed random numbers on the interval [0, 1], randp1(xbesti) and randp2(xbesti) are the random perturbation for positions of nests in xbesti. step 7: evaluate the new solutions’ fitness function based on the results of power flow analysis, determine the newly best value of each nest xbesti and the global best nest gbest by comparing the calculated fitness function from this new solutions with the stored fitness values in step 5, update the best value of each nest xbesti and the global best nest gbest, store the fitness values and the best fitness value. step 8: if the predefined maximum number of iterations itmax is reached, the computation is terminated and the results are displayed, else go to step 4. the flowchart of the proposed process is shown in figure 1. iv. numerical results the atc for each of the stipulated source to sink power transfers on two ieee systems (ieee 14-bus and ieee 24-bus) reliability is tested. the ieee 14-bus system consists of 5 generators and 20 lines as shown in figure 2, while there are 41 lines and 11generators in the ieee 24-bus system as shown in figure 3. the network and load data are given in [23]. based on experimental results, the optimal control parameters of csa have been selected for the 14-bus and 24-bus systems as: the number of nests for the two systems is 20 and 25 respectively. the rate of detection of alien eggs and the maximum number of iterations are 0.25 and 100 respectively for both systems. fig. 2. the ieee 14-bus system in order to apply the proposed methodology in security studies and in congestion management, atc values are computed in selected line outages. in the studies, the atc engineering, technology & applied science research vol. 10, no. 1, 2020, 5340-5345 5343 www.etasr.com duong et al.: available transfer capability determination for the electricity market using cuckoo … margin is limited by bus voltage magnitude in the range of 0.95-1.15pu. the variation in atc over the base state for both systems is studied with line outages, in line 16 (bus 13 to bus 14) in the ieee 14-bus system and in line 8 (bus 4 to bus 9) in the ieee 24-bus system. fig. 3. the ieee 24-bus rts system the atc results for each of the stipulated source to sink power transfers on the ieee 14-bus and 24-bus systems with and without line outage are tested by csa, ep, gwo and pso algorithms. from the results in tables i-iv and figures 4-9 it can be seen that csa has the ability to converge quickly while achieving better atc compared to ep, gwo and pso while the power on the branches and the voltage at the buses also meet the allowable limits as shown in figures 3 and 4. table i. atc with normal topology ieee 14-bus system source/sink bus no atc ep gwo pso csa 1/9 54.2131 54.6663 54.6714 55.4486 1/10 43.7002 44.5024 44.3598 44.8332 1/12 28.9543 29.1568 29.0006 29.0220 1/13 28.8554 29.0571 29.3684 29.5996 1/14 38.5578 38.4526 39.1232 39.4719 1/4 213.0554 214.1656 213.9675 215.3233 1/3 149.1062 152.4437 152.9997 153.1253 table ii. atc with normal topology ieee 24-bus system source/sink bus no atc ep gwo pso csa 23/15 790.9801 794.8945 794.9189 797.3823 22/9 375.4146 375.5291 377.2215 377.5662 22/5 249.8510 249.0834 251.1657 252.8519 21/6 65.3891 65.5217 65.9981 65.9995 18/5 250.2302 251.4353 251.9639 252.8634 the analysis results show that the csa algorithm is able to solve the nonlinear optimization problem of handling atc of power transactions between sources and sinks with equality and inequality constraints in the deregulated power system considering both thermal and voltage limits, and the ability of the algorithm to converge. fig. 4. power flow branch of the ieee 14-bus system without line outage fig. 5. bus voltage profile of the ieee 14-bus system without line outage fig. 6. convergence characteristics of csa compared to ep, gwo, and pso for the ieee 14 bus system without line outage table iii. atc with line outage topology for the ieee 14bus system source/sink bus no atc ep gwo pso csa 1/9 46.8778 48.7042 48.7277 50.0297 1/10 46.7321 49.9837 48.7654 50.8314 1/12 30.8796 34.1418 34.1167 34.1631 1/13 26.9986 32.4435 31.9989 33.8311 1/14 37.5423 38.2378 35.2742 38.6285 1/4 206.751 209.8131 207.324 210.365 1/3 148.903 150.778 150.228 151.770 engineering, technology & applied science research vol. 10, no. 1, 2020, 5340-5345 5344 www.etasr.com duong et al.: available transfer capability determination for the electricity market using cuckoo … fig. 7. convergence characteristics of csa compared to ep, gwo, and pso for the ieee 24-bus system without line outage fig. 8. convergence characteristics of csa compared to ep, gwo, and pso for the ieee 14-bus system with line outage table iv. atc with line outage topology for the ieee 24bus system source/sink bus no atc ep gwo pso csa 23/15 781.342 793.135 794.381 795.014 22/9 372.625 371.950 372.768 376.399 22/5 227.914 226.261 226.823 227.259 21/6 49.9771 51.0006 50.5363 51.1782 18/5 228.763 228.724 227.561 229.852 fig. 9. convergence characteristics of csa compared to ep, gwo, and pso for the ieee 24-bus system with line outage v. conclusions accurate atc determination in order to ensure system security while serving power transactions is one of the most challenging tasks in the electricity market. this paper has presented an implementation of the cuckoo search algorithm to solve the problem which is formulated as a nonlinear optimization problem with equality and inequality constraints for handling the atc of power transactions between sources and sinks in a deregulated power system considering both thermal and voltage limits. the results for the two systems have proved that the proposed csa has remarkable robustness in maximizing the atc. in all cases, the available transfer capability obtained by using csa is much higher than that of ep, gwo, and pso. thus, csa is one of the most effective methods for determining atc in an electric power system. references [1] m. r. salehizadeh, m. a. koohbijari, h. nouri, a. tascikaraoglu, o. erdinc, j. p. s. catalao, “bi-objective optimization model for optimal placement of thyristor-controlled series compensator devices”, energies, vol. 12, no. 13, article id 2601, 2019 [2] m. r. salehizadeh, a. rahimi-kian, k. hausken, “a leader–follower game on congestion management in power systems”, in: game theoretic analysis of congestion, safety and security, pp. 81-112, springer, 2015 [3] m. r. salehizadeh, a. r. rahimi-kian, m. oloomi-buygi, “securitybased multi-objective congestion management for emission reduction in power system”, international journal of electrical power & energy systems, vol. 65, no. 2, pp. 124-135, 2015 [4] m. oloomi-buygi, m. r. salehizadeh, “toward fairness in transmission loss allocation”, 2007 australasian universities power engineering conference, perth, australia, december 9-12, 2007 [5] y. ou, c. singh, “assessment of available transfer capability and margins”, ieee transactions on power systems, vol. 17, no. 2, pp. 463-468, 2002 [6] north american electric reliability council (nerc), available transfer capability definitions and determination, nerc, 1996 [7] p. venkatesh, r. gnanadass, n. p. padhy, “available transfer capability determination using power transfer distribution factors”, international journal of emerging electric power systems, vol. 1, no. 2, article id 1009, 2004 [8] h. farahmand, m. rashidi-nejad, m. fotuhi-firoozabad, “implementation of facts device for atc enhancement using rpf technique”, large engineering systems conference on power engineering, halifax, canada, july 28-30, 2004 [9] z. chen, m. zhou, g. li, “atc determination for the ac/dc transmission systems using modified cpf method”, international conference on critical infrastructure, beijing, china, september 20-22, 2010 [10] t. k. hahn, m. k. kim, d. hur, j. k. park, y. t yoon, “evaluation of available transfer capability using fuzzy multi-objective contingencyconstrained optimal power flow”, electric power systems research, vol. 78, no. 5, pp. 873-882, 2008 [11] m. rashidinejad, h. farahmand, m. f. firuzabad, a. a. gharaveisi, “atc enhancement using tcsc via artificial intelligent techniques”, electric power systems research, vol. 78, no. 1, pp. 11-20, 2008 [12] d. t. long, t. t. nguyen, n. a. nguyen, l. a. t. nguyen, “an effective method for maximizing social welfare in electricity market via optimal tcsc installation”, engineering, technology & applied science research, vol. 9, no. 6, pp. 4946-4955, 2019 [13] v. h. nguyen, h. nguyen, m. t. cao, k. h. le, “performance comparison between pso and ga in improving dynamic voltage stability in anfis controllers for statcom”, engineering, technology & applied science research, vol. 9, no. 6, pp. 4863-4869, 2019 [14] l. t. duong, t. t. nguyen, “network reconfiguration for an electric distribution system with distributed generators based on symbiotic engineering, technology & applied science research vol. 10, no. 1, 2020, 5340-5345 5345 www.etasr.com duong et al.: available transfer capability determination for the electricity market using cuckoo … organisms search”, engineering, technology & applied science research, vol. 9, no. 6, pp. 4925-4932, 2019 [15] t. nireekshana, g. k. rao, s. s. n. raju, “enhancement of atc with facts devices using real-code genetic algorithm”, electrical power and energy systems. vol. 43, no. 1, pp. 1276–1284, 2012 [16] r. m. idris, a. kharuddin, m. mustafa, “available transfer capability determination using bees algorithm”, 20 th australasian universities power engineering conference, christchurch, new zealand, december 5-8, 2010 [17] h. su, y. qi, x. song, “the available transfer capability based on a chaos cloud particle swarm algorithm”, 9 th international conference on natural computation, shenyang, china, july 23-25, 2013 [18] m. m. othman, a. mohamed, a. hussain, “available transfer capability assessment using evolutionary programming based capacity benefit margin”, international journal of electrical power & energy systems, vol. 28, no. 3, pp. 166-176, 2006 [19] d. s. ivan, “evolutionary algorithm for avaluating available transfer capability”, journal of electrical engineering, vol. 64, no. 5, pp. 291297, 2013 [20] x. s. yang, s. deb, “cuckoo search via lévy flights”, 2009 world congress on nature & biologically inspired computing, coimbatore, india, december 9-11, 2009 [21] m. shehab, a. t. khader, m. a. a. betar, “a survey on applications and variants of the cuckoo search algorithm”, applied soft computing, vol. 61, no. 12, pp. 1041-1059, 2017 [22] t. kang, j. yao, t. l. duong, s. yang, x. zhu, “a hybrid approach for power system security enhancement via optimal installation of flexible ac transmission system (facts) devices”, energies, vol. 10, no. 9, article id 1305, 2017 [23] http://www.pserc.cornell.edu//matpower (accessed on 7 june 2016) microsoft word 30-2924_s1_etasr_v9_n4_pp4480-4483 engineering, technology & applied science research vol. 9, no. 4, 2019, 4480-4483 4480 www.etasr.com panhyar et al.: influence of casting temperature on the structural behavior of concrete influence of casting temperature on the structural behavior of concrete muhammad arif panhyar department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan fahad ali shaikh department of civil engineering, mehran university of engineering and technology, jamshoro, pakistan syed naveed raza shah department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan ashfaque ahmed jhatial department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan abstract—concrete is the most preferred construction and building material and its demand is not expected to diminish in the near future. the properties of concrete are affected by various factors, one of them is the temperature at casting. this experimental work was carried out in order to study the effect of high temperature on workability, and compressive and flexural tensile strength of concrete. it was found that higher temperatures caused water content evaporation from the mix during casting, causing reduction in workability, but simultaneously increased the strength compared to concrete cast at controlled temperatures). keywords-structural behavior; temperature; compressive strength; flexural strength; casting temperature i. introduction concrete is extensively used as a construction material and it is the second highest consumed material around the world [1]. its popularity is mainly due to its durability, availability, cold resistance, chemical resistance, workability, and flexibility [2, 3]. nowadays, concrete consumption in the world is approximated to 2.5 tons per capita per year equal to 17.5 billion tons for a population of 7 billion [4]. concrete is a composite material and its properties depend on various factors such as proportioning, batching, mixing, transporting, pouring, and curing [5]. depending on the site conditions, concrete can be mixed manually or with the help of a mixing machine called mixer which can be transported with the help of wheel barrows or pumps. the curing process in concrete is an important factor because curing protects against the loss of needed moisture for hydration, enhances strength and reduces the hardened concrete’s permeability. curing is carried out by various methods, such as: ponding, steam curing, sprinkling water on concrete, covering surfaces with gunny bags, covering surfaces with membrane, and others (providing shades on concrete work, spreading wet sand etc.). concrete is a widely used commodity, which can be used in a variety of environments. concreting, though a relatively easy concept, is less understood sometimes and even small factors like temperature have a big role in its proper and satisfactory performance. temperature affects the properties of concrete, particularly when it varies during casting and curing. the guidelines for concreting in extreme weather conditions should be properly followed in order to acquire a serviceable product. concrete is cast under varying surrounding temperatures. concrete placement in winter is done at low temperatures and curing is done at even lower temperatures. in summer, concrete is frequently poured at high temperatures and cured at much higher temperatures. casting plays a key role in concrete construction and if not properly brought into action, it will surely have adverse effects on the slump (workability), compressive strength, and flexural tensile strength. throughout the casting of concrete, various factors should be taken into consideration which may affect its properties, preferably temperature. temperature directly affects workability, water demand, initial and final setting time, compressive and flexural tensile strength. by inspecting the influence of temperature variation, the behavior of concrete can be more easily identified. khairpur mirs’ is a city in northern sindh province of pakistan, which is considered as an average of the hot climate cities in northern sindh. the climate remains mostly hot for around 8 months in a year. furthermore, the temperature of khairpur mirs’ reached a record high of 49.5 o c during the heat wave of the 26th of may, 2010. the usual temperature varies approximately from 43.4 o c to 7.2 o c in summer and winter respectively [6]. high atmospheric temperature affects concrete’s properties by increasing the temperature of fresh concrete and causing a high-water demand, resulting in quick dehydration, which accelerates the initial settling and lowers the long term strength of concrete. high temperature increases the evaporation rate of freshly mixed concrete, resulting in lowering the effective water corresponding author: muhammad arif panhyar (arifali.panhyar@gmail.com) engineering, technology & applied science research vol. 9, no. 4, 2019, 4480-4483 4481 www.etasr.com panhyar et al.: influence of casting temperature on the structural behavior of concrete demand and hence lowering the effective water-cement (w/c) ratio [7]. keeping concreting continuous either in summer or in winter is important. there is an optimum temperature during the early-life of concrete which optimizes strength at later-ages [8]. in general, temperature was given less priority, it was neglected most of the times. temperature varies with time and area, therefore, its effects also vary with time and site location. when concrete is fresh, it is desirable to be workable. but sometimes due to conditions at site, the desirable workability is not obtained which results in the form of segregation, bleeding and loss of compressive strength. also, when there is a high ambient temperature at the casting place, then loss in workability occurs because of the accelerated evaporation process that is adjusted by adding excess water in the concrete mix. surely, this disturbs the w/c ratio which is directly proportional to concrete’s strength. if w/c ratio is increased, it would surely have adverse effects on concrete’s strength. often in summer the temperature may reach 45°c at day and 20°c at night. this change in temperature will adequately affect concrete’s properties. in hot and humid environmental conditions the concrete surfaces could get cracks. results in [9] show that the serviceability of hardened concrete and the mechanical properties of concrete are significantly affected by temperature. the factors which affect the concrete’s strength at high temperature can be divided in to two groups: properties of materials (aggregates, cement) and environmental factors such as temperature, duration of exposure, etc. [10]. authors in [11] worked on hardened concrete exposed to elevated temperatures [11]. when exposing reinforced concrete structures to risen temperatures, the structure starts deteriorating and could fail [12]. authors in [13] studied the curing regimes and temperature on the compressive strength of concrete. authors in [14] studied the effects of curing conditions on concrete’s properties. authors in [15] reported that exposing concrete to risen ambient temperature after casting will have a significant effect on its properties. long-term behaviors are affected temperature factor and should be investigated [16]. usually concrete testing is performed under controlled conditions in laboratory. in the field however, the concrete is prepaid and kept in service at a variety of temperatures. the range of concrete use has grown up considerably with many modern constructions being built in countries having a hot and humid climate. conventionally, the strength properties of concrete have been used as standard for determining its performance, although it is not necessary for concrete to have high strength, but it should have a long service life. it is known that the performance of concrete should be evaluated according to durability and strength under expected surrounding atmospheric conditions. keeping in view the research work carried out on concrete, only a few were carried out on the effects of casting temperatures on its properties. most researches were carried out under controlled conditions. therefore, an experimental study was conducted in order to learn the effects of khairpur mirs’ ambient temperature on the workability, compressive and flexural tensile strength of concrete during casting. the results were compared with the ones of conventional specimens. ii. materials and experimental procedure for this experimental study, type i ordinary portland cement was used. locally acquired fine and coarse aggregates had specific gravity of 2.667 and 2.7 respectively. mix design was done to determine the mix ratio, in order to achieve the target strength according to aci, which was determined to be 1:2.04:2.74 (1 part cement, 2.04 parts fine and 2.74 parts coarse aggregates), while the w/c ratio was 0.62. to determine the influence of temperature on the properties of concrete, it was cast at two different sites, one under controlled temperature of 26 o c inside the laboratory, while the other was cast outdoors, in open air where the temperature varied with respect to the time of casting. the casting of concrete was conducted at 1 hour intervals from 11:00 a.m. to 4:00 p.m. (outdoors). to determine the effect of increase in concrete temperature, a total of 6 batches were prepared outside and 1 batch of concrete in the laboratory. for each batch a total of 9 cubes of 150mm×150mm×150mm (3 cubes each for 3, 7 and 28 days of curing), while 6 beams of 500mm×100mm×100mm (3 beams for 7 and 28 days of curing each) were cast and were cured in water for the specified period. the workability was determined according to [17] and was recorded for the wet mix of each batch of concrete. the compressive strength testing of cube specimens was conducted after 3, 7 and 28 days of curing in accordance to [18], while flexural tensile testing was conducted on 7 and 28 days of curing in accordance to [19]. the ambient temperature was recorded during the casting of each batch. the concrete batch cast under controlled temperature was named b1 while the concrete batches cast under uncontrolled temperature and various times were named b-2 to b-7. iii. results and discussion a. workability workability is directly related to temperature. as the temperature increases, the water available in concrete starts evaporating which reduces workability as shown in table i. the slump values are also varying with temperature. figure 1 gives the graphical representation of the variation of slump with respect to time. from the results, it can be observed that the difference in the surrounding temperature has significant impact on workability. the concrete specimens which were cast under controlled temperature (b-1 batch) exhibited the highest slump, but in the outside casting (b-2 to b-7 batches), the workability decreases with increase in temperature. this is attributed to the evaporation of water, which caused the concrete to become dry thus directly effecting workability. b. compressive strength from the results shown in tables ii-iv for compressive strength testing at 3, 7 and 28 days respectively, it can be observed that the compressive strength of controlled specimen (b-1 batch) is significantly lower than of the specimens which were cast outside under uncontrolled temperature. this is attributed to the reduction in workability. the w/c ratio plays a significant role in achieving specified strength, the higher the w/c ratio the lower the strength that can be achieved. for this experimental work, though the w/c ratio was on the higher side, the difference in strength between the controlled and uncontrolled temperature specimens was significantly high, engineering, technology & applied science research vol. 9, no. 4, 2019, 4480-4483 4482 www.etasr.com panhyar et al.: influence of casting temperature on the structural behavior of concrete because in uncontrolled environment the water evaporates faster due to rise in temperature causing reduction in workability but simultaneously increasing strength. the variation in compressive strength is illustrated in figure 2. table i. workability results of concrete samples batch casting time (h) temperature ( o c) slump (mm) b-1 ---26 112 b-2 11:00 am 34 102 b-3 12:00 pm 35 98 b-4 01:00 pm 37 91 b-5 02:00 pm 38 87 b-6 03:00 pm 40 82 b-7 04:00 pm 42 76 fig. 1. slump variation versus temperature and time table ii. average compressive strength on 3 days batch casting time temperature ( o c) avg compressive strength (mpa) increase in strength w.r.t. control specimen b-1 (%) b-1 ----26 13.70 --- b-2 11:00 am 34 15.56 +13.59 b-3 12:00 pm 35 16.10 +17.52 b-4 01:00 pm 37 16.57 +20.94 b-5 02:00 pm 38 16.88 +23.21 b-6 03:00 pm 40 17.38 +26.86 b-7 04:00 pm 42 17.68 +29.05 fig. 2. variation in compressive strength of concrete table iii. av erage ompressive strength on 7 days batch casting time temperature ( o c) avg compressive strength (mpa) increase in strength w.r.t. control (%) b-1 ----26 19.85 --- b-2 11:00 am 34 22.11 +11.39 % b-3 12:00 pm 35 22.57 +13.7 % b-4 01:00 pm 37 22.85 +15.11 % b-5 02:00 pm 38 23.32 +17.48 % b-6 03:00 pm 40 23.96 +20.70 % b-7 04:00 pm 42 24.50 +23.40 % table iv. average compressive strength on 28 d ay s batch casting time temperature ( o c) avg compressive strength (mpa) increase in strength w.r.t. control (%) b-1 ----26 26.09 --- b-2 11:00 am 34 28.19 +8.05 % b-3 12:00 pm 35 28.46 +9.08 % b-4 01:00 pm 37 28.87 +10.65 % b-5 02:00 pm 38 29.11 +11.57 % b-6 03:00 pm 40 29.94 +14.76 % b-7 04:00 pm 42 30.56 +17.13 % c. flexural tensile strength the results of flexural tensile testing are shown in tables v and vi for 7 and 28 days of curing respectively, while the variation in flexural tensile strength is shown in figure 3. the results illustrate that with the increase in temperature during casting, the water content is reduced which causes reduction in workability. the reduction in workability in turn causes some issues while mixing or pouring the concrete into moulds, but it has the advantage of achieving higher strength compared to samples with better workability. this is evident from the results, where the control specimens (b-1 batch), which were cast under controlled temperature achieved higher workability but recorded significantly lower flexural tensile strength compared to the specimens of the b-2 to b-7 batches which were cast under uncontrolled temperature. fig. 3. variation in flexural strength of concrete engineering, technology & applied science research vol. 9, no. 4, 2019, 4480-4483 4483 www.etasr.com panhyar et al.: influence of casting temperature on the structural behavior of concrete table v. average flex ural tensile strength on 7 days batch casting time temperature ( o c) avg flexural tensile strength (mpa) difference in strength w.r.t. control (%) b-1 ----26 3.24 --- b-2 11:00 am 34 3.46 +6.96 % b-3 12:00 pm 35 3.60 +11.28 % b-4 01:00 pm 37 3.72 +15.00 % b-5 02:00 pm 38 3.86 +19.31 % b-6 03:00 pm 40 3.94 +21.79 % b-7 04:00 pm 42 4.07 +25.81 % table vi. average flexural tensile strength on 28 days batch casting time temperature ( o c) avg flexural tensile strength (mpa) difference in strength w.r.t. control (%) b-1 ----26 4.34 --- b-2 11:00 am 34 4.53 +4.38% b-3 12:00 pm 35 4.68 +7.83% b-4 01:00 pm 37 4.78 +10.14% b-5 02:00 pm 38 4.89 +12.67% b-6 03:00 pm 40 4.99 +14.98% b-7 04:00 pm 42 5.11 +17.74% iv. conclusions from the results, it can be concluded that: • the temperature has significant impact on the properties of concrete. • controlled temperature allows high workability to be achieved. uncontrolled temperature tends to cause water content to evaporate, thus causing significant loss in workability. • the reduction in workability caused by the increase in temperature, has significant impact on the compressive and flexural tensile strength of concrete. • at the peak recorded temperature of 42 o c, after 3 days of curing, the specimens cast outside were found to have 29.05% higher compressive strength than the specimens cast at the controlled temperature of 26 o c. after 28 days this increase in percentage was 17.13%. • the same behavior was observed in flexural strength. after 7 days, the flexural strength of the specimen cast outside at 42 o c was 25.81% higher than the one of the specimen cast at the controlled temperature of 26 o c. after 28 days of curing, this increase was 17.74%. this shows that as the temperature increases, the compressive and flexural strength of concrete increase but this diminishes with time. references [1] a. a. jhatial, s. sohu, n. k. bhatti, m. t. lakhiar, r. oad, “effect of steel fibres on the compressive and flexural strength of concrete”, international journal of advanced and applied sciences, vol. 5, no. 10, pp. 16-21, 2018 [2] a. a. jhatial, w. i. goh, k. h. mo, s. sohu, i. a.bhatti, “green and sustainable concrete–the potential utilization of rice husk ash and egg shells”, civil engineering journal, vol. 5, no. 1, pp. 74-81, 2019 [3] i. a. memon, a. a. jhatial, s. sohu, m. t. lakhiar, z. hussain, “influence of fibre length on the behaviour of polypropylene fibre reinforced cement concrete”, civil engineering journal, vol. 4, no. 9, pp. 2124-2131, 2018 [4] m. s. islam, m. s. ali, r. parvin, “mechanical properties of concrete made by fine aggregate obtained from dismantled concrete”, world journal of science and engineering, vol. 3, no. 1, pp. 71-88, 2018 [5] a. m. neville, properties of concrete, wiley, 1996 [6] climate-data.org, khairpur climate: average temperature, weather by month, khairpur weather averages, available at: https://en.climatedata.org/asia/pakistan/sindh/khairpur-1228/, accessed at may 10, 2019 [7] j. ortiz, a. aguado, l. agullo, t. garcia, “influence of environmental temperatures on the concrete compressive strength: simulation of hot and cold weather conditions”, cement and concrete research, vol. 35, no. 10, pp. 1970-1979, 2005 [8] p. klieger, “effect of mixing and curing temperature on concrete strength”, aci 53rd annual convention, dallas, usa, february 27, 1958 [9] k. a. soudki, e. f. e. salakawy, n. b. elkum, “full factorial optimization of concrete mix design for hot climates”, journal of materials in civil engineering, vol. 13, no. 6, pp. 427-433, 2001 [10] b. chen, c. li, l chen, “experimental study of mechanical properties of normal-strength concrete exposed to high temperatures at an early age”, fire safety journal, vol. 44, pp. 997-1002, 2009 [11] y. wu, b. wu, “residual compressive strength and freeze-thaw resistance of ordinary concrete after high temperature”, construction and building materials, vol. 54, pp. 596-604, 2014 [12] m. husem, “the effects of high temperature on compressive and flexural strengths of ordinary and high-performance concrete”, fire safety journal, vol. 41, pp. 155-163, 2006 [13] f. sajedi, “effect of curing regime and temperature on the compressive strength of cement-slag mortars”, construction and building materials, vol. 36, pp. 549-556, 2012 [14] a. s. a. ghatani, “effect of curing methods on the properties of plain and blended cement concretes”, construction and building materials, vol. 24, no. 3, pp. 308-314, 2010 [15] n. a. memon, f. r. abro, u. memon, s. r. sumadi, “effect of curing conditions and super plasticizer on compressive strength of concrete exposed to high ambient temperature of nawabshah, pakistan”, international journal of engineering research, vol. 3, no. 7, pp. 462464, 2014 [16] g. yaun, q. li, “the use of surface coating in enhancing the mechanical properties and durability of concrete exposed to elevated temperature”, construction and building materials, vol. 95, pp. 375-383, 2015 [17] british standard institution, en 12390-2 (2009): testing fresh concrete. slump-test, british standard institution, 2009 [18] british standard institution, en 12390-3 (2009): testing hardened concrete. compressive strength of test specimens, british standard institution, 2009 [19] british standard institution, en 12390-5 (2009): testing hardened concrete. flexural strength of test specimens, british standard institution, 2009 microsoft word etasr_v11_n4_pp7508-7514 engineering, technology & applied science research vol. 11, no. 4, 2021, 7508-7514 7508 www.etasr.com kassem et al.: a techno-economic viability analysis of the two-axis tracking grid-connected … a techno-economic viability analysis of the twoaxis tracking grid-connected photovoltaic power system for 25 selected coastal mediterranean cities youssef kassem department of mechanical engineering engineering faculty near east university nicosia, cyprus yousseuf.kassem@neu.edu.tr hüseyin gökçekuş department of civil engineering civil and environmental engineering faculty near east university nicosia, cyprus huseyin.gokcekus@neu.edu.tr hamza s. abdalla lagili department of civil engineering civil and environmental engineering faculty near east university nicosia, cyprus hamzasalem409@gmail.com abstract—generating energy from renewable sources, particularly solar energy, offers significant benefits and achieves a more clean and sustainable development. in the present paper, the potential of developing a 4.2kw grid-connected rooftop twoaxis tracking pv system in 25 selected coastal mediterranean cities located in different arabic countries is evaluated using retscreen software. the proposed system is serving the basic household energy needs according to the load profile from monthly electrical bills. it is found that the proposed system produces about 8824kw annually, which helps to reduce co2 emissions. also, the average energy production cost is assumed to range from 0.0337 to 00.0475$/kwh. it is concluded that the proposed system can provide an effective solution for energy poverty in developing regions with a very positive socio-economic and environmental impact. the small-scale grid-connected pv system will provide the domestic energy needs at a lower energy production cost than the electricity price grid-connected consumers pay. this study demonstrated that generating electricity from solar energy will help reduce the electricity tariff rates and the dependence on fossil fuels. keywords-coastal mediterranean cities; two-axis sun tracking system; solar energy potential; grid-connected; small scale pv system; retscreen i. introduction the energy sector is the most prominent of the economic crisis and the environmental disaster in arabic countries such as lebanon, syria, palestine, and libya [1]. this sector is the biggest waste producer and the primary cause of budget deficits and debt ballooning, in addition to being the primary cause of air pollution and related deaths. moreover, the electricity crisis has been increased in many arabic countries due to the population growth, the rising living standards, and the growing industry sectors, which have led to an increase of the energy demand, and the increased electricity cost associated with fossil fuel-based electrical energy production [2]. generally, most arabic countries do not suffer from poverty in electrical energy sources, such as oil, gas, sunlight, and wind. for instance, libya is a rich country in natural resources, however, it has faced power outages for several years due to the poor maintenance and civil war. the electricity crisis is not new in most developing countries and the electricity sector has suffered from decades of mismanagement, weak policies, and the absence of proper planning. this problem has been increased due to the dilapidation of old power stations, accompanied by sabotage operations. as a result, the hours of power cuts increased, ranging from 8 to 20 hours per day. for this reason, citizens are dependent on domestic power generators or small home generators, both of them adding financial burdens to the residents. nowadays, all countries are looking to utilize renewable energy resources instead of fossil fuels to mitigate climate change [3]. additionally, the utilization of renewable energies, such as solar, as power sources, can be an alternative solution for solving the electricity crisis in most countries and reducing the consumption of fossil fuels [4, 5]. globally, solar energy is one of the most popular alternative energy resources for electricity production. photovoltaic (pv) panels are used to convert sunlight into electricity. in the literature, utilizing the pv systems helps to meet the basic domestic needs globally, especially in the developing countries [6]. pv systems can be categorized as stand-alone systems or grid-tied systems for domestic and commercial settings. the grid-tied pv systems corresponding author: youssef kassem engineering, technology & applied science research vol. 11, no. 4, 2021, 7508-7514 7509 www.etasr.com kassem et al.: a techno-economic viability analysis of the two-axis tracking grid-connected … are generally installed with no mandatory requirement for storage in the regions/countries with stable grids [7]. the benefits of these systems are that they are simple to design, easily manageable, require less maintenance, and are costeffective. the disadvantage of a grid-tilt system is that its energy production is lower than the power produced by tracking pv systems. to maximize the amount of output power of the pv system, it must be adjusted to the changing position of the sun throughout the day [6]. solar tracking systems are utilized to maximize energy production by the pv systems [8]. solar tracking systems are classified based on movement capability (single-axis and two-axis) and control system (astronomically controlled systems and sensor-controlled systems) [9]. according to [10-12] the tracking systems (single-axis and two-axis) increased the energy production from 20 to 40%. the performance of grid-connected pv systems with various sun-tracking systems has been investigated by several scientific studies [13-15]. for instance, authors in [13] investigated the feasibility of a 5kw gridconnected pv system under different tracking systems and pv technologies in nahr el-bared, lebanon. the results demonstrated that the two-axis tracking solar system was an economical option for electricity production compared to other systems. authors in [14] evaluated the performance of the gridconnected solar system under different tracking systems in gulf cooperation council countries. the results showed that the vertical-axis and two-axis tracker system could produce 20% and 34% more power than the fixed-tilt systems. the benefit of grid-connected systems is that the excess electricity produced by these systems can be given back to the grid, which can help to reduce the electricity bills and solve the electricity crisis. the main scope of the current study is to present a techno-economic feasibility evaluation for 4.2kw grid-connected pv systems on the rooftops of household/residential buildings in coastal mediterranean cities in some arabic countries. the performance of the two-axis – tracking system for a grid-connected pv system has been analyzed using the retscreen software to show the benefits of solar energy utilization as a power source for solving the electricity crisis in developing countries. ii. materials and methods the solar energy potential in 25 coastal locations under mediterranean climate conditions is discussed based on a national aeronautics and space administration (nasa) database, which includes solar radiation (sr) and air temperature data. besides, the performance of the two-axis tracking system for grid-connected rooftop pv systems as a solution for the electricity crisis and reducing the electricity bills is investigated with the help of the retscreen software. a. location details and collected data in this work, 25 coastal mediterranean cities located in libya, lebanon, syria, palestine, tunisia, and algeria have been taken into consideration. the geographical coordinates of the selected cities are listed in table i. in the literature, the solar potential of different regions is usually evaluated using the nasa database. for example, authors in [16] assessed the potential of solar energy in various locations in nigeria using the nasa database. authors in [17] found that the nasa database showed good agreement with the measurement data of global solar irradiation. therefore, the solar potential of 25 coastal locations is assessed using the monthly nasa database. table i. coordinates of the selected cities country city latitude [°] longitude [°] libya az zawiyah 32.76 12.74 tripoli 32.89 13.19 al khums 32.65 14.27 misratah 32.33 15.10 surt 31.19 16.57 benghazi 32.12 20.09 turbruq 32.07 23.94 lebanon tripoli 34.43 35.84 beirut 33.89 35.50 syria tartus 34.90 35.89 al ladhiqiyah 35.61 36.00 palestine gaza strip 31.35 34.31 egypt port said 31.27 32.30 alexandria 31.20 29.92 marsa matrch 31.36 27.22 tunisia djerba modoun 33.81 10.85 gabes 33.89 10.10 sfax 34.74 10.76 sousse 35.82 10.63 tunis 36.81 10.18 algeria annaba 36.91 7.74 skikda 36.87 6.91 bejaia 36.75 5.06 algiers 36.70 3.06 oran 35.70 -0.63 b. two-axis tracking pv arrays in general, solar tracking systems are utilized to maximize energy production by the pv system due to the maximization of the incident beam radiation [18]. the rotation of these systems can be about a single axis or about two axes. maximum energy can be achieved using a two-axis solar system due to its total freedom of movement. in two-axis pv systems, the solar panels are mounted on the structure, which can move the modules in two axes [19] as shown in figure 1. for a two-axis pv system, two motors are required for the rotation of the axes [19]. thus, the panel’s orientation with the two-axis tracker system is dependent on the solar position. generally, this system is required a control module to direct it. the solar tracker pv systems utilize a sr sensor to control the system orientation [20]. moreover, the performance of the pv system depends on the parameters of the system components and weather. additionally, existing power producers are trying to increase the output power of the pv system by improving operation and maintenance (o&m) activities [20]. the o&m is considered one of the important aspects of a pv solar system. improving the o&m can help reduce the energy production cost and improve the impact returns on investment. furthermore, there are several issues that the pv system faces during its lifecycle, such as natural degradation, component failures, weather conditions, etc. [21]. therefore, a holistic approach can address these issues under the o&m aspect, which is divided into three categories (preventative maintenance, corrective maintenance, and condition-based engineering, technology & applied science research vol. 11, no. 4, 2021, 7508-7514 7510 www.etasr.com kassem et al.: a techno-economic viability analysis of the two-axis tracking grid-connected … maintenance). in fact, the tracking pv systems increase the o&m) due to the requirement of periodic checking to ensure the optimal performance of the system. fig. 1. characteristics of two-axis tracker movements. c. design of the pv power system to build the 4.2kw pv system, a mono-si-cs6x-300m pv module was selected. it is made of mono-crystalline-silicon cells with a maximum power of 300wp. a total number of 14 modules are required with an area of about 28m 2 . a fronius symo 4.5-3-m light 4.5 kw solar inverter with a capacity of 4.5kw and 98.6% efficiency was chosen in this study. the specifications of the selected pv panel and inverter are available at [22, 23]. d. simulation tool there are many simulation tools such as homer energy, retscreen, etc. that may be utilized to evaluate the energy production and levelized cost of energy (lcoe). the comparison between these simulation tools is available at [24]. in this study, homer is utilized to evaluate the economical feasibility of the proposed systems. retscreen is developed by natural resources canada (nrc). it utilizes the long-term monthly average meteorological data from the nasa database as a source of meteorological information for a specific location [3, 16]. in the present study, the most important economic indicators of financial analysis including net present cost (npc), cost of energy (coe), simple payback (sp), and equity payback (ep) are estimated with the retscreen software. also, the greenhouse gas (ghg) emission reduction, energy production, and capacity factor (cf) for the proposed system are determined. iii. results and discussion a. characteristics of solar energy in the selected locations generally, regarding pv panels and inverters, the characteristics of the installation, and the meteorological conditions (relative humidity, air temperature, solar radiation, etc.) are the major factors that influence the performance of the pv system. the meteorological conditions affecting the generating power by the pv system are mainly solar irradiance [25-27]. therefore, global sr data were analyzed to estimate the potential of solar energy in the selected cities. table ii summarizes the average horizontal monthly daily sr for the selected locations. it is found that the average horizontal monthly daily sr varied from 2.01kwh/m 2 /day to 8.50kwh/m 2 /day. the maximum and minimum values of sr are recorded in port said (in june) and skikda (in december) respectively. the highest and lowest annual sr are 5.87kwh/m 2 /day and 4.51kwh/m 2 /day for alexandria and skikda, respectively as shown in figure 2. the highest value of average temperature (at) was recorded in port said (21.23�) and the next highest in alexandria (20.79�). based on the value of sr at the selected locations, it is found that the solar resource of the selected locations is categorized as excellent (class 5) according to [16]. therefore, these locations are suitable for installing a pv system in the future due to their high value of sr. fig. 2. average sr and air temperature as a function of location. b. electricity generation and capacity factor sr and the number of clear sunny days are essential factors that influence the performance of the pv system including output power and cf [28, 29]. the monthly electricity generation (eg) from the proposed system is shown in table iii. it is found that the monthly eg is within the range of 390kwh-1125kwh. the maximum average eg occurs at alexandria during july with a value of 1125kwh, while the minimum value of 390kwh was recorded at january in beirut. furthermore, figure 3 shows the annual eg and cf from the proposed systems. it is found that the value of eg is within the range of 7628-10333kwh for pv systems with two-axis tracking systems. the maximum value of eg is recorded in alexandria while the minimum value is obtained in algiers. besides, it is found that the cf values vary from 20.73% to 28.08%. these observations can be supported by other scientific researches who analyzed the feasibility of a gridconnected pv system. for instance, authors in [30] found that the cf of their proposed pv system in oman was within the range of 16-23%. also, authors in [31] found that the cf of grid-connected pv systems with various technologies varied from 15.37% to 15.75%. authors in [32] found that the value of cf of grid-connected pv systems with different suntracking modes was within the range of 17.54 to 27.42%. moreover, the use of the two-axis instead of the fixed-tilt option significantly increases the generated electricity [32, 33]. therefore, it can be concluded that the value gotten from the present study for each location is compatible with the generally acceptable values. consequently, it is technically sustainable to build a grid-connected rooftop pv system in these locations. the results indicate that the variation of the eg and cf is a function of location. engineering, technology & applied science research vol. 11, no. 4, 2021, 7508-7514 7511 www.etasr.com kassem et al.: a techno-economic viability analysis of the two-axis tracking grid-connected … table ii. average daily solar radiation [kwh/m2/day] location jan feb mar apr may jun jul aug sep oct nov dec az zawiyah 2.69 3.86 5.14 6.41 7.15 7.90 8.10 7.26 5.74 4.18 2.99 2.38 tripoli-libya 2.67 3.66 4.79 6.15 6.98 7.67 7.79 7.05 5.52 3.96 2.75 2.35 al khums 2.79 3.67 4.75 5.83 6.52 7.14 7.34 6.50 5.17 3.97 2.89 2.45 misratah 3.07 4.09 5.36 6.57 7.24 7.90 8.07 7.37 5.96 4.60 3.31 2.77 surt 3.41 4.25 5.23 6.18 6.54 7.42 7.26 6.86 5.77 4.67 3.49 3.06 benghazi 2.87 3.87 5.18 6.56 7.26 7.92 7.94 7.26 5.96 4.55 3.26 2.63 turbruq 2.69 3.65 4.90 6.18 6.89 7.52 7.63 6.96 5.86 4.38 3.05 2.47 tripoli-lebanon 2.76 3.68 5.03 6.37 7.62 8.31 8.08 7.37 6.32 4.65 3.24 2.49 beirut 2.67 3.51 4.80 6.18 7.45 8.08 7.83 7.16 6.07 4.53 3.15 2.41 tartus 2.76 3.68 5.03 6.37 7.62 8.31 8.08 7.37 6.32 4.65 3.24 2.49 al ladhiqiyah 2.65 3.63 4.96 6.28 7.45 8.22 7.99 7.29 6.20 4.56 3.06 2.38 gaza strip 3.08 3.90 5.29 6.58 7.50 8.07 7.90 7.23 6.22 4.67 3.50 2.87 port said 3.24 4.08 5.46 6.79 7.77 8.44 8.10 7.54 6.53 5.02 3.68 2.96 alexandria 3.21 4.14 5.56 6.92 7.79 8.50 8.35 7.72 6.56 5.04 3.64 2.97 marsa matrch 2.74 3.66 4.98 6.24 7.05 7.89 7.82 7.16 5.94 4.35 3.12 2.50 djerba modoun 2.62 3.64 4.90 6.27 7.02 7.67 7.82 7.07 5.51 3.87 2.82 2.32 gabes 2.62 3.64 4.90 6.27 7.02 7.67 7.82 7.07 5.51 3.87 2.82 2.32 sfax 2.58 3.53 4.57 5.87 6.85 7.38 7.44 6.63 5.06 3.47 2.68 2.36 sousse 2.37 3.29 4.33 5.67 6.72 7.38 7.60 6.53 4.97 3.34 2.48 2.16 tunis 2.30 3.20 4.22 5.22 6.34 6.94 7.31 6.29 4.69 3.37 2.47 2.09 annaba 2.28 3.15 4.25 5.21 6.25 6.98 7.14 6.08 5.00 3.57 2.45 2.02 skikda 2.27 3.15 4.26 5.22 6.20 6.91 7.08 6.12 4.94 3.53 2.42 2.01 bejaia 2.38 3.31 4.44 5.46 6.41 7.12 7.23 6.38 5.08 3.66 2.51 2.06 algiers 2.48 3.38 4.59 5.69 6.49 7.20 7.13 6.44 5.28 3.82 2.63 2.15 oran 2.72 3.64 4.74 5.94 6.55 7.08 6.92 6.26 5.25 3.94 2.80 2.40 table iii. average monthly eg [kwh] location jan feb mar apr may jun jul aug sep oct nov dec az zawiyah 558 593 754 771 847 860 910 868 732 625 541 430 tripoli-libya 561 595 755 772 847 860 910 868 733 627 543 432 al khums 520 522 701 745 855 888 955 872 677 616 483 465 misratah 592 602 821 865 979 1011 1078 1028 811 753 581 553 surt 656 606 735 703 804 855 886 834 739 625 535 592 benghazi 536 558 785 859 975 1007 1056 1008 811 742 568 510 turbruq 483 511 725 799 918 950 1006 954 794 702 513 460 tripoli-lebanon 554 571 786 849 1055 1083 1085 1043 905 810 610 520 beirut 390 438 630 672 845 901 887 849 720 660 508 419 tartus 474 480 655 731 930 979 978 930 781 678 507 444 al ladhiqiyah 546 574 779 835 1021 1061 1066 1029 890 806 585 511 gaza strip 581 557 751 805 919 989 988 967 827 792 602 582 port said 613 583 827 891 1065 1094 1079 1053 903 831 647 580 alexandria 606 597 849 913 1070 1107 1125 1089 911 840 641 585 marsa matrch 532 540 794 854 979 1007 1031 993 837 754 572 519 djerba modoun 499 550 744 822 941 969 1030 973 743 609 487 453 gabes 581 564 745 763 905 897 945 873 724 686 586 572 sfax 508 542 690 766 917 926 970 902 675 535 471 488 sousse 466 505 651 739 899 928 999 888 668 518 436 446 tunis 498 479 680 754 869 921 971 911 739 695 572 518 annaba 463 493 649 675 830 874 933 823 688 591 449 426 skikda 457 490 649 675 821 864 924 829 676 579 438 420 bejaia 491 525 688 715 857 897 949 876 701 611 463 436 algiers 434 456 616 623 789 757 914 881 706 526 513 414 oran 598 594 772 830 936 939 991 946 788 679 551 525 c. performance of the proposed system the environmental impact and economic performance of the proposed system were evaluated. in this study, the financial parameters (table iv) are assumed based on other previous scientific studies in different countries. in the present study, the system cost is around $5000, with the estimation being based on recent market data. the estimation is consistent with cost prices available in the literature. table iv. financial parameters factor unit value inflation rate % 2.5 discount rate % 3 reinvestment rate % 9 project life year 25 debt ratio % 50 debt interest rate % 7 debt term year 20 electricity export escalation rate % 5 engineering, technology & applied science research vol. 11, no. 4, 2021, 7508-7514 ᔐᔐᔐᔐ page 7512 www.etasr.com kassem et al.: a techno-economic viability analysis of the two-axis tracking grid-connected … fig. 3. annual eg and cf as a function of location. table v lists the results of the economic performances of the proposed system. the obtained results showed that the value of npv is positive, which makes the project to be financially and economically feasible. moreover, it is observed that the developed pv system in algiers has the longest value of ep of 4.0 years, while alexandria and port said have the lowest ep value (2.8 years). besides, the maximum and minimum values of sp are recorded in algiers and alexandria. these results indicate that the pv projects in all locations make financial sense. additionally, the lowest value of epc is found in alexandria with a value of 0.0334$/kwh followed by tripoli-lebanon with a value of 0.0336$/kwh. it is found that tripoli-libya and algiers have the highest value of lcoe compared to other selected regions with a value of 0.0475 $/kwh and 0.0453 $/kwh respectively. in general, the electricity price depends on the amount of energy consumption. for instance, the energy cost calculation in lebanon starts from 0.0255$/kwh for 0-100kwh energy consumption, 0.04$/kwh for 100-300kwh, 0.0584$/kwh for 300-400kwh, 0.0875$/kwh for 400-500kwh, and 0.146$/kwh for energy consumption over 500kwh. in syria, it starts from 0.005$/kwh for 1-100kwh energy consumption, 0.007$/kwh for 101-200kwh, 0.01$/kwh for 200-400kwh, 0.015$/kwh for 401-600kwh, 0.015$/kwh for 601-800kwh, 0.061$/kwh for 801-1000kwh, 0.071$/kwh for 1001-2000kwh, and 0.081$/kwh for energy consumption over 2000kwh. in palestine, it ranges from 0.15$/kwh to 0.17$/kwh for energy consumption over 200kwh. the households are charged a flat rate at 0.045, 0.04, and 0.077$/kwh respectively in egypt, algeria, and tunisia. hence, the energy production cost of the proposed systems is competitive with the electricity company tariff in the selected countries except for libya. table v. economic performance of the proposed pv system for all selected locations location npv [$] sp [year] ep [year] alcs [$/year] coe[$/kwh] ga-ghg [tco2] az zawiyah 21505.8 5.9 3.5 1235.0 0.0407 5.40 tripoli-libya 14927.7 5.9 3.5 1003.4 0.0475 5.40 al khums 20883.3 6.0 3.6 1199.3 0.0416 5.27 misratah 25344.5 5.2 3.0 1455.5 0.0357 6.15 surt 21762.4 5.8 3.5 1249.8 0.0403 5.45 benghazi 24505.5 5.3 3.1 1407.3 0.0367 5.98 turbruq 22554.1 5.7 3.3 1295.2 0.0392 5.60 tripoli-libya 26215.9 5.1 3.1 1505.5 0.0336 6.98 beirut 19655.3 6.3 3.8 1128.8 0.0436 5.60 tartus 21747.5 5.8 3.5 1248.9 0.0403 5.15 al ladhiqiyah 25442.0 5.2 3.0 1461.1 0.0356 5.84 gaza strip 24324.8 5.3 3.1 1396.9 0.0369 4.28 port said 26941.3 4.9 2.8 1547.2 0.034 4.65 alexandria 27477.5 4.8 2.8 1578.0 0.0334 4.73 marsa matrch 24493.0 5.3 3.1 1406.6 0.0367 4.30 djerba modoun 22569.0 5.7 3.3 1296.1 0.0391 4.02 gabes 22640.7 5.7 3.3 1300.2 0.039 4.03 sfax 21175.8 6.0 3.6 1216.1 0.0412 3.82 sousse 20382.1 6.1 3.7 1170.5 0.0424 3.71 tunis 21883.5 5.8 3.4 1256.7 0.0401 3.92 annaba 19575.6 6.3 3.8 1124.2 0.0437 4.39 skikda 19340.5 6.4 3.9 1110.7 0.0441 4.35 bejaia 20601.0 6.1 3.6 1183.1 0.042 4.56 algiers 18710.7 6.6 4.0 1074.5 0.0453 4.24 oran 23642.9 5.5 3.2 1357.8 0.0377 5.09 the results demonstrated that the proposed system can help in solving the electricity crisis while simultaneously reducing ghg emissions. consequently, it can be concluded that the developed system provides a very good insight into the economic viability of the project for all regions. additionally, the obtained results demonstrated that the development of the proposed 4.2kw pv power system is economically acceptable due to the obtained favorable economic results. iv. limitations and conclusions installing pv systems has become increasingly attractive for residential consumers due to increasing electricity tariff rates while it reduces a country’s dependence on fossil fuels. the objective of the current study was to investigate the feasibility of a two-axis tracking pv system in coastal mediterranean cities located in different countries using the retscreen software. before starting the main conclusions in the present study, it is essential to acknowledge the limitations of this work. first, the assumed financial parameters were engineering, technology & applied science research vol. 11, no. 4, 2021, 7508-7514 7513 www.etasr.com kassem et al.: a techno-economic viability analysis of the two-axis tracking grid-connected … based on historical values in the literature. second, the influence of various parameters such as dust, irradiation intensity, air temperature, and relative humidity was neglected due to the limitations of the software. third, the cost of the proposed projects was estimated based on the existing cost in the literature. the findings from the present study showed the annual value of sr for the selected regions is within the range of 1645.85 to 2141.33kwh/m 2 . based on these data, the analysis indicates that the selected regions selected cities have the potential for the distribution of pv power systems in household/residential applications. moreover, the average annual energy output showed that the 4.2kw grid-connected pv system could produce 8824kwh, indicating that it can cover the required electricity needs for one house located in each selected city. these results are supported by the findings in [13]. based on the financial assumptions used in this study, the average energy production cost ranges from 0.0334 to 0.0475$/kwh for the developed system. thus, the energy production cost of the proposed system is competitive with the electricity company tariff in the selected countries, except for libya. the results of this paper demonstrate that a small-scale grid-connected rooftop pv system has the potential to solve the electricity crisis, reduce the consumption of fossil fuel, and reduce the environmental pollution by minimizing the emissions of co2. the conducted analysis showed that the small-scale grid-connected rooftop pv systems are found to be technically, economically, and environmentally feasible solutions for generating electricity and reducing the dependency on fossil fuels. acknowledgment the authors would like to thank the faculty of engineering, especially the mechanical engineering department, at 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qsifeng@163.com abstract—the ductility of prestressed concrete pier is studied based on response surface methodology. referring to the pervious prestressed concrete pier, based on box-behnken design, the ductility of 25 prestressed concrete piers is calculated by numerical method. the relationship between longitudinal reinforcement ratio, shear reinforcement ratio, prestressed tendon quantity, concrete compressive strength and ductility factor is gotten. the influence of the longitudinal reinforcement ratio, the shear reinforcement ratio, the prestressed tendon quantity and concrete compressive strength to curvature ductility is discussed. then the ductility regression equation is deduced. the result showed that the influence of the prestressed tendon quantity to the ductility of prestressed concrete pier is significant. with the increasing of the prestressed tendon quantity, the curvature ductility curved reduces. with the increasing of shear reinforcement ratio and compressive strength of concrete, the curvature ductility increases linearly. and the influence of the longitudinal reinforcement ratio to ductility of the prestressed concrete pier is insignificant. keywords-response surface methodology; experiment design; prestressed concrete; pier; ductility i. introduction the application of prestressed concrete (prc) pier has increased because of its efficiency and high quality. precast segmental construction methods can cut construction costs by reducing construction time while maintaining quality. in addition, because of the self-centering capability of prestressed tendon, prc pier could meet the performance requirement during the normal use stage as well as improve the seismic performance of a whole bridge [1]. many researchers have investigated the seismic performance of prc pier. hewes and priestley investigated the performance of unbonded posttensioned precast concrete segmental bridge columns under lateral earthquake loading [2]. in [3], authors studied the seismic performance, identify the key design variables, and evaluate the effect of different ground motions and different column configurations for a self-centering reinforced concrete column with unbonded prestressing strand placed at the center of the cross section. in [4], authors investigated the seismic performance of unbonded prestressed hollow concrete columns constructed with precast segments. in [5], authors tested several different pier bents in a four-span bridge earthquake simulation study. in [6], authors investigated the response of segment joints using detailed non-linear time-history analyses. a suite of ten near field earthquake records was used to determine the median joint response as well as to quantify the effect of vertical motion on the joint response. the authors showed that a prestressed bar could increase pier self reset capability and decrease the residual displacement of the bridge pier under earthquake. the mechanical properties of prc pier are relation to some parameters, such as the longitudinal reinforcement ratio, the shear reinforcement ratio, the prestressed tendon quantity and compressive strength of concrete. the parameters analysis can be conducted with the statistical analysis methodology. response surface methodology (rsm) represents a collection of statistical and mathematical techniques and it is often used for development, improvement and optimization of various processes, where certain response is influenced by several variables. in [7], authors used rsm to investigate the performance of corroding under-reinforced beams. in [8], authors adopted he rsm to create response surface functions of the specific energy for thin-walled columns. in [9], authors used rsm to estimate the representative fragility curves for horizontally curved steel, i-girder bridges in conjunction with monte carlo simulation. experimental design is widely used for controlling the effects of parameters in many processes. its usage decreases the number of experiments, using time and material resources. central composite design (ccd) and box behnken design (bbd) are usually adopted in rsm. ccds are a factorial or fractional factorial design with center points, augmented with a group of axial points [10]. bbd is a type of response surface design that does not contain an embedded factorial or fractional factorial design [11]. in [12], bbd was emp[loyed to optimize the indomethacin-loaded chitosan nanoparticle size. in [13], bbd was used to optimize the nanoscale retrograded starch formation. in [14], bbd was applied for fabrication of titanium alloy and 304 stainless steel joints. the present paper investigates the ductility of prestressed concrete pier through response surface methodology. the this work was supported by foundation of china scholarship council (201506060044, 201508210247); foundation of liaoning provincial department of education funded projects (l2014027) engineering, technology & applied science research vol. 6, no. 6, 2016, 1253-1257 1254 www.etasr.com wang et al.: a study on ductility of prestressed concrete pier based on response surface methodology influence of the longitudinal reinforcement ratio, the shear reinforcement ratio, the prestressed tendon quantity and concrete strength grade to curvature ductility is discussed. ii. response surface methodology response surface methodology (rsm) is a collection of statistical and mathematical methods that are useful for modeling and analysis engineering problems. response surface methodology was developed by box and collaborators in the 1950s [15]. the design procedure of response surface methodology is as follows [11, 16]:  designing of a series of experiments for adequate and reliable measurement of the response of interest.  choosing of the experimental design and carrying out the experiments according to the selected experimental matrix.  getting the experimental results by serial experiments.  mathematic–statistical treatment of the obtained experimental data through the fit of a polynomial function. a. mathematical model the simplest model which can be used in rsm is based on a linear function [17]. k 0 i i i=1 y=β + β x +εå (1) where β0, β1 represents the coefficients of the linear parameters, xi represents the variables, k is the number of variables, and ε is the residual associated with the experiments. to evaluate curvature, a second-order model must be used. in order to determine a critical point (maximum, minimum, or saddle), it is necessary for the polynomial function to contain quadratic terms according to the equation presented below[17]: k k k 2 0 i i ii i ij i j i=1 i=1 1 i j y=β + β x + β x + β x x +ε £ £ å å å (2) where bii, βij represents the coefficients of the quadratic parameter. b. experimental design the parameters analysis could be conducted with statistical analysis methodology. in this study, bbd was chosen. for bbd, the design points fall at combinations of the high and low factor levels and their midpoints. box and behnken suggested how to select points from the three-level factorial arrangement, which allows the efficient estimation of the first and second-order coefficients of the mathematical model. bbds have treatment combinations that are at the midpoints of the edges of the experimental space and require at least three continuous factors [18], shown in figure 1. because bbds often have fewer design points, they can be less expensive to do than central composite designs with the same number of factors. table i contains the coded values of the factor levels for bbd on three factors. fig. 1. bbd cube for 3 factors: (a) cube for bbd and three interlocking 3 factorial design, (b) points for bbd and three interlocking 3 factorial design: table i. bbd table for 3 factors number x1 x2 x3 1 -1 -1 0 2 1 -1 0 3 -1 1 0 4 1 1 0 5 -1 0 -1 6 1 0 -1 7 -1 0 1 8 1 0 1 9 0 -1 -1 10 0 1 -1 11 0 -1 1 12 0 1 1 c 0 0 0 iii. the ductility capacity of prestressed concrete pier a. constitutive relations 1) concrete the concrete damage plasticity (cdp) model was adopted [19]. a general constitutive relationship for cdp model is shown in figure 2, where m un ε and m un σ presents strain and stress of m-th tipping point, m pl ε is the concrete compressive plastic strain on m-th loading, dc is compressive damage factor, and dt is tensile damage factor. compression section was defined as [20]: (a) (b) engineering, technology & applied science research vol. 6, no. 6, 2016, 1253-1257 1255 www.etasr.com wang et al.: a study on ductility of prestressed concrete pier based on response surface methodology 2 c 0 0 0 0 c 0 u u 0 ε ε f 2 ε ε ε ε σ= ε-ε f 1-0.15 ε ε ε ε -ε ì é ùï æ öï ê ú÷çï ÷ £çï ê ú÷ç ÷ï çè øê úïï ë ûí ï é ùïï ê ú £ £ïï ê úï ë ûïî (3) where fc=uniaxial compressive strength of concrete, ε0=yield strain, εu=ultimate compressive strain. tension section was defined as t t t1.7 t t t ε ε σ=f ε ε ε ε a -1 + ε ε ³ æ ö÷ç ÷ç ÷ç ÷çè ø (4) where 2t ta =0.312f , tf = uniaxial ultimate tensile stress of concrete, tε = peak tensile strain of concrete [21]. fig. 2. constitutive relationship for cdp model 2) reinforcement bilinear kinematic (bkin) hardening of material was used to define the behavior of the steel bar. material properties for the bar were as follows [20]: elastic modulus εs=200gpa; yield stress fy=335mpa; yield strain εy=0.00168 and 0.1 εs as the slope of the hardening phase. bkin model for the steel bar behavior for unloading and reloading branches is shown in figure 3. fig. 3. constitutive relationship for reinforcement 3) pt strands in this study, the mechanical model of the pt strands was also defined as a bkin model [20], where elastic ratio of prestressing tendons es=195gpa, yield stress fy=1860mpa; yield strain εy=0.00954 and 0.1 es as the slope of the hardening phase. effective tensile stress σcon=800mpa which was equivalent to 43% of the ultimate tensile strength, and axial compression ratio u=22.7%. b. definition of ductility because of inelastic deformation capacity of reinforced concrete ductility members depends on cross section of plastic rotation capacity in plastic hinge zone, through responding to the ductility capacity of prestressed concrete could compute cross section curvature ductility coefficient [22]. a measure of the ductility of structures with regard to seismic loading is the displacement ductility factor defined as δu/δy ,where δu is the lateral deflection at the end of the post-elastic range and δy is the lateral deflection at first yield. a rotational ductility factor for members has been calculated by some dynamic analyses as [23] u φ y φ μ = φ (5) where φu=maximum curvature at the section and φy=curvature of the section at first yield, as shown in figure 4. fig. 4. moment-curvature relationship the curvature ductility coefficient of a structure is usually much bigger than its displacement ductility factor in the plastic hinge zone. the reason is that rotation of plastic hinge becomes the main deformation while yield occurring [24]. in this paper, members will yield if the outermost longitudinal tensile plain reinforcement of reinforced concrete members reach to the initial yield curvature. the ductility of prc pier are relation to the longitudinal reinforcement ratio, the shear reinforcement ratio, the prestressed tendon quantity and compressive strength of concrete. referring to pervious prestressed concrete pier, based on bbd, it is operable to analyze ductility of prc pier with fem. iv. case study one bridge pier circular cross section is 2 meters in diameter, just as shown in figure 5. the ratio of longitudinal reinforcement x1 would take the values of 0.80%, 1.00% and 1.20%. the shear reinforcement ratio x2 would take the values of 0.03%, 0.035% and 0.04%. the prestressed tendon x3 would engineering, technology & applied science research vol. 6, no. 6, 2016, 1253-1257 1256 www.etasr.com wang et al.: a study on ductility of prestressed concrete pier based on response surface methodology take the values of 15.27-10, 15.27-15 and 15.27-20. the concrete strength grade x4 would take the values of 30, 40 and 50. there are four factors with three level. base on bbd, the experiment design and ductility coefficient results y are shown in table ii. fig. 5. geometrical characteristic of the tested pier section table ii. the experiment design and results no. x1(%) x2(%) x3 x4(mpa) y 1 1.0 0.040 20 40 4.204 2 1.0 0.040 15 30 4.378 3 0.8 0.035 15 50 6.998 4 0.8 0.035 20 40 4.109 5 1.0 0.030 15 30 3.822 6 1.0 0.035 10 50 11.67 7 1.0 0.035 10 30 6.979 8 1.0 0.040 15 50 7.270 9 1.0 0.035 20 50 4.778 10 1.2 0.030 15 40 5.260 11 1.0 0.030 10 40 8.720 12 1.0 0.040 10 40 9.304 13 1.2 0.035 10 40 8.995 14 1.0 0.035 15 40 5.476 15 0.8 0.035 10 40 8.940 16 0.8 0.030 15 40 5.681 17 1.0 0.030 15 50 6.687 18 1.0 0.030 20 40 3.971 19 0.8 0.040 15 40 6.098 20 1.0 0.035 20 30 2.777 21 1.2 0.035 15 50 7.042 22 0.8 0.035 15 30 4.278 23 1.2 0.040 15 40 5.648 24 1.2 0.035 20 40 4.146 25 1.2 0.035 15 30 3.989 with statistical analysis and ignore insignificant quadratic term, the ductility regression equation is deduced. 1 2 3 4 2 2 3 3 4 1 2 2 2 3 =9.48720-4.05461x -55.14804x -1.04795x +0.35360x -3.51000x x -0.013450x x +1.81397x +2197.35294x +0.039947x y (6) based on (6), the influence of each factor to curvature ductility is discussed. the results are shown in figures 6-8. fig. 6. relationship between longitudinal reinforcement ratio, prestressed tendon and ductility factor fig. 7. relationship between shear reinforcement ratio, prestressed tendon and ductility factor fig. 8. relationship between concrete strength, prestressed tendon and ductility factor the results show that the influence of the prestressed tendon quantity to ductility of prestressed concrete pier is significant and the influence of the longitudinal reinforcement ratio to ductility of prestressed concrete pier is insignificant. with the increasing of the prestressed tendon quantity, the curvature ductility curved reduces. with the increasing of shear engineering, technology & applied science research vol. 6, no. 6, 2016, 1253-1257 1257 www.etasr.com wang et al.: a study on ductility of prestressed concrete pier based on response surface methodology reinforcement ratio and compressive strength of concrete, the curvature ductility linear increases. v. conclusion based on response surface methodology, the ductility of prestressed concrete pier is studied. according to box-behnken design, the ductility regression equation is deduced with statistical analysis. the influence of the longitudinal reinforcement ratio, the shear reinforcement ratio, the prestressed tendon quantity and concrete strength grade to curvature ductility is discussed. the results show that:  the prestressed tendon quantity to ductility of prestressed concrete pier is significant. with the increasing of the prestressed tendon quantity, the curvature ductility curved reduces.  with the increasing of shear reinforcement ratio and compressive strength of concrete, the curvature ductility linear increases.  the influence of the longitudinal reinforcement ratio to ductility of prestressed concrete pier is insignificant. references [1] p. m. davis, t. m. janes, m. o. eberhard, j. f. stanton, unbonded pretensioned columns for bridges in seismic regions, pacific earthquake engineering research center headquartered at the university of california, berkeley, 2012 [2] j. t. hewes, m. j. n. priestley, seismic design and performance of precast concrete segmental bridge columns, san diego, la jolla, california.: university of california 2002 [3] h. i. jeong, j. sakai, s. a. mahin, shaking table tests and numerical investigation of self-centering reinforced concrete bridge columns, berkeley, california.: university of california, berkeley, 2008 [4] r. yamashita, d. sanders, shake table testing and an analytical study of unbonded prestressed hollow concrete columns constructed 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saghaeian, f. nateghi, o. rezaifar, “comparison of using different modeling techniques on prediction of the nonlinear behavior of r/c shear walls”, ije transactions b: applications, vol. 27, no. 2, pp. 269282, 2014 [22] z. yang, y. zhang, m. chen, g. chen, “numerical simulation of ultra strength concrete-filled steel columns”, engineering review, vol. 33, no. 3, pp. 211-217, 2013 [23] b. a. suprenant, curvature ductility of reinforced and prestressed concrete columns, bozeman: montana state university, 1984 [24] a. namdar, x. feng, “economical considerations in the development of construction materials-a review”, engineering review, vol. 35, no. 3,pp. 291-297, 2015 microsoft word 12-3156_s_etasr_v9_n6_pp4933-4936 engineering, technology & applied science research vol. 9, no. 6, 2019, 4933-4936 4933 www.etasr.com ghabri et al.: performance optimization of 1-bit full adder cell based on cntfet transistor performance optimization of 1-bit full adder cell based on cntfet transistor houda ghabri leti laboratory national school of engineering of sfax sfax, tunisia houda.ghabri@gmail.com dalenda ben issa leti laboratory national school of engineering of sfax sfax, tunisia dalenda_benissa@yahoo.fr hekmet samet leti laboratory national school of engineering of sfax sfax, tunisia hekmet.samet@enis.rnu.tn abstract—the full adder is a key component for many digital circuits like microprocessors or digital signal processors. its main utilization is to perform logical and arithmetic operations. this has empowered the designers to continuously optimize this circuit and ameliorate its characteristics like robustness, compactness, efficiency, and scalability. carbon nanotube field effect transistor (cnfet) stands out as a substitute for cmos technology for designing circuits in the present-day technology. the objective of this paper is to present an optimized 1-bit full adder design based on cntfet transistors inspired by new cmos full adder design [1] with enhanced performance parameters. for a power supply of 0.9v, the count of transistors is decreased to 10 and the power is almost split in two compared to the best existing cntfet based adder. this design offers significant improvement when compared to existing designs such as c-cmos, tfa, tga, hpsc, 18t-fa adder, etc. comparative data analysis shows that there is 37%, 50%, and 49% amelioration in terms of area, delay, and power delay product respectively compared to both cntfet and cmos based adders in existing designs. the circuit was designed in 32nm technology and simulated with hspice tools. keywords-1-bit full adder; cntfet; pdp; low power; hspice i. introduction semiconductor technologies are in a constant innovation race to create a new functionality and meet growth-up expectations. implemented semiconductor devices for scientific, industry and consumers, are expected to offer high performance with high speed, scalability, and, especially, low power consumption. in embedded electronic products such as mobile phones, laptops and connected watches, power consumption is a key element that influences directly circuit operation. metal oxide semiconductor field effect transistors (mosfets) can’t no longer comply with moore’s law [2-3], which led to the need of finding alternative technologies. each technology has its advantages and disadvantages. carbon nanotube field effect transistor (cnfet) is the most promising technology with interesting advantages. it is widely adopted and has become one of the most interesting research areas [4, 5]. cnfet is flexible in overcoming challenges like ballistic transport, short channel effects, low off-current properties, etc. because the complete adder circuit is indispensable in any digital product, the performance of any digital circuit can be improved by enhancing it performance. efforts to optimize performance are continuous, efforts such as the conventional–complementary metal oxide semiconductor [1], the removed single driving full adder (rsd-fa) [6], the hybrid pass transistor logic with static cmos output drive (hpsc) [3], the 18 transistor 1-bit full adder [7], the hybrid multi-threshold full adder (hmtfa) [8], and the low power based cntfet [9]. the implementation of these adder circuits takes place using various logic families, therefore the above mentioned adders have different advantages and disadvantages. in this paper, a new schematic with 10t transistor is proposed, inspired from the new cmos full adder design [1]. after simulation and analysis, this design offers an interesting pdp with limited number of transistors. table i shows the comparison results for the proposed and the existing full adder designs implemented using cnfet and cmos based on power, delay, and power delay product parameters (pdp). the proposed full adder circuit was designed with cnfet technology simulated at 32nm with a voltage supply of +0.9v using the hspice tool. the model used is a stanford nano model. ii. background of cnfet among new technologies, cntfet is placed as one with the most potential thanks to its specific physical characteristics. it offers many advantages like quasi-ballistic transport due to high mobility, fast switching due to high carrier speed, and almost one-dimensional structure of carbon nanotube for better electrostatic control [10]. in fact, each carbon nanotube reacts as a channel contrary to mosfet, where the entire silicon acts as a channel [11]. the mobility in n and p types of cnfet is identical and the two types of transistor transfer the same driving current. this allows the creation of a completely novel logic not possible with mosfet transistors. iii. existing adder designs many full adder designs are available in the literature. among them, the 23t full adder cell, which is an improved version of the 18t adder block [12], combining two logics, pass-transistor and transmission gate. there are five inverter stages to have the final output (sum) causing a longer critical path and utilizing an important number of transistors. the corresponding author: houda ghabri engineering, technology & applied science research vol. 9, no. 6, 2019, 4933-4936 4934 www.etasr.com ghabri et al.: performance optimization of 1-bit full adder cell based on cntfet transistor logical operations are performed serially and not simultaneously. two different blocks are used to generate the sum and the cout. this impacts strongly the speed of this circuit and the consumed power. another interesting design is the hybrid full adder cell [12, 13]. two different circuits are used to generate simultaneously the sum and the cout output. two cascaded xor/xnor cells are used to generate the sum signal and many inverters are required. as a result, a huge number of transistors are used and the critical path becomes very long, causing speed problem. in order to solve this issue the cntcpl architecture was proposed [14]. because its critical path is composed of only two pass transistors, the delay is very short. in addition, using cntfet technology increases speed, and overcomes the inconvenience of non-full-swing nodes. although this design solves the problem of speed, it is not an appropriate choice for low-power applications. this design suffers from many issues, such as low driving capability caused by utilization of pass-transistor logic, high transistor counts due to duplicate blocks for sum and cout, and finally signal integrity problem caused by cascading blocks in series, especially in high frequencies. cntfa based on cntfet transistor is the last studied full adder design [14]. this circuit is composed in intermediate xor and xnor functions and pass-transistor logic. the generated xor/xnor signals are used as selectors in a multiplexer-based structure at the second stage to generate sum. sum and output carry are generated in parallel by a pass-transistor based block. this design has multiple merits like high-speed computation and low power consumption, but when facing high load capacitors, it suffers from downfalls due to its low driving capability. as discussed above, the known full adder circuits have many disadvantages and performance optimization to follow the growing expectation is an open research topic. in this context we propose a new cntfet full adder design trying to find a solution to some of these problems. iv. proposed full adder circuit inspired from the new cmos full adder design [1] we propose a 1-bit full adder based on 10 cntfet transistors that calculate the sum and carry using less transistors. the sum and carry of any full adder are achieved from the input bits including the previous stage carry. the expressions giving the relationship between the input and output bits are: sum = a ⊕ b ⊕ cin (1) carry = a.b + b.cin + a.cin (2) where a and b are the inputs, the outputs are sum and carry and cin represents the carry input, if any. the proposed full adder design requires 10 transistors and consists of two xor/xnor gates. the implemented circuit composed of two xor gates which are designed by using four transistors each is shown in figure 1. less transistor count results to less load capacitance values and so the switching power dissipation is less in this cntfet based full adder compared to other techniques. we are presenting the smallest full adder design in cntfet technology (figure 1). transistor number reduction allowed us a considerable gain in consumption and generally in pdp. the simulation results of the proposed full adder are presented in figure 2. to show the amelioration done by the proposed design we compared the simulation results with the best cntfet based adder in literature. comparison parameters were power, delay and pdp. the mathematical calculations needed to perform this comparison are explained below. fig. 1. the proposed full adder cell a. power consumption calculation pdp keeps a balance between delay and power, it is the multiplication result of the maximum delay and the average power consumption: pdp = max(delay)×p��� (3) power average is the sum of two powers: static power and dynamic and short-circuit power [5]. static power comes from biasing and leakage currents. the most important component of power consumption, the dynamic power, is a result of the load capacitances charging and discharging. the load capacitance, cload, can be presented as a mix of a fixed capacitance, cfix, and a variable capacitance, cvar, as follows: cload = cfix+cvar (4) where cfix is the technology-dependent due to diffusion capacitance and interconnect dependent capacitances, cvar is composed of the input capacitances of subsequent stages and a part of the diffusion capacitance at the gate output and can therefore be taken care of by proper transistor sizing. p���= ids×vdd×fc×cload (5) where ids is the drain to source current (a), vdd is the supply voltage (v), cload is the output load capacitance (f), and fc is the clock frequency (hz). b. calculation of propagation delay the adder is a fundamental element in most electronic systems. that is why the optimization of its response delay affects directly the speed of the whole system. the speed of the adder response is mainly dependent on the propagation delay of the carry signal which is usually minimized by reducing the path length of the carry signal. the delay is calculated from the time that the input signal reaches ½vdd to the time that the output signal reaches the same voltage level. engineering, technology & applied science research vol. 9, no. 6, 2019, 4933-4936 4935 www.etasr.com ghabri et al.: performance optimization of 1-bit full adder cell based on cntfet transistor fig. 2. output waveforms of the proposed full adder design in the present design, the carry signal is generated by controlled transmission of the input carry signal and either of the input signals a or b (when a=b). as the carry signal propagates only through the single transmission gate, the carry propagation path is minimized leading to a substantial reduction in propagation delay. the delay incurred in the propagation is further reduced by efficient transistor sizing and deliberate incorporation of strong transmission gates. based on this information, power consumption and pdp are calculated for the proposed design. in table i, the performance of the proposed full adder is compared with existing designs [9]. the number of transistors for the proposed full adder is 10. the calculated delay is 4ps. for 0.9 supply the power consumption is 0.073µw and the calculated pdp is 0.592 aj. table i. comparative analysis for number of transistors, delay, power, and pdp full adder transistor count power (µw) delay (ps) pdp (aj) c-cmos [2] 28 0.124 12.355 1.532 tga [13] 20 0.135 10.104 1.364 cpl [17] 1.33 0.84 0.38 tfa [18] 16 0.109 11.701 1.275 hpsc [3] 26 0.095 30.654 2.912 clrcl [15] 10 5.903 231.18 1364.65 ours1 [4] 28 0.163 10.866 1.771 hctg [5] 16 0.124 12.116 1.502 rsd-fa [6] 26 0.091 9.427 0.857 18t-fa [6] 18 0.088 8.93 0.785 hmtfa [7] 23 0.1216 16.909 2.056 1bfa16 [9] 16 .073 8.12 0.592 proposed 10 0.073 4 0.295 v. conclusions a novel full adder cell inspired from recent cmos design has been presented. although many designs have been presented recently with the aim of reducing the number of transistors, they suffer from serious problems such as pdp, and delay. although reducing the number of transistors intrinsically leads to less area and power consumption, the other performance parameters should be taken into consideration in order to make the circuit work properly in real conditions. simulation results prove that the proposed full adder exhibits improvement in area, delay, and pdp by approximately 37%, 50%, and 49% respectively compared to the best cntfetbased adder found in the literature. in future work, this design can be further extended for a 32-bit full adder implementation. references [1] c. venkatesan, s. m. thabsera, m. g. sumitrha, m. suriya, “analysis of 1-bit full adder using different techniques in cadence 45nm technology”, 5th international conference on advanced computing & communication systems, coimbatore, india, march 15-16, 2019 [2] n. h. e. weste, k. eshraghian, principles of cmos vlsi design: a system perspective, addison-wesley, 1988 [3] c. h. chang, j. gu, m. zhang, “a review of 0.18-µm full adder performances for tree structured arithmetic circuits”, ieee transactions on very large scale integration (vlsi) systems, vol. 13, no. 6, pp. 686-695, 2005 [4] m. a aguirre-hernandez, m. linares-aranda, “cmos full-adders for energy-efficient arithmetic applications”, ieee transactions on very large scale integration (vlsi) systems ,vol. 19, no. 4, pp. 718-721, 2011 [5] p. bhattacharyya, b. kundu, s. ghosh, v. kumar, a. dandapat, “performance analysis of a low-power high-speed hybrid 1-bit full adder circuit”, ieee transactions on very large scale integration (vlsi) systems, vol. 23, no. 10, pp. 2001-2008, 2015 [6] y. s. mehrabani, m. eshghi, “noise and process variation tolerant, lowpower, high-speed, and low-energy full adders in cnfet technology”, ieee transactions on very large scale integration (vlsi) systems, vol. 24, no. 11, pp. 3268-3281, 2016 [7] k. s. jitendra, a. srinivasulu, b. p. singh, “a new low-power full adder cell for low voltage using cnfets”, ieee 9th international conference on electronics, computers and artificial intelligence, targoviste, romania, june 29-july 1, 2017 [8] m. maleknejad, s. mohammadi, k. navi, h. r. naji, m. hosseinzadeh, “a cnfet-based hybrid multi-threshold 1-bit full adder design for energy efficient low power applications”, international journal of electronics, vol. 105, no. 10, pp. 1753-1768, 2018 [9] k. s. jitendra, a. srinivasulu, r. kumawat, “a low power high speed cntfets based full adder cell with overflow detection”, micro and nanosystems, vol. 11, no. 1, pp. 80-87, 2019 [10] m. h. moaiyeri, r. f. mirrzae, k. navi, a. momeni, “design and analysis of a high-performance cnfet-based full adder”, international journal of electronics, vol. 99, no. 1, pp. 113-130, 2012 [11] y. m. lin, j. appenzeller, p. avouris, “novel structures enabling bulk switching in carbon nanotube fets”, device research conference, 62nd drc., notre dame, usa, june 21-23, 2004 [12] m. moradi, r. f. mirzaee, m. h. moaiyeri, k. navi, “an applicable high-efficient cntfet -based full adder cell for practical environments”, 16th csi international symposium on computer architecture and digital systems, shiraz, iran, may 2-3, 2012 [13] r. f. mirzaee, m. h. moaiyeri, h. khorsand, k. navi, “a new robust and high-performance hybrid full adder cell”, journal of circuits, systems, and computers, vol. 20, no. 4, pp. 641-655, 2011 [14] m. h. moaiyeri, r. f. mirzaee, k. navi, a. momeni, “design and analysis of a high-performance cnfet-based full adder”, international journal of electronics, vol. 99, no. 1, pp. 113-130, 2012 engineering, technology & applied science research vol. 9, no. 6, 2019, 4933-4936 4936 www.etasr.com ghabri et al.: performance optimization of 1-bit full adder cell based on cntfet transistor [15] m. h. ghadiry, a. a. manaf, m. t. ahmadi, h. sadeghi, m. n. senejani, “design and analysis of a new carbon nanotube full adder cell”, journal of nanomaterials, vol. 2011, article id. 906237, 2011 [16] j. f. lin, y. t. hwang, m. h. sheu, c. c. ho, “a novel high speed and energy efficient 10-transistor full adder design”, ieee transactions on circuits and systems i: regular papers, vol. 54, no. 5 , pp. 1050–1059, 2007 [17] b. l. dokic, “a review on energy efficient cmos digital logic”, engineering, technology & applied science research, vol. 3, no. 6, pp. 552-561, 2013 [18] n. zhuang, h. wu, “a new design of the cmos full adder”, ieee journal of solid-state circuits ,vol. 27, no. 5, 840–844., 1992 microsoft word 12-3506_s_etasr_v10_n3_pp5648-5654 engineering, technology & applied science research vol. 10, no. 3, 2020, 5648-5654 5648 www.etasr.com cham et al.: hydrodynamic condition modeling along the north-central coast of vietnam hydrodynamic condition modeling along the northcentral coast of vietnam dao dinh cham institute of geography vietnam academy of science and technology hanoi, vietnam chamvdl@gmail.com nguyen thai son institute of geography vietnam academy of science and technology hanoi, vietnam nguyenthaison99@gmail.com nguyen quang minh institute of geography vietnam academy of science and technology hanoi, vietnam nguyenquangminh2110@gmail.com nguyen thanh hung key laboratory for river and coastal engineering vietnam academy for water resources hanoi, vietnam nthungpacific@gmail.com nguyen tien thanh dpt. of hydrometeorological modeling and forecasting thuyloi university hanoi, vietnam thanhnt@tlu.edu.vn abstract—an extremely dynamic morphology of the estuary is observed in the coastal regions of vietnam under the governing processes of tides, waves, and river system flows. the primary target of this paper is to provide insight into the governing processes and morphological behavior of the nhat le estuary, located in the north-central coast of vietnam. based on measured data from field surveys and satellite images combined with numerical model simulations of mike and delft3d, the influences of seasonal river flow, tides, and wave dynamics on the sediment transport and morphological changes are fully examined. the study showed that freshwater flow in the flood season plays a central role in cutting off the southern sandspit, maintain and shaping the main channel. the prevailing waves in winter and summer induce longshore drift and sediment transport in the southeast to northwest direction. in the low flow season, this longshore sediment transport is dominant, causing sediment to deposit on the southern side of the ebb tidal delta and elongating the southern sandspit which narrows the estuary entrance and reorients the main channel. keywords-hydrodynamics; morphology; delft3d; nhat le estuary; mike i. introduction coastal and estuarial morphological features highly depend on the combined influence and interplay of river flows, waves, tides, and currents. additionally, meteorological phenomena significantly affect the hydrodynamic and morphodynamic processes of estuarial and coastal zones [1]. especially in the tropics, the effects of atmospheric circulations on a synoptic scale on the precipitation regime and changes in temperature are carefully monitored [2-3]. the behavior of hydrologic processes is analyzed by hydrological models [4]. generally, these studies illustrate changes in river flows and evolutions of estuarial or oceanic features dominated by the effects of atmospheric circulations. the effects of dam construction on the morphology are investigated in [5]. authors in [6] used the deflt3d system [5] to study the fluvial erosion and to investigate the temporal evolutions of hydrodynamic processes. this system is widely applied in researches in hydrodynamics, sediment transport and wave modeling [8-12]. interaction of wave-current and tidal depth changes are considered in katama bay using combined models of deflt3d-flow and swan. these studies indicated a good reproduction of waves and currents. these studies mostly emphasize on the regions dominated by physical processes at a large scale. for many projects dealing with water resources and hydrodynamics, mike system [13] is applied [14-17]. the uncertainty strongly depends on a large range of data requirements and parameter values [18]. in other words, there is a need to further investigate the performance of mike for the estuary and coastal areas in the tropics like vietnam where the dynamics are very unstable. in the coastal zones of vietnam, human activities and natural environment changes lead to imbalance in the coastal processes, changes in dynamical action, and sediment transfer. so far, only a small number of studies have been conducted in this topic [19-20]. the nhat le estuary is selected as a study area, along the north-central coast of vietnam. it is located in quang binh province as shown in figure 1. it connects a drainage basin of 2647km 2 to the gulf of tonkin. under the governance of wave and river hydrodynamics in a tropical monsoon region, the morphology of the estuary and the adjacent coast are very dynamic and unstable. during the last ten years, the development of the southern sandspit posed difficulties for navigation, especially for the fishing boats entering the shelter areas during typhoons or rough sea conditions. since 1977, the northern and southern coasts have been eroded by the alternate attacks of the monsoon waves. many research and dredging projects have been invested and several coastal structures have been built to stabilize the estuary, but the problems remain, due corresponding author: nguyen tien thanh engineering, technology & applied science research vol. 10, no. 3, 2020, 5648-5654 5649 www.etasr.com cham et al.: hydrodynamic condition modeling along the north-central coast of vietnam to the fact that the main governing processes and the actual mechanism of the estuary’s morphological instabilities are still not clearly understood. therefore, the goad of this study is to comprehend the changes in bed-sea topography and the causes of estuary evolution, while additionally providing more insight into the main governing processes and the behavior of the morphology at the estuary based on measured data and numerical modeling of hydrodynamics, sediment transport, and morphological changes at the estuary. fig. 1. study area (screenshot from google earth, map data: esri, digital globe, geoeye, earthstar geographics, cnes/airbus ds, usda, usgs, aerogrid, ign, and the gis user community) ii. the study area the nhat le river is 85km long, origins from the truong son cordillera with two major tributaries, dai giang and kien giang, and discharges into the sea at dong hoi city. near the estuary the river has a width of about 400 to 500m, an average depth of 2 to 4.5m and a maximum depth of 7m. the river flow regime is strongly governed by the tropical monsoon climate regime with the two distinguish flood and dry seasons. the flood season lasts from september to december when the northeast monsoon winds carry moisture from the sea and cause considerable rainfall and river floods. also, torrential rain may occur from july to october due to severe typhoons coming from the western pacific basin. the flood season only lasts four months but produces 76% of the annual flow. the mean annual rainfall is about 2500mm. the dry season is characterized by a dry and hot climate due to the sheltering of the truong son cordillera from the southwest monsoon winds. the tidal regime in this area is semi-diurnal with a spring tidal range of 1.2-1.6m. due to the micro tidal regime, the tidal currents are also weak. the observed tidal currents along the coast are smaller than 0.5m/s. the wave climate strongly reflects the monsoon system. in the northeast monsoon season the prevailing wave direction is from northeast, the average wave height is 0.8-0.9m but the highest winter wave height can be 4.0-4.5m. in the summer, the dominant wave directions are southwest and southeast with an average wave height of 0.60.7m while the highest wave height can reach 3.5–4.0m. during major storms wave height may exceed heights of 6m. iii. materials and methodology a. materials instruments were used and installed at measurement stations. typically, the trimble r8s is used to create a topography on land [21]. jmcf-2000 and odom hydrotrac ii are used to create a topography of the seabed [22]. the primary instrument used for wave data collection was the nortek acoustic wave and current profiler (awac) [23]. field data at the nhat le estuary have been measured intensively by the authors themselves for projects of the institute of geography (e.g. project with the code vast 06.03/15-16) during the period from 2005 to 2016. the data include bottom topography, waves, tidal water level, river discharge, and sediment grain sizes. within this project, dong hoi hydrologic station is newly installed to measure tidal water level and discharge. the data include bottom topography, waves, tidal water level, river discharge, and sediment grain sizes. figure 2 shows the locations of stations including the dong-hoi hydrological station and awac deployments to measure waves. b. numerical modeling: set-up and boundary conditions the mike is an implicit finite difference model for one dimensional unsteady flow computation and can be applied to simulate surface runoff, flow, sediment transport, estuaries, water quality or floodplains [13]. for this study, mike 11hd package was applied [13]. the upstream boundary conditions include river flow discharge computed for 8 tributaries using rainfall-runoff model (i.e. nedbor astromnings model (nam)) [24] coupled with mike 11 [25]. the nam model is used as a module of mike 11 under the name of mike-nam. the output of nam (i.e. discharge) is used as upper boundary condition at 8 the tributaries for mike 11hd to compute the hydraulic boundaries. the upper boundary locations are shown in figure 2. this model was originally developed by the department of hydrodynamics and water resources at the technical university of denmark [26]. it is a conceptual model, describing the physical characteristics of the basin, on the basis of which it calculates rainfall flows. the nam is the conceptual hydrological model. its parameters and variables present the mean values for the entire basin. the input data for nam include the time series data of rainfall at kien giang hydrologic station (17°00'40.89"n, 106°44'09.94"e), time series of daily mean air temperature, wind speed, relative humidity, and solar radiation at dong hoi (meteo) (17°28'19.83"n, 106°37'27.32"e) to simulate daily evaportranspiration, and flow discharge for the catchments. the process-based numerical model system delft3d [7] primarily designed with a focus on applications of water flow and quality, was applied in this study. the ocean forcings (i.e. tidal, wave actions, and sediment transport) were simulated using the delft3d model, namely a couple of delft3d-flow and delft3d-wave using swan [7, 27-28] were applied to take into account the influences of tides, wave forcing, and river discharges. the flow model is a hydrodynamic component of delft3d with a three dimensional hydrodynamic and transport simulation program. it is applied to solve the depth-averaged non-linear shallow water equations for nonsteady flows. simulations of hydrodynamic, sediment transport engineering, technology & applied science research vol. 10, no. 3, 2020, 5648-5654 5650 www.etasr.com cham et al.: hydrodynamic condition modeling along the north-central coast of vietnam changes were conducted. the wave model is also a component of delft3d with two available modules of hiswa [29] and swan [27] as the second and third generation wave model, respectively. in this study, swan model was applied for wave propagation and transformation in near-shore. fig. 2. computational domain and grid the modules of rgfgrid and quickin combined within the delft3d system were used to create smooth, orthogonal curvilinear grids and interpolate the topographic data. figure 2 shows the model domain, computational grid, bathymetry at the estuary and locations of upstream flow boundaries and observation stations. the computational grid for the nhat le estuary and its rivers and adjacent continental shelf consists of 512×329 nodes. fine-grid resolution was used locally and coarse resolution was used away from the regions of interest. the maximum grid size at the offshore open boundary is about 300m. the depth is extended to -5m and -52m for the near-shore and offshore areas respectively. the grid areas are enlarged from about 3km up to about 40km for the boundary of near-shore and offshore far from the coastline respectively. grid cells in the main estuary channels are 15m in length, while grid cells in outer are up to 300m in length. the bathymetry for the fine grid mesh is taken from survey at 30m resolution in the nhat le estuary area and 500m resolution for offshore areas. the seaward open boundary forcings were assumed to be astronomical tides. based on the global ocean tide model tpxo 8.0 [30], ten tidal constituents of q₁, o₁, p₁, k₁, m₂, s₂, k₂, n₂, mf, mm were found to be dominant in the area and were used as the open boundary conditions of the model. note that the boundary conditions of wave model are deep-water wave parameters (i.e. significant wave height, peak wave period, mean wave direction) from wavewatch iii model [28]. for simulations of sediment transport, the parameters automatically adopted from [8-9, 32-33] were used. iv. results and discussion a. results at first the model performance of mike and delft3d system needs to be calibrated and validated. in the process of calibration, model parameters were modified to reduce the error between the simulated and observed discharges. the model parameters found during model calibration were kept in the process of validation. the measured flow data at kiengiang station were used to validate the rainfall-runoff and river flow model. figure 3 shows the discharge simulations of mike system for calibration and validation during the flood seasons of 2015 and 2016. it is observed that the difference between simulation and observation discharge at kien giang is negligible with nash-sutcliffe indices [26] of 0.89 (in 2015) and 0.98 (in 2016). it is significantly remarkable to provide well-fitted results of models against the measured data as shown in figure 3 at kien-giang station. the model calibration and validation showed that the timing of the peaks was captured well, but the model slightly underestimated the discharge value in november 2015 for calibration. the parameters of overland flow runoff coefficient (cqof) and time constants for routing overland flow (ck12) are most sensitive to the simulation results of discharge, followed by the maximum water content in root zone storage (lmax) and root zone threshold value for overland flow (tof) parameters. these parameters are defined on the basis of statistical performance indices (i.e. coefficient of determination). (a) (b) fig. 3. comparison between modeled and observed flow discharges at kien-giang station for the flood seasons in (a) 2015 and (b) 2016 the hydrodynamic model was calibrated for the period from 16 may to 20 may 2015 using the collected data at the awac station in the estuary. model validation is firstly performed using the water level, depth averaged current, and wave measurements at the awac station. figures 4-5 present a comparison between model predictions and measurements for water surface levels and depth averaged flow currents at awac station. the nash-sutcliffe indices for the efficiencies of the model versus data for water surface elevation, xand ycomponents of flow velocity are 0.96, 0.76 and 0.63 respectively indicating a good agreement between the model and the data. the model output is mostly influenced by the water level and discharge at the model boundaries and is especially sensitive to winds. besides water surface elevation and depth averaged flow currents, the comparison of wave engineering, technology & applied science research vol. 10, no. 3, 2020, 5648-5654 5651 www.etasr.com cham et al.: hydrodynamic condition modeling along the north-central coast of vietnam parameters including significant wave height, wave period, and wave direction between model and data also provides reasonable agreement (figure 6).the satellite images and field survey data were used to validate the simulations of the sediment transport. fig. 4. modeled (blue) and measured (red) water level at awac station (a) (b) fig. 5. comparison between modeled (blue) and measured (red) flow velocities for (a) xand (b) ycomponents at awac station (a) (b) (c) fig. 6. model prediction and measured data comparison for (a) significant wave height, (b) wave period, and (c) wave direction at awac station b. discussion based on the calibrated model, hydrodynamics and morphodynamics of the nhat le estuary were simulated and analyzed to investigate the influences of different governing processes such as tides, waves and river flows. firstly, a simulation of fresh water inflow and tides-only forcing was carried out. then a fully hydrodynamic model of all forcing (fresh water inflow, tides, winds and waves) was simulated. two simulation periods, may 2015 and september 2015, represented the different conditions in summer and winter respectively. 1) wave characteristics the model results of wave parameters were extracted at four different locations (p1 to p4) surrounding the entrance (figure 7(a)). wave roses for the period of 2015-2016 are plotted for these locations in figure 7(b). the purpose of this is to clarify the role of winds in affecting the wave characteristics. it is observed that the deep-water waves are prevailing from the east and north-northeast directions. when the waves are approaching the estuary, the dominant wave directions are east and northeast due to wave refraction. as the northeast waves are mostly normal to the coastline, the wave action would contribute mainly on the cross-shore sediment transport but not the long-shore sediment transport. therefore, the dominant eastern waves could be the major source in inducing longshore sediment transport in the estuary. due to the dominant eastern wave actions, the net long-shore sediment transport is directed in the southeast-northwest which elongates the southern sandspit and forces the main channel to head north. (a) (b) fig. 7. locations for wave extraction, (b) corresponding wave roses 2) estuary hydrodynamics figure 8 shows the peak velocities of ebb and flood tide velocities in three different situations: 1) tidal only forcing, 2) tides and northeast waves in winter monsoon season, and 3) tides and southeast waves in summer monsoon season. snapshots of the depth-averaged currents during flood and ebb tide periods show the strong velocities in the tidal channel at the entrance due to the restriction of the entrance because of the elongating southern sandspit. the combination of tides and fresh water inflow causes much stronger ebb tidal velocity than engineering, technology & applied science research vol. 10, no. 3, 2020, 5648-5654 5652 www.etasr.com cham et al.: hydrodynamic condition modeling along the north-central coast of vietnam flood tidal velocity (figures 8(a) and 8(d)). the strongest flow velocities during flood and ebb tides at the entrance have an important role in maintaining the entrance and orienting the main channel. away from the entrance, the flow currents decrease quickly over the ebb tidal delta. it can be seen that the tidal currents along the coast during the ebb tide are much stronger than during the flood tide, making the system to export sediments to the southern coast, i.e. the tidal currents transport fluvial sediment from the river mostly to the southern coast. fig. 8. peak velocities during flood tide (top) and ebb tide (bottom) in different tide and seasonal wave conditions (axes units are meters) in the case of wave present, the contribution of wave radiation stresses makes the flow field to be more complex. the results show that the long shore currents during the winter ne waves are much stronger than during the summer se waves but both wave conditions generate long shore currents and long shore sediment transport in the se-nw direction which cause the southern sandspit to elongate northwest. unlike the fresh water flow and tide only conditions, in the case of wave present both flood and ebb currents seem stronger and the flood currents are able to transport sediment from the ebb tidal delta and those delivered by long shore currents further landward thus reshaping the shores. the model results suggest that tidal and river flows dominate the main channel and the inner estuarine zone. especially during high river discharge events, which are frequent over winter months, river discharge and ebb tides flush sediment seaward and then the offshore tidal currents will transport the sediment to supply the southern coast. wave-induced circulations and alongshore currents prevail on the ebb tidal delta and in the near-shore region on both sides of the estuarine mouth. in the near-shore area away from the inlet, wave-induced circulation patterns are often driven by the interaction between the waves and the seabed. the strong wave radiation stress modifies the pattern of the depth-averaged velocity especially near to the coast and the sand bar due to wave breaking in this region. under the condition of combined currents and waves, the flow magnitude increases considerably in the tidal channel and particularly in shallow water depths. it is specially noted that coastal waves induced by currents (e.g. tidal currents) could reach up to 0.5m/s in most of the coastline. these currents combined with tidal and river flow produce a jet that can reach the depth of 10m in ebb tide conditions. 3) sediment transport and bottom changes sediment transport and bottom morphological changes are simulated for various conditions of hydrodynamic and wave forcings. sediment grain size is setup uniformly with d50=0.03mm based on bed core data. tides, waves, and river discharge are the main parameters that effect on the sediment transport and morphology responses. (a) (b) (c) fig. 9. erosion/accretion processes are displayed by (a) simulation modeling, (b) google earth image (screenshot from google earth, map data: image@2015 digital globe, image@2015 terrametrics and maxar technologies), and (c) survey data for the flood season in 2015 the simulations’ performance was well-fitted to the measured data during the high flow season. it is observed that sediment has pushed away from the estuary to the ebb tidal delta (figure 9). alongshore wave-driven and tidal currents engineering, technology & applied science research vol. 10, no. 3, 2020, 5648-5654 5653 www.etasr.com cham et al.: hydrodynamic condition modeling along the north-central coast of vietnam redistribute this sediment to accrete along the coastline. it is worth noting that during the low flow season, as a result of the long shore drift and sediment transport from the south which is weakly interrupted by the tides and river inflow, sediment continues to accumulate and deposit at the southern side of the ebb tidal delta and at the tip of the southern sandspit and causes the sandspit to develop northward (figure 10). (a) (b) fig. 10. erosion/accretion processes are displayed by (a) simulation modeling and (b) survey data for a low flow season (2015) v. conclusions this study presents the first attempt to fully couple hydrodynamic and morphodynamic models (mike and delft3d) for a better insight into the morphology evolution of nhat le estuary, vietnam. the simulations document a series of complexity trends under the ensemble effects of tides, waves, flows, and winds. the major physical processes governing the estuary morphology including tides, waves, and freshwater discharge were simulated. the model system was calibrated and validated using measured and observed data from 2005 to 2016. the simulations presented in this paper are, of course, limited to the particular sedimentary and morphological conditions of the nhat le estuary. although the findings are not considered with sedimentary and geological evolution at the upstream of nhat le river basin and at a regional scale of north-central coast of vietnam, they allow making hypotheses and conducting further research in a wider range. the results of the simulations are in accordance with the measured and observed data during the periods of calibration and validation. the results demonstrate that the seasonal variations of freshwater flow and ocean waves under the tropical monsoon regime significantly affect the behavior of the estuary morphology. the role of freshwater flow in the flood season is to cut off the southern sandspit, maintain, and shape the main channel. sediment from the river is exported to the ebb tidal delta due to the ebb dominant freshwater inflow and tidal currents. outside the estuary, ebb dominant tidal currents transport the sediment to the south and supply the southern coast. the prevailing waves in winter and summer induce long shore drift and sediment transport in the se-nw direction. in the low flow season, this long shore sediment transport is dominant which causes sediment to deposite on the southern side of the ebb tidal delta and elongates the southern sandspit to narrow the estuary entrance and reorient the main channel. acknowledgment this research was supported by projects vast 06.06/1920, kc08.16/16-20, and ndt.30.ru/17 protocol. references [1] g. masselink, “the effect of sea breeze on beach morphology, surf zone hydrodynamics and sediment resuspension”, marine geology, vol. 146, no. 1-4, pp. 115-135, 1998 [2] m. luo, n. c. lau, “synoptic characteristics, atmospheric controls, and long-term changes of heat waves over the indochina peninsula”, climate dynamics, vol. 51, no. 7-8, pp. 2707-2723, 2018 [3] n. t. thanh, n. h. son, “understanding shoreline and riverbank changes under the effect of meteorological forcings”, 10th international conference on asian and pacific coasts, hanoi, vietnam, september 26-28, 2019 [4] a. n. laghari, w. rauch, m. a. soomro, “a hydrological response analysis considering climatic variability”, engineering, technology & applied science 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engineering, technology & applied science research vol. 10, no. 2, 2020, 5512-5519 5512 www.etasr.com alkhafaji & izzet: prestress losses in concrete rafters with openings prestress losses in concrete rafters with openings falah jarass aied alkhafaji department of civil engineering college of engineering university of baghdad, iraq falahgaras@gmail.com amer farouk izzet department of civil engineering college of engineering university of baghdad, iraq amer.f@coeng.uobaghdad.edu.iq abstract—in this paper, experimental work was conducted to evaluate the losses in prestressing force of 13 (12 perforated and 1 solid) simply supported prestressed concrete rafters. all beams had the same dimensions and reinforcements. the tested beams were divided into four main groups and three additional subgroups were driven. these groups were classified according to size, number, and configuration of the openings, and the orientation of the posts (vertical or inclined). regarding the prestress losses that have been affected by the cross-section properties, the provision of the codes is applicable only to prismatic solid beams, so non-prismatic or moreover perforated beams also need to be studied. this paper aims to propose a method based on the same code provisions but taking into consideration the cross-section variation along the beam length. the proposed method divides the overall length of the rafter into a number of assumed prismatic segments with heights measured at centers. then, the overall prestress loss is found as the sum of these segments weighed by the ratios of the length of each beam segment to the overall length. the experimental results of the proposed method ranged from 84.749% to 95.607% denoting its validity. keywords-prestress losses; rafter beams; openings i. introduction the stresses in the tendons of prestressed concrete members are decreasing with time, but at a decreasing rate, and asymptotically level off after a long time. the total stress reduction during the lifespan of the member is called total prestress loss [1-3]. the reduction in the prestressing force can be grouped into two categories: • immediate elastic loss during the fabrication or construction process, including elastic shortening of the concrete, anchorage losses, and frictional losses. • time-dependent losses such as creep, shrinkage, and those due to temperature effects and steel relaxation, all of which are determinable at the service-load limit state of stress in the prestressed concrete element. an exact determination of the magnitude of these losses, particularly the time-dependent ones, is not feasible, since they depend on many interrelated factors. empirical methods of estimating losses differ with the different codes of practice or recommendations. the degree of rigor of these methods depends on the approach chosen and the accepted practice of record [4-5]. the presence of openings in gable reinforced concrete beams has many advantages such as flexibility, easier handling, and, most importantly, reduced overall weight. furthermore, concrete has very low to no maintenance cost and high fire resistance, therefore reinforced concrete gable beams can be used as a good alternative option to design roofs for warehouses, industrial buildings, and airplane hangars instead of steel sections [6-10]. the link structural elements (posts) between the upper and the lower chords of the rafter beam have many advantages such as avoiding vierendeel truss to prevent shear failure and allowing a beam to enhance its bending capacity and ductility [11]. the fact that concrete is not efficient in resisting tensile stress makes very difficult reaching a long span beam in design, so the addition of prestressing reinforcements has become necessary to reach span lengths which cannot be reached by using ordinary reinforcements [1213]. to estimate losses such as elastic shortening, creep, shrinkage, and relaxation in beams, the empirical methods recommended by the codes are only applicable to prismatic beams. no special recommendations have been included regarding rafter beams with or without openings. this study has proposed a method to estimate prestress losses in rafter beams, which are divided into a number of segments that are assumed to be prismatic along their lengths with heights measured at centers. ii. experimental investigation the experimental program consisted of casting and testing of 13 rafter beams, including 12 beams with openings (perforated) and one reference solid beam without openings. all the tested beams had the same rafter geometry, i.e. a rectangular cross-section of 100mm width and height of 400mm at center tapered to 250mm at the two ends, while the overall length was 3000mm with a clear span of 2800mm. figure 1 shows the geometrical details of the tested beams. figures 2 and 3 exhibit the details of the solid prestressed rafter concrete beam and the beams with openings respectively. mild steel reinforcement of 4, 6, and 12mm bar diameters were used while seven-wire low-relaxation strands, grade 270 with ø12.7mm diameter were used as prestressing steel. the tested beams were divided into four main groups (a, b, c, and d). these groups were classified according to the studied variables which are: size, openings number, posts inclination, and configuration of the openings. table i exhibits the grouping according to these variables as follows: corresponding author: falah jarass aied alkhafaji engineering, technology & applied science research vol. 10, no. 2, 2020, 5512-5519 5513 www.etasr.com alkhafaji & izzet: prestress losses in concrete rafters with openings • main groups to study the effect of openings’ width versus the number of openings along the beam length, it is worth to highlight that group a and b had vertical posts whereas group c had inclined posts. group a and c had the same upper and lower chords depth of 100mm whereas it was 75mm for group b. group d has been prepared in order to study the effect of the increasing of the opening area in the case of using the same number of circular openings. • subgroups group e has been driven to investigate the effect of increasing opening height or in other words decreasing depth of the upper and lower chords of the beam (beams have been taken from groups a and b). group f was driven to find the effect of post configurations linked between the upper and lower beam chords, i.e. the geometric shape of the quadratic openings (beams have been adopted from groups a and c). group g consists of beams with the same number of openings but with different openings configurations in order to compare circular and quadratic openings (beams have been chosen from groups a, b, c and d). a. measurements of prestress losses prestress losses were determined at different stages (at transfer of prestressing force and just before loading test). a special high accuracy electrical resistance measuring device was used for this purpose. electrical resistance strain gauges (fla-6-11, length=6mm) with gauge factor of 2.09±1%, and resistance of 120.4ω were fixed on the strand and bridged to the data logger. an initial reading was recorded on applying the prestressing force, and another reading was conducted before the load test. the electrical resistance is converted to strain through the following equation: 0 0 ir r kr ε − = (1) where ��=initial electrical resistance at the moment of prestress transfer, ��=electrical resistance immediately before testing, and �=strain gauge factor (for this type of strain gauge, �=2.09). through (1) the electrical resistance is converted to strain. this strain is compared with the strain calculated from the elongation which was measured immediately after applying the prestressing [14]. b. prestressing process for post-tensioning concrete gable beams, after attaining the age of 57 days for concrete, the prestressing process has been done according to the following sequence: • after fixing the strain gauges on the strand (7-wire strand, 12.7mm diameter), it was inserted through the pvc duct which has been embedded in the mold before concrete casting. • bridging the strain gauges wires to strain indicator (data logger) • attaching the predesigned end bearing steel plates with adequate grips at the beam ends. • applying the prestressing force (110kn) from one end according to the aci-318m-14 [15] limitations. • finally, releasing the jack and measuring the strand elongation and the strain which has been occurred in the strand. the corresponding strain was monitored and compared with the reading of the pressure gauge of the hydraulic jack. table i. details of tested beams group beam mark shape of openings number of openings total area of openings (mm 2 ) width of openings (mm) height of upper chord (mm) height of lower chord (mm) a pgb ----------0 --------------- pgt6 trapezoidal 6 180000 200 100 100 pgt8 trapezoidal 8 174000 150 100 100 pgt10 trapezoidal 10 144000 100 100 100 b pgb ----------0 --------------- pgth6 trapezoidal 6 240000 200 75 75 pgth8 trapezoidal 8 234000 150 75 75 pgth10 trapezoidal 10 195000 100 75 75 c pgb ----------0 --------------- pgp6 trapezoidal with inclined posts 6 154000 200 100 100 pgp8 trapezoidal with inclined posts 8 151000 150 100 100 pgp10 trapezoidal with inclined posts 10 138000 100 100 100 d pgb ----------0 --------------- pgc1 circular 8 184200 d 75 75 pgc2 circular 8 128000 0.83d 100 100 pgc3 circular 8 82000 0.67d 120 120 engineering, technology & applied science research vol. 10, no. 2, 2020, 5512-5519 5514 www.etasr.com alkhafaji & izzet: prestress losses in concrete rafters with openings fig. 1. geometrical details of the tested beams iii. experimental results and discussion the prestressing losses were monitored. these losses result from end anchorage slip, strand friction with the duct, strand relaxation and shrinkage, and creep of concrete. table ii shows the prestress losses and the residual prestress (effective prestress). it was observed that the losses ranged from 17.465% to 20.309% of the initial prestress depending on size, number of openings, posts inclination, and openings configuration. the effect of the considered parameters on the prestress losses are: for group a, b, and c, when the number of openings increases, the prestress losses decrease. this might be due to the minimization of total area of openings and increasing number of posts which have a positive effect on prestress losses and the behavior of the beam in general. the following comparison demonstrates the decreasing ratio in prestress losses with increasing number of openings: • group a: 2.558 and 4.33% for pgt8 and pgt10 beams respectively in relation to beam pgt6. • group b: 2.175 and 3.403% for pgth8 and pgth10 beams respectively in relation to beam pgth6. • group c: 2.888 and 4.764% for pgp8 and pgp10 beams respectively in relation to beam pgp6. • group d (circular openings) it can be noticed that, the prestress losses decrease with reducing size of circular openings. the decreasing ratio was 4.25% and 6.441% for gc2 and gc3 beams respectively in relation to gc1. • group e compares the beams of groups a and b. the decreasing depth of both upper and lower chords (group b) by 25% (elative to that of group a) led to reduced prestress losses by 3.824% for beam pgt6 related to beam pgth6 (group ei), 4.201% for beam pgt8 related to beam engineering, technology & applied science research vol. 10, no. 2, 2020, 5512-5519 5515 www.etasr.com alkhafaji & izzet: prestress losses in concrete rafters with openings pgth8 (group eii), and 4.749% for beam pgt10 related to beam pgth10 (group eiii) respectively. • group f consists of a comparison between the beams of groups a and c. the beams of the two groups have the same number of openings and post dimensions but they differ in their inclinations. the prestress losses were 0.438% for beam pgp6 related to beam pgt6 (group fi), 0.775% for beam pgp8 related to beam pgt8 (group fii), and 6.567% for beam pgp10 related to beam pgt10 (group fiii). (a) (b) fig. 2. (a) reinforcement details for solid rafter pgb, (b) section a-a (all dimensions are in mm) (a) (b) (c) fig. 3. (a) details of reinforcement for rafter with openings pgt6, (b) section b-b, (c) section c-c • group g consists of beams having eight openings but different configurations (circular and quadratic openings), with both opening shapes are restricted by the same chord depth. the results indicate a decrease in the prestress losses on the beams with circular openings in comparison with the beams with quadratic openings. the decrease ratios are: 2.488% for beam pgc2 related to beam pgt8 (group gi), 2.437% for beam pgc1 related to beam pgth8 (group gii), and 1.726% for beam pgc2 related to beam pgp8 (group giii). iv. prestress losses with the proposed method the variation in cross-section properties should be considered in order to calculate the prestress losses in solid or perforated rafter beams. the method suggests dividing a rafter beam into a set of segments that are considered as prismatic parts with heights measured at centers (figure 4). for the perforated beams, the number of segments should be chosen in a manner such that the segment is either solid or with openings. the overall prestress loss is found as the summation of the contributions of the beam subdivisions weighed by the ratio of the length of the beam segment to the overall length. the pgt6 beam has been taken as an example to show the steps of the estimation process in details. the same procedure was used for the other tested beams. 1) instantaneous losses a) anchorage seating loss usually long tendons will be less affected by seating loss. for short tendons, the seating loss should be detected and subtracted from the applied prestressing force [16]. assuming ∆a=1.5 mm and l=3000 mm and by (2): ���� �� �� (2) substituting we get ����=98.75mpa. b) elastic shortening no elastic shortening occurred because only one strand was used in each beam: ���� 0 c) friction losses the strand is straight therefore there is no curvature, α=0. assuming that wobble coefficient k=0.002, by (3) we get: ���� ����μ � � � �� (3) substituting we get: ����=6.25mpa. the stress remaining in the restressing strand after all instantaneous stresses is: ��� ��� � ����� � ���� � ����� (4) substituting we get: ��� =116-(105.8+6.25)=1003.95mpa. the net prestressing force is calculated by: �� ��� �� (5) substituting we get: �� ��� �� =99391n. 2) time dependent losses a) stage (i): losses after 24hr of the force transfer • relaxation loss: for t1=1hr, t2=24hr: ���! ��� "#$%&' (#$%&)*+ , ./0 ./1 � 0.554 (6) substituting we get: ���!=6.89 mpa. engineering, technology & applied science research vol. 10, no. 2, 2020, 5512-5519 5516 www.etasr.com alkhafaji & izzet: prestress losses in concrete rafters with openings table ii. prestress losses and stresses in prestressed concrete beams up to the moment of testing group beam's labeling prestress stress (mpa) age of beam at testing (days) age of beam transferred to testing (days) instantaneous losses after transfer (mpa) time dependent losses at testing (mpa) total prestress losses, (mpa) ∆pft residual prestress in strands, (effective prestress) (mpa) presstress loss/initial prestress (%) increasing ratio of losses% (1) main groups a pgb 1116 105 48 100.313 94.596 194.909 921.090 17.465 0 pgt6 1116 115 58 107.088 110.894 217.982 898.0176 19.533 11.837 pgt8 1116 120 63 105.494 106.912 212.406 903.594 19.033 8.9766 pgt10 1116 122 65 104.751 103.787 208.538 907.462 18.686 6.9922 b pgb 1116 105 48 100.313 94.596 194.909 921.091 17.465 0 pgth6 1116 123 66 105.122 121.528 226.650 889.350 20.309 16.284 pgth8 1116 125 68 104.244 117.476 221.720 894.280 19.867 13.755 pgth10 1116 127 70 105.208 113.729 218.936 897.063 19.618 12.327 c pgb 1116 105 48 100.313 94.596 194.909 921.090 17.465 0 pgp6 1116 128 71 101.489 115.539 217.028 898.972 19.447 11.348 pgp8 1116 129 72 97.996 112.764 210.760 905.240 18.885 8.1322 pgp10 1116 130 73 105.789 100.899 206.688 909.312 18.520 6.0427 d pgb 1116 105 48 100.313 94.596 194.909 921.091 17.465 0 pgc1 1116 131 74 98.013 118.303 216.316 899.684 19.383 10.982 pgc2 1116 132 75 97.727 109.396 207.123 908.878 18.559 6.2657 pgc3 1116 133 76 103.649 98.733 202.382 913.618 18.135 3.8338 secondary groups ei pgb 1116 105 48 100.313 94.596 194.909 921.091 17.465 0 pgt6 1116 115 58 107.088 110.894 217.982 898.018 19.533 11.837 pgth6 1116 123 66 105.122 121.528 226.650 889.350 20.309 16.284 eii pgb 1116 105 48 100.313 94.596 194.909 921.091 17.465 0 pgt8 1116 120 63 105.494 106.912 212.406 903.593 19.033 8.9766 pgth8 1116 125 68 104.244 117.476 221.720 894.240 19.867 13.755 eiii pgb 1116 105 48 100.313 94.596 194.909 921.091 17.465 0 pgt10 1116 122 65 104.751 103.787 208.538 907.462 18.686 6.992 pgth10 1116 127 70 105.207 113.729 218.937 897.063 19.618 12.327 fi pgb 1116 105 48 100.313 94.596 194.909 921.091 17.465 0 pgt6 1116 115 58 107.088 110.894 217.982 898.018 19.533 11.837 pgp6 1116 128 71 101.489 115.539 217.027 898.973 19.447 11.348 fii pgb 1116 105 48 100.313 94.596 194.909 921.091 17.465 0 pgt8 1116 120 63 105.494 106.912 212.406 903.594 19.033 8.977 pgp8 1116 129 72 97.997 112.764 210.761 905.240 18.885 8.132 fiii pgb 1116 105 48 100.313 94.596 194.909 921.091 17.465 0 pgt10 1116 122 65 104.751 116.464 221.215 894.785 19.822 6.640 pgp10 1116 130 73 105.789 100.899 206.688 909.312 18.520 6.043 gi pgb 1116 105 48 100.3134 94.596 194.9094 921.0906 17.465 0 pgt8 1116 120 63 105.4942 106.912 212.4062 903.5938 19.0328 8.9766 pgc2 1116 132 75 97.72652 109.396 207.1225 908.8775 18.5594 6.2657 gii pgb 1116 105 48 100.3134 94.596 194.9094 921.0906 17.465 0 pgth8 1116 125 68 104.244 117.476 221.72 894.28 19.8674 13.755 pgc1 1116 131 74 98.01274 118.303 216.3157 899.6843 19.3831 10.982 giii pgb 1116 105 48 100.3134 94.596 194.9094 921.0906 17.465 0 pgp8 1116 129 72 97.99647 112.764 210.7605 905.2395 18.8853 8.1322 pgc2 1116 132 75 97.72652 109.396 207.1225 908.8775 18.5594 6.2657 (1) 5678 �9:;<�( 5678 ��=>� 5678 ��=>� ∗ 100 • creep loss: ��a! 0 • shrinkage loss: ���b 0 • tendon stress at the end of stage i: �� ��� � ���! (7) substituting we get: �� 997.06mpa. b) stage (ii): losses after 58 days: • creep loss: �� ��� �� = 98.709kn rd ef�f (8) ẛh � � �0�f × -1 � :0' j0' 4 � kl0 :0ef (9) for part no.1: i=1, l1=0.6m (length of segment), x1=0.3m, y1= 0.15 0.3 1.45 × =0.031m, h1=0.25+y1=0.281m (height of sectional center of segment), b1=0.1m (beam width), a1=b1×h1=0.0281m 2 (cross section area of segment), so: i1= >)×b) *d =0.00018497m 2 , 1 1 2 2 0.00658mc c i i a r = = and m* = "b)d � nop, =0.0905m. taking as h=0.25m we have: engineering, technology & applied science research vol. 10, no. 2, 2020, 5512-5519 5517 www.etasr.com alkhafaji & izzet: prestress losses in concrete rafters with openings q* r* × s × ϫh =0.6kn/m and w2=0.0155kn/m. r is: � uvw(vx/yz0z[\×ϫ]d =0.963kn, and: md1 � × ^* � �q* × ^* × _* � qd × `'d × _d� 0.2617 ẛh � � �) �]) i "1 � :)'j)', � kl) :) eh� 7.75769mpa. with ẛh � i `0�=3.103mpa we have: ẛh ∑ ẛh � i `0�b�c* (10) �h 4700 i f�’h (11) i �/j�] (12) substituting in (10)-(12) we get: ẛh =7.718mpa, ec=29725, and n=6.65. for a posttensioned beam: kcr=1.6, so: ���a! i �a! ẛh (13) substituting we have ���a! =82.12mpa. the same steps are repeated for the other segments (portions) of the beam, and then the total prestress loss due to the creep is found after multiplying fcsi by li/l for all segments as in (10). the calculations are shown in table iii. • shrinkage loss: ���b� 2.8 i 10(m �no� eqr��1 � 0.06 v0�0 ��100 � �o�� (14) ���b ∑ ��no� i `��b�c* (15) for i=1, l1=0.6m, x1=0.3m, y1=31.034mm we get: h1=281.03mm, b1=100mm, vi=28103mm 2 , si=(b1+h1)× 2 =762.069mm 2 (surface area of segment), ksh=0.77, rh=70%, epsi=197500,and: ��no* 2.8 i 10 � 6 �no� eqrt "1 � 0.06v0�0, �100 � �o�� => ��no�=34.0994, while ��no* i `*� =13.6397845mpa and ��no ∑ ��no� i `��b�c* =34.48mpa. the same steps are repeated for the other segments of the beam, and then the total prestress loss due to shrinkage is the cumulative summarization of the ��no� multiplied by li/l for all parts as in (15). the calculations are shown in table iv. c) relaxation loss after 43 days fps=997.06mpa, t1=24hr, t2=1032hr, and δf6w ��� "#$%x' (#$%x)*+ , ./0 ./1 � 0.554=8.02mpa. the total losses are: ��yz ���n� � ��no � ����=124.622mpa ��: �� � ��yz=872.438mpa the same calculations are repeated for all beams. table v. shows the prestress losses by the proposed method and stresses in prestressed openings. for simplification reasons, the equivalent trapezoidal shape has the same area as the original opening and uniform posts are considered. the same simplification is used for group d, where equivalent rectangulars are positioned. table iii. calculation steps of creep loss for beam pgt6 (all dimensions are in m) (a) (b) (c) (d) fig. 4. dividing the beam to a set of segments. (a) details and number of segments, (b) section 1-1, (c) section 2-2, (d) section 3-3 part no. i li xi yi hi bi aci ici r 2 i ei pi mdi ẛcsi ẛcsi×l/l 1 1 0.6 0.3 0.031 0.281 0.1 0.0281 0.00018497 0.00658 0.0905 98.71 0.2597 7.75769 3.103 2 2 0.2 0.7 0.072 0.2 0.1 0.02 6.6667e-05 0.00333 0.05 98.71 0.5167 8.24952 1.1 3 3 0.1 0.85 0.088 0.338 0.1 0.0338 0.00032159 0.00952 0.119 98.71 0.585 7.04862 0.47 4 4 0.2 1 0.103 0.2 0.1 0.02 6.6667e-05 0.00333 0.05 98.71 0.6408 8.15642 1.087 5 5 0.1 1.15 0.119 0.369 0.1 0.0369 0.00041858 0.01134 0.1345 98.71 0.6849 6.72019 0.448 6 6 0.2 1.3 0.134 0.2 0.1 0.02 6.6667e-05 0.00333 0.05 98.71 0.7131 8.10221 1.080 7 7 0.05 1.425 0.147 0.397 0.1 0.0397 0.00052306 0.01316 0.1487 98.71 0.7134 6.45419 0.215 8 8 0.05 1.475 0.4 0.1 0.04 0.00053333 0.01333 0.15 98.71 0.7309 6.42646 0.214 ∑li 1.5 ẛcs 7.718 engineering, technology & applied science research vol. 10, no. 2, 2020, 5512-5519 5518 www.etasr.com alkhafaji & izzet: prestress losses in concrete rafters with openings table iv. calculation steps of shrinkage loss for beam pgt6 (all dimensions are in m) part no. l xi yi hi vi si ksh eps rh ∆fshi ∆fshi×li/ltotal 1 600 300 31.034 281.03 28103 762.069 0.77 197500 70 34.0994 13.639 2 200 700 200 20000 800 0.77 197500 70 35.1658 4.688 3 100 850 87.931 337.93 33793 875.862 0.77 197500 70 33.9463 2.263 4 200 1000 200 20000 800 0.77 197500 70 35.1658 4.688 5 100 1150 118.97 368.97 36897 937.931 0.77 197500 70 33.8785 2.2585 6 200 1300 200 20000 800 0.77 197500 70 35.1658 4.688 7 50 1425 147.41 397.41 39741 994.828 0.77 197500 70 33.8237 1.127 8 50 1475 400 40000 1000 0.77 197500 70 33.819 1.127 ∑l 1500 ∆fsh 34.482 table v. prestress losses based on the proposed method and stresses in prestressed concrete beams up to the moment of testing group beam instantaneous losses (1) time dependent losses (2) ∆pft (ii) fps fpe ∆pft (1)+(2) prestress loss/initial prestress (%) increasing ratio of losses% (1) at transfer (i) at the age of test (ii) ∆fpa ∆fes ∆fpf ∆fpr ∆fcr ∆fsh ∆fpr ∆fcr ∆fsh a pgb(ref) 98.75 0 6.25 6.89 0 0 7.65 76.47 33.975 118.095 997.06 878.965 229.985 20.608 0 pgt6 98.75 0 6.25 6.89 0 0 8.02 82.12 34.482 124.622 997.06 872.438 236.512 21.193 2.838 pgt8 98.75 0 6.25 6.89 0 0 8.18 81.54 34.48 124.2 997.06 872.86 236.09 21.155 2.654 pgt10 98.75 0 6.25 6.89 0 0 8.25 80.9 34.4 123.55 997.06 873.51 235.44 21.097 2.371 b pgb(ref) 98.75 0 6.25 6.89 0 0 7.65 76.47 33.975 118.095 997.06 878.965 229.985 20.608 0 pgth6 98.75 0 6.25 6.89 0 0 8.28 82.284 34.61 125.174 997.06 871.886 237.064 21.243 3.078 pgth8 98.75 0 6.25 6.89 0 0 8.33 81.703 34.609 124.642 997.06 872.418 236.532 21.195 2.846 pgth10 98.75 0 6.25 6.89 0 0 8.39 81.028 34.505 123.923 997.06 873.136 235.813 21.130 2.534 c pgb(ref) 98.75 0 6.25 6.89 0 0 7.65 76.47 33.975 118.09 997.06 878.965 229.985 20.608 0 pgp6 98.75 0 6.25 6.89 0 0 8.42 81.204 34.43 124.05 997.06 873.006 235.944 21.142 2.591 pgp8 98.75 0 6.25 6.89 0 0 8.45 80.84 34.43 123.72 997.06 873.34 235.61 21.112 2.445 pgp10 98.75 0 6.25 6.89 0 0 8.47 80.429 34.169 123.06 997.06 873.992 234.958 21.054 2.162 d pgb(ref) 98.75 0 6.25 6.89 0 0 7.65 76.47 33.975 118.095 997.06 878.965 229.985 20.608 0 pgc1 98.75 0 6.25 6.89 0 0 8.5 84.953 34.365 127.818 997.06 869.242 239.708 21.479 4.227 pgc2 98.75 0 6.25 6.89 0 0 8.53 80.915 34.23 123.675 997.06 873.385 235.565 21.108 2.426 pgc3 98.75 0 6.25 6.89 0 0 8.55 79.048 34.06 121.658 997.06 875.402 233.548 20.927 1.549 v. comparison between the experimental and the proposed method’s results as demonstrated in table vi, the experimental results converge to the ones of the proposed method. the ratio of experimental to the proposed method’s results ranged from 84.749% to 95.607% denoting the validity of the proposed estimation. table vi. result comparison group beam experimental loss proposed loss experimental loss / proposed loss % a pgb 194.909 229.985 84.749 pgt6 217.982 236.512 92.165 pgt8 212.406 236.09 89.968 pgt10 208.538 235.44 88.574 b pgb 194.909 229.985 84.749 pgth6 226.650 237.064 95.607 pgth8 221.720 236.532 93.738 pgth10 218.937 235.81377 92.843 c pgb 194.909 229.985 84.749 pgp6 217.028 235.944 91.983 pgp8 210.760 235.61 89.453 pgp10 206.688 234.958 87.968 d pgb 194.909 229.985 84.749 pgc1 216.316 239.708 90.241 pgc2 207.123 235.565 87.926 pgtc3 202.382 233.548 86.656 vi. conclusion • increasing the number of quadratic openings along the beam length from 6 to 8 and then to 10 decreased the prestress losses by an average of 2.54% and 4.166%, respectively. • the prestress losses decrease with reducing size of the circular openings by 17% and 33% from 4.25% to 6.441%. • decreasing the depth of both upper and lower chords for perforated beams by 25%, i.e. by increasing openings’ height, led to increase prestress losses by an average of 4.258%. • the average decrease in the prestress losses in beams having inclined posts in comparison with those having vertical ones was 2.593%. • the average losses decrease in prestressing force for beams with circular openings in comparison with that of quadratic ones was 2.217%. • the result of the proposed estimated method converges with the experimental results. this accordance ranged from 84.749% to 95.607%. engineering, technology & applied science research vol. 10, no. 2, 2020, 5512-5519 5519 www.etasr.com alkhafaji & izzet: prestress losses in concrete rafters with openings appendix �a area of net concrete section �� area of prestressed steel in tension zone �h modulus of elasticity of concrete �{o modulus of elasticity of prestressed steel ��� initial prestress stress in prestressed steel ��� stress in prestressed steel at jacking stage f’c cylinder concrete compressive strength at 28 days �� stress in prestressed steel at nominal flexural strength rh relative humidity |a second moment of area of net concrete section about an axis through its centroid � wobble coefficient md dead load moment �� initial prestress force μ curvature friction coefficient � total angular change of prestressing tendon profile in radians from tendon jacking end to any point x ∆a slip in tendon from anchorage ���� prestress losses due to anchorage seating ���� prestress losses due to elastic shortening ���� prestress losses due to friction δf6w prestress losses due to relaxation references [1] a. e. naaman, “computation of prestress losses”, in: prestressed concrete analysis and design, techno press 3000, pp. 445–514, 2004 [2] s. a. youakim, a. ghali, s. e. hida, v. m. karbhari, “prediction of long-term prestress losses”, pci journal, vol. 52, no. 2, pp. 116-130, 2007 [3] a. shokoohfar, a. rahai, “prediction model of long-term prestress loss interaction for prestressed concrete containment vessels”, archives of civil and mechanical engineering, vol. 17, no. 1, pp. 132-144, 2017 [4] e. g. nawy, “partial loss of prestress”, in: prestressed concrete: a fundamental approach, prentice hall, 5th edition, pp. 73–105, 2009 [5] d. m. h. al-fendawy, strengthening of reinforced concrete t-beams using external post-tensioning, msc thesis, university of baghdad, 2014 [6] m. a. mansur, k. h. tan, concrete beams with openings: analysis and design, crc press, 1999 [7] n. k. oukaili, a. shammari, “response of reinforced concrete beams with multiple web openings to static load”, fourth asia-pacific conference on frp in structures, melbourne, australia, december 1113, 2013 [8] v. n. baykov, e. e seagal, reinforced concrete structures, stroyizdat, 1991 [9] m. a. j. hassan, a. f. izzet, “serviceability of reinforced concrete gable roof beams with openings under static loads”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4813-4817, 2019 [10] m. a. j. hassan, a. f. izzet, “experimental and numerical comparison of reinforced concrete gable roof beams with openings of different configurations”, engineering, technology & applied science research, vol. 9, no. 5, pp. 5066-5073, 2019 [11] b. aykac, s. aykac, i. kalkan, b. dundar, h. can, “flexural behavior and strength of reinforced concrete beams with multiple transverse openings”, aci structural journal, vol. 111, no. 2, pp. 267-278, 2014 [12] p. s. samir, precast/prestressed concrete truss-girder for roof applications, msc thesis, university of nebraska-lincoln, 2013 [13] b. m. dawood, h. a. al-katib, “flexural strength of prestressed concrete beams with openings and strengthened with cfrp sheets”, international journal of scientific & technology research, vol. 4, no. 6, pp. 161-172, 2015. [14] m. m. mohammed, strength, cracking and deformability of partially prestressed concrete beams under repeated loading, phd thesis, university of baghdad, 2018 [15] aci-318, building code requirements for structural concrete (aci 318m-2014) and commentary, american concrete institute, farmington hills [16] p. zia, h. kent preston, n. l. scott, e. b. workman, “estimating prestress losses”, concrete international, vol. 1, no. 6, pp. 32-38, 1975 microsoft word 06-3598_s_etasr_v10_n4_pp5903-5913 engineering, technology & applied science research vol. 10, no. 4, 2020, 5903-5913 5903 www.etasr.com sasaki et al.: extracting problem linkages to improve knowledge exchange between science and … extracting problem linkages to improve knowledge exchange between science and technology domains using an attention-based language model hajime sasaki institute for future initiatives the university of tokyo tokyo, japan sasaki@ifi.u-tokyo.ac.jp amarsanaa agchbayar data artist inc. tokyo, japan amar@data-artist.com satoru yamamoto data artist inc. tokyo, japan yamamoto@data-scientist.com nyamaa enkhbayasgalan data artist inc. tokyo, japan enkhbayasgalan@mn.data-artist.com abstract—science and technology activities can be considered problem-solving activities, and scientific papers and patent publications can be viewed as providing explicit knowledge gained from the problem-solving of academia and industry respectively. however, even in the same field, the approach to the same problem is not consistent between a paper and the patented technology. the creation of information silos in science and technology generates inefficiency in human intellectual production. therefore, this study examines whether insights from technical problems can be shared with academics to solve scientific problems. we propose a concept to link the problems between these two domains using a linguistic approach for knowledge discovery that connects science and technology. we extracted scientific papers from the association for computational linguistics dataset, and patent literature from the derwent innovation platform. from these, pairs of problem defining sentences were identified and extracted using an attention-based language model. for example, we were able to extract examples of issues that do not necessarily arise from scientific papers, such as annotation difficulties in the analysis of social network data, but can be hinted at by patented techniques prior to the paper. these results suggest that scientific problems and industrial solutions can provide mutual insight. this knowledge discovery approach is recommended not only for benefiting corporate activities but also for grasping research trends. keywords-problem extraction; information matching; scientometrics; literature-based discovery (lbd); attention-based language model i. introduction science progress and technology change have become important issues on innovation and economics studies [1-3]. the way science and technology interact is a long-standing question. the knowledge flow in some areas, such as pharmaceuticals, can be effectively explained by linear models through basic research, applied research, development, and diffusion (production) [4-6]. linear models have been widely disseminated by academic institutions [7] lobbying for research funding, by economists [8] serving as expert advisors to policy makers and have been viewed as linear concepts of innovation by science and technology scholars [4]. on the other hand, recent research on innovation shows that such a linear model of innovation is insufficient to represent reality [5, 9-13]. the linear model does not consider the empirical evidence that technological change often results from experience and ingenuity rather than scientific theory and methods, the instrumental role of technological development in eliciting scientific explanation, and the importance of technology-based instruments for scientific research [14, 15]. it is sometimes pointed out that the linear model overlooks technology’s influence on the setting of the scientific agenda [16, 17]. innovation involves the transfer of knowledge between the scientific and industrial domains, as exemplified by the chain link model [11, 18, 19] and the network model [16]. of course, the linear model has the ability to explain innovation, and thus it not the all ideas that consider innovation to be a linear model are wrong [20], however, when the complexity of science and technology interactions is understood, it is undeniable that science pushes technology and technology pushes science. information retrieval research involving academic articles and patents has a long history [21-23]. information retrieval is defined as finding material (usually documents) of an unstructured nature (usually text) that satisfies an information need from within large collections (usually stored on computers) [24]. existing bibliometric methods regard research papers as representing scientific research and patents as representing innovation [25]. non-patent literature is sometimes used as a method for directly measuring the corresponding author: hajime sasaki engineering, technology & applied science research vol. 10, no. 4, 2020, 5903-5913 5904 www.etasr.com sasaki et al.: extracting problem linkages to improve knowledge exchange between science and … relationship between science and technology [22, 26, 27]. the patent examiner searches for prior non-patent literature based on the patent specification field. the number of non-patent literature is an indication of how the relating technology has already been mentioned in the context of the science domain. as mentioned earlier, the relationship between science and technology is not always straightforward and simple. traditionally, patent citations to papers have been comprehensively studied to understand the transfer of knowledge from science to technology [28]. however, the transmission from technology to science has not been well studied [29]. while patents contain detailed methodological information on successful innovations, references to patents are rarely found in applied science or science texts [29, 30, 31]. according to glanzel and meyer [29], the publications that have such reverse citations account for only 0.98% of all total publications between 1996 and 2000, of which 30% are in chemical-related fields. however, the absence of bibliographic references does not necessarily mean that technical and scientific knowledge are unrelated [16]. further, the explosive increase in scientific and technical knowledge can be problematic. there are over three million articles written in english [32]. regarding patents, there were 3.3 million patent applications in 2018, up 5.2% from 2017 for a ninth straight yearly increase [33]. in this context, it is becoming increasingly difficult for scientific papers and patents to fully reference each other. in every field, science and technology are fragmented into information silos, resulting in a condition in which one information system is unable to interoperate with other systems that are or should be associated with it. if debate proceeds only within the corresponding silos and information is not shared, even though the science and technology fields work on similar issues, the resources devoted to humankind’s intellectual activities will be significantly wasted. in this study, we focus on the possibility of extracting common needs between science and technology that have not been fully addressed by existing articles. there is an approach known as literature-based discovery (lbd) [34-37]. one way to determine the common needs between two fields by using knowledge discovery methods and involving bibliographic information is swanson’s abc model [38]. he succeeded in hypothesizing and verifying the unknown relationship between raynaud’s disease and fish oil based on bibliographic information. although scientific papers and patent publications are usually used as knowledge sources for lbd, most studies using this approach focus on discovering hidden links in the same domain (scientific papers for science domain, patent articles for technology domain). for example, one paper discussed the semantic similarities between gerontology and robotics based on the clustering of direct citation networks in the scientific inner domain [39]. meanwhile, other papers focus on knowledge discovery in a certain field in a cross-domain between scientific papers and patent publications. authors in [40] identified the commercialization gap between fields amply discussed in the science domain but not nearly as well discussed in the technology domain, using the photovoltaics-related knowledge field as an example; they created clusters based on direct citation networks between scientific papers and patent publications and calculated the semantic similarities among these clusters [41]. wang [42] also applied the same method for the micro biofuel field. considerable evidence indicates the importance of linking the same fields in the science and technology domains. several studies have revealed how science pushes technological development [21, 27, 43, 44]. thus, it is effective for industries to extract knowledge and contribute to the technology domain from the science domain [39]. scientific articles provide readers with a problem-solving process in terms of an objective and reproducible knowledge. the introduction, methods, results, and discussion (imrad) format for scientific articles has been gradually adopted since the 1940s [45]. it allows the problem-solving process to be described explicitly and enables the reporting of scientific activities to follow a more standard construction. the establishment of such a document structure greatly influences the research of vocabulary patterns of written language. authors in [46, 47] developed a way to analyze the structure of scientific and technological documents [45]. their methods can be used as a possible approach for the purpose of automatic classification, information extraction, and automatic summarization for scientific articles. the extraction of sentences related to problem-solving can also be used for science and technology articles. research on information retrieval from patent publications has also attracted considerable attention. many techniques have been proposed to classify text data of patent publications into problem and solution statements [48-50]. a subject–action– object (sao) structure can be recognized as a problem and solution pattern, which several patents have used [51-53]. authors in [54] attempted to extract and analyze sao structures to detect patent infringement. authors in [55] focused on the identification of rapidly evolving technological trends, and authors in [56] proposed a method to recommend research and development candidates by extracting the sao structure from problem–solution patterns of patent information. however, a few studies have described the relationships between problems and solutions extracted from papers. in this study, we will focus on this particular knowledge discovery issue. regarding extracting information from technical documents, researchers have attempted to extract expressions that represent technical features from patent publications and scientific articles as subtasks of the patent mining task of ntcir–8 (nii testbeds and community for information access research). this project aims at a large-scale evaluation for technologies that support the understanding and use of information, such as information retrieval, question answering, summarization, text mining, and machine translation, from a vast amount of information [57]. this extraction is also expected to be useful for the automatic creation of a technology trend map. however, as described above, because the terms used in patents are often more abstract or creative than those used in research papers to widen the scope of the claims, problem-extraction methods for patent publications are underdeveloped. on the other hand, based on the premise that the phrase “problem to be solved” in patent publications appropriately represents the technical problem, it is proposed that a more specific patent map can be created by paying attention to the sentence [58]. engineering, technology & applied science research vol. 10, no. 4, 2020, 5903-5913 5905 www.etasr.com sasaki et al.: extracting problem linkages to improve knowledge exchange between science and … there are many approaches to information retrieval using scientific and patent texts, but there are still problems and uncertainties regarding the defining keywords. in this sense, information extraction that does not solely rely on keywords is required. heffernan and teufel [59] showed that word embeddings, a technique in which words are represented as vectors, can be used as features to extract sentences related to problems and solutions, using the association for computational linguistics (acl) anthology as a dataset. they claimed that the detection of the problem and solution statements from papers can enable the comparison of similar papers and lead to the automatic generation of review articles. however, they do not describe their method’s application for cross-domain articles and also mention the linking of problem and solution statements as an area of future work. the current study aims to answer the question “is it possible to extract sentences that refer to the same problem (i.e. needs) from both the science and technology domains and obtain information that contributes to knowledge discovery across domains?” referring to if knowledge from patents can provide insight into the scientific issues being investigated. in this paper, the concept of inter-domain links for knowledge discovery using a linguistic approach is proposed. this study makes a concrete contribution to the literature because it demonstrates the possibility of building a needs-focused portfolio that includes both scienceand technology-related information by extracting appropriate sentences from scientific articles and patents. this study makes a concrete contribution to the literature because it shows it is possible to build a needsfocused portfolio that includes both scienceand technologyrelated information by extracting appropriate sentences from scientific articles and patents. for example, research articles often mention potential future studies, and knowledge can be obtained from existing patent information for these future investigations. thus, we show that not only does science support technology, but technology can support science. another contribution of this research is a model that extracts problem statements (sentences) from the paper without preparing clue words in advance, and performs better than the existing method [59]. to achieve this, it is hypothesized that the application of a model of language understanding that enables context-sensitive processing, which has been evaluated in the field of natural language processing, would be effective. ii. method a. overview the methodology of this study is outlined in figure 1. at first, data from scientific publications were taken from the acl database, whereas data from patent publications were taken from the derwent innovation platform, as shown in figure 1(1). problem statements for patents were then identified by whether they begin with the phrase “problem to be solved,” as shown in figure 1(2). for scientific articles, the problem statements from the sampled data are extracted, as shown in figure 1(3). finally, we calculated the semantic similarity between the scientific and technical problem statements, as shown in figure 1(4). these processes are described in more detail in the next section. fig. 1. method overview. b. dataset this section describes the data acquisition and preprocessing procedure shown in figure 1(1). we considered that scientific articles contain scientific knowledge and patent articles industry knowledge. we limited the papers/patents to the field of computational linguistics. the computations linguistics corpus of scientific articles is a subset of the acl anthology released in march 2016 and contains the full text of 22,878 articles. these data were parsed using parscit [60], and tokenization, sentencing, and dependency analysis were done with rasp parser [60]. we randomly sampled 2,500 articles engineering, technology & applied science research vol. 10, no. 4, 2020, 5903-5913 5906 www.etasr.com sasaki et al.: extracting problem linkages to improve knowledge exchange between science and … from this dataset, which is the same one used in [59] and is under the creative commons attribution license (cc-by). this allowed easy comparison of the classification performance with [59]. patent data were extracted from the derwent innovation platform provided by clarify analytics. computer science-related patent data classified as g06n were defined by the world intellectual property organization as “a computer system based on a particular computational model” in the international patent classification. a total of 38,718 filtered patent publications were extracted from the database. the “problem-solving concept” is a statement describing the problem solved by the patent [61-63]. patent gazettes often include important sentences that begin with the term “problem to be solved” [48]. thus, we extracted statements containing “problem to be solved” from patents. c. extraction of problem/solution sentences the way sentences were classified as shown in figure 1(2) is described in this section. we identified problem and solution sentences based on a previously established neural language approach by creating word embedding-based features [59]. word embedding involves mapping words to a vector space in order to capture the meaning of the word or grammatical structure. it is based on the distribution hypothesis that words having similar meanings will appear in similar contexts, that is, the appearance distribution of surrounding words [64, 65]. heffernan and teufel [59] proposed a supervised learning model that classifies given sentences into problem or notproblem sentences. they indicated that embedding-based features were effective for classifying these sentences [59]. in this study, we used a neural network language model focused on “attention” that has become common [66-68]. “attention” is a mechanism that allows machines to learn which vectors are important when there are multiple vectors. in other words, it informs the prediction model which part of the input data to focus on. we hypothesize that our method can extract problem sentences with higher accuracy by considering the entire context, whereas existing methods such as word2vec focus only on the area immediately before and after the clue word. in this study and by using this methodology, we constructed a model that determines whether a sentence is a problem statement based on whether it contains word with high probability to correspond to the problem. in this step, we conducted unsupervised and supervised learning. 1) unsupervised pre-training given the token � = ���, … ,� , the likelihood to be maximized in the standard stochastic language model is given by: �1 �� = ∑ ���� ��|��−�, … , ��−1; ��� (1) where � is the size of the window, and p is the neural network model with parameter� . here, � is adjusted by stochastic gradient descent. a model using the attention mechanism is given by: � �� = softmax!ℎ #$%& (2) where ' is the number of layers in the neural network, and #$ is the token embedding matrix. in this study, we utilized a published learning model in which a multi-layer transformer decoder is implemented as a language model [67, 69, 70]. 2) supervised fine-tuning parameter adjustment was performed through supervised learning using the modeled function that has been learned in (1). we implemented tasks to classify problem and nonproblem sentences as supervised learning tasks. assuming a dataset ( containing labels that contain a document consisting of a word string of input tokens )�, … , )* and a label + in each instance. for example, suppose that there is a group of words that constitute a sentence as input tokens. if it is a problem sentence, 1 is assigned to the label +, and 0 is substituted if it is not. this input passes through the previously learned model with an output layer with parameters for predicting +: � +|)�, … , )*� = softmax!ℎ,*#-& (3) below is a constraint that maximizes: �. (� = ∑ ���� +|)�, … , )*� /,-� (4) we conducted a five-fold cross-validation and comprehensive evaluation with the average value of the following four evaluation indices. • precision is the percentage of positive data that is actually positive: �012�3��' = %45$6789:9;$ %45$6789:9;$<=>,8$6789:9;$� (5) • recall is the percentage of what was actually positive and was predicted to be positive: ?12@�� = %45$6789:9;$ %45$6789:9;$<=>,8$a$b>:9;$� (6) • f-measure (f1 score) is the harmonic mean of the precision and recall: f1= .64$c9897 ∙e$c>,, 64$c9897 < e$c>,,� (7) • accuracy is the percentage of data actually predicted to be positive or negative: f22g0@2+ = %45$6789:9;$<%45$a$b>:9;$%45$6789:9;$<=>,8$6789:9;$<%45$a$b>:9;$<=>,8$a$b>:9;$ (8) d. clustering and similarity extraction here, the processing of clustering and extraction of similar problem pairs is described corresponding to figure 1(4). we vectorized the documents against the obtained scientific paper problem sentences and patent problem sentences respectively, and performed clustering. for clustering, we used the ward’s [71] method, which is a kind of hierarchical clustering. ward’s method repeats the procedure of merging any two clusters with the smallest increment in the sum of squares in the cluster. this clustering method has shown high performance regarding hierarchical clustering. additionally, term frequency-inverse cluster frequency (tf-icf) is calculated to extract the characteristic keywords for each cluster. the term frequency gives a measure of the importance of the term within the particular sentences. the inverse cluster frequency refers to a measure of the general importance of a term. the hijki of term � in cluster l is given as follows: engineering, technology & applied science research vol. 10, no. 4, 2020, 5903-5913 5907 www.etasr.com sasaki et al.: extracting problem linkages to improve knowledge exchange between science and … hijki = mn9,o ∙ �2n9 = mn9,o ∙ logr a cst u (9) where n is the total number of sentences. each cluster was labeled based on the resulting characteristic keywords and sentences. based on the dot products of embedded vectors of the obtained characteristic words, the similarities of problem sentences between the papers and patents were calculated. by focusing on problem-sentence pairs with high similarity, it is possible to manually confirm whether problem-solving information provided by the patents can be helpful to solve problems mentioned in scientific research papers. iii. results a. extracting problem sentences table ii shows several results of scientific paper problem sentences classified with this model. the actual problem sentences were labeled as “1.” non-problem sentences were labeled as “0.” the predicted result “1” means the sentence is predicted as a problem sentence. the predicted result “0” means the sentence is predicted as a non-problem sentence. table i shows the classification performance index. each number represents precision/recall/f_measure/accuracy, in that order. heffernan and teufel’s [59] results, whose study is the most similar to ours, are also shown for comparison. we were able to extract 2,385 sentences beginning with “problems to be solved” in patent publication abstracts. table iii represents an example of the actually extracted sentences. b. problem clusters in patents table iv shows a summary of the top ten clusters in the patents. each cluster name was manually chosen after reviewing all featuring sentences. the first cluster was labeled “information system” based on the problem sentences and keywords extracted by the tf-icf, as the clusters related to information processing and input information technology. the second cluster was labeled “memory efficiency and parameter optimization for neural networks,” with many problem statements addressing efficiency and optimization. the third cluster was named “data extraction and processing,” with many problem statements including challenges in data extraction. table i. classification performance precision recall f1 accuracy [59] 0.82 0.83 0.82 0.82 proposed 0.89 0.85 0.87 0.87 the fourth cluster, “knowledge systems and humans” focuses on knowledge rather than data and therefore features several issues related to human behavior. the fifth cluster, which is a knowledge system as well, is named “user and knowledge systems”, because many of the issue statements focus on the issues faced by users of the system. the sixth cluster was named “data classification,” with several problems focusing on classification, a machine learning task. the seventh cluster, “image recognition,” consists mainly of tasks that used images as data. the first bowl cluster was named “circuit of a neuron model” because many of its issues focused on circuit design using the nervous system. several task statements belonging to the ninth cluster focus on mathematical probabilistic tasks, and thus we named the cluster “estimating parameters, probabilities, calculation methods, and so on.” the tenth cluster is a concentration of issues in terms of control engineering and was named “data processing for control engineering.” the cluster name is representative of the set, and not all sentences matched the cluster name precisely. figure 2 shows the result of the vectorization of each document against the problem sentence in patents followed by compression in two dimensions and clustering. the results are shown in different colors for the top ten clusters in order of cluster size. other clusters are in gray. table ii. samples of extracted problem/non-problem sentences from scientific articles (n=10) sentences label predicted “this reduces the efficiency of the dynamic programming” 1 1 “this is expensive” 1 1 “should probably be treated separately, as a preposition modifier” 0 0 “creating these rules requires much cost and that they are usually domain-dependent” 1 1 “it is not capable of modeling bilexical dependencies on the right hand side of the rules” 1 1 “unsupervised constituency parsing is also an active research area” 0 0 “consuming very large parameter spaces” 1 1 “the time required to load and watch the videos” 1 0 “the need for large training data” 1 1 “the possible relationships that exist among the various factors” 0 1 table iii. samples of problem-related sentences in patents (n=5) problem sentences (example) application no. “problem to be solved is the neuron action potential calculation speed is slow in large-scale computer simulation process, the method of the invention can greatly improve the calculation speed of the action potential, while maintaining a relatively high precision, and it is very suitable for simulation of large-scale brain nerve network.” cn106447032a “problem to be solved: to decrease the number of sensors in use without a significant loss of control precision by constituting a 2nd control system by using a 1st and a 2nd control signal.” jp2000187504a “problem to be solved is to easily register information for specifying the symptom not only by type but also by designating an individually managed subject.” wo2008007442a1 “problem to be solved: to effectively recognize an object in a practical time, with practical accuracy and in a practical object range.” jp2001195381a “problem to be solved: to reduce the number of times of multiplication required for finding a covariant matrix for obtaining the coefficient of prediction for minimizing a square root error.” jp2001195586a engineering, technology & applied science research vol. 10, no. 4, 2020, 5903-5913 5908 www.etasr.com sasaki et al.: extracting problem linkages to improve knowledge exchange between science and … table iv. summary of top 10 clusters related to patent problem statements cluster id no. of sentences cluster name keywords cluster #1: 21 information system identification, information, abnormality, assisting, creation, semi-supervised, artificial, image, input, system cluster #2: 17 memory efficiency and parameter optimization problem, solve, difficult, included, that, capability, sample, network, neural, conventional cluster #3: 17 data extraction and processing extracting, analyzing, annotation, correlation, expected, pattern, data, added, data, stored cluster #4: 16 knowledge systems and humans personality, artificial, intelligence, person, human, realize, answer, concepts, defined, divided cluster #5: 16 user and knowledge systems knowledge, user, base, contents, concept, around, document, enormous, extracted, modeling cluster #6: 16 data classification classifying, classification, target, partial, support, enhancing, kind, source, high, unknown cluster #7: 15 image recognition monitoring, image, costs., evaluating, holding, interpretation, intention, generating, improving, attributes cluster #8: 14 circuit of a neuron model neuron, circuit, element., resistance, circuit, neural, output, network, element, bond cluster #9: 14 estimating parameters, probabilities, calculation methods and so on probability, calculation, similarity, arithmetic, unit, arbitrary, cluster, continuous, decision, independence cluster #10: 14 data processing for control engineering optimization, control, antenna, robust, ship, enhance, controller, service, efficiency fig. 2. hierarchical clustering dendrogram in patents. c. semantic similarity for all the obtained scientific paper and patent problem sentences, feature words were extracted based on tf-icf. the sentence similarity was calculated between the two different sources. table v shows the five pairs with high similarity. iv. discussion at first, the proposed model’s word selection and classification was described. in table ii, words and phrases such as “reduces the efficiency,” “expensive,” “it is not capable,” and “consuming” intuitively imply the suggestion of a problem. engineering, technology & applied science research vol. 10, no. 4, 2020, 5903-5913 5909 www.etasr.com sasaki et al.: extracting problem linkages to improve knowledge exchange between science and … table v. problem pairs with high semantic similarity between patent publications and scientific articles no. similarity scientific article problem sentences patent publication problem sentences #1 1.393 the present framework can handle only one anchor point (the question term) in the candidate answer sentence to provide a question sentence candidate presentation device and a program, which allow even a questioner unfamiliar to interview to extract data of good quality from an answerer #2 1.276 the computational complexity of working with svms to provide a re-learning method for support vector machine (svm) for improving accuracy of the svm and reducing computational complexity by using a few good samples #3 1.265 it requires the proportion of positive and negative examples in the test data be close to the proportion in the training data, which may not always hold, particularly when the training data is small to improve the accuracy of data classification of test data even if the number of training data is small #4 1.211 the unbalanced knowledge sources shared by human beings and a computer system to provide an experience transmission system making it possible to mutually share experiences of human beings #5 1.110 osn data come with no annotations, and it would be impossible to manually annotate the data for a quantitative analysis of selfdisclosure to provide an annotation data analysis technology of determining whether an annotation added to data relates to content of the data or not in the conventional sentence extraction from scientific articles and patents, such clue words must be manually collected in advance. however, this process is time-consuming and it is difficult to collect all clue words from thousands of documents. in addition, it can be difficult to determine whether a clue word indicates a problem. from table i, we can confirm that the evaluation scale in the proposed problem/non-problem classifier exceeds the existing model [59]. the pre-learning attention mechanism classified documents in context to see if the clue words indeed correspond to a problem. this suggests that sentence classification in the proposed model is performed better than through the word2vec approach, which examines only the words before and after the clue words. in table iii five sample sentences are presented, all using the “problem to be solved” as a clue word from the abstract information in the patent data. it can be seen that each patent shows the objectives to be addressed, such as the slow computation speed (cn106447032a) and the desire to reduce the number of sensors without decreasing the precision (jp2000187504a). table iv outlines the top 10 clusters resulting from these patent issue statements using ward’s method. especially after the second cluster, the focus is on relatively specific tasks, indicating that the clustering of task sentences has been performed properly. in the dendrogram shown in figure 2, the top 10 clusters are scattered, therefore, it is reasonable to understand that the top 10 clusters capture an overview of the issue awareness in the field. the third, fourth, and fifth clusters are close to each other. it can be seen from the keywords that both 4 and 5 are close in terms of knowledge and 3 and 5 are close in terms of extraction. from this dendrogram, it is possible to read the similarity of awareness of each other's issues. similar problem statements between article and patent texts (table v) are discussed below. pair #1: the article phrase was extracted from the following complete sentence: “a more serious limitation is that the present framework can handle only one anchor point (the question term) in the candidate answer sentence,” which comes from the section “shortcoming and extensions” of the paper “learning surface text patterns for a question answering system” [72]. this article examined an open-domain question answering system. the patent jp2011002872a has the most semantically similar problem sentences. this patent also refers to a question answering device and is related to interviewing problems stemming from human interviewers needing a sophisticated, adaptable interview technique. it is described as an effective way for handling multiple questions and extracting respondents’ true intentions in an interview by flexibly changing question order and depth according to the flow of conversation with respondents. based on the aforementioned problem, the invention proposes a mechanism for estimating topics of interest to respondents and presenting question candidates. in the scientific article problem sentence, the problem is that the machine making the question can only use a single viewpoint. although viewpoints vary depending on whether the subject asking questions is a machine or human, the information in the patent publication could provide inspiration for solving the scientific problem. pair #2: the article phrase was extracted from “the real drawback is the computational complexity of working with svms [support vector machines], thus the design of fast algorithm is an interesting future work,” describing a limitation of the paper titled “semantic role labeling via tree kernel joint inference” [73]. this sentence was described at the end of the conclusion as a future topic of research of the paper. the patent jp2011039831a contributes to reducing svm computational complexity. the title of this patent is “relearning method for support vector machine,” which provides a re-learning method for svm that can improve the accuracy of svm and reduce the computational complexity by using a small number of high-quality samples of svm for re-learning. while the patent itself was published in the 2011 public gazette, the applicant had published a basic patent titled jp200421590a—“re-learning method for support vector machine”—in 2004. this suggests that it is possible to solve the problems described as future work in a scientific paper published in 2006 through the industrial-technical level at the time. in other words, this finding indicates that science does not necessarily anticipate technology as represented by the linear model. pair #3: the article phrase was extracted from “one drawback of his algorithm is that it requires the proportion of positive and negative examples in the test data be close to the proportion in the training data, which may not always hold, particularly when the training data is small,” from the paper “semi-supervised learning for semantic parsing using support engineering, technology & applied science research vol. 10, no. 4, 2020, 5903-5913 5910 www.etasr.com sasaki et al.: extracting problem linkages to improve knowledge exchange between science and … vector machines” [74]. this sentence points out imbalanced data in the estimation algorithm proposed in [75]. in general, it is desirable that the data sizes of positive and negative examples are balanced in machine learning, especially for small datasets. the problem sentence of the corresponding patent, jp2002133389, proposes a method for improving the accuracy of data classification for test data even when the amount of training data is small. the paper was published in 1999 and the patent application in 2000. the imbalanced data problem was discussed in the artificial intelligence field around 2000. this pair is a good example of the information available at that time that could have been extracted by inter-domain knowledge-sharing and contributed to problem-solving. pair #4: the article phrase was extracted from “the bottleneck in artificial intelligence is the unbalanced knowledge sources shared by human beings and a computer system” in the paper “latent features in automatic tense translation between chinese and english” [76]. the paragraph with this sentence points out that the data that can be input into artificial intelligence mechanisms constitute only a small part of the data human beings can manage. the corresponding patent, jp20033233798a, provides a system for sharing human experience. at first glance, it seems the only common terms are “human being” and “system.” however, the problem at the core of this patent is that feelings and experiences cannot be sufficiently conveyed through the internet using only textbased document data. although the context is different, common to each problem are abstract concepts, including insufficient data. pair #5: the article phrase was extracted from “the challenge with such analysis is that osn [online social network] data come with no annotations, and it would be impossible to manually annotate the data for quantitative analysis of self-disclosure” in a paper titled “self-disclosure topic model for twitter conversations” [77]. this problem sentence points out the difficulty of annotating self-disclosure information on osns. data analysis of osns such as twitter had just begun at the time the article was written. this problem sentence appeared in the abstract and turned out to express the essential problem highlighted by the paper. the problem indicated by the corresponding patent jp2010237864a is that the annotation in such social annotation services contains much information unrelated to the essence of the content, so it is necessary to remove it. as to why this pair was extracted, it is clear that “annotation” is a common word in each sentence. it is also interesting that the common issue of social service was unintentionally extracted. even though the word “social” does not appear in the patent problem sentence, the common context can be extracted. thus, a patent published in 2010 dealt with a technical problem that would have provided a clue to the essential problem highlighted by a paper published in 2014. although such an evaluation must be qualitative, we confirmed in several pairs that certain knowledge is likely to be obtained from a patent whose problem corresponds to one raised by scientific research. v. conclusions science and technology research involves the exploration and exploitation of knowledge. scientific research strongly emphasizes “exploration” in the pursuit of new knowledge, while industrial technology has strongly emphasized the “exploitation” of the existing knowledge. however, it is natural in complex innovation processes that scientific knowledge involves new exploration through the exploitation of industrial technology. gardner [78] defines four concepts regarding the relationship between science and technology: 1) the “demarcation view” when both are considered independent, 2) the “idea state view” when science development precedes technology development, 3) the “materialist view” when the technology development precedes science development, and 4) the “interaction model” when science and technology develop interactively. in this study, we demonstrated the practicality of extracting problem sentences based on a language model and thus linking scientific and industrial knowledge. we collected data from scientific articles and patent publications related to information science (the natural language processing field). we proposed a model to extract problem-related phrases and confirmed that it shows higher performance than the existing models, especially for scientific articles. clustering was performed on each extracted problem sentence for both scientific articles and patent publications to categorize and map these problems. by determining the similarity between the paper and patent problem sentences, we extracted pairs with the same problem consciousness. after examining some of the pairs with high similarity, we could understand not only the reason for the common words but also the essential background of the problem. this approach showed the possible insight to be gained that would be difficult to obtain with only a keyword search. this research has several limitations. first, we did not fully consider the publication year of each of the papers and patents included in this study. for example, in pair #3, the scientific article was published in 2006 and the patent in 2011. thus, the patent presents information five years after the problem was described in 2006. in particular, knowledge is updated quickly in the information technology field and information becomes obsolete in about a year. we think this issue can be addressed by taking related information from documents published in the same year. for this, a sufficient dataset is required. we did not deal with this issue in this study, but it is essential for future work in this area. there is also room for improvement regarding the length mismatch of extracted problem sentences. information from some articles is extracted as phrase units, while patents have relatively long sentences, which would not be appropriate to compare. we also want to improve the method of calculating similarity. since a common word string is obtained for both sides, this gives a high degree of similarity, so it is arguable whether word-based extraction is necessarily appropriate. to capture a problem’s essence, a good approach may be to consider the similarity of collocations with a series of functions represented by sao as shown in section i. although there are several points to be improved, this research makes an important contribution. it developed a engineering, technology & applied science research vol. 10, no. 4, 2020, 5903-5913 5911 www.etasr.com sasaki et al.: extracting problem linkages to improve knowledge exchange between science and … practical model for identifying problem sentences from scientific papers and a method of utilizing the perspective of technology management. we showed the possibility of solving problems in scientific research by finding issues common to both science and industrial technology. identifying issues in science also contributes to the identification of important research topics, which can lead to insights into 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[78] p. gardner, “the representation of science-technology relationships in canadian physics textbooks,” international journal of science education, vol. 21, no. 3, pp. 329–347, mar. 1999, doi: 10.1080/095006999290732. authors’ profiles hajime sasaki is an associate professor at the institute for future initiatives, the university of tokyo. he received his ph.d. degree from the university of tokyo, and his m.s. degree from the tokyo institute of technology. his research interests include innovation management and data-driven decisionmaking. satoru yamamoto is the president and ceo of data artist inc., an ai solution company based in tokyo. he majored in ai at the university of tokyo. he aims to develop new and innovative ai solutions for various industries such as advertising, medicine, and finance. amarsanaa agchbayar is the cto of data artist inc. he majored in data mining at the university of tokyo. he is a bronze medalist in the international mathematical olympiad, and is presently leading an engineering team to develop new and innovative ai solutions for various industries. nyamaa enkhbayasgalan is a data scientist at data artist inc. he obtained his m.s. degree from tokyo institute of technology by majoring natural language processing. he has been involved in numerous projects utilizing ai technology. engineering, technology & applied science research vol. 8, no. 4, 2018, 3243-3248 3243 www.etasr.com le & vu: performance evaluation of traveling wave fault locator for a 220kv hoa khanh … performance evaluation of traveling wave fault locator for a 220kv hoa khanh-thanh my transmission line kim hung le the university of danang, university of science and technology, da nang, viet nam lekimhung@dut.udn.vn phan huan vu central power corporation, center electrical testing company limited, da nang, viet nam vuphanhuan@gmail.com abstract—this paper presents the traveling wave based fault location methods of sel-400l, and sfl-2000 available on the market for a 66.9km, 220kv hoa khanh-thanh my transmission line in central viet nam, such as single-ended, and doubleended, all of which rely on measurements from inductive cts and capacitive vts. focus was given on the building process of a matlab simulink model to evaluate these methods. current and voltage signals were sent to an analog chebyshev type ii filter which passes higher frequency signals at 3khz and rejects low frequencies signal at 50hz. after that, these output signals are used in clarke's transformation for getting 0 and α components. the detail coefficient of the selected components after dwt using db4 wavelet at decomposition level 1 can be used to determine the fault types, the direction of fault and propose a crest-wave comparison solution to identify exactly the adjacent bus' reflected wave from the fault point's reflected wave for the fault location. finally, the accuracy of fault location on the transmission line is reviewed by varying various parameters like fault type, fault location and fault resistance on a given power system model. keywords-transmission line; traveling wave fault locator; single ended method; double ended method; matlab/simulink i. introduction numerical relays are the most popular devices used for transmission line protection. they include fault location estimation based on impedance methods, which uses the voltage and current data measured in 50hz at one or more points along the power networks after the occurrence of a fault. typical impedance method’s error ranges from 2% to 5% depending on the relay model according to industry standards. however, the actual error is usually larger than 5% in practice operation manager at evn of viet nam [1]. it can be influenced by weather, high resistance ground faults, measurement errors, line impedance errors, mutual coupling, compensated lines, and other factors [2]. therefore, finding the accurate location of a fault constitutes a challenge in the power operator. selecting a new appropriate technology for a fault location application can be a daunting task so a performance evaluation is required when the evn wants to compare accuracy and finds the optimum and the most cost-effective one. in 2017, evn’s project installed a traveling wave fault locator (twfl) equipment kinkei sfl-2000, sel-400l for 220kv, 500kv transmission lines in substations such as son ha, thanh my, hoa khanh, hue, dong ha, tam ky, and doc soi in central viet nam. the project implementation plan followed 3 steps. the first step was setting up the twfl to work with single-ended method. the second step was synchronizing the twfls by the furuno gps/gnss clock receiver and using a configured communication channel. the twfls would send the traveling wave arrival information to f/l server that calculates the distance to fault base on doubleended method, display results and sends email to the operator. the third step, evn installs an npt communication network link between twfls as shown in figure 1. the twfls receive the remote traveling wave information that is necessary to provide an automatic fault location. sfl-2000’s accuracy is reported to be200m [3], whereas the accuracy for sel-400l is reported to be 2% [2]. although this issue was recognized by ptc2 as a good way to overcome the shortfalls of impedance-based methods, the sfl-2000 is not able to be used in step 1. so, if it is impossible to have communication between ends, the fault location cannot be implemented automatically by the f/l server. note that, the problem faced by the power system operator is manually collected traveling waves event reports from each substation. they lack skills to discriminate the reflection wave of fault point, the time of arrival of the wave for manual fault location estimation using the single-ended method because the reflected surge from the adjacent bus has the same polarity as the real fault point's reflected wave, so the confusion is inevitable. almost as many respondents said all the implementation and support work would be done by experienced professionals. consequently, evn needs to conduct a training session about the knowledge of the problem of fault location using traveling wave signals for communication technicians, field personnel, relay engineers, and analysis an in-depth review of all twfl system operations. in order to solve this issue, the paper focuses on twfl based double-ended and single-ended methods implemented in a 66.9km, 220kv hoa khanh–thanh my transmission line by matlab simulink. the proposed model has been assessed through several scenarios. results show that methods consistently and significantly yielded the accurate engineering, technology & applied science research vol. 8, no. 4, 2018, 3243-3248 3244 www.etasr.com le & vu: performance evaluation of traveling wave fault locator for a 220kv hoa khanh … location of the actual fault. ii. traveling wave based fault location methods the twfl can work based on current or voltage signals. it has two kinds of the traveling wave (tw) methods that are used for most fault locator systems. one is the single-ended, which captures data from the initial traveling wave and subsequent reflections at one terminal to calculate the fault location without requiring any information from the relay at the remote terminal. the other is double-ended, which requires data information from two terminals which are both equipped with a gps receiver to time tag the exact moment the traveling wave reaches each end of the line. fig. 1. traveling wave fault locator sfl-2000 on transmission line a. single ended method figure 2 for a fault at location f on a line of length l=66.9km (the bewley diagram is shown in figure 14). the fault is m (km) away from the hoa khanh terminal, that is suspected to be in the second half of the line hoa khanh-thanh my. a current tw is launched from the f at t0=40ms and arrives at the hoa khanh terminal at t1b. to discriminate the reflection wave of fault point, the number of samples in the selected window is limited to the interval from t1b to 40.825ms after the fault occurs. part of the wave transmission travels toward the bus da nang and then returns to the hoa khanh terminal at t’1a. it has opposite polarity with the first traveling wave (t’1a-t1b=constant). so we identify and eliminate false peak due to the effect of this wave. another part of the wave reflects, travels back toward the fault, reflects back from the fault, and then returns to the hoa khanh terminal at t2b. it has larger crest-current wave than the reflected surge from the thanh my terminal at t’1c with the same polarity. similarly, in the previously examined case, the fault is assumed to occur at the first half of the line as shown in figure 13 then the number of samples in the chosen window has limited the interval from t1b to 40.4125ms. now, the distance to the fault location from twfl b is [2]: 2 1( ) 2 b bv t tm    (1) wave propagation velocity is 1 11 243250 km/sv l c   (where l1=0.0013h/km is the inductance and c1=0.013μf/km is the capacitance of the propagation medium). when an external fault behind the hoa khanh terminal launches a traveling wave as shown in figure 3, the twfl b sees an initial wave behind it with t1b=t1, which travels across the transmission line to the thanh my terminal and is reflected back to the hoa khanh terminal after the known tw line propagation time (tl=0.275ms) with t2b=2×tl+t1. the twfl b displays l. fig. 2. single end twfl with internal fault fig. 3. single end twfl with external fault review: the single-ended method estimates the accurate fault location of an internal fault and does not require data synchronization. however, the accuracy of this method depends on the accuracy of l, v, sampling frequency, and errors in wave detection. if the impulse wave cannot be captured successfully or the impulse wave does not exist at all at the fault occurrence, the fault location will fail. for instance, strong buses on power system network influencing the voltage and current waveforms due to line impedances can reduce the amplitude of voltage waves making them harder to detect, and thus reducing the twfl accuracy [4]. b. double ended method when an internal fault f occurs at t0, waves generated at f run towards stations hoa khanh and thanh my (figure 4). the double-ended method determines the arrival time based on the rising point of surge waveform recorded at both end terminals (t1b at the hoa khanh, t1c at the thanh my) and then locates the fault point from the equation shown below [2, 3]. ( )1 1 2 2 2 v t tl l v tb cm         (2) we can calculate v using the line length l=66.9km and the arrival time of the surge generated by manually closing a circuit breaker at thanh my terminal as shown in figure 5 [3]: v=l/(t1b–t1c)=243270km/s. when an external fault behind the engineering, technology & applied science research vol. 8, no. 4, 2018, 3243-3248 3245 www.etasr.com le & vu: performance evaluation of traveling wave fault locator for a 220kv hoa khanh … hoa khanh terminal launches a traveling wave, the twfl b sees an initial wave with either positive or negative polarity with t1b=t1 which travels across the transmission line to the thanh my terminal. the twfl c sees the same initial wave tl=0.275ms later with opposite polarity (t1c=tl+t1). the distance to the fault location from twfl b is l. fig. 4. double ended twfl with internal fault fig. 5. calculate propagation velocity review: double-ended method requires data from both terminal ends to be synchronized. it estimates the accurate fault location of an internal fault. the accuracy of this method is effected by communication and precise timing stamp gps. this method is more expensive than the single-ended method. iii. power system under study recorded data from a real system are not available to evaluate the performance of the twfl. instead, the power system supplied from both ends can be modeled by matlab simulink software (figure 6). the overhead line hoa khanh– thanh my is 66.9km long, and the system nominal operating voltage is 220kv, 50hz. this model consists of: 1. the transmission line: three phase section lines are used to represent the distributed parameter transmission line. line sequence impedance is: rl1 =0.07(ω/km), rl0 =0.2164(ω/km). ll1 =0.0013(h/km), ll0 =0.0044(h/km). cl1 =0.013(μf/km), cl0 =0.0085(μf/km). 2. a load of 220kv, 56mw, and 34kvar is connected to the bus hoa khanh and thanh my. 3. three phase fault block to deduce fault types and fault resistance varies from 1 to 35 ohms. 4. three-phase measuring blocks to measure the three phase line and load current and voltage values. 5. a twfl model is located at hoa khanh bus. it has been developed for fault detection, fault classification, fault direction and fault location which will be presented in section iv. iv. traveling wave fault locator model this subsection helps to understand how the twfl works. the simulation model of the twfl has been designed with six functional flow block diagram (figure 7) by using simulink. fig. 6. power system model fig. 7. flowchart of travelling wave fault locator operation a. analog filter a fault generates current and voltage traveling waves that propagate along the overhead line. most of them contain a significant amount of high-frequency components. the twfl collects tws from conventional ct class 5p20, cvt class 3p. then it uses an analog chebyshev type ii filter to remove the fundamental component 50hz and a high-pass filter with a cutoff frequency of 3khz for phase currents and voltages. b. clarke’s tranformation to reduce the effect of mutual coupling between phases, this paper utilizes the clarke transformation to convert the three-phase currents and voltages into the α, ß and 0 mode components. for example, we use three sets of clarke components with reference to the a-phase, b-phase, and cphase of current signals, as follows [5]: 0 0 0 2 1 1 1 0 3 3 3 1 1 1 1 2 1 1 3 0 3 3 1 1 1 1 1 2 1 3 3 0 3 1 1 1 a a a b a c b a b b b c c a c b c c i i i i i i i i i i i i i i i i i i                                                                                        (3) c. discrete wavelet transform this function is developed by using an α mode and 0 (ground) mode component which capture voltages and current with a sampling rate of 10mhz at twfl a (uαa, u α b, u α c, i α a, iαb, i α c, ig), and twfl b (bus_b_i α a, bus_b_i α b, bus_b_i α c, bus_b_ig). by using dwt daubechies 4 mother wavelet (db4) engineering, technology & applied science research vol. 8, no. 4, 2018, 3243-3248 3246 www.etasr.com le & vu: performance evaluation of traveling wave fault locator for a 220kv hoa khanh … during the fault surges from the state steady sampled currents and voltages, we can rapidly extract the first level detail wavelet coefficients (cd1), frequencies up to 5mhz which is enough for the twfl transient frequency. now it is easy to determine the times of traveling wave occurrences (peaks can be observed on waveform) and to reveal their travel times between the point fault f and twfl. d. fault detection and fault classification under normal conditions, cd1 of phase a, b, c, and ground are zero (figure 8). under fault conditions, if the cd1 of ground is zero, the fault is identified as an ungrounded fault or as a grounded fault if it is nonzero. the cd1 of phase a, b, and c are available for all fault types. consider the ag fault occurring on the transmission line at time 40ms (figure 9). both reflection and refraction of the cd1 of current phase a and ground with the large amplitude occur at 40.0 to 40.8ms (or 2.0×105 to 2.04×105 samples). they are approximately twice as large as the cd1 of current phase b, c (healthy phases), and they have opposite polarity. consider the bc fault (figure 10), the cd1 of current phase b and c are also considerably larger than the cd1 in the healthy phase (a, ground), and these faulted phases have opposite polarities. based on information relationship between the squared cd1 magnitude of the first current traveling waves in each phase, the twfl can make fault type decisions that can be summarized in table i. fig. 8. the cd1 of phase a, b, c and ground at normal condition fig. 9. the cd1 of phase a, b, c and ground at ag fault e. direction fault the single-ended method can make a directional decision based on the polarity relationship between the first voltage and current traveling waves. for a fault on the transmission line in the forward direction, the voltage and current traveling waves observed by the relay have opposite polarity (figure 11). for a fault on the transmission line in the reverse direction, the voltage and current traveling waves observed by the relay have the same polarity as in figure 12. the double end method compares time-aligned current first tws at both ends of the protected line. for an external fault, a tw that entered one terminal with a given polarity leaves the other terminal with the opposite polarity exactly after δt=tl. for an internal fault, a tw that entered one terminal with a given polarity leaves the other terminal with the same polarity, δt<tl [2]. fig. 10. the cd1 of phase a, b, c and ground at bc fault table i. fault type classification fault type condition selection signal for fault location ag mag_a/mag_b>1.5 and mag_a/mag_c>1.5 and mag_g/mag_a>0.2 cd1_a bg mag_b/mag_a>1.5 and mag_b/mag_c>1.5 and mag_g/mag_b>0.2 cd1_b cg mag_c/mag _a >1.5 and mag_c/mag_b>1.5 and mag_g/mag_c>0.2 cd1_c ab mag_a/mag_c>1.5 and mag_b/mag_c>1.5 and mag_g/mag_a<0.2 and mag_g/mag_b<0.2 cd1_a or cd1_b bc mag_b/mag_a>1.5 and mag_c/mag_a>1.5 and mag_g/mag_b<0.2 and mag_g/mag_c<0.2 cd1_b or cd1_c ca mag_c/mag_b>1.5 and mag_a/mag_b>1.5 and mag_g/mag_c<0.2 and mag_g/mag_a<0.2 cd1_c or cd1_a abg mag_a/mag_c>1.5 and mag_b/mag_c>1.5 and mag_g/mag_a>0.2 and mag_g/mag_b>0.2 cd1_a or cd1_b bcg mag_b/mag_a>1.5 and mag_c/mag_a>1.5 and mag_g/mag_b>0.2 and mag_g/mag_c>0.2 cd1_b or cd1_c cag mag_c/mag_b>1.5 and mag_a/mag_b>1.5 and mag_g/mag_c>0.2 and mag_g/mag_a>0.2 cd1_c or cd1_a abc mag_a>1.5 and mag_b>1.5 and mag_c>1.5 cd1_a or cd1_b or cd1_c f. distance calculations because the frequency response for cts is better than for ccvts [4], we chose to use current signals for fault location. in the case when twfl identifies a forward or internal fault, both single end and double end methods are activated. we use matlab's find peaks function to find values and locations of cd1 maxima in a time period set according to the travel time of the line. the fault distance is given by (1) and (2). engineering, technology & applied science research vol. 8, no. 4, 2018, 3243-3248 3247 www.etasr.com le & vu: performance evaluation of traveling wave fault locator for a 220kv hoa khanh … fig. 11. curent and voltage polarities of phase a in fault forward direction fig. 12. curent and voltage polarities of phase a in fault reverse direction v. simulation results after building, the proposed model is ready to analyze the operation of twfl applied with variation in fault parameters such as fault type, fault location (from -5km to 65km), fault resistance from 1ω to 35ω (increasing the fault resistance seen at relay point as though moving away from the transmission line). the fault creation time is t0=40ms. figure 13 shows the phase currents captured at both terminals and a beley diagram for a bg fault with rf=10ω that is assumed to occur at a distance of 20km from hoa khanh bus (forward direction). twfl b calculates the fault location by the single-ended method with t1b=40.0836ms, t2b=40.2476ms, due to the traveling time taken by the fault to appear at the twfl b. based on the measured tw arrival times, an estimated from (1) fault location 19.9523km from the hoa khanh terminal emerged. in figure 14, results are shown where a bcg fault with rf=25ω at a distance of 45km from hoa khanh bus (forward direction). according to the traveling time taken by the fault to appear at the point t1b=40.1866ms, t2b=40.5566ms. the twfl b also uses the single-ended method to calculate fault location is 45.0016km. the double-end method’s (figure 15) performance is simpler than the single-ended one. in the case an ab fault occurs on the transmission line with rf=15ω at 10km, it calculates the distance to fault based on time tags of traveling wave records acquired at both ends of the faulty line. the first peak of hoa khanh terminal occurs at t1b=40.0426ms, the first peak of thanh my terminal occurs at t1c=40.2356ms, so the distance to the fault point f of twfl b estimate from (2) is 9.9762km. as shown in figure 16, an abc fault occurs on the transmission line at 35km, rf=15ω. according to the change in current waveforms during the fault, twfl b captured point t1b=40.1456s, twfl c captured t1c=40.1326s, thus the doubleend method of twfl b estimate is 35.0313km. some of the results for various fault cases are given in table ii respectively for bg, ab, bcg, and abc. fig. 13. phase current waves and bewley diagram explaining single ended method for a bg fault at 20km from the hoa khanh terminal fig. 14. phase current waves and bewley diagram explaining single ended mehtod for a bcg fault at 45km from the hoa khanh terminal fig. 15. phase current waves and bewley diagram explaining double ended method for ab fault at 10km from the hoa khanh terminal review: the simulation results show that single ended method locates faults with accuracy less than ±114m and double ended method locates faults with accuracy less than ±112m. engineering, technology & applied science research vol. 8, no. 4, 2018, 3243-3248 3248 www.etasr.com le & vu: performance evaluation of traveling wave fault locator for a 220kv hoa khanh … fig. 16. phase current waves and bewley diagram explaining double ended method for abc fault at 35km from the hoa khanh terminal table ii. test results of faults on transmission line phase actual fault location [km] fault resistance [ω] single end method estimated distance double end method estimated distance m [km] difference [m] m [km] difference [m] bg -5 1 / / 10 5 9.9733 -26.7 9.9762 -23.8 20 10 19.9523 -53.3 19.9495 -50.5 30 15 30.0416 41.6 29.9228 -77.2 40 20 40.015 15 39.967 -33 50 25 49.9883 -11.7 50.112 112 60 30 60.889 88.9 60.0859 85.9 ab -5 1 / / 10 5 9.9733 -26.7 9.9744 -25.6 20 10 19.9467 -53.3 19.9495 -50.5 30 15 30.0416 41.6 29.9228 -77.2 40 20 40.015 15 39.967 -33 50 25 49.9883 -11.7 50.112 112 60 30 59.9616 -38.4 60.0861 86.1 bcg -5 1 / / 5 5 5.114 114 5.109 109 15 10 14.960 -40 15. 0831 83.1 25 15 25.055 55 25.0578 57.8 35 20 35.028 28 35.031 31 45 25 45.016 16 45.0045 4.5 55 30 54.932 -68 54.9778 -22.2 65 35 64.9053 -94.7 64.9512 -48.8 abc -5 1 / / 5 5 4.9867 -13.3 5.109 109 15 10 14.96 -40 15.0831 83.1 25 15 25.055 55 25.0578 57.8 35 20 35.0283 28.3 35.0313 31.3 45 25 45.0073 7.3 45.0045 4.5 55 30 54.9806 -19.4 54.9778 -22.2 65 35 64.954 -46 64.9535 -46.5 vi. conclusions performance evaluation of twfl systems has become an increasingly important issue given its design, manufacturing, sale/purchase, use, upgrade, tuning, etc. in this study, a twfl model built into a 220kv transmission line that can be easily and reliably simulated on the matlab simulink software with 10mhz sampling frequency. the proposed model determines exactly fault types, fault direction and fault location. according to the obtained results, it has been shown that twfl is more accurate than the traditional impedance-based methods in relay protection. double-ended method is more accurate than singleended method. furthermore, the paper demonstrates a bewley diagram with the times of the current impulse wave at each terminal and results which are intended to help the operator transition from beginner to experienced professionals. this can assist in the research to eliminate factors of misoperation, contribute substantially to the safe, reliable, economical operation and maintenance of overhead transmission lines. acknowledgment authors would like to thank power transmission company no. 2, viet nam for allowing the use of fault location equipment for 220kv and 500kv transmission lines used in this study. references [1] k. h. le, p. h. vu, “a studying of single ended fault locator on sel relay”, ietec’13 conference, ho chi minh city, vietnam, december 4-6, 2013 [2] sel, sel t400l ultra high speed transmission line relay traveling wave fault locator high resolution event recorder instruction manual, 2018 [3] kinkei system corporation, surge type fault locator system specifications sfl 2000, 2016. [4] s. parmar, fault location algorithms for electrical power transmission lines methodology, design, and testing, msc thesis, delft university of technology, 2015 [5] b. kasztenny, a. guzmán, n. fischer, m. v. mynam, d. taylor, “practical setting considerations for protective relays that use incremental quantities and traveling waves”, 43rd annual western protective relay conference, washington, usa, october 18-20, 2016 microsoft word 23-3590_s_etasr_v10_n3_pp5713-5718 engineering, technology & applied science research vol. 10, no. 3, 2020, 5713-5718 5713 www.etasr.com nagao: an experimental study on the way bottom widening of pier foundations affects seismic … an experimental study on the way bottom widening of pier foundations affects seismic resistance takashi nagao research center for urban safety and security kobe university kobe city, japan nagao@people.kobe-u.ac.jp abstract—the resistance of a pier to horizontal loads, like seismic loads, is due to the flexural rigidity of its foundations and the horizontal subgrade reaction. in the event of a massive earthquake, the latter becomes very small because of the softening of the ground, while the structure may experience a large inertia force and lateral spreading pressure. therefore, structures with high seismic resistance are required in areas with high seismicity. when a wide caisson is used as a pier foundation, a rotational resistance moment caused by the vertical subgrade reaction acting on the foundation bottom can be expected. although this rotational resistance moment increases if the foundation is widened, in design practice the subgrade reaction coefficient is evaluated as being low under such circumstances. therefore, even if the foundation is widened, the rotational resistance moment does not increase greatly. rotational resistance commensurate with the increased construction cost due to foundation widening cannot be expected. in the present study, horizontal loading experiments were performed at one pier with a normal foundation and at one with widened at the bottom foundation, and the way that the widening affected the seismic performance was examined. the results show that compared with the normal foundation, the bottom-widened one experienced far less displacement and offered higher earthquake resistance. keywords-earthquake resistance; subgrade reaction; pier; displacement i. introduction a pier supports vertical loads (e.g. dead weight, cargo) by means of columnar foundations (e.g. piles) that penetrate to the bedrock, and resists horizontal loads (e.g. inertia forces during an earthquake) by means of (i) the flexural rigidity of the foundations and (ii) the horizontal subgrade reaction (sr). as ships have become bigger, so wharfs have had to be made deeper, and this increase in water depth results in increased seismic load. in addition, it has been noted that (i) lateral spreading pressure may act during a massive earthquake and (ii) the maximum lateral spreading pressure may exceed the one specified in seismic design codes [1]. many damages to pile foundations during the 1995 kobe earthquake have been reported [2], and a pier in kobe port buckled at points below the ground surface, which was caused by the lateral spreading pressure [3]. many other cases have been reported of wharfs being displaced laterally during earthquakes [4-7]. because a pier is strongly affected by ground deformation during an earthquake and experiences residual deformation even when its structural members are not damaged [8], the deformation performance of a pier against seismic loads is an important design criterion. the damage to the pile foundation becomes even greater when liquefaction occurs [9]. pier foundations comprise steel-pipe and reinforcedconcrete piles, and large-diameter caissons are also used when large earthquake loads are considered. when caissons are used as foundations, a rotational resistance moment (rrm) due to the vertical sr acting on the foundation base bottom is expected because of the wide foundations. in the event of a massive earthquake, the horizontal sr becomes very small because of the deterioration in ground stiffness [10]. however, because the foundations are embedded in a strong soil layer, the effect of lowered ground stiffness at the foundation bottom (fb) is small even during a massive earthquake, and a sufficient vertical sr can be expected. in addition, when caisson foundations are used, the area subjected to the vertical sr can conceivably be increased by widening the fb, thereby increasing the rrm to enhance the earthquake resistance. also, the seismic performance can be expected to increase because of the soil weight acting on the widened section. however, it has been noted that although the rrm increases as the foundations are widened, the sr coefficient used in the calculation of sr decreases with increasing foundation width [11-15]. in design practice, formulas for calculating the sr coefficient are used, which incorporate that effect [16]. when such formulas are used, the rrm does not increase greatly even if the foundations are widened, and therefore one cannot expect a rotational resistance that is commensurate with the increased construction cost due to the foundation widening. however, no studies to date have clarified the effect by experiments on the frame structure, and it is very important in the earthquake-resistant design of piers to examine how the foundation width affects the earthquake resistance. in the present study, experiments involving horizontal loading were performed on pier models with either a normal columnar foundation or one with widened fb, and how the latter affected the seismic performance was examined. also the differences in sr and displacement performance due to the widened fb are discussed. corresponding author: takashi nagao engineering, technology & applied science research vol. 10, no. 3, 2020, 5713-5718 5714 www.etasr.com nagao: an experimental study on the way bottom widening of pier foundations affects seismic … ii. method a. experiments outline in the experiments, a soil tank of 900mm (width) × 500mm (depth) was used as shown in figure 1, and a steel rigid frame model simulating a pier was installed in the ground as shown in figure 2. this pier model was loaded horizontally using a mega-torque motor. to avoid effects due to the soil being restrained by the side walls of the soil tank, the 150mm-deep pier model was installed in the central part of the 500mm-deep soil tank. steady braces were installed so that the horizontally elongated model would not tilt in the depth direction of the soil tank because of loading. figure 3 shows the specifications of the model. the normal type involves a rigid frame that has a columnar foundation with a circular cross section of 60mm diameter whereas the widened type involves a column that has the same diameter but whose base has been widened to 115mm. the dimensions of these models are based on a scaling factor (prototype/model) of 100 for the length considering the recent increases in wharf water depth. the normal and widened model weights are 0.142kn and 0.150kn respectively, the latter being heavier because it has a wider base. fig. 1. experimental soil tank fig. 2. model installation status the ground was prepared by air pluviation, using tohoku silica sand no. 6 in the dry state. although pier foundations penetrate solid ground, the ground shallower than the bearing stratum is usually soft. thus the model ground comprised an upper layer and a lower layer with relative densities of 42% and 77% respectively, corresponding to standard penetration test n-values of 5 and 33, respectively. the upper layer was 100mm thick and the lower layer was 135mm thick, thereby ensuring that the deformation in the lower soil layer was not constrained because of the rigid bottom plate of the soil tank. as shown in figure 1, the model foundation was embedded by 45 mm into the stronger lower layer. (a) (b) fig. 3. model specifications. (a) widened, (b) normal (unit: mm) by similitude [17], the horizontal loading rate on the model was determined to be 1/31.6 of the actual scale, in which the horizontal loading rate was 20cm/s as in [1]. the maximum displacement under loading was 10mm, which by similitude corresponds to an actual displacement of 10m. b. measured quantities the quantities measured in these experiments were the sr on the pier bottom, the horizontal and vertical displacements of the pier, and the horizontal load. time history data were recorded by a data logger. the sr on the fb was measured by installing earth pressure gauges on the model fb, two per leg in the widened type and one per leg in the normal type, on the basis of the relationship between the diameter of the earth pressure gauge and that of the model foundations. the horizontal and vertical displacements were measured by attaching a displacement gauge to the model as shown in figure 3. in the following, the loading side is referred to as the rear side, and the side where displacement occurs by loading is referred to as the front side. the measured data were subjected to (i) a fast fourier transform, (ii) low-pass filtering at 1hz, and then (iii) an inverse fast fourier transform to obtain smooth time history data as in [1]. pressure gauge 5 0 0 3 0 4 7 0 900 1 5 0 45 mega torque motor steady brace steady brace model 45 (unit: mm) 100 135 plan view side view mega torque motor engineering, technology & applied science research vol. 10, no. 3, 2020, 5713-5718 5715 www.etasr.com nagao: an experimental study on the way bottom widening of pier foundations affects seismic … iii. results a. load–displacement relationship figure 4 shows the time history of horizontal load (red) and horizontal displacement (blue). because the loading was carried out at constant displacement speed, the horizontal displacement increased linearly with time at the same rate for each type. the load increased over time, but the degree of increase was not constant. in both types, the load increase with time was large until around 1s when it became gradual. this was due to the change in the displacement mode of the pier around 1s: at first the rigid frame tilted because of the horizontal load, then, as the tilt increased, the horizontal resistance was reduced by the rear side leg floating up, whereupon sliding occurred. the final horizontal displacement was 10mm for both types, but the loads required to produce the final displacement differed, with the maximum load being 0.40kn for the widened type and 0.34kn for the normal type. the widened type was less likely to deform than was the normal type. (a) (b) fig. 4. time history of horizontal load and horizontal displacement the relationship between the horizontal displacement (dx) and the vertical displacement (dy) is shown in figure 5. the red line indicates the widened type and the blue line denotes the normal type. the vertical displacement is positive upward, and when the tilting occurs by horizontal loading, the model is displaced upward by rotation. a large vertical displacement occurred with horizontal displacement for the normal type, but the vertical displacement of the widened type was small. this occurred because it was difficult for the widened type to tilt because the rrm due to the vertical sr acting on the fb was large. fig. 5. relationship between horizontal and vertical displacement b. vertical subgrade reaction figure 6 shows the time history of the vertical sr on the fb. as described above, the widened type had two earth pressure gauges per leg, namely p1–p4 from front to rear. the normal type had one earth pressure gauge per leg, namely p1 in the front and p2 in the rear. in both types, the sr at the rear leg decreased sharply with increasing load: it became zero and the rear leg floated upon application of a horizontal load of 0.113kn in the widened type and 0.091kn in the normal type. (a) (b) fig. 6. time history of sr as a ratio to the dead weight, this load was 0.75 for the widened type and 0.64 for the normal type. the sr for p2 of the widened type, which was the rear side sr in the front leg, became zero when a horizontal load of 0.252kn was applied, which corresponded to 1.80 as a ratio to the dead weight. the front sr for p1 of the normal type did not increase significantly even if the load or displacement increased after the rear sr for p2 became zero. this was because the displacement mode changed from tilting to sliding. the widened type exhibited a similar tendency. 0.5 1 1.5 2 2.5 0 0.1 0.2 0.3 0.4 0 5 10 widened time(s) lo a d (k n ) d x (m m ) 0.5 1 1.5 2 2.5 0 0.1 0.2 0.3 0.4 0 5 10 normal time(s) lo a d (k n ) d x (m m ) 0 2 4 6 0 0.2 0.4 0.6 dx(mm) d y (m m ) 0.5 1 1.5 2 20− 0 20 40 60 80 100 0 0.1 0.2 0.3 0.4 widened time(s) p re ss u re (k p a ) lo a d (k n ) 0.5 1 1.5 2 20− 0 20 40 60 80 100 0 0.1 0.2 0.3 0.4 normal time(s) p re ss u re (k p a ) lo a d (k n ) engineering, technology & applied science research vol. 10, no. 3, 2020, 5713-5718 5716 www.etasr.com nagao: an experimental study on the way bottom widening of pier foundations affects seismic … iv. discussion a. vertical subgrade reaction characteristics when a rigid frame is subjected to horizontal loading, tilted displacement occurs first. we discuss how the tilted displacement characteristics differ between the normal type and the widened type. figure 7 shows the change in the distribution of the sr with the change in the applied load. the horizontal axis is the distance from the front end, and the stars mark the installation positions of the earth pressure gauges. the values in the legend are those of the horizontal load. when the load is small (0.02kn), the sr (p2, p4) at the rear side of each leg is larger than that at the front side (p1, p3) for both the front and rear side legs of the widened type. this occurs because in the widened type, the column is installed on the rear side rather than in the center of the base bottom, and the loading distribution of its dead weight is not uniform. although the front side sr (p1) increases with increasing horizontal load, there is no change in the rear side sr (p2) on the front side leg in the range of horizontal load up to 0.10kn. by contrast, the sr decreases on both rear sides (p3 and p4). (a) (b) fig. 7. distribution of sr in the normal type, the sr (p1) at the front increases with increasing loading and the sr (p2) at the rear decreases, but the p2 decrease is larger than the p1 increase. this is because the rigid frame does not rotate at the center of the span of the superstructure but does rotate at a point closer to the front than the center. by contrast, in the widened type, it is difficult to evaluate the rotational center in this state because the initial distribution of the dead weight is not uniform. therefore, we first averaged the initial values of the four srs from p1 to p4 and then subtracted their initial average values from the values of each sr. in addition, the values of the srs on the front and back side of each leg were averaged, and were plotted against the center of the earth pressure gauge installation position for each leg. the results are shown in figure 8, where the legend is the same as in figure 7. these results indicate that the rotational center is unchanged and constant regardless of the magnitude of the load, and that the rotational center position differs between the normal type and the widened type. in the widened type, the rotational center is close to the center of the superstructure span, namely at 0.47 times the span length from the front end, while in the normal type, the rotational center is at 0.37 times the span length from the front end. the arm length of the rrm is larger for the widened type than for the normal type, and therefore the rrm of the widened type is larger than that of the normal type. this is the effect of bottom widening. fig. 8. distribution of sr the rrm calculation is based on the sr distribution and the rotational center. the rrm values are plotted against the load in figure 9. the red line indicates the widened type and the blue line expresses the normal type. for a load of 0.1kn, the rrm is 0.045kn·m in the widened type and 0.035kn·m in the normal type, with the former being 1.28 times the latter. in design practice, sr distributions are calculated assuming that the foundation center of each leg is the rotational center when evaluating the seismic resistance of a pier. the sr distributions in such a conventional design differ greatly from the sr distributions revealed by this study, and the conventional design underestimates rrm of a pier as a frame structure because the arm length of rrm is evaluated as being short. fig. 9. rotational resistance moment b. displacement characteristics figure 10 compares the relationship between the loads and the horizontal displacement of the two types. the red line 0 100 200 300 400 500 0 20 40 60 widened distance(mm) su b g ra d e r e a c ti o n (k p a ) 0 100 200 300 400 500 0 20 40 60 widened distance(mm) su b g ra d e r e a c ti o n (k p a ) 0 0.05 0.1 0.15 0.2 0 0.02 0.04 0.06 load(kn) m o m e n t( k n m ) engineering, technology & applied science research vol. 10, no. 3, 2020, 5713-5718 5717 www.etasr.com nagao: an experimental study on the way bottom widening of pier foundations affects seismic … indicates the widened type and the blue line the normal type. for a given load, the widened type exhibits smaller horizontal displacement than the normal type. because the model weights differ between the normal and the widened type, as described above, the results of comparing the displacement characteristics in seismic coefficient form by dividing the horizontal load by the model weight are converted into values on the real scale according to the similitude [17] as shown in figure 10(b). the red line denotes the widened type and the blue line indicates the normal type. in the range of seismic coefficient of 0.4–0.6, the range of displacement ratio is 0.19–0.38, and the larger the seismic coefficient, the higher the seismic resistance of the widened type. in comparison with the rrm ratio, the difference between the two types is large for the horizontal displacement. therefore, the widened type can be said to have especially high horizontal displacement resistance. for vertical displacement, as shown in figure 11, the widened type (red) produces very little displacement in comparison with the normal type (blue). in the range of seismic coefficient up to 0.6, the displacement ratio is less than 2%. (a) (b) fig. 10. relationship between seismic coefficient and horizontal displacement fig. 11. relationship between seismic coefficient and vertical displacement v. conclusions in this study, in order to discuss how widening the bottom of pier foundations affects the seismic resistance, horizontal loading experiments were performed by installing two types of pier models in the ground, namely (i) a normal type with a leg diameter of 60mm and (ii) a widened type with a width of 115mm. the main conclusions drawn are outlined below. in a rigid frame subjected to horizontal load, tilted displacement occurs first, the vertical sr on the front side leg increases with increasing horizontal load, and the vertical sr on the back side leg decreases. the rotational center as a rigid frame is not at the center of the span but at a point closer to the front than the center of the span. the rotational center position differs between the normal type and the widened type. the widened type has a larger rrm arm length than the normal type because the rotational center is closer to the center of the span compared with that of the normal type. therefore, compared to the normal type, the widened type has a larger rrm which at maximum is 1.28 times the rrm of the normal type. in design practice, such vertical sr distributions cannot be reproduced, and the rrm is underestimated. when the amount of horizontal displacement with respect to the seismic coefficient is compared in terms of real scale, the widened type has 0.19–0.38 times the horizontal displacement in the range of seismic coefficient from 0.4 to 0.6 compared with the normal type. compared with the normal type, the widened type experiences less horizontal displacement, especially in the range of large seismic coefficient, and the widened type has remarkably high seismic resistance against the action of a massive earthquake. for vertical displacement, the widened type produces only 2% or less of the displacement of the normal type. acknowledgments the experiments were conducted with the help of rie yamaoka and daisuke shibata. this research was supported financially by jsps kakenhi grant no. jp18k04324 and oriental shiraishi co., ltd. references [1] t. nagao, d. shibata, “experimental study of the lateral spreading pressure acting on a pile foundation during earthquakes”, engineering, technology & applied science research, vol. 9, no. 6, pp. 5021-5028, 2019 [2] k. tokimatsu, y. asaka, “effects of liquefaction-induced ground displacements on pile performance in the 1995 hyogoken-nambu earthquake”, soils and foundations, vol. 38, no. special, pp. 163-177, 1998 [3] pianc, seismic design guidelines for port structures, a.a. balkema publishers, 2001 [4] g. mondal, d. c. rai, “performance of harbour structures in andaman islands during 2004 sumatra earthquake”, engineering structures, vol. 30, pp. 174–182, 2008 [5] r. a. green, s. m. olson, r. brady, b. r. cox, g. j. rix, e. rathje, j. bachhuber, j. french, s. 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ziaie-moayed, m. janbaz, “effective parameters on modulus of subgrade reaction in clayey soils”, journal of applied sciences, vol. 9, pp. 4006-4012, 2009 [15] j. lee, s. jeong, “experimental study of estimating the subgrade reaction modulus on jointed rock foundations”, rock mechanics and rock engineering, vol. 49, no. 6, pp. 2055–2064, 2016 [16] japan road association, specifications for highway bridges, part 4, substructures, japan road association, 2016 [17] s. iai, “similitude for shaking table test on soil-structure-fluid model in 1g gravitational field”, soil and foundations, vol. 29, no. 1, pp. 105118, 1989 microsoft word 07-3427_s1_etasr_v10_n3_pp5619-5626 engineering, technology & applied science research vol. 10, no. 3, 2020, 5619-5626 5619 www.etasr.com keltoum: model reference adaptive controller for lti systems with time-variant delay model reference adaptive controller for lti systems with time-variant delay ghedjati keltoum department of electrical engineering university ferhat abbas setif 1 setif, algeria ghedjat_keltoum@yahoo.com abstract—in this paper, a new direct model reference adaptive control procedure (dmrac) for linear time-invariant (lti) delay systems is presented with the use of the concept of the command generator tracker which expands the class of processes that can now be controlled with zero output error. the stability of the error between the system and the model is guaranteed by the lyapunov theory. the new algorithm is applied to control a perturbed delay system. matlab simulation examples are given to demonstrate the usefulness of the algorithm. keywords-adaptive control; asymptotic stability; time delay systems; dynamical uncertainties i. introduction the stability of time delay systems has been studied with the lyapunov–krasovskii and the lyapunov–razumikhin approach. these two concepts have been used in order to avoid the classical lyapunov method. authors in [1-3] give an overview of the stability of time delay systems with some advanced results. the rightmost roots of the characteristic are investigated in [4]. authors in [5] studied the control of an mimo nonlinear time delay system. stability analysis and stabilization for takagi–sugeno (t–s) fuzzy systems with time delay have been studied in [6, 7]. in [8], a delay-dependent stabilization condition was proposed for the stability of a class t–s fuzzy time-delay system using homogeneous polynomials scheme and polya's theorem with application on a truck-trailer model. authors in [9] investigated the pre-specified performance for time-varying delays using model reduction, fuzzy logic, and lmi techniques. the pid controller has also been used in the stability of the time-delay systems [10]. the developed method guarantees gain and phase margins besides stability. the introduction of adaptive control in uncertain time delay systems has been studied thoroughly. in [11], the author used the back stepping transformation where regulation was achieved despite the presence of partial measurements and disturbance. the adaptive identification of the parameters and the time delay of the time delay system were addressed in [12]. this identification is achieved with the use of the concept of transformation of the system in the parameterized form. the convergence of the identification error is guaranteed using the persistent excitation (pe) condition. also, finite time convergence was assured using the terminal sliding mode. in [13], the author applied a sliding mode controller to stabilize uncertain time-delay chaotic systems. the proposed controller was robust against time-delays, parameter uncertainties and disturbances. the h-infinity theory has also been used to control time-delay systems. in [14], time-delays appeared in the network used in the feedback loop. the delay-dependent stability criterion was derived from the lyapunov krasovskii function and the linear matrix inequality (lmi). the h2, hinfinity and the lmi concepts have been used for discrete time delay uncertain systems. authors in [15] used the past values of the states and the outputs, and were able to stabilize the system with time-varying delays. finite time stability of time-delay systems has been investigated in [7, 16-18] with the utilization of the homogeneity theory. the observer design of time delay systems was used in [19] for a switched singular system where two design methods were used and in [20], a luenberger-like observer has been used to estimate the unknown inputs for a large class of linear systems. the output regulation of timedelay systems has also been investigated in [21] by using the adaptive concept and the observer design using rbf neural network systems to approximate unknown functions. in [22] the well known lyapunov–krasovskii theorem was used to investigate the output stabilization for time-delay nonholonomic systems. the simple mrac of mimo plants was first proposed in [23]. this class of algorithms does not require full state access or satisfaction of perfect model conditions. asymptotic stability is ensured provided that the plant is almost strictly positive real (aspr). authors in [24] extended the original algorithm to a class of plants which violates this condition. this approach involved designing a supplementary feedforward filter to be included in parallel with the original plant resulting in a new augmented plant which had to satisfy the same strictly positive real condition. unfortunately, the tracking error was not the true difference between the plant and the model outputs since it included the contribution of the supplementary feedforward filter which led to an asymptotically stable error [25-28]. the application of adaptive fuzzy control can be found in [33, 34]. the authors considered the internal model for controlling dcdc converters. adaptive control is also used in many industrial fields, while authors in [35] used it for controlling uav systems. corresponding author: ghedjati keltoum engineering, technology & applied science research vol. 10, no. 3, 2020, 5619-5626 5620 www.etasr.com keltoum: model reference adaptive controller for lti systems with time-variant delay authors in [36] developed a saturated command for planar systems where the stabilization is achieved in finite time using just a simple proportional derivative corrector pd whose parameters are optimally adapted. this finite time stability is analyzed with lyapunov's theory and homogeneity concept. author in [37] aimed to replace a mechanical cam system with an electromagnetic actuator. the electromagnetic actuator creates a force which acts on the valve shaft and allows it to move linearly allowing the admission and exhaust of the explosion gas and therefore the combustion engine rotation. electromagnetic force is generated by making a velocity measurement without a speed sensor. the position is deducted adaptively according to the estimated speed. this adaptive technique improves the efficiency of the mechanical engine and its longevity. the same author in [38] follows up this work and tries to remedy the problems encountered by the classic pd corrector in the presence of noise at high frequencies by optimally approximating the pd corrector parameters. after finding an actuator’s model of electromagnetic valve actuator which replaces the classic mechanical valve actuator, the pd parameters are adjusted adaptively and on line with the variance minimization method. ii. direct model reference adaptive control the model reference adaptive control is considered for the non-linear plant: . 1 ( ) ( ) ( ( )) ( ) ( ) ( ) ( ) p p p p p p p p p p x t a x t a x t t b u t f x y t c x t τ= + − + + = (1) where ( ) p x t is the (n×1) state vector, up(t) is the (m×1) control vector, yp(t) is the (q×1) plant output vector, f(t) is an (n×1) vector of nonlinearities, ap, bp are matrices with appropriate dimensions, and τ(t) is the time delay that verifies assumption (2) as stated below. we assume that the parameters of the linear part of the plant model are uncertain, i.e. only known within certain finite bounds. the range of the plant parameters is assumed to be known and bounded with: _ ( , ) , , 1,...,ijp ij a a i j a i j n − ≤ ≤ = (2) _ ( , ) , , 1,...,ijp ij b b i j b i j n − ≤ ≤ = (3) • assumption 1: the non-linear function f(x) is lipschitz in its arguments, that means 1 2 1 2 ( ) ( )f x f x l x x− < − where l>0 is the constant of lipschitz, (.) is the euclidean norm and 1 2 ,x x belong to a compact set n rω∈ . • assumption 2 the derivative of the delay system τ(t) verifies: 1 d ( ) d t t τ τ≤ the objective of this paper is to find, without explicit knowledge of ap, bp, and for non-linear f(xp), the control up(t) such that the plant output vector yp(t) follows the reference model given by: . ( ) ( ) ( ) ( ) ( ) ( ) ( ) m m m m m m m m m m m m x t a x t a x t b u t b u t y t c x t τ τ τ τ = + − + + − = (4) the output ym is the desired response to the set point command um. the model incorporates the desired behavior of the plant, but its choice is not restricted. in particular, the order of the plant may be much larger than the order of the reference model. the ideal control law that generates perfect output tracking and ideal state trajectories is assumed to be a linear combination of the model states and the model input (see [29]). in our case, we suppose that the ideal state, its delay and the ideal input are related to the model state. its delay and the model input are related by: ( ) ( ) p m11 12 21 22 mp x t x (t)s s s s u (t)u t ∗ ∗      =            (5.0) the perfect output tracking means that the ideal output * ( )y t is equal to the output model ( ) m y t which means: * ( ) ( ) ( ) ( ) ( ) ( ) p p p p 11 m p 12 m m m m y t c x t c s x t c s u t y t c x t ∗= = + = = (5.1) taking into account (5.0) and that the ideal state * ( )x t verifies this relation and the assumption that the command um(t) is constant (in the case where the input is not a constant, we can always find a dynamic system to generate um(t) with a constant input), the derivative of * ( )x t can be written as: d ( ) d ( ( ) ( )) d d ( ( ) ( ) ( ) ( )) ( ) ( ) ( ) ( ) * p 11 m 12 m 11 m m m m m m m m 11 m m 11 m m 11 m m 11 m m x t s x t s u t t t s a x t a x t b u t b u t s a x t s a x t s b u t s b u t τ τ τ τ τ τ τ τ = + = + − + + − = + − + + − ( ) ( ) ( ) ( ( ) ( )) ( ( ) ( )) ( ( ) ( )) * * * p p 1 p p p p 11 m 12 m 1 11 m 12 m p 21 m 22 m a x t a x t τ b u t a s x t s u t a s x t s u t b s x t s u t τ τ = + − + = + + − + − + + (5.2) using (5.1)-(5.2), we obtain the following algebraic system: 2 0 11 m p 11 p 21 11 m p 12 p 22 11 m 1 11 11 m 1 1 p 11 m p 12 s a a s b s s b a s b s s a a s s b a s c s c c s τ τ = +  = +  =  =  =  = (5.3) which can be written as: engineering, technology & applied science research vol. 10, no. 3, 2020, 5619-5626 5621 www.etasr.com keltoum: model reference adaptive controller for lti systems with time-variant delay 0 0 0 p p11 m 11 m 11 12 11 m 11 m 1 21 22 pm a bs a s b s s s a s b a s s cc τ τ        =            (6) in the system (6) we have more unknowns than equations, so the solution almost always exists. when al, amτ, and bmτ are null, then the system and the model are without delay and we get the equations given in [29]. the adaptive control law based on the extended command generator tracker (cgt) approach is given by: ( ) ( ) ( ) ( ) ( ) ( ) ( ) p e y x m u m u t k t e t k t x t k t u t= + + (7) the adaptive law (7) has been applied for linear systems [30, 31]. here we aim to extend it to a linear time delay system described by (1) by adding a delay in the input and output in the model (4). the tracking error is given by: ( ) ( ) ( ) y m p e t y t y t= − and ( ) e k t , ( ) x k t and ( ) u k t are adaptive gains concatenated into matrix k(t) as : [ ]( ) ( ) e x uk t k t k (t) k (t)= (8) defining the vector r(t)(nr×1) as: ( ) ( ( ) ( )) t t t t m p m m r t y t y t x (t) u (t) = −  (9) the control up(t) is written in a compact form as: ( ) ( ) ( ) p u t k t r t= (10) where ( ) ( ) ( ) p i k t k t k t= + (11) ( ) ( ) ( ) . ( ) , 0 t p m p p p k t y t y t r t t t = − ≥  (12) . ( ) ( ) ( ) . ( ) , 0 t i m p i i k t y t y t r t t t = − >  (13) iii. stability study the first step of the demonstration is to design a positive definite quadratic form in the state variables ex(t) and ki(t) of the adaptive system. 1 i t − is assumed to be a symmetric positive definite matrix. then an appropriate choice of the lyapunovkrasovskii functional [32] is: ~ ~ 1 ( ) ( ) ( ) ( ) t t t x x x x t t t i i i v e pe e qe d tr s k k t k k s τ α α α − − = + +   − −   ∫ (14) where tr is the trace of a matrix. its time derivative is: . . . . ~ . 1 ( ) ( ) (1 ) ( ) ( ) 2 ( ) t t t x xx x x x t x x t ii i v e pe e pe e t qe t e t qe t tr s k k t k s τ τ τ − = + + − − − − +  −   (15) where p, q are symmetric positive definite matrices of size n×n, ~ k is a m×n matrix and s is a non-singular m×m matrix. since the matrix ~ k appears only in the function v and not in the control algorithm, it is called fictitious gain matrix. it has the same dimension as k where: ~ ~ ~ ~ e x up x m m k r k c e k x k u× = + + (16) the four gains ~ ek , ~ xk , ~ uk and ~ xrk are as ~ k fictitious. then we take the equation of the error using the fact that * x p p e x x= − to find: . * * * * 1 1 * * 1 * * * * 1 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) x p p p p p p p p p p p p p p p p p p p p p p p x x p p p p p e a x a x t b u f x a x a x t b u f x a x x a x t x t b u u f x f x a e ae t b u u f x f x τ τ τ τ τ = + − + + − − − − −    = − + − − −     + − + −   = + − + − +  − (17) if we set: * ( ) ( ) p p df f x f x= − and substitute * p u from (5.0) and p u from (7), we get: . 1 21 22 ( )x p x x p m m x m u m e p x e a e ae t b s x s u k x k u k c e df τ= + −  + − − − +  (18.a) 1 21 22 ( ) p x x t p m m i p x p a e ae t b s x s u k r c e r t r df τ= + − +  + − − +  (18.b) then the adaptive system is described by: [ ] dfrtrecrkusxsb teaeae p t xpimmp xxpx +−−++ −+= 2221 1 . )( τ (19) . t i p x i k c e r t= (20) substituting (19) and (20) in (15), we get: . 1 21 22 1 21 22 ~ 1 . ( ) ( ( ) ( 2 ( ) ( ) ( ) ( ) (1 ) ( ) ( ) t p x x p m m i xt p x p p x x p m m t x t i p x p t t t i i p x i t t x x x x a e ae t b s x s u k r v pe c e r t r a e ae t b s x s u e p k r c e r t r tr s k k t c e r t s e t qe t e t qe t τ τ τ τ τ − + − + + −  =   −   + − + +  +   − −     + − +   − − − − + df (21) we can write it as: engineering, technology & applied science research vol. 10, no. 3, 2020, 5619-5626 5622 www.etasr.com keltoum: model reference adaptive controller for lti systems with time-variant delay . 1 21 22 1 21 22 ~ 1 ( ) ( ) ( ) ( ) 2 ( ) ( ) t t t t x p x x x t t t t t t t t t t t t t t m p m p i p p x p p x t t x p x x x t t x p m m i p x p t t t t i i i x p t x v e a pe e t a pe x s b u s b r k b r t re c b pe e pa e e pae t e pb s x s u k r c e r t r tr s k k t t re c s e t q τ τ − = + − + + − − + + − + + − − +   − +   . ( ) (1 ) ( ) ( ) t x x x e t e t qe t dfτ τ τ− − − − + (22) knowing that for two vectors ( ,1)u l and (1, )v l have [ ]. .tr u v v u= therefore: . 1 1 21 22 21 22 ~ ( ) ( ) ( ) 2 ( ) (1 t t t t x p p x x x t t t x x x p m x p m t t t t t t x p i x p p x p m p x t t t t t t t t t t t m p x i p x p x p p x t t t x p i v e pa a p q e e t a pe e pae t e pb s x e pb s u e pb k r e pb c e r t r x s b pe u s b pe r k b pe r t re c b pe e c s s k k r df τ τ = + + + − + − + + − − + + − − + − + − . ) ( ) ( ) t x x e t qe tτ τ τ− − − (23.a) which means that: . 1 1 21 22 ~ . ( ) ( ) ( ) 2 ( ) 2 2 2 (1 ) ( ) ( ) t t t t x p p x x x t t x x x p m m t t t t t x p p x p x p p i t t t t x p x x v e pa a p q e e t a pe e pae t e pb s x s u e pb c e r t r e c s s pb k r e c s s k r e t qe t df τ τ τ τ τ = + + + − + − + +  − + −  − − − − − + by setting: t p p c gb p= and 1( )tg s s −= , the derivative of the lyapunov function becomes: . 1 1 21 22 ~ 1 . ( ) ( ) ( ) 2 ( ) 2 ( ) 2 (1 ) ( ) ( ) t t t t x p p x x x t t x x x p m m t t t t t t t x p p x p x p t x x v e pa a p q e e t a pe e pae t e pb s x s u e pb s s b pe r t r e c s s k r e t qe t df τ τ τ τ τ − = + + + − + − + + − − − − − − + (24) substituting ~ ~ ~ ~ r e x up x m m k k c e k x k u= + + in (24) we get: . ~ ~ 1 1 1 ~ ~ 21 22 . ( ) ( ) ( ) ( ) 2 ( ) 2 ( ) ( ) (1 ) ( ) ( ) t t e ex p p p p p p x t t t x x x x t t t t x p p x p t x ux p m m t x x v e p a b k c a b k c p q e e t a pe e pae t e pb s s b pe r t r e pb s k x s k u e t qe t df τ τ τ τ τ − =  − + − +   + − + − −  + − + −   − − − − + (25) thus, if we set: ~ ~ 21 22 ( ) ( ) 0x um ms k x s k u   − + − =   (25) or ~ 21x k s= and ~ 22u k s= (none of which is required for implementation), the derivative of v becomes: . ~ ~ 1 1 1 . ( ) ( ) ( ) ( ) 2 ( ) (1 ) ( ) ( ) t t e ex p p p p p p x t t t x x x x t t t t x p p x p t x x v e p a b k c a b k c p q e e t a pe e pae t e pb s s b pe r t r e t qe t df τ τ τ τ τ −  = − + − +   − + − − − − − − + (26) taking into account the assumption 2, the derivative of the lyapunov function verifies (27): . 1 1 1 1 1 ( ) ( ) (1 )( ) ( ) 2 ( ) t x x t x x t t t t x p p x p e t e tq pa v a p qe t e t e pb s s b pe r t r df ττ τ −      ≤     − −− −     − + (27) with ~ ~ 1 ( ) ( ) t e ep p p p p p q p a b k c a b k c p q= − + − + (28) from (12), tp is positive semi-definite, so (27) becomes: . 1 1 1 1 ( ) ( ) (1 )( ) ( ) t x x t x x e t e tq pa v df a p qe t e tττ τ      ≤ +    − −− −     (29) let’s take: ( ) ( ) x x x e t e e t τ   =  −  and 1 1 2 1 1 (1 ) t q pa q a p qτ   = − − −  (30) then (29) is rewritten as: . 2 t x x v e q e df≤ − + (31) when df is equal to zero, the error is asymptotically stable if and only if 2 2 t q q= is positive semi-definite. in the case where df is different from zero and satisfies the assumption 1, then the derivative of the lyapunov function verifies: . * 2 2 2 2 2 min 2 min 2 min 2 ( ) ( ) 0 ( ) t t t x x x x x x x x x x x x v e q e df e q e l x x e q e l e q e l e q e l e l e q λ λ λ ≤ − + ≤ − + − = − + ≤ − + ≤ − + ≤ ⇒ ≥ where min 2 ( )qλ stands for the lowest eigenvalue of 2 q which is a positive number since 2 2 0 t q q= ≥ . the last inequality implies that the error ex is ultimately uniformly stable, which means that it belongs to a compact set around the origin. this set can be rendered much lower if we select min 2 ( )qλ to be engineering, technology & applied science research vol. 10, no. 3, 2020, 5619-5626 5623 www.etasr.com keltoum: model reference adaptive controller for lti systems with time-variant delay large. one choice is given by 2 .q iα= where i is the identity matrix and α is a scalar positive number. finally the derivative of the lyapunov function is negative definite in ex if min 2 / ( ) x e l qλ≥ . since v(t) is a positive definite function, then the vector ex(t) and the matrix ki(t) are bounded. we summarize the stability concept in the following theorem: • theorem: the control given by (10), and the adaptive laws given by (11), (12) and (13) applied to the non-linear uncertain system (1) that verifies the assumption 1 lead to a asymptotically stable error between the system and the model if and only if there are two p, q matrices 0 t p p= > and 0tq q= ≥ such that: 1) the matrix 1 2 1 1 (1 ) t h pa q a p qτ   = −  − −  where ~ ~ ( ) ( ) t e ep p p p p p h p a b k c a b k c p q= − + − + is positive semi-definite for some matrix ~ ek . 2) ( ) t p pb gc= , 1( ) ,tg s s −= for a non-singular matrix s. 3) 2 1 2 1 2 1 2 ( ) ( ) , 0 f x f x l x x l x ,x r− < − > ∈ ~ ~ 2 1 2 1 2 1 2 ( ) ( ) ( ) 0, 0 , 0 ( ) ( ) , 0 , t e ep p p p p p t t p p i p a b k c a b k c p q i pb gc t t g g f x f x l x x l x ,x r α  − + − = −   = = ≥ > = > − < − > ∈ where rα +∈ , and i is the identity matrix. these relations imply that the feedback system is spr for large α, and so that the original linear system is aspr. iv. simulation during simulations, it is required that the output of the system tracks the output reference. the controlled system is given by: . 1 ( ) ( ) ( ( )) ( ) ( ) ( ) p p p p p p p p p x t a x t a x t t b u t y t c x t τ= + − + = with [ ]1 1 3 5 6 3 , , , 5 6 3 4 6 8 4 p a a b c       = = = =            . the transfer function of the reference model is given by: 2 ( ) 1 m g s s = + the eigenvalues of ap and a1 are given by: { }( ) -0.85; 5.85paλ = and { }1( ) 0.31; 12.68aλ = which means that the two matrices are instable. the model input is illustrated in figure 1, where 1 m u = from 0 to 20s and 1 m u = − from 20s to 40s. from 40s to 60s we have chosen a sinusoidal input given by ( ) 2sin( ) m u t t= and from 60s to 100s, another sinusoidal input, ( ) sin(t/3) m u t = , was selected. fig. 1. the model input ( ) m u t a. case 1: without perturbation in this case we supposed that the controlled system is not affected by noise measurement and actuator failure. the adjustable parameter is chosen to be 3,3 1 p i t t i= = × where 3,3 i is the identity matrix of order 3. figure 2 shows the two outputs where the output of the controlled system tracks the reference whatever is the model input. the controlled system is given in figure 3 where we can see that this command has the same form as the model input. the four gains are presented in figure 4. note that these gains are used to construct the controlled system input (see (11), (12) and (13)). these gains are bounded so the controlled system input is also bounded. b. case 2: with perturbation and 3,3 1 p i t t i= = × in this case, a noise measurement and an actuator fault are added, so the perturbed system is given by: . 1 ( ) ( ) ( ( )) ( ( ) ( )) ( ) ( ) ( ) p p p p p p p p p x t a x t a x t t b u t d t y t c x t n t τ= + − + + = + where d(t) is the actuator fault given by d(t)=1sin(2t), and n(t) represents the measurement noise given by n(t)=1sin(4t). the adjustable parameters are taken as in the previous case. figure 5 illustrates the outputs of the system and the model. it is clear that the tracking has been deteriorated due to the perturbation that has affected the system. figure 6 represents the control input where the controller is doing a big effort in order to damp the effect of the perturbation and let the system output track the reference model. 0 10 20 30 40 50 60 70 80 90 100 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 time s engineering, technology & applied science research vol. 10, no. 3, 2020, 5619-5626 5624 www.etasr.com keltoum: model reference adaptive controller for lti systems with time-variant delay fig. 2. outputs of the system and the model without perturbation fig. 3. the system command u(t) fig. 4. the gains ke, kx, and ku fig. 5. outputs of the system and the model with perturbation 3,3 1 p i t t i= = × fig. 6. the system command u(t) fig. 7. outputs of the system and the model with perturbation 3,3 10 p i t t i= = × 0 10 20 30 40 50 60 70 80 90 100 -4 -3 -2 -1 0 1 2 3 time s y ym 0 10 20 30 40 50 60 70 80 90 100 -1.5 -1 -0.5 0 0.5 1 1.5 time s 0 10 20 30 40 50 60 70 80 90 100 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 time s ke kx ku 0 10 20 30 40 50 60 70 80 -4 -3 -2 -1 0 1 2 3 time s y ym 0 10 20 30 40 50 60 70 80 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 time s 0 10 20 30 40 50 60 70 80 -4 -3 -2 -1 0 1 2 3 time s y ym engineering, technology & applied science research vol. 10, no. 3, 2020, 5619-5626 5625 www.etasr.com keltoum: model reference adaptive controller for lti systems with time-variant delay c. case 3: with perturbation and 3,3 10 p i t t i= = × in this case and in order to overcome the drawback that has appeared in the previous case, we augmented the adjustable parameter tp, ti as 3,310p it t i= = × . figure 7 shows a perfect tracking compared to figure 5 and figure 8 shows the effect of the controller in overcoming the perturbation and letting the system output track the reference model. note that this command is bounded and does not represent a high oscillation. figure 9 presents the gains that are bounded and they are adjusted to construct the system input. fig. 8. the system command u(t) fig. 9. the gains ke, kx, and ku v. conclusion this paper presents an adaptive command applied for a perturbed time delay system. the lyapunov’s theory has been addressed in order to achieve a robust command against the uncertainty which is inherent in all real systems. the simulation results confirm the robustness of the developed command. references [1] e. fridman, “tutorial on lyapunov-based methods for time-delay systems”, european journal of control, vol. 20, no. 6, pp. 271–283, 2014 [2] k. gu, v. l. kharitonov, j. chen, stability of time-delay systems, springer, 2003 [3] m. wu, y. he, j. h. she, stability analysis and robust control of timedelay systems, 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applied science research vol. 3, �o. 1, 2013, 349-351 349 www.etasr.com selvam and latha: a simple square rooting circuit based on operational amplifiers (opamps) a simple square rooting circuit based on operational amplifiers (opamps) k. c. selvam department of electrical engineering indian institute of technology, madras chennai – 600 036, india kcselvam@ee.iitm.ac.in s. latha department of electrical engineering indian institute of technology, madras chennai – 600 036, india latha@ee.iitm.ac.in abstract  a simple circuit which accepts a negative voltage as input and provides an output voltage equal to the square root of the input voltage is described in this paper. the square rooting operation is dependent only on the ratio of two resistors and a dc voltage. hence, the required accuracy can be obtained by employing precision resistors and a stable reference voltage. the feasibility of the circuit is examined by testing the results on a proto type. keywords-square-rooting; generators; comparators; switches; low pass filters i. introduction a need for obtaining the square root of a measured quantity is often met in the field of measurement and instrumentation systems [1]. especially techniques that involve the measurement of unknown signals buried in excessive noise by employing either a phase sensitive detector (psd) or a tracking amplifier invariably need a final square rooting stage [2]. a square rooting circuit is also required in certain methods of determining impedances under sinusoidal excitation as well as in case of obtaining the three vectors of a 3 phase power system. methods based on expensive and complex multipliers have been proposed in the past for realizing a circuit that provides an output voltage whose magnitude is the square root of the input voltage. square rooting circuits have been implemented with the use of different high performance active building blocks with second generation current conveyors [3], otas [4], second generation current controlled current conveyors (ccciis) [5], current differencing transconductance amplifiers (cdtas) [6] and current follower transconductance amplifiers (cftas) [7]. unfortunately, these reported circuits suffer from one or more of following disadvantages: (a) excessive use of the active/passive elements, especially external resistors [3-5], (b) use of a floating resistor, which is not convenient to further fabricate in ic [3] and (c) absence of linearly electronic controllability of output signal [3-7]. in this paper, a novel simple circuit for square rooting employing operational amplifiers (opamps) which eliminates all drawbacks of the previously mentioned methods [3-7], is proposed. though the scheme is simple, the expression for the output indicates that with a precision dc voltage as a reference and a pair of precision resistors, good accuracy can be achieved. ii. circuit description the circuit diagram of the proposed scheme is shown in figure 1. the sawtooth wave is generated by charging a capacitor at a specified rate and then rapidly discharging it with a switch. let us assume that at start, the charge and, hence, the voltage at the output terminal of operational amplifier oa1 is zero. since the inverting terminal of the operational amplifier oa1 is at virtual ground, the current through r1, namely vr/r1 amps, would flow through and charge capacitor c1. during this charging (till the output of oa1 reaches the voltage level of vr) the output of the operational amplifier oa2, configured to work as a comparator, is at the low state and switch s1 is kept open (off). as soon as the output of oa1 crosses the level of vr, e.g. after a time period t, the output of comparator oa2 goes high and switch s1 is closed (on). the s1 switch would then short the capacitor c1 and hence vs drops to zero volts. during the time period t we have, 1 1 1 1 1 r s r v v v dt t r c r c = =∫ (1) after a very short delay time td, required for the capacitor to discharge to zero volts, the comparator oa2 output returns to low and switch s1 is opened, thus allowing c1 to resume charging. this cycle, therefore, repeats itself at a period (t+td). the waveforms at cardinal points in the circuit of figure 1 are shown in figure 2. from (1) and the fact that at time t=t, vs=vr, we get: 1 1t r c= (2) as seen in figure 1, the comparator oa3 compares the sawtooth waveform thus generated with the output voltage vo etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 349-351 350 www.etasr.com selvam and latha: a simple square rooting circuit based on operational amplifiers (opamps) and provides at its output, a pulse train vk. the on time of this pulse train will be: (3) o r v d t v = this pulse train vk controls switch s2. switch s2 connects (a) vo to the low pass filter realized with the operational amplifier oa4 during on time ‘d’ and (b) zero volts during off time of pulse train vk. another pulse train vp is generated at the output of switch s2 with the same on time ‘d’, period t and max value vo. the output of the low pass filter realized with the operational amplifier oa4 will be the average value of pulse vp which is, 0 1 d f o v v dt t = ∫ o v d t = 2 (4)o r v v = considering kcl for node ‘j’ in the circuit of figure 1, we get: 1 3 2i i i+ = 1 3 f v i r = 2 3 5 4 o o i r v v v r v r r + = if r3 = r4 = r and r5 >> r 2 o i r v v v = 2 o i r v v v= o i r v v v= (5) thus the output voltage vo is proportional to the square root of the input voltage vi. iii. experimental results and conclusion the circuit shown in figure 1 was implemented and tested in our laboratory. lf 356 ics were used for all operational amplifiers. switches s1 and s2 were realized with cd 4053. the following values were set for different circuit components; vr=6 v, r1=200 kω, c1=470 pf, r3=r4=10 kω, r5=1 mω. voltage levels of ±7.5 v were chosen for the power supply. the test results are shown in table i. the accuracy of the proposed circuit strongly depends upon the sharpness and linearity of the sawtooth waveform. the offset voltages of all operational amplifiers are to be nulled for better performance of the circuit. the small variations in voltage vr will cause an error at the output; hence, a stable precision voltage source must be used as vr. however the small variations in the power supply will not affect the circuit at all. it should be noted here that the polarity of input voltage vi should only be negative and its maximum value should be less than vr. experimental results indicate the practical feasibility of the proposed circuit. acknowledgement the author is highly indebted to prof. dr. enakshi bhattacharya, prof. dr. v. jagadeesh kumar and dr. bharath bhikkaji of electrical engineering department, iit madras, for their constant encouragement throughout the work. he also thanks mr. mithun for manuscript formatting. table i. test results on the proto type square rooting circuit input volts -vi output voltage by experiment output voltage by calculation error in % 0.5v 1.711 1.732 -1.20 1.0v 2.420 2.449 -1.18 1.5v 2.959 3.000 -1.34 2.0v 3.414 3.464 -1.44 2.5v 3.829 3.872 -1.10 3.0v 4.200 4.242 -0.99 3.5v 4.525 4.582 -1.24 4.0v 4.820 4.890 -1.43 4.5v 5.125 5.196 -1.35 references [1] e. o. doebelin, measurement systems: application and design, mc graw hill, new york, 2004 [2] m. a. atmanand, “novel schemes for impedance measurement and their implementation through electronic circuits”, ph.d thesis, iit madras, 1996 [3] s. i. liu, “square-rooting and vector summation circuits using current conveyors”, iee proc. circuits., dev. syst., vol. 142, no. 4, pp. 223226, 1995. [4] v. riewruja, “simple square rooting circuit using otas”, electronics letters, vol. 44, no. 17, pp. 1000-1002, 2008 [5] c. netbut, m. kumngern, p. prommee, k. dejhan, “new simple square rooting circuits based on translinear current conveyors”, ecti tranasactions on elecrtrical eng., electronics and communication, vol. 5, no. 1, pp. 10-17, 2007. [6] w. tangsrirat, t. pukkalanun, p. mongkolwai, w. surakampontorn, “simple current mode analog multiplier, divider, square-rooter and square based on cdtas”, aeu-int. j. electron. commun., vol. 65, no. 3, pp. 198-203, 2011. [7] p. mongkolwai, d. prasertsom, w. tangsrirat, “cftabased current controlled current amplifier and its application”, 25th international technical conference on circuits/systems, computers and communications (itc-cscc 2010), pattaya, thailand, 2010. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 349-351 351 www.etasr.com selvam and latha: a simple square rooting circuit based on operational amplifiers (opamps) fig. 1. circuit diagram of square rooter fig. 2. associated waveforms of figure 1 authors profile k. c. selvam was born in 1968 in krishnagiri district of tamil nadu state, india. he graduated from the institution of electronics and telecommunication engineers, new delhi, in 1994. he got the best paper award by iete in 1996. at present he is working as technical staff in the controls and instrumentation laboratory, department of electrical engineering, indian institute of technology, madras, india. s. latha was born in 1967 in the vilupuram district of the tamil nadu state, india. she obtained a diploma in electronics and communication engineering from the periyar century polytechnic college, vallam, thanjavoor, tamil nadu, india in 1985. at present she is working as technical staff in the department of electrical engineering, indian institute of technology, madras, india. her research interests include microcontroller based digital measuring instruments. microsoft word 08-3094_s_etasr_v9_n6_pp4905-4911 engineering, technology & applied science research vol. 9, no. 6, 2019, 4905-4911 4905 www.etasr.com regis et al.: optimal battery sizing of a grid-connected residential photovoltaic system for cost … optimal battery sizing of a grid-connected residential photovoltaic system for cost minimization using pso algorithm nibaruta regis department of electrical engineering, pau institute of basic sciences, technology and innovation, nairobi, kenya nibaregis@gmail.com christopher maina muriithi school of engineering and technology murang’a university of technology nairobi, kenya cmmuriithi@mut.ac.ke livingstone ngoo faculty of engineering and technology multimedia university of kenya nairobi, kenya livingngoo@gmail.com abstract—this paper proposes a new optimization technique that uses particle swarm optimization (pso) in residential gridconnected photovoltaic systems. the optimization technique targets the sizing of the battery storage system. with the liberation of power systems, the residential grid-connected photovoltaic system can supply power to the grid during peak hours or charge the battery during non-peak hours for later domestic use or for selling back to the grid during peak hours. however, this can only be achieved when the battery energy system in the residential photovoltaic system is optimized. the developed pso algorithm aims at optimizing the battery capacity that will lower the operation cost of the system. the computational efficiency of the developed algorithm is demonstrated using real pv data from strathmore university. a comparative study of a pv system with and without battery energy storage is carried out and the simulation results demonstrate that pv system with battery is more efficient when optimized with pso. keywords-grid-connected pv; electricity surplus; sizing; battery energy storage; electricity prices; net metering; pso i. introduction nowadays electricity access plays a vital role and governments and private sector are investing in the electricity domain to ensure sustainable development. climate change and the relaxation of the electric energy market boosted the development of renewable energy integration in electric grids [1]. in many developing countries the reliable access to electricity is still a big challenge. grids are sometimes marked by limited supply and prevailing disruptions. due to this, some electricity users who especially own classical grid-connected pv systems do not derive a benefit from their installations considering the intermittent nature of the solar panel [2]. the hours of high pv production do not necessarily coincide with peak load demand hours. since customers usually experience frequent undesirable power cuts, it is possible that this issue will grow in the future. it is very important to look at alternative ways of minimizing the operational cost of a gridtied pv system. one of the alternatives is integrating optimally sized energy storages into a grid-connected pv system. there have been various contributions towards cost minimization and energy storage optimization where different approaches have been investigated. authors in [3, 4] used dynamic programing (dp), whereas in [5, 6] the optimization was performed by means of markov decision processes and fuzzy clustering method. authors in [7], presented an economic analysis of a pv system under a net-metering scheme. due to the randomness of renewable energy sources (res) and the serial characteristic of the decision problem in the analysis, a metaheuristic approach is preferred. whilst analytical methods usually endure some problems like slow convergence and dimensionality, metaheuristic-based optimizations are much more effective in handling large-scale nonlinear optimization problems. in [8], a genetic algorithm was developed to optimally size lead acid batteries that run under dynamic pricing strategies in both independent and aggregated ways. authors in [9] introduced a pso-based algorithm for optimally sizing constituents of a hybrid renewable system, aiming to maximize the energy production to cover the load at lowest cost and enhanced reliability. an improved firefly algorithm was proposed in [10] to optimally locate and size the battery energy storage system for mitigating the voltage rise in pvdg integrated distribution network. authors in [11] proposed a two layer optimization procedure using pso to optimize the battery size of a grid-tied pv system. authors in [12] conducted a comparative study between dp and pso for solving unit commitment problems. authors in [13] proposed a mechanism for minimizing the operation cost of a grid-tied system by optimizing the operation schedule of different energy sources in a residential complex energy system. the optimization was based on the invasive weed optimization technique (iwo) and the impact of selling and buying to/from the utility grid was considered. in this paper, storage optimization and cost minimization are based on pso. a grid-connected pv system with battery is presented with a configuration that allows the pv system owner to either sell or buy energy from the grid depending on the system’s output. the paper focuses on sizing the battery energy storage for a typical customer already owning a 5kw pv system in order to reduce daily electricity bills. corresponding author: nibaruta regis engineering, technology & applied science research vol. 9, no. 6, 2019, 4905-4911 4906 www.etasr.com regis et al.: optimal battery sizing of a grid-connected residential photovoltaic system for cost … ii. system modeling and problem formulation mathematical models of various components that are parts of this grid-connected pv system were developed in order to establish an optimal energy flow within the system. this energy flow approach is considered for the modeling process of the system’s components for a time step (δt) of one hour. the function of battery storage in a grid-tied pv system varies according to its configuration. some configurations use the direct charging method by charging the battery with pv panels dc voltage. in this paper, a different topology is set up in which the battery, the pv, the load and the grid are connected to the same ac bus as in figure 1. the battery is connected to the ac bus through an inverter/charge. the pv dc output is also fed to the ac bus via a three-phase dc/ac converter, which is modeled using a 3-level insulated gate bipolar transistor (igbt) bridge. b400_2 is a three-phase v-i measurement block serving as the common ac bus interconnecting the sources and the load. the grid is modeled as an ac source and functions as a swing bus to balance the power demands of the household or absorb pv power. power (positive sequence) block is used to monitor the active power exchange between the grid and pv system and serves for netmetering. an arbitrary household load of 3kw has been assumed in order to show how it is connected to the rest of the system. fig. 1. simulink model of the grid-connected pv system with battery an average hourly pv energy production along with the average hourly load consumption for the considered residence has been calculated and plotted in figure 2. the load energy used for simulation in this paper has a daily average of 12.15kwh whereas the pv energy output has a daily average of 21.443kwh. this means that only 56.6% of pv energy is consumed by the load and the rest must be sold to the grid. fig. 2. average hourly load and pv output throughout 2016 a. component modeling and data acquisition 1) pv array model the performance of the solar panels is highly governed by ambient temperature and solar irradiation. the optimal selection of a pv module with respect to the anticipated functional ambient conditions enhances the module’s performance and therefore increases energy production. for this work, a 5kwp pv array already installed on the top of a garage at strathmore university was considered. fig. 3. montly pv output power throughout 2016 the pv output is modeled as a linear power with respect to solar radiation [9, 13]: �����,�� � � � ��� (1) where � is the solar radiation at time interval �, is the pv panel area and ��� is the pv efficiency. the raw output data of the 5kwp pv array were collected from strathmore university, nairobi, kenya. the collected data were recorded hourly over the whole year of 2016 (figure 3). the module efficiency was taken as 14.91%. 2) battery storage capacity fading is normally estimated through real life experimentation by subjecting the battery to different charge/discharge rates, which can be hard and slow. an alternative way is the mathematical model which was developed based on arrhenius equation in [14]: ����� exp���������� (2) where ����� is capacity loss, is pre-exponential factor, �� is the processed energy, and !are the universal gas constant and temperature. in a practical scenario the battery charge and discharge rates change according to the grid and pv behavior, resulting in an increase of capacity fade with respect to increase in charge/discharge rate, "#� and temperature. the arrhenius equation of battery capacity fading has been adapted to take into account the charge and discharge rates of the battery. the proposed model depends on nominal capacity �%, charge rate �&' , discharge rate �&( , energy processed for charging �) , energy processed for discharging �* , the gas constant, and temperature. engineering, technology & applied science research vol. 9, no. 6, 2019, 4905-4911 4907 www.etasr.com regis et al.: optimal battery sizing of a grid-connected residential photovoltaic system for cost … �����) + exp,−� × �&' × �) × �% × ! ./+ 12 exp��(×345×�6×'7�×� �8 (3) this model has a particular advantage of being able to determine the capacity fade of the battery subjected to different charge-discharge rates. the various parameters of (3) can be found from the capacity loss data given by the battery manufacturers. the battery investment is taken as 200$/kwh [15] and the battery inverter cost has been estimated at 6006$/kw [16]. 3) grid electricity is expected to either be sold to the grid or purchased from it. for simplicity, we assume that the sellingpurchasing prices are equal at instant time � and we denote them as �39:);��,��. consequently, there is an electric power interchange between the utility grid and the pv system denoted by pgrid(t) such that: pgrid(t)<0 when electricity is sold to the utility grid and pgrid(t)>0 when electricity is bought from the grid. the system contains costs and benefits where costs account for the purchase of electricity from the grid and benefits account for selling electricity to the grid. the electric power exchange pgrid(t) in combination with the pv output power ppv(t) have to satisfy the power balance requirements as follow: �<9:*��� + ��������� = ����*��� + �=>���� �<9:*��� = ����*��� − ��������� + �=>���� (4) where �=>���� is the charging/discharging rate of the battery on the ac bus, and ����*��� is the load power. 4) residential load in a residential building, load appliances could have a fixed or a relatively flexible schedule, separating loads categories (lights and tvs from refrigerators and air conditioners). however, the details of load priorities are not analyzed in this work as a residential load profile has been collected from maisy database and adapted to the kenyan context. an hourly load profile for a residential building has been collected and plotted in figure 4. fig. 4. residential montly load profile throughout 2016 b. problem formulation and cost calculation the formulated problem is to minimize the sum of the different costs such as the cost of imported power, the cost of battery degradation, and the annualized inverter cost as expressed in (5): ?�@ a = b∑ ∑ �&'d��,�� + �'&��,��efgh%*gh i + �:j� (5) where �&'d is the cost of battery capacity loss, �'& is the energy cost and benefit, �:j� is the annualized battery inverter cost and �,� are day and time respectively. the pv system is considered as previously installed and its energy is already available to the sample customer. equation (5) emphasizes on the impact of battery capacity loss and electricity sell/purchase to/from grid on the overall running cost. it captures the effect of only the battery dc/ac inverter through �:j� (annualized inverter cost). in order to compare the running costs for grid-tied pv with battery storage and gridtied pv without battery storage, pv investment cost, pv dc/ac inverter cost, installation, and replacement cost are not considered. the reason is that those four variables are common for both cases. table i. input parameters parameter value unit pv capacity 5 kw pv efficiency �3k 14.91 % battery investment cost 200 $/kwh state of charge ("#�l:j,l�m) 30 and 90 % aging coefficient (n) 3 × 10�r n/a nominal charging rate 10 hrs self-discharging factor (s) 0.0000347 n/a pv inverter efficiency �:j� 97 % bat. inverter efficiency �=�f 94 % sampling time interval (tf) 1 hr annual real interest rate (�) 4 % battery charge/discharge eff. �)e/�*:�)e 90 % electricity charges 0.1583 off-peak 0.3560 on-peak $ the cost of the battery capacity fade for a given hour of the system operation is expressed as [6]: �&'d��,�� = &vw�*,f�×&xyz[\]^_`\]h�abcdxy (6) where 2'd��,�� is the battery capacity loss on day � at time �, 2:j�;�f�)��f is the battery investment cost and "#el:j is the battery minimum state of health. the battery has the following dynamic equation [17]: *�4�*,f� *f = �&��,�� (7) where �& is the battery energy and �&��,��>0 during battery charging state, �&��,��<0 during battery discharging state, and �&��,��=0 during battery inactive state. in order to take into account the battery aging effect, a battery usable capacity is considered after each sampling time and denoted as ����. obviously, at initial time �f the usable battery capacity is same as the battery nominal capacity �j. then �� �f� = �j. the above defined usable battery capacity is engineering, technology & applied science research vol. 9, no. 6, 2019, 4905-4911 4908 www.etasr.com regis et al.: optimal battery sizing of a grid-connected residential photovoltaic system for cost … updated at every sampling interval by subtracting a cumulative battery capacity loss �&������,�� from the battery nominal capacity as shown in (8): ���,�� = �j − �&������,�� �&������f� = 0 (8) therefore, the battery capacity loss on day � at time � can be expressed as: 2'd��,�� = �&������,�� − �&������,� − t�� (9) the model of the battery aging is [18]: *'4g`\\�*,f�*f = h −i × �&��,��, �j �&��,�� < 00 l�ℎnop�qn (10) using the conventional efficiency of the battery �& and the sampling interval t�, the above relation becomes: �&������,�� = r�&������,� − t�� �s×34�*,f�×tfu4 �j�2 < 0 �&������,� − t�� l�ℎnop�qn (11) where i is the battery aging coefficient. this expression simply indicates that for the battery-aging model, capacity loss is encountered only in the discharge process. thus, we can see that in (9), 2'd��,�� is equal to zero when the battery is charging. therefore, the calculation of cost of battery capacity loss in (6) entirely depends on the state of the battery, which is either charging or discharging. the battery state of charge is updated after each sampling period as: "#���,�� = "#���,� − t���1 − s�+ �)e 34�*,f�'�*,f�×k t� (12a) "#���,�� = "#���,� − t���1 − s�+ �*:�)e 34�*,f�'�*,f�×kt� (12b) equation (12a) is for battery charging and (12b) for discharging. ���,�� is the usable battery capacity. since the system allows purchasing and selling electricity from and to the utility grid, its operation contains both cots and benefits for the system owner that are combined and denoted together as �'& . costs account for energy bought from and benefits account for energy sold to the utility grid. equation (13) describes the mathematical expression of the cost of the energy exchanged: �'&��,�� = �39:);��,�� × �<9:*��,��t� (13) considering the two different scenarios that result from the reading on the net-meter, the above equation can be extended to account for the net power readings. it can be expressed as: 1 2 ( , ) {[ ( , ) ( , ) [ ( , ) ( , )]} cb price net price net e d t e d t p d t e d t p d t tδ = × + × (14) where �%;fh��,�� > 0 corresponds to the cost of buying power from the grid and �%;fw��,�� < 0 corresponds to expected benefits for selling excess power to the grid. � = b∑ ∑ ��9:);��,�� × �<9:*:l��9fefgh%*gh ��,��i (15) 2 = �∑ ∑ ��9:);��,�� × �<9:*;m��9fefgh%*gh ��,��� (16) where �<9:*:l��9f is the imported power from the grid and �<9:*;m��9f is the power exported to the grid. the capital recovery factor and the annualized battery cost can be calculated by (17) and (18) respectively: 2s��nox �sy��sz n{l|nox as{�lo �� a� = :�h}:�7�h}:�7�h (17) where � is the annual interest rate and ~ is the battery lifetime, and s@@�sz�nn� �s��nox {lq� = 2:j�;�f�)��f × � a (18) for easier calculations it is assumed that the prices for sales and purchases are identical. the system is subjected to a number of operational constraints: �&l:j ≤ �&��,�� 0 ≤ �&��,�� ≤ ���,�� "#�l:j ≤ "#���� ≤ "#�l�m "#e��� ≥ "#el:j (19) the total annual operation cost is therefore calculated as: 365 24 1 1 . .cos ( ( )) bcl cbd t inv an op t c e dt ac = = = + + ∑ ∑ (20) the lifetime of the battery is calculated in (21): battery lifespan �~� = 'y×k'4g`\\^�[�� (21) where �&������;�9 is the annual additive battery capacity loss. iii. particle swarm optimization algorithm particle swarm optimization is used to solve this optimization problem. the algorithm initializes the particles to search the best solution in the entire search space from the objective function [19]. in this study, the swarm is initialized as � = 1:@�ly where @�ly is the swarm size, taken as 30 particles. the particles refer to different random battery sizes from 100 to 3000ah. the number of iterations is set to a maximum of 20 and initialized as � = 1:?s��� where ?s��� is the maximum number of iterations. the inertia maximum and minimum weight is set to 0.9 and 0.2 respectively. the acceleration coefficients are assumed as 2. each particle is set to an initial zero velocity and for every particle (random battery size) the objective function is executed to compare the costs. each particle compares the target value with the best particle’s value, if the target value is lower, sets this value, and records the location of the corresponding particle [20]. velocities and positions are updated after each iteration [21]. each battery capacity has a position and each position has a velocity. the velocity of the �-th is updated by: |�,j;�� = p|�,��*� + {hohb��,�=;�f� − ���i + {wow (22) where |�,j;�� is the new velocity of the k-th particle at the j-th iteration, w is the inertia weight, |�,��*� is the old velocity of the k-th particle at the j-th iteration, {h and {w are the acceleration engineering, technology & applied science research vol. 9, no. 6, 2019, 4905-4911 4909 www.etasr.com regis et al.: optimal battery sizing of a grid-connected residential photovoltaic system for cost … constants, oh and ow are two random numbers in [0, 1]. the position of the the �-th is updated using (23): ��,j;�� ��,��*��h 0 |�,j;�� (23) where ��,lz� �-1 is the old position of the k-th particle at the previous iteration. in this study, the position x is the size and the velocity is the corresponding running cost. the objective function is to minimize the total operating cost f. the personal best of each battery is its size and the resulting operating cost. therefore, for every iteration, there is a corresponding battery size which, when integrated in this grid-connected pv system results in a minimum operating cost which is the global best. fig. 5. flow chart of the proposed pso algorithm iv. results and discussion in this simulation, the optimization algorithm computes the optimized battery size, the corresponding operation cost of the system, the additive battery degradation or capacity loss, and the battery lifespan. these different values are generated and compared with respect to two scenarios: a grid-connected system with and without battery energy storage. in both cases, we have distinguished import and export energies as �<9:* > 0 and �<9:* k 0 respectively. similarly, the battery charged and discharged energies are distinguished as �&�{ v 0 and �&�{ k 0 respectively. this is because the net-metering system needs to calculate the net power. a. grid-connected with battery energy storage in this pso-based optimization, a set of adequate numerical quantities for the pso parameters were chosen to get the algorithm quicker and faster. the population size was set to 30, the maximum number of iterations was set to 20, c1 and c2 were set to 2 and wdamp to 0.99. after initializing the parameters, the pso algorithm was utilized to compute the optimum battery size with respect to cost as depicted in figure 6. the dots represent the fitness values (total cost for a given battery capacity) and each of them represents a potential solution. according to figure 6(a), we can realize that a few points are close to the optimal battery size and could be mistaken as the best solution. this has been avoided by magnifying the bottom part of the figure and narrowing the search space to 1000-1600ah to highlight the final solution or the optimal battery size as 1200ah in figure 6(b). this optimal size is equivalent to 14.4kwh with a corresponding total annual cost or an annual income of 449.42$ to the pv system owner paid by the utility. the negative sign simply indicates that the exported energy to the grid was higher than the imported energy from the grid resulting in a benefit to the system owner. the capital cost of the 14.4kwh battery is calculated as 2880$ at a rate of 200$/kwh. the battery lifespan is calculated by (21) as 13.5 years and the battery recovery factor is found as 0.100143 by (17). the annualized battery cost or real battery capacity loss cost is then estimated as 288.4$ using the expression in (18). fig. 6. optimal battery capacity with respect to cost figure 7 shows the optimal energy flow within the system when a 14.4kwh battery storage is installed. the plots are for one sample day of the year (53 rd ) and we can realize that the load demand entirely depends on the grid during off-peak hours (00:00 to 7:00). pv power starts to be available after 7:00 and the peak production of 4.047kw is recorded at 13:00. the load takes only 0.799376kw out of 4.047kw and the excess 3.2476kw is fed to the grid to make profit. engineering, technology & applied science research vol. 9, no. 6, 2019, 4905-4911 4910 www.etasr.com regis et al.: optimal battery sizing of a grid-connected residential photovoltaic system for cost … fig. 7. optimal energy flow schedule for one day figure 8 illustrates how the energy varies in the battery and how the algorithm handles the constraint of "#� boundaries. according to this figure, battery discharges its energy to the utility grid from 8:00 until its state of charge reaches its minimum. the battery is kept inactive for one hour (13:00 to 14:00) then starts charging from pv until 16:00. the battery releases its energy to the utility grid again until its minimum "#�. from 18:00 to 22:00, the load is mostly relying on the grid and the battery is kept inactive. finally, during off-peak hours (22:00 forwards), the battery charges from the utility grid. we realize that the algorithm only discharges the battery at points where it is advantageous. fig. 8. soc variation of the battery during one regular day in figure 9, it can be seen that during the sampled day the additive battery capacity loss of this grid-connected pv-battery system increases during discharging time due to the aging effect described in (11). the additive battery capacity loss is 0.167318kwh at the start of the day and ends at 0.170278kwh totaling a daily additive battery capacity loss of 0.00296kwh or 2.96wh. the figure shows that the battery degradation increases only during discharge state from 8:00 to 13:00 and from 16:00 to 18:00. figure 10 reflects the convergence of the proposed pso algorithm to find the optimal solution for four independent runs with respect to costs. as depicted in this figure, optimal battery size is reached after about 10 iterations and the optimum solution converges to the same global best for the four runs. if the load demand is increased by 10% for each of the 8760 hours, the results show that the optimal battery capacity remains the same but the battery lifetime decreases by 3.7%. a change of 21% in the annual income is also recorded. if the load is decreased by the same percentage, the same proportions apply in favor of the owner. on the other hand, if the energy consumption is kept constant and the hourly power profile is decreased by 5%, the results show that the optimal battery capacity changes from 1200ah to 1100ah and the annual income of the pv system owner decreases by 24%. fig. 9. additive battery capacity loss during one day fig. 10. convergence of the pso for four independent runs b. grid-connected without battery energy storage if the system has no energy storage, the utility grid acts as both energy storage and energy source. during peak production, the energy surplus is injected to the utility grid. the system starts feeding energy to the grid immediately after the production exceeds load demand. during nights, cloudy days, or power cuts, the utility grid performs as an energy source to cover the load. fig. 11. energy flow for a typical day of the year engineering, technology & applied science research vol. 9, no. 6, 2019, 4905-4911 4911 www.etasr.com regis et al.: optimal battery sizing of a grid-connected residential photovoltaic system for cost … in figure 11, it can be seen that during the hours when the pv was unavailable, the load entirely relied on the grid. pv starts generating from 7:00, however, its energy is not enough to fully supply the load before 9:00. during this period, the grid continues to supply energy. between 9:00 and 17:00, pv energy exceeds the load demand and the excess is injected to the grid. according to the figure, out of 4.047kw of peak production recorded at 13:00, only 0.79937kw were consumed by the load and the excessive 3.2476kw were sold to the grid. from 19:00 and onwards the load is entirely covered by the grid. the optimization algorithm returned an annual benefit of 210.4384$ in favor of the system owner since only annual electricity cost and benefits are the costs involved in this type of configuration. v. conclusion the current paper presented a pso method for optimally sizing the energy storage of a grid-connected residential pv system. while satisfying a set of operation and optimization constraints, the goal was two-fold: to lower the amount of power import from the grid and to minimize the cost of battery degradation caused by the aging effect. the goals were achieved through optimally scheduling the battery operation. simulations were carried out for a system with battery storage and a system without battery storage. the results showed that electricity charges from utility and battery degradation costs highly influence the optimal battery capacity determination in a grid-tied pv system. results demonstrated that upon efficiently and optimally scheduling the battery operation, electricity bills can be significantly minimized. the system without battery returns lower benefits and its entire dependency on the utility grid during nights and cloudy days makes it less desirable. data availability the raw data used to get the results in this paper can be provided upon request. acknowledgment the authors acknowledge the african union (au) for funding this research through the pan african university. references [1] y. ru, j. kleissl, s. martinez, “storage size determination for gridconnected photovoltaic systems”, ieee transactions on sustainable energy, vol. 4, no. 1, pp. 68–81, 2013 [2] d. abdoulaye, z. koalaga, f. zougmore, “grid-connected photovoltaic (pv) systems with batteries storage as solution to electrical grid outages in burkina faso”, 1st international symposium on electrical arc and thermal plasmas in africa, ouagadougou, burkina faso, october 17-21, 2012 [3] y. riffonneau, s. bacha, f. barruel, s. ploix, “optimal power flow management for grid connected pv systems with batteries”, ieee 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anfis-based model to improve dynamic voltage stability”, engineering, technology & applied science research, vol. 9, no. 4, pp. 4384–4388, 2019 microsoft word 4-2994_s1_etasr_v9_n5_pp4596-4599 engineering, technology & applied science research vol. 9, no. 5, 2019, 4596-4599 4596 www.etasr.com bheel et al.: effect of tile powder used as a cementitious material on the mechanical properties … effect of tile powder used as a cementitious material on the mechanical properties of concrete naraindas bheel department of civil engineering mehran uet, sindh, pakistan naraindas04@gmail.com rameez ali abbasi department of civil engineering indus university, karachi, pakistan engr.rameez13@gmail.com samiullah sohu department of civil engineering quest campus, sindh, pakistan sohoosamiullah@gmail.com sohail ahmed abbasi department of civil engineering quest campus, sindh, pakistan engr.sohail63@gmail.com abdul wahab abro department of civil engineering mehran uet, sindh, pakistan ablwab82@gmail.com zubair hussain shaikh department of civil engineering mehran uet, sindh, pakistan azubair.shaikh56@gmail.com abstract—this study was undertaken to reduce the usage of cement in concrete where different proportions of tile powder as cement replacement were used. since in the manufacture of cement an exuberant amount of carbon dioxide is disposed of in the environment, this research aims to curtail the dependence on cement and its production. the objective of this work is to investigate the properties of fresh mix concrete (workability) and hardened concrete (compressive and splitting tensile strength) in concrete with different proportions of 0%, 10%, 20%, 30%, and 40% of tile powder as a cement substitute. in this study, a total of 90 concrete samples were cast with mix proportions of 1:1.5:3, 0.5 water-cement ratio, cured for 7, 14 and 28 days. for determining the compressive strength, cubical samples, with dimensions of 100mm×100mm×100mm, were cast, while for the determination of the splitting tensile strength, cylindrical samples with dimensions of 200mm diameter and 100mm height, were tested after 7, 14, and 28 days. the highest compressive strength of concrete achieved for tile powder concrete was 7.50% at 10% replacement after 28days of curing. the splitting tensile strength got to 10.2% when concrete was replaced with 10% of tile powder and cured for 28 days. it was also shown that with increasing percentage of the tile powder content, the workability of the fresh concrete increases. keywords-tile powder; cement replacement material; strength increase; cement use reduction i. introduction concrete is the most commonly used building material in the world. it consists of two parts: paste and filler. the paste comprises cement and water and sometimes other chemical additives, where the aggregate comprises sand and gravel. the paste ties the aggregates together. aggregates are moderately inert filler constituents which occupy 70% to 80% of the volume of concrete, therefore, it is expected to have effects on its properties [1]. for every ton of cement produced about one ton of carbon dioxide is released into the atmosphere. cement industry production corresponds to about 5% of global anthropogenic emissions of carbon dioxide. cement production is also related to dust, and noise [2, 3]. the necessity for more economical and environmentally friendly cement materials expanded the interest in other materials which can be used as substitutes to partially replace conventional portland cement [4-6]. the cost of natural resources is increasing constantly, leading to the search for alternatives, such as recycled materials, rice husk ash, sawdust ash [7], silica fume, fly ash, coal bottom ash [8], marble powder, millet husk ash, etc. also, ordinary portland cement (opc), is related to several diseases [9-11]. construction industry can be the final consumer of all waste tile powder and, thus, help solve this environmental problem [12, 13]. it is known that about 100 million tons of tiles are produced annually. fifteen to 30% of total production is turned into waste without recycling from the tile industry. tile powder has various advantages such as reduced cost, saving energy and reduced environment risks [14]. tile waste can be used in concrete to increase some of its properties like strength. various studies have been conducted on the use of by-products to increase their effectiveness [15, 16]. authors in [17] experimented on hardening concrete blended with 10%-30% of crushed tiles as replacement of coarse aggregates and 10%30% of granite powder used as fine aggregates. concrete samples were prepared and tested at 7, 14, 21, 28 and 90 days. in testing, it was found that compressive and splitting tensile strength were enhanced to about 8.02% and 41.6% respectively with addition of 20% crushed tile and 30% granite powder in concrete cured for 28 days. authors in [18] studied the hardening of concrete with inclusion of 10% and 20% waste tile powder used as a replacement of coarse aggregates and 10% and 20% of tile powder as replacement of fine aggregates. it was reported that the compressive strength was measured by 14.2% with addition of 10% waste tile powder and 20% of tile powder in concrete after 28 days. authors in [19] investigated hardened concrete with addition of 0%-50% crushed ceramic tile powder as cement substituent material. the compressive strength was measured by 18.3% at 28 days by using 30% of corresponding author: naraindas bheel engineering, technology & applied science research vol. 9, no. 5, 2019, 4596-4599 4597 www.etasr.com bheel et al.: effect of tile powder used as a cementitious material on the mechanical properties … crushed ceramic tile powder in concrete. the tiles were made of natural materials sintered at high temperatures. there were no damaging chemicals in the tiles. waste tiles can only cause pollution [20]. therefore, this study endeavors to use the tile powder produced in pakistan as a material that replaces cement. experimental work was carried out to find the influence of tile powder on the properties of concrete. ii. research methodology the aim of this experimental work was to check the properties of fresh concrete (workability) and the mechanical properties of hardened concrete such as compressive and splitting tensile strength with tile powder utilized as partial cement replacement material, with various percentages, in order to quantify the influences of tile powder in concrete and to know its impact on the mechanical properties of concrete. for this reason, there were two types of specific standards samples (cube, 100mm×100mm×100mm and cylinder 100mm diameter and 200mm height) were made in the structural and concrete laboratory. a total of 90 concrete samples were prepared with mix ratio of 1: 1.5: 3 in which 0.5 water-cement ratio was used and were cured for 7, 14, and 28 days as shown in table i. furthermore, the concrete cube samples were used for compressive strength tests and the cylindrical samples were used for splitting tensile strength tests under the british standard (bs) code. three specimens were cast for each proportion of tile powder and the average value was taken as the final result [6]. table i. concrete samples details samples tile powder percentage 7 days 14 days 28 days cube samples used for compressive strength testing 0% 3 3 3 10% 3 3 3 20% 3 3 3 30% 3 3 3 40% 3 3 3 total 15 15 15 cylindrical samples used for splitting tensile strength testing 0% 3 3 3 10% 3 3 3 20% 3 3 3 30% 3 3 3 40% 3 3 3 total 15 15 15 iii. materials used a. cement locally available opc was used in this experimental work under the brand name “pakland”. tests were conducted on cement as given in table ii. b. fine and coarse aggregates aggregates were obtained from the local market in the region of hyderabad, pakistan. fine aggregates passed from a 4.75mm sieve for removing unwanted materials and the coarse aggregates used in this work had a size of 20mm. various tests of fine and coarse aggregates were conducted in the laboratory for assuring the quality of materials as shown in table iii. table ii. cement tests tests results normal consistency 33% initial setting time 45 min final setting time 220 min table iii. properties of aggregates properties fine aggregates coarse aggregates fineness modulus 2.24 water absorption 1.30% 0.54% specific gravity 2.67 2.63 bulk density 120lb/ft 3 98lb/ft 3 c. tile powder tile waste is generated during the finishing and polishing of tiles in the industry. this waste was collected in the form of pest and after drying, hand crushing, and sieving through #300 sieves it can be used as cement replacement in concrete. d. water drinking water was used for mixing concrete in the laboratory. iv. results and discussion a. workability of fresh concrete the workability of concrete was measured with a slump cone in terms of slump reduction. the maximum slump value recorded was 88mm at 40% of tile powder and the minimum value was 58mm at 0% of tile powder as cement replacement. by carrying out the experimental work, it was shown that the workability of concrete gets proliferated with increasing quantity of tile powder [18, 21] as shown in figure 1. fig. 1. workability (fresh concrete) b. compressive strength of concrete the cubical samples (100mm××100mm) were tested to determine the compressive strength of the concrete’s various proportions of tile powder as cement replacement. at each proportion of tile powder, three concrete samples were cast and the average value was considered. the compressive strength of concrete improved by 7.50% at 10% of tile powder while it was decreased to about 12.60% when 40% of tile powder substituted cement in concrete cured for 28 days. the compressive strength of concrete was reduced at the initial engineering, technology & applied science research vol. 9, no. 5, 2019, 4596-4599 4598 www.etasr.com bheel et al.: effect of tile powder used as a cementitious material on the mechanical properties … stage of the curing period and increased at the final stages of curing period as presented in figure 2. fig. 2. compressive strength of concrete c. splitting tensile strength of concrete the cylindrical samples were used for determining the splitting tensile strength of concrete. at each proportion of tile powder, three concrete samples were cast and the average value was considered. the splitting tensile strength improved up to 10.20% when 10% of tile powder was used and it decreased to 8.0% when using 40% of tile powder as substituent for cement in concrete cured for 28 days. the splitting tensile strength of concrete reduced at the initial stage of the curing period and increased at the final stages of the curing period as displayed in figure 3. fig. 3. split tensile strength of concrete v. conclusions • maximum slump value was recorded as 88mm at 40% of tile powder and minimum slump value was 58mm at 0% of tile powder. it was observed that the workability of fresh concrete increased with the increase in the percentages of tile powder. • the compressive strength of concrete improved by 7.50% with 10% of tile powder and decreased by 12.60% at 40% of tile powder used as a substitute for cement in concrete cured for 28 days. the compressive strength of concrete was reduced at the initial stage of the curing period and increased at the final stages of the curing period. • splitting tensile strength increased to 10.20% at 10% of tile powder and decreased to 8.0% at 40% tile powder used as cement replacement in concrete cured for 28 days. references [1] s. mindess, j. f. young, d. darwin, concrete, prentice hall, 2003 [2] s. ghosal, s. moulik, “use of rice husk ash as partial replacement with cement in concrete-a review”, international journal of engineering research, vol. 4, no. 9, pp. 506-509, 2015 [3] n. d. bheel, s. l. meghwar, s. a. abbasi, l. c. marwari, j. a. mugeri, r. a. abbasi, “effect of rice husk ash and water-cement ratio on strength of concrete”, civil engineering journal, vol. 4, no. 10, pp. 2373-2382, 2018 [4] a. goyal, a. m. anwar, h. kunio, o. hidehiko, “properties of sugarcane bagasse ash and its potential as cement-pozzolana binder”, twelfth international colloquium on structural and geotechnical engineering, ain shams, 2007 [5] n. d. bheel, f. a. memon, s. l. meghwar, i. a. shar, “millet husk ash as environmental friendly material in cement concrete”, 5th international conference on energy, environment and sustainable development, jamshoro, pakistan, 2018 [6] n. d. bheel, s. a. abbasi, s. l. meghwar, f. a. shaikh, “effect of human hair as fibers in cement concrete”, international conference on sustainable development in civil engineering, jamshoro, pakistan, november 23-25, 2017 [7] s. a. mangi, n. jamaluddin, m. h. w. ibrahim, n. mohamad, s. sohu, “utilization of sawdust ash as cement replacement for the concrete production: a review”, engineering science and technology international research journal, vol. 1, no. 3, pp. 11-15, 2017 [8] s. a. mangi, m. h. w. ibrahim, n. jamaluddin, m. f. arshad, f. a. memon, r. p. jaya, s. shahidan, “a review on potential use of coal bottom ash as a supplementary cementing material in sustainable concrete construction”, international journal of integrated engineering, vol. 10, no. 9, pp. 28-36, 2019 [9] v. r. vummaneni, d. s. r. murty, m. a. k. reddy, “study on strength and behavior of conventionally reinforced short concrete columns with cement from industrial wastes under uniaxial bending”, international journal of civil engineering and technology, vol. 7, no. 6, pp. 408417, 2016 [10] n. bheel, s. l. meghwar, s. sohu, a. r. khoso, a. kumar, z. h. shaikh, “experimental study on recycled concrete aggregates with rice husk ash as partial cement replacement”, civil engineering journal, vol. 4, no. 10, pp. 2305-2314, 2018 [11] n. bheel, a. w. abro, i. a. shar, a. a. dayo, s. shaikh, z. h. shaikh, “use of rice husk ash as cementitious material in concrete”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4209-4212, 2019 [12] f. p. torgal, s. jalali, “compressive strength and durability properties of ceramic wastes based concrete”, materials and structures, vol. 44, no. 1, pp. 155-167, 2011 [13] e. fatima, a. jhamb, r. kumar, “ceramic dust as construction material in rigid pavement”, american journal of civil engineering and architecture, vol. 1, no. 5, pp. 112-116, 2013 [14] v. s. n. v. l. ganesh, n. c. rao, e. v. r. rao, “partial replacement of cement with tile powder in m40 grade concrete”, international journal of innovations in engineering research and technology, vol. 5, no. 7, pp. 34–39, 2018 [15] h. dullah, z. a. akasah, n. m. z. n. soh, s. a. mangi, “compatibility improvement method of empty fruit bunch fibre as a replacement material in cement bonded boards: a review”, iop conference series: materials science and engineering, vol. 271, no. 1, article id 012076, 2017 engineering, technology & applied science research vol. 9, no. 5, 2019, 4596-4599 4599 www.etasr.com bheel et al.: effect of tile powder used as a cementitious material on the mechanical properties … [16] i. s. yadav, laboratory investigations of the properties of concrete containing recycled plastic aggregates, msc thesis, thapar university, 2008 [17] m. padma, m. n. rao, “influence of granite powder as partial replacement of fine aggregate and crushed tiles as coarse aggregate in concrete properties”, international journal for modern trends in science and technology, vol. 3, no. 5, pp. 9-14, 2017 [18] c. h. kumar, k. a. ramakrishna, k. s. babu, t. guravaiah, n. naveen, s. jani, “effect of waste ceramic tiles in partial replacement of coarse and fine aggregate of concrete”, international advanced research journal of science, engineering and technology, vol. 2, no. 6, pp. 1316, 2015 [19] s. aswin, v. mohanalakshmi, a. a. rajesh, “effects of ceramic tile powder on properties of concrete and paver block”, global research and development journal for engineering, vol. 3, no. 4, pp. 84–87, 2018 [20] i. b. topcu, m. canbaz, “utilization of crushed tile as aggregate in concrete”, iranian journal of science & technology, transaction b, engineering, vol. 31, no. b5, pp. 561-565, 2007 [21] s. a. mangi, n. jamaluddin, m. h. w. ibrahim, a. h. abdullah, a. s. m. a. awal, s. sohu, n. ali, “utilization of sugarcane bagasse ash in concrete as partial replacement of cement”, iop conference series: materials science and engineering, vol. 271, no. 1, article id 012001, 2017 microsoft word 1-2933_s1 engineering, technology & applied science research vol. 9, no. 5, 2019, 4581-4585 4581 www.etasr.com bousselmi et al.: a novel high-gain quad-band antenna with amc metasurface for satellite … a novel high-gain quad-band antenna with amc metasurface for satellite positioning systems amira bousselmi microwave electronics research laboratory, faculty of sciences of tunis, tunis el manar university, el manar tunis, tunisia bousselmiamira@gmail.com ali gharsallah microwave electronics research laboratory, faculty of sciences of tunis, tunis el manar university, el manar tunis, tunisia ali.gharsallah@fst.utm.tn tan phu vuong imep – lahc, institute of microelectronics electromagnetism and photonics grenoble, france tanphu.vuong@gmail.com abstract—in this paper, a new design single feed multi-band antenna is presented. the proposed antenna is designed to operate at the 1.278ghz, 2.8ghz, 5.7ghz, and 10ghz frequency bands which cover the galileo satellite positioning system (1.278ghz), wlan (2.8ghz), wimax (5.7ghz) and the radar applications (10ghz), respectively. the antenna has a compact size, it is printed on an fr4 substrate of dimensions (60mm×27.5mm×1.67mm) placed on a ground plane of 60mm×17.5mm×0.035mm dimensions. to improve the radiation performance of the proposed antenna, an artificial magnetic conductor (amc) was used as a reflector plane with dimensions of 13.5mm × 13.5mm × 1mm. the simulated and measured results are in good agreement and show the significant improvement of the gain value of the multiband antenna with amc which is a required propriety for novel wireless communications systems. keywords-antenna design; multiband antenna; galileo; amc metasurface i. introduction due to the strong appearance of future generations of mobile communication systems, such as wireless local area network (wlan) and/or worldwide interoperability for microwave access (wimax), low cost, multiband, and compact size antennas are required [1-2]. in recent years, a new system of navigation has been developed by the european union named galileo which is expected to be rolled out in 2020. a high level of quality will be provided as part of the fee-based services offered to professionals, guaranteed global positioning service under civilian control [3-4]. it will be able to exchange with gps and glonass, the two other global satellite navigation systems [5]. for this reason, many techniques have been used recently to design planar multi band antennas [6-9]. in [6], a planar dual band monopole antenna has been proposed, the radiator of the antenna was consisted of a short stem connecting to two branches and generating two frequency bands at around 2.4 and 3.4ghz for wimax applications. in [7], a three band square slot antenna with symmetrical l strips has been discussed. the antenna was able to operate at 2.5, 3.5, and 5.2ghz, which include wlan and wimax. a four-band slot antenna was proposed in [8] using several stubs on the ultra-wideband slot radiator. although the size of the antenna was compact, a low gain of only -6 to -4dbi in the frequency band of 1.5 to 3 ghzwas achieved, which is not required for many practical uses. in this paper a quadband antenna is proposed. the planar antenna consists of two rectangular patches forming an l shape and implemented on an fr4 substrate and covered by ground plan. the size of the ground plan is reduced to generate the two first resonance frequencies. thus, the proposed design covers the galileo (1.278ghz), wlan (2.8ghz) bandwidth [2.793.1], wimax (5.7ghz) bandwidth [5.65-5.75] and radar applications (10ghz). measured and simulated results of the fabricated prototype are showing good agreement. then, in order to further improve the radiation performances of the proposed design, especially the gain, an artificial magnetic conductor (amc) structure acting as reflector plane was employed. the amc has been extensively used in recent decades for its outstanding advantages and its ability to increase the gain, efficiency and to reduce the size of antennas [9-11]. therefore, a significant improvement in the gain value at the four operation bands of the proposed quad band antenna with amc was figured out in both measurement and simulation. ii. quadband antenna without amc meta-surface a. antenna design the designed structure of the quad-band antenna is presented in figure 1 where the top and the bottom views are shown. the antenna is built on a fr-4 substrate with dielectric permittivity εr=4.4, loss tangent δ=0.025 and thickness equal to 1.6mm including the copper thickness of 0.035mm at both sides of the substrate. the size of the ground plane is reduced to obtain the quad-band operation where its dimension is 60mm×17.5mm×0.035mm. besides, two rectangular patch slots forming an l shape are created to generate both two higher resonant frequencies. to verify the proposed antenna design, a prototype is fabricated (figure 2) and measured. table i summarizes all the geometric parameters of the proposed design. b. results of the quad band antenna without amc the antenna was designed using the electromagnetic simulation software cst. a prototype was fabricated and corresponding author: amira bousselmi engineering, technology & applied science research vol. 9, no. 5, 2019, 4581-4585 4582 www.etasr.com bousselmi et al.: a novel high-gain quad-band antenna with amc metasurface for satellite … experimentally tested. the reflection coefficient of the fabricated quad-band antenna measured by a rohde schwarz zva 67 vector network analyzer is compared with the simulation results and shown in figure 3. a good agreement is observed between the results. the proposed design should operate at four frequency bands, 1.278ghz, 2.8ghz, 5.8ghz and 10ghz, whereas the measured ones are 1.3ghz, 2.82ghz, 5.5ghz and 9.5ghz, the small discrepancy obtained at the higher resonance frequency is attributed to the fabrication tolerances provided by the sma connector which are not considered in the simulation. more details about the simulated and the measured return losses results are recapitulated in table ii. (a) (b) (c) fig. 1. the geometry of the proposed quad band antenna: (a) top view, (b) bottom view (c) left side (a) (b) fig. 2. the fabricated prototype of the quad band antenna, (a) top view, (b) bottom view table i. antenna dimensions parameter value (mm) l 60 w 27.5 a 25.5 b 20.6 w a 1.90 w b 1.4 w1 17.5 fig. 3. measured and simulated s11 result of the proposed multiband antenna without amc table ii. measured and simulated return loss of the quad band antenna simulated measured first band (galileo) resonant frequency(ghz) 1.278 2.82 bandwidth (ghz) 0.15 0.15 matching level(db) -13 -23 second band (wlan) resonant frequency(ghz) 2.8 1.3 bandwidth (ghz) 0.31 0.58 matching level(db) -25 -9 third band (wimax) resonant frequency (ghz) 5.7 5.5 bandwidth (ghz) 1 1.2 matching level(db) -20.47 -15 fourth band (radars) resonant frequency (ghz) 10 9.5 bandwidth (ghz) 1.1 2.3 matching level(db) -30.7 -20 figure 4 shows the simulated 3d gain of the antenna without amc given at the four resonance frequencies. it is noted that the gain is about -4.24db in the lower band of 1.278ghz, -0.74db in the second band of 2.8ghz, 1.29db in the third band of 5.7ghz and 2.89db in the upper band of 10ghz. in addition, an omnidirectional radiation pattern is presented at all resonant frequencies. the proposed design achieves a low gain value, especially for the first two resonances, which may not be suitable for many modern communication applications. therefore, a solution to increase the gain value and the radiation performance of the design will be described below. c. parametric effect this section shows a parametric study for the elements of the antenna to understand their operation and the various radiating elements. the first parameter is the second slot width. for the first band, the parameter has no effect on the variation of the frequency. for the other three bands, if we increase the value of the parameter, the resonant frequencies of 2.8ghz, 5.7ghz and 10ghz increase. we find that 0 is the ideal value for optimizing the antenna. engineering, technology & applied science research vol. 9, no. 5, 2019, 4581-4585 4583 www.etasr.com bousselmi et al.: a novel high-gain quad-band antenna with amc metasurface for satellite … (a) (b) (c) (d) fig. 4. simulated gain of the proposed quad band antenna at the resonance frequencies, (a) 1.278ghz, (b) 2.8ghz, (c) 5.7ghz, (d) 10 ghz the second parameter is the width of the vertical slot, the change in this parameter from (0 to 3mm) shows the variation of the reflection coefficient for the proposed antenna. for the first band, the value of the parameter has no effect on the variation of the resonance frequency. for the second band, if we increase the value of b the resonance frequency decreases while keeping the same bandwidth. for the third band, if we increase the value of b then the bandwidth increases. the same stands for the last band with resonance frequency reduction. we find that b=1.5 is the ideal value for optimizing the antenna. the decrease of the length of the second slot reacts on the higher frequencies. iii. quad band antenna with amc metasurface for gain improvement the amc structure can be used as a reflector plane employed to improve radiation performance and antenna gain. indeed, these structures allow obtaining more compact antennas by favoring their directivity. a. design of the quad band antenna with amc generally, an amc is defined on the frequency band in which the phase of the reflection coefficient is given between −90° and 90°, i.e. in the frequency band where the interferences occur between the incident and the reflected wave [12]. this characterization is usually performed by illuminating with a plane wave at normal incidence and for an amc consisting of an infinite number of cells. to reduce the interaction between the amc and the antenna that will be associated with, it is important that the size of the unit cells composing the amc will be smaller than the dimension of the antenna. figure 5 presents the designed and fabricated prototype of the amc unit cell. (a) (b) (c) fig. 5. the proposed amc unit cell, (a) geometric (b) fabricated unit cell, (c) top view of the metasurface plan the amc structure consists of two rings where the inner ring allows the operation of the lower frequency and the outer engineering, technology & applied science research vol. 9, no. 5, 2019, 4581-4585 4584 www.etasr.com bousselmi et al.: a novel high-gain quad-band antenna with amc metasurface for satellite … ring provides the third resonance frequency. the radii of the outer and inner rings are equal to 9.7mm and 1.1mm, respectively. the amc cell is built on the rogers ro4003 substrate. to obtain the operation at the four desired frequency bands, the unit cell is arranged into a 2×4 array to form the amc plane, as shown figure 5(c). the overall quad-band amc structure with dimensions of 108mm×54mm consists of eight unit cells with dimensions 27mm×27mm. this configuration is selected through several parametric studies. the simulated result of the phase reflection of the amc unit cell used as a reference plane allows revealing its operating bands. the frequency bands are marked by the ± 90° variations around the 0° phase values, as shown in figure 6. hence, it can be noted that 0° of phase reflection is obtained at the 1.278, 2.8, 5.7 and 10ghz operating frequencies which correspond with the performances of the proposed quad –band antenna. fig. 6. reflection phase of the proposed amc unit cell b. results of the quad band antenna witht amc figure 7 presents the configuration of the proposed quad band antenna integrated with the amc plane surface. the distance of the spacing g given between the amc place and the antenna is well optimized to avoid the mutual coupling and also to keep the antenna as thin as possible. in practice, a foam substrate is used to separate the amc and the antenna. this configuration aims to improve the gain and efficiency of the antenna without reducing its bandwidth. fig. 7. fabricated multiband antenna placed above the amc plane the s-parameters of the quad band antenna with amc were tested by the vector network analyzer. the measured results of s11 of the antenna with the amc are compared with the obtained results without amc and are exhibited in figure 8. it can be observed that a good agreement is obtained which indicates that the emplacement of the amc surface does not perturb the resonance frequencies of the proposed antenna. fig. 8. measured results of the multiband antenna with and without the amc metasurface the radiation performance of the fabricated antenna with the presence of the amc is measured in an anechoic chamber. figure 9 compares the measured gain and directivity over the frequency of the proposed design in both discussed cases, with and without the amc plane. it is noted that a significant increase in the gain of more than 4db is observed at all the operating frequency bands. at the resonance frequencies 1.278, 2.8, 5.7 and 10ghz, the gain values are increased to 1.12, 4.5, 4.92 and 5.66db respectively. results indicate the expected behavior aimed by the emplacement of the artificial magnetic conductors. fig. 9. measured gain and directivity of the quad band antenna with and without amc metasurface the performances of the proposed quad band antenna and some other reported multi-band antennas [13-15] are compared in table iii. it is evident that the proposed design described in this study is characterized by high gain values which make it suitable for modern communication systems. engineering, technology & applied science research vol. 9, no. 5, 2019, 4581-4585 4585 www.etasr.com bousselmi et al.: a novel high-gain quad-band antenna with amc metasurface for satellite … table iii. comparison of the proposed quad-band antenna with other multi band antennas ref frequencies (ghz) gain (dbi) [13] tri band 2.46 2.33 3.59 3.134 5.69 2.89 [14] four band 1.5 -6 1.8 not reported 2.4 not reported 5.5 2.5 [15] four band 1.57 3.55 2.45 3.93 3.55 5.02 5.2 4.86 proposed 1.278 1.12 2.8 4.5 5.7 4.92 10 5.66 iv. conclusion the main objective of this paper is the design, fabrication and measurement of a new multiband antenna operating in the galileo e6, wlan, wimax and radar application bands. the design was fabricated and tested and the measured results showed a favorable agreement with the simulated ones. an amc metasurface was employed to increase the gain of the antenna by more than 4db at all operating frequencies. the proposed antenna is suitable for satellite positioning systems. references [1] t. y. wu, k. l wong., “on the impedance bandwidth of a planar inverted-f antenna for mobile handsets”, microwave and optical technology letters, vol. 32, no. 4, pp. 249-251, 2002 [2] l. m. mortensen, “growth responses of some greenhouse plants to environment. iii. design and function of a growth chamber prototype”, scientia horticulturae, vol. 16, no. 1, pp. 57-63, 1982 [3] m. c. huynh, w. stutzman, “ground plane effects on planar inverted-f antenna (pifa) 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novel switchable singleand multifrequency triple-slot antenna for 2.4-ghz bluetooth, 3.5-ghz wimax, and 5.8-ghz wlan”, ieee antennas and wireless propagation letters, vol. 9, pp. 534-537, 2010 [15] m. bod, h. r. hassani, m. m. samadi taheri, “compact uwb printed slot antenna with extra bluetooth, gsm, and gps bands ieee antennas and wireless propagation letters, vol. 11, pp. 531-534, 2012 [16] y. f. cao, s. w. cheung, t. i. yuk, “a multi-band slot antenna for gps/wimax/wlan systems”, ieee transactions on antennas and propagation, vol. 63, no. 3, pp. 952-958, 2015 microsoft word 7-3046_s_etasr_v9_n5_pp4612-4615 engineering, technology & applied science research vol. 9, no. 5, 2019, 4612-4615 4612 www.etasr.com tunio et al.: influence of coarse aggregate gradation on the mechnical properties of concrete, part i … influence of coarse aggregate gradation on the mechnical properties of concrete, part i: no-fines concrete zaheer ahmed tunio department of civil engineering quaid-e-awam university of engineering, science & technology, nawabshah, pakistan zaheerahmedtunio@gmail.com fahad-ul-rehman abro department of civil engineering, mehran university of engineering and technology, jamshoro, pakistan fahad.abro@gmail.com tariq ali department of civil engineering quaid-e-awam university of engineering, science & technology, nawabshah, pakistan tariqdehraj@gmail.com abdul salam buller department of civil engineering quaid-e-awam university of engineering, science & technology, larkana campus, pakistan buller.salam@quest.edu.pk muhammad ali abbasi department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan maliengrs@gmail.com abstract—it is an accepted fact that in concrete construction, the self-weight of the structure is a major part of its total load. reduction in the unit weight of the concrete results in many advantages. structural lightweight aggregate concrete (lwac) of adequate strength is now commonly used. in frame structures, the partition walls are free of any loading, where the construction of these non-structural elements with lightweight concrete of low strength would lead to the subsequent reduction of the overall weight of the structure. no-fines concrete is one of the forms of lightweight concrete and it is porous in nature. it can be manufactured similarly as normal concrete but with only coarse aggregates and without the sand. thus, it has only two main ingredients, the coarse aggregates, and the cement. the coarse aggregates are coated with a thin cement paste layer without fine sand. the current paper is a report of a detailed experimental study carried on nfc with fixed cement to aggregate proportion of 1:6 with 0.40 w/c (water-cement) ratio. coarse aggregate of various gradations(7mm-4.75mm, 10mm-4.75mm, 10mm-7mm, 13mm-4.74mm, 10mm-7mm, 13mm-4.75mm, 13mm-10mm, 13mm-7mm, 20mm-4.75mm, 20mm-7mm, 20mm-10mm, 20mm13mm), were used. specimens of standard sizes were cast to determine the compressive and splitting tensile strength after the specimens were cured in water up to the age of testing (28 days). keywords-no-fines; cement to aggregate mix proportion; unit weight; compressive strength; splitting tensile strength i. introduction concrete resulting by removing fine aggregates from normal concrete is termed as no-fines concrete (nfc), which is classified as a type of lightweight porous concrete. gravels known as coarse aggregates are coated with a thin layer of cement paste with no fine particles thus showing a two-phase material system. the coarse material is connected with a pointto-point network system with a small fillet of cement paste, holding particles together and giving strength to concrete [1]. nfc is usually used in parking areas [2], partition walls [3], as a contamination deterrent [4], in parking lots [5], and as brick material [6]. nfc pavements provide storm water management [7, 8] allowing water and air to percolate underground [9, 10]. generally, nfc has aggregate-cement ratios ranging from 6:1 to 10:1. normally nfc has w/c ranging from 0.28 to 0.40 [11]. in [11], it was concluded that the highest strengths were obtained with an aggregate-cement ratio of 7:1 and it has been concluded that when cement-aggregate ratio is increasing the strength properties are decreasing. the tensile and flexural strengths of nfc were significantly lower than those obtained from conventional concrete [12, 13]. the strength of nfc is less than normal concrete’s because of the existence of more voids with in its body [14]. nfc is different from conventional concrete which includes no-fine aggregates in the mixture. the coarse aggregates are combined with low water content with w/c ratio within the range of 0.25 to 0.35 for making nfc mixture with void contents ranging from 11% to 35% which results to high water and air permeability [15-17]. previously, nfc was developed with only one size of coarse aggregate gradation: 20mm-10mm, maintained by appropriate sieves [15]. the current study shows the influence of coarse aggregate gradation on the mechanical properties of nfc with different sizes of gravel. ii. experimental methodology the main aim of this study is to investigate the compressive and splitting tensile strength of no-fines concrete. the cementaggregate (c-a) proportions 1:6 of nfc were adopted. twelve corresponding author: abdul salam buller engineering, technology & applied science research vol. 9, no. 5, 2019, 4612-4615 4613 www.etasr.com tunio et al.: influence of coarse aggregate gradation on the mechnical properties of concrete, part i … different coarse aggregate gradations were used (details in table i). the nfc is cast with 0.4 w/c ratio. ordinary portland cement (opc) as per standard of astm c150 was used to manufacture the nfc and nc and cast the specimens of both concretes. the crushed stones used as coarse aggregates were obtained from the local market. they were washed and air dried and then they were sieved accordingly to achieve the specified aggregate gradations. potable water was used for casting and curing of the specimens. all the ingredients of each mix were batched accordingly following the proper mixing in an electric operated mixer. a total number of 60 cube specimens for nfc of standard size 150mm×150mm×150 mm, and 60 cylinders for nfc of standard size 150mm×300mm were cast. the specimens were demoulded after 24 hours of casting and were kept in a curing tank up to the age of testing. wet curing was applied. all specimens were tested after 28 days of curing. table i. batches details s. no. aggregate gradation (max-min)* (mm) 01 7-4.75 02 10–4.75 03 10–7 04 13–4.75 05 13–7 06 13–10 07 20–4.75 08 20–7 09 20–10 10 20–13 *nfc with gravel varying between max and min in mm. iii. results and discussion a. compressive strength of nfc the cubes were tested to measure the compressive strength of concrete. compressive strength tests were conducted in a universal testing machine (utm). the cubes were placed between the plates of utm and then load was applied gradually until the cubes were crushed. the load at crushing failure was recorded. the load is divided by the cross sectional area of the cube to determine the ultimate compressive stress using (1). the results of the average compressive strength are presented in table ii. ��� = � � (1) b. splitting tensile strength of nfc split cylinder test was carried out to measure the tensile strength of concrete. the cylinders were placed horizontal between two plates in the utm and load was applied gradually on the center of the cylinder until failure. the load at failure was recorded and calculations were made with (2) to determine tensile strength. the results of the average splitting tensile strength are presented in table iii. �� = � �� (2) c. unit weight in the unit weight test, the weight of the specimens was recorded before testing. the results are presented in table iv. from table iv, it is obvious that coarse gradation affects the unit weight of nfc. nfc with coarse aggregate gradation of 7mm-4.75mm had maximum density equal to 2089kg/m 3 , and with coarse aggregate gradation 13mm-10mm had the lowest, which was 1754kg/m 3 . the average unit weight of nfc was found to be 1883kg/m 3 . it may be observed that unit weight of nfc increases with the widening range of coarse aggregates. table ii. average compressive strength of nfc s. no. aggregate gradation (mm) average compressive strength fcu mpa psi 01 7–4.75 7.31 1059.95 02 10–4.75 4.27 619.15 03 10–7 11.12 1612.40 04 13–4.75 7.23 1048.35 05 13–7 6.87 996.15 06 13–10 3.29 477.05 07 20–4.75 4.66 675.70 08 20–7 7.56 1096.20 09 20–10 6.94 1006.30 10 20–13 5.17 749.65 maximum: 10–7 11.12 1612.40 minimum: 13–10 3.29 477.05 table iii. average splitting tensile strength of nfc s. no. aggregate gradation (mm) average tensile strength ft mpa psi 01 (7– 4.75) 0.85 123.25 02 (10–4.75) 1.02 147.90 03 (10–7) 0.92 133.40 04 (13–4.75) 1.23 178.35 05 (13–7) 1.13 163.85 06 (13–10) 0.89 129.05 07 (20–4.75) 1.28 185.60 08 (20–7) 1.26 182.70 09 (20–10) 1.08 156.60 10 (20–13) 1.05 152.25 maximum: 20–4.75 1.28 185.6 minimum: 7-4.75 0.85 123.3 table iv. average unit weight of nfc s. no. aggregate gradation (mm) average unit weight (kg/m 3 ) 01 7–4.75 2089 02 10–4.75 1820 03 10–7 1760 04 13–4.75 2021 05 13–7 1909 06 13–10 1754 07 20–4.75 1760 08 20–7 2009 09 20–10 1852 10 20–13 1852 maximum: 7–4.75 2089 minimum: 13–10 1754 engineering, technology & applied science research vol. 9, no. 5, 2019, 4612-4615 4614 www.etasr.com tunio et al.: influence of coarse aggregate gradation on the mechnical properties of concrete, part i … fig. 1. a cubic specimen before and after testing in utm fig. 2. a cylinder specimen before and after testing in utm fig. 3. compressive strength with various aggregate gradations and 1:6 c-a proportion at 0.4 w/c ratio it has been observed that the aggregate gradation significantly affects the compressive strength of concrete. the maximum compressive strength of nfc is 11.12mpa with 10mm-7mm size of coarse aggregate gradation, whereas the lowest compressive strength of nfc was 3.29mpa with 13mm10mm range of coarse aggregate gradation. the compressive strength of nfc with coarse aggregate gradation of 10mm7mm is increased by 51.12%, 162%, 52.12%, 61.86%, 236.62%, 47.08%, 60.23%, 115.08%, 120% as compared to gradation of 7-4.75, 10-4.75, 13-4.75, 13-7, 13-10, 20-4.75, 207, 20-10, and 20-13 respectively (in mm). it may be concluded that while producing the nfc, the gradation of the coarse aggregates may be considered properly if the compressive strength is a major parameter. like the compressive strength of nfc, its tensile strength is also greatly affected by the gradation of the coarse aggregates used. the maximum split tensile strength of nfc obtained was 1.29mpa with 20mm4.75mm size of coarse aggregate gradation and the minimum was 0.85mpa for the 13mm-10mm coarse aggregate gradation. the split tensile strength of nfc with coarse aggregate gradation of 20mm-4.75mm is increased by 50.58%, 25%, 39.13%, 4.06%, 13.27%, 43.82%, 1.58%, 18.5%, 20.9% for gradation of 7-4.75, 10-4.75, 10-7, 13-4.75, 13-7, 13-10, 20-7, 20-10, and 20-13mm, respectively. fig. 4. splitting tensile strength with various aggregate gradation and 1:6 c-a proportion at 0.4 w/c ratio iv. conclusions different gradations of coarse aggregate were used in nfc, and the effects on unit weight, compressive strength and tensile strength were studied. the results may be summarized as: • the maximum obtained unit weight was 2089kg/m 3 for nfc with aggregate gradation range of 7mm-4.75mm. the minimum obtained unit weight was 1.574kg/m 3 for nfc with aggregate gradation range of 13mm-10mm. the average unit weight was 1882.1882kg/m 3 which is approximately 21% of that of normal weight concrete which is 2400kg/m 3 . • the variation in the compressive strength of nfc due to coarse aggregate gradation ranged from 11.12mpa to 2.93mpa exhibited with n.f.c of coarse aggregate gradations of 10mm-4.75mm and 13mm-10mm respectively. • the tensile strength of n.f.c due to the different coarse aggregate gradations ranges between 0.85mpa-1.28mpa. • the behavior of nfc with various coarse aggregate gradations in terms of compressive strength and tensile strength is different because the compressive strength of nfc with 10mm-7mm coarse aggregate gradation is maximum whereas the tensile strength of nfc with coarse aggregate gradation of 20mm-4.75mm is minimum. engineering, technology & applied science research vol. 9, no. 5, 2019, 4612-4615 4615 www.etasr.com tunio et al.: influence of coarse aggregate gradation on the mechnical properties of concrete, part i … • the behavior of nfc with 7mm-4.75mm, 13mm-4.75mm, and 20mm-7mm coarse aggregate gradations in terms of compressive strength is approximately similar. • the behavior of nfc with 13mm-4.75mm and 20mm-7mm coarse aggregate gradations in terms of tensile strength is approximately similar. • it is observed from the results that coarse aggregate gradation has considerable effects on the compressive and tensile strength of concrete. • the relationship of nfc with various coarse aggregate gradations in terms of compressive strength and split tensile is different as compared to normal concrete. based on the results of this experimental study, it may be concluded that while producing nfc, the gradation of aggregates, c-a ratio and w/c ratio may be chosen appropriately particularly when the compressive strength is the major parameter of consideration. however, to a limited extent, unit weight and apparent texture also depend upon these factors. acknowledgment the authors are grateful to the quaid-e-awam university of engineering, science and technology for providing the research facilities. references [1] b. alam, m. javed, q. ali, n. ahmad, m. ibrahim, “mechanical properties of no-fines bloated slate aggregate concrete for construction application, experimental study”, international journal for computational civil and structural engineering, vol. 3, no. 2, pp. 302312, 2012 [2] r. lomte, “a review on study and analysis of strength, permeability and void ratio of pervious concrete”, international journal for research in applied science & engineering technology, vol. 6, no. 1, pp. 17171720, 2018 [3] a. muneeb, m. a. memon, m. a. bhutto, a. lakho, i. a. halepoto, a. n. memon, “effects of uncrushed aggregate on the mechanical properties of no-fines concrete”, engineering, technology & applied science research, vol. 8, no. 3, pp. 2882-2886, 2018 [4] s. ali, s. kacha, “correlation among properties of no fines concrete–a review”, international journal of advance engineering and research development, pp. 87-91, 2017 [5] g. yuvaraj, k. sundaravadivelu, p. vembuli, r. shankaranarayanan, e. ramya, “a study on compressive strength of pervious concrete by varying the size of aggregate”, international journal of engineering science and computing, vol. 7, no. 4, pp. 10149-10152, 2017 [6] k. b. thombre, a. b. more, s. r. bhagat, “investigation of strength and workability in no-fines concrete”, international journal of engineering and technical research, vol. 5, no. 9, pp. 390-393, 2016 [7] g. divya, l. reena, “an experimental stduies on behaviour of pervious concrete by using addition of admixtures”, international research journal of engineering and technology, vol. 4, no. 3, pp. 2366-2370, 2017 [8] p. p. pragnya, k. b. parikh, a. r. darji, “a review on experimental investigation of pervious concrete using alternate materials”, journal of emerging technologies and innovative research, vol. 4, no. 3, pp. 6870, 2017 [9] c. h. s. priyanka, “experimental analysis on high strength pervious concrete”, international journal of advances in mechanical and civil engineering, vol. 4, no. 2, pp. 9-13, 2017 [10] u. m. muthaiyan, s. thirumalai, “studies on the properties of pervious fly ash–cement concrete as a pavement material”, civil & environmental engineering, vol. 4, no. 1, article id 1318802, 2017 [11] k. r. balsaraf, d. r. kurhade, k. a. varpe, n. s. lohote, d. s. mehetre, “a review paper on no fines concrete”, international journal of engineering sciences & management, vol. 7, no. 1, pp. 293-303, 2017 [12] m. kovac, a. sicakova, “pervious concrete as a sustainable solution for pavements in urban areas”, 10th international conference environmental engineering, vilnius, lithuania, april 27-28, 2017 [13] d. s. shah, j. pitroda, “an experimental study on durability and water absorption properties of pervious concrete”, international journal of research in engineering and technology, vol. 3, no. 3, pp. 439-444, 2014 [14] i. barisic, m. galic, i. n. grubesa, “pervious concrete mix optimization for sustainable pavement solution”, iop conference series: earth and environmental science, vol. 90, article id 012091, 2017 [15] m. nallanathel, b. ramesh, p. h. vardhan, “effect of water cement ratio in pervious concrete”, journal of chemical and pharmaceutical sciences, vol. 6, pp. 200-203, 2017 [16] k. b. thombre, a. b. more, s. r. bhagat, “investigation of strength and workability in no-fines concrete”, international journal of engineering research & technology, vol. 5, no. 9, pp. 390-393, 2016 [17] w. t. kuo, c. c. liu, d. s. su, “use of washed municipal solid waste incinerator bottom ash in pervious concrete”, cement and concrete composites, vol. 37, pp. 328-335, 2013 [18] m. a. alam, s. naz, “experimental study on properties of no-fine concrete”, international journal of informative & futuristic research, vol 2, no. 10, pp. 3687-3694, 2015 microsoft word mousavi-ed.doc etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 461-466 461 www.etasr.com mahdiuon-rad et al.: analysis of pm magnetization field effects on the unbalanced magnetic … analysis of pm magnetization field effects on the unbalanced magnetic forces due to rotor eccentricity in bldc motors s. mahdiuon-rad department of electrical engineering, sahand university of technology, tabriz, iran s_mahdiuonrad@sut.ac.ir s. r. mousavi-aghdam department of electrical & computer engineering university of tabriz, tabriz, iran rmousavi@tabrizu.ac.ir m. reza feyzi department of electrical & computer engineering university of tabriz tabriz, iran feyzi@tabrizu.ac.ir m. b. b. sharifian department of electrical & computer engineering university of tabriz tabriz, iran sharifian@tabrizu.ac.ir abstract—this paper investigates both static and dynamic eccentricities in single phase brushless dc (bldc) motors and analyzes the effect of the pm magnetization field on unbalanced magnetic forces acting on the rotor. three common types of pm magnetization field patterns including radial, parallel and sinusoidal magnetizations are considered. in both static and dynamic eccentricities, harmonic components of the unbalanced magnetic forces on the rotor are extracted and analyzed. based on simulation results, the magnetization fields that produce the lowest and highest unbalanced magnetic forces are determined in rotor eccentricity conditions. keywordsfinite element method; single phase brushless dc (bldc) motor; static and dynamic eccentricity; unbalanced magnetic force i. introduction rotor eccentricity occurs when an unbalanced air gap exists between the stator and the rotor. therefore, an unbalanced magnetic flux density between the rotor and the stator is occurred, which is the main contributor to magnetically induced vibration and noise [1]. rotor eccentricity in a motor can be divided into three categories: static eccentricity, dynamic eccentricity, and their combination [2]. unbalanced magnetic force exists as long as there is eccentricity between the rotor and the stator, because a portion of the stator is closer to the permanent magnet of the rotor, thus generating a net attraction force acting on the rotor [3]. unbalanced magnetic force is also important because it has an exhausting effect on the bearings and also generates noise and vibration. on the other side, when eccentricity becomes large, the resulting unbalanced radial forces can cause stator-torotor rub, and this can result to stator and motor damage [4]. in a surface mounted permanent magnet motor, the permanent magnets act as air gaps (magnetically) between the iron in the stator and rotor. small changes in actual air gap length have a negligible impress on the motor effective air gap. this suggests that surface mounted pm motors may be less sensitive to rotor eccentricities than induction motors, and would be good candidates for applications where noise and vibration are significant [5]. therefore, a detailed study of unbalanced magnetic forces due to rotor eccentricity in such motors would be very useful. it should be noted that in the design of permanent magnet motors for high-precision applications, it is sometimes necessary to have a detailed analysis of the effect of rotor eccentricity [6]. in this paper pm magnetization field effects on the unbalanced magnetic forces due to both static and dynamic eccentricities in single phase bldc motors are analyzed. ii. static and dynamic eccentricity the external rotor permanent magnet motor with rotor eccentricity is schematically shown in figure 1. fig. 1. schematic of the external rotor pm motor with rotor eccentricity. the radial distance between the stator axis (o1) and rotor axis (o2) is defined as the eccentricity of the rotor and is denoted [2] by ge.   etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 461-466 462 www.etasr.com mahdiuon-rad et al.: analysis of pm magnetization field effects on the unbalanced magnetic … where e is the eccentricity ratio and g is the nominal air gap length. the eccentricity ratio has the following limit [2]: 10  e   static eccentricity with which the rotor is displaced from the stator center but is still turning upon its own axis o2 can be modeled by assuming ε and  as constants [2], that the position of the minimal radial air gap length is fixed in space and that there is a steady pull in one direction. this makes the unbalanced magnetic force difficult to be detected unless special equipment is used, which is impractical for motors in service. typical causes of static eccentricity include bearing wear, out of tolerance manufacturing and incorrect positioning of the rotor or the stator at assembly stage. dynamic eccentricity is where the rotor does not rotate on its own axis but does rotate on the stator axis and the center of the rotor is not at the center of rotation so that the point of minimum air gap rotates with rotor speed. this means that dynamic eccentricity is a function of space and time and can be treated by considering ε and  as functions of time and position. in this case the rotor center rotates around the stator center. dynamic eccentricity produces a radial magnetic pull that rotates at the mechanical speed of the motor and acts directly on the rotor. this makes the unbalanced magnetic force easier to detect by vibration or current monitoring [4]. dynamic eccentricity could be caused by a bent shaft, mechanical resonances at critical speeds, bearing wear, out of tolerance manufacturing, using fluid dynamic or aerodynamic bearings and misalignment of bearings. iii. different types of pm magnetization fields the single phase bldc motor geometry considered for simulation is shown in figure 2 [7]. different pm magnetization field patterns can give different air gap field distributions. therefore, the effect of pm magnetization field on the unbalanced magnetic forces due to rotor eccentricity of pm motor is investigated in this paper. for surface mounted permanent magnets, three common types of pm magnetization field patterns including radial, parallel and sinusoidal are considered as shown in figure 3. motor specifications are listed in table i. table i. motor specifications. stator inner diameter 18 mm stator outer diameter 42 mm rotor inner diameter 48 mm coil turns 72 number of pole 4 pm material ferrite rotor outer diameter 60 mm permanent magnet thickness 4 mm hc 200 ka/m br 0.25 t winding type concentrated winding rated speed 6000 rpm fig. 2. single phase bldc motor geometry. fig. 3. (a) radial magnetization (b) parallel magnetization (c) sinusoidal magnetization. iv. static eccentricity analysis and results unbalanced magnetic forces with eccentricity ratios of 0.3, 0.6 and 0.9 which are also known as radial magnetic forces, have been compared for various eccentricities. figure 4 shows the 2-d finite-element model of the single phase bldc motor used for the calculation of the unbalanced magnetic forces. the radial magnetic force on the rotor is calculated using maxwell stress tensor at every 3 degrees of rotor position period and a total number of 120 calculations are needed for the simulation of a complete revolution. radial magnetic forces on the rotor due to different eccentricities for parallel, radial and sinusoidal magnetization are shown in figures 5-7. in the static eccentricity analysis, the radial magnetic force directions are fixed in a complete revolution and magnitudes of these forces fluctuate between maximum and minimum values. it is shown that the average unbalanced magnetic force on the rotor and the force ripple increase with the eccentricity ratio. harmonic components of radial magnetic forces on the rotor for various eccentricity ratios are compared and shown in figure 8. harmonic components of radial magnetic force increase with the eccentricity ratio and 4th, 8th and 12th etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 461-466 463 www.etasr.com mahdiuon-rad et al.: analysis of pm magnetization field effects on the unbalanced magnetic … harmonic components are greater than other components as shown in figure 8. as mentioned earlier, in the case of static eccentricity, the position of the minimal radial air gap length is fixed in space. in other words, the part of the stator which is closer to the magnet is stationary and experiences different magnet polarity np times per revolution. where np is the number of magnet poles. this leads to npi  harmonics where i is a positive integer. fig. 4. 2-d finite-element model of the single phase bldc motor. fig. 5. radial magnetic forces on the rotor for parallel magnetization. fig. 6. radial magnetic forces on the rotor for radial magnetization. fig. 7. radial magnetic forces on the rotor for sinusoidal magnetization. fig. 8. comparison of harmonic components of radial magnetic forces on the rotor for parallel magnetization. the magnitude of the unbalanced magnetic force is known to be proportional to the amount of the eccentricity. therefore, an efficient way of comparing two bldc motors in terms of magnetic force characteristics is to assume the same amount of eccentricity in fem calculation and compare the magnetic force profiles [3]. the average of these forces are calculated for each case in order to compare the effect of eccentricity ratio e and different pm magnetization field patterns on radial magnetic forces simultaneously as shown in figure 9. the radial magnetic force on the rotor can be expressed as [8]:  22 02 1  bbf rr    where rb and b stands for radial and tangential component of magnetic flux density, respectively and 0 is the permeability of the air. from (3) it can be seen that the radial magnetic force is proportional to the square of air gap magnetic flux density. etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 461-466 464 www.etasr.com mahdiuon-rad et al.: analysis of pm magnetization field effects on the unbalanced magnetic … it can be shown that pm generates the highest air gap flux density for radial magnetization and the lowest air gap flux density for sinusoidal magnetization. therefore, radial magnetization gives the highest unbalanced magnetic force and sinusoidal magnetization offers the lowest unbalanced magnetic force on the rotor for all three different eccentricity ratios. fig. 9. comparison of averages of radial magnetic forces on the rotor. v. dynamic εccentricity αnalysis and ρesults in this section, dynamic eccentricity has been analyzed in the motor mentioned in section iii and unbalanced magnetic forces have been compared for various rotor eccentricity conditions with some available ratios of 0.3, 0.6 and 0.9. the calculation method of the radial magnetic force is similar to the one used in the case of static eccentricity explained in section iv. x and y components and also amplitudes of unbalanced magnetic forces on the rotor for parallel magnetization with different eccentricity ratios, are shown in figures 10-12. fig. 10. x components of unbalanced magnetic forces on the rotor due to dynamic eccentricity of rotor for parallel magnetization. fig. 11. y components of unbalanced magnetic forces on the rotor due to dynamic eccentricity of rotor for parallel magnetization. fig. 12. unbalanced magnetic forces on the rotor due to dynamic eccentricity of rotor for parallel magnetization. as shown in figures 10-11, x and y components of unbalanced magnetic forces have negative and positive values in a complete revolution in dynamic eccentricity and this means that these forces revolve with rotor rotation. the magnitudes of the unbalanced magnetic forces on the rotor increase with the eccentricity ratio. harmonic components of the unbalanced magnetic force x component on the rotor with eccentricity ratio of 0.3 are shown in figure 13. as illustrated, it can be seen that in the dynamic eccentricity analysis, in addition to the first harmonic, 3th, 5th, 7th, 9th and 11th harmonic components are greater than other harmonic components. the reason is explained as follows. in the case of dynamic eccentricity, the part of the rotor which is closer to the stator rotates with the rotor. thus, a rotating radial magnetic force is generated and modulated by the slots. this force can be expressed as [9]:     n i iir tilff 0 sin   etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 461-466 465 www.etasr.com mahdiuon-rad et al.: analysis of pm magnetization field effects on the unbalanced magnetic … where i , l and  are the integer, slot number and rotational speed respectively. x and y components of the magnetic force can be expressed as follows: )])1cos(( ))1cos(([ 2 1 )sin()sin( ))1[sin(( 2 1 )(sin)(cos 0 0 0 0 )])1sin((                      itil itilif itiliftf itil i f i til i ff n i n i y i n i n i x til t   where  is the angle between the stator rotation center and the rotor one. the above equations show that dynamic eccentricity leads to first harmonic ( 0i ) and 1il harmonic contents in the unbalanced magnetic force waveform. the harmonic analysis of the unbalanced magnetic force is of great importance to the vibration analysis of the motor because large vibration will be generated when the natural frequencies of the motor coincide with or are close to the frequency of the electromagnetic force or its harmonic frequencies. by comparing figures10 and 11, it can be deduced that the variation of y component of unbalanced magnetic force is similar to the x component variation. therefore, only the x component has been investigated in this paper. on the other side, results obtained for the x component of unbalanced magnetic force can be applied to the y component as well. fig. 13. harmonics of x component of unbalanced magnetic forces on the rotor for parallel magnetization. finally, amplitudes of x components of radial magnetic forces are calculated for each case in order to compare the effect of eccentricity ratio e and different pm magnetization field patterns on radial magnetic forces simultaneously. the results are shown in figure 14. fig. 14. comparison of amplitudes of x component of radial magnetic forces on the rotor. considering (3), radial magnetic force is proportional to the square of air gap magnetic flux density. therefore, with dynamic eccentricity radial magnetization produces the highest unbalanced magnetic force whereas sinusoidal magnetization generates the lowest unbalanced magnetic force on the rotor for all three different eccentricity ratios, as expected and shown in figure 14. vi. conclusion surface mounted pm motors may be less sensitive to rotor eccentricities than induction motors, and would be good candidates for applications where noise and vibration are significant but in the design of permanent magnet motors for high-precision applications, it is necessary to have a detailed analysis of the effect of rotor eccentricity. in this paper, static and dynamic eccentricities with eccentricity ratios of 0.3, 0.6 and 0.9, are analyzed in a single phase bldc motor. it can be seen from the simulation results that unbalanced magnetic forces acting on the rotor increase with the eccentricity ratio. further, in the case of static eccentricity radial magnetic forces consist of harmonics which are multiples of the rotor pole numbers and in the case of dynamic eccentricity consist of the first harmonic and the harmonics which are multiples of slot numbers plus or minus one. it is clearly shown that the radial magnetization generates the highest unbalanced magnetic force and sinusoidal magnetization produces the lowest unbalanced magnetic force acting on the rotor in a bldc motor. references [1] h. s. chen, m. c. tsai ,“effect of rotor eccentricity on electric parameters in a pm brushless motor with parallel winding connections”, journal of applied physics, vol. 105, no. 7, pp. 07f121-07f121-3, 2009 [2] u. kim, d. k. lieu, “magnetic field calculation in permanent magnet motors with rotor eccentricity: without slotting effect”, ieee transactions on magnetics, vol. 34, no. 4, pp. 2243–2252, 1998 etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 461-466 466 www.etasr.com mahdiuon-rad et al.: analysis of pm magnetization field effects on the unbalanced magnetic … [3] t. yoon, “magnetically induced vibration in a permanent-magnet brushless dc motor with symmetric pole-slot configuration”, ieee transactions on magnetics, vol. 41, no. 6, pp. 2173–2179, 2005 [4] s. rajagopalan, j. m. aller, j. a. restrepo, t. g. halbetler, r.g. harley, “analytic-wavelet-ridge-based detection of dynamic eccentricity in brushless direct current bldc motors functioning under dynamic operating conditions”, ieee transactions on industrial electronics, vol. 54, no. 3, pp. 1410-1419, 2007. [5] s. salon, k. sivasubramaniam, l. t. ergene, “the effect of asymmetry on torque in permanent magnet motors”, iemdc 2001, ieee electric machines and drives international conference , cambridge, usa, pp. 208-217, 2001 [6] z. j. liu, j. t. li, m. a. jabbar, “prediction and analysis of magnetic forces in permanent magnet brushless dc motor with rotor eccentricity”, journal of applied physics, vol. 99, no. 8, pp. 08r32108r321-3, 2006 [7] c. l. chiu, y. t. chen, w. s. jhang, “properties of cogging torque, starting torque, and electrical circuits for the single-phase brushless dc motor”, ieee transactions on magnetics, vol. 44, no. 10, pp. 23172323, 2008 [8] k. t. kim, s. m. hwang, g. y. hwang, t. j. kim, w. b. jeong, c. u. kim, “effect of rotor eccentricity on spindle vibration in magnetically symmetric and asymmetric bldc motors”, isie 2001, ieee international symposium on industrial electronics, pusan, south korea, vol. 2, pp. 967–972, 2001 [9] c. i. lee, g. h. jang, “experimental measurement and simulated verification of the unbalanced magnetic force in brushless dc motors”, ieee transactions on magnetics, vol. 44, no. 11, pp. 4377-4380, 2008 authors profile shahin mahdiuon rad received the b.sc. degree in electrical engineering from the university of zanjan, iran, in 2008, and the m.sc. degree, in 2011, in electrical engineering from the university of tabriz, iran. she is currently working toward the ph.d. degree in the faculty of electrical engineering, sahand university of technology. her research interests include control of electrical drives and electrical machines. seyed reza mousavi-aghdam received his b.sc. degree with first class honors in electrical power engineering from azarbaijan university of tarbiat moallem in 2009, tabriz, and m.sc. degree from university of tabriz with honor in 2011. he is currently working toward the ph.d. degree in the university of tabriz. his current research interests include design of electrical machines, electric drives and analysis of special machines. mohammad reza feyzi received his b.sc. and m.sc. in 1975 from the university of tabriz in iran with honors. he worked in the same university from 1975 to 1993. he started his ph.d. work at the university of adelaide, australia in 1993. soon after his graduation, he rejoined the university of tabriz. currently, he is a professor in the same university. his research interests are finite element analysis, design and simulation of electrical machines and transformers. mohammad bagher bannae sharifian studied electrical power engineering at the university of tabriz, tabriz, iran. he received the b.sc. and m.sc. degrees in 1989 and 1992 respectively from the university of tabriz. in 1992 he joined the electrical engineering department of the university of tabriz as a lecturer. he received the ph.d. degree in electrical engineering from the same university in 2000. in 2000 he rejoined the electrical power department of the faculty of electrical and computer engineering of the same university as assistant professor. he is currently professor of the mentioned department. his research interests are in the areas of design, modeling and analysis of electrical machines, transformers, electric drives, liner electric motors, and electric and hybrid electric vehicle drives. microsoft word 37-3465_s1_etasr_v10_n2_pp5547-5553 engineering, technology & applied science research vol. 10, no. 2, 2020, 5547-5553 5547 www.etasr.com alasadi et al.: efficient feature extraction algorithms to develop an arabic speech recognition system efficient feature extraction algorithms to develop an arabic speech recognition system abdulmalik a. alasadi dept. of computer science and it dr. babasaheb ambedkar marathwada university aurangabad, india dba.ora10g@gmail.com theyazn h. h. adhyani community college in abqaiq king faisal university saudi arabia taldhyani@kfu.edu.sa ratnadeep r. deshmukh dept. of computer science and it dr. babasaheb ambedkar marathwada university aurangabad, india rrdeshmukh.csit@bamu.ac.in ahmed h. alahmadi department of computer science taibah university saudi arabia aahmadio@taibahu.edu.sa ali saleh alshebami community college in abqaiq king faisal university saudi arabia aalshebami@kfu.edu.sa abstract—this paper studies three feature extraction methods, mel-frequency cepstral coefficients (mfcc), powernormalized cepstral coefficients (pncc), and modified group delay function (modgdf) for the development of an automated speech recognition system (asr) in arabic. the support vector machine (svm) algorithm processed the obtained features. these feature extraction algorithms extract speech or voice characteristics and process the group delay functionality calculated straight from the voice signal. these algorithms were deployed to extract audio forms from arabic speakers. pncc provided the best recognition results in arabic speech in comparison with the other methods. simulation results showed that pncc and modgdf were more accurate than mfcc in arabic speech recognition. keywords-speech recognition; feature extraction; pncc; modgdf; mfcc; arabic speech recognition i. introduction speech is the most commonly and widely used form of communication. many researches focus on developing reliable systems that can understand and accept commands through speech. nowadays computers are involved in almost every aspect of our life, and as communication between people is mostly vocal, people anticipate the same way of interaction with computers [1]. speech has the capacity to be an important mode of human-computer interaction, and the interest in developing computers that can accept speech as input is growing. the substantial research effort in global speech recognition and the increasing computational power at lower cost could result in more speech recognition applications in the near future [3]. arabic language is the most popular in the arab world, and the arabic alphabet is used in some other languages such as persian, urdu, and malaysian [2]. research in human-computer speech interaction has focused mostly on developing better technical speech recognition systems, and gains in precision and productivity [4]. this research applied three distinct feature extraction methods onto an arabic speech dataset, namely mel-frequency cepstral (mfcc), power-normalized cepstral coefficients (pncc) and modified group delay function (modgdf). the extracted features were classified by a support vector machine (svm). the results of these three feature extracting techniques were compared in order to get the most efficient and accurate output. the feature extraction techniques, having their own properties like modgdf, give additive and high-resolution signal. the additive property adds different functions in one group domain, and high-resolution property is used to sharpen the peaks of a group delay domain [5]. ii. background speech awareness and evaluation have captivated researchers from fletcher's early works [6] and the first voice identification devices [7], to present-day. nevertheless, high precision machine speech recognition can be achieved mostly in quiet settings, as the efficiency of a typical speech recognizer reduces significantly in loud settings [8]. environmental influence and other variables were explored in [9]. as technology progresses, speech recognition will be embedded in more devices used in everyday activities, where environmental variables perform a major part, such as mobile phone voice recognition applications [10], cars [11], integrated access control and information systems [12], emotion identification systems [13], application monitoring [14], disabled assistance [15], and intelligent technology. in addition to voice, many acoustic applications are also essential in diverse engineering issues [16–22]. a noise decrease method could be deployed to enhance efficiency in real-world noisy settings [23–26]. machine efficiency degrades on noise, corresponding author: theyazn h. h. adhyani engineering, technology & applied science research vol. 10, no. 2, 2020, 5547-5553 5548 www.etasr.com alasadi et al.: efficient feature extraction algorithms to develop an arabic speech recognition system channel variance, and spontaneous expressions further below than humans [27]. automatic speech recognition (asr) has not surpassed human efficiency in precision and robustness but we continue to avail from it by knowing the central values behind the identification of human speech (hs) [28]. despite the advancements in auditory processing and popular frontends for asr devices, only a few elements of noise handling in the auditory periphery are modeled and simulated [29]. for instance, common methods such as mfcc use auditory features like varying bandwidth filter bank and compression size. coefficients of perceptual linear prediction (plp) focus on perceptual processing by using curves of critical band resolution, corresponding loudness scaling, and cube root energy laws of listening linear prediction coefficients (lpc) [30]. synaptic adjustment could include an instance of auditory-motivated enhancements of voice depiction. standard mfcc or plp coefficients could be substituted by coefficients depending on some cochlear model in order to better represent human auditory periphery. the proposed model of synaptic adaptation in [31] showed important improvements in the efficiency of speech recognition. the pncc proposed in [32], was based on auditory processing, including new characteristics, using a nonlinearity of power-law, a noisesuppression algorithm relying on asymmetric filtering, and temporal masking. the experimental findings exhibited enhanced precision of acceptance, comparing to mfcc and plp. another strategy for feature removal was based on deep neural networks (dnn). the noise robustness of sound designs relying on dnn was evaluated in [33]. recurrent neural networks (rnn) for cleaning distorted input characteristics were applied in [34]. the use of lstm-rnns was suggested in [35] to manage extremely non-stationary additive noise. for solid voice recognition, an all-inclusive outline of profound teaching was presented in [36]. many researches utilized pncc and mfcc to extract the most significant features from speech signals [37-39]. group delay function (modgdf) was used to extract speech signals, being more efficient than mfcc. iii. method figure 1, shows the developed recognition system for evaluating the identification of arabic speech. fig. 1. proposed speech recognition system audio from arabic speakers was given as input to the system, and three feature extraction techniques, mfcc, pncc and modgdf, were applied to extract significant features of arabic speech. svm algorithm was used for training and classification, and performance measures were employed to evaluate these algorithms. iv. database a speech database was created, populated with utterances from volunteered yemeni students studying at dr. babasaheb ambedkar marathwada university, in aurangabad, india. tables i and ii, include the demographic information of the volunteers and the basic parameters of the recordings. table i. demographics of volunteers parameter values speaker type students (bsc, msc, phd) gender 35 male, 15 female basic language arabic accent standard and yemeni age group 20 35 country yemen environment dept. of cs & it table ii. basic recording parameters parameter value sampling rate 16000hz speakers dependent condition of noise normal accent arabic pre–emphasis 1-0.9/(z-1) window type hamming, 25ms window step size 20ms a. recording procedure the database was recorded using high quality headsets (sennheiser pc360) and praat software, in a quiet environment. speech samples were recorded in mono mode with 16000hz sampling rate. a microphone was placed at a distance of about 3cm from the volunteer’s mouth. table iii, displays the hardware and software used during the speech samples recording procedure. table iii. hardware and software details hardware software laptop hp elite book: (core i7 ,5th gen, 8gb ram, ssd 500gb) windows 10 headphone :sennheiser pc360 praat: 6102_win64 microphone b. isolated digits table iv shows the recorded arabic digits. c. isolated words isolated arabic words of the speech corpus were used. table v shows the arabic words related to learning. d. continuous sentences table vi shows the continuous sentence text corpus. five utterances were collected for each sentence. engineering, technology & applied science research vol. 10, no. 2, 2020, 5547-5553 5549 www.etasr.com alasadi et al.: efficient feature extraction algorithms to develop an arabic speech recognition system table iv. arabic digits digit pronunciation arabic writing 0 safer صفر 1 wahed َواِحد 2 ethnan اِْثنَان 3 thlathah ثَةzََث 4 arbaah أَْربََعة 5 khamsah َخْمَسة 6 settah ِستَّة 7 sabaah َسْبَعة 8 thamaneyah ثََمانِيَة 9 tesaah تِْسَعة table v. arabic words arabic word arabic pronunciation english word jameaah university جامعة koleyah collage كلية kesm department قسم taaleem education تعليم mauhader lecture محاضر modares teacher مدرس maamal lab معمل madah course مادة table vi. arabic sentences related to greetings english language arabic language when does registrations begin at the university? متى يبدأ التسجيل في الجامعة ؟ is there a graduate department? للدراسات العليا ؟ھل يوجد قسم what are the admission requirements? ما ھي شروط القبول ؟ is there a university website? ھل يوجد موقع الكتروني للجامعة؟ what are the available majors? ما ھي التخصصات المتوفرة ؟ the university has modern programs. حديثةالجامعة لديھا برامج the mission of the university is ambitious. رسالة الجامعة طموحة v. feature extraction algorithms feature extraction is vital for developing a speech recognition system. its main objective is to extract the most significant features for identifying arabic speakers. three feature extraction algorithms were applied: pncc, modgdf, and mfcc. a. power normalized cepstral cofficients (pncc) the pncc feature extraction algorithm for extracting features for speech recognition can be seen in [3]. pncc has two components: initial processing, and temporal integration for environmental analysis. 1) initial processing this processing uses a pre-emphasis filter in the form of: ����� 1�0.97��1 (1) subsequently, a short-time fourier transformation (stft) is conducted using hamming windows. the use of a dft volume of 1024 was intended to produce a length of 25.6ms, with 10ms between frames. by weighting magnitudesquared stft outputs, spectral power in 40 analysis bands was obtained for positive frequencies. center frequencies are also linearly spaced between 200hz and 8000hz using gamma tone filters in equivalent rectangular bandwidth (erb) [3]. 2) temporal integration for environmental analysis most speech recognition systems use length frames of analysis between 20 and 30ms. it is often found that longer analytical windows deliver greater noise modeling efficiency and environmental normalization [6], because of the facility related to most background conditions, and changes slower than the speaking-related instant power. in pncc processing, an estimate is made of a quantity referred to as “medium-time power” q[m,l] by calculating the running average of p[m, l], the power observed in a single frame of analysis, according to: '1 2 1 [ , ] [ ] m m m m m m q m l p m l + + = − = ∑ (2) where m is the index of the frame, and l is the index of the channel. b. modified group delay function (modgdf) this method was discussed in detail in [7-15]. it should be noted that the group delay feature is different from the phase spectrum, and it is defined as the phase negative derivative which can be used effectively to extract different system parameters when the signal is considered as a minimum phase signal. this is mainly so because a minimum phase signal’s magnitude spectrum is similar to each other and its group delay feature. figure 2, shows the process of modgdf algorithm for extracting speech features. the algorithm is described below. algorithm: modgdf feature extraction pseudocode input: speech x(n) output: modgdf (features vector) c(n) begin initialize parameters; apply the dft of the speech x (n) as x[k]; apply the dft of the speech n x (n) as y[k]; calculate group delay function where r and i represents real and imaginary parts; compute the spectrally smoothed spectra of x [k] and designate it as s [k]; compute modified group delay where s [k] is the smoothed version of x [k] and two new parameters α and γ are used to regulate the dynamic range of modgdf; apply the dct to get the modgd features; obtain modgd features vector (13 coefficients for each frame); end. fig. 2. feature extraction process of modgdf c. mel frequency cepstral coefficients (mfcc) mfcc is the mostly used method in speech technology development, as it is similar to the human auditory system [16], taking into account its characteristics. moreover, these engineering, technology & applied science research vol. 10, no. 2, 2020, 5547-5553 5550 www.etasr.com alasadi et al.: efficient feature extraction algorithms to develop an arabic speech recognition system coefficients are robust and reliable to variations of speakers and recording conditions. figure 3 shows the processing steps of mfcc for feature extraction. fig. 3. processes in mfcc feature extraction method pre-emphasis is the first step of mfcc, which produces energy, that was earlier compressed during sound generation, at a high frequency. framing uses narrower parts to trim the sound signals. windowing is used to avert discontinuity of the signals produced by the framing method. fast fourier transform (fft) is used for adapting a signal from time to frequency domain. filter bank is the overlapping band pass filter. the final process is the discrete cosine transform (dct) making the coefficients of mfcc [18]. mfcc is computed from speech signal using the following three steps: • compute the fft power spectrum of the speech signal • apply a mel-space filter-bank to the power spectrum to get energies • compute dct of log filter-bank energies to get uncorrelated mfcc’s the speech signal is first divided into time frames comprising of a random number of samples. in most systems, overlapping of frames is used to smooth transition from frame to frame. each time frame is then windowed with a hamming window to eliminate discontinuities at the edges [17]. the filter coefficients w(n) of a hamming window of length n are computed according to: �� � � 0.54�0.46cos��������, 0 � � ��1 �� � � 0, otherwise. (2) where n is the total number of samples, and n is the current sample. mel scale links perceived frequency or pitch of a pure tone to its actual measured frequency. humans discern better small changes in pitch at lower frequencies. integrating this scale makes the features match more closely to what humans hear. the formula for converting from frequency to mel scale is: �!� � 1125ln�1% & '(( � (3) while the formula to go back from mel’s scale to frequency is: ���)� � 700�exp� -���.��1� (4) vi. classification svm is principally a binary classifier, but with the following two approaches it can be extended to multi-class tasks, the first being 1-vs-all i.e. comparing each class to the rest and the second, 1-vs-1, i.e. each class to the other, separately [20]. in this study, the i-vs-all was used, consisting of multiple binary svms equal to the number of classes. every svm with each one of the classes against the rest of them is taught and taken into consideration when testing. the decision is eventually made based on the distance from all svms between the test data and the hyper planes. vii. simulation results several experiments were conducted, employing the speech database, for classification and recognition using mfcc, pncc and modgdf for feature extraction. training procedure used 60% of the data, while 40% were used for testing. the test procedure was implemented in matlab 2016, and screen shots are shown in figures 4 and 5. evaluation and testing was performed using accuracy rate, specificity, sensitivity, precision, and execution time. fig. 4. layout of the main system fig. 5. implementation a. analysis for arabic digits the feature extraction methods were applied on the digit samples, and the results are shown in table vii. table vii. svm results on digits feature extraction technique accuracy rate specificity sensitivity precision execution time (s) modgdf 90.3 94.5 50.5 72.7 16.39 pncc 97.5 98.6 87.6 88.7 54.8 mfcc 88.3 93.5 41.7 53.7 87.5 engineering, technology & applied science research vol. 10, no. 2, 2020, 5547-5553 5551 www.etasr.com alasadi et al.: efficient feature extraction algorithms to develop an arabic speech recognition system figure 6 illustrates the methods’ performance. as it can be observed, modgdf with svn obtained better results regarding time cost. pncc and mfcc with svn obtained good results, but their execution time was much higher. it is concluded that modgdf had lower time cost, as it reduced execution time complexity. table viii, shows the confusion matrix of pncc for the recognition of arabic digits. figure 7, displays a sample of modgdf with svm for the recognition of an arabic digit (“khamsah”). fig. 6. methods' performance on the recognition of arabic digits fig. 7. modgdf sample recognizing the arabic digit “khamsah” table viii. confusion matrix of digits usin g pncc/svm 19 0 0 0 0 0 0 0 0 0 0 19 0 0 0 0 0 0 0 0 0 2 17 0 0 0 0 0 0 0 1 0 1 17 0 0 0 0 0 0 0 1 0 0 18 0 0 0 0 0 0 1 1 0 0 17 0 0 0 0 0 0 0 2 0 1 16 0 0 0 2 0 1 1 0 1 1 13 0 0 1 0 0 3 0 1 0 1 13 0 0 0 0 1 0 0 1 0 0 17 b. analysis for arabic words table ix shows the results on the recognition of arabic words. the results of modgdf with svm are reported to be not satisfactory, but time cost is much lesser than the other feature extraction methods. pncc with svm performed better, but time cost turned out to be significantly more. the results are also shown in figure 8. table x shows the confusion matrix of pncc/svm for the recognition of arabic words. the confusion matrix has attested that pncc is more robust and demonstrates more strength to identify arabic words. figure 9 illustrates the performance of the pncc on the recognition of an arabic word (“dirham”). table ix. results on words feature extraction technique accuracy rate specificity sensitivity precision execution time (s) modgdf 89.3 94.1 46.8 58.6 12.3 pncc 95.15 97.3 75.8 79.2 49.5 mfcc 88.6 93.6 43.1 51.8 99.5 fig. 8. performance on the recognition of arabic words fig. 9. sample of pncc with the svm recognizing the arabic word “dirham” table x. confusion matrix of words usin g pncc/svm 19 0 0 0 0 0 0 0 0 0 2 17 0 0 0 0 0 0 0 0 2 2 15 0 0 0 0 0 0 0 2 1 1 15 0 0 0 0 0 0 2 0 3 2 12 0 0 0 0 0 1 1 2 2 0 13 0 0 0 0 1 3 1 0 0 0 14 0 0 0 0 0 0 1 2 0 0 16 0 0 0 1 1 1 0 0 0 0 16 0 2 0 0 0 0 0 2 2 1 12 c. analysis for arabic sentences table xi shows the performance results on the recognition of arabic sentences. as it can be observed, pncc with svm engineering, technology & applied science research vol. 10, no. 2, 2020, 5547-5553 5552 www.etasr.com alasadi et al.: efficient feature extraction algorithms to develop an arabic speech recognition system performed better, but had greater execution time. pncc had again the highest accuracy and lower execution time than mfcc. modgdf had the lowest execution time of 12.3s, and accuracy of 88.2, while mfcc showed again the lowest accuracy. the accuracy of pncc/svm can be also confirmed by its confusion matrix analysis of sentences in table xii. the confusion matrix shows that the pncc/svm is capable of recognizing sentences with satisfactory results. the results are also shown in figure 10, while figure 11 illustrates the performance of pncc on the recognition of an arabic sentence (“what are the available majors?”). table xi. results on sentences feature extraction technique accuracy rate specificity sensitivity precision execution time (s) modgdf 88.2 93.5 41.2 45.3 18.9 pncc 93.05 96.14 65.26 71.04 70.0 mfcc 86.0 92.2 30.0 49.48 125.0 fig. 10. feature extraction performance on arabic sentences fig. 11. sample of pncc/svm recognizing the arabic sentence “what are the available majors?” table xii. confusion matrix of sentences using pncc/svm 19 0 0 0 0 0 0 0 0 0 2 17 0 0 0 0 0 0 0 0 1 7 11 0 0 0 0 0 0 0 0 0 1 18 0 0 0 0 0 0 1 0 0 8 10 0 0 0 0 0 0 0 0 0 3 16 0 0 0 0 0 0 0 0 0 7 12 0 0 0 0 0 0 1 0 0 1 17 0 0 0 0 0 0 0 0 0 9 10 0 6 0 0 0 0 0 0 0 3 10 viii. conclusion in this paper, a speech recognition system for arabic language was presented, evaluating three feature extraction algorithms, namely mfcc, pncc, and modgdf, while an svm was used for the classification process. results showed that pncc was more efficient, while modgdf had moderate accuracy. pncc and modgdf fill the gaps in svm, as they both had greater accuracy than mfcc. pncc had a 93-97% accuracy rate, modgdf had 90% and mfcc had 88%. references [1] p. p. shrishrimal, r. r. deshmukh, v. b. waghmare, “indian language speech database: a review”, international journal of computer applications, vol. 47, no. 5, pp. 17-21, 2012 [2] s. k. gaikwad, b. w. gawali, p. yannawar, “a review on speech recognition technique”, international journal of computer applications, vol. 10, no. 3, pp. 16-24, 2010 [3] c. huang, t. chen, e. chang, “accent issues in large vocabulary continuous speech recognition”, international journal of speech technology, vol. 7, no. 2-3, pp. 141-153, 2004 [4] m. a. anasuya, s. k. katti, “speech 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cepstral coefficients based supervectors and i-vectors for small vocabulary speech recognition”, 2014 international joint conference on neural networks, beijing, china, july 6-11, 2014 [35] e. loweimi, s. m. ahadi, “a new group delay-based feature for robust speech recognition”, 2011 ieee international conference on multimedia and expo, barcelona, spain, july 11-15, 2011 [36] b. kurian, k. t. shanavaz, n. g. kurup, “pncc based speech enhancement and its performance evaluation using snr loss”, 2017 international conference on networks & advances in computational technologies, thiruvanthapuram, india, july 20-22, 2017 [37] t. fux, d. jouvet, “evaluation of pncc and extended spectral subtraction methods for robust speech recognition”, 23rd european signal processing conference, nice, france, august 31 – september 4, 2015 [38] a. kaur, a. singh, “power-normalized cepstral coefficients (pncc) for punjabi automatic speech recognition using phone based modelling in htk”, 2nd international conference on applied and theoretical computing and communication technology, bangalore, india, july 2123, 2016 [39] c. kim, r. m. stern, “feature extraction for robust speec recognition based on mmximizing the sharpness of the power distribution and on power flooring”, 2010 ieee international conference on acoustics, speech and signal processing, dallas, usa, march 14-19, 2010 [40] d. s. kim, s. y. lee, r. m. kil, “auditory processing of speech signals for robust speech recognition in real-world noisy environments”, ieee transactions on speech and audio processing, vol. 7, no. 1, pp. 55-69, 1999 microsoft word ismael-ed.doc etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 467-472 467 www.etasr.com mekhamer et al.: design practices in harmonic analysis studies applied to industrial electrical … design practices in harmonic analysis studies applied to industrial electrical power systems s. f. mekhamer faculty of engineering, ain shams university cairo, egypt saidfouadmekhamer@yahoo.com a. y. abdelaziz faculty of engineering, ain shams university cairo, egypt almoatazabdelaziz@hotmail.com s. m. ismael electrical engineering division, enppi cairo, egypt shriefmohsen@enppi.com abstract—power system harmonics may cause several problems, such as malfunctions of electrical equipment, premature equipment failures and plant shutdowns. accordingly, mitigation of these harmonics is considered an important target especially for industrial applications where any short downtime period may lead to great economic losses. harmonic analysis studies are necessary to analyze the current and voltage harmonic levels and check if these levels comply with the contractual or international standard limits. if the studies reveal that the preset limits are exceeded, then a suitable harmonic mitigation technique should be installed. harmonic analysis studies in the industrial electrical systems are discussed in many references. however, a comprehensive procedure for the steps required to perform a harmonic study is rarely found in the literature even though it is strongly needed for design engineers. this paper provides a comprehensive procedure for the steps required to perform a harmonic study in the form of a flowchart, based on industrial research and experience. hence, this paper may be considered as a helpful guide for design engineers and consultants of the industrial sector. keywords-harmonic analysis study; distortion; point of common coupling (pcc); variable frequency drive (vfd); resonance i. introduction due to the dramatic increase in the usage of nonlinear loads in industrial applications (mainly regarding variable frequency drives or vfds), the power system harmonics problems has gain in significance, representing a big obstacle against the wide application of vfds although they enhance system efficiency and provide great energy saving. the power system harmonics cause many harmful effects including:  overheating of generators, motors, transformers, and power cables that lead to early equipment failures  failure of capacitor banks  nuisance tripping to protection relays  interference to communication systems and sensitive electronic devices accordingly, the mitigation of the power system harmonics is of great importance in industrial electrical systems in order to increase system reliability, enhance operation economics, avoid unwanted equipment failure and process downtimes [1]. nowadays, industrial electrical systems contain a valuable amount of nonlinear loads. accordingly, power system studies for industrial plants should contain harmonic analysis studies beside short circuit, load flow and motor starting studies. the harmonic analysis studies for the industrial systems are discussed in [2], but the author did not focus on the guidelines of the harmonic study. also the authors did not introduce the various international standards that set the limits of the harmonic distortions. the goals of this paper can be summarized as follow: 1. to highlight the purpose of a harmonic analysis study 2. to highlight some guidelines for harmonic analysis studies 3. to provide a comprehensive description of the procedure required to perform a harmonic study 4. to introduce the international standards limits for the harmonic distortions ii. purpose of a harmonic analysis study nowadays, the applications of the nonlinear loads in the industrial plants grow rapidly and the percentage of these loads may be in the range of 30% to 50% of the total plant load. accordingly, the effects of harmonics within the electrical system and their impact on the electric utility and neighboring plants should be examined to avoid equipment damage and plant shutdowns. the following cases may necessitate performing a harmonic study [3]: 1. during the design stage of a project, if the amount of the nonlinear loads exceeds 25% of the total loads on a bus or a system, a harmonic analysis study is required to check the compliance with the contractual/ international harmonic limits 2. to solve harmonic-related problems such as failure of electrical equipment or malfunction of protective relays 3. if an existing plant is going to be expanded and a significant amount of nonlinear loads is going to be added, then a harmonic analysis study is required to verify the plant performance after the addition of these loads etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 467-472 468 www.etasr.com mekhamer et al.: design practices in harmonic analysis studies applied to industrial electrical … 4. if a capacitor bank is installed in any electrical networks that contain many nonlinear loads, then a harmonic analysis is required to check the possibility of resonance occurrence iii. guidelines for harmonic analysis studies a. harmonic sources all nonlinear loads are defined also as harmonic sources, as clearly shown in figure 1, because they draw non-sinusoidal currents when a sinusoidal voltage is applied. the nonlinear load acts as a source of harmonic currents in power system, thus causing voltage distortions at the various system buses due to the harmonic voltage drops across the system impedances. fig. 1. effect of a nonlinear load on the current waveform to perform a harmonic study, the design engineer must identify the available harmonic sources and the harmonic currents generated by these harmonic sources. there are three options available for the design engineer to determine the harmonic currents, as described below: a. to measure the generated harmonics from each harmonic source (time-consuming option, applicable only in case of existing plants) b. to calculate the generated harmonic currents by using suitable mathematical analysis (may require extensive manual and time-consuming calculations) c. to use typical values based on computerized softwares libraries or based on the available data from the nonlinear load's manufacturer practically, options (a) and (c) are the most used options and provide reasonable results. the following are the main sources of harmonics in industrial applications [4]: 1) saturable magnetic equipment: there are various saturable magnetic equipment that cause harmonic problems such as: a. rotating machines, rotating machines like induction motors may act as sources of the third harmonic currents when they are operating in abnormal or overloaded conditions. b. ballasts of discharge lamps, the discharge lamps like mercury vapor, high-pressure sodium and fluorescent lamps are dominant sources of the third harmonic currents. c. transformer harmonics, transformers create harmonics when they are overexcited. in addition, the transformer inrush currents may contain some even harmonics, but the duration is rather limited. d. generator harmonics, voltage harmonics are created from the synchronous generators due to the non-sinusoidal distribution of the flux in the air gap. selection of suitable coil-span factor (called also pitch factor) can significantly reduce the voltage harmonics from the generators. 2) power electronic devices: there are various power electronic devices that cause harmonic problems such as: a. variable frequency drives (vfds) used in fans and pumps b. switched mode power supplies (smps), used in instruments and personal computers c. high voltage dc transmission stations (hvdc) d. static var compensators e. uninterruptable power supply systems (ups) f. battery charger systems g. flexible ac transmission systems (facts) h. ac and dc arc furnaces in steel manufacturing plants b. resonance the inductive reactance increases as the frequency increases as follow: lfxl ...2    where: xl: inductive reactance f : system frequency l : inductance while the capacitive reactance decreases as the frequency increases as follows: )...2 cf(/ 1xc    where: xc: capacitive reactance c : capacitance due to the opposite characteristics of the inductive and capacitive reactances, there must be a frequency at which xl equals xc. this condition of equal and opposite reactances is called “resonance”. most of the power system elements are inductive. accordingly, the presence of shunt capacitors used etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 467-472 469 www.etasr.com mekhamer et al.: design practices in harmonic analysis studies applied to industrial electrical … for power factor correction or harmonic filtering can increase the probability of resonance occurrence. there are two types of resonance, the series resonance and the parallel resonance. the harmful effect of the series resonance may be the flow of excessive harmonic currents through the network elements. these excessive currents cause nuisance tripping to the protection relays, overheating of cables, motors, and transformers and premature failure to the electrical equipment. the harmful effect of the parallel resonance may be the presence of excessive harmonic voltages across the network elements. these excessive harmonic voltages cause dielectric breakdown of the electrical equipment’s insulation [3]. 1) series resonance: the series resonance occurs when an inductor and a capacitor are connected in series and they resonate together at a certain resonance frequency. an example of the series resonant circuit is shown in fig. 2. this ac circuit is said to be in resonance when the inductive reactance xl is equal to the capacitive reactance xc. fig. 2. ac circuit representing an example for the series resonance 2) parallel resonance: the parallel resonance occurs when an inductor and a capacitor are connected in parallel and they resonate together at a certain resonance frequency. there are many forms of parallel resonant circuits. a typical parallel resonant circuit is shown in figure 3. this circuit is said to be in parallel resonance when xl=xc similar to the series resonance. fig. 3. ac circuit representing an example for the parallel resonance c. tools of performing a harmonic analysis study: the harmonic analysis study can be performed by any of the following tools: a. manual calculations, which are limited to small-size networks since they are very complicated and susceptible to errors. b. field measurements, which are often used as a verification of the design, or as a preliminary diagnosis of a field problem. c. digital computer simulations, which nowadays are the most convenient and economical method for analyzing system harmonics d. power system modeling: at the presence of harmonics, the electrical system elements models must be updated to encounter for the presence of higher frequencies in the system rather than the power frequency (50 hz or 60 hz). details for electrical system elements models under harmonics distortions can be found in [3]. e. types of analyses performed during the harmonic analysis: there are two main types of analyses that could be performed during harmonic analysis [2]: a. current and voltage distortion analysis, in which the individual and total current and voltage harmonic distortions are calculated at the various buses then the results are compared with the relevant contractual limits. b. impedance versus frequency analysis, in which a plot of the system impedance at various buses is plotted against the frequency. this analysis is important in predicting the system resonances prior to energizing the electrical system. a peak in the impedance plot indicates a parallel resonance while a valley in the impedance plot indicates a series resonance. iv. steps of performing a harmonic analysis study if a harmonic analysis study is required to be performed due to any of the cases described in section (ii), the following steps should be followed: a. obtain the electrical system one-line diagram and highlight the available nonlinear loads, capacitor banks and medium voltage cables of long length within the industrial system. b. highlight the point of common coupling (pcc) which is the point that connects the industrial network with the utility or with the neighboring plant. c. highlight the in-plant system buses that are expected to be affected from harmonic distortions. d. gather the harmonics-related data of all nonlinear loads within the plant. e. obtain, from the utility company, the relevant data of current and voltage harmonics at the contractual pcc including the minimum and maximum short circuit fault levels and the permissible limits on voltage and current harmonics because the allowable harmonic limits vary from country to country. f. model the electrical network using any of the commercially available softwares such as the electrical transient analyzer program (etap). g. perform the harmonic analysis for the electrical network at the various possible operating scenarios. h. check the individual and total voltage and current distortion levels at the interested system buses and at the pcc. etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 467-472 470 www.etasr.com mekhamer et al.: design practices in harmonic analysis studies applied to industrial electrical … i. check the harmonic frequency spectrum, which is a plot of each individual harmonic value with respect to the fundamental value versus frequency. j. if the harmonic distortion results exceed the allowable limits, select an appropriate harmonic mitigation solution and the optimum insertion point for that solution. further details about this point are introduced in section (v). k. re-perform the harmonic analysis study after adding the harmonic mitigation technique to ensure compliance with the contractual / international harmonic limits. an extensive literature review over the past twenty years leads to the fact that there is no single article that summarizes the steps required to perform a harmonic analysis study even though the importance of this procedure for the design engineers. the comprehensive flowchart presented in figure 4 provides this novel helpful approach. v. selection of the harmonic filter's insertion point even if the design engineer selects the optimum harmonic mitigation technique for his plant, among the available harmonic mitigation solutions in the market [5], then the filter insertion point should be studied carefully as it greatly affects system performance [6]. as shown in figure 5, the possible filter insertion points can be classified into three categories as follow: a. local harmonic mitigation in this mode of mitigation, the shunt type (passive or active) harmonic filter is directly connected to the nonlinear load terminals. this mode is efficient if the number of nonlinear loads is limited and the power of each nonlinear load is significant compared to the total plant power. circulation of harmonic currents in the electrical network is avoided, thus the harmonic impact on the upstream network elements is minimized. b. semi-global harmonic mitigation in this mode of mitigation, the shunt type (passive or active) harmonic filter is connected to the input of the lv subdistribution switchboard. accordingly, the filter treats several sets of nonlinear loads. this type of compensation is ideal in presence of multiple nonlinear loads each having low rated power. a practical example of this mode is found in commercial buildings where a harmonic filter may be found on each floor of the building. c. global harmonic mitigation this mode of mitigation is more concerned with meeting the contractual harmonic limits at the (pcc) than the reduction of the in-plant harmonics. the major drawback of this mitigation mode is that the harmonic currents are allowed to circulate in the electrical network. thus, the various electrical elements within the plant will be subjected to harmful harmonic impact. vi. international harmonic standards the purpose of imposing strict limits on the harmonics emissions is to ensure that the current and voltage distortions at the pcc are kept sufficiently low. thus, the other customers connected at the same point are not disturbed. the international standards related to harmonic distortion limits can be classified as follows: a. standards specifying limits for individual nonlinear equipment  iec 61000-3-2 [7], which specifies the current harmonic limits for low voltage equipment that has an input current less than 16 a.  iec 61000-3-12 [8], which specifies the current harmonic limits for an equipment that has an input current between 16a and 75a  iec 61800-3 [9],which specifies the electro-magnetic compatibility (emc) requirements of the adjustable speed drive systems as noticed, the above standards are for small rating and low voltage harmonic loads only. in addition, the above standards do not set limits on the overall distribution network. b. standards specifying limits for electrical networks  ieee 519-1992 [10], this document introduces many useful recommended practices for harmonics control in electrical networks. this document is widely used in the industrial sector and many consultants/clients use the limits indicated in it as contractual limits within their specifications.  iec 61000-3-6 [11], this specification performs an assessment of the harmonic emission limits for distorting loads in medium voltage and high voltage power systems. up till now, this specification is not widely used in the industrial sector because it is rather new (punlished in 2008).  british engineering recommendation g5/4-1 [12], this document provides some helpful engineering recommendations for establishing the allowable harmonic limits of the voltage distortions in the united kingdom. vii. ieee 519-1992 harmonic limits a. harmonic current distortion limits harmonic current distortion limits are introduced in the ieee 519-1992. a summary of these current harmonic limits is shown in table i. setting limits for the current harmonic levels protects the utility company and the other utility consumers connected on the same feeder. where: isc : maximum short circuit current at pcc i1 or il: maximum demand load current (fundamental frequency component) at pcc etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 467-472 471 www.etasr.com mekhamer et al.: design practices in harmonic analysis studies applied to industrial electrical …   yes no no new plant existing plant harmonic analysis is not required end existing or new plant 1. gather all the required data about the existing harmonic sources. 2. make a survey about the harmonic related .problems within the plant 3. define the pcc. 4. perform site harmonic measurements at the pcc and at the system buses that contain the major nonlinear loads. 1. define the harmonic sources within the plant. 2. define the ratio of the nonlinear loads with respect to the total plant loads as follow: ratio = nonlinear loads (kva) / total plant loads (kva ratio of nonlinear loads with respect to the total plant loads ≥ 25% harmonic analysis is required. perform the following steps: 1. obtain the electrical system one-line diagram and highlight the available nonlinear loads, capacitor banks and long medium voltage cables within the industrial system. 2. highlight the point of common coupling (pcc). 3. highlight the in-plant system buses (or switchgears) that are foreseen to be affected from harmonic distortions. 4. gather the required equipment data, ratings and the harmonics related data of all the plant nonlinear loads. 5. obtain, from the utility company, the relevant data of current and voltage harmonics at the contractual pcc including the minimum and maximum short circuit fault levels and the permissible limits on voltage and current harmonics. 6. model the electrical network using any of the commercially available softwares such as the electrical transient analyzer program (etap). 7. perform the harmonic analysis for the electrical network at the various possible operating scenarios. 8. check the individual and total voltage and current distortion levels at the interested system buses and the pcc to ensure compliance with the contractual / international harmonic limits. voltage and current harmonic levels exceed the allowable c 1. evaluate the results of the harmonic study then select the optimum technical and economic harmonic mitigation technique. 2. select the optimum insertion point for the selected harmonic mitigation technique. 3. for a new plant, implement the selected harmonic mitigation technique in the network model then re-perform the harmonic analysis study. 4. for an existing plant, model electrical network of the plant after adding the selected harmonic mitigation technique then perform the harmonic analysis study. end c start yes fig. 4. a comprehensive procedure for the steps required to perform a harmonic analysis etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 467-472 472 www.etasr.com mekhamer et al.: design practices in harmonic analysis studies applied to industrial electrical … fig. 5. various insertion points for the harmonic filters it should be noted that all the power generation equipment are limited to these values of current distortion, regardless of the actual isc/i1 ratio. the ratio isc/il is the ratio of the short circuit current available at the (pcc) to the maximum fundamental load current. it is recommended that the load current (il) be calculated over any (15) or (30) min period and then averaged over the next (12) month period. table i. harmonic current distortion limits for general distribution systems (system voltages: from 120v to 69 kv) odd harmonic order h (%) individual current harmonic distortion (%) isc / i1 h < 11 11 ≤ h < 17 17 ≤ h < 23 23 ≤ h <35 h ≥ 35 total harmonic distortion thdi % < 20 * 4 2 1.5 0.6 0.3 5 20-50 7 3.5 2.5 1 0.5 8 50100 10 4.5 4 1.5 0.7 12 1001000 12 5.5 5 2 1 15 >1000 15 7 6 2.5 1.4 20 b. harmonic voltage distortion limits: the ieee 519-1992 defines the allowable voltage harmonic limits at the pcc. table ii summarizes the limits for the low voltage systems and table iii summarizes the limits for the medium and high voltage systems. where:  special systems: critical applications like hospitals and airports  dedicated systems: systems that contain only nonlinear loads it is important to highlight that the limits listed in table iii should be used as system design values for normal operation conditions (lasting more than one hour). for shorter operation periods, during start-ups or unusual transient conditions, these harmonic limits may be allowed to exceed by 50%. table ii. harmonic voltage distortion limits for low voltage distribution systems (system voltages: below 1 kv) allowable voltage thd special systems general distribution systems dedicated systems voltage thd (%) 3% 5% 10% table iii. harmonic voltage distortion limits for medium and high voltage distribution systems bus voltage individual voltage harmonic distortion (%) total voltage harmonic distortion (%) 69 kv and below 3 % 5 % from 69 kv to 161 kv 1.5 % 2.5 % 161 kv and above 1 % 1.5 % viii. conclusions harmonic analysis studies are necessary to analyze the current and voltage harmonic levels within any industrial electrical system and to check if these levels comply with the contractual or international standard limits. this paper provides a comprehensive approach for performing a harmonic study, presented in the form of a flowchart. in addition, this paper presents the current and voltage harmonic limits used in industrial systems. references [1] m. z. el-sadek, power system harmonics, 2nd edition, mukhtar press, egypt, 2007 [2] r. g. ellis, “harmonic analysis of industrial power systems”, ieee transactions on industry applications, vol. 32, no. 2, pp. 417-421, 1996 [3] ieee std 399-1997, recommended practice for industrial and commercial power systems analysis, ansi/ieee, 1997 [4] j. p. nelson, “a better understanding of harmonics distortions in the petrochemical industry”, ieee transactions on industry applications, vol. 40, no. 1, pp. 220-231, 2004 [5] s. f. mekhamer, a. y. abdelaziz, s. m. ismael, “technical comparison of harmonic mitigation techniques for industrial electrical power systems”, mepcon 2012, fifteenth international middle east power systems conference, paper id: 214, alexandria, egypt, 2012 [6] e. bettega, j. n. fiorina, cahier technique no. 183: active harmonic conditioners and unity power factor rectifiers, schneider electric, 1st edition, 1999 [7] iec std 61000-3-2, electromagnetic compatibility (emc)-part 3-2: limits for harmonic current emissions (equipment input current ≤16 a per phase, iec, 2009 [8] iec std 61000-3-12, electromagnetic compatibility (emc)-part 3-12: limits for harmonic currents produced by equipment connected to public low-voltage systems with input current >16 a and ≤ 75 a per phase, iec, 2011 [9] iec std 61800-3, adjustable speed electrical power drive systems-part 3: emc requirements and specific test methods, iec, 2004 [10] ieee std 519, recommended practice and requirements for harmonics control in electrical power systems, ansi/ ieee, 1992 [11] iec std 61000-3-6, electromagnetic compatibility (emc)-part 3-6: assessment of emission limits for the connection of distorting installations to mv, hv and ehv power systems, iec, 2008 [12] british engineering recommendation, planning levels for harmonic voltage distortion and the connection of nonlinear equipment to transmission systems and distribution networks in the united kingdom, g5/4-1, 2001 microsoft word 28-2658_s engineering, technology & applied science research vol. 9, no. 2, 2019, 4019-4026 4019 www.etasr.com nguyen et al.: green scenarios for power generation in vietnam by 2030 green scenarios for power generation in vietnam by 2030 vu h. m. nguyen faculty of electrical and electronics engineering ho chi minh city university of technology and education ho chi minh city, vietnam vunhm.ncs@hcmute.edu.vn cuong v. vo faculty of electrical and electronic engineering ho chi minh city university of technology and education ho chi minh city, vietnam cuongvv@hcmute.edu.vn luan d. l. nguyen department of urban engineering ho chi minh city university of architecture ho chi minh city, vietnam luan.nguyenleduy@uah.edu.vn binh t. t. phan faculty of electrical and electronics engineering ho chi minh city university of technology ho chi minh city, vietnam thanhbinh055@yahoo.com abstract—energy for future sustainable economic development is considered one crucial issue in vietnam. this article aims to investigate green scenarios for power generation in vietnam by 2030. four scenarios named as business as usual (bau), low green (lg), high green (hg) and crisis have been proposed for power generation in vietnam with projection to 2030. three key factors have been selected for these scenarios, namely: (1) future fuel prices, (2) reduction of load demand caused by the penetration of led technology and rooftop photovoltaic (pv) systems, and (3) the introduction of power generation from renewable sources. the least costly structure of power generation system has been found. co2 emission reduction of hg in comparison to the bau scenario and its effect on generation cost reduction are computed. results show that bau is the worst scenario in terms of co2 emissions because of the higher proportion of power generation from coal and fossil fuels. lg and hg scenarios show their positive impacts both on co2 emissions and cost reduction. hg is defined as the greenest scenario by its maximum potential on co2 emission reduction (~146.92mt co2) in 2030. additionally, selling mitigated co2 can make green scenarios more competitive to bau and crisis in terms of cost. two ranges of generation cost (4.3-5.5 and 6.07.7us$cent/kwh) have been calculated and released in correspondence with low and high fuel price scenarios in the future. using led lamps and increasing the installed capacity of rooftop pvs may help reduce electric load demand. along with the high contribution of renewable sources will make the hg scenario become more attractive both in environmental and economic aspects when the crisis scenario comes. generation costs of all scenarios shall become cheap enough for promoting economic development in vietnam by 2030. keywords-green; scenario; least cost; optimum power generation; vietnam i. introduction energy for sustainable development is one of the most crucial issues globally. in long-term energy planning, there are many uncertainty factors. in order to address the issue, green energy scenarios of iea, bp, and china have been built which are projected to 20-30 years ahead [1-3]. electricity usualy takes a high part of about 25% to 45% of total energy consumption. finding the optimum structure for a power system in a competitive market with many constraints of transmission lines, the rules of the market constitute a multiresearched topic [4-8]. vietnam has been considered as one of the most dynamic emerging countries with approximately 7% of annual gross domestic products (gdp) increase in the last 20 years. that development has led to up to 15% increase of the yearly nationwide electricity power demand [9]. it is currently a big issue of vietnam, relevant to the lack of primary fuels supplies. another obstacle for power generation in vietnam to meet the mentioned rapid economic development is environmental pollution [10]. summarizing, supplying electricity power to meet the development of the economy is one of the most urgent issues of vietnam. vietnam electricity corporation (evn) is a state-owned enterprise which is responsible for the whole country. evn is required to cooperate with other relevant energy institutes and departments to prepare and release multiscale development plans for the national power system, where the periodic master plan which projects the development plan for the next 15 to 20 years ahead is expected as the most important outcome. the most recent relevant release is decision no 428/qd-ttg on march 18 th 2016 [9]. three development scenarios for vietnam power system by 2030 have been proposed, namely base, high ratio of renewable energy, and high load demand scenarios. however, numerous dubiousness regarding historical input data, mathematical functions, and results of load demand forecasting have been identified from those three scenarios. that vagueness made forecasting results of [9]. not verifiable. the shifts in power consumption awareness and generation sources have created three new corresponding author: cuong v. vo engineering, technology & applied science research vol. 9, no. 2, 2019, 4019-4026 4020 www.etasr.com nguyen et al.: green scenarios for power generation in vietnam by 2030 factors which have a strong and direct effect on the power system: (1) the rapid growth of led lamp technology, (2) the withdrawing of nuclear power from the national electric power structure (since june 2016), and (3) the release of decision no. 11/qd-tags on april 14 th 2017 [11]. the above factors made the scenario in [9] become inappropriate. new scenarios with updated forecasting objectives by 2030 must be studied and introduced to fulfill [9]. the purpose of this paper is to propose two state-of-the-art concepts of green power generation scenarios for vietnam power system by 2030. new concepts are strongly based on: the uncertainty of future fuel price, the penetration of led technology and the increasing installed capacity of rooftop pv systems, and the difference in proportion of renewable energy exploited in vietnam power system. a least cost objective function and its constraints in correspondence with each scenario will be established. a software named lindo (linear, interactive, and discrete optimizer) is employed to figure the optimum structure of vietnam power generation system with projection to 2030. the scope of the study is the power generation system in vietnam only. the system is not yet capable to be put into a whole power system with constraints of trasmission lines and rules of a competitive maket. ii. method the scenarios are proposed based on uncertainty factors which have strong effects on sources (input) and load demands (output) of the power system. an objective function in terms of least cost and its constraints is employed to figure the optimum structure of vietnam power generation system. a. power generation scenarios three variable key factors have been selected for creating power generation scenarios: future fuel price, reduction of load demand caused by the penetration of led technology and rooftop pv systems, and the introduction of power generation from renewable sources. table i presents two scenarios of vietnam’s fuel price by 2030. proposals for the price of two common fuels used for power generation in vietnam (coal and gas) are computed. indicators show that there are big differences between the low and high scenarios. two models computed by the two prestigious institutes have approximately a difference of 100% [11, 12]. table i. fuel scenarios fuel price scenario 2020 2025 2030 coal ($/ton) high [12] 93.5 98.3 103.3 low [11] 41.8 44.4 48.2 gas ($/mbtu) high [12] 9.2 10.9 11.6 low [11] 4.9 5.5 5.7 since the price of led lamps has been dramatically reduced, they are considered as the best choice for replacing conventional lamps in existing and new constructions. the strong penetration of led lamps will lead to significant reduction of power load demand. assumptions of lighting load share and led penetration by 2030 are presented in table ii. decision no 11/qd-ttg [11] promoted the installation wave of residential rooftop pv systems in the south regions of vietnam. taking effect since june 1 st 2017, it was the first cornerstone of vietnam’s regulatory framework to encourage the development of solar energy utilization, which has been considered as one of the most effective ways to reduce the load demand. assumptions of the rooftop pv systems are shown in table iii. electric load demand scenarios resulted by the penetration of led lamp technology are shown in table iv. the high values are forecasted, while the low values are reduced by the penetration of led technology from 1.2% to 6.2% and 1.5% to 8.2%, respectively. table ii. assumptions of lighting load and led year 2020 2025 2030 lighting consumption (%) [9] 23 21 19 capacity factor of lighting 0.75 total lighting pmax (%) [9] 30.7 28.0 25.3 penetration of led (%) 10 30 65 energy reduction by led (%) 50 table iii. assumptions of rooftop pv systems year residential consumption [9] (%) penetration of rooftop pvs (%) low high 2020 34.75 2 2 2025 31.36 10 15 2030 28.63 20 30 table iv. assumptions of lighting load and led year demand (twh) pmax (gw) high [13] low reduction (%) high [14] low reduction (%) 2020 230.20 227.55 1.2 40.33 39.71 1.5 2025 349.95 338.93 3.2 60.84 58.28 4.2 2030 511.27 479.70 6.2 87.56 80.35 8.2 considering the combination of the development of rooftop pv systems and the penetration of leds, an option of deeply low load demand is proposed. a concept of cumulative reduction is presented in table v. it is noted that the rooftop pvs will take to the reduction of twh only while pmax is not affected because pmax normally occurs at evening (at around 7:00 pm). table v. cummulative electric load demand reduction by led and rooftop pv systems year demand low (twh) reduction (%) deeply low (twh) reduction (%) 2020 225.97 1.8 225.97 1.8 2025 328.30 6.2 322.98 7.7 2030 452.23 11.5 438.50 14.2 table vi indicates the maximum gwh and mw of power generation from renewable sources by 2030 [9]. however, the decision no. 2068/qd-ttg, issued on november 25 th 2015 [15] stipulated another option in which the values of exploitable renewable sources are much higher than the ones presented in table vi (see table vii). it is noted that high values of biomass are assumed to be reach up to 70% of that in [15] only. when combining those above factors, various scenarios are generated. four difference scenarios are proposed engineering, technology & applied science research vol. 9, no. 2, 2019, 4019-4026 4021 www.etasr.com nguyen et al.: green scenarios for power generation in vietnam by 2030 and shown in table viii: (1) business as usual (bau) is similar to what happened during the last 5 years in case of low fuel price, high load demand, and low sharing of renewable energy generation, (2) low green (lg) represents the case of low fuel price, low load demand, and high sharing of renewable energy, (3) high green (hg) is generated to perform the conditions of high fuel price, deeply low load demand, and high renewable energy, and (4) crisis scenario is the case of high fuel price, low load demand and low renewable energy. table vi. scenarios of low renewable energy [9] generation unit 2020 2025 2030 mini hydro twh 11.1 12.4 17.7 gw 3.8 5.2 6.8 biomass low twh 2.7 4.8 12.6 gw 0.5 0.9 2.4 wind low twh 2.1 4.0 12.0 gw 0.8 2.0 6.0 solar low twh 8.8 12.8 18.9 gw 6.1 8.0 12.0 table vii. scenarios of high renewable energy [15] generation unit 2020 2025 2030 biomass high (70% of [8]) twh 8.0 19.2 36.0 gw 1.5 3.6 6.9 wind high twh 2.7 6.0 15.4 gw 1.0 3.0 7.7 solar high twh 8.8 23.8 34.3 gw 6.1 15.0 21.8 table viii. proposed scenarios scenario fuel price load demand renewable energy bau low high low lg low low high hg high deeply low high crisis high low low vietnam’s economy has been performing well during the last 30 years. this boosts the electric load demand and therefore sustainable development solutions for energy supply must be considered. however, vietnam’s elasticity of electricity demand has still remained at a high value of more than 1.7 [9] due to the ineffective implementation of energy efficiency policies and frameworks, while the exploitation of renewable energy has been neglected. hence, energy scenarios have to be built comprehensively with aim to promote the exploitation of renewable energy and to reduce the electric load demand. these are the essential conditions to reform a green economy for vietnam. when the price of fuel increases, then the load demand must be reduced and renewable energy must be considered more seriously. this is a great opportunity for developing renewable energy in vietnam. b. objective function the objective function of the optimal structure for generation is the function where the power generation cost is minimized in 2020, 2025, and 2030. , , , , , , , . . min= →∑ y g y g q t y g q t y o w ce x (1) where g represents the type of generation (hydro, coal, gas, mini-hydro, biomass, wind, photovoltaic, import), q is the load pattern identified by number 1 to 8 (see table ix), t is the time of a day (from 1:00 to 24:00), y is the considered year (2020, 2025, 2030), ceg,y is the generation cost of power plant g at year y, xg,q,t,y is the least-cost generation power of power plant g, corresponding to the load pattern q at time t of the year y, and wy is the net present value coefficient, calculated by (2): 2014 1 1 ε − +  =  +  y y r w (2) where r is the interest rate, estimated at 8% per year, and ε is the inflation rate, estimated at 4% per year. the generation cost ceg,y [us$/kwh] of the power plant g at year y is calculated by: ( ), , , , , + + = ∑ g y g y g y g y g y f a mo ce q (3) where fg,y is the fuel price, ag,y is the yearly investment depreciation, mog,y, is the operation and maintenance cost, and qg,y is the power production of power plant g at year y [kwh]. the annual investment depreciation ag,y [us$/year] is calculated by: ( ) ( ) 0 0 3 , , , 0 . 1 10 1 1 + = × × × + − n g y g y g yn r r a i c r (4) where r0 is the oda interest rate, estimated at 3.8%/year, n is the lifetime of the power plant g, [year], ig,y is the investment cost per unit of a power plant g at year y, [us$/kw], and cg,y is the installed capacity of the power plant g at year y , [mw]. c. constraints the constraints of the suggested objective function are: load demand, upper limit of generation power, reserve power capacity, variable limitation of generation power between two consecutive hours, and capacity factor. 1) load demand in order to meet load demand, it is required for the total generation power to be equal with the load power demand: , , , , , =∑ g q t y q t y g x p (5) where pq,t,y is the load power demand for pattern q at the time t of year y. 2) maximum generation power the generation power of power plant g, corresponding to the load pattern q at time t of the year y must be lower than the maximum generation power of that power plant: max., , , , , ,qg q t y g q t y x x≤ (6) where tmax,q is the time that the power plant g operates at maximum power, corresponding to the load pattern q. engineering, technology & applied science research vol. 9, no. 2, 2019, 4019-4026 4022 www.etasr.com nguyen et al.: green scenarios for power generation in vietnam by 2030 the generation power at the time tmax,q for the load pattern q must be lower than the total installed capacity of the power plant g in the year y: max., , , ,qg q t y g y x c≤ (7) the power production of a power plant g in the year y must be lower than the upper capacity limit of that power plant: , max. ,g y g y q q≤ (8) where qmax,g,y is the maximum generation power of the power plant g in the year y. 3) maximum installed capacity the maximum installed capacity of power generations is decided by the upper limitation of input primary energies which can be exploited, and the funding sources which can be used for constructing new power facilities in certain years. the installed capacity of a power plant g in the year y must be lower than the maximum installed capacity of that plant at the same time: , max. ,g y g y c c≤ (9) 4) reserve power capacity to assure the reliability of the power system, the total installed capacity of generation facilities in the year y must be higher than the maximum demand power including reserve power: ( ), max.1 .α≤ +∑ g y y yc p (10) where pmax,y is the maximum power demand in year y, αy is the reserve limitation in the year y. reserve power capacity is closely related to the loss of load expectation (lole) which is chosen as an indicator of power system reliability in this study. values of αy do not include the installed capacity of renewable energy sources, i.e. biomass, wind, and solar generation. 5) capacity factor in each pattern of power load, the diurnal power generation of a power plant g must be less than its capacity factor multiplied by the theoretical power generation production: , , , , , 24. .≤∑ t g q t y g q g yx l c (11) where lg,q is the capacity factor of the power plant g corresponding to load pattern q. 6) limitation of generation power between two consecutive hours the relation between the probability of changing load power demand and the generation capacity of power plant g is presented as: ( ) ( ), , , , , , , , 1,1 . 1 .ρ ρ −− ≤ ≤ +g g q t y g q t y g g q t yx x x (12) where ρg is defined as the limitation of generation power variation between two consecutive hours of power plant g. iii. input data collection a. load pattern instead of using historical hourly data of power load, 8 load patterns, representing 8 typical groups of load profile in a year, are employed to minimize calculation time (table ix [16]). table ix. load patterns of vietnam power system [16] no. pattern 1 tet holidays 2 w: 1, 2 3 w: 3, 4, 5 4 w: 6, 7, 8 5 w: 9, 10, 11, 12 6 s & n: 1, 2 7 s & n: 3, 4, 5, 6, 7, 8, 9 8 s & n: 10, 11, 12 w: working day, s: sunday, n: national holiday b. maximum installed capacity maximum installed capacities of hydro, mini-hydro, coal, and gas generations are officially cited from [8] and [15] (table x). the maximum installed capacities of biomass, wind and pv are presented in tables vi and vii. table x. maximum installed capacity (gw) [8, 15] power generation 2020 2025 2030 hydro 18.16 18.63 21.22 coal 26.71 47.47 65.89 gas 9.47 17.55 23.23 mini-hydro 3.80 5.20 6.80 c. reserved capacity table xi presents the reserve margin and installed capacity of vietnam power system by 2030. it is worth noting that the reserved capacity does not include renewable energy sources. table xi. reserve margin and installed capacity [9] year lole target (h/y) reserve margin (%) demand pmax (gw) installed capacity (gw) high low high low 2020 24 25 40.33 39.71 50.41 49.64 2025 24 20 60.84 58.28 73.01 69.94 2030 24 20 87.56 80.35 105.07 96.42 d. capacity factor the fact that some power resources depend on climate and other natural conditions leads to dependence characteristics of capacity factor on natural conditions. for example, the capacity factor of a solar power plant depends on the variation of solar radiation, the capacity factor of a wind farm may be affected by the changes of wind speed, and the capacity factor of a hydro power plant will vary when the water flow alters. therefore, it is required to verify the exact capacity factor of each type of energy source before taking them into account. engineering, technology & applied science research vol. 9, no. 2, 2019, 4019-4026 4023 www.etasr.com nguyen et al.: green scenarios for power generation in vietnam by 2030 1) solar power plant in order to identify the capacity factor of a solar power plant, three important constraints must be accounted for: • sunny time: useful solar radiation could only be collected from 6:00 to 18:00. the other times, there may be some frail radiation in some regions but it cannot be used. • radiation intensity: solar radiation intensity varies continuously throughout the day. • geographical location: regions which have stable radiation duration are the central, highland and southern of vietnam [17]. therefore, it is recommended that solar power plants should be constructed around those regions. based on the solar radiation values of central and southern provinces presented in [17], the capacity factor of a solar power plant could be calculated. solar radiation of central coast area, and capacity factors of pv power plants are presented in table xii. 2) wind power plant at the height of 60m above sea level, wind energy could only be obtained effectively in ca mau, a mountainous province of highland, and some provinces of central coast area [18]. the biggest wind farm of the south east asia, tuy phong wind farm, is located in binh thuan province. however, because of the unstable wind speed, the generation power of tuy phong has high variations. based on forecasted wind speed [18], the capacity factor of a wind power plant located in vietnam could be computed. table xii presents the capacity factors corresponding to the monthly variation of wind speed in central coastal vietnam. 3) hydro and mini-hydro power plants as mentioned above, generation capacity of hydro and mini hydro plants strongly depends on water sources and rainfall. based on historical data involving climate conditions, annual average rainfall, and rainfall predictions, along with the assumption that there will be no unusual changes in the local natural conditions, the capacity factor of a hydro power plant could be calculated. regarding a mini hydro power plant, the current national regulations on dam design stipulate a very small limitation for height, leading to the result that generation power of a mini hydro power plant is closely connected to local rainfall. capacity factors of hydro and mini hydro power plants are presented in table xiii. 4) capacity factors of other power plants in theory, coal, gas, and biomass power plants can operate throughout the year. however, they need to be maintained periodically. it normally takes them at least 30 to 45 days per year to stop operating for maintenance or for accidental shutdown. therefore, in this research, the capacity factors of coal, gas, and biomass generations are proposed to be 0.8, as shown in table xiii. e. limitation of generation power variation between two consecutive hours of a power plant for solar and wind power plants, the generation ability between two consecutive hours totally depends on local natural conditions, i.e. wind speed changes or variations of solar radiation at different times of a day. table xii. solar radiation, wind speed in central coast area and pv, wind generation capacity factors [17, 18]] month solar wind solar radiation (kwh/m 2 .day) capacity factor [per unit] wind speed (m/s) capacity factor (per unit) 1 3.6 0.32 8.0 0.75 2 4.8 0.43 7.0 0.56 3 5.2 0.47 5.8 0.34 4 5.6 0.50 4.2 0.10 5 5.2 0.47 5.0 0.19 6 5.2 0.47 5.7 0.32 7 5.2 0.47 6.5 0.41 8 5.2 0.47 6.5 0.41 9 4.4 0.40 5.5 0.29 10 4.4 0.40 4.3 0.10 11 4.0 0.36 6.7 0.44 12 3.6 0.32 8.0 0.75 table xiii. generation capacity factors month no. of load pattern hydro minihydro wind pv coal, gas, biomass 1 1, 2, 6 0.51 0.20 0.75 0.32 0.8 2 1, 2, 6 0.48 0.20 0.56 0.43 0.8 3 3, 7 0.48 0.25 0.34 0.47 0.8 4 3, 7 0.82 0.72 0.10 0.50 0.8 5 3, 7 0.92 0.60 0.19 0.47 0.8 6 4, 7 0.76 0.78 0.32 0.47 0.8 7 4, 7 0.76 0.90 0.41 0.47 0.8 8 4, 7 0.92 1.00 0.41 0.47 0.8 9 5, 7, 8 0.82 0.75 0.29 0.40 0.8 10 5, 7, 8 0.58 0.60 0.10 0.40 0.8 11 5, 7, 8 0.58 0.27 0.44 0.36 0.8 12 5, 7, 8 0.58 0.21 0.75 0.32 0.8 1) wind power plant the generation capability between two consecutive hours depends on the changes of wind speed at the location where the wind-mill is constructed. however, the difference on wind speed between two consecutive hours is very small, at 1-2m/s (approximately 15%). 2) solar power plant as mentioned, two reasons which lead to the change of generation power between two consecutive hours of a solar power plant are the variation of solar radiation intensity during the day and the duration of sunny time per day. however, changes of solar radiation between two consecutive hours are still petite and accounted for around 15% as in the wind power case. table xiv presents the limitation of generation power variation between two consecutive hours of different types of power plants which may be called as the load traceability of power generation. table xiv. load traceability ratio of power generation (%) hydro coal gas biomass wind pv 10 20 60 20 15 15 engineering, technology & applied science research vol. 9, no. 2, 2019, 4019-4026 4024 www.etasr.com nguyen et al.: green scenarios for power generation in vietnam by 2030 f. co2 emissions and prices 1) co2 emission factor the emission factors of co2 for different energy sources in vietnam are shown in table xv. emission factors of wind energy and solar energy are cited from [20, 21]. table xv. co2 emission factors in vietnam unit coal gas biomass hydro pv wind [g-co2/kwh] 1,473 464 20 11 40 11.7 2) co2 prices although the clean development mechanism (cdm) issued by kyoto protocol (1997) has not been extended since 2012, international co2 trading market is still operating. selling prices of co2 in the global market are chosen at 18, 20, and 25 us$/short t-co2, for year 2020, 2025, and 2030, respectively. those are the lowest prices according to [22]. g. levelized cost in vietnam, renewable power plants will be offered a fixed selling tariff (table xvi). reference values relevant to investment, power factor, lifetime, fuel consumption per unit production, operation and maintenance cost, fuel price are included in table xvii. they are categorized as levelized cost. the values are cited from [9]. table xvi. electricity prices buyed by evn unit biomass [23] wind [24] pv [11] import [9] [us$cent/kwh] 7.4 7.8 9.35 6.02 table xvii. levelized cost of conventional power plants [9] indicator unit gas coal hydro 2020 2025 2030 2020 2025 2030 2020 2025 2030 investment us$/kw 1,224 1,660 1,660 1,400 1,850 1,850 1,500 1,500 1,500 energy consumption kcal/kwhe 2,457 1,870 1,870 2,098 1,720 1,720 lifetime yr 25 30 50 fixed o&m us$/kw.yr 24.5 28 28 42 43.5 43.5 5 5 5 variable o&m us$/mwhe 0.88 1.37 1.37 0.15 3 3 2 2 2 interest rate (wb-ida suf) % 3.8 fuel price – low us$/mbtu 4.88 5.46 5.69 1.6 1.7 1.9 fuel price – high us$/mbtu 9.16 10.9 11.6 3.6 3.8 4.0 heat value (lhv) 1000kcal/kg 9.8 8.5 8.5 6.5 6.5 6.5 iv. results when the input parameters are inserted into lindo software, optimal generation scenarios of installed capacity and power generation production based on different power sources for the years 2020, 2025, and 2030 are generated as final results. the following values are calculated: co2 emission capacity, electricity selling prices in case of non-purchasing mitigated-co2, and electricity selling prices with sharing by mitigated-co2 trading. a. installed capacity optimum installed capacity of power generation is presented in figure 1. fig. 1. optimum installed capacity hydro installed capacity is around 18.1gw, 18.6gw, and 21.2gw in 2020, 2025, and 2030 respectively reducing from 32% to 16.8%. it reaches its upper limit of installation and does not change through the scenarios. coal generation capacity on the other hand, is dramatically increased from around 15.817gw in 2020 to 24.6-29.3gw in 2025, and 38.9-49.9gw in 2030 changing its percentage of total capacity from about 27.8% to 40.6%. gas generation capacity is increased by years but not changed much through different scenarios at around 9.5gw in 2020, 15.6gw in 2025, and 23.2gw in 2030. in percentage of total, it varies in the range of 16.6% to 20.3%. the other generations are all reaching their upper limit installation. all scenarios have reserved capacity at more than 20% not including renewable sources. b. power generation production figure 2 illustrates the computed-results of optimum electricity generations. hydro generation reaches its upper limit from 66.3 to 68.6twh from 2020 to 2030 respectively decreasing its percentage from 35.8% to 13.9%. coal generation increases dramatically to meet the increasing load demand. the generation takes a very high percentage from 41.5% to 65.8%. gas generation shares 19% to 26.3% of total, depending on the years and scenarios. other generations are all reaching their upper limits. c. co2 emission capacity co2 emissions of the power generation system are shown in figure 3. bau scenario has the highest emissions of 188.9mtco2, 341.8mt-co2, and 516.9mt-co2 in 2020, 2025, and 2030 engineering, technology & applied science research vol. 9, no. 2, 2019, 4019-4026 4025 www.etasr.com nguyen et al.: green scenarios for power generation in vietnam by 2030 respectively. lowest emissions are resulted by the hg scenario and are reduced by 5.9% (2020), 20.4% (2025), and 28.4% (2030) compared to bau. this is caused by a considerable increase of renewable sources, and very low load demand. details of reduction in capacity of emissions are presented in table xviii. fig. 2. optimum power generation production fig. 3. co2 emissions table xviii. co2 reduction compared to bau scenario 2020 2025 2030 lg 11.14 62.04 127.74 hg 11.14 69.60 146.92 crisis 6.05 30.80 2.38 d. generation cost generation costs for both two cases of non-selling co2 emissions and selling mitigated co2 are shown in figure 4. two ranges of generation cost, 4.3-5.5 and 6.0-7.7 us$cent/kwh have been reached in correspondence with low and high fuel price future scenarios. it is demonstrated that selling mitigated co2 will help reduce the generation cost. maximum reduced cost is recorded in hg scenario in 2030 at 10% in case of non-selling mitigated co2. maximum amount of selling co2 emission reduction is 2.64 billion us$ in hg scenario in 2030. this helps generation cost of both hg and crisis scenarios to be nearly the same in 2030. selling mitigated co2 also makes generation cost of lg scenario in 2030 lower than that of bau. bau scenario has the same cost for both cases of selling and non-selling mitigated co2 as it has no emission reduction. fig. 4. electricity generation cost v. conclusion four projection scenarios of power generation by 2030 in vietnam have been proposed. three variable key-factors have been selected for creating the power generation scenarios: future fuel price, reduction of load demand caused by the penetration of led technology and rooftop pv systems, and the introduction of power generation from renewable sources. the scenarios named bau, lg, hg, and crisis are taken into account for finding the optimum structure of power generation system in terms of installed capacity and power generation production. co2 emission reduction compared to bau scenario and its effects on reducing generation cost are calculated with the aim to give an understanding of the magnitude of the impact of green scenarios on the power generation system. bau is the worst scenario in terms of co2 emissions because of the highest proportion of generation from coal and fossil fuels. it also leads to a poor energy security because thermal generations increase their generation share at about 62.6%, 72.5%, and 75.1% of total in 2020, 2025, and 2030, respectively. lg and hg scenarios show their positive impacts on co2 emissions and generation cost reduction. hg scenario is defined as the greenest one when renewable energy sources contribute 11.2% (2020), 15.5% (2025), and 19.4% (2030) of total generation. maximum emission reduction is about 146.92mt-co2 in hg scenario in 2030. additionally, selling mitigated co2 can make green scenarios more competitive to bau and crisis in terms of cost. two ranges of generation cost (4.3-5.5 and 6.0-7.7us$cent/kwh) have been reached in correspondence with the low and high fuel price scenarios. these generation costs are low enough to support future sustainable economic development in vietnam. replacing conventional electric lamps with led lamps and increasing the installed capacity of rooftop pvs may help reducing electric load demand. increasing the contribution of renewable generation will make the hg scenario become more attractive both in environmental and economic aspects when the crisis scenario comes. generation costs of all scenarios shall become engineering, technology & applied science research vol. 9, no. 2, 2019, 4019-4026 4026 www.etasr.com nguyen et al.: green scenarios for power generation in vietnam by 2030 cheap enough for promoting economic development in vietnam to 2030. references [1] iea, world energy outlook 2017, iea, 2017 [2] bp, bp energy outlook 2035, bp, 2015 [3] g. fan, n. stern, o. edenhofer, s. xu, k. eklund, f. ackerman, l. li, k. halding, the economics of climate change in china: towards a low-carbon economy, stockholm environment institute, 2011 [4] m. r. salehizadeh, “a. rahimi-kian, k. hausken, a leader–follower game on congestion management in power systems”, in: game theoretic analysis of congestion, safety and security, pp. 81-112, springer, 2015 [5] m. r. salehizadeh, s. soltaniyan, “application of fuzzy q-learning for electricity market modeling by considering renewable power penetration”, renewable and sustainable energy reviews, vol. 56, pp. 1172-1181, 2016 [6] m. r. salehizadeh, a. rahimi‐kian, m. oloomi‐buygi, “a multi‐attribute congestion‐driven approach for evaluation of power generation plants”, international transactions on electrical energy systems, vol. 25, no. 3, pp. 482-497, 2015 [7] m. r. salehizadeh, a. rahimi-kian, m. oloomi-buygi, “security-based multi-objective congestion management for emission reduction in power system”, international journal of electrical power & energy systems, vol. 65, pp. 124-135, 2015 [8] w. wangjiraniran, b. eua-arporn, “assessment of renewable energy penetration on power development plan in thailand”, journal of power and energy systems, vol. 5, no. 3, pp. 209-217, 2011 [9] n. t. dung, decision 428/qd-ttg, march, 18, 2016 of the prime minister of vietnam, revisions to the national power development plan from 2011 to 2020 with visions extended to 2030, 2016 [10] h. t. nguyen, “main drivers of carbon dioxide emissions in vietnam trajectory 2000-2011: an input-output structural decomposition analysis”, journal of sustainable development, vol. 11, no. 4, pp. 129147, 2018 [11] n. x. phuc, decision 11/qd-ttg, april, 14, 2017 of the prime minister of vietnam, support mechanisms for the development of solar power projects in vietnam, 2017 [12] department of energy & climate change uk, decc fossil fuel price projections, 2013 [13] v. h. m. nguyen, c. v. vo, k. t. p. nguyen, b. t. t. phan, “forecast on 2030 vietnam electricity consumption”, engineering, technology & applied science research, vol. 8, no. 3, pp. 2869-2874, 2018 [14] v. h. m. nguyen, c. v. vo, b. t. t. phan, “peak load forecasting for vietnam national power system to 2030”, journal of science & technology of technical universities – hanoi university of science and technology, no. 123, pp. 7-13, 2017 [15] n. t. dung, decision 2068/qd-ttg, november, 25, 2015 of the prime minister of vietnam, the development strategy of renewable energy of vietnam by 2030 with a vision to 2050, 2015 [16] v. h. m. nguyen, a. n. nguyen, c. v. vo, b. t. t. phan, “forecasting vietnam’s electric load profile to 2030”, journal of technical education science, vol. 49, pp. 51-57, 2018 [17] j. polo, s. martinez, c. m. fernandez-peruchena, a. navarro, j. m. vindel, m. gaston, l. r. santigosa, e. soria, m. v. guisado, a. bernados, i. pagola, m. olano, maps of solar resource and potential in viet nam, ministry of industry and trade of the socialist republic of vietnam, 2015 [18] aws truepower, wind resource atlas of vietnam, 2011 [19] v. v. cuong, “co2 life cycle emission factors of power generation in vietnam”, journal of science & technology of technical universities – hanoi university of science and technology, vol. 79, 102-107, 2010 [20] nrel, life cycle greenhouse gas emissions from solar photovoltaics, nrel/fs-6a20-56487, nrel, 2012 [21] r. c. thomson, g. p. harrison, life cycle costs and carbon emissions of wind power, university of edinburgh, 2015 [22] synapse energy economics, carbon dioxide price forecast, synapse energy economics inc., 2015 [23] ministry of industry and trade, decision 942/qd-bct, march, 11, 2016 of the minister of ministry of industry & trade, vietnam, avoiding cost appling for bimass power projects in 2016, 2016 [24] n. x. phuc, decision 39/2018/qd-ttg, september, 10, 2018 of the prime minister of vietnam, amending several articles of decision no. 37/2011/qd-ttg dated june 29, 2011 of the prime minister on provison of assistance in development of wind power projects in vietnam, 2018 microsoft word kardjilova-ed_r3.doc etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 424-428 424 www.etasr.com kardjilova et al.: influence of temperature on energetic and rheological characteristics… influence of temperature on energetic and rheological characteristics of plantohyd bio lubricants – a study in the laboratory krassimira kardjilova department of physics technical university of varna varna, bulgaria kardjilova@yahoo.com vlasta vozarova department of physics slovak university of agriculture of nitra nitra, slovak republic vlasta.vozarova@uniak.sk mihal valah department of physics slovak university of agriculture of nitra nitra, slovak republic michal.valach@uniag.sk abstract — this article presents the results of measuring the calorific value and the rheological characteristics of plantohyd bio lubricants. measurements were conducted under laboratory conditions with an ika c5000 calorimeter and a dv-3p anton paar digital viscometer. results are presented graphically. it is shown that the physical interpretation of energy values results and the dependence of rheological properties on temperature can be used to assess the quality of lubricants. keywords: plantohyd; calorific value; rheological characteristics; quality of lubricants. i. introduction biofuels and bio lubricants are widely entering the market, especially the liquid fuel market. biofuels and bio lubricants are compatible with existing engines and vehicles, but produced from organic material (waste agricultural products, sunflower, rapeseed oil, etc.). therefore, they are far more environment-friendly, whereas they are capable of producing similar energy values with ordinary fuels. plantohyd lubricants are products based on synthetic esters, providing an alternative to petroleum-based hydraulic oils (e.g. [1]). the main advantages of these lubricants are: • excellent composting 90% for 14 days; • excellent resistance to aging and oxidation; • good viscosity–temperature dependence. plantohyd hydraulic lubricants are suitable for all mobile and stationary hydraulic equipment in vehicles and industry. their use is recommended especially when there is a danger of leakage of hydraulic and lubricating oisl in soil, groundwater or surface water. to maintain their production properties, they must be used independently and not in combination with petroleumbased oils. they can be applied in a wide temperature range from -35 o c to +90 o c, covered by different plantohyd types. there is little information for the energetic values of different lubricants. changing other characteristics of the lubricants depending on temperature, pressure during use and storage conditions has also met limited investigation. measurements were conducted in the scientific laboratory of the department of physics of the slovak university of agriculture in nitra. we measured the specific heat of combustion of three plantohyd samples and of the dependence of rheological characteristics-dynamic viscosityη , kinematic viscosity ν , fluidity φ and density ρ on temperature .t measurement methods of thermophysical properties and their theoretical principles can be found in [2-5] ii. theoretical base basic physical processes that can be used to measure the influence of temperature on physical properties of lubricants are the hot wire method [2] and thermal analysis methods [6]. among the most common methods of thermal analysis are the thermo gravimetric analysis, the differential thermal analysis and the calorimetric differential compensatory difference. the main quantity studied in thermal analysis methods is the change in enthalpy h∆ [3, 7]. a. specific enthalpy (calorific value of fuels) the amount of energy generated when a unit mass of fuel is burned completely is known as the calorific value of the fuel. enthalpy is a measure of the energy content in a thermodynamic (td) system. for each balance state of the td system, specific enthalpy has a specific value. the value of enthalpy and its change depend on the initial and final state of the td system, rather than the intermediate states [4]. specific enthalpy is the enthalpy per unit mass[ ] kj h kg = . the change of specific enthalpy determines the heat released from the system at a fixed process. the release during the combustion of fuel energy transfers the products of combustion, which leads to a change in its enthalpy. enthalpy of combustion is defined as the difference between the enthalpy of the products and the enthalpy of etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 424-428 425 www.etasr.com kardjilova et al.: influence of temperature on energetic and rheological characteristics… reagents when complete combustion occurs at a given temperature and pressure [4]. in the combustion, the calorimeter technique is adopted to determine the enthalpy of combustion products that result from the fuel unit. enthalpy-energy diagrams, with graphical interpolation for intermediate values, can be used to determine the enthalpy of combustion products at different temperatures, excess air in the construction of thermal balance and the related thermo calculations of combustion. in many cases however, the enthalpy of combustion, which can be experimentally determined, is used for energetic analysis when the enthalpy formation data are not directly accessible fast and precise enough measurement of the specific enthalpy (calorific value of fuels) can be acquired with a c5000 calorimeter. b. rheological characteristics rheology is a branch of physics, which deals with the ways in which materials and fluids deform in response to applied forces or stress [8]. newton formulated the law for an ideal fluid: shear stress between layers is proportional to the velocity gradient, ∂u/∂y, in a direction perpendicular to the layers, in other words, the relative movement of layers. u y τ η ∂ = ∂ (1) here, the constant η is the coefficient of viscosity (viscosity) or dynamic viscosity. many fluids, such as water, satisfy newton's criterion and are known as newtonian fluids. non-newtonian fluids exhibit a more complex relationship between shear stress and velocity gradient. in some cases, the ratio of inertial resistance is calculated using fluid density ρ. kinematic viscosity is determined by: η ν ρ = (2) reciprocal value of viscosity determines the fluidity 1 η ϕ = (3) it is known that dynamic viscosity changes with temperature, which means that this impact will also occur in kinematic viscosity and fluidity. theoretical and experimental studies show that this dependence is exponentially or linearly decreasing for η and ν and linearly or exponentially increasing for φ [8, 9]. the dependencies are determined by the kind of the substance and the manner of processing and storage. this means that many different fluids are required in order to investigate the dependency of rheological properties on temperature. iii. model and method of measurement three samples of plantohyd (15s, 46s and 40n) were examined. measurements were made under laboratory conditions in air temperature t=21 o c, atmospheric pressure and normal humidity ω=56%. all calorie values are measured two times and all rheological three times. the presented results are average values. a. measurement of energy values measurements are performed with an ika calorimeter system c5000 control (c5040 calwin) [3, 7]. the selected operating condition is adiabatic. calibration of the apparatus is conducted before the measurement, in order to achieve a high degree of precision and accuracy the masses of the samples are measured with a digital balance accurate to 0.0001 g and then the samples are placed in a calorimetric bomb in which the combustion process takes place, under certain conditions. the specific heat of combustion is calculated based on data obtained for the mass of the samples, the heat capacity of the calorimeter and the temperature rise of the water in the calorimeter. b. measurement of rheological values measurements are made with a dv-3p anton paar digital viscometer, which is a rotational viscometer [8]. it holds and operates on the principle of measuring the torsion force as a function of resistance, which has a model for the rotation of the cylinder or spindle immersed in the sample. viscosity is calculated from the measured values. the combination of spindles (r2, r3) and speed allows an optimal choice for measuring viscosity. measurements of viscosity should be conducted in laminar flow, which requires a specific time (in our case 2 minutes). there should be no air bubbles in the model. it should have a uniform texture and should be free of mechanical impurities. the temperature must be constant throughout the volume of the sample. only under these conditions, the measured value of viscosity can be considered correct. the density of the samples is measured using the pycnometric method and a calibrated pycnometer with a volume of 50 ml. the dynamic viscosity of the three samples was measured at different temperatures. for the same temperature range, we measured the densities of the samples and calculated kinematic viscosity and fluidity. iv. results the energetic values of the three plantohyd samples are shown in table i. the kinematic viscosity and fluidity are calculated from the measured dynamic viscosity and density of the three samples. graphs are constructed using the grafer software, and the mode of the functional dependence and the coefficient of determination are calculated. the results are presented in table ii to viii and in figures 1 to 4. etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 424-428 426 www.etasr.com kardjilova et al.: influence of temperature on energetic and rheological characteristics… table i. measured energetic values of three plantohyd samples type ( )m g ( / )h j g / )(h mj kg 0.2363 37511 plantohyd 15s 0.5100 37345 37.428 0.2667 39521 plantohyd 46s 0.5554 39457 39.483 0.3334 39466 plantohyd 40n 0.5963 39378 39.417 table ii. measured values of , , ,η ν ϕ ρ plantohyd 15s ( ) o t c ρ 3 ( / )kg m η ( )mpa s⋅ ν 2 6( / 10 )m s − ⋅ φ 1 1 ( )pa s − − ⋅ -10 939.974 79.3 84.41 12.61 -5 937.897 75.8 80.87 13.19 0 934.776 62.4 66.77 16.03 5 931.656 57.1 61.26 17.51 10 928.537 51.2 55.17 19.53 20 922.298 45.9 49.79 21.79 30 913.980 35.5 38.84 28.17 40 908.781 24.0 26.41 41.67 50 902.542 21.7 23.99 46.08 table iii. measured values of , , ,η ν ϕ ρ plantohyd 46s ( ) o t c ρ 3 ( / )kg m η ( )mpa s⋅ ν 2 6( / 10 )m s − ⋅ φ 1 1 ( )pa s − − ⋅ -10 927.497 216.4 233.30 4.62 -5 926.457 166.3 179.50 6.01 0 925.417 122.5 132.37 8.16 5 924.378 102.2 110.55 9.78 10 922.298 84.6 91.70 11.81 20 913.980 61.2 66.95 16.34 30 907.741 50.9 56.05 19.65 40 900.462 43.2 48.01 23.15 50 896.303 37.6 41.95 26.59 table iv. measured values of , , ,η ν ϕ ρ plantohyd 40n ( ) o t c ρ 3 ( / )kg m η ( )mpa s⋅ ν 2 6 ( / 10 )m s − ⋅ φ 1 1 ( )pa s − − ⋅ -10 934.776 233.7 239.30 4.28 -5 937.696 174.7 186.30 5.37 0 930.616 132.3 142.16 7.56 5 926.457 93.7 10109 10.67 10 922.298 69.8 75.73 14.33 20 918.139 54.9 59.79 18.21 30 906.701 47.5 52.39 21.05 40 904.621 39.3 43.45 25.45 50 897.343 36.2 40.38 27.62 table v. results for functional dependence and coefficient of determination for density ( )f tρ = type equation association coefficient 15s y= -0.642x + 934.4 r 2 = 0.997 46s y= -0.566x + 924.8 r 2 = 0.974 40n y= -0.675x + 930.3 r 2 = 0.976 table vi. results for functional dependence and coefficient of determination for dynamic viscosity ( )f tη = type equation association coefficient 15s y= -0.000x 3 + 0.015x 2 1.369x + 64.87 r 2 = 0.986 46s y = -0.001x 3 +0.181x 2 6.447x + 129.4 r 2 = 0.997 40n y= -0.002x 3 + 0.236x 2 7.761x + 129.8 r 2 = 0.997 table vii. results for functional dependence and coefficient of determination for kinematic viscosity ( )f tν = type equation association coefficient 15s y= -1e-10x 3 + 2e-08x 2 1e-06x + 7e-05 r 2 = 0.985 46s y = -2e-09x 3 + 2e-07x 2 7e-06x + 0.000 r 2 = 0.997 40n y= -2e-09x 3 + 2e-07x 2 8e-06x + 0.000 r 2 = 0.997 table viii. results for functional dependence and coefficient of determination for fluidity ( )f tϕ = type equation association coefficient 15s y = 15.35e 0.022x r 2 = 0.983 46s y = 0.374x + 8.184 r 2 = 0.998 40n y = 0.411x + 8.547 r 2 = 0.984 fig. 1. dependence of density on temperature. fig. 2. dependence of dynamic viscosity on temperature. etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 424-428 427 www.etasr.com kardjilova et al.: influence of temperature on energetic and rheological characteristics… fig. 3. dependence of kinematic viscosity on temperature. fig. 4. dependence of fluidity on temperature. a. analysis of results the results for the energetic values show that they are very close for both plantohyd 46s and 40n and lower for 15s. constructed graphs of the dependence of density on temperature show a linear decreasing function for all three samples. dependence is: ( )tba −=ρ (4) where a and b are constants that depend on the type of substance. the values of densities fall in the following ranges: • plantohyd 15s: from 939.97 kg/m 3 at -10 0 c to 902.54 kg/m 3 at +50 0 c. • plantohyd 46s: from 927.50 kg/m 3 at -10 0 c to 896.30 kg/m 3 at +50 0 c. • plantohyd 40n: from 934.78 kg/m 3 at -10 0 c to 897.34 kg/m 3 at +50 0 c. it can be seen from the graphs that plantohyd 46s and 40n have slightly different densities after +400c, and that plantohyd 15s has the highest density values. our results for plantohyd densities are comparable to results given in reference books (for plantohyd 46s: 921 kg/m 3 , for plantohyd 40n: 922 kg/m 3 , data for plantohyd 15s were not found, but for plantohyd 32s density is 921 kg/m 3 ). the results for η show that dependence on t is not exponential and not linear. it rather follows a cubic decrease. dependence is: ( ) ( ) ( ) 2 3 c d t i t f tη = − + − (5) where c, d, f and i are constants that depend on the type of substance. the values of dynamic viscosity for plantohyd 46s and 40n are close: • plantohyd 46s: 216.4 mpa·s at -10 0 c to 37.6 mpa·s at +50 0 c. • plantohyd 40n: 233.7 mpa·s at -10 0 c to 36.2 mpa·s at +50 0 c. significantly, lower values of dynamic viscosity are for plantohyd 15s: 79.3 mpa·s at -10 0 to 21.7 mpa·s at +50 0 c. similar results can be seen for the dependence of kinematic viscosity on temperature. decreasing dependence is cubic. dependence is ( ) ( ) ( ) 2 3 g h t m t * tν = − + − (6) g, h, m and * are constants that depend on the type of substance. values for 46s and 40n are relatively close, and those for 15s are smaller. the results are as follows: • plantohyd 46s: 233.3·10 -6 m 2 /s at -10 0 c and 41.9·10 6 m 2 /s at +50 0 c. • plantohyd 40n: 239.3·10 -6 m 2 /s at -10 0 c and 40.4·10 -6 m 2 /s at +50 0 c. • plantohyd 15s: 84.4·10 -6 m 2 /s at -10 0 c and 23.9·10 -6 m 2 /s at +50 0 c. comparison of the results can be made with the given values of kinematic viscosity characteristics of those lubricants at 40 0 c. • plantohyd 46s: 48.8·10 -6 m 2 /s – our calculatted value is 48.01·10 -6 m 2 /s. • plantohyd 40n: 42·10 -6 m 2 /s our calculatted value is 43.4·10 -6 m 2 /s. • plantohyd 15s: no evidence for kinematic viscosity. the dependence of fluidity on temperature is a linearly increasing function of plantohyd 46s and plantohyd 40n. dependence is: ( )k l tϕ = + (7) dependence for plantohyd 15s is: ( )expk l tϕ = (8) , k and l are constants that depend on the type of substance. these functions are not differing significantly at temperatures from -10 0 c to +10 0 c. the obtained values for fluidity are: etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 424-428 428 www.etasr.com kardjilova et al.: influence of temperature on energetic and rheological characteristics… • plantohyd 46s: from 4.62 pa -1 ·s -1 at -10 0 c to 26.59 pa -1 ·s -1 at +50 0 c. • plantohyd 40n: from 4.28 pa -1 ·s -1 at -10 0 c to 27.62 pa -1 ·s -1 at +50 0 c. the dependence of fluidity on temperature for plantohyd 15s is an exponentially increasing function. the obtained values for fluidity are from 12.61 pa -1 ·s -1 at -10 0 c to 46.08 pa -1 ·s -1 at +50 0 c. v. conclusion lubricants are classified by their two main characteristics: viscosity and operational level the kinematic viscosity. the physical interpretation of the results of energy values and the dependence of rheological properties on temperature can be used to assess the quality of lubricants. using bio lubricants helps to lubricate the engine, providing longer engine and segment life. suitability for use of a bio lubricant is estimated with the help of certain criteria. as one of the roles of fuel and lubrication is its function, the change of its viscosity and its density are indicative of a change in quality. the viscosity values show the ability to withstand and protect against wear and corrosion. the results presented in this paper can be useful for manufacturers of similar synthetic oils and could be used by the automotive and mechanical engineering industry, which uses similar lubricants. further, the data obtained can be used in technological processes as well as for studying the physical properties of biо lubricants which would allow the development of new technologies using bioenergetics conversion and use of bio lubricants with better performance. references [1] fuchs europe schmierstoffe gmbh, “plantohyd s: environmentally-friendly, synthetic ester-based hydraulic and lubricating fluid (product information)”, pi 4-1274, pm 4 /03.08, 2008 [2] j. krempasky, fyzika, alfa, 1982 [3] v. vozarova, “study of processes and properties of materials by method of thermal analysis”, research and teaching of physics in the context of university education international conference, nitra, slovakia, pp. 141-144, june, 2007 [4] j. moran, n. shapiro, fundamentals of engineering thermodynamics, john wiley & sons, 1991 [5] p. haines, thermal methods of analysis: principles, appplications and problems, blackie akademic and proffessional, 1995 [6] a. blazek, termicka analiza, stnl, 1972 [7] m. valach, l. hires, “examination of viscosity and specific heat of combustion of biofuels”, physics–research–applications–education international conference, nitra, slovakia, pp.138-140, october, 2011 [8] m. bozikova, p. hlavac, selected physical properties of agricultural and food products, slovak university of agriculture, nitra, slovakia, 2010 [9] p. hlavac, “the rheologic properties of plum jam”, ptep journal of processing and energy in agriculture, vol. 11, no. 3, pp. 106-108, 2007 microsoft word 12-3301_s1_etasr_v10_n2_pp5406-5411 engineering, technology & applied science research vol. 10, no. 2, 2020, 5406-5411 5406 www.etasr.com espino & bellotindos: a system dynamics modeling and computer-based simulation in forecasting … a system dynamics modeling and computer-based simulation in forecasting long-term sufficiency: a philippine chicken meat sector case study ma. theresa m. espino engineering graduate program school of engineering university of san carlos cebu city, philippines and department of industrial engineering ateneo de davao university davao city, philippines mtmespino@addu.edu.ph luzvisminda m. bellotindos engineering graduate program school of engineering university of san carlos cebu city, philippines and center for research in energy systems and technologies university of san carlos cebu city, philippines lmbellotindos@usc.ed abstract—as the human population continues to grow, the global growth of the livestock sector will continue to rise as well. in the philippines, the demand for chicken meat is projected to triple by 2050. in this study, the increasing consumption and long-term sufficiency were evaluated with the use of the system dynamics concept. with system modeling and computer-based simulation techniques, the available data on chicken meat supply chain were processed considering that factors behave dynamically. the simulated model facilitated the forecasting of key variables which may drop sufficiency from 87% in 2015 to 60% by 2050 if no proper actions take place in the areas of production and consumption. as a whole, this study developed and demonstrated preliminary system dynamics-based and computer basedapproaches in order to understand the chicken meat sector. this showed that a dynamic systems-based paradigm shift in food and agricultural systems analysis can help address operational and strategic issues regarding food security. keywords-forecasting; system dynamics modeling; computerbased simulation; philippine chicken meat; sufficiency i. introduction as human population continues to grow by an approximately annual 1.1% percentage, the growth of livestock sector will continue to rise as well. the demand for meat is projected to grow by 70% in 2050 with 2005 as baseline. the poultry sector, which is basically chicken meat (cm) has the highest growth among meats at 121% [1]. it is a challenge for poultry sector to satisfy the demand and to align to the mandate on sustainable development goals (sdg). the sector has to comply primarily to food security as expressed in sdg #2 zero hunger [2]. one of the tools in achieving this is addressing food self-sufficiency, which is the ability to meet consumption needs, especially for staple food items such as meat, from domestic production rather than by importing. in addressing food security or food sufficiency, reliable forecasting is the foundation of all warning systems, in order to give decisionmakers enough time to plan and respond to red flag warnings. forecasting has to have a high degree of reliability to avoid false alarms. traditional popular forecasting techniques such as linear regression and multiple regression are used to examine the relationship between independent variable(s) and a dependent variable [3-6]. their usefulness is considerably acceptable for simple forecasting requirements. however, the outcomes are sometimes compromised, especially when the data are incomplete and correlation might be regarded as causation. to consider causation, system dynamics (sd) approach is more advantageous. sd is based on the synthesis of various concepts including operating theory, system theory, control theory, information feedback theory, decision-making theory, mechanical systems theory, and computer science. sd can model the system and analyze the system’s behavior given the desired parameters over time [7]. in contrast to traditional forecasting, sd models are more flexible in predicting complex phenomena due to their dynamic behavior [7, 8]. the sd models are more reliable since they can estimate the sensitivity of results to variables and employ stronger scenarios with the impact of significant changes in strategies or interventions. the process of establishing the model may seem complex at the initial model build-up stage. however, rigor and results can be more significant, especially in forecasting variables in dynamic systems. sd studies have been done in various industries [8, 9] and across agricultural and natural resources [10, 11]. on food supply chain systems, sd has already been applied in rice production [12-14] and food supply [15, 16], which makes it appropriate for the poultry sector. though these studies were done in food agricultural systems, they were not anchored to specific timelines of long-terms plans and sustainability goals on the respective countries. ii. philippine chicken meat sector in philippines, chicken is the most progressive animal enterprise. in 2017, the total chicken meat volume production corresponding author: m. t. m. espino engineering, technology & applied science research vol. 10, no. 2, 2020, 5406-5411 5407 www.etasr.com espino & bellotindos: a system dynamics modeling and computer-based simulation in forecasting … in philippines was 1,344.3 thousand metric tons (tmt). the industry volume is growing at 3.6% per annum during the last five years. a total inventory of 140.20 million birds for meat production has been recorded [17]. in terms of scale, the industry is characterized by “backyard” and “commercial” farms/installations. as described by sikap/strive foundation, rural families run the typical backyard farms, which comprise around 100 birds of native or improved breeds, which are raised primarily for their own consumption. on the other hand, commercial farms have at least 1,000 broilers, or combinations of at least 100 broilers and 100 layers [18]. the per capita consumption was 12.7kg in 2017, a 47% rise over a decade. the increase in local consumption is reported to be attributed to the changes in lifestyle, income and urbanization [19]. at present, the government tracks sufficiency expressed in selfsufficiency ratio (ssr), or the equivalent self-sufficiency level (ssl), an indicator of adequacy of local food production to satisfy the demand of the population. for chicken meat, the ssl at a national level was 92.82% in 2013 but declined to 84.67% in 2016 which is the lowest over a decade. the drop of 8.8% showed the widening gap of production and consumption. moreover, this indicated that around 15% of the demand was not satisfied in 2016 by local production, but was fulfilled through importation. however, ssl improved back to 96.1% in 2017 with the big improvement in local production [20]. total supply is augmented through importations. it registered 55.49 tmt in 2017. it has been increasing by 20132016 but declined in 2017, which was a manifestation that local production improved [21]. total production also utilized exports. the lowest level of exports was in 2017 at 355 metric tons which continued the downtrend since 2015 [17]. in terms of cost of production, the highest cost driver is feeds in both production systems. it accounts for about approximately 65 to 70% of total live broiler production [22]. soybean meal (sbm) is the major source of protein in feeds production. at present there is a limited soybean local production which only serves 8% of the country’s requirements [23]. on the other hand, most feed formulation uses maize as a primary source for energy. based on consolidated data in global livestock environmental assessment model (gleam), the baseline mix for broilers is 71% maize, 27% sbm, and 2% other additives. based on gathered field data, the average feed across stages is comprised of 51% maize, 25% sbm, 9% rice bran, 5% fish meal, 4% copra meal, 2% vegetable oil, and 4% other additives. for backyard production the baseline feed is 40% swill, 17.7% grass, 6% cassava, 4.4% maize, and the rest come from agriculture by-products [24]. however, field data showed that there is no comparable mix since different backyard operations have different feedings based on locale availability, practices, and capacity. the imported feed ingredients have more impact on broiler production. in terms of feeding, the average feed consumption is 2-2.5kgs per bird over a 30-day average rearing period while the amount is 3-3.9kgs per bird for backyard chickens over a period of 90 days. another challenge to improve in local production is technology. changes in production practices have increased productivity and capacity. for chicken production, this is represented by the broiler inventory and native breed inventory which describe the method and scale of production. based on field and gleam data, the average mortality rate is between 2-5% for broiler production, with a marketable average live weight of 1.6-1.2kg and carcass weight of 1.21.0kg over 30 days. on the other hand, the native breed inventory characterizes the typical backyard farms. backyard chicken would achieve a live weight of 1.3-0.9kg and a carcass weight of 1-0.70kg over a period of 90 days [18]. an extensive review on the related literature in philippines showed that no concrete studies have been done regarding meat production and consumption from a long-term sufficiency or sustainability perspective. this paper aims to answer the questions of “how do we evaluate the long term-sufficiency?” and “what are the factors that affect the long-term sufficiency of the philippine chicken meat sector”. with those in mind, the following key objectives are namely: to establish a dynamic model on the impact of increasing consumption to local production, to simulate consumption and production projections up to 2050, and to evaluate forecasts and their implications to sufficiency. the results of this paper can evaluate the model in terms of long-term sufficiency, sustainability, and stability to satisfy local consumption in the future in the philippine poultry sector. this can be used as a reference for planning, identifying opportunities, and conducting relevant researches to improve chicken meat production in view of achieving sdg 2 by 2050, the timeframe where sdgs and paris agreement are referred to. the model can help agricultural decision-makers and government agencies to come up with better programs to promote local agricultural economy and to provide better policies and programs to address issues related to food security. iii. methodology a. materials statistical data were taken from philippine statistics office, the official web-based system for food and agricultural statistical information in philippines [17] and the global meat consumption per country by oecd [1]. production related data were taken from the related literature and actual fieldwork and experiments conducted by the authors. regarding software, vensim, a simulation software for causal loop diagram (cld) [25] and stella (systems thinking for education and research) for stock and flow diagram (sfd) [26] were utilized. b. methods the sd model in this study was primarily anchored on the methodology presented in [7] that includes a three-step process: (a) formulation of the dynamic hypothesis, (b) implementation of the simulation, and (c) testing and validation. this was further expounded with specific steps as presented in figure 1, which serves as the framework of this study. this study is limited and focused to the forecasting of related variables and their implications by 2050. no policies or proposed action plans will be integrated in the model to demonstrate other functionalities. in ensuring a high level of accuracy of the model, validation was done with mean absolute percentage error (mape) [27, 28], a simple yet reliable statistical measure on forecast accuracy and error of models, as demonstrated in [29-31]. forecasting with less than 10% mape is considered engineering, technology & applied science research vol. 10, no. 2, 2020, 5406-5411 5408 www.etasr.com espino & bellotindos: a system dynamics modeling and computer-based simulation in forecasting … as highly accurate, with 10-20% as good, with 20-50% as reasonable and forecasting with mape greater than 50% is considered inaccurate [32]. validating the model was an iterative stage until the desired mape was achieved. fig. 1. framework of system modeling and simulation in forecasting longterm sufficiency iv. results and discussion a. dynamic hypothesis the analysis was centered on the factors that influence local production and consumption. production is basically driven by the technology or processes applied to the two methods of production, broiler and backyard, as quantified in their respective inventories. on the other hand, consumption is driven by the population and per capita consumption. the dynamic hypothesis is illustrated in the clp and further broken down to sfd. the timeframe considered is up to 2050, aligned to the timeframe of sdgs and paris agreement. 1) causal loop diagram (cld) cld is the visual representation of how variables in a system interact and interrelate. auxiliary variables were included in the cld that were simply calculations based on the stock and flows with some discrete event and agent-based modeling capabilities. to complete the cld, the polarity links were rationalized among factors, which were either positive (+) or negative (-). this signified the influence of one variable to the other relevant variables. in figure 2 the cld of chicken meat sufficiency is shown. the diagram was anchored on ssl, the state when local production satisfies local consumption. on the demand side, local consumption is driven by population and per capita chicken consumption. while on the supply side, local production is driven by both broiler and backyard production, which are influenced by their respective yield and inventory. surplus is included in the diagram, which is ideally the determinant for exportation should there be excesses and for importation should there be deficits in the supply chain. 2) stock and flow diagram (sfd) after cld, model building was done for the sfd. to ensure that stock and flows were defined accordingly, units were checked and equations were specified. there were 5 stocks identified, namely population, chicken per capita consumption, cm, broiler inventory, and backyard chicken inventory as shown in figure 3. the core stock in the system is cm, which is influenced by its inflow converter cm supply and outflow converter cm utilization. projection on population growth is available. for the other 3 growth rates, projections were based on 20 year historical performance data (19982017). included in the sfd are auxiliary variables on sbm usage and maize usage which are relevant in the study to evaluate the whole context of sufficiency given that they are imported production inputs. fig. 2. cause loop diagram of chicken meat production b. simulation to proceed with forecasting, the 4 relevant growth rate data were used as inputs in stella. with the equations set in the computer software, the values of the various variables in were generated from the equations in sfd indicated in figure 4. c. validation to validate the model, the actual consumption and production from 2008-2017 were compared to their equivalent simulated data as shown in table i. mape is 8.5% for consumption and 2.8 % for production, indicating that the whole model can be considered acceptable with a high level of accuracy. d. forecasting with the validated model, forecasts can then be generated from the sfd model. in figure 5, is the supply utilization accounts summary of actual and projected variables from 2010 to 2050 is presented. it is indicated that sufficiency level will drop to 60% by 2050, if no interventions take place. e. implications to long-term sufficiency the model showed that consumption will almost triple. also, it can be seen that there is no room for exportation in order to serve its own requirements. moreover, 40% of the requirements will be satisfied from chicken meat importations. this can be a red flag, knowing that chicken price has been rapidly increasing in the global market. engineering, technology & applied science research vol. 10, no. 2, 2020, 5406-5411 5409 www.etasr.com espino & bellotindos: a system dynamics modeling and computer-based simulation in forecasting … fig. 3. stock flow diagram of chicken meat production fig. 4. simulation equations of stock and flow diagram in the production side, broiler production is the driver, currently contributing at 75% of the volume and will continue and rise to 84% by 2050 as shown in figure 6. in figure 7, broiler inventory versus backyard chicken is shown. we can see that by 2025, broiler will outpace backyard production. further analysis for broiler chicken production and feeds usage may be necessary since the country cannot claim absolute sufficiency given that the main feed ingredients are imported, especially sbm and maize. with the projections, the importations of these two ingredients are expected to rise exponentially as shown in figure 8. this can be another red flag for instability in terms of resource management, operational efficiency, and cost control on imported inputs especially for broiler chicken. fig. 5. supply utilization accounts (2010-2050) it should be noted that the same feed raw materials are used for food and biodiesel, further increasing food-feed-fuel competition in terms of utilization [33]. to resolve this, the government should be looking already for alternative and 2010 2015 2020 2025 2030 2035 2040 2045 2050 production 1,041 1,278 1,316 1,473 1,630 1,787 1,944 2,100 2,257 imports 98.0 190.5 206.7 382.9 583.8 804.0 1,036 1,275 1,515 exports 5.5 3.7 consumption 1,134 1,465 1,523 1,856 2,214 2,591 2,981 3,376 3,772 % ssl 92% 87% 86% 79% 74% 69% 65% 62% 60% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 in t h o u sa n d m e tr ic t o n s engineering, technology & applied science research vol. 10, no. 2, 2020, 5406-5411 5410 www.etasr.com espino & bellotindos: a system dynamics modeling and computer-based simulation in forecasting … locally sourced feed inputs. on the other hand, backyard chicken volume contribution will drop from 25% to 16%, with its slow growth. perhaps, the industry must focus and identify the areas for improvement on its prevailing practices, methods, and systems and address them to increase productivity. it is also worth noting that the backyard chicken inventory is declining, which shows that backyard needs attention with its low productivity in both count and yield. table i. validation of simulation model year local cm consumption local cm production actual* simulation* error actual* simulation* error 2008 775.0 772.5 2.5 986.6 981.8 4.8 2009 798.5 812.0 13.5 1,001.7 1,014.1 12.4 2010 864.9 852.9 12.1 1,041.9 1,045.8 3.9 2011 921.8 895.2 26.6 1,089.0 1,077.5 11.5 2012 1,013.5 939.6 73.9 1,139.2 1,110.0 29.2 2013 1,058.9 986.1 72.8 1,197.4 1,143.2 54.2 2014 1,143.6 1,034.9 108.7 1,210.3 1,177.1 33.2 2015 1,211.0 1,086.0 125.0 1,278.8 1,211.8 67.1 2016 1,299.9 1,139.6 160.3 1,289.4 1,247.2 42.2 2017 1,498.7 1,195.2 303.5 1,344.3 1,282.8 61.5 mape 8.5% 2.8% * in thousand metric tons (tmt) the increasing consumption is driven by population and per capita consumption. interventions are more feasible in the per capita growth since it can be influenced by changes in eating pattern and lifestyle. in developed economies, awareness on sustainability issues on meat consumption are increasing such as reduction through practice of meatless days [34] and consumption of plant based meat substitutes and alternative protein sources [35]. perhaps, the industry can also embark on awareness, so that the consumers can somehow have the chance to make sustainable choices. with the model in place, decision makers can use the above implications in integrating proper interventions. other actions in the forms of technology improvements and consumer awareness can be conceptualized and tested in the model, which can project the relevant variables and check the level of sufficiency at specific timelines. hence, in the context of planning, the impact of short-term programs and long-term strategies up to 2050 can be evaluated in addressing food security. fig. 6. broiler and backyard chicken production (2020-2050) fig. 7. broiler and backyard chicken inventory (2020-2050) fig. 8. sbm and maize consumption (2020-2050) v. conclusion long-term sufficiency in this study was evaluated by system modeling and computer-based simulation forecasting. the simulated model projected a sufficiency drop to 60% by 2050 if no interventions take place in production and consumption. with the relevant variables in place in the model, this can be a sound basis in evaluating future scenarios and incorporating possible solutions. in conclusion, the developed dynamic model could be used to facilitate informed decisionmaking. initially, the process of establishing the model may seem complex in comparison with the traditional forecasting techniques. however, rigor and results can be more significant, especially for dynamic systems in the food and agriculture sectors. this study can encourage a paradigm shift in understanding dynamic factors and give decision-makers a better way of planning and addressing long-term sufficiency and food security concerns. acknowledgment the authors are grateful for the funding support given by engineering research and development for technology (erdt). due appreciation is also given to benjamin rubin for assisting in data processing. references [1] oecd, “meat consumption”, available at: http://www.oecd-ilibrary.org [2] un, “sustainable development goals”, available at: 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science and technology hanoi, vietnam vuong.dangquoc@hust.edu.vn abstract—this paper presents a subproblem approach with hconformal magnetostatic finite element formulations for treating the errors of magnetic shell approximation, by replacing volume thin regions by surfaces with interface conditions. these approximations seem to neglect the curvature effects in the vicinity of corners and edges. the process from the surface-tovolume correction problem is presented as a sequence of several subdomains, which can be composed to the full domain, including inductors and thin magnetic regions. each step of the process will be separately performed on its own subdomain and submesh instead of solving the problem in the full domain. this allows reducing the size of matrix and time computation. keywords-magnetostatic finite element formulation; magnetic scalar potential; magnetic field; magnetic shell; subproblem approach i. introduction the local fields in magnetic shells are approximated by a priori 1-d analytical distributions across the shell thicknesses [1, 2]. this means that the interior of volume thin regions is not meshed and is introduced by surfaces with impedance-type interface conditions (ics) linked to the inner-analytical distributions. this leads to negligible edges and corners of magnetic shells, increasing with thickness. in order to overcome this disadvantage, the sub-problem method (spm) for the magnetodynamic problem with dual formulation has been proposed for one-way coupling [3-10]. in this development, a subdomain technique based on the spm is extended for the hconformal magnetostatic finite element formulation in order to improve the local fields (magnetic scalar potential, magnetic flux density and magnetic field) appearing around the edges and corners of magnetic shells. the idea of the method is to perform subdomain solving in three steps (figure 1): • step 1: a lower subdomain attending with stranded inductors is first considered on a simplified mesh without any magnetic shells. • step 2: a shell with the very coarse mesh that does not contain stranded inductors anymore is then added. • step 3: a volume correction replacing the magnetic shell finite element (fe) by an actual thin region is introduced to improve shell inaccuracies. fig. 1. devision of a full domain into three steps. the relation between steps is constrained by volume source (vs) expressed changes of the material propoerties or surface sources (ss) presented changes of ics. in each step, the problem is independently solved in an individual sub-mesh and its surrounding without depending on other meshes, which allow to distinct mesh refinements. the method is applied on a practical problem. ii. magnetostatic problems a canonical magnetostatic problem q presented at step q is solved in a domain ω�, with boundary �ω� � γ� � γ�,� ∪ γ ,�. maxwell's equations, constitutive laws and boundary conditions (bcs) of the problem q give [3-11]: curl �� � ��,div�� � 0 (1a-b) �� � ���� � ��,� (2) corresponding author: vuong dang quoc engineering, technology & applied science research vol. 10, no. 4, 2020, 5953-5957 5954 www.etasr.com quoc: accurate magnetic shell approximations with magnetostatic finite element formulations by … � ∙ ��|г�,� = 0, �� ∙ �� !� = �",� (3a-b) where �� is the magnetic field (a/m), �� is the magnetic flux density (t), �� is the electric current density (a/m 2 ), �� is the magnetic permeability (h/m) and � is the unit normal exterior to ω�. the source field ��,� in (2) is a vs that accounts for volume changes of permeability (��) from the current problem to the next problem �$ (q =p), i.e.: ��,$ = %�$ − ��'��. (4) the notation [∙]!� = |!�+ − |!�, is the discontinuity of a quantity across the negative and positive sides of any interface -� in ω�. the field �",� is a ss between subdomains [3-10]. in addition, the magnetic field �� in (1a) is split in two parts ��,� and �.,�, i.e. �� = ��,� + �.,�, where �.,� is the reaction field and ��,� is a source magnetic field due to the imposed current density ��,� (curl ��,� = ��,�). iii. sequence of fe weak formulations a. weak formulation for inductor model step 1 (sp q) the magnetostatic weak formulation (�� − /) for step 1 (sp q) is obtained via the magnetic gauss's law (1b), i.e. [1, 2]: −%����,�, grad/� 2 ' 3� + %��grad/�, grad/� 2 ' 3� +< � ∙ ��, /� 2 >г�,�6!�+< −�� ∙ �� !� , /� 2 >!�= 0, (5) ∀/� 2 ∈ 9�,� :; %<�' where 9�,� :; %<�' is a function space presented in <� including the basis functions for /� as well as for the test function /� 2. notations of (. , . )>� and 〈. , . 〉a� are respectively the volume integral in <� the surface integral on γ�, of the product of their vector field arguments. the surface term < � ∙ ��, /� 2 >г�,�,b� in (5) is considered as a natural bc of type (3a), usually zero. b. weak formulation for magetnic shell model step 2 (sp p) the shell model (sp p) is defined via the last term in (5). the weak form of sp p, is [1, 2]: %�$grad/$, grad/$ 2 ' 3c +< � ∙ �$, /$ 2 >г�,c6!c +< �� ∙ �$ !c , /$ 2 >!c= 0, ∀/$ 2 ∈ 9�,� :; %<�' (6) the trace discontinuity term < �� ∙ �$ !c , /$ 2 >!c in (6) is given as [4]: < �� ∙ �$ !c , /$ 2 >!c= < �� ∙ �$ !c , /d,$ 2 >!c + < � ∙ �$|!c+, /e,$ 2 >!c+ (7) in addition, the term < �� ∙ �$ !f,$, /d,$ 2 >!f,$ in (7) is obtained from [1, 2]: < �� ∙ �$ !c , /d,$ 2 >!c = −< �$g$��,$, grad/$ 2 >!c +< �$g$grad/$, grad/$ 2 >!c (8) the remaining term < � ∙ �$|!c+, /e,$ 2 >!c+ in (7) is weakly presented via the surface source integral term, i.e.: < � ∙ �$|!c+, /e,$ 2 >!c+= −< � ∙ ��|!c+, /e,$ 2 >!c+= (��grad/�, grad/e,$ 2 )3c+h!c+ + (����,�, grad/e,$ 2 )3c+h!c+ = −�",� (9) the volume integrals in (9) are also limited to a single layer of fes on the positive side of <$ i touching -$ i [4-10]. by substituting (9) and (8) into (6), the weak form of sp p is rewritten as: (�$grad/$, grad/$ 2 )3c−< �$g$��,$, grad/$ 2 >гj,c + < �$g$grad/$, grad/$ 2 >гj,c− (��grad/�, grad/e,$ 2 )3c+ +(����,�, grad/e,$ 2 )3c+ = 0, ∀/$ 2 ∈ 9�,$ :; %<$' (10) at the discrete mesh, the source fields /� and ��,�, initially in mesh of sp q, have to be transferred to the mesh of sp p via a projection method [15-17]. c. weak formulation for volume correction step 3 (sp k) the weak form of sp k is finally established via a vs given by (2): (�kgrad/k, grad/k 2 )3l − ((�k − �$)grad/$, grad/k 2 )3l +(�k − �$)((��,$ − grad/k 2 ), grad/k 2 )3l + < � ∙ �k, /k 2 >г�,l6!l +< [� ∙ �k]!l , /k 2 >!l= 0 ∀/k 2 ∈ 9�,k :; (<k) (11) at the discrete mesh, the source quantities /$ and ��,$ in (11), defined in previous meshes (sp q and sp p) are also projected to the mesh of sp k via a projection method (see section d). in addition, the discontinuity of sp p in sp k has to be removed by fixing as: < [� ∙ �k]!l, /k 2 >!l= −< [� ∙ �$]!l, /k 2 >!l (12) d. transformation of solutions between sub-meshes as presented above, the source fields /� and �� obtained from the previous meshes of spi (e.g. sp q) are transferred to the mesh of sp p, i.e. [15-17]: (��,$6$.mn , � 2)3o,c = (��, � 2)3o,c, ∀� 2 ∈ 9�,$ : %<�,$' (13) where ∀�2 ∈ 9�,$ : %<�,$' is a curl-conform function space for the p-projected source ��,$6$.mn (the projection of ��,$6$.mn on mesh of sp p) and the test function �2 defined on <�,$. in the same way, the magnetic scalar potential /$, can project the grad of /� in the mesh of sp q to the mesh of sp p, i.e. [9]: (grad/�,$6$.mn , grad/ 2)3o,c = (grad /�, grad/ 2)3o,c ∀/2 ∈ 9�,$ :; %<$' (14) where /2 ∈ 9�,$ :; %<$' is the grad-conform function space for the p-projected source /�,$6$.mn (the projection of /� on mesh of sp p) and the test function /2 defined on <�,$. engineering, technology & applied science research vol. 10, no. 4, 2020, 5953-5957 5955 www.etasr.com quoc: accurate magnetic shell approximations with magnetostatic finite element formulations by … iv. application test the practical test is a shielded problem. it consists of a plate located in the middle of two stranded inductors carrying a magnetomovetive force of 1000 ampere-turns (figure 2). the magnetic shields (screen up and down) cover the plate and the stranded inductors, for �.,��p qe=1 and �.,$qrf =200. the test is performed in the 2-d case. as a sequence, the test at hand is performed in three steps. the solutions on the magnetic scalar potential / of each subdomain are illustrated in figure 3. an initial problem sp q including the stranded inductors alone is solved in a sub-domain without the shielding plate and screens up and down (figure 3(a), /�). fig. 2. geometry of a 2-d shielding problem (d=3÷7.5mm, lpl=2m, ls=2m+2d, hs=0.4m, hy=0.14m, cdx=0.8m, cdy=0.01m, cy=0.2m, cx=0.05m). (a) (b) (c) fig. 3. distribution of magnetic scalar potentials for (a) the stranded inductors alone sp q (/�), (b) addition of ts solution sp p (/$), and (c) volume correction sp k (/k) for thickness d=5mm). the shell approximation sp p that does not include the stranded inductors anymore is then added (figure 3(b), /$). the volume improvements covering the shielding plate and screen up and down are finally introduced to overcome the shell approximations [1, 2], for d=5mm, �.,��p qe =1 and �.,$qrf =200 (figure 3(c), /k ). in a similar way, the distribution of magnetic flux density for each subdomain obtained in each step is shown in detail in figure 4. the sequence from step 1 (sp q) → step 2 (sp p) → step 3 (sp k) is pointed out from top to bottom, for thickness d=5mm. (a) (b) (c) fig. 4. distribution of magnetic flux densities � = �(�� − grad /# for (a) stranded inductors alone sp q, (b) addition of the shell model sp p, and (c) volume correction sp k for thickness d=5mm. the significant errors on the magnetic flux densities of the shell approximation solution (sp p) along the plate are corrected by the volume correction (sp k) indicated in figure 5. the error reaches approximately 35% near the middle of the plate, for d=5mm (�.,��p qe=1 and �.,qrf =200). the volume engineering, technology & applied science research vol. 10, no. 4, 2020, 5953-5957 5956 www.etasr.com quoc: accurate magnetic shell approximations with magnetostatic finite element formulations by … solution is then checked to be similar to the reference solution in the computation from the traditional finite element method (fem) [12-14]. fig. 5. magnetic flux density on the shell solution, volume correction and reference solution along the plate, for d=5mm. (a) (b) fig. 6. ts inaccuracy on the magnetic flux density along the shielding plate (a) before making a correction and (b) after the correction for different values d. fig. 7. relative (improvement) correction of the magnetic flux density along the screen up for different values of d. the relative inaccuracy on the magnetic flux densities before making corrections is presented in figure 6 for various thicknesses. the error can reach 90% at the end regions of the plate, for d=7.5 mm, and 75% for smaller thickness d=3 mm for �.,��p qe=1 and �.,$qrf =200. accurate local improvement with volume correction sp k after improving are less than 15% for d=7.5mm near the plate end, or 10% for d=3 mm. it is worth noting that the error is less than 1% in the middle of the plate for both cases. the relative improvement (correction) of the ts magnetic flux along the screen up is presented in figure 7 for different screen thicknesses. it can reach a percentage up to 47% near the edge of the screen up, for d=7.5mm. it reduces to about 40% for d=5 mm, or 30% for d=3mm, with �.,��p qe=1 and �.,$qrf =200. v. discussion and conclusion in this research, a subdomain technique for coupling thin magnetic shells has been successfully developed with hconformal magnetostatic finite element formulations for improving the errors of the magnetic scalar potential, magnetic flux density, and magnetic flux around the edges and corners appearing from the magnetic shell approximation [1, 2]. the obtained results of the method were found to be quite similar to the reference solution in the computation of the traditional fem [12-14]. the proposed technique has been successfully carried out with a three step sequence. in the future, it could be extended to the case of multilayer-ts with different characteristics. the source-code of the method has been extended from the one subproblem method that was developed by the author with the help of patrick dular and christophe geuzaine at the deparment of electrical engineering and computer science, university of liege, belgium. it will be ran in the background of the getdp and gmsh (http://getdp.info and http://gmsh.info) as open source code. references [1] c. geuzaine, p. dular, and w. legros, “dual formulations for the modeling of thin conducting magnetic shells,” compel the international journal for computation and mathematics in electrical and electronic engineering, vol. 18, no. 3, pp. 385–398, jan. 1999, doi: 10.1108/03321649910274946. [2] c. geuzaine, p. dular, and w. legros, “dual formulations for the modeling of thin electromagnetic shells using edge elements,” ieee transactions on magnetics, vol. 36, no. 4, pp. 799–803, jul. 2000, doi: 10.1109/20.877566. [3] p. dular and r. v. sabariego, “a perturbation method for computing field distortions due to conductive regions with $\mmb h$ -conform magnetodynamic finite element formulations,” ieee transactions on magnetics, vol. 43, no. 4, pp. 1293–1296, apr. 2007, doi: 10.1109/tmag.2007.892401. [4] p. dular, r. v. sabariego, c. geuzaine, m. v. ferreira da luz, p. kuopeng, and l. krähenbühl, “finite element magnetic models via a coupling of subproblems of lower dimensions,” ieee transactions on magnetics, vol. 46, no. 8, pp. 2827–2830, aug. 2010, doi: 10.1109/tmag.2010.2044028. [5] p. dular, v. q. dang, r. v. sabariego, l. kahenbuhl, and c. geuzaine, “correction of thin shell finite element magnetic models via a subproblem method,” ieee transactions on magnetics, vol. 47, no. 5, pp. 1158–1161, may 2011, doi: 10.1109/tmag.2010.2076794. [6] v. q. dang, p. dular, r. v. sabariego, l. krahenbuhl, and c. geuzaine, “subproblem approach for thin shell dual finite element 0 0.2 0.4 0.6 0.8 1 1.2 -1 -0.5 0 0.5 1 m a g n e ti c f lu x d e n si ty 1 0 -3 (t ) position along the shielding plate (m) d=5mm, ts approximation d=5mm, correction d=5mm, reference 0 20 40 60 80 100 -1 -0.5 0 0.5 1 e rr o rs b e fo re c o rr e c ti o n b ( % ) position along the shielding plate (m) d=3mm d=5mm d=7.5mm 0.1 1 10 100 -1 -0.5 0 0.5 1 e rr o rs a ft e r c o rr e c ti o n b ( 1 0 -2 % ) position along the shielding plate (m) d=3mm d=5mm d=7.5mm 0 20 40 60 80 100 -1 -0.5 0 0.5 1 c o rr e c ti o n o f m a g n e ti c f lu x ( % ) position along the screen up (m) d=3mm d=5mm d=7.5mm engineering, technology & applied science research vol. 10, no. 4, 2020, 5953-5957 5957 www.etasr.com quoc: accurate magnetic shell approximations with magnetostatic finite element formulations by … formulations,” ieee transactions on magnetics, vol. 48, no. 2, pp. 407–410, feb. 2012, doi: 10.1109/tmag.2011.2176925. [7] d. q. vuong, “modeling of magnetic fields and eddy current losses in electromagnetic screens by a subproblem method,” tnu journal of science and technology, vol. 194, no. 1, pp. 7–12, 2019. [8] v. d. quoc and c. geuzaine, “using edge elements for modeling of 3-d magnetodynamic problem via a subproblem method,” science and technology development journal, vol. 23, pp. 439–445, feb. 2020, doi: 10.32508/stdj.v23i1.1718. [9] d. q. vuong and n. d. quang, “coupling of local and global quantities by a subproblem finite element method – application to thin region models,” advances in science, technology and engineering systems journal (astesj), vol. 4, no. 2, pp. 40–44, 2019, doi: 10.25046/aj040206. [10] p. dular, r. v. sabariego, m. v. ferreira da luz, p. kuo-peng, and l. krahenbuhl, “perturbation finite element method for magnetic model refinement of air gaps and leakage fluxes,” ieee transactions on magnetics, vol. 45, no. 3, pp. 1400–1403, mar. 2009, doi: 10.1109/tmag.2009.2012643. [11] v. d. quoc, “robust correction procedure for accurate thin shell models via a perturbation technique,” engineering, technology & applied science research, vol. 10, no. 3, pp. 5832–5836, jun. 2020. [12] s. koroglu, p. sergeant, r. v. sabariego, v. q. dang, and m. d. wulf, “influence of contact resistance on shielding efficiency of shielding gutters for high-voltage cables,” iet electric power applications, vol. 5, no. 9, pp. 715–720, nov. 2011, doi: 10.1049/iet-epa.2011.0081. [13] k. abubakri and h. veladi, “investigation of the behavior of steel shear walls using finite elements analysis,” engineering, technology & applied science research, vol. 6, no. 5, pp. 1155–1157, oct. 2016. [14] g. meunier, the finite element method for electromagnetic modeling. new york, ny, usa: john wiley & sons, ltd, 2010. [15] c. geuzaine, b. meys, f. henrotte, p. dular, and w. legros, “a galerkin projection method for mixed finite elements,” ieee transactions on magnetics, vol. 35, no. 3, pp. 1438–1441, may 1999, doi: 10.1109/20.767236. [16] p. e. farrell and j. r. maddison, “conservative interpolation between volume meshes by local galerkin projection,” computer methods in applied mechanics and engineering, vol. 200, no. 1, pp. 89–100, jan. 2011, doi: 10.1016/j.cma.2010.07.015. [17] g. parent, p. dular, f. piriou, and a. abakar, “accurate projection method of source quantities in coupled finite-element problems,” ieee transactions on magnetics, vol. 45, no. 3, pp. 1132–1135, mar. 2009, doi: 10.1109/tmag.2009.2012652. author’s profile vuong dang quoc received his phd degree in 2013 from the faculty of applied sciences at the university of liege in belgium. after that he came back to the hanoi university of science and technology in september 2013, where he is currently working as the director of the training center of electrical engineering, school of electrical engineering, hanoi university of science and technology. dr. vuong dang quoc’s research domain encompasses modeling of electromagnetic systems by coupling of subproblem method with application to thin shell models. microsoft word rev-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 155-161 155 www.etasr.com ateekh-ur-rehman and usmani: field engineers’ scheduling at oil rigs: a case study field engineers’ scheduling at oil rigs: a case study dr. ateekh-ur-rehman department of industrial engineering king saud university, riyadh, saudi arabia arehman@ksu.edu.sa yusuf usmani department of industrial engineering king saud university, riyadh, saudi arabia yusmani@ksu.edu.sa abstract— oil exploration and production operations face a number of challenges. professional planners have to design solutions for various practical problems or issues. however, the time consumed is often very extensive because of the large number of possible solutions. further, the matter of choosing the best solution remains. the present paper investigates a problem related to leading companies in the energy and chemical manufacturing sector of the oil and gas industry. each company’s field engineers are expensive and valuable assets. therefore, an optimized roster is rather important. in the present paper, the objective is to design a field engineers’ schedule which would be both feasible and satisfying towards the various demands of rigs, with minimum operational cost to the company. an efficient and quick optimization technique is presented to schedule the shifts of field engineers. keywordsfied engineers (fe); oil rigs; scheduling; uneven demand i. introduction scheduling is the allocation of resources over time to perform a collection of tasks. a workforce schedule that ensures appropriate service and production level is a key management function and has high practical importance. among the terms used, predictive scheduling describes the design of a schedule in advance whereas reactive scheduling describes the adaptation of the schedule according to actual events [1]. however, due to the exponential size of the scheduling problem it is extremely difficult to find good solutions to these highly constrained and complex problems [2]. further, providing the right people at the right time at the right cost whilst achieving a high level of employee satisfaction is another critical problem [2]. personnel scheduling, or rostering, is the process of constructing work timetables for the staff so that ab organization can satisfy the demand for its goods or services [2-3]. the origin of staff scheduling and rostering can be traced back to edie’s work on traffic delays at toll booths [4]. since then, staff scheduling and rostering methods have been applied to transportation systems, such as airlines and railways, health care systems, emergency services, such as the police, ambulance and fire brigade, call centers and many other service organizations such as hotels, restaurants and retail stores. therefore, extensive model and algorithm development has been carried out in the literature on crew scheduling and rostering in transportation systems, nurse scheduling in health care systems, and tour scheduling for various service systems. a focused review on applications of both personnel and vehicle scheduling can be found in [5] where scheduling objectives, constraints, and methodologies are surveyed for each application area. personnel scheduling has been a subject of investigation over the past 30 years with a survey in every decade. an application of such problems is presented in the following section. the present paper is concerned with the [r, n] days-off scheduling problem, where for a given cycle of n periods each field engineer is assign a work-stretch of r consecutive periods and break of ‘n-r’ consecutive periods. the focus is to address the issue related to uneven demand of field engineers for the oil rigs. the primary objective of the days-off scheduling problem is to minimize the workforce size, i.e., total number of field engineers assigned. the paper is organized into seven sections. section ii presents literature survey on days-off scheduling approaches. section iii presents the problem in detail. the uneven demands procedures for determining the minimum workforce size and assigning workers (field engineers) to days-off patterns are presented in sections iv and v with an example. section vi presents the case application of the model in an oil rig company. finally, the last section concludes with the discussion. ii. literature survey scheduling problems and their treatments are very diverse. the problem of designing a staffing schedule or roster (sometimes known as a tour) subject to a particular set of constraints was solved by williams [6]. early examples of the use of linear programming in scheduling problems were given by baker and magazine [7] and bartholdi et al. [8]. the solution of a problem with some similarities was also given by townsend [9]. an aspect of this problem was the existence of several different duties which had to be distributed fairly amongst crews. the rules governing the pattern of days on and days off were simpler. in aircrew scheduling, as described by ryan [10], with rosters used as inputs, one aspect of the technique was allocating rosters to staff. the problem solved in his paper was the finding of a feasible schedule. sydney [11] proposed the goal programming models for an integrated problem of crew duties assignment, for baggage services section staff. easton and rossin [12] used a heuristic approach to find improvements regarding the set of a feasible schedule. the problem considered by hung [13-14] had the added complication of non-homogenous labor force (one kind of etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 155-161 156 www.etasr.com ateekh-ur-rehman and usmani: field engineers’ scheduling at oil rigs: a case study worker can replace another, but not vice versa) factor. bechtold et al. [15] exemplify the approach of finding the few schedules, out of the numerous feasible schedules, which maximize certain desirable criteria. hojati and patil [16] considered the scheduling of heterogeneous part-time employees of service organizations. rafael [17] described how a simple procedure, combining random and greedy strategies with heuristics, has been successfully applied in assigning guard shifts to the physicians in a department. workforce scheduling problems are traditionally classified into three types i.e. shift scheduling, days-off scheduling, and roster scheduling. nanda and browne [18] provided a thorough survey of literature on these three types. narasimhan [19] reflected on multiple worker types, giving each worker two days off per week. emmons and burns [20] considered a workforce composed of n worker types, but assume a constant employee demand for all days of the week. the days-off scheduling model proposed by hung [21] was based on two assumptions. the first assumption is x workers are required on weekdays and y workers on weekends, and the second assumption was that each worker must have a out of b weekends off. alfares [22] presented a single-shift optimum solution technique for 3-day workweeks. similarly, alfares [23] extended the expression for the minimum workforce size, and included it as a constraint in the linear programming. backtracking techniques was used by musliu et al. [24] to obtain cyclic schedules (cyclic assignments of shifts to employees) that are optimal for weekends off, long weekends off and also in terms of the regularity of weekends off. some practical general scheduling applications can be found in the work of pinedo and chao [25], blazewicz [26], and pinedo [27]. the notion of skill is well known in the field of personnel scheduling [28]. ne´ron [29] consider the resource constrained scheduling problem where resources are staff members that have one or more skill. cai and li [30] considered the problem of scheduling staff with mixed skills. these papers tend to emphasize problems in which the same numbers of periods are worked each cycle. some attention is given to the important practical point of the period worked each cycle being contiguous. iii. problem definition the problem on hand is concerned with one of the leading companies in the energy and chemical manufacturing sector of the oil and gas industry. the company’s field engineers are typically one of its most expensive as well as one of its most valuable assets. therefore, scheduling needs focus on how to allocate field engineers to satisfy the forecasted requirement of field engineers on duty to cover the workload. questions that also needs answering are: what are the best roster assigning field engineers to shifts and which of them should cover a vacant shift? the objective is to reproduce (r, n) day’s on-off assigning problem, considering a ten week cycle. here for a given cycle of 70 consecutive days, each field engineer is assigned one work stretch of 42 consecutive workdays (i.e. break of 28 consecutive days off). the main objective is to reduce the cost by optimizing the field engineers’ schedule i.e. the total number of field engineers assigned. in order to reduce assignment cost, it is required to minimize the number of active days-off patterns. in the present paper, an added goal is to assign filed engineers to different rigs according to job requirement on particular oil rig. it is also evident from the literature survey, that there is the need to address issues related to mostly uneven demand of field engineers for the oil rigs. under such circumstances field engineers are assigned to different shift types, each involving a different pattern of “on” and “off” work periods, in such a way that the number of field engineers who are “on” in each period is sufficient to meet the demand in that period. the objective is to minimize the total cost of the shift. if the cost of field engineer to a shift is the same for all shift types, then the objective is to minimize the amount by which the capacity provided by the schedule exceeds the demand. the tool used is microsoft ms solver. thus, focus is given to scheduling field engineers to satisfy uneven demands of different oil rigs. the objective is to minimize the total cost of the shift. the formulation of even and uneven demand scheduling problem, the details of the solution and analysis are presented in the subsequent sections 4 and 5. iv. field engineers’ shifts scheduling formulation in practice, when there is a case of uneven demand of field engineers at oil rigs, the field engineers are scheduled to different shifts, involving a different pattern of “on” and “off” work periods, in such a way that the number of field engineers who are “on” in each period is sufficient to meet the demand in that period. the present paper is concerned with the [r, n] days-off scheduling problem, where for a given cycle of n periods each field engineer is assign a work-stretch of r consecutive periods and break of ‘n-r’ consecutive periods let’s consider a [r, n] days-off scheduling problem, where for a given cycle of n periods each field engineer is assign a work-stretch of r consecutive periods. there are ‘n’ schedule patterns. each field engineer is assigned to exactly one shift pattern, so that he/she will be on ‘n-r’ consecutive periods off. the scheduling for ‘m’ periods, where, i b = number of field engineer required on oil rigs during period i. j x = number of field engineer assigned to shift pattern j. i e =number of field engineer called on emergency in period i. j c = cost of a field engineer on normal duty assigned to shift pattern j. ei c = cost of a field engineer called on emergency in period i. the problem can be formulated as presented hereunder. etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 155-161 157 www.etasr.com ateekh-ur-rehman and usmani: field engineers’ scheduling at oil rigs: a case study let constraint matrix ][a a ij= , where row ‘i’ corresponds to period and column ‘j’ corresponds to shift pattern. so that, ij a = 1, if period i is an ‘on’ period in shift pattern j. = 0, otherwise. ∑∑ == += m 1i iei n 1j jj ecxcmin z subjected to ( ) .m……1,2, = ifor bexa ii n 1j jji ≥+∑ = ( ) .m……1,2, = ifor xexa n 1j ji n 1j jji ∑∑ == ≤+ ( )2,....n. 1, = j and ..m.……1,2 = ifor integer and 0e,x ij ≥ the objective function is to minimize the field engineer scheduling cost including the cost of calling the field engineers on emergency if required. there is the constraint that one should have enough field engineers to operate the rigs in each period. so, the first constraint set ensures that sufficient number of filed engineers is provided to meet or exceed the minimum demand of field engineers at oil rigs for the period. there is also another constraint that, a field engineer should be called on emergency duty only when he is on an off period. the second constraint limits the availability of field engineers on emergency basis in every period. the third constraint set place non-negativity and integer restriction on the decision variables. the application of the above formulation is illustrated with an example hereunder. a. computational illustration let’s consider the situation of a cycle of 10 weeks where field engineers are schedules on 6 weeks consecutive on shift and 4 weeks consecutive off shift. ms solver is used to find a schedule that uses the fewest number of field engineers and meets all weekly demands of field engineers at oil rigs. there is a need of certain number of field engineers to meet the oil rigs’ demand. a cycle consists of 10 periods. in other words there are 10 schedule patterns. for computational illustration as presented in table i, there are ten different schedule patterns (s1 to s10) each pattern have consecutive 4 weeks off (represented in column b). there are ten weeks (w1 to w10). as presented in table i, cell (c2:c11) in column c which have been set equal to zero at the start. ms excel refers to these cells as changing cells in ms solver. these changing cells are the number of field engineers required to meet demand. as the objective is to minimize cost (value in cell c15), it is calculated by multiplying total demand required during 10 week periods and pay per field engineer per day. ms solver refers to this as the “target cell” and it corresponds to the objective function defined. as presented in table i, cells d12 to m12 the allocation total field engineers for a period is calculated by multiplying and adding the number of workmen in cells c2:c11 with cells d2:d11 for result of cell d12 (d12=c1*d1+…..+c11*d11). the results of cells e12 through m12 will be calculated in same manners. the oil rig demands in these periods are entered in cells d13 to m13. using ms solver, the objective to minimize the cost for ten periods by optimizing the number of field engineers required to meet demand is calculated and presented in cell c15 of table i. ms solver acknowledges that a solution was found that appears to be optimal and the obtained results are presented in table i. from the results one can see that the number of employees in different schedule pattern is allocated. table i. scheduling of field engineer (fe) for different shift pattern using ms solver columns → rows↓ a b c d e f g h i j k l m week schedules 1 weeks off fe 1 2 3 4 5 6 7 8 9 10 2 s1 w1,w2,w3,w4 2 0 0 0 0 1 1 1 1 1 1 3 s2 w2,w3,w4,w5 3 1 0 0 0 0 1 1 1 1 1 4 s3 w3,w4,w5,w6 2 1 1 0 0 0 0 1 1 1 1 5 s4 w4,w5,w6,w7 1 1 1 1 0 0 0 0 1 1 1 6 s5 w5,w6,w7,w8 3 1 1 1 1 0 0 0 0 1 1 7 s6 w6,w7,w8,w9 1 1 1 1 1 1 0 0 0 0 1 8 s7 w7,w8,w9,w10 2 1 1 1 1 1 1 0 0 0 0 9 s8 w1,w8,w9,w10 1 0 1 1 1 1 1 1 0 0 0 10 s9 w1,w2,w9,w10 6 0 0 1 1 1 1 1 1 0 0 11 s10 w1,w2,w3,w10 0 0 0 0 1 1 1 1 1 1 0 12 total fe scheduled 21 12 10 14 13 12 14 14 14 11 12 13 weekly total demand of fe 12 10 14 12 12 14 14 14 10 12 14 cost/fe/week $3500 15 cost for 10 period $441000 etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 155-161 158 www.etasr.com ateekh-ur-rehman and usmani: field engineers’ scheduling at oil rigs: a case study the solution presented will not satisfy the oil company requirements to plan work shifts to approximately match the requests as per service. there is also the issue of how will the solution affect the utilization of personnel time, group morale and time required to perform customer service. the subsequent section presents field engineers’ scheduling using heuristic model. v. a heuristic approach any oil company wants to plan work shifts to approximately match the requests for the service. it is also concerned about the schedules affecting the utilization of personnel time, group morale and time required to perform the required service. in the present section, the same scenario as presented in section 4, which relates to 6 weeks on and 4 week off shift schedules to weekly numbers of field engineers available, is considered. a heuristic model is used to find a schedule that uses the smaller number of field engineers and meets all oil rigs’ demands. the requirements of the modelcan be formulated in the following question: what is the number of required field engineers and what ways could be used to reduce the amount of slack in the work shift schedules? thus, the model uses a “work shift heuristic procedure” to develop shift schedules for field engineers. the heuristic rule is stated as: choose two consecutive periods with least total number of field engineers required. in the case of ties, arbitrarily select a pair and continue. this heuristic was originally developed by baker and magazine [7]. for the problem on hand as presented in section 3, the company needs a field engineers’ schedule that provides six weeks on duty and four weeks off which minimizes the amount of total slack capacity. for simplicity let’s consider one cycle of 10 weeks and each week stands for seven working days. the number of workmen required in each week is the same as in cells d13 to m13 of table 1, the same is presented in table ii. the subsequent subsection presents the steps followed to illustrate the above mentioned heuristic approach using an example. a. steps step 1 find all the pairs of consecutive days that exclude the maximum daily requirements. select the unique pair that has the lowest total requirements for the 4 periods (weeks). periods 3 and 7 contains the maximum requirements (7), and periods 1, 2, 9 and 10 have the lowest total requirements. therefore, field engineer 1 is scheduled to work for period 3 to period 8 without a break, as presented in table ii. step 2 if a tie occurs, choose one of the tied pairs or ask the field engineer to make a choice and continue. table ii. field engineers (fe) schedule using heuristic approach week 1 2 3 4 5 6 7 8 9 10 total demand of field engineers 5 5 7 6 5 6 7 6 5 6 schedule of field engineer 1 off off on on on on on on off off net demand after 1 st iteration 5 5 6 5 4 5 6 5 5 6 schedule of field engineer 2 on on off off off off on on on on net demand after 2 nd iteration 4 4 6 5 4 5 5 4 4 5 schedule of field engineer 3 off off on on on on on on off off net demand after 3 rd iteration 4 3 5 4 3 4 4 3 4 5 schedule of field engineer 4 on on on on off off off off on on net demand after 4 th iteration 3 2 4 3 3 4 4 3 3 4 schedule of field engineer 5 off off off off on on on on on on net demand after 5 th iteration 3 2 4 3 2 3 3 2 2 3 schedule of field engineer 6 off off on on on on on on off off net demand after 6 th iteration 3 2 3 2 1 2 2 1 2 3 schedule of field engineer 7 on on on on off off off off on on net demand after 7 th iteration 2 1 2 1 1 2 2 1 1 2 schedule of field engineer 8 on off off off off on on on on on net demand after 8 th iteration 1 1 2 1 1 1 1 0 0 1 schedule of field engineer 9 on on on on on off off off off on net demand after 9 th iteration 0 0 1 0 0 1 1 0 0 0 schedule of field engineer 10 off on on on on on on off off off total total fe scheduled, c 5 5 7 7 6 6 7 6 5 6 60 total demand of fe, d 5 5 7 6 5 6 7 6 5 6 58 slack, c-d 0 0 0 1 1 0 0 0 0 0 2 etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 155-161 159 www.etasr.com ateekh-ur-rehman and usmani: field engineers’ scheduling at oil rigs: a case study step 3 subtract the requirements satisfied by the field engineer 1 from the net requirements for each period (week) the field engineer is to work and repeat step one. in continuation with above step it is observed that periods 1, 2, 9 and 10 has the lowest total requirements. therefore, field engineer 2 is scheduled to work for period 3 to period 8 as presented in table ii. step 4 repeat steps 1 through 3 until all the requirements have been satisfied. after field engineers 1, 2, and 3 have reduced the requirements, the period with the lowest requirements changes and field engineer 4 will be scheduled for periods 6, 7, 8, 9, 10 and 1. the above steps 1 to 3 are repeated until the schedule for individual field engineers can be planned such that all demands are met. the details are presented in table ii. the application of the above methods and the discussion is presented in the following section. vi. field engineers’ scheduling in an oil company: a case study the above presented model of uneven demand has been applied successfully at an oil company. the ultimate objective was to optimize the number of field engineers required to meet the demand and minimizing the total cost. the relevant data was collected for 6 months, from january 2009 to june 2009. it is observed that the numbers of field engineers available for oil rigs are twenty. the number of jobs “running” during this period was four to seven. two field engineers were required on each job. the schedule for each field engineer is considered as 42 days on shift / 28 days off shift (continuous 6 weeks on and 4 weeks off). the details of the data available and the scheduling cost without using any optimizing techniques are as presented in table ii. it’s observed that without using an optimization tool the field engineers are allotted throughout the shifts. because of this approach during a period of uneven demand the company had to call field engineers (particularly those that were on an off shift) back on duty on emergency call with higher bonuses. it was observed that field engineers were called on emergency duties twenty times during periods of high demand, whereas there were some incidences were demand was too low and the company was holding the field engineers on rigs without work, which is an idle cost incurred by the company. as presented in table ii the total cost incurred by the company without following an optimization technique for field engineer scheduling is found to be $1,169,000. after application of the proposed models it is observed that there is no need to call field engineers on emergency duty. the brief results obtained after the application of the proposed model are as presented in table iv. as presented in table iv, the total cost incurred by the company with following optimization techniques for field engineer scheduling is found to be $945,000. table iii. scheduling result and total cost before applying scheduling optimization techniques y e a r 2 0 0 9 m o n th w e e k 5 o . 5 o . o f jo b s f ie ld e n g in e e r s r e q u ir e d f ie ld e n g in e e r s p e r o n sh if t f ie ld e n g in e e r s p e r o ff sh if t t o ta l fi e ld e n g in e e r s f ie ld e n g in e e r s c a ll e d o n e m e r g e n c y f ie ld e n g in e e r s s e a ti n g id le 1 4 8 8 12 20 2 6 12 12 8 20 3 6 12 11 9 20 1 4 7 14 12 8 20 2 5 5 10 12 8 20 2 6 7 14 12 7 19 2 7 5 10 9 10 19 1 8 4 8 10 10 20 2 9 6 12 12 8 20 10 6 12 10 10 20 2 11 7 14 12 8 20 2 12 6 12 11 9 20 1 13 6 12 10 10 20 2 14 5 10 10 10 20 15 7 14 12 8 20 2 16 6 12 12 8 20 17 6 12 11 8 19 1 18 7 14 12 8 20 2 19 7 14 14 6 20 20 7 14 12 8 20 2 21 5 10 12 8 20 2 j a n u a r y t o j u n e 22 6 12 12 8 20 total 22 131 262 248 189 437 20 6 a. number of days per shift 7 b. cost per field engineer per day (if on duty) $500 c. extra cost per day if field engineer called on emergency duty $2000 d. total number of field engineers on normal shift 248 e. total number of field engineers called on emergency duty 20 f. total number of field engineers seating idle on normal duty 6 g. total cost of field engineers on normal duties = (a x b x d) $868000 h. total extra cost if field engineers called on emergency duty = (a x c x e) $280000 i. total cost for idle field engineers = (a x b x f) $21000 j. total cost for period = (g + h + i) $1169000 etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 155-161 160 www.etasr.com ateekh-ur-rehman and usmani: field engineers’ scheduling at oil rigs: a case study table iv. scheduling result and total cost after applying scheduling optimization techniques y e a r 2 0 0 9 m o n th w e e k 5 o . 5 o . o f jo b s f ie ld e n g in e e r s r e q u ir e d f ie ld e n g in e e r s p e r o n sh if t f ie ld e n g in e e r s p e r o ff sh if t t o ta l fi e ld e n g in e e r s f ie ld e n g in e e r s c a ll e d o n e m e r g e n c y f ie ld e n g in e e r s s e a ti n g id le 1 4 8 8 12 20 2 6 12 12 8 20 3 6 12 12 8 20 4 7 14 14 6 20 5 5 10 10 10 20 6 7 14 14 5 19 7 5 10 11 8 19 1 8 4 8 8 12 20 9 6 12 12 8 20 10 6 12 12 8 20 11 7 14 14 6 20 12 6 12 12 8 20 13 6 12 12 8 20 14 5 10 11 9 20 1 15 7 14 14 6 20 16 6 12 13 7 20 1 17 6 12 12 7 19 18 7 14 14 6 20 19 7 14 14 6 20 20 7 14 14 6 20 21 5 10 11 9 20 1 j a n u a r y t o j u n e 22 6 12 12 8 20 total 22 131 262 266 171 437 0 4 a. number of days per shift 7 b. cost per field engineer per day (if on duty) $500 c. extra cost per day if field engineer called on emergency duty $2000 d. total number of field engineers on normal shift 266 e. total number of field engineers called on emergency duty 0 f. total number of field engineers seating idle on normal duty 4 g. total cost of field engineers on normal duties = (a x b x d) $931000 h. total extra cost if field engineers called on emergency duty = (a x c x e) $00000 i. total cost for idle field engineers = (a x b x f) $14000 j. total cost for period = (g + h + i) $945000 vii. conclusion and discussion the present paper demonstrated the [r, n] days-off scheduling problem. the focus is to address the issue related to uneven demand of field engineers for the oil rigs. here the primary objective of the days-off scheduling problem was to minimize the workforce size, i.e., total number of field engineers assigned, in order to reduce the transportation costs. however, a model that does not consider demands, which may get cancel or amended unpredictably at the last moment due to unavoidable reason, faces limitations. as a result, the schedule of field engineers can be subjected to last minute changes. however, it is possible to minimize the number of field engineers required on site, which results in subsequent cost savings. on occasion, when field engineers are called (on emergency) for work before his or her days off the extra cost of transportation and payroll occurs. all these can be optimized by using the approach suggested in this paper. the company can benefit not only in terms of saving but also in terms of providing to its field engineers life quality leading to increased retention. generally, company’s planners may modify provisional work assignments and review business objectives at any time, since the working environment itself (weather, traffic conditions) is unpredictable. owing to limitations of the study, the present paper includes limited variables regarding field engineers’ scheduling. as a future goal, the above model can include added variables, such as stochastic demand of field engineers at oil rigs and working conditions. acknowledgment authors would like thank mr. vinod agrahari of the client organization for introducing them to this problem and his help specially in obtaining data. references [1] s. f. smith, “knowledge-based production management: approaches, results and prospects”, production planning & control, vol. 3, no. 4, pp. 350-380, 1992 [2] a. t. ernst, h. jiang, m. krishnamoorthy, d. sier, “staff scheduling and rostering: a review of applications, methods and models”, european journal of operational research, vol. 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[30] x. cai, k. n. li, “a genetic algorithm for scheduling staff of mixed skills under multi-criteria”, european journal of operational research, vol. 125, no. 2, pp. 359–369, 2000 engineering, technology & applied science research vol. 8, no. 3, 2018, 2892-2896 2892 www.etasr.com iqbal et al.: effect of maximum aggregate size on the bond strength of reinforcements in concrete effect of maximum aggregate size on the bond strength of reinforcements in concrete shahid iqbal department of civil engineering cecos university of it and emerging sciences peshawar, pakistan shahid.iqbalmce@gmail.com naqeeb ullah department of civil engineering cecos university of it and emerging sciences peshawar, pakistan naqibmarwat@hotmail.com ahsan ali department of civil engineering quaid-e-awam university college of engineering, science & technology larkana, pakistan ahsanone@gmail.com abstract-the bond between reinforcements and concrete is the only mechanism that transfers the tensile stresses from concrete to reinforcements. several factors including chemical adhesion, roughness and reinforcement interface and bar bearing affect the bond strength of reinforcements with concrete. this work was carried out considering another varying factor which is maximum aggregate size. four mixes of concrete with similar compressive strengths but different maximum aggregate sizes of 25.4mm, 19.05mm, 12.7mm and 9.53mm were used with the same bar size of 16mm. compressive strength, splitting tensile strength and bond strength for each concrete mix were studied. test results depict a slight increase in compressive and splitting tensile strength with decrease in maximum aggregate size. the bond strength remained at the same level with decrease in maximum aggregate size except at maximum aggregate size of 9.53mm when there was a drop in bond strength, despite better compressive and splitting tensile strengths. aci-318 and fib2010 codes equation for bond strength calculation work well only when the maximum aggregate size is 12.7mm and above. therefore, maximum aggregate size is critical for bond strength when smaller size aggregates are used. keywords-concrete; aggregate size; pullout test; bond strength i. introduction the role of the bond of reinforcement in concrete is of great importance. when the concrete member is loaded, tensile stresses from steel to concrete are transferred through the bond. therefore, to ensure the safety of concrete, proper bonding between reinforcing steel and concrete is essential when the concrete member cracks, tensile stresses are resisted by the reinforcement, reinforcement slip occurs which is resisted by friction and reinforcement bearing producing bond stresses [1]. bond behavior of steel reinforcements with concrete is an important aspect which affects the performance of reinforced concrete [2-6]. there are three main components of bond between reinforcements and concrete: friction, chemical adhesion and mechanical interlocking of deformations in steel bars. the factors affecting bond strength include strength and cover of concrete around reinforcement, geometry and yielding strength of reinforcement, embedded length, type of aggregates and admixtures used [1, 7-10] an increase of up to 20% in pullout load is reported with increase of concrete cover depth from 40mm to 70mm [9]. studying the effect of concrete cover on bond behavior, it is reported that the bond strength increases but the rate of increase decreases with the increase of concrete cover [10]. thus when concrete cover increases, initially the increase in bond strength is more pronounced to further increase in concrete cover. authors in [11] investigated the bond behavior of reinforcements in lightweight self-compacting concrete and reported 30% lower bond strength for all lightweight scc compared to normal weight concrete. corrosion also plays an import role in the bond performance. it is reported that there is a decrease in bond strength when corroded reinforcements are used [12]. for this purpose protective layers against corrosion may be used. it is reported that, galvanization of reinforcements can improve its resistance against carbonation and can extend the life of reinforced concrete structures [13]. investigating the effect of bar size on the bond strength of reinforcements in concrete, it is reported that bond strength of smaller bars (10mm diameter) is 21% higher than that of the larger bars (20mm) [1]. size of aggregate may be another bond influencing factor. to the best of our knowledge, there is limited literature available on the effect of aggregate size on the bond strength. therefore, this study is conducted to investigate the effect of aggregate size on the bond behavior of reinforcements in concrete. bond strength is calculated by dividing the maximum pullout load by the surface are of the reinforcement bar given by (1). μ = (1) where μ is bond strength, p is the maximum pullout load, l and d are embedded length and diameter of bar used. ii. materials and methodology a. materials used normal weight fine aggregates and crushed coarse aggregates, supplied by a local material supplier, were used. four different coarse aggregates having different maximum aggregate sizes i.e. 9.5mm, 12.5mm, 19mm, and 25mm were used (figure 1). the maximum sizes of the aggregates were engineering, technology & applied science research vol. 8, no. 3, 2018, 2892-2896 2893 www.etasr.com iqbal et al.: effect of maximum aggregate size on the bond strength of reinforcements in concrete selected on the basis of astm standard sieves. cem-i 42.5n cement, supplied by a local cement manufacturer (cherat cement) was used for all the concrete mixes. fig. 1. coarse aggregates b. experimental program fresh and hardened concrete properties were investigated for each mix. workability and density were investigated on the fresh concrete while compressive strength, splitting tensile strength and bond strength were studied on the hardened concrete. workability and density were found using [14] and [15] standards. six cylinder specimens 100mm in diameter and 200mm in height were casted from each concrete mix and cured in water tank as defined in [16]. three cylinders of each mix were tested for compressive strength as per [17] at 28 days concrete age, by application of constant loading rate of 0.25mpa/sec. three cylinder specimens of each concrete were tested for splitting tensile strength as per [18] at the concrete age of 28 days by load application at constant rate of 1mpa/min. three cube samples were casted embedded with 16mm diameter bars to test the bond strength as per [19]. the size of cube was kept at 150mmx150mmx150mm which is the most common cube size in concrete tests. these samples were cured in water tank for 28 days and tested in pullout test with pullout load applied at a constant rate of 0.1kn/sec. pullout test is a widely practiced and easy to perform test used to investigate the bond strength. it has been used by different researchers to study the factors affecting bond strength i.e. concrete compressive strength, size and geometry of reinforcement bars and active and passive confinement [20, 21]. the pull-out sample and testing assembly are shown in figure 2. iii. results and discussion a. concrete mix design trial mixes were conducted to finalize the concrete mix with maximum aggregate size of 25mm and target 28 day compressive strength of 20mpa. from previous studies [22-24] and trials of concrete compressive strength tests of each mix, it was observed that with the decrease in maximum aggregate size of coarse aggregates the compressive strength of concrete increases. the study aims at investigating the effect of aggregate size on the bond strength keeping all the other parameters constant. therefore, to achieve similar compressive strengths and compensate for this variation of compressive strength due to change in maximum aggregate size, the cement quantity was reduced by 2% for every consecutive reduction of coarse aggregate maximum size with increase in w/c ratio by 0.005. mix compositions for all the mixes are summarized in table i. the concrete mixes containing maximum aggregate sizes of 25mm, 19mm, 12.5mm and 9.5mm were nominated as mix-25, mix-19, mix-12.5 and mix-9.5 respectively. fig. 2. pull-out specimen and testing arrangement table i. concrete mix composition concrete type cement (kg/mᵌ) coarse aggregate (kg/mᵌ) fine aggregate (kg/mᵌ) water (kg/mᵌ) w/c ratio mix-25 400 800 880 192 0.48 mix-19 392 800 880 190 0.485 mix-12.5 384 800 880 188 0.49 mix-9.5 376 800 880 186 0.495 b. fresh concrete properties the test results for fresh concrete properties are presented in table ii. test results for fresh concrete properties indicate decrease in slump with decrease in maximum aggregate size while concrete density remains unchanged. the relation is graphically represented in figure 3. table ii. fresh concrete properties concrete type maximum coarse aggregate size (mm) slump (mm) concrete density (kg/m3) mix-25 25 89 2421 mix-19 19 83 2417 mix-12.5 12.5 78 2412 mix-9.5 9.5 65 2408 c. hardened concrete properties the test results for hardened concrete properties of all the concrete types are presented in table iii. instances of the tests of compressive strength, splitting tensile strength and pull-out strength tests that were conducted in the lab are shown in figure 4. 1) compressive strength the tests results for compressive strength of all concrete mixes are summarized in table iii. although the cement engineering, technology & applied science research vol. 8, no. 3, 2018, 2892-2896 2894 www.etasr.com iqbal et al.: effect of maximum aggregate size on the bond strength of reinforcements in concrete content decreased intentionally with decrease in maximum aggregate size to keep the compressive strengths of all concretes at the same level in order to study only the effect of maximum aggregate size on bond strength, there is still indication of increase in concrete compressive strength when the maximum aggregate size in concrete reduces. the relation is graphically shown in figure 5. fig. 3. fresh concrete properties variation table iii. hardened concrete properties concrete type maximum coarse aggregate size (mm) compressive strength (mpa) splitting tensile strength (mpa) bond strength (mpa) mix-25 25 21.22 2.76 7.76 mix-19 19 21.82 2.78 7.93 mix-12.5 12.5 21.95 2.97 7.88 mix-9.5 9.5 22.02 3.11 7.15 fig. 4. hardened concrete tests fig. 5. compressive strength variation 2) splitting tensile strength the test results for all concrete types are presented in table iii. similar to compressive strength, there is an increasing trend in splitting tensile strength with decrease in maximum aggregate size used despite the decrease in cement content. this trend is graphically presented in figure 6. fig. 6. splitting tensile strength variation 3) bond strength the main objective of this study was to investigate the effect of maximum aggregate size on the bond strength of reinforcements with concrete. results for bond strength are summarized in table iii calculated using (1). results indicate no major change in bond strength with decrease in maximum aggregate size. however, surprisingly, there is a drop in bond strength when maximum aggregate size of 9.5mm was used despite possessing the highest compressive and splitting tensile strengths among all the concretes used. the reason may be the decrease in locking provided by small aggregates to the pulled out bar. the failure pattern in all pullout specimens was by splitting of the concrete cover which is caused by wedging effect of bar deformations as shown in figure 7. fig. 7. pullout samples after bond failure the bond strength experimental results were compared with those calculated from different equations in the literature. four different equations were considered: (2)-(5) taken from [25-28] respectively. 0.25 0.2 0.33 0.1 , 2 max min max 20 6.54 ( ) ( ) [( / ) ( / ) 8 ] u split ck trf c c c k         (2) min min1/ 4 1/ 4 max [1.43 ( 0.54 ) 57.4 ] (0.1 0.9) c b s d b b c c t a f c l c d a f f c      (3) engineering, technology & applied science research vol. 8, no. 3, 2018, 2892-2896 2895 www.etasr.com iqbal et al.: effect of maximum aggregate size on the bond strength of reinforcements in concrete = 0.10 + 0.25 + 4.15 (4) = . . √ (0.88 + 0.12 ) (5) table iv. experiment and calculated bond strengths c on cr et e ty pe bond strength (mpa) experimental (2) (3) (4) (5) mix-25 7.76 7.87 7.83 7.34 7.25 mix-19 7.93 7.93 7.88 7.45 7.33 mix-12.5 7.88 7.94 7.89 7.47 7.35 mix-9.5 7.15 7.94 7.90 7.48 7.36 results indicate that there is no major impact of aggregate size on the bond strength of reinforcements in concrete when higher maximum aggregate sizes are used. equations (2) and (3) (from [25, 26]) are extremely good in predicting bond strength values while (4) and (5) (from [27, 28]) give slight conservative results. however, when the size of maximum aggregate reduces below 10mm, there is drop in experimental bond strength results despite better compressive and tensile strengths which may be due to lower resistance provided by smaller size aggregates to pulled out bars. this drop is not reflected in the equations used for bond strength calculations. as all the specimens failed by splitting, this phenomenon may have been more pronounced if concrete cover was increased to initiate pure pullout instead of specimen splitting. in that case, bigger size aggregates may induce more resistance to bars pulling out by locking compared to smaller size aggregates. the comparison of all values is shown in figure 8. the percentage variations of equation values were calculated with respect to the experimental results and are summarized in table v. equations (2) and (3) fit really well with the experimental values with less than 2% variation when 12.5mm and above maximum aggregate sizes are used. however, when the maximum aggregate size of 9.5mm was used, the variation was above 10%. the variations of (3), (4) with respect to the experimental values were in the range of ±5-7% for all values. fig. 8. bond strength variation and comparison table v. percentage variations c on cr et e ty pe percentage variations (2) (3) (4) (5) mix-25 1.42% 1% -5.4% -6.6% mix-19 0 -0.6% -6% -7.6% mix-12.5 0.76% 0 -5.2% -6.7% mix-9.5 11% 10.5% 4.6% 3% iv. conclusions the following conclusions have been drawn based on the experimentally performed study:  the workability of concrete decreases with decrease in maximum aggregate size used.  with increase in maximum aggregate size used in concrete, the compressive strength and splitting tensile strength decrease.  when higher maximum aggregate size of coarse aggregates values are used in concrete, there is no variation in bond strength but it reduces when maximum aggregate size of less than 10mm is used. this may be due to lower locking provided to pulled out bar by smaller aggregates. this may be more pronounced if splitting of samples is avoided by increasing concrete cover.  equations taken from [25, 26] for bond strength calculation work extremely well with higher maximum aggregate size concretes but do not work well when lower maximum aggregate sizes (<10mm) are used. aggregate size effect may be introduced in these equations for lower maximum aggregate size concretes to better reflect the actual bond strength. referencees [1] a. ali, s. iqbal, k. holschemacher, t. a. bier, “bond of reinforcement with normal-weight fiber reinforced concrete”, periodica polytechnica civil engineering, vol. 61, no. 1, pp. 128-134, 2017 [2] fib, “bond of reinforcement in concrete: state-of-art report”, bulletin no. 10, fib, 2000 [3] s. hong, s. k. park, “uniaxial bond stress-slip relationship of reinforcing bars in concrete. advances in material science and engineering”, advances in materials science and engineering, vol. 2012, article id 328570, 2012 [4] c. jiang, y. f. wu, g. wu, “plastic hinge length of frp-confined square rc columns”, journal of composites for construction, vol. 18, no. 4, 2014 [5] d. s. gu, y. f. wu, g. wu, z. s. wu, “plastic hinge analysis of frp confined circular concrete columns”, construction and building materials, vol. 27, no. 1, pp. 223-233, 2012 [6] d. guan, c. jiang, z. guo, h. ge, “development and seismic behavior of precast concrete beam-to-column connections”, journal of earthquake engineering, vol. 22, no. 2, pp. 234-256, 2016 [7] e. fehling, p. lorenz, t. leutbecher, “experimental investigations on anchorage of rebars in uhpc”, in: proceedings of hipermat 2012 3rd international symposium on uhpc and nanotechnology for high performance construction materials, pp. 533-540, 2012 [8] a. f. bingol, r. gul, “residual bond strength between steel bars and concrete after elevated temperatures”, fire safety journal, vol. 44, no. 6, pp. 854–859, 2009 engineering, technology & applied science research vol. 8, no. 3, 2018, 2892-2896 2896 www.etasr.com iqbal et al.: effect of maximum aggregate size on the bond strength of reinforcements in concrete [9] h. s. arel, s. yazici, “concrete-reinforcement bond in different concrete classes”, construction and building materials, vol. 36, pp. 78– 83, 2012 [10] b. bai, h. k. choi, c. s. choi, “bond stress between conventional reinforcement and steel fiber reinforced reactive powder concrete”, construction and building materials, vol. 112, pp. 825–835, 2016 [11] m. i. kaffetzakis, c. g. papanicolaou, “bond behaviour of reinforcement in lightweight aggregate self-compacting concrete”, construction and building materials, vol. 113, pp. 641–652, 2016 [12] x. fu, d. d. l. chung, “effect of corrosion on the bond between concrete and steel rebar”, cement and concrete research, vol. 27, no. 12, pp. 1811–1815, 1997 [13] p. pokorny, p. tej, m. kouril, “evaluation of impact of corrosion of hotdip galvanized reinforcement on bond strength with concrete – a review”, construction and building materials, vol. 132, pp. 271–289, 2017 [14] astm, “c143/c143m -15a: standard test method slump of hydrauliccement concrete”, in: annual book of astm standards, volume 04.02 concrete and aggregates, astm international, 2012 [15] astm, “c138/c138m-17a: standard test method for density (unit weight), yield and air content (gravimetric) of concrete”, in: annual book of astm standards, volume 04.02 concrete and aggregates, astm international, 2012 [16] astm, “c192/c192m-16a, “standard practice for making and curing concrete test specimens in the laboratory”, in: annual book of astm standards, volume 04.02 concrete and aggregates, astm international, 2012 [17] astm, “c39/c39m-18, standard test method for compressive strength of cylindrical concrete specimens”, in: annual book of astm standards, volume 04.02 concrete and aggregates, astm international, 2012 [18] astm, “c496/c496m-17, standard test method for splitting tensile strength of cylindrical concrete specimens”, in: annual book of astm standards, volume 04.02 concrete and aggregates, astm international, 2012 [19] rilem, “technical recommendations for the testing and use of construction materials”, taylor & francis, 1994 [20] r. eligehausen, e. p. popov, v. v. bertero, local bond stress–slip relationships of deformed bars under generalized excitations, report no. usb/eerc 83/23, earthquake engineering research center, university of california, berkeley, california, 1983 [21] b. s. hamad, “bond strength improvement of reinforcing bars with specially designed rib geometries”, structural journal, vol. 92, no. 1, pp. 3–13, 1995 [22] m. yaqub, i. bukhari, “effect of size of coarse aggregate on compressive strength of high strength concrets”, 31st conference on our world in concrete and structures, singapur, august 16-17, 2006 [23] n. a. a. hamid, n. f. abas, “a study on effects of size coarse aggregate in concrete strength”, jurnal teknologi, vol. 75, no. 5, pp. 51–55, 2015 [24] a. neville, “aggregate bond and modulus of elasticity of concrete”, materials journal, vol. 94, no. 1, pp. 71–74, 1997 [25] aci committee 408, “bond and development of straight reinforcing bars in tension (aci 408r-03)”, american concrete institute, 2003 [26] fib, model code 2010 first complete draft, vol. 1, 2010 [27] c. o. orangun, j. o. jirsa, j. e. breen, “a reevaluation of test data on development length and splices”, aci journal, vol. 74, no. 3, pp. 114–122, 1977 [28] m. r. esfahani, b. v. rangan, “bond between normal strength and high-strength concrete (hsc) and reinforcing bars in splices in beams”, aci structural journal, vol. 95, no. 3, pp. 272–280, 1998 microsoft word 35-2750_s_etasr_v9_n3_pp4261-4264 engineering, technology & applied science research vol. 9, no. 3, 2019, 4261-4264 4261 www.etasr.com saada et al.: application of stochastic analysis, modeling and simulation (sams) to selected … application of stochastic analysis, modeling and simulation (sams) to selected hydrologic data in the middle east nidhal saada civil engineering department, al-ahliyya amman university, amman, jordan n.saada@ammanu.edu.jo mustafa abdullah civil engineering department, al-ahliyya amman university, amman, jordan mrashied@ammanu.edu.jo arwa hamaideh water, environment and energy center, university of jordan, amman, jordan arwa.efb@gmail.com ali abu-romman civil engineering department, al-ahliyya amman university, amman, jordan a.aburuman@ammanu.edu.jo abstract—water resources in the middle east are very scarce and the management of these resources is a challenge. in this paper, the use of stochastic analysis, modeling, and simulation (sams) software package to selected hydrologic data in the middle east (namely jordan and saudi arabia) are explored. modeling and simulation experiments were conducted to test the capabilities of sams to be used for stochastic modeling and simulation in the middle east region. the hydrologic data used in this study consist of historic observed rainfall data of different lengths at various sites in jordan and saudi arabia. the models used in this study include: autoregressive moving average (arma) models, periodic autoregressive moving average (parma) models, multi-site contemporaneous autoregressive moving average (carma) models, and temporal disaggregation models. results indicate that sams can be used as a tool for stochastic modeling and simulation of hydrologic data in jordan and saudi arabia. it is important for managers and decision makers of water resources in these countries to be able to use sophisticated tools such as sams while deciding water management policies in these countries. keywords-stochastic analysis; modeling; simulation; hydrologic data i. introduction the region of middle east suffers from water resource scarcity. the situation is getting worse due to climate change, conflicts, wars, and economic and political instability. as a result, water resource management is a priority for the wellbeing of countries in the region. the use of sophisticated tools for better management of water resources is vital for that region. sams is a software package that deals with stochastic analysis, modeling, and simulation of hydrologic time series, and runs under windows operating system. the package is user friendly and consists of many menu and option windows which enable the user to choose among different available options. the current version of sams is sams 2007. sams capabilities can be classified into three categories: analysis of historic data, model fitting and parameter estimation, and synthetic data generation. the data analysis features of sams consist of: data plotting, checking the normality of the data, data transformation, and data statistical characteristics. sams has the capability of analyzing single site and multisite annual and seasonal data. the second application of sams is model fitting. it includes parameter estimation and model testing for alternative univariate and multivariate annual and monthly stochastic models. these include arma, parma, multisite arma, and disaggregation models [1]. the third main application of sams is data generation. data generation is undertaken based on the fitted models mentioned above. the statistical characteristics of the data are presented in graphical or tabular forms along with the historical statistics of the used data in fitting the models used. in this study, we explore the use of sams as a modeling and simulation tool in the middle east. for that purpose, selected hydrologic data from jordan and saudi arabia were used. providing water resource managers in the region with powerful modeling and simulation tools is vital for better management of water resources in the region. ii. methodology a. data used the data used in this study consist of the historic monthly and annual rainfall data for two stations in saudi arabia (surat obeida and malaki) and the standardized precipitation index (spi) data for five stations in jordan (table i). the data from surat obeida covered a period of 30 years from 1981 to 2010 while at malaki 27 years (1967–1993). the historic monthly rainfall data for the five stations in jordan were used to corresponding author: nidhal saada engineering, technology & applied science research vol. 9, no. 3, 2019, 4261-4264 4262 www.etasr.com saada et al.: application of stochastic analysis, modeling and simulation (sams) to selected … calculate the spi [2] for jordan by using files from the national drought mitigation center. b. models used 1) arma model the arma(p,q) model may be written as [3]: �� = � �� �� � p i=1 �� � � �� q i=1 (1) where �� represents the standardized process for year t, it has a mean=0 and variance ��� and is normally distributed, �� is the uncorrelated noise term with mean=0 and variance ��� and is also normally distributed. �� ,…. ,�� are the autoregressive parameters; �� ,…. ,�� are the moving average parameters. for example, for p=q=1, the arma(1,1) model becomes: �� � ������ �� � ������ (2) table i. data used station name data type period length (y) location malaki annual rainfall 1967-1993 27 asir, s.a. surat obeida monthly rainfall 1981-2010 30 asir, s.a. kufr sawm spi 1983-2013 31 irbid, jordan ras munif spi 1983-2013 31 irbid, jordan jarash spi 1983-2013 31 jarash, jordan swileh spi 1983-2013 31 swileh, jordan amman airport spi 1983-2013 31 amman, jordan s.a: saudi arabia 2) parma model the parma(p,q) model may be written as [4]: ��,� = � ��,� !,� � p i=1 ��,� � ��,� �!,� � q i=1 (3) where ��,� represents the standardized process for year υ and season τ, it has mean=0 and variance ���"�# and is normally distributed, ��,� is the uncorrelated noise term with mean=0 and variance ���"�# and is also normally distributed. ��,� ,…. ,��,� are the seasonal autoregressive parameters; ��,� ,…. ,��,� are the seasonal moving average parameters. specifically, for p=q=1, the parma(1,1) model becomes: ��,� � ��,���,��� ��,� � ��,���,��� (4) 3) carma model the carma model can be decoupled into component univariate models thus making the parameter estimation much easier than the full multivariate models [4]. the carma(p,q) model can be described as: $� � % &'$��'�'(� )� � % *')��' � '(� (5) where $� is a column vector for year t where each element represents the process (spi-12 at each site in this case). each element is normally distributed with mean=0 and variance �+�. &' are the diagonal autoregressive parameter matrices. *' are the diagonal moving average matrices, )� is a vector of residuals of the process at time t. they are uncorrelated in time but are correlated in space. equation (1) can be decoupled and written for each site as: $�, � � �', � '(� $��', )�, � � �', � '(� )��', (6) equation (2) represents the univariate arma(p,q) model for site i. for p=q=1, the arma(1,1) model at each site i can then be described as: $�, � ��, $���, )�, � ��, )���, (7) the residuals can be expressed as: )� � .� (8) where .� is a vector of random residuals that are uncorrelated in time and in space, and b is a parameter matrix. it can be shown that the covariance matrix of the residuals )� (g) can be expressed as [4]: / � --0 (9) where -0 is the transpose of matrix b. as such, the carma model implies that the cross-correlations between sites are preserved through the residuals [4]. notice also that the variances of the residuals (�1�) at each site are the diagonal elements in the g matrix [4] for each corresponding site. 4) disaggregation model the general lane’s temporal disaggregation model for a number of sites n can be expressed as [5]: ��,� � 2�3� -� )�,� 4���,��� (10) where ��,� is an n×1 column vector representing the seasonal series, n is the number of sites (n=1 in our case), 3� is an n×1 column vector representing the annual data series, )�,� is an (n×1) vector of uncorrelated normally distributed noise term. the model parameters a, b, and c can be estimated using the method of moments [5]. c. parameter estimation sams has two methods for parameter estimation. these are the method of moments (mom) and the least squares method (ls). authors in [1] provided more details about these methods and their calculations by sams. figure 1 shows a screenshot of the sams parameter estimation of an arma(2,1) model. fig. 1. sams parameter estimation for an arma(2,1) model. engineering, technology & applied science research vol. 9, no. 3, 2019, 4261-4264 4263 www.etasr.com saada et al.: application of stochastic analysis, modeling and simulation (sams) to selected … sams also provides the user with the ability for the estimation of the parma, carma, and the disaggregation models. d. stochastic simulation sams allows the user to run stochastic simulation experiments. once the model parameters are estimated, the user can generate synthetic data using the model. a user can specify the number of samples to generate and the length of each sample and sams will then generate the required data. figure 2 shows a screenshot of the sams generation of data from an arma model. the average statistics calculated from these generated series can then be compared with the historical data statistics. figure 3 shows such a comparison of the basic statistics such as mean, standard deviation etc. for an arma(2,1) model. additionally, sams provides a statistical comparison for the important drought related statistics such as the longest drough, deficit and surplus statistics, range, and hurst coefficient as shown in figure 4. sams also provides a statistical comparison for a number of other important statistics such as the correlation structure of the data. fig. 2. sams data generation window fig. 3. comparison between historic and generated basic statistics for an arma(2,1) model figure 5 shows a comparison of the serial correlation of the arma(2,1) model for malakai, saudi arabia. the ability of a certain model to preserve these statistics is important for water resources managers and decision makers. sams gives the managers the ability to try different models in a simple and easy manner. fig. 4. comparison between historic and generated drought and surplus related statistics for an arma(2,1) model. fig. 5. comparison between historic and generated serial correlation for an arma(2,1) model. iii. results and discussion sams was used to fit several arma models to the annual rainfall data at malakai in saudi arabia. table ii shows the parameter estimations for the arma(1,0), arma(1,1), and arma(2,1) models. the results shown are the mom parameter estimates. table ii. sams parameter estimation of arma models* model parameters arma(1,0) autoregressive parameters: ϕ1=0.514 variance of residuals: �1�=14108.7 arma(1,1) autoregressive parameters: ϕ1=0.742 moving average parameters: θ1=0.319 variance of residuals: �1�=13711.1 arma(2,1) autoregressive parameters: ϕ1=−0.008, ϕ2=−0.386 moving average parameters: θ1=−0.455 variance of residuals: �1�=13660.5 * for the annual rainfall at malakai, saudi arabia simulations were conducted for malakai, saudi arabia by generating synthetic time series data from the arma models mentioned above [6]. in each experiment 100 samples, each with length equal to the historical length of the series at malakai were generated from the arma models [6]. statistical comparison of historic and generated data revealed that the models were capable of preserving the statistics of historic data such as mean, standard deviation and serial correlation structure [6]. sams was also used for modeling and simulation of parma models to the monthly rainfall data for surat obeida, saudi arabia [7]. similarly, the temporal disaggregation model was also used for modeling and simulation purposes for surat obeida, saudi arabia [7]. results indicate that both parma and disaggregation model were capable of preserving the seasonal engineering, technology & applied science research vol. 9, no. 3, 2019, 4261-4264 4264 www.etasr.com saada et al.: application of stochastic analysis, modeling and simulation (sams) to selected … statistics of the data [7]. however, the disaggregation model was superior to the parma model in terms of preserving the underlying annual correlation structure of the data [7]. multisite carma(1,1) model was applied to the spi data for the five stations in jordan [8]. table iii shows the estimated autoregressive and moving average parameters and table iv shows the estimated variance-covariance matrix of the residuals. simulation experiments conducted by using the carma(1,1) model reveal that the model performed well in preserving the historical statistics of the observed data at each station. furthermore, the model was able to preserve the spatial cross correlation structure for the stations studied [8]. table v shows the historical and generated lag-0 cross correlations. based on the above results, sams can provide the user with a very powerfull tool to do sophisticated modeling and simulation of hydrologic data. this is very important for a water resource manager for his/her estimation, prediction and forecasting efforts for better management of water resources. table iii. fitted carma(1,1) model parameters for spi data in jordan station carma (1,1) model parameters autoregressive parameter (ϕ1) moving average parameter (θ1) kufr sawm 0.922 -0.008 ras munif 0.910 -0.031 jarash 0.917 0.090 swileh 0.938 0.082 amman airport 0.895 -0.006 table iv. residuals’ covariance matrix of the fitted carma(1,1) model, spi data, jordan station kufr sawm ras munif jarash swileh amman airport kufr sawm 0.148 0.134 0.134 0.112 0.128 ras munif 0.134 0.162 0.151 0.123 0.146 jarash 0.134 0.151 0.188 0.124 0.169 swileh 0.112 0.123 0.124 0.141 0.147 amman airport 0.128 0.146 0.170 0.147 0.196 table v. historical and generated lag-0 correlations of the spi-12 data station kufr sawm ras munif jarash swileh kufr sawm 1.0 (1.0) ras munif 0.87 0.86) 1.0 (1.0) jarash 0.80 (0.77) 0.86 (0.85) 1.0 (1.0) swileh 0.77 (0.72) 0.80 (0.77) 0.75 (0.71) 1.0 (1.0) amman airport 0.75 (0.70) 0.82 (0.81) 0.88 (0.87) 0.85 (0.83) generated values in parentheses iv. conclusion sams is a software tool that can be used for stochastic modeling and simulation of hydrologic data. several models were used in this study to fit different stochastic models (arma, parma, carma, and disaggregation models) to hydrologic data in jordan and saudi arabia. simulation experiments were conducted. synthetic data were geerated from the different fitted models by sams. sams provides the user the ability to compare the statistics of the generated data with the historic data. sams was proved to be a powerful and valuable tool that can be used by water resource managers in the middle east and should help them making better decisions in the management of the valuable and scarce water resources in that region. references [1] o. g. b. sveinsson, j. d. salas, w. l. lane, d. k. frevert, stochastic analysis, modeling, and simulation (sams), version 2007, user’s manual, colorado state university, 2007 [2] t. b. mckee, n. j. doesken, j. kleist, “the relationship of drought frequency and duration to time scales”, eighth conference of applied climatology, anaheim, usa, january 17–22, 1993 [3] j. d. salas, n. saada, c. h. chung, stochastic modeling and simulation of the nile river system monthly flows, hydrologic science and engineering program, department of civil engineering, colorado state university, 1995 [4] j. d. salas, n. saada, c. h. chung, w. l. lane, d. k. frevert, stochastic analysis, modeling, and simulation (sams), version 2000user’s manual, colorado state university, 2000 [5] w. l. lane, d. k. frevert, applied stochastic techniques: (personal computer version): user manual, bureau of reclamation, us department of interior, 1990 [6] n. saada, “simulation of long term characteristics of annual rainfall in selected areas in saudi arabia”, computational water, energy, and environmental engineering, vol. 4, no. 2, pp. 18-24, 2015 [7] n. saada, “time series modeling of monthly rainfall in arid areas: case study for saudi arabia”, american journal of environmental sciences, vol. 10, no. 3, pp. 277-282, 2014 [8] n. saada, a. abu-romman, “multi-site modeling and simulation of the standardized precipitation index (spi) in jordan”, journal of hydrology: regional studies, vol. 14, pp. 83-91, 2017 engineering, technology & applied science research vol. 8, no. 4, 2018, 3108-3112 3108 www.etasr.com ahmad et al. : effect of shear flow on crystallization of sydiotactic polypropylene/clay composites effect of shear flow on crystallization of sydiotactic polypropylene/clay composites naveed ahmad department of chemical and material engineering college of engineering northern border university arar, kingdom of saudi arabia elsayed fouad department of chemical and material engineering college of engineering northern border university arar, kingdom of saudi arabia farooq ahmad department of chemical and material engineering college of engineering, northern border university arar, kingdom of saudi arabia abstract-the high sensitivity of crystallization to shear flow is a subject of great research interest the last several years. a set of syndiotactic polypropylene/clay composite samples were used to examine the effect of shear flow on crystallization kinetics. this phenomenon alters both processing and material final properties. in the present work, the effects of clay contents and shear flow on the rate of flow induced crystallization were investigated using rheological technique. small amplitude oscillatory shear experiments were performed using advanced rheometric expansion system (ares). the crystallization rate is found to alter by both shear and clay contents in the polymer composites. keywords-shear flow; flow induced crystallization; syndiotactic polypropylene/clay composites; induction time; deborah number; crystallization kinetics i. introduction the enhancement in the rate of polymer crystallization due to the application of flow is known as flow induced crystallization. in other words flow induced crystallization can be defined as the process in which the rate of polymer crystallization is accelerated by the action of flow [1]. this phenomenon alters both processing and material final properties. the physics behind flow induced crystallization is simple. when a polymer is subjected to a flow, the polymer chains are oriented and stretched. this results to a decrease in the entropy or equivalent increase in free energy [2, 3]. this increase in free energy acts as a driving force and thus accelerates the polymer crystallization process by accelerating the rate of nucleation. in general, the process of crystallization occurs in two steps. in the 1st step, the formation of nuclei (stable nuclei) occurs, while in the 2nd step the subsequent growth of crystallite occurs. the flow has an effect on the first step of crystallization (nucleation stage) [1]. the flow mechanism induced crystallization has been explained very well in [2, 3]. the process can be explained as the stretching of long chains to form fibrous crystals. during the stretching process, distortion of chains from their most probable conformation results and hence a decrease in the conformational entropy occurs. if this deformation is maintained in this lower conformational entropy state, then less conformational entropy needs to be sacrificed by transforming to a crystalline state. the decrease in total entropy allows the crystallization to occur at high temperatures that will take place under quiescent conditions. normally, the formation of such fibrous morphology is accompanied by the formation of an epitaxial layer over and around the inner fiber giving rise to the so called shish-kebab kind of morphology [3]. a critical review shows that the outside, kebab like regions are essentially folded chain regions comprised of chains which do not crystallize during the orientation process [2-5]. while, in the inner shish region, the formation of folded chain discs occurs due to nucleation events taking place on the surface of extended chains. in the light of the above discussion, the enhancement in the rate of crystallization process by the shear flow is due to the enhancement in the rate of nucleation. numerous works regard nucleation kinetics [5]. according to [7], isothermal nucleation kinetics is expressed as: = ∆ − (∆ ) (1) where n=rate of nucleation, k=boltzmann’s constant, t=absolute temperature, ∆ =gl-gs=volumetric free energy difference between liquid and crystalline phase and k=constant containing geometrical and energetic factors of nucleus. it is generally accepted that the shear flow contributes to the free energy difference appearing in (2). ∆ = ∆ + ∆ (2) where ∆ and ∆ refer to the free energy contribution under quiescent and shear flow conditions respectively. in order to investigate the influence of flow on crystallization, a characteristic time for the crystallization is measured. this is usually called induction time. it is the time required for the steady state of nucleation to be reached. both induction time and nucleation rate are nearly inversely proportional. induction times can also be measured by detecting the sharp upturn in the viscosity vs time curve under constant shear rate [9]. the ratio between the induction time under quiescent and flow conditions can be defined as: engineering, technology & applied science research vol. 8, no. 4, 2018, 3108-3112 3109 www.etasr.com ahmad et al. : effect of shear flow on crystallization of sydiotactic polypropylene/clay composites = / = 1/1 + ∆ /∆ exp [ (∆ ) ] (3) where q and f refer to quiescent and flow conditions respectively. the dimensionless induction time is 1 under quiescent conditions, while it is less than 1 when the shear flow is applied .for steady shear flow ∆ = 3 γ ( ) (4) where de is deborah number. it is the product of the shear rate and the polymer reptation time. γ is dimensionless free energy, which is a function of de. in order to evaluate for a given polymer under isothermal flow conditions several material properties are needed. the quiescent free energy requires the knowledge of the thermodynamic melting temperature (tm) and latent heat of fusion (ho). ∆ = (1 − ) (5) values of the quiescent crystallization constant (k) and exponent (n) are required for calculating . besides this some values of rheological parameters of polymer melts like repetition time (td), entanglement density ( e) and molecular weight between entanglements (me) are also required. in case of polymer melting, the ability of the shear flow to produce conformation and morphological changes with respect to equilibrium and isotropic state results from the coupling between the shear flow intensity and relaxation behavior of the chain. according to the theory of repetition [6], chain segment conformation or orientation occurs only when the characteristic flow time (γ-1) is smaller than the repetition or disengagement time td. in the other words chain stretching is possible only when γ-1<tr<td. tr, and td are the rouse and disengagement times respectively. the effect of flow on the chain orientation and consequently on the flow induced crystallization has been explained in terms of a dimensional form by defining a deborah number for the system as: de=γ .td (6) the above discussion clearly mimics that for de<1, there will be no effect on the crystallization kinetics, whereas faster crystallization kinetics should be observed only in case of de>1. molecular structure factors like molecular weight, molecular weight distribution or polydispersity and tactility are the important structural properties in quantitatively determining the flow induced crystallization rate [8-10]. in case of monodisperse polymers, longer polymer chains will be more oriented than the shorter ones under the same flow conditions, as high molecular weight chain has longer relaxation times. the same applies on the polydisperse polymers. the presence of a long tail of molecular weight chains should enhance the flow induced nucleation rate. fiber pulling experiments on the long series of isotactic polypropylenes of different molecular weight were conducted [10]. it was found that the overall crystallization kinetics exponentially increased upon increasing polymer’s molecular weight at constant fixed shear rate [10, 11]. authors in [11] conducted rheological flow induced crystallization experiments on the isotactic polypropylene samples of different molecular weight and molecular weight distribution. they found an increase in the rate of crystallization by increasing the molecular weight of the samples at constant shear rate. furthermore, they found that after a combined thermo mechanical treatment which mainly caused a degradation of the high molecular weight tail, the effect of the shear rate on the crystallization rate was strongly reduced. in [14], authors obtained the same results by investigating the process using differential scanning calorimetry (dsc) technique. they performed experiments on both linear and branched chain polypropylene. long chain branched polypropylene showed accelerated crystallization kinetics in comparison with that of low branched level. the crystallization of long chain branched polypropylene was found more sensitive to shear flow than that of linear polypropylene during the induced period at low shear rates, which depicts that the longer relaxation time of the polymer chains played an important role in the nucleation of polypropylene under shear flow fields. in a nut shell an increase in molecular weight will produce a faster crystallization under given flow conditions. authors in [12] studied melt blended nanocomposites of pp/talc. nanocomposites of pp/talc were processed using an internal mixer. an elongational rheometer was used to generate well controlled different extensional flow conditions. samples were then characterized by waxs to reveal and quantify the fillers and polypropylene crystalline phase orientation. crystalline orientation of polypropylene was found to be strongly affected by the addition of talc under extensional flow and talc orientation. more recently, isotactic polypropylene (ipp) based single-polymer composites (spcs) were prepared by introducing ipp fibers into the molten or super cooled homogeneous ipp matrix [13]. the influences of fiber introduction temperature (ti) on the resultant morphology of transcrystallinity (tc) and mechanical properties of spcs were investigated via a polarized optical microscopy (pom) and a universal tensile test machine. the effects of interfacial crystallization on mechanical properties were also studied. the tensile strength of spcs was observed to increase firstly and to reach a maximum value at ti=160°c, and then to decrease with further increasing of ti. wide-angle x-ray diffraction (waxd), scanning electron microscopy (sem) and pom were employed to understand the mechanical enhancement mechanism. it is found that the enhanced tensile strength of spcs was strongly dependent on the synergistic effects of tc, high orientation degree of ipp fibers and good adhesion between the ipp fiber and the matrix. in the present work we studied the effect of clay loading and shear flow on the rate of crystallization of spp/clay composites using rheological technique. ii. experimental work a. materials samples of spp/clay composites with different contents of clay were used for the flow induced crystallization study. the diagnostic properties of the polymers are reported in table i. all the samples were synthesized in our chemistry department using solution mixing technique [15]. engineering, technology & applied science research vol. 8, no. 4, 2018, 3108-3112 3110 www.etasr.com ahmad et al. : effect of shear flow on crystallization of sydiotactic polypropylene/clay composites table i. list of all samples [15]. sample number sample name percentage of clay contents degree of syndiotacticity <%rrr> 1 spp-1 10% 2 spp-2 7.5% 3 spp-3 5% 4 spp 0 60 b. methodology the effects of shear flow and clay contents on the rate of crystallization (flow induced crystallization) were investigated by rheological technique using ares rheometer. before staring the flow induced crystallization experiments stability and range of shear stress were explored for each sample. after confirming the stability and determining the range of shear stress, the effect of shear flow on crystallization was examined at two different temperatures above and below the melting point. in case of spp-1, shear flow was applied at 145°c and 125°c, while in case of spp-3, the shear flow was applied at 120°c and 105°c. the procedure of the rheological flow induced crystallization experiments is explained below: 1. annealing of the polymer sample was carried out by time sweep test at 220°c for 20 minutes in order to clean the sample. 2. the polymer sample was cooled from 220°c to temperatures above melting temperature by temperature ramp test at a constant cooling rate of 40°c/min, 1 rad/s of frequency and at a strain of 1%. 3. different shear rates ranging from 0.01 to 0.25s-1 were applied at a specific temperature. 4. after the application of shear rate, temperature ramp test (crystallization test) was started within a time of 13 seconds. 5. in another set of experiments shear rate was applied at a temperature below melting point. different shear rates within the range (0.01 to 0.25s-1) were applied at 125°c and 105°c respectively for spp-1 and spp-3 respectively within the induction time for different periods of time (shear flow times). both sets of experiments were carried out for all samples. iii. results and discussion annealing of the samples by time sweep test at 220°c and 1rad/s was carried out for 20 minutes in order to investigate the stability and clean the sample completely from the spherulites and nuclei. time sweep test for spp-1 has been shown in figure 1. thermal stability of all samples was examined at 220°c and at 1rad/s of frequency. all the samples were found to be stable. after confirming the thermal stability, the stability of the samples was examined for different shear rates. all the samples were found stable in the range of 0.01 to 0.25s-1 of shear rates as shown in figure 2 for spp-1. crystallization behavior under quiescent conditions and at different shear rates was explored using the temperature ramp test from 220 to 125°c for spp-1. different shear rates were applied at 125°c after cooling from 220°c. in case of quiescent condition, no shear rate was applied at 125°c. in both cases of quiescent and flow induced crystallization, crystallization behavior was observed by cooling from 220°c to 125°c. changes in moduli dictate the process of crystallization. jump in the elastic modulus after the incubation and induction time is considered as the actual crystallization process. enhancement in the rate of crystallization was observed by the application of different shear rates. in another words the induction time is not the same in all cases. these findings have been exhibited graphically in figure 3. time sweep test at 220°c time (s) 0 200 400 600 800 1000 1200 1400 g ', g '' 0 2000 4000 6000 8000 10000 time(s) vs g' time(s) vs g'' fig. 1. time sweep test for spp-1 at 220°c. time (s) 0 100 200 300 400 500 600 s h e a r st re ss ( p a ) -2000 0 2000 4000 6000 8000 10000 12000 14000 16000 at 0.01 shear stress at 0.07 shear stress at 0.1 shear stress at 0.12 shear stress at 0.20 shear stress at 0.22 shear stress fig. 2. plot between time and shear stress for spp-1. in order to investigate the effect of shear flow on crystallization process, some other types of experiments were conducted on spp-11 and spp-5. in these experiments, different shear flows were applied within the induction time at temperatures below and above melting point after cooling from 200°c for all samples. each shear flow was applied for different periods of time ranging from 50 to 800 seconds depending upon on the induction time of the sample. a significant effect of shear flows was found on the crystallization kinetics. the characteristic deborah number was calculated from the relaxation time and shear flows. relaxation time was calculated by different methods. in all cases the deborah number was found greater than one (de>1), which verifies our experimental findings that the applied shear flow is able to orient the polymer chains. shear flow can be increased to the extent of making deborah number greater. in the present experimental work this attempt was made, but the sample was fou tha can inc on de she de ind inc for ind fig rate fig per com of beh dif our beh rat fou kin engineerin www.etasr und to come o at in the pres nnot be applie crease in the s e. the same eborah numbe ear flow time eborah numbe duction time d crease in cla rmation. the duction is show g. 3. crystalliz es for spp-1. g '( p a ) 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30 g. 4. crystalliz riods of time at 80 crystallizatio mposites at di shear flow in havior. the d fferent shear ra r findings of havior of spp tes. the effect und. increase netics. the rat ng, technology r.com out from the rh sent experime ed. deborah nu hear rate. in a trend was fou er was found e. the relatio er is shown i decreases with ay contents e relationship wn in figure 6 zation under quie 0 500 quscent crystalliza after 50s after 150 s after 300 s zation of spp-2 0°c. iv. c on measurem ifferent shear r n the range of eborah numbe ates was found f effect of sh p/clay compos of clay conten in clay conte te of crystalliz y & applied sci ahmad et a heometer plate ental set up h umber was fou all cases it was und in case o to increase w onship betwee in figure 5. h increasing o increases the p between c 6. escent conditions time 1000 1500 ation at a shear rate o conclusion ments perform rates show tha 0.01 to 0.25s er calculated fo d greater than hear flow on sites in the gi nts on crystall ents increases zation was fou ience research al. : effect of sh es, which conf higher shear und to increase s found greate f shear flow with increase i en shear flow it was found of the clay con e time of cr clay contents s and at differen 2000 2500 of 0.07 s-1 for d med on spp at there is infl s-1 on crystalliz for all the samp one, which ve the crystalliz iven range of lization kinetic s the crystalliz und to increase h v hear flow on c firmed flows e with er than times. in the ws and d that ntents. rystals s and nt shear different p/clay luence zation ples at erified zation shear cs was zation e with incr wit f stud dea ara [1] [2] [3] [4] [5] [6] vol. 8, no. 4, 20 crystallization o rease in clay c th increase in t d e 6.3x10 3.15x10 2.14x10 1.575x10 1.26x10 1.05x10 fig. 5. relati in d u c ti o n t im e ( s ) 0 200 400 600 800 1000 1200 1400 1600 fig. 6. relati authors wish dy by the anship of scie ar, kingdom o h. janeschitz-k promotor of nu rheological ac r. h. somani, lustiger, “shea isotactic polypr macromolecule r. h. somani, l precursor struct 20, pp. 8587–86 e. w. fischer macromolecule royal society o j. stejny, j. d characterization crystals”, journ 1979 s. t. milner, fluctuations in 81, no. 3, pp. 7 018, 3108-3112 of sydiotactic p contents. that the clay conten 0 100 200 0-4 0-4 0-4 0-4 0-4 0-4 shear flow tim onship between s clay 0 2 ionship between c acknowl h to acknowle grant no.68 entific researc of saudi arabia refer kriegl, e. ratajsk ucleation in poly cta, vol. 42, no. 4 , l. yang, b. s ar-induced molec ropylene: effects es, vol. 38, no. 4, l. yang, l. zhu, tures in entangled 623, 2005 r, m. stamm, m es in the condense of chemistry, vol dlugosz, a. ke n of the fibrou nal of materials s t. c. b. mc melts of linear po 725–728, 1998 2 polypropylene/c t's why induct nts. time (s) 300 400 500 me (s) vs de shear flow time an y contents (%) 4 6 8 clay contents vs in clay and contents ledgement dge the suppo 57-eng-2016 ch in northern a. rences ki, m. stadlbauer ymer melts: a qu 4, pp. 355–364, 20 s. hsiao, t. sun cular orientation s of the deform , pp. 1244–1255, b. s. hsiao, “flo d polymer melts”, m. dettenmair, ed phase”, in: far l. 68, 1980 eller, “electron us structure of science, vol. 14, leish, “reptatio olymers”, physica 3111 clay composites tion time decr 600 700 nd deborah numb 10 12 duction time and induction tim ort of this res 6-1-6-f from border unive r, “flow as an eff uantitative evalua 003 n, n. v. pogodin and crystallizat mation rate and s 2005 ow-induced shish, polymer, vol. 4 “organization o raday discussions microscope diffr poly (sulphur n no. 6, pp. 1291– on and contoural review letters s reases ber. me. earch m the ersity, ffective ation”, na, a. tion in strain”, -kebab 46, no. of the s of the raction nitride) –1300, -length s, vol. engineering, technology & applied science research vol. 8, no. 4, 2018, 3108-3112 3112 www.etasr.com ahmad et al. : effect of shear flow on crystallization of sydiotactic polypropylene/clay composites [7] j. i. lauritzen jr, j. d. hoffman, “formation of polymer crystals with folded chains from dilute solution”, the journal of chemical physics, vol. 31, no. 6, pp. 1680–1681, 1959 [8] s. acierno, n. grizzuti, h. h. winter, “effects of molecular weight on the isothermal crystallization of poly(1-butene)”, macromolecules, vol. 35, no. 13, pp. 5043–5048, 2002 [9] s. acierno, n. grizzuti, “flow-induced crystallization of polymer: theory and experiments”, international journal of material forming, vol. 1, pp. 583–586, 2008 [10] c. duplay, b. monasse, j. m. haudin, j. l. costa, “shear-induced crystallization of polypropylene: influence of molecular weight”, journal of materials science, vol. 35, no. 24, pp. 6093–6103, 2000 [11] s. vleeshouwers, h. e. h. meijer, “a rheological study of shear induced crystallization”, rheological acta, vol. 35, no. 5, pp. 391–399, 1996 [12] m. khalil, p. hebraud, a. mcheik, h. mortada, h. lakiss, t. hamieh, “elongational flow-induced crystallization in polypropylene/talc nanocomposites”, physics procedia, vol. 55, pp. 259–264, 2014 [13] l. zhang, y. qin, g. zheng, k. dai, c. liu, x. yan, j. guo, c. shen, z. guo, “interfacial crystallization and mechanical property of isotactic polypropylene based single-polymer composites”, polymer (uk), vol. 90, pp. 18–25, 2016 [14] f. hernandez sanchez, l. f. del castillo, r. vera-graziano, “isothermal crystallization kinetics of polypropylene by differential scanning calorimetry, i. experimental conditions”, journal of applied polymer science, vol. 92, pp. 970-978, 2004 microsoft word 29-2726_s_etasr_v9_n4_pp4474-4479 engineering, technology & applied science research vol. 9, no. 4, 2019, 4474-4479 4474 www.etasr.com mahessar et al.: flash flood climatology in the lower region of southern sindh flash flood climatology in the lower region of southern sindh ali asghar mahessar sindh barrages improvement project, sindh irrigation department, pakistan amahessar@yahoo.com abdul latif qureshi uspcas-w, mehran university of engineering and technology, pakistan alqureshi.uspcasw@faulty.muet.edu.pk insaf ali siming department of english, quest, nawabshah, pakistan insaf.siming@quest.edu.pk shafi muhammad kori uspcas-w, mehran university of engineering and technology, jamshoro, pakistan alqureshi.uspcasw@faulty.muet.edu ghulam hussain dars uspcas-w, mehran university of engineering and technology, jamshoro, pakistan ghdars.uspcasw@faculty.muet.edu.pk madeheea channa uspcas-w, mehran university of engineering and technology, jamshoro, pakistan madhachana.uspcasw@admin.muet.edu.pk abdul nasir laghari department of energy and environment engineering, quest, nawabshah, pakistan a.n.laghari@quest.edu.pk abstract-climate change impact is felt at a global scale. one of its results is the abnormal rain occurrence during monsoon season. in recent years, visible changes due to unusual weather events in pakistan’s hydrological cycle were observed in the form of intensification of the hydrological cycle with changing of precipitation events such as floods and prolonged droughts. hence, abnormal rainfall occurred in regions of southern and northern parts of sindh, like torrential river floods (2010), flash floods (2011-2012), unpredictable rainstorms, etc. causing loss of lives, damaging infrastructures and crops, structures, and inhabitant displacement. in 2011, heavy cumulative precipitation has been recorded in the southern sindh districts and the coastal belt of badin and the lbod and kotri surface drainage system achieved their extreme heights. another example of erratic rain occurred from september 8 to september 13, 2011 and produced an extraordinary discharge of about 14000 cusecs against the designed discharge of 4600 cusecs in the lbod and kotri surface drainage systems overtopping drains from several locations and wreaking havoc in the whole area of the southern part of sindh. keywords-climatology; rainfall; flood; lbod watershed area; drain carrying capacity; damages i. introduction climate variables such as rain, wind and temperature can sometime reach abnormal values and create natural disasters. these are termed as extreme events. changes in global precipitation estimate are a more complex and challenging task than the changes in temperature. extreme precipitation events often occur in populated areas causing disaster and affecting population. changes in extreme events such as torrential rainfall, cyclone, irregular temperatures, heat waves, prolonged droughts and floods are mainly caused by climate change [1, 2], and pakistan is one of the most vulnerable to climate change countries [3]. global climate change experts have identified pakistan as part of a zone that faces extreme changes in weather. climate change and environmental crises in vulnerable areas of pakistan indicate that 40% of the population is highly vulnerable to natural disasters [4]. developing countries including pakistan will be affected by serious droughts, floods, increasing temperatures, and lifethreatening events [5]. climate change risk is proposed to be an ambiguity related to the influence of climate change in specific areas of concern [6]. scientifically guesstimating the conceivable influences of future climate modification is the precondition to demeanor alteration activities. at primary period, the growing situation is regularly used to project the future influences of climate [7]. temperature will rise from 0.9 to 3.5°c by 2100, causing fluctuation in intensity, frequency and timing of rainfall, frequent hot days/nights occurrence and changed effects of biotic factors [8]. high temperature, reduction in rainfall occurrence, and an increase in the frequency of extreme climatic events are expected in the future climate of the tropics [5, 9]. the change in the weather disturbed life and cropping pattern. this expected deviation in climate has effects on the food chain and other segments through spatial and temporal scales [5, 10]. the frequency and severity of floods in some areas during the monsoon have serious impacts [12]. cyclone formations and irregularities in rainfall pattern are related consequences of global warming. global warming is closely linked to the seasonal atmospheric flow during the monsoon season with varying degree of uncertainty. irregular flooding is a serious repercussion of the monsoon season that damages infrastructure, human life and causes serious financial losses [11, 13]. the worst flood corresponding author abdul nasir laghari engineering, technology & applied science research vol. 9, no. 4, 2019, 4474-4479 4475 www.etasr.com mahessar et al.: flash flood climatology in the lower region of southern sindh disaster in the 80 year history of pakistan occurred in july 2010 with following heavy monsoon rains [14]. from july to september, the summer rainfall concentrates, which is generally a monsoon breath formed on the bengal bay reaching pakistan across india. another mechanism of summer monsoon rainfall is the flow of moisture from the arabian sea in the southwest and it will be activated in case of persisting depression. both phenomena strengthen the precipitation process and produce high intensity rainfall in a short time [15, 16]. coastal areas may suffer from increased tropical storm frequency and strength in the near future, while over 50,000 people may be displaced from pakistan's coastal deltas [17]. the southern part of sindh has been affected with strong rains, cyclones, high tides, causing damages in life, property, crops and causing waterlogging and soil salinity. kotri surface drainage and left bank outfall drain (lbod) system [3] were designed and constructed primarily aiming to provide effective drainage facilities to address the issues of waterlogging, salinity and generated rain runoff. this system fulfilled its purpose and provided rainwater release from its watershed area timely but a severe submergence of lands of badin district occurred during the erratic rainstorms of 1994 and 2003 ranging from 200 to 304mm respectively. the generated rain runoff exceeded the carrying capacity of lbod and kotri surface drainage system causing long term massive area submergence and damaging infrastructures and crops, while it increased the waterlogging problem. moreover, the components of the lbod system were overtopped at the heavy rain of 2006. from the historical rainfall data of 39 years of meteorological stations, table i shows the maximum rainfall in 24 hours in the watershed area of lbod and kotri surface drainage system. when the rainfall intensity is low there is no problem of safe disposal, but with high intensities that overcome the designed carrying capacity of the system, over extensive areas are submerged. the overall discharge passing through the outfall drains depends upon the weighted average rainfall for all the meteorological stations representing the entire catchment area. after the construction of kotri and lbod surface drainage systems, rainfall intensity of more than 100mm within 24h at one or more stations was recorded in 1994, 1999, 2003 and 2006 and caused severe damages [18]. the rain runoff during the monsoon in 2011 generated cumulative discharge of about 14000 cusecs while the designed carrying capacity of the lbod system was only 4600 cusecs, resulting in damages of the drainage system at several places and causing flooding in huge areas. ii. research study area the present study covered the watershed area of kotri surface drainage and lbod system which was designed to control the problems of waterlogging and salinity, and the generated rain runoff from benazirabad, sanghar, mirpurkhas districts and badin area in the left bank of indus river with the objective of improving the cultivable area of rohri and nara canals. the drainage system lies between 240 10' and 260 40' n and 680 09' and 690 26' e [19]. waterlogged and salinized lands will be reclaimed due to the construction of the drainage system [20], however, the performance of the system was found to be unsatisfactory during the monsoon rains in 2003 and 2006 causing the submerging of vast parts of badin. moreover, it was exacerbated during the ever highest rainfall intensity recorded from 29th august 2011 to 13th september 2011 as shown in figure 1. table i. maximum rainfall in sindh districts (mm) years hyderabad badin shaheed benazirabad chhor 1968 7.40 4.60 3.60 17.50 1969 3.00 0.00 13.20 4.10 1970 67.60 117.60 59.70 61.00 1971 18.00 42.20 8.60 51.30 1972 12.70 29.70 256.50 21.80 1973 21.80 35.60 17.30 32.80 1974 12.70 13.60 0.50 5.00 1975 29.10 61.00 52.00 40.00 1976 57.60 64.70 32.80 58.40 1977 47.40 60.80 22.00 88.60 1978 106.60 43.50 73.00 87.20 1979 41.60 241.00 64.00 29.00 1980 41.00 27.00 40.90 11.00 1981 17.70 138.00 51.20 42.20 1982 26.30 75.60 42.60 35.30 1983 101.70 67.40 48.20 119.90 1984 110.30 111.00 48.00 83.60 1985 30.70 55.70 35.90 97.60 1986 69.90 61.10 99.00 48.30 1987 14.20 0.00 0.00 23.70 1988 60.40 124.70 13.30 88.60 1989 79.20 95.40 27.50 86.60 1990 58.00 159.30 87.50 214.60 1991 6.50 36.00 26.00 20.00 1992 104.30 80.00 97.00 117.00 1993 27.00 119.00 29.20 123.40 1994 76.70 176.50 143.00 81.30 1995 31.20 88.00 72.20 60.00 1996 6.30 12.00 1.20 69.50 1997 12.00 31.00 30.00 36.30 1998 19.40 45.20 22.00 52.30 1999 36.10 113.50 8.00 107.20 2000 25.80 46.80 22.00 32.90 2001 40.50 26.10 16.80 70.40 2002 4.00 26.00 2.00 2.30 2003 71.00 150.40 61.00 137.20 2004 85.60 73.00 11.80 57.80 2005 15.40 23.00 26.30 32.10 2006 46.00 60.00 46.00 141.20 fig. 1. intensity of rainfall, 2011 engineering, technology & applied science research vol. 9, no. 4, 2019, 4474-4479 4476 www.etasr.com mahessar et al.: flash flood climatology in the lower region of southern sindh iii. methodology a walk through survey was conducted in the 2011 flood which damaged standing crops, communication infrastructure, irrigation and drainage systems, villages, towns and cities in the lower part of southern sindh and also changed the lake ecosystem. two to three feet of rainwater was observed to be standing in major roads and lowlands in various sindh areas. rainfall data of years 2011 and 2012 which were recorded at various rain gauge stations by the irrigation and the meteorological department were collected for computing rainfall statistics. the collected rainfall data have been analyzed in order to prepare the present and future strategy, and to customize flood management plans for controlling flood risk. iv. results and discussion most flash floods were caused from heavy rainfall. an understanding of flash flood climatology helps to develop tools to identify the risk of flooding and the likely timescale involved [21]. eventough abnormal rains and cyclones are nowadays common phenomena, they are major causes of damages. frequently heavy rains hit in 2010 the whole area of pakistan, in 2011 the southern part of sindh and in 2012 the northern part of sindh, but the mostly severe rainfall occurred in 1992, 1994, 2003 and 2006 in the same region of south sindh. figure 2 shows the rainfall occurring in badin, benazirabad and tharparkar chhor during the events of july and august of 1994. fig. 2. rainfall in lbod watershed area during the monsoon of 1994 august rains generated heavy runoff because the watershed area was already saturated and filled with water during july. the rain flood damaged crops, irrigation and drainage systems, road infrastructures, and cost many human lives. figure 3 shows the rainfall in badin, chhor and benazirabad for the same period of 20003. we see that the rainfall varied from 20 to 155mm but with a higher intensity in badin. it rained with severe intensity in the lower region of southern sindh during 2003 and with low intensity in the upper region of northern sindh. the first event of heavy rain occurred in 25-29 july and the second, in the lower region, on 26 august of 2003. the generated rain runoff was higher than the designed carrying capacity of the lower drainage system, so rainwater stagnated for months. this stagnant rainwater caused damages to agricultural lands and crops, infrastructure communication systems, and irrigation and drainage networks. figure 4 shows that rainfall variation during the monsoon of 2006. unusual rains occurred in badin, benazirabad and chhor area from 25 to 30 of july. the rain flood intensity was higher than the carrying capacity of the lower drainage system which flooded the entire area of the lower region and coastal belt. crops and communication systems were damaged in the affected area. the phenomenon of abnormal rainfall is often observed in the coastal area of southern sindh so the locals have become frequent victims of rain related disasters. figure 5 reveals that heavy rainfall in 2010 occurred in the catchment area of indus river from the glacier to arabian sea which caused many breaches in the protected banks of indus river and damages in communication infrastructures, buildings, crops, causing losses in human lives in the provinces of pakistan, i.e. kpk, punjab and sindh except baluchistan. fig. 3. rainfall in lbod watershed area during the monsoon of 2003 fig. 4. rainfall in lbod watershed area during the monsoon of 2006 fig. 5. rainfall in lbod watershed area during the monsoon of 2010 engineering, technology & applied science research vol. 9, no. 4, 2019, 4474-4479 4477 www.etasr.com mahessar et al.: flash flood climatology in the lower region of southern sindh however, rains in the lower region of the left side of indus in sindh province occurred with low intensity with 100mm in badin and 70mm in benazirabad (figure 5). hence, no loss of life and property occurred in 2010 in the lower region of sindh. figure 6 shows that heavy rainfall occurred in methi, badin, benazirabad and chhor in august-september of 2011 in the watershed area of the left bank command area of sukkur and kotri barrages. fig. 6. monsoon rainfall in lbod catchments, august-september, 2011 the recorded maximum rainfall was 300mm, occurred within 24 to 48 hours and was 8 to 10 times higher from the designed capacity of lbod and kotri surface drainage system. the main events occurred on august 11 and 29 and continued with intervals until september 13 when the highest rainfall in the history of sindh was recoded, which shows the unpredictable rainfall pattern in this area due to climate change. figure 7 exhibits the relation between normal and abnormal (2011) rainfall in pakistan, kpk, punjab, balochistan, and sindh. the highest rainfall deviation error among the provinces of pakistan was found in sindh. the rain floods of 2011 were unique in intensity, spread and simultaneous recurrence in the lower region of sindh province. fig. 7. percentage of deviation of 2011monsoon (july-august) figure 8 shows the recoded erratic rainfall in badin, mirpurkhas, mithi, umerkot, benazirabad and hyderabad (600mm, 820mm, 1100mm, 500mm and 300mm respectively). fig. 8. highest rainfall recorded in the districts of southern sindh in august-september of 2011 the intensity of rainfall was so high that not only damaged almost all the catchment area of the lbod system, but also other parts of sindh. the rainfall at the lower region during the july-august of 2011 interval is shown in figure 9. the rainfall water flooded lower region districts like badin, methi, nawab shah (benazirabad), mirpurkhas with highest intensity while the upper region districts such as jacobabad, larkana, sukkur, rohari, dadu, moin-jo-daro and dadu received low intensity and even less rains. as a result the rainstorm in the lower region affected all structural and non-structural activities. fig. 9. rainfall in sindh districts during july-august, 2011 in the northern part of sindh, there is a limited facility of surface drainage for agricultural runoff and waterlogged areas and existing surface drainage has no carrying capacity to drain out abnormal rains. the heavy rain flood of 2011 caused damage to crops, villages, towns, cities and road infrastructures. climatological flash flood events were recorded in 1992, 1994, 2003 and 2006 2010 and 2011 in southern and northern sindh, but events with high intensity were more frequent in the coastal part of the southern sindh. v. flood impact in lower sindh region heavy rainfalls caused disasters in the lower region of sindh and huge amounts of rainwater were accumulated in the land, villages and towns situated in the southern part of sindh. the local people made relief cuts in irrigation channels for saving mature crops and households on a temporary and short strategy basis. several breaches occurred in the banks of main and branch canals. major breaches occurred in fuleli canal, akram wah and nara canal system and also several breaches engineering, technology & applied science research vol. 9, no. 4, 2019, 4474-4479 4478 www.etasr.com mahessar et al.: flash flood climatology in the lower region of southern sindh occurred in the main and branch drains of the lbod system. almost all the drainage system was damaged and overtopped due to overwhelming rainfall intensity. the designed capacity of the spinal drainage was 4600 cusecs while the cumulative discharge was about 14,000 cusecs. the official land utilization statistics of sindh show that all cotton area, 50% of the rice and fodder crops, and a smaller percentage of sugarcane area were damaged. the statistics were worked out through the use of satellite remote sensing technology. the affected cotton area is 45.9 thousand ha and the production loss was estimated at around 0.34 million bales. the rice area damaged is estimated at 32.4 thousand ha and the rice production loss was estimated at 99.9 thousand tons. sugarcane crop was generally affected in a minor degree. the damages were estimated by suparco through satellite remote sensing. the cultivated area in sindh is 4.89 million ha. the net sown area over a year is 2.81 million ha and the fallow area over a year is 2.08 million ha. this is almost a ratio of 60% cropped area and 40% fallow area. however, in view of our assessments it is assumed that cropped area is 70% and fallow area is 30% [22]. vi. conclusions monsoon rains of 2011 were the most intense event in the history of pakistan. the heavy rainfall flash flooded the whole area of lower sindh. relief cuts were made in the irrigation and drainage network for saving crops and households but this worsened the situation, this water entered the spinal system, which was forced to deal with about 14000 cusecs discharge against the designed 4600 cusecs. this resulted to overtopping of the mirpurkhas main drain, spinal and doro puran outfall drain at various places, particularly at where the constructed drains intersect the dhoro puran natural water way. the major reason of this disaster was the small carrying capacity of the lbod system, but also we have to point out that the drainage system was chocked, the natural waterways were blocked by altered agriculture lands, construction of roads, having inadequate size and number of culverts and aqueducts over drains, consequently overtopping the drainage and irrigation networks. sindh irrigation and drainage authority (sida) and area water boards (awbs) have as goals to introduce reforms in the water sector and to restore equitable and reliable water delivery of the irrigation system. their functions are operation, maintenance and rehabilitation of canals, distributaries and minor networks, maintenance, rehabilitation and monitoring of the main drainage system, construction, operation and maintenance of the outfall drains, receiving effluent drainage water from awbs and convey it to the sea, maintain the flood protection infrastructure along river indus, and overall to act as the prime agent of change, advising awbs and farmer organizations (fos). it is concluded that to enhance the capacity of lbod and kotri surface drainage system for safe disposal of extraordinary rainfall from its watershed area, the best should be made from the use of the existing facilities and natural waterways based upon realistic hydro-meteorological analyses for draining out rainwater. facilities, monitoring tools, weather radars, and digital rain gauge stations must be provided in order to forecast more reliably heavy disasters, in order to perform more succesfully risk management and preparedness plans in southern sindh. acknowledgments authors are thankful to the sindh irrigation and drainage authority and the left canals area water board for providing the data and facilities for this research. references [1] m. a. melieres, c. marechal, climate change: past, present, and future, john wiley & sons, 2015 [2] a. a. mahessar, a. l. qureshi, g. h. dars, m. a. solangi, “climate change impacts on vulnerable guddu and sukkur barrages 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sun–climate connection”, journal of atmospheric and solar-terrestrial physics, vol. 73, no. 13, pp. 1980-1987, 2011 [14] y. y. loo, l. billa, a. singh, “effect of climate change on seasonal monsoon in asia and its impact on the variability of monsoon rainfall in southeast asia”, geoscience frontiers, vol. 6, no. 6, pp. 817-823, 2015 [15] a. a. mahessar, a. l. qureshi, a. baloch, “flood forecasting for the super flood 2010 in sukkur-kotri reach of indus river”, international water technology journal, vol. 3, no. 4, pp. 255-262,2015 [16] s. das, s. v. singh, e. n. rajagopal, r. gall, “mesoscale modeling for mountain weather forecasting over the himalayas”, bulletin of the american meteorological society, vol. 84, no. 9, pp. 1237-1244, 2003 [17] g. rasul, q. u. z. sixiong, z. sixiong, z. qingcun, “a diagnostic study of record heavy rain in twin cities islamabad-rawalpindi”, advances in atmospheric sciences, vol. 21, no. 6, pp. 976-988, 2004 [18] m. murshed, “does improvement in trade openness facilitate renewable energy transition? evidence from selected south asian economies”, south asia economic journal, vol. 19, no. 2, pp. 151-170, 2018 engineering, technology & applied science research vol. 9, no. 4, 2019, 4474-4479 4479 www.etasr.com mahessar et al.: flash flood climatology in the lower region of southern sindh [19] a. a. mahessar, k. c. mukwana, a. qureshi, m. ehsan, h. leghari, a. l. manganhar, “assessment of water quality of lbod system and environmental concerns”, quaid-e-awam university research journal of enginnering, science & technology, vol. 15, no. 1, pp. 32-39, 2016 [20] a. a. mahessar, a. l. qureshi, a. n. laghari, s. qureshi, s. f. shah, f. a. shaikh, “impact of hairdin, miro khan and shahdad kot drainage on hamal dhand, sindh”, engineering, technology & applied science research, vol. 8, no. 6, pp. 3652-3656, 2018 [21] c. a. gandarillas, m. saleh soomro, a. nazir, a. a. dasti baloch, a. turangzai, a. javed, b. a. shahid, d. veselinovic, f. samo, g. r. keerio, j. e. priest, k. ansari, k. h. soofi, m. silver, m. s. samo, n. ibrahim, r. tabassum, r. renfro, r. wilkins, s. u. zafar, s. ali soomro, s. m. akhtar, s. a. h. jagirdar, t. k. baloch, u. g. dar, z. saeed, z. habib, z. mangrio, regional master plan for the left bank of indus, delta and coastal, sindh irrigation and drainage authority, 2013 [22] suparco, pakisttan rain/flood 2011: report on flash floods, bbreaches in canals and damage to infrastructure & agriculture sectors in sind province, suparco, 2011 ab (w im con nec col un ada dra me ove an opt the alg con bas inf the ove rea mi rou pro app pac obs loc opt 802 qo are fun gat sin req sho dur engineerin www.etasr even a e si s bstract—the m wsn) in disast prove quality nsumption. lo cessary. with llected data is i ique form of o aptive routing awbacks of ac essages and l ercome by con n event-based timization (eb e performance gorithm is to i nsumption by sed on the b formation of no e sink (base sta erheads. ebc active 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ge of engineeri arashtra, india @rediffmail.com ge of a wirele is to discover (qos) and ness of nodes is the position ant colony opti method, which i eed packet de flooding, huge nce time. th tion informati alized energy ) algorithm is p the main focu and minimize tion and selecti pired routingring, data is ag h cluster head s a scalable a hich improves on of wsn as v, aco, aco ces energy n to improvem ease in packet d other algorith energetic path co) of the net ork increased p aodv; ch; clu ntroduction er of sensor n ow power cap ed in a partic or nodes (sn) ops as shown ations is that nication witho g algorithm do ience research an & kulkarni: usterin optim nt of w ing m ess sensor ne efficient routi to reduce e s also useful o n of sensor imization (aco is highly suitab livery. the pr overhead of c hese drawback ion of sensor efficient ant c proposed to en us of the pro the network e ing the optima -aco and lo ggregated and s (ch) which re and energy ef s qos, lifetim s compared to o using rssi consumption ment in throu drop which ha hms, i.e. autono h_with_ant c twork. use of packet drop. ustering; ebc; nodes. these pacity. these cular area for pass the data n in figure 1 t the sensor out failure for oes not consid h v event based c ng loc mizatio wirele etwork ing, to energy r even nodes, o) is a ble for rimary control ks are nodes. colony nhance oposed energy al path ocation sent to educes fficient me and o other i. the n by ghput, as been omous colony ieee ; lee; nodes multir data to the 1. the nodes r long der the loca whe algo solv qos effi is p enh clus biol nod a. hyb con nod ene netw reac pro vol. 8, no. 4, 20 clustering loca calized on for ess sen dr. ation informat ere stable com orithm is one ved [1-3]. the s and network therefore, an icient ant colo proposed. the hance qos, to ster formation logical inspire des. classical rou classical rou brid [4, 5]. r nsumption beh des in the ws ergy efficiency work perform ctive protocol tocols due to 018, 3177-3183 alized energy ef d ener perfo nsor n anju v d. y. patil in pune, mah anju_k64@ tion and thus mmunication is of the major p e main goals k lifetime and t fig. 1. w n event base ony optimizati e main focus o minimize n n and to selec ed routing-ac ii. rel uting protocol uting protoco routing proto havior of nod sn are supplie y is a major pr mance. takin s are more ef o less control 3 efficient ant co rgy ef ormanc networ v. kulkarni nstitute of tech harashtra, indi @yahoo.co.in cannot be use s important. s problems of se of wsn routi to reduce conn wsn architecture ed clustering ion (ebc_le of the propos network energy ct the optimal co and locati lated work ls ls are proact ocol has an des in a netw ed with a limit roblem that inf ng energy in fficient as com overheads. b 3177 olony optimizat fficient ce rk hnology a n ed in disaster selection of ro ensor network ing are to imp nectivity failur localized en e-aco) algor sed algorithm y consumptio path based o ion informatio tive, reactive impact on en work. since m ted energy ba fluences the ov nto considera mpared to proa both proactive tion… t areas outing to be prove re. nergy rithm is to on by on the on of e and nergy mobile attery, verall ation, active e and engineering, technology & applied science research vol. 8, no. 4, 2018, 3177-3183 3178 www.etasr.com chavan & kulkarni: event based clustering localized energy efficient ant colony optimization… reactive protocols are unaware of energy metrics and hence cause lowering of the battery energy of the nodes over the most heavily used routes in the network. b. localization based routing protocols location information for sensor networks by most routing protocols needs to calculate the distance between two particular nodes so that energy consumption can be calculated. according to the dependency of range measurements, the existing localization schemes can be categorized into two major categories: range-based approaches and range-free approaches. range-based and range-free schemes are again divided into anchor based and anchor free schemes. the anchor-free schemes do not assume that the node positions are known at first. on the other hand, the anchor-based schemes need some nodes that are aware of their positions (anchor nodes) to provide geographic information to unidentified nodes to localize [6]. c. location based bio-inspired routing algorithms various location-based routing algorithms have been proposed, nevertheless, they have a relative shortcoming: either not guaranteeing to find a way to the destination or locating a path which is much longer than the shortest path. position based ant colony (posant) routing algorithm is a collection of ant colony based routing algorithms that use the data about the position of nodes to improve the efficiency of an ant algorithm. contrary to other position based algorithms, this algorithm does not fail when the network contains nodes with different transmission range. posant is a multipath routing algorithm using gps to find position information which adds to cost of nodes and is not suited for indoor network [7]. location based ant colony optimization (lobant) algorithm uses distance to consider routing metrics due to received signal strength indicator (rssi), but energy aware metrics are not taken into account [8]. autonomous localization based eligible energetic path_with_ant colony optimization (aleep with aco) algorithm was developed in [9] by a combination of the advantages of the best exiting protocols. authors used the location of the nodes, adaptive transmission power (atp) and energy aware metrics to increase the efficiency of routing. after studying the related work, we came to conclusion and proposed an event based clustering localized energy efficient ant colony optimization (ebc_lee-aco) routing algorithm by combining the advantages of aco, rssi and clustering. iii. proposed scheme a. problem definition the main challenge of wsn is to discover efficient routing, as the sensor nodes are not static and change their position randomly. limited battery life is another issue. a disaster situation is one more challenge for wsn by which the communications in the network may fail and lead to excessive packet drop and can hang the network. for solving these problems, ebc_lee-aco algorithm is proposed, which is aco, based on geographical location with clustering approach. b. objectives  to find and reconstruct the optimal path for routing in disaster situations smoothly and quickly.  to reconstruct communication links in case of link failure.  to reduce network energy consumption by selecting the least distance from source to destination node with localized and clustering approaches.  to improve network qos.  to verify whether the proposed routing algorithm is more efficient than other routing algorithms like aodv, aco and aco using rssi and present aleep with aco routing algorithm. c. methodology to achieve the objectives we considered the following implementation steps:  design ebc_lee-aco routing algorithm by combining the advantages of aco, rssi and clustering.  simulate network considering variable number of nodes and variable node mobility.  this simulation will provide us data to perform network analysis of performance parameters like throughput, packet delivery ratio, packet drop and consumed energy.  compare above network parameters between the proposed algorithm and aodv, aco, aco using rssi algorithm and present aleep with aco algorithm.  network simulator 2 (ns2) is used for simulation. iv. current methods a. ad-hoc on demand distance vector (aodv) protocol as the name itself suggests, aodv protocol is an on demand routing protocol, which means that it determines a route to a destination only when a node wants to send a packet to that destination [10]. essential objectives of the algorithm are:  to broadcast discovery packets only when necessary using rreq message.  to perform local connectivity management, neighborhood identification and general topology maintenance using hello messages.  to spread data about changes in availability to neighboring nodes which will probably require the information using rerr message. aodv operation is divided into two phases, route discovery and route maintenance. b. ant colony optimization (aco) algorithm aco is a bio-inspired meta-heuristic algorithm introduced in [11, 12]. the main idea is to use ants as an inspirational source because they follow self-organizing principles which allow highly coordinated behavior. ants have collective learning intelligence. each ant communicates, learns and cooperates non-verbally with the others through pheromones. different kinds of ant’s algorithm can be inspired by different ant behaviors, e.g. foraging, labor division, brood sorting, and engineering, technology & applied science research vol. 8, no. 4, 2018, 3177-3183 3179 www.etasr.com chavan & kulkarni: event based clustering localized energy efficient ant colony optimization… cooperative transport [13, 14]. the basic rule of aco is the ability of ants to discover the shortest path between food sources and the anthill. in the beginning, the route the ants find may not be the shortest path, but with the passage of the time, more and more ants move cooperatively and the trail of their path becomes shorter and shorter until they get the shortest path. there are three phases of the ant based algorithm namely route discovery, route maintenance and route failure handling. c. ant colony optimization using received signal strength indicator (aco using rss) algorithm location aware aco routing is a high performance routing protocol for wsn design [15]. the main reason to seek location awareness in aco routing is the dynamic network topology causing frequent link breakup that causes the source node to spend most of its time in route setup and route maintenance. in location awareness in aco, each node will have a general idea about the network topology and its neighbors so that it can choose the nearest neighbor toward the destination [15, 16]. this new routing algorithm is based on aco and uses location as a parameter to enhance its efficiency. from the rssi value every node can determine the distance between nodes. in aco using rssi, the route is searched only when there is a collection of information packets to be sent from a source node (s), to a destination node (d), thus it is a reactive routing algorithm. sending the information packets will begin after a route from the source to the destination node is built up. before that, only forward ants are being exchanged with backward ants. to limit the time it needs to discover a route while keeping the quantity of generated ants as small as it could be expected under the circumstances, data about the position of nodes is utilized as a heuristic value [7, 8]. when there is a packet to be sent, the source starts a route discovery phase. at first, a route request (rreq) broadcasts to each one of the nodes from s to d. when the d gets the first rreq message, its answer is a route reply message to s. on receiving the rrep message, a node will extract rssi value from it and would calculate the location of the neighboring nodes and in turn the location of the destination. the routing table is updated with distance information between the nodes utilizing rssi value. every sensor node in the wsn has a memory block in which the leftover energy, the location data of the node, its neighbors and the base station are stored. route establishment using distance is described in [8, 20]. v. proposed methods a. ebc_lee-aco algorithm previous algorithms have some limitations such as: for proper monitoring, dense and large wsn will be used for different types of applications. there is a high probability of redundant data being recorded by neighboring nodes during an event. as many nodes might sense the same event, they will establish a route separately. routing algorithms based on ant colony are considered to have a high percentage in terms of packet delivery, but the drawback is overhead of the control messages required for discovering the route. cluster-heads use only forward route discovery control messages. their limitation is the dynamic topology of the network, which limits the bandwidth availability and energy constraints. to overcome these problems, clustering technique is used, as the clustering approach has an advantage of spatial reuse of resources to increase system capacity, data aggregation, reduce energy consumption etc. [17-19]. in the present research work an event based clustering localized energy efficient ant colony optimization (ebc_lee-aco) algorithm is proposed. the main focus of the proposed ebc_lee-aco algorithm is to minimize the energy consumption of the network by cluster formation and to select the optimal path based on the biological inspired routing aco and location information of nodes. b. three phases (stapes) of proposed algorithm 1) hop tree formation phase in wsn, data transmission takes place in multi-hop fashion where each node forwards its data to a neighbor node nearer to the sink. the node doesn’t have a full understanding of the network, but has only knowledge of its neighboring nodes. each node only knows the hop level in which it is in a hop tree [20]. in this phase, the distance metric used is the hop count (i.e. the number of nodes from a to b). the distances between the sink and different nodes are calculated. the algorithm is initiated by the sink node broadcasting a hop configuration message (hcm) to its neighboring nodes with a hop value. this hop value gets incremented every time the message is transmitted and is stored in their routing table. this process is continued until all the nodes are configured with a hop value within a tree. the hcm has two parts id and hoptotree (htt). id is the node identifier whereas the htt is the distance in hops. in this approach the sink node broadcasts hcms having values of htt as 1 and hop count 0. the receiving nodes forward messages to their neighboring nodes. initially all nodes set the value of htt as infinity. on receiving the hcm, each node compares the value of htt in the hcm with the value of htt that node already has in it. if the above conditions are met, then the node updates its internal stored values by the value of the field id as well as the value of the htt variable of the hcm. the node broadcasts the hcm with the new values. if the condition is not met which means that the node received the hcm from a shorter distance then the node discards it. the step described above occurs repeatedly until the whole network is configured. initially there is no recognized route and the value of htt variable has the smallest distance to the sink. when the first event is triggered the variable still stores the smallest distance, but a new route is established. after the event, the variable stores the lower among the 2 values: the distance to the sink or the distance to the closest already recognized route. hop tree formation phase is shown in figure 2. 2) cluster formation and cluster head (ch) selection phase when an event is detected by one or more nodes, the cluster formation and the cluster head selection algorithm gets started. a set of nodes that have detected an event forms a cluster. once clusters are formed, the next process is to select the cluster head within each cluster. the main process for forming the cluster is the selection of leader node which is called cluster head (ch) by using the cluster configuration message (ccm). ccm has four attributes (type, id, htt, state), where id is the sto fig netw the no sel bet cou i.e on tie wi me col the wh sam ch the nu red agg clu ac 3) rou coo wo des bei sea to loc rou no inv the me des no are me engineerin www.etasr e identifier of ores state value g. 2. flooding work where node if this is the e cluster head de or to the no lection 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destin over the route y analyzing th l an ant reache reates a stack, ng a fant e ergy with the t stination node timer called f time the d n nts, d will c e. ached, fant k and follows ollows the sta e sink to the so 3 efficient ant co me event form a cl ound in any o ) is generated h that was fol ontains rssi essage, rssi determining t l be updated. ts into two sec (bants). th ions is to take he other sec n collected by not create o he information the process s wards the sink ssemination. t nts to two p ghbor nodes ar the number o mone trail show these agents a tiates route nation at regula e to d based he routing tab es d. , pushing in tr each of the n threshold ener or sink receiv fet (forward node accepts calculate the o is converted i it. ack entries and ource. 3180 olony optimizat luster and select c of the neighb by d and is se llowed to reac value. when i value woul the location o for route sele ctions: forward he main reaso e the advantag ction i.e. ba y fants. base or update ro n and route cre starts with the k or base stati the s initiates ossible paths re closer to s f generated an ws the edge w are communic establishmen ar time interva on which no ble. this proce rip times for e nodes compare rgy. ves the first fa d expiration ti all fants. optimal path u into bant. b d traces the re tion… ch boring ent to ch d. each ld be of the ection d ants on to ge of ants ed on outing eation e ch ion to route from . the nts as weight cating nt by als. ode is ess is every es its ant, mer). with using bant verse engineering, technology & applied science research vol. 8, no. 4, 2018, 3177-3183 3181 www.etasr.com chavan & kulkarni: event based clustering localized energy efficient ant colony optimization… 8. pheromone edge updates depend upon the residual energy of the node and location. 9. once the optimal path is found, d backs up all possible paths in case the path is failed. vi. practical analysis this section presents a practical analysis of network performance metrics like throughput, packet delivery ratio, packet drop, consumed energy and node mobility. a. network scenarios and simulation parameters scenarios and simulation parameters are shown in table i. table i. scenarios and simulation parameters network parameters values routing protocol / algorithm aodv, aco, aco using rssi, ebc_lee-aco traffic patterns cbr (constant bit rate) network size 1000 × 1000 (x x y) mac protocol 802.11 initial energy 200j (for each node) simulation time 30s simulation platform ns-allinone-2.32 node variables number of nodes 10/30/60/100 node speed 3m/s variable mobility number of nodes 50 maximum speed 1/2/3/4/5 m/s b. results and analysis 1) results on varying number of nodes it is observed from figures 4 to 7 that for increasing number of nodes and constant mobility, throughput and packet delivery ratio decrease and consumed energy and the number of dropped packets increase because:  the probability of success in accessing the channel decreases,  as hop count increases, congestion and delay increases and collision and transmission error increase. fig. 4. throughput versus number of nodes fig. 5. pdr versus number of nodes fig. 6. packets drop versus number of nodes fig. 7. energy versus number of nodes 2) results of varying node mobility figures 8 to 11 show that for increasing mobility with constant nodes, throughput, packet delivery ratio and consumed energy decrease and packet drop increases because the probability of path breakage increases and the construction of a new path takes time. results show that the performance parameters of the network are improved by the use of the proposed ebc_lee-aco algorithm in comparison with aodv, aco and aco using rssi algorithms due to the following characteristics of the ebc_lee-aco algorithm: nodes 10 20 30 40 50 60 70 80 90 100 50 55 60 65 70 75 80 85 90 95 packet delivery ratio aodv aco aco rssi ebc lee aco p ac ke ts d ro p( n o. ) engineering, technology & applied science research vol. 8, no. 4, 2018, 3177-3183 3182 www.etasr.com chavan & kulkarni: event based clustering localized energy efficient ant colony optimization…  no back propagation.  multipath routing.  no packet flooding.  shortest distance routing.  ideal nodes.  reduce overhead.  data aggregation.  no redundant data transmission. fig. 8. throughput versus node mobility fig. 9. energy versus number of nodes vii. conclusions in this work, the ebc_lee-aco routing algorithm is implemented and the network performance, by varying number of nodes and node mobility, is analyzed. this algorithm is extensively compared to other algorithms like aodv, aco and aco-rssi by considering network metric parameters like throughput, packet delivery ratio, packet drop and consumed energy. simulation results show that the ebc_lee-aco algorithm outperformed the other algorithms in disaster situations. aco achieves better performance compared to aodv, as aco allows rerouting to another link in the case of existing link failure (no back propagation). aco using rssi routing algorithm improves the routing by minimizing the flooding of routing packets because, it has the location information of nearby nodes. fig. 10. pdr versus node mobility fig. 11. packet drop versus node mobility fig. 12. energy versus node mobility the ebc_lee-aco algorithm has achieved better performance due to clustering technique and location information of nodes. clustering data is aggregated and sent to the sink through ch which reduces overheads. also, location engineering, technology & applied science research vol. 8, no. 4, 2018, 3177-3183 3183 www.etasr.com chavan & kulkarni: event based clustering localized energy efficient ant colony optimization… information of nodes is useful to send data to shortest distance node in less time. the proposed algorithm reduces energy consumption by approximately 7%. an improvement in throughput, packet delivery ratio and increase in packet drop has been observed in comparison with present network routing algorithms, i.e. autonomous localization based eligible energetic path_with_ant colony optimization (aleep with aco) [9]. use of ieee 802.11 standard increased packet drop. hence, our ebc_lee-aco algorithm is useful for improvement in qos and reduction in energy consumption of the wsn. it is most suitable for information monitoring in disaster situations. the extension of the proposed algorithm will be considered for varying network areas as well as increasing number of nodes and mobility in future work. references [1] i. f. akyildiz, w. su, y. sankarasubramaniam, e. cayirci, “wireless sensor networks: a survey”, computer networks, vol. 38, no. 4, pp. 393–422, 2002 [2] j. yick, b. mukherjee, d. ghosal, “wireless sensor network survey”, computer networks, vol. 52, no. 12, pp. 2292–2330, 2008 [3] s. k. gupta, p. sinha, “overview of wireless sensor network: a survey”, international journal of advanced research in computer and communication engineering, vol. 3, no. 1, pp. 5201-5207, 2014 [4] a. k. gupta, h. sadawarti, a. k. verma, “review of various routing protocols for manets”, international journal of information and electronics engineering, vol. 1, no. 3, pp. 251-259, 2011 [5] h. s. a. hamatta, n. i. zanoon, r. m. al-tarawneh, “comparative review for routing protocols in mobile ad-hoc networks”, international journal of ad hoc, sensor & ubiquitous computing, vol. 7, no. 2, pp. 13-31, 2016 [6] a. mesmoudi, m. feham, n. labraoui, “wireless sensor networks localization algorithms: a comprehensive survey”, international journal of computer networks & communications, vol. 5, no. 6, pp. 45-64, 2013 [7] s. kamali, j. opatrny, “a position based ant colony routing algorithm for mobile ad-hoc networks”, third international conference on wireless and mobile communications (icwmc'07), guadeloupe, france, march 4-9, 2007 [8] r. vallikannu, s. e. jubin, “a location based aco routing algorithm for mobile ad hoc networks using rssi”, ieee international conference on communication and signal processing, chennai, india, april, 3-5, 2013 [9] r. vallikannu, a. george, s. k. srivatsa, “autonomous localization based energy saving mechanism in indoor manets using aco”, journal of discrete algorithms, vol. 33, pp. 19–30, 2015 [10] p. k. maurya, g. sharma, v. sahu, a. roberts, m. srivastava, “an overview of aodv routing protocol”, international journal of modern engineering research, vol. 2, no. 3, pp. 728-732, 2012 [11] m. dorigo, c. blum, “ant colony optimization theory: a survey”, theoretical computer science, vol. 344, no. 2-3, pp. 243–278, 2005 [12] c. blum, “ant colony optimization: introduction and recent trends”, physics of life reviews, vol. 2, no. 4, pp. 353–373, 2005 [13] s. binitha, s. s. sathya, “a survey of bio inspired optimization algorithms”, international journal of soft computing and engineering, vol. 2, no. 2, pp. 137-151, 2012 [14] o. deepa, a. senthilkumar, “swarm intelligence from natural to artificial systems: ant colony optimization”, international journal on applications of graph theory in wireless ad hoc networks and sensor networks, vol. 8, no.1, pp. 9-17, 2016 [15] x. wang, q. li, n. xiong, y. pan, “ant colony optimization-based location-aware routing for wireless sensor networks”, in: lecture notes in computer science, vol. 5258, pp. 109-120, springer, 2008 [16] c. dominguez-medina, n. cruz-cortes, “energy-efficient and locationaware ant colony based routing algorithms for wireless sensor networks”, 13th annual conference on genetic and evolutionary computation, dublin, ireland, pp. 117-124, july 12-16, 2011 [17] s. k. popat, m. emmanuel., “review and comparative study of clustering techniques”, international journal of computer science and information technologies, vol. 5, no. 1, pp. 805-812, 2014 [18] s. mahajan, p. k. dhiman, “clustering in wireless sensor networks: a review”, international journal of advanced research in computer science, vol. 7, no. 3, pp. 198-201, 2016 [19] s. k. gupta, n. jain, p. sinha, “clustering protocols in wireless sensor networks: a survey”, international journal of applied information systems, vol. 5, no. 2, pp. 41-50, 2013 [20] l. aparecido villas, a. boukerche, h. soares ramos, h. a. b. fernandes de oliveira, r. borges de araujo, a. a. ferreira loureiro, “drina: a lightweight and reliable routing approach for in-network aggregation in wireless sensor networks”, ieee transactions on computers, vol. 62, no. 4, pp. 676-689, 2013 microsoft word etasr_v10_n6_pp6418-6421 engineering, technology & applied science research vol. 10, no. 6, 2020, 6418-6421 6418 www.etasr.com phan: contractor's attitude towards risk and risk management in construction in two western … contractor's attitude towards risk and risk management in construction in two western provinces of vietnam van tien phan department of civil engineering vinh university vinh city, vietnam vantienkxd@vinhuni.edu.vn abstract—risk management is an important task in construction management that helps the contractor to actively identify, evaluate, control, and minimize negative impacts of risks on the project, thereby ensuring its effectiveness. people involved in the construction industry need to be well equipped with information and knowledge to manage risks adequately and systematically. the purpose of this research is to explore the attitude towards risk and risk management in construction projects of the vietnamese construction industry, with emphasis on the perspective of contractors. the research data are collected through a questionnaire associated with in-depth semi-structured interviews. the results indicate that the perception of risk within the vietnamese construction industry includes both threats and opportunities. the majority of professionals in the industry have a risk-neutral approach, contrary to previous research. the importance of implementing effective risk management is shared, in the planning and production phase while risk identification was perceived to be the most important out of the four core processes. keywords-contractor; risk; risk management; construction i. introduction risk management in construction is designed to plan, monitor, and control those measures needed to prevent exposure to risk. to do this, it is necessary to identify the hazard, assess the extent of the risk, provide measures to control the risk and manage any residual risks. the integration of an effective risk management is considered essential for the project’s success. construction projects are described as tremendously complex and uncertainty might arise from various sources. risk management is therefore becoming an extensive component of the project management in civil engineering in a pursuit to efficiently deal with unexpected risks and uncertainty. however, the managing of the adverse effects of risk and uncertainty in construction projects is rated ineffective, resulting in delays and a failure to meet quality and cost targets [1]. the aim of applying an efficient risk management procedure is to facilitate risk neutral decisions, resulting in superior performance. in order to obtain more information about risk and uncertainty of the construction project, different methods needed to be applied systematically [2]. although the application of various such techniques will not remove all risks, it ensures that the risks are assessed and managed in a manner allowing the overall objectives of the project to be achieved [3]. risk management in construction is identifying, analyzing, and taking steps to reduce or eliminate the exposures to loss faced by an organization or individual. the practice utilizes many tools and techniques, including insurance, to manage a wide variety of risks. this allows the project to be prepared for unavoidable issues with increased transparency [4]. this process is repeated continuously throughout the entire project life cycle due to the constant possibility of emerging risks. risk and uncertainty must be identified, assessed and responded from the earliest possible phases in order to achieve an efficiently dealt with when they arise [3]. the benefits of the process are the clearer understanding of the specific risks associated with the project, supported decisions by detailed analysis and a built-up of historical data that can be used to assist future risk management procedures. however, many contractors have still not realized the importance of applying risk management techniques as an integral part of the delivery of a project [1]. inefficient risk management has many causes, including the lack of formalized procedures, the discontinuity in different phases of the construction project, and the inadequate integration of knowledge management and interaction between processes and parties [1]. in place of the contractors, the responsibility to deal with risks is deciding if the risks should be reduced, avoided, transferred, or retained [6]. the contractor needs to understand the importance of risk and risk management capabilities to achieve effective risk implementation [7]. in this research, risk management in the vietnamese construction industry has been investigated, with focus being given on the attitude of the contractors towards risk and risk management techniques. the contractors participating in the survey were selected from small and large companies. the research is limited to the vietnamese construction organization in two main provinces in vietnam, vinh long and can tho. corresponding author: van tien phan engineering, technology & applied science research vol. 10, no. 6, 2020, 6418-6421 6419 www.etasr.com phan: contractor's attitude towards risk and risk management in construction in two western … ii. research methodology the research was carried out using a mixed method, in which both quantitative and qualitative data collection techniques and analytical procedures were used [8]. therefore, this form of survey integrates two types of data and the core assumption of this approach is that a combination of qualitative and quantitative methods leads to a better understanding of the problem [10]. mixed approach studies use multiple approaches in answering research questions, and are not restricted or limited [11]. previous research includes thorough understanding of the field of study and formulating research questions. the next step involves preparing a set of semistructured interview questions and building a questionnaire based on the theoretical framework. these steps are needed in order to achieve the purpose of this study, which is to understand the perceptions, knowledge, and practical implementations of risk management process in constructions in vietnam. the questionnaire was designed to identify attitudes, knowledge, and risk management application in the vietnamese construction industry. a survey strategy is associated with inference methodology and tends to be used for exploratory and descriptive research. it allows potential gathering of large amounts of data from a large population [8]. the purpose of descriptive research is to obtain an accurate representation of the person or situation, thus describing the characteristics of the phenomenon under investigation. a questionnaire is one of the most commonly used data collection techniques in surveys. each individual is provided with a questionnaire and is asked to answer the same set of questions, allowing a way to collect answers from a large sample before analysis [8]. a successful questionnaire should be short and simple [12]. simplified questions should be conducted in a logical sequence that moves from easier to more difficult. the questions provided in the survey may be open-ended allowing unlimited answers, bidirectional in which the answer is limited to a pair of alternatives such as yes or no, rating questions, and finally multiple-choice questions in which the respondents are asked to choose the most suitable option. the goal was to get an overall representation of the industry related to risk management. the questionnaire consisted of 29 questions divided into three parts. the first part was designed to collect background information and reveal respondents’ perceptions and attitudes towards risk management. the purpose of the second part was to explore ways to manage and transfer knowledge in the respective companies, and the third part covered practical risk management and implementation methods in the industry. an invitation was emailed to 336 vietnamese contractors a total of 43 responses were received, with a response rate of approximately 13%. the average response rate for external surveys is around 10-15%. about 70% of the respondents had more than 15 years of experience within the construction industry and the majority (88%) where contractors, 24% where developers and 2,38% where consultants. the size of the companies where equally represented, approximately 48% had more than 1000 employees while 52% had less than 1000 employees. iii. results the results of this study show the respondents’ perception of risks and how they view risk management in terms of importance. the respondents covered a variety of occupations in vietnamese construction industry, representing the overall picture of risk management perception and implementation, with their majority having more than 10 years of experience to enhance their credibly. contractors were the 78%, developers (clients) the 19%, and consultants the 13% of the participants. interviews were conducted only with contractors. an equal distribution among company sizes was attained in the data collection, as stated above. a difference of opinion related to the company size will merely be mentioned when a significant differentiation can be observed between them, otherwise an overall picture of the industry will be presented due to similar answers to the questions. the results indicate that the attitude among vietnamese contractors regarding risk is a combination of both opportunity and threat. this contradicts the results presented by [5] where the construction industry is predominantly risk averse. the overwhelming majority of the respondents in both the questionnaire and the interviews described themselves as being risk-neutral rather than riskaverse or risk-seekers, which coincides with previous studies. hence, their attitudes and perception of risk are in line with their risk approach profile as risk-neutral decision makers. one of the interviewees viewed risk as overall negative consequences depending on the type of risk, although he stated that an opportunity might be found when dealing with financial risks. however, the majority of respondents described risks as a mix of threat and opportunity since risks might lead to exploring other ways of managing hazardous situations which may be more prosperous. a. questionnaire the related part of the questionnaire consisted of the following questions: 1) how do you perceive risk within the construction industry? the answers show that the majority of respondents' attitudes toward risk were a combination of threats and opportunities, as shown in figure 1. only two respondents perceived risk only as a threat, two more respondents realized that the risk was something positive, that is only an opportunity. however, about 90% (30 people) of the respondents perceived the risks in the construction industry as a combination of both positive and negative associations. 2) what is your attitude in relation to tisk? about 5% of respondents feel they have a risk-seeking personality while 13% say they do not like risks. the majority, around 82%, has a risk-neutral approach and can balance between avoiding and seeking risks. therefore, a correlation between their cognitive traits and their attitudes is observable. 3) which stage/phase do you consider most important in risk management? respondents varied quite a lot when asked at what stage they considered the implementation of risk management to be the most important. the reason for this is probably the engineering, technology & applied science research vol. 10, no. 6, 2020, 6418-6421 6420 www.etasr.com phan: contractor's attitude towards risk and risk management in construction in two western … professional diversity among respondents because developers and consultants probably value the completion phase more in relation to construction and site managers consider planning and production risks in higher priority. however, the findings indicate that the majority consider the planning stage as the most important stage to implement risk management. this is followed by production, then conceptual stage and finally by the completion and finishing stages, as shown in figure 2. fig. 1. respondents risk perception (left) and respondent’s attitude in relation to risk. fig. 2. answers on “which stage do you consider most important for risk management?”. 4) which risk management process is most important? risk identification was perceived by the respondents as the most important risk management process as shown in figure 3. risk assessment, risk response, and risk monitoring phase are considered rather equally important with small variances in opinion. fig. 3. answer on “which risk management process is most important?”. the questionnaire revealed that the respondents perceived risk management to be most important during the planning and production rather than the conceptual and completion phases. the result illustrates that every phase is considered highly important since the planning and production phase didn’t exceed the other phases significantly. this outcome is probably caused by the fact that the participants came from various professions within the industry, in which different risks are considered. furthermore, out of the four core processes in risk management, the respondents viewed risk identification to be the most important while assessment, whereas response and monitoring where rather equally significant. this parallels the claim by [7] that the identification process might be viewed as the most crucial step. b. interviews the perception of risk management as the adoption of efficient processes of managing risks was shared among all the interviewees. risk management is crucial in order to achieve project objectives. the projects in the construction industry are filled with risks and uncertainty, thus it is essential to have an effective risk management process in place. the concept described in the literature facilitates the ability to maximize opportunities and simultaneously reduce threats. however, no universal standard or method can be observed among the respondents in the interviews, with the implementation of risk management varying in practice. nonetheless, four stages where considered as the core process within the construction industry even though there are many methodologies used for risk management [1]. the findings from the interviews revealed that even though the respondents didn’t have previous knowledge regarding theoretical models and processes they still had analogous organizational processes. hence, they were indirectly practicing risk management similar to the concepts described in the literature. the respondents described a general identification process in order to shed light on various risks followed by an assessment of the risks and a prioritization depending on impact and probability, which was determined by experience and discussion. this process is iterative and continuous throughout their projects, which is the essential information loop principal used when describing the use of an effective risk management implementation [2]. in terms of work environment risks, it was stated by one respondent that they made sure to manage a high impact risk scenario straightaway while low risks were allowed to be fixed during a longer time period. all respondents emphasized the importance of discovering risks as early as possible. iv. conclusions by preparing a set of semi-structured interview questions and by building a questionnaire based on the theoretical framework, the perceptions, knowledge, and practical implementations of risk management process in the construction industry in vietnam have been investigated. the questionnaire was designed to identify attitudes, knowledge, and risk management application in the vietnamese construction industry. the contractors participating in the questionnaire were selected from small and large companies in vinh long and can tho provinces. the perception of risk within the vietnamese construction industry includes awareness of threats and opportunities. the majority of the professionals in the industry have a risk neutral approach, a result that comes in contrast with the findings in [5]. the importance of implementing an effective risk management is shared, especially in the planning engineering, technology & applied science research vol. 10, no. 6, 2020, 6418-6421 6421 www.etasr.com phan: contractor's attitude towards risk and risk management in construction in two western … and production phases, while risk identification was perceived to be the most important of the four core processes. references [1] n. j. smith, t. merna, and p. jobling, managing risk: in construction projects, 2nd ed. hoboken, nj, usa: wiley-blackwell, 2009. [2] g. m. winch, managing construction projects, 2nd edition. chichester ; ames, iowa: wiley-blackwell, 2009. [3] k. potts, construction cost management: learning from case studies. london, uk: routledge, 2014. [4] m. schieg, “risk management in construction project management,” journal of business economics and management, vol. 7, no. 2, pp. 77– 83, jan. 2006, https://doi.org/10.1080/16111699.2006.9636126. [5] a. s. akintoye and m. j. macleod, “risk analysis and management in construction,” international journal of project management, vol. 15, no. 1, pp. 31–38, feb. 1997, https://doi.org/10.1016/s0263-7863(96)00035x. [6] j. liu, b. li, b. lin, and v. nguyen, “key issues and challenges of risk management and insurance in china’s construction industry: an empirical study,” industrial management & data systems, vol. 107, no. 3, pp. 382–396, jan. 2007, https://doi.org/10.1108/02635570710734280. [7] m. n. k. saunders, a. thornhill, and p. lewis, research methods for business students, 5th edition. new york, ny, usa: pearson, 2009. [8] a. f. serpella, x. ferrada, r. howard, and l. rubio, “risk management in construction projects: a knowledge-based approach,” procedia social and behavioral sciences, vol. 119, pp. 653–662, mar. 2014, https://doi.org/10.1016/j.sbspro.2014.03.073. [9] r. b. johnson and a. j. onwuegbuzie, “mixed methods research: a research paradigm whose time has come:,” educational researcher, vol. 33, no. 7, 2004, https://doi.org/10.3102/0013189x033007014. [10] p. t. nguyen and p. c. nguyen, “risk management in engineering and construction: a case study in design-build projects in vietnam,” engineering, technology & applied science research, vol. 10, no. 1, pp. 5237–5241, feb. 2020, https://doi.org/10.48084/etasr.3286. [11] m. s. shahbaz, a. g. kazi, b. othman, m. javaid, k. hussain, and r. z. r. m. rasi, “identification, assessment and mitigation of environment side risks for malaysian manufacturing,” engineering, technology & applied science research, vol. 9, no. 1, pp. 3852–3858, feb. 2019, https://doi.org/10.48084/etasr.2529. [12] a. chenarani and e. a. druzhinin, “a quantitative measure for evaluating project uncertainty under variation and risk effects,” engineering, technology & applied science research, vol. 7, no. 5, pp. 2083–2088, oct. 2017, https://doi.org/10.48084/etasr.1530. microsoft word mainier-ed.doc etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 479-482 479 www.etasr.com monteiro et al.: socio-environmental impacts associated with burning alternative fuels in clinker kilns socio-environmental impacts associated with burning alternative fuels in clinker kilns luciane p. c. monteiro escola de engenharia universidade federal fluminense niterói, rio de janeiro, brazil luciane@predialnet.com.br fernando b. mainier escola de engenharia universidade federal fluminense niterói, rio de janeiro, brazil fmainier@uol.com.br renata j. mainier prog. pós-graduação eng.civil universidade federal fluminense niterói, rio de janeiro, brazil renatajogaibmainier@msn.com abstract— the pollutants found in emissions from cement plants depend on the processes used and the operation of the clinker kilns. another crucial aspect concerns the characteristics of raw materials and fuels. the intensive use of fuels in rotary kilns of cement plants and the increasing fuel diversification, including fuels derived from coal and oil, from a multitude of industrial waste and from biomass, charcoal and agricultural waste (sugarcane bagasse, rice husk), is increasing the possibilities of combinations or mixtures of different fuels, known as blends. thus, there are socio-environmental impacts associated with the burning of alternative fuels in clinker kilns. in view of the growing trend of entrepreneurs who want to target the waste produced in their unit and of the owners of the cement plants who want to reduce their production costs by burning a waste with lower cost than conventional fuels, it is necessary to warn that a minimum level of environmental care should be followed regarding these decisions. it is necessary to monitor the points of emission from cement kilns and in the wider area influenced by the plant, in order to improve environmental quality. laboratory studies of burning vulcanised rubber contaminated with arsenic simulate the burning of used tyres in cement clinker kilns producing so2 and as2o3. keywordscement plants; arsenic; tyres; clinker kilns i. introduction co-incineration of waste in industrial clinker kilns is a practice that dates back to the time of the oil crisis and is currently being viewed as a coordinated action among industries and cement industries that generate waste, more contextualised in the environmental sphere and less in the energy sphere and considered by waste generators with the approval of environmental agencies, as a final solution for the disposal of their industrial waste. it should also be noted that in the manufacture of cement, as in any other large industrial activity, risks are associated with the scale of operations, i.e., they depend on the quantities of waste handled, transported, prepared, fed and incinerated and the degree of dangerousness of such materials. therefore, the scale of the enterprise determines the extent of risk exposure for workers, the surrounding population and the environment. the most commonly used cement is composed of 96% clinker and 4% gypsum by mass. the clinker is produced from the thermal treatment in rotary kilns at elevated temperatures of a rocky material usually containing 80% calcium carbonate (caco3), 15% silicon dioxide (sio2), 3% aluminium oxide (al2o3) and minor amounts of other constituents, such as iron, sulphur and others. these materials are found in limestone deposits often located near the site of the clinker kiln. the raw material is mixed and finely ground, before being subjected to a heating process that leads to the production of clinker [1, 2]. the minerals employed as raw materials for cement might be associated with a number of other secondary minerals, which might contain other contaminants in the form of complex salts or oxides. other dangerous contaminants to be highlighted include lead, copper, zinc, thallium, cadmium, chromium, nickel and arsenic. additionally, if burning chlorinated compounds, then fluoride and sulphide minerals might lead to problems of equipment corrosion and serious socio-environmental problems. ii. risks and contitions for co-processing industrial waste for the daily processing of 3600 tons of clinker, the main component of the cement kiln, a large capacity, an oil-fired rotary kiln is required, which would consume about 300 tons of fuel, or the equivalent of ten tanker truck loads. in brazil, the number of operating cement plants is 487 and among those, 30 have environmental licences for co-processing waste, consuming the equivalent of 39.48% of the total energy consumption of the country [3, 4]. around 1979-1981, the price of fuel oil tripled because of the national dependence on imported oil. a scheme was then introduced where the supply of fuel oil for industries, should not exceeding the consumption practiced in 1979. thus, incentives and subsidies were introduced for some alternative sources of fuel and heat energy, through the signing of protocols for the use of domestic coal for the steel, cement, paper and cellulose industries. in september 1979, the cement industry signed the "protocol reduction and replacement fuel oil consumption etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 479-482 480 www.etasr.com monteiro et al.: socio-environmental impacts associated with burning alternative fuels in clinker kilns in cement industry", which pledged to achieve by the end of 1984, the total substitution of fuel oil consumed by cement plants in their domestic production and to adopt energy conservation measures at the plant level. thus, in 1985, the cement industry had already replaced about 95% of its fuel oil consumption [3, 5]. according to ferrari [6], the basic assumptions for the use of waste in clinker kilns are:  not all types of waste may be used in cement clinker kilns owing to environmental restrictions (legislation) and to the manufacturing process of clinker  checking of the residue using partial replacement for fuel and/or as partial replacement of raw materials  the consideration that a residue might be considered as fuel and must provide heat to the process  if the residual considered for a partial replacement of the raw material should contain as major components: calcium, silicon, aluminium and iron. included in this case are material mineralisation and/or fluxes  assessment of physico-chemical characteristics. certain contaminants from waste should be in limited amounts in relation to the feeding rate of waste to the furnace  the maximum rate of feeding the waste to the clinker kiln is established by material balances, based on previous tests a. principal characteristics of the clinker kiln the clinker kiln should be adequate for the incineration of diverse industrial waste [6]. for example:  the oven must be able to operate at high temperatures, which is needed for the destruction of some hazardous organic wastes. the material in the kiln for production of cement clinker, must reach temperatures of 1400 – 1500 °c and the heating of the material requires a flame temperature of 3200 °c. the residence time at temperatures above 1100 °c is 6 to 10 seconds.  the need for turbulent gases in the furnace system with a reynolds number greater than 100,000; a condition that is highly favourable for the process of combustion and destruction of waste.  the clinker kiln has a basic environment that neutralises acid gases by the very nature of its raw materials.  the complete elimination of waste is expected, because the ash produced by incineration of residues is incorporated in the mass of the clinker produced.  stopping the waste stream following any mishap in relation to normal conditions of operation. the clinker kilns are necessarily a function of the basic relationship between the amounts of cao (calcium oxide) and sio2. thus, the cao/sio2 ratio must be greater than one, i.e., cao must be present in greater quantity than sio2, characterising the basics of the furnace system [6]. b. operations in cement plant licensed for the burning of industrial waste the cement manufacturing operation with residues using alternative fuels are based on two steps. 1) step 1: preparation and conditioning of waste fuel this step involves the following operations: receiving the waste, temporary storage, classification, segregation, mixing of different sources to form a blend with acceptable calorific value and finally, packaging in standard. 2) step 2: the co-processing this stage involves the following operations: overflow system, raising and feeding of waste packaged in patterns; system storage, mixing and transport of solid waste; storage system, pumping, transporting and injecting viscous mixture of waste; storage system, pumping, transportation and injection of liquid waste mixture. iii. monitoring the operation of a cement unit in relation to environmental contamination the environmental monitoring of a cement unit should be done by the industry and their records made available to the environmental control agencies based on the following guidelines. there should be periodic and non-periodic monitoring of parameters according to the composition of the waste that is fed to the furnace and among the sampling points critical to the control, such as:  sampling and analysis of the flue gases  sampling and analysis of clinker produced  reporting and documentation requirements of the environmental agency second controller  monitoring of air quality in the vicinity of the plant  control of the final specification of the cement produced when using industrial waste in the clinker furnace continuous monitoring is done by analysing and recording one or more parameters whenever the facility is in operation. in the furnace fuel particulate material, sox, nox, co and co2 are monitored. periodic monitoring is performed by analysing and recording particulate materials, sox, nox, fluoride, chlorine, metals, cyanides, pops (persistent organic compound) and vocs (volatile organic compounds). one has to consider the inclusion of a label stating that the cement being used was produced from the burning/co-incineration of waste, as well as an identification of the main types of contaminants expected in the product [7-9]. etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 479-482 481 www.etasr.com monteiro et al.: socio-environmental impacts associated with burning alternative fuels in clinker kilns iv. risks related to workers’ health, public health and the environment risks in the field of cement production are present in the form of occupational accidents with the introduction of industrial waste of any nature, which could cause immediate, acute toxicity to the workers following a break in the reliability of the process, irrespective of whether or not alternative fuels are used in the clinker furnace. as other forms of occupational risks, the cement units might impart a progressive chemical contamination to their workers that manifests over time. another risk related to cement production, concerns the character of environmental contaminants transferred, for example, through some climatic factor (wind and/or rain) to surrounding neighbourhoods and industrial units. there are risks related to the use of waste in cement from its place of origin to the final cement production involving all who participate in this operation. the characteristics of the technological process and the physico-chemical and toxicological properties of the raw materials and inputs employed in cement production, mean that cement plants pose risks to workers' health, public health and to the environment. these are mainly associated with exposure to the material in powder form that permeates the entire chain of production and from emissions of polluting substances, which occur continuously and even in small concentrations, characterise a chronic risk [1]. therefore, the entire cycle of the cement manufacturing process constitutes risk; the mining and processing of lime, the grinding and homogenisation of raw materials, the manufacture of clinker and the grinding and dispatch of the cement. throughout this process, there are emissions of particulate matter, consisting of the raw materials, clinker and cement, salt vapours, metal and gases formed in the combustion process and other missions generated elsewhere in the plant. the risk of further dissemination remains when using the cement end product. table i presents some metals found in solid waste and their consequences to human health. table i. metals vs risks contaminant solid waste disease cadmium solder, tobacco, batteries and cells. lung and prostate cancer, kidney injury. chromium industrial dyes, enamels, paints, steel and nickel alloys. asthma (bronchitis), cancer. nickel nickel-cadmium batteries, nickel electrowinning, castings. breast and lung cancer, sinuses. v. laboratory testing burning of vulcanised rubber containing arsenic the incineration of industrial residues in rotary kilns has been discussed across the world, because of the environmental problems caused to the atmosphere and the quality of the produced cement. this affects the sustainability of the cement industry because it has to guarantee the raw materials and fuels, as well as obey the environmental legislation. used tyres containing toxic contaminants are an example of this kind of fuel [11]. this experimental phase of the study was to simulate the burning of scrap tyres in cement clinker kilns generating gaseous environmental contaminants, such as arsenious oxide (as2o3) and sulphur dioxide (so2). the experimental method consisted of the preparation of rubber coupons (styrene-butadiene) with sulphur vulcanised to a high purity and contaminated with arsenic and sulphur. about 100 mg of finely grated coupons was placed in a porcelain crucible and subjected to firing at 1000 °c in a furnace with a controlled temperature heating rate (10 °c/min) and an atmosphere of helium and oxygen at a flow rate of 30 cm3/min, as shown in figure 1. fig. 1. equipment used for burning of rubber shavings: 1-voltage regulator, 2-nebuliser, 3-temperature indicator, 4-thermocouple, 5-heating mantle, 6-bottle containing sodium hydroxide solution the combustion gases were collected in a flask with a 2 m sodium hydroxide solution. the results of the burning of the rubber contaminated with sulphur and arsenic are shown in table ii. table ii. burning of the rubber contaminated with sulphul and arsenic gas burner outlet samples % sulphur in rubber % arsenic in rubber so2 mg/l as2o3 mg/l 1 11.13 ----1510 2 14.45 ----17450 3 11.13 4.46 1600 158 4 14.45 4.46 1570 164 5 14.45 16.65 17600 740 vi. conclusions based on the study, the following conclusions are considered as critical:  the majority of workers in the cement industry, as well as the residents in the neighbourhood of these factories are unaware of the origins and contents of waste fuels that are burned in the clinker ovens etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 479-482 482 www.etasr.com monteiro et al.: socio-environmental impacts associated with burning alternative fuels in clinker kilns  usually waste chemicals from various segments are mixed with sawdust to form a mixture based on economic value and with a calorific value viable for burning  there are no effective controls placed on the burning process and equipment used by the cement factories nor on the toxic gaseous contaminants generated during the burning process  laboratory analyses carried out on burning vulcanised rubber coupons contaminated with arsenic, simulating the burning of used tyres, generated significant levels of arsenic oxide (as2o3)  burning of scrap tyres in clinker kilns is not a recommended alternative for the disposal of this environmentally troublesome waste, especially because it can generate undesirable contaminants to the environment  negligent and irresponsible sales of industrial waste with undeclared toxic contaminants for incineration in industrial furnaces may occur  because of the dangers related to contamination of the cement produced from the use of industrial waste, its use should be avoided as much as possible in the absence of additional controls. references [1] m. achternbosch, k. r. bräutigam, n. hartlieb, c. kupsch, u. richers, p. stemmermann, m. gleis, heavy metals in cement and concrete resulting from the co-incineration of wastes in cement kilns with regard to the legitimacy of waste utilization, forschungszentrum karlsruhe gmbh, karlsruhe , 2003. [2] r. kikuchi, r. gerardo, “more than a decade of conflict between hazardous waste management and public resistance: a case study of nimby syndrome in souselas (portugal)”, journal of hazardous materials, volume 172, no. 2-3, pp. 1681-1685, 2009 [3] l. p. c. monteiro, avaliação do impacto ambiental associado à queima de resíduos industriais em fornos de clínquer: visão sob o prisma da educação ambiental, universidade federal fluminense, tese de doutorado, uff, outubro, 2007 [4] c. y. kawabata, h. savastano junior, j. souza-coutinho, “rice husk derived waste materials as partial cement replacement in lightweight concrete”, ciência e agrotecnologia, vol.. 36, no. 5, pp. 567-578, 2012 [5] j. g. silva, há emissões acrescidas na co-incineração de resíduos industriais perigosos em cimenteiras, universidade de coimbra, associação nacional de conservação da natureza, quercus, 2002 [6] r. ferrari, “co-processamento de resíduos industriais em fornos de clínquer”, companhia de cimento itambé, balsa nova, 2002 [7] p. shih, j. chang, h. lu, l. chiang, “reuse of heavy metal-containing sludges in cement production”, cement and concrete research, vol. 35, no. 11, pp. 2110-2115, 2005 [8] d. lemarchand, “cement kiln incineration associated to pre-treatment, a viable waste management solution”, congresso brasileiro de cimento, anais são paulo, 1999 [9] f. bagnoli, a. bianchi, a. ceccarini, r. fuoco, s. giannarelli, “trace metals and organic pollutants in treated and untreated residues from urban solid waste incinerators”, microchemical journal, vol. 79, no. 12, pp. 291-297, 2005 [10] f. b. mainier, b. p. salvini, l. p. c. monteiro , r. j. mainier, “recycling of tires in brazil: a lucrative business or an imported problem”, international journal of engineering and applied sciences, vol. 2, no. 3, pp. 19-28, 2013 microsoft word 31-3159_s_etasr_v9_n6_pp5037-5040 engineering, technology & applied science research vol. 9, no. 6, 2019, 5037-5040 5037 www.etasr.com hafeez et al.: a survey on the adaption of cms in pakistani universities a survey on the adaption of cms in pakistani universities abdul hafeez department of computer science smi university karachi, pakistan samreen javed department of computer science smi university karachi, pakistan anus bin murtaza department of computer science muhammad ali jinnah university karachi, pakistan abdul aziz department of computer science national university of computer and emerging sciences, karachi, pakistan syed muhammad hassan department of computer science smi university karachi, pakistan imtiaz hussain department of computer science smi university karachi, pakistan abstract—the use of campus management systems (cmss) has increased dramatically in pakistani universities, a huge amount of money has been invested in its development and deployment. the cms provides an integrated platform for managing academic activities, controlling process flows and provide online access to related information. it improves the efficiency and effectiveness of the universities and eventually improves the quality of teaching. however, it is very important to consider the attitudes and perceptions of faculty members and students towards the adoption of cms because they may affect the acceptance of this technology. the aim of this study is to investigate and highlight the user satisfaction level about the cms quality according to iso/iec 9126 standard. this work uses cross-sectional design as a primary research method, and data from 105 students and faculty members were collected from a pakistani public sector university using a questionnaire survey. the response of the respondents illustrates that the system functionality is good, reliable, usable, and efficient. however, some improvements are necessary in some areas such as understandability, learnability, operability, and attractiveness. keywords-software quality; software functionality, cms i. introduction information technology applications play a significant role in any organization or company [1]. they are controlling robots, helping in healthcare and commerce [2-4], they have also reached higher education in recent years under the name of cms [5] which basically are enterprise recourse planning (erp) programs for institutions [6, 7]. the cms improves the efficiency and effectiveness of the overall organization and ultimately improves the quality of teaching and learning. it shows the holistic picture of university processes [7]. in developing countries, public and private sector universities are facing competition in the higher education market, and want to use information and communication technology (ict) as an edge on other institutions [8]. in the ict landscape system, student-oriented processes are important because they reduce the operational cost, which is done when students independently manage their academic activities such as enrollment or acquiring information such as attendance and grades. through the integration of cms and web, these services are available any time. the importance of cms has also been recognized by the accreditation of institutions such as the higher education commission (hec) of pakistan which initiated the hec-funded deployment of cms on different public sector universities [9]. various universities in pakistan are implementing cms to handle their academic processes assessment and evaluation are conducted to improve the efficiency and effectiveness of any system. there are different kinds of evaluations such as (1) formative, which is performed during the development and (2) summative, which is performed after the completion of the system. it focuses on system’s effectiveness and if it meets the original requirements. this work evaluates the cms in four characteristics: functionality, reliability, usability, and efficiency. these characteristics are basically a part of iso/iec 9126-1 standard [10, 11] which focuses on 6 characteristics of software quality. however, the remaining two, portability and maintainability are not directly related to the end-users (students and faculty members). only cms features related to students and faculty such as student records, gradebook, student self-service, and faculty selfservice were considered in the current survey. a. functionality the functionality of the system concentrates the complete function list that should be provided by it. table i shows the subcharacteristics of functionality and the respected questions asked to the end-users. b. reliability reliability concerns the probability of error-free operation of the software and its ability to maintain its service delivery under specified circumstance. table ii shows the subcharacteristics of reliability and the respected questions asked to the end-users. corresponding author: abdul hafeez (ahkhan@smiu.edu.pk) engineering, technology & applied science research vol. 9, no. 6, 2019, 5037-5040 5038 www.etasr.com hafeez et al.: a survey on the adaption of cms in pakistani universities table i. functionality sub-characteristics characteristic sub-characteristics question functionality suitability can the cms do the required tasks? interoperability does the cms interact with another system? security does the cms prevent unauthorized access? accuracy does the cms give results as expected? table ii. reliability sub-characteristics characteristic sub-characteristics questions reliability maturity has a maximum number of errors in the cms been removed over time? fault tolerance is cms able to handle errors? recoverability after failure, can the cms continue working and recover lost data? c. usability usability is concerned about the software system’s ease of use and whether it is learnable. in usability, we focus on the user interface and how much the software system interface is easy to operate, easy to learn, and attractive to the end-users. table iii shows the sub characteristics of usability and the respected questions asked to the end-users. table iii. usability sub-characteristics characteristic sub-characteristics questions usability understandability does the user apprehend how to easily use the system? learnability can the end-user learn the system easily? operability can the user use the system without much effort? attractiveness does the system has a good look and feel? d. efficiency the efficiency concerns the resources’ utilization when performing the required operations such as memory, amount of disk space, processor, network, etc. table iv shows the subcharacteristics of efficiency and the respected questions asked to the end-users. table iv. efficiency sub-characteristics characteristics sub-characteristics questions efficiency time behavior how rapidly does the system respond and answer to queries? resource utilization does the system efficiently utilize system resources? ii. methodology a. research method there are various methods for evaluating software quality but selecting the correct one for evaluation depends on complexity and functionality. this study used the qualitative method for data collection and in order to understand the participants’ attitudes and experience. it is used in order to evaluate ideas, experience, and beliefs of the participants regarding the quality of the cms. b. participants in the survey, data were collected from n=105 students and faculty members. in the sample, 74% participants were male and 24% were female, while 20% were faculty members and 80% were students, out of which 59% were in their 4th year, 34% in their 3rd year and the rest were in their 2nd year, while the 1st year students were not selected due to their little experience on cms. c. data collection tools in this study, the evaluation form included two sections. the first section included demographic information, such as gender, age, and department, and the 2nd section consisted of the survey questions. the results showed that this method of assessment is effective in pointing various software quality issues in the cms. d. data analysis data were analyzed with spss to find how much the cms realized the four considered characteristics of the iso/iec 9126-1. the feedbacks of all sub-characteristic were combined, and the basic mean was obtained. e. validity and reliability in this study, for ensuring reliability, the data were collected through according to ethical research. in order to reach the utilization in the study, the faculty and students of pakistani university who experienced cms were selected. fig. 1. percentage distribution of cms product quality characteristics feedback table v. descriptive statistics quality characteristics n min max mean sd functionality 105 27 160 84 50.3 reliability 35 98 63 27.1 usability 50 126 84 32.5 efficiency 17 62 42 17.4 0 5 10 15 20 25 30 35 40 strongly agree agree may be disagree strongly disagree cms product quality characteristics functionality reliability usability efficency engineering, technology & applied science research vol. 9, no. 6, 2019, 5037-5040 5039 www.etasr.com hafeez et al.: a survey on the adaption of cms in pakistani universities f. results and discussion in this section, the data collected from the questionnaire survey are presented and analyzed statistically. in this work, a questionnaire was spread among faculty members and students who were familiar with the cms. in addition, interviews with some faculty members and students were conducted in order to validate the gaps in the questionnaire. figure 1 shows the detailed feedback regarding the quality characteristics of the cms. four items were combined to determine this factor, and the results are shown in table v. the minimum and maximum scores were 27 and 160, respectively. as it can be seen from table v, the overall mean is 84. so, it can be concluded that the faculty and students were satisfied with the functionality of the cms. table vi and figure 2 show the detail feedbacks on how the functionality of the cms works. as it can be seen in table vi, around 51.5% of the participants’ responses fall in the range of agree and strongly agree which shows satisfaction on the functionality of the studied system. it is worth mentioning that 23.8% of the participants were neutral on their response on the functionality of the system and 25.1% of the participants were unhappy with the functionality of cms and gave disagree and strongly disagree feedback. fig. 2. percentage distribution of cms functionality characteristics feedback fig. 3. percentage distribution of cms reliability characteristics feedback the reliability of the system was examined and the results are shown in table v. the minimum and maximum scores are 35 and 98 respectively and the mean is 63. it can be concluded that the faculty and students were not very much satisfied with the systems’ reliability. as it can be seen from the results in table vi and figure 3, 42.98% of the participants' responses fall in the range of agree and strongly agree which shows that the participants are moderately satisfied with the system’s efficiency. it is worth mentioning that 23.14% of the participants are neutral on their response and 33% consider the cms unreliable and give feedback as disagree and strongly disagree. the impact on the control of the system upon the freedom of use was examined and the results are shown in table v. the minimum and maximum scores were 50 and 126 and the mean was 84 which is near to minimum. as it can be seen from the results in table vi and figure 4, only 37% of the participants' responses fall in the range of agree and strongly agree which shows that the users were unsatisfied with the usability features. it is worth mentioning that 13% of the participants are neutral on their response on that feature and 49.2% of them consider that the cms is not easy to use and does not provide easy learning and gave feedback as disagree and strongly disagree. finally, the capability of the system to provide efficient usage was examined and the results are shown in table v. the minimum and maximum scores were 17 and 62 and the mean was 42. by this it can be concluded that the participants were moderately satisfied with the efficiency of the cms. table vi and figure 5 present the details of how the system efficiency responds to the user. as it can be seen from the results in table vi, 45.98% of the participants’ responses fall in the range of agree and strongly agree which shows that the participants are moderately satisfied with the system’s efficiency, 25.23% of the participants are neutral on their response and only 29% of them consider the cms as not efficient and give feedback as disagree and strongly disagree. fig. 4. percentage distribution of cms usability characteristics feedback fig. 5. percentage distribution of cms efficiency characteristics feedback 17 15 14 8 47 57 36 20 18 15 25 42 17 13 21 27 6 5 8 8 0 20 40 60 80 100 120 suitab ility sec urity accurateness interoperability f u n c ti o n a li ty strongly agree agree may be disagree strongly disagree 19 9 7 45 30 23 13 38 24 22 22 27 6 6 23 0 20 40 60 80 100 120 maturity rec overability fault tolerance r e li a b il it y strongly agree agree may be disagree strongly disagree 8 12 15 11 32 29 26 20 17 14 14 11 28 34 31 33 20 15 18 28 0 20 40 60 80 100 120 understandability learnability operability attractiveness u sa b il it y strongly agr ee agree may be disagree strongly disagree 18 15 28 34 24 29 24 20 10 7 0 20 40 60 80 100 120 time behav ior resource utilization e ff ic ie n c y strongly agr ee agree may be disagree strongly disagree engineering, technology & applied science research vol. 9, no. 6, 2019, 5037-5040 5040 www.etasr.com hafeez et al.: a survey on the adaption of cms in pakistani universities table vi. frequency statistics functionality sub-characteristics questions strongly agree agree maybe disagree strongly disagree n % n % n % n % n % suitability can the cms do the required tasks? 17 16.19 47 44.76 18 17.1 17 16.19 6 5.71 security does the cms prevent unauthorized access? 15 14.29 57 54.29 15 14.3 13 12.38 5 4.76 accuracy does the cms give results as expected? 14 13.33 36 34.29 25 23.8 21 20 8 7.62 interoperability does the cms interact with another system? 8 7.62 20 19.05 42 40 27 25.71 8 7.62 reliability maturity has a maximum number of errors in the cms been removed over time? 19 18.1 45 42.86 13 12.38 22 20.95 6 5.71 recoverability after failure, can the cms continue working and recover lost data? 9 8.57 30 28.57 38 36.19 22 20.95 6 5.71 fault tolerance is the cms able to handle errors? 7 6.67 23 21.9 24 22.86 27 25.71 23 21.9 usability understandability does the user apprehend how to easily use the system? 8 7.62 32 30.48 17 16.19 28 26.67 20 19.1 learnability can the end-user learn the system easily? 12 11.4 29 27.62 14 13.33 34 32.38 15 14.3 operability can the user use the system without much effort? 15 14.3 26 24.76 14 13.33 31 29.52 18 17.1 attractiveness does the system has a good look and feel? 11 10.5 20 19.05 11 10.48 33 31.43 28 26.7 efficiency time behavior how rapidly does the system respond and answer to queries? 18 17.1 28 26.67 24 22.86 24 22.86 10 9.52 resource utilization does the system efficiently utilize system resources? 15 14.3 34 32.38 29 27.62 20 19.05 7 6.67 iii. conclusion and recommendations this paper presented an evaluation of cms in four dimensions: functionality, reliability, usability, and efficiency. these characteristics are a major part of iso/iec 9126-1. from the evaluation, it was observed that there were no issues related to the functionality of the system regarding suitability, security, accuracy, and interoperability, with 51.5% of the participants’ responses falling in the range of agree and strongly agree. in addition, the results show that participants were moderately satisfied with the reliability of the system regarding maturity, recoverability, and fault tolerance, while around 43% of the participants agree and strongly agree with the reliability features of the cms. the participants were not very much satisfied from the usability features of the cms and only 37% of them agreed or strongly agreed with the effectiveness of usability features such as understandability, learnability, operability, and attractiveness. finally, it was observed that the participants were also moderately satisfied with the efficiency and around 43% of them agreed and strongly agreed with the questions regarding the efficiency features. as a conclusion, it is observed that most participants are satisfied with the cms quality characteristics, but it would be better to enhance its usability features. references [1] m. hemmati, h. hosseini, “effect of it application on project performance focusing on the mediating role of organizational innovation, knowledge management and organizational capabilities”, engineering, technology & applied science research, vol. 6, no.6, pp. 1221-1226, 2016 [2] m. ben ayed, l. zouari, m. abid, “software in the loop simulation for robot manipulators”, engineering, technology & applied science research,vol. 7, no. 5, pp. 2017-2021, 2017 [3] f. idachaba, e. idachaba, “robust e-health communication architecture for rural communities in developing countries”, engineering, technology & applied science research, vol. 2, no. 3, pp. 237-240, 2012 [4] m. odhiambo, p umenne, “net-computer: internet computer architecture and its application in e-commerce”, engineering, technology & applied science research, vol. 2, no. 6, pp. 302-309, 2012 [5] z. unal, a. unal, “evaluating and comparing the usability of web-based course management systems”, journal of information technology education, vol. 10, pp. 19-38, 2011 [6] g. sabau, m. munten, a. r. bologa, r. bologa, t. surcel, “an evaluation framework for higher education erp systems”, wseas transactions on computers, vol. 8, no. 11, pp. 1790-1799, 2009 [7] a. rainer, g. auth, “campus-management-system”, business & information systems engineering, vol. 52, no. 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artificial intelligence in agriculture applications of artificial intelligence in agriculture: a review ngozi clara eli-chukwu department of electrical & electronics engineering alex ekwueme federal university ndufu alike, ebonyi, nigeria ngozieli@gmail.com abstract—the application of artificial intelligence (ai) has been evident in the agricultural sector recently. the sector faces numerous challenges in order to maximize its yield including improper soil treatment, disease and pest infestation, big data requirements, low output, and knowledge gap between farmers and technology. the main concept of ai in agriculture is its flexibility, high performance, accuracy, and cost-effectiveness. this paper presents a review of the applications of ai in soil management, crop management, weed management and disease management. a special focus is laid on the strength and limitations of the application and the way in utilizing expert systems for higher productivity. keywords-artificial intelligence; agriculture; soil management; crop management; disease management; weed management; yield i. introduction agriculture is the bedrock of sustainability of any economy [1]. it plays a key part in long term economic growth and structural transformation [2-4], though, may vary by countries [5]. in the past, agricultural activities were limited to food and crop production [6]. but in the last two decades, it has evolved to processing, production, marketing, and distribution of crops and livestock products. currently, agricultural activities serve as the basic source of livelihood, improving gdp [7], being a source of national trade, reducing unemployment, providing raw materials for production in other industries, and overall develop the economy [8-10]. with the global geometric population rise it becomes imperative that agricultural practices are reviewed with the aim of proffering innovative approaches to sustaining and improving agricultural activities. the introduction of ai to agriculture will be enabled by other technological advances, including big data analytics, robotics, the internet of things, the availability of cheap sensors and cameras, drone technology, and even wide-scale internet coverage on geographically dispersed fields. by analyzing soil management data sources such as temperature, weather, soil analysis, moisture, and historic crop performance, ai systems will be able to provide predictive insights into which crop to plant in a given year and when the optimal dates to sow and harvest are in a specific area, thus improving crop yields and decrease the use of water, fertilizers, and pesticides. via the application of ai technologies the impact on natural ecosystems can be reduced, and worker safety may increase, which in turn will keep food prices down and ensure that the food production will keep pace with the increasing population. ii. consideration overview farming entails a great deal of choices and uncertainties. from season to season the weather varies, the prices of farming materials fluctuate, soil degrades, crops are not viable, weeds suffocate crops, pests damage crops, and the climate changes. farmers must cope with these uncertainties. although agricultural practice is broad, this research considers soil, crop, disease and weeds as major contributors to agricultural production. it is paramount to review the application of ai to agriculture in respect to soil, crop, diseases and pest management. • soil is a critical part of successful agriculture and is the original source of the nutrients used to grow crops. soil is the basis of all production systems in agriculture, forestry and fishery. soil stores water, nutrients and proteins in order to make them available for proper crop growth and development. • crop production plays a crucial role in nigeria’s economy. it does provide food, raw materials, and employment. in modern times, marketing, processing, distribution and aftersales service are also accepted as parts of crop production. in places where the real income per capital is low, emphasis is being laid on crop production and other primary industries. it is seen that increased crop production output and productivity tend to contribute substantially to the overall economic development of a country. it will hence be appropriate to place greater emphasis on further crop production development. • as agriculture struggles to support the rapidly growing population, plant diseases reduce crop production quantity and quality. agricultural losses due to post-harvest diseases can be disastrous. • weeds consist one of the major threats to all agricultural activities. weeds reduce farm and forest productivity, invade crops, smother pastures, and in some cases harm livestock. they aggressively compete with the crops for water, nutrients and sunlight, resulting in reduced crop yield and poor crop quality. corresponding author: ngozi clara eli-chukwu engineering, technology & applied science research vol. 9, no. 4, 2019, 4377-4383 4378 www.etasr.com eli-chukwu: applications of artificial intelligence in agriculture iii. soil management soil management is an integral part of agricultural activities. a sound knowledge of various soil types and conditions will enhance crop yield and conserve soil resources. it is the use of operations, practices and treatments to improve soil performance. urban soils may contain pollutants which can be investigated with a traditional soil survey approach [11]. the application of compost and manure improve soil porosity and aggregation. a better aggregation indicates the addition of organic materials that play an important role in preventing soil crust formation. it is possible to adopt alternative tillage systems to prevent soil physical degradation. the application of organic materials is essential to improve soil quality [12]. production of vegetables and other edible crops is often significantly affected by several soil-borne pathogens that require control through soil management [13]. sensitivity to soil degradation is implicit in the assessment of the sustainability of land management practices, with recognition of the fact that soils vary in their ability to resist change and recover [14]. a summary in ai soil management techniques is shown in table i. management-oriented modeling (mom) minimizes nitrate leaching as it consists of a set of generated plausible management alternatives, a simulator that evaluates each alternative, and an evaluator that determines which alternative meets the user-weighted multiple criteria. mom uses “hillclimbing” as a strategic search method that uses “best-first| as a tactical search method to find the shortest path from start nodes to goals [15]. knowledge of engineering for constructing the soil risk characterization decision support system (srcdss) involves three stages: knowledge acquisition, conceptual design and system implementation [16]. an artificial neural network (ann) model predicts soil texture (sand, clay and silt contents) based on attributes obtained from existing coarse resolution soil maps combined with hydrographic parameters derived from a digital elevation model (dem) [21]. the dynamics of soil moisture are characterized and estimated by a remote sensing device embedded in a higher-order neural network (honn) [22]. iv. crop management the crop management techniques are summarized in table ii. crop management starts with sowing, and continues with monitoring growth, harvesting, and crop storage and distribution. it is summarized as the activities that improve the growth and yield of agricultural products. in-depth understanding of class of crops according to their timing and thriving soil type will certainly increase crop yield. precision crop management (pcm) is an agricultural management system designed to target crop and soil inputs according to field requirements to optimize profitability and protect the environment. pcm has been hampered by lack of timely, distributed information on crop and soil conditions [26]. farmers must combine various crop management strategies to cope with water deficit resulting from soil, weather or limited irrigation. flexible crop management systems based on decision rules should be preferred. timing, intensity, and predictability of drought are important features for choosing among cropping alternatives [27]. table i. ai in soil management summary application technique strength limitation [15] mom minimizes nitrate leaching, maximizes production. takes time. limited only to nitrogen. [16] fuzzy logic: src-dss can classify soil according to associated risks. needs big data. only a few cases were studied. [17] dss reduces erosion and sedimentary yield. requires big data for training. [18] ann can predict soil enzyme activity. accurately predicts and classifies soil structure. only measures a few soil enzymes. it considers more classification than improving the performance of the soil. [19] ann can predict monthly mean soil temperature considers only temperature as a factor for soil performance. [20] ann it predicts soil texture requires big data for training. has restriction in areas of implementation. [21] ann able to predict soil moisture. the prediction will fail with time as weather conditions are hardly predictable. [22] ann successfully reports soil texture. it does not improve soil texture or proffers solution to bad soil texture. [23] ann cost-effective, saves time, has 92% accuracy requires big data. [24] ann can estimate soil nutrients after erosion. its estimate is restricted to only nh � . proper understanding of weather patterns helps in the decision-making process that will result in high and quality crop yield [28]. prolog utilizes weather data, machinery capacities, labor availability, and information on permissible and prioritized operators, tractors, and implements for evaluating the operational behavior of a farm system. it also estimates crop production, gross revenue, and net profit for individual fields and for the whole farm [30]. crop prediction methodology is used to predict the suitable crop by sensing various soil parameters and parameter related to the atmosphere. parameters like soil type, ph, nitrogen, phosphate, potassium, organic carbon, calcium, magnesium, sulfur, manganese, copper, iron, depth, temperature, rainfall, humidity [31]. demeter is a computer-controlled speed-rowing machine, equipped with a pair of video cameras and a global positioning sensor for navigation. it is capable of planning harvesting operations for an entire field, and then executing its plan by cutting crop rows, turning to cut successive rows, repositioning itself in the field, and detecting unexpected obstacles [32]. the use of ai in harvesting cucumber comprises of the individual hardware and software components of the robot including the autonomous vehicle, the manipulator, the end-effector, the two computer vision systems for detection and 3d imaging of the fruit and the environment and, finally, a control scheme that generates engineering, technology & applied science research vol. 9, no. 4, 2019, 4377-4383 4379 www.etasr.com eli-chukwu: applications of artificial intelligence in agriculture collision-free motions for the manipulator during harvesting [33]. field-specific rainfall data and weather variables can be used for each location. adjusting ann parameters affects the accuracy of rice yield predictions. smaller data sets required fewer hidden nodes and lower learning rates in model optimization [38]. table ii. ai in crop management summary application technique strength limitation [29] calex can formulate scheduling guidelines for crop management activities. takes time. [30] prolog removes less used farm tools from the farm. location-specific. [31] ann predicts crop yeild. only captures weather as a factor for crop yeild. [32] roboticsdemeter can harvest up to 40 hectares of crop expensive: uses a lot of fuel. [33] robotics has 80% success rate in harvesting crops slow picking speed and accuracy. [34] ann above 90% success rate in detecting crop nutrition disorder. a little number of symptoms were considered. [35] fuzzy cognitive map predict cotton yield and improve crop for decision management. it is relatively slow. [36] ann can predict the response of crops to soil moisture and salinity. considers only soil temperature and texture as factors. [37] ann and fuzzy logic reduces insects that attack crops. shows inability to differentiate between crop and weed. [38] ann can accurately predict rice yield. time-consuming, limited to a particular climate. v. disease management to have an optimal yield in agricultural harvest, disease control is necessary. plant and animal diseases are a major limiting factor regarding the increase of yield. several factors play role in the incubation of these diseases which attack plants and animals, which include genetic, soil type, rain, dry weather, wind, temperature, etc. due to these factors and the unsteady nature of some diseases causative influence, managing the effects is a big challenge, especially in large scale farming. table iii lists the ai applications in disease management available in the literature. to effectively control diseases and minimize losses, a farmer should adopt an integrated disease control and management model that includes physical, chemical and biological measure [39]. to achieve these is time consuming and not at all that cost effective [40], hence the need for application of ai approach for disease control and management. explanation block (eb) gives a clear view of the logic followed by the kernel of the expert system [42]. a novel approach of rule promotion based on fuzzy logic is used in the system for drawing intelligent inferences for crop disease management. a text-to-speech (tts) converter is used for providing capability of text-to-talking user interface. it provides highly-effective interactive user interface on web for live interactions [45]. a rule based and forward chaining inference engine has been used for the development of the system that helps in detecting the diseases and provide treatment suggestion in [46]. table iii. ai in disease management summary application technique strength limitation [42] computer vision system (cvs), genetic algorithm (ga), ann works at a high speed. can multitask. dimension-based detection which may affect good species. [42] rule-based expert, data base (db) accurate results in the tested environment. inefficacy of db when implementing in large scale. [43] fuzzy logic (fl), web gis cost effective, eco friendly. inefficiency due to scattered distribution. takes time to locate and disperse data. the location of the data is determined by a mobile browser. [44] fl web-based, web-based intelligent disease diagnosis system (widds) good accuracy. responds swiftly to the nature of crop diseases. limited usage as it requires internet service. its potency cannot be ascertained as only 4 seed crops were considered. [45] fl & tts converter resolves plant pathological problems quickly. requires high speed internet. uses a voice service as its multimedia interface. [46] expert system using rule-base in disease detection faster treatment as diseases are diagnosed faster. cost effective based on its preventive approach. time consuming. needs constant monitoring to check if pest has built immunity to the preventive measure. [47] ann, gis 95% accuracy internet-based. some rural farmers will not have access. [48] fuzzyxpest provides pest information for farmers. it is also supported by internet services. high precision in forecast. internet dependent. [49] web-based expert system high performance. internet and web based. [50] ann has above than 90% prediction rate. the ann does not kill infections or reduces its effect. vi. weed management weed consistently reduces the farmers’ expected profit and yield [51]. a report confirms a 50% reduction in yield for dried beans and corn crops if weed infestations are not controlled [51]. there is about 48% loss in wheat yield due to weed competition [52, 53]. these losses may at times rise up to 60% [54]. a study on the impact of weed on soybean showed about 8%-55% reduction in yield [55]. a study on yield losses in engineering, technology & applied science research vol. 9, no. 4, 2019, 4377-4383 4380 www.etasr.com eli-chukwu: applications of artificial intelligence in agriculture sesame crops accounts them to about 50%-75% [56]. the fluctuation in yield losses may be attributed to the length of exposure of the crops to the weeds [57, 58] and spatial heterogeneity of weeds [59]. beyond these, weed has both positive and negative effects to the ecosystem. according to the relative weed science society of america (wssa) report, weed effects include flooding during hurricane, some species of weeds can pave their way during rampant fire, some cause irreparable liver damage if consumed, and they muscle out plants or crops by competing for water, nutrients and sunlight. some weeds are poisonous and cause allergic reactions or even may threat public health. table iv lists a summary of the ai in weed managements uses. table iv. ai in weed management summary application technique strength limitation [61] ann, ga high performance. reduces trial and error. requires big data. [62] optimization using invasive weed optimization (ivo), ann cost effective, enhanced performance. adaptation challenge with new data. [63]. mechanical control of weeds. robotics. sensor machine learning saves time and removes resistant weeds. expensive. constant use of heavy machine will reduce soil productivity. [64] uav, ga can quickly and efficiently monitor weeds. has little or no control on weeds. expensive. [65] saloma expert system for evaluation, prediction & weed management. high adaptation rate and prediction level. requires big data and usage expertise. [66] support vector machine (svm), ann quickly detects stress in crop that will prompt timely site– specific remedies. only detects low levels of nitrogen. [67] digital image analysis (dia), gps has above 60% accuracy and success rate. its success was achieved after 4 years and as such, it is really time consuming. [68] uav high rate of weed detection within a short period of time. it is really expensive and requires vast human expertise. [69] learning vector quantization (lvq), ann high weed recognition rate with short processing time. the method of data input used affected the ai’s perfromance. an intensive management with herbicides has been deployed over the past decades to reduce its effect on crops. however, even with this management pattern, it was predicted that crop losses due to weed in western canada field crops are estimated to exceed $500 million annually [60], hence the need for a more expert weed management technique to compensate for this loss emerges [51]. a system can utilize an unmanned aerial vehicle (uav) -imagery to divide image, compute and convert to binary the vegetation indexes, detect crop rows, optimize parameters and learn a classification model. since crops are usually organized in rows, the use of a crop row detection algorithm helps to separate properly weed and crop pixels, which is a common handicap given the spectral similitude of both [64]. weed control in sugar-beet, maize, winter wheat, and winter barley, can be done by applying online weed detection using digital image analysis taken by an uav (drone), computer‐based decision making and global positioning system (gps)‐controlled patch spraying [67]. the drone in [68] travelled at a speed of 1.2km/h, with 58.10ms and 37.44ms execution time to find the tomato and weed locations to the spray controller respectively vii. curtailing challenges of ai in agriculture expert systems are tools for agricultural management since they can provide site-specific, integrated, and interpreted advices. however, the development of expert systems for agriculture is fairly recent, and the use of these systems in commercial agriculture is rare to date [70]. although ai has made some remarkable improvement in the agricultural sector, it still has a below the average impact on the agricultural activities when compared to its potentials and impacts in other sectors. more still need to be done to improve agricultural activities using ai as there are many limitations to its implementation. a. limitation: response time and accuracy a major attribute of an intelligent or expert system is its ability to execute tasks accurately in very short time. most of the systems fall short either in response time or accuracy, or even both. a system delay affects a user's selection of task strategy. strategy selection is hypothesized to be based on a cost function combining two factors: (1) the effort required to synchronize input system availability, and (2) the accuracy level afforded. people seeking to minimize effort and maximize accuracy, choose among three strategies: automatic performance, pacing, and monitoring [71]. b. limitation 2: big data required the strength of an intelligent agent is also measured on the volume of input data. a real-time ai system needs to monitor an immense volume of data. the system must filter out much of the incoming data. however, it must remain responsive to important or unexpected events [72]. an in-depth knowledge of the task of the system is required from a field expert and only very relevant data should be used improving the system’s speed and accuracy. the development of an agricultural expert system requires the combined efforts of specialists from many fields of agriculture, and must be developed with the cooperation of the growers who will use them [70]. c. limitation 3: method of implementation the beauty of any expert system lies on its execution methodology. since it uses big data, the method of looking-up and training should be properly defined for speed and accuracy. d. limitation 4: high data cost most ai systems are internet-based which in turn reduces or restricts their usage, particularly in remote or rural areas. engineering, technology & applied science research vol. 9, no. 4, 2019, 4377-4383 4381 www.etasr.com eli-chukwu: applications of artificial intelligence in agriculture the government can support farmers by designing a web service enabling device with lower tariff to uniquely work with the ai systems for farmers. also, a form of “how to use” orientation (training and re-training) will really help farmers adapt to the use of ai on the farm. e. limitation 5: flexibility flexibility is a strong attribute of any sound ai system. it is perceived that much progress has been made in applying ai techniques to particular isolated tasks, but the important theme at the leading edge of the ai-based robotics technology seems to be the interfacing of the subsystems into an integrated environment. this requires flexibility of the subsystems themselves [73]. it should also have expansive capabilities to accommodate more user data from the field expert. viii. the future of ai in agriculture global population is expected to reach more than nine billions by 2050 which will require an increase in agricultural production by 70% in order to fulfil the demand. only about 10% of this increased production may come from unused lands and the rest should be fulfilled by current production intensification. in this context, the use of latest technological solutions to make farming more efficient remains one great necessity. present strategies to intensify agricultural production require high energy inputs and market demands high quality food. 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novel-final-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 209-215 209 www.etasr.com yu and wang: a �ovel three dimension autonomous chaotic system with a quadratic … a novel three dimension autonomous chaotic system with a quadratic exponential nonlinear term fei yu college of information science and engineering hunan university changsha, china yufeiyfyf@yahoo.com.cn chunhua wang college of information science and engineering hunan university changsha, china wch1227164@sina.com abstract— a novel three dimension autonomous (3d) chaotic system with a quadratic exponential nonlinear term and a quadratic cross-product term is described in this paper. the basic dynamical properties of the new attractor are studied. the forming mechanism of its compound structure, obtained by merging together two simple attractors after performing one mirror operation, has been investigated by detailed numerical as well as theoretical analysis. finally, the exponential operation circuit and its temperature-compensation circuit, which makes the new system more applicable from a practical engineering perspective, are investigated. keywords3d chaotic system; exponential nonlinear term; exponential operation circuit; temperature-compensation circuit i. introduction since lorenz found the first chaotic attractor in a three firstorder autonomous ordinary differential equations (odes) when he studied the atmospheric convection in 1963 [1], many new three dimension (3d) chaotic attractors have been proposed in the last three decades, such as the rossler system [2], the chen system [3], the lü system [4], the liu system [5], and the generalized lorenz system family [6]. the complicated dynamic properties of these chaotic systems are all obtained by some quadratic cross-product nonlinearity terms at the righthand side in odes. recently, wei and yang [7] revealed a 3d autonomous chaotic attractor with a nonlinear term in the form of exponential function at the right-hand side in odes as x ay ax= −ɺ , y by mxz= − +ɺ , xyz n e= −ɺ , where the existence of singularly degenerate heteroclinic cycles for a suitable choice of the parameters was investigated. chaotic attractors with a quadratic exponential nonlinear term in three odes have never been found so far. in this paper, a novel chaotic attractor is proposed. it is a 3d autonomous system which relies on a quadratic exponential nonlinear term and a quadratic cross-product term to introduce the nonlinearity necessary for folding trajectories. the chaotic attractor obtained from the new system according to the detailed numerical as well as theoretical analysis is also the two-scroll attractor, exhibiting complex chaotic dynamics [5]. the chaotic attractor is similar to lorenz chaotic attractor, but not equivalent in the topological structure. nonlinear dynamic properties of this system are studied by means of nonlinear dynamics theory, numerical simulation, lyapunov exponents, poincare mapping, fractal dimension, continuous spectrum and bifurcation diagram. the compound structure of the two-scroll attractor obtained by merging together two simple attractors after performing one mirror operation is explored here. finally, the exponential operation circuit with temperaturecompensation of the new chaotic system is simply designed. ii. novel 3d autonomous chaotic system a novel 3d autonomous chaotic system is expressed as follows: ( ) , , , xy x a y x y bx cxz z e dz = −  = −  = − ɺ ɺ ɺ (1) where , , ,a b c d are all constants coefficients assuming that , , , 0a b c d > and , ,x y z are the state variables. there are six terms on the right-hand side but it mainly relies on two quadratic nonlinearities, one is a quadratic exponential nonlinear term and the other is a quadratic cross-product term, namely, xy e and xz , respectively. system (1) can generate a new chaotic attractor for the parameters 10, 40, 2, 2.5a b c d= = = = with the initial conditions [ ]2.2, 2.4, 28 t . the chaotic attractor is displayed in figure 1. it appears that the new attractor exhibits the interesting complex and abundant of the chaotic dynamics behavior, which is similar to lorenz chaotic attractor, but is different from that of the lorenz system or any existing systems. etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 209-215 210 www.etasr.com yu and wang: a �ovel three dimension autonomous chaotic system with a quadratic … fig. 1. phase portraits of the new attractor. iii. basic properties of the new system a. equilibria let: ( ) 0, 0, 0, xy a y x bx cxz e dz − =  − =  − = (2) if db c> and 0c ≠ , the system has two equilibria points, which are respectively described as follows: ( ) ( )( )ln , ln ,e db c db c b c+ , ( ) ( )( )ln , ln , .e db c db c b c− − − when 10, 40, 2, 2.5a b c d= = = = , we operate above those nonlinear algebraic equations and obtain that: ( )1.978,1.978, 20e+ , ( )1.978, 1.978, 20e− − − . for equilibrium point e + , system (1) are linearized, the jacobian matrix is defined as: 0 10 10 0 0 0 0 3.956 . 30.278 30.278 2.5 xy xy a a j b cz cx ye xe d + − −        = − − = −       − −    to gain its eigenvalues, we let 0i jλ +− = . these eigenvalues corresponding to the equilibrium point e + are 1 14.192λ = − , 2 0.846 +12.965iλ = and 3 0.846 -12.965iλ = . here 1 λ is a negative real number, 2 λ and 3 λ become a pair of complex conjugate eigenvalues with positive real parts. the equilibrium point e + is a saddle-focus point. and system (1) is unstable at this equilibrium point. and then, for the equilibrium point e − , its jacobian matrix equals to: 0 10 10 0 0 0 0 3.956 . 30.278 30.278 2.5 xy xy a a j b cz cx ye xe d − − −        = − − =       − − − −    the same we let 0i jλ −− = . these eigenvalues corresponding to the equilibrium point e − are 1 14.192λ = − , 2 0.846 +12.965iλ = and 3 0.846 -12.965iλ = . apparently 1 λ is a negative real number, 2 λ and 3 λ form a complex conjugate pair and their real parts are positive. the equilibrium point e − is also a saddle-focus point. and system (1) is unstable at this equilibrium point. by the above brief analysis, the two equilibrium points of the non-linear system are all saddle focus-nodes. b. symmetry and invariance it is easy to see the invariance of system under the coordinate transformation ( ) ( ), , , ,x y z x y z→ − − , i.e., the system has rotation symmetry around the z -axis [7]. c. dissipativity the three lyapunov exponents and the divergence of the vector field is: ( ) 3 1 , i i x y z le v a d f x y z= ∂ ∂ ∂ = ∆ = + + = − + = ∂ ∂ ∂ ∑ ɺ ɺ ɺ (3) where ( )1, 2,3ile i = denote the three lyapunov exponents of the system. note that ( ) 12.5f a d= − + = − is a negative value, so the system is a dissipative system and an exponential rate is: 12.5 . fdv e e dt −= = (4) from (4), it can be seen that a volume element 0 v is contracted by the flow into a volume element 12.5 0 t v e − in time t . this means that each volume containing the system trajectory shrinks to zero as t → ∞ at an exponential rate of 12.5− . therefore, all system orbits are ultimately confined to a specific subset having zero volume and the asymptotic motion settles onto an attractor [8]. etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 209-215 211 www.etasr.com yu and wang: a �ovel three dimension autonomous chaotic system with a quadratic … d. lyapunov exponent and fractional dimension the lyapunov exponents generally refer to the average exponential rates of divergence or convergence of nearby trajectories in the phase space. if there is at least one positive lyapunov exponent, the system can be defined to be chaotic. according to the detailed numerical as well as theoretical analysis and (3), the lyapunov exponents are found to be 1 1.459l = , 1 0l = and 3 13.959l = − . therefore, the lyapunov dimension of this system is: 1 1 2 31 1.459 2 2 2.104 13.959 j i i l j l l l d j ll = + + = + = + = + = − ∑ (5) equation (5) means system (1) is really a dissipative system, and the lyapunov dimensions of the system are fractional. having a strange attractor and positive lyapunov exponent, it is obvious that the system is really a 3d chaotic system. e. spectrum map, time domain and poincare maps the spectrum of system (1) exhibits a continuous broadband feature as shown in figure 2. figure 3 shows that the evolution of the chaos trajectories is very sensitive to initial conditions [9]. the initial values of the system are set to [ ]2.2, 2.399, 28 t for the solid line and [ ]2.2, 2.4, 28 t for the dashed line. fig. 2. spectrum of log x fig. 3. sensitivity of system (1) the poincare maps are shown in figure 4. from figure 4(a)-(b), it can be seen that the poincare maps consist of virtually symmetrical branches and a number of nearly symmetrical twigs. it is also found that the section of the attractor looks like some circles from poincare map as figure 4(c)-(d). f. the influence of system parameters from the above analysis, it is visible that the stability of system equilibria will be changed along with the change of system parameters, and the system will also be in different state. by using numerical simulation method, the change of system parameters and system conditions are analyzed below. we let a increasing when other parameters are fixed. figures 5 and 6 show the bifurcation diagram and lyapunov exponent spectrum versus increasing a . while a increases, the system is undergoing some representative dynamical routes, such as stable fixed points, chaos, quasi-periodic loops and period-doubling bifurcation, which are summarized as follows: • 0 1.35a< ≤ , system (1) is stable, as shown in figure 7(a). • 1.35 12a< ≤ , system (1) is chaotic, and there are several periodic windows in the chaotic band, as shown in figure 7(b)-(c). • 12 22a< ≤ , systems (1) are some quasi-periodic loops and also call a reverse period-doubling bifurcation window, as shown in figure 7(d). • 22 28.9a< ≤ , system (1) is chaotic, and there are several periodic windows in the chaotic band, as shown in figure 7(e). • 28.9 40a< ≤ , there is a reverse period-doubling bifurcation window too, as shown in figure 7(f). g. forming mechanism of this new chaotic attractor structure compound structures of the new system (1) may be obtained by merging together two simple attractors after performing one mirror operation. such an operation can be revealed through the use of a controlled system of the form: ( ) xy x a y x y bx cxz ky u z e dz = −  = − + +  = − ɺ ɺ ɺ (6) where u is a parameter of control and the value of u can be changed within a certain range. here, we still select the initial values of the system as [ ]2.2, 2.4, 28 t . when 3u = , the attractor evolves into partial but is still bounded in this time, the corresponding strange attractors are shown in figure 8a. when 5u = , the attractors are evolved into the single right scroll attractor, it is only one half the original chaotic attractors etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 209-215 212 www.etasr.com yu and wang: a �ovel three dimension autonomous chaotic system with a quadratic … in this time, the corresponding strange attractors are shown in figure 8b. then we select u to be a negative value. when 3u = − , the corresponding strange attractors are shown in figure 8c, the attractor evolves into partial but is still bounded in this time. when 5u = − , the corresponding strange attractors are shown in figure 8d, the attractors are evolved into the single left scroll attractor; it is only one half the original chaotic attractors in this time. fig. 4. poincaré maps in planes where (a) 0x = , (b) 0y = , (c) 15z = , (d) 10z = fig. 5. bifurcation diagram of system (1) with 0 < a < 40 fig. 6. lyapunov exponents spectrum of system (1) with 0 < a < 40 etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 209-215 213 www.etasr.com yu and wang: a �ovel three dimension autonomous chaotic system with a quadratic … iv. exponential operation circuit the exponential operation circuit is simply studied in this part. first, using the semiconductor pn-junction exponential volt-ampere characteristic, the exponential operation can be realized. then, in order to suppress temperature-drift, the technology of temperature-compensation is used in the exponential operation circuit. fig. 7. phase portraits of system (1) in y z− plane with ( ) ( ), , 40, 2, 2.5b c d = at initial values [ ]2.2, 2.4, 28 t : (a) 1a = , (b) 3a = , (c) 10a = , (d) 15a = , (e) 24a = , (f) 35a = fig. 8. phase portraits of system (6) in y z− plane at (a) 3u = , (b) 5u = , (c) 3u = − , (d) 5u = − . a. basic exponential operation circuit in actual application, we usually connect the collector with the base of bipolar junction transistor (bjt) to form a diode type. the exponential operation circuit is shown in figure 9. according to the relationship of c i and be u , we get: fig. 9. exponential operation circuit. etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 209-215 214 www.etasr.com yu and wang: a �ovel three dimension autonomous chaotic system with a quadratic … 1 , be t u u c e es i i i eα α   = =  −      (7) where α is the current amplification and 1α ≈ , es i and be u are the transistor parameters. when be t u u≫ , equation (7) is simplified to: , be t u u c es i i e≈ (8) then 0 1 1 1 . be i t t u u u u c es es u i r i r e i r e − = = = (9) b. exponential operation circuit with temperaturecompensation as is well known, es i and t u are functions of the temperature and very sensitive to temperature, so how to improve the temperature stability of the exponential operation circuit is an important problem that needs to be solved in actual application. here, two methods are applied. first we adopt a pair of bjts to eliminate the effect of es i , then we use the thermistor to compensate the influence of t u . figure 10 illustrates the exponential operation circuit with temperaturecompensation. the voltage of point a can be expressed as: 1 2 0 1 1 2 5 5 0 1 ln ln ln , a be be ref t es es ref t u u u u u u i r i r u r u u r = −   = −    = (10) here, the parameters of two bjts are equal ( 1 2es es i i= ). ref u is a reference voltage. when the value of 3 r was small, the output voltage 0 u can be expressed as: 3 3 4 5 0 1 , i t r u ref r r u u r u e r − • += (11) where 3 r is the positive temperature coefficient thermistor which use to compensate the temperature variations of t u . v. conclusion this paper presented a novel 3d autonomous chaotic system with a quadratic exponential nonlinear term. some basic properties of the system have been investigated. in addition, forming mechanisms of compound structures of the new chaotic attractor have been studied and explored. finally, the exponential operation circuit and its temperaturecompensation circuit of the chaotic system were simply designed. despite the abundant and complex dynamical behaviors of the new 3d autonomous system has been discussed in detail in this paper. but even more important, some analysis like control, synchronization and secure communication of the system will be taken into consideration in a future work. therefore, further research into the system is still important and insightful. fig. 10. exponential operation circuit with temperature-compensation references [1] e. n. lorenz, “deterministic non-periodic flow”, j. atmos. sci., vol. 20, no. 1, pp. 130-141, 1963 [2] o. e . rossler, “an equation for continuous chaos”, phys. lett. a, vol. 57, no. 5, pp. 397-399, 1976 [3] g. chen, t. ueta, “yet another chaotic attractor”, internat. j. bifur. chaos, vol. 9, no. 7, pp. 1465-1457, 1999 etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 209-215 215 www.etasr.com yu and wang: a �ovel three dimension autonomous chaotic system with a quadratic … [4] j. lü, g. chen, “a new chaotic attractor conined”, internat. j. bifur. chaos, vol. 12, no. 3, pp. 659-662, 2002 [5] c. liu, t. liu, l. liu, k. liu, “a new chaotic attractor”, chaos, solitons fractals, vol. 22, no. 5, pp. 1031-1038, 2004 [6] s. celikovsky, g. chen, “on the generalized lorenz canonical form”, chaos, solitons fractals, vol. 26, no. 5, pp. 1271-1276, 2005 [7] z. wei, q. yang, “dynamical analysis of a new autonomous 3-d chaotic system only with stable equilibria”, nonlinear anal.: rwa, vol. 12, no. 1, pp. 106-118, 2011 [8] w. zhou, y. xu, h. lu, l. pan, “on dynamics analysis of a new chaotic attractor”, phys. lett. a, vol. 372, no. 36, pp. 5773-5777, 2008 [9] d. sara, r. m. hamid, “a novel three-dimensional autonomous chaotic system generating two, three and four-scroll attractors,” phys. lett. a, vol. 373, no. 40, pp. 3637-3642, 2009 microsoft word etasr_v11_n4_pp7399-7404 engineering, technology & applied science research vol. 11, no. 4, 2021, 7399-7404 7399 www.etasr.com mugheri & keerio: an optimal fuzzy logic-based pi controller for the speed control of an induction … an optimal fuzzy logic-based pi controller for the speed control of an induction motor using the v/f method noor hussain mugheri department of electrical engineering quaid-e-awam university of engineering science and technology nawabshah, sindh, pakistan noorhussain@quest.edu.pk muhammad usman keerio department of electrical engineering quaid-e-awam university of engineering science and technology nawabshah, sindh, pakistan usmankeerio@quest.edu.pk abstract-the induction motor (im) is popular because of its low price, higher efficiency, and low maintenance cost. a comparative analysis of im speed controllers using voltage/frequency (v/f) control or scalar control (sc) is presented in this paper. sc is commonly used due to its ease of implementation, simplicity, and low cost. to decrease the difficulty and cost of hardware implementation, this paper proposes an optimal fuzzy proportional integral (fuzzy-pi) controller. firstly, the speed of im using the v/f control technique is discussed. then, speed control of im using a conventional pi controller is performed. finally, a simplified-rules fuzzy-pi controller is developed in matlab/simulink and its performance is compared with that of open-loop sc and the traditional pi controller. the performance of the simplified-rules fuzzy-pi controller is superior to that of an open-loop constant v/f control and a conventional pi controller. keywords-induction motor; constant v/f control; pi controller; optimal fuzzy pi controller i. introduction its low cost, simple structure, reliability, and good robustness have made the induction motor (im) a most attractive choice [1, 2] for industry applications. to change the speed of ims, frequency and voltage can be varied. in voltage/frequency (v/f) control, only their magnitudes are controlled. v/f control is easy to implement, it requires a small number of components, and can be employed in several applications such as variable speed pumps, fans, blowers, etc. [3]. normally, a proportional integral (pi) controller is employed for im speed control for most applications [4, 5]. but, the conventional pi controller has some disadvantages: its accuracy depends on the mathematical model, the system suffers fromnon-linearity, and it is very sensitive to parameter and temperature variations and to load disturbances [6, 7]. a fuzzy logic-based controller (flc) can overcome these disadvantages [8-10]. the flc does not need the model of the plant, can handle non-linearity, it is less sensitive to load disturbances, it produces human logic linguistic rules, and is robust [11-13]. authors in [14] suggested a 3-phase im speed control technique using constant v/f control. a simplified fuzzy rule-based flc can be easily implemented in hardware and performs better in comparison with the standard 25-rule flc [15]. d. asija proposed a standard 25-rule fuzzy-pi controller for im speed control using sc and concluded that the fuzzy-pi controller outperforms the traditional pi controller [16]. b. n. kar and k. b. mohanty presented a standard 49rule flc for im speed control by indirect vector control (ivc) and concluded that compared with the conventional pi controller, the proposed flc performs better with regard to change in load, settling time, and overshoot [17]. authors in [18] proposed a standard 49-rule flc based im speed control by ivc and concluded that flc performs better than the traditional pi controller with regard to load disturbances and changing reference speed. authors in [19] proposed and implemented a 3-phase im using v/f control. ii. proposed framework a simplified-rule fuzzy-pi controller using the v/f control technique is presented in this paper. various researchers proposed flc-based im speed control using standard 49 fuzzy rules, standard 25 rules, standard 9 rules, and simplified fuzzy rules [20-25]. in this paper, the standard 9 rules are simplified into 5 rules for the first time and the simplified-rule fuzzy-pi controller is developed and implemented for the speed control of a 3-phase im using constant v/f control. the rule base is selected using the trial and error technique. the proposed simplified fuzzy-pi controller reduces complexity and computational load, it is easily implemented, it is simple, and has better performance. figure 1 exhibits the diagram of the proposed framework. the dc supply voltage is converted into variable voltage and variable frequency by a metal oxide semiconductor field effect transistor (mosfet) inverter. the optimal fuzzy-pi controller gets feedback signals from an im. the method of speed control used here is the popular constant v/f control. the svpwm generator produces firing pulses to the inverter. the mosfet converts the dc supply voltage into variable ac by the svpwm method. corresponding author: noor hussain mugheri engineering, technology & applied science research vol. 11, no. 4, 2021, 7399-7404 7400 www.etasr.com mugheri & keerio: an optimal fuzzy logic-based pi controller for the speed control of an induction … fig. 1. the proposed framework. iii. constant v/f control with the recent developments in power electronics, variable voltage variable frequency ims are increasingly employed in a variety of industrial applications. the circuit diagram of v/f control is shown in figure 2. speed control of im is achieved using a 3-phase inverter. the frequency and applied voltage must be varied to maintain constant air-gap flux and to evade saturation of the im. the stator voltage and frequency are changed at the same time to keep v/f ratio constant. fig. 2. constant v/f control. iv. the fuzzy logic controller the flc is an intelligent controller that is very similar to human reasoning. it accepts crisp input, performs calculations, and then gives an output value [26]. the structural diagram of the flc is shown in figure 3. there are four steps for the implementation of an flc: fuzzification, inference engine, rule base, and de-fuzzification. the flc inputs are characterized by triangular membership functions (mfs) and 3 triangular mfs are used for output control. there are 9 rules out of which 5 are executed by the fuzzy inference system (fis). the triangular mfs for the flc system are shown in a figure 4. the mfs for two inputs and a single output are: positive (p), zero (z), and negative (n). fig. 3. the flc structural block diagram. (a) (b) (c) fig. 4. the triangular membership functions: (a) error (e), (b) change of error (∆e), (c) output control (∆u). table i shows the simplified rule base for the flc. for this application the mamdani type fis is chosen. the fuzzy logic process which is based on if-then rules is represented as follows: if n and p denote the error and change of error respectively then the output control will be denoted by z. table i. the simplified fuzzy rules for the flc e ∆e n z p simplified rules 1. if e is n and ∆e is z then ∆u is n 2. if e is z and ∆e is p then ∆u is p 3. if e is z and ∆e is z then ∆u is z 4. if e is z and ∆e is n then ∆u is n 5. if e is p and ∆e is n then ∆u is z p z p p z n z p n n n z -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 error d e g re e o f m e m b e rs h ip n z p -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 changeoferror d e g re e o f m e m b e rs h ip n z p -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 outputcontrol d e g re e o f m e m b e rs h ip n z p engineering, technology & applied science research vol. 11, no. 4, 2021, 7399-7404 7401 www.etasr.com mugheri & keerio: an optimal fuzzy logic-based pi controller for the speed control of an induction … fig. 5. the simulink diagram of the open loop v/f control-based im speed control. (a) (b) fig. 6. the open loop im speed control: (a) rotor speed, (b) electromagnetic torque. v. results and discussion figure 5 depicts the simulink diagram of the open loop im speed control using the svpwm technique. a 3-phase im is fed from an inverter and is connected with a dc voltage source. a mosfet inverter is modeled by a universal block and the im by an asynchronous machine block. a constant value of 11.9nm load torque is applied to the im shaft. a speed set point in rpm is applied to the v/hz block. the initially reference speed is 1725rpm and the final speed value is 1300rpm. the induction motor reaches a speed of 1275rpm. in this application, im does not reach the final speed of 1300rpm which is the required final value. the simulation results for open loop scalar control are shown in a figure 6. the simulink diagram of the traditional pi controller based im closed loop speed control using svpwm technique is shown in figure 7. the zeigler-nichols method is used in this paper for tuning the pi controller. to study the performance of the 3-phase im, two performance indices, i.e. rotor speed and electromagnetic torque are used. in order to achieve the actual im speed, feedback is used and it is compared to the im reference speed. the error is produced by the obtained difference of the two and the error is processed in a conventional pi controller which reduces it. the same reference step speed and load torque is used for the traditional pi controller. the simulink diagram of the simplified fuzzy-pi controller using sc is given in figure 9. the error signal and the change of error are the input of an intelligent controller. the fuzzy-pi controller produces the controlled output signal and provides it to the v/f control. 0 0.5 1 1.5 1250 1300 1350 1400 1450 1500 1550 1600 1650 1700 1750 time (sec) s p e e d ( re v /m in ) 0 0.5 1 1.5 5 6 7 8 9 10 11 12 13 14 time (sec) t o rq u e ( n m ) engineering, technology & applied science research vol. 11, no. 4, 2021, 7399-7404 7402 www.etasr.com mugheri & keerio: an optimal fuzzy logic-based pi controller for the speed control of an induction … fig. 7. the simulink model of the conventional pi controller based im speed control. (a) (b) fig. 8. the simulation results for conventional pi controller based im speed control: (a) rotor speed, (b) electromagnetic torque. here, the frequency varying device is the svpwm generator which uses the svpwm technique to produce firing pulses to the inverter and hence the frequency of the supply is changed w.r.t the voltage of the im. using the svpwm method, the mosfet inverter converts the dc supply voltage into variable ac. from figure 8, it is clear that the conventional pi controller reaches the final speed of 1300rpm. from figure 10, it is clear that the optimal fuzzy-pi controller also achieves the final speed of 1300rpm but with less settling time and without overshoot compared with a conventional pi controller and also better electromagnetic torque response is obtained. when compared with the existing literature, the proposed simplified fuzzy-pi controller uses the least number of fuzzy rules. the proposed intelligent controller employs a trial and error approach to minimize the fuzzy rules while achieving better im speed control performance. figure 11 depicts the speed response of the im with step speed reference with both controllers and constant v/f control. the performance analysis of both controllers and without any controller at a constant reference speed is given in table ii. table ii. performance analysis settling time (sec) overshoot (%) load (nm) conventional pi controller 1.440 0.307 11.9 optimal fuzzy-pi controller 0.980 0 without controller does not settle --- 0 0.5 1 1.5 1250 1300 1350 1400 1450 1500 1550 1600 1650 1700 1750 time (sec) s p e e d ( re v /m in ) 0 0.5 1 1.5 5 6 7 8 9 10 11 12 13 14 time (sec) t o rq u e ( n m ) engineering, technology & applied science research vol. 11, no. 4, 2021, 7399-7404 7403 www.etasr.com mugheri & keerio: an optimal fuzzy logic-based pi controller for the speed control of an induction … fig. 9. the simulink diagram of the optimal fuzzy-pi controller based im speed control. (a) (b) fig. 10. the simulation results for the optimal fuzzy-pi controller based im speed control: (a) rotor speed, (b) electromagnetic torque. vi. conclusion to reduce the computation load, the need of memory space, and to enable more easy hardware implementation an optimal fuzzy-pi controller using sc is successfully developed and simulated in this paper. the proposed optimal fuzzy-pi controller uses a minimum number of fuzzy rules. the simulation results show that the performance and speed response of the simplified-rule set fuzzy-pi controller surpass the ones of the open loop constant v/f control and the traditional pi controller. the optimal fuzzy-pi controller fully eradicates the overshoot of the conventional pi controller and the settling time is much smaller than that of the traditional pi controller. fig. 11. speed response of the 3-phase im with step speed reference with an initial value of 1725rpm and final speed reference of 1300rpm at 0.1s and 11.9nm load with optimal fuzzy-pi controller, conventional pi controller, and without controller. acknowledgement this research was funded by the quaid-e-awam university of engineering, science and technology, nawabshah, sindh, pakistan. 0 0.5 1 1.5 1250 1300 1350 1400 1450 1500 1550 1600 1650 1700 1750 time (sec) s p e e d ( re v /m in ) 0 0.5 1 1.5 5 6 7 8 9 10 11 12 13 14 time (sec) t o rq u e ( n m ) engineering, technology & applied science research vol. 11, no. 4, 2021, 7399-7404 7404 www.etasr.com mugheri & keerio: an optimal fuzzy logic-based pi controller for the speed control of an induction … appendix im electrical parameters power = 3hp , voltage = 220v, poles = 4, frequency = 60hz rs = 0.435ω, rr = 0.815ω ls = 2*2.0mh, lr = 2.0mh lm = 69.31mh j = 0.089 kg.m 2 references [1] a. bhowate, m. aware, and s. sharma, "predictive torque control with online weighting factor computation technique to improve performance of induction motor drive in low speed region," ieee access, vol. 7, pp. 42309–42321, 2019, https://doi.org/10.1109/ access.2019.2908289. 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[26] e. h. mamdani and s. assilian, "an experiment in linguistic synthesis with a fuzzy logic controller," international journal of man-machine studies, vol. 7, no. 1, pp. 1–13, jan. 1975, https://doi.org/10. 1016/s0020-7373(75)80002-2. microsoft word 33-3392_s_etasr_v10_n2_pp5524-5527 engineering, technology & applied science research vol. 10, no. 2, 2020, 5524-5527 www.etasr.com nadareishvili et al.: investigation of the visible light-sensitive zno photocatalytic thin films 5524 investigation of the visible light-sensitive zno photocatalytic thin films m. nadareishvili andronikashvili institute of physics ivane javakhishvili tbilisi state university, tbilisi, georgia malkhaz.nadareishvili@tsu.ge g. mamniashvili andronikashvili institute of physics ivane javakhishvili tbilisi state university, tbilisi, georgia mgrigor@rocketmail.com d. jishiashvili v. chavchanidze institute of cybernetics georgian technical university and condensed matter physics department andronikashvili institute of physics ivane javakhishvili tbilisi state university, tbilisi, georgia d_jishiashvili@gtu.ge g. abramishvili condensed matter physics department andronikashvili institute of physics ivane javakhishvili tbilisi state university, tbilisi, georgia gocha00007@mail.ru c. ramana university of texas at el paso el paso, usa rvchintalapalle@utep.edu j. ramsden university of buckingham united kingdom jeremy.ramsden@buckingham.ac.uk abstract—zno photocatalytic thin films deposited on a glass substrate are obtained by chemical spraying technique, and they are active in the visible light spectrum. optical studies have shown that zno thin films doped by nickel impurities absorb visible light at wavelengths from 400nm to 600nm. at the same time, this absorption rate increases with the increase of concentration of nickel impurities. at high concentration (5%), the absorption of light is reduced in the visible area, but after heat treatment at 600 0 c the light absorption in these samples improves, which allows us to conclude that the observed effect is caused by a violation of the homogeneity of the distribution of nickel impurities and the creation of agglomerates. decoration of zno thin film surfaces by silver clusters improves light absorption, as it happens to the nanopowders, but in the case of thin films, this effect is much smaller. experiments on methylene blue determine the significance of photocatalytic activity in the visible area of sun irradiation of zno thin films containing nickel impurities, which are obtained by chemical spraying technique. keywords—thin films; zno; impurities; photocatalysis; ecology i. introduction photocatalysis is the activation of reduction-oxidation (redox) reactions due to the influence of light. the reaction is connected to specific substances, called photocatalysts. photocatalysis can be used for the decomposition of water in hydrogen and oxygen and for the degradation of harmful substances in water and air under sun exposure [1]. as a result of light irradiation, a semiconductor photocatalyst particle generates electron-hole pairs that can reach the surface of the particle, enter in the redox reactions with environmental molecules and cause their dissolution, e.g. water dissolves into oxygen and hydrogen. hydrogen, obtained from water, can be used as an environmentally friendly fuel with the final product of its combustion being water again. photocatalysis can also decompose organic molecules, including bacteria, into the environment, and result in carbon dioxide, oxygen, and water. this is the main reason of the ongoing research for photocatalysis usage in hydrogen energy, ecology, and medicine [2-7]. the low efficiency of the reaction is the main challenge, which prevents the wide practical usage of photocatalysis. this is caused by two reasons: 1. low quantum yield brought by recombination of electrons and holes and 2. low level of visible light usage in photocatalysis, which has ten times more energy in the solar irradiation than its uv share, caused by the large width of energetic gap in a stable photocatalist. to improve the quantum yield, small clusters of different materials, so-called co-catalists, are coated on the surface of photocatalist particles, which capture electrons and holes, and thus, reduce the recombination [8]. introduction of various impurities in photocatalists, which decreases the width of energy gap is the main method of increasing the amount of visible light in the process of photocatalysis [9, 10]. a photocatalytic reaction occurs on the surface of the photocatalyst. therefore, photocatalysts are generally used in the form of powders to increase surface area. however, photocatalytic thin films are frequently needed as well, especially when the photocatalysts are used for environmental purposes, since these substances are often necessary in continuous flow systems, and it is very difficult to separate photocatalytic nanoparticles from a suspension. the thin photocatalytic films are also necessary to obtain self-cleaning surfaces, e.g. to create lamps that do not get attached with soot in automobile tunnels, smart window glasses, etc. corresponding author: m. nadareishvili engineering, technology & applied science research vol. 10, no. 2, 2020, 5524-5527 www.etasr.com nadareishvili et al.: investigation of the visible light-sensitive zno photocatalytic thin films 5525 currently, research is underway to create new photocatalytic thin films of various substances that are active in the visible region of solar radiation and therefore have improved efficiency. authors in [11] prepared pure cds and cu-doped cds thin films using the spray pyrolysis technique while 2%, 4% and 6% cu-contents were used for doping. reflectance and transmission measurements were studied in the spectral range of 200–1100nm to extract the optical properties variation upon copper doping. authors in [12] developed successful strategies on combining the versatility of mechanochemical synthesis with rf-sputtering for the controllable deposition of bivo4 thin films. photocatalytic activity experiments were performed for the degradation of rhodamine 6g (rh6g) dyes under visible light irradiation. authors in [13] investigated the long term stability and photocatalytic activity of cu2znsns4/tio2 thin film heterostructures, under simulated solar radiation, using phenol and imidacloprid as testing pollutants. our group conducted studies on the sensitization of thin photocatalytic films to visible light similar to those described above. zno photocatalytic thin films doped by nickel impurities and obtained by chemical spraying were studied. this choice was due to the fact that despite its relatively low photocatalytic efficiency, zno possesses a number of unique properties which make it one of the strongest candidates for industrial use, if it is sensitized to visible light and therefore has increased efficiency. these properties are: non-toxicity, direct forbidden gap at room temperature (3.37ev), decent optical properties, chemical resistance to photoreactions, low cost, etc. ii. experimental part zno thin films were deposited onto glass substrate at 460°c by spray pyrolysis [14]. undoped zno thin films were prepared using a zinc acetate precursor (c4h6o4zn. 2h2o) dissolved in 2-propanol to obtain a starting solution with a concentration of 0.1mol/l. nickel-doped zno thin films were prepared by adding a compound source of nickel chlorure hexahydrate (nicl2(6h2o), 99.9% purity) to the precursor solution while maintaining the acidity level for atomic percentages of [ni]/[zn] of 1,2,3,4,5 wt%. these samples are presented in figure 1. fig. 1. zno:ni thin film samples deposited on glass zno:ni thin films coated by silver clusters were obtained by a novel technology developed in the andronikashvili institute of physics at ivane javakhishvili tbilisi state university, which consists of depositing metallic clusters on the surfaces of the nanoparticles of fine powders [15, 16]. the technology was modified for ag nanoclaster deposition on the surface of zno:ni thin films. this inexpensive electroless technology proceeds at low temperatures (50-60 0 c) and hence it does not change either the coated material or the material of clusters itself. a solution of the following composition: agno3 – 0.7g/l, nh4oh – 7ml/l, naoh – 0.8g/l was prepared for this purpose. kna was added right before the experiment started. kna amount and deposition time determine the size of coated nanoclasters. scanning electron microscope (sem) and energy dispersive spectroscopy (eds) investigations were conducted on the sem tescan vega3 xmu, which is equipped with energy dispersive spectrometer (eds): oxford instruments, aztecone (figure 2). fig. 2. sem vega3 equipped with eds of oxford instruments iii. results and discussions light absorption increases in the visible area during the introduction of nickel impurity in zno thin films. when this process was observed, the detailed studies started by zno thin films been deposited on a glass substrate of uniform thickness, containing different amounts of ni impurities prepared beforehand, and their structure and optical spectra were studied afterwards. the concentration of ni impurities varied from 1% to 5% with a 1% step. the sem and eds investigation results of these samples are shown in figures 3 and 4 respectively. the sem image of the zno:ni thin film (figure 3) shows that the surfaces of the films are quite smooth. the eds image of the zno:ni thin film with 3% ni content (figure 4) points out the existence of other impurities apart from ni in the zno sample. fig. 3. sem image of the zno:ni thin film with 3% ni content and deposited on the glass engineering, technology & applied science research vol. 10, no. 2, 2020, 5524-5527 www.etasr.com nadareishvili et al.: investigation of the visible light-sensitive zno photocatalytic thin films 5526 fig. 4. eds spectrum of the zno:ni thin film with 3% ni content and deposited on the glass the zno:ni film sample may contain a part of these impurities while the rest of it may be in a glass substrate. to clarify this situation, the similar eds spectrum of the glass without zno:ni thin film was obtained, which showed that there were only ca and k additional impurities in the zno film itself. figure 5 shows the experimental results of the optical investigations. it has to be noted that there are no results below 400nm, because zno thin films have been deposited on the glass and hence the optical properties of the films in this area could not be studied because of the strong absorption of ultraviolet rays by the glass. the experiments have shown that the absorption of light by zno with the introduction of ni impurities increases with the increase of the concentration of ni impurities from 1% to 4%, in the visible area at the wavelength range of 400nm to 600nm. when the concentration of impurities increases further, e.g. at the nickel concentration of 5%, the light absorption decreases at this wavelength interval. figure 5 also shows that ni plays the main role in increasing the absorption of light in the visible area while the other impurities which exist in the zno film have considerably less influence in the existing amounts. fig. 5. dependence of the optical spectrum of zno thin films on the concentration of nickel impurities. curve-1: zno with 1% content of ni impurities, curve-2: zno with 2% ni, curve-3: zno with 3% ni, curve-4: zno containing 4% ni, curve-5: zno containing 5% ni, and curve-6: zno without nickel impurities the image on figure 5 is quite complicated, so to make this process more visible, the dependence of light absorption rate on the concentration of impurities at a specific wavelength of 450nm has been built for nickel-containing zinc oxides. figure 6 (continuous line) shows this dependence graph, which clearly indicates that as the nickel concentration increases up to 4% the absorption rate increases too, but at 5% it decreases sharply (continuous line and dot a). it was suggested that the reduction (shown on figure 6) in light absorption at high concentrations of impurities should have been caused by the inhomogeneous distribution of these impurities and by the creation of their agglomerates. in order to test this assumption, heat treatment was carried out on a sample containing 5% ni in vacuum at 600 0 c for 1 hour. the goal of the test was to remove the aforementioned agglomerates. figure 6 (dash line and dot b) shows the absorption value of this sample at a wavelength of 450nm after thermal treatment in a vacuum. as it is clear from figure 6, the absorbance has been increased sharply at 450nm after the vacuum thermal treatment at 600 0 c, confirming our assumption. fig. 6. dependence of light absorption of zinc oxides with nickelimpurities on nickel concentration at 450nm wavelength before heat treatment (continuous line and dota) and after heat treatment (dash line and dotb) as mentioned above, one of the main methods of increasing the quantum yield of photocatalyst nanopowders is to place different nano-size clusters on the surface of their particles which would capture photo-induced electrons and holes and reduce their recombination. to hit the goal in our case, silver clusters were placed on the surface of zno thin films with ni impurities and their optical properties have been investigated. figure 7 shows the results of the corresponding investigations: curve 1 corresponds to the absorption spectrum of zno thin film containing 3% of nickel impurities before decorating its surface with silver clusters and curve 2 does the same after decorating its surface. fig. 7. change of the absorption spectrum of zno thin film by decorating its surface with silver clusters. curve 1: the black circles show the absorption spectrum before zno thin film decoration. cutve 2: the black triangles show the absorption spectrum after the zno thin film was decorated with silver clusters there is an obvious increase in the light absorption after the clusters are applied to the surface, but the effect is much smaller than in the case of decorating nanopowders [17]. we suggest that the reason is that the surface area is much larger in the case of nanopowders than in the case of thin films. figure 8 shows the results of the investigation of the photocatalytic activity of the zno thin film with nickel impurities in the visible area of sunlight. methylene blue solution has been used to evaluate the photocatalytic activity. by changing the methylene absorption in this solution at 665nm wavelength, methylene degradation has been observed. two glass vessels of 5ml methylene blue were used for the experiment. it was spectrophotometrically established that the glass vessels hardly engineering, technology & applied science research vol. 10, no. 2, 2020, 5524-5527 www.etasr.com nadareishvili et al.: investigation of the visible light-sensitive zno photocatalytic thin films 5527 allowed the ultraviolet rays with less than 38nm wavelength to pass through. one vessel contained only a solution of methylene blue while another vessel contained the same solution of methylene blue with a thin layer of zno containing 4% nickel impurities deposited on glass substrates. the surface area of zno:ni thin film with 4% ni content was approximately 1cm 2 . both vessels were placed under the summer sunlight at 30 0 c for six hours. after each hour of solar irradiation the methylene blue solution from the glass vessels was placed in the spectrophotometer cuvette and the concentration of methylene blue was determined in the solution using methylene absorption peak value at 665nm wavelength. the spectrophotometer was pre-calibrated and the methylene concentration dependence on the absorption peak value was plotted. using this graph the concentration of methylene was determined according to the amount of absorption. the experiments showed that the concentration of methylene remained almost unchanged in the vessel without the zno thin layer, whereas the concentration of methylene gradually decreased in the vessel containing the zno thin layer. figure 8 illustrates the results. fig. 8. the graph of methylene blue degradation by the action of visible light. curve 1: without the thin film of zno in the vessel. curve 2: the vessel contained a thin film of zno with 4% nickel impurities iv. conclusion photocatalytic zno thin films active in the visible light were obtained by spray pyrolysis technique when hydrated ni chloride hexahydrate nicl2(6h2o) was added to the precursor solution. optical investigations have shown that ni impurities enhance the absorption of light by zno thin films in the visible area from 400nm to 600nm wavelength and this absorption increases with the increase of the concentration of ni impurities. also, it has been established that the formation of agglomerates of the impurities at high concentrations reduces the light absorption. the light absorption gets increased when the surfaces of zno thin films with ni impurities are decorated with silver clusters but the effect is much smaller than in the case of nanopowders. experiments on the determination of photocatalytic activity using methylene blue have shown that zno thin films with nickel impurities are characterized by photocatalytic activity in the visible area of sunlight. acknowledgment this work was supported by the shota rustaveli national science foundation of georgia (srnsfg) grant number stcu-2017-24 and the science and technology center in ukraine (stcu) grant n 7095. the authors are grateful to the professors of tunis el manar university a. mhamdi, k. boubaker and m. amlouk for kindly providing the research samples. references [1] m. kaneko, i. okura, photocatalisis science and technology, springer, 2002 [2] v. kumaravel, s. mathew, j. bartlett, s. c. pillai, “photocatalytic hydrogen production using metal doped tio2: a review of recent advances”, applied catalysis b: enviromental, vol. 244, pp. 1021-1064, 2019 [3] w. wang, g. huang, j. c. yu, p. k. wong, “advances in photocatalytic disinfection of bacteria: development of photocatalysts and mechanisms”, journal of environmental sciences, vol. 34, pp. 232–247, 2015 [4] h. a. maddah, “numerical analysis for the oxidation of phenol with tio2 in wastewater photocatalytic reactors”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3463-3469, 2018 [5] m. mahshidnia, a. jafarian, “forecasting wastewater treatment results with an anfis intelligent system”, engineering, technology & applied science research, vol. 6, no. 5, pp. 1175-1181, 2016 [6] z. y. ilerisoy, y. takva, “nanotechnological developments in structural design: load-bearing materials”, engineering, technology & applied science research, vol. 7, no. 5, pp. 1900-1903, 2017 [7] m. kalbacova, j. m. macak, f. schmidt-stein, c. t. mierke, p. schmuki, “tio2 nanotubes: photocatalyst for cancer cell killing”, physica status solidi (rrl)–rapid research letters, vol. 2, no. 4, pp. 194–196, 2008 [8] g. sadanandam, l. zhang, m. s. scurrell, “enhanced photocatalytic hydrogen formation over fe-loaded tio2 and g-c3n4 composites from mixed glycerol and water by solar irradiation”, journal of renewable and sustainable energy, vol. 10, pp. 034703-034708, 2018 [9] s. higashimoto, “titanium-dioxide-based visible-light-sensitive photocatalysis: mechanistic insight and applications”, catalysts, vol. 9, no. 2, pp. 201-209, 2019 [10] s. kaufhold, l. petermann, d. sorsche, s. rau, ““trojan horse” effect in photocatalysis: how anionic silver impurities influence apparent catalytic activity”, chemistry-a european journal, vol. 23, no. 10, pp. 2271-2274, 2017 [11] a. a. aboud, a. mukherjee, n. revaprasadu, a. n. mohamed, “the effect of cu-doping on cds thin films deposited by the spray pyrolysis technique”, the journal of materials research and technology, vol. 8, no. 2, pp. 2021-2030, 2019 [12] r. venkatesan, s. velumani, k. ordon, m. makovska-janusik, g. corbel, a. kassiba, “nanostructured bismuth vanadate (bivo4) thin films for efficient visible light photocatalysis”, materials chemistry and physics, vol. 205, pp. 325-333, 2018 [13] c. bogatu, m. covei, d. perniu, i. tismanar, a. duta, “stability of the cu2znsns4/tio2 photocatalytic thin films active under visible light irradiation”, catalysis today, vol. 328, pp. 79-84, 2019 [14] a. mhamdi, a. boukhachem, m. madani, h. lachheb, k. boubaker, a. amlouk, m. amlouk, “study of vanadium doping effects on structural, opto-thermal and optical properties of sprayed zno semiconductor layers”, journal of optik, vol. 124, pp. 3764–3770, 2013 [15] t. khoperia, g. mamniashvili, m. nadareishvili, t. zedginidze, “competitive nanotechnology for deposition of films and fabrication of powder-like particles”, ecs transactions, vol. 35, pp. 17-30, 2011 [16] t. khoperia, t. zedginidze, k. kvavadze, m. nadareishvili, “development of competitive nanotechnologies for solution of challenges in photocatalysis, electronics and composites fabrication”, 212th ecs meeting, washington dc, usa, october 7-12, 2007 [17] d. japaridze, d. daraselia, e. chikvaidze, t. gogoladze, m. nadareishvili, t. gegechkori, t. zedginidze, t. petriashvili, g. mamniashvili, a. shengelaya, “magnetic properties and photocatalytic activity of the tio2 micropowders and nanopowders coated by ni nanoclusters”, journal of superconductivity and novel magnetism, vol. 32, no. 10, pp. 3211-3216, 2019 microsoft word 35-3434_s_etasr_v10_n2_pp5534-5537 engineering, technology & applied science research vol. 10, no. 2, 2020, 5534-5537 5534 www.etasr.com bheel et al.: effect of sugarcane bagasse ash and lime stone fines on the mechanical properties of … effect of sugarcane bagasse ash and lime stone fines on the mechanical properties of concrete naraindas bheel department of civil technology h.c.s.t hyderabad, pakistan naraindas04@gmail.com abdul samad memon department of civil technology h.c.s.t hyderabad, pakistan samad.memon105@gmail.com imdad ali khaskheli department of civil technology h.c.s.t hyderabad, pakistan imdadali961@gmail.com noor muhammad talpur department of civil technology h.c.s.t hyderabad, pakistan mirnoor2018@gmail.com sher muhammad talpur department of civil technology h.c.s.t hyderabad, pakistan shermohd168@gmail.com muhammad awais khanzada department of civil technology h.c.s.t hyderabad, pakistan awais.khanzada145@gmail.com abstract—cement production releases huge amounts of carbon dioxide having a significant impact on the environment while also having huge energy consumption demands. in addition, the disposal and recovery of natural concrete components can lead to environmental degradation. the use of waste in concrete not only reduces cement production, but it also reduces energy consumption. the aim of this study is to evaluate the properties of fresh and hardened concrete by partially replacing cement with sugarcane bagasse ash (scba) and limestone fines (lsf). in this investigation work the cement was replaced with scba ash and lsf by 0% (0% scba+ 0% lsf), 5% (2.5% scba+ 2.5% lsf), 10% (5% scba+ 5% lsf), 15% (7.5% scba+ 7.5% lsf) and 20% (10% scba+ 10% lsf) by weight of cement. in this regard, a total of 60 samples of concrete specimens were made with mix proportion of 1:1.5:3 with 0.56 water-cement ratio. cube specimens were tested for compressive strength and cylindrical specimens were used for determining splitting tensile strength at 7 and 28 days respectively. the optimum result displayed that the crushing strength and split tensile strength increased by 10.33% and 10.10% while using 5% scba+ 5% lsf as a substitute for cement in concrete after the 28 th day. the slump value of concrete declined as the content of scba and lsf increased. keywords-limestone fines; sugarcane bagasse ash; cement replacement; enhance strength and reduce environmental issues i. introduction concrete is a man-made construction material, which is most commonly used for the construction of various civil engineering structures [1-3]. ordinary portland cement (opc) concrete is used in numerous structural applications and it is favorable for normal construction projects. however, due to some of its limitations, certain requirements have been difficult to satisfy especially in terms of strength and durability regarding complex structures. the need for the development of high-strength and high-performance concrete has extensively increased in order to meet the requirements for advanced and complex structures [4]. the development of high-strength concrete (hsc) requires a large amount of cement and the production of cement is considered as the most energyintensive component for the production of concrete [5]. co2 emissions during the production of cement are an environmental concern. it is a well-known fact that approximately one ton of co2 is released into the environment through one-ton production of opc cement. moreover, cement manufacturing is responsible for 5% to 7% of co2 emissions from industrial sources [6]. without compromising the performance of the concrete structures, the use of portland cement needs to be reduced in order to reduce co2 emissions related to cement production while the sustainability of construction needs to be taken into consideration [7-9]. partial substitutions of cement by a combination of cement replacing materials (crms) are advantageous not only from the economic point of view but also for their mechanical and microstructural characteristics [10]. the use of crms into concrete has gained popularity with emphasis on increasing the service life of concrete structures [11]. many crms are commercially available and can be used in concrete. some of the most common materials are sugarcane bagasse ash (scba) [12, 13], limestone fines (lsf), rice husk ash (rha) [14-16], silica fume (sf), etc. [17, 18]. in this experimental investigation, the combined influence of scba and lsf used as cement replacement materials in cement concrete was determined. scba is a sugar mill by-product found after burning bagasse, which in turn was originated after the sugar extraction from sugarcane. it has been tested for volcanic ash properties and improvements have been found in mortar and concrete, such as in crushing strength, durability, and water resistance in certain proportions [19]. lsf were collected from hyderabad and they can be used either as a cementitious material or as fine aggregates in concrete mix [20-22]. there are several studies corresponding author: naraindas bheel engineering, technology & applied science research vol. 10, no. 2, 2020, 5534-5537 5535 www.etasr.com bheel et al.: effect of sugarcane bagasse ash and lime stone fines on the mechanical properties of … conducted on the strength development of concrete containing scba and lsf. authors in [23] determined the influence of scba on the hardened concrete. concrete samples were prepared with 1:2:4 mix ratio and were tested for compressive and split tensile strength at 28 days. the test results advocated that the crushing and indirect tensile strength were enhanced by 7.90% and 14% at 10%. authors in [24] studied the effects of lsf content on concrete’s compressive strength and durability. they reported that increasing the amount of lsf in concrete enhances strength and decreases permeability. lsf concrete having 0.40w/b ratio performed better as compared to 0.50 and 0.60w/b ratio lsf concrete regarding strength development. the porosity and pore size of concrete were significantly decreased after 28 days. authors in [25] observed that the crushing and bending strength and permeability related properties were improved by using lsf in concrete. in the available literature there are a limited number of studies available on the individual and combined effects of scba and lsf as cement replacing material in concrete. several types of mineral admixtures are used in concrete but their effects on concrete properties with binary and ternary blends are not investigated in satisfying depth. the main aim of this paper is to investigate the combined effect of scba and lsf with cement on fresh and hardened concrete. since the compressive strength of concrete is an important parameter, and all other properties of concrete are judged on the basis of its compressive strength. in addition, statistical assessment on compressive strength of concrete using rsm has been performed in order to investigate the effectiveness of each material on the basis of its compressive strength. ii. research methodology this research study aimed to determine the fresh, physical and hardening properties of concrete by using of 0% (0% scba+ 0% lsf), 5% (2.5% scba+ 2.5% lsf), 10% (5% scba+ 5% lsf), 15% (7.5% scba+ 7.5% lsf) and 20% (10% scba+ 10% lsf) cement replacement materials in concrete. a total of 60 concrete samples of 1:1.5:3 mix proportions were prepared (30 cylinders and 30 cubes) with 0.56 water/cement ratio and were cured for 7 and 28 days. table i. concrete mixes id scba + lsf (%) f.a & ca (%) cement (%) water-cement ratio (%) 01 0%+0% 100 100 0.56 02 2.5%+2.5% 100 95 0.56 03 5%+5% 100 90 0.56 04 7.5%+7.5% 100 85 0.56 05 10% +10% 100 80 0.56 mix ratio 1:1.5:3 the variables cement (binder), coarse aggregates, fine aggregates, and water were considered. scba and lsf were used as crms and the concrete samples were tested on an utm. in this study, concrete cubes (100mm×100mm×100mm) ware cast and tested for compressive strength. similarly, cylinders (200mm×100mm) were tested for splitting tensile strength. moreover, the concrete specimens were tested for water absorption and concrete density after 28 days. three concrete samples were cast for each ratio, and the mean of the samples was considered as the ultimate result. the study was conducted in a laboratory of the department of civil technology, h.c.s.t hyderabad, sindh, pakistan [26, 27]. iii. materials used a. cement in this investigational study, opc was utilized with 33% normal consistency, and initial and final setting time of 46min and 160min respectively. b. fine and coarse aggregates hill sand was used as fine aggregates that passed through #4 sieves and crushed stones having 20mm in size were used as coarse aggregates. these aggregates were collected locally in the region of hyderabad. c. limestone fines (lsf) the lsf were collected from hyderabad. after collecting, they were sieved through #300 sieves to obtain fine powder form and then they were utilized as cementitious material in concrete mixes. d. sugarcane bagasse ash (scba) scba was collected from matiari sugar mill. after collecting, it was dried under the atmosphere and the dried ash was sieved through #300 sieves to obtain the desired ash. this desired ash was utilized as cement replacement in concrete. e. water drinking water was used. iv. results and discussion a. slump test slump test was studied based on slump losses using a standard slump cone in accordance with astm c 143-05. at 0% scba and 0% lsf, the maximum concrete slump is 65mm, and at 10% scba and 10% lsf, the minimum slump of fresh concrete is 29mm. the slump value reduced as the amount of scba and lsf increased as shown in figure 1. fig. 1. slump test results b. density of concrete the concrete samples were used to analyze the density of concrete with addition of several ratios of scba and lsf by engineering, technology & applied science research vol. 10, no. 2, 2020, 5534-5537 5536 www.etasr.com bheel et al.: effect of sugarcane bagasse ash and lime stone fines on the mechanical properties of … weight of cement on the 28 th day. the maximum value of 2380kg/m 3 was noted at 0% scba + 0% lsf and the minimum value of 2290kg/m 3 at 10% scba + 10% lsf after 28 days. the density of concrete reduced as the scba and lsf content increased as shown in figure 2. fig. 2. density of concrete c. water absorption the concrete samples were used to analyze the water absorption of concrete with addition of several ratios of scba and lsf by weight of cement at the 28 th day. it was recorded maximum (4.30%) at 10% scba + 10% lsf and minimum 2.50% at 0% scba + 0% lsf after 28 days. the water absorption of concrete augmented with increasing content of scba and lsf as shown in figure 3. fig. 3. water absorption of concrete d. compressive strength the cubical samples were checked for analyzing compressive strength of concrete. the optimum crushing strength was increased to 8.96% and 10.33% at 5% scba + 5% lsf and it was decreased by 9.80% and 6.40% at 10% scba + 10% lsf after 7 days and 28 days respectively as shown in figure 4. e. split tensile strength the cylindrical samples were checked for split tensile strength of concrete with several percentages of lsf and scba. the optimum indirect tensile strength was augmented by 8.20% and 10.10% at 5% scba + 5% lsf and was reduced by 9.84% and 4.04% at 10% scba + 10% lsf after 7 and 28 days respectively as displayed in figure 5. fig. 4. compressive strength of concrete fig. 5. split tensile strength of concrete v. conclusions the basic aim of this study was the utilization of scba and lsf as cement replacements in concrete and to determine their effect on the fresh and hardened concrete properties. from this research study, the following conclusions can be drawn: • at 0% scba and 0% lsf, the concrete slump is maximum (65mm), and at 10% scba and 10% lsf, the slump of fresh concrete is minimum (29mm). moreover, the slump value reduced as the amount of scba and lsf increased. • the density of concrete was maximum (2380kg/m 3 ) at 0% scba + 0% lsf and minimum (2290kg/m 3 ) at 10% scba+10% lsf after 28 days. the density of concrete reduced as the scba and lsf content increased. • water absorption of concrete was maximum (4.30%) at 10% scba + 10% lsf and minimum (2.50%) at 0% scba+0% lsf after 28 days. the water absorption of concrete increased as the amount of scba and lsf increased. engineering, technology & applied science research vol. 10, no. 2, 2020, 5534-5537 5537 www.etasr.com bheel et al.: effect of sugarcane bagasse ash and lime stone fines on the mechanical properties of … • the optimum crushing strength increased by 8.96% and 10.33% at 5% scba + 5% lsf and decreased by 9.80% and 6.40% at 10% scba + 10% lsf after 7 and 28 days respectively. • the optimum indirect tensile strength increased by 8.20% and 10.10% at 5% scba + 5% lsf and reduced by 9.84% and 4.04% at 10% scba + 10% lsf after 7 and 28 days respectively. references [1] m. uysal, v. akyuncu, “durability performance of concrete incorporating class f and class c fly ashes”, construction and building materials, vol. 34, pp. 170-178, 2012 [2] n. bheel, r. a. abbasi, s. sohu, s. a. abbasi, a. w. abro, z. h. shaikh, “effect of tile powder used as a cementitious material on the mechanical properties of concrete”, 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meghwar, r. a. abbasi, i. a. ghunio, z. h. shaikh, “use of sugarcane bagasse ash as cement replacement materials in concrete”, international conference on sustainable development in civil engineering, jamshoro, pakistan, december 5-7, 2019 [13] a. a. dayo, a. kumar, a. raja, n. bheel, a. w. abro, z. h. shaikh, “effect of sugarcane bagasse ash as fine aggregates on the flexural strength of concrete”, international conference on sustainable development in civil engineering, jamshoro, pakistan, december 5-7, 2019 [14] n. bheel, a. w. abro, i. a. shar, a. a. dayo, s. shaikh, z. h. shaikh, “use of rice husk ash as cementitious material in concrete”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4209-4212, 2019 [15] n. bheel, s. l. meghwar, s. a. abbasi, l. c. marwari, j. a. mugeri, r. a. abbasi, “effect of rice husk ash and water-cement ratio on strength of concrete”, civil engineering journal, vol. 4, no. 10, pp. 2373-2382, 2018 [16] n. bheel, s. l. meghwar, s. 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87-93, 2014 [25] c. aquino, m. inoue, h. miura, m. mizuta, t. okamoto, “the effects of limestone aggregate on concrete properties”, construction and building materials, vol. 24, no. 12, pp. 2363-2368, 2010 [26] n. d. bheel, s. a. abbasi, s. l. meghwar, f. a. shaikh, “effect of human hair as fibers in cement concrete”, international conference on sustainable development in civil engineering, jamshoro, pakistan, november 23-25, 2017 [27] a. n. khan, n. d. bheel, m. ahmed, r. a. abbasi, s. sohu, “use of styrene butadiene rubber (sbr) polymer in cement concrete”, indian journal of science and technology, vol. 13, no. 5, pp. 606-616, 2020 microsoft word 44-2929_s_etasr_v9_n4_pp4548-4553 engineering, technology & applied science research vol. 9, no. 4, 2019, 4548-4553 4548 www.etasr.com dung & phuong: short-term electric load forecasting using standardized load profile (slp) and … short-term electric load forecasting using standardized load profile (slp) and support vector regression (svr) nguyen tuan dung planning department, evnhcmc power company, ho chi minh, vietnam dp1526@gmail.com nguyen thanh phuong institute of engineering, hutech university of technology, ho chi minh, vietnam nt.phuong@hutech.edu.vn abstract—short-term load forecasting (stlf) plays an important role in business strategy building, ensuring reliability and safe operation for any electrical system. there are many different methods used for short-term forecasts including regression models, time series, neural networks, expert systems, fuzzy logic, machine learning, and statistical algorithms. the practical requirement is to minimize forecast errors, avoid wastages, prevent shortages, and limit risks in the electricity market. this paper proposes a method of stlf by constructing a standardized load profile (slp) based on the past electrical load data, utilizing support regression vector (svr) machine learning algorithm to improve the accuracy of short-term forecasting algorithms. keywords-short-term load forecast; regression model; standardized load profile; support vector regression i. introduction load forecasting is electrical systems is a topic that has been studied extensively. there are two main approaches in this area: traditional statistical methods of the relationship between the load and load-affecting factors (such as time series, regression analysis, etc.) and machine learning methods (a branch of artificial intelligence). statistical methods assume load data according to a sample and try to forecast the value of future loads using different time series analysis techniques. intelligent systems are derived from mathematical expressions of human behavior and experience. especially since the early 1990s, neural networks have been considered one of the most commonly used techniques in the field of electrical load forecasting, because they assume that there is a nonlinear function related to historical values and some external variables with future values may affect the output [1]. the approximate ability of neural networks has made their applications popular. in recent years, an intelligent calculation method involving support vector machines (svm) has been widely used in the field of load forecasting. authors in [2] used the support vector regression (svr) technique to solve the electrical load prediction problem (forecasting a maximum daily load for the next 31 days). this was a competition organized by eunite (european network on intelligent technologies for smart adaptive systems). the provided information included: the demand data of the past two years, daily temperature of the past four years and local holiday events. the data were divided into 2 parts: a part used for training (about 80%-90%) and the rest used for algorithm testing (about 20%-10%). the set of training inputs included data of previous day, previous hour, previous week, and the average of the previous week. since then, there have been several studies exploring the different techniques used for optimizing svr to perform load forecasting [3-10]. the main reason for using svm in load forecasting is that it can easily model the load curve, the relationship between the load and the dynamics of changing load demand. however, there are some problems encountered when the above algorithms are applied to real situations: • climate conditions always play an important role in load forecasting. they show the relationship between climate and load demand. when we do load forecasting for the post-test period, it is very difficult to forecast the values of weather and climate used as the input of the algorithm and these values are often not available. • electrical load samples include hidden elements, which tend to be similar to the previous load model. however, it will lead to a false forecast of the following days if the date pattern is different from the previous day or there is an event that impacts. therefore, the use of the dataset (training inputs include data of the previous day, the previous hour, the previous week, the average of the previous week) has many risks if the load models are not identical. • if the forecast time frame is greater than the past data frame (more than 7 days), there will be a lack of input to run the algorithm. • in addition, for asian countries (such as vietnam) that use lunar calendar, there are difficult and unpredictable issues as the lunar new year (usually in late january or early february), etc. there is a deviation between the solar calendar and the lunar calendar (the load models are not identical). therefore, it often leads the forecast results of algorithm for this period with large errors. this paper proposes a solution to build a standardized load profile (slp) based on the historical load dataset as a training corresponding author: nguyen tuan dung engineering, technology & applied science research vol. 9, no. 4, 2019, 4548-4553 4549 www.etasr.com dung & phuong: short-term electric load forecasting using standardized load profile (slp) and … dataset. this input dataset is combined with the svr algorithm to improve the accuracy of short-term forecast results, solve the problem of deviation between the solar and the lunar calendar, and overcome the input data frame. slp will be built for all 365 days and 8,670 hour cycles in a year. slp will be an important dataset during the training, testing and forecasting process. it will standardize load models by hours, days, seasons, and special day types (including lunar dates). therefore, slp will contribute to solve the above-mentioned difficulties and improve the quality of electrical load forecasting. ii. methodology observing the load profiles of february of ho chi minh city over the years (figure 1), we can see a huge fluctuation in the chart shape over the years. the results in the use of historical data for forecasting this period of time are extremely complicated. (a) (b) (c) fig. 1. the load profiles of february over the years: (a) 2016, (b) 2017, (c) 2018 in fact, the algorithms used to forecast in vietnam have to go through an intermediary stage in which the months are converted into regular months (without holidays and lunar new year). after, the forecast result will be reversed or the result will be accepted with a large error. this is a common problem in software provided by foreign countries. a. standardized load profiles (slp) while observing the load profiles of the days in a week and some special holidays of the year in ho chi minh city (figure 2), we see the difference between weekdays (from tuesday to friday) is not much and they have the same load chart. for the load profiles on monday, they are different from the normal days at 0:00 to 9:00, due to the forwarding demand from sunday. for load profiles on saturday, there is a change but not much compared to normal days. mainly the load demand decreases in the evening due to the start of weekends. particularly for load profiles on sunday, it is completely different from normal days (the demand for electricity is low). (a) (b) (c) fig. 2. typical load profiles on some days in a year when observing the load chart of the new year and the lunar new year, we see the difference completely, the graphs are almost flat, and the load demand is quite low because these are holidays. particularly on lunar new year, the load demand is the lowest, because this is the longest holiday of the year (from 6 to 9 days). slps are built by taking the value of the collected capacity in a 60-minute period divided by its maximum capacity. we need to build slp for 365 days per year. some typical slps are shown in figure 3. based on the slp of each cycle of the past data set, we can build the slp data set for future forecast periods. this should be accurate to each cycle, each type of day (weekdays, working days, holidays, etc.), each week, and each month. therefore, the slp is a special feature and is also an important input parameter of the svr (nn) training process to rebuild the load curves, from which we can estimate lost or not recorded data during the measurement process. b. support vector regression (svr) the feature of svr is that it provides us with a sparse solution. that is, to build the regression function, we do not need to use all the data points in the training set. the points that engineering, technology & applied science research vol. 9, no. 4, 2019, 4548-4553 4550 www.etasr.com dung & phuong: short-term electric load forecasting using standardized load profile (slp) and … contribute to the construction of the regression are called support vectors. the layering for a new data point will depend only on the support vectors [5–6]. (a) (b) (c) (d) fig. 3. slp of some days in a year: (a) sunday, (b) lunar new year, (c) saturday, and (d) a normal day. the regression function has the formula: ( ) ( ) t y f x w x b= = φ + (1) thus, the goal of svr training is to find w and b [7-10] for the training set {(x1, t1), (x2, t2), …, (xn, tn)} rr n ×⊂ . with a simple regression problem, to find w and b we have to minimize the normalized error function: 2 1 2 2 }{ 2 1 wty n n nn λ +−∑ = (2) where λ is a normalized constant. to get a sparse solution, we will replace the above error function with the ε-insensitive error function. the characteristic of this error function is that if the absolute value of the difference between the predicted value y(x) and the target value is less than ε (with ε>0) then the error is considered zero. now, we must minimize the normalized error function: 2 1 2 2 1 ))(( wtxyec n n nn +−∑ = ε (3) with ( ) ( ) ( ) t n ny x f x w x b= = φ + , c is a normalized constant like λ but is multiplied by an error function instead of 2 w . to allow some points outside the tube ε, we will add slack variables. for each data point xn, we need two liquid variables 0νξ ≥ and ˆ 0νξ ≥ , with 0νξ ≥ corresponding to the point that ( )n nt y x ε> + (outside and above the tube) and ˆ 0νξ ≥ corresponding to the point that ( )n nt y x ε< − (outside and below the tube). fig. 4. illustration for liquid variables ξn the condition for a destination point in the pipe is: n n ny t yε ε− ≤ ≤ + with yn=y(xn). using liquid variables, we allow destination points outside the tube (corresponding to liquid variables > 0) and thus the condition will now be: ˆ n n n n n n t y t y ε ξ ε ξ ≤ + + ≥ − − thus, we have an error function for svr: n 2 n n n 1 1ˆc ( w ) 2= ξ + ξ +∑ . our goal is to minimize this error function with constraints: ˆ0, 0 ˆ n n n n n n n n t y t y ξ ξ ε ξ ε ξ ≥ ≥ ≤ + + ≥ − − using the lagrange function and the karush-kuhn-tucker condition, we have the equivalent optimization problem: 1 1 1 1 1 ˆ ˆ( )( ) ( , ) 2 ˆ ˆ( ) ( ) n n n n m m n m n m n n n n n n n n n a a a a k x x a a a a tε = = = = − − − − − + − ∑∑ ∑ ∑ (4) engineering, technology & applied science research vol. 9, no. 4, 2019, 4548-4553 4551 www.etasr.com dung & phuong: short-term electric load forecasting using standardized load profile (slp) and … where k is the kernel function: )'()()',( xxxxk t φφ= . maximizing with constraints: 1 0 ˆ0 ˆ( ) 0 n n n n n n a c a c a a = ≤ ≤ ≤ ≤ − =∑ (5) from here, we have the regression function of svr: 1 ˆ( ) ( ) ( , ) n n n n n y x a a k x x b = = − +∑ (6) thus, for svrs using the ε-insensitive error function and the gaussian kernel function we obtain three parameters: the normalization coefficient c, the parameter γ of the gaussian kernel function, and the width of the pipe ε [7]. these parameters affect the forecast accuracy of the model and need to be selected carefully. • if c is too large, it will give a priority to the training error. it leads to a complex model and it is easy to be over fitting. if c is too small, it will give a priority to the complexity of the model. it leads to a too simple model and reduces forecast accuracy. • the meaning of ε is the same. if it is too large, there will be less support vectors, making the model too simple. on the other hand, if ε is too small, there are many support vectors, leading to complex models, which are more likely to be over fitting. • the γ parameter reflects the correlation between the support vectors and also affects the forecast accuracy of the model. c. research models the flowchart of the slp-svr forecasting algorithm is given in figure 5. fig. 5. flowchart of forecasting algorithm by slp – svr processed historical data (power consumption, capacity and temperature recorded in 24 cycles 60 minutes each) with the slp will be included in modules to build regression functions under svr, neural network (nn) algorithms to build regression functions. then we use the above dataset to check and evaluate the error of regression functions. after that, we choose the regression function with the smallest error to be used as regression function for the next forecast phase. the slp dataset in 24 cycles of the expected period (including holidays, etc.) and the forecasted temperature in 24 cycles of the corresponding period will be the input for the regression function that is selected to export forecast results in 24 cycles for a period of 7-30 days. iii. results and discussion a. input data: the article uses data from january 1 st , 2015, to november 17 th , 2018 of evnhcmc to run test models. after pretreatment, the dataset is divided into 2 parts: training set and testing set, in which the testing set is the last 30 days of the dataset. or the dataset is divided into phases to test the forecast results in different time periods. input data for training algorithms include: capacity (pmax/pmin) in 60-minute cycles, temperature (max/min) in 60-minute cycles, standardized load profiles of 24 hours of day and a list of holidays and lunar new year in the forecast year. a useful measurement parameter is the mean absolute percentage error (mape) which is used to evaluate the error of models. 1 mape 100 f t t t y y n y − = ∑ (7) the algorithms are programmed in matlab and the results are exported to excel files for data exploitation. b. svr models it is necessary to correctly select the input parameters to run svr models such as: normalization coefficient c, width of pipe ε and gaussian kernel function. the algorithm uses the same input dataset of models. some typical proposed svr model parameters are shown in table i. table i. svr model parameters model c ε kernel function svr 1 93.42 32.5 polynomial svr 2 500.32 0.01 gaussian svr 3 1 50.03 linear svr 4 100 0.01 linear c. rfr models a set of regression trees is used with each set of different rules to perform a non-linear regression. the algorithm builds a total of 20 trees, with a minimum leaf size of 20. the number of leaves is smaller or equal to the size of the tree to control overfitting and bring about high performance [13-14]. the algorithm uses the same input dataset of models. d. neural network models we used feedforward neural network models with the mentioned above input variables and training dataset. ahidden-layer network architecture with a class size of 10 and sigmoid activation function was used. at the same time, the usual neural network with 3-hidden-layer network architecture, engineering, technology & applied science research vol. 9, no. 4, 2019, 4548-4553 4552 www.etasr.com dung & phuong: short-term electric load forecasting using standardized load profile (slp) and … in which: the first hidden layer has a size of 10 nodes, the second hidden layer has 8 and the third hidden layer has 5 nodes. e. results and analysis 1) regression models test we run the forecast results for february of 2018 (the month of the lunar new year) to assess the degree of error of the models. the model included as inputs the data of the previous day, previous hour, previous week and the previous week average. processed historical data (power consumption, capacity, temperature recorded at 24 cycles of 1 hour) with the slp were included in modules to build regression functions under svr, neural network and random forest algorithms to build regression functions. fig. 6. regression models test table ii. checking errors of regression models results date ytr yts1 yts2 yts3 yts4 ytnn ytfeed ytrf 1/23/18 9.71 4.05 5.02 6.35 4.19 6.09 4.55 2.91 1/24/18 8.30 3.65 2.61 7.00 4.25 0.65 4.76 4.19 1/25/18 7.17 4.35 3.57 7.42 4.21 4.58 5.84 4.63 1/26/18 7.10 6.20 6.77 7.48 6.39 6.58 5.82 6.44 1/27/18 9.22 1.37 0.44 3.27 1.33 0.56 1.91 1.06 1/28/18 9.68 2.16 3.28 7.12 0.32 25.51 5.89 3.93 1/29/18 9.15 5.30 6.17 6.92 4.91 5.71 5.96 5.67 we chose the regression function with the smallest error to be used for the next forecast phase. the yts4 model was selected as a forecasting model. 2) forecast results for february of 2018 considering the model forecast results for february, we see a big difference between forecast and reality (figure 7). the reason is that we used the historical data of january of 2019 (714-30 days before the forecasting date) as the input for the training model. 3) results of testing svr models we see the results in figure 8 and table iii. 4) results of testing machine learning models we see the results in figure 9 and table iv. fig. 7. forecast results for the next 30 days fig. 8. svr models test table iii. results of checking errors of svr models date yts1 yts2 yts3 yts4 1/23/18 1.15 0.64 2.22 3.87 1/24/18 1.70 2.12 2.95 6.19 1/25/18 3.03 3.30 3.38 6.68 1/26/18 1.35 1.04 1.76 2.76 1/27/18 6.77 4.56 6.42 1.56 1/28/18 4.18 5.09 1.81 0.76 1/29/18 0.24 0.12 2.69 2.14 mape 2.63 2.41 3.03 3.42 fig. 9. machine learning models test engineering, technology & applied science research vol. 9, no. 4, 2019, 4548-4553 4553 www.etasr.com dung & phuong: short-term electric load forecasting using standardized load profile (slp) and … table iv. checking errors of machine learning models result date ytnn ytfeed ytrf 1/23/18 1.25 1.61 1.70 1/24/18 2.14 2.90 3.36 1/25/18 0.99 5.55 3.89 1/26/18 3.16 1.84 2.26 1/27/18 4.81 1.56 1.92 1/28/18 7.51 5.85 4.68 1/29/18 4.41 2.05 0.43 mape 3.47 3.05 2.60 5) results of testing regression models: we see the results in figure 10 and table v. fig. 10. regression test models table v. results of test models checking errors date ytr yts1 yts2 yts3 yts4 ytnn ytfeed ytrf 1/23/18 9.71 1.15 0.64 2.22 3.87 1.25 1.61 1.70 1/24/18 8.30 1.70 2.12 2.95 6.19 2.14 2.90 3.36 1/25/18 7.17 3.03 3.30 3.38 6.68 0.99 5.55 3.89 1/26/18 7.10 1.35 1.04 1.76 2.76 3.16 1.84 2.26 1/27/18 9.22 6.77 4.56 6.42 1.56 4.81 1.56 1.92 1/28/18 9.68 4.18 5.09 1.81 0.76 7.51 5.85 4.68 1/29/18 9.15 0.24 0.12 2.69 2.14 4.41 2.05 0.43 mape 8.62 2.63 2.41 3.03 3.42 3.47 3.05 2.60 we choose the regression function with the smallest error to be used as the regression function for the next forecast phase. the model yts2 is selected to be the forecasting model. 6) forecast results for february of 2018 we see the results in figure 11, where a definite improvement is observed. iv. conclusion we observed the experimental results in the forms of testing datasets (load datasets of the previous day, previous week, previous month and the dataset of slp), we saw that the results of the slp-svr models are closely to the actual value of february of 2018, while the results of the old model are in quite a large deviation. thus, we see that the use of slp as the input dataset for the modules of forecasting regression function is effective and gives forecasting results with low error. it solves the problem of deviation between the solar and the lunar dates, especially in the months of lunar new year. also it resolves the difference between the solar and lunar cycles. fig. 11. forecast results for the next 30 days references [1] m. h. m. r. shyamali dilhani, c. jeenanunt, “daily electric load forecasting: case of thailand”. 7th international conference on information communication technology for embedded systems, bangkok, thailand, march 20-22, 2016 [2] j. huo, t. shi, j. chang, “comparison of random forest and svm for electrical short-term load forecast with different data sources”, 7th ieee international conference on software engineering and service science, beijing, china, march 23, 2017 [3] l. c. p. velasco, c. r. villezas, p. n. c. phalang, j. a. a. dagaang, “next day electric load forecasting using artificial neural networks”, cebu city, philippines, december 9-12, 2015 [4] d. willingham, “electricity load forecasting for the australian market case study”, available at https://ww2.mathworks.cn/matlabcentral/ fileexchange/31877-electricity-load-forecasting-for-the-australianmarket-case-study?s_tid=fx_rc1_behav, 2016 [5] n. t. dung, t. t. ha, n. t. phuong, “comparative study of short-term electric load forecasting: case study evnhcmc”, 4th international conference on green technology and sustainable development, ho chi minh city, vietnam, november 23-24, 2018 [6] e. ceperic, v. ceperic, a. baric, “a strategy for short-term load forecasting by support vector regression machines”, ieee transactions on power systems, vol. 28, no. 4, pp. 4356-4364, 2013 [7] v. vapnik, the nature of statistical learning theory, springer, 1995 [8] s. gunn, support vector machines for classification and regression, technical report, university of southampton, 1995 [9] v. cherkassky, y. ma, “selection of meta-parameters for support vector regression”, international conference on artificial neural networks, madrid, spain, august 28-30, 2002 [10] d. basak, s. pal, d. c. patranabis, “support vector regression”, neural information processing – letters and reviews, vol. 11, no. 10, pp. 203– 224, 2007 [11] a. j. smola, b. scholkopf, “a tutorial on support vector regression, statistics and computing”, vol. 14, no. 3, pp. 199–222, 2004 [12] understanding support vector machine regression and support vector machine regression, available at: https://www.mathworks.com/help/ stats/understanding-support-vector-machine-regression.html [13] l. breiman, “random forests”, machine learning, vol. 45, no. 1, pp. 5-32, 2001 [14] l. breiman, j. h. friedman, r. a. olshen, c. j. stone, classification and regression trees. chapman & hall 1984 engineering, technology & applied science research vol. 8, no. 3, 2018, 2907-2913 2907 www.etasr.com abbassi et al.: a numerical-analytical hybrid approach for the identification of sdm solar cell … a numerical-analytical hybrid approach for the identification of sdm solar cell unknown parameters rabeh abbassi college of engineering, university of hail, saudi arabia and university of tunis, ensit, latice laboratory, tunisia r_abbassi@yahoo.fr attia boudjemline college of engineering, university of hail, saudi arabia a_boudjemline@hotmail.com abdelkader abbassi dept. of electrical engineering, university of tunis, ensit, lisier laboratory, tunisia abd_abbassi@yahoo.com ahmed torchani college of engineering, university of hail, saudi arabia and university of tunis, ensit, lisier laboratory, tunisia tochahm@yahoo.fr hatem gasmi college of engineering, university of hail, saudi arabia and university of tunis el manar, enit, tunisia gasmi_hatem@yahoo.fr tawfik guesmi college of engineering, university of hail, saudi arabia and university of sfax, enis, tunisia tawfiq.guesmi@gmail.com abstract—appropriate modeling and accurate parameter identification of solar cells are crucial in the optimization of photovoltaic (pv) systems. the single-diode model (sdm), consisting of an ideal current source, an ideal diode, a shunt resistor and a series resistor, is widely used to simulate the behavior of pv cells/panels. in this article, a hybrid approach for identification of solar cell sdm parameters is presented. this approach uses the inverse of the slope of the i-v curve under short-circuit and open-circuit conditions and combines numerical and analytical solutions. indeed, knowing that numerical methods require appropriate initial values, the main idea of the proposed approach is to provide these solutions by analytical methods. the comparison of obtained results with experimental ones, based on manufacturer’s datasheet, proves that the algorithm thus obtained requires less information from the manufacturer and improves significantly the parameter identification accuracy. keywords-solar energy; pv cell parameters; i-v and p-v characteristics; single-diode model i. introduction fossil fuels, i.e., oil, natural gas and coal, are the main sources of today’s energy, whose demand is increasing in an alarming rate [1, 2]. in the process of extracting and converting these materials to energy, they generate air and water pollution, land degradation and, consequently, cause of harm to the health and well-being of humans and animals [3]. in addition, fossil fuels are non-renewable, as they exist in finite amounts. it is quite obvious that, at the present high rate of exploitation, they will eventually deplete rapidly, becoming too expensive to extract [4]. so, we are faced with two enormous challenges: a decrease in the energy resources coupled with an increase in the damage to the environment [5, 6]. to mitigate these problems, efforts are being made worldwide by governments, national and international agencies, companies and research institutions to find other sources of energy that are renewable, sustainable, environment-friendly and not expensive [7-10]. in this respect, solar energy, in all its forms, has been identified as the most promising because it is plentiful, renewable, available in almost every country and harnessing it causes very little damage to the environment [10]. the most common method to exploit solar energy is via the photovoltaic (pv) effect, whereby the energy of the sunlight photons impinging on certain materials, is converted to electricity [11]. photovoltaic panels are intended to work outdoors and, as such, are exposed to varying environmental conditions, e.g., temperature and amount of solar insolence. in order to predict the performance of pv systems, designers need to know the different electrical parameters of the pv cells/panel measured in all sorts of conditions. unfortunately, pv manufacturers only provide some of the parameters at only one operating condition, referred to as standard test condition or stc [12]. to address this problem, designers and researchers resort to modeling the pv cells/panels in order to determine the vital intrinsic parameters. although the main equations derived from these models are basically the same, numerous methods and techniques with varying degrees of complexity have been developed and applied with great success to estimate the parameters. indeed, many review papers have been published to either summarize the salient features of these methods and/or to conduct a comparison between a few of them[13-20]. engineering, technology & applied science research vol. 8, no. 3, 2018, 2907-2913 2908 www.etasr.com abbassi et al.: a numerical-analytical hybrid approach for the identification of sdm solar cell … ii. pv module based on single-diode model a. pv cell model as mentioned above, it is of significant importance to know the performance of pv panels in different environmental conditions, e.g. solar irradiance and ambient temperature, before they are deployed in the field in order to maximize their output power [11, 21, 22]. in this respect, and due to the lack of information from datasheets, the intrinsic parameters that determine this performance need to be estimated. since it is not practically possible to test all manufactured solar cells/panels under all types of conditions, engineers resort to simulations which result in saving materials, time and labor [23-25]. a pv cell is basically a diode, a p-n junction made of two dissimilar semiconducting materials, whose top surface is exposed to sunlight. the photon energy is subsequently converted to electrical energy. as a result, the most commonly-used equivalent electric circuit that describes the operation of a pv cell is the single-diode model as shown in figure 1 (a) [26] and where the components are assumed ideal. in this model, i is the current delivered to the load and v is the voltage across the load. the current source represents the photoelectric current, iph, caused by the photons impinging on the solar cell. this current is assumed proportional to the solar irradiance and also depends on the cell’s temperature [11]. the diode in parallel with the current source represents the recombination current in the quasi-neutral regions [27]. the current source serves to forward-bias the diode. the single-diode model has been shown to result in the calculation, to a high degree of accuracy, of the electrical parameters that are characteristic of the pv cells. it is a good compromise between precision and simplicity [29]. furthermore, this model proved to be a very useful tool in optimizing the design of an entire pv system, including solar panels and control power electronics, and hence generating the maximum power possible. note that, over the years, other equivalent electrical circuit models with different degrees of complexity and accuracy, such as doubleand triple-diode ones, have been proposed depending on the desired outcomes; accuracy, time taken to simulate, etc. [11, 26, 27]. by applying kirchhoff’s current law to the equivalent circuit, which is a lossless model, the current at the terminals of the solar cell is expressed as: . .1 1t v qv v kt ph d ph o ph oi i i i i e i i e η η= − − − − −     = =         (1) where, io: diode reverse bias saturation or dark current (a) η: diode ideality factor, vt: thermal voltage (v) k: boltzmann’s constant (=1.381×10−23j/k) q: charge of an electron (=1.602×10−19coulomb) t: cell’s temperature in kelvin (k). equation (1) shows the well-known shockley diode equation. the diode reverse saturation current, io, originates from minority carriers (e.g., electrons in the p-region) that recombine in the depletion region. this current limits the current in the reverse bias operation mode [28]. the ideality factory, η, also known as the quality factor or emission coefficient, depends on the fabrication process and semiconductor material. it is typically between 1 and 2, depending on the dominant recombination mechanism [14]. the thermal voltage, vt, describes the voltage produced within the p-n junction due to temperature. at room temperature (300 k), vt ≈ 26 mv. a solar cell is characterized by its current-voltage (i-v) and power-voltage (p-v) curves. in order to generate accurate curves, one has to take into account the different losses associated with a cell/panel. examples of the origins of these losses are intrinsic material defects, manufacturing flaws and the contacts with the loads. consequently, a shunt resistor and a series resistor are added, as in figure 1 (b), to give a more realistic electrical model. fig. 1. equivalent circuit of (a) ideal (b) practical sdm pv cell model. the small series resistor rs represents the conductivity of the materials, the thickness of the various layers and the ohmic contacts between metal and semiconductor [27]. the large shunt resistor rsh represents the leakage current across the p-n junction when the diode is reverse-biased and usually originates from cell manufacturing defects [28]. taking into account the two resistors, (1) becomes: ph d shi i i i= − − (2) with exp 1dd o t v i i vη = −          (3) d sv v ir= + (4) s sh sh v ir i r + = (5) by substituting (3), (4), and (5) in (2), we obtain: exp 1s sph o t sh v ir v ir i i i v rη + + = − − −          (6) equation (6) describes the current-voltage relationship of the pv cell and is the main equation used to represent the single-diode electrical model of figure 1 (b) and also to plot the i-v and p-v curves. it is clear from (6) that, to calculate i as a function of v, the values of five parameters, namely, iph, io, rs, rsh and η need to be known. for most of the existing engineering, technology & applied science research vol. 8, no. 3, 2018, 2907-2913 2909 www.etasr.com abbassi et al.: a numerical-analytical hybrid approach for the identification of sdm solar cell … panels, if not all of them, these parameters are not supplied by the manufacturers and hence need to be estimated. b. proposed method parameters extraction to determine the five independent parameters, five independent equations are required. it is customary to use data extracted from the pv panel datasheet and sometimes from experiments performed on the cell/panel. in particular, three values are used: the short circuit current isc, the open-circuit voltage voc and the maximum power generated pmax measured at the standard test conditions, stc, where the panel’s ambient temperature is tc=25°c (298 k), the irradiance is 1000w/m2 and air mass am1.5 [11]. the values resulting from the solution of the five equations are then used in subsequent simulations which force the modeled i-v and p-v curves to pass through these main three points. in what follows, the asterisk (*) denotes values measured at stc. at open circuit: *0, oci v v= = and (6) becomes: * * * * * * exp 1oc ocph o t sh v v i i v rη = − +          (7) at short circuit: *0, scv i i= = and (6) becomes: * * * * * * * * * exp 1 0sc s sc ssc ph o t sh i r i r i i i v rη − + − + =          (8) substituting (7) in (8) results in (9): * * * * * * * * * * * exp exp 0oc sc s oc sc ssc o t t sh v i r v i r i i v v rη η − − − − =                (9) at the maximum power * * max : mp mpp i i v vand= = : and (6) leads to (10): * * * * * * * * * * * exp 1 0mp mp s mp mp sph o mp t sh v i r v i r i i i v rη + + − − − − =          (10) by substituting (7) in (10) the latter becomes: * * * * ** * * * * * * * 1 exp exp 0mp mp s oc mps ocmp o sh t t sh v i r v vr v i i r v v rη η + − + − − − =                   (11) the power delivered to the load is p vi= and its derivative with respect to the voltage v is: dp di i v dv dv = + (12) at the point of maximum power * mpp , * 0 mpp p dp dv = = and (12) becomes: * * 0mp mp di i v dv + = (13) the derivative of (6) gives: 1 1 1 exp 1ss o s t t sh v irdi di di r i r dv v dv v r dvη η + = − + − +                (14) at stc, and using (13) and (14), equation (15) is derived as follows: * * * * * * * * * * * * * * * 1 1 1 exp 1 0mp mp mp mp s mps o s mp t mp t sh mp i i v i r i r i r v v v v r vη η + − − − − =                   (15) the result is a set of four non-linear equations, (7), (9), (11) and (15), with five unknown variables, iph*, io*, rs*, rsh* and η*. consequently, a fifht equation is needed. the slope of the i-v curve at short circuit, i.e., ι=ιsc* and v=0, is approximately equal to the negative inverse of the shunt resistance rsho [15, 29]. in other words, * 0 1 sci i and v sho di dv r= = = − (16) with these values (14) will be rewritten as: * * * * * * * 1 1 1 exp sc s o sho s sh t t i r i r r r v vη η = + −       (17) in principle, rsho can be extracted from the i-v curve, but since datasheets do not provide numerical values for the data used to plot this curve, researchers use graphical methods to achieve this by means of a digitizer. however, inaccurate values can result, which in turn will affect the other extracted parameters. by assuming ( ) ( )* * * * * *exp 1o t sc s t shi v i r v rη η and * sho sr r , equation (17) will lead to the approximation * sho shr r≈ [21]. now, replacing rsho by rsh *, in (17) will lead to: * * * * * * * * 1 1 1 exp sc s o sh s sh t t i r i r r r v vη η = + −       (18) finally, (7), (9), (11), (15) and (18) constitute a set of five non-linear equations with five unknown variables iph*, io*, rs*, rsh*, η*. because these equations are inherently implicit and nonlinear, finding analytical solutions is not a trivial task [24-30]. approximations and simplifications are always used to arrive to some simple analytical solutions [25]. however, the set of transcendental equations is usually solved using numerical methods. these include curve-fitting, such as the levenbergmarquardt (lm) algorithm [29], and root-finding, such as the bisection and the newton-raphson methods [11, 21, 29]. to reach convergence, the numerical methods require good approximation of the starting values of the five parameters. to achieve this, analytical solutions are used. as a result, a variety of methods and techniques aiming at solving these non-linear equations have been devised, tested and published in the scientific literature over a few decades [12-22]. once these parameters are determined, usually at stc, other equations are used to estimate the response of the pv cell/panel at other operating conditions, i.e., temperature and solar irradiance. subsequently, (6) is used to generate the i-v curves for these operating conditions [11, 23, 26]. engineering, technology & applied science research vol. 8, no. 3, 2018, 2907-2913 2910 www.etasr.com abbassi et al.: a numerical-analytical hybrid approach for the identification of sdm solar cell … c. approximate analytical solutions from (9) the following expression for io* is derived: ( )( ) ( ) ( ) * * * * * * * * * * *exp exp s sh sc oc sh o oc t sc s t r r i v r i v v i r vη η + − = −       (19) the following acceptable assumptions and approximations are made. from experimental work, * * sh sr r , resulting in * *1 1.s shr r+ ≈ in addition, * * * sc oc shi v r and ( ) ( )* * * * *exp expoc t sc s tv v i r vη η [31]. equation (19) then becomes: ( )* * * *expo oc t sci v v iη= − (20) the shunt resistor shr has a high value, and is sometimes assumed infinite when modeling a pv cell. furthermore, in short-circuit mode, the diode is reverse-biased and hence its current can be neglected. consequently, the equality (21) is valid in all cases. * * ph sci i= (21) from the i-v and p-v curves, one can notice that * * oc mpv v− is small and with *shr being large, the following assumption: ( )* * * 0oc mp shv v r− ≈ is valid. hence, by substituting (20) and (21) in (11), we obtain (22): ( )( )* * * * * * *1 expmp mp oc mp s t sci v v i r v iη= − − +   (22) since rsh* is high and * *sh sr r , the term ( ) ( )* * * *1 1sh sh mp mpr r i v−   will be negligible and (15) becomes: ( ) ( ) ( )( )* * * * * * * * * * * *1 expmp mp t s mp mp mp oc mp s t sci v v r i v v v i r v iη η= − × − +      (23) taking the previous assumptions into consideration, (18) is transformed as: ( )2* * * * ** * * exp 0sh sc sc s ocs t t r i i r v r v vη η − − + =       (24) equation (22) can be rewritten as: ( ) ( )* * * * * * * *ln sc mp sc mp oc mp s ti i i v v i r vη− = − +   (25) by eliminating the term ( )* * * * *exp mp oc mp s tv v i r vη− +   from (22) and (23) and using (25), the following expressions for rs* and η* are obtained [21]: ( ) ( ) ( ) ( ) * * * ** * * * * * * * 2 ln 1 mp oc sc mpmp s mp mp sc mp sc mp v v i iv r i i i i i i − − = − − + −   (26) ( ) ( ) * * * * * * * * 2 ln 1 mp oc t mp sc mp sc mp v v v i i i i i η − = − + −   (27) equation (24) leads to: ( ) ( )( ) * * * * * * * *exp s sh sc t sc s oc t r r i v i r v vη η = − (28) once rs* and η* are computed using (26) and (27), their values will be used in (28) to calculate rsh. the calculated values of * * *, ands shr rη , are in turn used to calculate io * and iph * from (19) and (7), respectively. finally, and with the assumptions made, (7), (19), (26), (27) and (28) will constitute the approximated analytical solutions for the five parameters of the single-diode model for the pv cell/panel [32]. the estimated values of these parameters will be used as the starting values to solve numerically the implicit and nonlinear equations (7), (8), (11), (15) and (17) by the matlab ‘fsolve’ function based on l.m. algorithm. d. estimation of sdm parameters at operating conditions so far, the five sdm parameters were estimated at stc. however, in day-to-day applications, the conditions, especially the temperature and irradiance, are different from stc. moreover, the cell/panel parameters depend strongly on these conditions. therefore, it is crucial to evaluate the performance of the cell/panel at these real conditions. according to [12], the reverse saturation current io, the photocurrent iph and the shunt resistance rsh are expressed as follows: 3 * * * * 1 exp g go o e et i i t k t t    = −           (29) ( )* **ph ph i g i i k t t g  = + −  (30) * * sh sh g r r g = (31) where: t, g, eg and rsh are the temperature, irradiance, material band gap energy and shunt resistance at the operating condition, respectively, whereas, t*, g*, eg* and rsh* are the corresponding parameters at stc. the parameter ki is the temperature coefficient of the short-circuit current and k is botlzmann’s constant. iii. results and discussions in this section, the extraction of the parameters of the proposed model is carried out. the results of the proposed optimization algorithm are compared with the experimental results. the comparison is implemented under different conditions of irradiation and temperature. the studied method was applied to the suntech power ‘stp250s-20/wd’ monocrystalline silicon solar module and the multicrystalline tallmax module ‘tsm-pd14’. the five parameters of the model were estimated in accordance with the main steps presented previously. theoretical (or simulated) i–v and p-v curves derived from the developed approach were compared to experimental ones provided by the manufacturers, for different environmental conditions. the specifications of the ‘stp250s-20/wd’ and ‘tsm-pd14’ panels are depicted in table i. figures 2 and 3 show the i-v and p-v characteristics of the ‘stp250s-20/wd’ solar module at fixed module engineering, technology & applied science research vol. 8, no. 3, 2018, 2907-2913 2911 www.etasr.com abbassi et al.: a numerical-analytical hybrid approach for the identification of sdm solar cell … temperature (t=25°c) and under different irradiance levels (200, 400, 600, 800 and 1000w.m-2). the curves were overlaid on top of those obtained using the proposed method to highlight any discrepancies. the model curves match well with the experimental data except for a negligible gap registered at high solar radiation. similarly, figures 4 and 5 depict the experimental i-v and p-v curves of the multicrystalline tallmax solar module ‘tsm-pd14’. again, one can see that the simulated model curves match well with the experimental ones. figures 2, 3, 4 and 5 show the variation of isc (which is none other than iph) with the illumination. moreover, the increase in solar radiation causes a slight rise in the open-circuit voltage in addition to an increase in the maximum power generated by the panel. these results prove that the calculated data are extremely close to the experimental ones. fig. 2. single-diode model and manufacturer datasheet p-v curves for stp250s-20/wd at different irradiance levels (200, 400, 600, 800 and 1000w.m-2) and fixed module temperature (t=25°c). fig. 3. single-diode model and manufacturer datasheet i-v curves for stp250s-20/wd at different irradiance levels (200, 400, 600, 800 and 1000w.m-2) and fixed module temperature (t=25°c). fig. 4. comparison of single-diode model and manufacturer datasheet p-v curve for tsm-pd14 at different irradiance levels (200, 400, 600, 800 and 1000w.m-2) and fixed module temperature (t=25°c). fig. 5. comparison of single-diode model and manufacturer datasheet i-v curve for tsm-pd14 at different irradiance levels (200, 400, 600, 800 and 1000w.m-2) and fixed module temperature (t=25°c). table i. datasheet of suntech-power ‘stp250s-20/wd’ and tallmax module ‘tsm-pd14’ pv modules at standard test condition (stc) and nominal operating cell temperature (noct). datasheet parameters stp250s-20/wd tsm-pd14 at stc at noct at stc at noct pmp 250 183 325 242 vmp 30.7 27.9 37.2 34.5 imp 8.15 6.55 8.76 7.02 voc 37.4 34.4 45.9 42.6 isc 8.63 6.96 9.25 7.47 ki 0.05%/°c 0.05%/°c kv 0.34%/°c 0.32%/°c ns 60 72 after investigating the performance of the proposed approach under the effects of solar radiation, the effects of the temperature, which is a very important parameter, will also be evaluated. in order to predict a pv module i-v and p-v characteristics curves at different temperatures, for which data or i-v curves are not available, temperature coefficients (temperature coefficient of voc (kv) and temperature coefficient of isc and (ki)) were used. by using the sandia national laboratory database, the parameters isc(t), voc(t), imp(t), and vmp(t), at different temperatures can be determined. then, the obtained values enable the estimation of the those of η(t) , io(t), and iph(t). subsequently, the i-v and p-v curves at 0°c, 25°c, 50°c, and 75°c were generated for the panels ‘stp250s-20/wd’ and ‘tsm-pd14’ in figures 6-9. fig. 6. single-diode model and manufacturer datasheet p-v curves for stp250s-20/wd at different module temperatures (10, 20, 30 and 50°c) and fixed irradiance level (1000w.m-2). engineering, technology & applied science research vol. 8, no. 3, 2018, 2907-2913 2912 www.etasr.com abbassi et al.: a numerical-analytical hybrid approach for the identification of sdm solar cell … fig. 7. single-diode model and manufacturer datasheet i-v curves for stp250s-20/wd at different module temperatures (10, 20, 30 and 50°c) and fixed irradiance level (1000w.m-2). fig. 8. single-diode model and manufacturer datasheet i-v curves for tsm-pd14 at different module temperatures (10, 20, 30 and 50°c) and fixed irradiance level (1000w.m-2). fig. 9. single-diode model and manufacturer datasheet p-v curves for tsm-pd14 at different module temperatures (10, 20, 30 and 50°c) and fixed irradiance level (1000w.m-2). while increasing the temperature lead to a negligible increase in the photocurrent iph due to better light absorption, a noticeable decrease in the open-circuit voltage is observed. this is accompanied by a large reduction in the maximum power pmax which translates into a decrease in the available power. the superposition of the i-v and p-v curves obtained using the estimated parameters (of the single-diode model adopted in the work presented here) on top of those generated using the experimental data show very good agreement albeit negligible differences. iv. conclusions in this paper, a hybrid numerical-analytical approach was developed and programmed in matlab environment. its capability to estimate the unknown electrical parameters of pv modules using single-diode model (sdm) was validated by the experimental i-v and p-v data extracted 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research vol. 13, no. 4, 2023, 11210-11215 11210 www.etasr.com pervan et al.: mechanical stability analysis of the external unilateral fixation device due to the … mechanical stability analysis of the external unilateral fixation device due to the impact of axial pressure nedim pervan university of sarajevo, faculty of mechanical engineering, bosnia and herzegovina pervan@mef.unsa.ba (corresponding author) elmedin mesic university of sarajevo, faculty of mechanical engineering, bosnia and herzegovina mesic@mef.unsa.ba adis muminovic university of sarajevo, faculty of mechanical engineering, bosnia and herzegovina adis.muminovic@mef.unsa.ba enis muratovic university of sarajevo, faculty of mechanical engineering, bosnia and herzegovina muratovic@mef.unsa.ba muamer delic university of sarajevo, faculty of mechanical engineering, bosnia and herzegovina delic@mef.unsa.ba vahidin hadziabdic university of sarajevo, faculty of mechanical engineering, bosnia and herzegovina hadziabdic@mef.unsa.ba lejla redzepagic-vrazalica university of sarajevo, faculty of dentistry with clinics, bosnia and herzegovina lejlaredzepagic@yahoo.com received: 27 march 2023 | accepted: 7 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5888 abstract this study performed a mechanical stability analysis for the impact of axial pressure on an ultra x external unilateral fixation device applied to a tibia with an open fracture. the real construction of the fixation device was used to create a 3d geometric model using a finite element method (fem) model, which was made to perform structural analysis in the catia v5 (computer aided three-dimensional interactive application) cad/cae system. specific stresses and displacements were observed at points of interest using structural analysis. the focus was on the relative displacements of the proximal and distal bone segments in the fracture zone. these displacements were used to calculate the stiffnesses of the bone in the fracture zone and the fixation device itself. the results obtained provide the necessary information regarding the stability of the ultra x fixation device. keywords-external unilateral fixation device; specific stresses; relative displacements, stiffness; stability engineering, technology & applied science research vol. 13, no. 4, 2023, 11210-11215 11211 www.etasr.com pervan et al.: mechanical stability analysis of the external unilateral fixation device due to the … i. introduction during the recent years, there has been a considerable improvement in external fixation devices in terms of their construction variants, which have been experimentally investigated to provide information on their characteristics and advantages in terms of stability, stiffness, mechanical properties, and patient comfort during treatment. using software for 3d modeling and fem analysis to perform mechanical stability analysis is not a substitution for an experimental examination but is exclusively a tool for data comparison and validation. the experimental investigation of fixation devices is mainly based on biomechanical properties, along with the influence of specific parameters on the stability of the device [1]. the results of these investigations are reflected in certain values, such as von mises stresses, displacements, angular strains, and fixation device stiffnesses, and most of these studies provide results of the application of the fixation device [2-3]. in recent years, the most popular treatment for tibia fracture is by using intermediary fasteners [4]. in [5], the application of an external fixation device and intermediary fasteners was considered in an open tibia fracture taking into account the treatment time and other possible complications, such as the size, severity, etc. in [6], the stiffness of the fixation device was defined concerning the location of the fracture and the number of fasteners and pins. in [7], an analysis of the stiffness of the hoofman unilateral and uniplanar fixation device was presented along with its relation to the number of fasteners, trusses, and couplings. the stiffness of the device is determined by the loads that simulate normal walking conditions. in [8], a comparative study was conducted on two external fixation devices: the original hoffmann and the ao tabular device with four different construction solutions. in [9], the mechanical properties of the external pinless fixation device were experimentally investigated, comparing its results with the ao tabular and ultra x devices. this study concluded that the ao tabular devices are far superior in comparison with the other two solutions. in [10], the ilizarov fixation device was investigated experimentally. furthermore, many studies have analyzed the mechanical stability of structures [11-13]. this study aimed to investigate the mechanical properties of the ultra x external unilateral fixation device, applied to the openfracture tibia bone under the impact of axial pressure. the construction parameters taken into account were the stiffness of the device, the values of the maximum von mises stresses, and the displacements in specific points. ii. development of the cad/fem model the adjustable fixation device should be light, stiff, easy to implement, etc. such devices should be part of the first response at accident sites so that basic stabilization could be performed before transporting patients. figure 1 shows the howmedic ultra x external fixation device, which is one of the first modular fixation devices, and was used in the first gulf war in 1991. the components of the device are mostly made of metals, alloys, and plastics such as polymers and carbon fibers. the ultra x fixation device has a truss made of austenitic stainless steel x2crnimo17-12-2, while couplings and small and large spheres are made of polymeric materials, attributed with smaller strength, young's modulus, density, specific weight, and great forming properties. the upper and lower parts of the coupling and the fastening head are made of special polyvinyl chloride (pvc), which has high hardness and good mechanical properties. small and large spheres are made of polybutylene (pb), which has properties similar to pvc because it can be manufactured with any method of thermoforming, and therefore, it gives a lot of creativity during the shape-forming process. table i shows the mechanical properties of the unilateral ultra x fixation device [14]. fig. 1. the ultra x fixation device. table i. mechanical properties of the unilateral ultra x fixation device component name standard abbreviations (en) modulus of elasticity e (gpa) poisson's coefficient υ density ρ (kg/m3) yield strength σv (mpa) truss x2crnimo1712-2 230 0.29 8000 620 sphere >pb< 2.9 0.4 1290 coupling >pvc< 3.3 0.38 1380 0.2 fastener x5crni18-10 193 0.29 7900 205 half-pin x2crnimo1814-3 196.4 0.3 8000 800 the cad/fem model of the ultra x device was developed using catia v5 software. device components were defined and modeled in the part design environment and subsequently assembled in the assembly design environment. the general structural analysis module was used in the next step of model creation to complete the fem model and define the material for each component. the material of the bone fragments was assumed to be orthotropic with properties defined according to table ii [15-16]. after the materials were defined, the next step in fem processing was the discretization of the model and the definition of the finite element type. linear (te4) and parabolic (te10) elements were used for the model. the te4 elements were used for the spheres, while the rest of the components were discretized with the te10 elements. after the discretization was complete, it was necessary to define the constraints between the components of the device. the constraints used were the following: fastened connections between half-pins and bone segments, as shown in figure 2(a), and contact connections between other components, as shown in figure 2(b). in addition to defining the necessary constraints, it was also mandatory to define supports, as shown in figure 3. engineering, technology & applied science research vol. 13, no. 4, 2023, 11210-11215 11212 www.etasr.com pervan et al.: mechanical stability analysis of the external unilateral fixation device due to the … table ii. bone model mechanical properties property value longitudinal modulus of elasticity 22900 mpa tangential modulus of elasticity 10500mpa normal modulus of elasticity 14200 mpa poisson's coefficeint in the xy plane 0.29 poisson's coefficeint in the xz plane 0.19 poisson's coefficeint in the yz plane 0.31 shear modulus in the xy plane 6480 mpa shear modulus in the xz plane 6000 mpa shear modulus in the yz plane 3700 mpa density 1850 kg/m 3 the last step in creating the fem model was to define the axial load, which is applied as the surface load on the top surface of the upper bone segment. the upper bone segment is constrained so it can only move in the z-axis direction, i.e. the direction of the applied force. the lower bone segment is supported by a spherical joint (ball joint) through a virtual part (smooth virtual part). the spherical joint allows rotation around a predefined point (handle node), and all translations are restricted, as shown in figure 4. the axial load was set to 200 n, according to orthopedic recommendations and [17-18]. (a) (b) fig. 2. defining connection constraints: (a) fastened, (b) contact. fig. 3. fixation device model with constraints and supports. fig. 4. fixation device fem model with the applied load. iii. determination of stress, displacement, and stiffness during structural analysis, specific points were monitored to obtain values of principal and von mises stresses generated on the fixation device. the intensity of the equivalent one-axis stress, i.e. von mises stress, is often used in mechanics defined as [19-20]: �� = ��� = �3� = �� ��� − � � + �� − ��� + ��� − ��� � (1) apart from stresses, displacement values at the same points were monitored so the stiffness of the device can be defined as the ratio of the load and displacements. the device stiffness under the impact of axial load can be defined as [19, 21]: �� = ���� (2) where fp is the axial force (n), and δp is the axial displacement of the bone segments at the fracture zone (mm). the fixation device stiffness is an important parameter, but it doesn't give direct information about displacements at the fracture zone, so the fracture stiffness needs to be defined. this was achieved by determining displacements in the x, y, and z directions of the pair of adjacents points on the planes of the proximal and distal bone segments at the fracture zone. for these points, the resultant vector of relative displacement rmax has the highest value. accordingly, the total fracture stiffness is defined as the ratio of the load and the resultant relative displacement of the observed pair of points [22-23]: ��� = ��� = �� �������� !����"�� !����#�� (3) engineering, technology & applied science research vol. 13, no. 4, 2023, 11210-11215 11213 www.etasr.com pervan et al.: mechanical stability analysis of the external unilateral fixation device due to the … the relative displacements rd(x), rd(y), rd(z) of the observed points are defined as [24-25]: $%�&� = '��&� − '(�&� $%�)� = '��)� − '(�)� (4) $%�*� = '��*� − '(�*� where rd(x), rd(y), and rd(z) are the relative displacements for the points of bone segments (mm), dp(x), dp(y), and dp(z) are the displacements of the proximal bone segment (mm), and dd(x), dd(y), and dd(z) are the displacements of the distal bone segment in x, y, and z directions (mm). iv. results figure 5 shows the displacement vectors due to the maximum axial load, where the course, direction, and intensity of the vectors for the analyzed points can easily be noticed. table iii shows the components of the displacement vectors and the displacement values for the maximum axial load of 200 n. the stiffness of the construction is determined using (2), based on the axial displacement in the z-axis direction (straight surface at the top of the proximal bone), while the fracture stiffness requires displacements at the proximal and distal bone segments at the fracture zone in the x, y, and z directions. this is done by observing which pair of points will result in the highest displacements, as shown in figure 5 (detail a). fig. 5. displacement vectors for the specific points under the impact of maximum axial load. table iii. displacement and stiffness values displacement of the proximal segment (mm) displacement of the distal segment (mm) f r a c tu r e st if fn e ss ( n /m m ) c o n st r u c ti o n st if fn e ss ( n /m m ) load zone fracture zone fracture zone x y z dp(x) dp(y) dp(z) dd(x) dd(y) dd(z) cpp cp 0 0 -4.54 3.593 0.616 -4.76 3.744 0.701 0.246 39.89 44.05 figure 6 shows the von mises distribution. truss is an important component of the fixation device that needs to be considered in the structural analysis, which is loaded with eccentric pressure (simultaneous bending and pressure) for the truss amount σvm=318.62 mpa, which is also the global maximum. fig. 6. von mises stress distribution. due to axial pressure, the bone is bent around the y-axis. this induces the location of the maximum stress at the bone circumference, i.e. the location of the peripheral points with the x-axis, as shown in figure 7. fig. 7. von mises stress distribution for the fixation device truss. engineering, technology & applied science research vol. 13, no. 4, 2023, 11210-11215 11214 www.etasr.com pervan et al.: mechanical stability analysis of the external unilateral fixation device due to the … the intensities and the direction of principal stresses were monitored for the 10 most critical zones of the device construction, as shown in figure 8. table iv summarizes the values of principal and von mises stress for these points. fig. 8. principal stresses at the critical zones of the construction. table iv. stress values due to axial pressure load observed point principal stresses at critical points (mpa) von mises stresses at critical points (mpa) pm+ pmpm+ pm σ1 σ2 σ3 σ1 σ2 σ3 σνμ σνμ 1 198.0 -5.13 -14.4 -8.04 -11.2 -202 208.1 196.1 2 193.7 4.859 4.38 -3.35 -3.79 -175 191.1 174.8 3 203.4 11.83 7.18 -9.99 -14.2 -218 196.5 208.4 4 126.5 -6.46 -11.5 -3.22 -4.32 -185 135.6 183.7 5 205.6 10.64 7.23 -8.24 -13.8 -225 199.3 230.9 6 170.4 3.84 3.39 11.7 6.66 -145 169.2 145.5 7 218.8 13.95 9.70 -10.8 -12.3 -202 209.2 206.3 8 142.0 13.9 0.89 -3.02 -4.10 -163 147.2 162.5 9 315.4 1.07 2.20 0.42 -1.82 -322 318.8 317.3 10 302.9 1.41 0.51 6.36 5.89 -296 302.3 298.7 v. discussion the maximum displacement in the device construction due to the impact of the axial load is located at the end of the second schanz fastener and is 6.06 mm, as shown in figure 5. maximum displacements for the fracture zone are located at the edges of the proximal and distal bone segments, the values of which are given in table iii. when comparing these results with those of [26-27], it can be noticed that the ultra x external fixation device has significantly higher displacements (80100% higher) than the other such devices for the same case of applied load. displacements in the load zone are used as a basis for the stiffness of the fixation device, which was 44.05 n/mm. if this value is compared with other studies [23-24], it can be observed that the stiffness of the ultra x device is much lower (3-5 times) than that of other devices under the same load conditions. similarly, displacements in the fracture zone are used to calculate the fracture stiffness, which is 39.89 n/mm and is again 3-5 times lower compared than the values found in [26-27]. the results of the structural analysis show that the most critical zone of the fixation device construction is the middle of the truss where it establishes contact with large spheres. this zone is a load transfer zone, where the axial force is transmitted from the couplings to the truss through the schanz fasteners. the highest principal stresses, regarding the whole construction, were σ1=315.41 mpa (global maximum) for the positive values and σ3=-322.65 mpa (global minimum) for the negative values. both extreme values are located in the truss, have similar values, and are in correspondence with the results obtained in other studies [26-27]. it is also important to note that stresses in the fixation device construction satisfy the maximum permissible stress of the device material. vi. conclusion this study conducted a stability analysis on the ultra x external fixation device due to the impact of axial loads, developing a fem model. this model was used to observe the movements and displacements of the fracture and establish a connection between these phenomena with the stiffnesses of the fracture zone and the device itself. the analysis of the results obtained showed relatively large displacements compared to other studies for the same load conditions. this can be justified by the fact that a truss diameter of an ultra x device has a smaller cross-section, i.e. moment of inertia. lower displacement values could be expected for the hollow circle cross-sections of greater diameter, i.e. with an increased moment of inertia by moving away the material from the own axis of the element. this led to the conclusion that the mechanical stability of the ultra x fixation device is insufficient for application to fractures of the lower extremities. however, the ultra x device is recommended for traumas of the upper extremities due to its good properties, such as ease of implementation and small dimensions. in this case, weaker mechanical properties will not be a problem, as the upper extremities are subjected to significantly smaller loads. references [1] t. n. gardner, m. evans, and j. kenwright, "a biomechanical study on five unilateral external fracture fixation devices," clinical biomechanics, vol. 12, no. 2, pp. 87–96, mar. 1997, https://doi.org/10.1016/s02680033(96)00051-4. 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[27] n. pervan, e. mešić, a. j. muminović, m. delić, and e. muratović, "stiffness analysis of the external fixation system at axial pressure load," advances in science and technology. research journal, vol. 16, no. 3, pp. 226–233, jul. 2022, https://doi.org/10.12913/22998624/ 149599. engineering, technology & applied science research vol. 8, no. 5, 2018, 3332-3337 3332 www.etasr.com khoa & tung: modeling for development of simulation tool: impact of tcsc on apparent impedance … modeling for development of simulation tool: impact of tcsc on apparent impedance seen by distance relay ngo minh khoa faculty of engineering and technology quy nhon university quy nhon, binh dinh, vietnam ngominhkhoa@qnu.edu.vn doan duc tung faculty of engineering and technology quy nhon university quy nhon, binh dinh, vietnam doanductung@qnu.edu.vn abstract—the impact of thyristor controlled series capacitor (tcsc) on distance protection relays in transmission lines is analyzed in this paper. voltage and current data are measured and collected at the relay locations to calculate the apparent impedance seen by distance protection relays in the different operating modes of the tcsc connected to the line. short-circuit faults which occur at different locations on the power transmission line are considered in order to locate the fault for the purpose of evaluating the impact of tcsc on the distance protection relay. matlab/simulink simulation software is used to model the power transmission line with two sources at the two ends. voltage source, transmission line, tcsc, voltage and current measurement, and discrete fourier transform (dft) blocks are integrated into the model. simulation results show the impact of tcsc on the distance protection relay and determine the apparent impedance and fault location in the line. keywords-apparent impedance; distance relay; firing angle; tcsc; transmission line. i. introduction flexible alternating current transmission systems (facts) based on power electronics have been developed to improve the performance of weak alternating current (ac) systems and to make long distance ac transmission systems feasible [1, 2]. series compensation with tcsc has various applications in power system control such as readjustment of power flow, transient stability control, power oscillation damping control and sub-synchronous resonance mitigation because of its continuously varying reactance capability [3, 4]. the presence of a tcsc in fault loop affects both steady state and transient components of the voltage and current. moreover, variable capacitance or inductance in tcsc can lead to subsynchronous oscillations under overreaching distance protection and has an influence on the apparent impedance seen by distance protection relays [5, 6]. hence, a model for the development of a simulation tool that analyzes the impact of tcsc on distance protection relay in power transmission lines is necessary. authors in [7] proposed the fault direction estimation technique for a transmission line with a tcsc. a compensated line imposed problems to directional relaying schemes due to reactance modulation, current, and voltage inversion issues and tcsc-control action in order to estimate the direction of fault for a line with tcsc. authors in [8] considered tcsc as a dynamical device which had the response to disturbances based on its own control strategy. it concluded that not only tcsc affects the protection of its line, but also the protection of adjacent lines would experience problems. in [9], the impact of tcsc on the performance of conventional communication aided distance protection schemes was analyzed. authors also proposed new schemes for mitigating the impact of tcsc which used the information available at the substation to inhibit relay malfunctions. authors in [10] presented a new protective scheme for transmission lines compensated by tcsc. the scheme employed the averages of voltage and current, a new criterion was introduced to discriminate between forward and reverse faults. authors in [11] proposed a new high speed mho distance protection scheme for single line to ground faults in tcsc line in which fault voltage and current at relay point and firing angle from the tcsc substation were taken as the input for the mho relay. the objective of this paper is to model and analyze the impact of tcsc on the performance of based protection relays under normal operation and different single-phase to ground fault conditions. therefore, to address the aforementioned issues, this paper develops a simple power system model including a transmission line with a tcsc and single-phase to ground faults are investigated. according to the simulation results, the apparent impedance seen is calculated to analyze the impact of tcsc to distance protection relay on the line. ii. operation principles of tcsc tcsc is used in power systems to dynamically control the reactance of a transmission line in order to provide sufficient load compensation [12]. the benefits of tcsc are seen in its ability to control the amount of compensation of a transmission line, and in its ability to operate in different modes. these traits are very desirable since loads are constantly changing and cannot always be predicted. tcsc designs operate in the same way as fixed series compensation, but provide variable control engineering, technology & applied science research vol. 8, no. 5, 2018, 3332-3337 3333 www.etasr.com khoa & tung: modeling for development of simulation tool: impact of tcsc on apparent impedance … of the reactance absorbed by the capacitor device. the control scheme of a tcsc [13] is shown in figure 1. fig. 1. control scheme of tcsc. change of impedance of tcsc is achieved by changing the thyristor controlled inductive reactance of inductors connected in paralleled to the capacitor. the magnitude of inductive reactance is determined by the firing angle α, which can also be controlled continuously by the flowing amplitude of current reactor from maximum value to zero. firing angle switching thyristors can change inductive reactance controlled choke from a minimum value to, theoretically, infinite value. the tcsc equivalent reactance is as a function of its capacitive and inductive reactance parameters, and the firing angle [14, 15]:             1 2 2 ( ) 2 sin 2 cos tan tan                   tcsc cx x c c (1) where: 1    c lcx xc (2) 2 2 4   lc l x c x (3)   c l lc c l x x x x x (4)  c l x x  (5) an appropriate value for capacitance and inductance of a tcsc device is based on the net reactance of the transmission line and expected power demands in future. selection of capacitance and inductance values of tcsc can be summarized by the following steps:  step 1: select the degree of compensation (k).  step 2: calculate capacitive reactance (xc) and capacitance value of tcsc from (6) and (7), respectively. c tlx k x  (6) where xtl is the total reactance of the transmission line. the capacitance value of tcsc is given by (7): 1 2 c c fx   (7) where f is the fundamental frequency.  step 3: the choice of inductance value depends on the length of operating area required for inductive and capacitive region. it is decided by the factor , given in (5) by shifting the position of resonance region. finally, inductance value of tcsc is given by (8): 2 lxl f   (8) the tcsc capacitive and inductive reactance values should be chosen carefully in order to ensure that just one resonant point is present in the range of 90o to 180o. figure 2 shows the tcsc fundamental frequency reactance, as a function of the firing angle. fig. 2. tcsc fundamental frequency reactance characteristic curve. tcsc operates in different modes depending on when the thyristors for the inductive branch are triggered. the modes of operation are [16]:  blocking mode: thyristor valve is always off, opening inductive branch, and effectively causing the tcsc to operate as fixed series compensation.  bypass mode: thyristor valve is always on, causing tcsc to operate as capacitor and inductor in parallel, reducing the current through tcsc.  capacitive boost mode: forward voltage thyristor valve is triggered slightly before capacitor voltage crosses zero to allow current to flow through the inductive branch, adding to capacitive current. this effectively increases the observed capacitance of the tcsc without requiring a larger capacitor within the tcsc. the presence of tcsc systems with its reactor (xtcsc) has a direct influence on the total impedance of the protected line (zij), especially on the reactance xij and no influence on the resistance rij. the new setting zones (zone 1, zone 2, and zone 3) for a protected transmission line with tcsc connected at midline are: inductive mode 90olmax capacitive mode cmax180 o resonance mode lmaxcmax x lmax x bypass x c x cmax 90o lmax cmax 180 o  x tcsc 0 engineering, technology & applied science research vol. 8, no. 5, 2018, 3332-3337 3334 www.etasr.com khoa & tung: modeling for development of simulation tool: impact of tcsc on apparent impedance …  1 0.8 ij ij tcscz r jx jx       (9)    2 0.2ij ij tcsc jk jkz r jx jx r jx         (10)    3 1.2ij ij tcsc jk jkz r jx jx r jx        (11) where z1, z2, z3 are setting zones 1, 2 and 3, respectively, rij, xij are resistance and reactance of the protected line ij, respectively and rjk, xjk are resistance and reactance of the line jk which follows the line ij, respectively. iii. modeling of impact of tcsc on distance relay a. studied system description a 3-phase, 500kv, 400km long transmission line, as shown in figure 3, is investigated in this section. the transmission line has a tcsc at the sending end of the line. the transmission line and tcsc parameters are given in the appendix. inductance and capacitance of tcsc are determined by using the previous equations and they are also given in the appendix. by changing the firing angle from 150o to 180o, tcsc capacitive reactance calculated using (1) is shown by negative values in figure 4. tcsc provides 20% compensation at 180o (minimum), 69.53% compensation at 150o (maximum) firing angle. fig. 3. the transmission line with tcsc. fig. 4. tcsc capacitive reactance based on the firing angle. the studied power system has been simulated using matlab/simulink software. voltage and current data are collected at a sampling frequency of 1.0khz. samples of voltage and current signals are used to determine the phasors which are used to calculate the apparent impedance seen by the relay and to determine a fault in distance relay's zone of protection. dft is a tool for the phasor estimation of voltage and current signals. the algorithm for single-phase to ground (ph-g) fault is shown in figure 5. the algorithm can be explained by the following steps:  step 1: set system conditions including parameters of the sources and transmission line.  step 2: set single-phase to ground fault in the line.  step 3: acquire voltage and current from voltage transformers vts and current transformer cts.  step 4: computation of voltage vph and current iph phasor components using dft.  step 5: computation of the zero-sequence current phasor component i0.  step 6: computation of the apparent impedance seen by the distance relay as (12). 0   ph ph v z i ki (12) where vph, iph are the faulted phase voltage and current, respectively, i0 is the zero-sequence current component and  0 1 1 k z z z . z0, z1 are zero-sequence and positive-sequence line impedances per kilometer.  step 7: update the fault position and resistance and return to step 2.  step 8: finally, determine resistance and reactance r, x. fig. 5. the flow diagram for tripping characteristics. b. simulation results and discussion in order to verify the correctness of the modeling of impact of tcsc on the apparent impedance seen by distance protection relay, the system described in the previous section was modeled in matlab/simulink as shown in figure 6. in this model, the three-phase source blocks, source a and source b, implement a balanced three-phase voltage source with internal r-l impedance. the two voltage sources are connected in y with a grounded-neutral connection. the transmission line block implements a balanced three-phase transmission line model with parameters lumped in a pi section. the line parameters r, l, and c are specified as positiveand zerocb zsa line cb source b 21 zsb 21 a b fault source a tcsc 150 155 160 165 170 175 180 -80 -70 -60 -50 -40 -30 -20 -10 0  (degrees) x t c s c ( % ) -69.53 -31.82 -24.14 -21.41 -20.37 -20.04 -20.00 set system conditions set single-phase to ground fault acquiring voltage and current from vts and cts computation of voltage and current phasor components using dft computation of zero-sequence current phasor component i0 computation of apparent impedance z=v ph /(i ph +ki0) computation of resistance and reactance r, x update fault position and resistance start end engineering, technology & applied science research vol. 8, no. 5, 2018, 3332-3337 3335 www.etasr.com khoa & tung: modeling for development of simulation tool: impact of tcsc on apparent impedance … sequence parameters that take into account the inductive and capacitive couplings between the three phase conductors, as well as the ground parameters. the line is divided in two segments (segment 1 and segment 2) because the ph-g fault is located at mid-point of the line. the fault location can be changed by setting the length of the two segments. it is assumed that the fault location is at different positions on the line and it occurs at 0.4s in total simulation time of 2 seconds. moreover, the fault resistance is also changed from 0ω to 50ω in order to evaluate the impact of tcsc on the relay a. tcsc is modeled by using a series rlc branch block which can change its reactance parameters according to the equations presented in section ii. the firing angle is set to change the reactance of tcsc and simulate the changing apparent impedance seen by distance relay. however, the firing angles of tcsc, 180o, 155o, and 150o are used to measure the impact of tcsc on distance relay tripping characteristics in this study. fig. 6. simulated system a ph-g fault beginning at 0.4 seconds is established at the 100% of the line length and the fault resistance is set by zero (rf=0ω). four hypotheses (without tcsc in the line, with tcsc at the firing angle of 180o, 155o, and 180o) are simulated in the study. with total time of 2 seconds, the simulation results of this case, including the phase current, phase voltage, zerosequence current, and apparent impedance seen by the relay a are shown in figure 7. meanwhile, the voltage and current measurement data are acquired by vts and cts and are sampled by a specific period. the magnitude of faulted phase current at the relay a is shown in figure 7(a). at the beginning time of the fault (0.4 seconds), there is a transient period in the current magnitudes and then they are stable at their new steady state. because of the firing angle, the faulted phase current magnitudes are at different values as shown in figure 7(a). among these values, the current magnitude in the case with tcsc at the firing angle of 150o is the highest one and the current magnitude in the case without tcsc is the lowest one because the firing angle changes the reactance of tcsc. the magnitude of faulted phase voltage at the relay a is shown in figure 7(b). after the fault starts, the phase voltage magnitude decreases to new value. however, the voltage magnitude in the case with tcsc at the firing angle of 150o is the lowest one and the voltage magnitude in the case without tcsc is the highest one. the zero-sequence current is shown in figure 7(c). before the fault occurs, it is zero because the system is almost balanced. ph-g fault is applied at 0.4 seconds and the zerosequence current increases. the component is also used to calculate the apparent impedance seen by the relay a which is shown in figure 7(d). the apparent impedance seen by the relay a depends on the firing angle of tcsc. the impedance in the case with the presence of tcsc at the firing angle of 150o is the lowest one and the impedance in the case without tcsc is the highest one. fig. 7. apparent impedance for solid fault at 100% line length. 0 0.5 1 1.5 2 0 2 4 6 8 10 12 t (sec) (a) p hase current i p h (k a ) t csc  = 150o t csc  = 155o t csc  = 180o w it hout t csc 0 0.5 1 1.5 2 360 370 380 390 400 410 420 t (sec) (b) p hase volt age v ph ( kv ) w it hout t csc t csc  = 180o t csc  = 155o t csc  = 150o 0 0.5 1 1.5 2 0 100 200 300 400 500 600 700 800 t (sec) (c) zero-sequence current i 0 ( a ) w it hout t csc t csc  = 180o t csc  = 155o t csc  = 150o 0 0.5 1 1.5 2 0 50 100 150 200 250 300 350 400 450 t (sec) (d) apparent impendance z (  ) w it hout t csc t csc  = 180o t csc  = 155o t csc  = 150o (b) phase voltage (a) phase current (c) zero-sequence current (d) apparent impedance engineering, technology & applied science research vol. 8, no. 5, 2018, 3332-3337 3336 www.etasr.com khoa & tung: modeling for development of simulation tool: impact of tcsc on apparent impedance … in order to show the changing apparent impedance seen by the relay a according to the fault location, the fault is assumed to occur at different locations on the line by varying the length of two segments of the line. the locations range from 0 to 100% of the line length. in this situation, the apparent impedance seen by the relay a is shown in figure 8. it is clear that the apparent impedance without tcsc increases linearly by the fault location in the line. in the situation with tcsc, the apparent impedance seen by the relay a changes nonlinearly by the fault location in the line. with tcsc at the firing angle of 180o, 155o, and 150o an impedance resonance point occurs between the reactance of tcsc and the impedance of line. the point is the lowest impedance in its characteristic as shown in figure 8. therefore, the firing angle of tcsc has an influence on the apparent impedance seen by the relay a. fig. 8. apparent impedance according to fault location. in this work, high resistance faults are considered in order to investigate the influence of tcsc on apparent impedance seen by the distance relay a. the fault resistances are changed in the range of 0 to 50ω. because of the fault resistance, the apparent impedance will be changed as shown in figure 9. the curves in figure 9, including cases: without tcsc, with tcsc at the firing angle of 180o, 155o, and 150o are shown. this states that the modeling of the system can be used to analyze the impact of tcsc and the fault resistance on apparent impedance seen by the relay a comprehensively. fig. 9. apparent impedance according to fault resistance. the simulation results shown in figure 10 are the hybrid of fault location and resistance. the fault locations range from 0 to 100% of the line length and the fault resistances are set at 0, 10, 20, and 30ω. all faults simulated in this work are the ph-g fault that occurs at 0.2 seconds. the apparent impedance (z) seen by the relay a is separated to the resistance (r) and reactance (x). they are shown in impedance plane in which xaxis is the resistance and y-axis is the reactance. in addition, the mho characteristic of zone 1 is also plotted in order to identify the faults inside or outside zone 1. (a) without tcsc (b) tcsc α=1800 (c) tcsc α=1550 (d) tcsc α=1500 fig. 10. mho characteristic of distance relay according to the firing angle 0 20 40 60 80 100 0 20 40 60 80 100 120 l (%) z (  ) w it hout t csc t csc  = 180o t csc  = 155o t csc  = 150o 0 10 20 30 40 50 0 100 200 300 400 500 r f ( ) z (  ) w it hout t csc t csc  = 180o t csc  = 155o t csc  = 150o engineering, technology & applied science research vol. 8, no. 5, 2018, 3332-3337 3337 www.etasr.com khoa & tung: modeling for development of simulation tool: impact of tcsc on apparent impedance … the results in figure 10 are for the cases without tcsc and with tcsc with firing angle at 180o, 155o, and 150o. simulation results show that the firing angle of tcsc has an impact on the distance relay a. this can make the relay unable to operate correctly when the fault occurs because the point is outside of the zone 1. therefore, the zone 1 is modified according to the firing angle of tcsc to identify the fault correctly (figures 10(b)-(d)). iv. conclusion modeling for development of simulation tool of impact of tcsc on apparent impedance seen by distance protection relays has been proposed in this study. the algorithm for determining capacitance and inductance parameters of tcsc has been developed comprehensively and the method for calculating resistance and reactance seen by distance relay has been proposed. a 3-phase, 500kv transmission line in presence of tcsc which affects relay settings for fault conditions has been modeled and simulated in matlab/simulink. in the model, ph-g faults are applied in the line at different locations in order to evaluate the impact of tcsc on distance relays. simulation results show that the firing angle of tcsc has an impact on apparent impedance seen by distance protection relays. therefore, it is necessary for distance relay to adjust new settings in its mho characteristics and adapt to system conditions according to the firing angle of tcsc. appendix  the parameters of each source are: voltage at both sources: 500kv line-line rms, 50hz thévenin's resistance and inductance of: source a: r=0.8929ω, l=16.58mh source b: r=0.8929 ω, l=16.58mh phase angle between two ends: 10o  the parameters of the line are: length of line: 400km positive-sequence parameters: positive-sequence resistance: r1=0.01273ω/km positive-sequence inductance: l1=0.9337mh/km positive-sequence capacitance: c1=12.74nf/km zero-sequence parameters: zero-sequence resistance: r0=0.3864ω/km zero-sequence inductance: l0=4.1264mh/km zero-sequence capacitance: c0=7.751nf/km  the parameters of tcsc: capacitance: c=0.136mf inductance: l=10mh acknowledgment this work was supported by quy nhon university, code number of project: t2018.569.18. references [1] e. acha, c. r. fuerte-esquivel, h. ambriz-perez, c. angeles-camacho, facts modelling and simulation in power networks, wiley, 2004 [2] s. jamhoria, l. srivastava, “applications of thyristor controlled series compensator in power system: an overview”, 2014 international conference on power signals control and computations (epscicon), thrissur, india, january 6-11, 2014 [3] s. biswas, p. k. nayak, “state-of-the-art on the protection of facts compensated high-voltage transmission lines: a review”, high voltage, vol. 3, no. 1, pp. 21-30, 2018 [4] m. zellagui, a. chaghi, “impact of tcsc on measured impedance by mho distance relay on 400 kv algerian transmission line in presence of phase to earth fault”, journal of electrical systems, vol. 8, no. 3, pp. 273-291, 2012 [5] m. zellagui, a. chaghi, “impact of apparent reactance injected by tcsr on distance relay in presence phase to earth fault”, power engineering and electrical engineering, vol. 11, no. 3, pp. 156-168, 2013 [6] e. reyes-archundia, j. l. guardado, e. l. morenogiytia, j. a. gutierrez-gnecchi, f. martinez-cardenas, “fault detection and localization in transmission lines with a static synchronous series compensator”, advances in electrical and computer engineering, vol. 15, no. 3, pp. 17-22, 2015 [7] p. jena, a. k. pradhan, “directional relaying in the presence of a thyristor-controlled series capacitor”, ieee transactions on power delivery, vol. 28, no. 2, pp. 628-636, 2013 [8] m. khederzadeh, t. s. sidhu, “impact of tcsc on the protection of transmission lines”, ieee transactions on power delivery, vol. 21, no. 1, pp. 80-87, 2006 [9] t. s. sidhu, m. khederzadeh, “tcsc impact on communication-aided distance-protection schemes and its mitigation”, iee proceedings generation, transmission and distribution, vol. 152, no. 5, pp. 714728, 2005 [10] s. m. hashemi, m. t. hagh, h. seyedi, “high-speed relaying scheme for protection of transmission lines in the presence of thyristorcontrolled series capacitor”, iet generation, transmission & distribution, vol. 8, no. 12, pp. 2083-209, 2014 [11] a. maori, m. tripathy, h. o. gupta, “an advance compensated mho relay for protection of tcsc transmission line”, 6th ieee power india international conference (piicon), delhi, india, december 5-7, 2014 [12] k. k. sen, m. l. sen, introduction to facts controllers: theory, modeling and applications, new jersey: john wiley & sons, 2009 [13] s. bruno, g. d. carne, m. l. scala, “transmission grid control through tcsc dynamic series compensation”, ieee transactions on power systems, vol. 31, no. 4, pp. 3202-3211, 2016 [14] ieee standard 1534, ieee recommended practice for specifying thyristor controlled series capacitor, new york: ieee power and energy society, 2009 [15] s. meikandasivam, r. k. nema, s. k. jain, “selection of tcsc parameters: capacitor and inductor”, india international conference on power electronics, new delhi, india, january 28-30, 2011 [16] b. h. li, q. h. wu, d. r. turner, x. zhou, “modelling of tcsc dynamics for control and analysis of power system stability”, international journal of electrical power & energy systems, vol. 22, no. 1, pp. 43-49, 2000 microsoft word khalifeh-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 396-401 396 www.etasr.com khalifeh et al.: isolation of crude oil from polluted waters using biosurfactants pseudomonas bacteria isolation of crude oil from polluted waters using biosurfactants pseudomonas bacteria: assessment of bacteria concentration effects a. khalifeh islamic azad university science and research university tehran, iran anis.khalifeh@ yahoo.com b. roozbehani research center of petroleum university of technology abadan, iran b.roozbehani@ gmail.com a. m. moradi islamic azad university science and research university tehran, iran dr.oil@gmail.com s. imani moqadam research center of petroleum university of technology abadan, iran saeedeh.imani@ gmail.com m. mirdrikvand research center of petroleum university of technology abadan, iran mirdrikvand@ gmail.com abstract—biological decomposition techniques and isolation of environmental pollutions using biosurfactants bacteria are effective methods of environmental protection. surfactants are amphiphilic compounds that are produced by local microorganisms and are able to reduce the surface and the stresses between surfaces. as a result, they will increase solubility, biological activity, and environmental decomposition of organic compounds. this study analyzes the effects of biosurfactants on crude oil recovery and its isolation using pseudomonas sea bacteria species. preparation of biosurfactants was done in glass flasks and laboratory conditions. experiments were carried out to obtain the best concentration of biosurfactants for isolating oil from water and destroying oil-inwater or water-in-oil emulsions in two ph ranges and four saline solutions of different concentrations. the most effective results were gained when a concentration of 0.1% biosurfactants was applied. keywords-environmental decomposition; biological separation; biosurfactant; pseudomonas; concentration. i. introduction studies over optimum methodologies for elimination of oil and refinery products from sea ecosystems are growing rapidly worldwide. among applied physical and chemical methods, biological degradation is the most beneficial and economical one, in an environmental scope, for the elimination of oil pollutants [1]. fortunately, a great amount of oil is degraded via sea microorganisms. the amount of these microorganisms is comprehensively greater in polluted areas. as a result, preparing suitable conditions can accelerate such activities for oil recovery and separation. the microorganisms suitable for biological degradation can be obtained from polluted areas or in the lab, with proper conditions [2]. chromohalobacters, the bacteria that absorb oil pollutants, are advantageous since the released materials in their reactions are usually stable in salty solutions. owing to the fact that most oil resources are located in salty areas, these biosurfactants are effective and efficient for oil elimination. biosurfactants have always been applied in the revival and cleaning of polluted waters and hydrocarbons recovery. they can be applied as emulsioners, foam makers, moisturizers, and cleaners in the oil and petrochemical industry, environmental management systems and mining industries [3]. chemical theories of biosurfactants have been applied to oil industry for oil recovery and more importantly for increasing the efficiency of the recovery process [4-5]. biosurfactants attracted a great attention in environmental processes such as environmental cleaning of polluted waters and soil. biosurfactants appeared in such processes as they have some effects such as dispersion, and environmental friendly factors naming low toxicity and biodegradability [6]. in this study, biosurfactants were produced from local bacteria and their influence on decreasing pollutants’ concentration and their absorption from surroundings was analyzed. in addition, elimination of oil pollution from the area was accomplished as an environmental friendly method; it was done so that no oil residue remained after the cleaning. the oil was also recovered and used afterwards. this paper is going to analyze the effects of biosurfactants on biological degradation. the purpose of this study is to assess the influence of biosurfactants on environmental analysis of crude oil, using native bacteria separated from the mahshahr exporting port, in pilot design and in laboratory conditions. ii. materials and methods a. sampling samples were taken from mahshahr exporting port located at khur-musa near the persian gulf in khuzestan province, iran. they were kept in a temperature near that of incubator until the bacteria were isolated. salinity, ph and water etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 396-401 397 www.etasr.com khalifeh et al.: isolation of crude oil from polluted waters using biosurfactants pseudomonas bacteria temperature in the sample area were measured before and after sampling. b. substances and bacterial culture the basic field of crude oil environmental analysis tests includes the materials that are illustrated in table i along with their concentrations in the bacterial culture medium. table i. materials and their concentration in bacterial culture medium material concentration na2hpo4 2.2 gr/lit kh2 po4 1.4 gr/lit mgso4.7h2o 0.6gr/lit feso4.7h2o 0.02gr/lit nacl 10.0 gr/lit cacl2 0.08gr/lit yeast extract 0.02gr/lit nano3 1.0gr/lit glucose 2%v/v glucose was added to the culture plates as a carbohydrate source and nano3 and yeast extract as nitrogen sources. an amount of 1.5 milliliters of crude oil was eventually put through as the only hydrocarbon source. all experiments were carried out in 250 ml flasks. a volume of 100 milliliters from base culture medium including %2 v/v carbon hydrate source, 1 ml of hydrocarbon source and 0.02 gr/lit of yeast extract was poured into erlenmeyer flasks. an amount of 10 5 to 10 6 bacterial cells per each ml were inoculated into the erlenmeyer flasks. erlenmeyer flasks were left for a week in incubators of 120 revolutions per minute (rpm) rotation in a temperature of 32 °c. daily sampling was performed to define turbidity. besides, ph variations were measured every day and adjusted to the initial value. iii. designing the experiment in laboratory scale in this part of the study, the experiment was designed and performed in laboratory scale in order to assess amount of oil absorption by biosurfactants. ph variations and salinity effects were analyzed. a. ph in order to measure ph variation effects on crude oil environmental degradation, an amount of 10 5 to 10 6 pseudomonas bacteria per milliliters were injected into two 250 ml erlenmeyer flasks containing 100 ml of base culture medium including hydrocarbon and carbohydrate nutrients. phs of the mediums were adjusted on 8 and 8.5 respectively; the flasks were then kept in a temperature of 32 °c and rotation of 120 rpm in the incubator. ph variations were recorded everyday and then adjusted to the set point. figure 1 illustrates these variation effects. b. salinity effect eight 250 ml erlenmeyer flasks, each containing 100 ml of base bacterial culture medium, with salinities of 0.25%, 0.5%, 1%, and 2% were prepared. phs of the solutions were adjusted to 8-8.5; the test bacteria were then injected into the fields. erlenmeyer flasks were kept in the incubator with a temperature of 32˚ c and rotation rate of 120 rpm for a week. to assess the turbidity of solutions, sampling was done in 6 successive days. phs were also recorded daily and then adjusted to the initial amount [6]. iv. assessing the results a. bacteria cell growth and biosurfactant production the results of studies on pseudomonas bacterial cell growth represented crude oil consumptions as sources of carbon and energy. the results that were obtained after 5 days were similar to previous observations during production of these bacteria via these species [7]. the growth amount of most pseudomonas bacteria may be caused by more effective biodegradable features of pseudomonas compared to other species like bacillus. this fact comes after comparing nutrients; media culture situation and salinity in the other chemical cultivation studies [4]. figure 2 illustrates cell growth analysis using turbidity assessment in different concentrations of salt. b. analyzing diverse biosurfactant concentrations in crude oil segregation bacterial culture medium in this research exhibits great amounts of cell growth and more separation activity with concentration of 0.1% of biosurfactant just like those of [6]. no considerable increase in separation activity occurred at higher concentrations. biosurfactants were even identified in very low concentrations [8]. the maximum amount of bacterial degradation and oil separation species is 89% with a biosurfactant concentration of 0.1%. in this study, biosurfactants that were produced by these species in degradability test and oil segregation were used. biosurfactant effect analysis was done in concentrations of 0.25%, 0.5%, 0.15%, and 0.1% in various salinities. the best results was obtained in 0.1% concentration of biosurfactants, ph=8.5 and salinity of 1.0%. the results and comparisons are illustrated in figure 3. the total pollution amount considered is 1000 ppm and the figures show the results in proportion to the whole pollutions. c. analysis of separation and oil degradability in laboratory scale performing test stages in laboratory scale, in glass flasks, illustrated that maximum degradation and separation occurs when sources of phosphor and nitrogen are used in bacterial culture medium for biosurfactant production [9]. analyzing all parameters declares that the presence of biosurfactants is the most important factor that destroys oil-in-water emulsion drops. etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 396-401 398 www.etasr.com khalifeh et al.: isolation of crude oil from polluted waters using biosurfactants pseudomonas bacteria fig. 1. daily variations of ph in different salinities etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 396-401 399 www.etasr.com khalifeh et al.: isolation of crude oil from polluted waters using biosurfactants pseudomonas bacteria fig. 2. cell growth analysis using turbidity assessment in different concentrations of salt etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 396-401 400 www.etasr.com khalifeh et al.: isolation of crude oil from polluted waters using biosurfactants pseudomonas bacteria fig. 3. the amount of residue oil in the area per total pollution amount (1000ppm) etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 396-401 401 www.etasr.com khalifeh et al.: isolation of crude oil from polluted waters using biosurfactants pseudomonas bacteria v. iv. conclusion biosurfactants were applied to clean the polluted areas via the common strategy of being grown in bacterial culture plates and then added continuously to pollution sources. application of biosurfactant in oil recovery is one of the most important methods of recovering a substantial amount of oil residue. additions of biosurfactants increase degradation potential and oil segregation. results illustrated that bacterial cell production via biosurfactants was much more effective than chemical surfactants. biosurfactants were more advantageous due to their lower toxicity, native acceptance and biodegradability. acknowledgment special thanks to abadan refinery, petroleum university of technology and imam khomeini hospital for their friendly non ending helps. references [1] g. h. ebrahimipur, j. fuladi, a. ferdosi, “environmental factors’ effect assessment on crude oil separation via extreme haluphil oil eater bacteria producing biosurfactant pars q2 and gravimeter of oil cuts consumed by these bacteria in optimum conditions”, natural science journal, vol. 13, pp. 59-70, 2005 (in 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bacillus megaterium, corynebacterium kutscheri and pseudomonas aeruginosa", bioresource technology, vol. 102, no. 2, pp. 772-778, 2011 [7] r. thavasi, s. jayalakshmi, t. balasubramanian, i. m. banat, "production and characterization of a glycolipid biosurfactant from bacillus megaterium using economically cheaper sources", world journal of microbiology and biotechnology, vol. 24, no. 7, pp. 917925, 2008 [8] z. a. raza, z. m. khalid, i. m. banat, "characterization of rhamnolipids produced by a pseudomonas aeruginosa mutant strain grown on waste oils", journal of environmental science and health, vol. 44, no. 13, pp. 1367-1373, 2009 [9] b. kumari, s.n. singh, d.p. singh, “characterization of two biosurfactant producing strains in crude oil degradation”, process biochemistry, vol. 47, no. 12, pp. 2463–2471, 2012 microsoft word 18-2970_sx2_etasr_v9_n5_pp4673-4678_2 engineering, technology & applied science research vol. 9, no. 5, 2019, 4673-4678 4673 www.etasr.com nechadi: adaptive fuzzy type-2 synergetic control based on bat optimization for multi-machine … adaptive fuzzy type-2 synergetic control based on bat optimization for multi-machine power system stabilizers emira nechadi ferhat abbas setif 1 university setif, algeria emira.nechadi@univ-setif.dz abstract—a new, adaptive, fuzzy type-2 fast terminal, synergetic multi-machine power system stabilizer is proposed in this study, based on the bat algorithm. the time spent to reach the equilibrium point, from any initial state, is guaranteed to be finite. the adaptive fuzzy type-2 design is applied to estimate the unknown functions of a multi-machine power system. the parameters of the fast terminal synergetic control are optimized, using bat metaheuristic method. in order to test the robustness of the proposed stabilizer, three load conditions, of the multimachine power system are studied. a comparison of the proposed adaptive fuzzy type-2 synergetic power system stabilizer with bat conventional approach is presented, indicating improved performance. the control system stability is assessed by the second theorem of lyapunov and is proven to be asymptotically stable. keywords-adaptive fuzzy type-2 design; fast terminal synergetic control; bat algorithm; lyapunov stability; power system stabilizer i. introduction a power system must remain stable and capable of withstanding a wide range of disturbances, in order to provide secure and reliable services. in a power system, the active power depends on the phase angle between the sending and receiving-end voltages, whereas the reactive power depends on the voltage magnitudes. a dynamic model of the system can be described, by the relationships between active and reactive powers and the bus voltage and frequency [1]. in a stable power system, when synchronous generators are subjected to a disturbance, they either return quickly to their original state or to a new stable operating point. disturbances cause mechanical oscillations, which must be damped [2]. power systems are complex nonlinear systems that often exhibit low frequency oscillations, due to insufficient damping caused by adverse operating conditions, which can lead the underlying machine to lose synchronism [3]. power system stabilizers (pss) are designed to suppress these oscillations and improve overall stability by applying supplementary control through the excitation controller (avr) [4]. conventional pss, consisting of cascade connected lead–lag compensators derived from a linearized model of the power system around a certain operating point have long been used to damp oscillations, regardless of the varying loading conditions or disturbances. however pss control strategies based on linear models often fail to provide satisfactory results over a wide range of operating conditions [5]. authors in [4, 5] presented a comprehensive approach for tuning the conventional pss parameters and their effect on the dynamic performance of the power system. however pss designed to damp one single oscillation mode can produce adverse effects in other modes. several pss design techniques have been reported [6, 7]. pole placement or eigenvalues methods are used in [8-11]. classical optimization techniques failed to provide optimum pss parameters [12]. heuristic techniques, such as genetic algorithms (ga), have already been applied to pss design [13]. a particle swarm optimization (pso) algorithm has been used in [14], for optimizing pss parameters. research has been conducted in optimization using bat algorithm in [15, 16]. optimization of pss parameters, based on bat algorithm, has been also reported [17-19]. recently, a new synergistic control scheme, which combines control theory with heuristic optimization and computational intelligence methods, has emerged [20-22]. this study proposes an adaptive fuzzy type-2 fast terminal synergetic power system stabilizer. fast terminal’s synergetic control parameters are determined, using the bat optimization method, as shown in [23, 24]. adaptive fuzzy type-2 design is used to approximate unknown functions in the multi machine power system model. ii. fast terminal synergetic control in this section, the fast terminal synergetic (ftsyn) controller is developed for the following nonlinear singleinput/single-output (siso) system: ( ) ( )   += = utxgtxfx xx ,, 2 21 � � (1) where [ ] 2 21 rxxx t ∈= is the state vector, while ( )txf , and ( )txg , are unknown functions. in order to obtain the terminal convergence of the state variables, the following macrovariable is defined as a function of the state variables: 1 1 1 x x x λα βψ = + +� (2) corresponding author: emira nechadi engineering, technology & applied science research vol. 9, no. 5, 2019, 4673-4678 4674 www.etasr.com nechadi: adaptive fuzzy type-2 synergetic control based on bat optimization for multi-machine … where α, β are positive constants. with a proper choice of λ, α, β and given an initial state ( ) 00 1 ≠x , the dynamics of the macro variable will reach the equilibrium point in a finite time. the exact time to reach zero s t , is determined by: ( ) ( ) 1 1 01 ln 1 s x t λ α β α λ β − + =    −   (3) and the equilibrium point at 0 is a terminal attractor. introducing the typical constraint (4), the selected macrovariable is forced to evolve in a desired manner, despite the uncertainties and/or disturbances: 0,0 >=ψ+ψ ss tt � (4) where s t is a parameter to be chosen determining the rate of convergence to the attractor and can be made arbitrary small, considering only eventual control constraint. using (2) and (4), the macro-variable derivative is given as: ψ−=++ − s t xxxx 11 1212 λβλα�� (5) the fast terminal synergetic control is: ( ) ( )       ψ+++−= −− s t xxxtxftxgu 1 ,, 1 122 1 λβλα (6) to prove the stability of fast terminal synergetic control, consider the following candidate lyapunov function: ψψ= tv 2 1 (7) therefore: ψψ= �� tv (8) ( ) ( )( )1 122 ,, −+++ψ= λβλα xxxutxgtxf (9) 21 ψ−= s t (10) then: 0≤ i v� (11) iii. design of adaptive fuzzy type 2 synergetic control control law (6) ensures system stabilization and robustness, but it cannot be directly implemented, since functions ( )txf , and ( )txg , are not known. this can be overcome by approximating functions by two interval type-2 fuzzy adaptive systems. a fuzzy system that uses type-2 fuzzy sets and/or fuzzy logic and inference, is called a type-2 fuzzy system [25]. based on the universal approximation theorem, unknown functions ( )txf , and ( )txg , can be approximated by: ( ) ( ) f t f xxf θξθ =,ˆ (12) ( ) ( ) g t g xxg θξθ =,ˆ (13) where [ ] m21 ,...,θ,θθθ = is the parameters’ vector, [ ]t m21 ,...,ξ,ξξξ = is the vector of fuzzy basis functions (fbf), such that: [ ][ ] flfr t l t rf t θθξξθξ 2 1 = (14) [ ][ ] glgr t l t rg t θθξξθξ 2 1 = (15) where 1 2 t m l l l l ξ ξ ,ξ ,...,ξ =   , 1 2 t m r r r r ξ ξ ,ξ ,...,ξ =   , [ ]r 1r 2r mrθ θ ,θ ,...,θ= , and [ ]l 1l 2l mlθ θ ,θ ,...,θ= . this yields the minimum approximation error: u gf δδε += (16) where: ( ) ( ) * f t f xxf θξδ −= (17) ( ) ( ) * g t g xxg θξδ −= (18) and * f θ , * g θ are the optimal approximation parameters by letting: *~ fff θθθ −= (19) *~ ggg θθθ −= (20) the following control law: ( ) ( )       ψ+++−= −− st xxxtxftxgu 1 ,ˆ,ˆ 1 122 1 λβλα (21) under the adaptation laws: ( ) ff x θγξγθ 11 −ψ=� (22) ( ) gg x θγξγθ 22 −ψ=� (23) ensures the stability of the nonlinear system (1). the lyapunov function is chosen as: g t gf t f v θθ γ θθ γ ~~ 2 1~~ 2 1 2 1 21 2 ++ψ= (24) therefore : ( ) ( ) 1 2 1 1 1 t t f g s t t f f g g v x x u t θ ξ θ ξ ε θ θ θ θ γ γ   = ψ − − + − ψ    + + � �� � � � � (25) using (22) and (23): ψ+−−ψ−= εθθθθ g t gf t f st v ��� ~~1 2 (26) and given the following inequalities being valid: 2 * 2 1~~ 2 1~ ff t ff t f θθθθθ +−≤− (27) 2 * 2 1~~ 2 1~ gg t gg t g θθθθθ +−≤− (28) engineering, technology & applied science research vol. 9, no. 5, 2019, 4673-4678 4675 www.etasr.com nechadi: adaptive fuzzy type-2 synergetic control based on bat optimization for multi-machine … v� can be written as: 2 2 2 * * 1 1 1 2 2 1 1 2 2 t t f f g g s f g v t θ θ θ θ θ θ ε   ≤ − ψ + + +    + + ψ � � � �� (29) using: ( )222 2 1 22 1 εεε s s s s t t t t −ψ−+ψ=ψ (30) then: 2 2 2 2* * 1 1 1 2 2 2 1 1 2 2 2 t t f f g g s s f g v t t θ θ θ θ θ θ ε   ≤ − ψ + + +    + + � � � �� (31) and       +=       = 2 * 2 * 21 2 1 2 1 ,, 1 min gf st θθµ γγα (32) finally: 2 2 εµα s t vv ++−≤� (33) integrating (33) from 0 to t, yields: ( ) ( ) ( ) ( )0 2 0 2 0 vtd t dvtv t s t +++−≤ ∫∫ µττεττα (34) terms ( ) ττα dv t ∫ 0 and ( ) ττε dt t s ∫ 0 2 2 are bounded. it can be concluded that ψ and ψ� are bounded ( ∞∈ψ l and ∞∈ψ l� ). sinceε , f θ ~ and g θ ~ are bounded, hence )(tv is also bounded, guaranteeing the stability of the closed loop system. to optimize the synergetic parameters βα,, s t and λ, a fuzzy synergetic approach using bat algorithm is employed. the typical values of the optimized parameters are taken as [ ]2.005.0 − for s t , [ ]300100− for α , [ ]15050− for β and [ ]101− for λ . iv. bat οptimization αlgorithm bat algorithm is a relatively new meta-heuristic optimization method [23]. this algorithm exploits the so-called echolocation of bats. bats use sonar echoes to detect and avoid obstacles. they navigate by emitting high frequency sounds waves and detecting the time delay of the reflected waves. from the detected time delay, bats know how far away they are from the prey or the obstacle [25]. the algorithm, with the use of random walks (one solution is selected among the current best solutions and then the random walk is applied to generate a new solution for each bat), is presented in detail in [23, 24]. applying the bat optimization algorithm and after the optimization procedure, we find ts=0.1000, α=240, β=140 and λ=3. v. power system model the nonlinear power system model considered in this paper represents a synchronous machine connected to an infinite bus via a double circuit transmission line. a nonlinear representation of the power system, considered during a transient period after a major disturbance has occurred, is given by [18, 19]: ( ) ( )   +=∆ ∆=∆ uxgxfmp mp � �ω (35) where ω∆ is the speed deviation, em ppp −=∆ the accelerating power, m is the inertia coefficient, ru ∈ is the input, ( )xf and ( )xg are nonlinear functions and ( ) 0≠xg in the controllability region. the block diagram of a conventional lead-lag power system stabilizer is shown in figure 1. tw is the wash out time constant, t1i-t4i are the pss time constants and ki is the pss parameter of generator i. the optimal parameters of the conventional pss are obtained by bat method and are listed in table ii [19]. fig. 1. conventional power system stabilizer vi. simulation results to proof the robustness and effectiveness of the proposed optimal fuzzy synergetic pss, simulations were carried out under different operating conditions of the multi-machine power system. to demonstrate the stability enhancement achieved with the proposed stabilizer, a three-phase fault test is applied at bus 7 of the multi-machine power system, with duration of 60ms before its clearance. seven fuzzy sets were used for each variable of the proposed pss. the fuzzy sets for [ ]55.0.5730,2−∈∆p and [ ]1.81430.1086,-∈q are defined according to the membership functions shown in figures 2 and 3 respectively. three disturbance scenarios have been considered in the simulation, in order to test the robustness of the proposed control scheme. table i describes these three cases. in each case, the proposed stabilizer is compared with a bat cpss and an aft2 synpss. engineering, technology & applied science research vol. 9, no. 5, 2019, 4673-4678 4676 www.etasr.com nechadi: adaptive fuzzy type-2 synergetic control based on bat optimization for multi-machine … table i. cases of loading conditions for the system (pu) generator g1 g2 g3 light case p 0.9649 1.00 0.45 q 0.223 -0.1933 -0.2668 normal case p 1.7164 1.630 0.85 q 0.6205 0.0665 -0.1086 heavy case p 3.5730 2.20 1.35 q 1.8143 0.7127 0.4313 fig. 2. fuzzy sets for speed deviation fig. 3. fuzzy sets for accelerating power table ii. bat conventional power system stabilizer parameteters k t1 t3 batpss1 46.6588 0.4153 0.2698 batpss2 8.4751 0.4756 0.1642 batpss3 4.2331 0.2513 0.1853 the three-machine test system, used to examine the interarea oscillation control problem, is shown in figure 4 for light load case, in figure 5 for nominal load case and in figure 6 for a heavy load case. (a) (b) (c) fig. 4. light load scenario (a) (b) (c) fig. 5. normal load scenario engineering, technology & applied science research vol. 9, no. 5, 2019, 4673-4678 4677 www.etasr.com nechadi: adaptive fuzzy type-2 synergetic control based on bat optimization for multi-machine … (a) (b) (c) fig. 6. heavy load scenario the proposed stabilizer keeps the generator synchronized. three studies have been performed to investigate the effect of the proposed bat aft2 synpss. the results are compared with a bat cpss and an aft2 synpss. the fault is cleared and the proposed stabilizer helps the system to reach a stable operating point very quickly. vii. conclusion in this paper a bat algorithm was used in combination with an adaptive fuzzy type-2 terminal synergetic (bat aft2) to design a pss for a multi machine power system. the obtained results show that the proposed stabilizer is very effective and can cope with different loading conditions. the proposed stabilizer could rapidly damp oscillations that would eventually lead to a loss of synchronism. the simulation results demonstrate the superior performance of the proposed pss over the bat conventional power system stabilizer (bat cpss) and adaptive fuzzy type-2 synergetic power system stabilizer (aft2 synpss). references [1] f. p. demello, “concepts of synchronous machine stability as affected by excitation control”, ieee transactions on power appparatus and systems, vol. 88, no. 4, pp. 316-329, 1969 [2] k. tang, g. k. venayagamoorthy, “damping inter-area oscillations using virtual generator based power system stabilizer”, electric power systems research, vol. 129, pp. 126–141, 2015 [3] e. v. larsen, d. a. swann, “applying power system stabilizers part ii: performance objectives and tuning concepts”, ieee transactions on power apparatus and systems, vol. 100, no. 6, pp. 3025–3033, 1981 [4] p. kundur, n. j. balu, m. g. lauby, power system stability and control, mcgraw-hill, 1994 [5] p. m. anderson, a. a. fouad, h. 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kolesnikov, g. veselov, a. monti, f. ponci, e. santi, r. dougal, “synergetic synthesis of dc-dc boost converter controllers: τheory and experimental analysis”, seventeenth annual ieee applied power electronics conference and exposition, dallas, usa, march 10-14, 2002 [22] z. jiang, “design of a nonlinear power system stabilizer using synergetic control theory”, electric power systems research, vol. 79, no. 6, pp. 855–862, 2009 engineering, technology & applied science research vol. 9, no. 5, 2019, 4673-4678 4678 www.etasr.com nechadi: adaptive fuzzy type-2 synergetic control based on bat optimization for multi-machine … [23] x. s. yang, “a new metaheuristic bat-inspired algorithm”, nature inspired cooperative strategies for optimization, pp. 65–74, 2010 [24] x. s. yang, x. he, “bat algorithm: literature review and applications”, international journal of bio-inspired computation, vol. 5, no. 3, pp. 141–149, 2013 [25] e. nechadi, m. n. harmas, a. hamzaoui, n. essounbouli, “type-2 fuzzy based adaptive synergetic power system control”, electric power systems research, vol. 88, pp. 9–15, 2012 microsoft word 7-20-1-sm.doc etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 8-12 8 www.etasr.com pylarinos et al : automating the classification of field lc waveforms automating the classification of field leakage current waveforms d. pylarinos dept of ece university of patras patras, greece dpylarinos@yahoo.com k. siderakis dept of ee tei of crete heraklio, greece e. pyrgioti dept of ece university of patras patras, greece e. thalassinakis assistant director p.p.c. heraklion, greece i. vitellas director p.p.c. athens, greece abstract— leakage current monitoring is widely employed to investigate the performance of high voltage insulators and the development of surface activity. field measurements offer an exact view of experienced activity and insulators’ performance, which are strongly correlated to local conditions. the required long term monitoring however, results to the accumulation of vast amounts of data. therefore, an identification system for the classification of field leakage current waveforms rises as a necessity. in this paper, a number of 500 leakage current waveforms recorded on a composite post insulator installed at a 150 kv high voltage substation suffering from intense marine pollution, are investigated. the insulator was monitored for a period of 13 months. an identification system is designed based on the considered data employing fourier analysis, wavelet multiresolution analysis and a neural network. results show the large impact of noise in field measurements and the effectiveness of the discussed system on the considered data set. keywords-insulator; leakage current; field; neural network; wavelet; pattern recognition; std_mra i. introduction outdoor insulation is an important part of transmission and distribution systems, since a single insulator failure may cause an excessive outage of the power system. during operation, electric, mechanical, thermal and chemical stresses apply to outdoor insulators. one of the most influential mechanisms however, is the pollution phenomenon. the basic stages of the phenomenon as described in [1,2], are as follows: the first step is the accumulation of contaminants on the insulators’ surface. in the case of hydrophilic insulation (e.g. porcelain), the presence of a wetting mechanism (e.g. rain, fog, humidity) transforms the contaminants layer into a conductive film and the flow of leakage current (lc) on the surface is permitted. initially, this current is resistive and sinusoid but as activity advances distorted sinusoid current is recorded. the surface heats and dries up unevenly and areas of higher resistance, called dry bands, are formed. the voltage distribution along the insulator is altered. increased stress along the dry bands is observed and dry band arcs appear, which, under favorable conditions, may propagate and ultimately lead to a complete flashover of the insulator. the presence of the arc in the current path is indicated from the on-set time delay of lc waveform in every half-cycle, which causes a knee-like shape. polymer insulators and coatings are used to prevent film formation, and therefore suppress activity, due to their hydrophobicity. however, such materials experience cycles of hydrophobicity loss and recovery [3-7]. the phenomenon is highly correlated with environmental and surface conditions (temperature, wind, location etc) [1-8]. therefore, only field measurements can offer an exact view of the experienced activity and insulators’ performance. it should be noted that during a hydrophobicity loss period, the waveform shapes recorded on hydrophobic insulators are similar to those recorded on hydrophilic ones [8]. the main issue regarding field leakage current monitoring however, is that activity is rapid, rather rare and cannot be safely predicted. therefore, continuous long term field monitoring is required. the long term monitoring combined with the necessary high sampling rate results to the accumulation of vast amounts of data. further, field conditions exaggerate the noise factor and therefore a percentage of the gathered data may be incoherent [9]. in this paper, a data set of 500 lc waveforms recorded on an insulator located in the field during a period of 13 months, is investigated. an identification system capable of identifying four different types of waveforms is designed based on the considered waveforms. the identification system employs fourier analysis in order to identify noise generated waveforms, wavelet analysis and especially std_mra in order to extract patterns from activity portraying waveforms and a neural network to automate the identification process. ii. measurements setup the waveforms investigated in this paper have been recorded on a 150 kv post composite insulator located in the linoperamata 150 kv high voltage transmission substation of the greek network. the monitoring period was 13 months. the linoperamata substation is located next to the coast and suffers from intense marine pollution. the greek public power corporation (p.p.c.) has issued a large project to cope with the problem, and as a part of that project several insulators and coatings have been, or still are, monitored and investigated. some of the published results can be found in [8-11]. a schematic representation of the measuring apparatus employed to monitor leakage current is shown in fig. 1. etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 8-12 9 www.etasr.com pylarinos et al : automating the classification of field lc waveforms figure 1. a schematic representation of the lc measuring apparatus the measurement of leakage current is acquired by inserting in the lc path a collection ring and a hall sensor. the acquired data are transmitted to a central data acquisition system (daq) and sampling is performed at a rate of 2 khz. a user-defined time window is set (e.g. 24 hours) and the daq records one waveform for each time-window (e.g. one waveform per day). the waveform that is recorded is the one portraying the highest peak value. various time-windows have been applied during the 13 months of monitoring. each waveform has a length of 480ms which with a 2 khz sampling rate corresponds to 960 data points. the daq is periodically connected to a laptop in order for data to be retrieved. the matlab software has been employed for further processing of retrieved data and for the design and evaluation of the identification system. iii. wavelet analysis and the std_mra technique wavelets are a mathematical tool for signal analysis. extended wavelet theory can be found in [12,13]. wavelet analysis allows simultaneous time and frequency analysis of signals. a wavelet function is an oscillatory function, with an average value of zero and a band-pass like spectrum. the basic concept in wavelet analysis is to select an appropriate wavelet function ψ (the mother wavelet) and then perform the analysis of a signal using translated (shifted) and scaled (dilated) versions of the mother wavelet. the continuous wavelet transform is given by (1) where α represents the scale, b represents the position, and *ψ represents the complex conjugate of ψ . dt a bt tf a dtttff baba )()( 1 )()(, * ,, ∫∫ ∞ ∞− ∞ ∞− − ψ=ψ=ψ (1) in case a digitized signal and discrete values of a and b are used then the discrete wavelet transform is given by (2) where j sa 0 = , jkskab 0== and zjk ∈, . )()( 1 ),,( 0 0 0 ∫ ∞ ∞− ⋅− ψ= j j j s skt tf s bjfdwt (2) multiresolution analysis (mra) is a wavelet based filtering algorithm, which was created as a theoretical basis to represent signals that decompose in finer and finer detail [12,13]. the main idea is to use wavelet analysis to decompose the original signal in two parts: the approximation, which contains the lowfrequency part of the signal, and the details, which contains the high-frequency part. the first stage of decomposition will give the first level approximation (a1) which if decomposed will give the second level approximation (a2) and so on. detail analysis is performed with a contracted, high frequency version of the mother wavelet, while approximation analysis is performed with a dilated, low frequency version of the same wavelet. an example of mra performed in a lc waveform is shown in fig. 2. in this paper, the std_mra technique is used in order to extract patterns from lc waveforms. each lc waveform is decomposed in six levels using mra and the standard deviation (std) of the details (d1, d2, …, d6) extracted in each level of the mra is calculated. the normalized six-point vector, called std_mra vector, is then used as a pattern for the corresponding waveform. the std_mra vector is normalized because similar lc waveform shapes can portray various amplitudes. the mathematical expression of the standard deviation σ for a n-point vector x , is given in (3), where x is given in (4). considering that the shape of the mother wavelet should be similar to the shape of the signal, daubechies 4 wavelet is chosen as a mother wavelet. the form of the approximation and details during the mra is directly linked to the shape of the mother wavelet, which means that decomposition will produce daub4-like wavelets, as shown in fig. 2. the frequency band of approximation and details for each decomposition level is showed in table i. ∑ ∑ = = − − =− − = n i n i ii xx n xx n 1 1 22 1 2 )( 1 1 ))( 1 1 (σ (3) ∑ = = n i i x n x 1 1 (4) etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 8-12 10 www.etasr.com pylarinos et al : automating the classification of field lc waveforms figure 2. six level mra analysis of a lc waveform. a1-a6 shows the approximation and d1-d6 shows the details through levels 1-6. table i. frequency bands for different mra levels decomposition level approximation details 1 0~500 (hz) 500~1000 (hz) 2 0~250 (hz) 250~500 (hz) 3 0~125 (hz) 125~250 (hz) 4 0~62.5 (hz) 62.5~125 (hz) 5 0~31.25 (hz) 31.25~62.5 (hz) 6 0~15.625 (hz) 15.625~31.25 (hz) iv. activity portraying waveforms and extracted patterns three different categories for activity portraying waveforms were set after the investigation of the considered data set. sinusoid and distorted sinusoid current are described as type a. dry band arcs that are sustained for a limited number of half cycles are described as type b and excessive arcs that are sustained throughout the whole waveform are described as type c. an example of each type and the corresponding pattern derived from std_mra is portrayed in fig. 3,4 and 5 respectively. v. the artificial neural network artificial neural networks (ann) are highly parallel, adaptive learning systems that can learn a task by generalizing from case studies of the tasks. if a problem can be posed as a problem of mapping outputs to inputs, then an ann can be used as a black box that learns the mapping from examples of known cases of correlated inputs-outputs. the selection and the design of the ann was done considering the attributes described in [14-16] related to simplicity, speed and efficiency. among the various forms of ann architectures, the multilayer feed forward network with back propagation learning algorithm was chosen. this architecture (also known as multilayer perceptron architecture) is suitable for recognizing patterns that don’t evolve with time. figure 3. a type a waveform and it’s the std_mra pattern figure 4. a type b waveform and the std_mra pattern figure 5. a type c waveform and the std_mra pattern in order to identify categories that are located in the same area, but are not linearly separated (such as the patterns extracted in this study), one hidden layer is sufficient. the number of inputs etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 8-12 11 www.etasr.com pylarinos et al : automating the classification of field lc waveforms is six (equal to the elements of the pattern-vector) and the ann must identify 3 categories, therefore three output neurons are sufficient. each type is correlated to a three-element output vector easily separable from the others. type a to [1 0 0]’,type b to [0 1 0]’ and type c to [0 0 1]’. in order to minimize the risk of “trapping” the algorithm around a local minimum, the number of neurons per layer should decrease from the input layer to the output layer. hence, five neurons are selected for the hidden layer. the hyperbolic tangent function is chosen for the hidden layer for its speed and efficiency. the log-sigmoid function is chosen for the output layer in order to compress the outputs into the [0,1] domain. the learning algorithm used is the levenberg-marquardt due to its speed in the case of medium-sized anns. the train set consists of 4 type a waveforms, 3 type b waveforms and 6 type c. a schematic representation of the ann is illustrated in fig. 6. vi. noise generated waveforms noise generated waveforms can be attributed to various field related conditions (cable faults, equipment faults, operation of circuit breakers, switching of heavy loads etc) [9]. noise generated waveforms vary in form, and some typical waveforms are shown in fig. 7. those waveforms will lead to erroneous results if fed to the neural network. therefore, it is highly desirable to be identified and discarded at the early stages of the identification system, using deterministic criteria. the voltage frequency in the greek system is 50 hz and therefore the fundamental frequency of every leakage current waveform should be 50hz. this criterion can be used to discard waveforms as the first three in fig. 7. however, waveforms similar to the last one in fig. 7, can exhibit a 50hz fundamental. an example is shown in fig. 8. an amplitude criterion could be applied in order to discard such waveforms. however, a noise generated spike, can be superimposed on such waveforms, as shown in the first waveform of fig. 7, and thus allowing them to exceed any threshold. therefore, a simple low pass filter with a cut off frequency of 200hz is employed, in order to remove spikes while maintaining the main part of the waveform, and then an amplitude criterion is applied. figure 6. a schematic representation of the ann figure 7. noise generated waveforms figure 8. two noise generated waveforms and their frequency content vii. the identification system a block diagram of the identification system is shown in fig. 9. initially, the frequency content of each lc waveform is calculated using the fourier transform. if the fundamental frequency of the waveform differs from 50 hz then the waveform is attributed to noise. if the waveform exhibits a 50 hz fundamental, then it passes through the low-pass filter and the amplitude of the filtered waveform is calculated. if the amplitude of the filtered waveform is found smaller than 1 ma, then the waveform is attributed to noise. otherwise, std_mra is performed on the original waveform (not the filtered one). the extracted pattern (the std_mra vector) is then fed to the artificial neural network which identifies the waveform type. figure 9. block diagram of the identification system etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 8-12 12 www.etasr.com pylarinos et al : automating the classification of field lc waveforms viii. results and discussion the identification system was able to successfully identify all 500 waveforms and results are shown in table ii. the results show the significant impact of noise in field leakage current waveform monitoring. further it is shown that the discussed identification system can successfully recognise and further categorize activity portraying waveforms. table ii. number of waveforms per type waveform type �umber of waveforms noise 460 type a 9 type b 7 type c 24 sum 500 however, it should be mentioned that the design of the discussed identification system is based upon the considered data set, which is relatively small. further investigation of field waveforms is required. however, results show that the std_mra technique combined with neural networks can be applied in order to identify different types of field leakage current waveforms, although it is highly probable that further investigation may result to the modification of the system and possibly to the add of new categories. ix. conclusion leakage current monitoring is widely employed in order to investigate surface activity on high voltage insulators and to evaluate their performance, which are both strongly correlated to local conditions. field monitoring can offer an exact view of the insulators’ performance and the experienced activity. however, the necessary long term monitoring results to the accumulation of vast amounts of data and the implementation of an identification system rises as a necessity. in this paper a number of 500 waveforms recorded over a 13 month period on a 150 kv post composite insulator located at a 150 kv high voltage substation suffering from intense marine pollution, is investigated. an identification system is designed, capable of identifying four basic types of waveforms, including noise generated waveforms. results show that noise is significantly exaggerated in the field. in addition, it is shown that wavelet analysis, and especially the std_mra technique, combined with neural networks can be successfully employed to automate the classification of field leakage current waveforms. references [1] cigre wg 33-04, the measurement of site pollution severity and its application to insulator dimensioning for a.c. systems, electra no. 64, pp.101-116, 1979 [2] cigre wg 33-04, tf 01, a review of current knowledge: polluted insulators, cigre publications, 1998 [3] h. hillborg, u.w. gedde, “hydrophobicity changes in silicone rubbers”, ieee trans. dielectr. electr. insul., vol. 6, no. 5, pp.703-717, 1999 [4] z. jia, h. gao, z. guan, l. wang, j. yang, “study on hydrophobicity transfer of rtv coatings based on a modification of absorption and cohesion theory, ieee trans. dielectr. electr. insul., vol. 13, no. 6, pp. 1317-1324, 2006 [5] d.a. swift, c. spellman, a. haddad, “hydrophobicity transfer from silicone rubber to adhering pollutans and its effect on insulator performance, ieee trans. dielectr. electr. insul., vol. 13, no. 4, pp. 820-829, 2006 [6] s. kumagai, “hydrophobicity transfer of rtv silicone rubber aged in single and multiple environmental stresses and the behaviour of lmw silicone fluid”, ieee trans. power deliv., vol. 18, no. 2, pp. 506-516, 2003 [7] n. yoshimura, s. kumagai, s. nishimura, “electrical and environmental aging of silicone rubber used in outdoor insulation”, ieee trans. dielectr. electr. insul., vol. 6, no. 5, pp. 632-650, 1999 [8] k. siderakis, d. agoris,” performance of rtv silicone rubber coatings installed in coastal systems”, electr. power syst. res., vol. 78, issue 2, pp. 248-254, 2008 [9] d. pylarinos, k. siderakis, e. pyrgioti, e. thalassinakis, i. vitellas, “impact of noise related waveforms on long term field leakage current measurements”, ieee trans. dielectr. electr. insul., vol. 18, no. 1, 2011 [10] k. siderakis, d. agoris, s. gubanski, “salt fog evaluation of rtv sir coatings with different fillers”, ieee trans. power deliv., vol. 23, no. 4, pp. 2270-2277, 2008 [11] k. siderakis, d. agoris, j. stefanakis, e. thalassinakis, “influence of the profile on the performance of porcelain insulators installed in coastal high voltage networks in the case of condensation wetting”, iee proceedings, science, measurement and technology, vol. 153, no. 4 , p. 158-163, 2006 [12] s.g. mallat, “a theory for multiresolution signal decomposition: the wavelet representation”, ieee trans. pattern analysis and machine intelligence, vol. 11, pp. 674-693, 1989. [13] stephane mallat , a wavelet tour of signal processing, academic press, 1999 [14] s. haykin , neural networks: a comprehensive foundation, prentice hall , india 1999 [15] e. dermatas, pattern recognition, university of patras’ academic press, department of electrical and computer engineering, 1997 [16] c.m. bishop, neural networks for pattern recognition, oxford university press 1995 authors profile dionisios pylarinos was born in athens in 1981. he received a diploma degree in electrical and computer engineering from the university of patras in 2007. presently he is with the high voltage laboratory of the department of electrical and computer engineering at the university of patras. he has worked as a scientific consultant for ppc. his research interests include outdoor insulation, electrical discharges, signal processing and pattern recognition. kiriakos siderakis was born in heraklion in 1976. he received a diploma degree in electrical and computer engineering in 2000 and the ph.d. degree in 2006 from the university of patras. presently, he is an application professor at the department of electrical engineering, at the technological educational institute of crete. his research interests include outdoor insulation, electrical discharges, high voltage measurements and high voltage equipment diagnostics and reliability. eleftheria pyrgioti was born in 1958 in greece. she received her diploma degree in electrical engineering from patras university in 1981 and the ph.d. degree from the same university in 1991. she is an assistant professor at the department of electrical and computer engineering at the university of patras. her research activity is directed to high voltage, lightning protection, insulation coordination and distributed generation. emmanuel thalassinakis received the diploma in electrical and mechanical engineering and also the ph.d. degree from the national technical university of athens. after working for the ministry of the environment, in 1991 he joined the public power corporation (p.p.c.) where he is now assistant director of the islands network operations department. isidoros vitellas was born in 1954 in greece. he has a diploma in electrical engineering and the ph.d. degree in the same field. he is currently director of the islands network operations department in p.p.c. (public power corporation) athens, greece. engineering, technology & applied science research vol. 8, no. 3, 2018, 3041-3043 3041 www.etasr.com sohu et al.: flexural performance of concrete reinforced by plastic fibers flexural performance of concrete reinforced by plastic fibers muhammad tahir lakhiar faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia mtl.eng17@gmail.com samiullah sohu faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia sohoosamiullah@gmail.com imtiaz ali bhatti faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia engrimtiaz290@gmail.com nadeem-ul-kareem bhatti department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan knadeem_b@yahoo.com suhail ahmed abbasi department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan abbasi.suhail2009@gmail.com muhammad tarique department of civil engineering mehran university of engineering and technology jamshoro, sindh, pakistan mtarique181@gmail.com abstract—for sustainable development construction, recycle or reuse of waste materials is utilized. many researchers conducted tried to create an innovative green concrete, utilizing waste materials. the aim of this research is to contribute and promote the use of plastic waste in concrete. the concrete’s flexural and workability were investigated by using different percentages of 0%, 0.2%, 0.4%, 0.6%, 0.8% and 1% of plastic fibers in concrete. in this study, m15 grade concrete beams were casted and cured for 7 and 28 days to analyze the flexural performance and workability. the outcomes demonstrated that the workability was slightly reduced by the utilizing plastic fibers where flexural strength improved by 16.5% at 0.6% addition of plastic fibers in concrete. keywords-flexural strength; workability; plastic fibers; green concrete i. introduction concrete is a material widely utilized in construction industry due to its many benefits. it is feasible, durable and economical compared to other building materials [1-3]. flexural strength of concrete is minimum compared to compressive strength because concrete is brittle in nature [4]. to enhance the flexural strength, steel fibers are mostly used as reinforcement [5]. steel contributes to the carbon dioxide co2 emission in atmosphere during its manufacturing which contributes to global warming [6] and therefore, the need of sustainable green concrete raises day by day. concrete made from waste, which is more eco-friendly, is known as green concrete. in other words, green concrete is the concrete in which waste materials are utilized in order to save natural resources and thus decrease environmental pollution. in this type of concrete, waste material is used to at replace least one of its ingredients. if its production process does not affect the environment, production procedures, life cycle sustainability and quantity of cement are the key factors adopted to categorize whether a concrete is green or not [7, 8]. the main purpose of developing green concrete is to minimize co2 gas emissions which cause environmental pollution and to re-use waste materials, which create disposal problems. ii. materials and methodology a. materials for this experimental study, m15 grade concrete (1:2:4 ratio) was utilized with water-cement ratio constant at 0.55. the material properties of fine and coarse aggregates and cement are shown in tables i-iii. plastic fibers (figure 1) were utilized from 0%-0.6% with increment of 0.2%. ordinary portland cement was utilized for this research. b. methodology m15 grade concrete was casted incorporating 0%-1% with increment of 0.2% of plastic fibers. two concrete beam types were casted. one was conventional concrete beam which had 0% of plastic fibers (pf) and the other was plastic fiber concrete beam (pfc-b) which contained plastic fibers. fifty four beams were casted, three beams were tested for each proportions at each curing age. the beams, having size 150mmx200mmx1500mm, were tested for flexural strength at different water curing regimes of 7, 14 and 28 days. mixing was carried out utilizing a rotary mixer. the concrete mix workability was examined by standard slump test using standard slump cone and procedures according to astm c 143. all cubes were extracted from the molds after 24 hours and cured for the required age of testing. the concrete flexural str as c7 a. wo sho slig b. as out fig per engineerin www.etasr rength was tes stm followed 78/78m-18. table i s. n 0 02 03 04 table ii. s table s i slump test (a astm c 1 orkability of c own in table ghtly decrease ta convent pf pf pf pf p flexural stre flexural stre stm c78/78m tcomes of all gure 2. the rformance inc ng, technology r.com ted using thre d the overall i. materia no. t 1 water ab 2 specific 3 finess m 4 co . material . no. t 01 water a 02 specif 03 finess e iii. materi s. no. t 01 cons 02 specif 03 finess fig. 1. iii. result (astm c 143) 143 standard concrete. work iv. the resul ed incorporatin able iv. slu mixtures tional concrete b fc-b (0.2% pf) fc-b (0.4% pf) fc-b (0.6% pf) fc-b (0.8% pf) fc-b (1% pf) ength of beam ength test w m-18 standar l concrete mi outcomes de creased rapidly y & applied sci ee point flexur procedure d al properties of test r bsorption c gravity modulus olor lig properties of c test r absorption 1 fic gravity modulus ial properties o test re sistency 3 fic gravity 3 modulus plastic fibers ts and discus [9] was fal kability or slu lts show that t ng the plastic f ump flow of con slump beam 2 2 2 2 m as performed rd [10]. the ixes are show emonstrated t y by utilizing ience research ral loading tes escribed in a fine aggregate results 1.1% 2.6 2.96 ght brown oarse aggrega results 1.19% 2.68 6.15 of cement (o.p.c) esults 31% 3.14 1.18 sion llowed to ge ump flow resul the slump flow fibers in concr ncrete mix. values(mm) 32.37 30.34 29.50 28.24 26.32 25.65 d according t e flexural str wn in table v that beam fle plastic fibers h v sohu et al.: t. the astm es tes ) et the lts are w was rete. to the rength v and exural up to 0.8% the dec wat rap util pfc 2.54 plas flow the fou con [1] [2] [3] [4] [5] vol. 8, no. 3, 20 : flexural perfo % and then it flexural stren creased 1.5% ter curing, the idly up to 0.8 lized. after 28 c-b 16.52% 4% when 1% tabl mixtu conventional c pfc-b (0 pfc-b (0 pfc-b (0 pfc-b (0 pfc-b ( fig. 2. the workabil stic fibers we w. the flexura control samp und to be 0.6% ncrete in conte m. t. lakhiar, jhatial, a. a. a tensile strength vol. 8, no. 2, p z. li, advanced a. m. neville, p r. nagalakshm concrete with p aggregate with engineering re e. mello, c. properties with environmental 018, 3041-3043 formance of co decreased slig ngth of pfc-b when 1% of e flexural stren % and decrea 8 days water increased rap of pf were uti le v. flexu ures concrete beam 0.2% pf) 0.4% pf) 0.6% pf) 0.8% pf) 1% pf) flexural stren iv. co lity of concret ere added beca al strength inc ple. the opti % and it enhan xt of all other refer , n. mohamad, abdul samad, “e h”, engineering t pp. 2796-2798, 20 d concrete techn properties of con mi, “experimental partial replaceme h coconut shell”, esearch, vol. 4, n ribellato, e. m h fibers additio engineering, vol ncrete reinforc ghtly. after 7 b 11 % increas pf were utiliz ngth of pfc-b ased 1.42% wh curing, the f idly up to 0. ilized. ural strength o flexural st 7 days 14 1.96 2 2.08 2 2.13 2 2.18 2 2.15 2 1.93 2 ngth outcomes of onclusion te slightly red ause of the fi creased up to 1 imum percent nced the flexu mixes. rences m.a. b. shaikh, efffect of river in technlogy & app 018 nology, john wile ncrete, prentice h study on strength ent of cement w , international jo no. 1, 2013 mohamedelhassan, on”, international l. 8, no. 3, pp. 24 3042 ced by plastic f days water cu sed up to 0.8% zed. after 14 b 15.23% incre hen 1% of pf flexural streng 8% and decre of concrete trength (mpa) days 28 day 2.10 2.36 2.26 2.57 2.32 2.68 2.42 2.75 2.35 2.65 2.07 2.30 f all mixes duced when co ibers’ resistan 16.5% compar tage of fibers ural performan , a. a. vighio, ndus sand on co plied science res ey and sons inc., all, 2011 h characteristics o with fly ash and ournal of scient “improving co l journal of civ 9-254, 2014 fibers uring, % and days eased were gth of eased ys onsist nce to red to s was nce of a. a. oncrete search, 2011 n m25 coarse tific & oncrete vil and engineering, technology & applied science research vol. 8, no. 3, 2018, 3041-3043 3043 www.etasr.com sohu et al.: flexural performance of concrete reinforced by plastic fibers [6] y. wang, q. wang, y. hang, z. zhao, s. ge, “co2 emission abatement cost and its decomposition: a directional distance function approach”, journal of cleaner production, vol. 115, pp. 205-215, 2018 [7] a. baikerikar, “a review on green concrete”, j. emerging technol. innovative res. vol.1, no.6, pp. 472–474, 2014. [8] k. h. obla, “what is green concrete?”, the indian concrete journal, vol. 24, pp. 26-28, 2009 [9] astm international, astm c143/c143m-15, standard test method for slump of hydraulic-cement concrete), astm international, west conshohocken, pa, 2015 [10] astm international, astm c78/78m-18, standard test method for flexural strength of concrete (using simple beam with third-point loading), astm international, west conshohocken, pa, 2018 microsoft word 29-3468_s_etasr_v10_n4_pp6052-6056 engineering, technology & applied science research vol. 10, no. 4, 2020, 6052-6056 6052 www.etasr.com islam et al.: optimized controller design for an islanded microgrid using non-dominated sorting sine … optimized controller design for an islanded microgrid using non-dominated sorting sine cosine algorithm (nssca) quazi nafees ul islam electrical and electronic engineering department islamic university of technology gazipur, bangladesh quazinafees@iut-dhaka.edu saad mohammad abdullah electrical and electronic engineering department islamic university of technology gazipur, bangladesh saadabdullah@iut-dhaka.edu md. arif hossain electrical and electronic engineering department islamic university of technology gazipur, bangladesh arifhossain@iut-dhaka.edu abstract—in order to cope with the increasing energy demand, microgrids emerged as a potential solution which allows the designer a lot of flexibility. the optimization of the controller parameters of a microgrid ensures a stable and environment friendly operation. non-dominated sorting sine cosine algorithm (nssca) is a hybrid of sine cosine algorithm and non-dominated sorting technique. this algorithm is applied to optimize the control parameters of a microgrid which incorporates both static and dynamic load. the obtained results are compared with the results of the established non-dominated sorting genetic algorithm-ii (nsga-ii) in order to justify the proposal of the nssca. the average time needed to converge in nssca is 7.617s whereas nsga-ii requires an average of 10.660s. moreover, the required number of iterations for nssca is 2 which is significantly less in comparison to the 12 iterations in nsga-ii. keywords-multi-objective; nsga-ii; nssca; dynamic load; static load; spss; i. introduction renewable energy sources are often integrated in microgrids because they are environmentally friendly and are considered an answer to the fossil fuel scarcity. however, due to their unpredictable nature, renewable energy sources often hamper stability and may cause large frequency and voltage deviations in a microgrid [1]. the control parameters play a significant role for smooth and efficient operation of a microgrid. if there is any type of disturbance in the system, the selection of proper controller parameters and their tuning at optimized value ensures stable system operation [2]. thus, research is now focused in optimizing the controller parameters, load sharing, cost etc. of a microgrid with a view to enhance its stability, efficiency, and cost effectiveness [3, 4]. in this aspect, various optimization algorithms are often adopted because they can often identify the global optimum system and also have a better convergence probability [5, 6]. in single objective optimization (soo), the aim generally is to search for the best design or decision, which is expected to be the global solution of the optimization problem. but in the case of multiple objective optimization (moo), there may be one or more solutions which may be the best (global minimum or maximum) with respect to all objectives [7]. however, moo renders a greater flexibility to the designers than soo while selecting the most optimum result [8] because instead of presenting a single solution, moo provides a set of solutions known as the pareto front where none of the solutions dominates the others and thus the designer can choose any solution depending on his choice/requirements. various works have been conducted in optimizing the controller parameters of a microgrid. in [9], artificial fish swarm algorithm was used to optimize only the droop controller gains for controlling the frequency deviation in a microgrid operating in islanded mode but it did not optimize other controller parameters. authors in [10] used the moo nsga-ii in optimizing the controller parameters but lacked comparison analysis between existing works. in this regard, the present study proposes a new moo where sine cosine algorithm (sca) is combined with nondominated sorting technique to form the hybridized nondominated sorting sine cosine algorithm (nssca). basically sca is an soo which was first introduced in 2015 [11]. the incorporation of non-dominated sorting technique transforms this soo into an moo. the proposed nssca is being used to obtain global optimum control parameters for an islanded microgrid consisting of both static and dynamic load. the main focus of this study is to obtain a better dynamic performance during load variation by applying nssca. in order to establish the efficacy of the designed nssca, the results are compared with the ones of the established non-dominated sorting genetic algorithm (nsga-ii) [12]. ii. microgrid model in this study, an islanded microgrid as shown in figure 1, composed of two distributed generation (dg) units where one unit has static (r-l) load installed and an induction motor on the other unit is considered as the dynamic load. the complete microgrid model used in this study is adopted from [2, 13]. in microgrid modeling, inverter, loads, and network design are the three main parts. figure 2 shows the block diagram of an inverter connected to the microgrid along with its associated controllers. among the three controller units: power controller determines the frequency and magnitude of the output voltage reference for the voltage controller, voltage controller corresponding author: quazi nafees ul islam engineering, technology & applied science research vol. 10, no. 4, 2020, 6052-6056 6053 www.etasr.com islam et al.: optimized controller design for an islanded microgrid using non-dominated sorting sine … determines the inductor output currents’ reference using proportional integrator (pi) regulator after comparing the actual and reference voltage values, and finally the current controller supplies switching signals to the inverter. there are thirteen states for individual inverter units, i.e. twenty-six states in total for the two inverters, two states for static load model, two states for line network, and five states for the induction motor. the complete microgrid model used in this study is developed by incorporating the state space model of individual inverter, static load model, line network, and induction motor. the total number of state variables is eight as shown in (1). ∆�� � �∆�� ∆�� ∆ � ∆ ��� ∆ ��� ∆����� ∆����� ∆���� � (1) fig. 1. two dgs with static and dynamic load. fig. 2. block diagram of an inverter connected to microgrid. iii. problem formulation stable operation of a microgrid in islanded mode is an important aspect that needs to be ensured in order to acquire proper system output. the presence of both static and dynamic load in the microgrid creates challenges to its stable operation. moreover, controller parameters play a vital role in system stability. in this system, pi regulators are used to vary gains of both voltage and current controllers. these controller gains need to be fine-tuned within proper limits for stable operation of the microgrid. a. objective function the microgrid model used in this study has eight controller gain parameters as there are two inverters for two dgs and each inverter has a separate voltage and current controller unit. each voltage and current controller has separate pi regulators to control the controller gains. here, ����, ���� and ����, ���� represent the pi gains of the voltage controller of inverter-1 and inverter-2 respectively. similarly, ���� , ���� and ���� , ���� represent the pi gains of the current controller of inverter-1 and inverter-2 respectively. eigenvalue analysis provides information regarding damping characteristics of a system which plays an important role in system stability. if the eigenvalues of the states of the microgrid model move away from the imaginary axis and go in the left half of the s-plane, their real part becomes more negative, the damping performance of the system is improved, and system stability is ensured. the main objective of this study is to optimize the above-mentioned controller gains to obtain a stable performance. the objective functions are mentioned in (2) and (3) where � and ζ indicate the real part of the eigenvalues and the damping ratio respectively. ��������, !� � "#��$%�&$� # minimum+�, -. (2) ��������, !� � "/�$%�&$� # minimum+ζ, -. (3) n represents the total number of states, which is 35 for this study. for each of these states the � and / values will be evaluated so that both the objectives are satisfied. ��$%�&$� and /�$%�&$� specify the limit of objective functions [14]. these two objective functions are contradictory in nature which can be understood from (4) where ω represents the frequency of the states. from (4) it can be seen that if the magnitude of � increases then / becomes more negative i.e. it reduces and vice versa. /, � 0123124 5624 (4) the constraint for this study is given in (5) where controller gains are limited to a desired boundary which is obtained by performing root locus analysis in order to obtain a stable microgrid system with improved damping performance. 0 8 ����,� , ����,�, ����,�, ����,� 8 500 (5) b. proposed solution nssca, a novel hybridized optimization algorithm, is proposed in this study. the optimization technique is presented with the help of the flow chart in figure 3. the detailed steps of the algorithm are given below. step 1: initialize the system parameters and generate the initial set of population. the total number of iterations is also defined in this step. step 2: the fitness of the solutions is evaluated by the objective functions !� and !�. step 3: non-dominated sorting of the initial generation of population is carried out on the basis of fitness value. step 4: in this step, crowding distance and ranking of the population is done. step 5: the position of all the solution sets is updated by (6) and (7) following [11]. :�;5� � :�; < =� > sin+=� > |=a ��; # :�; |, =b 8 0.5 (6) :�;5� � :�; < =� > cos+=� > |=a ��; # :�; |, =b f 0.5 (7) where :�; is the current solution after the g;h iteration where the solution is along the �;h dimension. similarly ��; is the destination solution point after the g;h iteration along the �;h engineering, technology & applied science research vol. 10, no. 4, 2020, 6052-6056 6054 www.etasr.com islam et al.: optimized controller design for an islanded microgrid using non-dominated sorting sine … dimension. here, =� indicates the direction along which the solution will move, i.e. whether the solution will confine its movement within the space between the solution and the destination point or traverse beyond it. =� is updated using (8) where i is a constant and j is the maximum number of iterations. =� � i # g kl (8) =� is a random number [0, 2π] which indicates the distance of the movement of the solution inside or outside the destination and =a indicates a random weight in defining the effect of destination in distance calculation. if =a m 1 then the effect of the destination is emphasized and the opposite if =a 8 1 [11]. =b is a random number between �0, 1� which indicates which of (6) or (7) should be followed to update the position. fig. 3. flowchart of the nssca. step 6: in order to update the position of the solutions =� , =� , =a and =b need to be updated to reach the best destination point and determine the best solution. step 7: merge the new set of solution with the initial set of and then non-dominated sorting, crowding distance calculation and ranking of the merged set of solutions is applied until the maximum number of iterations is reached. step 8: the best possible position of the solution is determined after the final iteration and that position indicates the best solution iv. results and discussion a. eigenvalue analysis the ability of the proposed nssca algorithm in stabilizing the system was examined through eigenvalue analysis. the eigenvalues of different states obtained before and after optimizing the controller parameters using nssca are shown in table i. from the table, it can be observed that for some of the states∆ �� , ∆ �� , ∆���� and ∆�o�p$q the eigenvalues are positive which indicates their location on the right side of the s plane and thus instability to the system is introduced. after optimizing the controller parameters using nssca, it is observed that the obtained negative eigenvalues of the aforementioned states shifted their location from the right side to the left side of the s plane making the system more stable. table i. eigenvalue analysis index state eigen value of the state before optimization after optimization 1 ∆�� 2909410 + 12209388i -2909410 + 12209388i 2 ∆�� 2909410 12209388i -2909410 12209388i 3 ∆ � -3261123 + 8309127i -3261123 + 8309127i 4 ∆ �� -3261123 8309127i -3261123 8309127i 5 ∆ �� -55.194 + 45315i -19853 + 389577i 6 ∆ �� -55.194 45315i -19853 389577i 7 ∆ �� -352.417 + 44476.812i -19823 + 389227i 8 ∆���� -352.417 44476.812i 19823 389227i 9 ∆���� -4107.969 + 31524.405i -29070 + 318066i 10 ∆���� -4107.969 31524.405i -29070 318066i 11 ∆���� -5629.972 + 29764.098i -29078 + 318482i 12 ∆���� -5629.972 29764.098i -29078 318482i 13 ∆���� -8720.541 + 8365.113i -8277.936 + 20647.906i 14 ∆�� -8720.541 8365.113i -8277.936 20647.906i 15 ∆�� -6328.127 + 8624.675i -12555.159 + 18762.199i 16 ∆ � -6328.127 8624.675i -12555.159 18762.199i 17 ∆ �� -1291.429 + 0i -2209.282 + 504.685i 18 ∆ �� 213.426 + 784.754i -2209.282 504.685i 19 ∆ �� 213.426 784.754i -25.460 + 198.321i 20 ∆ �� -81.284 + 376.280i -25.460 198.321i 21 ∆���� -81.284 376.280i -157.538 + 0i 22 ∆���� -162.677 + 0i -1.092 + 55.904i 23 ∆���� -70.227 + 1.578i -1.092 55.904i 24 ∆���� -70.227 1.578i -70.694 + 0i 25 ∆���� -67.497 + 0i -67.571+ 1.586i 26 ∆���� 22.647 + 0i -67.571 1.586i 27 ∆�o�p$q 1.315 + 0i -2.187 + 0i 28 ∆�o�p$r -2.394 + 0i -0.369 + 0.044i 29 ∆�o�k�q -2.393 + 0i -0.369 0.044i 30 ∆�o�k�r -0.018 + 0.045i -1.686 + 0.009i 31 ∆�r% -0.018 0.045i -1.686 0.009i 32 ∆�q% -0.021 + 0i -1.686 + 0i 33 ∆�r& -0.329 + 0i -0.560 + 0i 34 ∆�q& -0.200 + 0i -0.701 + 0i 35 ∆so -0.202 + 0i -0.701 0i engineering, technology & applied science research vol. 10, no. 4, 2020, 6052-6056 6055 www.etasr.com islam et al.: optimized controller design for an islanded microgrid using non-dominated sorting sine … c. time domain simulation analysis in this section, the comparison among nsga-ii and nssca is presented based on the overshoot obtained from the step response of the inductor current (d-q), output voltage (dq), real power and reactive power for both dg-1 and dg-2 as shown in figure 4. considering the d-axis component of the inductor current of dg-1 as shown in figure 4(a), the percentage of overshoot in the case of nssca is much less compared to nsga-ii. when, the d-axis component of the inductor current is considered for dg-2, nsga-ii results in 25% overshoot compared to zero overshoot in the case of nssca. for both dg-1 and dg-2, when the step response of the q-axis component of the inductor current is considered, no overshoot is caused by nsga-ii and nssca. considering the step response of the output voltages (d-q) of both dg-1 and dg-2 as shown in figure 4(e)-(h), it can be observed that nssca causes less overshoot than nsga-ii with the only exception in case of the q-axis component of the output voltage of dg-2. for both dgs, the step response of the real and reactive power indicate that both the algorithms cause zero overshoot as depicted in figure 4(i)-(l). in the light of the above discussion, it can be concluded that nssca provides better step response compared to nsga-ii. fig. 4. step response. d. statistical tests in order to justify the uniqueness of each algorithm, independent samples’ t-test was performed to compare the equality of means using spss [15] statistical analysis software. the t-test was performed with respect to the total number of iterations required to complete the optimization process, the total execution time of the optimization process, and the total summation of the real part of the eigenvalues. while running the t-test, spss software generated the results of the f-test which indicate whether the data samples from the two grouping variables (i.e. nsga-ii and nssca in this case) possess equal variances or not. for the f-test, the null hypothesis assumes that the data samples from the two groups have equal variances and the alternative hypothesis assumes that the data samples have non-equal variances. the null hypothesis can only be rejected when the significant factor (p-value) of the f-test is less than 0.05. from the results summarized in table ii, it can be observed that the p-value of the f-test is greater than 0.05 only in case of the total summation of the real part of the eigenvalues. thus, the data sets of nsga-ii and nssca possess non-equal variances in terms of total number of iterations and total execution time. the corresponding t-test results are also summarized in table ii. in the case of the t-test, the null hypothesis assumes that the means of two data sets are equal and as the alternative hypothesis it is assumed that the means of two data sets are not equal. if the significant factor (p-value) of the t-test is less than 0.05, then the null hypothesis can be rejected. from table ii it can be observed that there is a significant difference between the two algorithms with respect to the total number of iterations and the execution time as for both cases the p-value of the t-test is less than 0.05, whereas, with respect to the total summation of eigenvalues the null hypothesis cannot be rejected as the p-value of the t-test is greater than 0.05. however, from the data presented in table engineering, technology & applied science research vol. 10, no. 4, 2020, 6052-6056 6056 www.etasr.com islam et al.: optimized controller design for an islanded microgrid using non-dominated sorting sine … iii, the total summation of the eigenvalues in the case of nssca is slightly higher compared to nsga-ii which indicates that nssca ensures slightly better stability to the system. from the above analysis, it can be concluded that each algorithm possesses unique characteristics. considering the mean values of the total number of iterations, total execution time, and total summation of eigenvalues of both algorithms, nssca was found to exhibit significantly better performance. table ii. comparison between nsga-ii and nssca based on the f-test and t-test results parameters f-test t-test for equality of means f sig. mean diff. t df sig. (2-tailed) total iterations 60.035 0.000 10.133 6.177 29.273 0.000 total summation of eigenvalues (real) 2.477 0.121 30941 1.356 58 0.180 execution time 38.545 0.000 3.043 2.155 33.202 0.039 table iii. group statistical data of nsga-ii and nssca parameters algorithm mean standard deviation standard error mean total number of iterations nsga-ii 12 8.965 1.637 nssca 2 0.615 0.112 total summation of eigenvalues (real) nsga-ii -12709275 68444 12496 nssca -12740216 104560 19090 execution time nsga-ii 10.660 7.468 1.363 nssca 7.617 2.015 0.368 v. conclusion in this study, the non-dominated sorting technique was merged with the sine cosine algorithm (sca) in order to develop a multi-objective optimization algorithm named nssca. this algorithm was applied to optimize the controller gains of a two bus microgrid model. the microgrid model was developed considering static load in one of the buses and an induction motor as dynamic load in the other bus. the performance of nssca in optimizing the controller gains was compared with nsga-ii by applying nsga-ii for the same two-bus system. from the comparative study in terms of eigenvalue analysis, time domain analysis, and statistical tests it was observed that nssca performs better in stabilizing the system by optimizing controller gains. the computations done by nssca were significantly faster compared to nsga-ii in terms of both required number of iterations and execution time. thus, nssca can be considered as a prospective algorithm in optimizing the controller gains of a microgrid model. references [1] a. m. howlader et al., “a minimal order observer based frequency control strategy for an integrated wind-battery-diesel power system,” energy, vol. 46, no. 1, pp. 168–178, oct. 2012, doi: 10.1016/j.energy.2012.08.039. [2] n. pogaku, m. prodanovic, and t. c. green, “modeling, analysis and testing of autonomous operation of an inverter-based microgrid,” ieee transactions on power electronics, vol. 22, no. 2, pp. 613–625, mar. 2007, doi: 10.1109/tpel.2006.890003. [3] l. s. coelho and v. c. mariani, “combining of chaotic differential evolution and quadratic programming for economic dispatch optimization with valve-point effect,” ieee transactions on power systems, vol. 21, no. 2, pp. 989–996, may 2006, doi: 10.1109/tpwrs.2006.873410. [4] r. eslami, s. h. h. sadeghi, and h. a. abyaneh, “a probabilistic approach for the evaluation of fault detection schemes in microgrids,” engineering, technology & applied science research, vol. 7, no. 5, pp. 1967–1973, oct. 2017. [5] s. sinha and s. s. chandel, “review of recent trends in optimization techniques for solar photovoltaic–wind based hybrid energy systems,” renewable and sustainable energy reviews, vol. 50, pp. 755–769, oct. 2015, doi: 10.1016/j.rser.2015.05.040. [6] e. e. miandoab and f. s. gharehchopogh, “a novel hybrid algorithm for software cost estimation based on cuckoo optimization and knearest neighbors algorithms,” engineering, technology & applied science research, vol. 6, no. 3, pp. 1018–1022, jun. 2016. [7] k. prabakar, f. li, and b. xiao, “controller hardware-in-loop testbed setup for multi-objective optimization based tuning of inverter controller parameters in a microgrid setting,” in 2016 clemson university power systems conference (psc), clemson, sc, usa, mar. 2016, doi: 10.1109/psc.2016.7462824. [8] m. fadaee and m. a. m. radzi, “multi-objective optimization of a stand-alone hybrid renewable energy system by using evolutionary algorithms: a review,” renewable and sustainable energy reviews, vol. 16, no. 5, pp. 3364–3369, jun. 2012, doi: 10.1016/j.rser.2012.02.071. [9] a. ibrahim, y. jibril, and y. s. haruna, “determination of optimal droop controller parameters for an islanded microgrid system using artificial fish swarm algorithm (afsa),” international journal of scientific & engineering research, vol. 8, no. 3, pp. 959–965, mar. 2017. [10] r. wang et al., “optimized operation and control of microgrid based on multi-objective genetic algorithm,” in 2018 international conference on power system technology (powercon), guangzhou, china, nov. 2018, pp. 1539–1544, doi: 10.1109/powercon.2018.8601845. [11] s. mirjalili, “sca: a sine cosine algorithm for solving optimization problems,” knowledge-based systems, vol. 96, pp. 120–133, mar. 2016, doi: 10.1016/j.knosys.2015.12.022. [12] k. deb, a. pratap, s. agarwal, and t. meyarivan, “a fast and elitist multiobjective genetic algorithm: nsga-ii,” ieee transactions on evolutionary computation, vol. 6, no. 2, pp. 182–197, apr. 2002, doi: 10.1109/4235.996017. [13] a. kahrobaeian and y. a.-r. i. mohamed, “analysis and mitigation of low-frequency instabilities in autonomous medium-voltage converter-based microgrids with dynamic loads,” ieee transactions on industrial electronics, vol. 61, no. 4, pp. 1643–1658, apr. 2014, doi: 10.1109/tie.2013.2264790. [14] s. r. mudaliyar and s. s. sahoo, “comparison of different eigenvalue based multi-objective functions for robust design of power system stabilizers,” international journal of electrical and electronic engineering & telecommunications, vol. 1, no. 2, 2015. [15] spss inc. released 2007. spss for windows, version 16.0. chicago, spss inc. microsoft word 24-2630_s engineering, technology & applied science research vol. 9, no. 2, 2019, 3998-4001 3998 www.etasr.com eli-chukwu & onoh: experimental study on the impact of weather conditions on wide code … experimental study on the impact of weather conditions on wide code division multiple access signals in nigeria ngozi clara eli-chukwu department of electrical & electronics engineering, alex ekwueme federal university, ndufu-alike, ebonyi, nigeria ngozieli@gmail.com g. n. onoh electrical & electronics engineering, enugu state university of science and technology, enugu, nigeria onohgn@gmail.com abstract—in cellular network activities, before a site is integrated it is expected that each cell of the site meets the nigerian communication commission (ncc) standard of ≥98% for both service accessibility and call completion rate which in turn depicts a ≤2% in both blocked call rate (bcr) and dropped call rate (dcr). it is suggested that weather conditions have a very strong negative effect on the performance of wideband code division multiple access (wcdma) network as it could lead to signal attenuation or change the polarization. in this paper, we study the impact of weather conditions on wcdma network in nigeria. to achieve this, network samples (log-files) were collected weekly during a driving test in enugu state nigeria for a period of five years for both rainy and dry seasons, in which blocked and dropped calls were extracted. results show that during adverse weather conditions, bcr and dcr rise greater than 8% and 4% respectively. although with a slight relationship between the weather conditions, the weather condition during the dry season has a better-blocked call rate of 8.76% in comparison with the rainy season with 12.89%. calls tend to drop more during the dry season. from the outcome of the experiment, a model was developed for predicting an unknown network call statistics variables. keywords-blocked call; cellular; dropped call; dry season; rainy season; weather; wcdma i. introduction in cellular networks, trying for optimization is considered a constant. one of the major reasons for constant optimization is the weather. often, weather conditions affect major key performance indicators (kpi) such as accessibility and retainability used by operators and subscribers to assess network performance. during various weather conditions, it is expected for the wcdma cellular network to maintain its performance and meet the nigerian communication commission (ncc) threshold of both bcr and dcr ≤2%. this paper studies the impacts of weather conditions on wcdma network and compares them. gsm signal strength varies with respect to weather parameters. tropospheric delays such as humidity, pressure and temperature affect the strength of the transmitted signal [1]. distance estimation based on the received signal strength of a wireless radio is susceptible to radio propagation conditions, particularly during periods of precipitation [2]. movement of mobile station (ms) affects the signal received from the base transceiver system (bts). decreased signal reception conditions, if the channel is exposed to rain, occur. rain attenuation as color noise affects signal quality, mainly 3g network signal transmission, and can be grouped into drizzling rain, straight form, medium, heavy convective and storms, have the effect of their own in the process of signal transmission. [3]. many wireless sensor networks operating outdoors are exposed to changing weather conditions, which may cause severe degradation in system performance. therefore, it is essential to explore the factors affecting radio link quality in order to mitigate their impact [4]. there is a relationship between atmospheric conditions and speech quality [5]. since the cellular gsm networks are one of the most commonly used communication technologies today, the quality of speech in these networks is a topic of great significance. many advances and approaches have been introduced in the field of speech quality during the last decade, most of them focusing on ip networks, where speech quality is influenced by every single network node through which the communication passes. there is a bond between speech quality in gsm networks and weather conditions and a greater bond between rain density and speech quality [6]. the most classical approach of determining rain attenuation for radio-wave frequency has been to theoretically determine the specific attenuation. at frequency over 10ghz, rain and precipitation can influence the attenuation a lot. the effect of atmospheric attenuation between the source and destination over wireless communication is of major concern and proper site visit and control method are required so that the performance can be increased [7]. rainfall is a natural phenomenon whose temporal and geographical distribution varies widely. wireless communications suffer losses in network quality during rainfall which can affect the regional communication for a while. growing concerns of climatic change also encourage the study of the effects of natural phenomena like rainfall on other measurable parameters corresponding author: ngozi clara eli-chukwu engineering, technology & applied science research vol. 9, no. 2, 2019, 3998-4001 3999 www.etasr.com eli-chukwu & onoh: experimental study on the impact of weather conditions on wide code … [8]. the link availability of outdoor radio systems is often affected by atmospheric conditions such as rain and snow. the effects of rainfall on wireless transmissions are particularly noticeable at data rates. as the rate of rainfall increases, more disruption is caused to the outdoor link [9]. some dependencies between weather conditions and receive level were studied in [10]. there is a relationship between refractivity from rainfall and propagation of the gsm radio signal as greater refractivity means lower signal quality and vice versa [11]. the gsm technology is the most widely utilized communication standard which it is now coming to its bandwidth limitations especially in big cities and densely populated areas. under such circumstances, even a minor weather change could be a decisive factor causing changes in the quality of service [12]. attenuation in tropical regions is underestimated by existing prediction methods based on experimental data from temperate climates [13]. sunny and rainy weather conditions have firstorder main effects on user equipment [14]. the significance here is that various forms of precipitation such as rain, snow, cloud and fog absorb and scatter electromagnetic energy leading to attenuation in its signal strength. harmattan precipitation intensity may be so great that visibility at ground level is reduced to less than a hundred meters while inflicting attenuation significantly [15]. certain combinations of the constituents in weather can cause radio signals to be heard hundreds of miles beyond the ordinary range of radio communications. tropical weather has significant effects on radio signal where the highest correlation values for each factor are 0.70756 for solar radiation, 0.6285 for humidity, 0.4344 for wind speed, 0.3850 for rain rate, and 0.3339 for temperature [16]. terrestrial and earth-space links operating at bands higher than 10ghz inevitably suffer severe signal degradation due to rain fade, particularly in the tropics [17]. this study focuses on ascertaining and comparing the impact of various weather conditions on wcdma network. ii. experimental setup a. method the drive test method was used to characterize the network [18]. the experimental setup uses the testing equipment for mobile system (tems) v13.0 software installed on a laptop, a tems mobile phone, a gps and a power inverter. voice calls were made for 120secs on the mtnn network by the mobile phone. the test covered the enugu metropolis in enugu state, nigeria for a period of 5 years, covering both rainy and dry seasons. b. network characterization parameter although the experimental technique reports many parameters, the parameters of interest are bcr and dcr. bcr explains the rate at which the user equipment (ue) is unable to access the network when a call is attempted. it is expressed as: %��� = ���∗ �� � (1) where ��� is the number of blocked calls and ��� the number of successful calls. dcr is the rate at which established calls ends abruptly without the knowledge of both call originator and terminator: %��� = ���∗ �� �� (2) where ��� is the number of is dropped calls and ��� is the number of successful calls. c. network characterization results table i shows the call statistics and radio environment results for the five year period. table i. call statistics kpi result from network characterization. year weeks rainy season dry/harmattan season bcr dcr bcr dcr 2015 wk1 7.14 3.66 7.43 2.06 wk2 3.19 3.12 2.1 2.27 wk3 1.01 2.6 1.01 3.07 wk4 3.04 1.96 2.23 2.98 wk5 10.25 3.9 3.75 2.43 wk6 5.54 2.88 3.29 2.7 wk7 5.1 2.11 3.02 1.97 wk8 3.87 3.04 1.98 2.45 2016 wk9 3.47 4.1 2.56 5.7 wk10 5 3.72 9.41 5.32 wk11 16.75 8.62 2.19 3.14 wk12 8.96 5.46 4.98 9.42 wk13 12.85 5.47 3.46 6.81 wk14 17.19 8.18 2.27 5.12 wk15 24.35 11.3 11.21 7.07 wk16 22.13 2.63 13.75 7.73 2017 wk17 23.35 7.47 13.81 9.94 wk18 10.43 4.37 8.21 5.59 wk19 14.29 4.7 13 4.84 wk20 21.55 4.05 31.87 8.77 wk21 29.53 3.91 3.34 2.52 wk22 30 5.84 8.98 5.83 wk23 35.22 7.5 12.39 8.38 wk24 30.15 5.7 12.44 7.37 2016 wk25 2.46 4.65 16.53 5.45 wk26 1.69 3.36 4.76 4.27 wk27 2.91 1.72 1.27 1.28 wk28 29 4 5.06 2.67 wk29 24.63 5.91 31.76 7.47 wk30 23.08 4.39 31.3 4.5 wk31 6.59 7.27 7.73 8.98 wk32 3.01 2.35 4.88 2.65 2017 wk33 5.05 5.7 6.93 5.53 wk34 10.11 3.45 9.91 3.73 wk35 16.92 5.47 9.04 12.31 wk36 17.54 5.35 10.11 5.75 wk37 7.07 6.65 12.37 6.67 wk38 5.91 4.05 8.74 5.71 wk39 8.38 5.2 4.88 3.82 wk40 7.11 6.11 6.34 4.07 iii. results and analysis a. blocked call rate analysis first, a correlation test is performed on the bcr results for both rainy and dry seasons to ascertain their nature of relationship existing between them. the correlation test is denoted with �� ranges from -1 to 1 [19]. �� = �� ��� � ��� ( �"�) (3) engineering, technology & applied science research vol. 9, no. 2, 2019, 3998-4001 4000 www.etasr.com eli-chukwu & onoh: experimental study on the impact of weather conditions on wide code … the result (rs=0.453) shows there is a slight positive relationship between the bcr for both rainy and dry seasons, such that a rise in rainy season bcr leads to a rise in dry season bcr: μ%�& '()* = 12.8955 , μ�%'()* = 8.7573 . a statistical approach for testing the hypothesis is used to ascertain if there is a difference in population means between the bcr during the rainy and dry seasons. hypothesis: 3�: μ% 5 μ� = 0 3�: μ% 5 μ� 7 0 (4) decision rule: accept h0 if 8��9 : 8( ;< �"=)�>(?) , otherwise reject. test statistic: 8��9 = (@;"@�)ab;��;<b���� ~ 8( ;< �"=)�>(?) (5) 8��9 = 2.796 e 8( ;< �"=)�>(?) = 1.664 (6) conclusion: there’s a statistical significant difference between the blocked call rate for the rainy and dry seasons. the graph in figure 1 shows that the rate of blocked calls during rainy season is higher than the dry/hammattan season. this result is obvious in weeks 21, 23 and 25 respectively. fig. 1. rainy and dry season bcrs b. drop call rate analysis applying (3)-(5) the dcr we get rs=0.524. with rs there is a slight positive correlation between the dcrs of both rainy and dry seasons: μ%�& 'g)* = 4.798 and μ�%'g)* = 5.2085 , 8��9 = 51.129 e 8( ;< �"=)�>(?) =1.664. conclusion: there’s no statistical significant difference between the dcrs of rainy and dry seasons. the graph in figure 2 shows that there is a statistical equal rate of dropped calls during rainy and dry/hammattan seasons. all through the test period, the average marginal difference (amd) of the dcr was 51 k lm�g)* k 1. fig. 2. rainy and dry season dcrs c. comparative kpi analysis friedman test is a non-parametric test of hypothesis approach for repeated measure analysis of variances which is used when the same parameter has been measured under different conditions on the same subjects [20]. hypothesis: 3�: �*()* = �n()* = �*g)* = �ng)* = 0 3�: �*()* = �n()* 7 0 (6) decision rule: accept h0 if op�9q� e o�&r and reject if otherwise [20]. s���9 = �=� *�� t ��� u(u<�) 5 3v(w x 1) ~ s�( ,u)�>(?) (7) op�9q� = 0.05 e o�&r. = 0 conclusion: there’s no statistical significant difference between the bcr and dcr for rainy and dry seasons. d. multiple linear regression multiple linear regression is a statistical approach that models the relationship between two or more explanatory variables and a response variable by fitting a linear equation to the observed data [20]. all the values of the independent variable x are associated with the values of the dependent variable y. the model is expressed as: z& = �� x ��[&�x..x �\[&\ x ]& (8) z& = 2023.437 5 0.084[� x 0.756[= x 0.415[^ x 0.555[_ where z& =years, [� =rainy bcr, [= =dry bcr, [^ =rainy dcr and [_ =dry dcr. the above linear regression model can be used for prediction. iv. conclusion in cellular network activities in nigeria, before site integration, it is expected that each cell of the site meets the ncc standard of ≥98% for service accessibility and call completion rate which in turn depicts a ≤2% in the bcr and engineering, technology & applied science research vol. 9, no. 2, 2019, 3998-4001 4001 www.etasr.com eli-chukwu & onoh: experimental study on the impact of weather conditions on wide code … dcr. these results are achieved during seasonal changes. this paper points out the impact of varying weather conditions on wcdma network performance. the results showed that during adverse weather conditions, the bcr and dcr rise greater than 8% and 4% respectively. although with a slight relationship between the weather conditions, the weather conditions during the dry season have a better bcr of 8.76% than the rainy season with 12.89%. calls tend to drop more during the dry season. a regression model was developed for predicting unknown network call statistics variables. optimization actions that will protect against the effects of weather conditions on service accessibility and retainability should be considered in future studies. references [1] t. s. dalip, v. kumar, “effect of environmental parameters on gsm and gps”, indian journal for science and technology. vol. 7, no. 8, pp. 1183-1188, 2014 [2] s. h. fang, y. s yang, “the impact of weather condition on radiobased distance estimation: a case study in gsm network with mobile measurement”, ieee transactions on vehicular technology, vol. 65, no. 8, pp. 6444-6453, 2015 [3] m. s. yadnav, i. w. sudiartha, “simulation of broadcast level signal mobile station 3g network rain condition”, asia pacific conference on multimedia and broadcasting, bali, indonesia, november 17-19, 2016 [4] j. luomal, i. hakala, “effects of temperature and humidity on radio signal strength in outdoor wireless sensor networks”, computer science and information systems, vol. 5, pp. 1247-1255, 2015 [5] m. voznak, j. rozhon, “influence of atmospheric parameters on speech quality in gsm/umts”, international journal of mathematical models and methods in applied sciences, vol. 6, pp. 575-582, 2012 [6] j. rozhon, p. blaha, m. voznak, j, skapa, “the weather impact on speech quality in gsm network”, in: computer networks, communications in computer and information science, vol. 291 springer, 2014 [7] m. c. kestwal, s. joshi, l. s. garia, “prediction of rain attenuation and impact of rain in wave propagation at microwave frequency for tropical region”, international journal of microwave science and technology, vol. 2014, article id 958498, 2014 [8] s. sabu, s. renjmol, d. abhiram, b premlet, “effect of rainfall on cellular signal strength: a study on the variation of rssi at user end of smartphone during rainfall 2017 ieee region 10 symposium, cochin, india, july 14-16, 2014 [9] b. fong, p. b. rapaiic, g. y. hong, “effects of rain attenuation on wireless transmission of frame relay traffic”, the 8th international conference on communication systems, singapore, november 28, 2002 [10] j. skapa, m. dvorsky, l. michalek, r. sebesta, p. blaha, “k-mean clustering and correlation analysis in recognition of weather impact on radio signal”, 35th international conference on telecommunications and signal processing, prague, czech republic, july 3-4, 2012 [11] l. ali, i. alam, a. a. s. syed, m. yaqoob, “various meterological parameters effect on gsm radio signal propagation for a moderate area”, 2017 international conference on frontiers of information technology, islamabad, pakistan, december 18-20, 2017 [12] p. blaha, j. rozhon, m. voznak, j. skapa, “correlation between speech quality and weather”, in: soft computing models in industrial and environmental applications. advances in intelligent systems and computing, vol. 188, springer, 2014 [13] l. a. r. da silva mello, e. costa, r. s. l. de souza, “rain attenuation measurements at 15 and 18 ghz”, electronics letters, vol. 38, no. 4, pp. 197-198, 2015 [14] c. li, x. luo, c. zhang, x. wang, “sunny, rainy, and cloudy with a chance of mobile promotion effectiveness”, marketing science, vol. 36, no. 5, pp. 762-779, 2017 [15] d. d. dajah, n. parfait, “a consideration of propagation loss models for gsm during harmattan in n’djamena (chad)”, international journal of computing and ict research, vol. 4, no. 1, pp. 43-48, 2010 [16] n. h. sabri, r. umar, m. m. shafie, s. n. a. s. zafar, r. mat, a. sabri, z. a. ibrahim, “correlation analysis of tropical rainforest climate effect on radio signal strength at kusza observatory, terengganu”, advanced science letters, vol. 23, no. 2, pp. 1268-1271, 2015 [17] a. f. ismail, m. r. islam, j. din, a. r. tharek, n. l. i. jamaludin, “investigation of rain fading on a 26ghz link in tropical climate”, 6th international conference on telecommunication systems, services, and applications, bali, indonesia, october 20-12, 2011 [18] n. c. eli-chukwu, g. n. onoh, “improving service accessibility (cssr) in gsm network using an intelligent agent-based approach”, international journal of computer engineering in research trends, vol. 4, no. 11, pp. 478-486, 2017 [19] p. k. sahu, s. r. pal, a. k. das, estimation and inferential statistics, springer, 2015 [20] m. r. spiegel, l. j. stephens, theory and problems of statistics, mcgraw-hill, 1999 engineering, technology & applied science research vol. 7, no. 2, 2017, 1478-1481 1478 www.etasr.com shukla et al.: a modified approach of optics algorithm for data streams a modified approach of optics algorithm for data streams m. shukla department of computer engineering marwadi education foundation & r. k. university, rajkot, india madhu.ce@gmail.com y. p. kosta department of computer engineering marwadi education foundation rajkot, india ypkosta@gmail.com m. jayswal department of computer engineering marwadi education foundation rajkot, india, mjmeghnesh@gmail.com abstract-data are continuously evolving from a huge variety of applications in huge volume and size. they are fast changing, temporally ordered and thus data mining has become a field of major interest. a mining technique such as clustering is implemented in order to process data streams and generate a set of similar objects as an individual group. outliers generated in this process are the noisy data points that shows abnormal behavior compared to the normal data points. in order to obtain the clusters of pure quality outliers should be efficiently discovered and discarded. in this paper, a concept of pruning is applied on the stream optics algorithm along with the identification of real outliers, which reduces memory consumption and increases the speed for identifying potential clusters. keywords-two phase; cluster quality; clustering technique; pruning; time and space complexity; threshold value i. introduction traditional data mining methods are not that successful in case of huge data streams, as off-line mining is not applicable. there are some requirements for clustering algorithms. fast processing of data points and identification of outliers must be clear and precise [1]. data uncertainty is an added issue. different data type should be treated differently which is also an issue. an arbitrary shape of clusters makes hard to distinguish the accurate shape of the cluster [2]. there are many different applications like network traffic analysis, sensor network, internet traffic etc. that produce stream data [20]. random sampling, sliding window, histograms, multi-resolution methods, sketches and randomized algorithm are some basic data sampling techniques for mining data streams [13]. classification of stream data is possible with algorithms such as the hoeffding tree, the concept adaptive very fast decision tree (cvfdt), the very fast decision tree (vfdt), and the classifier ensemble approach. accuracy, efficiency, compactness, separateness, purity, space limitation and cluster validity are an important issue in the aspect of clusters quality. different types of clustering methods like partitioning, hierarchical methods, model based, density based, grid based, constraint-based and evolutionary methods etc. are used for clustering stream data. various algorithms are developed for clustering in data streams. micro-clustering algorithms for data streams are as follows: den stream algorithm, stream optics algorithm, hdd stream algorithm [19] etc. density grid-based algorithms for data streams are as follows: d-stream algorithm, mr-stream algorithm, dengris algorithm[19] etc. table i gives a basic mapping of several existing algorithms that contains the description of their advantages and disadvantages. clustering is a key task in data mining. there are various other additional challenges by data streams on clustering such as one pass clustering, limited time and limited memory. along with this, finding out clusters with arbitrary shapes is very much necessary in data stream applications. density-based clustering method is of significant importance in clustering data streams, as it has the tendency to discover arbitrary shape clusters as well as outliers. in density based clustering, a cluster is defined as areas of higher density than the remaining data set. clustering algorithms requires very tedious calculations for detecting the outliers. handling noisy data, limited time and memory, handling evolving data, and handling high dimensional data are also to be considered. an outlier is defined as a data point which shows abnormal behaviour to the system and it is application dependent. in stream data mining the data points are huge in number thus it may be possible that during clustering of such data points few of the data points which does not belong to clusters or does not take part in clustering due to its distance from the cluster will be termed as outliers. it is required to remove such data points. as data generation is continuous and fast, a structure should be established to handle the mining process. clustering provides a solution to such types of issues in stream data mining ii. proposed architecture in this paper a modification is applied on the stream optics algorithm by applying a pruning method and setting a threshold value cut off points for data dynamically. the extension of the most basic density algorithm (dbscan) is optics which is based on the ordering point in the stream data mining. its concept is to continuously increase the given cluster till the density in the neighborhood cross some of the threshold value. for each data point in a given cluster from the group of the cluster, the neighborhood of given radius has to contain at least a minimum number of points. one of the important advantages of this method is that it can find clusters of arbitrary shapes and can be used to filter out engineering, technology & applied science research vol. 7, no. 2, 2017, 1478-1481 1479 www.etasr.com shukla et al.: a modified approach of optics algorithm for data streams noise. it considers clusters as dense regions of the objects in the data space which are separated by low-density regions. for interactive and automatic cluster analysis this algorithm determines an augmented cluster ordering. an ordering of clusters is done to obtain basic clustering information and deliver the intrinsic clustering architecture. the core distance represents the smallest value from the core. the reachability distance considers the greater value of the core distance of the second object and the euclidean distance between the two objects. this creates an ordering of the objects in a database and stores the suitable reachability distance and core distance for each object. the major drawback of the optics method is that if there is no core object the reachability distance between two objects is undefined. the same basic scheme is applied for the stream optics algorithm modified with the addition of an iterative property of the threshold value and with the concept of pruning in order to optimize and time complexity. table i. approach, advantages, and disadvantages of existing algorithms algorithm approach advantages disadvantages stream [1] partitioning space and time complexity is low. it does not have flexibility of computing the clusters at user defined time periods. clu-stream [2] partitioning & hierarchical it provides flexibility of computing the clusters at user defined time periods. does not support concept drift and gives the clusters of arbitrary shapes. hpstream [3] partitioning & hierarchical high dimensional projected clustering of data stream an average number of projected dimension parameters and number of clusters requires detail domain knowledge. den-stream [4] density based gives arbitrary shape clusters. deleting and merging of the micro clusters does not allow release of any memory space. d-stream [5] density and grid based it supports density decaying and monitors evolving behaviour for real time data streams. does not support handling of multiple dimensional data e-stream [6] hierarchical high performance then other algorithm user complexity of setting high number of parameters dbscan [7] density based can analyze the cluster for large dataset inputting the parameter setting is very much difficult stream-optics [8] density based plotting of cluster structure based upon time. for cluster extraction it is not supervised technique mr-stream [9] density based improves the performance of the clustering. in high dimensional data, it lacks its working hdd-stream [10] density based high dimensional data is clustered. it takes more amount of time in searching the neighbor clusters. dengris [11] density based using sliding window model the distribution of recent most records are captured precisely no evaluation to show its effectiveness compared with other state off art algorithms. somke [12] density based use in non-stationary data efficiently and effectively. cannot handle unbalance data. leaden-stream [13] density and grid based it supports density decaying and monitors evolving behaviour for real time data streams. does not support handling of multiple dimensional data pod – clus [14] model based supports concept evolution and data fading computation and updating of pairwise distance takes a lot of time in data streams birch [15] hierarchical overcomes the inability to undo what was done in previous step does not perform well if the cluster is not in spherical shape. spe-cluster [16] partitioning based solve the problem of specifying the number of cluster. cannot discover arbitrary shape clusters. cobweb [17] model based it identifies the outliers effectively. it does not provide compact representation. data stream input in the form of small chunks is called data chunks. here a windowing concept is used because stream data are huge. data are fitted into a window frame and then passes ahead. different parameters like window size, threshold value, and radius are set by the user. after that, an one-way online process is used in which data chunks are fitted into the window and then the clustering process is applied. in the online phase, micro-clustering is performed and basic dbscan algorithm is used. the micro clustering is done by the selection of the centroid with nearest data point's i.e. cluster mean value of object. the output of these will be the data points with k cluster and n objects. the clustering is done based on distance. these will now be input to the offline phase with the parameters like core distance, epsilon and fixed value of min point, generating distance. the proposed scheme is depicted in figure 1. in the offline phase, the stream optics algorithm is used for clustering. macro clustering takes place and the data points form clusters of good quality. two phase work is required because due to the nature of data streams. points which have not yet been part of any clusters are distinguished by giving them weight. for every new iteration, this value will be incremented to make sure it is part of real outlier. based on the application of a threshold value, points termed as real outliers are detected. thus the node or the data points, which are outliers, will be pruned off which will reduce the memory consumption and the time taken for generation of the potential clusters. these will improve the engineering, technology & applied science research vol. 7, no. 2, 2017, 1478-1481 1480 www.etasr.com shukla et al.: a modified approach of optics algorithm for data streams purity of the potential clusters. for each threshold value set the whole dataset is been checked with the prime motto of maintaining the quality of the clusters. the algorithm is broken down in steps in figure 2. iii. results & discussions various parameters like cluster purity, number of clusters, ssq, threshold, memory and time consumption are evaluated. then these evaluated parameters are used for comparison and performance evaluation. net beans is used for the simulation studies in our research work. the forest cover type data set and sensor data set are used for evaluation and algorithms are computed for 50000 and 100000 data records respectively. different threshold values were tested and an optimum value was chosen in each case (3 for the the forest cover type data set and 14 for the sensor data set). tables ii to v sum up the results. fig. 1. the proposed scheme fig. 2. the proposed algorithm table ii. overall result summary of forest cover dataset with different parameter at various threshold values before pruning. threshold value maximum time (sec) maximum memory (mb) number of cluster sum of squared error no. of noise points purity 1 44427 171.46 22 1.31 19 93.02 2 44327 163.09 23 1.21 19 92.13 3 44162 138.99 21 1.46 12 91.29 4 43966 128.56 25 1.35 15 91.35 5 44636 137.21 24 1.42 10 93.82 6 44172 138.18 21 1.38 17 92.95 table iii. overall result summary of forest cover dataset with different parameter at various threshold values after pruning threshold value maximum time (sec) maximum memory (mb) number of cluster sum of squared error no. of noise points purity 1 43783 145.46 16 1.15 23 95.53 2 43643 132.09 16 1.02 22 95.68 3 43580 110.99 13 1.02 17 95.87 4 43480 100.56 14 1.00 21 95.17 5 43939 109.21 14 1.06 16 95.42 6 43172 111.18 9 1.18 20 95.34 table iv. overall result summary of sensor dataset with different parameter at various threshold values before pruning threshold value maximum time (sec) maximum memory (mb) number of cluster sum of squared error no. of noise points purity 2 15499 53.06 21 1.27 17 92.33 10 15370 57.06 23 1.47 20 93.80 13 15434 52.06 25 1.33 13 91.08 14 15498 58.06 24 1.09 16 93.61 15 15156 54.06 25 1.29 12 93.33 2 15499 53.06 21 1.27 17 92.33 table v. overall result summary of sensor dataset with different parameter at various threshold values after pruning threshold value maximum time (sec) maximum memory (mb) number of cluster sum of squared error no. of noise points purity 2 14938 27.06 17 1.02 19 95.74 10 14797 26.21 9 1.09 24 94.94 13 14704 27.12 7 1.07 19 95.52 14 14938 27.06 8 1.02 19 96.29 15 14578 27.06 6 1.08 16 95.31 16 14704 26.08 6 1.07 15 94.96 iv. conclusion handling data streams shows increased complexity due to their constant, huge and potentially infinite nature. working with data streams challenges the memory, space, time and handling changes along with speed and multiple source of data generation. thus, the algorithms used for offline data mining and management may prove insufficient in such application and variations may be required. such a variation of the optics algorithm is proposed in this paper. simulations are performed, results are discussed and an overall improvement is documented. references [1] l. o’callaghan, n. mishra, a. meyerson, s. guha, r. motwani “streaming-data algorithms for high-quality clustering”, 18th engineering, technology & applied science research vol. 7, no. 2, 2017, 1478-1481 1481 www.etasr.com shukla et al.: a modified approach of optics algorithm for data streams international conference on data engineering, pp. 685-694, february 26march 1, 2002 [2] c. c. aggarwal, j. han, j. wang, p. s. yu, “a framework for clustering evolving data streams”, international conference on very large databases, vol. 29, pp. 81-92, 2003 [3] c. c. aggarwal, j. han, j. wang, p. s. yu, “a framework for projected clustering of high dimensional data streams”, thirtieth international conference on very large data bases, vol. 30, pp. 852-863, 2004 [4] f. cao, m. ester, w. qian, a. zhou, “density-based clustering over an evolving data stream with noise”, siam international conference on data mining and secure data management (sdm), vol. 6, pp. 328-339, 2006 [5] li-xiong, h. hai, g. yun-fei, and c. fu-cai, “rdenstream: a clustering algorithm over an evolving data stream”, international conference on information engineering and computer science, pp. 1-4, december 1920, 2009 [6] k. udommanetanakit, t. rakthanmanon, k. waiyamai, “e-stream: evolution-based technique for stream clustering”, lecture notes in computer science, vol. 4632, pp. 606-616, 2007 [7] c. dharni, m. bnasal, “an improvement of dbscan algorithm to analyze cluster for large datasets”, ieee international conference on mooc innovation and technology in education (mite), pp. 42-46, 2013 [8] m. ankerst, m. m. breunig, h. kriegel, j. sander, “optics : ordering points to identify the clustering structure”, acm sigmod, vol. 28, no. 2, pp. 49-60, 1999 [9] l. wan, w. k. ng, x. h. dang, p. s. yu, and k. zhang, “density-based clustering of data streams at multiple resolutions”, acm transactions on knowledge discovery from data (tkdd), vol. 3, no. 3, pp. 1-28, 2009 [10] i. ntoutsi, a. zimek, t. palpanas, p. kröger, h. kriegel, “density-based projected clustering over high dimensional data streams”, society of industrial and applied mathematics (siam) international conference on data mining, pp. 987-998, 2012 [11] a. amini, t. y. wah, “dengris-stream: a density-grid based clustering algorithm for evolving data streams over sliding window”, international conference on data mining computer engineering, pp. 206211, 2012 [12] y. cao, h. he, h. man, “somke: kernel density estimation over data streams by sequences of self-organizing maps”, ieee transactions on neural networks learning systems., vol. 23, no. 8, pp. 1254-1268, 2012. [13] a. amini, t. y. wah, “leaden-stream: a leader density-based clustering algorithm over evolving data stream”, journal of computer communication, vol. 1, no. 5, pp. 26-31, 2013 [14] p. p. rodrigues, j. gama, j. p. pedroso, “odac: hierarchical clustering of time series data streams”, ieee transaction on knowledge data engineering , vol. 20, no. 5, pp. 615-627, 2008 [15] t. zhang, r. ramakrishnan, m. livny, “birch: an efficient data clustering databases method for very large”, acm sigmod record, vol. 25, no. 2, pp. 103-114, 1996 [16] e. keogh, s. chu, d. hart, m. pazzani, “an online algorithm for segmenting time series”, international conference on data mining, pp. 289-296, 2001 [17] kavita, p. bedi, “clustering of categorized text data using cobweb algorithm”, international journal computer science and information technology research, vol. 3, no. 3, pp. 249-254, 2015 [18] m. khalilian, n. mustapha, “data stream clustering: challenges and issues”, international multi conference of engineers and computer scientists, vol. 1, hong kong, march 17-19, 2010 [19] a. amini, t. y. h. saboohi, “on density-based data streams clustering algorithms:a survey”, journal of computer science and technology, vol. 29, no. 1, pp.116-141, 2014 [20] m. shukla, y. p. kosta, p. chauhan, “analysis and evaluation of outlier detection algorithms in data streams”, ieee international conference on computer, communication and control (ic4), pp. 1-8, september 1012, 2015 [21] p. chauhan, m. shukla, “a review on outlier detection techniques on data stream by using different approaches of k-means algorithm”, ieee international conference on advances in computer engineering and applications (icacea), pp. 580-585, 2015 [22] m. kamber, j. han, data mining: concepts and techniques, second edition, elsevier, 2001 engineering, technology & applied science research vol. 8, no. 2, 2018, 2834-2838 2834 www.etasr.com ibrahim: accuracy of bit error probability for w-cdma system using code tree accuracy of bit error probability for w-cdma system using code tree anwar hassan ibrahim department of electrical engineering qassim university, college of engineering buraydah, saudi arabia dr.anwar@qec.edu.sa abstract—w-cdma is radio access utilized for 3g cell frameworks. a code tree allocation scheme is one of the most explored channelization techniques, used to improve system performance and capacity through adjustable data rates. this work investigates the accuracy of bit error probability for wcdma system using code tree orthogonal variable spreading factor (ovsf) codes, compared to pseudo-noise (pn) codes under various noise conditions, such as additive white gaussian noise (awgn) and random noise (rn). results are carried out theoretically and by computer simulation. the simulation includes the scenario of simple model representation for wcdma system. it was concluded that, the system has better performance using ovsf compared with pn code under different noisy channels. keywords-w-cdma; ovsf code; pn code; awgn; rn; bit error probability (bep) i. introduction data spreading in w-cdma systems is done by the application of a signal independent code. the code choice affects the framework execution. the more extended the code, the higher the preparations picked up, which empowers the system to permit more clients in the framework. then again, a bigger preparation, infers the use of more transfer speed in wcdma [1]. a good w-cdma planning model for communications development reduces the complexity of solutions in order to integrate them into the same channel by using code division multiple access (cdma), data, and web services. 3g wireless standards use w-cdma to meet high data rates and variable rate requirements. the proposed scenario initially attempts to assign request codes to the system, and then tries to allocate them to user access. in order to achieve high bit error rate accuracy [2, 3], different data must be used by different user connections with variable operation rates and ovsf. in terms of implementation, it is better to have different spreading factors from the same branch of the tree to avoid chip level buffering [4]. the more the channel is used, the more noise is produced [5]. furthermore, the scenario studies the efficiency performance of ovsf code tree in wcdma system under two different data under noise comparing to pn code. w-cdma is a flexible system, supporting variable data rates and services. the flexibility of using ovsf as channelization code increases the ability of supporting variable data rates for each transceiver and makes simpler hardware usage [6]. ii. ovsf code tree a. orthogonality the tree structure code method is usually assigned to certain users with different data rates orthogonally. the design of ovsf codes has different lengths on different levels and different spreading factors, related to the information rate multiplied by the entire code word [7]. two codes are supposed to be orthogonal when their inner product is zero. for example, the characterized code of (1, 1, 1, 1) and (1, 1, -1, -1) are orthogonal. their product is zero as shown below: (1*1)+(1*1)+(1*-1)+(1*-1)=0 b. code tree definition ovsf codes have been introduced for 3g communication systems. spectrum spreading is attained by plotting each bit (1 or -1) into an allocated code categorization. figure 1 shows the tree structure [8]. ovsf codes are continuously powering data rates with respect to the lowest simple rate. the potential rates supported are: rb, 2rb, 4rb, 8rb, etc, with rb meaning “rate bit”, and the break becomes greater as the rate growths. in particular cases it may over-serve by a greater rate [6]. fig. 1. ovsf code structure c1(1) = [1] c2 (1) = [c1(1) , c1(1)] = [1,1] c2 (2) = [c1(1) , c1(1) ] = [1,-1] c4 (2) = [c2(1) , c2(1) ] = [1,1,-1,-1] c4 (3) = [c2(1) , c2(1) ] = [1,-1, 1, -1] c4 (4) = [c1(1) , c1(1) ] = [1,-1,-1,1] c4 (1) = [c2(1) , c2(1) ] = [1,1,1,1] . … … … … . . cn (1) = [cn/2 (1) , cn/2 (1)] cn (2k 1) = [cn/2 (k) , cn/2 (k)] cn (2k) = [cn/2 (k), cn/2 (k)] cn (n) = [cn/2 (n/2), cn/2 (n/2)] … . … . engineering, technology & applied science research vol. 8, no. 2, 2018, 2834-2838 2835 www.etasr.com ibrahim: accuracy of bit error probability for w-cdma system using code tree c. code tree algorithm different distribution code factors, means different code extents. the general idea is to enable the merging of changed messages with alternative spreading factors and retain their orthogonality. code dimensions are needed to be orthogonal. the analysis below shows the workability of the algorithm. the process of the first section in the tree is 1. for each level, there are two conceivable sub-levels, represented as top and bottom sub divisions. the top sub division is constructed by repeating the root of the sub-division twice. so in this case the top sub-section of (1) would be (1, 1) and the bottom sub division is assembled by self-inverse of (1), and it would be (1, -1). at each section, all the codes are the rows of a hadamard matrix with the fundamentals mapped to polar arrangement. the type of code tree depends on the chosen code through the design in figure 2. if sf=8, the other level can’t be used [9]. iii. pn-code algorithm a pseudo-noise (pn) used for direct sequence spreading code consists of nds components, named chips. these chips require 2 values: either -1/1 or 0/1. the bit classifications are used unless specified otherwise. each data symbol is mutual with a single comprehensive pn-code, the direct sequence is identical to the code-length. pn sequences are periodic structures that have similar behavior with noise [10]. this code is generated by using shift registers, module adders represented by xor gates and feedback loops. figure 2 shows the scenario for generating pn code. fig. 2. shift register of pn code generation the extreme dimension of a pn sequence is defined by the size of the register and the structure of the feedback system. an n bit sequence created can consist of up to 2n different groupings of zeros and ones. meanwhile the feedback system achieves linear processes, if all the inputs of the flip-flops are zero, the result of the output from the feedback system will also be zero. consequently, the entirely zero grouping will always stretch zero output for all following clock cycles, so the system avoids including it in the sequence. hence, the determined length of several pn sequences is 2n-1 and classifications of that extent are called maximum-length arrangements or msequences. this became preferable. feedback outlines for msequences are organized and can be found in functions created in matlab. the signal is usually multiplied by a pn code. a pn code is a classification of chips valued as -1 and 1 (polar sequence) or 0 and 1 (non-polar sequence) and has similar noise properties. to create a pn code in the proper way, at least one shift-register should be actively fast. as long as the length of the code in such a shift-register is n equal, the result in (1) will represent the period nds of the above mentioned scenario for the length of the code: nds=2n-1 (1) this code is used to determine the frequency spectrum that the produced signal will lodge. it regulates and controls the spreading arrangement of the system. iv. proposed system the system model is illustrated in figure 3. fig. 3. illustrattion fo the proposed system model this section details the developed simulation methodology to evaluate the performance of ovsf code tree. the simulation results demonstrate the code performance for several configurations in different channel environments, which are given. the system consists of two channels where users fed their data into a diversity receiver [11]. in the receiver, the transmitted data are recovered and checked for errors [12]. the simulation study investigates a scenario with undesired channel condition, aiming to examine the refusal of the ovsf code tree to accept this condition and to calculate the probability of error. v. bit error probability an important application of spread spectrum structures is multiple access infrastructures, in which several users have to access the channel [13]. the probability of error performance in the receiver part is presented. the antenna component separation and the functioning environment parameters (such as random noise (rn) and additive white gaussian noise engineering, technology & applied science research vol. 8, no. 2, 2018, 2834-2838 2836 www.etasr.com ibrahim: accuracy of bit error probability for w-cdma system using code tree (awgn) generation), in overall space-path multiplicity expanse can be directly assessed. every one of spreading waveforms is assigned to one equivalent bit vectors. consequently, each independent message bit to be transferred on the n-th signaling interval is allocated to a defined transmit antenna. the number of n-th user's data transmitted by transmit antenna k on the n-th signaling is multiplied by spreading waveform . the composite channel improvement among transmit antenna k and receive antenna j on the n-th signaling interval ∝ . different users are allocated single sets of spreading waveforms [14] w = c t − nt (2) = 1, 2, … . t and (cmx= ∅ when m≠1) the designation for these decision variables and how they are joined together is the subject of the spreading technique used by the transmitter. the kth matched filter output on receive antenna j and signaling interval n is and the xth channel gain matrix, then the decision variables of are given by equation 3. u = ∑ e b ∝ + n , k = xn k ≠ x (3) in addition, we make the usual assumption that power control is used to enable all users’ transmissions that reached the user of interest with the same power. under these conditions, it can be shown, that the receiver bit error probability can be approximated [15]. )( snrqpe  (4) where 2 2 ( ) ( )e a tb eb p q q no no   (5) 11( ) 3 2 k no snr n eb   (6) in which k is the number of users and n is the number of chips per bit (the processing gain). the main idea of this paper is to identify the system implemented to assess the performance of the ovsf code tree and pn code under channel environment. we are assuming that the same power control can be used by all users. under these conditions, it provides the receiver bit error probability calculated approximately in simple system built. therefore, it characterizes the number of chips contained in one data bit. complex processing gain (pg) required more spreading factor. orthogonal variable spreading factor code tree does not have the greatest spreading behavior and the process of spreading depends on user data rate. nevertheless the pn sequences need to have more spreading factor, since their power spectral density is focused on a small number of the selected discrete frequencies. vi. results figures 4-5 show the accuracy of the bit error probability. figure 4 shows the pe versus eb/no for the constant processing gain and varying number of users. it is found that the error is approached for every case shown. for example, if 8 users are active and pe of 10-2 is desired, it cannot be achieved no matter what eb/no is used. this is one of the drawbacks of w-cdma by using code tree or pn code. the average error in w-cdma system, by using ovsf code tree, will be approximately less than the pn code. it is also found that, with more users and larger processing gain, the more accurate the approximation. the other advantage of ovsf code tree is that the variable data give the user an opportunity to introduce the system as well as if it were in good condition. figure 4 explains pe versus eb/no for wcdma system using pn code. the number of users is 4 and the processing gain=4. figure 5 shows pe versus eb/no for wcdma system using orthogonal variable spreading factor under distributed users (the number of users is changing when the processing gained is constant). fig. 4. bep for the system using pn code fig. 5. user distribution for given bep figures 6-9 give detail comparison between the original data transmitted and received for both types of noise (awgn and rn) for ovsf and pn. as a result of adding awgn to the w-cdma system with ovsf code, a 25% error in the transmitted data is detected at the receiver as shown in figure 6. in figure 7, rn is added to the w-cdma system with ovsf code tree and a 18.75% error occurs. figure 8 shows a comparison between the original transmitted and received data when adding rn to the w-cdma system with pn code. in that case a 31.25% error in the data transmitted was detected at engineering, technology & applied science research vol. 8, no. 2, 2018, 2834-2838 2837 www.etasr.com ibrahim: accuracy of bit error probability for w-cdma system using code tree the receiver. adding awgn to the w-cdma system with pn code, a 37.5% error in the data transmitted was detected by the receiver as shown in figure 9. table i shows the summarization of data error occurrence in the receiver without filtering and using different codes and different noises. table i. clarify error occurrence in the receiver type of code type of noise error occur ovsf awgn 25% rn 18.75% pn awgn 37.5% rn 31.25% fig. 6. data transmitted vs data received for ovsf and awgn fig. 7. data transmitted vs data received for ovsf and rn fig. 8. data transmitted vs data received for pn and rn fig. 9. data transmitted vs data received for pn and awgn vii. conclusion results have shown that in the orthogonal variable spreading factor, the error is obtained by applying awgn and rn were 25% and 18.75%, respectively. this indicates that rn effect is less than the awgn effect. however, in the pn, the error obtained by applying awgn and rn are 37.5% and 31.25% respectively confirming that, rn effect is less than awgn effect in the system. to conclude, the lowest effect of noise channel in the system will be achieved by applying the rn introduced by ovsf tree. the low cross-correlation standards between the codes is easy to the strain of a data message detection. references [1] p. singh, g. soni, “performance analysis of wcdma link using qpsk & qam modulation schemes based on vector signal transceiver 5644r & labview 2012”, international conference on control, instrumentation, communication and computational technologies (iccicct), kumaracoil, india, december 16-17, 2016 [2] m. matthe, n. michailow, i. gaspar, g. fettweis, “influence of pulse shaping on bit error rate performance and out of band radiation of generalized frequency division multiplexing”, international conference on communications workshops, sydney, nsw, australia, pp. 43–48, june 10-14, 2014 [3] n. michailow, s.krone, m. lentmaier, g. fettweis, “bit error rate performance of generalized frequency division multiplexing”, 38th ieee vehicular technology conference (vtc fall), quebec, canada, september 3-6, 2012 [4] p. bah1, a. farrago, i. chlamtac, “resource assignment for integrated service in wireless atm networks”, international journal of communication systems, vol. 11, no. 1, pp. 29-41, 1998 [5] m f. alsharekh, m. islam, a. h. ibrahim, r. khan, s. habib, “bit error rate performance of rfid signal in sdr communication”, journal of applied sciences, vol. 16, no. 4, pp. 161 -166, 2016 [6] t. minn, k.-y. siu, “dynamic assignment of orthogonal variable spreading factor codes in w-cdma”, ieee. journal on selected areas in communications, vol. 18, no. 8, pp. 1429-1440, 2000 [7] n. cardona, a. navarro, “w-cdma capacity analysis using gis based planning tools and matlab simulation”, first international conference on (conf. publ. no. 471) 3g mobile communication technologies, london, uk, march 27-29, pp. 230-234, 2000 [8] c. w. wu, r. q. huang, “ovsf code management schemes on ad hoc networks”, ieee international conference on communications (ieee cat. no.04ch37577), paris, france, vol. 7, pp. 4152-4156, june20-24, 2004 [9] r. g. winch, telecommunication transmission systems: microwave, fiber optic, mobile cellular radio, data, and digital multiplexing, mcgraw-hill, inc., ny, usa, 1993 engineering, technology & applied science research vol. 8, no. 2, 2018, 2834-2838 2838 www.etasr.com ibrahim: accuracy of bit error probability for w-cdma system using code tree [10] f. liu, a.-j. chen, c.-b. xiang, h.-j. song, “the intelligent monitoring method based on spectral correlation pseudo wcdma”, 4th international conference on computer science and network technology, harbin, china, pp. 1294-1298, december 19-20, 2015 [11] r. e. ziemer, w. h. tranter, principles of communications systems modulation and noise, john wiley & sons, 2014 [12] c. d'amours, a. o. dahmane, “bit error rate performance of a mimocdma system employing parity-bit-selected spreading in frequency nonselective rayleigh fading”, international journal of antennas and propagation, vol. 2011, article id 516929, 2011 [13] m. shen, g. li, h. liu, “effect of traffic channel configuration on the orthogonal frequency division multiple access downlink performance”, ieee transactions on wireless communications, vol. 4, no. 4, pp. 1901-1913, 2005 [14] z. deng, y. liu, j. liu, x. chen, a. argyriou, z. xu, s. ci, “crossnetwork and cross-layer optimized video streaming over lte and wcdma downlink”, ieee symposium on computers and communication (iscc), messina, italy, pp. 868-873, june 27-30, 2016 [15] y.-c. tseng, c.-m. chao, “code placement strategies for wideband cdma ovsf code tree management”, ieee transactions on mobile computing, vol. 99, no. 4, pp. 293-302, 2002 microsoft word 27-2939_s_etasr_v9_n5_pp4724-4728 engineering, technology & applied science research vol. 9, no. 5, 2019, 4724-4728 4724 www.etasr.com al-shammari & darwish: in-depth sampling study of characteristics of vehicle crashes in saudi arabia in-depth sampling study of characteristics of vehicle crashes in saudi arabia naif khalaf al-shammari mechanical engineering department, university of hail, hail, saudi arabia naif.alshammari@uoh.edu.sa saied mohamed hassan darwish industrial engineering department, king saud university, riyadh, saudi arabia darwish@ksu.edu.sa abstract—it is imperative for any traffic safety enhancing effort to collate and analyze detailed data about crashes. this article describes a study that investigated all aspects related to motor vehicle crashes resulting in human injuries or deaths in riyadh. the database consisted of 295 collisions involving 331 vehicles, 596 fatalities (car passengers and pedestrians) and 2,454 injuries with abbreviated injury scale (ais) ≥ 1. results show that only 15.1% of all vehicle occupants were wearing seatbelts at the time of collision which is reflected in having most injuries occurring to upper parts of the body and the spine. it is also reflected in a high incidence rate of 0.22 fatalities per crash. the average age of victims was 33 years with three quarters of them being males. results also show that human actions, like reckless driving, over speeding, and sudden lane deviations were the causes of most collisions. it is concluded that in order to improve traffic safety conditions in riyadh and in the whole country, a change in driving culture of all road users is needed. this can only come with improved awareness of the risks involved among road users, better law enforcement and other engineering and hi-tech countermeasures like smart red lights. keywords-motor vehicle crashes; riyadh; casualties; spinal injuries; driving behavior; injury prevention i. introduction and background the kingdom of saudi arabia (ksa) is located in southwestern asia and is the largest country in the middle east. it occupies about the fourth-fifths of the area of the arabian peninsula with a total area of 2,250,000km 2 [1] and an estimated population of 34.14 million by the end of 2019 [2]. the oil boom experienced in saudi arabia over the past seventy years resulted in a sharp increase in living standards and massive urban development. this inevitably led to a significant increase in the asphalted road network length from a few thousand kilometres in mid-twentieth century to currently more than 71,500km. the number of motor vehicles has also increased from 144,000 cars in 1970 to almost 19 million with approximately 800,000 vehicles being imported every year [2, 4]. this increase in living standards has also resulted in a large increase in the number of traffic crashes and, subsequently, in a tragic jump in the number of deaths due to these crashes. it is estimated that road crash deaths account to 6.53% of the total deaths in saudi arabia [3]. also, about one quarter of all cases transported by the saudi red crescent society (srcs) ambulances over the last 20 years were due to road crashes [8]. the official saudi annual average mortality rate from road crashes for the period of 2010-2018 is estimated to be 19.25 per 100,000 population [2, 7], which is among the highest in the world [5]. moreover, the rank of saudi’s fatality rate based on its motorization level (vehicles/population) is found to be 11.23 which is approximately three times higher than the average of developed countries [9, 20]. furthermore, an estimated loss of between 2.2% and 4.7% of the national income due to traffic crashes has been suggested for saudi arabia [10, 11]. this deteriorating situation poses a serious threat and has a serious negative effect on economic growth, especially as the majority of losses are among the younger generation knowing that the average age of drivers in saudi arabia is 26.7 years [12, 13]. the problem of road crashes has attracted significant research in the last few decades in most developed countries resulting in a reduction of the size of the problem [21-23]. however, one of the most serious problems facing traffic safety improvement effort in most of developing countries such as saudi arabia is the lack of epidemiological studies that analyze the extent and the gravity of this problem [5]. conducting in-depth prospective or retrospective studies involving extensive data collection are also essential in developing safety regulations and programs aiming to reduce road crashes and to minimize the resulting human and economic loss [13, 14, 20]. this study comes to fill in some of these gaps in that it aims to do an indepth retrospective analysis of crashes that led to human losses or injuries in riyadh over a period of 18 months. ii. methodology this study was carried out in the city of riyadh, the capital of saudi arabia, and surrounding region (known as greater riyadh area). riyadh is a large metropolis with an area of 1782km 2 and a population of approximately 8 million people, around a quarter of the total population of saudi arabia [2]. over the last 10 years, the city of riyadh recorded an average annual population growth rate of 3.53%. riyadh has a modern road network system but its traffic management system is not fully developed. out of 957,125 new registered vehicles in saudi arabia in 2016, 129,513 were found in the greater riyadh area. it is estimated that there are about seven million trips daily in the city, with over 85 percent by private car. bus trips only represent two percent of the total, whilst goods movements make up the remainder [4, 16]. the study corresponding author: naif khalaf al-shammari engineering, technology & applied science research vol. 9, no. 5, 2019, 4724-4728 4725 www.etasr.com al-shammari & darwish: in-depth sampling study of characteristics of vehicle crashes in saudi arabia population consisted of motor vehicle collisions in greater riyadh area that resulted in an injury of ais ≥ 1 of one or more vehicle occupant(s) and/or pedestrian(s) between september 2017 and february 2019 (18 months). the data collection procedure entailed performing an in-depth technical examination of vehicles, extracting related information from police records and collecting detailed injury information from medical archives. each vehicle was inspected and photographed extensively both internally and externally. where possible, the damage profile of the vehicle was measured so that severity indicators known as collision delta-v (∆v) and/or equivalent test speed (ets) were used [17]. the rollover speed and impact speed on pedestrians were reconstructed based on the physical evidence present at the scene. for pedestrian crashes, the procedure developed by nhtsa [18] and ccis [14, 15] was followed. impact direction was classified based on the standardized collision deformation classification (cdc) code as recommended by ‘sae practice j224b’ [6]. this method used the principal direction of force of the impact (pdof). directions were front (pdof = 1, 11 and 12), side (pdof = 2, 3, 4, 8, 9 and 10) and rear (pdof = 5, 6 and 7). vehicle body types were classified into two categories. the first category included passenger cars, light trucks and vans and the second included sport utility vehicles (suvs). vehicles were also classified according to curb weight (small for weight less than 1,089kg, mid-size cars weighting 1,090 – 1,587kg, or large weighting more than 1,588kg). information including age, gender, restraint use, and seating position was obtained for each attended casualty. the use of airbags and seatbelts was primarily determined through crash scene vehicle inspection, police records, and interviews. details of the injuries were obtained from medical and emergency department records. injury severity was classified according to the ais rev 2005 [19]. descriptive statistics, bar chart, pearson χ 2 test, one-way analysis of variance and association analysis (cross tabulation) were used, where applicable, to present and assess the data. also, mann-whitney u and median tests were used for comparisons of means. spss version 23 was used for this purpose. significance level was set at 0.05. iii. results and analysis in saudi arabia, the number of road accidents and the resulting human and financial losses are still enormous. the official statistics show that 22,545 people were killed and 69,018 were injured as a result of the 533,380 accidents that happened on saudi roads during the last three years [7]. the average fatalities and injuries per accident were 0.22 and 0.68 respectively. this means that one person dies and 3 people get injured for every 4 accidents. table i presents the recent statist of accidents, fatalities and injuries of road traffic accidents in saudi arabia. table i. vital statistics of rtas in ksa durin g 2017-2019 year non-fatal accidents fatal accidents serious injuries fatalities 2017 511,649 38,120 21,731 9,031 2018 438,068 33,199 22,420 7,489 2019 327,597 30,217 24,867 6,025 total 1,277,314 101,536 69,018 22,545 over the study period, a total of 295 collisions involving a total 331 motor vehicles have qualified to be included in the current study. in those 295 collisions, there were 596 casualties including 568 vehicle passengers and 28 pedestrians who received between them a total of 2,454 injuries (ais ≥ 1). a. collision characteristics figure 1 presents the type of collisions in this study. out of those 295 collisions, 61.2% were collisions between vehicles, 14.54% due to colliding with fixed objects, 10.9% due to motor vehicle rollover, 10.9% due to motor vehicles hitting pedestrians and 2.9% due to colliding with camels. maximum number of accidents was recorded on thursdays and minimum on sundays. this may be attributed to the increase in activities during weekend and decrease suddenly after. figure 2 shows the severity of accidents for various impacts. police records show that 6% of the crashes as slight, 53.5% as serious, and 40.5% as fatal crashes. crosstabulating severity of crashes over impact reveals that almost all fatal and serious crashes had either frontal or lateral impact. it was found that there is an association between the severity of accident and the type of impact. the majority of accidents happened within the carriageway. the site of accident does not affect the type of impact. almost 61% of the accidents were recorded on the highways in urban areas. there is no statistically significant relationship between impact direction and the area of accident. most of frontal impacts (62%) and side impacts (73%) frequently occurred on straight roads and slope layouts. there was a statistically significant relationship between the type of impact and road layout. the distribution of weather condition at the time of crash is presented in table ii. fig. 1. distribution of collisions by type table ii. distribution of crash by weather condition weather conditions percentage fine no high winds 68.8 dust 12.7 raining, no high winds 11.7 raining and high winds 4.4 fine and high winds 1.8 fog or mist 0.6 the majority of accidents occurred in fine weather conditions (69%). the weather conditions had a significant effect on the types of impacts. most severe crashes due to traffic accidents occurred on lit roads or during day time. pedestrian crossing facilities are crucial as some of the areas engineering, technology & applied science research vol. 9, no. 5, 2019, 4724-4728 4726 www.etasr.com al-shammari & darwish: in-depth sampling study of characteristics of vehicle crashes in saudi arabia are reserved for parking, gardening, etc. and some areas should not be accessible by pedestrians. more than half of the pedestrian collisions occurred on the nearside of drivers. fig. 2. impact direction vs. severity of the accident b. vehicle characteristics there were 331 vehicles involved in the accidents considered in this study. the type of vehicle has the potential of playing an important role in causing accidents and their consequences. passenger cars form the vast majority of traffic crashes (87%). the direction or location of impact plays an important role on the severity and type of injury. figure 3 shows the distribution of types of impact for crashes between vehicles. it can be seen that frontal impact represents 62.6%, side impact 18.9%, top/bottom impact 10.9% and rear end impact 7.6%. fig. 3. direction of impact for vehicle crashes most of the vehicles were small size cars (55%) followed by medium size cars (41%). the statistical analysis showed that there is an association between the type of impact and vehicle size as presented in figure 4. hatchback was the motor vehicle with most traffic crash-induced injuries (60%). table iii shows the major causes attributed to the vehicle crashes in ksa. the causes have been categorized according to driver, vehicle, and road. the drive behavior was responsible about most of these accidents (93.80%), followed by technical defects (5.30%) and roads works (0.90%). the major causes of accidents by driver’s action were found to be careless driving (24%), over speeding (21.6%) and sudden deviation (16.6%) accounting for 61% of car accidents in this study. of the sampled vehicles, the unacceptable condition of tires, brakes, and lights accounted for 43%, 36%, and 8% of all vehicle faults respectively. analyzing tire-related collisions lead to aging defects, unacceptable tread depth and illegal tires being the most common types of defective tires contributing 37%, 21%, and 14% of tire-related collisions respectively. fig. 4. impact direction vs. type of vehicle table iii. distribution of crash causes crash cause percentage driver’s violations (93.80%) over speed 21.4 run traffic light 9.4 wrong overtaking 3.4 wrong u-turn 1.9 wrong parking 1.5 alcohol 4.4 falling asleep 0.6 exhaustion 1.1 careless driving 24.6 driving on the wrong side of the road 1.7 stop sign crossing 1.9 disobeying priority rules 3.4 sudden deviation 16.6 tailgating 0.4 recklessness driving 1.5 vehicular faults (5.30%) bad tires 2.28 brakes defects 1.90 lights faults 1.12 roads obstacles (0.90%) total 100% c. causlaty charatcteristics as stated earlier, the 295 crashes included in the current study resulted in 596 casualties. casualty medical details were collected from hospital records, emergency medical service providers and trauma centers. three quarters of injuries due to traffic crashes were males. the average age of the victims was 33.2 (stdev=17.3) years. people aged 15-44 years sustained the bulk of traffic crash-related injuries (66%). in this study, 568 occupants were included. figure 5 shows that the majority of injured occupants were drivers (54.2%) followed by front seat passengers (20.1%). only 15% of vehicle occupants who sustained an injury were restrained. restraint use was found to reduce significantly the injury severity. out of the 596 engineering, technology & applied science research vol. 9, no. 5, 2019, 4724-4728 4727 www.etasr.com al-shammari & darwish: in-depth sampling study of characteristics of vehicle crashes in saudi arabia casualties included in the current study, 57.7% were admitted to hospital, 6.7% were treated as outpatients, 24.9% died upon arrival to hospital and 10.7% died before admission (figure 6). out of those admitted to hospitals 71.6% had ais level of 2, 13.2% of 3 and 15.2% level or 4+. fig. 5. position of vehicle occupants during the crash fig. 6. place of death for victims in the study d. injury characteritsics most of injury details of the 596 casualties were collected from the medical records of the main hospitals in riyadh where the casualties were admitted and the severity of each injury was assessed using the ais scale. in total, there were 2,454 injuries (with ais > 1) and 596 casualties. table iv shows a summary of the severity of the injuries for each type of collision. as can be noted, 25.2% of injuries due to collisions with fixed objects and 23.1% of injuries due to collisions with other vehicles lead to injuries of ais ≥ 4. this reflects the greater risk of injury upon hitting a fixed object or a vehicle as compared to hitting a pedestrian (16.2%), in case of rollover (13.1%) and hitting a camel (13.1%). there were a total of 588 head injuries recorded. pearson χ 2 test revealed that there is a significant association between head injury severity and impact direction (p=0.001). most of severe head injuries (with ais ≥ 3), mainly believed to be injuries to the cervical spine, occurred in front and lateral impacts. it was found that most of the head injuries in frontal impact occur due to head contact with the windscreen and frame while in lateral impacts occur due to contact with the side rail above the window. it was also noticed that injuries to the cervical spine are mainly non-contact ones occurring due to high forces being transmitted to the spine. a total of 87 face injuries were recorded in the crashes analyzed in this study. as the vast majority of face injuries had ais ≤ 2, pearson χ 2 test result gave a non-significant relationship between face injuries and ais value (p > 0.05). also, there were 487 thorax injuries recorded. pearson χ 2 test revealed that there is a significant relationship between thorax injury severity and impact direction (p < 0.05) where most thorax injuries occurred in frontal and lateral impacts. the abdomen injuries were 400. the relationship between the abdomen injury severity and impact direction was examined. pearson χ 2 test revealed that there is no significant relationship between abdomen injury severity and impact direction (p > 0.05). it can be seen also that more than 80% of abdomen injuries had ais ≤ 3. in total, there were 329 recorded injuries to the limbs. cross tabulation of limb injury severity and impact type was found to be significant (p < 0.001) with lateral impact crashes resulting, generally speaking, in higher ais level than other crash types. table iv. distribution of severity of injuries accordin g to collision types impact ais 1 2 3 4 5 6 rollover n=239 36.8% 37.2% 12.9% 9.2% 3.3% 0.6% vehicle n=1597 28.5% 28.6% 19.8% 11.6% 6.8% 4.7% fixed object n=393 31.6% 24.4% 17.8% 12.4% 9.1% 4.7% pedestrian n=179 36.9% 37.4% 9.5% 8.3% 4.4% 3.5% camel n=4 69.6% 17.4% 2.2% 4.3% 4.3% 2.2% iv. discussion and conclusions high losses due to road traffic crashes in saudi arabia highlighted earlier can be reduced by introducing intervention measures. such measures have helped to decrease the rates of road crashes in motorized countries like uk, australia, sweden, and usa [5]. in this study detailed information on 295 collisions that occurred in the city of riyadh and resulted in an injury of ais ≥ 1 were analyzed. the results show that most of the casualties were young in age, 75% of them were males, and 54% were drivers. this can be attributed to the fact that this group of drivers accepts greater risk than others which is reflected through their lower rate of seatbelt use, higher rate of reckless driving and their greater proneness to disobey traffic rules than others [10, 12]. over half of the injuries sustained are head and cervical, and a significant number of those involve cord damage. thoracic and lumbar spinal injury is predominately fracture, without associated cord damage [9, 20]. while at all levels of injury severity, car to car impacts accounted for about 61% of the collisions in the study. it was interesting to note that a third of injuries (34%) were caused due to collisions with vehicles other than cars [15]. this suggests that these injuries may not be adequately addressed by the european or us test standards and tests since the mass and the height of the test barrier in either test cannot compare to the mass and height of a standard european/us heavy goods vehicle [17, 20]. also for crash characteristics, it was found that the majority of crashes leading to deaths or injuries in riyadh were from frontal impact, recorded on highways, in urban areas, in the presence of road light or sun light and on engineering, technology & applied science research vol. 9, no. 5, 2019, 4724-4728 4728 www.etasr.com al-shammari & darwish: in-depth sampling study of characteristics of vehicle crashes in saudi arabia straight roads, while they occurred in fine weather conditions. such findings can be further justified when reported causes of these crashes are considered [21-23]. moreover, only 15.1% of vehicle occupants were reported to be restrained in police records regarding the 568 casualties. this explains the high rates of upper body (mainly in head and thorax) injuries reported in hospital records of the same casualties. even injuries to the spine occurred, reportedly, as result of head contact during which a translational force is transmitted along the spine from the head [13, 20]. keeping in mind the good road network that exits in greater riyadh area, it is therefore concluded that human behavior is the main contributor to these crashes. although it was clear that human behavior is responsible for the majority of crashes, assessing crash vehicle characteristics revealed that some technical problems are also contributing to the high road crash rate. improper maintenance of tires and brakes as well as underinflated, illegal or ageing tires were the most commonly recorded crash causes related to vehicle characteristics, which is in-line with previous research studies. this study demonstrated several important aspects that should be addressed in order to improve the state of safety in saudi arabia. a detailed database would give strong indicators to policy makers as of the state of road safety and how the related issues are emerging. it is also recommended for future research work to incorporate crash analysis and reconstruction to better understand how crashes happen in saudi arabia and what can be done to minimize their number and severity. acknowledgment this study was supported by king abdulaziz city for science and technology general directorate of research grants program (grant number at-34-220). references [1] ministry of culture and information, the kingdom of saudi arabia: a welfare state, cultural affairs releases, ministry of culture and information, 2008 [2] gastat, “statistical yearbook for the years 1391-1439h (1970 2018), general authority for statistics (gastat), 2018 [3] a. s. al-ghamdi, road traffic accidents in saudi arabia: causes: effects, and solutions, riyadh: king abdulaziz city for science and technology, 1999 (in arabic) [4] ministry of transport, transportation statistics: annual publications of transportation statistics for the years 1391-1439h (19702018), ministry of transport, saudi arabia, 1970-2018 [5] who, global status report on road safety 2015, world health organization, 2015 [6] sae international, collision deformation classification j224_ j224_201702, sae, 2017 [7] ministry of interior, traffic statistics: annual publications of road accident statistics for the years 1391-1437h (19702016), ministry of interior, general traffic department, 2016 [8] srcs, first aids statistics: annual publications of saudi red crescent statistics for the years 1391-1439h (19702018), red crescent, ministry of health, saudi arabia, 2018 [9] n. k. al-shammari, “typical cases of crash reconstruction and injury casuation in saudi arabia”, national traffic safety conference 2019: (present and future), riyadh, saudi arabia, march 11-13, 2019 [10] h. a. mohamed, “estimation of socio-economic cost of road accidents in saudi arabia: willingness-to-pay approach (wtp)”, advances in management & applied economics, vol. 5, no.3, pp. 4361, 2015 [11] ada, “the economic cost of road traffic accidents in the kingdom of saudi arabia. riyadh”, the high commission for the development of arriyadh (ada). 2010 [12] k. m. sarma, r. n. carey, a. a. kervick, y. bimpeh, “psychological factors associated with indices of risky, reckless and cautious driving in a national sample of drivers in the republic of ireland”, accident analysis & prevention, vol. 50, pp. 1226–1235, 2013 [13] s. bendak, “compliance with seat belt enforcement law in saudi arabia”, international journal of injury control and safety promotion, vol. 14, no. 1, pp. 45-48, 2007 [14] a. m. hassan, r. guo, c. e. n. sturgess, y. hu, “road traffic accident data collection and analysis for road safety research”, 4 th international conference on traffic safety, changsa, china, 2005 [15] m. mackay, a. m. hassan, “age and gender effects on injury outcome for restrained occupants in frontal crashes: a comparison of uk and us data bases”, in: annual proceedings, association for the advancement of automotive medicine, vol. 2000 pp. 75-91, aaam, 2000 [16] ada, background of the riyadh public transport network, the high commission for the development of arriyadh (ada), 2016 [17] n. johnson, assessment of crash energy–based side impact reconstruction accuracy, msc thesis, virginia polytechnic institute and state university, 2011 [18] nass, crashworthiness data system, national accident sampling system, july 2016 [19] aaam, the abbreviated injury scale, 2015 revision, association for the advancement of automotive medicine, 2015 [20] n. k. al-shammari, motor vehicle spinal injuries: simulation and crash investigation, lap lambert academic publishing, 2012 [21] m. touahmia “identification of risk factors influencing road traffic accidents”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2417-2421, 2018 [22] a. detho, s. r. samo, k. c. mukwana, k. a. samo, a. a. siyal, “evaluation of road traffic accidents (rtas) on hyderabad karachi m-9 motorway section”, engineering, technology & applied science research, vol. 8, no. 3, pp. 2875-2878, 2018 [23] a. detho, s. r. samo, k. c. mukwana, i. a. memon, u. a. rajput, “proposed remedies to prevent road traffic accidents (rtas) on highways in pakistan”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3366-3368, 2018 autho rs profile dr. naif k. al-shammari holds a bsc and an msc in mechanical engineering from king saud university, saudi arabia, and a phd in biomechanics from the university of birmingham, uk. in 2005 he joined the birmingham automotive safety centre (basc). his current research interests focus on crash injury of real world accidents including biomechanics of impacts, vehicle collision performance, and epidemiology of traffic crashes. he has held the post of principle crash analyst and was working as a researcher in the co-operative crash injury study team (ccis) at the university of birmingham. he has published more than 17 papers and technical reports. his major fields of specialization are computer modeling, robotics and artificial intelligence. prof saied darwish got his phd in the area of industrial engineering from birmingham university, uk in 1987. he has a distinct inter-disciplinary background and has been working in the areas of computer aided design and finite element analysis. he has published more than 70 research papers in international journals and over 100 in various conferences. he holds 3 patents in various countries including the us, european union, china, singapore and japan while another 6 applications are in various stages of processing. prof. darwish has supervised 5 phd students, ~70 bsc/msc students for their thesis works and at present eleven students are working with him for their phd degrees. he is an active member of more than 15 international societies of mechanical and industrial engineers around the world. microsoft word 23-3054_s1_etasr_v9_n6_pp4996-5000 engineering, technology & applied science research vol. 9, no. 6, 2019, 4996-5000 4996 www.etasr.com al-zahrani: on the statistical distribution of packets service time in cellular access networks on the statistical distribution of packets service time in cellular access networks ali y. al-zahrani department of electrical and electronic engineering university of jeddah jeddah, saudi arabia ayalzahrani1@uj.edu.sa abstract—a cellular communication system is divided into two main parts, core network, and radio access network. this research is concerned with the radio access network part which consists of multiple-cells, each served by a central located base station. furthermore, the users in each cell are considered to be uniformly distributed inside the cell. in the downlink context, the users’ packets usually arrive at the base station via fiber optic and then are relayed to the users via radio waves of certain frequency/ies. the speeds of delivering users’ packets vary, depending on the users’ location. in this paper, the actual distribution of the service time over different users whose locations are uniformly distributed in a cell served by one base station is analytically found. simulation results are presented to validate the derived model. keywords-wireless network; cumulative distribution function; probability density function; packet service time; resource allocations i. introduction deploying a wireless system can be quite costly. therefore, vendors and operators do extensive simulations before deploying any system to make sure that it is going to work properly as anticipated, and hence the investment will pay off. a key issue for drawing useful insights out of these numerical experiments (i.e. simulations) is the accuracy of the models that represent different parts of the system. in the cellular radio access network (ran) where each cell is served by one central base station (bs), users are usually distributed within the cell according to a uniform distribution. in addition, the users’ packets arrive to the base station via fiber optic channels, and are relayed to the users via wireless radio channels [1, 2]. from queuing theory perspective, when the packets arrive at a service facility according to poison distribution (i.e. the packets interarrival time is an exponential random variable), and being serviced in a time that is exponentially distributed, then the resulted queue is denoted by m/m/1. m stands for “memoryless” which is a property of the exponential distribution, and 1 indicates the existence of only one server in the facility. this model is the simplest among different queue models [3]. bs may be looked at as the service facility which serves the incoming packets by relaying them to their respective users. this paper aims to show that the resulting queue in the bs cannot be m/m/1 as some researchers assume [4, 5]. since the backhaul of the bs is connected to a single reliable fiber optic channel, the inter-arrival time of the packets to the bs may be modeled as an exponential random variable [6]. on the other hand, the time required to send packets is a random variable, but cannot be modeled as exponentially distributed because these packets belong to many users with different channels to the bs. hence, the packets are delivered with completely different data rates. the main contributions of this paper are: • the statistical distribution of the service time required to deliver packets from the bs to the users is analytically derived. • a function for generating service time samples, which is a very useful tool for simulation purposes, is provided. • the statistical distribution of the service rate under the described system setup is also derived. • the impact of the derived service time distribution is highlighted from the queuing theory perspective. ii. system description in a typical cell of a radius r, as shown in figure 1, users are distributed within the cell according to a uniform distribution. hence, users generally experience different pathloss due to their different distances d from the bs. furthermore, since the bs backhaul is a reliable fiber optic link, the users’ packets arrive to the cell bs according to the poisson distribution with an average rate of λ packets per second. for simplicity, we assume that the considered bs has one frequency channel fc which is allocated/shared among users’ packets over time domain according to the first-in-firstout policy (fifo). considering the bs as the router which routes the arrived packets to their respective users, the service time required to send each packet depends on the channel gain from the bs to the packet’s destination. the channel gain g from a user distant from the bs by d (m) is � = � ���� �� , where � is a constant ( c = a� � � ������ , with �� being the overall antenna gain, and �� the signal wavelength), �� is the reference distance, and α is the pathloss exponent. finally, we assume the size of each packet is � bits. corresponding author: ali y. al-zahrani engineering, technology & applied science research vol. 9, no. 6, 2019, 4996-5000 4997 www.etasr.com al-zahrani: on the statistical distribution of packets service time in cellular access networks fig. 1. a radio access network iii. system analysis since the mobile users are uniformly distributed within the cell, the distance d from the base station to any randomly selected user is a random variable (rv) whose cumulative distribution function (cdf) can be found as follows. considering only the users with the cell, the probability that a typical user is within an area of radius � such that �� < � < � is given by: ��� ��!" ��$% !� !�&�!" !� ! &' �ℎ '' %��) % "" = * * + �, �+ �-.���/(�� − ���) = * 2/ + �+���/(�� − ���) solving the above equation yields the cdf of the distance from the bs the a randomly selete user: 45 (�) = 6[8 ≤ �] 45(�) = ; 0 '&� � ≤ ���=>��=?=>��= '&� �� ≤ � ≤ �1 '&� � ≥ � , (1) where � is any typical distance and � is the radius of the cell. thus, the average channel gain c from the base station to any randomly selected user is a random variable and can be defined as a function of the distance 8: c = � d��8 e�, therefore, the cdf of the channel gain can be found as [9]: 4�(�) = 6[c ≤ �] = 6 f� d��8 e� ≤ �g = 6[8�h/� ≥ �h/���] = 6 f8 ≥ ���h/��h/� g = 1 − 6 f8 ≤ �� d��eh/�g = 1 − 45 j�� d��e h�k substituting (1) into the last equation yields: 4�(�) = 1 − lmm n mmo 0 '&� �� � pq�h/� ≤ �� d���rs�t/ue=>��=?=>��= '&� �� ≤ �� �pq�h/� ≤ �1 '&� �� �pq�h/� ≥ � (2) after rearranging (2), we obtain the cdf of the channel gain of a randomly selected user as follows: 4�(�)= = lmn mo 0 '&� � ≤ � ���? ��1 − ��=vp=/u>q=/uwq=/uv?=>��=w '&� � ���? �� ≤ � ≤ �1 '&� � ≥ � (3) assuming the system applies capacity achieving code, the throughput of a given user, whose channel gain is g, will be x = y"&�� �1 + [q\]�� , where ^ is the a constant transmit power, y is the channel bandwidth, and _� is the noise singlesided power spectral density. furthermore, the service time required to transmit one packet of l bits over one frequency band, form the bs to a randomly selected user is a random variable ` = ab. the cdf of the service time 4c(�) is derived as follows: 4c(�) = 6[` ≤ �] = 6 d �y "&�� �1 + ^cy_�� ≤ �e = 6 f �y� ≤ "&�� d1 + ^cy_�eg = 6 fc ≥ d2 a\h − 1ey_�^ g = 1 − 6 fc ≤ d2 a\h − 1e y_�^ g ⟹ 4c(�) = 1 − 4� j�2 klm − 1�\]�[ n (4) substituting (3) into (4) yields the cdf of the service time over one frequency channel as shown below: fp(t) = lm mm n mmm o 0 for t ≤ uvwxy=�hz {|}~�� k �=�>�(�)�(�) for uvwxy=�hz {|}~�� ≤ t ≤ uvwxy=jhz{|d��� e�}~� k 1 for t ≥ u vwxy=jhz{|d��� e � }~� k (5) where � = ��=?=>��=, and ℎ(�) = �2 klm − 1� =u �\]� �=u. engineering, technology & applied science research vol. 9, no. 6, 2019, 4996-5000 4998 www.etasr.com al-zahrani: on the statistical distribution of packets service time in cellular access networks a. generating service time samples for simulation purposes, it is sometimes required to generate samples of service time. the inverse-transform technique can be used for generating samples of service time. since 4c(�) ∈ [0,1] , and is a monotone non-decreasing function, _ samples of the service time can be generated by: � �̀ = 4c>h(��)���h] , where 4c>h is the inverse of the cdf in (5), and ������h] are randomly generated samples that follow the uniform distribution over the interval [0,1] . below, we explicitly find 4c>h: � = � p=/u>�(c)�(c) ��(c)� = ��/� − ℎ(`) ℎ(`)��� + 1� = ��/� ℎ(`) = �p=/u�z� �2 kl� − 1��/� �\]� ��/� = �p=/u�z� solving for ` yields: ` = 4c>h(�) = a\��q=jhz� �����u/= r�l��n (6) thus, (6) is a direct simulation tool for generating samples of the service time required to send a packet of � bits from the bs to a randomly selected user. b. service time probability density function (pdf) from (5), the pdf of the service time can be found: 'c(�) = �v��(h)w�h (7) = lmn mo� >��(h)p =u�=(h) '&� a\��q=�hz �rl��� ≤ � ≤ a\��q=jhz�rd��� eul�� k0 &�ℎ ���$ (8) where: ℎ′(�) = �(�(h))�h = − �\]�� ��/� �a�¡(�)\� (�) klmd� klm>he=¢uu h= after some mathematical manipulations, the pdf of the service time can be rewritten as shown bleow: 'c(�) = lmn mo£ hh= �2=¤m − 2>u¤m �> =�uu '&� a\��q=�hz �rl��� ≤ � ≤ a\��q=jhz�rd��� eul�� k0 &�ℎ ���$ (9) where £ = ���/� � �\]���/� �a�¡(�)\� , and , = a\(�z�). note that both £ and , are constant. let the limits of the service time wheren the pdf is non zero be: �� = a\��q=�hz �rl���, and �¥ = a\��q=jhz�rd��� eul�� k. then, the first two moments of the service time are given by [9]: ¦[`] = £ * h§h� hh d2=¤m − 2>u¤m e> =�uu �� (10) ¦[`�] = £ * h§h� d2=¤m − 2>u¤m e> =�uu �� (11) c. density function of the service rate in certain occasions, we are sometimes interested in service rate rather than service time. the service rate (s) is a discrete random variable which represents the number of transmitted packets in one second. in this subsection, we introduce the cdf and pdf of service rate. clearly, the relation between service time and service rate is t=1/s. therefore, the cdf of the service rate can be found as: 4̈ ($) = 6[© ≤ $] = 6[1̀ ≤ $] = 1 − 6[` ≤ 1$] = 1 − 4c(1$) by substituting (5) in the above equation, we obtain the cdf of the service rate over one frequency channel as follows: 4̈ ($) = lmm mn mmm o 0 '&� $ ≤ \��q=jhz �rd��� eul�� k a (� + 1) ª(�)> ���tp=/uª(�) '&� \��q=jhz�rd��� e u l�� k a ≤ $ ≤ \��q=�hz �rl���a 1 '&� $ ≥ \��q=�hz �rl���a , (12) where «($) = ℎ(h�). furthermore, the pdf of the service rate is given by: '̈ ($) = = lmn mo£v2�¬� − 2>�¬�w>=�uu '&� \��q=jhz �rd��� eul�� k a ≤ $ ≤ \��q=�hz �rl���a 0 &�ℎ ���$ . (13) the average service rate can be found by [9]: ©̅ = ® $ £v2�¬� − 2>�¬�w>�z�� �$ hh� hh§ d. the impact of the derived service rate the bs usually has a number of orthogonal frequency channels through which the transmitters within the bs can transmit the packets to the respective users. when all radio frequencies are assigned to only one transmitter which transmits all packets in a fifo fashion, then, according to the queuing theory [3], this kind of queue is called m/g/1 queue. m indicates a markovian arrival model, in which the packet engineering, technology & applied science research vol. 9, no. 6, 2019, 4996-5000 4999 www.etasr.com al-zahrani: on the statistical distribution of packets service time in cellular access networks inter-arrival time follows an exponential distribution while g indicates a general service model where the packet service time follows an arbitrary distribution as the one shown in (5), and “1” indicates that only one transmitter is in service. when � < ©̅, the utilization of the bs transmitter is ¯ = °̈̅ , which quantifies the proportion of time the bs transmitter is busy in the long run. moreover, the system will be stable since ¯ < 1, and the steady-state parameters of this m/g/1 queue will be as follows [12]: • packet average delay: ± = h̅̈ + °(h/¨̅=z²�=)�(h>³) , (14) where ´c� is the variance of the packet service time t. • average number of packets in the bs: _ = ¯ + ³=(hz²=¨̅=)�(h>³) (15) • probability of zero packets at the bs: 6. = 1 − ¯ if, however, the service model was not general (g), but rather markovian (m) (as it is usually erroneously assumed), then the steady-state parameters would have been [12]: • packet average delay: ± = 1©̅ − � • average number of packets in the bs: _ = ¯1 − ¯ • probability of n-packets at the bs: 6¡ = ¯¡(1 − ¯) these quantities, which are based on loose assumptions, are misleading as they are completetly different than the actual pararmeters shown in (14) and (15). note that the true packet average delay in (14) is directly proportional to the variance of the service time which indicates that the packet delay increases as the variation in service time increases. thus, as the users become more scattered in the cell, then their service time, which depenends on the distance from the bs, will vary more. one way to reduce ´c� is by dividing the set of all radio frequencies into n subsets assingend to n transmitters for serving n packets simultanously. in addition, each transmitter should serve packets related to users at approximately the same distance from the bs (i.e. a group of user apart from the bs by � ± ¶). iv. numerical experiment in this section, the results of computer simulation are shown and discussed. the simulation is conducted in accordance with the system setup explained above. the simulation parameters are shown in table i. the simulated network architecture is shown in figure 2, where the bs (red star) is located at the cell center and all users (black dots) are uniformly distributed in the cell. matlab version r2013a was used. the simulation started by randomly choosing the location of each user (i.e. its distance from the base station and its angle with respect to the central point of the cell). then, the channel of each user was estimated via calculating the signal path loss and small scale fading. by knowing the user channel, data rate can be estimated, and so the required time for delivering each packet. the objective was to measure the required time for delivering each packet, and then draw the cdf of these samples using the matlab command cdfplot, and finally comparing the result with analytical cdf found in (5). table i. simulation parameters parameters value unit system frequency 2.5 ghz channel bandwidth 30 khz pathloss exponent (·) 3.52 – reference distance (��) 20 m cell radius 500 m transmit power (^) 0 dbm noise power spectral density -174 dbm/hz overall antenna gain 0 db packet size (�) 1500 bits fig. 2. a simulated cell with 500m radius figure 3 shows different graphs for the analytical and the simulated cdfs of the time required to relay the packets to the users. the analytical cdf is a simple graph of 4c(�) described by (5) while the simulated cdf is based on the data drawn from the simulation. as depicted in the figure, the simulated cdf fits the analytical cdf. in addition, as the number of users increases, the precision of the fitness increases further, simply because the analytical cdf is based on the limit (i.e. the number of users tends to infinity). this result clearly proves the accuracy of the statistical model of the packet service time proposed in (5). furthermore, figure 4 shows a comparison between the analytical pdf portrayed by (9) and the histogram of the service time results drawn from the simulation. the analytical pdf clearly matches the result of the simulation. this shows that the derived statistical model is realistic and closely matches the data-based results. engineering, technology & applied science research vol. 9, no. 6, 2019, 4996-5000 5000 www.etasr.com al-zahrani: on the statistical distribution of packets service time in cellular access networks fig. 3. comparisons between analytical cdf and simulated cdf: (a) 100 users/cell, (b) 500 users/cell, (c) 1000 users/cell, (d) 2000 users/cell fig. 4. comparison between analytical pdf and the histogram of the packet service time v. conclusion in this paper, the correct statistical model of the time taken by the bs to relay a user’s packet was derived. we showed that it is completely different than exponential distribution as it might be assumed. furthermore, we showed how this can be handy and beneficial in numerical experiments involving the cellular system. finally, we derived a direct closed form of the cdf and pdf of the service rate measured in packets per seconds. these results may be beneficial in developing new methods for radio resource management aiming at reducing the waiting time at the bs. references [1] t. s. rappaport, wireless communication: principles and practice, prentice hall, second edition, 2002 [2] a. goldsmith, wireless communication, cambridge university press, first edition, 2005 [3] d. p. bertsekas, r. g. gallager, data networks, prentice-hall, 1992 [4] k. son, h. kim, y. yi, b. krishnamachari, “base station operation and user association mechanisms for energy-delay tradeoffs in green cellular networks”, ieee journal on selected areas in communications, vol. 29, pp. 1525-1536, 2011 [5] h. kim, g. de veciana, x. yang, m. venkatachalam, “·-optimal user association and cell load balancingin wireless networks”, ieee/acm transactions on networking, vol. 20, no. 1, pp. 177-190, 2002 [6] d. niyato, e. hossain, “adaptive fair subcarrier/rate allocation in multi rate ofdma networks: radio link level queuing performance analysis”, ieee transactions on vehicular technology, vol. 55, no. 6, pp. 1897– 1907, 2006 [7] a. y. al-zahrani, “modelling and qos-achieving solution in full-duplex cellular systems”, international journal of computer networks & communications, vol. 10, pp. 117–135, 2018 [8] s. buyukcorak, g. k. kurt, o. cengaver, “a probabilistic framework for estimating call holding time distributions”, ieee transactions on vehicular technology, vol. 63, no. 2, pp. 811–821, 2014 [9] a. leon-garcia, probability and random processes for electrical engineering, addison-wesley, 1994 [10] m. azhar, a. shabbir, “5g networks: challenges and techniques for energy efficiency”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2864-2868, 2018 [11] l. scalia, k. k. t. biermann, c. choi, w. kellerer, “power-efficient mobile backhaul design for comp support in future wireless access systems”, 2011 ieee conference on computer communications workshops, shanghai, china, april 10-15, 2011 [12] j. banks, j. s. carson ii, b. l. nelson, d. m. nicol, discrete-event system simulation, prentice hall, fourth edition, 2005 authors profile ali y. al-zahrani received his bsc in electrical engineering (with honors) from king fahad university of petroleum and minerals (kfupm), dhahran, saudi arabia, in 2002 and his msc and phd degrees in electrical and computer engineering from carleton university, ottawa, on, canada, in 2010 and 2015 respectively. he is currently an assistant professor at the department of electrical and computer engineering, university of jeddah, saudi arabia. from 2002 to 2007 he worked as an electrical engineer at the saudi basic industries corporation (sabic). his research interests include radio resource allocation and interference management in wireless communication systems, dsp and massive mimo. microsoft word 02-3679_s1_etasr_v10_n5_pp6165-6171 engineering, technology & applied science research vol. 10, no. 5, 2020, 6165-6171 6165 www.etasr.com abdulkareem: identification of oil-gas two phase flow in a vertical pipe using advanced … identification of oil-gas two phase flow in a vertical pipe using advanced measurement techniques lokman a. abdulkareem department of petroleum engineering college of engineering university of zakho duhok, iraq lokman.abdulkareem@uoz.edu.krd abstract−the characteristics of flow configuration in pipes are very important in the oil industry due to its role in governing equipment design. in vertical risers, many flow configurations could be observed such as bubbly, slug, churn, and annular flow. in this project, two tomographic techniques have been applied simultaneously to the flow in a vertical riser: the electrical capacitance tomography (ect) technique and the capacitance wire mesh sensor (wms) technique. the employed pipe diameter was 50mm and the superficial studied velocities were 0.06-3.0m/s for gas and 0.06-0.4m/s for oil. several techniques have been used to analyze the output data of the two tomography techniques such as time series of cross-sectional averaged void fraction, probability density function (pdf), image reconstruction, and liquid hold-up profile. the averaged void fractions were calculated from the output signal of the two measurement techniques and plotted as functions of the superficial velocity of the gas. the flow patterns were identified from the pdf of the averaged void fraction. in addition, it was found that both tomographic techniques are reliable in identifying the flow regimes in pipes. keywords-insert void fraction; electrical capacitance tomography; wire mesh sensor; two phase flow i. introduction multiphase flow of gas-liquid mixtures in vertical pipes occurs in industrial equipment and applications such as petroleum industry, boilers, chemical plants, heat transfer equipment with change of phases, nuclear reactor technology, and geothermal energy production. two phase flow is a challenging subject due to the complexity of the form in which the fluids exist inside the pipes [1]. the prediction of occurring characteristics such as liquid hold up and gas void friction during the two phase gas/liquid flow in pipes is of particular interest to the nuclear, petroleum, and chemical industries. in some petroleum industry units, obtaining accurate inflow performance relations is difficult due to its multiphase behavior [2]. the most important parameters in multiphase flow are flow regimes and void fraction [3]. therefore, the understanding of any process in multi-phase flows depends on the identification of flow regimes. as a result, identification of flow regimes is an excellent start for developing techniques that predict gas and liquid hold up, mass and heat transfer, and finally pressure drop. therefore, the main aim of this study is the characterization of two-phase flow in vertical pipes. ii. experimental arrangement the study of multi-phase gas-liquid flow requires accurate measurements of each phase velocity and phase fraction. the experimental facilities and equipment setup used in this study are described in [3] and shown in figure 1. the project measurement technique that has been installed and used on the vertical facility technique is the novel embracing capacitance wire mesh sensor (wms) [4]. this device is designed in the research center of helmholtz centrum dresden rossendorf (hzdr), germany. fig. 1. block diagram of the facility. iii. probability density function the probability density function (pdf) of the void fraction time series has been used to classify the various flow patterns corresponding author: lokman a abdulkareem engineering, technology & applied science research vol. 10, no. 5, 2020, 6165-6171 6166 www.etasr.com abdulkareem: identification of oil-gas two phase flow in a vertical pipe using advanced … observed in our previously performed experiments [5]. typical examples for bubbly, slug, and churn patterns are given in figure 2. this data corresponds to a liquid superficial velocity of 0.06m/s and gas superficial velocities of 0.06-5.33m/s respectively. the slug flow regime is characterized by twin peaks corresponding to the liquid slug and the taylor bubble. a single peak existing at a low void fraction is typical of bubbly flow. the pdfs of the conditions of flow rate of oil uls=0.06 and 0.4m/s and gas superficial velocity of 0.06-5.33 m/s are illustrated on 3 dimensional graphs in figure 3. fig. 2. probability density function versus gas superficial velocity. (a) (b) fig. 3. the pdfs from: (a) electrical capacitance tomography and (b) wire mesh sensor. the pdf at the lowest gas flow rate shows a single peak at low void fraction, typical of bubbly or homogeneous flow. as the gas velocity increases, this first peak moves to higher void fractions. in addition, a second peak at a much higher void fraction begins to grow. this second peak is typical of slug flow and represents the emergence of taylor bubbles. for slug flow, the results from electrical capacitance tomography sensor show a clearer peak than those of wire-mesh sensors. the axial gap between the electrodes is 2mm for wire-mesh sensor, therefore the wire-mesh sensors measure almost instant void fraction at a plane, whilst electrical capacitance tomography probes measure average void fraction over the 13 zones. iv. mean void fraction the mean void fraction of two probes for vertical flow has been plotted against the superficial gas velocity in figure 4. the measurements were conducted under liquid velocity of 0.06m/s and different gas rates. as can be seen from figure 4, at low gas rates, there is a good agreement between the two curves. however, after the gas superficial velocity reached 1.4m/s, the mean void fraction curve in ect probe has moved higher than the wms curve. fig. 4. mean void fraction of two probes vs. superficial gas velocity. v. void fraction profile the wire-mesh sensor measuring system provides time and cross-sectional resolved information about the spatial distribution of phases. the information can be used to obtain many parameters such as space and time averaged void fractions, radial profiles of time averaged void fraction, and cross-sectional averaged time series of void fraction in the pipe. time averaged resolved radial gas void fraction profiles were examined for various gas and liquid superficial velocity values. figure 5 shows the curve shapes of oil-air flow. all peak values are located in the pipe center and increase with increasing gas superficial velocity. these curve shapes are developed by the appearing of relatively large gaseous structures located in the pipe center. this is expected as the flow rates fall in the center peak region [6]. vi. time series of cross-sectional averaged void fraction time series is a calculation method that is used as adjunct to identify and analyze the types of flow pattern inside a vertical pipe. the wms provides time and cross-sectional resolved information about the spatial distribution of the phases. the time series of cross-sectional average void fraction allows detecting essential features of the flow [7]. effectively, the time series data show the variation of void fraction with time for each performed run which detects the time each bubble passes through the sensors and is transferred to the output device which in turn records the time taken for each bubble. engineering, technology & applied science research vol. 10, no. 5, 2020, 6165-6171 6167 www.etasr.com abdulkareem: identification of oil-gas two phase flow in a vertical pipe using advanced … (a) (b) fig. 5. radial, time-averaged void fraction profiles for different gas superficial velocities and (a) 0.06m/s, (b) 0.4m/s liquid superficial velocity. examples of time series of cross-sectional average void fraction obtained from wms tomography technique are shown in figure 6 which explains the difference between bubble size and the amount of gas-liquid inside the pipe. however, the time series method of measurements by itself is not sufficient for identifying the types of flow pattern. other parameter methods are needed, such as pdf, frequency and mean void fraction techniques. with the presence of these parameters, the detection of flow pattern type is more accurate. the flow pattern types for vertical pipe are bubbly flow, cup bubble flow, slug flow, and churn flow. (a) (b) (c) (d) fig. 6. time series of cross-sectional average void fraction for (a) bubbly flow, (b) cup bubble, (c) slug flow, and (d) churn flow. vii. iimage reconstruction electrical capacitance tomography (ect) produces images of permittivity distribution of the mixture of two fluids inside pipes. the permittivity distribution is displayed as a series of normalized pixels located on a 32×32 square pixel grid using an appropriate color scale of graduated blue/green/red to indicate the normalized pixels permittivity [8]. the pixel values corresponding to the lower permittivity material used in the calibration of the sensor have zero value and are displayed in blue whereas pixels corresponding to the higher permittivity material have the value of 1 and are displayed in red. the normalized permittivity distribution corresponds to the fractional concentration distribution of the higher permittivity material. the method which has been used for reconstruction images is known as linear back projection (lbp) and is based on a set of forward and inverse transforms. several slice images of reconstruction data have been constructed for captured data. figure 7 shows examples of reconstruction of tomographic images for different superficial oil and gas velocities. the images from the figure are in agreement with the visual observations. the images in figure 8 show the transition of a few different flow regimes processed with both visualization techniques. fig. 7. tomographic images for flow for different velocitird of liquid and gas. (a) (b) fig. 8. visualization of (a) electrical capacitance tomography and (b) wire-mesh sensor data. it has been experimentally observed that bubbles start forming up at low flow rates. gradual slug flow occurs due to the increase in the superficial velocity. with further increase in engineering, technology & applied science research vol. 10, no. 5, 2020, 6165-6171 6168 www.etasr.com abdulkareem: identification of oil-gas two phase flow in a vertical pipe using advanced … velocity, the pattern progresses, into churn flow with moderate to high turbulence. preliminary results obtained using this technique have proved the ect system as a powerful tool for exploring transient multiphase phenomena in gas–liquid [9]. viii. three dimension plots two and three dimension plots of surface contours of the permittivity of the material inside the pipe have been generated by the ect system. the plot3d software allows the capacitance data to be captured and the ptl ect32 software to be displayed as a set of multiple 2-d image frames and to be viewed in 2 or 3d. the 3d plotting extends the flow visualization of the structure of the flow into the third dimension axially along the pipe. it does this by projecting the structures axially based on the velocity as they pass through the sensor planes. figure 9 shows an example of 3d data captured by the ect sensor. fig. 9. 3d plot of liquid concentration. the wire mesh sensors (wmss) employed in this study are capable of providing the taylor bubble shapes by creating a 3d reconstruction of the flow as shown in figure 10. the deformation of a taylor bubble is also related to the stresses generated from the translational motion. as a result, as the mixture velocity increases it can be observed that the taylor bubble is totally broken when the gas superficial velocity reaches 1.4m/s. this phase interaction mechanism might be the reason why, as reported in [10], liquid structures inside the gas core of the taylor bubble (wisps) have been found to exist in the churn flow regime. fig. 10. taylor bubble shapes in 3d. ix. liquid hold up profile ect is a system which processes capacitance data captured by a twin plane ect sensor to produce velocity and flow profiles and overall flow data for a mixture of 2 dielectric materials. it generates instantaneous concentration (hold up) profiles of the flow inside the ect sensor, at two axial measurement locations (planes) for each frame of capacitance data. these concentration profiles can be calculated for a relatively small number of zones in the flow cross-section. figure 11 shows the average concentration (expressed as a percentage of the zone when full, in the nominal range 0100%) for the selected zone at each of the two measurement planes as a function of time. the green trace corresponds to the average zone concentration at plane 1 and the red trace corresponds to the average zone concentration at plane 2. cross-correlation techniques can then be used to derive the instantaneous velocity in each zone from the concentration profiles at the 2 measurement planes. the overall flow profile can also be calculated from the concentration and velocity profiles. fig. 11. time variation of liquid hold up in four marked zones from the two probes. x. structure velocity structure velocities have been calculated from the cross correlation of the two void fraction signals from two planes of the ect sensor. the transient time between the two planes was measured and divided by the distance between the two planes. figure 12 shows the variation of structure velocity against mixture velocity for all conditions for vertical flow. in addition, the experimental data have been compared with the nicklin equation. the dash line curve in the figure is the correlation proposed by [11]. it shows that increasing the mixture velocity leads to increasing in structure velocity. however, at liquid rate of 0.06m/s and gas rate of 1.9m/s, the structure velocity starts to decrease. the reason of this case is the change in flow engineering, technology & applied science research vol. 10, no. 5, 2020, 6165-6171 6169 www.etasr.com abdulkareem: identification of oil-gas two phase flow in a vertical pipe using advanced … pattern from slug to churn. in addition, the experimental structure velocity is higher than the nicklin curve. fig. 12. structure velocity vs. mixture velocity of gas, for different liquid flow rates. xi. frequency analysis frequency analysis is a very important technique on the predication of slug flow characteristics. accurate designing of separation in two phase flow depends on the reliable predication of slug frequency. the frequency of the data can be found by power spectrum density (psd) analysis. psd shows how the power of a signal or time series is distributed with frequency. mathematically, according to the wiener-khinthine theorem, the psd has been obtained by using fast fourier transform (fft) of auto covariance function and auto correlation of time series signal. the auto covariance function of a signal x(t) is given by: 1 1 ( ) [ ( ) ] [ ( ) ] n xx t r t x t x x t t x n = ∆ = − ⋅ + ∆ −∑ (1) where 1 1 ( ) n t x x t n = = ∑ . the psd is then obtained from: 2)2exp()( 1 )( 1 0       = ∑ = = n t xxxx fitr n fp τπ (2) the autocorrelations for one run are shown in figure 13. as can be seen, in auto covariance function and fft there is a single dominant peak which is about 1.2hz. figure 14 shows the effect of gas flow rate on frequency. as can be seen there are break points at bubbly flow to slug and slug to churn transition. the frequency slightly increased with increasing gas flow rate until velocity reached about 0.5m/s and then the frequency starts to decrease due to change in flow regimes from bubbly to slug flow. however, the frequency slightly decreases in slug flow region for higher gas flow rates. xii. discussion this section concentrates on the discussion of the results obtained in the previous sections. also, the results of the present study are compared with the results obtained in [13]. (a) (b) (c) fig. 13. (a) psd vs. frequency, (b) auto correlation vs. time delay, (c) time series of void fraction for usg=0.4m/s and usl=0.27m/s. fig. 14. frequency against superficial velocity of gas, for different liquid rate flows. a. average void fraction analysis in figure 15, the variation of average void fraction with gas superficial velocity is shown. the behavior in present work is compared with the results obtained in [13] with silicone oil in pipes of the same diameter. i can be seen that the results follow a comparable trend. minor differences can be explained by the difference in electrode configurations which brings about a time delay. b. probability density function the pdf obtained from the void fraction time series suggested that the flow was bubbly, slug, and churn. the results observed in the present study have been compared with the results obtained in [13]. three velocities were used for engineering, technology & applied science research vol. 10, no. 5, 2020, 6165-6171 6170 www.etasr.com abdulkareem: identification of oil-gas two phase flow in a vertical pipe using advanced … comparison (figures 16-18). it can be clearly seen that the pdfs obtained for both studies are of similar character. fig. 15. result comparison between the current study and [13]. fig. 16. current study and [13] comparison of pdfs at 0.003m/s. fig. 17. current study and [13] comparison of pdfs at 0.001m/s. fig. 18. current study and [13] comparison of pdfs at 0.02m/s. c. dominant frequency analysis the variation of dominant frequencies with gas superficial velocity was compared to the pattern obtained in [13]. the comparison is shown in figure 19. the plot trend obtained in the present study was found to be significantly different from that obtained in [13]. here the frequency was found to fluctuate with superficial gas velocity unlike the one obtained in [13]. this fluctuation in frequency value is mainly due to disturbances caused by noise. fig. 19. comparison of dominant frequencies. d. structure velocity the structure velocity was found to vary linearly with the gas superficial velocity as shown in figure 20, implying the flow inside the tube to be slug. the bubble velocities obtained in the present study were compared with the bones obtained in [13] and it was seen that their magnitudes are very similar. this suggests that the bubble behaviors of both liquids can be considered to be similar. fig. 20. comparison of structure velocity. xiii. conclusion two advanced instrumentations were used to examine and investigate the characteristics of two-phase flow in vertical pipes. experiments were performed in a mixture of gas and oil, revealing good agreement in the flow pattern behavior with similar studies. the ect has the capability to measure velocity non-intrusively, and is able to show detailed void fraction and velocity profile information for flows. the 3d shape of the bubble was reconstructed from wms and ect data. the structure velocity shows similar trends when compared with [11]. pdfs used as in [5] have been used to identify the flow patterns. acknowledgment the author would like to thank the multiphase flow research center in the department of petroleum engineering, college of engineering, university of zakho for funding and supporting this research project. engineering, technology & applied science research vol. 10, no. 5, 2020, 6165-6171 6171 www.etasr.com abdulkareem: identification of oil-gas two phase flow in a vertical pipe using advanced … references [1] b. j. azzopardi, gas-liquid flows. new york, ny, usa: begell house, 2006. 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[12] e. q. bashforth, j. b. p. fraser, h. p. hutchison, and r. m. nedderman, “two-phase flow in a vertical tube,” chemical engineering science, vol. 18, no. 1, pp. 41–46, jan. 1963, doi: 10.1016/0009-2509(63)80004-4. [13] m. m. mustafa, “investigation of gas-liquid flow in vertical pipes by using wire-mesh sensor & measuring the viscosity flow of fluids using bs/u/m viscometers,” ph.d. dissertation, university of zakho, zakho, iraq, 2013. engineering, technology & applied science research vol. 9, no. 1, 2019, 3726-3733 3726 www.etasr.com benmoussa et al.: a multi-criteria decision making approach for enhancing university accreditation … do not alter header & footer. they will be completed during editing a multi-criteria decision making approach for enhancing university accreditation process nezha benmoussa signals, distributed systems and artificial intelligence laboratory, enset mohammedia, university of hassan ii, mohammedia, morocco nbnezhabenmoussa@gmail.com abir elyamami signals, distributed systems and artificial intelligence laboratory, enset mohammedia, university of hassan ii, mohammedia, morocco abir.elyamami@gmail.com khalifa mansouri signals, distributed systems and artificial intelligence laboratory, enset mohammedia, university of hassan ii, mohammedia, morocco khmansouri@gmail.com mohammed qbadou signals, distributed systems and artificial intelligence laboratory, enset mohammedia, university of hassan ii, mohammedia, morocco qbmedn7@gmail.com elhoussein illoussamen signals, distributed systems and artificial intelligence laboratory, enset mohammedia, university of hassan ii, mohammedia, morocco illous@hotmail.com abstract— this paper is an attempt to provide an accreditation training process model by the criteria established by the national agency for evaluation and quality assurance of higher education and training. the aim is to minimize rejection returns or revisions of the training record. the main feature of our contribution is the use of multi-criteria decision making (mcdm) approaches for calculating the suitability of proposed courses. therefore, our contribution will is concretized by the analysis of various decision support multi-criteria methods, the modeling of the general accreditation process of university courses, the development of a risk management matrix concerning the launch of new courses and the application of topsis (technique for order of preference by similarity to ideal solution) on a sample of courses according to internal and external criteria, collected during interviews in moroccan universities. result analysis shows that the proposed model allows a better prioritization of training and thus avoids the abrupt closure of courses because of lack of material or human resources. keywordsdecision support; mcdm; accreditation; risk management matrix; topsis i. introduction decision-making generates very important industrial and economic issues affecting management and competitiveness of organizations. prioritizing and optimizing all actions are two key factors of effective decision-making. universities face the challenge of resources and investment optimization to avoid any negative impact on the management of training projects and their performance. they are always looking for innovation so that they may be able to meet the needs of the market and to encourage scientific research. all interviewed managers assume that taking an effective decision in advance, requires a preliminary study of any educational proposal. multi-criteria decision making (mcdm) methods, are increasingly used in various fields like natural resource management, environment and spatial planning, making possible to rely on science while taking managerial decisions and to drive decision-making processes in organized systems [1]. whether strategic, global, operational or local, decision making is generally made to manage organizations consistently: quantitatively (number of products or services offered), and qualitatively (development of standards, establishment of a charter). therefore, making a decision requires different alternatives that must be evaluated according to one or more criteria in order to determine the optimum [2]. these alternatives and indicators help enormously in decision-making and are a great contribution to the evolution of future steps to take. decision support is a scientific approach to decisionmaking problems that arise in any socio-economic context in which the two main factors are the decision-maker who governs the decision-making process, and the responsible of study who intervenes at least on 1 of the 3 important levels, namely the modeling of the decision problem, the design or adaptation of a procedure for exploiting the model and the elaboration of a prescription from the solution(s) [3]. formerly, decision support was designed to find the solution to a given problem. today, it decently offers answers in the form of recommendations to decision-makers of a decision-making process and allows them to make better choices [4]. operational research (or) offers a variety of decision support tools and the most complex decisions and resource optimizations are possible through a number of algorithmic approaches that iteratively build a solution, descent heuristics that seek a global optimum from a given solution and metaheuristics that break down objectives to ease decision-making. these purely algorithmic resolution methods in the decisionmaking domain resolve in time, efficiently and quickly, to a solution or choice [5]. indeed, or is a discipline of scientific methods that help the making of a decision. it refers to notions corresponding author: n. benmoussa engineering, technology & applied science research vol. 9, no. 1, 2019, 3726-3733 3727 www.etasr.com benmoussa et al.: a multi-criteria decision making approach for enhancing university accreditation … do not alter header & footer. they will be completed during editing that map our contemporary semantic and legal territory to the image of big data, e-reputation, or predictive algorithms [6]. multicriteria decision support is a major area of study of or involving several schools of thought, mainly american [7]. these are mathematical methods to choose the best solution or the optimal solution among a whole set of solutions. in this paper, we contribute by analyzing various mcdm methods, modeling the general process of accrediting academic training and developing a risk management matrix for the launch of new courses and the application of topsis on a sample of courses according to internal and external criteria, collected during interviews for an effective decision-making process within moroccan universities. ii. mcdm methods multicriteria decision aid (dma) was created in the 1970s. it has aroused interest through its innovative approach starting with single-criteria analysis followed by the weighting of criteria and their aggregation procedures varied in decision problems [8]. most conventional mcdm methods use parameters derived from the decision maker's preferences. these parameters are often used for weight calculation, quantifying the importance of each criterion in the multicriteria decision process. this domain is broken down into two subdomains: • madm (multi-attribute decision making) for selecting the best alternative in a predetermined set of alternatives. • modm (multi-objective decision making) concerning the selection of the best action in a continuous or discrete decision space. multi-objective optimization is a branch of modm [9]. authors in [10] specify that in a multi-criteria decision support process, the main objective is not to find a solution, but to build or create a tool considered as useful in the decisionmaking process. since then, the mcdm methods are more and more used including maxmin, maxmax, saw, ahp, topsis, smart and electre [11] in order to make a choice, to classify or to sort out for an effective decision making. the mcdm's progression goes through 6 steps as shown in figure 1. fig. 1. general steps of mcdm methods the test steps are important because they give an accurate assessment of the indicators. if the indicator’s quality isn’t conformed to the goals, it must be redefined and the test must be recommenced. below we present some decision support methods which will be the object of a concise description specifying their functioning and their limits. topsis will be more detailed since it constitutes the implementation tool of the data of our case study “accreditation and training management”. the analyzed methods’ advantages and limitations are shown in table i. a. ahp (hierarchical process analysis) ahp is a semi-quantitative method that has been developed in [12] and its computer version “expert choice” software was introduced in the us in 1985. it is based on the comparison of pairs of options and criteria by structuring in a logical coherence: • classes, criteria and hierarchical weights. • sub-criteria and ranks by priority. this involves making pairs of elements of each hierarchical level with an element of the higher hierarchical level. this step makes possible to build comparison matrices. the values of these matrices are obtained by the transformation of judgments into numerical values according to the saaty scale [13], while respecting the principle of reciprocity: 𝑃𝑐(𝐸𝐴, 𝐸𝐵) = 1 𝑃𝑐(𝐸𝐵,𝐸𝐴) (1) b. smart (simple multiple attribute rating technique) smart is similar to ahp, it has been developed since 1971 as a hierarchical structure created to assist in defining a problem and in organizing criteria. the difference between a value tree and a hierarchy in ahp is that the value tree has a true tree structure, allowing one attribute or sub-criterion to be connected to a higher level criterion. its main steps are: • put the criteria in decreasing order of importance. • determine the weight of each criterion. • normalize the relative importance coefficients between 0 and 1: sum the importance coefficients and divide each weight by this sum. • measure the location of each action on each criterion (uj (αi)). evaluations actions are on a scale ranging from 0 (plausible minimum) to 100 (plausible maximum). • determine the value of each share based on the following weighted sum: 𝑈(𝑎𝑖) = ∑ 𝜋𝑗𝑢𝑗(𝑎𝑖) 𝑛 𝑗=1 , i=1, 2… m (2) • classify actions in decreasing order of u(αi). c. topsis topsis was presented in [14] and developed later in [15, 16]. it is worth noting that it corresponds to the hellwig taxonomic method of ordering objects [17]. the main advantages of this method are: it is a simple, rational, comprehensible concept, and it has intuitive and clear logic that represents the rationale of human choice. in this method, two alternatives are hypothesized: the ideal solution that has the engineering, technology & applied science research vol. 9, no. 1, 2019, 3726-3733 3728 www.etasr.com benmoussa et al.: a multi-criteria decision making approach for enhancing university accreditation … do not alter header & footer. they will be completed during editing best solution for all attributes and the negative ideal solution for the one which has the worst attribute values. topsis method performs prioritization of alternatives based on their geometric distance from the positive-ideal and negative-ideal solution. it reduces the need of pair comparisons and the limitation of capacity may not significantly dominate the process. therefore, it would be appropriate for cases with a large number of criteria and alternatives, especially when objective or quantitative data are determined [18]. topsis breaks down the decision into different stages: 1) formation of decision matrix criterion outcomes of decision alternatives are collected in a decision matrix. the matrix rows represent decision alternatives, with matrix columns representing criteria. a value found at the intersection of row and column in the matrix represents a criterion outcome: a measured or predicted performance of a decision alternative on a criterion. c1cjcn x= 𝐴1 ⋮ 𝐴2 ⋮ 𝐴𝑚 [ 𝑥11 ⋮ ⋯ … 𝑥1𝑗 ⋮ … 𝑥1𝑛 ⋮ 𝑥𝑖1 ⋮ … … 𝑥𝑖𝑗 ⋮ … 𝑥𝑖𝑛 ⋮ 𝑥𝑚1… … 𝑥𝑚𝑗 … … 𝑥𝑚𝑛 ] 𝑚×𝑛 (3) where, xij is the performance rating of alternative i with respect to criterion j, ai is ith alternative and cj is the jth criterion. 2) formation of weight matrix different importance weights to various criteria may be awarded by the decision maker independently or by entropy method. these importance weights form the weight matrix: w=[w1 …..wj …..wn] (4) 3) normalization of performance rating units and dimensions of performance ratings under criteria differ. for comparison, these performance ratings are converted into dimensionless units by normalization using the following equations: ( ) ij ij ij i x x max x = (5) for benefit criteria j and ( )ij i ij ij min x x x = (6) for non-benefit criteria j finally, the normalized decision matrix is formed: =x a1 ⋮ ai ⋮ am [ x̅11 ⋮ ⋯ … x̅1j ⋮ … x̅1n ⋮ x̅i1 ⋮ … … x̅ij ⋮ … x̅in ⋮ x̅m1 x̅mj x̅mn] m×n (7) 4) determination of the positive ideal and negative ideal solution a+ = (ai1 + ,ai2 + , … … … … … … . . , aim + ), aij += max 1≤i≤m (aij), j=1, 2…, n (8) a− = (ai1 − ,ai2 − , … … … … … … . . , aim − ), aij −= min 1≤i≤m (aij), j=1, 2…., n (9) 5) calculation of the separation measures using the n-dimensional euclidean distance the separation of each alternative from the positive ideal solution is given as: 𝐷𝑖 +=√∑ 𝑊𝑗(𝑎𝑖𝑗 + − 𝑎𝑖𝑗) 2𝑛 𝑗=1 (10) similarly, the separation from the negative ideal solution is given as: 𝐷𝑖 −=√∑ 𝑊𝑗(𝑎𝑖𝑗 − − 𝑎𝑖𝑗) 2𝑛 𝑗=1 (11) 6) step6: calculation of the ratio for each alternative, calculate the ratio ri as: 𝑅𝑖 = 𝐷𝑖 − 𝐷𝑖 + + 𝐷𝑖 − i = 1, 2. . . . . . m (12) 7) rank alternatives in increasing order according to the ratio value of ri d. electre i & ii electre i (elimination and choice translating reality) was developed in 1968 and electre ii in 1971 [19]. both versions are based on the notions of concordance and discordance. electre is a non-compensatory method of multicriteria decision support. in reality, the decision maker is often undecided, his preferences evolve because the decision is the result of a process of micro decisions. the optimum can only be achieved if three conditions are met: • the different strategies (projects) proposed to the decision maker are distinct. • strategies stability over time is present. • comparability is transitive. e. electre iii electre iii is based on a fuzzy logic and a constructive approach which classifies actions. it favors [20]: • dialogue between the different factors in the decisionmaking process. • weighting of criteria by factors expressing preferences on resource management strategies. • consideration of uncertainty in the evaluation of actions by pseudo-criteria. f. electre iv this method assumes that all pseudo-criteria are of equal importance. it involves two outranking relations like electre ii but only one set of veto thresholds and the notion of concordance is translated by a notion of majority of criteria in the absence of any weighting. engineering, technology & applied science research vol. 9, no. 1, 2019, 3726-3733 3729 www.etasr.com benmoussa et al.: a multi-criteria decision making approach for enhancing university accreditation … do not alter header & footer. they will be completed during editing table i. mcdm methods: advantages and limitations ahp popular method that has been subjected to criticism regarding the explosion of the number of pairwise comparisons in case of a complex problem, the reversal of rank (order of priority of the actions) in case of addition or deletion and the introduction of biases by the association of a numerical scale on the semantic scale which is restrictive. currently, ahp is subject to several extensions such as the consideration of uncertainty (stochastic ahp) and blur (fuzzy ahp) in the expression of judgments. smart similar to ahp and easy to exploit but requires a priori articulation of preferences, and evaluation of actions on a single scale (cardinal scale). it is compensatory and has been developed in criterium decision plus 3.0 and decide right for automatic management. topsis easier method to apply and responsive to the decision maker's wishes. however, the attributes must be cardinal in nature, preferences are fixed a priori. on the other hand, if all the actions are bad, the method proposes the best of these bad actions. electre i it formalizes well the process of human reasoning, but has the disadvantage of using quantization weights of the importance of different criteria. despite the contribution of this method, the decision maker still faces the difficult task of providing quantization weights. electre ii it replaces the classic upgrade relationship with two new relationships, namely strong upgrade and weak upgrade. electre iii it introduces the notion of pseudo-criteria that replace the classical criteria. the pseudo-criteria are modeled by functions whose expression is close to the membership functions known in the field of fuzzy logic. electre iv is distinguished by its ability to dispense with the weights associated with each criterion. however, this benefit is tempered by the need to determine a “credibility degree” associated with each outranking relationship used. gra uses a specific concept of information. it defines situations with no information as black, and those with perfect information as white. neither of these idealized situations ever occurs in real world problems. situations between these extremes are described as being grey, hazy or fuzzy. promethee gaia unlike the outranking relation constructed by the electre method, which is purely binary, the relation constructed by promethee is a valued upclass relationship: one action outclasses another with a numerical preference intensity. in 1989, gaia provided a descriptive complement to promethee rankings. using a graphical representation of the multicriteria problem, the decision maker can easily understand which choices are possible and which trade-offs are required to make a good decision. promethee-gaia require less parameterization while remaining as efficient. it makes possible to stay closer to the real decision problem, to better describe it and to carry out sensitivity analyses. g. gray relational analysis (gra) also called deng's gray incidence analysis model [21], gra uses a specific concept of information. it defines situations with no information as black, and those with perfect information as white. however, neither of these idealized situations ever occurs in real world problems. in fact, situations between these extremes are described as being gray or fuzzy [22]. the scope of the gray system involves agriculture, ecology, economics, meteorology, medicine, history, geography, industry, earthquake, geology, hydrology, irrigation, strategy, military affairs, sport, traffic, management, materials science, environment, biological protection, judicial system. h. promethee preference ranking organization method for enrichment of evaluations (promethee) is a part of the family of upgrade methods that allow two particular mathematical treatments: partial storage (promethee i) and complete storage (promethee ii). with their descriptive complement geometrical analysis for interactive aid they are better known under the names promethee and gaia1 [23]. they are multi-criteria decision-support methods that belong to the family of methods of outreach initiated by the electre methods. promethee and gaia methods offer a prescriptive and descriptive approach to the analysis of discrete multicriteria problems covering several areas. in fact, 217 scientific articles from 100 journals mention their fields of application on environmental management, hydrology and water management, commercial and financial management, chemistry, logistics and transport, manufacturing and assembly, energy management and other topics such as medicine, agriculture, education, design, government, and sport [24, 25]. iii. research methodology the proposed approach concerns the field of higher education in general and the moroccan universities in particular. it meets the obligation to set up indicators before launching a new course. indeed, the objective of this study is to contribute to the optimization of resources and especially the evaluation of existing training as well as the decision-making concerning those to be accredited. for the understanding of the accreditation process, we modeled the demands management standard and developed the corresponding risk management matrix. in addition, we studied university specifications and conducted interviews with university officials on the basis of internal and external criteria that are essential for the training. these data will be presented and commented. for the evaluation of our proposal, we applied topsis on a course sample. a. model of accreditation of innovative university courses the compliance with the standards and criteria stipulated by the national agency for evaluation and insurance quality of higher education and scientific research (aneaq) is essential for the acceptance of the training proposed by any institution. the following model presents the general process for the processing of accreditation requests for training and the main conditions to be taken into consideration in order to avoid the return of refusals or major revisions: at least 1 teacher per higher grade, the appropriate hourly volume in theory and practice as well as internships and partnerships to prepare profiles for the professional world as shown in figure 2. b. risk management matrix the interviewees unanimously expressed the usefulness of the designed risk management matrix which specifies not only the main risks to be considered, but also the responsibility and actions to be taken to make the decision effective. they have completed it and have judged that these risks are to be minimized or even avoided and must be taken into consideration before any training proposal (table ii). engineering, technology & applied science research vol. 9, no. 1, 2019, 3726-3733 3730 www.etasr.com benmoussa et al.: a multi-criteria decision making approach for enhancing university accreditation … do not alter header & footer. they will be completed during editing fig. 2. processing process for training accreditation applications table ii. risk management matrix risk probability rating severity rating priority rating responsibility action to be taken lack of classrooms 3/5 4/5 12/25 university construction enlargement lack of human resources 4/5 4/5 16/25 establishment continuing education session lack of equipment 4/5 5/5 20/25 establishment/ university acquisition the risk management matrix in table ii clearly shows that teaching resources and human resources are the most important according to their respective ratings of 20/25 and 16/25, which is explained by the risk of lack of rooms that can be solved by adequate automatized planning or an expansion of the establishment. thus, the managers must establish a policy of continuous training of human resources permanently according to the evolution of the market and an adequate budgetary strategy relating to the educational equipment necessary for each department. to make the study relevant, we have defined, in addition to these indicators, internal and external criteria based on program specifications and interviewee responses. c. internal and external criteria table iii provides the main internal criteria of moroccan university courses, the main objective of the departments is the adequacy of the proposals with the university strategy which aims to reach 100% in terms of innovation and development in order to meet the expectations of the market and encourage scientific research. table iii illustrates the results of the interviews based on the specifications and the actual estimate for each of the criteria according to the specifications. we were able to determine 7 internal and 3 external criteria. the internal ones are part of the school's strategy and are the key to the success of the existing training and future ones. externally, these are the conditions to be respected for alignment with the standards put in place concerning requests for accreditation of new training. these criteria will allow university officials to detect, qualitatively and quantitatively, the defects and report on the improvement of the situation and good planning. in addition to the ratings in the risk management matrix and standards in the accreditation processing model, the vision will be clear in identifying priority areas for improvement to avoid inefficient decision-making. the external criteria are shown in table iv and are complementing the internal ones in order to prepare competent profiles in adequacy with the socioeconomic status and respect for the aneaq standards. they concern especially the rank of human resources, the hourly amount and the content which must be theoretical and practical. table iv shows that the partnership is essential and must be developed for all courses in order to gain knowledge of the market and easy integration in active life and internships. it is therefore necessary to maximize the agreements and partnerships with companies and administrations. internal and external criteria, partnership and internships considerably influence the decision to be taken and constitute the key to evaluate existing training cards and launching new training. they will be implemented via topsis in order to conclude with recommendations of interest for our universities. table iii. main internal criteria criteria motivation human resources technical resources course innovation market needs team experience class rooms work shops equipment bdcc 95% 95% 50% 100% 65% 30% 40% glsid 90% 80% 65% 90% 65% 40% 45% mli 85% 80% 65% 90% 65% 35% 40% gmsi 75% 85% 70% 90% 70% 50% 45% sid 70% 80% 75% 75% 65% 40% 40% gecsi 80% 85% 65% 90% 70% 45% 45% gmasi 75% 80% 70% 90% 70% 50% 45% table iv. external criteria alignment with standards partnership traineeship grade vh content 2 pes 100% t/p yes yes 3 pa 100% t/p yes yes 2 pa 100% t/p yes yes 1 pa 100% t/p not yet yes 4 pa 100% t/p not yet yes 3 pa 100% t/p not yet yes 1 pa 100% t/p yes yes 1 pa 100% t/p not yet yes d. topsis implementation after the identification of the alternatives and criteria, the results of our interviews will be implemented under the mcdm topsis in order to identify the importance coefficients and prioritize the best decision. we will then calculate the weighted scores for each of the formations according to the standardized criteria and values in order to prioritize and optimize the different formations. 1) formation of decision matrix the choice of alternatives and criteria is the most important step in decision making. indeed, selecting the key indicators is a basis that will allow university officials to prioritize and optimize actions for better management. the alternatives and criteria codes are presented in figure 3. 2) formation of weight matrix in table v we see the selected alternatives and the scoring engineering, technology & applied science research vol. 9, no. 1, 2019, 3726-3733 3731 www.etasr.com benmoussa et al.: a multi-criteria decision making approach for enhancing university accreditation … do not alter header & footer. they will be completed during editing of each alternative on different criteria. the dataset is used as decision matrix and then the normalized decision matrix is calculated (table vi). fig. 3. codification of internal and external criteria table v. weight matrix aij c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 a1 95 95 50 90 65 30 40 43 1 1 a2 95 100 65 100 80 80 45 43 1 1 a3 85 80 65 90 65 35 40 38 1 1 a4 75 85 70 90 70 50 45 38 0 1 a5 70 80 75 75 65 40 40 43 0 1 a6 80 85 65 80 70 45 45 26 0 1 a7 75 80 70 90 70 50 45 38 1 1 3) determination of positive and negative ideal solutions positive and negative ideal solutions, 𝐴+and 𝐴− are defined according to the normalized decision matrix (table vii). 4) calculation of the separation measures for each competitive alternative the separation distance is calculated in table viii. 5) ratio calculation the relative closeness of each location to topsis ideal solution is measured in table ix. 6) classify actions the alternatives are ranked in decreasing order (table x). table vi. performance rating rij a1 0.43 0.41 0.29 0.39 0.35 0.23 0.35 0.42 0.50 0.38 a2 0.43 0.44 0.37 0.43 0.44 0.61 0.40 0.42 0.50 0.38 a3 0.39 0.35 0.37 0.39 0.35 0.27 0.35 0.37 0.50 0.38 a4 0.34 0.37 0.40 0.39 0.38 0.38 0.40 0.37 0.00 0.38 a5 0.32 0.35 0.43 0.32 0.35 0.31 0.35 0.42 0.00 0.38 a6 0.37 0.37 0.37 0.34 0.38 0.34 0.40 0.25 0.00 0.38 a7 0.34 0.35 0.40 0.39 0.38 0.38 0.40 0.37 0.50 0.38 table vii. positive and negative ideal solutions vmax a+ 0.43 0.44 0.43 0.43 0.44 0.61 0.40 0.42 0.50 0.38 vmin a0.32 0.35 0.29 0.32 0.35 0.23 0.35 0.25 0.00 0.38 table viii. separation measures course code smin smax a1 0.546676 0.420843 a2 0.686478 0.057166 a3 0.53037 0.379255 a4 0.240516 0.568416 a5 0.231595 0.61971 a6 0.161789 0.609396 a7 0.554413 0.276441 table ix. ratio values course code coefficients ranking a1 0.923127 1 a2 0.667281 2 a3 0.583065 3 a4 0.565028 4 a5 0.297325 5 a6 0.272047 6 a7 0.209792 7 table x. ranking values course coefficients ranking glsid 0.923127 1 gmasi 0.667281 2 mli 0.583065 3 bdcc 0.565028 4 gmsi 0.297325 5 sid 0.272047 6 gecsi 0.209792 7 iv. discussion compensatory methods such as topsis allow trade-offs between criteria, where a poor result in one criterion can be negated by a good result in another. it provides a more realistic form of modeling than non-compensatory methods. using topsis, the collected results respond to our problematic, which aims to innovate in the field of university training, whether initial or continuous, and above all to prioritize and optimize actions in order to remedy the difficulties encountered before, during and after the launch of a new course. figure 4 illustrates the degree of prioritization of different courses according to the studied criteria. fig. 4. prioritization the result of the proposed method shows that the first 4 courses are favored by several factors that can be summarized in: 9 2 .3 1 % 6 6 .7 3 % 5 8 .3 1 % 5 6 .5 0 % 2 9 .7 3 % 2 7 .2 0 % 2 0 .9 8 % glsid gmasi mli bdc c gmsi sid ge c si engineering, technology & applied science research vol. 9, no. 1, 2019, 3726-3733 3732 www.etasr.com benmoussa et al.: a multi-criteria decision making approach for enhancing university accreditation … do not alter header & footer. they will be completed during editing • relevant course modules • interesting potential of human resources • strong demand for these specialties on the market however, for all courses, we must focus on the material and teacher’s specialties constraints. in addition, some modules may be enriched, deleted or replaced. the results show that the engineering, industry and big data rank first in relation to others because all criteria are fulfilled. this explains why, before launching a new course, we have to focus on the indicators studied and evaluate the limits of the human and material resources which are at the origin of the success of any course. in addition, we must prioritize these courses because they are innovative and meet current and immediate market expectations. admittedly, they require more teaching resources and considerable experience in the field, but the situation can be improved by setting up performance tools such as balanced scorecards. our method allowed the evaluation of possible alternative solutions for the continuous improvement of the performance of the studied formations. the proposed framework can help universities identify the strengths and weaknesses of their human and material resources. it also makes it easier for decision-makers to plan future strategies to develop educational courses and identify the best practices for each course while respecting current strategies, the job market, and the technological evolution. v. conclusion the main goal of this study was to provide a decisionmaking tool for effective management of the initial and continuing training map. we focused on the case of multicriteria decision-making in the system of applications for accreditation of innovative training in order to prioritize decisions and the incessant changes in the labor market. it should be noted that the interaction between the different stakeholders (decision makers, department heads and teachers) is always present. in this context, we opted for mcdm methods in general and topsis in particular, which uses precise parameters to calculate the performance for each studied element. using this tool, we were able to quantify the internal and external criteria identified from specifications and interviews. these indicators were determined and can be expanded in the future according to the academic needs and standards. they allowed us to to enable decision-makers to target the best alternative and also to correct those that are interesting but have lower results. in conclusion, the multicriterion aspect and the proposed approach combining the analysis of internal/external criteria via the topsis tool, made possible to select and prioritize the actions to be taken for an effective decision. these coefficients will help university officials in determining the value of different alternatives in order to focus human and material resources on the emergencies to be addressed and the innovative trainings to be planned. when it comes to future work, this same approach can be completed by a calculation of weights of each of the criteria announced or taken over with fuzzy topsis or promethee gaia for more details, especially the management of uncertainties and sensitivity of situations through a prescriptive and descriptive approach, and scorecards for helping in decision-making. references [1] m. diaby, f. valognes, a. clement-demange, “utilisation d’une methode multicritere d’aide a la decision pour le choix des clones d’hevea a planter en afrique”, biotechnologie, agronomie, societe et environnement, vol. 14, no. 2, pp. 299-309, 2010 (in french) [2] d. vanderpooten, aide multicritere a la decision concepts, methodes et perspectives, ens cachan, 2008 (in french) [3] s. b. mena, “introduction aux methodes multicriteres d’aide a la decision”, biotechnologie, agronomie, societe et environnement, vol. 4, no. 2, pp. 83-93, 2000 (in french) [4] j. ninin, l. mazeau, “la recherche operationnelle: de quelques enjeux juridiques des mecanismes d’aide a la decision”, lex electronica, vol. 22, pp. 57-79, 2017 (in french) [5] d. c. porumbel, “algorithmes heuristiques et techniques d’apprentissage applications au probleme de coloration de graphe”, phd thesis, université d'angers, 2009 (in french) [6] b. roy, regard historique sur la place de la recherche operationnelle et de l’aide a la decision en france, universite paris-dauphine, 2006 (in french) [7] t. l. saaty, “decision making with the analytic hierarchy process”, international journal of services sciences, vol. 1, no. 1, pp. 83-98, 2008 [8] b. roy, h. aissi, robustesse en aide multicritere a la decision, universite paris-dauphine 2008 (in french) [9] a. appriou, “methodologie de la gestion intelligente des senseurs”, traitement du signal, vol. 22, no. 4, pp. 305-306, 2005 (in french) [10] b. roy, d. bouyssou, aide multicritere a la decision: methodes et cas , economica, 1993 (in french) [11] m. hanine, o. boutkhoum, a. tikniouine, t. agouti, “application of an integrated multi-criteria decision making ahp-topsis methodology for etl software selection”, springerplus, vol. 5, pp. 1-17, 2016 [12] t. l. saaty, l. g. vargas, models, methods, concepts & applications of the analytic hierarchy process, springer, 2001 [13] f. tscheikner-gratl, p. egger, w. rauch, m. kleidorfer, “comparison of multi-criteria decision support methods for integrated rehabilitation prioritization”, water, vol. 9, no. 2, pp. 1-28, 2017 [14] d. ozturk, f. batuk, “technique for order preference by similarity to ideal solution (topsis) for spatial decision problems”, isprs 4th international workshop, trento, italy, march 2-4, 2011 [15] a. mardani, a. jusoh, k. nor, z. khalifah, n. zakwan, alireza, “multiple criteria decision-making techniques and their applications”, economic research-ekonomska istrazivanja, vol. 28, no. 1, pp. 516571, 2015 [16] t. jolanta, z. edmundas, t. zenonas, p. vainiunas, “multi-criteria complex for profitability analysis of construction projects”, economics and management, vol. 16, pp. 969-973, 2011 [17] z. edmundas, m. abbas, t. zenonas, j. ahmad, n. khalil, “development of topsis method to solve complicated decision-making problems”, international journal of information technology & decision making, vol. 15, no. 3, pp. 645-682, 2016 [18] g. o. odu, o. e. charles-owaba, “review of multi-criteria optimization methods – theory and applications”, iosr journal of engineering, vol. 3, no. 10, pp. 1-14, 2013 [19] d. ayadi, optimisation multicritere de la fiabilite: application du modele de goal programming avec les fonctions de satisfactions dans l’industrie de traitement de gaz, phd thesis, universite d’angers, 2010 (in french) [20] k. solecka, “electre iii method in assessment of variants of integrated urban public transport system in cracow”, transport problems: an international scientific journal, vol. 9, no. 4, pp. 83-96, 2014 engineering, technology & applied science research vol. 9, no. 1, 2019, 3726-3733 3733 www.etasr.com benmoussa et al.: a multi-criteria decision making approach for enhancing university accreditation … do not alter header & footer. they will be completed during editing [21] l. sifeng, c. hua, c. ying, y. yingjie, “advance in grey incidence analysis modelling”, 2011 ieee international conference on systems, man, and cybernetics, anchorage, usa, october 9-12, 2011 [22] f. y. ma, “analysis of energy effinciency operational indicator of bulk carrier operational data using gray relation method”, journal of oceanography and marine science, vol. 5, no. 4, pp. 30-36, 2014 [23] s. greco, m. ehrgott, j. r. figueira, multiple criteria decision analysis: state of the art surveys, springer, 2005 [24] s. c. deshmukh, “preference ranking organization method of enrichment evaluation promethee”, international journal of engineering science invention, vol. 2, no. 11, pp. 28-34, 2013 [25] m. zare, c. pahl, h. rahnama, m. nilashi, a. mardani, o. ibrahim, h. ahmadi, “multi-criteria decision making approach in e-learning: a systematic review and classification”, applied soft computing, vol. 45, pp. 108-128, 2016 microsoft word 14-3340_s_etasr_v10_n2_pp5419-5422 engineering, technology & applied science research vol. 10, no. 2, 2020, 5419-5422 5419 www.etasr.com belkhir: simple implementation of a fuzzy logic speed controller for a pmdc motor with a low cost … simple implementation of a fuzzy logic speed controller for a pmdc motor with a low cost arduino mega kamel salim belkhir department of electrical engineering faculty of technology university ferhat abbas setif 1 setif, algeria ksbelkhir@univ-setif.dz abstract—control of the permanent magnetic direct current pmdc motor is a common practice, hence the importance of the implementation of the pmdc motor speed controller. the results of a fuzzy logic speed controller for the pmdc motor rely on an appropriate base. as the dimension of the rules increases, its difficulty rises which affects computation time and memory requirements. fuzzy logic controller (flc) can be carried out by a low-cost arduino mega which has a small flash memory and a maximum clock speed of 16mhz. it is realized by three membership functions and each was divided into three memberships. the results of the flc are satisfactory, revealing superior transient and steady-state performance. in addition, the controller is robust to speed mode variations. keywords-fuzzy logic; pmdc motor; arduino mega i. introduction permanent magnetic direct current pmdc motors have long been commonly used in the industry control area, due to their high performance and the fact that the torque is directly proportional to the field flux, which means that the speed can be adjusted by the terminal voltage [1]. in classical pid controllers, proportional, derivative, and integral control actions are applied together. they are simple in construction, and are appropriate to control the processes with well-defined mathematical models. generally, the exact model is not available, so the conventional pid controller may not be the best choice [2-5]. to overcome this problem, flc is proposed. the flc does not rely on a mathematical model [6]. it can be successfully functional to control nonlinear systems using basic engineering logic [7-8]. with the rapid developments of microprocessors and semiconductor materials, many classical and intelligent control techniques can be applied to control the speed of the dc motor in order to achieve high performance. a minor overshoot and quicker response of motor speed signal were stated in the fuzzy pid control compared to the classic pid control [9]. the neuro-fuzzy controller performed better compared to the pid controller in different loads [10]. compared h2 and h∞ control methods for a dc motor [11], adaptive robust control method for dc motor [12], and speed control of a dc motor used hybrid control methods [13]. these techniques offer a good instrument for the control of nonlinear systems that are hard to model. when choosing flc parameters, several problems occur. among the proposed solutions, adaptive controllers are able to adjust to reach optimum performance [14-17]. however, as the number of rules and large membership functions for fuzzy logic increase, calculation speed and memory storage become serious problems [18-19], so the need for excessive memory and high speed capacity materials for the implementation becomes necessary. fuzzy-logic controllers require more processing power to work in real time as the number of inputs/outputs of the controller increases. in this case, conventional microprocessors are not adequate for most real-time applications. in [20], in order to control the system, quanser q8 data acquisition card along with high performance computers were used for sending analog signals and getting encoder signals. in [21], the data exchange with the pc was provided by a ni usb-6812 daq card, which sent the signals that it received from the feedback tacho generator and control signals to the dc motor control module. in both cases vast resources were used for the control of dc motor. in this concern, the main contribution of the current work is the implementation of the proposed flc controller on the conventional and low cost arduino mega board. the board uses the three membership functions and each membership function’s inputs were divided to three memberships. ii. control strategy the pmdc motor simulink program given in figure 1 was implemented by using the following structures. the inputs of flc are the error speed e and its derivative de by subtracting pmdc motor speed value ω from the reference speed value ω * . e (t) and de (t) for each sampling time t are given as: ���� = �∗���− ���� (1) ���� = ���� − ��� − 1� (2) the output dv is the change in armature voltage v is: ���� = ���� − ��� − 1� (3) corresponding author: kamel salim belkhir engineering, technology & applied science research vol. 10, no. 2, 2020, 5419-5422 5420 www.etasr.com belkhir: simple implementation of a fuzzy logic speed controller for a pmdc motor with a low cost … fig. 1. control speed strategy the linguistic terms used to represent input and output are defined by three variables: negative (n), zero (z) and positive (p). triangular and gaussian membership functions are used. agreeing to the rated speed of the pmdc motor, the interval of discourse of the speed error is between -3000rpm/mn and 3000rpm/mn. the supported rules are shown in table i. table i. final rules e de n z p n n p p z n z p p n n p after adjustments, the final membership functions are obtained (figure 2). the defuzzification method is used at the center of gravity of the membership function dv. (a) (b) (c) fig. 2. input and output membership functions: (a) error speed, (b) change in error speed, (c) change in armature voltage iii. hardware implementation the hardware block diagram is shown in figure 3 and the hardware implementation in figure 4. a matlab program was used to transfer the flc algorithm to the arduino mega card (figure 5) which received the feedback signal from the tachometer and sent signal in the form of pwm to the pmdc motor via dc-dc converter module. the motor specifications ares illustrated in table ii. the pmdc motor was set at noload, 30% load, and 95% load. fig. 3. hardware blok fig. 4. hardware implementation fig. 5. arduino mega table ii. pmdc motor parameters rated power 3.8w rated voltage 20v rated speed 3000rpm iv. experimental results an experiment test was set to demonstrate the performance of the flc. the output voltage was 0-3v to control the motor speed 0–3000rpm. engineering, technology & applied science research vol. 10, no. 2, 2020, 5419-5422 5421 www.etasr.com belkhir: simple implementation of a fuzzy logic speed controller for a pmdc motor with a low cost … (a) (b) (c) (d) (e) fig. 6. operation at various speeds and loads: (a) 1000rpm, 0%, (b) 2000rpm,0%, (c) 2600rpm, 0% (d) 1000rpm, 30%, (e) 1800rpm, 95% the aim was to make the pmdc motor operate at a constant speed for various loads. in order to test whether the system could remain at a constant speed under no-load, the motor was operated at 1000rpmm 2000rpm, and 2600rpm (figure 6(a), 6(b) and 6(c) respectively). it was observed that oscillations were low. also it was shown that the motor achieves the desired speed in less than 5s for overshoot less than 30%. as a next step, the motor was operated at 1000rpm under 30% load at 24s (figure 6(d)) and 1800rpm under 95% load at 22s (figure 6(e)). in the latter case, even though the motor was almost loaded, the flc controller keep the speed constant with no oscillations. the pmdc motor was regulated by the controller and still rotated at the desired speed. the fuzzy controller was capable to realize intelligent control for each speed. explicitly, the speed overshoot and the swings were small. v. conclusion in this paper, a low cost flc controller was designed to control the speed of a pmdc motor. the design extremely diminishes the necessary hardware to the simple conventional arduino mega and on the other hand, the used program was rather simple. in contrast with some distinct fuzzy controllers with several rules and membership functions running on computer systems, a simple flc controller using a small number of rules and a simple implementation program were able to control the speed of the pmdc motor. the controller shows good performance in tracking the reference speed and in terms of reducing steady state error. references [1] n. matsui, “sensorless pm brushless dc motor drives”, ieee transactions on industrial electronics, vol. 43, no. 2, pp. 300-308, 1996 [2] a. w. nasir, i. kasireddy, a. k. singh, “real time speed control of a dc motor based on its integer and non-integer models using pwm signal”, engineering, technology & applied science research, vol. 7, no. 5, pp. 1980-1986, 2017 [3] m. ndje, j. m. nyobe yome, a. t. boum, l. bitjoka, j. c. kamgang, “dynamic matrix control and tuning parameters analysis for a dc motor system control”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3416-3420, 2018 [4] l. a. gadeh, “outline of a new approach to the analysis complex systems and decision processes”, ieee transactions on systems, man, and cybernetics, vol. smc-3, no. 1, pp. 28-44, 1973 [5] e. gowthaman, c. d. balaji, “self tuned pid based speed control of pmdc drive”, 2013 international mutli-conference on automation, computing, communication, control and compressed sensing, kottayam, india, march 22-23, 2013 [6] r. kushwah, s. wadhwani, “speed control of separately excited dc motor using fuzzy logic controller”, international journal of engineering trends and technology, vol. 4, no. 6, pp. 2518-2523, 2013 [7] a. h. o. ahmed, “optimal speed control for direct current motors using linear quadratic regulator”, journal of science and technology, vol. 13, no. 3, pp. 32-38, 2012 [8] d. drainkov, h. hellendoorn, m. reinfrank, an introduction to fuzzy control, springer-verlag, 1993 [9] z. z. liu, f. l. luo, m. h. rashid, “speed nonlinear control of dc motor drive with field weakening”, ieee transactions on industry applications, vol. 39, no. 2, pp. 417-423, 2003 [10] s. v. s. r. pavankumar, s. krishnaveni, y. b. venugopal, y. s. kishore babu, “a neuro-fuzzy based speed control of separately excited dc motor”. international conference on computational intelligence and communication networks, bhopal, india, november 26-28, 2010 [11] y. shi, j. huang, b. yu, “robust tracking control of networked control systems: application to a networked dc motor”, ieee transactions on industrial electronics, vol. 60, no. 12, pp. 5864-5874, 2013 engineering, technology & applied science research vol. 10, no. 2, 2020, 5419-5422 5422 www.etasr.com belkhir: simple implementation of a fuzzy logic speed controller for a pmdc motor with a low cost … [12] z. li, j. chen, g. zhang, m. g. gan, “adaptive robust control for dc motors with ınput saturation”, iet control theory & applications, vol. 5, no. 16, pp. 1895-1905, 2011 [13] s. h. kim, k. ishiyama, “hybrid speed control of a dc motor for magnetic wireless manipulation based on low power consumption: application to a magnetic wireless blood pump”, ieee transactions on magnetics, vol. 50, no. 4, article id 5000307, 2014 [14] a. fereidouni, m. a. s. masoum, m. moghbel, “a new adaptive configuration of pid type fuzzy logic controller”, isa transactions, vol. 56, pp. 222–240, 2015 [15] h. acikgoz, “speed control of dc motor using interval type-2 fuzzy logic controller”, international journal of intelligent systems and applications in engineering, vol. 6, no. 3, pp. 197-202, 2018 [16] a. ramya, m. balaji, v. kamaraj, “adaptive mf tuned fuzzy logic speed controller for bldc motor drive using ann and pso technique”, iet the journal of engineering, vol. 2019, no. 17, pp. 3947–3950, 2019 [17] d. k. panicker, m. r. mol, “hybrid pi-fuzzy controller for brushless dc motor speed control”, iosr journal of electrical and electronics engineering, vol. 8, no. 6, pp. 33-43, 2013 [18] l. t. ngo, d. d. nguyen, l. t. pham, c. m. luong, “speed up of interval type 2 fuzzy logic systems based on gpu for robot navigation”, advances in fuzzy systems vol. 2012, article id 698062, 2012 [19] d. k. chaturvedi, r. umrao, o. p. malik, “adaptive polar fuzzy logic based load frequency controller”, international journal of electrical power & energy systems, vol. 66, pp. 154-159, 2015 [20] a. avcu, a. f. bozkurt, k. erkan, i. kurt, s. sezer, “comparison of ipd and fuzzy logic velocity control in two degree of freedom dc motor system”, international journal of engineering science and application vol. 2, no. 1, pp. 1-7, 2018 [21] i. kandilli, “real-time speed controlling of a dc motor using fuzzy logic controller”, pamukkale university journal of engineering sciences, vol. 23, no. 5, pp. 543-549, 2017 engineering, technology & applied science research vol. 8, no. 4, 2018, 3287-3293 3287 www.etasr.com benmoussa et al.: web information system for the governance of university research web information system for the governance of university research khaoula benmoussa information system engineering research group national school of applied sciences abdelmalek essaadi university tetouan, morocco majida laaziri information system engineering research group national school of applied sciences abdelmalek essaadi university tetouan, morocco samira khoulji information system engineering research group national school of applied sciences abdelmalek essaadi university tetouan, morocco kerkeb mohamed larbi information system engineering research group faculty of sciences abdelmalek essaadi university tetouan, morocco abstract—technology development has proved crucial in analyzing and processing the volume of scientific information that is generated today. governments are developing scientific and technical information systems that, beyond a database, are a real tool for supporting research management and decisionmaking in the field of science and technology policy. for the development of higher education in morocco, the ministry has focused on projects for the management and development of university research. for this purpose, abdelmalek essaadi university developed an efficient application dedicated to the management of collaborative extranet called simarech (moroccan information system of scientific research), in order to support, organize and structure all academic activities. it will enable all university stakeholders to use a digital workspace specific to their roles, to access and share information, and interact and engage in national scientific research. this article presents an overview of research management systems and the design and development of simarech, which is designed as a tool for monitoring research conducted by a university or other institutions. keywords-simarech platform; web information system; management of research; university scientific research i. introduction governments want high-level universities because the modern economy is based on scientific research and highly skilled human capital. each university must have a clear and evidence-based understanding of the institution's research performance in relation to its objectives and mission [1]. since research is a central function, the university must evaluate its research performance, something that will help the decision making about which research areas to support or build [2]. it will also help university leaders to understand the institution's position in relation to global and national standards of research production. for a good piloting of scientific research, an information system becomes a mandatory condition to manage better investments in science in order to evaluate the performance of research and to establish a solid policy for the development of scientific research [3]. to this end, moroccan universities have decided to adopt the digital application called simarech set up by abdelmalek essaadi university, which aims to develop an information system initiative whose ultimate goal is to support researchers and enhance their scientific activities. the incorporation of simarech into moroccan universities has contributed to a significant increase in the number of active researchers, the quantity of research projects in progress, the external and internal funds obtained and the number of publications in indexed journals. simarech can be defined as a set of people, processes and equipment designed, built, operated and maintained to collect, record, process, store, retrieve and display information about the activities and results produced by the researchers in their development centers or in collaboration with other national or international institutions. ii. global research management systems overview global research management has benefited greatly from the development of research management systems that reflect the research results generated in universities and research centers, organizations, institutions, etc. the development or improvement of a research information system requires a comparative study of similar existing systems and as well as taking into account remarks from researchers or users of the system. a. research management systems in latin america table i shows an overview, the advantages and the disadvantages of the respected systems (sgi, sicytar). b. research management systems in europe the same applies in table ii regarding the european research management systems (sica, graal, iris). engineering, technology & applied science research vol. 8, no. 4, 2018, 3287-3293 3288 www.etasr.com benmoussa et al.: web information system for the governance of university research table i. latin american research management systems systems overview advantages cons sgi (chile) developed in 2001 at the university of talca to support the academic activities of their researchers [4]. includes a range of information services for the exclusive use of specific users of university researchers, aims to have a set of indicators and related statistics of available research capabilities, stays informed in the results of academic research, exchange knowledge at national and international level, allows visitors to the sgi platform to view the researchers' cv [4-6]. limited to the management of university research. limited to the management of research projects and indexed publications. [4] sicytar (argentina) sicytar was established in 2002, in order to facilitate and unify the access to information on scientists, technicians and their jobs [11]. keeps a unified cvar register constantly updated [9]. produces through the infosicytar service of the platform detailed statistical information to develop indicators and evaluate science and technology policies, for exclusive use by the institutions of national system of science, technology and innovation [10] provides the buscar tool for networking among researchers, as well as government and commercial sectors accessible to all visitors [7]. there is not an identifier to distinguish the user from the system, it is accessible to everyone, a researcher or other from any country can create an account and provide false information, something that makes the statistics information withheld questionable [8]. table ii. european research management systems systems overview advantages cons sica (spain) sica was born as a research project in 2001, through a cooperation agreement between the ministry of education and culture of the government of andalusia and the university of granada to meet the specific needs of the organizations of operational management to promote research and technological development in spain [13, 15]. assists management in general and those responsible for science policy especially in decision-making, provides updated information from individual researcher programs, flexible mechanisms for management and maintenance on an ongoing basis, establishes an authorized knowledge base with standardized criteria in the evaluation and quality of the results of the scientific activity, encourages the transfer of results between different types of information [13, 15]. accessible to everyone, all people (researchers or other) have the opportunity to create an account and enrich the sica database with information which may be wrong [12, 13]. the evaluation of research by this system is imprecise. graal (france) graal is a software program launched in 2000 by the interuniversity computing center of grenoble. its management was then entrusted to a group of scientific interest (gls) bringing together the public partners concerned [16]. presents and manages in a coherent way the research units within the university including the personnel and their scientific activities, manages the monitoring of financial means and international activities within the university [16]. limited just to the research management of university research units [16]. iris (italy) adopted in 2015 by the university of l'aquila in italy, it is a platform of data management on research activities, was designed to meet the needs of academic institutions and research. it is now installed in seven establishments outside italy [17]. iris aims to collect, manage and store the results of the scientific research of the university, professors, researchers, the fellows of research, specialization and phd students, as well as administrative staff members can access the platform using their credentials to catalog their published research, iris aims to control the results of research and to improve the visibility of the university's production, has five different modules integrated through standard protocols and interfaces, one of the main components of iris is dspace-cris, an open source solution that can also be used as a standalone system [17, 19]. does not allow managing and evaluating of research activities of each unit independently of the other [20] . c. the globally recognized research information management system (rims) rims project is an initiative funded by dst and powered by infoed. authors in [21, 22] described rims as a potential new category of services for libraries. rims is an integrated online system for managing grants and the administration of ethics in research projects and research activities. it provides researchers, administrative and executive staff with a single point of reference for these aspects of research projects [22, 24]. the software is used by more than 600 academic, medical and scientific institutions around the world [21, 22, 24, 25]. iii. simarech the moroccan information system of scientific research (simarech) aims to collect, manage and store research (research, professional, educational and international activities) at national level. its modular nature and flexibility of its data model facilitate the processing, organizing and transmission of information in accordance with international standards. the development team has worked to develop a scalable and customizable application that aligns with local, national and international research policies, and recognizes the autonomy of universities in terms of governance of the scientific research [25]. simarech has taken into consideration the advantages and disadvantages of the previously presented systems. a. general simarech was created at abdelmalek essaadi university in 2008 to help develop the research potential by highlighting the scientific production and know-how of researchers. simarech can also be used as an assessment tool and could help decision making. initially, the system was structured to include a range of services for the exclusive use of specific users based on their pro res str rel has mo wa inc and act situ and eva sel all res un to sec pat 1) ma adm       2) un  engineerin www.etasr ofile, with resp sulting from rategic level th lated statistics s been designe oroccan mana ay the institut cluding the pe d the monito tivities [26]. s uation and a d material res aluation of res lf-evaluation a ows for a tran sponsible of a iversity admin print docume ctions: index tents, etc. [27] administrati simarech i aintaining inn ministrative pr reducing the streamlining providing au access to i compliance. improving th demands of a making the understand a processes. making the p status, inform between univ university p simarech ha iversities and promote a 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web r. the create of the c. ts and eation th the sults. n and versity rsity. argely cts the es and e tool on one given nds of ate the search rsity’s st and , with nce in eer of higher ing to entific a, n. a. or the ocedia ometric ges and iety for 9-1935, [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] vol. 8, no. 4, 20 b information s n. barts, infoc pilotage de la r université paul i. f. palomo, c investigación tecnológica, v universidad de spanish) j. e. p. latour, la investigación distrito de nue chimbote, 2014 buscador sicy (in spanish) sicytar http://cvar.sicyt cvar, availab spanish) ] nuevo sitio d argentino mi available at: ht de-informacion ] sistema de info available a de_ciencia_y_t ] guia de usu /help/index.htm ] f. m. solis cab una experiencia (in spanish) ] sistema de i https://sica2.cic ] p. desfray, g. architecture”, morgan kaufm ] amue, “gestio recherche, app (in french) ] a. bollini, m. m managing the research, vol. ] v. zwass, mana ] cineca inter information sys ] universita, de information sy institutional-res ] l. dempsey, “ service catego information-ma ] acrl, “keep systems”, a keeping_up_wi ] m. hasan, n. m hassan, “deve management international c systems (icrii ] m. mangena, “ project”, avai launch-of-resea 2008-02-26, 20 ] university of https://www.new research-system about-rims 018, 3287-3293 system for the g centre recherche : recherche d’un é l cézanne-aix-ma c. g. veloso, r. en la universi ol. 18, no. 1, pp. e talca, informe implementacion n tecnologica en evo chimbote, 20 4 (in spanish) ytar, available a identificación tar.mincyt.gob.ar/ ble at: http://ww el sistema de i nisterio de cienc ttp://www.mincyt n-de-ciencia-y-tecn ormacion de cien at: https://ww tecnología_arge uario de sica ml?anexo_iii.htm ( brera, “el sistema a pionera en espa informacion cie ca.es/# raymond, “mo in: modeling e mann, 2009 on de la recherch plication des act mennielli, s. mor research life-cy 4, no. 4, pp. 738agement informat runiversity cons stem, cineca, 2 egli studi di m ystem), available search-informatio “research inform ory”, available anagement-system ping up with.. available at: th/rims, 2016 maarop, g. n. sam eloping a succ system for re conference on re is), langkawi, m “launch of rese ilable at: http: arch-information-m 08 newcastle, aus wcastle.edu.au/re ms/research-inform 3 governance of système d’infor tablissement de r arseille iii, 2008 f. schmal, “sis idad de talca, 97-106, 2007 (in gestion universi de un sistema inf el i.s.t.p. carlo 014, universidat, at: http://sicytar.m de usuario /auth/index.jsp (in ww.mincyt.gob.ar información de cia, tecnología e t.gob.ar/noticias/n nologia-argentino ncia y tecnologi ww.ecured.cu/sis ntino (in spanish a2, available a (in spanish) a de informacion c ana”, madri+d, n entifica de and odels for phase c enterprise archi he, application d tivit es laboratoir rnati, d. t. palme ycle”, universal -743, 2016 tion systems, wm sortium, iris, 2015 messina, iris ( e at: http://www n-system mation managem at: http://orwe ms-a-new-service. research info http://www.al my, h. i. baharum ess model of esearch affiliated esearch and inno malaysia, august 1 earch information ://www.polity.org management-syst stralia, “about esearch-and-innov mation-manageme 3292 f university res mation, outil d’a recherche, phd t (in french) stema de gestión chile”, inform n spanish) idad de talca, 20 formatico de gest os salazar rome , catolica los a mincyt.gob.ar/bus o, available n spanish) r/accion/cvar-646 ciencia y tecn innovacion produ nuevo-sitio-del-si o-11530 (in spani a argentino – ec stema_de_inform h) at: https://sica2.c cientifica de and no. 22, pp. 12-18 dalucia, availab c: information s tecture with to es activit gestion res laboratoires” er, “iris: suppor journal of educa m. c. brown, 199 institutional re (institutional re w.unime.it/it/ricerc ment systems a eblog.oclc.org/res -category/, 2014 ormation 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science research vol. 9, no. 4, 2019, 4433-4439 4433 www.etasr.com karkush et al.: magnetic field influence on the properties of water treated by reverse osmosis magnetic field influence on the properties of water treated by reverse osmosis mahdi o. karkush civil engineering department university of baghdad baghdad, iraq mahdi_karkush@coeng.uobaghdad.edu.iq mahmoud d. ahmed civil engineering department university of baghdad baghdad, iraq mahmoud_baghdad@yahoo.com salem m. a. al-ani civil engineering department university of baghdad baghdad, iraq salimalani39@yahoo.com abstract—the current study is focused on reviewing the rapid growing of magnetic water use in different science fields and in measuring the influence of several intensities of magnetization on the chemical and electrical properties of tap water treated by reverse osmosis. this work includes water circulation for 24h in magnetic fields of intensities 500, 1000, 1500, and 2000g. the magnetization of water increases some ions in the water such as mg, k, na, cl, and sio2 and decreases ca and so3. the main application of magnetic water is the improvement of the geotechnical properties of soft and swelling soil through precipitation of calcite in pores which increases the bond between soil particles and the strength of the soil. keywords-magnetic field; water; cheimical properties; electric properties; reverse osmosis i. introduction water is a polar molecule in a v-shaped order of dipoles. magnetic water is defined as raw or treated water passed through magnetic field of various intensities and circulation periods. water properties include magnetic sensitivity and when subjected to a magnetic field, these properties change. the changes could be of negative or positive impact according to the use. water meniscus is not homogeneous and depends on the applied pressure and temperature. magnetization can affect the two forces that control the water structure, chemical hydrogen bond and van der waal’s forces, where magnetization can break down its structure, reduce the linkage angle and increase solubility [1, 2]. it is found that the magnetic field changes the size of the water clusters which in turn changes the physical properties of water [3, 4]. increase in the intensity of magnetic field causes decrease of the surface tension of tested water samples, which reduces the capillary rise of water [5]. the magnetic field application in wastewater has improved its physical and biological property performance in terms of solid-liquid separation through aggregation of colloidal particles and improvement of bacterial activity [6]. the compression strength of concrete produced using magnetic water is increased by 10%-23% compared to the concrete mixture prepared with plain tap water [7]. the circulation of raw salt water in magnetic field of 2000g intensity increased the k, mg, na, and al cations and decreased anions (cl and so3). the results of the treatment of irrigation water by magnetic field showed beneficial effects on the germination of seeds, plant growth and development, and crop yield [8]. authors in [9] investigated the effects of magnetization on the ability of magnetite (fe3o4) nanoparticles, synthesized by chemical co-precipitation, in removing metal ions from water. the nanoparticles of magnetite are promising potential adsorbents and exhibit remarkable reusability for removal of metal ions from water and wastewater. the effect of magnetic field dependent viscosity on free convection heat transfer of a nanofluid in an enclosure considering brownian motion had been studied in [10], where the bottom wall had constant heating flux. the results showed that the nusselt number is an ascending function of the rayleigh number and the nanoparticle volume fraction, but it is a descending function of viscosity parameter and hartmann number. there was significant decrease in salinity measured in terms of electrical conductivity (ec), na, and cl content, in soil irrigated with saline water treated by magnetization. in contrast, there were created non-significant effects on mg 2+ and hco3̄ . the deficiency or high cost of potable water pushed farmers to use saline water for irrigation, but the saline water needed to be treated before use. the test results showed that salt contents in soil increased with increasing depth in the column of soil treated with magnetic water where the salts moved deeper during the treatment process [11]. the top layer of soil is very important in agriculture [12]. the influence of magnetization of water on the rate of calcite precipitation and formation on the membranes of reverse osmosis process had been studied in [13]. tests were conducted on tap water using a module of spiral wound with reverse osmosis membranes. the results did not show any effect for magnetization on the precipitation and formation of calcite. the present study is focused on reviewing the applications of magnetized water in different science fields, especially in water treatment and improvement of the chemical and geotechnical properties of soil. also, the influence of magnetic field of several intensities on the chemical and electrical properties of water treated by reverse osmosis and ozone has been studied. this water can be used in improving the geotechnical properties of swelling soils. ii. magnetic water applications the magnetized water has many applications in different science fields and in industry, especially in green technology. corresponding author: mahdi o. karkush engineering, technology & applied science research vol. 9, no. 4, 2019, 4433-4439 4434 www.etasr.com karkush et al.: magnetic field influence on the properties of water treated by reverse osmosis the circulation of water in magnetic field can change some of its properties. these changes may be useful in industries associated with water properties like ph, surface tension, electrical resistivity, viscosity, and calcite formation inhibition. magnetized water has many applications in green technology, e.g. in the remediation of contaminated soil and water. also, magnetized water can be used as injection fluid in oil recovering areas [14]. a. water purification the treatment of water can be classified according to its source: domestic, natural, and wastewater. according to the quality of water, a specific plan of action will be adopted for reuse, treatment, or disposal. the treatment of water depends on the type and the specifications of effluents. the available techniques of water purification are adsorption, catalytic processes, biotechnology, membrane treatment, ionizing radiation, and magnetization processes. high gradient magnetic separator (hgms) is a technique commonly used in the separation of particles [15-18]. the application of a magnetic field across a column of water will produce a magnetic gradient along the column and will attract magnetized particles to the surface and help trap these particles, so the collection of particles depends on the magnetic gradient, particle size, and maybe their shape. b. wastewater treatment there are many chemical, physical, and biological techniques used for wastewater treatment. the quantity of wastewater is mainly related to the size of population and the level of development. rapid industry development and growing population produce different types of wastewater which require different types of technology for reuse or treatment. the magnetic field have been used in treatment of wastewater for several purposes such as the removal of colors, heavy metals, suspended solids and turbidity, organic compounds, and toxic chemicals [19-21]. however, more research is required in this field. c. formation of calcium carbonate (caco3) the formation of caco3 has the attention of many researchers because of its wide range of applications in engineering processes, e.g. as cementing agent, adsorbent material, and brightener filler [22-26]. the sedimentation of caco3 causes damages and operational problems such as blocking of pipes, clogging of membranes, and efficiency decay in heaters. several methods have been used to prevent precipitation of caco3 (scaling) such as water decarbonization through electrochemical processes and addition of acid and chemical inhibitors. keeping in mind that chemical treatment may be harmful to public health, therefore, physical techniques have been developed to avoid the use of chemicals. one of these techniques is the magnetic treatment of hard water [2627]. the precipitation of different types of crystals under the existence of a magnetic field proved that caco3 is considered the most thermodynamically stable crystal at standard temperature and pressure and forms thick layers that are difficult to be removed mechanically [28-30]. improvement and remediation of soil is considered one of the important fields in geotechnical engineering. the application of magnetic field to the water circulated through weak, swelling or contaminated soils may help to build bonding between particles of soil through precipitation of calcite in soil pores. these bonds depend mainly on the quantity of calcite precipitated in the pores and the ability of calcite in absorbing the contaminants from soil. d. synthesis of phas from biomass sludge the application of magnetic field on bacteria cultivations enhanced their growth [31-33], depending on the gradient of magnetic field and the type of existing microorganisms. many studies investigated the effects of magnetization on the growth of microorganisms, yet the synthesis of polyhydroxyalkanoates (phas) under a magnetic field has not been investigated in details. also, carbon waste such as activated sludge can be used to reduce the cost of processing [34-37]. using acetate of concentration more than 200cmmol/l can prevent cell growth and pha formation [38]. therefore, magnetization treatment can be used to enhance the production of pha under unfavorable conditions. e. magnetic water treatment in agriculture the magnetization of water changes its chemical and physical properties and these changes will affect the soil-waterplant-system. the irrigation of soil with magnetic water will increase the available alkalines such as na, k, and mg significantly. the magnetic susceptibility of nutrients will determine its behavior under the magnetic field. generally, the molecules in nonmagnetic water are in loose state, but they cluster together due to attraction forces provided by magnetization. these forces may help pollutants, especially the toxic ones, to move inside the water molecule cluster. also, the large structure of water molecule clusters or toxic molecules can clog the membrane when they pass through a membrane cell [39-41]. the magnetization of water will prevent the toxic agents from entering its structure, therefore the magnetic water is considered as a bio friendly fluid. using magnetic water in agriculture will help increase crop yield and benefit the health of biomass. using magnetic water will help conserve fresh water supplies for the expected water crisis [39, 40, 42]. iii. materials and methods pure water as a dipolar and associative liquid can alter its intermolecular bonds under the application of magnetic field and transform to a metastable state [43]. the magnetic field will affect both physical and chemical processes of crystallization and dissolution of water molecules [44]. there are two main different types of magnetic field effects. the direct field which affects the biochemical reactions and the indirect field which affects the surroundings [45]. in the first type of magnetic field, the concern might be the possible genetic influences on living organisms, but the second type of magnetic field may have secondary effects such as temperature, pressure, or mechanical stirring. in the present study, the water container was made from plastic fiber (acrylic) material. the used water pump has the following properties: 25w power, 18m head, 1000l/h flow rate, and ac 220v, 50hz and the provided magnetic fields were 500, 1000, 1500, and 2000g in a with plastic tube of 12mm diameter. all these parts were connected together in a basin of water containing 10l of water engineering, technology & applied science research vol. 9, no. 4, 2019, 4433-4439 4435 www.etasr.com karkush et al.: magnetic field influence on the properties of water treated by reverse osmosis treated by reverse osmosis (ro) as shown in figure 1. the water magnetization device was supplied from a local factory. water treated with ro will be the reference for comparison. the procedure of magnetization of water can be easily described by putting 10l of the reference water in the plastic box. the box is supplied with a submersible pump and the magnetization equipment is fixed on the top of the box. the submersible pump is connected to the magnetization equipment by the 12mm tube. the circulation of water in the magnetic field was continued for 5 days, but the water’s most chemical and electrical properties remained approximately constant after 24h. the practical use of water magnetic treatment is based on certain changes in its physical and chemical properties. intensification and stabilization of small initial changes in properties can occur with the help of intermediate mechanisms increasing many times these changes. water tank submersible pump power supplyregulator regulator ph meter magnets tube tube direction of flow fig. 1. schematic diagram of the magnetic system. table i. water analysis methods parameter symbol specification ph ph value astm, d1293 electrical conductivity ec astm, d1125 total alkaline alkaline astm, d1067 total dissolved salts tds astm, d5907 silicon dioxide sio2 astm, d859 chloride content cl¯ astm, d512 sulfate so4 astm, d516 magnesium, calcium mg, ca, astm, d511 sodium na astm, d4191 potassium k astm, d4192 in most cases, such intensification is inherent to heterogeneous systems and their phase transitions. for example, the slightest stimulation of crystal formation can cause avalanche irreversible bulk crystallization, with all the process consequences. a slight decrease in the hydration degree of solid particles under certain conditions can lead to their mass coagulation, significant improvement in filtration, etc. the tested chemical and electrical properties of water are listed in table i. iv. results and discussion previous studies demonstrated that magnetic water treatment influences the molecular and physicochemical properties of water that alter its quality. the effects of magnetic treatment on irrigation water include increasing the number of crystallization centers and altering the free gas content [33]. the factors affecting the magnetization process are flow rate, circulation time, magnetic field intensity, carbonate water hardness of more than 50mg/l, and the concentration of hydrogen ions in water at ph value>7.2. to determine the influence of magnetic field intensity on the properties of water, several intensities ranging from 500g to 2000g produced by common lab devices were applied to water treated by ro. the circulation of water in the magnetic field continued for 5 days, but almost all properties remained constant after 24h. experimental studies have shown that magnetic treatment can increase the number of crystallization and modulates the free gas content of the solution [46]. magnetic treatment on water plays important role in different procedures influencing the crystallization process such as association, dissociation, and nucleation rates [29, 33, 47] a. effects of magnetization on ph pure water is considered neutral when having a ph value of 7 at room temperature (25°c), where the amounts of h + ions and oh¯ ions are equal. water becomes more volatile as a result of magnetic processing due to the weakening of the hydrogen bonds between its molecules [48]. the magnetic process can change the ph of water [49]. decrease in ph is caused by the formation of calcite nuclei resulting from the liberation of h + ions. �� � � � � � ⇌ � � �� � (1) � � �� � � � � ��� � (2) �� � � ��� � ⟶ ���� � � � (3) fig. 2. concentration of ph vs magnetic field intensity figure 2 shows the variation of ph under magnetic field of different intensities. when water passed through the magnetic field, the ph value increased by 6% to 34.34% when the magnetic field intensity increased from 500g to 2000g under 6,4 6,8 7,5 7,9 8,6 0 2 4 6 8 10 0 500 1000 1500 2000 p h v a lu e magnetic field (g) engineering, technology & applied science research vol. 9, no. 4, 2019, 4433-4439 4436 www.etasr.com karkush et al.: magnetic field influence on the properties of water treated by reverse osmosis constant flow rate of 1000l/h. for flow rate higher than 2160l/h, the ph value was stable under various magnetic fields [50]. according to the results, the ph value increases with increasing magnetic field intensity, which means absorption of h + ions and increasing number of oh¯ ions in the water. these finding were confirmed by previous studies, but with increasing percentage of 0.53% to 5.6% [51-53], this difference is mainly due to the quality of the used water and the physicochemical parameters. b. effects of magnetization on alkalines the alkaline metals are basic when dissolved in water with ph value greater than 7.0. generally, the water forms more carbonate without magnetization which accelerates the precipitation of calcite. magnetic field inhibits the precipitation of bicarbonates, and inhibits the formation of calcites, but the magnetization increases the precipitation of na, k, and mg. mostly, the alkaline metals increase with increasing magnetic field intensity. also, the magnetic field induces faster proton transfer from hydrogen carbonate to water due to the inversion spin of protons in the diamagnetic field of salts. figure 3 shows the variation of alkaline concentration with different intensities of magnetic field, where the alkaline concentration increased from 238% to 450% when the magnetic field increased from 500g to 2000g. the test results demonstrated significant increase in the concentration of alkaline minerals with increasing magnetic field intensity. the alkalines may be affected by flow velocity. the intensity of magnetic field did not affect the alkaline content at the highest flow velocity, but had significant effects on the content of alkaline at low flow velocity [54]. fig. 3. concentration of alkalines vs magnetic field intensity figure 4 shows the variation of concentration of alkaline minerals: magnesium (mg), calcium (ca), sodium (na), and potassium (k) with different magnetic field intensities. the concentration of mg and k in water increased significantly with increased magnetic field intensity. na does not occur freely in nature and is prepared chemically from compounds. na salts are highly soluble in water. the concentration of na increased significantly when the magnetic field intensity increased. the ph value increases with increasing magnetic field intensity and the concentration of ca ions decreased. in other words, the high precipitation of caco3 makes a significant drop in the calcium content. the magnetic field inhibits the growth of crystal particles [54]. the concentration of ca decreases with increasing magnetic field intensity. fig. 4. concentration of mg, na, ca, and k vs magnetic field intensity c. effects of magnetization on chloride chloride (cl − ) is an anion formed when the cl element gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. chloride salts are very soluble in water. figure 5 shows the variation of cl¯ concentration with different magnetic field intensities. the concentration of cl¯ increased by 20, 45, 75, 100% for magnetic field of 500, 1000, 1500, and 2000g intensity respectively fig. 5. concentration of cl¯ vs magnetic field intensity d. effects of magnetization on silicon dioxide silicon dioxide (sio2) is a chemical compound extensively found in quartz, sand, and in living organisms. this compound is not very reactive because the polarity of its molecule is zero. silica is a major compound of sandy soils having many uses in chemical, electronic and pharmaceutical industries. fig. 6. concentration of sio2 vs magnetic field intensity 16 54 70 81 88 0 20 40 60 80 100 0 500 1000 1500 2000 a lk a li n e (m g /l ) magnetic field (g) 0 5 10 15 20 25 30 35 40 0 500 1000 1500 2000 m in e ra l c o n te n t (% ) magnetic field (g) mg content na content ca content k content 20 24 29 35 41 0 10 20 30 40 50 0 500 1000 1500 2000 c l¯ (m g /l ) magnetic field (g) 2,1 2,7 3,3 3,7 4,1 0 1 2 3 4 5 0 500 1000 1500 2000 s io 2 (% ) magnetic field (g) engineering, technology & applied science research vol. 9, no. 4, 2019, 4433-4439 4437 www.etasr.com karkush et al.: magnetic field influence on the properties of water treated by reverse osmosis figure 6 shows the variation of sio2 concentration with different intensities of magnetic field, where sio2 concentration increased by 28, 57, 76, and 95% when the reference water passed through magnetic field of of 500, 1000, 15000, and 2000g intensity respectively. e. effects of magnetization on electrical conductivity (ec) ec is the reciprocal of electrical resistivity. it represents the material’s ability to conduct electric current. figure 7 shows the change in ec for different magnetic field intensities at a flow rate of 1000l/h, where ec increased from 56 to 264µs/cm with increasing intensity of magnetic field from 0 to 2000g. the flow rate does not have a significant effect on ec [54]. the ec depends on the ion content. it is observed that decreasing the content of ca with increasing intensity of magnetic field causes increase in the ec [54]. fig. 7. ec vs magnetic field intensity f. effects of magnetization on total dissolve solids (tds) tds is a measure of the dissolved inorganic and organic substances present in a liquid in molecular, ionized or microgranular suspended form. specific types of tds mainly include calcium, magnesium, potassium, sodium, bicarbonates, chlorides, iron, lead and sulfates. the common sources of dissolved solids in water come from weathering of rocks and erosion of earth’s surface. many minerals are soluble in water, so high contents will be accumulated over time through the constantly reoccurring process of precipitation and evaporation. groundwater usually has higher contents of tds than surface water, due to longer duration of contact with the underlying rocks and sediments. figure 8 shows the variation of tds content with different magnetic field intensities. we can see that the tds content in magnetized water increases with increasing magnetic field intensity. fig. 8. concentration of tds vs magnetic field intensity g. effects of magnetization on sulfate sulfate (so4) is a polyatomic anion found in water. the sulfate compounds occur from the oxidation of sulfite ores, the presence of shales, and industrial wastewater. sulfate is considered one of the most common dissolved salts in rainwater. figure 9 shows the variation of so4 concentration with different magnetic field intensities, where the circulation of water in a magnetic field causes decreasing in the so4 content with increasing magnetic field intensity. fig. 9. concentration of so4 vs magnetic field intensity v. conclusion the results of the present study showed that the circulation of water in a magnetic field increases the ph which indicates increasing water alkalinity. the nucleation of alkaline content increased from 16mg/l for reference water to 88mg/l for water treated with magnetic field of 2000g intensity. also, the magnetic treatment reduces the nucleation of calcium mineral and sulfate content. the results from this research are focused on the influences of magnetic field of varying intensity on the chemical and electrical properties of water treated by reverse osmosis. the experiments changed the content of ions in water as follows: • after the use of magnetic treatment, ph, ec and tds increased with increased magnetic field intensity. • some positive and negative ions such as mg, k, na, cl, alkaline, and sio2 increased. • some positive and negative ions such as ca and so4 decreased. • the strength of soil could be improved by this method without using chemical additives to the soil through calcite precipitation. the amounts of sulfate in magnetic field decreased, which is useful to protect concrete from erosion, but the magnetization causes increase in the content of chloride which attacks the reinforcement steel of foundation and causes corrosion. references [1] y. wang, h. wei, z. li, “effect of magnetic field on the physical properties of water”, results in physics, vol. 8, pp. 262-267, 2018 [2] d. r. ambashtaa, m. sillanpaa, “water purification using magnetic assistance: a review”, journal of hazardous materials, vol. 180, no. 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conditioners”, annals of faculty engineering hunedoara-international journal of engineering, vol. 11, no. 4, pp. 147-157, 2013 [54] l. jiang, j. zhang, d. li, “effects of permanent magnetic field on calcium carbonate scaling of circulating water”, desalination and water treatment, vol. 53, no. 5, pp. 1275-1285, 2015 microsoft word 1-2551-6848-1-ed_s engineering, technology & applied science research vol. 9, no. 2, 2019, 3871-3880 3871 www.etasr.com arhin & gatiba: predicting injury severity of angle crashes involving two vehicles at unsignalized … predicting injury severity of angle crashes involving two vehicles at unsignalized intersections using artificial neural networks stephen a. arhin howard university transportation research and data center washington, dc, usa adam gatiba howard university transportation research and data center washington, dc, usa abstract—in 2015, about 20% of the 52,231 fatal crashes that occurred in the united states occurred at unsignalized intersections. the economic cost of these fatalities have been estimated to be in the millions of dollars. in order to mitigate the occurrence of theses crashes, it is necessary to investigate their predictability based on the pertinent factors and circumstances that might have contributed to their occurrence. this study focuses on the development of models to predict injury severity of angle crashes at unsignalized intersections using artificial neural networks (anns). the models were developed based on 3,307 crashes that occurred from 2008 to 2015. twenty-five different ann models were developed. the most accurate model predicted the severity of an injury sustained in a crash with an accuracy of 85.62%. this model has 3 hidden layers with 5, 10, and 5 neurons, respectively. the activation functions in the hidden and output layers are the rectilinear unit function and sigmoid function, respectively. keywords-crashes; unsignalized intersection; artificial neural network; injury severity i. introduction even though intersections constitute a relatively low proportion of the facilities of transportation systems, a significant number of crashes occur at these locations, especially in urban areas. in california for instance, an annual average of 1.5 crashes occur at unsignalized intersections in rural locations, compared to an average of 2.5 crashes per year in urban locations [1]. data from the world health organization (who) reveal that 1.25 million people die annually worldwide in road crashes. the economic cost of these deaths is estimated to be approximately $260 billion per year [2]. in the united states, there were a total of 37,456 fatalities in road-related crashes reported in 2016 [3]. though most of these crashes occurred on road segments, a significant number occurred at or near intersections. out of the total of 52,231 fatal crashes in the united states in 2015, approximately 4.4% (2,298) of the crashes occurred at stopcontrolled intersections, while 7.5% (3,917) of the crashes occurred at intersections controlled by traffic signals. intersections without any type of traffic control device recorded the highest number of fatal crashes (4,227) [4]. several studies have investigated the causes of these crashes. these causes are either driver-induced, or occur due to road geometry, road defects, vehicle defects and atmospheric or weather conditions. various countermeasures have been proposed and/or implemented to reduce the occurrence of crashes at intersections, which in some instances have been successful. in order to effectively reduce the frequency and mitigate the severity of intersection related crashes, it is necessary to explore the predictability of these crashes based on the pertinent factors and circumstances that might have contributed to the occurrence of these crashes. several studies have resulted in the development of mathematical models that predict crashes on roadways in general and, in a few instances, at unsignalized intersections in particular. these mathematical models include linear regression and machine learning methods. given the varying characteristics of intersections, it is necessary to develop models that are focused and specific to a particular set of conditions. this study therefore focuses on the development of models to predict the severity of right-angle crashes involving two vehicles at unsignalized intersections in urban centers using anns. ii. literature review a. contributory factors for intersection-related crashes there are many factors that determine the degree of injury sustained by people involved in crashes at unsignalized intersections. however, it is shown that only certain factors are statistically significant predictors. authors in [5] assessed the degree of injury sustained by drivers involved in angle collisions in relation to the fault status of drivers. the results of the study showed that drivers who were not at fault tended to sustain more severe injuries than those who were at fault. it was further determined that injury severity was affected by factors including time of year, speed limit, age, gender, restraint/helmet use, and alcohol/drug use. authors in [6] concluded that the road surface condition (wet or dry) was a significant predictor of injury severity. additionally, female drivers are more likely to sustain severe injuries than male drivers. crashes at urban areas were determined to result in less serious injuries than crashes at rural areas [6]. also, traffic volume on a major road is a significant predictor of crashes at unsignalized intersections [7]. corresponding author: stephen a. arhin (saarhin@howard.edu) engineering, technology & applied science research vol. 9, no. 2, 2019, 3871-3880 3872 www.etasr.com arhin & gatiba: predicting injury severity of angle crashes involving two vehicles at unsignalized … the geometric characteristics and features of unsignalized intersections have also been found to be potential explanatory variables in crash prediction models. authors in [8] predicted the frequency of accidents at unsignalized intersections in urban areas using negative binomial models. it was concluded that besides traffic exposure functions such as traffic flow, which usually significantly predict crashes, intersection geometrics, absence of street lighting and dedicated left-turning lanes are positively correlated with accident frequency at intersections. typical geometric characteristics included number of lanes on major road, width of lanes, and presence of median on intersecting roads. the study further revealed that tintersections with yield control had a much lower accident potential than those with stop control. b. crash prediction models several modeling techniques have been employed to predict crashes at intersections. 1) linear regression models linear regression modeling is an approach to establish a relationship between scalar responses, also called dependent variables, and other explanatory (or independent) variables. model parameters are estimated using a data set of values of the response and explanatory variables. the model is usually fitted to the observed data set using the least square approach. linear regression models take the form: �� = �� + �� �� + � � + ⋯+ �� � + ؏� (1) where, yi is the i th dependent variable, β1, β2… βp are estimated parameters, xi1, xi2…xin are the predictor variables of the i th dependent variable and ؏� is the error term. the error term is an independent and normally distributed random variable with mean of zero and a variance greater than zero. linear regression modelling has been applied in several studies to establish various relationships between the frequency of injury crashes and other traffic characteristics. authors in [9] investigated the relationship between the number of injuries or property damage only (pdo) crashes that occur annually at intersections and traffic and environmental factors. the crash records (ranging from 1984 to 1987) of 2,488 intersections in california were sampled. the linear regression analysis employed in this study was conducted in two levels. in the first level, a simple linear regression model was developed with injury/pdo crashes per year as the response variable and traffic intensity, expressed in millions of vehicles entering the intersection per year from all approaches, as the predictor variable. in the second model, additional information such as design, traffic control, proportion of cross street traffic, and environmental features were included as predictor variables. the results of the analysis showed that the accuracy of the model improved as more predictors variables were added. though linear regression models are easy to use and interpret, it has been shown that they are not ideal for crash predictions. crashes are usually sporadic and random in nature and hence are not best fitted by linear relationships. also, the assumption that the error term is normally distributed is not accurate for crash predictions which are usually discrete and non-negative. further, some factors have been determined to strongly correlate with each other, thus introducing multicollinearity thereby invalidating such linear models [10]. in overcoming the shortcomings of the linear regression models, generalized linear models (glms) have been used to model crashes at intersections. glms are a flexible generalization of the ordinary linear regression that can accommodate the non-normal distributed error terms. the most common forms of generalized linear models used in crash prediction models are the negative (nb) model and the ordered probit model (opm) 2) negative binomial model nb models are a generalization of the poisson regression. unlike the poisson models where the variance of the distribution of the response variables is equal to its mean, in nb models, the variance differs from the mean. nb models have been found to be suitable for crash predictions due to the nature of the dependent variables in such analysis. usually the response required is the number of crashes at a specific location. such responses are nonnegative integers and generally follow the nb distribution. the distribution is given by the following poisson-gamma distribution: ��(y=yi |ui,α)= ɼ(������) ɼ(���)ɼ(����) ( ����������) ���( ����������) �� (2) where, u is the mean of the dependent variable y, β is an estimated parameter to be estimated, α is the heterogeneity parameter, and xi is the i th the predictor variable. authors in [11] investigated the relationship between crash frequencies and factors such as traffic conditions, geometric and operational characteristics or roadways, and weather conditions using data of crashes that occurred from 2004 to 2010 on a motorway in auckland. the nb regression model developed had a goodness of fit, ρ 2 of 0.119. additionally, several individual predictors such as length of road segments, aadt, number of lanes and shoulder width were found to be significant predictors of the model. 3) ordered probit models the ordered probit model (opm) is used in developing models which have an ordered response. this approach in modeling data employs the use of the probit link function. the latent continuous metric underlying the ordinal responses observed are partitioned into a series of regions corresponding to the ordinal categories. generally, the probability of obtaining a particular outcome is given by: ��(�� = �| !) = "#$ (%&'(�)) (��"#$�%&'(�)�) − "#$�%&��'(�)����"#$�%&��'(�)�� (3) where, yi is an observable ordinal variable, xi is a vector of exogenous variables, β is a vector of unknown parameters to be estimated and and τj is the threshold associated with the j th ordinal partition interval which are assumed to be of ascending order. opm has been applied in the development of several crash prediction models which seek to predict injury severity based on several factors. authors in [12] developed an opm that sought to relate the severity of crashes experienced at freeway exits. crash data for 326 locations in florida were sampled. the results of the study indicated that the factors which significantly influenced crash severity included mainline engineering, technology & applied science research vol. 9, no. 2, 2019, 3871-3880 3873 www.etasr.com arhin & gatiba: predicting injury severity of angle crashes involving two vehicles at unsignalized … lane number, length of ramp, difference of speed limits between mainline and ramp, light condition, weather condition, surrounding land type, alcohol/drug involvement, road surface condition, and crash type. the model developed had a goodness of fit of 0.019 and a chi-squared goodness of fit value of 95.63. 4) empirical bayes refinement of the glm crash estimates made with glms are susceptible to regression-to-the-mean. the regression to mean occurs when a randomly large number of accidents during a period is normally followed by a reduced number of accidents during a similar after period, even if no measure has been implemented. the glms do not account for this effect. hence, to improve the accuracy of the predictions made with glms, the empirical bayes (eb) method is usually applied. the eb method compensates for the regression-to-the-mean bias by pulling the crash count towards the mean. thus, prior data (observed crash counts) are combined with the predicted crash frequency from the glm to calculate a corrected value. the corrected value is expected to lie somewhere between the observed crash frequency and the predicted frequency from the glm. this is expressed as: ( )1 observed crashes frequencye weight weightµ= × + − × (4) where, e is the corrected value, and µ is the average number of crashes (determined from the glm) [13]. 5) artificial neural networks (anns) anns are mathematical models inspired by the biological neural networks in the human brain. anns are used in engineering to perform complex tasks such as pattern recognition, forecasting, data compression and classification. the effectiveness of an ann is based on its ability to approximate both linear and nonlinear functions to a required degree of accuracy using a learning algorithm, and to build ‘‘piece-wise’’ approximations of the functions [14]. classification or forecasting using anns involves training and learning procedure, where, historical data (a set of input data with known outputs) is presented to the network. usually large amounts of such data are required for the training of the network. the network goes through a learning process by constructing a network of inputs and outputs, and weights assigned to each mapping are adjusted at each iteration. the method by which these weights and bias levels of a network are updated is determined by the learning rule used. thus, the learning rule helps a neural network to learn from the existing conditions and improve its performance. there are several learning rules used in training neural networks. notable among the rules are the hebbian, perceptron (error-correction), delta, correlation and outstar learning rules [15]. however, the most common known rule is the multilayer perceptron (mlp). mlp basically consists of three layers: input layer, hidden layer, and output layer. mlp is a feed forward network in which information flows from the input layer through the hidden to the output layer to produce the outcome. these layers have interconnected nodes (neurons). the interconnections are assigned weights (representing information flow) which are computed using mathematical functions. the outputs for specific inputs are obtained by adjusting the weights to minimize the errors between the output produced and the desired output by error-back propagation. the mlp is known to be a universal approximator because of its ability to approximate continuous functions on a compact set of real numbers with little assumption made. activation functions, also called transfer functions, are an essential component of anns. activation functions are models in the output neurons of the ann which introduce non-linearity into the network. they function by calculating the weighted sum of their inputs and adding a bias, then deciding whether a neuron should be activated or not. the three most common types of activation functions used in an ann are the sigmoid, the hyperbolic tangent, and the rectified linear unit [16]. authors in [17] utilized anns to develop a model to show the relationship between crash severity on urban highways, and traffic variables such as traffic volume, flow speed, human factors and road, vehicle and weather conditions. the study showed that mlp with feed forward back propagation networks provided the best results compared to other learning methods. network architecture with 2 hidden layers with 17 and 7 neurons respectively were determined to be the best. mean square errors (mse) within acceptable range of 3% to 4% were achieved. also, correlation coefficients of 86% to 87 % were achieved. iii. methodology a. study area this study is based on data obtained in the district of columbia (dc). the capital of the usa, washington, dc is divided into four (equal) quadrants areas: northwest (nw), northeast (ne), southeast (se), and southwest (sw) which are further divided into eight wards. as of july 2018, the population of dc was about 702,455 with a growth rate of approximately 1.41% [18]. the city is highly urbanized, and it’s ranked the sixth most congested city in the united states with each driver spending an average of 63 hours in traffic annually [19]. it has a land area of 68.34mi 2 and a total of 1,503 miles of roadway comprised of local roads, collector roads, minor arterials, principal arterials, freeways and interstates [20]. also, the city has about 7,700 intersections of which 1,450 are signalized [21]. the american society of civil engineers’ 2017 infrastructure report card reported that about 95% of the roads in dc are in poor condition [22]. b. the crash database system crash prediction models are data dependent and as a result the accuracy of the developed models depends largely on the quality of the available crash data. to ensure that a reliable model is developed, this research utilized traffic crash data from the district department of transportation’s (ddot’s) crash database called traffic accident reporting and analysis systems version 2.0 (taras2). the district of columbia metropolitan police department (mpd) records traffic crash information at the scene of crashes electronically on a police department form number 10 (pd-10) crash reporting form. the crash data is then downloaded through secure servers from mpd into ddot’s database and are then processed and made available in taras2, which is an oracle-based application. taras2 contains data fields that can be broadly categorized engineering, technology & applied science research vol. 9, no. 2, 2019, 3871-3880 3874 www.etasr.com arhin & gatiba: predicting injury severity of angle crashes involving two vehicles at unsignalized … under vehicle characteristics, environmental conditions, roadway characteristics, traffic exposure characteristics, as well as crash location, date, time, crash type, crash severity and information on of persons involved. c. data extraction and encoding nine years of crash data (2008-2015) were queried and extracted from taras2. the data were then filtered to obtain angle crashes involving two vehicles at unsignalized intersections. further, the extracted data were cleaned by identifying and removing duplicate and incomplete crash records and irrelevant data fields. in all, 3,307 data points were extracted and used for analysis. the extracted data set contained the following fields: accident complaint number, main street name, side street name, year of accident, month of accident, time of accident, day of week, quadrant of accident occurrence, type of collision, road surface condition, street lighting condition, lighting condition, weather condition, traffic condition, traffic control type, drivers’ age, drivers’ gender, contributing circumstances, and injury severity. only numerical data can be analyzed by anns. hence, qualitative data must be converted to quantitative data. thus, both input and output data must be encoded into either real or integer values. secondly, binary method (0 and 1) of encoding has been determined to yield better results since it minimizes the loss functions values with respect to the models’ parameters. the loss value determines how well the model fits the data set. the lower the loss function value the better the model fits the data set. table ii presents the variables and coding scheme used in this study. d. types of collision the crash types considered for this study are angle collisions. three types of angle collisions are specified: rightangle, right turn, and left turn collisions. • right-angle collision: this type of collision occurs when the side of one vehicle is impacted by the front of another vehicle which is traveling in a direction at right angle to the direction of the former vehicle. figure 1 depicts a rightangle collision at an intersection. • right turn collision: this type of collision occurs when a vehicle turning right at an intersection is impacted by a vehicle from the other intersecting road. figure 2 depicts a right turn collision. • left turn collision: this type of collision occurs when a left turning vehicle at an intersection is impacted by a vehicle from the oncoming traffic. figure 3 depicts a left turn collision. e. injury severity the outcome variable describes the degree of injury severity sustained by persons involved in a crash. the crash database specifies five degrees of injury severity: no injury, complain, non-disabling injury, disabling injury and fatal. due to the insignificant percentage of fatal and disabling injury crashes in the data set, all complain, injury and fatal crashes were categorized as injury crashes. table i shows the levels of crashes used in the analysis. fig. 1. right-angle collision fig. 2. right turn collision fig. 3. left turn collision table i. levels of injury severity injury severity level no injury non-injury complain injury non-disabling injury disabling injury fatal f. data standardization to achieve accurate predictions from machine learning models it is necessary that variables used in developing the models are of equal scale. also, most optimization algorithms minimize the loss function converge faster when variables are of the same scale. the method of scaling used on this data set is standardization. the raw scores (of the encoded data) are converted to standard scores by subtracting the mean of each variable from the raw score of each observation and then dividing the difference by the standard deviation of the variable. by doing so, the variables are transformed to have a mean of zero and a unit variance. the standardized value, z, of each score of each variable is given by (5): _ )/(z x x σ= − (5) where, 6 is the mean of the variable, x is the encoded score of each observation of a variable and σ is its standard deviation. engineering, technology & applied science research vol. 9, no. 2, 2019, 3871-3880 3875 www.etasr.com arhin & gatiba: predicting injury severity of angle crashes involving two vehicles at unsignalized … table ii. variable encoding variable variable name code variable variable name code day of crash lighting condition x1 monday 1-present, 0-otherwise x26 dark 1-present, 0-otherwise x2 tuesday 1-present, 0-otherwise x27 dark lighted 1-present, 0-otherwise x3 wednesday 1-present, 0-otherwise x28 daylight 1-present, 0-otherwise x4 thursday 1-present, 0-otherwise weather condition x5 friday 1-present, 0-otherwise x29 clear 1-present, 0-otherwise x6 saturday 1-present, 0-otherwise x30 rain 1-present, 0-otherwise x7 sunday 1-present, 0-otherwise x31 snow 1-present, 0-otherwise time of day x32 traffic condition 0-low, 1-medium, 2-high x8 a.m. peak (06:00 – 10:00) 1-present, 0-otherwise traffic control type x9 off peak (10:00 – 15:00) 1-present, 0-otherwise x33 stop 1-present, 0-otherwise x10 p.m. peak (15:00 – 19:00) 1-present, 0-otherwise x34 yield 1-present, 0-otherwise x11 evening (19:00 – 00:00) 1-present, 0-otherwise x35 none 1-present, 0-otherwise x12 night (0000 – 0600) 1-present, 0-otherwise contributing circumstances of driver 1 quadrant x36 no violation d1 1-present, 0-otherwise x13 nw 1-present, 0-otherwise x37 alcohol/ drug use d1 1-present, 0-otherwise x14 sw 1-present, 0-otherwise x38 speeding d1 1-present, 0-otherwise x15 ne 1-present, 0-otherwise x39 stop/ yield sign violation d1 1-present, 0-otherwise x16 se 1-present, 0-otherwise x40 improper maneuvering d1 1-present, 0-otherwise x17 bn 1-present, 0-otherwise contributing circumstances of driver 2 type of collision x42 no violation d2 1-present, 0-otherwise x18 right angle 1-present, 0-otherwise x43 alcohol/ drug use d2 1-present, 0-otherwise x19 left turn 1-present, 0-otherwise x44 speeding d2 1-present, 0-otherwise x20 right turn 1-present, 0-otherwise x46 improper maneuvering d2 1-present, 0-otherwise road surface condition x47 distraction d2 1-present, 0-otherwise x21 wet 1-present, 0-otherwise x22 dry 1-present, 0-otherwise x48 age of driver 1 1-present, 0-otherwise street lighting x49 age of driver 2 1-present, 0-otherwise x23 light off 1-present, 0-otherwise x50 gender of driver 1 0-female, 1-male x24 light on 1-present, 0-otherwise x51 gender of driver 2 0-female, 1-male x25 none 1-present, 0-otherwise y1 injury severity 0-no injury, 1-injury g. development of models the process of classification by ann is an iterative process of weight adjustments based on information flow that mimics the functioning of neurons in the human brain. the steps below describe in detail how models for crash injury severity classification were developed using ann: • selection of network architecture. • training of neural network. • testing and evaluation of model. 1) selection of network architecture the network architecture was first set up. a multi-layer perceptron (mlp) feedforward ann was adopted to develop classification models. an mlp consists of at least three layers: an input layer, hidden layer(s) and an output layer. each layer consists of nodes or neurons. the neurons of each layer are interconnected with those of the succeeding layer. also, the neurons of the hidden and output layers are embedded with nonlinear activation functions. the mlp ann architecture used in this research consists of an input layer with 44 neurons (each neuron represents each of the input variables, xi in table ii) and an output layer with 1 neuron, which is the target or dependent variable, y. the number of hidden layers and neurons varied for several iterations until the optimal numbers of hidden layers and neurons which produced the best model were obtained. figure 4 shows the mlp ann architecture used in developing the model. fig. 4. mlp ann 2) training of neural network training of the neural network by backward propagation was carried out in the following sequence: • presentation of training dataset to the network: the training dataset was imported into the network to commence training. the vector of independent variables was fed into each input neuron connected to neurons of the first hidden layer. the training process was initialized by randomly engineering, technology & applied science research vol. 9, no. 2, 2019, 3871-3880 3876 www.etasr.com arhin & gatiba: predicting injury severity of angle crashes involving two vehicles at unsignalized … selecting weights for all interconnections between the neurons of the input and hidden layers. • forward computation: the forward propagation was then implemented by multiplying the weights with the values of the input neurons and the sum products are stored in the corresponding neurons of the hidden layer. the weighted sums are subsequently transferred into an activation function and based on the output of the functions, the neuron is either activated or not. mathematically this can be expressed as: 789 = ∑ ;8�9 � (9'�)< �=� (6) �89 = ф��78� (7) where, 789 is the weighted sum in jth neuron of the lth hidden layer, ;8�9 is the weight coefficient of the jth neuron of the lth layer that is fed from the i th neuron in layer l-1, � (9'�) the output of th i-th neuron in the previous layer l-1, �8 is the output of the of the j th neuron in layer l-1, ф� is the activation function which is a rectilinear unit function in the hidden layers and a sigmoid function in the output layer. hence for the last layer (output layer) l=l, �8?(@) = ab (8) where, ab is the output of the n-th iteration. • computation of error: the error of the j th neuron of the n th iteration is then computed as c8(@) = d8(@) − ab(@) ¨ (9) where, d8 is the target output. • backward computation: the weights in the network are adjusted based on a local gradient, σ, which is a function of the error, e, and computed as follows: e89(@) = c8?(@) фf g78?(@)h (10a) for neuron j in the output layer l, and e89(@) = c8?фf g789(@)h∑ ei (9��)(@);i8 (9��)(@)i (10b) for neuron j in the hidden layer l, where, k is the succeeding neuron in layer l+1 and фf(·) is the derivative of the function ф(·). the weights in the network are then adjusted by the given relation: ;8�9 (@ + 1) = ;8�9 (@)b + kl;8�9 (@)b(@ − 1)m + ne89(@)�� (9'�)(@) (11) where η is the learning-rate parameter and α is the momentum constant. • iteration: the procedures in the three previous steps are repeated for batches of 3 observations per iteration until the stopping criteria of 100 epochs is met. figure 5 illustrates the training process. 3) model testing and evaluationl after the training of the network for the required number of epochs (100), the model was tested using the test dataset. the accuracy of the model was evaluated by the confusion matrix. the number of hidden layers and neurons in the network architecture was varied and the training process was repeated. this iterative process was done until the model with the best performance was achieved. fig. 5. ann training process 4) model evaluation the performance of each of the models was assessed using the test dataset. the results were then evaluated by using the data generated by a confusion matrix (cm). a cm contains information about actual and predicted classifications done by a classification system. each row of the cm represents the instances of an actual class and each column represents the instances of a predicted class. table iii shows the confusion matrix for a two-class classifier. table iii. confusion matrix total no. of observations predicted negative positive actual negative true negative (tn) false positive (fp) positive false negative (fn) true positive (tp) the entries of the cm are defined as follows: true positive (tp) instances are positive and correctly classified as positive, true negative (tn) instances are negative and correctly classified as negative, false positive (fp) instances are negative but wrongly classified as positive, and false negative (fn) instances are positive but wrongly classified as negative. based on the cm, the following measures were computed to evaluate the models developed. • accuracy (ac): the accuracy is the proportion of the total number of predictions that were correctly classified. it is computed as: ac=(tn+tp)/(tn+fp+fn+tp) (12) • error rate (er): the error rate is the rate at which predictions will be misclassified: er=1-ac (13) • sensitivity (s): it is the proportion of positive cases that were correctly identified: s=tp/(fn+tp) (14) engineering, technology & applied science research vol. 9, no. 2, 2019, 3871-3880 3877 www.etasr.com arhin & gatiba: predicting injury severity of angle crashes involving two vehicles at unsignalized … • precision (p): it is the proportion of the predicted positive cases that were correct: p=tp/(fp+tp) (15) • f-measure (f): it is a measure of the accuracy of the test model computed using s and p. the value of f ranges from 0 to 1, where 1 shows an excellent model and 0 shows a bad model. fmeasure is calculated as: f=2(s·p)/(s+p) (16) h. analysis software the classification models of all three machine learning techniques were developed by using the high-level generalpurpose programming language python. especifically, the anaconda python distribution was used. this is an open source distribution with standard and robust libraries for data processing, analysis and machine learning applications. the numpy and pandas libraries were imported to facilitate data preprocessing. also, tensorflow and keras libraries were imported to develop the ann models. in addition, the descriptive statistics of the data were obtained using ibm statistical software for social scientist (spss). iv. results a. descriptive statistics tables iv and v present the descriptive statistics of the data set. the frequencies of categorical variables are presented in table iv, while table v presents the mean and standard deviation of the continuous variable age. it can be observed from table iv that the highest number of crashes (1,252) occurred during the off-peak period, from 10:00a.m. to 3:00p.m., while the least number of crashes (176) occurred at night, between 12:00am to 6:00am. most of the crashes occurred on tuesdays, wednesdays and thursdays while sundays recorded the least number of crashes. the northwest quadrant of washington d.c. recorded the highest number of crashes (1,167). right-angle collision was the most frequent occurring crash type. most of the crashes occurred under daylight, clear weather and light level traffic conditions. though most crashes were as a result of no violation on the part of one or both drivers, distracted driving and stop/yieldsign violation were also reported as comparatively high contributing circumstances. among the drivers involved, 3,936 were male and 2,678 were female. of the 3,307 recorded crashes, 1,274 resulted in injury. it is observed that the rate of injury crashes was highest during the night (41.24%), on fridays (41%), and in the northeast quadrant (40.44%). most were right turn collisions (40.69%), absent street lights (39.52%), rainy weather (50.57%), under light traffic conditions (54.78%). intersections controlled by yield signs also recorded the highest rate (70.59%) of injury crashes. this is complemented by the fact that the highest rates of injury crashes were a result of at least one driver’s failure to comply with a stop/yield sign. thus, the contributing circumstance which resulted in the highest rate (69.94%) is stop/yield sign violation. crashes in which at least on driver was a female recorded the highest rate of injury crashes. a correlation analysis was conducted to investigate the relations between age and injury severity. the results are presented in table vi. the spearman’s rho of -0.52 was found to be statistically significant (p=0.03). this implies that, the severity of a crash increased with decreasing age of drivers involved in the crash. table iv. crash frequencies no factor level crashes total injury noninjury injury rate (%) 1 period of day a.m. peak 730 296 435 40.49 off peak 1252 466 785 37.25 p.m. peak 776 298 478 38.4 evening 373 142 230 38.17 night 176 73 104 41.24 2 day of week monday 265 102 163 38.49 tuesday 566 228 338 40.28 wednesday 957 371 586 38.77 thursday 657 243 414 36.99 friday 400 160 240 40 saturday 261 90 170 34.62 sunday 201 80 122 39.6 3 quadrant northwest 1,167 442 725 37.87 northeast 858 347 511 40.44 southwest 226 76 150 33.62 southeast 984 382 602 38.82 boundary 72 27 45 39.13 4 type of collision right angle 1,338 530 808 39.61 left turn 1,217 438 779 39.61 right turn 752 306 446 40.69 5 street lighting condition lights off 2,503 967 1,536 38.63 lights on 680 258 422 37.94 none 124 49 75 39.52 6 lighting condition dark 757 15 727 2.02 dark (lighted) 581 193 388 33.22 day light 1,967 1,063 906 53.99 7 weather condition clear 2,350 921 1,429 39.19 rain 609 308 301 50.57 snow 348 45 303 12.93 8 traffic condition light 2,178 1,193 985 54.78 medium 808 71 737 8.79 heavy 321 71 737 8.79 9 traffic control type stop sign 2,504 1,066 1,450 42.37 yield sign 604 132 55 70.59 none 187 76 528 12.58 10 gender of driver 1 male 1,621 419 1,202 25.85 female 1,686 855 831 50.71 11 gender of driver 2 male 2,315 1,026 1,289 44.32 female 992 248 744 25 12 contri. circum. of driver 1 no viloation 1,700 869 831 51.12 alcohol 159 0 159 0 distracted 682 122 560 17.89 speed 430 134 296 31.16 stop/yield sign violation 310 148 162 47.74 improper maneuver 24 2 22 8.33 13 contri. circum. of driver 2 no viloation 1,041 7 764 0.91 alcohol 160 0 160 0 distracted 996 408 588 40.96 speed 276 7 269 2.54 stop/yield sign violation 672 470 202 69.94 improper maneuver 161 112 49 69.57 14 injury severity 3,307 1,274 2,033 38.52 engineering, technology & applied science research vol. 9, no. 2, 2019, 3871-3880 3878 www.etasr.com arhin & gatiba: predicting injury severity of angle crashes involving two vehicles at unsignalized … table v. driver age statistics factor mean standard deviation min. max drivers age 42.56 15.73 14 86 table vi. age-injury severity corelation analysis factor test statistic (spearman’s rho) p-value age of driver -0.52 0.03 b. spatial distribution of crashes this section presents the results of the spatial analysis of the crashes using arcgis pro software program. the spatial analysis performed included the spatial distribution of crashes based on injury severity and a kernel density analysis for injury crashes. the spatial distribution and density of crashes are shown in figures 6 and 7, respectively. figure 7 shows that most of the crashes were located in the nw quadrant. this covers the downtown and central business district of washington dc. figure 7 also shows that higher densities of injury crashes are in the same region of washington dc. fig. 6. spatial distribution of crashes [source: arcgispro] fig. 7. kernel density of injury crashes [source: arcgispro] c. results of classification of crashes twenty-five distinct ann models were developed using the training dataset. each model was trained with batches of 3 observations per iteration until the stopping criteria of 100 epochs was met. the performance of each model was then evaluated using the test data set (which constitutes of 25% of the total dataset). the performance of the models after training and testing are presented in tables vii and viii respectively. the tables show the number of models explored and the structure of the neural network. the performance measures (accuracy, error rate, sensitivity, precision and f-measure) of each model were computed and are also presented. table vii. results of training ann model network arch. ac er s p f hidden layer no. no. of neurons 1 1 20 0.9181 0.0819 0.8995 0.8892 0.8943 2 1 15 0.9032 0.0968 0.9162 0.8454 0.8794 3 1 5 0.8649 0.1351 0.8366 0.8170 0.8267 4 1 3 0.8573 0.1427 0.8461 0.7961 0.8203 5 2 25-20 0.9585 0.0415 0.9455 0.9465 0.9460 6 2 20-25 0.9472 0.0528 0.9435 0.9213 0.9322 7 2 20-15 0.9512 0.0488 0.9874 0.8964 0.9397 8 2 15-20 0.9258 0.0742 0.9539 0.8668 0.9083 9 2 10-15 0.9157 0.0843 0.9529 0.8473 0.8970 10 2 15-10 0.9302 0.0698 0.9445 0.8826 0.9125 11 2 5-10 0.8722 0.1278 0.8785 0.8067 0.8411 12 2 10-5 0.9060 0.0940 0.8953 0.8654 0.8801 13 2 6-3 0.8685 0.1315 0.8628 0.8086 0.8349 14 2 3-6 0.8597 0.1403 0.8440 0.8020 0.8224 15 2 2-2 0.8427 0.1573 0.8304 0.7767 0.8026 16 3 30-20-25 0.9516 0.0484 0.9832 0.9170 0.9490 17 3 25-30-20 0.9689 0.0311 0.9204 0.9565 0.9381 18 3 20-15-20 0.9402 0.0598 0.9916 0.8926 0.9395 19 3 15-20-15 0.9404 0.0596 0.9644 0.8916 0.9266 20 3 15-10-15 0.9293 0.0707 0.9738 0.8692 0.9185 21 3 10-15-10 0.9310 0.0690 0.8995 0.8677 0.8833 22 3 5-10-5 0.9115 0.0885 0.8859 0.8270 0.8554 23 3 10-5-10 0.9102 0.0898 0.9414 0.8293 0.8818 24 3 6-4-2 0.9159 0.0841 0.9058 0.8374 0.8702 25 3 6-2-6 0.9237 0.0763 0.9058 0.8547 0.8795 the accuracy, sensitivity, precision and f-measure (f) performance measures range from 0 to 1, with values closer to 1 showing models with better performance measures and conversely values closer to 0 showing worse performance measures. in contrast, models with error rates (er) closer to 0 are better than models with error rate closer to 1. the results of the analysis in table vii show that after the training of the models, the accuracy ranged from 84.87% to 96.89%. model 17 produced the best classification accuracy (96.89%) with a corresponding error rate of 3.11%, while model 15 produced the worse accuracy (84.87%) with a corresponding error rate of 15.73%. model 7 had the highest sensitivity (s) measure, while model 15 had the least sensitivity measure. with regards to the precision measure, model 17 was the most precise (p) model with a precision of 0.9565, while model 15 was the least precise one. model 16 recorded the highest f-measure of 0.9490, while the lowest f-measure was recorded by model 6. the variation of performance measures with varying models is shown in figure 8. table viii presents the results of evaluation of the trained models using the test data set. the results show that the accuracy (after testing) of the models ranged from 76.54% to 85.62%. model 22 produced the best classification accuracy (85.62%) with a corresponding error rate of 14.38%, while model 6 produced the worse accuracy. model 14 had the highest sensitivity measure, while model 16 had the least sensitivity measure. with regards to the precision measure, model 15 was the most precise model with a precision of 0.7850, while model 18 was the least precise model with a engineering, technology & applied science research vol. 9, no. 2, 2019, 3871-3880 3879 www.etasr.com arhin & gatiba: predicting injury severity of angle crashes involving two vehicles at unsignalized … precision of 0.6882. model 15 recorded the highest f-measure of 0.7875, while the lowest f-measure was recorded by model 6. the variation of performance measures with varying models is shown in figure 9. fig. 8. variation of performance measures for training dataset using ann table viii. results of testing ann model network arch. ac er s p f hidden layer no. no. of neurons 1 1 20 0.8005 0.1995 0.7900 0.7200 0.7534 2 1 15 0.8114 0.1886 0.7492 0.7587 0.7539 3 1 5 0.7896 0.2104 0.7524 0.7164 0.7339 4 1 3 0.8295 0.1705 0.7806 0.7781 0.7793 5 2 25-20 0.7872 0.2128 0.7210 0.7256 0.7233 6 2 20-25 0.7654 0.2346 0.7116 0.6900 0.7006 7 2 20-15 0.7836 0.2164 0.7304 0.7147 0.7225 8 2 15-20 0.7787 0.2213 0.7179 0.7112 0.7145 9 2 10-15 0.7944 0.2056 0.7586 0.7224 0.7401 10 2 15-10 0.7715 0.2285 0.7429 0.6890 0.7149 11 2 5-10 0.8198 0.1802 0.7680 0.7656 0.7668 12 2 10-5 0.7993 0.2007 0.7524 0.7339 0.7430 13 2 6-3 0.8174 0.1826 0.7774 0.7561 0.7666 14 2 3-6 0.8114 0.1886 0.8276 0.7233 0.7719 15 2 2-2 0.8356 0.1644 0.7900 0.7850 0.7875 16 3 30-20-25 0.8440 0.1560 0.6865 0.7252 0.7053 17 3 25-30-20 0.8256 0.1744 0.7398 0.7024 0.7206 18 3 20-15-20 0.8100 0.1900 0.8025 0.6882 0.7410 19 3 15-20-15 0.8300 0.1700 0.7837 0.7163 0.7485 20 3 15-10-15 0.8511 0.1489 0.7367 0.7460 0.7413 21 3 10-15-10 0.8532 0.1468 0.7712 0.7546 0.7628 22 3 5-10-5 0.8562 0.1438 0.7586 0.7586 0.7586 23 3 10-5-10 0.8457 0.1543 0.7524 0.7385 0.7453 24 3 6-4-2 0.8406 0.1594 0.8119 0.7379 0.7731 25 3 6-2-6 0.8340 0.1660 0.7868 0.7233 0.7538 fig. 9. variation of performance measures for testing dataset using ann v. discussion the study sought to develop classification models to predict injury severity of angle crashes involving two vehicles at unsignalized intersections using anns. a total of 3,307 reported crashes from 2008 to 2015 were extracted from a crash database and used in the analysis. of the total number of crashes, 1,272 resulted in injury and/or fatality, while the remaining 2,035 crashes were non-injury crashes. the spatial distribution of the crashes showed that the downtown area of washington dc experienced the highest frequency of crashes. also, most of the crashes occurred during off-peak periods and under light traffic conditions. right angle collisions were the most frequent collision type. the combination of driver contributing circumstances which result in injury were stop/yield sign violation by one driver, and no violation on the part of the other driver. the accuracy of classification models developed using ann generally tends to increase as the number of hidden layers increases. models with higher accuracies were attained with three hidden layers. model 22 was the most accurate (85.62%) for predicting injury severity of angle crashes at unsignalized intersections. this model has 3 hidden layers with 5, 10, and 5 neurons respectively. the activation function in the hidden layers is the rectilinear unit function and the activation function in the output layer is the sigmoid function. the confusion matrix of this model is presented in table ix. we can see that 51.5% of the crashes were correctly classified as non-injury crashes, while 10.3% were wrongly classified as injury crashes. similarly, 29% of the crashes were correctly classified as injury crashes while 9.2% were wrongly classified as non-injury crashes. f-measure, is a combined measure for both precision and sensitivity. f-measures of the ann models generally ranged between 0.7 and 0.8, and the higher values of f-measure were achieved with two hidden layers. models 15 and 22 are the most accurate ann models for predicting injury severity of angle crashes at unsignalized intersections. table ix. confusion matrix of model 22 total no. of observations predicted negative positive actual negative 431 77 positive 77 242 vi. conclusion and recommendation in conclusion, the most accurate ann model for predicting the severity of an injury sustained in a crash is a model with 3 hidden layers with 5, 10, and 5 neurons. the activation functions in the hidden and output layers are the rectilinear unit function and sigmoid function. this research explored the ann machine learning technique. future research can explore other techniques such as decision trees, k-nearest neighbors and linear discriminants. also, other types of crashes can be explored at unsignalized intersections. further, these analyses could be extended to signalized intersections. references [1] t. r. neuman, r. pfefer, k. l. slack, k. k. hardy, d. w. harwood, i. b. potts, d. j. torbic, e. r. k. rabbani, national cooperative highway engineering, technology & applied science research vol. 9, no. 2, 2019, 3871-3880 3880 www.etasr.com arhin & gatiba: predicting injury severity of angle crashes involving two vehicles at unsignalized … research program: guidance for implementation of the aashto strategic highway safety plan, transportation research board, 2003 [2] world health organization, global status report on toad safety 2015, who, 2015 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vol. 2, no. 2, pp. 92-94, 2014 [19] office of the state superintendent of education, “new u.s. census bureau numbers officially put dc’s population over 700,000”, available at: https://osse.dc.gov/release/new-us-census-bureau-numbersofficially-put-dc%e2%80%99s-population-over-700000, 2018 [20] t. winship, “the 10 us cities with the worst traffic”, available at: https://www.businessinsider.com/the-10-us-cities-with-the-worst-traffic2018-2, 2018 [21] district department of transportation, “ddot by the numbers”, available at: https://ddot.dc.gov/page/ddot-numbers [22] american society of civil engineers, repord card for d.c.’s infrastructure, asce, 2016 microsoft word 35-3160_s_etasr_v9_n6_pp5062-5065 engineering, technology & applied science research vol. 9, no. 6, 2019, 5062-5065 5062 www.etasr.com memon et al.: controlling the defects of paint shop using seven quality control tools in an … controlling the defects of paint shop using seven quality control tools in an automotive factory imdad ali memon department of mechanical engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan engineerimdad@yahoo.com ahmed ali department of electrical engineering sukkur iba university sukkur, pakistan ahmed.shah@iba-suk.edu.pk munawar ayaz memon department of electrical engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan engr.mam@gmail.com umair ahmed rajput department of mechanical engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan engr.umair@quest.edu.pk saeed ahmed khan abro department of electrical engineering sukkur iba university sukkur, pakistan saeed.abro@iba-suk.edu.pk ahsan ali memon department of mechanical engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan 15el06@quest.edu.pk abstract—seven quality control (7qc) tools are used for reducing defects during manufacturing. these tools are highly effective in productivity and quality improvement. in this case, the study of the 7qc tools was applied in an automotive factory in order to reduce paint shop defects. within four months the production line was inspected, defects were categorized and the 7qc tools were successfully applied, reducing the overall defect rate by 70%. although every tool was important, the cause and effect diagram was responsible for finding the root causes of the defects. keywords-defects reduction; productivity improvement; paint shop; 7qc tools i. introduction the seven quality control (7qc) tools are highly useful for improving productivity, resolving problems in the quality operational process and delivery [1, 2]. the 7qc tools are applied for improving the performance of the production processes, solving problems at any stage [3, 4]. solving problems by the 7qc tools reduces cost, while they cannot be replaced by any other complex decision-making support system [5]. the level of defects or problems in the product is associated with the process conditions. if the process is under control limit then the product is useful, while when the process is out of control the product has demerits resulting to rejection, rework or scrap [6]. these problem solving tools are directly beneficial for customers too, as quality products entail the vast reduction of defects, while this process reduces cost. improving the quality of the product is very important for any company and its endurance in the market. the 7qc tools can be used in the production processing line ensuring the reduction of defects while suggesting improvements [7]. statistical process control (spc) tools used to hold the position of 7qc tools. these tools have played an important role in the reduction of variations in many industries [8]. many studies focused on these tools which were found very effective regarding problem solving in many industries. a comparative study was conducted between them and the new 7qc tools [8]. it has been reported that there are more than two spc techniques, namely the ishikawa diagram (cause and effect diagram) and the spc control charts which were also applied in automotive industry. the study in [9] focused on the defects in shocker seals of the automotive industry. the rejection level was reduced from 9.1% to 5% and 95% process capability was achieved. the control chart alone was applied to automotive components and monitored process capability. it was reported that the defect level has been reduced using a data acquisition system. the automated inspection method was adopted and offline spc method was converted into the online method in [10]. in many companies, more complex quality tools were used, but they were not highly effective and also they were not able to examine defects at a proper level [11]. in today’s challenging environment, every organization should apply proper productivity improvement tools. this paper presents a case study of the application of the 7qc tools in an automotive factory. initially, the factory used partially some of the tools without getting fruitful results. a goal to apply all the 7qc tools and understand their implementation mechanism was set, focusing on the identification and reduction of the defects occurring in the paint shop. an inspection point of the paint shop was used in order to collect, assess and analyze data. ii. related work the 7qc tools are applicable to any kind of industry regardless of size and capacity [11, 12]. these techniques (flow chart, pareto diagram, check sheet, control chart, histogram, corresponding author: imdad ali memon engineering, technology & applied science research vol. 9, no. 6, 2019, 5062-5065 5063 www.etasr.com memon et al.: controlling the defects of paint shop using seven quality control tools in an … scatter plot, cause-and-effect diagram) aim to control quality parameters such as methods, machine, equipment, and products. hence, these tools reduce the loss and give more profit [13]. in [7], the 7qc tools were used for reducing the rejection of shift fork. the total rejection was reduced from 16.66% to 0.65%, saving rs 303.000 per year. in [14] the cost impact of the application of real time spc in hardwood sawmills was investigated. in [15], some of the basic statistical tools were selected, such as pareto diagram, control chart and histogram, studying their impact on the overall process performance, cost and product quality. in [16], the importance of the 7qc tools was examined, showing a continuous quality improvement process in an automotive industry, while in [17] those tools were used for productivity improvement. many companies adopted spc tools and continued the implementation of process control in manufacturing industries. these techniques fulfill the customer requirements for highquality products at low price. manufacturing firms use spc to analyze their impact, isolate problems, monitor the outcome and process parameters for achieving quality goals [18, 19]. moreover, the spc process can enhance problem solving and performance [9, 20]. paint is a dispersion of pigments. it is used as filler in a fluid vehicle. the fluid vehicle includes a liquid binder that was solidified during cure. it has the capability to serve as a liquid carrier, viscosity reducing aid, and also provide healthy application distinctive [21]. drying oil, volatile thinner, and paint have been developed by mixing, grinding, thinning, straining operations [22] iii. materials and methods data collection started from the assessment of the automotive factory, through frequent visits. after visual inspection, defects were categorized in four types: dust, floatation, scratch, and improper paint. then, defects having a direct impact on the car body were focused. therefore, a check sheet was developed for finding the root cause of paint defects, applying the cause and effect diagram technique. this technique is very useful for the reduction of body section defects [23, 24]. data were collected through the check sheet for four months, using the same pattern. these data can be simulated, as reported in [25]. iv. results αnd discussion a. application of the 7qc tools • flow chart (qc tool 1): it was developed for collecting data from the paint shop. the defects observed at paint shop are of four types: scratch, dust, improper paint and floatation. • check sheets (qc tool 2): after identifying the defects, the next step is data collection. the check sheets were developed for collecting defect data for further analysis, and were designed focusing on attributted data, providing simple checkmarks, where check inspectors marked defect occurences. the check sheets mentioned different types of defects in the paint shop. data were collected from november 2015 to february 2016. • histograms (qc tool 3): histograms were created using excel. the histograms display variation levels and process capability. occurrence frequency of each defect was displayed in a monthly histogram between november 2015 to february 2016, as shown in figure 1. fig. 1. histogram for paint shop defects • pareto diagrams (qc tool 4): a pareto diagram shows the defects in descending order of occurrences. the pareto diagram is also monitoring the defects cumulative frequency level occurrences on its secondary axis. the red trend line shows the defect cumulative percentage level. defects occurring at a high level should be given priority. the pareto diagrams are displayed in figure 2. fig. 2. pareto charts of paint shop defects for (a) nov-15, (b) dec-15, (c) jan-16 and (d) feb-16 • cause and effect diagram (qc tool 5): the cause and effect diagram helps in discovering the root causes of the problem. this tool can point out the defects and their reasons. the preliminary data collected through check sheets showed a high frequency of defects in november and december 2015. cause and effect diagrams were developed and applied in the paint shop. using check sheets the data were collected for january 2016 and february 2016, engineering, technology & applied science research vol. 9, no. 6, 2019, 5062-5065 5064 www.etasr.com memon et al.: controlling the defects of paint shop using seven quality control tools in an … showing considerable reduction in paint defects, due to control on root causes as pointed out in figure 3. • scatter diagram (qc tool 6): this tool was used for the study and evaluation of the impact of each parameter to another. fig. 4 shows the scatter diagram of the paint shop. this diagram shows time in weeks and the number of defective bodies. in the first eight weeks, the defect rate was too high, while after finding the root cause of defects through cause and effect diagram, it was observed that the occurrence rate of defective bodies was reduced. fig. 3. cause and effect diagram for paint shop of: (a) improper paint, (b) floatation, (c) scratch, and (d) dust fig. 4. scatter diagram • p-chart (qc tool 7): the p-chart was based on the number of paint defect occurrences using binominal distribution. the process, running either in statistical control or not, can be pointed by the p-chart. it also pointed out that the changes occurred in the defective items when process measurement took place. b. overall defect reduction figure 5 shows the np control chart for the paint shop, where the blue line shows the defect rate, the green line shows the upper control limit, the red line shows the center and the purple line shows the lower control limit. nine weeks after the implementation of the 7qc tools, the defections were drastically reduced. figure 6 shows the impact on the defect rate before and after the implementation of 7qc tools in the paint shop. 122 defects occurred during the first month and 155 occurred during the second. after using the 7qc tools the defects were reduced to 83 during the third month and to 47 during the fourth. fig. 5. np control chart fig. 6. reduction of defects after the application of the 7qc tools v. conclusion this research investigated the application of the 7qc tools for the reduction of defects it an automotive factory. the initial flow chart was developed and check sheets were designed for data collection on inspection points. it was observed that the highest frequency defects were seen in november and december, 2015. after using the cause and effect diagram, the defects reduced substantially. during the fourth month (february 2016) total defects reduced by 70%, comparing to the first month, from 155 to 47. every tool played an important role in the defect reduction, but the cause and effect diagram was very useful for finding the cause and its effect. the main contribution of this study is to highlight all the possible defects or errors affecting production in manufacturing industries. references [1] j. c. benneyan, “the design, selection, and performance of statistical control charts for healthcare process improvement”. international journal of six sigma and competitive 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l. chew hernandez, l. viveros rosas, r. f. retes mantilla, g. espinosa martínez, v. velazquez romero, “supply chain cooperation by agreed reduction of behavior variability: a simulation-based study”, engineering, technology and applied science research, vol. 7, no. 2, pp. 1546–1551, 2016 microsoft word 6-2754_s_etasr_v9_n4_pp4342-4348 engineering, technology & applied science research vol. 9, no. 4, 2019, 4342-4348 4342 www.etasr.com le & vu: performance evaluation of a generator differential protection function for a numerical relay performance evaluation of a generator differential protection function for a numerical relay kim hung le the university of danang university of science and technology da nang, vietnam lekimhung@dut.udn.vn phan huan vu central power corporation central electrical testing company limited da nang, vietnam vuphanhuan@gmail.com abstract-this paper describes the advantages and disadvantages of a generator differential protection relay system which uses double slope characteristics of areva p343, abb reg670, sel300g and ge g60. a buon tua srah hydropower plant in vietnam was selected as an example for the relay setting calculations of these characteristics. the performance of the introduced relay model was tested at various fault conditions in matlab/simulink. the results apply to the problems of solving the performance of the relay accurately and with reliable differential protection against internal faults, and keeping the generator stable on all external faults and in normal conditions. the simulation simplifies the process of selecting the relay and protection system. this can improve the quality of the protection system design early, thereby reducing the number of errors found later in the operation. keywords-generator; differential protection function; slope 1; slope 2; matlab/simulink i. introduction the synchronous generator is the most important element of a power system. generator faults are considered serious since they may cause severe and costly damages to insulation, windings, and stator core. the large short circuit currents cause large current forces, which can damage other components in the power plant, such as the turbine and the generator-turbine shaft, or even initiate explosion and fire. in addition, if the generator is tripped in connection to an external short circuit, it can give an increased risk of power system collapse. to limit the damages in connection to a stator winding short circuits and abnormal operating conditions, generators need to be protected as much as possible by a proper protection system [1]. nowadays, there are a variety of numerical different protective relays on the market which include many functions in one unit, and provide metering, communication, and generator protection. these protective relays help us to simplify the protection implementation in circuit design and setting calculations. although there is quite an agreement among protection engineers as to what constitutes the necessary protection and how to provide it, there are still many differences of opinion in certain areas. as protection system complexity increases with ieds connected to the hydropower plant, the evaluation of effective protection relay becomes a need for well-designed algorithms that can allow or deny arranged trip of generator, field circuit, and neutral breakers (if used) through a lockout relay based on decisions, to enable fault isolation. among them, generator differential protection function (f87g) is one of the most critical protection applications. it is mainly employed for the protection of stator windings of generator against earth faults and phase-to-phase faults. it is also of great importance that the f87g does not trip for external faults when the large fault current is fed from the generator. the need to evaluate f87g with individual different characteristics has been well known to generator protection engineers. the techniques, methods and practices to provide this coordination are well established but scattered in various textbooks, papers, and in manufacturer’s user manuals [2]. author in [1] evaluated the performance of the f87g of the sel 300g generator protection relay which was employed to protect the particular low resistance grounded 555mva generator represented in the real-time simulation model of the rscad generic software. authors in [3] considered the f87g and simulated this function using simulink. authors in [4] described the effects of damages in secondary circuits and the influence on disoperation of differential protection micom p633 of the unit generator–transformer in simulink. authors in [5] conducted performance evaluation of the f87g by using a dynamic model of atp/emtp software for a large steam turbine synchronous generator. authors in [6] used atpemtp package to simulate and generate fault data which were processed in matlab to implement relay logic for detecting internal faults in the stator windings of f87g. authors in [7] used an anfis algorithm in simulink to design a f87g. the technical manuals of schneider p343, abb reg670, sel300g and ge g60 relay protections are in [9, 11, 14, 15] respectively. the works on detailed settings guidance [10, 12, 13, 16] allow protective relaying engineers to have a clear understanding of which methods are available on every relay protection, what input parameters are required for each method and the expected results of each. in practice, the worst condition of unbalanced secondary currents is realized when the current transformer (ct) in the faulted circuit is completely saturated and none of the other cts suffers a reduction in ratio. it is a universal differential protection problem for an unwanted trip of the generator [8]. besides, there is a possibility that corresponding author: phan huan vu engineering, technology & applied science research vol. 9, no. 4, 2019, 4342-4348 4343 www.etasr.com le & vu: performance evaluation of a generator differential protection function for a numerical relay someone with unauthorized access might infiltrate the relay and reconfigure incorrect settings instructing it to release a false trip signal without the existence of a fault. when these types of misoperation risks go undetected, it is very easy for operators to mistakenly believe that their relay protection is secure. hence, the question that operators need to ask is: “how confident am i that my relay protection is reliable and secure?”. therefore, the purpose of this paper is to provide a single document that can be used to calculate relay setting parameters with multi-vendors, to answer the most frequently asked questions about f87g considering the buon tua srah hydropower plant in vietnam. in addition, a matlab/simulink model to check four generator differential characteristics to the plant will be checked while simulating fault cases. it will equip the reader with the knowledge to choose the most suitable vendor for his or her project. ii. generator differential protection function this section shows how an f87g characteristic is constructed and how it works. selection rules for setting parameters are discussed. as an example, figure 1 illustrates the schematic diagram for the implementation of the main generator protection of a buon tua srah hydropower plant. line side cts and neutral side cts are both ends of the stator winding which are wye-connected. the f87g relies on measurements of the currents of the protected generator in order to calculate differential and biased currents which are then utilized to make tripping decisions. on low-impedance grounded machines, this scheme can detect phase-to-phase, phase-to-ground, and three-phase faults. equations (1) and (2) show the mathematical definition of the differential and biased currents, respectively, which are employed by various vendors such as schneider, abb, sel, and ge. fig. 1. differential protection relay connection with a generator. the differential current: || _ 2 _ 1 iii diff += (1) the biased current: 2 |||| _ 21 _ ii i bias + = (2) based on these values of ibias and of idiff, the trip/restrain characteristics are applied in the vendors of protection relay which has a three-step shape (two slopes and one pickup level) as in figure 2. the differential current pickup setting (is1, idmin, 87op, pickup) should avoid the maximum unbalance current under normal load condition which is mainly caused by ct error, the normal current error (kct_err) must be less than 5% the operating current for the 5p20 type ct, and we should multiply by a reliable coefficient krel that is normally equal to 1.5. this setting can be set as low as 5% of the rated generator current, to provide protection for as much of the winding as possible [10]. fig. 2. differential protection characteristics slope1 setting (k1, slopesection2, slp1, and slope1) is set to ensure sensitivity to internal faults at normal operating current levels. the criterion for setting this slope is to allow maximum expected ct mismatch error when operating at maximum permitted current. in this case, it combines the kct_err. the relay pickup accuracy (krelay_err) can be obtained from the instruction manual of the relay, and an operating margin (kmargin) of 5% is typically provided in order to increase the security of the differential protection scheme [13]. the purpose of the slope2 setting (k2, slopesection3, slp2, slope2) is to increase the security of the differential protection scheme during heavy through-fault conditions. it can result in severe saturation of a ct. when a ct saturates, it can no longer trustworthy reproduce the primary current with a scale factor on the secondary side of the ct. as a result, a very high differential current may be obtained under this fault condition. the slope2 setting is typically set higher than the slope1 setting. relay setting calculation is an important task for a power plant before operating. the parameter in this calculation is used for the setting of the relay protection equipment of the power plant. choosing the slope of a differential relay has been more art than science. manufacturer’s guidelines tend to be qualitative or empirical in nature. they are based on the manufacturer’s experience and knowledge of his/her design [9], as shown in the above f87g using trip/restrain characteristics. we can calculate detailed adjustable settings by using the generator parameters as in table i [10]. a. schneider p343 [11, 12] is1 is calculated to avoid maximum unbalance under normal load and the k1 should be 0% to assure the sensitive under normal operating current. . . 1 1.5 (2 0.05) 2116.5 0.127, 2500 rel err ct g n s k k i i ct × × × × × = = = so, 0.2a is proper. ibias slope2 idiff pickup slope1 break1 break2 (d). ge g60 irt slope1 slope2 iop o87p irs1 u87p (c). sel 300g zone3 slope section2 slope section3 idiff ibias idmin endsection1 endsection2 zone1 zone2 (b). abb reg670 ibias idiff is1 k1 is2 k2 (a). areva p343 engineering, technology & applied science research vol. 9, no. 4, 2019, 4342-4348 4344 www.etasr.com le & vu: performance evaluation of a generator differential protection function for a numerical relay the is2 should be the same with ct rating current or generator’s 120% nominal current. ct rating current is 2500a, so is2=2500a, the secondary value is is2=1a. the k2 is normally to avoid external max unbalance current under max throughout fault near protection zone. this max unbalance current can be calculated according to: iunb.max=krel×kap×kcc× kerr.ct×i (3) max (3) where the external three phase short circuit current is: (3) . " 2116.5 4.045 0.2093 2500 g n max d i i x ct = = = ×× . the ct type factor kcc should be 0.5 when same type ct for each side, or be 1 when different type ct for each side. in this paper, we select 0.5. the non-periodic factor is kap=1.5~2.0. in this paper, we select 2.0. so: iunb.max=1.5×2×0.5×0.1×4.045=0.6068. according to the equation: . 1 (3) 2 0.6068 0.2 2 0.1336 4.045 1 unb max s max s i i k i i − − = = = −− , we suggest selecting k2=0.2. the f87g operates when idiff exceeds is1 and the percentage of ibias, defined by a slope setting (k1, k2). it can be calculated using the following: idiff>k1×ibias+is1 where ibias ≤is2 idiff >k2×ibias–(k2−k1)×is2 +is1 where ibias>is1 table i. parameters of buon tua srah hydropower plant parameters values rated capacity 50.6 mva normal current ig.n 2116.5a rated voltage 13.8kv frequency 50hz pt ratio of the terminal of the generator 13.8 0.11 0.11 0.11 3 3 3 line ct ratio 2500/1 neutral ct ratio 2500/1 rated current secondly 0.8466a synchronous reactance xd 99.28% transient reactance x’d 28.27% sub transient reactance x’’d 20.93% synchronous reactance xq 62.88% negative reactance x2 23.60% static negative current i2∞ 250a transient negative current i 2 2t 40s krelay_err sel300g is 2%, g60 is 1%, p434 is 5%, and reg670 is 2% b. abb reg670 [9, 10] the pick-up value (idmin) is: . . min 1.5 (2 0.05) 2116.5 0.127 2500 rel err ct g n d k k i i ct × × × × × = = = we set idmin=0.2ig.n. in section1, the risk of false differential current is very low. this is the case, endsection 1 is set to experience value: . 0.5 0.5 2116.5 sec 1 0.4233 2500 g n i end tion ct × × = = = a slopesection2 is proposed to be set to 30%. breakpoint 2 set to experience value: . 3 3 2116.5 sec 2 2.5398 2500 g n i end tion ct × × = = = slopesection3=80%. it is supposed to cope with false differential currents related to current transformer saturation. the f87g operates when idiff exceeds a threshold idmin and a percentage of ibias: ( )2 1 when 1 2 diff dmin bias bias i i slopesection i endsection endsection i endsection > + × − ≤ ≤     ( ) ( ) 2 2 s 1 3 2 ] when 2 [ diff dmin bias bias i i slopesection endsection end ection slopesection i endsection i endsection > + × − + × − ≥ c. sel300g [13, 14] the slope1 setting can be calculated as: 1 2 _ _ct err relay err margin slp i k k= × + + (4) slp1=2×5%+2% +5%=17%, so 20% is proper. o87p setting is calculated using the guidance shown in equation: o87p=0.5∗slp1=0.1 the slp2 setting is fixed to 100%, the turning point between slope1 and slope2 defined by the value irs1 is fixed to 3.0 per unit. the purpose of the unrestrained differential element pickup setting (u87p) is to detect the very high differential current that clearly indicates a fault inside the differential protection zone. the u87p setting is set to 10 per unit as recommended by the relay manufacturer. the criteria for internal and external faults can be seen from the differential characteristic and are described below: 87 where 87 1/ diff bias i o p i o p spl> ≤ 1 1 when 87 1/ diff bias bias rs i i slp o p spl i i> × < < ( ) 12 1 2 when diff bias b rbi s sa iasi i slp slp slp i i i> × + − × ≥ d. ge multilin g60 [15, 16] . . 1.5 0.02 2116.5 0.025398 2500 rel er n g nk i ipickup ct × × × × = = = , so 0.1a is proper. slope1 is set at 15% starting from 0.04 (rc). the break1 setting should greater than the maximum overload expected for the machine: .1.05 1.05 2116.51 0.88893 2500 g nibreak ct × × = = = , so it is set at 1.2 slope2 is set at 80 %. the break2 setting is set at 3 or 4. it provides security from misoperation for maximum fault and resulting maximum ct error condition. the criteria for internal and external faults can be seen from the differential characteristic and are described below: engineering, technology & applied science research vol. 9, no. 4, 2019, 4342-4348 4345 www.etasr.com le & vu: performance evaluation of a generator differential protection function for a numerical relay where 1/ diff bias i pickup i pickup slope> ≤ 1 when 1 1 / diff bias bias i slope i pickup slope i break> × < < 2 3 0 1 2 3 ≥ + × + × + ×diff bias bias biasi c c i c i c i when 1 2, where:< <biasbreak i break 2 2 0 3 2 ( 1 2) 1 2 ( 1 2) slope slope break break c break break × − × = − × 2 2 1 3 2 1 ( 1 1 2 4 2 ) ( 1 2) slope break break break break break c break break × × + × + × = − 2 2 3 1 2 (4 1 1 2 2 ) ( 1 2) slope break break break break break break break × × × + × + − − 2 2 2 3 2 ( 1 2) ( 1 1 2 2 ) ( 1 2) slope slope break break break break c break break × − × + × + = − ( ) ( ) 3 3 2 1 1 2 ( 1 2) slope slope break break c break break − × + = − and idiff>slope2×ibias when ibias≥break2 all setting parameter results are calculated based on the best manufacturer practices that are adjusted to compensate for ct ratio error mismatch and ct response via a dual slope characteristic typically as shown in figure 7. review: the numerical algorithm of the f87g is very similar to motor differential protection. it is also principally simpler than that of the power transformer differential protection. no phase shifts, and no transformation ratios, typical for power transformers, must be numerically allowed for. the suggested protection for instantaneous and sensitive protection for generator internal faults is presented in [17]. the variable slope percentage differential relay is a widely used form of differential relaying for generator protection. in this type of relay, the percentage slope characteristic may vary from about 10% at low values of through current up to 100% or more at high values of through current. a p434 is more sensitive than another relay with k1=0% during light internal faults and relatively low sensitivity (k2=20%) during heavy external faults. iii. power system under study matlab/simulink tool is useful for the basic understanding of power system protection, particularly for new engineers. it helps them to model the f87g system behavior under normal and fault conditions. in this section, the f87g performance is tested on the 13.8kv, 50.6mva synchronous generator, connected with 220kv through a 51mva, d11yn step-up transformer as shown in figure 3. a. the generator the generator is represented by its impedance and an ac source, required for the system supply. it is located at the point where one side can easily be grounded. a resistor of 0.5ω, which exists in the actual grounded generator neutral, is not represented. this assumption does not have a significant influence on the study. fig. 3. power system model b. current transformer models current phasors at both ends of stator windings are 2500/1a 5p20 30va which are performed the current transformer excitation test, measured the ct winding resistance and ct current-ratio automatically by the vanguard ezct2000 test set in central electrical testing company limited. all of the ezct’s test leads can be connected to the ct output terminals, eliminating the need for lead switching during testing. test voltage output is automatically raised and lowered by the ezct without any operator intervention. once the test is completed, test results can be printed and excitation curves can be plotted on the built-in 4.5-inch wide thermal printer as in figure 4. fig. 4. v-i curve of ct 2500/1 a knee type iec 10/50 standard [18]: vpk=1401.44v, ipk=0.0124a, ct ratio: 2485.885/1a, error: 0.5646%, ex v=99.6v, ex i=0.02a, phase angle: 0.120, ct pole: in phase, and winding res: 13.94ω. the proposed mathematical current transformer model is shown in figure 5 and is based on the ct saturation theory and calculator presented by the ieee power system relaying and control committee (psrc) and the practical testing results of ct by vanguard ezct-2000 test set above (see [19] for more details). engineering, technology & applied science research vol. 9, no. 4, 2019, 4342-4348 4346 www.etasr.com le & vu: performance evaluation of a generator differential protection function for a numerical relay fig. 5. a mathematical current transformer model c. different protection relay model by performing the essential computations given in section ii, we got the four models of f87g relay (p343, reg670, sel300g, g60) which are connected on ct’s secondary side at both ends of the generator (il, in). after that, these signals were calculated using recursive discrete fourier transform algorithm. these are combined with setting parameters sending to s-function block. this block has been developed for detecting generator stator winding internal faults. if the output from the s-function block is equal to zero, this means that there is no fault in the stator winding of the generator, otherwise, the stator winding of the generator has a fault. the inside simulink model of f87g block is shown in figure 6. fig. 6. differential protection relay p434 block d. three phase fault block three phase fault block f1 and f2 generate fault types and fault resistance varying from 1ω to 35ω which are inside the protected zone, and out of the protected zone, respectively. iv. simulation results after the building of the proposed model has been completed, it is ready to analyze the operation of f87g applied under three cases below. in the first case, the normal condition shows the phase current waveforms captured at both terminal in=il=2200a, ct error ≈0%, idiff≈0a and all relays have not generated trip signal. the trajectory of the operating point can be seen by the relay lied the restrain zone (figure 7). fig. 7. current waves, ct error, trip signals and trajectory of operating point for normal condition in the second case, the internal fault occurs at 0.16s on the terminal of phase ‘abg’ stator winding as shown in figure 8. the phase currents captured at both terminals in=2ka, il=1ka and remain in the same phase, ct error ≈0%, idiff≈8a. according to change in current waveforms during the fault, the trajectory of the operating point moves quickly into trip zone, which results in a tripping at 0.178s (reg670), 0.1832s (sel300g and g60), 0.1835s (p434). in the third case, a threephase fault occurs at 0.1s on the terminal of a synchronous generator that is external to the stator winding. if the cts have no error, then currents at both ends of stator windings remain in the same value and opposite phase, and idiff≈0a. unfortunately, during fault conditions as shown in figure 9, cts do not always perform ideally, since core saturation may cause a breakdown of a ratio (in=20ka, il=1.8ka). such core saturation usually from 0.13s to 0.15s is the result of a dc transient in the primary fault current, total burden impedance zb=150ω and may be aggravated by the residual flux left in the core by a previous fault. the trajectory of the operating point moves into the trip zone of p434, sel300g, and reg670. after that, it comes back to the restrain zone at 0.23s. therefore, in order to provide additional security against maloperations during this event, the relay incorporates saturation detection logic. when saturation is detected, the engineering, technology & applied science research vol. 9, no. 4, 2019, 4342-4348 4347 www.etasr.com le & vu: performance evaluation of a generator differential protection function for a numerical relay element will make an additional check on the angle between the neutral and line current. if this angle indicates an internal fault then tripping is permitted. in this case, the generator does not trip because the differential relay does not a response to the fault since the fault happens out of the protected zone. fig. 8. current waves, ct error, trip sinals and and trajectory of operating point for internal fault condition (abg fault) review: the simulation results show that under the no-fault condition and external fault then the relay does not trip; under a fault condition, the trip signal is taken. in another way the characteristic results are very sensitive to internal faults and insensitive to ct error currents during severe external faults. v. conclusions in order to verify the deployed generator protection scheme is working as designed after field installation, this paper is discussed with a buon tua srah hydropower plant example. the paper provides calculation on appropriate a pickup threshold, slope and breakpoint settings for an f87g function available from today’s modern multifunctional generator protection ieds such as p434, reg670, sel300g, and g60. it also presents important aspects of generator protection system analyzing at different conditions which are simulated on a synchronous machine stator winding in matlab/simulink. this software shows the two cts’ current waves, and the different and restraint current trajectories on the relay characteristics. it tells the user how far the different locus intrudes into the trip zone. according to the obtained results, it has been shown that the ieds operate safe and reliable. fig. 9. current waves, ct error, trip sinals and and trajectory of operating point for external fault condition (abc fault) acknowledgment the authors would like to thank the central electrical testing company limited, vietnam for allowing the use of the test record of current transformer, setting the calculations of hydropower plants used in this study. references [1] y. t. huang, investigating the performance of generator protection relays using a real-time simulator, msc thesis, university of kwazulu-natal, 2013 [2] d. reimert, protection relaying for power generation systems, taylor & francis group, 2006 [3] m. v. sudhakar, l. k. sahu, “simulation of generator protection using matlab”, ieee international conference on smart technologies and management for computing, communication, controls, energy and materials, chennai, india, august 2-4, 2017 [4] k. kadriu, g. kabashi, l. ahma, “misoperation of the differential protection during the dynamic processes of faults in the secondary protection circuit. differential protection modeling with matlab software and fault simulation”, 5th wseas international conference on power systems and electromagnetic compatibility, corfu, greece, august 23-25, 2005 [5] w. yousef, m. a. elsadd, a. y. abdelaziz, m. a. badr, “performance evaluation of generator-transformer unit overall differential protection in large power plant”, international journal on power engineering and energy, vol. 9, no. 3, pp. 869-877, 2018 [6] n. w. kinhekar, s. daingade, a. kinhekar, “current differential protection of alternator stator winding”, international conference on power systems transients, kyoto, japan, june 3-6, 2009 [7] r. mohemmed, a. cakir, “modeling and simulation of differential relay for stator winding generator protection by using anfis algorithm”, international journal of scientific & engineering research, vol. 7, no. 12, pp. 1668-1673, 2016 engineering, technology & applied science research vol. 9, no. 4, 2019, 4342-4348 4348 www.etasr.com le & vu: performance evaluation of a generator differential protection function for a numerical relay [8] ieee, c37.102 guide for ac generator protection, ieee, 2006 [9] abb, generator protection reg670 application manual, abb, 2012 [10] abb engineering (shanghai) ltd, #1, #2 g-t unit protection setting calculations for buon tua srah hydro power plant, abb engineering, 2009 [11] schneider electric, micom p343 generator protection relay-technical manual, schneider electric, 2011 [12] ecidi-alstom consortium, cscs system protection parameter calculation, vnss4-c3-9-001 /a, ecidi-alstom consortium, 2010 [13] xj electricity co., generator relay protection setting calculation instruction, xj electricity co., 2010 [14] sel, sel-300g multifunction generator relay instruction manual, sel, 2018 [15] ge digital energy, g60 generator protection system-instruction manual, ge digital energy, 2015 [16] ge grid automation, application book-ct requirements for ge multilin relays, ge grid automation, 2016 [17] i. brncic, z. gajic, s. roxenborg, adaptive differential protection for generators and shunt reactors, abb power technologies ab, 2007 [18] central electrical testing company limited, “the test record of current transformer 2500/1a, 5p20 30va, 04/17/2014”, 2014 [19] k. h. le, p. h. vu, “testing and evaluation of factors affecting the current transformer saturation”, journal of science and technology, thai nguyen university, vol. 189, no. 13, pp. 129-134, 2018 (in vietnamese) microsoft word 10-3-2759_s1_etasr_v9_n4_pp4367-4370 engineering, technology & applied science research vol. 9, no. 4, 2019, 4367-4370 4367 www.etasr.com alghamdi: creep resistance of polyethylene-based nanocomposites creep resistance of polyethylene-based nanocomposites abdulaziz s. alghamdi mechanical engineering department, college of engineering, university of hail, hail, saudi arabia asbg945@hotmail.com abstract—the purpose of this work is to investigate the effects of carbon black (cb), carbon nanotubes (cnts) and nanoclay sheets addition on the creep behavior of polyethylene-based nanocomposites synthesized with an in-house processing method. a blend of 75 wt.% uhmwpe and 25 wt.% hdpe, abbreviated to u75h25, was used as the hybrid pe matrix to accommodate the nanofillers. a 0.5 wt.% of cb, cnts or nanosheets clay was embedded separately into the blend matrix in order to improve the creep resistance. the scanning electron microscope (sem) and transmission electron microscope showed that the nanofillers were homogeneously dispersed in the u75h25. the addition of just 0.5 wt.% nanoclay resulted in a significant increase in the creep resistance of the polyethylene blend. conversely, the addition of cb or cnts caused a reduction in the creep resistance. the embedding of cnts into the matrix resulted in creep behavior almost close to the creep behavior of pure uhmwpe. the burger’s model was employed to understand the effect of the nanoparticle addition on the creep mechanism. keywords-uhmwpe; hdpe; polymer; creep; nanocomposite; polyethylene i. introduction polyethylene (pe) is the most widely used thermoplastic because of its outstanding mechanical properties, such as moisture absorption, chemical resistance, high toughness and ease of processing [1]. it was found that the incorporation of various nanofillers can lead to a significant improvement in the polyethylene composite properties which can be used in many applications such as packaging, electrical and thermal energy storage, automotive, and biomedical [1-6]. recently, new polyethylene nanocomposites have been developed with the use of various processing methods, different types, and amounts of reinforcements [7-16]. these nanocomposites can be a cost-effective alternative to the high cost advanced composites and can be widely used in various industrial applications [1]. however, achieving uniform dispersion of the nanoparticles is still an important scientific and technological challenge in nanocomposite fabrication. poor dispersion of the nanofillers, weak interaction between the filler and the matrix, and agglomeration can lead to the reduction of the mechanical properties [9]. in [10], it was found that the embedding of mwcnt and nanoclay into the polyethylene matrix increased significantly hardness, elastic modulus and indentation resistance of polyethylene-based nanocomposites. in this work, different types of nanofillers with different geometric shapes were used in order to improve the creep resistance of the uhmwpe/hdpe. the volume of fractions was kept at low percentage to minimize the effect of agglomeration, especially for cb and cnt. the creep response was analyzed using the burger’s model. ii. experimental work a. materials the materials tested in this study were uhmwpe/hdpe blended polymers with various nanofillers. nascent uhmwpe powders (sabic®uhmwpe3548) were purchased from sabic, having an average molecular weight of 3×106mol/g. hdpe powders (exxonmobil tm hdpe hma014) were purchased from ico ltd. carbon black (cb) powder with the commercial product name, black pearls ® 4040 (bp4040) and average particle diameter of 28nm was provided by cabot corporation. natural hectorite nanoclay was supplied by elementis specialties. multi-wall nanotubes (mwnt) with diameters in the range of 5nm to 50nm, were provided by nanocyl. butylated hydroxytoluene and tris (nonylphenyl) phosphate, supplied by sigma-aldrich, were used as primary and secondary antioxidants, to maintain the long term thermal stability and melt processing stability, respectively. b. processing an in-house pre-mix technology was used to incorporate the nanofillers into the uhmwpe and hdpe powders. a twinscrew extruder was then used to blend the uhmwpe and hdpe powders pre-mixed with 0.5wt.% of cb, carbon nanotubes (cnt) or nanoclay to form nano-filled uhmwpe/hdpe composites. a blend of 75wt.% uhmwpe and 25wt.% hdpe, abbreviated to u75h25, was used as the hybrid pe matrix to accommodate the nanofillers. during processing, the mixing temperature was controlled using five zones from feeding port to die, the processing parameters are shown in table i. compression moulding was used to mould the nanocomposite materials. the raw material was placed into a mould (100mm×100mm×1.65mm), and then heated to 190ºc, which is higher than the melting point of the composite (approximately 135ºc). various mould pressures (154, 232, corresponding author: abdulaziz s. alghamdi engineering, technology & applied science research vol. 9, no. 4, 2019, 4367-4370 4368 www.etasr.com alghamdi: creep resistance of polyethylene-based nanocomposites 309, and 386mpa) were studied in order to optimize material properties such as hardness and crystallinity. various holding times at maximum pressure (10, 15 and 30min) were also used to identify the most appropriate moulding parameters. the optimal moulding pressure and holding time were 309mpa and 15min respectively, which resulted in the highest values of hardness and crystallinity. after compression moulding, the mould was cooled to room temperature with the use of water. then, the specimens were cut from the plaques into a dumbbell shape using a die punch cutter with the following dimensions: 75mm overall length, 25mm length of narrow parallel-sided portion, 12.5mm width at the ends, 4mm width of narrow portion and 1.65mm thickness. table i. processing method parameters extruder speed (rpm) processing temperature (ºc) zone 1 zone 2 zone 3 zone 4 die cooling 190 220 250 260 270 280 water c. mechanical testing and characterization. in order to characterize the nanofiller dispersion and the microstructure of the u75h25 nanocomposites, several experimental techniques were used. these included differential scanning calorimetry (dsc), scanning electron microscopy (sem) and transmission electron microscopy (tem). dsc, (ta instruments, shimadzu dsc60) was used to analyze the effect of different compression moulding parameters and nanofiller types on the crystallinity of the blend and nanocomposites. the specimens, with average mass of 5±0.2mg, were sealed in aluminium pans and heated from 20ºc to 180ºc at a rate of 10ºc per minute. the mass fraction degree of crystallinity was then determined by comparing the heat of fusion with that for fully crystalline polyethylene at the equilibrium melting point (290kj/kg) [17]. the surface morphology was investigated using a leo 440 sem from leo electron microscopy ltd and philips xl30 esem-feg from fei company. the dispersion of the nanofillers was studied after fracturing the samples in liquid nitrogen, and then coating them using platinum. a jeol 2000fx tem from jeol ltd. was used to analyze the dispersion of nanofillers into the blend matrix. tensile creep tests were carried out using an instron 3366 tensile testing machine from instron corporation) at room temperature (22±2ºc). d. burger’s model. creep modeling and analysis is important to determine time response, which leads to understanding chain dynamics. the burger’s model, which is a combination of kelvin-voigt and maxwell elements, is the most used model to describe the linear viscoelastic behavior of composites. the total strain as a function of time can be obtained from (1) [18]: ε� = � �� + �� 1 − e �� �� � + ��� t (1) where em and ηm are the elastic and viscous components of maxwell model, τ=ηk/ek is the retardation time taken to produce 63.2% of the total deformation in the kelvin unit, ηk and ek are elastic and viscous components of kelvin model. iii. results and discussion a. nanofillers dispersion figure 1 shows the sem images for the microstructure of u75h25/nanofillers. it can be seen that cb, nanoclay and cnts are dispersed homogenously in the u75h25 matrix. however, small agglomeration of the cb nanofillers can be observed, which can lead to a reduction of load carrying capacity between cb and the polymer matrix. similarly, these cb nanofillers agglomerations have been observed in the tem image, as seen in figure 2(a). moreover, figure 1(c) shows good dispersion of cnts into the polyethylene matrix. single clay nanosheet and cnt can be seen in figures 2(b) and 2(c), respectively. this indicates a uniform distribution of both clay nanosheets and cnts into the blend matrix. (a) (b) (c) fig. 1. sem images for the microstructure of (a) u75h25-0.5wt.%, (b) u75h25-0.5wt.% clay, and (c) u75h25-0.5wt.% cnts engineering, technology & applied science research vol. 9, no. 4, 2019, 4367-4370 4369 www.etasr.com alghamdi: creep resistance of polyethylene-based nanocomposites (a) (b) (c) fig. 2. tem images for the microstructure of (a) u75h25-0.5wt.%, (b) u75h25-0.5wt.% clay, and (c) u75h25-0.5wt.% cnts b. thermal analysis table ii presents the dsc results for u75h25 and its nanocomposites. it can be seen that the addition of 0.5wt.% cb nanoparticles has no effect on crystallinity, however crystallinity is increased significantly with the addition of 0.5wt.% clay nanosheets. the incorporation of 0.5wt.% cnts resulted in a slight reduction in the crystallinity value. these changes in the crystallinity values can be attributed to the effect of nanofiller shapes and the interaction between the nanofillers and the polyethylene matrix. table ii. thermal propertis of hdpe-based nanocomposites materials crystallinity % uhmwpe 53.3 u75h25 55.3 u75h25-0.5wt.% cb 55.2 u75h24-0.5wt.% clay 69 u75h25-0.5wt.% cnt 50 c. tensile creep results figure 3 shows the effect of the blending of hdpe on the creep resistance of uhmwpe and the effects of the addition of nanofillers on the creep resistance of u75h25 blend. it can be seen that blending 25wt.% of hdpe with 75wt.% uhmwpe resulted in an increase in the creep resistance by 32%. this can be proposed to the influence of hdpe chains and spherulite properties on the mobility during creep. the viscoelastic behavior in semi-crystalline polymers such as uhmwpe and hdpe is a combination of crystalline and amorphous phase’s mobility and the changes in these microstructures can lead to significant variation in the polymer properties. the addition of cb and cnts nanofillers resulted in a reduction in the creep resistance of the u75h25 blend. this can be attributed to the agglomerations of the nanofillers, which lead to a reduction in the surface to volume ratio and apply as defects in the microstructure. polyethylene is a nonpolar polymer; therefore, the interaction between the nanofillers and the polyethylene matrix is almost weak. this can affect the effectiveness of load transfer between the matrix and the nanofiller, which then affects mechanical properties. however, the addition of 2d plate-like nanofillers showed a significant improvement in the creep resistance of the polyethylene blend. the addition of only 0.5wt.% of clay nanosheets resulted in 22% increase in the creep resistance. this can be attributed to the good dispersion, interaction between nanoclay and polyethylene matrix, the increase in crystallinity and the plate-like shape of nanoclay. fig. 3. effect of gnss addition on the micro-hardness values. d. constitutive modeling as shown in figure 3, curves fitting are in a satisfactory agreement with the experimental data. the data were fitted to the burger’s model, all parameters being obtained by minimizing the sum of the squared differences between the actual and calculated strains, using the solver in excel. table ii shows the berger’s model parameters that indicate an increasing in the values with blending 25wt.% hdpe with 75wt.% uhmwpe. further increasing can be observed with the addition of plate-like clay nanosheets. the elasticity em and the stiffness of the amorphous phase ek of the blend have increased by 32% by the addition of nanoclay. the parameter ηm represents the irrecoverable creep strain, which also engineering, technology & applied science research vol. 9, no. 4, 2019, 4367-4370 4370 www.etasr.com alghamdi: creep resistance of polyethylene-based nanocomposites increased with the addition of nanoclay. this indicates that a reduction in the dashpot flow can occur, which leads to a reduction in the permanent deformation. however, retardation time, where τ is the delayed response to the applied stress for the u75h25-0.5wt.% clay, is less than the retardation time for the blend and the uhmwpe. conversely, the addition of cb and cnts nanofillers to the blend matrix shows a reduction in elasticity, stiffness and in the irrecoverable creep strain. table iii. burger’s model parameters material em ηm (x10 3 ek τ ηk (mpa) mpa.s) (mpa) (s) (mpa.s) uhmwpe 445 381 561 56.1 31472.1 u75h25 617 605 789 53.4 42132.6 u75h25-0.5wt.% cb 558.7 480 724 52.3 37865.2 u75h24-0.5wt.% clay 907 629 1020 37.7 38454 u75h25-0.5wt.% cnt 497 445 626 53.6 33553.6 iv. conclusion the main findings in this work are summarized as follows: • blending 25wt.% of hdpe with 75wt.% uhmwpe resulted in a significant increase in the creep resistance. • the addition of low weight fraction of plate-like nanoclay leads to further improvement in the creep resistance of the u75h25 blend. • the embedding of cb and cnts into the blend matrix resulted in a reduction in the creep resistance, which can be attributed to the weak interaction between the filler and the polyethylene matrix. moreover, the agglomeration of these types of nanofillers can reduce the surface to volume ratio, which can significantly affect the load transfer between the matrix and the filler. • elasticity, stiffness and the irrecoverable creep strain have increased with the addition of plate-like nanoclay. references [1] p. n. khanam, m. a. a. maadeed, “processing and characterization of polyethylene-based composites”, advanced manufacturing: polymer & composites science, vol. 1, no. 2, pp. 63-79, 2015 [2] a. sari, “form-stable paraffin/high density polyethylene composites as solid–liquid phase change material for thermal energy storage: preparation and thermal properties”, energy conversion and management, vol. 45, no. 13–14, pp. 2033–2042, 2004 [3] k. m. manu, s. soni, v. r. k. murthy, m. t. sebastian, “ba(zn1/3ta2/3)o3 ceramics reinforced high density polyethylene for microwave applications”, journal of materials science: materials in electronics, vol. 24, no. 6, pp. 2098–2105, 2013 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publications, 1989 microsoft word 16-3600_s engineering, technology & applied science research vol. 10, no. 4, 2020, 5974-5978 5974 www.etasr.com nguyen et al.: nonlinear inelastic analysis of 2d steel frames nonlinear inelastic analysis of 2d steel frames an improvement of the plastic hinge method phu-cuong nguyen faculty of civil engineering ho chi minh city open university ho chi minh city, vietnam cuong.pn@ou.edu.vn binh le-van faculty of civil engineering ho chi minh city open university ho chi minh city, vietnam binh.lv@ou.edu.vn son dong tam vo thanh faculty of civil engineering ho chi minh city open university ho chi minh city, vietnam son.dtvt@ou.edu.vn abstract—in this study, a new method for nonlinear analysis of 2d steel frames, by improving the conventional plastic hinge method, is presented. the beam-column element is established and formulated in detail using a fiber plastic hinge approach. residual stresses of i-shape sections are declared at the two ends through fibers. gradual yielding by residual stresses along the member length due to axial force is accounted for by the tangent elastic modulus concept. the p-δ effect is captured by stability functions, whereas the p-∆ effect is estimated by the geometric stiffness matrix. a nonlinear algorithm is established for solving nonlinear problems. the present study predicts the strength and behavior of 2d steel frames as efficiently and accurately as the plastic zone method did. keywords-fiber plastic hinge; nonlinear algorithm; residual stress; stability functions; steel frames i. introduction nowadays, direct design for steel frames is permitted by the modern design codes. a direct design including the effects of geometric nonlinearity, inelasticity of materials, imperfections, residual stress, etc. is accounted directly and simultaneously in advanced analysis. there are usually two methods for advanced analysis: plastic hinge methods [1-15] and plastic zone methods [3, 16-25]. authors in [14, 15, 22, 23, 26] invented a spring element for accounting stiffness of beam-to-column connections for nonlinear behavior analysis of steel frames with flexible connections. recently, authors in [27-29] tried to investigate the behavior of steel frames with the effects of connections. author in [30] investigated the effect of the iranian standard no. 2800 on the elastic and inelastic behavior of dual steel systems by using the nonlinear pushover analysis of commercial software sap2000. up to now, in spite of the developments in computer science and technology, plastic zone methods are still expensive for the daily engineering design of steel frames. plastic hinge methods are more simple, efficient in computational time, and with acceptable accuracy, so they are suitable for practical design. plastic hinge methods have been studied widely from 1980 to 2000 [1-8]. authors in [1, 3] used hermite interpolation functions to predict the displacements of beam-column elements. plastic hinges were assumed to concentrate at the two elemental ends. for considering geometric nonlinearity, the beam-column elements were divided into many short-elements. residual stresses and imperfections were not accounted for in direct analysis. authors in [6, 7] used a five-order interpolation function for considering the second-order effects of beam-column elements. the plasticity of cross-sections at the two ends of the element is modeled by two springs using the section assemblage concept. the tangent stiffness matrix of a structural system is established by integrating the stiffness of beam-column elements and the stiffness of springs. authors in [10] derived a finite element formulation for a beam-column element that had an arbitrarily plastic hinge along the element length. authors in [9] proposed a second-order inelastic large-deflection analysis method using only one element per member, including three plastic hinges in one member. in 2014, liu et al. [13] also proposed an arbitrarily-located plastic hinge element for direct analysis of planar steel frames. their method was directly developed from the initial out-ofstraight element. king et al. [5] proposed a second-order inelastic analysis method for steel frames. this method employed stability functions for predicting the second-order effects accurately. gradual yielding at plastic hinges accounted for using lrfd’s interactive equations. gradual yielding by residual stresses along the member length due to axial force was calculated by the crc tangent modulus concept. one element was used for modeling. in 2002, ziemian and mcguire [8] improved the result of plastic hinge method using modified tangent modulus formulation. the result was nearly identical with the sophisticated plastic zone method in some examples, but the method should be verified even more with different problems. the plastic hinge method of [5] is effective and saves computational time because it uses only one element per member. however, residual stresses at two plastic hinges are not considered in the analysis, and in some problems, the result has a significant error when compared with the ‘exact’ solutions using plastic zone methods. this study tries to develop a new plastic hinge method which can capture the nonlinear behavior of steel frames accurately. the proposed method employs the fiber discretization of a cross-section. stability functions and the geometric stiffness matrix are utilized for accounting for the second-order effects. a nonlinear static algorithm implementing the generalized displacement method is established for solving nonlinear problems. by some examples, the present method is proved to be reliable and straightforward for tracing the nonlinear behavior of 2d steel frames. corresponding author: phu-cuong nguyen engineering, technology & applied science research vol. 10, no. 4, 2020, 5974-5978 5975 www.etasr.com nguyen et al.: nonlinear inelastic analysis of 2d steel frames ii. behavior of the beam-column element a. p δ− effect stability functions studied in [31] were utilized for predicting the p δ− effect. with one element for the member, it is efficient to economize sources and analysis time. the force-displacement relationship using the incremental form of a 2d beam-column element can be written as: 1 2 2 1 / 0 0 0 0 i i j j p a i ei m s s l m s s δ θ θ ∆ ∆ ∆ = ∆ ∆ ∆                         (1) where p∆ , im∆ , and jm∆ are the axial force and moments, δ∆ , iθ∆ , and jθ∆ are the axial movement and rotations, a is the sectional area, i is the moment of inertia around the z axis, l is the elemental length, e is the young’s modulus of the steel, and 1s and 2s are stability functions. b. fiber plastic hinge figure 1 illustrates the fiber plastic hinge method. in this method, two ends, i and j, of the element are monitored regarding the behavior of stress and strain of fibers. the forcedisplacement relation of a 2d element considering both the p δ− effect and plasticity can be formulated as in (2): 2 2 1 2 1 2 2 2 1 1 / 0 0 0 ( (1 )) 0 ( (1 )) t i i j i j i j j i j j i a i p e i s m s s l s m s s s s δ η η η η θ θ η η η η       ∆ ∆         ∆ = − − ∆       ∆ ∆       − −     (2) where iη and jη are scalar parameters accounting for gradual yielding of fiber hinges. fig. 1. fiber plastic hinge method. they are estimated as: ( )2 1 n tii i i i i i t e a y i e i η = + = ∑ (3) ( )2 1 n tji i i i i j t e a y i e i η = + = ∑ (4) where n is the sum of fibers on the sections at i and j, tiie and tjie are the tangent modulus of the th i fiber at i and j, ia is the area of the th i fiber, ii is the moment of inertia of the th i fiber, iy is the center coordinate of the th i fiber, shown in figure 1, and te is the tangent modulus of an element. c. residual stresses from [5], the crc tangent modulus te is applied with the aim to consider the effects of residual stresses along the length. this effect is similar to the spread of plasticity on the length due to axial force, formulated as: te e= for 0.5 yp p≤ (5) 4 1t y y p p e e p p   = −      for 0.5 yp p> (6) where py is squash load. eccs residual stress [2] is admitted as initial condition to fibers, as shown in figure 2. d. fiber state the cross-section ends of the element are divided into several fibers n for considering gradual yielding of two fiber plastic hinges at i and j, as shown in figure 1. fibers are monitored and their behavior (stress, strain) is updated. if the fiber is yielded, its elastic modulus is equal to zero. axial strain ε∆ and curvature χ∆ of cross-section, and section forces are written as: sectional force vector: { }tn m∆ ∆ (7) sectional deformation vector: { }tε χ∆ ∆ (8) the sectional deformation vector is estimated as: ( ) 1 1 1 2 1 1 n n i i i i i i i n n i i i i i i i i i e a e a y n m e a y e a y i ε χ − = = = = − ∆ ∆ = ∆ ∆ − +                       ∑ ∑ ∑ ∑ (9) engineering, technology & applied science research vol. 10, no. 4, 2020, 5974-5978 5976 www.etasr.com nguyen et al.: nonlinear inelastic analysis of 2d steel frames fig. 2. eccs residual stress pattern. e. p − ∆ effect the elemental tangent stiffness matrix is written as: [ ] [ ] [ ] 3 5 3 3 3 5 5 5 t e gt k t k t k × × × ×  = +     (10) where the transformation matrix [ ] 3 5 t × of the element is formulated as: [ ] 3 5 1 0 0 0 0 0 1 0 1/ 1/ 0 0 1 1/ 1/ t l l l l × −   = −   −  (11) and gk   is the geometric stiffness matrix: 2 2 5 5 2 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 i j i j g i j i j m m m m l l k m m p p l ll m m p p l ll × + + − = + − + − −                           (12) iii. nonlinear solution the nonlinear solution algorithm invented by yang and shieh [32] is developed to find a solution to the structural system. yang and shieh’s method is one of the most efficient and stable numerical methods. it can easily capture the problems with several critical points. the equilibrium equation of steel frames is: { } { } { }1 1ˆi i i ij j j jk d p rλ− −  ∆ = +  (10) where 1 i jk −   is the tangent stiffness matrix, { } i jd∆ is the displacement vector, { }p̂ is the consultation load vector, { }1ijr − is the residual force vector, ijλ is the load coefficient. iv. examples and discussion a. column flexural buckling figure 3 illustrates a simply supported steel column under axial compression. young’s modulus is e=200000mpa and poisson’s ratio of steel is v=0.3. a horizontal load is put in the middle of the column for considering geometry imperfection. fig. 3. simply supported column. fig. 4. load-deflection curves of the column. the load-deflection curves of the column captured by the present study and abaqus are plotted in figure 4. by one element per column, the presented method can predict precisely the behavior and strength of the column, but abaqus overestimates the strength by 10.6%. abaqus needs more than five elements for obtained accuracy. this example illustrates the accuracy of the presented study in predicting the second-order effect. b. portal steel frame vogel [3] invented the portal steel frame for benchmark second-order inelastic methods. nguyen and kim [25] proposed a plastic zone method for analyzing this frame. the frame configuration is described in figure 5. the elastic modulus is e=205000mpa, the yield stress of the steel is σy=235mpa. the cross-sections are hea340 and heb300. authors in [3, 25] used 50 elements for columns and 40 elements for the beam for analyzing the frame, while this present program uses one element for beam-column members, and i-shape cross-sections have been meshed into 24 fibers for flanges and 18 fibers for the web. the load-deflection curve of the present study closely matches with vogel’s result, as plotted in figure 6. nguyen and kim’s result is lower than vogel’s result: -2.05% error is obtained when compared with p 0.004p w 8 x 3 1 2 .5 m 2 .5 m engineering, technology & applied science research vol. 10, no. 4, 2020, 5974-5978 5977 www.etasr.com nguyen et al.: nonlinear inelastic analysis of 2d steel frames vogel’s result. the collapse load coefficient of the different applied methods is listed in table i. less than 0.8% error of the present study is achieved when comparing with vogel’s result. analyzing this problem on a computer, with a configuration of intel core i7-7500 4cpus 2.70ghz and 16gb ram, the analyzing time is only 15s. this shows the accuracy and computation speed of the proposed method. fig. 5. portal steel frame. table i. collapse load coefficient for portal frame method collapse load coefficient error (%) [3] 1.022 – [25] 1.001 -2.05 present study 1.014 -0.78 fig. 6. load-deflection curves of portal frame. c. six-story steel frame the six-story steel frame plotted in figure 7 was firstly analyzed by vogel in [3]. vogel used both plastic zone and plastic hinge methods, chan and chui [7] used the refined plastic hinge method, nguyen and kim in [22] used a fiber beam-column method and in [25] the plastic zone method. all the columns are inclined with an angle of ψ = 1/450. properties of steel are e=205000mpa and σy=235mpa. in the present study, five elements for beams and one for columns were used for modeling. figure 8 and table ii show the results predicted by various methods. in this frame, the predicted load-deflection curve of various methods is not much different. the load-deflection curve of the present study is almost identical to vogel’s plastic zone method. the critical strength predicted by the proposed method (1.116) has less than 0.45% error when compared with vogel’s result (1.111) using the plastic zone method. analyzing this problem on the same intel computer, it takes only 53s, showing that the proposed program is accurate and efficient in predicting the nonlinear behavior and the strength of 2d steel frames. fig. 7. six-story steel frame. fig. 8. load-deflection curves of a six-story frame. table ii. collapse load coefficient for a six-story frame method collapse load coefficient error (%) [3] 1.111 – [25] 1.100 -0.99 present study 1.116 +0.45 v. conclusion a second-order inelastic analysis program based on the finite element method for 2d steel frames has been developed successfully. the effects of p-δ, p-∆, inelasticity of materials, residual stresses, and imperfections have been accounted for the nonlinear analysis by the generalized displacement method. the proposed method is simple, accurate, and efficient in predicting the strength and behavior of steel frames. the 4.0 m 5 .0 m 2800 kn 35 kn ∆ h e b 3 0 0 2800 kn h e b 3 0 0 hea340 ψ = 1/400 ψ 0.0 0.2 0.4 0.6 0.8 1.0 0 5 10 15 20 25 l o a d c o e ff ic ie n t horizontal deflection (mm) vogel nguyen and kim present study 6.0 m6.0 m 49.1 kn/m 49.1 kn/m 49.1 kn/m 49.1 kn/m 49.1 kn/m 31.7 kn/m ipe400 ipe360 ipe330 ipe300 ipe300 ipe240 h e b 2 2 0 h e b 2 2 0 h e b 2 2 0 h e b 2 2 0 h e b 1 6 0 h e b 1 6 0 h e b 2 6 0 h e b 2 6 0 h e b 2 4 0 h e b 2 4 0 h e b 2 0 0 h e b 2 0 0 6 x 3 .7 5 m = 2 2 .5 m ∆ = 1/450ψ = 10.23 knf 1 = 22.44 knf 2 f 2 f 2 f 2 f 2 ψ ψ 0.0 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[32] y.-b. yang and m.-s. shieh, “solution method for nonlinear problems with multiple critical points,” aiaa journal, vol. 28, no. 12, pp. 2110– 2116, 1990, doi: 10.2514/3.10529. microsoft word etasr_v13_n3_pp10765-10768 engineering, technology & applied science research vol. 13, no. 3, 2023, 10765-10768 10765 www.etasr.com doan van: application of advanced deep convolutional neural networks for the recognition of road … application of advanced deep convolutional neural networks for the recognition of road surface anomalies dong doan van science and technology application for sustainable development research group, ho chi minh city university of transport, vietnam dongdv@ut.edu.vn (corresponding author) received: 28 march 2023 | revised: 8 april 2023 | accepted: 14 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5890 abstract the detection of road surface anomalies is a crucial task for modern traffic monitoring systems. in this paper, we used the yolov8 network,a state-of-the-art convolutional neural network architecture, for real-time object recognition and to automatically identify potholes, cracks, and patches on the road surface. we created a custom dataset of 1044 road surface images in vietnam, each of which was annotated with pavement anomalies, and the yolov8 network was trained with this dataset. the results show that the model achieved an accuracy of 0.56 map at a threshold of 0.5, indicating its potential for practical application. keywords-road surface anomalies; convolutional neural networks; digital image processing; transportation i. introduction identifying anomalies on road surfaces such as potholes, cracks, and bumps is an important factor in creating conditions for road maintenance, providing a better driving experience, and reducing the risk of accidents (collisions, falls, etc.) [1-5]. analyzing data related to the condition of streets promptly can help make better decisions about transportation spending [4]. the anomalies on the road surface are repaired when they are reported by citizens or when a major incident occurs. however, a real-time reaction system that automatically detects various anomalies on urban and national roads does not exist. systems for identifying anomalies on roads can be divided into three categories: vision-based, sensor-based, and 3d reconstruction methods [6]. the sensor-based method mostly uses sensor data to identify road anomalies. authors in [5] compared the decision tree (dt) and support vector machine (svm) algorithms for classifying abnormalities on the road using data measured from acceleration and gyro sensors. authors in [7] used inertial sensor datasets collected in different contexts to detect and classify abnormalities on road surfaces (e.g. dirt roads, cobblestones, and asphalt roads). based on the reported results, the proposed convolutional neural network (cnn) model achieved the best performance with an accuracy of 93.17%. authors in [8] developed a hybrid method combining threshold-based signal processing techniques and machine learning algorithms to form a near real-time road anomaly detection system. on the other hand, the technique that uses 3d reconstruction to anticipate the shape of the road anomalies and evaluate their volume through stereo-vision technology is considered the most precise of the three methods. however, this method is more costly and difficult to identify when potholes are filled with water or dirt than other approaches. for instance, authors in [9] developed a pixel-level road surface anomaly detection approach based on stereo vision and deep learning. specifically, the vehicle-mounted photography system was used to capture both parallel and oblique photos to generate a 3d pavement point-cloud model. stereo-vision technology was employed in the 3d reconstruction phase to process the input images. point-cloud calibration relied on a pca algorithm, and various orthoimages, including color, depth, and overlapped images, were generated during the 3d data-processing phase. to identify pavement cracks and potholes in the orthoimages, a modified u-net deep-learning technology was utilized for segmentation. their approach achieved significant results: 0.9632 precision, 0.9552 recall, and 0.9592 f1 score. the vision-based method uses images to identify the presence of abnormalities through image processing algorithms. the advantage of this method is that it does not require direct access to the location of the abnormalities on the road, making it easy to detect multiple objects at the same time through traffic monitoring cameras or cameras on mobile devices. for example, authors in [10] proposed a real-time automatic pavement crack and pothole recognition system using a mobile device. the proposed system achieved only 0.7 precision, recall, accuracy, and f1 score. recently, deep learning techniques have gained widespread application in diverse fields [11-14]. these methods have also been employed in the identification of road surface anomalies, leveraging their strengths such as accurate detection and the ability to handle engineering, technology & applied science research vol. 13, no. 3, 2023, 10765-10768 10766 www.etasr.com doan van: application of advanced deep convolutional neural networks for the recognition of road … intricate data. for example, authors in [1] discussed a deep learning algorithm for detecting potholes on road surfaces. the algorithm employed a cnn with 9 layers. however, the method is not suitable for real-time applications because it cannot be used for online video processing. authors in [2] developed a system based on yolov2 [15] network to detect potholes on roads. however, their system can only run offline and cannot be used in real-time applications. additionally, the system's accuracy only reached 82.5%. authors in [16] proposed a lightweight cnn model based on a modified mobilenetv2 [17] that can operate on edge devices. the proposed system is capable of performing pixel-wise crack detection on streets. the common drawback of the image processing methods mentioned above is that they cannot meet real-time operational criteria. therefore, in this article, we propose a method that used yolov8, an advanced cnn model capable of real-time object detection with high accuracy. the proposed method can detect abnormalities on the road surface such as potholes, cracks, and road patches. the technical contributions of this paper can be summarized as:  to the best of our knowledge, this paper is the first that applies the state-of-the-art yolov8 architecture to road anomaly detection.  the proposed method can detect in real time various types of anomalies such as potholes, cracks, and patches.  the empirical results suggest that the proposed method can be applied in practical settings with suitable modifications. ii. road anomalies dataset we constructed a road surface dataset consisting of 1044 images collected from random roads in vietnam. figure 1 shows some examples from the dataset. the data were taken at different times and weather conditions, resulting in a wide range of lighting and shadow conditions. this is the biggest challenge for abnormal road detection methods based on image processing. the dataset has a total of 1044 images and was divided into 967 images for training of the network and 77 images for model evaluation. each image was labeled with three kinds of anomalies namely potholes, cracks, and road patches. the instance distribution is presented in figure 2. iii. methodology a. yolov8 network released at the beginning of 2023, yolov8 is the latest generation of the yolo network, in particular, and is currently the most efficient model in tasks such as classification, detection, and segmentation of objects [18]. in object detection tasks, yolov8 can achieve superior results and faster processing times than other models thanks to its combination of optimization techniques and improvements. specifically, the yolov8m model achieved a 50.2% map score on the coco dataset, which is higher than its predecessors [18]. also, the model requires fewer parameters than the others. fig. 1. examples in the dataset. fig. 2. distribution of road anomalies in the dataset. yolov8 utilizes advanced techniques in the object detection field such as decoupled head and anchor-free detection. also, novel ideas, such as mosaic stopping strategy that skips mosaic augmentation for the last 10 epochs, were introduced. the modifications compared to yolov5 [18, 19] are:  the c3 module was replaced with the c2 module 5. engineering, technology & applied science research vol. 13, no. 3, 2023, 10765-10768 10767 www.etasr.com doan van: application of advanced deep convolutional neural networks for the recognition of road …  the first 6×x6 conv was replaced with a 3×3 conv in the backbone.  the first 1×1 conv` was replaced with a 3×3 conv in the bottleneck.  decoupled head was used and the objectness branch was deleted. this technique separates the classification and regression tasks into two separate subnetworks, each with its own set of parameters [11, 20]. fig. 3. evaluation results of proposed model. fig. 4. visualization of the results in real-time application. b. experimental environment the proposed yolov8 model was trained for 200 iterations with a batch size of 8. due to the relatively small sizes of the objects of interest, the input image size increased from 640×640 to 1280×1280. all experiments were run on a computer with the following configuration:  gpu nvidia rtx3050 4 gb vram  cpu amd ryzen 5 5600h, 3.3 hz  16 gb ram iv. results and discussion the performance of the anomaly detection model on the road is shown in figure 3. specifically, the model’s precision achieved 84%, and the average accuracy was 56.8% at a confidence threshold of 0.5. the recall criterion, which indicates the ability to detect all objects present in the image, achieved 60% score. the visualized results of the evaluation set can be observed in figure 4. the results show that the model is capable of detecting anomalies such as potholes, cracks, and patches on the road with high accuracy. engineering, technology & applied science research vol. 13, no. 3, 2023, 10765-10768 10768 www.etasr.com doan van: application of advanced deep convolutional neural networks for the recognition of road … v. conclusion in this paper, the utilization of the advanced yolov8 convolutional neural network architecture to address the issue of detecting road anomalies was discussed. the study shows that the proposed model's performance is promising, with map of 0.56 at the threshold of 0.5, suggesting that it can be applied in practical settings with suitable modifications. we intend to gather additional road data and further finetune the model to achieve better results in the future. references [1] v. pereira, s. tamura, s. hayamizu, and 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[2] k. e. an, s. w. lee, s.-k. ryu, and d. seo, "detecting a pothole using deep convolutional neural network models for an adaptive shock observing in a vehicle driving," in 2018 ieee international conference on consumer electronics (icce), las vegas, nv, usa, jan. 2018, https://doi.org/10.1109/icce.2018.8326142. [3] j. m. celaya-padilla et al., "speed bump detection using accelerometric features: a genetic algorithm approach," sensors, vol. 18, no. 2, feb. 2018, art. no. 443, https://doi.org/10.3390/s18020443. [4] f. seraj, b. j. van der zwaag, a. dilo, t. luarasi, and p. havinga, "roads: a road pavement monitoring system for anomaly detection using smart phones," in big data analytics in the social and ubiquitous context, 2016, pp. 128–146, https://doi.org/10.1007/978-3319-29009-6_7. 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[9] j. guan, x. yang, l. ding, x. cheng, v. c. s. lee, and c. jin, "automated pixel-level pavement distress detection based on stereo vision and deep learning," automation in construction, vol. 129, sep. 2021, art. no. 103788, https://doi.org/10.1016/j.autcon.2021.103788. [10] a. tedeschi and f. benedetto, "a real-time automatic pavement crack and pothole recognition system for mobile android-based devices," advanced engineering informatics, vol. 32, pp. 11–25, apr. 2017, https://doi.org/10.1016/j.aei.2016.12.004. [11] h. d. quy, n. n. son, and h. p. h. anh, "deyolov3: an optimal mass detector for advanced breast cancer diagnostics," in computational intelligence methods for green technology and sustainable development, 2023, pp. 325–335, https://doi.org/ 10.1007/978-3-031-19694-2_29. 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[15] j. redmon and a. farhadi, "yolo9000: better, faster, stronger," in 2017 ieee conference on computer vision and pattern recognition (cvpr), honolulu, hi, usa, jul. 2017, pp. 6517–6525, https://doi.org/ 10.1109/cvpr.2017.690. [16] g. doğan and b. ergen, "a new mobile convolutional neural networkbased approach for pixel-wise road surface crack detection," measurement, vol. 195, may 2022, art. no. 111119¸https://doi.org/ 10.1016/j.measurement.2022.111119. [17] m. sandler, a. howard, m. zhu, a. zhmoginov, and l.-c. chen, "mobilenetv2: inverted residuals and linear bottlenecks." arxiv, mar. 21, 2019, https://doi.org/10.48550/arxiv.1801.04381. [18] g. jocher, a. chaurasia, and j. qiu, "yolo by ultralytics." jan. 2023, [online]. available: https://github.com/ultralytics/ultralytics. [19] g. jocher et al., "ultralytics/yolov5: v7.0 yolov5 sota realtime instance segmentation." zenodo, aug. 22, 2022, https://doi.org/10.5281/ zenodo.7347926. [20] z. ge, s. liu, f. wang, z. li, and j. sun, "yolox: exceeding yolo series in 2021." arxiv, aug. 05, 2021, https://doi.org/10.48550/ arxiv.2107.08430. microsoft word 13-875-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1274-1279 1274 www.etasr.com zeghib and chaker: efficiency of a solar hydronic space heating system under the algerian climate efficiency of a solar hydronic space heating system under the algerian climate ilhem zeghib energy physics laboratory department of physics, brothers mentouri university constantine, algeria imita75@yahoo.fr abla chaker energy physics laboratory department of physics, brothers mentouri university constantine, algeria chakamine@yahoo.fr abstract—hydronic heating systems supplied by renewable energy sources are one of the main solutions for substituting fossil fuel and natural gas consumption. this paper presents the development of modeling and analysis of a solar hydronic heating system in an existing single-family house built in 1990’s heated by low-temperature radiators. the simulation has been used to study the potential of using this system under climatic conditions in algeria. and for this purpose, a component based on the simulation model for the thermal behavior of each component of the system are carried out in order to evaluate the economic performance for this system. the system is compared, with a conventional high-temperature boiler system. the results indicated that single-family houses could be heated with solar hydronic heating and provided an acceptable level of thermal comfort in the room with 22°c, according to the results of the analysis, the solar energy covers only 20.8% of the total energy consumption in a single-family house. furthermore, the thermal performance of the heating conventional system can be largely improved up to 15%. keywords-solar collector; low temperature heating; solar heating; indoor temperature; efficiency i. introduction in algeria, energy consumption in the building sector accounts for almost 40% of the total final energy use [1] with heating and hot water being responsible for almost 60% of that [1]. this high consumption has led to opt for new low-energy buildings and to retrofit old ones, and take measures such as using additional insulation, tight building envelopes, or energysaving equipments. all these measures help reduce the season and space heating load and provide an opportunity to use lowtemperature heating systems. these systems usually work with a maximum supply water temperature of 45°c. so a new generation of hydronic heating systems operating at low temperatures and employing renewable energy sources such as geothermal sources and solar energy has emerged. in [2], authors show that renewable sources of heat can be integrated into the district heating system without problems and contribute to the fossil-free heating sector. in [3], the author studied the technical and economical potential to use solar energy in the finnish district heating system. the function of a district heating system connected to the solar collector field was simulated with the trnsys (transient system simulation tool) software. the results show that solar collectors could provide the 10% of the yearly heat production. in the existing single-family house, we can make very significant savings by replacing or supplementing an old system with a solar heating system. the objective is to meet the heating needs using the least possible energy auxiliary, valorize a performance enhancement of solar energy. for this purpose, integration of the solar thermal system should be relatively simple: all that will need to be done is to replace the boiler of a traditional heating fluid with a storage tank heated with a set of solar panels and existing conventional radiators with oversized radiators (low temperature). in this paper, we are studying the dynamic behavior of the solar hydronic space system is represented by a mathematical model corresponding to an energy balance of each element of the solar system, collector, tank and the radiators. ii. system description a. heating system a schematic diagram of the solar hydronic space heating system used in the present study is shown in figure 1. the solar space heating system consists of the flat plate collectors, a hot water storage tank, the piping, the controllers, and the auxiliary heating system [4]. the load distribution system consists of low temperature radiators and two pumps to transfer the energy to the storage and to the load. the circulating water from the collector transmits its heat to the storage tank water where it is stored in the form of a sensitive heat until it can be used. an auxiliary heater (gas boiler) is connected to the storage tank to supplement solar heating, when needed to meet temperature requirement of the load. in our study, the heat production system is the combination of solar collectors and a gas boiler. when water temperature in the storage tank is high enough for space heating, solar collectors are used as the only heat source can deliver hot water directly to the low temperature radiators. in this respect, auxiliary heater operates only when the temperature of the water in the tank is lower than 45°c which will reduce the boiler energy. engineering, technology & applied science research vol. 6, no. 6, 2016, 1274-1279 1275 www.etasr.com zeghib and chaker: efficiency of a solar hydronic space heating system under the algerian climate fig. 1. schematic diagram of solar low heating system b. hydronic distribution system the component parts of a solar-water distribution system are similar to that of a conventional heating system. the hydronic systems use pipes and circulation pumps to distribute heated water throughout the house. a heat distribution grid can transfer heat from the tank to the low-temperature radiator. the low-temperature hydronic heating concept can be extended to existing houses by replacing existing radiators with low temperature radiators and changing the design operating conditions from 70/60/20°c to 50/40/20°c [3]. in our study, the length and height of the radiators are kept the same but their depth is changed. this meant that while all the original radiators were type 21, the low-temperature radiators were type 33 [5]. as such, replacing the radiators is very easy because the radiators can be connected to the existing piping system without any changes. iii. modeling system components the simulation procedure involves casting mathematical models for each system component and then combining these models consecutively to accomplish the complete simulation. thermal models compute each component exit temperature (collector, storage tank, low temperature radiator) and system performance, were estimated every minute. a. thermal analysis 1) solar collector two flat-plate collectors, a 1.5 m² gross surface area each, were used for the collection of solar energy. the collectors have been installed facing south and inclined at an angle of 45°c from the horizon for maximum gain during winter collection. the mathematical model describes the flat-plate solar collector system considering the transient properties of its different zones. in the proposed model, the analyzed control volume of the flat-plate solar collector contains one tube that is divided into five nodes (glass cover, air gap, absorber, fluid and insulation) perpendicular to the liquid flow direction. the collector efficiency is defined as the ratio of usable heat energy extracted from a collector by the heat transfer fluid during any time period to the solar energy striking the cover during that same time period [6]: dtia dtq t t gc t t u c    2 1 2 1  (1) 2) water storage tank a stratified storage tank was used in this simulation, a mathematical model for heat transfer in the storage tank based on the one-dimensional transient heat transport equation by convection and conduction along the prevailing flow direction of the storage tank. in multi-node modeling, the tank is divided into n nodes or sections, with energy balances written for each node. the energy equation takes into account the energy gain from the collector, the energy loss in the surrounding, and utilized by the load. this results in n differential equations to be solved simultaneously to obtain the temperature of each node [7]. in our study the tank is divided into 150 nodes. thermal efficiency at tank [9]: s dis s q q  (2) where disq is the heat transferred to the distribution system is defined by: slosssdis qqq , (3) the energy storage in the tank is related to the mass and the difference between the initial and final temperature of water in the storage tank can be expressed as [10]: )( 1 ,1, 1 ,, isis n i isiss ttcpm n q    (4) the heat losses from the tank is given by [11]  aisisis n i sloss ttau n q   ,,, 1 , 1 (5) 3) auxiliary heating system the auxiliary heating system used in conjunction with a solar heating system is of the plain/traditional type. although engineering, technology & applied science research vol. 6, no. 6, 2016, 1274-1279 1276 www.etasr.com zeghib and chaker: efficiency of a solar hydronic space heating system under the algerian climate the auxiliary boiler can be controlled in different ways, normally the auxiliary heater in series would be used to the temperature of the water from storage only when the water temperature in the storage tank is too low to meet the heating requirement in the house, and has a desired temperature of 45°c. the auxiliary efficiency was calculated as : gazcaz sso bur au au pcim ttcpm q q . 1, . . )(   (6) auq the useful energy transmitted by the auxiliary to the hot water, bruq the energy used by the burner. 4) pipe heating the task of the distribution system is to connect all various components of the heating system. the pipes distribute a heating medium lose some it to the surroundings. this heat loss causes undesired cooling of the medium in the pipes; how they can be acceptable if the pipes are placed within a heated space. however, this form of heat transfer is undesirable, and it cannot be regulated and may not be required for most of the time. the efficiency of the pipes heating:           ctif q q q q ctif q q q q s au ploss au p s dis ploss dis p pi 451 451 1, , 1, ,  (7) the heat emissions of pipes are calculated is following [12]: )(.., nmfccploss ttylq  (8) where cy is the linear thermal transmittance, cl is the total length of pipes. mft is the pipes inner temperature and nt is the interior temperature. 5) low-temperature radiators the level of water temperature supplied to the heat emitter in buildings plays a major role in primary energy consumption. the main principle of a low-temperature heating system is to provide the same thermal comfort as a medium-temperature heating system, while using a lower supply temperature. the radiators for low temperature systems are physically and technically the same as traditional panel radiators. the only key factor which changes is sizing. normally manufacturers' data sheets will quote radiator output when there is a temperature difference (water to air). if a radiator is required to run at a lower temperature than normal, its size must be increased to compensate for this temperature difference. the water return temperature through radiators based on actual heat emission and inlet water temperatures is calculated by [13]: )()()( . rsbrrsrepr rs r ttuattcm dt dt c  (9) the emission efficiency is giving by : p re re q q  (10) 6) eenergy demand in the house the energy balance of a house is characterized by energy losses and gains, energy losses are transmission and ventilation and these losses can be fully or partly compensated by energy gains. different sources of energy gains can be utilized, such as internal energy gains caused by appliances and users as well as solar gains through openings. in this study, the energy need of the house during the heating is estimated using the equations in thermal regulation for algerian buildings. the need of useful heat depends on thermal qualities of its envelope (thermal resistances), and its losses by ventilation. the energy need for heating is giving by [14]: glosh qnqq . (11) where losq is the total heat transfer for heating mode, gq are the total heat gains for the heating, n is the dimensionless gain utilization factor. the house is modeled as a multi-zone model (each room is modeled as an individual zone). the rooms are heated at a uniform indoor temperature at all times. the room can be modeled as a single heat capacity element. a differential equation is then written relating the heat flow to the room to time derivative of the indoor temperature and the house heat capacity. the indoor temperature of room is calculated by: )( 11 ,sup, blosb b net b b qq c q cdt dt  (12) b. energy performance analysis the performance indices of energy evaluated in this study include: energy collected, energy delivered and supply pipe losses, solar fraction, collector efficiency and system efficiency. 1) solar fraction the solar fraction is the amount of energy provided by the solar technology divided by the total energy required. it can be calculated from the equation below [15]:     auxs s qq q sf (13) where sq the solar energy produced, auxq auxiliary heating requirement. engineering, technology & applied science research vol. 6, no. 6, 2016, 1274-1279 1277 www.etasr.com zeghib and chaker: efficiency of a solar hydronic space heating system under the algerian climate 2) system efficiency the efficiency of heating systems is increasingly important because of the increasing need to save energy. the major characteristic parameter for estimating the efficiency of the hydronic heating is heat loss factor. the main parts of a heating system, generation, storage, distribution and emission, all have some losses. the distribution losses caused by pipes in unheated area are calculated as non-recoverable losses and losses in heated rooms contribute as recoverable losses. emission losses consist of heat loss due to non-uniform temperature distribution, heat loss due to heat emitter position and heat loss due to control indoor temperature. the tolal systems efficiency is calculated dy [16] repiauinst s  ... (14) iv. results and discussion the thermal performance of a solar space heating system is usually estimated by computer simulation, taking into consideration local climatic conditions and energy load. the simulation input parameters include climatic conditions of adrar (27.10 n, 0.17 e, altitude: 279 m) in algeria. the weather data are obtained from in-field measurements, using a weather station, the measured radiation and ambient temperature for 1 min intervals over a 96 h optimization interval are shown in figure 2. a calculation code is set up and developed in fortran language for the resolution of the thermal balance equations for different component of the solar space heating. the program determine every minute the temperature of the collector, the storage tank, the radiators and energy needed for heating. for the hydronic system, we determine the pipe heat losses, the global efficiency of the solar space heating system. the system was analyzed and optimized over a period of four days from 16th to 19th february. fig. 2. variation of solar radiation in this study, the heated water from solar collectors is stored in a tank for a week without use. the goal is to increase the tank temperature to 55°c, after we used the water from that tank for heats the space water radiators. figure 3 shows the variation of the outlet water temperature in the tank and inlet and outlet temperature of the radiators. when water temperatures at the outlet of tank is less than 45°c, water goes to auxiliary heater to be heated and to be send to the radiators. this occurs when the solar radiation is not sufficient to heat and if the water storage temperature is over 45 ° c the radiators are heated by hot water from the storage tank. fig. 3. water temperature of the radiators and the storage tank in figure 4, the energy need for heating of the house is shown for 4 days. it is noticed that heating energy profile is quite similar to ambient temperature profile. in general, heating energy and the ambient temperature are inversely proportional to each other: the higher the heating energy the lower ambient temperature, and vice versa. it may be noted that during the night the heating needs are greater in the living room that two room, its maximum value of 1.2 kw. there is a slight difference of the heating needs in the three rooms between 14.00 h and 10.00 h this is obviously caused by effect of the solar gains on the internal conditions, which are different according to orientation of the room. fig. 4. variation of energy need for heating during the 4 days from figure 5, it has been observed clearly that daily solar fraction is maximal when the storage temperature is higher than 45°c, the radiators are heated by hot water from the storage tank. when the temperature is below 45°c, the auxiliary heater is activated, and daily solar fraction starts to decrease with decreasing storage temperature. as it can be observed from figure 6 the monthly solar fraction decreases from november to january and then increasing until march. during november and march, the solar energy is relatively low but it this coincides with heating requirements which are low. during december and january, the solar fraction decreases and at the same time the contribution of the solar thermal systems to the supply of energy is reduced. moreover engineering, technology & applied science research vol. 6, no. 6, 2016, 1274-1279 1278 www.etasr.com zeghib and chaker: efficiency of a solar hydronic space heating system under the algerian climate it was estimated that the annual solar fraction for this system is about 20.8%. figure 7 illustrates the variation of the indoor temperatures in the rooms in the house (living room, room1 and room 2) for four days. it should be noted that the internal temperature profile is quite similar to ambient temperature profile, the temperature is maximum in the middle of the day and minimum for the night, or heating needs are important. they vary between 17°c and 23°c for three rooms, for a minimum ambient temperature at 7°c. there is a slight difference temperature of living room and two rooms between 10.00h and 14.00h, this is due to the fact that the living room main facade faces south while the two rooms are oriented to the north. fig. 5. variation of daily solar fraction and tank temperature fig. 6. variation of monthly solar fraction, annual energy needs and solar energy produced fig. 7. room air temperature during 4 days figure 8 shows a comparison of indoor room temperature in the room 1 between solar heating and conventional heating. it is observed that temperatures are similar (difference of 0.5°c) and they range between 16 and 23°c. we can deduce that solar heating systems can provide a ideal temperature inside the house. figure 9 shows a comparison of total system efficiency between solar heating and conventional heating. we note that the performance of solar heating systems is higher than conventional heating systems by 15%.this seems logical when the heating system is too hot, the head losses from production units, distribution pipes and radiators are important, therefore, their performance decreases. it should be noted that the system efficiency profile is quite similar to indoor room temperature profile, the system efficiency is maximum in the middle of the day and minimum for the night. fig. 8. comparison of indoor room temperature between conventional and solar heating fig. 9. comparison of space heating efficiency between conventional and solar heating the potential savings offered by solar thermal systems are difficult to calculate exactly and depend on a large range of factors. these include: initial system cost (depending on size, quality of parts and installation), the energy source that you are replacing (coal, gas). solar heating systems usually cost more to purchase and install than conventional water heating systems. in this study the total cost of the solar heating system was 300000 da. this figure includes the cost of installation and all parts (solar collectors, controller, pipes, hot water tank). however, regulators and piping distribution system are not included in the calculation of costs as they are part of conventional system. the annual saving offered by this system in the first year of operation is about 3661 kilowatts hours / year, corresponding to 366 m 3 of natural gas. we can deduce that the space solar heating in algeria offer modest savings, because the per unit cost of gas is fairly cheap and the prices engineering, technology & applied science research vol. 6, no. 6, 2016, 1274-1279 1279 www.etasr.com zeghib and chaker: efficiency of a solar hydronic space heating system under the algerian climate for natural gas exported by algeria are 20 times less expensive than the international prices (equal to 4.191da / kwh (1 euro = 122.43 da )). v. conclusion system modeling and computer simulations are employed in order to investigate the potential of using a solar hydronic space heating system under the algerian climate. the developed mathematical analysis is utilized to study the performance of the proposed system. results showed that this system provide on average, more than 20.8% of a house’s heating energy. furthermore, the thermal performance of the heating conventional system can be largely improved to 15%. moreover, the system was capable of sustaining a stable and comfortable indoor temperature in rooms with 22°c. the results indicate that, considering the cost of solar heating systems and the fuel prices today, a hydronic heating system that integrates solar heating is not yet cost-effective in the algerian circumstances, especially as the expected pay-back periods tend to be very long. this result proves that this technology is preferred for countries with higher gas price. references [1] k. imessad, r. kharchi, “experimental study of a combined solar system for floor heating”, renewable energy, vol. 18, no. 3, pp. 399405, 2015 [2] m. brand, s. svendsen, “renewable-based low-temperature district heating for existing buildings in various stages of refurbishment”, energy , vol. 62, pp. 311-319, 2013 [3] m. leskinen, “the use of solar energy in a district heating system in finland : case study of six district heating plants”, new and renewable technologies for sustainable development, pp. 313-324, 2002 [4] m. bojic, s. kalogirou, k. petronijevic, “simulation of a solar domestic water heating system using a time marching mode”, renewable energy, vol. 24, pp. 441-452, 2002 [5] www. chappee.com, 2015 [6] y. kim, k. thu, “thermal analysis and performance optimization of a solar hot water plant with economic evaluation”, solar energy, vol. 86, pp. 1378-1389, 2012 [7] z. f. li, k. sumathy, “performance study of a partitioned thermally stratified storage tank in a solar powered absorption air conditioning system”, applied thermal engineering, vol. 22, pp. 1207-1216, 2002 [8] i. zeghib, a. chaker, “modeling and simulation of a solar thermal system for domestic space heating using radiators low temperature”, international journal of renewable energy research, vol. 1, no. 5, pp. 266-276, 2015 [9] c. j. porras-prieto, f. r. mazarron, “influence of required tank water temperature on the energy performance and water withdrawal potential of a solar water heating system equipped with a heat pipe evacuated tube collector”, solar energy, vol. 110, pp. 365-377, 2014 [10] m. arslan, “thermal performance of a vertical solar hot water storage tank with a mantle heat exchanger depending on the discharging operation parameters”, solar energy, vol. 116, pp. 184-204, 2015 [11] h. wang, c. qi, “performance study of underground thermal storage in a solar-ground coupled heat pump system for residential buildings”, energy and buildings, vol. 40, pp. 1278-1286, 2008 [12] s. ntsaluba, b. zhu , “optimal flow control of a forced circulation solar water heating system with energy storage units and connecting pipes”, renewable energy, vol. 89, pp. 108-124, 2016 [13] l. haiyan, p. valdimarsson lamberto, “district heating modelling and simulation”, 34th workshop on geothermal reservoir engineering, 2009 [14] l. tronchin, k. fabbri, “energy performance building evaluation in mediterranean countries: comparison between software simulations and operating rating simulation”, energy and buildings., vol. 42, pp. 18621877, 2010 [15] e. kazanavicius, a. mikuckas, “the heat balance model of residential house”, information technology and control , vol. 35, pp. 391-396, 2006 [16] m. maivel, j. kurnitski, “low temperature radiator heating distribution and emission efficiency in residential buildings”, energy and buildings, vol. 69, pp. 224-236, 2014 microsoft word 16-2728_s_etasr_v9_n3_pp4154-4158 engineering, technology & applied science research vol. 9, no. 3, 2019, 4154-4158 4154 www.etasr.com pamplona & alves: mitigating air delay: an analysis of the collaborative trajectory options program mitigating air delay: an analysis of the collaborative trajectory options program daniel alberto pamplona air transportation department aeronautics institute of technology sao jose dos campos, brazil pamplonadefesa@gmail.com claudio jorge pinto alves air transportation department aeronautics institute of technology sao jose dos campos, brazil claudioj@ita.br abstract—congestion is a problem at major airports in the world. airports, especially high-traffic ones, tend to be the bottleneck in the air traffic control system. the problem that arises for the airspace planner is how to mitigate air congestion and its consequent delay, which causes increased cost for airlines and discomfort for passengers. most congestion problems are fixed on the day of operations in a tactically manner using operational enhancements measures. collaborative trajectory options program (ctop) aims to improve air traffic management (atm) considering national airspace system (nas) users business goals, particularities faced by each flight and airspace restrictions, making this process more flexible and financially stable for those involved. in ctop, airlines share their route preferences with the air control authority, combining delay and reroute. when ctop is created, each airline might decide its strategy without knowledge of other airline’s flights. current solutions for this problem are based on greedy methods and game theory. there is potential space to improve. this paper examines ctop and identifies important strategic changes to atm adopting this philosophy, particularly in brazil. keywords-ctop; collaborative trajectory options; air traffic management; atm i. introduction air delay is an existing problem in most airports around the world, bringing higher cost to the airlines and discomfort to the passengers. this type of inefficiency brings economic consequences for all stakeholders involved in the airline business. authors in [1] reported that flights in europe overdue to airspace inefficiencies and capacity bottlenecks are delayed 10 minutes on average per flight. it is estimated that, on average, consumer benefits per flight due to airspace modernization will count for €32 with higher levels for business passengers. in the next 20 years the projected demand for civil aviation market varies from 32,600 [2] new aircrafts (freighter and passenger) to 38,050 airplanes [3]. single-aisle airplanes are expected to command the largest share of the new deliveries, with an estimated need of 26,730 airplanes [2]. the total fleet is expected to double in 15 years. in this context, some cities are expected to concentrate the air demand with long-haul and regional traffic, creating global hubs. the air traffic growth is concentrated in a few cities. in latin america, since 2007, 45% of the traffic growth is accounted by just 10 airports. these airports are not just transport hub exchanges but they arise as the cornerstones of new urban and economic global centers [4]. delay is one of the consequences of this flight concentration and is a constant problem in most big airports. in 2014, the average delay per delayed (add) flight in europe was 26 minutes. in 2013, 7.9% of all flights in brazil were delayed more than 30 minutes, and 3.1% were delayed more than 60 minutes. in 2010, 24% of all flights in europe and 18% of all flights in usa were delayed more than 15 minutes [5, 6]. more than half of delays are caused by airline factors such as technical problems, baggage delays, and passenger related problems. the second largest portion (22%) is due to air traffic flow control management (atfcm) problems. the third largest portion is related to airport problems (16%) and the last portion is related to the weather (9%) [6]. due to capacity constraints, there is a growing necessity for changes in the air traffic system to accommodate the increasing traffic demand. the fundamental shift in atm paradigm will be from clearance-based air traffic control (atc) to trajectory-based atc operations. this new type of trajectory will include new constraints, for example target time of arrival (tta), that will improve its predictability and as consequence, and facilitate air traffic controllers’ work. there are differences in the capacity constraints for the usa and europe. for us, the major capacity constraints are founded at major airports and in the terminal airspace around them. in the other hand, in europe the en route airspace presents capacity constraints [7]. according to [8] there are four performance objectives: (a) airspace design for more capacity, with an increase of 73% in 2020, when compared to the 2005 panorama. in the long term, there will be three times more air space capacity; (b) three times improvement in air safety for 2020 and a ten times increase in the longer term; (c) decrease of 10% on the environmental impact per flight due to atm; (d) decrease of 50% to atm costs per flight. as [9] reminds, atm is foremost about safety. ii. a cooperative environment between airlines and air traffic authorities in 2003, during the 11th air navigation conference, it was agreed upon icao members that it was necessary to evolve towards a more collaborative environment. key to this philosophy is the notion of global information utilization, corresponding author: daniel alberto pamplona engineering, technology & applied science research vol. 9, no. 3, 2019, 4154-4158 4155 www.etasr.com pamplona & alves: mitigating air delay: an analysis of the collaborative trajectory options program management and interchange. this new philosophy aims to evolve to a holistic, cooperative and collaborative decisionmaking environment. despite the differences between the members, the actions are balanced to achieve equity and access. the following members comprise the atm community: (a) airport community, (b) airspace providers, (c) airspace users, (d) atm service providers, (e) atm support industry, (f) international civil aviation organization (icao), (g) regulatory authorities, and (h) states. in this context of collaboration the collaborative air traffic management (catm) arises [10]. iii. collaborative air traffic management collaborative atm (catm) is an attempt to accommodate aircraft operator preferences to the maximum extent possible with restrictions imposed only when an actual operational need exists. catm tries to adjust the atc system to meet real-time demands. the main objective is to give the aircraft operator the opportunity to participate in the decisions rather than the atc authority arbitrary defining the restrictions. this means that all airspace operators can work together and collaborate on the decision making [11]. the first implementation of catm is the collaborative decision-making (cdm). a. collaborative decision-making cdm began in us in 1993 when faa and major air space users started a cooperative environment. before 1993, faa used flight schedules published in the official airline guide (oag) to forecast preliminary air traffic demand prior to operator’s route request. the milestone of cdm was when the industry agreed to share its information, providing real-time, day-of-operations schedules [12]. the notion was that both the service provider (faa) and the system users (airlines) could benefit from cooperation [13]. it was 1995 when cdm was officially launch in the us, when faa and the industry group defined roles and responsibilities and the foundation for a collaborative air traffic management system was laid [12]. cdm is structured in the following manner: the basis of the cdm process is: (a) common situational awareness: where all parties must know the constraints, with a shared view of the constraints in the system. above is the (b) distributed planning: where all parties must be able to react to the constraints in a manner where decisions are made at the most appropriate point. in the top is the (c) analytical capability: where all parties must measure what happened in order to improve the system and is the pillar of the collaborative paradigm [13]. in europe, cdm was implemented in early 2000’s as airport cdm (a-cdm), because virtually all european airports have slot controls and scheduled operations generally are within airport capacities [14, 15]. today, cdm is well developed in europe and usa [16]. allied with this collaborative environment, air traffic flow management (atfm) programs were created to reduce the scale and cost during times of adverse weather and heavy traffic demand [15]. b. air traffic flow management (atfm) atfm is a function of atm established with the objective of contributing to a safe, orderly and expeditious flow of traffic while minimizing delays. the purpose of atfm is to balance air traffic demand with airspace and/or airport capacity to ensure the most efficient use of the airspace system [17]. to achieve those objectives of optimum flow traffic, the following measures include, but are not limited to: a) allocating and updating departure slots, (b) allocating and updating arrival slots, (c) allocating and updating en route slots, (d) re-routing of traffic, (e) alternate flight profiles, (f) minutes-in-trail assignments, (g) mile-in-trail assignments, (h) airborne holding, and (i) ground-holding [17]. atfm programs developed to handle problems in the en route airspace have been quite successful in mitigating the cost of disruptions, although their success has been limited due to inflexibilities in incorporating flight operator´s specific needs and adapting to changing weather and traffic conditions [18]. recently, the nextgen and sesar programs are looking for a shift in the atc method moving for trajectory-based operations (tbo). linked to this, faa has recently implemented a new atfm program, ctop [18, 19]. iv. trajectory-based operations a trajectory can be defined as the four-dimensional flight path of an aircraft through space and time (4d). the tbo concept means a move from base method atc to a trajectorybased system of atm. in this new concept, the aircraft will be assigned flexible and negotiated trajectories and the atc will have to manage those routes, with the air traffic controllers performing a strategic traffic flow coordinator. this will allow maximum utilization of available airspace and providing advanced navigational capabilities for those aircrafts flying for example rnp trajectories [11]. for operating in this new concept, these will be necessary: (a) the aircraft will be required to transmit and receive aircraft and navigational data in a precise manner, (b) new surveillance equipment, (c) improved aircraft avionics capabilities, (d) advanced automation systems, and (e) automated conflict probes. enabling tbo requires interactive and integrated decisions and control actions spanning each time horizon to include capacity management, flow contingency management and trajectory management. a critical requirement is the air navigation service provider (ansp) enabling the stakeholder access and common awareness of the air traffic system capacity and constraints, in the present and future (predicted) situation. ctop provides through trajectory option set (tos) an initial foundation of the tbo [20]. tbo is the new atc concept that moves from a base method to a trajectory-based method. collaborative trajectory options program (ctop) is one of the atm initiatives and it is associated with the idea of a constrained area. inside the ctop, there is the trajectory options set (tos) a set of trajectories that are chosen by the airlines in a constrained area and the four-dimension trajectory (4dt) that is a flight path of an aircraft through space (three-dimension) and time (one-dimension) [21]. a. collaborative trajectory options program ctop relates to the idea of a constrained area. ctop is one of many new traffic management initiatives been developed within catmt and is a part of the nextgen and sesar initiatives. ctop is a method of managing demand through constrained airspace. in ctop, customers are allowed to communicate their preferences in a tos. the customers can choose between route and delay [19]. ctop is used anywhere engineering, technology & applied science research vol. 9, no. 3, 2019, 4154-4158 4156 www.etasr.com pamplona & alves: mitigating air delay: an analysis of the collaborative trajectory options program there is a constraint in the air traffic system. the most common constraints are weather and air traffic volume. the ctop program provides greater flexibility for the airspace planner in managing capacity by allowing ground delays and re-routes to be considered together. according to [18] ctop has similarities with the previous en route atfm programs with the difference that it considers flight operator´s submitted en route resources preferences. b. trajectory options set a tos will allow the airlines to manage a flight by telling the atc the route and delay options that the clients are willing to accept. the tos may contain multiple trajectories options, with different routes, altitude or speed per trajectory. the difference between a flight plan and a tos is that the flight plan contains a single request with a defined route, altitude and speed. tos may contain multiple trajectory options, with each one of the options, containing routes, altitudes or speeds [19]. in the current air traffic control system (atcs) the pilot determines through a flight plan the flight’s objective (destination airport) and how to reach it, deciding which route is best, the proposed altitude, the cruising airspeed, the time of departure, climb and descent profiles. to control an airplane while flying, the pilot can be qustioned by the air traffic controller if the parameters requested in the flight plan form are maintained or can determine the aircraft’s flight profile by interpreting the flight track, azimuth and altitude information displayed on the radar scope [11]. in the current atc configuration, the system aims to satisfy each pilot’s request for a specific route or altitude. it may be necessary to apply procedural restrictions to ensure positive aircraft separation. the constant use of air space restrictions results in increased fuel use, increased flight times, loss of flexibility, and, occasionally, reduced traffic flow. in the other hand, great care must also be taken to not overload the air controller. the routine imposition of procedural restrictions reduces the controller’s workload, and consequently decreases the potential loss of separation between aircrafts and decreases the number of planes flying in an area. these procedural restrictions tend to keep an aircraft at inefficient altitudes. since the constrained aspect is the controller’s capacity to coordinate clearances and predict separation conflicts, and not airspace saturation, an automated process would reduce the need for rigid procedural restrictions on system capacity. in this aspect, manual air traffic control procedures need to be improved with computer-based decision support systems for the atc to become more efficient and capable. the aircraft separation is nowadays human dependent, maintained by air traffic controllers who use radar screens to visualize aircraft flight paths, make subjective judgements as future aircraft positions and potential conflicts, and mentally develop alternate flight paths [11]. the operators must express their preferences among different flight options, which must be expressed in terms of a relative trajectory cost (rtc). each option will be evaluated based on customer’s preference expressed by the rtc [19]. the rtc of a flight option is an expression of the number of minutes of delay that would have to be imposed upon the operator’s most preferred trajectory option before some other flight option becomes a desirable alternative. upon submitting a tos, the ctop and cacr algorithms assign routes and/or ground delay to flights by attempting to provide the operator a minimum adjusted cost. the minimum adjusted cost is the sum of the delay assigned to a flight plus its rtc, while ensuring that traffic is limited within the program flow constrained area (fca) to a specified capacity [20]. the fundamental principle behind ctop and tos is the four-dimension trajectory. c. four-dimension trajectory four-dimension trajectory (4dt) is the pillar of the new atm, whereby time-based operations progress to trajectorybased operations and in the long term achieve performancebased operations. a 4dt is defined as a precise description of an aircraft path in space and time. waypoints are used to represent specific steps along the path, which is earthreferenced with a proper latitude and longitude [7]. what distinguishes a 4dt is that the path contains altitude description for each waypoint and indications about the time at which the trajectory will be executed. some waypoints in the 4dt path may be associated with controlled time of arrival (cta) or required time of arrival (rta). in a cta, it may be assigned a target time of arrival (tta). the aircraft must meet this tta requirement within a specified time of tolerance. the cta represents a time window for the aircraft to pass through a specific waypoint. it is normally used to regulate traffic flows entering congested en route/arrival/departure airspace. the main idea is to establish a sequence of spatial and temporal windows. this sequence will represent milestones to meet during flight execution [22]. to achieve the desired rta, aircraft’s speed must be adjusted and regulated along the trajectory to arrive at a specific waypoint at a specified time, improving the predictability of the aircraft-flying path. the problem is that the time of arrival over a fixed point is not a function of aircraft´s airspeed alone, but it depends upon the winds and temperature that the aircraft will encounter in its route [23]. in europe, in the sesar program, the 4dt is often called reference business trajectory (rbt). the term reference is used because once a trajectory is chosen, it will become the reference trajectory which the airspace user agrees to fly and all the service providers agree to facilitate with their respective services. this name difference is basically caused by the european consortium which wants a more collaborative environment, where trajectories are agreed between all the atm stakeholders, for example atc, airports, airlines, military and general aviation. this 4dt will be executed gateto-gate by the aircraft [7]. sesar’s and nextgen’s core concept is to structure atm around aircraft tbo. to achieve this milestone, it is necessary for the aircraft to achieve the 4dt with accuracy/reliability, to accurately and fast pass information via data link, huge improvements in surveillance capabilities are demanded as well as automation and decision support tool capabilities and huge improvements in computer/equipment processing power and speed [9]. the 4d concept is consistent within icao aviation system block upgrade (asbu) and with icao global air navigation plan and global air traffic management operational concept. some authors divide 4dt in two phases: initial 4dt (i4dt) and full 4dt (4dt). the objective of an i4dt is to optimize the arrival phase of a flight at an airport. engineering, technology & applied science research vol. 9, no. 3, 2019, 4154-4158 4157 www.etasr.com pamplona & alves: mitigating air delay: an analysis of the collaborative trajectory options program to achieve this goal, the airborne and ground trajectories must be synchronized around a common unique reference designated by a 2d point or metering fix (mf) and a time constraint. the trajectory negotiation process begins when the aircraft is about 200nm or 40 minutes from its destination. the negotiation is made via a data link between the atc and the aircraft and includes the standard terminal arrival route (star) and approach procedures applicable to the metering fix. the final 4dt is a lateral route with altitude, speed and time constraints over waypoints in the trajectory [24]. for the implementation of the i4dt function onboard, the following avionics systems are necessary: (a) cockpit display systems: it must display relevant data related to the engagement and monitoring of the 4dt, (b) flight management system: the onboard computed prediction and the system performance requirements are consistent, (c) communication system: must be able to manage the ads-contract and the controller-pilot data link communication (cpdlc) applications. an information management platform is necessary to allow this entire collaborative environment. the system wide information management (swim) platform will provide the infrastructure and services necessary to deliver network-enabled information access to a multitude of atm system users. the system must integrate with a variety of legacy sub-system over many years. swin is described as a framework enabling authorized applications and services to reliably and securely share information. swin will allow the necessary trajectory functions exchange functions. this will permit a system coordinated 4dt plans [23]. v. future scope figure 1 shows the most important metrics for result comparison of the 4dts in the key performance areas. fig. 1. metrics for 4dt comparison to achieve tbo environment, the following technologies are considered necessary: (a) advanced flight management system (fms) capabilities: 4dt can only exist with accurate (cta) capabilities. the key factors that impact system accuracy are wind and temperature data. (b) data communication: the voice communication channel between atc and cockpit will not be sufficient to handle the amount of traffic. it will be necessary to introduce data communication that will decrease the controller’s workload. one of the key aspects is the balance between the new airspace capacity and the controller task load [7]. atm system depends critically on the rate that controllers can process aircraft through airspace sectors [9]. (c) ads-b: this technology will replace the radar as surveillance instrument. (d) air traffic control decision support tools: there is a necessity to implement decision support tools (dst) for air traffic controllers. dst will be necessary to provide air traffic controllers with acceptable levels of workload. dst will have to handle the trajectories predicted for the system, and will allow to share and negotiate 4dt, and keep the traffic separated. they will be able to have the capability of conflict detection and resolution. the ctop, which started on march 2014, is a new concept for traffic flow management (tfm). however, some characteristics could be brought to brazil to be implemented, as a future program. the application of preferential routes to ifr has the objective of optimizing the airspace’s use and allowing the better planning of flights. also, it intends to reach better use of aircraft’s rnav navigation systems to keep air traffic flow and its high safety standards. these preferential routes could be used as initial routes in the tos since they are the most advantageous for air traffic service (ats) provider and airline companies. since these routes represent the optimized routes, they represent for airline companies the fastest routes representing lesser cost, and for ats provider represent that flights will follow routes which are contained in sectors which could absorb the increase in traffic flow. another important step towards the ctop implementation would be the observation of airspace’s characteristics, such as certain regions which present degraded weather conditions. one possible application is at the rio de janeiro and sao paulo air terminals, as shown in figure 2. this is the region with the largest aircraft movement in brazil. due to its geographical proximity and air movement growth trend, it is estimated that in the coming decades, there will be an increase in flight delay. fig. 2. possible implementation in brazil this could be done through the assessment of meteorological maps and through the experience of air traffic controllers and other workers in the sector. this analysis would allow identifying the most common constrained areas in the brazilian airspace and it would be an initial step to create the alternative routes to be part of the tos. then, the use of fasttime simulation could allow identifying the cost of each engineering, technology & applied science research vol. 9, no. 3, 2019, 4154-4158 4158 www.etasr.com pamplona & alves: mitigating air delay: an analysis of the collaborative trajectory options program trajectory relative to one another. cost parameters such as travelling time and fuel burn could be evaluated and they would compound the relative cost for each trajectory. validating the trajectories with all stakeholders is an important step to ensure that tos satisfies their needs. vi. conclusion in 15 years, the total commercial fleet is expected to double and some cities are expected to concentrate air demand with long-hauls and regional traffic creating global hubs. delay is one of the consequences of this flight concentration and due to capacity constraints there is a growing necessity for changes in the air traffic system to accommodate the increased traffic demand. air traffic flow management aims to balance traffic demand with airspace. the purpose of atfm is to balance air traffic demand with airspace and/or airport capacity to ensure the most efficient use of the airspace system. a fundamental change will be from clearance-based atc to trajectory-based atc operations and the implementation of the ctop. ctop aims to improve air traffic management considering national airspace system users business goals, particularities faced by each flight, and airspace restrictions, making this process more flexible and financially stable. tbo will be a fundamental pillar in this new operational scenario and will permit more and extreme use of accessible airspace. with its increasing demand for air transportation, brazil, especially rio de janeiro and sao paulo region, is a serious candidate for the implementation of such technologies. this district is the one with the biggest airplane deployment in brazil. because of its land closeness and air deployment pattern, it is assessed that in the coming decades, there will be an expansion in flight delay. besides air saturation, the full operational implementation of new technologies is also necessary. research is undergoing to embed all the needed capabilities in sesar and nextgen operational environment. references [1] g. burghouwt, r. lieshout, t. boonekamp, v. van spijker, economic benefits of european aairspace modernization, seo amsterdam economics, 2016 [2] airbus, global market forecast 2014-2034, 2015 [3] boeing, current market outlook 2015-2034, 2015 [4] v. bamberger, m. blondel, mega-aviation cities’ project, arthour d. little, 2013 [5] brazilian national civil aviation agency (anac), air transport yearbook, 2014 [6] european organisation for the safety of air navigation (eurocontrol), 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a. hopkins, “enabling a modernized nas atm infrastructure in support of trajectory based operations”, 2012 integrated communications, navigation and surveillance conference, herndon, usa, april, 24-26, 2012 [21] b. vaaben, j. larsen, “mitigation of airspace congestion impact on airline networks”, journal of air transport management, vol. 47, pp. 54-65, 2015 [22] p. brooker, “a 4d atm trajectory concept integrating gnss and fms?”, the journal of navigation, vol. 67, pp. 617-631, 2014 [23] j. klooster, k. wichman, o. bleeker, “4d trajectory and time-of-arrival control to enable continuous descent arrivals”, aiaa guidance, navigation and control conference and exhibit, honolulu, usa, august 18-21, 2008 [24] l. h. mutuel, p. neri, e. paricaud, “initial 4d trajectory management concept evaluation”, tenth usa/europe air traffic management research and development seminar, chicago, usa, june 10-13, 2013 microsoft word reffas-ed-r2.doc etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 452-460 452 www.etasr.com reffas et al.: analysis of void growth and coalescence in porous polymer materials… analysis of void growth and coalescence in porous polymer materials coalescence in polymer materials sid ahmed reffas djillali liabes university of sidi bel abbes, algeria reffas_ahmed@yahoo.fr mohamed elmeguenni djillali liabes university of sidi bel abbes, algeria elmeguennimohamed@yahoo.fr mohamed benguediab djillali liabes university of sidi bel abbes, algeria benguediab_m@yahoo.fr abstract— the use of polymeric materials in engineering applications is growing more and more all over the world. this issue requests new methodologies of analysis in order to assess the material’s capability to withstand complex loads. the use of polyacetal in engineering applications has increased rapidly in the last decade. in order to evaluate the behavior, the damage and coalescence of this type of polymer, a numerical method based on damage which occurs following several stages (nucleation of cavities, their growth and coalescence in more advanced stages of deformation) is proposed in this work. a particular attention is given on the stress-strain and the volumetric strain evolution under different triaxiality and for three initial void shapes. its application to polyacetal allows approving this approach for technical polymers. finally, this method allow us to compare the obtained results of basic calculations at different triaxiality and to discuss their possible influence on the initial size and the geometrical shape of the porosity on the material failure. keywordsvoid growth; coalescence; representative elementary volume( rve); ductile; polyoxymethylene (pom); acetal i. introduction in the plastics industry, technical polymers are widely used in engineering components which may experience complex mechanical loadings. the understanding of their intrinsic mechanical behavior to evaluate the mechanisms of damage and coalescence, is of prime importance in order to make better choices in the design of all components. over recent years, considerable attention has been focused on the analysis of plastic deformation of the ductile materials and solid polymers. the deformation processes involved in the plastic deformation of the ductile materials have been widely investigated by several authors [1-19], however, most studies conducted on solid polymers are based on the same criteria. phenomenological laws have been proposed by some researchers [20-25] and other studies have been based only on the mechanical behavior of polymers in large scale deformation [26-36]. research efforts have been devoted to understanding the mechanisms of voids growth and coalescence and to developing micro-mechanical models for better describing the ductile fracture of polymers. probably the best-known expansion plasticity model is the one introduced by gurson [20], later modified by tvergaard and needleman [37-39]. the gurson model was derived based on the assumption that the deformation mode of the matrix material surrounding a void is homogenous. it can therefore predict the material softening behavior due to the nucleation and growth of voids, but has no intrinsic ability to predict the shift of a homogenous deformation mode to a localized mode by void coalescence. for our work, the representative elementary volume (rve) method has been chosen, where the stress depends on the deformation, the strain rate and the stress triaxiality effect. this law has been used successful to characterize the behavior of a great number of polymers with an empirical criterion, like the critical void volume fraction. in this study, a numerical simulation on the basis of the model of an elementary cell is presented. firstly, the unit cell model which is used to predict the response of a material consisting of a periodic assembly of rve is briefly described. secondly, a method developed for the calculation of cells while maintaining a constant triaxiality during the loading is described. this method allows us to compare results of basic calculations for all triaxiality used in this study and to summarize the effects of the various geometrical parameters on the void coalescence in the acetal material (polyoxymethylene or pom). finally, the relevant features which should be taken into account in the application of an accurate constitutive rve model are discussed with a particular attention paid on volumetric strain, damage and their evolutions for all triaxiality. ii. material and numerical procedure the void matrix material is characterized by a model type of material (pom). the yield stress of the virgin matrix material σ0 is set to be 55 mpa. the elastic properties of the model material are taken as e=2900 mpa and ν=0.4. the results obtained using the standard tensile tests are presented in figure 1. the objective of these tests is to demonstrate the strain-rate effect on the response and fracture under large deformation of the pom material. tests were conducted on an etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 452-460 453 www.etasr.com reffas et al.: analysis of void growth and coalescence in porous polymer materials… instron machine. an optical measurement system was used to control the strain-rate and measure the local strain in the specimen section. the mechanical tests were achieved at thre strain rates of 10 -1 , 10 -2 and 10 -3 at room temperature (23 °c). the pom material exhibits an influence of strain rate on the nonlinear behavior. in order to observe this effect, and to quantify it, an overview of the strain-rate effect on the true stress-strain curves is firstly analyzed. figure 1 indicates that the response of this material is similar to other polymers seen in the literature on the viscoelastic evolution. however, the overall response looks like ductile materials. in this response, the curve shows a proportional limit followed by a maximum at which necking takes place. it is common to term this maximum as the yield stress in polymer materials. fig. 1. experimental true stress – strain curves during pom at 23°c (10-1 s-1; 10-2 s-2 and 10-3 s-3). after experimental testing, results show that the behavior of the pom has the same evolution with ductile materials. so, for a first approach, a law already used for metals is applied. the objective is to verify the relevance of this law to this type of polymer. in the present work, the rate-independent power law strain hardening material is applied. the flow stress of the virgin matrix material is described as: 0 0 (1)1 n p f ε σ σ ε           = + where σf is the flow stress, εp the equivalent plastic strain, σ0 the yield stress, ε0= σ0 /e the yield strain, and n the plastic strain hardening exponent. three moderate hardening exponents n have been used to verify a good relationship and representation with the experimental curve (n = 0.01, 0.05 and 0.08). in the idea of good representation, two pre-strain cases have been considered (1.5% and 2.5%). the pre-strain here means the permanent strain after unloading. pre-strain induces strain hardening and residual stress in the void model as well as void growth and void shape changes. in order to separate the strain hardening effect from the one due to void shape changes, ellipsoidal, and spherical voids with a void volume faction equivalent to the one at the end of pre-strain history and a homogenous pre-strained matrix material have been analyzed. figure 2 compares the virgin material with the three moderate hardening exponents in (a) and the two homogenous pre-strained matrix materials in (b). it should be noted that in this study, n=0.05 and 1.5% of pre-strain have been chosen. the stress-strain curve of the material shown in figure 2 is obtained by trimming the virgin material curve by the specified pre-strain level. the elastic properties of the pre-strained materials are kept identical to the virgin material. 0 20 40 60 80 0 0,1 0,2 0,3 true strain tr u e s tr e s s ( m p a ) experimental curve n=0.01 n=0.05 0.08 0 20 40 60 80 0 0,1 0,2 0,3 true strain tr u e s tr e s s experimental curve prestrain = 0 prestrain = 1.5% prestrain = 2.5% fig. 2. matrix material properties used in the analyses: a) the plastic strain hardening exponent (n); b) the pre-strain variability for the virgin material (a) (b) etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 452-460 454 www.etasr.com reffas et al.: analysis of void growth and coalescence in porous polymer materials… figure 3 shows the quarter unit cell model used in the study. the model has been used previously for various studies on the void coalescence behavior [40-46]. the model is axisymmetric and the stress ratios ρ=σx/σy are kept constant in both the pre-straining analysis and subsequent analyses. the model was analysed in a load-controlled manner and abaqus-riks method has been applied [47]. nodal constraints were applied such that the left and top boundaries remain vertical and horizontal during the analysis. (a) (b) fig.3. a voided unit cell model and the region analyzed numerically: a) a voided unit cell model and; b) one quarter of the unit cell model. for the axisymmetric problem considered the stress triaxiality can be calculated from the stress ratio α: ( 2) 1 2 3(1 ) h eq σ αβ σ α += = − where σh is the hydrostatic stress and σeq the von mises equivalent stress. the initial radius and height of the model are denoted as lx0, ly0, ry0 and rz0 and represent the initial radii of the void. the results are based mainly on the case with an initial void volume fraction of 1%. voids with different initial shapes (spherical, prolate, and oblate) but same initial void volume fraction are also considered (figure 4). the initial and current void aspect ratios are defined as: 0 0 0 ( 3 ) z y y z r s r r s r          = = (a) (b) (c) fig. 4. three initial void shapes considered in the study: a) spherical void with s = 1; b) prolate void with s = 4; c) oblate void with s = 0.25. the microscopic strain and cauchy stress tensors inside the matrix are denoted by small letters ε and σ, whereas the macroscopic strain and stress tensors are denoted by the capital letters ε and σ. the overall deformation of the cell model can be calculated from the normal displacements of the outer faces. because of the symmetry of the problem on hand, the macroscopic total logarithmic strain tensor ε and cauchy stresses tensor σ possess the same principal directions, which are the radial and axial directions. the tensor ε is qualitatively given by: ( ) (4)y y x x z zp ze e e e e e e e= ⊗ + ⊗ + ε ⊗ the macroscopic asymmetric radial (e1) and axial (e2) deformations are defined by the following expressions: 1 1 0 2 2 0 (5) ln 1 ln 1 a y a z u e l u e l                           = + = + for the purpose of specifying the overall plastic deformation of the cell model, we choose the effective strain ee defined by: 2 1 ( 6 ) 2 3e e e e= − as an independent variable for presenting most results. the macroscopic stress tensor σ is qualitatively given by: ( ) (7)y y x x z zp ze e e e e eς = σ ⊗ + ⊗ +σ ⊗ with the remote true principal stresses σy in both y and x directions, and σz in z-one. they are calculated at any instant as the average reaction forces at the cell faces per momentary areas through. 0 2 0 (8) 1 2 z y ly y z lz l y z y l z zy t dz l yt dy l                    = = σ = σ = ∫ ∫ etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 452-460 455 www.etasr.com reffas et al.: analysis of void growth and coalescence in porous polymer materials… where t is the stress vector. the corresponding effective von mises stress σe and hydrostatic stress σh result from: (9 ) 1 2 3 ze y z yh           σ = σ − σ σ = σ + σ and the overall stress triaxiality β of the stress state is defined as the ratio: 21 1 1 2 (1 0) 3 3 1 z yh e z y αβ α                      σ σ + σ += = = σ −σ − σ w ith (1 1)y z α σ = σ the stress triaxiality equals 1/3 (or α=0) for simple uniaxial tension and 0 (or α=-0.5) for pure shear. figure 5 shows the evolution of stress ratio α versus the triaxiality β used in the study. -1 -0,7 -0,4 -0,1 0,2 0,5 0,8 1,1 0 0,5 1 1,5 2 2,5 3 3,5 triaxiality st re ss r a ti o fig.5. evolution of stress ratio versus the triaxiality. iii. method of analysis in as much as the unit cell is subjected to axisymmetric deformation, the analysis of its evolution is performed using a cylindrical coordinate system with an orthonormal frame denoted by (ex, ey, ez) along y-radial, x-ortho-radial and z-axial axis. in the initial undeformed configuration, the unit cell is a cylinder with diameter 2ly0 and height 2lz0. the voids are assumed to be spheroidal initially with radius ry0 and half length rz0. the void is oblate if ry0 > rz0, and prolate if ry0 < rz0. the particular case of a spherical void with radius ry0 corresponds to the situation for which ry0 = rz0. the void volume fraction f is defined as the ratio of the total void volume to the unit cell volume. the void volume fraction can be calculated in two ways: the first is by numerical integration of the points along the surface of the void volume; a second criterion is by using the approximate formula proposed by koplik and needleman [41]. this relationship has been proposed assuming the matrix plastically incompressible. the initial cell geometry is completely characterized by the void volume fraction, the void aspect ratio and the cell aspect ratio which their initial values, f0, s0 and λ0 are respectively defined by: 2 0 0 0 0 0 2 (12) 3 y z y z r r f l l                 = 0 0 0 (13)z y l l λ = as a consequence of the lattice periodicity, all outer planes of the unit cell have to behave only as rigid moveable planes in coordinating directions during the process of loading. the faces at y = lyo and z = lzo will have a uniform normal displacements and their mutual orientations will be maintained. these requirements impose the unit cell to remain a cylinder during the finite strain deformation process. this feature is attained by assessing the deformation via an imposed homogeneous elongation (uz a ) of the corner a in the axial direction and monitoring its homogeneous radial displacement (uy a ) by multipoint constraints. the cylinder is thus characterized in an arbitrary state by: 0 0 (14) a y yy a z zz l l u l l u      = + = + because of these constraints, only one quarter geometry of the unit cell model (0≤ y ≤ lyo; 0≤ z ≤ lzo) needs to be analyzed and is drawn in figure 3-b. to satisfy the axisymmetric conditions and to ensure periodicity of the cell arrangements, the boundary conditions of the quadrant dealing with displacements read, uy = 0 along the axis, uz = 0 on the bottom and uy = uy a on the lateral surface, uz = uz a on the top. the actual void volume fraction f is calculated whether using numerical integration from the updated coordinates of the nodes at the void–matrix interface during the deformation of the unit cell, or using the following approximate analytic formula proposed in (8). ( )0 01 1 (15) ev v f f v v ∆= − − − ( ) ( )0 3 1 1 (16)with e h v f v e ν−∆ = − σ where the ratio of the current volume v of the unit cell to its initial volume v0 is given by: ( ) 2 0 0 2 0 0 0 (17) a a y zy z y z l u l u v v l l       + + = etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 452-460 456 www.etasr.com reffas et al.: analysis of void growth and coalescence in porous polymer materials… ∆v e is an approximate correction term for the elastic expansion change in cell volume due to the imposed hydrostatic stress σh. it was checked that the two methods yield very close results within the range of our calculations. it should be mentioned however, that (16) does not hold in the case of porous matrix. on the other hand, it should be kept in mind that this approximation will be used in the transient analysis of the cell model to provide the starting loading for which, as will be seen later, it turns out that the stress triaxiality drops down quickly and then have to be corrected. iv. numerical results and discussion in order to evaluate the proposed transient analysis for axisymmetric cell model simulations, a series of calculations have been conducted. figure 6 shows the mesoscopic radial strain versus equivalent strain curves for the case with an initial void volume fraction of 1% and for all triaxiality proposed in this study from 0.33 to 3. a global view of these results indicates that there is rather a reasonably good agreement between the results. however, it is seen from these curves that a difference exists in the nature of the response especially in the coalescence. in general, the cell model elongates in the vertical direction and contracts in the radial direction. during the plastic deformation and void growth, an approximate linear relation can be observed. this linear relation indicates a homogenous deformed state. when the deformation reaches a critical state a sudden shift from the relatively homogenous deformation state to a uniaxial straining state can be seen. this shift depicts the onset of void coalescence. computations were carried out for all cell models, whereby the extreme values of stress triaxialty from 0.33 to 3 were investigated. the most interesting outcome of the cell models is the overall mesoscopic hardening and failure behavior. this relation is expressed in term of the invariants of the equivalent stress versus equivalent strain. figure 7(a) displays variations of the equivalent stress as a function of the equivalent strain. the onset of void coalescence corresponds to a marked change of the slope of the curves. the transition is most sharp at low stress triaxiality, where the triaxiality effect is marked. it has all also been shown that after the onset of void coalescence the falling equivalent stress– strain curves is nearly linear, except for the high triaxiality (2 and 3). figure 7(b) exhibits the variations of the volumetric strain as a function of the equivalent strain. void coalescence induces an increase in the void growth rate and a transition in the void shape evolution. after the onset of void coalescence, the volumetric strain growth is significantly larger. the end of the coalescence process in a polymer material usually consists of the failure of the remaining ligament by microcleavage, crystallographic shearing, or with the help of the second population of smaller voids, rather than volumetric void growth until impingement. -0,6 -0,5 -0,4 -0,3 -0,2 -0,1 0 0 0,2 0,4 0,6 0,8 1 1,2 1,4 equivalent strain ra d ia l s tr a in β = 0.33 β = 0.6 β = 1 β = 2 β = 3 f 0=1% fig. 6. radial strain versus equivalent strain for different stress triaxiality. f 0 =1% 0 20 40 60 80 100 0 0,2 0,4 0,6 0,8 1 equivalente strain e q u iv a le n t s tr e s s ( m p a ) β = 0.33 β = 0.6 β = 1 β = 2 β = 3 0 0,1 0,2 0,3 0,4 0 0,2 0,4 0,6 0,8 1 equivalente strain v o lu m e tr ic s tr a in β = 0.33 β = 0.6 β = 1 β = 2 β = 3 f 0=1% fig.7. cell model results for spherical void in different stress triaxiality: a) equivalent stress versus equivalent strain; b) volumetric strain versus equivalent strain (a) (b) etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 452-460 457 www.etasr.com reffas et al.: analysis of void growth and coalescence in porous polymer materials… in the previous results we note a reduction of the void diameter which depends on the triaxiality occurred in the course of loading. to study the influence of this additional condition on the mechanical behavior of the cell, we have chosen three cases of void volume fraction (1%, 5% and 10%) with different initial shapes (spherical, prolate, and oblate) (figure 4). computations were carried out for all cell models, whereby the extreme values of stress triaxialty from 0.33 to 3 is investigated. figure 8 shows the evolution of the mesoscopic equivalent stress versus equivalent strain curves and summarizes the effects of the various geometrical parameters on void coalescence; the three cases of void volume fraction (1%, 5% and 10%) with different initial shapes (spherical, prolate, and oblate) for all triaxiality. here the equivalent stress and strain are chosen, because both are relevant coalescence parameters. all the cells were loaded with a prescribed triaxiality β=0.33 to 3. several comments can be made concerning the void coalescence. the onset of void coalescence depends strongly on the relative void spacing as can be discerned by comparing cells (1% spherical with β=0.33) and (1% spherical with β=3), which have an identical void shapes and initial porosity. the effect can be seen in another way by comparing cells (5% or 10% prolate) and (5% or 10% oblate) for all triaxiality, which has been chosen with roughly similar void spacing. the cells have not a similar coalescence strain for the same initial void volume fractions and different shapes. the conclusion to be drawn is that heterogeneity in the void distribution inherited from prior working or processing plays a major role in the coalescence of the material. void spacing is not the only influential parameter as can be seen when comparing figure 9-a and figure 9-e (spherical; 5% and 10% prolate or oblate). in these comparisons, a higher level of triaxiality builds up in the ligament of cell and accelerating localization of the coalescence. for a similar cell aspect ratio, cells (10% prolate) and (10% oblate) also have significant differences between the slopes after the onset of void coalescence, due to the differing initial porosity and void shape. the analysis of the stress and strain fields inside several void cells has shown that voids start interacting with each other well before the onset of void coalescence. figure 9 compares the critical stress and strain obtained at the moment of the coalescence as a function of the triaxiality for the different geometrical parameters on void coalescence in all cases. in general, stress triaxiality has a negative effect on the coalescence stress and strain. it is interesting to observe that both the void shapes have a strong influence on the reduction of the coalescence stress and strain. v. conclusion in order to summarize the observed results in this paper, and to confirm predictions of the rve model, we have noted some conclusions. when the peak equivalent stress strain appears at the outer boundary; the void coalescence starts. the microscopic coalescence criterion is practical and has been applied to determine the coalescence. however, this observation further verifies the plastic limit load theory for void coalescence, and the void coalescence occurs when a plastic limit load state of the void cell model has been reached. the void coalescence behavior effect is strongly dependent on the stress triaxiality and the initial void shape. for prolate and oblate voids smaller than 5%, the critical stress and the strain coalescence effect can be neglected. at high stress triaxiality cases the reduction in coalescence stress – strain due to the initial voids higher than 5% can be very significant. for an initially spherical void with β = 3, the reduction in coalescence strain can be as large as 70%. in comparison, the stress triaxiality effect of the coalescence strain of oblate voids is the largest. the absolute reduction of coalescence strain seems to be dependent of stress triaxiality. finally, it can be noted that the predictions show promising results, and these calculations show that the constitutive equations for damage evolution are required, and the determination of onset and continuation of a triaxiality is based on the initial porosity shape. etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 452-460 458 www.etasr.com reffas et al.: analysis of void growth and coalescence in porous polymer materials… β = 0.33 0 20 40 60 80 100 0 0,2 0,4 0,6 0,8 1 equivalente strain e q u iv a le n te s tr e s s ( m p a ) f0 = 1% spherical f0 = 5% prolate f0 = 10% prolate f0 = 5% oblate f0 = 10% oblate β = 0.6 0 20 40 60 80 100 0 0,2 0,4 0,6 0,8 equivalent strain e q u iv a le n t s tr e s s ( m p a ) f0 = 1% spherical f0 = 5% prolate f0 = 10% prolate f0 = 5% oblate f0 = 10% oblate β = 1 0 20 40 60 80 0 0,2 0,4 0,6 equivalent strain e q u iv a le n t s tr e s s ( m p a ) f0 = 1% spherical f0 = 5% prolate f0 = 10% prolate f0 = 5% oblate f0 = 10% oblate β = 2 0 20 40 60 0 0,05 0,1 0,15 0,2 0,25 equivalente strain e q u iv a le n te s tr e s s ( m p a ) f0 = 1% spherical f0 = 5% prolate f0 = 10% prolate f0 = 5% oblate f0 = 10% oblate β = 3 0 10 20 30 40 50 0 0,05 0,1 0,15 0,2 equivalente strain e q u iv a le n te s tr e s s ( m p a ) f0 = 1% spherical f0 = 5% prolatel f0 = 10% prolatel f0 = 5% oblate f0 = 10 oblate fig. 8. cell model results for three initial void shapes (spherical; prolate and oblate): (a) β =0.33; (b) β =0.6; (c) β =1; (d) β =2; (e) β =3. (a) (b) (c) (d) (e) etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 452-460 459 www.etasr.com reffas et al.: analysis of void growth and coalescence in porous polymer materials… 0 20 40 60 80 100 0 1 2 3 triaxiality c ri ti c a l e q -s tr e s s ( m p a ) f0 = 1% spherical f0 = 5%prolatel f0 = 10% prolatel f0 = 5% oblate f0 = 10% oblate 0 0,2 0,4 0,6 0,8 1 0 1 2 3 triaxiality c ri ti c a l e q -s tr a in f0 = 1% spherical f0 = 5% prolatel f0 = 10% prolatel f0 = 5% oblate f0 = 10% oblate fig. 9. cell model results: a) critical stress versus triaxiality; b) critical strain versus triaxiality. references [1] a. a. benzerga, j. besson, a. pineau, “coalescence-controlled anisotropic ductile fracture”, journal of engineering materials and technology, vol. 121, no. 2, pp. 221-229, 1999 [2] a. a. benzerga, “micromechanics of coalescence in ductile fracture”, journal of the mechanics and physics of solids, vol. 50, no. 6, pp. 1331-1362, 2002 [3] a. a. benzerga, j. 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international journal of plasticity, vol. 20, no. 2, pp. 255-268, 2004 [47] w. brocks, d. z. sun, a. hönig, "verification of the transferability of micromechanical parameters by cell model calculations with viscoplastic materials", vol. 11, no. 8, pp. 971-989, 1995 microsoft word etasr_v11_n4_pp7405-7410 engineering, technology & applied science research vol. 11, no. 4, 2021, 7405-7410 7405 www.etasr.com shamsan & almuhanna: intersystem interference study between medical capsule camera endoscopy … intersystem interference study between medical capsule camera endoscopy and other systems in co-channel and adjacent bands zaid ahmed shamsan electrical engineering department college of engineering imam mohammad ibn saud islamic university (imsiu) riyadh, saudi arabia shamsan@ieee.org khalid almuhanna electrical engineering department college of engineering imam mohammad ibn saud islamic university (imsiu) riyadh, saudi arabia kalmuhanna@imamu.edu.sa abstract—the ultra-high frequency (uhf) band occupies a very vital region in the spectrum and is becoming very congested because many applications use it. the capsule camera (capcam), an ultra-low power wireless device, is a short range device (srd) application that utilizes the uhf spectrum for medical endoscopy and it is designed to operate at the 430-440mhz frequency band range. this study will focus on the interference between the capcam and other systems operating in the frequency of 435mhz and adjacent bands. other systems that can operate in this band include non-specific srd and radiolocation services such as airborne radar and ground radar stations. the minimum coupling loss (mcl) method is implemented in this study. the findings showed that restricted distances between the capcam and other services must be considered when the capcam is in use. this should be done to avoid harmful interference from the capcam especially in the case of radiolocation services. keywords-capcam; airborne radar; ground radar; interference; mcl method i. introduction wireless medical capsule endoscopy (wmce) is a new generation of medical short range device (srd) applications, which are characterized by operating in ultra-low power and short distance applications. the capsule camera (capcam) is a main component of the ultra-low power wmce application. the capcam endoscopy is a practice recommended by doctors that uses a miniature wireless camera to take images of a patient’s digestive tract as it passes through it. the endoscopy camera is placed within a small capsule (approximately the same size as a vitamin pill) that the patient swallows. the camera takes pictures as the capsule passes through the patient's digestive system and transfers them wirelessly to a recorder carried by the patient [1]. the capcam is a medical diagnostic tool designed to operate in the uhf range including the frequency band of 430-440mhz [2]. this frequency band is occupied by several services such as radiolocation services, amateur radio services, non-specific srds (nsrds), land mobile services, and earth exploration-satellite services. therefore, the possibility of interference occurring between these systems and the capcam service is something that needs to be investigated. as a result of the interference, system performance deterioration may occur. depending on the properties of various wmce systems and the method of treatment, many contraindications are set by manufacturers. such a contraindication is the electromagnetic radiation represented by the interference of the capcam with other wireless devices (or intersystem interference). based on previous studies and the manufacturers’ recommendations, these contraindications include the effect on the cardiac pacemakers or other implanted electro-medical devices, creating strong electromagnetic fields on devices such as magnetic resonance imaging (mri), etc. [3, 4]. more broadly, in this paper, the intersystem interference between the capcam service and other systems is controlled in a primary-secondary operating basis, where the capcam service is a secondary service and the other systems are considered the primary services [5]. comprehensively, when the srds (as a secondary service) operate in shared bands, they are not permitted to cause harmful interference to radio services (primary). so, in general, srd cannot claim protection from interference caused by radio communication services as defined by the international telecommunication union radio regulations (itu-rr) [6]. further, this means that the capcam must not cause interference to the other primary services. therefore, this paper will study the effect of the capcam service on other services. both co-channel interference and adjacent channel interference will be examined in line of sight (los) and nonlos (nlos) environments. ii. intersystem interference scenarios this section provides a summary of the proposed interference scenario between the capcam and other systems that share the same frequency band of 430-440mhz. the services/systems involved in this study are described in detail. corresponding author: zaid ahmed shamsan engineering, technology & applied science research vol. 11, no. 4, 2021, 7405-7410 7406 www.etasr.com shamsan & almuhanna: intersystem interference study between medical capsule camera endoscopy … a. interference scenario the interference scenario is shown in figure 1. the capcam service is assumed to be operating in the 430440mhz frequency band and shares it with other services (radiolocation and nsrd) according to the itu-rr's article 5 [5] and the european common allocations (eca) [7]. the frequency allocation for the 430-440mhz band regarding radiolocations services (airborne and ground radars) and srd are shown in table i. it can be realized that the proposed use of the capcam application operating in the frequency band of 430-440mhz would lead to affecting both radiolocation and nsrd systems. this study will investigate this impact in order to coordinate the use of the capcam with radiolocation and nsrd systems. table i. the itu-r spectrum allocation for the capcam, radiolocation, and nsrd services in the 430-440mhz band itu rr allocation frequency band (mhz) radiolocation 430-433.05 radiolocation, nsrd 433.05-434.79 radiolocation 434.79-440 fig. 1. the interference scenario of capcam with other services. fig. 2. the scenario of capcam and dr as a wmce application. it is assumed that the capcam service (the interferer) is utilized inside a medical building such as a hospital and causes interference to three discrete outdoor wireless systems (airborne radar, ground radar, and nsrd), which can be termed as interfered services (figure 1). in the following subsections, a brief description of these systems, as well as the capcam service are presented. b. the capcam service it is a relatively new application of medical srds that can perform medical tests of patients with specific digestive conditions without causing bleeding or sedation hazard involved by traditional endoscopy [2]. the crucial part of the new application is a disposable tiny optical imaging camera imbedded in a capsule. the capcam is given to the patient to swallow and while it moves through the patient’s digestive tract it sends images to a receiver (data recorder-dr) outside the patient’s body as shown in figure 2. c. non-specific srds nsrds are devices for wireless telegraphy including telemetry, tele-command, alarms, and data transmission. telemetry services use radio communication for automatically indicating or recording measurements at a distance from the measuring instrument. tele-command services use radio communication for the transmission of signals to create, modify or dismiss functions of equipment at a distance; and the alarms are devices used for alarm systems, including social, security, and safety alarms [8]. d. radiolocation radiolocation services are defined as radio-determination services for the purpose of position determination. radiodetermination is defined as the determination of the position, velocity, and/or other characteristics of an object by the propagation properties of radio waves [9, 10]. the airborne radar [11], is a radar on a plane used to detect objects moving at very low speeds whereas ground radar is used for fixed, mobile, or transportable operations. iii. interference calculation methodoolgy the method proposed to calculate the intersystem interference from the capcam and other systems is the standard minimum coupling loss (mcl) which consists of attaining the critical minimum propagation losses required to avoid interference. once the total losses are obtained, it is straightforward to determine a matching minimum separation distance depending on a given propagation model. the propagation model used for the assessment of the separation distance is the free space model as well as indoor penetration losses due to the natural work of the capcam from the indoor environment and emitting power into the outdoor environment. the free space wave propagation model is given by [12]: � � ������ �� � � � (1) where � denotes the received interference power at the interfered system (radiolocation or nsrd systems), �� denotes the transmit power from the interferer system (the capcam service), �� and �� are the gain of the transmitter and receiver antenna respectively, � � denotes the correction factor of bandwidth between the capcam and the interfered system, and ���� is the channel propagation loss due to the free space (outdoor) environment and the indoor penetration loss. the expression in (1) can be represented using the decibel scale as follows [13]: � � �� � ����� � � � � ���� (2) where ���� is the free space loss due to the free space environment (��) and the indoor penetration loss ��. the �� engineering, technology & applied science research vol. 11, no. 4, 2021, 7405-7410 7407 www.etasr.com shamsan & almuhanna: intersystem interference study between medical capsule camera endoscopy … loss mainly depends on the wavelength of the traveling signal, �, either in los or nlos environments, and the distance between the transmitter and receiver � . �� is based on the material type used to construct the hospital building. therefore, the ���� factor can be defined for the los and nlos as follows: ���� � �� � �� (3) when the signal travels in a los outdoor environment, the loss ���� is given by (4) for true urban propagation prediction [14, 15]: ����(���) � 32.45 � 20log(&�) � �� (4) if the signal travels in an nlos outdoor environment, the loss ���� is given by: ����('���) � 32.45 � 20log(&) � 35log(�) � �� (5) where the frequency & is in mhz and the distance � is in km. in this study, both interference situations (co-channel and adjacent channel interferences) will be considered in both propagation environments. iv. system parameters the main parameters for the considered systems for the capcam, nsrd, airborne radar, and ground radar are shown in tables ii and iii. it is worth mentioning that the radiations from the capcam may not be highly uniform throughout the whole channel bandwidth except within the co-channel frequency (at around 10mhz). also, 10db is assumed as the body loss which is applied to distinguish the power levels inside/outside the body. table ii. main parameters of the interferer system (the capcam) value parameters 430-440mhz frequency of operation 10mhz single channel rf bandwidth -30dbm maximum erp of the transmitter 2.15db antenna gain -40dbm erp outside patient's body -50dbm/100khz maximum erp density outside patient's body 8-12h single use of activity cycle 10db building penetration loss table iii. main parameters of interfered systems ground radar airborne radar nsrd parameters 1 1 0.250 channel bandwidth, mhz 38 22 -2.85 rx antenna gain, db -115.9 -114.9 -110 rx interference threshold, dbm �/) � −6 �/) � −6 c/i�8 rx protection criteria, db 8 >9000 3 height above ground level, m v. results and discussion this section of the paper analyzes and discusses the results of the coordination between the capcam and the considered systems that share the frequency band of 430-440mhz. a. the capcam and nsrd systems since the nsrd is set to run in the frequency band 433.05434.79mhz, the operating carrier frequency is assumed as 433.91mhz. the channel propagation will be affected by the penetration loss of 10db as well as the loss in the los and nlos environments. the values of interference levels from the capcam service into the nsrd service versus the separation distances using co-channel frequency are shown in figure 3. this figure illustrates that the minimum distance in the los environment is about 322m whereas it is 27.6m in the nlos dense urban areas. at these distances, minimum power will be detected according to the nsrd receiver sensitivity which is 110dbm/25khz. figure 3 shows that as the distance increases the interference level from the capcam into the nsrd receiver decreases due to the propagation effect for both los and nlos. however, the interference level drastically decreases in nlos compared to the los environment. to allow for proper coordination between the capcam system and the nsrd system the required margin in the co-channel frequency band is depicted in figure 4. it can be seen from figure 4 that as the distance increases, the required margin decreases linearly in the log scale. in figure 4, we can notice that the required margin is 0db at the separation distances of 322m and 27.6m for los and nlos respectively. the reason is that at these distances the received power is equal to the nsrd receiver sensitivity of -110dbm. before reaching the aforementioned distances, the interference power is high and can cause deterioration in nsrd receiver performance. therefore, it is required to keep that distance in consideration regarding the operation of the capcam and nsrds services. fig. 3. the interference from the capcam into the nsrd in the cochannel frequency band. on the other hand, by shifting the capcam carrier frequency by 10mhz the two systems will operate under the adjacent channel band scenario. this is illustrated in figures 5 and 6. in figure 5, the interference level from the capcam service is 102m in los areas, while the distance in nlos dense urban areas is only 15m and lower than that of los environment. these findings are confirmed in figure 6, which shows the power margin in both areas. this shows that the power margin is 0db at the above mentioned distances due to the received power being equivalent to the nsrd receiver sensitivity. from the findings of the operation of the capcam and nsrd services, it can be concluded that the interference in te rf e re n c e ( d b m ) engineering, technology & applied science research vol. 11, no. 4, 2021, 7405-7410 7408 www.etasr.com shamsan & almuhanna: intersystem interference study between medical capsule camera endoscopy … power in nlos is less than in the los environment. this variation in interference power is due to the environment in the nlos blocking the interference power from the capcam from reaching the interfered system receiver in its entire strength. the los environment allows the interference signal power to travel with no obstacles in its path. moreover, the minimum distance required to operate the capcam and nsrd services simultaneously in the same area with no harmful interference using the co-channel frequency band is higher compared to the distance using the adjacent channel. this occurs due to the fact that the emitted power from the capcam service in the case of the adjacent channel frequency band is less than the power emitted in the case of the co-channel band by 10db. thus, the decrease in the interference emission power is transferred into decreasing the distance that enough harmful interference signal can reach the affected receiver of the nsrd. this finding is consistent with the findings of [16]. fig. 4. the required margin for coordination of the capcam and the nsrd in the co-channel frequency band. fig. 5. the interference from the capcam to the nsrd in the adjacent channel frequency band. b. the capcam and airborne radar systems here, the affected service is the airborne radar while the interferer is the capcam service. the airborne radar receiver has an interference threshold of –114.9dbm. figures 7 and 8 illustrate the interference power level with the distance increasing between the two systems in co-channel and adjacent channel frequency bands respectively. both figures show that the distance required in los is higher than that required in nlos areas. in addition, the minimum distance in the cochannel band is higher than that in the adjacent channel band. in the co-channel scenario the distance is 1563m and 67.5m, while in the adjacent channel scenario it is 494.5m and 36m for los and nlos respectively. also, in figures 9 and 10, the power margin is depicted for the same scenarios, in which 0db is the margin at the abovementioned distance. at greater distances, the power margin is negative which means it allows the airborne radar to run with no interference acting on it from the capcam. fig. 6. the required margin for the coordination of the capcam and the nsrd in the adjacent channel frequency band. fig. 7. the interference from the capcam to the airborne radar in the cochannel frequency band. fig. 8. the interference from the capcam to the airborne radar in the adjacent channel frequency band. m a rg in ( d b ) in te rf e re n c e ( d b m ) m a rg in ( d b ) in te rf e re n c e ( d b m ) in te rf e re n c e ( d b m ) engineering, technology & applied science research vol. 11, no. 4, 2021, 7405-7410 7409 www.etasr.com shamsan & almuhanna: intersystem interference study between medical capsule camera endoscopy … c. the capcam and ground radar systems for this scenario, the receiver has an interference threshold that is lower than that of the airborne radar, which is –115.9dbm. the findings shown in figures 11 and 12 present the interference levels with the distance between the capcam and ground radar services. it is found that the minimum distance at which the two systems can operate together with no harmful interference is 1754m and 72m for the co-channel frequency band in the los and nlos environments respectively. the minimum distance decreases using the adjacent channel band are 555m and 39m in the los and nlos environments respectively. moreover, figures 13 and 14 show the required power margin between the received interference from the capcam service and the maximum interference threshold. therefore, at the abovementioned distances, this margin is 0db, and before the ground radar cannot work. for instance, in distances less than 1754m and 555m the ground radar may not operate properly if the capcam service operates at the same time. fig. 9. the required margin for the coordination of the capcam and the airborne radar in the co-channel frequency band. fig. 10. the required margin for the coordination of the capcam and the airborne radar in the adjacent channel frequency band. table iv summarizes the results from the presented scenarios. it shows that the ground radar service is the most affected among other services due to the maximum interference threshold and its higher antenna gain. although, the exceptionally low deployment density of the capcam services and the short time period of single-use of the capcam devices, compared with many other srd applications, distance should be taken into account. another important point in this study is that it assumes that the patient treated by the capcam is separated by only one wall from the considered devices/services. in practical situations there may be many walls or partitions, which can contribute to more propagation loss that may allow the operation of the capcam with other services without interferences. fig. 11. the interference from the capcam to the ground radar in the cochannel frequency band. fig. 12. the interference from the capcam to the ground radar in the adjacent channel frequency band. fig. 13. the required margin for the coordination of the capcam and the ground radar in the co-channel frequency band. m a rg in ( d b ) in te rf e re n c e ( d b m ) in te rf e re n c e ( d b m ) m a rg in ( d b ) engineering, technology & applied science research vol. 11, no. 4, 2021, 7405-7410 7410 www.etasr.com shamsan & almuhanna: intersystem interference study between medical capsule camera endoscopy … fig. 14. the required margin for the coordination of the capcam and the ground radar in the adjacent channel frequency band this paper illustrates new findings on the coordination of operating a capcam system with radiolocation and nsrd services, which are investigated in order to eliminate possible interferences to those services. this study considered the effect of building penetration loss, adjacent channel interference, and long coverage distance which makes this study more technically sound compared to the work in [2]. ultimately, the findings of this paper aim to decrease the required restrictions that should be taken into account for the capcam service to run harmlessly besides other wireless services. table iv. minimum physical separation between the capcam and other systems iin los and nlos environments physical separation (m) environment channel type with ground radar with airborne radar with nsrd 1754 1563 322 los co-channel 72 67.5 27.6 nlos 555 494.5 102 los adjacent channel 39 36 15 nlos vi. conclusion this paper presents a study of the medical capsule camera endoscopy (capcam) and other systems in the 430-440mhz band using the mcl approach. the study covered los and nlos areas using co-channel and adjacent channel frequency bands. it has been found that 1754m is the maximum distance for the three systems as a conservative protection distance in the case of the co-channel frequency band. the minimum distance for the three services is 555m in the adjacent channel scenario within a los environment. in the case of nlos, the physical separation distances decrease dramatically. more studies may be recommended to investigate and analyze the effect of different practical situations with different building construction materials, stories, and designs. acknowledgment the authors would like to thank the deanship of scientific research at imam mohammad ibn saud islamic university (imsiu) for the financial support of the project under the grant no. 18-11-14-001. references [1] d. v. moyer, t. p. smith, j. g. erd, d. a. luebke, and k. l. tuma, "ingestible device with propulsion capabilities," us20200405129a1, dec. 31, 2020. [2] "coexistence of wideband ultra-low power wireless medical capsule endoscopy application operating in the frequency band 430440 mhz," ecc, ecc report 267, 2017. [3] d. bandorski et al., "contraindications for video capsule endoscopy," world journal of gastroenterology, vol. 22, no. 45, pp. 9898–9908, dec. 2016, https://doi.org/10.3748/wjg.v22.i45.9898. [4] s. dubner, y. dubner, h. rubio, and e. goldin, "electromagnetic interference from wireless video-capsule endoscopy on implantable cardioverter-defibrillators," pacing and clinical electrophysiology: pace, vol. 30, no. 4, pp. 472–475, apr. 2007, https://doi.org/10.1111/ j.1540-8159.2007.00695.x. [5] "article 5 frequency allocations," itu radio regulations. https:// life.itu.int/radioclub/rr/art05.htm (accessed jul. 03, 2021). [6] erc recommendation of 1997 on relating to the use of short range devices (srd). erc, 2021. [7] "the european table of frequency allocations and applications in the frequency range 8.3 khz to 3000 ghz (eca table)," erc, erc report 25, 2020. [8] etsi en 305 550 v2.1.0 (2017-10) short range devices (srd); radio equipment to be used in the 40 ghz to 246 ghz frequency range; harmonised standard for access to radio spectrum. etsi, 2017. [9] "assessment of the technical feasibility of introducing very narrow channel spacing in some existing plans, in guard bands and center gaps of fws channel arrangement at 6 ghz and 10 ghz," ecc, ecc report 215, 2014. [10] m. almutiry, "uav tomographic synthetic aperture radar for landmine detection," engineering, technology & applied science research, vol. 10, no. 4, pp. 5933–5939, aug. 2020, https://doi.org/ 10.48084/etasr.3611. [11] g. w. stimson, stimson’s introduction to airborne radar, 3rd ed. edison, nj, usa: scitech publishing, 2014. [12] t. s. rappaport, wireless communications: principles and practice, subsequent edition. upper saddle river, nj, usa: prentice hall, 2001. [13] recommendation itu-r p.530-17: propagation data and prediction methods required for the design of terrestrial line-of-sight systems. geneva, switzerland: itu, 2017. [14] recommendation itu-r p.525-4: calculation of free-space attenuation. geneva, switzerland: itu, 2019. [15] recommendation itu-r p.1411: propagation data and prediction methods for the planning of shortrange outdoor radiocommunication systems and radio local area networks in the frequency range 300 mhz to 100 ghz. geneva, switzerland: itu, 2019. [16] k. kimani and m. njiraine, "cognitive radio spectrum sensing mechanisms in tv white spaces: a survey," engineering, technology & applied science research, vol. 8, no. 6, pp. 3673–3680, dec. 2018, https://doi.org/10.48084/etasr.2442. m a rg in ( d b ) microsoft word 33-3100_s_etasr_v9_n6_pp5047-5055 engineering, technology & applied science research vol. 9, no. 6, 2019, 5047-5055 5047 www.etasr.com eyadeh & al-ta'ani: performance study of wireless systems with switch and stay combining diversity … performance study of wireless systems with switch and stay combining diversity over α-η-µ fading channels ali a. eyadeh communication engineering department yarmouk university irbid, jordan aeyadeh@yu.edu.jo mohammad n. al-ta'ani communication engineering department yarmouk university irbid, jordan mohd.taani89@gmail.com abstract—in this paper, we consider a switch and stay combiner (ssc) diversity scheme operating over α−η−µ fading channel. new and closed-form expressions for the average output snr (asnr), the moment-generating function (mgf), the outage probability (p_out), and the average symbol error rate (aser) for m-ary quadrature amplitude modulation (qam) signaling are derived. the expressions are obtained in terms of the wellknown bivariate fox’s h-function (bfhf). it is worth pointing out that the bfhf and the bivariate meijer’s g-function (bmgf) have recently been used extensively in wireless communications literature to study the system's performance. the evaluated results are plotted for channel parameters of interest, and the effect of fading severity on the combiner performance is studied. moreover, the results are shown to match those previously reported in the literature for other channel models such as η−µ as a special case, which confirms the validity of the obtained expressions. also, insights on the optimal choice of the switching threshold are provided. keywords−switch and stay combiner ssc diversity; α−η−µ fading channel; m-ary qam; average output snr (asnr); moment-generating function (mgf); outage probability (pout) i. introduction there are many distributions that describe properly the statistics of the mobile radio signal. the long-term signal variation is acknowledged to follow the lognormal distribution, whereas the short-term signal variation is described by various other distributions such as hoyt, rayleigh, rice, nakagami-m, and weibull. it is typically accepted that the path strength at any extend is characterized by short-term distributions over a spatial dimension of a few hundred wavelengths, and with the aid of the lognormal distribution over areas with larger dimensions. the α−η−µ distribution is a generic fading distribution used to signify the small-scale variation of the fading signal. channel multipath fading is an important consideration when designing a wireless communication system, therefore fading mitigation techniques are needed. diversity combining is an effective technique used to mitigate fading and improves the performance of wireless systems over a fading channel. there are various types of diversity combining techniques used in practice [1], for example selection combining (sc), equal gain combining (egc), maximal ratio combining (mrc) and switched diversity combining (sdc). two strategies can be used in sdc: switch and stay combining (ssc) which is considered in this paper, and switch and examine combining (sec). in an ssc diversity system, the receiver selects a branch until its signalto-noise ratio (snr) drops below a predetermined threshold. when this happens, the combiner switches to another branch and stays there regardless of whether the snr of the original branch is above or below the predetermined threshold. several works have been conducted on the analysis of ssc scheme over fading channels including [2-14]. in [2-5], the performance of ssc for non-coherent binary frequency shift keying (bfsk) and noncoherent m-ary frequency shift keying (mfsk) over correlated nakagami-m and rician fading channels was studied. in [6], the performance of non-coherent mfsk with selection and switched diversity was analyzed over a hoyt fading channel. the performance of correlated rician fading channels and correlated weibull fading channels with ssc diversity was evaluated in [7] and [8] respectively. the performance of a dual-branch ssc systems over nakagami-m, correlated α–µ, correlated η–µ and correlated generalized-k (kg) fading channels were studied and analyzed in [9-14]. popular fading distributions have been derived assuming a homogeneous diffuse scattering field, resulting from randomly distributed point scatters. the assumption of a homogeneous field is truly an approximation because the surfaces are spatially correlated characterizing a non-linear environment. with the aim at exploring this non-homogeneity, two new fading distributions, κ−µ and η−µ have been discussed in [15, 16], and to discover the non-linearity of the propagation medium, which was also addressed more currently in a new proposed common fading distribution, the α−µ distribution [17]. the α−η−µ distribution is an accepted distribution for a short-time fading model. the probability density function (pdf) of α−η−µ distribution is in the shape of three parameters α, η and µ, which are associated to the nonlinearity of the environment, the scattered wave power ratio between the inphase, and quadrature components of each cluster of multipath corresponding author: ali a. eyadeh engineering, technology & applied science research vol. 9, no. 6, 2019, 5047-5055 5048 www.etasr.com eyadeh & al-ta'ani: performance study of wireless systems with switch and stay combining diversity … and the number of multipath clusters in the environment respectively. the α−η−µ model includes, as special cases, other short-time fading distributions, like rayleigh, nakagami-m, nakagami-q (hoyt), weibull, η–µ and one-side gaussian distribution. by setting α=2, it reduces to η–µ distribution. furthermore, from η–µ fading distribution, nakagami-m model could be obtained in two cases: first for η→1, with nakagami parameter m being expressed as μ=m/2, and second for η→0, with parameter m being expressed as μ=m. it is well-known that η–µ distribution reduces to hoyt distribution, when µ=1, with hoyt parameter q defined as q=(1-η)/(1+η). from the hoyt distribution the one-sided gaussian is obtained for q→+1 or q→−1 (η→0 or η→∞). in the same way, by equating the in-phase and quadrature components variances, namely by setting η=1, rayleigh distribution is derived from hoyt. also, weibull distribution could be obtained as a special case of the α-η-µ model by setting corresponding values to the parameters µ=1and η=1. in [18], α−η−µ and α-κ-µ distributions have been discussed. the performance analysis of wireless communication over α-η-µ fading channel has been investigated in [19], where the outage probability, pdf and cdf of the received signal to interference ratio were derived. the performance analysis of α-η-µ fading channel is carried out in [20], when the communication is subjected to influence of co-channel interference. in [21], the performance of digital communication systems that operate over α−η−µ fading channels was analyzed and evaluated. specifically, exact closed-form analytical expressions for mgf, cdf, average channel capacity, and asep for different coherent and noncoherent modulation schemes were derived. switched diversity combining schemes such as ssc are less complex diversity combining schemes, as ssc does not require channel estimation at the receiver, and minimizes the switching rate required the available diversity branches. though this diversity combining scheme was already examined over different fading channels including rayleigh, rician, nakagami, etc., analysis over fading distributions such as α-η-µ is not available in the literature. in this paper, we derived novel and closed-form expressions for asnr, outage probability (pout), mgf, and the aser for the m-ary quadrature amplitude modulation (qam) scheme, of a dual-branch ssc operating over generalized α−η−µ fading channels. the expressions are obtained in terms of the bivariate fox’s hfunction (bfhf). it is worth pointing out that the bfhf and the bivariate meijer’s g-function (bmgf) have recently been used extensively in the wireless communications literature when studying the systems’ performance. the evaluated results are plotted for channel parameters of interest, and the effect of fading severity on the combiner performance is studied. our derived expressions are valid for arbitrary values of the fading parameters α, η and µ. other short-time fading distributions, like rayleigh, nakagami-m, nakagami-q (hoyt), weibull, η–µ and one-side gaussian distribution, are derived from our results as special cases. ii. system model and output statistics in this paper, we focus on the performance evaluation of ssc systems over α-η-µ fading channels. in these dual-branch diversity systems the receiver selects a branch until its snr drops below a predetermined threshold. when this happens, the combiner switches to another branch and stays there regardless of whether the snr of the original branch is above or below the predetermined threshold. a. the � − � − � distribution 1) probability density function: we assume that the channel envelope r follows the α-η-µ distribution. the probability density function (pdf) of the channel under consideration is given as [22]: ���� = � √������� ���������������������� ���� !�� "�����̅������� $%&���'����� � (1) where γ�) = * +,-. exp�−+ d+34 is the gamma function, 56�∙ is the modified bessel function of the first kind and arbitrary order 8, α > 0, � > 0, ℎ = �.>? �@ ? , a = �.-?� @ ? , η>0, and �̅� represents the �-root mean value of the envelope �. to derive the cumulative density function (cdf) of the snr, we need first to derive the pdf for the snr. as such, we define the instantaneous snr, b, as [23]: b = b̅ ���̅�� (2) where b̅ = cd�̅�eeb/no and eb/no is the energy per bit to the noise power spectral density ratio. after performing random variable transformation using (1) and (2) [24], then the pdf of b is obtained as: �f�b = √� � � ������f���������������g���h �� h��� i j�� "����f���������klmg��'h��h��� i (3) the unified pdf defined in (3) can be written in terms of the fox’s h-function as [21]: �f�b = � �������f����������!�� "����f��������� × a4,..,4 o����-" f��f��� p -�4,. q a.,�.,. o@�" f �� f��� p ���,.���-��,.�,���-�,.�q (4) where a&,rs,td. e is the fox’s h-function [25]. 2) the cumulative distribution function the cdf of b with its corresponding pdf defined in (3) can be derived using the main definition of the cdf, which is given by [1] as: vf = * �f�w xwf4 (5) for arbitrary values of µ, the cdf of b in (5) can be expressed as [18]: vf�b = 1 − z� g"� , [���f��f��� i (6) engineering, technology & applied science research vol. 9, no. 6, 2019, 5047-5055 5049 www.etasr.com eyadeh & al-ta'ani: performance study of wireless systems with switch and stay combining diversity … where z��\,] = √� ��̂���.-_� �j�� _���� * `�� 5�-���\`� exp�−`� x`3a denotes the yacoub integral [15]. hence, the cdf of b is obtained as: vf�b = �.-��'�� �j���>. b2�ℎ �ff����d�� × φ� o�, �;2� + 1; − �1 "��b2�ℎ �ff����d , −�− "�� b2�ℎ �ff����dq (7) where φ� is the confluent lauricella function [26]. 3) the moment generating function (mgf) the mgf for the α−η−µ fading channels is obtained using the bfhf as [21]: hf�i = � �������j�� "���� �j f� �������� × h.,4:4,.;.,�4,.:.,4;.,. m ����-" �j f� ��@�" �j f� �� n �.-����>���;��,���:-;���,.�-:�4,. ;��-��,.�,���-�,.�o (8) b. output statistics of the ssc system: the pdf, cdf and mgf of the received snr at the output of a dual-branch ssc system over α−η−µ fading channels are derived in this section. 1) the pdf of the received snr if biip denotes the snr at the output of an ssc combiner, and bq denotes the predetermined switching threshold, to derive the pdf of ssc of the output snr, we first derive the cdf of the output snr, vfjjr�b , in terms of cdf of individual branch snr,vf�b , as [1]: vfjjr�b = s vf�bq vf�b , b < bqvf�b − vf�bq + vf�bq vf�b , b ≥bq (9) therefore, the cdf for a dual branch α-η-µ fading channels with ssc diversity is obtained by inserting (7) into (9) as: vfjjr�b = suvf�b , b < bqvf�b − u + u vf�b , b ≥bq (10) where u = vf�bq = �.-��'�� �j���>. b2�ℎ �fvf� ���d�� × φ� o�,�; +1; − �1 + "�� b2�ℎ �fvf� ���d, − �1 − "�� b2�ℎ �fvf� ���dq differentiating vfjjr�b with respect to b, we get the pdf of the snr at the output of the ssc combiner, �fjjr�b , in terms of cdf vf�b ,and the pdf �f�b of the individual branch snr as [1]: �fjjr�b = wxhyyz�f wf = svf�bq �f�b , b < bq{1 + vf�bq |�f�b , b ≥bq (11) the pdf �fjjr�b , for fading channels with ssc diversity is found by inserting (7) with respect to bq, and one of the pdf expressions (3) or (4) into (11) as: �fjjr�b = su �f�b , b < bqd1 + ue �f�b , b ≥bq (12) where u = vf�bq as mentioned previously in (10). 2) the mgf of the received snr the mgf with ssc diversity receiver, operating over α-η-µ fading channels is obtained using the pdf in (12) that is [1]: hfjjr�i = * e-jf�fjjr�b xb34 = d1 + vf�bq e hf�i − * e-jf �f�b xb fv4}~~~~�~~~~��� (13) where hf�i is the mgf for an individual branch under α-η-µ fading channel which is derived in (8). to obtain an expression for hfjjr�i in (13), we need to solve the second term integral 5.. to calculate the integral 5. in (13) we insert (4) in 5. as: 5. = � �������j�� "����f��������� * b����>���-.fv4 × h4,..,4 o����-" f��f��� p -�4,. q h.,�.,. o@�" f �� f��� p � ��,.���-��,.�,���-�,.�q × h4,..,4 �ib � -�4,. � xb (14) note that (14) is found by expressing the exponential function in 5., in terms of the fox’s h function [25]. using the definition of fox’s h function [25], (14) is written as: 5. = � �������j�� "����f��������� � .����� × * * * γ�w. b����-" f��� d -�� �^���� × j��-��>���j���-���j���>�-��� b@�"f��� d -�� γ�w� �i -�^ × �* b����>��-��-���-�^-. xb fv4}~~~~~~~�~~~~~~~��� � xw.xw�xw� (15) the inner integral in (15) with respect to b (i.e.,5. can be solved using the power integration rule: 5. = * b����>��-��-���-�^-. xb fv4 engineering, technology & applied science research vol. 9, no. 6, 2019, 5047-5055 5050 www.etasr.com eyadeh & al-ta'ani: performance study of wireless systems with switch and stay combining diversity … = fv����������������^����>��-��-���-�^ (16) by using the identity γ�` + 1 = ` γ�` [27], then (16) can be written as: 5. = fv����������������^ j�����>��-��-���-�^�j�����>��-��-���-�^>.� (17) now, substituting (17) into (15) yields: 5. = � �������fv��������j�� "����f��������� � .����� × * * * γ�w. b����-" fv��f��� d -�� �^���� × j��-��>���j���-���j���>�-��� b@�"fv �� f��� d -�� γ�w� �i bq -�̂ × j�����>��-��-���-�^�j�����>��-��-���-�^>.� xw.xw�xw� (18) using a.1 from [28], then the inner integral 5. is found in terms of the bfhf as: 5. = � �������fv��������j�� "����f��������� × h.,.:4,.;.,�;4,.4,.:.,4;.,.;.,4 �� ��� �����-" fv��f��� @�"fv��f���i bq nn �.����>���;��,��,.�:-;���,.�;�-����>���;��,��,.�:�4,. ;��-��,.�,���-�,.�;�4,. �� ��� � (19) in conclusion, a closed form expression of the hfjjr�i , is obtained as: hfjjr�i = �1 + vf�bq � � �������j�� "�����j f� �������� × h.,4:4,.;.,�4,.:.,4;.,. m ����-" �j f� ��@�"�j f� �� n �.-����>���;��,���:-;���,.�-:�4,. ;��-��,.�,���-�,.�o − � �������fv��������j�� "����f��������� × h.,.:4,.;.,�;4,.4,.:.,4;.,.;.,4 ��� ��� ����-" fv��f���@�"fv��f���i bq nn �.-����>���;��,��,.�:-;���,.�;�-����>���;��,��,.�:�4,. ;��-��,.�,���-�,.�;�4,. ��� ��� (20) iii. performance analysis of the ssc system many important measures characterize the performance of communication systems in fading environments, such as the average symbol error probability (asep), the asnr or the pout, can be determined by averaging appropriate performance functions over the distribution of the effective snr at the receiver-side. in this section a detailed performance analysis, in terms of pout, asep and asnr, for ssc diversity receivers operating over α-η-µ fading channels is presented. a. outage probability the outage probability is the probability that the snr at the output of the ssc falls below a threshold level, b��, which is found by replacing b in vfjjr�b with b�� as in 9.241 in [1]: ����jjr(b�� = ��dbjjr ≤ b��e = vfjjr�b�� (21) since the sdc is considered as an optimal implementation of the switched diversity system, then the optimal switching threshold in the minimum outage probability is: bq,�&� = b��, and because the outage probability of a dual-branch sc is ����jr (b�� = d vf�b�� e 2 [1], then the outage probability of a dual-branch ssc system with an optimal switching threshold is [1]: ����jjr(b�� = ����jr (b�� = d vf�b�� e � (22) where vf�b�� is (7) after replacing b with b��. as a result, a closed form expression of the ����jjr ( b�� is obtained after inserting (7), after replacing b with b��, into (22) as: ����jjr(b�� = �.-��'�� ���j���>. �� b2�ℎ�f�'f� ���d @� × bφ� o�, �; 2� + 1; − �1 + "��b2�ℎ �f�'f� ���d , −�1 − "��b2�ℎ �f�'f� ���dqd�(23) b. average output snr the average snr at the ssc output, b̅jjr , is a useful performance measure serving as an excellent indicator for the overall system fidelity, and it can be obtained by averaging b over �fjjr�b [1]: b̅jjr = * b �fjjr�b xb = d1 + vf�bq e b̅ − * b �f�b xb fv4}~~~�~~~� �� 34 (24) differentiating (24) with respect to bq and setting the result to zero, it can be easily shown that b̅jjr is maximized when the switching threshold is set to bq,�&� = b̅ . to obtain an expression for b̅jjr in (24), we need to solve the second term integral 5�. following similar steps as in (13) and using 2.57 from [28], 5� is found in terms of the bfhf as: 5� = � ������� fvα���������j�� "���� f��������� × h.,.:4,.;.,�4,.:.,4;.,. ��� ������-" fv α� f��� @�"fvα� f��� n n �-����>���;��,���:-;���,.� �-.-����>���;��,���:�4,. ;��-��,.�,���-�,.���� �� (25) finally, a closed form expression of the b̅jjr is obtained as: b̅jjr = �b̅ + b̅ vf�bq � − � ������� fvα��µ������j�� "���� f��������� engineering, technology & applied science research vol. 9, no. 6, 2019, 5047-5055 5051 www.etasr.com eyadeh & al-ta'ani: performance study of wireless systems with switch and stay combining diversity … × h.,.:4,.;.,�4,.:.,4;.,. ��� ������-" fv α� f��� @�"fv α� f��� n n �-����>���;��,���:-;���,.� �-.-����>���;��,���:�4,. ;��-��,.�,���-�,.���� �� (26) c. average symbol error probability in this section, the asep for m-ary qam signaling of a dual-branch ssc operating over a generalized α-η-µ fading channel is derived. for m-qam modulation scheme, the average sep is obtained using the following averaging process [1]: pr�e = * p��e 34 f ��¡�γ dγ (27) where �j�c is the conditional sep for square m-qam signals whose constellation size m is given by m= 2£ with k even. from 8.10 in [1], �j�c is given by: p��e = 2 a erfc�¨b γ � − a�erfc��¨b γ � (28) where erfc(x) is the complementary error function, (i.e. ª��p�` = �√� * ª-��∞% x+, [1]), \ = 1 − .√« and ] = ���¬��« ��«-. . although (28) is obtained for square constellations, it gives a good approximation for m for general qam constellations with m= 2£ points which are either in the shape of a square (k is even), or in the shape of a cross (k is odd) [1]. as a result, and after substituting (28) into (27), for m-qam modulation scheme, the average sep can be found as: pr�ª = d1 + vf�bq e × g* 2 \ ª��p�¨] b � �f�b xb34}~~~~~~~~�~~~~~~~~��^ − * \ �ª��p��¨] b � �f�b xb34}~~~~~~~~�~~~~~~~~��­ i − ®¯ 2 \ ª��p�¨] b � �f�b xbfv4}~~~~~~~~�~~~~~~~~��° − ¯ \�ª��p��¨] b � �f�b xbfv4}~~~~~~~~�~~~~~~~~��± ² �29 differentiating (29) with respect to bq and setting the result to zero [1], it can be shown that there is a generic expression for bq,�&� , for which the average error rate is minimal. in general, this bq,�&� will be a solution of 9.254 in [1], but explicit closed-form solutions will not always be possible to obtain. in this case, one must rely on numerical root-finding techniques to find an accurate solution for the optimum threshold. to find the asep for m-qam modulation scheme for ssc, we need to find the integrals, 5�, 5@, 5 ́and 5µ in (29). these quantities are derived in terms of the bfhf as: 5� = � _ � ������� √¶ j�� "���� �· f� �������� × h�,.:4,.;.,�4,�:.,4;.,. × �� �� ����-" �· f� �� @�" �· f� �� nn ���-����>���;��,���,�.-����>���;��,���:-;���,.� �-����>���;��,���:�4,. ;��-��,.�,���-�,.� �� �� (30) 5@ = _�� ������� ¶ j�� "���� �· f� �������� × h�,.:4,.;.,�;.,�4,�:.,4;.,.;�,4 × �� �� �����-" �· f� �� @�" �· f� ��1 nn �.-����>���;��,��,.�,���-����>���;��,��,.�:-;���,.�;�.,. �-����>���;��,��,.�:�4,. ;��-��,.�,���-�,.�;�4,. ,���,.��� �� � (31) 5´ = � _ � ������� fv��������√� j�� "���� f��������� × a.,.:4,.;.,�;.,�4,.:.,4;.,.;�,4 × �� �� ������-" fv �� f��� @�"fv�� f���] bq n n �.-����>���;��,��,.�:-;���,.�;�.,. �-����>���;��,��,.�:�4,. ;��-��,.�,���-�,.�;�4,. ,���,.� �� �� �� (32) 5µ = \�� ℎ���>�� bq����>��� ¸ γ�� a�-�� b̅����>��� × h.,.:4,.;.,�;.,�;.,�4,.:.,4;.,.;�,4;�,4 × �� �� �� �����-" fv�� f��� @�"fv�� f���] bq] bq n n �.-����>���;��,��,.,.�:-;���,.�;�.,. ;�.,. �-����>���;��,��,.,.�:�4,. ;��-��,.�,���-�,.�;�4,. ,���,.�;�4,. ,���,.� �� �� �� � (33) a closed form expression of the pr�ª has been obtained, which is given as: pr�ª = �1 + vf�bq � × � � _ � ������� √¶ j�� "���� �· f� �������� h�,.:4,.;.,�4,�:.,4;.,. × m ����-" �· f� �� @�" �· f� �� n ���-����>���;��,���,�.-����>���;��,���:-;���,.� �–����>���;��,���:�4,. ;��-��,.�,���-�,.� o − _�� ��� ���� ¶ j�� "���� �· f� �������� h�,.:4,.;.,�;.,�4,�:.,4;.,.;�,4 × �� �� �����-" �· f� �� @�"�· f� ��1 nn �.-����>���;��,��,.�,���-����>���;��,��,.�:-;���,.�;�.,. �-����>���;��,��,.�:�4,. ;��-��,.�,���-�,.�;�4,. ,���,.��� �� � º »¼ −( � _ � ������� fv��������√� j�� "���� f��������� h.,.:4,.;.,�;.,�4,.:.,4;.,.;�,4 × �� �� ������-" fv �� f��� @�"fv�� f���] bq n n �.-����>���;��,��,.�:-;���,.�;�.,. �–����>���;��,��,.�:�4,. ;��-��,.�,���-�,.�;�4,. ,���,.��� �� �� _�� ������� fv�������� � j�� "���� f��������� h.,.:4,.;.,�;.,�;.,�4,.:.,4;.,.;�,4;�,4 �� �� �� �����-" fv�� f��� @�"fv�� f���] bq] bq n n �.-����>���;��,��,.,.�:-;���,.�;�.,. ;�.,. �–����>���;��,��,.,.�:�4,. ;��-��,.�,���-�,.�;�4,. ,���,.�;�4,. ,���,.� �� �� �� � º »» »¼ (34) engineering, technology & applied science research vol. 9, no. 6, 2019, 5047-5055 5052 www.etasr.com eyadeh & al-ta'ani: performance study of wireless systems with switch and stay combining diversity … iv. results and discussion in this section the ����, asnr and asep of a dual-branch ssc system over α-η-µ fading channels are presented using several numerical examples. the results are obtained using (23), (26) and (34). the optimum switching threshold was applied in each example. to validate our results, we plot in figures 1, 2 and 6, the abep for coherent bpsk and coherent bfsk, the ����, and asnr over η–µ and hoyt (nakagami-q), which are deduced from our results reported in [6, 12]. the results exactly match the results reported in figures 5 and 6 in [12], figure 5 in [6], figure 1 in [12], figure 4 in [6], and figure 2 in [12] respectively, which validates our work. the corresponding results for one-sided gaussian and nakagami-m fading channels are presented as special cases of α-η-µ fading channels. figure 1 presents the abep for coherent bpsk and noncoherent bfsk for some special cases of fading channels. figure 2 presents the outage probability with and without diversity over α-η-µ fading channels vs the normalized outage threshold (b��/b̅ for different values of α, η and µ. for α=2, η=0.5, µ=0.5 and �b��/b̅ =0db, it is shown that ����jjr(b�� with diversity decreases (improves) by 41% when compared to the outage probability without diversity. fig. 1. abep for coherent bpsk and coherent bfsk for some special cases of fading channels fig. 2. outage probability of a dual-branch ssc system over α-η-µ fading channels versus normalized outage threshold �b��/b̅ figures 3 and 4 show the effect of fading parameters on the outage probability ����jjr(b�� with average snr b̅ = 10db and b�� =5db. when α and (or) µ increase(s), they result in improved system performance. for example, in figure 3, when η=2 (fixed) and µ=1.5 (fixed), the ���� jjr(b�� is approximately decreased by 54% when α is decreased from 1.1 to 0.7. in figure 4, when α=1.5 (fixed) and η=0.9 (fixed), ���� jjr(b�� is approximately decreased by 57% when µ is decreased from 1.5 to 1. also, as η increases, ���� jjr(b�� increases. for example, in figure 3, when α=2 (fixed) and µ=1.5 (fixed), ���� jjr(b�� is approximately increased by 31% when η decreases from 2.5 to 1.5. this occurs for higher values of η. it is clear from the above discussion that ���� jjr(b�� improves by increasing α and µ, and degrades by increasing η, because of the following reasons: parameter µ represents the multipath in each cluster, so, when µ increases the receiver will have more copies of the same transmitted signal, so ���� jjr(b�� improves. parameter α represents the power exponent of the sum of multipath components, therefore, as α increases, ���� jjr(b�� improves. the fading parameter η represents the correlation coefficient between the in-phase and quadrature components of each cluster of multipath. therefore, as η increases the correlation coefficient increases, and then the ���� jjr(b�� degrades. fig. 3. outage probability of a dual-branch ssc system over α-η-µ fading channels versus parameter α fig. 4. outage probability of a dual-branch ssc system over α-η-µ fading channels versus parameter µ engineering, technology & applied science research vol. 9, no. 6, 2019, 5047-5055 5053 www.etasr.com eyadeh & al-ta'ani: performance study of wireless systems with switch and stay combining diversity … figure 5 shows the normalized average output snr of a dual-branch ssc system over fading channels �b̅jjr/b̅) versus the parameter α for different values of η and µ. figure 6 shows the b̅jjr/b̅ as a function of µ for different values of α and η. both figures are plotted at bq 0 db. the results presented in figure 5 show that as α increases, the b̅jjr / b̅ decreases, resulting in a reduced diversity gain. for example, in figure 5, when η=1.5 (fixed) and µ=0.5 (fixed), b̅jjr / b̅ for α=1.4 is approximately decreased by 7% compared to α=0.6. we note similar observations for the effect of the fading parameter µ in figure 6. the results indicate that as µ increases, the b̅jjr/b̅ is degraded. for instance, when α=1.5 (fixed) and η=2.2 (fixed), b̅jjr /b̅ for µ=1.8 is nearly decreased by 7.5% compared to µ=0.8. in contrast to α and µ, it is obvious from figures 5 and 6 that as the value of η increases, b̅jjr/b̅ increases. for example, in figure 6, when α=1 (fixed) and µ=1.5 (fixed), b̅jjr/b̅ for η=2.2 is approximately increased by 1.5% compared to η=1.2. this effect of η occurs for higher values of η. fig. 5. normalized average output snr of a dual-branch ssc system over α-η-µ fading channels �b̅jjr/b̅) versus parameter α fig. 6. normalized average output snr of a dual-branch ssc system over α-η-µ fading channels �b̅jjr/b̅) versus parameter µ a graphical illustration of the impact of the switching threshold on b̅jjr for different values of α, η and µ is depicted in figure 7. this figure is plotted with respect to average snr b̅ 10 db. obviously, we get the best performance for bq bq,�&� b � . figure 8 shows the average sep of 16qam of a dual-branch ssc system over α-η-µ fading channels versus the average snr �b̅ for different values of α, η and µ, for switching threshold bq=5db. the curves in figure 8 are categorized into different sets according to the average snr value. each combination of the parameters α, η and µ represents different channel model which justifies that each curve has different rate of change behavior within the same set. as expected, the asep performance improves as input branch snr b̅ increases. the asep for a single branch � �� � � fading (no diversity) is also appeared in figure 8. as shown, the system performance is improved under ssc diversity. for example, when α=1.5 (fixed), η=1.5 (fixed), µ=2 (fixed) and b̅ =10db (fixed), the asep under ssc diversity is approximately decreased by 59% compared to the asep for a single branch. fig. 7. average output snr of a dual-branch ssc system over α-η-µ fading channels �b̅jjr) versus the switching threshold ( bq . fig. 8. asep of 16-qam of a dual-branch ssc system over α-η-µ fading channels versus average snr�b̅ figures 9 and 10 show the effect of the fading parameters on the asep. the average snr b̅ 10db and bq 5db. as α and (or) µ increase(s), the system performance improves. for example, in figure 9, when η=2(fixed) and µ=1(fixed), the asep reduction is about 39% when α increases from 0.6 to 0.95. figure 10 shows the effect of the parameter µ on the asep. for α=0.5(fixed) and η=1.1(fixed), the asep reduction is about 33% when µ increases from 0.75 to 1.35. in contrast with α and µ, it is clear that as η decreases, the asep improves. engineering, technology & applied science research vol. 9, no. 6, 2019, 5047-5055 5054 www.etasr.com eyadeh & al-ta'ani: performance study of wireless systems with switch and stay combining diversity … for instance, in figure 9, when α=0.6 (fixed) and µ=1(fixed), the asep reduction is about 10.5% when η decreases from 2.5 to 0.9. note that, this effect occurs for higher values of η. fig. 9. asep of 16-qam of a dual-branch ssc system over α-η-µ fading channels versus α fig. 10. asep of 16-qam of a dual-branch ssc system over α-η-µ fading channels versus µ fig. 11. asep of a dual-branch ssc system over α-η-µ fading channels versus the average snr �b̅ for multi levels of qam in figure 11, we plot the asep of a dual-branch ssc system over α-η-µ fading channels versus the average snr �b̅ for multi levels of qam: 4, 8, 16, 32, 64 and 128. figure 11 is plotted for fixed values of α, η and µ (α=2, η=1.5 and µ=2), and for bq 3db. the degradation in the asep is obvious with increasing values of m-ary of qam. the asep get an improvement with increasing the average snr �b̅ . v. conclusions in this paper, a dual-branch ssc diversity scheme operating over α-η-µ fading channel has been examined. new and closed-form analytical expressions were derived for asnr, mgf, ���� , and asep for m-ary qam signaling. expressions for the optimum adaptive switching thresholds were also derived. some of these expressions were obtained in terms of the well-known bivariate fox’s h-function (bfhf). the results p are shown to match those previously reported in the literature for other channels models such as η−µ model as a special case, which confirms the validity of the obtained expressions. using numerical examples, we observed that the dual-branch ssc system has improved the performance of pout, asnr, and asep for m-ary qam signaling. the pout and asnr of the ssc diversity system improve, as α and (or) µ increase(s), with η kept constant. the asnr also improves, as η increases, with α and µ kept constant. however, increasing α and µ improves the system performance more than η. references [1] m. k. simon, m. s. alouini, digital communication over fading channels: a unified approach to performance analysis, john wiley & sons, 2000 [2] a. a. a. dayya, n. c. beaulieu, “analysis of switched diversity systems on generalized-fading channels”, ieee transactions on communications, vol. 42, no. 11, pp. 2959–2966, 1994 [3] a. a. a. dayya, n. c. beaulieu, “switched diversity on microcellular rician channels”, ieee transactions on vehicular technology, vol. 43, no. 4, pp. 970–976, 1994 [4] s. haghani, n. c. beaulieu, “post detection switch-and-stay combining in nakagami-m fading”, ieee vehicular technology conference, los angeles, usa, september 26-29, 2004 [5] s. haghani, n. c. beaulieu, “revised analyses of postdetection switchand-stay diversity in rician fading”, ieee transactions on communications, vol. 54, 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letters, vol. 13, no. 6, pp. 411-413, 2009 [24] p. z. peebles, probability, random variables, and random signal principles, 4th edition, mcgraw-hill, 2000 [25] a. p. prudnikov, y. a. brychkov, o. i. marichev, integrals and series: special functions, crc press, 1990 [26] a. erdelyi, higher transcendental functions, mcgraw-hill, 1953 [27] i. s. gradshteyn, i. m. ryzhik, table of integrals, series and products, 7th edition, academic press, 2007 [28] a. m. mathai, r. k. saxena, h. j. haubold, the h-function: theory and application, springer, 2010 microsoft word 38-3435_s_etasr_v10_n4_pp6109-6115 engineering, technology & applied science research vol. 10, no. 4, 2020, 6109-6115 6109 www.etasr.com mleke & dida: a web-based monitoring and evaluation system for government projects in tanzania … a web-based monitoring and evaluation system for government projects in tanzania: the case of ministry of health mpawe nicodem mleke school of computational and communication sciences and engineering the nelson mandela african institution of science and technology arusha, tanzania mlekem@nm-aist.ac.tz mussa ally dida school of computational and communication sciences and engineering the nelson mandela african institution of science and technology arusha, tanzania mussa.ally@nm-aist.ac.tz abstract—monitoring and evaluation systems are used by organizations or governments to measure, track progress, and evaluate the outcomes of projects. organizations can improve their performance, effectiveness, and achieved results in project success by strengthening their monitoring and evaluation systems. moreover, various studies reveal the need for information and communication technology systems in monitoring and evaluation activities. despite the advantage of the tools, most organizations do not employ computerized monitoring and evaluation systems due to their cost and limited expertise whereas those having these systems lack a systematic alert mechanism of the projects' progress. currently, the ministry of health, community development, gender, elderly, and children of tanzania monitors and evaluates its projects manually facing the risks and consequences of delayed project completeness. in this study, the evolutionary prototyping approach was used to develop the proposed system. this study describes the development of a web-based monitoring and evaluation system that aims to solve the monitoring and evaluation challenges, simplify works, generate quality data, and provide timely successful project implementation. the developed system was tested and evaluated against the user’s requirements and was positively accepted to be deployed at the ministry of health. keywords-health projects, monitoring and evaluation system; web-based, ministry of health i. introduction monitoring and evaluation (m&e) systems are used to improve the performance of projects and achieve positive results in project activities. m&e is essential in helping planners, implementers, managers, policymakers, and donors to understand and obtain the information they need to make informed assessments about project processes or operations [1]. project activities are usually executed over a fixed period of time, with the aim of achieving desired outcomes or specific goals [2]. project monitoring is essential for giving feedback about project progress to the beneficiaries involved in the project, implementers, and the donors who fund the project. furthermore, project evaluation is necessary for making judgments about the activities of the project and informing program decisions. evaluation determines the efficiency, effectiveness, sustainability, impact, whether projects have met their targets, and helps to identify areas of improvement. moreover, by sharing the project output to others, m&e creates knowledge in project management and promotes accountability to donors, stakeholders, and citizens [3]. the tanzanian government has recently shown significant efforts in improving the lives of its citizens, by initiating and implementing different projects and programs in community empowerment and health [4]. in tanzania, the basic health care services are equitable, qualitative, affordable, accessible, gender-sensitive, and sustainable and are supposed to be taken care by the ministry of health, community development, gender, elderly and children (mohcdgec). projects initiate at mohcdgec, but there is a lack of m&e systems for tracking their implementation progress in order to improve data quality, performance, reduce paperwork, and achieve good results. ii. background information currently, m&e of government projects at the mohcdgec is done manually, and as a result, there are risks encountered due to the lack of timely adoption of remedial actions. non-uniformity is observed in data collection, reporting, and management for different projects sponsored by different donors within the ministry [5]. having an electronic system for providing accurate and timely m&e information can be one of the solutions to this problem. among the challenges faced by the national malaria control program (nmcp) was coordinating the collection of m&e information [6]. moreover, lack of coordination among partners, agencies, ministries and information communication and technology departments was highlighted in the health sector strategic plan iii (2009–2015). the strategic plan further showed a lack of m&e activities in epidemics such as aids/hiv, tuberculosis (tb) and malaria due to poor infrastructure of the healthcare system and inefficiencies [7]. although the donor-funded health projects reported an increasing demand on the use of electronic m&e systems to reduce workload, improve data corresponding author: mpawe nicodem mleke engineering, technology & applied science research vol. 10, no. 4, 2020, 6109-6115 6110 www.etasr.com mleke & dida: a web-based monitoring and evaluation system for government projects in tanzania … quality, data analysis, accurate reports, and data access [7], such systems are not available at the ministry of health. this study intends to support the mohcdgec by developing an electronic m&e system for government projects in order to track progress, report status, and give alerts and warning information. moreover, this study will simplify the data collection process, generate qualitative data for planning and evaluation, facilitate successful project implementation, and provide feedback mechanisms between stakeholders, employees, and donors. iii. related work m&e assists governments and organizations to extract data from past and ongoing activities, provides reports on projects' progress, and measures whether the project is meeting its objectives or progressing in the right direction. without m&e, it is impossible to judge if the project work is going in the right direction and what future efforts might be required [1]. traditionally, m&e focused on assessing input with the implementation processes. today, m&e focuses on assessing the factors that contribute to the development output, outcome, partnerships, advocacy, coordination, and policy advice. project managers are required to apply the information gained from m&e to improve project activities and strategies. better decisions in projects lead to greater accountability to the stakeholders and help improving project activity performance. close partnership with stakeholders creates knowledge sharing, skills, learning, capacity, project decision planning, provides valuable feedback, and makes a positive contribution to the effectiveness of development [1]. a project can be successful by good decision making and cooperative relationships [8]. having project planning and project management teams keeps the judgment of ongoing project activities, monitors progress, solves the challenges in case of gaps in planned goals, and improves project performance. the performance of a project is influenced by project management capabilities, cost, quality, time, risk management, communication skills, and human resources [9]. an unesco report indicates that governments or organizations have the systems for data collection for measuring the outcomes which have achieved on a project or program and can be simple or sophisticated but their results are poor due to lack of electronic m&e systems. it further shows that in the developed world only a few countries are implementing projects by using m&e systems [10]. authors in [11] proposed an m&e system for the organization and employee evaluation for the ministry of trade and industry in egypt. the system, not only provided regular reports but also assisted the top management to get feedback from employees and customers, eventually increasing employee performance. in [12], a web-based tool was used to support the collection and reporting of data for learning, research, and teaching in education. the tool was needed by students, instructors, and researchers for education project design, student progress evaluation, and as a feedback tool. this tool can be adopted at the mohcdgec to simplify the implementation of health project activities and provide feedback to different stakeholders. authors in [13] studied web-based construction for projects and a tool to monitor their performance was developed to support the project manager to measure and manage people, time, client satisfaction, cost communication, and quality. the purpose of this tool was to reduce the time used to collect data, dissemination and data incompatibility that was occurring in different software or systems. however, the system had cost implications in ensuring reliable security, preventing downtime and facilitating constant monitoring. the developed m&e system in [14] allows monitoring and evaluating road projects and public works for philippines government. the information is being secured and cannot be deleted or altered because of the administrator who updates and edits the data. the sokoine university of agriculture in tanzania has developed a webbased m&e system. the adoption of this electronic system helps knowing project progress, learning from achievements, coordinating and managing the project activities. overall, the designation of this system helps detecting risks that may occur and it gives early warnings to the coordination office and project’s team members. that system has additional functionalities allowing researchers and project team members to submit their reports electronically [15]. the literature review reveals that most government/organizations do not employ computerized m&e systems and those having these systems lack a systematic early informing mechanism of the projects' progress. this study aims to develop a web-based m&e system for health projects in order to keep track of the implementation progress, report the project status, and give appropriate warning alerts thus contributing to the completion of the project's goals. iv. methods a. system development approach in this study, data were collected at the mohcdgec in dodoma and dar es salaam regions, where various projects are monitored and evaluated. interviews, document reviews and focus group discussions were used to analyze the current m&e system for government projects. the requirements for the proposed system were analyzed and participants agreed to have an electronic m&e system for government projects in tanzania. to develop the proposed system for government projects, the evolutionary prototyping approach was used because it allows changes in every phase [16]. it improves the prototype system, reduces the software risks, minimizes work, and critical and serious defects during the system testing. b. tools and technologies used in system development 1) hypertext pre-processor (php) it used for database connection and manipulation and carries website duties such as authentication, password handling, and forum managing. it can be embedded into hyper text makeup language (html) code [17]. in this study, php was used to accept the data from the client and send them to the relational database management system (rdbms) for storage. it ensures the security of the user who logs in by maintaining the user session across the pages. further, it was used to connect the developed system to the mysql database. engineering, technology & applied science research vol. 10, no. 4, 2020, 6109-6115 6111 www.etasr.com mleke & dida: a web-based monitoring and evaluation system for government projects in tanzania … 2) mysql it is a back-end rdbms that handles database commands or instructions. it handles large databases efficiently by employing different programs to support the administration [18]. during this study, a mysql database was developed to help m&e and other project members to store, retrieve and manage data. furthermore, different access privileges and password encryptions were used to enhance security through host-based verification. 3) javascript it is a scripting language that allows client-side data validation before the data are submitted to a database. the client-side validation is important as it saves time, reduces the workload of the server, allows the server to concentrate on lowlevel verification and data processing [10]. in this study, apart from validation, javascript libraries such as jquery and chart.js were employed to improve data presentation in plotting graphs, and handling tabular data and the date text field. 4) hypertext markup language (html) in the development of this system, html [20] was used for the purpose of displaying the web pages and other multimedia/information which are displayed on a web browser. 5) apache web-server it is highly customized to meet the need for different environments by using modules and extensions. apache is a cross-platform software that works on both windows and unix servers, it is reliable, secure, and fast [21]. 6) integrated development environment (ide) for this study, the ide used was net beans. it is an opensource integrated development environment used for application development. it provides the wizard, editors, and templates which help creating applications in programming languages like php and java and can be installed in operating systems such as windows, macos, solaris and linux [22]. c. user acceptance testing user acceptance testing was conducted to validate the proposed system if it met the project's requirements at mohcdgec. questionnaires were given to twelve respondents including four m&e staff, two ict staff, four project members, one project manager and one accountant to gather feedback on the validity of the system. v. results and discussion a. system requirements for implementing the proposed system, functional and nonfunctional requirements were collected and are shown in table i and table ii respectively. b. the architecture of the proposed system based on the study findings, the proposed system was successfully developed. it contains three modules: a project registration module, a project tracking module, and a project status module. this study intended to develop a tool to track and report the status of projects and allow prompt actions to mitigate the encountered challenges and risks. figure 1 presents the architecture for the proposed system. table i. functional requirements system users (actors) description system administrator will be able to login to the system and register all users/members. is responsible for defining and giving different privileges to the users of the system, for maintaining, and for updating the system. every user must have a username and password. project manager will be able to register a new project to the system, including code number and title/type of project, location and timeframe/period of the project, source of the project fund and all partners/support/donor funds and project activities. m&e officers add/update indicators for project activities and targets of the project, in a quarterly or year basis. m&e will review and check the data which are entered by program members to track the progress of the project and to measure performance and generate quarterly or yearly reports depending on the nature of the project. accountant officers add/update financial documents for project activities and verify if the accounting function was correctly captured. project members program members or project teams will have the privilege to perform their specific tasks of entering data/information in weekly, monthly or quarterly basis. all registered users users will be able to view the deadline warnings, the status and report of the projects and alert information before/after the project is completed. donors/ partners they will be able to provide feedback from the generated report. further, they will view various reports from the projects they support. they can see the progress of reports and enquire more information from the project manager if needed table ii. non functional requirements quality factor description performance the system will be required to support many terminals simultaneously without failure and handle multiple users without contradiction or break by using a fast server to handle traffic and provide crossbrowser compatibility. usability users must be satisfied with the usability of the website without any specialized training and be able to complete different tasks without failure. reliability the system should be capable of maintaining its performance.. security the system will protect services and information from external attacks using authentication, authorization, and encryption. interoperability the system will be interoperable with existing systems at the ministry. other systems must be able to fetch data from it and it should be able to read structured documents such as xml. maintainability the maintenance or any modification to the system will not cause the website to shut down more than once in 24 hours. recovery the system will be able to recover after some damages. flexibility the system will have the ability to add the new notification/status of projects before and after the deadline engineering, technology & applied science research vol. 10, no. 4, 2020, 6109-6115 6112 www.etasr.com mleke & dida: a web-based monitoring and evaluation system for government projects in tanzania … fig. 1. architecture of the proposed system. c. data flow diagram the dataflow diagram is used to show how data will flow between actors [23]. in this study, the level 0 (context diagram) shows the flow of information between the developed system and external entities (figure 2). data flow diagram (level 1) presents the flow of information for all processes involved in each stage and their stored data when the process is completed. figure 3 presents the data flow diagram for the developed system. fig. 2. context diagram. d. the developed pmes the developed web-based tool, named project m&e system (pmes) for government projects is organized into six sections, namely account, settings, project details, project implementation, reports, and system log. these sections grouped several functionalities to simplify navigation. the developed web application for government projects allows only registered users to access the system. the home or dashboard page shows the status of the projects/project information including the initiated, implemented, completed, delayed projects and alert/warning information displayed on the dashboard. the dashboard page (figure 4) helps all system users to understand the progress of each project and minimize potential problems or solve the project challenges on time. this will help the ministry of health to complete projects within the allocated time. all registered system users can view the status of the project, but not other system menus. registered users need the administrator’s permission to access other menus based on their user roles. in the pmes, only system administrators can browse and access all system menus. the project detail section, has various functionalities including project registration, project sponsors, project members, project activities, and uploaded project reports. project manager and m&e team have access to the project detail section. to register a new project, the project manager enters the new project details including the title/type of the project, code number, location, start date, end date, and project and project activities. moreover, the project manager registers the project sponsor, project members, and fills the amount of money sponsored by the project. this is done by selecting their members, donor and positions since they were already registered by the system administrator. lastly, in the project details menu, project manager and m&e officer can upload various project reports. the reports may include information about project activities at any time they are needed, quarterly, annually or based on the agreed project format. this will allow users to know the reports of various projects and have access to feedback from decision making/ partnership/sponsors. figure 5 shows the page for entering the project details. the project implementation section enriches the particular project entered in the project section. it houses pmes functionalities including entering field data, setting indicators, entering indicator achievement, setting a budget and finally entering activity expenditure. in the system, the m&e officer is responsible for adding or updating the indicators of project activities on a quarterly basis or depending on the nature of the project. as a part of monitoring, the m&e officer is able to set indicators for each project activity, monitor its progress and enter the score of a particular indicator. figure 6 presents the form for uploading activity execution attachment. fig. 3. data flow diagram. engineering, technology & applied science research vol. 10, no. 4, 2020, 6109-6115 6113 www.etasr.com mleke & dida: a web-based monitoring and evaluation system for government projects in tanzania … fig. 4. dashboard. fig. 5. project details page. fig. 6. form for uploading an activity execution attachment. engineering, technology & applied science research vol. 10, no. 4, 2020, 6109-6115 6114 www.etasr.com mleke & dida: a web-based monitoring and evaluation system for government projects in tanzania … fig. 7. the indicator performance for project activity. project reports section has the reports needed by the various stakeholders, including reports on project details, field data, indicator performance, activity expiry, financial information, and project members. it is important for m&e officials to monitor the progress of all projects. the indicator performance section offers the m&e team the ability to evaluate the success of activities within the projects. it uses both tabular data and bar graphs to demonstrate the performance of an indicator. while the tabular data present the target and achievement of certain indicators, the graph shows the indicator performance in percentage. figure 7 presents the indicator performance for project activity. e. user acceptance validation to gather feedback from the system users, the users were trained in the pmes and were given three days to familiarize with it. the users were then registered into the pmes for proceeding with using and interacting with the system in their different roles. in the project detail menu, the project manager was allowed to log in, reset the account, and register project details. in the project implementation menu, the m&e officer was allowed to login and add the different project performance indicators. the accountant added the budget and sub-budget of the project activities, and the project member uploaded the attachment for activity which has been executed and any needed details or explanation. the other functionalities in pmes included viewing the list of projects with all associated details and status. furthermore, a questionnaire was distributed to the system evaluators and their comments, views, perception and recommendations about the pmes were asked. the questionnaire results were calculated on the mean score based on a four-point likert scale (4 = strongly agree, 3 = agree, 2 = disagree and 1 = strongly disagree) as shown in table iii. the mean score for each validated feature was above 3.5 which indicates that the majority of the respondents accepted the developed system, and they will be able to continue using it in their projects in order to improve the project implementation performance. lastly, the users report that they will recommend the tool or its extensions to fit other minister/organization m&e projects. table iii. system’s user acceptance validation result validation features mean score the pmes satisfies the m&e requirements of health projects. 3.75 the pmes is easy to access. 3.75 the interface of this pmes system is interactive. 3.83 the system contents are learned, understand and easy to operate. 3.75 the pmes will reduce the workload and paperwork in health projects. 3.91 the pmes will improve health project data handling in a specific time. 3.83 the pmes will improve the m&e process of the different health projects on time. 3.75 the pmes will improve the report generation, 3.67 the pmes will be useful and help in accessing health projects at the ministry. 3.91 i think, i will continue using this pmes. 4 i don’t think there is a need for having training support to operate this system. 3.91 f. discussion the mohcdgec currently relies on manual or paperbased systems in m&e of project activities, revealing a number of challenges in their operation such as poor information sharing and underperformance. some previous studies indicate that there is a need for web-based tools to monitor and evaluate project activities, simplify data collection, accommodate information sharing among stakeholders and improve the projects’ performance. after the system’s development, the results of user acceptance testing indicate that the developed pmes will help reducing the presented challenges. there is a need for pmes to be adopted at the mohcdgec to minimize manual work, improve cooperation among ministry departments, stakeholders, donors and, partners. moreover, the developed system will improve the quality of data, simplify the process of data collection and improve the progress of projects of the ministry of health in tanzania. engineering, technology & applied science research vol. 10, no. 4, 2020, 6109-6115 6115 www.etasr.com mleke & dida: a web-based monitoring and evaluation system for government projects in tanzania … vi. conclusion in this study, a tool was developed that will help the ministry of health to monitor and evaluate various project activities, thus remedying challenges such as delay of data submission during project implementation and data loss which usually occur in the paper-based data collection on a monthly or quarterly basis. the developed system will be useful to different stakeholders including project managers, project members, decision-makers, policymakers and m&e officers in tracking the projects’ progress, in the health domain as a tool for better and more informed decisions. acknowledgment the authors wish to thank the ministry of health and social welfare. this study was funded by the african development bank. references [1] handbook on monitoring and evaluating for results evaluation office. one united nations plaza new york, ny 10017, usa: evaluation office, united nations development programme, 2002. 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[23] l. svobodová and m. černá, “project management model with designed data flow diagram: the case of ict hybrid learning of elderly people in the czech republic,” in computational collective intelligence, cham, 2018, pp. 399–408, doi: 10.1007/978-3-319-984469_37. microsoft word etasr_v11_n4_pp7477-7482 engineering, technology & applied science research vol. 11, no. 4, 2021, 7477-7482 7477 www.etasr.com daithankar & ruikar: analysis of the wavelet domain filtering approach for super-resolution videos analysis of the wavelet domain filtering approach for video super-resolution mrunmayee v. daithankar electronics engineering department walchand college of engineering sangli, maharashtra, india mrunmayeed30@gmail.com sachin d. ruikar electronics engineering department walchand college of engineering sangli, maharashtra, india ruikarsachin@gmail.com abstract-the wavelet domain-centered algorithms for the superresolution research area give better visual quality and have been explored by different researchers. the visual quality is achieved with increased complexity and cost as most of the systems embed different preand post-processing techniques. the frequency and spatial domain-based methods are the usual approaches for super-resolution with some benefits and limitations. considering the benefits of wavelet domain processing, this paper deals with a new algorithm that depends on wavelet residues. the methodology opts for wavelet domain filtering and residue extraction to get super-resolved frames for better visuals without embedding other techniques. the avoidance of noisy highfrequency components from low-quality videos and the consideration of edge information in the frames are the main targets of the super-resolution process. this inverse process is carried with a proper combination of information present in lowfrequency bands and residual information in the high-frequency components. the efficient known algorithms always have to sacrifice simplicity to achieve accuracy, but in the proposed algorithm efficiency is achieved with simplicity. the robustness of the algorithm is tested by analyzing different wavelet functions and at different noise levels. the proposed algorithm performs well in comparison to other techniques from the same domain. keywords-observation model; super-resolution; video quality parameters; wavelet residuals; wavelet domain processing i. introduction super resolution (sr) is a leading field of digital signal processing (dsp) with wide applicability in electronic imaging such as biomedical, forensics, surveillance, satellite imaging, etc. not only for better picturing but for proper data extraction, there is a need for high-quality images which are not readily available every time. an expensive high-resolution (hr) imaging system has restrictions on the sensor's capacity, the optics fabricating machinery, memory, and the sensor’s transmission bandwidth. physical up-gradation has almost reached its limits, so the solution is to develop effective ways to overcome the hardware limitations of the imaging systems. this leads to the sr concept and related developments. many authors [1-5] explored the sr concept, its recent applications, limitations, and scope for improvements. the concept aims to produce hr frames from successive low-resolution (lr) images or frames by applying dsp techniques in a proper sequence. some of the work related to sr is summarized below. the main contributions of the current paper are: • an introduction of the sr concept with the required basics. • a selection of a proper wavelet function through analyzing the simulation results for future work. • analysis of the proposed work with different noise levels and wavelet functions to check the robustness of the algorithm. • the establishment that the combination of low-frequency components and wavelet residuals for high-frequency details like edges leads to increased efficiency in comparison with the state-of-the-art techniques. ii. literature review a. super-resolution with the observation model the inverse process to carry out high-quality images or frames from their low-quality versions using digital image processing techniques is known as sr. the original hr version of the scene gets degraded by different factors like warping (w), blurring (b), aliasing or down-sampling (d), and additional noise (n) by the environment or by imaging devices. this degradation process results in the lr version of the images. the sr issue is an ill-posed problem, i.e. it has no particular solution and it doesn’t have a particular mathematical expression. researchers have tried to convert this ill-posed problem into a well-posed one in order to get a solution [1, 2]. even these trials do not represent the exact issue but helped obtain nearby versions and their solutions. for representing the sr concept mathematically, let us assume the following: x is the original hr image, with yk kth lr images/frames, where k is the number of observations. d is the decimation matrix, b is the blurring matrix, wk the warping matrix, and nk the additional noise. so, the mathematical expression of the observation model is represented in (1): yk = dbwkx+nk (1) the generalized observation model is represented in figure 1. the observation model shows the exposures of the lr frame from the high-quality frame due to some degradation factors. corresponding author: mrunmayee v. daithankar engineering, technology & applied science research vol. 11, no. 4, 2021, 7477-7482 7478 www.etasr.com daithankar & ruikar: analysis of the wavelet domain filtering approach for super-resolution videos the sr process is to get back the high-quality frames by restoring the degraded data using dsp techniques. this reverse process is carried out with different algorithms developed for different applications. the techniques for sr are mainly classified by their domain: spatial, frequency, and wavelet [36]. each domain has its advantages and disadvantages based on the application field. the next section summarizes some recent literature regarding sr. fig. 1. general sr observation model. b. super-resolution process categorization the categorization of the sr process is based on the domains in which the technique is developed. the techniques in the frequency field deal with the frequency element as an image trait. the frequency-domain approach is depending on shifting, aliasing, and band limitation of the signal [3–6]. the very first approach of sr was in the frequency area [7]. the routine equations that narrate the hr representation to the perceived vitiated pictures were framed with approximating the comparative moves among a series of down-sized, aliased, and without noise lr images. this process was protracted in [8] by recommending a biased least squares result upon the theory that the distortion and noise individualities are identical for all lr pictures. authors in [9] presented the dct centered image quality improvement algorithm. the dct has the benefits to attain a notable improvement in picture quality even for frequently posed cases. a foremost benefit of the frequency province-centered sr approaches is that they are habitually hypothetically straightforward and rational in calculations. the most elementary way to boost the resolution of a picture is spatial domain interpolation methods. the set of pixels estimates new pixels either by considering neighboring pixels or averaging the pixel values. these methods are known as nearest neighbor, bilinear, and bicubic interpolation. the composite interpolation methods are cubic b-spline interpolation method [10], new edge-directed interpolation (nedi) [11], and edge-guided interpolation (egi) [12]. for the spatially grounded sr approaches, uneven interpolation methods are some of the utmost innate approaches with moderately minimal computational difficulty. the frequency and spatial-based domain methods have their advantages and disadvantages as well. wavelet transform (wt) based methods give frequency components as well as spatial statistics which produce results more encouraging than the previous transforms. the same theory was investigated in [13]. the discrete wt and gabor wavelet combination also give promising results in the superresolution construction of satellite images, explored in [14]. the wavelet domain-centered sr restoration methodology can examine and manipulate global and local features at coarseand fine-scale respectively. among the confronts in sr, one needs to uphold or retrieve the real edges of entities in the interim condensing noise, which is commonly challenging to be realized instantaneously using frequency-centered processes due to the parallel reaction of edges and noise in the frequency range. this leads to embedding wt and edge-preserving algorithms like egi [15]. the combination of the keren algorithm for image registration, dwt, and nedi to improve the edges in the frames was explored in [16]. the appealing assets of wt, for instance, density, multi-resolution, and locality are valuable for probing actual-world motions. wt recommends a substitute solution to examine exact edges and noise individually. a collective statement of wtcentered techniques is that the lr frame is the quality truncated frequency subordinate band constructed by the wt of the picture [17]. the difference in wavelet decomposed sub-bands with actual low-resolution image, interpolation is the technique given in [18] for the reconstruction of images. authors in [19] recommended the sr method for the degraded frame with dwt and stationary wt (swt). yet, these accessible ways have partial execution in a range of noise stages, motion planes, wavelets, and the total of consumed frames. still, the researchers are showing interest in wavelet domain processing for the better performance of the algorithms. iii. the proposed wavelet-domain video sr process enhancing video quality in frequency and spatial domains is the traditional way, but nowadays the wavelet domain processing has become a trend due to the benefits of both domains embedded in one. the proposed algorithm is used basically for the analysis of the effect of the use of wavelets in the super-resolution process. the proposed technique uses the benefits of wavelet domain processing such as low frequency and high-frequency separation with the help of well-known wavelet families. the flow of work for the proposed methodology is divided into two parts: (a) degradation process and (b) upgradation process. these processes are presented in figures 2 and 3. a. degradation process naturally, the quality of images or video frames are degraded during the acquisition process due to many factors like noise in the acquisition process or environment, hardware quality, etc. many times, due to less storage and transmission capacity, the images/videos are compressed which leads to degradation. dealing with degraded quality data means inefficient information processing, less effective analysis, and lower quality visuals. the degradation process of the input video frames is shown in figure 2. fig. 2. degradation of input video frames. engineering, technology & applied science research vol. 11, no. 4, 2021, 7477-7482 7479 www.etasr.com daithankar & ruikar: analysis of the wavelet domain filtering approach for super-resolution videos in the proposed method, the original high-quality video frames are degraded by some factors like downsampling and addition of noise and are referred to as lr frames. the process is shown in figure 3. the degradation process of the proposed method can be communicated mathematically by modifying (1) to: yk = dx + nk (2) the steps followed in the degradation process are given in the form of a descriptive pseudo code in figure 3. fig. 3. frame degradation pseudocode. these lr frames are used as input in the upgradation process. b. upgradation process: the use of the wavelet transform is the frequency domain filtering of an input image, without any other noise removal technique. if only wavelet domain filtering is applied then it affects the output. this effect is analyzed for frame or image quality enhancement. the sr area has attracted the attention of researchers, as it enables the use of conventional image acquisition systems as it is with some post-processing. it reduces the cost of exchange of traditional systems by new technology. the simple and general steps involved in the superresolution process are shown in figure 4. fig. 4. sr of input lr video frames. the steps involved in the upgradation process are shown in the pseudocode of figure 5. fig. 5. frame upgradation pseudocode. iv. video quality measurement parameters a. peak signal to noise ratio (psnr) the psnr is a measure of the fraction among the highest signal power and the distortion of the noise that alters the superiority of its interpretation. since maximum signals include a vast range of intensity, the psnr is typically articulated in the logarithmic scale, whereas mean square error (mse) is offered by: mse � � �� ∑ ∑ x�i, j� � y�i,j��������������� (3) psnr � 20log�� " #$%& √#() * (4) where x represents the original image or frame, y denotes the matrix data of the corrupted image or frame, m gives the number of the pixel lines of the images, and n signifies the number of columns in the pixel image [1]. b. structural similarity (ssim) parameters like luminance, contrast, and structure are important to check the similarity between the original and super-resolved frames. collecting all these terms together we get the structural similarity (ssim) index [16, 20]. if the measurement of similarity is considered between images or frames x and y with the same size then the equation for ssim will be: ssim � ,�-&-./012,�3&./042,-&4/-.4/012,3&4/3.4/042 (5) where, μ6 and μ7 are the averages of x and y, σ6� and σ7� are variances of x and y, and σ67 is the covariance of x and y. c� and c� are constants [1]. v. experimental results and discussion the projected sr method based on the wavelet domain is verified on renowned noncopyrighted videos. the reason behind considering these videos is that they represent an easy engineering, technology & applied science research vol. 11, no. 4, 2021, 7477-7482 7480 www.etasr.com daithankar & ruikar: analysis of the wavelet domain filtering approach for super-resolution videos way to assess the functioning of our technique with other state of the art algorithms which have already taken these videos as input. the results disclosed here are on the "foreman" video. the video collections were extracted from an open database from xiph.org [23] which contains non-copyrighted and copyrighted type videos (to avoid copyright issues, the authors of the current paper considered only non-copyrighted videos). the frames were separated for further processing. the original high-resolution video was resized to 512×512 pixels. grounded on the observation prototype, the entered lr frames had dimensions of 128×128 pixels after down-sampling and were more degraded by the addition of different noise levels. the noise used to degrade frames was gaussian noise with specific snr. the aimed algorithm was executed in matlab (r2018b). the results and analysis are divided into three parts are explained below: • comparison of the proposed algorithm with existing techniques. • analysis of the planned algorithm with diverse noise levels. • analysis of the projected algorithm with different wavelet functions. a. comparison of the proposed algorithm with existing techniques the evaluation of the average values of psnr and ssim results for the proposed method and other techniques is shown in table i. the values from the table itself declare the prominence of the proposed algorithm. the most important characteristic is the simplicity, when concidering its efficiency. the algorithms used for comparison have many pre-processing and hybrid approaches which makes them more complex than the proposed algorithm. the reason behind this elevated performance is that the dwt-centered sr algorithms are further useful to regain the high-level frequency particulars of the specific degraded frames. the real borders are appropriately maintained and noise is eliminated by filtering purposes. for the "foreman" frames, even though the psnr and ssim results attained by the proposed method are greater than the other methods', the performance gain can be boosted by adding other edge preservation and direct mapping techniques. figure 6 shows the behavior of sr methods concerning the average psnr and ssim values. the most important quality metrics, i.e. ssim, have shown a substantial increase by the proposed algorithm. table i. comparative analysis of the proposed algorithm with existing methods method nearest bicubic nedi [11] dwtdiff [18] dwtswt [19] srdwt [16] proposed quality metrics avg. psnr 20.89 22.02 21.19 18.97 19.83 23.88 24.9 avg. ssim 0.61 0.7 0.7 0.47 0.50 0.84 0.897 b. analysis of the proposed algorithm with diverse noise levels the robustness of the proposed algorithm is validated with different noise levels, varying from 50db to 25db with a step of 5db. the sampled noisy frames of the "foreman" video are shown in figure 8. the frames were already down-sampled by a scale of 1/4th to the original. the db1 wavelet function was used. fig. 6. comparative analysis of the proposed algorithm with other sr methods. table ii. results for different noise levels noise in db 50 45 40 35 30 25 avg. psnr 25.01 25.01 25 24.98 24.9 24.68 avg. ssim 0.9067 0.9064 0.9057 0.9036 0.8970 0.8774 the average psnr and average ssim values after upgrading the quality are shown in table ii. figure 7 shows the graph for quality metrics with different noise levels. it can be seen that the proposed algorithm gives better results in a variety of noise levels. the psnr values are not affected much but the ssim values have significantly decreased. this can be concluded as the addition of noise significantly affect structural similarities. fig. 7. effect of different noise levels on super-resolution process. c. analysis of the proposed algorithm with different wavelet functions the literature provides different wavelet functions which have been tried with varying results. to check and analyze the variation in the efficiency of the proposed algorithm according to the wavelet function, all the parameters were kept stable and the noise level at 30db. in the literature, the daubechies family is explored in the super-resolution process, but not all functions are used except db2, db7/9 which are having wide applicability. this paper utilized db1, db2, db7, and db9 wavelet functions engineering, technology & applied science research vol. 11, no. 4, 2021, 7477-7482 7481 www.etasr.com daithankar & ruikar: analysis of the wavelet domain filtering approach for super-resolution videos for the proposed algorithm. the results are tabulated in table iii. figure 8 shows the graph for the proposed algorithm using different wavelet functions. table iii. analysis of the proposed algorithm with different wavelet functions wavelet function db1 db2 db7 db9 avg. psnr 24.9 21.79 14.18 13.58 avg. ssim 0.897 0.8582 0.6774 0.6455 the db1/haar function gives the most promising results due to its component reconstruction capability. many researchers prefer db2 for decomposition and reconstruction purposes, but in this case, db1 provides more efficacy in reconstruction while being simpler than the db2. fig. 8. effect of different wavelet functions on the sr process. the surveyed recent papers show that there is still a scope for efficiency improvement in object detection areas like face [21] and logo [22] recognition. the decision of recognition is based on the processes applied to the input data. but input pictures with low quality increase the complications in the final decision making. to avoid such circumstances, quality details in the input data are needed. this mends the interest in the sr area. vi. conclusion the current paper explored a simpe algorithm for the analysis of the effect of wavelet domain filtering in visual quality upgradation of low or degraded videos. this technique is based on wavelet residual mapping and interpolation. the robustness of the wavelet filtering approach is investigated for different noise levels and different wavelet functions and it can be said that the proposed algorithm surpasses the other popular methods from the same domain. simplicity and efficiency are the two main advantages of the proposed algorithm. the purpose behind developing this algorithm is to reduce the complexity. as the mapping of low-frequency information with wavelet residues gives promising results, the embedding of the wavelet domain with neural networks for learning this sr mapping will hopefully succeed. references [1] m. v. daithankar and s. d. ruikar, "video super resolution: a review," in icdsmla 2019, singapore, asia, 2020, pp. 488–495, https://doi.org/10.1007/978-981-15-1420-3_51. [2] m. v. daithankar and s. d. ruikar, "video super resolution by neural network: a theoretical aspect," journal of computational and theoretical nanoscience, vol. 17, no. 9–10, pp. 4202–4206, jul. 2020, https://doi.org/10.1166/jctn.2020.9045. [3] g. pandey and u. ghanekar, "a compendious study of super-resolution techniques by single image," optik, vol. 166, pp. 147–160, aug. 2018, https://doi.org/10.1016/j.ijleo.2018.03.103. [4] l. yue, h. shen, j. li, q. yuan, h. zhang, and l. zhang, "image superresolution: the techniques, applications, and future," signal processing, vol. 128, pp. 389–408, nov. 2016, https://doi.org/10.1016/ j.sigpro.2016.05.002. [5] d. thapa, k. raahemifar, w. r. bobier, and v. lakshminarayanan, "a performance comparison among different super-resolution techniques," computers & electrical engineering, vol. 54, pp. 313–329, aug. 2016, https://doi.org/10.1016/j.compeleceng.2015.09.011. [6] j. tian and k.-k. ma, "a survey on super-resolution imaging," signal, image and video processing, vol. 5, no. 3, pp. 329–342, sep. 2011, https://doi.org/10.1007/s11760-010-0204-6. [7] r. y. tsai, "multiframe image restoration and registration," advances in computer vision and image processing, vol. 11, no. 2, pp. 317–339, 1984. [8] s. p. kim, n. k. bose, and h. m. valenzuela, "recursive reconstruction of high resolution image from noisy undersampled multiframes," ieee transactions on acoustics, speech, and signal processing, vol. 38, no. 6, pp. 1013–1027, jun. 1990, https://doi.org/10.1109/29.56062. [9] s. rhee and m. g. kang, "dct-based regularized algorithm for highresolution image reconstruction," in international conference on image processing, kobe, japan, oct. 1999, vol. 3, pp. 184–187 vol.3, https://doi.org/10.1109/icip.1999.817096. [10] x. zhang and y. liu, "a computationally efficient super-resolution reconstruction algorithm based on the hybird interpolation," journal of computers, vol. 5, no. 6, pp. 885–892, 2010. [11] x. li and m. t. orchard, "new edge-directed interpolation," ieee transactions on image processing, vol. 10, no. 10, pp. 1521–1527, oct. 2001, https://doi.org/10.1109/83.951537. [12] l. zhang and x. wu, "an edge-guided image interpolation algorithm via directional filtering and data fusion," ieee transactions on image processing, vol. 15, no. 8, pp. 2226–2238, aug. 2006, https://doi.org/ 10.1109/tip.2006.877407. [13] h. ji and c. fermuller, "robust wavelet-based super-resolution reconstruction: theory and algorithm," ieee transactions on pattern analysis and machine intelligence, vol. 31, no. 4, pp. 649–660, apr. 2009, https://doi.org/10.1109/tpami.2008.103. [14] a. muthukrishnan, j. charles rajesh kumar, d. vinod kumar, and m. kanagaraj, "internet of image things-discrete wavelet transform and gabor wavelet transform based image enhancement resolution technique for iot satellite applications," cognitive systems research, vol. 57, pp. 46–53, oct. 2019, https://doi.org/10.1016/j.cogsys.2018.10.010. [15] s. izadpanahi and h. demirel, "motion based video super resolution using edge directed interpolation and complex wavelet transform," signal processing, vol. 93, no. 7, pp. 2076–2086, jul. 2013, https://doi.org/10.1016/j.sigpro.2013.01.006. [16] w. witwit, y. zhao, k. jenkins, and s. addepalli, "global motion based video super-resolution reconstruction using discrete wavelet transform," multimedia tools and applications, vol. 77, no. 20, pp. 27641–27660, oct. 2018, https://doi.org/10.1007/s11042-018-5941-5. [17] a. temizel, "image resolution enhancement using wavelet domain hidden markov tree and coefficient sign estimation," in ieee international conference on image processing, san antonio, tx, usa, oct. 2007, vol. 5, pp. v-381-v–384, https://doi.org/10.1109/icip.2007. 4379845. [18] h. demirel and g. anbarjafari, "discrete wavelet transform-based satellite image resolution enhancement," ieee transactions on geoscience and remote sensing, vol. 49, no. 6, pp. 1997–2004, jun. 2011, https://doi.org/10.1109/tgrs.2010.2100401. [19] h. demirel and g. anbarjafari, "image resolution enhancement by using discrete and stationary wavelet decomposition," ieee transactions on image processing, vol. 20, no. 5, pp. 1458–1460, may 2011, https://doi.org/10.1109/tip.2010.2087767. [20] z. wang, a. c. bovik, h. r. sheikh, and e. p. simoncelli, "image quality assessment: from error visibility to structural similarity," ieee engineering, technology & applied science research vol. 11, no. 4, 2021, 7477-7482 7482 www.etasr.com daithankar & ruikar: analysis of the wavelet domain filtering approach for super-resolution videos transactions on image processing, vol. 13, no. 4, pp. 600–612, apr. 2004, https://doi.org/10.1109/tip.2003.819861. [21] y. said, m. barr, and h. e. ahmed, "design of a face recognition system based on convolutional neural network (cnn)," engineering, technology & applied science research, vol. 10, no. 3, pp. 5608–5612, jun. 2020, https://doi.org/10.48084/etasr.3490. [22] a. alsheikhy, y. said, and m. barr, "logo recognition with the use of deep convolutional neural networks," engineering, technology & applied science research, vol. 10, no. 5, pp. 6191–6194, oct. 2020, https://doi.org/10.48084/etasr.3734. [23] "xiph.org : derf’s test media collection." https://media.xiph.org/ video/derf/ (accessed aug. 02, 2021). authors profile mrunmayee v. daithankar is working as a senior research fellow by attaining the national doctoral fellowship promoted by the all india council of technical education (aicte), delhi. she is carrying out her research in electronics engineering at walchand college of engineering sangli, maharashtra (india), under the guidance of dr. sachin d. ruikar. her research interests lie in the areas of image/video processing and neural networks. before joining the fellowship, she worked as an assistant professor for three and a half years in sinhgad institute’s college of engineering, pandharpur. she has completed her graduation in electronics and telecommunication engineering from sveri’s c.o.e, pandharpur, in 2011. in 2014, she received her postgraduate degree in electronics engineering from sinhgad institute’s c.o.e, pandharpur, affiliated to solapur university, solapur. sachin d. ruikar has received a graduate degree in electronics and telecommunication from the government engineering college, aurangabad, under the aegis of dr. b. a. m. u. aurangabad, in 1998. he has received thepostgraduate degree in electronics and telecommunication engineering from government engineering college, pune university, india in 2002. he has completed his ph.d. in the electronics under shri guru gobind singh institute of engineering technology, srtmu nanded, in 2013. presently, he is working as an associate professor in electronics engineering at walchand college of engineering, sangli, maharashtra. his research interests include image denoising with wavelet transforms, image fusion, image painting and image superresolution. microsoft word 38-2972_s_etasr_v9_n4_pp4520-4524 engineering, technology & applied science research vol. 9, no. 4, 2019, 4520-4524 4520 www.etasr.com shamsan et al.: micrometer and millimeter wave p-to-p links under dust storm effects in arid climates micrometer and millimeter wave p-to-p links under dust storm effects in arid climates zaid a. shamsan electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university, riyadh, saudi arabia zashamsan@imamu.edu.sa moath alammar electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university, riyadh, saudi arabia moath14121@hotmail.com abdullah alharthy electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university, riyadh, saudi arabia abdullah-alharthy@outlook.sa abdulaziz aldahmash electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university, riyadh, saudi arabia aziz.dahmash@gmail.com khalid. a. al-snaie electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university, riyadh, saudi arabia kalsnaie@imamu.edu.sa abdulaziz m. al-hetar faculty of engineering and information technology, taiz university, taiz, yemen alhetaraziz@gmail.com abstract—a dust storm is the main attenuation factor that can disturb receiving radio signals in arid climate condition as in saudi arabia. this paper presents a study on the effect of dust storms on the received radio frequency power in a homogenous environment in the city of riyadh. a number of micrometer and millimeter wave links have been considered along with several measured dust storm data to investigate the dust storm effects. the results showed that dust storm can critically influence the communication link and this effect grows up as the physical distance between the transmitter and the receiver increases. the negative effect of the dust storm apparently appears at highfrequency bands allocated for the next communication generation (5g) which imposes finding solutions to mitigate the effects of this phenomenon. keywords-dust storm; millimeter waves; arid climate; attenuation; receiver sensitivity i. introduction in the fifth generation (5g) wireless networks, which are expected to be introduced around 2020, there will be some changes, including dramatic changes in the design of different layers for the next generation communication systems. massive multiple input multiple output (mimo) systems, filter bank multi-carrier (fbmc) modulation, relaying technologies, and millimeter-wave (mmwave) communications have been considered as some of the strong candidate techniques for the physical layer design of 5g networks [1]. the frequency spectrum represented by mmwave bands is most likely to be used in 5g networks, while mmwave capability can provide a huge amount of spectrum resources. regardless of the high data rate possibly offered by mmwave, quite a lot of practical difficulties in its use in mobile networks are evident. these difficulties include large path loss, low penetration capability, narrow beam width, fading phenomena due to rain and sand storms, or fading loss due to diffraction, etc. [2-5]. rain and snow attenuation are predominant factors in regions such as america, europe and other continental areas, while sand and dust storms are observed in some arabic countries, such as saudi arabia, and arid parts of australia, and dry states such as texas and arizona. dust storms occur when there are two conditions: the first one is the existence of dry and disjointed soil with no vegetation cover, and the second is high speed wind. the mechanics of the emergence of a dust storm can be explained as follows: when convection currents are created due to the heating of the earth surface, the air above the earth surface becomes warm and then rises up as convection currents. this causes variations in atmospheric pressure and heat, and leads relatively cold winds to be pushed to replace the previous convection currents site, which in turn make dust rise up and carry soil grains up to a level that is proportional to wind power and soil dryness and disintegration. nowadays, prediction of dust storms has become easy given the availability of metrological data [6]. however, a significant concern in this matter is the fading or signal attenuation caused by the sand storms. the attenuation factor is varying according to regional meteorological conditions. authors in [7] focused on dust storm attenuation as a uniform distribution of a specific geometric shape. in this paper, we estimate the attenuation caused by a dust storm, especially on p-to-p terrestrial signals and recommend a solution to avoid power loss due to attenuation over the 5g frequencies. the saudi capital riyadh, located on the center of the saudi desert, is experienced with continuous sand storms. the statistics for the number of sand storms per year in saudi arabia during the period 2010-2017 show that the number of sand storms per year ranges between corresponding author: zaid a shamsan engineering, technology & applied science research vol. 9, no. 4, 2019, 4520-4524 4521 www.etasr.com shamsan et al.: micrometer and millimeter wave p-to-p links under dust storm effects in arid climates 83 in 2014 and 212 in 2012 [8]. among the last observed stand storms, some of them were so strong that the visibility was very low. for example, a huge dust storm engulfed riyadh city and covered most of its parts on the 10th of march 2009 [9]. it stayed for hours after it started, and visibility highly diminished from kilometers to just very few meters within thirty seconds. in this study, we assume the worst case scenario in which a uniform distribution of dust storm has been considered in order to be in the safe side of received signal prediction. ii. method and proposed scenario the wireless point to point (p-to-p) link is proposed to be within an urban area in riyadh city. the transmitter is placed in al-washm at a level of 603.6m above sea level (asl) while the international king khalid airport (ikka) at 623.7m (asl) has been considered to be the receiver point, see figure 1. fig. 1. google map showing ikka and al-washm sites in riyadh (google llc). the distance between the two points is 34.750km. riyadh area is considered as an arid area, characterized by dust and sand storms. thus, the signal potentially undergoes the sand storm effect. this scenario is shown in figure 2. fig. 2. the proposed scenario (dust storm environment) the p-to-p has been installed and the system specifications (transmitter and receiver parameters) have been defined with the help of the radio mobile tool [4-5] and the channel propagation is assumed to be free space in order to study the worst case scenario. the power is calculated at the receiver under the influence of a homogenous dust storm. then, the received power has been calculated under the abovementioned effects. the received power and the receiver sensitivity are compered and the results are collected. this method is summarized in the flow chart shown in figure 3. fig. 3. the flow chart for the proposed method system installing has been carried out by defining the main specification of the p-to-p system with the help of the radio mobile tool, and the propagation channel loss has been computed using friis’ formula. in this formula, we can compute the receiver power, when the following parameters are known: transmitter power �� , gain of the transmitter and receiver antenna �� and �� , respectively, and the channel propagation loss l. firiis’ formula is given by: �� � ����� �� (1) where ��� is the free space loss which mainly depends on the wavelength of the travelling signal �, and the distance between the transmitter and receiver �. this factor can be defined as: ��� � ��� � � ���� � (2) where � is the light speed and � is the frequency of the p-to-p link signal. for dust storm effect estimation, due to the fact that when an object (rain drop/particle) is illuminated by a wave, some of the incident power is absorbed and another part is scattered. thus, the attenuation due to the dust storm can be explained in terms of scattering cross-section of a single particle [10, 11]. the total attenuation, in db, caused by a dust storm over a link has a length of l can be given as: � � � �� ��� �� (3) this solution can be executed by either rayleigh approximation or mie solutions [12]. due to the fact that rayleigh approximation is based on the assumption that !≪�, it is difficult to use it for frequencies bigger than 37ghz [13], while mie solution has not that limitation and can be used to predict attenuation in various frequency bands with high reliability particularly at higher frequencies. therefore, this paper proposes the mie model [14] to be used to estimate the engineering, technology & applied science research vol. 9, no. 4, 2019, 4520-4524 4522 www.etasr.com shamsan et al.: micrometer and millimeter wave p-to-p links under dust storm effects in arid climates dust attenuation �� , in db/km, as a function of the signal wavelength �, visibility $, radius of dust particles %, and dielectric constants of the dust particles for the real and imaginary parts ε' and ε'', respectively. �� � 94.3*+ ,.� + 3721.2*3 ,-4 .�4 + 23381*6 ,-7 .�7 (4) where *+, *3 and *6 are constants whose values depend on the real (ε') and imaginary (ε'') parts of the dielectric constant of the particles. these constants are: *+ � 8ɛ:: ;ɛ:<3=><ɛ::> (5) *3 � ɛ?? @ 8 a bɛ:><bɛ::><�ɛ:c3� d;ɛ:<3=><ɛ::>]> + + +a + + 6d;3ɛ:<6=><�ɛ::>] a +f (6) *6 � � 6 d gɛ:c+h>;ɛ:<3=<i3gɛ:c+hgɛ:<3hcjk<ɛ::7 d;ɛ:<3=><ɛ::>]> ] (7) visibility $ can be expressed in terms of particle density as: $ � a.a×+� m7 n,-> (8) where o is the dust particle number per volume unit of air in the unit of particles per cubic meter and ! is the radius of dust particles in meters. iii. system specification and parameters the key parameters for the point to point link system are listed in table i. various frequencies were used to study the dust storm effects. receiver sensitivity for each link with different frequency has also different values. in addition, values of dielectric constant vary with each carrier frequency operation. table i. the main parameters of p to p links link 3 [4] link 2 [15] link 1 [15] parameters 38, 60, 100 26 3.9 frequency, ghz 43.01 18 32 transmitter power, dbm -103.02 -77 -69 receiver sensitivity, dbm 17 40 40 transmitter antenna gain, db 50 transmitter height, m 2 40 40 receiver antenna gain, db 30 receiver height, m 0.16 waveguide loss, db/m 34.725 physical link separation, km ɛ? � 3.50 ɛ?? � 1.64 ɛ? � 4.56 ɛ ?? = 0.25 ɛ ? = 4.56 ɛ ?? = 0.25 dielectric constants measurements of dust storm have been carried out and readings were recorded and are listed in table ii [16]. the measurements have been carried out in riyadh with the use of passive collectors manufactured according to the astmd1739 [17]. each collector/bucket has an open topped cylinder with vertical sides and a flat bottom, its minimum diameter is 15cm with a depth of 2-3 times the diameter. the buckets are located at different heights above ground on the receiving tower. the collected dry samples were mixed in a watch-glass and then few drops of distilled water have been added in order to sediment the mixture. the resulted slurry is diluted up to approximately 100ml, and then it was boiled with low pressure to separate any superfluity air bubbles. a system called sedimentation balance was used to record particle weight that fell in the sedimentation fluid in terms of height and time. finally, stokes law was used to calculate the particle diameter d. table ii. dust storm measurement readings visibility (km) particle average diameter (µm) 0.6 21.25 1 15.3 2 9.8 4 8.2 iv. results and discussion this part of the paper analyzes and discusses the computed received power at ikka receiver antenna from a transmitter at al-washm zone under various dust storm measurements in riyadh. from the readings in table ii, it can be seen that there are four measurement categories. the first one is with visibility of 0.6km and particle radius of 21.25µm. this case seems the worst case because the signal experienced higher particle radius and lower visibility. whereas in the rest three cases, the particle radius decreases and visibility increases. table iii shows the corresponding free space loss due to signal propagation for ikka and al-washm sites. in table iv, the results of sand storm attenuation indicate that the signal fading is directly and inversely proportional to particle radius size and visibility degree. when a dust storm is strong then the visibility degree is low and the signal fading becomes high and vice versa, whereas when the particles radius size is small the signal fading becomes also small. table iii. free space propagation loss link 3 link 2 (26ghz) link 1 (3.9ghz) 100 ghz 60 ghz 38ghz 161.3164 158.8176 154.8503 151.5541 135.0759 lfs (db) table iv. dust storm attenuation of the link paths ae (µm) v(km) ad (db/km) link 1 (3.9ghz) link 2 (26ghz) link 3 38ghz 60ghz 100ghz 21.25 0.6 0.0526 1.1663 3.0939 4.8849 8.1414 15.3 1 0.0226 0.5035 1.3365 2.1103 3.5171 9.8 2 0.0073 0.1632 0.4324 0.6759 1.1264 8.2 4 0.0031 0.0676 0.1788 0.2828 0.4713 the distance versus power received for link1 is depicted in figure 4 on which power decreases when distance increases. figure 4 also shows that when the particle radius of dust increases and visibility decreases, then attenuation will increase. in addition, it can be seen that the power received is always greater than the receiver sensitivity which is -69dbm, and this means there is no effect of the dust storm on the receiver performance due to the fact that the link 1 employs a microwave carrier frequency of 3900mhz. the power level is about -27dbm, i.e. there is a margin of 42db from the receiver sensitivity. on the other hand, if the carrier frequency is increased to 26ghz as shown in figure 5, there will be not much difference in terms of the receiver performance, but the power margin is decreased to 19dbm. the relation of low visibility and large dust particle size with received power starts engineering, technology & applied science research vol. 9, no. 4, 2019, 4520-4524 4523 www.etasr.com shamsan et al.: micrometer and millimeter wave p-to-p links under dust storm effects in arid climates to be clear in figure 5 in which the worst case leads to weaken received power. all four cases in links 1 and 2 are good enough to receive the signal power from transmitter at 34.7km with no critical fading created by the sand storm. in figure 5, the power received value for all cases is approximately in the range between -58.3 and -57.19db, which is greater than the sensitivity, so the signal quality is good enough to be received. fig. 4. physical distance versus received power for link1. fig. 5. physical distance versus received power for link 2. regarding link3, we have another three cases with three different frequencies: 38, 60 and 100ghz with a fixed receiver sensitivity of 103.02dbm for all cases. using 38ghz, at the receiver palace ikka, the power signal will be received under all four dust storm conditions, as shown in figure 6. however, at 13km distance after the ikka (d=48km) the receiver will not be able to sense the transmitted signal especially for the worst dust storm condition of visibility of 0.6km and dust particle size of 21.25µm. the situation will be worse when the link uses 60ghz. in this case, restrictions on using this frequency should be considered spatially when the visibility is lower than 600m and 1000m. for these two conditions (with visibility of 0.6 and 1km), the signal can’t be captured by the receiver due to the fact that the power level of the received signal, 107.4 and 103.4dbm respectively, is lower than the receiver sensitivity at ikka, as shown in figure 7. the signal at ikka, for the other two cases (with visibility of 2 and 4km), will not be affected because the power received is -101.3 and -100.8dbm for visibility of 2 and 4km, respectively. however, the signal will deteriorate after about 10km from ikka (i.e. at a distance greater than 44km from the transmitter). for the link3 with carrier frequency of 100ghz as shown in figure 8, the signal will not be received for all visibility cases due to high dust attenuation. the power level at ikka is about -117.2, -109.7, -106.6 and -105.8dbm for visibility of 0.6, 1, 2 and 4km, in the same order. the maximum distance between the transmitter and the receiver with sensitivity of -103.02dbm is 15.5, 20, 24 and 27km for visibility of 0.6, 1, 2 and 4km, respectively. fig. 6. the physical distance versus power received for link3 at 38ghz. fig. 7. the physical distance versus power received for link3 at 60ghz. fig. 8. the physical distance versus power received for link3 at 100ghz. therefore, as a solution, the use of an rf relay system every 15.5, 20, 24 and 27km for all abovementioned visibility conditions of the same order is suggested. also, the transmitter power can be increased during dust storms to compensate the attenuation. in addition, data rate reduction, adjusting modulation and coding techniques are also mitigation solutions that can be used to mitigate the problem. v. conclusion this paper presents a study of the dust storm effect on communication channel performance in the arid area of engineering, technology & applied science research vol. 9, no. 4, 2019, 4520-4524 4524 www.etasr.com shamsan et al.: micrometer and millimeter wave p-to-p links under dust storm effects in arid climates riyadh, saudi arabia. measured dust storm data have been employed to investigate this factor. it was shown that severe dust storm may result to radio link interruption due to dust attenuation, especially in high frequency, large communication link, low visibility and large particle size conditions. these situations need technical mitigation schemes such as using an rf relay system, power control and/or adaptive modulation. references [1] e. basar, “index modulation techniques for 5g wireless networks”, 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environment (1967), vol. 21, no. 12, pp. 27232725, 1987 [17] astm, astm d1739-70: standard method for collection and analysis of dustfall, astm d1739-70, 1982 microsoft word 18-3394_s engineering, technology & applied science research vol. 10, no. 2, 2020, 5441-5447 5441 www.etasr.com sabir et al.: towards a new model to secure iot-based smart home mobile agents using blockchain … towards a new model to secure iot-based smart home mobile agents using blockchain technology badr eddine sabir laboratory of watch for emergent technologies fst, hassan i university settat, morocco b.sabir@uhp.ac.ma omar bouattane laboratory of ssdia enset, university of hassan ii casablanca mohammedia, morocco o.boattane@gmail.com mohamed youssfi laboratory of ssdia enset, university of hassan ii casablanca mohammedia, morocco med@youssfi.net hakim allali laboratory of watch for emergent technologies fst, hassan i university settat, morocco hakim-allali@hotmail.fr abstract—the internet of things (iot) is becoming an indispensable part of the actual internet and continues to extend deeper into the daily lives of people, offering distributed and critical services. mobile agents are widely used in the context of iot and due to the possibility of transmitting their execution status from one device to another in an iot network, they offer many advantages such as reducing network load, encapsulating protocols, exceeding network latency, etc. also, the blockchain technology is growing rapidly allowing for the addition of an approved security layer in many areas. security issues related to mobile agent migration can be resolved with the use of blockchain. this paper aims to demonstrate how blockchain technology can be used to secure mobile agents in the context of the iot using ethereum and a smart contract. the transactions within the blockchain are used to detect the malevolent mobile agents that could infiltrate the iot systems. the proposed model aims to provide a secure migration of mobile agents to ensure security and protect the iot applications against malevolent agents. the case of a smart home with multiple applications is applied to verify the proposed solution. the model presented in this paper could be extended to a wider selection of iot systems outside of the smart home. keywords-internet of things; smart home; blockchain; ethereum; smart contract; solidity; multi-agent systems; mobile agents i. introduction iot is growing exponentially in the area of telecommunications and it will be an indispensable part of the future internet [1-4]. it is referring to an approach where an extensive number of physical objects are interconnected and connected to the internet [5]. it is a part of pervasive and ubiquitous computing networks offering distributed and transparent services [6]. iot enables heterogeneous devices to interconnect to support various applications to serve users with different requirements [7-8] and is considered to be a good way to achieve smart city [9-10]. mobile agents are widely used in the context of the iot and due to the possibility of transmitting their execution status in an iot network, they offer many advantages such as reducing network load, encapsulating protocols and exceeding network latency. an agent-oriented infrastructure enables flexible coordination between iot devices including robots, smartphones, and sensors. agentbased systems enable cognitive management without constant human intervention [11-12]. functionalities such as smartness, autonomy and dynamicity are required for iot based infrastructure and can be offered by the presence of agents [11]. besides using agents, processing can be performed closer to actual data sources to reduce the cost of processing [13]. the use of mobile agents in an iot network is highly recommended due to their advantages [14]. authors in [7] showed that mobile agents can be represented by mobile javascript code (agentjs) that can be modified at run-time by agents that are processed by a modular and portable agent platform jam in a protected sandbox environment encapsulating agent processes. the proposed approach enables agents to migrate between different host platforms including web browsers by migrating the program code of the agent, embedding the state and the data of an agent, too, in an extended json+ format. authors in [4] presented mobile agents based on web technologies in the context of iot. in the proposed approach, agents can move between different devices, and if necessary, it is also possible to clone agents to create numerous instances. this model enables the creation of increasingly complex configurations, where device and context-specific decisions can also be taken. this approach increases the flexibility of the system design and evolution of iot since the new code can add new functionalities and adapt the device to new requirements. moving code and especially agents can also be used to add autonomous intelligence to systems. authors in [15] propose a distributed software-defined multi-agent architecture for unifying iot applications. this corresponding author: badr eddine sabir engineering, technology & applied science research vol. 10, no. 2, 2020, 5441-5447 5442 www.etasr.com sabir et al.: towards a new model to secure iot-based smart home mobile agents using blockchain … architecture can tackle the main challenges that the iot faces, including heterogeneity, interoperability, scalability, flexibility, and security of iot applications. authors in [16] present an architecture based on mas, soa, and semantic web technologies to automate the integration and management of devices in iot environment. a prototype system was implemented and tested in a simulated environment of a manufacturing context. in this context, the system demonstrated the ability to adapt incorporating new features and flexibility. in [17], a framework for iot was presented which uses mobile agents for information transfer. the proposed approach can update information like the availability and usability of services dynamically. it also has speech processing modules to provide solutions using voice-based commands and prompts. mobile agents are widely used in the field of iot. therefore, the questions of how to ensure security during the process of migration of the mobile agents and protect the iot application against malevolent agents arise. authors in [18] describe four kinds of threat scenarios faced while using mobile agents: agent corrupts the platform (acp), platform corrupts agent (pca), agent corrupts agent (aca) other malicious entities (third-party programs) corrupt agent (oca). in this paper, we present an architecture model to secure mobile agents and protect them against different types of threats in the context of the iot. the proposed model aims to provide a secure migration of mobile agents to ensure security and protect the iot applications against malevolent agents using a smart contract [19]. the data in the blockchain is unchangeable once published and can help neutralize any attempt to altering the agent code source. the blockchain approach provides the logging of events in a tamper-proof manner which allows us to detect any mobile agent that has turned malicious. it can be used to provide high trust in secure transactions in a heterogeneous network [20]. once such a mobile agent is detected, the security agent isolates and destroys it. the case of a smart home can be a very suitable application of iot to verify the proposed solution, as it involves a variety of devices and parameters to be connected [21], however, the presented model could be extended to a wider selection of iot systems. ii. related work in this section, the related work is described with regard to the security of mobile agents in a multi-agent environment. authors in [13] provide a methodology to improve brosmap and make it a lightweight protocol to fulfill the needs of multiagent based iot systems in general. they offer a new eccbrosmap which is equivalent in security with the rsabrosmap and implement both rsa-brosmap and eccbrosmap before presenting a comparative performance study and implementation results of ecc-brosmap against rsa-brosmap. authors in [22] illustrate the use of mobile agent systems in distributed applications in the domain of ambient intelligence. they focus on the ability to improve privacy by hiding information using the agent architecture. the shown scenario clarifies the necessity to consider the particular security requirements of mobile agents. authors in [23] introduce agent identity in distributing the symmetric key to the newly attached agents of the platform. during the registration of the agent and its services at the platform, it must obtain the key from the key distribution process. the authors proposed a novel idea in fixing the identity of the agent for getting its shared key from the key distribution process. every trusted agent in a platform has a tiny hardware called usb dongle, which is password protected. it is configured during the initial environment formation. authors in [24] propose a security framework that can be effectively used to protect agents from attacks by malicious hosts. the framework is based on restricting the access level of the agent according to the trust level that is assigned to the current host. certain methods can only be executed on certain hosts that are minimally trusted. methods that cannot be executed on a host are kept encrypted. data are also selectively accessible according to the trust placed on the host. in traditional security methods, discovering the determined private key is enough for message decryption that can be done through malicious attacks to the network nodes or listening to communication links. accessing the private key can be considered as the endpoint of a malicious process. authors in [25] propose an approach to improve private key security using two strategies: encrypting the private key using an encryption algorithm (aes algorithm is used in this paper) and breaking the encrypted private key into different units. a secure authentication model based on ibc for the multi-agent of a single domain, giving a second authentication model based on ibc for multi-agent of multi-domain was proposed in [26]. authors in [27] described the general security requirements for mobile agent systems and existing security measures. especially, they pointed out some weaknesses in the field of protecting the carried data of mobile agents. to mitigate this issue, they implemented a trust and reputation management to provide a secure path for mobile agent data protection. our work aims to present a simple approach to guarantee the security of the migration of mobile agents in an iot network by ensuring maximum flexibility and without degrading performance. iii. background a. blockchain technology in 2008 the blockchain was first propagated through bitcoin [28] to assure all parties that the payer had the means to satisfy the debt before concluding any transaction [29]. basically, bitcoin was created with blockchain technology to transfer money, but now blockchain is used in many other areas. a blockchain [28] is a decentralized distributed database that maintains a continuously growing list of data in a public or a private peer-to-peer network. duplicated to all the peer nodes of the network, blockchain offers a secured system, between untrusted collaborators, which everyone on the network can check and interact with, but no one can control or alter. this allows the blockchain to be a trustworthy source without the requirement of a third-party [30]. a blockchain is a series of blocks. every block has itw own cryptographic hash code, previous block hash, and its data [31]. as shown in figure 1, each block in the blockchain is connected to the previous block, containing a hash of the previous block. as a result, the engineering, technology & applied science research vol. 10, no. 2, 2020, 5441-5447 5443 www.etasr.com sabir et al.: towards a new model to secure iot-based smart home mobile agents using blockchain … history of transactions on the blockchain cannot be altered or deleted without completely changing the content of the blockchain [32]. a blockchain network is formed by one or more nodes. a node can be any electronic device (a computer, a telephone, etc.) if it is connected to the internet and has an ip address, and each node has a complete and separate copy of the blockchain. all these nodes connect to form a blockchain network. a transaction is not sent to the network but rather to a network node that it communicates with the other network nodes. fig. 1. simplified diagram of a blockchain network the blockchain has several characteristics, among which we can cite [33]: • decentralization: in the blockchain, third parties are not required to verify transactions. consensus algorithms and cryptographic mechanisms are used to maintain data consistency on blockchain networks. • persistency: it is not possible to delete transactions that have already occurred. • auditability: each transaction on the blockchain refers to the previous transaction. this makes it easy to verify and track each transaction. b. ethereum ethereum is a blockchain platform which surpasses some limitations of bitcoin [19]. it allows users to run distributed applications in a decentralized manner. this means that applications running on ethereum are available everywhere and every time [34-35]. ethereum has several elements, the most important of them are [36]: • account: every account on ethereum has a 20-byte address and consists of four parts, namely nonce-counter, storage, ether balance, and contract code. • transaction: transaction in ethereum refers to a signed data package that stores messages. • technology used: ethereum uses several technologies including web technology, client/node implementation, and data storage. • consensus algorithm: ethereum has 3 types of consensus algorithms, namely proof stake (pos), proof of authority (poa), and proof of work (pow). the most common one is pow. the underlying principle in this consensus algorithm is the complicated mathematical puzzles which consume a certain amount of power to find the solution but whose verification is comparatively fast and easy. the process of finding a solution to the puzzle is known as mining, while the nodes executing this process are known as miners. if the miner manages to find the solution (hash), the new block is formed, which is distributed on the network and if validated, the blocks get added, extending the chain. the protocols used for generating the hash for every block are cryptographic hash algorithms like sha256 which compute the hash of the current block considering metadata like the hash of the previous block. this makes each hash unique and any attempt to change the content or metadata of a block will result in an entirely different hash generating a diversion in the chain [30]. c. smart contract it was introduced in 1994 and defined a smart contract as a computerized transaction protocol that executes the terms of a contract [37]. translating contractual clauses into code and embedding them into a property that can self-enforce them was suggested in [38]. within the blockchain context, smart contracts are scripts recorded on the blockchain [39]. since they reside on the chain, they have a unique address. we trigger a smart contract by addressing a transaction to it. it then executes independently and automatically in a prescribed manner on every node in the network, according to the data that were included in the triggering transaction [40]. the nodes in the network interact with the contract by requesting the functions of the contract code once it is deployed on the network. smart contracts are invulnerable and cannot be altered, even by the author, once deployed on the network. smart contracts on ethereum are written in a high-level language and compiled via the ethereum virtual machine. the most used programming language is solidity [41] which we will use to write our own smart contracts. iv. proposed model in recent years, we have witnessed an impressive development of the iot home devices. home automation is a system controlled by a smart device. it can control home appliances such as lights, fans, air conditions, smart security locks, etc [42]. many companies such as google home, amazon echo, and samsung smartthings have released innovative new products that allowed these devices to become widely available. while these devices have a variety of benefits, they also introduce a new target for potential security threats [43]. device providers do not think about device security, supposing that devices in the home environment are trustworthy, and since the consumers do not have the resources to protect themselves from targeted security attacks on their home network, it becomes vulnerable to a variety of potential security threats. so, there is a real need for an intelligent and efficient home security model. a. components of the proposed model the proposed model shown in figure 2 aims to provide a migration of mobile agents while ensuring security and engineering, technology & applied science research vol. 10, no. 2, 2020, 5441-5447 5444 www.etasr.com sabir et al.: towards a new model to secure iot-based smart home mobile agents using blockchain … protection of the iot application against malevolent agents by ensuring non-repudiation and their integrity using blockchain technology. the main components of our model are: • agents: an agent can be attached to a source device to collect information or perform actions on the source device. an agent can migrate to another device keeping its state to perform operations on the destination device. • smart device: extremely useful devices that are making our daily life easier [44] allowing users to configure, access and, control iot devices through a user-friendly interface. fig. 2. proposed model architecture • whitelist: it contains hashes of transactions returned by the ethereum network after the registration of a new agent. an agent identifier (aid) is associated with a transaction hash. • iot gateway: a user can access and control the iot devices using a smart device by accessing the iot gateway. the gateway is responsible for authenticating and monitoring communication between devices, requesting the security agent in the event of an agent migration. • security agent: mainly performs the operations of registering the source code hash of agents who wish to migrate to other devices in the blockchain network and of the verification of the agents after their migration to guarantee integrity, authentication and non-repudiation agents. • iot device: in our architecture, the iot device is a piece of hardware with a sensor. • securityagent.sol: it is a smart contract that provides two functions: o registermobileagent (aid, agenthash): this function allows sending a transaction to the blockchain network to register the source code of the agent. the function takes in two parameters, the hash of the source code of the agent (agenthash) and the agent identifier (aid) and returns the identifier of the transaction recorded in the blockchain (tranactionhash). o retrieveagenthash (transactionhash): this function allows us to recover the hash of an agent's source code from the blockchain network. the function takes the identifier of the transaction that allowed registering the hash of the source code of the agent and returns the hash of the source code of the agent. this smart contract is developed in solidity, which is a contract oriented language, used for writing smart contracts that can be deployed on an ethereum virtual machine. it follows an object-oriented approach and supports features like inheritance and complex data types. • solidity compiler: securityagent.sol is what we call “contract definition”. this code is not executed on the ethereum network, thus we need to compile our “contract definition” using a “solidity compiler” which will produce two separate files. a file which will contain “byte code” which will then be deployed on the ethereum network in the form of a contract instance using in our case truffle which is a development environment and a testing framework that helps the automatic compilation and deploying of contracts on blockchain, and is also used to deploy contracts on a private ethereum blockchain. the compilation will produce an “application binary interface (abi)”. this abi will be used to call the functions exposed by the smart contract instance deployed in the ethereum network using the web3 library. ethereum provides an interface with the ethereum network for developers in the web3.js api. this allows applications to interpret events sent from the ethereum network and to submit transactions to the network [45]. b. secure communication between agents the diagram shown in figure 3 illustrates the migration steps of an agent from a temperature sensor to a smart device in chronological order: • the mobile agent measures and collects information from the temperature sensor. • the mobile agent requests the iot gateway to migrate to the smart device. • the security agent generates the hash of the source code of the mobile agent. • the security agent invokes the “registermobileagent” function of the secureagent.sol smart contract, with passing in parameters the hash of the mobile agent source code and the aid of the agent. • the hash of the agent source code is registered in blockchain ethereum network. engineering, technology & applied science research vol. 10, no. 2, 2020, 5441-5447 5445 www.etasr.com sabir et al.: towards a new model to secure iot-based smart home mobile agents using blockchain … • the result of this operation is an identifier of the transaction validated on the blockchain in the form of a hash of the transaction. • the security agent registers the hash of the transaction in the whitelist by associating it with the aid of the mobile agent for which the source code has been saved in the blockchain. • the iot gateway allows the mobile agent to migrate. • after the migration and the generation of graphs in the smart device, the mobile agent requests to return to the temperature sensor. • the iot gateway requests the security agent to verify the integrity and the authentication of the mobile agent after its migration. • the security agent retrieves the transaction identifier from the whitelist passing in the aid of the mobile agent. fig. 3. sequence diagram: migration of an agent • the security agent invokes the “retrieveagenthash” function of the securagent.sol smart contract passing the transaction identifier. • the hash of the source code of the mobile agent stored in the blockchain is returned to the security agent. • the security agent compares the hash recovered from the blockchain with the current mobile agent hash. • if the hashes are same, then the security agent allows the mobile agent to return to the sensor temperature. • else the security agent destroys the mobile agent. v. conclusion this document presents an overview of the current state of research in the field of mobile agent security in a multi-agent environment, and the utility of employing mobile agents in iot systems such as reducing network load, protocol encapsulation and exceeding network latency. an architecture using the blockchain technology has been presented in this document to secure mobile agents and protect them against different types of threats in the context of the iot using a smart contract deployed in a private ethereum network. the smart home use case with multiple iot devices using mobile agents was applied to verify and explain the proposed solution. though this document presents the smart home use case, there is a potential for this model to be extended to other types 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aperture radar for landmine detection muhannad almutiry electrical engineering department northern border university arar, saudi arabia muhannad.almutiry@nbu.edu.sa abstract—the development of the unmanned aerial vehicle (uav) and communication systems contributed to the availability of more applications using uavs in military and civilians purposes. anti-personnel landmines deployed by militia groups in conflict zones are a life threat for civilians and need cautious handling while removing. the uav tomographic synthetic aperture radar (tsar) can reconstruct three-dimension images of the investigation domain to prescreen nonmetallic landmines. a nonmetallic landmine cannot be detected using conventional ground penetrating radars when the scattering field is undetected due to the dielectric permittivity. in this paper, imaging the underground for detecting landmine using tsar is proposed. the tsar has the capability of prosing the data in discrete mode regardless of the altitude of uav’s radar. a landmine is always buried less than a feet depth. l-band frequency is used to provide high resolution and to penetrate deep in dry soil. more than one uavs are used to multistatic scan the investigation space. the geometric diversity of multistatic distribution of the sensors will provide more information about the buried nonmetallic landmines, certain features, and their location. the data collected from the sensors will align with the geolocation data obtained from the uav’s system for processing. dynamic flying can be used to predict the electromagnetic response of the scattering field to create a dynamic matching filter using the green’s function under first-order born approximation. the occurring air-soil interference has been removed as an unwanted reflection from the ground while keeping the signal coming from underground. using the born approximation assumption created an ill-posed linear system solved by the conjugate gradient algorithm. simulation results are presented to validate the method. keywords-radar; rf tomography; uav; synthetic aperture radar i. introduction there were an estimated one hundred million landmines positioned in many countries by 2009, while their number is increasing by 2 million landmines annually [1, 2]. these hidden weapons pose a serious threat to the civilians living in these regions. while efforts are been conducted to remove these mines, at the ongoing rate of clearance it will take an estimated 1100 years to eradicate them and perform ordinances of unexploded mines through the use of conventional methods of detection such as ground-penetrating radar (gpr) [3]. tsar exhibits three primary attributes that set it apart from alternative sensors: a wide accumulated angle, low-frequency band, and small bandwidth. these attributes facilitate a more effective penetration of the soil, the development of synthetic aperture radar (sar) images that are of a higher resolution, and enable the radar to cover more extensive areas. as such, tsar represents a promising technology for the ongoing efforts to find land mines from a safe distance. moreover, tomography has been effectively employed in many medical and scientific fields. for example, computed tomography (ct) is frequently used to assist diagnosis. the tomographic set of scanning is exploiting the spatial diversity as an x-ray beam is concentrated and scanning in multiple angles around the object is conducted in order to provide the 3-d features [4]. the attenuation that occurs as the object is passed is calculated by the detectors (x-ray receivers) that are facing the x-ray tube. at each point at the circular geometry, the radiation dose that is received relates to an estimation of the attenuation of the object in the direction of the transmission. according to the projection-slice theorem [5] for a given angle position the fourier transform of the signal that is subsequently received relates to a slice of the two-dimensional (2-d) fourier transform. during the process of the ct, a one-dimensional (1d) fft is first performed. this is then processed into a 2-d image that displays the distribution of the attenuation in a polar arrangement. after that, the polar format is transformed into a cartesian format via an interpolation step. the final image is developed via a 2-d inverse that results in the presentation of the 2-d object attenuation map at every position of interest. several studies [6-8] have demonstrated that it is possible to formulate spotlight sar spectral analysis based on azimuth in a comparable technique similar to the tomographic set of medical x-ray scanning [9, 10]. the radar tomographic set is based on linking the radars in one processing network, where it can be expanded to further application [11, 12]. furthermore, the stripmap mode can be performed using a similar process to tomographic processing based on the scanning trajectory [13]. as a result of the small variations in the angles that are of interest during sar processing, more algorithms have been developed for effective image reconstruction [14]. at a high level, the development of the synthetic aperture that is employed in sar represents a tomographic technique. when x-ray tomography is performed, it is not possible to achieve 3corresponding author: muhannad almutiry engineering, technology & applied science research vol. 4, no. 4, 2020, 5933-5939 5934 www.etasr.com almutiry: uav tomographic synthetic aperture radar for landmine detection d imaging. instead, 2-d processing is performed in iterations spanning multiple positions on the object by performing minor step parallel readings of the receiver and transmitter set. this form of ct can be applied to detect mines due to the mutlistatic tomographic radar that can process signals at any evaluation beam level, where a discrimination process can be applied to classify a landmine from a variety of objects at a selected area that is potentially prescreening. having the ability to detect and image objects that are buried in the ground is essential in a range of commercial, military, and civilian settings, i.e. for the exploration of natural resources and detection of tunnels [15]. below-ground imaging techniques that are currently in use have the ability to identify both metallic and nonmetallic artifacts that exhibit higher conductivity than soil [16, 17]. the use of electromagnetic waves to image objects that are located below the ground represents a non-damaging approach to the detection, surveillance, and imaging of below-ground features and irregularities. the performance of below-ground imaging is performed using a process of radio wave transmission and scattering by which radio waves are passed through the ground by the transmitter system, which subsequently measures the waves that are reflected from the targets and determines the effects that the various materials have on the transmitted radio waves. the data that are reflected from the area of interest are primarily received by passing a surface antenna around a circular framework. pulses are transmitted from the airborne uav’s radar downward-looking to the ground with a data link connection for effective and accurate processing. the main difficulty in this scenario is the capturing of the signal caused by reflections of the surface. when the targets are deeply buried, it is easy to separate the surface clutter signal from the target signal. in such cases, it is easy to separate signals using range gating techniques. if the target is very close to the surface, range gating is ineffective because the clutter signal from the surface and the target will be received almost at the same time. thus, the problem is to promote the separation of target signals and ground clutter. tsar can operate at ultranarrow bandwidth (unb) or even at a single frequency in pulse form to reduce the attenuation when these pulses penetrate the ground and come into contact with an underground landmine. the signal attenuation is associated with the bandwidth. the radar system employs a supercomputer to undertake real-time digital processing of the scattering data field collected. when covering large environments, the data rate is substantial, and so a single receiver system using a single frequency is required for realtime processing employing existing down-link hardware. the surface antenna assembles the scattering field data that are reflected and subsequently undergo processing for detection and imaging. dynamic green’s function is used to eliminate the strong surface clutter. in dynamic green’s function technique, the processing of the landmine imaging is done by using just a single frequency. the technique explores an image of a below-ground item that is reconstructed through the application of tsar and 3-d sar using matched filter calculations based on aviation data that permit the collection of circular data collection. ii. land mine detection using electromagnetics land mines are currently detected through the use of metal detectors that evaluate the disruption of a radiated electromagnetic field from the presence of underground metallic objects. one of the primary drawbacks of this approach is that any scrap metal activates the alarm. as such, it represents an inefficient approach to the detection of land mines due to the high rate of false alarms [18]. the gpr is used to transmit electromagnetic waves that penetrate the ground to sense the underground from the reflections that occur at the discontinuities of the dielectric constant. due to its ability to penetrate the ground, ultra-wide band synthetic aperture radar (uwb sar) has emerged as a promising technology that can identify landmines in a large area of land without putting human lives at risk [19-20]. however, like metal detectors, gpr can trigger false alarms due to the presence of irregularities in the soil, for instance, rocks and roots, when hidden markov models were used to classify the background from plastic-cased or completely nonmetal landmines [21-23]. a further issue with gpr is that it is not as effective in terms of detection of smaller mines that are in shallow locations because the soil-surface reflection disguises their response [1, 24]. the x-ray backscattering approach is based on the notion that soil and mines have different attenuation, which leads to detecting landmines [25] although the x-ray generators that are employed in this approach are huge and heavy and require high amounts of power to achieve sufficient penetration. as such, this does not represent a portable method [26]. furthermore, as radiation is involved, its acceptance is limited. the millimeter-wave radar (mmwr) approach is dependent on the concept that the soil has low reflectivity and high emissivity at certain frequencies, while metals have the opposite characteristics [27, 28]. active mmwr employs a source of excitation, but mmwr relies purely on the temperature of the environment. as such, while mmwr represents a promising approach for the detection of metallic objects, it is not effective in the detection of plastic artifacts. iii. related work a number of methods of signal processing have been put forward for improving landmine gpr system performance, including forward scattering radar classification [29], background subtraction, clean algorithm [30], kalman filters [31], likelihood ratio test [32], wavelet packet decomposition [33], and additional two-dimensional filtering [34]. the majority of these methods depends on estimating the background signal through green’s function or calculating a mean value for the unprocessed data collected by gpr and then subtracting the estimated background signal from the received signal. such methods have been widely used for gpr applications but are a compromise at best. an alternative approach that does not need background data has been suggested in [35]: rather than being dependent on background scene data, we can gate out ground reflections, estimate the corresponding parameters, and use this for modeling and subtracting wall contributions from the received data. gpr designed for the detection of buried landmines through multiple probes of the ground across the target area has a similar problem caused by clutter reflection, i.e. reflection engineering, technology & applied science research vol. 4, no. 4, 2020, 5933-5939 5935 www.etasr.com almutiry: uav tomographic synthetic aperture radar for landmine detection from the ground’s surface. this approach involves the application of matched filters for eliminating ground clutter, which can be estimated at the phase center of the scattering field. while gpr requires special filtering, these two challenges have two substantial differences. firstly, for gpr, clutter signals arise from echoes caused by the air/soil medium differences. this means the strong ground clutter will mask the landmines which are very close to the surface. those buried deep down will not be shielded by clutter. secondly, as the clutter/landmine scatting signal is significantly overlapped within frequency domains, filtering will also attenuate the landmine reflection. for numerous gpr applications, the inverse problem of imaging a whole medium is not practical. the inverse problem will generally be nonlinear even when the forward problem is linear. additionally, the inverse problem is generally ill-conditioned, and we have to apply an inversion technique to regularize the solution. in this case, we employ techniques centered in matched filter methodology based on dynamic green’s function for the detection of significant changes in patterns within the cluttered environment, e.g. the appearance/disappearance of targets/target motion, with no knowledge of the background medium. iv. methodology the proposed dynamic green’s function is based on rf tomography imaging introduced at [15, 36]. the tsar model incorporates an electromagnetics source that is mounted into a uav located at an instant time at ��� . the instant time can be determined by combining the information from the global positioning system (gps) and the radar signal to determine the exact distance form the ground. there are many methods to support accurate fly level information, such as lidar. the electromagnetic field radiates toward the ground which is known as the ��� incident field in terms of the target. the area of interest that needs to be constructed for the image is discretized where more than one uav can scan. the target is positioned at �� about 0.1m under the strong ground clutter, and the scattering field �� is comparable to the way of radiating from the airborne uav transmitter. this scattered field, which is known as �� , is recorded by a receiver at ��� . the ��� and �� will have the same polarization unless the target has no properties of changing the reflection polarization. additionally, each respective object is assumed to be isotropic due to the ground environment where the ��� and �� together form the total electric field ���� as: ���� = �� + ��� (1) the incident field can be formed as green’s function with knowing the aviation and sensor parameters to given ���, ��� , and �� as follows: ��� = �ωμ�����,��� (2) the green’s function �����,��� is giving the calculated electromagnetic response at any point in the area of interest with respect to �� , and k is the wavelength number: �����,��� = �� + ∇∇��� ���� ! " # $� %&'�!"(�$' (3) in order to obtain the dynamic green’s function to remove strong air-soil clutter, the propagation number needs to be updated due to the soil dielectric properties. now, we calculate the ground clutter respace above the area of interest ��) as: ��) = )*+, (4) where prf is pulse repetition frequency and c is the speed of light. the green’s function to calculate the clutter �)����,��� is giving the calculated electromagnetic response at any point in the area of interest with respect to ��) : �)���),���� = �� + ∇∇��� ���' $.# / ' %&'�$.(�/ ' (4) the scattered field can be obtained in the integral form of respect to the object function 0���� and the total electric field ���� as follows: �1)2ω,���,���3 = ∭����,����0����e����ω, ���6�� (5) it is not possible to solve the scattered field, �� , from (5) because it is incorporated in ���� and becomes a nonlinear integral equation, as outlined in (1). the incident field can be calculated using (4) and by applying the first-order born approximation to linearize. in addition, 0���� is an unknown element within the imaging problem. it is multiplied by the other unknown, �� that is incorporated in the ���� . it is possible to apply the born approximation to the total electric field ���� to substitute the incidence field ��� to linearize the integral equation as: �1)27,���,��� 3 = ∭����,����0����e���7,���6�� (6) the incident field can be substituted with (2) to produce: �1)2ω,���,���3 = ∭�����,�������,����0����6�� (7) we need now to update the green’s function in the integral by the clutter green’s function: �1)2ω,���, ���3 = ∭�)���), ���������, �������,����0����6�� (8) discretizing (8) to have more flexibility to be adopted into airborne processing while calculating the green’s function as we collect the scattering field in different aviation level and trajectory by dividing the area of interest into p pixels as follows: �1)2ω,���,���3 ≅ 9:0����; ≅ ∑ {�)���), ��� ������,�������,����0����>�?> (9) equation (9) can be mathematically considered in a matrix form to provide an effective and rapid process in digital signal processing in form: ��� = 9��� ⋅ 0 (10) to obtain the object function 0, we will solve (10) as an inverse problem that is an ill-posed and ill-conditioned linear system representing the forward scattering model. however, (9) can only be used to determine single measurements as it relates to a particular orientation and transmitter location, engineering, technology & applied science research vol. 4, no. 4, 2020, 5933-5939 5936 www.etasr.com almutiry: uav tomographic synthetic aperture radar for landmine detection receiver orientation location, orientation, and frequency. in the event any of these parameters are reformed, there is a requirement to obtain a new measurement. as such, there is a need to modify (9) in response to any variations by compiling a set of (q=1, q) airborne uav’s measurements for each divided pixel p as [8, 9]: ab� =  db�ee0b�ee + db�ef0b�ef + db�gh0b�ei + ⋯   +db�fe0b�fe + db�ff0b�ff + db�fi0b�fi + ⋯ (11) +db�ie0b�ie + db�if0b�if + db�ii0b�ii each d value in (11) can be calculated by appropriately reorganizing and modifying (10). expanding the equation outlined above to all pixels in the area of interest and all potential measurement patterns, q, we have: k�>��*�⋮ mno p measurementvector�scattered field� k�>>) �>>b �>>�>*) �>*b �>*⋯�*>) �*>b �*>�**) �**b �**⋯⋮ ⋮ ⋱ mdeeeeeeeefeeeeeeeegh ijjjjjjjjkjjjjjjjjldynamic green's function 2matching filter3 ⋅ st>t*tuvnw p contrastvector2image3 (12) where e is the measured scattering field data collated at various uav’s aviation level, the matched filter h is the calculated green’s function response for the transmitter and the receiver at each z pixel in the area of interest grid, and w is the unknown object function. the inversion technique to recover the object function is given by: w = h(>o (13) the inversion of the ill-posed matrix at (12) can be obtained using the conjugate gradient (cg) algorithm, which is much faster compared to other inversion algorithms such as algebraic reconstruction techniques (art). the inversion algorithm can be done after the prescanning of the area of interest to do offline processing. real-time processing is doable due to independent measurement in discrete form analysis, where the pixels of the area of interest are updated at each scan. v. simulation results the simulation of the landmine detection using uav tsar has been done using feko, which is a computational em simulation software tool. in this simulation, we first need to check the accuracy of the calculated dynamic green’s function, whether it really can estimate the ground clutter or not in order to update the matched filter. in figure 1, we calculated the scattering field at using the same parameters for green’s function and feko simulation, which appear matching at the phase and amplitude of the reflected signal. the matching between the calculated and simulated scattering field indicates an exact update for the dynamic green’s function in the system to predict the effect of the clutter in the received signal. the accuracy of the calculated green’s function will eliminate the clutter by updating the matched filter. furthermore, obtaining the range distance between the uav and the ground improves the accuracy of the calculated clutter response at the matching filter. we are using the simulated radar scattering single received at l-band 500mhz bandwidth to obtain the range distance. the exact range distance of the radar and the measured range distance are shown in figure 2, which can provide the accurate calculation of the clutter response using the green’s function. we placed the radar first at 2.4m then we measured the range distance by the received scattering field. then, we increased the aviation level from the ground by 0.4m to find if the measured range is matching the flying level. as shown in figure 2, the flying level was increased by 0.4m for each position and the measured radar range matched the exact range. for landmine imaging, we show two scenarios with the same number of sensors at two different flying patterns. the operation frequency of both scenarios was at 2ghz. fig. 1. comparing the accuracy of the calculated scattering field. fig. 2. determining the flying ground level using uav radar. in the first scenario, the scattering field from constant circular trajectory flying pattern was simulated as shown in figure 3, while snapshotting the received scattering field at 969 locations around the measurement domain to mimic the airborne uav’s collecting data. the measurement domain contains three cylinders placed 0.075 from the center at shown in figure 4. each cylinder has a diameter of 0.0375m and a height of 0.05m. after the data of the single 2ghz frequency d b engineering, technology & applied science research vol. 4, no. 4, 2020, 5933-5939 5937 www.etasr.com almutiry: uav tomographic synthetic aperture radar for landmine detection were stored at a scattering field vector in multiple snapshot locations, we started to calculate the dynamic green’s function based on the distance obtained from radar range at 500mhz bandwidth at l-band to be added into the matching filter matrix. since the inversion is an ill-posed condition, the inversion between the scattering filed vector and the matching filter matrix has been done using the cg algorithm. the reconstructed xy-plane image of the measurement domain is shown in figure 5 in which the pixel size is 0.00375m. fig. 3. uav collecting data at constant flying attitude. fig. 4. three cylinders at the measurement domain using feko simulation. in the second scenario, we collected snapshot data at erratic flying pattern as shown in figure 6. the snapshot data of the scattering field were collected at a circular trajectory from different flying levels at 969 different locations around the measurement domain. we used a multistatic scanning mode to apply different uav scannings at the same time. the operation frequency is 2ghz with a wavelength of 15cm. the measurement domain contains five cylinders placed in the scene, as shown in figure 7. each cylinder has a diameter of 0.375m spaced equally by 0.075m at the x-axis and y-axis. the x-y plane in figure 8 is the cross-sectional of the z-plane at 0, and the pixel size is 0.00375m. the objects at the measurement domain appear as weak reflections due to the distance between the transmitters and the receivers, the varying uav flying pattern, and the number of snapshot measurements, as shown in figure 8. fig. 5. the reconstructed tsar of three cylinders at the measurement domain. fig. 6. the erratic flying pattern scenario of the uav. fig. 7. five cylinders at the measurement doamin using feko simulation. after collecting the scattering field, the inversion process has been done using the cg algorithm to obtain the object function from the matching filter matrix that has been calculated due to each snapshot position and direction through the green’s function. the inversion produced the final z -a x is ( m e te r) engineering, technology & applied science research vol. 4, no. 4, 2020, 5933-5939 5938 www.etasr.com almutiry: uav tomographic synthetic aperture radar for landmine detection reconstructed image. the final reconstructed image can be extended into a 3-d model image. fig. 8. the reconstructed tsar image of the measurement domain. vi. conclusion in the middle east there are more than 50,000 landmines buried randomly under the saudi-yemeni border, posing a fatal threat for the civilians. unfortunately, most of the buried mines are nonmetallic, which are challenging to be detected in a large area by conventional methods. a large area needs to be prescreened for landmines before it becomes safe to use. nevertheless, the synthesis array antenna is the output of a radar sensor onboard an aircraft to increase the airborne radar aperture length. the image formation algorithm generates the output image based on the collected signals, where the matched filter will apply autocorrelation to the input signal. overall, sar will treat the clutter as a processed signal to form an image. appropriate sar image requires high bandwidth and aperture parameters to obtain the desired resolution. on the other hand, soil losses degrade the penetrating depth based on the frequency and bandwidth for more underground sensing applications using sar techniques. in the tomographic sar mode, the data are collected as multistatic geometry exploiting the spectral/spatial diversity. furthermore, the multistatic decouple the relation between frequency forming the image and the radiated frequency. tsar can be formed by using the ultranarrow band (unb) at l-band to give more resolution than the conventional sar, where nbu reduces the signal attenuation for more penetration depth. for uav’s tsar, the measurement vector presents the collected signal in a multistatic mode. the matched filter is the electric field response at any flying location and direction, and the contrast vector (the object function) is the pixel weight. the idea based on exploit microwave signals to create an image of an object or prescreening underground. the operation frequency based on the applications (e.g. more microwave image resolution, less penetrating depth) where we are imaging based on tomography techniques. the tomographic sar techniques solve the contrast function of an object or land (image) as an inverse problem considering the received signal with its response in the medium. for our application, we need less bandwidth to increase the penetrating depth and obtain higher resolution. the uav’s tsar techniques were recording the aviation information and linked it to the recorded scattering field as discrete data. however, these methods exploit the spectral/spatial diversity, where the soil losses are always a problem for penetrating signals, but unb gives more 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[36] m. c. wicks, “rf tomography with application to ground penetrating radar,” in conference record of the forty-first asilomar conference on signals, systems and computers, pacific grove, ca, usa, nov. 2007, pp. 2017–2022, doi: 10.1109/acssc.2007.4487591. engineering, technology & applied science research vol. 8, no. 3, 2018, 2958-2962 2958 www.etasr.com tunio et al.: performance and emission analysis of a diesel engine using linseed biodiesel blends performance and emission analysis of a diesel engine using linseed biodiesel blends m. m. tunio department of energy and environment engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan mureed.tunio@gmail.com m. r. luhur department of mechanical engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan luhur@quest.edu.pk z. m. ali department of chemical engineering mehran university of engineering and technology jamshoro, pakistan zeenat.ali@faculty.muet.edu.pk u. daher department of chemistry govt. degree (boys) college sakrand, pakistan oooga82@gmail.com abstract—the core object of this study is to examine the suitability of linseeds for biodiesel production. the performance of an engine at different proportions of linseed blends with petrodiesel and the amount of emissions rate were investigated. initially, linseed biodiesel was produced through transesterification process, and then it was mixed with petrodiesel fuel (d100) blends at volumetric ratios of 10% (lb10), 20% (lb20), and 30% (lb30). the properties of linseed biodiesel and its blends were investigated and compared with petro-diesel properties with reference to astm standards. it has been observed that the fuel properties of produced biodiesel are within astm permissible limits. the specific fuel consumption (sfc) of lb10 blend has been found lesser compared to lb20 and lb30. sfc of d100 is slightly less than that of all the blends. the brake thermal efficiency (bte) of lb30 is greater than that of pure diesel d100 at maximum load and greater than that of lb10 and lb20. the heat dissipation rate in all linseed blends is found to have been less than that of d100. carbon monoxide, carbon dioxide and nox emissions of linseed blends are mostly lower in comparison with d100’s. among all blends, lb10 was found more suitable alternative fuel for diesel engines and can be blended with petro diesel without engine modifications. it can be concluded that cultivation and production of linseed in pakistan is very promising, therefore, it is recommended that proper exploitation and use of linseed for energy production may be encouraged through pertinent agencies of pakistan. keywords–linseed oil; transesterification; diesel-biodiesel blends; engine performance; emission analysis i. introduction the demand of energy sources is increasing day by day due to population growth, urbanization and industrialization. fossil fuels are conventional energy sources and are used for power production for a long time. however, they are finite sources of energy and cannot be replenished once consumed. environmental consequences are also major drawbacks of fossil fuel consumption. therefore, it is an inevitable to explore alternative energy sources which must be environmental friendly to fulfill growing energy demand [1]. out of all agricultural sources, linseed is preferable because of its reasonable availability and easy accessibility, especially in sindh and punjab pakistan provinces [2]. pakistan is an energy deficient country, as demand is larger than production capacity. energy shortage and frequent load shedding have created a chaotic situation in every corner of the country [3]. the government of pakistan is encouraging and promoting research and efforts to utilize renewable energy sources to supplement fossil fuels. pakistan has a good potential of edible and nonedible crops for biodiesel (bio-energy) production. among all non-edible feed stocks, linseed is recognized to be one of the most suitable sources for biodiesel production as it is an oil seed bearing plant [4]. linseed oil is a non-edible vegetable oil and is considered as a potential alternative fuel for the compression ignition engines. it is a sulfur free, non-aromatic, nontoxic, and oxygenated oil. moreover, pakistani government is eager to introduce blended petroleum (with biodiesel) at a national level in order to meet the increasing energy demand. it was decided that 5% by volume of diesel will be blended with biodiesel up to 2015 and gradually the analogy will increase up to 10% in 2025 [5]. however, this has not been achieved yet due to the delay in large scale biodiesel production level, less foreign investment and lack of infrastructure facilities. linseed (linum usitatissimum l.) locally known as “alsi” is an annual winter plant grown for fiber and oil. it is a herbaceous annual-type plant that is cultivated in 59 countries for its fiber as well as its oil [6]. linseed contains oil at 35-45% by weight and is high in unsaturated constitutes [7]. in pakistan, linseed is cultivated on marginal and sub-marginal lands under irrigated conditions. linseed is cultivated in punjab and sindh provinces in 762 and 2929 hectares of land respectively, and its whole country cultivation was around 3691 hectares during 2014-15. the quantity of linseed production was 2622 tons during 2014. its yield in kg per hectare was 758 in sindh and 697in punjab, while its national average yield during 2014-15 was 710kg/ha [8]. various chemical properties and characteristics of linseed seeds, extracted oil and biodiesel produced decide its suitability for the replacement of petro diesel in internal combustion engines and other industrial applications. this study aimed to produce linseed biodiesel using indigenous linseed seeds and to examine the performance of a die exh pro kin val eff coo em ca pm kn cri att exc lin and dif lin sin me scr giv lin me en at im rem col ste oi est a. it equ the we bio me for me hou dri b. die la die 30 lin (m in engineerin www.etasr esel engine by haust emissio operties of pro nematic viscos lue. the pe ficiency (bte olant were eva mission, nitrog arbon monoxi m10 were also own as a maj itical air pollut ention to the cellent alterna i the experim nseed oil as raw d emission c fferent blends nseeds were pu ndh, pakistan. ethods like s rew press meth ves more yield nseed oil was echanical expe nergy and env t first, the lins mpurities, forei maining on th llected in air erilized, washe l’s free fatty terification. transesterifi linseed biod was produce uipped with ermometer wit ere made at odiesel yield. echanical stirr r 30 minutes. ethyl ester wa urs. the crude ied to remove blend prepa emissions the blends o esel were p aboratory. the esel at volume % (lb30) as nseed biodiese model dwe-6/ table i [12]. ng, technology r.com y using its diffe on rates. the oduced biodie sity, cetane n erformance p e), fuel cons aluated at vary gen dioxide ide (co), car analyzed. the jor contributor tant [9]. the o e synthesis of ate of petroleum ii. materi mental work p w material. it a characteristics s and compar urchased from . the linseed solvent extrac hod. the screw ds and so it w extracted wi eller of the bi vironment en seed seeds we ign particles a he outer seed’ r sealed glas ed with doubl y acid level fication proces diesel was pro ed using a fi mechanical th cork reflux different mol the mixture w er by keeping at the end of as transferred e methyl ester its moisture co raton, engine of varying rati prepared at e linseed bio etric ratios of s shown in fi el were tested /10–js–dv). t y & applied sci tunio erent blends w study include esel, such as d number, pour arameters, li sumption, and ying loads. re (no2), nitrog rbon dioxide e emission of p r to global wa objective of thi f linseed biod m diesel, espec als and meth produced biod also investigat of linseed m red them with m the local mar oil can be ob ction, enzyma w press metho was adopted [ ith the help o iofuel laborat ngineering, qu ere cleaned in and adhered a s surface. th ss bottles wh le distilled wa l was reduce ss duced through ive hole lid r stirrer, temp x condenser. v lar ratio to o was agitated w g its speed at 6 f the transester into a separa r was washed w ontent and unw e performance io of linseed b room tempe odiesel was b f 10% (lb10) igure 1. the on a slow sp the specificat ience research et al.: performa with petro dies es physcio-che density, flash point, and ca ike brake th d heat carrie garding exhau gen oxides (n (co2), pm2 particulate ma arming as wel is study was to diesel, which cially in pakis hods diesel using re ted the perform methyl ester h petro diesel rkets of hyder btained by dif atic extraction od is preferabl [10, 11]. the of the screw tory, departm uest, nawab n order to avo agrochemical s e extracted oi hich were al ater and oven ed through h transesterific reactor which perature cont various experi obtained max with the help 600rpm under rification, the ating funnel f with water and wanted reagen e and exhaust biodiesel and erature in b blended with ), 20% (lb20 different blen peed diesel en tions are ment h v ance and emiss el and emical point, lorific hermal ed by ust gas nox), 2.5 & atter is ll as a o draw is an stan. efined mance using l. the rabad, fferent n and le as it crude press ment of bshah. oid the sprays il was lready dried. single cation. h was troller, iments ximum of the r 55°c crude for 24 d then nts. petrobiofuel petro 0) and nds of ngine, tioned lubr and in incr of 3 of t was con per con and tem gas var dio pm no a. pro bio ceta ceta 52. disc sul vol. 8, no. 3, 20 sion analysis of tabl par m numbe s compr starti o max rotati coo dyn flo the engine ricating system d several senso an integrated reased gradua 3kw. the incr the engine fro s measured by nsumption wa rformance para nsumption (bs d outlet temper mperature and s analyzer 350 rious flue gas xide (co2), a m10 were dete . 531s. i fuel properti the results o oduced linseed diesel was fou ane number a ane number w 5, which is m covered to be lfur was found 018, 2958-2962 of a diesel engi fig. 1. linse le i. diese rameter type model er of cylinder bore stroke ression ratio ing method output xium load ional speed oling type amometer ow meter comprises m, fuel supply ors which are manner [12] ally (step: 0.75 rease of load om 2200 to 1 y an eddy cur as measured ameters like s sfc), lubricat ratures, suctio thermal effici 0 xl testo-met emissions like and nitrogen ermined by pa ii. results ies and engine of the proper d biodiesel are und to have low and flash poi was found to b more than the a e more in lb2 d less in all b ine using linse eed biodiesel blen el engine specifi specificat horizont dwe-6/10-j 1 80mm 95mm 23:01 manual 8.5 ps 3kw 2200rpm water coo eddy current elec float typ of several y system, wa attached with ]. the load o 5kw) from zer on the engine 200. the pow rrent electric d on volumetri speed, torque, tion oil tempe on and exhaust iency were exa ters were used e carbon mono oxides (nox) articulate met s and discuss e performance rties of the d shown in tab wer viscosity int. in blend be 53.5, where astm standar 20 and lb30 blends than th 2959 eed biodiesel b nds ications [12] ion tal s-dv l m oled ctro brake pe systems such ater cooling sy measuring de on the engine ro to the maxi e decreases the wer output (to dynamometer. ic basis [12, brake specific erature, water t pressures, ex amined. more d for the analy oxide (co), ca ) [14]. pm2.5 ter aerocet m sion e different blend le ii. the prod and density, h lb10, maxi eas, in lb20 it rd. flash poin 0 than petro d hat in 100% d blends h as ystem evices e was imum e rpm orque) fuel 13]. c fuel inlet xhaust eover, ysis of arbon 5 and model ds of duced higher imum t was nt was diesel. diesel. th all les cal ble fou the po out fou wa lb app the out ble ble lb and wit ble wo b. no em am qu car bio engineerin www.etasr he calorific val fuel propertie ss kinematic v lorific values. end compared und better than e ones reporte wer output wa q de kinematic v total a c fig. 2. b figure 3 sho tput for the d und to increas as found great b20 at maxim plied in intern ermal efficienc t by coolant ends. the hea ends than that b20 and lb30 d lb10. thi thout heating ends. lubricat ould be econom exhaust emi table iii sho ox no, no2, p missions of bi mong vehicula antities of rbonaceous m ofuels the env ng, technology r.com lues were with es of lb10 bl viscosity, high b10 was fou d to lb20 and n petro diesel. ed in [15-16] as examined b quality paramete ensity at 15oc kg/ viscosity at 40oc sulfur %wt flash point o c acid number mgk pour point oc cetane number alorific value mj brake power versu ows the deviat different blend se with increas ter than that mum load. lb nal combustio cy. figure 4 sh (hc) versus at dissipation r of d100. at z , whereas at fu s reveals tha resultantly w tion oil consum mical for the o issions ows the exhaus pm2.5 and pm iodiesel blend ar fuels, petro particulate material [17]. a vironmental im y & applied sci tunio hin permissibl lend were foun her cetane num und to be mo d lb30. all b the results w ]. engine per by load variatio tabl ers /lit (mm2 / sec) koh/gm j/kg us brake specific f tion of bte v ds of linseed b se of brake po of pure diese b30 blend co on (ic) engin hows the varia s brake powe rate was found zero load lb10 ull load lb30 at the engine with the use o mption could b operation of ic st emissions su m10 by load. i ds were comp o-diesel produ matters, wh as a result, by mpacts can be ience research et al.: performa le limits. gene nd better in te mber, even ele ore suitable fe blend samples were found sim rformance or on. the variat le ii. fuel allowable limit 0.88 1.9–6.0 0.05 max 130 min 0.80 max -15 to +5 47 mini 37.5 42.80 fuel consumption versus brake p biodiesel. bte ower. bte of el d100, lb1 ould be pract ne due to its h ation of heat c er for the dif d less in all li 0 recorded les had less than can run smo of linseed bio be less, theref c engines. uch as co, co in this study ex pared with die uces slightly hich consist the use of alt e reduced. by h v ance and emiss erally, erm of evated easible s were milar to brake tion in spe diff 0.7 wit blen max spe properties of li ts diesel 100 0.8401 3.06 0.735 74 0.249 0 52 44.2 power e was lb30 0 and tically higher carried fferent inseed ss than lb20 oothly odiesel fore, it o2 and xhaust esel’s. larger ts of ernate using dies lb resp whi 0.7 less in con dec f fi flue vol. 8, no. 3, 20 sion analysis of ecific fuel co ferent fuel bl 5kw power, th the increas nd found less ximum brake ecific fuel cons inseed biodiesel 0% lb 100 0.8809 4.17 0.0093 172 1.22 -3 45 42.85 sel the pm2.5 20 and lb30 pectively. sim ile in lb10, 32mg/m3 respe ser than diesel fuel-rich zon ntains more o creased [18]. fig. 3. brake p g. 4. brake po co is a form e gases, whic 018, 2958-2962 of a diesel engi onsumption (s lends is show sfc was fou se of brake p s as compare power d100 sumption (sfc l and blends % lb 10% 9 0.8945 3.57 3 0.125 74 1.48 -9 53.5 41.8 5 were record emissions wer milarly, pm1 , lb20 and ectively. gene l’s. the pm f nes and high oxygen than d power versus brak ower versus heat mation mixtur h when put t ine using linse sfc) versus wn in figure und maximum power. howev ed to lb20 a performed w c). % lb 20% 0.8509 3.67 0.113 78 1.59 -9 52.5 41.5 ded 0.09mg/m re 0.002, 0.04 10 was obse lb30 were erally biodiese formation proc h temperatures diesel, thereby ke thermal efficie carried out by co re of temperat together contr 2960 eed biodiesel b brake power 2. in genera m, and it decre ver, sfc in l and lb30. a well with respe lb 30% 0.8561 3.81 0.1007 81 1.64 -6 50.5 40.8 m3, whereas l 40 and 0.010m rved 2.157m 1.356, 1.308 el’s pm emissi cess mainly o s. since biod y pm emissio ency for the test fu olant for the test ture and unbu rol the rate of blends r for al, at eased lb10 at the ect to lb10, mg/m3 mg/m3, and ion is occurs diesel on is uels fuels urned f fuel engineering, technology & applied science research vol. 8, no. 3, 2018, 2958-2962 2961 www.etasr.com tunio et al.: performance and emission analysis of a diesel engine using linseed biodiesel blends decomposition and oxidation [19]. all biodiesel blends provide lesser co emissions compared to petro diesel. lb10 blend gave slightly lower emission than lb20 and lb30. similar results were also reported in [19-20]. the percentage of carbon dioxide (co2) emission was found increasing with the increase of biodiesel ratios at full load condition but remained lower than that of petro diesel. the nitrogen oxide levels (nox) is an exhaust emission of diesel engines. it could create health hazards, when it is inhaled. it can cause many diseases, like tuberculosis, severe headache, respiratory problems, lung cancer, nausea, skin cancer etc. [21]. the nox emissions of all blends were found lower than that of petro diesel. among all blends, lb20 blend emission was much lower than the ones of lb10 and lb30. this reveals that the linseed biodiesel is feasible using blend forms for nox reduction. similarly, other pollutant results, like no2, no and co2 remained lower than that of 100% diesel. table iii. comparison of exhaust emissions parameters diesel lb10 lb20 lb30 engine load (%) 25 50 75 100 25 50 75 100 25 50 75 100 25 50 75 100 pm2.5 (mg/m3) 0.14 0.16 0.66 0.60 0.02 0.04 0.012 0.002 0.02 0.03 0.005 0.04 0.005 0.029 0.056 0.010 pm10 (mg/m3) 0.87 0.84 1.52 2.15 0.52 0.73 0.31 1.35 0.42 0.58 0.74 1.30 0.36 0.39 0.42 0.73 no2 (ppm) 9.30 8.10 8.88 8.98 8.50 3.10 1.20 0.05 6.70 1.50 0.70 0.40 1.80 3.90 0.20 0.15 nox (ppm) 98.0 79.0 37.0 77.0 48.0 59.0 65.0 30.0 57 66.0 63.0 11.0 46.0 88.0 45.0 15.0 co (ppm) 425 480 510 530 182 188 269 365 161 200 201 328 210 235 264 372 no2 (ppm) 65.0 73.0 70.0 68.0 40.0 55.0 64.0 29.0 51.0 65.0 63.0 60.0 45.0 55.0 65.0 60.0 co2 %(ppm) 4.2 3.4 3.5 4.82 1.69 2.17 2.65 2.93 1.70 2.34 2.73 3.44 1.59 2.36 3.00 3.68 iv. conclusions linseed biodiesel was produced through transesterification process using indigenous linseeds. the produced biodiesel was blended with petro-diesel fuel (d100) at different volumetric ratios of 10% (lb10), 20% (lb20), and 30% (lb30). the fuel properties of produced biodiesel were found within astm permissible limits. the specific fuel consumption of lb10 blend was found less than that of lb20, and lb30. bte of lb30 is greater than pure diesel’s d100 at the maximum load. the heat dissipation rate was found less in all blends of linseed than that of d100. this reveals that the diesel engines can run smoothly without heating with the use of linseed blends. both particulate matters pm2.5 and pm10 results were investigated and it was found that pm emission is drastically less than petro-diesel’s at all loads. the co2 and nox emissions of linseed blends were found lower when compared to petro diesel fuel. among all blends, lb10 was found to be more suitable alternative fuel for diesel engines and can be blended with petro diesel without engine modifications. it was also observed that cultivation and production of linseed in pakistan is very promising therefore it is recommended that the proper exploitation and use of linseed for energy production may be encouraged by the relevant agencies of pakistan. references [1] s. kumar, a. pal, a. baghel, “an experimental analysis of biodiesel production from linseed oil”, international journal of engineering technology, management and applied sciences, vol. 3, no. 2, pp. 133140, 2015 [2] s. ali, m. a. cheema, m. a. wahid, a. sattar, m. f. saleem, “comparative production potential of linola and linseed under different nitrogen levels”, crop & environment, vol. 2, pp. 33-36, 2011 [3] m. asif, “sustainable energy options for pakistan”, renewable and sustainable energy reviews, vol. 13, no. 4, pp. 903-909, 2009 [4] s. a. r. kazmi, a. h. solangi, s. n. a. zaidi, jatropha curcas l. cultivation experience in karachi pakistan, joint study preliminary report of pakistan agricultural research council and pakistan state oil, 2003 [5] a. b. awan, z. a. khan, “recent progress in renewable energy–remedy of energy crisis in pakistan”, renewable and sustainable energy reviews, vol.33, pp. 236-253, 2014 [6] food and agriculture organization of the united nations, food and agriculture organization corporate statistical database, available at: http://www.fao.org/faostat/en/#home, accessed: 03/02/2018. [7] f. ullah, a. bano, s. ali,“optimization of protocol for biodiesel production of linseed (linum usitatissimum l.)oil”, polish journal of chemical technology, vol. 15, no. 1, pp. 74-7, 2013 [8] m. amjad, oilseed crops of pakistan pakistan agricultural research council, islamabad, 2014 [9] c.-j. ruan,w.-h. xing, j. a. t. da silva, “potential of five plants growing on unproductive agricultural lands as biodiesel resources”, renewable energy, vol. 41, pp. 191-199, 2012 [10] p. beerens, screw-pressing of jatropha seeds for fuelling purposes in less developed countries”, msc thesis, eindhoven university of technology, ministerio de ambiente y energía, 2007 [11] m. m. tunio, s. r. samo, z. m. ali, k. chand, “comprehensive study of jatropha (jatropha curcas) biodiesel production and its prospectus in pakistan”, sindh university research journal (science series), vol. 48, no. 1, pp. 209-212, 2016 [12] tokyo meter co, operational manual of single cylinder slow speed diesel engine research and test bed, model: dwe-6/10-js –dv, 2002 [13] k. singh, m. y. sheikh, y. b. mathur, “performance study of a vcr diesel engine fueled with diesel and low concentration blend of linseed oil biodiesel”, international journal of emerging technology and advanced engineering, vol. 4, no. 4, pp. 295-299, 2014 [14] testo, testo 350 m/xl 454 instruction manual, 2002 [15] s. r. samo, m. m. tunio, “production and characterization of biodiesel from indigenous linseed herb”, international journal of current trends in engineering & research” vol. 2, no. 8, pp. 91-97, 2016 [16] a. m. ashraful, h. h. masjuki, m. a. kalam, i. r. fattah, s. imtenan, s. a. shahir, h. m. mobarak, “production and comparison of fuel properties, engine performance, and emission characteristics of biodiesel from various non-edible vegetable oils: a review”, energy conversion and management, vol. 80, pp. 202-228, 2014 [17] r. sattanathan, “production of biodiesel from castor oil with its performance and emission test”, international journal of science and reseach,vol. 4, no. 1, pp. 273-279, 2015 [18] m. h. shojaeefard, m. m. etgahni, f. meisami, a. barari, “experimental investigation on performance and exhaust emissions of castor oil biodiesel from a diesel engine”, environmental technology, vol. 34, no. 13-14, pp. 2019-2026, 2013 engineering, technology & applied science research vol. 8, no. 3, 2018, 2958-2962 2962 www.etasr.com tunio et al.: performance and emission analysis of a diesel engine using linseed biodiesel blends [19] s. k. mahla, a. birdi, “performance and emission characteristics of different blends of linseed methyl ester on diesel engine”, international journal on emerging technologies, vol. 3, no. 1, pp. 5559, 2012 [20] m. ozcanli, h. serin, o. y. saribiyik, k. aydin, s. serin, “performance and emission studies of castor bean (ricinus communis) oil biodiesel and its blends with diesel fuel”, energy sources, part a: recovery, utilization, and environmental effects, vol. 34, no. 19, pp. 1808-1814, 2012 [21] m. m. krishna, k. v. krishna, “experimental investigations of comparative performance and exhaust emissions of linseed biodiesel fuelled di diesel engine with low grade lhr combustion chamber”, international journal of advanced scientific and technical research, vol. 5, no. 4, pp. 180-197, 2014 engineering, technology & applied science research vol. 8, no. 3, 2018, 2897-2900 2897 www.etasr.com lucas and huebner: numerical simulation of single-phase and two-phase flows in separator vessels … numerical simulation of single-phase and twophase flows in separator vessels with inclined halfpipe inlet device applied in reciprocating compressors fagner patrício lucas department of mechanical engineering university of minas gerais belo horizonte, minas gerais, brazil engfagner@gmail.com rudolf huebner department of mechanical engineering university of minas gerais belo horizonte, minas gerais, brazil rudolf@ufmg.br abstract—this paper aims to apply computational fluid dynamics (cfd) to simulate air flow and air flow with water droplets, as a reasonable hypothesis for real flows, in order to evaluate a vertical separator vessel with inclined half-pipe inlet device (slope inlet). thus, this type was compared to a separator vessel without inlet device (straight inlet). the results demonstrated a different performance for the two types in terms of air distribution and liquid removal efficiency. keywords-inlet device; separator vessel; computational fluid dynamics; reciprocating compressor; single and two-phase flow i. introduction the reciprocating compressor is widely used in industry, being an important machine to compress all gas types. however, the liquid fraction ingestion is one of the main causes of unavailability problems due to the “liquid hammer effect” that increases, quickly, the loads in the piston, piston rod, connection rod, crosshead, crosshead pin and other parts. as result, it can lead to their mechanical failure. according to [1], liquid can enter the compressor cylinder due to the impurity from other systems, the gas condensation in the suction piping or by handling low boiling point gas or wet gas during compression process. this context motivated the api-618 code (reciprocating compressors for petroleum, chemical and gas industry services) to recommend the use of separator vessels, in the suction of first stage and between stages, for removing 99% of droplets of 10µm or larger since the dispersed flow (or mist flow) is the most typical standard flow present in compressor unit. therefore, separator vessels have two important devices in order to capture all droplets through the gravitational deposition and inertial impaction mechanisms. the first, called inlet device, minimizes the droplet shearing, improves the downstream gas velocity distribution and, thus, maximizes the liquid removal efficiency, mainly in the gravitational deposition area [2]. the second, known as mist eliminator (or demister), removes the droplets in three steps: inertial impaction, coalescence and detaching of the droplets from the surface of wire due to the gravitational force [3]. this paper investigated numerically a vertical separator vessel, with inclined half-pipe inlet device and wire mesh mist eliminator, through single-phase and two-phase simulations, and finally the results were compared to a vertical separator vessel without inlet device and the same design of wire mesh mist eliminator. ii. materials and methods a. governing equations the following equations were used in the mathematical model of the numerical simulation [4]. the mass equation can be described as: ( ) 0u t       (1) where ρ (kg/m3) is the fluid density, u (m/s) is the fluid velocity and t is time. the momentum equation is:   ( ) t u uu p f          (2) where  (n/m²) is the viscous stress tensor, f (n) is the airwater droplets interaction force and p (pa) is the air pressure. b. souders-brown equation this equation is the most common method to sizing separator vessels and can be defined by the force balance applied on a droplet in an upwards-flowing in a fluid field, as described (figure 1) [5]. max. l air air k             (3) where k(m/s) is the separation factor (or souders-brown velocity), ρl and (kg/m³) ρair are the water and air density respectively and vmax is the maximum air velocity. maximum engineering, technology & applied science research vol. 8, no. 3, 2018, 2897-2900 2898 www.etasr.com lucas and huebner: numerical simulation of single-phase and two-phase flows in separator vessels … air velocity from (3) can be used to define the internal diameter of the separator vessel for the proposal air flow. the other dimensions (length and nozzles) were defined by practical methods from reciprocating compressors manufacturers. fig. 1. the forces acting on a droplet in a upwards-flowing c. cfd modeling the commercial cfd package ansys® cfx 15 was used in the present study, for solving the governing equations and the geometry was made in computer-aided design (cad) software. a pc processor with four cores was used, with 3.4ghz processor frequency and 8gb ram. the typical run times were around 7h. the mesh generated has unstructured tetrahedrons grids with 1,115,883 nodes and an inflation was considered close to the surface of the fluid volume to capture the details of the flow. the gas phase was taken to be air, with ρair=1.07kg/m³, qair=0.07m³/s and tair=25ºc. the liquid phase was assumed to be water and, thus, it was considered mwater=2.78e-3kg/s. 1,000 water droplets were divided in five diameters: 10µm, 50µm, 100µm, 150µm and 200µm. for the air and water droplets flow, the restitution coefficient was 0.15 for perpendicular collision and 0.30 for parallel collision. the values were defined based on the weber number according to [6]. figure 2 shows the separator vessel used in the cfd simulation for the present work. fig. 2. the separator vessel sized for the cfd simulation the study concentrated in the open space between “plane 1” and “plane 2” (figure 2). thus, the wire mesh mist eliminator was included in the modeling as a porous body with a resistance factor that lead to a pressure drop according to hazen-dupuit-darcy equation [7]. 2    c kh p (4) where p (pa) is the pressure drop, h (m) is the mist eliminator thickness, ρ is the air density and κ and c are dimensionless coefficients (obtained experimentally). figure 3(a) shows the computational domain for a separator vessel without inlet device and figure 3(b) shows the computational domain for the same separator vessel, but with inclined halfpipe inlet device. fig. 3. computacional domain for a separator vessel: (a) without inlet device and (b) with inclined half-pipe inlet device. the dimensions of the vessel are described in table i and the boundary conditions used in the cfd simulation are described in table ii. table i. dimensions of the model dimension (figure 3) value unit internal diameter 400 mm “plane 1” to “plane 2” 887.32 mm “plane 1” to “enmf i” 700 mm “plane 1” to “enmf ii” 712.32 mm table ii. boundary conditions boundary position boundary condition inlet cross section through the inlet nozzle uniform velocity profile, turbulence model (k-ε) outlet cross section of the separator vessel, some space above the packing bed (plane 2 of figure 3) free outlet water sump liquid surface considered flat (plane 1 of figure 3) no shear wall vessel wall and nozzle wall adiabatic for mass and energy. porous body plane enmf i or enmf ii pressure drop model engineering, technology & applied science research vol. 8, no. 3, 2018, 2897-2900 2899 www.etasr.com lucas and huebner: numerical simulation of single-phase and two-phase flows in separator vessels … iii. simulation results and discussion a. effect of the inlet device on uniformity of air flow the profile of air velocity was numerically determined for both types of separator vessels. the first type is the vessel without the inlet device, also called straight inlet, and the second type is the vessel with the inclined half-pipe inlet device, also called slope inlet. in this step of simulation, the support ring, used to assembly the wire mesh mist eliminator in the vessel, was not considered. thus, the vessel section has 400mm internal diameter, being the plane “enmf i” (figure 3) the aimed section to evaluate the air distribution. figure 4 shows the air vertical velocity for the two types of separator vessels. fig. 4. distribution of the air vertical velocity in the section “enmf i” placed 10.32mm below the wire mesh mist eliminator for: (a) the straight inlet and (b) the slope inlet. it is clear that both types presented a concentrated air flow along the wall which created a non-uniform air flow. however, it is necessary to quantify this distribution by the variation coefficient, widely used in the chemical process industries to evaluate structured, unstructured packing and distributor, with the following equation [8-10]: 5,02 _ _ 1 1                       u uu a a c i n i i t v (5) where cv (dimensionless) is the variation coefficient, n is the number of the cells, ai (m²) is the area of the cell i, at (m²) is the total area of the transversal section, ui (m/s) is the air velocity in cell i and u is the average air velocity:    n i ii t ua a u 1 _ 1 (6) the obtained variation coefficients were 2.67 and 2.34 for the straight and slope inlet respectively. thus, the results showed that the vessel with the inclined half-pipe inlet device (slope inlet) allowed a slightly better air distribution compared to the straight inlet. however, both types presented a high air velocity in some areas, above the limit of 3.25m/s (3). this condition is undesirable for phase separation. b. effect of the support ring on uniformity of air flow figure 5 presents the air vertical velocities for the separator vessels considering the support rings of wire mesh mist eliminators. it can be observed that maximum velocities decreased, but the straight inlet obtained a lower value compared to the slope inlet. the variation coefficients were 0.34 and 0.81 for straight and slope inlet, respectively. thus, it is clear that the support rings influenced the air distribution, mainly for the straight inlet due to the deviation of the air flow along the wall. the air velocity in the straight inlet remained below the limit of 3.25m/s. therefore, this configuration presented better results for the two parameters: air distribution and good condition for phase separation. fig. 5. distribution of the air vertical velocity in the section “enmf ii” placed 1.0mm below the wire mesh mist eliminator for: (a) the straight inlet and (b) the slope inlet. c. effect of the inlet device on liquid removal efficiency the path lines of water droplets for two kinds of inlets were determined by cfd analysis and the results are shown in figure 6. as observed, the slope inlet removed almost all water droplets above 10µm due to the coalescence of them in the bottom of the vessel. table iii shows a lower number of droplets escaped for the vessel with slope inlet. it is important to explain that the number of droplets that escaped, described in table iii, represents the phase separation in the sections “a” and “b” in figure 2. in real conditions, the remained droplets will be removed by the wire mesh mist eliminator. fig. 6. the path lines of the water droplets for: (a) the straight inlet and (b) the slope inlet. engineering, technology & applied science research vol. 8, no. 3, 2018, 2897-2900 2900 www.etasr.com lucas and huebner: numerical simulation of single-phase and two-phase flows in separator vessels … table iii. numbers of water droplets that escaped from the separator vessels droplet diameter numbers of water droplets (straight inlet) numbers of water droplets (slope inlet) 10 µm 121 152 50 µm 48 0 100 µm 17 1 150 µm 8 0 200 µm 2 0 total 196 153 d. effect of the inlet device on liquid removal efficiency the slope inlet presented a better efficiency compared to the straight inlet (table iv). table iv. liquid removal efficiency from the separator vessels water mass flow (straight inlet) water mass flow (slope inlet) input (kg/s) 2.78e-3 2.78e-3 output (kg/s) 5.45e-4 4.25e-4 removed (kg/s) 2.23e-3 2.35e-3 efficiency (%) 80.38 84.69 e. effect of the support ring on liquid removal efficiency the liquid removal efficiency of the slope inlet was increased after the inclusion of the mist eliminator support ring (table v). table v. liquid removal efficiency from the separator vessels with support rings. water mass flow (straight inlet) water mass flow (slope inlet) input (kg/s) 2.78e-3 2.78e-3 output (kg/s) 2.67e-4 1.92e-4 removed (kg/s) 2.51e-3 2.59e-3 efficiency (%) 90.39% 93.09% iv. conclusions in this study, cfd simulation was employed to simulate an air flow through the separator vessels with straight inlet and slope inlet (or with inclined half-pipe inlet device). the results showed that the uniformity of air flow and the liquid removal efficiency in a separator vessel were affected by the inlet device and the support ring of the mist eliminator. the slope inlet improved the liquid removal efficiency in the air gravity separation section. in the other hand, the straight inlet had a better air distribution with a suitable vertical velocity for phase separation. in this type of vessel, the internal diameter may be minimized since the air velocity (1.64m/s) stayed below the limit of 3.25m/s. the obtained results showed that the computational fluid dynamics is an important approach to evaluate the performance of separator vessels. references [1] b. g. s. prasad, “effect of liquid on a reciprocating compressor”, journal of energy resources technology, vol. 124, no. 3, pp. 187-190, 2002 [2] m. bothamley, “gas/liquid separators: quantifying separation performance part 1”, society of petroleum engineers, vol. 2, no. 4 2013. [3] h. t. el-dessouky, i. m. alatiqi, h. m. ettouney, n. s. al-deffeeri, “performance of wire mesh mist eliminator”, chemical engineering and processing: process intensification, vol. 39, no. 2, pp. 129-139, 2000 [4] f. m. white, viscous fluid flow, mcgraw-hill, inc., 1991 [5] m. souders, g. g. brown, “design of fractionating columns i. entrainment and capacity”, industrial & engineering chemistry, vol. 26, no. 1, pp. 98-103, 1934 [6] b. p. v. d. wal, static and dynamic wetting of porous teflon® surfaces, department of polymer chemistry, university of groningen, nova zelândia, 2006 [7] t. helsør, h. svendsen, “experimental characterization of pressure drop in dry demisters at low and elevated pressures”, chemical engineering research and design, vol. 85, no. 3, pp. 377-385, 2007 [8] s. r. darakchiev, “gas flow maldistribution in columns packed with holpack packing”, bulgarian chemical communications, vol. 42, no. 4, pp. 323–326, 2010 [9] z. olujic, “comparison of gas distribution properties of conventional and high capacity structured packings”, chinese journal of chemical engineering, vol. 19, no. 5, pp. 726-732, 2011 [10] t. petrova, n. v. bancheva, s. darakchiev, r. popov, “quantitative estimates of gas maldistribution and methods for their localization in absorption columns”, clean technologies and environmental policy, vol. 16, no. 7, pp. 1381-1392, 2014 engineering, technology & applied science research vol. 8, no. 3, 2018, 3079-3083 3079 www.etasr.com halepoto et al.: analysis of retransmission policies for parallel data transmission analysis of retransmission policies for parallel data transmission imtiaz ali halepoto department of computer systems engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan halepoto@quest.edu.pk intesab hussain sadhayo department of telecommunication engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan intesab@quest.edu.pk muhammad sulleman memon department of computer systems engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan sulleman@quest.edu.pk adnan manzoor department of information technology, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan adnan@quest.edu.pk shahid bhatti department of information technology, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan shahidmsit12@gmail.com abstract—stream control transmission protocol (sctp) is a transport layer protocol, which is efficient, reliable, and connection-oriented as compared to transmission control protocol (tcp) and user datagram protocol (udp). additionally, sctp has more innovative features like multihoming, multistreaming and unordered delivery. with multihoming, sctp establishes multiple paths between a sender and receiver. however, it only uses the primary path for data transmission and the secondary path (or paths) for fault tolerance. concurrent multipath transfer extension of sctp (cmt-sctp) allows a sender to transmit data in parallel over multiple paths, which increases the overall transmission throughput. parallel data transmission is beneficial for higher data rates. parallel transmission or connection is also good in services such as video streaming where if one connection is occupied with errors the transmission continues on alternate links. with parallel transmission, the unordered data packets arrival is very common at receiver. the receiver has to wait until the missing data packets arrive, causing performance degradation while using cmt-sctp. in order to reduce the transmission delay at the receiver, cmt-sctp uses intelligent retransmission polices to immediately retransmit the missing packets. the retransmission policies used by cmt-sctp are rtx-ssthresh, rtxlossrate and rtx-cwnd. the main objective of this paper is the performance analysis of the retransmission policies. this paper evaluates rtx-ssthresh, rtx-lossrate and rtxcwnd. simulations are performed on the network simulator 2. in the simulations with various scenarios and parameters, it is observed that the rtx-lossrate is a suitable policy. keywords-cmt; cmt-sctp; retransmission policies; sctp; parallel transmission i. introduction the most commonly used protocols of the transport layer of the osi model are udp and tcp. udp is a connectionless and unreliable transport layer protocol. udp sends data in the form of short messages, which are called datagrams, in a network. udp is a connectionless protocol, which means that there is no need to establish a connection between the sender and receiver. in terms of reliability, the tcp is the most widely used protocol today. a recently introduced protocol for the transport layer is sctp, which is reliable and connection-oriented. sctp is very similar to tcp and udp in terms of operations. it transmits multiple streams of data simultaneously between two endpoints that have established a connection. sctp is more efficient and more powerful in its design when compared to peer protocols. cmt-sctp extension enables a sender to simultaneously transmit data over various paths, which increase the overall transmission throughput. the competitor protocol to cmtsctp is multipath tcp, which is also in design phase. parallel transmission is very common in the development of mobile applications such as video streaming, online gaming, ecommerce, collaborative scientific projects and voip, that require faster data transmission and downloading data rate. the parallel transmission through cmt-sctp uses more than one physical interface, for example the parallel transmission of data between two mobile phones uses two interfaces. one interface transmits using 4g and one interface transmits using wifi. sending data through two interfaces increases throughput compared to sending data through one interface. the use of more interfaces also increases the internet availability of a mobile phone. cmt-sctp is in development process, and some issues such as transmission errors and recovery are challenging. the parallel transmission using cmt-sctp causes unordered data packet arrival at the receiver. the data travels in parallel through different paths, the data along a fast path may reach the receiver earlier than the data sent along a slow path. to solve the problem an immediate retransmission of the missing data is mandatory for smooth transmission. in order to reduce the transmission delay at the receiver, cmtengineering, technology & applied science research vol. 8, no. 3, 2018, 3079-3083 3080 www.etasr.com halepoto et al.: analysis of retransmission policies for parallel data transmission sctp utilizes some retransmission policies to quickly retransmit the missing data packets to the receiver. the main work of this paper is to evaluate retransmission policies for the performance analysis. there are five traditional retransmission policies of a cmt-sctp sender. rtx-same and rtx-asap are very simple and outdated by the three newer policies. obtained results show that rtx-loss rate is better in terms of performance than rtx-cwnd, and rtx-ssthresh. for the simulation setup a realistic network scenario is proposed. in the scenario, both paths with similar characteristics and dissimilar characteristics are tested. an example of dissimilar paths is parallel transmission using mobile phone via 4g and wifi. to extend the simulation for more real networks, a loss rate is added in the paths to reflect the scenario of transmission errors. this research suggests the suitable retransmission policy as well as a base knowledge to design a new retransmission policy for cmt-sctp. ii. retransmission policies the retransmission policies used by cmt-sctp are:  rtx-same: in this retransmission policy data packet retransmission is expected to the similar node. it utilizes just a single path to send data packets to the same destination until that particular node is proved dead.  rtx-asap: the sender retransmits missing data packets to a number of ip addresses. the receiver ip address that provides the congestion window (cwnd) space is the retransmission address. if multiple destinations provide cwnd space then the sender selects one randomly.  rtx-cwnd: in this policy the sender retransmits the data packets to the ip address with the largest cwnd and to a random ip if cwnds are equal.  rtx-ssthresh: in this retransmission policy the sender is retransmitting data packets to the destination with the largest slow start threshold. in case of destinations with equal slow start threshold value, the ip address is chosen randomly.  rtx-lossrate: in this retransmission policy, the sender retransmits data a node with lowest path loss. random selection is done in case of nodes with equal loss rates. iii. simulation model simulations have been carried out using network simulator 2 (ns-2) in which cmt-sctp extension is available. the proposed scenario consists of one sender and one receiver. there are two paths used between the sender and receiver. in order to create these two paths the sender and the receiver are both configured as multihomed hosts. each host is equipped with two interface cards. when the simulation begins the sender transmits the data in parallel along the two paths. the first step is setting up the ns-2 working parameters according to the proposed scenario. ns-2 has many default (fixed) parameters and many changeable parameters that are configured according to the proposed topology. in this research work, two scenarios are proposed as depicted in table i. the first one includes paths of no packet loss. the second includes paths with packet loss. four experiments are executed with the three cmt-sctp retransmission policies. the simulation time is 300 seconds for each policy. the policies used are rtxssthresh, rtx-cwnd, and rtx-lossrate. for each policy the simulation is repeated for 20 times and the average results are plotted. the protocol used is cmt-sctp. throughput is used as the evaluation parameter. the remaining parameters like the size of congestion window, buffer size at sender and receiver and the value of slow start threshold are set to the default settings of ns-2. table i. simulation parameters scenario without loss rate scenario with 10% loss rate # bandwidth, delay # bandwidth, delay 1 path 1:2-20mbps, 1ms path 2: 20mbps, 1ms 1 path 1: 2-20mbps, 1ms path 2: 20mbps, 1ms 2 path 1:22-40mbps, 1ms path 2: 20mbps, 1ms 2 path 1: 1-100mbps, 1ms path 2:1-100mbps, 1ms 3 path 1:5-50mbps, 200ms path 2: 1mbps, 200ms 3 path 1: 1mbps, 10100ms path 2: 1mbps, 1ms 4 path 1:1mbps, 10-100ms path 2: 1mbps, 1ms 4 path 1: 1mbps, 1-100ms path 2:1mbps, 1ms iv. results & discussion a. experiments without loss rate the plots in figure 1 show the performance of different retransmission policies executed without applying any kind of packet loss on the paths. four scenarios are proposed with different bandwidth and delay values as shown in table i. in the first scenario (figure 1(a)) the policies are evaluated based on the bandwidth and the propagation delay changes. the bandwidth on path 2 or secondary path is kept to a fixed value, while the bandwidth on path 1 or primary path varies from 2 to 20mbps. the three policies behave very similar. their starting performance is rather low from 2mbps to 16mbps and suddenly the throughput increases which is caused by the sudden increase in the congestion window. figure 1(b) shows that there is a relationship between the bandwidth and the transmission throughput. in this experiment, a large value of bandwidth is used. in experiment 2 the retransmission rate of rtx-ssthreshold and rtx-cwnd is very similar. however, due to the bandwidth availability (large bandwidth) the retransmission rate of rtx-loss rate is greater than the rates achieved with the other two policies. experiment on a large bandwidth with longer delay values is performed in the scenario 3. it is observed that, when the delay is longer the impact of retransmission policy is less because the retransmission timer expires sooner no matter which retransmission policy is applied. the same is observed in experiment 4, where a small bandwidth value is used and the delay value varies from 10ms to 100ms on path 1. the experimentation with no loss rate shows that the bandwidth plays a key role in increasing the transmission throughput. the rtx-lossrate policy improves the throughput with the increase in the bandwidth. on the other hand, propagation delay is a less significant parameter for the choice of retransmission policy. moreover, the proposed scenario is very simple. b. err add con del engineerin www.etasr (a) ex (c) (d) exp fig. 1 experiments in reality, the rors. so, in th dition of prog nfigured to b lay on path ng, technology r.com xperiment 1: ban (b) experiment ) experiment 3: d eriment 4: small . scenario of with loss ra ere are chance his scenario th grammed loss be 10%. in ex 2 are kept 2 y & applied sci ndwidth variation 2: large bandwid delay variation on bandwidth with l f two paths withou ate es of data loss he experiment rate on path xperiment 1, 20mbps and ience research hale on path 1 dth n path 1 longer delay ut loss rate due to transm s are repeated 1. the loss r the bandwidth 1ms. wherea h v epoto et al.: an mission d with rate is h and as the ban the betw betw (d) f lo exp ban (fig vol. 8, no. 3, 20 nalysis of retran ndwidth on pat delay remain ween 2mbps ween the polic (a) ex (b) expe (c) experiment 3 ) experiment 4: b fig. 2. scenar when the b ossrate reac periment is sl ndwidth on p gure 2(b)). 018, 3079-3083 nsmission polic th 1 changes fr ns constant on and 8mbps th cies as show in xperiment 1: band eriment 2: bandw : bandwidth varia bandwidth variatio rio of two paths w andwidth is ches the throu lightly modifi path 1 increa in this expe 3 cies for paralle from 2mbps to n 1ms. when b here is no no n figure 2(a). dwidth variation o width variation on ation on both path on on both paths with added loss ra larger than 8 ughput of 2.6 ied in experim ases from 22 eriment rtx 3081 el data transm o 20mbps, how bandwidth is oticeable differ on path 1 both paths. hs with longer del with larger bandw ate of 10% on path 8mbps, the r 8mbps. the g ment 2, wher 2mbps to 40m x-ssthresh ission wever small rence lay width h 1 rtxgiven e the mbps hold engineering, technology & applied science research vol. 8, no. 3, 2018, 3079-3083 3082 www.etasr.com halepoto et al.: analysis of retransmission policies for parallel data transmission produces the lowest throughput. in the same experiment, the rtx-cwnd, due to the large bandwidth the sender continuously increases the congestion window but due to the limitation in the buffer size of receiver the throughput at maximum reaches 0.84mpbs. the throughput of rtxlossrate is greater than the other two policies. experiment 3 (figure 2(c)) is an example of two paths with similar characteristics i.e., same bandwidth and delay. the bandwidth on path 1 and 2 varies from 1mbps to 100mbps. longer delay is used i.e. 100ms. the trend in terms of throughput for the retransmission policies is the same. initially with the increase in the bandwidth, the transmission rate also increases because at this point there are fewer chances of retransmissions and higher chances of successful transmissions due to the congestion window availability. in experiment 4 the bandwidth has a small value of 1ms delay (figure 2(d)). the results of experiment 4 are very similar to that of experiment 3. this shows that on similar path characteristics the performance of all the retransmission policies remains similar. however, the experiment on paths with different characteristics, rtxlossrate is the preferable policy for the data transmission. v. related work authors in [1] evaluated five retransmission polices of cmt-sctp on a simple scenario where a sender transmits data to a receiver simultaneously through two paths. according to their observations rtx-lossrate, rtx-cwnd, rtxssthresh are the best policies. they also suggested that in future, further work should be a new policy that must consider the loss rate into account [2, 4, 5, 11]. the concept of integrated policy is proposed in [3, 10]. the work in [6, 7, 17] highlighted the role of the retransmission policy and suggested improvements in path selection while transmitting and retransmitting the data. many authors evaluated sctp and cmt-sctp [8, 9, 12] and highlighted that a good policy also reduces the buffer-blocking problem. the retransmission policies are also used for the evaluation of the cmt-sctp extensions [13] along with other parameters. authors in [14] related the importance of retransmission policies with the problem of handoff in wireless mobile networks. authors in [15, 16] analyzed different failure scenarios of sctp and their impact on the use of retransmission policies. the issue of retransmission or efficient transmission may also be solved by the design of routing protocols [18]. vi. conclusion the trend of parallel transmission of data in order to obtain greater throughput is increasing. parallel transmission is also useful in the development process of mobile applications for emergency services where a device is connected with more than one networks. one of the promising protocols for the parallel transmission is the cmt-sctp. transmission errors are common, particularly in parallel transmission where the immediate solution is the retransmission of data. for that, cmt-sctp uses retransmission policies such as rtxlossrate, rtx-cwnd and rtx-ssthreshold. the current research compared the aforementioned retransmission policies in realistic network conditions where changes in bandwidth and delay are applied. moreover, the programmed loss rate is introduced in the paths in the simulations. the results of simulations suggest that for similar path characteristics all of the retransmission policies behave the same. however, on the paths with added random data loss, rtx-lossrate improves the throughput compared to rtxcwnd and rtx-ssthreshold. the research may be extended to the evaluation of cmt-sctp with other parallel transmission protocols such as multipath tcp. references [1] j. r. iyengar, p. d. amer, r. stewart, “retransmission policies for concurrent multipath transfer using sctp multihoming”, 12th ieee international conference on networks, singapore, vol. 2, pp. 713-719, ieee, 2004 [2] j. r. iyengar, p. d. amer, r. stewart, “receive buffer blocking in concurrent multipath transfer”, in ieee global telecommunications conference (globecom'05), st. louis, usa, vol. 1, p. 6, ieee, 2005 [3] a. l. caro, p. d. amer, r. r. stewart, “retransmission schemes for end-to-end failover with transport layer multihoming”, in ieee global telecommunications conference, globecom'04, vol. 3, pp. 1341 1347, ieee, 2004 [4] j. liu, h. zou, j. dou, y. gao, “reducing receive buffer blocking in concurrent multipath transfer”, in 4th ieee international conference on circuits and systems for communications, shanghai, china, pp. 367371, ieee, 2008 [5] p. natarajan, n. ekiz, p. d. amer, r. stewart, “concurrent multipath transfer during path failure”, computer communications, vol. 32, no. 15, pp. 1577-1587, 2009 [6] i. a. halepoto, f. c. lau, z. niu, z, “concurrent multipath transfer under delay-based dissimilarity using sctp”, in ieee second international conference on computing technology and information management (icctim), pp. 180-185, ieee, 2015 [7] i. a. halepoto, scheduling and flow control in cmt-sctp, hku theses online (hkuto), 2014 [8] p. natarajan, j. r. iyengar, p. d. amer, r. stewart, “concurrent multipath transfer using transport layer multihoming: performance under network failures”, in military communications conference, milcom 2006, washington, dc, usa, pp. 1-7, ieee, 2006 [9] j. r. iyengar, p. d. amer, r. stewart, “concurrent multipath transfer using transport layer multihoming: performance under varying bandwidth proportions”, in ieee military communications conference, milcom 2004, monterey, usa, vol. 1, pp. 238-244, ieee, 2004 [10] h. shen, c. wang, w. ma, d. zhang, “research of the retransmission policy based on compound parameters in sctp-cmt”, in 2nd international conference on information technology and electronic commerce (icitec), dalian, china, pp. 25-28, ieee, 2014 [11] a. l. caro jr, p. d. amer, r. r. stewart, “retransmission policies for multihomed transport protocols”, computer communications, vol. 29, no.10, pp. 1798-1810, 2006 [12] t. yang, l. pan, l. jian, h. hongcheng, w. jun, “reducing receive buffer blocking in cmt based on sctp using retransmission policy”, in ieee 3rd international conference on communication software and networks (iccsn), xi'an, china, pp. 122-125, ieee, 2011 [13] y. cao, c. xu, j. guan, “a record-based retransmission policy on sctp's concurrent multipath transfer”, in 2011 international conference on advanced intelligence and awareness internet (aiai 2011), shenzhen, china, pp. 67-71, ieee, 2011 [14] f. siddiqui, s. zeadally, “sctp multihoming support for handoffs across heterogeneous networks”, in: 4th annual communication networks and services research conference (cnsr 2006), moncton, nb, canada, ieee, 2006 [15] a. l. caro jr, j. r. iyengar, p. d. amer, g. j. heinz, r. r. stewart, “using sctp multihoming for fault tolerance and load balancing”, acm sigcomm computer communication review, vol. 32, no.3, p.23, 2002 engineering, technology & applied science research vol. 8, no. 3, 2018, 3079-3083 3083 www.etasr.com halepoto et al.: analysis of retransmission policies for parallel data transmission [16] a. l. caro jr, p. d. amer, j. r. iyengar, r. r. stewart, “retransmission policies with transport layer multihoming”, in: 11th ieee international conference on networks, sydney, australia, pp. 255-260, ieee, 2003 [17] i. a. halepoto, f. c. m. lau, z. niu, “scheduling over dissimilar paths using cmt-sctp”, in: seventh international conference on ubiquitous and future networks (icufn), sapporo, japan, pp. 535-540 ieee, 2015 [18] n. h. bhangwar, i. a. halepoto, s. khokhar, a. a. laghari, “on routing protocols for high performance”, studies in informatics and control, vol. 26, no. 4, pp. 441-448, 2017 microsoft word 42-3002_s_etasr_v9_n4_pp4538-4542 engineering, technology & applied science research vol. 9, no. 4, 2019, 4538-4542 4538 www.etasr.com malkanthi & perera: particle packing application for improvement in the properties of compressed … particle packing application for improvement in the properties of compressed stabilized earth blocks with reduced clay and silt s. n. malkanthi department of civil engineering university of ruhuna sri lanka snmalkanthi@cee.ruh.ac.lk a. a. d. a. j. perera department of civil engineering university of moratuwa sri lanka asoka@uom.lk abstract—soil as a building material has been used in different forms such as mud, adobe, rammed earth and bricks. the present study focuses on producing compressed stabilized earth blocks (csebs) giving attention to the particle size distribution in the soil mixture. the literature established that compressive strength significantly depends on clay and silt content and 25% of clay and silt produce optimum results while no attention has been given to the amount of other, larger particles. soil grading refers to the combination of different-size particles in a soil mixture. the correct selection of sizes in the correct proportion may cause improvements in cseb properties. this paper explains the application of particle packing technology for the improvement of cseb properties. the theoretical concepts provide a continuous particle size distribution, and the soil used for the experiments also has a continuous particle size distribution. the soil used in the experiments was subjected to washing to reduce the clay and silt content. separated clay and silt and large particles of different sizes were added to the mixture to match particle size distribution to the optimization curves as explained in particle packing theories. the experimental results show that the cseb properties can be significantly improved by modifying particle size distribution to fit the suggested optimization curves. according to the results, the compressive strength improved by more than 50% with different amounts of cement stabilization. significant improvements in the dry densities and water absorption ratios of blocks were observed with this particle size modification. keywords-cement stabilized earth blocks; soil washing; particle packing; optimization curves; compressive strength i. introduction earthen materials are been used in civil engineering construction worldwide with different forms, such as mud, adobe, rammed earth and bricks. csebs are earthen materials made of soil that are stabilized with different additives, such as cement, fly ash, and lime. csebs have been investigated as a building material for their advantageous properties. compressed earth blocks represent a cost-effective and environmentally friendly alternative building material to traditional masonry elements [1]. in practice, csebs are made of earth stabilized with up to 10% cement and pressed either using a hand-operated press or a hydraulically operated, machine-driven press [2]. csebs are available as bricks, blocks, interlocking blocks and hollow blocks. earthen constructions have many advantages, such as thermal comfort, local employment creation and minimal impact on the environment [3]. the use of earthen constructions is not limited to developing countries, even in developed countries, such as australia, approximately 20% of the new building market is occupied with earth-based construction projects [4]. clay and silt content, cement percentage, and soil grading used for cseb production influence the properties of cseb [5]. soil grading refers to a combination of different size particles in a soil mixture. the selection of the correct sizes in the correct proportion may improve cseb properties. correct sizes and proportion can be better explained with the theory of particle packing. with this background, the aim of this paper is to explain the application of particle packing technology for the improvement of cseb properties. to achieve this aim, the following objectives were considered: • the properties of csebs made with different soils and different particle size distributions were tested. • the soil grade was modified to fit the optimization curve for cseb production, and the improvements in block properties with different amounts of cement stabilization were assessed. ii. literature review a compressed earth block (ceb), also known as a pressed earth block or a compressed soil block, is a building material made primarily from soil compressed at high pressure to form blocks. a mechanical press is used to form blocks out of an appropriate mix of fairly dry inorganic subsoil, non-expansive clay and aggregates. if the blocks are stabilized with a chemical binder such as portland cement, they are called csebs [6]. there are different methods of producing building walls using soil, such as with csebs, wattle and daub materials, rammed earth walls, and cob, or in the recent past, mud blocks [7]. compared to major masonry units such as burnt bricks and cement blocks, csebs have considerable advantages related to corresponding author: s.n. malkanthi engineering, technology & applied science research vol. 9, no. 4, 2019, 4538-4542 4539 www.etasr.com malkanthi & perera: particle packing application for improvement in the properties of compressed … environmental effects. author in [8] mentions low energy consumption and the use of recyclable material. authors in [3] explained the advantages of using cseb in developing countries, as the bricks do not need plastering because they have a finish that is the same as that for wire-cut bricks, hence significantly saving in cost. the major challenges with cseb have been researched by many studies considering strength and durability. the amounts of clay and silt are the main factors that act both positively and negatively with the properties of csebs. a. strength of csebs compressive strength has become a fundamental and universally accepted unit of measurement to specify the quality of masonry units. authors in [9] showed the relationship between the clay and silt content and the compressive strength for different soil-cement ratios. in the test results of [9], the compressive strength displayed an increasing tendency with decreasing clay content and, as expected, it was high for high cement contents. however, other researchers used a minimum clay content limited to 15% [2, 10]. based on their experiments, the compressive strength has tendency to increase with decreasing fines content for different amounts of cement. author in [9] concluded that high compressive strength can be achieved when the plasticity index is low and with 10% cement. however, he tested blocks made with soil having a minimum clay content of 15%. it was also shown in [5], that a compressive strength of more than 10n/mm 2 can be achieved, even with a low plasticity index, when the clay content is between 10% and 15%. the mechanical properties of soil blocks with fiber reinforcement for two different soil types have been investigated in [11]. both soils had more than 40% clay and silt content. for these soil types, the maximum compressive achievement was limited to 3n/mm 2 , even with fiber reinforcement. authors in [12] reported compressive strengths of 1.2, 1.9 and 2.4n/mm 2 with 5%, 8% and 10% cement, respectively, when the soil plasticity index is 13.4. authors in [13] reported compressive strength results of 2.8 and 1.2n/mm 2 for csebs with 7.5% cement and soil having a plasticity index of 12.6 and 14.4 respectively. however, they did not consider any durability issues. in general, csebs with a minimum clay content of 15% have been tested in many studies, but the amount of larger particles has not been considered, which is the main focus of this paper. b. application of particle packing technology for csebs soil properties are the dominant factor of csebs’ properties. different researcher groups found different soil particle combinations, ingredients, etc. particle packing technology is an important aspect of concrete technology to select appropriate sizes and shapes of aggregates. the purpose of this section is to review particle packing technology, its application in different areas, and to match it to csebs. particle packing technology considers optimizing the right sizes and amounts of various particles to increase particle density [14]. additionally, the packing of aggregates for concrete is the degree of how well the solid particles of the aggregates are packed in terms of packing density [15]. the packing density is defined as the ratio of the solid volume of the aggregate particles to the bulk occupied volume. at first, large particles fill the container with large voids and smaller particles are added to reduce the voids. then, tiny particles are filled to further reduce voids and increase density [16]. when well-graded soil is used for csebs, it increases the strength property of the soil blocks. smaller particles should be selected to fill the voids between large particles to increase packing density. the concept of particle packing optimization has been used in the field of concrete technology, such as highperformance concrete [17] and interlocking paving block development [18]. authors in [17, 18] focused on an ideal grading curve that represents the grading with the greatest density. these ideal curves help to perform mixture proportion optimization since it is easy to modify the total particle size distribution by adjusting the ingredient proportions. most studies on particle packing use one of the following particle optimization methods: • optimization curves: groups of particles with a specific particle size distribution are combined in a way that the total particle size distribution of the mixture is closest to an optimum curve. the following are such optimization curves [14, 19]: �(�)= � ��� � � (1) where p(d)=size cumulative distribution function, d=considered particle diameter (m), dmax=maximum particle diameter in the mixture (m), q=parameter (0.33-0.5) which adjusts the curve for fineness or coarseness. authors in [19] utilized (1) with q=0.5 and as per [14]. others have suggested values of q in the range of 0.33-0.5. equation (1) was modified with the adjustment factor q=0.37 for optimum packing [20]: min max min ( ) qq qq d d p d d d − = − (2) author in [21] proposed a maximum density line that provides a guide to blend aggregates and obtain maximum density [21]. authors in [14] showed that when the packing density is high, high compressive strength can be achieved. • particle packing models: these models are analytical models that calculate the overall packing density of a mixture based on the geometry of the combined particle groups. these models are discrete, hence, they consider the definite sizes of different particles. • discrete element models: these models simulate the virtual particle structure from a given size distribution. considering the nature of the above-mentioned three optimization methods, an optimization curve is used to compare the soils used in this study. iii. research methodology as the main consideration of this paper, focus was given on particle packing concepts. first, different soil types were checked for clay and silt content. specifically, a wet sieve analysis test was performed in accordance with astm 117 [22] to determine the clay and silt percentage of the tested soil engineering, technology & applied science research vol. 9, no. 4, 2019, 4538-4542 4540 www.etasr.com malkanthi & perera: particle packing application for improvement in the properties of compressed … samples. csebs were cast from all the tested soil types. based on the research scope, one soil type was selected. the selected soil was washed in order to reduce clay and silt content. in this study, washed soil contained 5% clay and silt. this washed soil was used to produce csebs, and its grading was modified to match the particle packing concept by adding large-size particles that were separated from the same soil earlier. then, previously separated clay and silt (fines) were added to create fine particle percentages of 5%, 7.5% and 10%. for each fines content, 4%, 6%, 8% and 10% cement content was used as stabilizer. for each combination, 10 blocks were cast, resulting in a total of 120 blocks. blocks of 150mm×150mm×150mm were prepared using a commercially available cement sand block-making machine. both vibration and compaction were applied for block casting. the vibration time was regulated based on the preliminary test conducted. cast blocks were cured using wet gunny bags and sprinkling water for 7 and 28 days. the cast blocks were tested to determine their dry and wet compressive strengths, dry density and water absorption, as per sls 1382 (part 2) [23]. each soil block was placed carefully in the testing machine below the center of the upper bearing block, and load was added until failure. using the load at failure, the compressive strength could be determined. figure 1 shows the testing procedure and cast blocks. fig. 1. cast blocks and compressive test procedure the dry density of the blocks was determined after keeping the blocks in the oven for more than 24h at 105 0 c. each specimen was oven-dried to a constant mass, weighed and measured to determine its dry density. � = �������(��) ������(��) �10� (3) to determine the water absorption of the blocks, the ovendried test specimens were immersed in water for 24h and the increase in the mass of each oven-dried test specimen was calculated and expressed as a percentage of the specimen’s initial dry mass. = !�"���"�� ���$�%� ��� ����(�)&'(�) ��� ����(�)'(�) ��� ����(�) �100 (1) iv. testing the particle packing applicability initially, five soil types designated as s1, s2, s3, s4 and s5 were selected for preliminary testing. the s1 soil is industrially washed soil. the s3 and s5 soils are naturally available lateritic soils. the s2 and s4 soils were derived by washing of the s3 and s5 soils, respectively, to reduce clay and silt content. table i denotes the soil grading distribution for each soil. figure 2 shows a comparison with optimization curves based on the theoretical grading curves explained above. all the theoretical curves were considered within the particle size region of 0.075mm to 12mm. table i. soil grading distribution soil type particle size 0-0.075 0.075-2.0 2.0-6.0 6.0-12.0 s1 5 82 9 3 s2 23 24 23 30 s3 35 25 15 25 s4 19 28 20 33 s5 40 30 10 25 fig. 2. comparison of the particle distribution of the used soil with the theoretical distribution these five types of soil with the same cement content added (6%) were used for block casting, and the cast blocks were tested after 28 days for wet and dry compressive strength, block density and water absorption. considering the presented soil types and optimization curves, the particle size distribution of soil types s2 and s3 are closer to the optimization curves. a. cseb properties vs optimization curves five selected soil types were used for cseb manufacturing. table ii gives the tested properties for cast csebs. among the studied soil types, blocks made with soil types s2 and s3 have comparatively high dry and wet compressive strength. however, the other properties of the blocks do not have the highest values but are within the acceptable range specified by [23-25]. these standards define compressive strength values under three grades and those are grade 1 (strength value is above 6.0mpa), grade 2 (4.0-6.0mpa) and grade 3 (2.84.0mpa). the minimum density is 1750kg/m 3 and the maximum water absorption is 15%. blocks made with s1 soil type have high density but low strength. therefore, blocks with s1 were tested with different cement contents, and the results are shown in table iii. the s1 soil has 5% fines after washing of the originally available soil. figure 3 shows the graphical representation of these results. engineering, technology & applied science research vol. 9, no. 4, 2019, 4538-4542 4541 www.etasr.com malkanthi & perera: particle packing application for improvement in the properties of compressed … table ii. block properties (6% cement) soil type fines % compressive strength (mpa) dry density (kg/m3) water absorption (%) 28-day dry 28-day wet s1 5 1.06 0.55 1956 9.5 s2 19 3.01 1.55 1854 12.9 s3 23 2.95 0.82 1778 19 s4 33 1.98 0.69 1713 18.5 s5 40 0.99 0.25 1481 31 table iii. block properties varying cement content cement % compressive strength (mpa) dry density (kg/m 3 ) water absorption (%) 7-day dry 28-day dry 28-day wet 4 0.56 0.71 0.47 1820 10.0 6 0.85 1.06 0.55 1956 9.5 8 1.95 2.26 1.27 1956 10.2 10 3.96 4.49 3.42 1940 8.75 fig. 3. compressive strength of soil blocks with 5% fines, 20% quarry dust, and s1 soil although the soil gradation does not match the available optimization curves, the strength can still be improved with cement addition. however, many past studies highlighted that more than 10% cement is not economical. therefore, this study concerns soil grading near the optimization curve at low cement content. therefore, the available s1 soil type was modified by adding larger particles to match the power line for cseb production, and those blocks were tested. the final soil grading is shown in figure 4 with the corresponding comparison to the optimization curves. this modified soil was used to cast blocks with varying cement content. additionally, the influence of adding quarry dust was tested with 20% quarry dust and 0% quarry dust. figure 5 shows the 28-day dry compressive strength for blocks made with modified s1 soil and 0% and 20% quarry dust for varying cement and fines content. we see that maximum compressive strength for all fines contents can be achieved with 10% cement content. also, the use of quarry dust for the mixture does not have a significant influence on strength. the wet compressive strength, dry density and water absorption results for the tested blocks are shown in table iv. the water absorption ratio clearly shows a notable improvement when optimizing particle packing. the dry density values also show that all the blocks made with upgraded soil arrangements achieve values of more than 1800kg/m 2 . the sls 1382 minimum value is 1750 kg/m 2 . fig. 4. particle size distribution of the modified soil fig. 5. 28-day compressive strength results of soil blocks with modified soil table iv. blocks’ dry density and water absorption soil type clay and silt % cement % 28-day wet compressive strength (mpa) dry density (kg/m3) water absorption % s1 washed soil to obtain 5% fines, 20% quarry dust 5.0 4 0.47 1820 10.0 6 0.55 1956 9.5 8 1.27 1956 10.2 10 3.42 1940 8.75 s1* and 20% quarry dust 5.0 4 1.17 2009 8.43 6 1.26 2009 9.2 8 2.75 2009 7.7 10 5.26 2023 5.1 s1* and 0% quarry dust 5.0 4 0.88 1911 9.3 6 2.73 2009 7.1 8 4.54 2009 7.3 10 5.65 2018 7.1 s1* 7.5 4 0.7 1890 11.3 6 1.19 1961 10.1 8 5.11 2009 7.5 10 7.69 2055 6.8 s1* 10.0 6 3.2 1917 8.7 8 3.8 1865 8.7 10 5.9 1893 8.5 s1*: s1 modified to match the power line by larger particle addition v. conclusion compressed stabilized earth blocks (csebs) have been considered a key researched masonry unit over the past few decades. many researchers have concluded that the compressive strength increases with decreasing clay and silt content. however, most researchers focused on the clay and silt content only. their attempts focused on reducing clay and silt engineering, technology & applied science research vol. 9, no. 4, 2019, 4538-4542 4542 www.etasr.com malkanthi & perera: particle packing application for improvement in the properties of compressed … content by adding different soil, sand, etc. further, studies of the influence of other larger particle sizes have not been extensively performed. this study focused on rearranging the particle distribution of the soil to match the optimization curves while reducing the clay and silt content by soil washing. csebs produced with this rearranged soil showed improvements in their block properties. for this study, the soil was rearranged for three different clay and silt contents: 5%, 7.5% and 10%. the results show that high compressive strength can be achieved with 7.5% clay and silt content and 8% and 10% cement contents. most of the compressive strengths are acceptable for grade i blocks, as per sls 1382. the dry density and water absorption ratio were also higher than the specified values in sls 1382. this study mainly considered the strength characteristics of csebs. many studies have been conducted on the durability of csebs with comparatively high clay and silt contents. nevertheless, improvements are needed to enhance the durability of cseb walls. clay and silt content consist the main barrier to achieve the expected durability performance. therefore, this research will be extended to test the durability issues of csebs with low clay and silt contents. acknowledgment this research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. the authors would like to acknowledge the support given by mr. d.m.n. l dissanayaka, technical officer of structural testing laboratory, mr. h.t.r.m. thanthirige, technical officer of building materials laboratory, and mr. t.p.d.g.i. yohan, technical officer of structural dynamics and health monitoring laboratory, university of moratuwa, sri lanka. references [1] j. d. sitton, b. a. story, “estimating soil classification via quantitative and qualitative feild testing for use in constructing compressed earth blocks”, procedia engineering, vol. 145, pp. 860-867, 2016 [2] k. heathcote, “compressive strength of cement stabilized presses earth blocks”, building and research information, vol. 19, no. 2, pp. 101105, 1991 [3] c. jayasinghe, a. perera, s. west, “the application of hand moulded stabilised earth blocks for rural houses in sri lanka”, international earth building conference, sydney, australia, january 19-21, 2005 [4] m. segetin, k. jayaraman, x. xu, “harakeke reinforcement of soil– cement building materials: manufacturability and properties”, building and environment, vol. 42, no. 8, pp. 3066-3079, 2006 [5] b. v. v. reddy, m. s. latha, “influence of soil grading on the characteristics of cement stabilised soil compacts”, materials and structures, vol. 47, no. 10, pp. 1633-1645, 2013 [6] https://en.wikipedia.org/wiki/compressed_earth_block [7] c. udawatta, r. azoor, r. halwatura, “manufacturing framework and cost optimization for building mud ccncrete blocks (mcb)”, 16th conference of the science council of asia: mobilization modern technologies for sustainable development in asia, colombo, sri lanka, may 30-june 1, 2016 [8] d. j. haris, “a quantitative approach to the assessment of the environmental impact of building materials”, building and environment, vol. 34, no. 6, pp. 751-758, 1999 [9] p. j. walker, “strength, durability and shrinkage characteristics of cement stabilised soil blocks”, cement & concrete composites, vol. 17, no. 4, pp. 301-310, 1995 [10] a. perera, c. jayasinghe, “strength characteristics and structural design methods for compressed stabilized block walls”, international masonry society, vol. 16, pp. 34-38, 2003 [11] h. danso, d. b. martinson, m. ali, j. b. williams, “physical, mechanical and durability properties of soil building blocks reinforced with natural fibres”, construction and building materials, vol. 101, no. 1, pp. 797–809, 2015 [12] c. m. chan, l. p. low, “development of a strength prediction model for “green” compressed stabilised 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to concrete for sustainable development”, organization, technology and management in construction: an international journal, vol. 5, no. 2, pp. 844-852, 2013 [18] h. a. c. k. hettiarachchi, w. k. mampearachchi, “validity of aggregate packing models in mixture design of interlocking concrete block pavers (icbp)”, road materials and pavement desing, vol. 20, no. 2, pp. 462474, 2017 [19] w. b. fuller, s. e. thompson, “the laws of proportioning concrete”, asian journal of civil engineering transport, vol. 59, no. 2, pp. 67143, 1907 [20] j. e. funk, d. r. dinger, coal grinding and particle size distribution studies for coal-water slurries at high solids content, empire state electric energy research corporation, 1980 [21] t. c. powers, the properties of fresh concere, wiley, 1968 [22] astm, astm c 117 (2009): standard test method for materials finer than 75-µm (no. 200) sieve in mineral aggregates by washing, astm, 2009 [23] sri lanka standard institution, sls 1382 (2010): specification for compressed stabilized earth blocks: part 2 test methods, sri lanka standard institution, 2010 [24] sri lanka standard institution, sls 1382 (2010): specification for compressed stabilized earth blocks: part 1 requirements, sri lanka standard institution, 2010 [25] sri lanka standard institution, sls 1382 (2010): specification for compressed stabilized earth blocks: part 3 guildlines on production, design and construction, sri lanka standard institution, 2010 microsoft word 04-3524_s1_etasr_v10_n4_pp5889-5895 engineering, technology & applied science research vol. 10, no. 4, 2020, 5889-5895 5889 www.etasr.com soomro et al.: simulation-based analysis of a dynamic voltage restorer under different voltage sags … simulation-based analysis of a dynamic voltage restorer under different voltage sags with the utilization of a pi controller abdul hameed soomro electrical engineering department quaid-e-awam university of engineering science & technology campus larkano, pakistan hameedsoomro13@yahoo.com abdul sattar larik electrical engineering department mehran university of engineering. & technology jamshoro, pakistan sattar.larik@faculty.muet.edu.pk mukhtiar ahmed mahar electrical engineering department mehran university of engineering & technology jamshoro, pakistan mukhtiar.mahar@faculty.muet.edu.pk anwar ali sahito electrical engineering department mehran university of engineering & technology jamshoro, pakistan anwar.sahito@faculty.muet.edu.pk izhar ahmed sohu universty of tun hussein onn malaysia izharahmedsohu@gmail.com abstract-power quality problems are becoming a major issue. every utility company consumer desires to receive steady-state voltage, i.e. a sinusoidal waveform of constant frequency as generated at power stations, but the influence of disturbances in the shape of sags and swells, interruptions, transients and harmonic distortions which affect power quality, resulting in loss of data, damaged equipment, and augmented cost. the most powerful voltage disturbance is the sag voltage. in this paper, a dynamic voltage restorer (dvr) is proposed for sag voltage compensation. it is cost-effective and protects critical loads in a good manner from balanced or unbalanced sag voltage. control strategy (such as a pi controller) is adopted with dvr topology and the performance of such a device with the proposed controller is analyzed through simulation in matlab/simulink. three types of faults are utilized, which are available in matlab/simulink pack, for obtaining the sag voltage. the specific range of total harmonic distortion percentage is also discussed. after the result validation of the dvr topology in matlab/simulink, it has been seen that the proposed topology is able to compensate the sag voltage of any type of fault and reduce the unbalancing and voltage distortions of the grid. keywords-dynamic voltage restorer (dvr); voltage source inverter (vsi); faults; power quality i. introduction globally, power quality problems are becoming a major issue. the distribution system network supplies voltage to consumers for utilization [1, 2]. every consumer desires to receive a steady state voltage, i.e. a sinusoidal wave form of constant frequency as generated at power stations but disturbances produced on the distribution system [3] result in distorted waveforms, which create a difficulty in the operation of electrical and electronic equipment in industries risking production loss, restarting expenses, and breakdown [4]. voltage disturbances are sag and swell voltage, unbalance voltage, voltage fluctuations, small and large interruptions, harmonic distortions, and transients [5]. the most powerful disturbance is sag voltage: it is defined as a decrease in voltage from 10% to 90% for durations up to one minute [6]. mostly voltage sags are observed during the start of an induction motor, the energization of a transformer, system faults, or nonliner loads [7-9]. the problem of sag voltage can be avoided through the application of voltage compensation devices such as a dynamic voltage restorer (dvr) [10, 11]. ii. dynamic voltage restorer dvr is a commonly used device for sag voltage compensation. the dvr is connected in series to the sensitive loads and adds the needed voltage when necessary. dvr voltage sag compensation is a cost effective method applicable in small and large loads up to 45mva or even larger [9]. dvr is mainly composed of components such as the voltage source inverter (vsi), a voltage injection device, a filter, an energy storage device, and a controlling device [12, 13]. figure 1 shows the proposed dvr topology. corresponding author: abdul hameed soomro engineering, technology & applied science research vol. 10, no. 4, 2020, 5889-5895 5890 www.etasr.com soomro et al.: simulation-based analysis of a dynamic voltage restorer under different voltage sags … fig. 1. proposed dvr iii. dvr components a. energy storage unit through this commonly used in dvr topology unit, low and high values of voltage are compensated and the efficiency of dvr increases. usually batteries, superconducting magnetic and super capacitor energy storages are utilized as energy storage units [12-14]. b. voltage source inverter this is the most valuable component in dvr topology. it allows supplying the necessary voltage to the load for compensation. vsi is composed of power electronic components and has the capability of changing the direct current (dc) into a sinusoidal current (ac) with the desired amplitude, frequency and phase angle supplied by the energy storage unit. vsi is switched on through dc voltage supply of small input impedance and output voltage is independent of load current [9]. c. filter dvr is a non-linear device because of its semiconductor components. this would result in distortion in the output voltage waveforms. to avoid the problem of distorted wave forms, a filter is employed to get distortion free voltage to the load [9, 12, 15]. d. voltage injection device a voltage injection device such as the power transformer is employed in dvr topology and connected with each phase individually. its main purpose is to add the needed voltage to the load. better performance and reliability of voltage injection transformer is based on the selection of mva rating, impedance and turns ratio [9, 14]. e. by-pass switch large current flows after the occurrence of fault on the power system will result in excessive current flows through the dvr, so it is essential to give another path to the current. this can be achieved through the by-pass switch. f. controlling device the controller has an imperative role in any system. in dvr, the controller is contributed to the role of an observer of bus-bar voltage. if voltage sag is detected then it closes the bypass switch and the required voltage is added to the load. iv. dvr operating modes the dvr operates in three modes [9, 16], which are presented below. a. standby mode the dvr is not supplying voltage to the load during this mode but due to transformer reactance it may inject some voltage for voltage drop compensation [9]. b. protection mode faults on the power system result in the flow of heavy currents which result in damaging the dvr [9]. so, protection of the dvr is necessary by using protective devices such as breakers [17, 18]. c. injection mode when a voltage sag is sensed, the dvr comes into operation very quickly [15] and the required voltage value is added to the load. in this way, the voltage sag is compensated [9]. v. voltage injection techniques there are four voltage injection techniques employed in dvr topology [19]: a. pre-sag technique this technique is superior, because through it, the voltage difference before and after the sag is added to the load but it needs an energy storage unit of large capacity because of the un-controlled injected active power. b. phase advance technique in this technique, dvr use of real power is trimmed-down through the reduction in power angle. c. voltage tolerance with minimum energy technique in this technique, we can retain the load voltage in the patience area of less variation of voltage magnitude. d. in-phase voltage injection technique in this technique, the non-variable value of load voltage is achieved despite different phase angles of pre-sag and load voltage due to in-phase association of the added voltage with supply voltage. vi. proposed methodology a. voltage sag calculation source voltage and source reactance (�� and ��) are shown in the equivalent circuit in figure 2 and loads such as �� and �� are supplied through two feeders named �� and �� . under normal operating condition, the supply current � and pre-sag voltage at the common coupling point are shown in (1): � � � � � �� ��������� � � �� ��������� (1) where � is the impedance of the load, �� is the feeder reactance magnitude, and � is the supply current. when abnormal conditions occur (fault on feeder ��) the result is the flowing of large load and supply current. equations (2)-(3) show the supply voltage and fault current at the common coupling point. engineering, technology & applied science research vol. 10, no. 4, 2020, 5889-5895 5891 www.etasr.com soomro et al.: simulation-based analysis of a dynamic voltage restorer under different voltage sags … �� �� � �,���� �� (2) �,���� ! ���� ��� � ���������� (3) it has been seen that, the voltage across f2 is decreased because of the large voltage drop, also called sag voltage, produced across the �� (source reactance). figure 3 shows the equivalent circuit where the dvr is connected and adds the needed voltage �"�# to the critical load to compensate the value of sag voltage. fig. 2. sag voltage calculation. fig. 3. voltage injection through the dvr. fig. 4. proposed one line diagram. figure 4 shows the one line diagram of the 11kv, 50hz power system, which generates voltage, the three winding power transformer of star grounded/delta/delta, which supplies voltage to two transmission lines. these two transmission lines supply voltage to two distribution systems and these two supply voltages are stepped down to 0.4kv through the distribution transformer which is connected in star and delta. the faulty feeder where different faults will occur at point x is connected through bus-a and the neighboring feeder where sensitive loads are connected is represented by bus-b. the dvr performance is authenticated by applying different types of faults with 130ms fault time. b. voltage total harmonic distortion power quality (system output voltage) is well defined through total harmonic distortion (tdh) method. a 5% or less voltage tdh is acceptable when the voltage magnitude is up to 69kv. the border line for single frequency voltage harmonic is 3% [21]. equations (4)-(5) show the voltage tdh calculated at the common coupling point, where the harmonic number is symbolized by h and the phase order is symbolized by p, so p is equal to a, b, c [22, 23]. $%&' ()"*� �()"*+�()", (4) $%&�. /∑ 12� �� .1��3�. 4100 (05) c. voltage sag indice sag voltage and recovered voltage quality is pointed-out through sag voltage indices which are very sensitive to voltage disturbances and provide a precise response on the performance of the system. the below mentioned indices are also conversed in simulation outcomes. 1) detroit edison sag score (ss): for contracts between utilities and customers, the first utilized index was s detroit edison sag score. it is defined by [24]: 55 1 � ����+��, (6) where ��, �7 and �8 are the phase voltages. if we get the outcome of 55% near to 0, then we can say that, after sag voltage compensation, the recovered voltage is better. 2) voltage sag lost energy index (vslei) this type of index provides the lost energy (w) when a reduction in voltage is observed for short duration. the same is applied to the load as shown in (7): : ∑ �. ∑ $.; ; 4 <1 � � �=>?@=�a b -.�d (7) where e f, g, h , �. is the phase voltage during the occurrence of sag and $. is the sag period (ms) for every phase [25]. when the calculations are carried out for the three phases, the required energy is added to the phases individually. 3) phase voltage unbalance rate (pvur) pvur [25] is given by: e�ij k�lmn�n*o ��*� 4 100 (8) where �q shows the variation in phase voltage from ��'r. vii. dvr control algorithm in this study, the pi controller is proposed for the dvr and parks transformation stu method is used for the generation of the reference voltage as shown in (9) to the series voltage source inverter to search for and maintain the load side voltage at its actual value. v represents the angular frequency (rad/s). engineering, technology & applied science research vol. 10, no. 4, 2020, 5889-5895 5892 www.etasr.com soomro et al.: simulation-based analysis of a dynamic voltage restorer under different voltage sags … through this method, the three phase voltages are easily controlled because of the transformation from three phase to two voltage components (wx and wy) while the zero sequence components of phases fgh are neglected. as shown in control block diagram in figure 5, free wave distortion is basically generated through a phase locked loop (pll) circuit [26]. z �q �[ �u \ �]̂ ^̂ _ 2 sin vd 2 sinevd � �fg 2 sinevd � �fg2 cos vd 2 cosevd � �fg 2 cosevd � �f g 1 1 1 jk kk l m �� �7 �8 n (9) fig. 5. dvr controller scheme. the dvr controller is employed to observe the load voltage on bus-bar and the load voltage components are compared with dq components. when the voltage is trimmeddown, an error signal is produced between the measured and the reference voltage to activate the controller whereas the output signal is produced from the proposed controller to add the needed voltage to the load. in-order to get a distortion-free output voltage, it is necessary to add a filter. in this study, a lc low pass filter is proposed for the suppression of harmonic distortion and switching signals of 5.5khz for frequency modulation are considered. pulse width modulation (pwm) technique is used for vsi for the production of three 50hz phases at load terminals. an igbt switching device for vsi is selected for the study of the dvr operation. viii. simulation results the controller’s performance under harmonic distortions and non-linear load is analyzed by applying three conditions in matlab simulation scenarios. the applied mathematical statistics is available in [26]. the three fault conditions which are applied to the system to evaluate the performance of dvr are presented in table i and are discussed below. table i. fault conditions condition fault type condition i three phase to ground fault condition ii double line to ground fault condition iii single line to ground fault • fault condition i: under this fault condition, the system will be in type a voltage sag. the value of voltage sag is equal in the three phases (balanced voltage sag condition). • fault condition ii: under this fault condition, the system will be in types e, f, and g sag voltage depending on the transformer connection between fault point and bus. if the measured bus is with &/pr transformer then the observed sag voltage is of the f type. • fault condition iii: under this fault condition, the system will be in types b, c, and d sag voltage, depending on the value and direction of healthy phases. when a change in direction is observed with no change in magnitude, then we can say that the system is under voltage sag of c-type. table ii. dvr system stricture s.no strictures value 1 line resistance 1.0ω 2 line inductance 5.8mh 3 line frequency 50hz 4 phase voltage of the load 220v 5 per phase power of the load 100ws 6 per phase inductive power of the load 0.3kvar 7 per phase capacitive power of the load 0.6kvar 8 turns ratio of injection transformer 1:1 9 dc voltage 200v 10 filter inductance 70mh 11 filter resistance 0.2ω 12 filter capacitance 5.0µf fig. 6. voltage vs time in faulty feeder at fault condition i. fig. 7. un-compensation of voltage vs time at fault condition i. fig. 8. voltage compensation vs time at fault condition i. fig. 9. voltage vs time of faulty feeder at fault condition ii. for observing voltage sags, each fault condition is applied to the system for 130ms. table iii shows the outcome when the voltage sag is not compensated. table iv shows the outcome when the voltage sag is compensated after the application of the dvr. it has been seen that, thdv% and pvur% are as per [25]. so it is observed that the proposed topology is suitable for sag voltage compensation under three conditions (in condition i-50%, in condition ii-24.2% and in condition iiiengineering, technology & applied science research vol. 10, no. 4, 2020, 5889-5895 5893 www.etasr.com soomro et al.: simulation-based analysis of a dynamic voltage restorer under different voltage sags … 1.85%). figures 6–14 show the voltage waveforms (faulted, un-compensated and compensated voltage waveforms) under the three fault types. table iii. system outcome after voltage sag occurence stricture fault condition i ii iii $%&��% 4.20 3.20 0.94 $%&�7% 8.10 8.15 0.98 $%&�8% 8.61 2.90 0.44 $%&�% 6.95 4.80 0.80 e�ij% 8.94 16.32 1.48 55% 50.01 24.23 1.87 �5qr s 47.48 17.20 0.02 table iv. system outcome after voltage sag compensation stricture fault condition i ii iii $%&��% 0.48 0.99 0.57 $%&�7% 1.79 1.7 0.56 $%&�8% 1.70 1.10 0.010 $%&�% 1.29 1.25 0.38 e�ij% 0.50 0.70 0.02 55% 1.99 0.69 0.23 �5qr s 0.0020 0.000320 0.0000020 fig. 10. un-compensation of voltage in volts versus time at condition-ii. fig. 11. compensation of voltage vs time at fault condition ii. fig. 12. voltage vs time of faulty feeder at fault condition iii. figure 15 shows the voltage thdv% of the energy storage capacity. it has been seen that the smallest value of voltage thdv% is achieved by the utilization of 200dc voltage. the variation of ss% according to the change of energy storage capacity is shown in figure 16. it has been seen that 200dc voltage is a suitable choice which attains the lowest ss%. figure 17 shows the pvur% according to the change in produced energy after the compensation as per change of storage capacity. it has been seen that 130dc voltage is the smallest voltage which is able to meet the terms of the ieee standard 112-1991 with less than 2% of phase unbalance rate. fig. 13. un-compensation of voltage vs time at falut condition iii. fig. 14. compensation of load voltage vs time at fault condition iii. the dvr is connected to the linear load. fig. 15. variance of $%&�% in competition with energy storage. fig. 16. variation of 55% in competition with energy storage . fig. 17. variation of e�ij% in competition with energy storage. table v. system outcome after voltage sag occurence with linear and non linear loads stricture fault condition i ii iii $%&��% 5.49 3.97 4.39 $%&�7% 7.49 9.68 5.67 $%&�8% 9.60 3.35 5.58 $%&�% 7.52 5.67 5.19 e�ij% 7.90 14.58 1.24 55% 50.63 30.99 12.00 �5qr s 47.73 18.57 0.57 engineering, technology & applied science research vol. 10, no. 4, 2020, 5889-5895 5894 www.etasr.com soomro et al.: simulation-based analysis of a dynamic voltage restorer under different voltage sags … table vi. system outcomes after voltage sag compensation with of linear and non linear loads stricture fault condition i ii iii $%&��% 0.83 2.39 1.17 $%&�7% 1.83 3.02 1.07 $%&�8% 1.96 1.30 1.63 $%&�% 1.53 2.23 1.29 e�ij% 0.51 1.35 0.13 55% 2.03 2.20 0.31 �5qr s 0.001 0.0069 0.000 ix. conclusion voltage sag is a critical problem which affects a distribution system network causing loss of data, damaging equipment, reducing production loss, and increasing cost. in this paper, a dynamic voltage restorer is proposed for voltage sag compensation as a cost effective solution that protects critical loads in a good manner from balanced or un-balanced voltage sag. control strategy (i.e. a pi controller) is adopted within the dvr topology and the performance of such a device with the proposed 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[24] r. a. barr, v. j. gosbell, and i. mcmichael, “a new saifi based voltage sag index,” in 2008 13th international conference on harmonics and quality of power, oct. 2008, pp. 1–5, doi: 10.1109/ichqp.2008.4668806. engineering, technology & applied science research vol. 10, no. 4, 2020, 5889-5895 5895 www.etasr.com soomro et al.: simulation-based analysis of a dynamic voltage restorer under different voltage sags … [25] “ieee standard test procedure for polyphase induction motors and generators,” ieee std 112-1991, 1991, doi: 10.1109/ieeestd.1991.114383. [26] s. h. e. a. aleem, a. m. saeed, a. m. ibrahim, and e. e. a. el-zahab, “power quality improvement and sag voltage correction by dynamic voltage restorer,” international review of automatic control (ireaco), vol. 7, no. 4, pp. 386-393–393, jul. 2014, doi: 10.15866/ireaco.v7i4.2160. etasr paper format engineering, technology & applied science research vol. 9, no. 2, 2019, 4053-4056 4053 www.etasr.com al-khazaal et al.: study on the removal of thiosulfate from wastewater by catalytic oxidation study on the removal of thiosulfate from wastewater by catalytic oxidation abdulaal z. al-khazaal chemical engineering and materials engineering department, northern border university, arar, saudi arabia abdulaal.alkhazaal@nbu.edu.sa farooq ahmad chemical engineering and materials engineering department, northern border university, arar, saudi arabia farooq.amin@nbu.edu.sa naveed ahmad chemical engineering and materials engineering department, northern border university, arar, saudi arabia naveed.ahmad@nbu.edu.sa abstract-wastewater streaming from industrial plants, including petroleum refineries, chemical plants, pulp and paper plants, mining operations, electroplating operations, and food processing plants, can contain offensive substances such as cyanide, sulfides, sulfites, thiosulfates, mercaptans and disulfides that tend to increase the chemical oxygen demand (cod) of the streams. in the present work, removal of thiosulfate from wastewater by catalytic oxidation using aluminum oxide as a catalyst was studied. four main factors were considered, namely the initial thiosulfate concentration, the hydrogen peroxide concentrations, the amount of the catalyst and the operating temperatures. the analysis of thiosulfate and sulfate was carried out by using uv visible spectrophotometer. an empirical rate equation was developed. keywords-thiosulfate oxidation; kinetic model; catalytic oxidation; wastewater treatment i. introduction sulphur can be found in a variety of oxidation states, with three oxidation states of −2 (sulphide and reduced organic sulphur), 0 (elemental sulphur) and +6 (sulphate) being the most significant in nature. thiosulfate is often produced from an incomplete oxidation of sulfides (pyrite oxidation) or partial reduction of sulfate. the reactions that lead to thiosulfate formation are [1]: 8h2s + 4o2 → s8 + 8h2o (1) h2s + 3/2o2 → 2h + + so3 2 (2) so3 2+ 1/8s8 → s2o3 2 (3) h2s + 2o2 → 2h + + so4 2 (4) 2s2+ 3/2o2→ s2o3 2 (5) so4 + 5h + → ½s2o3 + 5/2h2o (6) thiosulfates are stable in neutral or alkaline solutions, but not in acidic solutions, due to their decomposition to sulfite and sulfur, the sulfite being dehydrated to sulfur dioxide: s2o3 2−(aq) + 2h+(aq) → so2(g) + s(s) + h2o (7) this phenomenon could cause a rise of water ph, increasing enrichment of s2-and s0 in pore water, and finally plant death and inhibition of nitrification by sulfide toxicity, while the thiosulfates are a very aggressive species regarding metal corrosion. [2] based on [3], it was found that the concentration of thiosulfate in refinery wastewater is about 174ppm and for other wastewater, the thiosulfate concentration is about 2050ppm. according to [4], the traditional method of treating thiosulfate containing wastes is by oxidation to sulfate which can be accomplished either chemically by using oxidizing agents (e.g. peroxide) and oxidation catalysts (e.g. complexed copper (ii)), or biological using aerobic processes such as activated sludge systems. several aerobic and anaerobic microorganisms have the ability to utilize thiosulfate and other sulfur species as sources of energy. the most important aerobic microorganisms are sulfur chemolithoautotrophic bacteria (sulfur autotrophs), which use various reduced forms of sulfur as energy sources (electron donors) and oxygen as the electron acceptor. the final product of the complete dissimilatory oxidation of these compounds is sulfate. in [5], authors removed sulfide from wastewater by oxidizing it to sulfate using hydrogen peroxide in the presence of iron oxide catalyst. they synthesized iron oxide catalyst using the sol-gel technique and used different analytical techniques including scanning electron microscopy (sem), fourier transform infrared spectroscopy (ft-ir), thermal gravimetric analysis (tga) and energy dispersive x-ray spectroscopy (edx). their results were further explained by a kinetic study. authors in [6] studied the treatment of wastewater containing thiosulfate by photo oxidation. they treated thiosulfate containing wastewater by aeration in the presence of uv light and found that the treatment process thus accelerates. they explained their results by carrying out a kinetic study of the process. authors in [7] explored the treatment of sulfidic wastewater by aeration in the presence of ultrasonic vibration. they examined the oxidation of sulfide by aeration in the presence of ultrasonic vibration and found that the oxidation process was faster. kinetics of the treatment process was also studied. author in [8] studied the oxidation of thiosulfate in the presence of ultrasonic vibration. the process was studied at different initial thiosulfate concentrations, different ultrasonic vibrations and at different hydrogen peroxide dosages. the results were further explained by studying the kinetics of the treatment process. corresponding author: abdulaal z. al-khazaal http://en.wikipedia.org/wiki/alkali http://en.wikipedia.org/wiki/sulfite http://en.wikipedia.org/wiki/sulfur http://en.wikipedia.org/wiki/sulfur_dioxide engineering, technology & applied science research vol. 9, no. 2, 2019, 4053-4056 4054 www.etasr.com al-khazaal et al.: study on the removal of thiosulfate from wastewater by catalytic oxidation ii. experimental work a. materials solutions with different thiosulfate concentrations were prepared synthetically. sodium thiosulfate of 60% purity was used to prepare the test solutions. the changes in thiosulfate and sulfate concentrations were examined by the dr-5000 uvvisible spectrophotometer. distilled water was used to prepare the test solution. the analysis of sulfate was carried out by dr5000 uv-visible spectrophotometer using barium chloride as a reagent [5-8]. b. catalyst preparation aluminum oxide (al2o3) catalyst was prepared from aluminium chloride and ammonium hydroxide by the sol-gel technique. aluminum oxide was used as a catalyst for the treatment of wastewater containing thiosulfate. the aluminum oxide prepared by the sol-gel technique was dried in the oven for 24h before use [5]. c. methodology oxidation of thiosulfate was carried out in a jacked glass reactor. the carried out experiments were divided into four groups. first the process was explored at different initial thiosulfate concentrations (700ppm, 1400ppm, 2100ppm and 2800ppm). the second experiment was carried out at hydrogen peroxide loading (0.8, 1.6, 2.4, 3.2 molar). in the third experiment, the treatment process was explored at different catalyst loadings (0.25g, 0.50g, 1.0g and 1.5g). finally, the effect of temperature was explored. the process was repeated at 35oc, 45 oc, and 55oc. iii. results and discussion a. effect of initial thiosulfate concentration the process was carried out at four different initial thiosulfate concentrations. catalyst and h2o2 amounts were kept constant throughout the experiments, 0.25g and 0.8 molar respectively. the experiment was conducted at room temperature (25oc). figures 1 and 2 clarify that the rate of sulfate formation or/and thiosulfate drop increases as the initial concentration of thiosulfate increases. an increase in the initial thiosulfate concentration increases the amount of thiosulfate ions per sample to be reacted and form sulfate ions. thus the formation of the sulfate ions increases. this finding shows that initial thiosulfate concentration is one of the main components in the rate law of this advanced oxidation process. b. effect of hydrogen peroxide concentration the treatment process was also explored at different hydrogen peroxide loadings. the results are shown graphically in figures 3 and 4. we see that the concentration of sulfate formation and/or thiosulfate drop increases as the concentration of h2o2 increases from 0.8 to 1.6 molar. while, the formation of the sulfate ions is less as the h2o2 increases to 2.4 molar and 3.2 molar. these results showed that the optimum concentration for h2o2 in this experiment is 1.6 molar because most of thiosulfate ions were being consumed. the reason for this is that h2o2 mainly functions as the agent to produce hydroxyl radical that reacts in the thiosulfate oxidation process. furthermore, the slope of the graph indicated the formation of sulfate ions which increases quickly at the first three readings for all h2o2 concentration and the slope starts to decline and become constant afterwards. fig. 1. thiosulfate concentration versus time for different thiosulfate concentrations. catalyst loading: 0.25g, h2o2: 0.8m. fig. 2. concentration of sulfate formation for different thiosulfate concentrations versus time. catalyst loading: 0.25g, h2o2: 0.8m. fig. 3. concentration of sulfate formation for different molar h2o2 concentrations versus time. catalyst loading: 0.25g, initial thiosulfate concentration=1400ppm. c. effect of catalyst loading the effect of catalyst loading was investigated. figures 5 and 6 show different catalyst loadings ranging from 0.25 to 1.5g used to explore the treatment process. the sulfate formation or/and thiosulfate drop were found to increase with increasing concentration of the catalyst, reaching the highest value of 1320mg/l and 630mg/l respectively, and then became constant. this may be due to the fact that when most of thiosulfate ions have reacted, the addition of higher quantities of catalyst would have no effect on the reaction. engineering, technology & applied science research vol. 9, no. 2, 2019, 4053-4056 4055 www.etasr.com al-khazaal et al.: study on the removal of thiosulfate from wastewater by catalytic oxidation fig. 4. concentration of thiosulfate for different molar h2o2 concentrations versus time. catalyst loading: 0.25g, initial thiosulfate concentration=1400ppm. fig. 5. concentration of sulfate formation versus time for different catalyst amounts. h2o2: 0.8m, initial thiosulfate concentration=1400ppm. fig. 6. concentration of thiosulfate versus time for different catalyst amounts. h2o2: 0.8m, initial thiosulfate concentration=1400ppm. d. effect of temperature the temperature of the reaction is important to the efficiency of the reaction. figures 7 and 8 describe the influence of temperature on the treatment process. with increase in temperature from 350c to 450c we found that the sulfate formation only shows an increment at the first three readings. after that it starts to decrease for the temperature of 35oc, and remains constant for 45oc. however, when the temperature is further increased to 55oc, sulfate formation and/or thiosulfate drop is found to suppress. from these results it can be concluded that the optimum operating temperature for this h2o2 advanced oxidation process with al2o3 catalyst is between 25oc and 45oc. fig. 7. concentration of sulfate formation versus time in various temperatures. h2o2: 0.8m, initial thiosulfate concentration=1400ppm, catalyst loading=0.25g. fig. 8. concentration of thiosulfate versus time in various temperatures. h2o2: 0.8m, initial thiosulfate concentration=1400ppm, catalyst loading=0.25g. e. kinetic study an empirical rate equation was developed. the orders with respect to all reactants and for the overall reaction were determined. the reactants were hydrogen peroxide (h2o2) and thiosulfate ion (s2o3 2-). when a catalyst is used the reaction rate may be stated on a catalyst weight basis. thus, the rate of the reaction becomes: rate=-k[ s2o3 2-]α [h2o2] β[al2o3] γ (8) k=ae(-ea/rt) (9) where k is the reaction rate constant and α, β and γ are the reaction orders for s2o3 2, h2o2 and al2o3 respectively. from (8)-(9), we can see that the rate is proportional with [s2o3 2-]α, [h2o2] β and [al2o3] γ. the mathematical relations of this explanation are shown below, with rate α being [ s2o3 2-]α, rate β being [h2o2] β, and rate γ being [al2o3] γ. thus: rα=[s2o3 2-]α (10) lnrα=αln[s2o3 2-] (11) rβ=[h2o2] β (12) lnrβ=β ln [h2o2] (13) rγ=[al2o3] γ (14) lnrγ=γ ln [al2o3] (15) using the above equations, rates and orders with respect to each reactant are calculated. the orders of reaction with respect to thiosulfate, hydrogen peroxide and catalyst were found to be 0.421, 0.556 and 0.558 respectively. the order of reaction with engineering, technology & applied science research vol. 9, no. 2, 2019, 4053-4056 4056 www.etasr.com al-khazaal et al.: study on the removal of thiosulfate from wastewater by catalytic oxidation respect to hydrogen peroxide was found by plotting the rate of reaction against concentration of hydrogen peroxide as shown in figure 9 which is the logarithmic plot of the rate of the reaction of thiosulfate oxidation and hydrogen peroxide concentration. the slope of the plot gives us the order of reaction with respect to hydrogen peroxide. using arrhenius equation, activation energy was found to be 3507kj/mol. fig. 9. plot of the reaction order with respect to h2o2. iv. conclusion thiosulfate from wastewater can be removed by catalytic oxidation using hydrogen peroxide as an oxidant. the following points can be concluded from this study:  the reaction rate depends on the reactant species which are thiosulfate and h2o2 in this project. however, compared to thiosulfate, the concentration of hydrogen peroxide has a bigger effect on the reaction rate.  the amount of catalyst also played an important role in supporting the rate of formation of sulfate ions. increasing the amount of catalyst increases the rate of reaction.  temperature affects the treatment process. however, increase in temperature above 45oc has no positive effect on the progress of treatment process. the optimum temperature of the treatment process is in the range of 25oc to 45oc.  the treatment process is also affected by the dose of hydrogen peroxide. dosage of higher hydrogen peroxide from a certain limit increases only the level of hydroxyl ions and has no fruitful effect on the treatment process. the optimum dosage of hydrogen peroxide in the current study was found to be 1.6m.  the rate of the reaction is also influenced by the initial thiosulfate concentration. increase in the initial concentration of thiosulfate increases the rate of the reaction.  the orders of reaction for all reactants were found positive, which means that increase in their initial concentration will increase the rate of the reaction. references [1] r. h. dinegar, r. h. smellie, v. k. la mer, “kinetics of the acid decomposition of sodium thiosulfate in dilute solutions”, journal of the american chemical society, vol. 73, pp. 2050-2054, 1951 [2] t. yan, removal of cyanide, sulfides and thiosulfate from ammonia containing wastewater by catalytic oxidation, us patent, no. 5360552, 2001 [3] dionex, determination of thiosulfate in refinery and other wastewaters, application note 138, dionex, 2001 [4] d. c. schreiber, s. g. pavlostathis, “biological oxidation of thiosulfate in mixed heterotrophic/autotrophic cultures”, water research ,vol. 32, no. 5, pp. 1363-1372, 1998 [5] n. ahmad, s. maitra, b. k. dutta, f. ahmad, “remediation of sulfidic wastewater by catalytic oxidation with hydrogen peroxide”, journal of environmental sciences, vol. 21, no. 12, pp. 1735-1740, 2009 [6] n. ahmad, f. ahmad, i. khan, a. daud khan, “studies on the oxidative removal of sodium thiosulfate from aqueous solution”, arabian journal for science and engineering, vol. 40, no. 2, pp. 289-293, 2015 [7] f. ahmad, n. ahmad, a. z. al-khazaal, i. alenezi, “remediation of sulfidic wastewater by aeration in the presence of ultrasonic vibration”, engineering, technology & applied science research, vol. 8, no. 3, pp. 2919-2928, 2018 [8] f. ahmad, “a new approach for the removal of thiosulfate from wastewater”, international journal of chemical and enviromental engineering, vol. 3, no. 5, pp. 303-308, 2012 [9] f. ahmad, n. ahmad, s. maitra, “treatment of sulfidic wastewater using iron salts”, arabian journal for science and engineering, vol. 42, no. 4, pp. 1455-1462, 2017 https://www.sciencedirect.com/science/article/pii/s100107420862481x https://www.sciencedirect.com/science/article/pii/s100107420862481x https://link.springer.com/article/10.1007/s13369-014-1473-0 https://link.springer.com/article/10.1007/s13369-014-1473-0 i. introduction ii. experimental work a. materials b. catalyst preparation c. methodology iii. results and discussion a. effect of initial thiosulfate concentration b. effect of hydrogen peroxide concentration c. effect of catalyst loading d. effect of temperature e. kinetic study iv. conclusion references microsoft word 17-2661_s engineering, technology & applied science research vol. 9, no. 2, 2019, 3959-3964 3959 www.etasr.com demetillo & taboada: real-time water quality monitoring for small aquatic area using unmanned … real-time water quality monitoring for small aquatic area using unmanned surface vehicle alexander t. demetillo college of engineering and information technology caraga state university butuan city, philippines atdemetillo@carsu.edu.ph evelyn b. taboada school of engineering university of san carlos cebu city, philippines evelynbtaboada@gmail.com abstract—most developing countries depend on conventional water quality monitoring methods which are usually expensive, complicated, and time-consuming. in recent years, stationary and portable water quality monitoring and a mobile surface vehicle have increased the utilization of on-site water measurements and monitoring. the first has the disadvantage of small coverage area while the second has its cost and operational complexity. this paper addresses these issues by placing materials and equipment used in fixed online water quality monitoring and using a customized and low-cost unmanned surface vehicle. the measurements are taken automatically on the equipment onboard the unmanned surface vehicle (usv), transmitted wirelessly to a pc-based remote station or nearby stations and saved there in a dedicated database. the overall system comprises a commercial water quality sensor, a gsm and zigbee module for a wireless communication system, a low-cost mobility platform, and the location/positioning system. during testing, all captured data like water quality parameters, location, and other essential parameters were collated, processed and stored in a database system. relevant information from the usv can be viewed on a smartphone or a computer. the usv was also tested to conduct unmanned water quality measurements using the preinputted navigation route which shows a good result in navigation and data transmission. water bodies with calm water such as lakes and rivers can use the usv, in a stand-alone mode or as a part of a networked sensor system. keywords-unmanned surface vehicle; water quality monitoring; wireless transmission i. introduction because of population increase, industrialization and climate change, water demand is increasing at an alarming rate [1-3]. the sources of potable water are limited and vulnerable, thus the need for water quality monitoring in rivers, lakes, and other freshwater bodies is becoming a more pressing issue [4]. there is a growing demand to implement a mechanism to enhance the effectiveness of existing water quality monitoring methods. mostly, water quality information gathering uses traditional or manual methods for various reasons ranging from lack of technology capacity, human resources and financial constraints [5-7]. these techniques or methodologies are usually accurate and inexpensive, but suffer from various disadvantages like the loss of vital information during transport, limited samples, and cost-effectiveness. they cannot perform real-time monitoring which could mitigate or prevent uncertain happenings in a particular area [8]. nowadays, some advanced countries perform water quality monitoring using innovative technologies like utilizing an electrochemical sensor which can give water quality information in real-time [10-11], maximizing the advantages of recent technology by combining electrochemical sensors with wireless communication technology [11]. the system automatically senses data, transmits it to the notification node and will alarm if the parameters exceed their limits. authors in [12] successfully demonstrated a method of deployment of a wireless sensor network with a mechanism to reduce traffic between base and remote stations for water quality monitoring wherein stationary stations could detect essential water parameters in real time. gathered data were transmitted every five minutes to the base station through multi-hoop routing using a flooding routing protocol. however, the stationary platform also has the disadvantages of high cost of covering the whole study area [13], of provision of sensors in every sampling point and lack of mobility [14]. with these, the development of a mobile technology which will take advantage of the water quality monitoring capability of the stationary sensors and add mobility to enhance coverage, effectiveness, and efficiency of water monitoring is necessary [15]. usv technology with sensors on board could cater and house more research tools, thus improving the methods of water quality monitoring. mobile vehicles in a marine or aquatic area could further increase the coverage of an automated water quality monitoring system with its ability to transfer from one location to another thus increasing the spatial and temporal measurement capability of the whole system. they can provide protection (housing and floatation) to the electronic equipment needed for monitoring and getting samples of the research area. with the advancement of computational ability, options for more monitoring equipment on board the usv increased through the utilization of new and innovative sampling methods [17, 18]. this led to the increasing trend of using different approaches, design, and implementation in a mobile vehicle for wqms endeavor. among many types of water surface vehicles for water and environmental monitoring, autonomous underwater vehicle corresponding author: alexander t. demetillo engineering, technology & applied science research vol. 9, no. 2, 2019, 3959-3964 3960 www.etasr.com demetillo & taboada: real-time water quality monitoring for small aquatic area using unmanned … (auv), unmanned surface vehicle (usv), and autonomous surface vehicle (asv) are the most widely used [18]. asv has the capabilities of large-area monitoring and worry-free unmanned navigation which is the ideal scenario for water quality monitoring, but comes with a high cost [19], while auv also can be a handy tool, especially in dangerous areas, but has also a high price along with its complex operation and setup [20]. usvs offer the advantages of being less expensive and having simpler supervision compared to uav, while they are easy to customize for a hybrid operation depending on the actual situation of the study area like an obstacle or floating objects which can be hardly detected using automation. several aquatic mobile vehicles have been developed for water quality monitoring with some enhancements like customized platforms to fit the actual conditions of the area [21], communication systems [22], and energy systems and mechanisms to cater the much-needed power of the vehicle [24, 25]. some known usv projects for water quality monitoring include bathymetric survey [25], data acquisition system on large fish and marine mammal movements [26], research on marine inhabitant activities [28-30], coastal environmental monitoring and pollutant tracking [13], emergency response and survey of damages [30], data acquisition and sampling for sea water and air [31]. authors in [33] focused on the improvement of surface vehicle platforms, communications and coordination, propulsion, control and other crucial improvements. they covered basic important wqm parameters ranging from temperature to sodium with data being wirelessly transmitted to a nearby computer system for storage. authors in [34] proposed another low-cost usv water quality monitoring, but with emphasis on inland water resources, while authors in [35] studied a multi-robot system approach to monitoring coastal waters, rivers, and lagoons in real-time with added features for the monitoring of heavy metal concentrations. measurement of marine important parameters like partial pressure and sea-air fluxes of co2 were conducted in [36]. the usv in [37] collects water samples in different water depths, places them in different water containers, and brings the samples for laboratory analysis. a remote-controlled watercraft with an automatic calibrator for sensors that need frequent calibration like ph was studied in [38] and low-cost bathymetry and depth monitoring in real time were performed in [25]. small water bodies like lakes and rivers usually have shallow waters which are difficult and too expensive for an environmental ship to monitor. operations in shallow waters require having a low draft and protection mechanism for the propellers. usv is able to operate in shallow waters with possible floating materials and plants such as water lilies, fish pens, and other barriers. with constraints for its total weight, it only allows a very minimalistic payload to be onboard the usv like a sensor, communication and navigational equipment with their electronics parts. the usv aims to provide a low-cost method capable of bringing information about water physicochemical parameters in real-time. this real-time monitoring can be an aid to the traditional or conventional methods of water quality monitoring which have high sensitivity, but seldom perform satisfyingly for budgetary constraints and other reasons. instead, usv utilization would make up continuous monitoring systems essential in the investigation and characterization of some water quality parameters like ph and temperature which have very inconsistent characteristics. received data can be further analyzed and may serve as input to decision making. this study focuses on the design of an unmanned mobile vehicle for water quality monitoring with consideration of the actual requirements and scenarios of the target area which is lake mainit, philippines. its main features are its affordability and adaptability to the field of study. ii. materials and methods the primary goal of the usv is to give an alternative method in water quality monitoring in dangerous areas and high-risk jobs. to collect data in hard to reach areas [19], to improve the data collection frequency, which if done manually could lead to expensive and laborious endeavor. figure 1 shows the diagram of the proposed system in which data collection is automated. figure 2 shows the usv prototype during its first testing. boat materials available in the area were used for creating its body and motor and its controllers are commercially available wq sensors from atlas scientific (ph and temperature) making this design ready for replication. also, to make it affordable, open source software was utilized. this software is used to receive and accumulate data acquired from the onboard sensors of the usv as an input interface for navigational operation setup, and to download the predefined usv direction. the system is divided in four subsystems, namely usv platform, automated sensor system, application software, and a base station. fig. 1. diagram of mobile water quality monitoring fig. 2. usv prototype engineering, technology & applied science research vol. 9, no. 2, 2019, 3959-3964 3961 www.etasr.com demetillo & taboada: real-time water quality monitoring for small aquatic area using unmanned … a. construction most of the materials used in the catamaran-type usv are available online or in the local market. the main goal of this research is to build a floating and mobile platform that can perform water quality monitoring in a sizeable aquatic area that is too large for the deployment of stationary sensors and too risky and difficult for manual sampling. usv design considers affordability, replicability and flexibility to cater to an actual field situation. the usv was designed and built in the center for robotics, automation and fabrication technology (craft) of caraga state university in butuan city, philippines. it is an enhancement of the previous project for wqm which uses buoy as floating material, but in a permanent location. the area to be covered is set to be 5km 2 per day with the need to sample/measure water in at least 1-meter depth. these requirements are in consideration with the area of the lake mainit of caraga region in the philippines where mining activities are rampant. these facts led to a consideration of a minimum speed of 1 nautical mile (0.5m/s), and a maximum weight of 40kg. a catamaran-type of construction was chosen for its proven stability on water, which allows easy control. the usv can be operated using remote control or can be automated depending on the location of the area and the distance it will cover. the operator might opt for remote-controlled operation if the area is small and there is a presence of an obstacle or floating materials or species that might destroy or damage the usv propeller, the casing or onboard sensors. the automatic operation fits with considerable area coverage with no obstruction or floating objects. the operator can design a mission plan and define its coordinates for the sampling location. with these, deployment makes data gathering unmanned and automated in dangerous and difficult to reach areas. b. electronic module in terms of electronic components, the usv system comprises of two subsystems: usv unit and ground control station with corresponding electronic equipment. the ground control station comprises of a computer system (laptop/pc) and wireless transceivers linking with the usv. the ground control has also the path/direction application program used in updating the usv path and pointing of sampling if needed. communication module comprises of telemetry, xbee, and rc modules. the data related to the mobility of the usv are catered by the ardupilot using telemetry. xbee module is used to transmit the gathered data to the nearest station while the remote controller (rc) module is used for the manual navigation control of the usv. it used a customized mission planner using an open source program powered by arduino ide to control the navigational operation of the usv. for a continuous operation, a mission plan must be downloaded to the microcontroller before the start of the mission. the automated operation used a compass board and gps module as a means to follow the predefined navigational route. sensing of data is the same with the stationary sensor methodology. the sensor determines the value and after proper conditioning and boosting it will be transferred to the microcontroller for preprocessing and will be sent to the wireless transceiver for transmission to the nearest stations or pre-defined cellphone numbers. wireless transmission is done through an xbee technology for short distance and gsm/gprs transceiver for long-distance transmission. arduino ide is the software used to configure the microcontroller (arduino mega 2560), xbee short distance communication and gsm/gps setup for long distance transmission. xbee module provides wireless connectivity to devices using end-point solutions. xbee uses ieee 802.15.4 networking protocol which is common to low power clustering communication setups. for long distance transmission and reception of data a gsm module is used. it has a library which mimics an arduino board to perform operations same as an ordinary gsm powered cellphone like receiving and sending messages and connect to the local telecommunication companies. the gsm/gprs transceiver has a built-in modem that facilitates data transfer from a serial port to the gsm network. it will receive data at the controller by another xbee. an open source program will process this data using microsoft visual studio flat form to facilitate userfriendly display and storage. a triple-axis magnetometer compass board hmc5883l (honeywell) and a neo-6m gps module (ublox) control the navigation system of the usv, designed to cover all functions for unmanned operation using a pre-programmed mission plan. the body of the usv platform utilizes marine plyboard with painting to safeguard the usv onboard electronic components. a wooden material houses the battery and other electronic components and connected to 1.5m (from head to tail) by 1m wide catamaran boat type. the usv can carry a maximum payload of 40kg. finally, the wireless transceiver and sensor calibration were completed before testing the whole system in the actual application. the water sensor unit is the primary component of the mobile water quality monitoring system. in this research, it employed two sensors from the atlas scientific company for measuring ph and temperature. with the built-in flexibility of arduino microcontroller, it can add more number of electrodes depending on the needs. ph and temperature sensors have their interface circuits which are also provided by the manufacturer. only the temperature sensor is connected directly to the analog pin of the microcontroller. it utilized a customized motherboard to connect all electronic components to the microcontroller. also, the board allows other modules and circuits, while having a feature to isolate the sensor individually and eliminate issues of noise. to maintain accuracy, electrodes are calibrated based on the manufacturer standards and using their own calibration solutions. the microcontroller unit is the main part of the usv and makes it unique among other aquatic mobile vehicles. it has pins which can expand its utilization. it comprises of a hardware microcontroller and a software program that guides the operation of the microcontroller with the rest of the usv parts. this research uses arduino mega 256, the most expandable arduino microcontroller to accommodate capability and future expansion of the system. same with the early variant of the arduino microcontroller, it has an opensource electronics prototyping platform, flexible, easy-to-use hardware, and user friendly programming environment [39]. the usv preprocess the data using the preprogrammed commands downloaded to the microcontroller. the developed software program uploaded into the microcontroller memory sets the sensor node to measure the water quality parameter at engineering, technology & applied science research vol. 9, no. 2, 2019, 3959-3964 3962 www.etasr.com demetillo & taboada: real-time water quality monitoring for small aquatic area using unmanned … predetermined time intervals. the data are always copied in an sd card before transmission as backup data storage. c. software the software for all usv electronic modules controlled by the microcontroller is written in arduino ide while microsoft visual studio (ide) was used to develop the windows application that interfaces the usv output to the computer systems in the base station. figure 3 shows the flowchart of the usv software. it uses the windows application to receive data from the serial port that connects the communication link of the usv. first, the microcontroller initializes all the components and waits for the gps to be ready before it navigates using either the preprogrammed path or through remote control. fig. 3. usv program flowchart for rc operation, all programming comes from manual input of the operator which converts a string of commands and processes by the microcontroller for execution like direction, points of sampling, etc. in the autonomous method, the microcontroller sets the destination points, navigates, gets the current position of the usv from the gps, reads the sensors, and sends and logs data. with the destination point encoded, the microcontroller navigates until it reaches home location. d. usv datalogger for easy data transfer from the usv to base station a data logger was designed. figure 4 shows the software application interface for the usv which was developed using visual studio. it was designed in such a way that it will display the incoming data in a tabulated form. also, it provides a mechanism of updating the path of the usv using a simple inputting of values through a graphical interface. the usv’s time to stay and gather data before it will navigate or move to another location can change through this logger. all necessary inputs are displayed for the user to review. iii. results and discussion after a laboratory bench testing of the different parts of the system, the usv was assembled. navigation trials were conducted in order to check if specifications were followed. a series of tests were also conducted for its autonomous navigation. laboratory tests included measurements of the quality of communication between the control unit and the usv, and the interruption of the radio link. the results of the connection measurements conform to the minimum standards. fig. 4. usv interface application a. navigation testing upon the construction of the vessel prototype, testing followed in the creek found inside the university campus. maneuvering capabilities, vessel stability, and navigation speed were tested. the results of maneuvering capabilities and stability were outstanding since the catamaran was stable and could rotate almost around its axis. the average navigation speed was 1knot, while 180° turn was achieved in less than 15s. also, testing the range of the radio link, stability, and behavior of the boat at some water disturbances that mimic small sea waves was conducted. tests showed that the radio link range in the open sea is about 150m. fig. 5. usv’s path b. wqm sensor testing a calibration process was conducted to the electrochemical sensors in the lab for their accuracy and functionality. calibration solution interface and isolation circuit from atlas scientific were utilized to calibrate and test the ph electrodes. for field testing, freshly calibrated electrodes from the lab were installed on the usv side platform. a series of final tests of the electronic component implemented were conducted before the engineering, technology & applied science research vol. 9, no. 2, 2019, 3959-3964 3963 www.etasr.com demetillo & taboada: real-time water quality monitoring for small aquatic area using unmanned … actual operation. the configuration of the water quality sensor was the same with the one used in the laboratory. the usv was programmed to measure a minute after its arrival at the designated testing point or on the points/area where the operator wanted to make the measurement. figure 5 shows the data received from the usv. it shows the effectivity of the system by accurately displaying important wqms parameters, which include ph, temperature, time, date etc. it validates that the system performs following the specifications of the electronic component and the usv delivers its primary function which is to protect components from water intrusion. the test also did not encounter a significant problem except the periodic gsm signal. the display works well on pcs, laptops, and smart mobile phones. with these, the onboard water sensor and its peripherals can provide the needed resources, thus giving stakeholders an alternative method on how to conduct water quality monitoring continuously. fig. 6. sample of the output of the system iv. conclusions with changing water environment, the need for a low-cost and mobile method of measurement is increasing. in this research, the design and development of a low-cost mobile vehicle as a tool to carry water sensors and transmit their results wirelessly was successfully implemented. utilization of easy to find sensors, locally available materials for the usv parts, and development of customized integrated software using open source technology are the main advantages of the system when compared with commercial usvs. laboratory and on-site results show the usv’s capability to conduct water quality monitoring in a lake and other small bodies of water. temperature ph, time and date were transmitted. in conclusion, this system has the potential to enhance reporting and information dissemination regarding the status of water quality. acknowledgement authors wish to thank the scholarship funding given by the department of science and technology through its engineering research and development for technology (erdt) program and the caraga state university for allowing the 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nigeria, september 29-october 1, 2014 microsoft word 4-2633_s_etasr_v9_n3_pp4100engineering, technology & applied science research vol. 9, no. 3, 2019, 4100-4104 4100 www.etasr.com mohammed et al.: sanitary landfill siting using gis and ahp sanitary landfill siting using gis and ahp a case study in johor bahru, malaysia habiba ibrahim mohammed department of geoinformatics, faculty of built environment and surveying, universiti teknologi malaysia, johor, malaysia mydearhabiba@yahoo.com zulkepli majid department of geoinformatics, faculty of built environment and surveying, universiti teknologi malaysia, johor, malaysia zulkeplimajid@utm.my yamusa bello yamusa school of civil engineering, universiti teknologi malaysia, malaysia, and department of civil engineering, nuhu bamalli polytechnic, zaria, nigeria yamusabello@yahoo.com mohd farid mohd ariff department of geoinformatics, faculty of built environment and surveying, universiti teknologi malaysia, johor, malaysia mfaridma@utm.my khairulnizam m. idris department of geoinformatics, faculty of built environment and surveying, universiti teknologi malaysia, johor, malaysia khairulnizami@utm.my norhadija darwin department of geoinformatics, faculty of built environment and surveying, universiti teknologi malaysia, johor, malaysia norhadija2@utm.my abstract—one of the major problems affecting municipalities is solid waste management. there is a difficulty in selecting suitable sites for waste disposal as it involves different factors to be considered before site selection. currently, waste generation in johor bahru has steadily increased over the last few years and the only existing sanitary landfill is reaching its capacity limits, which means that a new sanitary landfill site needs to be constructed. in this study, geographic information system (gis) and analytical hierarchy process (ahp) methods were utilized with the integration of dynamic data such as future population and projection of waste production in order to provide suitable sites for the construction of a sanitary landfill in the study area. thirteen criteria were considered for this study, namely water bodies, soil, geology, slope, elevation, residential areas, archeological sites, airports, population, road, railway, infrastructure, and land use. ahp was used to determine the weights for each criterion from the pairwise comparison matrix. consistency index and consistency ratio were checked and confirmed to be suitable. the results obtained from ahp were assigned to each criterion in gis environment using weighted overlay analysis tool. the final potential site map was produced, and the three most suitable potential landfill sites were identified. keywords-geographic information system; analytical hierarchy process; landfill siting; sustainable solid waste management i. introduction the most significant part of urban planning is identifying a desirable location for municipal solid waste disposal [1]. however, serious environmental problems or health hazards can arise from landfill locations and the disposing methods [2]. the greatest concerns associated with landfill environmental impacts are linked to its effects on ground and surface water, air, soil, odor emission, and issues regarding solid waste transportation [3]. in the majority of developed and developing countries, the most common technique adopted for solid waste disposal is sanitary landfill [4-5]. other methods are composting and incineration, but the landfill is the oldest and most common technique. due to landfills, a lot of problems have risen in the waste management sector [6]. there is a need for effective and efficient solid waste management to prevent public health hazards or negative environmental impact. global population increase and rapid industrialization mean an increase in the volume of waste. managing the waste produced by a city has become more complex [7]. getting rid of waste using landfills has become an unavoidable component of the entire solid waste management framework, regardless of reduction, reuse, and recycling activities and practices, there will always be a need for the transfer of the remaining waste into the landfill. the goal of a site selection exercise is to find the optimum location that satisfies a number of predefined criteria. locating a suitable and sustainable sanitary landfill site is very tedious, complex, and time consuming because it involves various different fields of knowledge (environmental, economic, political, social, technical, and engineering). gis has been used as a system for management, manipulation, representation and analysis of geospatial data to facilitate and cut down costs in a site selection process [8]. according to [9], gis is an ideal tool because of its ability to manage large amounts of spatial data acquired from different sources. the utilization of gis for a preliminary screening is normally carried out by classifying an individual map, based on selected criteria, into exactly defined classes or by creating buffer zones around geographic features to be protected [10]. meanwhile, multi-criteria decision analysis (mcda) investigates a number of possible choices for a siting problem, taking into consideration multiple criteria and conflicting objectives [6]. among the mcda methods, ahp [11] is the most common and popular, used to identify criteria corresponding author: yamusa bello yamusa engineering, technology & applied science research vol. 9, no. 3, 2019, 4100-4104 4101 www.etasr.com mohammed et al.: sanitary landfill siting using gis and ahp weights using a pairwise comparison matrix [12]. ahp is an mcda technique used in solving different decision-making problems. it was developed with the aim of dealing with manycriteria complex decisions [13, 14]. also, ahp is a wellstructured mathematical and psychological method of organizing and analyzing complex decisions [15]. this method is widely used by decision-makers and researchers in understanding problems and choosing the solution which is best for their goal [16]. technological development, globalization and population growth have accelerated the dynamics of the urbanization process in developing countries. suitable solid waste sites must match with the rapid urbanization process [17]. currently, waste generation in johor bahru has steadily increased over the last few years. waste generation in johor bahru is about 1.06kg/person/d and according to estimations is expected to rise to 1.4kg/person/d by 2025 [18]. solid waste produced in johor bahru has risen to nearly 30% from 2005 to 2010 and is estimated to rise to 50% by 2025 [19]. in this study, gis and ahp were used with the integration of dynamic data such as future population and projection of waste production in order to provide suitable sites for the construction of a sanitary landfill in the study area, providing long-term solution to solid waste management. ii. materials and methods a. study area the study area is situated in the southernmost part of the peninsular malaysia. it lies within latitude 1°29′0″n and longitude 103°44′0″e, with a total land area of about 220km 2 . it covers the administrative boundary of the johor bahru (jb) which is the capital city of johor, malaysia. b. population growth rate and waste generation the population of the study area was generated according to the estimated population of jb from the statistics department of malaysia [20]. table i. population and solid waste projection for jb [21] s/no year population solid waste (tons/year) 1 2010 815,600 315,556 2 2015 952,052 406,574 3 2020 1,104,843 520,215 4 2025 1,493,400 763,128 from table i, we can see that the calculated sum of the projected solid waste from 2010 to 2025 is drastically increasing. according to iskandar malaysia blueprint (2010), estimated land requirements based on 1,000 tons per day capacity and landfill lifespan of 15 year is 100 hectares excluding buffer. this justifies the need for locating new sanitary landfill sites to sustainably contain solid waste. c. data collection and processing landfill siting criteria guidelines such as integrated solid waste management blueprint for iskandar malaysia [21] and national strategic plan for solid waste management [22] were adopted. three main criteria were used which were divided into 13 sub-criteria. the data used in this study were collected from various sources: jb administrative boundary and land use/land cover map was acquired from the iskandar regional development agency. the geological map was derived from a scanned geological map of peninsular malaysia published by the director general of geological survey, malaysia (1985). road, water body, and railway maps were extracted from digitization of the topographical map series 4551 published in 1996. all the data are geo-referenced according to the kertau rso projection system. data from the us geological survey global visualization viewer (usgs glovis) digital elevation model (dem) needed for this study were accessed from their online archive http://glovis.usgs.gov/. aster gdem with spatial resolution of 30m was used to extract elevation and slope information of the studied area. erdas imagine software was used in processing and analyzing satellite images. arcgis software was used for digitizing and spatial data analysis. considering secure and reliable distance to landfill site in order to allocate the buffer zones for each layer was based on governmental guidelines, experts’ judgment, and local and international references. each criterion was categorized into classes, and each class was given a suitability score from 0 to 10 where 0 means that the area is unsuitable and 10 means that it is most suitable. distancing, reclassification and overlay analysis were undertaken in gis, using the spatial analyst tool arcgis. in order to evaluate the site selection criterion, ahp was used to measure the relative importance weight of each criterion. d. buffers buffer zones for each criterion were first created in accordance with the structural hierarchy criteria for the decision-making tree. these zones were calculated based on the landfill siting guidelines and related reviews. the buffer zones for water bodies, residential areas, archeological sites, airport, roads, railways and infrastructures were generated at various distances of 1000m, 2000m, 1500m, 3000m, 1500m, 1000m, and 150m. furthermore, slope, elevation, soil and geology maps were divided in different classes of suitability from less to most suitable. land use such as public facilities, educational sites, agricultural land, forest and vacant land were assigned with scores of 0, 0, 6, 3, and 10 respectively. pairwise comparison was then applied in order to determine the relative importance of each alternative in terms of each criterion. this is been measured according to a numerical scale of 1 (equal importance) to 9 (extreme importance). this procedure enables the decision maker to assess the contribution of each factor to reach the objective independently, thus simplifying the decision-making process [23]. iii. results and discussion in this study, a total of 13 criteria were used for the sanitary landfill site selection analysis. criterion map layers were extracted from different map sources including topographic sheets, geological and soil maps, land use/land cover maps, and dem. the land use/land cover maps were used to obtain a five layer (residential, airport, archeological, infrastructures, and population) criteria-based map. dem was used to derive the elevation and slope map of the area while topographic sheets were used to get roads, water bodies, and railways. all the data (map layers) were geo-referenced according to the kertau rso engineering, technology & applied science research vol. 9, no. 3, 2019, 4100-4104 4102 www.etasr.com mohammed et al.: sanitary landfill siting using gis and ahp projection system with 30m resolution pixels. criteria weights were obtained using the ahp pairwise comparison matrix based on expert’s judgment. a. implementation of ahp using ahp, the problems were broken down in hierarchical order, thus making it easier to be analyzed independently. after the construction of the hierarchy, systematic evaluation of the different criteria by pairwise comparison was done creating the pairwise comparison matrix. values have been assigned according to a numerical scale of 1 (equal importance) to 9 (extreme importance). this will enable the decision makers to assess the contribution of each factor to reach the objective independently through this comparison, thus simplifying the decision-making process [23]. b. deriving priorities (weights) for the criteria criteria importance may vary. the next step in ahp is weighting the criteria, because when siting a sanitary landfill not all the criteria are of equal importance. therefore, pairwise comparison is necessary for the relative importance weight of the criteria used by applying the saaty numerical scale of 1 to 9. the upper triangular of the matrix is filled with the values of comparison criteria above the diagonal of the matrix. the lower triangular matrix was completed by the contents of the upper diagonal part of the matrix reciprocally. the element of row � and column � is ����, and the lower diagonal is completed by applying: ��� = ��� (1) the values of c (i=1,2,3….m and j=1,2,3…. n) are used to signify the performance values in terms of the i-th and j-th element in a matrix [24-25]. thus, the complete comparison matrix for solving any decision-making problem and deriving weight for each criterion can be represented in a decision matrix as follows: � � � � � ���� ��� ��� ���� ��� ��� ���� ��� ��� ��� � � ������� (2) experts’ decisions were entered in the comparison matrix and the weight of each criterion was used to evaluate the best potential sites for the sanitary landfill site in the area (table ii). table ii. pairwise comparison matrix criteria r e si d e n ti a l w a te r b o d ie s g e o lo g y s o il s l a n d u se s lo p e e le v a ti o n r o a d in fr a st r u c tu r e a ir p o r t p o p u la ti o n a r c h e o lo g ic a l r a il w a y weights residential 1 3 4 3 5 5 7 7 5 7 2 5 8 0.239 water bodies 0.33 1 2 3 5 4 5 5 4 5 2 5 9 0.168 geology 0.25 0.50 1 2 3 3 4 4 3 4 4 3 6 0.121 soils 0.33 0.33 0.50 1 3 3 1 3 4 4 4 3 5 0.099 land use 0.20 0.20 0.33 0.33 1 2 3 3 2 3 2 2 4 0.067 slope 0.20 0.25 0.33 0.33 0.50 1 2 2 2 2 3 2 3 0.056 elevation 0.14 0.20 0.25 1 0.33 0.50 1 2 3 2 2 3 2 0.054 road 0.14 0.20 0.25 0.33 0.33 0.50 0.50 1 1 2 2 2 2 0.036 infrastructure 0.20 0.25 0.33 0.25 0.50 0.50 0.33 1 1 3 3 2 3 0.046 airport 0.14 0.20 0.25 0.25 0.33 0.50 0.50 0.50 0.33 1 2 3 2 0.033 population 0.50 0.50 0.25 0.25 0.50 0.33 0.50 0.50 0.33 0.50 1 2 2 0.038 archeological 0.20 0.20 0.33 0.33 0.50 0.50 0.33 0.50 0.50 0.33 0.50 1 2 0.025 railway 0.12 0.11 0.16 0.20 0.25 0.33 0.50 0.50 0.33 0.50 0.50 0.50 1 0.018 furthermore, from the result of the weighting obtained, it was revealed that residential areas and water bodies are the most important criteria while railway was the least important. c. eigenvector the eigenvectors of each row were calculated with the multiplication of each value of a given criteria in a column and same row of the original pairwise comparison matrix and then applying this to each row as shown in (3) [26]: ��� = ��� × � � × � …× � ��� (3) where ��� is the eigenvalue for row �, � is the total criteria number used in row � . the normalized eigenvector of the matrix, known as priority vector, was calculated from the pairwise comparison matrix by normalizing its eigenvalues to 1 as shown in (4): !� = ��� ∕ �#$� = 1��&� (4) these eigenvectors reflect weights of preferences [27] and can be defined as a method of normalized arithmetic averages [26]. the relative importance of the compared criteria was also computed from the values of the eigenvector [28]. λmax is the highest eigenvalue of preference matrix. it was acquired from the addition of the products of multiplication between each element of the priority vector and the sum of columns of the reciprocal matrix (5). '�() = * +,� �����. /��. (5) where ��� is the criteria summation of a single column and ,� is the corresponding value of the priority vector for each criteria weight in the comparison pairwise matrix. d. consistency check once the weight has been calculated, it is important to check for consistency. this is because the values used for the engineering, technology & applied science research vol. 9, no. 3, 2019, 4100-4104 4103 www.etasr.com mohammed et al.: sanitary landfill siting using gis and ahp computation of the weight are obtained from different opinions with different perspectives, therefore there is a possibility to encounter errors in the final stage of computation in the matrix [29]. the consistency index (ci) was computed using (6), '�() is the greatest eigenvalue of preference and n is the total number of the compared criteria: �0 = �1 �() 2����2 � (6) calculation of consistency ratio (cr) was done by dividing the value of ci by the random consistency index (ri) [11]. ri is derived from the mean ci element gotten as a result of random simulation of the comparison pairwise matrix: �3 = 454 (7) where cr should be ≤0.10 for weight consistency check. if cr≥0.10 a revision in the judgement ahp matrix is required [30-31]. for this study, the cr value is 0.088, meaning that there is consistency in the ahp matrix, and the weights assigned to the criteria can be used for analysis [32]. e. sanitary landfill suitability evaluation to find suitable potential areas for a sustainable sanitary landfill, the sum of the 13 weighted criteria thematic layers was put in the gis environment using arcgis software. criteria weights were assigned to each map layer which is in reclassified raster format using the map algebra tool based on: 6� = ,��7. × ��� (8) where ai is the suitability index for area i, wj is the relative importance weight of criterion, cij the grading value of area i under criterion j and n is the total number of criteria [32]. the ci value for this study is 0.137 and the cr value is 0.088 meaning that there is consistency in the ahp matrix and the weights assigned to the criteria can be used for analysis [32, 34]. map algebra tool in the arcgis spatial analyst tool box was used to produce the final output map of the potential sites. the map was divided into four different categories: unsuitable, less suitable, suitable, and most suitable. the map in figure 1 shows the distribution of the selected areas based on suitability where the most suitable are considered sites of higher priority. from the result of this map, it was found that most of the study area, 57% was unsuitable, 9% less suitable, 23% suitable and 11% most suitable. moreover, to get the most suitable sites, the potential site map was then imported to the condition toolset in the spatial analyst tool in arcgis to identify the most suitable or highest priority sites for the determination of the best potential sites. from the most suitable sites, the best potential sites were identified by filtering the most suitable sanitary landfill layers. thus, the output layer, in raster format, was converted into vector and then the areas that did not have an intersection with water bodies and railway were selected. based on experts’ judgment, using ahp criteria weighting and gis analysis, 3 candidate sites appear to be the best from environmental, economic, and social perspectives (figure 2). these sites fulfil the requirements for a sanitary landfill siting with a distance of at least 1000m away from roads, 1500m from residential areas, and far away from public and educational facilities. fig. 1. map of potential sanitary landfill sites. fig. 2. best potential sanitary landfill sites map. furthermore, after the integration of gis and ahp, the final map was then converted to keyhole markup language (.kml) file format which was used in the google earth pro for further accuracy check, from which the 3 most suitable potential sites were selected among the most suitable class. the coordinates of these sites were taken from the google earth pro for field check to determine the accuracy and precision of the sites. iv. conclusion rapid population growth and increase in economic and commercial activities have resulted to large increase of solid waste produced daily/annually. gis and mcda with 13 evaluation criteria were applied in this study for assessing the possible potential sites for sanitary landfill in johor bahru, malaysia. ahp was used in calculating the relative importance weights of the criteria, which were assigned in the final suitability map production. the most important criteria for this study were residential areas with 23.9% and water bodies with 16.8%, while the least important criterion was railway with 1.8%. based on experts’ judgment, using the ahp criteria engineering, technology & applied science research vol. 9, no. 3, 2019, 4100-4104 4104 www.etasr.com mohammed et al.: sanitary landfill siting using gis and ahp weighting and gis analysis, 3 most suitable potential sites were identified among the various sites from the most suitable class in the final map. each of these sites fulfilled the necessary requirements of selection guidelines with a distance of at least 1000m from water bodies and roads, 1500m from residential areas, and far away from public and educational facilities. these sanitary landfill sites can serve as backups for the existing one that is almost attaining its maximum capacity. finally, for the construction of the final sanitary landfill site, further geotechnical and hydrological analysis is required to prevent groundwater contamination caused by leachate. references [1] s. bahrani, t. ebadi, h. ehsani, h. yousefi, r. maknoon, “modeling landfill site selection by multi-criteria decision making and fuzzy functions in gis, case study: shabestar, iran”, environmental earth sciences, vol. 75, no. 4, pp. 337, 2016 [2] m. sharholy, k. ahmad, g. mahmood, r. c. trivedi, “municipal solid waste management in indian cities a 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pastor-ferrando, f. garcia-garcia, “an analytic network process approach for siting a municipal solid waste plant in the metropolitan area of valencia (spain)”, journal of environmental management, vol. 91, no. 5, pp. 1071-1086, 2010 [33] m. eskandari, m. homaee, s. mahmodi, “an integrated multi criteria approach for landfill siting in a conflicting environmental, economical and socio-cultural area”, waste management, vol. 32, no. 8, pp. 15281538, 2012 [34] p. v. gorsevski, k. r. donevska, c. d. mitrovski, j. p. frizado, “integrating multi-criteria evaluation techniques with geographic information systems for landfill site selection: a case study using ordered weighted average”, waste management, vol. 32, no. 2, pp. 287-96, 2012 microsoft word 19-3055_s_etasr_v9_n5_pp4679-4684 engineering, technology & applied science research vol. 9, no. 5, 2019, 4679-4684 4679 www.etasr.com added et al.: miniaturized chipless rfid tags based on periodically loaded microstrip structure miniaturized chipless rfid tags based on periodically loaded microstrip structure maha added physical department, university of tunis el manar, tunis, tunisia maha.added@gmail.com safa chabaan physical department, university of tunis el manar, tunis, tunisia safa.chebaane90@gmail.com karima rabaani physical department, university of tunis el manar, tunis, tunisia rabaanikarmia@hotmail.fr noureddine boulejfen research center for microelectronics and nanotechnology, technopole of sousse, sousse, tunisia nboulejf@ucalgary.ca abstract—a compact chipless radio frequency identification (rfid) tag-based on slow-wave technology is introduced in this paper. the tag consists of a resonant circuit based on open stub resonators periodically loaded by shunt stubs allowing a coding capacity of 9 bits and operating in a frequency range from 2 to 4ghz. the receiving and transmitting antennas of the tag are particularly designed to minimize the tag size as much as possible. the proposed tag presents a robust bit pattern with a compact and fully printable structure using fr4 substrate for a low-cost tag. keywords-chipless rfid tag; slow-wave technology; coding capacity i. introduction radio frequency identification (rfid) is one of the most rapidly growing segments of modern automatic capture and identification. however, conventional chipped rfid systems have many limitations related to the use of the chip such as high cost, susceptibility in harsh environments, short life of the chip battery packs, etc. to overcome these limits, chipless rfid systems appear where the tag is a fully passive microwave structure and its encoding data depends only to its geometry [1]. frequency domain chipless rfid tags use spectral signature to encode data [6]. frequency domain tags are classified into two main families, the rcs-based tags and the retransmission-based tags. the rcs-based tags use resonant antennas that receive the signal and send it back with the tag signature [1-7]. generally, they can reach a high coding capacity with a compact size. in [1], a compact rcs-based tag using resonant antennas in c form was proposed. the reported tag offers a coding capacity of 20 bits operating in a frequency range from 2 to 4ghz and with an overall size of 25×70mm². however, the rcs-based tags generally have a short reading range [2, 3] and a strong mutual coupling, which limits the data encoding capacity [4]. concerning the retransmission-based tags [8-13], single or double antennas are used to receive and transmit the signal. the spectral signature of the tag is obtained by a resonant circuit with multiple resonators where each of them creates a notch or a peak around a given frequency point. the chipless tag introduced in [13] is a retransmission-based tag using spiral resonators that allow the coding of 35 bits in a frequency band ranging from 3.1 to 7ghz. even if retransmission-based tags usually have an important size, this type of chipless tags has a robust bit pattern and ensures a large reading range compared to the rcs-based tags thanks to the use of independent antennas for both transmission and reception. in this paper, the miniaturization technique based on the slow wave approach has been used to design a 9-bit compact retransmission-based tag operating in a frequency band of 2 to 4ghz. for a complete chipless tag, dual crosspolarized monopole antennas were designed and connected to the resonant circuit to establish a communication link with the interrogator. ii. tag design the retransmission-based tag presented in this paper consists of a resonant circuit of nine resonators connected to two cross polarized antennas, one for the transmission and the one for the reception. as it is shown in figure 1, a basic chipless rfid tag structure can be composed of the known resonant circuit based on quarter-wave open stub resonators and two identical ordinary rectangular monopole antennas. the overall dimensions of the basic chipless rfid structure are around 119×73mm². a. resonant circuit design 1) basic resonant circuit structure a basic structure of a resonant circuit can be based on the known quarter-wave open stub resonators as shown in figure 2. this structure has been realized using the fr4 substrate with corresponding author: maha added engineering, technology & applied science research vol. 9, no. 5, 2019, 4679-4684 4680 www.etasr.com added et al.: miniaturized chipless rfid tags based on periodically loaded microstrip structure thickness h=0.4mm, dielectric constant ɛr=4.7 and loss tangent tgδ=0.019. as presented in the figure 2, the initial design of the prototype contains 9 open stub resonators equally spaced with 1mm apart to avoid mutual coupling. the length of each resonator is equal to λg/4 at its corresponding resonant frequency, where λg is the wavelength in the substrate. the resonance frequency is independent from the width of the resonator [9, 16]. the parameters of each resonator in the basic multi-resonantor are given in table i. fig. 1. basic chipless rfid tag structure fig. 2. basic resonant circuit structure, g1=46 mm, g2=25 mm a tuning process using agilent ads momentum software has revealed that high q resonances can be obtained with a 15ω feed line, such that wb=4mm. thus, a taper impedance transformer is required to match the input impedance of the resonant circuit to 50ω. the length of the taper section is equal to λg/4 with respect to the lowest operating frequency. in this work, the appropriate length of the impedance transformer section is found to be lt=14.5mm. the resonant circuit response exhibits 9 resonance frequencies and thus a coding capacity of 9 bits, where the operating frequency range is between 2 and 4.5ghz. the overall dimensions of the obtained circuit are about 46×25mm². 2) miniaturized resonant circuit structure starting from the basic resonant circuit described above, a slow wave structure is used to reduce the size of the initial circuit while keeping the same electrical behavior. periodically loading transmission lines with shunt capacitances can increase their effective electrical length [14]. using this concept, significant size reduction of several passive microwave components have been achieved. for instance, the technology of periodically loaded slow wave microstrip lines has been used in [14] to miniaturize the size of branch-line and rate-race couplers and in [15] to design miniaturized single-band twoway and dual-band two-way wilkinson power dividers. in this paper, slow-wave structure is developed for the miniaturization of chipless rfid tags. based on the slow-wave concept, a conventional microstrip line with a given length is substituted for a shorter microstrip line loaded with equally spaced capacitances terminated to ground. the role of the loading capacitances is to slow down the wave propagation within the microstrip line. this results in a longer effective electrical length compared to an unloaded microstrip line. based on this approach one can accurately determine the values of the loading capacitances cp and their spacing d to guarantee the desired electrical behavior while reducing the line length. let’s consider an unloaded lossless transmission line with characteristic impedance zc_un and a phase velocity vp_un given by [15] such as: ��_�� � �� (1) �_�� � �√� (2) where l and c are the line inductance and capacitance of the transmission line respectively. loading periodically the transmission line with equally spaced shunt capacitors cp allows the reduction of its effective characteristic impedance zc_lo and phase velocity vp_lo. for a spacing d between the capacitors less than the signal wavelength, zc_lo and vp_lo are given by [15] as: ��_�� � � � ���� (3) �_�� � ��� � ���� � (4) equation (4) shows the reduction of the phase velocity vp_lo compared to that of the unloaded line. this means that an effective electrical length can be achieved using a transmission line with a shorter physical length. the effective electrical length of the loaded line is expressed as: φ��= ������_�� = !"#�$ �% & �� � (5) where n is the number of the loading capacitors and "# is the angular frequency of interest. using (1)-(5) we can determine the value of cp and the spacing d of the loading capacitors: ! � '(_��)�� ��_*+� ��'(_*+ (6) %� � )���'(_*+,-'(_��,�� ��'(_*+,'(_�� (7) to obtain an entirely planar circuit, the loading capacitances cp can be realized using open-circuit stubs by applying the following formula [15]: %� � �./*0'(_./*0��_./*0 for ����_./*0 123�4 ≪ 1 (8) where lstub, zc_stub and vp_stub are the length, characteristic impedance and phase velocity of the stub respectively. engineering, technology & applied science research vol. 9, no. 5, 2019, 4679-4684 4681 www.etasr.com added et al.: miniaturized chipless rfid tags based on periodically loaded microstrip structure 3) design considerations to achieve the highest possible reduction, the impedance of the unloaded line zc_un should be at its highest possible value which is obtained by choosing the lowest possible microstrip width that can be manufactured. in addition, to minimize the crosstalk between stubs, the spacing d must be greater than 3h where h is the height of the substrate. this condition (d≥3h) can be relaxed by placing the stubs on both sides of the line. taking into account these design considerations, the resulting slow wave structure can be duplicated for all the resonators of the proposed resonant circuit. depending on the frequency of resonance of each resonator a corresponding stub length is required. as previously mentioned, to obtain the highest possible line length reduction (l/lqwl), the characteristic impedance of the unloaded microstrip line zc_un should be at its highest value, so its width should be at the lowest possible value. in this work, the width of all the unloaded microstrip lines is fixed to wun=0.2mm allowing a characteristic impedance of 94ω. for a planar structure, the capacitances cp implemented using open stubs with a similar width for all the resonators and length that varies from one resonator to the other as described by (8). to avoid mutual coupling between the stubs, the spacing d is fixed to 0.6mm for all resonators and stubs are alternatively placed on both sides of the line as shown in figure 3. the number of sections n is chosen to be the same for all the resonators. consequently, different resonance frequencies can be obtained by changing the stub length lstub. fig. 3. slow wave resonant circuit, g3=46mm, g4=14mm table i illustrates the resonance frequencies, the parameters of each quarter-wave resonator with the capacitance and stub length of its corresponding slow-wave structure. knowing that d=0.6mm and n=14, the length of the unloaded stub for all the resonators is l=n×d=8.4mm. figure 3 shows the slow wave structure based resonant circuit. the spacing between resonators is fixed such as to avoid the coupling effect and to ensure the stability of the resonance frequencies when changing the configuration pattern of the resonant circuit. the dimensions of the slow wave structure based resonant circuit are 48×14mm² offering a size reduction of 41.6% compared to the basic resonant circuit. to validate the obtained values of cp and lstub, the simulation of both circuits is performed without considering the coupling effect using agilent ads simulator. the comparison between the transmission responses of the basic quarter-wave length based resonant circuit and the slow wave structure based one is illustrated in figure 4, which shows a good match between the two responses, which validates the calculated values and the slow-wave structure efficiency with a size reduction of 41.6% while keeping the same coding capacity and operating frequency range. the simulated and measured transmission responses of the proposed slow wave based resonant circuit in the presence of coupling effects are discussed in section iii. table i. physical and electrical parameters of the slow wave based resonators vs quarter-wavelen gth resonators quarter-wavelength resonator slow wave resonator res. freq. (ghz) lqwl (mm) w (mm) zc_qwl (ω) 78 (pf) 9:;<= (mm) l e n g th r e d u c ti o n (% ) res1 2.28 18.9 1.16 39.7 0.257 2.8 55.5 res2 2.52 17.23 1 43.8 0.201 2.2 51.2 res3 2.72 16.08 0.88 47.4 0.164 1.8 47.7 res4 2.919 15.05 0.789 50.6 0.137 1.5 44.2 res5 3.07 14.3 0.724 53.2 0.118 1.3 41.6 res6 3.25 13.64 0.654 56.3 0.1 1.1 38.5 res7 3.459 12.9 0.583 60 0.08 0.9 34.9 res8 3.716 12.07 0.507 64.4 0.063 0.7 30.4 res9 4.045 11.18 0.426 70.1 0.045 0.5 24.9 fig. 4. comparison between the transmission responses of quarter-wave resonant circuit and based slow wave resonant circuit without considering the coupling effect b. antenna designs omni-directional monopole uwb antennas are generally used for signal reception and transmission in chipless tags (figure 1). these antennas are known by their relatively big size, which further increases the overall size of the tag. 1) receiving antenna for a miniaturized antenna structure, an omni-directional monopole uwb antenna with a slow wave feed line has been designed. the structure of the proposed antenna using the slow wave based feed line is presented in figure 5. the addition of slots in the ground plane is required to improve the reflection response of the antenna. the positions, forms, and dimensions of the slots are chosen according to the surface current density in the antenna. the dimensions of the antenna have been reduced to 26×44mm². the simulated and measured responses of the proposed antenna are presented and discussed below. 2) transmitting antenna the transmission antenna of the tag is designed in a way to minimize as much as possible the size of the tag while keeping its horizontal polarization to avoid cross talk between transmitted and received signals. therefore, as shown in figure 6, a rectangular monopole uwb antenna with a bended feed engineering, technology & applied science research vol. 9, no. 5, 2019, 4679-4684 4682 www.etasr.com added et al.: miniaturized chipless rfid tags based on periodically loaded microstrip structure line is used. the bending of the feed line allowed a good space management of the entire tag. however, it resulted in a ground plane shape modification leading to performance degradation. to overcome this problem some feed line length tuning has been performed. figure 6 shows the final shape and the design parameters of the transmitting antenna. fig. 5. structure of receiving antenna based on slow wave feed line: ygnd2=14.54mm, lp=2.5mm, wp=1mm, lf=7mm, wf=0.5mm, ef=2mm, ff=1mm, we=2.2mm,;le=1mm, b2=27mm, a2=22mm fig. 6. transmitting antenna structure: xr=39mm, yr=36mm, y1=5.5mm, y2=14.25mm, y3=5mm, y4=50.25mm, x1=10mm, x2=24.25mm, x3=2.4mm, wan2=0.7mm figure 7 presents the new tag structure using the designed antennas. the size of the whole tag is about 66.5×55mm² allowing a miniaturization of 58.2% compared to the basic structure tag described in figure 1. to study the mutual coupling effect between antennas and to fix the spacing threshold between the two radiating elements, each antenna is excited by a plane wave and simulated independently in the presence of the other antenna. fig. 7. final chipless rfid tag structure: g7=66.5mm, g8=55mm iii. results and discussion so far, to build up a clearer picture of the real behavior of the resonant circuit, an electromagnetic simulation that considers the coupling effects is required. therefore, a simulation using cst studio suit has been performed for different tag codes. for the experimental validation of the proposed miniaturization approach, the developed resonant circuit has been fabricated in the all-one configuration as shown in figure 8(a). then its transmission coefficient has been measured in the 1.5-5ghz frequency band. figure 8(b) shows a good agreement between the measured and the cstsimulated (with coupling) transmission coefficients. (a) (b) fig. 8. slow wave based resonant circuit: (a) realized resonant circuit, (b) simulated and measured responses each resonator branch of the resonant circuit operates at a correspondent frequency allowing a coding capacity of 9 bits. when all the resonators are connected to the main transmission line the resulting tag code is set to 111111111 and the resonance frequencies are: 2.28ghz, 2.58ghz, 2.8ghz, 3ghz, 3.22ghz, 3.41ghz, 3.63ghz, 3.85ghz, and 4.26ghz. each bit in the code is set or reset by connecting or disconnecting the corresponding resonator branch from the main transmission line. as presented in figure 9, res2, res4, res6 and res8 are disconnected from the transmission line to set the tag code to 101010101. after the preliminary validation using the all-one realized resonant circuit, a comparison between the simulated and measured results has been performed for the resonant circuit with the tag code set to 101010101. as revealed by figure 10 a good agreement between the measured and the simulated results has been observed. fig. 9. chipless rfid tag configuration with tag code set to 101010101 engineering, technology & applied science research vol. 9, no. 5, 2019, 4679-4684 4683 www.etasr.com added et al.: miniaturized chipless rfid tags based on periodically loaded microstrip structure fig. 10. simulated and measured transmission responses of the resonant circuit with tag code set to 101010101 as a next stage, a comparison between two different measured tag codes has been performed. figure 11 includes the measured transmission responses of resonant circuits with tag codes set to 111111111 and 101010101. the figure shows clearly that the resonance frequencies are quite stable even if the tag code changes, which demonstrates the coding robustness of the proposed resonant circuit. fig. 11. measured transmission responses of resonant circuits with tag codes set to 111111111 and 101010101 for experimental validation purposes, the designed slow wave based antenna has been fabricated and measured over the 1.5 to 5ghz frequency band. the fabricated antenna is presented in figure 12(a) while figure 12(b) illustrates the simulated and the measured reflection coefficients. according to the measured reflection coefficient illustrated in figure 12(b), the proposed antenna is well matched between 1.6ghz and 4.5ghz, which covers the operating frequency band of the proposed resonant circuit. furthermore, the radiation efficiency, the radiation pattern and the gain of the proposed antenna have been simulated. as it is shown in figure 13(a), the radiation efficiency of the antenna is around 70% for the entire operating frequency band. the simulated radiation pattern of the antenna, illustrated in figure 13(b), is omnidirectional with a gain around 2.2dbi which confirms that the designed antenna is suitable for rfid applications. (a) (b) fig. 12. (a) realized receiving antenna, (b) simulated and measured reflection coefficient (a) (b) fig. 13. radiation efficiency and radiation pattern of the slow wave based antenna: (a) radiation efficiency, (b) the radiation pattern at h and e plane respectively regarding the transmitting antenna described in figure 6, the corresponding simulated and measured reflection coefficients are illustrated in figure 14(b) showing that the operating bandwidth of the antenna is between 2.2ghz and 4.3ghz which is also adequate to the frequency range of the multi resonant circuit. the radiation pattern of the antenna presented in figure 15 is almost omnidirectional and the gain in the operating frequency range is about 2.2dbi, which confirms that the designed antenna is suitable for rfid applications. table iii presents a comparison between different rfid chipless retransmission-based tags including this work. (a) (b) fig. 14. transmitting antenna: (a) realized transmitting antenna, (b) comparison of simulated and measured reflexion response of the transmitting antenna 1.5 2 2.5 3 3.5 4 4.5 5 x 10 9 -30 -25 -20 -15 -10 -5 0 frequency (hz) s 1 1 ( d b ) simulation measurement engineering, technology & applied science research vol. 9, no. 5, 2019, 4679-4684 4684 www.etasr.com added et al.: miniaturized chipless rfid tags based on periodically loaded microstrip structure (a) (b) fig. 15. radiation pattern of the transmitting antenna: (a) h-plane, (b) e-plane table ii. comparison between different chipless tags ref. used approach coding capacity frequency range (ghz) size [9] triangle microstrip filter 6 bits 4-7 150×30mm² (without antennas) [10] microstrip open resonators 8 bits 2-4 80×60mm² (with antenna) [12] siw 1 bit 10.5-11 10×10mm² (without antennas) this work slow wave resonator 9 bits 2-4 66×55mm² (with antennas) fig. 16. the realized proposed chipless rfid tag iv. conclusion in this paper, a slow-wave structure was used to miniaturize a rfid chipless retransmission-based tag. firstly, a slow-wave structure based multi-resonator has been developed and a size reduction of 41.6% was reached compared to the quarter-wave open stub resonators. the developed multi resonator includes nine open stub resonators periodically loaded by shunt stubs. the resonance frequency of each resonator depends only on the length of its shunt stubs. the nine resulting resonance frequencies lay in the 2.28 to 4.26ghz range. simulation results not included in this paper revealed that with the use of the roger 4003c substrate instead of the fr4 one can further reduce the size of the nine bit multi-resonator and improve its behavior. therefore, a miniaturized rectangular monopole uwb antenna, which is used as the receiving antenna of the tag, has been designed using a slow-wave structure, while respecting the required operating frequency range and allowing omnidirectional pattern. with a good space management of the whole tag, a reduction of more than 58% has been obtained compared to the basic tag structure which demonstrated the efficiency of the used approach for designing miniaturized chipless rfid tags. references [1] a. vena, e. perret, s. tadjini, “a fully printable chipless rfid tag with detuning correction technique”, ieee microwave and wireless components letters, vol. 22, no. 4, pp. 209-211, 2012 [2] m. a. islam, n. c. karmakar, “a novel compact printable dualpolarized chipless rfid system”, ieee transactions on microwave theory and techniques, vol. 60, no. 7, pp. 2142-2151, 2012 [3] h. s. jang, w. g. lim, k. s. oh, s. m. moon, j. w. yu, “design of lowcost chipless system using printable chipless tag with electromagnetic code”, ieee microwave and wireless components letters, vol. 20, no. 11, pp. 640-642, 2010 [4] i. jalaly, i. d. robertson, “capacitively-tuned split microstrip resonators for rfid barcodes”, european microwave conference, paris, france, october 4-6, 2005 [5] m. martinez , d. v. d. weid, “compact slot-based chipless rfid tag”, ieee rfid technology and application conference, tampere, finland, september 8-9, 2014 [6] m. s. bhuiyan, n. karmakar, “chipless rfid tag based on splitwheel resonators”, 7th european conference on antennas and propagation, gothenburg, sweden, april 8-12, 2013 [7] c. m. nijas, u. deepak, p. v. vinesh, r. sujith, s. mridula, k. vasudevan, p. mohanan, “low-cost multiple-bit encoded chipless rfid tag using stepped impedance resonator”, ieee transactions on antennas and propagation, vol. 62, no. 9, pp. 4762-4770, 2014 [8] c. s. hartmann, “a global saw id tag with large data capacity”, ieee ultrasonics symposium, munich, germany, october 8-11, 2002 [9] c. m. nijas, r. dinesh, u. deepak, a. rasheed, s. mirdula, k. vasudevan, p. mohanan, “chipless rfid tag using multiple microstrip open stub resonators”, ieee transactions on antennas and propagation, vol. 60, no. 9, pp. 4429-4432, 2012 [10] m. e. jalil, m. k. a. rahim, n. a. samsuri, r. dewan, “chipless rfid tag based on meandered line resonator”, ieee asia-pacific conference on applied electromagnetics, johor bahru, malaysia, december 8-10, 2014 [11] h. e. matbouly, n. boubekeur, f. domingue, “a novel chipless identification tag based on a substrate integrated cavity resonator”, ieee microwave and wireless components letters, vol. 23, no. 1, pp. 52-54, 2013 [12] s. moscato, r. moro, m. bozzi, l. perregrini, s. sakouhi, f. dhawadi, a. gharsallah, p. savazzi, a. vizziello, p. gamba, “chipless rfid for space applications”, ieee international conference on wireless for space and extreme environments, noordwijk, netherlands, october 3031, 2014 [13] s. preradovic, n. c. karmakar, “design of fully printable planar chipless rfid transponder with 35-bit data capacity”, european microwave conference, rome, italy, september 29-october 1, 2009 [14] k. w. eccleston, s. h. m. ong, “compact planar microstripline branchline and rat-race couplers”, ieee transactions on microwave theory and techniques, vol. 51, no. 1, pp. 2119-2125, 2003 [15] j. s. hong, m. j. lancaster, “capacitively loaded microstrip loop resonator”, electronics letters, vol. 30, no. 18, pp. 1494-1495, 1994 [16] k. rawat, f. m. ghannouchi, “a design methodology for miniaturized power dividers using periodically loaded slow wave structure with dualband applications”, ieee transactions on microwave theory and techniques, vol. 57, no. 12, pp. 3380-3388, 2009 [17] c. zhou, h. y. d. yang, “design considerations of miniaturized least dispersive periodic slow-wave structures”, ieee transactions on microwave theory and techniques, vol. 56, no. 2, pp. 467-474, 2008 microsoft word final-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 416-423 416 www.etasr.com ilic et al.: analysis of video signal transmission through dwdm �etwork based on a quality… analysis of video signal transmission through dwdm network based on a quality check algorithm s. ilic dpt. of elec. and comp. engineering university of prishtina kosovska mitrovica, serbia sinisa.ilic@ pr.ac.rs b. jaksic dpt. of elec. and comp. engineering university of prishtina kosovska mitrovica, serbia branimir.jaksic@ pr.ac.rs m. petrovic dpt. of elec. and comp. engineering university of prishtina kosovska mitrovica, serbia mile.petrovic@ pr.ac.rs a. markovic dpt. of telecommunications university of nis nis, serbia acomarkovic87@ yahoo.com v. elcic dpt. of information technology university of slobomir p bijeljina, bosnia and herzegovina vanja.elcic@ gmail.com abstract — this paper provides an analysis of the multiplexed video signal transmission through the dense wavelength division multiplexing (dwdm) network based on a quality check algorithm, which determines where the interruption of the transmission quality starts. on the basis of this algorithm, simulations of transmission for specific values of fiber parameters are executed. the analysis of the results shows how the ber and q-factor change depends on the length of the fiber, i.e. on the number of amplifiers, and what kind of an effect the number of multiplexed channels and the flow rate per channel have on a transmited signals. analysis of dwdm systems is performed in the software package optisystem 7.0, which is designed for systems with flow rates of 2.5 gb/s and 10 gb/s per channel. keywords – ber parameter; q factor; dwdm network; amplifying section i. introduction dense wavelength division multiplexing (dwdm) is a technology that allows multiplexing of multiple optical carrier signals on a single optical fiber by using different wavelengths for transmission of various information. the smallest attenuation of the signal in the optical fiber is achieved by applying the wavelength of 1550 nm or by using the "third optical window" [1-4]. dwdm systems allow the expansion of the existing capacity without laying additional fibers in optic cables. the capacity of the existing system is expanded using multiplexers and demultiplexers at the ends of the system [5-6]. for the successful transmission of optical signals over long distances, doped fiber amplifiers with erbium (edfa erbium doped fiber amplifier) are used. erbium is a rare element and, when excited, it is emitting the light at a wavelength of 1,54 µm, which is the wavelength at which the attenuation of signal power is minimal. weak signals enters the erbium doped fiber, in which light is injected by lasers pumps. this light excites erbium atoms, and the atoms are releasing the accumulated energy in a form of additional light with wavelength around 1550 nm. as this process continues through the fiber, the signal is amplified. edfa is available in the c and l windows but with quite narrow range (1530-1560 nm) [7-8]. edfa can amplify optical signals as much as they can be multiplexed in a given range until a strong enough signal is received. when the level of the signal at the input is reduced, the signal can not step up all multiplexed signals. ii. ber and q factor the performance of an optical communication system is specified by the bit error ratio (ber) [7-8]. ber is the probability that the impulse is interpreted incorrectly (i.e. a logical '1' is detected as '0' and vice versa). thus, a ber of 10 -6 corresponds to an average of one error per million bits. the ber value depends on the characteristics of the laser source and the transmission route. with the increase of the flow in optical systems, in both systems with standard single mode optical fiber and systems with special purpose fiber, effects of spontaneous emission, polarization mode dispersion, chromatic dispersion, optical fiber nonlinearities and noise in the receiver are increasing. therefore, ber measurement is of great importance when more adequate results are in question [7-8, 9]. the criteria used in optical receivers is that ber is less than 10 -9 . for a fluctuating signal received at a decision circuit, sampling is performed at time . d t the sampled value of the signal i varies from one bit to another around the mean value 1 i or 0i , depending on whether the bit is corresponding to 1 or etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 416-423 417 www.etasr.com ilic et al.: analysis of video signal transmission through dwdm �etwork based on a quality… 0 in the bit stream. the decision circuit compares sampled values with the threshold value d i and calls the bit 1 if d i i> or 0 if d i i< . an error occurs if d i i< for bit 1 or if d i i> for bit 0. both errors can be included in the definition of error probability as [7-8]: ber (1) (0 / 1) (0) (1 / 0)p p p p= + (1) where (1)p and (0)p are the probability of receiving bits 1 and 0, respectively, (0 / 1)p is the probability that 0 was decided when 1 was received and (1 / 0)p is the probability that 1 was decided when 0 was received. if the probability of occurrence of bits 1 and 0 are equal, then (1) (0) 1 / 2p p= = and ber is given by: [ ] 1 ber (0 / 1) (1 / 0) 2 p p= + (2) ber with the optimum adjustment for decision threshold depends only on the parameter q : ( )2exp q / 21 q ber 2 2 q erfc π −  = ≈    (3) and erfc is short for complementary error, defined by [10]: ( ) ( )∫ +∞ −= x dyyxerfc 2 exp . (4) the parameter q can be written as [1-2]: 0 1 0 1 q i i σ σ + = + (5) where 2 1 σ , 2 0 σ are noise variance corresponding to the symbols 1 and 0, respectively. an approximate form of ber is obtained by using the asymptotic expansion ( )q / 2erfc and is quite accurate for q 3> . iii. system model and algorithm analysis of the dwdm transmission system was performed using the software package optisystem 7.0 [11]. the algorithm used for the quality check of the dwdm transmission is presented in figure 1. the quality check algorithm applies to a fixed flow rate r. the parameters that vary are the number of dwdm channels (8 to 512) and the length of the amplifying section as (km), at whose ends edfa amplifiers are placed. the parameter that is being evaluated is the q factor, which shows whether the transmission quality is good. the boundary value for this factor is q 6.= fig. 1. algorithm for the evaluation of quality of dwdm transmission network during the design stage. the algorithm consists of a sub-cycle and a main cycle, for which the number of execution varies. the sub-cycle (blue line in figure 1) refers to the number of shares and the number of its executions depends on the values of the q factor for a variable number of shares and constant number of dwdm channels. the main cycle (red line in figure 2) refers to the number of dwdm channels, contains a sub-cycle for each section and it is repeated seven times, for three values of n (n = 8, 16, 32, 64, 128, 256, 512). at the beginning there are eight channels (n=8). after multiplexing (constant flow per channel , n dwdm channels), the signal is sent to an amplifying section as (a km in length). the q factor is calculated for the given values of as, r and n. if the condition q 6> is met, quality transmission is achieved and then the number of shares is increased by 1 (a extra km). after that, the algorithm will start from the part related to the calculation of q , that is the sub-cycle (blue line in figure 1) will be repeated until the condition q 6> is met. when the condition is not met, the sub-cycle is not repeated, and the current n and as values are the values for which high-quality transmission is not possible. once the subcycle is ended, the number of channels n will double and the etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 416-423 418 www.etasr.com ilic et al.: analysis of video signal transmission through dwdm �etwork based on a quality… algorithm is starting from the beginning, i.e., from the part that is refering to the multiplexing of the flow r with increased value of n dwdm channels. again, the cycle starts from one section, the length of a a km, but for double the value of the number of dwdm channels. the previous sub-cycle will be repeated as many times as needed to achieve the required quality during the transfer. once the sub-cycle is ended, the cycle will be repeated with double the number of dwdm channels and it will be examined whether the current value of channels is n<513, since this is the condition for ending the main cycle. the algorithm is applied for the specific values of the optical fiber system defined by the itu g.652 standard [1213]. two systems are observed, the first with a flow rate of 2.5 gb/s, and the second with a flow rate of 10 gb/s. the system is analyzed for 16, 32 and 64 dwdm channels, while the length of the amplifying section ranges from 40 to 80 km. the dispersion characteristics of the fiber are given in table i, and the diagram of the dwdm network analyzed in optisystem is given in figure 2. fig. 2. 16-channels dwdm network. power emitted by each source is 5 dbm. after receiving the digital signals, multiplexing is performed in dwdm multiplexers. the frequency of each channel is separated by 1 ghz. then a multiplexed signal is sent through an optical fiber where on every a km a edfa amplifier is set, with the following parameters: gain = 20 db, power = 15 dbm. since the system works in the third optical window, the attenuation along the length of the fiber is 0.2 db/km. on the receiving side, demultiplexing of the signals is done using dwdm demultiplexer running at the same frequency as the dwdm multiplexer. at the receiver, a ber analyzer is set to determine the values for ber and q , based on which one can determine the performance of the transmission system. results showed that the change of ber and q depends on the length of the fiber, i.e. on the number of the amplifying shares, and they also showed what kind of an effect the number of multiplexed channels and the flow rate per channel have on signal transmission. iv. simulation results table ii and table iii provide the ber parameter for flow per channel at 2.5 gb/s and 10 gb/s, respectively. based on the obtained values of ber, the graphs shown in figures 3-7 were drawn, showing that the value of the q factor decreases with the change in the number of dwdm channels and the length of the amplifying section. the purple dashed straight line represents the limit at which signal transmission quality distorts. if the limit of the quality transmission is a ber value of 10 -9 and q 6,= when the number of dwdm channels incerases quality transmission can be achived only if the the length of the section is reduced. decrease of the q factor is much more pronounced in the first amplifying sections, while with the greater number of them, q factor becomes approximately constant. table i. dispersion characteristics of the analyzed fibers 5ame value units mode group velocity dispersion include normal third-order dispersion include normal dispersion data type constant normal frequency domain parame not include normal dispersion 16.75 ps/nam/km normal dispersion slope 0.075 ps/nm^2/km normal beta 2 -20 ps^2/km normal beta 3 0 ps^2/km normal etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 416-423 419 www.etasr.com ilic et al.: analysis of video signal transmission through dwdm �etwork based on a quality… table ii. ber parameter values for the flow per channel of 2.5 gb/s 5umber of amplifying section 5 u m b e r o f d w d m c h a n n e ls l e n g th o f a m p li fy in g se c ti o n 1 2 3 4 5 6 7 8 9 10 40 km 2.80e-183 2.84e-087 1.73e-063 3.36e-055 4.07e-043 2.41e-039 5.17e-029 1.95e-023 3.62e-020 5.16e-020 50 km 1.18e-182 2.35e-089 1.32e-053 1.14e-036 9.29e-027 7.67e-020 6.60e-018 2.05e-015 7.41e-013 3.05e-011 60 km 8.59e-174 1.78e-082 4.22e-056 2.64e-039 1.87e-035 6.12e-026 2.39e-019 1.49e-015 5.02e-014 6.67e-012 70 km 8.68e-167 1.89e-112 4.95e-054 1.45e-036 9.72e-030 1.46e-026 1.66e-022 1.97e-017 3.49e-014 8.96e-015 16 80 km 5.56e-166 3.68e-101 1.99e-063 1.68e-026 7.88e-011 0.0014 1 1 1 1 40 km 1.17e-177 5.63e-076 5.28e-062 7.10e-044 3.13e-039 6.55e-032 2.76e-026 2.54e-023 4.82e-019 8.02e-017 50 km 5.85e-160 2.27e-065 8.52e-047 2.52e-036 9.97e-025 4.74e-019 2.72e-016 2.67e-013 7.72e-012 2.88e-010 60 km 5.36e-169 1.64e-074 1.94e-051 2.82e-034 6.68e-024 1.66e-020 3.20e-017 3.24e-014 1.09e-012 1.51e-010 70 km 7.79e-164 2.58e-068 7.24e-042 1.33e-029 1.09e-022 3.94e-020 8.12e-016 8.13e-014 1.58e-012 1.16e-010 32 80 km 1.78e-164 3.14e-081 9.84e-047 1.21e-021 7.66e-009 0.0047 1 1 1 1 40 km 1.92e-067 1.41e-048 2.73e-043 1.82e-030 6.28e-026 3.22e-023 5.43e-022 2.45e-018 2.68e-018 2.52e-016 50 km 9.73e-065 1.35e-044 1.55e-039 4.96e-029 3.15e-023 1.02e-018 2.31e-015 3.90e-013 5.85e-011 3.13e-010 60 km 7.22e-065 8.84e-051 1.05e-043 2.53e-034 7.13e-024 3.33e-017 7.13e-015 2.90e-013 6.41e-013 3.88e-010 70 km 5.19e-061 2.77e-045 5.63e-029 1.36e-024 5.17e-022 2.52e-017 4.53e-015 8.40e-014 2.12e-011 2.05e-010 64 80 km 1.83e-061 1.94e-038 7.81e-024 8.37e-014 1.25e-008 0.0051 1 1 1 1 table iii. ber parameter values for the flow per channel of 10 gb/s 5umber of amplifying section 5 u m b e r o f d w d m c h a n n e ls l e n g th o f a m p li fy in g se c ti o n 1 2 3 4 5 6 7 8 9 10 40 km 1.25e-145 6.34e-069 3.76e-040 4.23e-028 1.08e-018 2.27e-013 1.82e-009 0.0014 0.0024 0.0028 50 km 3.78e-138 3.18e-059 9.42e-031 5.51e-018 1.29e-011 1.18e-008 0.0007 0.001 0.0017 0.0021 60 km 6.96e-142 9.46e-049 6.03e-024 5.67e-015 7.68e-009 0.0005 0.0009 0.002 0.0026 0.0034 70 km 3.51e-126 6.01e-055 3.25e-023 1.39e-010 0.0005 0.0014 0.0016 0.0021 0.0028 0.0032 16 80 km 1.80e-117 5.72e-040 1.65e-014 0.0009 0.0018 0.0414 1 1 1 1 40 km 3.31e-094 6.37e-066 1.81e-036 1.29e-026 1.99e-017 4.63e-013 3.16e-009 0.0016 0.0026 0.0031 50 km 8.33e-090 3.97e-048 8.41e-025 2.06e-016 1.98e-010 8.55e-008 0.0009 0.0012 0.0024 0.0032 60 km 1.25e-080 2.15e-039 5.70e-021 1.87e-013 4.01e-008 0.0006 0.0012 0.0025 0.0037 0.0059 70 km 2.47e-080 4.65e-032 8.55e-016 1.54e-009 0.0008 0.0014 0.0019 0.003 0.0034 0.0046 32 80 km 1.31e-070 1.20e-030 3.97e-012 0.0009 0.0031 1 1 1 1 1 40 km 5.602e-048 3.31e-047 2.02e-030 3.29e-023 4.42e-017 3.50e-012 3.61-008 0.0026 0.0028 0.0032 50 km 6.32e-045 2.04e-034 7.28e-023 6.46e-015 4.73e-010 0.0006 0.001 0.0012 0.0028 0.0046 60 km 2.40e-044 1.75e-033 8.84e-019 1.83e-010 0.0007 0.0007 0.0012 0.0026 0.0035 0.0059 70 km 3.26e-044 1.84e-028 4.34e-014 4.36e-009 0.0011 0.0015 0.0031 0.0037 0.0037 0.0044 64 80 km 6.10e-045 3.13e-020 1.88e-009 0.0014 0.0043 1 1 1 1 1 fig. 3. changing the q factor for length of the amplifying section 40 km. fig. 4. changing the q factor for length of the amplifying section 50 km. etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 416-423 420 www.etasr.com ilic et al.: analysis of video signal transmission through dwdm �etwork based on a quality… fig. 5. changing the q factor for length of the amplifying section 60 km. fig. 6. changing the q factor for length of the amplifying section 70 km. fig. 7. changing the q factor for the length of the amplifying section 80 km. the given figures shows that with an increasing length of the amplifying section for the system of 10 gb/s there is no major change in quality with the larger length of signal transmission. in the case of the system of 2.5 gb/s, increasing the length of the amplifying sections means that there will be degradation of transmission quality. figures 8-13 show the eye diagram for the dwdm transmission system for an amplifying section length of 80 km, for 16, 32 and 64 channels and with a flow rate per channel of 2.5 gb/s and 10 gb/s. closed lines represent sectors with ber values of 10 -8 to 10 -12 . a) b) c) fig. 8. the eye diagram for flow rate per channel 2.5 gb/s and 16 dwdm channels: a) 80 km, b) 240 km, c) 400 km. etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 416-423 421 www.etasr.com ilic et al.: analysis of video signal transmission through dwdm �etwork based on a quality… a) b) c) fig. 9. the eye diagram for flow rate per channel 2.5 gb/s and 32 dwdm channels: a) 80 km, b) 240 km, c) 400 km. a) b) c) fig. 10. the eye diagram for flow rate per channel 2.5 gb/s and 64 dwdm channels: a) 80 km, b) 240 km, c) 400 km. a) b) c) fig. 11. the eye diagram for flow rate per channel 10 gb/s and 16 dwdm channels: a) 80 km, b) 240 km, c) 400 km. etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 416-423 422 www.etasr.com ilic et al.: analysis of video signal transmission through dwdm �etwork based on a quality… a) b) c) fig. 12. the eye diagram for flow rate per channel 10 gb/s and 32 dwdm channels: a) 80 km, b) 240 km, c) 400 km. a) b) c) fig. 13. the eye diagram for flow rate per channel 10 gb/s and 64 dwdm channels: a) 80 km, b) 240 km, c) 400 km. v. conclusion based on a quality check algorithm, used for calculation of the distance at which the transmission quality is lost and for calculating the number of dwdm channels at which the optical signal will be distorted, simulations of the network for specific values are conducted. an analysis of the ber parameter and the q factor shows that the length of the amplifying section, the flow rate per channel and the number of dwdm channels affect the transmission quality. results showed that ber and q are changing with the change in length of an amplifying section. decrease of q is much more pronounced in the first amplifying section, while with the greater number of sections, it becomes approximately constant. a conclusion was made: with increasing length of the amplifying section for the system of 10 gb/s there is no major change in quality with the larger length of signal transmission. in the case of the system of 2.5 gb/s, increasing the length of amplifying sections means that there will be degradation of transmission quality. acknowledgment this work was done within the research project of the ministry of science and technological development of serbia tr35026 and iii47016. references [1] k. m. sivalingam, s. subramaniam (eds), optical wdm networks: principles and practice, kluwer academic, norwell, ma, 2000 [2] m. t. fatehi, m. wilson, optical networking with wdm, mcgraw-hill, new york, 2001 [3] m. stefanovic, d. milic, “an approximation of filtered signal envelope with phase noise in coherent optical systems”, journal of lightwave technology, vol .19, no. 11, pp. 1685-1690, 2001 [4] i. djordjevic, m. stefanovic, “performance of optical heterodyne psk systems with costas loop in multichannel environment for nonlinear second-order pll model”, journal of lightwave technology vol. 17, no.12, pp. 2470-2479, 1999 [5] r. ramaswami, k. sivarajan, optical networks: a practical perspective, 2nd ed., morgan kaufmann publishers, san francisco, 2002 [6] i. p. kaminow, t. li, a. willner (eds), optical fiber telecommunications v, elsevier/academic press, 2008 [7] g. agrawal, nonlinear fiber optics, 2nd ed., academic press, 2001 [8] g. agrawal, fiber-optic communication systems, 3nd ed., wiley, 2002 [9] e. g. sauter, nonlinear optics, john wiley & sons, inc., new york etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 416-423 423 www.etasr.com ilic et al.: analysis of video signal transmission through dwdm �etwork based on a quality… [10] m. abramowitz, i. a. stegun, handbook of mathematical functions, dover, new york, 1970 [11] optiwave-design software for photonics, optisystem-optical communication system and amplifier design software, http://www.optiwave.com/products/system_overview.html (accessed 03.11.2012) [12] international telecommunication union, “optical fibers, cables and systems”, itu-t manual, 2009 [13] international telecommunication union-itu-t g.652, “series g: transmission systems and media, digital systems and networks. transmission media and optical systems characteristics: characteristics of a single-mode optical fibre and cable”, itu, 2009 authors profile sinisa ilic graduated at faculty of electrical engineering in pristina 1992 in the field of electronics and telecommunication. as b.sc. engineer he worked at television and radio pristina. he received his m.sc. at faculty of electrical engineering in belgrade in the field of digital transmission of information and defended phd thesis at university of pristina in the field of digital signal processing and computer engineering. he is teaching now databases, design of information systems, infrastructure of e-commerce and biomedical informatics at faculty of technical sciences in university of pristina located in kosovska mitrovica. his areas of interest are: databases, information systems, biomedical informatics, multimedia, digital signal processing. he is author and co-author of many scientific papers published in journals and presented at international conferences. he is also involved in several educational projects and in several commercial projects related to introduction of public finance management information systems. branimir jaksic is assistant at the department of electronic and computing engineering, faculty of technical sciences in kosovska mitrovica, serbia. he is phd candidate in the faculty of electronic engineering, university of nis, serbia. areas of research include optical and satellite communications. he has authored several scientific peer-reviewed papers on the above subject. mile petrovic is full professor at the department of electronic and computing engineering, faculty of technical sciences in kosovska mitrovica, serbia. areas of interest include telecommunications television techniques. he has authored over 50 scientific peer-reviewed papers and a large number of projects and patents. he is a member of the technical program committee and reviewer for several international journals and symposia. aleksandar markovic is phd candidate in the faculty of electronic engineering, university of nis, serbia. his research interests are statistical communication theory and optical communications. he has published several journal publications on the above subject. vanja elcic is assistant at the university slobomir p in bijeljina, bosnia and herzegovina. his areas of interest include information technology and telecommunications. he has authored several scientific peer-reviewed papers in the field of information technology and telecommunication. engineering, technology & applied science research vol. 8, no. 5, 2018, 3355-3359 3355 www.etasr.com laaziri et al.: information system for the governance of university cooperation information system for the governance of university cooperation majida laaziri information system engineering resarch group national school of applied sciences abdelmalek essaadi university tetouan, morocco samira khoulji information system engineering resarch group national school of applied sciences abdelmalek essaadi university tetouan, morocco khaoula benmoussa information system engineering resarch group national school of applied sciences abdelmalek essaadi university tetouan, morocco kerkeb mohamed larbi information system engineering resarch group faculty of sciences abdelmalek essaadi university tetouan, morocco abstract—recognizing the impact of international cooperation in science and technology, all higher education institutions prioritize strategic partnerships. if setting up a partnership is important, its management, monitoring and evaluation of cooperation actions, regular communication among partners, and the ability to allow all parties to monitor the functioning of the partnership are more important. for good co-operation management, an information system becomes a mandatory condition. abdelmaleek essaadi’s university team has set up an information system for the governance of a university cooperation called simacoop, to support cooperation between governments and universities, and to facilitate the process of partnership management. this system also helps in identifying the shared vision and goals of the partnership members and develops documents that define the partnership terms. in addition, simacoop has put in place procedures for maintaining and monitoring the partnership evolution [1]. the purpose of this article is to give a general presentation on simacoop’s design and development for the governance of university cooperation. keywords-information system; the governance of university cooperation; simacoop platform; object-oriented methodology; uml i. introduction moroccan universities and research institutions face the challenge of synchronization with the demands and expectations of modern society while reinforcing their actions on international level. a large academic and research university is not any more a sufficient condition to provide access to high quality education, if it does not cooperate with other major universities and organizations at national and international level. for this reason, all higher education institutions give importance to university cooperation, which enables the development of innovative international partnerships, student mobility, establishment of relationships and networks, experience and knowledge exchange, and generation of ideas and knowledge. in addition, university cooperation requires effective management to ensure the continuity of constructive and productive relations [2], and to allow all considered parties to monitor the functioning of the partnership. in this context and with the evolution of information systems in different fields, the abdelmaleek essaadi university (aeu) set up a tracking information system for the management of university cooperation called simacoop. ii. simacoop generalities simacoop is a monitoring system designed to support governments and universities in the cooperation, partnership and student exchange plans and programs, and to improve communication, collaboration and integration between universities and their partners, performance management, strategic planning, research performance evaluation and establishing of a sound policy for the development of the institutional relationship[3]. simacoop offers a range of services, it mainly gives the university and its partners the possibility to: do a follow-up of the activities of the cooperation projects, do a follow-up of cooperation agreements and their results, and get personalized follow-up of foreign students (figure 1). it notifies the user of the dates of the cooperation project activities, whether they are imminent or behind schedule, and informs them of the dates of the agreements in force and the non-renewable agreements. thus, this system can detect the strong points of cooperation in order to overcome its weaknesses, benefit from the exchange of experience, skills and competences, and raise the level of efficiency and productivity, monitor the implementation, the extent to which each party fulfills its obligations and commitments, and the respect of cooperation agreements with partner missions and their strategic objectives [1]. simacoop is a coherent information system centered in a global platform integrating several services that meet the administrative and academic needs (figure 2). engineering, technology & applied science research vol. 8, no. 5, 2018, 3355-3359 3356 www.etasr.com laaziri et al.: information system for the governance of university cooperation fig. 1. simacoop features a. administrative  makes the partnership management process easier.  facilitates the work of the administration and allows it to accomplish its mission.  provides reliable, relevant and instant information  provides better partnership management.  follows the strategic objectives of the partnership.  detects successful actions and challenges.  allows regular communication among partners.  provides information about the evolution of the partnership.  ensures monitoring and evaluation of cooperation actions. b. academic  measures the evolutions and the consequences of the decisions taken.  helps the actors of the partnership in their activities.  schedules and controls the tasks of the partnership process.  allows effective communication.  adds depth and breadth to its impact on the scientific community.  identifies the shared vision and goals of the partnership members.  develops documents that define the partnership terms.  follows-up the partnership as it evolves.  allows all parties to follow the functioning of the partnership.  maintains constructive and productive relationships.  evaluates research.  shares and exchanges information.  reduces cost.  takes advantage of the exchange of experience, skills and competences.  raises the level of efficiency and productivity.  improves the quality of data reported by the institutions management. fig. 2. administrative and university services of simacoop iii. object-oriented methodology object-oriented technology is a new methodology that is widely applied in the field of software development. objectoriented methodology (oom) is a supreme technique for solving complex problems by ripping the problem into subtasks. oom is a new approach to system development that encourages and facilitates the reuse of software components. by using oom, higher productivity, lower maintenance costs and better quality can be achieved [4, 5]. oom requires objectoriented techniques to be used during system analysis, design, and implementation. this methodology allows to determine what the system objects are, how they behave over time or in response to events, and what responsibilities and relationships an object has to other objects. object-oriented analysis allows seeing all the objects in a system, their commonalities, their differences and the way the system handles objects [6, 7]. during design, the overall architecture of the system is described. during the implementation phase, the class objects and interrelations of these classes are translated and effectively coded. there are several object-oriented development methods (ooms). in the design of our information system, we used the object modeling technique (omt) because it is the most developed one, and covers a good part of the system development cycle. omt is an object-oriented software development methodology given by james rumbaugh. this methodology describes a method of analysis, design and implementation of a system using an object-oriented technique. it is a fast and intuitive approach to identify and model all the objects that constitute a system [8]. omt consists of three basic models, each capturing important aspects of the system, namely the object model which describes the static, structural and system data, the dynamic model that describes the temporal, behavioral and control aspects of the system and the functional model that describes the transformational and functional aspects of the system [9, 10]. omt methodology supports the entire life cycle of the system, according to five main phases [11-13]. a. system analysis as in any other system development model, system analysis comes first. in this phase, the developer interacts with the system user to know the user's needs and analyzes the system engineering, technology & applied science research vol. 8, no. 5, 2018, 3355-3359 3357 www.etasr.com laaziri et al.: information system for the governance of university cooperation to understand how it works. on the basis of this study, the analyst prepares a model of the desired system. this model is purely based on what the system needs to do. at this stage, the implementation details are not taken into account. only the model of the system is prepared on the basis of the idea that the system consists of a set of interacting objects. the important elements of the system are underlined. b. system design system design is the next stage of development, where the overall architecture of the desired system is decided. the system is organized as a set of subsystems interacting with each other. when designing the system as a set of interacting subsystems, the analyst considers the specifications observed in the system analysis as well as the user-imposed requirements. the analysis of the system consists in perceiving the system as a set of interacting objects. a larger system can also be seen as a set of smaller interacting subsystems that are themselves composed of a set of interacting objects. when designing the system, the focus is on the objects that constitute the system, not on the processes that are running in the system. c. object design in this phase, the details of system analysis and system design are implemented. the objects identified in the design phase of the system are designed. in this phase, the implementation of these objects is decided in the form of required data structures and interrelationships between objects. this concept is known as class creation. in this phase of the development process, the designer decides classes in the system based on these concepts. it decides whether classes should be created from scratch, whether existing classes can be used as is, or new classes can be inherited. d. implementation during this phase, the class objects and interrelations of these classes are translated and effectively encoded using an object-oriented programming language. the required databases are created and the entire system is transformed into an operational system. e. testing this phase aims to test the system in implementation. three cases are produced and used:  test cases: what to test in the system.  test procedures: the procedures that allow running the test.  test components: the environment needed to actually perform the test cases. iv. ooad with an uml, omg standard. object oriented analysis and design (ooad) is a technical approach used in the analysis and design of the system through the application of paradigm and object-oriented concepts, including visual modeling, applied throughout the cycle system development [8]. it models a system as a group of objects. one of the most used notations to represent the objects of a system and how they interact with each other is the unified modeling language (uml). object management group (omg) for object-oriented modeling, standardized uml in 1997. it is a graphical language for data modeling and processing (objectoriented), that allows the specification, representation and construction of computer system components, it combines widely accepted concepts from a number of object-oriented modeling techniques and is inherited from several other methods like omt [14]. it is intended to model information systems and covers the different phases of an object development (analysis, design and implementation) [15, 16]. it improves and facilitates communication, representation and understanding of object solutions [4]. v. system architecture design the design of the system architecture is how system functionality is to be provided by the system components, where the system represents a set of components that perform the defined functions [17]. the design process of the information system architecture focuses on the decomposition of the system into different components and their interactions to satisfy functional and non-functional requirements. figure 3 provides an overview of the design and development of the simacoop information system. fig. 3. simacoop architecture according to figure 3, the realization of the simacoop information system was based on the functionality of the symfony framework and the architecture of the mvc paradigm. thanks to symfony's functionalities, our system has benefited from a well-structured modular workspace with a clear and maintainable code, the code is separated in three layers according to the mvc model, it is characterized by an object-relational mapping layer (orm) and a data abstraction layer, ensuring data separation, display, processing, and actions [18]. vi. result in the simacoop information system, there are three types of actors who can access the platform: project manager, dean, university president. their functions are different, so each actor corresponds to a space in the platform as follows: a. project manager’s space simacoop offers the project manager an account to enter the general information of his cooperation project, the information of the project partners, the activities, the expenses and the budget (figure 4 [3]). engineering, technology & applied science research vol. 8, no. 5, 2018, 3355-3359 3358 www.etasr.com laaziri et al.: information system for the governance of university cooperation fig. 4. project manager’s space simacoop allows the project manager to:  follow the activities of cooperation projects.  manage projects better.  communicate with other partners (government, universities, national and international institutions, ...).  be notified of project activities that are imminent or delayed.  exchange and share information and cooperation documents with other project managers. b. dean's space simacoop offers the dean of the institution an account that enables him to introduce his information as project manager and to add the project managers belonging to his institution in the simacoop platform, the validation of their partnership activities, and all the partners of his establishment (figure 5 [3]). fig. 5. dean’s space simacoop allows the dean to:  manage the budget and the expenses of the cooperation projects and the partnership agreements.  follow the agreements and conventions of the institution over time.  make a personalized follow-up of the foreign students of the establishment.  download the annual report of the activities of the cooperation projects and partnership agreements of the institution.  exchange information and share cooperation documents.  provide visibility to all project managers at the institution, and all national and international partners.  be advised of the dates of activities carried out, unrealized projects and the agreement dates that are in force or renewed.  follow the evolution and the execution of the actions of the partnerships of the establishment.  detect successful partnership actions and challenges.  ensure the continuation of constructive and productive relationships. c. university administrator's space simacoop offers the president of the university an account for two roles: he can introduce his information as project manager and he is also the manager of the platform. he has total visibility on the database, his task is to manage the entire system, and he is in charge of creating and validating the accounts of all the project managers who belong to the institutions from his university in the simacoop platform. therefore, he specifies the access rights of each user (figure 6 [3]). fig. 6. administrator space simacoop allows the president to:  validate the accounts of the project managers of the university.  ensure the smooth running of all agreements and partnership agreements of the university.  order the budgets and expenses of cooperation projects and the university.  check and accredit all the information concerning all cooperation partnerships of the university.  download the annual report of the projects and cooperation partnerships of the university. vii. conclusion the use of information systems in the university has become a reality, and a central part of its operation, because they provide universities with management tools that meet their needs, and help all users in their activities. they schedule and control tasks and they enable effective communication. as the problems faced by university communities become more complex, the idea of a management information system on university cooperation can be very promising. through partnerships, the university can contribute and benefit from the efforts of other higher education institutions. through a cooperative information system, universities can accelerate engineering, technology & applied science research vol. 8, no. 5, 2018, 3355-3359 3359 www.etasr.com laaziri et al.: information system for the governance of university cooperation learning and disseminate skills and knowledge. in addition, they can add depth and breadth to their impact on the scientific community. references [1] m. laaziri, k. benmoussa, s. khoulji, k. mohamed larbi, “simacoop: a framework application for the governance of university cooperation”, transactions on machine learning and artificial intelligence, vol. 5, no. 4, pp. 785-794, 2017 [2] r. de vry, g. watson, “university of delaware’s faculty-it partnership: educational transformation through teamwork”, the technology source, available at: http://technologysource.org/article/ university_of_delawares_facultyit_partnership/ [3] simacoop, available at: http://simacoop.uae.ac.ma/ [4] u. a. khan, i. a. al-bidewi, k. gupta, “object-oriented software methodologies: roadmap to the future”, international journal of computer science issues, vol. 8, no. 5, pp. 392-396, 2011 [5] m. r. b. prakash, h. s. chandrasekharaiah, “an object oriented perspective for ac/mtdc system simulation”, ieee international conference on intelligent system application to power systems, orlando, usa, january 28-february 2, 1996 [6] h. lee, c. lee, c. yoo, “a scenario-based object-oriented methodology for developing hypermedia information systems”, ieee 31st hawaii international conference on system sciences, kohala coast, hi, usa, january 9, 1998 [7] r. chalmeta, t. j. williams, f. lario, l. ros, “developing an objectoriented reference model for manufacturing”, ifac proceedings volumes, vol. 30, no. 1, pp. 351-356, 1997 [8] s. hong, g. van den goor, s. brinkkemper, “a formal approach to the comparison of object-oriented analysis and design methodologies”, ieee 26th hawaii international conference on system sciences, wailea, hi, usa, january 8, 1993 [9] j. osis, o. ivasiuta, p. rusakovs, “advanced object-oriented modeling techniques for large scale systems”, ifac proceedings volumes, vol. 31, no. 20, pp. 787-792, 1998 [10] r. h. bourdeau, b. h. c. cheng, “a formal semantics for object model diagrams”, ieee transactions on software engineering, vol. 21, no. 10, pp. 799-821, 1995 [11] ukessays, two object oriented methodologies booch and rambaugh information technology essay, available at: https://www.ukessays.com/ essays/information-technology/two-object-oriented-methodologiesbooch-and-rambaugh-information-technology-essay.php [12] m. p. selvan, k. s. swarup, “object methodology techtorial”, ieee power energy magazine, vol. 3, no. 1, pp. 18-29, 2005 [13] visual basic tutorials, object oriented methodology life cycle model, available at: http://www.freetutes.com/systemanalysis/sa2-objectoriented-methodology.html [14] g. booch, j. rumbaugh, i. jacobson, the unified modeling language user guide, addison wesley, 1998 [15] s. servigne, “conception, architecture et urbanisation des systemes d’information”, in: encyclopædia universalis, encyclopædia britannica, 2008 (in french) [16] o. glassey, j. l. chappelet, comparaison de trois techniques de modélisation de processus : adonis , ossad et uml, institute de hautes etudes en administration publique, 2002 (in french) [17] tutorials point, ooad object oriented system, available at: https://www.tutorialspoint.com/object_oriented_analysis_design/ooad_o bject_oriented_system.htm [18] symfony 4.0 documentation, available at: https://symfony.com/ doc/current/index.html microsoft word 20-3680_s1_etasr_v10_n4_pp5998-6003 engineering, technology & applied science research vol. 10, no. 4, 2020, 5998-6003 5998 www.etasr.com nguyen et al.: backstepping control for induction motors with input and output constrains backstepping control for induction motors with input and output constraints tung lam nguyen department of industrial automation university of science and technology hanoi, vietnam lam.nguyentung@hust.edu.vn thanh ha vo department of electrical engineering university of transportation and communications, hanoi, vietnam vothanhha.ktd@utc.edu.vn nam duong le department of electrical engineering quy nhon university quy nhon, vietnam lenamduong@qnu.edu.vn abstract−in practice, the applied control voltage for an induction motor drive system fed by a voltage source inverter has a limit depending on the dc bus capacity. in certain operations such as accelerating, the motor might require an excessively high voltage value that the dc bus cannot supply. this paper presents a control solution for the bounded control input problem of the induction motor system by flexibly combining a hyperbolic tangent function in a backstepping control design procedure. in addition, the barrier lyapunov function is also employed to force speed tracking error in a defined value. the closed-loop system stability is proven, and the proposed control is verified through numerical simulations. keywords-backstepping; barrier lyapunov funtion; induction motor; foc i. introduction induction motors have been serving as a major workforce in various industrial applications [1, 2] due to their robustness and ease of maintenance. despite the fact that technologies used in induction motor drive systems are well-established, the drive system still draws control researchers’ attention due to its complicated dynamical properties [3, 5]. in the two most common induction motor drive control techniques, flux oriented control (foc) [6] based schemes are widely used when compared to direct torque control (dtc) structure [7]. foc renders the induction motor as a direct current motor in terms of decoupling torque producing and flux forming process. there have been many attempts to control the induction motor based on foc, from classical pid control [2] to advance nonlinear strategies including model predictive control [8], sliding mode control [9], fuzzy-neural approach [10], and genetic algorithm [11]. thanks to its systematic design and the ability to cope with system nonlinearities, backstepping method is intensively used in the induction motor drive. authors in [12] successfully employed backstepping integrated with a high-gain observer for stabilizing the motor drive without information on the rotor speed, flux, and load torque. in order to compensate system uncertainties, backstepping was combined with a recurrent neural network to enhance tracking performance in induction servo systems [13]. a similar approach can be found in [14] where a radial basis function neural network was used. the proposed control guarantees system stability and bounded signals. exploiting the robustness of sliding mode control, authors in [15] designed a backstepping sliding mode control for dealing with lumped uncertainties in linear induction motor drives. the effectiveness of the proposed control is verified numerically and experimentally. in [16], adaptive backstepping control supported by a fuzzy system for integral action was developed for a linear induction motor. simulation study showed the control ability to cope with parameter variations and load disturbances. in the quest of compensating system mechanical parameters such as unknown viscous coefficient and load torque, an adaptive backstepping algorithm was designed in [17]. other applications of backstepping control in induction motor drive can be seen in [18, 19]. the aforementioned researches mainly focus on ways to improve the dynamical responses of the induction motor drive closed-loop system regardless the limitations of the control inputs. it is clearly that in certain circumstances, the motor might require exceeded voltage value that the dc bus cannot supply. if the required voltage is not satisfied, it results in system performance degradation. in this paper, a method is introduced to tackle the problem by manipulating backstepping control with the assistance of a virtual control defined through a hyperbolic tangent function for limiting the control input in a specified value determined by the capacity of the dc bus. in addition, the paper also integrates barrier lyapunov function in the design steps in order to force the speed tracking error falling in a desired range. ii. mathematical model formulation the mathemathetical model of the induction motor is well defined, for more detailed derivation please refer to [20]. the induction motor model in the d-q reference frame is obtained as in (1) where: 2 1 m s r l l l σ = − is the leakage factor, s s s l t r = the stator time constant, r r r l t r = the rotor time constant, mr r l k l = , 2 s r rr r r kσ = + , ' l t r σ σ σ σ = , m sds r rd l i t ω ω ψ = + the slip estimation, ω is the mechanical rotor speed, zp is the number of pole pairs, j is the rotor and load lumped inertia, tl the load torque, rdψ corresponding author: tung lam nguyen engineering, technology & applied science research vol. 10, no. 4, 2020, 5998-6003 5999 www.etasr.com nguyen et al.: backstepping control for induction motors with input and output constrains the rotor flux, and , , : m r s l l l mutual, rotor, and stator inductance. , , , ' ' ' 2 ' ' 1 1 1 1 1 1 1 1 1 1 1 ( ) 3 3 (1 ) 2 2 sd sd s sq rd sd s r r s sq s sd sq rd s r rq sq r s rd sd rd s rq r r m m p rd sq p s rd sq r di i i u dt t t t l di i i dt t t u t l d i dt t t l m z i z l i t σ σ ω ψ σ σ σ σ σ σ ω ωψ σ σ σ σ ψ σ σ ψ ψ ω ω ψ ψ σ ψ   − − = − + + + +      − − = − − + −    − + + = − + − = = − −              (1) the first two equations characterize motor current dynamics. the last two equations denote motor flux forming process and equation of motion. it can be observed that the induction motor given in (1) is a coupled and nonlinear system. the block diagram representation of the induction motor is given in figure 1. ⊗ ⊗ ⊗ ⊗ × × × × ÷ (1 ) t st σ σ+ 1 m r l t s+ p z sj • • • • • • • 1 1 1 m r m r l tl ts σ σ − + m r l t 3 2 m p r l z l sd u sq u q d e − m e m e d q e − rd ψ r ω ω sd i sq i s ω + + + − − − 1 1 1 m r m r l tl ts σ σ − + l m + + m m (1 ) t st σ σ+ 1 s lσ 1 s lσ rd ψ fig. 1. structure of the induction motor in dq-coordinates. iii. backstepping controller design with control input and output constrains a. magnetic flux control design the control objective is to drive the motor magnetic flux to a desired value in such a way that the tracking error stays in a predefined range. in order to achieve this objective, the tracking error is defined as follows: ' 1 1 rdref z x ϕ= − (2) and a lyapunov candidate function is: 2 1 2 2 1 1 log 2 b b d k v k z = − (3) taking the time derivative of v1 gives: 1 2 1 2 2 1 ( ) d d b d z x q v k z − = − � � (4) at this point, x2 is considered as a control input, the error between x2 and the desired control value is defined as: 2 2 1 z x α= − (5) where a1 is the virtual control. substituting (5) into (4) gives: 1 2 1 1 2 2 1 ( ) d d b d z z a q v k z + − = − � � (6) equation (6) suggests that the virtual control can be selected as: 1 1 1 1 2 2 2 1 ( ) d d b d q x a c z x k z − = + + − � � (7) the virtual control renders 1 v� as: 2 1 1 1 1 2d d v c z z z= − +� (8) to deal with the coupling term 1 2 z z and force 2 z to zero, we propose a lyapunov candidate function as: 2 2 2 1 1 2 d v z v= + (9) the derivative of v2 will have the following form: 2 2 1 1 1 2 2 2d d d d d v c z z z z z= − + + � (10) taking the derivative of (5) we have: 2 2 2 1 1 1 1 1 2 1 1 2 2 2 1 1 ( )( ) 2 ( ) d b d d k d q x k z z z z c z k z − − − = − − − �� �� � � � (11) substituting the first and second equations (10) to (11) results in: ( ) ( ) ( ) 2 2 1 12 2 1 1 2 1 1 2 12 2 1 1 2 1 2 12 2 2 1 1 1 1 1 1 ( ) 1 1 1 1 1 ( ) ( ) 2 1 1 ( ) s sd r b d d r r rr b d d d d r r b d z x x x u t t tt k z x x c x x q t t t tt k z z x x q q t tk z σ σ σ σ σ ω σ σ − = − + + + − − − + − − − + − − − − � � � �� (12) from (10) and (12) the control signal can be achieved guaranteeing x1 converges to dq with the dynamical error confined in a range defined by kb. another control objective is to specify the control input subject to a limitation. it is necessary to consider input constrains in the control design since the applied voltage is supplied from an inverter whose output voltage is practicallye limited. toward this end, the limitation of the output voltage is described as a tangent function. ( ) tanh( ) sd m m u g u u υ υ≡ = (13) where m u is the control limit. the design of sd u is passed to the construction of ϑ . equation (13) results in: engineering, technology & applied science research vol. 10, no. 4, 2020, 5998-6003 6000 www.etasr.com nguyen et al.: backstepping control for induction motors with input and output constrains ( ) ( )g g υ υ υ υ ∂ = ∂ �� (14) the control design of sd u is subject to sd m u u≤ is a shift to a task of finding a virtual signal u1 defined by: ( ) 1 1 g g uυ υ − ∂ = ∂ � (15) to proceed we define: ( )3 2 2sdz u gα υ α= − ≡ − (16) from (12) and (16) the virtual control a2 can be selected as: 2 2 2 2 1 1 1 12 2 1 1 1 2 12 2 1 1 2 1 1 2 1 2 12 2 2 1 1 2 2 1 ( )( ( ( ) 1 1 1 1 ( ) ( ) 1 1 2 1 1 ( ) ( ) ( ) ) r b s r b r r b r r d d r r b r r d x l t k z z x t k z t x x x t t k z t t z c x x q x x q t t k z t t q c z σ σ α σ ω σ σ = − − + − + − − + − − − + − − + − − − − + � � �� (17) virtual control a2 renders 2v � as: 2 2 2 1 1 2 2 2 32 2 1 1 1 ( ) b r s v c z c z z z k z t lσ = − − + − � (18) in order to remove the coupling term related to 2 3 z z and drive ( )g υ to track a2, a lyapunov candidate function is proposed as follows: 2 3 3 2 1 2 v z v= + (19) the derivative of (19) yields: 2 2 3 1 1 2 2 2 3 3 32 2 1 1 1 ( ) b r s v c z c z z z z z k z t lσ = − − + + − � � (20) taking the derivative of (16) and substituting the result into (20), we can finally get the virtual control that guarantees bounded control input as: 1 2 2 3 32 2 1 1 1 ( ) b r s u z a c z k z t lσ = − + − − � (21) substituting the proposed control into (20) gives: 2 2 2 3 1 1 2 1 3 3 0v c z c z c z= − − − ≤� (22) and the design process for magnetic flux is completed. b. speed control design the speed control design with input and output constrains is carried out in the same manner as in the previous section. for the sake of abstract presentation, control design steps are summarized in this section as follows: 1 3 ref t x ω= − � (23) 2 1 1 1 4 2 2 1 1 ref b x d t x k t ω β − = − + − − �� (24) 2 4 1 t x β= − (25) 2 2 1 1 1 4 2 2 12 2 1 1 1 4 2 1 12 2 2 2 1 1 1 1 2 1 1 4 1 4 1 2 22 2 2 1 1 ( ) 1 ( ( ) ( ) 1 1 ( ) ( ) ( ) 2 ( ) ( ) ) ( ) s b m s m b refm b r r b m m ref ref b j l k t k x x x x k x j k t t k x x x t j k t t t k t t k x x k x x d d t k t j j σ σ σ β ω ω σ ω ω ω − − = − − − − − + − − + − − + − + − + − � � � (26) 3 2 2 ( ) sq t u gβ υ β= − = − (27) 1 2 2 2 3 32 2 1 1 ( ) m b s k x u t d t k t j l β σ = − + − − � (28) where 1 ,β 2 β are virtual controls and t1, t2, t3 are the backstepping design errors in each step. the control signal guaranteeing bounded input and output is u2. iv. simulation results a. settings simulations were conducted on an im machine with the structure control for induction motor shown in figure 2. the space vector modulation is used for the inverter part. ,rψ ,rω and , i r are flux, speed, and dq-current controllers, respectively. simulation parameters are given in table i. in the simulation, two control schemes were implemented: conventional and input-output embedded backstepping controls. table i. simulation parameters rated power pnom 2.2kw speed motor nnom 2880prm rated phase current inom 4.7arms number of pole pairs zp 1 rotor resistance rr 0.42ω stator resistance rs 0.37ω rotor inductance lr 34.25mh stator inductance ls 34.41mh mutual inductance lm 33.1mh total inertia j 0.001kgm 2 b. simulation procedure at t=0s, magnetic current is created and at t=2s the system speeds up to 1200rpm. in the simulation scenario, a sudden torque with rated value of 1.5nm is applied on the motor shaft. the results of the simulation of stator current and speed controllers using conventional backstepping control method and backstepping with control input and output constrains are shown in figures 3-8 where (a) represents the response of conventional backstepping and (b) represents the backstepping with input and output constraints. the proposed backstepping controller is applied to the induction motor. the coefficients are chosen as: c1=1000, c2=1000, c3=5150, c4=1000, d1=500, d2=500, d3=1000, and d4=500. engineering, technology & applied science research vol. 10, no. 4, 2020, 5998-6003 6001 www.etasr.com nguyen et al.: backstepping control for induction motors with input and output constrains fig. 2. backstepping control with output and input contraints. in the simulation result, the control signal constraint is selected as: 2 2 160v s sd sq u u u= + ≤ (29) constraints on dq are determined according to rectangular approximation: max max 2 and 1 3 3 dc dc sq sd v v u uα α= = − (30) where vdq=300v and a=0.8. this condition implies that control inputs must satisfy: max sq sq u u≤ and max sd sd u u≤ (31) the designed controller can also limit the system’s output through the value kb. this helps us to control the overshoot of the system. in the simulation, we set the value kb=0.1. (a) (b) fig. 3. speed response. for the system controlled by the conventional backstepping method, we set the dc bus voltage to 300v dc v = . this implies that there is no hard limit applied in this case. on the contrary, the dc bus voltage is restricted to 160v when the induction motor drive system is regulated by backstepping control with input and output constraints. in both cases, simulation results show that the two approaches provide good tracking performance with fast response time as can be seen in figure 3. (a) (b) fig. 4. voltage response usd. (a) (b) fig. 5. voltage response usq. (a) (b) fig. 6. stator current responses isd. engineering, technology & applied science research vol. 10, no. 4, 2020, 5998-6003 6002 www.etasr.com nguyen et al.: backstepping control for induction motors with input and output constrains (a) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 -5 0 10 15 20 isq* isq i s q [ a ] (b) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 time[s] -5 0 10 15 20 is q [ a ] isq* isq fig. 7. stator current responses isq. (a) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 40 80 100 160 200 us us* time[s] u s [v ] (b) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 time[s] 0 40 80 120 160 u s [ v ] us us* fig. 8. voltage us response. it is noted that at 2s the motor accelerates to 1200rpm. this speeding action requires a considerably large quadrature current and voltage (figures 4(a), 5(a), 6(a), and 7(a)), resulting in us reaching 180v in the case of the conventional method as shown in figure 8(a). meanwhile, due to the fact that the control inputs are tied to 160v, the us measured values when the backstepping with input and output limitation action is suppressed well below 120v (figures 4-8(b)). the results show technical meaning when the system requires large control input when fast accelerating or deaccelerating in the face of limited dc bus capacity. the speed tracking also indicates that the overshoot remains in the bounded set specified by 0.1. b k = we see that the controller designed by this method helps the drive system respond well in accordance with the set values. however, the disadvantage of this method is that it is difficult to select the optimal coefficients for the controller, the design process of calculating control signals requires many derivative steps leading to a large volume of calculations. v. conclusion the paper proposes a control mechanism backboned by backstepping control to avoid voltage saturation in induction motor drive systems. the hyperbolic tangent is embedded in the control design to deal with the voltage saturation problem. this approach differs from other works where either torque producing or flux forming voltage is sacrificed when the input voltage enters the saturation zone. the simulation results show that the control can suppress the control input voltage in the prescribed domain while maintaining the tracking error due to the help of the barrier lyapunov function. in future research, we aim at deploying the proposed control in an experimental rig. references [1] x. shi, h. li, and j. huang, “a practical scheme for induction motor modelling and speed control,” international journal of control and automation, vol. 7, pp. 113–124, apr. 2014, doi: 10.14257/ijca.2014.7.4.11. 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[13] c. m. lin and c. f. hsu, “recurrent-neural-network-based adaptivebackstepping control for induction servomotors,” ieee transactions on industrial electronics, vol. 52, no. 6, pp. 1677–1684, dec. 2005, doi: 10.1109/tie.2005.858704. [14] j. yu, y. ma, b. chen, h. yu, and s. pan, “adaptive neural position tracking control for induction motors via back stepping,” international journal of innovative computing, information and control, vol. 7, no. 7, pp. 4503–4516, jul. 2011. engineering, technology & applied science research vol. 10, no. 4, 2020, 5998-6003 6003 www.etasr.com nguyen et al.: backstepping control for induction motors with input and output constrains [15] f.-j. lin, p.-h. shen, and s.-p. hsu, “adaptive backstepping sliding mode control for linear induction motor drive,” iee proceedings electric power applications, vol. 149, no. 3, pp. 184–194, may 2002, doi: 10.1049/ip-epa:20020138. 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[20] n. p. quang and j.-a. dittrich, vector control of three-phase ac machines: system development in the practice, 2nd ed. berlin heidelberg: springer-verlag, 2015. microsoft word 21-2857_s_etasr_v9_n4_pp4428-4432 engineering, technology & applied science research vol. 9, no. 4, 2019, 4428-4432 4428 www.etasr.com usman: an efficient depth estimation technique using 3-trait luminance profiling an efficient depth estimation technique using 3trait luminance profiling imran usman college of computing and informatics saudi electronic university riyadh, saudi arabia i.usman@seu.edu.sa abstract—this paper presents an efficient depth estimation technique for depth image-based rendering process in the 3-d television system. it uses three depth cues, namely linear perspective, motion information, and texture characteristics, to estimate the depth of an image. in addition, suitable weights are assigned to different components of the image based on their relative perspective position of either the foreground or the background in the scene. experimental results on publicly available datasets validate the usefulness of the proposed technique for efficient estimation of depth maps. keywords-depth estimation; 3d tv; dibr; depth image; 3-d warping i. introduction with the advancement of technology in recent decades and the reduced cost of hi-tech hardware, a wide range of new possibilities is realizable as the demand for enhanced viewing experience in the 3d field. in recent years, there has been rapid progress in the fields of image capturing, coding and display which brings the realm of 3d closer to reality than ever before [1]. real, 3d world incorporates a third dimension (z-axis) that defines depth. depth is perceived by human vision in the form of binocular disparity. as human eyes are located at slightly different positions, different views of the real world are perceived which are then used by the human brain to reconstruct the depth information of the scene. a 3d display takes advantage of this phenomenon, creating two slightly different images of every scene and then presenting them to the individual eyes. with an appropriate disparity and calibration of parameters, a correct 3d perception can be realized. in the field of 3d, one of the important steps is to generate the 3d content itself. for this purpose, special cameras have been designed to generate 3d models directly. for example, a stereoscopic dual-camera uses co-planar configuration of two monoscopic cameras. depth information is computed using binocular disparity. another example is the depth range camera. the examples mentioned above are used for direct generation of the 3d content. on the other hand, there is a tremendous amount of data in 2d which can be converted into 3d. unfortunately, the conventional 2d camera does not provide any information about the depth in the image. thus, developing a method for estimating an image’s depth map close to the real depth map has become of prime interest [2, 3]. once accurately estimated, the depth map can then be used to construct the 3d image using techniques such as depth image based rendering (dibr). authors in [4] used the concept of tensor voting at two different levels for depth estimation in a semi-automatic sparseto-dense structure aware depth estimation method. authors in [5] proposed a collaborative deconvolutional neural network to concomitantly model semantic segmentation and single-view depth estimation for mutual benefits. authors in [6] proposed a two-stage depth estimation technique based on dense feature extractor and a depth map generator. the dense feature extractor extracts multi-scale information from input image while keeping the feature maps dense. these multi-scale features are then fused by the depth map generator using a defined attention mechanism. authors in [7] proposed a method for depth estimation corresponding to every viewpoint of a dense light field. their proposed algorithm computes the disparity for every viewpoint by taking occlusions into consideration. it also preserves the continuity of the depth space and prior knowledge on the depth range is not required. authors in [8] proposed a network for depth estimation combining encoder-decoder architecture with adversarial loss. authors in [9] proposed a depth estimation framework based on deep convolutional neural network. it is based on depth prediction and depth enhancement sub-networks. all the mentioned works are computationally extensive and resource hungry. in this work, we propose a simple idea of depth profiling based on three depth cues, namely linear perspective, motion detection and texture characteristics, to estimate the depth of an image. ii. the proposed depthmap estimation technique in order to generate the depth map, three cues are observed: motion information, linear perspective and texture characteristics. in motion information, the temporal difference is taken between the two consecutive frames and then thresholding is applied. in linear perspective, the vanishing line or the vanishing point [3] is used to find the points that are farthest in the image. corresponding to these, gradient depth values are assigned. texture characteristics are determined and analyzed. in addition, this work further demonstrates the use of corresponding author: imran usman engineering, technology & applied science research vol. 9, no. 4, 2019, 4428-4432 4429 www.etasr.com usman: an efficient depth estimation technique using 3-trait luminance profiling bilateral or gaussian filter for smoothing of the depth map to achieve better results. figure 1 presents the general architecture of the proposed technique in a flow diagram. the details of the proposed technique are presented in the following subsections. reference image current image temporal difference between current and reference image locating vanishing line/ point in the current image moving object border detection defining foreground and background objects by thresholding gradient depth map mapping texture characteristics of the current image merged depth map bilateral smoothing filter depth map dibr technique left view right view anaglyph fig. 1. general architecture of the proposed technique a. motion information the human brain pays more attention to the things that are in motion than to those which are static. so, information in the form of video (objects in motion) is more understandable and clearer than steady images. objects that are far away, or are distant, seem to be static or moving very slowly when we look at them while we are in motion, whereas the objects that are nearer to us move fast when observed from a moving source. this effect is known as motion parallax. things closer to us seem to move rapidly while the objects far away move slowly or are at rest. keeping this fact into consideration, we use the approach of temporal difference to find out objects that are moving or are in a state of rest. by doing so, the objects are assigned to the foreground domain and the background domain in an image by assigning threshold values to the points in the image. the formula for finding the temporal difference is: 1 ( , ) ( , ) c c i j i jρ ρ −∆ = − (1) where c ρ is the current frame pixel at ( , )i j and 1c ρ − is the reference frame pixel at point ( , )i j . after calculating the temporal difference between the frames, the values are compared with the threshold value. the threshold values are computed as: 1, ( , ) 0, c if i j otherwise ∆ > ∂ ∆ =    (2) where c ∂ is the standard deviation given as: 1 1 ( ) 1 m c i im ρ ρ = ∂ = − − ∑ (3) where m is the total number of pixels and ρ is the mean of total pixels in a frame. from the first two equations, moving objects are found. in depth map, the pixels value ranges from 0 to 255, whereby 0 represents the farthest point and 255 shows the nearest point in the image. in the algorithm, the values of temporal difference show which objects are static in the image and which are in motion. if the temporal difference between each pixel of the current frame and the reference frame is less than the standard deviation of the frame, then those pixels are assigned with the value 0. this denotes that these sets of points belong to the background (farthest region). similarly, if the temporal difference generates a value greater than the threshold value, the pixels are assigned with higher gray level values, indicating that these points belong to the foreground (nearest region) of the image. in this cue the frame or image is separated between two parts: the foreground and the background. b. linear perspective objects that are placed far away subtend a very small angle in our eye which the mind interprets as being the farthest in the scene. parallel lines in the image, like the long railway tracks running in the image, provide linear perspective that helps to see objects in three-dimensional view. linear perspective is also a depth cue related to texture gradient and relative size. in every image, when observing closely, we find either the vanishing line or point. the vanishing point is the farthest point in the image where all parallel lines converge. in terms of graphical perspective, it is a point in the image plane that is defined by a line in the space. the vanishing line in an image is defined as a set of vanishing points which are all located in one line. the vanishing line or point represent the farthest point in the image which ultimately gives the depth information. in this work, the vanishing line or point are located empirically using different tools. this algorithm, in general, discusses three possibilities for the occurrence of vanishing point/line. after finding the vanishing point/line, depth gradient values are assigned accordingly. these are discussed below in detail in three different cases. 1) case i: if horizontal line exists this case is applied when only a horizontal vanishing line appears. pixels above the vanishing line are assigned ‘0’ gray level and the pixels below this line are assigned lighter shades engineering, technology & applied science research vol. 9, no. 4, 2019, 4428-4432 4430 www.etasr.com usman: an efficient depth estimation technique using 3-trait luminance profiling of the gray level (1-255), since they move away from the vanishing line. 2) case ii: if a vanishing point appears on the left part of the image the approach used for assigning gradient value in this case is to first divide the image into two portions, left and right respectively. when the vanishing point appears on the left side of the frame, the upper left corner of the image is assigned ‘0’ level of gray. consequently, the upper right part of the frame is assigned ascending values of gray from 0 to 255. the lower left corner of the frame is assigned ascending values of gray level from darker to lighter shades of the gray scale. finally, the lower right part of the frame is assigned ascending values of gray ranging from 0 to 255 diagonally. the following are the four regions in which the image is divided after locating a vanishing point for the assignment of gradient values. • upper left regions: (1 : ,1 : ) 0image i j = (4) where i and j are the coordinates of the vanishing point in the image. • lower left region: (1 : ,1 : ) 0image i j = (5) where i and j are the vanishing point coordinates in the image and m is the total number of rows in the image. • upper right region: 0 (1: , 1: ) 255 image i j n gradient values+ =    (6) where i and j are vanishing point co-ordinates in the image and n is the total number of rows in the image. • lower right region: 0 ( 1: , 1: ) 255 image i m j n gradient values+ + =    (7) 3) case iii: if a vanishing point appears on the right part of the image the upper right corner of the image is assigned ‘0’ value of gray level, and the upper left part of the frame is assigned ascending values of gray from 0 to 255. similarly, the lower right corner of the frame is assigned ascending values of gray level from darker to lighter shades of the gray scale. the left lower part of the frame is assigned ascending values of gray ranging from 0 to 255 diagonally. the details of the four regions are given below. • upper right regions: (1 : , 1: ) 0image i j n+ = (8) where, i and j are the co-ordinates of the vanishing point in the image and n is the total number of columns in the image. • lower right region: 0 ( 1: , : ) 255 image i m j n gradient values+ =    (9) where, i and j are vanishing point coordinates in the image, m is the total number of rows in the image, and n is the total number of columns. • upper left region: 0 (1: , 1:1) 255 image i j gradient values− =    (10) where, i and j are vanishing point coordinates in the image . • lower right region: 0 ( 1: , 1:1) 255 image i m j gradient values+ − =    (11) c. texture characteristics texture characteristics of an image also provide very important clues about the depth of the image. it is a common observation that when any object is placed closer, it gives more details about its color, shape, brightness etc. the objects that are located at some distance, or are located very far away are hard to be determined in terms of their brightness and contrast. their details might get lost, get blended in the background and may even seem to be a part of the background itself. this common observation adds up value to the importance of texture characteristics in finding the nearer and the farthest objects in an image providing us with depth information. the texture characteristics of an image include brightness, luminance, hue and chrominance. it has been discovered that human perception gives priority to brightness, hue, and chrominance [10]. brightness is the characteristic of the visual perception which helps in recognizing whether the object is reflecting or radiating light or not. it is also termed as an attribute that tells us about the luminance of an object. objects present in the foreground usually have greater value of brightness as compared to the objects present in the background. so, greater values of brightness are assigned to the objects in the foreground and lesser values to the objects present in the background of an image. the quantity of light that is absorbed or reflected from the object is described as luminance, which is a property defining color. hue shows the wavelength of the energy band of the light at which it has maximum value. chrominance is the remaining component of the color arrangement when luminance is removed from it. converting images into gray scale gives us the values of pixels demonstrating texture characteristics [11]. converting images into gray scale means removing the rgb contents from the image and assigning each pixel values between 0 to 255 according to its characteristics. d. merging the three cues to generate the depth map the three depth cues (motion detection, linear perspective and texture characteristics) are used to estimate the depth of the engineering, technology & applied science research vol. 9, no. 4, 2019, 4428-4432 4431 www.etasr.com usman: an efficient depth estimation technique using 3-trait luminance profiling image. in order to convert a 2d image into 3d, the image is divided into two parts: background and foreground. while merging the cues for estimating the values in depth map, more values are assigned to the objects present in the foreground of the image, whereas the objects present in the background of the image are assigned smaller weights. this is done because objects present in the foreground of the image receive more attention by human brain than objects in the background. cue merging to generate depth map is divided into the following two cases. 1) case i: foreground for the foreground region, the depth is calculated as: f mo mo lin lin depth depth depthω ω= × + × (12) where, mo depth and lin depth are the depth values extracted in motion information and linear perspective cues respectively, mo ω is the weight assigned to the motion information cue, and lin ω is the weight assigned to the linear perspective cue. as discussed earlier, moving objects get more attention from the human visual system, hence, higher weights are assigned to the depth values calculated in motion information cue i.e. 0.7 mo ω = . the value assigned to linear perspective cue is 0.25 lin ω = . these values are determined and assigned empirically after subjective tests of the human visual system. 2) case ii: background for the background region, the depth is calculated as: lin lin tex texb depth depth depthω ω= × + × (13) where, tex depth and lin depth are the depth values calculated in texture characteristics and linear perspective respectively. linear perspective dominates gradient depth values for generating depth in static objects and background, therefore, a higher weight value is assigned to it and a lower weight value is assigned to texture characteristics. hence, 0.7 lin ω = and 0.25 tex ω = . the final depth map is generated by combining the results of these two cases. f b depth depth depth= + (14) e. smoothing of the depth map in order to reduce noise in the generated depth map while preserving its edges, and to achieve a smooth depth map, bilateral filters [12] are used (other filters, e.g. gaussian, can also be used). another strategy to effectively remove noise is to use a bilateral filter along with directional gaussian kernels which are edge-dependent for the non-hole regions. in addition, considering the similarity of the depth pixels, a trilateral filter can be selectively used in combination according to the type of pixels. iii. results and discussion the proposed technique is implemented in matlab using an intel core i7 3.4ghz processor with 8gb ram. for experimentation, we used the middlebury 2005 dataset [13] which is comprised of a number of different images having a variety of depth perspectives. these images also contain the corresponding stereo images and the created anaglyph images. the anaglyph images are created by either using the stereo images, or by using the center image and the associated depth map. figure 2 presents some of the images from the middlebury dataset and their associated depth maps. these random images show daily life objects with different depth perspectives. the images are rectified and radial distortion has been removed. the depth maps are created using a focal length of 3740 pixels, and a baseline of 160mm, while the intensity and disparity values are kept at 60. more details on other parameter settings can be found in [13]. (a) i (b) i (a) ii (b) ii (a) iii (b) iii (a) iv (b) iv fig. 2. sample images from the middlebury dataset [13]. (a) i-iv are the original images, and (b) i-iv are the corresponding depth maps. table i presents the performance comparison of the proposed technique and the depth maps from the middlebury data set for art, books, computer, dolls, and drumsticks images. for comparison, we assume the depth maps from the middlebury data set as the standard depth maps corresponding engineering, technology & applied science research vol. 9, no. 4, 2019, 4428-4432 4432 www.etasr.com usman: an efficient depth estimation technique using 3-trait luminance profiling to the scene and compare them with the luminance profiled depth maps generated through the proposed technique. we used peak signal to noise ratio (psnr) and structural similarity index measure (ssim) as comparison metrics between the estimated depth map and the original depth map. it can be observed from table i that the proposed technique yields an acceptable level of similarity compared with the standard depth maps for all of the selected images. table i. performance comparison of the proposed technique and the depth maps from middlebury dataset depth map image name psnr ssim art 28.970 0.689 books 28.516 0.651 computer 29.387 0.713 dolls 29.146 0.704 drumsticks 28.632 0.701 figure 3 shows the average performance comparison of the proposed technique and the standard depth maps using a number of images from the middlebury data set. it is to be noted that for the purposes of comparison and display, the values of psnr are scaled down using a dividing factor of 30 in order to bring them close to the values of ssim. once again, it can be observed that the proposed technique produces depth maps that are in acceptable range of similarity and luminance profiling as compared to the original depth maps. fig. 3. average performance comparison of the proposed and standard technique on depth maps iv. conclusion this work presents a simple depth estimation method which is computationally fast and resource efficient. the proposed technique utilizes linear perspective, motion detection and texture characteristics to estimate the luminance profiling of an image scene. in motion information, the temporal difference is taken between two consecutive frames and then thresholding is applied. in linear perspective, the vanishing line or the vanishing point are used to find the farthest points in the image. corresponding to these, gradient depth values are assigned. texture characteristics are determined and analyzed in order to estimate the depth map. finally, bilateral filters are used to smooth the depth map. the experimental results show that the depth maps generated through the proposed technique are of acceptable quality and can be used in real world applications. acknowledgment the author acknowledges saudi electronic university’s help and financial support. references [1] j. son, b. javidi, s. yano, k. choi, “recent developments in 3-d imaging technologies”, journal of display technology, vol. 6, no. 10, pp. 394-403, 2010 [2] l. zhang, w. j. tam, “stereoscopic image generation based on depth images for 3d tv”, ieee transactions on broadcasting, vol. 51, no. 2, pp. 191-199, 2005 [3] a. almansa, a. desolneux, s. vamech, “vanishing point detection without any a priori information”, ieee transactions on pattern analysis and machine intelligence, vol. 25, no. 4, pp. 502-507, 2003 [4] b. wang, j. zou, y. li, k. ju, h. xiong, y. f. zheng, “sparse-to-dense depth estimation in videos via high-dimensional tensor voting”, ieee transactions on circuits and systems for video technology, vol. 29, no. 1, pp. 68-79, 2019 [5] j. liu, y. wang, y. li, j. fu, j. li, h. lu, “collaborative deconvolutional neural networks for joint depth estimation and semantic segmentation”, ieee transactions on neural networks and learning systems, vol. 29, no. 11, pp. 5655-5666, 2018 [6] z. hao, y. li, s. you, f. lu, “detail preserving depth estimation from a single image using attention guided networks”, 2018 international conference on 3d vision (3dv), verona, italy, september 5-8, 2018 [7] x. jiang, m. l. pendu, c. guillemot, “depth estimation with occlusion handling from a sparse set of light field views”, 25th ieee international conference on image processing, athens, greece, october 7-10, 2018 [8] m. carvalho, b. le saux, p. trouve-peloux, a. almansa, f. champagnat, “on regression losses for deep depth estimation”, 25th ieee international conference on image processing, athens, greece, october 7-10, 2018 [9] x. duan, x. ye, y. li, h. li, “high quality depth estimation from monocular images based on depth prediction and enhancement subnetworks”, ieee international conference on multimedia and expo, san diego, usa, july 23-27, 2018 [10] k. ghosh, s. k. pal, “some insights into brightness perception of images in the light of a new computational model of figure–ground segregation”, ieee transactions on systems, man, and cybernetics part a: systems and humans, vol. 40, no. 4, pp. 758-766, 2010 [11] m. song, d. tao, c. chen, x. li, c. w. chen, “color to gray: visual cue preservation”, ieee transactions on pattern analysis and machine intelligence, vol. 32, no. 9, pp. 1537-1552, 2010 [12] a. v. le, s. w. jung, c. s. won, “directional joint bilateral filter for depth images”, sensors, vol. 14, no. 7, pp. 11362-11378, 2014 [13] http://vision.middlebury.edu/stereo/data/scenes2005/[accessed: 21-apr2019] microsoft word 10-3343_s_etasr_v10_n2_pp5396-5401 engineering, technology & applied science research vol. 10, no. 2, 2020, 5396-5401 5396 www.etasr.com lam et al.: simulation models for three-phase grid-connected pv inverters enabling current … simulation models for three-phase grid-connected pv inverters enabling current limitation under unbalanced faults le hong lam faculty of electrical engineering the university of danang—university of science and technology da nang, vietnam lhlam@dut.udn.vn tran dai hoang phuc faculty of electrical engineering the university of danang—university of science and technology da nang, vietnam 105150107@sv.dut.edu.vn nguyen huu hieu faculty of electrical engineering the university of danang—university of science and technology da nang, vietnam nhhieu@dut.udn.vn abstract—normally unbalanced grid voltage dips may lead to unbalanced non-sinusoidal current injections, dc-link voltage oscillations, and active and/or reactive power oscillations with twice the grid fundamental frequency in three-phase gridconnected photovoltaic (pv) systems. double grid frequency oscillations at the dc-link of the conventional two-stage pv inverters can further deteriorate the dc-link capacitor, which is one of the most important limiting components in the system. proper control of these converters may efficiently address this problem. in such solutions, current reference calculation (crc) is one of the most important issues that should be coped with the reliable operation of grid-connected converters under unbalanced grid faults. therefore, this paper proposes and simulates crc methods and presents the results in order to improve the quality of the grid-connected pv system under unbalanced grid voltage fault. keywords–photovoltaic (pv) systems; unbalance voltage; two– stage converters; power oscillation; dc–link voltage oscillation i. introduction with the fast increase of grid-connected pv generation [1, 2], pv systems should contribute to the grid stability by providing ancillary services, beyond the basic power delivery. the new grid requirements demand the grid-connected pv systems, singleor three-phase, to have the capability to operate in power factors other than unity. also, based on the recently revised grid codes, pv inverters are preferred to stay connected during grid voltage faults [3-6]. when a fault happens, the converter has to detect the incident and respond quickly to the disturbance to mitigate the adverse effects on the inverter, the equipment connected to the grid, and the upstream system. indeed, the revised grid codes require the pv systems to inject a certain amount of reactive power in case of low voltage fault [7, 8]. these issues are now gaining more consideration in pv systems, as the power capacity of an individual pv system is also increasing. detection of voltage sags, current limitation, current reference calculation [9], active and reactive power oscillation, and dc-link voltage oscillation are such important issues. besides, they are the key issues to the proper operation of grid-connected pv converters under faults. among them, crc plays the most important role to satisfy the grid requirements, especially under unbalanced grid faults. in current researched methods, d-q methodology is commonly implemented under grid voltage faults [3-6, 10] although it is quite complex since it requires building blocks to convert the signals and calculate the frequency as the phase lock loop (pll), dual second order generalized integrator based frequency-locked loop (dsogi–fll). the aforementioned active power oscillation can have a negative impact on the reliable operation of the grid-connected pv converters. in two-stage pv converters, where a dc-dc converter operates as maximum power point tracking (mppt) [11], it is common that a pi controller determines the active power reference. thus, in case that the injected active power starts fluctuating, the pi controller cannot follow its sinusoidal variations because the pv power injected to the dc-link is constant. as a result, the dc-link voltage will fluctuate with the same frequency of the injected active power [12]. notably, due to the high failure rates of the electrolytic capacitors of the two-stage pv converters, the system reliability is challenged. this is worsened by dc-link voltage ripples. in this paper there are two main contributions: (i) dc link ripples during unbalanced faults are reduced with proper control of dc-dc converter and (ii) the impact of the pv systems on the distribution grid is analyzed and a control strategy is proposed for the pv using calculation methods referenced in the static αβ reference frame to reduce the complexity of the control structure and more efficient instead of using moving d-q reference frames. moreover, the deprecating power of the main grid can be made by changing the power factor of wind generators [13-15]. this control strategy may offer a new solution to solve the voltage sag issue on a power system due to the pv plants connected to the grid by streaming their reactive power to the grid to enhance its power quality. ii. system operation this section analyzes the inverter operation under normal and abnormal conditions for a three-wire three-phase pv system. the two-stage three-phase system shown in figure 1 corresponding author: le hong lam engineering, technology & applied science research vol. 10, no. 2, 2020, 5396-5401 5397 www.etasr.com lam et al.: simulation models for three-phase grid-connected pv inverters enabling current … includes a boost converter and a full-bridge inverter interconnected through the dc-link capacitor. pv array boost converter v dc 2 v dc 2 c c dc dc s4 s3 s6 s2 s5s1 a c b lcl filter va v b vc fig. 1. two-stage three-phase grid-connected pv system. the formulation is performed in the stationary reference frame (srf). the conversion from the three-phase system into the srf is as: ��� = ������ = �� 1 − �� − ��0 √ � − √ � � � ������� (1) where ��, �� are the voltages in the srf from ��, ��, ��. the apparent power s is written as: � = �. �∗ = � + �� (2) since under normal conditions the grid voltages and loads are balanced, there will not be any oscillatory components in the active and reactive components of the power and the injected current is completely sinusoidal. however, under unbalanced conditions, the ns components will appear in both current and voltage vectors. thus, the apparent power is rewritten as: � = ���. ���∗ = ���! + ���" #. ���! + ���" #∗ = ���! . ���! ∗ +���! . ���" ∗ + ���" .���! ∗ + ���" . ���" ∗ (3) in which ���! , ���" are derived from: ���! = �� $1 − %% 1& ��� (4) ���" = �� $1 %−% 1& ��� (5) where % = '"()/� is a 90°-lagging phase-shifting operator applied to the time domain [16]. similarly, ���! , ���" are achieved following (4) and (5): ���! = �� $1 − %% 1& ��� (6) ���" = �� $1 %−% 1& ��� (7) in (3), there are four terms in the apparent power formulation. ���! . ���! ∗ = ��! + ���!#. ��! + ���!#∗ = ��!��! + ��!��! +� ��!��! − ��!��!# = �� + ��� (8) ���! . ���" ∗ = ��! + ���!#. ��" + ���"#∗ = ��!��" + ��!��" +� ��!��" − ��!��"# = �� + ��� (9) ���" . ���! ∗ = ��" + ���"#. ��! + ���!#∗ = ��"��! + ��"��! +� ��"��! − ��"��!# = � + �� (10) ���" . ���" ∗ = ��" + ���"#. ��" + ���"#∗ = ��"��" + ��"��" +� ��"��" − ��"��"# = �+ + ��+ (11) the constant and oscillating parts of the total active and reactive power are written as: � = �, + � (12) �, = �� + �+ = ��!��! + ��!��! + ��"��" + ��"��" (13) �= �� + � = ��!��" + ��!��" + ��"��! + ��"��! (14) � = �, + � (15) �, = �� + �+ = ��!��! − ��!��! + ��"��" − ��"��" (16) �= �� + � = ��!��" − ��!��" + ��"��! − ��"��! (17) where � and � are the total active and reactive power, and �,, �,, �-, �are the constant and oscillating parts in the active and reactive power. under balanced voltage sag faults, there is no ns in the voltages and currents, thus there are no oscillatory components in the active and reactive power. however, during unbalanced faults, the ns components appear in the voltages and currents. from (12) and (15), it is concluded that the active and reactive power have a constant part named �0 and �0. also, there are two oscillating parts in the active and reactive power, denoted as �. and �.. fundamentally, in the pv power systems, all the active power generated by the pv panels is delivered to the dc-link. this active power is continuously processed by the inverter and injected into the grid. if the active power generated by the inverter is less than the power injected to the dc link from the pv source, the dc link voltage will increase. proper control is needed to synchronize the power flow from the pv source to the grid by regulating the dc link voltage. accordingly, in the case that the injected active power has double grid frequency oscillations, the dc-link voltage will inevitably oscillate with the same frequency. double grid frequency oscillations of the dc-link voltage have a negative impact on the life cycle of the capacitive dc-link. iii. proposed control strategy in this section, a new control strategy to overcome the unbalance grid voltage based on the current reference generation (crg) is presented and a current limitation scheme is used to warranty the overcurrent issue. a. current reference generation in order to eliminate active power oscillations, (14) has to be zero. in (14) and (17), �, and �, are equal to the average active power ( �/01 which is the output of the dc-link regulator) and reactive power (�/01 which is calculated during grid faults) references. these values are continuously calculated by the control algorithm. the control goal is to eliminate the oscillatory components from the active power, while allowing reactive power to oscillate with the double grid engineering, technology & applied science research vol. 10, no. 2, 2020, 5396-5401 5398 www.etasr.com lam et al.: simulation models for three-phase grid-connected pv inverters enabling current … frequency. hence, �is considered equal to 2 ��!��" − ��!��"#. accordingly, (17) is rewritten as: �= ��!��" − ��!��" + ��"��! − ��"��! = 2 ��!��" − ��!��"# (18) ��!��" − ��!��" − ��"��! + ��"��! = 0 (19) furthermore, (13), (14), (16), (19) are written as: 34 44 5 ��! ��! ��" ��"��" ��" ��! ��!��! − ��! ��" − ��"−��" ��" ��! − ��! 67 77 8 344 45��!��!��"��"677 78 = 9�/010�/010 : (20) a formulation for generating sinusoidal currents to deliver a certain amount of active and reactive power [3, 17, 18] is obtained as: ��! = ;<=>?">@ �/01 − ;<a=>?!>@ �/01 (21) ��" = − ;<b>?">@ �/01 − ;<ab>?!>@ �/01 (22) ��! = ;c=>?">@ �/01 − ;ca=>?!>@ �/01 (23) ��" = − ;cb>?">@ �/01 − ;cab>?!>@ �/01 (24) ���d��d� = �0 − 11 0� ������ (25) ef = ��!� + ��!� (26) eg = ��"� + ��"� (27) where ��d, ��d are the orthogonal voltages of the srf voltage vectors. the srf currents are driven from the average value of the active and reactive power. these references determine the peak-peak value of the oscillations on the reactive power. accordingly, a general formulation is obtained as: ��h = ;<=";<bi;<=j!;c=jk!i;<bj!;cbjk �/01 (28) ��h = ;c=";cbi;<=j!;c=jk!i;<bj!;cbjk �/01 (29) ��l = − ;<a= !;<abi;<a= j!;ca= jk!i;<ab j!;cab jk �/01 (30) ��l = − ;ca= !;cabi;<a= j!;ca= jk!i;<ab j!;cab jk �/01 (31) in which, ��h, ��h, ��l, ��l are the active and reactive currents in the srf. b. current limitation scheme in order to prevent the overcurrent failure, a new efficient current limiting method is proposed. the rated power of the converter must be updated once a voltage sag is detected. this is called new nominal power (nnp). normally, under voltage sag faults, the nnp value is less than the nominal power of the converter, which depends on the voltage sag depth. therefore, nnp is achieved as: mm� = n>?"n>@>opqr � (32) where � is the apparent power or the nominal power of the power converter, e��s0 is the base voltage, which is equal to the root-mean-square (rms) value of the line-line grid voltage. on the other hand, according to the voltage sag depth, the reactive power can be calculated as: t�/01 = 0 efu > 0.9�/01 = � × 1.5 × 0.9 − efu# 0.2 < efu < 0.9�/01 = 1.05 × � efu < 0.2 (33) with efu being calculated as: efu = �;<j!;cj>opqr (34) given the nnp and reactive power of q, the maximum allowed active power �[�\ for the inverter to inject to the grid while avoiding overcurrent can be achieved as: �[�\ = nmm�� − �� (35) for operation of the converter under very deep voltage sags, nnp will have a low value, since nef − neg becomes small. therefore, under a deep voltage sag, the condition is: if � > mm� → � = mm� and �[�\ = 0 (36) vpu pmax p* vpu<0.9 no yes fault signal =1 pmax < p* enable signal = 0 compare signal = 1 no yes calculate pmax, nnp, qref pmax non mppt mppt enable signal = 1 fig. 2. flowchart of the proposed control algorithm the dc-dc converter operates as the mppt–p&o, the dc-dc converter should switch to the non-mppt mode in case a grid fault occurred and the inverter could not inject the maximum pv power. the flowchart in figure 2 summarizes and clarifies the control system. if efu < 0.9 the voltage sag detection block will generate a fault signal activating the mm�, �[�\, �/01 calculator block. then, for a comparison between �[�\ and �∗, a comparator signal will be generated there is an and block, in which, if the comparator signal and engineering, technology & applied science research vol. 10, no. 2, 2020, 5396-5401 5399 www.etasr.com lam et al.: simulation models for three-phase grid-connected pv inverters enabling current … fault signal are equal to 1, the dc-dc converter switches to the non-mppt. in this case, the fault signal is 1, while the comparator signal remains zero. mppt may continue working under abnormal operation when the fault exists in the grid. iv. control structure design a control structure was implemented in matlab/simulink [19]. it should be noted that the proposed strategy control is mainly in voltage source inverter (vsi) and current controller. since, these modules play an important role in creating the reference current to balance voltage after faults. a. voltage source inverter in connected grid mode, the vsi controller [20] power flow comes from the pv system to respond to the requirements of the grid, and control the voltage on the capacitor abc of dc– link. active power is required from the grid reference given �/01 from ebc voltage regulator. meanwhile, reactive power �/01 is calculated according to the current limit to stabilize the voltage on the ac bus. figure 3 shows the schematic diagram of the ebc voltage control loop, the quantity to be controlled because it is proportional to the energy stored in the capacitor. dc voltage on the capacitor is stable thanks to the energy balance through (ignoring losses in vsi): �h> = �bc + �d (37) where �h> is the power from the pv, �bc is the power on the capacitor, and �d is the power inject to the grid. vdc vdc_ref (.) 2 (.) 2 + kv(s) + ppv p ref fig. 3. diagram control eef voltage when the voltage on the dc capacitor is stable, the value of the �bc is considered as zero: �h> = �d (38) equation (38) indicates that the controlling �d will be controlled through the �d to achieve the desired value. then, the referenced currents g�/01 and g�/01 are calculated through the reference power value from (39) and (40) and then they are taken to the current control. ��/01 = ;<=";<bi;<=j!;c=jk!i;<bj!;cbjk �/01 − ;<a= !;<abi;<a= j!;ca= jk!i;<ab j!;cab jk �/01 (39) ��/01 = ;c=";cbi;<=j!;c=jk!i;<bj!;cbjk �/01 − ;ca= !;cabi;<a= j!;ca= jk!i;<ab j!;cab jk �/01 (40) fig. 4. control structure of vsi [9] (the non mppt mode is ignored) b. current controller the current controller in figure 5 (current separator) has the aim to control and coordinate the active and reactive power. its components involve ghi'j and gki'j to control active power and reactive power. after calculating the index modulations lh , lk from the current controller, a block converts from the srf h − k to the natural reference frame (nrf) mnf. a clark transformation matrix will be used to convert lh , lk into lmnf index modulation. the control signals are included in the lmnf model of the vsi model to control power and achieve the desired value. the current control using with pi formulas are: eo� = e� + g�/01 − g�# iph + qrs k (41) eo� = e� + g�/01 − g�# iph + qrs k (42) + ++ + pi pi × ÷ × ÷ v v v /2 m m i α i β i α α β α β dc ref i β ref fig. 5. current controller v. simulation results in order to verify the proposed control strategy, a simple pv system connected to the pcc is used as shown in figure 6. in this simulation, a boost converter is connected to the pv and, as mentioned above, it is driven to track mpp. the output of the vsi is connected to the secondary side of distribution transformers (400v). the system is built on matlab/simulink [19]. the main parameters of the system are presented in table i. here, the simulation scenario is that a fault occurs at t=0.515s, thus voltages on phase a and phase b fall 50%. the grid parameters of the simulation are shown in figure 7 including the voltage of three phases without the engineering, technology & applied science research vol. 10, no. 2, 2020, 5396-5401 5400 www.etasr.com lam et al.: simulation models for three-phase grid-connected pv inverters enabling current … proposed control strategy (figure 7(a)), the injected current when applying the proposed control strategy to fix the unbalance voltage (figure 7(b)), and the three phase voltage with the proposed control strategy (figure 7(c)). fig. 6. model simulation table i. simulation parameters description simulation parameters symbol value maximum power of pv systems �f; 100kwp grid line-line voltage (rms) ed 381v dc–link voltage es� 500v resistance of the ac filter of the vsi t1 0.75mω inductance of the ac filter of the vsi u1 100µh capacitor of the dc–link as� 0.2f grid frequency j 50hz (a) (b) (c) fig. 7. grid parameters: a) pcc voltage before injecting reference current, b) pv system current injected to the grid under fault occurrence, c) pcc voltage after injecting reference current when fault occurred, efu dropped to 0.69, and the system switched to operate under fault mode (figure 4) since efu z 0.9 at the time of the error. e� and e� were halved, the current of phase a and phase b increased but phase c remained stable. after current reference was injected at t=0.515s, the voltage at the connection point (point of common couplingpcc) restored the three-phase loads to the rated value as shown in figure 7(c). moreover, the proposed control strategy guarantees that the oscillation of the dc-link voltage is acceptable. figure 8 shows the output data of the system including the active power and reactive power in figure 8(a) and 8(b), the active power reference of the inverter in figure 8(c), and the oscillation of the voltage of dc-link in figure 8(d). because the system is operating in sheltered mppt p&o algorithm [11], the output active power of the system remains at the maximum value shown in figure 8(a). when unbalanced voltage sag was detected, the system responded and corrected the error immediately releasing reactive power to the grid in order to fix unbalances (figure 8(b)). (a) (b) (c) (d) fig. 8. the power output parameters of the system: a) active power injected to the grid, b) reactive power injected to the grid, c) active power reference, d) voltage of dc – link at t=0.515s, active power reference is required to be injected to the grid depending on the capacity of pv controlled under p&o algorithm. as shown in figure 8(c), the dc–link voltage started to oscillate with the frequency of active power but maintained stability in 500v (figure 8(d)). under fault engineering, technology & applied science research vol. 10, no. 2, 2020, 5396-5401 5401 www.etasr.com lam et al.: simulation models for three-phase grid-connected pv inverters enabling current … conditions, the pv systems were injecting 100kwp active power to the grid and reactive power is 59.3kvar. vi. conclusion the simulation results of the proposed strategy control of the current reference generation show that the proposed control strategy has been successful in detecting voltage sags and in properly responding to fault conditions of a 100kwp gridconnected pv system. the proposed control strategy removes the active power and voltage oscillations in the dc-link. therefore, the voltage at the pcc is restored to the nominal value ensuring power quality. acknowledgment this work is funded by the ministry of education and training, vietnam, code: b2019-dna-13. references [1] j. hossain, a. mahmud, renewable energy integration: challenges and solutions, springer science & business media, 2014 [2] m. a. aman, s. ahmad, b. noor, f. w. karam, “mitigating the adverse impact of un-deterministic distributed generation on a distribution system considering voltage profile”, engineering, technology & applied science research, vol. 8, no. 3, pp. 2998--3003, 2018 [3] a. junyent-ferre, o. gomis-bellmunt, t. c. green, d. e. soto-sanchez, “current control reference calculation issues for the operation of renewable source grid interface vscs under unbalanced voltage sags”, ieee transactions on power electronics, vol. 26, no. 12, pp. 37443753, 2011 [4] p. a. n. garcia, j. l. r. pereira, s. carneiro, jr., v. m. da costa, n. martins, “three-phase power flow calculations using the current injection”, ieee transactions on power systems, vol. 15, no. 2, pp. 508-514, 2000 [5] t. khatib, w. elmenreich, modeling of photovoltaic systems using matlab: simplified green codes, wiley, 2016 [6] a. e. alvarez, a. junyent-ferre, o. gomis-bellmunt, “active and reactive power control of grid connected distributed generation systems”, in: modeling and control of sustainable power systems. green energy and technology, pp. 47-81, springer, 2012 [7] a. von jouanne, b. banerjee, “assessment of voltage unbalance”, ieee transactions on power delivery, vol. 16, no. 4, pp. 782-790, 2001 [8] f. shahnia, a. ghosh, g. ledwich, f. zare, “voltage unbalance reduction in low voltage distribution networks with rooftop pvs”, 20th australasian universities power engineering conference, christchurch, new zealand, december 5-8, 2010 [9] e. afshari, g. r. moradi, r. rahimi, b. farhangi, y. yang, f. blaabjerg, s. farhangi, “control strategy for three-phase grid-connected pv inverters enabling current limitation under unbalanced faults”, ieee transactions on industrial electronics, vol. 64, no. 11, pp. 8908-8918, 2017 [10] z. yan, y. xue, x. p. zhang, “pi parameters determination in dq decoupling control of vsc terminals”, 13th iet international conference on ac and dc power transmission, manchester, uk, february 14-16, 2017 [11] n v. tan, d. m. quan, t. a. tuan, p. v. kien, l. h. lam, h. h. long, “so sanh cac thuat toan bat diem cong suat cuc dai bang phuơng phap mo phong va thuc nghiem”, tap chi khoa hoc va cong nghe, vol. 2, no. 11, pp. 64-68, 2018 (in vietnamese) [12] h. wang, f. blaabjerg, “reliability of capacitors for dc-link applications in power electronic converters: an overview”, ieee transactions on industry applications, vol. 50, no. 5, pp. 3569-3578, 2014 [13] n. h. hieu, l. h. lam, “using double fed induction generator to enhance voltage stability and solving economic issue”, ieee international conference on sustainable energy technologies, hanoi, vietnam, november 14-16, 2016 [14] n. h. hieu, l. h. lam, c. t. luu, t. q. tuan, “effects of dfig wind power generation on vietnam power system operation”, ieee eindhoven powertech, eindhoven, netherlands, june 29-july 2, 2015 [15] a. b. lajimi, s. a. gholamian, m. shahabi, “modeling and control of a dfig-based wind turbine during a grid voltage drop”, engineering, technology & applied science research, vol. 1, no. 5, pp. 121-125, 2011 [16] p. rodriguez, r. teodorescu, i. candela, a. v. timbus, m. liserre, f. blaabjerg, “new positive-sequence voltage detector for grid synchronization of power converters under faulty grid conditions”, 37th ieee power electronics specialists conference, jeju, south korea, june 18-22, 2006 [17] r. teodorescu, m. liserre, p. rodriguez, grid converters for photovoltaic and wind power systems, wiley, 2011 [18] s. chattopadhyay, m. mitra, s. sengupta, “clarke and park transform”, in: electric power quality. power systems, springer, 2011 [19] mathworks, “simulation and model-dased design”, available at: https://www.mathworks.com/products/simulink.html. [20] a yazdani, r iravani, voltage-sourced converters in power systems, wiley, 2010 microsoft word etasr-khromov.doc etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 320-324 320 www.etasr.com khromov and kawalla: simulation of a steel wire straightening taking into account … simulation of a steel wire straightening taking into account nonlinear hardening of material ilya khromov dept. of technical mechanics and science of machines sevastopol national technical university sevastopol, ukraine i.v.khromov@sevntu.com.ua rudolf kawalla institute of metal forming tu bergakademie freiberg freiberg, germany rudolf.kawalla@imf.tu-freiberg.de abstract—straightening is used to ensure the straightness of a rod workpiece as well as to redistribute or reduce the residual stresses in a finished product. the accuracy of modeling the operation of this kind plays an important role when manufacturing high quality ropes and cables of a small diameter. the physical model of alternating wire bending in a straightener has been considered in the paper. computer methodology has been developed to calculate deflected mode and internal bending moment in a cross section of a wire at the different stages of deformation, which allowed taking into account nonlinear hardening of the material. keywordselastic-plastic deformation; deflected mode; nonlinear hardening; straightener i. introduction straightness is one of the most vital quality factors when manufacturing metal ropes and cables of a small diameter. it is evaluated by the residual curvature diameter of the loose length of a finished product. the value of the parameter mentioned depends significantly on the initial curvature of a wire used in cable/rope twisting. with the view of curvature reduction and technological stress redistribution different types of machining are applied in the process of production, straightening relates to the operations of this kind. despite the fact that straightening seems to be a rather simple process in terms of mechanical implementation, it is difficult enough to find thorough analysis of the process simulation related to steel wire rope production. the earliest works on solving technological problems and designing the forming process of twisted products were focused on calculations in the absence of computers, so they were based on a very rough simplification. for example, dorodnykh [1] and tulenkov [2] used a non-hardening model of material when modeling straightening process. guericke and et al. [3, 4] proposed the use of a linear hardening model to describe the behavior of a wire being deformed by rollers of a straightener, which refined significantly the numerical calculations. lee et al. [5] applied fem to simulate the straightening of metal cord using the software package abacus. the same approach was employed by k. k. adewole and s. j. bull [6] when studying alternative bending of a flat wire. very often there is no possibility to apply existent program packages for technological problem solving and a research team has to develop their own specialized procedures for finding the optimal deformation parameters when designing technological processes for steel rope manufacturing. however, in such cases, technical articles are usually limited to a brief description of the models used and focus more on explaining the interface features of the developed software [7]. in this paper, the authors tried to describe in more detail the main stages of developed computer methods for calculating the deflected mode of a steel wire while straightening and taking into account its real stress-strain diagram. ii. operation purpose and physical model of the process straightening is a multiple alternating elastic-plastic bending of a rod workpiece on the rolls of a straightener, as shown in figure 1. this kind of machining is used to ensure the straightness of a rod workpiece as well as to redistribute or reduce the residual stresses in a finished product. theoretical analysis and calculation of setup modes for a straightener (i.e. center-to-center distances horizontally ha and vertically va ) are based on the physical model of the process, its graphical scheme shown in figure 2 as a multistep diagram )(km x . while being straightened, the rod is subjected to pure bending deformation. however, alternating deformation behavior leads to a considerable complication of the mathematical model of this process. intermediate positions of random cross section of a rod workpiece moving along the straightener are marked with points 1,2,…,7 in figure 1a. respective deflected modes of the cross section are shown in figure 2b as points 1-7. separate stages of elastic-plastic deformation (lines 02, 23, 34, 45) appear to be described by different nonlinear integral functions as ),( 1, kkm iix  , where i is the number of the stage of bending deformation. at the two final stages (lines 56 and 67 in figure 2b) the diagram has linear character ),( 55, kkm x . in this case, the physical model allows to set down an implicit equation for defining unknown values of the workpiece research has been carried out under financial support by daad. etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 320-324 321 www.etasr.com khromov and kawalla: simulation of a steel wire straightening taking into account … curvature at the four intermediate stages of bending 5432 ,,, kkkk . it might be given on condition that there is no residual curvature of a finished product (straightness condition) 0),(),,,,( 55,5432057  kkmkkkkkmm x . (1) missed relations between parameters 5432 ,,, kkkk can be ascertained from kinematic and technological problem specification. due to the implicit form of the equation (1) mathematical modeling of the process comes to step-by-step numerical computation and construction of the curve under figure 2b for the variable set of required parameters 5432 ,,, kkkk . the algorithm of iterative procedure should ensure the fulfillment of (1) as the final result. thus the main problem of the straightening process design is to guarantee that there is no internal bending moment and residual curvature in the finished product through several stages of elastic-plastic alternating bending of a rod workpiece. a) b) fig. 1. a) kinematic scheme of the process and b) appearance of the device for straightening a long-length product fig. 2. a) loading condition and b) deformation diagram of a wire in the course of straightening iii. experimental stress-strain diagram of a steel wire, approximation function stress-strain and shear diagrams have fundamental significance not only for obtaining initial information relating to the material behavior under simple types of loading, they also form the basis for constructing mathematical models for deformable body of any configuration under different types of complex loading. a real stress-strain diagram of a wire of 1,1 mm in diameter made of steel c60 with ultimate strength of 1750u  mpa has been applied for further simulation. it was obtained in the set of tests conducted at the institute of metal forming, tu bergakademie freiberg. mechanical properties for steel wire samples are shown in a table 1. table i. mech anical properties of wire m ad e of steel c60 young’s modulus, mpa tensile strength, mpa elongation, % yield strength, mpa 190000 1750 1,5 1020 according to the analysis made in [8], it is reasonable to describe the experimental stress-strain diagram of a steel wire using the following combined analytical function             )]1(1[,,)( )1( yy y   abeif , (2) where y , y yield stress and strain, a, b invariables determined by three base points of the experimental diagram (for this curve 312,0a , 821,0b ). in this case approximation function almost completely matches the experimental points of the )( diagram (figure 3). fig. 3. experimental stress-strain diagram and approximation function etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 320-324 322 www.etasr.com khromov and kawalla: simulation of a steel wire straightening taking into account … iv. methods of computer simulation of a wire straightening process in accordance with the classification provided in [9] modeling of the straightening process comes to solution of the direct problem of technological mechanics of a rod. in this case, having known the equations for the trajectory of deformation of the longitudinal axis of a rod it is necessary to determine the stress state and internal forces under the arbitrary value of a certain process parameter (e.g. curvature of a rod) the final stress state and rod form i.e. the technical parameters of the finished product are assumed to depend on the history of its deformation in all operations of technological process. in this connection, the method of mathematical simulation should include stepwise calculation of deflected mode changes of the rod material taking into consideration its non-linear properties. when modeling plane sections hypothesis is applied [10], as well as the following hypotheses and theories are accounted:  discrete model is used when cross section of a rod is divided into finite number of elementary areas. stresses at every point of the area are supposed to be constant. therefore, one part of the cross section might be at the elastic stage while the other is at the plastic one;  material behavior under pure tension is described by piecewise function (2);  at the plastic stage, the theory of plastic flow is used for calculating stresses. due to this theory, the final stresses depend on the trajectory of deformation while equations describing plastic deformation are differential relations that are nonintegrable analytically [11];  as criterion for plasticity, the condition of tangential stress intensity (von mises condition) is applied. every stage of deformation is divided into a number of steps with curvature increment k . the algorithm supports multiple step-by-step calculation of the stresses on the basis of the unified procedure elaborated previously by khromov [12]. having calculated the stress value the internal bending moment can be defined according to the integral formula   f x dfym  . (3) the main difference of the proposed procedure for stress calculation at the plastic deformation stage is the fact that the nonlinear hardening of the material has been taken into account when solving plastic flow equations. in this case hardening modulus and hardening coefficient depend on accumulated intensity of plastic deformation. considering (2) at the optional loading stage, they are determined as follows:                        1 y y )ln(, ,       aabeeif d d e , (4)                          1 y y )ln(, 1 , )(      aabif e e . (5) the flowchart of the general algorithm is shown in figure 4. it includes several one-type cycles executed in consecutive order, their number being equal to the number of alternating bending stages. data files of internal bending moment, curvature and normal stresses are formed in the course of calculation. after program finishing, the files can be read and processed using built-in functions of standard mathematical program packages. fig. 4. flowchart of the general algorithm for solving the problem of alternating bending. etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 320-324 323 www.etasr.com khromov and kawalla: simulation of a steel wire straightening taking into account … v. results and disscusion figures 5 and 6 represent an example of simulating the fourfold straightening process for a steel wire of 1,1 mm in diameter. calculations and data file forming have been carried out for three values of initial curvature of a wire ( 5,20 k m-1, 50 k m-1, 100 k m-1) using the procedure developed in microsoft visual basic. the curvature value at the end of a single stage of straightening is unknown. it should be determined by means of the condition that internal bending moment xm and residual wire curvature at the end of the process would be equal to zero under optional value of the initial curvature 0k . in this example, the deformation value for all three initial curvatures remained the same at the separate step of bending. the data files with the calculated arrays of normal stress, bending moment and curvature were processed using the mathematical package mathcad. as it is shown in figure 5, in this numerical calculation the function )(km x comes to the coordinate origin with the accuracy sufficient for practical calculations when initial curvature 5,20 k m-1, 50 k m-1. for 100 k m -1 the final value of the moment is not zero. in this case, it is necessary either to increase the value of the bending deformation at the first stage, or add one more step of bending to ensure the output condition 0xm . fig. 5. dependence )(km x calculated for three values of initial curvature figure 6 represents diagrams for ),( yx stress distribution along the cross section of a wire for three values of initial curvature. the left part of it shows initial stresses when curvilinear wire is straightened at the entrance to the straightener. stress diagram is linear, outer fiber stresses reach maximum values. after straightening normal stresses are redistributed, stress diagram becomes complex. however, initial maximum stresses are reduced 2-3 times. even for the case of 100 k m -1 residual stresses do not exceed 300 mpa and this value could be decreased more by adding one more stage of bending. a) b) fig. 6. graphical stress analysis of a wire when a) entering and when b) leaving the straightener vi. conclusion the technique developed provides a method for choosing the necessary number of bending cycles at the stage of technological procedure designing based on real properties of a material as well as for visual evaluation of distribution of stresses in cross section of a wire at different stages of deformation. further the different elements described can be used for modeling one of the perspective operations of machining which is a rotating straightening. acknowledgment authors appreciate dipl.-ing. marcel graf for technical support while preparing and making experiments. etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 320-324 324 www.etasr.com khromov and kawalla: simulation of a steel wire straightening taking into account … references [1] b. dorodnykh, “method for calculation of set-up parameters of deforming device when manufacturing two lay ropes”, mining journal, no. 9, pp. 60-66, 1959 [in russian] [2] f. tulenkov, “change of stress condition of a wire in the process of straightening”, steel ropes, no. 2, pp. 367-372, 1965 [in russian] [3] w. guericke, m. paech, e. albert, “simulation of the wire straightening process”, wire industry, no. 8, pp. 613-620, 1996 [4] w. guericke, “material model describing cyclic elastic-plastic deformation of roller levelling and straightening processes”, steel research int., vol. 80, no. 4, pp. 281-287, 2009 [5] j. s. lee, h. huh, j. bae, j. lee, d. kim, “design optimization of roller straightening process for steel cord using response surface methodology”, materials processing and design; modeling, simulation and applications; numiform '07; proceedings of the 9th international conference on numerical methods in industrial forming processes. aip conference proceedings, volume 908, pp. 581-588, 2007 [6] k. k. adewole, s. j. bull, “simulation of the wire reverse bending test”, journal of civil engineering and construction technology, vol. 3, no. 1, pp. 116-126, 2012 [7] m. paech, “the positioning of straightening rolls”, wire, vol. 52, no. 2, pp. 82-83, 2002 [8] i. v. khromov, “methods for selecting parameters of exponential for stress-strain diagram of a steel rope wire”, sevntu journal. mechanics, power engineering, ecology, no. 87, pp. 12  15, 2008 [in russian] [9] i. v. khromov, “classification of processes of plastic working of rod workpieces with permanent cross-sectional shape”, sevntu journal. mechanics, power engineering, ecology, no. 106, pp. 31-34, 2010 [in russian] [10] v. d. da silva, strength of materials, 2006 [11] a. s. kobayashi, s. n. atluri, “analytical mechanics of solids”, springer handbook of experimental solid mechanics, pp. 3-16, 2008 [12] i. v. khromov, “analysis of the stressed state of a circular thin-walled cylinder under complex loading and with nonlinear hardening of the material”, strength of material, vol. 41, issue 3, pp. 278-284, 2009 microsoft word 11-3276_s_etasr_v10_n1_pp5157-5163 engineering, technology & applied science research vol. 10, no. 1, 2020, 5157-5163 5157 www.etasr.com nagao: seismic amplification by deep subsurface and proposal of a new proxy seismic amplification by deep subsurface and proposal of a new proxy takashi nagao research center for urban security and safety kobe university kobe, japan nagao@people.kobe-u.ac.jp abstract—codes of practice and ground motion prediction equations involve ground structure proxies to account for seismic amplification. although the ground consists of both shallow and deep subsurface, proxies are mainly related to the shallow subsurface as it is shallow subsurface information that is mostly available. however, as deep subsurface seismic amplification is not negligible, it may not be appropriate to use shallow subsurface proxies. in this study, the relationship between shallow and deep subsurface seismic amplification factors is discussed on the basis of s-wave velocity profile data from japanese kik-net strong-motion observation system stations. the correlation between typical proxies such as the average s-wave velocity of the top 30m of the ground surface and the seismic amplification factor was examined. although there was a negative correlation between the two, the degree of the correlation was weak. a new proxy showing stronger correlations with the seismic amplification factor is proposed and its effectiveness is demonstrated. keywords-seismic amplification; vs30; s-wave velocity; deep subsurface i. introduction earthquake ground motions are amplified as they propagate through the ground, thus differences in ground characteristics are considered in design earthquake ground motions and ground motion prediction equations (gmpes). the concept of using surface soil conditions to select design earthquake ground motions and gmpes has been pervasive for years since [1]. a typical ground structure proxy to account for seismic amplification is the average s-wave velocity from the surface down to 30m beneath the surface (vs30). vs30 can be easily calculated from ground data without seismic response analysis and a correlation between vs30 and seismic amplification has been noted [2, 3]. for this reason, although discussions on the appropriateness of using vs30 as a proxy continue [4, 5], vs30 is widely used at present and has been introduced as a proxy in national earthquake hazards reduction program (nehrp) [6], aashto [7], eurocode8 [8], and various other models [9, 10] and gmpes [11, 12]. note that the ground’s natural period is used as a proxy in japanese codes of practice [13, 14]. the ground consists of shallow and deep subsurface layers, and the boundary between the shallow and deep subsurface layers is referred to as engineering bedrock. this is a rigid layer with shear rigidity that does not deteriorate even during strong earthquakes. both vs30 and the natural period are mainly related to the shallow subsurface. s-wave velocities are approximately 100m/s in soft soil, 300m/s or more in stiff soil, 500m/s or more in rock, and 700m/s or more in engineering bedrock. however, the seismic bedrock beneath the deep subsurface layer can have s-wave velocities of 3000m/s or more. the degree of seismic amplification depends greatly on s-wave velocity changes in the ground, with the shallow subsurface having a velocity change of about a factor of two to four and the deep subsurface change being approximately a factor of five. therefore, the deep subsurface often has a greater seismic amplification than the shallow subsurface. some studies have pointed out the importance of deep subsurface to seismic amplification [15], and others have claimed that accurate evaluation of deep subsurface seismic amplification is important for assessing seismic ground motion [16]. however, the s-wave velocity structure from the engineering bedrock to the seismic bedrock varies greatly from site to site, and ground structures down to the seismic bedrock at many sites have not been clarified in detail. for this reason, few studies have systematically discussed deep subsurface seismic amplification, and none have tested the validity of explaining shallow and deep subsurface seismic amplification in proxies related to the shallow subsurface such as vs30. this study discusses the differences in seismic amplification between shallow and deep subsurface layers using information on actual ground structures and determines the optimal proxy for seismic amplification. for simplicity, the shallow and deep subsurface will be described as characteristics of the deep subsurface hereinafter. ii. method in this study, kik-net [17] was targeted, which is a network of strong-motion observation seismographs developed in japan. vertical-array strong-motion observation is performed on the ground surface and underground at kik-net sites, with sensors installed deeper than the engineering bedrock in boreholes in rock or stiff soil. seismic ground motion amplification factors can be discussed by analyzing the spectral ratios of strongmotion records from the ground surface and in the borehole. however, as most of the observation points do not reach the seismic bedrock in their boreholes, only those amplifications corresponding author takashi nagao engineering, technology & applied science research vol. 10, no. 1, 2020, 5157-5163 5158 www.etasr.com nagao: seismic amplification by deep subsurface and proposal of a new proxy with deep subsurface degrees of effect that differ from point to point can be discussed. therefore, in this study we calculate and discuss theoretical amplification factors based on the swave velocity structure from the ground surface to the seismic bedrock. s-wave velocity structure from the ground surface to the borehole sensor’s installation depth is obtained using p-s logging data at the kik-net sites. for the s-wave velocity structure from the borehole sensor installation depth to the seismic bedrock, s-wave velocity structure information from the japan seismic hazard information station (j-shis) [18] is used. thus, s-wave velocity structure from the ground surface to the seismic bedrock is obtained by combining kik-net and j-shis s-wave velocity structure information. in this study we used 615 data points. figure 1 shows the cumulative distributions of shallow and deep subsurface depths, with the red line indicating shallow subsurface and the blue line denoting the deep subsurface. the cumulative probability for sites with a shallow subsurface depth of less than 30m is 62%. although more than half of the sites include deep subsurface information in vs30, the percentage of that information in the total is not very high. kik-net stations are often installed at sites with thin deposits such as mountainous areas [19], but only two sites have deep subsurface depths of 30m or less, and more than 50% of the sites have deep subsurface depths of 400m or more, with 30% exceeding 1000m. sites with shallow subsurface thicknesses of 2m or less are generally regarded as rock or stiff soil sites, 94% of the data points are from deep subsurface depths deeper than 100m and 27% points have depths deeper than 1000m. it is obvious that there are limitations in expressing the seismic amplification using shallow subsurface proxies. fig. 1. cumulative layer thickness distributions of shallow and deep subsurface vs30 is the time-averaged s-wave velocity of the top 30m of the ground and is expressed as: vs30 = 30 / σ (hi /vsi) (1) where hi is the thickness of soil layer i (m), and vsi is the swave velocity of soil layer i (m/s). the nehrp [6] classifies ground types into five groups (class a–e) based on vs30 (table i). japanese highway bridge design specifications [13] classify ground types into three groups (types 1 to 3) based on the natural period of shallow subsurface (table ii). the numbers in parentheses in tables i and ii indicate the percentage of data points included in each category. nehrp class c sites are relatively common in this study. as for correlation with japanese highway bridge design specifications, type 1 ground, which corresponds to hard ground, is the most common at 80%. the reason for this is that kik-net stations are mainly installed in areas with relatively thin deposit layers [19]. shallow and deep subsurface transfer functions were calculated using sh-wave multiple-reflection theory under an assumption of horizontally stratified ground to evaluate the seismic amplification factor. for the quality factor (q) representing inelastic damping, the values shown in table iii were used in accordance with j-shis [18]. regarding obtained transfer functions, we focused on the 0.1–10.0hz range as that frequency range strongly influences structure and ground stability during earthquakes, and examined maximum amplitude frequencies (peak frequencies) and peak amplitudes. table i. ground type classifications in nehrp site class vs30 (m/s) a (1) 1500 < vs30 b (12) 760 < vs30 ≤ 1500 c (57) 360 < vs30 ≤ 760 d (28) 180 < vs30 ≤ 360 e (2) vs30 ≤ 180 table ii. ground type classification in japan’s highway bridge design specifications ground type natural period: ts (s) 1 (80) ts ≤ 0.2 2 (17) 0.2 < ts ≤ 0.6 3 (3) 0.6 < ts table iii. quality factor vs (m/s) q vs < 600 60 600 ≤ vs < 1000 100 1000 ≤ vs < 2000 150 2000 ≤ vs <3000 200 3000 ≤ vs 300 iii. examples of s-wave velocity profiles and seismic amplification factors figure 2 shows the s-wave velocity profiles of the sites under consideration, with aomh13, ibrh10, and szoh42 selected as examples of points having low vs30 values, hrsh02, ngsh01, and sigh03 selected as medium points, and fkih01, iskh06, and oith06 are selected as high vs30 value examples. the numbers in parentheses after the station code are the vs30 values of each site. in the low vs30 group, swave velocity reaches 1500m/s at a depth of 224m at station szoh42. in contrast, the s-wave velocity is only about 400m/s at 200m at aomh13 and ibrh10. for the medium vs30 group, the s-wave velocity exceeds 2000m/s at 30m and reaches 3000m/s at 150m at hrsh02, whereas at ngsh01, the s-wave velocity reaches 1900m/s at 18m without showing large increase until 1000m. for sigh03, the s-wave velocity is 530m/s at 30m and does not exceed 2000m/s until 350m. for the high vs30 group, the s-wave velocity exceeds 2000m/s at 20m at fkih01, whereas at oith06 the s-wave velocity 1 10 100 1 10 3 × 1 10 4 × 0 0.2 0.4 0.6 0.8 1 depth(m) c u m u la ti v e p ro b a b il it y engineering, technology & applied science research vol. 10, no. 1, 2020, 5157-5163 5159 www.etasr.com nagao: seismic amplification by deep subsurface and proposal of a new proxy reaches 1700m/s at 100m. at iskh06, the s-wave velocity does not exceed 2000m/s until 260m. in summary, even for the same vs30 values, s-wave velocity structures down to the seismic bedrock vary greatly from point to point. fig. 2. s-wave velocity profile figure 3 shows the transfer functions for the respective points, where the red solid lines denote shallow subsurface transfer functions and the blue solid lines represent deep subsurface transfer functions. for the low vs30 group, the shallow subsurface (fs) and deep subsurface (fd) peak frequencies are generally consistent, but deep subsurface peak amplitudes (ad) are much larger than shallow subsurface values (as), with amplification factor ratios ranging from 1.7 to 2.6. furthermore, for the station ibrh10, although the deep subsurface transfer function shows a large amplification of approximately 10 at 0.3hz and 0.7hz, there are no clear peaks in the shallow subsurface transfer functions. the fs and fd roughly agree with each other at the three points where vs30 is moderate, but ad is 1.5–2.2 times greater than as. at the three points where vs30 is large, fd and fs agree with each other at ibrh10, but the shallow subsurface amplification factor is almost 1, whereas the deep subsurface transfer function shows a large amplification at several frequencies. additionally, peaks can be seen at frequencies lower than the three points exemplified as a medium vs30 at 2.2hz at stations iskh06 and 0.73hz at station oith06. at fkih01, the ad is 17.7, which is the second largest ad after szoh42 among the nine points shown. thus, because of differences in deep subsurface s-wave velocity structures, the amplification factors greatly differ even for similar vs30 values. fig. 3. transfer function iv. results and discussion a. relationship between shallow and deep subsurface peak amplification factors figure 4 shows the relationship between as and ad which are plotted on the horizontal and vertical axes respectively. plotting on a double logarithmic chart shows a positive 0 1 10 3 × 2 10 3 × 3 10 3 × 4 10 3 × 0 800 600 400 200 0 aomh13(154) ibrh10(144) szoh42(153) vs(m/s) d e p th (m ) 0 2 10 3 × 4 10 3 × 0 800 600 400 200 0 hrsh02(391) ngsh01(398) sigh03(393) vs(m/s) d e p th (m ) 0 2 10 3 × 4 10 3 × 0 800 600 400 200 0 fkih01(716) iskh06(721) oith06(712) vs(m/s) d e p th (m ) 0.1 1 10 0 2 4 6 8 10 aomh13 frequency(hz) a m p li tu d e 0.1 1 10 0 5 10 15 ibrh10 frequency(hz) a m p li tu d e 0.1 1 10 0 10 20 30 szoh42 frequency(hz) a m p li tu d e 0.1 1 10 0 5 10 15 20 hrsh02 frequency(hz) a m p li tu d e 0.1 1 10 0 5 10 15 ngsh01 frequency(hz) a m p li tu d e 0.1 1 10 0 5 10 15 20 fkih01 frequency(hz) a m p li tu d e 0.1 1 10 0 1 2 3 4 5 iskh06 frequency(hz) a m p li tu d e 0.1 1 10 0 2 4 6 8 sigh03 frequency(hz) a m p li tu d e 0.1 1 10 0 1 2 3 4 5 6 oith06 frequency(hz) a m p li tu d e engineering, technology & applied science research vol. 10, no. 1, 2020, 5157-5163 5160 www.etasr.com nagao: seismic amplification by deep subsurface and proposal of a new proxy correlation between the two peak amplification factors, however, the variation is large. figure 5 shows the frequency distribution of peak amplification factor ratios. the solid line represents a probability density function assuming a lognormal distribution, and the distribution of the peak amplification factor ratios can be approximated by a lognormal distribution. the mean value was 2.39 and the standard deviation was 0.74. it was thus shown that the assessment of deep subsurface seismic amplification is crucial for properly evaluating earthquake ground motions and gmpes. the characteristic of the lognormal distribution is that the distribution’s right-side tail is heavy and the maximum ratio value is as large as 5.64. the red broken line in figure 4 represents the regression equation (2) obtained by performing a linear regression analysis on double logarithmic plots with a determination coefficient of 0.76. log ad = 0.484 + 0.766 log as (2) fig. 4. relationship between as and ad fig. 5. frequency distribution of peak amplification ratio b. relationship between peak frequency and peak amplification factor figure 6 shows the relationship between peak frequency and peak amplification factors. both shallow and deep subsurface show large scatters between frequency and amplification, with no correlation observed. a low peak frequency indicates a thick deposit layer or soft deposit layer at the site, and the amplification factor is assumed to be large. however, this is not the case in practice. at station aomh13, although fs, fd are as low as 1hz, as is 5.0 and ad is 8.6, and the amplification factors are lower than at ngsh01, which have a fs, fd values of 4.5hz, as 6.9, and ad of 17.7. the reason for this is the difference in the deposited layer thickness. although the s-wave velocity is low and the deposited layer is very thick at aomh13, peak amplification is not large due to damping effects. this means that the peak amplification factor is determined by complex combinations of parameters such as swave velocity and layer thickness in each soil layer, and the peak frequency of the ground is not an appropriate proxy for seismic amplification. fig. 6. relationship between peak frequency and peak amplification factor c. relationship between vs30 and peak amplification factor figure 7 shows the relationships between vs30 and as, ad. for vs30, there is less variation with as and ad than with peak frequency, and there is a weak negative correlation. in particular, the variation is small where vs30 exceeds 1000m/s. therefore, it can be said that vs30 is appropriate as a seismic amplification proxy for nehrp class a sites. however, in regions where vs30 is less than 1000m/s, the variation is large, with particularly large variations from 760m/s to 500m/s, but it is reduced in regions where vs30 is 500m/s or less. the reason for this reduction in variation is that ad has an upper limit value limited to approximately 20, whereas the ad lower limit value is increased when vs30 decreases. therefore, the reduced variation where vs30 is 500m/s or less does not necessarily indicate a strong correlation between vs30 and peak amplification. as a result, ad has the largest variation in nehrp class c sites, which differs slightly from the as case as as is 1 in many cases at sites with a large vs30. however, the 1 10 100 1 10 100 amp. shallow a m p . d e e p 0 2 4 6 0 20 40 60 80 100 amp. ratio fr e q u e n c y 0.1 1 10 1 10 100 frequency shallow(hz) a m p . sh a ll o w 0.1 1 10 1 10 100 frequency deep(hz) a m p . d e e p engineering, technology & applied science research vol. 10, no. 1, 2020, 5157-5163 5161 www.etasr.com nagao: seismic amplification by deep subsurface and proposal of a new proxy variation is also very large from 500m/s to 760m/s. the red broken line in figure 7 represents the regression equation obtained through linear regression analysis (3), (4). log as = 2.865 0.877 log vs30 (3) log ad = 3.173 0.858 log vs30 (4) the determination coefficients are 0.40 for as and 0.49 for ad, which are not high. however, ad had a slightly higher determination coefficient than as despite vs30 being considered an indicator of shallow subsurface geological structures. the reason is that the variation of as is greater than that of ad on the logarithmic scale under the same vs30 condition. furthermore, because kik-net stations used in this study are installed in locations with relatively thin deposits [19], approximately 40% of the points had deep subsurface appearing at less than 30m beneath the surface. therefore, it is considered that the relatively large number of points with deep subsurface information included in vs30 led to high correlations between amplification factors by deep subsurface and vs30. as a method of regression analysis, a constraint condition may be considered such that ad becomes 1 when vs30 becomes 2000m/s. however, the determination coefficient is lower than the determination coefficient resulting from (3) and (4). fig. 7. relationship between vs30 and peak amplification factor v. proposal of a new proxy the reason why vs30 and peak amplification show negative correlations is that vs30 is high at rocky sites with a low amplification factor, and vs30 is low in soft sediment sites with a high amplification factor. the results described above also indicated a negative correlation between the two parameters, but the variation was very large. to solve this problem, we compared the amplification factors of three ground structures with different s-wave velocity contrasts in top 30m and the same vs30 at 300m/s, as shown in table iv. the deep subsurface transfer function is illustrated in figure 8. case 1, which has the highest s-wave velocity contrast, shows the largest ad, and case 3, which has the lowest contrast, shows the smallest ad. the same results were obtained for as. vs30 has a certain effectiveness as an index for simply expressing the complicated ground structure to 30m of the surface layer, but information on the impedance contrast is not necessarily sufficiently expressed by only vs30. therefore, in this study, we propose a modified vs30 that corrects vs30 using the impedance contrasts of the ground surface to 30m as: 30 30 30s mod d vs vs vs vs = ⋅ (5) where vs30mod is the modified vs30, vss is the s-wave velocity of the ground surface, and vsd30 is the s-wave velocity 30m beneath the surface. fig. 8. transfer function table iv. model ground structure case 1 case 2 case 3 h (m) vs (m/s) h (m) vs (m/s) h (m) vs (m/s) 5 100 10 200 50 300 45 500 40 400 50 1000 50 1000 50 1000 2500 2500 2500 h: layer thickness a comparative study of the correlation between the modified vs30 and peak amplification factor yielded an s-wave velocity ratio between the ground surface and 30m of 0.5 power. figure 9 shows the relationship between the modified vs30, vs30, and ad for the model ground. the red circle denotes the modified vs30 and the gray triangle indicates the vs30. the use of the modified vs30 clarifies the negative correlation between the average s-wave velocities and peak amplifications. the relationship between the modified vs30 and peak amplification factor is illustrated in figure 10. the 100 1 10 3 × 1 10 4 × 1 10 100 vs30(m/s) a m p . sh a ll o w 100 1 10 3 × 1 10 4 × 1 10 100 vs30(m/s) a m p . d e e p 0.1 1 10 0 5 10 15 case 1 case 2 case 3 frequency(hz) a m p li fi c a ti o n engineering, technology & applied science research vol. 10, no. 1, 2020, 5157-5163 5162 www.etasr.com nagao: seismic amplification by deep subsurface and proposal of a new proxy variation is reduced compared to the relationship of vs30 with both as and ad. in particular, because the increasing tendency in the variation for a specific vs30 range is alleviated, the new proxy is applicable for all ground categories. the red broken line in figure 10 represents the regression equation obtained using a regression analysis ((6)-(7)): log as = 2.734 0.948 log vs30mod (6) log ad = 2.853 0.844 log vs30mod (7) the obtained determination coefficients are 0.63 for ad and 0.61 for as, which are significantly larger than the vs30 regression equations. thus, the modified vs30 is more useful as a seismic amplification proxy than vs30. fig. 9. relationship between vs30, modified vs30, and ad fig. 1. relationship between modified vs30 and peak amplification factor vi. conclusion in this study, the theoretical seismic amplification characteristics of shallow and deep subsurface were examined using p-s logging data from the kik-net strong-motion observation network and deep ground data from j-shis. in this study the following conclusions were obtained: • the deep subsurface to shallow subsurface seismic amplification ratios have a mean of 2.39 and a standard deviation of 0.74, and seismic amplification considering only the shallow subsurface underestimates the seismic amplification of the whole ground. assessment of the deep subsurface’s amplification characteristics is crucial for properly evaluating earthquake ground motions and gmpes. • examining the correlation between the typical proxies and seismic amplification factors demonstrated that the shallow subsurface peak frequency is not correlated with seismic amplification factors, and vs30 shows a weak negative correlation with seismic amplification factors. however, vs30 varies greatly relative to seismic amplification factors. to reduce this variation, we proposed a modified vs30 that considers the s-wave velocity ratios of the ground surface at the depth of 30m. the variation in the relationship between the modified vs30 and the seismic amplification factor is reduced compared with that using the conventional vs30. therefore, seismic amplification factors can be evaluated more accurately with the modified vs30 than the conventional vs30. acknowledgments the author appreciates kik-net and j-shis for providing the ground structure data. references [1] h. b. seed, c. ugas, j. lysmer, “site-dependent spectra for earthquakeresistant design”, bulletin of the seismological society of america. vol. 66, no. 1, pp. 221-243, 1976 [2] r. d. borcherdt, “estimates of site-dependent response spectra for design (methodology and justification)”, earthquake spectra, vol. 10, no. 4, pp. 617–653, 1994 [3] r. dobry, r. d. borcherdt, c. b. crouse, i. m. idriss, w. b. joyner, g. martin, m. s. power, e. e. rinne, r. b. seed, “new site coefficients and site classification system used in recent building seismic code provisions”, earthqake spectra, vol. 16, no. 1, pp. 41–67, 2000 [4] s. castellaro, f. mulargia, p. l. rossi, “vs30: proxy for seismic amplification?”, seismological research letters, vol. 79, no. 4, pp. 540–543, 2008 [5] v. w. lee, m. d. trifunac, “should average shear-wave velocity in the top 30m of soil be used to describe seismic amplification?”, soil dynamics and earthquake engineering, vol. 30, no. 11, pp. 1250–1258, 2010 [6] building seismic safety council, nehrp recommended provisions for seismic regulations for new buildings and other structures, part 1: provisions (fema 368), federal emergency management agency, 2001 [7] aashto (american association of state highway and transportation officials), guide specifications for lrfd seismic bridge design, second edition with 2014 interim, aashto, 2014 [8] cen, eurocode8. design of structures for earthquake resistance. part1: general rules, seismic actions and rules for buildings. final draft pr en1998, european committee for standardization, cen, 2003 0 200 400 6 8 10 12 14 vs30(m/s) p e a k a m p li tu d e 10 100 1 10 3 × 1 10 4 × 1 10 100 modified vs30 (m/s) a m p . sh a ll o w 10 100 1 10 3 × 1 10 4 × 1 10 100 modified vs30 (m/s) a m p . d e e p engineering, technology & applied science research vol. 10, no. 1, 2020, 5157-5163 5163 www.etasr.com nagao: seismic amplification by deep subsurface and proposal of a new proxy [9] building seismic safety council, recommended provisions for seismic regulations for new buildings and other structures, part 1: provisions. report no. fema-450, fema, 2003 [10] american society of civil engineers (asce), minimum design loads for buildings and other structures, tandards asce/sei 7-10, 2010 [11] j. x. zhao, j. zhang, a. asano, y. ohno, t. oouchi, t. takahashi, h. ogawa, k. irikura, h. k. thio, p. g. somerville, y. fukushima, y. fukushima, “attenuation relations of strong ground motion in japan using site classification based on predominant period”, bulletin of the seismological society of america, vol. 96, no. 3, pp. 898–913, 2006 [12] t. kanno, a. narita, n. morikawa, h. fujiwara, y. fukushima, “a new attenuation relation for strong ground motion in japan based on recorded data”, bulletin of the seismological society of america, vol. 96, no. 3, pp. 879–897, 2006 [13] japan road association, specifications for highway bridges, part5, seismic design, ver. 2012, maruzen co., ltd., 2016 [14] t. narafu, y. ishiyama, r. ison, j. sakuma, h. kato, s. kita, “outline and features of japanese seismic design code”, 16th world conference on earthquake engineering, santiago chile, january 9-13, 2017 [15] d. m. boore, w b. joyner, “site amplifications for generic rock sites”, bulletin of the seismological society of america, vol. 87, no. 2, pp. 327-341, 1997 [16] y. fukushima, t. nagao, “variation of earthquake ground motions with focus on site amplification factors: a case study”, engineering, technology & applied science research vol. 9, no. 4, pp. 4355-4360, 2019 [17] s. aoi, k. obara, s. hori, k. kasahara, y. okada, “new strong-motion observation network: kik-net”, eos, transactions of the american geophysical union, vol. 81, 2000 [18] h. fujiwara, s. kawai, k. x. s. hao, n. morikawa, h. azuma, “j-shis: an integrated system for sharing information on national seismic hazard maps for japan”, 16th world conference on earthquake engineering, santiago chile, january 9-13, 2017 [19] y. okada, k. kasahara, s. hori, k. obara, s. sekiguchi, h. fujiwara, a. yamamoto, “recent progress of seismic observation networks in japanhi-net, f-net, k-net and kik-net”, earth planets and space, vol. 56, no. 8, pp. 15-28, 2004 microsoft word 11-2730_s1_etasr_v9_n3_pp4131-4135 engineering, technology & applied science research vol. 9, no. 3, 2019, 4131-4135 4131 www.etasr.com rind et al.: particle crushing effect on the geotechnical properties of soil particle crushing effect on the geotechnical properties of soil touqeer ali rind department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan touqeerali@muetkhp.edu.pk hemu karira department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan engr.hemu07civil@gmail.com ashfaque ahmed jhatial department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan ashfaqueahmed@muetkhp.edu.pk samiullah sohu department of civil engineering, quaid-e-awam university of engineering, science and technology, larkana campus, larkana, sindh, pakistan engr.samiullah@quest.edu.pk abdul razzaque sandhu department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan abdulrazzaque@muetkhp.edu.pk abstract—foundations are considered as the backbone of a structure. most of the times, the foundation is laid on the soil. for the foundation design of any structure, we need to know beforehand the soil conditions such as shear strength and permeability. these parameters help us determine the bearing capacity of the soil. the soil conditions are determined by performing various laboratory tests such as shear box test or triaxial shear test. however, we cannot design the foundation considering these data as the ground conditions will change once the loads are applied to the soil as there are some soil particles with angularity or sharp edges will break. once they will break, soil conditions will not remain the same as they were before since the gradation will change. this work is carried out in order to know the impact soil breakage brings to the soil (granular soil). for this purpose, actual ground conditions were simulated in the laboratory by applying one-dimensional compression to soil particles for about 45 minutes in a universal testing machine (utm). different crushing loads to soil particles were applied and the change in the soil behavior was monitored. it was found that due to particle breakage of soil, the engineering properties of sand altered. this research work aims to analyze the effect of particle breakage only in the case of sand. keywords-shear strength; permeability; shear box test; bearing capacity; crushing load i. introduction granular soils like sand get crushed when subjected to heavy loading conditions. these materials are commonly used in the compacted sub-grade of flexible or rigid pavements, embankments, dam foundations and other structures [1]. different granular materials in foundation engineering have different compositions, water content, unit weight, particle size distribution, etc. [2]. when granular materials are subjected to heavy loadings, the particles of soil get crushed and particle breakage occurs [3]. particle breakage of granular material can occur at different stress levels for different materials [5, 6]. it can occur due to heavy load on soil caused by pile driving, highway embankments, offshore structures, etc. [4]. once particle breakage occurs, the soil conditions alter as the gradation of soil changes. particle breakage occurs when highly loaded particles crush into smaller pieces. we know soil properties are associated with particle size, so a change of properties would occur as a result of soil particles’ breaking. a few soil particles may break immediately upon load application, while others may break after a very long time. it is important to know the changes occurring in the geotechnical properties as the soil is subjected to loading for very long time. a precaution must be taken into consideration before the construction of structures is carried out. the geotechnical properties may include particle size distribution (psd), specific gravity, density, void ratio, shear strength etc. psd of soil has major effects on the design of earth fill dams and embankments [7-9]. a granular soil material has a particle size ranging from 0.001mm to 1000mm like granular sand [10]. after crushing, when the particle size distribution is changing, changes may occur in permeability, shear strength, deformation and other granular soil properties [11]. this research work aims to determine the changes that will occur on the engineering properties of sand when it is subjected to crushing under different loading conditions. ii. problem statement for structure design the consideration of particle breakage is important. the success of a project doesn’t rely upon designing the foundation on laboratorial or in-situ test data. there must be a margin kept for the consideration of particle breakage as the soil is supposed to sustain the desired load for very long and with the passage of time different particles will break due to which soil properties change. thus there is a need of determining the effects of particle breakage on engineering corresponding author: touqeer ali rind engineering, technology & applied science research vol. 9, no. 3, 2019, 4131-4135 4132 www.etasr.com rind et al.: particle crushing effect on the geotechnical properties of soil properties of sand due to crushing of its particles at different loading conditions. in this work, the granular sand passing from a 4.75mm sieve and retaining on 0.075mm sieve was crushed at 5mpa, 10mpa, 15mpa and 20 mpa one-dimensional loads in a utm machine. iii. research methodology to simulate the actual conditions of ground (that is when a structure transmits a load onto the soil) in the laboratory we used a special mould known as “pressure mould” in which we kept sand and applied compressive forces with the help of the utm to break the soil particles. the soil was crushed at different loads (5mpa, 10mpa, 15mpa and 20mpa) and for each state of the soil, tests were performed in the same conditions to analyze the effect of particle breakage in to the geotechnical soil properties. a. material properties 1) grain-size distribution the sizes of soil grains and their distribution vary greatly [12-15]. the grain-size distribution of coarse-grained soil is generally determined by sieve analysis. for a fine grained soil, the grain-size distribution can be obtained by hydrometer analysis. 2) sieve analysis sieve analysis is conducted by taking a measured amount of dry, well-pulverized soil and passing it through a stack of progressively finer sieves with a pan at bottom. the amount of soil retained on each sieve was measured, and the cumulative percentage of soil passing through each sieve was determined. 3) relative density in granular soils, the degree of compaction in the field can be measured according to the relative density, given as: dr� ������ ��������� 100 (1) where emax=void ratio in soil in loosest state, emin=void ratio in soil in densest state, and e=in situ void ratio. the relative density of soil can also be expressed in terms of dry unit weight or: dr={ � �� ��� � ����� ��� }* � ��� � 100 (2) where rd=in situ dry unit weight, rdmax=dry unit weight in densest state corresponding to emin, and rdmin=dry unit weight in loosest state corresponding to emax. 4) hydraulic conductivity the voids between soil grains allow water to flow through them. knowledge of this procedure is required in order to design earth dams, determine the quantity of seepage under hydraulic structures and dewater foundations before and during their construction [16]. the following equation for calculating the velocity of flow of water through a soil was proposed in 1856: v=ki (3) where v=darcy velocity, k=hydraulic conductivity, i=hydraulic gradient=dh/l. 5) shear strength soils are essentially frictional materials. they are comprised of individual particles that can slide and roll relative to one another. in the discipline of soil mechanics, it is generally assumed that the particles are not cemented. one consequence of their frictional nature is that the strength depends on the effective stresses in the soil. as the effective stress increases with depth, so in general will the strength [17]. shear strength of the soil is the internal resistance per unit area that the soil mass offers to resist failure and sliding along any plane inside it. mohr in 1900 proposed these failure criteria. the limiting shear stress that may be applied to any plane in the soil mass is found to be given by an equation of the form: τ=c+σn tan ϕ (4) where c=cohesion and ϕ=friction angle. since this research was limited to sand only, so we will not discuss other geotechnical parameters such as atterberg limits and soil consolidation. b. experimental procedure 1) sample preparation the followed procedure to prepare a sand sample from the bulk of soil having a mixed variety of different soils is given below. we knew that the sand has maximum particle size of 4.75mm and minimum particle size of 0.075mm, so the first step was to sieve the soil from a no. 4 sieve, to remove all gravel and larger particles. the second step was to wash the soil sample through a no. 200 wash sieve (0.075mm aperture), to remove all the silt and clay particles. washing of the soil should be carried out in small quantities until the water passed from the sieve is clean and clear of any particles. the soil (consisting of sand only) was then dried out by placing in the oven for 24 hours (or it may be dried out by the hot plate procedure discussed later). the dried sample should be kept in a safe place so that dust particles would not mix with it. for this research, 200kg of pure sand were prepared. the sieves used for sample preparation are shown in figure 1. fig. 1. no. 4 sieve and no. 200 washing sieve 2) crushing of sand samples the sand particles were crushed by applying loads of 5mpa, 10mpa, 15mpa, and 20mpa for 45 minutes. for the crushing of soil particles, a special mould was used (pressure mould) consisting of a base plate onto which a circular metallic ring (15cm diameter, and 15cm height) opened from both sides is placed, and a loading rim which was placed on top of the engineering, technology & applied science research vol. 9, no. 3, 2019, 4131-4135 4133 www.etasr.com rind et al.: particle crushing effect on the geotechnical properties of soil mould system containing the soil to be crushed. the soil was limited by the quantity determined using another cylindrical container (with a capacity of 3.27kg). the soil was then transferred to the mould arrangement and then a loading rim was placed. once the mould setup was prepared, it was placed in the utm as shown in figure 2. for this research work 30kg of crushed soil at each loading was obtained. each loading intensity was applied on the soil for 45 minutes. then, the soil was removed and the mould was refilled by fresh uncrushed soil and the same loading conditions were applied. the procedure was repeated until we got the required amount of crushed soil for each load the uncrushed soil was crushed by applying the same procedure at 5mpa 10mpa, 15mpa and 20mpa. (a) (b) (c) (d) (e) (f) fig. 2. different components of the pressure mould placed in the utm: (a) base plate, (b) pressure mould, (c) cylinderical container, (d) loading rim, (e) pressure mould filled with sand, and (f) pressure mould placed in utm iv. results and discussion a. psd the psd of sand crushed at 5mpa, 10mpa, 15mpa and 20mpa loads was calculated separately. merging all the particle size distribution curves at each loading conditions we observe that the percentage of finer soil is increased in the upper sieves as the crushing load is increased. this applies to bottom sieves also, but the effect is not that much as smaller particles are very difficult to break as shown in figure 3. b. specific gravity or density it was observed that due to crushing the minimum and maximum dry density of particles was reduced. as the crushing of particles is increased by the application of more load, the density of soil particle is further reduced as shown in table i. fig. 3. effect on the psd curve due to crushing of sand table i. effect on sand density s.no soil condition ρdmin ρdmax ρdavg 1 uncrushed 1.59 1.88 1.735 2 crushed at 5mpa 1.57 1.87 1.72 3 crushed at 10mpa 1.56 1.85 1.705 4 crushed at 15mpa 1.54 1.83 1.685 5 crushed at 20mpa 1.51 1.81 1.66 c. e-k curve we can see that the soil permeability (k) is reducing as the particle crushing is increasing by increasing the crushing load. also, we can see that for the same voids ratio (e) in each soil condition, we get different permeability values (figures 4-5). fig. 4. e-k curve of soil in different states (crushed and uncrushed) fig. 5. effect on the permeability of soil due to crushing at e=0.6 engineering, technology & applied science research vol. 9, no. 3, 2019, 4131-4135 4134 www.etasr.com rind et al.: particle crushing effect on the geotechnical properties of soil d. shear strength the shear strength of soil in all conditions (crushed and uncrushed) was determined by applying a normal load of 8.5kg and 10.5kg. the weight of the soil was taken as 102gm in each case. the results are shown in figures 6-10. fig. 6. effect on the shear envelop of the soil due to crushing fig. 7. shear displacement vs.shear stress under normal load of 8.5kg fig. 8. shear displacement vs. vertical displacement under normal load of 8.5kg fig. 9. shear displacement vs. shear stress under normal load of 10.5kg fig. 10. shear displacement vs. vertical displacement under normal load of 10.5kg v. conclusion crushing of particles did bring changes in the geotechnical properties of soil. the following conclusions can be made from this research work: • the gradation (psd) of soil changed. increase in crushing load on soil particles increases the percentage of finer particles from various sieves, especially the ones with larger aperture size increased. • specific gravity of particles was reduced as the particle breakage increased by applying a greater crushing load. also, the maximum and minimum dry density of soil reduced as the crushing load kept on increasing. • the permeability of particles also reduced when the crushing load increased. even when the voids ratio stayed the same, the permeability of soil, either in crushed or in uncrushed state, was different, and kept reducing as the crushing load was increasing. • shear box test results revealed details about the changes occurring in the sand due to crushing. it was observed that dense sand behaved like loose sand as particle breakage was induced. thus, some precautionary measures must be taken while designing the foundations of a structure, as the original properties of soil will change once the structure is built and the particles will break due to structural load. precautionary measures might be taken in the form of considering a significant reduction in the friction angle of soil while designing the foundation as the structure will transfer load onto the soil for very long time thus inducing significant particle breakage. or we may apply greater factor of safety in determining the safe bearing capacity of the soil, as the bearing capacity of the soil is determined by considering shear parameters. references [1] l. e. vallejo, z. chik, “the evolution of crushing in granular materials and its effect on their mechanical properties”, proceedings of the 16th international conference on soil mechanics and geotechnical engineering, millpress science publishers/ios press, 2006 [2] m. l. chen, g. w. jian, b. gan, w. h. jiang, j. w. zhou, “physical and compaction properties of granular materials with artificial grading behind the particle size distributions”, advances in materials science and engineering, vol. 2018, pp. 1-20, 2018 engineering, technology & applied science research vol. 9, no. 3, 2019, 4131-4135 4135 www.etasr.com rind et al.: particle crushing effect on the geotechnical properties of soil [3] o. h. al hattamleh, h. h. al-deeky, m. n. akhtar, “the consequence of particle crushing in engineering properties of granular materials”, international journal of geosciences, vol. 4, no. 7, pp. 1055-1060, 2013 [4] t. a. rousan, o. al hattamleh, r. a. dwairi, “effect of inherent anisotropy on shear strength following crushing of natural aqaba subgrade sand”, jordan journal of civil engineering, vol. 5, no. 3, pp. 431-445, 2011 [5] j. p. hyslip, l. e. vallejo, “fractal analysis of the roughness and size distribution of granular materials”, engineering geology, vol. 48, no. 34, pp. 231-244, 1997 [6] j. yang, x. d. luo, “exploring the relationship between critical state and particle shape for granular materials”, journal of the mechanics and physics of solids, vol. 84, pp. 196-213, 2015 [7] b. b. mandelbrot, the fractal geometry of nature, w. h. freeman and company, 1983 [8] j. j. wang, d. zhao, y. liang, h. b. wen, “angle of repose of landslide debris deposits induced by 2008 sichuan earthquake”, engineering geology, vol. 156, pp. 103-110, 2013 [9] m. rieu, g. sposito, “fractal fragmentation, soil porosity, and soil water properties: i. theory”, soil science society ofamerica journal, vol. 55, no. 5, pp. 1231-1238, 1991 [10] z. y. ma, f. n. dang, h. j. liao, “numerical study of the dynamic compaction of gravel soil ground using the discrete element”, granular matter, vol. 16, no. 6, pp. 881-889, 2014 [11] g. lumay, n. vandewalle, “compaction of anisotropic granular materials: experiments and simulations”, physical review e, vol. 70, no. 5, 2004 [12] m. a. martin, m. reyes, f. j. taguas, “an entropy like parameter of particle size distributions as packing density index in complex granular media”, granular matter, vol. 19, no. 1, p. 9, 2017 [13] w. choi, y. son, j. park, s. noh, t. bong, “an in-vestigation on crushing and particle size distribution characterizes of bottom ash as compaction energy”, 2013 world of coal ash (woca) conference, lexington, usa, april 22-25, 2013 [14] h. shahnazari, r. rezvani, “effective parameters for the particle breakage of calcareous sands: an experimental study”, engineering geology, vol. 159, pp. 98-105, 2013 [15] m. s. lim, d. c. wijeyesekera, a. zainorabidin, i. bakar, “the effects of particle morphology (shape and sizes) characteristics on its engineering behaviour and sustainable engineering performance of sand”, international journal of integrated engineering, vol. 4, no. 4, pp. 27-37, 2012 [16] m. a. martin, m. reyes, f. j. taguas, “estimating soil bulk density with information metrics of soil texture”, geoderma, vol. 287, pp. 66-70, 2017 [17] f. casini, g. m. viggiani, s. m. springman, “breakage of an artificial crushable material under loading”, granular matter, vol. 15, no. 5, pp. 661-673, 2013 microsoft word 10-876-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1258-1263 1258 www.etasr.com suarez-dominguez et al.: homogeneous and stratified liquid-liquid flow effect of a viscosity reducer homogeneous and stratified liquid-liquid flow effect of a viscosity reducer: i. comparison in parallel plates for heavy crude e. j. suarez-dominguez e. f. izquierdo-kulich a. rodríguez-valdez laboratorio de mecanica y materiales fadu universidad autonoma de tamaulipas tampico, tamaulipas, mexico edgardo.suarez@uat.edu.mx departamento de quimicafisica f. q. universidad de la habana la habana, cuba elenaik@fq.uh.cu facultad de ingenieria universidad nacional autonoma de mexico ciudad de mexico, mexico arodriguezv@ii.unam.mx f. solorio-ordaz a. e. chavez-castellanos a. palacio-perez facultad de ingenieria universidad nacional autonoma de mexico ciudad de mexico, mexico fjso@unam.mx facultad de ingenieria universidad nacional autonoma de mexico ciudad de mexico, mexico aechavez@unam.mx facultad de ingenieria universidad nacional autonoma de mexico ciudad de mexico, mexico apalaciop@ii.unam.mx abstract—production of heavy crude oil in mexico, and worldwide, is increasing which has led to the application of different methods to reduce viscosity or to enhance transport through stratified flow to continue using the existing infrastructures. in this context, injecting a viscosity improver that does not mix completely with the crude, establishes a liquid-liquid stratified flow. on the basis of a parallel plates model, comparing the increase of flow that occurs in the one-phase case which assumes a complete mixture between the crude and the viscosity improver against another stratified liquid-liquid (no mixing between the oil and compared improver); it was found that in both cases there is a flow increase for the same pressure drop with a maximum for the case in which the flow improver is between the plates and the crude. keywordsstratified flow; velocity profile; heavy oil i. introduction transporting heavy oil has gained significant interest due to high viscosity and operational problems such as high pumping costs, heavy fractions deposition and other phase changes [1-3]. the study of velocity profiles is very important because these effects are directly related to the pumping power and transport costs [4], as well as the design of monitoring pipeline [5]. although frequently emulsions are used to improve pipeline transport [6, 7] and viscosity reducers are injected [8], few studies have examined the effects related to the shape of the injected fluid and dosing of products in the crude oil. most of the time the research focuses on pump dimensioning [9, 10] limiting the capacity to use the same infrastructure for heavier fluids. it is important to consider the mechanism that determines the transport of a compound injected to a fluid to reduce its viscosity. this can determine the effectiveness of its action and interaction effects that are set at the molecular level and that modify the rheological properties. [11-14]. in this regard, it has been found that the injection of a liquid into the inner periphery of a pipeline can substantially improve the flow of transported fluid [15, 16]. various numerical methods [18, 19] and theoretical simulation models have been proposed to explain this effect [17]. studies have also been carried out focusing on the involvement of surface tension exerted by the flow improvers and leading to an oil phase dispersion increase and the consequent influence in viscosity [20-22]. however, there are not papers reporting the effects of injection of other liquids on flow enhancement, as in the case of highly viscous fluids such as heavy and extra heavy crude, that generally maintain a laminar flow. a liquid-liquid stratified flow can be established if mechanical mixing between the oil and the chemical is not presented, as when oil extraction is performed by the reservoir natural pressure, or the flow improver is injected at a later point or away from the pump discharge. the aim of this work is to model theoretically the behavior of a system consisting of crude oil and flow improver moving between two parallel plates considering three different conditions: i) complete mixing between the two fluids, so that we have a single-phase system of lower viscosity, ii) no mixing between the crude oil and the flow improver, establishing a stratified system with only one interface between them iii) engineering, technology & applied science research vol. 6, no. 6, 2016, 1258-1263 1259 www.etasr.com suarez-dominguez et al.: homogeneous and stratified liquid-liquid flow effect of a viscosity reducer establishing a stratified flow where one of the fluids is in the center and the other in the duct walls, creating two interphases. ii. mathematical model the mathematical model used to predict the velocity profiles and the total flow related with the volume fraction of the flow improver is based on the equations of continuity and change in cylindrical coordinates, in all cases considering i) newtonian flow with constant density and viscosity, ii) isothermal system, iii) laminar flow regime and iv) steady state. schemes corresponding to the cases to be considered are shown in figures 1-3. the distance x between the plates is to be considered much less than the width y, so that one can assume that the momentum transport occurs preferentially in the x direction, while the liquid moves in the direction z. to quantify the effect of the flow improver on total flow is determined by the relationship: 12 1 q q= q and 12 1 2q =q +q (1) where the subscript 1 refers to the crude and the subscript 2 refers to the flow improver. q12 represents the homogenous mix of the two substances. q1 represents the flow of oil; q allows to quantify the flow increase because of the flow improver injection, for the same pressure drop. fig. 1. case a: single-phase flow consisting of the mixture of oil and the flow improver. fig. 2. case b: no mixing between the oil crude and the flow improver, so that the system behaves as a two-phase stratified flow with a single interface between the fluids fig. 3. case c: one of the fluids is injected in the center, such that stratified flow is developed with two interfaces between the fluids a. case a when a complete mix is produced between crude oil and the flow improver, either via a mixing tank or an injection prior to pumping, blend viscosity decreases. many empirical equations exist to describe this effect. the ones proposed by lederer: 2 12 2 1 μ lnμ =g ln +1 μ (2) ( ) 2 2 2 2 σy g = σ 1-y +y σ=0.5-0.004t (3) and kendall and monroe: 3 1 22 3 1 11 3 1 12  xx (4) respectively, are classical results, which can be used for mix of oil and improver flows [23, 24]. in this paper, (2) is used in order to describe the system behavior when a complete mix is produced because of experimental results showed this is one of the higher correlation mixing rule [25]. from the considerations set, we obtained that the velocity profile established in this system is described by the partial differential equation: 2 2 p d v =μ z dx ¶ ¶ (5) where p is pressure and v is the fluid velocity. defining the dimensionless parameter γ: x γ= α (6) and: 2 p φ=α z ¶ ¶ (7) equation (5) is written in the form: 2 2 d v -φ=μ dγ (8) with the boundary conditions: ( ) ( ) v 0 =0 v 1 =0 (9) differential equation (8) has an analytical solution, and considering (9), velocity profile is obtained: ( )2 1 φ v= γ-γ 2 μ (10) from the velocity profile, volumetric flow is obtained for the single-phase case ( ) y 1 2 0 0 1 φ q= γ-γ dγdy 2 μ æ ö÷ç ÷ç ÷÷çè øò ò and therefore: engineering, technology & applied science research vol. 6, no. 6, 2016, 1258-1263 1260 www.etasr.com suarez-dominguez et al.: homogeneous and stratified liquid-liquid flow effect of a viscosity reducer 1 φ q= y 12 μ (11) taking into account equations (1), (2) y (11) yields: ( ) ( ) ( )( ) 1 2 2 1 2 2 0.5-0.004t y μ μ1-y 10.5-0.004t +y μ q= exp ln +1 æ ö÷ç ÷ç ÷ç ÷çè ø (12) b. case b the system of differential equations describing spatial velocity profile of a stratified flow with a single interface between the fluids is given by: 2 1 1 2 d v -φ=μ dγ for 0<γ<α (13) 2 2 2 2 d v -φ=μ dγ for α<γ<1 (14) near of the wallsm it is considered that velocity is zero, therefore: ( ) ( ) 1 2 v 0 =0 v 1 =0 (15.a) the others boundary conditions are stablished taken into account the continuity of velocity and shear stress on interface α, in such way that: ( ) ( ) ( ) ( ) 1 2 1 2 v α =v α τ α =τ α (15.b) where  is fluid shear tensor, defined: dv τ=-μ dx (16) the differential equations (13) and (14) have, in this case, the solution: ( ) 1 22 16 2 1 γ1 μ2v γ =c +c γφ for 0<γ<α (17) ( ) 2 26 15 2 2 1 2 γ μv γ =c +c γφ for α<γ<1 (18) where: ( )( ) ( ) ( )( ) ( ) ( ) ( ) ( ) 22 2 1 1 2 15 2 1 1 2 2 1 1 2 16 1 1 1 2 1 2 26 2 1 1 2 c =0 μ -α μ -μφ c = 2μ μ -α μ -μ μ -α μ -μφ c = 2μ μ -α μ -μ μ -μ α α-1φ c = 2μ μ -α μ -μ (19) to find the  value that corresponds to the interphase position, the flow values are determined as a function of : ( )( ) ( ) 22 1 1 2 1 1 1 1 2 μ -α μ -μ1 α 3 q = yφ -α 6 μ 2 μ -α μ -μ æ ö÷ç ÷ç ÷ç ÷çè ø (20) ( ) ( ) ( )( ) ( )( ) ( ) ( ) ( )( ) ( ) 2 1 1 2 1 2 2 2 2 1 1 2 1 1 2 μ -α μ -μ μ -μ α α-11 yφ 3 q = 1-α 1+α +3 1+α+α (21) 6 μ 2 μ -α μ -μ μ -α μ -μ æ ö÷ç ÷ç ÷ç ÷ç ÷÷çè ø and from defining the volume fraction of the injected flow improver y2 = q2/q12 relative to the total two-phase flow,  is cleared from the equation: ( ) ( )2 22 1 1 2 1 22 1 4 2 4 3 2 2 2 1 2 1 2 1 2 μ -2αμ +4αμ +α μ -α μy =μ α-1 1-y α μ -μ α μ -2μ α μ +3μ α μ (22) after determining the value of the position of the interface for a fraction of the injected liquid ratio, relationship between the total biphasic flow and single phase flow of crude oil is determined: ( )( ) ( ) ( ) ( ) ( )( ) ( )( ) ( ) ( ) ( )( ) ( ) 2 2 1 1 2 1 1 1 2 2 1 1 2 1 2 2 2 1 1 2 1 1 2 μ -α μ -μα 3 q=2μ -α μ 2 μ -α μ -μ μ -α μ -μ μ -μ α α-11-α 3 +2μ 1+α +3 1+α+α (23) μ 2 μ -α μ -μ μ -α μ -μ æ ö÷ç ÷ç ÷ç ÷ç ÷ç ÷ç ÷ç ÷÷ç ÷çè ø æ ö÷ç ÷ç ÷ç ÷ç ÷ç ÷ç ÷ç ÷÷ç ÷çè ø c. case c following the same methodology as in case b, but considering two interfaces among fluids, the velocity profile that is set for two-phase flow, where one fluid is in contact with both plates, (figure 3) is obtained: ( ) a 22 16 1 2 2 a γ μv γ =c +c γφ for 0<γ<α (24) ( ) a 22 16 2 a 1 2 γ μv γ =c +c γφ for β<γ<1 (25) ( ) b 26 15 2 b 1 2 γ μv γ =c +c γφ for α<γ<β (26) where: ( )( )( ) ( ) 22 b a b 15 a b 16 a a b 26 a b c =0 μ + μ -μ α+βφ c = 2 μ μ 1 φ c = 2 μ αβ μ -μφ c =2 μ μ (27) in this case there may be two possibilities. first is that the flow improver moves inside (in the centre) and the crude is in contact with both plates. in which case we obtain: engineering, technology & applied science research vol. 6, no. 6, 2016, 1258-1263 1261 www.etasr.com suarez-dominguez et al.: homogeneous and stratified liquid-liquid flow effect of a viscosity reducer ( ) ( ) ( )( )( ) ( ) ( ) ( )( ) 2 2 2 1 1 22 2 2 2 2 1 μ β-α 3μ α+β -2αβμ + μ -3μ α +βy = 1-y β-1 2β+1 -α 2α-3 (28) ( ) ( ) ( )( ) ( ) ( ) ( )( )( ) 2 2 2 2 2 1 1 2 2 q= β-1 2β+1 -α 2α-3 1 + β-α 3μ α+β -2αβμ + μ -3μ α +β μ (29) second case is if oil flows through the inside and the flow improver is in contact with both plates: ( ) ( ) ( )( ) ( ) ( ) ( )( )( ) 2 2 2 1 2 2 2 1 1 2 2 β-1 2β+1 -α 2α-3y =μ 1-y β-α 3μ α+β β +α 3μ -μ -2αβμ (30) ( ) ( ) ( )( )( ) ( ) ( ) ( )( ) 2 21 1 1 2 2 2 1 2 21 2 μ 1 q= β-α 3μ α+β β +α 3μ -μ -2αβμ μ μ μ + β-1 2β+1 -α 2α-3 μ (31) iii. results and discussion the results obtained with the model were based on a crude with viscosity 1 = 35 pa.s and a flow improver with viscosity 2 = 0.007 pa.s. to make the study, the velocity profile was analyzed considering φ=1 for a flow improver volume fraction of 0.03. results predicted by the model are shown in figures 4.a, 4.b, 4.c y 4.d. it is appreciated that when there is mixing between the two liquids (case a) the speed of transport is increased significantly compared with that achieved in the absence of flow improver. if there is no mixing, we see a welldefined interface between the two flows, where the speed reached in the liquid layer corresponding to the flow improver is significantly higher than the phase of crude oil (case b), but is lower than that reached with complete mixing. when the flow improver is injected in the center (case c.1), even when the speed is increased, this increase is less pronounced than the corresponding liquid-liquid stratified flow with a single interface, while a further increase occurs when the flow improver is in contact with both plates. as shown in figure 5, the model predicts different behavior between the volume fraction and flow improvement is achieved for the same pressure drop depending on the form of injection. thus very significant increases are achieved when the enhancer is in contact with the walls. this apparently is because it has significantly lower viscosity than crude, so that the shear stress on the wall of the plates decreases, which is manifested in increased flow for the same pressure drop. in correspondence with this, the smallest increase in flow is achieved for the case where the crude oil is in contact with both plates. however, this two interfaces model between fluids has two limiting factors: the first is that there is no explicit criteria established by the asymmetry of the same (distance from each of the interfaces), and it only has a flow ratio to determine the height of the interface, so that the asymmetry must be defined to make other predictions. the second limitation is that it is necessary to define under what conditions interfaces can be established because in horizontal ducts, the density difference between both flows favors the formation of a stratification. when cases a and b are compared, it can be seen that in both cases there is an increased flow. although this increase is more marked when mixing, it is still advisable to inject the flow improver before pumping. the results in terms of flow profiles are consistent with those obtained in [16, 26-27]. the maximum possible flow is the flow improver and oil crude substituted in (1), such that q=5000; it can be seen that the better effect is around 95%. fig. 4. velocity profiles predicted by the model. case a: complete mix with the fraction of flow improver as parameter. case b: stratified flow with a single interface. case c: stratified flow with two symmetrical interfaces. 1 the oil crude is located in contact with both plates; 2. the flow improver is in contact with both plates iv. conclusion the injection of a flow improver always causes an increase of fluid flow for the same pressure drop, where the increased magnitude order, from lowest to highest, is: stratified flow with two interphases, which is crude oil that is in contact with the walls; stratified flow with an interface between the two flows; complete mixing between the two fluids with the establishment of a single phase flow of lower viscosity and two interfaces case a case b case c.2 case c.1 engineering, technology & applied science research vol. 6, no. 6, 2016, 1258-1263 1262 www.etasr.com suarez-dominguez et al.: homogeneous and stratified liquid-liquid flow effect of a viscosity reducer stratified flow where the flow improver is in contact with the plates. these results indicate that the way in which the injection of the flow improver and the existence of mechanical mixing with oil crude occur influences the overall enhancement effect. the model has as limitation that it cannot explicitly set the conditions under which the formation of two interfaces occurs, so that oil flows through the center, which may reasonably be expected if similar fluids densities are obtained. it is necessary to develop technologies that allow the injection to be made in the wall with subsequent increase in improved operating systems extraction and transportation of crude oil. 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020 0.022 0.024 0.026 0.028 0.030 13.2 13.4 13.6 13.8 14.0 14.2 14.4 14.6 14.8 15.0 y q 0.005 0.010 0.015 0.020 0.025 0.030 6.56 6.57 6.58 6.59 6.60 6.61 6.62 6.63 y q 0.005 0.010 0.015 0.020 0.025 0.030 1.840 1.845 1.850 1.855 1.860 y q 0.005 0.010 0.015 0.020 0.025 0.030 4756 4758 4760 4762 4764 4766 4768 y q fig. 5. behavior of flow increase with respect to the volume fraction of improver acknowledgment the authors would like to thank the consejo nacional de ciencia y tecnología (conacyt) of mexico, project number 166923 for the support and prof. lynda kay deckard for editing this paper. references [1] r. santos, w. loh, a. bannwart, o.trevisan, “an overview of heavy oil properties and its recovery and transportation methods”, brazilian journal of chemical engineering, vol. 31, no. 3, pp. 571-590, 2014 [2] z. huang, h. lee, m. senra, h. fogler, “a fundamental model of wax deposition in subsea oil pipelines”, alche jornal, vol. 57, no.11, pp. 2955-2964, 2011 [3] z. tian, w. jin, l. wang, z. jin, “the study of temperature profile inside wax deposition layer of waxy crude oil in pipeline”, frontiers in heat and mass transfer, vol. 5, no. 5, pp. 1-8, 2014 [4] r. martínez-palou, m. de lourdes mosqueira, b. zapata-rendón, e. mar-juárez, c. bernal-huicochea, j. de la cruz clavel-lópez, j. aburto, “transportation of heavy and extra-heavy crude oil by pipeline: a review”, journal of petroleum science and engineering, vol. 75, no. 3-4, pp. 274-282, 2011 [5] r. thorn, g. johansen, b. hjertaker, “three-phase flow measurement in the petroleum industry”, measurement science and technology, vol. 24, no. 1, pp. 1-19, 2013 [6] h. laurencio-alfonso, y. delgado-drubey, “influencia de la temperatura en las propiedades reológicas de la emulsión de petróleo pesado”, minería y geología, vol. 24, no. 2, pp. 1-12, 2008; “influence of temperatura in the rheologic properties of heavy petroleum emulsion”, mining and geology, vol. 24, no.2, pp.1-12, 2008 [7] r. pal, 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métodos computacionales, 2003 case a case b case c.1 case c.2 engineering, technology & applied science research vol. 6, no. 6, 2016, 1258-1263 1263 www.etasr.com suarez-dominguez et al.: homogeneous and stratified liquid-liquid flow effect of a viscosity reducer [19] m. lotfi, m. karbaschi, a. javadi, “dynamics of liquid interfaces under various types of external perturbations” current opinion in colloid & interface science, vol. 19, no. 4, pp. 309-319, 2014 [20] w. manning, g. lind, “data analysis and discussion of product interface size on a batched crude oil pipeline”, psig annual meeting, 6-9 may, baltimore, maryland, usa, pipeline simulation interest group, 2014 [21] s. hasan, m. ghannam, n. esmail, “heavy crude oil viscosity reduction and rheology for pipeline transportation”, fuel, vol 89, pp. 1095-1100, 2010 [22] r. silva, d. almeida, r. rufino, j. luna, “applications of biosurfactants in the petroleum industry and the remediation of oil spills”, int. j. mol. sci., vol. 15, pp. 12523-12542, 2010 [23] e. lederer, “viscosity of mixtures with and without diluents”, proc. world pet. congr. lond., vol. 2, pp. 526–528, 1933 [24] a. palacio-pérez, v. gonzalez-davila, “analisis del efecto de un bioreductor de viscosidad”. proyecto sener-conacyt no. 166223, global report, mexico, 2013 [25] g. centeno, g. sánchez-reyna, j. ancheyta, j.a. muñoz, n. cardona, “testing various mixing rules for calculation of viscosity of petroleum blends”. fuel, vol. 90, no. 12, pp. 3561-3570, 2011 [26] fs. arafin, n. al-habsi, s. rahman, “transport properties and model-based dynamical properties of omani crude oils”, arabian journal of geosciences, vol. 5 no. 5, pp. 1085-1092, 2015 [27] s. arafin, s. mujibur rahman, “exact solution for velocity profile of flow of multilayer immiscible liquids”, physics and chemistry of liquids, vol. 53, no. 1, pp. 84-103, 2015 engineering, technology & applied science research vol. 7, no. 3, 2017, 1685-1693 1685 www.etasr.com njah and el hamdi: a constrained multi-objective learning algorithm for feed-forward neural … a constrained multi-objective learning algorithm for feed-forward neural network classifiers mohamed njah control and energy management laboratory (cem lab) digital research center of sfax, tunisia mohamed.njah@enig.rnu.tn ridha el hamdi control and energy management laboratory (cem lab) digital research center of sfax, tunisia ridha.elhamdi@enig.rnu.tn abstract—this paper proposes a new approach to address the optimal design of a feed-forward neural network (fnn) based classifier. the originality of the proposed methodology, called cmoa, lie in the use of a new constraint handling technique based on a self-adaptive penalty procedure in order to direct the entire search effort towards finding only pareto optimal solutions that are acceptable. neurons and connections of the fnn classifier are dynamically built during the learning process. the approach includes differential evolution to create new individuals and then keeps only the non-dominated ones as the basis for the next generation. the designed fnn classifier is applied to six binary classification benchmark problems, obtained from the uci repository, and results indicated the advantages of the proposed approach over other existing multi-objective evolutionary neural networks classifiers reported recently in the literature. keywords-fnn classifier; constrained multi-objective optimization; pareto dominance criterion; differential evolution i. introduction the problem of classification is perhaps one of the most widely studied in the data mining and machine learning communities. classification tasks are widely used in real-world applications, including handwritten characters, detection of faces in images, medical diagnosis and several other tasks [1]. moreover, there are a large number of computational classification systems that are commonly used for classification, such as probabilistic methods, decision trees, rule-based methods, instance-based methods, svm techniques, and neural networks [2, 3]. all these modeling techniques tackle the problem of dividing between two or more classes. classification problems involving multiple classes can be addressed in different ways. one of the most popular techniques consists in dividing the original dataset into twoclass subsets, learning a different binary model for each new subset. this work focuses on feed-forward neural network (fnn) based classifiers for solving two-class classification tasks, that is, classifiers that assign patterns to one of two different classes, typically denoted as positive and negative classes. fnn based classifiers [4] have attracted a lot of research effort during the last 20 years, and they are still one of the hottest research topics in the field of machine learning because of their learning and generalization capability. this however does not imply that a fnn can easily learn the underlying functional mapping between the input data and the desired output. in fact, the main drawbacks of fnns are problems associated with local minima and the slow convergence of the learning process. population-based stochastic search approaches, such as evolutionary algorithms (ea), have been proposed to address the problem of the optimal design of the whole (i.e., input vector, structure, and weights) fnn, since such methods are particularly useful for dealing with complex problems having large search spaces with many local optima. a comprehensive review of these approaches can be found in [5]. however, the use of ea in fnn does not emphasize the trade-off between complexity and accuracy of the fnn based classifier. this trade-off is a wellknown problem in the multi-objective optimization field. in recent years, pareto-based multi-objective algorithms [6] have been adopted for the design of fnn and they have attracted much interest, with promising results. such approaches are usually implemented by means of error minimization while controlling the complexity of the model [6]. in addition, it is generally known, in the framework of binary classifiers, that the sensitivity and the specificity which express, respectively, how well the system classifies patterns belonging to the positive class and to the negative class are also conflicting objectives [7]. therefore, to deal with this antagonism, the use of multi-objective optimization within the evolutionary neural network classifier seems an expected headway. this paper proposes a new constrained multi-objective optimization algorithm (cmoa) to achieve a solution to the learning of a fnn based classifier, characterized by good generalization properties. hence, the primary goal in cmoa is to find or to approximate the set of pareto optimal solutions [8] that results into trade-offs among learning performance (expressed in terms of sensitivity and specificity) and complexity. however, this pareto front includes unacceptable solutions. indeed, it is well known that for each application we could, beforehand, attribute a threshold on the learning engineering, technology & applied science research vol. 7, no. 3, 2017, 1685-1693 1686 www.etasr.com njah and el hamdi: a constrained multi-objective learning algorithm for feed-forward neural … f m = 2*recall*precision recall + precision precision = tp tp + fp and recall = tp tp + fn   1 1 (2)mf min f performance of the desired neural network. if the learning performance is greater than some value, the associated classifier is then considered as unacceptable solution. therefore, cmoa aim at splitting objective space into two areas separating the acceptable solutions from unacceptable ones and uses a specific constraint handling technique based on a self-adaptive penalty procedure in order to direct the entire search effort towards finding only pareto optimal solutions that are acceptable. ii. related works several approaches have been proposed to address the problem of the optimal design of neural network based classifier such as constructive [9], pruning [10], regularization [11] and population-based stochastic search approaches [4]. these approaches, usually, jointly minimize network complexity and empirical error in the form of a single lossfunction that usually consists of an error cost function and a regularizer. although this may result in good generalization models, they are highly dependent on user defined training parameters. in addition, it is generally known that error and complexity are conflicting objectives [6], e.g. reducing the approximation error often leads to an increase of the complexity of the model and consequently, no single optimal solution exists that optimizes all the objectives simultaneously. this viewpoint led to the development of multi-objective machine learning (moml) methods [6]. in recent years, several studies discussed the use of multiobjective approaches, as more promising algorithms, for automatic design of nn-classifiers. in [12], authors proposed a multi-objective evolutionary algorithm called pde (pareto differential evolution), for vector optimization problems. pde algorithm includes differential evolution to create new individuals and then keeps only the non-dominated ones as the basis for the next generation. from the onset of the pde algorithm, and almost in parallel, memetic (i.e. evolutionary algorithms (eas) augmented with local search) pareto artificial neural network (mpann), which is a version of pde with a local search algorithm, was developed in [13] to optimize the number of hidden nodes and the training of anns. in [14], an mpann is applied to breast cancer diagnosis and promising results have been obtained. in [15], pde is used to generate a pareto optimal set of artificial neural networks that act as controllers for the legged locomotion of a quadrupedal robot simulated in a 3-dimensional, physics-based environment. other studies have focused on the problem of multiobjective optimization of nn-classifiers as powerful tools in the domain of face detection [16]. according to [17], the developed hybrid evolutionary algorithm using either scalar fitness or the nsga-ii selection scheme [18] successfully solves the problem of reducing the number of hidden neurons of the nn-classifier without loosing detection accuracy. more recently, in [6] authors provided an overview of the existing research on pareto-based multi-objective learning algorithms. a number of machine learning case studies are provided to show the main benefits of the pareto-based approach versus single-objective learning. three approaches of pareto-based multi-objective ensemble generation are compared and discussed, in terms of how to generate classifiers, how to choose which classifier among them and which ones have formed the ensemble. pareto-based multi-objective algorithms have been also adopted for the design of radial basis function networks (rbfns) and they have attracted much interest in recent years, with promising results [19-21]. in [22], authors studied the use of specific techniques for selecting the best artificial neural model with sigmoid basis units from a multiobjective evolutionary algorithm called mpdenn algorithm based on the pde algorithm [12] and on the local search algorithm irprop [23]. these techniques are based on choosing the best models for training in the two objectives, the correct classification rate and the minimum sensitivity. these techniques are compared with three standard selection methodologies with very promising results. iii. background materials a. performance measures in the framework of fnn based classifiers, the accuracy of a classifier is, usually, evaluated in terms of percentage of correct classifications, and the objective of a classifier identification process is to maximize this percentage. this objective might not be appropriate for the application domains characterized by highly imbalanced distributions of patterns, with positive cases composing just a small fraction of the available data used to train the classifier, or when the cost of misclassification of the positive patterns is different from the cost of misclassification of the negative patterns [24]. in order to avoid these deficiencies, other evaluation measures [25] have been defined in the literature. generally, these evaluation metrics are built from a confusion matrix (table i). table i. confusion matrix for a two-class classification task decision: prediction class positive negative true class positive true positives (tp) false negatives (fn) negative false positives (fp) true negatives (tn) based on the confusion matrix, a popular measure has been proposed [7] as one of the most relevant metric to imbalanced data. this measure, called f-measure (fm), is defined as the harmonic mean of recall and precision: (1) where the recall, also known as sensitivity or true positive rate, refers to the proportion of samples belonging to the positive class (true positives), which were correctly predicted as positive. precision is the proportion of true positive samples among all samples that are predicted as being positive. b. pareto fitness assignment the two objectives that are considered, under the cmoa approach, to control the learning performance and the complexity of the fnn based classifier are: engineering, technology & applied science research vol. 7, no. 3, 2017, 1685-1693 1687 www.etasr.com njah and el hamdi: a constrained multi-objective learning algorithm for feed-forward neural … s i = n i n η = 1− r a r a = nb of acceptable solutions population size 31 20 ( ( )) 0.5 (8) 1 pp p c i i i i if y f y y y else ìï + £ï= í ïïî 31 2 1 ( ) [0 (7) ,1]pp pc i i i i p i x f x x if u cr x x else ìï + £ï= í ïïî { }2 2min (3)f w= the minimization of the l2_norm of hidden-layer weights (f2) is a conventional manner to control the size of the network complexity [26]. in our problem formulation, we use only one hidden layer of neurons, as dictated by the universal approximation capability theorem for neural networks [27]. the cmoa approach includes differential evolution [28] to create new individuals and then keeps only the non-dominated ones as the basis for the next generation. the population is sorted according to the pareto dominance concept [6]. once a pareto front is built, each individual i in the pareto front (a nondominated solution) is assigned a fitness value fi. (4 1 ( 1) )ii i s if i is an acceptable solution f s otherwiseh ì +ïï= í ï +ïî the fitness value of an individual i depends on its strength value si[0, 1], representing the number of solutions it dominates, divided by the population size n. (5) if the individual is unacceptable, a penalty factor [0, 1] is used. (6) where in (4), 1 is added to ensure that the fitness value of an individual is greater than zero. this is quite interesting because not only individuals that correspond to the two extremes of the pareto front may have null strength values (they are not dominated by any of the individuals of the population) but also individuals that correspond to the middle of the pareto front, especially in last generations. moreover, the use of a selfadaptive penalty (sap) procedure based on the penalty factor  is very promising since it requires no parameter tuning. the method keeps track of the percentage of acceptable individuals in the population (as illustrated in figure 1) to determine the amount of penalty applied to unacceptable individuals. if there are a few acceptable individuals in the whole population (usually in early generations), a penalty factor (1σφάλμα! τα αντικείμενα δεν μπορούν να δημιουργηθούν από την επεξεργασία κωδικών πεδίων.) is applied to unacceptable solutions. otherwise, a penalty factor (0) is used. as discussed earlier, cmoa aims at splitting objective space into two areas, separating the acceptable solutions from unacceptable ones and uses a constraint handling technique based on a self-adaptive penalty method so as to direct the entire search effort towards finding only pareto optimal solutions that are acceptable. c. differential evolution differential evolution (de) [28] is a simple, but powerful algorithm that simulates natural evolution combined with a mechanism of generation of multiple search directions based on the distribution of solutions (vectors) in the current population. in de, a child is generated applying the crossover operator to three parents (p1, p2 and p3). the resultant child is a perturbation of the main parent (p1). aonly 12 percent of solutions are acceptable b68 percent of solutions are acceptable fig. 1. illustration of fitness computation for cmoa with regard to the percentage of acceptable solutions if we consider xip1, xip2 and xip3 the ith parametric genes respectively of parents p1, p2 and p3, the ith parametric gene of the child c (i.e. xic) is generated as follows: where f[0, 1] is an amplification factor also called "differential weight". cr is the rate of crossover and u is a random fraction in the [0, 1] interval. once the child parametric genes are generated, we proceed to apply the same principle of differential evolution for structural genes to determine the structure of the child to generate. if we consider yip1, yip2 and yip3 the ith structural genes respectively of parents p1, p2 and p3, the ith structural gene of the child c (i.e. yic) is generated as follows [22]: engineering, technology & applied science research vol. 7, no. 3, 2017, 1685-1693 1688 www.etasr.com njah and el hamdi: a constrained multi-objective learning algorithm for feed-forward neural … yes randomly initialize the population by individuals of different sizes stop = false evaluate each individual in the population using the pareto dominance criterion identify non-dominated individuals from next pareto front the number of the non-dominated individuals > 3 identify these individuals compute the fitness values (equation 4) of identified non-dominated individuals delete all individuals who are not identified (dominated individuals) from the population. (let e : the number of deleted individuals) accept = false, i = 0 population size = n or stop = true randomly select three distinct individuals (parents) p1, p2 and p3 no no yes yes no the main parent (p1) is the individual with the greatest crowding distance more than one individual have the same greatest fitness value the main parent (p1) is the individual with the greatest fitness value no yes generate a child from the three parents using differential evolution compute the fitness value (equation 4) of the generated child place the child into the population according to the replacement procedure remove dominated and not acceptable solutions stop = false select the solution with the best generalization error end start fig. 2. overall flowchart of cmoa iv. constrained multi-objective optimization algorithm (cmoa) the proposed cmoa approach can be described as shown in figure 2. the algorithm starts generating a random population of individuals of different sizes. the population is sorted according to the non-domination concept and dominated individuals are removed from the population. the remaining non-dominated solutions are retained for reproduction. as the de strategy requires at least three different non-dominated individuals, we allow the algorithm to consider the nondominated individuals of the second pareto front if the first edge is composed of only one or two individuals. three parents are selected at random. the individual with the best fitness value (4) is considered as the main parent and the other two as supporting parents. if more than one parents share the same best fitness value, a crowding distance measure [18] was used engineering, technology & applied science research vol. 7, no. 3, 2017, 1685-1693 1689 www.etasr.com njah and el hamdi: a constrained multi-objective learning algorithm for feed-forward neural … to select the main parent in order to produce and maintain welldistributed solutions. a child is generated from the three parents and is placed into the population according to a replacement procedure (figure 3). this process continues until the population is completed.the replacement procedure is used so as to ensure convergence of the algorithm. in fact, it attempts, from one generation to another:  to improve the quality of the pareto frontier by adding at least one offspring individual that dominates his main parent.  or to increase the number of pareto optimal solutions on the pareto frontier by adding at least one offspring individual that is non-dominated with respect to the current subpopulation of parents. in other words, the generated child should not, therefore, be dominated neither by v1 nor by v2, where v1 and v2 are the two non-dominated individuals neighbours with regard to the generated offspring. iterations are terminated when none of the e generated offspring individuals satisfy the condition of the replacement procedure (e is the same number of deleted individuals in the current population). for the application of the proposed method, we have to select only one preferred solution. to facilitate the selection task, dominated and unacceptable solutions are removed at the end of the multi-objective optimization. the best representative solution is, then, chosen from the remaining pareto frontier individuals based on the generalization error computed on a test set. v. experimental results the cmoa approach was developed and implemented using xcode version 7.2 under a mac os x 10.11.2 workstation. to examine the performance of cmoa, we consider six benchmark classification problems, selected from the uci repository. table ii gives a brief description of the selected datasets. fig. 3. replacement procedure table ii. description of the selected datasets dataset patterns attributes % positive % negative breast cancer 683 9 35 65 australian card 690 14 44.5 55.5 ionosphere 351 34 64.1 35.9 german 1000 61 70 30 pima 768 8 34.9 65.1 heart 270 13 44.45 55.55 figure 4 and figure 5 show the effect of the application of the self-adaptive penalty (sap) procedure on the final solutions. these results are achieved using respectively the first and the second dataset. these two figures show clearly that the sap procedure discards unacceptable solutions. their number becomes very limited at the end of calculations, when the sap procedure is applied. however, when the sap procedure is not applied to the algorithm, the proportion of unacceptable solutions remains hight and this influences the quality of the solution obtained at the end of calculation. in terms of computational time, the total number of generations in both cases (using or without sap) does not seem to differ much. in order to know how competitive the proposed method is, we decided to compare it against two relevant pareto-based multiobjective learning algorithms called mpann and mpensga2. mpensga2 (memetic pareto evolutionary nsga2) was introduced in [29]. it tries to boost two conflicting main objectives: the best model in accuracy and the best model in sensitivity. concretely, a memetic version of nsga2 [18], which introduces the irprop+ algorithm [23] as a local optimizer adapted to the softmax activation function and the cross-entropy error function, designs the anns architecture finding an adequate number of neurons in the hidden layer and an adequate number of connections along with their corresponding weights. the comparison was conducted using a stratified holdout procedure with 30 runs, where approximately 75% of the patterns were randomly selected for the training set and the remaining 25% for the test set. in each execution, once the first pareto front is calculated, we chose the extreme values in training, that is, the best individual in the two objectives that are considered. in this paper, we denote :  m1: the methodology using the proposed cmoa approach and the extreme chosen individual is the one that has better learning performance (2).  m2: the methodology using the proposed cmoa approach and the extreme chosen individual is the one that has better complexity of the fnn based classifier (3).  m3: the methodology using the mpensga2 approach and the extreme chosen individual is the one that has better entropy.  m4: the methodology using the mpensga2 approach and the extreme chosen individual is the one that has better sensitivity. engineering, technology & applied science research vol. 7, no. 3, 2017, 1685-1693 1690 www.etasr.com njah and el hamdi: a constrained multi-objective learning algorithm for feed-forward neural … alast population (498) using sap blast population (511) without sap fig. 4. effect of the use of the self-adaptive penalty (sap) procedure on the final solutions (breast cancer) alast population (490) using sap blast population (500) without sap fig. 5. effect of the use of the self-adaptive penalty procedure on the final solutions (australian card)  m5: the methodology using the mpann approach and the extreme chosen individual is the one that has better error (mse).  m6: the methodology using the mpann approach and the extreme chosen individual is the one that has better ann complexity (number of hidden units). table iii presents the values of average and standard deviation for accuracy and sensitivity for the testing set of each dataset obtained for the best models in each run. statistical results achieved from mpensga2 and mpann are obtained from [29]. a first analysis of the results, illustrated in table iii, shows that the performance of the proposed method is competitive or comparable to both mpann and mpensga2. from a statistical point of view, these comparisons are possible because we use the same partitions of the datasets. in other cases, it is difficult to justify the equity of the comparison procedure. the results reported in table iii show also that the developed method cmoa achieves slightly better standard deviation in most datasets. it is interesting to see the small standard deviation for the test performances, which indicates consistency and stability of the used method. the proposed approach is also compared against three multi-objective learning algorithms, proposed in [19, 20] for the design of radial basis function networks (rbfns). these algorithms are named memetic pareto particle swarm optimization based rbfn (mppson), memetic elitist pareto non-dominated sorting genetic algorithm based rbfn (mepgan) and memetic elitist pareto non-dominated sorting differential evolution based rbfn (mepden). these algorithms have been tested based on two and three objective functions. the first one (f1) is the accuracy based on meansquared error (mse) on the training set. the second objective function (f2) concerns the complexity of rbf network and is computed based on the number of hidden nodes in the hidden layer. the last one (f3) concerns also the complexity of the network and is computed based on the norm of the centers and weights of the rbf network. the comparison was carried out on the same datasets used in both this paper and those two references [19, 20], i.e. the first and the last two datasets shown in table ii. the results were obtained by 10-fold crossvalidation for all datasets. each dataset is divided into ten subsets of equal size. one subset is used as the testing dataset, and the other nine subsets are used as the training dataset. engineering, technology & applied science research vol. 7, no. 3, 2017, 1685-1693 1691 www.etasr.com njah and el hamdi: a constrained multi-objective learning algorithm for feed-forward neural … breast cancer pima heart cmoa 97,46 78,95 87,28 mppsonf1f2 97,66 77,34 85,2 mppsonf1-f3 97,81 78,25 85,54 mepganf1f2 96,78 72,78 79,07 mepganf1-f3 97,8 68,35 80,79 mepdenf1f2 96,93 77,07 84,17 mepdenf1-f3 97,66 78,76 87,54 cmoa cmoa cmoa mppso nf1f2 mppso nf1f2 mppso nf1f2 mppso nf1-f3 mppso nf1-f3 mppso nf1-f3 mepg anf1f2 mepg anf1f2 mepg anf1f2 mepg anf1-f 3 mepg anf1-f 3 mepg anf1-f 3 mepd enf1f2 mepd enf1f2 mepd enf1f2 mepd enf1-f 3 mepd enf1-f 3 mepd enf1-f 3 0 10 20 30 40 50 60 70 80 90 100 a cc ur ac y amean testing accuracy breast cancer pima heart cmoa 97,5 61,21 87,28 mppsonf1f2 97,08 60,36 82,53 mppsonf1-f3 97,48 60,36 86,21 mepganf1f2 96,25 45,2 66,76 mepganf1-f3 96,65 20,37 67,69 mepdenf1f2 96,67 58,86 80,22 mepdenf1-f3 97,08 61,5 83,19 cmoa cmoa cmoa mppso nf1f2 mppso nf1f2 mppso nf1f2 mppso nf1-f3 mppso nf1-f3 mppso nf1-f3 mepg anf1f2 mepg anf1f2 mepg anf1f2 mepg anf1-f 3 mepg anf1-f 3 mepg anf1-f 3 mepd enf1f2 mepd enf1f2 mepd enf1f2 mepd enf1-f 3 mepd enf1-f 3 mepd enf1-f 3 0 10 20 30 40 50 60 70 80 90 100 se n si ti vi ty bmean testing sensitivity breast cancer pima heart cmoa 97,96 89,2 92,1 mppsonf1f2 97,07 84,4 84,38 mppsonf1-f3 97,97 87,8 85 mepganf1f2 97,08 87,11 89,38 mepganf1-f3 98,42 94 91,88 mepdenf1f2 97,08 86,2 87,5 mepdenf1-f3 97,98 88 91,25 cmoa cmoa cmoa mppso nf1f2 mppso nf1f2 mppso nf1f2 m ppson f1-f3 mppso nf1-f3 mppso nf1-f3 mepg anf1f2 mepg anf1f2 mepg anf1f2 mepg anf1-f 3 mepg anf1-f 3 mepg anf1-f 3 mepd enf1f2 mepd enf1f2 mepd enf1f2 mepd enf1-f 3 mepd enf1-f 3 mepd enf1-f 3 75 80 85 90 95 100 sp ec i ic it y cmean testing specificity fig. 6. performance comparisons of the proposed and existing methods on the testing set engineering, technology & applied science research vol. 7, no. 3, 2017, 1685-1693 1692 www.etasr.com njah and el hamdi: a constrained multi-objective learning algorithm for feed-forward neural … this train and test process is repeated so that all subsets are used as a testing dataset. the summary of performance comparisons of proposed and existing methods on the testing set is shown in figure 6. it can be observed from figure 6 that, for the breast cancer dataset, there are no significant differences between the analyzed methods in terms of accuracy and sensitivity. however, in terms of specificity, it can be observed that the proposed cmoa approach outperforms algorithms using two objective functions (mppsonf1f2, mepganf1f2 and mep denf1f2) and is competitive to algorithms using three objective functions (mppsonf1-f3, mepganf1-f3 and mepdenf1-f3). for pima and heart datasets, cmoa is better or at least competitive to other algorithms except mepganf1f2 which has demonstrated the best specificity values (94 %) for pima dataset. however, for this dataset, mepganf1f2 performs poorly, in terms of accuracy and sensitivity, with respect to other algorithms. vi. conclusion this study constructs a novel methodology for implementing pareto-based multi-objective optimization within the evolutionary neural network classifier. using six binary classification benchmark problems, obtained from the uci repository, the proposed approach was shown to be competitive to older works. the results gave also a useful insight on the impact of using the self-adaptive penalty (sap) procedure. for future work, we will evaluate the performance of the proposed method on regression problems. another interesting issue that rises from this work is how to extend the proposed methodology to work with other kind of classifiers. table iii. mean testing accuracy c(%) and sensitivity s(%) for the different methods breast cancer method c(%) s(%) m1 97.52±0.21 97.14±0.48 m2 97.17±1.06 97.29±0.36 m3 95.87±0.61 90.94±1.68 m4 95.60±0.85 90.72±1.84 m5 96.04±1.08 92.75±3.40 m6 96.27±1.00 93.30±3.36 australian card method c(%) s(%) m1 87.87±0.81 87.11±0.36 m2 87.89±0.41 86.74±0.78 m3 88.07±1.57 86.13±2.73 m4 88.25±1.39 86.84±2.00 m5 87.59±1.18 85.95±1.98 m6 87.78±2.49 85.83±4.43 ionosphere method c(%) s(%) m1 92.37±0.21 83.04±1.01 m2 92.33±0.21 82.44±0.33 m3 92.65±2.22 82.41±5.36 m4 92.08±2.30 82.40±4.14 m5 91.10±2.37 79.17±5.99 m6 91.10±2.37 79.17±5.99 german method c(%) s(%) m1 77.17±0.66 74.56±0.98 m2 75.87±0.61 74.64±0.28 m3 75.31±1.44 51.16±4.10 m4 71.55±1.87 86.80±3.11 m5 73.61±1.80 48.89±5.33 m6 73.76±1.77 48.76±5.44 pima method c(%) s(%) m1 78.93±0.51 71.24±0.68 m2 78.42±0.71 71.21±0.24 m3 78.99±2.81 60.45±2.59 m4 76.96±2.09 72.69±3.07 m5 78.54±2.80 59.65±3.71 m6 78.28±2.03 58.86±3.86 heart method c(%) s(%) m1 83.81±0.61 85.04±0.43 m2 83.57±0.63 84.94±0.27 m3 78.28±1.76 61.89±2.09 m4 77.50±1.73 62.67±2.38 m5 76.91±1.10 62.68±2.21 m6 76.91±1.10 62.68±2.21 references [1] c. aggarwal, data classification: algorithms and applications, 1st edition. chapman and hall/crc, 2014 [2] r. ramli, h. arof, f. ibrahim, m. y. i. idris, a. s. m. khairuddin, “classification of eyelid position and eyeball movement using eeg signals”, malaysian journal of computer science. vol. 28, no. 1, pp. pp. 28-45, 2015 [3] s. m. a. kalaiarasi, s. gopala, c. ali, t. jason, “artificial neural network tree approach in data mining”, malaysian journal of computer science, vol. 20, no. 1, pp. 51-62, 2007 [4] v. chaitali, b. nikita, m. darshana, “a survey on various classification techniques for clinical decision support system” international journal of computer applications, vol. 116, no. 23, pp. 14–17, 2015 [5] a. azzini, a. g. b. 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with neural networks: the size of the weights is more important than the size of the network”, ieee transactions on information theory, vol. 44, no. 2, pp. 525–536, 1998 [27] g. dreyfus, j. martinez, m. samuelides, m. b. cordon, f. badran, s. thiria, l. herault, réseaux de neurones: méthodologie et application, eyrolles, 2004 [28] r. storn, “differential evolution research-trends and open questions”, studies in computational intelligence, vol. 143, pp. 1-31, 2008 [29] j. c. fernandez caballero, f. c. h. josé martinez, p. a. gutiérrez, “sensitivity versus accuracy in multiclass problems using memetic pareto evolutionary neural networks”, ieee transactions on neural networks, vol. 21, no. 5, pp. 750–770, 2010 microsoft word 39-3316_s_etasr_v10_n1_pp5314-5319 engineering, technology & applied science research vol. 10, no. 1, 2020, 5314-5319 5314 www.etasr.com filipova-petrakieva & shopov: electrical device protection from overvoltage in a dc power supply … electrical device protection from overvoltage in a dc power supply network fast-acting protection, realized by an “artificial” short circuit in the input of the protected device simona filipova-petrakieva department of theory of electrical engineering faculty of automatics technical university of sofia sofia, bulgaria petrakievas-te@tu-sofia.bg jordan shopov department of electrical apparatus faculty of electronics and automation technical university of sofia sofia, bulgaria shopov@tu-sofia.bg abstract—in the present paper a protective device based on the so-called “artificial” short circuit in the input of the network, is proposed. to ensure the necessary time for switching on the protection, the increased power supply voltage is delayed to reach in the input of the protected device by additional inductance l, which is connected in series to the power supply. as a result of this forced short circuit, the dc-power supply is switched off by a standard protective circuit-breaker. the short circuit is realized by a fast-acting semi-conductor device (e.g. diac + thyristor, etc.). the controlling signal is formed as a voltage across a capacitor that is a part of rc-circuits connected in parallel to the dcpower supply network. an analytical expression for this voltage, using a classical method for transient analysis, is obtained. the main aim is to determine the exact time of switching on the protection. the research is confirmed with simulations by orcad pspice under the exact values of the elements in the rccircuits considered. two rapid increase cases in the power supply voltage are considered: positive jump and linear increase. the suggested solution is applicable for overvoltage protection of different electrical devices. the electrical scheme, based on the electronic components, ensures a fast-acting breaking, which guarantees secure protection. based on the analytical expressions, the synthesis of the circuit for control and protection is made and the respective values of its elements are calculated. keywords—electrical engineering; electronics; overvoltages; short circuit’s protection by electronic unit; transients analysis by classical method i. introduction many electrical devices have one dc-power supply (either from a current rectifier or from a special network) [1]. during normal operation they are subjected to variations of power supply network parameters. this can lead to exceeding the maximum admissible values guarantying the normal operation of these devices. overvoltage in the dc-power supply network occurs due to different atmospheric influences, switching on and off of large consumers, etc. the normal operation of a number of electrical devices deteriorates and sometimes overvoltage is the cause of damage or breakdown. so, the purpose of this work is to suggest a simple electrical scheme for overvoltage protection. it only consists of rc-groups (figure 1). it guarantees greater reliability than similar protection solutions that use additional electronic elements or controllers [2-5]. the main disadvantage of most of the existing solutions is that they are designed to protect low power and low voltage consumers [6-8]. an additional advantage of the proposed solution is that it can be applied to form the level of the control signal activating the protection at both low and high voltages only by an elementary change in the values and parameters of the elements in the rc groups. there are also simple solutions designed for specialized protection with a specific form of voltage (e.g. dc + triangle voltage form [9]). authors in [10] discuss a variety of protection schemes to ensure protection from faults causing overvoltage supplying some electronic elements working in low voltages. a simple method for protecting the analog channel from overvoltage is resistive input attenuation ahead of a precision operational amplifier. ic device junctions, such as base-collector and jfet gate-source junctions, don't exhibit the same degradation in performance upon breakdown and the input current should be 5ma. overvoltage protection can be achieved using cmos channel protectors. it is possible to break ground loops by using digital isolation techniques. to eliminate a possible damage, a protection based on the so-called “artificial” short circuit in the power supply input of the convertor with semiconductor device s (figure 1) is used. the convertor discharges both from voltage and current which is the main advantage of this method. it is also faster than the protections realized by switching off from the power supply with standard commutation apparatus [11]. in figure 1, a fast-acting commutation apparatus s (e. g. diac + thyristor) that carries out a short circuit in the input of the protected electrical device is shown. a protecting breaker k connected in series with the power supply [11-13] is also shown in this figure. rc-circuits are connected in parallel to s. they form the time and the parameters of the switching off corresponding author: simona filipova-petrakieva engineering, technology & applied science research vol. 10, no. 1, 2020, 5314-5319 5315 www.etasr.com filipova-petrakieva & shopov: electrical device protection from overvoltage in a dc power supply … signal realizing the short circuit. the protected device is marked with “el. device”. fig. 1. a short circuit protection on the input of the convertor the proposed protection is analyzed below. the parameters of the control signal and its variation in order to ensure effective protection are determined. the necessary parameters for different input signals of the circuit can be realized with the variation of the elements’ values. afterwards, an analytical solution for the voltage across the common node of the two discussed rc-circuits during an unexpected change of the power supply voltage is suggested. this change determines both the time dependence of the processes and the parameters of the control signal intended for the commutation apparatus s that carries out a short circuit in the input of the protected device. the classical method for transient analysis is applied [14, 15]. the results from the solution are confirmed with illustrative examples by computer orcad pspice simulations. the paper concludes with remarks about the advantages and disadvantages of the proposed protection and with some perspectives for a future research. ii. problem statement the principal scheme of the proposed protection from overvoltage in dc-power supplying network is shown in figure 2. the processes in the circuits that form both the parameters of the signals and the moments of switching on the protection are very significant. it is necessary to determine the connection between the times and the parameters of the scheme’s elements in order to make a correct choice of their values in each specific case of power supply overvoltage. the fact is that different devices have different parameters, different power supply voltages, etc. in an emergency, the power supply voltage of a given electrical device can rapidly increase. to limit this increase a protective system is necessary to be applied. in the considered case the system is an electric scheme that generates a switching off protective signal applying to a fast commutation apparatus s. in the control circuit of s the device (e.g. diac – not shown in figure 2) is included. it actuates when the voltage in the main node of c1 and c2 exceeds the definite value. the parameters of both the signal and the reaction time of the protection depend on the specific scheme solution and the ratio of the values of the elements. the control signal is proportional to the voltage across the r2c2group. it is essential to have a capacitor in which a sufficient amount of energy is accumulated to activate the protection. when the necessary parameters of the control pulse are reached, the apparatus s switches on and the power supply of the protected electrical device acts as a short circuit. as a result, the input current increases and reaches a value that causes the opening of the breaker к and the power supply voltage is switched off. an additional inductance l can improve the effectiveness of the protection (figure 2(b)). the inductance delays the moment when the increased supply power voltage is switched on at the input of the device. in this way an extra time is ensured for switching on the apparatus s and switching off the breaker k due to the increase of the input current. (a) (b) fig. 2. protective circuit from overvoltages in dc-power supply network: (a) default, (b) with additional inductance l for overvoltage protection this method is better than the laplace transform [16] because on each step of the solution the physical interpretation of the result can be visualized. iii. analytical solution to the transients via classical method in the present paper, an analytical solution based on the classical method (using a set of ordinary differential equations) for determining the transient of the voltage 2 ( ) c u t (figure 3) is proposed. this transient appears when the power supply voltage increases rapidly and the electrical device should be protected. two cases of power supply overvoltage are considered: • positive jump of the power supply voltage (figure 4(а)) ( )1 0( ) vu t u u= > . • linear increasing the power supply voltage (figure 4(b)) ( )0( ) . vu t u kt= + since the studied electric circuit consists of two parallel rc-groups connected in series, then the transients are of the 1 st u r r c c s el. device r k u r r c c s el. device r k u r r k c c s el. device r l engineering, technology & applied science research vol. 10, no. 1, 2020, 5314-5319 5316 www.etasr.com filipova-petrakieva & shopov: electrical device protection from overvoltage in a dc power supply … order. so, in both cases mentioned above, the transient 2 ( ) c u t satisfies the aperiodic law: ( ) 2 ( ) . v trans t t c u t ae − = (1) where the time constant is: ( ) ( ) ( )1 2 1 2 1 2 . , s r r c c t r r + = + . the initial conditions also are the same for both cases: ( ) ( ) 2 2 0 2 1 2 . (0 ) (0 ) v c c u r u u r r + −= = + (2) fig. 3. input protection rc-circuit (a) t (s) u (t) (v) 0 u 0 u 1 (b) t (s) u (t) (v) 0 u 0 fig. 4. (a) positive jump of the power supply voltage, (b) linear increase of the power supply voltage however, the new steady states are different: • if ( )1 0( ) vu t u u= > , then ( ) ( ) 2 1 2 1 2 . ( ) v steady statec u r u t r r = + (3a) • if ( )0( ) . vu t u kt= + , then: ( ) ( ) ( ) ( ) 2 0 2 1 2 0 2 1 2 1 1 1 2 22 1 2 . . ( ) . . . . . . v steady statec u r k u t t r r u r k r r r rc r c k r r = + + + + −   + (3b) the final solution about the transient is: ( ) 2 2 2 2 ( ) ( ) ( ) . ( ) v trans steady state steady state c c c t t c u t u t u t ae u t − = + = = + (4) for each of the analyzed cases the following results are obtained: • when ( )1 0( ) vu t u u= > ⇒ ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 1 2 1 2 0 1 2 1 2 1 2 1 2 1 2 . ( ) v . . s steady statec u r u t r r u u r a r r r r c c t r r = + − = + + = + (4а) • when ( )0( ) . vu t u k t= + ⇒ ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 0 2 1 2 0 2 1 2 1 1 1 2 22 1 2 0 2 1 2 2 1 1 2 1 2 1 2 1 2 1 2 . . ( ) . . . . . v . . . . s steady statec u r k u t t r r u r r r r rc r c k r r u r r r c rc k a r r rr c c t r r = + + + + + −   + − = + + = + (4b) in the present paper the proposed power supply overvoltage protection will switch on (the commutation apparatus s will be a short circuit in the input of the protected device) when the threshold value of the capacitor voltage has been reached, i.e. 2 ( ) transc threshold u t u= . iv. illustrative example a scheme for power supply overvoltage protection is considered (figure 2). without some special considerations the power supply voltage of u0=300v is chosen. note that in normal operation the power supply voltage can deviate up to 20% from the nominal one, i. e.: ( ) [ ] ( )0 300 20 % 240, 360 vu v= ± = . the protection has to be set in such a way that it switches on only when the upper bound of the power supply voltage is exceeded.the commutation apparatus s has to switch on when the threshold voltage uthreshold=20v according to the chosen semi-conductor element (e.g. diac), which watches on the value of the control signal (in the common point of the rc-groups. 0 15 threshold u u η = = (5) u(t) r r k c c u (t) 2 engineering, technology & applied science research vol. 10, no. 1, 2020, 5314-5319 5317 www.etasr.com filipova-petrakieva & shopov: electrical device protection from overvoltage in a dc power supply … the relation between the resistors 1 r and 2 r is given by: 1 2 2 15 r r r η + = ≤ (6) to ensure a normal exploitation, the voltage across the capacitor c2 has to be smaller than the threshold voltage of switching on the commutation apparatus s, i.e.: ( ) ( ) 2 2 0 2 1 2 . 0 0 c c threshold u r u u u r r + −= = ≤ + (7) 10.424 v 20v< (7a) on the base of (6) and (7), (7a), the values of the resistors r1=100kω and r2=3.6kω are determined. the capacitances of the capacitors c1 and c2 determine the speed of variation and the time of the transients. the latter fade away faster when these values are smaller, because in this case the time constants are also smaller. the specific values are determined based on the following condition: the energy stored in the capacitor c2 has to be enough to activate the apparatus s. the switching time depends on the thyristor and it is up to tens of microseconds. as an illustration of the process, the following values are chosen: c1=2nf and c2=200nf. the analysis of the two considered cases follows. • positive jump of the power supply overvoltage (figure 4(a)), when u(t)=u1=600v • linear increasing of the power supply overvoltage (figure 4(b)), when u(t)=u0+kt=300+50000t (v). simulations with orcad pspice were conducted. the scheme and the results are shown in figures 5-7. fig. 5. simulation of the overvoltage protective circuit in a dc-power supply voltage the time for switching on the proposed protection for both cases of overvoltage in the power supply network is analytically calculated by (4), (4а) and (4b) and it is determined by the simulations’ graphs. the results are shown in table i. the relative errors from the analytical solution and from the simulations for both cases are 12.99% and 0.33% respectively. table i. time for switching on the protection input power supply voltage analytical solution simulation solution u(t)=u1=600v 1.77 (ms) 1.54 (ms) u(t)=u0+kt=300+50000t 6.02 (ms) 6 (ms) fig. 6. voltage 2 ( ) c u t in a positive jump of the dc-power supply voltage engineering, technology & applied science research vol. 10, no. 1, 2020, 5314-5319 5318 www.etasr.com filipova-petrakieva & shopov: electrical device protection from overvoltage in a dc power supply … fig. 7. voltage 2 ( ) c u t in a linear increasing dc-power supply voltage v. conclusion in the present paper, a method of control and protection of the electrical devices (usually electronic) from overvoltage in power supply network is suggested. it is realized by a short circuit in the input of the protected device. the proposed approach for dc surge protection is based on basic theoretical knowledge. its innovation is the simple calculation of the time for activating the protection by using the classical transient analysis method without the need for mathematical processing using matlab or other similar software. another major advantage is that this scheme is applicable to arbitrary values of the supply voltage and its form: dc-jump, linear, saw, etc. unlike other schemes (with a resistive divider only), the use of rc-groups in this work increases the sensitivity of the offered protection. it can also be used to form control and protection signals at both low and high voltages in low and high power consumers. to ensure the necessary time for switching on the protection, the increased power supply voltage is delayed to reach the input of the protected device by an additional inductance l, which is connected in series to the power supply. two cases of rapid increase of the power supply voltage are considered: positive jump and linear increase. analytical expressions for the voltage 2 ( ) c u t which determine the moment of switching on the protection are given for each case. the expressions are obtained using the classical method for transient analysis. the main advantage of the classical method for transient analysis is that in each step of the solution, one should take in mind the physical interpretation of the processes considered while it is not necessary when using other known methods such as laplace transform, duhamel’s integral, state space method, fourier transform, etc. one disadvantage of the classical method for transient analysis is the tedious and long description during the solution. based on the analytical expressions, the synthesis of the circuit for control and protection is made and the respective values of its elements are calculated. the respective moments for switching on the protection are determined analytically and by simulations. the resulting relative errors are 12.99% and 0.33%, respectively. this shows that the simulations confirm the final analytical solution. the differences are due to the different rounding methods applied during the calculations. a possible perspective for future research of the problem considered in this paper is to obtain the analytical expression for the control signal to the commutation apparatus s, using duhamel’s integral. acknowledgment the authors are grateful to the scientific research sector of the technical university of sofia for their financial support. references [1] m. h. rashid, power electronics handbook, 4 th edition, pp. 27-54, elsevier, 2018 [2] h. v. nguyen, h. nguyen, m. t. cao, k. hung le, “performance comparison between pso and ga in improving dynamic voltage stability in anfis controllers for statc”, engineering, technology & applied science research, vol. 9, no. 6, pp. 4863-4869, 2019 [3] d. n. truong, v. t. bui, “hybrid pso-optimized anfis-based model to improve dynamic voltage stability”, engineering, technology & applied science research, vol. 9, no. 4, pp. 4384-4388, 2019 [4] d. d. tung, n. m. khoa, “an arduino-based system for monitoring and protecting overvoltage and undervoltage”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4255-4260, 2019 [5] on semiconductor, ncp346, overvoltage protection ic, semiconductor components industries llc, available at: https://www.onsemi.com/ pub/collateral/ncp346-d.pdf engineering, technology & applied science research vol. 10, no. 1, 2020, 5314-5319 5319 www.etasr.com filipova-petrakieva & shopov: electrical device protection from overvoltage in a dc power supply … [6] http://www.learningaboutelectronics.com/articles/overvoltageprotection-circuit.php [7] https://www.electroschematics.com/overvoltage-protection-circuit/ [8] https://www.sunpower-uk.com/glossary/what-is-over-voltage-protection/ [9] https://electronics.stackexchange.com/questions/452529/overvoltageprotection-circuit-for-5v-limit [10] w. jung, w. kester, j. bryant, j. buxton,w. freeman, “overvoltage protection – section 9.4”, in: data conversion handbook, pp. 793-822, newnes, 2005 [11] m. mintchev, electric arc breaking with contactless elements in electrical devices for low voltage, msc thesis, sofia, bulgaria, 1987 (in bulgarian) [12] m. mintchev, p. penchev, contactless apparatus, technica, 1976 (in bulgarian) [13] m. mintchev, n. trifonov, manual for contactless apparatus design, technica, 1987 (in bulgarian) [14] l. r. neuman, k. s. demirchian, basic of theoretical electrical engineering: linear electric circuits’ theory, vol. 1, no. 2, energy, 1976 (in russian) [15] g. cherneva, p. ivanov, “approaches for modeling electronic schemes with key elements”, меchanics transport communications, vol. 16, no. 3, article id 1710, pp. vii-60-vii-66, 2018 (in bulgarian) [16] k. milanov, h.. antchev, “fast-acting protection of a semiconductor converter by means of short-circuiting thyristor”, 10th electrical engineering faculty conference, santa marina, sozopol, bulgaria, september 11-14, 2018 authors profile simona filipova-petrakieva was born in sofia, bulgaria in 1971. she received her bsc and msc in electronics and automatics in the technical university of sofia, bulgaria (1994). she defended a phd thesis in electrical engineering, electronics and automatics, theory of electrical engineering there (2005). from 2009 she teaches as an associate professor in the department of theory of electrical engineering, faculty of automation, tu-sofia, bulgaria. her research interests include theory of electrical engineering, cluster analysis, graphs theory, interval methods for analysis and synthesis of linear circuits and systems, discrete event systems, and discrete structures in mathematics. she teaches theory of electrical engineering and discrete structures in mathematics. she is a reviewer for many scientific journals, such as the journal of abstract and applied analysis, the journal of applied numerical mathematics, the journal of mathematical communication, the arabian journal for science and engineering, etc. yordan metodiev shopov was born in gulabnik, bulgaria, (1943). he received his bsc and msc in electrical machine and apparatus in the technical university of sofia, bulgaria (1969). he defended a phd thesis in electrical engineering, electronics and automatics, theory of electrical apparatus there (1978). from 1995 he teaches as an associate professor in the department of electrical apparatus, faculty of electrical engineering, tu-sofia, bulgaria. his research interests include power supply current sources, plasma technologies, telecommunication power sources, converters for electro-technologies, and testing stends and devices for stabilization the ac voltage and home electrical appliances. he teaches electrical apparatus, industrial technologies, production technologies, technologies in electrical engineering and electronics, circuit design, power electronics, contactless apparatus, and home appliances. invention: “device for reversely supplying of the loads with back e.m.f.”. microsoft word 02-al ammar.doc etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 84-89 84 www.etasr.com al-ammar: application of using hybrid renewable energy in saudi arabia application of using hybrid renewable energy in saudi arabia essam a. al-ammar department of electrical engineering king saud university saudi arabia essam@ksu.edu.sa nazar h. malik department of electrical engineering king saud university saudi arabia nmalik@ksu.edu.sa mohammad usman department of electrical engineering king saud university saudi arabia musman@ksu.edu.sa abstract— one of the major world wide concerns of the utilities is to reduce the emissions from traditional power plants by using renewable energy and to reduce the high cost of supplying electricity to remote areas. hybrid power systems can provide a good solution for such problems because they integrate renewable energy along with the traditional power plants. in kingdom of saudi arabia a remote village called al-qtqt, was selected as a case study in order to investigate the ability to use a hybrid power system to provide the village with its needs of electricity. the simulation of this hybrid power system was done using homer software. keywordshybrid, renewable energy, homer, photovoltaic, wind energy i. introductđon renewable energy or “green energy” is defined as the energy generated from natural resources such as sunlight, wind, rain, and geothermal heat, which are renewable. hybrid power systems usually integrate renewable energy sources with fossil fuel based generators to provide electrical power. they are generally independent of large electric grids and are used to feed loads in remote areas. hybrid systems offer better performance, flexibility of planning and environmental benefits compared to the diesel generator based stand-alone system. hybrid systems also give the opportunity for expanding the generating capacity in order to cope with the increasing demand in the future [1-4]. remote areas provide a big challenge to electric power utilities. hybrid power systems provide an excellent solution to this problem as one can use the natural sources available in the area e.g. the wind and/or solar energy and thereby combine multiple sources of energy to generate electricity. a village in the kingdom of saudi arabia, called al-qtqt, was selected as a case-study to investigate the most suitable combination of power sources for the hybrid power system. a simulation is done using homer software [5], and the details of this study are described in this paper. ii. hybrđd power systems hybrid power systems usually integrate renewable energy sources with fossil fuel, (diesel/petrol) based generators to provide electrical power and traditional diesel system acting as back-up in case of lack of the primary source [2]. they are generally independent of large centralized electric grids and are used in remote areas. in these systems, it is possible for the individual power sources to provide different percentages of the total load. for instance, on a cloudy and windy day, when the solar panels are producing low levels of electricity, the wind generator can compensate by producing more electric power. there are generally two accepted hybrid power system configurations: 1. systems based mainly on diesel generators with renewable energy used for reducing fuel consumption. 2. systems relying on the renewable energy source with diesel generators used as a backup supply for extended periods of low renewable energy period or in cases of high load demand [1, 4]. a hybrid power system, as the one shown in figure 1, has the ability to provide 24-hour grid quality electricity to the load. such a system offers better performance, flexibility of planning and environmental benefits compared to the diesel generator based stand-alone system. the operational and maintenance costs of the diesel generator can therefore be decreased thereby improving the performance of operation. further, less fuel is used. the system also gives the opportunity for expanding its capacity in order to cope with the increasing demand in the future. this can be done by increasing either the rated power of the diesel generator, renewable generator or both of them. the advantages of using renewable energy sources for generating power in remote areas are obvious. the cost of transported fuel is usually expensive for such locations. further, using fossil fuel has many concerns on the issue of climate change and global warming. the main disadvantage of a standalone power system using renewable energy is that the availability of renewable energy has daily and seasonal fluctuations which results in difficulties in regulating the output power to cope with the varying the load demand [3]. etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 84-89 85 www.etasr.com al-ammar: application of using hybrid renewable energy in saudi arabia fig. 1. hybrid power systems iii. simulation of hybrid power system using homer software in order to design a mini-grid hybrid power system, one has to be provided with information for the selected location. typical information’s required are; the load profile that should be met by the system, solar radiation for pv generation, wind speed for the wind power generation, initial cost for each component (diesel, renewable energy generators, battery, converter), cost of diesel fuel, annual interest rate, project lifetime, etc. then using these data one can perform the simulation to obtain the best hybrid power system configuration. one of the available tools for this purpose is the homer software from nrel [3]. a. homer simulation procedure homer simulates the operation of a system by making energy balance calculations every hour for each of the 8,760 hours in a year. it finds the least cost combination of components that meet the specified electrical and thermal loads. homer simulates thousands of system configurations, optimizes for life cycle cost, and generates results of sensitivity analyses for most situations [6]. thus homer helps to perform analysis and answer many design questions such as: • which technologies are most cost-effective? • what size should the components have? • what happens to the project’s economics if costs or loads change? • can the renewable sources supply the load? b. village selection the objective of this study was to select a village in a remote area in the kingdom of saudi arabia to study the feasibility of using hybrid power system to supply the load of the village throughout the year. al-qtqt village was chosen for this purpose. it is located at 24°28'36.16"n 46°15'0.86"e and it is about 100 km from riyadh city. fig. 2. annual load profile for this village figure 2 shows the load profile for this village [8]. the simulation process of the hybrid power system for the chosen village was analyzed to see if using the hybrid power system will be feasible or not. it is important to note that this village is already connected to the grid and one additional objective was to see the effect of using hybrid power system and to determine if the village can depend on it. for the chosen village, the renewable energy sources e.g. the solar and wind data is given in table 1 [9]. etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 84-89 86 www.etasr.com al-ammar: application of using hybrid renewable energy in saudi arabia table i. the solar radiation & wind speed readings for the village clearness daily radiation wind speed months index (kwh/m2/d) (m/s) january 0.633 4.310 3.000 february 0.658 5.205 3.000 march 0.639 5.930 3.600 april 0.616 6.422 3.600 may 0.643 7.091 3.000 june 0.678 7.596 3.700 july 0.654 7.254 3.500 august 0.661 7.010 3.500 september 0.691 6.660 2.500 october 0.675 5.598 2.200 november 0.661 4.646 1.100 december 0.626 4.033 2.800 iv. case studies figure 3 shows the general configuration of the hybrid system investigated. when designing the system, different scenarios and conditions need to be considered to simulate all possible cases. each selected case examines the system under a specified set of conditions. case 1: solar plus grid without any constrains this case represent the current condition of the system where the village connected to the grid and the solar is added to the system to see the feasibility of the solar usage but without any constrains imposed. case 2: solar and wind plus grid without any constrains in this case the wind was also added to the system and the specification in homer software was still without any constrains. this was done to see the effect of adding a wind turbine to the system case 3: solar and wind plus grid but with constrains this case represents the same system as the previous case, but it was required that the system should use a minimum renewable fraction. the minimum renewable fraction was varied from 0 % to 50 %. if a wind turbine was removed from the system, then it translates to the case of solar plus grid but with constrains. case 4: diesel, solar and wind without grid and any constrains this case represents the ideal condition for the system where the village is off the grid and the system depends only on the hybrid power plant without any constrains of using a specific portion of renewable energy in the output power from the power plant. case 5: diesel, solar plus wind without grid but with constrains this case is similar to case four but constraints were imposed to use a pre specified percentage of renewable energy in the output power. v. results and discussion the simulations of different cases shows that there are only two main cases i.e. case 3 and case 4 which are of interest. this is due to the fact that the other cases produce only one output, which is the grid, and this is due to not using any constrains in homer software. it is important to note that tariff of electricity are very low in saudi arabia. therefore, if there are no constraints, grid supply will be the most economical for the consumer. for case 3 and case 5 the optimal system types are shown in figure 4 and figure 5. as shown in these figures, the optimal system of the village is the solar and grid only (without wind) because the wind turbines are not feasible for wind speed of less than 3 m/s. in most cases, the wind speed in this village is close to this minimum. thus one will not expect much contribution from the wind turbines in the hybrid system. to obtain the optimal percentage of minimum renewable fraction from economical point of view there are various output costs that must be considered. these are plotted versus the minimum renewable fraction in figures 4a, 4b whereas figure 4c provides the co2 emission values. from the curves of figure 4 it is clear that a minimum renewable fraction (min. rf) of 15%-35% provides the optimal range for costs and emission. further, from figure 5a we can note that at 30% min. rf, the total cost for the system is minimum. although the cost of energy increases with the increase of min. rf, the emissions decrease. table 2 includes a summary of the costs for the system when the min. rf is 30%. here the optimal system consists of solar and diesel. to obtain the optimal percentage of minimum renewable fraction from economical point of view there are various output costs which are plotted versus the minimum renewable fraction as shown in these figures the curves show that the range of 10% -30% of min. rf gives the optimal range for the costs and emissions. in figure 5a it is shown that, at 0% ,the best choice economically is the diesel only system. however, as shown in figure 5b and figure 5c at 20% the system will use more renewable energy, the emissions will be less than the lower values for min. rf and the coe will be slightly higher. table 2 summarizes the costs for 20% of minimum renewable fraction, while table 3 shows a summary of emissions. fig. 3. hybrid power system configuration etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 84-89 87 www.etasr.com al-ammar: application of using hybrid renewable energy in saudi arabia vi. conclusđons to reduce the emissions from traditional power plants, by using renewable energy, and to decrease the high cost of supplying electricity to remote areas, hybrid systems are of considerable importance. hybrid systems are one of the most promising applications of renewable energy technologies in remote areas, where the cost of grid extension is high. since the price of fossil fuel increases with the distance of the location, hybrid energy systems could be an appropriate technology to reduce fuel consumption and environmental hazards. applications of hybrid systems range from small power supplies for remote households providing electricity for lighting or water pumping and water supply to village electrification for remote communities. homer software can be used to analyze and simulate the possible alternatives to decide for the best choice. a village in the kingdom of saudi arabia was selected for the study described in this paper. the load profile of the village as well as the solar emission and wind speed data were used as the inputs to the software. . different scenarios and conditions were considered to cover possible states of the system in the village. five case studies were designed and simulated. the output of the simulation helps to choose the optimal case for the system and the optimal percentage of minimum renewable fraction. it is shown that the optimal case is the solar and grid combination and it represent a system connected to the grid with the addition of using renewable energy. the chosen percentage of minimum renewable fraction, considering cost and emissions, was 30%. table ii. summary of the costs cases costs case 3 case 5 total capital cost($) 20,200,000 16,602,000 total npc($) 55,482,580 35,107,348 total o&m cost($/yr) 2,543,109 43,464 total fuel cost($/yr) 0 1,086,972 total ann. cost($/yr) 4,340,220 2,746,333 coe($/kwh) 0.184 0.116 table iii. emissions of grid only system & hybrid power system emissions (kg/yr) pollutant grid only system hybrid power system carbon dioxide 14,943,271 10,713,995 carbon monoxide 0 0 unburned hydrocarbons 0 0 particulate matter 0 0 sulfur dioxide 64,786 46,450 nitrogen oxides 31,684 22,716 . fig. 4. optimal system type fig. 5. optimal system type etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 84-89 88 www.etasr.com al-ammar: application of using hybrid renewable energy in saudi arabia fig. 4a. total annual cost vs. min. rf fig. 5a. total annual cost vs. min. rf fig. 4b. coe vs. min. rf fig. 5b. coe vs. min. rf fig. 4c. co2 emission vs. min. rf fig. 5c. co2 emission vs. min. rf etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 84-89 89 www.etasr.com al-ammar: application of using hybrid renewable energy in saudi arabia references [1] y. bhikabhai, “hybrid power systems and their potential in the pacific islands”, sopac miscellaneous , report no. 406 , 2005. [2] g. delvecchio, m. guerra, c. lofrumento, f. neri, “a study for optimizing a stand-alone hybrid photovoltaic-diesel system to feed summer loads”, international conference on renewable energy and power quality, icrepq, spain, pp. 167-168, 2005. [3] a. a. setiawan , c. v. nayar, “design of hybrid power system for a remote island in maldives”, the proceedings of the homer webcast nrel usa, 2006. [4] e. mohamed, “hybrid renewable energy systems for the supply of services in rural settlements of mediterranean partner countries hyress project”, 4th european conference pv-hybrid and mini-grid 2008. [5] national renewable energy laboratory (nrel), “homer – analysis of mircopower system options”, https://analysis.nrel.gov/homer/default.asp. [6] national renewable energy laboratory (nrel), “homer the mircropower optimization model fact sheet”, pp. 1-2, 2005. [7] arabic cnn, “egypt enter the era of alternative energy by " kremat " solar station" ,translated from arabic, http://arabic.cnn.com/2009/mme/12/18/kremat.egypt/index.html. [8] saudi electric company, “load profile for al-qtqt village”, 2010. [9] national aeronautics and space administration (nasa), “solar and wind data for al-qtqt village”, 2009. [10] s. m. shaahid, m. a. elhadidy, “technical and economic assessment of grid-independent hybrid photovoltaic–diesel–battery power systems for commercial loads in desert environments”, research institute king fahd university of petroleum and minerals, pp. 9, 2006. microsoft word 44-3604_s_etasr_v10_n3_pp5851-5856 engineering, technology & applied science research vol. 10, no. 3, 2020, 5851-5856 5851 www.etasr.com khoso et al.: a new and efficient nonlinear solver for load flow problems a new and efficient nonlinear solver for load flow problems amjad hussain khoso department of electrical engineering mehran university of engineering and technology jamshoro, pakistan khosoamjadhussain@gmail.com muhammad mujtaba shaikh department of basic sciences and related studies, mehran university of engineering and technology jamshoro, pakistan mujtaba.shaikh@faculty.muet.edu.pk ashfaque ahmed hashmani department of electrical engineering mehran university of engineering and technology jamshoro, pakistan ashfaquehashmani1@gmail.com abstract—load flow (lf) analysis is a fundamental and significant issue in electric power systems. because of the nonlinearity of the power mismatch equations, the accuracy of the nonlinear solvers is important. in this study, a novel and efficient nonlinear solver is proposed with active applications to lf problems. the formulation of the proposed method (pm) and its workflow and mathematical modeling for its application in lf problems have been discussed. the performance of the pm has been validated on the ieee 14-bus and 30-bus test systems against several existing methods. the simulation results show that the pm exhibits higher order accuracy, faster convergence characteristics, smaller number of iterations, and lesser computation times in comparison with the other benchmark methods. keywords-electric power system; load flow; gauss-seidel; newtonraphson; fast decouple; power perturb; efficient method i. introduction most mathematical models arising in science and engineering are complex and nonlinear in nature. nonlinear models relate the unknown quantity implicitly within an equation or a system of equations. such models cannot be solved using traditional analytical methods, and demand the use of efficient and stable numerical methods to yield the approximate solutions to the desired accuracy [1, 2]. such models arise in different areas of science and engineering, for example the colebrook’s equation is a nonlinear model to find pipe flow systems friction factor implicitly when pipe relative roughness and flow reynolds number are known [3, 4], chemical combustions problem, nasa’s wind satellite problem [1], and the power flow analysis model of a system comprising of buses [5]. lf study is the constant flow analysis of a power system. lf study is important for existing power systems and consequent optimum performance, and is crucial in planning to expand power systems. lf studies serve as a basis in different aspects associated with power systems, for example power flow optimization, continuation and online transmission [5-7]. new methods with robust solutions and fast convergence are still searched and these fast methods for the lf problems are needed in the field of power systems, particularly for optimal power factor extraction and improvement, maximum power point tracking in solar photovoltaic systems [8], power electronics with stability and control [7, 9], steady-state and transient stability of power systems [10-13]. one of the old methods for solving the lf problem was the gauss-siedel (gs) method [5, 14-15]. the main drawbacks of the gs method are that it requires a large number of iterations and that it converges slowly. due to these drawbacks, another most commonly used method is the newton-raphson (nr) method, which was proposed for lf studies to overcome the convergence problems of the gs [1416]. in industrial applications, nr method is used widely and it is known as the standard lf method. but, nr method’s ability of fast convergence starts to deteriorate when the size of the power system increases. for improving the convergence of the nr method, new methods such as fast decoupled (fd) and power perturb (pp) [17-18] methods became popular. in this paper, a new and efficient nonlinear solver for scalar nonlinear equations and vector systems is proposed. the application of the pm has been done on the lf problem. the performance of the pm is compared with different widely used benchmark lf methods on ieee-14 and ieee-30 bus standard test systems [19]. through numerical simulations and results, the ascendancy of the pm over gs, nr, fd, and pp methods has been established from the view-points of higher order accuracy, lower power mismatch errors, lesser number of iterations, and computational time. ii. load flow problem formulation an electric network model of the power system has the objective of efficiently solving voltage and power issues of the network at various buses. the lf study gives information about the magnitude and the angle of the voltage, active power in form of real power, passive component of power, i.e. reactive power and power losses for each bus of the power scheme. the bus-wise equations of power (real and reactive) mismatch can be generally described as: ∆�� = ���ℎ − ∑ |�� ||� ||�� | cos(�� − � − �� )���� (1) ∆�� = ���ℎ − ∑ |�� ||� ||�� | sin(�� − � − �� )���� (2) where ∆pi = mismatch in active power at i bus, ∆qi = mismatch in reactive power at i bus, psch = injected active power at i bus, qsch = injected reactive power at i bus, vi∠δi = corresponding author: muhammad mujtaba shaikh engineering, technology & applied science research vol. 10, no. 3, 2020, 5851-5856 5852 www.etasr.com khoso et al.: a new and efficient nonlinear solver for load flow problems complex voltage at i bus, yij∠θij = ijth entry of the admittance matrix, and n = number of power system buses. consider another equation: x = {δpv ∪ δpq ∪ vpq} (3) where δpv and δpq represent the vectors of voltage polar angle at pv and pq buses, whereas vpq is the magnitude of voltage at pq buses. equation (3) defines the unknown array containing the variables of the lf study to be determined. the size of the unknown vector is given by (4): nx = npv + 2npq (4) where, npv and npq are the pv and pq buses numbers, respectively. the iterative algorithm for determining the unknowns is stopped as soon as the pre-specified error tolerance has been achieved, which can be defined in terms of maximum absolute value of mismatch in the powers from (1) and (2), as: max{|∆pi| ∪ |∆qi|} ≤ ε ∀ i (5) equation (5) defines a stopping condition of the lf problem in achieving at most ε error. in the general form of the nonlinear system, (1) and (2) are usually described as: �( ) = 0 (6) iii. some existing methods for lf problems a. gauss-seidel (gs) method the gs method is well-known as the method of successive approximations. the nonlinear system of equations to be solved can be defined by rearranging (6) as: = �( ) (7) let (") be the starting approximation at kth iteration for the unknown x, then the numerical scheme is "#� = �( (")) (8) when the absolute mismatch of any two consecutive iterates is within the desired accuracy bound $, then the desired solution is obtained [12]. b. newton-raphson (nr) method the nr method is used to solve nonlinear scalar equations and systems. given a particular bus system, its lf is often analyzed by the nr method, which is easy to execute and has simple calculations. to consider the solution of a non-linear algebraic equation, with x as a variable, and if x 0 is the starting guess for the solution, then the taylor’s series development of f(x) in the vicinity of initial guess can be truncated to the first order derivative term to yield the nr iterative scheme for each iteration (k) to get the new estimated x as: "#� = " − %(&')%((&') (9) k = 0,1,2,… to solve the nonlinear system (6), we may write (9) as: ("#�) = (")−)& ( ("))*��( (")) (10) where )& is an invertible matrix of first order partial derivatives, usually known as the jacobian matrix. the process defined in (10) continues until the desired accuracy level has been achieved. iv. proposed method motivated from some recent studies of new time-efficient and convergent nonlinear solvers of different engineering problems [1, 3, 4, 17], a two-step method is proposed which is cubically convergent to solve scalar nonlinear equations, nonlinear systems, and the conventional lf problem arising in electrical power systems. a. algorithm of the pm the iterative procedure in the pm involves two steps per iteration to solve (6). the pm uses only one additional midpoint of the jacobian matrix to calculate each iteration when more than one is used in [17]. the main equations of the pm in scalar form are (11) and (12). +(") = (") − %(&('))%((&(')) (11) ("#�) = (") − %(&('))%((,-[&(')#/(')]) (12) where k = 0,1,… b. pm formulation for the lf problem equations (11) and (12) for (6) become: +(") = (") + ∆+(") (13) where ∆+(") = −)&2 (")3 *��( (")) and ("#�) = (") + ∆ (") (14) where ∆ (") = −)& 4 1 27 (") + +(")89 *� �( ") finally, for nonlinear systems, and hence for the lf problem (1)-(5), the pm can be extended as: +(") = (") − )&2 (")3 *��( (")) (15) ("#�) = (") − )& :�; 7 (") + +(")8< *� �( ") (16) the complete process of the pm when applied to solve lf problems is described by the flow chart of figure 1. having obtained the bus and line data of a power system, the pm approaches the solution. the process terminates as soon as the desired accuracy level has been achieved. v. results and discussion the pm is validated on two well-known bus systems: ieee 14and 30-bus test systems’ data [18, 19]. both test systems are parts of the us power system [19]. the 14-bus system engineering, technology & applied science research vol. 10, no. 3, 2020, 5851-5856 5853 www.etasr.com khoso et al.: a new and efficient nonlinear solver for load flow problems comprises of 5 positions described by generators and condensers. on the other hand, the 30-bus system contains a combination of synchronous condensers and generators [18]. the numerical simulations have been performed in matlab with standard double precision arithmetic and the error tolerance was set at most 1e-08. the pm and its performance have been compared with other conventional methods: gs, nr, fd and pp. fig. 1. flow chart of the pm the results of the pm for the ieee 14-bus system are shown in table i, with details about bus-wise voltage profiles with magnitudes (p.u) and angles (p.u) respectively, along with simulated real and reactive powers across generation and load, in mw and mvar. the comparison of the voltage profiles, in form of magnitude and angles, obtained by the pm and other methods are displayed in figures 2 and 3 on ieee 14-bus data, respectively. the pm provides optimal results similar to the other methods’ with better precision and accuracy. the voltage magnitudes have been almost higher than those from all other methods. of all methods, a dissimilar behavior has been observed for pp on ieee 14-bus data for magnitude and angle of voltages across all buses. for solving the nonlinear voltage equations of ieee 14-bus power system for the preset error tolerance the pm takes only 6 iterations, whereas nr, pp, fd and gs, respectively require, 11, 59, 74, and 182 iterations, as shown in figure 4. figure 5 shows the computational time (in seconds) of all methods for the same system. maximum errors are shown in figure 6. the nr and pm methods take almost the same execution time on several runs of the program, whereas the highest time was found for the fd method. table i. pm simulation results for the ieee 14-bus system bus bus voltage power (real p and reactive q) magnitude (p.u.) angle (p.u.) generation load p q p q 1 1.060 0.000 159.22 38.174 30.380 17.780 2 1.045 -1.513 232.00 0.120 0.000 0.000 3 1.010 -13.641 0.000 63.353 131.880 26.600 4 0.992 -10.429 0.000 0.000 66.920 10.000 5 0.999 -8.744 0.000 0.000 10.640 2.240 6 1.070 -17.435 0.000 60.714 15.680 10.500 7 1.032 -15.028 0.000 0.000 0.000 0.000 8 1.090 -15.028 0.000 35.849 0.000 0.000 9 1.008 -17.461 0.000 0.000 41.300 23.240 10 1.006 -17.871 0.000 0.000 12.600 8.120 11 1.028 -17.821 0.000 0.000 4.900 2.520 12 1.036 -18.623 0.000 0.000 8.540 2.240 13 1.027 -18.643 0.000 0.000 18.900 8.120 14 0.990 -19.494 0.000 0.000 20.860 7.000 fig. 2. comparison of voltage magnitude for ieee-14 data fig. 3. comparison of voltage angle for ieee-14 data the simulation results for the ieee 30-bus system by the pm in form of bus-wise voltage magnitudes and voltage angles profiles along with simulated real and reactive powers across generation and load are shown in table ii. the comparison of the voltage magnitude and angles for all methods on the ieee 30-bus data are shown in figures 7 and 8, respectively. engineering, technology & applied science research vol. 10, no. 3, 2020, 5851-5856 5854 www.etasr.com khoso et al.: a new and efficient nonlinear solver for load flow problems fig. 4. iterations taken by all methods for the ieee 14-bus system fig. 5. computational time (s) by all methods for the ieee 14-bus system fig. 6. maximum errors for all methods for the ieee 14-bus system the pm provides optimal results similar to other methods in this case too with better precision and accuracy. the voltage magnitudes have been almost higher than those of the other methods. again the pp method shows different results for the ieee 30-bus system in both magnitude and angle voltages across all buses. for solving the nonlinear ieee 30-bus power system data for the desired error bound, the pm takes only 4 iterations, whereas nr, pp, fd and gs, respectively require, 5, 24, 71, and 93 iterations, as shown in figure 9. figure 10 shows the computational time (in seconds) for all methods for the same system, whereas maximum errors are shown in figure 11. the nr and pm methods take almost the same execution time, with pm taking ascendancy minimum most of the program runs, whereas the highest time was found for the fd method. table ii. pm simulation results for the ieee 30-bus system bus bus voltage power (real p and reactive q) magnitude (p.u) angle (p.u) generation load p q p q 1 1.060 0.000 260.99 -17.021 0.000 0.000 2 1.043 -5.497 40.000 48.822 21.700 12.700 3 1.022 -8.004 0.000 0.000 2.400 1.200 4 1.013 -9.661 0.000 0.000 7.600 1.600 5 1.010 -14.381 0.000 35.975 94.200 19.000 6 1.012 -11.398 0.000 0.000 0.000 0.000 7 1.003 -13.150 0.000 0.000 22.800 10.900 8 1.010 -12.115 0.000 30.826 30.000 30.000 9 1.051 -14.434 0.000 0.000 0.000 0.000 10 1.044 -16.024 0.000 0.000 5.800 2.000 11 1.082 -14.434 0.000 16.119 0.000 0.000 12 1.057 -15.302 0.000 0.000 11.200 7.500 13 1.071 -15.302 0.000 10.424 0.000 0.000 14 1.042 -16.191 0.000 0.000 6.200 1.600 15 1.038 -16.278 0.000 0.000 8.200 2.500 16 1.045 -15.880 0.000 0.000 3.500 1.800 17 1.039 -16.188 0.000 0.000 9.000 5.800 18 1.028 -16.884 0.000 0.000 3.200 0.900 19 1.025 -17.052 0.000 0.000 9.500 3.400 20 1.029 -16.852 0.000 0.000 2.200 0.700 21 1.032 -16.468 0.000 0.000 17.500 11.200 22 1.033 -16.455 0.000 0.000 0.000 0.000 23 1.027 -16.662 0.000 0.000 3.200 1.600 24 1.022 -16.830 0.000 0.000 8.700 6.700 25 1.019 -16.424 0.000 0.000 0.000 0.000 26 1.001 -16.842 0.000 0.000 3.500 2.300 27 1.026 -15.912 0.000 0.000 0.000 0.000 28 1.011 -12.057 0.000 0.000 0.000 0.000 29 1.006 -17.136 0.000 0.000 2.400 0.900 30 0.995 -18.015 0.000 0.000 10.600 1.900 fig. 7. comparison of voltage magnitude methods for ieee-30 data fig. 8. comparison of voltage angle by all methods for ieee-30 data from the exhaustive simulations and consequent comparison of results, an encouraging performance of the new methods gs nr fd pp pm 0 20 40 60 80 100 120 140 160 180 200 methods gs nr fd pp pm 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 number of iterations 1 2 3 4 5 6 7 10 -15 10 -10 10 -5 10 0 10 5 gs nr fd pp pm engineering, technology & applied science research vol. 10, no. 3, 2020, 5851-5856 5855 www.etasr.com khoso et al.: a new and efficient nonlinear solver for load flow problems and efficient pm has been established for lf problems with successful validation on ieee 14 and ieee 30 test bus systems against conventional methods. the pm exhibits higher order accuracy and better convergence characteristics than known benchmark methods gs, nr, fd and pp. the pm converges quickly, takes lesser computational time, and has a lower iteration count in comparison with the other methods. fig. 9. iteration number comparison for the ieee 30-bus system fig. 10. computational time comparison for the ieee 30-bus system fig. 11. maximum errors comparison for the ieee 30-bus system vi. conclusion in this paper, a new iterative nonlinear solver, referred to as pm, was proposed for lf problems. the mathematical model of pm for solving the lf problems was presented. the structural approach of the pm to efficiently solve nonlinear equations of lf problems was systematically presented and worked out. the performance of the pm against other benchmark lf solvers was tested on ieee 14and 30-bus systems’ test data, through numerical simulations on matlab. the main advantages of our pm are its better convergence properties, less computational time, and smaller iteration number when compared with the standard lf methods. acknowledgement the authors would like express their gratitude to the mehran university of engineering and technology authorities for their support. references [1] h. a. abro, m. m. shaikh, “a new time-efficient and convergent nonlinear solver”, applied mathematics and computation, vol. 355, pp. 516-536, 2019 [2] f. l. alvarado, “bifurcations in nonlinear systems-computational issues”, ieee international symposium on circuits and systems, pp. 922-925 ,1990 [3] m. m. shaikh, s. u. r. massan, a. i. wagan, “a new explicit approximation to colebrook’s friction factor in rough pipes under highly turbulent cases”, international journal of heat and mass transfer, vol. 88, no. 3, pp. 538-543, 2015 [4] m. m. shaikh, s. u. r. massan, a. i. wagan, “a sixteen decimal places’ accurate darcy friction factor database using non-linear colebrook’s equation with a million nodes: a way forward to the soft computing techniques”, data in brief, vol. 27, article id 104733, 2019 [5] b. stott, “review of load-flow calculation methods”, proceedings of the ieee, vol. 62, pp. 916–929, 1974 [6] v. ajjarapu, computational techniques for voltage stability assessment and control, springer, 2010 [7] p. kundur, power system stability and control, mcgraw-hill, 1993 [8] v. bhan, a. a. hashmani, m. m. shaikh, “a new computing perturband-observe-type algorithm for mppt in solar photovoltaic systems and evaluation of its performance against other variants by experimental validation”, scientia iranica, vol. 26, pp. 3656-3671, 2019 [9] n. e. akpeke, c. m. muriithi, c. mwaniki, “contribution of facts devices to the transient stability improvement of a power system integrated with a pmsg-based wind turbine”, engineering, technology & applied science research, vol. 9, no. 6, pp. 4893-4900, 2019 [10] z. a. shahani, a. a. hashmani, m. m. shaikh, “steady state stability analysis and improvement using eigenvalues and pss: a case study of a thermal power plant in jamshoro, pakistan”, engineering, technology & applied science research, vol. 10, no. 1, pp. 5301-5306, 2020 [11] o. kahouli, b. ashammari, k. sebaa, m. djebali, h. h. abdallah, “type-2 fuzzy logic controller based pss for large scale power systems stability”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3380-3386, 2018 [12] g. shahgholian, a. fattollahi, “improving power system stability using transfer function: a comparative analysis”, engineering, technology & applied science research, vol. 7, no. 5, pp. 1946-1952, 2017 [13] d. v. ngo, k. v. pham, d. d. le, k. h. le, k. v. huynh, “assessing power system stability following load changes and considering uncertainty”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2758-2763, 2018 [14] s. mallick, d. v. rajan, s. s. thakur, p. acharjee, s. p. ghoshal, “development of a new algorithm for power flow analysis”, international journal of electrical power & energy systems, vol. 33, no. 8, pp. 1479–88, 2011 [15] m. ebeed, s. kamel, f. jurado, “determination of ipfc operating constraints in power flow analysis”, electrical power & energy systems, vol. 81, pp. 299–307, 2016 [16] w. f. tinney, c. e. hart, “power flow solution by newton’s method”, ieee transactions on power apparatus and systems, vol. pas-86, no. 11, pp. 1449–60, 1967 methods gs nr fd pp pm 0 10 20 30 40 50 60 70 80 90 100 methods gs nr fd pp pm 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 number of iterations 1 2 3 4 5 6 7 10 -15 10 -10 10 -5 10 0 10 5 gs nr fd pp pm engineering, technology & applied science research vol. 10, no. 3, 2020, 5851-5856 5856 www.etasr.com khoso et al.: a new and efficient nonlinear solver for load flow problems [17] m. tostado, s. kamel, f. jurado, “developed newton-raphson based predictor-corrector load flow approach with high convergence rate”, international journal of electrical power & energy systems, vol. 105, pp. 785-792, 2019 [18] h.saadat, power system analysis, pearson, 2011 [19] university of washington, power systems test case archive, available at: https://labs.ece.uw.edu/pstca/ authors profile amjad hussain khoso has a be of electrical engineering from mehran university of engineering and technology, jamshoro, pakistan. at present, he is pursuing his me from the same department. muhammad mujtaba shaikh is working as an assistant professor (mathematics) in the department of basic sciences and related studies, mehran university of engineering and technology. he received his phd from the institute of mathematics and computer science, university of sindh, jamshoro, pakistan in 2017. he has been awarded with gold and silver medals in bs (mathematics) degree in 2009. he is an active researcher having an impact factor of over 20 according to most reputed journal citations reports by thompson reuters. he has profound knowledge on computational methods and statistical analysis, and has been involved in teaching and research in these fields. his research fields include optimization, numerical integration, applied and computational mathematics, and mathematical problems in engineering. he is also an active member of supply chain and operations management (scom) research group at mehran university of engineering and technology. besides, a number of research scholars are working under his supervision in ms, mphil, me and phd programs. ashfaque ahmed hashmani has a be from mehran university of engineering and technology, a me from singapore, and a phd from university of duisbergessen. at present, he is a professor and chairman at the department of electrical engineering, mehran university of engineering and technology. his fields of interest are: power system stability and control, nonlinear control and applications, robust control of power and energy systems. engineering, technology & applied science research vol. 9, no. 2, 2019, 4037-4043 4037 www.etasr.com ghaly et al.: design and modeling of a radiofrequency coil derived from a helmholtz structure design and modeling of a radiofrequency coil derived from a helmholtz structure sidi m. ahmed ghaly electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university, riyadh, saudi arabia smghaly@imamu.edu.sa khalid. a. al-snaie electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university, riyadh, saudi arabia kalsnaie@imamu.edu.sa asad. m. ali electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university, riyadh, saudi arabia asadali@ imamu.edu.sa abstract—this paper focuses on radiofrequency (rf) coils that can produce a high electromagnetic field homogeneity to be used for magnetic resonance imaging (mri) applications. the proposed structure is composed of four wire loops symmetrically located on an ellipsoidal surface. the main objective of this work is to improve field homogeneity compared to a standard helmholtz coil. numerical simulation was carried out to assess the rf electromagnetic field behavior of the proposed coil. different electrical modeling and simulations were investigated, particularly the study of the whole modeling of the proposed structure taking into account all the couplings between the loops. the proposed coil was evaluated and compared with the standard helmholtz coil. simulation and experimental results confirmed the good performance of the developed coil in terms of electromagnetic field homogeneity, efficiency, sensitivity, and quality factor. keywords-radiofrequency coils; modeling; simulation; design; electromagnetic field homogeneity; impedance measurements; mri i. introduction since the demonstration of the nuclear magnetic resonance (nmr) phenomenon in 1946, the number of its applications grows steadily [1-3]. nmr imaging is based on the study of the magnetization modifications of the nuclei of a subject substance to a precise magnetic environment [4], in particular, a very strong magnetic field. the field homogeneity is needed over the observed area and it has been shown that the quality of the image obtained is, in particular, a function of the intensity of the applied static magnetic field and the homogeneity of the radiofrequency electromagnetic field produced by the transmitting coil and associated with the receiving coil [5-7]. the electromagnetic field homogeneity of radiofrequency coils is usually better with multiple radiating elements, of identical or different attributes [8, 9], and their design can be accordingly optimized. for example, birdcage coils [8] are the most popular in mri, they show outstanding performance in terms of magnetic field and signal-to-noise ratio (snr), and have a sufficient number (usually greater than 8) of parallel radiating strands, often periodically placed on the surface of a cylinder. the optimization of rf coils is the subject of continuous research. currently, inductive coupling problems between radiating elements (conductors) are largely taken into account, and this task is partly facilitated for periodic structures [10-12]. for rf coils that do not have a specific periodicity, optimization and implementation are more challenging. this is the case of helmholtz coils [13] which consist of two coaxial circular coils separated by a distance equal to their radius. an improvement in the homogeneity of the field passes necessarily by the addition of coaxial turns. thus, original structures, generally contained in a spherical and ellipsoidal envelope and having four or more free element loops have already been proposed [10-12] and very interesting properties in terms of homogeneity and sensitivity are obtained. a certain number of possibilities nevertheless remain to be analyzed. this research work considers aspects related to electronic instrumentation and in particular, the design, modeling and optimization of rf coils for magnetic resonance imaging, presenting a certain simplicity of implementation and having good homogeneity of rf electromagnetic field. more precisely, the optimization and modeling of a symmetrical coil with four coaxial circular loops producing effective sixth order homogeneity of electromagnetic field are presented. in fact, the proposed structure includes only two coaxial circuits. in nmr imagery, we have already demonstrated the advantages of the free element four-coil system [10, 11] that provides fourth order homogeneity. in this work, the main objective is to increase the sensitivity of the coil and reduce the number of tuned loops from four to two, which can be done by connecting the two loops positioned in the same side in series with a shared tuning capacitance. this configuration looks like a distributed helmholtz coil. this work, which includes modeling, simulations and experimental results, intends to be an important input for rf coils resulting from helmholtz structure which can be used for mri applications. ii. electrical modeling in this section the electrical modeling of the proposed coil that includes all inductive and capacitive couplings will be discussed. the electrical modeling of the structure is necessary to demonstrate its operation and feasibility. the proposed structure is shown schematically in figure 1. the proposed structure has the advantage to reduce the number of tuned corresponding author: sidi m. ahmed ghaly engineering, technology & applied science research vol. 9, no. 2, 2019, 4037-4043 4038 www.etasr.com ghaly et al.: design and modeling of a radiofrequency coil derived from a helmholtz structure circuits from four to two by connecting the two loops positioned in the same side with a shared tuning capacitance for each single circuit (two series circuits). this choice facilitates the comparison with the preceding proposed structures [10, 11]. thus, the developed coil looks like a distributed helmholtz coil. to confirm the feasibility of such a coil configuration, a whole electrical model of the four-loop system compelling all capacitive and inductive couplings is investigated. the coupling mode of the rings is an inductive coupling [14] between all loops and a capacitive coupling [15] between adjacent left or right loops (connected in series). the equivalent electrical diagram of the system in the ideal case (without losses) is shown in figure 2. fig. 1. structure of the proposed coil fig. 2. electrical diagram for the proposed coil (without losses) because of the probe symmetry, there are some obvious simplifications: inductances l4=l1, l3=l2, capacitances c1=c2, mutual inductances m34=m12 and m24=m13. as for the helmholtz coils [13] and using kirchoff`s voltage law, the two electrically isolated circuits crossed by the currents i1 and i2 are characterized by the following equation system: [ 𝑍 𝑗(𝑀14 + 𝑀23 + 2𝑀13)𝜔 𝑗(𝑀14 + 𝑀23 + 2𝑀13)𝜔 𝑍 ] [ 𝐼1 𝐼2 ] = [0 0 ] (1) two modes of resonance can be distinguished: a co-current symmetrical mode with i1=i2, which is the mode of interest and a mode counter current which is not symmetric with i1=-i2 (gradient mode). for the co-current mode (the mode of interest), (1) can be reduced to: 𝑍𝐼1 + 𝑗(𝑀14 + 𝑀23 + 2𝑀13)𝜔𝐼2 = 0 (2) introducing the coupling coefficients kij [16], the resonance equation becomes: 1 2 12 1 2 2 13 1 2 14 1 23 2 2 2 1 ( ) c l l k l l k l l k l k l  + + + + + = (3) thus, it has a real positive solution: 𝑓1 = 1 2𝜋√𝐶(𝐿1+𝐿2 +2𝑘12√𝐿1𝐿2+2𝑘13√𝐿1𝐿2+𝑘14𝐿1+𝑘23𝐿2) (4) for the counter-current mode (i1=-i2), there is a frequency of: 𝑓2 = 1 2𝜋√𝐶(𝐿1+𝐿2 +2𝑘12√𝐿1𝐿2−2𝑘13√𝐿1𝐿2−𝑘14𝐿1−𝑘23𝐿2) (5) as for the helmholtz coil, it is necessary to ensure sufficient decoupling of the modes by separating the loops sufficiently. iii. optimization of the field homogenity for the calculation of the electromagnetic field (b1) produced by the proposed structure which consists of two symmetric elements and has small dimensions compared to the wavelength, the superposition principle can be applied to obtain the total electromagnetic field [17]. the component along the y axis of the magnetic field shown in figure 1 produced by a thin ring of wire, of radius a, positioned in the xz plane, centered on the origin o and carrying a current i is easily determined by using biot-savart’s law [18]: 0 1 3 2 2 2 1 y b y     =     +       (6) the extension to the proposed structure permits to obtain the total field b1y along the coil axis as shown: 𝐵1𝑦 = 𝜇ₒ𝐼 ∑ 1 2𝛼𝑖(1+[ 𝑦−𝑦𝑖 𝛼𝑖 ] 2 ) 3 2 4 𝑖 (7) where yi is the ordinate of the position of the loop i on the axis and αi is the radius of the loop (i). due to the symmetry of the structure, b1y component can be expressed as a taylor expansion around the origin [19]. the odd orders of the function b1y should be zero and the taylor’s expansion gives the even. for a given ellipsoidal structure, the symmetry returns the computation parameters to two and thus, the spacing between the loops (inner or outside rings) or the diameter of the loops can be adjusted. the angles αi can be introduced with respect to the axis (oy), i.e. for loops 1 and 2, angles α1 and α2 (α1<α2) and for loops 3 and 4, angles π-α2 and π-α1 respectively as shown in (8). it should be noted that the field calculation depends only on the geometry of the coils. 𝐵1𝑦 = 2𝐼𝜇ₒ {( 𝑠𝑖𝑛𝛼1 3 𝑎1 ) + ( 𝑠𝑖𝑛𝛼2 3 𝑎2 ) + (( 𝑠𝑖𝑛𝛼1 2 𝑎1 ) 𝑃91 (𝑐𝑜𝑠𝛼1)) ( 𝑦 𝑟1 ) 8 + (( 𝑠𝑖𝑛𝛼2 2 𝑎2 ) 𝑃91 (𝑐𝑜𝑠𝛼2)) ( 𝑦 𝑟2 ) 8 +. . } (8) indeed, on the electrical level, the transformation ratio between currents is forced to one and it is possible to modify the solution by simply scaling factor. after the numerical calculations, there is a certain range of possibilities for fourth order homogeneity field which advantageously presents a unique and optimal six-order solution for the proposed coil. there is a unique solution for which the six-order derivative of engineering, technology & applied science research vol. 9, no. 2, 2019, 4037-4043 4039 www.etasr.com ghaly et al.: design and modeling of a radiofrequency coil derived from a helmholtz structure the electromagnetic field (b1) is zero. for this optimal case, the secondary geometric data for the proposed coil are given in table i. table i. secondary geometric data for the proposed coil main axis a (cm) secondary axis b (cm) α1 (rad/deg) α2 (rad/deg) 3.042 2.459 0.734/42.09 1.299/74.42 the eccentricity e is given by: 𝑒 = √1 − ( 𝑏2 𝑎2 ) = 0.587 (9) according to table i, the taylor expansion in (8) can be reduced to: 𝐵𝑖𝑦 = (𝐼𝜇ₒ/2){106.3-1.247 10 15 𝑦8 + ⋯} (10) figure 3 shows the obtained dimensions of the ellipsoidal coil and the corresponding normalized electromagnetic field profile: fig. 3. (a) dimensions of the proposed structure, (b) normalized field profile it is clear from figure 3(b) that profile widths at 1% and 10% can be calculated and compared with those obtained from helmholtz coil shown in table ii. table ii. profile widths at 1% and 10% for both coils (helmholtz and proposed) structure profile width at 1%(cm) profile width at 10%(cm) helmholtz 1.50 2.89 proposed 2.92 4.44 by comparison with helmholtz coil, the proposed structure has a significant increase in the profile. thus, in considering uniformity of 1%, profile width has increased approximately 97% and at 10% uniformity the profile width increased 58% more than the helmholtz coil. the performance described above is very general and does not depend on the size of the coils. indeed, it suffices to apply a simple scale factor to the ellipsoidal structure to obtain coils with the same performances. iv. simulation in this part, the electrical behavior of the system will be investigated for the proposed structure (ellipsoidal coil). the system comprises of four coaxial wires with inductive coupling between all loops and capacitive coupling between adjacent left or right loops. it consists of two identical tuned circuits resonant at the same frequency. a. one tuned circuit having two rings coupled in series in this case, assume a circuit tuned at frequency f0 and consisting of two rings with inductances l1 and l2 mutually coupled as shown in figure 4. fig. 4. two mutually coupled inductances in the case without losses, the value of the self-resonance frequency is given by: 𝑓0 = 1 2𝜋√(𝐿1+𝐿2 +2𝑘12√𝐿1𝐿2)𝐶 (11) b. case of the proposed structure (2 tuned circuits): coaxial wire loops are characterized by their selfinductance and their mutual inductances, which depend at high frequencies on the geometrical configuration: loop diameter, wire diameter, and distances between the loops [20]. the two tuning capacitors are supposed to be identical. if we consider that the proposed structure is sourced by an ideal voltage source, then the equivalent electrical diagram is shown in figure 5. fig. 5. electrical diagram for the proposed coil (with losses) the tuning capacitor is determined from the established formula of the resonance frequency f1 of the coil as shown in (2). for the co-current mod, the tuning capacitor is deduced as: 𝐶 = 1 2𝜋2𝑓1 2(𝐿1+𝐿2 +2𝑘12√𝐿1𝐿2+2𝑘13√𝐿1𝐿2+𝑘14𝐿1+𝑘23𝐿2) (12) the resonance frequency f1=100.24mhz is the larmor frequency at static magnetic field b0=3t [7]. table iii presents (a) (b) engineering, technology & applied science research vol. 9, no. 2, 2019, 4037-4043 4040 www.etasr.com ghaly et al.: design and modeling of a radiofrequency coil derived from a helmholtz structure the data necessary for the preliminary adjustment of the ellipsoidal structure obtained from the equivalent electrical model in figure 5. tuning capacitor c and self-resonance frequency f0 of tuned circuits are presented in table iv. table iii. electrical parameters and tuning elements parameters (inductances li coupling kij) l1=l4 l2=l3 k12 k13 k14 k23 proposed structure 83.3 117.6 0.16 0.06 0.02 0.20 table iv. tuning elements f0 c 108.37mhz 9.269pf the simulation results give the quality factor of the proposed structure which equals to 305 with losses when r1=r2=0.82ω. figure 6 presents the simulation of the input impedance curve of the proposed structure. as seen, there are two resonance series: at 100mhz and 123mhz. as the quality factor is high, then the energy absorbed at f0 is low. on the other hand, since r is small, the energies absorbed at f1 and f2 are relatively large [7]. for the resonance frequencies, table v compares the simulation results with the theoretical (without losses) for the ellipsoidal coil. fig. 6. simulation of the input impedance vs frequency curve for the ellipsoidal coil. table v. simulation and theoretical results without losses ellipsoidal structure modes of resonance 1 2 theoretical f1 (mhz) 100.24 118.85 simulation f1 (mhz) 100.23 118.98 a simulation of the currents variations in the ellipsoidal coil which includes two circuits only (carrying currents ic1 and ic2) is given in the figure 7. it should be noted that at the two resonance frequencies f1 and f2, the currents ic1 and ic2 have maximum magnitude (almost identical) and the difference between the two modes remains essentially at the phase level: in-phase currents for f1 and in opposition of phase for f2. c. matching of the coil at 50ω: the proposed coil is matched using an inductive coupling [14]. this kind of matching uses an attack loop with the same dimensions as the first loop of the proposed coil and this attack loop is tuned to f1 as shown in figure 8. fig. 7. simulation of the currents variation vs frequency for the ellipsoidal coil. fig. 8. matching of the ellipsoidal coil with inductive coupling the attack coil is inductively coupled with the four loops of the structure. the matching of the coil at 50ω is performed by optimizing the coupling loop position. the associated coupling coefficients (k0i, i=1, .., 4) allowing the matching are presented in table vi. the simulation of the matching at 50ω (figure 9) gives a corresponding distance between the attack loop and the ellipsoidal coil equal to 2.56cm. the inductive coupling results in an impedance inversion: the series resonance modes become parallel. table vi. associated coupling coefficients coupling kij k01 k02 k03 k04 ellipsoidal structure 0.0736 0.0216 0.0096 0.0018 fig. 9. μagnitude of the input impedance vs frequency.simulation of the matching for the ellipsoidal coil at f1=100mhz, r=50ω. engineering, technology & applied science research vol. 9, no. 2, 2019, 4037-4043 4041 www.etasr.com ghaly et al.: design and modeling of a radiofrequency coil derived from a helmholtz structure v. experimental part in this part, we present the experimental results obtained with the developed coils (helmholtz and ellipsoidal). we conducted out-of-field tests using a network analyzer. relative measurements of the rf electromagnetic field (b1) along the main axis of the coils were carried out and were compared with those found in theory. a. prototype dimensions to facilitate comparisons, both standard helmholtz coil and the proposed (figure 10) had the same radial diameter d equal to 4.80cm (table vii). table vii. coil dimensions diameter distances structure inner loops outer loops inner loops outer loops helmholtz 4.80 -2.40 - ellipsoidal 4.80 3.60 1.33 4.05 (a) (b) fig. 10. the developed (a) helmholtz and (b) ellipsoidal coils b. matching and tuning of the coils it is possible to proceed directly to the tuning of the coils, but it requires a certain control of the various influential parameters (stepwise adjustment of the tuning capacitors). the tuning of each loop at f0 is performed individually by shorting the other loops and bringing it closer to a test loop. by predetermination of fo (see (4)), a vacuum presetting of the coil is carried out. figure 11 gives an explanatory diagram. fig. 11. individual tuning of ellipsoidal coil figure 12 shows the variations of the module and phase of the input impedance seen by the source as a function of the frequency. fig. 12. photograph of the tuning of the ellipsoidal coil two parallel resonance frequencies are observed for the ellipsoidal coil. table viii gives the comparison between the values of the experimental measured frequencies (with losses) and those in theory (without losses) for the ellipsoidal coil: table viii. experimental and theoretical values ellipsoidal coil resonance mode i 1 2 fi theoretical (mhz) 100.25 118.85 fi experimental (mhz) 100.24 117.91 it can be observed that we have almost the same value of the frequency f1, while there is a small error for the other frequencies. for the last mode of resonance, the error is almost 3% for the ellipsoidal coil. impedance matching allows optimal energy transfer between coils and the transmission and reception system [14]. for optimal transfer in the coaxial transmission cable during excitation, the impedance of the system should be 50ω [14]. the matching of the coils can be realized, either using capacitors (capacitive coupling) or using a coupling loop (inductive coupling). in our case, we opted for the matching by inductive coupling because it allows having a electrically balanced circuit. the matching of the coil is achieved by optimizing the position of the attack loop with the coil. thus, the value of the distance to have an impedance of 50ω is equal to 1.9cm (1.91cm in theory) for the ellipsoidal coil. the impedance curve obtained for the matched ellipsoidal coil with impedance measurements using network analyzer is given in figure 13. fig. 13. impedance curve obtained for the matched ellipsoidal coil engineering, technology & applied science research vol. 9, no. 2, 2019, 4037-4043 4042 www.etasr.com ghaly et al.: design and modeling of a radiofrequency coil derived from a helmholtz structure c. results comparative tests have been carried out between the ellipsoidal and helmholtz coils. thus, relative field measurements along the axis of the coils were made using a small test loop connected to the network analyzer. figure 14 shows the measurement bench. we were able to take the electromagnetic field along the axis of the coils (oy). the curves of this normalized field produced by both coils are given in figure 15. fig. 14. the measurement bench fig. 15. the curves of the normalized field produced by both coils to compare the axial profiles, we determined the relative widths of the lobe at 10%. thus, compared to the helmholtz coil, the relative width of the lobe at 10% is 1.54 times larger for the ellipsoidal coil (see table ix), which is in accordance with the theoretical forecasts (table ii). similarly, for the same absorbed power, it is possible to check the efficiency of the coils [22]. compared to the helmholtz coil, the center field is 1.42 times larger for the ellipsoidal coil as shown in table ix. by scanning with frequency and using two sufficiently distant coils (one transmitting and the other receiving), an improvement of the quality factor of 47% for the ellipsoidal coil is noted. it is increased from 215 for the helmholtz coil to 316 for the ellipsoidal coil (table ix). table ix. coil performance comparison coil helmholtz ellipsoidal relative widths of lobe at 10% 1 1.54 efficency 1 1.42 quality factor 215 316 vi. conclusion we presented the design and testing of a prototype magnetic resonance imaging coil composed of two free distributed elements contained in an ellipsoidal envelope and connected directly in series via a tuning capacitor. compared to classic helmholtz coils, the goal was to improve the homogeneity of the rf electromagnetic field produced by the coil to get an effective sixth order homogeneous field. a whole complete electrical modeling of the prototype coil was investigated, taking into account all couplings (inductive and capacitive). for a given resonance frequency, predetermination of the tuning frequency of the coil’s elements is performed, as well as the calculation of the associated tuning capacitors. the matching of the prototype coil by inductive coupling allowed great flexibility for settings and a real simplicity of design. comparative tests and measurements between a reference helmholtz coil and the prototype coil with the same radial diameter, have been carried out and were in good agreement with the theoretical predictions. thus, the observed width of the field homogeneity lobe at 10% is considerably increased for the proposed coil. a significant improvement in the quality factor was also observed for the ellipsoidal coil. moreover, for the developed ellipsoidal coil, efficiency and signal-to-noise ratio are higher as well. these good performance values for the ellipsoidal prototype coil give motivation to test the coil with load (with real samples) for mri applications. acknowledgment authors would like to thank the deanship of academic research at al imam mohammad ibn saud islamic university for the financial support of the project: no 371411/1437h. references [1] f. remeo, d. i. hoult, “magnet field profiling: analysis and correcting coil design”, magnetic resonance in medicine, vol. 1, no. 1, pp. 4465, 1984 [2] c. e. hayes, w. a. edelstein, j. f. schenck, o. m. mueller, m. eash, “an efficient, highly homogeneous radiofrequency coil for whole-body nmr imaging at 1.5 t”, journal of magnetic resonance, vol. 63, no. 3, pp. 622-628, 1985 [3] j. t. vaughan, h. p. hetherington, j. o. out, j. w. pan, g. m. pohost, “high frequency volume coils for clinical nmr imaging and spectroscopy”, magnetic resonance in medicine, vol. 32, no. 2, pp. 206-218, 1994 [4] k. asher, n. k. bangerter, r. d. watkins, g. e. gold, “radiofrequency coils for musculoskeletal mri”, topics in magnetic resonance imaging, vol. 21, no. 5, pp. 315-323, 2010 [5] q. x. yang, s. li, m. b. smith, “a method for evaluating the magnetic field homogeneity of a radiofrequency coil by its field histogram”, journal of magnetic resonance, series a, vol. 108, no. 1, pp. 1-8, 1994 [6] s. li, q. x. yang, m. b. smith, “rf coil optimization: evaluation of b1 field homogeneity using field histograms and finite element calculations”, magnetic resonance imaging, vol. 12, no. 7, pp. 10791087, 1994 [7] b. gruber, m. froeling, t. leiner, d. w. j. klomp, “rf coils: a practical guide for nonphysicists”, journal of magnetic resonance imaging, vol. 48, no. 3, pp. 590-604, 2018 [8] j. mispelter, m. lupu, a. n. m. r. briguet, nmr probeheads for biophysical and biomedical experiments: theoretical principles & practical guidelines, imperial college press, 2006 [9] b. j. dardzin, s. s. li, c. m. collins, g. d.williams, m. b. smith, “a birdcage coil tuned by rf shielding for application at 9.4 t”, journal of magnetic resonance, vol. 131, no. 1, pp. 32-38, 1998 [10] s. m. a. ghaly, s. s. al-sowayan, “a high b1 field homogeneity generation using free element elliptical four-coil system”, american journal of applied sciences, vol. 11, no. 4, pp. 534-540, 2014 engineering, technology & applied science research vol. 9, no. 2, 2019, 4037-4043 4043 www.etasr.com ghaly et al.: design and modeling of a radiofrequency coil derived from a helmholtz structure [11] s. m. a. ghaly, k. a. al-snaie, s. s. al-sowayan, “design and testing of radiofrequency spherical four coils”, modern applied science, vol. 10, no. 5, pp. 186-193, 2016 [12] s. m. a. ghaly, k. a. al-snaie, o. k. mohammad, “spherical and improved helmholtz coil with high b1 homogeneity for magnetic resonance imaging”, american journal of applied sciences, vol. 13, no. 12, pp. 1413-1418, 2016 [13] j. wang, s. she, s. zhang, “an improved helmholtz coil and analysis of its magnetic field homogeneity”, review of scientific instruments, vol. 73, no. 5, pp. 2175-2179, 2002 [14] m. decorps, p. blondet, h. reutenauer, j. p. albrand, c. remy, “an inductively coupled, series tuned nmr probe”, journal of magnetic resonance, vol. 65, no. 1, pp. 100-109, 1995 [15] j. murphy-boesch, a. p. koretsky, “an in vivo nmr probe circuit for improved sensitivity”, journal of magnetic resonance, vol. 54, no. 3, pp. 526-532, 2003 [16] r. f. lee, r. o. giaquinto, c. j. hardy, “coupling and decoupling theory and its application to the mri phased array”, magnetic resonance in medicine, vol. 48, pp. 203-213, 2002 [17] c. m. collins, z. wang, “calculation of radiofrequency electromagnetic fields and their effects in mri of human subjects”, magnetic resonance in medicine, vol. 65, no. 5, pp. 1470-1482, 2011 [18] y. e. esin, f. n. alpaslan, “mri image enhancement using biot–savart law at 3 tesla”, turkish journal of electrical engineering & computer sciences, vol. 25, pp. 3381-3396, 2017 [19] d. m. ginsberg, m. j. melchner, “optimum geometry of saddle shaped coils for generating a uniform magnetic field”, review of scientific instruments, vol. 41, no. 1, pp. 122-123, 2010 [20] h. fujita, t. zheng, x. yang, m. j. finnerty, s. handa, “rf surface receive array coils: the art of an lc circuit”, journal of magnetic resonance imaging, vol. 38, no. 1, pp. 12-25, 2013 microsoft word etasr_v11_n5_pp7635-7640 engineering, technology & applied science research vol. 11, no. 5, 2021, 7635-7640 7635 www.etasr.com mahdi et al.: a multipath cluster-based routing protool for mobile ad hoc networks a multipath cluster-based routing protocol for mobile ad hoc networks mohammed a. mahdi computer science and information department college of computer science and engineering university of ha’il ha’il, saudi arabia wsabi3@gmail.com tat-chee wan school of computer science universiti sains malaysia penang, malaysia tcwan@usm.my adnan mahdi school of electrical and electronic engineering, universiti sains malaysia, malaysia and college of computer science and engineering, university of hafr al batin, saudi arabia adnanmhdi@gmail.com mohamed a.g. hazber computer science and information department, college of computer science and engineering university of ha’il ha’il, saudi arabia m.hazber@uoh.edu.sa badiea abdulkarem mohammed computer engineering department college of computer science and engineering university of ha’il ha’il, saudi arabia b.alshaibani@uoh.edu.sa abstract-a manet (mobile ad-hoc network) is a group of mobile network nodes dynamically forming a network without any pre-existing infrastructure. multi-path routing protocols in manets try to discover and use multiple routes between source and destination nodes. multipath routing is typically used to reduce average delay, increase transmission reliability, provide load balancing among multiple routes, and improve security and overall qos (quality of service). in this paper, the cluster based routing protocol (cbrp), which is a single path manet protocol is enhanced to use multiple paths. the traffic will be distributed among multiple paths to reduce network traffic congestion and decrease delay. an analytical model is used for multipath and single path cbrp routing protocols in manets to estimate the end-to-end delay and queue length. the analytical results show that the average delay and average queue length in multipath cbrp are less than the average delay and queue length in single path cbrp. keywords-manet; routing protocols; single path; multi path; cbrp i. introduction a mobile ad-hoc network (manet) is a collection of wireless mobile nodes/routers. the nodes dynamically form a temporary network without the use of any existing network infrastructure or centralized administration. the mobile nodes are equipped with wireless interfaces that utilize radio channels to communicate with each other, without the need for centralized management [1]. manets can be used in classrooms, battlefields, and disaster recovery situations [1, 2]. routing protocols are an important part of any network. they play the main role for any communication in the network and they are used to establish and correct efficient routes among a pair of network nodes and to deliver messages in a timely manner [3-5]. routing protocols in manets are differentiated in terms of hop-by-hop or source routing, reactive or proactive approach, single path or multipath, distance vector or link state, and unicast or multicast [6]. multipath routing is a technique to overcome the problems of frequent topological changes and link instability because the use of multiple paths could diminish the effect of possible link failures between the nodes [7, 8]. thus, multipath routing protocols of wireless ad-hoc networks are superior over conventional single-path ad-hoc routing protocols [9] because the multipath routing protocols reduce end-to-end delay, provide more reliable network services, allow load balancing among multiple routes, provide higher aggregate bandwidth, improve security, and overall they improve the quality of service (qos) [10, 11]. various multipath routing protocols have been proposed for wireless ad hoc networks. a multipath routing protocol based on the source routing protocol dsr is the salvage capable opportunistic node-disjoint multipath routing (snmr) [12]. a multipath routing protocol based on the ad hoc on-demand routing scheme is the ad hoc on-demand multipath distance vector (aomdv) [3, 10]. ii. manet routing protocols manet routing protocols based on the schemes of discovering and maintaining paths are classified into three classes: reactive, proactive, and hybrid [13, 14] (figure 1). in terms of reactivity, they are classified as reactive or proactive, and regarding the number of paths as single or multi-path. the reactive method is more efficient than the proactive method. the most common-known reactive routing protocols in manets (single-path and multipath) are described below. corresponding author: mohammed a. mahdi engineering, technology & applied science research vol. 11, no. 5, 2021, 7635-7640 7636 www.etasr.com mahdi et al.: a multipath cluster-based routing protool for mobile ad hoc networks a. manet single-path routing protocols manet single path routing protocols mainly intend to maintain a single route between a source and a destination node. the most popular routing protocols of this type are aodv, dsr, and cbrp. fig. 1. manet routing protocol taxonomy. 1) dynamic source routing (dsr) dsr [15, 16] is an on-demand routing protocol that is based on the concept of source routing. it is a simple and an efficient routing protocol, specifically designed for use in multi-hop wireless ad hoc networks. it consists of two mechanisms, route discovery and route maintenance, that work together to allow nodes to discover and maintain routes from the sources to arbitrary destinations in network. dsr computes the paths when necessary and then maintains them. it applies on-demand schemes for both path discovery and path maintenance. thus, it makes the routing overhead traffic to scale automatically to the actual needed size, which is considered as its main advantage. 2) ad hoc on-demand distance vector (aodv) aodv [17] is a reactive on-demand routing protocol that allows dynamic, self-starting, multi-hop routing among mobile nodes desiring to establish and maintain an manet. it is essentially a combination of dsr and dsdv (destination sequenced distance vector) protocol. aodv uses the basic on-demand mechanisms of route discovery and route maintenance as in dsr and a next hop routing model with sequence numbers and periodic beacons to discover and maintain routes of dsdv. also, when the ad-hoc network topology changes, an aodv sequence number method is used to avoid long-term loops. moreover, aodv allows the mobile nodes to obtain routes quickly and does not require maintaining routes that are not in active communication. 3) cluster-based routing protocol (cbrp) cbrp [18-20] is a hierarchical on-demand routing protocol that uses source routing, like dsr, to avoid forming loops. cbrp is an efficient, scalable, and robust routing protocol for manets. it features more advantageous metrics than existing routing protocols, its overhead is less and its throughput is higher than aodv's. the cbrp is designed to be used in medium-to-large manets. cbrp groups the nodes of a network into several clusters. each cluster has a cluster head which coordinates data transmission within the cluster and with other clusters. there are four possible states of the node in the cluster: normal, isolated, clusterhead, and gateway. figure 2 shows these states. one of the advantages of cbrp is that only cluster heads exchange routing information, therefore the number of control overhead transmitted through the network is far less than the traditional flooding methods. other features of cbrp [20] are: • distributed operation is fully used. • during the dynamic route discovery process there is less flooding traffic. • explicit exploitation of uni-directional links that would otherwise be unused. • broken paths can be repaired locally without route rediscovery. • sub-optimal routes can be shortened as they are used. fig. 2. cluster based routing protocol (cbrp). b. manet multi-path routing protocols multi-path routing protocols try to discover a multiple route from the source node to the destination node. multipath routing can effectively improve reliability, end-to-end delay, and achieve load balancing, but it is more complicated than single path routing [11]. most multipath routing protocols proposed for wireless ad hoc networks are based on reactive routing. they are mostly created on the basis of dsr and aodv. 1) ad hoc on-demand multipath distance vector routing (aomdv) aomdv [3, 10] extends the aodv protocol to compute multiple paths between the source and the destination during route discovery. multiple paths are computed to guarantee that the route is loop-free and disjoint. the aomdv protocol calculates multiple loop-free paths, where every node maintains an advertised hop count for each destination node. therefore, loop freedom is accomplished, and the advertised hop count represents the maximum hop count for all multiple paths. aomdv has three novel aspects compared to other on-demand multipath protocols. first, it does not have high intermodal coordination overhead. second, it ensures disjointness of alternate routes via distributed computations without the use of source routing. finally, it computes alternate paths with minimal additional overhead. engineering, technology & applied science research vol. 11, no. 5, 2021, 7635-7640 7637 www.etasr.com mahdi et al.: a multipath cluster-based routing protool for mobile ad hoc networks 2) salvage capable opportunistic node-disjoint multipath routing (snmr) snmr [12] is based on dsr. in snmr, a route discovery attempt, a primary path, and a node disjoint route are created between the source and the destination node along with alternative routes for the intermediate nodes of the primary route. snmr reduces the overhead caused by duplicate rreq broadcasting in creating multiple routes and recovers quickly from connection failures due to its packet salvaging ability. minimum overhead, node disjoint multipath, non-duplicate rreq rebroadcasting, and packet salvaging are the main advantages of snmr protocol. a bloom filter is used in snmr for space saving. within the primary route, the intermediate nodes are compressed in a bloom filter containing their hashed addresses. snmr uses the hashed node address to check the presence of a node in the bloom filter. therefore, an intermediate node can check if a neighboring node is included in the primary path or not. iii. the proposed multipath cbrp this paper focuses on the enhancement of cbrp routing protocol to work as a multipath routing protocol with improved qos. a. overview multipath cbrp routing protocol extends the single path cbrp to use multiple paths in distributing traffic from the source node (s) to destination node (d). cbrp is selected due to its above mentioned features. for example, cbrp has less routing overhead and higher throughput than the aodv protocol. cbrp repaires broken links locally without rediscovery, which leads to the reduction of broken links in the network and increased qos. on the other hand, cbrp has higher average delay than aodv. therefore, it should be enhanced to reduce the average delay. the proposed multi path cbrp (mp-cbrp) improves the qos in manets. mp-cbrp uses the idea of disjoint paths to distribute data packets over multiple routes. this distribution increases packet delivery ratio, data throughput, and reduces the average delay and queue length because it decreases congestion. an analytical model is used for multipath cbrp routing protocol and single path cbrp routing protocol to estimate the end-to-end delay and queue length. fig. 3. the proposed multipath cbrp routing protocol (mp-cbrp). as shown in figure 3 two paths are discovered from the source node (s) to destination node (d). data traffic λ is distributed through these two paths, divided to λ1 and λ2. the λ1 is sent through path1 and λ2 is sent through path2. s is the source node and d the destination node. ch is the cluster head, rreq is the route request, rrep the route reply and rc is the route cache. the pseudo code of the proposed mp-cbrp is illustrated in figure 4 and the flow diagram of the proposed mp-cbrp is shown in figure 5. fig. 4. pseudo code of the proposed mp-cbrp. b. network model to obtain the average delay and queue length for multipath cbrp, let us characterize the disjoint multipath network as follows: • the network with n disjoint path resources is characterized by the set of values � � ��1,�2,�3,� ,…,��� for the individual resources. a resource could be the data transmission capacity of the given communication channel. • the set � � 1, 2, 3,. . , ,…, �� represents the average arrival rate distribution across the set of the resources (�). • the set � � ��1,�2,�3,…,� ,…,��� represents the delay of values that applied on each of the n paths when the distribution of the traffic along the paths is λ, and the distribution of the resources along the paths is µ. • the set � � ��1,�2,�3,…,� ,…,��� represents the queue length values experienced on each of the n paths engineering, technology & applied science research vol. 11, no. 5, 2021, 7635-7640 7638 www.etasr.com mahdi et al.: a multipath cluster-based routing protool for mobile ad hoc networks when the distribution of the traffic along the paths is λ, and the distribution of the resources along the paths is µ. according to the above assumption, and using the queuing model m/m/1 queue [21] the delay (� ) and queue size (� ) can be calculated as: � � � ����� (1) � � �� ���� and � � �� �� (2) fig. 5. flow diagram of the proposed mp-cbrp. iv. results and discussion the results are shown in the form of graphs. graphs show the comparison between single path cbrp and mp-cbrp with two paths, based on the terms of average delay and queue length. values of average arrival rate (λ): 0.1, 0.3, 0.5, 0.7, 0.9 are used for all the nodes in the network model of mp-cbrp and service rate µ=1. a. average delay average delay is calculated by (1). figures 6 and 7 illustrate the average delay for single path and mp cbrp routing protocol. two paths have been considered for the mp cbrp, and two different scenarios have been considered. 1) average delay scenario 1 traffic is split equally between the two paths in the mp cbrp model. figure 6 shows that the average delay for mp cbrp is lesser than the average delay of single path cbrp using different arrival rates. 2) average delay scenario 2 traffic is not split equally between the two paths in mp cbrp model. the traffic for path 1 is 30% and for path 2 is 70%. figure 7 shows that the average delay of mp cbrp is lesser than the average delay of single path cbrp using different arrival rates. fig. 6. average delay for single path cbrp and equally divided traffic mp cbrp. fig. 7. average delay for single path cbrp and mp cbrp using 30% traffic for path1 and 70% traffic for path 2 engineering, technology & applied science research vol. 11, no. 5, 2021, 7635-7640 7639 www.etasr.com mahdi et al.: a multipath cluster-based routing protool for mobile ad hoc networks figure 8 shows the results of average delay for scenario 1 and scenario 2. the average delay for mp-cbrp in scenario 1 is better than the average delay for mp-cbrp in scenario 2 due to the high network congestion in scenario 2. fig. 8. average delay for single-path cbrp and mp-cbrp (scenarios 1 and 2). b. average queue length the average queue length is calculated by (2). figures 9 and 10 illustrate the average queue length for single path cbrp and mp cbrp. two paths have been considered for cbrp multipath, and two different scenarios have been considered. fig. 9. average queue length for single path and mp cbrp for scenario 1. 1) average queue length scenario 1 the traffic is split equally between the two paths in mp cbrp. figure 9 shows that the average queue length for mp cbrp is better than the average queue length in single path cbrp that uses different arrival rates. 2) average queue length scenario 2 traffic is not split equally between the two paths in mp cbrp model. the traffic for path 1 is 30% and for path 2 is 70%. figure 10 shows that the average queue length for mp cbrp is better than average queue length in single path cbrp that uses different arrival rates. figure 11 shows the results of average queue length for scenario 1 and scenario 2. the queue length of mp-cbrp in scenario 1 is better the average queue length of mp-cbrp in scenario 2 due to the high network congestion in scenario 2. fig. 10. average queue length for single path and mp cbrp for scenario 2. fig. 11. average queue length for single-path cbrp and mp-cbrp (scenarios 1 and 2). v. conclusion this paper proposes the enhancement of the single path cbrp manet protocol to work as an mp routing protocol. the mathematical model using the m/m/1 queueing model was used to evaluate the performance of mp-cbrp and single path cbrp routing protocols. the results show that the average delay and average queue length in mp-cbrp are better than the average delay and average queue length in single path cbrp. in the future, the network simulator (ns) will be used to evaluate the mp-cbrp. engineering, technology & applied science research vol. 11, no. 5, 2021, 7635-7640 7640 www.etasr.com mahdi et al.: a multipath cluster-based routing protool for mobile ad hoc networks references [1] m. al mojamed, "integrating mobile ad hoc networks with the internet based on olsr," wireless communications and mobile computing, vol. 2020, oct. 2020, art. no. e8810761, https://doi.org/ 10.1155/2020/8810761. 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[21] c. h. ng and s. boon-hee, queueing modelling fundamentals: with applications in communication networks, vol. 2. wiley, 2007. microsoft word 30-3479_s_etasr_v10_n2_pp5505-5511 engineering, technology & applied science research vol. 10, no. 2, 2020, 5505-5511 5505 www.etasr.com danikas et al.: some factors affecting the breakdown strength of solid dielectrics: a short review some factors affecting the breakdown strength of solid dielectrics: a short review m. g. danikas democritus university of thrace school of engineering department of electrical & computer engineering xanthi, greece g. e. vardakis democritus university of thrace school of engineering department of electrical & computer engineering xanthi, greece r. sarathi indian institute of technology madras department of electrical engineering chennai, india abstract—this paper refers to some factors affecting the breakdown strength of solid insulating materials. solid insulating materials play a most important role in the high voltage industry. factors, such as area effect, crystallinity, impregnation with liquids, temperature, the role of interfaces and mechanical stressing, are investigated and commented upon. keywords-solid dielectrics; solid insulation; breakdown strength; crystallinity; amorphous regions; temperature; interfaces; mechanical stressing i. introduction solid insulating materials are essential for the good functioning of high voltage equipment in most applications [13]. such materials include traditional materials, such as paper, as well as polymeric materials and – more recently – polymer nanocomposites. various factors, such as the shape of electrodes, their area, the applied electric field, gap spacing, the structure and type of polymeric materials, their molecular weight, types of additives, water and gas content, type of voltage waveform used, pressure of the impregnant (if any), have an effect on the breakdown strength of solid dielectrics. in the following sections a short review of some of the aforementioned factors will be given. ii. area effect of the electrodes the influence of the area of the electrodes affecting the breakdown strength of high voltage insulation in general is well known, especially from the research with insulating liquids [4, 5]. such a phenomenon exists also when investigating the breakdown strength in solid dielectrics. as was shown quite early, an area effect exists since larger area electrodes include more defects or weak points. larger electrode areas result in lower breakdown strength, as was shown in experiments with teflon films [6]. larger electrodes also produce shorter average breakdown times [6]. authors in [7], worked with spherical and cylindrical electrodes at power frequency and indicated that a pronounced area effect exists since much lower breakdown strength results were obtained with cylindrical depressions [7]. early breakdown studies were somehow related with the notion of “intrinsic electric strength”, a notion prevalent at that time [8]. later research indicated that this notion was erroneous and that the so-called intrinsic breakdown strength was not a property characterizing the insulating solids [9]. as is written in [9], “this word “intrinsic” reflecting history in that early theories stimulated belief in the existence of a physical constant, independent of geometry, electrode material, voltage waveform, and determined by molecular and/or crystal structure and temperature. the concept, is not supported by experiment”. admittedly, one cannot find much data on the electrode area effect on the breakdown strength of solid dielectrics. however, the general lines that are followed in the other categories of insulating materials, are also followed in the case of solid dielectrics, namely that the breakdown strength depends on the configuration of the electrodes, that the physical shape of the electrodes gives the variation of the breakdown voltages, and that the above mentioned quantities define the electric field distribution [10]. iii. crystallinity earlier experiments with various types of organic insulating materials indicated that the breakdown strength of polyethylene was not affected by doubling its crystallinity [11]. polystyrene, however, a partially aromatic polymer, showed a considerable reduction in the breakdown strength by increasing the ordered structure of the polymer (4.9mv/cm was the average breakdown strength for isotactic polystyrene pressed film compared to 7.1mv/cm for atactic polystyrene pressed film). the isotactic character of the polystyrene gives a crystallisable polymer, which permits a favorable geometry for interaction between the adjacent benzene rings [11]. other researchers, investigating the dielectric properties of thermally aged biaxially orientated polypropylene (bopp), observed that surface degradation was much faster than the bulk degradation although the total thickness of the films was no more than 25µm. they also showed that the morphological nature of bopp films changed during thermal aging. the crystallinity of bopp increased by thermal aging since recrystallization of part of the amorphous phase occurred. the interfacial domain of crystalline and amorphous phases may play a significant role for various properties of semi-crystalline polymers including breakdown strength [12]. during aging, changes in the chemical structure of polymers may alter processes such as softening or melting above their glass transition temperature and consequently, changes in their chemical structure may corresponding author: m. g. danikas engineering, technology & applied science research vol. 10, no. 2, 2020, 5505-5511 5506 www.etasr.com danikas et al.: some factors affecting the breakdown strength of solid dielectrics: a short review occur. less obvious physical effects, such as secondary crystallization in partially crystalline materials may occur and may cause increased stiffness and structural relaxation in an amorphous component rendering thus densification and embrittlement possible [13]. an important point is made in [14], where it is remarked that “a polymer melt has structural viscosity, i.e the macromolecules are orientated according to the shear velocity. [since] non-newtonian polymer melt displays a velocity distribution that is more uniform in the central section of the flow [and] the velocity gradient close to the boundary surface is higher … salient orientations and stretchings of the macromolecules occur in these zones …[consequently] orientations [that] are initially retained in the insulation and are frozen during the cooling process by reduction of the chain mobility and crystallization” may cause inhomogeneities with a subsequent effect on breakdown strength. on the other hand, swelling of a polymer – in case of impregnation with liquid – may be reduced by some factors such as crystallinity. authors in [15] reported that the breakdown strength of both polythene and polypropylene depends mainly on their semi-crystalline structure and the presence of defects rather than their chemical structure, since the two polymeric materials have similar values of breakdown strength. the preponderant role of defects was also emphasized in [16, 17], since defects can vary from those of molecular dimensions up to gross defects arising from inclusions. in a more recent publication, performing tests on polyethylene terephthalate (pet) with ac voltage, it was remarked that the breakdown strength is reciprocal to the longest free path [18]. although the authors of [18] did not specifically study the relation between material crystallinity and breakdown strength, they tacitly imply the relation between the two aforementioned quantities. furthermore, they noted that in thicker films, the boundaries between amorphous and crystalline parts can be a cause of inhomogeneities, thus reducing breakdown strength. more recently, authors in [19] investigated both ceramic (al2o3, tio2, srtio3,and batio3) and polymeric materials (pmma, polystyrene and n-butyl acetate) and used the so-called dielectric breakdown toughness (gbd) which is related to the critical energy release necessary to initiate the unstable growth of the longest conducting filament in the sample surface [19]. evidently, such a quantity is related also to the very structure of a polymer. since a polymer consists of amorphous and crystalline regions, some sort of cause that will modify the relation between these two regions, will necessarily have an influence on the breakdown strength. the microhardness (mh) of a polymeric material can be expressed as mhc = αh + (1-α)ηa (1) where hc and ha are the hardness values of the crystalline and amorphous regions respectively and α is the volume fraction of the crystalline region [20]. authors in [20] showed that the microhardness of a polymer decreases with temperature, with the decrease following an exponential law of the type: h = h0·e -βt (2) where h0 is a constant, t is the temperature ( o c), and β is the coefficient of thermal softening. according to [20], a decrease in microhardness is mainly associated to the softening of the crystalline region. an increase in the thickness of amorphous region – and therefore a decrease in crystallinity – will result to a decrease of the breakdown strength of the insulating material [21, 22]. on the other hand, working with poly (ether ether ketone) – peek, which is a high temperature insulating thermoplastic, it was observed that the breakdown strength decreased by increasing the crystalline/amorphous ratio of the polymer [23, 24]. the author attributed this to the fact that increased crystallinity introduces breakdown pathways not present in the amorphous material. investigating bopp samples, researchers relatively recently remarked that the breakdown strength increased substantially when the initially spherulitic morphology was transformed into a highly ordered fibrillar network structure of densely packed lamellar crystallites aligned parallel to the film surface [25]. in accordance with the above, it was reported by other researchers that with dc high voltage, the breakdown strength increases with increasing crystallinity because the free volume of polyethylene becomes smaller as the crystallinity increases [26]. thus the free path of electrons decreases and it is more difficult for them to accelerate. consequently, there is an increase in breakdown strength. it is evident from the above that the effect of crystallinity on the breakdown strength of polymers depends on the very chemical structure of the materials as well as on the defects that may be included. iv. impregnation effect impregnation of solid insulation with appropriate liquids is necessary in order to avoid the risk of partial discharges and/or early breakdown. the impregnating liquids must have a suitable viscosity, so that they can impregnate micro-cavities that may exist in the solid insulation [1]. it has been established that an impregnated system prepared without sufficient care against contamination and/or possible micro-cavities may be subject to several mechanisms, which may cause its ultimate deterioration [16]. quite early it was shown that the nature of the impregnating liquid is most important for the electrical behavior of a composite insulating system. the breakdown strength of low density polyethylene (ldpe) extruded film was reported to be lower when the film was immersed into odichlobenzene than when it was immersed into transformer oil or chlorinated biphenyls. many pre-breakdown discharges were evident in the o-dichlorobenzene in contrast to either the transformer oil or the chlorinated biphenyls [11]. silicone oil or diethyleneglycol were shown to impregnate xlpe cable insulation better since they both indicated considerable improvement in breakdown strength. such liquids exhibited a 50% or even better increase in impulse and ac breakdown strength. this improvement was attributed to the moderation of the fatigue mechanism when liquid replaced gas in the microspaces and consequently to a reduction in the energy of ionic or electronic deteriorative process [27]. in further studies, other researchers continued working on xlpe cables considering filling the microporosities in xlpe with appropriate gases (such as sf6). they showed that the ac breakdown strength as well as the partial discharge behavior improved [28]. in [15], dc and impulse breakdown strength of polypropylene increased by impregnation with suitable dipolar engineering, technology & applied science research vol. 10, no. 2, 2020, 5505-5511 5507 www.etasr.com danikas et al.: some factors affecting the breakdown strength of solid dielectrics: a short review liquids (hexachlorodiphenyl –hcp, trichlorodiphenyl – tcp, dibutyl phthalate-dp) at both room and liquid-air temperatures. the breakdown strength of polythene impregnated with chlorinated diphenyl was also found to increase at room temperature under impulse conditions. high stability is required from the combination of polymeric insulation and the impregnant since they have to resistant to thermal degradation and to oxidation [29, 30]. low viscosity oils are preferable because of their better impregnation when in contact with polymers. moreover, low viscosity oils absorb gas more easily than heavily viscous oils [31]. as was pointed out more recently, “the gas absorption property of an impregnating liquid together with its viscosity determines to a very great extent the partial discharge performance of the liquid impregnated system” [32]. a low viscosity and high gas absorption capacity oil is always desirable in order to have low discharge activity and consequently a high breakdown strength. a combination of polymer and of a low viscosity absorbing liquid was proposed several years ago. that was a combination of uniaxially orientated polyethylene (uope) and dodecylbenzene (ddb) oil [33-35]. experimental results indicated that since collision impact of electrons accelerated in the free volume is the dominant cause for electrical tree initiation, liquid impregnation is a promising way to improve the performance of polymeric materials and to rise the breakdown strength [36]. swelling of the polymer is another parameter determining the behavior of a composite insulation and must be avoided since the breakdown strength of the composite insulation can be seriously deteriorated. previous work on this has shown that the ac breakdown strength of a polypropylene laminated paper/oil combination decreases as swelling worsens [37]. similar conclusions were reached with another composite insulating system consisting of uope/ddb oil [33-35]. in [38], the problem of solid/liquid combination was attacked from another angle, namely that of the interface and also in terms of the water content. it was concluded that the breakdown voltage is reduced more dramatically when temperature is low and water content is also low. swelling of polypropylene (pp) films with rapeseed oil was not that significant and, moreover, the oil impregnation rose the breakdown strength from 640v/µm to 810v/µm. this rise was attributed to the diffusion of the rapeseed oil into the pp film. with oil diffusion, the pp foil structure becomes more regular as the free volume of the dielectric is filled with the impregnant. therefore the electric field distribution in the case of applied voltage becomes more homogeneous and thus the breakdown strength of the pp foils increases [39]. the advantages of rapeseed oil (good impregnation, good resistance to aging) were also reported in [40]. it must be noted, however, that rapeseed oil lacks w.r.t. aging vegetable oil which has excellent resistance to aging [41]. v. temperature effect temperature has long been recognized of having a significant effect on the breakdown process of solid insulating materials. quite early it was reported, among other types of deterioration, the thermal depolymerization of polymeric insulating materials. at elevated temperatures, polymer chains break into smaller units and this can happen even when oxygen is not present [42]. more recently, some other researchers, investigating oil filled kraft-paper cable at high temperature for a long time, reported that there will eventually be a failure because of saturation of the impregnant by gas formed as a result of thermal degradation of the cellulose [43]. experiments with polyethylene films indicated that the breakdown strength decreases with increasing temperature. as an explanation, it was put forward the electron thermal runaway in localized electron system caused by the interaction with conduction electrons [21]. other researchers looked at the temperature effect from another interesting viewpoint, namely that of the temperature influence during sample preparation. in this case, temperature may greatly influence the morphology of a polymer and also the field necessary for tree initiation. as ambient temperature increases, both tree initiation and breakdown occur at lower stresses [44]. experiments with low-density polyethylene (ldpe) samples of various thicknesses showed that in the range of 80 o to 100 o c, breakdown strength increased. above and below this temperature range, the slope of temperature dependence of breakdown strength was observed to be negative. such a behavior could be explained by suggesting that the input energy rate from impulse voltage is partly devoted to melt the crystalline lamellae increasing thus the amorphous parts and decreasing the electron mobility. consequently, an increase of the electric stress is needed to trigger a breakdown [45]. orientated polymers seem to be more stable than nonorientated polymers. however, as mentioned in [29], orientated polymers may be subjected to a rapid shrinkage above a critical temperature. degradation of uope films has been observed several years ago, especially when these are combined with ddb oil [33-35]. besides the fact that such a composite system (uope/ddb oil) starts having problems at about 110 o c, oils with aromatic constituents can cause crazing to polymers much more easily than polybutene oil [46, 47]. on the other hand, polybutene oil has poorer gas absorbing characteristics, its absorption rate of hydrogen being equal to 1/9 of that of the ddb oil [48]. regarding composite solid/liquid insulating systems, it is worth noting that, in earlier decades some researchers investigating the gassing characteristics of mineral oils, reported that an increase in temperature leads to an increase in gas absorption as well as in gas evolution [49, 50]. elevated temperature tests turn out to give lower breakdown strength, which may be due to an increase of the thickness of the amorphous region of the polymer and to the greater solubility and diffusivity of the gaseous byproducts. greater solubility and diffusivity in turn will sustain discharges of a certain magnitude and will possibly cause discharges of an even larger magnitude, which will erode the polymer with accelerating rate and will eventually lead to failure [33-35]. measurements with dc voltages showed that the breakdown strength of fluorinated parylene (pa-f) decreased with increasing temperature from ambient up to 350 o c. the authors attributed the decrease to the fact that the thermal energy induces changes leading to the acceleration of free electrons. moreover, as the temperature increases, the trapped engineering, technology & applied science research vol. 10, no. 2, 2020, 5505-5511 5508 www.etasr.com danikas et al.: some factors affecting the breakdown strength of solid dielectrics: a short review electrons are freed more easily with less electric field needed. a further contributing factor to the decrease of the breakdown strength is the decrease of the material density due to the free volume increase [51]. such an interpretation is in agreement with previous publications [52, 53]. the interpretations of [5153] are not fundamentally different from the interpretations given earlier [45]. the free volume increase, the accumulation of internal heat and of the space charges cause an increasing electric field distortion with increasing temperature and thus they become the contributing factors for the decrease of breakdown strength of xlpe with dc voltages [54]. in [55], polyethylene terephthalate (pet) showed a decrease of breakdown strength going up from 33 o c to 73 o c because of – as the authors claimed – the activation of thermal breakdown pathways [55]. such an approach is not radically different from the interpretation given in [21]. the work performed with thin and thick dielectric films introduced yet another parameter. it was observed that while the breakdown strength decreased with increasing temperature, such a decrease was less noticed with thicker samples than with thinner samples. it was suggested that the breakdown strength is less sensitive to temperature for thicker samples because the electromechanical mechanism is the dominant mechanism for the dielectric breakdown [56, 57]. on the other hand, their interpretation for the dependence of the thinner samples was similar to the interpretation put forward in [51]. vi. the role of interfaces interfaces play a significant role in determining the breakdown strength of solid dielectrics. differing phases may also play a role. the interfacial domain between crystalline and amorphous phases may well determine the various properties of semi-crystalline polymeric materials [58]. interfacial breakdown was studied with a variety of electrode systems. paper and transformer oil were used as insulation. when the paper was not carefully dried, interfacial breakdown would occur [59]. in [59], however, was also noted that with a carefully prepared paper-oil interface, breakdown did not necessarily took place at the interface. such observations were also made later with silicone rubber interfaces [60]. modern insulating systems, such as those with solid dielectrics, did not avoid problems of interfaces, since there were interfaces of semi-conducting sheaths with the main insulation or the inclusion of microcavities and/or impurities [61, 62]. the role of microcavities at interfaces between solid and solid dielectric was treated in [63]. microcavities between solid dielectrics, especially with the applied field parallel to the interface, enhance the risk of low breakdown strength. such risk may be avoided if a mechanical pressure is applied to the two solids. mechanical pressure (i.e. contact pressure) implies a better contact between the two surfaces and consequently, a better interface [64, 65]. in [66], the same research group claimed that lubricated interfaces offer higher breakdown strength than nonlubricated interfaces. moreover, in silicone rubber-silicone rubber interfaces, despite the fact that air voids are the limiting factor, the injection of liquids/gels to air voids is of vital importance for high breakdown strength. authors in [64-66] confirmed the observations and conclusions of earlier works [67, 68]. in a further work, one of the authors of [66] distinguished between vented and enclosed cavities at an interface between solid-solid dielectrics, and he proposed the idea that discharges inside such cavities may develop to streamers, which in turn will lead to breakdown. the gas pressure inside the enclosed cavities is likely to increase as a function of the change in the size of the cavity, the extent of which is dependent on the contact pressure and elastic modulus. increased gas pressure, in turn increases the discharge field strength of the cavities according to paschen’s law [69]. the threshold electric field for partial discharge initiation depends primarily on the solid dielectric under stress, when the surrounding medium is air or liquid. this threshold field was shown to be much lower in the case of solid-air interfaces than in the case of solid-liquid interfaces. such experimental data indicated the importance of impregnation with liquids [70]. quite early research pointed out that prolonged heating in a composite solid-liquid insulating system affects mainly the solid component, and in the case of paper-oil system, a significant increase of acidity was observed. evidently, the increase of acidity of the oil after prolonged heating in the presence of paper was due to the degradation of the paper and not to the alteration of the oil [71]. furthering and extending the thoughts of [71], it was shown later that – with polycarbonate impregnated with low viscosity mineral oil – ionizable impurities in mineral oil enhance space charge losses. the latter in turn causes the lowering of breakdown strength [72]. the importance of ionic carriers for the dielectric behavior of a polypropylene/oil system was also noticed in [73]. considering the role of interfaces on lapped taped polymers (such as hdpe, polypropylene, and nylon impregnated with supercritical helium) authors in [74] indicated that there is no tendency for the discharges and breakdown to concentrate in butt gaps adjacent to the metal conductor. the butt gaps next to the conductor were no more frequently the seat of breakdown than the butt gaps in the interior of the insulation. in this respect, the authors in [74] reached similar conclusions with the authors in [59, 60]. more recently, the importance of the difference between the permittivities of the solid dielectric and the liquid insulant was emphasized w.r.t the electric field applied parallel to the interface. as the solid dielectric has – as usually is the case – a higher permittivity than the liquid, the initial streamer will convert to breakdown as the strong attractive force causes the streamer to settle on the interface. parallel high permittivity liquid immersed dielectrics accelerate the charge transport between the electrodes [75]. the conclusions of [75] are in accordance with those published earlier, where it was remarked that the flashover mechanism is initiated in the liquid immediately adjacent to the spacer/liquid interface as a consequence of electric-field intensification induced by permittivity mismatching between the solid and the liquid [76]. as noted elsewhere, breakdown strength depends on the quality of the interfaces. due attention must be paid to the choosing of the materials for specific applications and to the construction of the composite insulating system. interfaces in the conventional insulating systems, can be considered as the weak aspects of such systems. without the need of an exaggeration, one can conclude that the problems arising in engineering, technology & applied science research vol. 10, no. 2, 2020, 5505-5511 5509 www.etasr.com danikas et al.: some factors affecting the breakdown strength of solid dielectrics: a short review high voltage applications are for the most part problems of interfaces [77]. vii. mechanical stressing in the context of the present paper we will not deal with mechanical stressing and its effect on electrical trees in solid dielectrics (since this topic has been dealt before [78]) nor we will deal with internal residual mechanical stresses. the aim here is to somehow mention several studies in relation to the mechanical stressing to the breakdown strength of soli dielectrics. about four decades ago, it was shown that both dc and impulse breakdown strength of polythene increased by compression. the effect of changing from an uncompressed to a compressed sample was an increase of 38% in the mean breakdown strength (from 0.61 to 0.84gv/m) [15]. indications of the influence of mechanical stressing on the breakdown strength of polythene were given even earlier, when it was noted that its impulse strength at 80 o c was much higher than the breakdown strength of the same material tested under the same temperature with a slowly applied electric stress [79]. the beneficial effect of compressive stresses can be understood on the basis of an initial increase of density, which results in closing up voids and to increase molecular packing. on the other hand, the compressive stresses may cause the breakage of tie-bonds and create defects. this is the reason for which, experiments with pet and epoxy resin showed that, although initially there was an increase of breakdown strength, subsequently it decreased. tensile stresses may cause crack initiation and growth. such stresses may cause defects at the amorphous-lamellae interfaces of semi-crystalline polymers (such as polyethylene and polypropylene) [80]. the observations of [80] confirmed previous research, where it was indicated that elongation causes a decrease of breakdown strength for both ldpe and hdpe, no matter what sort of voltage was applied (ac, dc, and impulse). the authors attributed the decrease to defects produced by mechanical stretching [81]. confirmation of [80], as to the perplexing effect of compressive stresses on polymers, was reported recently [82], where the authors investigated the breakdown strength of an acrylic dielectric elastomer. the authors especially emphasized on the relation between the electrode configuration and the applied compressive stresses. tensile stresses may have a beneficial effect with some polymeric materials since they tend to decrease thickness and consequently to increase breakdown strength. such data were given with transparent silicone polymers in [83]. a recent report tackled the problems of both tensile and compressive stresses. it stated that when the silicone rubber is subjected to a tensile stress, the molecular chains are stretched in the stress direction leading to fracturing. on the contrary, when a compressive stress is applied, the molecular chains come closer and they generate more attraction bonds and consequently more stabilization in the silicone rubber structure [84]. in yet another recent publication, it was reported that the accumulated damage is higher in the case of tensile stress than in the case of compressive stress, whereas the space charge, free volume and partial discharges increase in the presence of tensile stresses and decrease in the presence of compressive stresses [85]. viii. some general remarks in this paper, a brief review on some factors affecting the breakdown strength of polymeric materials is given. although effects such the area effect are more or less clear by now, other factors, such as the role of crystallinity, need further clarification. as was noted recently, the effect of polymer crystallinity on breakdown strength is a problem of carrier mobility in general. as carrier mobility increases, breakdown strength decreases. therefore polymers with higher crystallinity have lower breakdown strength than those with lower crystallinity. on the other hand, if polymers have a lot of small crystallites (even if crystallinity is large), inter-crystal boundaries may reduce mobility, and therefore increase breakdown strength. detailed states of polymers (morphology, impurities, crystal-amorphous boundary conditions, density of boundaries, length of crystals and amorphous regions) play a crucial role [86]. carrier mobility also increases as temperature increases in both crystalline and amorphous regions and drastic increase in mobility is anticipated especially in the amorphous regions [86]. the influence of mechanical stresses is also a subject in need of further exploration since with tensile stresses there is a critical value for crack formation, whereas with compressive stresses there is the possibility of breakage of tiebonds and of creation of defects. ix. conclusions the present paper deals with some factors affecting the breakdown strength of polymeric materials. factors such as the area of the electrodes, the polymer crystallinity, the impregnation of polymers, the temperature effect, the quality of interfaces, and the effect of mechanical stresses are investigated and commented upon. in the context of this brief review, only conventional polymers were considered. references [1] d. kind, h. karner, high-voltage insulation technology, springer, 1985 [2] m. s. naidu, v. kamaraju, 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model library of technological mining equipment an integrated model for technological processes of underground coal mining in stoping face was developed. the main goal of simulation for coal mining technological processes in stoping face is the evaluation of productivity of a cutter-loader depending on different factors like the technical parameters of the cutter-loader, size of the longwall face, geophysical state of the coal seam. keywords-coal mining; simulation system; visual interactive simulation; longwall mining system i. introduction many coal mines face problems while making decisions to increase productivity, improve coal production planning, use new mining equipment and new perspective technologies for coal mining. the most suitable way to solve these problems is simulation. a large number of publications on the use of simulation to support decision making on the design, development and optimization of coal mines testifies the importance of these problems [1-8]. to solve these problems the simulation system mtss [9] was developed. it is a visual interactive and process-oriented discrete simulation system intended to develop and execute the technological processes of models. a distinguishing feature of the simulation system is its orientation towards users who are experts in a particular subject area (process engineers, mining engineers) but do not have experience in usage of universal simulation systems. fast model development is carried out due to the visual-interactive interface and specialized model libraries of technological equipment for specific subject areas. the simulation system mtss provides the user with the following options: visually interactive model construction with a graphical editor, setting model parameters, various modes of model execution, 2d and 3d model visualization. mtss uses 2d as a graphical editor and 2d, 3d visualization of model execution. to simulate the technological processes in coal mines in mtss the specialized libraries of technological equipment for such mine subsystems as an underground conveyor network, a pumping subsystem, and a power supply subsystem were developed. with the use of the specialized libraries a number of models of these subsystems for underground coal mines in kuznetsk coal basin (russia, western siberia) were created [10]. in this article a new specialized library of models of mining equipment in the stoping face is considered. the second section provides a mathematical model of the technological process of coal mining in the stoping face. the third section describes the simulation model of the technological process of coal mining in the stoping face developed using the new specialized library of models and the results of its implementation. ii. the mathematical model of productivity of the cutter-loader the theoretical advance speed of a cutter-loader is [11, 12]: 1 1 2 2 3 4 5 6 3 0 c os k k k k k k n n v fp p sin s d n       (1) where v — the speed of the cutter-loader, n — the power of the effector motor, η — the efficiency of the effector reduction gearing, n1 — the cutting tools in the cutting line, k1 — the coefficient of the horsepower input to cutterloader travel, f — the cutter-loader and transporter friction coefficient, p — the cutter-loader weight, α — the angle of inclination of the cutter-loader. “plus” and “minus” in front of the cutter-loader weight specify the cutter-loader movement up and down the longwall, respectively. s — the weighted average of the coal cutting resistance, d —the diameter of the augers, n2 — the cutting tools that synchronously cut the face, k2 — the coefficient of squeeze which takes into account the cutting force decrease due to the ground pressure. engineering, technology & applied science research vol. 8, no. 3, 2018, 3060-3063 3061 www.etasr.com okolnishnikov: an mtss based underground coal mining simulation model k3, k4, k5, k6 are the coefficients for the cutting angle, the cutting tool width, the cutting tool dulling and the cutting tool shape, respectively. among the above mentioned parameters the coal cutting resistance s influences the motion rate the most. the coal cutting resistance is considered to be invariable in a certain vast area and is defined by data obtained while drilling the geological prospecting well with (2) 1 ( )c c r r c r k m f m f s m m    (2) where mc, mr — the coal mass and the rock mass respectively, fc, fr — the coal hardness and the interbed rock hardness respectively, k — a certain coefficient. in the case of several geological prospecting wells s is calculated with the inverse distance weighting method according to (3). 2 1 2 1 , 0 ( , ) , 0 n i i i in i i i i d s if d s x y d s if d               (3) where n — the number of wells nearest to stoping face that are taken into account while calculating, si — the coal cutting resistance in i-th well calculated with (2), di — the distance between the i-th well and the mining face with current position (x,y), calculated with (4) 22 )()( iii yyxxd  (4) where (xi , yi) — the coordinates of the ith well. while one-way operating of the cutter-loader the time of one way is: 1 1 one way scr end one cut end one cut scr t t t t l l t v v            (5) where l — the length of the longwall face, v1 — the speed of the cutter-loader movement up the longwall determined by (1), vscr — the speed of the cutter-loader movement when scraping operation is performing, tend one cut — the time of the cutter-loader at the end of the longwall face by one-way operating. while shuttle operating of the cutter-loader the time of one cycle is: 1 2 1 2 2 2shuttle end end l l t t t t t v v       (6) where l — the length of the longwall face, v1, v2 — the speeds of the cutter-loader movement up and down the longwall determined by (1), respectively, tend — the time of the cutter-loader at the end of the longwall face by shuttle operating. while one-way operating of the cutter-loader the productivity of the cutter-loader per time twork is : work one way one way mrlт a т     (7) where γ — the average mean density of the rock mass, m — the working-bed height, r — the cutter–loader cut width. substituting v1 from (1) into (5) and tone way from (5) into (7) we get: 2 2 3 4 5 6 1 1 +co 3 s 1 0 scr work one way end one cut mrт a f sdn k k k k k tp psin n n k v l           (8) while shuttle operating of the cutter-loader the productivity of the cutter-loader per time twork is: 2 work shuttle shuttle mrlт a т   (9) substituting v1, v2 from (1) into (6) and tshuttle from (6) into (9) we get: 2 2 3 4 5 6 1 1 cos + 30 work shuttle end mrт a fp sdn k k k k k t n n k l      (10) iii. integrated simulating model of stoping face operations in the frames of simulation system mtss, a specialized library of simulating models of mining equipment (a conveyor, a cutter-loader, a self-moving roof support etc.) used in coal mining in stoping face was implemented. using the specialized library of simulating models of mining equipment an integrated model for technological processes of underground coal mining in stoping face was developed. the integrated model involves the following interactive models:  a coal seam model,  a cutter-loader model moving up and down the longwall face,  a model of a self-moving roof support,  a model of a flight conveyor. engineering, technology & applied science research vol. 8, no. 3, 2018, 3060-3063 3062 www.etasr.com okolnishnikov: an mtss based underground coal mining simulation model all parameters of the mine equipment models correlate with the parameters of the actual mine equipment operating at one of the coal mine in in kuznetsk coal basin. the goals of the simulation for coal mining technological processes in stoping face are:  the evaluation of productivity of a cutter-loader depending on different factors including the variety of geophysical conditions of the coal seam,  the input data acquisition (input coal stream) for operating of the belt conveyor network model of the coal mine. generally, in the stoping face the following factors influence the productivity of the cutter-loader:  the geophysical state of the coal seam,  the advance speed of the cutter-loader,  the technical characteristics of the cutter-loader,  the delays at the end of the longwall face,  the delays associated with the movement of the roof support,  the delays associated with the flight conveyor,  the delays associated with the belt conveyor,  the delays associated with the increase of methane release,  the delays associated with equipment failures,  regulation conditions and maintenance etc. in this paper, the influence of the first six factors of the cutter-loader productivity was studied. since the main factor influencing the cutter-loader productivity is the state of the coal seam (the coal cutting resistance) which restricts the advance speed of the cutter-loader, the subject of the research is the detailed simulating of one-way operating and shuttle operating of the cutter-loader together with roof supports movement depending on the geophysical state of the coal seam. under these conditions the top speed and the cutter-loader productivity were calculated with (1) and (7). figure 1 shows the coal seam model with two geological prospecting wells. figure 2 shows the integrated model of underground coal mining technological processes in stoping face carried out with simulation system mtss. the coal seam with two geological prospecting wells is painted over. the areas with reduced resistance are painted in a lighter tone. the belt conveyor and power lines are designated in the main window. the equipment parameters and operation modes can be set interactively in the parameters window. the control buttons are entered in the main window: to start the cutter-loader; to stop the cutterloader. with the developed simulation model of the technological process of underground coal mining in the stoping face a series of experiments was performed. for oneway and shuttle operations the average productivity of the cutter-loader was calculated, depending on the length of the longwall face. all experiments were carried out under equal conditions of the passage of the cutter-loader for a certain depth into the coal seam. fig. 1. the 3d coal seam model with two geological prospecting wells. fig. 2. the main window of the stoping face model. engineering, technology & applied science research vol. 8, no. 3, 2018, 3060-3063 3063 www.etasr.com okolnishnikov: an mtss based underground coal mining simulation model the obtained results are presented in the form of graphs in figure 3. the obtained results allow us to conclude the following:  the shuttle operation of coal mining in the stoping face is more productive in comparison with the one-way operation.  increasing the length of the longwall face, beginning from a certain value, does not significantly affect the increase in the productivity of the cutter-loader. fig. 3. the dependence of the productivity of the cutter-loader on the length of longwall face. iv. conclusion the extension of the considered simulation model of the stoping face operation is assumed to be carried out in the future. models of aerogasdynamics of methane-air flow in a long stope and models of a belt conveyors subsystem, a ventilating subsystem and a power supply subsystem of the coal mine will be additionally included into the integrated model of the stoping face operation. the mtss simulation system can be used not only for simulation of the existing coal mining technologies, but also for simulation of perspective robotized technologies and staffless coal mining technologies. acknowledgement this research was partially financially supported by the russian foundation for basic research (project 16-07-01179). references [1] a. salama, j. greberg, h. schunnesson, “the use of discrete event simulation for 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science research, vol. 6, no. 3, pp. 993-999, 2016 [11] a. a. ordin, a. a. metel’kov, “optimization of the fully-mechanized stoping face length and efficiency in a coal mine”, journal of mining science, vol. 49, no. 2, pp. 254-264, 2013 [12] a. a. ordin, a. a. metel’kov, “analysis of longwall face output in screw-type cutter–loader-and-scraper conveyor system in underground mining of flat-lying coal beds”, journal of mining science, vol. 51, no. 6, pp. 1173-1179, 2015 microsoft word etasr_v11_n6_pp7867-7874 engineering, technology & applied science research vol. 11, no. 6, 2021, 7867-7874 7867 www.etasr.com iftikhar et al.: evaluating the performance parameters of cryptographic algorithms for iot-based … evaluating the performance parameters of cryptographic algorithms for iot-based devices umar iftikhar computer and information systems engineering dept. ned university of engineering and technology karachi, pakistan maria waqas computer and information systems engineering dept. ned university of engineering and technology karachi, pakistan kashif asrar computer and information systems engineering dept. ned university of engineering and technology karachi, pakistan syed abbas ali computer and information systems engineering dept. ned university of engineering and technology karachi, pakistan abstract-nowadays, terabytes of digital data are generated and sent online every second. however, securing this extent of information has always been a challenging task. cryptography is a fundamental method for securing data, as it makes data unintelligible for attackers, offering privacy to authorized clients. different cryptographic algorithms have different speeds and costs that make them suitable for different applications. for instance, banking applications need outrageous security amenities, as they utilize superior algorithms having greater requirements, while gaming applications focus more on speed and cost reduction. consequently, cryptographic algorithms are chosen based on a client's prerequisites. this study compared des, aes, blowfish, and rsa, examining their speed, cost, and performance, and discussed their adequacy for use in wireless sensor networks and peer-to-peer communication. keywords-des; aes; blowfish; rsa i. introduction cryptography is the study of utilizing math to conceal messages and has been around since the inception of human civilizations. from the hand-ciphers used thousands of years ago, to electronic ciphers used in modern commercial applications and war, mankind utilized cryptography to ensure the secrecy of information. the advance of programmable computers necessitated more complex cryptographic algorithms and expanded their application domain to secure data confidentiality and integrity, user authentication, and prevention of cyber-attacks [1]. today, there is a wide variety of powerful encryption algorithms, offering different combinations of speed, security, and computational resources. all efforts in this area converge to the single goal of making the encryption secure at the best cost to performance ratio [26]. cryptographic algorithms are characterized as symmetric or asymmetric, depending on the keys they utilize. data encryption standard (des) was developed in the '70s and is considered to be the pioneer symmetric algorithm, using fixed key lengths. its most prominent successors are tripledes (3des) and advanced encryption standard (aes), with the latter being the most preferred today. blowfish is another popular symmetric scheme that uses variable key length, while river ciphers also belong in this group. in the asymmetric category, rivest-shamir and adleman (rsa) and elliptic curve cryptography (ecc) are the undisputed kings [7]. many researchers investigated these strategies to track down the best in terms of execution cost [2-21]. authors in [10] compared the strengths and weaknesses of each algorithm. they compared experimentally the most significant encryption algorithms on metrics like memory usage, time consumption, and the avalanche effect, concluding that each one has a separate set of domain-wise strengths. blowfish was the most economical in terms of time and memory usage, aes had the most cryptographic strength, and des was the most bandwidthefficient. this study extends the analysis with exclusive emphasis on decryption efficiency, as it can be a useful factor for selecting an encryption algorithm in certain domains. additionally, these algorithms were examined for their adequacy on wireless sensor networks and peer-to-peer communication. ii. the investigated and implemented cryptography algorithms during this study the des, aes, rsa, and blowfish algorithms were implemented in java. the source code used for the evaluation of each algorithm including its description, methodology, and execution pattern is exhibited along with the block diagrams of the main functions of each algorithm. a. des des is based on symmetric key square code and uses a 56bit key in 64-bit blocks [7]. des has 16 phases, also named as rounds [2], and uses the following functions: • a zor function that takes a stream and generates an integer result corresponding author: umar iftikhar (umariftikhar@neduet.edu.pk) engineering, technology & applied science research vol. 11, no. 6, 2021, 7867-7874 7868 www.etasr.com iftikhar et al.: evaluating the performance parameters of cryptographic algorithms for iot-based … • the en_box function that generates an array • the s_box that takes a 48-bit input and returns a 32 bit output • the f_permute that uses a loop to return permuted data • the fn_function that uses xor to return a xorstream • a user_input function to get key bits and data bits fig. 1. des sub-key generation. the function definitions are: def zor(left,xorstream): xorresult = np.logical_xor(left,xorstream) xorresult = xorresult.astype(int) return zorresult def en_box(right_data): expanded_data = np.empty_data(48) j = 0 for i in ebox: expanded_data[j] = right[i-1] j+=1 expanded_data = list(map(int,expanded_data)) expanded_data = np.array(expanded_data) return expanded_data def f_permute(topermute): permuted_data= np.empty_data(32) e = 0 for f in f_pbox: permuted_data[j] = topermute[f-1] e+=1 return permuted_data def fn_function(right_data,rkey): expanded_data = e_box(right_data) xored = xor(expanded_data,rkey) sboxed = sbox(xored) xorstream = f_permute(sboxed) return xorstream fig. 2. des block diagram. fig. 3. des round block diagram. engineering, technology & applied science research vol. 11, no. 6, 2021, 7867-7874 7869 www.etasr.com iftikhar et al.: evaluating the performance parameters of cryptographic algorithms for iot-based … fig. 4. des function block diagram. b. aes aes is a symmetric key square code algorithm that was developed as a replacement for des. aes utilizes three key sizes of 128, 192, and 256 bits, and uses 128-bit blocks that can be encrypted in one go, as it is much faster than des. encryption and decryption in aes are performed in multiple rounds. the number of rounds used for the encryption or decryption varies with the key size between 10, 12, and 14 for 128, 192, and 256 keys respectively. aes consists of 3 steps that contain different combinations of specified operations [4]. the step by step procedure for aes algorithm is: • initialize the constructor function • change _of _key uses a text to matrix function along with a control structure to generate a list of round keys • the encryption gets a plain state from text to matrix and returns the matrix to text • the decryption gets the cipher state object and uses multiple returns matrix to text • round_key_addition, _rounding_ encrypt, and a few more functions are used to generate the final output the function definitions are: def text_to_matrix(text_data): matrix_data = [] for e in range(16): byte = (text >> (8 * (15 e))) & 0xff if e % 4 == 0: matrix_data.append([byte_data]) else: matrix_data[e / 4].append(byte_data) return matrix_data def matrix_to_text(matrix_data): text_data = 0 for e in range(4): for f in range(4): text |= (matrix_data [e][f] << (120 8 * (4 * e + f))) return text def round_key_addition(self, r, k): for e in range(4): for f in range(4): s[e][f] ^= k[e][f] fig. 5. aes block diagram. engineering, technology & applied science research vol. 11, no. 6, 2021, 7867-7874 7870 www.etasr.com iftikhar et al.: evaluating the performance parameters of cryptographic algorithms for iot-based … def _rounding_encrypt(self, state_matrix_data, key_matrix_data): self.__sub_bytes_data(state_matrix_data) self.__shift_rows_data(state_matrix_data) self.__mix_columns_data(state_matrix_data) self.__add_round_key_data(state_matrix_data, key_matrix_data) the encryption steps are: • add round key: data are straightforwardly xored with the round key or the code key of 128 pieces. • sub bytes: breaks the input into bytes and then passes it via a substitution box. unlike des, aes has the same sbox for all bytes. returns a 4×4 matrix. • shift rows: the rows of the obtained matrix from the sub bytes are shifted left. since it's a 4×4 network, the fourth column is moved threefold, the third is moved twice, the second is shifted once, and the first remains unshifted. hence, each n-th row will be shifted (n-1) times. • mix columns: interchanges the columns via a mathematical function to get the output. the above steps may be applied in reverse to get the deciphered text. c. rsa rsa was named after its 3 donors, rivest–shamir– adelman. the key length must be greater than 1024 bits and the plain text to encrypt must be at least 512 bits. since it utilizes mathematic prime number calculations, it has very high encryption and decryption times and consumes a lot of computational power [20]. the private key is generated in the pkcs#8 format, whereas the public key uses the x.509 format. fig. 6. rsa encryption. the step by step procedure of rsa is: • two large prime numbers are selected • a pair of public and private keys is generated. • the user enters a message to be encrypted • the encrypt_data_message function takes two arguments (public key and message) to generate the encrypted text. • the private key can be used to decrypt the data message. fig. 7. rsa decryption. fig. 8. rsa key generation. engineering, technology & applied science research vol. 11, no. 6, 2021, 7867-7874 7871 www.etasr.com iftikhar et al.: evaluating the performance parameters of cryptographic algorithms for iot-based … the function definitions are: def encrypt_data_message(pk, plaintext): key, n = p_k cipher_text = [pow(ord(char), key, n) for char in plaintext] return cipher_text def decrypt_data_message(pk, cipher_text): key, n = p_k aux = [str(pow(char, key, n)) for char in ciphertext] plain = [chr(int(char2)) for char2 in aux] return join(plain) d. blowfish blowfish is a symmetric key square code with a variable key length from 32 to 448 bits and a block size of 64 bits. blowfish is faster than des and is considered a promising encryption algorithm. blowfish's advantages are its speed, the fewer memory requirements, whereas it is straightforward and more secure as it uses variable key length [5]. blowfish is a block cipher having a variable order_of_byte which finds out the number of bytes and uses the big-endian byte order. the functions per_array and sub_boxes are used to define array and substitute boxes. two static methods are used, namely data_encrypt and data_decrypt, to get the encrypted and decrypted data. the function definitions are: def data_encrypt(l, r, p, s1, s2, s3, s4, u4_1_pack, u1_4_unpack): for p1, p2 in p[:-1]: l ^= p1 a, b, c, d = u1_4_unpack(u4_1_pack(l)) r ^= (s1[a] + s2[b] ̂ s3[c]) + s4[d] & 0xffffffff r ^= p2 a, b, c, d = u1_4_unpack(u4_1_pack(r)) l ^= (s1[a] + s2[b] ^ s3[c]) + s4[d] & 0xffffffff p_penultimate, p_last = p[-1] return r ^ p_last, l ^ p_penultimate def data_decrypt(l, r, p, s1, s2, s3, s4, u4_1_pack, u1_4_unpack): for p2, p1 in p[:0:-1]: l ^= p1 a, b, c, d = u1_4_unpack(u4_1_pack(l)) r ^= (s1[a] + s2[b] ̂ s3[c]) + s4[d] & 0xffffffff r ^= p2 a, b, c, d = u1_4_unpack(u4_1_pack(r)) l ^= (s1[a] + s2[b] ^ s3[c]) + s4[d] & 0xffffffff p_first, p_second = p[0] return r ^ p_first, l ^ p_second def __init__(self, key, byte_order = "large", p_array = pi_p_array, s_boxes = pi_s_boxes): 1) sub-key generation keys should be ready before data encryption or decryption. the variable-length key is produced using k1, k2, k3 … kn, where [1 ≤ n ≤ 14] and every k has 32-bits. key length can be anything from 32 to 448 bits. the p-array has eighteen 32cycle sub-keys: p1, p2… p18. four s-boxes or replacement boxes are used, each having 256 entries, and all 256 elements are of 32bits. s1 s0, s1, … s255 s2 s0, s1, … s255 s3 s0, s1, … s255 s4 s0, s1, … s255 the sub-keys are produced as: • instate the p-exhibit and four s-boxes with a static string. this string contains the hexadecimal digits of π. • the main component in the p-exhibit (p1) is xored with the initial 32 pieces of the key k1, the second component in the p-cluster (p2) is xored with the second 32 pieces of the key k2. rehash until every p-cluster component is xored with the key pieces. • encode every string by blowfish encryption calculation utilizing the sub keys from p1 to p18. • change p1 and p2 with the yield of the third step. • utilize the adjusted sub keys to encode the yield of the third step. • change p3 and p4 with the yield of the fifth step. this interaction proceeds until the whole of the p-cluster is changed. 2) data encryption the following steps are used for data encryption in the blowfish algorithm: • the 64-bit plain content is isolated into two sections, left 32-bit and right 32-bit. • the left 32-bit is xored with p1 and the yield is shipped off. blowfish function f is additionally utilized as right 32digit for the next round • the yield of capacity f is xored with the right 32-digit and the result is utilized as the left 32-bit of the next round. • this cycle is continued for 18 rounds, and the left and right output of round 18 are joined to give a 64-bit figure text. 3) blowfish function blowfish function (f) uses the following process: engineering, technology & applied science research vol. 11, no. 6, 2021, 7867-7874 7872 www.etasr.com iftikhar et al.: evaluating the performance parameters of cryptographic algorithms for iot-based … • the 32-bit input is divided into four 8-bit data, one for each s-box. • the s-boxes substitute 8-bit data into 32-bits. • the output of the first two s-boxes is added. • the result of the third step is xored with the output of sbox 3. • the result of the fourth step is added to the yield of s-box 4. • the result of the fifth step is the final output. fig. 9. blowfish block diagram. fig. 10. blowfish function f block diagram. iii. evaluation parameters each encryption strategy has advantages and disadvantages. specific details, such as speed and cost requirements, should be examined before choosing an appropriate cryptographic algorithm for an application. this section describes the parameters used to evaluate those algorithms. a. encryption time encryption time is the time needed to transform a plaintext to ciphertext and depends on three parameters: key size, plaintext block size, and mode. in this study, encryption time was estimated in milliseconds (ms). εncryption time impacts a framework's implementation, as shorter encryption time makes the framework more quick and responsive. b. decryption time decryption time is the time needed to convert ciphertext into plaintext. like encryption time, shorter decryption time increases a framework's responsiveness and speed. decryption time is also measured in ms. c. memory used each algorithm requires a different amount of memory space to execute. the memory size needed depends upon the number and kind of calculations, key size, and presentation vectors and affects system's cost. d. avalanche effect a desirable property of cryptographic algorithms is when a slight change in input changes the output significantly. this property is called dissemination or torrential slide impact. this is assessed using hamming distance, via the following equation: ��������� � ��� � �� ��� �������� � ��� ���� (1) e. entropy irregularity or vulnerability is a significant property in cryptography since data should not be speculated by an attacker. entropy is a measure of irregularity in data. higher entropy is essential for a more intricate connection between key and ciphertext. this property is called disarray and is determined by shannon's formula. iv. implementation the encryption and decryption algorithms of aes, des, rsa, and blowfish algorithms were implemented in java. java has packages that provide extensive support for aes and des. three parameters were identified for each algorithm: memory used in kbs, encryption and decryption times in ms. four different plain texts were used for each algorithm. v. results and discussion a. encryption time the result comparison is exhibited in figure 11. it can be noticed that blowfish has the sortest encryption time. b. decryption time as it can be noted from figure 12, decryption time is generally lesser than encryption time, while the rsa engineering, technology & applied science research vol. 11, no. 6, 2021, 7867-7874 7873 www.etasr.com iftikhar et al.: evaluating the performance parameters of cryptographic algorithms for iot-based … decryption requires longer and the blowfish requires lesser time. fig. 11. encryption time in ms for each algorithm. fig. 12. encryption time in ms for each algorithm. c. memory used memory utilization specifies the memory usage in both the encryption and decryption processes. figure 13 shows that rsa consumed more memory, due to its longer key length and two-step process nature, as it generated a pair of public and private keys before encryption. fig. 13. memory used by each algorithm. fig. 14. memory used in encryption by each algorithm. the decryption memory usage comes to be negligible (almost 0) when compared to encryption. the snapshots in figures 15-19 show the outputs observed after encrypting and decrypting a text. fig. 15. aes algorithm output. fig. 16. des algorithm output. fig. 17. rsa key generation step. fig. 18. rsa output. fig. 19. blowfish output. vi. conclusion every cryptographic algorithm has its strengths and weaknesses. rsa is comparatively costly in terms of time and power consumption. blowfish is effective for applications that require fast and secure communication, as it has lesser encryption and decryption times. aes is a very secure algorithm with a tradeoff of more memory usage and encryption time, whereas des has a lesser memory footprint. moreover, since decryption time is considerably lesser than encryption time, it requires less computational power making it highly effective in electronic devices having power consumption and battery life as crucial parameters [21]. for example, the control signals sent to sensors in wireless sensor networks that must be encrypted to avoid attacking or eavesdropping [6]. since those sensors' operation depends heavily on battery life, decryption algorithms can be used without significantly increasing power consumption or memory usage. references [1] p. patil, p. narayankar, d. g. narayan, and s. m. meena, "a comprehensive evaluation of cryptographic algorithms: des, 3des, aes, rsa and blowfish," procedia computer science, vol. 78, pp. 617–624, jan. 2016, https://doi.org/10.1016/j.procs.2016.02.108. [2] a. jeeva, d. v. palanisamy, and k. kanagaram, "comparative analysis of performance efficiency and security measures of some encryption algorithms," international journal of engineering research and, vol. 2, no. 3, pp. 3033–3037, may 2012. [3] h. o. alanazi, b. b. zaidan, a. a. zaidan, h. a. jalab, m. shabbir, and y. al-nabhani, "new comparative study between des, 3des and aes within nine factors," vol. 2, no. 3, p. 6, mar. 2010. engineering, technology & applied science research vol. 11, no. 6, 2021, 7867-7874 7874 www.etasr.com iftikhar et al.: evaluating the performance parameters of cryptographic algorithms for iot-based … [4] r. tripathi and s. agrawal, "comparative study of symmetric and asymmetric cryptography techniques," international journal of advanced foundation and research in computer, vol. 1, no. 6, jun. 2014. 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[20] e. s. i. harba, "secure data encryption through a combination of aes, rsa and hmac," engineering, technology & applied science research, vol. 7, no. 4, pp. 1781–1785, aug. 2017, https://doi.org/ 10.48084/etasr.1272. [21] a. s. alshammari, "comparison of a chaotic cryptosystem with other cryptography systems," engineering, technology & applied science research, vol. 10, no. 5, pp. 6187–6190, oct. 2020, https://doi.org/ 10.48084/etasr.3745. microsoft word 17-3440_s_etasr_v10_n3_pp5678-5682 engineering, technology & applied science research vol. 10, no. 3, 2020, 5678-5682 5678 www.etasr.com khan et al.: a review of software risk analysis with the use of classification techniques software risk analysis with the use of classification techniques: a review muhammad naeem ahmed khan independent researcher islamabad, pakistan mnak2010@gmail.com aamir mehmood mirza department of computer science baluchistan university of information technology, engineering and management sciences, quetta, pakistan mirza.aamir@buitms.edu.pk imran saleem school of professional advancement university of management and technology lahore, pakistan imran.saleem@umt.edu.pk abstract—risk analysis and management is a critical aspect of the software development process. various risks are associated with every phase of the software development lifecycle. the early identification of risks in each phase of software development coupled with mitigating plans can help to reduce the cost of the product and increase software quality. this study aims to explore various tools and techniques used in the literature of analyzing and managing risks. most risk analysis techniques have been applied in the requirement analysis phase, so there is a scarcity of tools supporting automated risk analysis. accommodating various types of risk factors to predict the software risks reduces the accuracy of the classifier. keywords-risk analysis; software risk; classification techniques i. introduction a software risk is a threat that could have a negative effect on software quality, delay the project or exceed the budget. it is necessary to identify various types of risk to a software project during the early phases of software development life cycle (sdlc). software risk poses serious threats to the software quality as the desired functionality may be compromised. the specific areas of sdlc which are affected by risks are software development, testing, and maintenance phases. software quality can be ensured by forecasting the risks that an existing software project can face. for this purpose, we use defect prevention, defect reduction, and defect containment. defect prediction is necessary to forecast the presence of defects in software modules. for defect prediction, we use historical data of the past projects and assess how many software defects are likely to present in the current projects. the purpose of this study is to find the merits and the demerits of the different classification techniques that have been applied for defect prediction. a critical review showing the usefulness of the various classification techniques on different types of software project datasets has been conducted in this report. developing an efficient software fault/risk prediction method is a highly demanding challenge. software fault/risk prediction plays an important role in analyzing software quality and balancing software development cost. early and accurate prediction of software risk has become a critical issue to project success. many researchers have proposed different prediction approaches such as an artificial neural networks, fuzzy logic, decision tree, bayesian network (bn), etc. to overcome the problem of risk in software development. as the demand for good software quality is increasing, increased software size and complexity may lead to increasing software faults which require identification at the early stages of sdlc. ii. literature review authors in [1] address the way risks affect different software development efforts. the study explores the causes of different risks with the use of a bn. the study combines expert knowledge and v-structure discovery algorithm to generate a bn that performs causality analysis to manage software project-related risks and to improve prediction accuracy. causality analysis is more useful than correlated analysis as the later approach does not help in effective risk planning. the objective of the study is to combine risk analysis and risk control for effective software risk management. authors employ expert knowledge to build a bayesian network in order to identify risks. the study is focused on three critical risk factors, namely inadequate requirements, lack of user cooperation, and poor project planning. however, 27 equally important risk factors were identified and bayesian network is efficient only for small datasets. involving many variables makes it more complex and different to understand. the way risks affect the analysis and design stages of sdlc is addressed in [2], in which a methodology called statebased risk assessment approach is explored, which is used to estimate risks for different states of a component and estimates the risk for the overall scenario on the basis of the entire component. the study introduced an inter-component state dependence graph that is used to estimate the complexity and severity of risk assessment. at first, complexity estimates, for the state of the component within the system, are made. then, the severity for the component within the scenario is decided using the three hazard technique: functional failure analysis, software failure mode and effect analysis, and software fault tree analysis. the objective of the study is to estimate the overall system risks that are based on the scenario risk and the state collaboration test model of the system (scotem). corresponding author: aamir mehmood mirza engineering, technology & applied science research vol. 10, no. 3, 2020, 5678-5682 5679 www.etasr.com khan et al.: a review of software risk analysis with the use of classification techniques authors in [3] address how risk analysis and planning are difficult to manage effectively. the authors explore an empirical integration of intelligent decision support model for software project risk analysis and planning. the study has two main contributions: an integration framework for intelligent software risk planning (if-isprp) and for minimizing the impact of project risks and a method called mmakd (many to many actionable knowledge discovery) for complex risk planning. both the framework and the method are integrated to support effectively control software project-related risks. the objective of the study is to combine risk analysis and risk planning modules to control risks. the study assumes that different risk actions can be executed simultaneously where practically this is not possible as risks are managed in some order. authors in [4] explore different types and categories of risk and their effects on the software project. the authors elaborate on different aspects and characteristics of risk systematically. they also suggest a software tool for risk assessment for supporting better and quicker decisions. the study combines different types of risk and categories of risk with their characteristics. a tool called risk is used for determining how an event occurs and to evaluate what consequences it can have on project performance. the study explores risk analysis, focusing on quantitative risk analysis, for making a better decision of what kind of risk has occurred. the objective of the study is to identify different types of risks and categorize them. the way project cost and duration are making the budget estimation difficult for software risk management when trying to develop a high-quality software system is addressed in [5]. the study improves software process risk management by using the software process model with risk management and cost. the study proposes a measurement model that combines process risk management and trustworthiness metrics. the study suggests two metrics, one for software risk management performance and another for trustworthiness that help the project manager to control risks for every software development process. the objective of the study is to improve software risk management, enhancing trustworthiness by avoiding cost overrun and delays in software development and also, to use cost control modules that help improving the software risk management process. authors in [6] explored the field of risk management using a knowledge management conceptual framework, called knowledge-based risk management for identifying how knowledge management helps improving effectiveness. timely identification of risk helps improving the overall implementation and the quality of the product. handling risks early in software development helps to reduce the cost of the product while minimizing delays. the study suggests integrating knowledge management activities for risk management and for this purpose, a framework is proposed. risk occurrence at the early stages of software development and its effect on the success of the final product is explored in [7]. to achieve quality software products in the shortest time, the goal-driven software development risk management model (gsrm) model is presented that is used to identify and analyze goals, risk, and treatment actions at the early stages of the sdlc. the study presents a layer-based modeling framework that supports software development risk management. it performs activities by using suitable tasks, methods and techniques. the framework is categorized into five dimensions. the objective of the study is to explore risk at early sdlc by using a method called goal-driven software development risk management (gsrm), that performs a treatment action at the early stages of the process, particularly in the requirement phase. the way faults affect software quality and cost is addressed in [8]. the study combines fuzzy measures to generate concepts connected to the fuzzy integral to achieve better prediction performance of the software module. the objective of the study is to minimize cost and improve the software development process by early prediction of fault-prone software. the authors employ object-oriented metrics and method level metrics for constructing a model that establishes the relationship between software metrics and fault-prones and does not require expert knowledge. using fuzzy integral for software fault prediction provides significant advantages due to its ability. the major limitation of the proposed approach is that it is computationally extensive and building a model using this technique requires a lot of effort. author in [9] addresses how risky software projects affect the overall project success and software risk results, schedule and cost overload. the study explores accuracy evaluation criteria and performance charts to predict whether the project is risky by using a three-layered neural network with back propagation. the study proposes an algorithm which can understand complex patterns with a three-layered neural network architecture. the purpose of using complex datasets is to build a predictive model for the risky nature of projects. the objective of the study is to control risk at an early stage of the software development and minimize cost and time of software construction, while improving the performance of the project. authors in [10] explore different classification approaches for the purpose of software defect prediction. the objective of the study is to create a cost-sensitive artificial neural network (ann) by using the abc algorithm for efficient software defect prediction. the study suggests the expected cost of misclassification (ecm) technique for converting an ann into a cost-sensitive learner. the study utilizes n-fold crossvalidation technique to determine the performance of the proposed classifier. authors divide the performance of classifiers into two subsections, regardless and regarding cost sensitivity. both metrics are used for comparison with other studies. the study proposes a classifier for the software defect prediction problem. authors in [11] explore how the estimation of risk at the early stages of software development affects reliability and software cost. the study suggests a new fuzzy rule base algorithm for the validation of the proposed fuzzy rule base model while data of 20 actual software projects have been used. the objective of the study is to predict faults at the early stages of sdlc, i.e. requirement analysis phase or design phase for developing highly desirable software with optimal cost. authors in [12] address how risk and potential failure affect systems, products, and processes. the study suggests that failure mode and effect analysis (fmea) can identify failures engineering, technology & applied science research vol. 10, no. 3, 2020, 5678-5682 5680 www.etasr.com khan et al.: a review of software risk analysis with the use of classification techniques in a system by a risk priority number (rpn) which lacks some deficiency and affects effectiveness. the objective of the study is to identify potential failure modes, evaluate their effects and causes, and find the solution to eliminate or reduce the occurrence of failures by using the proposed topsis approach. fmea techniques lack effectiveness because two different failure modes may have the same rpn but could have different risk implications, and fmea doesn’t differentiate between risk implications. to overcome this issue the tosis method has been applied to properly manage the risk. topsis is based on linguistic terms with their rating of failure modes. the limitation of the proposed approach is that it involves both subjective and objective analysis. author in [13] explores how the fault proneness affects software quality. a logistic regression method and six machine learning methods (decision tree, support vector machine, group method of data handling method, artificial neural network, cascade correlation network, and gene expression programming) are analyzed and compared in order to find the relationship between static code metrics and fault proneness. the objective of the study is to develop good quality software by using machine learning methods for analyzing and predicting faults in the early phases of sdlc. the author compared the predictive facility of the models by using area under curve (auc) that measures receiver operating characteristic (roc). the results of lr and machine learning (ml) methods were compared in the use of two datasets. as a result, the ml method was found to perform better than lr. authors in [14] address the way defects affect software maintenance, accuracy, trustworthiness, and evolution. the study explores a defect prediction classification model to reduce the defects that affect the performance of a project or product. this study finds an extension of the ordinal association to relational association rules that predict whether the software module is or not defective and performs an experiment to evaluate the proposed classification model, which is based on relational association rule mining and compares it with other software detection approaches. the objective is to build defect-free high-quality software by identifying and predicting defects. authors in [15] address how a two-way decision method causes high misclassification error rates and costs. the study suggests three-way decisions to overcome the problem of twoway decision that includes two kinds of actions based on software defect prediction. in each experiment, 10-fold crossvalidation has been performed to show that the proposed method reduces errors and cost. authors in [16] proposed the tgr model to define risk features in requirement engineering, based on the original tropos and risk analysis methodologies. the approach encourages the development of numerous costbased, risk-based and goal-based solutions. this analysis could find the best solution that meets the demands of lower costs and risks. the study also implemented a prototype application to prove the concept. the application takes as input various goals, events and responses and produces various combinations of solutions to enable end-users to select the best one. risk management in open source software (oss) is addressed in [17]. one of the key technologies for achieving shorter time-to-market and better quality of the software system is the reuse of software components from third-party vendors. such modules, also known as off-the-shelf components, come in two types: commercial-off-the-shelf and oss components. to make an effective use of oss components, it is important to find how to change the development processes and methods. the study suggests many measures that may be implemented for process improvement and risk reduction depending on the open-source software components, though not all are necessary for a project. machine learning techniques are employed to build a model predicting potentially faulty modules with respect to their metric data within a given set of software modules [18]. to that end, the naive bayesian classification is used as authors have argued that in many complex real-world situations, naive bayesian performs better than techniques such as decision trees. the data sets used in the experiments are organized into two categories, i.e. learning datasets and prediction datasets. risk factors are analyzed using the proposed model to enhance the risk assessment process. risk management has also been used in project management. the main aim of the authors in [19] was to understand the principles of risk assessment in order to establish a model for risk management of it projects. the proposed conceptual model is based on a synthesis of the pmbok guide and the risk management framework of pmi by incorporating different areas of expertise extracted from these manuals. integrating these principles allows the early start of the risk management phase in the project by including key stakeholders in the lifecycle, regularly assessing project threats during the project lifecycle, and creating risk reduction strategies to better match projects with the company's strategy. the effects of uncertainty on the project and the risk event as a consequence of uncertainty are analyzed in [20]. the uncertainty index is proposed as a quantitative measure for assessing project uncertainty. this is done by using entropy as an indicator of system disorder and lack of information. using this index, the uncertainty of each activity and its increase due to risk effects and changes in project uncertainty as a function of time can be assessed. the proposed solution is implemented and analyzed as a case study. the results can be useful for project managers and other stakeholders in selecting the most effective methods for controlling uncertainty and risk management. iii. critical evaluation a critical analysis of selected studies is provided in table i. iv. conclusion in this study, we reviewed the latest research pertaining to software risk assessment, software fault prediction, and risk management. the aim of the study was to discover various classifiers that have been tried for defect prediction. commonly used classification techniques are ann, abc algorithm, fuzzy integral, fuzzy hybrid topsis approach, bn, fuzzy rule base model, etc. for classification, various types of software project datasets have been used. it is worth mentioning that some researchers combined risk analysis and risk control mechanisms for effective software risk management engineering, technology & applied science research vol. 10, no. 3, 2020, 5678-5682 5681 www.etasr.com khan et al.: a review of software risk analysis with the use of classification techniques table i. critical evaluation of selected studies ref area of focus model and tools used algorithms and datasets used sdlc phases covered risk dimensions risk categories and factors identified validation parameters [6] software project risk analysis and management probabilistic model bn with following causality constraints: 1. expert knowledge 2.v-structure discovery requirement organization environment user risks requirement risks project complexity planning and control team test categories: 6 factors: 27 accuracy (10-fold cross-validation) [10] rm process and integrating knowledge management activities for rm a conceptual framework called kbrm. km processes and risk response planning to mitigate risks. knowledge-based risk management model (kbrm) all risk response planning categories: 1 improves project effectiveness ]16[ risk on analysis of sdlc a state-based risk assessment approach. scotem functional failure analysis, software failure mode and effect analysis, software fault tree analysis design scenario risks, risks at analysis and design stages categories: 2 experiments to prove efficiency and comparison with existing methods. ]11[ manageability of risk analysis and planning. an integrative framework (if-isprp). mmakd analysis and planning phase organization environment. user risks. requirement risks. project complexity. planning and control. team test. categories: 6 factors: 27 includes a number of cost minimal risk cost actions. ]14[ risks at the early stages of the software development process. gsrm. layer based modeling framework early stages risk treatment actions at early stages. categories: 1 factors: 17 explore risks to build a high-quality software product. ]9[ different risk types and categories and their effects on a project. software tool risk for supporting better and quick decisions. all qualitative risk analysis quantitative risk analysis the study focuses on quantitative risk analysis. categories: 2 developes and highlights the importance of automated risk analysis software. ]3[ software risk management to produce high-quality software software process model with risk management and cost. measurement model. trustworthy software process software development process product trustworthiness all calculations of software risk management performance and trustworthiness values categories: 2 control risk for every subprocess of the software development process. [1] fault-prone effect software quality and software cost. fuzzy integral object-oriented metrics method-level metrics fuzzy integral classifier. nasa provided promise and data program repository all predicting fault-prone software categories: 1 minimizes cost and improves software development process by early prediction of fault-prone software. ]7[ software risk result schedule and cost overload ann omron dataset early stages requirement, estimation, planning, team organization, and project management categories: 5 factors: 22 100% accuracy with the nn model and 87.5% when using logistic regression. ]8[ software defect prediction issues affecting sdlc ann, ecm abc algorithm 5 datasets all prediction software defect/risk categories: 1 n-fold crossvalidation technique ]4[ risk estimation at the early stages of development affecting reliability and cost fuzzy rule based model fuzzy rule based algorithm requirement phases. analysis phase and design phase requirement fault density, requirement stability, review, inspection, walkthrough, experience of requirement team categories: 4 performance of fault prediction ]5[ risk and potential failure affect systems, products, processes topsis fmea all potential failure modes. categories: 1 eliminate or reduce failure occurrence. [15] fault proneness affects software quality logistic regression 6 ml methods auc d t, svm, g m dhm, ann, ccn, and gep. ar1 and ar6 datasets all static code metric and fault proneness categories: 2 10-fold crossvalidation engineering, technology & applied science research vol. 10, no. 3, 2020, 5678-5682 5682 www.etasr.com khan et al.: a review of software risk analysis with the use of classification techniques ]17[ defects affect software maintenance, accuracy, trustworthiness, and evolution. -ordinal association. -relational association rules. -dprar -nasa datasets all predicting software defects/faults categories: 1 accuracy (cross validation) ]12[ three-way decision two-way decision method. three-way decision method 11 nasa datasets. six algorithms for comparison. all defect prone modules. non defect prone modules. deferment modules. categories: 3 10-fold crossvalidation ]13[ risk assessment in requirement engineering tgr requirement cost, risk prioritization, cost risk analysis categories: several observations made in terms of cost and cost and risk. riskbased priority of candidate solutions. ]2[ risk assessment for oss risk breakdown structure all quantitative risk analysis matrix categories: 5 factors: 12 risk response actions for oss. [18] analyze risk factors and enhance the risk assessment process naïve bayes classification naïve bayes algorithm all potentially defected modules within a given set of software modules categories: 1 85.77 % accuracy when using naïve bayes and 82.81% when using nns. references [1] y. hu, x. zhang, e. w. t. ngai, r. cai, m. liu, “software project risk analysis using bayesian networks with causality constraints”, decision support systems, vol. 56, pp. 439–449, 2013 [2] m. ray, d. p. mohapatra, “risk analysis: a guiding force in the improvement of testing”, iet software, vol. 7, no. 1, pp. 29–46, 2013 [3] y. hu, j. du, x. zhang, x. hao, e. w. t. ngai, m. fan, m. liu, “an integrative framework for intelligent software project risk planning”, decision support systems, vol. 55, no. 4, pp. 927–937, 2013 [4] z. kremljak, c. kafol, “types of risk in a system engineering environment and software tools for risk analysis”, procedia engineering, vol. 69, pp. 177–183, 2014 [5] j. li, m. li, d. wu, h. song, “an integrated risk measurement and optimization model for trustworthy software process management”, information sciences, vol. 191, pp. 47–60, 2012 [6] s. alhawari, l. karadsheh, a. n. talet, e. mansour, “knowledge-based risk management framework for information technology project”, international journal of information management, vol. 32, no. 1, pp. 50–65, 2012 [7] s. islam, h. mouratidis, e. r. weippl, “an empirical study on the implementation and evaluation of a goal-driven software development risk management model”, information and software technology, vol. 56, no. 2, pp. 117–133, 2014 [8] c. jin, s. w. jin, “applications of fuzzy integrals for predicting software fault-prone”, journal of intelligent fuzzy systems, vol. 26, no. 2, pp. 721–729, 2014 [9] w. m. han, “discriminating risky software project using neural networks”, computer standard & interfaces, vol. 40, pp. 15–22, 2015 [10] o. f. arar, k. ayan, “software defect prediction using cost-sensitive neural network”, applied soft computing, vol. 33, pp. 263–277, 2015 [11] s. chatterjee, b. maji, “a new fuzzy rule based algorithm for estimating software faults in early phase of development”, soft computing, vol. 20, no. 10, pp. 4023–4035, 2016 [12] h. c. liu, j. x. you, m. m. shan, l. n. shao, “failure mode and effects analysis using intuitionistic fuzzy hybrid topsis approach”, soft computing, vol. 19, no. 4, pp. 1085–1098, 2015 [13] r. malhotra, “comparative analysis of statistical and machine learning methods for predicting faulty modules”, applied soft computing, vol. 21, pp. 286–297, 2014 [14] g. czibula, z. marian, i. g. czibula, “software defect prediction using relational association rule mining”, information sciences, vol. 264, pp. 260–278, 2014 [15] w. li, z. huang, q. li, “three-way decisions based software defect prediction”, knowlegde-based systems, vol. 91, pp. 263–274, 2016 [16] s. n. bhukya, s. pabboju, “software engineering: risk features in requirement engineering”, cluster computing, vol. 22, no. s6, pp. 14789–14801, 2019 [17] n. d. linh, p. d. hung, v. t. diep, t. d. tung, “risk management in projects based on open-source software”, 8th international conference on software and computer applications, penang, malaysia, february, 2019 [18] k. suresh, r. dillibabu, “designing a machine learning based software risk assessment model using naïve bayes algorithm”, taga journal, vol. 14, pp. 3141--3147, 2018. [19] a. e. yamami, s. ahriz, k. mansouri, m. qbadou, e. illoussamen, “representing it projects risk management best practices as a metamodel”, engineering, technology & applied science research, vol. 7, no. 5, pp. 2062-2067, 2017 [20] a. chenarani, e. a. druzhinin, “a quantitative measure for evaluating project uncertainty under variation and risk effects”, engineering, technology & applied science research, vol. 7, no. 5, pp. 2083-2088, 2017 microsoft word etasr_v13_n4_pp11204-11209 engineering, technology & applied science research vol. 13, no. 4, 2023, 11204-11209 11204 www.etasr.com hamasur & abdalrahman: the effect of tool’s rake angles and infeed in turning polyamide 66 the effect of tool’s rake angles and infeed in turning polyamide 66 shawbo a. hamasur department of mechanical engineering/production, college of engineering, sulaimani polytechnic university, iraq shawbo.ali.h@spu.edu.iq rzgar m. abdalrahman department of mechanical engineering/production, college of engineering, sulaimani polytechnic university, iraq rzgar.abdalrahman@spu.edu.iq (corresponding author) received: 28 march 2023 | revised: 15 may 2023 | accepted: 17 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5891 abstract polyamide pa66 has been adopted by a variety of industries, and engineering fields. it is used in machinery part production due to its good properties. machining is the most commonly used processing technique when high quality of part dimension and surface is required. there is a lack of knowledge about the impact of the tool’s rake angles when turning polyamide pa66, therefore, this study aims to define an optimal condition that can provide the highest performance in machining polyamide pa66 at the lowest cutting force. the impact of the tool’s side rake angle, back rake angle, and cutting depth on cutting force was studied during turning polyamide pa66 with the hss tool. three levels were considered for each variable and taguchi's orthogonal array (oa) was used to design nine test configurations. the tests were performed experimentally on a conventional lathe machine. the resultant cutting force was calculated as the response data. the values were converted to signal-to-noise (s/n) ratio to facilitate the analysis using the taguchi method and analysis of variance (anova). accordingly, the cutting depth showed the greatest impact on cutting force (57.12%), followed by the side rake angle (27.9%) and back rake angle (8.21%). an optimal condition set to turn polyamide pa66 at the lowest cutting force (fc) is identified as 1 mm depth of cut, side rake angle αs = 21°, and back-rake angle αb = 8°. finally, the optimal condition set was evaluated by conformation tests, and the results agreed with the calculations to a large extent. keywords-polyamide pa66; hss cutting tool; back rake angle; side rake angle; cutting depth; anova; cutting force i. introduction nowadays, plastics have gained interest in manufacturing various parts of machines due to their good resistance to wear and corrosion, in addition to their low density, coefficient of friction, and high productivity [1, 2]. polyamide pa66, for instance, is an important thermoplastic type, which is most frequently used in producing power transmission elements (e.g. bearings, cams, worm wheels, gears and bearing cages, slide bearings, gear box parts, and wheel covers parts) in the machinery of different technical sectors including aircraft, automobile, and robotics [3, 4], because, compared to other polymer kinds and despite the aforementioned physical and mechanical properties, it is superior in strength, rigidity, heat stability, chemical resistance, while being a strong noise dampener and electrical insulator [5]. pa66 was introduced as toothbrush filament in 1938 [6]. polyamides pa66 is one of the most well-known plastics. it consists of two monomers of dicarboxylic and diamine acids [7]. pa66 is a polycondensation product of hexamethylene diammonium and adipate salt. it is created by removing water from reaction of several species of diamine and diacid [8]. plastics are less frequently machined. however, the machining process is advised when the quantity of the produced pieces does not warrant the expense of molds [9, 10]. furthermore, machining the plastic materials is recommended when high quality components with high surface finish and dimensional precision are required [11]. the main aims of the modern machining processes are achieving low power consumption, machining cost, cutting time, cutting force, and stresses with high dimension accuracy, surface quality, tool life, and productivity [12, 13].the produced cutting forces that act on the cutting tools during the machining are the key component of the machining process responses, their amount has a decisive effect on energy consumption, vibration creation, and the quality of the machined part and cutting tool life [14, 15]. machining plastic materials needs special processing circumstances to provide acceptable product quality and high engineering, technology & applied science research vol. 13, no. 4, 2023, 11204-11209 11205 www.etasr.com hamasur & abdalrahman: the effect of tool’s rake angles and infeed in turning polyamide 66 cutting performance. therefore, this study investigates the effect of tool back rake angle, side rake angle, and cutting depth on the magnitude of cutting force as response data when turning polyamide pa66. the aim is defining the most proper conditions that ensure lowest cutting force. three levels are considered for each test parameter and the statistical method of anova is applied for analyzing the obtained response data. ii. literature review many machining factors, including cutting conditions and tool geometry, have been considered by researchers to assist in mastering plastic machining, especially polyamide pa66. for instance, authors in [16] investigated the machinability of pa66 polyamide during precision turning at various feed rates. they applied four coated tools of chemical vapor deposition (cvd) coated carbide, polycrystalline diamond (pcd), and iso grade k15 uncoated cemented carbides with and without chip breaker. the findings showed that when turning polyamide pa66 with the k15-kf carbide tool the highest force was recorded, followed by similar results for cvd and pcd, and the lowest force was recorded with the k15 carbide. authors in [17] performed an experimental and analytical research to examine the surface quality, effective cutting force, and specific cutting pressure under the impact of three test variables of feed, depth of cut, and cutting speed during machining polyamide pa66. the obtained response data were optimized with anova. the statistical results indicated that the feed is the most affecting factor on surface finish followed by cutting speed and cutting depth. the most effective factor on cutting force was the cutting depth (d) followed by feed (f) and cutting speed (v). for a specified cutting force it was v, f and d, respectively. authors in [18] studied experimentally the effect of cutting speed, feed rate, depth of cut, and tool nose radius, when turning polyamide pa-6. minitab software was used to compile and evaluate the experimental results. their results show that the feed rate is the most effective factor followed by the cutting depth and tool nose radius, while cutting speed had very little effect on the average surface roughness. authors in [5] utilized uncoated cemented carbide tools with three different tool nose angles to study the impact of the cutting-edge angles, including angle and nose radius, on the cutting force during turning polyamide pa66. the obtained statistical results concluded that when the included angle is 35° and the simultaneous cuttingedge angles are 45°, the lowest cutting force that offers the most acceptable turning performance was achieved. additionally, they concluded that the 0.2 mm tool nose radius had the least impact on �� . authors in [19], during turning polyamide pa66, discovered that cutting depth and feed rate have the greatest impact on cutting force. they concluded that as the cutting depth and feed rate rise, the cutting force does as well. the effects of tool nose radius on tool life, cutting force, temperature, and surface quality were studied in [20] during precise turning of polyamide. the results showed that the cutting force increases with the increase of tool nose radius, while the surface roughness increases with the increase of feed rate and decrease of the tool nose radius. the researchers performed an experimental and analytical investigation to indicate the influence of feed rate on each of the chip compression ratio, chip deformation, friction angle, shear angle, normal stress, and shear stress of polyamide pa66 during the turning process. they applied uncoated carbide tools without a chip breaker. they concluded that the cutting force presented high values due to the ductile behavior of pa66 polyamide, which is soft and adheres to the tool’s rake face. generally, comparable conclusions were reached when the merchant model's findings were contrasted with the experimental values [21]. authors in [22] applied artificial neural networks (anns) with improved harmony search algorithm (ihsa) to determine the optimal cutting parameter set to minimize surface roughness when turning polyamide material. they tested the effect of cutting speed, feed rate, depth of cut, and tool nose radius and found the values of 65.03 m/min, 0.049 mm/rev, 1mm, and 0.8mm, respectively, as the optimal set. the conclusion of the literature review is that the cutting tool geometry, especially the side and back rake angles, has received less attention in the literature than other aspects of machining of the plastic materials despite its importance in regulating chip formation and flow to reduce cutting forces. therefore, the current study takes the tool's side and back rake angles with infeed amount into account to define their effectiveness ratio and their optimal set values that provides the lowest cutting force, when turning polyamide pa66. iii. methodology a. materials and preparation of the cutting tools and specimens high-speed steel (hss) of 12 mm thickness, grade aisi m2, hs 6-5-2 with 62-65 hrc, ςασ selected for preparing different cutting tools with the proposed geometries of the current study, as shown in figure 1. the tool angles were grounded manually on a tool grinding machine, type excel, cv7, nw9, iso 9001, with a swiveling vice, type vertex, that moves on multiple axes. all the processed tool angles, especially the variables, were checked during and after preparation by the optical projector comparator type mitutoyo ph-a14 and angle protractors type mitutoyo with sequential accuracies of 2 minutes and 0.4 minutes to ensure the required tool geometries were obtained exactly. fig. 1. the prepared nine hss cutting tools. the workpiece material in this study was a polyamide pa66 bar of 750 mm length and 100 mm diameter, supplied by beijing feng teng ltd company, china. the mechanical and physical properties of pa66 are presented in table i. as shown engineering, technology & applied science research vol. 13, no. 4, 2023, 11204-11209 11206 www.etasr.com hamasur & abdalrahman: the effect of tool’s rake angles and infeed in turning polyamide 66 in figure 2, the planned 27 samples were prepared with the dimensions illustrated in figure 3. initially, the bar diameter was reduced to 95 mm to ensure producing concentric samples and to reduce the workpiece chattering during testing. the dimensions were checked during and after the sample preparation by precise digital vernier calipers. fig. 2. prepared samples on the polyamide pa 66 bar. fig. 3. dimensions of the prepared samples. table i. main characteristics of pa66 [5] properties units tested values density g/cm 3 1.14 tensile strength mpa 60 coefficient of linear expansion 1/ᵒc 78×10 -5 impact strength j/m 2 1400 rockwell hardness kgf / mm 2 m70-80 water absorption 0.8% b. test devices the tests were performed on a universal lathe machine type cu630-3000, serial number 1270 with a 15 hp driving motor. a dial gauge was mounted at the back of the cross slide to further ensure the compound rest accuracy. the cutting forces were measuring by a 3d (x, y, z) dynamometer of 500 kg (5000n) capacity and 1 kgf (10 n) resolution. the device was provided by unitech scales and measurements pvt. ltd. india. it consists of strain gauges as sensing elements connected by a whetstone’s based 350 ω bridge. the software tool viewer v2.1was installed on a computer to log the received data from a data acquisition system connected to the dynamometer. in order to guarantee the correctness of the tests results, the lathe machine and all the used equipment in this test rig (figure 4) were subjected to calibration and maintenance. fig. 4. test devices. c. design of the experiments in the current study, the back (αb) and side (αs) rake angles of the cutting tool along with the cutting depth (figure 5) [23], were selected as variables during turning polyamide pa66. the other tool geometries, i.e. nose radius, side and end cutting edge angles, cutting speed, and feed rate, were kept constant at 1 mm, 3°, 12°, 300 rpm, and 0.25 mm/rev, respectively. three levels were proposed for each variable (table ii). consequently, in order to perform the lowest test number for investigating the quality properties, the standard taguchi’s l9 (3×3) orthogonal array (oa) was applied to design 9 experiment combinations, as shown in table iii. the values of all the variables and constant parameters were suggested according to the literature and specific test results. the test of each designed experiment was repeated at least three times to ensure the accuracy of the results. fig. 5. single point cutting tool geometry. table ii. proposed parameters and their levels factors unit levels 1 2 3 side rake angle (��) a ° 7 14 21 back rake angle (��) b ° 0 4 8 cutting depth c mm 1 2 3 d. analysis of variance cutting force (fc) is an essential evaluator for the machining performance, therefore it is regarded as the response engineering, technology & applied science research vol. 13, no. 4, 2023, 11204-11209 11207 www.etasr.com hamasur & abdalrahman: the effect of tool’s rake angles and infeed in turning polyamide 66 variable in the current study. after performing the planned tests, the mean square deviation (msd) of the fc results in each trail (table iii), were determined as [19]: ��� � ∑ � �� �� (1) the smaller the fc value, the lower the power consumption and the vibration and the higher the tool life and product quality [20]. accordingly, in order to facilitate the evaluation of the lb features of the proposed characters, the basis of "smaller is better" (lb) was considered to convert the msd values to signal to noise ratio (s/n) by [24]: s/n = 10 � ��� � ����� (2) table iii. designed experiments according to taguchi’s l9 oa trail no. parameters and levels response variable a b c msd s/n ratio n db 1 1 1 1 95.1 -39.6 2 1 2 2 140 -42.9 3 1 3 3 154.5 -43.8 4 2 1 2 129.5 -42.2 5 2 2 3 132.5 -42.4 6 2 3 1 80 -38.1 7 3 1 3 130 -42.3 8 3 2 1 73.6 -37.3 9 3 3 2 73 -37.3 the average performance of each specified level of the variables is defined by the mean of the s/n ratios of the trails that contain the entire level, as presented in table iv. also, the difference between the highest and lowest average performance of each variable was determined to define its rank and importance. based on the results showed in table iv, the anova statistical method was applied to define the individual significance of the proposed variables in influencing the response data of cutting force as shown in table v. table iv. average performance of the variable levels level �� (°) �� (°) cutting depth (mm) a b c 1 -42.1 -41.4 -38.3 2 -40.9 -40.9 -40.8 3 -39.0 -39.7 -42.8 ���� ��!" 2.0 1.7 4.5 ranking 2 3 1 table v. anova results source degrees of freedom sum of squares variance variance ratio percentage contribution dοf ss v f-test p % a 2 15.0 7.5 4.1 27.9 b 2 4.4 2.2 1.2 8.2 c 2 30.7 15.3 8.5 57.1 residual error 2 3.6 1.8 1.0 6.8 total 8 53.7 iv. results figure 6 presents the attributes of the machining force components for a test in the first trail when turning a polyamide 66 sample. it shows that the tangential force (�# ) is the largest, and each of the feed (�$ ) and infeed (�� ) component values are almost a quarter of the ft value. all the force components initiate at point (a), where the cutting edge, as illustrated in figure 7(a), is initially contacting the sample. the forces are noticeably rising simultaneously with increasing the workpiece/cutting edge contact length to its maximum value at point (b) and remains constant till point (c). therefore, the effective values of �# , �$ , and �� in each test, were calculated as their averages in this period. after point (c), the forces start dropping inconsistently due to the gradual reduction of the contact length. the inconsistent drop is the result of spinning instead of cutting the remained weak triangular section layer of the material, as illustrated in figure 7(b). the effective cutting force (�� ) in the current study is calculated as the resultant of the effective components of �# , �$ , and �� by [25]: f&='f( � ) f* � ) f+ � (3) fig. 6. cutting force results of a test in the first trail (, =7°, ,. = 0°, d =1mm). (a) (b) fig. 7. the cutting pass during the tests. fig. 8. the remained layer of the work material at the sample end (a) before and (b) after spinning. engineering, technology & applied science research vol. 13, no. 4, 2023, 11204-11209 11208 www.etasr.com hamasur & abdalrahman: the effect of tool’s rake angles and infeed in turning polyamide 66 the average performance of the s/n of each variable’s level is presented in figure 9. accordingly, the optimal combination of ,-, ,. , and the infeed can be defined as the third level of , (a3 = 21°), third level of ,. (b3 = 8°), and first level of cutting depth (c1=1mm), represented as a3b3c1. the significance of the proposed factors of cutting depth, side rake angle, and back rake angle in addition to their role in turning pa66 with the lowest cutting force value are determined by the anova. table v defines the anova results of all the variables. the contribution percentage results, shown in figure 10, illustrate that the cutting depth contributes by 57.12% in affecting the cutting force and it is the most important factor, followed by the side rake angle, which has an effectiveness of 27.9%, and the back rake angle which has the least impact of 8.21%. fig. 9. average performance of the variable levels. fig. 10. contribution percentage of the factors in affecting the ��, besides the residual error. while the deduced optimal combination set of a3b3c1 did not exist in the 9 designed tests in this study, its value in s/n ratio was predicted as [19]: /01# =t/n + (a3 – t/n) + (b3 – t/n) + (c1 – t/n) (4) accordingly, the calculated response value of the optimal set is -35.67 db (60.76 n), which is smaller than the lowest value in table iii. this confirms the validity of the concluded optimal condition set. then, the confidence value of 90% was depended to determine the confidence interval (c.i.) of ± 0.97 db by [19]: 2. 4. 5'��1, 7�� � �89 :9⁄ � (5) the c.i. value shows that the experimental performance of the defined optimal set will be between -34.30 db (51.88 n) and -36.26 db (65.16 n). finally, the �� value of the confirmation test of 59 n (-35.41 db) was obtained. it confirms the correctness of the concluded optimal combination set, because the deduced experimental �� value is within the confidence limits of the expected value. v. discussion the experimental results of this research showed that the most effective factor on cutting force is the cutting depth, in accordance with the findings in [17, 19, 20]. authors in [5] obtained lowest cutting force at lowest simultaneous cuttingedge angles of 45° without noticing inconsistent drop in the forces at the end of the cutting passes, as was occurred in the current study. that can be interpreted due to the fact that the large approach angle reduces the amount of remained material layer at the end of the passes. the optimal set obtained in this study not only facilitates the cutting of pa66 with minimal force, but also enables machining pa66 with lowest power consumption, machining cost, cutting time, cutting stresses and highest part quality, tool life, and productivity. the produced cutting forces are an essential evaluator for the aforementioned machining performances as deduced in [22]. vi. conclusion this study aimed to find an optimum combination set of cutting depth, side rake angle, and back rake angle for turning polyamide pa66 at the lowest cutting force (�� ) value. three levels for each variable were considered. taguchi’s l9 oa was applied to set the experiments. the obtained �� results were transferred to signal to noise ratio (s/n) to facilitate analyzing by anova and the following were concluded:  the cutting depth has the maximum contribution factor of 57.12% in generating the resultant cutting force. the side rake angle has an effect of 27.9%, while the back rake angle has the lowest contribution of 8.21%.  the optimum condition set of factor combination that provides minimal cutting force is the cutting depth of 1 mm, side rake angle of 21˚, and back rake angle of 8˚.  the experimental confirmation test result of the �� value confirmed the correctness of the concluded optimal condition and its expected result. acknowledgment the authors are greatly thankful to the staff of the workshops and the metal cutting lab of the mechanical engineering department, polytechnic university, sulaimani, for their help and support. special thanks go to mr. barzan talib for his advice and guidance. nomenclature c.i. confidence interval n number of observations of the results f variance ratio 7� error dof 7� <9 �$ feed force = from taguchi's table and its always 1 �� radial force s/n signal to noise ratio �# tangential force t sum of the s/n ratio <9 degree of freedom of the error term 89 variance of the error term engineering, technology & applied science research vol. 13, no. 4, 2023, 11204-11209 11209 www.etasr.com hamasur & abdalrahman: the effect of tool’s rake angles and infeed in turning polyamide 66 msd mean square deviation � resulting value of the cutting force n total number of trials or number of s/n ratio ,. back rake angle :9 effective number of replications , side rack angle references [1] n. dusunceli and o. u. colak, "the effects of manufacturing techniques on viscoelastic and viscoplastic behavior of high density polyethylene (hdpe)," materials & design, vol. 29, no. 6, pp. 1117–1124, jan. 2008, https://doi.org/10.1016/j.matdes.2007.06.003. 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[25] m. rizal, j. a. ghani, and a. z. mubarak, "design and development of a tri-axial turning dynamometer utilizing cross-beam type force transducer for fine-turning cutting force measurement," sensors, vol. 22, no. 22, jan. 2022, art. no. 8751, https://doi.org/10.3390/s22228751. microsoft word 44-3101_s_etasr_v9_n5_pp4824-4829 engineering, technology & applied science research vol. 9, no. 5, 2019, 4824-4829 4824 www.etasr.com eisa osman et al.: application of fvsi, lmn and cpf techniques for proper positioning of facts … application of fvsi, lmn and cpf techniques for proper positioning of facts devices and scig wind turbine integrated to a distributed network for voltage stability enhancement shaheer hashim eisa osman department of electrical engineering, pan african university, institute for basic sciences technology and innovation, nairobi, kenya shaheerkapo2017@gmail.com george k. irungu department of electrical engineering, jomo kenyatta university of agriculture and technology, nairobi, kenya girungu@jkuat.ac.ke david k. murage department of electrical engineering, jomo kenyatta university of agriculture and technology, nairobi, kenya davidkinyua76@gmail.com abstract—induction power generators are the most popular wind energy conversion systems (wecs) because they do not require synchronization units. however, they usually draw a huge quantity of reactive power during disturbances. hence, incorporating wind power into power networks may cause voltage instability. this paper presents the usage of statcom and sssc facts devices for voltage stability enhancement of a distribution network with a squirrel cage induction generator (scig) wind power turbine. the continuation power flow (cpf) approach is utilized as a tool to determine the most suitable position of scig in the system. also, voltage stability indices (fvsi and lmn) are employed to estimate the stability margin of the system by figuring the weakest transmission lines and buses in order to locate the appropriate position where the facts devices should be installed. a comparison of the suitability of the facts devices to restore system stability was evaluated under 3phase fault conditions. the results illustrated that statcom behaves better than sssc when the system is restoring from a fault. simulations and voltage stability assessment were carried out on the ieee 14 bus test scheme using the psat simulation software package. keywords-squirrel cage induction generator (scig); voltage stability analysis; continuation power flow (cpf); voltage stability indices (vsi); statcom; sssc facts devices; psat i. introduction the integration of wind energy conversion systems (wecs) in electrical power systems can help boosting voltage stability. wecs perform a major role in regulating the electric power flow and enhance the system voltage profiles [1]. recently, there has been an increase in the use of wecs because the cost of generating electricity using this technology is cheaper compared to other technologies [2]. currently, several scientific studies have been done on incorporating a squirrel cage induction generator (scig) wind power turbine into an electric power system during normal operation and emergencies [3]. by relying on both the wind turbine and operational features of the distribution system, the incorporation of wind power generators can have negative or positive effects on the system’s stability and electric power losses [1, 4]. therefore, it will be necessary to analyze the influence of the considered scig wind power systems with the other electric power system elements. the scig was among the first induction generators to be used in wind farms. this generator can also be used in systems with high penetration of wind energy because of features like simple rotor framework and minimal maintenance costs [5]. operators had experienced many challenges in incorporating wind energy conversion systems in power systems because induction generators always absorb huge amounts of reactive power from the system during normal operation and during disturbances leading to the problem of voltage collapse [5]. voltage collapse occurs when a significant portion of the system has very low voltage profiles that can lead to an incomplete or overall blackout of the system [6]. in order to alleviate the negative impacts of high-level penetration of the wind power conversion system, various means can be used such as the instalment of facts devices which have already been considered as one of the most effective solutions to overcome the voltage stability problem [7]. facts devices refer to flexible alternating current transmission systems which can be able to inject or consume reactive power into/from the system [8]. several researchers have examined the utilization of scig wind turbines for various functions corresponding to enhancing voltage profiles and reducing electrical power losses [1] as well as increasing the loadability of the system [7]. the computational continuation power flow technique has been utilized on an ieee 30 bus test system to find the best position in the wind energy conversion system that will result in system’s stability enhancement [9] and to get an appropriate position of statcom as indicated in [10]. various studies have been carried out using numerous voltage stability indices (vsi) such as fast voltage stability index (fvsi), line stability index (lmn) for several purposes such as determining the corresponding author: shaheer hashim eisa osman engineering, technology & applied science research vol. 9, no. 5, 2019, 4824-4829 4825 www.etasr.com eisa osman et al.: application of fvsi, lmn and cpf techniques for proper positioning of facts … proper placement of svc and statcom [11], identifying the weakest buses and lines in order to set up fact devices [12]. the main contributions of the current paper are: (a) the cpf approach is presented to examine the influence of scig wind turbine on various regions of the ieee 14 bus test system for system voltage stability analysis, (b) the fvsi along with lmn indices are presented for the suitable positioning of statcom and sssc facts devices for voltage stability improvement. ii. wind energy placement a. squirrel cage induction generator (scig) the scig model is driven by a constant speed wind turbine. it is also known as a short-circuit induction generator that could be coupled straight to the electric grid. the configuration and the mathematical equations of the dynamic scig wind turbine type are based on the induction motor equivalent circuit [4, 13], that could be expressed in a synchronously rotating real-imaginary frame (r-m) linked with the system reference point angle. therefore, the maximum power output obtained by the wind power turbine can be expressed mathematically as [13]: � = � � ��� ��λ�� (1) where ρ is the air density, s is the swept area by the wind turbine, v is wind speed, cp defines the performance coefficient, λ is the ratio of tip speed of the turbine blade, and β is the pitch angle. at lower wind speed levels, the performance coefficient relies simply on the ratio of tip speed rather than the pitch angle that would be equal to zero. this coefficient corresponds to the aerodynamic output of the wind turbine providing the highest power output. b. continuation power flow method (cpf) this particular technique is utilized to measure the maximum loadability point (lambda) of the system. essentially in cpf technique there are two phases. the first phase, known as the predictor step, is responsible for forecasting the next value of lambda (λ) in the case where it shifts from the base condition point. the second step attempts to correct the value which has been forecasted in the initial phase [14]. the purpose of the cpf method is to keep track of the solutions as the loading parameter λ varies. this parameter is termed a loading point or (factor) which is utilized to the system mw distance from a primary operating point to the voltage collapse point where the voltages will become critical. the parameter modifies load powers as in [1]. iii. voltage stability indices there a number of strategies used to assess the system voltage stability which is obtained by the application of indices such as the fvsi index and lmn index that are capable of identifying the critical lines and corresponding weak buses by measuring the reactive power and voltage of the transmission lines in which the system stability may have been violated [15]. the basic mathematical formulas for fvsi and lmn employ the general two-bus electric power line model presented in [10]. a. fast voltage stability index (fvsi) the principle behind this index can be illustrated from (2). the more the fvsi is close to 1 in that particular transmission line, the more the system will tend to lose stability. ���� = � ��� � �� �� ��� ≤ 1 (2) where zij is the impedance of the transmission line between bus i and bus j, xij is the reactance between bus i and bus j, qj is the reactive power that flows to bus j, vi is the sending-end voltage. b. line voltage stability index (lmn) this index is derived by [20]. upon examination of (3), it can be noted that if the index is≤ 1, the system becomes stable otherwise it’s unstable. ��� = � ��� �� �� � � �� �!"#� ≤ 1 (3) where θ is the line angle and δ is the difference between a sending-end angle and receiving-end angle. iv. facts devices overview the operation of an alternating current power transmission line is generally limited by the constraints of the electrical power parameters. fact devices are a novel technology that applies power electronics for controlling voltage, impedance, phase angle, current, active and reactive power during normal and contingency events in order to improve the system controllability, stability and hence increase the power transfer capabilities of the system transmission line. facts devices may either be connected in series or shunt. their behaviors depend on the proper position across the transmission lines and buses. in a two-bus transmission line, the active power and the current flowing through the transmission line can be controlled as stated in [8, 16]. a. static synchronous compensator (statcom) statcom is a voltage source converter (vsc) that is connected in parallel to the bus for the purpose of providing dynamic reactive power and thus regulating the system voltage. both statcom and synchronous condenser have the same functionality. they can deliver or consume the reactive power for the system. the basic statcom topology can be found in [17]. statcom is shunt-connected and therefore functions to control the voltage at the connecting bus with respect to the reference by adjusting the voltage and angle of the internal voltage source. when e=v, the reactive current output is zero. when e>v, the current will flow to the converter from the ac system, absorbing reactive power, whereas when e<v, the currents will flow through the converter to the ac system generating reactive power. when δ=0, the reactive current absorbed (ir) is given by: �$ = %"� &'(� (4) engineering, technology & applied science research vol. 9, no. 5, 2019, 4824-4829 4826 www.etasr.com eisa osman et al.: application of fvsi, lmn and cpf techniques for proper positioning of facts … b. static synchronous series compensator (sssc) sssc is basically consisting of a vsc, a coupling transformer and a voltage source. the flow of the power can be regulated by controlling the magnitude of the voltage source (vc) and hence, control the active and reactive power flow in the network. sssc is connected in series to power transmission lines through a transformer and this is the only difference with statcom [17]. the steady-state power in the absence of the energy source between vc and the dc side is shown by: �)� ∗ = 0 (5) this equation illustrates that vc is in quadrature with the flowing current i, meaning that there are two operating modes for reactive power compensation (capacitive mode and inductive mode) depending on the phase displacement between the vc and i. so, generally �) ∧ = �)�cos 0 1 2 sin 0�5 (∅ (6) where γ is the angle by which �) ∧ lags the current, ∅ is line current phase angle. v. description of the system model in this study, the basic ieee 14 bus test system as indicated in figure 1 has been considered. fig. 1. illustration of the standard ieee 14-bus test system with wind incorporated to bus 14 the system comprises of two synchronous power generators, three synchronous condensers, joined together by using numbers of twenty transmission lines to supply eleven load buses [11]. the scig model from the psat library is employed on this simulation. the chosen mva and rated frequency are 100mva and 50hz respectively. the wind farm comprises of 25 units of 2mw, 0.69kv, 50hz, a scig type with 15m/s average wind speed is integrated to the standard ieee 14 bus system by adding an extra pv bus type at bus 15 through a power transformer. a standard pq type is utilized for the loads while the generator limitations are dismissed. the scig and wind turbine data used in wind farms simulation are found in [18]. the simulation has been executed with the use of psat. psat is a power system analysis toolbox incorporating various tools such as load flow analysis (lfa), time domain simulation (tds) and continuation electrical power flow (cpf) [19]. employing the cpf method of psat, the system voltage stability is examined. vi. simulation, results, and discussion to examine the effects of wind power integration on voltage stability, the simulation was carried out in various stages. a. identifying the proper location of the wind turbine in this stage, the scig wind power turbine model from the psat library was used. the location was identified as an outcome of the cpf approach, on which the system stability was enhanced and electric power losses were minimized. the cpf approach is used to identify voltage levels along with the maximum loadability element of the presented system after introducing the scig wind turbine into the system. from the ieee 14 bus dynamic model base case, a cpf is performed and the voltage profiles were obtained. figure 2 shows that buses 9, 10, 11, 13, and 14 are the critical buses. among them, bus 14 is considered the most critical one due to the small value of the voltage profile which is 0.69p.u. fig. 2. the voltage profiles of the basic case using cpf method the active power-voltage (p-v) curve of each bus is obtained through the employment of cpf approach, in which cpf starts with primary operating point and then expanding the load to the maximum loading point. figure 3 illustrates the p-v curve of each weak bus of the basic case. maximum loading factor or (point) which is where the jacobian matrix turns out to be singular, takes place at λ=1.7p.u. bus 14 is demonstrated as the weakest load bus that needs voltage support. fig. 3. shows the ieee 14 bus p-v curves of the basic case engineering, technology & applied science research vol. 9, no. 5, 2019, 4824-4829 4827 www.etasr.com eisa osman et al.: application of fvsi, lmn and cpf techniques for proper positioning of facts … the maximum loading point for the modified system with the wind generator located at bus 14 happened at λ=1.72p.u, and this is due to the positioning of the wind generator at the weak bus. when the wind energy conversion system is connected at bus 14, there is an increase in the maximum loading factor of the system and an improvement in the voltage levels in the weak buses as shown in figure 4. fig. 4. the voltage levels of the integrated system using cpf method b. the modified ieee 14 bus system under 3-phase fault the considered test system has been divided into three areas which are high voltage side, medium voltage side and low voltage side based on the working voltages 69kv, 18kv, 13.8kv respectively of the ieee 14 bus system. on this stage a three-phase fault has been applied on bus 1 which represents the high voltage side, bus 8 which represents the medium voltage side, and on bus 14 which represents the low voltage side. the 3-phase fault occurred at the 1.0s instant and was cleared at the 1.25s instant. to examine the effects of the threephase fault on the system, the electrical variables active power, reactive power, and voltage have been monitored on the wind bus which represents bus 15. from the results shown in figure 5, during the occurrence of the faults at bus 14 the voltage dropped from 1.045p.u to almost 0p.u and therefore, the acceleration of the wind rotor reduced making the transmitted active power by the wind generator to the system equal to 0p.u as shown in figure 6. fig. 5. voltage profiles response at the wind bus with fault applied at bus 1, bus 8, and bus 14 it was noted that when the fault was cleared the system attempted to restore back to its original operating point making the scig wind power generator to absorb a huge reactive power amount equal to -0.8p.u from the distribution portion of the system as shown in figure 7. when the fault occurred at bus 14 the wind system became unstable. this was because the reactive power demanded by the scig wind turbine was not enough for the rotor magnetization of the wind generator, while in the other fault cases (fault at bus 1 and bus 8) the wind system kept its stability although reactive power had been consumed. fig. 6. active power transmitted by a wind turbine with fault applied at bus 1, bus 8, and bus 14 fig. 7. reactive power transmitted by wind turbine with fault applied at bus 1, bus 8, and bus 14 c. determination of the weakest lines and buses for an integrated system with the wind at bus 14 from sub-section b it is evident that the scig wind turbine required huge reactive power when the fault was close to the wind bus. also, the distribution part as shown in figure 5 describing the installed wind turbine has some nodes needing reactive power support which may lead to instability. therefore, it is recommended to apply the vsi for the integrated ieee 14 bus system, to determine the weakest lines and corresponding buses for reactive power support. 1) procedures of computing the vsi the steps that have been followed are: • perform the newton-raphson method for the integrated ieee 14 bus test system and obtain the load flow report. • from load flow results and by the use of (7) and (8) the fvsi and the lmn for all buses and lines of the system are computed. • the reactive power at the receiving-end bus for the selected load bus progressively increases until the load flow process fails to converge to a solution. this is followed by the calculation of fvsi. engineering, technology & applied science research vol. 9, no. 5, 2019, 4824-4829 4828 www.etasr.com eisa osman et al.: application of fvsi, lmn and cpf techniques for proper positioning of facts … • the line index with the highest values shall be taken out as the most significant weak line with reference to a bus. • another load bus is chosen and the previous procedures are repeated. 2) calculation of fvsi and lmn for the integrated ieee 14 bus system. figure 8 shows the obtained values from the calculation of fvsi and lmn. fig. 8. bar graph of the calculated values of fvsi, lmn of the integrated ieee 14 bus test system. the modified system has 21 transmission lines, but only 15 transmission lines have been considered. this is because they connect load buses, which are line numbers 4, 5, 7, 8, 9, 11, 12, 13, 15, 16, 17, 18, 19, 20, and 21. among the considered lines, the ones with the highest values (greater or equal to 0.04) of fvsi and lmn have been taken as critical lines, which are lines 8, 9, 11, 12, 13, 15, 18 and 20 as shown in figure 8.the results showed that load bus 14 is the weakest bus and exposed to voltage instability. it has the lowest maximum allowable reactive power of 63mvar compared to the other load buses as shown in figure 9. bus 14 has three lines connected to it and the weakest line with respect to load bus 14 is the line 13-14. hence this implies that any absorption of 63mvar or more will tend to voltage collapse. fig. 9. maximum allowable reactive power on load buses d. comparison of the facts devices used at this stage, two types of facts devices, statcom and sssc facts devices, were compared. by the utilization of psat platform, the time domain simulation (tds) approach have been examined to evaluate the performance of facts when a three-phase fault occurs at bus 14. 1) performance of statcom and sssc facts devices during a three-phase fault. the scenario that was discussed in sub-section b has been repeated again with the presence of 100mva sssc and statcom facts devices. sssc is connected to line 20 (between bus 13 and bus 14) and statcom is connected to bus 14. comparison analysis between the sssc and statcom has been made based on the responses of the electrical variables voltage, active and reactive power with respect to the considered system under three-phase faults. figure 10 shows the voltage responses of the wind bus before and after the connection of sssc and statcom facts devices. it is evident that the system was able to revert back to the normal operation and this is attributed to the consumed reactive power amount by scig wind turbine that has been generated from sssc and statcom facts devices making the system stable. although both types of facts devises performed well in the system, statcom settled down before sssc. this is attributed to the effectiveness of statcom at low voltage levels which has made the system stability better than when using sssc. with regards to active power response, sssc has better performance than statcom as shown in figure 11. statcom oscillated higher and delayed in the settlement compared to sssc. fig. 10. voltage responses at wind bus 15 with fault applied at bus 14 fig. 11. active power responses at wind bus 15 with fault applied at bus 14 finally, the analysis was extended to the reactive power response that was delivered by both facts devices. figure 12 shows the reactive power drawn by the scig wind turbine. as mentioned above, the instability occurred because of scig wind turbine reactive power absorption goes more than 63mvar. therefore, in sssc and statcom cases even if the reactive power demand goes beyond 63mvar these devices were able to support the excess reactive power demand which makes the system stable. statcom reacted faster than sssc. furthermore, statcom started to settle down before sssc. engineering, technology & applied science research vol. 9, no. 5, 2019, 4824-4829 4829 www.etasr.com eisa osman et al.: application of fvsi, lmn and cpf techniques for proper positioning of facts … fig. 12. reactive power responses at wind bus 15 with fault applied at bus 14 vii. conclusion the computation of vsi of the standard ieee 14 bus after the integration of the scig wind power turbine was calculated along with the comparative investigation of statcom and sssc facts devises. the results were drawn for simulations with the scig wind power turbine incorporated to the distribution network at bus 14. there was an enhancement of the voltage levels at some load buses with a difference of 0.2p.u, and the loadability margin increased from 1.7 to 1.72. there was also a reduction in the active and reactive electric power losses from 1.3p.u and 5.18p.u to 0.97p.u and 3.59p.u respectively. furthermore, there was a massive reactive power amount at the time of fault occurrence. the weak parts of the system were determined and the maximum permissible reactive power for load buses was computed. to prevent voltage collapse, statcom and sssc have been employed and comparatively statcom provided more effective outcomes than sssc. references [1] z. h. a. tameemi, k. m. abuwaleda, h. m. almukhtar, m. k. abbas, “voltage stability enhancement based on dg units”, electrical engineering, vol. 100, no. 4, pp. 2707–2716, 2018 [2] j. b. v. c. subrahmanyam, p. a. bandana, k. bhanupriya, c. shashidhar, “renewable energy systems: development and perspectives of a hybrid solar-wind system”, engineering, technology & applied science research, vol. 2, no. 1, pp. 177–181, 2012 [3] m. benchagra, m. hilal, y. errami, m. ouassaid, m. maaroufi, “modeling and control of scig based variable-speed with power factor control”, international review on modelling and simulations, vol. 4, no. 3, pp. 1007–1014, 2011 [4] d. devaraj, r. jeevajyothi, “impact of fixed and variable speed wind turbine systems on power system voltage stability enhancement”, iet conference on renewable power generation, edinburgh, uk, september 6-8, 2011 [5] h. li, z. chen, l. han, “comparison and evaluation of induction generator models in wind turbine systems for transient stability of power system”, international conference on power system technology, chongqing, china, october 22-26, 2006 [6] p. kundur, power system stability and control, mcgraw hill, 1994 [7] a. rashad, s. kamel, f. jurado, “stability improvement of power systems connected with developed wind farms using sssc controller”, ain shams engineering journal, vol. 9, no. 4, pp. 2767–2779, 2018 [8] i. n. muisyo, k. k. kaberere, “utilization of facts devices in power systems : a review”, sustainable research and innovation conference, nairobi, kenya, may 2-4, 2018 [9] o. l. bekri, m. k. fellah, “optimal placement of wind farms for enhancing voltage stability using cpf analysis”, deuxieme conference internationale sur l’electrotechnique, l’electronique, l’automatique et la maintenance, november 24-25, 2015 [10] a. s. telang, p. p. bedekar, “application of voltage stability indices for proper placement of statcom under load increase scenario”, world academy of science, engineering and technology international journal of energy and power engineering, vol. 10, no. 7, pp. 998–1003, 2016 [11] i. i. ali, m. n. mohsen, “enhancement voltage stability of the iraqi power grid using shunt facts devices”, engineering and technology journal, vol. 34, no. 13, pp. 2527–2550, 2016 [12] s. kumar, a. kumar, n. k. sharma, “a novel method to investigate voltage stability of ieee-14 bus wind integrated system using psat”, frontiers in energy, pp. 1–9, 2016 [13] s. ahsan, a. s. siddiqui, “dynamic compensation of real and reactive power in wind farms using statcom”, perspectives in science, vol. 8, pp. 519–521, 2016 [14] k. bhumkittipich, c. j. ngurn, “study of voltage stability for 22kv power system connected with lamtakhong wind power plant, thailand”, energy procedia, vol. 34, pp. 951–963, 2013 [15] a. oukennou, a. sandali, “assessment and analysis of voltage stability indices in electrical network using psat software”, eighteenth international middle east power systems conference, cairo, egypt, december 27-29, 2016 [16] r. jadeja, s patel, s. k. chauhan, “statcom–a preface to power quality in power systems performance”, engineering, technology & applied science research, vol. 6, no. 1, pp. 895–905, 2016 [17] k. r. padiyar, facts controllers in power transmission and distribution, new age international publishers, 2007 (in india) [18] p. anusri, k. c. s. thampatty, “mathematical modeling of the squirrel cage induction generator based wind farm for sub-synchronous resonance analysis”, indian journal of science and technology, vol. 9, no. 38, pp. 1–7, 2016 [19] f. milano, “an open source power system analysis toolbox”, ieee transactions on power systems, vol. 20, no. 3, pp. 1199–1206, 2005 [20] m. moghavvemi, f. m. omar, “technique for contingency monitoring and voltage collapse prediction, iee proceedings generation, transmission and distribution, vol. 145, no. 6, pp. 634-640, 1998 microsoft word 36-2662_s engineering, technology & applied science research vol. 9, no. 2, 2019, 4062-4065 4062 www.etasr.com ali et al.: distributed file sharing and retrieval model for cloud virtual environment distributed file sharing and retrieval model for cloud virtual environment munwar ali department of information technology shaheed benazir bhutto university shaheed benazirabad, pakistan mazardari@gmail.com nouman q. soomro department of software engineering muet szab campus khairpur mirs, pakistan noumansoomro@muetkhp.edu.pk huzaifa ali department of computer science comsats university islamabad lahore campus lahore, pakistan huzaifaali14@gmail.com ahsan awan department of computer science comsats university islamabad lahore campus lahore, pakistan ahsanawan12322@gmail.com mohsin kirmani department of computer science comsats university islamabad lahore campus lahore, pakistan mohsin007kirmani@gmail.com abstract—cloud-based storage services are multiplying and are being adapted mostly for data storage. at the same time, many potential problems pertaining to data storage and security are being addressed. this research provides the architecture for splitting user data and the solution in retrieving different data chunks, stored on different cloud storages. by doing this, not only the load on a single server is reduced but security and storage are efficiently used. data would be stored and retrieved in slices, hence the chances of data forgery are diminishing. file processing will be faster as split parts would be fetched from different clouds, enabling parallel processing. keywords-cloud computing; data security; file sharing; distributed system i. introduction cloud computing is being adapted by many organizations due to its dynamic scalability and virtualized resources [1]. cloud computing, particularly cloud storage, has been proven in multiple real-world cases to simplify information technology (it) operations helping companies to save millions of dollars. the era of big data would not be possible without the emergence of highly scalable cloud storage [2]. cloud storage provides ease to users in a variety of ways like providing faster accessibility, rapid deployment, accessibility, and data security, backup and recovery. due to the extensive use of cloud, problems pertaining to it are becoming noticeable [3]. the load on the servers is getting heavier and the system must look for more advisable methods to minimize it. for that purpose, distributed file systems and cloud storage come handy and address many of the problems discussed above. in these, a dataset is divided into small chunks and these chunks are then stored over different servers to minimize the load on any single server, hence increasing efficiency and security [4]. goals that have been achieved by data distribution include fault tolerance, ability to store bigger data and managing them efficiently, append operations on file allowance, and reliable communication among different machines. however, attention is still needed on the domain of retrieval of distributed data in their complete original form. this project focuses on data, stored onto different servers, distribution and retrieval. this can be achieved by the help of an information retrieval method which will facilitate us by maintaining the order of data slices for the same file, so while fetching they can be arranged into the complete original file. several schemes have been proposed in context of file splitting and sharing, but the proposed scheme focuses on the following points. • to design a hybrid multi-cloud model to improve cloud efficiency and provide a secure environment. • a data distribution technique and splitter is used to encrypt and split data into chunks. • to develop an efficient and intelligent method for the retrieval of split file chunks into its original form. corresponding author: nouman q. soomro engineering, technology & applied science research vol. 9, no. 2, 2019, 4062-4065 4063 www.etasr.com ali et al.: distributed file sharing and retrieval model for cloud virtual environment ii. related work security as a service (saas) provides the opportunity to divide data into chunks for security enhancement. when they are divided, each chunk is then encrypted and stored onto different databases [5]. but this technique has a serious issue which is the linked list based distribution of the data. the tail of each node of the linked list contains information of the next node. so, if one node is hacked, it will give information of all the other nodes. security is provided by isolating the process of decryption and encryption to a third party, so the data is encrypted using a secured co-processor [5]. cloud systems have provided ease to users in many ways like storing data, running applications, data recovery, and flexibility. cloud also includes risk of data integrity, network dependency and centralization. this is the main reason many why big companies restrain from using clouds as primary storage. csa, enisa and nist published general security guidance and recommendations, for cloud usage to provide some level of protection ranging from physical security to network/system/application security [6]. the idea of distributed computing turns is gaining popularity over the last few years. data storage is a critical and important research field in distributed computing. in [4], authors presented the idea of distributed computing and distributed storage and the design of distributed storage right off the bat. authors in [8] developed a dynamic load balancing algorithm to balance the load across the storage nodes during the expansion of private cloud storage. authors in [9] addressed encryption challenges by the use of tanked searchable symmetric encryption. authors in [7] implemented data integrity protocols to detect data corruption. authors in [10] discussed cloud computing and its service models, cloud security issues, challenges, and analyzed various solutions with ttpa and studied their benefits in terms of data integrity, access control mechanism, and data confidentiality. authors in [11] provided a knn classification method, a privacy preserving protocol which accesses data in database using encryption and solved input record query of data mining. iii. research methodology a. data splitting and encryption techniques cryptography is a secure communication technique used when there is a presence of malicious third-parties—known as adversaries. encryption which is a main module of cryptography uses an algorithm and a key to transform an input known as plaintext into an encrypted output called ciphertext. algorithm will always decrypt the cipher text/block into plaintext if the same key is provided. the encryption algorithm is considered secure because if any of the encrypted data (cipher block) is lost, information from this block cannot be retrieved until the encryption key is given. 1) data encryption • symmetric encryption: this is the simplest kind of encryption that involves only one secret key to cipher and decipher information. symmetrical encryption is an old and known technique. the secret key that can either be a number, a word, or a string of random letters. it is blended with the plain text of a message to change the content in a way. the sender and the recipient should know the secret key to encrypt and decrypt the messages. • asymmetric encryption: asymmetric algorithms use two keys, one to encrypt the data, and the other key to decrypt. these inter-dependent keys are generated together. one is labeled as the public key and is distributed freely. the other is labeled as the private key and must be kept hidden. • hash: a hash function is a mathematical function that takes input/data of an arbitrary length and then generates fixed length hash based on the input. it is easily calculated, but it is very difficult to generate the original data if the hash value is not known. 2) data splitting cryptography splitting is an algorithm that splits the input/data into a number of chunks. splitting is done at bit level. a secure key is used to control splitting and splitting is done randomly. 3) data security algorithms blowfish, aes, rc4, des, rc5, and rc6 are used for encryption to enhance security. the most widely used algorithms are aes-128, aes-192, and aes-256. the technique that we are using is the aes (advanced encryption standard)-256 which has the advantages of low memory cost, high speed, same key used to encrypt and decrypt, and the cipher and plain blocks are of the same size. 4) cryptographic data splitting algorithm pseudo code: start get filepath call: doencryption declare counter: 1 decalre sizeoffile: 1024 * 1024 declare buffer: array[sizeoffile] declare filename: getfilename() declare bytesamount: 0 declare bufferinputstream: bis do until bytesamount=bis.read(buffer)> 0 declare filepartname: (filename + counter) declare file newfile: file(filepartname) declare fileoutputstream: out(newfile) out.write(buffer, 0, bytesamount) while loop end stop 5) merging of file chunks algorithm pseudo code start get filechunks call: dodecryption declare file: into declare fileoutputstream: fos(into) declare bufferoutputstream: mergingstream(fos); repeat for file f: filechunks files.copy(f.topath(), mergingstream) end for loop stop 6) distribution of a a file into chunks engineering, technology & applied science research vol. 9, no. 2, 2019, 4062-4065 4064 www.etasr.com ali et al.: distributed file sharing and retrieval model for cloud virtual environment the uploaded file will be encrypted first and then broken down into a number of chunks according to the number of public clouds available. 7) placement of chunks on different clouds these encrypted chunks will be stored on different public clouds and the server id of each chunk on which it is stored is fetched. 8) maintaining log file a log file will be maintained having information about the number of registered users and uploaded files, along with the number of chunks and the cloud reference on which is stored for each chunk. figure 1 shows the system flow of the proposed technique. figure 2 shows the architecture of the proposed technique. fig. 1. system flow diagram fig. 2. proposed model architecture iv. results and discussion in this section, the proposed model is compared with the plain file system. the comparison is based on time. the total time taken by the proposed model is the accumulated sum of receiving, encryption, splitting and transferring times. a. proposed file distribution model table i shows the total time taken by different modules (receiving, encryption, splitting and transferring) when users upload files of different size. the smallest file (3.73mb) takes a total processing time of 17499ms whereas the largest file (25.3mb) takes52638ms. however, total time also depends on bandwidth, cpu, and memory. table i. file processing time of fdm file size (mb) receiving time (ms) encryption time (ms) splitting time (ms) transferring time(ms) total (ms) 3.73 12013 527 15 5471 17499 18 63003 103 58 13925 76986 17.8 59720 118 54 20457 80231 25.3 41749 594 67 10822 52638 16.2 28409 97 91 8891 37391 b. plain file distribution system table ii shows the total time taken by the plain file distribution system (pfs) when users upload files of different sizes. total time is inversely proportional to the bandwidth. table ii. file processing time of pfs file size (mb) receiving time (ms) total time (ms) 3.73 12013 12013 18 63003 63003 17.8 59720 59720 25.3 41749 41749 16.2 28409 28409 a detailed comparison between the proposed and the plain file system is shown in figure 3. the proposed system looks a bit complex and took more processing time as compared to the pfs. it is understood that computational complexity can be compromised for data security purposes. the proposed system is more secure than the pfs. fig. 3. processing time comparison between the proposed and the pfs c. result analysis from the above results, it is concluded that the total time taken by the proposed distributed file system is increased by only a few seconds. this time is utilized in taking security measures (i.e. encryption, splitting) and in efficient storage utilization. to achieve high security, one must compromise on time. table iii shows the time consumption difference between the proposed and the plan file system. the proposed distributed file system is technically compared with google file system (gfs) and the saas model. table iv shows the comparisons. table v shows the comparison of the proposed distributed file system with the saas model. engineering, technology & applied science research vol. 9, no. 2, 2019, 4062-4065 4065 www.etasr.com ali et al.: distributed file sharing and retrieval model for cloud virtual environment table iii. result analysis total time of the proposed file system (ms) total time of plain file system (ms) difference(ms) 17499 12013 29512 76986 63003 13983 80231 59720 20511 52638 41749 10889 37391 28409 8982 table iv. comparison of proposed model with gfs gfs proposed model consists of single master server, multiple chunk servers and clients. consists of private clouds along with multiple public clouds master manages all the system data and file directory structure. manages all operations including signup and login request, file distribution, encryption, maintaining log files and deploying chunks onto public servers. a client interacts with the master server for metadata only and interacts with chunk servers directly for all other data. a client interacts with the private server only. a client is not required to communicate directly with the public servers because the private server will be responsible for carrying out the client’s request. divides files into fixed size chunks of 64mb each. there is no restriction on the chunk size. the file division is based on the number of public clouds available. each chunk is replicated on three public chunk servers. there is no replication of chunks ensuring data integrity. table v. comparison of proposed model with saas saas proposed model has three major parts (header, tail, and encrypted data). uses only encrypted data. header contains all the important details including encryption technique, total number of chunks, total size of chunks, chunk number and a unique user id. log file (database) will maintain all important details.. tail will contain reference to the next chunk. next chunk can be identified from the log file. a third party does encryption and decryption. user can select between multiple encryption techniques. private cloud is responsible for encryption and decryption. user has no choice over the encryption technique. log file contains the record of the user data and helps to identify the first chunk. log file will contain the total number of chunks along with server ids log file will be maintained in master database and all the data will be dumped into random databases. log file will be maintained in the master cloud and all the data chunks will be saved into slave clouds. enhances the security of the encrypted data by distributing the data within the cloud. master and slave clouds. user can directly interact with the master cloud only. communication takes place between master and slave clouds. the proposed model has some characteristics which differentiate it from the previous models/techniques. these are: • user cannot directly communicate with slave clouds, which ensures data security. • the proposed model does not give privilege of encryption technique to user which ensures reliability. • the proposed model contains all information about data chunks and their order in secured log files • the proposed model doesn’t involve any third party for encryption which is more trustworthy whereas saas model depends upon third parties for encryption techniques. • the proposed model is a hybrid model consisting of multiple clouds in which one is the master (private) and others are slaves (public). v. conclusion the distributed file system is a very efficient way of partitioning data and storing them to multiple clouds. in that way the load on a single cloud is reduced and the performance is increased. it also helps in creating a secure way for file retrieval and processing, hence managing and protecting user's data. the main concern of the project is the efficient distribution of data and their retrieval in correct order. references [1] r. m. babu, “secure storage and retrieval of big data on distributed cloud environment”, international journal of applied engineering research, vol. 11, no. 10, pp. 7063-7071, 2016 [2] j. broberg, s. venugopal, r. buyya, “market-oriented grids and utility computing: the state-of-the-art and future directions”, journal of grid computing, vol. 6, no. 3, pp. 255–276, 2008 [3] j. tang, y. cui, q. li, k. ren, j. liu, r. bayya, “ensuring security and privacy preservation for cloud data services”, acm computing surveys, vol. 49, no. l, article no 13, 2016 [4] k. liu, l. j. dong, “research on cloud data storage technology and its architecture implementation”, procedia engineering, vol. 29, pp. 133-137, 2012 [5] c. p. ram, g. sreenivaasan, “security as a service (sass): securing user data by coprocessor and distributing the data”, trendz in information sciences & computing, chennai, india, december 17-19, 2010 [6] t. sivashakthi, d. n. prabakaran, “a survey on storage techniques in cloud computing”, international journal of emerging technology and advanced engineering, vol. 3, no. 12, pp. 125-128, 2013 [7] v. ukey, n. mishra, “dataset segmentation for cloud computing and securing data using ecc”, international journal of computer and information technologies, vol. 5, no. 3, pp. 4210-4213, 2014 [8] k. gabhale, n. jadyal, a. more, v. bhalekar, v. v. dakhode, “data partitioning technique to improve cloud data storage security”, international journal of advanced research in computer and communication engineering, vol. 5, no. 3, pp. 24-26, 2016 [9] n. m. anuradha, g. a. patil, “secure and efficient data retrieval in cloud computing”, international journal of engineering research & technology, vol. 4, no. 4, pp. 2278-0181, 2015 [10] p. h. atulkumar, p. a. atulkumar, “a review of addressing storage correctness in cloud computing with trusted third-party auditor”, international journal of research in engineering & advanced technology, vol. 1, no. 2, pp. 1-4, 2013 [11] v. goutham, p. a.. reddy, k. sunitha, “k-nearest neighbor classification on data confidentiality and, privacy of user’s input queries”, international journal of advanced research in computer and communication engineering, vol. 5, no. 7, pp. 704-708, 2016 microsoft word 25-21-3005_s_etasr_v9_n5_pp4712-4717 engineering, technology & applied science research vol. 9, no. 5, 2019, 4712-4717 4712 www.etasr.com alomari: effect of the presence of basements on the vibration period and other seismic responses of… effect of the presence of basements on the vibration period and other seismic responses of r.c. frames jamal ahmad alomari civil engineering department, al-ahliyya amman university, amman, jordan j.alomari@ammanu.edu.jo abstract—the soil-structure interaction (ssi) of r. c. building frames including basements below ground level has been the subject of extended research, mostly in the form of theoretical dynamic analysis. there are different issues concerned with this type of work, as e.g. the location of the base of the structure. usually, the base of the structure in dynamic analysis or according to the codes is the level at which the lateral displacement is zero. according to this definition, and with the presence of basement floors and the soil mass below, the ground level may not be the base of the structure. the soil stiffness around basement walls has a great effect on the lateral displacement of the basement floor. another issue is the effect of the presence of the basement floors on the dynamic behavior of the structure. a third issue is the effect of the soil around the basement walls and the soil mass below the foundation in general, which is known as the ssi. in this paper, 3-dimensional regular building frames subjected to seismic loading are analyzed using sap2000 software. the first frame is a 5-floor, 3-d frame without including the soil mass below the raft foundation and without a basement floor. the second frame is the same frame with a basement floor and with consideration of the soil mass below the raft foundation and around the walls of the basement floor. the third frame is the same frame with consideration of the soil mass below the raft foundation but without the basement floor. results of the seismic time history analysis and ubc97 response spectrum analysis are presented and discussed. keywords-soil-structure interaction; soil stiffness; basement floor; seismic analysis; period of vibration; time history analysis; response spectrum analysis i. introduction this paper aims at studying the effect of the presence of basements, including soil-structure interaction (ssi), on the seismic behavior of rc buildings during earthquakes. conventionally, basement floors have been considered safe during earthquakes, and seismic structural analysis has been conducted to neglect their presence during earthquake excitation. designers usually consider the structure base at the ground level, and carry out the designs assuming the structure has a fixed base at the ground level, neglecting the presence of the underground floors. in this context, the base of a structure is the level at which the lateral displacement is zero [3]. this issue has been the subject of a lot of theoretical analysis [2-4]. the building codes of practice lack any structural analysis procedures for including the effect of basements with ssi during seismic excitation. they consider the base of the structure is at ground level neglecting the presence of basement floors. for example, ubc97, item 1629.8.2, “simplified static”, for calculating the base shear, considers the height of a structure measured from ground level and excludes the presence of the basement floors from height calculations, although the presence of basement floors has a considerable effect on the structure behavior during seismic excitation. periods of vibration, base shear, member forces, and story drifts are considerably changed when ssi and basement floors are considered. ii. literature review authors in [5] carried out an analysis of a 3d, 12+g, rc building frame including 2 basements. they compared the results with the results of the building without basements. they found that due to the presence of basements, roof displacements and base shears were reduced. the period of vibration for the building with basements was found lower than that of the one without basements. authors in [6] studied the effect of the basement on the seismic response of high-rise buildings and the effect of the seismic loads on the member forces of the basement by studying the behavior of a g+15 rc building with basements under seismic loading. authors in [2] investigated the behavior of a g+12 rc building with two basements and shear walls under seismic excitation. they compared the responses, base shear, story drift, axial forces, and periods of vibration, for buildings with and without basement walls. authors in [4] studied the effect of basements on the structure behavior by carrying out seismic analysis of a 3d model of a 12-story rc building with 4 basements using sap200. they carried out static, modal, and time history analysis, and concluded that base shear, bending moment and acceleration were reduced, whereas time period and displacement were increased. authors in [3] carried out structure–soil models for 2and 6story buildings built on soft soil deposits, with and without basements, using time domain dynamic analysis. they concluded that the earthquake response of structures with basements is less damaging than without basements. the buildings with basements showed better corresponding author: jamal ahmad alomari engineering, technology & applied science research vol. 9, no. 5, 2019, 4712-4717 4713 www.etasr.com alomari: effect of the presence of basements on the vibration period and other seismic responses of… resistance to earthquakes than the buildings without basements as was observed after the earthquakes occurring in turkey. iii. frames and soil description to study the effect of the presence of basements and the soil-structure interaction on the dynamic behavior of rc structures, 3 building frames are considered: • case 1 is a 3-d building frame without consideration of the soil below the raft foundation and without a basement floor, called hereinafter as bare frame, as shown in figure 1. • case 2 is a 3-d building frame with consideration of the soil below the raft foundation and with a basement floor as shown in figure 2. • case 3 is a 3-d building frame with consideration of the soil below the raft foundation but without a basement floor as shown in figure 3. figure 4 shows a plan of the building frame for all of the three frames mentioned above. fig. 1. case 1: section of bare frame showing some joints and member numbers at x-z plane at y=3m fig. 2. case 2: section of building frame including the soil below raft foundation with one basement floor. selected joints and members numbers are shown on x-z plane at y=3m fig. 3. case 3: section of building frame including the soil below raft foundation without a basement floor. selected joint and member numbers are shown on x-z plane at y=3m fig. 4. plan of the building frame at the level of z=21m showing the raft foundation elements each of the frames is a 3d frame. the plan is 12×12m. case 1 is the bare frame without the soil mass, and without a basement floor. case 3 is the frame with the soil mass below foundation but without a basement floor. both these cases consist of 5 floors with 3.0m height for each floor. case 2 is a frame that includes a basement floor and the soil mass below the raft foundation, and the soil around the basement floor. case 2 consists of 6 floors including a basement floor surrounded with soil mass on all four sides. the soil mass is modeled by 24 thick shell layers of 1.0m thickness. the layers are divided into 1.0m×1.0m thick shell elements. in plan, the soil mass is 26m×26m, such that it extends 7m on each side of the building plan on all four sides. the soil material stiffness is considered 100mpa. the edge joints of the soil mass are considered fixed in the analysis and as such, the rock bed limits are realized at the soil mass boundaries. all columns are 0.5m×0.5m, and all beams are 0.32m deep × 1.2m wide. the building frames are built on a raft foundation of 0.5m thickness. the raft elements are considered as 0.5m thick × 4.0m wide beam elements. the basement walls are 0.25m thick, they are modeled as thin shell elements, and they are divided into 1.0m×1.0m elements. the soil is considered in contact with the basement walls around the building. connection between the soil and raft elements and the basement wall elements is realized by compression link elements known as gap elements in sap2000 software. such elements are active in compression and have no other effect on the structure’s behavior. the stiffness of the gap elements is engineering, technology & applied science research vol. 9, no. 5, 2019, 4712-4717 4714 www.etasr.com alomari: effect of the presence of basements on the vibration period and other seismic responses of… considered as 166770kn/m 2 . concrete compressive strength of all concrete sections is 21mpa. the beams are assumed to carry a uniform load of 15kn/m. frames are analyzed for ubc 97 response spectrum, with values of ca=0.4, and cv=0.4, and damping of 5%. the frames are also being subjected to time history analysis using n-s el centro ground acceleration in the x direction using modal analysis solution and srss technique. the results of the analysis are used to compare the structures’ responses for column shears, base shears, periods of vibration, and story displacements. all analysis is carried out using sap200 software. iv. results and discussion sap2000 software was used to analyze the three described building frames using ubc97 response spectrum and time history analysis was conducted using the n-s el centro acceleration record. figure 5 shows the mode shape number 3 of the 3-d frame. fig. 5. mode shape number 3 in a 3d view 1) first vibration periods table i shows the first 12 periods of vibration of the frames. it can be seen that the fundamental period of vibration of the bare frame is shorter than that of the other two frames. table i. vibration periods of the three building frames period no case 1 case 2 case 3 1 0.477267 0.503704 0.529412 2 0.477267 0.501569 0.527399 3 0.425421 0.435116 0.439127 4 0.150058 0.244263 0.286942 5 0.150056 0.232681 0.277906 6 0.13518 0.224227 0.27273 7 0.082466 0.206354 0.252434 8 0.082459 0.196641 0.222605 9 0.075614 0.18969 0.217581 10 0.057678 0.185846 0.212107 11 0.055327 0.176478 0.193702 12 0.055317 0.172078 0.190033 comparing the fundamental periods of vibration of cases 1 and 3, (0.477s, and 0.529s) indicates that the ssi adds flexibility to the building frame. this result is in agreement with the findings of [7]. structural building codes do not consider the effect of the ssi when they calculate the base shear value. therefore, such codes in fact overestimate the value of the base shear since the value of the fundamental period of vibration appears in the denominator in their equations, such as in equation 30-4 of the ubc97 code (v=cv.i.w/r.t). comparing 1/0.477=2.096 with 1/0.529=1.890 reveals that there is an increase in the base shear by (2.096–1.890)/1.890×100%=10.9%. however, when a basement floor is added to the building frame, as in case 2, the fundamental period of vibration becomes shorter (0.504s). the stiffness added by the basement walls adds stiffness to the structure and causes this reduction in the period of vibration. 2) shear at the base of the structure table ii shows the base shear value for the three frames resulting from the analysis. the base shear is in fact the structure base reaction as known in [8]. it acts at the base of the structure which is the level at which the lateral displacement is zero. for the bare frame, it is the foundation level. for the other two frames, it is the bottom of the soil mass, which is 26m below the foundation level. the big difference in the values of the base shear occurs due to the huge mass of the soil included in the analysis. table ii. base shear in of the three building frames method of analysis case 1 (kn) case 2 (kn) case 3 (kn) ubc97 416.15 30692.69 29499.54 max base shear in the x direction 272.866 6816.67 9144.55 min base shear in the x direction -396.455 -12721.90 -14835.02 3) column shear forces tables iii-v show the values of shear force in some columns of the three frames resulting from ubc97 and time history analysis. from table iii, it can be seen that shear force in columns of the building frame with basement (case 2), is much smaller than the one without a basement (case 3), especially for the upper floor columns. this indicates that the presence of basements reduces shear forces in columns. this can also be concluded by the results shown in tables iv and v. this result is in agreement with the findings of [9]. on the other hand, comparing the column shear force values for cases 1 and 3 (including ssi effect), it can be seen that the consideration of ssi effect produces more shear forces in columns. therefore, it should be noted that this contradicts with the belief that ssi effects produce a decrease of the forces in structures. this is in agreement with [10]. figures 6 and 7 show the table values in graphical form. table iii. columns shear forces of the 3 building frames ubc97 method of analysis case 3 (kn) case 2 (kn) case 1 (kn) column 7.99 4.07 4.76 269 19.06 10.26 10.73 268 24.34 14.50 14.72 267 26.80 17.50 17.70 266 27.16 24.34 22.48 265 18.56 187 engineering, technology & applied science research vol. 9, no. 5, 2019, 4712-4717 4715 www.etasr.com alomari: effect of the presence of basements on the vibration period and other seismic responses of… table iv. max. column shear forces of the 3 cases resulting from time history analysis in the x direction time history analysis in the x direction case 3 (kn) case 2 (kn) case 1 (kn) column no. 3.49 2.84 2.47 269 10.12 7.34 6.26 268 14.60 10.60 8.93 267 18.73 13.08 11.90 266 21.44 18.10 16.48 265 10.55 187 note: column 187 is a basement column table v. min. column shear forces of the 3 cases resulting from time history analysis in the x direction time history analysis in the x direction case 3 (kn) case 2 (kn) case 1 (kn) column no. -2.21 -2.26 -2.16 269 -6.37 -5.77 -5.54 268 -9.18 -8.25 -7.97 267 -11.78 -10.06 -10.03 266 -13.51 -13.96 -13.13 265 -0.23 187 note: column 187 is a basement column fig. 6. shear force in selected columns for the frames resulting from ubc97 response spectrum fig. 7. maximum shear force in some columns for the frames from time history analysis in the x direction 4) joints displacement the lateral displacement of the joints on the extreme of one side of the frames is chosen as a parameter to study the effect of both the presence of a basement floor, and the ssi on the seismic behavior of the structures. the lateral displacements of the joints on the right –hand side of the frames on the x-z plane at y=3m are tabulated for the three frames resulting from the ubc97 response spectrum and time history analysis. tables vi-viii show these displacements. table vi. joint displacements of the 3 building frames as result from the ubc97 analysis ubc97 analysis case 3 (mm) case 2 (mm) case 1 (mm) joint number 11.26 7.10 6.49 38 9.80 6.37 5.78 54 7.67 5.13 4.58 70 5.28 3.46 2.97 86 3.48 1.56 1.18 102 3.20 0.25 0.00 118 0.33 13806 table vii. maximum joint displacements of the 3 building frames max. displacement resulting from time history analysis case 3 (mm) case 2 (mm) case 1 (mm) joint no. 8.72 5.22 4.18 38 7.84 4.71 3.77 54 6.43 3.83 3.06 70 4.56 2.61 2.04 86 2.45 1.22 0.84 102 1.11 0.15 0.0 118 0.14 13806 table viii. minimum joint displacements of the 3 building frames min. displacement resulting from time history analysis case 3 (mm) case 2 (mm) case 1 (mm) joint number -5.55 -4.05 -3.61 38 -4.99 -3.64 -3.24 54 -4.10 -2.95 -2.59 70 -2.92 -2.00 -1.70 86 -1.59 -0.91 -0.68 102 -0.08 -0.08 0.00 118 -0.07 13806 note: joint 13806 is a corner basement joint. joint 118 in case 1 is a fixed joint a close study of the three tables shows that the least lateral displacement is in the fixed base structure (case 1).when soilstructure interaction is considered in the analysis, as in cases 2 and 3, it is obvious that the ssi effect produces a significant increase in the story drifts compared to the fixed-base frame. the flexibility of the soil mass below foundation produces a remarkable lateral displacement at the foundation level as shown for joint 118 in tables vi and vii. joint 118 in case 1 is a fixed joint with a zero lateral displacement. the same joint, in case 2 has a lateral displacement of 0.25mm due to the presence of the basement walls. the base of the structure in case 2 is at the basement bottom not at the ground level as in the fixed base frame of case 1. moreover, comparing the displacements at the top of frames of cases 2 and 3 (at joint 38), the effect of the presence of the basement floor reduces the top story drift by a considerable percentage. this can be seen in the following simple calculations: the reduction of the top of frame lateral displacement due to the presence of basement is: engineering, technology & applied science research vol. 9, no. 5, 2019, 4712-4717 4716 www.etasr.com alomari: effect of the presence of basements on the vibration period and other seismic responses of… (11.26–7.10)/7.10×100%=59%. that is to say, the presence of a basement floor reduces the top story drift of case 2 by 59% when ubc97 response spectrum analysis is used. when the time history analysis is used, the reduction is equal to 67%: (8.72–5.22)/5.22×100%=67% (see table vi). similarly, it is possible to find the effect of the ssi on the story drift by comparing the displacements of cases 1 and 3. when ubc97 response spectrum analysis is used, ssi increases the top story drift by 73%: (11.26–6.49)/6.49×100%=73% (table vi). when time history analysis is used, the top story drift increases by 50%: (8.72-4.18)/4.18×100%=50% (table vi). the story displacements in table viii show similar results. therefore, it can be concluded that the frames with ssi included exhibited much larger story drifts than the fixed base structures. moreover, the presence of a basement floor reduces the story drifts by a big percentage. in both cases, there are many factors affecting the changes in the story drifts, including the number of basement floors, the extension of the soil mass below, on the sides of the foundation and on the sides of the basement floors, the properties of the soil mass, the properties of the link gap elements, and the properties of the basement walls. figures 810 show the results in graphical form. fig. 8. joint displacement at selected joints of the three frames resulting from ubc97 response spectrum analysis fig. 9. joint displacement at selected joints of the three frames resulting from time history analysis in the x direction fig. 10. maximum joint displacement at selected joints of the three frames resulting from ubc97 response spectrum analysis v. conclusion three regular rc frame buildings have been analyzed by ubc97 response spectrum and time history analiiysis using the n-s el centro acceleration record. the aim was to study the effect of the basement floor and the soil-structure interaction on the dynamic response of the buildings. from the results the following conclusions can be drawn: • when the ssi and the presence of basement floors are included in the dynamic analysis of structures, as compared to fixed base structures, the changes in the values of the story drifts, periods of vibrations, columns shear forces, and other structures’ responses, are too large to be ignored. • there are many factors affecting the extent of the effects of the ssi and the basement floors on the dynamic behavior of structures. these include the number of basement floors, the soil mass extension below and around the structures, the properties of the soil mass, the basement wall properties, the type of connection between the soil mass and the structure elements, the regularity of the frames, and the type of seismic excitation. therefore, more research is still needed in order to conclude at any governing formulas to quantify such effects for code writing. • for the three frames considered with different conditions of soil, and basement floor, it is concluded that the ssi imparts flexibility to the structures, the story drifts increased by 50% or more, and the column shear forces increased by unequal percentages, with the upper floors columns experiencing more increase in the shear force than the lower columns. • for the two frames of considered cases 2 and 3, the presence of a basement floor has a remarkable effect on the structure seismic analysis, and caused the top floor lateral displacement to be reduced by 59% and 67% for the ubc response spectrum and time history analysis respectively. it is concluded that the presence of a basement floor reduces the floor drifts by a large amount, and therefore underground basements are beneficial to the structures. engineering, technology & applied science research vol. 9, no. 5, 2019, 4712-4717 4717 www.etasr.com alomari: effect of the presence of basements on the vibration period and other seismic responses of… references [1] d. j. kelly, “location of base for seismic design”, structure magazine, vol. 2009, no. 12, pp. 8-11, 2009 [2] b. raghava maheedhar, m. arun kumar, s. nagarjuna, c. v. siva rama prasad, “analysis and design of g+12 storey building with shear wall effect with two basements”, international research journal of engineering and technology, vol. 5, no. 5, pp. 396-401, 2018 [3] n. caglar, s. sert, m. s. imbabi, a. h. serdar, “the effect of a basement story on the earthquake response of rc buildings constructed on soft surface soil”, 3rd international symposium on innovative technologies in engineering and science, valencia, spain, june 3-5, 2015 [4] n. chandran, a. p. rajan, s. syed, “seismic analysis of building with underground stories considering soil structure interaction”, international journal of emerging technology and advanced engineering, vol. 4, no. 11, pp. 112-117, 2014 [5] m. arun kumar, b. raghava maheedhar, g. janakiram goud, “comparative study on analysis and design of g+12 stories building with and without basement walls of two basements”, international journal of engineering and techniques, vol. 4, no. 2, pp. 240-245, 2018 [6] j. sravani, v. a. reddy, “earthquake analysis of high raised rc framed building by response spectrum method”, international journal of trend in research and development, vol. 4, no. 1, pp. 580-585, 2017 [7] h. turkia, n. lahbari, “a analytical model for vibration period with ssi of r/c structures”, iosr journal of mechanical and civil engineering, vol. 12, no. 2, pp. 110-120, 2015 [8] https://www.csiamerica.com/products/sap2000 [9] r. c. ravi kumar, s. sameer, p. sandeep reddy, “a study on the behavior of a multi-storied building with soil-structure interaction”, arpn journal of engineering and applied sciences, vol. 11, no. 23, pp. 13760-13765, 2016 [10] o. bogdan, d. m. ghiocel, d. cretu, “seismic-soil-structure interaction (ssi) effects for a different type of buildings in dense urban area”, second european conference on earthquake engineering and seismology, istanbul, turkey, august, 25-29, 2014 authors profile jamal alomari is an assistant professor of structural engineering, teaching at al ahliyya amman university in the civil engineering department. his main scientific intersts lie in the area of dynamic analysis and earthquake engineering of structures. microsoft word 32-2634_s1 engineering, technology & applied science research vol. 9, no. 2, 2019, 4044-4047 4044 www.etasr.com memon et al.: defect reduction with the use of seven quality control tools for productivity … defect reduction with the use of seven quality control tools for productivity improvement at an automobile company imdad ali memon department of mechanical engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan engineerimdad@yahoo.com qadir bakhsh jamali department of mechanical engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan qjamali@quest.edu.pk abdul sattar jamali department of mechanical engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan jamali_sattar@quest.edu.pk muhammad kashif abbasi department of mechanical engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan muhammadkashif@quest.edu.pk nisar ahmed jamali department of mechanical engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan nisarjamali101@gmail.com zahid hussain jamali department of mechanical engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan zahidhussain0804@gmail.com abstract—the goal of zero defects is pursued by many manufacturing and service companies. in this regard, statistical tools are being used for defect reduction leading to productivity improvement. in this work, seven traditional qc tools (flow chart, check sheet, histogram, pareto chart, cause, and effect diagram, scatter diagram and control chart) have been developed and implemented in an automobile company to assess and improve the defect reduction level in the assembly line. chassis and trim lined were selected for data collection to assess and improve the defect level for productivity improvement. it was found from the results that after the successful implementation of the qc tools, the defect level reduced by 90% (from 132 to 13 defects) at the chassis line. similarly, the defect level was reduced by 80% (from 157 to 28 defects) at the trim line. the automobile company implemented only a few of the seven qc tools in their assembly line. it is suggested that the company may need to manage a mechanism for the implementation of all seven qc tools in every section of the company. keywords-vehicle inspection department (vid); chassis line; tim line; 7 qc tools i. introduction statistical process control (spc) plays a major role in the reduction of variations in any manufacturing and service enterprise. the problem solving tools used in spc, called the “management seven” [1], are traditional management tools, namely check sheets, histogram, pareto chart, cause and effect diagram, scatter diagram and control chart. these tools are very popular and are commonly called the 7 qc tools. their applications for quality improvement are found in almost all manufacturing and service organizations. many researchers have done successful implementations of these tools in their work. they were implemented in jordan industry in [2]. the major causes of non-conformities and the root causes of quality problems were specified, and possible remedies were proposed. continuous improvement techniques are currently used in multiple usa industries. the 7 old tools were compared with new 7 tools in [3]. spc tools such as cause and effect diagram and control charts were implemented in automotive industry. the study in [4] dealt with defects in shocker seals of an automotive industry. the percentage of rejection reduced from 9.1% to 5% after the implementation of spc. the results in [5] showed that the improvement in production processes saved materials and money. the inspection process was made automated and offline spc was converted into online spc in [6]. qc tools were used in manufacturing taper shank drills in taper shank drill industry. check sheet, pareto diagram, histogram, cause and effect diagram, control chart, run chart and scatter diagram were implemented for productivity improvement in [7]. highlighted research articles and case studies on the implementation of spc tools in manufacturing industry are reviewed in [8]. a framework for quality improvement was developed by the authors in [9] using some tools like pareto chart and fish bone diagram of critical problems. in [10], authors achieved better control in solving the problems of dimensional variations in 3-cylinder metric block casting using pareto analysis, cause and effect diagram, brain storming, why-why analysis. they suggested remedies which result in quality improvement [10]. the role of the 7 qc tools is obvious even in the increase in customer demand looking for better product quality [11]. some significant improvements were also observed after spc tools implementation in process potential capability (cp), process actual capability (cpk) and in defective parts per millions (dpm) [12]. corresponding author: qadir bakhsh jamali engineering, technology & applied science research vol. 9, no. 2, 2019, 4044-4047 4045 www.etasr.com memon et al.: defect reduction with the use of seven quality control tools for productivity … ii. materials and methods the initial activity was to assess the assembly line of an automobile company through frequent visits for the conformation of the defect level in the vehicle assembly line. two inspection points, chassis line and trim line were identified for data collection by the vehicle inspection department (vid). chassis line included wheels section, whole frame engine section with fuel wiring and battery wiring. trim line included a combined portion of shade, seats and dashboard. the frequency of defects was observed at both lines. a. flow chart (qc tool-1) the chassis and trim lines of vid were monitored for data collection. eight types of defects (hand brake wire does not drag, wire harness air booster lh side does not insert, brake oil pipe touches with chassis lh side, clutch oil pipe is not in alignment, fuel pipe touches fuel tank, engine hood damage found, exhaust pipe air wire bkt channel is not settled, compressor pipe is rusted and galvanizing process is not done) were found in chassis line. it was decided by looking the severity of defects that only two defects, namely engine hood damage (ehd) and compressor pipe rusted (cpr) were studied. similarly, four types of defects were found in trim line and only two, door improper sealed (dis) and footstep assembly stud impression (fasi) were taken for analysis based on the severity level of their occurrences. b. check sheets (qc tool-2) after identification of the inspection points for data collection, check sheets were developed to collect or mark the defective data for further analysis. check sheets are the most basic tool out of the seven. check sheets are forms especially prepared to enable data to be collected simply by checking marks. check inspectors used these sheets during checking or inspecting e.g. checking the occurrences of defects. the check sheets can be used for both numerical data and attributed data. in this research work, check sheets were designed and used for attributed data e.g. the number of different types of defects found on the chassis and trim lines. data were collected through check sheets for four months, from november 2015, to february 2016 for both lines. c. histograms (qc tool-3) histograms were developed based on the data collected through check sheets to display the variation and capability of the process. the frequency of individual defects using histograms for the four months of data collection for chassis and trim lines was developed through excel as shown in figure 1. the frequency of defects observed during november and december was high because the 7 qc tools were not implemented properly. after the application of the 7 qc tools a considerable reduction in defects was observed in january and february. the same pattern in defects reduction was observed in trim line defects as shown in figure 2. d. pareto diagrams (qc tool-4) pareto diagrams represent quality problems and their associate cost in order of their significance. a bar graph identifies the defects shown in descending order of magnitude of occurrences. it differs from histogram in the sense of mentioning the cumulative frequency of defects on its secondary axis and in the trend line showing the cumulative percentage of defects. high frequency of defects occurring can be prioritized using this chart. the pareto diagrams of defects for chassis and trim lines are shown in figures 3 and 4 respectively. fig. 1. histograms for chassis line decfects fig. 2. histograms for trim line defects (a) (b) fig. 3. pareto chart for chasssis line defects: (a) ehd, (b) cpr the pareto chart for ehd represents that 55% of defects occurred during december, 2015, while 76% occurred in november and december. the cpr defect percentage in the november was 50%. the pareto chart for dis shows that 59% occurred in november, while the accumulative percentage of november and december was 77%. fasi defect’s percentage engineering, technology & applied science research vol. 9, no. 2, 2019, 4044-4047 4046 www.etasr.com memon et al.: defect reduction with the use of seven quality control tools for productivity … in december was 47% and the accumulative percentage for november and december was 79%. (a) (b) fig. 4. pareto chart for trim line defects: (a) dis, (b) fasi e. cause and effect diagram (qc tool-5) it is used for analyzing the causes of problems which occur in products, processes or systems. the reasons of defects at chassis and trim lines can be easily identified by this tool. the initial data from the check sheets for november and december, 2015 found that the defect level was very high. therefore, cause and effect diagram was used to find the defects’ root causes. data were also collected through check sheets for january and february, 2016 to check any improvement in defect level. the cause and effect diagram for both lines for the selected defects is shown in figures 5 and 6 respectively. (a) (b) fig. 5. cause and effect diagram for chassis line defects (a) ehd, (b) cpr f. scatter diagram (qc tool-6) its purpose is to study and evaluate the inter relationship between two characteristics. the effect of one characteristic on the other can be observed by the use of a scatter diagram. the number of defects with respect to time was observed for chassis line and trim line as shown in figure 7 and 8 respectively. we see that defects had negative correlation with time. (a) (b) fig. 6. cause and effect diagram for trim line defects: (a) dis, (b) fasi d e fe c te d b o d ie s fig. 7. scatter diagram for chassis line defects d e fe c te d b o d ie s fig. 8. scatter diagram for trim line defects g. p-chart (qc tool-7) p-chart is a data analysis technique for determining if a measurement process has gone out of statistical control. it is sensitive to changes in the number of defective items in the measurement process. the “p” stands for the mean number of successes of a binomial distribution. the p-control charts for chassis and trim lines are shown in figures 9 and 10 respectively. the biggest reduction in defect level was observed in week 7 in chassis line and week 9 in trim line. compressor pipe rusted (cpr) environment made of weak planning method material improper inserting humidity due to the drops engine hood damage (ehd) man weak material tool method material series of process placing of tools hammering footstep assembly stud impression (fasi) location worker places tools tools method man improper assembling of parts proper placement irrelevant tools user door improper sealed (dis) material poorly assembled design method man proper processing not flexible material not proper design engineering, technology & applied science research vol. 9, no. 2, 2019, 4044-4047 4047 www.etasr.com memon et al.: defect reduction with the use of seven quality control tools for productivity … d e fe c ti v e f ra c ti o n fig. 9. control chart for chassis line d e fe c ti v e f ra c ti o n fig. 10. control chart for trim line iii. defect reduction after application a considerable improvement has been observed after the application of the 7 qc tools in both lines. the defects before and after the application of the 7 qc tools in chassis and trim lines are shown in figures 11 and 12 respectively. fig. 11. reduction in defects in chassis line fig. 12. reduction of defects in trim line iv. conclusion this research studied the reduction of defects in an assembly line of a vid department of an automobile company. it was observed that the highest frequency of defects in chassis line (ehd and cpr) was 132 defects in december of 2015 (before the application of the 7qc tools) and the lowest defect number (13) was found in february of 2016 (after the application of the 7qc tools). the overall improvement in the reduction of the defects for chassis line was 90%. regarding the trim line, there were 157 defects in november, 2015 and 28 in february, 2016. the overall improvement in the reduction of defects for the trim line was 82%. acknowledgment authors would like to thank the automobile company for giving access at their assembly lines and data, and the yu, ksa and quest nawabshah, pakistan for the facilities for data analysis. some data of the company are kept private in accordance with our confidentiality agreement. references [1] d. c. montogmery, introduction to statistical quality control, john wiely and sons, inc., 1997 [2] r. h. fouad, a. mukattah, “statistical process control tools: a practical guide for jordian industrial organizations”, jordian journal of mechanical and industrial engineering, vol. 4, no. 6, pp. 693-700, 2010 [3] j. v. kovach, e. a cadney, c. c. elrod, “the use of continuous improvement techniques. a survey-based study of current practices”, international journal of engineering, science and technology, vol. 3, no. 7, pp. 89-100, 2011 [4] d. r. prajapati, “implementation of spc techniques in automotive industry: a case study”, international journal of emerging technology and advanced engineering, vol. 2, no. 3, pp. 227-241, 2012 [5] m. aichouni, “on the case of the basic quality tools for the improvement of the construction industry: a case study of a mixed concrete production process”, international journal of civil and environmental engineering, vol. 12, no. 5, pp. 28-34, 2012 [6] t. v. u. kiran kumar, “spc tools in automobile component to analyze inspection process”, international journal of advanced research in electrical, electronics and instrumentation engineering, vol. 2, no. 1, pp. 624-630, 2013 [7] p. j. patel, s. c. shah, s. makwana, “application of quality control tools in taper shank drills manufacturing industry: a case study”, international journal of engineering research and applications, vol. 4, no. 2, pp. 129-134, 2014 [8] p. s. parmar, v. a. desphande, “implementation of spc techniques in industry: a review”, journal of emerging technologies and innovative research, vol. 1, no. 6, pp. 583-587, 2014 [9] a. hussain, q. w. ahmed, i. haq, “improving productivity and quality in smes of pakistan”, technical journal, university of engineering and technology, taxila, pakistan, vol. 20, no. 2, pp. 103-114, 2015 [10] a. b. vante, g. r. naik, “quality improvement for dimensional variations in sand and casting using quality control tools”, international journal of innovative research in science, engineering and technology, vol. 4, no. 8, pp. 6917-6926, 2015 [11] d. g. pendokhare, t. quazi, p. s. kulkarni, “redesign and manufacturing by using dmadv method”, international journal of research in engineering and technology, vol. 4, no. 2, pp. 144-149, 2015 [12] n. afzaal, a. aftab, s. khan, m. najamuddin, “to analyze the use of statistical tools for cost effectiveness and quality of products”, iosr journal of humanties and social science, vol. 20, no. 1, pp. 47-57, 2015 microsoft word 7-2556_s1 engineering, technology & applied science research vol. 9, no. 2, 2019, 3905-3908 3905 www.etasr.com gorenekli & becerikli: development of electronic water meter based on wireless network and rf development of electronic water meter based on wireless network and rf kasim gorenekli isu general head office it department, kocaeli metropolitan municipality, kocaeli, turkey kgorenekli@isu.gov.tr yasar becerikli computer engineering department, engineering faculty, kocaeli university, kocaeli, turkey ybecerikli@kocaeli.edu.tr abstract—the global need for water is increasing. water must be used more economically in order to be sustainable. water consumption per capita in turkey is below the world regarding its geographical location. manual reading water meters are inconvenient and time-consuming, they have low accuracy, they are very slow and resource wasting. using wireless communication will mitigate these unwanted states. consumers will be able to observe their water consumption in real time and be able to compare with the average water consumption in their district. with this system water pressure of whole pipes could be observed. keywords-remote meter reading; sustainable and qualified service; water loss; wireless and rf network; smart water meter; accurate and high performance i. introduction in accordance with regulations issued by the ministry of water affairs, municipalities are responsible for 30% of drinking water losses, and in the following 4 years they should reduce them to 25%. the first project initiated to pursue these regulations throughout turkey is the kocaeli, izmit district drinking water project for reduction of loss. the increase in population, which results in more residential areas being constructed, constantly expanding industry sites, and utility companies seeking billing systems for residential and industrial environments to require less human interaction, necessitates the reduction in the cost of implementing a water-metering system. smart water meter systems increase time efficiency and adequacy, since bills are delivered timely and more accurately. another advantage is that the system can be adapted for use in other domains such as gas or electricity [1-3]. water distribution network monitoring provides the opportunity for automatic billing data collection, rejecting unauthorized connections, infrastructure security (tampering), leak detection [4], and water quality monitoring. in real life scenarios, the drive-by scenario is problematic as the readout procedure might fail and urbanized area range limitations due to signal attenuation are present, resulting in the need for a repeated drive-by. the target of authors in [5] was to optimize energy consumption of all these components. the optimization will give a positive impact on cost minimization and on the prolongation of battery life time. it will simplify the deployment of wireless sensor networks for monitoring the water distribution networks. simplified packet repeater principle showed great results during trial network deployment and reduced overall installation costs by minimizing the required gateway nodes that need direct network connections. the proposed case does not consider such a solution. a pseudo autonomous system is tuned for minimal operational costs, including maximization of non-stoppable service uptime by maximization of battery lifetime. in [6], authors focused on implementing a smart water management system to assist users in obtaining real-time data for real-time analysis. the system provides the user with realtime data for water consumption. it also creates various visual graphs of the collected data and represents them in a readable manner to the customer. the scope of the paper does not allow it to focus on the continuous development of analogue water meters for greater accuracy or to consider how the raw data can be linked to the billing utility system. automatic measurement systems make life easier for science and technology. the use of these systems saves time, minimizes human error factors, reduces costs, and provides ease of analysis and management. the economic use of water consumption and the reduction of leaks are inevitable. the automatic measuring system is the development of a radio frequency based water meter or a module to be connected to the measuring device. in this way, instantaneous water consumption, and device intervention will be monitored remotely and the necessary intervention will be made immediately. ii. related work authors in [5] showed the use of wireless sensors in water distribution networks and focused on the energy consumption and the consistency of data in wireless communications. communication is achieved by adding fixed electric routers to the points where meters cannot be reached. improved protocol was used for low energy consumption compared to mobile ad hoc network. despite the traditional point-to-point communication, the wireless sense network (wsn) is able to save data by sending only data that needs to be moved to the external network using its own account capability [7]. the work done in [6] about the advanced sense network research group is focused on the economical use of water. one solution is to retrieve data via physical cable. it is observed that this is not practical in terms of time and cost. alternatively, the corresponding author: k. gorenekli engineering, technology & applied science research vol. 9, no. 2, 2019, 3905-3908 3906 www.etasr.com gorenekli & becerikli: development of electronic water meter based on wireless network and rf wireless communication is used between water meter and gateways. ldbrs (low data bit rate sense) proposes the use of zigbee [8] using ieee 802.15.4 protocol. modbus-rtu and iec 61107 mode c communication protocols are used frequently in remote meter reading systems [9]. iii. communication networking smart water meters must be accurate and fast enough to serve a large number of subscribers. bidirectional communication should be used. utility companies should therefore implement smart water metering which should be capable to support geographically spread modules. remedy of latency, fastness, accuracy, security and reliability are the specifications which are compulsory. network topology refers to the physical and logical placement of computers in the local area network (lan). physical topology specifies how all devices in the network are connected to each other and what kind of cable is used. there are several network topologies. five common topologies are described below. a. bus topology all devices are connected to each other via a main cable and all devices have access to it. the cable used is usually a coaxial cable. devices on the line must make sure that the line is completely empty before sending data, otherwise there will be conflicts. data are sent to all devices connected to the line, but only the target device receives them. it is the topology with the lowest performance [10]. b. star topology in star topology, each device on the network is connected directly to central connectors called switches or hubs. data go through the central connector (switch or hub) to the destination. it is the central connector that manages and controls all functions of the network. c. mesh topology in mesh topology all nodes in the network are connected to each other. this topology is also called complex topology. mesh does not need to use any distributors. on the other hand, the routing process has a significant share in the mesh. that is, the paths of the data packets should be defined in advance. this is the most secure network topology. since there is a connection between each point, data transfer can be hidden. for example, while two computers are exchanging data among themselves, others cannot see these data. mesh-type networks are always in communication. the corruption of any connection doesn’t affect the other connections. if any cable breaks, the network will continue to run by using another path and no computer will be out of the network. therefore, this network is preferred when communication breakdown is dangerous. the mesh also provides short response time. mesh has and some disadvantages. as the number of computers to be connected increases, the number of cables increases exponentially. this increases the complexity and cost because each new computer will need to establish new separate lines with the other computers on the network. therefore, mesh connection is not preferred in large-scale networks. it is mostly used in special places and small networks. it has a limited usage area. d. tree topology it is often used to link networks in star topology. the networks can thus be enlarged. the branches of a tree represent networks in different topologies, and they are interconnected with the tree's body. many working groups can be put together. when the backbone cable is broken, network traffic on the partitions is affected. it is difficult to install and edit [11]. e. ring topology all devices in the ring topology are connected to each other in a ring shape and each device has two separate neighbors. the devices on the line are visited one by one with the help of a token until data reach the target [12]. iv. proposed algorithm and sensor network structure a wi-fi based network is created with 3 raspberry pi’s [10]. one of them is also used as a hotspot. another raspberry pi is used as a gateway to which the network is connected through rf (radio frequency). rasbian (based on linux) is used on these raspberry pi’s. for easiness to learn and compatibility reasons, python language is used. time periods mentioned below are saved in a file and can be changed by the user. the block diagram is shown in figure 1 and the flowchart in figure 2. fig. 1. block diagram of the system fig. 2. flow chart of the system the implemented software steps from the flow chart have the following functions: • ips of the active modules in the network are searched and saved for future use. this is done by all modules daily. • getting and saving in a file the track of current water meter index (every 30 minutes) engineering, technology & applied science research vol. 9, no. 2, 2019, 3905-3908 3907 www.etasr.com gorenekli & becerikli: development of electronic water meter based on wireless network and rf • sharing index data with neighbor modules through wi-fi (or rf) every 3 hours. by this way every module saves the data from all modules in the same network. • the collected data from the modules are sent to the gateway through rf once per day. • if there is a problem in the transmission between the central module in the network and the gateway, another path is used according to the closest ip from the central module. • the result’s data are displayed on web pages (figure 3). fig. 3. displaying indexes of all three raspberry pi’s in web pages. fig. 4. debian installed on raspberry pi 3 module with rf added the energy consumption in wireless communication is important. the lifetime of the battery can be calculated according to the equations below [5]: ���� � ����.� � ����. � ����. ��� � (1) ���� � ������������ � ���� 1000 � ���� �������� � � �� 1000 � ����. ��� � (2) ��� .� � � !�"�#$ � 1000 � ���%&�%'()*' !�+���� �������� � ������()*"�#$ (3) where: tawm : average working time of microcontroller, (ms) iavg.m : average current of the microcontroller, (ma) iavg.t : average current of transmitter, (ma) iavg.losses: average losses of circuit, (ma) tmc : microcontroller working cycle, (ms) imc : microcontroller current at working cycle, (ms) itc : transmitter current at working cycle, (ma) tawt : average transmitting time of transmitter, (ms) ttc : transmitter working cycle, (ms) cnew : capacity of fully charged battery, (mah) c10y : estimated capacity of new battery after 10 years caused by self-discharge, (mah) tbath : estimated sensor node lifetime, (h) as an example, package size is 23 bytes, baud rate is 4800bps and time period is 15 minutes. by using the above equations the battery lifetime is calculated as follows: ��, � -.�/0/�� � 1000 � 38 34 (4) � � � 24 7 � 900.000 34 (5) ��, 9 40 34 (6) ����. 9 80 3: (7) ��,� 9 20 34 (8) ��� 9 16 34 (9) ��� 9 3 3: (10) ����. ��� � 9 5=: (11) ���� � -��>����� � 3 � 1000 � 0� ?����� � 80 � 1000 � 5 9 12.25 =: (12) ��� .� 9 ���� � --@��-.-@ 9 183673 7 9 21 bcde4 (13) 4800 baud rates with the package size of 23 bytes converted into bits shown in (4). if the above equations are processed the lifetime of this battery will be about 21 years as shown in (13). v. conclusion in this paper, four modules are used to create a network. a wifi network is created among the modules in the same building. an extra module for hotspot is not used. according to the mesh topology, the data of all modules are sent among themselves in the same network. the module with the lowest ip sends the whole data to the gateway via rf. in case of transmission failure the module which has the next ip takes this responsibility over. there are some technologies like sigfox, zigbee, gsm, lte and lora with their own advantages and disadvantages. three parameters are considered which are low energy, long distance and license. in our case lora technology was used. it is possible to detect the water leaks by using this system. the amount of leakage is the difference between the amount of water supplied and the total amount of water used. the less the water consumption, the easier the engineering, technology & applied science research vol. 9, no. 2, 2019, 3905-3908 3908 www.etasr.com gorenekli & becerikli: development of electronic water meter based on wireless network and rf detection of water leakage. minimum use of water is observed during night hours. the hourly recordings at the night make the detection of the water leakage easier. this study covers the district of izmit, which has 160.000 subscribers. vi. future work this work can be adapted to the iot (internet of things) technology. by using this technology the number of gateways will be decreased. in addition, temperature, pressure and humidity data might be detected. energy might be supplied by adding tribunes before water meter. tank levels can be increased to keep the water pressure of subscribers at the same level. if there is water consumption when the subscriber is outside, the system may inform him and also turn the water meter off automatically. references [1] f. benzi, n. anglani, e. bassi, l. frosini, “electricity smart meters interfacing the households”, ieee transactions on industrial electronics, vol. 58, no. 10, pp. 4487-4494, 2011 [2] m. li, h. j. lin, “design and implementation of smart home control systems based on wireless sensor networks and power line communications”, ieee transactions on industrial electronics, vol. 62, no. 7, pp. 4430-4442, 2015 [3] a. m. abu-mahfouz, t. o. olwal, a. m. kurien, j. l. munda, k. djouani, “toward developing a distributed autonomous energy management system (daems)”, africon 2015, addis ababa, ethiopia, september 14-17, 2015 [4] a. nasirian, m. f. maghrebi, s. yazdani, “leakage detection in water distribution network based on a new heuristic genetic algorithm model”, journal of water resource and protection, vol. 5, no. 3, pp. 294-303, 2013 [5] k. kondratjevs, a. zabasta, n. kunicina, l. ribickis, “development of pseudo autonomous wireless sensor monitoring system for water distribution network”, ieee 23rd international symposium on industrial electronics (isie), istanbul, turkey, june 1-4, 2014 [6] m. j. mudumbe, a. m. abu-mahfouz, “smart water meter system for user-centric consumption measurement”, ieee 13th international conference on industrial informatics (indin), cambridge, uk, july 2224, 2015 [7] g. hu, x. zhang, w. qian, p. yan, z. hu, “a routing protocol for low energy wireless sense network”, 2006 iet international conference on wireless, mobile and multimedia networks, hangzhou, china, november 6-9, 2006 [8] e. yuksel, design of a zigbee architecture for telemetering, msc thesis, istanbul university, 2010 [9] e. s. suzer, remote metering techniques and sample software for modbus-rtu, iec 61107 mode c protocols, mcs thesis, fen bilimleri enstitusu, 2006 (in turkish) [10] m. rouse, “tree network”, available at: https://searchnetworking. techtarget.com/definition/tree-network [11] a. shekhar, “what is tree topology? advantages and disadvantages of tree topology, available at https://fossbytes.com/tree-topologyadvantage-disadvantage, 2016 [12] cosum park, “temel ag topolojileri”, available at: http://www.cozumpark.com/blogs/network/archive/2008/04/29/temelag-topolojileri.aspx, 2008 (in turkish) authors profile kasım gorenekli in 1996 he finished computer engineering at yildiz technical university in istanbul. he is doing his msc degree of computer engineering at kocaeli university and at the same time he is working at kocaeli metropolitan municipality as a computer engineer. married, he has four children and five grandchildren. yasar becerikli received his bsc degree from the electronics and communication engineering department at yildiz technical university in 1991, his msc degree from the electronics and communication engineering department of the istanbul technical university in 1994, and his phd from the electrical and electronics engineering department at the sakarya university in 1998. he was a research assistant at sakarya university, turkey, from 1992 to 2000, an assistant professor of computer engineering at kocaeli university, from 2000 to 2005, and he served as an associate professor at kocaeli university, from 2005 to 2011. currently, he works as a professor of computer engineering in kocaeli university. he served as a senior researcher at marmara research center (mrc), from 2003 to 2004. his current research interests include intelligent systems and control, neurofuzzy systems and optimal control, computational intelligence, optimization theory/deep learning, wavelet networks, stochastic process control, medical/signal and image processing, uavs and pattern reconnition, fpga based embedded systems. dr. becerikli serves as associate editor of eurasip journal on advances in signal processing, eurasip journal on image and video processing, and advances in fuzzy systems and also serves as a reviewer for more than 30 journals. microsoft word 24-2974_s_etasr_v9_n5_pp4706-4711 engineering, technology & applied science research vol. 9, no. 5, 2019, 4706-4711 4706 www.etasr.com zemzemi & boulejfen: behavioral modeling and digital predistortion of 2x2 mimo wireless … behavioral modeling and digital predistortion of 2x2 mimo wireless transmitters with enhanced multivariable polynomials imene zemzemi department of physics, university of tunis el manar, tunis, tunisia imizemzmi@gmail.com noureddine boulejfen research centre for microelectronics and nanotechnology technopole of sousse, sousse, tunisia nboulejf@ieee.org abstract—in this paper we propose a novel concept named enhanced multivariable memory polynomials (emvp) for the behavioral modeling and linearization of multiple input multiple output (mimo) transmitters in the presence of linear (lc) and nonlinear (nlc) coupling effects. the proposed model improves the linearization performance of the conventional multivariable memory polynomials (mvp) model. its performance is experimentally compared with the ones of three popular polynomial models. emvp model has succeeded in offering better linearization of mimo transmitters, with fewer coefficients, compared to the conventional models. experimental results showed improvement in adjacent channel power ratio (acpr<-60dbc) and normalized mean square error (nmse<-45db) for lte signal excitation with 10mhz bandwidth, in the presence of both linear and nonlinear couplings of 20db. keywords-behavioral modeling;digital pre-distortion (dpd); multiple-input multiple-output (mimo); enhanced multivariable memory polynomials (emvp) i. introduction in 5g wireless communication systems, billions of connections could exist concurrently for various data transmission types [1, 2]. mimo transmitters are considered as a feasible solution to fulfill these high requirements [3–15]. mimo systems deal with simultaneous transmission and reception of multiple signals, through the same radio channel and frequency bandwidth, by exploiting multipath propagation. [6–12]. moreover, mimo systems have been developed to handle concurrent dual-band signals [13–17]. despite their efficiency in terms of data transmission rates, mimo transmitters suffer from several problems. on top of the nonlinearity and memory effects, inherited from single inputsingle output (siso) transmitters, mimo systems suffer from the coupling between adjacent amplification branches. this crosstalk [8] becomes stronger in mmic implementation of mimo transmitters. in the published literature crosstalk is classified as linear (lc) and nonlinear (nlc) [9–11]. in [6– 20], digital predistorters (dpd) have been used to reduce the distortion effects of mimo systems. in [9], the crossover model (mcr) is based on the summation of two nonlinear siso models. this model has the advantage of low amount of coefficients, but its performance degrades in the presence of strong crosstalk (nlc and/or lc of levels over -30db). in [10], a robust model based on multivariable polynomials (mvp) has been presented. this model is capable of handling memory effects, as well as strong linear and nonlinear crosstalk, with a cost of a large amount of coefficients and high complexity. in [11], a curtailed version of the mvp based model (cmvp) has been developed through the elimination of certain terms, by considering only the nonlinear crosstalk. this model, and its corresponding dpd, is able to reach almost the same performance as the mvp based model with less coefficients. therefore, mvp and cmvp models are assumed as good references for measuring the performance of the proposed model. in this paper, we propose a robust polynomial model for the digital predistortion of mimo systems, named as the enhanced multivariable polynomials (emvp) model. this new model is based on the enhancement of the mvp model’s efficiency by adding properly selected intermodulation and cross terms. ii. polynomial modeling of mimo transmitters in siso transmission systems, rf power amplifiers are critical components in terms of energy consumption, nonlinearity and memory effects that cause signal distortion. mimo power amplifiers inherit these effects, while exhibiting an additional coupling effect between amplification branches. in fact, input signals are transmitted at the same time and carrier frequency through transmitter paths. the resulting coupling depends on certain parameters, such as pa nonlinearity, power of input signals, and integration density which is exponentially increasing in modern communication systems like 4g and 5g networks. to compensate for coupling, pa nonlinearity and memory effects, a 2d dpd with reasonable complexity and performance compromise is required [3]. figure 1 shows the proposed diagram of a 2x2 mimo dpd system, based on the indirect learning architecture where ui(n), yi(n) and zi(n) represent the baseband input signal, the pa output signal and the predistorted signal of the amplification branch i respectively. crosstalk is caused by the coupling between different transmitter’s paths or due to the corresponding author: imene zemzemi engineering, technology & applied science research vol. 9, no. 5, 2019, 4706-4711 4707 www.etasr.com zemzemi & boulejfen: behavioral modeling and digital predistortion of 2x2 mimo wireless … leakage through the common lo, classified lc and nlc. nlc occurs at the pa input path while lc occurs at the pa output. fig. 1. architecture of a 2x2 mimo transmitter with dpd two coupling scenarios will be considered in order to properly assess the performance of the proposed dpd. it can be expected that performance will degrade when crosstalk at input is stronger than 20db. this is expected to occur for high integration density, foreseen in 4g systems and beyond [3]. for comparison purposes, two recently published dpds, based on multivariable polynomial models, will be simulated. a. multivariable memory polynomial model (mvp) in order to enhance model’s accuracy for mimo transmitters with strong crosstalk, an inclusive mimo polynomial model has been proposed in [10]. the output of each amplification branch is modeled considering only nlc mimo transmitter’s input. the output of the mvp 2x2 mimo model can be written as: 1 ( )( ) .1 , , 1 1 2 0 0 0 1 ( ).2 , , 2 2 1 0 0 0 ( ) ( ) ( ) ( ) ( ) ( ) ( ) m k k k q qi i k q m m k q m k k k q qi k q m m k q j j j j j j ny b u u u b u u u − − = = = − − = = = = ∑ ∑ ∑ +∑ ∑ ∑ (1) where k is the nonlinearity order, m is the memory depth, ( ,1) , , i k q mb and ( ,2) , , i k q mb are the coefficients of each model’s branches, u1(n) and u2(n) are input signals and ( ) ( ) i mvpy n is the i th output of the mimo transmitter, with i={1,2}. mvp model has a relatively high number of coefficients and is expected to exhibit good performance. b. curtailed multivariable memory polynomial model (cmvp) the output y (i) of the 2x2 cmvp based model is given by: 1 ( ) .1 , 1 1 0 0 /2 1 .2 , 2 2 0 0 /2 1 ( ).3 , , 1 1 2 0 1 1 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) m k ki i k m m k m k ki k m m k m k k k q qi k q m m k q j j j j j j j y n b u u b u u b u u u − = = − = = − − = = = = ∑ ∑ +∑ ∑ + ∑ ∑ ∑ (2) with u1(n) and u2(n) being the input signals, k the non-linearity order, m the memory depth, .1 , i k mb , .2 , i k mb and .3 , , i k q mb the model coefficients, and y (i) (n) the output of the amplification branch i. the complexity of cmvp based model is way less than mvp, with comparable performance. c. proposed model (emvp) mimo transmitters’ model aims to predict precisely pa nonlinearity and memory effects, as well as lc and nlc between pa branches. hence, the model’s complexity is increasing with the strength of these undesired effects. a compromise between accuracy and complexity is very helpful on implementing any model. in this context, we propose emvp mimo model that eliminates the even nonlinear terms, while adding all cross terms between input signals and intermodulation terms of the main transmitted channels. thus, the output of the proposed model, including both lc and nlc, can be expressed as: ( ) ( ) ( ) ( ) ( ) ( ) i i i l nl y n y n y n= + (3) where ( ) ( ) i nl y n is the output component with cross terms that model the non-linear crosstalk, given by: 1 2( ) 2( ) .1 1 1 2 0 0 0 1 2( ) 2.2 2 2 1 0 0 0 , , , , ( ) ( ) ( ) ( ) ( ) ( ) ( ) m k k k q qi i nl m k q m k k k q qi m k q k q m k q m y n u j b u j u j u j b u j u j − − = = = − − = = = = ∑ ∑ ∑ + ∑ ∑ ∑ (4) however, �� ��� predicts lc, which, for a 2x2 mimo transmitter in the presence of lc, can be given by: 1 2 2( ) .3 1 1 1 2 , 1 0 1 1 2 2.4 2 2 1 2 0 1 , ( ) ( ) ( ( ), ( )) ( ) ( ) ( ( ), ( )) ( ) m k ki i l k m m k m k ki m k k m y n u j u j u j b u j u j u j u j b u j − − = = − − = = = ∆∑ ∑ + ∆∑ ∑ (5) with * * 1 2 1 2 2 1( ( ), ( )) ( ) ( ) ( ) ( )u j u j u j u j u j u j∆ = + , ( )* being the conjugate operator, j=n-m, is the output of channel 1, u1(n) and u2(n) are the input signals, k the nonlinearity order defined as (nonlinearity degree+1)/2 and m is the memory depth. thus, the output of a transmitter path can be expressed as: 1 2( ) 2( ) .1 1 1 2 0 0 0 1 2( ) 2.2 2 2 1 0 0 0 1 2 2.3 1 1 1 2 , 1 0 1 1 2 2.4 2 2 1 2 1 , , , , , ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ( ), ( )) ( ) ( ) ( ( ), ( )) ( ) m k k k q qi i m k q m k k k q qi m k q m k ki k m m k k ki m k k q m k q m k m y n u j b u j u j u j b u j u j u j u j u j b u j u j u j u j b u j − − = = = − − = = = − − = = − − = = ∑ ∑ ∑ + ∑ ∑ ∑ + ∆∑ ∑ + ∆ ∑ 0 m = ∑ (6) where .1 , , i p q m b , .3 , i p m b , .2 , , i p q m b and .4 , i p m b are model’s coefficients. emvp model includes all cross terms and intermodulation terms of signals in transmitter’s output. we added in (2) two terms for each nonlinearity order k. the model is expected to perform well with limited memory depths, as it will be demonstrated below in experimental validation. table i presents the expressions that calculate the number of coefficients for the three considered models. figure 2(a) shows the variation of these numbers as a function of the model’s nonlinearity order for a constant memory depth m=3. figure 2(a) reveals that the amount of mvp model’s coefficients engineering, technology & applied science research vol. 9, no. 5, 2019, 4706-4711 4708 www.etasr.com zemzemi & boulejfen: behavioral modeling and digital predistortion of 2x2 mimo wireless … augments exponentially with nonlinearity order, as compared to cmvp and the proposed emvp models that exhibit comparable behavior. table i. number of coefficients for 2×2 mimo models model number of coefficients cmvp ( ) ( / 2) 2 1 ( / 2)* 2 floor k m k floor k   + +    mvp ( )( )1 1k k m+ + emvp ( )( )( )( ) ( ) 3 1 1 1 4 k k m km m + + + + − + d. models’ identification model’s identification is a critical procedure. in fact, model’s coefficients need to be carefully estimated in order to reach the highest performance on any given behavioural model. there are different parameter identification strategies such as the least squares (ls) algorithm, which is widely used to identify polynomial models with linear parameters. however, iterative procedures such as recursive least squares (rls) can be used for models with no linear parameters. in order to use the ls identification procedure expressions in (1), (2) and (4) are reformulated into matrix form as: (i) (i) (i) y =b c (7) where y (i) is the n×1 vector representing samples of the i th pa output and b (i) is the n×s data matrix, relative to branch i, that includes nonlinear input terms obtained from model’s input. c (i) is an s×1 vector containing model coefficients for branch i, where s is the overall model size. for simplicity, i subscript will be dropped in subsequent equations. data matrices for the models are given below: (1) (1.1) (1.2) (1.3) (1.4) b b b b b emvp emvp emvp emvp emvp  =    (8) (1) (1.1) (1.2) b b b mvp mvp mvp  =    (9) (1) (1.1) (1.2) (1.3) b b b b cmvp cmvp cmvp cmvp  =    (10) where each row of the component matrices (corresponding to one time index j n m= − ) is given by: (1.1) ( ) ( 1) 1 1 1 2 1 2 b ( ) ( )... ( ) ( ) ( ) ... ( ) ( ) k q q k mvp n u j u j u j u j u j u j − − =   (11a) (1.2) ( ) ( 1) 2 2 2 1 2 1 b ( ) ( )... ( ) ( ) ( ) ... ( ) ( ) mvp k q q k n u j u j u j u j u j u j − − =   (11b) (1.1) ( 1) 1 1 1 1 1 b ( ) ( )... ( ) ( ) ... ( ) ( ) k k cmvp n u j u j u j u j u j − =   (12a) (1.2) ( /2 1) 2 2 2 2 2 b ( ) ( )... ( ) ( ) ... ( ) ( ) k k cmvp n u j u j u j u j u j − =   (12b) (1.3) ( ) ( /2 1) 1 1 1 2 1 2 b ( ) ( )... ( ) ( ) ( ) ... ( ) ( ) k q q k cmvp n u j u j u j u j u j u j − − =   (12c) 2( ) 2 (1.1) 1 1 1 2 2( 1) 1 2 ( ) ( ) ( ) ( ) b ( ) ( ) ( ) k q q kemvp u j u j u j u j n u j u j − −    =    … … (13a) 2( ) 2 (1.2) 2 2 2 1 2( 1) 2 1 ( ) ( ) ( ) ( ) b ( ) ( ) ( ) k q q emvp k u j u j u j u j n u j u j − −    =    … … (13b) ( ) (1.3) 2( 1) 1 1 1 1 2 b ( ) ( )... ( ) ( ) ( ), ( ) k emvp n u j u j u j u j u j − = ∆   (13c) ( ) (1.4) 2( 1) 2 2 2 1 2 b ( ) ( )... ( ) ( ) ( ), ( ) k emvp n u j u j u j u j u j − = ∆   (13d) after constructing model’s matrices, as outlined above, coefficients are typically extracted using ls [19] as: ( ) ( ) ( ) ( ) -1 h( ) ( ) c b b b y i i h ii i ls ∧ = (14) ( ) c i ls ∧ is obtained by the pseudo inverse of matrix b (i) , with h being the operator denoting the hermitian transpose. ls method has been extensively used to extract parameters of behavioral models and dpds. however, it is known to suffer from numerical stability issues due to the matrix inversion step when large ill-conditioned model matrices are involved. iii. numerical stability analysis numerical stability of the model’s identification procedure, using the ls algorithm, mainly relies on the conditioning of the observation matrix (b (i)h b (i) ). inverting ill-conditioned matrix results in inaccurate and dispersive coefficients that reduce the performance of the corresponding dpd. this problem becomes more severe when implementing dpd in a fixed point calculation environment such as dsp and fpga hardware. this would require large word length, which increases the cost of practical system realizations [20]. a good metric for the matrix condition is the condition number is given by: 1 2 2 b bρ −= × (15) where b is the square observation matrix to be inverted and || ||2 operator refers to the 2-norm. figure 2(b) presents the condition number of the observation matrices for the three considered models as a function of the nonlinearity order with constant memory depth m=3. the figure shows that the emvp model has the lowest condition number for all k, which reveals the stability and the robustness of the proposed model compared to cmvp and mvp. table ii lists the condition numbers for the three models, for different memory depths. once again, the proposed model has shown its superiority for all combinations of (m, k). table ii. condition number for the 2×2 mimo case memory depths models k 1 5 9 11 m=0 mvp 1.05 8.02.10 06 4.41.10 13 1.12.10 17 cmvp 1.05 3.62.10 06 8.95.10 13 3.19.10 17 emvp 1.05 4479.2 1.53.10 07 1.08.10 09 m=3 mvp 2.01.10 10 3.86.10 12 1.98.10 18 1.72.10 20 cmvp 2.01.10 10 7.16.10 12 1.98.10 18 4.27.10 20 emvp 2.01.10 10 1.01.10 10 2.27.10 13 6.11.10 14 m=5 mvp 8.38.10 15 1.07.10 17 2.93.10 20 3.77.10 21 cmvp 8.38.10 15 8.42.10 17 3.41.10 20 7.79.10 21 emvp 8.38.10 15 1.06.10 16 9.78.10 16 1.31.10 18 engineering, technology & applied science research vol. 9, no. 5, 2019, 4706-4711 4709 www.etasr.com zemzemi & boulejfen: behavioral modeling and digital predistortion of 2x2 mimo wireless … (a) (b) fig. 2. (a) number of coefficients as a function of the nonlinearity order k for m=3, (b) condition number as a function of k and m=3. iv. experimental validation a. experimental setup experimental setup used for both dpd extraction and mimo forward modeling is illustrated in figure 3, where two complex baseband signals are generated and fed into two synchronized rohde & schwarz smbv100a vector signal generators, to produce the input rf signals with the same carrier. two identical power amplifiers rf mini-circuits zhl42 constitute the dut setup, while two cross-connected couplers are used to produce a path of 20db coupling between the input signals. couplers are placed in front of the pas for nonlinear coupling and after them for a linear one. input rf signals are independent lte signals centered on 2.14ghz with 10mhz bandwidth, -8db average power and 11db peak-toaverage power ratio (papr). mimo system’s rf outputs are converted to intermediate frequency (if) signals. an adq214 analog-to-digital converter (adc) samples if signals with 400mhz sampling rate and 14 bit resolution. indirect learning architecture (ila) is used following the same methodology as in [10, 11]. fig. 3. setup diagram b. model and dpd performance metrics 1) normalized mean square error (nmse) time domain nmse [22, 23] has been used in order to evaluate the accuracy of the proposed mimo model in predicting transmitter output. nmse is expressed as: 2 1 10 2 1 ( ) ( ) 10log ( ) n ms s est s n db n ms s n y nt y nt nmse y nt = =   −   =        ∑ ∑ (16) where yms(nts) and yest(nts) are the measured and predicted outputs respectively. typically, values below -40db are desirable for nmse [10-11]. 2) adjacent channel power ratio (acpr) in order to study the linearization performance of a dpd, the acpr metric is commonly used [22, 23]: 2 . 2 . ( ) ( ) adj ch db main ch y f df acpr y f df = ∫ ∫ (17) acpr can be evaluated for the adjacent channels above and below the main frequency band known as the upper and lower acpr in units of dbc (db below the carrier). |y(f)| 2 is the power spectral density of the y(n) output. c. results the performance of the proposed emvp model was evaluated against cmvp and mvp models, in terms of forward modeling and dpd. coupling scenarios shown in table iii were considered for the evaluation procedure. table iii. coupling scenarios scenarios crosstalk levels (db) nlc lc scenario 1 20 0 scenario 2 20 20 1) forward modeling performance evaluation results of emvp model using a mimo transmitter are shown in tables iv and v. nmse and the amount of coefficients are measured for nonlinearity order k=11. table iv presents the nmses for the first scenario. results reveal that the nmse of the emvp model is the lowest with an average of 3-4db lower than mvp and cmvp. in addition, emvp and cmvp have the same number of coefficients. however, emvp model achieves maximum nmse performance for a memory depth of m=3, while mvp and cmvp reach their best nmse performance for m=5. table v presents the nmses for the second scenario. once again, the proposed model exhibits better performance, with an nmse of -45.28db compared to mvp and cmvp, which did not drop below -42.10db. in order to further investigate the models’ convergence behavior and respective sensitivity, emvp and cmvp were extracted while sweeping the value of engineering, technology & applied science research vol. 9, no. 5, 2019, 4706-4711 4710 www.etasr.com zemzemi & boulejfen: behavioral modeling and digital predistortion of 2x2 mimo wireless … k for memoryless (m=0) and memory models with m=3. obtained results for the two scenarios are shown in figure 4. it is clear that emvp can reach better nmse performance (-45db) and offers the fastest convergence for a similar number of coefficients. table iv. nmse for the first measurement scenario table v. nmse for the second measurement scenario models m number of coefficients nmse (db) y (1) y (2) mvp 3 528 -41.97 -41.25 5 792 -42.10 -41.96 cmvp 3 208 -41.05 -40.90 5 312 -41.40 -41.33 emvp 3 208 -45.28 -45.12 5 312 -45.32 -45.21 (a) (b) fig. 4. the nmse for surfaces as a function of the k and m values for different model, (a) scenario 1 (b) scenario 2 2) dpd results after evaluating the performance of the proposed multivariable polynomials in the reverse modeling, a dpd is built to linearize the mimo transmitter. in this experiment, lc and nlc are set to 20db and the linearization experiment was performed two times, covering the two scenarios defined in table iii. figure 5 presents the power spectral densities of the two output signals, with and without dpd, for the two coupling scenarios. τhe proposed dpd exhibited the lowest the highest linearization performance for both scenarios, which confirms the obtained acprs. figures 5(c) and 5(d) show a small reduction in dpd’s performance in the presence of linear coupling, even though the proposed dpd maintained its superiority over mvp and cmvp dpds. (a) (b) (c) (d) fig. 5. power spectral density (psd) of the dut output with and without dpd (a) channel 1, scenario 1, (b) channel 2, scenario 1, (c) channel 1, scenario 2, (d) channel 2, scenario 2 models m number of coefficients nmse (db) y (1) y (2) mvp 3 528 -44.05 -43.99 5 792 -44.76 -44.46 cmvp 3 208 -43.05 -43.15 5 312 -43.97 -43.42 emvp 3 208 -46.93 -47.05 5 312 -47.11 -47.15 engineering, technology & applied science research vol. 9, no. 5, 2019, 4706-4711 4711 www.etasr.com zemzemi & boulejfen: behavioral modeling and digital predistortion of 2x2 mimo wireless … table vi. comparison of acpr(dbc) for mimo dpd transmitter with different measurement scenarios models m number of coefficients acpr (dbc) y (1) y (2) scenario 1 mvp 5 792 -52.83 -52.23 cmvp 5 312 -50.74 -51.74 emvp 3 208 -63.02 -62.02 scenario 2 mvp 5 792 -51.83 -51.53 cmvp 5 312 -50.75 -51.10 emvp 3 208 -62.05 -61.25 v. conclusion this paper proposed a new behavioral memory polynomial model and a digital predistorter for 2x2 mimo transmitters. this model includes nonlinear and cross terms, in order to reach a good compromise between efficiency and complexity. robustness and stability of the model parameter identification procedure have been numerically validated for different nonlinearity orders and number of memory branches. the choice of polynomial cross terms has led to a good dpd performance, in the presence of strong linear and nonlinear crosstalk. the proposed mimo dpd offers very competitive performance, compared to other recent publications, with no additional computational or hardware complexity. references [1] j. gozalvez, “samsung electronics sets 5g speed record at 7.5 gb/s [mobile radio]”, ieee vehicular technology magazine, vol. 10, no. 1, pp. 12-16, 2015 [2] p. pirinen, “a brief overview of 5g research activities”, 1st international conference on 5g for ubiquitous connectivity, akaslompolo, finland, november 26-28, 2014 [3] e. g. larsson, o. edfors, f. tufvesson, t. l. marzetta, 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“behavioral modeling of concurrent dual-band transmitters based on radially-pruned volterra model”, ieee communications letters, vol. 19, no. 5, pp. 751-754, 2015 [14] e. zenteno, d. ronnow, “mimo subband volterra digital predistortion for concurrent aggregated carrier communications”, ieee transactions on microwave theory and techniques, vol. 65, no. 3, pp. 967-979, 2017 [15] n. naraharisetti, p. roblin, c. quindroit, s. gheitanchi, “efficient leastsquares 2-d-cubic spline for concurrent dual-band systems”, ieee transactions on microwave theory and techniques, vol. 63, no. 7, pp. 2199-2210, 2015 [16] y. liu, j. j. yan, p. m. asbeck, “concurrent dual-band digital predistortion with a single feedback loop”, ieee transactions on microwave theory and techniques, vol. 63, no. 5, pp. 1556–1568, 2015 [17] s. a. bassam, a. kwan, w. chen, m. helaoui, f. m. ghannouchi, “subsampling feedback loop applicable to concurrent dual-band linearization architecture”, ieee transactions on microwave 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window size in classification of epileptic short-term eeg signals using a brain computer interface software katerina d. tzimourta medical physics laboratory, university of ioannina ioannina, greece ktzimourta@cc.uoi.gr loukas g. astrakas medical physics laboratory, university of ioannina ioannina, greece astrakas@uoi.gr anna maria gianni computer engineering dpt, technological educational institute of epirus, kostakioi, arta, greece anna.maria.gianni@gmail.com alexandros t. tzallas computer engineering dpt, technological educational institute of epirus, kostakioi, arta, greece tzallas@teiep.gr nikolaos giannakeas computer engineering dpt, technological educational institute of epirus, kostakioi, arta, greece giannakeas@teiep.gr ioannis paliokas information technologies institute, centre for research and technology hellas thessaloniki, greece ipaliokas@iti.gr dimitrios g. tsalikakis informatics and telecommunications eng. dpt, university of western macedonia, kozani, greece dtsalikakis@uowm.gr markos g. tsipouras informatics and telecommunications eng. dpt, university of western macedonia, kozani, greece mtsipouras@uowm.gr abstract— the complexity of epilepsy created a fertile ground for further research in automated methods, attempting to help the epileptologists’ task. over the past years, great breakthroughs have emerged in computer-aided analysis. furthermore, the advent of brain computer interface (bci) systems has facilitated significantly the automated seizure analysis. in this study, an evaluation of the window size in automated seizure detection is proposed. the eeg signals from the university of bonn was employed and segmented into 24 epochs of different window lengths with 50% overlap each time. statistical and spectral features were extracted in the openvibe scenario and were used to train four different classifiers. results in terms of accuracy were above 80% for the decision tree classifier. also, results indicated that different window sizes provide small variations in classification accuracy. keywords-epilepsy; eeg; seizure detection; window size; brain computer interface i. introduction epilepsy is a devastating brain disorder followed by seizures, which are repetitive episodes of temporary interruption or disturbance of communication between neurons. many people experience seizures without a clear cause and almost one-third of the epileptic patients suffer from refractory seizures [1]. the latest facts render epilepsy a life-threatening disorder and a major factor responsible for mortality in developed and developing countries [2]. depending on the brain areas that participate during epileptic activity, seizures are divided into two fundamental types: partial (affects only a single brain area) and generalized (affects more than one region). these two main types are subdivided forming a bigger list of several seizure types [3]. the electroencephalogram (eeg) is used to monitor and diagnose epilepsy. the brain activity is monitored through the eeg which is usually performed in a well-equipped hospital. the electrodes are either attached to the surface of the skull (scalp eeg – seeg) or placed invasively inside the brain (intracranial eeg – ieeg). furthermore, the eeg recording is usually performed after a seizure episode and before the next seizure occurrence (interictal period). rarely an eeg recording captures the seizure onset (ictal period) and it usually happens in a 24-hour monitoring. the complexity of eeg recordings and the huge amount of data, led to the development of methods for detecting different patterns of brain activity [4] and automated seizure analysis [5]. generally, these methods follow a pattern recognition approach, which contains feature extraction and classification. the signal is usually decomposed in epochs of specific duration in an attempt to better capture the transient occurrences of the eeg. several time-frequency analysis methods have been proposed such as discrete wavelet transform [6-8], wigner-ville distribution [9], empirical mode decomposition [10-11] etc. significant features are extracted from the decomposed signal and are then used to train a classifier. usually, the raw signal is initially analyzed in epochs of small duration and the window size is of primary importance in automated seizure detection. recent breakthroughs in computer-aided analysis initiated the development of brain computer interface (bci) systems, which are more user-friendly and provide direct communication with the user’s brain in real-time without any possible movement [12]. in this work, a method for seizure det ana ava dif ov cal cas tra sig tes op com mi win un dec fea fea fig an tra dep a. ord of ee vo gro con dur engineerin www.etasr tection and t alysis is pres ailable databa fferent lengths erlap. signifi lculated and e ses were creat ained and teste in this work gnal processing sting various en-source so mmunication inimum of pro ndow size in niversity of composed in atures were e atures were u gure 1 a flowc example of aining parame picted in figur fig. 1. a the databas the databas der to investig eeg segment eg recording lunteers and ouped in five ntaining of 10 ration marked ng, technology r.com t the investigat sented. the e ase was used s, ranging fro ficant statistic employed to t ted in the open d the four clas ii. materi k, the openvi g and the we classifiers. t oftware desig with the brain ogramming ski n eeg signa bonn was u various epoch extracted in t used to train chart of the pro f the openvi eters which u re 2. a flowchart of the se e university gate the windo ts that were se gs, which w 5 epileptic p subsets, deno 00 single-chann d as z, o, n y & applied sci tzimourta et al. tion of wind eeg recordin and decomp om 1 to 24 cal and spec train four clas n-source softw ssifiers. ials and met ibe bci soft eka environm the openvibe gned to be n, by a broad ills. to investi l analysis, th used. the e hs of differen the openvib four remark oposed method ibe scenario used to train proposed three-s of bonn [14] ow length. th elected and cu were acquired patients. the oted as a, b, nel eeg segm n, f and s, ience research : evaluation of dow size in ngs from a p posed in epoc seconds with tral features ssifiers. in tot ware openvib thod tware was use ment for trainin e [13] is an used for range of users igate the role he database o eeg signals nt sizes and s be scenario. kable classifie d is presented. that contain n the classifie step methodology ] was employ he database co ut out of conti d from 5 h eeg segmen , c, d and e ments of 23.6-s , respectively h v f window size i signal public chs of h 50% were tal, 24 e that ed for ng and easy, direct s with of the of the were everal these ers. in also, ns the ers is yed in onsists inuous ealthy nts are e each second y. the sam wer pre emp set cha as g pro sub lab z o n f s b. dec sec epo epo eac seg 13 vol. 8, no. 4, 20 in classificatio mpling frequen re visually re sented in tab ployed to crea is a class (z allenging and m good classifica oblem. fig. 2. part o table bset bel type of eeg recording z seeg o seeg n ieeg f ieeg s ieeg time epochin in the ope composed in e ond with 0.5 oching” was u ochs from 1 to ch time. in to gments ranging seconds overla 018, 3093-3097 on of epileptic s ncy of the dat emoved. more ble i. in this st ate the proble z-o-n-f-s). t many studies ation results as of the openvibe i. summar g subjects healthy healthy epileptic epileptic epileptic ng envibe desi epochs of cons 5 seconds ove used to confi o 24 seconds w otal, 24 xml g from 1 secon ap. short-term ee ta is 173.61hz e details abou tudy, all the 5 em of five cla this particular [15-17] have a s the ones obta scenario for the “ ry of the bonn d subjec relaxed in an aw op relaxed in an aw cl seizure-free fr hemisphere of z seizure-free from z seizure act epilepto igner the ee secutive secon erlap. the plu figure the dur with 50% seco l files were nd up until 24 3094 eg signals usin z and any art ut the databas 500 segments asses, wherein r problem is attempted to o ained from a b “f” eeg segment database ct’s state wake state with ey pened wake state with ey losed from the opposite the epileptogenic zone m the epileptogen zone tivity from the ogenic zone eg signals nds, starting fr ugin “time b ration of the onds epoch ov created with seconds with ng … tifacts e are were each more obtain binary ts. es es c nic were rom 1 based eeg verlap eeg 0.5 engineering, technology & applied science research vol. 8, no. 4, 2018, 3093-3097 3095 www.etasr.com tzimourta et al.: evaluation of window size in classification of epileptic short-term eeg signals using … c. feature extraction a set of 8 features was extracted in each epoch, forming the feature vector that used in the classification. the plugins “univariate statistics” and “spectral analysis” were employed in the openvibe scenario to compute four time-based features namely:  mean value,  variance,  range (maximum value – minimum value),  median value, and four spectral features based on fast fourier transform being:  the spectrum amplitude (the power of the signal) in alpha band (8-12hz),  the spectrum amplitude in beta band (12-25hz),  the spectrum amplitude in theta band (4-8hz),  the spectrum amplitude in delta band (1-4hz), the resulting feature set was used to train four well-known classifiers, being naïve bayes, multilayer perceptron, support vector machines and decision tree. d. classification to evaluate the proposed method and the window size in classification results, four of the most sophisticated supervised classifiers were used. 1) naïve bayes (nb) naïve bayes (nb) is a simple classifier that combines a probability model with a decision rule. the classifier operates on the simplest assumption that the features are conditionally independent and is based on bayes decision theory, wherein the posterior probability of each class is calculated by the likelihood and the prior probability [15]. the ultimate goal of the classifier is to minimize the probability of classification error and maximize the posterior probability. a small number of training data is needed for the classifier to estimate the necessary classification parameters and in conjunction with the less time complexity, this simple classifier has preferred in complex classification problems. 2) multilayer perceptron (mlp) the multilayer perceptron (mlp) classifier is a neural network with at least three layers of nodes. mlp utilizes the backpropagation techniques for training and maps non-linear input data into a space, where it becomes linearly separable. in order to train a mlp classifier and perform correct pattern classification, the connection weights after each processing of data are adjusted, based on the comparison between the error in the output and the expected result [15]. 3) support vector machines (svm) support vector machines is a machine learning technique for linear and non-linear classification problems. the nonlinear input data is projected into a high-dimension feature space in order to be linearly separated. this projection is performed by the kernel function, which can be either a linear or a polynomial function, the radial basis function or the sigmoid kernels. the gap that separates the data is called hyperplane and the major goal of the algorithm is to find the optimal separating hyperplane that maximizes the distance between the data and minimizes the classification error [15]. in our experiments, the radial basis function was used. 4) decision tree (dt) a decision tree (dt) classifier is a straightforward classifier based on a series of decision rules. the root node of the tree is displayed at the top and is successively connected with other nodes through links or branches, until no further links to other nodes exist (leaf nodes). according to the dt classifier, only one link can be followed each time and the subsequent node becomes the root node of the next sub-tree. the procedure is repeated until a leaf node is reached, leading to no further decision and the category label is read [15]. iii. results and discussion the four classifiers were trained and tested according to the 10-fold cross-validation technique. to evaluate the classification results of the experiments and thus, the window size the accuracy was calculated from the correctly classified instances: = (1) the obtained statistical results of the 24 experiments for each classifier are presented in table ii. table ii. results epoch (sec) overlapping (sec) correctly classified instances (%) nb mlp svm dt 1 0.5 59.11% 72.41% 67.51% 85.95% 2 1.0 63.67% 75.56% 70.35% 79.06% 3 1.5 66.37% 78.02% 70.46% 82.05% 4 2.0 67.47% 78.73% 70.11% 83.50% 5 2.5 68.97% 79.47% 68.87% 83.60% 6 3.0 70.32% 81.72% 70.00% 84.87% 7 3.5 70.23% 81.10% 69.21% 85.45% 8 4.0 70.03% 80.17% 68.55% 85.17% 9 4.5 71.90% 80.91% 68.45% 85.19% 10 5.0 72.11% 77.75% 63.63% 83.83% 11 5.5 72.08% 83.15% 68.10% 85.48% 12 6.0 73.33% 81.95% 68.46% 85.39% 13 6.5 73.52% 81.03% 67.44% 83.72% 14 7.0 74.01% 81.23% 67.83% 84.25% 15 7.5 75.29% 81.98% 68.34% 82.71% 16 8.0 75.61% 83.35% 66.57% 84.51% 17 8.5 74.58% 83.53% 68.19% 83.75% 18 9.0 75.85% 82.39% 67.72% 82.31% 19 9.5 75.37% 82.18% 68.31% 82.60% 20 10.0 75.57% 83.00% 67.87% 81.23% 21 10.5 81.23% 82.79% 67.62% 84.46% 22 11.0 76.48% 82.04% 68.87% 82.82% 23 11.5 77.34% 82.24% 68.16% 83.77% 24 12.0 77.55% 81.70% 68.82% 85.63% engineering, technology & applied science research vol. 8, no. 4, 2018, 3093-3097 3096 www.etasr.com tzimourta et al.: evaluation of window size in classification of epileptic short-term eeg signals using … the best classifier for epochs of 1 second with 0.5 seconds overlap, is dt with 85.95% followed by mlp with 72.41%, svm with 67.51% and nb with 59.11%. for epochs lasting 2 seconds with 1 second overlap, the best classifier is dt with 79.06%, followed by mlp (75.56%) and svm (70.35%) and the worst classifier is nb with 63.67% accuracy. for windows of 3 seconds with 1.5 seconds overlap and 4 seconds with 2 seconds overlap, dt remains the best classifier (82.05% and 83.50% respectively) and the lowest accuracy (66.37% and 67.47% respectively) is obtained with nb as well. for the next 12 window sizes the dt outperforms (ranging from 82.71% to 85.48%) and the lowest values (ranging from 63.63% to 70%) are obtained with svm. at the same time, mlp indicates accuracy ranging from 77.75% to 83.35%, whereas nb shows lower accuracy, ranging from 68.97% to 75.61%, and in some cases perform almost the same with svm (for windows of 5sec and 6sec duration). for the next 4 window sizes the dt and the mlp presents almost the same accuracy and none of the two classifiers is considerably better than the other. accuracy for nb is about 75% for these four window sizes and svm does not exceed 68%. finally, for the last four window sizes, dt is the best classifier (ranging from 81.23% to 85.63%) followed by mlp (ranging from 82.04% to 83%), nb (ranging from 75.57% to 81.23%) and svm (ranging from 67.62% to 68.87%). the smooth and small changes of the obtained results for each classifier and the comparison between their performances are depicted in figure 3. from figure 3 it can be observed that while the window size is increasing, the classification results for nb, mlp and dt are slightly higher, without great variations (in most cases not greater that 3%). the lowest accuracy for nb and mlp is 59.11% and 72.41% and the highest 81.23% and 83.53%, respectively; however, despite the big difference between the lowest and highest values, the intermediate values range from 1% to 3%. the best classification accuracy is provided with dt with lowest value 79.06% (2 seconds window with 1 second overlap) and highest 85.63% (24 seconds with 12 seconds overlap) whereas svm showed the worst classification accuracy (lowest value 63.63% and highest 70.46%). also, the best accuracy for dt, mlp and nb (above 80%) is obtained for windows of 21 seconds with 10.5 seconds overlap, whereas the svm seemed to be the weakest classifier compared to the others. the epoch duration has also been a focus point for several researchers. recently [16], a method based on dynamic principal component analysis (dpca) and energy was proposed. the authors evaluated four window sizes of the eeg segments, being 64, 128, 256 and 512 samples per window (approximately 0.37, 0.74, 1.47 and 2.95 seconds respectively). results showed minor increase when signals were segmented in 512 samples epochs per window. in [17], authors conducted 4 experiments to find the optimal window size between 4 options. in the presented method the permutation entropy was calculated from nonoverlapping epochs of 0.25, 0.5, 0.75 and 1 second and was used to train a svm classifier. results in terms of f1 score showed small deviation (about 5% for overall f1 score). an extension of the above mentioned approach was presented in [18] wherein the same group of authors investigated among other, whether the overlapping plays significant role in seizure detection or not and they proposed a method based on weighted permutation entropy (wpe). in this approach, 200 signals of the bonn database were employed and segmented in epochs of approximately 0.35 seconds duration with overlap (ov) (128 samples per window) and without overlap (nov) (164 samples per window). the method was evaluated on svm and artificial neural network (ann) classifier and results indicated that epochs with 50% overlap provided slightly higher accuracy (2.25% overall accuracy for svm and ann). in our experiments, 24 window sizes are evaluated and the classification accuracy slightly arises as the window size increases for all classifiers. the best classifier is dt with accuracy ranging from 79.06% to 85.95%, followed by mlp ranging from 72.41% to 83.53%, svm from 67.51% to 70.46% and nb from 59.11% to 75.61%. a comparison table is presented in table iii. table iii. comparison table reference window size signal analysis features classifier classification problem performance metrics [16] 4 non-overlapping window sizes ranging from 0.37-2.95 sec dynamic principal component analysis energy 1-nn z-s zonf-s accuracy: 99.9%-100% [17] 4 non-overlapping window sizes ranging from 0.25-1 sec raw segmented data weighted permutation entropy svm z-s o-s n-s f-s average f1 values for each window size: 0.866 0.917 [18] 0.35 sec nonoverlapping window raw segmented data weighted permutation entropy svm z-o-n-f-s nov accuracy: 90.63 92.88% 0.35 sec with 50% overlap window ov accuracy: 91.63 93.88% this work 24 overlapping windows with 50% overlap ranging from 124sec raw segmented data mean, range, variance, median, spectral amplitude in alpha, beta, delta, theta band naïve bayes, mlp, svm, dt z-o-n-f-s nb accuracy: 59.11% 81.23% mlp accuracy: 72.41% 83.53% svm accuracy: 63.63% 70.46% dt accuracy: 79.06% 85.63% fig ml stu mo me ext dec cha exp do co com sig fu sec win wa abo win wh [1] [2] [3] [4] [5] [6] [7] engineerin www.etasr g. 3. results i lp, yellow: nb, p epilepsy is udies have foc ost of the stu ethodology, w traction and composition anges of the periments indi not have a sig onsequently, a mputational t gnificant par urthermore, the conds with 10 ndow length f as 23.6 second ove 24 secon ndow size ca hich are closer world health o o. devinsky, preventing ep vol. 86, no. 8, i. e. scheffer, guilhoto, e. h perucca, t. classification o for classificati 521, 2017 s. segkouli, i “study of eeg cognitive dec computing par a. t. tzallas, astrakas, s. k detection meth i. guler, e. d signals classifi biomedicine, v y. kumar, m. dwt based fu neurocomputin ng, technology r.com t in terms of accur purple: svm) iv. co constantly un cused on seiz udies, the auth which contain classification is very imp e eeg recor icated that sm gnificant impa a smaller nu time of the c rameter in e best window 0.5 seconds ov for seizure pre ds, 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dependen iew e, vol. 64, n dis, “epileptic s is”, ieee transa 13, no. 5, pp. 70 sed on teager e ks”, qscience co rma, “a novel g detection”, com pp. 2-18, 2016 assification, john mponent analysis ations to epileptic olume 2014, arti ic seizure detect on entropy and s nference (cibec rid automated det mputers & ele soltesz, p. benqu diction and interve urophysiology: o aphic society, v ng … , a. t. pileptic ium on seizure neural , pp. 1y using medical genetic mputer pilepsy ess and noy, o. atform virtual nments, , c. e. nsional nce on no. 6, seizure actions 03-710, energy onnect, genetic mputer wiley s with c eeg icle id tion in upport c), pp. tection ectrical uet, p. ention: official vol. 32, engineering, technology & applied science research vol. 8, no. 3, 2018, 2914-2918 2914 www.etasr.com asma and amiri: using association rules to enrich arabic ontology using association rules to enrich arabic ontology asma ksiksi technologies of information laboratory (lr-siti) national engineering school of tunis (enit) tunis, tunisia asma.ksiksi@gmail.com hamid amiri technologies of information laboratory (lr-siti) national engineering school of tunis (enit) tunis, tunisia hamidlamiri@gmail.com abstract—in this article, we propose the use of a minimal generic base of associative rules between term association rules, to automatically enrich an existing domain ontology. initially, nonredundant association rules between terms are extracted from an arabic corpus. then, the matching of the candidate terms is done through the matching between the concepts of the initial ontology and the premises of the association rules, with three distance measures that we define. keywords-ontology; automatic enrichment; association rules i. introduction ontology is a tool for representing knowledge and reasoning that serves the organization of a set of concepts in a specific field, as well as the relations between these concepts [1-3]. ontologies are regularly subject to updates and changes. performing these updates manually is an expensive and timeconsuming task as it mobilizes experts in the field to identify and classify new vocabulary items in the ontology. to accelerate this process of evolution and adaptation and to take away any form of subjectivity, recent research has focused on the implementation of semi-automatic and automatic ontology enrichment techniques. the majority of approaches, often based on statistical or linguistic tools, focus on adding new concepts and/or relationships between them. the ontology enrichment process can be divided into two stages: the search for new concepts and relations and the placement of these concepts and relationships within the ontology [3]. the general process is depicted in figure 1. several works have focused on this process of enrichment of ontologies, addressing one or more of its stages: • extraction of representative terms in a specialized field. • identification of lexical relations between terms. • placement of new terms in an existing ontology in these works, the term ontology takes several meanings like thesaurus, taxonomy or more generally controlled vocabulary. the work dealing with the extraction of candidate terms in the ontology enrichment process is based on statistical and syntactic methods. statistical methods select terms according to their distribution in the corpus [1-3], as well as other measures such as mutual information, “the probability of the appearance of the word a knowing that the word b has appeared”, or else measures calculating the probability of occurrences of a set of terms [4-6]. these different propositions make it possible to identify new ontology elements, but do not allow their placing in the ontology, without human intervention. syntactic methods aim at determining the grammatical function of a word or a group of words within a sentence. they are based on the hypothesis that grammatical dependencies reflect semantic dependencies. these techniques lead to the proposition of new concepts, linked by relations that are not yet semantically identified. regarding the identification of concepts and relationships and their placement in the ontology, the extraction of ars is one of the major techniques proposed by the data mining community. many other works propose the use of frequent correlations which can exist between the terms of a corpus. these approaches consist most often of extracting ars between candidate terms, previously identified by statistical or syntactic tools [7]. at the end of the process, authors get a set of ars, describing the existence of a relationship between two concepts [8-10]. fig. 1. general process of ontology enrichment. in this paper, we propose a methodology for building a conceptual network formed by the combination of two types of knowledge, namely, knowledge present in the initial ontological structure specific to a domain and represented by semantic links, and knowledge derived from the minimal generic base of associative rules (ars) between terms, essentially representing correlations that are appreciated by statistical measures. ii. existing techniques for ontology enrichment a. existing approaches to discover candidate concepts we distinguish two types of methods for the discovery of candidate concepts: engineering, technology & applied science research vol. 8, no. 3, 2018, 2914-2918 2915 www.etasr.com asma and amiri: using association rules to enrich arabic ontology • statistical methods: they select the terms according to their distribution in the corpus [1-3], as well as other more complex measures such as mutual information, tf-idf, etc., or the use of statistical distributions of terms [4]. these different propositions make possible to identify new ontology elements, but do not make possible placing them in the ontology, without tedious human intervention [12]. • syntactic methods: they aim to determine the grammatical function of a word or group of words within a sentence. they are based on the hypothesis that grammatical dependencies reflect semantic dependencies [13]. they define in a sentence, the verb (v) as being the relation which links the subject (s) to the complement (c). they thus have the disadvantage of identifying only the relationships labeled by the verbs. some approaches also use syntactic patterns [12]. the extracted terms illustrate the new candidate concepts for enrichment, but also the existence of relations between them. however, these relationships are not labeled semantically. moreover, no measure evaluating semantically new added relations is calculated. b. existing approaches to the concept placement in ontology after the discovery of the candidate terms, it is essential to detect the relations between these new terms and those which link them to the initial ontology. in [2], authors propose a statistical approach based on the frequent co-occurrence of candidate terms with terms of the initial ontology. the major drawback of this work lies in the fact that they do not allow the precise addition of new concepts and relations in the ontological structure [14]. other approaches in the literature suggest using search techniques data [10, 11, 13]. the work in [4, 15], is based on a classification method in order to bring together the candidate terms contained in the texts of the concepts present in the ontology. the principle is similar to that explained in the approaches of [1, 15], which group together terms by a clustering method according to their number of occurrences within the corpus. however, these methods do not detect the relations between the candidate terms, i.e., these new terms can therefore be added only by human intervention. in addition, several studies propose the use of frequent correlations that exist between the terms of a corpus. these approaches consist of extracting rules association [7] between candidate terms [8-10]. at the end of the search process, a set of ars between terms is generated. each rule expresses the existence of a relationship between two concepts of the domain. this process of enrichment remains semiautomatic because on the one hand the number of derived ars is very important and on the other hand, a human intervention is necessary to semantically define the relations discovered and to name them. iii. association rules association rule mining is a famous knowledge discovery technique for finding associations between items from a transaction database. its definition varies according to the three main currents initiated by the following: author in [16] defines rules of statistical implication to help educationalists find relationships between acquiring basic notions in class, authors in [17] are more interested in orderly representation of concepts with informative implications, authors in [18] favored optimized extraction of ars in large databases. subsequently, these forms have known extensions in several directions. the binary properties are no longer required, we can now make ars with digital properties [19, 20]. to avoid the vast increase of rule extraction time, more efficient algorithms have been proposed [21]. the semantics of the rules have been refined through many quality indices [22], which helps the user to choose the most appropriate rules for his needs. navigation and queries by using an appropriate language have been developed [23] to facilitate the exploration of this set of rules. ars present conditional relationships between the attributes of a database. they represent an implication of the form a→b where a and b are an itemsets. the set of items a is called antecedent and b consequent of the rule which provides information about the existing relations between a and b. it expresses how objects or items are related to each other, and how they can be grouped together. the first step of extraction in the association rules mining is finding out the frequent itemset which is called candidate (te). this transaction can be measured by two statistic measurements called support and confidence. the support (sup(a→b)) is defined as the relative frequency of transactions in the data set d that contains the itemsets a and b. d t}bet t a:d{t b) sup(a = b)sup(a ⊆⊆∈ =∪→ (1) the confidence (conf(a→b)) of a rule measures the reliability of the inference given by rules. sup(a) b)sup(a =b)conf(a ∪ → (2) then, the important association rules are filtered from the candidate itemsets. a rule r is available only if sup(a→b)>minsup and conf(a→b)> minconf where minsup represents the threshold of support and minconf represents the threshold of confidence. these two values are specified by the user. a. process for association rules extraction the process of extracting association rules consists of several phases ranging from data selection and preparation to result interpretation (figure 2). several works have focused on this process of enrichment of ontologies, addressing one or more of its stages: • data selection and preparation (cleaning): in this phase, the database data used for the extraction of the association rules are selected and the transformation of these data into an extraction context occurs. this phase is necessary to be able to apply rule extraction algorithms to different kinds of data from different sources, to concentrate the search on the useful data and to minimize extraction time [24]. to have significant rules the extraction of morphological analysis of engineering, technology & applied science research vol. 8, no. 3, 2018, 2914-2918 2916 www.etasr.com asma and amiri: using association rules to enrich arabic ontology each word must follow the order described in [25] and shown in table i • generation of association rules: is carried out from the frequent itemsets generated previously. in general, the generation of association rules is done directly, without access to the extraction context, and the cost of this phase in execution time is therefore low compared to the cost of extracting frequent itemsets. • visualization and interpretation: this phase consists in the visualization of the association rules extracted from the context and their interpretation. thus the domain expert can judge their relevance and usefulness. table i. representative schema of an arabic word structure enclitic suffix schematic body prefix proclitic base post radical near_base fig. 2. process of association rules. iv. proposed approach this stage consists in bringing closer to our initial ontology, that will be noted as o, the terms which appear in the premises of the candidates rules of the base of the sequential rules. these terms are identified as candidate concepts for enrichment. • definition 1: an ontology is a quadruplet o=(cd, ≤c, r, ≤r) where cd is the set of concepts of the domain, ≤c is the partial order defined on cd, r is the set of relations defined on cd×cd and ≤r is the partial order relation defined on r. we consider that a formal extraction context is a triplet k=(d, t, r) where d represents a finite set of documents from the corpus c, t is a finite set of terms and r a binary relation. each pair (d,t)∈r means that the document d∈d contains the term t∈t. • definition 2: a termset is a non-empty set of terms denoted by (t1, t2 ... tk). an associative rule r is valued by two statistical metrics, namely support and trust [18]. the support of the associative rule r: ti→tj, denoted by supp (r), expresses the frequency with which the two termsets ti and tj co-occur together in corpus c. the confidence of r, denoted by conf(r), expresses the conditional probability for a document to contain termset tj, knowing that it contains the termset ti. an associative rule is valid if its confidence is greater than or equal to the minimum confidence threshold noted by minconf. fig. 3. process of enrichment of ontology by using association rules. a. extraction of the ontology and creation of the generic base we use the gen-mgb algorithm [26] for the extraction of the generic base of ra no redundant mgb. this base is characterized by its significant compactness, i.e., it contains a minimal core of ars, from which all the redundant and valid rules can be deduced by means of a complete and valid axiomatic system [26, 27]. by considering the context of text extraction k, we adapt the definition of the mgb base given in [26] to the problem of ontology enrichment. we remind that non-redundant ars have one only term of the domain in the premise [28]. k k 1 k m g b = { r : t t | c o n f(r ) m in c o n f t = { t ,..., t } t } m g b = → ≥ ∧ ⊆ (3) we use then a semi-automatic tool such as protege 2000 [29] for the ontology o construction from co corpus. it is validated downstream by a domain expert. the evaluation of the semantic link between o concepts are computed from the proposed similarity measure in [30] that takes into account both the depth of concepts in the hierarchy of concepts and the structure of the latter. thus, the similarity between two concepts c1 and c2 of the ontology o is calculated as [30]: 1 2 1 2 (2 × depth(c)) simwu(c ,c )= (depth(c )+ depth(c ) ) (4) where depth (ci) corresponds to the depth level of the concept ci and c represents the most specific concept that generalizes c1 and c2 in o. b. adopted approach for the ontology enrichment the enrichment process we propose is iterative and includes the following steps: 1) calculation of the candidate concepts for the enrichment we compute for each concept ci of ontology o the set of the candidate concepts to be connected to ci. this set includes the terms figuring in the conclusions of the valid associative rules whose premise is ci as well as those of the redundant rules [31]. engineering, technology & applied science research vol. 8, no. 3, 2018, 2914-2918 2917 www.etasr.com asma and amiri: using association rules to enrich arabic ontology according to the example shown in figure 4, the candidate concepts for enrichment related to the concept c1 are {c10, c12, c5, c15}. fig. 4. example of calculating candidate concepts. 2) placement of the new concepts this step consists in placing the candidate concepts while preserving the coherence of the concepts and pre-established relations in the initial ontology. this makes possible not to add relational redundancies in the case of a concept being candidate to be related to several concepts of ontology o [32]. figure 5 shows the addition of the new concepts c10 and c11 and the displacement of c15 because conf(c1⇒c15)>conf(c7⇒c15). 3) calculating the neighborhood of ci and distance measurements we define the notion of neighborhood of a concept of the ontology o as: • definition 3: the neighborhood of a concept represents the set of corners connected to it in the ontology, by one or more valid association rules [32]. the relations between ci and its neighbors, are evaluated on the basis of a statistical metric that we call measure of distance between ci and its neighborhood, and denoted by disto mgb. it is computed according to the measure of confidence of associative intervening during the ontology enrichment and the measures of similarities calculated between the concepts of the initial ontological structure [33]. fig. 5. example of placement of candidate concepts. the measure of distance that we define is calculated according to three possible cases [34]: • case 1: if the two concepts ci and cj come from the base c then disto c(ci, cj)=conf(r: ci⇒cj). • case 2: if the two concepts ci and cj belong initially to ontology o then disto c(ci, cj)=simwu(ci, cj). the similarity between the two concepts c1 and c2 of ontology o is calculated as in (3). • case 3: if ci is a concept added to the ontology o and it is related to the concept ck of the initial ontology o in a way that disto mgb(ck, ci)=conf(r:ck⇒ci)=β then any concept cx of the ontology o in relation to ck such that simwu(ck, cx)=α, is also in relation with ci. in this case, the distance measure is mixed, i.e., disto mgb (ci, cx)=α×β. the three cases are illustrated in figure 3. thanks to this enrichment technique we are able to add new concepts and relationships. fig. 6. example of a figure caption. v. conclusion various ontology enrichment techniques have been proposed in the literature. their limitations come from the fact that they do not allow the entire enrichment process without the intervention of the domain expert. in this article, we presented an automatic ontology enrichment process with a generic base of associative rules. the originality of our approach is that it exploits the maximum of concepts for enrichment without resorting to a priori knowledge. its advantage is that it allows the learning of the distance represented by any relation of the enriched ontology. references [1] e. agirre, o. ansa, e. hovy , d. martinez, “enriching very large ontologies using the www”, ecai 2000 workshop on ontology learning, berlin, germany, august 2000 [2] a. faatz, r. steinmetz , “ontology enrichment 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601-602, morgan kaufmann, 1991 [32] d. j. abadi, a. marcus, s. r. madden, k. hollenbach, “scalable semantic web datamanagement using vertical partitioning”, 33rd international conference on very large data bases, vienna, austria, pp. 411-422, september 23-27, 2007 [33] p. gamallo, m. gonzalez, a. agustini, g. lopes, v. s. de lima, “mapping syntactic dependencies onto semantic relations”, proceedings of the ecai 2002 workshop on machine learning and natural language processing for ontology engineering (olt’2002), lyon, france, pp. 15-22, 2002 [34] f. cerbah, ”learning highly structured semantic repositories from relational databases”, lecture notes in computer science, vol. 5021, pp. 777-781, springer-verlag, 2008 microsoft word 11-3166_s_etasr_v9_n6_pp4925-4932 engineering, technology & applied science research vol. 9, no. 6, 2019, 4925-4932 4925 www.etasr.com duong & nguyen: network reconfiguration for an electric distribution system with distributed … network reconfiguration for an electric distribution system with distributed generators based on symbiotic organisms search thanh long duong faculty of electrical engineering technology industrial university of ho chi minh city ho chi minh city, vietnam duongthanhlong@iuh.edu.vn thuan thanh nguyen faculty of electrical engineering technology industrial university of ho chi minh city ho chi minh city, viet nam nguyenthanhthuan@iuh.edu.vn abstract—this paper proposes a method of network reconfiguration based on symbiotic organisms search (sos) algorithm for reducing power loss of the electric distribution system. the sos is a recent developed meta-heuristic algorithm inspired from the symbiotic interaction strategies of organisms for surviving and propagating in the ecosystem. compared to other algorithms, sos does not need any control parameters during the searching process. the advantages of the proposed sos method have been validated in two electric distribution systems. three network cases have been considered for each system, consisting of performing network reconfiguration on the system without distributed generator (dg) placement, the system installed type-p dgs and the system installed type-pq dgs. the comparison results with particle swarm optimization and other previous methods show that the proposed sos can be a promising technique for the problem of electric network reconfiguration. keywords-symbiotic organisms search; electric distribution system; network reconfiguration; active power loss i. introduction power loss in electric distribution systems (edss) takes a high portion in the total power loss of the electricity system. there are lots of techniques for reducing power loss such as distributed generation placement [1], capacitor placement [2-4], and network reconfiguration. among these methods, network reconfiguration is the most efficient. it is implemented by transferring a part of the load from some branches to others through changing the status of switches located on each branch. the result of network reconfiguration method is a radial topology of eds that satisfy constraints such as the limits of node voltage and branch current. from its introduction [5], the problem of network reconfiguration has been solved by many methods. they can be divided into two main groups: heuristic and metaheuristic. the first main group includes methods based on knowledge of operating the edn and technical strategies. typical methods in this group are grouped in branch and bound methods and branch exchange methods. the idea of branch and bound method is that the edn is modeled by a purely resistive network. initially all switches are closed. gradually the switches on the branches with the smallest currents are opened step by step until the radial topology of the edn is reached [6]. in the branch exchange method, initially all switches are closed and then an open switch is replaced by a closed switch for reducing power loss [7]. the advantages of this method group are that they are easy to implement and the knowledge related to these methods is very close to the area of operating eds. however, the obtained results are usually local extremes. in addition, changing the objective function is difficult for solving the problem of network reconfiguration. the second group method includes methods based on metaheuristic algorithms. they are usually inspired from phenomena of nature or society. the main advantage of this method group is that they are very efficient for handling constraints and different objective functions. compared to the former group, the later has the ability to provide a sufficiently good solution to the problem of network reconfiguration. thus, more and more new metaheuristic algorithms have being applied to this problem such as genetic algorithm [8], particle swarm optimization (pso) algorithm [9-11], gravitational search algorithm (gsa) [12], fireworks algorithm (fwa) [13], runner root algorithm (rra) [14, 15], and cuckoo search algorithm (csa) [16, 17]. however, for solving the problem of network reconfiguration by this method group, the issue of adjusting the control parameters of the algorithms has to be faced, e.g. for applying the ga to the problem of network reconfiguration, the rates of selection and mutation have to be tuned, for applying the pso, two constants c1 and c2 in the equation of velocity of particles have to be selected etc. therefore, it is worth considering the application of recent developed metaheuristic algorithms which have less control parameters, for solving the network reconfiguration problem. symbiotic organisms search (sos) is inspired from the symbiotic interaction strategies of organisms for surviving and propagating in the ecosystem [18]. compared to other metaheuristic algorithms, the biggest advantages of sos are that it does not require specific algorithmic parameters for operations. in sos, from each organism in the ecosystem, four new organisms are generated based on mutualism, commensalism, and parasitism phases. two new organisms are used for updating the initial organism and the other two corresponding author: thuan thanh nguyen engineering, technology & applied science research vol. 9, no. 6, 2019, 4925-4932 4926 www.etasr.com duong & nguyen: network reconfiguration for an electric distribution system with distributed … organisms are used for updating the other organisms in the ecosystem. in [18], sos has been used to solve 26 benchmark functions and has outperformed other algorithms such as ga, pso, etc. recently, sos has been applied in many areas such as construction engineering, power or energy optimization engineering problems [19]. in the latter, sos has been successful applied in the problems of optimal placement and sizing of distributed generators (dgs) [20, 21], reduction of power loss of a transmission system [22], capacitor placement [23], economic emission dispatch problem [24], and optimal power flow [25]. for the problem of network reconfiguration, sos has been used in [26]. however, in this study, the solution vector of sos (called sos1) for the problem is expressed by the state of all the electric switches in the eds. the normally closed electric switches are shown by the one state and vice versa, the open electric switches are represented by the zero state. coding technique makes the solution vector become large and makes sos ineffective for finding optimal network configuration. in this paper, the proposed method based on sos is used to solve the problem of network reconfiguration to find the optimum eds configuration for power loss reduction. the solution vector of the problem is only presented by the open switches in integer form. the applied method was tested on the 33-bus and 69-bus systems and the obtained results were compared with the ones of other techniques. the main contributions of this paper can be summarized as: • sos is adapted to solve efficiently the network reconfiguration problem. • the performance of sos is effectively applied on different electric distribution systems, namely the eds without dgs and with different types of dgs. • sos can find the optimal radial topology of eds for all cases, with higher success rate than the other methods mentioned in the literature. ii. the problem of network reconfiguration the power loss of eds is determined by the sum of the power losses of each branch of the system. although having mesh structure, edss always operate in radial topology. so, there are branches that contain switches in the open state with no current flow. therefore, the total power loss of the eds is determined by: ∆� = � ���� �� �� � ��� ��� (1) where ��� is a number of branches of the eds, �� is the i-th branch’s resistance, pi and qi are respectively the active and reactive power flow on the i-th branch. �� is a coefficient which is equal to zero for an open branch and one for a close branch, and �� is the ending voltage of the i-th branch. equation (1) is subjected to the following constraints: • radial network constraint: the radial topology of eds must be maintained and no load nodes have not to be served. in this study, the empirical formula from [27] is used to check whether the candidate configuration is radial or not: det(�) = �−1 !� 1, �#$%#& 0, (!) �#$%#& (2) where det(a) is the determinant of matrix a. a is a (branch x node) matrix presenting a connection of eds. • node voltage constraint: the voltage magnitude at each node must lie in the permissible range [�*�+,�*,-] to keep power quality. in general, �*�+,�*,are usually set equal to [0.95, 1] pu: �*�+ ≤ �/ ≤ �*,0%)ℎ 2 = 1,2, . .��56 (3) where ��56 is the total number of nodes in eds. • branch current constraint: the current magnitude of each branch of eds must lie in their permissible range to avoid over load: 7� ≤ 7*,-,� 0%)ℎ % = 1,2, . .��� (4) iii. sos for network reconfiguration sos is based on the interactive behavior of organisms in nature. many species living in nature have a reliant relationship with other species, called symbiosis. commonly, there are three popular reliant relationships in nature, mutualism, commensalism, and parasitism [18-19]. the main procedures of sos for the problem of network reconfiguration problem are described below. a. initializating candidate solutions similarly to other metaheuristic algorithms based on population, sos also generates an initial population of organisms termed as the ecosystem. each organism represents a candidate solution of the optimization problem. the degree of adaptation of each organism in the ecosystem is reflected by its fitness value. the process of creating the initial population of organisms is implemented as: 8� = 89:;,< +�#($ ×?8@�a@,< −89:;,/b (5) where xi (i=1,2… n) is an organism in the ecosystem. 8@�a@,< and 89:;,< are the upper and lower limits of the control variable k (k=1, 2, …, d) of the organism, n and d are the population size and the dimension of the problem. the control variables of the network reconfiguration problem are the switches located in each branch of the eds. therefore, the control variables used in sos for the network reconfiguration problem are presented under integer form. in addition, the search space of each control variable is also determined by closing the corresponding initial open switch xinitial,k. by closing xinitial,k, a loop occurs in the eds called loopk. all the switches in this loop are candidate open switches for the control variable xi,k. it is clear that the size of loopk is the upper limit of the control variable xi,k and the lower limit of the control variable xi,k is one, which is the first position in loopk. in other words the control variables of the network reconfiguration problem are the position of switches in each loop created by closing one by one the initial open switches in the eds. therefore, in the initialization state, the ecosystem is generated as: 8� = roundg89:;,< +�#($×?8@�a@,< −89:;,/bh (6) engineering, technology & applied science research vol. 9, no. 6, 2019, 4925-4932 4927 www.etasr.com duong & nguyen: network reconfiguration for an electric distribution system with distributed … where round is a function that rounds each element of xi to the nearest integer. from the initial population of organisms, the radial topology of each organism is checked and if it is satisfied, the power flow is run to calculate its fitness function. then, based on the fitness value, the best organism xbest of the ecosystem is found. if the radial topology of organism xi is not satisfied, a very high value is assigned to its fitness function value. b. generating new solutions based on mutualism strategy in nature, mutualism helps in gaining benefits for both participating organisms in the ecosystem. an example of this strategy can be seen from the relationship between flowers and bees. from this metaphor, the organism xi in the population will interact with the organism xj which is selected randomly from the population to create two new solutions as in (7). participating in the mutualism strategy, both organisms gain benefits. the radial topology of the two new organisms is checked and if it is satisfied, the power flow is run to calculate their fitness function. then, if their fitness values are better than the one before interaction, the organisms xi and xj will be updated: i8�,+j; = roundk8� +rand(0,1)× (8�jmn −opjqn:� ×rs1)t8/,+j; = roundg8/ +rand(0,1)×(8�jmn −opjqn:� ×rs2)h (7) opjqn:� is determined by (8). bf1 and bf2 are the benefit factors representing for level of benefit of each organism determined by: opjqn:� = u �uvw (8) �rs1 = round (1 +rand�)rs2 = round (1 + randw) (9) c. generating new solutions with commensalism strategy in nature, many birds live on bigger herbivores. this is a typical example of commensalism. in this strategy, a species will benefit while the other derives neither benefit nor harm. the organism xi will benefit from the commensal interaction between organism xi and xj. to implement this strategy, organism xj is selected randomly from the ecosystem to interact with xj as presented in (10) for creating a new organism. then, organism xi will be updated only if the fitness of the new organism is better than that of xi before the interaction. 8�,+j; = roundg8� +rand(−1,1)×(8�jmn − 8/)h (10) d. generating new solutions with parasitism strategy contrary to commensalism strategy, in the parasitism one species will benefit while the other species as a host will be a victim and even may die. in sos, organism xi is considered as a parasite. it modifies randomly some control variables to create a new organism called 8 ,�,m�nj. therefore, 8 ,�,m�nj is first assigned by xi, and then some of the control variables of 8 ,�,m�nj are modified by (11). note that the number of control variables of 8 ,�,m�nj is also selected randomly. the organism xj which is considered a host is selected randomly. if the fitness function value of the new organism created from xi is better than that of the organism xj, it will replace the position of xj in the ecosystem. in other words, xj will be killed by xi. 8 ,�,m�nj,< = roundg89:;,< + �#($ × ?8@�a@,< −89:;,<bh (11) after performing mutualism, commensalism, and parasitism for the organism xi, the best organism is updated at the end. then, the next organism in the ecosystem is considered until the whole population interacts with the three strategies. the process of searching new solution is stopped if the maximum number of organism evaluations is reached. the flowchart of the proposed sos for the network reconfiguration problem is given in figure 1. begin set parameters: size of ecosystem (eco_size), maximum fitness evaluation (mfe) generate randomly population of organisms by (6) calculate fitness function value of each organism by checking radial topology, running power flow to calculate the power loss, voltage and current profile identify the best electric network configuration (xbest) set number of iterations (iter) and number of fitness evaluation (fe) equal to zero iter = iter + 1; i = 1 select randomly xj from the ecosystem (i ≠ j) generate two new organisms xi,new and xj,new by (7) calculate fitness function value of two new organisms by checking radial topology, running power flow to calculate the power loss, voltage and current profile increase the fe by two: fe = fe + 2 update xi and xj: if xi,new is better than xi then xi is updated by xi,new and if xj,new is better than xj then xj is updated by xj,new i = eco_size ? i = i + 1 fe ≥ mfe ? yes no no output: the best electric network configuration xbest finish yes select randomly xj from the ecosystem (i ≠ j) generate one new organism xi,new by (10) calculate fitness function value of xi,new by checking radial topology, running power flow to calculate the power loss, voltage and current profile increase the fe by one: fe = fe + 1 update xi: if xi,new is better than xi then xi is updated by xi,new select randomly xj from the ecosystem (i ≠ j) create xparatise by copying xi and modifying control variables by (11) calculate fitness function value of xparatise by checking radial topology, running power flow to calculate the power loss, voltage and current profile increase the fe by one: fe = fe + 1 update xj: if xparatise is better than xj then xj is updated by xparatise update the best electric network configuration xbest fig. 1. sos for the network reconfiguration problem iv. numerical results to demonstrate the efficiency of the proposed method, the application of sos for network reconfiguration is implemented in matlab 2016a, executed on a personal computer intel(r) core(tm) i5-2430 at 2.4ghz with 4gb ram. the performance of sos is evaluated in a 33-node and a 69-node system. also, network reconfiguration based on the wellknown pso algorithm was implemented on the same personal computer in order to compare its results with the proposed method’s. engineering, technology & applied science research vol. 9, no. 6, 2019, 4925-4932 4928 www.etasr.com duong & nguyen: network reconfiguration for an electric distribution system with distributed … a. the 33-node test system the 12.66kv, 33-node test system contains 1 feeder and 32 load nodes. the system’s data are taken from [28]. the five initial open switches are {s33, s34, s35, s36 and s37} causing power loss of 202.6863kw. the diagram of the system for the initial configuration is given in figure 2. the control parameters of sos and pso consisting of eco_size, pop_size and mfe are set to 10, 40 and 2000 respectively. 1 2 3 1 4 5 6 7 8 19 20 21 33 91011 12 22 35 18 19 20 21 8 7 6 5 4 3 2 910 11 13 14 1534 12 14 13 16 17 18 33 36 15 16 17 26 27 28 25 26 27 32 29 29 23 24 25 37 22 23 24 31 30 32 31 30 29 fig. 2. the 33-node test system three cases were considered for the 33-node test system: • case-1: performing network reconfiguration on the system without dg placement. • case-2: performing network reconfiguration on the system with installed type-p dgs which inject only real power such as fuel and photovoltaic cells. • case-3: performing network reconfiguration on the system with installed type-pq dgs which inject real and reactive power like synchronous machines. the calculated results on the 33-node test system for the case-1 are shown in table i. the total power loss (∆p) of the system has been reduced from 202.6863kw to 139.9823kw by applying the proposed sos method. this minimal power loss value is achieved by opening switches {s7, s9, s14, s28, s32}. the minimal voltage amplitude (vmin) has been raised from 0.9131p.u. before reconfiguration to 0.94124p.u. after sos reconfiguration. in comparison with pso, in case-1, pso found the optimal configuration but in 50 runs pso has only achieved the optimal solution 5 times corresponding to 10%, while sos achieved the optimal configuration 38 times corresponding to 76%. the maximal (fitmax), average (fitmin) and std of the fitness function values (fit) of sos were also lower than those of pso in 50 runs. furthermore, the running time of sos was 1.2228s lower than pso’s. the average, minimal and maximal convergence trends of sos and pso in 50 runs for case-1 are shown in figure 3. in 50 runs, the average convergence trend of sos is much closer to the minimal convergence trend than of pso. this means that in each run, sos usually tends to convergence to lower fitness values than of pso. as shown in table ii, the results achieved by sos are identical to those obtained by improved selective binary pso (isbpso) [29] and fwa [13]. regarding the comparison with rra [14], power loss obtained by sos is 0.4323 higher than by rra, however the minimal voltage amplitude of network configuration obtained by sos is more improved than by rra. table ii shows that the network configuration obtained by sos1 does not satisfy the radial topology due to the existing ten open switches of {22, 23, 24, 30, 31, 32, 33, 34, 35, 37} in the optimal solution. this configuration will make some nodes in the system not supplied with power. the power loss obtained by sos1 is 175.3337kw which is also higher than that of the proposed sos. table i. results of case-1 of the 33-node system after 50 independent runs item initial sos pso opened switches 33, 34, 35, 36, 37 7, 9, 14, 28, 32 7, 9, 14, 28, 32 ∆p (kw) 202.6863 139.9823 139.9823 vmin (p.u.) 0.9131 0.94124 0.94124 fitmax 159.5083 194.1428 fitmin 148.7392 148.7392 fitaverage 150.2977 161.4816 std of fit. 3.0475 8.2984 successful rate (%) 76 10 run time (sec) 4.3819 5.6047 table ii. comparison of sos with other methods in the 33node system for case-1 method opened switches ∆p (kw) vmin (p.u.) sos 7, 9, 14, 28, 32 139.9823 0.94124 sos1 [26] 22, 23, 24, 30, 31, 32, 33, 34, 35, 37 175.3337 isbpso [29] 7, 14, 9, 32, 37 139.55 0.9378 csa [17] 7, 9, 14, 28, 32 139.9823 0.94124 rra [14] 7, 14, 9, 32, 37 139.55 0.9378 fwa [13] 7, 9, 14, 28, 32 139.9823 0.94124 fig. 3. convergence trends of sos and pso in 50 runs for the 33-node test system in case-1 in the case of the test system with three type-p dgs installed with sizes of 0.7798mw, 1.1251mw and 1.3496mw at node 14, 24 and 30. the reconfiguration results are presented in table iii. the power loss has been reduced from 74.2576kw of the initial configuration to 61.4474kw after the reconfiguration with the opening of {s7, s8, s9, s36 and s37} switches. the obtained result from sos is 1.5326kw lower than the one obtained from csa. in this case, pso also found the optimal configuration but in 50 runs, pso only achieved the optimal solution 3 times corresponding to 6%. meanwhile, sos achieved the optimal configuration 28 times corresponding to 56%. similarly, the maximal, average and std of the fitness function values of sos were also lower than engineering, technology & applied science research vol. 9, no. 6, 2019, 4925-4932 4929 www.etasr.com duong & nguyen: network reconfiguration for an electric distribution system with distributed … those of pso in 50 runs. furthermore, the running time of sos was 1.3612s lower than pso’s. the convergence trends of proposed sos and pso in 50 runs for case-2 are shown in figure 4. table iii. results of case-2 of the 33-node system after 50 independent runs item initial sos pso csa [17] opened switches 33, 34, 35, 36, 37 7, 8, 9, 36, 37 7, 8, 9, 36, 37 8, 9, 27, 33, 36 dg size in mw (node) 0.7798 (14); 1.1251 (24); 1.3496 (30) ∆p (kw) 74.2576 61.4474 61.4474 62.98 vmin (p.u.) 0.9778 0.97865 0.97865 0.9826 fitmax 61.9765 63.328 fitmin 61.4474 61.4474 fitaverage 61.503 62.007 std value of fit. 0.1015 0.3742 successful rate (%) 56 6 running time (sec) 3.9691 5.3303 fig. 4. convergence trends of sos and pso in 50 runs for the 33-node test system in case-2 similarly to case-2, the comparison of sos and pso in case-3 shown in table iv also leads to the conclusion that sos is better than pso in terms of successful rate, quality of fitness function values, and running time. for the network with three type-pq dgs with sizes of 0.5314+j0.3147mw, 0.5030+j0.1485mw, 1.0403+j0.9996mw at node 12, 16 and 30, after reconfiguration sos gained the optimal configuration in 32 runs corresponding to 64% while pso did it only in 2 runs. the maximum, average and std of the fitness function values of sos were respectively 19.635, 18.9885 and 0.2518 while they were 21.3489, 19.5861 and 0.4703 for pso. moreover, the running time of sos was 1.3668s lower than pso’s. the average, minimum and maximum convergence trends of proposed sos and pso in 50 runs for case-1 are shown in figure 5. the power loss of the optimal configuration obtained by sos was also 6.3120 lower than that of the method based on grey wolf optimizer (gwo) [30]. the voltage profile of the system achieved by the proposed sos technique is shown in figure 6. in the initial configuration there are many nodes with lower voltage magnitude than the permissible range such as node 6-18 and 27-33. most of them have been improved after the reconfiguration by sos in case-1. only nodes 18, 30-33 have voltage magnitude lower than 0.95 p.u. in case-2 and case-3, the voltage magnitudes of all the nodes are within the permissible range. the current profile of the 33node system before and after reconfiguration is shown in figure 7. from the figure we can see that the currents of all branches are within the permissible range and the branches carrying high load such as branches 1 to 5 have reduced loads after the reconfiguration. fig. 5. convergence trends of sos and pso in 50 runs for the 33-node test system in case-3 table iv. results of case-3 of the 33-node system after 50 independent runs item initial sos pso gwo [30] opened switches 33, 34, 35, 36, 37 6, 14, 21, 28, 32 6, 14, 21, 28, 32 7, 9, 14, 32, 37 dg size in mva (node) 0.5314+j0.3147 (12); 0.5030+j0.1485 (16); 1.0403 + j0.9996 (30) ∆p (kw) 26.0931 18.8366 18.8366 25.1486 vmin (p.u.) 0.9807 0.98638 0.98638 fitmax 19.635 21.3489 fitmin 18.8366 18.8366 fitaverage 18.9885 19.5861 std of fit. 0.2518 0.4703 successful rate (%) 64 4 run time (sec) 4.0591 5.4259 fig. 6. voltage profile of the 33-node test system before and after reconfiguration b. the 69-node test system the 12.66kv, 69-node test system contains 1 feeder and 68 load nodes. the system’s data are taken from [31]. the five initially open switches {s69, s70, s71, s72 and s73} caused power loss of 224.8871kw. the diagram of the system for the initial configuration is given in figure 8. the control parameters of sos and pso selected for the 69-node test system are similar to those of the 33-node test system. as in the engineering, technology & applied science research vol. 9, no. 6, 2019, 4925-4932 4930 www.etasr.com duong & nguyen: network reconfiguration for an electric distribution system with distributed … 33-node test system, the three aforementioned cases were also considered. fig. 7. current profile of the 33-node test system before and after performing reconfiguration the simulation results on the 69-node test system for case-1 are shown in table v. the total power loss of the system has been reduced from 224.8871kw to 98.5875kw after performing reconfiguration. this minimal power loss value is achieved by opening switches {s14, s57, s61, s69 and s70}. in comparison with pso, in case-1, pso achieved the optimal solution 12 times in 50 rounds corresponding to 24% while sos achieved the optimal configuration 23 times corresponding to 46%. the maximum, average and std of the fitness function values of sos were lower than those of pso in 50 runs. furthermore, the running time of sos was 2.421s lower than pso’s. the average, minimal and maximal convergence trends of the proposed sos and pso in 50 runs for case-1 are shown in figure 9. as shown in the figure, in 50 runs the average convergence trend of sos converged to lower values than pso and was much closer to the minimal convergence trend than pso. as presented in table vi, the results achieved by sos are identical to those obtained by csa [17]. in comparison with fwa [32] and adaptive shuffled frogs leaping algorithm (asfla) [33], the power loss obtained by sos is the same with that of fwa and asfla. fig. 8. the 69-node test system in the case of the test system with three type-p dgs installed with sizes of 0.6022, 0.3804 and 2mw at node 11, 18 and 61, the reconfiguration results are presented in table vii. the power loss has been reduced from 72.4343kw of the initial configuration to 41.1317kw after reconfiguration with the opening of {s14, s57, s64, s69 and s70} switches. the power loss obtained from sos is identical to that obtained from csa. pso also found the optimal configuration but achieved it only 2 times in 50 runs. meanwhile sos achieved the optimal configuration 21 times corresponding to 42%. similarly, the maximal, average, and std of the fitness function values of sos were lower than those of pso. furthermore, the running time of sos was 2.7578s lower than pso’s. the convergence trends of proposed sos and pso in 50 runs for the case-2 are shown in figure 10. fig. 9. convergence trends of sos and pso in 50 runs for the 69-node test system in case-1 table v. results of case-1 of the 69-node system after 50 independent runs item initial sos pso opened switches 69, 70, 71, 72, 73 14, 57, 61, 69, 70 14, 57, 61, 69, 70 ∆p (kw) 224.8871 98.5875 98.5875 vmin (p.u.) 0.9092 0.9495 0.9495 fitmax 105.6075 143.9785 fitmin 99.1169 99.1169 fitaverage 100.7601 110.2838 std of fit. 2.5010 13.4530 successful rate (%) 46 24 run time (sec) 13.3928 15.8138 table vi. comparision of sos with other methods in the 69node system for case-1 method opened switches ∆p (kw) vmin (p.u.) sos 14, 57, 61, 69, 70 98.5875 0.9495 csa [17] 14, 57, 61, 69, 70 98.5875 0.9495 asfla [33] 14, 56, 61, 69, 70 98.59 0.9495 fwa [32] 14, 56, 61, 69, 70 98.59 0.9495 table vii. results of case-2 of the 69-node system after 50 independent runs item initial sos pso csa [17] opened switches 69, 70, 71, 72, 73 14, 57, 64, 69, 70 14, 57, 64, 69, 70 14, 58, 64, 69, 70 dg size in mw (node) 0.6022 (11); 0.3804 (18); 2 (61) ∆p (kw) 72.4343 41.1317 41.1317 41.13 vmin (p.u.) 0.9890 0.98283 0.98283 0.9828 fitmax 42.2749 44.7133 fitmin 41.1317 41.1317 fitaverage 41.4486 43.0842 std of fit. 0.4794 0.8452 successful rate (%) 42 4 run time (sec) 12.2278 14.9856 engineering, technology & applied science research vol. 9, no. 6, 2019, 4925-4932 4931 www.etasr.com duong & nguyen: network reconfiguration for an electric distribution system with distributed … the comparison of sos and pso in case-3 for the 69-node test system presented in table viii also leads to the similar conclusion that sos is better than pso in terms of successful rate, quality of fitness function values and running time. for the network with existing three type-pq dgs with sizes of 0.0871+j0.2096, 1.4155+j1.0131 and 0.5643+j0.3856mw at nodes 68, 61, and 27 respectively, after reconfiguration, sos gained the optimal configuration in 18 runs corresponding to 36% while pso did it only in 7 runs. fig. 10. convergence trends of sos and pso in 50 runs for the 69-node test system in case-2 table viii. results of case-3 of the 69-node system after 50 independent runs item initial sos pso gwo [30] opened switches 69, 70, 71, 72, 73 10, 14, 17, 56, 72 10, 14, 17, 56, 72 14, 57, 61, 69, 70 dg size in mva (node) 0.0871+j0.2096 (68); 1.4155+j1.0131 (61); 0.5643+j0.3856 (27) ∆p (kw) 15.77 7.6707 7.6707 8.4784 vmin (p.u.) 0.984 0.9934 0.9934 fitmax 7.9488 8.7164 fitmin 7.6707 7.6707 fitaverage 7.7247 7.9065 std of fit 0.0840 0.24383 successful rate (%) 36 14 run time (sec) 10.7863 14.24 maximal, average and std of the fitness function values obtained by sos were lower than those of pso. moreover the running time of sos was also lower. the average, minimal and maximal convergence trends of pso and the proposed sos in 50 runs for case-3 are shown in figure 11. the power loss of the optimal configuration obtained by sos was 0.8077kw lower than gwo [30]. fig. 11. convergence trends of sos and pso in 50 runs for the 69-node test system in case-3 the voltage profile of the 69-node system achieved by the proposed sos technique is shown in figure 12. in the initial configuration there were many nodes with lower voltage magnitude than the permissible range, such as nodes 57-69. most of them improved after reconfiguration by sos in case-1. only the node 61 had voltage magnitude of 0.9495 which was a bit lower than the lower permissible limit. in case-2 and case3, the voltage magnitude of all nodes was within the permissible range. fig. 12. voltage profile of the 69-node test system before and after performing reconfiguration v. conclusion this paper presents a method of network reconfiguration based on sos for finding the optimal electric network configuration with minimal power loss. the effectiveness of the proposed sos method is evaluated on a 33-node, and a 69node test system. three cases of 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patnaik et al.: an experimental study of greenhouse gas concentration on the maximum power point … an experimental study of greenhouse gas concentration on the maximum power point of solar pv panels bhabani patnaik school of electrical engineering kiit deemed to be university bhubaneswar, india bhabani.twinkle@gmail.com sarat chandra swain school of electrical engineering kiit deemed to be university bhubaneswar, india scs_132@rediffmail.com ullash kumar rout department of electrical engineering college of engineering and technology, bhubaneswar, india ullashrout@rediffmail.com abstract−the energy demand increases along with demographic and development growth. india is the second-most populous country in the world and most of its population needs more energy as its human and energy development indices are rather low. so, the country depends on cheaper sources of energy which have ample effects on the environment. many energy sources are polluting, but solar energy is pollution-free and its availability is abundant with zero cost. solar photo voltaic (pv) technology is the best technology to harness electricity. the effect of varying environmental factors regulates the performance factors of this technology. its efficiency mainly depends on the concentration of greenhouse gases (ghgs), ambient temperature, module temperature, incoming solar radiation intensity, and pv material composition. to understand the behavior of solar panels on maximum power point under various ghgs concentrations, three experiments were conducted. one in normal atmospheric co2 concentration and two in higher co2 concentration chambers. keywords-solar pv; ghgs; co2 concentration; otc; mpp i. introduction as of 2019, 35% of india's installed electric generation is from renewable sources [1], which is globally the largest producer percentage. even though india is committed by the paris agreement that by 2030, 40% of its total electric energy will be generated from non-fossil fuels, it targets to achieve 57% by 2027. until the end of 2019, india's total renewable energy capacity was 130.68gw which is 35.7% of its total electricity generation [2]. the government of india has focused on solar pv systems due to their reliable and cost-effective nature [3]. especially in india, the climatic conditions are suitable for this technology because it needs higher solar irradiation as input to acquire better output at standard test conditions [4]. nowadays, different types of solar pv modules are used (polycrystalline, monocrystalline, etc.) [5]. the output of a solar pv depends on various factors like greenhouse gases (ghgs), module material, panel area, cable thickness, climatic conditions (humidity, temperature), etc. [6]. due to the growing population and the climate change, ghgs also increase vigorously. ghgs include co2, ch4, no2, sf6, o3, perfluorocarbons (pfcs), water vapors, etc. out of all these gases, ch4 and co2 have the highest effect due to their higher concentrations in the atmosphere (16% and 65% respectively). it can be concluded that it is necessary to produce more green electricity as the climatic changes [7]. ii. the concentration of co2 in the atmosphere the concentration of co2 in the atmosphere ranges from 380 to 420ppm, to an average of 400ppm. it has been shown that the polluting gases from fossil fuels and industry will grow by 3.2% by 2020. the burning of fossil fuels such as coal, petroleum products, and natural gas produces co2. it is observed that the rate of growth is increasing day by day due to the heavy demand for energy production and transportation [8]. in this paper, a higher concentration of co2 was taken to analyze the performance of solar pv panels under these climatic conditions because as the co2 concentration increases, so is the demand of renewable energy (i.e. especially solar pv technology). from figure 1, we can see the rate of growth of co2 in every 10 years. fig. 1. the increasing rate of co2 concentration. iii. experimental analysis an experimental analysis has conducted in the national rice research institute, cuttack. they had built special chambers, known as open top chambers (otcs) [9], where the concentration of co2 is kept higher than its atmospheric concentration (400ppm).two otcs were made with two corresponding author: bhabani patnaik engineering, technology & applied science research vol. 10, no. 5, 2020, 6200-6203 6201 www.etasr.com patnaik et al.: an experimental study of greenhouse gas concentration on the maximum power point … different concentrations of co2, 550ppm and 575ppm respectively. the experiment was carried out for three days (10 a.m. to 4 p.m.) in dry season (oct-15-2019 to oct-17-2019). the otcs were used for conducting the co2 enrichment experiment. they were arranged in the field with a block design which is rectangular in shape (6m×4m×3m). these chambers are made up of transparent polycarbonate sheets with about 80 to 90% transparency. the upper part of the otc is open. the temperature for all the chambers was recorded with a digital thermometer. pure co2 gas was blown (2.5kg/cm 2 ) inside the otcs through perforated polyvinyl tubes regulated by solenoid valves. the co2 data logging, sampling and the concentration of each co2 on each otc were performed by a personal computer (pc) through an automatic digital meter and a microcontroller. figures 2-3 show the design of open-top chambers and the system where the co2 concentration, temperature and humidity were recorded. fig. 2. otcs with different co2 concentrations. fig. 3. the recording system. in order to evaluate the performance of the solar pv panels under higher co2 concentrations, three 20w pv modules were kept in three different otcs. the experimental set-up of each chamber is given in figures 4-6. each module was kept in its respective chamber and the measuring instruments were kept outside, so that the effect of co2 on the solar pv panel could be properly analyzed. fig. 4. solar pv panel under otc 1 with 575ppm co2 concentration. fig. 5. solar pv panel in otc 4 with 550ppm co2 concentration. fig. 6. solar pv panel on atmospheric co2 concentration of 400 ppm. the solar pv module description and the required instruments for the experiment are given in tabular form in table i. the experiment was conducted in order to acquire knowledge of the effect of higher concentrations of co2 on the performance of a solar pv module. the experimental analysis has continued for three days and the data were properly engineering, technology & applied science research vol. 10, no. 5, 2020, 6200-6203 6202 www.etasr.com patnaik et al.: an experimental study of greenhouse gas concentration on the maximum power point … synthesized and analyzed. in this paper, the data of only a single data are shown, representing the best outcome from the three-day experiment. table i. required instruments for the experiment instruments required range unit solar panel 20w 3 ampmeter 0-1a (dc) 3 voltmeter (multimeter) 0-100v (dc) 3 rheostat 0-145ω 3 solar meter measuring irradiation 1 solar pv stand tilt angle-22deg. 3 thermometer 0500 0 c. 3 table ii. solar pv module specifications parameter specification maximum power 20w maximum voltage 18.25v maximum current 1.10a open circuit voltage 21.96v short circuit current 1.17a cell technology polycrystalline dimension (mm) (356×490×20) iv. results all the data were taken simultaneously for the three systems on a sunny day. voltage, current, ambient temperature, and module temperature of all setups were taken each hour from 10 am to 4 pm. the maximum power point (mpp) was traced from these data. in figure 7, the data were taken at 10 am when the irradiation was 715w/m 2 , in figure 8, at 11 am when the irradiation was 850w/m 2 , in figure 9, at noon when the irradiation was 915w/m 2 , in figure 10, the data were taken at 1 pm when the irradiation was 750w/m 2 , in figure 11, the data were taken at 2 pm when the irradiation was 660 w/m 2 , in figure 12 at 3 pm with 550 w/m 2 irradiation, and in figure 13at 4 pm when the irradiation was 400w/m 2 . fig. 7. pv characteristics at 10 am. fig. 8. solar pv characteristics at 11 am. fig. 9. solar pv characteristics at 12 am. fig. 10. solar pv characteristics at 1 pm. fig. 11. solar pv characteristics at 2 pm. engineering, technology & applied science research vol. 10, no. 5, 2020, 6200-6203 6203 www.etasr.com patnaik et al.: an experimental study of greenhouse gas concentration on the maximum power point … fig. 12. solar pv characteristics at 3 pm fig. 13. solar pv characteristics at 4 pm. v. discussion we can verify from the graphs that as the irradiation increases, the temperature of the panel also increases but at the same time, the increase of co2 concentration has a major effect on the temperature of the solar panel. at 10 am, the maximum power of the solar panel at 575ppm co2 was 3.85w, at 550ppm it was 4.125w, and at 400ppm it was 4.5w. similarly, at 11 am the maximum power of the solar panel at 575ppm was 4.03w, at 550ppm was 4.074w whereas at 400ppm it was 4.509w. we can see that when the panels were under the highest radiation (noon time), the maximum power of solar panel at 575ppm was 4.53w, at 550ppm was 4.585w whereas at 400ppm it was 4.816w. similarly, we can observe at every hour of that day the output maximum power or mpp of the solar pv module at 550ppm is less than the mpp of the pv module at 400ppm (ambient). and the module which is kept at 575ppm gives less mpp than the module kept at 550ppm. it should be noted that the same irradiance is absorbed by all the panels and that the data were taken simultaneously. due to the higher co2 concentration, the ambient temperature of 550ppm and 575ppm otcs was higher than the ambient temperature of the panel with 400ppm co2 concentration. due to the increase in the ambient temperature of the otcs, the solar pv module temperature increased, which effected the mpp of the panel as shown in figures 7-13. a small increase of the ambient temperature affects disproportionately the panel temperature and thus the maximum power of the solar pv panel is gradually decreasing. vi. conclusion in 2000, the concentration of co2 in the atmosphere was 366ppm, and now (2020) the concentration of co2 is 400 to 405ppm. meanwhile, the demand for solar pv energy is increasing dramatically. research in many aspects is conducted to get maximum efficiency from the solar pv panels. there are many factors present in the atmosphere by that affect the efficiency of solar pv panels. from this experimental analysis it was observed that due to the higher concentration of co2, the ambient temperature increases, and a small increase in ambient temperature has many effects on the panel efficiency. the temperature is inversely proportional to the module output power. so at standard test conditions, the solar panel gives maximum efficiency where the temperature should be 25 0 c. thus it is necessary to maintain the module temperature at 25 0 30 0 c in order to have better efficiency and performance with higher solar irradiance. acknowledgement the authors like to thank the national rice research institute, cuttack, odisha for providing the necessary set-up for the experiments. references [1] t. v. krishna, m. k. maharana, and c. k. panigrahi, “integrated design and control of renewable energy sources for energy management,” engineering, technology & applied science research, vol. 10, no. 3, pp. 5857–5863, jun. 2020. [2] a. s. saidi, m. b. slimene, and m. a. khlifi, “transient stability analysis of photovoltaic system with experimental shading effects,” engineering, technology & applied science research, vol. 8, no. 6, pp. 3592–3597, dec. 2018. [3] a. gholami, a. saboonchi, and a. a. alemrajabi, “experimental study of factors affecting dust accumulation and their effects on the transmission coefficient of glass for solar applications,” renewable energy, vol. 112, pp. 466–473, nov. 2017, doi: 10.1016/j.renene.2017.05.050. [4] k. v. vidyanandan, “an overview of factors affecting the performance of solar pv systems,” energy scan (a house journal of corporate planning, ntpc ltd.), vol. 27, pp. 2–8, feb. 2017. [5] b. patnaik, s. c. swain, and u. k. rout, “effect of colour spectrum and plastic on the performance of pv solar system,” international journal of recent technology and engineering, vol. 8, no. 4, pp. 10843–10846, nov. 2019, doi: 10.35940/ijrte.d4373.118419. [6] b. patnaik, s. c. swain, and u. k. rout, “modelling and performance of solar pv panel with different parameters,” in applications of robotics in industry using advanced mechanisms, cham, 2020, pp. 250–259, doi: 10.1007/978-3-030-30271-9_23. [7] h. wang, b. w. ang, and b. su, “a multi-region structural decomposition analysis of global co2 emission intensity,” ecological economics, vol. 142, pp. 163–176, dec. 2017, doi: 10.1016/j.ecolecon.2017.06.023. [8] r. heede, “tracing anthropogenic carbon dioxide and methane emissions to fossil fuel and cement producers, 1854–2010,” climatic change, vol. 122, no. 1, pp. 229–241, jan. 2014, doi: 10.1007/s10584013-0986-y. [9] a. kumar, a. k. nayak, r. p. sah, p. sanghamitra, and b. s. das, “effects of elevated co2 concentration on water productivity and antioxidant enzyme activities of rice (oryza sativa l.) under water deficit stress,” field crops research, vol. 212, pp. 61–72, oct. 2017, doi: 10.1016/j.fcr.2017.06.020. microsoft word 20-2943_s_etasr_v9_n5_pp4685-4688 engineering, technology & applied science research vol. 9, no. 5, 2019, 4685-4688 4685 www.etasr.com alomari: the effect of mass, depth, and properties of the soil below the raft foundation on the … the effect of mass, depth, and properties of the soil below the raft foundation on the seismic performance of r.c. plane frames jamal ahmad alomari civil engineering department, al-ahliyya amman university, amman, jordan j.alomari@ammanu.edu.jo abstract—soil structure interaction (ssi) has been the subject of numerous studies. the foundation soil has a definite effect on the performance of structures during seismic excitation. recent studies show that the effect of soil-structure interaction ssi may be detrimental to the structure during seismic excitation. in this study, the effect of consideration of the soil below foundation and its depth, and the soil modulus of elasticity on the response of structures is investigated. the number of mode shapes considered has an effect on the accuracy of the values of structure response. a structural model consisting of an 8-story reinforced concrete frame resting on raft foundation, and including the soil below the raft is analyzed. the frame is analyzed using sap2000 software, and time history and modal analysis are carried out with varying values of both soil depth and soil modulus of elasticity. the soil below the foundation is connected to the raft elements by gap links. gap element links are compression–only members with appropriate stiffness, which are active only in compression. modal analysis results show that the periods of vibration decrease as the modulus of elasticity of the soil increases. periods of vibration of the frame without the soil mass consideration are less than those when the soil mass below the raft is considered, and they increase with increased depth of foundation to a certain limit. the structures response in the form of columns shear forces and story displacements are also evaluated under the variable parameters considered. keywords-ssi; soil mass depth; number of mode shapes; seismic; period of vibration; soil modulus of elasticity; column shear force; story displacement; gap link i. introduction the effect of soil-structure interaction on the performance of structures during seismic excitation has been the subject of extensive research, mostly theoretical rather than experimental due to the self-evident difficulty of experimental work. it is well known that the soil mass below the structure foundation and the structure have a mutual effect on each other during earthquake excitation. this is known as soil-structure interaction (ssi). the soil in general has non-linear properties both in geometric and material behavior. however it is considered as consisting of layered linear shell elements in this analysis. its flexibility and deformation during earthquakes have an immediate and sometimes detrimental effect on the structure’s behavior. the flexibility of the soil mass may amplify ground shaking and change the structure response dramatically. design practice usually treats the structures as fixed at the base and ignores the flexibility and settlement of the soil mass below. moreover, the number of mode shapes considered in the seismic analysis affects the accuracy of the values of the structure response, such as story displacement, and column shear forces. the effect of higher modes of vibration on the structure response using fixed-base structures without consideration of the soil mass below has been studied in depth. this paper considers the effect of consideration of higher modes on the structure response during time history analysis with due consideration of the ssi. the codes of practice usually specify a minimum number of mode shapes to be considered to arrive to a certain level of accuracy. in fact, this minimum is different for different parameters such as the story displacement and column shear forces. this paper tries to show the effect of the depth of soil mass, and its properties on the structure response during seismic excitation, as well as the minimum number of modes needed to arrive at a certain level of accuracy for the structure responses while including ssi. ii. literature review authors in [1] studied the local site effects excluding ssi for midrise moment resisting frames of 5, 10, and 15 story heights with 2 soil types having shear wave velocity less than 600m/s. they concluded that excluding the fact that the ssi cannot adequately guarantee the structure safety for structures higher than 5 stories resting on soft soils. authors in [2] carried out theoretical research on multi-floor frames with various parameters of the soil below foundation and number of stories to show the effect of ssi effects on the dynamic properties of the frames. they compared the results with the fixed –base structures. they research concluded that as the soil stiffness increases, the fundamental period for the structural model decreases, and that the fundamental period for the structural model is not only a function of building height but also a function of ssi. authors in [3] carried out a theoretical study on a 8-story reinforced concrete frame on raft foundation corresponding author: jamal ahmad alomari engineering, technology & applied science research vol. 9, no. 5, 2019, 4685-4688 4686 www.etasr.com alomari: the effect of mass, depth, and properties of the soil below the raft foundation on the … including the soil mass below to study the effect of ssi on the settlement of the structure, bearing pressure, and bending moments in the raft and stresses on slabs. authors in [4] analyzed a 15-story r. c. moment resisting frames founded on soft soils, with bedrock depths of 10, 20, and 30 meters. the performance of the fixed base frame in the form of the story drift was compared with that of the frame with soil-structure interaction. they concluded that increasing the bedrock depth increases lateral deflections and inter-story drifts of the structures. authors in [5] considered 3 types of buildings for dynamic analysis. these were a shear building with constant columns stiffness, a shear building with variable columns stiffness, and a flexural building, without considering ssi. their analysis aimed at finding the number of mode shapes considered to arrive at 5% and 10% levels of accuracy for the values of base shear and top story shear forces. they concluded to simple formulas that keep the relative errors of the building response within the specified percentages. authors in [6] studied a finite element model of a 2-story plane frames with soil-structure interaction under dynamic loading considering a wide range of shear wave velocity of the soil. they concluded that ssi influences all modes of the structure and particularly the vertical modes. they also concluded that dynamic ssi generally leads to lower eigen frequencies for the coupled structure. iii. structure description and method of analysis the reinforced concrete plane frame shown in figure 1 consists of 8 floors. the beams are 1.0m×0.3m and the columns are 0.5m×0.5m. the frame rests on reinforced concrete raft foundation of 0.7m thickness, modeled as beam elements with dimensions of 3.96m×0.7m. the raft beam elements are further divided into 0.66m long beam elements. the concrete has a compressive strength of 27.57mpa. the soil below the raft is modeled as layered shell elements, with 2.5m depth of each layer, and with varying modulus of elasticity. soil shell elements are connected to the raft elements via compression-only gap element links. these are active in compression only otherwise they have no effect on the structure. they are assigned little stiffness values. the soil boundary joints are considered fixed. as such, the bedrock layer is realized at the bottom and at the sides of the soil layers. the depth of the soil mass varies from 7.5m to 30m. the soil properties in the form of its modulus of elasticity are varied from a value of 60mpa to a value of 300mpa. this range of values is typical for soils ranging from dense sands to hard rock [7]. the frame described is subjected to typical gravity loads. linear time history analysis using the modal solution type of the frame, foundation and soil below is carried out. the n-s el centro time history acceleration is used with a scale factor of 0.1. iv. results and discussion the first 10 periods of vibration of the frame against the soil modulus of elasticity are shown in table i. it is observed that the periods decrease as the modulus of elasticity of the foundation soil increases. this observation is in agreement with the findings of [3, 8]. more runs of sap2000 [10] were carried out to investigate the effect of varying number of modes on the accuracy of the frame response of story displacement, and column shear forces. for this purpose, the frame is analyzed using time history acceleration of the n-s component of el centro record scaled to 0.1 using the modal solution type. the soil modulus of elasticity is considered 100,000mpa for all runs for this purpose. table ii shows the displacements of some joints of the structure using different number of modes, and table iii shows the shear forces in selected columns of the frame with varying number of modes. fig. 1. reinforced concrete plane frame and soil below the raft foundation of 7.5m depth table i. vibration periods vs soil modulus of elasticity e of soil (mpa) 60 80 100 120 140 200 260 300 period no 1 0.618159 0.589168 0.571294 0.559174 0.550416 0.534432 0.525701 0.52179 2 0.194967 0.17763 0.17113 0.168536 0.167237 0.165596 0.164947 0.164694 3 0.157704 0.149354 0.138538 0.128471 0.120041 0.103119 0.097416 0.096526 4 0.131757 0.119397 0.110484 0.10405 0.099759 0.094192 0.087192 0.081987 5 0.099767 0.094051 0.092901 0.091626 0.089659 0.080809 0.073206 0.069746 6 0.093854 0.085042 0.076805 0.071145 0.068919 0.068237 0.067867 0.067174 7 0.086504 0.075461 0.067935 0.064997 0.063532 0.054391 0.049573 0.050197 8 0.074895 0.066347 0.061014 0.059412 0.056321 0.048 0.045486 0.044027 9 0.062798 0.05976 0.055354 0.051622 0.04826 0.041115 0.03813 0.036902 10 0.037754 0.03641 0.034435 0.032522 0.030664 0.026159 0.031023 0.031177 engineering, technology & applied science research vol. 9, no. 5, 2019, 4685-4688 4687 www.etasr.com alomari: the effect of mass, depth, and properties of the soil below the raft foundation on the … table ii. joint displacement at selected joints no. of modes 1 2 3 5 7 10 20 30 50 joint 33 0.0300 0.038 0.0312 0.0363 0.0374 0.03815 0.0382 0.0382 0.0382 joint 37 0.0940 0.0164 0.162 0.155 0.151 0.1458 0.155 0.155 0.155 joint 40 0.0121 0.0224 0.235 0.242 0.244 0.2405 0.240 0.240 0.240 table iii. shear force in selected columns number of modes 1 2 3 5 7 10 20 30 50 column 29 joints 32-33 314.2 488.6 364.2 400.00 354.8 394.4 394.4 394.4 394.4 column 33 joints 36-37 138.4 305.3 377.4 347.3 182.5 199.8 199.8 199.8 199.8 column 36 joints 39-40 19.7 -18.7 86.4 136.1 176.3 110.1 110.1 110.1 110.1 the “exact” response of the frame can be considered as the one using all modes of vibration. it is possible to calculate the relative error in the response by taking the difference between the “exact” value and the value including a reduced number of mode shapes. from tables ii and iii, it is seen that including 20 mode shapes in the calculations of the displacements and column shear forces produced zero percent errors. however, usually, it is sufficient to include few of the mode shapes in the calculations depending on the desired accuracy. the level of accuracy depends on the element of the structure under consideration in addition to two other factors, namely the modal contribution factor and the spectral coordinate [9]. from table ii, it is observed that including 5 modes in the calculations of the lateral displacements produces errors of -5%, 0%, and +0.83% for joints 33, 37, and 40 respectively. as for the shear forces in columns, including 7 mode shapes in the calculations produces errors of -10%, -8.7%, and +60.1%. it is clear that the shear forces in columns require more mode shapes than the displacements for acquiring the same accuracy. the height of the member or joint under consideration above the base of the structure is another factor affecting the accuracy of the response. the error percentage in the top floor displacement is less than in the lower joints displacements for the same number of modes. this is not the same for shear forces in columns where the top floor columns require more modes to be included than the lower columns for the same accuracy. these findings are in agreement with the findings of [3, 5]. v. effect of including the soil mass below the raft and the soil mass depth to investigate the effect of including the soil mass below the raft, and the effect of its depth on the period of vibration, the same frame is analyzed first without the soil mass, i.e. bare frame, and then with soil depths of 7.5m, 15.0m, 22.5m, and 30.0m (figure 2). table iv shows the periods of vibration of the bare frame, and with the above mentioned soil depths. comparing the periods of vibration of the bare frame with that of the structure with 7.5m deep soil mass, it is observed that there is an increase of around 15% in its value. more depth of the soil mass increases the period length but to a limited value. this also depends on the value of the soil modulus of elasticity. in other words, soil flexibility imparts flexibility to the structure, and this effect is more pronounced with soft soils having a shear wave velocity of 600m/s or less [1]. vi. mode shapes for completeness, figure 3 shows some of the mode shapes of the structure with a soil depth of 30m. it is obvious from the deformation of the soil below the raft foundation, e.g. mode shape number 5, how the structure performance is affected (a) (b) fig. 2. (a) the plane frame without the soil mass below the raft foundation, and (b) the frame with soil depth of 22.5m (a) (b) (c) fig. 3. mode shapes (a) 1, (b) 2, and (c) 5 engineering, technology & applied science research vol. 9, no. 5, 2019, 4685-4688 4688 www.etasr.com alomari: the effect of mass, depth, and properties of the soil below the raft foundation on the … table iv. first 10 periods of vibration of the frame shown in figure 1 with varying soil depth below the foundation period no. period (s) without soil below the raft with soil depth=7.5m* with soil depth=15m* with soil depth=22.5m* with soil depth=30m* 1 0.495405 0.571294 0.576505 0.576701 0.576707 2 0.163307 0.17113 0.177173 0.179174 0.179683 3 0.094817 0.138538 0.154888 0.159159 0.162008 4 0.068374 0.110484 0.131925 0.145083 0.1533 5 0.054196 0.092901 0.110795 0.125378 0.133296 6 0.046517 0.076805 0.097386 0.116624 0.109966 7 0.042821 0.067935 0.088106 0.094202 0.095989 8 0.039289 0.061014 0.068064 0.078491 0.082779 9 0.014975 0.055354 0.061655 0.065283 0.06561 10 0.010402 0.034435 0.04612 0.053339 0.055881 * e=100000 mpa vii. conclusion based on the findings of this study, the following conclusions can be drawn: • consideration of the soil mass below the raft foundation of r. c. framed structures increases the length of periods of vibration. • increasing the depth of the soil mass below the raft foundation increases the periods of vibration up to a limited value depending on the soil modulus of elasticity e. for the considered case where e=100,000 mpa, soil mass depth of 10m is enough to arrive at the maximum effect of the soil mass on the values of periods of vibration, beyond which periods remain constant. • the type of soil below foundation, measured by its modulus of elasticity, has an increasing effect on the structure response as its modulus of elasticity is decreasing. soft soils with low modulus of elasticity impart more flexibility to the structures than stiff soils • it was found that shear forces in columns require consideration of more mode shapes than story displacements in order to arrive at the same level of accuracy as compared to the “exact” value, which is the one including the total number of mode shapes. • the shear force in higher floor columns requires more mode shapes than in the lower columns to be included in the solution to arrive at the same level of accuracy. • the displacement at lower floors requires more mode shapes to be included in the solution to arrive at the same level of accuracy, and that is opposite to the case of shear force in columns. • the seismic demand of the structure should take account of the soil mass beneath structures including its properties and depth in order to avoid underestimation of the base shear calculated according to the equations stipulated in the codes of practice. references [1] b. fatahi, s. h. r. tabatabaiefar, b. samali, “soil-structure interaction vs site effect for seismic design of tall buildings on soft soil”, geomechanics and engineering, vol. 6, no. 3, pp. 293-320, 2014 [2] s. e. abdel raheem, m. m. ahmed, t. m. a. alazrak, “evaluation of soil–foundation–structure interaction effects on seismic response demands of multi-story mrf buildings on raft foundations”, international journal of advanced structural engineering, vol. 7, no. 1, pp. 11-30, 2015 [3] b. moczar, z. polgar, a. mahler, “a comparative study of soil-structure interaction in the case of frame structures with raft foundation”, materials and geoenvironment, vol. 63, no. 1, pp. 1-8, 2016 [4] b. fatahi, s. h. reza tabatabaifar, a. s. hokmabadi, b. samali, “significance of bedrock depth in dynamic soil-structure interaction analysis for moment resisting frames”, 2nd international conference on performance-based design in earthquake geotechnical engineering, taormina, italy, may 28-30, 2012 [5] o. a. lopez, m. cruz, “number of modes for the seismic design of buildings”, earthquake engineering and structural dynamics, vol. 25, no. 8, pp. 837-855, 1996 [6] m. papadopoulos, r. van beeumen, s. francois, g. degrande, g. lombaert, “computing the modal characteristics of structures considering soil-structure interaction effects”, procedia engineering, vol. 199, pp. 2414–2419, 2017 [7] r. obrzud, a. truty, the hardening soil model –a practical guidebook, zace services ltd, 2012 [8] s. lamar, c. fortoul, “brick masonry effect in vibrations of frames”, in: proceedings of the 4th world conference on earthquake engineering, vol. 2, pp. 91-98, 1969 [9] a. k., chopra, dynamics of structures theory and applications to earthquake engineering, prentice hall, 2017 [10] https://www.csiamerica.com/products/sap2000 microsoft word 15-2858_s1_etasr_v9_n4_pp4392-4396 engineering, technology & applied science research vol. 9, no. 4, 2019, 4392-4396 4392 www.etasr.com al-mashaqbah et al.: utilizing upper arm images in determining body mass index and nutritional status utilizing upper arm images in determining body mass index and nutritional status sami f. al-mashaqbah dept. of biomedical systems and medical informatics, hijjawi faculty for engineering technology, yarmouk university, irbid, jordan sami.m@yu.edu.jo walid al-zyoud biomedical engineering dept., school of applied medical sciences, german jordanian university, amman, jordan walid.alzyoud@gju.edu.jo awad al-zaben dept. of biomedical systems and medical informatics, hijjawi faculty for engineering technology, yarmouk university, irbid, jordan azaben@yu.edu.jo abstract—body mass index (bmi) is the most widely used index for determining the fitness status of an individual. midd-upper arm circumference (muac) is another commonly used anthropometric index, providing a simple measurement widely used for nutrition level screening. however, building a massive population database based on both bmi and muac measurements is time-consuming and may introduce errors due to instrumentations and different operators. in this paper, a measurement technique of bmi from photographic images of the upper arm is presented. three parameters are measured from the subject photos with a scale attached, and these are upper arm length, sagittal plane middle arm thickness (smt), and frontal plane middle thickness (fmt). different parameters are derived from the smt and the fmt. these parameters are used to study the correlation and measurements agreements with the bmi. it is found that all parameters related to smt correlate very well with the bmi with correlation coefficients of more than 90%. in addition, the smt measurement limits (both upper and lower) are acceptable and within the clinical significance range. finally, the receiver operating characteristics analysis of both smt and muac has been evaluated. the findings show that smt is slightly better than muac since it gives excellent sensitivity (94.7%) without compromising the specificity (88.5%) when compared to the muac results. keywords-bmi; obesity; sagittal plane i. introduction as technology increased our quality of life, it led to a sedentary lifestyle and increased the prevalence of overweight or obesity in a global scale [1]. there is a metric difference between overweight and obesity in terms of the mass of the human body. according to the world health organization (who), obesity is defined as a medical condition where the fat mass of the human body is excess to the point that might negatively affect health. overweight is being fat in a degree between healthy and obese. the association between obesity and the increased risk of developing a wide range of chronic diseases such as cardiovascular diseases, diabetes mellitus, and even cancer has been reported and raised public health concerns [2-4]. currently, one of the most common methods to classify people based on their anthropometric (height and weight) characteristics is the body mass index (bmi), an index that reflects an individual’s body fatness [5]. bmi is calculated by dividing the body mass in kilogram by the squared body height in meters [6]. the who obesity classification is based on bmi [7] which is widely adopted [8]. four categories have been adopted: underweight: if the measured bmi is in the range 15-19.9, normal: if it is in the range 20-24.9, overweight: if it is in the range 25-29.9, and obese if it is more than 30. there are other obesity classification systems with alternative terms. for example, the one suggested in [9], was not similar to the who-bmi system in terms of the categories cutoff points. in 1997, the obese category has been divided by the international obesity task force into three categories as shown in table i [10]. table i. bmi categories [10] categories bmi range underweight 15-19.9 normal weight 20-24.9 overweight 25-29.9 obesity class i 30-34.9 class ii 35-39.9 class iii ≥40 obesity is the term describing excessive accumulated amount of triacylglycerols in the adipose tissue of the human body. from an anatomical and physiological point of view, obesity is called adiposity. adiposity studies on public health are dominantly based on population surveys, something that makes bmi as a direct fat indicator quite debatable due to differences in variables including gender, age, ethnic group, and race [11-13]. it is worth mentioning that fat accumulation in different areas of the human body might be related to several pathophysiological indicators including inflammations, metabolic disorders, stress, and cardiovascular dysfunctions [14]. despite this limitation, bmi is still the most widely used index for determining one’s fitness status. on the other hand, the muac, which is another commonly used anthropometric index, provides a simple measurement that is widely used for nutrition level screening. muac has been used as a nutritional index in elderly, impatient, infants, children, university students, and pregnant women [15-19]. however, building a massive database of different populations to be used in corresponding author: sami f. al-mashaqbah engineering, technology & applied science research vol. 9, no. 4, 2019, 4392-4396 4393 www.etasr.com al-mashaqbah et al.: utilizing upper arm images in determining body mass index and nutritional status determining the nutrition status of the public based on both bmi and muac measurements is time-consuming. furthermore, these techniques may introduce errors due to instrumentations and different operators. in this study, a novel imaging approach is proposed in order to study the association between the bmi and anthropometric measurements of the upper arm, to find the best parameters that can be used to represent bmi in the sense of correlation and measurement agreement, and to compare the sensitivity and specificity of these parameters to muac. this method can be used in cases of disabilities where it is difficult to perform traditional measurements of height and weight. furthermore, it provides a fast way to find bmi at temporary refugee camps and whenever the needed instruments are not available. ii. database and method photos of the subject in three positions are taken: sagittal plane position with the elbow flexed at 90 o with their palm facing upward, sagittal plane with their hands at the sides, and frontal plane with their hands at the sides as shown in figure 1. fig. 1. (a) standing on the sagittal plane with the elbow flexed at 90 o with palm facing upward, (b) standing on the sagittal plane with hands at the sides, (c) frontal plane with hands at the sides. the upper arm length is measured relatively to the scale used in the photographic setup. two parameters are then measured from the two other relative photos. these are the sagittal plane middle thickness (smt) and the frontal plane middle thickness (fmt). the measured parameters are used to derive a set of parameters shown in table ii. in addition, subjects were asked to wear sleeveless shirts on top and to be barefoot. a digital weight scale was used to measure the weight of each subject. the height of the subjects was measured using a measuring tape attached to the wall while the subject stands on the floor at a right angle to the wall. while their right elbow was flexed at 90 o , a measuring tape was used to measure the distance between the lateral tip of the acromion and the most distal point on the olecranon, which is considered as the upper arm length (ual). the mid-upper arm was located and marked using a pen. a flexible measuring tape was used to measure the mid-arm circumference (muac) at the marked mid-point. a vernier was used to measure the smt and the fmt. after taking informed consent, 45 healthy young male individuals with an average age of 22.25 years, ranging from 19.5 to 26.58, participated in this study. among them, 26 subjects were normal weighted with a bmi between 18 and 25, ten subjects were over weighted with bmi between 25 and 30, and nine subjects were obese with a bmi greater than 30. table ii. calculated parameters iii. results the actual bmi is calculated from the well-known relation of the measured weight and height. this bmi is compared to the parameters measured and derived (table ii) after scaling. the null hypothesis is that the two measurements are not linearly related. figure 2 shows the correlation analysis and the bland-altman plot [20, 21] of the measured muac versus bmi. the correlation analysis and the bland-altman plots of the sagittal plane parameters versus bmi are shown in figure 3. similarly, figure 4 shows the correlation analysis and the bland-altman plots of the other parameters derived from both sagittal and frontal images versus the bmi. figure 5 shows the receiver operating characteristics of muac and smt. the corresponding optimal cutoff-point analysis is shown in figure 6. the results show an area under the curve (auc) of 0.973 and 0.966 for muac and smt, respectively. furthermore, the optimal cutoff point of overweight for smt is 11.2cm with a sensitivity of 94.7% and specificity of 88.5%, while the optimal cutoff point of overweight for muac is 30cm with a sensitivity of 100% and specificity of 84.7%. parameter description equation pcirc mid-arm circular perimeter based on sagittal middle and frontal middle thicknesses. π�smt�fmt�2 pellip mid-arm elliptical perimeter based on sagittal middle and frontal middle thicknesses. 2 � �� � � ��� � 8 acircsagittal mid-arm circular crosssectional area based on sagittal middle thickness. � ��2 � � acirc mid-arm circular crosssectional area based on sagittal middle and frontal middle thicknesses. � �� � ���4 � � aellip mid-arm elliptical crosssectional area based on sagittal middle and frontal middle thicknesses. 4π �smt2 � �fmt2 � engineering, technology & applied science research vol. 9, no. 4, 2019, 4392-4396 4394 www.etasr.com al-mashaqbah et al.: utilizing upper arm images in determining body mass index and nutritional status (a) (b) fig. 2. correlation analysis and bland-altman plot of muac versus bmi. iv. discussion the current work aimed to investigate the usefulness of using images of the upper arm in determining bmi and nutritional status. several parameters have been measured and derived from the images of the sagittal and frontal planes of the upper arm. these parameters’ relationship to bmi is evaluated using two statistical measures: the correlation coefficient and the measurement agreement presented by bland-altman plots. the correlation coefficient values revealed a solid relationship between bmi and all parameters. the correlation coefficients were 0.926, 0.936, 0.855, 0.916, 0.916, and 0.906 for smt, acircsagittal, pcirc, acirc, pellip, and aellip respectively. the best correlation corresponds to these parameters derived from a sagittal image (smt and acircsagittal). however, the correlation is between one variable and another, not the differences. hence it is not recommended as a standalone method for assessing the comparability between methods [20]. therefore, bland-altman plots were used to describe the agreement between each parameter and bmi. in the blandaltman plot, the difference between the paired measurements is plotted against the mean of the two measurements [20, 21]. the result shows that the smt measurement agreement with bmi is better than with other parameters. (a) (b) fig. 3. correlation analysis and bland-altman plots of parameters derived from sagittal plane: (a) smt, (b) acircsagittl engineering, technology & applied science research vol. 9, no. 4, 2019, 4392-4396 4395 www.etasr.com al-mashaqbah et al.: utilizing upper arm images in determining body mass index and nutritional status (a) (b) (c) (d) fig. 4. correlation analysis and bland-altman plots of parameters derived from sagittal plane image panel (a) pcirc versus bmi panel, (b) acirc versus bmi panel, (c) pellip versus bmi panel, and (d) aellip versus bmi. muac was measured, and the correlation and the measurement agreement were evaluated against bmi. compared to smt, the result shows that the smt measurements agreement is better than the muac’s, given that the corresponding correlation coefficient is slightly lower than that of the upper arm circumference. finally, the receiver operating characteristics of both smt and muac were evaluated. the results show a slightly higher auc area of 0.973 for muac compared to 0.966 for smt. moreover, the sensitivity was 100% for muac and 94.7% for smt. however, the specificity was higher for smt with a value of 88.5% compared to 84.7% for muac. this shows that smt performs better than muac since it gives excellent sensitivity without compromising for specificity. the current data are based on healthy subjects without any health issues except obesity. therefore, special attention should be given when applying the proposed approach on people who are suffering from inflammations, metabolic disorders, stress, and cardiovascular dysfunctions, which may cause local changes in the shapes of specific areas of the human body, such as the lower and upper extremities, due to fat accumulation. engineering, technology & applied science research vol. 9, no. 4, 2019, 4392-4396 4396 www.etasr.com al-mashaqbah et al.: utilizing upper arm images in determining body mass index and nutritional status fig. 5. receiver operating characteristics of smt and muac. (a) (b) fig. 6. (a) optimal cutoff smt and (b) optimal cutoff of muac. estimation of the bmi and the nutritional status using a sagittal plane image of the upper arm provides an indirect, easy, fast, and low-cost method. this method can be used in cases of disabilities, where it is difficult to perform traditional measurements of height and weight. furthermore, it provides a fast way to find bmi whenever the needed instruments are not available or in temporary refugee camps. the technique used in the current research can be further investigated using automated image processing calculations. using an automated system can make easier to build a massive database of varying population to be used in determining the nutritional status of the public. moreover, this technique eliminates instrumentation errors and variability due to different operators. references [1] m. m. finucane, g. a. stevens, m. j. cowan, g. danaei, j. k. lin, c. j. paciorek, g. m. singh, h. r. gutierrez, y. lu, a. n. bahalim, f. 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ahmed, m. i. hossain, “assessment of under nutrition of bangladeshi adults using anthropometry: can body mass index be replaced by mid-upper-arm-circumference?”, plos one, vol. 10, no. 4, article id e0121456, 2015 [16] p. nguyen, u. ramakrishnan, b. katz, i. g. casanova, a. e. lowe, h. nguyen, h. pham, t. truong, s. nguyen, r. martorell, “mid-upper-arm and calf circumferences are useful predictors of underweight in women of reproductive age in northern vietnam”, food and nutrition bulletin, vol. 35, no. 3, pp. 301-311, 2014 [17] t. khadivzadeh, “mid upper arm and calf circumferences as indicators of nutritional status in women of reproductive age”, eastern mediterranean health journal, vol. 8, no. 4-5, pp. 612-618, 2002 [18] r. chakraborty, k. bose, s. koziel, “use of mid-upper arm circumference in determining undernutrition and illness in rural adult oraon men of gumla district, jharkhand, india”, rural remote health, vol. 11, no. 3, article id 1754, 2011 [19] v. a. leandro-merhi, j. luiz braga de aquino, j. gonzaga teixeira de camargo, “agreement between body mass index, calf circumference, arm circumference, habitual energy intake and the mna in hospitalized elderly”, journal of nutrition health and aging, vol. 16, no. 2, pp. 128132, 2012 [20] j. m. bland, d. g. altman, “statistical methods for assessing agreement between two methods of clinical measurement”, lancet, vol. 1, no. 8476, pp. 307-310, 1986 [21] d. giavarina, “understanding bland altman analysis”, biochemia medica, vol. 25, no. 2, pp. 141-151, 2015 microsoft word 23-2158_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3427-3431 3427 www.etasr.com laaziri et al.: development of the intelligent tutoring system for the use of university … outlining an intelligent tutoring system for a university cooperation information system majida laaziri information system engineering research group, national school of applied sciences, abdelmalek essaadi university, tetouan, morocco khaoula benmoussa information system engineering research group, national school of applied sciences, abdelmalek essaadi university, tetouan, morocco samira khoulji information system engineering research group, national school of applied sciences, abdelmalek essaadi university, tetouan, morocco kerkeb mohamed larbi information system engineering research group, faculty of sciences abdelmalek essaadi university, tetouan, morocco abstract—international opening of universities and research institutions is essential in the development of their research and innovation activities. abdelmalek essaadi university (aeu) attaches crucial importance to partnership and international cooperation, and actively participates in national and international cooperation and exchange programs. in order to manage the monitoring and evaluation of its cooperation activities as it evolves, the university has set up a system of information on the governance of university cooperation for proper management and managing better partnerships. when setting up a new information system, end-user training in this new management tool is a very important part of this process. for this reason, the university has adopted the idea of developing an intelligent tutoring system. this system will be based on the moodle platform and will be fully automated and adaptable to the needs of each learner. this article presents the basic design of the intelligent tutoring system incorporated in the management information system of university cooperation simacoop of our university and shows the feasibility of the intelligent tutoring system around an information system. keywords-information system; learning process; intelligent tutoring system; simacoop; moodle i. introduction computer science has played an important role in spreading and sharing knowledge. information and communication technologies (icts) have greatly promoted the dissemination and sharing of knowledge and expertise [2, 3], and improved our ways of informing and communicating. this technological emergence has revealed a new way of learning known as elearning. it is based on access to online, interactive and sometimes personalized training that develops skills, while making the learning process independent of time and place [4]. since the beginning of e-learning, artificial intelligence techniques have been tested to increase the learning experience, and have led to the emergence of a new field known as intelligent tutoring systems (itss) which refers to the concepts and methods of artificial intelligence and cognitive psychology. an its consists of making an artificial tutor available to learner [5], and aims to provide immediate and personalized instructions and feedback [6]. the main agents targeted by most of these systems are students. aeu has many information systems designed and implemented to improve the management practices within the university. among these systems, a new information system is recently set up for the management of the university cooperation [1]. it is important to mobilize human and financial resources on the technical aspects of a new information system, however, the university must also integrate the goal of effective and efficient use of this new application. for this reason, the need to develop an intelligent learning system dedicated to its teachers and administrative staff emerged. this learning system is to facilitate the use of the new information system, and at the same time reduce administrative costs and save time. the current paper describes the latest part of previous work published in [7-8]. ii. aeu: a brief insight abdelmalek essaadi university (aeu) occupies an important place in the educational scene in morocco, it has exceptional potential, and is open to global exchanges [9]. it offers a wide range of accredited training in many disciplines and at all levels. the training is essentially organized according to the lmd (license master doctorate) teaching architecture of higher education and is organized in four areas: science and technology, humanities and social sciences, law, economics and management, and medical and pharmaceutical sciences. it brings together, in addition to the presidency, eight faculties and five schools, more than 197 branches, and includes more than 954 research professors, 539 administrative and technical staff and more than 86000 students [10]. in addition, despite its young age, aeu has developed an interesting and promising research potential. research at the aeu is now structured within 5 doctoral studies centers, 21 laboratories, 12 groups and 42 research teams accredited by the university council (uc). international activity has been defined in the university's development strategy as a priority axis. currently, aeu has more than one hundred collaboration agreements with universities in europe, america, asia and the arab world. in this context, a significant mobility of research, administrative engineering, technology & applied science research vol. 8, no. 5, 2018, 3427-3431 3428 www.etasr.com laaziri et al.: development of the intelligent tutoring system for the use of university … staff, students and teachers has been triggered in both directions, in the context of both research projects and cooperation programs. a large number of students, especially sub-saharan students, undertake, under cooperation agreements, their higher education in different institutions. all this predisposes the university to play an important role internationally [11]. like all universities, in the context of modernization, aeu has many information systems. the utility of these information systems is that all university members (teachers-researchers, administrative staff, students) and its partners have the information they need analogous to their user status. iii. governance information system of university cooperation strengthening trust and exchange among all its partners is one of the goals of aeu, which gave cooperation an exceptional potential. it is based in particular on national and international partnerships aimed at supporting the development and quality of higher education and research system, in particular the scientific and engineering courses sought by the socio-economic community. currently, aeu has more than one hundred collaboration agreements with other universities. each year the university responds to several calls for international cooperation projects, actively participates in exchange programs, which allow it to develop its training offer, increase student mobility abroad, increase the number of scholarship recipients and to intensify the framework agreements. university cooperation requires effective management in order to monitor and coordinate the various activities of this cooperation and to ensure the continuity of constructive and productive relations. it is for this reason that an information system in the university has become a compulsory condition for a good steering of the cooperation and the management of better partnerships, and to establish a solid policy for the development of the institutional relation. in order to achieve this goal the university has set up the simacoop information system for the management of university cooperation [1, 7-8, 12]. this system has been deployed for the following reasons: • difficulties in identifying cooperative activities carried out by teachers individually, institutions independently and the presidency. • difficulties to follow cooperation agreements in time and their results. • difficulties in making a personalized follow-up of foreign students. simacoop is a monitoring system that supports governments and universities cooperation plans. it facilitates the partnership management process signed between the university and its various partners, tracks the implementation of the partnership and the extent to which each party is meeting its obligations and commitments and respecting agreements and memoranda of understanding to partner missions and their strategic objectives. its scope is to improve communication, collaboration and integration between universities and their partners. simacoop is a coherent information system centered in a global platform that generally integrates three main aspects of university cooperation governance connected to a university database [1]: • the management of university cooperation projects, including partners, activities, budget and expenses. • the management of agreements and conventions (including signatories of agreements, actions and budget). • personalized monitoring of foreign students. this system is dedicated mainly to project managers, administrators of institutions and universities, and contains tabs that manage: • information on cooperation projects, partners contributing to the project, activities, budget and project expenses. • information on agreements and conventions signed by the university. • information about foreign students, who benefit from cooperation agreements. it is enriched with a warning system, which informs the project managers and the administrative personnel of the dates of the activities, the imminent ones, those which present a delay of realization, the convention dates, and non-renewable agreements. after the deployment of simacoop, aeu organized training tours within the university's institutions and meetings to train teachers and administrative staff in the use of simacoop and how to take advantage of its features. but despite the university's efforts to have its staff adapt to the system, some of them had difficulties and problems accessing the system services, and their training was not sufficient, even if the system integrates an intuitive and user-friendly interface. for this reason, the university has thought to develop an intelligent tutoring system for the personnel training on the operation of the system. iv. intelligent tutoring system a. generalities in classroom, the course is the same for everyone, there is no individualization. teachers guide learners and need to perceive their needs in order to improve teaching. however, in group tutoring environments, the one-to-one time spent by teachers on each learner decreases considerably. for this reason, some learners prefer the use of a tutoring learning system with which they can learn at their own pace [12]. recently, the use of information and communication technologies in education has increased considerably. icts are considered a synonym for modernization, especially in the field of university teaching-learning since they provide advanced and up-to-date technological tools and applications. the ict adoption strengthens the teaching process, facilitates and improves the effectiveness of learning, research and scholarly communication, promotes knowledge building and ensures that the learner becomes cognitively active and takes cognitive action in developing his skills. the rapid advancement of information technology has provided new learning methods, environments and innovative ways not only for the engineering, technology & applied science research vol. 8, no. 5, 2018, 3427-3431 3429 www.etasr.com laaziri et al.: development of the intelligent tutoring system for the use of university … dissemination of knowledge but also for the exploration of learning strategies that foster the building of skills [14]. icts have the power to complement, enrich and positively transform learning and teaching process, fill learning gaps, improve quality and relevance of learning, enhance inclusion and improve learning, administration and governance while they facilitate administrative transactions [3, 15-16]. with the emergence of icts, a new training approach, or more precisely a new way of learning, has emerged called e-learning. elearning enhances the quality of training as an advanced learning process in which learners acquire new skills or knowledge through information and communication technologies [17-18]. it is intended to help the acquisition of personalized knowledge adapted to the speed and pace of progression of the individual learner. the range of existing elearning applications includes [4]: • price management systems, a field mostly covered by industrial products. • intelligent tutorial systems, adaptive hypermedia, a highly oriented research area. • collaborative tools used for learning, videoconferencing, etc. • digital exams, online quizzes, etc. among these teaching processes, there is a tutoring system that helps learners in their progression adapted to their current level of knowledge, called a system of intelligent tutorials, which uses techniques derived from artificial intelligence based on the theory of learning and cognition to assist the learner in solving a problem, analyzing responses and cognitive diagnoses. the intelligent tutoring system (its) is a very useful tool to support and enhance learning process, it is designed to simulate the behavior and advice of a human tutor in order to emulate an artificial tutor [5, 19]. this tutor should be able to solve the same problems as those posed to the learner. he could thus follow the reasoning of the learner and understand his mistakes. this artificial tutor provides immediate and personalized instructions and comments. the goal of the its is to enable a learner to learn by his own. in general, it alternates between the phases in which the learner conducts the exercise and the tutor validates the actions, and the phases in which the tutor performs the tasks and explains them to the learner [20]. its interacts directly with students and performs many pedagogical functions usually reserved for teachers or tutors while providing access to high quality education for each learner. any its usually includes a “domain model” that knows what to teach, “a pedagogical model” that knows how to teach, “a learner model” that can personalize learning with respect to it, and “a model of the interface”, i.e. the visible means allowing the interrelation between the learner and the system [12, 21-22] (figure 1). in any its, the assessment of learner acquisition of knowledge is a primary task, this assessment is necessary to adapt learning materials and activities to learners' abilities [13, 23]. knowledge assessment is a systematic process of collecting, analyzing and interpreting data. to evaluate the acquisition of knowledge, different techniques can be used by the system, such as tests or exercises, questions, etc. fig. 1. classic conceptual architecture of an its b. its development our main goal is to design an its that meets the needs of the university's faculty and administrative staff and provides an advanced learning environment, adapted to their current level of knowledge. its purpose is to provide instant, personalized instructions and comments without the intervention of a human tutor. the formation process of our system consists of five different tasks [24]: • objective choosing. • realization of the learner characteristics. • realization and use of ideas on learning and motivational learning. • choosing and using the means to learn (methods and techniques). • evaluate the learning achievements of the learner. within the university there are three types of users who can access the simacoop information system: project managers, research professors, and administrative staff. their missions are differentiated in the information system, and the use of the latter does not represent the same difficulties for them. each user has a defined role in the simacoop information system, associated with a usage profile in the system representing all the functionalities that the user can access. this profile determination plays an important role in the design of our its in order to specify the training to which the user/learner will have to participate. the its will have a resource base that includes all training elements according to the profile of the enrolled users. each of these users is subjected to a set of controls during the registration in order to know their preliminary achievements and present them the attributes of their profile. this tutoring system will guide them in training according to their individual achievements and objectives, and will present the skills that the learner will have acquired after a training action. the system will be divided into different modules based on the classical modules of an its indicated above. these modules are at the same time independent and linked in input and output allowing their separate evolution. the system will be able to model learners' profiles using an “enrollment and evaluation” module that will evaluate the learner's knowledge and will update his profile. to learn about the level of the learner, the system will offer the learner some tests to pass. these tests will in fact be added by the expert (expert model), and attached to the resources to allow the engineering, technology & applied science research vol. 8, no. 5, 2018, 3427-3431 3430 www.etasr.com laaziri et al.: development of the intelligent tutoring system for the use of university … follow-up of the learning and the update of the profile (figure 2). fig. 2. steps followed for profile modeling c. implementation tool at present, there is a vast choice of e-learning development solutions that allow easy communication of information and interoperability of applications. the choice of a platform to develop our solution is motivated by problems of maximum adaptability to our needs and criteria. moodle meets our needs perfectly, enjoys a good reputation and many successful implementations in the education field. the determining factors in its favor are: its ease of use, it is free and, especially, its possibility of developing and integrating new tools through its open source license. moodle is an abbreviation for “modular object-oriented dynamic learning environment”. it is an online learning platform, an lms (learning management system), freely licensed to create communities, and educate around content and educational activities. in a content management system, moodle adds a few pedagogical and communicative functions creating an online learning environment: this application makes it possible to create, via network, interactions between pedagogues, learners and teaching resources [25-27]. moodle has a very broad community of users, it is scalable, robust, stable and interoperable, and there are no problems with the content portability. it is characterized by [28]: • user-friendly interface for all user types. • several languages can be used simultaneously in the various courses of the same platform. • filters make it easy to use media files within moodle pages. • detailed usage reports for each learner help supervising learning efforts. • moodle facilitates the dynamic management of a course with a calendar. each course is a portal composed of blocks that the tutor can display as he wishes, avoiding information overload. • it has many features shared with other online training platforms: forums, resource manager, tests and nine turnkey modules. it also includes a module for creating tests. the questions created with this module can be shared and reused in different test contexts. • it is very flexible, it was designed from the beginning in a modular way that makes it possible to meet the needs of an isolated trainer as an academic institution. all these features of moodle favor developing a fully automated and adaptable teaching system for the use of simacoop information system, which will give this system the main features of an its. it will communicate through the moodle platform with three main user types who have the right to access the system to perform various actions: • an administrator who manages the use of the system and its database. • a learner who follows the training through the system. • a teacher who accesses the system for consultation and adds educational resources to the database. v. conclusion the information systems in the university have become indispensable, helping the university staff (administrative staff, teachers and students) in their activities and in the accomplishment of their missions. in the implementation of an information system, a multidimensional vision must be apprehended. in this article, we have emphasized the place of the learning dimension within the university, and more specifically the feasibility of a system of intelligent tutoring around the information system. this learning is instrumented by the use of ict and artificial intelligence concepts, and taking it into account from the design phase of the information system would better integrate the learning object. the introduction of new learning technologies such as itss for university staff around their daily management tools is a real challenge today. acknowledgment this research was supported by the information system engineering research group. references [1] m. laaziri, k. benmoussa, s. khoulji, k. m. larbi, “simacoop: a framework application for the governance of university cooperation”, transactions on machine learning and artificial intelligence, vol. 5, no. 4, pp. 785-794, 2017 [2] m. gaha, realisation d’un agent tuteur intelligent conscient, msc thesis, universite du quebec a montreal, 2008 (in french) [3] w. j. pelgrum, n. law, ict in education around the world: trends, problems and prospects, unesco, international institute for educational planning, 2003 [4] s. azough, e-learning adaptatif: gestion intelligente des ressources pédagogiques et adaptation de la formation au profil de l’apprenant, phd thesis, universite mohammed v rabat (in french) [5] b. de lievre, c. depover, p. dillenbourg, “quelle place accorder au tuteur systeme et au tuteur humain dans un processus d’industrialisation?”, distances et savoirs, vol. 3, no. 2, pp. 157-181, 2005 (in french) [6] r. juarez-ramirez, r. navarro-almanza, y. gomez-tagle, g. licea, c. huertas, g. quinto, “orchestrating an adaptive intelligent tutoring system: towards integrating the user profile for learning improvement”, procedia – social and behavioral sciences, vol. 106, pp. 1986-1999, 2013 [7] k. benmoussa, s. khoulji, m. laaziri, k. m. larbi, “web information system for the governance of university research”, engineering, technology & applied science research, vol. 8, no. 4, pp. 3287-3293, 2018 [8] m. laaziri, s. khoulji, k. benmoussa, k. m. larbi, “information system for the governance of university cooperation”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3355-3359, 2018 engineering, technology & applied science research vol. 8, no. 5, 2018, 3427-3431 3431 www.etasr.com laaziri et al.: development of the intelligent tutoring system for the use of university … [9] presentation de l’universite abdelmalek essaadi, available at: http://www.ensat.ac.ma/guide/02presentationuae.htm (in french) [10] universite abdelmalek essaadi, available at: http://uae.ma/ website/index.php (in french) [11] abdelmalek essaadi university, projet de developpement 2015-2018, 2015 (in french) [12] simacoop, available at: http://simacoop.uae.ac.ma/ [13] a. ramirez-noriega, r. juarez-ramirez, y. martinez-ramirez, “evaluation module based on bayesian networks to intelligent tutoring systems”, international journal of information management, vol. 37, no. 1a, pp. 1488-1498, 2017 [14] n. perreault, “role et impact des tic sur l’enseignement et l’apprentissage au collegial – i”, pedagogie ccollegiale, vol. 16, no. 3, pp. 3-10, 2003 (in french) [15] m. v. tikam, “impact of ict on education”, international journal of information communication technologies and human development, vol. 5, no. 4, pp. 1-9, 2013 [16] a. pani, realisation d'un prototype de didacticiel d'apprentissage de la notion d' amortissement enclasse de premiere g2, university of yaounde i, bsc thesis, eecole normale superieure de yaounde, 2009 (in french) [17] m. baklouti, e-learning : presentation, aspects, enjeux et avenir, msc thesis, university of sfax, 2002 (in french) [18] g. b. nganmini-asatsop, la mesure de la qualite percue d’un dispositif de e-learning, phd thesis, université nancy 2, 2009 (in french) [19] m. bessagnet, m. f. canut, “sur la conception de tuteurs intelligents ...”, le bulletin de l’epi, vol. 56, pp. 95-110, 1989 (in french) [20] m. beggas, modelisation par un systeme multi-agents d’un hypermedia educatif adaptatif dynamique, msc thesis, centre universitaire d'eloued, 2005 (in french) [21] s. petrovica, m. pudane, “simulation of affective student-tutor interaction for affective tutoring systems : design of knowledge structure 2 related work”, international journal of education and learning systems, vol. 1, pp. 99-108, 2016 [22] edutech wiki, “systeme tutoriel intelligent”, available at: https://edutechwiki.unige.ch/fr/système_tutoriel_intelligent (in french) [23] h. n. m. ferreira, t. brant-ribeiro, r. d. araujo, f. a. dorca, r. g. cattelan, “an automatic and dynamic knowledge assessment module for adaptive educational systems”, ieee 17th international conference on advanced learning technologies, timisoara, romania, july 3-7, 2017 [24] j. dabolins, j. grundspenkis, “the role of feedback in intelligent tutoring system”, applied computer systems, vol. 14, no. 1, pp. 8893, 2013 [25] moodle, “moodledocs”, available at: https://docs.moodle.org/34/en/ main_page [26] “moodle : plate-forme d'apprentissage en ligne”, available at: http://eole.ac-dijon.fr/documentations/2.4/partielles/html/applications web/co/moodle-base.html (in french) [27] b. benyounes, evaluation de la fonctionnalite et l’utilisabilite de la plateforme d’apprentissage moodle : une approche du genie logiciel, msc thesis, universite du quebec a montreal, 2009 (in french) [28] multi acces formation, “moodle: la plateforme d’apprentissage en ligne moodle”, available at https://multiacces.com/fr/multiacceslms/ pourquoi-moodle (in french) microsoft word 27-2764_s_etasr_v9_n3_pp4213-4217 engineering, technology & applied science research vol. 9, no. 3, 2019, 4213-4217 4213 www.etasr.com buller et al.: 24-hour fire produced effect on reinforced recycled aggregates concrete beams 24-hour fire produced effect on reinforced recycled aggregates concrete beams abdul hafeez buller department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan ah.buller@quest.edu.pk bashir ahmed memon department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan bashir_m@hotmail.com mahboob oad department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan engrmahbooboad04@gmail.com samiullah sohu department of civil engineering, quaid-e-awam university of engineering science & technology, campus larkana, pakistan sohoosamiullah@gmail.com abstract—in this article, the effect of prolonged fire (24-hour duration) on reinforced concrete beams made with recycled aggregates from demolished concrete was experimentally investigated. demolished concrete was used recycled coarse aggregates in equal proportion with natural coarse aggregates. normal and rich mix concrete with water-cement ratio equal to 0.54 were used. as a control specimen, beams with all-natural aggregates were also cast to compare with the results of the proposed beams. all beams were cured for 28 days and exposed to fire at 1000°c in an oven for 24 hours. after the elapse of this fire period, the beams were allowed to air cool, followed by testing till failure in a universal load testing machine. comparison of the test results shows that rich mix concrete beams more reduction in flexural strength, more increase in maximum load carrying capacity and deflection than normal mix beams. the maximum reduction in flexural strength was 32.41% for beams cast with 50% rca and rich mix. although the fire duration used in this study is rare, yet the outcome provides guidelines for taking proper decisions for retrofitting/strengthening of the fire affected structure before putting it back in service. keywords-green concrete; fire effect; flexural behavior; demolished waste; recyclable aggregates i. introduction green concrete, particularly the concrete produced by using demolished concrete as aggregates has a wide acceptance among researchers and the construction industry, because it is environment friendly, reduces environmental hazards, reduces waste management issues by its on-site consummation in new concrete, and it is less costly. however, its properties and behavior to various effects should be well understood to develop good confidence level on the material, which in turn will lead to assurance of strength and durability during the service life of the structure. fire is among several hazards, natural or accidental, which a structure may meet. fire not only affects the appearance by damaging the cladding but due to thermal stresses and high temperature, affects strength. fire would affect the green concrete made with demolished concrete as aggregates. green concrete on the other hand is a relatively new material, thus its behavior should be studied particularly at elevated temperatures for longer duration to set the guidelines for industry and researchers. several researchers are actively engaged in evaluating the properties and behavior of green concrete made with demolishing waste [1-3]. author in [1] reviewed the recent developments regarding the use of demolishing waste in new concrete with respect to challenges, recycling and behavior of green concrete. authors in [2] reviewed the properties, strength parameters and property numerical equations of green concrete evaluated by several researchers among the available state-ofthe-art on the subject. authors in [3] also reviewed the state-ofthe-art, particularly with regard to the waste generated due to heavy floods in bh serbia. based on the available research about the material, they concluded that waste can be used to produce conventional and even high-quality concrete subjected to the properties of aggregates from waste. compressive strength of concrete with demolished concrete as coarse aggregates in different dosages has been studied in [4]. from the experimental results, the authors found that 50% replacement of natural aggregates is the optimum dosage. with this replacement the reduction in strength is minimum. the flexural behavior of reinforced recycled aggregate concrete beams was studied with the use of normal and rich mixes in [5] and [6] respectively. based on the laboratory findings, the authors observed that the flexural behavior of green concrete beams is in good agreement with the conventional concrete beams. also, they observed that the deflection in the proposed beams remained within the allowable limits of approximate deflection given by aci-318. towards the evaluation of effect of fire on green concrete, several attempts have been made using different temperatures and fire durations. green concrete cubes made with demolished corresponding author: abdul hafeez buller engineering, technology & applied science research vol. 9, no. 3, 2019, 4213-4217 4214 www.etasr.com buller et al.: 24-hour fire produced effect on reinforced recycled aggregates concrete beams concrete as coarse aggregates have been used in [7] to check the effect of 1000°c for 6h. the authors used different dosages of recyclable aggregates. the compressive strength test results of these fire exposed cubes revealed that with 50% replacement the reduction in compressive strength is minimum. the compressive strength of recycled concrete exposed to 500°c temperature for 1h has been investigated in [8]. however, the authors used 75% replacement of natural coarse aggregates and compared the results with conventional concrete made with different water-cement ratios. based on the test results by ultrasonic and resonance frequency test, the authors observed that the proposed concrete at the above mentioned temperature and duration performs well in comparison with the conventional concrete of low water-cement ratio. the compressive strength of concrete cubes made with 0% to 100% (with increment of 25%) recycled aggregates and heated in electronic oven at 50°c, 100°c, 200°c, 300°c, and 400°c for 8h has also been studied in [11]. the tests’ results showed 38% average reduction in strength for all replacements when heated up to 200°c and 45% residual strength when heated from 300°c to 400°c. in a similar study, but with different natural aggregate replacement percentages from 0% to 50% [15], specimens were heated from 200°c to 800°c. from the test results, the authors concluded that the performance of the recycled aggregate concrete was comparable with the one of conventional concrete. author in [9] used 50% and 100% replacement of natural coarse aggregates with recyclable aggregates to produce green concrete. the specimens were heated to 600°c and 800°c. after heating, the specimens were checked for strength and modulus of elasticity. the authors observed 10% increase in compressive strength of green concrete with 50% rca and 50% reduction to 100% replacement of natural coarse aggregates. however, they reported no influence of elevated temperature and natural coarse aggregates replacement percentage on the elastic modulus. the authors further reported a strong correlation between the elastic modulus and the square root of compressive strength. authors in [10][10] checked the mechanical properties of 204 concrete cylinders made with recycled concrete aggregates, river gravel and limestone aggregates. the authors used different dosages of the aggregates and heated the cylinders at 20°c, 250°c, 500°c and 750°c. from the test results of compressive and tensile strength, elastic modulus, damage and cracking, they found the proposed concrete to have good performance. also, they argued that even at the temperature of 750°c, the proposed concrete did not exhibit any disintegration of the ingredients. in addition to the above, the behavior of fiber reinforced recycled aggregate concrete [12] and geopolymer coated aggregate concrete [13] have been studied. a constitutive theory for recycled aggregate concrete subject to elevated temperatures has been presented in [14]. it may be noted, that a good number of research findings has been published about the properties of recycled aggregate concrete, yet little work is available regarding the effect of high temperatures on recycled aggregate concrete, particularly the effect of longer fire duration (24h). this motivated the work presented in this study. it combines the use of recyclable aggregates from demolished concrete and the effect of a 24h fire on reinforced concrete beams. it is anticipated that the outcome of the work will set suitable guidelines for the researchers in understanding the behavior of recycled concrete exposed to longer fire durations. ii. materials and testing for recycled aggregates, old demolished concrete of an about 50-year old school building was obtained in the shape of large blocks. the large pieces were manually reduced to size approximately equal to 20mm. to ensure well graded aggregates in concrete mix, gradation of both recycled and natural aggregates was done in accordance to astm standards. the obtained results are shown in tables i (recycled aggregates) and ii (natural aggregates). both sets are plotted in figure 1. additionally, abrasion test on both types of aggregates was also performed as per the procedure given by astm c131-89. the los angeles abrasion value for natural aggregates was recorded equal to 18.3% and 26.7% for recycled aggregates. the recycled aggregates exhibited 8.4% more abrasion than natural aggregates. this is mainly due to the old mortar attached with the recycled aggregates. attempt has been made to separate the mortar powder and pieces, then the abrasion of recycled aggregates was recorded 5.7% more than the one of natural aggregates. the dosage of recycled aggregates used was 50%. the selection of this dosage is based on the conclusions of [4]. table i. grad ation of recacled coarse aggragates # sieve (mm) weight retained (g) cumulative wt. ret. (g) retained (%) passing (%) 1 31.5 0.00 0.00 0.00 100.00 2 25 95.00 95.00 4.48 95.52 3 19 978.00 1073.00 50.61 49.39 4 12.5 742.00 1815.00 85.61 14.39 5 9.5 262.00 2077.00 97.97 2.03 6 4.75 31.00 2108.00 99.43 0.57 7 2.36 7.00 2115.00 99.76 0.24 8 pan 5.00 2120.00 100.00 0.00 table ii. gradation of natural coarse aggregates # sieve (mm) weight retained (g) cumulative wt. ret. (g) retained (%) passing (%) 1 31.50 0.00 0.00 0.00 100.00 2 25.00 55.00 55.00 2.49 97.51 3 19.00 945.00 1000.00 45.25 54.75 4 12.50 680.00 1680.00 76.02 23.98 5 9.50 487.00 2167.00 98.05 1.95 6 4.75 37.00 2204.00 99.73 0.27 7 2.36 0.00 2204.00 99.73 0.27 8 pan 6.00 2210.00 100.00 0.00 to reinforce the beams, 4#4 steel bars were used with two bars in tension and compression zones. to ensure the shear capacity of the beams, #3 ties at 150mm center-to-center were used throughout the length of the beam (figure 2). the size of all beams was kept the same. a total of 24 beams were cast for the purpose. the details of the beams with respect to curing age, concrete mix and dosage of recycled aggregates are given in table iii. after casting the reinforced concrete beams in standard fashion and water curing for 28 days, all the beams were exposed to fire for 24h in an oven made for the purpose. the source of fire was wood and it took almost 1.5h to reach 1000°c, and then the temperature was maintained. during the engineering, technology & applied science research vol. 9, no. 3, 2019, 4213-4217 4215 www.etasr.com buller et al.: 24-hour fire produced effect on reinforced recycled aggregates concrete beams process of heating the temperature was regularly monitored using a digital thermometer (figure 3). after the elapse of 24h the source of fire was cutoff and the beams were left in the oven for a day to avoid sudden attack of atmospheric moisture. then, the beams were tested until failure under central point load (figure 4) as per the recommendations of astm c293 [17]. fig. 1. gradation of ra and na fig. 2. model dimensions fig. 3. temperature monitoring fig. 4. beam mounted on the utm table iii. specimen details mix rca % no of beams w/c ratio curing (days) 1:2:4 50 6 0.54 28 0 6 0.54 28 1:1.5:3 50 6 0.54 28 0 6 0.54 28 during the load testing, deflection and cracking were monitored. at failure crack, the pattern was recorded and the flexural strength of the beams was computed using a numerical formula given by the above mentioned astm standard. iii. results and discussion the maximum load attained by the reinforced concrete beams is plotted in figure 5. average peak load, average deflection, and average flexural strength exhibited by the six beams of the group are given in table iv. from this table it may be observed that reinforced concrete beams cast with allnatural aggregates and normal mix showed less maximum load than the beams of the other groups. considering the maximum load of these beams as control value, the rc beams cast with normal mix and 50% rca exhibited 23.57% reduction. in contrast to normal mix, rich mix beams cast with all-natural aggregates showed 5.67% reduction in average peak load, while 32.41% reduction in average peak load was recorded for the beams cast with rich mix and 50% recycled aggregates. after fire exposure for 24h, beams showed reduced maximum load. the rich mix beams of both natural and recycled aggregates exhibited reduction in load in comparison to normal mix beams. even the rich mix concrete beams cast with recycled aggregates showed 3.34kn less maximum load when compared to normal mix beams with the same percentage of recycled aggregates. therefore, more attention should be given to fire exposed (particularly prolonged fire) structural members cast in rich mix. fig. 5. maximum load figure 6 shows the graphical comparison of the maximum deflection observed by all beams in each group. in this figure, the increasing trend of deflection may be observed. the maximum deflection is observed in beams cast with 50% rca and rich mix and is equal to 12.2mm. the value in comparison to aci-318 maximum allowable deflection is about 2.5 times larger. observation of average values of the deflection shows that normal mix rc beams cast with all-natural aggregates due to exposure to fire showed 9.66mm deflection. this is double engineering, technology & applied science research vol. 9, no. 3, 2019, 4213-4217 4216 www.etasr.com buller et al.: 24-hour fire produced effect on reinforced recycled aggregates concrete beams than the aci-318 allowable values. considering it as base value, rc beams cast with 50% rca and normal mix exhibited 9.92% more deflection. 8.02% and 20.10% increase in deflection was also recorded for rich mix beams cast with 0% and 50% rca. the load-deflection pattern for normal and rich mix beams are shown in figures 7 and 8 respectively. it may be observed that the trend of load-deflection is the same for all beams except the peak values of the parameters. fig. 6. maximum deflection fig. 7. load vs deflection of normal mix beams fig. 8. load vs deflection of rich mix beams table iv. parameter av arage v alues mix rca (%) load def fs 1:2:4 0 37.80 9.66 15.12 1:2:4 50 28.89 10.62 11.56 1:1.5:3 0 35.66 10.43 12.89 1:1.5:3 50 25.55 11.60 10.22 the average values of the computed flexural strength are given in table iv. considering 0% rca, normal mix reinforced concrete beams as control specimen, the average flexural strength attained by rich mix concrete beams of 0% and 50% dosage of rca is shown in figure 9. like the reduction in peak load, the reduction in flexural strength is recorded with maximum reduction equal to 32.41% in rich mix beams with 50% dosage. it is 20.73% smaller than its counterpart with all-natural aggregates. fig. 9. average flexural strength (rich mix vs normal mix) due to the long fire exposure and cooling process, several hair line cracks appeared on the surface of the beams which made difficult the monitoring of the first crack during testing. therefore, the crack pattern after failure was recorded. the observations show shear cracks in most of the specimens with few beams showing both flexural and shears cracks. shear cracks were dominant in all beams. therefore, the failure mode of the beams is considered as shear failure. iv. conclusion based on the experimental observations of the reinforced concrete beams exposed to 24-hour fire at 1000°c, the following observations are made. • normal mix reinforced concrete beams exhibited more residual strength than rich mix reinforced concrete beams. • due to fire exposure, beams exhibited reduction in maximum load carrying capacity. • addition of recycled aggregates added more reduction of maximum load carrying capacity. • increasing trend of deflection is recorded in all beams. • load-deflection behavior of all beams is similar, except peak values. engineering, technology & applied science research vol. 9, no. 3, 2019, 4213-4217 4217 www.etasr.com buller et al.: 24-hour fire produced effect on reinforced recycled aggregates concrete beams • maximum of 32.41% reduction in flexural strength of rich mix reinforced concrete beams cast with 50% dosage of recyclable aggregates is recorded in comparison to beams cast will all-natural aggregates and normal mix. • shear failure in all beams was observed. although 24-hour fire is a rare occasion, yet the proposed beams showed minimum of about 68% residual strength. therefore, the performance of the beams is comparable with conventional concrete’s. hence, the outcome of this research provides experimental information and sets guidelines regarding the effect of prolonged fire on green concrete made with demolished concrete as coarse aggregates. references [1] b. a. memon, “recent development on use of demolished concrete as coarse aggregates”, international journal of emerging technology and innovative engineering, vol. 2, no. 1, pp. 1–11, 2016 [2] b. g. fonteboa, s. seara-paz, j. d. brito, i. g. taboada, f. m. abella, r. v. silva, “recycled concrete with coarse recycled aggregates. an overview and analysis”, materiales de construccion, vol. 68, no. 330, 2018 [3] m. malesev, v. radonjanin, g. broceta, “properties of recycled aggregate concrete”, contemporary materials, vol. 2, pp. 239-249, 2014 [4] m. oad, b. a. memon, “compressive strength of concrete cylinders using coarse aggregates from old concrete”, 1st national conference on civil engineering, modern trends and advancements, pakistan, april 28–29, 2014 [5] m. oad, a. h. buller, b. a. memon, n. a. memon, “flexural stressstrain behavior of rc beams made with partial replacement of coarse aggregates with coarse aggregates from old concrete: part-1: 1:2:4 ratio”, engineering technology and applied science research, vol. 8, no. 3, pp. 3048-3053, 2018 [6] m. oad, a. h. buller, b. a. memon, n. a. memon, s. sohu, “flexural stress-strain behavior of rc beams made with partial replacement of coarse aggregates with recyclable concrete aggregate: part-2: rich mix”, engineering technology and applied science research, vol. 8, no. 5, pp. 3338-3343, 2018 [7] a. h. buller, b. a. memon, “effect of fire on strength of concrete cubes with rca as coarse aggregates”, 1st national conference on civil engineering-modern trends and advancements, pakistan, april 28–29, 2014 [8] c. j. zega, a. a. di maio, “recycled concrete exposed to high temperatures”, magazine of concrete research, vol. 58, no. 10, pp. 675-682, 2006 [9] f. u. a. shaikh, “mechanical properties of concrete containing recycled coarse aggregate at and after exposure to elevated temperatures”, structural concrete, vol. 19, no. 2, pp. 400-410, 2018 [10] s. r. sarhat, e. g. sherwood, “residual mechanical response of recycled aggregate concrete after exposure to elevated temperatures”, journal of materials in civil engineering, vol. 25, no. 11, 2013 [11] i. adebakin, t. ipaye, “effect of elevated temperature on the compressive strength of recycled aggregate concrete”, journal of engineering sciences, vol. 5, no. 9, pp. 2278-9472, 2016 [12] g. m. chen, y. h. he, h. yang, j. f. chen, y. c. guo, “compressive behavior of steel fiber reinforced recycled aggregate concrete after exposure to elevated temperatures”, construction and building materials, vol. 71, pp. 1-15, 2014 [13] a. gupta, s. ghosh, s. mandal, “coated recycled aggregate concrete exposed to elevated temperature”, global journal of researches in engineering – civil and structural engineering, vol. 12, no. 3, 2012 [14] g. etse, s. m. vresh, m. ripani, “constitutive theory for recycled aggregate concretes subjected to high temperature”, construction and building materials, vol. 111, pp. 43-53, 2016 [15] g. gowda, b. s. rao, s. m. naik, “behavior of recycled aggregate concrete on exposed to elevated temperature”, international journal of civil engineering, vol. 4, no. 6, pp. 5-13, 2017 [16] astm, active standard astm c131/c131m: standard test method for resistance to degradation of small-size coarse aggregate by abrasion and impact in the los angeles machine, astm, 2008 [17] astm, active standard astm c293/c293m-16: standard test method for flexural strength of concrete (using simple beam with centerpoint loading), astm, 2008 [18] a. h. buller, m. oad, b. a. memon, “flexural strength of reinforced concrete rac beams exposed to 6-hour rire: part 2: rich mix”, engineering technology and applied science research, vol. 9, no. 1, pp. 3813-3816, 2019 microsoft word 22-3527_s_etasr_v10_n3_pp5706-5712 engineering, technology & applied science research vol. 10, no. 3, 2020, 5706-5712 5706 www.etasr.com lam et al.: mobile-based hospital bed management with near field communication technology mobile-based hospital bed management with near field communication technology a case study meng chun lam center for artificial intelligence technology (cait) faculty of information science and technology universiti kebangsaan malaysia bangi selangor, malaysia lammc@ukm.edu.my masri ayob center for artificial intelligence technology (cait) faculty of information science and technology universiti kebangsaan malaysia bangi selangor, malaysia masri@ukm.edu.my jun yang lee ifast fintech solutions kuala lumpur, malaysia junyang0822@gmail.com norizal abdullah center for artificial intelligence technology (cait) faculty of information science and technology universiti kebangsaan malaysia bangi selangor, malaysia norizal.abdullah23@gmail.com faizal amri hamzah department of emergency medicine hospital canselor tuanku muhriz ukm medical center kuala lumpur, malaysia vit_ron@yahoo.com siti sarah mohd zahir department of emergency medicine hospital canselor tuanku muhriz ukm medical center kuala lumpur, malaysia sarahirissa821@gmail.com abstract—bed management is one of the most crucial tasks in a hospital. a desktop-based (pc) information technology system has been widely adopted to assist this operation. the fixed location and the limited amount of available pcs shared among staff for different routine tasks can cause delays in bed information updating and therefore delays to the bed management processes. with the penetration of smartphones, a mobile-based application becomes a reliable alternative solution for bed management to complement the existing system. smartphones offer a few benefits, especially mobility because users can update the information from any place and at any time. our aim was to study the applicability of a mobile-based application for assisting bed management operation. the application consisted of ward-based bed information visualization, bed information updating, and ward information updating modules. observation and interviews with expert users were performed to outline the required functions of the application. on a likert 1-5 scale, the mobile application achieved a mean score of 3.45 for usefulness, 3.40 for ease of use, and 3.42 for satisfaction. meanwhile, the respondents were also concerned about the mobile data consumption of the app, which took up 45.8% of the negative feedback. on the positive side, the respondents agree that the mobile application helps them in the bed management operation. keywords-bed management; mobile application; usability study; hospital management i. introduction the increase of human population density put pressure on hospitals in providing adequate services to accommodate patients. one of the most important facilities in a hospital is the number of available hospital beds. limited or problematic bed capacity can cause overcrowded situations in outpatient departments due to the prolonged waiting time of bed assignment to patients. the shortage of beds or inefficient bed management in hospitals is a common problem. some of the common factors that cause bed shortage or delays in the process of patient discharge are: family members being unable to accompany patients home upon discharge, patients waiting for family members to collect their medications and documents, and delays of information in the communication to the bed manager on the status of beds [1]. to overcome this issue, hospital canselor tuanku muhriz (hctm) improved the patient discharge process by introducing a discharge lounge. the patient who is in good condition is directed to the discharge lounge with the approval of a doctor. patients are waiting comfortably to be taken by their family members within the lounge facilities. hence, the bed in the ward will be corresponding author: meng chun lam engineering, technology & applied science research vol. 10, no. 3, 2020, 5706-5712 5707 www.etasr.com lam et al.: mobile-based hospital bed management with near field communication technology available for new patients. unfortunately, the process of updating the bed utilization status is often delayed due to the limited availability of personal computers (pcs) for the staff. the existing bed management system in hctm is a web-based system. the system is integrated with other common operations or modules including patient registration, admission, discharge, bills, medication, etc. the staff has to access the system via a pc, the fixed location and amount of available pcs limits the staff’s accessibility. hence, the staff members often need to queue for using the shared pcs which are utilized for various routine tasks. also, all the modules are web-based, and the user interface of the system is not designed for mobile view. therefore, it is not a mobile-friendly system because the user interface does not show and align probably in a smartphone. a potential solution is to enhance the bed management system to maximize resource utilization and avoid hospital overload. a bed management information system can be helpful [2]. it allows bed managers to make easier, faster, and more accurate decisions. the number of smartphone users is growing rapidly. with the advent of smartphone and internet technology, smartphonebased applications have been applied to areas such as banking [3], environmental monitoring [4], and healthcare services [5]. near field communication (nfc) is a wireless sensor technology available in a smartphone, using contactless shortrange communication devices. it consists of two main components: a tag that contains information and a reader-writer that is able to extract and put information from and to the tag [6]. nfc is a set of standards for smartphones and similar devices for creating radio communication when brought in proximity, normally no more than a few centimeters [7]. nfc is available on a smartphone where the reader is placed into the phone’s shell. the bed information can be embedded in the nfc tag and thus it allows instant information access when the equipped smartphone is in its proximity. this paper aims to identify the applicability of a smartphone-based mobile application with nfc technology to facilitate the bed management process at the hctm. the developed bed management mobile application (bmma) is a high-fidelity prototype that allows a non-technical person like a nurse or a doctor to instantly see the flow, user interface, and test the bed management mobile application. thus, users can judge how well it meets their expectations and facilitates their work. the contribution of this research is the bmma using the nfc approach and its evaluation. ii. background hospital bed availability is an important asset, especially for intensive care units (icus), coronary care units (ccus) or emergency departments. it is an essential hospital job to coordinate the allocation of patients over the unoccupied hospital beds [8]. a. mobile application in health care utilizing mobile applications for hospital management including the research to study the level of acceptance of mobile health applications [9] is an open research subject with many areas of interest [9-14]. even though the smartphone is a popular device, capable of performing technology-based tasks, its use might not be welcome in a hospital. authors in [9] confirmed that a mobile health application is generally accepted by the public to be integrated with the existing system of a hospital. their study suggested eight factors that need to be considered when implementing mobile applications which were hedonic motivation, performance, expectancy, social influence, effort expectancy, price value, habit, facilitating conditions, and behavior. to increase the effective and efficient care of the hospital, authors in [10] proposed a bringyour-own-device (byod) concept to allow hospital staff to use their own devices to access the hospital system. the byod guideline included role-based access control, apps to work on internal or virtual private networks, it required apps to use a minimal cache, and enforced automatic logoff to prevent data leakage. an example of a developed mobile application included mphasis [11]. it has been developed and utilized to monitor the vital signs of patients based on several sensors. it can notify medical personnel in case of emergencies, hence manually and frequently checking on the patient can be reduced. authors in [12] designed a smartphone program-based system to help doctors to track alzheimer's disease patients’ condition. the application alerts the patient when to consume medicine based on the schedule provided by the doctor. a mobile application for diabetes patients [13] can be seen as a personal health care system. it is a tool to record daily test results and track long term health condition changes. authors in [14] concentrated on mobile application design to deliver an efficient health care system. by using this app, users can find in-city hospital information, cabin data, make cabin booking payments, accept smart tips on selecting the right hospital, locate a physician, call for emergency services, receive information on first aid and notifications from the drug alarm system, calculate their body mass index (bmi), receive information on health care, data about support and drugs, prescription reminders, etc. such mobile applications will be an essential part of the next generation of ubiquitous and pervasive healthcare systems. this study aims to have an initial exploration of the feasibility of applying a smartphone-based mobile application for managing beds at hctm. b. current situation hctm, previously known as pusat perubatan universiti kebangsaan malaysia, is a hospital merged with the hospital of universiti kebangsaan malaysia and the faculty of medicine, universiti kebangsaan malaysia. in order to understand the situation and the operations of the hospital, a series of interviews and discussions with different members of the staff including nurses, doctors, and information technology officers were conducted. there are many clinical systems that have been designed for the hctm to ensure a smooth procedure flow for the hospital operations. one of the known modules is the bed management system. it is used to view and update the status of beds in wards. the system allows the hospital staff to view the availability of a bed in a ward and handle the admission and the discharge process of a patient. after a few discussions and meetings with the information technology officer and the end-users (nurses), it was realized that the running functions fulfilled the requirements of the daily engineering, technology & applied science research vol. 10, no. 3, 2020, 5706-5712 5708 www.etasr.com lam et al.: mobile-based hospital bed management with near field communication technology bed management operation. however, no work has been done in the form of a smartphone-based mobile application in any module of the existing hctm system. in hctm, a bed manager from each ward is responsible to update the information/status of bed availability. the pc in the ward is the main terminal for accessing the bed management system. it is shared with the other staff members. sometimes, the bed manager was forced to wait the other users to complete their tasks on the pc. hence, a physical logbook still exists to keep track of the record and the information from there is put in the system later, when the pc is not occupied. the ward receives a bed booking start with the requests from the clinic or the emergency department. the bed manager at the ward should record or start the reservation using the existing desktop-based bed managing system. in this step, the bed manager is required to select and record the patient information and other relevant information such as the doctor in charge, diet preferences, etc. in the system. however, the manager is often unable to do it on the spot in the desktop-based system because the pc in the ward might not be available. hence, managers are forced to record the information in the logbook and put the information in the system later. the manual recording is causing the information to be not transparent and delayed. in other words, the system does not show the real and updated information in a real situation, which could cause problems, e.g. it might confuse the nurses at the clinic and the emergency department on the bed availability in a ward. the system could show that there are beds available, when there are not. therefore, nurses have to keep calling the ward to get the latest bed information. in addition, after the patient arrives in the ward, the bed manager should update the status of the bed from reserved to occupied. the bed managers are also nurses that have the responsibility to take care of the patients once they arrive in the ward. they will accompany and settle down a patient at the bed before they update bed information. once the patient is in the good condition and ready to discharge, the in-charge doctor would write the discharge summary and the nurse will make the bed available in the system. all the process should be done through the system because the captured information will be used for decision making. the consequences of delayed and inaccurate information can be a crowded emergency department (ed) with patients waiting for a bed in the ward, delays in the clinical process for patients, miscommunication between different departments/wards and wrong decision making from the management team. hctm has been looking for a way to reduce the bed turnaround time. one of the solutions that they have looked into was improving the patient bed management workflow. in this research, focus is given on the exploration of using a mobile application to assist the bed management process. c. existing bed management system three existing bed management systems [16-18] were analyzed and compared with the developed and proposed bed management mobile application (bmma). table i provides a comparison of system features and functions between the previous systems and the proposed mobile application. most of the existing systems are desktop-based. some system interfaces are simple and neat. however, they are not following the current design trend, while the developed bmma follows the material design [15] which is a mobile design principle that provides smooth interaction with the mobile application. the advantages and limitations in the comparison served as guidelines to develop the bmma. table i. comparison of the proposed app and previo us systems features/functions wise bed manager [16] bedwatch®bed control system [17] blueberry in-patient management system [18] developed bmma display bed information main function main function sub-function main function color-code bed allocation ✓ ✓ ✓ ✓ summarize ward’s bed information ✓ x ✓ ✓ summarize discipline’s bed information x x x ✓ mobile application x ✓ x ✓ user interface outdated design simple and neat outdated design material design [15] complexity easy to use with drag and drop function easy to use with predefined input method time-consuming. requires a lot of information from users easy to use with predefined input method nfc technology x x x ✓ 1) wise bed manager wise bed manager is a web-based system developed by wise technologies ltd. the system displays online information of beds and patients based on the room number through a web browser. icons or illustration of bed and color code were utilized to arrange the user interface element in a tidy way. the wise bed manager system is easy to use, and the information is straightforward and easy to understand. the system also has a drag-and-drop function that makes patient access to the ward easier through the system [16]. 2) the bedwatch® bed control system bedwatch® bed control is a multi-platform bed management system. the system can show the current state of a bed via devices connected to the internet such as computers, smartphones, and tablets. through these devices, users can view and update information such as the bed status in a ward. it helps different types of users as it can engage with a number of different parties such as nurses, bed managers, and cleaners. the status of the bed can be updated in a short time because the person dealing with the bed can make updates with a smartphone [17]. 3) the blueberry in-patient management system engineering, technology & applied science research vol. 10, no. 3, 2020, 5706-5712 5709 www.etasr.com lam et al.: mobile-based hospital bed management with near field communication technology the blueberry in-patient management system is a webbased system developed by blueberry consultants ltd. the system includes functions such as bed management, patient tracking, and letter issuing. the system is complex and requires users to input different types and varying amounts of information. it has a simple graphical user interface and provides user convenience in accessing the ward, patient, and bed information [18]. iii. method a bed management mobile application with nfc technology for the hctm was designed and developed. the purpose of the mobile application is to complement the existing bed management system in the hospital in order to improve bed management efficiency. the main function of the mobile application consists of updating and viewing the bed status based on discipline and ward. the following subsection discusses the details of the bed management mobile application, includes the system architecture, entityrelationship diagram, and the user interface. a. system architecture the system architecture is shown in figure 1 the bed management mobile application used a simple two-tier architecture in which the application contains the presentation and application layer. a server is utilized to store data and information such as bed, ward, and staff information. mobile applications are mainly used to present relevant data in a userfriendly user interface. an internet connection is important in enabling the communication between the mobile application and the user. besides that, the nfc tag is available on the wall of the bed, so bed managers can easily access the tag and update the status of the bed, thus the bed’s updating process is speeded up. users of the system can be managers, doctors, and nurses. the nurse can view and update the bed status, while doctors and managers can only view the bed status. fig. 1. the architecture of the bed management mobile application b. entity-relationship diagram (erd) the erd is a graph that depicts the logical structure of a database. after the entities in the bed management mobile application are identified, the diagram is provided to show the relationships between the entities. attributes of the entities are also indicated in the diagram. figure 2 shows the erd for the design of the proposed app. its entities are: bed, ward, patient, additional information, nfc, and staff. the relationship between entities can be identified. for example, one patient will have one bed and one bed will have one nfc tag in the hospital. also, one ward will have many staff members, much additional information, and have many beds. fig. 2. the erd c. bed management mobile application the bmma is built on the android platform. the main functionality includes: 1) the ability to view the status of beds based on discipline and ward, 2) the ability to update the status of a bed, 3) the ability to obtain the “pending list” and the “additional information” of a bed. the pending list function allows the nurse to select the current number of patients pending to be admitted into the ward. through the application, another user can also view the number of pending lists of the ward without the need to call a certain ward for bed availability confirmation. the additional information allows the nurse to add a short information message to a bed or ward (e.g. “the fan is not working”). figure 3 shows the screenshots of the bmma. with the use of nfc tags, users can scan the tag through their smartphone and get the information of the bed from the server based on the bed’s id information stored in the tag. (a) (b) (c) fig. 3. user interface of the bmma: (a) landing page, (b) bed information based on a specific ward, (c) user interface for bed status update engineering, technology & applied science research vol. 10, no. 3, 2020, 5706-5712 5710 www.etasr.com lam et al.: mobile-based hospital bed management with near field communication technology iv. experimental design the main goal of the experiment is to gather early feedback about the developed bmma for the hctm. a 5-point likert scale (ranging from 1 for strongly disagree to 5 for strongly agree) with questions about its usefulness, ease of use, and satisfaction was used [19]. the ease of use and usefulness are the two main factors that affect the user's intention to use new technology [20, 21]. open-end questions about the positive and negative aspects of the mobile application were also asked. the invited participants were 150 and the assessment was conducted on a voluntary basis. at first, the operation of the bmma in checking and updating the status of beds was demonstrated. the session continued with 20 minutes of exploration of the bmma among the participants themselves. the participants could freely check or update bed status using the bmma during that session. finally, the participants were asked to answer the five-point scaled questionnaire and the open-end questions. a follow-up face to face interview section was also conducted after a week of usage with three selected levels of participants, namely a junior nurse, a senior nurse, and a head nurse. v. results and discussion from the 150 participants, 113-136 complete responses were received analogous to the different sections of the questionnaire. for example, 113 participants answered the question regarding their phone operating system, 136 participants responded to the working experience question and 127 participants fully answered the tam question along with the satisfaction factor. they all were nurses of different levels (executive, junior, senior, and head nurses). as shown in table ii, the age of the participant ranged from 23 to 48. in terms of working experience, 63% of the participants had more than 10 years of experience. 82% of the participants were using android phones and samsung, oppo, vivo, and xiaomi were the most preferred brands. the rest of the 18% of the participants were ios users. table ii. demographic data of participants items category number of complete responses (n=115-135) n (%) age 21-30 42 (31) 31-40 61 (45) 41-50 32 (24) working experience (years) 1-5 33 (24) 6-10 18 (13) 11-15 25 (19) 16-20 53 (39) 21-25 6 (5) operating system android 94 (82) ios 21 (18) mobile service provider celcom 48 (36) umobile 32 (25) maxis 27 (20) digi 14 (10) others 14 (10) a. usability results to measure the level of performance of each factor, a set of merits was adapted from [22]. a mean score falling between 1.0-2.32 is considered poor and requires improvement, 2.333.65 represents the average and requires consideration to make improvements, and 3.66-5.0 is considered good. a total of 127 received questionnaires were considered fully answered. the results are shown in table iii. the cronbach’s alpha value for each factor is more than or equal to 0.9 while the suggested benchmark is 0.7 [23]. therefore, all the items used to measure the constructs are reliable. the mean for all three factors was between 3.40-3.45. the mean score received from the user’s evaluation for the usefulness factor was 3.45, for the ease of use was 3.40, and for satisfaction it was 3.42. based on the questionnaire result, the developed bmma lied in the average zone and required attention for further improvement. b. subjective feedback the follow-up face to face interview section confirmed the average result of the questionnaire. in general, the feedback received from the interview section was divided into two parts: the app and app requirement perspectives. in terms of the app perspective, the users expected the developed bmma to be linked to the existing web system. hence, the users required inputting the information either in the web or in the app platform to avoid the repeating process. other than that, the bmma did not have not a role-based restriction, thus they were worried about the possibility the bed status information to be updated by unauthorized parties. for example, only the responsible nurses in the medical ward should able to update the bed status for the medical ward, while the nurses from other wards should be able to only view the bed status. due to the above reasons, users thought it of not being user-friendly. in terms of the app requirement perspective, the users were worried about the internet/data connection when using the bmma in their daily tasks, due to the limited internet coverage by the mobile internet service provider or the fact that the signal might be not sufficient. besides that, the phone capacity such as storage, battery, processor and the operating system were the factors that they were concerned about. many users asked questions about the ios version. they were also worried of the public reception of the fact that they would be using the phone while working. this feedback from the interview section was supported by the result of the open-end questions. a total of 48 feedbacks were received from the open-end question related to the negative feedback and the results are shown in table iv. even though there were a few limitations required to be solved, users are looking forward to the complete version of bmma. considering the positive feedback (table v), 46.4% of participants thought that the mobile application was easy, 23.2% found usefulness in its flexibility and transparency regarding bed information (23.2%) among wards. a mobile app system would certainly be helpful in daily tasks of the 10.7% while 8.9% commented that it would speed up the information update and browsing process. this research aimed on the exploration and the possibility of using a mobile application to assist the bed management process in hctm. a major goal was to find the acceptance of the staff in the use of a mobile application in their daily operations and the major challenges to implement the mobile application operation. a prototype was developed for the proof of concept and to get early feedback about utilizing the mobile engineering, technology & applied science research vol. 10, no. 3, 2020, 5706-5712 5711 www.etasr.com lam et al.: mobile-based hospital bed management with near field communication technology app system in the hctm in the near future. therefore, the current version of bmma in this study provided limited functionality: it focused on viewing and updating the bed status. information regarding patient, doctor, meal, and medical data was not able to be associated in this version. to make it more practical, the bmma should have all the functions of the existing system. nonetheless, the current developed bmma served well as a tool to allow nurses to imagine the use of smartphone-based application in the bed management process. table iii. evaluation results construct mean + sd cronbach's alpha usefulness 3.45 ± 0.63 0.94 u1 the application helps me to accomplish tasks more quickly. 3.37 ± 0.63 u2 the application makes the ward information exchange in the discipline ward convenient. 3.55 ± 0.57 u3 the application saves time. 3.44 ± 0.68 u4 the application helps me to do my job more easily. 3.41 ± 0.67 u5 the application meets my job needs. 3.41 ± 0.65 u6 the application is useful in my job. 3.50 ± 0.59 ease of use 3.40 ± 0.58 0.90 eu1 i can use the application easily without written instructions (manual). 3.39 ± 0.62 eu2 i find it easy to get the application to do what i want it to do. 3.34 ± 0.58 eu3 it is easy for me to remember how to update the bed status using the application. 3.43 ± 0.57 eu4 i find this application easy to learn. 3.43 ± 0.62 eu5 i find this application easy to use. 3.43 ± 0.54 satisfaction 3.42 ± 0.56 0.91 s1 the application works the way i want it to work. 3.29 ± 0.55 s2 i can read the text in this application clearly 3.50 ± 0.52 s3 i am satisfied with the interface of the application. 3.39 ± 0.52 s4 i like the color theme of the application. 3.50 ± 0.53 s5 i feel i need to have the application. 3.48 ± 0.65 s6 the application is pleasant to use. 3.45 ± 0.57 s7 i am satisfied with the use of the application. 3.33 ± 0.56 table iv. negative feedback negative factors number (n =48) n (%) internet/mobile network data 22 (45.8) added workload 8 (16.7) ios 3 (6.3) not user-friendly 3 (6.3) phone hanging 2 (4.2) role-based access 2 (4.2) lack of device 2 (4.2) phone storage 2 (4.2) misunderstanding from outsiders 2 (4.2) cost 1 (2.1) battery 1 (2.1) the participants are looking forward to the complete version of the bmma. it certainly solves the problem of limited desktop computer access of the existing web-based system. nurses can access the bed management system through their smartphones with an internet connection. a pilot version of the bmma was launched and evaluated. the role-based restrictions, the integration with the existing web system, and other important functionality issues are in the app’s design. the bring-your-own-device (byod) policy [10] will be adopted to ensure the protection of patient data. table v. positive feedback positive factors number (n =56) n (%) easy 26 (46.4) updated and transparent information 13 (23.2) helpful 6 (10.7) saves time 6 (10.7) speeds up task 5 (8.9) vi. conclusion a smartphone-based mobile application, the bed management mobile application (bmma), is proposed to complement the existing web system in hospital canselor tuanku muhriz (hctm) regarding bed management. bmma allows the user to view and update the bed information anytime and anywhere which is a more convenient approach than the existing pc-based system. a feasibility study of applying mobile application in hctm has been carried out. based on the study’s findings the main os platform using by the nurses in hctm is android while the participants mostly used the four major mobile network service providers in malaysia. hence, the future mobile application development should consider internet connectivity of these four providers inside the hctm’s buildings. other than that, the usability questionnaire received an average result. however, users gave an overall positive feedback and agree that the mobile application will be helpful for them in executing their routine tasks in bed management. they are looking forward to having a mobile application to help them. acknowledgment this study is a part of a research funded by the ministry of higher education (mohe) (frgs/1/2018/ict04/ukm/02/4) and the universiti kebangsaan malaysia (ap-2017-007/2). references [1] w. j. phua, m. y. h. low, n. venkatarayalu, j. koh, “nfc-based smart notification system for hospital discharge process and bed management”, ieee international conference on service operations and logistics, and informatics, singapore, july 31-august 2, 2018 [2] e. iadanza, a. luschi, a. ancora, “bed management in hospital systems”, in: world congress on medical physics and biomedical engineering 2018, springer, 2019 [3] z. u. rehman, f. a. shaikh, “critical factors influencing the behavioral intention of consumers towards mobile banking in malaysia”, engineering, technology & applied science research, vol. 10, no. 1, pp. 5265-5269, 2020 [4] s. zafar, g. miraj, r. baloch, d. murtaza, k. arshad, “an iot based real-time environmental monitoring system using arduino and cloud service”, engineering, technology & applied science research, vol. 8, no. 4, pp. 3238-3242, 2018 [5] a. s. m. mosa, i. yoo, l. sheets, “a systematic review of healthcare applications for smartphones”, bmc medical informatics and decision making, vol. 12, article id 67, 2012 engineering, technology & applied science research vol. 10, no. 3, 2020, 5706-5712 5712 www.etasr.com lam et al.: mobile-based hospital bed management with near field communication technology [6] a. z. z. zay, r. m. nor, m. j. m. razi, t. mantoro, m. a. ayu, “nfc based attendance: more than just a touch”, jurnal teknologi, vol. 78, no. 9-3, pp. 69-78, 2016 [7] a. d. potgantwar, v. m. wadhai, “a standalone rfid and nfc based healthcare system”, international journal of interactive mobile technologies, vol. 7, no. 2, pp. 73-79, 2013 [8] f. noonan, j. o’brien, e. broderick, i. richardson, j. walsh, “hospital bed management practices: a review”, 12th international joint conference on biomedical engineering systems and technologies, prague, czech republic, february 22-24, 2019 [9] m. k. a. azzam, m. b. alazzam, m. k. al-manasra, “mhealth for decision making support: a case study of ehealth in the public sector”, international journal of advanced computer science and applications, vol. 10, no. 5, pp. 381-387, 2019 [10] s. u. a. ayubi, a. pelletier, g. sunthara, n. gujral, v. mittal, f. c. bourgeois, “a 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december 17-18, 2016 [15] i. g. clifton, android user interface design: implementing material design for developers, addison-wesley, 2015 [16] wise technologies, wise bed manager, available at: http://www.bedmanager.com [17] the bedwatch, bed control system, available at: http://www.bedwatch.com/products/bed-control/ [18] blueberry health, blueberry in-patient management system, available at: https://www.blueberry-health.co.uk/patientcaresystems/projectexamples/ inpatientmanagementsystem [19] a. m. lund, “measuring usability with the use questionnaire”, usability interface, vol. 8, no. 2, pp. 3-6, 2001 [20] f. d. davis, “perceived usefulness, perceived ease of use, and user acceptance of information technology”, mis quarterly, vol. 13, no. 3, pp. 319-340, 1989 [21] m. h. alanazi, b. soh, “behavioral intention to use iot technology in healthcare settings”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4769-4774, 2019 [22] h. mohamed, h. m. judi, n. sahari, m. n. yaman, n. a. abdul, “penilaian kualiti penyampaian perkhidmatan pasca siswazah: satu kajian di sebuah universiti awam”, journal of quality measurement and analysis, vol. 14, no. 1, pp. 45-54, 2018 (in malay) [23] r. f. devellis, scale development: theory and applications, sage, 2016 microsoft word 03-3612_s_etasr_v10_n4_pp5882-5888 engineering, technology & applied science research vol. 10, no. 4, 2020, 5882-5888 5882 www.etasr.com nagao & fukushima: sourceand site-specific earthquake ground motions sourceand site-specific earthquake ground motions application of a state-of-the-art evaluation method takashi nagao research center for urban safety and security kobe university kobe city, japan nagao@people.kobe-u.ac.jp yasuhiro fukushima department of disaster mitigation and facility maintenance eight-japan engineering consultants inc. okayama city, japan fukushima-ya@ej-hds.co.jp abstract—seismic codes stipulate earthquake ground motions by considering the seismicity and seismic amplification properties of the ground at the target site. however, the effects of source, path, and site amplification characteristics are not sufficiently anticipated in seismic codes. regarding the source and path characteristics, earthquakes that have the strongest influence on the target site should be considered specifically, and, concerning seismic amplification, the effects of not only a shallow subsurface but also a deep subsurface should be considered. this article takes the design spectra of japanese highway bridges as an object and compares them with the spectra produced by a ground motion prediction equation and the sourceand site-specific spectra evaluated using a state-of-the-art method. the results show that the spectra differ greatly. in this way, the necessity of the application of a state-of-the-art technique in the evaluation of source, path, and site amplification characteristics is demonstrated. keywords-earthquake ground motion; site amplification factor; strong-motion simulation i. introduction earthquake ground motion (egm) is affected by source, path, and site characteristics. codes of practice take those characteristics into account in various ways when developing principles of seismic design. regarding the first two characteristics, aashto design specifications for bridges [1] and nehrp-recommended seismic provisions for buildings [2] apply site-specific hazard analyses to reflect the effects of source and path characteristics on egms. eurocode 8 [3] classifies the seismicity of the site according to the surface wave magnitude of the associated earthquake, and design coefficients for egms are specified according to the seismicity of the site of interest. the japanese specifications for highway bridges (jshb) [4] classify the focal mechanisms of earthquakes into inter-plate earthquakes and shallow crustal (inner-plate) earthquakes, as well as specify the egms for each focal mechanism. the egms are then multiplied by a region coefficient according to the seismicity of the site of interest. the japanese technical standard for buildings also specifies egms and region coefficients [5]. one of the problems in the application of hazard analysis when evaluating egms for seismic design is that the analysis only provides a probabilistic egm corresponding to the magnitude of reference earthquakes. therefore, specific source characteristics such as directivity effects due to the rupture process in the fault plane [6] cannot be considered. the egm recommendations of the jshb are also not site-specific, because data of massive earthquakes obtained from all over the country are used. regarding the site amplification characteristic, almost all the seismic codes and ground motion prediction equations (gmpes) consider the amplification only in relation to a shallow subsurface. aashto, nehrp, and eurocode 8 classify site conditions according to surface soil types and vs30, which is the average shear-wave velocity of the top 30m of the site. the jshb and japanese building codes classify ground conditions in accordance with the natural period of the shallow subsurface, from the ground surface down to the engineering bedrock. here, engineering bedrock is a stiff soil whose shear-wave velocity exceeds 300m/s. it has been observed that the effect of a deep subsurface should be considered [7–10] and an evaluation of the amplification of shallow subsurfaces alone greatly underestimates the amplification values at the relevant sites [9, 10]. recent achievements in the field of earthquake engineering have enabled the introduction of strong-motion simulation techniques such as a semi-empirical method using a characterized source model [11, 12]. when conducting a strong-motion simulation, evaluation of source, path, and site amplification characteristics by using a state-of-the-art method is very important for sourceand site-specific egms. this study aims to address the necessity of the appropriate consideration of the said characteristics for egms by showing the difference in egms evaluated via conventional methods and those evaluated by a state-of-the-art method. ii. conventional egm a. egm in the jshb the jshb stipulate six types of egm as the maximum credible egm at the target site, namely, the combination of two kinds of source characteristics (the inter-plate type and the inner-plate type) and three kinds of ground conditions. corresponding author: takashi nagao engineering, technology & applied science research vol. 10, no. 4, 2020, 5882-5888 5883 www.etasr.com nagao & fukushima: sourceand site-specific earthquake ground motions regarding earthquake type, inter-plate type egms were defined in relation to the 1923 kanto earthquake, the 2003 tokachi-oki earthquake, and the 2011 off the pacific coast of tohoku earthquake. inner-plate type egms were defined in relation to the 1995 kobe earthquake. the standard egms are multiplied by a region coefficient in the range of 0.7–1.2. although the region coefficient is used to reflect the seismicity of the site of interest, there has been no reported evidence supporting that value. the ground condition is classified by the natural period of the shallow subsurface, as shown in table i. figure 1 shows the standard 5% damped egms. table i. ground type classification ground type natural period t (s) type i t < 0.2 type ii 0.2 ≤ t < 0.6 type iii 0.6 ≤ t fig. 1. standard egms. b. gmpes gmpes are widely used to evaluate egms in accordance with the magnitude of the reference earthquake and the surface condition of the target site. many gmpes have been proposed to date [13, 14]. this study employs the gmpe proposed by [13], wherein egm is calculated by: ( )( ) ( )( ) ( ) ( ) ln ln exp ln a w w c h r i s sl k msst s t am bx x c dm e h h f s s s x c s δ= + − + + − + + + + + + (1) where sa(t) is the 5% damped response spectrum (cm/s 2 ), mw is the moment magnitude, x is the shortest fault distance (km), h is the focal depth (km), and δ is a dummy variable equal to 0 for h < hc and 1 for h ≥ hc, with hc as a depth constant. a, b, c, d, and e are the regression coefficients for the period t(s). fr, si, and ss are the source type coefficients, where fr is applied to a reverse fault-type inner-plate earthquake, si is applied to an inter-plate earthquake, ss is applied to an intraslab earthquake, and 0 is used for all other kinds. ssl is the magnitude-independent path correction term for intra-slab earthquakes, ck is the site classification coefficient, and smsst is the correction factor of the magnitude-squared term for each source type. we refer the reader to [13] for details. iii. target sites four sites from the strong-motion observation network knet [15] were chosen as target sites in this study: gnm001 (i), ymg019 (i), fko011 (ii), and koc014 (iii). the number in the parentheses is the ground type according to the jshb. the reference earthquakes for each site are: an inter-plate type in the form of the nankai trough megathrust earthquake (also known as the nankai trough earthquake) for ymg019 and koc014, an inner-plate type earthquake along the fault zone of the left bank of the katashina river (katashina river fault earthquake) for gnm001, and an inner-plate type earthquake along the fault zone of the north edge of the saga plain (saga plain fault earthquake) for fko011. the region coefficients provided in the jshb for egms at those sites are: 1.0 for gnm001, 0.8 for ymg019, 0.7 for fko011, and 1.2 for koc014 [4]. iv. sourceand site-specific egms a. method overview we applied a semi-empirical method for the evaluation of sourceand site-specific egms. the used method is also called the statistical green’s function method [11], and we referred to [16] for the specific calculation procedures. this method divides the strong motion generation area (smga) in a fault plane into sub-faults and evaluates the larger egm as the summation of the small egms caused by the sub-faults. an smga is also called the asperity in the literature. a fourier transform of the small egm (u(f), green’s function) is obtained with the following equation: ( ) ( ) ( ) ( ) ( ) / ( )u f s f p f g f o f o f= × × × (2) where s(f) is the source spectrum, p(f) is the path spectrum, g(f) is the site amplification spectrum, o(f) is the fourier spectrum of the small earthquake observed at the target site, and f is the frequency. it is emphasized that source, path, and site amplification characteristics need to be source and site specifically evaluated as will be described in the following section. b. source characteristics the source spectrum was obtained with reference to [17] as: 2 0 3 (2 ) ( ) 1 ( / )4 e cs m f s f r fs prtitn f fv θφ π πρ = ⋅ ⋅ ⋅ ⋅ + (3) where rθφ is the radiation coefficient, fs is the amplification due to the free surface (=2), prtitn is a reduction factor accounting for the partitioning of energy into two horizontal components (=0.71 in this study), m0e is the seismic moment of the small earthquake, ρ is the density, vs is the shear-wave velocity, and fc is the corner frequency of the small earthquake. corner frequency fc is calculated based on [18, 19] as: 0.66 / c s e f v s= (4) where se is the area of the sub-fault. 0.1 0.5 1 5 10 1 5 10 50 period (s)response accelerat ion (m/s2 ) inter-plate type type i ground type ii ground type iii groundinner-plate type type i ground type ii ground type iii ground engineering, technology & applied science research vol. 10, no. 4, 2020, 5882-5888 5884 www.etasr.com nagao & fukushima: sourceand site-specific earthquake ground motions the summing of the waveforms of the small earthquakes, in accordance with the rupture process, yields the waveform of the large earthquake [20, 21]. this study refers to the government of japan’s cabinet office [22] for the arrangement of smgas and source parameters setting methods for the nankai trough earthquake. figure 2 illustrates the arrangements of smgas and rupture starting points for ymg019 and koch014. the smgas were arranged so that the egm were largest at the target sites. the rupture starting point was set by analyzing the estimated starting point of the previous events [22]. figures 3 and 4 exhibit the arrangements of smgas and the rupture starting points for the saga plain fault earthquake and katashina river fault earthquake respectively. the rupture starting points were set so that the waveforms at the target sites became as large as possible due to the directivity effect. the source parameters were set by referring to [23, 24]. (a) (b) : smga : rupture starting point fig. 2. arrangements of the smgas and rupture starting points for the nankai trough earthquake: (a) for ymg019 (downdip case), (b) for koc014 (west case). c. path characteristics the path spectrum was obtained by [17] on the following equation: 1 ( ) exp s fr p f r qv π  = −    (5) where r is the hypocentral distance, q is the quality factor along the propagation path, vs is the shear-wave velocity, and f is the frequency. the quality factor in (5), which expresses the inelastic attenuation of seismic motion, is known to be frequency dependent and differs from area to area [25]. this study employed the quality factor proposed in previous studies by focusing on the area and earthquake types, as shown below: • the nankai trough earthquake [26]: q( f )=152f 0.38 (6) • the saga plain fault earthquake [27]: q( f )=104f 0.63 (7) • the katashina river fault earthquake [26]: q( f )=166f 0.76 (8) : smga : rupture starting point fig. 3. arrangements of the smgas and a rupture starting point for the saga plain fault earthquake. : smga : rupture starting point fig. 4. arrangement of an smga and a rupture starting point for the katashina river fault earthquake. d. site amplification characteristics site amplification is the amplification of egms from the seismic bedrock to the ground surface and it is known to differ from site to site. the present study employed two kinds of site amplification factors: (i) empirically obtained site amplification factors using the spectral inversion technique [28–30] and (ii) amplification factors obtained using the multiple reflection theory and assuming a horizontally layered half-space with a vertically incident sh wave (1d amplification). spectral inversion is a method that separates the source, path, and site amplification characteristics from the observed egm. site 0 200km100km50kmymg0190 50 100 200 (km) 0 200km100km50km koc0140 50 100 200 (km) 0 20km10km5km fko0110 5 10 20 (km) 0 20km10km5km gnm0010 5 10 20 (km) engineering, technology & applied science research vol. 10, no. 4, 2020, 5882-5888 5885 www.etasr.com nagao & fukushima: sourceand site-specific earthquake ground motions amplification factors obtained by spectral inversion [31] are known to be larger than those obtained by 1d amplification [9], because factors affecting seismic amplification, such as 3d effects, cannot be considered in 1d amplification calculations. in addition, precise reproduction of the seismic motion by use of site amplification factors by the spectral inversion was demonstrated in [16]. in the calculation of 1d amplification, shear-wave velocity profiles from the ground surface to the seismic bedrock and quality factors were evaluated by referring to [10]. figure 5 shows the shear-wave velocity profile at each site. although the sediment depth at three of the sites (fko011, gnm001, and ymg019) is almost identical (150m), the shear-wave velocity profiles above the seismic bedrock greatly differ among the sites. at koc014, the sediment depth is 600m, which is significantly deeper than at other sites. fig. 5. shear-wave velocity profiles. figure 6 compares the site amplification factors evaluated by the two methods in the range of 0.1–10hz, as this is an important frequency range for engineering practices. for simplicity, the shallow and deep subsurface will be described as characteristics of the deep subsurface hereinafter. the black line indicates the spectral inversion, the red line denotes 1d amplification by a deep subsurface, and the green line expresses 1d amplification by a shallow subsurface. we will discuss the differences individually. ymg019 is a hard rock site, and shear-wave velocity exceeds 2km/s at 11m depth. thus, amplification factor observation by 1d analysis made no significant difference because the amplification factor by the shallow subsurface was unity, while the amplification factor by the deep subsurface was also unity below 1hz and increased only a little above 1hz. the maximum amplitude was 1.4 at 10hz. in contrast, amplification by spectral inversion showed an amplitude of approximately 2 below 3hz, which was larger than that demonstrated by 1d amplification. the maximum amplitude was 6.0 at 6.4hz, which was considerably different from the results of 1d amplification. (a) (b) (c) (d) : amplification by the spectral inversion : 1d amplification by a deep subsurface : 1d amplification by a shallow subsurface fig. 6. comparison of the site amplification factors: (a) ymg019, (b) koc014, (c) fko011, and (d) gnm001. 0 1000 2000 3000 4000 0 100 200 300 400 500 600 depth (m) vs (m/s) ymg019 koc014 fko011 gnm001 0.1 0.5 1 5 10 0.5 1 5 10 50 100amplification factor frequency (hz) 0.1 0.5 1 5 10 0.5 1 5 10 50 100amplification factor frequency (hz) 0.1 0.5 1 5 10 0.5 1 5 10 50 100amplification factor frequency (hz) 0.1 0.5 1 5 10 0.5 1 5 10 50 100amplification factor frequency (hz) engineering, technology & applied science research vol. 10, no. 4, 2020, 5882-5888 5886 www.etasr.com nagao & fukushima: sourceand site-specific earthquake ground motions concerning koc014, the results of amplification using the three methods were similar, with a first-order peak around 1hz, but the amplitudes were significantly different. peak amplitudes at the first-order peak frequencies were: 60 using spectral inversion, 10 using 1d amplification with a deep subsurface, and 3.3 using 1d amplification with a shallow subsurface. the amplitude result from using spectral inversion was much larger than that obtained from using 1d analysis with a deep subsurface below 3hz. the amplitude measurement from using 1d analysis with a shallow subsurface was much smaller than those obtained using the other two methods. regarding fko011, the result of the amplification factor by using spectral inversion was like that of 1d amplification with a deep subsurface, but the amplitude measurement from spectral inversion was much larger, especially below 3hz. as with other sites, the result of 1d amplification with a shallow subsurface was much smaller than the other amplifications. gnm001 is a rock site whose shearwave velocity is 600m/s at a depth of 10m, and it exceeds 2km/s at 130m. the 1d amplification factor by a shallow subsurface is unity below 3hz and increased to 3 at 10hz. 1d amplification by a deep subsurface showed peaks at 2.4, 5.1, and 8.5hz with a maximum amplitude of 6.6 at 5.1hz. the amplification effect above 1hz was considerably larger when compared with that of the shallow subsurface. amplification by spectral inversion showed a comparatively small amplitude below 4hz and then increased to 20 at 10hz. in summary, the site amplification factor results from using spectral inversion are larger than those from using 1d amplification with a deep subsurface. using 1d amplification with a shallow subsurface produced the smallest results. it was inferred that the use of 1d amplification with a deep subsurface for waveform evaluation may result in an underestimation of the intensity of the egm. it is very clear that the use of 1d amplification with a shallow subsurface alone can lead to the evaluation of egms on the dangerous side, thus the present study does not use the said method hereafter. another important point to note is the difference in the amplification factors of the spectral inversion among the sites. sediment sites (fko011 and koc014) show large amplitudes, whereas rock sites (ymg019 and gnm001) show small amplitudes. the difference in the amplitude is much larger than that assumed by 1d amplification. this is attributed to the 3d amplification characteristics as mentioned above. e. nonlinear characteristics of the shallow subsurface a shallow subsurface exhibits nonlinear characteristics during a strong earthquake. therefore, the effects of nonlinear characteristics of a shallow subsurface were evaluated using the following processes: (i) obtain the input seismic motion at the engineering bedrock level via the deconvolution process using the multiple reflection theory along with the initial shear modulus of the soil (a linear earthquake response analysis), (ii) conduct an equivalent-linear earthquake response analysis [32, 33] considering the nonlinear characteristics of the soil [34], and (iii) obtain the waveform at the ground surface. v. results and discussion figure 7 compares the horizontal, two-component (ns and ew) synthetic 5% damped calculated egms. (a) (b) (c) (d) : sourceand site-specific egm : egm with 1d amplification : egm using a gmpe : egm according to the jshb fig. 7. comparison of the response spectra: nankai trough earthquake (a) at ymg019 and (b) at koc014, (c) saga plain fault earthquake at fko011, and (d) katashina river fault earthquake at gnm001. 0.1 0.5 1 5 10 0.5 1 5 10 50 period (s)response acceleration (m/s 2 ) 0.1 0.5 1 5 10 0.5 1 5 10 50 period (s)response acceleration (m/s 2 ) 0.1 0.5 1 5 10 0.5 1 5 10 50 period (s)response acceleration (m/s 2 ) 0.1 0.5 1 5 10 0.5 1 5 10 50 period (s)response acceleration (m/s 2 ) engineering, technology & applied science research vol. 10, no. 4, 2020, 5882-5888 5887 www.etasr.com nagao & fukushima: sourceand site-specific earthquake ground motions regarding egms for ymg019, the egm according to the jshb is relatively small because the region coefficient is as low as 0.8, however it still overestimates the egm when compared with sourceand site-specific egm because the site amplification factor at ymg019 is small. 1degm conversely underestimates egm, and the egm of a gmpe is generally consistent with sourceand site-specific egm. on the other hand, koc014 is a site where the region coefficient is as large as 1.2, but because of the large site amplification factor, the jshb underestimate the egm when compared with source and site-specific egm in the period range of 3s or less. the 1degm and gmpe results also underestimate the egm when compared with sourceand site-specific egm. fko011 corresponds to an area where the region coefficient is as small as 0.7. however, because the magnitude of the reference earthquake is 7.5 and the site amplification factor is large, the jshb underestimate the egm in the period range of 5s or less when compared with sourceand site-specific egm. the 1degm and gmpe results also underestimate egm. gnm001 corresponds to an area where the region coefficient is 1.0. however, the magnitude of the reference earthquake is 6.8, which is a little smaller than that of other large earthquakes, and the site amplification factor is small except in the high frequency region. therefore, the egm results of the jshb overestimate the egm when compared with sourceand sitespecific egm in the period range of 0.15s or more. 1degm also overestimates egm in the period range of 0.15–1.5s. gmpe results also overestimate the egm in the period range of 0.2 to 2 s. based on the above, it can be said that egms vary greatly depending on the calculation methods used. conventional methods do not consider deep subsurface amplification and therefore often overestimate or underestimate egm when compared with sourceand site-specific egm. for a rational egm evaluation, it is important to evaluate the egm source and site specifically by using the state-of-the-art method described above. vi. conclusions in this study, sourceand site-specific egm results of interplate and inner-plate earthquakes were estimated using a stateof-the-art method targeting various site amplification factor points and compared them with egm results from the jshb and gmpes. as a result, it was made clear that although the jshb consider the earthquake type, ground type, and region coefficients, the way it treats the source, path, and site amplification characteristics is insufficient. gmpes are widely used to simply evaluate egm; however, estimated egms may differ significantly from sourceand site-specific egm because the same three characteristics are not properly considered. infrastructure must be appropriately constructed and maintained, but in order to do so, the load effects on it must be appropriately evaluated, and infrastructural investments should be optimized regarding the seismic hazard at each site. therefore, the evaluation of egm using a state-of-the-art method is extremely important. acknowledgment the authors would like to thank the national research institute for earth science and disaster prevention, japan for providing k-net strong motion records and ground structure data. references [1] aashto guide specifications for lrfd seismic bridge design (2nd edition) with 2012, 2014 and 2015 interim revisions, aashto, washington, d.c., u.s.a, 2014. 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[30] j. boatwright, j. b. fletcher and t. e. fumal, “a general inversion scheme for source, site and propagation characteristics using multiply recorded sets of moderate-sized earthquakes,” bulletin of the seismological society of america, vol. 81, no. 5, pp. 1754-1782, 1991. [31] a. nozu, and t. nagao, “site amplification factors for strong-motion sites in japan based on spectral inversion technique,” (in japanese), technical note of the port and airport research institute, no. 1102, 2005. [32] m. sugito, “frequency-dependent equivalent strain for earthquake response analysis of soft ground,” proceedings of the is-tokyo, ’95, the first international conference on earthquake geotechnical engineering, tokyo, 1995. [33] i. suetomi and n. yoshida, “damping characteristics of soil deposits during strong ground motions,” in proc. second int. symposium on the effect of surface georogy on seismic motion, yokohama, japan, dec. 13, 1998, pp. 765-772. [34] s. yasuda and i. yamaguchi, “dynamic soil properties of undistrubed samples,” (in japanese), proc.of 20th annual conference of jssmfe, nagoya, japan, jun. 10-12, 1985, pp. 539-542. microsoft word chikouche-r2.doc etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 433-439 433 www.etasr.com mohammed chikouche et al.: variable gain pi controller design for speed control of a dfim variable gain pi controller design for speed control of a doubly fed induction motor using state-space nonlinear approach t. mohammed chikouche dpt of electrotechnics, university of saida, algeria tarekchi@yahoo.fr a. mezouar dpt of electrotechnics, university of saida, algeria a.mezouar@yahho.fr t. terras dpt of electrotechnics, university of saida, algeria t_tahar2000@yahoo.fr s. hadjeri dpt of electrotechnics djillali liabes university of sidi bel abbes, algeria shadjeri2@yahoo.fr abstract—this paper presents a comparison between a variable gain pi controller and a conventional pi controller used for speed control with an indirect field orientation control of a doubly fed induction motor (dfim), fed by two pwm inverters with a separate dc bus link. by introducing a new approach for decoupling the motor’s currents in a rotating (d-q) frame, based on the state space input-output decoupling method, we obtain the same transfer function (1/s) for all four decoupled currents. thereafter, and in order to improve control performance, the vgpi controller was used for speed regulation. the results obtained in matlab/simulink environment illustrate the effectiveness of the technique employed for the decoupling and for speed regulation. keywords: doubly fed induction motor (dfim); input output decoupling; field-oriented control; variable gain pi controller; conventional pi controller. appendix dfim doubly fed induction motor. vgpi variable gain pi. s, r stator and rotor indices, d,q indices of the orthogonal components direct and quadrature. x complex variable such as: [ ] [ ]ximjxrex += . sr , rr stator and rotor resistances. sl , rl stator and rotor inductances. rs t,t stator and rotor time constant. σ leakage factor )llm1( rs 2 sr−=σ . srm mutual inductance. θ the electrical rotor position. rs ,θθ statoric flux position, rotoric flux position. ω the mechanical rotor frequency. ω mechanical speed. sω electrical stator frequency. p number of pole pairs. emt electromagnetic torque. rt load torque. j moment of inertia. ƒ friction coefficient. rated data of the simulated doubly fed induction motor: rated values: 1.5kw; 220/380v-50hz; rated parameters: ω75.1rs = ω68.1rr = h295.0ls = h104.0lr = h165.0m = 0.2p = mechanical constants 2 m.kg01.0j = .s.i00.0f = i. introduction the progress accomplished, in the few past years, in power electronics has made the doubly fed induction motor (dfim) an industrial standard due to its low cost and high reliability [1, 2]. the dfim is an electrical three-phase asynchronous machine with wound rotor accessible for control. since the power handled by the rotor side (slip power) is proportional to the slip, the energy requires a rotor-side power converter which handles only a small fraction of the overall system power [3, 4]. it is very attractive for both energy generation and high power drive applications. in recent years, there has been a great amount of activity on back stepping control approach in ac drive fields [3].the non linear control approach shows better precision and stability. however, its major problem is its sensitivity to motor parameter variations and load disturbance. dfim control issues are traditionally handled by fixed gain proportional integral (pi) controllers. however, the fixed gain controllers are very sensitive to parameter variations and cannot provide good dynamic performance. so, the controller etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 433-439 434 www.etasr.com mohammed chikouche et al.: variable gain pi controller design for speed control of a dfim parameters have to be continually adapted [5]. the vgpi controller gives better results in case of parameter variations for nonlinear systems. so, the dfim is an ideal candidate to test its performance [6, 7]. the present work is about field-oriented control with vgpi controller of a dfim employing the state space decoupling method.the vector control of the dfim with two independent converters has been studied in several works recently. the linearization of the nonlinear model of the machine can be done in different manners with various terms of compensation [5, 6]. in this paper, a nonlinear state space is proposed to ensure the decoupling of the multi-variables system input-ouput that constitutes the dfim. the paper is organized as follows: in section ii the dfim model is illustrated. section iii contains the field-oriented control of a dfim based on the sate space decoupling method. section iv is focused on the control speed of the dfim using the vgpi controller. in section v, simulations of the control system performed by matlab are presented and discussed. ii. dfim dynamic model the dynamic model of the dfim in a (d-q) synchronous rotating frame is given by the following voltages equations:       ++= ++= rr r rrr ss s sss j dt d irv j dt d irv φω φ φω φ (1) expressions of the fluxes are given by:    += += ssrrrr rsrsss imil imil φ φ (2) from (1) and (2) the all currents state model is written as follows:        −++−= −++−= s rs rsr r r s rs ssr r r r r rs rsr s s r rs rsr s s ss v ll rm v l 1 i ll rm i l r dt rid v ll rm v l 1 i ll rm i l r dt id σσσσ σσσσ (3) the mechanical equation is expressed by (4): rem t p ƒ t dt d p j −−= ωω (4) with: ωω .p= and the electromagnetic torque is given by: ( )∗= rsmsrem iiipmt (5) so, the equation for the speed variation becomes: ( ) t p ƒ iiipm dt d p j rsmsr −−= ∗ ωω (6) iii. vector control strategy of dfim by state space decoupling a. rotor flux oriented the principle for this type of control consists in orienting the flux into the machine, to the rotor, to the stator or in the air gap. conventionally, we work with an orienting on the d axis. the in quadrature axis will therefore carry the current that will participate in the creation of the electromagnetic torque in the machine [6, 8-9] rdrrq ; φφφ == 0 (7) then: sq r sr rq i l m i −= (8) the magnetization of the machine allows to impose the rotor flux module, so we distinguish two strategies [6, 10]: • working with a unitary power factor to stator or to rotor, which implies that one of the two currents sdi or rdi will be null, with: sdsrrd im=φ • split the magnetizing current equally between the two converters, that is : 2 d rdsd i ii == , with: ( ) 2 d srrrd i ml +=φ (9) the choice of 0 rd i = , gives the same expression for the flux to the stator and to the air gap. in addition, the expression depends only on sr m , and with a unitary power factor at the rotor. fig. 1. rotor flux oriented on the d axis etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 433-439 435 www.etasr.com mohammed chikouche et al.: variable gain pi controller design for speed control of a dfim b. currents decoupling state space b.1. principle of the method: consider the following multivariable system:    = += cxy buaxxɺ with [ ] [ ] [ ]tm21 t m21 t n21 m m n y...yyy u...uuu x...xxx u y x = = =      ℜ∈ ℜ∈ ℜ∈ (10) the objective is to determine a state space of the form: lvxku d +−= , with m v ℜ∈ (11) v denotes the new input vector, which decouples the system, in a way that the output iy (i=1 to m) depends only on the input v. the output iy is written: xcy ii = where ic is the i-th row of the matrix c . let us derive iy a few times in order to bring up the command. we call characteristic index noted iδ , the number of derivation it takes in order to bring up the command. we then have successively for each output i:          ≠+= ==+== ==+== ==+== − )0buac( :with buacxacy 0buac:withxac )buax(acxacy 0abuc:withxac )buax(acxacy 0buc:withaxc )buax(cxcy iiii i 1 ii )( i 2 i 3 i 2 i 2 i )3( i i 2 iiii iiiii δχδδ ⋮ ɺɺɺ ɺɺɺ ɺɺ (12) that we can still write in matrix form: u bac bac bac x ac ac ac y y y 1 m 1 2 1 1 m 2 1 )( 2 )( 2 )( 1 m 2 1 m 2 1 m 2 1               +               =               − − − δ δ δ δ δ δ δ δ δ ⋮⋮⋮ (13) that is: ubxay *+= ∗∗ (14) with m y ℜ∈∗ , mma ×∗ ℜ∈ and mmb ×∗ ℜ∈ . we seek a control law vlxku dd +−= such as vy = ∗ . the looped system is written as: ( ) ( ) vlbxkbavlxkbxay dddd ∗∗∗∗∗∗ +−=+−+= (15) to obtain vy =∗ we must have 1lb d = ∗ and 0kba d =− ∗∗ . if the matrix ∗ b is invertible, the choice of : ( ) ∗−∗= abk 1d and ( ) 1 bl −∗= (16) gives: vy =∗ that is: )s(v s 1 )s(y i1i i + = δ (17) b.2 application to the dfim: we search to exploit this method for decoupling the currents of the machine projected on a (d-q) rotating frame [6, 11, 12]. starting from (3) and choosing a state vector equal to the output vector, formed of four currents of the machine. the input vector is formed of supply voltages. then we obtain the following expression: cxy buaxx = +=ɺ (18) with: [ ]trqrdsqsd iiiix = the state vector (for all currants) and [ ]trqrdsqsd vvvvu = the input vector voltages.                 −− +−−− −−−− +− = 2s46 s264 351s 53s12 aaa aaa aaaa aaaa a ω σ ω ω ω σ ω ω ωωω ωωω (19)             − − − − = 23 23 31 31 00 00 00 00 bb bb bb bb b             = 1000 0100 0010 0001 c (20) where: σ σ− = 1 a ; s s 1 l r a σ = ; r r 2 l r a σ = rs srr 3 ll mr a σ = ; rs srs 4 ll mr a σ = ; s sr 5 l m a σ = ; r sr 6 l m a σ = ; s 1 l 1 b σ = ; r 2 l 1 b σ = rs sr 3 ll m b σ = ; rs 2 sr ll m 1 σ σ −= etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 433-439 436 www.etasr.com mohammed chikouche et al.: variable gain pi controller design for speed control of a dfim the choice of x = y makes the system completely controllable and observable. in applying the decoupling method on this system, it follows that: 0;i i =∀ δ and     = = − − abk bl d d 1 1 (21) vy =∗ , therefore: s 1 )s(v )s(y i i = (22) the four currents are decoupled and thus governed by the same transfer function in open loop: s)s(g 1= . c. design the control loops c.1 currents control the currents are decoupled and then we can consider a state space correction with the method of placement of poles. the principal schematic diagram of this correction is given by the figure 2. fig. 2. current regulation by state spaces to ensure the same response for the current loop, the next choice can be adopted.             == k000 0k00 00k0 000k kl (23) so the transfer function of each current closed loop will be of the form: ( ) ks k sh + = (24) c.2 speed control the mechanical equation is given by: ƒ em r d j t t dt ω = − ω − (25) the orientation of the rotor flux on the d axis, and the hypothesis of working with 0, rd i = confer on the electromagnetic torque the following expression: rqrdsdrqsrem ipiipmt φ−=−= (26) as we proceed to the magnetization of the machine before applying a speed reference, rdφ can be replaced by its reference rdrefφ in the relation (26), therefore: rqemrqrdrefem ikipt =−= φ (27) and rrqem tƒik dt d j −−= ω ω (28) with emk being the torque constant. thus, the transfer function of the speed will be expressed by: ( ) ( ) ( )st jsƒ 1 si jsƒ k s rrq em + − + =ω (29) the magnitude ( )str plays the role of a disturbance input for speed, the principal input being ( )sirq . the block diagram of the regulation will be in conformity with that of figure 3. fig. 3. speed control chain iv. vgpi controller in dfim speed control a. vgpi controller structure the use of pi controllers to command a doubly fed induction motor’s speed is often characterized by an overshoot in tracking mode and a poor load disturbance rejection. this is mainly caused by the fact that the gains of the controller cannot be set to solve the overshoot and load disturbance rejection problems simultaneously. overshoot elimination setting will cause a poor load disturbance rejection, and rapid load disturbance rejection setting will cause important overshoot or even instability in the system. to overcome this problem, the use of vgpi controllers is proposed. a vgpi controller is a generalization of the classical pi controller where the proportional and integrator gains vary etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 433-439 437 www.etasr.com mohammed chikouche et al.: variable gain pi controller design for speed control of a dfim along a tuning curve. each gain of the proposed controller has four tuning parameters [13-15]: • gain initial value or start up setting which permits overshoot elimination. • gain final value or steady state mode setting which permits rapid load disturbance rejection. • gain transient mode function which is a polynomial curve that joints the gain initial value to the gain final value. • saturation time which is the time at which the gain reaches its final value. the degree n of the gain transient mode polynomial function is defined as the degree of the variable gain pi controller. if e(t) is the signal input to the vgpi controller the output is given by : ∫+= t ip d)(ek)t(ek)t(y 0 ττ (30) with: ( )      ≥ <+        − = spf spi n s pipf p tt if k tt if k t t kk k (31)      ≥ <        = sif s n s if i tt if k tt if t t k k (32) where pik and k pf are the initial and final values of the proportional gain pk and kif is the final value of the integrator gain ki. the initial value of ik is taken to be zero. it is noted that a classic pi controller is a vgpi controller of degree zero. the vgpi unit step response is given by:        ≥      + −+ <              + +−+ = ssifpf s n s if pipfpi tt if t 1n n tkk tt if t t t 1n k kkk )t(y (33) if stt 〈 the classical pi unit step response is a linear curve beginning at pfk and finishing at pf s pik t k+ whereas the vgpi unit step response ( )0≠n varies along a polynomial curve of degree 1+n beginning at pik and finishing at )1n(ktk ifspf ++ . if stt ≥ , the unit step responses of a pi and vgpi controllers are both linear with slope ifk . from these results, one can say that a vgpi controller has the same properties with a classical pi controller in the permanent region with damped step response in the transient region. a vgpi controller could then be used to replace a pi controller when we need to solve the load disturbance rejection and overshoot problems simultaneously. the vgpi controller in vector control of dfim is used as presented in figure 4. fig. 4. the structure of vgpi controller in dfim vector control the tuned vgpi controller is given by: (34) 1.5 0.4 if t 1 1.9 if 1 14 if t 1 14 if 1 p i t k t t k t         + <= ≥ < = ≥      v. simulation results the dfim used in this work is a 1.5 kw-50hz motor, whose parameters are given in the appendix. the global schema of the state-space nonlinear control of a dfim using vgpi controllers is presented in figure 5. a. speed reversal of rated value in order to make a comparison between the behavior of the conventional pi controller and that of the vgpi controller, studied under different operating conditions, a direct start of the motor under no load is realized with a set point of 157 rad/s followed by an inversion of the rotation direction at time t = 3s, external perturbations are introduced by a sudden application of a 10n.m nominal charge at t = 1s and removed at t = 2s. etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 433-439 438 www.etasr.com mohammed chikouche et al.: variable gain pi controller design for speed control of a dfim fig. 5. block diagram of dfim speed control using a state space nonlinear approach. the results given by figures 6-7 show excellent performance in regulation for the vgpi controller with very good monitoring of the reference speed. this will result in a much lower tracking error than that obtained using the conventional pi structure. note also that the orientation of the rotor flux is fully realized; furthermore, the developed electromagnetic torque reproduces its reference satisfactorily. it can also be noted that the low sensitivity and disturbance rejection are excellent for the vgpi controller which also provides better performance in terms of speed and time disturbance rejection. b. robust control for different values of rotor resistance in order to verify the robustness of vgpi regulator under motor parameters variations, we have simulated the system with rotor resistance variation (increase at 50% of nominal value rotor resistance). figures 8-9 show the responses speed and rotor flux in the test of robustness for different values of rotor resistance. the results indicate that the vgpi regulator is insensitive to the resistance change, which results in zero influence on the torque and rotor flux. an increase of the resistance does not have any effect on the performances of the proposed controller. the vgpi controller rejects rapidly the rotor resistance disturbance. by comparing these results, one can say that varying the gains of a classical pi controller transforms it to a high performance robust controller. a linear variation of the gains (first degree vgpi controller) gave important amelioration. one can mention the setting time value which was almost divided by four or the speed overshoot which was totally eliminated. better performances could be obtained using higher degree vgpi controllers. fig. 6. simulted results of speed control of dfim using vgpi fig. 7. response of the two components of the rotor flux etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 433-439 439 www.etasr.com mohammed chikouche et al.: variable gain pi controller design for speed control of a dfim fig. 8. test of robustness results for rotor flux for different values of rotor resistance: nominal case and +50%. fig. 9. test of robustness results using vgpi for different values of rotor resistance: nominal case and +50%. vi. conclusion in this paper, we presented the principle of speed control of a double-fed induction motor using a variable gain pi speed controller. taking advantage of the accessibility of the current measurement of the motor, a new approach was discussed to allow the decoupling of its currents in a rotating (dq) frame. this principle is based on an input-output decoupling by state space feedback that will serve to obtain very simple currents transfer functions, and therefore, a simplified calculation of the correction. subsequently, we demonstrated the improvement made by the variable gain pi speed controller on the performance of the dfim compared to the conventional pi controller. simulation results demonstrate that vgpi controller outperforms the classical pi controller. further, that the given first degree vgpi controller eliminates overshoot. the simulation results showed a remarkable behaviour of the vgpi controller during regulation and tracking, with a significantly better disturbance rejection than the classic pi controller. simulation results have shown correct rotor flux oriented control behaviour and superior speed tracking performances. the vgpi regulator provides robustness against rotor resistance variation and insensitivity to load torque disturbance as well as faster dynamics with negligible steady state error at dynamic operating conditions. references [1] g. salloum, r mbayed, m pietrzak-david, b de fornel, “mixed sensitivity h∞ control of doubly fed induction motor”, isie 2007, ieee international symposium on industrial electronics, pp. 1300-1304, vigo, spain, june 4-7, 2007 [2] a. l. nemmour, r. abdessemed, a. khezzar, l. louze, m. boucherma, “the input-output linearization control scheme for a doubly-fed induction motor drive”, icem 2008, 18th international conference on electrical machines, vilamoura, portugal, september 69, 2008 [3] l. yuan, h. feng-you, y. zong-bin, "study on sliding mode speed control with fuzzy approach for doubly-fed induction motor", ieee international conference on control and automation, pp. 2171-2175, christchurch, new zealand, december 9-11, 2009. [4] s. drid, m. tadjine, m. s. nait-said, “nonlinear feedback control and torque optimization of a doubly fed induction motor”, journal of electrical engineering, vol. 56, no. 3-4, pp. 57-63, 2005 [5] a. chaiba, r. abdessemed, m.l bendaas, a. dendouga, “performances of torque tracking control for doubly fed asynchronous motor using pi and fuzzy logic controllers”, journal of electrical engineering, no. 2, vol. 5, article no. 5.2.4, 2005 [6] g. salloum, contribution à la commande robuste de la machine asynchrone à double alimentation (contribution at the robust control of doubly fed induction motor), phd thesis, national institut polytechnic of toulous, france, 2007 [7] b. allaoua, a. abderrahmani, b. gasbaoui, a. nasri, "the efficiency of particle swarm optimisation applied on fuzzy logic dc motor speed control", serbian journal on electrical and engineering, vol. 5, no. 2, pp. 247-262, 2008 [8] s. drid, m. tadjine, m.s. nait-said, “robust backstepping vector control for the doubly fed induction motor”, iet control theory & applications, vol. 1, no. 4, pp. 861-868, 2007 [9] d. ben attous, y. bekaka, "speed control of a doubly fed induction motor using fuzzy logic techniques", international journal on electrical engineering and inforrmatics, vol. 2, no. 3, pp. 179-191, 2010 [10] s. k. el khil, i. slama-belkhogja, m. pietrzak-david, b. de formel, “a fault tolerant operating system in a doubly fed induction machine under inverter short-circuit faults”, iecon 2006, 32nd annual conference on ieee industrial electronics, pp. 1125-1130, paris, france, november 710, 2006 [11] m. s. vicatos, j. a. tegopoulos, “a doubly-fed induction machine differential drive model for automobiles”, ieee transactions on energy conversion. vol. 18, no. 2, pp. 225-230, 2003 [12] p-e. vidal, m. pietrzak-david, f. bonnet, “mixed control strategy of a doubly fed induction machine”, electrical engineering, vol. 90, no. 5, pp. 337-346, 2008 [13] a. miloudi, “ etude et conception de régulateurs robustes dans différentes stratégies de commandes d’un moteur asynchrone”, phd thesis, universtity of mohamed boudiaf of oran, algeria, 2006 [14] a. miloudi, e. a. a. radadi, a. d. draou, “a variable gain pi controller used for speed control of a direct torque neuro fuzzy controlled induction machine drive”, turkish journal of electrical engineering & computer science, vol. 15, no. 1, pp. 37-49, 2007 [15] a. miloudi, e. a. a. radadi, a. d. draou, y. miloud, “simulation and modelling of a variable gain pi controller for speed control of a direct torque neuro fuzzy controlled induction machine drive”, pesc 04, ieee 35th annual power electronics specialists conference, vol. 5, pp. 34933498, aachen, germany, june 20-26, 2004 microsoft word 25-2732_s engineering, technology & applied science research vol. 9, no. 4, 2019, 4452-4456 4452 www.etasr.com lima& huebner: optimization of air distribution in a baghouse filter using computational fluid … optimization of air distribution in a baghouse filter using computational fluid dynamics wagner ferreira lima universidade federal de minas gerais departamento de engenharia mecanica belo horizonte, brazil wagnerferreiral@yahoo.com.br rudolf huebner universidade federal de minas gerais departamento de engenharia mecanica belo horizonte, brazil rudolf@demec.ufmg.br abstract—baghouse filters are used to reduce the emission of pollutants in the atmosphere. with the stricter environmental regulations and the need to avoid the emission of pollutants into the atmosphere, the demand for better results in terms of collection efficiency and filtration rises. a good performance of a baghouse filter is closely linked to the correct flow distribution inside it, whether in the hopper or in the bags. other important variables for good performance are internal speed, filtration rate (rap), pressure drop, cleaning efficiency, etc. the upgrading of existing bag filters to current standards is a major challenge for the industry, generally due to, among other factors, emission regulations and common physical and dimensional constraints of the existing equipment. computational fluid dynamics analysis (cfd) can help deal with this problem because it makes possible to perform several analyzes at a lower cost and with great result accuracy when compared with the traditional approaches. in this work, the analysis of an existing bag filter, which presents serious problems of premature discharging of components due to nonuniformity in the internal distribution of the flow, is performed. this analysis has several steps, among them, documentation survey, field survey, flow and pressure drop measurements (pressure differential between the clean side and the dirty side of the filter) with the aid of cfd, with the objective to raise pressure and velocity and to identify possible dimensional changes to improve flow uniformity. keywords-baghouse filter; flow distribution; flow uniformization; computational fluid dynamics (cfd); internal flow i. introduction existing environmental standards have become increasingly restrictive because of growing concerns about climate change, employee and public health. thus, the need emerged to control air quality, minimizing the amount of atmospheric pollutants released by the industrial sector. in this context, environmental protection systems have become increasingly important within industrial facilities, with the purpose of exhausting gases from the production process, containing particulate matter, providing separation and disposing of clean gases (particulate free) or containing particulate matter within the allowable limits. the baghouse filter is the most used in the industry because it has high collection efficiency (above 99%) for inhalable particles. direct impaction is used as a particle capture mechanism. the gas mixture is exhausted by an exhaust system, which can be installed before or after the filter, passing through a pipeline network until it reaches the filter itself, forcing the mixture containing the particles through the filter material (bag filter). the mixture passes through its pores and most of the particles are retained on its surface. it is necessary to remove them from time to time to avoid the formation of a very thick layer that would make the passing of air difficult (increase of the loss of charge). in this work, a bag filter installed to exhaust and treat gases from the storage and transportation of raw materials (coke, iron ore and sinter) from a blast furnace is studied. the filter, since its installation, shows a premature wear of the bag filters, which causes a series of other problems such as constant need for interventions, high cost of replacement of bag filters, premature wear of the exhaust system, etc. in order to reduce the above mentioned factors, a case study of this filter will be carried out with the aid of fluid dynamics simulation (cfd), considering the great potential of this technique for the solution of engineering problems. fig. 1 baghouse filter ii. literature review the atmospheric pollutants are defined as any form of matter or energy with intensity and in quantity, concentration, time or characteristics not in accordance with the established levels, and which render or may render the air: improper, harmful or offensive to health, public or damaging to the material, the fauna and flora or harmful to the security, use, and enjoyment of the property and to the normal activities of the community [1]. atmospheric pollutants can be classified initially according to their physical state: particulate matter, corresponding author: wagner ferreira lima engineering, technology & applied science research vol. 9, no. 4, 2019, 4452-4456 4453 www.etasr.com lima& huebner: optimization of air distribution in a baghouse filter using computational fluid … gases and vapors. solid or liquid particles emitted by sources of air pollution or even those formed in the atmosphere, such as sulfate particles, are called particulate matter and, when suspended in the air, are called aerosols. particulate matter particles can be classified by their size which is determined by the particle formation process and are directly associated with their health effects. particles smaller than 10µm are called inhalable, while those with aerodynamic diameter less than 2.5µm are commonly called respirable. both are of great interest because of their effects on human health [2]. they can also be classified in dusts (of cement, asbestos, cotton, street dust), fumes (of lead, aluminum, zinc, ammonium chloride), smoke (combustion particles of fossil fuels, asphalt materials or wood, containing soot, liquid particles and, in the case of wood and coal, a mineral fraction), and mists (liquid particles). according to [2] there is evidence of the association of particulate matter present in the air with effects on the respiratory and cardiovascular systems of the exposed population. inhalable particles can penetrate the respiratory system, while the finer, respirable ones can also affect the heart and lungs causing serious health impacts. a. treatment of emissions reduction in the amount of generated pollutants can be achieved by the following measures: • equipment use within its rated capacity. • good operation and proper maintenance of the equipment. • enclosures of sources, etc. after exhausting all efforts with measures as mentioned above, without having achieved the necessary reduction in the generation of pollutants, it is necessary to use the equipment for treatment of the emissions (equipment of control of pollutants filters). there are several types of equipment for this purpose, however, this work will be limited to the filter type of pulse jet baghouses. b. baghouse filter baghouse filters are widely used for the control of emissions of particulate matter in industries and present high efficiency, generally above 99%, for fumes and dust above 0.1µm. they are a very complex installation and operation equipment. some items that show the complexity of these devices are listed below: • they treat abrasive gases at high temperatures and high speeds. • they are closely related to the steelmaking process. • operational failures can lead to significant material losses and safety-critical situations. • they are designed by adapting existing process conditions and are often not prepared for the future. • they adapt to layout and available spaces. • they consume a significant amount of water and/or energy. • their maintenance is difficult and time consuming. c. filtering process a brief description of the operating principle of the filter follows. the passage of the gaseous mixture containing the particles through a porous filter material, the gas passing through its pores and the particles, for the most part, are retained on its surface, which from time to time has to be withdrawn to avoid the formation of a very thick layer (cake), which would disturb the passing of gas (increase of the loss of charge). at the beginning of the filtration process, the collect begins with the collision of the particles against the fibers of the filter media and their subsequent adherence to them. as the process continues the layer of particles (cake) collected increases, becoming the collection medium and increasing the efficiency of the process. according to [4], as the particles are collected by the bags, the loss of charge (pressure drop) through the filter media increases until the moment it reaches a predetermined value or a fixed filtration time, where it is necessary, from the economic point of view, and operational to clean the bags. the bags need to be periodically cleaned to avoid excessive pressure drop on the baghouse filter. when the bags are cleaned, a layer of residual dust remains to act as a filter for the smaller particles. the baghouse filter is composed of a series of components, the main of them are: • captors • pipeline, dampers, orifice plates • entrance plenum • dirty tube • bags and cages • cleaning air chamber • cleaning air distribution system • cleaning system, manifold, blowpipe, valves • exhaust system, outlet duct, fan, casing and chimney d. design of a baghouse filter generally, the baghouse filter design is based on the manufacturer's experience with similar processes and applications. a configuration of inlet ducts and filter geometry is adopted, and it is assumed, for calculation purposes, that the flow at the inlet is uniform and that all the bags are subject to the same values of velocity and pressure, which in practice is not true. the author in [5] showed that the design of the filter directly influences the velocity distribution in the bags and that a filter with inhomogeneous distribution provides areas with filtration velocities higher or lower than the filtration rate by design. the existence of too high speed regions can cause premature wear of the baghouses. poor flow distribution can promote non-uniformity in the cake, since higher filtration speeds are responsible for the formation of more compact and more difficult to remove cakes [6], as opposed to lower filtration rates. therefore, the cleaning of the bags may be deficient, since the baghouse set and the surface of each baghouse are subject to filtration cakes of different characteristics. engineering, technology & applied science research vol. 9, no. 4, 2019, 4452-4456 4454 www.etasr.com lima& huebner: optimization of air distribution in a baghouse filter using computational fluid … e. computational fluid dynamics numerical simulation in fluid mechanics and heat transfer, known as cfd (computational fluid dynamics), has an impressive development over the last 20 years [7]. initially used as a tool for analyzing physical problems at the level of scientific research, it is currently recognized as a powerful tool for solving important engineering problems. improving the flow behavior of the fluid inside a bag filter is an engineering problem. there are three ways to develop a project or analyze a problem: analytical methods, numerical methods (numerical experimentation) and laboratory experimentation [7]. out of these, the numerical simulation has been notable for its ability to solve complex problems, with complex geometries and general contour conditions, presenting results quickly. iii. research methodology a. characterization of the problem since the baghouse filter’s operational start, it has been showing a marked wear of the filtering units (bags) shown in figure 2. the cost of maintenance and procurement of spare is high, due to the need for constant interventions for the exchange of damaged bags. fig. 2 worn baghouses b. field survey the data acquisition step was performed in the plant's premises where the baghouse filter is installed and operating. the obtained data were used as input parameters in the numerical model, for its calibration. numerical simulation and modeling steps were performed using the ansys spaceclaim and cfx software, respectively, available and licensed in this plant. the filter to be studied is a pulsed jet type, and its data are listed in table i. drawings were drawn up, the equipment available history was studied and photographic records were made. data were collected in order to obtain enough information to validate the model, the boundary conditions adopted and the simulations to be performed. a data collection chamber was chosen considering the ease of access and the positioning of the measuring points. c. mathematical modeling in this section a brief description will be developed of how the modeling and the numerical simulation were done using fvm (finite volume methods) to obtain the response variables of interest. for the modeling step the ansys spaceclaim 19.2 (2018) software was used. figure 3 shows the model of the original chamber of the baghouse filter. for the mesh generation, ansys meshing software was used (figure 4). figure 5 shows the generated mesh data. fig. 3 model of the filter chamber fig. 4 computational mesh generated fig. 5 generated mesh data for this case, the domain was determined to be fluid with air at 25°c and no particulates. the simplifying assumptions regarding flow conditions are listed below with their respective justifications: • permanent flow: the properties of the fluid can be considered constant in time. • incompressible fluid: the fluid can be considered incompressible since the mach number is less than 0.3, the flow is permanent and isothermal. • isothermal conditions: the studied baghouse filter exhausts conveying belts and silos in an open place. the air was considered to have temperature of 25°c and therefore the effects of thermal exchange can be neglected. • the filter is divided into 8 chambers with medium inlet. for this work, air was considered uniformly divided between engineering, technology & applied science research vol. 9, no. 4, 2019, 4452-4456 4455 www.etasr.com lima& huebner: optimization of air distribution in a baghouse filter using computational fluid … the 8 chambers. a symmetry hypothesis was used to facilitate the work. • hypothesis of the fluid as continuous: a fluid can be treated as a continuous distribution of matter. • the bags were not simulated due to the complexity of geometry, meshes and computational resource. the objective of this work is to find a better distribution of the pressure profile and velocity within the dirty air chamber of the bag filter, so the variables to be evaluated will be the velocity in the three directions ��=(�1, �2, �3) and pressure �, because there is no heat transfer or chemical reactions. to do so, the following laws will be considered: • mass conservation principle: the mass of a fluid in the system is preserved. • newton's second law: the rate of change of momentum is equal to the sum of the forces in a fluid particle. iv. results a. analytical results table i shows the results obtained by analytical calculations for the original geometry. table i. baghouse filter data and analytical results parameter value unit volumetric gas flow rate 600,000.00 m³/h bag diameter 130.00 mm bag length 6,000.00 mm filtering area per bag 2.45 m² number of compartments 12 un number of bags per row 32 un number of compartments 8 un total number of bags 3,072.00 un total filter area 7,527.76 m² filtering velocity 1.33 m/min filtering velocity in cleaning 1.52 m/min maximum can velocity bags + cages distance between centers direction of flutes 180 mm internal dimension of filtration region direction of flutes 5.94 m distance between centers direction of the air manifold 180 mm internal dimension of the filtration region direction of the air manifold 2.34 m transversal area of filtration region 111.20 m² sum of the areas of the bottoms of the bags or pulse pleats 40.78 m² transversal area of the filtration region available for gas rise 70.42 m² can velocity 2.37 m/s can velocity in cleaning 2.95 m/s b. original geometry in figure 6, the streamlines are shown reaching the opposite side of the hopper inlet. it is observed that the velocity collides with the wall with values close to 20m/s, which for a typical application are about 10 times higher than the recommended one. strong recirculation in the bottom of the hopper is also observed, which causes undesirable effects for the efficiency of the filter. fig. 6 current lines on the opposite side of the hopper inlet in figure 7 we can see the velocity profile in a plane just before the baghouses. it is observed that the highest velocity values are on the opposite side of the hopper inlet, it is where there is greater wear and consequent change of baghouses, which agrees with the data collected in the field. it is also observed that the flow is not evenly distributed. fig. 7 profile of velocities in the plane just before the baghouses the ascent velocity (can velocity) has average values of 2.3m/s and can reach 2.9m/s when the chamber is cleaned. the simulation showed values in the order of 11.19m/s on the opposite side to the entrance in the hopper and values close to zero in the distant regions of the entrance. recirculation is also observed in the lower part of the hopper. this recirculation is very damaging to the system, because in addition to recirculating the powder that is already fallen in the hopper, it also causes loss of energy by the turbulent dissipation. studies show that the formation of the cake in the bags is not uniform, just as the pressure drop is not uniform either. the high-speed value inside the filter, besides causing an overload of a part of the filter, still cause the entrance of particulate material in the interstice of the baghouse. this material is not removed by the cleaning system and causes increase in pressure drop, which leads to premature wear of the filter’s baghouses. c. proposed geometry changes in the hopper inlet plenum in the baffle frame will be carried out, as shown in figure 8. the angle of entry of the lower part of the plenum was changed and a baffle was added in the curve of the plenum. the number of baffles was decreased, and the angle increased from 15° to 20°, as shown in figure 8. this was necessary because of the high velocity values in the plenum curve before entering the hopper. engineering, technology & applied science research vol. 9, no. 4, 2019, 4452-4456 4456 www.etasr.com lima& huebner: optimization of air distribution in a baghouse filter using computational fluid … fig. 8 proposed geometry the velocity profile of the proposed geometry is shown in figure 9. it is observed that there is a significant reduction in the speed values within the baghouse filter. the input speed, which was close to 20m/s, is now close to the recommended value which is approximately 7m/s. figure 10 shows a uniform distribution of the pressure field in the selected study regions. fig. 9 velocity profile for the proposed alternative geometry fig. 10 pressure profile for the presented alternative v. conclusion cfd technique was used to investigate the reduction of the consequences generated by the non-uniform distribution of the flow inside the baghouse filter, and thus to find the best solution with optimized time and cost. during the design of the filter, we assumed the averages of the calculated variables are constant, but in practice, this was not verified. a simulation of the baghouse filter model was carried out according to the original design and the results were as suspected: high gas inlet velocity in the hopper, very high-rise velocity and uneven flow distribution, causing overflow on the back side of the hopper inlet, and non-uniform velocity and pressure profile. several tests were carried out by altering the dimensions of the existing baffle frame in order to improve the flow inside the filter with a lower pressure drop to obtain the best speed field, especially in the region just before the start of the baghouses. it was found that in this case, due to the high inflow velocity in the hopper, changes in the baffle frame were not causing significant effects. there was an improvement in the distribution of the gases, but not enough to solve the problem. simulations were carried out through cfd analysis, and it was concluded that it was necessary to increase the angle and the area where the flow enters the hopper, and to change the angle of the baffle frame. after analysis of the alternatives, it was concluded that the alternative which represents the most significant gain in the velocity field is shown in figure 8. in table ii the main parameters studied in this work for the tested models are listed. table ii. comparison between the studied parameters model parameters original proposed entering velocity [m/s] 17.78 9.85 velocity on the opposite side [m/s] 17.67 9.59 velocity in the lower plane [m/s] 11.74 0.03 velocity in the central plane [m/s] 7.14 5.32 velocity in the upper plane [m/s] 5.19 4.04 velocity in the symmetry plane 17.74 10.93 in table ii we can see that there is a reduction of approximately 45% in the main monitored parameters, and in the others an average reduction of 30% was found. this change did not cause a significant change in the recirculation of the flow in the region of deposition of particulate material in the hopper, which can generate the resuspension of the powder. this was presented as the best alternative due to the gains in the uniformity of the pressure and velocity fields at the entrance of the hopper and in the region immediately below the baghouses, where the rate of gas rise is characterized. references [1] conama resolution no 3, june 28, 1990, available at: http://www.braziliannr.com/brazilian-environmental-legislation/conamaresolution-3-90/ [2] world health organization, air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide: global update 2005, who, 2006 [3] united states environmental protection agency, particulate matter, available at: http://www.epa.gov/airquality/particlepollution/index.html [4] d. vallero, fundamentals of air pollution control, elsevier, 2008 [5] r. b. damian, “desenvolvimento de um sistema de filtragem compacto para usinas de asfalto”, 10th brazilian congress of thermal sciences and engineering, rio de janeiro, brazil, november 29-december 3, 2004 [6] e. r. tognetti, influencia das condicoes operacionais na formacao e remocao de tortas de filtracao de gases, msc thesis, federal university of sao carlos, 2007 (in prortugese) [7] c. r. maliska, transferencia de calor e mecanica dos fluidos computacional, ltc, 2004 (in prortugese) ab th cur im fea to sig can als fea par dat ex pro po pro bio spe is s req ana sig lou a. rep pro engineerin www.etasr usi departm fac a dr. bstract—voice hey are used in rrent study a plemented an ature array gen identify the vo gnal type or si n produce a u so showed that ature extraction keywords-wav rameters digital signa ta currently xamples of th 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dio file as an o stored in a composed into fig. 2. sa there are tw ono signal is a arranged in o nal and its va own in figure 3 (a) mon fig. 3. f voice signal a the voice p culated to form y or signature nal. the set of estimated mu 018, 3153-3156 wave equation ct digi ziad partment of c aculty of engin al-balqa ap amma dr.ziad.alqa nalogue audio ng the audio output (figure digital form, a series of sam ampling and quan wo types of d a one-channel one column ar alues are arran 3. no signals first 10 samples o analysis and parameters me m a voice key is then used f parameters in u of the popula 6 n to extract dig ital sig al-qadi omputer engi neering techn pplied univers an, jordan adi@bau.edu.j signal by appl file as an inp 2). when ana each digital mples [1-3]. ntization to produ dss, mono a signal and it rray. stereo fil nged in a two (b) ster of (a) s8 and (b) c voice signal p entioned in [ or signature. t to identify or ncludes: ation [4]. 3153 gital signal fea gnal neering nology sity jo lying sampling put and the d alogue sound w audio file ca ce digital signal and stereo sig s amplitude v le is a two-ch o column arra eo signals cow wave files parameters [4], can be e the obtained v r retrieve the v atures g and digital waves an be gnals. values annel ay as easily voice voice engineering, technology & applied science research vol. 8, no. 4, 2018, 3153-3156 3154 www.etasr.com al-rawashdeh & al-qadi: using wave equation to extract digital signal features  estimated sigma [5].  peak factor (crest factor (cf)) [5].  dynamic range [6-8].  power spectral density (psd) [4, 9]. a matlab code was written to calculate the above mentioned parameters [4] for different voice signals and the implementation results are shown in table i. the code used was: %computing sigma, mu, peak fact, dynamic range % get a section of the sound file %[x,fs] = waveread('ziadyes.wav', [20000 65001]); [x,fs] = audioread('s8.wav'); xxx=x; % sigma and mu estimation [u s] = normfit(x); sigma = num2str(s); zs1=sigma mu = num2str(u); zs2=mu % computing of the peak (crest) factor rms = sqrt(mean(x.^2)); x = abs(x); peak = max(x); q = 20*log10(peak/rms); qstr = num2str(q); zs3=qstr % computing of the dynamic range maxval = peak; x(x==0)=[]; minval = min(x); d = 20*log10(maxval/minval); dstr = num2str(d); zs4=dstr %calculating power spectral density fs = 32e3; t = 0:1/fs:2.96; x = audioread('dog.wav'); pxx = periodogram(x); hpsd = dspdata.psd(pxx,'fs',fs); % create a psd data object. psd1=mean(hpsd.data);zs5=psd1 table i, shows the implementation results. ii. methodology a. wave εquation the wave equation [10, 11] takes the form shown in (1): 2 ,2 = 2 2 ,2 (1) where /c e  is the velocity. usually a discrete equation is considered in the form of the equation with finite difference of second order as shown in (2): 2 2 = 2ℎ2 +1 − 2 + −1 (2) if c=1 and h=1, then (3) can be applied: 2 2 = +1 − 2 + −1 (3) equation (3) can be solved by applying convolution between the array x=[1 -2 1] and the voice signal (laplace operator). b. method the proposed method is based on the wave equation and the following algorithm shows the sequence of operations to be implemented to generate voice features. 1. get the original voice signal data matrix (one column matrix for mono voice signal, or two column matrix for stereo voice signal). 2. reshape the voice signal data to one row array. 3. apply the convolution between laplace operator and the row array. 4. check each value in the convolution results. 5. if the value is greater than zero, add 1 to a local minimums count. 6. if the value is equal to zero, add 1 to a stable count. 7. if the value is less than zero, add 1 to a local maximums count. 8. save the 3 counts as a features array for the voice signal. iii. implementation and experimental results a matlab code was written to implement the proposed method using several experiments. clc close all clear all [x,fs] = audioread('cow.wav'); [s1 s2]=size(x) tic zz=reshape(x,s1*s2,1); dd=[1 -2 1]; zz1=filter2(dd,zz); ff1=sum([zz1<0]); ff0=sum([zz1==0]); ff2=sum([zz1>0]); toc in experiment 1, the word “zero” spoken by a person was taken and its wave file was then recorded using the same sampling frequency (12500), but with a different number of samples. table ii, shows the implementation results of experiment 1. figure 4 shows (a) one of the voice signals wave and (b) the obtained second derivative of this signal. in the experiment 2, different animal voices with different sizes and different sampling frequencies were taken and manipulated. results of this implementation are shown in table iii. from the results shown in tables i-iii, the following are noted:  each voice file was obtained from a unique feature array, and thus, such a unique array can be easily used to identify the voice signal. each obtained feature for each voice file is unique, thus each feature array can be used as a key to identify the voice signal. engineering, technology & applied science research vol. 8, no. 4, 2018, 3153-3156 3155 www.etasr.com al-rawashdeh & al-qadi: using wave equation to extract digital signal features  any change (even very small) will be reflected on the corresponding feature array, and consequently will produce another new feature array.  figure 4 clearly indicates that the proposed method can be used for voice signal smoothing.  finally, the proposed method can be used to generate a key for any type of voice signal (mono or stereo) with any size and any sampling frequency. the third experiment was carried out in order to compare the efficiency between the proposed method and the voice signal parameters. different wave files were taken and processed by both methods. feature array generation time was calculated using cpu processing time. table iv, shows the implementation results of experiment 3. the results strongly reveal that the proposed method can reduce the feature extraction processing at least 28 times and accordingly can be considered to be more efficient than the voice signal parameters methods described in the literature [4-5]. table i. calculated voice signal parameters voice sigma mu peak (crest factor, cf) dynamic range power spectral density (psd) calculation time (s) s1 0.090572 0.001204 15.4313 60.7982 0.0026 0.2366 s2 0.17885 -0.000242 14.0642 65.3405 0.0102 0.2376 s3 0.14246 -0.000229 14.4525 63.7525 0.0065 0.2391 s4 0.10539 0.0012252 13.5841 60.2668 0.0035 0.2346 s5 0.12479 0.0012236 13.2751 61.4252 0.0050 0.2342 s6 0.088082 -0.000240 16.2567 61.3809 0.0025 0.2359 s7 0.11217 0.0012188 13.9156 61.14 0.0040 0.2356 s8 0.12832 -0.000714 13.1212 61.5132 0.0052 0.2329 table ii. results of experiment 1 voice signal number of samples features number of local max stable number of local min s1 12544 5185 2423 4936 s2 14080 5743 2450 5887 s3 18944 8091 2675 8178 s4 15872 7087 1795 6990 s5 16384 6915 2503 6966 s6 16896 6788 3074 7034 s7 14592 6142 2477 5973 s8 14336 6193 1615 6528 table iii. results of experiment 2 voice signal size number of samples frequency sampling (fs) features number of local max stable number of local min cow 30964*2 16000 30689 5 31234 bird 78588*2 44100 63759 21867 71550 dog 46069*2 44100 41300 7590 43248 dolphin 39294*2 44100 39972 3968 34648 donkey 118994*2 44100 112979 10988 114021 duck 205536*2 44100 192594 27020 191458 elephant 22517*2 44100 21957 1769 21308 (a) (b) fig. 4. voice signal and 2nd derivative table iv. results of experiment 3 voice calculation time (s) parameters (1) calculation time (s) 2nd derivative (2) speedup=(1)/(2) s1 0.2366 0.008166 28.9738 s2 0.2376 0.007583 31.3332 s3 0.2391 0.007616 31.3944 s4 0.2346 0.007489 31.3259 s5 0.2342 0.007429 31.5251 s6 0.2359 0.007413 31.8225 s7 0.2356 0.007441 31.6624 s8 0.2329 0.007394 31.4985 cow 0.7429 0.008937 83.1263 dog 0.7674 0.009850 77.9086 iv. conclusion in the current research, a method based on the wave equation designed to extract voice signal features was proposed. the experimental results showed that the extracted 0 5000 10000 15000 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 voice signal amplitude time a m p lit u d e 0 5000 10000 15000 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 2nd derivative of voice signal amplitude time a m p lit u d e engineering, technology & applied science research vol. 8, no. 4, 2018, 3153-3156 3156 www.etasr.com al-rawashdeh & al-qadi: using wave equation to extract digital signal features feature array for each voice signal is unique and can be used as a key to identify the voice signal. the proposed method suits any type of voice signal with any size and any sampling frequency. moreover, it was shown that the feature array is very sensitive to any changes in the voice signal. the comparison between the proposed method’s experimental results and other methods, like the voice signal parameters method described in [4-5], proved that our new proposed method is faster. references [1] r. szabo, a. gontean, i. lie, “sound based coin recognition and clapper”, 16th international conference on soft computing (mendel), pp. 509–516, june 23-25, 2010. [2] a. k. paul, d. das, m. m. kamal, “bangla speech recognition system using lpc and ann”, seventh international conference on advances in pattern recognition (icapr), kolkata, india, pp. 171– 174, february 4-9, 2009 [3] r. szabo, a. gontean, “human voice signal synthesis and coding”, ifac proceedings volumes, vol. 46, no. 28, pp. 336-341, 2013 [4] k. μ. matrouk, a. alhasanat, h. alasha'ary, z. alqadi, h. m. alshalabi, “speech fingerprint to identify isolated word-person”, world applied sciences journal, vol. 31, no. 10, pp. 1767-1771, 2014 [5] r. m. stern, f. h. liu, y. ahshima, t. m. sullivan, a. acero, “multiple approaches to robust speech recognition”, darpa speech v natural language workshop, pp. 274–279, harriman, 1992 [6] p. chatzimisios, c. verikoukis, i. santamaría, m. laddomada, o. hoffmann, mobile lightweight wireless systems, second international icst conference, mobilight, barcelona, spain, 2010, springer, 2011 [7] b. wu, j. zhu, f. n. najm, “dynamic range estimation”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 25, no. 9, pp. 1618-1636, 2006 [8] b. wu, j. zhu, f. n. najm, “an analytical approach for dynamic range estimation”, 41st design automation conference, san diego, usa, july 7-11, 2005 [9] s. miller, d. childers, probability and random processes, academic press, pp: 370-375, 2012 [10] f. gouyon, f. pachet, o. delerue, “classifying percussive sounds: a matter of zero-crossing rate”, cost g-6 conference on digital audio effects (dafx-00), verona, italy, december 7-9, 2000 [11] a. fichtner, s. m. hanasoge, “discrete wave equation upscaling”, geophysical journal international, vol. 209, no. 1, pp. 353–357, 2017 [12] v. e. tarasov, “discrete wave equation with infinite differences”, applied mathematics & information sciences letters, vol. 5, no. 2, pp. 41-44, 2017 authors profiles dr. ayman y. al-rawashdeh was born on 01 january 1970 in jordan. he received his diploma degree in 1995 and phd degree in 2008 in the field of mechatronics engineering. currently he works as an assistant professor at the electric power engineering department, faculty of engineering technology, al-balqa applied university, jordan. his main interests include renewable energy, drive system analysis, simulations and signal processing. ziad al-qadi was born on 09 march 1955 in jordan. he received his diploma degree in 1980 and phd degree in 1986 in the field of computer engineering. currently he is a professor at the computer engineering department, faculty of engineering technology, al-balqa applied university, jordan. his main interests include signal processing, pattern recognition, algorithms, modelling and simulations. microsoft word 24-3278_s1_etasr_v10_n1_pp5228-5232 engineering, technology & applied science research vol. 10, no. 1, 2020, 5228-5232 5228 www.etasr.com boubaker et al.: prediction of daily global solar radiation using resilient-propagation artificial … prediction of daily global solar radiation using resilient-propagation artificial neural network and historical data: a case study of hail, saudi arabia sahbi boubaker department of electronics engineering university of hail hail city, saudi arabia s.boubaker@uoh.edu.sa souad kamel department of computer & network engineering, university of jeddah jeddah, saudi arabia skamel@uj.edu.sa mourad kchaou department of electrical engineering university of hail hail, saudi arabia m.kchaou@uoh.edu.sa abstract—in this paper, several different feed forward artificial neural networks (ffanns) were used for forecasting the oneday-ahead global horizontal irradiation (ghi) in hail region, saudi arabia. the main motivation behind predicting ghi is that it is a critical parameter in sizing and planning photovoltaic water pumping systems. the novelty of the proposed approach is that it employs only the historical values of the ghi itself as explanatory variables and a fast training algorithm (resilientpropagation). in terms of performance metrics, the rp-trained ffanns provided better results than quasi-newton (bfg) algorithm trained ffanns for almost all the studied combinations of the ffann structure. it has been also shown that increasing the number of neurons per layer didn’t improve the performance. medium structures with fast training algorithms are recommended. keywords-global horizontal irradiation (ghi); forecasting; feed-forward artificial neural network (ffann); resilientpropagation (rp) training algorithm i. introduction hail region (saudi arabia) has a semi-arid climate where solar energy is abundant, while water needs to be pumped from relatively deep wells. due to the new electricity pricing policy adopted in saudi arabia at the beginning of 2018, where the price of one kwh increased from 0.05sar to 0.18sar (1usd=3.75sar), solar energy can constitute an alternative solution replacing classical electricity. predicting as accurately as possible the future amounts of solar energy is of high importance in designing stand-alone or grid-connected solar plants. given the fact that solar energy resources measurement stations remain relatively expensive, one solution is the design of computerized numerical forecasters. moreover, global horizontal irradiation (ghi) is characterized by a high level of variability due to the climatic and geographical factors affecting it. accordingly, researchers have resorted to mathematical models to describe such complex and uncertain relationships. an increasing interest in more reliable and accurate forecasting approaches has been observed among the solar energy research community during the last few years. various techniques have been used in the literature to forecast ghi including time-series (ts) and machine learning (ml). artificial neural networks (anns) as flexible tools having high capabilities to map inputs (patterns) to outputs (targets) are popular in the domain of forecasting. however, accuracy is found to be varying from one study to another and to be highly related to the nature and size of the available datasets. the present paper focuses on forecasting the ghi in hail region using different structures of a feed-forward ann (ffann) based only on the historical records of the ghi itself. thus, the ghi is expressed as a symbolic form ghi(t)=f(ghi(t-1), ghi(t-2), …, ghi(t-d)). this form is a dynamic description of the next day ghi. once this form is identified, it will be used in a recursive manner to predict the future value of the ghi. based on trial-and-error procedure, different ffann structures, input combinations, and training algorithms have been explored in order to improve the accuracy and reduce the computational burden. it should be noted that the results presented in this paper are a part of a complete study aiming at sizing, implementing and controlling a pilot photovoltaic water pumping system (pvwps) in hail, saudi arabia. ii. literature review in this section, a critical discussion is presented in order to situate the contribution of our paper. for predicting daily global solar radiation in arid northwest of china, a back-propagation ann tuned by particle swarm optimization (bp-pso) has been investigated in [1], using data from eight meteorological stations. the bp-pso has shown good performance with a coefficient of determination r 2 varying between 0.5630 and 0.9678. sunshine duration has been found to be the most affecting global solar radiation. however, the study presented a kind of now-casting (assessment) exercise rather than a forecasting (prediction) one. based on multiple neural networks and using a photovoltaic panel (pv) model associated with an irradiance forecast, a pv yield prediction system has been presented in [2]. the designed ghi forecaster has shown a mean absolute percentage error (mape) of 3.4% on a sunny day and 23% on a cloudy for stuttgart, germany. the developed approach is found to corresponding author: sahbi boubaker engineering, technology & applied science research vol. 10, no. 1, 2020, 5228-5232 5229 www.etasr.com boubaker et al.: prediction of daily global solar radiation using resilient-propagation artificial … require a large meteorological data set which is usually unavailable. a quaternion-valued neural network (qvnn) based method has been developed for forecasting ghi in [3]. presenting the meteorological variables to the quaternion domain in a unique variable including the latitude, the longitude and the time indexes has resulted on three times reduction of the input-output layers which decreased computation time. this method has been successfully applied on real datasets from tamarnasset, algeria. several empirical equations and ann-based algorithms were used for estimating the solar radiation for stations of aristotle university, greece [4]. using daily meteorological data such as temperature, radiation and humidity as explanatory variables, ann and multi-linear regression (mlr) have been found able to improve the accuracy. prediction and forecasting of monthly mean daily ghi has been implemented using anns. nonlinear autoregressive (nar) with exogenous input (narx) and hybrid time-series have been evaluated in selected regions from nigeria. the hybrid model involving the current month number has been found to be the most accurate and reliable. in fact, the coefficient of determination (r 2 ) has reached 0.96 in abuja when using the hybrid model [5]. since solar radiation is scarcely measured in turkey, an approach using ann, adaptive neuro-fuzzy inference system (anfis), and mlr was implemented in order to forecast ghi in [6]. using a variance factor analysis procedure, calendar month number, average temperature, average relative humidity and extraterrestrial radiation have been found the most affecting ghi variables. ann was more accurate outperforming anfis, mlr and a set of empirical equations. a hybrid approach including wavelet multi-resolution procedure combined to ann has been used in [7] for modeling solar radiation. wavelets have been applied to the original time-series and decomposed them into simple parts. after that, various ann types (mlp, anfis, narx and generalized ann (grnn)) have been used to reconstruct the original signals. the coefficient of determination r 2 has been improved (6.84%) for the mlp and the rmse (2.78%) for the grnn without wavelet transformation. the case study was abudhabi, united arab emirates. further testing was declared to be interesting in other geographical locations. for sizing a stand-alone pv system at almadinah, saudi arabia [8], a radial-basis ann has been utilized for predicting global solar radiation. the rbf using the sunshine duration and the temperature as explanatory variables has provided a coefficient of determination of 98.80%. a set of artificial intelligence methods including anns have been compared when used for assessing global solar radiation in 12 locations over iran in [9]. the group method handling data (gmhd) has been found to outperform the other methods in terms of r 2 , rmse and mse. ann-based methods combined to several feature selection techniques have been devised for predicting one-day-ahead ghi in different locations in saudi arabia [10]. further improvements will be obtained when taking into consideration the uncertainties of the used data. a backpropagation ann (bpnn) optimized by genetic algorithm (ga) and pso for predicting daily diffuse solar radiation in beijing, china has been implemented in [11]. based on several external variables such as temperature and humidity, the psobpnn has been found to be more accurate than ga-bpnn and bpnn. combining bpnn to a global optimization algorithm has helped in overcoming the problem of local search algorithms based on gradient descent. one can conclude that the accuracy of the obtained results is strongly linked to factors such as the size and quality of datasets, the geographic location, the climatic conditions and the design of the method itself. it could be also noted that combined methods look to be more suitable since they allow superposing the advantages of each one of the individual methods. iii. materials and methods the data used to perform this study were collected from king abdullah city for atomic and renewable energy (kacare) in saudi arabia. about two years of daily ghi covering the period from january 1, 2015 to november 30, 2016 from a measurement station located in hail city (figure 1) were utilized. the data were divided into subsets: 85% were used for training and 15% for testing of the ann models. fig. 1. hail region location a. ann pprinciples basically, anns are computing agents that have the ability to imitate the human brain functions. structurally, an ann is composed of nodes, weights and activation functions. in its basic form, an ann includes three layers (input, hidden and output). the main strength of an ann is that given a set of inputs (patterns) and outputs (targets), it performs a training process to map the inputs to the outputs. this process is called training which can be supervised or unsupervised. b. anns used in our study in this study, we considered the case where the one-dayahead ghi is affected only by its own previous values. thus, the ann inputs are respectively ghi(t-1), ghi(t-2), …, ghi(t-d). the output is the ghi(t) and d is the model order (figure 2). the number of neurons in each layer is determined by trial-and-error procedure. the basic multi-layer perceptron (mlp) [14] was used first with a small number of neurons. if the ann fails to provide good performance, the number of hidden layers and the number of their neurons are increased in a reasonable manner. weighted-inputs are summed with biases engineering, technology & applied science research vol. 10, no. 1, 2020, 5228-5232 5230 www.etasr.com boubaker et al.: prediction of daily global solar radiation using resilient-propagation artificial … and fed to a transfer function which converts them to an output of the input layer. this output plays after the role of input to the next layer. this process is repeated until reaching the last layer (commonly called output layer). in general, an ann operates following seven steps: data collection, dataset pre-processing, creation of the network structure, configuration of the network, definition of the ann training parameters, training and testing of the ann. fig. 2. proposed ffann for predicting ghi the multi-layer ffann is described by the following set of equations: a1 = f1 (w1,1x+b1) a2 = f2 (w2,1a1+b2) . aj = fj (wj,j-1aj-1+bj) . an = fn (wn,n-1an-1+bn) (1) where: a j , j=1:n are the outputs of the respective layers. a 1 is the output of the input layer and a n is the output of the output layer), w j,j-1 are the weights of the j th layer, b j are the biases of the j th layer, f j is the transfer function of the j th layer. tangent sigmoid (tansig) and logsig are commonly used for input and hidden layers whereas purelin is usually used for the output layer. it should be noted that n=3 layers (1 input, 1 hidden and 1 output) are used in most cases. if the number of hidden layers is more than one, we will be in the case of deep learning (a special class of machine learning). during the training phase, the training algorithm updates iteratively the ann weights as in (2): w(k) = w(k-1) + 2α∆w(k-1)x t (2) where k is the iteration index, α the learning rate and ∆w(k-1) is the error function related to the weights. in practice, it is very difficult to choose the suitable training algorithm in terms of accuracy and computation time. the choice is conditioned depending on many factors including the quality and size of the datasets, the number of weights and biases to be adjusted, the level of accuracy and the complexity of the problem to be solved. commonly, levenberg-marquardt (lm), scaled-conjugate gradient (scg) and resilient propagation (rp) are used. iv. results and discussion all computations are carried out using matlab2013a run on an intel core i3 processor with a cpu of 2.40ghz with 4gb ram. first, the collected data were pre-processed by dividing them by the maximum value of the daily ghi. the aim of this operation is to transform them into values within the interval [0, 1] which is most suitable for the ann activation functions. at the end of the training and the validation phases, the results are multiplied by the same maximum value to return-back to their regular values. to evaluate the performance of the developed ann algorithms, three performance metrics, namely the mean absolute percentage error (mape), the coefficient of determination (r 2 ) and the rmse were used (see [13, 14] for definitions and details). after several runs, a three-layer (1 input, 1 hidden and 1 output) ann was adopted. the number of neurons in each layer varied. the resilient-propagation (rp) and the quasi-newton (bfg) are used as training algorithms. the tansig and the linear transfer functions (purelin) have been used respectively for the input, hidden and output layers. several combinations of inputs have been roughly tested. it has been found that better results were obtained when using the six previous daily ghis as inputs for forecasting the one-dayahead ghi. the obtained results for some combinations of ann structures are summarized in table i for the training and testing phase, in table ii for the training phase and in table iii for the testing phase. table i. performance o f the trainin g and testin g ph ases case # ann structure training algorithm mape r 2 rmse 1 (10, 5, 1) bfg 6.8554 0.8594 6.7894 2 (10, 5, 1) rp 7.7818 0.8112 7.8657 3 (20, 15, 1) bfg 5.1914 0.9166 5.2281 4 (20, 15, 1) rp 6.9134 0.8576 6.8316 5 (50, 30, 1) bfg 7.9008 0.8069 7.9563 6 (50, 30, 1) rp 5.6850 0.9058 5.5566 jan. 1, 2015 to nov. 30, 2016 table ii. performan ce o f the train in g phase case # ann structure training algorithm mape r 2 rmse 1 (10, 5, 1) bfg 6.9162 0.8606 6.8871 2 (10, 5, 1) rp 7.9192 0.8129 7.9784 3 (20, 15, 1) bfg 4.7008 0.9363 4.6561 4 (20, 15, 1) rp 6.9653 0.8597 6.9087 5 (50, 30, 1) bfg 8.1239 0.8050 8.1450 6 (50, 30, 1) rp 5.3614 0.9157 5.3549 jan. 1, 2015 to aug. 26, 2016 table iii. performance o f the testin g phase case # ann structure training algorithm mape r 2 rmse 1 (10, 5, 1) bfg 6.3815 0.7840 6.0898 2 (10, 5, 1) rp 6.7113 0.7098 7.0590 3 (20, 15, 1) bfg 9.0127 0.6188 8.0899 4 (20, 15, 1) rp 6.5091 0.7698 6.2873 5 (50, 30, 1) bfg 6.1631 0.7506 6.5435 6 (50, 30, 1) rp 7.5339 0.7337 6.7616 aug. 27, 2016 to nov. 30, 2016 to investigate the performance of the ffann for forecasting daily ghi in hail region, six cases have been engineering, technology & applied science research vol. 10, no. 1, 2020, 5228-5232 5231 www.etasr.com boubaker et al.: prediction of daily global solar radiation using resilient-propagation artificial … considered. three levels of investigations have been drawn. at first, the effect of the ann structure was studied (more particularly the number of neurons per layer). then, the used training algorithm in terms of convergence characteristics, result accuracy, and training time and finally, the performance of the ann for different data subsets (training and testing subset, training subset, and testing subset). by analyzing the results of case#1 and case#2 where a relatively small number of neurons have been utilized, we can conclude that the bfg algorithm performs better than the rp algorithm. by increasing the number of neurons per layer (case#3 and case#4), an improvement of performance for both training algorithms for the three data subsets has been obtained. however, the rp training algorithm has provided better results during the testing phase (mape=6.5091, r 2 =0.7698 and rmse=6.2873). this result is very interesting since it concerns the testing phase because naturally the training dataset has to provide good agreement when used in testing phase. the relatively high number of neurons (case#5 and case#6) didn’t improve the results for the bfg algorithm in the three subsets. in addition, the bfg algorithm took a lot of time in training the ann (in case#6, the training time was more than one hour). the rp algorithm was way faster than the bfg. based on the above described results, it can be concluded that for a small number of neurons per layer it is better to use the quasi-newton (bfg) algorithm. for a medium number of neurons, rp can be chosen for its fastness and bfg can be chosen for its accuracy. in the case of high numbers of neurons, the rp training algorithm performs better in terms of computation time. figures 3 and 4 show the graphs of the forecasted ghi, the observed (real) ghi, and the scattered plot of the obtained results during the testing phase. fig. 3. forecasted and observed ghi for the testing phase (ffann trained by resilient-propagation algorithm) v. conclusions the suitability of ffanns to predict daily ghi was evaluated using data from the king abdullah city for atomic and renewable energy (kacare) station located in hail college of technology. fig. 4. scattered plot (case#6) the obtained results were compared with the use of statistical criteria such as mape, r2, and rmse. the best results were recorded when using a medium structure (20, 15, 1) of neurons for the input, hidden and output layers and the quasi-newton (bfg) training algorithm. however, the resilient-propagation (rp) algorithm is recommended for structures with high number of neurons in different layers. further improvements will be achieved in future works by using deep learning (dl) algorithms with more data. also, other explanatory variables such as climatic conditions and storm effects will be investigated. the results of this study can be extended to photovoltaic power system modeling as in [15]. acknowledgment the authors would like to thank hail university for providing the grant number 160811 to support this study. references [1] y. zhang, n. cui, y. feng, d. gong, x. hu, “comparison of bp, psobp and statistical models for predicting daily global solar radiation in arid northwest china”, computers and electronics in agriculture, vol. 164, article id 104905, 2019 [2] s. p. durrani, s. balluff, l. wurzer, s. krautter, “photovoltaic yield prediction using an irradiance forecast model based on multiple neural networks”, journal of modern power systems and clean energy, vol. 6, no. 2, pp. 255–267, 2018 [3] l. s. saoud, f. rahmoune, v. tourtchine, k. baddari, “a novel method to forecast 24 h of global solar irradiation”, energy systems, vol. 9, pp. 171–193, 2018 [4] v. z. antonopoulos, d. m. papamichail, v. g. aschonitis, a. v. antonopoulos, “solar radiation estimation methods using ann and empirical models”, computers and electronics in agriculture, vol. 160, pp. 160–167, 2019 [5] c. g. ozoegwu, “artificial neural network forecast of monthly mean daily global solar radiation of selected locations based on time series and month number”, journal of cleaner production, vol. 216, pp. 1-13, 2019 engineering, technology & applied science research vol. 10, no. 1, 2020, 5228-5232 5232 www.etasr.com boubaker et al.: prediction of daily global solar radiation using resilient-propagation artificial … [6] h. citakoglu, “comparison of artificial intelligence techniques via empirical equations for prediction of solar radiation”, computers and electronics in agriculture, vol. 118, pp. 28-37, 2015 [7] s. hussain, a. alalili, “a hybrid solar radiation modeling approach using wavelet multiresolution analysis and artificial neural networks”, applied energy, vol. 208, pp. 540-550, 2017 [8] m. benghanem, a. mellit, “radial basis function network-based prediction of global solar radiation data: application for sizing of a stand-alone photovoltaic system at al-madinah, saudi arabia”, energy, vol. 35, pp. 3751-3762, 2010 [9] a. khosravi , r. o. nunes, m. a. h. assad, l. machado, “comparison of artificial intelligence methods in estimation of daily global solar radiation”, journal of cleaner production, vol. 194, pp. 342-358, 2018 [10] m. almaraachi, “investigating the impact of feature selection on the prediction of solar radiation in different loactions in saudi arabia”, applied soft computing, vol. 66, pp. 250-263, 2018 [11] x. xue, “prediction of daily diffuse solar radiation using artificial neural networks”, international journal of hydrogen energy, vol. 42, pp. 28214-28221, 2017 [12] s. boubaker, “identification of nonlinear hammerstein system using mixed integer-real coded particle swarm optimization: application to the electric daily peak-load forecasting”, nonlinear dynamics, vol. 90, no. 2, pp. 797-814, 2017 [13] s. boubaker, “identification of monthly municipal water demand system based on autoregressive integrated moving average model tuned by particle swarm optimization”, journal of hydroinformatics, vol. 19, no. 2, pp. 261-281, 2017 [14] s. shah, h. n. nagraja, j. chakravorty, “ann and anfis for short term load forecasting”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2818-2820, 2018 [15] f. mavromatakis, y. franghiadakis, f. vignola, “modeling photovoltaic power”, engineering, technology & applied science research, vol. 6, no. 5, pp. 1115-1118, 2016 microsoft word 15-2686_s_etasr_v9_n3_pp4148-4153 engineering, technology & applied science research vol. 9, no. 3, 2019, 4148-4153 4148 www.etasr.com mahessar et al.: environmental impact assessment of the tidal link failure and sea intrusion on … environmental impact assessment of the tidal link failure and sea intrusion on ramsar site no. 1069 ali asghar mahessar sindh barrages improvement project irrigation department, government of sindh sindh, pakistan amahessar@yahoo.com abdul nasir laghari department of energy and environment, quaid–e–awam university of engineering, science and technology, nawabshah, pakistan a.n.laghari@quest.edu.pk sumeera qureshi department of analytical chemistry, university of sindh, jamshoro, pakistan s.dr582@gmail.com insaf ali siming department of basic sciences and related studies, quaid–e–awam university of engineering, science and technology, nawabshah, pakistan insaf.siming@quest.edu.pk abdul latif qureshi us-pakistan centers for advanced studies, mehran university engineering & technology, jamshoro, sindh, pakistan latif.qureshi@faculty.muet.edu.pk faheem akhtar shaikh department of chemical engineering, quaid–e–awam university of engineering, science and technology, nawabshah, pakistan faheemakhtar86@yahoo.com abstract—this paper presents the impact on the ramsar site no. 1069 that receives fresh water by the kotri drainage system. at present, the complex faces threats by effluents from the left bank outfall drain (lbod) system and from saline seawater intrusion during high tides. these threats have destroyed the ecosystem of the lakes cholari, mehro, pateji and sanhro belonging to the complex. the total present lake area, maintained at the cholari weir crest level, is about 170km 2 . the lakes are expanding, available data shows that there is an increase up to 700% in the original lakes’ area, from 6058 to 41220 acres from 1954 to 1977. this is mainly caused by the operation of kotri barrage surface drainage system and has positive impact on lakes’ ecology because the drainage effluent is of marginal salinity. the rapid increase in the lakes’ area, of about 40% within 2 years after the functioning of the tidal link with saline effluents from lbod and sea intruded water have changed the ecology of the area. this posed significant impact on the ecosystem. conversely, a similar rise in water level due to sea intrusion has nearly doubled the surface area and reposed a negative impact on the system. these lakes were giving shelter to a wide variety of local and migratory birds and had aquatic biodiversity. hence, parts of sanhro and mehro dhands have been recognized by the ramsar convention. keywords-tidal link; sanhro and mehro dhands; lbod; ecosystem; sea intrusion i. introduction tidal link is the component which makes the lbod unique among drainage projects in pakistan and probably in the world. the saline water must be disposed of in such a way that it could not damage other areas or fresh water bodies. with the ever-growing awareness of the need to protect the natural environment, disposal to lakes, rivers or natural depressions has become unacceptable. the tidal link allows strongly saline effluents to flow directly to the sea. it extends from the end of the kadhan pateji outfall drain (kpod) to the sir tidal creek [1]. prior to the construction of the tidal link the water of pateji/cholri dhand area was maintained at a level of approximately 5 feet above mean sea level by a natural land bar separating it from the rann of kutch. since the construction of the kotri surface drainage system in the 1960s, the dhands have become an environmentally important wildlife sanctuary, and also support a thriving fishing industry [2].the spinal drain was constructed to dispose drainage water into sea via the tidal link [3]. the southerly section of the lbod system was constructed in 1995 having length of 25 miles. it has a point of junction from kpod to its outfall in sir creek [4]. disasters that commonly occur in fast succession are cyclones, heavy rainfall, floods and droughts. manmade disasters have affected the coastal population badly as well [5]. however, in several parts of badin district, saline water has brought land degradation and submergence of the area due to failure of the system to meet the desired results. coastal wetlands are of pivotal importance to human activities and natural systems [6, 7]. however, it is challenging to determine quantitative measure values for the wetlands due to several factors such as complicated hydro-biological functions, corresponding author: abdul nasir laghari engineering, technology & applied science research vol. 9, no. 3, 2019, 4148-4153 4149 www.etasr.com mahessar et al.: environmental impact assessment of the tidal link failure and sea intrusion on … socioeconomic context and diversity [8]. policy suggests that both market and non-market values of the wetlands can be considered into account during decision making. globally, 50% reduction has been seen in the wetlands [9]. one third of the species are dependent on wetlands [10]. the urbanization and climate change are bringing about the wetlands at the brink of degradation [11, 12]. sinatry and shakoor dhands lie at the pakistan-india border and are fed by dhoro puran. the area is swampy at the location of tidal link and is covered with large interconnected water bodies such as cholri, pateji sanhromehro, and khadi dhands [13]. after the construction of the lbod, the natural flow of the water was altered and the waters from the 3 dhands flow into the cholri and cholri weir via shah samando creek and runn of kutch into the open sea [14]. it is worth mentioning that more than two dozen breaches have taken place in the tidal link drain after the cyclone 2a. the cholri weir controlling the water level in dhands was damaged and completely washed out during the cyclone. this altered water flows and water exchange and affected the water emancipations from the lbod in the area [14]. a sharp incline angle of the bank of the tidal link drain near rd–93 was observed due to the impact of the cyclone 2a at various locations. the water from the arabian sea and from the indian territory now directly enters into the tidal link drain. the movement of the water is unrestricted from the tidal link drain to adjacent dhands and vice versa [15]. when the water salinity was tested at different rds, high values were recorded at rd–114, rd–124, rd–93 and rd–74, indicating sea water presence. there has been a free exchange of water between dhands due to the washing away of tidal link drain at different places [15]. the high amount of salinity of the rann of kutch affects the salinity of tidal link canal left bank as it flows through its breaches. at least up to 1997, the salinity conditions stayed favorable in dhands. presently, the range of salinity conditions goes from those typical for sea water to the hyper saline pateji dhand. ii. study area the drainage water across pateji dhand and cholri into the arabian sea via shah samando creek is delivered by the man made tidal link drain. the research study area is located at latitude of 24 o 29'7162''n and longitude 68 o 60'5430''e. the length of tidal link is 41km starting from its juncture point with kpod in the northeast upto the shah samando creek in the southwest. the tidal link is built in such a way that it can transport about 3,118 cusecs of drainage water. the alignment of the tidal link passes across pateji and cholri dhands which are linked with mehro and sanhro dhands. these dhands have drained the excess water into the rann of kutch. tidal link now blocks this drainage. iii. materials and methods the ph and salinity values of tidal link and dandhs were measured on site. a. ph meter the hi 8014 measures ph with temperature compensation. it measures qrp as well. different modes of measurements can be switched by the user. b. refrectometer the salinity and specific gravity of sea water can be measured using this device. c. failure of constructed cholri weir the design of the weir was in such a way that it could flow in either direction to the tidal cycle having a cresl level of 4.5ft and length of 18000ft. the water level in the dhands must not exceed the limit of 6ft. as a comparison, the designed water levels in the incoming karo ghungro and fuleliguni outfall drains are 10 and 11ft [16]. d. cyclone 2a, 19th may 1999 in this area, rainfalls and cyclones are common phenomena, responsible for causing damage to the tidal link and infrastructures. before cyclone 2a, the creeks were connected to the sea 50m away from the main city of badin [17]. iv. results and discussion there is a 700% increase in original dhands area from 6058 to 41220 acres from 1954 to 1977 due to the operation of kotri barrage surface scheme. this has positive impact on dhands ecology because the drainage effluents are of marginal saline. but the rapid increase in the dhands area of about 40% within 2 years after the functioning of the tidal link with saline effluents from lbod and sea intruded water have been changing the ecology of the area. table i. dhands area before tidal link construction dhand name area acres extended area acres (1997) 1954 1977 1991 cholri 300 5715 5560 60,000 mehro 620 9575 9730 sanhro 975 16525 15908 bakradi 234 620 in mehro bakar 1575 600 in pateji pateji 2354 5714 6332 mandhar not exist 2471 4300 narahi not exist dry dry 6058 41220 41800 60,000 a. sources of dhands water supply the sources of water supply of the area are mainly from the tail end channels of fuleli and pinyari canal of kotri barrage. the area is also supplemented by outfall drains. kadhan-pateji, karo gunghro and fulleli guni discharge into the dhands area. these drains carry effluents from agricultural lands and storm water during monsoon rains from a total catchment area of more than 2000 sq. miles. karo-gunghro outfall drain and ahmed rajo branch drain discharge into sanhro dhand. fuleligunni outfall drain discharges into mehro dhand. some sub drains and branch drains of kadhan-pateji outfall system discharge via kpod into the pateji dhand (table ii). table ii. discharges of kotri surface drains in tidal area drain name out fall discharge (cusecs) fulleli guni outfalls drain mehro dhand 2550 ahmed rajo branch drain mehro dhand 80 karo gunghro outfalls drain sanhro dhand 1768 kpod tidal link 3626 engineering, technology & applied science research vol. 9, no. 3, 2019, 4148-4153 4150 www.etasr.com mahessar et al.: environmental impact assessment of the tidal link failure and sea intrusion on … b. impact of tidal link on the dhand complex in 1995, the tidal link was built so that it could withdraw 3 million tons of salt and 0.7 million acre feet of sewage into the sea per year. issues were brought up concerning the operation of the tidal link drain such as saline water flow rates, water movements and their influence upon the dhands and coastal wetlands. in order to sustain the area ecology, a long (1800ft) weir was constructed on the norther bank of tidal link and the south limb of cholri dhand. the drain of the tidal link does not flow through any agricultural lands. the cholri weir contributes in maintaining the water balance and quality in dhands. the water samples were collected from different areas (figures 1-4) which were affected by the high tide of sea (before the construction of the tidal link) and were sent to the sindh university for analysis in 1997. the ph values of all samples have been found within permissible limits except the sample from sanhro. the electric conductivity was higher at cholri, fuleli tidal-129rd. the other samples were within permissible limits. the measured chloride content was in the range of 1000 to 40000ppm, and the salinity was relatively low in most of the samples. fig. 1. ph values before the construction of the tidal link fig. 2. electric conductivity before the construction of the tidal link c. cyclone 2a and tidal link damages the monsoons dominate the coastal zone of indus delta from july to september. most of the damages to infrastructures are caused by cyclones and heavy rainfalls in this area. the cyclone 2a damaged the tidal link severely. this calamity left the banks of 56 locations with partial breaches. the system could not sustain the storm water due to its failure. the sweet to saline water dhands like mehro, kadan pateji, sanhro and cholri were turned saline due to seawater intrusion. fig. 3. cloride values before the construction of the tidal link fig. 4. salinity values before the construction of the tidal link before cyclone 2a the creeks were connected to the sea water 50km away from the main badin city. the sea water approached many villages at a distance of 35km from the main city. water samples were collected in 2001 from different locations/areas (figures 5-8) affected by high sea tides before the construction of the tidal link and were sent to sindh university for analysis. the results showed that ph values of all samples were within permissible limits except the sample from sanhro. the electric conductivity was higher in the samples from cholri, fuleli tidal-129rd, while the other samples were within permissible limits. the measured chloride content was in the range of 2000 to 16000mg/l. salinity refers to the total amount of soluble salts in the water. it is expressed in ds/m at 25 o c. excess soluble salts present in water can change its chemical and physical characteristics. salinity has been used here as a main indicator for sea water intrusion. the salinity recorded during 2001 shows that cholri and pateji dhands were generally as saline as sea water (34000ppm), and that sanhro and mehro dhands were of low salinity (6000ppm) although still well above the salinity of canal water (450ppm). kpod water had also low salinity (5000ppm) in winter. there is no dilution source for the dhands and adjoining agricultural fields resulting to salt accumulation on the dhands bed, intrusion on land and spreading on the area through winds. engineering, technology & applied science research vol. 9, no. 3, 2019, 4148-4153 4151 www.etasr.com mahessar et al.: environmental impact assessment of the tidal link failure and sea intrusion on … fig. 5. ph values after the construction of the tidal link fig. 6. electric conductivity after the construction of the tidal link fig. 7. cloride values after the construction of the tidal link fig. 8. salinity values after the construction of the tidal link d. seawater intrusion tidal link probably, the main cause of the excess amount of salinity in the tidal link drain is the water exchange between dhands and the high salinity adjoining creeks. the seawater from shah samando creek has now extended up to rd-55 and beyond. according to the visible topographic changes, the outfall of the tidal link has shifted from rd-155 to an area between rd-93 and rd-125. the water salinity in tidal link drain at various rds ranged from 30 to 45ppt, the water salinity at rd-93 varied between 30 and 44ppt, but mostly remained between 30 and 35ppt. lower water salinity indicates the influence of kpod water in the tidal link drain. no brackish water/fresh water was observed to enter dhands or the tidal link drain. e. seawater intrusion in dhands the area between the high tidal zone and the agricultural lands contains a few but huge dhands. the water in these dhands varies from sweat to saline. high amount of salinity in the dhands is probably the result of seawater mixing with the tidal link and the decreased flows in a few of the kotri drains (fuleli and karo). the flow from kotri drains consequently ends up in the tidal link via narri sanhro and mehro dhands. evaporation may be an effective factor for balancing the water level in dhands. the polluted streams from sugar factories and others may pose a serious threat to them. figures 9-13 show the values of surface water salinity per year. water quality has been improved by the recent rainfall flood in 2011. due to the inter-connection of sea water with cholri weir, the narri and associated dhands aren’t suitable for accumulating fresh or rainfall water. fig. 9. salinity of mehro dhand fig. 10. salinity of sahro dhand engineering, technology & applied science research vol. 9, no. 3, 2019, 4148-4153 4152 www.etasr.com mahessar et al.: environmental impact assessment of the tidal link failure and sea intrusion on … fig. 11. salinity of pateji dhand fig. 12. salinity of cholri dhand fig. 13. salinity of sahro, mehro, cholri and pateji dhands f. satellite images of the dhand area the total area covered by the dhands (cholri, pateji, sanhro, and mehro) is about 153 sq. miles. these dhands are interconnected naturally via open narrow channels. various species of migrating birds from siberia to north pole, aquatic life of fish and plants rely on these dhands for their survival. fig. 14. satellite image of the tidal link area, 21 oct. 1989 fig. 15. satellite image of the tidal link area, 3 feb. 1999 compared to the 1989 image (figure 14) of the tidal link, the natural vegetation/swamps have vanished in 1999 (figure 15). when compared to 1999, a massive water body appears to have shrunk in the southern part of kadhan, cholri and pateji dhands. tidal link drain appears to have stopped water inflow from irrigation canals draining to cholri and patrji to kadhan and thus converted them to wet mud flats. g. environmental and socioeconomic impact dhand water attracts thousands of migratory birds from siberia and europe from november until the end of march. dhands serve as feeding grounds, only few of the migratory birds species breed there. the dhands are rich in aquatic life, they produce large numbers of shrimps and fish, which depend on fresh and sea water during their life cycle. crops cultivated in the years 1993 to 1998 in the affected area in rabi (november to may) are: wheat, barely, vegetables, mustard seed, sunflower, hurbo and maize fodder. in kharif (may to october) are: maize fodder, rice, sugar cane and vegetables. fish farming is active and growing in this area, with the majority of the workforce belonging to the fisher community. the main stakeholders of the area are small landowners, harees (tenants) and laborers. they are involved in agriculture, small business, livestock, fishing, and various manual labor occupations. information collected shows that the numbers of small and medium landowners are the majority. the majority of farmers holds lands below 12.5 acres. v. conclusions the dhands are an environmental concern, they possess estuary ecology and maintain a biodiversity of flora and fauna. the concept of the cholri weir was to maintain 5ft water depth in the dhands and give way overflow water to the tidal link, in order to maintain the ecology of the area. the effect of the natural disaster of the 1999 cyclone, high tides during the 2000 quake, the 26 may 2001 storm and the 2003, 2006 and 2011 heavy storms further damaged tidal link. they have completely shattered the system from shah samando creek to seerani drain. the satellite images show the completely wash away picture of the tidal link. there is a free way of sea flooding during high tides and rough weather particularly in monsoon season from shah samando creek. these conditions along with drought triggered seawater intrusion in the area severely demaged the area’s ecology. agricultural fields, fresh water reserves and fishing activities have been reduced. dhand water attraction of migratory birds declined. inhabitants have to travel far away from their homes in search of basic commodities such as food, water, firewood, fodder, etc. something that directly impacts human life in this area. wild engineering, technology & applied science research vol. 9, no. 3, 2019, 4148-4153 4153 www.etasr.com mahessar et al.: environmental impact assessment of the tidal link failure and sea intrusion on … life pattern has changed, the seasonal migrating has not been seen in this area since long, particularly after the failure of the tidal link. sweet water fish have been replaced by saline water species whose majority is carnivore, their colonies are continuously increasing and eventually they will lead the remaining native species to extinction. generally, the ground water is saline and the residents are depended on the occasionally available canal water or are forced to purchase water from venders. the contaminated water causes various diseases like diarrhea, jaundice, abdominal and skin diseases, which are common in the area. concluding, the failure of the tidal link had a serious impact in the life of common people. acknowledgement the authors are thankful to the sindh irrigation and drainage authority and sindh barrages improvement project for providing the facilities to conduct this research work. references [1] m. e. habib, environmental study of seawater intrusion around tidal link, msc thesis, mehran university of engineering and technology, 2013 [2] world bank left bank outfall drain project talking pakistan’s waterlogging and salinity problems, 1997 [3] s. h. n. rizvi, j. baquer, i. raza, “disposal of saline surface drain to inter-tidal delta, arabian sea using gravity gradient”, canadian 1999 coastal conference, victoria, canada, may 19-22, 1999 [4] a. l. qureshi, s. n. chandio, s. m. kori, “performance evaluation of surface drains in lbod project area: a case study of spinal drain”, 1st national seminar on drainage in pakistan, jamshoro, pakistan, august 16-18, 2000 [5] national institute of oceanography, hydraulic monitoring of the tidal link drain, quarterly progress report (april – june ‘99), 1999 [6] r. e. heimlich, k. d. wiebe, r. claassen, d. gadsby, r. m. house, wetlands and agriculture: private interests and public benefits. agricultural economic report no. 765, resource economics division, economic research service, u.s. department of agriculture, 1998 [7] w. j. mitsch, j. g. gosselink, wetlands, van nostrand reinhold, 1993 [8] p. f. scodari, wetlands protection: the role of economics, environmental law institute, 1990 [9] united nations environmental programme (unep), the status of the nigerian coastal zones, 2007 [10] g. asibor, “wetlands: values, uses and challenges”, paper presented to the nigerian environmental society at the petroleum training institute, effurun, nigeria, november 21, 2009 [11] n. o. uluocha, i. c. okeke, “implications of wetlands degradation for water resources management: lessons from nigeria”, geojournal, vol. 16, pp. 151–154, 2004 [12] r. akpofure, environmental sciences: an introduction, kraft books, 2009 [13] j. r. schubel, “estuarine circulation and sedimentation: an overview”, in: marine geology and oceanography of arabian sea and coastal pakistan, pp. 113-136, von nostrand reinhold company, 1984 [14] national institute of oceanography, hydraulic monitoring of the tidal link drain, quarterly progress report (october – december 2000). national institute of oceanography, 2000 [15] national institute of oceanography, hydraulic monitoring of the tidal link drain, quarterly progress report (october – december 2001). national institute of oceanography, 2001 [16] wapda, physical monitoring of lbod stage-1 project. revised work plan and cost estimates 1995/96 to december 1997, directorate of scarps monitoring (south), 1995 [17] m. e. leghari, developing sustainable management plan for water supply and sanitation in coastal area of badin, msc thesis, mehran university of engineering and technology, 2013 microsoft word 01-tarvor2-ed2.doc etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 133-138 133 www.etasr.com tarnavsky and vorozhtsov: cloud computing in science and engineering and the “scishop.ru” … cloud computing in science and engineering and the “scishop.ru” computer simulation center gennady a. tarnavsky institute of computational mathematics and mathematical geophysics, siberian branch of the russian academy of sciences novosibirsk, russia gennady.tarnavsky@gmail.com evgenii v. vorozhtsov khristianovich institute of theoretical and applied mechanics, siberian branch of the russian academy of sciences novosibirsk, russia vorozh@itam.nsc.ru abstract—various aspects of cloud computing applications for scientific research, applied design, and remote education are described in this paper. an analysis of the different aspects is performed based on the experience from the “scishop.ru” computer simulation center. this analysis shows that cloud computing technology has wide prospects in scientific research applications, applied developments and also remote education of specialists, postgraduates, and students. keywords-cloud computing; information technologies; internet; computer simulation i. introduction one can identify cloud computing as a unique direction among the various developments of advanced information technologies. it should be noted that the cloud is one of the internet symbols. the purpose of the present work is to give a general review of cloud computing and to illustrate an example based on the internet cloud portal, “scishop.ru” computer simulation center. a. the ideology of cloud computing cloud computing is a rapidly developing and promising direction of contemporary informatics. the ideology of cloud computations lies in transferring, to a considerable extent, the arrangement for computations and the processing of data from personal computers to worldwide web servers. the concept of cloud computing is based on the internet being capable of meeting the demands of users as they are generated and also processing data within wide ranges of users’ requests. for example, the google apps system provides applications for business in the online regime, the access to which occurs with the aid of internet browsers, and all software and data are stored in the google servers whereas the google chrome operation system (os) is based entirely on cloud computing. in addition, the microsoft corporation has developed its new version of the os windows azure whose segments are based nearly entirely on cloud technologies. in particular, ms office is stored in ms servers, with a free (licensed) access provided to clients on their request. this frees the users from the need to install the system in their own computers and to support its functioning in the future. the resource demands for pcs and even for workstations for collective use, decrease substantially when using cloud computing. the cloud computing direction is exceptionally promising for the development of remote education in different branches of knowledge as well as for computer modeling in the remote access regime. therefore, one should expect in the near future a massive appearance of cloud web resources. b. technologies of cloud computing cloud computing contains a specialized spectrum of processing and transferring data technologies with computer resources being provided to the user as internet services. the user has access to data, which are permanently stored in web servers, only as a client during the internet sessions. the information (and process results) can be stored on personal computers, notebooks, netbooks, smartphones, etc. until now, one can identify several basic technologies (models) of cloud computing: ● infrastructure as a service (iaas). ● platform as a service (paas). ● data as a service (daas). ● software as a service (saas). ● workplace as a service (waas). ● all as a service (aaas). within the framework of the iaas, paas, daas, saas, and waas models the customers pay for the software lease (the aaas model), that is its use via the web interface, rather than for the possession of the software itself. thus, in contrast to the classical scheme of licensed software purchase, the customer does not need to invest large funds for the acquisition of the product and for a computer platform suitable for its installation and for its future efficient operation. the customer has only relatively low periodic expenses in the form of user charges which can always be interrupted (and renewed) based on the need for the software. etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 133-138 134 www.etasr.com tarnavsky and vorozhtsov: cloud computing in science and engineering and the “scishop.ru” … c. cloud computing in internet the process of the transfer of computational complexes conventionally involved the purchase of computer codes (in some cases also the program texts), from the developers, by the future user and their installation on his computer. for a faultfree and smooth operation of the program, the user should have a similar operation environment, including the systems for the visualization of digital data. the stage of program installation can be very complex and often causes many difficulties whose surmounting may require considerable and non-productive expenses of intellectual efforts and time. the cloud form of using the computational complexes solves all problems related to the installation of the acquired program product. it should be noted that the right of use of program complexes rather than their sale is kept in mind here. the electronic forms of trade in the internet, including the trade of computer programs, are already fairly well developed. a special computer simulation center site named “scishop.ru” is currently being developed. the program complexes are hosted in this center together with all of their attributes: the processing system for the preparation of tasks, the processing system for the execution of tasks (the execution of computational operations) and the postprocessing system for the output of the obtained information in digital and graphical forms. the user has only to formulate its own computational task by inputting the necessary numerical data and start its computation. the problem solution will be provided for the user upon termination of computations. user's comfort during their stay at the center is ensured via client support. in economic terms, such a method of operation of program complexes means their leasing from the resource developers rather than their purchase. ii. sites providing users a direct computer simulation in internet remote access regime in the near future, one should expect mass appearance of internet sites at which the simulation of subject-oriented large scientific and applied problems related to numerical integration of complex nonlinear equations systems will be carried out. the “scishop.ru” computer simulation center [1, 2, 3] is such an internet site, providing (at present) solutions for problems of high-speed aerodynamics [4, 5, 6, 7], computational astrophysics [8], and the design of nanostructured semiconductor materials [9, 10] the direct numerical computations of problems formulated and started by the visitor of the site are carried out at the center, without an intermediate procedure of the purchase of computational complexes and installation on the visitor’s computer. it should be emphasized that all interfaces have been debugged and “tuned” properly and no problems regarding the operation of acquired programs arise when placing the processing systems. the functioning of complexes is troublefree within the indicated ranges of the variation of parameters (note that one can ask on the site forum at any time any question and get an explanation). one more advantage of this approach is that the user is freed from the necessity of buying the often costly hardware, which is necessary for the execution of needed computations [11]. the user “leases” the hardware from the developers of the site only for the time needed for the solution of his problem. summarizing the above brief survey one can state the following: the cloud computing concept is a very promising direction of infocommunication technology and constantly gain a more and more widespread application range. the introduction of the cloud concept in science and engineering is yet delayed, but one may predict a mass appearance of cloud portals of computer simulation in the future, since cloud computing provides appealing advantages regarding the “consumption” of program products compared to conventional commercial sales. it should be noted however that, besides technological problems, special problems of copyright and intellectual property may arise [12]. iii. “scishop.ru” computer simulation center the “schishop.ru” computer simulation center is an internet cloud portal (figures 1 and 2). the goal of the development of the computer simulation center (http://www.scishop.ru) is the development and improvement of new techniques for scientific knowledge dissemination, based on advanced infocommunication technologies for the process, storage, transfer and protection of information. fig. 1. main page of the internet center for computer simulation (a fragment). • the center is designed for the realization of advanced needs in the commercialization of scientific products. it aims to the solution of fundamental problems related to various scientific, technological, social, and psychological aspects etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 133-138 135 www.etasr.com tarnavsky and vorozhtsov: cloud computing in science and engineering and the “scishop.ru” … of the development and promotion of specialized web resources. • the center structurally consists of two segments: center-1 and center-2. • the center includes four big information-computation complexes (iccs) “impact”, “flow”, “astra”, and “nano” , as shown in figures 3-6. fig. 2. main page of the section “center-1”. a. services provided by center-1 • the following services are provided for the visitor of center-1: 1. access to the libraries containing scientific papers on declared themes. 2. access to tabular and/or graphical databases containing the results of computer simulation of some spectrum of computer tasks. 3. access to the processing systems enabling the client to organize and conduct the computer simulation of problems which are of interest to him. 4. access to sites of leading russian and foreign journals in corresponding branches of knowledge. 5. access to “forum'” for consultations and discussion of problems. • in the non-commercial regime, the visitor has access to the demo versions of center-1 systems. for a full-scale access, the visitor has to register and transfer payment. • the center’s system for receiving payment accepts payments from any electronic payment systems (webmoney, yandex.money, e-gold, etc.) included in the “robokassa” consortium. a system for receiving payments using credit bank cards and mobile telephony sms has also been developed and is currently being verified. fig. 3. base page of the section of the icc “impact” “high-velocity internal aerodynamics: computation of shockwave structures in a scramjet diffuser”. b. services provided by center-2 • center-2 is intended for storing program developments in various branches of knowledge, without theme limitations. the content of this section can be provided by specialists having the copyright for these information resources. • all specialists in the area of computer simulation in any knowledge branches, that wish to promote their work on commercial basis, are invited for cooperation with center2. specialists wishing to place their scientific products at center-2 have to study the conditions, get in touch with the administration of the center and sign an agreement. one can learn more about all aspects of the center functions in the special section “publications” using the corresponding hyperlink from the site main page. all cloud technologies iaas, paas, daas, saas, waas, and aaas are used at the “scishop.ru” portal in its different segments. etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 133-138 136 www.etasr.com tarnavsky and vorozhtsov: cloud computing in science and engineering and the “scishop.ru” … fig. 4. base page of the section of the icc “flow” “high-velocity external aerodynamics: the computation of the flow around the objects in the atmosphere of earth and mars”. c. “infrastructure as a service” (iaas) technology the computer simulation center provides internet infrastructure and portal infrastructure: • apparatus means (servers, the systems for storing the data, client systems, net facilities). • operation systems and the system software (the means of virtualization, automation, and control). • multi-functional segments of the portal content (the switches of regimes, gateways, etc.). d. “software as a service” (saas) technology the information-computational complexes provide the client with the following characteristics: • complexes are used in the remote access regime. • multi-communication (several clients may use the same complex simultaneously). • support of complex systems is included in the payment. • modernization of complexes occurs smoothly and invisibly for clients. e. “data as a service” (daas) technology the center provides to the client the library, tabular, and graphical databases, which contain: • theoretical materials and the texts of published papers. • digital results of executed computations of scientific and applied problems and their visualization. the client is provided with the necessary control of data flow and information protection concerning the transfer of data via the net. fig. 5. base page of the section of the icc “astra” “computational astrophysics: simulation of the dynamics of processes in the inter-galactic gas and protoplanet clouds”. f. “workplace as a service” (waas) technology the center provides maximum comfort for scientific research to clients and reduces the costs for the operation of the clients’ own workstations, by “replacing” them with a virtual environment of centralized infrastructure (employing the supercomputer of the siberian branch of the russian academy of sciences). g. “all as a service” (aaas) technology the program complexes of the center may be used both free of charge (demo versions) and on commercial basis: • access to full-scale functioning of the center is granted after the visitor's registration in the specialized “book of record” and after the visitor transfers the user charge via the electronic payment systems. • the specialized “robokassa” bank system is used for payment transfers, which ensures the use of more than 20 electronic payment systems (webmoney, yandex.money, internet.money, etc.). etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 133-138 137 www.etasr.com tarnavsky and vorozhtsov: cloud computing in science and engineering and the “scishop.ru” … • a system has been introduced, enabling the payments with the use of mobile telephony sms. payment transfer safety, routing transparency, the necessary messages for the client and the currency conversion in different electronic payment systems, is ensured by the special structures of the “robokassa” system and has been checked during the trial operation of the computer simulation center. fig. 6. base page of the icc “nano” “microelectronics: computer support of the design of nano-structured semiconductor materials”. h. arrangement of computations and information flows on the portal. “data file cruise” dfc technology the comfort of the client's stay at the internet center and a convenient use of its segments (the bibliographic section, databases and especially the processing systems), are the most important attributes of any program complex. the systems for the preprocessing preparation of tasks (the input of parameters and the start of processing systems) are organized in a clear, convenient, and simple form, which does not cause any ambiguous interpretation and difficulties even for users with small experience. operations are performed by the user in the remote access regime at the computer simulation center via the worldwide web rather than in the user’s own computer during the installation of the complex. this gives the visitor of the center the opportunity to study the computational complex in the real time regime, organize the solution of the task of interest, and obtain the result of computer studies. the computational complex transfer usually involves the acquisition of licenses, documentation, and computer codes. after that, the user installs the purchased product on his own computer. this may cause difficulties in general, due to various reasons, ranging from the use of different versions of operation systems to the peculiarities of the seller’s and buyer’s supporting systems. such problems become obsolete with the placing of the processing systems at the center. significantly enhanced cloud computing methodology is incorporated at the creation of the web resource “scishop.ru”. in general, cloud computing methodology usually assumes that the information flow moves only in two directions: from the client's browser to the internet server and back. one can call the developed new organization of information flows in “scishop.ru”, the dfc (data files cruise) technology. this technology has a much larger number of motion directions of information flows: from the client's browser to the “scishop.ru” internet server to the entrance in the supercomputing center (ip1 address) to the exit from the supercomputing center (ip2 address) to the “scishop.ru” internet server and back to the client's browser. the client can take the obtained solution file either directly at the portal “scishop.ru” or at the indicated ip2 address. it is planned to implement subsequently a third variant: the transfer of the solution at an address indicated by the client. the dfc technology is a big advantage for the computer simulation center because the client, possibly a scientific researcher or applied designer, may not be familiar with system programming. this way the user can focus on the physical or technological meaning of his problem, without unjustified and excessive time expenses and intellectual effort for the formation of the computational task. to avoid any misunderstandings it should be noted that the procedure of using the supercomputer in the remote access regime is sufficiently well known, however, quite a different thing is meant here: the creation of the files for the access to the supercomputer, the execution of computations, and solution transfer at the indicated address is done by the systems of the “scishop.ru” automatically, without the client's participation. it is possible subsequently to also use other supercomputing centers on an alternative and/or combined basis. iv. positive and negative aspects of cloud computing cloud computing application gives rise to a number of complex problems, with several positive and negative arguments. the following positive and negative factors of cloud computing can be identified: • positive factors for developers: 1. efficient struggle against the non-licensed use of programs since the product itself does not reach the customer. 2. relative ease of detection and suppression of unauthorized access of several users under the same login. 3. substantial reduction of costs for the development and introduction of technical and consulting support for each customer. etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 133-138 138 www.etasr.com tarnavsky and vorozhtsov: cloud computing in science and engineering and the “scishop.ru” … • positive factors for users: 1. no need for software installation in the workplaces of the users since access to the software is performed via a plain browser. 2. drastic reduction of the expenses for the unwrapping of the system in an institution. 3. reduction of costs for technical support and renewal of unwrapped systems, including the case of their total absence. 4. quickness of introduction, due to the absence of time expenses for system unwrapping. 5. clarity and predictability of payments. 6. possibility of obtaining a higher level of software servicing. • negative factors for the developers: 1. cloud computing is by no means applicable to all functional problems. 2. since the main economy of the provider's resources is reached at the expense of the scale, the cloud computing approach may prove inefficient for a small number of clients. 3. the cloud computing approach is inefficient if it is necessary to perform an in-depth individual adaption to each customer. • negative factors for customers: 1. attachment to a single developer and its hosting site. 2. instability of the provider's work may lead to impossibility of long-term planning and deadline wrecking. 3. undesirability of using the cloud computing for projects of strict confidentiality because of a high risk of information leaking from the service provider and the impossibility of controlling the process. 4. difficulty of improving the quality of the services in the current operation regime. 5. need for a permanent internet connection with a fairly high speed of data transfer. an important issue is the confidentiality problem. the scientific and technological process in any country and, naturally, in russia has certain “niches” of closed themes where information leaking is extremely undesirable. the outside skilled specialist can easily determine by a number of signs the direction of the research theme. this may obliterate the application of cloud computing for the given objectives in principle despite the wide spectrum of positive factors. regarding the developer, one of the main shortcomings of cloud computing is the high cost of entering the market. to provide a competitive price to the client the developer needs the “scale effect”, that is a large number of potential clients. this way small projects with a convenient very low payment, may have large profit rates depending on the number of clients. v. conclusions in the present paper, we have briefly investigated the ideology, technologies, and problems regarding the cloud computing concept, considering the example of the “scishop.ru” computer simulation center, a pioneer of a new form of scientific knowledge dissemination. this center is designed for direct use of program complexes of mathematical modeling of processes in various scientific areas, providing the possibility of a direct execution of computations in the internet remote access regime. such a form has wide prospects of application in scientific research as well as applied developments for the remote education of specialists, 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[2] g. a. tarnavsky, e. v. vorozhtsov, “computer simulation center in internet”, cornell university, new york, 2011. http://arxiv.org/abs/1101.0664. [3] g. a. tarnavsky, “cloud computing: content, infrastructure, and technologies of the arrangement of information flows of the computer simulation center scishop.ru” (in russian), investigated in russia, vol. 13, no. 001, pp. 1–29, 2010. http://zhurnal.ape.relarn.ru/articles/2010/001.pdf. [4] g. a. tarnavsky, a. g. tarnavsky, k. v. gilev, “informationcomputation internet center “aeromechanics”. the first line: program complex “shock”” (in russian), numerical methods and programming, vol. 6, no. 1, pp. 27–48, 2005. [5] g. a. tarnavsky, “shock-wave modes of flow at the inlet to the diffuser of a hypersonic scramjet engine: the effect of flight altitude and velocity”, high temperature, vol. 43, no. 1, pp. 58–72, 2005. 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[12] s. b. zhibinov, g. a. tarnavsky, “computer simulation center in internet: problems of copyright and intellectual property of the content” (in russian), investigated in russia, vol. 12, no. 073, pp. 953–967, 2009. http://zhurnal.ape.relarn.ru/articles/2009/073.pdf. microsoft word 38-3486_s_1_etasr_v10_n2_pp5554-5560 engineering, technology & applied science research vol. 10, no. 2, 2020, 5554-5560 5554 www.etasr.com ben khedher et al.: numerical comparison of triangular and sinusoidal external vibration effects on … numerical comparison of triangular and sinusoidal external vibration effects on the 3d porous drying process nidhal ben khedher mechanical engineering department university of hail hail, saudi arabia and national school of engineers of monastir, university of monastir monastir, tunisia rzig ramzi thermal and energy systems studies laboratory national school of engineers of monastir university of monastir monastir, tunisia ibrahim a. alatawi mechanical engineering department college of engineering university of hail hail, saudi arabia abstract—drying is one of the most energy-intensive industrial processes. one of the techniques aiming to reduce energy consumption is the vibration technique which is generally employed to intensify the heat and mass transfer process. in this respect, this paper presents a three-dimensional numerical model to study the external vibration effects on the drying process of a porous medium. the model is based on a comparison of heat and mass transfer phenomena that arise during vibrating drying of unsaturated porous medium for two cases: triangular and sinusoidal external vibrations. the three-dimensional unstructured control volume finite element method (cvfem) is employed to simulate the vibrating drying. numerical results of the time evolution of temperature, liquid saturation, pressure, and water content are compared and analyzed for the two cases. keywords-external vibration; vibrating drying; unsaturated porous medium; cvfem i. introduction the problem of intensification of heat and mass transfer in porous media has attracted considerable attention over the last years. this interest has been motivated by a large domain of industrial applications, including food, wood, paper, building, ceramic, etc. to solve this problem, more efficient technologies have been employed. the development of the vibration phenomenon in porous media has been an emerging subject in many fields of science and engineering. the vibration phenomenon has been found to enhance heat and mass transfer process and to improve systems efficiency. for many years research has been interested in heat and mass transfer during the drying process which is one of the oldest processes in porous media, characterized by coupled heat and mass transfer phenomena. however, the consumption of high quantity of energy during porous solids drying has made it an interesting subject in scientific and technological range with a variety of industrial applications. also, high cost and long execution time of experimental studies made the numerical simulation widely employed to analyze the drying process. in consequence, research focuses on the employment of more efficient technologies to intensify the drying process [1]. recently, several methods have been developed as the technique of drying with ultrasonic [2] and later with acoustic [3] frequencies. these two techniques present many disadvantages such as high noise level and low energy efficiency. consequently, the vibration is an important alternative gaining increasing [4]. authors in [5] investigated the influence of airborne ultrasound conditions on drying. moreover, authors in [6] studied the drying intensification by vibration. also, authors in [7] studied the vibration effect on convection excitation in fluid and porous layers. recently, authors in [8] conducted a numerical analysis of the effect of vertical vibrations on heat and mass transfer through natural convection in a partially porous cavity. more recently, authors in [9] developed a 3-d numerical model to study the vibration effects on the drying process. the motivation of this study is that the vibration is a new technology for the amelioration of drying process which deserves to be further studied and analyzed. the aim of the present paper is to offer a numerical study that can explain the external vibration effects on the drying process through a comparison between two configurations of vibration (triangular and sinusoidal vibrations). in this context, a 3-d numerical model is employed to describe the coupled heat and mass transfer phenomena during vibrating drying of unsaturated porous plate. the numerical results of studying the effects of the two types of vibration on the drying process are presented and analyzed. ii. governing equations the proposed model is based on a numerical problem treating a comparison of external vibration effects of hot air on heat and mass transfer during the drying of unsaturated porous medium. the physical domain is a porous plate composed of three phases (solid, liquid and gas). the geometry of the plate can be seen in figure 1. corresponding author: nidhal ben khedher (n.khedher@uoh.edu.sa) engineering, technology & applied science research vol. 10, no. 2, 2020, 5554-5560 5555 www.etasr.com ben khedher et al.: numerical comparison of triangular and sinusoidal external vibration effects on … fig. 1. dimensions and geometry of the porous plate the numerical model is a comparison of heat and mass transfer during the drying process for three configurations of drying (hot air velocity):  classical drying (without vibration): 10 m sav  (1)  with triangular vibration:   m sav a t b   (2) with: 3 , 0; 0 3 6 2 , 3 ; 3 3 3 2 , 3 ; 3 v v v v v v v v v v v v v a t a b t t a t t a b a t t a t a b a t t t                       with sinusoidal vibration:  sin(2 )a v vv a f t m s     (3) where  10 m sv va a  is the maximum amplitude of vibrating velocity, t is the time,  0.2sv vt t  and  5hzv vf f  are respectively the period and the frequency of vibrating velocity and a is the acceleration. the periodic evolution of hot air velocity for the two configurations of vibrating drying (triangular and sinusoidal) are presented in figure 2. fig. 2. evolution of hot air velocity during a period for triangular and sinusoidal vibrations referring to the theory given in [10-12], various mathematical versions have been employed to describe the drying phenomenon for porous media. a. thermodynamic relations the partial pressure of the vapor is equal to its equilibrium pressure:  ,v veqp p t s (4) where s is the liquid saturation defined by: 𝑆 = (5) the gaseous phase is assumed to be an ideal mixture of perfect gases: 𝑃 = 𝑅𝑇; 𝑖 = 𝑎 (6) 𝑃 = 𝑃 + 𝑃 𝜌 = 𝜌 + 𝜌 the vapor pressure is given by: = 𝑒𝑥𝑝 (− . . . . . ) (7) the presented model has the following assumptions:  the porous plate is homogenous and isotropic.  the three phases (solid, liquid, and gas) are in local thermodynamic equilibrium.  the gaseous phase is thermodynamically ideal.  the terms of tortuosity and dispersion are considered as diffusion terms.  the work of compression and the viscous dissipation are negligible.  the radiative heat transfer is negligible. based on the above assumptions, the macroscopic equations for the heat and mass transfer that arise during the drying of porous medium can be derived. b. generalized darcy's law the average velocities of gaseous and liquid phases, which are noted respectively as gv and lv , are obtained from darcy's law which is generalized by using the relative permeability (calculated as the ratio between the intrinsic permeability and the effective permeability).  the gaseous phase: 𝑉 = − 𝛻𝑃 (8) the gaseous velocity is calculated without taking into consideration the gravitational effect.  the liquid phase: engineering, technology & applied science research vol. 10, no. 2, 2020, 5554-5560 5556 www.etasr.com ben khedher et al.: numerical comparison of triangular and sinusoidal external vibration effects on … 𝑉 = − 𝛻 𝑃 − 𝑃 − 𝜌 𝑔 (9) where 𝑃 = 𝑃 − 𝑃 is the capillary pressure. c. mass conservation equations  the gaseous phase: for this phase the average density is not constant. in this case, the mass conservation equation is given by: + 𝛻 𝜌 𝑉 = �̇� (10) where 𝜌 is the intrinsic average density of the gas phase which is considered as an ideal mixture of perfect gases.  the vapor phase: + 𝛻(𝜌 𝑉 ) = �̇� (11) 𝜌 𝑉 = 𝜌 𝑉 − 𝜌 𝐷 𝛻 (12) 𝐷 represents the coefficient of the effective diffusion of the vapor in the porous medium. this coefficient takes into account the resistance to the diffusion due to tortuosity and the effects of constriction.  the liquid phase: assuming that liquid density is constant, the mass conservation equation of the liquid phase is: + 𝛻(𝑉 ) = − ̇ (13) where �̇� is the mass rate of evaporation which is the volume fraction of liquid phase. d. energy conservation equation 𝜌𝐶 𝑇 + 𝑑𝑖𝑣 𝜌 𝐶 𝑉 + ∑ 𝜌 𝐶 𝑉, 𝑇 = 𝛻 𝜆 . 𝛻𝑇 − ∆𝐻 . �̇� (14) where ∆𝐻 is the latent heat of vaporization at temperature 𝑇(𝐾) , 𝜆 and 𝜌𝐶 are respectively the effective thermal conductivity and the constant pressure heat capacity of the porous medium and 𝜌𝐶 is given by: 𝜌𝐶 = 𝜌 𝐶 + 𝜌 𝐶 + 𝜌 𝐶 + 𝜌 𝐶 (15) where 𝜌 𝐶 , 𝜌 𝐶 , 𝜌 𝐶 and 𝜌 𝐶 are the mass heat capacities of the plate solid matrix, liquid, vapor, and air. iii. solution procedure cvfem has been widely employed to simulate heat and mass transfer in porous media [13, 14]. consequently, this method is employed to solve the equation set with boundary conditions [15, 16]. a. creation of 3-d meshing the free mesh generator gmsh [17] is employed to create the 3-d meshing of the porous plate (figure 3). afterwards a fortran code is developed to describe the coupled heat and mass transfer phenomena that arise during vibrating drying of porous plate. fig. 3. three-dimensional porous plate meshing iv. boundary conditions the variables (temperature, saturation and pressure) are initially uniform in the porous plate (figure 4). fig. 4. drying conditions on the exchanging faces (right, left, top, front and back faces), we can write: 𝜆 〈 〉 + 𝛥𝐻 𝜌 〈𝑉 〉𝑛 = ℎ (〈𝑇〉 − 𝑇 ) (16) the mass flow corresponding to evaporation and to the evacuation of water is a function of the vapor density difference and mass transfer coefficient: [𝜌 〈𝑉 〉 + 〈𝜌 〉 〈𝑉 〉]𝑛 = ℎ (𝐶 − 𝐶 ) (17) the gaseous pressure on the exchanging face is equal to the atmospheric pressure: 〈𝑃 〉 = 𝑃 (18) since the plate is placed on the swing of the dryer, the bottom face does not exchange heat with the hot air. then, we assume that the bottom face (y=0) is adiabatic and impermeable. 𝜆 〈 〉 + 𝛥𝐻 𝜌 〈𝑉 〉𝑛 = 0 (19) [𝜌 〈𝑉 〉 + 〈𝜌 〉 〈𝑉 〉]𝑛 = 0 (20) 〈 〉 = 0 (21) the convective mass and heat transfer coefficients are given by the following equations [18]. the convective mass transfer coefficient [m/s]: 4 / 5 1/ 3 , 0.023a b e c m c d r s h l     (22) engineering, technology & applied science research vol. 10, no. 2, 2020, 5554-5560 5557 www.etasr.com ben khedher et al.: numerical comparison of triangular and sinusoidal external vibration effects on … the convective heat transfer coefficient [w/m2°c]: 4 / 5 1/ 30.023 e r t c r p h l      (23) the validity of these equations is: 55 10er  0.6rp  0.6cs  with: a a c e a v l r    a a r a c p    , a c a b s d   where lc=0.02m is the characteristic length of porous plate and da,b is the vapor diffusion in air obtained by: 4 2 1 , , 0.26 10a b vap aird d m s        (24) the numerical code is validated in [9, 13]. v. numerical results and discussion in this section, a 3-d numerical model is employed to study the effects of externals vibrations (triangular and sinusoidal vibrations) on coupled heat and mass transfer during the drying of unsaturated porous plate. the purpose of this study is to analyze the simulation results illustrating the 3-d coupled mechanisms that take place during the vibrating drying. the results are presented for three different configurations of drying:  classical drying (without vibration)  triangular vibrating drying  sinusoidal vibrating drying for the three cases, the three drying conventional phases are noticed (figures 5-7):  the transient heating phase: this phase is characterized by the evolution of the temperature of the material to the wet bulb temperature accompanied by the evaporation a short period in time. also, a slight depression takes place in this first period.  the constant drying rate phase: all the heat supplied to the plate is consumed by the evaporation of water to the solid surface whose temperature is evolving to the wet bulb, it homogenizes and remains constant. moreover, the gas depression reduces without canceling.  the decreasing drying rate phase (first and second periods): this time period is characterized by evaporation inside the environment and diffusion to the surface. also, the air diffuses towards the inside. fig. 5. comparison of the evolution of temperature fig. 6. comparison of the evolution of liquid saturation fig. 7. comparison of the evolution of pressure the drying conditions for simulation are presented in table i. table i. simulation drying conditions 𝑻𝒂𝒎𝒃 [ oc] 𝑻𝒊𝒏𝒊 [ oc] 𝑺𝒊𝒏𝒊 [%] 𝑪𝑽𝒂𝒎𝒃 𝑷𝒂𝒎𝒃 [atm] 𝑷𝒊𝒏𝒊 [atm] 100 20 50 0.01 1 1 engineering, technology & applied science research vol. 10, no. 2, 2020, 5554-5560 5558 www.etasr.com ben khedher et al.: numerical comparison of triangular and sinusoidal external vibration effects on … in figures 5-7, we see a comparison of the time evolution of temperature, saturation and pressure between the three configurations of drying. in figure 5, it is observed that the profile of temperature for the triangular vibrating drying is more rapid than for the two other drying configurations. consequently, this configuration implies a rapid drying time. moreover, the isenthalpic phase (second phase of drying) is clearly longer for the sinusoidal vibrating drying. this delay in time is explained by the fact that the heat and mass transfer coefficients take more time to reach their maximum compared to the triangular vibration. here, we can conclude that not all air vibration types will surely improve the drying process, but the vibration type should be carefully chosen. moreover, the vibration period is an important parameter which should be optimized. in this context, the influence of this parameter was detailed in [9]. figure 6 exhibits a comparison of the time evolution of liquid saturation. from this figure, it is clearly noted that the triangular vibrating drying presents a gain of time since the liquid saturation drops more rapidly than the other configurations. this gain in time is due to the presence of the triangular vibration which encourages the heat and mass transfer by forcing the liquid inside the plate to move to the exchanging faces, and consequently to be dried more rapidly. figure 7 depicts the evolution in time of the gaseous pressure for the three configurations of drying (classic, triangular and sinusoidal vibrations). from this figure, it can be noted that the pressure profiles have three different peaks with the more rapid and intense peak corresponding to the triangular vibrating drying while the sinusoidal vibration has the slowest and the weakest gaseous pressure. this behavior is justified by the reasons above which are the time evolutions of heat and mass transfer coefficients which are slower compared to the triangular one. to be really sure of which vibration type is better, the comparison of time evolution of water content is presented in figure 8. as expected, the triangular vibration performs better. the triangular vibration forces all the liquid in the porous plate to migrate to the exchanging faces. consequently, it encourages the evaporation and the diffusion to the surface. in this context, this type of drying encourages the coupled heat and mass transfer to be more intense and rapid, implying a rapid and intense drying. fig. 8. comparison of the evolution of water content to explain more the three dimensional effects of the two configurations of external vibration, it is interesting to exhibit the spatiotemporal evolutions of temperature, saturation and pressure during the drying process. in order to better represent the spatial distribution of different variables for the three cases, the slices view after two hours of drying of temperature, saturation and pressure are shown in figures 9-11. figure 9 depicts a 3-d comparison of the temperature distribution along the drying process. referring to this figure, and compared to the two other cases, the triangular vibrating drying is the most intense. however, the energy is driven within the plate due to the heat conduction and the presence of the triangular vibration forces the liquid water to be evaporated at the surface of the medium and the moisture moves out of the board dues to the diffusion. moreover, the sinusoidal vibrating drying presents the lowest evolution of temperature in the whole porous plate. (a) (b) (c) fig. 9. comparison of the temperature distribution the during drying process (time=2h) for (a) classical, (b) triangular, (c) sinusoidal drying the presence of three orthogonal exchange faces forces the moisture content to be very low at the corner. during drying time, only the core of porous plate retains a high value of moisture content (classical drying) (figure 10). referring to the result presented in figure 10, the sinusoidal vibrating mode of drying retains the highest amount of water in the core of the porous medium. as a result, it presents the lowest gaseous pressure compared to the other cases. engineering, technology & applied science research vol. 10, no. 2, 2020, 5554-5560 5559 www.etasr.com ben khedher et al.: numerical comparison of triangular and sinusoidal external vibration effects on … (a) (b) (c) fig. 10. comparison of the saturation distribution during the drying process (time=2h) for (a) classical, (b) triangular, (c) sinusoidal drying moreover, for the triangular vibration case the liquid water extraction from the core of the porous plate is accelerated, and then dried more rapidly at the exchanging faces. consequently, the gas pressure in the core of the porous medium is intense forcing the water to migrate to the exchanging faces (figure 11). from the presented results (figures 9-11), we can conclude that the drying process becomes more rapid and intense with the triangular vibration which forces the liquid inside the porous plate to migrate to the exchanging faces in order to be dried more rapidly than the two other modes of drying. vi. conclusions in the present study, a 3-d numerical simulation has been developed to analyze the heat and mass transfer mechanisms that arise during vibrating drying. in order to quantify these effects, two types of external vibration of hot air are tested: triangular and sinusoidal vibrations. consequently, three configurations of drying of unsaturated porous medium (classical drying, triangular and sinusoidal vibrating drying) are studied. referring to the numerical results, these two modes of vibration are characterized by two effects which are totally inverse: the triangular vibrating drying is characterized by a rapid and intense evolution during the drying process, while the sinusoidal vibration leads to slow and weak drying rate. this behavior can be explained by the fact that the resultant heat and mass transfer coefficients take more time to reach their maximum during the sinusoidal vibration and they remain low for a longer time during the vibration period. (a) (b) (c) fig. 11. comparison of the pressure distribution during the drying process (time=2h) for for (a) classical, (b) triangular, (c) sinusoidal drying acknowledgement the authors would like to thank the deanship of the scientific research of the university of hail, saudi arabia for funding and supporting the research project (grant n°0160823). nomenclature a acceleration of hot air [𝑚𝑠 ] 𝐴 maximum amplitude of hot air velocity [𝑚𝑠 ] ca specific heat of the air [𝑘𝐽𝑘𝑔 𝐾 ] cp specific heat at constant pressure [𝑘𝐽𝑘𝑔 𝐾 ] 𝐶 specific heat of the vapor [𝑘𝐽𝑘𝑔 𝐾 ] 𝐷 , diffusion coefficient [𝑚 𝑠 ] 𝑓 vibration frequency [hz] 𝑔 gravitational acceleration [𝑚𝑠 ] engineering, technology & applied science research vol. 10, no. 2, 2020, 5554-5560 5560 www.etasr.com ben khedher et al.: numerical comparison of triangular and sinusoidal external vibration effects on … ℎ convective mass transfer coefficient [𝑚𝑠 ] ℎ convective heat transfer coefficient[𝑤𝑚 ℃ ] k intrinsic permeability [m²] 𝐿 characteristic length of plate [m] ma molar mass of air [𝑘𝑔𝑚𝑜𝑙 ] mv molar mass of vapor [𝑘𝑔𝑚𝑜𝑙 ] m evaporation rate [𝑘𝑔𝑠 ] 𝑛 outward normal vector p pressure [pa] pc capillary pressure [pa] 𝑃 partial pressure of saturated vapor [pa] r gas constant [𝐽𝑚𝑜𝑙 𝐾 ] r the average radius of curvature of the menisci s liquid saturation [%] t temperature [k] 𝑇 vibration period [s] t time [s] 𝑉 air velocity [𝑚𝑠 ] greek symbols 𝜀 porosity 𝜀 volume fraction of liquid phase 𝜇 dynamic viscosity [𝑘𝑔𝑚 𝑠 ] 𝜗 kinematic viscosity [𝑚 𝑠 ] 𝜌 density [𝑘𝑔𝑚 ]  conductive transfer coefficient [𝑤𝑚 ℃ ] 𝜎 surface tension [𝑁𝑚 ] ∆𝐻 vaporisation latent heat [𝐽𝑘𝑔 ] subscripts 0 initial condition a air eff effective g gas l liquid v vapour dimensionless groups 𝑅𝑒 reynolds number 𝑃𝑟 prandtl number 𝑆𝑐 schmidt number references [1] g. musielak, d. mierzwa, j. kroehnke, “mechanisms of drying acceleration by ultrasounds”, 19th international drying symposium, lyon, france, august 24–27, 2014 [2] v. acosta, j. bon, e. riera, a. pinto, “ultrasonic drying processing chamber”, physics procedia, vol. 70, pp. 854-857, 2015 [3] s. j. kowalski, “ultrasound in wet materials subjected to drying: a modelling study”, international journal of heat and mass transfer, vol. 84, pp. 998-1007, 2015 [4] j. kroehnke, j. szadzińska, e. radziejewska-kubzdela, r. biegańskamarecik, g. musielak, “ultrasoundand microwave-assisted convective drying of carrots: process kinetics and product's quality analysis”, ultrasonics sonochemistry, vol. 48, pp. 249-258, 2018 [5] s. m. beck, h. sabarez, v. gaukel, k. knoerzer, “enhancement of convective drying by application of airborne ultrasound: a response surface approach”, ultrasonics sonochemistry, vol. 21, pp. 2144-2150, 2014 [6] j. colin, w. chen, j. casalinho, m. e. a. ben amara, s. ben nasrallah, m. stambouli, p. perre, “drying intensification by vibration: fundamental study of liquid water inside a pore”, 21thinternational drying symposium, valencia, spain, september 11-14, 2018 [7] e. a. kolchanova, n. v. kolchanov, “vibration effect on the onset of thermal convection in an inhomogeneous porous layer underlying a fluid layer”, international journal of heat and mass transfer, vol. 106, pp. 47-60, 2017 [8] e. h. zidi, a. hasseine, n. moummi, “the effect of vertical vibrations on heat and mass transfers through natural convection in partially porous cavity”, arabian journal for science and engineering, vol. 43, pp. 21952204, 2018 [9] r. rzig, n. ben khedher, s. ben nasrallah, “a 3-d numerical heat and mass transfer model for simulating the vibration effects on drying process”, heat transer asian research, vol. 46, pp. 1204-1221, 2017 [10] a. v. luikov, “systems of differential equations of heat and mass transfer in capillary porous bodies (review)”, international journal of heat and mass transfer, vol. 18, no. 1, pp. 1–14, 1975 [11] s. whitaker, “a theory of drying”, advances in heat transfer, vol. 13, pp. 119-203, 1977 [12] n. ben khedher, “numerical study of the thermal behavior of a composite phase change material (pcm) room”, engineering, technology & applied science research, vol. 8, no. 22, pp. 26632667, 2018 [13] r. rzig, n. ben khedher, s. ben nasrallah, “three-dimensional simulation of mass and heat transfer in drying unsaturated porous medium”, heat transfer research, vol. 48, no. 11, pp. 985-1005, 2017 [14] a. latreche, m. djezzar, “numerical study of natural convective heat and mass transfer in an inclined porous media”, engineering, technology & applied science research, vol. 8, no. 4, pp. 3223-3227, 2018 [15] b. r. balliga, s. v. patankar, “a new finite-element formulation for convection–diffusion problems”, numerical heat transfer, vol. 3, no. 4, pp. 393-409, 1980 [16] b. r. balliga, s. v. patankar, “a control-volume finite element method for two-dimensional fluid flow and heat transfer”, numerical heat transfer, vol. 6, no. 3, pp. 245–261, 1983 [17] c. geuzaine, j. f. remacle, “gmsh: a 3-d finite element mesh generator with built-in preand post-processing facilities”, international journal for numerical methods in engineering, vol. 79, no. 11, pp. 1309–1331, 2009 [18] f. p. incropera, d. p. de witt, t. l. bergman, a. s. lavine, fundamentals of heat and mass transfer, john wiley & sons, 2002 microsoft word 32-2558_s engineering, technology & applied science research vol. 9, no. 1, 2019, 3832-3835 3832 www.etasr.com sandhu et al: effect of river indus sand and recyclable concrete aggregates as fine and coarse … effect of river indus sand and recycled concrete aggregates as fine and coarse replacement on properties of concrete abdul razzaque sandhu department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs, pakistan abdulrazzaque@muetkhp.edu.pk muhammad tahir lakhiar faculty of civil and environmental engineering, universiti tun hussein onn malaysia, 86400 parit raja, batu pahat, malaysia mtl.eng17@gmail.com ashfaque ahmed jhatial department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs, pakistan ashfaqueahmed@muetkhp.edu.pk hemu karira department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs, pakistan engr.hemu07civil@gmail.com qadir bakhsh jamali department of mechanical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, sindh, pakistan qjamali@quest.edu.pk abstract—as the demand for concrete rises, the concrete materials demand increases. aggregates occupy 75% of concrete. a vast amount of aggregates is utilized in concrete while aggregate natural resources are reducing. to overcome this problem, river indus sand (ris) and recycled concrete aggregate (rca) were utilized as fine and coarse aggregate respectively. the aim of this experimental investigation is to evaluate the workability, and compressive and tensile strength of concrete utilizing ris and rca. concrete samples of 1:2:4 proportions were cast, water cured for 7, 14, 21 and 28 days, and tested for compressive and tensile strength. the outcomes demonstrate that concrete possessed less workability when ris and rca were utilized. it was predicted that compressive strength of concrete would reduce up to 1.5% when 50% ris and 50% rca were utilized in concrete and 11.5% when natural aggregate was fully replaced by ris and rca, whereas the tensile strength decreased up to 1.60% when 50% by 12% respectively. keywords-compressive strength; split tensile strength; workability; river indus sand (ris); recycled concrete aggregates (rca) i. introduction concrete is the one of the most utilizable products in construction manufacturing industry. concrete has great durability, serviceability and availability compared to other building materials [1, 2]. residential houses, skyscrapers, bridges, pavements and dams are mostly being constructed using concrete [3]. nowadays it has become the major construction building material [4]. the main ingredients used to manufacture concrete are binder (cement), aggregates (coarse and fine), water and admixtures [5]. aggregates are non-chemical reactive materials in concrete. they occupy 6075% of the concrete’s total volume. their texture, shape and sizes play a vital role in fresh and hardened concrete properties [6-7]. in construction industry, the aggregates are mostly obtained from natural resources [8]. high energy is used to obtain these aggregates and natural resources are utilized [9]. gradual depletion of natural resources has forced construction industry to focus more on sustainability and utilization of waste materials [10]. in this study, ris and demolished concrete waste, commonly known as recycled concrete aggregates (rca), were utilized and partially and fully replaced fine aggregates and coarse aggregates respectively. workability, compressive and tensile strength of concrete were analyzed in context of conventional concrete. ii. literature review though concrete is considered as the backbone of any country’s infrastructure [11, 12], the use of natural resources in the manufacturing of concrete has raised environmental concerns. to overcome such concerns, the performance of concrete by replacing sand and coarse aggregate with other alternative sources has been examined. authors in [13] analyzed the experimental performance of concrete by partially replacing sand with foundry sand with various proportions of fine aggregates (10%, 20%, 30%, 40% and 50% by mass) at various curing ages (7 days, 14 days and 28 days). the conclusion confirmed that 30% replacement was optimum. compressive upsurges decline beyond that. authors in [14] observed the slump flow and hardened state strength performance of concrete at 10%, 20%, 30%, 40%, and 50% partially replacement of foundry sand to natural sand. the results revealed that the slump flow of 30% replacement was satisfactory and the strength performance was boosted among corresponding author: a. r. sandhu engineering, technology & applied science research vol. 9, no. 1, 2019, 3832-3835 3833 www.etasr.com sandhu et al: effect of river indus sand and recyclable concrete aggregates as fine and coarse … the other proportions. authors in [15] experimentally examined the strength (compressive, split tensile strength and flexural strength) behavior of concrete while utilizing foundry sand as fine aggregate replacement. foundry sand was replaced at various fractions 0, 15%, 25% and 35% with natural sand. the outcomes defined that the 25% replacement exhibited maximum strength among other percentages. ris was used in [16] as fine aggregate replacement in concrete of various grades. fine aggregates were fully replaced in m15, m20 and m25 grade concretes and their tensile strength was compared with concrete containing no replacement. it was determined that workability reduced significantly while the tensile strength was 1% to 2% lower than the conventional concrete’s in all grades, suggesting that ris would be utilized in order to conserve natural fine aggregates. authors in [17] inspected the material and mechanical characteristics of concrete adding rca as partially replacement of natural coarse aggregates at various fractions: 0%, 35%, 50% and 65%. the outcomes revealed that the rca has less specific gravity and high water absorption in context to natural aggregates. also, compressive and flexural behavior was analyzed. the compressive and flexural strength reduced up to 35% compared to conventional concrete. authors in [18] conducted an experimental study on concrete incorporating rice husk ash as cement and rca as coarse replacement. concrete with full coarse aggregate replacement with rca and with full coarse aggregate replacement with rca along with 10% rha as cement replacement was analyzed and compared with control concrete. it was determined that the workability reduced with the use of rca and further declined when rha was used. it was further noticed that 100% rca concrete showed significantly lower compressive and tensile strength compared to control concrete. interestingly the 10% rha + 100% rca concrete showed increase in strength, suggesting that incorporation of rca can be beneficial if it is used along with other materials. authors in [19] analyzed experimentally the performance of concrete using rca as coarse aggregate replacement at 20%, 40%, 60%, 80% and 100%. mechanical and surface characteristics, permeability and greenhouse gases valuation were also evaluated at 7 and 28 days of curing. the results describe that by adopting rca the mechanical performance was lower compared to conventional concrete’s. permeability was maximum when rca was incorporated in concrete in terms of conventional concrete. greenhouse gases investigation expressed that the co2 emission of this 100% rca mix was 24% lesser than the control mix. based on the above literature review, in this study ris was utilized as fine aggregate replacement whereas rca was adopted as coarse aggregates. iii. research methodology a. materials cement from the brand lucky, an ordinary portland cement cem i 42.5n that obeys astm c0150-04ae01, was chosen for this study. in this research two types of aggregates (aggregates obtained from hill and rca) were utilized. the material properties of aggregates obtained from hill were: the fines modulus of coarse aggregates was 3.18%, water absorption was 1.59%, and the specific gravity was 2.58 whereas the rca had fines modulus 2.91%, water absorption 2.39% and specific gravity of 2.32. hill sand possessed fines modulus of 3.10%, water absorption 1.2% and specific gravity of 2.46. and rsi had fines modulus 2.14%, water absorption 3.62 and specific gravity 2.46. b. experimental procedure and mix proportions the 1:2:4 mix design ratio for 3000 psi strength concrete was used for this study. two different kinds of concrete mix were made, one was conventional concrete utilizing natural aggregates and the other was concrete incorporating ris as fine aggregates and rca as coarse aggregates. the aggregates were 50% partially and fully replaced with ris and rca as fine and coarse aggregates respectively. the concrete cubes were cast and tested for compressive strength at curing ages of 7, 14, 21 and 28 days and for the split tensile strength test the cylinders were cast for different curing ages 7, 14, 21 and 28 days. concrete mixing was done by a semi-automatic rotary mixer. slump flow of both concrete mixes was analyzed according to the method described in [20]. compressive strength of both concretes was tested according to the overall method defined in [21] and split tensile strength was tested according to [22]. iv. results and discussion a. workability to check the workability of concrete, astm c 143 was followed. the workability outcomes of both concretes are given in table i showing that workability declines along with ris and rca percentage. table i. workability mixture slump value (mm) conventional concrete 33.34 50% ris and 50% rca concrete 27.4 100% ris and 100% rca concrete 22.8 b. compressive strength to check the compressive strength, astm c39 was fallowed. the compressive strength outcomes are shown in table ii and illustrated in figure 1. the results demonstrate that by utilizing ris and rca the strength is reduced because the interlocking between the particles is not as strong and in utilizing ris because a huge number of clay particles are present reducing the cement chemical hydration. table ii. average compressive strength mixture compressive strength (mpa) 7 days 14 days 21 days 28 days conventional concrete 14.21 18.36 20.18 21.09 50% ris and 50% rca concrete 12.42 16.69 18.98 20.79 100% ris and 100% rca concrete 11.32 15.61 17.72 18.91 at 7 days water curing, the compressive strength of 50% ris and 50% rca concrete and ris and rca concrete, reduces by 14.41% and 25.53% respectively. at 14 days water curing, the compressive strength of 50% ris and 50% rca concrete and ris and rca concrete, reduces by 10% and 17.61% respectively. at 21 days water curing the compressive strength of 50% ris and 50% rca concrete and ris and rca engineering, technology & applied science research vol. 9, no. 1, 2019, 3832-3835 3834 www.etasr.com sandhu et al: effect of river indus sand and recyclable concrete aggregates as fine and coarse … concrete, reduces by 6.32% and 13.88% respectively and at 28 days water curing the compressive strength of 50% ris and 50% rca concrete and ris and rca concrete, reduces up to 1.44% and 11.52% respectively. fig. 1. average compressive strength ss. curing age. c. split tensile strength to check split tensile strength, astm c496 was fallowed. the split tensile strength test results are presented in table iii and illustrated in figure 2. the outcomes describe that by adopting ris and rca the tensile strength is decreased because the ris contains more clay particles causing the bonding between the particles to weaken while rca are lighter than natural aggregates and the concrete becomes more brittle. hence, while utilizing ris and rca, the split tensile strength is decreased. table iii. average split tensile strength mixture split tensile strength (mpa) 7 days 14 days 21 days 28 days conventional concrete 1.49 2.12 2.42 2.53 50% ris and 50% rca concrete 1.34 1.84 2.28 2.49 100% ris and 100% rca concrete 1.25 1.72 1.95 2.27 fig. 2. average tensile strength vs. curing age. at 7 days water curing, the tensile strength of 50% ris and 50% rca concrete and ris and rca concrete was reduced by 11.19% and 19.20% respectively, at 14 days curing it was reduced by 13.20% and 23.26% respectively, at 21 days by 6.14% and 24.10% and at 28 days it was reduced by 1.60% and 11.45% respectively. v. conclusion it can be concluded that when 50% ris and 50% rca were utilized in concrete the slump value was less than conventional concrete’s whereas when ris and rca fully replaced natural aggregates the slump value was even lower. for improvement in slump flow, certain chemical admixtures should be utilized. from the mechanical properties results, compressive strength of 50% ris and 50% rca concrete decreased up to 1.5% compared to conventional concrete at 28 days of curing. concrete compressive strength was reduced up to 11.5 % when ris and rca fully replaced natural aggregates at 28 days curing. tensile strength decreased up to 1.60% compared to conventional concrete when 50% ris and 50% rca were utilized at 28 days curing. the concrete tensile strength reduced up to 12% compared to conventional concrete when ris and rca fully replaced natural aggregates at 28 days of curing. references [1] e. aprianti, “a huge number of artificial waste material can be supplementary cementitious material (scm) for concrete production -a review part ii”, journal of cleaner production, vol. 142, no. 4, pp. 4178-4194, 2017 [2] z. li, “introduction to concrete” in: advanced concrete technology, john wiley and sons, 2011 [3] a. a. jhatial, s. sohu, n. k. bhatti, m. t. lakhiar, r. oad, “effect of steel fibres on the compressive and flexural strength of concrete”, international journal of advanced and applied sciences vol. 5, no. 10, pp. 16 -21, 2018 [4] m. t. lakhiar, s. sohu, i. a. bhatti, n. k. bhatti, s. a. abbasi, m. tarique, “flexural performance of concrete reinforced by plastic fibers”, engineering, technology & applied science research, vol. 8, no. 3, pp. 3041-3043, 2018 [5] a. m. neville, properties of concrete, pp. 400-407, prentice hall, 2011 [6] c. s. poon, z. h. shui, l. lam, h. fok, s. c. kou, “influence of moisture states of natural and recycled aggregates on the slump and compressive strength of concrete”, cement and concrete research, vol. 34, no. 1, pp. 31-36, 2004 [7] a. omoregie, o. e. alutu, “the influence of fine aggregate combinations on particle size distribution, grading parameter, and compressive strength of sandcrete blocks”, canadian journal of civil engineering, vol. 33, no. 10, pp. 1271-1278, 2006 [8] m. t. lakhiar, n. mohamad, s. sohu, a. a. jhatial, m. oad, “mechanical properties of concrete containing river indus sand and recyclable concrete aggregate”, civil engineering journal, vol. 4, no. 8, pp. 1869-1876, 2018 [9] d. k. bangwar, a. saand, m. a. keerio, m. a. soomro, a. n. laghari, “replacement of coarse aggregate with locally available brick aggregate”, engineering, technology & applied science research, vol. 7, no. 6, pp. 2266-2267, 2017 [10] a. a. jhatial, w. i. goh, n. mohamad, s. sohu, m. t. lakhiar, “utilization of palm oil fuel ash and eggshell powder as partial cement replacement a review”, civil engineering journal, vol. 4, no. 8, pp. 1977-1984, 2018 [11] a. a. jhatial, s. sohu, m. t. lakhiar, j. shahzaib, a. a. buriro, “effectiveness of locally available superplasticizers on the workability and strength of concrete”, civil engineering journal, vol. 4, no. 12, pp. 2919-2925, 2018 [12] a. khitab, m. t. arshad, f. m. awan, i. khan, “development of an acid resistant concrete: a review”, international journal of sustainable engineering, technology & applied science research vol. 9, no. 1, 2019, 3832-3835 3835 www.etasr.com sandhu et al: effect of river indus sand and recyclable concrete aggregates as fine and coarse … construction engineering and technology, vol. 4, no. 2, pp. 33-38, 2013 [13] a. d. raval, a. pamnani, a. i. kachwala, “foundry sand: utilization as a partial replacement of fine aggregate for establishing sustainable concrete”, international journal of engineering sciences & research technology, vol. 4, no. 1, pp. 308-311, 2015 [14] k. amrutha, s. adharsh, k. ashirwad, k. fareen, m. najila, r. praseedha, “partial replacement of fine aggregate by used foundry sand in concrete”, international research journal of engineering and technology, vol. 4, no. 3, pp. 165-169, 2017 [15] d. r. bhimani, j. pitroda, j. j. bhavsar, “used foundry sand: opportunities for development of ecofriendly low cost concrete”, international journal of advanced engineering technology, vol. 4, no. 1, pp. 63 -66, 2013 [16] m. t. lakhiar, n. mohamad, m. a. b. shaikh, a. a. vighio, a. a. jhatial, a. a. a. samad, “effect of river indus sand on concrete tensile strength”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2796-2798, 2018 [17] f. r. salehlamein, m. solikin, i. sunarjono, “effect of recycled coarse aggregate on concrete properties”, international journal of innovative research in science, engineering and technology”, vol. 4, no. 1, pp. 19060-19068, 2015 [18] n. bheel, s. l. meghwar, s. sohu, a. r. khoso, a. kumar, z. h. shaikh, “experimental study on recycled concrete aggregates with rice husk ash as partial cement replacement”, civil engineering journal, vol. 4, no. 10, pp. 2305-2314, 2018 [19] s. p. yap, p. z. c. chen, y. goh, h. a. ibrahim, k. h. mo, c. w. yuen, “characterization of pervious concrete with blended natural aggregate and recycled concrete aggregates”, journal of cleaner production, vol. 181, pp. 155-165, 2018 [20] astm, astm c143/c143m-15, standard test method for slump of hydraulic-cement concrete), astm international [21] astm, astm c39/c39m-18, standard test method for compressive strength of concrete, astm international [22] astm , astm c496/c496m -17, standard test method for splitting tensile strength of cylindrical concrete specimens, astm international . microsoft word 4-2-2700_s_etasr_v9_n4_pp4334-4337 engineering, technology & applied science research vol. 9, no. 4, 2019, 4334-4337 4334 www.etasr.com rajamohan et al.: treatment of diesel oil contaminated soil by ex-situ bioremediation treatment of diesel oil contaminated soil by ex-situ bioremediation natarajan rajamohan faculty of engineering, sohar university, sohar, oman rnatarajan@su.edu.om rajasimman manivasagan department of chemical engineering, annamalai university, tamil nadu, india simms@rediffmail.com fatma al fazari faculty of engineering, sohar university, sohar, oman fatmafazari1000@gmail.com abstract—treatment of oil-polluted soil is a challenging problem faced by all refineries and petrochemical industries. in this research study, bioremediation of diesel oil contaminated soil was conducted for diesel concentration ranging from 5% to 20%. the physicochemical characteristics of diesel oil contaminated soil were studied. the effects of soil amendments, namely coconut ash powder, biofilter activated sludge, and npk fertilizer, on total petroleum hydrocarbon removal efficiency were studied. the maximum total petroleum hydrocarbon removal efficiency achieved was 94.5% when 4g npk, 40g of activated sludge and 40g of coconut ash powder per 1000g of contaminated soil were used. the studies on the effect of temperature confirmed the optimal temperature as 35°c. the parametric studies confirmed that the degradation efficiency decreased with increase in diesel oil concentration. keywords-bioremediation; fertilizer; sludge;diesel;efficiency i. introduction pollution caused by oil spills is a critical problem occurring near petrochemical plant sites. treatment of oil contaminated soil can be handled by physical, chemical or combined techniques. the effectiveness of these techniques highly depends on the hydrocarbon fractions present and their solubility properties. bioremediation of soils contaminated by hydrocarbons is recognized as an alternative method having advantageous characteristics. bioremediation technologies either in-situ or ex-situ utilize the natural potential of microorganisms to degrade complex contaminants [1-3]. different organisms are employed using various techniques of bioremediation according to the hydrocarbons present in the contaminated soil. as the composition of each type of oil is unique, there are different ways to deal with them through microbes and flora. bioremediation is operated naturally or with addition of microbes and fertilizers [4-6]. the microorganisms which can decompose or transform the chemical substances present in petroleum and petroleum derivatives are enriched though the optimal supply of nutrients. spilled crude oil affects physicochemical properties of the soil such as temperature, structure, nutrient status and ph. the successful implementation of a bioremediation process usually needs the application of strategies customized for the specific environmental conditions of the contaminated site [7, 8]. crude oil forms a layer on the surface of the soil and this oil film acts as a physical barrier between air and soil thereby causing a breakdown of soil texture followed by soil dispersion [4]. the light hydrocarbon fractions of the crude oil evaporate while the greasy fractions permeate slowly into the soil and are slowly biodegraded by microbes which naturally inhabit the soil [5]. crude oil spills of diversified composition are considered as a difficult substrate mix as the microorganisms could not have resistance for all the pollutants. the objectives of this study are diesel oil contaminated soil treatment and the study of the effects of relevant variables on the bioremediation efficiency. ii. materials and methods a. chemicals the components used in the bioremediation of crude oil contaminated soil are organic manure composed of activated sludge, coconut powder shell and inorganic fertilizer. the inorganic fertilizer (npk-15-15-15) which is composed of nitrogen, phosphorus and potassium (k) was purchased from a local agro-chemical shop. b. preparation of contaminated soil soil samples were collected from a site near sohar port and were screened by sieving to 2mm to remove heavier fractions. twenty kg of sieved soil were weighted and distributed equally in 20 plastic boxes, each containing 1kg of soil. subsequently, the 20 boxes were divided into 4 groups of 5 boxes each. samples of known quantity of diesel oil were weighed and well mixed with the soil in the first box to prepare the 5% desired concentration. similarly, the other samples of desired concentrations were prepared. a sample of activated sludge from the biofilter used for treating benzene was taken and used as a microbial source. the isolated sludge was dried in an oven to evaporate the remaining water and crushed well to fine powder. the coconut shells were collected from a nearby farm and dried for 3 weeks in sunlight. the dried coconut shells were burned until they were totally converted to ash. the coconut shells ash was sieved to obtain fine particles of 2mm size. c. ex-situ bioremediation procedure the soil samples were dug to a depth of 0-15cm. the excavated top soil, unlike the activated sludge and coconut corresponding author: natarajan rajamohan engineering, technology & applied science research vol. 9, no. 4, 2019, 4334-4337 4335 www.etasr.com rajamohan et al.: treatment of diesel oil contaminated soil by ex-situ bioremediation powder shell ash was sun dried for three weeks and ground using a mortar and a pestle. the samples were sieved using a 2mm standard mesh sieve and were measured using by an electronic weighing balance. this remediation experiment was carried out in a well perforated 1.5lt plastic container with an estimated depth of 6cm. crude oil concentration was prepared at levels of 5, 10, 15 and 20% (by mass). the individual cells were mixed with the aid of a stirrer. stirring was conducted every four days for eight weeks. during this period, the samples from the 20 labeled cells were taken to the laboratory for analysis of total hydrocarbon content, once in a week. the physicochemical properties and total petroleum hydrocarbon (tph) were analyzed using standard methods [9, 10]. iii. results and discussion a. physicochemical properties of contaminated soil the physical and chemical properties of the contaminated soil are presented in table i. the soil samples were analyzed and found to have acidic properties with moderate moisture content. table i. contaminated soil physicochemical properties parameter value ph (water/soil=5/1) 5.80 moisture content (%) 17.40 toc (%) 14.20 tph (mg/kg) 38425.25 b. effect of coconut shell powder on tph removal efficiency in this set of experiments, the influence of coconut shell powder addition on tph removal efficiency was studied by adding coconut shell powder in the ratio of 40g/1000g contaminated soil. the experiments were repeated with samples with 5% to 20 % diesel oil concentration. the experiments were conducted at ambient temperature of 34°c. the results obtained from the experiments are presented in figure 1 and indicated that tph removal efficiency decreased as diesel oil concentration increased. the microbial culture present in the soil degraded 5% diesel oil polluted soil faster and the maximum removal efficiency achieved was 49.1%. the tph removal efficiency of the experiments conducted with 10% diesel oil polluted sample was 35.6%. the removal efficiencies achieved with 15% and 20% samples were very low due to the excessive pollutant load on the microbial community. above a certain concentration, diesel oil is highly resistant to biodegradation. the importance of soil amendments is described in [12]. c. effect of activated sludge and coconut shell powder on tph removal efficiency in this set of experiments, the effect of the addition of two soil amendments, namely biofilter activated sludge and coconut shell powder, on diesel oil removal efficiency was studied by adding equal quantities of the two components in the contaminated soil samples. the experiments were conducted with 1000g soil samples polluted with 5% to 20% diesel oil concentration. the data from figure 2 describe that the tph removal efficiency increased due to the addition of biofilter activated sludge. an improvement of approximately 10% was observed due to the increased microbial population present in the activated sludge. the biofilter activated sludge contained microorganisms acclimated to hydrocarbons and contributed to better removal percentages. but, the efficiency decreased when the diesel oil percentages increased. the tph removal efficiency was around 50% in the diesel oil concentration range 5%-10% and later on decreased to 36.9% which could be due to the excessive pollutant loading resistance to microbial degradation. fig. 1. effect of coconut shell powder addition on tph removal fig. 2. effect of activated sludge and coconut shell powder addition on tph removal d. effect of npk fertilizer on tph removal efficiency the influence of addition of npk fertilizer on tph removal efficiency was studied by adding 4g of npk fertilizer to the contaminated soil samples. the results shown in figure 3 indicate that the addition of npk fertilizer to the contaminated soil samples enhanced the removal efficiency compared to the previous experiments on coconut powder and sludge addition. the maximum removal efficiency achieved with 5% and 10% diesel oil contaminated soil samples was 74.9% and 51% respectively. the tpd removal efficiency achieved with 15% and 20% diesel oil samples was 27.2% and 14.2%, respectively. the lack of organic feeding material was reported to limit the oil degradation [13, 14]. e. effect of activated sludge, npk and coconut shell powder on tph removal efficiency in this set of experiments, the influence of addition of three additives on total petroleum hydrocarbon removal efficiency was studied by adding 40g of activated sludge, 40g of coconut shell powder and 4g of npk fertilizer to 1000g of contaminated soil in 4 different samples which had 5% to 20% diesel oil concentration. the experiments were conducted under an average ambient temperature of 34°c. the obtained engineering, technology & applied science research vol. 9, no. 4, 2019, 4334-4337 4336 www.etasr.com rajamohan et al.: treatment of diesel oil contaminated soil by ex-situ bioremediation results, shown in figure 4, inferred that the addition of these 3 amendments resulted in high tph removal efficiency for the 5% and 10% diesel oil concentration samples. the percentage of removal efficiency decreased as diesel oil concentration increased. the 5% sample showed the highest removal efficiency of 94.5%, followed by 79.5% by the 10% sample. however, the removal efficiency achieved with the 15% and 20% samples was less than 50% due to higher diesel oil concentration. studies on bioremediation of diesel oilcontaminated soil using bio stimulation reported similar results [15]. fig. 3. effect of npk fertilizer on tph removal fig. 4. effect of activated sludge, npk fertilizer and coconut shell powder on tph removal f. temperature effect on tph removal efficiency temperature is reported as a controlling factor for biodegradation of petroleum hydrocarbons. extreme temperatures inhibit the enzymatic functioning of most microorganisms and will also reduce the action of enzymes in a diesel oil spilled environment. with decrease in temperature, the rates of degradation decrease probably because of the decreased rates of enzymatic activity and increased oil viscosity. temperature also affects the solubility of hydrocarbons. although hydrocarbon biodegradation can occur over a wide range of temperatures, the rate of biodegradation generally decreases with decreasing temperature. the effect of temperature on tph removal was studied with 10% diesel oil contaminated soil over a period of 8 weeks. the highest removal efficiency achieved was 89.5% when the temperature was 38°c and the tph removal efficiency decreased to 79.5% at 35°c. at the highest temperature of 40°c, the tph removal efficiency decreased to 68.5%. the decrease in efficiency at higher temperatures was due to the thermal resistance and inhibition to microbial action. the effect of mesophilic temperature on tph removal was studied and 70% removal was reported after 12 weeks [12]. fig. 5. effect of operating temperature on tph removal. iv. conclusions this study investigated and proved that bioremediation of diesel oil contaminated soil is feasible with nutrient addition. the contaminated soil amended with activated sludge, npk fertilizer and coconut shell powder showed the highest percentage (99%) of total petroleum hydrocarbon degradation when 5% diesel oil contaminated soil was used. with increase in diesel oil concentration, the degradation efficiency decreased. the findings of this study showed that the rate of biodegradation depends majorly on soil nutrient availability. both organic and inorganic fertilizers proved to enhance the multiplication of indigenous microbes thus enabling rapid biodegradation of contaminants in the soil. acknowledgment sohar university is gratefully acknowledged for providing the required facilities. references [1] m. gavrilescu, k. demnerova, j. aamand, s. agathos, f. fava, “emerging pollutants in the environment: present and future challenges in biomonitoring, ecological risks and bioremediation”, new biotechnology, vol. 32, no. 1, pp. 147-156, 2015 [2] b. sharma, a. k. dangi, p. shukla, “contemporary enzyme based technologies for bioremediation: a review”, journal of environmental management, vol. 210, pp. 10-22, 2018 [3] s. rayu, d. g. karpouzas, b. k. singh, “emerging technologies in bioremediation: constraints and opportunities”, biodegradation, vol. 23, no. 6, pp. 917-926, 2012 [4] r. natarajan, j. al-sinani, s. viswanathan, r. manivasagan, “biodegradation of ethyl benzene and xylene contaminated air in an up flow mixed culture biofilter”, international biodeterioration & biodegradation, vol. 119, pp. 309-315, 2017 [5] u. kingsley, t. pekdemir, m. copur, “surfactants treatment of crude oil contaminated soils”, journal of colloid and interface science, vol. 276, no. 2, pp. 456-464, 2004 [6] f. a. orji, a. a. ibiene, e. n. dike, “laboratory scale bioremediation of petroleum hydrocarbon–polluted mangrove swamps in the niger delta using cow dung”, malaysian journal of microbiology, vol. 8, no. 4, pp. 226-235, 2012 [7] j. ayotamuno, r. b. kogbara, s. ogaji, s. d. probert, “bioremediation of a crude-oil polluted agricultural-soil at port harcourt, nigeria”, applied energy, vol. 83, no. 11, pp. 1249-1257, 2006 [8] y. wang, j. feng, q. lin, x. lyu, x. wang, g. wang, “effects of crude oil contamination on soil physical and chemical properties in momoge engineering, technology & applied science research vol. 9, no. 4, 2019, 4334-4337 4337 www.etasr.com rajamohan et al.: treatment of diesel oil contaminated soil by ex-situ bioremediation wetland of china”, chinese geographical science, vol. 23, no. 6, pp 708–715, 2013 [9] s. mrayyan, m. n. battikhi, “biodegradation of total organic carbons (toc) in jordanian petroleum sludge”, journal of hazardous materials, vol. 120, no. 1-3, pp. 127-134, 2005 [10] r. r. bruce, a. klute, “the measurement of soil moisture diffusivity”, soil science society of america journal, vol. 20, no. 4, pp. 458-462, 1955 [11] n. das, p. chandran, “microbial degradation of petroleum hydrocarbon contaminants: an overview”, biotechnology research international, vol. 2011, articleid 941810, 2011 [12] r. m. hesnawi, f. s. mogadami, “bioremediation of libyan crude oilcontaminated soil under mesophilic and thermophilic conditions”, apcbee procedia, vol. 5, pp. 82-87, 2013 [13] c. h. chaineau, c. yepremian, j. f. vidalie, j. ducreux, d. ballerini, “bioremediation of a crude oil-polluted soil: biodegradation, leaching and toxicity assessments”, water, air & soil pollution, vol. 144, no. 14, pp. 419-440, 2003 [14] m. chorom, h. s. sharifi, h. motamedi, “bioremediation; fertilizer; heterotrophic bacteria; crude oil; normal paraffin”, iranian association of environmental health, vol. 7, no. 3, pp. 319-326, 2011 [15] x. yaohui, l. mang, “bioremediation of crude oil-contaminated soil: comparison of different biostimulation and bioaugmentation treatments”, journal of hazardous materials, vol. 183, no. 1-3,pp. 395401, 2010 microsoft word etasr_v13_n4_pp11432-11436 engineering, technology & applied science research vol. 13, no. 4, 2022, 11432-11436 11432 www.etasr.com najim: synthesis and electrical behavior of sodium doped monoclinic srsio3 synthesis and electrical behavior of sodium doped monoclinic srsio3 mohd najim department of electrical and electronic engineering, college of engineering, university of jeddah, saudi arabia mngalib@uj.edu.sa (corresponding author) received: 5 april 2023 | revised: 11 june 2023 | accepted: 26 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5893 abstract the operating temperature of solid oxide fuel cells, oxygen division membranes, and oxygen sensors is determined by oxide-ion electrolytes. there is a strong incentive to reduce the operating temperature in solid oxide fuel cells, from 800°c to 500°c. the use of low-cost na+ instead of k+ as dopant in monoclinic srsio3 offers a wider solid solution range (0.1<x< 0.5) in sr1-xnaxsio3-δ and obtains an oxide ion conductivity of 10 -2 scm -1 at 600°c, reducing the temperature of a smooth transition to full impairment of mobile oxide ions. for electrochemical characterization, the flat surfaces of the pellets were pasted with silver (ag) paste and then sintered at 1200°c for 24 hours. the production of the na2si2o5 phase was observed for most compositions due to thermal treatment. crystallization of na2si2o5 from glass was obtained in single-step calcination at 850°c after synthesis in an acetone medium, resulting in the highest conductivity. although double calcination reduced conductivity, it improved thermal stability. due to its low activation energy and lack of crystallization of other silicates, this material showed maximum conductivity after long-standing maturity at 600°c. ethanol was used in place of acetone for powder assimilation and double calcination was also performed. keywords-solid oxide fuel cell; electrolyte; conductivity; activation energy, srsio3 i. introduction electrochemical energy conversion devices, such as solid oxide fuel cells (sofcs), have been extensively studied as a potential technology for a wide range of applications, including large-scale stationary and portable power generators for both civilian and military applications [1]. the yttria stabilized zirconia (ysz) electrolyte used in conventional sofcs has a suitable power density but also has the strong drawback of operating at high temperatures (~1000°c) [2]. on the other hand, high operating temperatures cause complicated difficulties for materials, such as the choice of materials and their chemical and physical compatibility with the restrictions of cell components for interconnects and seals, resulting in high cell manufacturing costs [2]. in this sense, the discovery of alternative electrolytes that can provide adequate performance in the so-called in-between temperature range of 500-700°c is one of the most crucial concerns for the widespread commercialization of sofcs [3-4]. several materials have been studied for intermediate temperature sofcs, including doped ceria represented as oxide-ion conductors and lagao3 and proton conductors signified by doped baceo3 [4]. in addition to these oxides, doped strontium silicate with the general formula sr1-xaxmo3-δ (a = na, k and m=si/ge) has attracted a lot of attention for its highest oxygen ion conductivity [5-7]. the main reason for the conductivity in sr1xnaxsio3 is that na doping in srsio3 forms oxygen vacancies through which oxygen ion flows [8-9]. as evidenced by nmr spectroscopy, due to the steric pause of large sr2+ and na+ ions, conductivity was related to the development of the oxygen opportunity without changing the composition of srsio3 [8]. oxygen ions, which normally promote conduction, are not present in rare-earth oxyapatites. several studies challenged these conclusions by highlighting the crucial role that glassy phases play in the na2o-sio2 system [6-9]. specifically, conduction in sr1-xnaxsio3 (sns) due to na + ion movement in the amorphous phase was observed by solid-state nmr spectroscopy investigations [10-11], and x-ray diffraction (xrd) analysis revealed constrained doping of na in srsio3 [12-13]. conductivity appeared to be significantly affected by the crystallization of na2si2o5 after some processing at approximately 650°c [12-13]. some studies described how the amalgamation process and processing situations affect the structure and conducting qualities of alkali-doped srsio3 and srgeo3 [14]. in large amounts, most of the materials investigated were made by a traditional solid-state method that involved mixing silica with acetone na and sr carbonates [1214]. spark plasma sintered (sps) powders generated using the solid-state method create single-phase materials with tiny grains and strong ionic conductivity [15]. this study demonstrated that processing, in particular precursor reaction conditions and thermal properties, must have a major impact on phase composition and, subsequently, electrical properties. so, this study used a solid-state reaction to create sr1-xnaxsio3 (x = 0.0 and 0.45). engineering, technology & applied science research vol. 13, no. 4, 2022, 11432-11436 11433 www.etasr.com najim: synthesis and electrical behavior of sodium doped monoclinic srsio3 ii. experimental part the solid-state reaction method approach was used to create powders of sr1-xnaxsio3 (x=0.0 and 0.45), indicated as sns. wet ball milling with zirconia balls combined stoichiometric quantities of sr and na carbonates and nanometric sio2 in ceramic jars. to investigate the effects of solvent on na inclusion and glassy phase development, three dissimilar dispersion media with growing polarity, acetone c3h6o, ethanol c2h6o, and distilled water h2o, were used. slurries were stored at 4°c after 24 hours of milling to acquire the final reaction result, and then the dry particles were sieved and heated to high temperatures in the air. the final product was produced by: �1 � ����� � � �� � � �� → ����� ��� �� ��/ � �1 � � � � (1) the composition with the highest conductivity for only x = 0.0 and x = 0.45 [2] was made with ethanol and water. additionally, all compositions were "aged" in the air for 24 hours at 1200°c to further confirm their stability and to permit the crystallization or devitrification of any glassy phase. the powders obtained were compacted into pellets for conductivity testing that were generally 0.2 cm thick and 1 cm in diameter. powder xrd with a philips x'pert diffractometer (cu kαradiation = 1.5418 å) with bragg brentano reflection geometry seemed to verify its chemical phase purity. sem was used to study the microstructures (shape and surfaces) of the powder and pellets at an accelerating voltage of 20 kv (jeol, jsm5610). the composition and apparent regularity of the compounds were confirmed by energy-dispersive x-ray (edx) spectroscopy using a probe connected to the sem. the samples were heated at a rate of 2°c/min while subjected to thermo-gravimetric analysis (tga) in an air atmosphere (airflow: 20 cm3/min). oxide ion conductivity was measured in an ambient atmosphere using a solartron impedance analyzer (model 1287) with two probes at frequencies between 1 hz and 10 mhz and an ac amplitude of 10 mv. two pt-blocking electrodes were produced by coating pt paste (from heraeus) over the two faces of the pellets and firing them for an hour at 800 °c. all measurements were taken at temperatures ranging from 300 to 800°c. to estimate the intercept to the real z′ axis of a low-frequency semicircle, conductivity was calculated by extrapolating the difference between the source and the extrapolation of the intercept to the real z′ axis. iii. results and discussion figure 1 shows the xrd patterns of srsio3 and sr0.55na0.45sio3 at ambient temperature. both materials are monoclinic with a single-phase structure [16]. a high temperature (~1100c) is needed for the parent srsio3 to eliminate impurities such as sr2sio4 and sio2 and produce the single phase. the presence of voids is indicated by the broad flat top at 2~ (12-17) for srsio3. however, for sr0.55na0.45sio3, these flat tops become peaks. peak splitting is observed for sr0.55na0.45sio3 at higher 2>40, due to a disorder imposed on the parent srsio3 [16]. the disorder in na doping into srsio3 may be due to stress and vacancy formation. in sr0.55na0.45sio3, the monoclinic phase formation is controlled by both the sio2 layers and the amorphous sio2 matrix, as opposed to srsio3 where only the sio2 layers regulate the monoclinic phase growth [16]. edx was used to examine the formulations of the sr1-xaxsio3-δ (a = na). figure 2 shows sem micrographs and figure 3 shows the edx profile of sr0.55na0.45sio3-δ. fig. 1. xrd pattern of srsio3 (with structure) and sr55na0.45sio3-δ. fig. 2. fe-sem image of sr0.55na0.45sio3−δ. fig. 3. edx plot of sr0.55na0.45sio3−δ. engineering, technology & applied science research vol. 13, no. 4, 2022, 11432-11436 11434 www.etasr.com najim: synthesis and electrical behavior of sodium doped monoclinic srsio3 the sem analysis demonstrated the dense structure of the grains that ranged in size from 5 to 10 μm. on the other hand, the grains were in good contact due to the well-sintered pellets. the edx analysis, shown in figure 3, confirms the composition and superficial homogeneity (on the surface, not deep) of the material. the archimedean principle produced pellets with a density of 97% of the theoretical density of the substance in water. it is difficult to estimate the oxide ion conductivity of the undoped sample, as srsio3 is an electrical insulator within the measured temperature range and the conductivity is not due to the doped srsio3 but due to the narich phase (na2si2o5). figure 4 shows the complex impedance spectra of sr0.55na0.45sio3-δ at various temperatures. the bulk and grain boundary response was reflected in an apparent semicircle at high frequencies, while the electrode response was reflected in an apparent semicircular with a spike at low frequencies [17-18]. total conductivity and not individual responses can be measured from bulk and grain boundaries if there are no clearly defined high-frequency semicircles [19]. due to the high density of the pellet, the lack of a semicircle at high frequencies suggests that the contribution of the relative grain boundary to the resistance is almost minimal at high temperatures, as shown in figure 4 [20-21]. the intercept of the low-frequency semicircle or the spike on the real (z′) axis is used to represent the bulk crystal conductivity in the spectrum in the non-appearance of a high-frequency semicircle [22]. the investigated system sr1-xnaxsio3-δ, for x = 0.45, achieved conductivity σ ≥ 10-2 scm-1 at a lower temperature than sr1-xkxsi1-ygeyo3-δ by shifting a smooth variation in activation energy centered at 550°c in sr0.8k0.2si0.5ge0.5o3-δ to a slightly lower temperature [22]. the potential for protonic conduction was expected in the investigated electrolytes due to the existence of absorbed water or hydroxide content, which was revealed by tga measurement [16]. figure 5 shows the tga plots of sr0.55na0.45sio3-δ. sr0.55na0.45sio3-δ had a negligible weight decrease at 400°c, possibly due to the vaporization of the adsorbed water. fig. 4. impedance plot of sr0.55na0.45sio3-δ at 500 (with electrical circuit) and 700°c. the lack of weight loss at high temperatures (~ 400°c) due to the loss of lattice oxygen may be responsible for the improved electrical conductivity. ions from absorbed water strongly approve the absence of any protonic conductivity at 400°c in the sample. however, it was unclear whether oxygen vacancies existed in the lattice or whether the sample sr0.55na0.45sio3-δ produced oxygen interstitials since there was little or no water adsorption. glass transition and glass melting features are absent in srsio3 and glassy phase formation in nadoped srsio3. when it formed, other phases such as sr2sio4 and sio2 were always present, proving that it is impossible to create pure oxygen-stoichiometric srsio3 in a single monoclinic phase [23]. the overall conductivity of the system can be calculated as the sum of na+ conduction in the glassy phases in the strontium sodium silicate. it is impossible to say whether the sr0.55na0.45sio3-δ or glass contributes more to conduction in the sample. separation of two contributions is not possible in impedance diagrams because only one semicircle is present, and an additional investigation using different methods would be necessary to clarify this characteristic. table i shows the conductivity and activation energy of similar studies [23-25]. fig. 5. tga plot of sr0.55na0.45sio3−δ. table i. comparative study of conductivity and activation energy sample σ scm -1 at 700c activation energy (ea) in ev srsio3 1.5 × 10 -3 0.35 sr0.6na0.4sio3 (1.4-6.3) × 10 -3 (0.16-0.49) la0.9ba0.1ino3 3.0 × 10 -3 0.88 la0.9ca0.1ino3 1.6 × 10 -3 0.81 figures 6 and 7 show the variation of conductivity with temperature, indicating its dependence. conductivity increases as temperature rises, showing that the movement of oxygen ion vacancies is speeding up [26-28]. the following equation was used to determine conductivity: � = � �� (2) where t is thickness, a is the area, and r is the resistance of the pellet. as can be observed, the experimental data and the recorded temperatures are nicely matched by a straight line [27-29], implying that the arrhenius formula can be used to express conductivity: � = (��/�) �� (−!�/"#�) (3) where ea is the activation energy, kb is boltzmann's constant, and σ0 is the pre-exponential factor. comparing the results of this study with [30], the observed conductivity is lower in this study. the same disparity was found in [31-33]. sr0.55na0.45sio3 has an activation energy of engineering, technology & applied science research vol. 13, no. 4, 2022, 11432-11436 11435 www.etasr.com najim: synthesis and electrical behavior of sodium doped monoclinic srsio3 0.39 ev and its conductivity at 700c is higher (1.73×10-2 scm1) than that of other solid electrolytes such as la0.9sr0.1in0.8mg0.2o3 (10 -3 scm-1), la0.9k0.1ga0.9mg0.1o3 (7.65×10-3 scm-1), and la0.9ca0.1ino3 (1.6×10 -3 scm-1) [34-38]. finally, it can be concluded that sr0.55na0.45sio3 is a low-cost, rare-earth-free composite system, with a na-rich amorphous phase (na2si2o5) in the grain and na-srsio3 along the grain borders. fig. 6. arrhenius plot for sr55na0.45sio3-δ conductivity. fig. 7. conductivity variation of sr0.55na0.45sio3-δ with temperature. iv. conclusion in this study, srsio3 and sr0.55na0.45sio3 were produced using solid-state processes. srsio3 acts as an insulator over the temperature range studied, and sr0.55na0.45sio3 has strong ionic conductivity. xrd and sem studies revealed that there are two phases in sr0.55na0.45sio3: intragrain srsio3 and intergrain na2si2o5. tga indicated 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[38] l. madani, k. s. belkhir, and s. belkhiat, "experimental study of electric and dielectric behavior of pvc composites," engineering, technology & applied science research, vol. 10, no. 1, pp. 5233–5236, feb. 2020, https://doi.org/10.48084/etasr.3246. microsoft word 38-3108_s_etasr_v9_n5_pp4789-4794 engineering, technology & applied science research vol. 9, no. 5, 2019, 4789-4794 4789 www.etasr.com ta & dang: a redundant recurrent cerebellar model articulation control system for industrial … a redundant recurrent cerebellar model articulation control system for industrial applications van-phuong ta department of automatic control hcmc university of technology and education ho chi minh city, vietnam phuongtv@hcmute.edu.vn xuan-kien dang graduate institute hcmc university of transport ho chi minh city, vietnam dangxuankien@hcmutrans.edu.vn abstract—because of increasing reliability requirements of the applications in industrial areas, the control systems must guarantee the stability and robustness during operation and continuously maintain control and supervisory process. in order to meet the above requirements, this study proposes a redundant recurrent cerebellar model articulation control system (rrcmacs) for controlling industrial applications, in particular the water level and the pressure in a tank. therein, the stability and the robustness of the applications are guaranteed by the recurrent cerebellar model articulation controller (rcmac) and the redundant solution maintains continuously control and supervisory process. to adapt industrial applications, a programmable logic controller (plc) was used to build the control system and industrial networks were used to transfer data between the control system and field devices. keywords-recurrent cerebellar model articulation controller (rcmac); redundancy system; industrial communication network; uncertainties; non-linear system i. introduction stability control of level and pressure in a tank are crucial tasks in industrial applications [1-3]. because of the effects of the uncertainties due to dynamic perturbations and signal noises, the dynamic model of these systems cannot be completely obtained [4-7]. consequently, model-based controllers cannot achieve the desired performances [8-10]. to overcome these disadvantages, advanced controllers such as fuzzy logic controller (flc) [11, 12], sliding mode control (smc) [13, 14], neural networks (nn) [15, 16], and wavelet neural network (wnn) [17-21] have been developed and have achieved impressive results in dealing with uncertain systems. in the above-mentioned advanced controllers, however, there are still difficulties in designing the control systems. for the flc, the selection of fuzzy sets and rules is dependent on the prior experience of the system. in the smc, selection boundary of uncertainties or disturbance is a trade-off between stability and chattering phenomena. for the nn and wnn, the selection of the number of neurons and hidden layers to achieve good performance and learning requirements is extremely difficult in practical applications. cerebellar model articulation controller (cmac) is a learning structure that mimics human brain [22]. the cmac has been developed and adopted for uncertain non-linear multiple-input and multiple-output (mimo) systems due to properties such as fast learning, good generation capability, and simple computation. the augmented effectiveness in applications of the cmacs when compared to nns has been proved [23-26]. in recent researches, the wavelet function and recurrent technique were incorporated into the cmac to improve the learning capability and dynamic response of the traditional cmac [27-30]. the above adaptive, intelligent controllers can deal with the uncertainties and non-linear characteristic of the systems to achieve the desired performance. the industrial applications of these controllers, however, have been limited. in addition, the redundant solution has not been mentioned to continuously maintain control and supervisory process. this paper proposes an rrcmacs to achieve the desired responses and continuously maintain control and supervisory process. the recurrent cerebellar model articulation (rcmac) is designed to keep the stability and the robustness, and the redundant solution aims to maintain the continuous working of the control system. to meet the requirements of the industrial area, the plc was used to build the control system and industrial networks were used to transfer data between the control system and field devices. ii. system description a. structure and operation of the redundant system the structure of the redundant system and a photograph of its implementation are shown in figures 1 and 2 respectively. the redundant system includes a primary station (ps) and a standby station (ss), which continuously maintain the control and supervisory process of the control system. in particular, the system used devicenet network to control and monitor the pressure and water level in a tank. the controlnet network was used to transfer diagnostic information between the ps and ss to take over control as satisfying prescribed conditions. at the beginning of the process, the station that started earlier takes the role of the ps and takes control over the system, while the other station works as the ss. during operation, if the ps corresponding author: van-phuong ta engineering, technology & applied science research vol. 9, no. 5, 2019, 4789-4794 4790 www.etasr.com ta & dang: a redundant recurrent cerebellar model articulation control system for industrial … faults, the ss will take over to maintain control and the supervisory process of the system. in addition, the rcmac was utilized to guarantee the stability and robustness of the system during operation. the rcmac was downloaded to both stations, thus the effectiveness of the control and supervisory process was the same with in both stations. fig. 1. structure of the redundant system fig. 2. experiments of the rcmacs b. control takeover during operation, the controllers monitor the working conditions of each other. a “heartbeat” parameter is used to measure the strength of the controllers. when this parameter falls down under a prescribed threshold, it means the controllers are having faults while handling the system. in particular, assuming that the ps owns the control system at the beginning of the process, it monitors the connections of the devices in the system during operation. if there are fault connections suddenly inhibiting these devices, the ss can communicate with them in order to control the system. in addition, the ss always monitors the status of the ps. whenever the ps has problems with connections, the ss immediately takes over control of the system. figure 3 describes the process of control takeover between the ps and ss. the flowchart of control takeover is shown in figure 4. iii. rcmac along with continuously maintaining the control and supervisory process of the system, stability and robustness of the system are also a crucial task in the industrial applications. this duty is handled by the rcmac. the dynamic model of practical applications is extremely difficult to define. fig. 3. take over control between two cpu fig. 4. the flowchart of control takeover in this study, the dynamic equation of the pressure control system and the water level control system are identified by the matlab tool. the linearized dynamic models, including uncertainties of the system are given by (1) and (2), respectively: y(t)+0.045y(t)+0.0017y(t)+ud(t) = 0.0045u(t)�� � (1) y(t)+0.00035y(t)+0.001y(t)+ud(t) = 0.165u(t)�� � (2) where u(t) andy(t) are control signal and the pressure in the tank or water level. ud(t) is the lumped uncertainties and linearization error. equations (1) and (2) can be rewritten in state equation form as: 0 0 t t t x= f (x) + g (x)u + ud(x) y = x; = x x       �� � x (3) engineering, technology & applied science research vol. 9, no. 5, 2019, 4789-4794 4791 www.etasr.com ta & dang: a redundant recurrent cerebellar model articulation control system for industrial … in the case of 0 f (x) , 0 g (x) , and well-known uncertainties (x)ud , an ideal controller can be designed as [27, 30]: -1 0 d 0 1 2i g (x) y f (x) ud(x) k e+k eu = − − +  �� � (4) where 1 2 k , k are selected to the error dynamic equation 1 2 ke+ e+k e = 0�� � satisfying the hurwitz criterion. however, the uncertainties, ud(x) cannot be defined in the practical systems, thus the ideal controller i u does not guarantee the desired performance. to deal with the uncertainties, a proposed control system is depicted in figure 3. in this system, the recurrent cerebellar model articulation controller urcmac is combined with a compensator controller ucc to achieve stability and robustness. therein, the urcmac is developed to mimic the ideal controller and by its learning capability to achieve stability while the compensator controller is designed to attenuate efficiently the effects of uncertainties to obtain robustness. the total proposed control system has the following form: rcmac cci u = u -u -u (5) the control diagram and the structure of the rcmac are shown in figures 5 and 6 respectively. the rcmac aims to learn the uncertainties, ud(x) , which always exist in practical applications, in order to minimize the errors of the system. to reduce the number of the variables in the computation of the control system, error, derivation of error, and integral of error are integrated to form the error sliding surface, s which is minimized by the rcmac during learning [30]. according to the learning capability of the rcmac, the error sliding surface will converge to zero at the appropriately selected learning rate. however, due to the uncertainties’ effects, the error sliding surfaces often oscillate around zero point and easily diverge in the presence of disturbances or noise. therefore, a compensator controller was combined with the rcmac to guarantee the robustness of the system during operation [28, 30]. this rcmac (figure 6) includes input space s , association memory space a , receptive field space r , weight memory space w , and output spaces o . the function value of each space in the rcmac is represented as [30]: rik i rik ik s (t) = s (t)+w µ (t -1) (6) ( ) 2 ri ik ik rik 2 ik s -m µ (s ) = exp σ        (7) n ik ik rik i=1 µb = (s )∏ (8) nj nnk j jk ik rik j=1 k=1 i=1 µo = w (s )∑∑ ∏ (9) the parameters of the controller are adjusted by the rcmac’s learning to achieve good performance in the presence of the lumped uncertainties ud(x) . fig. 5. control diagram of the rcmac fig. 6. structure of the rcmac in this paper, ts s� is selected as an error function and the back-propagation algorithm is utilized to adjust the parameters of the controller as follows: 0 ism rcmac cc t t t t d 1 2 ( ) (x)( ) ( s s s s s ud(x) k e+k e) = − − + + − − +�� � � 0 f x g u u u x (10) i t t rcmac kj w w kj rcmac kj n t w 0 ik ri i=1 s s s s w η η w w η s (x)( µ (s )) ∆ ∂∂ ∂ = − = − ∂ ∂ ∂ = ∏ � � u u g (11) ( ) t t rcmac ik ik m m ik rcmac ik ik ri ikt m 0 kj 2 ik µs s s s m η η m µ m s -m η s (x)w 2 σ ∆ ∂ ∂∂ ∂ = − = − ∂ ∂ ∂ ∂ = � � u u g (12) engineering, technology & applied science research vol. 9, no. 5, 2019, 4789-4794 4792 www.etasr.com ta & dang: a redundant recurrent cerebellar model articulation control system for industrial … ( ) t t rcmac ik ik σ σ ik rcmac ik ik σ kj 2 ri ikt 3 ik µs s s s η η µ η (x)w s -m s 2 σ ∆σ σ σ ∂ ∂∂ ∂ = − = − ∂ ∂ ∂ ∂ = � � 0 u u g (13) ( ) rik rik rik t t rcmac ik ri rik w w rik rcmac ik ri rik w kj ri ikt i(k-1)2 ik µ ss s s s w η η w µ s w η (x)w s -m s 2 µ σ ∆ ∂ ∂ ∂∂ ∂ = − = − ∂ ∂ ∂ ∂ ∂ = � � 0 u u g (14) to maintain the robustness of the control system as the error function is tending to zero, a sliding mode control-based compensator controller can be designed as: -1 cc 0 ˆu = g (x)btanh(s) (15) wherebis the error boundary and b̂is an estimation of b. in practical industrial applications, the error boundary cannot be exactly measured. moreover, selecting the boundary error is a trade-off between the output chattering phenomenon and the stability of the control system. consequently, the error boundary is estimated in this study as [28, 30]: b b̂ = η s � (16) with the estimating rule given in (15), the stability of the system is guaranteed in the sense of lyapunov-like lemma [31]. iv. experimental results a. water level stability control system the water level control system is represented in figure 7. the system includes a pump powered by a devicenet network-controlled inverter. the water level in the tank is monitored by a level transmitter (lt). the lt’s signal is connected to the inverter. all processes are performed by the control stations via the devicenet network. data in the control stations are monitored by computers and a human machine interface (hmi) via an ethernet network. the initial parameters of the rcmac of the control system are: w m σ wr b k η = η = η = η = η = 0.001,n = 7 1 2 k = 0.035,k = 0.054 m [ 0.6 0.4 0.2 0 0.2 0.4 0.6]= − − − w [ 0.4 0.25 0.15 0 0.15 0.25 0.4]= − − − [0.3 0.3 0.3 0.3 0.3 0.3 0.3]σ = rik w [ 0.4 0.25 0.15 0 0.15 0.25 0.4]= − − − the response of the water level in the tank is shown in figure 8. the experimental result shows that the rcmacs can control the water level in the tank and achieve different desired set points. besides, the redundant solution guarantees the continuous control and supervisory process in case the controllers get faults. in particular, during the operation, if the ps is in the program mode, fault or outage power, the ss will take over the control of the system and maintain the process continuously. fig. 7. water level control system fig. 8. the response of the water level in the tank b. pressure stability control system the pressure stability control system is presented in figure 9. the system includes a pressure pump powered by a devicenet network-controlled inverter. the pressure in the tank is qualified by a pressure transmitter (pt). the pt’s signal is connected to the inverter. all processes are performed by the control stations via the devicenet network. fig. 9. pressure stability control system engineering, technology & applied science research vol. 9, no. 5, 2019, 4789-4794 4793 www.etasr.com ta & dang: a redundant recurrent cerebellar model articulation control system for industrial … the initial parameters of the rcmac are the same with the case of water level control. the experimental results of the pressure stability control system are shown in figure 10. the experimental results prove that the rcmacs can control the pressure in the tank and achieve the desired different references in reality. along with achieving good responses, the redundant solution also guarantees the continuous control and supervisory process in case of fault in the controllers. fig. 10. the response of the pressure in the tank v. conclusion and future work water level control system and pressure stability control system were controlled to achieve the desired trajectories by the redundant recurrent cerebellar model articulation control system. the parameters of the controller were learned and turned in real time, and the stability and robustness of the control system are guaranteed in the lyapunov sense. the exchange data between the control stations and the field devices were transferred via the industrial devicenet network. this solution not only reduces the effects of noise and signal attenuation during operation, but also increases the distance between the control stations and sensors and actuators. furthermore, the redundant solution was proposed in this study to maintain continuously the control and supervisory process. two control stations were used to operate concurrently. whenever one station faults, the other will quickly take over control of the system. therefore, the 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industrial electronics, vol. 59, no. 4, pp. 2024-2033, 2012 microsoft word 05-3686_s_etasr_v10_n5_pp6183-6186 engineering, technology & applied science research vol. 10, no. 5, 2020, 6183-6186 6183 www.etasr.com pham et al.: squeeze flow of a newtonian fluid under different test speeds squeeze flow of a newtonian fluid under different test speeds hong son pham faculty of construction vinh university vinh city, vietnam phamhongson1977@gmail.com xuan hung vu faculty of construction vinh university vinh city, vietnam xuanhungkxd@vinhuni.edu.vn van tien phan faculty of construction vinh university vinh city, vietnam vantienkxd@vinhuni.edu.vn abstract-in this paper, the squeeze flow behavior of newtonian fluid was investigated with a series of squeeze tack laboratory experiments. the newtonian fluid was squeezed out radially between two parallel and circular plates. from the flow curves obtained in the squeeze tack experiments, rheological parameters such as yield stress in tension and in squeeze, have been investigated. the results indicate that the values of yield stress in squeeze and in tack of the testing material are relatively small. these values gradually decrease with increasing sample thickness. this shows that the squeezing and tacking process does not affect the testing material, glucose in this case. although the experimental results are not much, a linear relationship can be found between tensile and squeeze stress of newton fluid in the experiment. this is especially evident at low test speeds. keywords-squeeze flow technique; glucose; yield stress; newtonian fluid i. introduction newtonian fluid is a viscous liquid, obeying the newton’s law of internal friction, which means that the tangential stress and velocity gradient are linearly dependent on each other. the scale factor between the two is called viscosity. a newton fluid has a constant viscosity. however, most liquids we know have changes in their viscosity and do not really fit the exact definition. in fact, almost all salts, molten polymer materials, blood, toothpaste, paint, corn starch and many other liquids are non-newton liquids. the investigation of the behavior of these materials is very important, especially in the state of flow. in construction, to study the rheological properties of construction materials, 1-point measurement method is usually used, which is the method of measuring slump. this method has the limitation of not fully evaluating material characteristics in shear [1, 2]. there should be another method of measuring more characteristics, tracking the variation of those features over time, etc. these methods should be thoroughly investigated, first of all with newtonian fluids. squeeze–tack test has been used for characterizing the squeeze flow of materials between two rigid plates. the test material was firstly squeezed to an initial set-up thickness, then it was relaxed for about 2 minutes and finally it was pulled out at a constant velocity. during the experiment, the total force was measured. measured squeeze stress is the average value over the sample diameter at the time of calculation. during the squeeze flow experiments, the geometrical properties of two parallel rigid plates strongly affect the squeeze flow. sliding wall phenomenon would result in a decrease of the viscous force and a profound effect on shear thickening pastes. surface microchannels can accelerate squeezing flow of a fluid in a thin gap between parallel plates. the squeeze flow experiment of newtonian fluids is important for understanding the characteristic of the shear thickening materials under shearing and towards more efficient applications. the squeeze-tack test can simultaneously evaluate the properties of a material under compression and tensile stress. at the same time, strong viscoelasticity can be observed during the transition. similar to the tensile behavior, squeeze behavior should also be an important aspect to comprehend the structure evolution of a material. at the same time, shear viscosity is closely associated with the inner structure evolution. critical shear rate of the test material strongly increases with the increasing gap in a simple shear flow. to this end, studying the shear viscosity in the squeeze mode will contribute to the understanding of the rheological properties under moving boundary. therefore, it is necessary to investigate the squeeze flow behavior of newtonian materials comprehensively. in this paper, the properties of a newtonian material were characterized with the squeeze flow experiment. the test material was placed between two parallel rigid spheres. the typical load vs. displacement profile was determined and was used to obtain the rheological parameters of the testing material, including squeeze and tack stress. the separating velocity’s values were 2mm/s, 20mm/s, and 200mm/s. the material thickness was 1mm, 2mm, 3.5mm, and 5mm. the squeeze speed was 20mm/s and 200mm/s. ii. apparatus squeeze tests have been widely used to determine the flow properties of highly viscous pastes (food, cosmetic, polymers, composites, ceramic pastes and others) [3-5], as it overcomes some of the common problems of conventional rheometry such as slip, disruption of plastic materials and the difficulty to load very thick and fiber-containing fluids in rotational devices [6]. squeezing technique can characterize cementitious materials by compressing of a cylindrical specimen between two parallel surfaces by controlled force or displacement rate. this method has been previously used by various researchers for corresponding author: van tien phan engineering, technology & applied science research vol. 10, no. 5, 2020, 6183-6186 6184 www.etasr.com pham et al.: squeeze flow of a newtonian fluid under different test speeds characterizing the rheological behavior of cement pastes [4], herschel bulkley fluid [6], bingham plastic [7], etc. the typical load vs. displacement profile of a constant velocity squeeze flow experiment was determined in [8] and is used to obtain the rheological parameters of testing materials, including yield stress and viscosity. direct measurements of yield stress are uniquely performed by stress-controlled rheometry [9, 10]. squeeze flow tests carried out with constant displacement velocity do not allow such direct measurements [6, 11] since the material flow occurs regardless of the existence of the material’s yield stress, unless the force required to overcome this value exceeds the load limit of the testing device. in the present work, the testing material is firstly compressed/squeezed between two parallel surfaces until a predefined thickness, followed by a relaxation period of 1.5min, and is finally separated with a predefined tack velocity (figure 1). a typical curve of squeeze-tack can be seen in figure 2 in [12], in which three periods can be observed, including compression, relaxation and traction. fig. 1. a squeezing tack experiment in process. it is possible to conduct indirect yield stress determination by the extrapolation of the flow curves in the squeeze stage of the experiment. the yield stress is calculated by dividing the maximum force recorded by the area at that time. the formula is as follows: � � � �� max � (1) where as is the average area of the testing sample at the moment that the recorded load is max: as= � � = � � � � � (2) and h is the predefine thickness of the test mortar, r is the radius of the sample and h’ is the mortar’s thickness at the moment of the maximum squeeze force. similar calculations with the yield stress at tensile stage can be performed in order to investigate the variation of the material’s resistance in tack measurement. iii. results and discussion a controlled stress experiment was performed in order to plot the relationship between shear rate and shear stress. the results in figure 2 indicate that the test material is newtonian. fig. 2. flow curves of the experimental results determine that the testing material is newtonian. the recorded squeeze forces obtained in the squeeze step are shown in figure 3. each subfigure corresponds to a different initial material thickness (1mm, 2mm, 3.5mm, and 5mm). during the squeeze phase, the test material was squeezed to the previous set-up thickness and the normal forces were recorded as a function of displacement/time. the squeeze stress was then calculated. from the obtained graphs, it is possible to evaluate the role of the sample thickness to the rheological properties of the material by displaying the force relational graphs over time on the same general chart. from each of the graphs in figure 3, the maximum tensile force value, corresponding to the yield tensile stress, will be calculated using (1). fig. 3. the squeeze force obtained in the squeeze experiments. 0 20 40 60 80 100 0 0.5 1 1.5 2 2.5 3 3.5 4 glucose aller retour s h e a r ra te ( 1 /s ) stress (pa) engineering, technology & applied science research vol. 10, no. 5, 2020, 6183-6186 6185 www.etasr.com pham et al.: squeeze flow of a newtonian fluid under different test speeds figure 4 represents the evolution of tack forces versus time obtained when h=1mm and h=3.5mm. the indicator s corresponds to the squeeze speed and t to the tack speed, so s20 t20 means that the squeeze speed is 20mm/s and the tack speed is 20mm/s, etc. (a) (b) fig. 4. flow curves obtained in the squeeze experiments. fig. 5. the relations between tack stress and squeeze stress. as can be easily seen in figure 4, the greater the drag speed, the greater the drag force. for example, with a 1mm sample thickness, the top two curves are obtained when pulling is conducted at a speed of 200mm/s, followed by two curves obtained when pulling is conducted at 20mm/s and finally at 2mm/s. the greater the drag speed, the faster the drag force reaches its maximum and the curve obtained after crossing the maximum point will become steeper. from these curves it is possible to determine many rheological characteristic values of materials such as yield stress, viscosity, etc. however, in the current research, only the stress of test materials in squeeze step and those in tack are investigated. figure 5 represents the relationship between tack stress and squeeze stress of glucose. it is possible to see distinct areas on the graph, corresponding to the different material thickness values. the more the sample thickness increases, the more this area is closer to the origin. this shows that at a large thickness of the specimen, the yield stresses when pulled and when pressed are very small. when the specimen thickness is smaller (i.e. 1mm and 2mm), in order to squeeze the specimen to a given thickness or to pull the specimen, a much larger force is required to overcome the drag. this result can be explained by the arrangement of material particles when pulled or pressed at low speed. when considering the relationship between the two types of stresses when fixing pressing speed (figure 5), at the same tensile speed, the relationship between compressive stress and tensile stress is linear when the tensile speed is low. in contrast, when the tensile speed is large (200mm/s), the slope of the straight line changes, decreasing gradually as the sample thickness is reduced. (a) (b) fig. 6. tack stress versus squeeze stress at different squeeze speeds. iv. conclusions the squeeze flow is a simple and effective method for the rheological characterization of materials in a wide range of consistencies, providing important information regarding the rheological behavior of materials in practical applications. from the flow curves obtained in the squeeze tack experiments, 0 50 100 150 200 250 1 2 3 4 5 6 7 8 1mm s200_t200 s200_t20 s200_t2 s20_t200 s20_t20 s20_t2 f o rc e ( n ) time (sec) -10 0 10 20 30 40 50 60 1 2 3 4 3.5 mm 3.5mm_s200_t200 3.5mm_s200_t20 3.5mm_s200_t2 3.5mm_s20_t200 3.5mm_s20_t20 3.5mm_s20_t2 f o rc e ( n ) time (sec) 0 0,005 0,01 0,015 0,02 0,025 0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 1mm 2mm 3,5mm 5mm t a c k s tr e s s ( n /m m 2 ) squeeze stress (n/m2) 0 0,005 0,01 0,015 0,02 0,025 0 0,005 0,01 0,015 0,02 0,025 squeeze 20 mm/min s20_t2 s20_t20 s20_t200 t a c k s tr e s s squeeze stress 0 0,005 0,01 0,015 0,02 0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 squeeze 200 mm/min s200_t2 s200_t20 s200_t200 t a c k s tr e s s squeeze stress engineering, technology & applied science research vol. 10, no. 5, 2020, 6183-6186 6186 www.etasr.com pham et al.: squeeze flow of a newtonian fluid under different test speeds the rheological parameters, including yield stress in tension and in squeeze, have been investigated. the results indicate that the yield stresses of the testing material are relatively small. these values gradually decrease with increasing sample thickness. this shows that the squeezing and tacking process does not affect the testing material, in this case glucose. although the experimental results are far from been characterized as complete, a linear relationship can be found between the tensile and the compressive stress of a newton fluid in the experiment.this is especially evident at low test speeds. references [1] p. banfill, “use of the viscocorder to study the rheology of fresh mortar,” magazine of concrete research mag concr res, vol. 42, no. 153, pp. 213–221, jan. 1990, doi: 10.1680/macr.1990.42.153.213. [2] p. v. tien, “influence of re-dispersible powder on the properties of mortars,” journal of materials and engineering structures, vol. 1, no. 1, pp. 2–10, 2014. [3] j. engmann, c. servais, and a. s. burbidge, “squeeze flow theory and applications to rheometry: a review,” journal of non-newtonian fluid mechanics, vol. 132, no. 1, pp. 1–27, dec. 2005, doi: 10.1016/j.jnnfm.2005.08.007. [4] o. campanella and m. peleg, “squeezing flow viscosimetry of peanut butter,” journal of food science, vol. 52, no. 1, pp. 180–184, aug. 2006, doi: 10.1111/j.1365-2621.1987.tb14000.x. [5] b. h. min, l. erwin, and h. m. jennings, “rheological behaviour of fresh cement paste as measured by squeeze flow,” journal of materials science, vol. 29, no. 5, pp. 1374–1381, mar. 1994, doi: 10.1007/bf00975091. [6] k. kardjilova, v. vozarova, and m. valah, “influence of temperature on energetic and rheological characteristics of plantohyd bio lubricants – a study in the laboratory,” engineering, technology & applied science research, vol. 3, no. 3, pp. 424–428, jun. 2013. [7] j. d. sherwood and d. durban, “squeeze-flow of a herschel–bulkley fluid,” journal of non-newtonian fluid mechanics, vol. 77, no. 1, pp. 115–121, may 1998, doi: 10.1016/s0377-0257(97)00099-2. [8] f. a. cardoso et al., “experimental developments of the squeeze flow test for mortars,” in rheology and processing of construction materials, cham, 2020, pp. 182–190, doi: 10.1007/978-3-030-225667_22. [9] b. belahcene, a. mansri, and a. benmoussat, “investigation on the rheological behavior of multigrade oil under the effect of organic and inorganic impurities,” engineering, technology & applied science research, vol. 4, no. 6, pp. 711–713, dec. 2014. [10] g. h. meeten, “yield stress of structured fluids measured by squeeze flow,” rheologica acta, vol. 39, no. 4, pp. 399–408, aug. 2000, doi: 10.1007/s003970000071. [11] t. phan and d. d. nguyen, “influence of squeezing rate on yield stress and viscosity of fresh mortar,” engineering, technology and applied science research, vol. 10, no. 4, pp. 5921–5924, aug. 2020 [12] v. t. phan, “evaluation of some rheological properties of xanthan gum,” engineering, technology and applied science research, vol. 10, no. 5, pp. 6172-6175, oct. 2020. engineering, technology & applied science research vol. 7, no. 2, 2017, 1515-1522 1515 www.etasr.com liaghat et al.: evaluating the effects of dam construction on the morphological changes of… evaluating the effects of dam construction on the morphological changes of downstream meandering rivers (case study: karkheh river) ali liaghat civil engineering department engineering faculty, shahid chamran university of ahvaz iran arash adib civil engineering department engineering faculty, shahid chamran university of ahvaz iran hamid reza gafouri civil engineering department engineering faculty, shahid chamran university of ahvaz iran abstract—the establishment of stability in rivers is dependent on a variety of factors, and yet the established stability can be interrupted at any moment or time. one factor that can strongly disrupt the stability of rivers is the construction of dams. for this study, the identification and evaluation of morphological changes occurring to the karkheh river, before and after the construction of the karkheh dam, along with determining the degree of changes to the width and length of the downstream meanders of the river, have been performed with the assistance of satellite images and by applying the cche2d hydrodynamic model. results show that under natural circumstances the width of the riverbed increases downstream parallel to the decrease in the slope angle of the river. the average width of the river was reduced from 273 meters to 60 meters after dam construction. this 78% decrease in river width has made available 21 hectares of land across the river bank per kilometer length of the river. in the studied area, the average thalweg migration of the river is approximately 340 meters, while the minimum and maximum of river migration measured 53 and 768 meters, respectively. evaluations reveal that nearly 56% of the migrations pertain to the western side of the river, while over 59% of these migrations take place outside the previous riverbed. by average, each year, the lateral migration rate of the river is 34 meters in the studied area which signifies the relevant instability of the region. keywords-erosion; dam; meander; morphology; cche2d hydrodynamic model. i. introduction after the construction of any dam, the fluvial regime of the river is subjected to consequential change and its system or pattern of erosion may undergo metamorphosis. dam construction alters the amount of sediment production, retention and transportation of the sediments in the system. this causes changes in the pattern of erosion and thus can alter the channel’s morphology in both short and long term periods. it can further change the morphological qualities of the bed and banks, which influence the amount of water transportation and the rise and fall in the elevation of the bed, ultimately resulting in the spread of flooded regions surrounding the river. all of the above can be attributed to the produced effect of morphological changes occurring to the river. the change in the direction of meanders is one of the most prominent problems regarding the instability of rivers. this change in the meander direction can seriously threaten the success of projects that are aimed at controlling floodwater. the threat can be explained by the fact that as meanders change their course and migrate, some installations such as levees and lateral floodcontrolling installations tend to lose their functionality [1]. in sections of meanders, there is a high gradient of change in the distribution of velocity along the length of the river, when considering the water velocity of the inner bend of the meander towards its outer bend. due to the continuous change in the bend’s radius of curvature, fluvial parameters are more complex in meander sections than in straight river sections [2]. in [3], authors stated that the most important feature of fluvial structure in meandering rivers is the inverted vortex direction of secondary flow cells at the peak of curvature, considered before and after the occurrence of flood. the intensity and direction of vortex for these secondary flow cells have a significant effect on the morphology of the bed and banks, besides affecting the distribution of flow velocity along the length and across the width of the river. in [4], 20 meandering reaches were analyzed over a 128-km-long river reach located in the middle part of the karoon river, iran. the results of a paired t-test showed that river width and meander neck length have significantly changed during the study period (1989–2008), with an increase of + 3.5 m for width and a decrease of 274 m for length. in [5], it was suggested that the feedback mechanism between in-channel sedimentation and bank erosion may affect channel morphology. here, the pattern of the bar area, bank erosion, and morphology of the gravel-bed dunajec river upstream from the czorsztyn reservoir, constructed in 1997 in southern poland were analyzed from aerial images (1982–2012). in [6], authors examined spatial variation in channel morphology and bed sediment character upstream and downstream of four run-of-river dams in illinois. results show that the four dams do not create major discontinuities in channel morphology or sediment character. engineering, technology & applied science research vol. 7, no. 2, 2017, 1515-1522 1516 www.etasr.com liaghat et al.: evaluating the effects of dam construction on the morphological changes of… silt/clay content of bed material at the four sites is higher upstream of the dams than downstream, but this size fraction generally is a minor component by weight of the sediment samples collected. an applicable instance whereby satellite images are used for study is the assessment of geometrical changes that occur to the meanders over a period of time. usually, as the rivers reach a flooded state, the water level rises and progresses more towards the banks. eventually, after the flooding ensues, various sizes of patches of land alongside the river become immersed in water. the repetitive evaluation of satellite images provides a convenient means for the discrimination of geometric changes to the river. the amounts by which a dam affects the morphology of the downstream river, is largely dependent on the strategy of the dam and the features of the downstream river. examples of studies in this field include the long term changes in the bed of the rio grande river as a result of establishing irrigation installations [7-8], geometrical, hydraulic changes in the downstream of the hapcheon dam [9], the effect of daily pulses of flow that originate from the dam on the hwang river [10], evaluating the effect of the englebright dam on the downstream morphology [11] and evaluation of the effect of functionality of the keystone dam on the morphology of the arkansas river [12]. it appears that the first research on the geomorphologic changes of rivers resulting from the construction of dams was conducted by petts in the late 1970s which significantly influenced the future of relevant research in the field [13-14]. dams can influence the fluvial pattern and the sediment load of the river. upstream the reservoir of dams, the local groundwater level rises. rivers that feed a reservoir deposit their load in their beds in the vicinity of the reservoir and as forms of delta inside the reservoir bed. sedimentation reduces the slope of the riverbed and increases the elevation of the bed, thereby increasing the risk of flooding. in addition to the change in the length and width of the river channel, the occurrence of erosion in subordinate streams and in the stream’s origins can be greatly influenced by changes in the basal ground level of the channel [5-18]. in [19], authors described the geometric shape of the river as a reflection of its discharge, sedimentation and the hydrological conditions of the flow. their research focused on the role of a unit factor in evaluating the geometric pattern of the river, but seldom considered systematically the geomorphic conditions and geological setting of the river, altogether, along its route. in [20], authors applied the model of meander migration in the southern river of virginia and compared the development and migration of meanders within the alluvial domains of sandy beds and rocky beds. the research showed that over 45% of regions the erosion model predicted to be eroded would eventually then actualize in field observations of erosion. in [21], authors evaluated the mechanism of cutoff formation along the length of big meanders by considering the topography of the floodplain and its floodwater dynamics. their research claimed that reasons such as rapid changes in the capacity of river sections, which commonly result from the construction of dams and the sudden surge of floodwater, can generate meander cutoffs. in [22], authors assessed the stages by which morphodynamic meanders are formed. the mechanism of meander formation based on hydrodynamic forces was discussed along with realizing the patterns of change in the geometry of meanders. in [23-25], the corriolis effect on the making of meanders under laboratory conditions was simulated this research aims to evaluate how the construction of the karkheh dam affects morphological changes in the downstream meandering section of the karkheh river. for this purpose, morphological changes of the karkheh river before and after dam construction was evaluated by satellite images, along with determining the degree of changes to the length and width of river meanders downstream the karkheh by assistance of the cche2d hydrodynamic model. in this research, evaluations are made regarding the effects of dam construction on the hydraulic features and morphological characteristics downstream the karkheh river. in this method, the changes in hydraulic shapes of the river between two stations, namely paye-pol and abdolkhan (downstream the karkheh dam) were modeled by the cche2d model and the transition in plane and cross-section was considered in addition to the morphological changes in the river during the time span between the years 1996 and 2011 which were determined based on making comparisons between the relevant satellite images. the karkheh dam is the biggest dam in iran and in the middle east which was completed for exploitation in 2002. this dam is one of the world’s biggest earth dams, which is located 22 kilometers north-west of the city of andimeshk in the khuzestan province of iran. the karkheh river is the third biggest river in iran in terms of discharge, after the karoon and dez rivers. ii. district of study in order to simulate the fluvial pattern for the purpose of analyzing the hydraulics of meanders, a section of the karkheh river (downstream the karkheh dam and the hydrometric station of pay-e-pol) was selected for this study. figure 1 displays the location of the pay-e-pol station on the karkheh river, and figure 2 shows the district selected for this study on the river. fig. 1. the location of the pay-e-pol station on the karkheh river. engineering, technology & applied science research vol. 7, no. 2, 2017, 1515-1522 1517 www.etasr.com liaghat et al.: evaluating the effects of dam construction on the morphological changes of… fig. 2. location of the selected domain of study for the karkheh river. iii. methods and materials the stages of this research were: (i) to find the hydraulic processes of the flow and to determine its relevant features, besides simulating the transportation of sediments in the karkheh river through the application of the cche2d software and the calculations of hydraulic parameters pertaining to the flow and the transportation of sediments; (ii) to compare the results obtained by simulations of the model of hydrodynamic sections and that of the identical spots, before and after the construction of the karkheh dam (via the assistance of satellite images) with the aim of determining the effects of dam construction on the river; (iii) to calculate the length of the river as it contributes to the river’s instability and to show the morphological condition of the river, before and after dam construction. equations pertaining to flow, herein, concerned open flow channels which are relevant to the essentials of shallow waters. therefore, the influence of fluvial vertical motion is not so much important in this circumstance, and for this reason the averaged two-dimensional equations are of suitable precision and functionality which address the depth of a river in most cases of simulating the hydraulics of the flow. the averaged equations used for the depths of the fluvial system for its turbulent flows are presented as the equations in the cche2d model [24]: continuity equation of flow: 0 )()(          y hv x hu t z (1) equations of momentum (movement): ( )( )1 yyxx bx cor hhu u u z u v g f v t x y x h x y h                       (2) uf hy h x h hx z g y v v x v u t v cor byyyyx                          )()(1 (3) in these momentum equations, especially in (2), the reynolds stresses can be predicted with the help of the boussinesq hypothesis according to the following [25]: x u vtxx    2 (4)             x v y u vtyxxy  (5) y u vtyy    2 (6) it is necessary to grid the environment for the discretization of partial differential equations governing the model in relation to water and sediments via numerical methods (figure 3). the process involves gridding the selected domain via the cche2d mesh generator model by algebraic and numerical methods. then, the produced grids is assessed by the mdo and ado functions. after calibrating and assessing the grids, it was observed that the environment gridded with i=30 and j=200 displayed less error in comparison with gridding by other values of ‘i’ and ‘j’. table i demonstrates the precision of gridding. generally, grids are more precise when the values of the mdo and ado functions are less. table i. calibrating and assessing the produced grids. fig. 3. type of the produced grids of the selected domain. a. analysis of the daily discharge hydrograph of the flow in the model one of the most important factors in determining the mechanism of floodwater hydrograph combinations and the condition of a river system at times of flood is the temporal delay between the peak discharge of floodwaters of upstream and downstream districts of the river which directly affects the peak discharge of the overall floodwater. the peak of floodwater hydrograph is important in terms of hydraulic conductivity, regardless of the volume of floodwater function (mdo) function (ado) ( j ) value ( i ) value no. 8.23 9.46 200 20 1 6.30 5.32 300 15 2 2.40 1.12 200 30 3 engineering, technology & applied science research vol. 7, no. 2, 2017, 1515-1522 1518 www.etasr.com liaghat et al.: evaluating the effects of dam construction on the morphological changes of… hydrograph, which posit the peak discharge of the hydrograph as the base for the engineering of river installations and designs. for this purpose, the relevant scale and condition of the river under critical situations of flooding which indicate the degree to which the surrounding lands of the river become flooded and immersed in water are factors determined by the peak discharge of the floodwater hydrograph. however, the influential factor affecting the erodibility of the riverbed and banks is mostly the long-term effect of discharge within a specified amount of time. in this research, the hydrograph of flow discharge pertaining to a time span of three consecutive years was obtained from the hydrometric station upstream the river, and its information was regarded as the input data for the model. a three-year time span was considered for the time preceding the construction of the dam, and a three-year time span was studied to consider the condition after dam construction. the preconstruction period of three years was from september 1993 to august 1996, and the post-construction period of three years was from september 2008 to august 2011. this pattern of time-span selection has been practiced in previous research too [26]. figure 4 shows the hydrograph of three consecutive years before and after the construction of the karkheh dam. fig. 4. the hydrograph of three consecutive years before and after the construction of the karkheh dam. determination of manning’s roughness coefficient can be done by the d50 value of materials which constitute the structure of riverbed and banks. the strickler equation is also involved in the relevant calculations. 6 1 50047.0 dn  (7) where n is manning’s coefficient value, d50 is the average size of alluvial particles (m). the method of calibrating the surface level of water was applied for calibration and assessment of the model. to correlate the calculated amount of sediment discharge with the actual amount of sediment discharge, it was supposed that the manning coefficient which was obtained from the calibration of surface water level remains valid for this stage too. accordingly, it was realized that the calculated values matched quite suitably with the actual values observed in the experimental field. table ii displays the manning coefficient in the model for various domains. b. correlations between flow discharge and sediment discharge, the amount of suspended load and bed load in the cche2d model the equation that best fits the optimum curve congruent with the data of flow discharge and sediment discharge of the jelogir and pay-e-pol stations can be presented as in the following formula. the formula (8) is used for sediment data pertaining to the time before the dam was constructed, and formula (9) is used for sediment data of after when the dam was constructed [27, 28]. 4027.2032.0 ws qq  (8) 357.20364.0 ws qq  (9) where qw is the flow discharge in m 3/s and qs is the sediment discharge expressed in ton/day. table ii. manning’s roughness coefficient of the river before and after the construction of the dam. the transportation of materials in a river occurs in the form of bed load and suspended load, in either case it depends on the size of particles and the velocity or other qualities of the flow. the presence of various kinds of sediments (sand, silt and clay) in the alluvial system is partially due to the process of selective transportation wherein particles are arranged in their movements. this leads to the fact that the process is related to the selective motion of various sediment particles which have an incipient motion that is nearly equal to the shear stress in the bed, but which the particles can be extensively transported when a higher degree of shear stress rules. accordingly, (10) and (11) can be used for the input data of bed load and suspended load in the cche2d model [27, 28]. 7932.51102.0  blqw (10) 2085.737.48  slqw (11) where qw is the flow discharge measured in m3/s and bl is the bed load and sl is the suspended load expressed in ton/day. c. grain size gradation of bed load sediments the relationship between grain size of sediments and the hydraulic conditions of the flow was determined by the help of the flow discharge diagram in relation to the percentage of three different types of sediment particles in the bed load, namely gavel, sand and fine grains. the composition of sediment particles of the karkheh river was 93.26% sand, 4.63% gravel and 2.08% of fine grains (silt-clay). figure 5 shows the diagram of gradation for average grain size of sediment particles in the studied district of the karkheh river. in the studied district of the river, the karkheh river exhibits diverse widths along its course and sections. the river is very wide in some sections (having an extensive floodplain) and has manning’s roughness coefficient in 2011 manning’s roughness coefficient in 1996 distance from pay-e-pol st. (km) reach no. 0.035 0.034 12.3 1 0.039 0.039 20.1 2 0.040 0.038 30.9 3 engineering, technology & applied science research vol. 7, no. 2, 2017, 1515-1522 1519 www.etasr.com liaghat et al.: evaluating the effects of dam construction on the morphological changes of… tall banks in some other sections. therefore, in most occasions, massive floodwaters may partially stream off the river’s main course and thus cause errors in the measurement and documentation of the floodwater by downstream hydrometric stations. but to solve this problem, a wide domain of river sections was selected which also included the river’s floodplain. under these circumstances, the model can yield actual and logical results on a two-dimensional basis. fig. 5. the diagram of gradation for average grain size of sediment particles. iv. results and discussion it is common knowledge that rivers are influenced by various factors and variables that cause them change in their dimension, direction and pattern. these changes have temporal and geographical dimensions and are affected by the discharge of flow and sediments, the features of input sediments to the system and grain size of the bed materials (of river bed and banks). metamorphosis of rivers can be gradual and continuous in the long-term approach, or it can be sporadic and sudden if considered under certain circumstances in the short-run [2931]. the results of these changes in this research are as follows: a. changes to the widths of the river by measuring the widths of the riverbed obtained by results of the model in different seasons through the course of the river, the trend of change for the widths of the riverbed can be achieved. under natural conditions, the widths of the riverbed increases towards the downstream of the river’s course, parallel to the decline in the river’s slope angle along the length of the river. figure 6 and table iii show that the width of the river has been reduced considerably because of dam construction. the overall domain of the studied district measured 31 kilometers long. there were 34 sections considered along the district, and the summarization of results is presented in 6 domains (table iii). the average widths of the river before dam construction was 273 meters, its maximum and minimum widths were 589 and 75 meters, respectively. the average widths of the river became 60 meters after dam construction, the maximum and minimum of widths after dam construction were 86 and 30 meters, respectively. therefore, by an approximate reduction of 78% in the widths of the river, nearly 21 hectares of land, per each kilometer of river length, was released from floodwater. this value pertains to the floodwater with a return period of two years. table iii. average widths of the river before and after the construction of the dam. average widths of river (m) zone distance end of reach from pay-e-pol st. (m) 1996 year 2011 year 1 5138 219.4 51.4 2 10852 423.1 60.3 3 15085 289.1 57.4 4 20060 191.6 61.2 5 25111 215.9 57.3 6 30982 291.0 71.9 b. changes to the plane of the river and lateral migration when there occurs a considerable change in the amount of flow discharge and sediment load in a meandering river, the plane of the river also undergoes considerable change as a consequence, over the specified amount of time. in table iv, the migration of the river’s thalweg is shown in addition to its direction and status in comparison with the primary conditions of the riverbed. in the studied district, the average thalweg migration of the river is approximately 340 meters, and its maximum and minimum are 768 and 53 meters, respectively. table iv. the thalweg migration of the river before and after the construction of the dam. sum thalweg migration input and output old riverbed (m) sum thalweg migration with the primary conditions (m) right direction left direction input old riverbed output old riverbed average thalweg migration (m) distance end of reach from pay-e-pol st. (m) zone 2855 2283 2850 2288 68.4 5138 1 0 5714 1633 4081 408.5 10852 2 3004 1229 2244 1989 356.9 15085 3 3706 1269 2366 2609 430.5 20060 4 5051 0 2281 2770 373.0 25111 5 3464 2407 3768 2103 369.4 30982 6 18080 12902 15142 15840 sum engineering, technology & applied science research vol. 7, no. 2, 2017, 1515-1522 1520 www.etasr.com liaghat et al.: evaluating the effects of dam construction on the morphological changes of… figure 6 shows the changes in plane and the lateral migration of the river in the studied domain, and figure 7 shows the diagram for thalweg migration of the river. results show that over 51% of migrations occurred to the west side of the river, and over 58% of these migrations took place outside the old riverbed. the analysis of results shows that there is an average lateral migration of 34 meters occurring to the river each year, in the studied district, which signifies the instability of the region. fig. 6. the changes in plane and the lateral migration of the river in the studied domain. fig. 7. the diagram for thalweg migration of the river c. changes to the longitudinal profile and the level of riverbed the slope angle along the length of the river is first controlled by the conditions and features of topographic and geological characteristics of the watershed region. the slope, however, would change gradually as a result of erosion and disintegration of materials. with increasing the slope value the erosion level of the river bed will be increased and visa versa (because of the velocity of water). this concludes to a condition that the slope of the river becomes the summation result of water flow effects and the influences of topographic and geological parameters (figures 8 and 9). fig. 8. changes to the longitudinal profile before the construction of the dam. fig. 9. changes to the longitudinal profile after the construction of the dam. the equations for the longitudinal profile of the studied district, before and after dam construction, can be expressed as in (12) and (13), where el is the height of the riverbed (m), and d is the distance to the pay-e-pol station (m). 9794.0 13.103 2 051    r el e de (12) 9589.0 34.102 2 051    r el e de (13) d. changes to the cross-section of the water level to illustrate the cross-section of the water level, the results of the model’s performance was derived correspondingly in a congruent manner regarding the period preceding dam construction and the period after it. by comparing the crosssection of the floodwater between the pre-construction and post-construction periods, it is evident that the level of water in the river has declined in most sections, because of dam construction. figures 10 and 11 show that in both cases of pre and post-construction periods of the dam, the fluctuations in the river’s depths are sporadic in relation to the distance from the station, but generally these changes exhibit a trend of increase in the river’s depths by the longer distance from the station, in both cases of pre and post construction periods of dam construction. one reason for this increase in the river’s depth can be explained by the reduction in the river’s slope angle and the occurrence of sedimentation downstream the selected domain of the river. fig. 10. changes to the cross-section of the water level before the construction of the dam. engineering, technology & applied science research vol. 7, no. 2, 2017, 1515-1522 1521 www.etasr.com liaghat et al.: evaluating the effects of dam construction on the morphological changes of… fig. 11. changes to the cross-section of the water level after the construction of the dam. v. conclusions metamorphosis of rivers can be gradual and continuous in the long-term approach, or it can be sporadic and sudden if considered under certain circumstances in the short-run. under natural conditions, the widths of the riverbed towards downstream the river’s course is increased, when the river’s slope angle decreases. in this case, significant changes occurred after the construction of a dam. the average widths of the river reduced from 273 meters to 60 meters. by an approximate reduction of 78% in the widths of the river, nearly 21 hectares of land, per each kilometer of river length, was released from floodwater. this value pertains to the floodwater with a return period of two years. in the studied district, the average thalweg migration of the river is approximately 340 meters, and its maximum and minimum are 768 and 53 meters, respectively. results show that over 51% of migrations occurred to the west side of the river, and over 58% of these migrations took place outside the old riverbed. there is an average lateral migration of 34 meters occurring to the river each year, in the studied district, which signifies the instability of the region. with respect to the assessment of the model’s results, the bed profile of the river has thus reached a relative degree of stability, and the channel’s slope angle is not significantly different when comparing between 1996 and 2006. therefore, dam construction did not have a considerable effect on the general changes to the slope angle along the length of the river. the equation for the longitudinal profile of the studied domain of the river, before and after dam construction, is expressed in two exponential functions with coefficients of r2=0.96 and r2=0.98 which shows the reduction of the river’s slope angle towards downstream the river and correlates with the shulitz equation for changes in the slope angle along the river’s route. the fluctuations in the river’s depths are sporadic in relation to the distance from the station, but generally these changes exhibit a trend of increase in the river’s depths by the longer distance from the station, in both cases of pre and post construction periods of dam construction. results suggest that the studied region of the karkheh river is characterized by instability, in between the distance from the pay-e-pol station up to 40 km downstream of it. therefore, future changes to the course of the river are anticipated to happen in the studied district. results pertaining to the migration and movement of various sections of the river also confirm the strong likelihood of change that can occur to the river’s course in the future. references [1] w. r. white, r. bettes, e. paris, “analytical approach to river regime”, asce journal of the hydraulics division, vol. 108, no. 10, pp. 1179-1193, 1982 [2] k. c. patra, s. k. kar, a. k. bhattacharya, “flow and velocity distribution in meandering compound channels”, asce journal of hydraulic engineering, vol. 130, no. 5, pp. 398-411, 2004 [3] d. a. ervine, k. babaeyan-koopaei, r. h. j. sellin,“two-dimensional solution for straight and meandering overbank flows”, asce journal of hydraulic engineering, vol. 126, no. 9, pp. 653-669, 2000 [4] s. yousefi, h. r. pourghasemi, j. hooke, o. navratil, a. kidová, “changes in morphometric 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below the hapcheon re-regulation dam, south korea”, international journal of river basin management, vol. 8, no. 2, pp. 139–150, 2010 [10] y. h. shin, p. y. julien, “effect of flow pulses on degradation downstream of hapcheon dam, south korea”, asce journal of hydraulic engineering, vol. 137, no. 1, pp. 100-111, 2011 [11] n. b. dam, yuba river development project ferc project no. 2246, 2011 [12] c. a. lott, r. l. wiley, r. a. fischer, p. d. hartifield, j. m. scott, “interior least tern (sternula antillarum) breeding distribution and ecology: implications for population-level studies and the evaluation of alternative management strategies on large, regulated rivers”, ecology and evolution, vol. 3, no. 10, pp. 3613-3627, 2013 [13] s. a. brandt, “classification of geomorphological effects downstream of dams”, catena, vol. 40, no. 4, pp. 375-401, 2000 [14] j. c. stevaux, d. p. martins, m. meurer, “changes in a large regulated tropical river: the paraná river downstream from the porto primavera dam, brazil”, geomorphology, vol. 113, no. 4, pp. 230-238, 2009 [15] i. overeem, a. j. kettner, j. p. m. syvitski, “impacts of humans on river fluxes and morphology”, treatise of geomorphology, vol. 9, no. 8, pp. 828-842, 2013 [16] g. e. grant, j. c. schmidt, s. l. lewis, “a geological framework for interpreting downstream effects of dams on rivers”, in a peculiar river, water science and application vol. 7, , vol. 7, no. 8, pp. 203-219, 2003 [17] n. surian, m. rinaldi, “morphological response to river engineering and management in alluvial channels in italy”,geomorphology, vol. 50, no. 4, pp. 307-326, 2003 [18] n. c. nelson, s. o. erwin, j. c. schmidt, “spatial and temporal patterns in channel change on the snake river downstream from jackson lake dam, wyoming”, geomorphology, vol. 200, no. 5, pp. 132-142, 2013 [19] a. zámolyi, b. szĕkely, e. draganits, g. timár, “neotectonic control on river sinuosity at the western margin of the little hungarian plain”, geomorphology, vol. 122, no. 4, pp. 231-243, 2010 [20] p. narinesingh, j. e. pizzuto, applying a model of curvature-driven bend migration developed for alluvial rivers to a gravel-bedded engineering, technology & applied science research vol. 7, no. 2, 2017, 1515-1522 1522 www.etasr.com liaghat et al.: evaluating the effects of dam construction on the morphological changes of… river with reaches of exposed bedrock, agu fall meeting abstracts, 2009 [21] j. a. constantine, s. r. mclean, t. dunne, “a mechanism of chute cutoff along large meandering rivers with uniform floodplain topography”, geological society of america bulletin, vol. 122, no. 6, pp. 855-869, 2010 [22] i. güneralp, r. a. marston, “process–form linkages in meander morphodynamics: bridging theoretical modeling and real world complexity”, progress in physical geography, vol. 36, no. 6, pp. 718746, 2012 [23] m. kurowski, “procedural generation of meandering rivers inspired by erosion”, the 20th international conference in central europe on 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[25] j. guo, p. y. julien, “shear stress in smooth rectangular open-channel flows”, asce journal of hydraulic engineering, vol. 131, no. 1, pp. 30-37, 2005 [26] h. avila, g. vargas, r. daza, “susceptibility analysis of river bank erosion based on exposure to shear stress and velocity combined with hydrologic and geomorphologic variables”, asce world environmental and water resources congress, 2014 [27] m. shafai bajestan, h. hassanzadeh, n. m. esfahani, investigation of sedimentology and estimation of yearly sediment yeild in karkheh river, khuzestan water & power authority (kwpa), technical report, 2010 [28] m. ghomeshi, result of sedimentation types analysis (case study: kharkhe river, khuzestan water & power authority (kwpa), technical report, 2005 [29] l. b. a. michalik, t. tekielak, “the relationship between bank erosion, local aggradation and sediment transport in a small carpathian stream”, geomorphology, vol. 191, no. 2, pp. 51-63, 2013 [30] s. bandyopadhyay, k. ghosh, s. k. de, “a proposed method of bank erosion vulnerability zonation and its application on the river haora, tripura, india”, geomorphology, vol. 224, no. 2, pp. 111-121, 2014 [31] j. l. grimaud, d. chardon, v. metelka, a. beauvais, o. bamba, “neogene cratonic erosion fluxes and landform evolution processes from regional regolith mapping (burkina faso, west africa)”, geomorphology, vol. 241, no. 3, pp. 315-330, 2015 microsoft word 24-2311_s1 engineering, technology & applied science research vol. 8, no. 5, 2018, 3432-3438 3432 www.etasr.com sun et al.: analysis of bilateral trade flow and machine learning algorithms for gdp forecasting analysis of bilateral trade flow and machine learning algorithms for gdp forecasting jingwen sun school of international and public affairs, columbia university, new york, usa jingwensun321@gmail.com yuan suo school of social sciences, university of california, irvine, usa suoyuandl@163.com seeha park hankuk academy of foreign studies yongin, south korea seehalemon@gmail.com tianze xu college of liberal arts and sciences, university of connecticut, storrs, usa constans_x@163.com yizhu liu pius xi catholic high school, milwaukee, usa yizhuliupius@yeah.net weiqi wang lawrence woodmere academy, new york, usa weiqiwanglwa@163.com abstract—the terms imports and exports describe goods and services traded between countries. countries import goods they cannot produce domestically or can obtain at a lower cost from another country. according to the world trade organization (wto) reports, the u.s. is the world’s largest importer based on capital investment, followed by the e.u., china, germany, and japan. for exports, china leads the world with an official trade amount of $1.904 trillion in 2013. e.u. ranks second, followed by u.s., germany, and japan. trade in goods and services is defined as a change in ownership of material resources and services between economies. trade indicators include the sale of goods and services as well as barter transactions or goods exchanged and are measured in million usd, the percentage of gdp for net trade, and the annual export and import growth. this study analyzes imports and exports of all countries for the 1960-2017 period and evaluates the correlations in trade statistics to predict future imports and exports. since the gdp for any country depends mainly on trade, this study examines trade data and compares various machine learning algorithms to forecast a country’s gdp. keywords-imports; exports; gdp; trade statistics; gdp forecast i. introduction trade data include exports, imports, and trade balance. in general, international trade represents the economic activity of a country related to some economic relationship with another country. a series of such activities forms a country’s trade balance. the trade volume of a country indicates the country’s collective effect of macroeconomic policies. analyzing this effect from international trade policies requires data on the country’s exports and imports and the long-run equilibrium relationship between these two variables. here, there always is the effect of time lag on trade volume since any change in a country’s import/export demand does not happen quickly, and therefore, trade data require a deep analysis [1]. one factor in explaining trade remains the comparative advantage. however, some new factors such as consumer preferences, advantages in the economy of scale, and the use of global production have emerged, and such factors may alter international trade patterns. in addition, bilateral trade is important in understanding the consequences of international trade [2]. economies that are oriented mainly toward trade must carefully analyze their bilateral trade data since international trade flow and its direction, composition, and linkages require bilateral as well as multilateral analyses. therefore, data should always be carefully examined in any empirical analysis [3]. several studies have analyzed exports, imports, the economy, and their relationships, including cointegration between exports and imports [4, 5], long-run trade elasticity in less developed countries [6], cointegration in specific groups of countries [7], and related technical issues [8]. some studies have investigated the importance of exports and imports in forming the economy and improving the quality of life [9]. there are various methods for determining the importance of exports and imports in the economy and analyzing their impacts on economic growth. one uses simple (and sometimes multiple) regression between these three variables and other factors, and another employs causality, determining the factors and causes as well as inverse causality. some studies have used var and vec models to exclude this causality problem. a cointegration test has verified a long-run equilibrium relationship between gdp, exports, and imports in tunisia [10], finding these two variables to influence economic growth and thus highlighting their importance. a study of the nigerian economy has suggested economic growth to be determined by exports, imports, labor, and the exchange rate and posited their cointegration, also showing positive relationships of exports and labor to economic growth and negative effects of imports and the exchange rate on the economy [11]. a study of the ethiopian economy has revealed that the growth rate of real exports has a positive relationship with the rate of economic growth, analyzing that, although the effect is non-significant in the short run, there is a strong long-run relationship between engineering, technology & applied science research vol. 8, no. 5, 2018, 3432-3438 3433 www.etasr.com sun et al.: analysis of bilateral trade flow and machine learning algorithms for gdp forecasting these two variables [12]. these studies show that exports and imports have great impacts on economic growth. economic growth is typically represented with gdp, gdp per capita, trade balance, consumption, investment, and government spending. in addition to the impact on economic growth, exports and imports are important for other reasons. an example is the model of innovation and trade, which predicts positive shocks in exports can facilitate more productive and innovative firms. here the accompanying rent from the innovation effort of companies increases with the firm’s market size, known as the market size effect [13]. a country’s gdp is a primary indicator of the country’s economy. gdp represents the worth (in dollars) of all goods and services produced and imported/exported over a period of time. this is measured relative to previous gdp. an increase in gdp shows the growth of a country’s economy, and this figure is considered a key benchmark for the country’s economy. the u.s. has the largest gdp in the world, followed by china, japan, germany, the u.k., france, and india. in most cases gdp measurement is complicated. in simple terms, gdp is the income earned (gross profit) and expenditure spent by a country, and since it is considered relative to countries, exports and imports play a vital role in deciding a country’s gdp. gdp can be calculated as the total spending on all final goods and services (consumption of goods and services (c) + gross investments (i) + government purchases (g) + (exports (x) imports (m)), i.e. gdp=c+i+g+(x-m). ii. world trade data statistics trade statistics represent a unique dataset for modern economies. trade data statistics can indicate economic geography and provide insights into economic development and globalization. international trade plays an important role in a wage-based economy. international trade data provide insights into global relationships between countries as well as information on the relationship between local and regional economies [14]. statistical data confirm that trade has continued to support economic growth and development, helping to reduce poverty around the world. world merchandise exports have increased in value by about 32% since 2006, reaching usd 16 trillion in 2016. at the same time, world exports of commercial services have accelerated by about 64%, reaching a total of usd 4.77 trillion [15]. the importance of world trade data statistics is clear, but its usefulness depends on various factors such as data availability, analysis requirements, and data accuracy. therefore, measuring trade statistics must adhere to the standard international trade classification [16]. this is important since insufficient data or analysis may cause misinterpretation of variables. according to the world fact book, the world’s top exporter is china with the total export of $2.157 trillion in 2017, followed by the e.u. with $1.929 trillion in 2016 and the u.s. with $1.576 trillion in 2017 [17]. for top import countries, the world fact book ranks u.s. as the leader with $2.352 trillion of total imports in 2017, followed by e.u. with $1.895 trillion in 2016 and china with $1.731 trillion in 2017 [18]. germany and japan followed. the total import for germany was $1.104 trillion in 2017, and japan was $625.7 billion in 2017. for exports, germany exported $1.401 trillion in 2017, and japan, $683.3 in 2017 [17, 18]. the top 18 world imports and exports can be seen in [19]. cars top the list, with germany as the largest exporter and the u.s. as the top importer. refined petroleum follows, with the u.s as a sole leader in both exports and imports. the list also includes goods such as pharmaceuticals, gold, crude petroleum, telephone, broadcasting equipment, diamonds, petroleum gas, and aircrafts [20]. iii. literature review authors in [23] proposed a machine learning model for predicting agricultural commodity prices over one-, two-, and three-month periods ahead. they used the multivariate relevance vector machine based on bayesian learning for regression and compared the performance of the mvrvm model to that of multiple-output artificial neural networks. authors in [24] applied data mining to detect relationship patterns in customs administration data with market prices and current exchange rates in ethiopia and discovered association rules to generate note worthy import/export patterns. they used datasets from the ethiopian revenue and customs authority, central statistics agency, and the national bank of ethiopia and applied the weka tool for data analysis purposes, and the results verified that imported textile was significantly related to the market price and the currency exchange rate. they also concluded the apriori algorithm as the fastest one in discovering association rules. authors in [25] predicted bilateral trade flow, an important economic indicator, by using the gravity model of trade with a fully connected feed-forward neural network. they experimented with machine learning models by varying hidden layers and neurons in each hidden layer and found that fully connected feed-forward neural networks can improve the gravity model’s prediction performance. they also proposed that the lstm model may yield better results than fully connected neural networks for time series data. author in [26] used machine learning and data mining techniques for publicly available commodity data and forecasted country gdp, finding a correlation between exportimport data and gdp. he considered commodity trade and gdp as inputs to the algorithm and designed a model to predict gdp for another day with the given commodity trade for the new day. he used a multi-class support vector machine with a genetic algorithm based on a fuzzy set and artificial neural network to predict gdp. authors in [27] implemented a backpropagation neural network based on a genetic algorithm for port throughput forecasting. they used a 12-year dataset such that 11 years of data was used for simulations/training and the final year was used for forecasting. they verified the proposed hybrid model, the ga-bp forecasting model, to show better accuracy but it took longer to converge. authors in [28] proposed a new machine learning approach for price modeling using a neural network with an advanced signal-processing tool. they used the proposed model to forecast prices of commodities such as coal, crude oil, and electricity and employed a mixture of a gaussian neural network, showing significant improvements relative to other popular models. authors in [29] constructed a garch model using an artificial neural network and evaluated its ability to forecast stock market volatility. they compared the engineering, technology & applied science research vol. 8, no. 5, 2018, 3432-3438 3434 www.etasr.com sun et al.: analysis of bilateral trade flow and machine learning algorithms for gdp forecasting performance of their model to that of other popular volatility models for various international stock indices. authors in [30] proposed a model to predict future gold rates based on 22 market variables using machine learning techniques. they collected data from various online sources and implemented a linear regression model using artificial neural networks with the rapid miner tool. authors in [31] proposed a unified modeling framework to justify the empirical regularity in the international trade network and analyzed the international trade network each year with exports of the country with other countries. they constructed a basic model with a directed weighted network for unified modeling. iv. machine learning in global trade data machine learning applies artificial intelligence (ai) to automatically learn and improve from experience without being specifically programmed. machine learning focuses on the development of computer programs for accessing and learning from data. the process of learning begins with observations or data, including examples, direct experience, and instructions, to identify certain patterns in data for making better decisions. the main aim is to allow the computer to learn automatically without human intervention and engage in appropriate actions. ai and machine learning represent a good way for financial institutions to optimize margin valuation adjustment (mva), which can be performed through the assistance of machine learning by reducing margins for derivatives through a combination of “executing pairs of offsetting derivative trades” and “executing offsetting strategies with the same dealer” [21]. by choosing the best combination of the initial margin, machine learning reduces trades in a given period of time, and the basis for this is the degree of initial margin reduction in the past from various combinations of trades [20]. financial institutions emphasize cost-effective means for regulatory requirements, such as efficient trade execution, data reporting, and prudent regulation. in this regard, ai can be used to obtain information and process orders, and machine learning can help create “trading robots” that can respond quickly to market changes. therefore, such innovations can be used by firms to estimate financial impacts more accurately and minimize trading costs [20]. v. methodology a. datasets the data for this research study is gathered from [32]. the data consisted of yearly import/export data from 217 countries for the 1960-2017 period. data were collected from the bop (balance of payments) statistics yearbook and presented in usd. several missing data points were identified as a result of no substantial import/export participation by some countries during early years. therefore, the data for the last 43 years were considered in this study (i.e., 1975-2017). the data containing the top 10 countries in imports and exports were extracted from the primary data source for the analysis. the data (in billion usd) were used for further analysis. tables i and ii present the import and export data, respectively, for the study period. datasets show the u.s. as leading both imports and exports from 1975 to 2017. therefore, it is evident that the u.s. had the highest gdp and the gdp was growing at a constant pace. for better understanding, the import and export datasets are plotted in figures 1 and 2 respectively. fig. 1. increase in imports. table i. imports (in billon $) for 1975-2017 year canada colombia germany uk israel india netherlands sweden us s. africa 1975 42 3 94 64 7 7 40 21 120 12 1976 47 3 108 66 7 6 44 23 149 11 1977 49 3 123 74 8 7 51 24 180 10 1978 53 4 149 88 9 9 60 25 208 12 1979 63 4 193 115 11 12 76 35 248 15 1980 71 6 222 134 12 17 88 40 291 23 1981 79 7 195 122 13 18 76 36 310 26 1982 67 7 186 119 12 18 72 34 299 21 1983 74 6 181 118 12 18 70 32 323 18 1984 88 6 178 123 12 18 70 33 399 19 1985 93 6 184 128 12 19 73 35 410 13 1986 99 6 226 148 13 20 86 41 449 15 1987 107 6 271 183 17 23 104 51 501 18 1988 128 7 298 222 18 26 114 58 546 21 1989 141 7 319 233 18 29 119 62 580 21 1990 148 7 412 264 21 30 142 71 616 22 1991 152 7 452 251 23 28 146 66 610 22 1992 157 9 485 267 24 30 157 68 656 23 1993 168 12 420 255 27 31 144 56 713 24 1994 183 14 464 284 31 38 159 66 802 27 1995 199 16 559 327 36 49 210 81 891 34 1996 209 17 553 355 38 55 211 85 956 34 engineering, technology & applied science research vol. 8, no. 5, 2018, 3432-3438 3435 www.etasr.com sun et al.: analysis of bilateral trade flow and machine learning algorithms for gdp forecasting year canada colombia germany uk israel india netherlands sweden us s. africa 1997 237 19 537 380 38 59 206 85 1040 35 1998 241 18 565 396 36 60 217 90 1100 33 1999 259 14 579 419 41 63 223 91 1230 31 2000 287 15 595 440 47 74 231 97 1450 34 2001 268 17 587 439 44 72 231 87 1370 32 2002 271 16 589 471 43 76 243 91 1400 33 2003 295 17 726 529 45 93 286 113 1510 44 2004 337 21 858 625 53 131 363 134 1770 59 2005 385 26 934 686 59 182 392 149 2000 69 2006 430 31 1080 784 63 225 441 169 2220 84 2007 471 38 1250 841 75 279 522 204 2360 98 2008 508 46 1410 867 85 379 595 226 2550 108 2009 412 40 1130 677 64 328 486 167 1970 83 2010 500 49 1270 753 77 439 532 197 2350 103 2011 568 64 1500 840 93 553 615 233 2680 123 2012 587 70 1410 844 93 580 600 221 2760 124 2013 586 71 1480 869 92 560 618 224 2760 122 2014 585 76 1510 915 95 554 632 231 2870 116 2015 531 65 1310 840 85 492 552 200 2760 100 2016 513 55 1330 804 90 472 555 202 2710 90 2017 548 57 1460 838 97 561 619 222 2900 100 table ii. exports (in billon $) for 1975-2017 year canada colombia germany uk israel india netherlands sweden us s. africa 1975 39 3 103 60 4 6 43 21 130 11 1976 45 3 119 63 5 7 47 22 142 10 1977 48 4 137 76 6 8 52 23 152 12 1978 54 4 166 92 7 9 60 27 178 15 1979 64 5 198 117 8 10 75 34 223 20 1980 75 6 217 146 9 12 87 39 272 29 1981 81 5 200 136 9 12 81 36 294 24 1982 80 5 201 128 9 13 78 34 275 21 1983 86 4 192 121 9 14 75 34 266 21 1984 100 6 193 122 10 14 76 36 291 20 1985 101 5 207 132 10 13 79 37 289 19 1986 102 7 272 144 12 14 92 44 310 20 1987 112 7 326 175 14 16 109 53 349 26 1988 132 7 358 191 15 18 122 60 431 27 1989 142 8 379 199 16 21 128 63 487 26 1990 149 9 457 239 18 23 153 71 535 28 1991 149 10 443 240 17 24 157 70 578 27 1992 155 10 473 254 20 25 169 72 617 28 1993 168 10 421 246 21 28 160 62 643 30 1994 189 11 468 277 24 32 178 74 703 31 1995 218 13 571 322 28 39 235 96 794 35 1996 233 14 573 352 30 41 236 101 852 36 1997 249 15 563 383 32 45 231 101 934 37 1998 253 14 594 384 33 46 240 105 933 35 1999 283 14 594 393 38 52 242 106 970 34 2000 328 16 601 409 47 60 247 112 1080 37 2001 310 16 622 401 41 63 248 105 1010 36 2002 304 15 680 421 40 71 260 107 979 37 2003 329 16 819 480 44 85 322 131 1020 48 2004 382 20 1000 563 54 116 410 161 1160 59 2005 431 25 1080 622 59 155 446 174 1290 69 2006 465 29 1240 719 63 193 499 199 1460 80 2007 502 35 1480 765 73 240 593 235 1650 94 2008 536 44 1640 781 84 305 673 257 1840 103 2009 392 39 1300 625 70 261 550 188 1580 84 2010 469 46 1440 689 82 348 603 220 1850 108 2011 547 64 1690 799 95 446 692 262 2130 127 2012 551 69 1630 792 93 444 679 249 2220 118 2013 556 68 1710 813 98 468 711 253 2290 113 2014 568 65 1780 854 100 486 727 257 2380 110 2015 492 46 1580 790 94 429 632 225 2260 97 2016 476 42 1600 749 97 430 641 225 2210 92 2017 511 48 1740 802 102 488 714 240 2330 104 engineering, technology & applied science research vol. 8, no. 5, 2018, 3432-3438 3436 www.etasr.com sun et al.: analysis of bilateral trade flow and machine learning algorithms for gdp forecasting fig. 2. increase in exports. with the growth in imports and exports of all countries identified, as shown in these plots, data analysis was conducted using linear regression to identify the correlation coefficient and other performance measures. b. data analysis the gdp of any country is dependent on import and export data since these factors make the greatest contributions to the country’s economy, and several algorithms have been implemented for the analysis of trade data. therefore, this study focused on analyzing import and export data. the study initially employed linear regression, followed by a comparison with other machine learning algorithms. here, preprocessed data from 10 countries were used as the input for linear regression, and the results for export and import datasets were obtained as shown in tables iii and iv, respectively. table iii. exports analysis for top 10 countries country cc mae rmse rae (%) rrs(%) canada 0.9642 40.606 46.7947 25.1067 25.8104 colombia 0.8346 8.3626 10.8224 49.9367 53.1576 germany 0.9375 162.9892 195.2004 32.1998 33.721 india 0.8353 78.3047 90.7998 54.2975 53.1019 israel 0.9484 9.2247 10.3887 31.6044 30.7659 netherlands 0.933 72.6982 84.1967 34.3541 34.8714 s. africa 0.8842 13.7084 16.464 43.1783 45.1946 sweden 0.942 22.7929 27.3736 31.1841 32.5885 uk 0.9639 61.4828 70.191 25.9338 25.899 us 0.9566 184.4345 211.1925 29.5354 28.3296 cc: correlation coefficient, mae: mean absolute error, rmse: root mean square error, rae: relative absolute error, rrse: root relative squared error table iv. imports analysis for top 10 countries country cc mae rmse rae (%) rrs(%) canada 0.9585 44.3818 51.9594 27.3267 27.6743 colombia 0.8578 9.0713 11.2877 48.4398 49.8184 germany 0.9447 130.7667 154.7405 31.125 31.8091 india 0.8272 94.3616 110.4496 54.8779 54.241 israel 0.9562 7.6478 8.748 29.0447 28.426 netherlands 0.9347 62.5513 71.9923 34.2352 34.4388 south africa 0.8703 15.8974 18.4622 46.8866 47.7568 sweden 0.9344 20.9784 25.3766 32.8641 34.5429 uk 0.9628 67.9066 77.7684 25.9899 26.2868 us 0.9639 221.3444 249.555 25.9518 25.8817 cc: correlation coefficient, mae: mean absolute error, rmse: root mean square error, rae: relative absolute error, rrse: root relative squared error from these import and export tables, it can be observed that the correlation coefficient is close to 1, indicating a strong positive linear relationship. however, the rmse is slightly high in some cases. since the dataset consisted of only 43 instances (last 43 years of data), the linear regression model showed good correlations and high rmse values. therefore, further analysis using other machine learning algorithms was conducted with import and export datasets from the u.s. and germany. vi. results and discussion to investigate on the best-performing machine learning algorithms for a better analysis of trade data and to forecast country gdp, this study considered 5 machine learning algorithms: • linear regression (lr) • rbf regressor (rbf) • support vector machine (svm) • regression by discretization (rd) • reduced error pruning tree(rep) the u.s. and germany import and export datasets were used as input datasets. a 10-fold cross-validation method was implemented to select training and testing datasets. here correlation coefficients, root mean squared error, relative absolute error, and root relative squared error were considered as performance measures. a two-tailed test with a 0.05 confidence level was conducted and the results for these four performance measures are respectively shown in tables vviii. table v shows the correlation coefficients obtained for 4 datasets in the experiment with 5 algorithms. the table shows that the rbf algorithm generated better models with high correlation coefficients, followed by rd, lr, svm, and rep. table vi (relative absolute error analysis) shows that rbf generated models with much smaller errors than lr and svm. the results for rd lie between rbf and rep results. therefore, rbf can be considered to perform well with respect to the relative absolute error measure. table v. correlation coefficient analysis data set lr rbf svm rd rep germany_exports 0.97 0.99 0.97 0.97 0.96 germany_imports 0.97 0.99 0.97 0.97 0.96 us_exports 0.98 0.99 0.98 0.99 0.97 us_imports 0.98 0.99 0.98 0.99 0.97 table vi. relative absolute error analysis data set lr rbf svm rd rep germany_exports 35.46 13.78 35.85 20.99 22.45 germany_imports 34.41 15.57 32.05 21.36 23.81 us_exports 34.21 12.02 33.16 16.60 22.30 us_imports 29.38 9.58 30.72 16.36 20.82 table vii. root mean squared error analysis data set lr rbf svm rd rep germany_exports 187.53 86.55 195.54 118.76 139.53 germany_imports 146.63 78.10 149.10 105.87 119.36 us_exports 205.34 83.24 237.78 111.97 155.62 us_imports 247.66 106.71 262.79 156.85 202.58 engineering, technology & applied science research vol. 8, no. 5, 2018, 3432-3438 3437 www.etasr.com sun et al.: analysis of bilateral trade flow and machine learning algorithms for gdp forecasting table viii. root relative squared error analysis data set lr rbf svm rd rep germany_exports 36.13 15.43 36.88 22.80 26.56 germany_imports 33.85 16.69 33.01 23.69 26.95 us_exports 30.89 12.26 33.36 16.81 23.58 us_imports 28.26 11.45 29.47 17.66 23.25 table vii (root mean squared error) and table viii (root relative squared error) also verify rbf as providing better results than the other algorithms. although rms values are high (with a smaller dataset), rbf obtains 60% better results than lr. the performance plots for the above measures using the rbf algorithm are shown in figures 3-6. fig. 3. correlation coefficienet. fig. 4. mean absolute error. fig. 5. root mean squared error given these measures, the rbf algorithm is shown to provide good performance with a gain of about 60%. the results demonstrate that rbf outperformed the other four algorithms and that the models generated using rbf produced better results in forecasting of country gdp. fig. 6. root relative squared error vii. conclusions trade analysis results show a strong positive linear relationship in trade statistics. imports and exports increased linearly with the world engaging in increased trade activity. in particular, the u.s., china, japan, and india have made remarkable progress in the past decade in both exports and imports. this study takes two different directions. the first direction is the analysis of the top 10 import/export countries to show the correlation in trade data, and the second is to investigate different machine learning algorithms to identify the best algorithm for the prediction of trade data and country gdp. here the weka data analysis tool was used for data analysis, and the experiments were conducted using five machine learning algorithms. the results show that all five algorithms exhibited good correlations but that the rbf algorithm outperformed the other algorithms. this suggests that the rbf algorithm may perform well in forecasting trade data to predict a country’s gdp. references [1] j. uddin, “time series behavior of imports and exports of bangladesh: evidence from cointegration analysis and error correction model”, international journal of economics and finance, vol. 1, no. 2, pp. 156162, 2009 [2] i. s. kim, s. liao, k. imai, “measuring trade profile with granular product-level trade data”, available at: https://imai.fas.harvard.edu/ research/files/bigtrade.pdf, 2018 [3] r. sen, “analyzing international trade data in a small open economy: the case of singapore”, asean economic bulletin, vol. 17, no. 1, pp. 23-35, 2000 [4] m. bahmani-oskooee, h. j. rhee, “are imports 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indicators, available at: https://data.worldbank.org/ indicator microsoft word 13-3347_s_etasr_v10_n2_pp5412-5418 engineering, technology & applied science research vol. 10, no. 2, 2020, 5412-5418 5412 www.etasr.com ullah & altamimi: panic detection in crowded scenes panic detection in crowded scenes ahmed b. altamimi college of computer science and engineering university of hail hail, saudi arabia altamimi.a@uoh.edu.sa habib ullah college of computer science and engineering university of hail hail, saudi arabia h.ullah@uoh.edu.sa abstract—a crowd is a gathering of a huge number of individuals in a confined area. early identification and detection of unusual behaviors in terms of panic occurring in crowded scenes are very important. panic detection comprises of formulating normal scene behaviors and detecting and identifying non-matching behaviors. however, panic detection and recognition is a very difficult problem, especially when considering diverse scenes. many methods proposed to cope with these problems have limited robustness as the density of the crowd varies. in order to handle this challenge, this paper proposes the integration of different features into a unified model. discriminant binary patterns and neighborhood information are used to model complex and unique motion patterns in order to characterize different levels of features for diverse types of crowd scenes, focusing in particular on the detection of panic and nonpedestrian entities. the proposed method was evaluated considering two benchmark datasets and outperformed five existing methods. keywords—crowd analysis; anomaly detection; congestion; bottleneck identification i. introduction crowd scene analysis is major problem in computer vision. the challenges of crowd scene analysis are found in gatherings which attract many people, such as sports, festivals, social, political and religious gatherings. important problems and security concerns are raised in huge crowds. therefore, dealing with the crowd scenes is a very challenging problem in the subfield of video surveillance, due to the complex behaviors of individuals. a method developed for this purpose could be deployed for detecting critical crowd levels, people counting, and anomalies in such environments. detecting panic situations in such scenes becomes extremely important for crowd control and safety. furthermore, in public gatherings, it is important to know the ongoing situation and the behavior of people attending an event, as it can provide useful information for future event planning and public space design. this study aims at detecting panic and non-pedestrian entities representing abnormal behaviors in crowd scenes, integrating robust features into a unified model. the structure of the proposed method consists of the discriminant binary pattern (dbp) [1] and the neighborhood orientation information [2]. these features are combined and classified using a multi-class support vector machine [3]. in the crowd scene context, different feature integration could represent individuals, and patterns that reflect the collective behavior of crowd arise from the interaction of individuals. this kind of modeling deals with the challenges of crowded scenes in terms of various distributions, sparseness, consistency and inconsistency of the scene. many computer vision based methods have been proposed to detect panic and other anomalies in crowded scenes. however, most of them are modeled to address a specific scene, while different representations of motion and appearance are analyzed with different techniques. the proposed method explores the properties of abnormal situations, considering both the anomalies in terms of panic and non-pedestrian entities. this method computes dense motion trajectories from input videos. considering the computed trajectories, different features are combined into a unified hybrid model. furthermore, the underlying complex motion information is explored, which can formulate complex events in the crowd. this information consists of mid-level characteristics that model the distance between low and highlevel features for representing anomalous situations. the proposed hybrid features do not limit the type of features or scenes, enabling the extension of the technique to broader research fields. for experimental evaluation, the method is applied on two widely used benchmark datasets. additionally, the proposed technique is compared with five existing methods, namely the spatio-temporal texture model (sttm) [4], the abnormal crowd behavior model (acbm) [5], and the spatio-temporal volume based methods: mixture of dynamic texture (mdt) [6], data mining for anomaly (dma) [7], and optical flow and texture for anomaly (ofta) [8]. ii. literature review recently, deep learning methods have shown promising results in different applications in the field of computer vision. therefore, different computer vision and deep learning based methods have been successfully employed to solve problems related to crowded scenes in real time [9-11]. crowded scenes can be categorized on gathering locations, e.g., congested urban areas, historical events organized in museums, music and fun concerts, arrival and departure zones in airports, and different sports in stadiums. various proposed methods can generally help safety, security staff and administrators in identifying security methods. different crowd analysis methods consider the input data in different ways. for example, some methods process videos from stored archives. the methods corresponding author: habib ullah engineering, technology & applied science research vol. 10, no. 2, 2020, 5412-5418 5413 www.etasr.com ullah & altamimi: panic detection in crowded scenes introduced in [12, 13] extract frames from video cctv cameras. some researchers introduced unified frameworks for crowd congestion analysis, individual counting, crowd flow analysis on pedestrian pathways, crowd fight analysis, panic and bottleneck detection during exit and entrance [14-16]. in [17], a hybrid method was used to analyze crowd from different angles, such as crowd moving in different directions, computing statistics related to a static crowd, calculation of areas covered by potential crowd, and crowd’s social behavior analysis in the form of groups or as a whole. this technique could be deployed to take into account different aspects in public locations, considering a unified framework. moreover, the techniques introduced in [18-20] could be used to direct crowd flow to avoid stampede or other adverse events. in addition, crowd analysis approaches driven by tracking techniques [21-23] can be exploited to track suspicious individuals in a congested area, in order to ensure security. the tracking driven technique in [24] could be used to understand how individuals are behaving and moving in crowded scenes. these techniques can be used to divert crowd flows in public places to avoid congestion and stampede. in general, crowd analysis methods can be divided into two categories. in the first, each entity in the crowd is considered individually and they are combined to model crowd behavior. however, these methods can only be considered when the scene is not occupied by a very dense crowd. in the second category, methods treat the whole crowd as a single entity. these techniques perform very well in dense crowded scenes. the techniques in [25-27] fall in the first category, and they can be utilized to track individual people in the crowd, calculate the waiting time of a static crowd, compute the length of individuals in a queue, count the number of people in crowded scenes, and analyze people’s engagement in crowd scenes. the techniques presented in [28-30] fall in the second category, and they can help security staff and administrators to have in insight into a crowd scene and get the essence of the behavior as a whole. different methods have been proposed in dealing with the problems of crowd analysis considering different factors such as individual tracking, abnormal situation detection, flow analysis, and situation awareness. the method proposed in [31] combines different data from different sensors to get more accurate localization of the target in the crowded scene, introducing a modified ensemble of kalman filters to deal with a high degree of nonlinearity. the method in [6] detects and recognizes anomalies in crowded scenes using features related to the appearance and the dynamics of the crowd, considering both temporal and spatial information to compute mixtures of dynamic textures. the model presented in [32] uses a multiscale deep convolutional neural network to count the number of individuals in a single image with arbitrary crowd density and perspective. authors in [33] presented an aggregation of ensembles considering pre-trained convnets and a pool of classifiers in order to detect anomalies in crowded scenes. their approach was inspired by the concept that a set of different fine-tuned cnns represents various levels of semantic characterization, and therefore encodes a very rich set of robust features. the method in [34] was an agent-based crowd simulation model that exploited a path planning strategy. different elements, including traveling distance and turning angle, can be used efficiently for path planning in crowded scenes. an inspiration of momentum from physics was exploited in [35], integrating foreground information with an object’s motion, based on background subtraction, feature computation, behavior identification, and anomaly detection. authors in [36] discussed various approaches for the analysis of both high and low density crowds to facilitate personal mobility, safety, and security, enabling assistive robotics in crowded scenes. this study demonstrated the main challenges and solutions for the analysis of unified behaviors, in order to explore interpersonal relations and social interaction of people in crowd scenes. authors in [37] investigated a confined set of socio-cognitive crowd behaviors, discovering the interrelated connection between the movements of individuals to analyze different crowd behaviors. this was a layered approach segmenting visual analysis and semantic crowd behaviors. table i. methods, feature models and datasets used ref. publication date features/model dataset [9] 2017 statistical ucd [11] 2018 nested motion pets2009umn [12] 2019 spatio-temporal collected data [13] 2019 intra-frame classification www crowd [19] 2019 social model cuhk crowd [20] 2019 depth information ucf [23] 2019 texture features pnnl parking [24] 2019 spatio-temporal ucf crowd [26] 2016 simulation features mall dataset [27] 2019 entropy features crowd dataset [29] 2019 probabilistic model umn crowd [6] 2010 dynamic texture ucsd [33] 2020 aggregation of ensembles collected data [35] 2019 histogram features ucsd, pets [7] 2018 visual features www crowd [8] 2019 optical flow features cuhk crowd [38] 2016 holistic features pnnl parking [39] 2011 low-level features collected data [40] 2011 adaptive features umn [4] 2019 spatio-temporal cuhk crowd a method based on artificial bacteria colony was investigated in [7], where the optical flow of frames was exploited to get the foreground segments with entity motions as layers. surveillance problems using image processing and machine learning techniques were studied in [8], exploring algorithms of identifying abnormal crowd behaviors, proposing a unified method for anomaly detection, considering both crowd motion and texture-based analysis. a deep learning method was proposed in [41], calculating crowd density from individual images representing different crowd densities, exploiting both deep and shallow fully convolutional networks to estimate the density map of a crowd image. this method is good in encoding both high level semantic information and low level features. authors in [42] analyzed stationary crowd by computing the duration of a static foreground pixel. for this purpose, they used dynamic constraints, spatial and temporal features, and mixed partials. authors in [38] used holistic features for crowd anomaly detection, fusing together different features including crowd collectiveness, conflict, density and mean motion speed. authors in [43] mapped a given crowd scene to its density, avoiding people occlusion in dense crowd, foreground and background similarities, and huge changes in camera viewpoints. in [44] a combined framework was engineering, technology & applied science research vol. 10, no. 2, 2020, 5412-5418 5414 www.etasr.com ullah & altamimi: panic detection in crowded scenes presented to deal with the different elements of a crowd scene, including people counting, abnormal behavior detection, and different crowd density. a contextual pyramid technique was presented in [45] to produce a robust map of crowd density and people count, by using both global and local contextual features. recently, some advanced deep learning methods [46, 47] were presented, which could improve the performance of crowd analysis techniques. the modeling of complex crowd scenes using deep elman neural network architecture in [46], could extract in a better way the complex structure of a crowd, and emulate perfectly such dynamic systems. iii. proposed method panic detection and non-pedestrian entity localization is a challenging task due to its associated complexities. for this purpose, discriminative features are explored [1]. there is a lack in researches that efficiently assess the underlying structure of crowd scenes, investigating the most discriminant pattern representation of abnormal situations. this study’s purpose is to exploit the connection between the motion feature extraction and their discriminability, proposing an integrated model characterized by the discriminative power of combining different features. this framework renders a deep insight into the optimal feature extraction for anomaly detection. this study avoids the modeling of traditional features that use single-type representation and features unable to encode the motion and crowd structure information. moreover, this study is exploiting local neighborhood features. a refined feature [2] combines more information of the intrinsic structure and is effective for crowd scene analysis. the method’s flow diagram is shown in figure 1. fig. 1. proposed method's flow diagram the effectiveness of the selected features is not limited to abnormal situation detection, they could also be widely used in many other applications in the field of computer vision and machine learning. the proposed method computes repetitions of different orientations in localized areas of a crowd video. this framework gets some inspiration from edge orientation histograms [48], scale-invariant feature transform descriptors [49], and shape contexts. a significant difference lies in the unification of completely different features, as the model is formulated on a dense grid of all pixels in each frame. the intuition behind the feature unification was that localized crowd pattern appearance and layout within a video frame could be formulated by the distribution of intensity and orientation information. previous studies [50-52] extracted different types of orientation features. however, this study investigated the important discriminability of feature unification for generalized purposes, exploring a model to characterize the discriminative power of various types of orientations, so that more discriminative features can be fused together. the proposed method is effective and compact for abnormal situation detection. hence, it demonstrates complex and unique motion patterns, and it could be considered as a mid-level hierarchy to integrate the space between low and high-level information in order to capture complex crowd events. features represent motion information in the neighborhood of the region under observation. the most significant ability of this method is the unification of features in the local neighborhood. crowd scene layout (i.e. appearance structure of the scene) captures reliable information in a reasonable neighborhood, discovering important hints to recognize various events of interest in crowds. the conventional techniques extract gradient locations and orientation information for feature modeling. the proposed method differs from these as it considers the difference between each pixel and the center one, within local windows of its eight neighbors to produce different orientation features, whereas conventional techniques are confined to only horizontal and vertical. therefore this kind of conventional modeling cannot be effectively applied without any distinction in the significance and the influence of different orientations. the proposed refined features improve the local scene description ability, enhancing the intrinsic structure of the crowd scenes. in this method, each frame is extracted from the crowd video. it is worth noticing that each class label for each event in the scene is considered. abnormal situations in each crowd video consist of multiple abnormal events. inspired by [1], the abnormal situation is extracted through the discriminant binary pattern (dbp). dbp can model the scene changes and implicitly formulate the multiple dominant features, as: 𝜁 = exp −𝜋 + cos 2𝜋𝜇(𝑥𝑐𝑜𝑠𝜃 + 𝑦𝑠𝑖𝑛𝜃) (1) where 𝜁 represents the function to extract direction information. the potential feature will maximize this response, and it can be considered as the prominent direction feature of the abnormal situation. in (1), 𝜖 and 𝜌 represent the standard deviations of the data surrounding the position x and y. the convolution between 𝜁and a video frame i is represented by: 𝜉 (𝑥, 𝑦) = 𝜁 ∗ 255 − 𝐼(𝑥, 𝑦) (2) where * represents the convolution operation, and functions 𝜁 and 𝜉 obtain convolved results for each pixel of the video frame. in order to identify individual pixels related to abnormal situations in the crowded scene, the following modeling is performed: 𝜃 𝐼(𝑥, 𝑦) = 𝑎𝑟𝑔𝑚𝑎𝑥𝜉 (𝑥, 𝑦) (3) where 𝜃 represents the orientation of the pixel under observation. equation (3) characterizes the connection between the direction feature extraction and the discriminability of the abnormal situation. to enhance the method’s encoding ability, it is consolidated as [2]: engineering, technology & applied science research vol. 10, no. 2, 2020, 5412-5418 5415 www.etasr.com ullah & altamimi: panic detection in crowded scenes 𝛽 = {𝛼 − 𝛼 , 𝛼 − 𝛼 , 𝛼 − 𝛼 , 𝛼 − 𝛼 , . . , 𝛼 − 𝛼 } = {𝛾 , 𝛾 , 𝛾 , 𝛾 , 𝛾 , 𝛾 , 𝛾 , 𝛾 } (4) where 𝛼 represents the central pixel and 𝛼 , 𝛼 , 𝛼 , 𝛼 , . . , 𝛼 represent the neighboring pixels. the intensities of non-unit neighboring pixels are obtained by arithmetic operations, using their adjacent pixel values. next, the intensity difference between each neighboring pixel and the central pixel is computed. differences are concatenated to a difference vector that represents the scene. in fact, for each frame, this information is extracted densely for all 9×9 neighborhoods. features in (3) and (4) are combined into a unified framework as shown in: λ = ∑ ∑ (exp − 𝜃 − 𝛽 ) (5) this equation considers the entire features of the scene and gathers the statistics of local regions to embed more local information and strengthen the robustness of representing complicated crowd motion patterns for abnormal situation detection. the classification of a crowded scene into normal and abnormal situations, involves exploiting a multi-class support vector machine [3]. two benchmark datasets were used and the training parts of these datasets consist of panic situation and non-pedestrian entity detection. therefore, a function that shows at most ε deviation from the actually chosen labels for the training data of both datasets is required. this function was intended to be very flat according to the training data of both datasets. in order to elaborate the theoretical background, errors are not considered as long as they are less than ε. the importance of this theory arises from the fact that it is desired to ensure that error lies in some acceptable margin during the classification process of different abnormal events. to start the classification procedure according to the multi-class support vector machine, a linear function is considered as: 𝑓(𝑥) =< 𝑤, 𝑥 > +𝑏 𝑤𝑖𝑡ℎ 𝑤𝜖 𝜒, 𝑏 𝜖 ℝ (6) where <. , . > represents the dot product. smoothness in this equation is related to the convergence of the smaller w, and this is only possible by minimizing its norm. this process belongs to convex optimization formulation according to: minimize ‖ω‖ subject to y −< w, x > −b ≤ ϵ < w, x > +b − y ≤ ϵ (7) according to (7), convex optimization is possible if enough training data are available. for this reason, two benchmark datasets were used to train the multi class support vector machine, taking full advantage of the convex optimization process. standalone features without integration are not very effective, since the physical structure of crowd scene changes over a temporal window. in addition, single type of features is very sensitive to background and illumination changes, scale variations, and crowd flow direction. to handle these problems, the integration of different robust and reliable features should be explored. for instance, entities in the crowd scattered in the scene with a still background, consist a very challenging environment in terms of modeling different events. therefore, a method based on single type of features suffers if the uncertainty in crowd flow increases over a large scale, such as a uniform crowd flow versus a random one. the outcome of the traditional and single type of features would be unreliable in such situations. moreover, if the flow of the crowd is in one direction and it changes randomly due to the occurrence of either panic situation or a non-pedestrian entity, the same features would behave differently. therefore a unified model for different features is needed, modeling the random flow of crowd and being robust to different variations. the proposed method can effectively cope with these issues. iv. results the detailed experimental analysis procedure utilized the widely used benchmark datasets ucsd [53] and umn [54]. these datasets are properly annotated benchmarks for the analysis of abnormal detection and localization in crowded scenes. ucsd consists of anomalous entities represented by non-pedestrian entities in scenes. the videos of this dataset were captured with a cctv camera fixed at an elevation, at a resolution of 238×158 at 10fps, overlooking people in pedestrian pathways. non-person objects in pathways and anomalous pedestrian motion patterns are treated as abnormal situations. in this dataset, the abnormal entities are bikers, skaters, small carts, and people walking across a pathway or in the park. the video clips in the dataset are divided into 2 subsets: ped1 and ped2, and each one is associated with a different crowd scene. videos recorded from each scene were categorized into different clips, each of them consisting of about 200 frames. ped1 consists of 34 training and 36 testing videos. ped2 consists of 16 training and 14 testing videos. in each video, the ground truth annotation includes a binary flag per frame, showing whether an anomalous entity is present. moreover, there is a subset consisting of 10 videos with manually produced pixel-level binary masks, which recognize the parts or sub-parts consisting of abnormal events with clear boundaries. this was generated for performance analysis, with respect to the ability of anomaly localization and segmentation. sample images from the ucsd dataset are depicted in figure 2. in the top row, non-pedestrian entities are shown, which are not allowed in these pedestrian pathways. fig. 2. pedestrians walking with other entities present. images from ucsd © svcl qualitative and quantitative experimental analyses were performed. the qualitative results are shown in figure 3, where engineering, technology & applied science research vol. 10, no. 2, 2020, 5412-5418 5416 www.etasr.com ullah & altamimi: panic detection in crowded scenes the top row shows sample frames taken from four video sequences. the bottom row shows the anomalous entities annotated and highlighted in light blue. the bicycle riders in the bottom row are detected as anomalous entities, since they are not allowed to use the pedestrian pathways. similarly, a vehicle is detected in the bottom left frame. fig. 3. the top row shows sample frames taken from four video sequences. the bottom row shows anomalous entities annotated and highlighted in different colors. images from ucsd © svcl for the quantitative analysis, table ii presents the area as a roc curve (auc) of the tested methods, in which a larger auc score shows improved classification results. as it can be noted, the proposed method outputs competitive results against the five reference methods. table ii. ucsd: auc performance comparison method sttm [4] acbm [5] mdt [6] dma [7] ofta [8] proposed auc 0.77 0.74 0.77 0.73 0.69 0.81 moreover, experimental analysis in the form of equal error rate (eer) was performed. figure 4 shows the results in graphs for the five references and the proposed method. blue and red graphs represent the results for ped1 and ped2 subsets respectively. we can see that the proposed method has smaller eer errors compared to the five reference methods. fig. 4. ucsd dataset: frame level equal error rate comparison the umn dataset presents both normal and abnormal crowd video sequences. this dataset comprises of three indoor and outdoor scenes, showing 11 different scenarios of panic events. the dataset consists of 7739 frames in total, with resolution of 320x240 pixels. each video starts with normal human behaviors, such as walking or standing. figure 5 depicts sample images from the umn dataset. fig. 5. people walking and standing. images from [54], © university of minnesota qualitative results for the umn dataset are depicted in figure 6, where the top row shows sample frames taken from four video sequences. the bottom row shows anomalous entities annotated and highlighted in light blue. panic is detected and highlighted when pedestrians start running in different directions. table iii shows the area under a roc curve (auc) of the five references and the proposed method. again, the proposed method has larger auc score than the referenced methods. fig. 6. umn dataset: normal frames and panic detection on them. images from [54], © university of minnesota table iii. umn: auc performance comparison method sttm acbm mdt dma ofta proposed auc 0.91 0.75 0.84 0.87 0.79 0.93 experimental analysis in the form of eer was performed, considering the umn dataset. figure 7 shows the results provided for the five references and the proposed method. blue engineering, technology & applied science research vol. 10, no. 2, 2020, 5412-5418 5417 www.etasr.com ullah & altamimi: panic detection in crowded scenes and red graphs represent the results for the first two and the following two video sequences of the umn respectively. as can be noted, the proposed method has smaller eer errors compared to the five reference methods. fig. 7. umn dataset: frame level equal error rate comparison v. conclusion many diverse approaches have been proposed to solve the problem of panic detection and anomaly identification. however, most of them are designed to work on specific scenes, where different representations of motion and appearance are analyzed with different models. in this study, the properties of abnormal situations were considered specifically as anomalies in terms of panic, and more general, as anomalies in terms of non-pedestrian entities. abnormal entities are rare things with unexpected appearance or motion patterns. for anomalous situation detection including panic and non-pedestrian entities, a novel technique was proposed, where dense motion trajectories were computed from the crowd input videos. considering the computed trajectories, a set of robust features was designed considering hog, hof, and mbh. motion atoms were explored for compact encoding of motion patterns in crowded scenes, representing distinguished motion patterns of crowds. in fact, motion atoms are mid-level characteristics to fuse the distance between low and high-level features for capturing anomalous situations. since an anomalous situation is described from the view of a feature set, the proposed method can be utilized in different surveillance scenes. moreover, hybrid features and motion atoms do not limit the type of features or the type of scenes, which helps in extending the proposed technique to broader research fields. the experimental results demonstrated that the proposed approach is effective for real crowd videos containing various types of normal and abnormal activities, in terms 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lima, p. t. saito, f. m. lopes, p. h. bugatti, “classification of texture based on bag-of-visual-words through complex networks”, expert systems with applications, vol. 133, pp. 215-224, 2019 [53] statistical visual computing lab–uc san diego, “ucsd anomaly detection dataset”, available at: http://www.svcl.ucsd.edu/projects/ anomaly/dataset.htm [54] university of minnesota, “monitoring human activity”, available at: http://mha.cs.umn.edu/ microsoft word 02-3317_setasr_v10_n2_pp5352-5360 engineering, technology & applied science research vol. 10, no. 2, 2020, 5352-5360 5352 www.etasr.com el ame et al.: openings effect on the performance of reinforced concrete beams loaded in bending … openings effect on the performance of reinforced concrete beams loaded in bending and shear fouad el ame civil engineering department pan african university institute for basic sciences technology and innovation, nairobi, kenya elame50@gmail.com john n. mwero department of civil and construction engineering university of nairobi nairobi, kenya mwero@uonbi.ac.ke charles k. kabubo department of civil and construction engineering jomo kenyatta university of agriculture and technology, nairobi, kenya kabcha2001@gmail.com abstract—transverse openings are often provided to reinforced concrete beams to accommodate utility ducts and pipes. this technique is usually adopted to avoid the creation of dead space in structures caused by extended dropped ceilings and leads to significant cost saving. on the other hand, the provision of openings through a beam creates a reduction in its strength and affects serviceability. in this study, ten reinforced concrete beams were cast using c30 concrete. material characterization and engineering properties tests were carried out to ensure compliance with the requirements provided by the codes of practice. the effect of vertical positioning and size of openings was investigated through subjecting the beams to a four-point bending test after 28 days of curing. maximum load capacity, first cracking load, and deflections at mid-span were recorded and crack pattern and failure mode were evaluated. test data showed that openings of depth greater than 0.4d significantly affect the beams’ strength and lead to earlier cracking, while the failure mode remains essentially the same, a diagonal tension crack through the opening except for opening of 0.5d size where the failure occurred by a sudden formation of two independent shear cracks above and below the opening. when holes were located above the centroid of the section, the beams exhibited a lesser deflection characterized by the absence of plastic deformation. furthermore, a significant reduction in strength was recorded compared to cases where the positioning of openings was in tension chords. this was validated using equations from the aci code of reinforced concrete design. keywords-circular openings; rc beams; opening size; vertical location; four-point bending test; strength; serviceability i. introduction in practice, the accommodation of services like telephony, water supply, air conditioning, electricity, and sewage requires the provision of a network of ducts and pipes. most frequently, pipes and tubes are positioned underneath the soffit. the aesthetic implications involve using a suspended ceiling for covering, which creates extra dead spaces in each floor [1]. the provision of openings in beams is a practical solution to avoid extended dropped ceilings, which leads to an economical design and significant cost savings, especially in multistory buildings. the presence of openings produces changes in the behavior of the beams. openings might be of circular, rectangular, or undefined shape, while in most cases they are placed near the supports where shear stresses are high. research on perforated beams has started early in the 1960s while trying to comprehend the theory of beams with openings considering various involved parameters. an opening of a circular shape is large when its diameter is greater than 40% of the beam’s effective depth (d), while the square opening is considered large if the height exceeds 0.25d [2, 3]. authors in [4] tested 27 reinforced concrete beams with openings of different shape, size, and horizontal location and reported that placing holes in flexure zone has lesser impact on the beam performance compared to when the holes are placed in the shear zone. additionally, circular openings caused the least reduction in ultimate load compared to the other shapes. the regions around the opening experience stress concentration at the corners and possibly transverse cracks. moreover, the stiffness of the beam can be reduced, which leads to an excessive deflection against the service load and also affects the internal moment and forces distribution throughout the beam [5-7]. according to authors in [3], openings in beams are a source of potential weakness. failure traverses the openings except the case in which the opening is too close to the support. authors in [8], after an experimental program on perforated beams, reported that the openings make the beams fail prematurely by an unexpected propagation of an inclined crack in compression chord. many experimental and analytical studies have been carried out on the effect of openings on beams considering various variables. this research focuses on varying the vertical position of the openings in order to understand the influence of the reduction in the concrete area at compressive and tension chords. the opening size is also a researched parameter. ii. materials and methods a. material characterization 1) fine aggregates river sand was obtained locally from nairobi, kenya. in this study, gravel was checked for conforming the requirements of british standard [9], carried out tests were: sieve analysis, specific gravity, water absorption, moisture content, bulk density, and voids content. the test results are presented in table i and figure 1. corresponding author: fouad el ame engineering, technology & applied science research vol. 10, no. 2, 2020, 5352-5360 5353 www.etasr.com el ame et al.: openings effect on the performance of reinforced concrete beams loaded in bending … table i. characterization of fine aggregates test test method result specific gravity bs812: part 2 2.41 water absorption bs812: part 2 2.951% moisture content bs812: part 109 0.13% bulk density bs en 1097-3 1680.1kg/m 3 voids calculation bs en 1097-3 35.72% fig. 1. fine aggregates particle size distribution 2) coarse aggregates the gravel was obtained locally from nairobi, kenya and was checked for conforming the requirements of [9]. tests carried out were: sieve analysis, specific gravity, water absorption, moisture content, bulk density, and voids content. the test findings are shown in table ii and figure 2. table ii. characterization of coarse aggregates test test method result specific gravity bs812: part 2 2.86 water absorption bs812: part 2 3.88% moisture content bs812: part 109 0.14% bulk density bs en 1097-3 1508.5kg/m 3 voids calculation bs en 1097-3 42.2% fig. 2. coarse aggregates particle size distribution particle size distribution, specific gravity on a saturated and surface dried basis, bulk density, and void content for both aggregates fall within the recommended intervals. therefore the aggregates are suitable for use in construction, hence, in this study. 3) cement the used cement is portland cement 42.5, which is highly recommended for structural carrying elements according to bs en 197-1:2000 [10]. 4) steel high tensile steel bars conforming to astm-15-65 [11] were adopted for this project. longitudinal reinforcement was of type t12 with a measured yield stress of 538mpa. stirrups were type t6 with average yield stress equal to 405mpa. b. mix proportion and engineering properties the mix design used in the current study was prepared as described in [12] for a target strength of 30mpa. slump test was carried out as shown in [13] to check the workability in the mix. mean compressive strength for 7, 14, and 28 days test was conducted on cubes as described in [11] to observe the strength development while tensile strength was also measured. modulus of elasticity was determined based on the uniaxial stress-strain curve obtained from a standard test cylinder. table iii. engineering properties property result slump 72mm compressive strength at 28 day 30.25mpa tensile strength at 28 day 2.8mpa modulus of elasticity 25,125mpa c. specimen the specimen design was done as demanded in [14]. loading assumptions were taken in order to make the case study near to the reality. the simply supported beam had 2m span, 150mm width, and 200mm depth. concrete strength was 30mpa. the main bars were t12, while the shear reinforcements used were t6 with a strength of 538n/mm² and 405n/mm² respectively (figure 3). fig. 3. beam details d. test procedure this research considered two variables: the size and the vertical position of the openings. the three proposed locations engineering, technology & applied science research vol. 10, no. 2, 2020, 5352-5360 5354 www.etasr.com el ame et al.: openings effect on the performance of reinforced concrete beams loaded in bending … were 0.5, 0.55, and 0.6 times the effective depth of the beam while the horizontal location was kept constant at 300mm from the supports. the choice of these vertical locations is supported by the question on how the reduction in concrete area within the different chords of the section will affect the serviceability and strength in beams. the proposed opening diameters were 0.3, 0.4, and 0.5 times the effective depth d. test samples were allocated with codes for simplification. vertical locations 0.5d, 0.55d, and 0.6d are respectively denoted as v1, v2, and v3. while openings size was coded using the equivalent diameter in mm. 50, 65, 80 are respectively indicating 0.3d, 0.4d, and 0.5d. beams are divided into three sets according to the vertical location. the control beam is represented as cb. table iv. beams' codes set code control beam cb 1st set pbv1-50 pbv1-65 pbv1-80 2nd set pbv2-50 pbv2-65 pbv2-80 3rd set pbv3-50 pbv3-65 pbv3-80 all the samples were subjected to a four-point bending test. each beam was loaded by two symmetrical concentrated loads applied approximately at the span’s thirds. this type of test is adopted in order to have a beam type ii behavior, which ensures that the span to depth ratio (s/d) is controlled to fall between 2 and 5, making the beam exposed to flexure and shear at the same time [15]. a hydraulic jack of 400kn capacity was used to apply the load at the beam tip. a load cell of 200kn capacity was used to measure the applied load accurately. the gradually increasing load was applied until the failure of the beam. a linear variable differential transducer (lvdt) was used to measure the deformation at the beam midspan. a photo of the monotonic loading test set-up is shown in figure 4. fig. 4. test configuration iii. results and discussion crack pattern and failure mode were observed, and deflections at mid-span were recorded at each increment of loading until failure. the impact of openings on the static behavior of the beams considering the variables of focus was evaluated. the outputs of the tests were compared to those of the control specimen a. ultimate load figure 5 shows a comparison of the ultimate load the control beam could withstand with the maximum load capacity of each group of tested specimen. the control beam, which has no perforations, has utterly failed when the applied load reached 65kn. (a) (b) (c) fig. 5. ultimate and first cracking soad: (a) set 1, (b) set 2, (c) set 3 the first set of beams with openings sized 0.3d (figure 5(a)) exhibited changes in terms of the ultimate load capacity in function of the position of openings. when transverse holes were inserted above the centroid, the beam failed at 58kn, with a 10.77% reduction in strength relative to the reference beam. specimens pbv2-50 and pbv3-50 exhibited higher loadcarrying capacities since the recorded load at collapse was 61kn and 64kn respectively. the reduction in strength was small compared to specimen pbv1-50 (6.15% and 1.54% respectively. the provision of openings in the upper fibers of the beam (pbv1-50) decreases the contribution of concrete to the overall strength at the opening section. the holes reduce the engineering, technology & applied science research vol. 10, no. 2, 2020, 5352-5360 5355 www.etasr.com el ame et al.: openings effect on the performance of reinforced concrete beams loaded in bending … area necessary for the development of a full compressive stress block which made the opening periphery subjected to a strain concentration. consequently, the collapse occurred at a smaller load compared to the solid beam. in contrast, concrete is not expected to resist tensile stresses, and the existence of an opening in the bottom chords (pbv3-50) did not highly affect the load-carrying mechanism because concrete would have cracked anyway in flexure. figure 5(b) and table v show that the ultimate load capacity of pbv1-65 and pbv2-65 significantly decreased to 55kn and 60kn, which were respectively 15.38% and 7.69% less than the control’s (65kn). similarly to pbv1-50, this is caused by the reduction in the area of the compressive stress block caused by the openings. on the other hand, when the openings were located below the mid-depth, pbv3-65 performed a better response with a strength diminution of 3.08%. from figure 5(c) and table v, it can be observed that the increase in the size of the openings to 0.5d leads to a significant decrease in collapse load by at least 12.31%, as was the case for pbv3-80 while samples pbv1-80 and pbv2-80 recorded a maximum load capacity equivalent to 53kn and 52kn, which is 18.46% and 20% less than the solid beam respectively. in proportion to the depth of the opening, the contribution of concrete to shear resistance is assumed to decrease at the opening region, in addition to the disturbance created in developing the usual bending stress flow resulting in a high reduction in the load-carrying mechanism. it is concluded that the presence of openings with a diameter less than or equivalent to 40% of the effective depth of the beam does not result in high reduction in the ultimate load capacity, except in cases where the openings are located above the centroid of the section. on the other hand, openings with a diameter greater than 0.4d lead to a reduction of at least 12.31% in the collapse load. besides, it is noted that when the openings are located below the centroid, the reduction in strength is not as remarkable as if they are located adjacent to the compression chord. b. first cracking load the presence of cracks in a reinforced concrete member usually indicates damage. in reinforced concrete beams, the concrete starts cracking when the tensile stress reaches or exceeds its tensile strength. authors in [16] distinguishe between active and passive cracks. a crack is said to be active when its width evolves according to the stresses. then it affects the mechanical properties and the transfer mechanism of the forces within the member. a crack is said to be passive when its width no longer varies appreciably even when it is subjected to various stresses, although this type of cracks usually decreases the deformability of the beams. in this study it was ensured that the concrete tensile properties were kept uniform to all samples, as well as the amount and pattern of reinforcements. therefore, changes in the cracking behavior were originated from the presence of transverse openings and their positions. the first cracking load of each of the tested specimens can be seen in figure 5. the control beam experienced the first cracks at a load of 53kn, which is when the beam reached 81.54% of its ultimate load capacity. the cracks were narrow of a flexural nature at the soffit of the beam. additionally, it was observed that the width of the corresponding cracks did not change as the load increased. in the first group of perforated beams with 0.3d openings, the cracking behavior remained mostly the same compared to control, as the first cracks propagated in the flexure zone at 48kn, 49kn, and 50kn, for pbv1-50, pbv2-50, and pbv3-50 respectively which keeps the first cracking in the range of 7881% of the ultimate load. figure 6 shows that varying the vertical location induced slight changes. it was noticed that these cracks had an active character as their width kept evolving relatively to loading as well as their propagation which extended to the compressed fibers. this gives an indicator that openings introduced a change in the transfer of the internal forces. figure 5(b) indicates the cracking load for beams with openings of 0.4d. the load at the first crack for pbv1-65 did not differ noticeably from that of control, while a change was recorded for pbv2-65 and pbv3-65 (77-73% of the ultimate load). figure 6 illustrates that as the openings move toward the tensile chord, the concrete subjected to tension undergoes cracking at an earlier stage. similarly to the first set, cracks were narrow and vertical located at the soffit of the beam. it can be concluded that having drilled openings in the tension chord decreases the resistance of the beam to tensile stresses although the split-tensile strength of concrete is the same for the three samples. when the diameter of the openings reached 0.5d, the first cracks appeared at an earlier loading range, specifically at 77.36%, 76.92%, and 73.68% of the ultimate load for pbv1-80, pbv2-80, and pbv3-80 respectively. the cracks were also of a flexural nature at midspan. the width and length of these cracks kept developing until failure, which decreased the deformability of the beam and led to failure at a smaller collapse-load compared to the control beam. fig. 6. ultimate load to cracking load ratio generally, the propagation of the first crack was found to be affected by the presence of the openings and their vertical position. the conclusions based on the results are: • the presence of openings at the bottom chords weakens the resistance of concrete to tensile stresses and leads to an earlier cracking. this would disrupt the distribution of engineering, technology & applied science research vol. 10, no. 2, 2020, 5352-5360 5356 www.etasr.com el ame et al.: openings effect on the performance of reinforced concrete beams loaded in bending … stresses within the concrete and the stress transfer mechanism from concrete to reinforcements. • for the same vertical location, circular openings with a diameter equivalent or greater than 0.4d, lead to an earlier cracking to at least 77% of the ultimate load. • neither the size nor the position of the openings affects the nature of the first crack. it remains a narrow flexural crack at the soffit of the beam. c. load vs deflection deflection in beams is simply defined as the displacement from its initial position in the direction of the applied load. it is a function of the applied load, the length of span, the flexural rigidity, and the flexural ductility. a high load is necessary to cause a certain deflection at the elastic range to a beam with high flexural rigidity. a beam is said to be ductile when it can perform a large plastic deformation prior to failure or fracture. from the structural safety point of view a good ductility would provide the beam with a much better chance of survival when it is overloaded or subjected to accidental impact. in current codes of practice and in this study, the flexural ductility was controlled by designing the beam as under-reinforced. in this section, the result data of load-deflection curves are discussed from the rigidity and ductility points of view. table v indicates the maximum deformation observed on the beams, and figure 7 compares the load-deflection response of the control beam with other three groups of beams. table v. ultimate load and maximum deflection sample ultimate load (kn) difference percentage (%) deflection at mid-span (mm) cb 65 37.00 pbv1-50 58 10.77 27.00 pbv2-50 61 6.15 28.00 pbv3-50 64 1.54 30.00 pbv1-65 55 15.38 20.00 pbv2-65 60 7.69 22.00 pbv3-65 63 3.08 26.00 pbv1-80 53 18.46 15.00 pbv2-80 52 20.00 16.00 pbv3-80 57 12.31 17.00 the cb exhibited a good load-deflection behavior, as its response is composed of the three essential stages before the collapse: elastic, elastoplastic, and plastic stage. when the load increased, the deflection started to increase elastically until the first crack at 52kn, which was followed with a series of flexural cracks, the response shifted to plastic deformation before the complete failure at 65kn. the recorded maximum deflection of the cb was 37mm which can be classified as a ductile failure because the beam deformed plastically. the load-deflection curves for set 1 beams are presented in figure 7(a). the perforated beams with a diameter equivalent to 0.3d performed a behavior identical to that of the control. the beams had an ability to deform plastically before the collapse, although there was a slight reduction in terms of maximum deflection. thus, it can be concluded that openings of 0.3d size influence neither the rigidity nor the ductility of the beams. figure 7(b) illustrates that specimen pbv3-65 kept a response similar to cb, despite that the maximum deflection decreased to 26mm. in contrast, as the openings move above the mid-depth it was observed that the failure became more brittle as the deformation in the plastic range was small. moreover, the deflection diminished to 20mm and 22mm for pbv1-65 and pbv2-65 respectively. (a) (b) (c) fig. 7. load vs. deflection: (a) set 1, (b) set 2, (c) set 3 engineering, technology & applied science research vol. 10, no. 2, 2020, 5352-5360 5357 www.etasr.com el ame et al.: openings effect on the performance of reinforced concrete beams loaded in bending … from figure 7(b), it can be seen that the elastic response of specimen pbv3-50 was not influenced by the presence of the openings, only that the plastic deformation decreased recording a maximum deflection of 26mm. in contrast, pbv1-65 and pbv2-65 deflected more at the elastic range compared to the solid beam under a similar load, which indicates a reduction in the beams’ rigidity, hence their stiffness. moreover, the beams exhibited a brittle failure and a small deformation in the plastic range. the maximum deflections were 20mm and 22mm for pbv1-65 and pbv2-65 respectively. similarly, the three beams with openings diameter 0.5d had a similar behavior which is characterized by a greater elastic deflection and smaller plastic deformation. the maximum deflections at collapse load were 15mm, 16mm, and 17mm for pbv1-80, pbv2-80, and pbv3-80 respectively. the elastic behavior of the beams is governed by the following matrix: � � � ∗ � (1) where p refers to the applied load, u is the induced displacement, and k is the stiffness of the system. the stiffness is a function of rigidity in addition to the length of the member, and the rigidity is a function of material (e) and geometric properties (i). the provision of openings decreases the moment of inertia. hence, the beams became less stiff and had a larger elastic deflection. on the other hand, the absence/decrease in plastic deflection is related to the effect of openings on the stress-transfer mechanism between concrete and steel. to ensure that a certain level of ductility is achieved, the beams were designed as under-balanced so that steel could be fully stretched. with the openings located adjacent to the compressive chords, concrete in compression was subjected to higher stresses, which caused failure before steel in tension yields. d. crack pattern and failure mode figure 8 shows the crack profile of the beams at the collapse load. when the load was applied to the cb, the deformation began to develop slightly. after the concrete failed in tension, the beam started cracking at a load of 53kn. the first cracks were narrow and vertical at the mid-span. as the beam continued to deflect, flexural fissures kept propagating, until 59kn where a crack initiated diagonally from the tensile fibers and reached the compression chord which had caused a splitting in the concrete and consequently the beam collapsed. the mode of failure was a diagonal tension-type characterized by ductility and large deflection. the beams with diameter 0.3d openings had different modes of failure compared to control. pbv1-50 and pbv2-50 started to deflect and as the load increased, vertical cracks propagated in the lower end of the segment. the vertical cracks near the openings started to deviate and gather into a 45° wide diagonal crack which elongated to reach the compressed fibers causing failure. both samples were found to suffer from excessive cracks, and high damage in the concrete, which may be explained by the influence of the openings on the balance between the tensile and the compressive stress resultants due to the positioning of the openings close to the compression stress block. (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) fig. 8. crack pattern at failure: (a) cb, (b) pbv1-50, (c) pbv2-50, (d) pbv3-50, (e) pbv1-65, (f) pbv2-65, (g) pbv3-65, (h) pbv1-80, (i) pbv280, (j) pbv3-80 the response of over-reinforced concrete beams where the assumption that steel yields before concrete is not valid, hence concrete crushes before the steel reaches its yield point, is supported by the data discussed earlier in this paper. pbv3-50 had a more ductile behavior since its plastic deflection was larger than the deflection of the other two samples. as with the cb, the mode of failure is caused by a diagonal tension crack passing through the opening. pbv1-65 had a similar behavior to pbv1-50, except that the deflection was low. the failure mode was a typical diagonal tension failure. in contrast, pbv265 and pbv3-65 suffered cracking at an earlier stage. the cracks were limited in the soffit of the beams until two wide diagonal cracks suddenly appeared below and above the fracture openings. similarly, the provision of openings with a depth equivalent to 0.5d in the third set of samples divided the section into segments. hence, the collapse was caused by the formation of two independent diagonals below and above the openings. this phenomenon is distinguished for rc beams with large aperture and is denoted as a frame-type failure in reference to the independent behavior of the segments above engineering, technology & applied science research vol. 10, no. 2, 2020, 5352-5360 5358 www.etasr.com el ame et al.: openings effect on the performance of reinforced concrete beams loaded in bending … and below the holes which resembles a structural behavior of frames. the cracks that caused the collapse in this group gave no visual warning and were developed suddenly. hence, the failure was brittle with a small deflection. moreover, a high local deformation in the opening periphery was observed, caused by the stress concentration in that region. the applied factored moment mu at the center of the opening from the global action is resisted by the usual bending mechanism, that is by the couple formed by the compressive and tensile stress resultants nu in the members above and below the opening. the presence of the 0.4d and 0.5d openings created a disequilibrium between the two resultants which caused a rotational effect in the opening region. on the other hand, authors in [1] demonstrated that he applied shear vu is distributed between the two members in proportion to their cross-sectional areas. thus, they behave independently. based on the test data, it is evident that the presence of openings affects the crack pattern and the failure mechanism. the beams with opening diameter less than 0.4d exhibit a ductile behavior and undergo extensive damage in concrete. the failure is originated from a tension-diagonal crack that passes through the openings. on the other hand, beams with 0.4d or greater openings exhibit a brittle behavior. the collapse type is a frame-type failure due to the disequilibrium induced between the stress resultants. e. flexure and shear capacities as discussed above, it is clear that the introduction of openings does not alter the load carrying mechanism as long as the openings are located within the tension zone of the beam because concrete there would have cracked anyway at ultimate flexure. consequently, the strength of the beam is not affected. this has been confirmed by several researchers in the past such as the authors in [18]. in this section, the equations from [20] were used under the common theories of rc beams subjected to bending and shear. 1) flexural strength at collapse load, according to the usual flexural strength theory, the applied factored moment mu from the global action is resisted by the usual bending mechanism, that is, by the couple formed by the compressive and tensile stress resultants nu. the strain and stress distributions across a section at ultimate are shown in figure 9. fig. 9. conditions at ultimate test data showed that if the opening is placed in such a way that it cuts the material from the compression zone, it reduces the concrete area required for the development of the full compressive stress block at ultimate. as a result, nu decreases. let us consider specimens cb and the beams of set 3. at ultimate, (2) is used to get the compressive stress resultant: � � 0.85 �’� ba (2) � � 220.81kn the presence of openings in specimens pbv1-80, pbv280, and pbv3-80 reduces the compressive resultant as shown in figure 10. fig. 10. compressive resultant for cb and set 3 it can be observed that having an opening of 0.5d size decreased the compressive stress resultant by at least 16%. this reduction is higher when the perforation moves upward toward the compressive surface. the stress resultant nu through the opening section is therefore decreased which led the beams to fail at the same region. evidently, this explains why the beams of set 3 exhibited much smaller deflection, prior to reaching the full potential capacity. 2) shear strength having an opening in the segment leads to a reduction in its depth, affecting the shear resistance in that segment. in this section shear capacities for solid and perforated sections with different diameters are computed and compared. the aci code [20] design method for shear requires that: vn >vu where vn is the nominal shear strength given by combining two components vc and vs, and vu is the applied shear force. at the center of the opening vu=32.5kn. the simplified expression of vc is given by [20]: �� � 1 6 √�′��� the expression of vs is developed using a 45° truss model while assuming that shear reinforcements yield at the collapse. the general correlation for vs is given as the sum of vertical and diagonal stirrups vsv and vsd. in the current study diagonal stirrups are not involved therefore: �� � ��� !�"� # (4) a) the control beam from (3) the contribution of concrete to the shear strength engineering, technology & applied science research vol. 10, no. 2, 2020, 5352-5360 5359 www.etasr.com el ame et al.: openings effect on the performance of reinforced concrete beams loaded in bending … is vc=20.38kn, while (4) is used to get the shear strength attributed to shear reinforcements around the openings vs=13.01kn. the nominal shear strength that can be provided by a solid section is therefore 33.39kn. therefore the condition vn >vu is applied for specimen cb. b) pbv1-80 section through the opening in case of a perforated segment, the opening depth is deducted from the simplified expression of vc as follows: �� � 1 6 √� ′ ��$� % �&' (5) vc becomes 10.38kn, while vs remains the same with the solid section. the reduction in the contribution of concrete to the shear capacity is not affected by the vertical location. figure 11 shows the nominal shear capacity of the beams through the opening per size. it is observed that with the presence of openings the shear strength of the beam decreases by at least 18.7%. therefore, the direction of the principal tensile stress changes from horizontal to a direction inclined to the longitudinal axis of the beam through the perforation. since concrete is weak in tension, this diagonal tensile stress eventually leads to what is basically known as diagonal tension failure of a beam. adding too much shear reinforcement doesn’t seem adequate as failure may also occur by crushing of the concrete in a diagonal direction. fig. 11. the nominal shear capacity per opening size iv. conclusions the main findings of this study are: • the provision of openings in the bottom chords with a diameter less than 40% of the beam’s effective depth brings no significant changes in terms of ultimate load capacity or first crack instant. • circular openings with a diameter equal or greater than 40% reduce the beam’s strength and lead the beam to premature cracking. • when openings with a diameter not greater than 0.4d are introduced below the centroid, the beam retains both the elastic and the plastic deflections, allowing a certain degree of ductility. in contrast, openings with size more than 0.4d make the beam behavior limited at the elastic range with a smaller alarming deflection. • when the openings are located in compression fibers, the behavior of the beam becomes more brittle with less plastic deformation. besides, the concrete in the upper fibers undergoes extensive damage and the beam cracks more than usual. • when the depth of the openings is equal to or greater than 0.4d, the type of failure changes from a beam-type failure to a frame type that occurs suddenly without significant previous signs. (in case of openings of size 0.4d, this applies when the location of the openings is not above the centroid). • openings located above the mid-depth reduce the area necessary for the formation of the rectangular compressive stress block, which leads to a smaller flexural capacity. consequently, the beam will exhibit less curvature, hence less deflection. v. recommendations further research work can focus on: • investigating the effect of drilling openings in existing reinforced concrete beams. • strengthening the periphery of the openings using sisal mat polymer composite. • proposing an optimized reinforcement scheme to prevent diagonal tension failure and control the cracks. • for openings located in the compression chord, replacing pvc pipes which are typically used for inserting circular openings with steel tubes which may have reinforcing actions and more resistance to compressive stresses. acknowledgements the authors will like to thank the african union commission, under the flagship program of pan african university, institute for basic science, technology and innovation (pausti) and the africa-ai-japan project for funding this research. references [1] m. a. mansur, “design of reinforced concrete beams with web openings”, asia-pacific structural engineering and construction conference, kuala lumpur, malaysia, september 5-6, 2006 [2] s. amiri, r. masoudnia, “investigation of the oppening effects on the behavior of concrete beams without additional reinforcement in opening region using fem method”, australian journal of basic and applied sciences, vol. 5, no. 5, pp. 617–627, 2011 [3] m. a. mansur, “effect of openings on the behaviour and strength of r/c beams in shear”, cement and concrete composites, vol. 20, no. 6, pp. 477–486, 1998 [4] s. a. a. sheikh, “flexural behaviour of rc beams with opening”, concrete research letters, vol. 5, no. 2, pp. 812–824, 2014 [5] s. m. allam, “strengthening of rc beams with large openings in the shear zone”, alexandria engineering journal, vol. 44, no. 1, pp. 59–78, 2005 [6] s. amiri, r. masoudnia, a. a. pabarja, “the study of the effects of web openings on the concrete beams”, australian journal of basic and applied sciences, vol. 5, no. 7, pp. 547–556, 2011 engineering, technology & applied science research vol. 10, no. 2, 2020, 5352-5360 5360 www.etasr.com el ame et al.: openings effect on the performance of reinforced concrete beams loaded in bending … [7] j. v. amiri, m. h. alibygie, “effect of small circular opening on the shear and flextural behavior and ultimate strength of reinforced concrete beams using normal and high strength concrete”, 13th world conference on earthquake engineering, vancouver, canada, august 1-6, 2004 [8] w. b. siao, s. f. yap, “ultimate behavior of unstrengthen large openings made in existing concrete beams”, journal of the institution of engineers, vol. 30, no. 3, pp. 51–57, 1990 [9] british standards, bs 882 (1992): specification for aggregates from natural sources for concrete, british standards, 1992 [10] european standard, en 197-1 (2000): cement-part 1: composition, specifications and conformity criteria for common cements, european standard, 2000 [11] astm a1096/a1096m-15 (2015): standard test method for evaluating bond of individual steel wire, indented or plain, for concrete reinforcement, astm a1096/a1096m-15, 2015 [12] d. c. teychenne, r. e. franklin h. c. erntroy, design of normal concrete mixes, bre press, 1997 [13] k. hover, “testing hardened concrete”, publication #c930727, the aberdeen group, 1993 [14] r. s. narayanan, k. r. wilson, r. j. w. milne, manual for the design of reinforced concrete building structures to ec2, the institution of structural engineers, 2000 [15] g. n. j. kani, “the riddle of shear failure and its solution”, aci journal proceedings, vol. 61, no. 4, pp. 441-468, 1964 [16] association francaise de normalisation, structure-repair and strengthening of concrete engineering structures-treatment of cracks and protection of concrete-specifications for the technique and materials used, association francaise de normalisation, 2014 [17] r. c. murthy, g. s. palani, n. r. iyer, “residual strength evaluation of unstiffened and stiffened panels under fatigue loading”, structural durability & health monitoring, vol. 5, no. 3, pp. 201-226, 2009 [18] h. a. abdalla, a. m. torkey, h. a. haggag, a. f. a. amira, “design against cracking at openings in reinforced concrete beams strengthened with composite sheets”, composite structures, vol. 60, no. 2, pp. 197204, 2003 [19] t. ozbakkaloglu, m. saatcioglu, “rectangular stress block for highstrength concrete”, aci structural journal, vol. 101, no. 4, pp. 475-483, 2004 [20] american concrete institute, aci 318-95 (1995): building code requirements for structural concrete and commentary, american concrete institute, 1995 microsoft word 33-2948_s_etasr_v9_n4_pp4495-4499 engineering, technology & applied science research vol. 9, no. 4, 2019, 4495-4499 4495 www.etasr.com chigvinadze et al.: vibrating reed study of superconducting cuprates fabricated by superfast melt … vibrating reed study of superconducting cuprates fabricated by superfast melt quenching in a solar furnace j. chigvinadze department of condensed matter physics, andronikashvili institute of physics, ivane javakhishvili tbilisi state university,tbilisi, georgia chigvinadze@yahoo.com v. tavkhelidze department of condensed matter physics, andronikashvili institute of physics, ivane javakhishvili tbilisi state university,tbilisi, georgia tawge@yahoo.com g. i. mamniashvili department of condensed matter physics, andronikashvili institute of physics, ivane javakhishvili tbilisi state university,tbilisi, georgia mgrigor@rocketmail.com g. donadze department of condensed matter physics, andronikashvili institute of physics, ivane javakhishvili tbilisi state university,tbilisi, georgia donadze_g@yahoo.com j. v. acrivos department of chemistry, san jose state university, san jose, usa jacrivos@earthlink.net d. gulamova institute of materials science spa “physics-sun” of academy of science, tashkent, uzbekistan gulamova@uzsci.net abstract—in this study, the potential possibilities of the precision of the vibrating reed method for the evaluation of the тс of superconducting precursors in an htsc bi-pb-sr-cu-o system were investigated. a special technology for obtaining these samples by using solar energy for melting and following superfast melt quenching was applied to increase their internal inhomogeneity, allowing to receive high-quality textural ceramic samples of bi1,7pb0,3sr2can-1cunoy (n=2-30) showing critical temperatures of superconducting precursor transitions above bulk тс. to determine critical temperatures of superconducting precursors above bulk тс for the first time, the original vibrating reed method of studying these multiphase samples in an applied magnetic field was used. it was shown that this method has sensitivity to superconducting diamagnetism making possible to reveal new superconducting precursor phases above bulk tc. keywords-htsc; solar energy; superfast quenching; vibrating reed technique; ctitical temperature of superconducting transition; high-temperature superconducting phases; pinning i. introduction after the discovery of high-temperature superconductors (htsc) in 1986, great efforts were made to the further increase the critical temperature of superconducting transition тс with aim to reach room temperatures. such a discovery would cause the emergence of new htsc materials with тс higher than the ones of liquid nitrogen (~77k) and hydrogen (19к) (tc in ybacuo and mgb2, correspondingly) opening great possibilities for their applications in electronics and energetics. from this point of view, particular interest attracts the bi-pbsr-ca-cu-o system, because it is characterized by high тс=107к and the record high second critical magnetic field нс2 ~150t. our group has undertaken research on the possibility to increase the тс of this system [1-5]. in [1-3, 5] the melt technology for obtaining bi-pb-sr-cu-o htsc ceramics using solar energy for melting and subsequent superfast melt quenching for increasing of internal inhomogeneities was developed, allowing the receiving of homogeneous, highquality, textured ceramic samples with controllable microstructure and pinning centers. in [4], hot shock wave consolidation technology was used to produce bi-pb-sr-cacu-o compositions with increased internal inhomogeneity and for studying their superconducting precursor phases by torsional magnetometry method. this time, for increasing internal inhomogeneity we used solar melting and following superfast quenching technology. previous measurements of pinning and dissipation processes were carried out in the andronikashvili institute of physics using an original vibrating torsion mechanical magnetometry method to study the torsion oscillations of samples in an applied magnetic field realized using an automated multipurpose device [6] and standard methods of magnetic and electric parameter measurements. it was showed that samples obtained using the suggested solar technology were multiphase containing phases with higher critical temperatures тс reaching ~200к. but the concentration of new htsc phases appeared to be so small that for more precision assessments it was necessary to find alternative and more sensitive methods. one of such methods could be the vibration reed (vr) method for the first time developed in works of our group and then independently [7]. as the frequency and dissipation of vr could be measured with high precision, the vr method exceeds in sensitivity a conventional accorresponding author: g. i. mamniashvili engineering, technology & applied science research vol. 9, no. 4, 2019, 4495-4499 4496 www.etasr.com chigvinadze et al.: vibrating reed study of superconducting cuprates fabricated by superfast melt … susceptometer, and besides, it is contactless. using the vr method one could study the elastic coupling between the abrikosov vortex lattice and the crystal lattice even in micron sized grains inserted in the normal matrix. the field dependence measurements of vr resonance frequency and dissipation could be used for the precision investigation of the first critical magnetic field нс1 temperature dependence without the introduction of free parameters, along with the energy distribution character caused by the motion of the abrikosov vortex lattice. in [8], the example of successful application of the vr method for investigation of two-phase bi-ca-sr-cu-o superconducting ceramics and the precision assessment of their bulk critical temperatures тс were presented. the vr method was used for the first time to determine critical temperatures of superconducting precursors above bulk тс. so, the aim of the current work is to determine critical temperatures of superconducting precursors above bulk тс. we used for the first time the original vr method to study these multiphase samples in an applied magnetic field. it was shown that this method has sensitivity to superconducting diamagnetism sufficient to reveal new superconducting precursor phases above bulk tc. ii. results and discussion for the study of high-temperature superconductors, we used a setup consisting of a cryostat with a block-holder of the sample, placed in the gap of a permanent magnet, and an electronic part. the electronic part of the setup contains a mechanical spectrometer developed in the andronikashvili institute of physics operating at a frequency of ~1khz [9], and instruments for powering the permanent magnet and creating a weak (~0.5mt) alternating magnetic field on the sample. the high sensitivity of the equipment provides measurements of the natural frequency of the sample f with an accuracy of ~0.1%. figure 1 shows actual devices/set up view and measuring cell photos. figure 2 shows the principal electronic circuit of the installation. (a) (b) fig. 1. (a) actual devices/set up photo, (b) measuring cell. fig. 2. electronic block-diagram of the installation. the basis of the operation of a mechanical spectrometer is the electrostatic method of exciting bending oscillations of a sample having the shape of a rectangular plate. the electronic equipment of the spectrometer allows measurements in the mode of self-excitation of samples at their natural resonant frequency. the electrode, located in the immediate vicinity of the sample, makes up with the capacitance included in the oscillating circuit of the high-frequency generator, and serves simultaneously to excite and detect oscillations of the sample. measurements of the resonance frequency fr of the oscillation of the sample allow the determination of the elastic modulus e according to: 2r d e f k l ρ = (1) where d is the thickness of the sample, l is the length of the oscillating plate, e is the modulus of elasticity, ρ is the density of the sample, and k is a constant coefficient. figure 3 shows the block-holder of the superconducting sample. it is made of ultrapure copper and is placed in a low-temperature cryostat. fig. 3. block-holder block-holder provides oscillations of a superconducting sample in constant and alternating magnetic fields without affecting it by mechanical deformations. this is achieved by the fact that the metal substrate acts as a vibrator of a mechanical spectrometer, cut in the shape of e character, and engineering, technology & applied science research vol. 9, no. 4, 2019, 4495-4499 4497 www.etasr.com chigvinadze et al.: vibrating reed study of superconducting cuprates fabricated by superfast melt … the superconducting sample is glued to the tip of its middle reed. as a substrate, high-purity niobium is specially selected. in the temperature range from nitrogen to 200k, which is of interest to us, there are no anomalies of the elastic modulus and a very low level of oscillation energy dissipation (∼5×10 -4 ). figure 4 shows a cryostat placed in the gap of a permanent magnet and operating in the temperature range from 80k to 500k. in figure 4: 1) the block-holder with the sample is rigidly fixed on the console of ultrapure copper. 2) the tank into which liquid nitrogen is poured is integrated with the console. 3) a furnace is wound in the lower part of the console. these allow to measure both the temperature spectra and the field dependences of the elastic modulus in the temperature range of 80-500k. 4) the poles of the permanent magnet are located on both sides of the cryostat and can be moved so that the direction of the constant field h relative to the sample plane can be changed at any angle. fig. 4. cryostat to study the dynamics of the abrikosov vortex, a lattice in htsc is provided for the creation of a relatively weak exciting magnetic field, oscillating with a certain frequency. in order to create such a field, 5 especially wound helmholtz coils are placed inside the cryostat, covering the block-holder. the location of the coils in the immediate vicinity of the sample allows the creation of a sufficiently strong alternating field on it by using a standard low-frequency generator. the alternating field h created by the helmholtz coils can also be directed at different angles that were combined with application of solar energy and superfast quenching melt technology [1-5]. amorphous precursors and their use make possible the manufacturing of high-density low porous texturized ceramics with given dimensions of grains. starting mixtures of nominal composition were prepared from previously annealed bi2о3, pbo, srco3, caо, cuо high purity powders. the synthesis by solar melting and the following superfast quenching was realized using as a heating source the concentrated solar flux in a solar furnace. the phase composition of samples was determined by x-ray phase analysis. the form of superconducting samples used in the experiments was such that their size in the direction of the magnetic field was less than the depth of its penetration. in this case, the abrikosov magnetic vortices (av) penetrated the sample through in the direction of the magnetic field. the variation of the square of the resonant oscillation frequency (f 2 ) of the sample can be considered in the framework of the so-called magnetomechanical approach [7] according to which, when the superconductor is displaced relative to the external magnetic field h, acts as a restoring mechanical force on each “pinned” magnetic vortex. as a result, the oscillation frequency of the entire sample changes by ∆f(h), depending on the density of the fixed vortices, the moment of inertia of the superconductor and its volume. measuring the dependence of the elastic modulus of the substrate-sample system (in units of f 2 ) on the magnitude of the magnetic field gives information about the elastic interaction of the av with the crystal lattice. this is a convenient method for determining the magnitude of the vortex pinning force, especially by measuring the labusch parameter, which determines the slope of the pinning potential curve. in addition, the dependence f 2 (h) provides a simple and convenient method for determining the value of the lower critical magnetic field нс1. figure 5 shows the dependence of f 2 (h) of sample (2267), taken at t=88k, while its superconducting transition temperature is тс=97к. fig. 5. field dependence of the square of the natural frequency of the sample (2267) the anomaly f 2 (h) at 42mt shows the moment of the magnetic field vortex penetration into the sample, i.e. нс1. an increase in f 2 corresponds to an increase in the number of avs with an increase in h. by the slope of this curve, one can judge the pinning force in this particular sample. one could also study the phase transitions in the abrikosov vortex lattice. as an example, figure 6 shows the field dependences of a singlephase polycrystalline sample of erba2cu3o7-δ prepared according to standard technology. according to the temperature dependence of the electrical resistance ω (figure 6), the temperature and width of the superconducting transition were determined: тс=91.2k and ∆тс=0.8k respectively. the dependences of f 2 (h) were measured in the superconducting state of the sample at t=79k. two different dependencies were taken. in the first case, the sample oscillated only in an external constant magnetic field, (curve □). in the second case, along with the constant magnetic field, from the very beginning the engineering, technology & applied science research vol. 9, no. 4, 2019, 4495-4499 4498 www.etasr.com chigvinadze et al.: vibrating reed study of superconducting cuprates fabricated by superfast melt … sample was affected by a weak, h=0.5mt alternating magnetic field of low frequency (curve ■). on the first curve (□) of the dependence f 2 (h), at н=173mt, there is a feature characteristic of order-disorder phase transformations. this feature indicates that when h=173mt and higher, av exist in the sample in the form of ordered lattice. if during the taking of the field dependence a variable magnetic field h acts on the sample, then the feature on the f 2 (h) curve is not observed. this is due to the fact that the alternating magnetic field constantly shakes the vortices in the sample, preventing their ordering in the lattice. in this work, the temperature dependence of the square of the natural frequency f 2 (h) of an htsc sample oscillating in a magnetic field is used to obtain information about the phase composition of high-temperature superconducting precursors above тс. when a superconducting vr is subjected to applied fields and temperature variations, a step-like increase in the resonant frequency ∆f=f−fo compared to its normal state value fo is observed near or below the upper critical magnetic field нс2(t), when flux lines are rigidly pinned to vr. this is due to the diamagnetic surface currents flowing in the superconductor and producing diamagnetic restoring force proportional to the mxh torque. this feature when applied above tc completely removes normal-state contributions and thus allows tracing the diamagnetic signal above tc with great precision. prior to the measurements, the samples were cooled to a nitrogen temperature in an external magnetic field, after which the temperature dependences of f 2 were taken during a slow, ≈1k/min, heating. in order to separate the effects associated with the penetration of av into the superconducting sample from the effects of the niobium substrate proper, we measured the temperature dependence of f 2 of pure niobium. figure 7 shows the dependence of f 2 (t) of a niobium substrate without an htsc sample taken in an 300mt external magnetic field. fig. 6. field dependence of f 2 of oscillation of the sample erba2cu3o7-δ: □ – h = 0, ■ h = 0.5mt. t=79k it is seen that the f 2 (t) curve, in the temperature range from nitrogen to 170k, has a uniform slope and does not contain any features. figure 8 shows the dependence of f 2 (t) of sample (2267) taken in an external magnetic field of 300mt. the curve contains a single feature at t=97k. such features on the f 2 (t) dependence are typical for phase transition points, the 97k point is the sample transition temperature from normal to superconducting state. there are no other features on the curve, this means that the sample (2267) is monophase. another picture is observed on the f 2 (t) curve of the sample (2-2-1920), shown in figure 9. on dependencies taken at a magnetic field of 300mt during the heating process, 4 features were observed. this means that in the sample (2-2-19-20), along with the main superconducting phase and the transition temperature of 104k, there are inclusions of other superconducting phases with higher transition temperatures: 118, 127 and 151k. fig. 7. temperature dependence of f 2 of a niobium substrate in a magnetic field of 300mt. fig. 8. temperature dependence f 2 of oscillations of the monophase sample (2267) in a magnetic field of 300mt fig. 9. temperature dependence of f 2 of the multiphase sample (2-2-19-20) in a magnetic field of 300mt engineering, technology & applied science research vol. 9, no. 4, 2019, 4495-4499 4499 www.etasr.com chigvinadze et al.: vibrating reed study of superconducting cuprates fabricated by superfast melt … iii. conclusions we investigated the potential possibilities of the vibrating reed method for the evaluation of тс of superconducting precursors in an htsc bi-pb-sr-cu-o system. we applied a special technology for obtaining these samples using solar energy for their melting and subsequent uperfast melt quenching for increasing their internal inhomogeneity, allowing the receiving of high-quality textural ceramic samples of the bi1,7pb0,3sr2can-1cunoy (n=2-30) system showing critical temperatures of superconducting precursor transitions above bulk тс. to determine the critical temperatures tc of superconducting precursors above bulk тс we used for the first time the original vibrating reed method to study this multiphase samples in an applied magnetic field. it was shown that this method has sensitivity to superconducting diamagnetism making possible to reveal new superconducting precursor phases above bulk tc. acknowledgment this work has been supported by the shota rustaveli national science foundation grant stcu-2016-51 & stcu grant n 6317. references [1] j. g. chigvinadze, j. v. acrivos, s. m. ashimov, d. d. gulamova, t. v. machaidze, d. uskenbaev, “temperature dependence investigation of dissipation processes in strongly anisotropic high-temperature superconductors of bi-pb-sr-ca-cu-o system synthesized using solar energy”, epitoanyag, vol. 61, pp. 104-108, 2009 [2] d. d. gulamova, d. g. chigvinadze, j. v. acrivos, d. e. uskenbaev, “obtaining and studying the properties of high-temperature superconductors of homologous series of bi1.7pb0.3sr2can-1cunoy (n=49), under influence of solar energy”, applied solar energy, vol. 48, pp. 135-139, 2012 [3] j. g. chigvinadze, j. v. acrivos, s. m. ashimov, d. d. gulamova, g. donadze, “superconductivity at т≈200 k in bismuth cuprates synthesized using solar energy”, available at: https://arxiv.org/ftp/arxiv/papers/1710/1710.10430.pdf, 2017 [4] j. chigvinadze, s. ashimov, g. mamniashvili, g. donadze a. peikrishvili, b. godibadze, “on the nature of superconducting precursors in bi-pb-srca-cu-o compositions fabricated by hot shock wave consolidation technology”, engineering, technology & applied science research, vol. 8, no. 3, pp. 3032-3037, 2018 [5] j. g. chigvinadze, s. m. ashimov, j. v. acrivos, d. d. gulamova, “critical temperature of the superconducting transition of individual phases of multiphase bismuth cuprates after cooling in a magnetic field to a temperature of 77 k”, low temperature physics, vol. 45, no. 4. pp. 386-394, 2019 [6] s. m. ashimov, d. g. chigvinadze, “torsion balance for studying anisotropic magnetic properties of superconducting materials”, instruments and experimental techniques, vol. 45, no. 5, pp. 431-435, 2002 [7] p. esquinazi, “vibrating superconductors”, journal low temperature physics, vol. 85, no. 3-4, pp. 139-232, 1991 [8] a. gupta, p. esquinazi, h. f. braun, “vibrating-reed studies on nonsingle-phase bi-ca-sr-cu-o superconducting ceramics”, physical review b, condensed matter, vol. 39, no. 16, pp. 12271–12274, 1989 [9] v. a. melik-shakhnazarov, i. a. naskidashvili, “a device for an automated recording of internal friction in metals”, pribory i tekhnika eksperimenta, vol. 1, pp. 81-84, 1967 (in russian) microsoft word 41-3441_s__etasr_v10_n2_pp5570-5575 engineering, technology & applied science research vol. 10, no. 2, 2020, 5570-5575 5570 www.etasr.com alshammari: probabilistic evaluation of a power system’s reliability and quality measures probabilistic evaluation of a power system’s reliability and quality measures badr m. alshammari department of electrical engineering college of engineering university of hail hail, saudi arabia bms.alshammari@uoh.edu.sa abstract—reliability and performance quality measures computed so far are deterministic in nature. they represent one operating state (a snapshot of the system conditions) in which the required demand and generation and transmission capacities are known with 100% certainty. in this paper a general and coherent formulation is presented, which can be used to account for the randomness associated with the load level as well as the availability of generation and transmission capacities. the general probability formulation can be used to calculate various reliability indices and quality measures. the paper describes the new approach for computing probabilistic evaluation (expected value) of the reliability indices and performance quality measures and presents illustrative applications. the methodology used in this paper constitutes a new line of research in the probabilistic reliability evaluation of a system where the derived system-wide performance quality indices are capable of classifying and exhibitionistic areas of deficiencies, bottlenecks and redundancies in large-scale power grids. keywords-probabilistic reliability; evaluation; quality; power systems i. introduction the competitive electricity market is subjected to an increasing amount of uncertainties such as the demand forecast uncertainty, electricity price volatility, reliability of the generation groups, economic growth uncertainties, and changing environmental and social impacts on the energy sector [1-2]. in addition to considerations of these uncertainties, planners also need to balance the technical requirement of the system and the requirements from investors who aim at profit maximization [3-5]. there is a general utilization of reliability models throughout the world as the advantages of probabilistic methods over the deterministic approaches of planning, designing, operating and maintaining electric utility systems have clearly been recognized [6]. as has happened with many power system disciplines, the prime interest in system security, adequacy, and reliability has gradually shifted from completing and refining the theoretical basis, through developing suitable computational tools for demonstrating the capability and practicality of the methodologies, to upgrading the computational tools to handle the large-scale nature of present power systems and, finally, to relate various security, quality and reliability indices to the practical concerns of utility engineers and executives regarding supply and/or transmission deficiencies as well as the risk associated with ignoring such deficiencies [7-10]. methods for computing probabilistic contingency-based reliability and performance quality indices have previously been published in [11-17]. these methods are based on a combined contingency analysis and reliability evaluation scheme which integrates both the contingency effect and its probability of occurrence into one routine of analysis [18-19]. in the current work, similar analysis will be used to compute the expected values of different system reliability and performance quality indices. in this context, a “contingency scenario” or a system “demand level” are regarded, in a more general sense, as a “state”, which occurs with certain probability and represents a given demand value and an availability pattern of various capacities in the system. this paper shares the results of a recent major industry supported research and development study in which a novel framework was developed [2] for evaluating performance quality indices associated with power system generation demand balance. in this paper, the optimization technique based on three metaphors (dimensions) representing the relationship between available generation capacities and required demand levels, is presened. the novel formulation presented in this paper can accommodate the randomness associated with the load level and the availability of generation and transmission capacities. ii. problem formulation a. power system network model let nb be the number of buses in the power network, where nb=nl+ng, with nl and ng being the number of load and generator buses respectively. also, in the network model used, nt is the number of transmission branches (lines and transformers). in order to facilitate the subsequent formulation, it is assumed without loss of generality, that the load buses are numbered as 1, 2, ...,nl followed by generator buses as nl+1, .., nl+ng, where nl+ng=nb. for example, the sample power system shown in figure 1 has nb=4, ng=2, nl=2 and nt=5. now, let a=(nb×nt) be the bus incidence matrix representing the connectivity pattern between buses and lines. the entries of a are 0, 1 or -1. therefore, an element abt=1 if bus b is feeding a transmission branch t, abt=-1 if bus b is fed from a branch t, and abt=0 otherwise. in the current analysis, the a matrix is partitioned row-wise into al and ag associated respectively with load and generator buses. the rows of a (or columns of corresponding author: badr m. alshammari engineering, technology & applied science research vol. 10, no. 2, 2020, 5570-5575 5571 www.etasr.com alshammari: probabilistic evaluation of a power system’s reliability and quality measures at) represent groups of buses while the columns of a (or rows of at) represent groups of transmission links. we also note that for practical large-scale networks, the matrix a is extremely sparse. fig. 1. a sample power system [8] b. performance quality assessment although the basic definitions pertaining to system performance quality are simple to state and often seem intuitive at first glance, care should be exercised in order to recognize some subtle differences in the definition and formulation of the composite performance quality indices. let 𝑃 be a vector of nt elements representing transmission branch capacities, 𝑃 a vector of nl elements of peak bus loads, and 𝑃 a vector of ng elements representing generator capacities 𝑃 . for simplicity of notation, we shall use 𝑃 to denote a general element t of the vector 𝑃 (rather than the more strict notation of 𝑃 ). similarly, we shall use 𝑃 and 𝑃 to denote the general elements of 𝑃 and 𝑃 respectively. however, when confusion may occur, we will use the strict notation of 𝑃 , 𝑃 and 𝑃 . now, consider the schematic configurations of figure 2(a) which depicts the transfer connectivity between generations through transmission to load. (a) (b) (c) fig. 2. g-t-l transfer connectivity [8] if, for example the local generation capacity 𝑃 at bus g exceeds the corresponding transmission capability ∑ 𝑃∈ in figure 2(b), where tg denotes the set of transmission branches connected to generator bus g, then using the terminology introduced in the previous section, we may say that a positive amount of (𝑃 − ∑ 𝑃 )∈ of generation beyond bus g has been bottled (blocked from usage). we should note that such a definition applies to a specific scenario of system configuration (the a-matrix) and loading conditions. for example, in the above discussion, we assumed that the set tg does not represent any of pre-defined contingency scenarios. that is, tg represents the full transmission capacity at bus g. in addition to the above definitions, we also define, using similar notation, the following vector for later use: 𝑃 =vector of generation site capacities, which represents the maximum future expanded generation capacity that could be available at the same generation site. the novel framework applied in this paper is based on the original work in [2], in which three dimensions were introduced to represent the relationship between certain system generation capacity and the demand. these tropes relate to the following demand fulfillment issues:  need of capacity for demand fulfillment  existence of capacity (availability for demand fulfillment)  ability of capacity to reach the demand the first trope defines whether the capacity is needed, the second defines whether the capacity exists, and the last defines whether the capacity can reach (delivered to) the demand. the eight possible combinations associated with the 0/1 (yes/no) values of the three tropes, are illustrated in table i. generation quality indices are defined in terms of the previously defined “1/0” states indicating the (needed, exists, can-reach) true/false values associated with each quality metaphor. we shall use the symbol qgijk to indicate the generation quality index state. also, in the following expressions, we shall use min {x, y,..., z} to indicate the minimum of x, y, .., z. the notation <x> will be used to denote max {0, x}, which is the maximum of x and zero (=x if x>0, or 0 otherwise). table i. illustration of quality assessment tropes not needed (l = 0) needed (l > 0) cannot reach can reach cannot reach can reach redundant qg010 surplus qg011 bottled qg110 utilized qg111 exist (c>0) saved qg000 spared qg001 deficient qg100 short-fall qg101 not-exist (c=0) table i summarizes the considered quality indices, namely the utilized generation capacity (q111), bottled generation capacity (q110), shortfall generation capacity (q101), deficit generation capacity (q100), surplus generation capacity (q011), redundant generation capacity (q010), spared generation capacity (q001), and saved generation capacity (q000). c. linear program formulation in the computational scheme of [2], the integrated system quality assessment is performed via solving a master linear programming problem in which a feasible power flow is established which minimizes the total system load not served (lns) subject to capacity limits and flow equations. the master engineering, technology & applied science research vol. 10, no. 2, 2020, 5570-5575 5572 www.etasr.com alshammari: probabilistic evaluation of a power system’s reliability and quality measures linear program, which utilizes the network bus incidence matrix a, is formulated as: 1 objective function= (minimize ( ) ) with respect to , , and subject to: , 0 , 0 , ln l l l g t l l l l t g g g g t t t t f p p p p p p p a p p p p p p p p p                            p (1) an optimization software package (cplex) has been used to solve the master linear program. the overall process of the evaluation of power systems reliability and quality measures is summarized in the flowchart in figure 3. fig. 3. flow chart of the proposed methodology d. probabilistic reliability indices the power system can be described, for the purpose of composite reliability and performance quality assessment, by the three-component model in which generation, transmission, and load are considered as multi-state elements of the power system. for a given operating state m, the values of the network variables will be the solution of the maximum load-supply optimization problem described in the previous section. also, let fm be the probability of operating state m (the sum of fm for all m, including base-case scenario is 1). then, the loss of load may be defined as: 𝐿𝑂𝐿𝑃 = ∑ 𝐿𝑂𝐿𝑃( ) (2) where: 𝐿𝑂𝐿𝑃( ) = 𝑀𝑎𝑥 {𝑌 𝐿𝑂𝐿𝑃 ( ) } (3) represents the system loss of load probability for any operating state m (load levsrl, loss of generation and/or transmission capacities) in the power grid, 𝐿𝑂𝐿𝑃 ( ) = 𝜆 𝑓 (4) represents the loss of load probability at bus  for operating state m, 𝜆 ( ) = 0 𝑖𝑓 𝑃 ( ) ≤ 𝑃 1 𝑖𝑓 𝑃 ( ) > 𝑃 (5) and p o denotes the scheduled (required) load at load bus . also, in (2), ms denotes the number of all possible states. iii. probabilistic evaluation the reliability and performance quality indices computed so far are deterministic in nature, i.e. they represent one operating state in which the required demand and the generation and transmission capacities are known with 100% certainty. a. proposed formulation in real life, load variations occur randomly and contingencies cause some generation and/or transmission capacities to be lost (become unavailable). in other words, neither the load levels nor the generation or transmission capacities are known with absolute certainty. they are rather subject to random variations and consequently the calculated reliability and performance quality indices are all subject to random variations where only expected values of these indices can be evaluated. for example, the load variations, which are accounted for using the so-called “load-duration curves” can be used to calculate the expected value of the lns, which is widely known as the expected load not-served (elns). on the other hand, the randomness in the generation and transmission capacity availability are accounted for using the so-called forced-outage rates (or availability rates) associated with various facilities. consequently, the expected values of the performance quality indices qg111, qg110, qg101, etc. can be evaluated using the modeled randomness of the system load as well as the generation and transmission capacity availabilities as will be outlined in this section. methods for computing probabilistic contingency-based reliability and performance quality indices have previously been published [7]. these methods are based on a combined contingency analysis and reliability evaluation scheme which integrates both the contingency effect and its probability of occurrence into one routine of analysis. in the present work, similar analysis will be used to compute the expected values of different system performance quality indices. in this context, a “contingency scenario” or a system “demand level” are regarded, in a more general sense, as a “state” which occurs with certain probability and represents a given demand value and availability pattern of various capacities in the system. b. simulation results consider the sample power system in figure 4. the system consists of two generators, namely g1 and g2, with a total capacity of 100mw and connected to two load buses, with a engineering, technology & applied science research vol. 10, no. 2, 2020, 5570-5575 5573 www.etasr.com alshammari: probabilistic evaluation of a power system’s reliability and quality measures total required load of 115mw, via five transmission lines. in this illustrative example, the availability of the two generating units are assumed as 0.9 and 0.8, respectively (forced outage rates of g1 and g2, respectively). also, for simplicity, all transmission lines are assumed to have availability of 0.85. the system load is assumed to have three possible levels, namely 35mw, 75mw, and 115mw with probability of occurrence 0.5, 0.3 and 0.2 respectively. fig. 4. a 4-bus sample power system the combined generation/transmission state probability table associated with the generation and transmission capacities of this system, along with the reliability and performance quality indices lns, qg111 and qg110 are shown in table ii for the 35mw load level. the rows of table ii represent various operating states. the first three columns of table ii represent the well-known generation capacity outage probability table (copt) [20]. the next five columns (t1 to t5) represent the copt for the transmission facilities of this system. column ( ∑ 𝑃 ) is the total generation available capacities for each operating state shown in the table. the column (∑ 𝑃 ) represents the actual total generation as calculated from the solution of the master linear program for various operating states. similarly, the next three columns represent the associated values of the indices lns and qg111 and qg110 respectively. when these values are multiplied by the operating state probability shown in the next column, they produce the expected values of these indices as outlined in the last three columns of the table, namely elns and eqg111 and eqg110. using the generation state availabilities shown in table ii, the discrete probability density functions of various capacities and indices can be evaluated and displayed. these discrete density functions show the overall probabilities of occurrence associated with given capacities or indices. for example, the probability density function of the generation capacity (state probabilities) for this system are depicted in figure 5. fig. 5. probability density of generation capacity for system figure 6 shows the probability density of the utilized generation capacity (qg111) at 75mw load, while figure 7 shows the probability density of bottled generation capacity (qg110) at 115mw load and the probability density of surplus generation capacity (qg011) for this system at 35mw load is shown in figure 8. table iii summarizes the expected values of various performance quality and reliability indices for this system. fig. 6. probability density of qg111 for a system at 75mw load fig. 7. probability density of qg110 for a system at 115mw load fig. 8. probability density of qg011 for a system at 35mw load the discrete probabilities of figure 7 for qg110 at 115mw load reveal that the highest probability is associated with generation bottling of 15mw and not with zero as would be expected for well-designed systems. this indicates a general weakness (shortage) in the installed transmission facilities as compared with the existing generation capacities and required load. the discrete probabilities of figure 8 for qg011 show two distinct high probabilities of occurrence at both 0 and 50mw surplus levels. this is mainly due to the fact that most of the main facilities (generators and transmission lines) are available (outage does not occur) which means that the network could deliver all the available generation (not needed) to the load side. on the other hand, at qg011=0, most of the main facilities (generators and transmission lines) are not available (outage), especially g1, t1 and t2, meaning that the network either doesn’t has the capacity of generation over the required load or it is incapable to deliver the available generation (not needed) through transmission lines to the load side. in this regard, the maximum value of the probability density of the qg111 for the system occurs at 75mw load level as shown in figure 8. engineering, technology & applied science research vol. 10, no. 2, 2020, 5570-5575 5574 www.etasr.com alshammari: probabilistic evaluation of a power system’s reliability and quality measures  gp  gp table ii. performance quality indices for the test system at 35mw load # 1g 2g 1t 2t 3t 4t 5t lns 111gq 110gq probability elns 111geq 110geq 1 1 1 1 1 1 1 1 100 85 0 35 0 0.319468 0 11.18137 0 2 1 1 1 1 1 1 0 100 52 10 25 10 0.056377 0.563767 1.409417 0.563767 3 1 1 1 1 1 0 1 100 85 0 35 0 0.056377 0 1.973184 0 4 1 1 1 1 1 0 0 100 52 30 5 30 0.009949 0.298465 0.049744 0.298465 5 1 1 1 1 0 1 1 100 85 0 35 0 0.056377 0 1.973184 0 6 1 1 1 1 0 1 0 100 40 10 25 10 0.009949 0.099488 0.248721 0.099488 7 1 1 1 1 0 0 1 100 85 0 35 0 0.009949 0 0.348209 0 8 1 1 1 1 0 0 0 100 40 30 5 30 0.001756 0.05267 0.008778 0.05267 9 1 1 1 0 1 1 1 100 55 0 35 0 0.056377 0 1.973184 0 10 1 1 1 0 1 1 0 100 52 10 25 10 0.009949 0.099488 0.248721 0.099488 11 1 1 1 0 1 0 1 100 55 3 32 3 0.009949 0.029846 0.318362 0.029846 12 1 1 1 0 1 0 0 100 52 30 5 30 0.001756 0.05267 0.008778 0.05267 13 1 1 1 0 0 1 1 100 55 0 35 0 0.009949 0 0.348209 0 14 1 1 1 0 0 1 0 100 40 10 25 10 0.001756 0.017557 0.043892 0.017557 15 1 1 1 0 0 0 1 100 55 15 20 15 0.001756 0.026335 0.035114 0.026335 16 1 1 1 0 0 0 0 100 40 30 5 30 0.00031 0.009295 0.001549 0.009295 17 1 1 0 1 1 1 1 100 45 0 35 0 0.056377 0 1.973184 0 18 1 1 0 1 1 1 0 100 12 23 12 23 0.009949 0.228823 0.119386 0.228823 19 1 1 0 1 1 0 1 100 45 0 35 0 0.009949 0 0.348209 0 20 1 1 0 1 1 0 0 100 12 30 5 30 0.001756 0.05267 0.008778 0.05267 21 1 1 0 1 0 1 1 100 45 0 35 0 0.009949 0 0.348209 0 22 1 1 0 1 0 1 0 100 0 35 0 35 0.001756 0.061449 0 0.061449 23 1 1 0 1 0 0 1 100 45 5 30 5 0.001756 0.008778 0.05267 0.008778 24 1 1 0 1 0 0 0 100 0 35 0 35 0.00031 0.010844 0 0.010844 25 1 1 0 0 1 1 1 100 15 20 15 20 0.009949 0.198977 0.149232 0.198977 26 1 1 0 0 1 1 0 100 12 23 12 23 0.001756 0.040381 0.021068 0.040381 27 1 1 0 0 1 0 1 100 15 20 15 20 0.001756 0.035114 0.026335 0.035114 28 1 1 0 0 1 0 0 100 12 30 5 30 0.00031 0.009295 0.001549 0.009295 29 1 1 0 0 0 1 1 100 15 20 15 20 0.001756 0.035114 0.026335 0.035114 30 1 1 0 0 0 1 0 100 0 35 0 35 0.00031 0.010844 0 0.010844 31 1 1 0 0 0 0 1 100 15 20 15 20 0.00031 0.006197 0.004647 0.006197 32 1 1 0 0 0 0 0 100 0 35 0 35 5.47e-05 0.001914 0 0.001914 33 1 0 1 1 1 1 1 85 70 0 35 0 0.079867 0 2.795343 0 34 1 0 1 1 1 1 0 85 52 10 25 10 0.014094 0.140942 0.352354 0.140942 35 1 0 1 1 1 0 1 85 70 0 35 0 0.014094 0 0.493296 0 36 1 0 1 1 1 0 0 85 52 30 5 30 0.002487 0.074616 0.012436 0.074616 37 1 0 1 1 0 1 1 85 70 0 35 0 0.014094 0 0.493296 0 38 1 0 1 1 0 1 0 85 40 10 25 10 0.002487 0.024872 0.06218 0.024872 39 1 0 1 1 0 0 1 85 70 0 35 0 0.002487 0 0.087052 0 40 1 0 1 1 0 0 0 85 40 30 5 30 0.000439 0.013168 0.002195 0.013168 41 1 0 1 0 1 1 1 85 40 0 35 0 0.014094 0 0.493296 0 42 1 0 1 0 1 1 0 85 40 10 25 10 0.002487 0.024872 0.06218 0.024872 43 1 0 1 0 1 0 1 85 40 18 17 18 0.002487 0.04477 0.042283 0.04477 44 1 0 1 0 1 0 0 85 40 30 5 30 0.000439 0.013168 0.002195 0.013168 45 1 0 1 0 0 1 1 85 40 10 25 10 0.002487 0.024872 0.06218 0.024872 46 1 0 1 0 0 1 0 85 40 10 25 10 0.000439 0.004389 0.010973 0.004389 47 1 0 1 0 0 0 1 85 40 30 5 30 0.000439 0.013168 0.002195 0.013168 48 1 0 1 0 0 0 0 85 40 30 5 30 7.75e-05 0.002324 0.000387 0.002324 49 1 0 0 1 1 1 1 85 30 5 30 5 0.014094 0.070471 0.422825 0.070471 50 1 0 0 1 1 1 0 85 12 35 0 35 0.002487 0.087052 0 0.087052 51 1 0 0 1 1 0 1 85 30 5 30 5 0.002487 0.012436 0.074616 0.012436 52 1 0 0 1 1 0 0 85 12 30 5 30 0.000439 0.013168 0.002195 0.013168 53 1 0 0 1 0 1 1 85 30 5 30 5 0.002487 0.012436 0.074616 0.012436 54 1 0 0 1 0 1 0 85 0 35 0 35 0.000439 0.015362 0 0.015362 55 1 0 0 1 0 0 1 85 30 5 30 5 0.000439 0.002195 0.013168 0.002195 56 1 0 0 1 0 0 0 85 0 35 0 35 7.75e-05 0.002711 0 0.002711 57 1 0 0 0 1 1 1 85 0 35 0 35 0.002487 0.087052 0 0.087052 iv. conclusions a general and coherent formulation is presented which can be used to account for the randomness associated with the load level and the availability of generation and transmission capacities. the general probability formulation can be used to calculate various reliability indices and quality measures. the paper describes the new approach for computing the probabilistic evaluation (expected value) of the reliability indices and performance quality measures and presents engineering, technology & applied science research vol. 10, no. 2, 2020, 5570-5575 5575 www.etasr.com alshammari: probabilistic evaluation of a power system’s reliability and quality measures illustrative applications. the expected values of reliability indices, such as the expected load not-served (elns) and the expected values of performance quality indices: utilized generation capacity (eqg111), bottled generation capacity (eqg110), shortfall generation capacity (eqg101), deficit generation capacity (eqg100), surplus generation capacity (eqg011), redundant generation capacity (eqg010), spared generation capacity (eqg001), and saved generation capacity (eqg000) are calculated in this paper with the established flow pattern, based on the solution of the basic linear program . table iii. expected value of reliability and quality perfomance indices index elns eqg111 eqg110 eqg101 eqg100 value (mw) 21.44 43.56 12.90 6.85 0.99 index eqg011 eqg010 eqg001 eqg000 value (mw) 15.11 17.14 34.03 25.36 the general framework and formulation introduced in this paper can be applied to practical power systems. also, it can be applied to a system under normal operation or subject to contingencies with certain or random occurrences. in this paper, the optimization technique based on three metaphors (dimensions) representing the relationship between available generation capacities and required demand levels was utilized. the novel formulation presented in this paper can accommodate the randomness associated with the load level as well as the availability of generation and transmission capacities, in this case, the expected values of reliability indices and the expected values of performance quality measures. acknowledgment this work was supported by the university of ha'il. references [1] r. billinton, e. khan, “a security based approach to composite power system reliability evaluation”, ieee transactions on power systems, vol. 7, no. 1, pp. 65-72, 1992 [2] m. a. el-kady, b. m. alshammary, “a practical framework for reliability and quality assessment of power systems”, journal of energy and power engineering, vol. 3, no. 4, pp. 499-507, 2011 [3] h. jun, y. zhao, p. lindsay, p. kit, “flexible transmission expansion planning with uncertainties in an electricity market”, ieee transactions on power systems, vol. 24, no. 1, pp. 479-488, 2009 [4] s. d torre, a. j. conejo, j. contreras, “transmission expansion planning in electricity markets”, ieee transactions on power systems, vol. 23, no. 1, pp. 238-248, 2008 [5] b. m. alshammari, “assessment of reliability and quality performance using impact of shortfall generation capacity index on power systems”, engineering, technology & applied science research, vol. 9, no. 6, pp. 4937-4941, 2019 [6] d. o. koval, a. a. chowdhury, “outage data concepts for generation and transmission equipment”, ieee power engineering society general meeting, montreal, canada, june 18-22, 2006 [7] m. a. el-kady, b. a. alaskar, a. m. shaalan, b. m. al-shammri, “composite reliability and quality assessment of interconnected power systems”, international journal for computation and mathematic in electrical and electronic engineering, vol. 26, no. 1, article id ssd05pes-12, 2007 [8] b. m. alshammari, m. a. el-kady, y. a. al-turki, “computer-aided optimization of power system performance quality indices”, 3rd global conference on power control and optimization, gold coast, australia, february 2-4, 2010 [9] b. m. alshammari, m. a. el-kady, y. a. al-turki, “power system performance quality indices”, european transactions on electrical power, vol. 21, no. 5, pp. 1704–1710, 2011 [10] o. kahouli, b. ashammari., k. sebaa, m. jebali, h. hadj abdallah “type-2 fuzzy logic controller based pss for large scale power systems stability”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3380-3386, 2018 [11] p. jirutitijaroen, c. singh, “reliability constrained multi-area adequacy planning using stochastic programming with sample-average approximations”, ieee transactions on power systems, vol. 23, no. 2, pp. 405-513, 2008 [12] r. billinton, d. huang, “effects of load forecast uncertainty on bulk electric system reliability evaluation”, ieee transactions on power systems, vol. 23, no. 2, pp. 418-425, 2008 [13] m. de jong, g. papaefthymiou, p. palensky, “a framework for incorporation of infeed uncertainty in power system risk-based security assessment”, ieee transactions on power systems, vol. 33, no. 1, pp. 613–621, 2018 [14] b. m. alshammari, m. a. el-kady, “probabilistic assessment of power system performance quality”, journal of energy and power engineering, vol. 4, no. 5, pp. 372-379, 2012 [15] s. gope, a. k. goswami, p. k. tiwari, “transmission congestion management using a wind integrated compressed air energy storage system”, engineering, technology & applied science research, vol. 7, no. 4, pp. 1746-1752, 2017 [16] m. de jong, g. papaefthymiou, p. palensky, “a framework for incorporation of infeed uncertainty in power system risk-based security assessment”, ieee transactions on power systems, vol. 33, no. 1, pp. 613–621, 2018 [17] b. m. alshammari. “evaluation of power system reliability levels for (n-1) outage contingency”, international journal of advanced and applied sciences, vol. 6, no. 11, pp. 68-74, 2019 [18] e. tomasson, l. soder, “improved importance sampling for reliability evaluation of composite power systems”, ieee transactions on power systems, vol. 32, no. 3, pp. 2426–2434, 2017 [19] m. de jong, g. papaefthymiou, p. palensky, “a framework for incorporation of infeed uncertainty in power system risk-based security assessment”, ieee transactions on power systems, vol. 33, no. 1, pp. 613–621, 2018 [20] r. billinton, r. n. allan, reliability assessment of large electric power systems, kluwer acadmic publisher, 1988 microsoft word 20-3404_s_etasr_v10_n2_pp5452-5458 engineering, technology & applied science research vol. 10, no. 2, 2020, 5452-5458 5452 www.etasr.com alkahtani et al.: human interruption management in workplace environments: an overview human interruption management in workplace environments: an overview mohammed alkahtani industrial engineering department king saud university riyadh, saudi arabia moalkahtani@ksu.edu.sa mustufa haider abidi advanced manufacturing institute king saud university riyadh, saudi arabia mabidi@ksu.edu.sa ali ahmad louisiana community and technical college baton rouge, la, usa ali.ahmad.phd@gmail.com saber darmoul industrial engineering department king saud university riyadh, saudi arabia sdarmoul@ksu.edu.sa shatha samman global assessment inc. orlando usa shatha.samman@gmail.com mageed ghaleb industrial engineering department king saud university riyadh, saudi arabia mghaleb@ksu.edu.sa abstract—interruptions are unexpected breaks that introduce new tasks on top of ongoing activities. in work environments, interruptions occur when operators and decision-makers have to deal simultaneously with several stimuli and information sources and have to make decisions so as to maintain the flow of activities at a satisfactory level of performance or quality of service. the causes and effects of interruptions and their subsequent management strategies in workplace environments have been researched in the past, however, only a few review articles are available to report on current advances in this area, to analyze contributions, and to highlight open research directions. this paper offers an up-to-date review and a framework for interruptions and interruption management strategies. the current approaches to identify, report, and manage interruptions in a variety of workplace environments are reviewed and a description of environmental characteristics that favor the occurrence of interruptions and influence interruption management in workplace environments is provided. various approaches to classify and model the different types of interruptions and their cause-consequence relationships are discussed and the strategies to manage interruptions and approaches to measure human performance when dealing with interruptions are analyzed. based on these insights, several guidelines to manage interruptions in workplace environments are provided, and future research directions are highlighted. keywords-interruptions; interruption management strategies; workplace environments i. introduction a workplace environment consists of everything that forms a part of an employee’s involvement with the work itself, such as the relationships with co-workers and supervisors, working equipment and devices, working tasks, etc. workplace environment can be any place including a home-office to a large office building or factory [1]. in several workplace environments, it is important to make sure that the trade remains competitive and prosperous [2]. balancing between staff collaboration in workplaces and the cost of interruption is a hard question with which workplaces struggle [3]. this problem is becoming even more critical where corporations are evaluating means to escalate yield while mitigating in-house costs [4]. in [5], interruptions were defined as breaks in action that introduce new tasks, often unexpectedly and unplanned, on top of an ongoing activity. handling interruptions is a part of interruption management, which has been defined as the detection, interpretation, and integration of interruptions within ongoing task performance [6]. interruptions can have substantial effects on job performance and employee welfare [7]. the importance of reducing the negative consequences of interruptions in any working environment makes interruption management an important consideration. although interruptions and interruption management have stimulated a lot of research in recent years, only a few studies address the recent advances in this field. to the best of our knowledge, the most recent review was conducted in 2010 [8], which focused on interruptions and interruption management in healthcare settings. the main findings reported were: interruptions happen regularly in all healthcare sceneries, interruptions in healthcare have only been explored from the perspective of the individual being interrupted, and few studies inspected the cognitive inferences of interruptions. this article provides a review and a framework to analyze literature on interruptions and interruption management strategies in workplace environments. common causes of interruptions in workplace environments are discussed, and a classification into two sections is suggested: interacting with information and communication technologies and performing office-related activities. the current approaches to identify, report, and manage interruptions are studied. then, a description of environmental characteristics that favour the occurrence of interruptions and influence interruption management in workplace environments is provided. finally, corresponding author: mohammed alkahtani engineering, technology & applied science research vol. 10, no. 2, 2020, 5452-5458 5453 www.etasr.com alkahtani et al.: human interruption management in workplace environments: an overview the article strategies to manage interruptions are described and analyzed and a stage model of interruption management that can be used when dealing with interruptions is proposed. the article concludes by suggesting guidelines for interruption management in workplace environments and highlighting future research directions. ii. workplace environments the term workplace represents the physical location where a human is working or employed. author in [9] classified workplaces according to personality types and occupations into realistic type work environments, investigative type work environments, artistic type work environments, social type work environments, enterprise type work environments, and conventional type work environments. a properly designed workplace assists an organization’s tactical business plans, permits staff to accomplish their work competently and efficiently, symbolizes and exemplifies the ethics and beliefs of the company, and is environmentally healthy [10]. properly designed workplaces possess the following features: interference-free work, collaborative and spontaneous interaction, concentrated teamwork and meetings, personal work style promotion, workstation personalization, customized thermal control, access to sunshine, control of brightness, clear way finding, adjacencies that support work flow, up gradation with latest technology, ergonomic accommodation, and expression of organizational culture [10]. interruptions in a workplace may have a negative impact on well-designed workplace features. as a result, they can have a direct effect on the efficiency, well-being and safety, comfort, attentiveness, job satisfaction, and confidence of staff at the workplace. therefore, identifying factors that result in interruptions and effective strategies to manage interruptions may reduce the negative impacts of interruptions in workplace environments. typical workplace examples where interruptions occur are banks [11] and construction sites [12] or hearlthcare [13-15]. iii. interruption causes in workplace environments interruptions are an omnipresent part of work environments. they are a result of the need to maintain the flow of activities in the workplace, while handling with a number of stimuli and data sources at the same time [16-19]. interruptions can be broadly classified, according to their cause, into external or internal interruptions [5, 20, 21]. the classification can vary from a workplace environment to another. for example, in air traffic control, communication with the pilot might be considered as an external interruption, while talking with a cabin crewmember entering the flight deck might be considered as an internal interruption [22, 23]. in general, external interruptions can be a result of alerts, notifications or environmental cues. one type of internal interruption, called self-interruptions, is related to decisions to halt a current activity to attend an alternative task owed to individual thought processes [24]. intended breaks are not considered as interruptions. several factors may result in interruptions in workplace environments, such as interacting with information and communication technologies, which is known as human computer interaction (hci) [5, 20, 21], and performing general office-related activities [25-27], and multitasking. for a more detailed discussion regarding the causes of interruptions in workplace environments and their effects on human performance, refer to [28, 29]. a. interacting with information and communication technologies interacting with information and communication technologies and communicating with monitoring and control systems can result in interruptions in workplace environments [5, 20, 21, 30]. in hci, interruptions may enable performance on straightforward tasks, while preventing performance on difficult tasks [31]. authors in [20] reported that workers may shift tasks every three minutes as a result of interruptions [20]. after a survey of 1000 senior executives, authors in [32] stated that unwanted interruptions comprise 28% of a worker's day. authors in [33] reported that undesired disruptions cause workers to take up to 30% more time to finish the task and commit up to two times the number of errors. authors in [34, 35] studied self-imposed interruptions in computer-based tasks, and found that it is common for people to use a number of programs/applications simultaneously. authors in [36] studied email interruptions and their influence on people’s attention. the results indicated that individuals choose tactics for realizing a task according to the particular factors of the task or objective. they suggested that email interruptions are manageable when they do not deviate a person’s focus away from a central task, and do not compel the receiver to deal with the interruption. in addition, people use a wide range of different tactics for dealing with email interruptions and those strategies vary based on the circumstantial factors afforded by the task or email. authors in [37] evaluated the use of short email messages in computer related tasks, and found that the practice of one-line electronic mail messages decreases the interruption time for both sender and receiver. authors in [38] found that the customized settings for the notification method of incoming electronic messages, in many email clients, may result in some reduction of the computer-based interruptions. authors in [18] investigated the use and impact of instant messaging (im) tools in the workplace. the authors proposed that while the use of im may result in interruptions, it can lead to enhanced communication quality and the development of a sense of trust among coworkers. authors in [39] reported that interruptions result into a decrease in quality of work during difficult and creative writing tasks. authors in [19] conducted experiments to evaluate the influence of im interruptions on knowledge worker task performance. task performance was determined using two factors, task accurateness and task completion time. the designed tasks were classified as symbolic (manipulation of distinct sets of symbols) and spatial (creating connections between sets of symbols). their results showed that instant massaging interruptions have no effect on task accuracy, but have a significant effect on task completion time. authors in [40] reported that a ringing phone’s interruption at an inconvenient instant can be very disrupting to the present task or social condition. authors in [41] conducted a study on cell phone usage. the investigation of 1201 incoming calls showed that most of the time “who” is calling was used (87.4%) by persons to make cautious call handling decisions (n=834), contrary to the interrupter’s existing local social (34.9%) or cognitive (43%) circumstances. engineering, technology & applied science research vol. 10, no. 2, 2020, 5452-5458 5454 www.etasr.com alkahtani et al.: human interruption management in workplace environments: an overview b. performing office-related activities office-related activities are day-to-day tasks related to planning and scheduling, distribution and logistics, personnel, financial, record keeping and billing, and many other activities within a company. interruptions can occur during the performance of these activities as a result of insufficient employee education (or unawareness) about interruptions and their consequences [42], noises from conversations and other offices [25-27, 38, 43], high traffic areas [44], and disturbance by visitors for staff working either on high cognitive load activities or on tasks with tight timelines [42, 43]. authors in [42] reported that in any company, interruptions may occur as a result of insufficient employees’ education regarding this matter. thus, educating employees about may assist in decreasing their influence. the authors also reported that teaching staff about the adverse effects of interruptions results into a decline in interruptions by 30%. they also reported that interruptions could occur as a result of disturbance by visitors. thus, the authors suggested the use of “do not disturb” (or similar) signs in time and focus demanding workplaces. the authors’ suggestion had substantial improvements in user’s performance and contentment. authors in [43] studied the preferences of staff working on critical and tight timelines, and recommended assignment of independent working space for employees working on jobs with strict deadlines. some studies addressed noise as a widespread cause of interruptions in workplace environments [25-27, 38, 43]. several strategies have been reported to decrease the influence of such interruptions. for example authors in [43] suggested the use of alternative sounds such as ambient background office music that could counterbalance chatty noises and control the distractions in the office. authors in [38] reported that the use of ear buds/headphones undoubtedly restricts the different conversations and other office noises [38]. authors in [25-27] suggested that office organization might be needed in case it is feasible to define loud and silent zones. moreover, the degree of noise within these zones should be known. thus it will provide a reason to move staff members so that the noise is more uniformly dispersed through the workplace. in many workplace environments, high traffic areas may exist and can cause interruptions. isolating these areas can reduce the impact of disruptions in the workplace [44]. authors in [17] examined the consequences of interruption frequency, task intricacy, and individual characteristics on mental load and consequently decision-making performance on monetary tasks. the outcomes showed that task complexity and interruption frequency have significant influence on performance. authors in [38] identified different kinds of interruptions for workplace related tasks, explored the circumstantial features near these interruptions, and identified methods that could be used to mitigate the adverse effects of interruptions. they found that most of the time interruptions occur mainly from colleagues. disruptions are a noteworthy problem in the workplace, and most of the interruptions at all stages were associated with ontask business activities. authors in [45] investigated the idea of users deferring interruptions at points of higher workload until times of lower workload. their study showed that during periods of lower workload, users swapped to the interrupting task 94% of the time. iv. interruption management strategies interruptions stand as an important research area. with the advances in information and communication technologies, the amount of interruptions on day-to-day basis is also rising [38]. interruptions are a ubiquitous component of the workplace, and have the capability to be perilous, particularly in cognitively intensive knowledge workplace environments [46]. if they are not handled in an effective and efficient way, they can lead to health, safety, and performance problems [47]. figure 1 presents a cause and effect diagram that illustrates why interruptions take place in workplace environments. fig. 1. a cause and effect diagram of interruptions in workplace environments interruptions can be controlled in several manners, including denial, postponement, and prompt partial processing [48]. handling interruptions is a part of interruption management, which has been defined by as the detection, interpretation, and integration of interruptions within ongoing task performance [6]. the importance of having an environment with minimum interruptions effect is what makes interruption management an important issue in human multitasking environments. a task-independent interruption management system (ims) was developed with an objective to interrupt users at low-workload moments in order to minimize the disruptiveness of interruptions [49]. in interruption-failure modes and effects analysis (i-fmea) [50], the interruptionrelated failure modes are assessed in terms of risk, worker efficiency, and patient satisfaction. this strategy helps identify interruptions that may be delayed (i.e. reflecting relatively low risk, average effect on patient satisfaction, and average additional work). several strategies for managing interruptions can be found in the literature. for example, authors in [6] proposed a 4-stage model for interruption management: interruption detection, interruption interpretation, interruption integration, and dismiss with in-hand task performance. authors in [51] identified four strategies for handling interruptions: (a) before starting the interruptive task complete in-hand task, (b) postpone the interruptive task so as to finish the main task (i.e. asking a caller to wait on hold), (c) recognize the matter of the interruptive task and then finish the main task engineering, technology & applied science research vol. 10, no. 2, 2020, 5452-5458 5455 www.etasr.com alkahtani et al.: human interruption management in workplace environments: an overview before finalizing the interruptive task, and (d) process the interruptive task instantly, quitting the in-hand task that will be accomplished later [51]. author in [52] proposed four different strategies for managing interruptions: (a) instantaneous, (b) planned, (c) negotiated, and (d) facilitated. authors in [46] addressed a set of stages to handle an interruption: identifying the interruption, understanding what the interruption contains, assimilating the interruption into the present work task and then continuing with the in-hand task. figure 2 depicts the proposed stage model for interruption management, modified from [46]. fig. 2. proposed stage model of interruption management strategy, modified from [46] to manage an interruption, first there is a need to identify the aspects that make interruption an encumbrance. next, an interruption management strategy can be applied [53]. the challenge in handling an interruption is in how to manage it in order to cause minimal harm and at the utmost advantage. the tactic must not be more disrupting than the interruption itself [54]. table i provides a summary of literature findings pertaining to interruption management strategies that can be used as a theoretical foundation for human interruption management in workplace environments. v. discussion, conclusions and future work this paper provides a systematic review of human interruption management in workplace environments. the review concentrates on the interruption causes in workplace environments and on the strategies to handle and manage those interruptions. it starts by defining workplace environments, and introduces features of a well-designed workplace environment, and how interruptions might impact these features. interruptions are defined in the context of workplace environments, and interruption causes are discussed. the causes of interruptions are classified into two broad sections namely: interacting with information and communication technologies (known as hci), and performing office-related activities. in hci there are several causes of interruptions such as phone ringing, emails, and instant messaging. in officerelated activities, there are several causes like lack of awareness, and noises from conversations and other offices, disturbances by visitors, and by high traffic areas. recovering from interruptions takes longer than one can think. some interruptions may look insignificant in nature, however they have long term impact and cause delays and reduce productivity. workplace interruptions are an inescapable problem that results into compromised efficiency, productivity, and accuracy [57]. an experimental study [58] was conducted with a hypothesis that people’s productivity decreases when interrupted compared to when they have not been interrupted. the results showed that the interruptions engineering, technology & applied science research vol. 10, no. 2, 2020, 5452-5458 5456 www.etasr.com alkahtani et al.: human interruption management in workplace environments: an overview reduce productivity and increase the probability of errors. some studies showed that interruptions increase stress levels [59-61]. authors in [62] analyzed the effect of interruptions on task performance, annoyance, and anxiety. the results revealed that interruptions have disrupting effects on both emotional state and productivity. however, some studies showed that interruptions have benefits sometimes, such as walking in nature for some time reduce stress and increases creativity, etc. [63-65]. table i. summary of literature findings in interruptions management expected interruptions proposed procedures suggestions and clarifications source emails and email messages customize settings various email clients have personalized settings for the reporting of inward email messages. [38] keep them short and pretty encourage the use of short messages. the practice of one-line email messages decreases the interruption time for both sender and receiver. [37] instant messaging only if necessary in tasks of little or modest mental load with numerous natural breakpoints, instant messaging can be allowed. [25, 55, 56] self-imposed interruptions better if working on the primary task switching though occupied by the goal of the main task could be better. [25, 26, 35] high traffic areas be aware of their impact isolating high traffic areas to reduce the impact of disruptions. [44] noises from conversations and other offices ear buds/headphones the use of ear buds/headphones definitely restricts noise disturbances. [38] background music the use of ambient background workplace music may balance the conversational noise and control the disturbances in the workplace. [43] office organization and restructuring mounting various sound measurement devices all over the office would be achievable to specify if loud and silent regions exist and their noise level. the outcomes may divulge substantial differences between places and offer explanation in rearranging staff so that the noise is more uniformly dispersed all through the workplace. [25-27] disturbance by visitors “back in 10 minutes” place “do not disturb” (or similar) signboards in the workplace of developers/programmers working on high cognitive load tasks. the use of these signs has substantial improvements in user performance and satisfaction. [42] interruptions during tasks with tight timelines quiet working rooms allocate independent offices for employees working on strict timelines. [42, 43] interruptions caused by unawareness educate staff educating staff about the amount of interruptions that are taking place at all stages of the company. [42] this paper describes the current approaches and strategies to identify, report, and manage interruptions. based on these strategies, the paper proposes a stage model of interruption management that can be considered as a summary of the analyzed strategies to manage interruptions. finally, a summary of literature findings pertaining to interruption management strategies was provided. the summarized strategies can be used as a theoretical foundation for human interruption management in workplace environments. future research includes the empirical evaluations of the proposed strategies. comparison studies should be conducted to determine the most suitable strategy to use for a certain environment. moreover, such studies might be applied to different workplace environments, with the intention of assessing the efficacy of the suggested strategies. acknowledgment this project was funded by the national plan for science, technology and innovation (maarifah), king abdulaziz city for 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annoyance, and anxiety in the user interface, university of minnesota, 2001 [63] m. czerwinski, e. horvitz, s. wilhite, “a diary study of task switching and interruptions”, conference on human factors in computing systems, vienna, austria, april 24-29, 2004 [64] j. m. hudson, j. christensen, w. a. kellogg, t. erickson, ““i’d be overwhelmed, but it’s just one more thing to do”: availability and interruption in research management”, conference on human factors in computing systems, minneapolis, usa, april 20-25, 2002 [65] j. jin, l. a. dabbish, “self-interruption on the computer: a typology of discretionary task interleaving”, conference on human factors in computing systems, boston, usa, april, 2009 microsoft word etasr_v11_n4_pp7417-7423 engineering, technology & applied science research vol. 11, no. 4, 2021, 7417-7423 7417 www.etasr.com shamsan: statistical analysis of 5g channel propagation using mimo and massive mimo technologies statistical analysis of 5g channel propagation using mimo and massive mimo technologies zaid ahmed shamsan electrical engineering department college of engineering imam mohammad ibn saud islamic university (imsiu) riyadh, saudi arabia shamsan@ieee.org abstract—multiple input multiple output (mimo) and massive mimo technologies play a significant role in mitigating five generation (5g) channel propagation impairments. these impairments increase as frequency increases, and they become worse at millimeter-waves (mmwaves). they include difficulties of material penetration, line-of-sight (los) inflexibility, small cell coverage, weather circumstances, etc. this paper simulates the 5g channel at the e-band frequency using the monte carlo approach-based nyusim tool. the urban microcell (umi) is the communication environment of this simulation. both mimo and massive mimo use uniformly spaced rectangular antenna arrays (ura). this study investigates the effects of mimo and massive mimo on los and non-los (nlos) environments. the simulations considered directional and omnidirectional antennas, the power delay profile (pdp), root mean square (rms) delay spread, and small-scale pdp for both los and nlos environments. as expected, the wide variety of the results showed that the massive mimo antenna outperforms the mimo antenna, especially in terms of the signal power received at the end-user and for longer path lengths. keywords-mimo; massive mimo; millimeter-waves; channel propagation; path loss exponent; rms delay spread; received power i. introduction massive multiple input multiple output (mimo) and millimeter-waves (mmwaves) are two key technologies of 5g wireless systems that deliver high data rates, support multiple users, and provide very low latency. the use of mmwaves for the 5g systems is still in the experimental stage. classically, the mmwaves belong to the frequency spectrum from 30 to 300ghz [1]. some frequency bands of the first part of this frequency spectrum, up to 100ghz (as well as the traditional wireless mobile generation bands) are dedicated to the 5g system because they offer a huge amount of unutilized or under-utilized spectrum frequencies, compared to the lower bands. the e-band (71-76 and 81-86ghz) [2, 3] can be represented by 73ghz and it is one of the main frequencies allocated to 5g systems. it is well recognized that the spectral bandwidth is directly proportional to the amount of transmitted data rate. however, using the mmwaves for mobile communication exposes several propagation challenges, e.g. signal attenuation, coverage area limitations, and, most notably, high penetration losses. due to the higher frequency of mmwaves, free space loss is much higher especially when an isotropic antenna is used, and many materials cause very high absorption loss, while diffraction is less noticeable. consequently, mmwave signal goes under high blockage, and most of the time propagation tends to be line-of-sight (los) based [4]. to mitigate mmwave disadvantages, several technologies have been introduced, such as small cell coverage, beamforming, mimo and massive mimo antennas, etc. massive mimo-ofdm has been considered as one of the most desired technologies for broadband wireless systems and is worldwide recognized as the 5g wireless communication basis. it is more flexible and adaptable to stay active, especially if developed for a high number of antennas or massive mimo [1, 3]. this paper will discuss the 73ghz channel and signal propagation using mimo and massive mimo technologies in urban microcell area. in [5], the 73ghz frequency band proved to be power-efficient and robust against atmospheric variations. both omnidirectional and directional channel models were used due to the fact that they are widely adopted by the industry and researchers for proper designing of wireless systems and antenna arrays in supporting massive mimo systems by employing spatial diversity and/or beamforming gain respectively [6, 7]. for this purpose, the monte carlo approachbased nyusim simulator (nyusim v3.0) was utilized to apply mimo-orthogonal frequency-division multiplexing (ofdm) and massive mimo technologies and generate channel impulse responses (cirs) from both omnidirectional and directional channel models at 73ghz [8-10]. this simulator can be also used in the thz band [11]. ii. mimo and massive mimo technologies generally, three methods can be planned to improve the wireless network efficiency, namely deploying extreme access points, using wide frequency spectrum, and increasing the spectral efficiency. the foreseen wireless systems will utilize small base station coverage and thus will require by default many access points to cover all considered areas. also, new spectral bands will be exploited to support the efficiency of the wireless network. however, the spectral efficiency always corresponding author: zaid a shamsan engineering, technology & applied science research vol. 11, no. 4, 2021, 7417-7423 7418 www.etasr.com shamsan: statistical analysis of 5g channel propagation using mimo and massive mimo technologies needs to be maximized in a given frequency band. the spectral efficiency equals to the total bits that can be sent per second in each unit of bandwidth (bits/s/hz) which ultimately contributes in improving the throughput (th) [12]: �� � �� ��� (1) where �� is the bandwidth (hz) and �� is the spectral efficiency (bits/s/hz). a recognized technique to raise the spectral efficiency is to exploit the concept of multiple antennas at the transceivers. communication with multiple antennas leads to send out multiple streams which in turn cause multiplexing gain that significantly improves the capacity of communication. therefore, the use of mimo antennas as a diversity method is able to improve the communication reliability. the useful characteristics of the mimo technology allowed its incorporation to the new generation wireless systems (4g, 5g, and 6g). figure 1 shows the mimo technology concept for point to point link. fig. 1. mimo technology for point to point link (upand down-link). in each channel of the mimo technology, one vector is transmitted and another is received. if an additive white gaussian noise (awgn) at the receiver (rx) exists, shannon theory gives the following equations for the spectral efficiency of the link (in b/s/hz): �� � log� ��� ��� � �� �� (2) �� � log� ��� ��� � � ��� � log� ��� ��� � ���� (3) where � is the number of bs antennas, k is the number of terminal antennas, � is an � �� matrix for the channel frequency response between the base station (bs) array and the terminal array, and ��� and ��� are the signal-to-noise ratios (snrs) for the uplink and downlink, which are proportional to the corresponding total radiated powers. the spectral efficiency values in (2) and (3) involve that the rx must know �, however the transmitter (tx) does not require knowing �. if the tx attains channel state information (csi), the performance will be enhanced. the spatial multiplexing gain has been exploited and the mimo was developed to the multiuser mimo (mumimo), where the number of users is concurrently functioned by one bs supported by multiple mimo antennas [13-16]. by equipping the bs with more antennas, more degrees of freedom can be provided and therefore, more users can concurrently connect in the same resource of time-frequency. consequently, a large sum throughput can be attained. when a bs is enhanced with 100 or more antennas concurrently (mumimo system) to serve tens (or more) of users in the same time-frequency resource, this system is termed as a massive mimo, very large mu-mimo, hyper-mimo, or fulldimension mimo [12]. precisely, in contrast, mu-mimo systems support a large number of wireless broadband terminals using a large number of bs antennas whereas, massive mimo is a type of mu-mimo system where antennas (hundreds/thousands) concurrently serve wireless broadband terminals (tens/hundreds) in the same frequency resource as shown in figure 2. assuming that terminals in mu mimo/massive mimo have a single antenna as shown in figure 2 in which the bs serves k terminals, let � be a matrix of � � � matching the frequency response between the bs array and the � terminals. the sum spectral efficiencies of the upand down-link are expressed by: �� � log�|�� ������| (4) �� � max $%&' ∑ $)*+%),log�|�� ����./��| (5) where 0 � 101,. . . ,5�6 7 , ��� is the uplink snr per each terminal, and ��� is the downlink snr. the calculation of downlink capacity needs a solution of the convex optimization problem. the attaining of csi is essential to (4) and (5). the bs must identify the channels in the uplink, and each terminal has to be informed its allowed transmission rate individually, while in the downlink, the bs and the terminals must have csi [17]. fig. 2. massive mimo system (upand down-link). iii. models of channel propagation the nyusim simulator uses two main integrated models: the free space path loss (pl) model and the statistical spatial channel model (sscm). the close-in (ci) free space pl model used in this paper as shown in (6) is based on friis’ and bullington’s research work that set wireless propagation fundamental principles, where the path loss depends on the environment with a reference distance and includes an additional attenuation component [18-19]: 89:;<=,>?@a � 32.4 20log+'<=a 10flog+'<>?@a 9g hi:; (6) where = is the operation frequency (ghz), f denotes the path loss exponent (ple), >?@ is the three-dimension (3d) distance engineering, technology & applied science research vol. 11, no. 4, 2021, 7417-7423 7419 www.etasr.com shamsan: statistical analysis of 5g channel propagation using mimo and massive mimo technologies between the tx and rx, and >' is the free space reference distance, ranging between 1m and 5m (1m in this paper), provided that >?@ ≥ >'. the term hi:; represents the gaussian random variable with zero-mean and standard deviation σ in db, while 9g denotes the atmospheric conditions attenuation factor [1, 8], and >?@ is defined as in (6). the adopted model of the channel (closed-in path loss) uses a small number of parameters compared to that of 3gpp/itu channel models while it can estimate a wide range of microwave and mmwave frequencies, physical separation paths, and scenarios with better performance, better stability, and fewer parameters. the ple is confidentially relevant to the environment where the communication system works. it has different values for different pl models which are developed through numerical schemes combined with empirical approximations of experimental data obtained in channel sounding measurements. for instance, for the urban microcell (umi) scenario and in the case of los free space environment, the ple is set to be 2 with a shadow fading standard deviation of 4.0db, whereas these two parameters are respectively set to 3.2 and 7.0db in the nlos environment. in the sscm model, time clusters and spatial lobes are employed to model the omnidirectional cir, and power spectra of both angle of departure (aod) and angle of arrival (aoa). time clusters contain multipath components moving closely in time, and the ones which arrive from different angular directions in a short excess delay time. spatial lobes are the main directions of arrival or departure components that arrive or depart within several hundreds of nanoseconds. in the sscm model, multiple paths within a time cluster can arrive at unique pointing angles that can be detected by directional antennas with high gain [1, 18]. in fact, the number of clusters of the mmwave signals should not be large due to the fact that this can cause an imprecise spectral efficiency prediction. thus, the number of time clusters is in the range 1–6, whereas the spatial lobes are between 2 and 5 [18]. iv. communication scenarios with mimo and massive mimo several studies on mimo and massive mimo have been conducted in order to develop and improve the technology of communication [1, 20-22]. the proposed communication scenario is a communication link in an urban microcell system at 73ghz using 4×4 mimo and 64×64 massive mimo technologies. it is assumed that both the tx and rx are equipped with 4 mimo or 64 massive mimo antenna elements comprising uniformly spaced rectangular antenna arrays (ura) with �k and �l antenna elements in the elevation domain and azimuth domain, in that order [23]. the adopted antenna patterns are based on table 7.3-1 of [24]. for ofdm technique, each subcarrier has an mimo channel coefficient which will be generated through paramount parameters of each solvable multipath component. the mimo channel coefficients �m,n,�<=a between the �o tx antenna and the k th rx antenna for the subcarrier = are expressed through the following equation [1, 8]: �m,n,�<=a = ∑ pn,q,mrstu,),v × rws�xyzu,),vm × rws�x�[n \]^_`u,),va ×rws�x�bq\]^_cu,),va (7) where d represents the def resolvable solvable multipath component, α represents the amplitude of the channel gain, φ is the phase of the multipath component, g is the time delay, >7 and >h denote the antenna element spacing at the tx and rx respectively, whereas i and j represent the azimuth aod and aoa correspondingly. it is assumed that the number of carriers is 1601 (the frequency interval between adjacent subcarriers is 500khz and the bandwidth is 800mhz, therefore, (800mhz/500khz) + 1 = 1601 subcarriers). v. the main parameters in table i, the tx and rx antenna types, simulation conditions, propagation parameters, and system components are tabulated. the results of applying the assumed values in table i will be discussed in the next section. table i. key parameters and simulation conditions [1, 8, 9, 18, 25, 26] parameter value parameter value operation frequency (ghz) 73 tx and rx antenna gain (dbi) 24.9 no. of tx and rx antenna elements in massive mimo 64×64 no. of massive mimo antenna elements per row 8 system bandwidth (mhz) 800 tx and rx array type ura no. of tx and rx antenna elements in mimo 4×4 tx and rx antenna elevation hpbw 8.6 o tx and rx antenna azimuth hpbw 10.9 o no. of mimo antenna elements per row 2 tx power (dbm) 30 tx and rx antenna spacing 0.5k barometric pressure (mbar) 1013.25 ofdm subcarrier spacing (khz) 500 humidity 50% no. of ofdm subcarriers 1601 temperature 20 o c polarization co-pol vi. results and discussion figures 3(a)-(d) explain the substantial difference in the omnidirectional and directional path loss at different environments and number of antenna elements at 300m separation distance between the tx and rx and operation frequency of 73ghz. these figures are produced using the nyusim tool, where the pl, ple(n), and directional shadow fading standard deviation are demonstrated for 4 los and nlos cases. each figure illustrates the pl, n, and directional standard deviation. it can be seen that the tx antenna gain and rx antenna gain for the urban microcell are assumed to be the same (24.9dbi). from figure 3(a), it can be noticed that the omnidirectional path loss at 300m is roughly 123.5db using mimo in los environment, while it increases to 164.4db with mimo in nlos environment at the same distance (figure 3(b)). this means that there is a very large difference of 40.9db in the pl in the case of los compared to nlos. on the other hand, the omnidirectional pl massive mimo is approximately 116.6db in los environment, while it increases to 153.3db in nlos environment at the same distance as displayed in figures 3(c) and 3(d) respectively. the difference between the two environments is approximately 36.7db. table ii shows a comparison among the 4 cases of the systems used in the simulations. it can be stated that the pl in the case of mimo in nlos is the largest, while the lowest pl occurs using massive mimo in los environment. table ii shows the difference in omnidirectional pl among the system scenarios. engineering, technology & applied science research vol. 11, no. 4, 2021, 7417-7423 7420 www.etasr.com shamsan: statistical analysis of 5g channel propagation using mimo and massive mimo technologies (a) (b) (c) (d) fig. 3. omnidirectional and directional path loss tx-rx separation distance for an urban microcell scenario (a) 4×4 mimo los, (b) 4×4 mimo nlos, 64×64 massive mimo los, (d) 64×64 massive mimo nlos. table ii. difference in omnidirectional pl among the system scenarios description difference in omnidirectional pl (db) systems mimo los mimo nlos massive mimo-los massive mimo-nlos mimo-los ----40.9 6.9 -29.8 mimo-nlos 40.9 ---47.8 11.1 massive mimo-los -6.9 -47.8 ----36.7 massive mimo-nlos 29.8 -11.1 36.7 --- to study the effect of the directional antenna compared to the omnidirectional antenna, the worst case of mimo system is considered to investigate its impact on the rms delay spread. this scenario is shown in figure 4 for the los environment in which the maximum separation distance between the tx and the rx is 0.5km. the directional antenna clearly seams that it causes less rms delay spread. figure 4 shows that the maximum rms delay spread is 2.8ns when the rx is located at 400m whereas the minimum rms delay spread is about 0.3ns at a separation distance of 250ns and 450ns from the tx. in contrast, the omnidirectional antenna causes grater rms delay spread for all cases. the maximum rms delay spread for the omnidirectional antenna is 24ns at 100m whereas the minimum value of the antenna, 9.5ns, is at 500m. these results reveal that the rms delay spread resultant from omnidirectional antenna is always greater than that of the directional antenna. moreover, figure 4 indicates that there is very small fluctuation in the delay generated by the directional antenna, however, the omnidirectional antenna generates a high rms delay fluctuation. the same scenario is shown in figure 5 for the mimo system to investigate the impact of the nlos environment on the rms delay spread. the rms delay spread values in figure 5 are higher than that in figure 4. in addition, the fluctuations of rms delay spread values in the nlos environment are higher than that in the los environment which creates more stable delay. furthermore, this result is similar for either omnidirectional or directional antenna type, the general effect of nlos does not change. for example, the directional rms delay shown in figure 6 for nlos is almost higher than that of los except very few cases where the rms delay is higher than that of nlos by a very small value of rms delay spread. this is true due to the fact that the nature of nlos environment is filled with several reflectors, scatters, diffracted materials, etc. fig. 4. omnidirectional and directional rms delay spread for a los urban microcell scenario. engineering, technology & applied science research vol. 11, no. 4, 2021, 7417-7423 7421 www.etasr.com shamsan: statistical analysis of 5g channel propagation using mimo and massive mimo technologies fig. 5. omnidirectional and directional rms delay spread for a nlos urban microcell scenario. fig. 6. directional rms delay spread for mimo system in los and nlos urban microcell scenario. the ple confidentially describes the environment where the tx and rx are situated. it is an important parameter to indicate the propagation environment nature. in figure 7, at 73ghz, the ple for the mimo system in omnidirectional los and nlos urban microcell scenario is shown. its values in los environment range between 2.6 and 1.8 which manifests a stronger power profile, while in nlos environment, its values are between 3.1 and 4.6, leading to a weaker power profile. additionally, figure 7 shows that the ple is more stable for los, especially for longer distances between the tx and rx, whereas less stability is shown for the nlos case even for higher communication distances. the received power for mimo and massive mimo systems is illustrated in figure 8. this figure indicates that the received power is inversely proportional to the distance between tx and rx. as the distance increases, the path attenuation loss also increases which causes the signal power to diminish. on the other hand, for smaller separation distances between tx and rx, both mimo and massive mimo behave in an approximately similar way for los and nlos. however, for longer distances, the massive mimo system outperforms the mimo system because the power in the massive mimo has a very narrower beam than in the mimo system, which means more active antenna means, more focused energy, and thus less attenuation. figure 8 also shows that the average improvement of the received power in massive mimo compared to mimo is roughly 14% for long distances between 300 and 500m. furthermore, massive mimo system in los provides better performance than nlos. fig. 7. ple for mimo system in omnidirectional los and nlos urban microcell scenario. fig. 8. received power for mimo and massive mimo systems in omnidirectional los and nlos urban microcell scenario. fig. 9. small scale pdps at 73ghz in umi los with 300m terrestrial separation and 4×4 mimo system. figures 9-12 show the small scale power delay profile (pdp) of the omnidirectional antenna using mimo-los, mimo-nlos, massive mimo-los, and massive mimonlos systems respectively. in figures 9 and 10, it can be seen that there are 4 groups of omnidirectional components received at the rx antenna and separated according to a specific value of the wavelength λ. the antenna spacing of tx or rx is adjusted to be 0.5λ even in the case of massive mimo. the 4 groups are caused by the fact that the rx uses 4 antenna elements for a 4×4 system. from figures 9 and 10 it is also observed that the received power (dbm) decreases as propagation time delay rms increases and that there is a noticeable gap between different multipath components as rms delay spread increases. also, due to the fact that the rx uses 64 antenna elements for engineering, technology & applied science research vol. 11, no. 4, 2021, 7417-7423 7422 www.etasr.com shamsan: statistical analysis of 5g channel propagation using mimo and massive mimo technologies the 64×64 system, as illustrated in figures 11 and 12, it can be realized that there are 64 component groups at the rx antenna. fig. 10. small scale pdps at 73ghz in umi nlos with 300m terrestrial separation and 4×4 mimo system. fig. 11. small scale pdps at 73ghz in umi los with 300m terrestrial separation and 64×64 massive mimo system. fig. 12. small scale pdps at 73ghz in umi nlos with 300m terrestrial separation and 64×64 massive mimo system. as a comparison, it is worth noticing that the strongest signal power for the 4 systems can be arranged in descending order as follows: (i) massive mimo-los (figure 11), (ii) mimo-los (figure 9), (iii) massive mimo-nlos (figure 12), and (iv) mimo-nlos (figure 10). moreover, in the case of nlos for both mimo and massive mimo, it is noticed that less number of components in each group will be received at the rx as shown in figures 10 and 12, due to the fact that in the nlos environment there are many blockage materials that act as signal attenuators and add losses to the signal power which in turn reaches the rx with very low power, such that it can not be detected. in figures 9 and 11, there are a lot of components in the case of los environment because no blockage material disturbs the signal power when it travels from the tx to rx. this environment does not impact highly the signal power, thus many components arrive to the rx with higher magnitude than the one in the case of nlos situation. vii. conclusion this paper applied the mimo and massive mimo techniques to analyze the 5g propagation channel at 73ghz in an urban microcell scenario. the two systems, 4×4 mimo and 64×64 massive mimo, have been assumed to examine the channel characteristics within two environment types, los and nlos. extensive simulations have been carried out through the monte carlo approach-based nyusim tool. the findings showed that the received power in 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[26] a. a. alzamil, "assessment of uplink massive mimo in scattering environment," engineering, technology & applied science research, vol. 10, no. 5, pp. 6290–6293, oct. 2020, https://doi.org/10.48084/ etasr.3743. engineering, technology & applied science research vol. 8, no. 3, 2018, 2998-3003 2998 www.etasr.com aman et al.: mitigating the adverse impact of un-deterministic distributed generation on a … mitigating the adverse impact of un-deterministic distributed generation on a distribution system considering voltage profile muhammad aamir aman electrical engineering department iqra national university peshawar, pakistan sanaullah ahmad electrical engineering department iqra national university peshawar, pakistan babar noor electrical engineering department iqra national university peshawar, pakistan fazal wahab karam electrical engineering department, comsats university, abbottabad, pakistan abstract—electric power systems are enforced to operate near to their stability limit due to the fast increase in power demand. therefore, voltage stability has become a primary concern. the main cause of voltage variations is the imbalance between generation and consumption. in order to mitigate variations in voltage profile, most of the modern electric power systems are adopting new emerging technologies such as distributed generation (dg). validation of standard voltage optimization is a difficult task when dg is integrated to medium and low voltage networks. integration of dg will have diverse impacts on voltage levels when connected un-deterministically to the electric distribution system. this paper analyzes both the impacts of undeterministic large and small size dg on voltage profile. feasible solutions by incorporating reactors and increasing cross sectional area of cables, variation in voltage profile were mitigated. detailed simulations were performed in etap by modeling and evaluating kohat road grid station situated in peshawar, pakistan. the results anticipated that this approach can be useful to ensure standard voltage profile and better utilization of undeterministic dg units. keywords-electric power system; distributed generation; voltage profile; synchronous; induction; generator i. introduction as energy demand increases, the complexity of power system networks also rises [1]. distributed generation (dg) is steadily becoming a viable option. dg is generation at distribution level which can be classified into two major groups, renewable (non-conventional) and non-renewable (conventional) energy sources [2]. voltage control equipment in the distribution network mostly considers unidirectional power flow, from the transmission network to step down substations and then to the low voltage distribution network. voltage may drop from the standard level due to different factors like line losses or line impedances. injecting dg on the distribution system may have a significant impact on power flow, voltage profile, and fault current levels. voltage is increased due to the power generated by dg injected in the distribution system, which may cause variation in the voltage profile [3]. by injecting dg, power flow becomes bidirectional. the impact depends upon the placement and size of the dg unit. power system operation might be harmfully affected by installing a dg unit, if definite least possible values for control, injection and location are not retained. for positive impacts, dg must be appropriately synchronized with the operational system and feeder scheme. integration of dg and its impact on the system is relative to feeder demand and capacity therefore the coordination of dg with the system must be optimized to avoid these issues [4]. this study demonstrates the impact of distribution system components on voltage profile violation caused by dg integration. this study is validated through etap. six busbar distribution systems are selected as test cases, which are modeled and analyzed in etap. two cases are formulated using un-deterministic small and large size dg units. firstly, cross sectional area of conductors is increased and voltage profile is evaluated, considering the injection of a small size dg unit. secondly, reactors are installed to analyze its effect on voltage profile considering a large size dg unit. ii. dg impact on distribution system dg supports voltage rise at the termination of the feeder. though, where the dg is introduced, it may raise the voltage above the standard limits. voltage may be greater at the consumer amenities than on the primary side of the distribution transformer and may even go above the voltage higher limits. this means that both high and low service voltage can take place due to the mismatch of dg with the radial power stream. an unacceptable voltage profile is produced, when a small extent of dg power is connected at the wrong location, while a very huge quantity of dg power permits satisfactory operative conditions. so, for better voltage profile dg units must be placed at the optimal location. injection of dg may cause negative impacts on the system e.g. voltage rise issues. the nondeterministic or probabilistic dgs are installed at the client’s location. their parameters such as optimal location, size, and type are not known. injecting a huge amount of undeterministic dgs to the system causes problems regarding voltage rise issues. erratic operation may cause too wide voltage variation. this variation is undesirable and must be kept within the prescribed limits (i.e. declared voltage ±6%).voltage regulating equipment is installed at different locations to achieve this limit. different solution methods are engineering, technology & applied science research vol. 8, no. 3, 2018, 2998-3003 2999 www.etasr.com aman et al.: mitigating the adverse impact of un-deterministic distributed generation on a … proposed by various researchers. there is a huge amount of elements between a power plant and customers’ premises. voltage control equipment’s are used for two reasons at more than one location in the system. the first reason is that in the transmission and distribution system there is a significant voltage drop due to the widespread power network and the second reason is the divergent load characteristics of the numerous circuits of the power system. this voltage control equipment may be installed with generators in series, or with each feeder in series or even with bus bars. in this research work, reactors are installed at different locations to minimize voltage rise problems. reactors are used to limit the voltage level by adding additional reactance to the system. compared to ohmic resistance, these reactors are designed with a coil with large inductance. the reactor’s winding must be solidly braced. system efficiency is changed in a very small amount if a small reactor resistance is added to the system. inclusion of dg can impact the system voltage profile. injection of dg can improve the voltage where the voltage dip and blackout are of concern for service providers. however dg may complicate the equipment used for regulation and deviate the voltage above or below acceptable limits. in this paper, dg is injected on a radial distribution system and its impact is analyzed. the dg unit is injected on locations where the voltage profile is not that good. researchers showed that inappropriate selection of dg size and location may have adverse impact on the system [5]. dg location and load parameters affect greatly the voltage profile of the system. when dg is operated in voltage control mode the feeder reactance is negligible [6]. it is necessary for utilities to choose an optimum location for dg injection so that the voltage profile will be improved and system losses will reduce [7]. iii. mathematical modeling and the newtonraphson method steady state analysis is used for power systems because of their slowly operating changing nature. transients occurred from disruption are assumed in the steady state as unchanging. the operation tool for the steady state analysis is known as power flow analysis. in load flow analysis the voltage magnitude and phase angle, flow of active and reactive power throughout the network at all buses can be find. different techniques are used for solving the power flow equations, newton-raphson method is discussed below. taylor’s series expansion for a function of two or more variables is the basis for the newton-raphson method for solving load flow problems. the method begins the problem’s solution involving only two equations and two variables. then the extension of the analysis to the solution of load flow equation will be discussed. let us consider the equation of a function of two variables, z1 and z2 equal to a constant c1 as f1 (z1, z2) = c1 (1) similarly the second equation becomes f2 (z1, z2) = c2 (2) initially estimates of the solution of these equations is z1(0) and z2(0). the corrections ∆ (0) and ∆ (0) must be added to z1(0) and z2(0) for the correct solution. c1 = f1 (z1, z2) = f1 (z1(0) + ∆ (0), z2+ ∆ (0)) (3) c2 = f2 (z1, z2) = f2 (z1(0) + ∆ (0), z2+ ∆ (0)) (4) now the problem is to find ∆ (0) and ∆ (0). expanding (3) and (4) in taylor’s series we get: c1 = f1(z1(0), z2(0)) + ∆ (0) |(0) + ∆ (0) |(0) + ⋯ (5) c2 = f2(z1(0), z2(0)) + ∆ (0) |(0) + ∆ (0) |(0)+ ⋯ (6) partial derivatives of order greater than one will be neglected. so, writing (5) and (6) in matrix form will become: − ( ( ), ( )) − ( ( ), ( )) = ∆ ( )∆ ( ) (7) where partial derivatives of the square matrix are known as jacobian “j” or j(0) in this case. f1 (z1(0), z2(0)) is the calculated value of k1 for the estimated values of z1 (0) and z2 (0). if ∆c1 (0) is selected as the specified value of c1 minus the calculated value of c1 and also for ∆c2 (0). ∆ ( )∆ ( ) = j (0) ∆ ( )∆ ( ) (8) for a total of n buses the calculated voltage at any bus a where pa and qa are given as: va = [ – ∗ -∑ ] (9) is obtained from the following equation: pa – jqa = ( +∑ ) va* (10) where n≠a. if n is permitted to equals to a, pa – jqa = va* ∑ (11) pa = va* ∑ (12) qa = img {va*∑ } (13) equation (13) evaluates reactive power qa for the better previous voltage values at the buses. qa is substituting in (10) to get a new ya. voltage at bus and line admittances in polar form is: va = |va| < ; vn = |vn| < ; = |ykn| < by substituting these in (11) we get: pa – jqa = ∑ < + (14) pa = ∑ cos ( + ) (15) and qa = -∑ sin ( + ) (16) now, by comparing (8) with the power system, ∆ ( )= ∆ = – ∆ ( )= ∆ = – engineering, technology & applied science research vol. 8, no. 3, 2018, 2998-3003 3000 www.etasr.com aman et al.: mitigating the adverse impact of un-deterministic distributed generation on a … ∆ ( ) = ∆ ( ) ∆ ( ) = | ( )| the jacobian “j” contains the partial derivative of real and reactive power. the basic iterative procedure is as follows:  begin with the preceding case result.  calculate the divergence and end it where the bound of acceptance value outstrips.  power flow calculation for the jacobian, update value and return to step ii. iv. analysis of test feeder circuit an 11kv residential radial distribution feeder located at kohat road peshawar, khyber pakhtunkhwa, pakistan is considered for analysis. electrical transient analyzer program (etap) is used for analysis of the selected radial distribution feeder. etap is user friendly, and has the capability to perform analysis related to distribution generation. this 11 kv radial feeder is energized from a bus bar of 132 kv with the help of a 31.5/40 mva transformer. the source for this radial feeder is the 132 kv bus bar and is shown as power grid with a short circuit capacity of 2100 mva. the base for these calculated data is 100 mva. seven distribution transformers are connected to seven different sizes of lumped loads with a lagging power factor of 0.85 in this radial feeder. for interconnection of buses with each other, cables are used. the type of cable used in this system is 3-phase overhead aluminum conductor having insulation of cross-linked polyethylene. the length for each conductor is taken as 50 0m with a cable class percentage of 100%. v. modeling of distributed generation units synchronous and induction generators are used as dg units in this research paper. these units will be operated and analyzed under different conditions. to analyze the effect of dg unit on the radial distribution system, different unit types have been placed at different locations. a. without dg unit. in this case the system analysis will be conducted without dg injection to the system. this analysis will act as a reference case for the other cases. the impact of dg on residential distribution system will be studied. b. injecting a small amount of un-deterministic dg units. in this case a small amount of dg units will be injected in the system and its impact will be analyzed. for improvement of system voltage profile the cross-sectional area (csa) of the conductors will vary and its impact on the system will be analyzed. by increasing csa of the conductor the resistance of the conductor decreases and hence the voltage profile will improve at the bus bars. this case consists of two situations, the worst situation is taken first i.e. by injecting small undeterministic dg units and no change in the conductor’s csa and existing csa mm2 are taken. in the second case, the csa of the conductors has been upgraded by increasing the size of the cross-sectional area. c. injecting a huge amount of un-deterministic dg units. by injecting a huge amount of un-deterministic dg units to the distribution system, the impact on voltage profile will be analyzed. in this case reactors are used for the improvement of voltage profile. reactors are designed as coils with high inductance. vi. test cases a. case-i the results of load flow analysis of the radial distribution network in case-i are shown in figure 1. no dg unit is injected to the system. as mentioned above, this case is taken as a reference for the other cases. fig. 1. with no dg unit injection to the system. b. case-ii in this case a small dg unit will be injected in the system and its impact will be analyzed. when a small dg unit is injected in the system there is no change in the voltage profile, so for the betterment of voltage profile the size of the conductor csa is increased. two situations are taken in this case: at first the worst situation is taken i.e. by injecting the small dg unit in the existing system with no change in the conductor csa while in the second case the size of the csa will be upgraded by increasing the size of cross-sectional area of the conductor. in the following manner the voltage profile will be analyzed. 1) injecting a small amount of un-deterministic dg units and keeping existing csa mm2 for the radial distribution system in this situation the dg unit is injected in the existing system with no change in the size of the csa of the conductors used in the radial distribution system. the load flow analysis results for the first situation of case-ii are shown in figure 2. the load requirement is fulfilled by the power grid and undeterministic dg. this is taken as reference for the second situation. real time condition and voltage levels at different engineering, technology & applied science research vol. 8, no. 3, 2018, 2998-3003 3001 www.etasr.com aman et al.: mitigating the adverse impact of un-deterministic distributed generation on a … bus bars are shown in figure 2. in table i the drops in voltage from one bus to another are shown as percentages. fig. 2. injecting dg without change in the cross-sectional area of the conductors. table i. case-ii: bus voltage in percentage of the system with existing csa branch/ circuit id % bus voltage from to line 12 100.0 96.6 line 23 96.6 93.9 t1 96.6 93.3 line 34 93.9 92.0 t2 93.9 90.6 t3 93.9 90.1 line 45 92.0 90.7 t4 92.0 88.3 line 56 90.7 90.4 t5 90.7 87.2 t6 90.7 87.9 t7 90.4 87.1 2) upgrading csa in this situation the system has been upgraded by increasing the size of the csa of the conductors. the csa is taken as 185mm2 for the conductors used in the radial distribution system. the load flow analysis results are shown in figure 3. the load requirement is fulfilled by the power grid and the undeterministic dg unit. real time condition and levels of voltage at different bus bars are shown. comparing voltages from the first situation, voltage profile is much better and clear improvement can be seen. in table ii the drop in voltage from one bus to another are shown. voltage profile is much better and clear improvement can be seen. c. case-iii in this case, a huge amount of un-deterministic dgs is injected in the radial distribution network and its impact on the system is analyzed. two situations are taken in this case, in first the un-deterministic dgs are installed at busbar-3. this is recognized as the worst situation because it would produce voltage profile problem. in the second situation the rectors are connected across the busbar 2, 3 and across the transformer secondary and busbar3. fig. 3. cross-sectional area of the conductors are upgraded. table ii. case-ii: bus voltage in percentage of the system when upgrading existing csa branch/ circuit id % bus voltage from to line 12 100.0 99.2 line 23 99.2 98.6 t1 99.2 95.9 line 34 98.6 98.2 t2 98.6 95.4 t3 98.6 95.0 line 45 98.2 97.9 t4 98.2 94.7 line 56 97.9 97.8 t5 97.9 94.5 t6 97.9 95.2 t7 97.8 94.7 1) by injecting s huge amount of un-deterministic dgs at busbar-3 under this operating strategy the maximum dg output coincides with minimum load condition. this case is taken for the purpose that what will happen if consumers are freely allowed to install dgs on their premises. the load flow analysis results are shown in figure 4. real time condition and levels of voltage at different bus bars are shown. in table iii the drops in voltage from one bus to another are shown in percentage. 2) installing reactors to improve voltage profile the voltage profile is improved by installing reactors. reactors may be connected in series with the generators, in series with each feeder and in bus-bars depending on the requirement of the system. two reactors are placed here, the first one is connected in series with the secondary of the transformer and the second one is connected in series with line 23. the load flow analysis results are shown in figure 5. the voltage level at different bus bars is shown. the voltage profile engineering, technology & applied science research vol. 8, no. 3, 2018, 2998-3003 3002 www.etasr.com aman et al.: mitigating the adverse impact of un-deterministic distributed generation on a … is much better and clear improvement can be seen. in table iv the drops in voltage from one bus to another are shown. fig. 4. installing un-deterministic dgs at busbar-3. fig. 5. installing reactors for voltage improvement. vii. results and discussion in table v the real and reactive power, injected by the grid and dg units, is shown. a. voltage profile analysis when different types of dg units are injected to the system they cause different impact on voltage profile. 1) case-i no dg unit is injected in this case. there is clear decrease in voltage profile from source to load as shown in figure 6. the voltage level is decreased due to line impedance. table iii. case-iii: bus voltage in percentage of the system by injecting huge amount of un-deterministic dg units branch/ circuit id % bus voltage from to line 12 100.0 103.1 line 23 103.1 108.1 t1 103.1 99.9 line 34 108.1 107.7 t2 108.1 105.1 t3 108.1 104.7 t10 108.1 99.4 line 45 107.7 106.6 t4 107.7 104.4 line 56 106.6 106.5 t5 106.6 103.4 t6 106.6 104.0 t7 105.5 103.5 cable11 99.4 100.6 cable12 100.6 101.5 cable13 101.5 102.3 cable14 102.3 102.8 cable15 102.8 103.0 table iv. case-iii bus voltage by injecting huge amount of undeterministic dg units branch/ circuit id % bus voltage from to line 12 100.0 99.9 line 23 96.0 92.6 t1 99.9 96.6 x11 99.9 92.6 line 34 96.0 95.5 t2 96.0 92.8 t3 96.0 92.3 x9 96.0 90.1 line 45 95.5 95.1 t4 95.5 92.0 line 56 95.1 95.0 t5 95.1 91.6 t6 95.1 92.4 t7 95.0 91.8 cable11 78.4 85.8 t10 78.4 90.1 cable12 85.8 86.9 cable13 86.9 87.8 cable14 87.8 88.4 cable15 88.4 88.6 table v. injection of real and reactive power from dg units and grid case situations dg injected power grid injected power mw mvar mw mvar 1 1 0 0 6.805 4.449 2 1 1.5 0 7.045 4.436 2 1 1.5 0 6.637 4.460 3 2 25 -15.5 -9.411 26.469 3 2 25 -15.5 -4.209 34.057 2) case-ii in this case the small size un-deterministic dg unit is injected with no change in the size of the csa of the conductors used in radial distribution system in first situation, and in second situation the size of the csa of the conductor is increased. by increasing csa the resistance of the conductor is engineering, technology & applied science research vol. 8, no. 3, 2018, 2998-3003 3003 www.etasr.com aman et al.: mitigating the adverse impact of un-deterministic distributed generation on a … decreased and hence we get better results by improving voltage profile. the result obtained from both situations is shown in figure 7. the up gradation of csa shows the best voltage profile. 3) case-iii in this case a large amount of un-deterministic dg units is injected in the system. by doing so, the voltage level raises or sometimes it reduces below standards. in this case the voltage raises above the limit. reactors are used to level down the voltage profile. both results before and after the reactors installation are shown in figure 8. when reactors are installed the voltage profile is improved. fig. 6. radial feeder voltage arrangement. fig. 7. impacts of voltage profile by injecting un-deterministic dg unit and increasing csa of conductor. viii. conclusion and future work voltage stability is a prime utility responsibility. dg may increase or decrease the voltage level from standard limit depending upon the nature, size and placement of the dg unit. after injecting un-deterministic dg units to the distribution system and analyzing different cases, in this research work it is concluded that by increasing the csa of distribution cables the voltage level can be improved to standard voltage while introducing reactors can decrease the voltage level to standard voltage. csas of distribution cable are increased when the injection of dg units doesn’t affect the voltage profile while reactors are introduced when dg units increase the voltage level above the standard. in future, the impacts of different conventional and also un-conventional dg units can be analyzed considering harmonics and reliability. acknowledgment authors gratefully express their thanks to the electrical engineering department of iqra national university, pakistan for their assistance and support. fig. 8. impact on voltage profile by injecting un-deterministic dg units and installing reactors. references [1] m. o. alruwaili, m. y. vaziri, s. vadhva, s. vaziri, “impact of distributed generation on voltage profile of radial power systems”, 2013 ieee green technologies conference, denver, usa, pp. 473-480, ieee, 2013 [2] p. c. chen, r. salcedo, q. zhu, f. de leon, d. czarkowski, z. p. jiang, r. e. uosef, “analysis of voltage profile problems due to the penetration of distributed generation in low-voltage secondary distribution networks”, ieee transactions on power delivery, vol. 27, no. 4, pp. 2020-2028, 2012 [3] d. caples, s. boljevic, m. f. conlon, “impact of distributed generation on voltage profile in 38kv distribution system”, 2011 8th international conference on the european energy market, zagreb, croatia, pp. 532536, ieee, 2011 [4] q. sun, z. li, h. zhang, “impact of distributed generation on voltage profile in distribution system”, international joint conference on computational sciences and optimization, (cso 2009), sanya, hainan, china, pp. 249-252, ieee, 2009 [5] v. van thong, j. driesen, r. belmans, “interconnection of distributed generators and their influences on power sytem”, international energy journal vol. 6, no. 1 part 3, pp. 3-127−3-140, 2005 [6] l. ramesh, s. p. chowdhury, s. chowdhury, a. a. natarajan, c. t. gaunt, “minimization of power loss in distribution networks by different techniques”, international journal of electrical computer engineering, vol. 3, no. 4, pp.661-667, 2009 [7] m. aamir aman, s. ahmad, a. ul asar, b. noor, “analyzing the diverse impacts of conventional distributed energy resources on distribution system”, international journal of advanced computer science and applications, vol. 8, no. 10, pp. 390–396, 2017 microsoft word etasr_7-1_1391-1397.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1391-1397 1391 www.etasr.com liaghat and tavanpour: a study of the formation of velocity counter lines and secondary (spiral)… a study of the formation of velocity counter lines and secondary (spiral) flows in different cross sections of different arcs ali liaghat shiraz branch islamic azad university shiraz, iran nima tavanpour shiraz branch islamic azad university shiraz, iran abstract—the mechanical properties of flow are very complex in channel arcs. therefore, dynamic numerical models of fluids are considered effective tools in predicting such flow fields. in this study, the numerical model was validated by the measures of a uniform u-shaped arc with a width of 0.6 meter. then two similar u shaped arcs, divergent and convergent, were simulated by a three-dimensional numerical model with variable widths from 0.6 to 0.75 meters and 0.6 to 0.45 meters. validating the numerical model by measured data in the uniform 180-degree arc showed that the model can simulate the flow field in the uniform arc very well. results regarding several parameters such as rout of maximum velocity, maximum velocity line, water level variations, power of spiral flow, existence of a rotating cell are stated and discussed. keywords-arc; secondary flow (spiral); velocity counters; ssiim three-dimensional numerical model i. introduction simulation of flow patterns is the most interesting subject in river engineering and sedimentation studies [1]. predicting rivers’ behavior on bends is obviously the focus of interest, as most rivers have meandrous form. for meandrous rivers, flow patterns are too complex as flow mechanics has different characteristics on bends compared to straight channels. in general, forces influencing flows at a bend include centrifugal force due to non-uniformity of vertical velocity profile, and combine with flow curve, cross-sectional stresses, and radius gradient of pressure caused by lateral slope of water surface [2]. synchronous effects of such forces create a flow called helical flow. many studies have been performed to investigate the flow characteristics and patterns in 180° bends with solid beds, of which [3] is the earliest, but substantially criticized for setting the radial velocity component at zero. rozovskii [4] was among the first researchers who performed comprehensive studies in this field. the most important result rozovskii obtained was that the velocity distribution belongs to a 3-d flow, and that the velocity component exists in radius direction. mosonyi and gotz [5] were the first who paid attention to the manner of distribution of helical flow strength and its changes along channel. they showed that secondary flow can be well described by its strength changes. they reported the presence of second cycle of secondary flow near internal bend, which only occurs at b/h <10 ratios. leschziner and rodi [6] presented their 3-d numerical model by using the finite differences method. the most important result these researchers reported was the effect of lengthwise pressure gradient on flow pattern in swift bends. in [7], authors exercised the effect of secondary flow on depth-averaged equations by using stress diffusion matrix and studied flow pattern in 1800 bend with rigid bed through their 2-d numerical model. their research indicated the effect of secondary flow on the origin of maximum velocity along channel. booij modeled the structure of secondary flow in 1800 bend by using large eddy simulation method [8]. the most important point of his research was that disturbance turbulence k  model fails to model the rotation against direction of secondary flow near external wall. in [9], authors did extensive research in this field. in [10], authors developed a 2-d model to compute the diffusion term in convection equation of suspended sediments, which increase efficiency of 2-d models to simulate the secondary flows in channel bends. they studied the over-time bed evolution in 1800 river bends with ssiim 3-d model [10]. in [11], authors developed a 2-d numerical model which describes the hydrodynamic, sediment transportation and bed changes in river bends. in [12], authors investigated the flow characteristics such as effect of secondary flows on velocity distribution and path of longitudinal maximum velocity in 90o bends with constant width and solid bed. in their research several parameters (e.g., stream wise and vertical velocity profile, bed shear stress distribution, stream wise and span wise slopes of water surface and helical flow strength) were compared in 1800 divergent and uniform bends. ii. mathematical model and methods navier-stokes equations for viscous and turbulent noncompressible fluid flows include continuity equation (1) and momentum conservation equation (2) are written as follows [1]: ( )0 1, 2, 3 (1)i i du i dx = = engineering, technology & applied science research vol. 7, no. 1, 2017, 1391-1397 1392 www.etasr.com liaghat and tavanpour: a study of the formation of velocity counter lines and secondary (spiral)… 1 ( ), 1, 2, 3 (2)i ij ij i j j j u u u p u u j t x x d r r ¶ ¶ ¶ + = = ¶ ¶ ¶ where ui is the average velocity component in xi direction; ρ is the density of water; p is pressure; δij is the kroncker delta, which is 1 if i = j and 0 otherwise; and xi and xj are the general space dimensions. the last term in (2) is reynolds stress, which represents the transport of momentum that can be attributed to turbulence. the reynolds stress is often modeled with the boussinesque approximation: 2 ( ) . . (3) 3 ji i j t ij j i uu u u k x x dd r ru r d= + ¶ ¶ where ut is eddy viscosity k-ε model calculates the eddy viscosity as 2 (4)t k c   k is turbulent kinetic energy defined by 1 (5) 2 i jk u u= k is modeled as (6)ti k i i k j k k k u p t x x x u e s é ùæ ö¶ ¶ ¶ ¶÷çê ú÷+ = + -ç ÷ê úç ÷ç¶ ¶ ¶ ¶è øê úë û where pk is given by (7) ji i k t j j i uu u p x x x u æ ö¶¶ ¶ ÷ç ÷ç= + ÷ç ÷÷¶ ¶ ¶çè ø the dissipation of k is denoted ε, and modeled as 2 1 2 (8) t i k i i j u c p c t x x x k ke ee ne e e e e s é ùæ ö¶ ¶ ¶ ¶÷çê ú÷+ = + -ç ÷ê úç ÷ç¶ ¶ ¶ ¶è øê úë û in (4) through (8), cμ ’, σk, σε, cε1 and cε2 are empirical constants, which were determined experimentally to be 0.09, 1.0, 1.3, 1.44, and 1.92, respectively [13]. boundary conditions for the navier-stokes equation (e.g., boundary condition for inflow, outflow, the water surface and the bed/wall) are similar to the diffusion-convection equation. dirichlet boundary conditions have to be given at the inflow boundary, which is relatively straightforward for velocity. usually it is more difficult to specify the turbulence. to specify the eddy viscosity, it is possible to estimate the shear stress ( ) at the entrance bed using a given velocity. then, the turbulent kinetic energy k at the entrance bed is determined by: (9)k c     with the eddy viscosity ut and turbulent kinetic energy k at the bed, (4) gives the value of ε at the bed. if k is assumed to vary linearly from the bed to the surface, then (4), together with the profile of the eddy viscosity, can be used to calculate the vertical distribution of ε. a zero gradient condition was used for outflow boundary. the free surface is computed using a fixed-lid approach, with zero gradients for all variables. the location of fixed lid and its movement as a function of time and the water flow field are computed by pressure and bernoulli algorithm. the algorithm is based on pressure field. it uses the bernoulli equation along the water surface to compute the water surface location based on fixed point downstream of bend in this study. the wall law for rough boundaries [14] was used as a boundary condition for bed and wall: * 1 30 ln( ) (10) s u y u kk = where u* is the shear velocity, u is the velocity at the center of the grid cell closest to the bed, κ is a constant equal to 0.4, y is the distance from the wall to the center of the grid cell, and ks is wall roughness. iii. results and discussion a. verification of 3-d numerical model the experimental data is extract from a channel with 180o bend used in pirestani’s lab studies [15]. figure 1 show convergent and divergent 180o bends studied in this paper, which has a mesh size 91x91x7 in longitudinal, transverse and vertical direction, respectively. mentioned bend has two straight paths, upstream and downstream, which were 7.2 m and 5.2 m long, respectively. its wall and bed is made of plexiglas with wall roughness of 0.0001 m (ks=0.0001 m). the flow pattern was studied at a flow rate of 30 l/s and a water depth of 0.15 m at the channel entrance, and, in order to verify numerical modeling, the results from modeling in the bend with uniform 0.6m width were compared with pirestanie’s lab results [14], as shown in figures 2 to 4. it should be noted that in pirestani’s research, flow velocities were measured at different depths in 91 cross sections along the bend with a two dimensional portable emissions measurement systems (pems). a b fig. 1. grid sample used in this study (a) convergent bend and (b) divergent bend to find the optimal mesh size, grid independency investigations have performed. so that the mesh size has changed from 71x12x7 in longitudinal, transverse and vertical direction, respectively as a coarse mesh to finest mesh size 351x35x15. by comparison of maximum and minimum velocities, pressure and turbulent kinetic energy in different mesh finally the mesh size 91x91x7 was selected as the optimal engineering, technology & applied science research vol. 7, no. 1, 2017, 1391-1397 1393 www.etasr.com liaghat and tavanpour: a study of the formation of velocity counter lines and secondary (spiral)… mesh size. power low and second order upwind methods for discretization of convectional term were used. the result showed no significant difference between the velocity profiles calculated by two methods. there for in continue the power low method used. fig. 2. comparison of vertical velocity profile (continuous line) with measurement data (points) in 180o cross section. fig. 3. comparison of velocity profiles profile (continuous line) at the plane near water surface (h=0.145m) in different cross sections with lab data (points). fig. 4. comparison of velocity profiles profile (continuous line) at the plane near water surface (h=0.145m) in different cross sections with lab data (points). figures 2 through 4 indicate that velocity profiles calculated by numerical modeling are in complete agreement with labmeasured data. statistical indicators (e.g., erms and em) were used to compare values of calculated and measured velocities at a plane of h = 0.145 m: 2 1 1 [ ] (11) n rms m i p i i e v v n = = -å where erms is root mean square of error, em is mean error, n is number of measurement data, vmi and vpi are the values of the ith measured and calculated velocities, respectively. results of statistical comparison are presented in table i. the low values of erms and em in the table indicate numerical model simulates well flow field in uniform bend. table i. statistical indicator between calculated and measured velocities at plan near water surface cross section 170o 130o 90o 40o 10o statistical indicator 0.042 0.043 0.048 0.042 0.074 erms (m/s) 0.012 0.015 0.018 -0.009 -0.066 em (m/s) b. comparison of vertical velocity profiles in this paper, the results from a convergent channel bend with a width ranging from 0.6 m at the beginning of the bend to 0.45 m at the end of the bend, divergent channel bend with a width ranging from 0.6 m to 0.75 m were compared with those of a channel with uniform 0.6 m width in order to compare flow characteristics of uniform channels with divergent and convergent ones. vertical velocity profiles were taken into account on two cross sections, i.e. sections 45o, 135o (figure 5). at both cross sections vertical velocity profiles show lower values in divergent bend than in uniform and convergent one, because velocity will decrease in divergent bend due to bend width bend expanding and we have opposite of this situation in convergent bend. also, maximum and minimum of vertical velocity profile is seen at dimensionless distance of 0.75 m and 0.08 m from internal wall of channel. additionally, vertical velocity profiles at 45o cross section are close together for the three types of the bends, while at 135o cross section the difference between them is more significant. (b) 135o cross-section (a) 45o cross-section fig. 5. comparison of vertical velocity profiles at different cross sections of uniform, divergent and convergent bends. c. comparison of lengthwise velocity profiles in the bends figure 6 shows the trends of changes in lengthwise velocity profile at the plane near water surface for three types of bend channels. in all cross sections the values of velocity in divergent bend shows slower velocity than in the uniform bend and the uniform bend velocity is slower than convergent bend due to bend expanding and decreasing in discharge per unit width. this difference will increase with the distance from the beginning of the bend. also, lengthwise velocity profile have the same shape in three type of bends which shows that the maximum lengthwise velocity occurs near the internal wall at the beginning of the bend and after entering the bend, it migrates gradually toward the external wall. table ii discuses about comparison of differences between values of velocities in uniform and divergent bends and also uniform and convergent bends. in all cross sections we see more decreasing of lengthwise velocity in internal bend rather engineering, technology & applied science research vol. 7, no. 1, 2017, 1391-1397 1394 www.etasr.com liaghat and tavanpour: a study of the formation of velocity counter lines and secondary (spiral)… than external bend. this more decreasing of lengthwise velocity in internal bend rather than external bend is almost constant and about of 5% to 7% and with pasting from beginning of bend to end of bend, it hasn’t any considerable changes. (b) 90o cross-section (a) 40o cross-section (d) 180o cross-section (c) 130o cross-section fig. 6. comparison of velocity profiles at plane near water surface (h=0.145m) for different cross section of uniform, divergent and convergent bends. table ii. comparison percentage of lengthwise velocity difference between bends at plan near water surface cross section 180o 130o 90o 40o bend cross section 21% 19% 14% 8% internal bend 5% 12% 9% 3% external bend divergent 27% 24% 19% 10% internal bend 19% 15% 13% 7% external bend convergent figure 7 shows the path of occurring maximum velocity at the plane near water surface in different bends. as shown, maximum velocity cuts the centerline of channel at about 55o cross section within uniform bend and this occurs at about 30o40o cross section within convergent channel, while this occurs at about 50o cross section within divergent channel and its difference with uniform one is the maximum velocity line has a smoother path in the uniform rather than in the divergent bend. this means that in the divergent bend, maximum velocity line cuts the centerline of channel in a straight mood and faster than other bends tangent with external wall of bend in 80o cross section and stay in this situation to end of bend. in addition, the maximum velocity line is tangent to the external wall of uniform and convergent bend between 90o to 100o and stay in this situation to the end of bend. this indicates that in convergent bend, centrifugal force dominates over flow field increases at less distance from the beginning of the bend. in other words, effect of lengthwise pressure gradient dominates to effect of secondary flow strength at a less distance from beginning of the bend, so maximum velocity disposes toward external wall at closer distance from the beginning of the bend. moreover, in both cases, maximum velocity becomes tangent to the bend external wall near 100o cross section and remains in this state until it reaches the end of the bend. fig. 7. comparison of maximum velocity paths at plane of h = 0.145 m for uniform, divergent and convergent bends. d. comparing helical flow strength helical flow strength is employed to examine the trend of secondary flow dissipation along channels. this concept was defined by mosonyi and gotz (1973) as (13) [5]: 2 2 (13)sp v da i u da = ò ò where u and v are lengthwise and widthwise velocity components respectively, and da is area of each cells. also, a program is developed for calculating helical flow strength in vb language. figure 8 indicates the changes of helical flow strength along bends. regarding this figure, for three types of channels, the strength of helical flow reaches its maximum value at about 60° cross section, and this section is the same area where secondary flow dominates lengthwise pressure gradient, resulting in transverse transfer of lengthwise momentum. after secondary flow grows and reaches its perfect growth at 60° cross section, the strength of helical flow assumes a decreasing trend. also, because divergent channel lengthwise velocity is lower than the uniform one and lengthwise velocity in uniform channel is lower than the convergent one along the bed, denominator in (13) is longer for channels with convergent bends; as a result the maximum helical flow in divergent, uniform and convergent bend is higher respectively. also, the maximum of helical flow strength in uniform channel is 10.55% lower than divergent one. fig. 8. changes of helical flow strength along bend at flow rate of 30 l/s. engineering, technology & applied science research vol. 7, no. 1, 2017, 1391-1397 1395 www.etasr.com liaghat and tavanpour: a study of the formation of velocity counter lines and secondary (spiral)… e. comparing water surface lengthwise and widthwise slopes in figure 9, changes of longitudinal slope of water surface were shown for external wall, center line and internal wall of bends. in all of channels, longitudinal slope of water surface forms before reaching the bend. this phenomenon is caused by the change in lengthwise momentum movement direction due to flow entering into the bend, causing a short interval to be affected before the bend entrance. then, once the bend is reached, water surface faces relative positive and negative changes at the external wall and the internal wall, respectively, due to the effect of the centrifugal force. in all of channel at about 30° cross section, the trend of water surface rising at the external wall is positive, then it begins to decrease, and reaches near zero after the curve, in all cases. the water surface varying trends are clearly different for the channels. the range of water surface elevation changes is much wider in the convergent channel than in the uniform channel. more decreasing in water level in convergent channel rather than uniform one is due to effect of narrowness on flow. with decreasing of channel width, the discharge rate per unit of cross section will increase and water level is decreasing considering specific energy diagram. also, water level changes in the uniform and convergent channel is decreasing (negative longitudinal steep) and it's increasing for the divergent channel (positive longitudinal steep). this means that water level will generally decrease in the internal wall, center line and external wall of the uniform and convergent bend when moving forward, but will increase in the divergent one. table iii shows the decreasing percentage of water level in vicinity of external wall of uniform bend in comparison with divergent bend. as seen, the percentage of water level differences in these two bend will increase with moving from beginning of the bend. fluctuation changes can be observed on the water surface by careful looking at the flow pattern at the end of uniform bend (the enlarged part in figure 9), which is caused by the straightening of the bend path. this phenomenon was not observed at the exit of the convergent and divergent bend. it can be seen from figure 10 that the widthwise elevation difference of the water surface occurs before the beginning of the bend. such an elevation difference increases after the flow enters the bends and decreases as the flow approaches the exit of the bend, reaching zero shortly after the flow exits the bend. fig. 9. trend of lengthwise water surface changes at internal and external walls of uniform, convergent and divergent channels d = distance from the beginning of channel (m), h*= dimensionless water depth ratio. table iii. decreasing percentage of longitudinal water surface level for external wall of uniform bend in comparison with uniform bend cross section decreasing water level (%) bend cross section (o) 0.1 0 0.2 10 0.3 20 0.4 30 0.5 40 0.5 50 0.6 60 0.7 70 0.8 80 0.8 90 0.9 100 1.0 110 1.1 120 1.2 130 1.3 140 1.3 150 1.4 160 1.5 170 1.6 180 fig. 10. lengthwise changes of transverse water surface elevation difference (ds*), d = distance from the beginning of channel (m). at the beginning of the bend, the widthwise water surface elevation difference is larger in the divergent, uniform and convergent channel, respectively. at the end of the bend, this amount is larger in the uniform, convergent and divergent channel, respectively. uniform bend have an almost same widthwise water surface elevation difference, from beginning to end of the bend in channel. f. comparing flow lines at different levels at flow length as can be seen in figure 11, the pattern of flow lines are almost the same for all of bends but with moving toward the end of divergent bend, flow lines take distance from each other and it shows the decreasing in discharge per unit of width. opposite of this situation take place in convergent bend. for the all of channels, the path of stream lines moves toward the external wall of the channel at the plane near the water surface. water particles begin to move from the internal wall of the bend entrance, proceed toward the external wall, and ultimately strike against the channel’s external wall downstream. the pattern of stream lines is slightly affected by the secondary flow at this channel’s average-depth plane, and nearly follows its curve. at the plane near the bed of the uniform channel, the engineering, technology & applied science research vol. 7, no. 1, 2017, 1391-1397 1396 www.etasr.com liaghat and tavanpour: a study of the formation of velocity counter lines and secondary (spiral)… pattern of stream lines excessively deviates toward the internal wall of the bend and water particles do not follow the bend. therefore, if there were mobile particles on the bed of the bend, it is expected that they would be washed out downstream toward the internal wall. at the entrance of the bend, the rate of particles’ deviation at the plane near the bed is higher than that near the water surface, the reason for which is the presence of one-way flow toward the internal wall at the channel bed as well as the higher intensity of secondary flow at lower flow levels than at upper ones. as can be seen in the channel with a convergent bend, the overall pattern of stream lines is almost identical to that of the channel with the uniform bend, except that in the convergent bend, due to gradual reduction of the channel width and increasing discharge per unit of width, the stream lines move closer together. (a) uniform channel (b) convergent channel (c)divergent channel fig. 11. comparison of stream lines in uniform and convergent channels bends. g. comparison of bed shear stress distribution although the study of bed variation requires concurrent examination of fluid flow and bed sedimentation as well as their interaction, it is possible to predict erosion and sedimentation patterns for mobile beds by taking the distribution of bed shear stress into account. as can be seen in figure 12, there is a region of maximum shear stress in both uniform and convergent channels from which mobile bed particles begin to move shortly after the experiment is initiated. the reason for the creation of such a high-stress region is a high-velocity gradient existing here, which is caused by movement of a high-velocity core toward the external wall and its expansion at the plane near the bed. this point can be well interpreted by the changes in the high-velocity core at the 180° cross-section. as figure 12 indicates, at the end of the bend, bed shear stress exhibits higher values in convergent channel and subsequent straight channel than in the same region of channel with uniform bend; the value of maximum bed shear stress is longer in convergent bend than in uniform bend. the reason for that is nothing but the flow impressionability from channel's gradual narrowing. that is, lengthwise flow velocity; hence bed shear stress increase due to this section narrowing. (a) uniform channel (b) convergent channel (c) divergent channel fig. 12. comparisons of bed shear stress in uniform and convergent bends for flow rate 30 l/s. also, it can be observed that width and length of the region with high bed shear stress are larger at the end of convergent bend than those at the same region of uniform bend. in addition, more attention to distribution of high velocity core at the bottom of channel of this region indicates the mentioned changes in bed shear stress be expected for convergent channels. the region with high bed shear stress which seen at the middle of the uniform bend is not seen in channel with divergent bend. the reason for that is decreasing of velocity due to effect of channel expansion. iv. conclusion in this study, the numerical model was first verified using measured data on the bend with a uniform bend width. statistical comparison of the calculated and measured velocities at a plane near the water surface shows that the maximum erms and em are equal to 0.074 m/s and –0.066 m/s, respectively, indicating good agreement between measured and calculated velocities in the uniform bend. flow characteristics and patterns were compared in the uniform, convergent and divergent 180º bends. velocity profile shows higher lengthwise velocity at the 45º and 135º cross-sections in convergent, uniform and divergent bend, respectively. for the convergent channel, the maximum velocity path crosses the channel centerline near the water surface (h = 0.145 m) at about the 30º to 40º cross-section, while this occurs at about 50o cross section within divergent channel and about 55º for uniform one. the varying range of the water surface elevation is much wider for the convergent channel than for the uniform and divergent one. in general, the widthwise water surface elevation difference is larger in the convergent channel than in the uniform one due to the existence of larger centrifugal force in the convergent channel. also, water level changes in uniform and convergent channel is decreasing (negative longitudinal steep) and it's increasing for divergent channel (positive longitudinal steep). in all of bends, the strength of the helical flow reaches its maximum value at about the 60° crosssection. the helical flow strength is higher in the divergent, uniform and convergent channel, respectively, and the maximum of helical flow strength in uniform channel is 10.55% lower than divergent one. moreover, no counterrotating cell is observed at the 135° cross-section in convergent channel. in both uniform and convergent channels, a region with maximum bed shear stress is observed at the bend exit, but at the end of the convergent bend, bed shear stress shows higher values than those in the same region in the channel with engineering, technology & applied science research vol. 7, no. 1, 2017, 1391-1397 1397 www.etasr.com liaghat and tavanpour: a study of the formation of velocity counter lines and secondary (spiral)… a uniform bend. the pattern of flow lines are almost the same for all of bends but with moving toward the end of divergent bend, flow lines take distance from each other and it shows the decreasing in discharge per unit of width. opposite of this situation take place in convergent bend. references [1] n. rüther, computational fluid dynamics in fluvial sedimentation engineering. ph. d. dissertation, norwegian university of science and technology, trondheim, norway, 2006 [2] v. t. chow, open channel hydraulics, mcgraw-hill, new york, 1959 [3] c. e. mockmore, “flow around bends in stable channels”, transactions of the american society of civil engineers, vol. 109, no. 1, pp. 593618, 1994 [4] i. l. rozovskii, flow of water in bend of open channel, institute of hydrology and hydraulic engineering, academy of sciences of the ukrainian ssr, kiev, 1957 [5] e. mosonyi, w. gotz, secondary currents in subsequent model bends. proceedings of the international association for hydraulic research international symposium on river mechanics, asian institute of technology, bangkok, 1973 [6] m. a. leschziner, w. rodi, “calculation of strongly curved open channel flow”, journal of the hydraulic division, vol. 105, no.10, pp. 1297-1314, 1979 [7] h. c. lien, j. c. yang, k. c. yeh, t. y. hsieh, “bend-flow simulation using 2d depth-averaged model”, journal of hydraulic engineering, vol. 125, no. 10, pp. 1097-1108, 1999 [8] r. booij, “measurements and large eddy simulations in some curved flumes”, journal of turbulence, vol. 4, no. 1, pp. 8-16, 2003 [9] n. r. b. olsen, a three-dimensional numerical model for simulation of sediment movements in water intakes with multiblock option, department of hydraulic and environmental engineering, norwegian university of science and technology, trondheim, norway, 2006 [10] s. l. huang, y. f. jia, s. y. wang, “numerical modeling of suspended sediment transport in channel bends”, journal of hydrodynamics, vol. 18, no. 4, pp. 411-417. 2006 [11] l. begnudelli, a. valiani, b. f. sanders, “a balanced treatment of secondary currents, turbulence and dispersion in a depth-integrated hydrodynamic and bed deformation model for channel bends”, journal of advances in water resources, vol. 33, no. 1, pp. 17–33, 2010 [12] m. naji abhari, m. ghodsian, m. vaghefi, n. panahpur, “experimental and numerical simulation of flow in a 90° bend”, journal of flow measurement and instrumentation, vol. 21, no. 3, pp. 292-298, 2010 [13] b. e. launder, d. b. spalding, “the numerical computation of turbulent flows”, computer methods in applied mechanics and engineering, vol. 3, no. 2, pp. 269-289, 1974 [14] h. schlichting, boundary layer theory. 7th ed. new york: mcgrawhill, 1979 [15] m. pirestani, study of flow and scouring patterns at intake entrance of curved canals, ph. d. dissertation, azad islamic university, tehran, iran, 2004 microsoft word 16-3168_s_etasr_v9_n6_pp4956-4961 engineering, technology & applied science research vol. 9, no. 6, 2019, 4956-4961 4956 www.etasr.com khalifa & mahamid: causes of change orders in construction projects causes of change orders in construction projects walid m. a. khalifa civil engineering department hail university, saudi arabia and fayoum university, egypt khalifawalid@yahoo.com ibrahim mahamid civil engineering department prince mugrin university medina, saudi arabia imahamid@ymail.com abstract—change orders are usually issued to cover variations in the scope of work, material quantities, design errors, and unit rate changes. this study discusses variations in public construction projects in saudi arabia by investigating their causes, studying their effects on the project, identifying the beneficial parties, and suggesting remedies to alleviate the related problems. tasks included conducting a field survey via a questionnaire. it was determined that the top five causes of change orders from contractors’ view are: owner’s additional works, errors, and omissions in design, lack of coordination between construction parties, defective workmanship, and owner financial difficulties. keywords-change orders; variation orders; construction; contractors; consultants i. introduction in the last thirty years, saudi arabia has experienced a huge growth in the field of construction, due to the wealth created by the oil industry and the economic impetus it has given the country. this has resulted in very rapid growth and transformations during that period. the high living standards of the people of saudi arabia have generated many manufacturing and building employment opportunities. the growth of towns accelerated as a result of high population growth. large and complex projects have been built, attracting contractors and construction companies from all over the world. most of those contractors and their companies lack sufficient understanding of the social, cultural and physical environment of saudi arabia. this situation coupled with inexperienced owners has led to inadequate designs resulting in many changes to plans, specifications, and contract terms. the construction industry and its parties are associated with high degree of risk. risk in construction has been the object of attention because of time and cost overruns associated with construction projects [1]. the change orders were proved to be one of the main factors leading to cost and time overrun in construction projects. these changes are inevitable in any construction project. needs of the owner may change in the course of design or construction, market conditions may impose changes to the parameters of the project, and technological developments may alter the design and the choice of the engineer. the engineer’s review of the design may bring about changes to improve or optimize the design and hence the operation of the project. further, errors and omissions in engineering or construction may force a change. these and other factors necessitate changes that are costly and generally un-welcomed by all parties. consideration must be given to this problem from the early stages of the project. a contract change clause is added to define the way that owner, consultant, and contractor will handle changes. a procedure must be set to process a change from its conceptual development until it materializes in the field. given the fact that an adversarial atmosphere usually exists between the parties in the construction industry, a change must be managed well in order to minimize its cost, schedule and consequential effects that can lead to enormous cost and schedule overruns. a change order is a written order to the contractor, signed by the owner, and issued after execution of the contract, authorizing a change in the work or an adjustment in contract sum or contract time. changes in designs and contract documents usually lead to change in contract price or schedule. changes also increase the possibility of contractual disputes. in general, changes present problems to all parties involved in the construction process. there are many reasons for issuing construction change orders in large building construction contracts. it might be a result of further development of the owner’s requirements. it can be a result of non-availability, slow delivery of required materials or correction of contract document errors and omissions. identifying the causes of change orders is very important in order to avoid potential changes in future projects or to minimize their effects. the aim of this research is therefore to study the causes of construction change orders in construction projects in hail in saudi arabia. this study will assist both owners and contractors to plan effectively before starting a project and during the design phase to minimize and control changes and change effects. this study will also lay the foundation for further research on the subject. the objectives of the study can be divided into three categories. the first is to identify the main causes of construction change orders in saudi arabia. the second is to identify the severity of those causes. the third is to suggest remedies to alleviate related problems. ii. literature review change orders have long been an inherent part of the construction industry. the execution of a construction project without a change is a rare occasion. change normally arises as a result of some causes attributed to the different parties involved in the project execution. upon acknowledging its existence, the change – or variation is formally regularized by the issuance of a change order which is a document describing corresponding author: walid m. a. khalifa engineering, technology & applied science research vol. 9, no. 6, 2019, 4956-4961 4957 www.etasr.com khalifa & mahamid: causes of change orders in construction projects the scope of the change and its impact on both cost and/or time. if no agreement is reached between the parties of the project on the change, it turns into a claim or dispute that may negatively affect the execution of the project and curtail its chances of successful completion. change order is work added to or deleted from the original scope of work of a contract which alters the original contract amount or completion date [2]. the change has been defined as any deviation from an agreed upon well-defined scope and schedule [3]. the words “change order” conjure strong feelings of negativity for all involved in construction projects. owners do not like them because they generally feel they are paying for the mistakes of others. contractors may believe that change orders disrupt workflow and require additional paperwork and time. in other cases, contractors would find in change orders a mean to improve their outcome of the project. however, it is generally accepted that consultants, contractors, and owners agree that projects would be better without change orders. change orders strain the relationships of owners, engineers, contractors, subcontractors, and others involved in the construction process, also adding cost and schedule delay. changes on one project can also affect other unrelated projects by tying up resources that are committed elsewhere. negative relationships between the parties are another by-product of changes on a project. not only workflow is disrupted, but also trying to get quick responses quotes, shop drawings, and many other things required to get back schedule causes a strain on working relationships [4]. authors in [5] investigated 21 causes and 11 potential impacts of change orders. nine practices were reported to management and control of change orders. the study identified 11 important causes and 7 important impacts. it was further concluded that the consultant is the most responsible party for change orders. the overall average increase in total cost of construction projects due to change orders was found to be 11.3%. the research concluded that change of project scope due to owner requirements is the most important cause and cost overruns are the most important impacts of change orders in those projects. changes during construction of projects are inevitable in most construction projects and change orders are issued to correct or modify the original design or scope of work. the corrections or modifications are carried out for many reasons including changes in scope made by the client and as a result of change requests made by the consultant due to design errors or new findings. the contractor makes use of the different interpretations of the contract clauses or loose ends in the scope or design to improve his profit margin. most of change orders issued during the construction period are major causes of time and cost overruns, disruption, and disputes. in some cases, change orders cause confusion and lead to detrimental effect on the environment. yet, no unique method is available for avoiding or managing them effectively. the conventional approach is to include a percentage of the project cost as a contingency in the contract budget for their occurrence. authors in [6] studied the influencing factors on 31 highrise projects in indonesia and found that design changes is one of the most important factors causing time overrun. authors in [7] conducted a survey to determine and evaluate the relative importance of the significant factors causing delays in hong kong construction projects. the survey covered 83 previously identified delay factors. the study classified the reasons for delays based on the role of the parties in the local construction industry (clients, consultants or contractors) and the type of projects. the results indicated 5 principal causes of delays: poor site management and supervision, unforeseen ground conditions, low speed of decision making involving all project teams, client-initiated variations, and necessary variations of works. author in [8] found that user changes are one of the main causes of delay in 130 public projects in jordan. authors in [9] used a survey to identify the most important causes of delays in construction projects. the research revealed that the most important factors were: owner interference, inadequate contractor experience, financing and payments, labor productivity, slow decision making, improper planning, and subcontractors. author in [10] reported 5 key elements that burden projects: payments, authority, change orders, work schedule, and contract documents. author in [11] divided the causes of delay into two broad categories: excusable delays and nonexcusable delays. excusable delays were more oriented to the client or consultant causes, while nonexcusable delays were related to the contractor. design change was mentioned as a cause in excusable delays. the research suggested a list of remedies for the causes of both categories. authors in [12] carried out field survey and identified 6 construction conflicting factors pertinent in korean context. change order was the third factor causing conflict in construction projects. authors in [13] conducted a questionnaire survey in malaysia and identified 10 causes of delay. the first three causes were: contractor’s improper planning, contractor’s poor site management, and inadequate contractor’s experience. authors in [14] reported that changes in design as well as defects and correction in design as factors that resulted in cost and time overruns. authors in [15] conducted a field survey on time performance of different construction projects in saudi arabia. they identified 73 causes of delay in the 76 projects surveyed, but the most common cause of delay identified by all three parties (clients, consultants, and contractors) was the “change order”. authors in [16] studied the causes of 1,038 change orders issued for a national highway project in taiwan. their study revealed that the design insufficiency of geologic survey, site survey, and planning are the major causes of change orders. a method that can be used to solve potential lawsuit problems caused by change orders in construction projects was provided in [17]. the method developed the hybrid ann-cbr model (hacm), the ai branches of artificial neural networks (ann) and case based reasoning (cbr). the research was based on the litigation archives evaluating 31 cases. it is confirmed that the model hacm performs well especially for those medium sized construction projects. authors in [18] studied the variations in public construction projects in oman. the study determined that the client’s additional works and modifications to design were the most important factors causing change orders, followed by the nonavailability of construction manuals and procedures. the suggested remedial actions were the revision of registration of consulting offices would be the most important action followed by establishing standard documents for design procedures and building a national database about soil conditions and services. engineering, technology & applied science research vol. 9, no. 6, 2019, 4956-4961 4958 www.etasr.com khalifa & mahamid: causes of change orders in construction projects authors in [19] investigated the change orders for public and private construction projects in kuwait using a questionnaire surveying comprising 385 engineers representing the construction industry for the owners, contractors, and consultants. the results of the questionnaire indicated that the owner is the most responsible party causing changes due to change of plans by the owner which cause increase in project’s cost. the study put the first control as checking all changes to design documents. authors in [20] identified the most common factors responsible for cost escalations in construction industry in pakistan using a questionnaire survey for clients, consultants, and constructors. the study results showed that financial problems, slow payments, and inflation were the topranked identified factors responsible for cost escalation in the construction industry of pakistan. authors in [21] adopted a quantitative approach to find the main causes of time overrun in the construction of building project and its possible mitigation measures. the study revealed that the main causes of time overrun in construction projects can be concluded as the financial issues faced by the contractor, contractor’s inexperience, weather impacts, late delivery of materials, mistakes in design, shortage of skilled labor, incompetent subcontractor and mistakes in time estimation. mitigation measures were also proposed. iii. research methodology twenty one factors that might affect orders in construction projects were defined through a detailed literature review. the factors were tabulated into a questionnaire form. the draft questionnaire was discussed with some parties involved in construction projects to evaluate and modify its content. recommendations for minimizing change orders in construction projects were emphasized in view of the results of the study. a. questionnaire design the questionnaire was divided into two main parts. part i was related to general information. contractors and consultants were further requested to answer questions pertaining to their experience in the construction industry. part ii included the list of the identified causes of change orders in construction projects as shown in table i. table i. list of change order causes no. cause of change orders no. cause of change orders 1 owner’s additional works 12 value engineering 2 error and omissions in design 13 unavailability of skills 3 lack of coordination 14 defined project objective 4 defective workmanship 15 differing site conditions 5 owner financial difficulties 16 new government regulations 6 change of plans by owner 17 unavailability of equipment 7 contractor financial difficulties 18 substitution of material or procedures 8 changes in design 19 conflict between contract and document 9 safety considerations 20 technology changes 10 contractor desire to improve his financial conditions 21 weather conditions 11 owner change of schedule for each factor a question was asked: what is the degree of severity of this cause on change orders? degree of severity was categorized as follows: very high, high, moderate, low and very low (on 5 to 1 point scale). b. data analysis the information collected from the questionnaire was analyzed statistically in excel. the statistical methods that were used for calculating and presenting the survey results are discussed below. 1) ranking the suggested change orders causes in construction projects are ranked by the measurement of the severity index [22]. regarding the severity index, a formula is used to rank causes of cost overrun based on their impact level as identified by the participants: severity index (%) = ∑ a (n/n)∗100/5 (1) where, a is the constant expressing weighting given to each response (ranges from 1 for very low up to 5 for very high), n is the frequency of the responses and n is the total number of responses. accordingly, if all participants answer one factor to be of “no influence”, then the severity index is 0, which means that this factor is not relevant. on the other hand, if all answer that it is of “very high influence”, then the severity index is 100, which means that this factor is very highly relevant. table ii shows the possible ranges for the severity index and the corresponding impact level. the severity index for all causes was calculated according to (1) from contractors’ and consultants’ view. table ii. severity index scale and the corresponding impact level range (%) 0 < 20 20-40 40-60 60-80 80-100 impact level no influence very low low moderate high very high 2) importance rank correlation the correlation coefficient is used to measure the extent of which two variables are linearly related. spearman rank correlation factor was used to measure the degree of agreement between contractors and consultants on the severity and frequency index for factors affecting quality in construction projects. equation (2) was used for the calculation of the spearman rank correlation [23]: rs = 1 – [6∗∑d 2 /(n 3 – n)] (2) where rs is the spearman rank correlation coefficient (the agreement between contractors and consultants), d is the difference between the ranks on one variable and the ranks on another variable, and n is the number of causes. iv. results presentation and analysis a. general characteristics of respondents the questionnaire was sent out to a total of 40 contractors and 40 consultants, asking their contribution in ranking the identified 21causes in terms of severity using an ordinal scale. engineering, technology & applied science research vol. 9, no. 6, 2019, 4956-4961 4959 www.etasr.com khalifa & mahamid: causes of change orders in construction projects a total of 30 contractors and 25 consultants filled the questionnaire with response rates of 75% and 63% respectively. participating consultants and contractors have an average of more than 10 years of experience. simple random sampling was used to select the participants from an available list. b. ranking of change orders causes the causes under each group are ranked by the measurement of severity according to (1). the severity index and ranking of all investigated change orders causes in construction projects in saudi arabia from contractors’ view and consultants’ view are listed in table iii. the results show that both contractors and consultants ranked the followings as the top causes of change orders in construction projects in saudi arabia: 1. owner’s additional works 2. error and omissions in design 3. lack of coordination table iii. ranking of change orders causes cause contractors' view consultants' view severity index rank severity index rank owner’s additional works 82.03 1 86.67 1 error and omissions in design 79.23 2 83.33 2 lack of coordination 77.69 3 81.33 3 defective workmanship 76.14 4 67.33 7 owner financial difficulties 72.09 5 72.00 4 change of planes by owner 64.81 6 66.67 10 contractor financial difficulties 62.39 7 65.33 13 change in design 61.15 8 68.00 6 safety consideration 59.68 9 67.33 8 contractor desire to improve his financial conditions 58.91 10 66.67 11 owner change of schedule 58.52 11 67.33 9 value engineering 56.29 12 66.00 12 unavailability of skills 55.28 13 62.67 17 defined project objective 51.14 14 55.33 21 differing site conditions 51.06 15 70.00 5 new government regulations 50.18 16 65.33 14 unavailability of equipment 48.16 17 61.33 20 substitution of material or procedures 48.12 18 64.00 15 conflict between contract and document 46.74 19 63.33 16 technology change 46.32 20 62.67 18 weather conditions 46.25 21 62.00 19 c. statistical analysis statistical analysis and participants’ responses indicate that contractors and consultants highly agree on the severity of these causes e.g. owner’s additional works, which is the top ranked cause, has standard deviation of 0.79 and 0.79 from contractors and consultants, respectively. it also has coefficient of variation of 17% and 22.69% from contractors and consultants respectively. responses also show that most of the participants specify it as high affecting cause (i.e. 75% of the participating consultants and 80% of the participating contractors said that it has high to very high impact level). table iv presents the statistical analysis for the severity responses of change orders causes as assessed by contractors and consultants. the table contains the computation of the standard deviation (sn) and coefficient of variation (c.v.). table iv shows that the sn and c.v. have reasonable values. a visual indication got from the scatter diagram (figure 1) is that the data have good compactness, indicating that there is a good data consistency and agreement on the severity of the identified causes. figure 2 shows the sn of the identified causes for consultants’ responses. the figure shows good data compactness and a good internal consistency and agreement on the severity of the identified causes. visual comparison between figures 1 and 2 indicate that the contractors’ data has better compactness than the consultants’ data and so there is better internal agreement and consistency in the contractors input than the consultants’. table iv. statistical analysis for the severity of change orders causes cause contractors’ responses consultants’ responses sn c.v. (%) sn c.v. (%) owner’s additional works 0.79 17.00 0.78 22.69 error and omissions in design 0.98 34.40 0.68 30.50 lack of coordination 1.02 20.27 1.04 36.78 defective workmanship 0.81 40.33 1.34 38.14 owner financial difficulties 0.98 24.07 0.80 31.35 change of planes by owner 1.04 21.29 0.86 31.18 contractor financial difficulties 0.74 21.35 0.76 26.80 change in design 0.71 30.17 0.76 23.06 safety consideration 0.83 28.77 0.67 23.59 contractor desire to improve his financial conditions 1.17 34.28 0.78 36.74 owner change of schedule 0.89 31.14 0.63 31.27 value engineering 1.04 33.09 1.07 39.33 unavailability of skills 1.23 37.25 0.64 40.19 defined project objective 0.76 28.83 0.74 38.48 differing site conditions 0.91 53.76 0.74 43.13 new government regulations 0.95 47.34 1.00 33.87 unavailability of equipment 1.00 35.11 0.86 34.21 substitution of material or procedures 0.74 26.79 0.79 26.80 conflict between contract and document 1.11 36.59 0.70 39.45 technology change 0.87 41.20 1.10 37.98 weather conditions 0.98 26.99 0.85 32.13 fig. 1. mean value vs. standard deviation for contractors’ responses engineering, technology & applied science research vol. 9, no. 6, 2019, 4956-4961 4960 www.etasr.com khalifa & mahamid: causes of change orders in construction projects fig. 2. mean value vs. standard deviation for consultants’ responses d. rank correlation spearman correlation was used to determine the association among the parties included in this study. this test is used to find and compare how well the contractors and consultants agree on the severity of the causes affecting change orders construction projects. by applying (2), then: rs = 1 – ((6∗5808)/ (52 3 – 52)) = 0.75 (3) the value of rs is close to +1 which indicates good agreement between consultants and contractors on the ranking of change orders causes. v. summary and recommendations the causes of change orders in construction projects in saudi arabia were discussed in a field survey which studied the severity of the causes of change orders. twenty one causes of change orders were identified. the field survey included 30 contractors and 25 consultants. the top five severe causes of change orders as seen from contractors’ view were: 1. owner’s additional works 2. error and omissions in design 3. lack of coordination 4. defective workmanship 5. owner financial difficulties the top five severe causes of change orders as seen from consultants’ views were: 1. owner’s additional works 2. error and omissions in design 3. lack of coordination 4. owner financial difficulties 5. differing site conditions the value of the spearman’s rank correlation coefficient of 75% indicates that there is relative good agreement between contractors and consultants on the severity rank of the change orders causes. the statistical analysis of the data shows the following: (1) no participant response specified any cause with no influence on the change orders and (2) no causes had severity index less than 30%. these indicate that the identified causes are highly relevant to the problem of change orders in construction projects in saudi arabia. in spite of the good data consistency and agreement between the surveyed participants on the severity of the identified change orders causes, there are some sources of uncertainty, these might be: • misunderstanding of the questions by the respondents. • answering from different backgrounds, especially for consultants who have experience in many construction types such as building, utilities, etc. and so they may be biased to a construction type. the following remedial steps are recommended to be followed in order to improve the management of construction projects in saudi arabia: • a standard manual with a check list for design of projects should be developed to regulate all stages/steps including feasibility study, design, tendering, tender evaluations, and project awarding. this document should be implemented by a specialized governmental unit. • a specialized national technical unit should be established to study and evaluate overall construction practices in saudi arabia, to establish a construction procedure manual, and to follow-up on its implementation. • a national database system about soil, underground services, and weather conditions should be developed and made available for all concerned parties. • the registration of consulting companies and contractors should be reviewed from time to time to ensure the competence of their present technical and financial capabilities. • the client should prepare a well-defined brief document about his/her needs before entering the design stage. this can be done either by carrying out a feasibility study or circulating a questionnaire to the end users of the project and also conduct enough deliberation about the project’s final intended use. • clients should hire well-experienced technical staff members that can advise and help in decision making on a timely manner. • unlike what happened during the sudden rise in oil prices, the government should plan the projects in a fashion that does not lead to the contractors being overloaded by the number of projects with a shortage of qualified staff, especially engineers, which adversely affect the quality and time scheduling of works. further study can be conducted as: • similar studies can be done for other types of construction projects, such as road construction, utility, building construction, dam construction, and public construction. • detailed studies can be done in order to evaluate the involvement and effect of a specific party or resource of construction project on change orders in construction projects. engineering, technology & applied science research vol. 9, no. 6, 2019, 4956-4961 4961 www.etasr.com khalifa & mahamid: causes of change orders in construction projects acknowledgment this research was funded by the deanship of scientific research at the university of hail, saudi arabia, under the contract 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overrun in construction of building projects in pakistan”, engineering, technology & applied science research vol. 9, no. 1, pp. 3762-3764, 2019 [22] i. mahamid, a. bruland, n. m. dmaidi, “causes of delay in road construction projects”, journal of management in engineering, vol. 28, no. 3, pp. 300-310, 2012 [23] d. l. harnett, j. murphy, introductory statistical analysis, addisonwesley publishing company, 1975 authors profile walid m. a. khalifa received his bsc in civil engineering from cairo university of egypt in 1988, and his phd in water resources and environmental hydrology from cairo university in 2000. he is currently an assistant professor in hail university, saudi arabia, and fayoum university, egypt. his research interests include predictive water quality and hydrodynamics in surface water bodies and also in reinforced concrete water structures. ibrahim mahamid received his bsc in civil engineering from birzeit university of palestine in 2001, and his phd in construction engineering and project management from norwegian university of science and technology (ntnu), norway in 2011. he is currently an associate professor in prince mugrin university, saudi arabia. his research interests include construction management and surveying. engineering, technology & applied science research vol. 8, no. 3, 2018, 2985-2990 2985 www.etasr.com gharnali and alipour: mri image segmentation using conditional spatial fcm based on … mri image segmentation using conditional spatial fcm based on kernel-induced distance measure babak gharnali department of computer engineering islamic azad university, buinzahra branch buinzahra, iran babakgharnali.ai@gmail.com siavash alipour department of electrical and electronic engineering malek-ashtar university of technology tehran, iran siavash.alipur@gmail.com abstract—fuzzy c-means (fcm) clustering is the widest spread clustering approach for medical image segmentation because of its robust characteristics for data classification. but, it does not fully utilize the spatial information and is therefore very sensitive to noise and intensity inhomogeneity in magnetic resonance imaging (mri). in this paper, we propose a conditional spatial kernel fuzzy c-means (cskfcm) clustering algorithm to overcome the mentioned problem. the approach consists of two successive stages. first stage is achieved through the incorporation of local spatial interaction among adjacent pixels in the fuzzy membership function imposed by an auxiliary variable associated with each pixel. the variable describes the involvement level of each pixel for construction of membership functions and different clusters. then, we adapted a kernelinduced distance to replace the original euclidean distance in the fcm, which is shown to be more robust than fcm. the problem of sensitivity to noise and intensity inhomogeneity in mri data is effectively reduced by incorporating a kernel-induced distance metric and local spatial information into a weighted membership function. the experimental results show that the proposed algorithm has advantages in accuracy and robustness against noise in comparison with the fcm, sfcm and csfcm methods on mri brain images. keywords-image segmentation; mri; fuzzy c-means; noise i. introduction segmentation is an essential preprocessing step in computer-guided medical image analysis and diagnosis [1]. it helps doctors extract soft tissue regions from the respective organs of the human body for surgical decisions, abnormality detection and therapy management. mri is one of the most eminent medical imaging techniques and segmentation is a critical stage in the investigation of mri images. some factors complicate segmentation in medical images such as noise, normal anatomic variation, post-surgical anatomic variation, vague and incomplete boundaries, variation of contrast, inhomogeneities in the boundaries of the object of interest, motion blurring artifacts and so on [2]. to address these difficulties, clustering methods have been extensively studied and widely used in mis, with promising results [3]. among the different clustering methods devised in the past for medical images, the fuzzy c-means (fcm) algorithm has proved its efficacy. unlike hard clustering methods, like k-means algorithm, which assign pixels exclusively to one cluster, the fcm algorithm allows pixels to have relation with multiple clusters with varying degree of memberships. the main disadvantage of the fcm is that it is sensitive to noise and inhomogeneity which leads to erroneous segmentation results and undesired visual quality in case of mri brain image data. to overcome the problems of traditional fcm algorithm, many researchers modified the objective function by considering different criteria and presented more efficient and robust clustering algorithms [4-8]. authors in [9] introduced a class of robust non-euclidean distance measure for the objective function to enhance the robustness of the original fcm clustering algorithm and to reduce noise and outliers. enhanced fcm is proposed in [10] to fasten the segmentation process as well as to reduce the noise effect. to deal with the inhomogeneity problem, many algorithms have been proposed by adding correction steps before image segmenting [11,12] or by modeling the image as the product of the original image and a smooth varying multiplier field [13,14]. in [15], authors introduced a novel energy term based on multilayer structure of local intensity information to segment images with intensity inhomogeneity. authors in [16] proposed a region-based method using a local similarity factor to enhance the performance in segmenting images with intensity inhomogeneity and noise. authors in [7] proposed a conditional spatial fuzzy c-means clustering algorithm (csfcm) to address the fcm problem. the csfcm algorithm incorporates conditioning effects, imposed by some auxiliary (conditional) variables, as well as spatial information into the final membership function to improve robustness to the noise and inhomogeneity, providing thereby superior segmentation results. in this paper, we propose a conditional spatial kernel fuzzy c-means (cskfcm) clustering algorithm that can effectively segment mri brain images with the presence of noise and intensity inhomogeneity. the proposed algorithm incorporates a kernel-induced distance to replace the original euclidean distance in csfcm algorithm which leads to better results. it is shown that the proposed algorithm has better segmentation results on simulated or real mr images corrupted by noise and other artifacts than the standard algorithms such as csfcm. the rest of the paper is organized as follows: in section ii, we engineering, technology & applied science research vol. 8, no. 3, 2018, 2985-2990 2986 www.etasr.com gharnali and alipour: mri image segmentation using conditional spatial fcm based on … briefly introduce the cskfcm method to prepare the description of our proposed segmentation framework which is explained in section iii in detail. the experimental results and conclusions are presented in sections iv and v respectively. ii. background fcm clustering [17-19] is an unsupervised technique that has been successfully applied to feature analysis, clustering, and classifier designs in fields such as astronomy, geology, medical imaging, target recognition, and image segmentation. the fcm algorithm, where the correlation between the neighboring pixels is not considered, fails to generate accurate clusters. authors in [7] proposed a conditional spatial fuzzy c– means algorithm (csfcm) to address this issue. this mechanism ensures that if the neighboring pixels share similar characteristics, the center pixel should have higher probability of being grouped to the same cluster as the neighboring pixels. thus, the algorithm takes the level of involvement of a pixel into a cluster by considering its neighborhood. a local membership function is defined as follows: 𝑈𝑖𝑘 = 𝑓𝑖𝑘 ||(𝑥𝑖)−(𝑣𝑖)|| 2 𝑚−1/ ∑ ||(𝑥𝑘)−(𝑣𝑐)|| 2 𝑚−1𝐶 𝑐=1 () 𝑓𝑖𝑘 = ∑ µ𝑖𝑘𝑗∈𝑁(𝑥𝑘) 𝑀 () where fik is the conditioning variable which defines the level of involvement of pixel 𝑋𝑖 into the ith cluster by considering its neighborhood in a spatial domain. n(xk) is the square box having the pixel xi as its center and m is the number of pixels in the box. the membership value function of the csfcm is the combination of the global membership values μik and the local membership values uik as following: 𝑍𝑖𝑘 = (µ𝑖𝑘) 𝑝𝑈𝑖𝑘 𝑞 ∑ (µ𝑐𝑘) 𝑝(𝑈𝑐𝑘) 𝑞𝐶 𝑐=1 () 𝑊𝑖 = ∑ 𝑧𝑖𝑘 𝑚𝑁 𝑘=1 𝑥𝑘 ∑ 𝑧𝑖𝑘 𝑚𝑁 𝑘=1 () where p and q are the parameters to control the relative importance of both global and local membership functions. figure 1 displays the full explanation of the csfcm method. iii. proposed algorithm the csfcm algorithm employs squared-norm in similarity measurement which is effective in grouping “spherical” clusters. in fact, due to the use of nonrobust euclidean distance, it leads to nonrobust results. in this paper, based on the recognized power of the “kernel method” [20, 21] in recent machine learning community, we present a kernelized csfcm algorithm to address this issue. unlike the csfcm algorithm which adopts the squared-norm distance metric in the objective function, the proposed algorithm uses a kernel-induced metric and is shown to be more robust to noise and outlier than classical algorithms. here, we adapted a kernel-induced distance to replace the original euclidean distance in the csfcm. by replacing the inner product with an appropriate “kernel” function, one can implicitly perform a nonlinear mapping to a higher-dimensional feature space without increasing the number of parameters. the philosophy of the “kernel method” is that every (linear) algorithm that only uses scalar products can be extended to the corresponding (nonlinear) version of this algorithm which is implicitly executed in a higher feature space through kernels [22]. input: set values for the number of cluster c, the degree of fuzziness m=2, q=2, q=2 and the error ∈. 1. initialize randomly the centers of clusters 𝑉 𝑖 (0) . 2. initialize randomly the centers of clusters 𝑊 𝑖 (0) . 3. j=1. 4. repeat a. j= j+1 b. calculate membership values𝑈(𝑗) using the cluster centers𝑣 𝑖 (𝑗−1) as follows : µ𝑖𝑘 = 1 ||(𝑥𝑖 ) − (𝑣𝑖 )|| 2 𝑚−1/ ∑ ||(𝑥𝑖 ) − (𝑣𝑐 )|| 2 𝑚−1𝐶 𝑐=1 c. calculate conditional spatial membership values 𝑢 𝑖𝑘 (𝑗) using the cluster centers𝑣 𝑖 (𝑗=1) as follows : 𝑈𝑖𝑘 = 𝑓𝑖𝑘 ||(𝑥𝑖 ) − (𝑣𝑖 )|| 2 𝑚−1/ ∑ ||(𝑥𝑘 ) − (𝑣𝑐 )|| 2 𝑚−1𝐶 𝑐=1 where 𝑓𝑖𝑘 = ∑ µ𝑖𝑘𝑗∈𝑁(𝑥𝑘) 𝑀 d. calculate weighted membership values𝑧 𝑖𝑘 (𝑗) as follows : 𝑍𝑖𝑘 = (µ𝑖𝑘 ) 𝑝𝑈𝑖𝑘 𝑞 ∑ (µ𝑐𝑘 ) 𝑝(𝑈𝑐𝑘) 𝑞𝐶 𝑐=1 e. update joint cluster value 𝑊 𝑖 (𝑗) as:𝑊𝑖 = ∑ 𝑧𝑖𝑘 𝑚𝑁 𝑘=1 𝑥𝑘 ∑ 𝑧𝑖𝑘 𝑚𝑁 𝑘=1 f. update centers𝑉𝑖 (𝑗) as: 𝑉𝑖 = ∑ µ𝑖𝑘 𝑚𝑁 𝑘=1 𝑥𝑘 ∑ µ𝑖𝑘 𝑚𝑁 𝑘=1 5. until‖𝑊𝑖 (𝑗) − 𝑊 𝑖 (𝑗−1) ‖ <∈ 6. return the cluster center wi and membership value 𝑍𝑖𝑗 : 1,2, … , 𝐶; 𝑘: 1,2, … , 𝑁 fig. 1. the csfcm algorithm a kernel in the feature space can be represented as a function k below: 𝐾(𝑥, 𝑦) = 〈𝛷(𝑥), 𝛷(𝑦)〉 () where φ stands as implicit nonlinear map, and <φ(x), φ(y)> denotes the inner product operation. in the csfcm objective function, we express the distance function using inner product space. by constraining ourselves to the euclidean distance in ||φ(xk)-φ(vi)|| the squared distance is computed in the kernel space using a kernel function. here we use only the gaussian rbf kernel for simplicity. so, if we employ the nonlinear map with the gaussian kernel substitution in the csfcm objective function, the global and local membership function of csfcm can be rewritten as follows: µ𝑖𝑘 = 1 (1−k(𝑥𝑘,𝑣𝑖 )) 2 𝑚−1/ ∑ (1−k(𝑥𝑘,𝑣𝑐 )) 2 𝑚−1𝐶 𝑐=1 () engineering, technology & applied science research vol. 8, no. 3, 2018, 2985-2990 2987 www.etasr.com gharnali and alipour: mri image segmentation using conditional spatial fcm based on … 𝑈𝑖𝑘 = 𝑓𝑖𝑘 (1−k(𝑥𝑘,𝑣𝑖 )) 2 𝑚−1/ ∑ (1−k(𝑥𝑘,𝑣𝑖 )) 2 𝑚−1𝐶 𝑐=1 () where k(x, y)=φ(x)tφ(y) is an inner product gaussian rbf kernel function, and k(x, y)=exp[-(||x-y||2)/2σ2]. moreover, cluster centers can be rewritten as follow: 𝑣𝑖 = ∑ 𝑢𝑖𝑘 𝑚𝐾(𝑥𝑘,𝑣𝑖)𝑥𝑘 𝑛 𝑘=1 ∑ 𝑢𝑖𝑘 𝑚𝐾(𝑥𝑘,𝑣𝑖) 𝑛 𝑘=1 () according to (6)-(8), the data point is endowed with an additional weight 𝐾(𝑥𝑘 , vi), which measures the similarity between 𝑥𝑘 and vi based on their effects with respect to the pixels’ distance. it means that the kernel function gives more weight to nearer pixels and vice versa. the proposed cskfcm algorithm is be summarized in the figure 2. input: set values for the number of cluster c, the degree of fuzziness m=2, q=2, q=2 and the error ∈. 1. initialize randomly the centers of clusters v i (0) . 2. initialize randomly the centers of clusters w i (0) . 3. j=1. 4. repeat a. j= j+1 b. calculate membership valuesu(j) using the cluster centers𝑣 𝑖 (𝑗−1) as follows : µ𝑖𝑘 = 1 (1 − k(𝑥𝑘 , 𝑣𝑖 )) 2 𝑚−1/ ∑ (1 − k(𝑥𝑘 , 𝑣𝑐 )) 2 𝑚−1𝐶 𝑐=1 c. calculate kernel conditional spatial membership values 𝑢 𝑖𝑘 (𝑗) using the cluster centers 𝑣 𝑖 (𝑗=1) as follows : 𝑈𝑖𝑘 = 𝑓𝑖𝑘 (1 − k(𝑥𝑘 , 𝑣𝑖 )) 2 𝑚−1/ ∑ (1 − k(𝑥𝑘 , 𝑣𝑖 )) 2 𝑚−1𝐶 𝑐=1 where𝑓𝑖𝑘 = ∑ µ𝑖𝑘𝑗∈𝑁(𝑥𝑘) 𝑀 d. calculate weighted membership values 𝑧 𝑖𝑘 (𝑗) as follows : 𝑍𝑖𝑘 = (µ𝑖𝑘 ) 𝑝𝑈𝑖𝑘 𝑞 ∑ (µ𝑐𝑘 ) 𝑝(𝑈𝑐𝑘) 𝑞𝐶 𝑐=1 e. update joint cluster value𝑊 𝑖 (𝑗) as: 𝑊𝑖 = ∑ 𝑧𝑖𝑘 𝑚𝑁 𝑘=1 𝑥𝑘 ∑ 𝑧𝑖𝑘 𝑚𝑁 𝑘=1 f. update centers 𝑉𝑖 (𝑗) as:𝑣𝑖 = ∑ µ𝑖𝑘 𝑚𝐾(𝑥𝑘,𝑣𝑖 )𝑥𝑘 𝑁 𝑘=1 ∑ µ𝑖𝑘 𝑚𝐾(𝑥𝑘,𝑣𝑖 ) 𝑁 𝑘=1 5. until‖𝑊𝑖 (𝑗) − 𝑊 𝑖 (𝑗−1) ‖ <∈ 6. return the cluster center 𝑊𝑖 and membership value 𝑍𝑖𝑘 : 1,2, … , 𝐶; 𝑘: 1,2, … , 𝑁 fig. 2. the proposed cskfcm algorithm iv. experimental results this paper performs two groups of experiments to evaluate the proposed algorithm qualitatively and quantitatively. the qualitative evaluation compares the output of the proposed algorithm with the following algorithms: fcm [23], sfcm [24], and csfcm [7].the quantitative evaluation shows the final output with the reference segmented image and compares the segmentation results of the proposed method with three fuzzy-based mentioned algorithms along the same line based on ground-truth images. the quantitative evaluation is computed based on dice criteria [25,26]. the dice factor which is common in image segmentation has been measured for segmentation algorithms as a quantitative evaluation. the experiments and performance evaluation were carried out on three different datasets. one is a simple synthetic image, another is the classical simulated brain database borrowed from mcconnell brain imaging centre of the montreal neurological institute, mcgill university [27], and the last one is an mr image borrowed from [2]. the original images are stored in gray scale space. these images are commonly used in papers [28, 29–34] for image segmentation purposes and the algorithms compared have employed these images in their experiments. next, the setting of parameters, the comparison of algorithms and the evaluation of each performance are explained in detail. a. setting experimental parameters the max iteration, 𝑡𝑚𝑎𝑥 , was considered 200. the parameters in the fcm based methods were set as follows: (i) the weighting exponent was set to be m=2 since it had been shown to be the most effective one [35]. (ii) the termination criteria was set to be ε=0.01 since most reports showed good success with ε ∈[0.01, 0.0001] [ 36 ]. (iii) the gaussian rbf kernel width as proposed method parameter was set to be σ=150 since it showed better results than other σ values [36]. moreover, the parameters in the csfcm [7] method were set as follows: (i) the parameters of weighted membership function were set to be p=2 and q=2 since it had been shown that the algorithm provides superior results using these values [csfcm]. (ii) the size of the neighborhood was set to n(xk)=9 (3 × 3 window centered around each pixel). b. qualitative evaluation the synthetic image is shown in figure 3(a). it contains a two-class pattern corrupted by gaussian noise with mean=0, variance=0.02. figures 3(b)-(e) show the segmentation results of fcm, sfcm, csfcm and the proposed cskfcm respectively. as shown in figure 3(b), without spatial constraints, the fcm cannot separate the two classes. although, the sfcm and csfcm employ the correlation between the neighboring pixels, they fail to generate accurate clusters as shown in figures 3(c) and (d). by comparing figure 3(d) with the others, we can see that the proposed cskfcm method provides a better segmentation result than its counterparts. note that because of the injection of the kernel, cskfcm needs more execution time than csfcm, and correspondingly, cskfcm is slower than csfcm. typically, the algorithms without kernel are several times faster than those with injection of kernels. the next experiment is designed to evaluate the performance of the proposed method on a t1-weighted simulated brain image with the presence of noise and intensity inhomogeneity. the target is to segment different tissue regions: cerebrospinal fluid (csf), grey matter (gm) and white matter (wm). figure 4 shows the segmentation results of a t1weighted mr image (slice 100, figure 4(a) with 7% noise and 20% inhomogeneity. figure 4(b)–(d) shows the segmented regions of the csf, gm and wm, respectively by the fcm engineering, technology & applied science research vol. 8, no. 3, 2018, 2985-2990 2988 www.etasr.com gharnali and alipour: mri image segmentation using conditional spatial fcm based on … algorithm. figures 4(e)–(g) show the segmented regions of the csf, gm and wm, respectively by the sfcm algorithm. figures 4(h)–(j) show the segmented regions of the csf, gm and wm, respectively by the csfcm algorithm. figures 4(k)– (m) show the segmented regions of the csf, gm and wm, respectively by the proposed cskfcm algorithm. (a) (b) (c) (d) (e) fig. 3. comparison of segmentation results on a synthetic image corrupted by gaussian noise with variance=0.02. (a) the original image, (b) using fcm, (c) using sfcm, (d) using csfcm, and (e) using cskfcm the last row of figure 4 shows the result of the proposed algorithm. it can be seen that this algorithm performs well for the mri brain image with the presence of noise and intensity inhomogeneity. however, the rest fails in most situations and also several artifacts are present in the segmented regions of the csf, gm and wm. the reason is that the cskfcm attempts to unify the intensity and spatial information as a whole and it employs a kernel-induced new metric to replace the euclidean norm in the original space. consequently, it shows less susceptibility to noise. in the last experiment of this section, we tested the performance of the proposed cskfcm algorithm on another mri image data from [2] corrupted by gaussian noise with mean=0, variance=0.003 as shown in figure 5(a). the second to fifth rows of figure 5 show segmentation results by fcm, sfcm, csfcm, and cskfcm respectively. by comparing them, we can see that the proposed method provides a better segmentation result than its counterparts. c. qualitative evaluation to evaluate the results of brain mri mage segmentation, it is necessary to make a quantitative evaluation of different algorithms. the comparisons are illustrated using the dice similarity coefficient (dsc) [11, 23] as a similarity criterion, which is defined by: dsc(ωs, ωr) = 2area(ωs∩ ωr) (area(ωs)+area(ωr)) () (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l) (m) fig. 4. segmentation results of the csf, gm and wm (from left to right) by the different algorithms on a t1-weighted mri brain image with 7% noise and 20% inhomogeneity (a). (b)–(d): fcm algorithm; (e)–(g): sfcm algorithm; (h)–(j): csfcm algorithm and (k)–(m): the proposed cskfcm algorithm. in (9), ωs is the final segmented region and ωr is the corresponding reference region. this coefficient varies from 0 to 1 and measures the degree of agreement between the two regions. it is 1 if the two regions are identical and 0 when they are completely different. table i gives the segmentation accuracy of four methods in figure 3(a) based on ground-truth image in figure 6(a), where the segmentation accuracy is computed using the dice similarity coefficient. table ii shows the results of applying the dice similarity coefficient for three segmented parts of the simulated mri brain image in figures 2(a): csf, gm and wm using the fcm, sfcm, csfcm and the proposed method. the second row of figure 6 shows the reference or the region of interest (roi) of the csf, gm and wm regions of the brain image in figure 4(a). table iii shows the results of applying the dice similarity coefficient for the wm segmented parts of the mri brain image in figure 3(a) engineering, technology & applied science research vol. 8, no. 3, 2018, 2985-2990 2989 www.etasr.com gharnali and alipour: mri image segmentation using conditional spatial fcm based on … using the fcm, sfcm, csfcm and the proposed method. figure 4(e) shows the reference of the wm region of the brain image in figure 5(a). from tables i-iii, it can be seen that the best results in term of the dice coefficient (highest value) are achieved by our proposed method. in addition, by comparing the csfcm and the proposed cskfcm results from the tables, we can see the advantages in using the kernel-induced metric to replace the original euclidean norm metric in csfcm objective function. (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l) (m) fig. 5. segmentation results of the csf, gm and wm (from left to right) by the different algorithms on an mri brain image contaminated with gaussian noise (mean=0 and variance=0.003)(a). (b)–(d): fcm algorithm. (e)–(g): sfcm algorithm. (h)–(j): csfcm algorithm. (k)–(m): proposed cskfcm algorithm. (a) (b) (c) (d) (e) fig. 6. ground-truth segmentation of images. a roi of the synthetic image in figure 4(a). (b)-(d): csf, gm and wm roi of the simulated brain image in figure 4(a). (e): wm roi of the brain image in figure 5(a) table i. computation dice similarity coefficients (figure 3(a)) fcm sfcm csfcm proposed method figure. 1a 0.9560 0.9856 0.9904 0.9982 table ii. computation dice similarity coefficients (figure 4(a)) fcm sfcm csfcm proposed method csf 0.9560 0.9856 0.9904 0.9982 gm 0.8423 0.8623 0.8930 0.9086 wm 0.8621 0.8876 0.9030 0.9191 table iii. computation dice similarity coefficients (figure 5(a)) fcm sfcm csfcm proposed method wm 0.8015 0.8230 0.8446 0.8594 v. conclusion in this paper, a new approach for segmentation of corrupted by noise mri images has been presented. the proposed algorithm is based on incorporating the kernel method and the spatial information into the final membership function of the fcm to effectively segment mr images corrupted by noise and inhomogeneity. we assessed the effectiveness of the proposed algorithm, qualitatively and quantitatively, on synthetic and mr images available in segmentation data-bases that are commonly used in papers. in the qualitative evaluation, the output of the proposed algorithm was compared with the fcm, sfcm and csfcm methods in noisy cases. the quantitative evaluation was calculated based on the dice factor. experimental results demonstrate that the proposed algorithm produces better results by successfully detecting the object engineering, technology & applied science research vol. 8, no. 3, 2018, 2985-2990 2990 www.etasr.com gharnali and alipour: mri image segmentation using conditional spatial fcm based on … boundaries and also is more robust to gaussian noise than other fuzzy clustering algorithms in segmenting mri images. references [1] j. s. duncan, n. ayache, “medical image analysis: progress over two decades and the challenges ahead”, ieee transactions on pattern analysis and machine intelligence, vol. 22, no. 1, pp. 85-106, 2000 [2] t. dietenbeck, m. alessandrini, d. friboulet, o. bernard, “creaseg: a free software for the evaluation of image segmentation algorithms 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kao, j. c. gore, z. ding, “minimization of region-scalable fitting energy for image segmentation”, ieee transactions on image processing, vol. 17, no. 10, pp. 1940-1949, 2008 [35] j. c. bezdek, j. keller, r. krisnapuram, n. pal, fuzzy models and algorithms for pattern recognition and image processing, springer science & business media, vol. 4, 1999 [36] d. -q. zhang, s.-c. chen , “a novel kernelized fuzzy c-means algorithm with application in medical image segmentation”, artificial intelligence in medicine, vol. 32, no. 1, pp. 37-50, 2004 microsoft word 39-2766_s_etasr_v9_n4_pp4525-4529 engineering, technology & applied science research vol. 9, no. 4, 2019, 4525-4529 4525 www.etasr.com hii et al.: ecg noise reduction with the use of the ant lion optimizer algorithm ecg noise reduction with the use of the ant lion optimizer algorithm kiew hui hii faculty of electrical & electronics engineering, university of malaysia pahang, pekan, pahang, malaysia qhui_0906@hotmail.com vigneswaran narayanamurthy faculty of electrical & electronics engineering, university of malaysia pahang, pekan, pahang, malaysia vigneswaran@ump.edu.my fahmi samsuri faculty of electrical & electronics engineering, university of malaysia pahang, pekan, pahang, malaysia fahmi@ump.edu.my abstract—the electrocardiogram (ecg) signal is susceptible to noise and artifacts and it is essential to remove that noise in order to support any decision making for automatic heart disorder diagnosis systems. in this paper, the use of ant lion optimizer (alo) for optimizing and identifying the cutoff frequency of the ecg signal for low-pass filtering is investigated. generally, the spectrums of the ecg signal are extracted from two classes: arrhythmia and supraventricular. baseline wander is removed by a moving median filter. a dataset of the extracted features of the ecg spectrums is used to train the alo. the performance of the alo is investigated. the alo-identified cutoff frequency is applied to a finite impulse response (fir) filter and the resulting signal is evaluated against the original clean and conventional filtered ecg signals. the results show that the intelligent alo-based system successfully denoised the ecg signals more effectively than the conventional method. the accuracy percentage increased by 2%. keywords-ant lion optimazation (alo); electrocardiogram (ecg); finite impulse response (fir); cutoff frequency i. introduction the first clear electrocardiogram (ecg) signal was obtained in 1895. since then, ecg analysis became a standard and trustworthy technique of detecting cardiac defects [1], while cardiovascular diseases (cvds) are the world’s leading cause of death. the number of cvd victims may decrease if timely medical treatment is well organized. in telecardiology applications, it is necessary to facilitate high-resolution ecg signals for proper diagnosis [2]. ecg is an electrical signal from the heart. when the blood is pumping in the circulatory system, this mechanism generates a sequence of electrical signals. the noise in the ecg signal is important to be reduced [3], otherwise the signal’s morphology will be interrupted, the diagnosis will be harder [2] and the precision of the time and the amplitude of the measurement will be reduced [3]. it is essential to verify what kinds of noise contaminate the ecg signal so that they can be removed effectively and obtain the noise-free clear ecg morphology. as ecg is a very sensitive and low frequency heart signal, the real amplitude and duration of the signal can be changed by many different types of noise and interference. ecg signals are mostly affected by high frequency, electrode noise, muscle artifacts noise, baseline wander, composite noise and power line interference. but in this research, focus was given in high frequency since the ecg is a low frequency signal. for better analysis of ecg, the removal of noise becomes an important part of pre-processing [4]. the normal range for the frequency of the ecg is 0.01hz100hz and it is found that 90% of the spectral energy lies between 0.25hz–35hz. in this paper, the ant lion optimization is used to find the cutoff frequency to remove the noise of the ecg. ii. biosignal acquisition and processing techniques there are several techniques on noise filtering. one is the electronics design and the development of the circuit. authors in [5] worked on an automatic noise cancellation method using a 3-axis mems accelerometer to recover signals corrupted by body movement as one of the most significant sources of motion artifacts. the preliminary results from the bench tests and the laboratory setup demonstrate that the goal of the highperformance wearable ppg is viable and feasible. authors in [6] used the tina to run simulations and dc source to mimic the noise. the result of the reduction on the complexity and the power consumption showed an excellent performance. authors in [7] described a digitally assisted noise cancellation method for a coupled electrocardiogram (ecg) sensor. this sensor using an insulated electrode could measure ecg through an insulator such as clothing without direct skin contact. they used the noise feedback method to improve the availability of a capacitive coupled ecg sensor to decrease the noise caused by body movement. measurement results showed that the ecg noise can be suppressed. sensor improvement is one of the solutions on noise canceling. authors in [8] restructured the electrodes to noncontact, capacitive ecg measurements and both gradiometer designs were compared with standard ecg recording methods and showed detection mismatch employing an open source beat detection algorithm. authors in [9] proposed the normalized signed regressor lms (nsrlms) algorithm to remove ecg noise. efficient noise reduction, especially of the nonstationary noise was, achieved. adaptive filters change their coefficients with the continuous change of signal, providing optimum noise removal features for non-stationary signals. corresponding author: kiew hui hii engineering, technology & applied science research vol. 9, no. 4, 2019, 4525-4529 4526 www.etasr.com hii et al.: ecg noise reduction with the use of the ant lion optimizer algorithm authors in [10] used the adaptive filter algorithm rls to cancel various noises in ecg signals. the simulation results depicted that rls algorithm performed well in removing noises from the ecg signals [10]. there were many ways to try to get a clear ecg signal, starting with the design of the electronics devices of the equipment or the improvement in the structure of the electrodes and the sensors of the wearable devices. excellent results for cancelling the noise of various artifacts have been obtained by filtering algorithms. the use of advanced signal processing techniques like alo can help finding the cutoff frequency, which will help in canceling noise stage. the cutoff frequency is applied to a fir filter for getting the original and clean ecg signal [11]. the advantages of stochastic algorithms like alo are that they can avoid local solutions more easily than the deterministic algorithms and they are rather simple to implement. an adaptive filtering technique for denoising ecg signal based on genetic algorithm (ga) and tuned sign-data least mean square (sd-lms) algorithm was proposed in [12]. the author used ga to optimize the step size to obtain a better snr value. authors in [13] worked on obtaining clean heart signals. in this work, an adaptive filter was designed with the stochastic artificial bee colony (abc) algorithm. by using abc an adaptive filter was designed for eliminating the distortions in the ecg signal. authors in [14] proposed a pso-based approach, which aims at optimizing the performances of svm classifiers in terms of classification accuracy by detecting the best subset of available features and solving the tricky model selection issue. automatically identifying the cutoff frequency of the ecg signal was studied in [15]. the optimum cutoff frequency was used in low-pass filtering. a dataset of the extracted features of the ecg spectrums was used to train a psonn (particle swarm optimization neural network) in [16]. the optimum cutoff frequency was applied to an fir filter and the signal was evaluated against the original. as a result, it was shown that the psonn is trustworthy and fast for automatically identifying cutoff frequency. the clean data were compared to the psonn filtered signals showing that the proposed method was suitable for heart disorder diagnosis. in this research, the ant lion optimizer (alo) algorithm has been chosen because it performs better than other stochastic algorithms like genetic algorithm (ga) and particle swarm optimizer (pso) [17-18]. alo also helps in saving cost by minimizing losses [11]. authors in [19] used alo to design antenna arrays by optimizing the excitation current amplitudes of array elements. alo is able to get the optimum value of the cutoff frequency, and not only the values but also the location and size [20]. it mimics the hunting mechanism of the ant lion, which is a searching method to find the optimal feature set maximizing classification performance. the proposed model is evaluated using different evaluation criteria on 18 different data sets [18]. alo approach uses less fitness function evaluations, it does not get trapped into local minima and offers promising convergence characteristics [21]. iii. methodology a. ant lion optimizer alo algorithm mimics the interaction between ant lions catching their prey and trap ants. it contains five steps to catch prey. the first stage is ant lions walking randomly, then they build their traps and make sure the ants are trapped. when the ants fail into the holes, the ant lions catch their prey. the last step is ant lions re-building traps and waiting for their prey to come again. 1) ant random walks the first step of the alo optimizer is the random walk of ants. the equation below is used to normalize and update the position by time: �� � = ��� ���×(�� �� ) (�� ��) + �� (1) where �� and �� indicate the minimum and maximum of the random walk, �� and �� are the minimum and maximum of the i-th variable at the t-iteration [22]. 2) trapping the trapping of the ants depends on the pits of the ant lion modeled as below: �� � = �������� � + �� (2) �� � = �������� � + �� (3) where �� indicates the minimum of the t-th iteration, the vector including the maximum of all variables at t-th iteration is represent by ��. both equations show the walking of ants around one ant lion which is selected in the form of a hyper sphere [22]. 3) building traps a roulette wheel is used in the alo algorithm to build up and optimize the ant lions’ fitness. this mechanism is giving the fitter ant lion to have a higher chance on catching ants [22]. 4) sliding ants towards the ant lions the ant lion fitter can build up better trapping pits. the deeper the trap, the easier is for ants to slide down towards the ant lion. equations (4)-(5) indicate the radius of the pit trap. at this stage, ants try to escape when they start sliding down. based on the mathematical modeling, the radius of the trap keeps decreasing as they go deeper [22]: � � = � � (4) � � = � � (5) where i is a ratio, � � is the minimum of all variables at t-th iteration, and � � represents the vector at the t-th iteration. 5) catching prey and rebuilding the pit as an ant reaches the bottom of the pit, the ant lion catches its prey. this is the final stage of the ant lion algorithm optimization. but an ant may escape if it is fitter. at the same time, the ant lion has to update its position to get a chance of engineering, technology & applied science research vol. 9, no. 4, 2019, 4525-4529 4527 www.etasr.com hii et al.: ecg noise reduction with the use of the ant lion optimizer algorithm hunting new prey [22]. this condition forms the equation as below: �������� � = ���� � � (���� �) ! ��������� �� (6) b. elitism elitism indicates the best ant lion in terms of fitness. the fitness of ant lion gives the best solution for the ant lion algorithm: ra and re represent the random walk of the ant lion and the elite at the t-th iteration. anti indicates the position at the i-th ant at the t-iteration [22]. ���� � = " � � +" # � 2 (7) to implemented the fir filter requires the cutoff frequency (%�) and the filter order. since the order is the width of the window, higher order brings sharper response in the signal [15]. the equation of the fir filter is: �& = ∑ ()* �+,& ./ 0)12 (8) where the �& is sum of the n terms, and k is the data point. c. flow chart figure 1 shows this study’s flow chart. the input signal is collected from the mit-bih database. two heart diseases (arrhythmia and atrial fibrillation) were put in the filtering process. in this research, 10 datasets would be used for each disease. each of the diseases contains 1000 data points. since the data consist of high frequency, a median filter was used to reduce the high frequency of the noisy ecg. the next step was feature extraction by fast fourier transform (fft) to convert the time domain signal into frequency domain. as the noisy ecg signal is formed in the frequency domain, the cutoff frequency can be determined. after the fourier transform, the analysis proceeds to alo algorithm. by implementing the equation of ant lion algorithm, the optimum cutoff frequency is obtained. the optimum result is termed as “elitism”. if the elitism does not fulfill the range of the frequency, the optimization needs to be repeated. an fir filter is implemented with the optimized cutoff frequency on the noisy signal to get the clear ecg as a result. iv. results and discussion the results were divided into several parts which were noisy ecg signal database pre-processing stage, median moving filter approach, transformation of the signal from time domain to frequency domain, fourier transform, and alo optimization. the optimized cutoff frequencies from the alo optimization were applied on the fir filter in order to get better ratio signal to noise ratio (snr) values. there were two types of ecg diseases in the data: arrhythmia and atrial fibrillation were used for feature extraction of the ecg signal. the sampled data of the arrhythmia were 20000, and the first 10000 were divided into 10 sets of samples, each set containing 1000 samples. the extracted arrhythmia features are shown in figure 2. the sampling frequency %3 for this signal was 360hz. fig. 1. flow chart of the research fig. 2. arrhythmia ecg noisy signal fig. 3. time signal after filtering the cutoff frequency played an important role, because it was used into the fir filtering. table i shows the results of the conventional method. ant lion algorithm helped in optimizing the best score of cutoff frequency. the fft helped in finding the cutoff frequency which was used in filtering and the results are given in table ii. equation (9) shows the transform: �& = ∑ ()* �+,& ./ 0)12 (9) where xk is sum of the n terms, and k is the data point. the main function of the median filter reduced noise on the pre-processing stage. it helped in smoothing the signal of the noisy ecg and assisted the filtering process more effectively. in figure 4, the blue colour signal indicates the original noise engineering, technology & applied science research vol. 9, no. 4, 2019, 4525-4529 4528 www.etasr.com hii et al.: ecg noise reduction with the use of the ant lion optimizer algorithm signal and the green color signal is the filtered signal by the moving median filter. the original signal contained many spikes and the r-peak was high before filtering. after implementing the moving median filter, the amplitude of the r peak reduced. fig. 4. comparison between the filtering using median filtering. (a) blue line: original ecg signal, (b) green line: filtered ecg signal table i. normalized cutoff frequency with snr data set signal type normalized cutoff frequency snr1 (db) 1 arrhythmia 0.16 26.9993 2 arrhythmia 0.43 93.2363 3 arrhythmia 0.09 23.3543 4 arrhythmia 0.06 23.7472 5 arrhythmia 0.07 21.5048 6 arrhythmia 0.04 22.3169 7 arrhythmia 0.01 24.8268 8 arrhythmia 0.03 22.4479 9 arrhythmia 0.02 23.5868 10 arrhythmia 0.03 23.2509 11 atrial fibrillation 0.95 66.4295 12 atrial fibrillation 0.43 61.0999 13 atrial fibrillation 0.52 62.2211 14 atrial fibrillation 0.16 27.7318 15 atrial fibrillation 0.61 56.5778 16 atrial fibrillation 0.11 19.4273 17 atrial fibrillation 0.95 59.6059 18 atrial fibrillation 0.04 23.7628 19 atrial fibrillation 0.73 64.8241 20 atrial fibrillation 0.01 21.0842 table ii. optimized cutoff frequency with snr data set signal type normalized cutoff frequency snr2 (db) 1 arrhythmia 0.1646 27.3131 2 arrhythmia 0.4315 95.2403 3 arrhythmia 0.0936 23.4540 4 arrhythmia 0.0649 23.8389 5 arrhythmia 0.0780 21.6872 6 arrhythmia 0.0492 22.4329 7 arrhythmia 0.0169 24.8516 8 arrhythmia 0.0382 22.5248 9 arrhythmia 0.0210 23.5924 10 arrhythmia 0.0317 23.2650 11 atrial fibrillation 0.9560 66.8004 12 atrial fibrillation 0.4363 62.2693 13 atrial fibrillation 0.5233 62.3098 14 atrial fibrillation 0.1685 28.2561 15 atrial fibrillation 0.6115 56.7816 16 atrial fibrillation 0.1138 19.5668 17 atrial fibrillation 0.9585 60.3111 18 atrial fibrillation 0.0430 23.7975 19 atrial fibrillation 0.7329 65.8605 20 atrial fibrillation 0.0103 21.0850 the ant lion algorithm mimics the interaction between ants and ant lions. at the initial steps the ants are walking randomly and ant lions walk in certain areas (like the cutoff frequency was calculated in a certain range). the ant lion algorithm found the best cutoff frequency and gave a high snr, as can be seen by comparing tables i and ii. in figure 5 we can see the comparison of the conventional method (white) and the alo optimization (black) in finding the actual cutoff frequency. the y-axis shows the snr. we can see that the alo algorithm had a higher snr percentage. fig. 5. snr percentage between the conventional method and the alo v. conclusion this paper presented a newly developed method in the identification of the cutoff frequency. one of the objectives of this research was to apply a fir filter and a moving median filter to reduce the high-frequency noise of the ecg data samples. the morphology of the ecg was maintained. the aim of this research was to identify and optimize the cutoff frequency using the ant lion algorithm. the target was achieved through alo optimization in matlab. from the simulations, the optimized cutoff frequency was successfully retrieved in higher than the conventional method’s snr. the proposed method’s cutoff frequency performance was with the conventional cutoff frequency of feature extraction of the signal. the optimum cutoff frequencies’ result shows that the proposed method reduced more noise than the conventional method. acknowledgement the authors are grateful to the university of malaysia pahang and the ministry of education of malaysia for supporting this collaboration work under the scholarship grs 140329. references [1] n. singh, s. ayub, j. p. saini, “design of digital iir filter for noise reduction in ecg signal”, 5th international conference and computational intelligence and communication networks, mathura, india, september 27-29, 2013 [2] m. n. salman, p. t. rao, m. z. u. rahman, “novel logarithmic reference free adaptive signal enhancers for ecg analysis of wireless cardiac care monitoring systems”, ieee access, vol. 6, pp. 4638246395, 2018 [3] y. a. altay, a. s. kremlev, “analysis and systematization of noise arising by long-term recording of ecg signal”, ieee conference of russian young researchers in electrical and electronic engineering, moscow, russia, january 29-february 1, 2018 engineering, technology & applied science 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distribution systems with distributed generators using antlion optimizer”, nineteenth international middle east power systems conference, cairo, egypt, december 19-21, 2017 [21] s. verma, v. mukherjee, “optimal real power rescheduling of generators for congestion management using a novel ant lion optimiser”, institution of engineering and technology generation, transmission & distribution, vol. 10, no. 10, pp. 2548-2561, 2016 [22] s. mirjalili, “the ant lion optimizer”, advances in engineering software, vol. 83, pp. 80–98, 2015 engineering, technology & applied science research vol. 9, no. 2, 2019, 3965-3970 3965 www.etasr.com japitana & burce: a satellite-based remote sensing technique for surface water quality estimation a satellite-based remote sensing technique for surface water quality estimation michelle v. japitana school of engineering, university of san carlos, cebu city and college of engineering and geosciences, caraga state university, butuan city, philippines mvjapitana@carsu.edu.ph marlowe edgar c. burce school of engineering, university of san carlos cebu city, philippines mcburce@yahoo.com abstract—remote sensing provides a synoptic view of the earth surface that can provide spatial and temporal trends necessary for comprehensive water quality (wq) monitoring and assessment. this study explores the applicability of landsat 8 and regression analysis in developing models for estimating wq parameters such as ph, dissolved oxygen (do), total dissolved solids (tds), total suspended solids (tss), biological oxygen demand (bod), turbidity, and conductivity. the input image was radiometrically-calibrated using fast line-of-sight atmospheric analysis (flaash) and then atmospherically corrected to obtain surface reflectance (sr) bands using flaash and dark object subtraction (dos) for comparison. sr bands derived using flaash and dos, water indices, band ratio, and principal component analysis (pca) images were utilized as input data. feature vectors were then collected from the input bands and subsequently regressed together with the wq data. forward regression results yielded significant high r2 values for all wq parameters except tss and conductivity which had only 60.1% and 67.7% respectively. results also showed that the regression models of ph, bod, tss, do, and conductivity are highly significant to sr bands derived using dos. furthermore, the results of this study showed the promising potential of using rsbased wq models in performing periodic wq monitoring and assessment. keywords-spectral; reflectance; radiance; water quality modelling; geoinformatics i. introduction water is among the most important resources. however, water bodies are under acute seasonal scarcity due to the increased rate of human intervention and human-induced modification of natural processes [1]. periodic monitoring and assessment of water quality (wq) help to develop management strategies to control surface water pollution [2]. governmentsponsored wq monitoring programs usually employ field measurements and collection of water samples for subsequent laboratory analysis in a traditional way. while such conventional approach to wq monitoring data is accurate at a specific location and time, in most cases, it cannot provide enough information on overall wq. water monitoring data and reports in the philippines usually only have point-specific datasets which lack spatiotemporal trends that are rather vital in the monitoring, assessment, and identification of water management strategies. also, though this in-situ measurement offers high accuracy, it is not feasible to provide a simultaneous wq database on a regional scale [3]. fortunately, the emerging technologies of geoinformatics, particularly remote sensing (rs) and geographic information system (gis), provide useful tools for a comprehensive wq assessment and management. remote sensing datasets offer a synoptic view of ongoing earth surface processes which allows an evaluation of the pressures placed on aquatic ecosystems [4]. scientific findings towards understanding wq by employing rs techniques are highly effective. such techniques are valuable in monitoring upstream land use and land cover changes and spread [5], deriving rs empirical models to aid wq monitoring and assessment[2, 6-8], and mapping the spatial distribution of wq parameters using gis [2, 9]. moreover, satellite images have been used successfully in water management protocols such as to conduct inventory and water balance assessment [10-12], to assess flood areas [13], and for wq change detection and monitoring [14, 15]. there is no restriction on obtaining and using landsat satellite imagery [16]. landsat satellite series are widely used to establish relationships between wq parameters of surface waters and spectral reflectance [17-20]. authors in [21] showed that satellite-based regression models can be derived using images acquired with a maximum of ±15 days offset from the date of in-situ water sampling. however, there are recommendations of a narrower time difference of ±5 days [22], ±4 days [23], ±3 days [21], and ±1 day [22, 24] between the sampling date and the acquisition date of the image. for this study, an offset of ±5 or lesser days is set in the selection of satisfactory (less cloud cover) satellite images. regression analysis is one of the widely used methods to determine spectral reflectance and wq parameter relationship by selecting derived regression models with high r2 value [6, 16, 19, 25]. a wide range of studies proved the potential of using satellite datasets in deriving wq models which include physicochemical water parameters [18, 24, 26], nutrient concentrations [20], and heavy metals [27]. for instance, authors in [17] applied regression modelling to develop algorithms for estimating tss, ph, bod, and chlorophyll-a. hence, in this study, wq algorithms are developed using a combined regression and remote sensing approach. the objective of this study is to determine the potential of using corresponding author: michelle v. japitana engineering, technology & applied science research vol. 9, no. 2, 2019, 3965-3970 3966 www.etasr.com japitana & burce: a satellite-based remote sensing technique for surface water quality estimation do not alter header & footer. they will be completed during editing landsat 8 images combined with field measurements to predict selected wq indicators. to derive wq regression models, this study utilizes various raw, pre-processed, and post-processed landsat 8 bands and in-situ wq data and employs regression analysis. ii. study area tubay river is one of the principal rivers in agusan del norte, philippines which is classified as a class a water body. its headstream is the main outlet of lake mainit, and the river traverses within the municipalities of jabonga, santiago, and tubay. there are two major tributaries of the river, one at its upstream portion and the other at the mid-downstream part. the river plays a vital role in the economic development of the said municipalities, as manifested by its diverse uses that include irrigation and other agricultural uses, fisheries, livestock production, and various domestic uses and tourism. the river is also a receptor of domestic solid and liquid wastes and other non-point sources of polluted waters [28]. figure 1 shows the location of tubay river and the terrain within the study area. fig. 1. the study area showing the location of tubay, agusan del norte and the location of emb water quality monitoring points. iii. materials and methods the 2014-2015 wq monitoring data of the environmental management bureau (emb) were utilized in this study. to explore the relationships between wq indicators and spectral data, we employed the latest addition in the landsat series which is the landsat 8 oli. landsat 8 images with acquisition dates with a ±5-day difference to the water sampling dates of the emb were downloaded through usgs earth explorer. the general methodology applied in this study is shown in figure 2. fig. 2. high level abstraction of processes and data flow. fig. 3. the procedure flow for pre-processing the landsat 8 oli image. in the pre-processing part, we employed radiometric correction to remove errors in the raw pixel values (digital numbers, dn) of the landsat image and convert the pixels into radiance or reflectance using the flaash tool. a detailed procedure of transforming dn into at-sensor radiance and surface reflectance is covered entirely in [29]. the general form of the equation for computing toa reflectance (rtoa) is shown in (1) and (2): 𝐿′𝜆 = 𝑀𝜌 ∗ 𝑄𝐶𝐴𝐿 + 𝐴𝜌 (1) 𝐿𝜆 = 𝐿′𝜆 cos 𝜃⁄ 𝑆𝐸 (2) where l΄λ is toa spectral radiance, qcal is the quantized calibrated pixel values in dn, mρ is the band-specific multiplicative rescaling factor, band-specific aρ is the additive scaling factor, θse is the local sun elevation angle, and lλ is the toa reflectance. then, atmospheric correction was employed to transform toa radiance or reflectance bands into surface reflectance using two types of pre-processing methods to investigate which method is the most appropriate for extracting rs-based wq models. the first method is to apply the flaash atmospheric correction [30] automatically while the second method employs dos [31]. band math computations were finally applied to surface reflectance bands using the two approaches to complete the post-flaash and post-dos procedure. then the raw, radiance and reflectance images were used to perform pca and band ratios for deriving two water indices. to enhance the spectral appearance of water bodies, modified normalized difference water index (mndwi) and normalized difference water index (ndwi) variants were derived using (3)-(5). band ratio (br) was also obtained using band 1 and band 5 by applying (6): 𝑀𝑁𝐷𝑊𝐼 = (𝜌3 − 𝜌6) (𝜌3 + 𝜌6)⁄ (3) 𝑁𝐷𝑊𝐼1 = (𝜌3 − 𝜌5) (𝜌3 + 𝜌5)⁄ (4) 𝑁𝐷𝑊𝐼2 = (𝜌5 − 𝜌6) (𝜌5 + 𝜌6)⁄ (5) 𝐵𝑅 = 𝜌1 𝜌5⁄ (6) where 𝜌1 is the ultra-blue (coastal/aerosol) band, 𝜌3 is the green band, 𝜌5 is the nir band, and 𝜌6 is the swir 1 band of the landsat 8 oli image. engineering, technology & applied science research vol. 9, no. 2, 2019, 3965-3970 3967 www.etasr.com japitana & burce: a satellite-based remote sensing technique for surface water quality estimation do not alter header & footer. they will be completed during editing all images were then resized to contain only the region of tubay river as study area. we then extracted feature vectors from each raw image and transformed satellite images using the geographic locations of the monitoring stations of emb. then, all pixel values were organized and tabulated to be used for regression analysis. during the regression, two fitting methods were applied using the spss 16.0 software, the enter method and the forward (step-up) method. in the first method, all variables with high correlation to the wq parameter are fitted in the regression model while the forward method only includes variables that explain a significant amount of additional variance in the model and output all possible regression models with significant r2 values. iv. experimental results quarterly wq monitoring data for the years 2014 and 2015 were available during this study. from these datasets, only 7 physical wq parameters were considered during this study: ph, do, bod, tss, tds, conductivity and turbidity. among the available satellite images in the study area, only the landsat 8 oli images acquired during april 19, 2015 were utilized since they qualified the ±5 day difference and the minimal cloud cover criteria. hence, the emb april 14, 2015 wq data (shown in table i) were utilized for statistical rs modelling. a total of 7 raw bands, 7 pre-processed bands using flaash, 7 pre-processed bands using dos, 18 principal component (pc) bands, 3 water indexes, and 1 br were used in this study. this results in a total of 43 variables to be considered in the regression analysis. statistical results showed that 6 variables or image bands were found to be highly correlated to all physical under consideration wq parameters. these variables include mostly image bands atmospherically corrected using dos. these variables were fitted in the respective wq regression models using the enter method in spss which all resulted to an r2 value of 100%. table ii shows all the regression models (enter method) derived using various rs datasets. table i. water quality data of tubay river, april 14, 2015 stn. do (mg/l) bod (mg/l) tss (mg/l) tds (mg/l) ph conductivity (ms/cm) turbidity (ntu) 1 7.3 0.7 5 1,510 7.65 2.25 1.21 2 7.8 0.7 4 112 7.93 1.72 81.6 3 8.1 0.8 8 116 7.95 0.165 85.3 4 8.0 0.8 24 86 8.20 0.125 92.5 5 7.4 0.6 12 92 8.03 0.140 66.3 6 7.4 0.7 0.0 97 8.03 0.149 51.0 7 7.6 0.5 48 97 8.14 0.149 55.3 source: emb (2015) the first run of forward regression analysis did not output a statistical model for do and turbidity. in this method, out of the 6 significant variables identified in previously, only 3 were found to be substantial in the derived wq regression models. these are the br, pc4 of surface reflectance bands calibrated using dos (pc4_sr2), and the pc5 of surface reflectance bands calibrated using flaash (pc5_sr1). forward regression analysis results showed that the models for tds, bod, and ph yielded the highest r2 values of 96.8%, 89.3%, and 89.0%, respectively. the resulting regression models also showed the strong association of br to water ph, tds, and conductivity. also, the pc reflectance band 4 is highly significant to both bod and tss regression models, although the r2 value of the tss regression model is only 60.1%. moreover, forward regression analysis for tds resulted in two models. the first model with the highest r2 value of 96.8% has br and pc1_sr1 as predictors while the second model shows that tds can also be estimated using only br as a predictor with an r2 value of 77.6%. table ii. remote sensing-based regression models (enter method) for selected wq parameters. model no. dependent predictors and coefficients r 2 % 1 do 7.961+65.873×pc5_sr138.644×sr2b1+58.405×pc4_sr2+1.56 0×ndwi2-1.378×br+9.507×rtoab7 100 2 ph 8.128+42.442×pc5_sr113.18×sr2b1+4.891×pc4_sr2+0.943× ndwi2-0.754×br+7.343×rtoab7 100 3 bod 0.285+10.063×pc5_sr17.258×sr2b1+32.07×pc4_sr2+0.573× ndwi2+0.017×br+3.089×rtoab7 100 4 tss 15.184+7311.307×pc5_sr12681.941×sr2b13467.17×pc4_sr2+168.64×ndwi2+2 1.174×br+1525.531×rtoab7 100 5 tds 75475.527×pc5_sr123045.975×sr2b155739.039×pc4_sr2+2118.343×ndwi 2+4404.119×br+24777.549×rtoab7 100 6 turbidity 183.783+3031.118×pc5_sr1480.841×sr2b1+4903.518×pc4_sr264.447×ndwi2-258.509×br681.372×rtoab7 100 7 conductivity 2.726+18.552×pc5_sr1+33.248×sr2b 1-110.85×pc4_sr2– 12.795×ndwi2+2.775×br19.44×rtoab7 100 sr1=surface reflectance bands calibrated using post-flaash, sr2=surface reflectance bands calibrated using post-dos, b#=band number, pc=principal component then, we evaluated back the wq datasets for do and turbidity since the first run of the forward regression analysis did not yield models for these wq parameters. the wq data in table i showed that it has the lowest level (1.21) of turbidity at station 1 which is located at the mouth of the river. this suggests low flows during the measurement and that the water was relatively clear. this situation is also evident even 5 days after the wq measurement as shown in the zoomed-in images (true color image and histogram-stretched true color image) from the landsat (figure 4). at the mouth of the river, we can observe in figure 4(a) that the pixels depict greenish color while it is light blue in figure 4(b). in the upper stream of the river, turbid water appears dark (near black) in the normal rgb image. on the other hand, it is very dark blue in the enhanced rgb image applied with histogram equalization. tds level at station 1 is extremely high and exceeds the 1000mg/l minimum standard. this tds concentration may indicate pollution and may pose danger to aquatic life. the tds is a measure of dissolved solid materials in the river water that includes salts, some organic materials, and a wide range of other things from nutrients to toxic substances [32]. despite the high concentration of tds at station 1, its do level passed the minimum criteria of denr, indicating that there is enough engineering, technology & applied science research vol. 9, no. 2, 2019, 3965-3970 3968 www.etasr.com japitana & burce: a satellite-based remote sensing technique for surface water quality estimation do not alter header & footer. they will be completed during editing amount of oxygen dissolved in the water to support aquatic life. the very extreme turbidity and tds values in station 1 may indicate a different scenario since station 1 is located at the mouth of the river. to avoid any uncertainties during the modelling process, station 1 data for turbidity and tds were excluded. considering the relationship between wq parameters, we also included them in each run of the regression analysis. indeed, a new set of regression models were derived for do and turbidity. table iii shows all the derived rs-based models using regression analysis (forward method) including do and turbidity. (a) (b) fig. 4. the subset or zoomed in images of landsat 8 acquired april 19, 2015, showing the downstream river: (a) true color rgb image (b) enhanced true color rgb composite image by employing histogram equalization. table iii. remote sensing based regression models (forward method) for selected wq parameters. model no. dependent predictors and coefficients r2 % standard estimate error 1 do 7.446+0.008× turbidity11.59×sr2b1 88.5 0.828 2 ph 8.339-0.827×br 89.0 0.060 3 bod 0.382+28.746×pc4 _sr2 90.0 0.041 4 tss 53.2573633.719×pc4_sr2 60.1 11.55 5 tds 90.1241911.396×pc6_sr1 84.6 5.113 6 tds 84.7343465.448×pc6_sr1+4 07.034×pc3_sr2 99.5 1.025 7 turbidity 37.985×do+4742.646 ×pc5_sr1295.309×pc3_sr142.973×pc2_sr2220.624 100.0 0.026 8 turbidity 39.985×do+4548.48 6×pc5_sr1213.951×pc3_sr1228.288 99.8 1.051 9 turbidity 36.176×do+3334.53 6×pc5_sr1-198.601 96.5 4.076 10 conductivity 3.682×br-0.882 67.7 0.570 sr1=surface reflectance bands calibrated using post-flaash, sr2=surface reflectance bands calibrated using post-dos, b#=band number, pc=principal component the do regression model yielded an r2 of 88.5% with turbidity and surface reflectance band 1 derived using postdos method (sr2 b1) as predictors, while the regression for turbidity resulted in 3 models with very high r2 of 100%, 99.8%, and 96.5%, respectively. the regression model for turbidity with highest r2=100% has 4 predictors which are pc 3 and pc 5 of surface reflectance bands corrected using postflaash method (pc3_sr1 and pc5_sr1), do, and pc 2 of surface reflectance bands corrected using dos method (pc2_sr2). with these regression modelling results for turbidity and do, the significant predictors that were included in the models confirmed the high correlations found between turbidity and do. as observed in table ii, using enter regression, 4 of the most significant variables are band images applied with post-dos correction and its derivatives (e.g., pca, ndwi2, and br). in particular, these are the surface reflectance band 1, pc band 4, ndwi2, and br and then, 2 more bands, toa reflectance band 7 and pc 5 of surface reflectance, using post-flaash (pc5_sr1). this implies that the surface reflectance bands processed using post-dos correction, the toa reflectance band 7, and pc5_sr1 are practically useful in developing wq algorithms using enter regression analysis. however, in table iii, when forward regression analysis was employed, only 1 to 2 image bands were found to be significant for each rs-based wq model. two of the 6 significant bands (i.e. toa reflectance band 7 and the ndwi2) using enter regression were already not included as predictors in the models determined by forward regression analysis. it can be observed that the resulting predictors of each regression model can be easily associated with the type of calibration method used. for example, the rsbased regression models for ph, bod, tss, do, and conductivity involve predictors representing image bands derived using post-dos calibration. the second regression model for tds, on the other hand, involved surface reflectance bands derived from both post-dos and post-flaash. while tds (1st model) and turbidity regression models include image bands derived using post-flaash method. regarding the goodness of fit, wq models obtained remarkable r2 values except tss and conductivity with 60.1% and 67.7%, respectively. this proves the potential of employing image processing and regression modelling in deriving rs-based wq models. we compared the performance of the developed models in this study to other regression models derived from remote sensing data with moderate resolution like landsat series [14, 16, 19, 23], and from other satellite sensors with high resolutions like worldview-2 [18] and aster [26]. we also took note of the atmospheric correction method and other post-processing techniques. as observed in table iv, the r2 values of the algorithms developed in this study for ph, turbidity, tss, and bod are better than the ones from the other models presented in previous studies using landsat images. this holds true even when our developed models for do, ph, and tss are compared to regression models based on a 2-meter resolution worldview-2 image. it is interesting to note that the turbidity model performance of this study is comparable to the model derived using aster with a 15-meter resolution. overall, we can conclude that the developed regression models using doscorrected landsat 8 bands can reliably estimate water parameters such as do, ph, tss, and bod, while tds and turbidity can be estimated using flaash-corrected landsat 8 images. this comparison result suggests that a free satellite engineering, technology & applied science research vol. 9, no. 2, 2019, 3965-3970 3969 www.etasr.com japitana & burce: a satellite-based remote sensing technique for surface water quality estimation do not alter header & footer. they will be completed during editing image like landsat series can be a reliable input image if the right pre-processing method is employed. table iv. comparison of regression model performances between wq models dependent variable processing method(s) model performance reference predictors r2 % do dos turbidity and b1 88.5 this study dos b1, b3, b4, b5, b7 93.0 [16] n/a b3, b6, b7 44.0 [18] ph dos, band ratio b1, b5 89.0 this study dos b3, b4, b5, b6 81.53 [16] flaash b8, b9 95.06 [26] n/a b3, b4, b5, b6, b7 60.7 [18] turbidity flaash, pca do, pc3, pc5 99.8 this study dos b4, b5 64.2 [16] flaash b2, b3, b4, b5 98.6 [23] flaash b1, b2, b3 99.8 [26] dos b1, b2, b3 46.1 [19] conductivity dos, band ratio b1, b5 67.7 this study dos b2, b3, b4, b6 69.9 [16] flaash b3, b4, b8 99.6 [26] tss dos, pca pc4 60.1 this study dos b1, b2, b3 24.4 [19] flaash b2, b3, b4, b5 98.8 [23] n/a b1, b3, b5 b6, b7 38.8 [18] tds dos/flaash, band ratio, pca b1, b5, pc2_sr1 96.8 this study flaash b3 99.7 [26] bod dos, pca pc4 89.3 this study dos b1, b2, b3 70.7 [14] n/a b2, b6, b7 47.6 [18] v. conclusion and recommendations this study aimed to develop rs-based models of landsat 8 images by employing regression analysis. the results of this study showed a strong correlation between in-situ wq readings and rs-based datasets in tubay river. forward regression analysis results showed that the models for turbidity, tds, do, bod, and ph yielded the highest r2 values of 99.3%, 96.8%, 94.1%, 89.3%, and 89.0%, respectively, while tss and conductivity have r2 values of only 60.1% and 67.7% respectively. these models will be beneficial in estimating wq parameters and predicting seasonal changes. this study demonstrated promising results in estimating wq parameters in which if further validated with multi-temporal datasets, can be considered for the development of an operational rs-based monitoring and assessment system that can be escalated at a regional and national scale. from the model comparison results, this study can conclude that it is not necessary to acquire high resolution and commercial satellite images since a free satellite image like landsat series can be a reliable input image if the right pre-processing method is employed. we further suggest that the government’s wq monitoring campaigns will be planned to coincide with the dates of landsat image acquisitions in the respective areas. in this way, more water characterization data with matching satellite images can be utilized in deriving more reliable empirical wq models, as well as in the model validation. acknowledgment this paper was supported by an engineering research and development for technology grant of the philippine’s department of science and technology. authors would like to thank james earl b. cubillas for his technical assistance and the center for resource assessment, analytics, and emerging technologies of caraga state university for providing a workspace to download and pre-process the landsat images. references [1] f. mushtaq, a. c. pandey, “assessment of land use/land 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“water quality index with missing parameters”, international journal of research in engineering and technology, vol. 2, no. 4, pp. 609-614, 2013 authors profile michelle v. japitana is an associate professor the college engineering and geosciences (cegs), caraga state university and is currently a doctor of the engineering program of the university of san carlos. she received her bsc degree in geodetic engineering from caraga state university in 2003 and her msc in remote sensing from the university of philippines. her research interests include resource mapping, environmental monitoring, and rs-gis applications. marlowe edgar c. burce is an associate professor of the university of san carlos. he finished his phd (2012) and msc (2009) in biosystems sustainability at hokkaido university, japan. he also received his msc in information technology in 2005 and bsc in computer engineering at the university of san carlos. his research interests include precision agriculture, field robotics, remote sensing, management information systems, application and systems programming, programmable logic controllers, microcontrollers and embedded systems. microsoft word 18-881-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1303-1306 1303 www.etasr.com abdul-niby et al.: a simple phase shifting technique for an injection locked oscillator a simple phase shifting technique for an injection locked oscillator mohammed abdul-niby school of engineering the australian college of kuwait, kuwait m.nibi@ack.edu.kw mamoon alameen school of engineering the australian college of kuwait, kuwait m.radiy@ack.edu.kw hania baitie school of engineering the australian college of kuwait, kuwait h.baitie@ack.edu.kw abstract— in self oscillating systems, locking of the oscillators can take place for injected signals close in frequency to nth harmonics of the free-running frequency. in this paper, we present a simple design for digital phase shift control by using a harmonically injection locked oscillator (ilo) of 35mhz frequency. phase shifters at high frequencies are essential in many communication system applications such as frequency synthesis, quadrature signal generation and phase locked loops (plls). keywords-injection locked oscillator; injection locking; phase shifter i. introduction in self oscillating systems, oscillators locking can occur when signals close in frequency to nth harmonics of the freerunning frequency are injected [1-5]. the superharmonic injection locked oscillator is designed and implemented using a colpitts oscillator which has a free-running frequency of 35mhz. this frequency is used as the intermediate frequency (if) in low capacity fm-fdm and psk-pcm communication systems. for very practical reasons, the colpitts oscillator is injected with the 2nd harmonic signal’s frequency i.e. 70mhz to achieve locking. the frequency range in which injection locking happens is called “locking range”. injection locking also happens when the injected frequency is close to the harmonic or subharmonic of the free-running oscillator frequency i.e. nωo or ωo/n [1-3]. the use of q superharmonic injection-locked oscillator as frequency divider was discussed in [6], whereas a precise digital phase shifter using a phaselocked loop was investigated in [7]. in [8], authors presented a multiphase injection-locking (il) technique and its application in the locking range extension in multiphase injection-locking oscillators (ilos) for terahertz (thz) signal generation. ii. proposed architecture the proposed phase shifting technique is shown in figure 1. by injecting a signal harmonically related to the oscillator free-running frequency, a dual function of locking and phase shifting may be achieved. the magnitude of frequency shift and rate of change of phase is controlled by the pulse amplitude, while the pulse duration controls the length of time for which the total phase change can be obtained. fig. 1. injection locked oscillator (ilo) with phase control pulses model iii. analysis of the proposed phase shifting technique figure 2 shows the time domain waveform of the ilo in locked and unlocked conditions. in this method the oscillator is forced to operate outside the locking range. this way of detuning is developed through the use of a varactor diode connected in parallel with the oscillator tuned circuit. the varactor diode act as a variable capacitor when the bias voltage is varied hence controls the oscillator free-running frequency. the oscillator free-running frequency is controlled by applying a control pulse to the varacor diode. the amplitude of the pulse should cause sufficient detuning to force the oscillator to operate at new frequency outside the locking range. as this condition is achieved, then proper pulse duration should be chosen to obtain the required phase shift such that the condition constantft is valid, where t is the pulse duration an ∆f is the frequency detuning. after applying the unipolar pulse to the varactor diode, the oscillator will be running at a phase of ∆φ relative to its previous locked phase. in order to prove that the unipolar pulse can cause the required phase shift, let us find the relation between t and ∆f that is satisfying our requirement to obtain a phase shift in the ilo frequency. with reference to figure 2, we can proceed as follows: engineering, technology & applied science research vol. 6, no. 6, 2016, 1303-1306 1304 www.etasr.com abdul-niby et al.: a simple phase shifting technique for an injection locked oscillator fig. 2. the time domain waveform of the ilo in locked and unlocked conditions. for t < to i.e. before applying the unipolar pulse, the oscillator is in a locked condition and the oscillator locked signal is: ( ) cosv t v tw= (1) and the locking signal is: ( ) cosl lv t v n tw= (2) at the beginning of the pulse at t=to, the ilo is forced to operate at some )(   frequency outside the locking i.e. xlma   . the ilo output  tv becomes:   tvtv )cos(   (3) the phase at the instant when  ott is:     oo tt   (4) the end of the pulse i.e. at t=to+t, the phase is:     tttt oo   (5) the phase accumulation during the pulse duration t can be found from the difference between equations (4) and (5):       tttt oo   (6) if the pulse had not been applied, the phase accumulation of the ilo output signal for the same time t elapsed would be: to   (7) thus, the resultant phase shift due to  in t can be obtained from equations (6) and (7): ftto   2 (8) clearly, one can see from equation (8) that the phase shift depends on the product of frequency detuning and the pulse duration. for constant phase shift, the named product should be kept constant. under the continuous drive of the locking signal, the oscillator will return to its locked condition at the end of the pulse and running at frequency f with the new phase. for immediate (no transient) return to the locked condition,  must be equal to the integer multiple of the period of the locking signal. since the later is 2π/n with respect to the ilo signal period ( 2 ), then the following condition must be satisfied: n k 2  (9) k = 1, 2, 3, …. comparing equation (8) and (9) we find: constant n k ft (10) iv. circuit design and operation figure 3 shows the schematic diagram of the designed injection locked oscillator. the oscillator is designed to operate at 35mhz; the total capacitance in the oscillator tuned circuit is chosen to be 60pf while the inductance is calculated from the formula of the free running frequency 1 lcw = . it is found that l = 0.35µh, thus the coil of 10 turns wounded side by side on a plastic bobbin of 4mm diameter with tuning ferrite core. for the ilo oscillator, an integrated circuit ul1111n (14 pins dil) was used, in such integrated circuit there are five transistors, two of these are in differential pair and three separate transistors. the phase shift control pulses are applied to the varactor (ba124) which is reversed biased by -6v supply through a potentiometer as shown in figure 3. fig. 3. schematic diagram of the designed injection locked oscillator with phase control pulses. v. experimental measurements it is necessary to conduct a set of static measurements on the proposed ilo circuit to examine its parameters and ability of achieving phase shifting. these measurements are engineering, technology & applied science research vol. 6, no. 6, 2016, 1303-1306 1305 www.etasr.com abdul-niby et al.: a simple phase shifting technique for an injection locked oscillator essential in setting the proper operation of the phase shift control. a. varactor static capacitance–voltage characteristic (ba124) the static capacitance–voltage characteristic of the varactor is shown in figure 4. fig. 4. static characteristic (cv vs vr) of the ba124 varactor diode. pulses shown are applied to control the capacitance. b. measurement of the ilo locking band as a function of the locking signal voltage measurement of locking band or locking ranges as a function of locking signal voltage is performed for harmonic locking (n=2). locking band bl (bl = 2∆flmax) measurements help in deciding what locking signal level should be injected to obtain a locking range less than the fixed frequency detuning caused by the applied control pulse of 4v amplitude. the measurement is done by setting zero locking signal voltage and adjusting the varactor operating point at 2v by the preset pot (figure 3). the oscillator free-running frequency is then tuned to 35 mhz by the inductance core, and tuning signal to 70 mhz. setting the locking signal to a certain voltage vl (below the oscillator voltage vo) starting from a very small locking signal level, then detuning the locking signal and observe the spectrum of the ilo output then recording lower and upper frequencies at which the unlock occur. the frequency limits of locking and locking band curves are plotted in figures 5 and 6. vi. conclusion a simple ilo based phase shifting technique is presented. the presented architecture consists of a colpitts oscillator running at an intermediate frequency of 35mhz and a 2nd harmonic frequency injected signal. the proposed ilo attains a large locking range of about 0.88mhz. the proposed design was demonstrated and tested successfully; the obtained results are very satisfactory. the essential features of this technique are: 1. the use of unipolar pulses which are preferable due to the possibility of using ttl in processing such pulses. 2. the use of a varactor diode as a controlled reactive element in the oscillator tuned circuit to force the ilo to operate at a frequency outside the looking range. 3. the proposed circuit of the injection locked oscillator can be used frequency divider. apart of the above mentioned features, the proposed technique has a disadvantage which is the need of supplying the locking signal at the second harmonic of the oscillator output frequency. this may be impractical especially at high microwave frequencies. fig. 5. ilo output frequency versus locking signal voltage. fig. 6. locking band as a function of the voltage of the locking signal. acknowledgment the authors appreciate the continuous support of the australian college of kuwait in conducting this research work. engineering, technology & applied science research vol. 6, no. 6, 2016, 1303-1306 1306 www.etasr.com abdul-niby et al.: a simple phase shifting technique for an injection locked oscillator references [1] r. adler, “a study of locking phenomena in oscillators”, proceedings of the ire, vol. 34, no. 6, pp. 351-357, 1946 [2] k. kurokawa, “injection locking of microwave solid-state oscillators”, proceedings of the ieee, vol. 61, no. 10, pp. 1336–1410, 1973 [3] l. j. paciorek, “injection locking of oscillators”, proceedings of the ieee, vol. 53, no. 11, pp. 1723–1727, 1965 [4] h. l. stover, “theoretical explanation of the output spectra of unlocked driven oscillators”, proceedings of the ieee, vol. 54, no. 2, pp. 310– 311, 1966 [5] m. armand, “on the output spectrum of unlocked driven oscillators”, proceedings of the ieee, vol. 57, no. 5, pp. 798–799, 1969 [6] h. r. rategh, t. h. lee, “superharmonic injection-locked frequency dividers”, ieee journal of solid-state circuits, vol. 34, no. 6, pp. 813– 821, 1999 [7] j. austin, j. r. forrest, “a precise digital phase shifter using a phaselocked loop”, electronics letters, vol. 14, no. 8, p. 254–255, 1978 [8] h. wang, k. sengupta, rf and mm-wave power generation in silicon, academic press, elsevier, 2016 microsoft word 14-3607_s engineering, technology & applied science research vol. 10, no. 4, 2020, 5358-5366 5358 www.etasr.com kassem et al.: solar energy potential and feasibility study of a 10mw grid-connected solar plant … solar energy potential and feasibility study of a 10mw grid-connected solar plant in libya youssef kassem department of mechanical engineering engineering faculty near east university nicosia, cyprus yousseuf.kassem@neu.edu.tr huseyin camur department of mechanical engineering engineering faculty near east university nicosia, cyprus huseyin.camur@neu.edu.tr osama a. m. abughinda department of mechanical engineering engineering faculty near east university nicosia, cyprus osama1984amma@gmail.com abstract—libya is currently interested in utilizing renewable energy technologies to reduce the energy dependence on oil reserves and greenhouse gas (ghg) emissions. the objective of this study is to investigate the feasibility of a 10mw gridconnected pv power plant in libya. nasa data are used to analyze the global horizontal irradiation, direct normal irradiation, and air temperature of 22 selected locations in libya and to evaluate the potential of solar energy. retscreen software is used to estimate the energy production, ghg emissions, and financial parameters for the 22 locations. based on the solar atlas map, it is noticed that the highest global horizontal irradiation is in the southern part of libya, which ranged from 2100 to 2500kwh/m 2 . these results indicate that libya has a huge solar energy potential that can be used to generate electricity. moreover, based on techno-economic results, it is observed that the highest electricity generation of 22067.13mwh is recorded at al kufrah and the lowest at al jabal al akhdar with a value of 17891.38mwh. furthermore, al kufrah and murzuq are the best locations for the future installation of pv power plants from annual energy and the economic parameters point of view. the maximum value of power that can be generated by the plant was estimated to be 22.06gw. keywords-libya; nasa data; solar energy potential; retscreen; techno-economic analysis i. introduction energy is an indispensable need, which was met with the consumption of conventional fossil fuels until quite recently. however, the use of fossil fuels has polluted the environment and contributed to the climate change due to greenhouse gas (ghg) emissions [1]. the environmental problems resulting from the increasing fossil fuel consumption encouraged researchers to investigate alternative sources of energy that would be able to generate energy while protecting the environment [2-4]. solar energy has become an important alternative source of energy because it is clean, cost-effective, and readily available. solar energy can be converted to electricity by photo voltaic (pv) modules. the utilizing of pv systems has met the electricity demand in many countries. many studies investigated the potential for solar energy to generate power in various countries. for example, authors in [5] assessed the feasibility analysis of a 6mw grid-connected pv power plant in six states in nigeria. authors in [6] evaluated the technical viability of 1mw grid-connected at the pekan campus and gambang of ump in peninsular malaysia by using pvgis and pvwatt software. the author in [7] analyzed the feasibility of 1mw grid-connected pv power plant in cyprus. the results indicated that the capital expenditure of the pv park is a critical parameter for the viability of the project, in the case where no feed-in tariff is available. authors in [8] evaluated the potential of developing 5mw gird-connected pv power plants in eight selected cities in the southern coast of iran using retscreen software. the results showed that the southern coast of iran has a huge potential and presents actual market opportunities for investors to develop grid-connected pv projects. authors in [9] assessed the performance of a 6.4kw grid-connected pv system for household buildings in three regions in northern cyprus using simulation software (pvgis, pv*sol, and pvwatts). the results showed that solar pv power was a feasible solution for supplying power and reducing the volume of co2 emissions. authors in [10] presented the feasibility of 10mw gridconnected pv plants at 44 sites in saudi arabia. the author in [11] studied the feasibility of a pv grid-tied energy system in jos, nigeria by using homer. the results showed that the system could produce energy of 331.536gwh/year with a capacity factor of 40.4% from solar energy. a. renewable energy potential in libya libya is now experiencing an energy crisis because of the power cuts that persist for seven years without proven solutions. the electricity service is worsening in libya. because of libya's ongoing civil war, the country has faced a chronic power shortage, and various power plants have been damaged, which has caused a reduction in generation capacity in most populated areas. the libyan electricity sector depends on a public network linking each power station to provide energy demand to all regions of libya. the total produced electrical energy in generation stations during 2012 reached 33,980gwh. in 2017, the general electricity company of libya (gecol) stated that the available products for the network were 4,900mw, while the demand reached 6,500 mw, with a deficit of 130mw in the east and 1,470mw in the west. as a result, the power outage crisis has increased in most corresponding author: youssef kassem engineering, technology & applied science research vol. 10, no. 4, 2020, 5358-5366 5359 www.etasr.com kassem et al.: solar energy potential and feasibility study of a 10mw grid-connected solar plant … of the regions in libya, i.e. the western region has five to eight hours of blackouts per day whereas the eastern region has 1 to 4 hours of blackouts per day. according to the gecol statistics, the peak load was 7000mw in 2016. the electricity of libya is nationalized under the control of the ministry of energy. the power plants in libya are thermal power plants. there are several power plants in libya, the most important of which are west of tripoli (600mw), east of tripoli (1400mw), misrata (600mw) and tobruk (740mw). also, gecol stated that it is expected that the maximum load will increase to 10,795mw by 2020, then to 14,834mw by 2030 and 21,669mw by 2050. these estimates are based on an optimistic assumption of the recovery of the libyan economy, and the increase in demand from the industry and energy sector in particular. therefore, it can be concluded that the amount of co2 and greenhouse gas emissions released will rise as a result of increasing energy consumption. additionally, the electricity consumption demand in libya will increase in the long term [12], which indicates that the amount of fossil fuels used for electricity production will increase in the future. therefore, alternative energy sources, such as wind or solar energy could be the best solution to reduce fossil fuel demand and co2 emissions in the country. libya is a country rich in renewable energy sources, particularly solar energy, as the annual average solar radiation of the horizontal surface ranges from 5.5kwh/m 2 in the coastal strip regions to 7.0kwh/m 2 in the southern regions [13]. numerous studies have investigated the potential of renewable energy, especially solar energy, in libya. authors in [14] investigated the current utilization and the future of renewable energy in libya by conducting interviews with managers, consultants, and decision-makers from different government organizations. the results demonstrated that renewable energy could be the solution to cover some of the energy demand in the country. authors in [15] examined the potential use of renewable energy sources for improving the current and future energy situation in libya. the results indicated that renewable energy systems could produce energy and achieve cost-saving and reduce co2 emissions. authors in [16] investigated the feasibility of replacing the grid-connected hps-lamp street lighting system with a solar-powered led street lighting system for a 4km road in libya. the results indicated that the stand-alone solar-powered led lighting system reduces co2 emissions, saves fuel, and is economically feasible. authors in [17] proposed photovoltaic-solar water heating and photovoltaic-photovoltaic/thermal systems for replacing the electrical heater and reducing the peak load demand in libyan electric grid for households. authors in [18] evaluated the feasibility of a 14mw pv plant in houn city, libya. the results showed that it is economically feasible and sustainable. authors in [19] assessed the mean monthly solar radiation and sunlight duration to analyze the characteristics of radiation and duration sun rays over tripoli in libya. they concluded that solar energy can be considered as a major source of renewable energy in libya and there is a need to attract investors to renewable energy technology by strengthening the existing infrastructure and laws. moreover, according to [20], solar power will definitely help to solve the electricity supply problem. authors in [21] provided an overview of the future of renewable energy in terms of solar and wind energy utilization in libya. the results showed that libya has a huge renewable energy potential especially solar and wind, which could be used for various purposes such as electricity generation, communication systems, and mechanical activities. authors in [22] developed a 50mw pvsolar plant in al-kufra, libya. the results indicated that the energy output was found to be 114gwh/year with a payback time of 2.7 years. in addition, libyan minister of electricity stated that libya intends to build a solar power station to reduce by one-fifth its electricity needs from fossil fuels [23]. besides, according to a member of the board of directors of the general electricity company in southern libya, the libyan government aims to construct a 100mw pv system to solve the electricity problem in southern libyan cities [24]. moreover, according to the vision of the renewable energies and environment (reeo), the desert renewable energy project is one of the most promising projects in the world, which aims to supply europe with energy extracted from the solar irradiation in north africa, mainly libya, and middle east. the project can produce 250gw per year, thus preventing the emission of 150,000 tons of carbon dioxide. in summary, most of the researchers investigated the potential of solar in different parts of libya. they found that libya has a great potential for harnessing solar energy, which could be used to generate electricity. besides, the studies indicated that electricity generated from solar energy could help reducing the electricity sector's emissions and fossil fuel consumption. however, none of these studies analyzed the solar energy potential to examine the best location for the future installation of a pv system in libya. in addition, none of these papers assessed the sustainability of a 10mw gridconnected pv plant in a suitable location in libya using retscreen software, which is a vital tool in project decision making where the uncertainty of any project is analyzed by predicting the future return of the renewable energy project for sustainability. b. scope of the study the literature review reveals a clear lack of evaluation of solar potential in different locations in libya in order to examine the best location for the future installation of a pv system. furthermore, there is a clear lack of exploring the potential of a 10mw grid-connected solar pv system generation. as mentioned above, according to gecol, it is expected for the maximum load to increase to 10,795, 14,834, and 21,669mw by 2020, 2030, and 2050 respectively. therefore, the primary goal of this study is to draw a solar energy roadmap that aims to decrease the electricity consumption generated by diesel fuel between 30% and 50% by 2030 when the excepted load will reach 14,834mw. besides, this paper aims to greatly reduce the ghg emissions of the country. therefore, the potential of exploiting solar energy in 22 regions in libya is evaluated. moreover, this study provides technical, environmental, and economic aspects of the 10mw grid-connected pv system for the regions in order to provide solutions to accommodate the increasing energy demand and to improve living quality in urban areas due to the rapid urbanization of the region. in addition, the engineering, technology & applied science research vol. 10, no. 4, 2020, 5358-5366 5360 www.etasr.com kassem et al.: solar energy potential and feasibility study of a 10mw grid-connected solar plant … production of electricity using solar systems can protect the environment. for this purpose, retscreen expert software was utilized to validate the techno-economic 10mw gridconnected solar pv system in the regions. ii. materials and methods a. locations in this study, 22 regions located in different parts of libya were chosen as case studies. information for the geographical locations of the selected cities is listed in table i. table i. locations of the studied regions region latitude (°n) longitude (°e) al butnan 30.178 24.053 al jabal al akhdar 32.48 21.70 al jabal al gharbi 30.705 13.223 al jifarah 32.786 13.163 al jufrah 28.006 16.743 al kufrah 23.33 22.084 al marj 31.911 21.14 al marqab 32.407 13.86 al wahat 29.157 21.750 an nuqat al khams 32.718 11.990 az zawiyah 32.763 12.726 benghazi 32.129 20.082 darnah 32.759 22.638 ghat 26.020 10.434 misratah 32.375 15.090 murzuq 24.535 15.25 nalut 30.613 10.67 sabha 27.033 14.43 surt 31.206 16.584 tripoli 32.897 13.17 wadi al hayat 26.423 12.718 wadi ash shati' 27.602 12.864 b. design of the pv power system according to [25], the parameters that are considered of most importance in designing a pv solar plant are: • power generating factor (pge): ��� � ��� � � ������������ ��� � �� � ���� ��� ����� � � ��� (1) • energy demand (ed): �� � ������ ����� !"#�� �$ %&& &�%'� (2) • solar pv energy required (spver): (�)�* � ��*��+( (3) • pv module sizing: ,�"%& -%"" !�%. �%"#�� � ��� /0 ��� 12 �3�� � 4 ��� 1��� ���� 5 ��� (4) �) �'�&� �#6� � 7�� � 8 �� 4� 9 ���1/0 ���4�� 4�:� ���1 (5) • inverter sizing: ;�<��"�� �#6� � ��*�=%�"�� �$ �%$�"� (6) where ��* is peak energy requirement, �+( is energy lost in the system and the factor safety is 1.3 [25]. c. pv plant layout fifty hectares of land are usually needed in order to install a 10mw solar pv plant. for the proposed pv system, canadian solar mono-si cs6x-300m with an output power rating of 300w has been considered due to its high efficiency. to build the 10mw grid-connected pv plant in the chosen location, 33500 of the selected modules are required, as calculated with (5). furthermore, the inverter size is estimated as 13mw. fourteen units of central inverters of sunny central 850cp xt were utilized. each selected inverter has a capacity of 954kw. the total capacity of 13.356mw was used for the proposed pv system to convert dc into ac power. the grid-connected pv system configuration is shown in figure 1. fig. 1. components of the grid-connected solar plant. d. pv solar panels the solar panels, composed of a number of solar cells, are used to change the sunlight into direct current using semiconducting materials. in general, when the solar radiation falls on the solar cell, the anti-reflective layer effectively traps the incident light by enhancing its transition to the next layers. on the other hand, the positive gaps move to the conduction area of the positive strip, resulting in a potential difference between the surfaces of the two-link. the two surfaces can be connected by an electrical conductor to obtain an electric current in an electrical circuit, where electrons pass through the negative to the positive link, and thus light energy is converted into electrical energy. in this study, monocrystalline pv panels are used. table ii tabulates the characteristics of the used pv panels. table ii. characteristics of used pv panels electrical characteristics at (stc) value watts (stc) 300w watts (ptc) 217w max power voltage (vmpp) 36.5v max power current (impp) 8.22a open circuit voltage 45.0v short circuit current 8.74a max system voltage (ul) dc 600v efficiency 15.63% e. power conditioning units generally, pv panels convert solar radiation energy to electrical energy and the electricity is produced in the form of direct current (dc). therefore, the dc current must be converted to alternating current (ac). for this purpose, inverters are used. the specifications of the applied inverter used in this study are presented in table iii. engineering, technology & applied science research vol. 10, no. 4, 2020, 5358-5366 5361 www.etasr.com kassem et al.: solar energy potential and feasibility study of a 10mw grid-connected solar plant … table iii. electrical properties of the selected inverters type modular power switch max. dc power 954kw max. input voltage 1000v mpp voltage range 681e850v/625e850v rated input voltage 681v max. input current 1400a max. dc short-circuit current 2500a rated power (@ 25℃) 935kva nominal ac voltage/nominal ac voltage range 386v/348v-443v max. output current/max. total harmonic distortion 1411a/0.03 max. efficiency/european efficiency/cec efficiency 98.6%/98.4%/98.5% f. power evacuation for the proposed 10mw grid-connected solar plant, transformers with a rated power of 1.5mva were utilized. the pv system is integrated into the grid by a dc/ac inverter, a step-up transformer, and an evacuating line of 33kv. the evacuation of power demands the reliability of the distribution system to be 99.5%. the efficiency of the transformer is almost 97% g. simulation software used pvgis (photovoltaic geographic information system) is widely used for evaluating the performance of solar pv power plants. the european commission has developed a web application with a geographical location interface for analyzing “solar resource geographical evaluation and performance of photovoltaic technology”. this tool contains a package, which includes solar radiation databases, performance evaluation methods, and estimates of economic parameters including electricity cost. pvgis allows the user to choose the pv technology to be used in the system, enter system capacity requirement for installation and enter the permissible total system losses. it also allows the user to choose the slope or tilt angle and azimuth angle of the pv module. in order to assess the technical, economic, and environmental impact of renewable energy projects, retscreen program was used. retscreen is a clean energy management program to ensure energy efficiency, renewable energy, co-generation analysis, and continuous energy performance analysis. retscreen is a useful tool for analyzing and assessing the viability of a gridconnected renewable energy system. in this study, important economic measures are the net present value (npv), the internal rate of return (irr), the flat energy cost (lcoe), the payback period (pb), the annual life cycle savings (alcs), and the benefit-cost ratio (b-c) which are calculated using the retscreen. figure 2 presents the outline of the methodology used by the retscreen expert software. • net present value (npv): ?�) � ∑ abcde fbg�hi (7) • levelized cost of energy (lcoe): +jk� � ��l �5 ���� �m� ��5���l�� �5 ����� ����2 1��� �� �m� ��� ��5���l� (8) • the internal rate of return (irr): k � ∑ abcdenoofbg�hi (9) • simple payback (sp): (� � apnqrasbsteauvwveaxyeaz[z\pra]&_ea`asb\ (10) • equity payback (ep): �� � ∑ j�g�hi (11) • annual life cycle savings (alcs): c+j( � g/0d tedp d cdftfgh (12) • ghg emission reduction cost (grc): �*j � ija�∆z[z (13) • benefit-cost ratio (b-c): lmj � g/0ecdp5nfacdp5nfa (14) • capacity factor (cf)): j= � /]ao/�pqri (15) where ���� is the energy generated per year, � is the installed capacity, n is the project life in years, j� is the after-tax cash flow in year n, r is the discount rate, c is the total initial cost of the project, $ is the debt ratio, b is the total benefit of the project, ;� is the incentives and grants, j��� is the annual energy savings or income, j� 4 is the annual capacity savings or income, jos is the annual renewable energy (re) production credit income, jqtq is the ghg reduction income, j�&u is the yearly operation and maintenance costs incurred by the clean energy project, j5��� is the annual cost of fuel, which is zero for renewable projects, and ∆qtq is the annual ghg emission reduction. fig. 2. standard analysis in retscreen software. engineering, technology & applied science research vol. 10, no. 4, 2020, 5358-5366 5362 www.etasr.com kassem et al.: solar energy potential and feasibility study of a 10mw grid-connected solar plant … iii. results and discussion a. global solar resources two parameters, namely global horizontal irradiation (ghi) and direct normal irradiation (dni) are used to analyze the solar resource in libya. the annual averaged ghi, dni, and temp values for all the locations are provided in table iv. the values of ghi were found to vary from 2020.807kwh/m 2 to 2308.587kwh/m 2 . the maximum and minimum annual values of ghi are recorded in al kufrah and tripoli, with a value of 2308.587kwh/m 2 and 2020.807kwh/m 2 respectively. furthermore, it is found that the highest annual value of dni of 2429.203kwh/m 2 occurs in misratah and the lowest value (2267.607kwh/m 2 ) is recorded in darnah. additionally, it is noticed that the maximum and minimum value of air temperature is recorded in ghat and al jabal al akhdar with a value of 25.047 o c and 17.298 o c respectively. table iv. annual ghi, dni and temp for all selected regions regions ghi [kwh/m 2 ] dni [kwh/m 2 ] temp [℃℃℃℃] al butnan 2110.6 2294.8 22.8 al jabal al akhdar 2035.3 2309.2 17.3 al jabal al gharbi 2101.8 2323.5 21.5 al jifarah 2187.2 2350.2 22.6 al jufrah 2187.2 2350.2 22.6 al kufrah 2308.6 2394.4 23.4 al marj 2068.9 2314.1 21.6 al marqab 2069.9 2375.7 20.6 al wahat 2131.4 2309.3 23.8 an nuqat al khams 2049.0 2373.6 22.9 az zawiyah 2060.5 2420.7 23.2 benghazi 2065.6 2400.5 21.4 darnah 2058.9 2267.6 20.3 ghat 2206.3 2311.8 25.0 misratah 2061.5 2429.2 22.1 murzuq 2248.5 2318.7 24.3 nalut 2080.5 2274.0 22.7 sabha 2145.1 2271.8 24.8 surt 2117.7 2416.1 22.4 tripoli 2020.8 2397.3 22.3 wadi al hayat 2211.1 2330.9 23.4 wadi ash shati' 2166.1 2295.9 24.6 b. simulationrresults of energy generation and capacity factor in this study, pvgis software is used to find the optimum slope angle and azimuth angle for all selected locations in libya. table v lists the optimum angle for the future installation of a pv system for all chosen locations. retscreen is utilized to investigate the feasibility of a grid-connected 10mw pv system in the selected locations. the mean monthly electricity generation from the proposed system is shown in table vi. figure 3 illustrates the annual electricity exported to the grid from the proposed pv system. it is observed that the highest annual electricity generation of 22067.128mwh is recorded at al kufrah and the lowest one of 17680.901mwh is obtained at al marqab. moreover, based on the results of electricity generation for al kufrah and al marqab (see table vi), it is noticed that the maximum monthly electricity generation is achieved in july with a value of 1986.72mwh for al kufrah and 1847.528mwh for al marqab. the minimum monthly electricity generation is recorded in december for al marqab and al kufrah. the capacity factor (cf) for the proposed pv project for all chosen locations is presented in figure 4. table v. optimum angles for pv systems location slope angle [°] azimuth angle [°] al butnan 29 -6 al jabal al akhdar 28 -7 al jabal al gharbi 30 -7 al jifarah 30 -3 al jufrah 27 -6 al kufrah 22 -5 al marj 29 -8 al marqab 30 0 al wahat 28 -5 an nuqat al khams 31 -4 az zawiyah 30 -3 benghazi 29 -2 darnah 28 -4 ghat 26 -6 misratah 30 -4 murzuq 24 -7 nalut 30 -6 sabha 26 -7 surt 29 3 tripoli 30 4 wadi al hayat 27 0 wadi ash shati' 28 -2 fig. 3. annual electricity exported to the grid for all selected locations. fig. 4. cf for all locations. the maximum capacity factor is observed for the climatic conditions of al kufrah with a value of 25.07%. the values of cf are within the range 20.08%-25.07%. these values indicate that the selected regions are suitable for developing pv projects. the results of the annual energy exported to the grid and their cf in each city in libya are compatible with the engineering, technology & applied science research vol. 10, no. 4, 2020, 5358-5366 5363 www.etasr.com kassem et al.: solar energy potential and feasibility study of a 10mw grid-connected solar plant … acceptable values [10, 26] and hence, it is technically sustainable to build and operate solar pv plants in the selected regions based on the technical viability of the solar system. c. simulation results of financial and emission reduction analysis economic analysis is essential in order to know if the project is economically viable and sustainable. studying the economic viability of pv power plant benefits and informs both investors and policymakers. the financial analysis worksheet of retscreen software includes some financial parameters like inflation rate, discount rate, reinvestment rate, debt ratio, debt interest rate as input variables. based on the input variables, simple payback, equity payback, net present value (npv), annual life cycle savings (alcs), and levelized cost of electricity were determined. table vii shows the financial parameters including inflation rate, discount rate, debt ratio, debt interest rate, and project life which are used as input variables for assembly to be economically feasible. table vi. mean monthly electricity exported to the grid in mwh from the proposed pv system for all selected regions month al butnan al jabal al akhdar al jabal al gharbi al jifarah al jufrah al kufrah al marj al marqab jan. 1482.45 1019.00 1137.54 1234.86 1305.08 1587.19 1190.31 1161.49 feb. 1532.75 1122.34 1323.06 1362.68 1454.17 1727.04 1294.09 1221.70 mar. 1808.01 1543.41 1733.07 1660.70 1823.52 1977.31 1715.83 1565.76 apr. 1858.58 1717.82 1786.08 1695.56 1840.12 1917.34 1847.94 1649.98 may. 1925.64 1840.15 1828.81 1717.70 1862.01 1977.39 1907.59 1730.37 jun. 1941.69 1851.44 1828.21 1692.20 1852.40 1942.22 1898.76 1733.37 jul. 1990.48 1912.75 1977.69 1783.46 1965.28 1986.72 1990.33 1847.53 aug. 1973.41 1825.05 1903.45 1749.74 1931.31 1986.00 1959.44 1757.98 sep. 1875.02 1617.19 1667.62 1605.74 1694.00 1908.28 1744.61 1509.14 oct. 1787.17 1401.08 1471.30 1384.86 1645.74 1909.36 1588.51 1368.89 nov. 1492.16 1084.45 1140.12 1209.22 1332.55 1644.73 1258.60 1098.46 dec. 1395.02 956.69 1036.59 972.08 1189.02 1503.55 1118.96 1036.23 month al wahat an nuqat al khams az zawiyah benghazi darnah ghat misratah murzuq jan. 1344.84 1131.85 1121.16 1199.03 1095.93 1708.74 1308.39 1575.42 feb. 1495.15 1308.28 1300.75 1300.83 1217.36 1756.72 1386.79 1710.57 mar. 1793.38 1709.27 1705.56 1722.05 1639.14 1936.71 1784.12 1969.93 apr. 1814.05 1813.11 1816.07 1852.16 1787.48 1855.74 1859.89 1899.62 may. 1878.66 1883.10 1891.56 1910.15 1915.47 1729.51 1911.88 1897.24 jun. 1896.32 1892.96 1904.02 1900.78 1939.33 1669.57 1899.34 1891.20 jul. 1978.18 2006.89 2017.62 1992.77 2015.16 1827.65 2011.52 1977.58 aug. 1962.10 1946.14 1951.76 1963.15 1933.42 1848.92 1982.71 1983.57 sep. 1778.01 1679.92 1678.75 1750.10 1730.47 1730.30 1745.93 1848.98 oct. 1718.07 1457.72 1450.79 1596.42 1490.30 1747.30 1615.68 1839.03 nov. 1418.04 1162.27 1152.28 1267.29 1173.66 1556.77 1295.03 1604.16 dec. 1209.80 1021.90 1011.22 1127.98 1006.26 1612.43 1212.14 1484.67 month nalut sabha surt tripoli wadi al hayat wadi ash shati' jan. 1387.45 1398.51 1371.93 1245.03 1517.70 1428.35 feb. 1544.91 1517.54 1486.18 1370.03 1634.83 1539.58 mar. 1909.76 1859.00 1858.57 1666.24 1918.52 1869.55 apr. 1915.71 1806.54 1852.67 1699.41 1859.38 1801.19 may. 1813.48 1742.48 1860.13 1720.87 1773.15 1726.66 jun. 1823.95 1781.60 1846.30 1695.48 1757.20 1759.97 jul. 1927.75 1898.81 1961.08 1786.96 1882.92 1877.79 aug. 1957.52 1861.55 1938.07 1753.29 1861.94 1851.15 sep. 1739.24 1710.85 1716.92 1610.29 1786.41 1714.41 oct. 1632.32 1724.00 1695.64 1391.14 1787.48 1744.61 nov. 1408.61 1377.89 1395.14 1218.08 1453.56 1404.58 dec. 1249.98 1261.15 1256.48 980.89 1406.55 1290.30 table vii. financial parameters factor unit value inflation rate % 8 discount rate % 6 reinvestment rate % 9 project life year 25 debt ratio % 70 debt interest rate % 0 debt term year 25 electricity export escalation rate % 5 based on the input variables the npv, alcs, and other financial parameters were calculated by the retscreen software. according to [27], npv and the payback period are the main economic viability factors in order to measure a pv project. according to our analysis, the npv values for all regions are positive (see figure 5), which indicates that the proposed project is estimated to be financially and economically feasible [10, 27]. the simple payback period which is the length of time that will take to recoup the project's initial investment is shown in figure 6. the proposed pv project in al marqab region has the longest payback period of engineering, technology & applied science research vol. 10, no. 4, 2020, 5358-5366 5364 www.etasr.com kassem et al.: solar energy potential and feasibility study of a 10mw grid-connected solar plant … 15.91 years followed by the one in al jabal al akhdar region with 15.72 years, while al kufrah region has the shortest payback period of 12.75 years. in addition, al marqab has the highest equity payback of 6.31 years, while the one in al kufrah has the least with 4.79 years. furthermore, it is found that al kufrah region has the lowest cost of electricity of 0.06564$/kwh followed by murzuq region with a value of 0.0668$/kwh, while al marqab has the highest electricity cost of 0.0819$/kwh as shown in figure 7. further analysis of the project was carried out by estimating the value of the alcs of the developed pv plants. figure 8 presents the results of this analysis for all selected regions. the proposed pv project in al kufrah region has the highest alcs of 2375881.48 $/year followed by the one in murzuq region with 2309133.84$/year, while al marqab region has the lowest alcs of 1615756.51$/year. fig. 5. net present value in $ for all locations. fig. 6. simple payback and equity payback in years. fig. 7. energy production cost in $/kwh for all locations. the emission analysis worksheet was used to calculate the ghg emission reduction resulting from carrying out the solar pv installation. the software calculates the gross annual ghg emission reduction for each of the 22 regions as shown in figure 9. the project in al kufrah region has a maximum ghg emission reduction of 14025.28t co2. it is followed by the project in murzuq region whereas the least emission reduction is obtained from the project in al butnan region. fig. 8. annual life cycle saving in $/year for all locations. fig. 9. emission reduction results. iv. successful policies for supporting solar pv power systems renewable energy policies depend on a country's geography, population density, technical and financial capacity, and sovereignty obligations that govern deployment and development of its renewable energy sources [28]. in order to develop and promote renewable technologies and especially solar pv technology in a country, different policy suggestions and interventions are required. generally, the successful renewable policy or market needs five steps that make up the policy design cycle, which are [28, 29]: • defining renewable energy sources targets • identifying an appropriate strategy to reach the targets • implementing the strategy • enforcement and monitoring • evaluation of compliance additionally, a successful renewable policy or market depends on the technology-specific financial support [30]. however, there are some obstacles in using renewable energy in developing countries in general and libya in particular, which are classified into financial, institutional, and technical constraints. financial and economic constraints are considered the most important factors that affect utilizing renewable energy technologies as generation power in developing countries. these constraints are concentrated in the high capital cost of renewable energy projects with a lack (or absence) of financing mechanisms, in addition to the misconception that investing in such projects represents a financial risk. also, some banks and financing sources may not encourage loans and investments in emerging fields compared to traditional energy projects, and this supports that investments in engineering, technology & applied science research vol. 10, no. 4, 2020, 5358-5366 5365 www.etasr.com kassem et al.: solar energy potential and feasibility study of a 10mw grid-connected solar plant … renewable energy fields may not be of clear in-kind value, and may not be economically attractive (cost-benefit analysis) when compared with other investment opportunities. therefore, the government can encourage investment in new and renewable energy fields by: • setting environmentally oriented policies such as exempting or reducing taxes on energy production from renewable and environmentally friendly sources, and setting taxes and fines on more polluting sources. • providing financial assistance and support and ensuring project loans that drive towards the use of renewable resources. • setting and developing standards and legislation related to new and renewable sources within the concept of all concerned partners. • reconsidering petroleum products pricing systems and linking them to fuel quality. these must be held in addition to taking into account detailed project proposals that include a description of procedures, mechanisms and the proposed implementation schedule for the project, determining technical needs, techniques, equipment, and expertise needed for implementation, estimating the total value of investments and their terms, and assessing the direct and indirect financial benefits of the project. moreover, public awareness is categorized as one of the constraints of utilizing renewable energy technology. the lack of interest in using renewable sources for energy production and a misunderstanding of the nature of the work and applications of renewable energy technologies by the parties concerned and society at large is a major impediment to relying on clean sources for energy production. this obstacle strengthens the general feeling among institutions and individuals that there is little benefit in endeavors related to the environment and the feasibility of using systems that depend on varying natural phenomena (such as the sun and wind). here, the role of information and awareness emerges to push towards the rehabilitation of individual and public opinion towards a correct concept of energy production from clean and environmentally friendly sources, bearing in mind that awareness is not limited to the media campaigns of the public and its encouragement to switch to new and renewable energy technology only. rather, it should extend to repeated training and technical education through training programs, scientific seminars, workshops, and conferences for engineers and technicians, and decision-makers in the field of energy and transportation, which help clarifying economic, environmental, and technical facts in these areas. v. conclusions the problem of power outages continues to trouble the people of libya since the civil war destroyed the substructure and transmission of the only source of electricity, while the quantities of fuel needed to operate the generation stations are reducing. this situation poses a challenge to the besieged libyans and forced them to resort to many alternative options such as bringing small generators, storing electricity in car batteries, etc. however, the widening circle of generator users in libya has left an atmosphere of noise and pollution not seen before, which prompted several researchers to investigate the potentiality of solar energy to generate electricity. therefore, the investigation of the feasibility of a 10mw grid-connected pv system was made in this study. to achieve this, retscreen software was utilized to determine the financial parameters and reduction of co2 emissions. the main findings of the current study are: • the annual average global horizontal irradiation of libya is within the range of 1900-2700kwh/m 2 . the highest global horizontal irradiation is in the southern part of libya, ranging from 2100 to 2500kwh/m 2 . these results indicate that libya receives a huge amount of solar energy that can be used to generate electricity. • the values of ghi varied from 2020.807kwh/m 2 to 2308.587kwh/m 2 . the maximum and minimum annual ghis are recorded in al kufrah and tripoli, with values of 2308.587kwh/m 2 and 2020.807kwh/m 2 , respectively. • it was found that the highest annual value of dni of 2429.203kwh/m 2 occurs in misratah 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[30] r. haas, c. panzer, g. resch, m. ragwitz, g. reece, and a. held, “a historical review of promotion strategies for electricity from renewable energy sources in eu countries,” renewable and sustainable energy reviews, vol. 15, no. 2, pp. 1003–1034, feb. 2011, doi: 10.1016/j.rser.2010.11.015. microsoft word 36-3007_s_etasr_v9_n5_pp4775-4782 engineering, technology & applied science research vol. 9, no. 5, 2019, 4775-4782 4775 www.etasr.com louarem et al.: an efficient active and reactive power control of dfig for a wind power generator an efficient active and reactive power control of dfig for a wind power generator sabah louarem department of electrical engineering, laboratory dac hr, ferhat abbas university setif 1, algeria slouarem@univ-setif.dz tarek bouktir department of electrical engineering, ferhat abbas university setif 1, algeria tbouktir@univ-setif.dz djamel eddine chouaib belkhiat department of physics, laboratory dac hr, ferhat abbas university setif 1, algeria djamel.belkhait@univ-setif.dz saad belkhiat department of electrical engineering, laboratory dac hr, ferhat abbas university setif 1, algeria sbelkhiat@univ-setif.dz abstract—during the last decade, wind energy gained much importance as an energy source in power systems. dfig energy is one of the most widely accepted types of renewable energy generation because of its several benefits. this paper presents a comparative study on the performance of different control strategies for dfig wind turbines: proportional––––integral (pi), artificial neural networks (ann), ��, and adaptive fuzzy pi controller. simulation results show that dfig’s performance, dynamic response, and robustness against machine parameter variations are improved with ��control technique. keywords-wind energy; dfig; pi controller; ann controller; �� controller; adaptive fuzzy pi controller i. introduction in the last few years, severe environmental problems attracted the world’s attention to renewable energy utilization [1]. renewable energy sources, safe and reliable for the environment, are locally available energy sources [2]. among them, wind power has received considerable attention [3]. wind energy conversion systems (wecs) can be classified in two categories: variable and fixed-speed wecs. among these techniques, variable speed wind generators are frequently used compared to fixed-speed systems because of their efficient energy production, improved power quality and dynamic performance during grid faults [4]. in this context, the doublyfed induction generator (dfig) has proved its worth as a powerful solution to improve the power rating of wind [4-5]. several control algorithms have been proposed to improve dfig-based wind turbine system’s behavior during normal operation [6]. most of these control laws were generally based on the vector control concept. for instance, decoupled control of active and reactive power in a dfig-based wind energy conversion system with conventional pi controllers has been proposed in [7]. the main disadvantage of this kind of controllers is that they require accurate knowledge of machine’s parameters [8]. to address this issue, several studies focused on advanced and robust controllers have been conducted. for example, predictive functional control (pfc) [9] was proposed in order to reduce the incidence of machine’s parameter variations. in the same context, a predictive power controller synthesized by using a linearized state-space model of dfig has been proposed in [10]. the design of an adaptive fuzzy gain scheduling of proportional integral controller (afgpi) has been performed in [11] to address the issue of parameter changes and satisfactory power response was obtained, compared to the conventional pi controller. a neuronal controller has been designed in [12] to control the rotor currents of dfig. the robustness of the proposed controller has been tested when the stator and the rotor selfinductances increased by 20%. another robust h� control design, based on a vector control strategy, has been carried out in [13] for the purpose of controlling active and reactive power flow between dfig and the grid. the tracking control performance of the proposed controller was evaluated by modifying the machine's parameters. the obtained simulation results were satisfactory, showing the robustness of the h� compared to the conventional pi controller. recently, a robust power command based on the active disturbance rejection control (adrc) for dfig used in a wecs system has been designed in [14]. simulation results showed that the proposed adrc controller had the best performance in terms of robustness against machine's parameter variations. in the dfigs, the stator is directly connected to the grid and the rotor is connected to the grid via the machine’s and grid’s inverters. in this paper, a comparative study of four kinds of controllers (pi, ann, h� and adaptive fuzzy pi controllers) is performed for the purpose of driving the power flowing between the stator of the dfig and the grid. corresponding author: sabah louarem engineering, technology & applied science research vol. 9, no. 5, 2019, 4775-4782 4776 www.etasr.com louarem et al.: an efficient active and reactive power control of dfig for a wind power generator ii. modeling of the wind turbine conversion system the diagram of the dfig-based wind turbine is shown in figure 1, where rsc and gsc are respectively the rotor side converter and the grid side converter. fig. 1. basic configuration of a dfig wind turbine a. wind turbine model the fraction of power extracted from the wind by a wind turbine is usually referred by the symbol � , which stands for the coefficient of performance or power coefficient. the actual mechanical power output � of a wind turbine is given as [1516]: � � � . �. �. ��� ��, �������� (1) where, � is the mechanical output power of the turbine �� , � is the air density �!" #�⁄ , � is the rotor radius �# , and � is the blade pitch angle �%&" . the power coefficient expresses the rotor aerodynamics as a function of both tip speed ratio � and pitch angle of the rotor blades �. the tip speed ratio is defined as the ratio between the blade tip speed and the wind speed, expressed as [17]: � � '()*+, (2) where . is the rotor speed �/0% and ����� is the wind speed �#/2 . in order to determine � , the following generic equation is used [18-19]: � � 30.5 6 0.0167. �� 6 2�;. 2<= > ?.�@ab. � c.deb.��fe��g 6 0.00184. �� 6 3�. �� 6 2� (3) b. modeling of the doubly-fed induction generator concordia and park’s transformation will be applied to the three-phase model of the ig. dynamic voltages equations in an arbitrary %– l reference frame are following [20-21]. the stator voltage equations are: mn� � �non� p ��q �rn�� 6 .nrnsmns � �nons p ��q 3rns; 6 .nrn� (4) the rotor voltage equations are t mu� � �uou� p ��q �ru�� 6 �.n 6 .u�rusmus � �uou� p ��q 3rus; 6 �.n 6 .u�ru� (5) the stator current of dfig was decomposed into active and reactive component via the coordinate transformation and the field-oriented vector transformation. in order to regulate the power of the dfig based wind turbine system, the vector control strategy is used. it consists of using the flux orientation, such as stator flux orientation (sfo) [7-22]: mn� � 0 and mns � mn � .nrn. the active and reactive powers at the stator side and rotor side of the dfig are given as: t n � 6mn vwvx ousyn � z[ \xvx 6 zxvwvx ou� (6) ]̂̂ _ ^̀̂ mu� � �u. ou� p abu 6 vwcvx d �ef-�q 6".n abu 6 vwcvx d ous mus � �u. ous p abu 6 vwcvx d �efg�q p ".n abu 6 vw cvx d ou� p ".h vw.ixvx (7) in steady state, the second derivative terms in (7) are neglected and the third term constitutes cross-coupling tams. t mu� � �u. ou� 6 ".n abu 6 vw c vx d ous mus � �u. ous p ".n abu 6 vw cvx d ou� p ".h vw.ixvx (8) iii. controller synthesis a. pi controller synthesis figure 2 shows the block diagram of the system controlled with the pi controller. the terms ! and !� represent the proportional and integral gain respectively. the ratio b/a represents the transfer function to be controlled, where j and k are presently defined as follows: j � bn�u p lbn abu 6 vw cvx d and k � 6b�mn (91) the response time of the controlled system will be fixed to 10ms. this value is sufficient for our application, while a lower value could involve transients with important overshoots. the calculated terms are given in [7-23]. fig. 2. system with pi controller the transfer function of the open loop becomes: m�l� � 6 no pwqxapfpxrpwcds (10) engineering, technology & applied science research vol. 9, no. 5, 2019, 4775-4782 4777 www.etasr.com louarem et al.: an efficient active and reactive power control of dfig for a wind power generator the transfer function of the closed loop is expressed by: t�l� � asuf (11) where vu is the response time. now, we express the controller gains correction based on the settings of the machines and the response time as follows: ]_ `w � 6 uf vxxvfepwcpx yvwzxw� � 6 uf (fvxvwzx (12) b. ann controller synthesis ann models are inspired from the basic framework of the brain [24-25]. in this study, the ann controller was performed by using the nftool of matlab. the dfig-based wind turbine is simulated with the pi controller. the data, before and after the controller are computed and saved. after that, the network training was done for 10 iterations. the hidden layers contained 40 neurons. fig. 3. neural network structure c. design of the t� controller in this section, we present the t� mixed-sensitivity synthesis method for robust tracking control design. the main idea consists of synthesizing the controller by minimizing t�’s performance. as mentioned above, the quotient b/a represents the transfer function to be controlled. thus, we can define the tracking error, the input control and the output as: &�2� � z�2�{/&|�2� (13) }�2� � !�2�z�2�{/&|�2� (14) {�2� � ~�2�{/&|�2� (15) where z�2� � xo p ��n���n� !�2�y e is the sensitivity function and ~�2� � ��n���n� !�2� xo p ��n���n� !�2�y e is the closed-loop transfer function. we are interested in designing the controller !�2�. for that, we will consider the t� mixed-sensitivity design problem illustrated in figure 4, where, � �2� and ���2� are selected as loop-shaping weights. hence, the tracking control design is considered as an optimization problem which consists of finding a stabilizing controller !�2� to minimize the following cost function: �� � �2�z�2����2�!�2�z�2���� (16) fig. 4. s/ks mixed-sensitivity minimization the design weights � �2� and ���2� were selected as: � �2� � �bbbna�b (17) ���2� � b.bb�dncb.bbbdncadna bb (18) by using the robust control toolbox of matlab, we obtain the following controller: ( ) 4 3 8 2 10 11 4 6 3 10 2 11 12 2.98 10 3.00 10 2.7 10 4.20 10 1.25 10 1.23 10 6.19 10 7.34 10 s s s k s s s s s − × − × − × − × = + × + × + × + × (19) d. adaptive fuzzy o controller synthesis the adaptive fuzzy o controller scheme is given in figure 5. the fls inputs are the errors (e) in active, reactive, and rate of change in active and reactive power error �%&�. the output of the fuzzy controller is %}. in contrast to the controller where controller parameters ( w and w� gains) are tuned in a predefined way [30], fls is used to tune the w and w� parameters of the pi so that the controller can keep up with parametric changes and reference signals can be tracked. fig. 5. pi control system with fuzzy gain adapter the fuzzy sets are defined as: nb is negative big, nm is negative medium, ns is negative small, zr is zero, ps is positive small, pm is positive medium, pb is positive big, b is big and s is small. the max-min reasoning method and the center of gravity defuzzification method are used [31]. the values of ! � and !�� are determined by a set of fuzzy rules of the form designed fuzzy gain scheduling controller has two inputs and two outputs. ! � � �oe�ow+,�ow��e�ow+, (20) !�� � �+e�+w+,�+w��e�+w+, (21) iv. simulation results comparative simulations of the controllers were performed in matlab. the proposed control algorithm’s nominal parameters are indicated in the appendix. it was first tested in ideal mode and driven to 1500rpm. the different controllers engineering, technology & applied science research vol. 9, no. 5, 2019, 4775-4782 4778 www.etasr.com louarem et al.: an efficient active and reactive power control of dfig for a wind power generator were tested and compared by two different criteria, namely reference tracking performance, and robustness by varying the system parameters. a. reference tracking in ideal conditions mode simulation results of active and reactive power using the classical pi controller, an ann controller, the proposed h� controller and the proposed adaptive fuzzy pi controller are shown in figure 6. as expected, both active and reactive powers have been produced with good accuracy. moreover, they can track the desired reference after a finite time interval and the answers are without overshoots for different controllers. fig. 6. active and reactive power behavior fig. 7. zoom in active and reactive power behavior figure 7 shows a zoom view of active and reactive power behavior from 0 to 0.005s to compare the response times of all controllers. we can notice a quicker response time for ann and h� controllers. in the same context, we notice that the system controlled by the pi controller evolved to a steady state with an important response time in comparison with the other controllers. fig. 8. evolution of cumulative tracking error functions in order to show which controller has the best steady state accuracy, we graph the evolution of the following cumulative tracking error functions: �~�� � � � n 6 nu���%�, � ∈ �0 22 qb (22) �~�� = � �yn − ynu���%�, � ∈ �0 22 q b (23) as shown in figure 8, the h� controller has the best steady state accuracy in comparison with the other controllers. in contrast to the h� controller, the conventional pi controller has low steady state accuracy. b. robustnes we are interested in evaluating the robustness of the different controllers against parameter variation for parameters such as the inductances bn, bu, the mutual inductance b� and the resistance �u. the controllers’ performances are compared according to rise time, maximum peak overshoot and settling time. we test the robustness of the controllers against mutual inductance variations. figure 9 and table i present the simulation results for a parametric variation in the order of -10%. unlike the adaptive fuzzy pi controller and the h� controller, we can remark that the ann and pi controllers lose their performance regarding maximum overshoot. fig. 9. active and reactive power behavior with -10% mutual inductance variation engineering, technology & applied science research vol. 9, no. 5, 2019, 4775-4782 4779 www.etasr.com louarem et al.: an efficient active and reactive power control of dfig for a wind power generator table i. comparison of the response parameters �b� − 10%� active power controller rise time (s) maximum overshoot (%) settling time (s) pi 0.0102 29.43 0.0541 ann 0.0018 7.62 0.0023 �� 0.0023 0.77 0.001 adaptive fuzzy pi 0.0024 0.01 0.0042 reactive power pi 0.0102 19.20 0.0252 ann 0.0005 7.62 0.0021 �� 0.0005 1.20 0.0010 adaptive fuzzy pi 0.0024 0.14 0.0042 in order to refine our study, we tested the robustness of the proposed controllers against a mutual inductance variation in the order of -25%. the simulation results are presented in figure 10 and table ii. we can note that the pi and ann controllers lose their performance in response time with undesirable maximum overshoots and only adaptive fuzzy pi controller and h� controller can resist this parametric variation with a slight superiority for h� controller in terms of response time. fig. 10. active and reactive power behavior using h� and adaptive fuzzy pi controllers with -25% mutual inductance variation table ii. comparison of the response parameters �b� − 25%� controller rise time (s) maximum overshoot (%) settling time (s) active power �� 0.0014 1.95 0.0057 adaptive fuzzy pi 0.0060 0.61 0.0104 reactive power �� 0.0015 2.96 0.0058 adaptive fuzzy pi 0.0060 0.70 0.0106 in the same way, the robustness of the proposed controllers against rotor inductance variations was tested. two deep simulations have been performed (figures 11 and 12). the first one concerns a variation in the order of +10% and the second a variation in the order of +25%. the results are shown in tables iii and iv respectively. note that only two controllers have resisted the second test with slight superiority regarding response time for the h� controller. regarding stator inductance variations, the simulation results are shown in tables v and vi. as in the preceding cases, only the h� and the adaptive fuzzy pi controllers can resist the high stator inductance variation. fig. 11. active and reactive power behavior with 10% rotor inductance variation table iii. comparison of the response parameters �bu + 10%� active power controller rise time (s) maximum overshoot (%) settling time (s) pi 0.0066 11.94 0.0414 ann 0.0011 0.37 0.0012 �� 0.0003 0.40 0.0005 adaptive fuzzy pi 0.0013 0.0023 reactive power pi 0.0060 17.76 0.0427 ann 0.0003 17.16 0.0013 �� 0.0003 0.78 0.0005 adaptive fuzzy pi 0.0013 0.25 0.0024 fig. 12. active and reactive power behavior using h� and adaptive fuzzy pi controllers with +25% rotor inductance variation engineering, technology & applied science research vol. 9, no. 5, 2019, 4775-4782 4780 www.etasr.com louarem et al.: an efficient active and reactive power control of dfig for a wind power generator table iv. comparison of the response parameters �bu + 25%� controller rise time (s) maximum overshoot (%) settling time (s) active power �� 0.0007 0.93 0.0011 adaptive fuzzy pi 0.0028 0.31 0.0106 reactive power �� 0.0007 1.54 0.0038 adaptive fuzzy pi 0.0028 0.18 0.0011 fig. 13. active and reactive power behavior using the four controllers with +10% variation of bn table v. comparison of the response parameters �bn + 10%� active power controller rise time (s) maximum overshoot (%) settling time (s) pi 0.0066 11.51 0.0411 ann 0.0010 0.36 0.0012 �� 0.0003 0.39 0.0005 adaptive fuzzy pi 0.0024 0.01 0.0042 reactive power pi 0.0068 17.11 0.0424 ann 0.0003 18.86 0.0012 �� 0.0003 0.74 0.0005 adaptive fuzzy pi 0.0013 / 0.0023 table vi. comparison of the response parameters �bn + 25%� controller rise time (s) maximum overshoot (%) settling time (s) active power �� 0.0007 0.90 0.0011 adaptive fuzzy pi 0.0028 0.01 0.0049 reactive power �� 0.0007 1.30 0.0011 adaptive fuzzy pi 0.0003 1.80 0.0052 finally, regarding the rotor resistance variation, which is the result of the rotor heating, a deep simulation was performed by considering a rotor resistance variation in the order of 100%. the simulation results are shown in figure 15 and the controllers’ performances are summarized in table vii. thus, we can see that the different controllers can drive the system to track the reference signals. in other words, the active and reactive powers follow correctly the reference signals. fig. 14. active and reactive power behavior using the h�and adaptive fuzzy pi controller with +25% variation of bn. table vii. comparison of the response parameters ��u + 100%� active power controller rise time (s) maximum overshoot (%) settling time (s) pi 0.00220 1.17 0.02330 ann 0.00020 0.10 0.00020 �� 0.00003 0.39 0.00007 adaptive fuzzy pi 0.0002 / 0.00050 reactive power pi 0.00240 5.15 0.1500 ann 0.00005 24.37 0.1498 �� 0.00001 71.37 0.1499 adaptive fuzzy pi 0.00004 3.01 0.1500 as far as the active power is concerned, it is clear that the h� controller has the best rise time and settling time when compared with the other controllers. however, concerning reactive power, the controller performances are almost identical to those of the ann controller with a slight superiority for h� controller. in a nutshell, the simulation results presented in this work have shown that the h� controller has the best steady state accuracy compared with the other controllers. regarding the robustness against parametric variation, the h� and adaptive fuzzy pi controllers have the best tracking performance and robustness with a slight superiority of the h� controller. v. conclusion in this paper, the control of doubly fed induction generator (dfig) based wind energy conversion has been studied. the dfig’s stator was directly connected to the grid and the rotor was connected to the grid via the machine’s and grid’s inverters. the design of four control strategies, namely pi, ann, adaptive fuzzy pi, and h� controller, has been presented and discussed. the engineering, technology & applied science research vol. 9, no. 5, 2019, 4775-4782 4781 www.etasr.com louarem et al.: an efficient active and reactive power control of dfig for a wind power generator obtained results showed that the h� controller is the best to drive the dfig’s stator and to track perfectly the active and reactive power references with very good tracking performance, namely low-rise time, low settling time, and high steady-state accuracy. the h� controller seems more robust than all other controllers against parameter variations. fig. 15. active and reactive power behavior using the four controllers with +100% variation of �u appendix rating of the wind turbine power p=1.5mw radius r=35.5m inertia j=1000kg.m 2 gear box ratio 90 damping coefficient f=0.0024nm.rad -1 wound rotor induction machine power 1.5mw stator voltage vs=398/690v rotor voltage vr=225v p � wind turbine parameters blades radius r=35.25m gain of gearbox g=90 air density ρ=1.225kg/m 3 references [1] b. yang, x. zhang, t. yu, h. shu, z. fang, “grouped grey wolf optimizer for maximum power point tracking ofdoubly-fed induction generator based wind turbine”, energy conversion management, vol. 133, pp. 427-443, 2017 [2] s. v. varzaneh, m. abedi, g. b. 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[30] m. brahim, i. bahri, y. bernard, “real time implementation of h infinity and rst motion control of rotary traveling wave ultrasonic motor”, mechatronics, vol. 44, pp. 14–23, 2017 [31] z. y. zhao, m. tomizuka, s. isaka, “fuzzy gain scheduling of pid controllers”, the first ieee conference on control applications, dayton, usa, september 13-16, 1992 [32] a. g. aissaoui, a. tahour, m. abid, n. essounbouli, f. nollet, “a fuzzy-pi control technique designed for power control of wind turbine based on induction generator”, advanced materials research, vol. 875877, pp. 1676-1682, 2014 microsoft word 29-2733_s_etasr_v9_n3_pp4225-4229 engineering, technology & applied science research vol. 9, no. 3, 2019, 4225-4229 4225 www.etasr.com buller et al.: flexural behavior of reinforced rac beams exposed to 1000°c fire for 18 hours flexural behavior of reinforced rac beams exposed to 1000°c fire for 18 hours abdul hafeez buller department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan ah.buller@quest.edu.pk mahboob oad department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan mahbooboad04@gmail.com bashir ahmed memon department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan basher_m@hotmail.com abstract—in order to meet the socio-economic demands around the globe, construction industry not only consumes concrete at a very fast pace but also yields huge amounts of construction and demolishing waste. the phenomenon gives rise to environmental issues due to production of concrete ingredients and due to dumping of the waste. therefore, one of the solutions is the production of green concrete utilizing demolished waste. this research work studies the effect of prolonged fire (18 hours) on the flexural behavior of reinforced concrete–recycled aggregate beams. the beams were using 50% replacement of natural coarse aggregates with demolished concrete. the beam samples were cast as both normal and rich mix concrete and were cured for 28 days. after curing, the beams were exposed to fire at 1000°c in a purpose made oven, followed by testing in a universal load testing machine under central point load. the test results show that the proposed beams (cast with rich mix) exhibited about 22% reduction in flexural strength. the failure mode of the beams was observed as shear failure. keywords-green concrete; fire effect; flexural behavior; demolished waste; recyclable aggregates i. introduction fire is one hazard a structure may face during its lifetime. it not only affects a structure’s appearance, but also deteriorates its strength. therefore, a fire damaged structure needs careful examination and proper retrofitting. this requires investigation of the effects of fire, fire duration, temperature gain and behavior of reinforced concrete members during and after fire. on the other hand, to meet the socio-economic development, old or short height structures are demolished to build new, higher, structures, particularly in city centers. the demolishing of the structures generates massive waste, raising, among others, environmental issues. green concrete, the concrete made with demolishing waste, is one of the solutions. this research work studies the use of demolished concrete as coarse aggregates in new concrete and the effect of prolonged fire (18hour duration) on it. author in [1] highlights the challenges and issues regarding aggregates along with possible solutions. the author also summarized different aspects of recycled aggregates and investigations on concrete made with these aggregates. similar work is also done in [1, 2] but for composite members. authors in [4, 13] used different dosages of demolishing waste in making concrete cubes for strength checking after exposing to fire at 1000°c for different durations. they observed that at 50% replacement of the natural coarse aggregates, the compressive strength of the concrete is within acceptable limits. authors in [5, 6] used 50% replacement of natural coarse aggregates with demolished concrete to check the flexural strength vs strain of reinforced concrete beams. in depth experimental investigations showed comparable performance with specimens made from conventional concrete. combined use of wollastonite and recycled waste as partial replacement of cement and coarse aggregates is reported in [7]. additionally, silica was used in 10% by weight to check performance under elevated temperatures (20°c-800°c) among other properties. the results showed that the wallastonite had adverse effects on strength and durability but positive effect on flexural and tensile strength, whereas, the recycled waste as coarse aggregates performed well. authors in [8] used ilmenite and baryte concretes for the study of the effects of fire on heavy weight concrete used in nuclear structures as shield, and investigated the strength after exposing the samples in fire for 1 to 3 hours at 250°c to 950°c. the results showed that ilmenite concrete was more fire resistant than baryte and normal concrete. further testing revealed that addition of foam or increased air entrapped percentage led the concrete with better performance than other types as nuclear radiation shield. water throwing on burning objects is the most common firefighting method, however other methods may also be used. to this end, authors in [9] studied different cooling methods and their effect on the residual strength of concrete. the authors exposed concrete members to fire from 300°c to 900°c. they used water throwing, immersion in water, covering by plastic and slow cooling (up to 224 days) and tested strength properties. based on the obtained results they outlined strength changes and related matters related to the subject matter. ramp slab of a shopping mall damaged due to accidental fire was investigated in [10] from the retrofitting point of view. various research groups have also studied the effects of fire on the thickness of concrete cover in residential structures [14], the effects of high temperature on physical and corresponding author: abdul hafeez buller engineering, technology & applied science research vol. 9, no. 3, 2019, 4225-4229 4226 www.etasr.com buller et al.: flexural behavior of reinforced rac beams exposed to 1000°c fire for 18 hours mechanical properties [15], and reinforced concrete structural material [16]. the discussion above shows the importance of the subject and the variation in results and exploration of the parameters for different condition, which motivated this project on the evaluation of the effects of fire on reinforced concrete beams made with partial replacement of natural coarse aggregates with demolished concrete exposed to prolonged 18hour fire. ii. materials and testing the demolished concrete used in this research work was obtained from a demolished 50 year old school building in the shape of large blocks (figure 1). these blocks were manually hammered to obtain aggregates of 25mm in size (figure 2). the cracked particles were screened and separated carefully (figure 3). sieve analysis of both natural and recyclable aggregates was done to have well graded aggregates. fig. 1. demolished concrete fig. 2. hammering process fig. 3. cracked particles as old mortar is attached with the demolished concrete and requires more water in the concrete mix to ensure workability, water absorption test of recyclable and natural coarse aggregates was done in standard fashion. the water absorption of natural coarse aggregates was obtained equal to 1.80% and that of recyclable aggregates was equal to 3.92%. accordingly, the water demand in concrete mix was adjusted. twenty four reinforced concrete beams were prepared using 1:2:4 (normal mix) and 1:1.5:3 (rich mix). in each concrete mix 50% beams were cast with all-natural coarse aggregates and 50% with equal proportion of the natural and recyclable aggregates following the conclusions of [3, 12]. to reinforce the beams, 2#4 deformed steel bars were used both in tension and compression zones along with #3 bars as shear reinforcement at 150mm center to center along the beam length. the size of all beams was taken equal to 900mm×150mm×150mm. the prepared beams (figure 4) were cured for 28 days by fully immersing in water, and were air-dried for 24 hours. all the beams were then exposed to fire for 18 hours in a purpose made oven (figure 5) at 1000°c. burnable wood was used as the source of fire. it was observed that 1 hour was required to reach the temperature of 1000°c, which was then maintained for the required duration of time. after the elapse of fire duration, the fire source was cut off and beams were left in the oven for 24 hours to avoid sudden attack of atmospheric moisture. fig. 4. beam samples fig. 5. oven engineering, technology & applied science research vol. 9, no. 3, 2019, 4225-4229 4227 www.etasr.com buller et al.: flexural behavior of reinforced rac beams exposed to 1000°c fire for 18 hours fig. 6. beam testing finally, all the beams were tested in a universal testing machine under central point load in accordance with [11] (figure 6) until failure. during the testing load, deflection and cracking were monitored at regular intervals. the flexural capacity of the beams was then computed using the numerical expression given in [11]. the obtained results for the beams cast with all-natural coarse aggregates (g1) and 50% recyclable aggregates (g2), with normal mix are given in tables i and ii respectively. similarly, table iii lists the test results of reinforced concrete beams cast with rich mix and all-natural coarse aggregates (g3) while the results of reinforced concrete beams cast with rich mix and equal proportion of natural and recyclable aggregates (g4) are given in table iv. all beams were exposed to fire for 18 hours. table i. test results-group g1 s. no beam no load (n) deflection (mm) flexural strength n/mm² psi 1 19 45279 8.40 18.11 2626.18 2 20 41360 8.05 16.54 2398.88 3 21 45836 8.30 18.33 2658.49 4 22 45570 7.90 18.23 2643.06 5 23 45365 8.10 18.15 2631.17 6 24 45697 8.30 18.28 2650.43 average 44851.17 8.18 17.94 2601.37 table ii. test results-group g2 s. no beam no load (n) deflection (mm) flexural strength n/mm² psi 1 49 36650 9.05 14.66 2125.70 2 50 37235 9.15 14.89 2159.63 3 51 36870 9.2 14.75 2138.46 4 52 36272 9.0 14.5 2103.8 5 53 36560 9.15 14.62 2120.48 6 54 36980 9.0 14.792 2144.84 average 36761.17 9.13 14.70 2132.15 table iii. test results-group g3 s. no beam no load (n) deflection (mm) flexural strength n/mm² psi 1 109 45145 9.50 18.06 2618.41 2 110 42120 9.05 16.85 2442.96 3 111 42730 9.10 17.09 2478.34 4 112 45216 9.65 18.09 2622.53 5 113 43976 9.45 17.59 2550.61 6 114 45225 9.55 18.09 2623.05 average 44068.67 9.38 17.63 2555.98 table iv. test results-group g4 s. no beam no load (n) deflection (mm) flexural strength n/mm² psi 1 79 35125 10.10 14.05 2037.25 2 80 35070 10.25 14.03 2034.06 3 81 35235 10.35 14.09 2043.63 4 82 33840 10.20 13.54 1962.72 5 83 32480 10.25 12.99 1883.84 6 84 35350 10.45 14.14 2050.30 average 34516.67 10.27 13.81 2001.97 iii. results and discussion the load and deflection recorded are graphically shown in figures 7-10 for groups g1-g4 respectively. it may be observed that the load-displacement pattern of the beams within and across the group is similar except peak values. fig. 7. load vs displacement – g1 beams fig. 8. load vs displacement – g2 beams fig. 9. load vs displacement – g3 beams engineering, technology & applied science research vol. 9, no. 3, 2019, 4225-4229 4228 www.etasr.com buller et al.: flexural behavior of reinforced rac beams exposed to 1000°c fire for 18 hours fig. 10. load vs displacement – g4 beams the comparison of maximum load attained is shown in figure 11. the same relationship between g3 and g4 beams is shown in figure 12. it may be observed from these graphs that due to induction of recyclable aggregates, normal mix beams exhibit 19.06% reduction in maximum load, whereas, the same for rich mix concrete beams is equal to 21.82% with respect to its counterpart. it may be noted that the rich mix concrete beams exhibited more reduction in maximum load capacity (14.4%) than normal mix beams due to fire exposure. this is mainly attributed to the larger cement content in these beams. fire loss of moisture from the body of concrete weakens the bond leading to reduction of load carrying capacity. therefore, more care should be taken while considering rich mix concrete with recycled aggregates and fire exposure. fig. 11. maximum load – g2, g1, g4 beams fig. 12. maximum load – g3 and g4 beams all the beams containing recycled aggregates showed reduction in flexural strength with the same percentage decrease as peak load. the results of the deflection showed increase for both normal and rich mix concrete beams. normal mix beams with recycled aggregates exhibited 17.61% increase in comparison to their counterpart cast with all-natural aggregates. whereas, mix concrete beams with recycled aggregates recorded equal increase to 9.48%. in comparison to aci-318 specified approximate allowable deflection values, the deflection at failure in normal mix beams tripled and in rich mix beams doubled. therefore, rich mix concrete beams showed better performance regarding deflection in comparison to normal mix reinforced concrete beams. cracks and cracking pattern at failure were also observed during testing. due to fire exposure, several surface cracks were presented even before the start of the test, therefore it was difficult to monitor the first crack due to loading. crack pattern after failure was observed as diagonal cracks from center towards supports or near to supports, with arching action in some of the specimens. therefore, the failure mode of the beams was identified as shear failure (figure 13). fig. 13. cracking in beams iv. conclusion the presented experimental study aimed to evaluate the effects of 18-hour fire on reinforced concrete beams cast with 50% dosage of both natural and recycled aggregates. normal and rich mix concrete were used in reinforced concrete beams. control specimens with all-natural aggregates were cast to compare the results. after exposure to fire, all beams were tested for peak load, deflection and cracking. the obtained flexural strength of the proposed beams was 19.06% and 21.82% reduced for normal and rich mix beams respectively. at failure, increase in deflection up to three times than approximate allowable deflection by aci-318 and shear failure were observed. although 18 hours of fire is a prolonged duration, the loss of flexural strength or peak load is about 22%. this reduction is due to the combined effects of recycled aggregates and exposure to fire, therefore may be considered a reasonably low value. however, proper retrofitting decision should be taken before putting the structure back in service. references [1] b. a. memon, “recent development on use of demolished concrete as coarse aggregates”, international journal of emerging technology and innovative engineering, vol. 2, no. 1, pp. 1–11, 2016 engineering, technology & applied science research vol. 9, no. 3, 2019, 4225-4229 4229 www.etasr.com buller et al.: flexural behavior of reinforced rac beams exposed to 1000°c fire for 18 hours [2] w. li, j. xiao, c. shi, c. s. poon, “structural behavior of composite members with recycled aggregate concrete–an overview”, advances in structural engineering, vol. 18, no. 6, pp. 919-938, 2015 [3] m. oad, b. a. memon, “compressive strength of concrete cylinders using coarse aggregates from old concrete”, 1st national conference on civil engineering-modern trends and advancements, pakistan, april 28–29, 2014 [4] a. h. buller, b. a. memon, “effect of fire on strength of concrete cubes with rca as coarse aggregates”, 1st national conference on civil engineering-modern trends and advancements, pakistan, april 28–29, 2014. [5] m. oad, a. h. buller, b. a. memon, n. a. memon, “flexural stressstrain behavior of rc beams made with partial replacement of coarse aggregates with coarse aggregates from old concrete: part-1: 1:2:4 ratio”, engineering technology and applied science research, vol. 8, no. 3, pp. 3048-3053, 2018 [6] m. oad, a. h. buller, b. a. memon, n. a. memon, s. sohu, “flexural stress-strain behavior of rc beams made with partial replacement with recyclable concrete aggregates: part-2: rich mix”, engineering technology and applied science research, vol. 8, no. 5, pp. 33383343, 2018 [7] s. a. zareei, f. ameri, p. shoaei, n. bahrami, “recycled ceramic waste high strength concrete containing wollastonite particles and micro-silica: a comprehensive experimental study”, construction and building materials, vol. 201, pp. 11-32, 2019 [8] k. sakr, e. elhakim, “effect of high temperature or fire on heavy weight concrete properties used in nuclear facilities”, 6th arab conference on the peaceful uses of atomic energy, cairo, egypt, december 14–18, 2002 [9] a. a. a. de souza, a. l. moreno jr, “the effect of high temperatures on concrete compression strength, tensile strength and deformation modulus”, ibracon structures and material journal, vol. 3, no. 4, pp. 432-448, 2010 [10] p. knyziak, r. kowalski, j. r. krentowski, “fire damage of rc structures of a shopping center”, engineering failure analysis, vol. 97, pp. 53-60, 2019 [11] astm, active standard astm c293/c293m-16: standard test method for flexural strength of concrete (using simple beam with centerpoint loading), astm, 2008 [12] a. h. buller, m. oad, b. a. memon, “flexural strength of reinforced concrete rac beams exposed to 6-hour fire: part 2: rich mix”, engineering technology and applied science research, vol. 9, no. 1, pp. 3813-3816, 2019 [13] h. sabeur, m. saillio, j. vincent, “thermal stability and microstructural changes in 5 years aged cement paste subjected to high temperature plateaus up to 1000 °c as studied by thermal analysis and x-ray diffraction”, heat and mass transfer, 2019 [14] f. kigha1, j. a. sadeeq, o. s. abejide, “effects of temperature levels and concrete cover thickness on residual strength characteristics of fire exposed reinforced concrete beams”, nigerian journal of technology, vol. 34, no. 3, pp. 429–437, 2015 [15] q. xie, l. zhang, s. yin, b. zhang, y. wu, “effects of high temperatures on the physical and mechanical properties of carbonated ordinary concrete”, advances in materials science and engineering, vol. 7, pp. 1-10, 2019 [16] l. o. onundi, m. b. oumarou, a. m. alkali, “effects of fire on the strength of reinforced concrete structural members”, american journal of civil engineering and architecture, vol. 7, no. 1, pp. 1-12, 2019 microsoft word 41-3060_s_etasr_v9_n5_pp4808-4812 engineering, technology & applied science research vol. 9, no. 5, 2019, 4808-4812 4808 www.etasr.com hamid et al.: acsis: authentication system based on image splicing acsis: authentication system based on image splicing soomaiya hamid center for computing research, jinnah university for women, karachi, pakistan soomaiya.hamid@juw.edu.pk narmeen zakaria bawany center for computing research, jinnah university for women, karachi, pakistan narmeen.bawany@juw.edu.pk shahzeb khan department of computer science, fast national university of computer and emerging sciences, pakistan k153005@nu.edu.pk abstract—text-based passwords are widely used for the authentication of digital assets. typically, password security and usability is a trade-off, i.e. easy-to-remember passwords have higher usability that makes them vulnerable to brute-force and dictionary attacks. complex passwords have stronger security but poor usability. in order to strengthen the security in conjunction with the improved usability, we hereby propose a novel graphical authentication system. this system is a picturebased password scheme which comprises of the method of image splicing. authentication data were collected from 33 different users. the usability of the method was evaluated via a comparison between the number of correct and incorrect authentication attempts and time taken. additionally, a comparison was made between our proposed method and a complex text-based password authentication method using the authentication success rate. authentication using image splicing proved to be resilient to brute-force attacks since the processing of images consumes a voluminous password space. the evaluation of the usability revealed that graphical passwords were easy-to-remember, resulting in a higher number of correct attempts. the proposed method produced 50% higher success rate compared to the text-based method. findings motivate the use of the proposed method for securing digital assets. keywords-secured authentication; brute force attack; graphical authentication; picture-based authentication; image splicing; graphical passwords i. introduction secure authentication is a major concern in computerized system security. most of the current authentication systems employ text-based passwords. in these systems, an alphanumeric string is used for preventing an unauthorized access [1]. the major issue in using alphanumeric passwords is that they are typically hard to remember as the use of a lengthy and complex password makes it more difficult to recall. therefore, in order to make passwords more memorisable, people use short and simple passwords. this in turn leads to increase in system vulnerability as these passwords can be cracked easily using simple tools [2-4]. various techniques [57] exist that can exploit the vulnerabilities present in simple passwords. dictionary attacks are the most common type of attacks on simple passwords [8, 9]. to overcome the problem of using complex passwords, alternate methods are designed such as biometric systems [5] for secure authentication. however, they are expensive since their installation requires extra hardware. studies prove that from the age of 62 and above finger print quality decreases [10, 11]. therefore, biometric systems often fail to match the impressions of elderly people. moreover, biometric systems are not applicable in all scenarios, such as during the authentication in webservers or applications. besides all these problems, biometric passwords cannot be changed, due to which personal identification of the user is exposed. studies have proved that human memory is good in memorizing pictures as compared to text [12-14]. subsequently, this paper introduces an alternate solution that provides a method for secure authentication using picturebased passwords. this in turn supports a suitable way to remember a complex password. picture-based passwords come under the category of graphical authentication systems. in these systems passwords are involved with the processing of images. [15-17] users can enter and select from the images which makes it easier than to remember passwords [18]. besides the user point of view, graphical passwords also provide a better security against attacks. for creating secure system graphical passwords may need more clicked points to recognise [19-21]. a problem in using graphical passwords is that, the authentication requires a massive pool of images in order to make the process secure. the storage and processing of images requires huge memory size. another problem in using graphical passwords is the extensive consumption of time taken for authentication compared to using textual passwords. some methods use image hashes to reduce the authentication time [22-25]. hashing is a process that modifies a password before storing it into a database. the hashing process is irreversible that makes it difficult for an unauthorized entity to steal the password from the database. an example is a graphical authentication method developed in [22]. in this method, a user is required to recognize pre-selected images in a sequence. a server stores the seeds of these images in a text file, which is a time-consuming process. authors in [23] modified this algorithm by using an sha-1 hash function that enabled less memory consumption and increased security. cued click-points belong to one such technique that is based on selecting cue points on a single image for authentication. authors in [26, 27] revealed high success rate of secure authentication using the corresponding author: soomaiya hamid engineering, technology & applied science research vol. 9, no. 5, 2019, 4808-4812 4809 www.etasr.com hamid et al.: acsis: authentication system based on image splicing cued click-points based on a two week recall study. authors in [28] used distinct shape, color, and type of images from a predefined set to authorize a user. authors in [29] also used color code authentication. in [28, 30] a user had to recognize previously selected images from a set of random images for logging into the system. authors in [31] proposed an alignment based graphical password system to authenticate a user. they used a spin wheel that was rotated by the user until a combination of images was achieved. real user corporation developed an algorithm called “passface”, which was enhanced in [32, 33]. this method worked by matching a sequence of face images and random face images. however, the passwords were predictable since image sequences were obvious. a similar method was developed in [27]. in this method, a user had to recognize a pre-selected object between 1000 crowded objects in a picture. a downside of this method was that, the log-in process was too slow. in order to quicken the log-in process, an assisted graphical password method was proposed that used approximation of pre-selected locations in a picture [18]. the idea was further extended into a ‘passpoint’ system 35] who calculated the amount of tolerance around each chosen pixel for authentication. the paper introduces a novel approach for secure authentication using picture-based passwords along with the cue-point technique. the method generates a combination of a large set of images that is used as a password for authentication. the log-in speed is enhanced using sha-1 hashing and image splicing. ii. system overview this paper proposes a picture-based password scheme which is flexible because the solution accepts any type of picture, e.g. nature images, paintings or daily life pictures. the block diagram of the proposed system in figure 1 shows the entire work-flow of the system. fig. 1. a schematic diagram of the picture-based authentication system first time registration process has two phases. in the first phase, a screen is presented to the user where the user is required to enter a user name and a unique pin code. in phase 2, the user is required to upload an image on the system. the system divides the image into 500 slices in a 20x25 grid. in this paper each slice is termed as a “cue point”. the user is then required to select a single cue point out of the 500 slices. hash code is computed for the selected cue point and stored in the database. the image uploading and cue point selection process is repeated five times in order to complete the registration process. in the authentication phase, the user is authenticated by the username and the pin code added during phase 1 of the registration. after successful authentication, all five images are presented to the user, one by one, where the user is required to select the cue points chosen before. after successful registration of conventional username and pin code, the system performs the steps as shown in figure 1, to complete the picture based registration process which is described in the following sub sections. a. data acquisition this system requires images from the user as an input. in the first step, system prompts the user to upload five images of his/her own choice in five consecutive steps (the system supports jpeg, gif or png formats). in each step, the uploaded image is saved by the system for further processing. this image is presented to the user at the time of authentication. the images for initial testing are used from the open source image databases morguefiles [36] and shutterstock [37]. b. image splicing once an image is uploaded to the system, a twodimensional array of bitmap type is initialized. the size of the array is kept 20x25 which is capable of holding 500 objects of bitmap type. the height and width of each bitmap is calculated. each bitmap is represented by b with height of bh pixels and width of bw pixels. the total height ih of an input image i is the sum of heights of all bitmaps as shown in (1). similarly, the total width of bitmap is calculated as the width of all bitmap images, equal to the width iw of the input image i as shown in (2). after the bitmap size calculation the uploaded image is mapped to the array of bitmaps where a portion of the uploaded image of height bh and width bw is stored in each bitmap b. these bitmaps are placed in a matrix as shown in figure 2. �� � ∑ �� �� � (1) �� � ∑ �� � � (2) fig. 2. sliced grid view of the user's selected image c. feature extraction the most important feature, cue point selection, is extracted at this step. cue point is a part of the original user uploaded image which has been sliced by the system in the previous step of image splicing and is now selected by the user as a part of password from the grid shown in figure 2. this single slice of engineering, technology & applied science research vol. 9, no. 5, 2019, 4808-4812 4810 www.etasr.com hamid et al.: acsis: authentication system based on image splicing the picture is used to authenticate the user on a recall technique. when the user clicks on the cue point, the system processes it transparently. therefore no change appears on the screen so the people around are unable to look at the selection in a glance. without selecting the cue point, the user is unable to proceed further. after selecting the cue point user clicks the add button as shown in figure 2, to complete the round. then, a preview of the selected pictures is shown in selected images section so that the user can see a list of pictures he/she had selected. this step is repeated in all 5 rounds. if the user quits before completing the 5 rounds, the system will terminate the registration process and delete the incomplete data. after successful registration, the user can authenticate by only selecting cue points from the pictures that were added at the registration time. d. hashing to make the system more secure, user input data is encrypted with hashing algorithms making it impossible to decrypt, in case of an unauthorized entity getting access to the database. in this system sha-256 algorithm is used which has 2256 possible combinations. in the user registration process, once the user selects the cue point, the system computes the hash of the selected cue point using the secure hashing algorithm sha-256 to ensure the security of user information stored in the database. sha 256 generates a 128-bit key which helps increasing the key size for secure authentication. in the authentication phase the user selects the cue point on a recallbased technique. all images are presented to the user iteratively where he/she has to select that cue point which was selected at the time of registration. then the hash is computed and the system proceeds to the next round. when all 5 rounds are completed, hashes are compared with the database records. e. user identification at the start of the authentication process, the user is required to provide the name and unique pin code added at the time of registration. once the conventional username and pin code verification is completed, the user is presented with all the images added at the time of registration. subsequently, the user is asked to select the cue points that were selected at the time of authentication. each image hash of the selected cue points is computed using sha-256 and is compared with the hash value already stored in the database. on successful match of hashes, the user is authenticated by the system. in case of a hash mismatch, the session is terminated by the system, declaring an unauthorized access and the authentication window is closed. figure 3 shows the complete working model of the system. iii. experimental setup to perform our experiments a laboratory environment was created where people were asked to register themselves into the system for later authentication. an evaluator monitored how people were interacting with the system. this system was evaluated for different age groups, where the majority of the testing data set was acquired from 20-40 year old users who were the students of computer science department of fast national university of computer and emerging sciences and jinnah university for women. fig. 3. proposed system work flow: (a) the registration phase for a new user. (b) the steps required for authentication into the system. iv. testing and result analysis the proposed methodology suggests that, on an input of one picture, the system created 500 sub images (slices), which made 500 possible cue points of that particular picture. the system required 5 pictures with 500 slices of each picture. at the authentication phase if the hash of cue points was compared at every round, the possible combinations become 5x500=2500 which is very small to protect the authentication from brute force attacks. therefore, the hash was compared after the completion of all 5 rounds. this technique made the system more powerful because it made 5005 possible combinations that resulted in tens of trillions values which constitute a huge data set for an attacker to predict the password. the proposed system was tested by a group of people (20 to 40 years old), in lab environment. users selected pictures and performed registration and authentication process by following the rules which were learned before the testing session. instructions were also provided on the system’s screen. users were asked to register and authenticate to the system. each user had to make ten attempts while the time taken in the authentication process was recorded. only the authentication time was recorded as the registration is an one-time activity. the success rate was also recorded. the data of correct and incorrect attempts were collected and it was found that alphanumeric passwords were less memorable than graphical passwords. according to the results shown in table i, a higher rate of incorrect attempts was noticed in alphanumeric engineering, technology & applied science research vol. 9, no. 5, 2019, 4808-4812 4811 www.etasr.com hamid et al.: acsis: authentication system based on image splicing passwords and a lower rate of zero incorrect attempts was found regarding graphical passwords. this proves that users found graphical passwords more convenient to remember. users were excited about the system and took this survey as playing a game in order to examine their memory strength. some users used few techniques to remember the tiles (slices) while some used the attraction points of the pictures. only a few of them were those who were tired of remembering the cue points in the beginning attempts of the survey. table i. incorrect attempt comparison incorrect attempts alphanumeric authentication graphical authentication all 8 4 zero 12 22 half 1 1 three 2 2 two 3 2 one 7 2 it is a fact that whenever a new system is proposed in the market, people find it difficult to adopt it in the beginning, but later on, they get impressed by the new approach and ultimately adopt it [3]. for the comparative study we designed an alphanumeric password system with hard restrictions to obtain a strong password and asked users to try some new passwords. in the strong password credentials we accepted at least 10 characters long combination passwords comprising of 1 numeric digit, 1 uppercase letter, 1 lowercase letter and 1 special character. we noticed that the majority of the users used password structure like username1234+ or username@1234. they derived an easier way to break the combination password rules and to memorize it. when a user types his/her username in password and 1234 digits, the password becomes more guessable and can be affected by social engineering attacks. from the comparative study, we found that graphical authentication process took a little longer time than the alphanumeric password process. according to the results of this research, graphical authentication took 13 seconds in average while alphanumeric authentication took 11.9 seconds. note that the alphanumeric scheme is wellknown and the most commonly used process for authentication and that the graphical authentication process proposed in this paper was definitely new to the users. these observations reveal that although graphical authentication took a little more time, it also provided a highly secure password space which provided greater chances to memorize a strong password as compared to the text based password method. these findings support the studies which reported that pictures have a high tendency to be memorized by the human brain. v. conclusion and future work in conclusion, a graphical password technique was developed for user authentication. our findings suggest that this system had improved the capability of remembering complex passwords in terms of pictures. a user had to memorize only five points in five images and the system automated these five images into tens of trillions combinations. this huge set of combinations made it harder for brute force attacks to crack a password. this paper also provided a comparative study of the effectiveness of the proposed system. according to the results, the graphical authentication process has 50% more success rate than the text-based password method. the proposed system provides secure authentication using images and eliminates the use of textual passwords. capitalizing the ability of humans to remember images, this system has the advantage over textual passwords in terms of remembering complex passwords in the simplest way. future work includes using a dynamic number of slices per image. it can be suggested that 100 or 50 slices will not make the system vulnerable for brute force attack. this will increase cue point dimensions which helps users who are not eligible to remember small cue points and do not have a need of high security. this might decrease the number of image-slices but still the number of possible combinations will be enormous. the system can be enhanced by adding a module to prevent it from shoulder surfing attack for which fake pointers could be used with different colors for confusing the attacker. an analysis on big data and picture resolution is also required, to analyze its effects on hash function or brute force attack. the system can be further modified by 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20-3530_s_etasr_v10_n3_pp5694-5699 engineering, technology & applied science research vol. 10, no. 3, 2020, 5694-5699 5694 www.etasr.com duc et al.: imperfect roll arrangement compensation control based on neural network for web … imperfect roll arrangement compensation control based on neural network for web handling systems dinh nguyen duc school of electrical engineering hanoi university of science and technology hanoi, vietnam dinh.nguyenduc201297@gmail.com ly tong thi hanoi university of science and technology and hanoi university of industry hanoi, vietnam ttly.haui@gmail.com tung lam nguyen school of electrical engineering hanoi university of science and technology hanoi, vietnam lam.nguyentung@hust.edu.vn abstract—the speed and tension control problem of a web handling system is investigated in this paper. from the system equations of motion, we developed a backstepping-sliding mode control for web speed and tension regulation tasks. it is obvious that the designed control depends heavily on roll inertia information. dissimilar to other researches that were based on the assumptions of rolls with perfect cylindrical form with the rotating shafts of the rolls considered properly aligned, the novelty of this paper is the presentation of a neural network to compensate the effects of imperfect roll arrangement. the neural network design is based on the radial basis function (rbf) network estimating the uncertainty of roll inertia. the information on estimated inertia is fed into a backsteppingsliding mode controller that ensures tension and velocity tracking. the control design is presented in a systematical approach. closed loop system stability is proven mathematically. the tracking performance is shown through several simulation scenarios. keywords-roll-to-roll; web handling system; backstepping; sliding mode control; radial basis function (rbf); adaptive control i. introduction numerous practical applications associated with web handling systems such as flexible displays, color-shifting, lighting, solar cells, etc. utilizing roll-to-roll (r2r) systems are becoming prevalent in industry [1-5]. several papers have been published to enhance speed and tension control with various control algorithms based on the system dynamic modeling illustrated in [2, 3]. sliding mode control (smc) [6] is employed in [7], in which tension observers are introduced to eliminate the requirement of loadcells. backstepping control is applied in [8–11] to counter the nonlinearity effects in r2r systems. an indirect tension control is proposed in [12], where the web tension is manipulated indirectly via distance information between two consecutive rolls. the experimental results show a moderate level of tension while tracking performance and high position control accuracy. authors in [13] designed a tension coupling compensator based on active disturbance rejection control. the main advantage of this method was its simple approach. the elasticity of the web material is the most challenging problem in tension control. in [14], the phenomenon is tackled by a h-infinity robust control with varying gains. the control shows robustness against varying roll radius and inertia. some effects of the transmission system such as backlash and flexible motor-roll coupling are considered in [15, 16]. it is evident that roll inertia information is essential for control system design [17–19]. conventionally, the roll inertia depends on roll shape and web thickness. in practice, roll eccentricity and deformation exist and lead to false estimations. the robustness of the closed loop system against roll eccentricity is presented in [20]. however, when the parameters of the system are accompanied by system uncertainties, the proposed controllers can hardly guarantee efficiency and quality control in production. hence, it is strictly essential to develop an adaptive controller that deals with the problem of varying roll inertia for the control of the r2r systems. a neural network is a powerful tool which can address the complex requirements of the system, requirements that other techniques could hardly solve. in this paper, by taking the advantages of backstepping and sliding mode control (bsmc) [21], a new control approach which uses bsmc integrated with an rbf neural network [22] (rbfn-bsmc) is proposed for the building of an r2r adaptive control system considering the presence of imperfection roll arrangements. the contribution of this paper can be summarized as: i) the proposal of a nonlinear backstepping-sliding mode control for web handling systems, ii) the realization of an rbf based adaptive mechanism for compensating roll inertia uncertainty. ii. bsmc for roll to roll web systems a. r2r web system modeling the single-span r2r web control system shown in figure 1 contains an unwinder, a rewinder and a loadcell subsystem with idle rollers. input torqueses are applied on the unwinder and rewinder. the following assumptions are made: • web slippage and deformation are totally ignored. • loadcell dynamics and friction are not taken into account. • the web obeys hook’s law. corresponding author: tung lam nguyen engineering, technology & applied science research vol. 10, no. 3, 2020, 5694-5699 5695 www.etasr.com duc et al.: imperfect roll arrangement compensation control based on neural network for web … • actuator dynamics are ignored. fig. 1. single-span web control system the non-linear dynamic equations of the single-span r2r web control system are [3]: 1 2 3u u uc c t cω ω τ= + +� (1) 4 5 6u r rt c c t cω ω ω= + + � (2) 7 8 9r r rc t c cω ω τ= + +� (3) where 1 , u u b c j = 2c , u u r j = 3 1 , u c j = − 4 ,uc kr= − 5 , rr c l = − 6 ,rc kr= 7 , r r r c j = 8 , r r b c j = − 9 1 . r c j = in the above equations of motion, (1) and (2) present the dynamics of unwinding and rewinding section, and (3) describes tension dynamics between the two rolls. the relations between the total moment of inertia, operating radius, web thicknes, and roll speed are described by: 0( ) 2 u u u h r t r θ π = − ( )4 40 0 2 u u u u r r j j πρω − = + 0( ) 2 r r r h r t r θ π = + ( )4 40 0 2 r r r r r r j j πρω − = + where t is web tension, ju and jr are the moments of inertia of the unwind and rewind rolls, ru and rr are radii of the unwind and rewind rolls, bu and br are the coefficients of vicious friction of the unwind and rewind rolls, k is the spring constant of the web, l is the total web length, h is web thickness, ρ is web density, ωu, ωr are the unwinding and rewinding roll speeds, and θu, θr, are unwinding and rewinding roll positions. b. backstepping sliding mode control the controller’s purpose is keeping web tension and web speed at the desired values. web speed is controlled through tracking the angular velocity. this section uses the sliding algorithm based on backstepping technique to design the controller. the design steps are: step 1: the tracking error variables are defined as bellow: dt t t= − (4) u u udω ω ω= − (5) r r rdω ω ω= − (6) where td and ωrd are the desired web tension and the desired rewind web angular velocity respectively, ωud is an unknown function serving as a virtual control that will be designed in such a way that t tends to td. step 2: the control signal ωud is determined such that the web tension tracks the desired value. equation (2) can be rewritten as: 4 5 6u r rt c c t cω ω ω= + + � (7) to regulate the tension error 0t → , virtual control ωud is chosen as: ( )5 6 1 4 1 ud r rc t c k t c ω ω ω= − + + (8) where k1 is a positive gain. the proposed lyapunov candidate function is: 21 2 tv t= (9) using (7) and taking the time derivative of (9) we obtain: ( )4 5 6t u r rv t c c t cω ω ω= + +� (10) replacing ωu by ωud from (8) results in: 2 1 0tv k t= − ≤ � step 3: based on backstepping technique, the control signal τu, τr will be determined in order to drive ωu to track ωud, and ωr to track ωrd asymptoticaly. from (1), (3), (5), and (6) we obtain the error equations: 1 2 3u u u udc c t cω ω τ ω= + + − � � (11) 8 7 9r r r rdc c t cω ω τ ω= + + − � � (12) the sliding surfaces are defined as: u us ω= (13) r rs ω= (14) the proposed lyapunov candidate function is: 21 2 u uv s= (15) differentiating (15) gives: u u uv s s= �� (16) the control signal is calculated as: engineering, technology & applied science research vol. 10, no. 3, 2020, 5694-5699 5696 www.etasr.com duc et al.: imperfect roll arrangement compensation control based on neural network for web … u ueq uswτ τ τ= + (17) where ueqτ is the control component making 0us = � and uswτ is the control component ensuring 0.us ≤ � from (11), it is straightforward to get ueqτ as: ( )1 2 3 1 ueq u urc c t c τ ω ω= − + − � (18) in order to guarantee 0us ≤ � , the signal usw τ is proposed to be: ( )2 3 satusw u k s c τ = − (19) where k2 is a positive gain. from (11), (13), (16)-(19) we get: ( )2 sat 0u u uv k s s= − ≤� similarly, the control signal rτ is generated by taking the total reqτ and rswτ , where: ( )8 7 9 1 req r rrc c t c τ ω ω= − + − � (20) ( )3 9 satrsw r k s c τ = − (21) where k3 is a positive gain. it should be highlighted that the designed controls depend on the calculated roll inertia which is based on the assumption of a perfectly prismatic roll shape and ideal rotating shaft alignment. this assumption does not always hold in practical applications. iii. adaptive bsmc for the uncertainties of the roll to roll web system in practice, roll eccentricity and deformation as demonstrated in figure 2 might occur [3]. fig. 2. roll eccentricity and deformation this phenomenon leads to miscalculated moments of inertia of the unwind and rewind rolls, hence some system parameters are unknown: 1 2 3 7 8, , , , ,c c c c c and 9.c the designed input torques given in (22)-(25) indicate a strong dependence on the accuracy of acquired inertia. inaccurate information on roll inertia can deteriorate control performance. it is necessary to develop a strategy to retrieve unwinding and rewinding sections. in order to tackle this problem, a mechanism based on the rbf network is proposed to estimate these parameters. the inputs of the neural network are ωu, ωr and the outputs are ˆ ˆ,u rj j which are the estimated inertia values. the neural network is trained online in order to force the error between the actual and the estimated values to approach zero. w is defined as the ideal weight and ŵ as its estimation the error of ideal and estimated weights is: ˆw w w= −� (22) then, j and ĵ can be writen as: ˆ ˆ, ˆ t t t j w h j w h j j j w h = = = − =� � (23) where h is the vector output of the hidden layer with its transfer function defined as: 2 2 1 2 2 2 2 1 2 2 1 exp exp u i r i i i n u i r i jj c c b h c c b ω ω ω ω =  − + −  −    =  − + −  −     ∑ where n is the number of neurons of the neural network. under the condition of uncertain roll inertia, control signals that are derterminded in the above section can be rewritten as: ( )( )1 2 2 3 1 ˆ ˆ ˆ sat ˆ u u ud uc c t k s c τ ω ω= − + − +� (24) ( )( )8 7 3 9 1 ˆ ˆ ˆ sat ˆ r r rd rc c t k s c τ ω ω= − + − +� (25) where 1 2 3 7 8ˆ ˆ ˆ ˆ ˆ, , , , ,c c c c c and 9̂c are the estimated values of 1 2 3 7 8, , , , ,c c c c c and 9,c respectively, since these constants depend on roll inertia. the objective of this control design is to identify the laws for unwinding and rewinding rolls. replacing ,uτ rτ with ˆ ,uτ r̂τ in (11) and (12) we obtain: ( )2 ˆ satu uu ud u u u j j s k s j j ω= − � � � (26) ( )3 ˆ satr rr ur r r r j j s k s j j ω= − � � � (27) the lyapunov candidate function for u s becomes: ( )2 11 1 tr 2 2 t u u u u u uv j s w f w −= + � � (28) where fu is a fit positive matrix. taking the time derivative of (28) we get: ( )2 11 ˆtr 2 t u u u u u u u u uv j s j s s w f w −= + + � �� � � (29) d i o ro o engineering, technology & applied science research vol. 10, no. 3, 2020, 5694-5699 5697 www.etasr.com duc et al.: imperfect roll arrangement compensation control based on neural network for web … substituting (26) into (29) yields: ( ) ( )2 12 ˆ1 ˆsat tr 2 tu u u u u u u ud u u u u u u j j v j s j s k s w f w j j ω −   = + − +     � � � � �� after some fundamental operations, it can be shown that: ( ) ( ) 2 2 1 1 ˆ sat 2 ˆtr u u u u u u t u u u ud u v j s j k s s w f w h sω− = −  + +    � � � � � (30) equation (30) suggests that the updated law can be selected as: ˆ u u u ud uw f h sω= − � � (31) with the selected updated law uv � can be rewritten as: ( )2 2 1 ˆ sat 2 u u u u u uv j s j k s s= − � � it is noted that 0uj ≤ � , thus 0.uv ≤ � the proposed candidate lyapunov function for rs is: ( )1 2 tr1 2 2 t r r r r r r w f w v s j − = + � � (32) where fr is a fit positive matrix. taking the time derivative of (36) yields: ( ) ( )( )11 2 2 trtr 2 t t r r r rd r r r r r r r r r r r w f w h sw f w j v j j j j ω ω − − + = − − + � �� �� � � � � (33) similarly, the updated law for neural network weight is chosen as: ˆ r r r rd rw f h sω= − � � (34) the update law renders rv � becomes: ( )1 2 3 2 trˆ 2 t r r r r r r r r j w f wj v k s j j − = − − � � � � in addition, 0rj ≥ � , thus rendering 0.rv ≤ � iv. simulation results in this section, the performance of the proposed control and estimation mechanism is demonstrated through a numerical simulation. to adequately evaluate the effectiveness of the control system, there will be two simulation cases: with constant inertia and with added disturbance to the inertia. the parameters of the r2r system are utilized as: 0 0.04m, u r = 0.00002533kgms/rad, 1m, u r b b w= = = 0 0 1kg/m/s, u r j j= = 0 0.3m, 0.015m, 0.00002m, r l r h= = = and k = 200kg/m. the parameters of the controller are chosen as: k1=5, k2=10, k3=10. in the simulation, the performance of the bsmc controller was compared with the adaptive rbfn-bsm controller’s. the reference web speed was 0.2m/s and the desired web tension tref = 2n. bsmc receives full information of the web transport system while rbfn-bsmc must estimate the information of the model. (a) (b) fig. 3. system response with constant roll inertia. (a) web tension, (b) web speed (a) (b) fig. 4. input torques with constant roll inertial. (a) rewinding roll, (b) unwinding roll when the roll inertia is pre-identified, both bmsc and rbfn-bmsc produce accurate and fast tension and speed responses as shown in figures 4 and 5. engineering, technology & applied science research vol. 10, no. 3, 2020, 5694-5699 5698 www.etasr.com duc et al.: imperfect roll arrangement compensation control based on neural network for web … fig. 5. roll inertia disturbance (a) (b) fig. 6. system response with varying roll inertia. (a) web tension, (b) web speed (a) (b) fig. 7. input torques with varying roll inertia. (a) rewinding roll, (b) unwinding roll however, the required input torque for rbfn-bmsc is lower than bmsc’s. it is interesting to note that in this situation, rbfn-bmsc provides better tension tracking performance. the effectiveness of the proposed rbfn-bmsc is validated when the system is subject to unknown varying inertia. it is assumed that the roll inertia disturbance is the one given in figure 5. as can be seen in figure 6, the tracking result of rbfn-bmsc is still guaranteed. without precise information of roll inertia, the bmcs shows its weakness in following the reference. figure 7 indicates that under varying roll inertia, bmsc input torque fluctuates with high amplitude. keeping in mind that full information of the roll to roll model is difficult to be obtained in real conditions, thus rbfn-bsmc law is more suitable for industrial applications than bsmc. v. conclusion in this paper, a controller which combines the backstepping method with sliding mode control was proposed for web transport systems. in the proposed controller the estimator based on the rbf neural network was utilized for approximating system uncertainties. simulation results show that the control system achieves both tracking and adaptation. furthermore, when using rbf neural network, the controller does not require the precise description of the plant, thus the proposed controller is highly capable to be used in industrial applications. future research focus on system generalization to multi-section web tension and a tension sensorless control will be proposed along with the experimental work. acknowledgements this research is supported by the hanoi university of science and technology under the research grant t2018-pc053. references [1] k. okada, t. sakamoto, “adaptive fuzzy control for web tension control system”, 24th annual conference of the ieee industrial electronics society, aachen, germany, august 31-september 4, 1998 [2] k. m. chang, c. p. weng, “modeling and control for a coating machine”, jsme international journal series c mechanical systems, machine elements and manufacturing, vol. 44, no. 3. pp. 656–661, 2001 [3] c. g. kang, b. j. lee, “stability analysis for design parameters of a rollto-roll printing machine”, international conference on control, automation and systems, seoul, south korea, october 17-20, 2007 [4] c. g. kang, b. j. lee, “mimo tension modelling and control for roll-toroll converting machines”, ifac proceedings volumes, vol. 41, no. 2, pp. 11877-11882, 2008 [5] t. sakamoto, y. fujino, “modelling and analysis of a web tension control system”, ieee international symposium on industrial electronics, dubrovnik, croatia, july 10-14, 1995 [6] s. drakunov, v. utkin, “sliding mode observers. tutorial”, 34th ieee conference on decision and control, new orleans, usa, december 1315, 1995 [7] n. r. abjadi, j. soltani, j. askari, g. r. a. markadeh, “nonlinear sliding-mode control of a multi-motor web-winding system without tension sensor”, iet control theory and applications, vol. 3, no. 4, pp. 419–427, 2009 [8] b. bouchiba, a. hazzab, h. glaoui, f. m. karim, i. k. bousserhane, p. sicard, “backstepping control for multi-machine web winding system”, journal of electrical engineering and technology, vol. 6, no. 1, pp. 59– 66, 2011 [9] t. t. tran, k. h. choi, “a backstepping-based control algorithm for multi-span roll-to-roll web system”, the international journal of advanced manufacturing technology, vol. 70, no. 1–4, pp. 45–61, 2014 engineering, technology & applied science research vol. 10, no. 3, 2020, 5694-5699 5699 www.etasr.com duc et al.: imperfect roll arrangement compensation control based on neural network for web … [10] t. t. tran, k. h. choi, d. e. chang, d. s. kim, “web tension and velocity control of two-span roll-to-roll system for printed electronics”, journal of advanced mechanical design, systems, and manufacturing, vol. 5, no. 4, pp. 329–346, 2011 [11] k. h. choi, t. t. thanh, d. s. kim, “a precise control algorithm for single-span roll-to-roll web system using the back-stepping controller”, ieee international symposium on industrial electronics, seoul, south korea, july 5-8, 2009 [12] n. nevaranta, m. niemela, j. pyrhonen, o. pyrhonen, t. lindh, “indirect tension control method for an intermittent web transport system”, 15th international power electronics and motion control conference, novi sad, serbia, september 4-6, 2012 [13] s. liu, x. mei, f. kong, k. he, “a decoupling control algorithm for unwinding tension system based on active disturbance rejection control”, mathematical problems in packaging engineering, vol. 2013, article id 439797, 2013 [14] h. koc, d. knittel, m. d. mathelin, g. abba, “modeling and robust control of winding systems for elastic webs”, ieee transactions on control systems technology, vol. 10, no. 2, pp. 197–208, 2002 [15] r. v. dwivedula, p. r. pagilla, “effect of backlash on web tension in roll-to-roll manufacturing systems: mathematical model, mitigation method and experimental evaluation”, ieee international conference on control applications, hyderabad, india, august 28-30, 2013 [16] l. t. thi, l. n. tung, c. d. thanh, d. n. quang, q. n. van, “tension regulation of roll-to-roll systems with flexible couplings”, international conference on system science and engineering, dong hoi, vietnam, july 20-21, 2019 [17] f. mokhtari, p. sicard, “decentralized control design using integrator backstepping for controlling web winding systems”, 39th annual conference of the ieee industrial electronics society, vienna, austria, november 10-13, 2013 [18] j. k. chen, z. p. yin, y. l. xiong, j. z. quan, “a hybrid control method of tension and position for a discontinuous web transport system”, international conference on information and automation, zhuhai, china, june 22-24, 2009 [19] x. m. xu, w. x. zhang, x. l. ding, m. zhang, s. h. wei, “design and analysis of a novel tension control method for winding machine”, chinese journal of mechanical engineering, vol. 31, article id 101, 2018 [20] k. c. lin, “observer-based tension feedback control with friction and inertia compensation”, ieee transactions on control systems technology, vol. 11, no. 1, pp. 109–118, 2003 [21] z. b. duranay, h. guldemir, s. tuncer, “fuzzy sliding mode control of dc-dc boost converter”, engineering, technology & applied science research, vol. 8, no. 3, pp. 3054–3059, 2018 [22] g. s. fesghandis, a. pooya, m. kazemi, z. n. azimi, “comparison of multilayer perceptron and radial basis function neural networks in predicting the success of new product development”, engineering, technology & applied science research, vol. 7, no. 1, pp. 1425–1428, 2017 microsoft word armaos-ed3.doc etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 473-478 473 www.etasr.com armaos: a study of joint cost inclusion in linear programming optimization a study of joint cost inclusion in linear programming optimization panagiotis armaos civil & structural engineer, msc steel construction iraklion, greece parmaos@hotmail.com abstract— the concept of structural optimization has been a topic or research over the past century. linear programming optimization has proved the most reliable method of structural optimization. global advances in linear programming optimization have been powered to include joint cost, self-weight and buckling considerations. a joint cost inclusion scopes to reduce the number of joints existing in an optimized structural solution, transforming it to a practically viable solution. the topic of the current paper is to investigate the effects of joint cost inclusion, as this is currently implemented in the optimization code. using intelliform software, a structured series of problems were set and analyzed. the joint cost tests examined benchmark problems and their consequent changes in the member topology, as the design domain was expanding. results are discussed. the distinct topologies of solutions created by optimization processes are also recognized. finally an alternative strategy of penalizing joints is presented. keywords-joint cost inclusion; linear programming optimization; structural optimization; intelliform i. introduction the term optimization is used to describe the process through which the performance of an objective function is improved toward some optimal point or points. michell [1] was the first to suggest and develop theories concerning the optimal layout of structural frames, more than a century ago. michell’s theories were then applied in benchmark problems which where later named michell type problems. according to [2] optimization has two distinct parts: (1) the process of improvement and (2) the optimal point. each of them has to be studied separately. often in optimization procedures the focus is being placed solely upon the target, the optimal point, while the interim performance is being neglected. in more complex systems with multiple objectives, reaching the optimum becomes less important. the most important goal of optimization is the search for improvement and therefore focus should be placed on methods of improvement. the objective of structural layout optimization is to minimize the volume and weight of structural members that are required to carry a specific load. with several methods being invented, linear programming optimization stands out for its accuracy and reliability. in structural optimization the term design space is used to define the initial borders in which all possible nodes are included. the number of nodes may vary but the coordinates of the nodes or members can not extend outside this design space. additionally all forces that are applied must be enclosed within this space. the optimum solution reached after the optimization process very often includes numerous members and consequently many nodes. that makes the optimum solution impractical for real structure design modeling. it is the scope of joint cost inclusion in optimization processes to reduce the number of actual joints associated with an optimized structural solution. in order to give a greater picture of optimization research into finding optimum solutions, the following visualization concept is adopted. the aims of any optimization method are mainly three. firstly, theoretical accuracy is unquestionably a goal of all optimization methods. secondly, the size of the problems that can be solved with optimization methods needs to be large. finally, if an optimization method is to lead to a practical design tool for structural arrangements, it should be able to incorporate realistic aspects of structural engineering design practice. in an imaginary chart each of the three aims, could be represented as an axis. the optimum point is the point where all three goals are satisfied completely. figure 1 is the result of this visualization. the performances of linear optimization (lp) and other non-linear (non-lp) methods are being compared. studying the inclusion of joint costs will help increasing of the performance of linear programming optimization towards more realistically approached structural layouts. ii. the concept of joint cost inclusion solutions given from optimization analysis usually contain a very large number of nodes and members. from a constructors view, solutions like that are unmanageably complex and ineffective to be built, for several reasons. the joints of a real construction can not link more than a few members, where in the optimal solution, very often, thousands of elements may be assumed to be linked on a single node. furthermore, optimum solutions include many short members; some of them contribute insignificantly, but can greatly increase the complexity of fabrication. the main reason though etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 473-478 474 www.etasr.com armaos: a study of joint cost inclusion in linear programming optimization that solutions with a large number of nodes can not represent a real structure is the joint construction cost. it is widely known that the cost of constructing joints is relatively high and that increases with its complexity. therefore, the cost of material saved in the optimization analysis can be easily outweighed by the fabrication complexity. a solution thus including a large number of joints, although optimum by weight, would be economically ineffective. a. introducing joint costs an approach of dealing with this problem is the introduction of a penalty for every joint in the structure. parkes [3] published a paper presenting a method, according to which joints can be taken into account in the optimization process. his suggestion was surprisingly simple and effective. in an optimization process the objective function is the volume of the structure and if the joints had to be a part of this objective function, a volume penalty had to be adjoined to them. parkes suggested that a joint of an element is accounted as an extra length of each member, say j (cost of a joint) and can be represented as a joint radius j. this way joints connecting many members will have large volume and therefore be excluded during the optimization process. according to the defined joint cost the solution will include more or less complicated joints. this technique implied that only a change in the member lengths should be implemented by a constant value j, and that complied with the linear optimization programming principle, since it included only a constant term. this approach of penalizing joints has been adopted in intelliform software, which was created by researchers of the university of sheffield and was used for the following tests. fig. 1. optimization goals and method performances iii. problem series a: michell type wheel a. problem description the first problem examined was a 2d rectangular design space with two supports (pinned and roller) at the bottom of the domain. the relative dimensions are 2 to 1 with the long dimension parallel to x axis. a single load was applied at the middle bottom node and had a negative unit value. the design domain is illustrated at figure 2. fig. 2. design space with 2:1 length ratio this problem was named problem a and was studied for four design domains of increasing size. therefore problems ai, aii, aiii and aiv had design spaces of 20x10, 30x15, 40x20 and 60x30 nodes accordingly. the parameter joint cost j was examined for a typical range of values from j=0.0 to j=1,000,000. tests were not conducted with a constant change of j value, since that proved to be ineffective for tracking the exact j value of topology change. instead of that, tests were made much more densely in areas of possible topology changes. for example, j values of 0.1, 0.2, 0.4,.…..0.8, 1.0 were tested and noticed that a change in topology occurred between 0.8 and 1.0. in order to track the exact j value that generated the change of topology, tests with more dense values in that region were conducted. finally for value of 0.99 no topology change occurred and therefore that is assumed to occur for a j value of 1.0. the topology change is named ‘stage’. the typical topology stages of problem ai are illustrated in figure 3, with the joint cost value and the volume increase they correspond to. for intermediate values of joint cost j, the topology of the solution does not change. the topology changes that occur as the joint cost increases are presented in figure 4. from the chart can be seen that the relation between volume and joint cost follows a step function. on the chart, the topology layout of the solution is placed next to each step thus making clear the stages of simplification that occur. it can also be seen the slight topology change that occurs from stage (c) to (d) when the joint cost increases exponentially. at this point the term simplicity of the structure has to be defined. the aim of joint cost inclusion is to result in optimal solutions that include fewer joints. if a solution includes fewer joints it can be considered simpler. therefore a measure of the simplicity of a solution can be inversely the number of joints, etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 473-478 475 www.etasr.com armaos: a study of joint cost inclusion in linear programming optimization (1/number of joints) or simply 1/n. another way of representing the effect of joint cost in structural solutions is by plotting the imaginary measure of structural simplicity against joint cost. this visualization is attempted in figure 5. (a) j=0 v=3,1570852924 (b) j=1 volume up by 3,104636% (c) j=2 volume up by 5,134993% (d) j=4 volume up by 11,0411% (e) j=1000000 volume up by 18,64438% fig. 3. simplification stages of problem aiii fig. 4. volume increase against joint cost 1/37 minimum joint structure 1/7 1/6 1/5 1/4 0,1 1 10 100 joint cost value j s im p li c it y o f s tr u c tu re ( 1 /n ) fig. 5. simplicity of structure against joint cost it can be seen from the previous chart that the solutions never converge to the simplest structure of four joints. although parkes [3] considered as the simplest structural arrangement, that of four nodes for this problem, the current joint cost criterion could not lead to this structure. this surprising finding was examined further and proved with hand calculations, and will be discussed in the next section. b. proof of non-convergence the fact that no problem solution could converge to the simplest structure of four joints required further investigation which enriched the knowledge on the actual effect of joint cost. all the models could effectively track the simplification stage or figure 6(a), a simple truss of five joints and equal angles. as the joint cost was increasing, structural solutions illustrated a tendency towards the structural arrangement of figure 6(b). for any infinitely large value of joint cost the arrangement of figure 6(c) did not appear. a) b) c) fig. 6. structural arrangements the equilateral truss solution (a) was calculated by hand and was found to have a volume of 2 3 3.4641v   for the case of all angles being 60o. solution (b) was found having a volume of v= 4.0 for zero joint cost. when the joint cost formulation was included, that volume was according to (1). v(b)= 4+(3+2 2 ) j (1) solution (c) was also analyzed by hand calculations and surprisingly its volume was also v= 4.0 for zero joint cost. with joint cost that turned to equation (2). v(c)= 4+(4+2 2 ) j (2) it can be easily noticed that the total volume of solution (b) will have a lower value than solution (c) for any joint cost j value. the optimization program therefore will never result in solution (c) since solution (b) will always posses lower volume. the latter contradicts with the expected simplification stages, since a structure with fewer joints is anticipated for a very high joint cost. it is inferred therefore that current joint cost inclusion is ineffective in creating always simpler topologies. an alternative joint penalty is presented further on this paper. etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 473-478 476 www.etasr.com armaos: a study of joint cost inclusion in linear programming optimization iv. problem series b: cantilever the second problem examined with intelliform was a cantilever with different lengths. with that problem series, the relation of increasing one dimension of the design space was studied. the ratio of the design space is 1/x with x taking values 0.5, 1.0, 2.0, 3.0, 4.0. a unit load was applied at the tip of the cantilever at the middle node. the vertical dimension of the design space was set to 20 nodes and the problems were as following: bi 10x20, bii 20x20, biii 40x20, biv 60x20 and bv 80x20 nodes. in figure 7 the design space is shown. fig. 7. design space of problem b it was noticed that type b problems always reached the simplest solution, that of three joints, for a definite value of joint cost j. therefore values of joint cost problems did not have to expand to high numbers. it is chosen that the topology simplification stages of problem biv, 20x60 nodes, are illustrated, with their corresponding volume increase, in figure 8. (a) j=0 v=13,6368865492 (b) j =1 volume up by 2,316614% (c) j=2,0 volume up by 4,784589% (d) j=10 volume up by 7,509586% (e) j=11 volume up by 13,6848% (f) j=13 volume up by 35,68689% fig. 8. simplification stages of problem biv similarly to the previous problem the complete topology simplification sequence is illustrated at figure 9, where next to each stage, the corresponding topology is adjoined. it was noticed that the volume increases rapidly when simpler solutions are created. the first stage eliminated a large number of nodes with a relatively small volume penalty. this is also visible in figure 10, where the simplicity of the structure is plotted against the joint cost increase. fig. 9. volume increase against joint cost 1/729 1/14 1/7 1/3 1/5 minimum joint structure 0 5 10 15 joint cost value j s im p li c it y o f s tr u c tu re ( 1 /n ) fig. 10. simplicity of structure against joint cost the results of the analyses are being commented and discussed at the following chapter. v. result and discussion an overall assessment of the results of the problems examined came to a series of conclusions about the effect of joint cost inclusion in linear programming optimization. the current method of including joint cost into optimization is that suggested in [3] and did not always provided satisfactory results. those along with further notes on the problems examined are listed below:  the first topology change (stage) occurred always for a joint cost value of j=1.0. that was a fact for all problems, irrespectively to the geometry of the domain, support location or loads. the first stage in all the cases eliminated a large number of joints in the structure.  no model of problems ai-iv could track the solution of 4 joint-triangle, figure 6(c) as presented in [3]. this matter was further investigated in section 3.2.  in type a problems the main simplification stages are three. those stages where not always tracked by the problems. more specifically problem ai skipped the first stage while other failed to produce a clear topology. x 1 etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 473-478 477 www.etasr.com armaos: a study of joint cost inclusion in linear programming optimization instead of that, a double frame appeared as a solution, as shown in figure 11. fig. 11. double frame appearance that may have been caused by two reasons: either a node was not present at the desired location so a single frame could be created, or in the optimization program two distinct topologies with different number of nodes are recognized as equal. after further investigation it was found that both parameters affect the appearance of double frames. it was proven that the joint cost inclusion criterion does not actually penalize joints, but short members. furthermore, it did not eliminate effectively the number of joints.  joint cost in relation to domain size: it was noticed that after the first stage which occurred for a joint cost j=1.0 later stages did not occur at the same joint cost value for all models. more specifically, for larger domains the transition of stages where shifted to higher joint costs. it was noticed that a topology stage is defined by the required volume increase of the structural arrangement rather than the value of joint cost j.  the associated volume increase for the final simplification stage, that of three joints figure 8(f), in the case of type b problems was significantly increased as the domain expanded horizontally. it can be inferred therefore that designing with optimization considerations can be of great benefit for large cantilever type structures as stadium roofs. vi. suggestion of an alternative joint penalty introduction the joint cost as currently incorporated in linear programming optimization proved that it does not penalize effectively the number of actual joints. an actual joint penalty would allow us to track all the possible simplification stages. an alternative strategy of penalizing joints is therefore suggested in this paper. ideally each active joint of the structure should have an equivalent volume penalty. the difficulty of such a volume equivalence implementation in linear programming arises from the fact that in lp all nodes are supposed to be joints, fully connected. no distinction is therefore possible for the actual joints of the structure. a function is therefore required, that when implemented in the optimization process, can distinguish the actual joints and define their affect in the final optimization solution. the function that possessed the desired behavior, modified in order to include a relative joint penalty parameter is presented in (3). , 1 1( )j k n i i j p f p v e    (3) where kjpv , is the volume equivalence of joint k, fi is the force in member i and pj is the relative penalizing factor with positive values the proposed volume equivalent of all joints is directly added with the volume of the structural elements and taken into account into optimization process. the total volume formulation is presented in (4). , 1 j k n ptotal members i v v v    (4) the plot in figure 12 shows the suggested joint penalty for different values of pj and sums of forces. it can be seen that by altering the penalty factor pj the influence of volume penalty can be controlled 0 1 2 3 4 1 4 7 10 13 16 19 22 25 28 31 34 37 40 joint volume penalty s u m o f m e m b e r fo rc e s o f a j o in t. pj=4 pj=3 pj=2 pj=1 pj=0.2 fig. 12. joint penalty for different values of parameter pj by including the suggested joint penalty into optimization processes it can be shown that the convergence discussed previously in section 3.2 can occur for a definite number of joint cost. that is depicted in figure 13. fig. 13. proof of convergence with suggested joint penalty etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 473-478 478 www.etasr.com armaos: a study of joint cost inclusion in linear programming optimization vii. conclusions the study of joint cost inclusion in linear programming optimization had a scope of revealing the effect of joint cost parameter j in different problems, as well as the simplification stages that emerge. by exploring the ways a joint cost inclusion simplifies an optimal solution, a link is created between theoretically optimum and practically buildable structures. through this approach linear programming optimization is led towards more realistic concepts of structural solutions. however, the current way of joint cost implementing, in some occasions, proved inefficient in generating simpler solutions in the sense of decreasing joints. this in-depth study of joint cost effect in optimization process resulted in the suggestion of an alternative joint penalty integration, which illustrated inspiring results in small scale topology problems. concluding, it is believed that with constant research and development, linear programming optimization will be able to provide a design tool to practical engineers and guide towards a more optimized structural practice. references [1] a. michell, “the limits of economy of material in frame-structure”, philosophical magazine series 6.,vol 8, no. 47, pp. 589–597, 1904 [2] d. e. goldberg, genetic algorithms in search, optimization and machine learning, addison-wesley, reading, massachusetts, 1989 [3] e. w. parkes, joints in optimum frameworks, international journal of solids and structures, vol. 11, no. 9, pp.1017-1022, 1975 microsoft word 23-2864_s1_etasr_v9_n4_pp4440-4447 engineering, technology & applied science research vol. 9, no. 4, 2019, 4440-4447 4440 www.etasr.com hekmet & izzet: performance of segmental post-τensioned concrete beams exposed to high fire … performance of segmental post-τensioned concrete beams exposed to high fire temperature h. m. hekmet department of civil engineering al-farabi university college baghdad, iraq maithem_haider@yahoo.com a. f. izzet department of civil engineering university of baghdad baghdad, iraq amer.f@coeng.uobaghdad.edu.iq abstract—the present study illustrates observations, record accurate description and discussion about the behavior of twelve tested, simply supported, precast, prestressed, segmental, concrete beams with different segment numbers exposed to high fire temperatures of 300°c, 500°c, and 700°c. the test program included thermal tests by using a furnace manufactured for this purpose to expose to high burning temperature (fire flame) nine beams which were loaded with sustaining dead load throughout the burning process. the beams were divided into three groups depending on the precast segments number. all had an identical total length of 3150mm but each had different segment number (9, 7, and 5 segments), in other words, different segment lengths. to simulate genuine fire disasters, the nine beams were exposed to high-temperature flames for one hour along with the control specimens. the selected temperatures were 300°c (572°f), 500°c (932°f), and 700°c (1292°f) as recommended by the standard fire curve (astm–e119). the specimens were cooled gradually at ambient laboratory conditions. the performance of the prestressed segmental concrete beams through the burning process was described with regard to the beams camber, spalling, and occurred deterioration. keywords-burning temperature, fire flame; gradual cooling; segmental beam i. introduction segmental box girder bridges represent one major recent development in bridge engineering. this method of construction has many advantages like substantial economical savings due to the possibility of weather-independent segment production, shorter construction periods, simple element assembly at job site, replace ability of tendons, the concreting and prestressing operations are independent, small light segments, the profiling of the main external steel is easier to check, and the friction may be reduced [1]. the strength of reinforced concrete (rc) and prestressed concrete decreases after fire exposure. the basic fire safety objectives are to protect life and prevent failure. following a fire, even if no collapse occurs, there is always a possibility of fire-induced damage. this research seeks to give an explanation and a simplified estimation of fire-induced damages produced in precast segmental prestressed concrete (spc) beams via monitoring experimentally the behavior of internally prestressed precast concrete segmental beams with selective parameters such as segment length, number of joints between segments, and the exposure to different burning temperatures. authors in [2, 3] presented the results of nonlinear finite element analysis on segmental concrete beams with external tendons. authors in [4] investigated the structural behavior of dry joined externally prestressed segmental (eps) beams under combined stresses, i.e. bending, shear and torsion stresses. it was found that the presence of torsion in beams reduces the vertical load and vertical deflection at the onset of nonlinearity, failure load and further, it would alter the failure mechanism. a reduction in the load-carrying capacity of eps beams can be compensated by higher pre-stressing and by increasing stirrup reinforcement in the joint regions and to ensure serviceability. the joints in the supported regions should still be sufficiently pre-stressed under service load conditions. previous works dealt with high temperature residual mechanical properties of concrete, mild steel and prestressing steel and how high temperature residual properties affect the ultimate strength of the element. authors in [5] studied the mechanical properties of high-performance concrete (hpc) and the normal-strength concrete (nsc) after exposure to high temperature. the residual compressive strength was examined after the concrete specimens were subjected to a temperature of 800°c. authors in [6] compared the strength and durability performance of normal and high-strength pozzolanic concretes including silica fume, fly ash, and blast furnace slag at high temperatures up to 800°c. authors in [7] reported that concrete can suffer large damage when exposed to fire, although it has low heat conductivity. author in [8] stated that concrete materials have significant variations, therefore the structural fire safety capacity of concrete is very complex. prestressed normal strength concrete (nsc) and high-strength concrete (hsc) exposed to fire require constitutive relationships to offer active modeling and to meet particular fire performance standards for fire-resistant prestressed concrete behavior. in this research, formulations were proposed to estimate the parameters that affect the behavior of unconfined prestressed concrete at high temperatures. authors in [9] studied the mechanical properties of prestressing wires through and after the exposure to fire. the results were compared with the existing ones from the relevant literature and design codes, and empirical formulas were suggested. researchers concluded that although the prior examinations provided beneficial results for corresponding author: h. m. hekmet engineering, technology & applied science research vol. 9, no. 4, 2019, 4440-4447 4441 www.etasr.com hekmet & izzet: performance of segmental post-τensioned concrete beams exposed to high fire … the mechanical characteristics of prestressing steel at high temperatures, the information found was somewhat scattered and still inadequate. ii. spc beams set up the experimental program consisted of twelve simply supported segmental prestressed concrete beams divided into three groups depending on the precast segments number. all the spc beams were selected and designed with 3150, 400 and 400mm length, depth and width, respectively. the first group consisted of spc beams with 9 segments (350mm segment length), the second group with 7 segments (450mm segment length), while the last group had 5 segments (630mm segment length). figure 1 shows the schematic shape of the spc beams for each group. figure 2 demonstrates the details of the two opposite contact surfaces of reinforced concrete precast segments, which have been used to assemble the spc beams, the first consisted projections as shear connecters (keys), in contrast the other consisted pits to engage with the projections. (a) (b) (c) fig. 1. schematic shape and dimensions of the tested spc beams: (a) group i, (b) group ii, (c) group iiii the reinforcement details for the three groups are illustrated in figure 3. the deformed 8mm diameter bar of 486 and 640mpa, its yield stress and ultimate strength, were respectively used for the longitudinal and ties reinforcement. side view of the shear keys precast reinforced concrete segments fig. 2. configuration of spc beam segments (all dimensions in mm) fig. 3. reinforcement details of segments for each group of the tested spc beams the tested spc beams passed through two stages of manufacturing. first, the segments of each beam had been cast (using the short line method) and cured, after reaching the specified concrete strength of 40mpa, the segments were assembled together in groups. after that, eccentric prestressing force of 120kn was applied from one end after insertion of low relaxation 7-wires strand (12.7mm diameter), grade 270, in the plastic tube which had been fixed before casting. the adopted prestressing force was selected so that it satisfied the limits of the aci 318m-14 code. table i lists the suggested variables. two stages of experimental tests were carried out on the spc beams. iii. exposure to fire test three spc beams of each group (with its control specimens) were exposed to high temperatures of 300, 500, and engineering, technology & applied science research vol. 9, no. 4, 2019, 4440-4447 4442 www.etasr.com hekmet & izzet: performance of segmental post-τensioned concrete beams exposed to high fire … 700°c while applying uniformly a constant dead load of 3.22kn/m by using nineteen concrete blocks, 50kg each for similar exposure period of 1h after reaching the target temperature. after that, all beams were allowed to cool at ambient laboratory temperature. the burning stage comprised of positioning the spc beams above their idealized simply supported ends, and the deflection due to the constant dead load and the camber change due to fire were measured using a dial gauge of 0.002mm/div sensitivity. the temperature was monitored by a digital thermometer reader with three thermocouple sensor wires type k (nickel-chromium/nickelalumel), which can be used at temperatures up to 1100°c. the sensors were set at three points with equal distances in the top region between the furnace cover and the spc beam at the mid, right and left of the top case of the furnace. the fire flame test procedure is illustrated in figures 4 and 5. table i. segmental prestressed concrete beams burning temperature (°c) segment length (mm) segment number specimen group unburned 350 9 segments spc-9-r group i 300 350 9 segments spc-9-300 500 350 9 segments spc-9-500 700 350 9 segments spc-9-700 unburned 450 7 segments spc-7-r group ii 300 450 7 segments spc-7-300 500 450 7 segments spc-7-500 700 450 7 segments spc-7-700 unburned 630 5 segments spc-5-r group iii 300 630 5 segments spc-5-300 500 630 5 segments spc-5-500 700 630 5 segments spc-5-700 fig. 4. furnace schematic shape and burning process fig. 5. burning process iv. results and discussion a. camber at prestressing stage the effect of the prestressing force, combined with the beam self-weight, causes a net upward deflection at the midspan of the prestressed beam before superimposed dead and live loads are applied. the spc beams camber was measured with a mechanical dial gauge of 0.002mm/div set in the midspan of the beam while the prestressing process was performed. the results, exhibited in table ii, show a significant camber decrease with decreasing number of segments. it reveals a decrease percentage in the average camber by 79% for spc beams of 7 segments (group ii) and 62% for spc beams of 5 segments (group iii) compared with the spc beams of 9 segments (group i). the regular cracks performed in the segmental beams are comprehended by the dry joints that affect the behavior of camber, due to the high stiffness of beams with the small number of joints in the spc beams with less number of segments. b. deflection due to superimposed load nineteen concrete blocks for each specimen were placed over the length of the spc beams during the period of exposure to burning temperature. the measured deflections, listed in table ii, were set under the beam while these blocks were set above the spc beams. the results show a conflicting relation between the deflection and the number of segments composing the spc beam, in other words between the spc beam stiffness and the number of segments. table ii. initial prestressing camber after applying sustain load on spc beams group no. in it ia l p r e s tr e ss in g c a m p e r ( m m ) a v e r a g e p r e s tr e ss in g c a m b e r ( m m ) r e s id u a l in it ia l p r e s tr e ss in g c a m b e r % s u p e r im p o s e d lo a d d e fl e c ti o n (m m ) n e t c a m b e r b e fo r e b u r n in g ( m m ) g ro u p i spc-9-r 2.9 2.9 100 spc-9-300c° 2.8 0.36 2.44 spc-9-500c° 3.1 0.36 2.74 spc-9-700c° 3 0.36 2.64 g ro u p i i spc-7-r 2.3 2.3 79 spc-7-300c° 2.2 0.27 1.93 spc-7-500c° 2.4 0.27 2.13 spc-7-700c° 2.2 0.27 1.93 g ro u p i ii spc-5-r 1.8 1.8 62 spc-5-300c° 1.6 0.2 1.4 spc-5-500c° 1.8 0.2 1.6 spc-5-700c° 1.9 0.2 1.7 c. thermal test results the burning process comprised of setting fire until reaching the target temperature, then, after an exposure period of 1h to the target temperature the fire was turned off and a gradual cooling was performed by removing the furnace cover case and engineering, technology & applied science research vol. 9, no. 4, 2019, 4440-4447 4443 www.etasr.com hekmet & izzet: performance of segmental post-τensioned concrete beams exposed to high fire … lefting the spc beams with their control specimens in the ambient air (lab conditions). 1) compressive strength of concrete (ƒ′c) authors in [6] reported that there are three testing methods available to find the residual compressive strength of the concrete at high temperatures: stressed test, unstressed test, and unstressed residual strength test. the first two methods opt to find concrete strength during high temperatures, while the last is excellent for determining the residual properties after exposure to high temperature. it was observed that the third method gives less strength and is therefore more appropriate for obtaining limiting values. this method has been adopted to find the residual concrete strength. the test results of compressive strength, as shown in table iiii for the 150mm specimens showed reducing in the compressive strength results with increasing burning temperature. table iii. fire effects on compressive strength* ƒcu (mpa) ƒ′c * (mpa) average residual strength % ƒ′c ** (mpa) residual strength [8] t e m p e r a tu r e o c ambient 42 33.6 100 33.6 100 300 39 31.2 93 32.1 95.5 500 28 22.4 67 24.4 72.6 700 16 12.8 38 13.9 41.4 * ƒ′c cylindrical compressive strength by using 0.8 converting factor ** post fire concrete strength proposed equation by [8] the loss of strength was characteristically varying depending from the burning temperature. up to 300°c, only a small portion of the original strength was lost, about 7%. severe loss in the strength mostly happened within the range of 500-700°c burning temperature and was 33%-62%, respectively. the proposed equations [8] are compared in table iii with the test results. it is clear that there is a good agreement between the experimental results and the values given by the proposed equations. the compressive strength (figure 6) exhibits a rapid decrease above 300°c, due to the dehydration of calcium hydroxide in the cement which begins when the temperature reaches about 400°c, generating more water vapor and also causing an additional significant reduction in the physical strength of the material [10]. the residual strength exhibits a rapid decrease above 300°c as shown in figure 7. fig. 6. burning temperature versus compressive strength fig. 7. burning temperature versus residual strength 2) properties of steel reinforcement bars concrete structural properties after exposure to high temperature cannot be reversed to the original values. in contrast, steel structures usually return approximately to their original condition after cooling. this is caused by irreversible transformations in the chemical and physical properties of the cement itself [10]. authors in [11] reported that when a temperature increment occurs, a significant drop in the value of steel yield strength and steel modulus of elasticity emerges. however, when the structure is cooled down, reinforcing steel properties usually recover the most of their original condition. so, real deterioration happens when the reinforcement in some structural elements becomes useless due to the failure of bar anchorage after exposure to fire. authors in [12] reported two distinguished types of tensile tests of steel at high temperatures to find material properties: transient-state and steady-state tests. in the transient-state tests, the test specimen is under constant load and under constant temperature rise. the heating rate in the transient state tests is 20°c/min. temperature and strain are measured during the test. while in the steady-state tests, the test specimen are burned up to a definite temperature. a tensile test follows. the steady state tests can be carried out either as strain or as load controlled. the steady-state test is more adequate than the transient-state test and therefore that method is more frequently used. the second test method was conducted in this research: three reinforcing steel specimens were burned at different burning temperatures. after cooling stage, tensile tests were carried out. table iv lists the burning effect on the properties of steel reinforcement bars. mechanical properties of the steel reinforcement bars after burning at temperature of 300°c were not affected, but a significant drop in the value of steel reinforcement properties was observed at burning temperatures of 500 and 700°c. table iv. fire effects on the properties of steel bars yield tensile stress (mpa) residual yield tensile stress % ultimate tensile stress (mpa) residual ultimate tensile stress % t e m p e r a tu r e o c ambient 486 100 640 100 300 484 100 630 98 500 462 95 602 94 700 379 78 461 72 the percentages of residual yield tensile stress and ultimate tensile strength were 95.78 and 94.72% at 500°c and 700°c experimental results [8] experimental results [8] engineering, technology & applied science research vol. 9, no. 4, 2019, 4440-4447 4444 www.etasr.com hekmet & izzet: performance of segmental post-τensioned concrete beams exposed to high fire … respectively. the results are in good agreement to the ones obtained in [13-15]. 3) strand the behavior of the prestressing strand is not like that of mild steel, where by cooling, the material will restore less amount of its original state. the effect of burning on the properties of strand is summarized in table v. the results reveal that, the mechanical properties of the strand were not affected at burning temperature of 300°c, but at 500°c and 700°c effects were observed, as was also by other studies. authors in [16] reported the same observation and added that, prestressing steel losses almost or all of its non-linear behavior at temperatures above 500°c. authors in [9] reported that the prestressing steel properties were more sensitive than reinforcing steel bar properties at identical fire temperatures. equations for calculating yield and ultimate residual stress of prestressing strand where proposed. the loss percentages of 79.42% and 76.43% of the residual yield stress and residual ultimate tensile strength at temperature 500°c and 700°c were observed respectively. they are in good agreement with the findings in [9]. table v. fire effect on the properties of prestressing strand y ie ld t e n si le s tr e ss ( m p a ) r e s id u a l y ie ld te n s il e s tr e ss % u lt im a te te n s il e s tr e s s (m p a ) r e s id u a l u lt im a te t e n s il e s tr e s s % [9] residual yield % residual ultimate % t e m p e ra tu re o c ambient 1720 100 1860 100 100 100 300 1700 99 1850 99 100 100 500 1359 79 1414 76 82.7 80 700 722 42 800 43 47.5 44 4) camber at burning and cooling stage spc beams of different segment lengths but identical in total length were subjected to fire test (table i). sustain load (3.22kn/m) was applied on the spc beams simultaneously with the exposure to high temperature. the furnace temperature was applied as recommended by astm–e119. the beams passed through three stages within burning and cooling cycle. at the first stage, they reached the target temperature of 300˚c, 500˚c or 700˚c. this took approximately 5, 7 and 12min respectively. then, the temperature was stabilized for 1h. at the final and cooling stage, the spc beams were cooled gradually by the ambient air (lab conditions). the effects of the three stages on the mid span camber for all beams are summarized in table vi. camber versus time history for the spc beams of groups i, ii and iii are shown in figures 8, 9 and 10 respectively. these figures elucidate that, increasing burning temperature in the first and second stages lead to steep increase in spc camber, while a gradual camber decreasing in the third stage occurs the structure of the prestressed concrete beam exhibits upward curvature (camber) due to the eccentric prestressing force, which compressed the concrete at the lower zone (chord) of the prestressing force position and stretching the upper concrete zone (chord). the fire was positioned at the base of the furnace towards the lower face of the spc beam, in other words, exposing a concrete beam to high temperature under sustain eccentric load led to increase in the deterioration in higher camber, despite applying external load. this denotes that the effect of temperature was more on concrete than on steel reinforcement. the structural response of beams exposure to burning can be grouped into three stages as mentioned before. in stage 1 (heating stage), concrete and strands are subject to very little degradation. the cambers in all spc beams increase gradually and these cambers result from the generation of thermal strains caused by high thermal gradients that occur in the initial stage of fire exposure. fig. 8. camber vs time for group i beams at different temperatures fig. 9. camber vs time for group ii beams at different temperatures fig. 10. camber vs time for group iii beams at different temperatures in the second stage, within the 1h of fire exposure at the target temperature, as temperature increased in the internal layers of concrete, camber increased significantly caused by reduction in thermal concrete strength due to the formation of internal hair cracks. the interference of thermal effect into the internal layers attributed to concrete’s degradation of strength and modulus of elasticity more than that of strand. then camber increased at a higher pace. in addition, camber increment is essentially attributed to high creep strains engineering, technology & applied science research vol. 9, no. 4, 2019, 4440-4447 4445 www.etasr.com hekmet & izzet: performance of segmental post-τensioned concrete beams exposed to high fire … subsequent from high temperatures in concrete which is composed of different materials and strands. the value of maximum camber at the end of the second stage is shown in table vi. we can see that with increasing burning temperature, the maximum camber value of spc beams increased. at the end of stage 2 at 500˚c and 700˚c the maximum camber was 165% and 335% for spc beams of 9 segments (group i), compared with that burned at 300˚c. whereas, it was 181% and 388% and 181% and 409% for spc beams of 7 segments (group ii) and beams of 5 segments (group iii) respectively. the difference in the behavior (camber) of beams at each group is shown in figures 8-10. the camber (upward deflection) increases during the heating period and reaches its maximum at the end of stage 2. the upward movement of the spc beam is probably explained by the reduction of concrete’s resistance at the location of cracking and spalling, so the residual force in the prestressing tendons caused the segmental beams to move upwards. it can be seen that at the same burning temperatures the deterioration decreases with decreasing number of segments. exposing spc beams of 7 and 5 segments to 300˚c revealed that, the decrease in maximum camber at the end of stage 2 was 80% and 64% respectively while for spc beams with 9 segments it was 88%, and 70% for group ii and 93%, and 78% for group iii at 500˚c, and 700˚c burning temperatures respectively. these comparisons exhibit that increased burning temperature increased the camber through the exposure period (burning stage), whilst increased segment number increased the maximum camber and decreased the beam stiffness. table vi. camber at the end of each stage of burning and cooling process for all spc beams group no. initial camber (mm) heating stage heat stability for 1 hr cooling stage final camber (mm)* residual camber % duration (min) variation camber (mm) accumulative camber (mm) duration (min) variation camber (mm) accumulative camber (mm) duration (min) variation camber (mm) i spc-9-r spc-9-300c° 2.44 0-5 +0.2 2.64 5-65 +2.0 4.64 65-245 -0.9 3.74 153 spc-9-500c° 2.74 0-7 +0.5 3.24 7-67 +3.3 6.54 67-380 -1.9 4.64 169 spc-9-700c° 2.64 0-12 +1.0 3.64 12-72 +6.7 10.34 72-520 -4.1 6.24 236 ii spc-7-r spc-7-300c° 1.93 0-5 +0.1 2.03 5-65 +1.6 3.63 65-245 -0.7 2.93 152 spc-7-500c° 2.13 0-7 +0.3 2.43 7-67 +2.9 5.33 67-380 -1.6 3.73 175 spc-7-700c° 1.93 0-12 +0.9 2.83 12-72 +6.2 9.03 72-520 -3.9 5.13 266 iii spc-5-r spc-5-300c° 1.4 0-5 +0.07 1.47 5-65 +1.27 2.74 65-245 -0.67 2.07 150 spc-5-500c° 1.6 0-7 +0.2 1.8 7-67 +2.3 4.1 67-380 -1.2 2.9 182 spc-5-700c° 1.7 0-12 +0.8 2.5 12-72 +5.2 7.7 72-520 -3.4 4.3 253 * final camber equals to the sum of initial camber and final camber variation. + sign denotes increased value. sign denotes decreased value. at the end of the third stage the camber had a value higher than before burning. the ratio between the final camber after burning and the initial prestressing camber before burning is called the residual camber. the values of the residual camber are shown in table vi. in general, decreasing camber of prestressed concrete beams is a sign of increasing losses in prestressing force. increasing camber indicates that deterioration could happen in concrete strength whilst the prestressing force is not affected. increased temperature had a bad effect on the residual camber, denoting that more deterioration occurred. the increased percentage in the residual camber for the beams of 9 segments (group i) was 153%, 169%, and 236% for burned beams at 300˚c, 500˚c, and 700˚c respectively compared to the initial camber before burning. for the beams of 7 (group ii) and 5 segments (group iii) it was 152%, 175% and 266%, and 150%, 182% and 253% for the same burning temperatures respectively. comparing the effect with the number of segments shows that the camber increases with increasing number of segments. exposing spc beams composed of 7 and 5 segments to 300˚c decreased the final camber at the end of burning and cooling cycle by 78% and 56% respectively. for spc beams with 9 segments it was decreased by 80%, and 63% for group ii and 82% and 69% for group iii, at 500˚c and 700˚c respectively. figures 11-13 show the camber difference of beams with different number of segments for the tested burning temperatures. fig. 11. camber-time plot of spc beams with different segment number during burning at 300˚c and cooling cycle fig. 12. camber-time plot of spc beams with different segment number during burning at 500˚c and cooling cycle engineering, technology & applied science research vol. 9, no. 4, 2019, 4440-4447 4446 www.etasr.com hekmet & izzet: performance of segmental post-τensioned concrete beams exposed to high fire … fig. 13. camber-time plot of spc beams with different segment number during burning at 700˚c and cooling cycle 5) spalling and cracking patterns during the burning test a distinct network of minor cracks occurred in spc beams exposed to high temperature burning, however no main crack was testified. cracking sounds were heard in some of the beams at around 15min after the start of the burning test that were mainly caused by spalling. at around 100ºc, spalling started to appear, surface cracks were noticed and continued to develop until the final stage. figures 14-16 show an appearance comparison of the beams after the exposure to fire. as mentioned before, the spc beams were composed of different number of segments, and the burning nozzles were positioned at the lower base of the beams. these facts elucidate that due to the irregularity of fire distribution, deterioration was noticed at some segments more than others and that this difference had marginal effects on the distribution of hairline cracks on the beam surfaces. at 300ºc the beams exhibited spalling cracks at some regions on the surface of the beam depth and at the edges near the fire source (figure 14). short cracks occurred in all the surfaces of the spc beams and were concentrated in the joint positions between beam segments. (a) specimen spalling at 300ºc (b) specimen hairline at 300ºc fig. 14. spalling and surface hairline cracks in surface (bottom fiber) of specimens near the fire at 300ºc at 500ºc the spc beams have suffered spalling at some regions in the surface and edges near to the fire source and surface hairline cracks were observed (figure 15). it is clear that the spalling effects at the bottom surface of the beams were deeper than those of specimens at 300ºc and the surface hairline cracks were more and longer. hairline cracks at this temperature went deeper between segments in the joint positions and occurred in the bottom surface at prestressing steel position. naturally, the spalling was observed in the spc beams burned at 700ºc. the map-cracking and separation of concrete cover were more and deeper. after cooling, the spalling and the network of minor cracks in specimens increased as exhibited in figure 16. (a) specimen spalling at 500ºc (b) specimen hairline at 500ºc fig. 15. spalling and surface hairline cracks in surface (bottom fiber) of specimens near the fire at 500ºc (a) specimen spalling at 700ºc (b) specimen hairline at 700ºc fig. 16. spalling and surface hairline cracks in surface (bottom fiber) of specimens near the fire at 300ºc author in [17] reported that between 100ºc and 200ºc of a slow temperature rise, the first effects in concrete will occur due to high thermal stresses caused from fast heating and pressure caused by moisture evaporation inside the porous concrete, which the concrete structure is not able to dissipate. engineering, technology & applied science research vol. 9, no. 4, 2019, 4440-4447 4447 www.etasr.com hekmet & izzet: performance of segmental post-τensioned concrete beams exposed to high fire … these movements cause the development of cracks and the eviction of pieces from the surface layers of the beam material. at 300ºc, concrete starts to shrink at a faster rate and surface relatively short hairline cracks begin to form. the surface moisture evaporates faster than it can be replaced by rising bleed water, leading the surface to shrink more than the inside concrete. as the internal layers of concrete inhibit the shrinkage of the surface layer, stresses grow which exceed the concrete’s tensile strength, causing the surface cracks. the aggregates start to deteriorate at temperatures between 500ºc to 700ºc because calcium hydroxide starts to dehydrate at that temperature range. calcium hydroxide is a hydration output of most portland cements, the quantity being dependent at the specific cement being utilized. v. conclusions • the camber due to prestressing force decreases with decreasing number of segments. the percentage decrease in the average camber was 79% and 62% for spc beams of 7 and 5 segments compared with beams of 9 segments for beams having the same total length and cross section. • the fact that the fire was positioned at the base of the furnace toward the lower face of the spc beams, i.e. the beams were exposed to high temperature under sustain eccentric prestressing force, led to increase in deterioration and to higher camber regardless of the applied external downward load. this denotes that the effect of temperature on concrete was more than that on steel reinforcement. • increasing burning temperature in the first and second stages led to steep increase in the spc camber, while a gradual camber decreasing was observed in the third stage (cooling stage). • for identical spc beams made up of 9 segments, the value of maximum camber at the end of target temperature period increased at burning temperature 500˚c, and 700˚c by 165%,and 335% compared with the one at 300˚c. likewise, it was 181% and 388% and 181% and 409% for spc beams of 7 and 5 segments for the same burning temperatures. correspondingly, the camber at this stage compared to the initial value was 182%, 220%, and 354% for spc beams of 9 segments at 300˚c, 500˚c, and 700˚c, respectively. likewise, it was 183%, 236%, and 421% and 191%, 244%, and 406% for spc beams of 7 and 5 segments at the same burning temperatures respectively. • increasing burning temperature had a bad effect on the residual final camber at the end of burning and cooling cycle, denoting more deterioration occurred. the increase percentage in the residual camber for spc beams of 9 segments was 153%, 169%, and 236% for burned beams at 300˚c, 500˚c, and 700˚c respectively compared to the initial camber before burning. whilst, for spc beams of 7 and 5 segments it was 152%, 175% and 266%, and 150%, 182% and 253% for the same temperatures. • comparing the effect of segment number on the residual camber of post fire spc beams, the results show that, camber decreases with decreasing number of segments. exposing spc beams composed of 7 and 5 segments to 300˚c decreased the final camber by 78% and 56% respectively compared to that of 9 segments. it decreased by 80% and 63%, and 82% and 69% for spc beams composed of 7 and 5 segments compared to 9 segments at 500 c, and 700˚c respectively. references [1] m. al-gorafi, a. ali, i. othman, m. jaafar, m. anwar, “externally prestressed monolithic and segmental concrete beams under torsion: a comparative finite element study”, iop conference series: materials science and engineering, vol. 17, 2011 [2] c. sivaleepunth, j. niwa, d. nguyen, t. hasegawa, y. hamada, “shear carrying capacity of segmental prestressed concrete beams”, doboku gakkai ronbunshuu e, vol. 65, no. 1, pp. 63-75, 2009 [3] d. nguyen, k. watanabe, j. niwa, t. hasegawa, “modified model for shear carrying capacity of segmental concrete beams with external tendons”, doboku gakkai ronbunshuu e, vol. 66, no. 1, pp. 53-67, 2010 [4] m. algorafi, a. ali, i. othman, m. jaafar, m. anwar, “experimental study of externally prestressed segmental beam under torsion”, engineering structures, vol. 32, no. 11, pp. 3528-3538, 2010 [5] y. chan, x. luo, w. sun, “compressive strength and pore structure of high-performance concrete after exposure to high temperature up to 800°c”, cement and concrete research, vol. 30, no. 2, pp. 247-251, 2000 [6] c. poon, s. azhar, m. anson, y. wong, “comparison of the strength and durability performance of normaland high-strength pozzolanic concretes at elevated temperatures”, cement and concrete research, vol. 31, no. 9, pp. 1291-1300, 2001 [7] b. georgali, p. tsakiridis, “microstructure of fire-damaged concrete. a case study”, cement and concrete composites, vol. 27, no. 2, pp. 255259, 2005 [8] f. aslani, “prestressed concrete thermal behaviour”, magazine of concrete research, vol. 65, no. 3, pp. 158–171, 2013 [9] l. zhang, y. wei, f. au, “mechanical properties of prestressing steel at elevated temperature and after cooling”, australasian conference on the mechanics of structures and materials, southern cross university, australia, december 9-12, 2014 [10] i. fletcher, s. welch, j. torero, r. carvel, a. usmani, “behaviour of concrete structures in fire”, thermal science, vol. 11, no. 2, pp. 37-52, 2007 [11] m. abramowicz, r. kowalski, “residual mechanical material properties for the reassessment of reinforced concrete structures after fire”, 9th international conference on modern building materials, structures and techniques, vilnius, lithuania, may 16-18, 2007 [12] j. outinen, p. makelainen, “mechanical properties of structural steel at elevated temperatures and after cooling down”, fire and materials, vol. 28, no. 24, pp. 237-251, 2004 [13] w. dias, “some properties of hardened cement paste and reinforcing bars upon cooling from elevated temperatures”, fire and materials, vol. 16, no. 1, pp. 29-35, 1992 [14] k. umran, fire flame exposure effect on some mechanical properties of concrete, msc thesis, babylon university, 2002 [15] m. kadhum, “effect of burning by fire flame on the behavior of reinforced concrete beam models”, journal of babylon university, vol. 21, no. 5, 2011 [16] j. j. myers, w. l. bailey, “seven-wire low relaxation prestressing tendon subjected to extreme temperature: residual properties”, international journal of engineering research and science & technology, vol. 4, no. 3, pp. 223-239, 2015 [17] r. jansson, “fire spalling of concrete – a historical overview”, matec web of conferences, vol. 6, article id: 01001, 2013 microsoft word 02-singh-ed.doc etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 295-301 295 www.etasr.com singh and sharma: preparation of bimetallic pd-co nanoparticles on graphene support for use as … preparation of bimetallic pd-co nanoparticles on graphene support for use as methanol tolerant oxygen reduction electrocatalysts ravindra nath singh department of chemistry, centre of advanced study banaras hindu university, varanasi, india rnsbhu@rediffmail.com chandra shekhar sharma department of chemistry, centre of advanced study banaras hindu university, varanasi, india shekhar3040@rediffmail.com abstract— graphene-supported (40-x) wt% pd x wt% co (0≤x≤13.33) alloys/composites have been prepared by a microwave-assisted polyol reduction method and been investigated for their structural and electrocatalytic properties for the oxygen reduction reaction (orr) in 0.5 m h2so4 at 298 k. the study demonstrated that the bimetallic pd-co composite nanoparticles are, in fact, alloy nanoparticles with fcc crystalline structure. partial substitution of pd by co (from 3.64 to 13.33 wt%) in 40 wt% pd/graphene decreases the lattice parameter as well as the crystallite size and increases the apparent catalytic activity, the latter, however, being the greatest with 8 wt% co. the orr activity of the active 32 wt% pd 8wt% co is found to be considerably low when it was deposited on the support multiwall carbon nanotubes under similar conditions. the rotating disk electrode study indicated that the orr on 32 wt% pd 8 wt% co/gns in 0.5 m h2so4 follows approximately the four-electron pathway. keywordsgraphene-supported composite; oxygen reduction reaction;microwave-assisted polyol reduction method; electrocatalytic properties. i. introduction among various direct liquid fuel cells (dlfcs), the direct methanol fuel cell (dmfc) has received the most intensive attention. considerable improvements have been made in its performance [1-4], however, one of the main obstacles for the commercialization of dmfc is the methanol crossover from the anode to the cathode compartment through the solid polymer electrolyte membrane (spem) [5-6]. platinum is the best cathode material known for the oxygen reduction reaction (orr) due to its high work function ability to cause appreciable oxygen reduction, and good resistance to dissolution [7]. however, due to high cost and limited availability in nature, pure platinum material is not commercially viable. also, pt catalysts have high intrinsic activities to both orr and mor (methanol oxidation reaction) and therefore, the efficiency of pt-based cathode materials decreases by the interference of oxidation of alcohol present in the cathodic compartment during the cell operation. recently, pd-based cathode catalysts have attracted much attention because pd possesses properties similar to those of pt (same group of the periodic table, same crystal structure, and similar atomic size) and, as similar to pt, it has also a four electron pathway for orr [8]. the cost of pd is currently about onethird of pt and it is, at least, 50 times more abundant than pt [9]. in addition, it has negligible electrocatalytic activity towards mor in acidic mediums [10]. several carbon-supported pd-based bimetallic cathode materials have already been reported [11-16]. graphene is an allotrope of carbon (like diamond, fullerene, carbon nanotubes (cnt) etc.) having sp2-hybridized carbon atoms forming two dimensional monolayer sheets possessing high surface area [17] and excellent electronic mobility at room temperature [18-19]. compared to other carbon supports used for obtaining active fuel cell catalysts, it is low cost and has large surface area [17, 20-21] and much lower production cost [20, 22]. however, the investigation of graphene as a metal catalyst support in fuel cells is very limited. singh and awasthi [23] obtained 20 wt% pd nanoparticles dispersed on graphene nano sheets (gns), nanocarbon powders (nc) and multiwalled carbon nanotubes (mwcnts) and demonstrated that the electrocatalytic activity of 20 wt% pd/gns for methanol electrooxidation was significantly higher than that of 20 wt% pd/mwcnts or 20 wt% pd/nc in 1 m koh +1 m ch3oh. recently, graphene has also been used as a support for pt to investigate the electrocatalytic activity and durability towards the orr. the result showed the enhanced electrocatalytic activity and durability of graphene-supported metal electrodes compared with cnt or amorphous carbon supported electrodes [24-25]. this has been attributed to the intrinsic graphitization degree of graphene and the enhanced metal catalyst-support interaction. very recently, rao et al. [26] synthesized graphene-supported pt3co and pt3cr alloy nanoparticles. they found the orr activity of the pt3m (m = co and cr)/graphene 3-4 times higher than that of pt/graphene. the high catalytic performance of pt3m alloys is ascribed to the inhibition of formation of hydroxyl species on pt surface by alloying. in this paper, we obtained pd nanoparticles (nps) dispersed on gns for the orr in acid solutions. preliminary investigations showed that the 40 wt% pd/gns electrode has the greatest orr activity in 0.5 m h2so4. to enhance the etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 295-301 296 www.etasr.com singh and sharma: preparation of bimetallic pd-co nanoparticles on graphene support for use as … orr activity of the electrode further, pd-co bimetallic nanoparticles with varying co/pd ratios (i.e. 1:10, 1:6, 1:4 and 1:2) by weight were deposited on gns and their structural and electrocatalytic activities in arand o2-saturated 0.5 m h2so4 with and without containing methanol were investigated. the investigation of orr, to our knowledge, has not been reported on graphene-supported pd-based bimetallic nps in acid solutions. ii. experimental a. catalyst preparation home made graphite oxide (gox) is taken as the precursor for the preparation of gns. gox was prepared by a modified hummers and offemmans method [27-28] and reduced to gns by the nabh4 reduction method [23, 29]. a known amount of gns is dispersed into ethylene glycol, sonicated the dispersion for one hour and then added required volumes of 1.0 mm pdcl2 (prepared in 0.05 m hcl), and 8.4 mm cocl2. .6h2o solutions and again sonicated the whole content for one hour for proper mixing. the mixture, so obtained, was maintained at ph~10 using koh solution, sonicated for 15 min and subsequently placed in a microwave oven at 800 watt for 5 min and then left overnight at room temperature. the black solid residue was separated from the mixture through ultracentrifugation, washed with acetone and finally dried in a vacuum oven [26, 33]. the total metal (co+pd) loading on the graphene was 40 wt%. bimetallic nanoparticles prepared insitu are 36.36 wt% pd3.64 wt% co, 34.28 wt% pd 5.72 wt% co, 32 wt% pd 8 wt% co and 26.67 wt% pd 13.33 wt% co. for simplicity in representation, only ’%’ is written in place of ‘wt%’ throughout the text hereafter. for comparison, 40% pd/mwcnt composite was also prepared under similar experimental conditions. b. characterization of catalyst x-ray diffraction (xrd) powder patterns of the electrocatalysts were recorded at the sweep rate of 3o min-1 on an x-ray diffractometer (thermo electron) using cukα as the radiation source (λ=1.5418å). morphology of the electrocatalyst has been studied by transmission electron microscope (tem: jeol, jem 2100). c. electrode preparation the ink was prepared by mixing 3 mg of electrocatalyst in 600 µl of the ethanol-water (2:1) mixture ultrasonically. 30 µl of ink was placed on the glassy carbon electrode (gc: area = 0.5 cm2) and dried in air to evaporate the solvent. then, 10 µl of 1% nafion solution (alfa aesar) was dropped over the dried catalyst layer to cover it. the catalyst loading on gc (metal+gns) was 0.3 mg cm-2 and accordingly, the metal loading was 0.12 mg cm-2. pretreatment of the gc electrical contact with the catalyst overlayer and electrode mounting were carried out as described in [31, 32]. d. electrochemical studies a three-electrode one-compartment pyrex glass cell was used to carry out electrochemical investigations. the saturated calomel electrode (e0=0.242v vs. she) and a pure pt-foil (area~8 cm2), were used as the reference and auxiliary electrodes, respectively. the reference electrode was separated from the electrolyte by a bridge in order to prevent cl contamination of the electrolyte. however, all potentials in this study refer to that of the reversible hydrogen electrode (rhe). electrochemical studies namely cyclic voltammetry (cv) and linear sweep voltammetry (lsv) were carried out by a computer controlled potentiostat/galvanostat (eg & g par model: 273a). cvs and lsvs of electrocatalysts were recorded in aras well as o2-saturated 0.5 m h2so4 solution with and without containing 1 m ch3oh. iii. results and discussion a. xrd/ sem/tem the xrd powder patterns of 40% pd/gns and (40-x)% pd x% co (0≤x≤13.33) composite electrodes recorded between 2θ = 20 and 2θ = 80° are shown in figure 1. fig. 1. xrd patterns of pd/gns and pd-co/gns composites. the xrd pattern of 40% pd/gns shows the three characteristic peaks of pd at 2θ≈40°, 46.5° and 68.2°, which correspond to planes (111), (200) and (220), respectively. thus, 40% pd nanoparticles dispersed on gns [23, 33] follows the fcc crystalline structure. the xrd patterns of bimetallic composites of pd and co also display the above three diffraction peaks but, they are found to shift slightly to a higher 2θ value with respect to the corresponding peak observed in the case of pd/gns catalyst, the magnitude of shift in 2θ values being 0.5-1° with 3.6-13.3 % co addition in the composite. the shift of peaks to a higher angle and the absence of reflection corresponding to co in the xrds of pd-co composites reveal the alloy formation between pd and co, which is caused by the incorporation of co in the pd fcc structure. the broad peak between 2θ=24 and 26˚ is the characteristic peak corresponding to the (002) plane for graphene. the lattice parameter (δ) and the mean crystallite size (s) of pd nanoparticles in all four catalysts have also been determined. the most intense diffraction peak of pd corresponding to the plane (111) was employed to determine etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 295-301 297 www.etasr.com singh and sharma: preparation of bimetallic pd-co nanoparticles on graphene support for use as … the pd crystallite sizes (s) by using the scherrer formula. the lattice parameter was calculated by using (1): )( 4 222 2 2 2 qkhsin ++= δ λ θ (1) where λ is the cukα radiation wave length, 1.5418 å, δ is the lattice parameter and h, k, q are the lattice index parameters [34]. estimates of s and δ for pd are ~5.7 nm and 0.390 nm, ~3.7 nm and 0.389 nm, ~3.6 nm and 0.387 nm, and ~3.4 nm and 0.385 nm in 40% pd/gns, 36.36% pd 3.64% co/gns, 32% pd 8% co/gns and 26.27% pd 13.33% co/gns respectively. thus, results show that as the co content increases in pd-co alloy, both the mean crystallite size [11, 16] and the lattice parameters [11, 34] decrease. the decrease in value of the lattice parameter might result from a lattice contraction upon alloying [11]. studies of xrd and raman spectroscopy [23] and sem/tem [30] of gns used in this investigation have already been reported in our previous communication. sem/tem images exhibited wrinkled and folded features for graphene. results of tem, xrd and raman spectroscopy showed the formation of three-layer graphene [23]. tem images of 40% pd/gns, 26.67% pd 13.33% co/gns and 32% pd 8% co/gns are depicted in figure 2(a-f). these figures show good dispersion of pd and pd-co particles on gns. at some places, however, there are also some concentrated regions which may be due to presence of functional groups on the gns in significant amount [35]. some dark contrast within the pictures are also seen which probably may be due to bragg orientation of metal particles. there is also possibility of overdeposition of metal nanoparticles which may cause mass contrast. the average particles size measured by tem pictures of 40% pd/gns, 26.67% pd 13.33% co/gns and 32% pd 8% co/gns were ~6.3, ~4.3 and ~4.8 nm, respectively, which are close to values of the crystallite size obtained from the xrd study. b. cyclic voltammetry (cv) cvs of (40-x)% pd x% co/gns (0≤x≤13.33) composites have been recorded at the scan rate (v) of 50 mv s-1 in the potential region from -0.058 to +1.542 v vs. rhe in 0.5 m h2so4 with and without containing methanol at 298 k. cvs were recorded under ar-saturated electrolyte conditions and reproduced in figures 3 and 4. features of curves shown in figs. 3 and 4 are similar, regardless of the nature of the electrode and electrolyte. therefore for simplicity in representation, only three representative curves for the electrocatalysts , namely 40% pd/gns, 32% pd 8% co/gns and 26.67% pd 13.33% co/gns are shown in figures 3 and 4. figure 3 gathers cvs of 40% pd/gns, 32% pd 8% co/gns and 26.67% pd 13.33% co/gns electrodes in arsaturated 0.5 m h2so4. the oxidation-reduction peaks observed in the potential region, from 0.342 to -0.058 v vs. rhe, are produced due to the adsorption/desorption of hydrogen [36]. the wave-like shape of voltammograms on the positive-going scan and prior to the commencement of o2 evolution reaction can be ascribed to a slow electrochemical oxidation of the palladium surface into palladium (ii) oxide [37]. a relatively strong cathodic peak observed at e = 0.5560.615 v vs. rhe on the negative-going scan is caused due to the reduction of palladium (ii) oxide, formed under anodic condition, into palladium metal [23, 33, 34, 38]. the relatively larger anodic peak, observed in the potential range between 0.058 v and 0.342 v vs. rhe, for the pd/gns catalyst in comparison with those for pd-co/gns catalysts (figure 3) might indicate the dissolution of adsorbed hydrogen into bulk pd. the addition of co within the catalyst might restrain dissolution of hydrogen into bulk pd-co/gns as compared to pure pd catalyst [10]. it is known that unlike pt, the bulk pd can absorb hydrogen [38] and so, the charge of a monolayer of adsorbed hydrogen is difficult to determine in the case of pd. therefore, the electrochemically active surface areas (easas) of the pdco/gns composite electrodes have been measured by determining the coulombic charge (q/mc) for the reduction of palladium oxide [30, 38]. q has been determined by integrating the oxide reduction peak. the easa of the electrode was then estimated using the relation easa=q (mc)/s (mc cm-2), where s is the proportionality constant. a charge value of 0.405 mc cm-2 is assumed for reduction of pdo monolayer [23, 30, 33, 39]. the easa values of catalysts (in ‘cm2’), thus estimated, are listed in table 1. fig. 2. tem images of 40% pd/gns (a and b), 26.67% pd 13.33% co/gns (c and d) and 32% pd 8% co/gns (e and f). etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 295-301 298 www.etasr.com singh and sharma: preparation of bimetallic pd-co nanoparticles on graphene support for use as … fig. 3. cyclic voltammograms of pd/gns and pdco/gns composites in ar-saturated 0.5 m h2so4. scan rate = 50 mvs -1 & t = 298 k. fig. 4. cyclic voltammograms of pd/gns and pdco/gns composites in ar saturated 0.5 m h2so4 1 m ch3oh. scan rate = 50 mvs -1 & t = 298 k. table i. electrocatalytic properties of (40-x)% pd x% co nanoparticles dispersed on gns in 0.5 m h2so4; geometrical area of the electrode = 0.5 cm2 ; metal loading (l) = 0.12 mg cm-2 , temp. 298 k. 1 0 2 ×× ×× l / m g c m -2 e a s a apparent current at e = 0.20 v / x / w t% pd co q / m c c m 2 c m 2 m g -1 p d m a m a m g -1 p d 1 0 2 ×× ×× s p e c if ic a c ti v it y / m a c m -2 0 12 0 16 39.5 658 0.33 5.5 0.84 3.64 10.9 1.1 18 44.4 823 0.53 9.8 1.19 5.72 10.3 1.7 19 46.9 920 0.71 13.9 1.51 8.00 9.6 2.4 23 56.8 1183 0.79 16.4 1.39 13.33 8.0 4.0 6 14.8 380 0.42 10.7 2.83 the observed easa of a particular electrocatalyst has also been normalized with respect to the actual pd mass taken in that electrocatalyst. based on values of the easa, the catalysts investigated follow the order: 32% pd 8% co/gns > 34.28% pd 5.72% co/gns > 36.36% pd 3.64% co/gns > 40% pd/gns > 26.67% pd 13.33% co/gns features of cvs of pd-co/gns composites recorded in arsaturated 0.5 m h2so4 containing 1 m ch3oh shown in figure 4 are also similar to those recorded in absence of methanol under similar experimental conditions (figure 3); they do not show any characteristic current peak for the electrooxidation of alcohol. thus, results show that pd-co bimetallic composites are perfectly immune to the mor in acid solutions and can be used as methanol tolerant reduction reaction electrocatalysts. c. electrocatalytic activity linear sweep voltammetries (lsvs) of (40-x)% pd x% co/gns (0≤x≤13.33) composites have been recorded in the potential region from + 0.842 to + 0.042 v vs. rhe at the scan rate (v) of 5 mv s-1 in arand o2saturated 0.5 m h2so4 at 298 k. curves, so obtained, are reproduced in figure 5. fig. 5. linear scan voltammograms of pd/gns and pdco/gns in o2saturated 0.5 m h2so4. scan rate = 5 mvs -1& t = 298 k. lsvs of electrocatalysts in ar-saturated 0.5 m h2so4 were similar and seem to have very little (i.e. negligible) current contributions towards the electroreduction of oxygen. a typical lsv curve for the 32% pd 8% co/gns catalyst in ar-saturated 0.5 m h2so4 is shown in figure 5. voltammograms in o2saturated solution depicted in figure 5 show that among the bimetallic pd-co composites, the 32% pd 8% co/gns electrode is the greatest active while the 26.67% pd 13.33% co is the least active electrode for the orr. based on values of the orr current density noted from figure 5 at a constant potential, e=0.442 v vs. rhe, different electrocatalysts can be put in the activity order: 32% pd 8% co/gns (1.58 ma cm-2) > 34.28% pd 5.72% co/gns (1.42 ma cm-2) > 36.36% pd 3.64% co/gns (1.06 ma cm-2) > 26.67% pd 13.33% co/gns (0.84 ma cm-2) > 40% pd/gns (0.66 ma cm-2). the enhanced catalytic activities observed in the case of pd-co composites in comparison with pure pd may be attributed to the alloying of pd and co followed by a lattice compression (i.e. reduction in pd-co bond). the lattice compression results in shift of d-band center, which has an effect on surface activity of pd sites. it has already been shown by dft calculation that the compression of a pd lattice in alloy produces the downshift of the d-band center energy [40]. the etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 295-301 299 www.etasr.com singh and sharma: preparation of bimetallic pd-co nanoparticles on graphene support for use as … increase in the specific activity of the electrode with co introduction for pd shown in table 1 also indicates modification in the electronic properties of the electrode material in favour of electrocatalysis of the orr. the decrease in the apparent orr activity at the higher co addition (13.33%) can be ascribed to somewhat lowering of percentage of pd in the bimetallic alloy. also, blocking of some active pd sites at higher co additions cannot be ruled out. to examine the influence of the catalyst support, the 32% pd 8% co alloy nanoparticles were also obtained on mwcnts and investigated as electrocatalyst for the orr under similar experimental conditions as employed in the study of the same alloy catalyst obtained on the gns support. lsv curves shown in figure 6 indicate that the orr performance of the pd-co alloy is greatly improved when obtained on the gns support rather than on mwcnts. also, the onset of the reduction wave gets shifted toward the higher positive potential (figure 6), which can be ascribed to greatly enlarged geometrical surface area and better electron transport properties of the gns support. fig. 6. linear scan voltammograms of 32 % pd 8 % co supported on gns and mwcnts in o2-saturated 0.5 m h2so4. scan rate = 5 mvs -1 & t = 298 k. the most active bimetallic catalyst, 32% pd 8% co/gns, of the investigation was also deposited at the disk (dia. 0.3 cm) of a rotating disk electrode (rde) and lsv curves at the slow scan rate of 2 mv s-1 and varying rotations were recorded in o2saturated 0.5 m h2so4 at 298 k. lsv curves, so obtained, are shown in figure 7. the observation of lsv curves of the electrode at varying rotations indicates that at the higher potential region the orr is a mixed diffusion–kinetic controlled process. therefore, the overall measured disk current density (j) was determined by using the relation [4142], dk jjj 111 += (2) where jk and jd represent the currents, controlled by electron transfer kinetics and mass transport (mainly diffusion) properties, respectively. fig. 7. linear scan voltammograms of 32 % pd 8% co/gns at varying rotations in o2-saturated 0.5 m h2so4; scan rate = 2 mvs -1; & t = 298 k. the analysis of catalytic current as a function of rotation rate was done with the help of the koutecky-levich relation [43]: 2 1 111 ωbjj k += (3) where ω is the electrode rotation in revolutions per minute (rpm) and b is the levich constant given by [44]: 6 1 3 2 22 2.0 1 − = ν oo dnfc b (4) where 0.2 is a constant, co2 is the concentration of o2 dissolved in the bulk electrolyte, n is the number of electrons transferred per molecule of o2 reduced, f is the faraday constant, do2 is the diffusion coefficient of oxygen in solution, ν is the kinematic viscosity of sulphuric acid. the kinetic values, with respect to activation and diffusion, have been calculated by constructing the linear kouteckylevich, l-k, (i.e. 1/j versus 1/ω1/2) plots at different constant potentials, as shown in figure 8, and measuring the intercept (1/j=1/jk for 1/ω 1/2 = 0) and slope (= 1/b) of these linear curves. values of jk and b, so obtained, are listed in table 2. fig. 8. 1/j versus 1/ω1/2 plots constructed from fig.7 at constant potentials. etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 295-301 300 www.etasr.com singh and sharma: preparation of bimetallic pd-co nanoparticles on graphene support for use as … values of slope listed in table 2 seem to slightly decrease with the increase of the cathodic overpotential; the average value of the slope being 8.44± 0.45 x 10-2 ma-1 cm2 rpm1/2 in the potential range, 0.4-0.3 v vs. rhe. the average slope, thus determined, is somewhat lower than the theoretical slope, 9.41 x 10-2 ma-1 cm2 rpm1/2 [44]. the theoretical slope was computed by using (5) and considering n=4, f=96485 coulomb, co2=1.1x10 -6 mol cm-3, do2=1.4x10 -5 cm2 s-1, ν=1.0x10-2 cm2 s-1, electrolyte=0.5 m h2so4. thus, the result shows that the orr in 0.5 m h2so4 follows an 3.6 (≈4) electron pathway in the potential region, 0.30-0.40 v vs. rhe. zhang et al [45] also found similar parallel straight lines for kl plots indicating four-electron reduction of o2 on pt/pd (111) surface in 0.1 m hclo4. recent studies of orr on pd0.5nixse(0.5-x) [46], pd deposited on porous carbon paper [47], irco/c [44] and pd nanoparticles/mwcnts [48] in h2so4 solution also exhibited a four-electron charge transfer pathway for electroreduction of o2 to h2o. table ii. estimate of kinetic values for orr at the catalytic film of 32% pd 8% co/gns on glassy carbon disk (0.3 cm dia.) in 0.5 m h2so4; scan rate :2 mv s -1, rotation speed :1600 rpm temp. 298 k. e/v jk /ma cm -2 slope b/ ma cm -2 rpm -1/2 jd ( = b ωωωω 1/2 )/ ma cm -2 0.40 3.42 8.9 0.112 4.48 0.38 3.92 8.8 0.114 4.56 0.35 4.37 8.4 0.119 4.76 0.33 4.90 8.1 0.123 4.92 0.30 5.43 8.0 0.125 5.00 iv. conclusion the study shows that incorporation of co into pd produces a solid solution (i.e. alloy) with reduced lattice parameter as well as the particle size. all the alloy catalysts exhibited better electrocatalytic performance than the pure pd catalyst, the orr activity, however, being the greatest with 32% pd8 % co/gns catalyst. it is worth-mentioning that all the pd-co bimetallic catalysts of the present investigation are good methanol tolerant cathodes. further, the graphene displays much superior performance compared to mwcnts as a metal catalyst support material. acknowledgement the financial support received, to carry out the investigation, from the council of scientific and industrial research (csir), government of india through research grants (ref. no. 01(2320)/09-emr-ii) is gratefully acknowledged. authors thank dr. divesh n. srivastava, central salt & marine chemicals research institute, bhavnagar (india) and prof. r. s. tiwari, physics department, b.h.u. 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deemed to be university bhubaneswar, india mkmfel@kiit.ac.in chinmoy kumar panigrahi school of electrical engineering kalinga institute of industrial technology deemed to be university bhubaneswar, india panigrahichinmoy@gmail.com abstract—growing population and expanding industry set off the demand for electrical energy and issues, such as the problem of peak load demand, emerge. to balance the supply and load demand problem, the energy management system has the vital role of electric peak shaving with the integration of microgrid into the utility grid. the combination of demand-side management with storable energy sources helps us resolve the matters concerned with the peak load demand. however, in a microgrid, whenever the distributed energy sources are interconnected, the dc bus link voltage will vary due to the inherent behavior of each source as they mainly depend on geographical conditions. this work proposes voltage droop control strategy to keep the dc bus link voltage at a constant value. also, it gives an overlook of the present power sector scenario of india and a reassessment of the demand side management system and how it is utilized in electrical peak shaving. keywords-demand side management; droop controller; energy management system; microgrid; peak load demand i. introduction electrical energy is the backbone and the most essential factor for world growing technology and economic development. load demand due to generation and consumption mismatch problems is a major issue of the perpetually expanding utility grid. with the help of the available fossil fuels to generate adequate power to satisfy the load demand, the problem of greenhouse gas emissions emerged. overcoming issues like greenhouse gas emissions, led to the utilization of renewable energy sources (ress) for electrical energy generation. we use ress to reduce the problem of demand requirement that occurs due to the mismatch in generation and consumption. globally, over 70% of generation is done by using fossil fuels like (coal, oil, nuclear, etc.), while in india the percentage is 80% [1]. the supply demand may increase up to 40-50% in the next one or two decades. if the energy demand increases gradually in the next few decades, the energy generation by using the bulk amount of fossil fuels is not a feasible solution, because these sources may drain quickly and by using fuels like coal for power generation in thermal power plants will release more amount of pollutant gases like so2 and nox. because of these pollutant gases, there is a change in environmental conditions. so to reduce these problems, res have been utilised, and they are leaping power generation, especially sources like solar and wind energy system (excluding hydropower plants), having an ability to recharge at every time instant. however, at present in india, only 17% of the demand is supplied by ress, even though the scope and ability to increase the generation of renewable energy exist. ress take an all-important share in india’s energy generation sector [2]. however, due to their irregularity in nature, ress do not always help in reducing the peak demand when generation and consumption mismatch problems occur. even sometimes while penetrating to the grid, we can see the problem occurring due to the extensive integration of wind and solar generation in the distribution and transmission network. high solar irradiance and wind speed when the demand is low can cause issues like voltage regulation, frequency regulation, and system losses in the distribution and transmission networks [3]. solutions for these issues should overcome by bringing into effective action the comparison of the demand side management (dsm) and energy storage system (ess). dsm provides a platform for peak demand by shifting loads from peak-time period to the off-peak-time period and also controls the loads during renewable energy generation. if the generation from res is more than the demand, it manages the excess amount of energy generated by ress by utilizing ess, and the energy is pushed back to the utility grid during the peak period of the supply demand. the dsm is not only used to reduce peak demand and shifting of loads but also to support distributed generation (microgrids) to consume the power generated by small-scale ress for local loads instead of transmitting long distances. the ess can offer high flexibility in a state of charging and discharging at the time of peak and off-peak periods so that the problem of demand in supply can be distributed equally. we can also use ess to reduce fluctuations and issues regarding voltage and frequency regulation. in microgrids (mgs), when integrating two more sources, the main issue is the voltage regulation of the dc bus link voltage, which it cannot be kept consistent. this study mainly focuses on maintaining voltage regulation and constant dc bus link voltage with the help of a corresponding author: teki vamsee krishna engineering, technology & applied science research vol. 10, no. 3, 2020, 5857-5863 5858 www.etasr.com krishna et al.: integrated design and control of renewable energy sources for energy management voltage droop controller for power management when two energy sources (solar and wind energy with ess) penetrate the system. ii. literature review energy management system (ems) plays a crucial role in present power systems. ems is used to optimize the most complex and vital technical creations in the electrical power system. an essential step in energy management systems is operating different energy sources to overcome issues concerned with the mismatch of generation and consumption to reduce electrical peak shaving. ems has taken various forms such as generation side management (gsm), industrial energy management system (iems), demand-side management (dsm), building energy management system (bems), home energy management system (hems). however, when compared with other topologies, dsm plays the most vital role in the present power systems scenario with scheduling loads according to supply demand. the main aim of the dsm scheme is to get the final load curve as close as possible to the standard load curve. combining dsm with an ess allows reducing the mismatch problem and the fluctuations and frequency regulation when distribution generating units penetrate the utility grid. there are some useful studies in the field of mgs and distribution generating units. authors in [4] developed a smallscale mg-based hybrid system, consisting of solar and wind energy with a battery storage system. the operation of an mg by controlling different sources and with the help of an energy management algorithm verified with rtds increased the system performance of the mg. they used a cascaded pi controller to control the dc link voltage by taking an average value and generating corresponding reference current signals to various converters. the drawback of the ems method is that when the load demand increases, it dedicates the developed algorithm to the standalone system and exercises load shedding. authors in [5] proposed deterministic energy management for mgs, used for feature solar photovoltaic with bss installation, which gives more flexibility to the distribution network. the management has functioned in two parts according to their characteristics, but because of variations in geographical conditions, the output power from res fluctuates, which results in the variation of grid’s voltage and frequency regulations. to overcome these issues, the authors implemented a hybrid supercapacitor battery-based pv active generator to offer energy reserves with fewer fluctuations and to balance power fluctuations coming from the pv active generator and primary frequency control. in ems, dsm is the best field to optimize the problems related to peak demand. dsm has the potential to improve the energy system at the side of demand [6]. dsm’s main advantage is that it is less expensive to influence the load intelligently by scheduling the load according to the demand and availability of supply (direct and indirect approach) instead of constructing new generating units or by providing the ess. the indirect dsm approach is a time-varying price signal, which influences load according to the peak time, known as demand response (dr). we can remark it as complicated for the consumer end to use a time-varying tariff scheme, in a realtime pricing policy. in [7], a game-theoretic model was proposed to optimize the demand and to decrease the consumer’s electricity bill around 20%. dsm strategy is utilized to optimize resources with the game-theoretical model to schedule the appliances according to the time of use (tou). the control model optimizes the user’s electricity bill, according to the tou: in the peak period the prizes are high and vice versa. the biggest challenge with the implementation of the tou is that a problem from the consumers end may emerge when the price is updated in every cycle, which may be more or less equal to 1 hour. spinning reverse is seen as the primary and secondary control, as the active output power directly depends on frequency. grid state and frequency can be restored with added active power. the biggest challenge the power plants face is when, because of the loads, they act as a reverse or virtual negative spinning. droop control or some other control management are used to correlate the power consumption with the grid state. an adaptive power flow control has been proposed in [8], used to reduce the electrical peak grid demand and to increase the penetration of res to reduce the mismatch between generation and consumption. apfc aims to control the appliances, consuming the most amount of power and the bss was charged or discharged according to the power demands. integrating res does not mean that it can reduce the peak demand at the time of imbalance between supply and demand. however, penetrating a high level of pv energy into a distribution network with strong irradiance and low demand can cause issues. combing ess with dsm is one of the best solutions in overcoming those issues. to get the benefits of the system, the authors have focused on control management. apfc uses the historical data on grid demand, pv data and load demand data as inputs to decide the dsm and battery charge or discharge mode to balance the demand and supply. thus, the average peak demand was reduced to 35% and the share of pv generation was increased up to 64%. to reduce fluctuations requires storing energy to achieve proper regulation when penetrated with res. authors in [9] presented a power management and control technique for a standalone hybrid system with flywheel energy storage system usually alternating in nature. the controller output is the reference voltage, used to switch the power converter with space vector pulse width modulation to keep the dc bus link voltage. frequency regulation used to be conducted by synchronous generators, but now it is gradually taken over by power converts as virtual synchronous generators (vsgs) [10], which act as an interface between the res and the utility grid. droop and vsg controller were used to control the inner voltage. in modern power systems, power converters are used to transfer maximum power from ress without frequency regulation. the hybrid energy storage system comprises of a battery and an ultra-capacitor to achieve power management. the authors of [10] did not consider the quick changes in the load demand situations though. in the future smart grid, dsm will play a vital role by scheduling and managing the loads in a smart way to reduce electrical peak demand. for scheduling appliances, authors in [11] used an evolutionary dsmbased algorithm for scheduling loads of end users according to the demand. to reduce issues like peak demand, they develop two engineering, technology & applied science research vol. 10, no. 3, 2020, 5857-5863 5859 www.etasr.com krishna et al.: integrated design and control of renewable energy sources for energy management approaches for promoting energy-efficient technology, later known as dr. a new home energy system (hes) model based on tou scheme was developed with and without ress, to reduce electrical peak demand. the authors did not discuss the benefits of load scheduling of multiple houses to utility and end-user comfort, addressing the case of a single house instead. distributed emss become more popular for smart appliance scheduling. when the demand varies regarding time, the use of a bss is studied to decrease the cost of the demand for consumers. however, variations to the supply and demand (especially when dealing with ress), effect the action of charging and discharging efficiency of storage devices, reducing dc bus link voltage at peak time which is not kept constant [12, 13]. in [14], a droop control method is used for a standalone mg for ems to support the generator output power for stable operation. the dc bus link voltage also kept constant by taking the reference value from the output voltage magnitude and phase angle. the droop controller identifies the reference values from two sets of specific droop characteristics to get optimal output power. the authors considered only the standalone system and did not discuss the operation of droop controller when it was operated in grid-connected mode and the benefits of controlling for reactive power-sharing. to reduce peak demand, a mixed-integer nonlinear programming technique was used in [15]. the authors developed an adaptive neural fuzzy inference system (anfis) based microcontroller to schedule the appliances according to the demand. we should remark that the overall control of the energy system becomes a big challenge and demand response is also not a fully automated solution for scheduling the appliances. in order to reduce power demand, one solution is to penetrate renewable sources to the utility grid. authors in [16] did so considering solar energy only. in [17], dynamic programming (dp) was used for optimal power flow management, which helps in penetrating pv power to the utility grid for peak shaving. ess is the best solution that reduces the fluctuations in output power. in this, they mainly concentrated on a small amount of energy with high peak demand, which can buffer by the battery storage system. the literature review on demand-side management with the combination of energy storage systems gave some worth mentioning conclusions: • when ress penetrate the utility grid, the change in renewable generation and load can cause variation in dc bus link voltage. • as the ress are based on geographical conditions, they can cause issues like output power fluctuations, voltage and frequency regulation, and circulating current within the system. • droop control method is used to reduce the active and reactive power variation by taking reference set points from output voltage magnitude and frequency. it is also used to keep the sharing of reactive power in ac mg at balance and maintain dc bus link voltage at its nominal value. iii. role and control strategy of energy management in smart grids, ems consists of functions used to monitor, measure, and control the supply of demand centrally [18-25]. ems is used to forecast load data, operate and manage sources in order to reduce the supply demand. ress are useful and helpful at the time of peak demand for electrical peak shaving, either connected to the distribution network (small-scale) or to the transmission, network (large scale). they also increase the complexity of the network to supply uninterrupted power to load. however, the integration of large-scale renewable energy to the utility grid creates challenges to the traditional grid as these depend on weather conditions. the development in ems will reduce the issues when ress are integrated. renewable energy generation, such as solar, wind, etc., is formed as an mg, taking an essential role in the eps to produce energy with the other generating units (coal, nuclear, etc.) for reducing peak demand. these energy sources with a combination of ess, power converters and communication between sources made the grid power system network more complicated. to increase power system network stability and controllability requires many communications links and data, creating communication burdens and decreasing the protection scheme’s performance. nowadays, with the smart grid utilization, household-level distributed ems due to its ability in scheduling appliances in a quick manner reduces the burden of data communication [12]. mgs play an active role in the market and energy producers and consumers are now known as prosumers which control and manage power demand. there are three main categories in the mg control strategy: centralized, decentralized and distributed (household-level). in a power system network, economic dispatch is centralized, as the data are collected from all the energy stations and are forwarded to the central controller unit. the decentralized control method has its control and can take decisions according to local power demands. it also provides stability in small-scale generating units. in the distributed control method, the information is shared among peer mgs by two-way communication to achieve optimisation. in the present power sector, the use of mgs is increased due to the significant issue of power demand. however, one of the significant issues in the mg is the uncertainty of power supply due to the use of ress. with the combination of ess and dsm, power demand can reduce by scheduling the appliances according to the supply demand. dr’s use changes the consumer’s electric bill prices over time periods and results in electrical peak shaving. recently, hems also became a part of the smart power system in the utilisation level. it gathers information from household appliances to optimize supply and demand problems. hems was also used to hold the household appliances hastily. hems manages appliances and energy supply to improve the power system’s reliability. iv. droop control method mgs comprise more than one dg units, which can operate either in standalone or grid integrated mode, causing issues and creating challenges to operators. an mg comprises the solar pv system, the wind energy system and a battery energy storage system integrated into the utility grid through dc/dc buck/boost converter to extract maximum power from the engineering, technology & applied science research vol. 10, no. 3, 2020, 5857-5863 5860 www.etasr.com krishna et al.: integrated design and control of renewable energy sources for energy management ress which are interfaced to the point of common coupling through the dc/ac power converter circuit. we connect local loads at pcc, as it can operate the mg in any of its modes. droop control [26-27], became one of the most promising control techniques in the present mg scenario for parallel operation of converters due to the absence of a communication line between the dg units while minimizing the circulating current between converters [28]. the wireless droop controller is used mostly for load sharing as it has the advantage to avoid critical communications lines when two converters are operated in parallel. another type of controller is master-slave droop controller (wired droop controller), which has the drawback that when more than two converters operate in parallel, the primary converter (acting as the master) is used to control the dc bus link voltage and transmits the reference signal to the other converters (slave converters). if the primary converter fails, the total system will shut down. in the voltage droop control, they interface each converted to a common point and each converter responds individually and calculates how much energy has to supply or consume and maintains the output voltage of the dc bus link voltage at its nominal value. however, the drawbacks of the conventional droop control are that its performance is poor with ress and it has certain limits like slow transient response, voltage regulation, etc. authors in [29] addressed a detailed review of droop control strategy. voltage droop control regulates the inverter output voltage and frequency when sharing active and reactive power. droop control is widely used in complex power generation and transmission. the line diagram of the transmission line (inverter connected to pcc) is shown in figure 1, while (1) and (2) give the active and reactive powers transmitted across a lossless line. fig. 1. inverter connected at pcc sin ev p x φ= (1) 2 cos ev v q x φ = (2) pv f ev = (3) ( ) qx e v e ≈ (4) assuming the power angle is tiny, from (3) and (4) it is derived that the reactive power mainly depends on the power angle and moves through the limits of the output voltage. output voltage amplitude and frequency can define the droop characteristics shown in figure 3. we use this method to control the active power flow by taking frequency as a set point from each inverter unit, instead of considering the inverter output power. fig. 2. two inverters connected to the load 1 k pω ω ∗ = (5) 2 e e k q ∗ = (6) in grid-connected mode we have: * ( ) 1 k p pω ω ∗ = (7) ( ) 2 e e k q q ∗ ∗ = (8) fig. 3. voltage droop controller in (5) and (6), ω* and e* are the set points for the output voltage amplitude and the angular frequency at the no-load condition and k1 and k2 are the droop controller gain coefficients for amplitude and frequency. p* and q* are the reference setpoints obtained from real power vs frequency and from reactive power vs voltage amplitude [14]. we represent these droop controller equations in figure 3. when the frequency falls from its limits, the output power generated is increased, something that shows that increase in the load demand and requirement of more active power. however, when two converters operate in parallel with the same droop control characteristics a fall in the frequency occurs which results in a simultaneous increase in the active output power. the increase in the output power counteracts the fall in frequency and the system settles down in a steady-state point on droop controller characteristics. so, the droop controller allows the converters that operate in parallel to share the load with no disturbances. we applied this technique to the voltage droop controller shown in figure 4 to maintain the dc bus link voltage. however, the design and stability of a dc bus link voltage controller are not discussed thoroughly in this paper. engineering, technology & applied science research vol. 10, no. 3, 2020, 5857-5863 5861 www.etasr.com krishna et al.: integrated design and control of renewable energy sources for energy management fig. 4. voltage droop controller v. simulation model, results, and discussion a. microgrid configuration the overall system configuration of the proposed mg is shown in figure 5. fig. 5. simulink mg model table i. system specifications simulation result parameters parameters symbol output ratings specification of the solar photovoltaic module maximum pv power ppv 14kw maximum pv voltage vpv 500v maximum pv current ipv 28a open circuit voltage voc 32.9v of each cell (360 cells in 1 module) short circuit current isc 8.21a (single module) specification of wind turbine maximum power pwt 14kw maximum voltage vwt 500v maximum current iwt 28a specification of bess (lead-acid battery) battery voltage vbat 200v battery rated capacity c r ah 40ah maximum battery capacity c max ah 41.66ah fully discharge current vch, idch 217.76v, 8a other system specifications dc bus link voltage vdc 500v connected load-1 pl1 3kw connected load-2 pl2 3kw the system comprises a common dc bus and an ac bus of 500v. various components are connected to the dc bus, and different loads are supplied by the ac bus for residential or commercial use. solar pv and wind turbine power are considered as the main sources, grid power as the primary source of power supply, and bss is considered as the backup source for peak load demands. we have connected the solar pv source with the help of a buck converter, and wind turbine power is first converted to dc with the help of a rectifier circuit and is connected to the bus using a buck converter. a bss with a rated capacity listed in table i is also connected to the dc-link bus by a bi-directional converter. by using a dc/ac converter, the entire dc supply is inverted to ac and used to feed the local loads at pcc while integrated to the utility grid. b. results and discussion the performance of the hybrid model designed with pv, wind turbine, and ess is verified with the use of the variablestep solver (ode23tb) in simulink for a time interval of 1s. the parameters of the model are listed in table i. considering the integration of solar and wind power to a utility grid, we mainly concentrated on the dc bus link voltage when two or more energy sources are interconnected with each other. as res depends on geographical and weather conditions, the output power will fluctuate with varying solar irradiance and wind speed. to extract maximum power from these sources, a dc/dc converter with the help of a particular mppt technology is used. however, when interconnecting two sources the voltage at the dc bus link is going to fluctuate due to the flow of circulating current in the system. when there is a change in irradiance or wind speed or a change in load, the output obtained from these sources will also change, affecting the bus voltage. to keep the dc bus link voltage, we used a droop control strategy. we considered the voltage droop controller shown in figure 4, and we modelled both solar and wind energy sources at 500v, as shown in figures 6 and 7. fig. 6. solar energy dc output voltage fig. 7. wind energy dc output voltage simulations were done with changes in wind speed and solar irradiance. wind speed was considered to range between 8-12m/s and solar irradiance between 700-1000w/m 2 . we mainly focused on providing a constant voltage at the dc bus link, which is connected to the ress and to achieve power balance by maintaining it at a constant value. however, the engineering, technology & applied science research vol. 10, no. 3, 2020, 5857-5863 5862 www.etasr.com krishna et al.: integrated design and control of renewable energy sources for energy management voltage regulation of the system is affected by various disturbances, e.g. interconnecting two or more sources, weather changes, changing in loads, etc.. the droop coefficients k1 and k2 take the small values of 0.32 and 0.7 for all generating units in this model for simplicity (as we are concentrated on voltage) and a reference voltage of 500v is set in the controller. in figure 8, the purple line shows the dc bus link voltage when two sources are interconnected and the voltage is maintained at 500v. by maintaining the dc bus link voltage at a constant value, the mg operation under grid-connected mode at a constant load of 6kw and with variation in the solar irradiation and wind speed, the output voltage of inverter and active and reactive power of the system are shown in figures 9 and 10. we observe that the droop controller took less than 0.2s to maintain 500v with k2=0.7. fig. 8. dc bus-link voltage fig. 9. inverter line voltage (vab) fig. 10. active and reactive power of the system vi. conclusion renewable energy sources depend on environmental conditions and can cause variations in the output voltage, which may lead to changes in the dc bus link voltage and increase of the circulating currents in parallel operating converters. the flow of circulating currents will affect the degradation of battery state of charge. the main aim of control is to keep the dc bus link voltage constant with the help of a voltage droop controller by taking reference setpoints from the voltage droop characteristics. simulations were conducted with varying wind speed and solar irradiation. the results show that the design of the proposed mg with voltage droop control can successfully maintain the dc bus link voltage at a constant value throughout the system operation. the droop controller allows the converters to share the currents with no interdisturbance on controlling the load when they operate in parallel. this control method also reduces the active and reactive power variation by maintaining reference set points from output voltage magnitude in a stable condition. this paper mainly focused on demand-side management and voltage droop control due to its simplicity in operation, which is used to interconnect more than one distributed generation sources in a microgrid. references [1] wikipedia, electricity sector in india, available at: https://en.wikipedia.org/wiki/electricity_sector_in_india [2] wikipedia, renewable energy in india, available at: https://en.wikipedia.org/wiki/renewable_energy_in_india [3] t. v. krishna, 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research, vol. 8, no. 5, pp 3392-3397, 2018 microsoft word 368_ced_r2.doc etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 483-487 483 www.etasr.com soto-cabán and law: using resistivity measurements to determine anisotropy in soil and … using resistivity measurements to determine anisotropy in soil and weathered rock sandra soto-cabán department of physics and engineering muskingum university new concord, oh, usa ssoto@muskingum.edu eric law department of geology muskingum university new concord, oh, usa ericlaw@muskingum.edu abstract— this study uses electrical resistivity measurements of soils and weathered rock to perform a fast and reliable evaluation of field anisotropy. two test sites at new concord, ohio were used for the study. these sites are characterized by different landform and slightly east dipping limestone and siltstone formations of pennsylvanian age. the measured resistivity ranged from 19 ω·m to 100 ω·m, and varied with depth, landform, and season. the anisotropy was determined by a comparison of resistance values along the directions of strike and the dip. measurements showed that the orientation of electrical anisotropy in the shallow ground may vary due to fluid connection, which is determined by the pore geometry in soil and rock, as well as by the direction of fluid movement. results from this study indicated that a portable electrical resistivity meter is sensitive and reliable enough to be used for shallow ground fluid monitoring. keywordssoil resistivity; resistance; soil anisotropy; resistivity measurements i. introduction the hydrological anisotropy of soil and weathered rock beneath it is an important issue in many studies and applications. while the change of anisotropy may be expected in a vertical soil profile and rock stratification, the change of anisotropy along a horizontal layer of soil or rock is usually much less obvious. however, the horizontal variation of anisotropy is also a significant feature and has been demonstrated in several studies e.g. [1-5]. measuring the electrical resistivity of the ground is a nondisturbing geophysical method that is commonly used to explore the properties of soil and rock. it has been extensively used in various environmental and engineering studies [6-9]. in [9], the authors demonstrated that if some ground variables can be monitored, then the on-field electric resistivity method is a good alternative to other much more expensive and difficult methods for quantitatively monitoring the moisture distribution of ground shallower than 10 meters. this method can be used to identify the direction of horizontal anisotropy in the soil by measuring and comparing the resistivity along profiles of different directions at the same locality. moisture content is one of the major factors in determining ground resistivity [9, 10]. ground moisture condition depends on several other factors, such as weather, season, types of soil and rock [9, 11, 12]. as a consequence, the value of resistivity, particularly for shallow ground, may change quickly and significantly with time and ground conditions. since the anisotropy is expressed by the ratio of resistivity values along different directions, common factors that will affect resistivity, such as moisture content, weather conditions, groundwater chemistry, and time will be cancelled out, and the difference on the ratios will only reflect the variation of controlling factors. the purpose of this study is to use a portable resistivity meter to take measurements of soil resistivity, and to determine the nature of anisotropy of shallow ground up to a depth of 20 feet. measurements of ground resistivity and anisotropy are described and interpreted. ii. methodology a. resistivity meter and measurements soil resistivity testing was performed using the 4-point wenner array method [13]. this method is the most used test method to measure the resistivity of soil for electrical grounding design. the wenner array, illustrated in figure 1, consists of a line of four equally spaced electrodes. current is injected through the outer electrodes c1 and c2, and potential is measured between the inner electrodes p1 and p2. the resistivity meter used is model h-4385 made by humboldt mfg© [14]. based on [13], the pin separation should be approximately 20 times larger than the pin depth in the soil. pin depth is important to properly measure the resistivity of deeper ground. the resistivity of soil using the wenner array can be calculated using 2 v a i   (1) where a is the electrode separation, v is the difference in potential between p1 and p2, and i is the current flowing between c1 and c2. using ohm’s law, v/i=r. the value of r is given by the meter and thus ρ can be calculated using (1). etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 483-487 484 www.etasr.com soto-cabán and law: using resistivity measurements to determine anisotropy in soil and … fig. 1. wenner array. the resistivity meter used is model h-4385 made by humboldt mfg© b. testing sites measurements of soil resistivity were taken at two different locations in new concord, ohio. site 1 is a small flat area on the top of a hill. site 2 is a lithology controlled slope. the slope surface is tilted 30° toward east. the soil profile at both sites received minimum disturbance. however, at site 1, there was an east-west oriented, 5 feet deep utility trench, which was dug and backfilled about 12 years ago. soils over the test area are derived from rocks of the upper pennsylvanian conemaugh formation. in general, the bottom of site 2 is not deeper than 5 feet. the bedding of bed rock has a ns strike with a few degree dip toward the east. the strata include the ames limestone and siltstone layers above and below the limestone. the ames limestone is a 3-feet thick fresh crystalline packstone, which has no appreciable permeability. however, the slab shape limestone has been weathered through along joints and becomes isolated slabs of 1 to 5 meters in diameter. at both sites, the limestone is located between weathered siltstone layers. soil resistivity in both sites was measured using the 1d wenner array along both ns and ew direction of selected locality. resistivity at site 1 was measured in two different seasons, summer and winter, to acquire seasonal contrast. for measurements taken during the summer, additional readings were taken along profiles of n45e and n45w. at each array, the average resistance to the depths of 10, 15 and 20 feet was measured. ground conditions of both sites were seasonally dry in the summer. in winter, the ground was cold and moist, but not frozen. iii. results a. resistivity the results of resistivity values calculated from the measured resistances in site 1 during winter are summarized in figures 2 and 3. fig. 2. resistivity values in site 1 measured in the ns direction in winter. fig. 3. resistivity values in site 1 measured in the ew direction in winter. during the summer months, resistance measurements where taken in the ns, ew, and n45e directions. pin separations of 1.524 m (5 feet) and 3.048 m (10 feet) where used. results are presented in figure 4. fig. 4. resistivity values in site 1 measured in different directions in summer. the ew* direction means that measurements were taken where the profile runs along a dug and refilled utility trench of 4 feet deep. the resistivity at site 1 varied from 40 ω·m to 100 ω·m. this range of value is at the low end of common fresh sedimentary rocks reported in [15]. considering that all the measured material is soil and weathered rock, resistivity at the low end of normal range was expected. a a a a/20 c2 c1 p1 p2 etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 483-487 485 www.etasr.com soto-cabán and law: using resistivity measurements to determine anisotropy in soil and … a 1.524 m (5 feet) deep utility trench was dug and back filled at site 1 in 2001. a sequence of measurements were taken around this trench and are identified in figure 4 as the ew* direction. the resistivity on the trench profile at 1.524 m (5 feet) and 3.048 m (10 feet) depth was measured. to provide a comparison, resistivity was also measured along the same direction, but with a 0.9144 m (3 feet) offset to the undisturbed ground (ew direction in figure 4). the data shows that resistivity along the disturbed ground is 8 ω·m to 6 ω·m, lower than that of the undisturbed ground. measurements in site 2 where taken during the summer. soil in site 2 is similar to the soil in site 1 but it has a sloped surface tilted 30° toward east. the measured values of resistivity ranged from 19 ω·m to 28 ω·m, as shown in figure 5. the data have narrower variation and measured resistivity values are significantly lower than the measured resistivity values in site 1. these values were taken during the dry season, but the lower resistivity suggests that the ground probably has higher moisture content. consider that site 2 is a 30° eastfacing slope, and is where shallow groundwater accumulates and exits. the significantly lower resistivity reflects the effect of a slope on surface moisture. fig. 5. resistivity values in site 2 measured in different directions in summer. fresh carbonate rock has resistivity around 300 ω·m [15] which is much higher than any measured resistivity in this study. the shallow dense ames limestone layer in the studied area does not raise the resistivity values beyond the range of the surrounding weathered siltstones. this could imply that the limestone is significantly fractured and therefore, it does not hinder the passage of electric current. this interpretation was confirmed by the observation on many constructions made in the neighborhood of the study area. the excavations showed that the limestone layer has been weathered through and is broken into slabs approximately 2 by 3 meters or smaller. b. anisotropy in this study, the degree of anisotropy is evaluated by comparing the resistivity along the strike of the formation to that along the dip of the formation. the attitude of rock formation is the same at both sites, and has strike approximately in ns and dip a few degrees toward east. if the ratio is within ±10% of 1, then it is taken as a lack of anisotropy. the larger the ratio (i.e. larger than 1), the stronger the anisotropy. absolute values of degree of anisotropy were not assigned to the resistivity ratios. when the activity ratio is significantly larger than 1, it means that the resistivity along the ew profile is lower. this is interpreted as that the ew direction has better moisture connectivity of pore fluids. it implies that either the pore spaces are better connected or the moisture is moving across the pore spaces along the ew direction. for site 1, the resistivity ratios are presented in table i. table i. resistivity ratios site 1 (ns/ew) shallow (< 3.048 m; 10 ft) deep ( ≥ 3.048 m; 10 ft) winter 0.94-1.04 1.45-2.00 summer 0.84 1.29 the data show that when the pin separation is shorter than 6.096 m (20 feet), there is a lack of anisotropy down to 3.0484.572 m (10-15 feet) deep at site 1 during the winter time. when the pin separation is extended to 6.096 m (20 feet), resistivity became lower, but the degree of anisotropy significantly increased. higher resistivity was shown along the ns direction. this suggested that ground moisture became higher in the deeper ground, which reduced the resistivity. also, the moisture connection in pore spaces is better along the ew direction, which is the direction of the formation dip. this feature is interpreted as that in the winter (wet) season, the moisture in the shallow ground is stagnant, but the moisture is moving toward east in the deeper ground. in the summer time, the degree of anisotropy at the shallow ground becomes significant. this is shown in table ii. table ii. resistivity ratios in summer summer (ns/ew) shallow deep site 1 0.84 1.29 site 2 1.11 0.77 the data further indicates that for both sites in the winter and summer seasons, the anisotropy remained similar in direction at the deeper ground. the anisotropy at the shallow ground changed from insignificant in winter to ew enhanced, which is the opposite direction to that in the deeper ground, during the summer time. at site 1, the anisotropy shown in the summer dry season in the shallow ground indicates a better pore fluid connection along the direction of strike, which is the ns direction. this interpretation agreess with [16, 17]. during the wetter winter season, more abundant pore fluid obscured this trend and made the shallow ground seems isotropic. on the other hand, the moisture in the deeper ground is always moving toward the east. this shows the ew anisotropy in both the wetter winter and the drier summer for the deeper ground. the higher amount of flow makes a stronger anisotropy during the winter time. also, the shallow ground along the trench is also lacking anisotropy (0.97 ratio), but the undisturbed ground shows significant anisotropy (0.84). these data suggest that the etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 483-487 486 www.etasr.com soto-cabán and law: using resistivity measurements to determine anisotropy in soil and … material along the disturbed trench is more porous and homogenous than that on the undisturbed ground. at site 2, in addition to the significantly lower resistivity, the anisotropy is also significant in both shallow and deep grounds. the direction of anisotropy is not only opposite in direction between the shallow ground and the deeper ground, but is opposite to that in site 1 at the same time (table ii). in the shallow ground, which is less than 1.524 m (5 feet) deep, resistivity is lower along the direction of dip (ew). at ground deeper than 3.048 m (10 feet), resistivity becomes lower along the direction of strike (ns). this switch of anisotropy suggests that ground moisture is moving down the slope (and the dip) near surface, but is lacking movement in deeper ground. iv. conclusions this study measured the resistivity of soil and underlay weathered rock down to 6.096 m (20 feet) deep. it included the unsaturated zone and the shallow saturated zone. the measurements were taken along the strike and the dip directions of the rock formation. the ratio of resistivity along the two directions filtered out common factors that change the value of resistivity, but preserved the factors that affect the anisotropy. the abundance of moisture in the unsaturated zone and the direction of moisture movement in the saturated zone were two major factors. measured data suggested that the electrical resistivity and anisotropy of shallow ground, less than 6.096 m (20 feet) deep, are easily changed by conditions of depth, landform, geological structure and weather. resistivity is also sensitive to the soil and rock conditions. the best illustration of the sensitivity is the comparison of resistivity along a 12-year old utility trench and its adjacent undisturbed ground. as a result, the method used in this study is useful in indicating minute variations of moisture conditions due to various reasons, and it can serve as a quick field method to check contemporary hydrological condition of shallow ground. while the resistivity at site 1 is several times higher than that at site 2, the degree of anisotropy is approximately the same, even though the direction of anisotropy got reversed with depth during the time of testing, since the anisotropy is measured by the ratio of resistivity. due to the difference of landform which affected the direction of moisture flow, the variation of anisotropy at the two sites more likely reflects the characteristics of pore geometry and the movement of pore fluid. this study shows that the anisotropy is clearly indicated along the bedding plane. resistivity data show that when the pore fluid in soil and shallow rocks is stagnant, the moisture in the pore space is better connected along the strike direction than that along the dip direction. this result is in agreement with the study of pore space geometry [18-20]. however, when the pore fluid starts to move due to either pore saturation or hydraulic pressure from a slope, it will produce a better electric conductivity along the direction of water movement. in this case, it is the dip direction that has a key role. since the degree of water saturation in the unsaturated zone is easily modified by the weather and season, the direction of electrical anisotropy may also be changed when moisture conditions are changed. references [1] a. anandarajah, n. kuganenthira, “some aspects of fabric anisotropy of soil”, geotechnique, vol. 45, no. 1, pp. 69-81, 1995 [2] m. bała, “evaluation of electric parameters of anisotropic sandy-shaly miocene formations on the basis of resistivity logs”, acta geophysica vol. 59, no. 5, pp. 954-966, 2011 [3] r. p. chapuis, d. e. gill, “hydraulic anisotropy of homogeneous soils and rocks: influence of the densification process”, bulletin of the international association of engineering geology, vol. 39, no. 1, pp. 75-86, 1989 [4] j. l. collins, m. e. everett, b. johnson, “detection of near-surface horizontal anisotropy in a weathered metamorphic schist at llano uplift (texas) by transient electromagnetic induction”, physics of the earth and planetary interiors, vol. 158, no. 2-4, pp. 159-173, 2006 [5] c. t. petersen, a. trautner, s. hansen “spatio-temporal variation of anisotropy of saturated hydraulic conductivity in a tilled sandy loam soil”, soil and tillage research, vol. 100, no. 1-2, pp. 108-113, 2008 [6] v. c. goyal, s. niwas, p. k. gupta, “theoretical evaluation of modified wenner array for shallow resistivity exploration”, ground water, vol. 29, no. 4, pp. 582-586, 1991 [7] j. w. lane jr, f. p. haeni, w. m. watson, “use of square-array directcurrent resistivity method to detect fractures in crystalline bedrock in new hampshire”, groundwater, vol. 33, no. 3, pp. 476-485, 1995 [8] m. u. osakuni, t. k. s. abam, “shallow resistivity measurement for cathodic protection of pipelines in the niger delta”, environmental geology, vol. 45, no. 6, pp. 747-752, 2004 [9] b. f. schwartz, m. e. schreiber, t. yan “quantifying field-scale soil moisture using electrical resistivity imaging”, journal of hydrology, vol. 362, no. 3-4, pp. 234-246, 2008 [10] l. chen, z. yin, p. zhang “relationship of resistivity with water content and fissures of unsaturated expansive soils”, journal of china university of mining and technology, vol. 17, no. 4, pp. 537-540, 2007 [11] z. s. abu-hassanein, c. h. benson, l. r. blotz, “electrical resistivity of compacted clays”, journal of geotechnical engineering vol. 122, no. 5, pp. 397–406, 1996 [12] v. a. rinaldi, g. a. cuestas, “ohmic conductivity of a compacted silty clay”, journal of geotechnical and geoenvironmental engineering, vol. 128, no. 10, pp. 824–835, 2002 [13] f. wenner, “a method of measuring earth resistivity”, bulletin of the bureau of standards, vol. 12, pp. 469-478, 1916 [14] humboldt manufacturing company ®, “resistivity-meter”, http://www.humboldtmfg.com/resistivity_meter.html, 2013 [15] b. s. badmus, e. a. ayolabi, j. a. olowofela, s. a. adisa, t. o. oyekunle “current variation in electrical resistivity probing using wenner and schlumberger arrays in a basement terrain”, j.ournal of geophysics and engineering, vol. 2, no. 2, pp. 118-125, 2005 [16] p. domnesteanu, c. mccann, j. sothcott, “velocity anisotropy and attenuation of shale in under-and overpressured conditions”, geophysical prospecting, vol. 50, no. 5, pp. 487-503, 2002 [17] m. l. stewart, a. l. ward, d. r. rector, “a study of pore geometry effects on anisotropy in hydraulic permeability using the latticeboltzmann method”, advances in water resources, vol. 29, no. 9, pp. 1328–1340, 2006 [18] c. a. grattoni, r. a. dawe, “anisotropy in pore structure of porous media”, powder technology, vol. 85, no. 2, pp. 143-151, 1995 [19] e. kuusela, j. lahtinen, t. ala-nissila, “sedimentation dynamics of spherical particles in confined geometries”, physical review e, vol. 69, no. 6, pp. 066310-1–066310-9, 2004 [20] l. esteban, y. geraud, j.l. bouchez, “pore network connectivity anisotropy in jurassic argillite specimens from eastern paris basin (france)”, physics and chemistry of the earth, vol. 32, no. 1-7, pp. 161-169, 2007 etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 483-487 487 www.etasr.com soto-cabán and law: using resistivity measurements to determine anisotropy in soil and … authors profile dr. sandra soto-cabán received her bachelor’s and master’s degrees in electrical engineering from university of puerto rico, mayagüez campus, and her ph.d. degree in electrical engineering from michigan state university, east lansing, mi. currently she is an assistant professor of engineering in the department of physics and engineering at muskingum university, new concord, ohio, usa. dr. soto-cabán is a senior member of the institute of electrical and electronics engineers (ieee) and a member of the american society of engineering education (asee). she is also a member of the engineering honor societies tau beta pi and eta kappa nu. her research interests include electromagnetic simulation of underground contaminants, material characterization, and engineering education. dr. eric law received his ph.d. degree in geology in 1984 from case western reserve university, cleveland, ohio, usa. currently works as an associate professor in the geology department of muskingum university at new concord, ohio. his most recent research is focused on the role of mechanical erosion on limestone. microsoft word etasr_7-1_1387-1390.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1387-1390 1387 www.etasr.com dragan: a numerical proof of concept for thermal flow control a numerical proof of concept for thermal flow control valeriu dragan computational fluid dynamics department national research and development institute for gas turbines, comoti bucharest, romania drvaleriu@gmail.com, valeriu.dragan@comoti.ro abstract— in this paper computational fluid dynamics is used to provide a proof of concept for controlled flow separation using thermal wall interactions with the velocity boundary layer. a 3d case study is presented, using a transition modeling shear stress transport turbulence model. the highly loaded single slot flap airfoil was chosen to be representative for a light aircraft and the flow conditions were modeled after a typical landing speed. in the baseline case, adiabatic walls were considered while in the separation control case, the top surface of the flaps was heated to 500 k. this heating lead to flow separation on the flaps and a significant alteration of the flow pattern across all the elements of the wing. the findings indicate that this control method has potential, with implications in both aeronautical as well as sports and civil engineering applications. keywords-heat transfer; cfd simulation; flow control; high lift device i. introduction controlling flow attachment on aerodynamic surfaces is one of the main engineering subjects of recent years. from aircraft wings [1] or thrust vectoring [2] to both radial [3] or axial [4] flow turbomachinery and even synthetic jets in sports vehicles [5] and buildings [6], having the ability to control boundary layer separation opens new possibilities for design and operation. this paper deals with a theoretical concept for flow control which has been tested, using state of the art cfd methods, with advanced turbulence modeling. in [7], a multitude of traditional flow control methods is described and commented. thin wall jets have been used for circulation control as well as supercirculation [8]. additionally, more recent development of piezo-electric [9] actuators, unsteady passive actuation [10] or even plasma actuators [11] have made their way to high technology readiness levels, providing viable alternatives for aerodynamicists in various fields of engineering. conventionally, heating was used on aircraft wings to reduce the reynolds number near the wall of the wing in order to diminish turbulent friction. indeed the theoretical background this technique is rooted in provides an optimal point in which virtually all flow near the wall is essentially laminar. however, the power consumption associated with the heating as well as the advent of natural laminar airfoils [12] has made this all but useless for airline applications. smaller aircraft and drones have been fitted with similar technologies – in the same traditional sense. due to their small characteristic length, uav propellers have been shown to be positively influenced by surface heating [13]. as far back as the 1980’s, the prospect of using heated airfoils for improved aerodynamic performances was explored [14]. the typical applications rely on the lowering of the reynolds number through the local increase in fluid viscosity as the result of heating. in this way, the friction coefficient becomes a function of temperature. however, in the proposed embodiment of this method, a spoiler-like behavior is sought without the need for geometry variations. such a method could be used for small aerial vehicles for both rolling maneuvers and landing, without the requirement for complex and heavy moving parts, thus increasing reliability and reducing overall weight. 0 (1) w y u y t m = ¶ = ¶ 3 / 2 0 0 0 (2) t st t t s m m + = + æ ö÷ç ÷ç ÷÷çè ø re (3) v cr m ¥ ⋅ = a previous study confirmed that, for airfoils with low camber and viscous dominated drag, a careful distribution of wall temperature can lead to a serious reduction in the drag coefficient as well as a marginal increase in lift coefficient [15]. ii. computational fluid dynamics case setup the current paper uses state the of the art k-omega sst rans model, with additional equations for compensating the laminar to turbulent transition and curvature correction to obtain a proof of concept case for the use of thermal actuation for boundary layer separation. a highly loaded airfoil was considered, with typical single-slot flaps and gurney type element on the trailing edge. in the baseline case adiabatic noslip walls were used whereas in the thermal trimming case, the top surface of the flaps was set to a uniform surface temperature of 500 k. surface roughness was considered null, bearing in mind that the rugosity itself will (in a real life application) promote the mixing of the turbulent boundary engineering, technology & applied science research vol. 7, no. 1, 2017, 1387-1390 1388 www.etasr.com dragan: a numerical proof of concept for thermal flow control layer and therefore increase the heat transfer. the geometry of the airfoil and flaps was constructed using an eppler s1223 for the main airfoil and flaps with a 10 mm gap between the two and a combined chord of 300 mm. the setting angle of attack for the main airfoil is 0° and the flaps is set at 40°. this airfoil has been chosen due to its high loading and low drag [16]. since this is a preliminary study, seeking an additional validation of the theoretical principle behind the separation control, the cfd study was conducted using rans methods. having said this, the case presents a 3d domain albeit with periodic conditions while the turbulence model was chosen in such a way that transition from laminar to turbulent as well as relaminarisation could be theoretically captured. furthermore, grid sensitivity tests were performed on three grids with increasing cell density (i.e. baseline, baseline x23, baseline x26). the current mesh was the result of the analysis of the trends of the three grids with respect to lift, drag and moment coefficient. another relevant aspect is that the first cell (nearest to the wall) was kept constant for all four cases, insuring the same y+ for every case. the fluid considered was the classical redlichkwong which has a built in wall temperature correlation. figures 1 and 2 depict the blocking structure, near wall cell distribution and the y+ distribution for both presented cases. fig. 1. blocking structure for the adiabatic and heated cases as stated, the turbulence model employed was the transition sst-rc k-omega [17], as implemented in ansys fluent v17. as seen, the near wall mesh meets the criteria y+ for k-omega models, in particular for the one used. since the reynolds number is expected to decrease with temperature, the cell size used in the adiabatic case was considered and proven to be sufficiently small to also cover the heat transfer case. the method used to calculate the first cell size was through the equation below [18] where h is the first cell height, ν is the kinematic viscosity and τw is the wall shear stress. (4)w y h t n + = one of the key elements of the heat transfer simulation is the interaction between the velocity boundary layer with the thermal boundary layer. multiple tests have been reported in the literature, concluding that the sst [19] and sa [20], which both model the boundary layer without wall functions, are best suited for the heat transfer [21]. fig. 2. the y+ distribution for the adiabatic and heated cases in terms of boundary conditions, the solid surfaces were considered smooth walls, with no slip condition, the sides of the domain were considered periodical and the velocity inlet was set along the ox axis at a magnitude of 50 m/s with an isa atmosphere as a reference. the cfl condition was set to a value of one unit, in order to correctly capture the physical phenomena of heat convection through the boundary layer. iii. results and discussions as is the case with all flapped airfoils, the increase in the overall lift coefficient is owed to the change of pressure distribution around the main airfoil as a result of the secondary airfoil (flaps) disturbance in the flow. by shifting the leading edge stagnation point, the flaps makes to airfoil behave as if the angle of attack had been increased, but without the danger of destabilizing the flow on the top of the main foil. the shift of the le stagnation point has two main components, the first of which being the deceleration on the underside of the foil, the second reason is more subtle and has to do with the interaction with the flow on top of the flaps itself. since the flow on the top of the flaps acts similarly to a curved wall jet, the entrainment effects on the flow circulating on the top of the main foil contributes to the apparent increase in angle of attack. in the heated version however, this entrainment occurs to a flaps suction side has the most significant difference engineering, technology & applied science research vol. 7, no. 1, 2017, 1387-1390 1389 www.etasr.com dragan: a numerical proof of concept for thermal flow control significantly lesser degree, meaning that its contribution to this apparent aoa increase will be negligible. fig. 3. velocity magnitude field in the midspan section without (top) and with flow thermal-induced flow separation (bottom) figure 3 provides an interesting behavior (particular to this type of flow control) in which the flaps no longer manages to perturb the flow in the same manner. notice that, although the underside flow pattern remains virtually the same, the topside flow is significantly different. it is this difference that leads to the differences in lift and drag seen in the figure below. figures 4-6 shows bar charts of the results. fig. 4. overall lift and drag breakdown for the two considered cases as shown increased drag is experienced by the stalled flaps due to the thermal trimming is in fact the result of a double influence. equally the positive flaps drag is increased whereas the negative drag of the main airfoil is decreased. it must be said that the negative drag on the main foil arises due to the pseudo-incidence that the flaps induces. this negative drag is always going to be canceled out and surpassed by the added positive drag of the flaps, even if it is not stalled. unfortunately, in this case, the negative drag component on the main airfoil is inextricably linked to the lift force on the respective section. therefore, if we pursue the diminishing of the overall lift we will have to accept the diminishing of the negative drag. hence, the only avenue for further optimization of this arrangement will have to rely on the flaps pressure drag and, to some extent, on the main airfoil skin friction drag perhaps with the classical heating described in [7]. further, it can be seen that both the main and flap airfoils lead to significant decreases in their respective lift force, to approximately 70% in the case of the main and 60% for the flaps. this is due primarily to the diminishing of the circulation on the top side of both the airfoil elements as downstream diffusion is significantly decreased hence impeding the acceleration of the upstream flow. the gurney element also registers an influence, however it is marginal when viewed only on the element itself. fig. 5. drag force breakdown for the two cases fig. 6 lift force breakdown on the components iv. conclusions the paper deals with the prospect of using skin thermal influences on the velocity boundary layer in order to induce separation, essentially stalling an airfoil which (under normal circumstances) would have no stall tendencies. in our case, a conventional highly loaded airfoil with single slotted flaps was used as a benchmark. the topside of the flaps, when heated, induced boundary layer separation on the flaps which in turn led to the change of the overall characteristics of the entire assembly. since the mach number was low, comparable to streamline curvature acceleration due to apparent angle of attack thermal induced separation on flaps upper surface engineering, technology & applied science research vol. 7, no. 1, 2017, 1387-1390 1390 www.etasr.com dragan: a numerical proof of concept for thermal flow control typical landing speeds of civilian aircraft [22], the influence upstream of the flaps is quite visible on the main foil. a breakdown of aerodynamic forces on the components of the assembly revealed that the lift and drag contribution of the flaps on the overall force is only part of the trimming. by looking at the flow pattern around the main airfoil, we can observe that the velocity distribution corresponds to a state where the flaps would be extended at a lower angle. although the lift has been successfully reduced by using the proposed method, the drag penalty appears to be (at least in part) linked to it. hence, the main direction in which the drag can be reduced would be to use the minimization of the pressure drag on top of the flaps though the use of conventional curved wall jets [23]. although both theoretical [24] and empirical efforts [25] have been made to model the boundary layer velocity distribution on such flows, the addition of a wall temperature as a factor will most certainly require further study and modeling. references [1] d. miklosovic, r. imber, m. britt-crane, “measurements of midspan flow interactions of a low-aspect-ratio circulation control wing”, journal of aircraft, vol. 53, no. 6, pp. 1969-1974, 2016 [2] j. páscoa, a. dumas, m. trancossi, p. stewart, d. vucinic, “a review of thrust-vectoring in support of a v/stol non-moving mechanical propulsion system”, open engineering, vol. 3, no. 3, pp. 374-388, 2013 [3] i. malael, h. dumitrescu, a. dumitrache, “methods for improve the performance of the turbomachines using the flow control”, aip conf. proc., vol. 1389, 2011 [4] m. g. de giorgi, e. pescini, f. marra, a. ficarella, “experimental and numerical analysis of a micro plasma actuator for active flow control in turbomachinery”, asme turbo expo 2014: turbine technical conference and exposition, germany, june 16-20, 2014 [5] m. n. sudin, m. a. abdullah, s. a. shamsudin, f. r. ramli, m. m. tahir, “review of research on vehicles aerodynamic drag reduction methods”, international journal of mechanical and mechatronics engineering, vol. 14, no. 2, pp. 35-47, 2014 [6] s. j. kang, j. park, k. y. oh, j. g. noh, h. park, “scheduling-based real time energy flow control strategy for building energy management system”, energy and buildings, vol. 75, pp. 239–248, 2014 [7] m. gad-el-hak, flow control: passive, active, and reactive flow management, cambridge university press, 2007 [8] v. ciobaca, j. wild, “an overview of recent dlr contributions on active flow-separation control studies for high-lift configurations”, aerospace lab journal, vol. 6, 2013 [9] l. iorga, h. baruh, i. ursu, “refined analysis of the piezoelectric pseudo-active control for helicopter blades vibration”, 46th aiaa/asme/asce/ahs/asc structures, structural dynamics and materials conference, usa, april 18-21, 2005 [10] s. endrikat, b. roentsch, j. c. little, l. taubert, c. f. de luzan, e. j. gutmark, i. j. wygnanski, “physics and control of the flow over a generic trapezoidal wing planform”, 54th aiaa aerospace sciences meeting, usa, january 5-8, 2016 [11] x. zhang, h. x. li, y. huang, w. b. wang, “wing flow separation control using asymmetrical and symmetrical plasma actuator”, journal of aircraft, 2016 [12] r. w. barnwell, m. y. hussaini, natural laminar flow and laminar flow control, springer verlag, 2012 [13] d. a. kessler, r. johnson, a. t. corrigan, s. qidwai, m. merrill, j. thomas, “modeling low-reynolds-number flow over rough airfoils", 54th aiaa aerospace sciences meeting, usa, january 5-8, 2016 [14] l. maestrello, f.f. badavi, k. w. noonan, an application of active surface heating for augmenting lift and reducing drag of an airfoil, nasa technical memorandum 100563, 1988 [15] v. dragan, “influences of surface temperature on a low camber airfoil aerodynamic performances”, incas bulletin, vol. 8, no. 1, pp. 49–60, 2016 [16] m. s. selig, j. j. guglielmo, “high-lift low reynolds number airfoil design”, journal of aircraft, vol. 34, no. 1, pp. 72-79, 1997 [17] g. kalitzin, g. medic, g. xia, “improvements to sst turbulence model for free shear layers, turbulent separation and stagnation point anomaly”, 54th aiaa aerospace sciences meeting, usa, january 5-8, 2016 [18] f. m. white, fluid mechanics, 7th edition, mcgraw-hill, 2009 [19] k. tsukamoto, y.horiuchi, k. sugimura, s. higuchi, “conjugate heat transfer analysis in an actual gas turbine rotor blade in comparison with pyrometer data”, asme turbo expo 2014: turbine technical conference and exposition, germany, june 16-20, 2014 [20] s. allmaras, f. johnson, p. spalart, “modifications and clarifications for the implementation of the spalart-allmaras turbulence model”, 7th internaitonal conference on computational fluid dynamics iccfd7, hawai, july 2012 [21] g. zigh, j. solis, computational fluid dynamics best practice guidelines for dry cask applications, nureg, 2012 [22] m. janic, “modeling effects of different air traffic control operational procedures, separation rules, and service disciplines on runway landing capacity”, journal of advanced transportation, vol. 48, no. 6, pp. 556– 574, 2014 [23] m. burnazzi, r. radespiel, “synergies between suction and blowing for active high-lift flaps”, ceas aeronautical journal, vol. 6, no. 2, pp 305–318, 2015 [24] m. trancossi, a. dumas, d. vucinic, “mathematical modeling of coanda effect”, sae technical paper no. 2013-01-2195, 2013 [25] v. dragan, “implementation of a correction factor for the pohlhausen laminar boundary layer applied on the ceva curved wall jet model”, incas bulletin, vol. 5, no.3, pp. 61-67, 2013 engineering, technology & applied science research vol. 8, no. 3, 2018, 3064-3072 3064 www.etasr.com hdhibi et al.: effect of single oxide fluxes on morphology and mechanical properties of atig on … effect of single oxide fluxes on morphology and mechanical properties of atig on 316 l austenitic stainless steel welds abdeljlil hdhibi mechanical engineering department college of engineering prince sattam bin abdulaziz university al kharj, saudi arabia and preparatory engineering institute of nabeul (ipein), tunisia a.hedhibi@psau.edu.sa kamel touileb mechanical engineering department college of engineering prince sattam bin abdulaziz university al kharj, saudi arabia k.touileb@psau.edu.sa rachid djoudjou mechanical engineering department college of engineering prince sattam bin abdulaziz university al kharj, saudi arabia r.djoudjou@psau.edu.sa abousoufiane ouis mechanical engineering department college of engineering prince sattam bin abdulaziz university al kharj, saudi arabia a.ouis@psau.edu.sa mohamed lamjed bouazizi mechanical engineering department college of engineering prince sattam bin abdulaziz university al kharj, saudi arabia my.bouazizi@psau.edu.sa jamel chakhari mechanical engineering department college of engineering prince sattam bin abdulaziz university al kharj, saudi arabia j.chakhari@psau.edu.sa abstract—tungsten inert gas (tig) is a wide common process used in fabrication due to its low cost equipment, high quality and accuracy welds but has low productivity related to the low penetration depth in single pass. a new perspective, the activated tungsten inert gas (atig), in which the same equipment as tig is used, except that a thin layer of activated flux is deposited on a workpiece surface. in this work, eight kinds of oxides were tested on 316l austenitic stainless steel. three levels of welding current were used to study the effect of different activating fluxes on weld bead geometry and mechanical properties. x-ray photoelectron spectroscopy (xps) was used for the first and the second level energy for different atig welds to analyze the relationship between the weld shape and oxygen content in welds. the experimental results showed that the weld profile is related to the thermodynamic stability of selected oxides and in relation to the energy provided. atig with tio2, sio2, mno2 oxides presented the deepest welds followed by cr2o3, fe2o3, and zno. finally zro2, cao oxides had no effect on the weld depth. the atig welded joint showed better tensile strength than tig. the atig hardness measurements carried out showed also better if not the same as tig weld except for the silicon oxide weld. results of the impact test showed that, except for the titanium dioxide tio2 which has a good benefit, the weldment using the other oxide fluxes exhibits worse withstanding to sudden shock than tig welding. keywords-atig; austenitic stainless steel; weld shape; mechanical properties i. introduction tig welding uses a non-consumable tungsten electrode and an inert gas. in this process, an electric arc is formed between the tungsten electrode and the base metal. however, there are a few limitations of the tig welding process, like low penetration depth, and if the workpiece thickness is greater than 3mm joint edge preparation and multiple passes are required to fill the joint completely. tig welds are also affected by cast-tocast compositional variation in the base metal being welded [1, 2]. these limitations can be overcome by using atig welding. this technic was invented in the 1960’s by researchers at the paton electric welding institute (pwi) in ukraine [3, 4]. few data are available in the open literature about the activating flux composition. such data are very important to determine the weld penetration improvement. the mechanism related to deep penetration is linked to: a. arc constriction [5-7] this phenomenon can occur by two means:  the interaction between the peripheral negative charge (electrons outside the arc) and the neutral particles (atoms and molecules) formed from the dissolution of flux components causes the constriction of the arc, leading to the increase of the welds depth.  the flux acts as insulating layer reducing the current density of the outer arc radius and increases the current density in the center as well as magnetic force (lorentz engineering, technology & applied science research vol. 8, no. 3, 2018, 3064-3072 3065 www.etasr.com hdhibi et al.: effect of single oxide fluxes on morphology and mechanical properties of atig on … force) in the weld pool which lead to the increasing of weld depth. b. marangoni convection [8-10] during tig welding, without surfactants elements like sulfur, oxygen, selenium, and tellurium, the surface tension gradient is negative and the convection movement is centrifugal leading to a shallow penetration. the addition of activated flux induces an inversion of the convection current and changes the sign of the surface tension resulting in a centripetal convection movement, to the increase of penetration depth. high sulfur percentage weld beads are sensitive to centerline cracking and heat affected zone (haz) cracking. on the other hand, very low sulfur content can lead to irregular weld penetration. for acceptable penetration without a risk of crack, the sulfur range should vary from 0.005% to 0.030% for 316 stainless steel with the suggested creq/nieq ratio range from 1.43 to 1.9 [11]. this element can be provided as pasted flux on the workpiece to improve the depth of welds [12]. on the other hand, the addition of 500ppm of so2 in shield gas improves the d/w ratio by 80% [13]. as for selenium, an addition of 0.1% by weight of se in steel reduces its superficial tension by 30% [14]. while the variations of o2 range from 600ppm to 1200ppm, can lead to an increase of penetration from 15% to 45% for the 1010 steel [15]. the activation of the cited elements is limited by a reversal temperature beyond which they don’t affect the weld morphology [14]. authors in [16] showed that oxygen as active element is active in pure liquid iron in the range of 150-300ppm. above this range the temperature coefficient of surface tension becomes zero or negative leading to shallow and wide weld bead. according to a study [17], the oxygen content in the weld metal in the range of 70ppm-300ppm, can increase the geometric parameter d/w from 1.5 to 2 times. many works have been conducted using single flux (oxide or halide type) to study their individual effect on the morphology and the mechanical properties [12, 18-25]. due to the complexity of the reactions in the weld pool and interconnection with the welding arc, a single component flux cannot meet a good morphology and mechanical properties requirements. on the other hand, several studies were conducted in order to find the suitable flux compositions. binary fluxes have been developed in order to get optimum percentages of binary flux components that can improve the aspect and the shape as well as the mechanical properties of welds [1, 27-29]. in addition, other studies were devoted to ternary flux where statistical programs were used to develop a formulation on the percentages of the ternary flux components to enhance depth and mechanical properties of welds [30] as well as the effect of the welding parameters and the flux on weld bead geometry, angular distortion and mechanical properties. in this study, eight different kinds of oxide fluxes (cr2o3, fe2o3, cao, zno, zro2, sio2, mno2 and tio2) were used to investigate the effect of single component flux on the morphology, and mechanical properties of 316l stainless steel tig welds. this study contributes to the understanding of the phenomena that occur in the weld pool. ii. experimental procedure this work was conducted on 316 l stainless steel. the tensile strength of the material is 618mpa, vickers hardness is 180hv and melting point is about 1440oc. table i lists the chemical compositions of this steel. plates 6mm in thickness were cut into 204mmx204mm to have test samples for mechanical testing and weld morphology (figure 1). acetone was used to clean and remove dust and contamination. table i. chemical composition of 316l stainless steel ss 316 l percentage c % 0.018 mn % 1.30 si % 0.43 p % 0.034 s % 0.0029 cr % 16.78 ni % 10.00 mo % 2.005 n ppm 321 ti % 0.0042 cu % 0.2082 co % 0.226 fig. 1. different test specimens on welded plate eight different kinds of oxide fluxes were used. table ii lists the melting and boiling temperature of the different oxides. thermodynamic stability of selected oxides is showed in table iii where the stability decreases from left to right. products have been heated separately in furnace at 150ºc for 1 hour to eliminate humidity. the powder has been mixed with acetone (1:1 ratio) forming a paste. a brush was used to apply the mixture on the plain surface to be welded. the acetone was allowed to evaporate, so only the flux powder was left on the metal surface. the coating density of flux was about 78mg/cm2, and the flux layer thickness about 0.2mm. a tig welding machine was used. a water-cooled torch with a standard 2% thoriated tungsten electrode rod having diameter of 3.2mm has been used for the experiments. the torch was mounted on a motorized carriage as shown in figure 2. three series of tests have been carried out with three levels of welding currents (150amp, 540kj/m-180amp, 680kj/m, 200amp, 800kj/m).the welding parameters selected for tig welding are listed in table iv. after welding, the samples were cut as shown in figure 1, far from the welding starting point to be sure that the arc welding was stabilized. etching operation is necessary to reveal the morphology of the welds and for hardness measurements. solution of one volume of water and 2 volumes of engineering, technology & applied science research vol. 8, no. 3, 2018, 3064-3072 3066 www.etasr.com hdhibi et al.: effect of single oxide fluxes on morphology and mechanical properties of atig on … hydrochloric acid (hcl) and one volume of nitric acid (hno3) was used for etching. the tensile tests were conducted at room temperature. the tests were carried out with a computer control electro-hydraulic servo universal testing machine model waw-300e and the impact tests with the impact testing machine model jbs-500. vickers hardness measurement was performed with a digital hardness tester model hvs-50. the tensile, impact, and hardness test were conducted only with 180amp welds (second energy level). fig. 2. experimental setup of tig welding with flux paste (a motorized carriage, torch–workpiece). table ii. melting and boiling temperature of used oxides oxides tm(ͦc ) tb (ͦ c) cr2o3 2435 3000 fe2o3 1540 1987 cao 2613 2850 zno 1975 1975* zro2 2715 4300 sio2 1713 2950 mno2 535 540* tio2 1843 2972 *decomposition temperature of oxides table iii. thermodynamic stability of selected oxides in decreasing order cao zro2 tio2 sio2 cr2o3 zno fe2o3 mno2 table iv. welding parameters welding speed 15cm/min welding current (150-180-200)amp arc length 2mm electrode tip angle 60 ͦ shield gas on work piece argon with flow rate 12l/min shield gas back side argon with flow rate 5l/min welding mode direct current electrode negative iii. results and discussion a. oxygen content xps was used to analyze the surface chemistry of sectional weld bead, especially the percentages of oxygen remaining in weld bead. the result obtained with the flux sio2 is reported in figure 3. results for two energy levels series for different fluxes are reported in table v. fig. 3. oxygen spectrum in atig welded bead with sio2 flux table v. percentages of o in atig weld bead flux e=540kj/m e=680kj/m sio2 4.99 6.29 tio2 10.19 9.57 fe2o3 11.07 7.33 mno2 10.9 8.84 cr2o3 23.95 11.89 zno 11.8 10.32 zro2 16.85 8.53 cao 28.52 10.44 b. effect of the energy level e=540kj/m regarding the fluxes of cao and zro2, it can be seen that the quantity of oxygen remaining in weld bead is relatively high. this is due to their high thermodynamic stability. with this level of energy there is no or very small quantity liberation of oxygen in weld pool. the melting point of those oxides is very high comparatively to parent metal (tm316l =1440oc) the gradient of temperature is high, so a high energy is needed to melt them: δt (zro2-316l)=2715-1440=1275oc δt (cao-316l)=2613-1440=1173oc as for the flux of cr2o3 it is characterized by its high melting and boiling temperature, a lot of energy is necessary to melt or vaporize it, that’s why a quantity of oxygen remains in the weld bead. cr2o3 has moderate thermodynamic stability. δt (cr2o3-316l)=2435-1440=995oc as for the fluxes of zno, mno2, and fe2o3, they have low stability, but manganese dioxide, with its low melting point of 535oc, can liberate easily its oxygen. δt (zno-316l)=1975-1440=535oc (less energy required to melt it) δt (fe2o3-316l)=1540-1440=100oc (easy to melt) finally, the fluxes sio2, tio2: their standard gibb's energies of formation as well as their boiling point are close. δt (sio2-316l)=1713-1440=273oc 0.00e+00 1.00e+05 2.00e+05 3.00e+05 4.00e+05 5.00e+05 020040060080010001200 c ou nt s / s binding energy (ev) survey 5 scans, 2 m 16.1 s, 200µm, cae 200.0, 1.00 ev fe2p cr2p ni2p3 mo3do1s ar2pc1s engineering, technology & applied science research vol. 8, no. 3, 2018, 3064-3072 3067 www.etasr.com hdhibi et al.: effect of single oxide fluxes on morphology and mechanical properties of atig on … δt (tio2-316l)=1843-1440=403oc, so less energy is required to melt them. c. effect of the energy level e=680kj/m in this case, the low level of oxygen remaining in weld bead means that the oxygen was liberated. this element contributes to having centripetal convection of weld bead leading to full penetrated welds. maybe there is some oxygen trapped in the weld bead due to the lack of protection effectiveness of the melt. iv. weld morphology: the weld morphology is characterized by the penetration depth d and the bead width w. a. effect of different fluxes on weld morphology with a current of 150amp e=540kj/m figure 4 shows the morphology of tig welds with and without fluxes and figure 5 shows the width to depth penetration. it can be seen that tio2, sio2 and mno2 oxides permit to get total penetration weld bead followed by cr2o3, fe2o3 and zno with good penetration of around 5mm. finally moderate penetration welds occur with zro2 and cao oxides. the depth to width ratio r is greater than 0.7 for tio2, sio2, cr2o3 oxides and close to 0.7 for mno2. it decreases to 0.55 for fe2o3 and zno. but it goes down to 0.4 for zro2 and cao. zro2 and cao oxides behave as pure metals promoting a wide and shallow weld bead. on the other hand, tio2 and sio2, and at a less degree cr2o3, significantly increase the weld depth to weld bead width ratio. b. effect of different fluxes on weld morphology with a current of 180amp e=680kj/m as revealed with xps analysis, increasing the welding current increases the temperature in weld pool leading to more liberation of oxygen. four fluxes out of eight (tio2, sio2, fe2o3 and mno2) presented total penetration of welds as shown in figure 6. in this case, the positive tension gradient temperature coefficient controls the melt metal movement in the weld. c. effect of different fluxes on weld morphology with a current of 200amp e=800kj/m the penetration is total for almost all oxides used except zirconium and calcium oxides as shown in figure 7. in this case, the movement of liquid is from the center to the edges. fig. 4. morphology of tig and atig welds (i=150a, v=15cm/min) fig. 5. width to depth ratio of tig and atig welds (i=150a, v=15cm/min) fig. 6. morphology of tig and atig welds (i=180a, v=15cm/min) v. oxide effectiveness with provided energy the efficiency of oxides is represented by the ratio r. the welding current level represents the energy level supplied to the melt. this energy indirectly represents the temperature reached in the melt. normally, each oxide has an optimum temperature where it completely fulfills its role. figure 8 shows that the coefficient r is more important with current 180a in the cases of tio2, sio2, fe2o3, mno2, cao but zno and cr2o3 oxides are more efficient with a current of 200a, and finally zro2 oxide is efficient with a current of 150a. figures 9 and 10 show micrographs of weld beads. fig. 7. morphology of tig and atig welds (i=180a, v=15cm/min) fig. 8. width to depth ratio of tig and atig welds (i=150,180 ,200a, v=15cm/min) engineering, technology & applied science research vol. 8, no. 3, 2018, 3064-3072 3068 www.etasr.com hdhibi et al.: effect of single oxide fluxes on morphology and mechanical properties of atig on … tig weld bead atig weld with sio2 flux atig weld with tio2 flux atig weld with fe2o3 flux atig weld with mno2 flux atig weld with cr2o3 flux atig weld with zno flux atig weld with zro2 flux atig weld with cao flux fig. 9. weld beads using different mono-oxides flux with 180a, 15cm/min vi. effect of oxide fluxes on mechanical properties a. tensile test the configuration and size of the tensile specimens were prepared according to astm e8m-04 for the tensile test as shown in figure 11. figure 12 presents the results for the tensile strength of tig weldment with and without fluxes. it can be clearly seen that the tensile strength obtained by using activating fluxes exhibit are better than those of tig welding. according to [23, 31, 32], the delta ferrite is formed during atig welding. the delta-ferrite has a body-centered cubic (bcc) crystal structure, which has a higher mechanical strength than that of the austenitic fcc structure. it was seen that the content of ferrite number is greater during the atig welding than in tig welding. it was also observed that during the atig the delta-ferrite content in the weld metals was increased, and showing a positive effect in increasing the tensile strength. b. hardness test the location of the measurements across the weld cross section is shown in figure 13. the values used are the average of four measurements.results showed the same trends as the tensile strength results that the oxide flux did not affect the hardness of welds. the hardness of atig welds is equal or above of the tig welding hardness reading, except atig silicon oxide flux weld hardness (165hv) which is less to tig weld bead hardness (176 hv) as shown in figure 14. in the other hand hv hardness of mno2, cr2o3 and zro2 are bigger than the hardness of parent metal (180hv). c. impact test figure 15 presents the results for the experimental results for the impact test at weld zone of tig weldment with and without fluxes. the specimens were prepared according to astm e23 for the impact test as shown in figure 16. it can be observed that, except for the titanium dioxide tio2, the weldment using the other oxide fluxes exhibits a worse withstand to sudden shock than those of tig welding. this may be attributed to two reasons: (a) the level of oxygen trapped in the weld pool while welding or due to decomposition of oxides as revealed by xps analysis and (b) the formation of the ferrite content in atig welds decreases to sudden impact loads. figure 17 presents the results of the experimental results for the impact test at heat affected zone haz of tig weldment with and without fluxes. it can be engineering, technology & applied science research vol. 8, no. 3, 2018, 3064-3072 3069 www.etasr.com hdhibi et al.: effect of single oxide fluxes on morphology and mechanical properties of atig on … observed that a drastic reduction in the impact toughness, probably due to a formation of sigma phase and coarser ferrite and austenite grains. atig with cr2o3 flux, i=150a atig with cr2o3 flux, i=180a atig with cr2o3 flux, i=200a atig with fe2o3 flux, i=150a atig with fe2o3 flux, i=180a atig with fe2o3 flux, i=200a atig with zno flux, i=150a atig with zno flux, i=180a atig with zno flux,i=200apms fig. 10. weld beads using different levels of current intensity (150180 -200a), welding speed 15cm/min fig. 11. test specimen for the tensile test engineering, technology & applied science research vol. 8, no. 3, 2018, 3064-3072 3070 www.etasr.com hdhibi et al.: effect of single oxide fluxes on morphology and mechanical properties of atig on … fig. 12. uts of tig and atig welds (i=180a, v=15cm/min) fig. 13. hardness test locations on weld bead fig. 14. vickers hardness for tig and atig welds at weld zone (i=180a, v=15cm/min) fig. 15. energy absorbed for tig and atig welds at weld zone (i=180a, v=15cm/min) vii. microstucture during welding, weld metal cools so rapidly that the transformation of delta ferrite to austenite is not complete, so, more delta ferrite is retained in the weld metal after solidification. the arc voltage increases when the activated tig process was used knowing that the heat provided to weld pool is proportional to the voltage. the longer the element in the flux has the ability to influence the voltage, the higher the energy supplied. the measurement of ferrite content in the austenite matrix was performed using areas image processing software from microvision as shown in figure 18 (a)-(d). the study has been conducted on different atig welds and tig conventional weld. results show a ferrite content equal to 6.8 for tig. on the other hand there is an increase in ferrite content when using oxide fluxes which vary from 6.9 for mno2 to 8.4 for sio2 as shown in figure 18. the increase of deltaferrite content explains the increase of hardness and strength of the atig welds. (a) (b) fig. 16. test specimen for the impact test (a) weld zone, (b) haz fig. 17. energy absorbed for tig and atig welds at haz (i=18a, v=15cm/min) viii. conclusion this study was conducted on atig welding of austenitic 316l. eight oxide fluxes were investigated. the results are summarized as follows:  xps analysis shows that the percentage of oxygen in the welds decreases with the increase of current welding intensity. this contributes to increase the energy supplied to the melt. this can be explained by the fact that the oxides decompose and the oxygen atoms are transferred to the liquid weld pool allowing to centripetal melt convection.  the oxides which are characterized by melting and boiling point close to those of the base metal should be chosen, like sio2, tio2, cr2o3, and fe2o3 whose melting and boiling points are close to the ones of austenite stainless steel 316l. it is not a major criterion but it helps to get better welding without loss of energy.  oxide fluxes with high thermodynamic stability and high melting points are not advisable to use for austenitic stainless steel (tm=1440 ͦ c), like zro2 and cao. engineering, technology & applied science research vol. 8, no. 3, 2018, 3064-3072 3071 www.etasr.com hdhibi et al.: effect of single oxide fluxes on morphology and mechanical properties of atig on … tig: delta ferrite content fn=6.8 atig with flux: mno2delta ferrite content fn=6.9 atig with flux: tio2 delta ferrite content fn=7.1 atig with flux: sio2 delta ferrite content fn=8.4 fig. 18. delta-ferrite content for tig weld (a) and atig welds (b,c,d). sem. magnification 2500 x.  the optimal geometric ratio of efficiency r is achieved when i=180a, v=15cm/min and arc length=2mm for the 316l stainless steel using oxide fluxes such as si2o, tio2, fe2o3, and mno2.  the tensile strength of atig welds are above the tig or parent metal tensile strength (618mpa). this is due to the formation of delta ferrite which is characterized by its high mechanical strengths.  the hardness of the welded zone was not affected by the addition of active fluxes.  except for the titanium dioxide tio2, the weldment using other oxide fluxes exhibits worse withstanding to sudden shock compared to those of tig welding. this is probably due to oxygen content in welds and the delta ferrite formation. funding and acknowledgement this work is supported by the deanship of scientific research in prince sattam bin abdulaziz university ksa under the research project number 2017/01/7373. authors acknowledge his collaboration and thank dr. ibrahim ali alsayed for his help in performing xps analysis. references [1] h. y. huang, s. w. shyu, k. h. tseng, c. p. chou, “evaluation of tig flux welding on the characteristics of stainless steel”, science and technology of welding and joining, vol. 10, no. 5, pp. 566–573, 2005 [2] s. w. shyu, h. y. huang, k. h. tseng, c. p. chou, “study of the performance of stainless steel a-tig welds”, journal of materials engineering 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structural analysis of wood and steel bungalows a contemporary house proposal: structural analysis of wood and steel bungalows yenal takva department of architecture, faculty of architecture, gazi university, turkey yenaltakva@gazi.edu.tr cagatay takva department of architecture, faculty of architecture and design, ataturk university, turkey cagataytakva@atauni.edu.tr (corresponding author) fulya goksen department of architecture, faculty of architecture, gazi university turkey fulyagoksen@gazi.edu.tr received: 1 april 2023 | revised: 18 april 2023 | accepted: 2 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5896 abstract the housing typologies that meet shelter and other basic needs are diverse, and bungalows are one of them. these buildings are generally single-story and mostly use wooden building materials. this paper introduces a new construction technique using steel, which is more durable than typical wooden bungalow houses. this design aimed to create a new building stock based on the logic of mass production, where modular steel bars can be prefabricated and transported to the construction site. an architectural design with a steel construction instead of a wooden one and a hexagonal plan instead of a rectangular one was developed. structures designed with wooden and steel materials were compared using the structural analysis method. structural analysis of the construction designs using wood and s235 steel grade was performed with the sap2000 software. the structures were evaluated according to displacement, modal analysis periods, and self-weight, and their static suitability was tested. this new architectural design was developed because steel can maintain its strength for a long time compared to wood and has a higher modulus of elasticity. the results showed that wood and steel materials exhibit similar behavior under the same cross-sections, but the steel structure has come to the forefront as it is lighter than wood in terms of self-weight. keywords-building design; bungalow; house; steel construction; structural analysis; wood construction i. introduction the concept of home has a different meaning for each person, as some people define it as a living space while others define it as a place of entertainment, rest, and sleep. considering the house as a sheltering need is an indicator of its main function [1]. the origin of single-family houses dates back 2,000 years [2]. as the world population increases, housing production increases to meet current demands in the housing sector [3]. parameters such as awareness, sense of responsibility, and waste management should be considered along with the increase in housing production [4]. high productivity, efficiency, quality, and sustainable steps are nowadays widely considered in the construction sector [5-6]. sustainable architectural approaches to environmental problems are being developed for new houses to be built [3, 7]. bungalows account for one such house type. in general, singlestory bungalows without stairs form a living space [8]. since this living space consists of a single space, it can have a simple basic geometry, or it can be produced from parametric plans using various shapes [9]. colony-shaped portable bungalow prototypes have been used in the construction of modern houses [10]. several studies have been conducted on bungalows. in 1999, a bungalow was designed in malaysia with a photovoltaic panel system installed on its roof, and energy tests were carried out [11]. a study conducted in great britain showed that heating costs in detached houses and bungalows were higher than those in apartments [12]. performance and economic analyses were performed with photovoltaic panels for a bungalow house in damansara, malaysia in [13]. noise analysis was carried out in bungalow houses in the context of acoustics in england, evaluating environmental and socio-economic factors [14]. thermal comfort tests and experiments were carried out in a detached bungalow-type house in ireland using smart algorithms [15]. in building design, the use of materials is also important. in [16], wood and steel-reinforced concrete were engineering, technology & applied science research vol. 13, no. 3, 2023, 11032-11035 11033 www.etasr.com takva et al.: a contemporary house proposal: structural analysis of wood and steel bungalows evaluated in housing construction in terms of energy use and emissions. in [17], the mechanical properties and manufacturing technologies of engineered wood and bamboo composite materials were investigated and compared. in [18], cross-laminated timber and concrete slab flooring were analyzed in terms of structural performance, cost, and greenhouse gas emissions. the use of different approaches in building designs requires considering different parameters. integration of different parameters improves the architecture, engineering, and construction (aec) industry. in addition to material differentiation, design phases [19-20], cost analyses [21-23], and entrepreneurial views [24] also contribute to the aec industry. as most of the bungalow studies are focused on energy, it can be observed that the structural analysis studies on bungalows and material comparison are limited. this study presents a contemporary bungalow proposal, performing a design and structural analysis comparison of a bungalow made of wooden and steel materials and hexagonal form, by bringing a new perspective to bungalows in traditional materials and forms. the structural analyses of the constructions designed with wood, which is a traditional building material, and s235 steel class were compared using the sap2000 software and the finite element method. this software offers 2d and 3d modeling possibilities, from simple to complex geometries, that accelerate the engineering processes [25]. ii. materials and methods bungalow houses are usually built with wooden materials. this study used s235 steel, which is a frequently used and long-lasting building material [26-27]. the reason for choosing steel is its robustness, its ability to be used in frame systems, and its potential for improved aesthetics and functionality. although wooden construction materials are also used in frame systems, when compared to steel in the same span, the material cross-section is larger and does not provide an effective solution. while there are common structural steel types such as s235 (st37), s275 (st44), and s355 (st52), s235 unalloyed structural steel has higher strength, is used by steel manufacturers and designers in turkey, and is wider than other steel types [28]. figure 1 shows the flowchart of this study. fig. 1. flow chart of the study. the displacements in the x and y directions were calculated under self-loads, considering weights for the structural analysis of the wooden and steel structures. the required strength for the system and elements was determined according to different critical load combinations, specifically: g+q, 1.4g, and 1.2g+1.6q. the mode values were also used to determine the dynamic state of the designs. fixed support was used for the elements of the structures that rest on the ground. steel construction profiles can be produced in square, rectangular, and pipe forms. for the steel cross-section, a hollow circular steel structural element was chosen to avoid sharp ends in frame systems and provide ease of application. similarly, the wooden structure used circular structural elements. the wood and steel construction elements had a pipe section of 500mm in diameter, and the steel construction elements had a wall thickness of 15mm. table i shows the properties of the structural wood and steel used in the designs. table i. properties of structural materials w o o d density 0.800kg/m3 shear modulus 3800n/mm2 modulus of elasticity 9.8gpa (9800mpa) poisson's ratio 0.3 s t e e l density 7,850kg/m3 minimum yield strength of steel 235n/mm2 modulus of elasticity 200gpa (200000mpa) poisson's ratio 0.286-0.315 (0.3 taken.) shear modulus 8100kn/cm2 tensile strength 360–510mpa iii. case study – bungalow house bungalow houses can be used in the countryside and provide the opportunity to live a life in touch with nature. today, the importance of nature is more evident in the city centers due to the dense construction and population. this study considered a steel-built design, which is an innovative and sustainable building material that does not take up much space. the design focused to keep the construction area small on the land by increasing the vertical elevation of the structure. to this result, the upward-rising structure was expanded, and the architectural spaces were increased. structural elements must be modular manufactured for easier transport. in the design, the steel elements that form the frame of the building should be manufactured as modular and transported to the construction site. the geometry of the structure was formed from a regular hexagon, which allows steel members of equal length to be produced modularly. the durability and the cost of the two types of structures were investigated. figure 2 shows the appearance of the designed bungalows. fig. 2. the exterior and the location of the bungalow. engineering, technology & applied science research vol. 13, no. 3, 2023, 11032-11035 11034 www.etasr.com takva et al.: a contemporary house proposal: structural analysis of wood and steel bungalows figure 3 shows the structural design. the structure rises 12m on a regular hexagonal plan, covers a 1212m area, and has an expanded frame with a 1.5-meter-long cantilever. after raising 6m, the frame of the structure narrows, and a square horizontal frame of 66m was obtained at the top level of 12m. the building structure was completely formed from wooden and s235 steel structural materials. a beam was added between the two longest corners of the regular hexagon geometry at the 6-meter level. wooden and steel construction elements were connected with rigid connections. fig. 3. the structure of the bungalow and the connections of the steel elements. the total mass and rigidity of the structure with the incoming loads affect the amount of displacement. in addition, the calculation of vibration periods plays an important role. in steel frames, the material and its diameter along with the thickness of the wall cause these values to vary [29]. the elastic properties of the structure should also be considered during the design phase [30]. using displacement data, the static and dynamic properties of buildings are analyzed for safety [31], while displacement also changes the performancebased designs [32]. table ii shows the values of the building structures according to the displacement analyses. table ii. displacements under self-loading w o o d δx δy δz displacement under self-loads -0.42mm displacement in the x-direction 1.35mm 0.7mm displacement in the y-direction 2.04mm 0.98mm s t e e l displacement under self-loads -0.33mm displacement in the x-direction 1.53mm 0.76mm displacement in the y-direction 2.13mm 1.05mm the performance analysis identified the period values of the system. mode values are defined as the values of the natural vibration period on the principal axes of the structure [33]. the mode concept plays a role in showing the deformation patterns of periods. modal analysis is also essential for determining structural damage [34]. in the mode values, the first three values of the natural vibration period with the highest mass participation are considered. the connection points of the bar elements also play an active role in the mode values [35]. this study examined the first three mode values that provide the most mass participation in terms of mode value. horizontal and vertical vibration periods may occur in three-dimensional structures. a high period value means low rigidity, as there is an inverse proportional situation. at this point, a comparison between the period value and stiffness can be made. table iii shows the mode values of the structural system. the total weights of the structures having the same geometry and crosssections of the structural elements were obtained. by looking at the total weight values, inferences can be made about the costs. table iv shows the weights of the wood and steel structure designs. table iii. deformations and first natural vibration periods wood mode-1 mode-2 mode-3 0.09s 0.09s 0.06s steel mode-1 mode-2 mode-3 0.31s 0.28s 0.21s table iv. total weights of structures (kg) self weight of the systems wood steel 6805kg 3467kg iv. conclusion building construction techniques vary according to the characteristics of the buildings. there are also different construction techniques in houses. structure materials used in houses have changed from the past to the present. the use of local materials, which are found predominantly in the construction area, is dominant in the construction of buildings. the use of local materials is at the forefront in bungalows, which form one of the housing types. these structures have been used in different combinations throughout history. it is possible to encounter this situation in the need for luxury housing or accommodation for refugees. this study presented a new architectural design for such buildings. the design used high-strength steel for the construction due to its innovative and durable characteristics. the proposed steel design was evaluated by comparing it with a similar wooden one. structural analyses were performed on the two bungalow designs. at first, the displacement of the structures under selfloads was examined. due to the tests carried out toward gravity and along the x and y-axis, it was observed that the maximum displacement values were in the y-axis direction. considering the displacement values obtained, it can be inferred that the proposed steel system provides positive feedback. the modal analysis results showed that an 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[35] d. d. quinn, "modal analysis of jointed structures," journal of sound and vibration, vol. 331, no. 1, pp. 81–93, jan. 2012, https://doi.org/ 10.1016/j.jsv.2011.08.017. microsoft word 42-3110_s_etasr_v9_n5_pp4813-4817 engineering, technology & applied science research vol. 9, no. 5, 2019, 4813-4817 4813 www.etasr.com hassan & izzet: serviceability of reinforced concrete gable roof beams with openings under … serviceability of reinforced concrete gable roof beams with openings under static loads maryam abdul jabbar hassan college of engineering, department of civil engineering, university of baghdad, baghdad, iraq maryemaj123@gmail.com amer farouk izzet college of engineering, department of civil engineering, university of baghdad, baghdad, iraq amer.f@coeng.uobaghdad.edu.iq abstract—this paper presents an analytical study on the serviceability of reinforced concrete gable roof beams with openings of different sizes, based on an experimental study which includes 13 concrete gable roof beams with openings under static loading. for deflection and crack widths under static loading at service stage, a developed unified calculation procedure has been submitted, which includes prismatic beams with one opening subjected to flexure concentrated force. the deflection has been calculated with two methods: the first method calculated deflections via relevant equations and the second was direct stiffness method in which the beam is treated as a structural member with several segments constituting the portions with solid sections and those with sections crossed by the opening. the crack width was calculated with the aci code’s equation with a proposed magnification factor equal to 1.125. the analytical results were compared with the experimental ones and a good agreement was obtained. keywords-serviceability; gable roof beam; deflection; crack width; static loads i. introduction concrete has relatively low material costs, good high fire resistance, and low to no maintenance cost. for these reasons reinforced concrete gable beams can be used as an alternative preferred option to support roofs of warehouses, industrial buildings, and airplane hangars. the presence of openings in gable beams has many advantages, such as easier handling or overall weight reduction, but the insertion openings in a solid beam would directly affect beam behavior as the opening would essentially cause a sudden drop in the beam cross section dimensions which would in turn reduce the overall stiffness of the beam which may result in extreme deflections under service loads. gable beams are non-prismatic beams or beams of variable cross-section which make the calculation of the moment of inertia more complicated [1]. the presence of openings would lead to further complication. to the best of our knowledge, there is no literature regarding the deflection of reinforced concrete gable roof beams with openings. therefore, this research is an attempt to present an analytical study of the deflection for rc gable roof beams with openings based on previous studies of prismatic beams with one opening. authors in [2] presented a simple method to evaluate the deflection at service stage of simply supported beams with openings. the upper and lower chords of opening behave as struts framing on sides of the opening into rigid abutments. the effective length le is equal to the distance between full-depth stirrups on the sides of opening. the point of contra flexure is assumed at mid-length of each strut, so that each half of upper and lower chords bends as a cantilever. authors in [3] proposed a rigorous method to calculate the deflection of beams with openings. in this methodology, the beam is treated as a structural member with several segments constituting the portions with solid sections and those with sections crossed by the opening. an equivalent stiffness is adopted for the latter segments and the beam can be analyzed using methods such as the direct stiffness method. both previous methods have been used to calculate the deflection of prismatic beams with only one rectangular opening. in the present study an attempt was made to develop these methods to calculate deflection for gable beams with openings of different sizes. crack width is one of the major serviceability requirements of concrete structures, concrete’s low tensile strength leads to crack occurrence in reinforced concrete under service loads. cracking control is essential for the acceptable appearance and durability of concrete structures, particularly those subjected to aggressive environment [4]. the aci 318m-1995 code [5], considered that the permissible maximum crack widths at service stages for exterior and interior exposure conditions are 0.3mm and 0.4mm, respectively. authors in [6] examined the influence of circular openings on the structural behavior of concrete beams. the adopted parameters were: the opening diameter, the location of the opening, the reinforcement type and place, and the concrete compressive strength. the main findings were that the ultimate strength reduction and the pattern of cracking were magnified in normal concrete beams, when the opening diameter exceeded the one-third of the beam's depth. the diameter and the opening location are the main parameters that affect the strength of concrete. it is preferable to use inclined bar reinforcement around the opening, to control the cracks and restrict their width. using inclined bar reinforcement and stirrups in the upper and lower chords of the opening is necessary to increase the ultimate shear strength. for beams with openings, wide cracks appear close to the end of chord members at the opening corner due to stress concentration at these zones [7-11]. corresponding author: maryam abdul jabbar hassan engineering, technology & applied science research vol. 9, no. 5, 2019, 4813-4817 4814 www.etasr.com hassan & izzet: serviceability of reinforced concrete gable roof beams with openings under … ii. deflection at service load a. equation method maximum deflection under working loads is generally required to be in agreement with code provisions. in the present analysis, service load is taken as the experimental ultimate load divided by a factor of 1.7 as recommended by [3, 12]. a simple method to estimate the mid-span deflection of simplysupported beams with openings is suggested in [2]. the maximum deflection of the beam can be calculated as: � � �� � ����� ��� � � ����� ��� � � ⋯ (1) where δw is the mid-span deflection of the beam in the absence of openings and δv is the relative displacement of one end of the opening with respect to the other end under the action of v, which may be obtained as: �� � � ��� �� �� ���� ��� (2) where ec is the modulus of elasticity of concrete. under service load, it is the moment of inertia of the upper chord which may be based on gross concrete section, while ib is the moment of inertia of the lower chord which can be conservatively based on a fully cracked section. the effective length le of the struts is conservatively taken as the distance between the full-depth stirrups on each side of the opening (as mentioned previously). in the present study an attempt has been drawn to calculate the deflection of the tested beams under service loads applying the above equations as follows: ps=assumed service load= �� 1.7! , v=corresponding shear force= �" 2! , le=the effective length of opening=lopening+50mm, ec=modulus of elasticity of concrete from testing=26870mpa, it=the moment of inertia of the upper chord= $∗ &� �� , ib=the moment of inertia of the lower chord=0.1it, and δw=the midspan deflection of the beam with span l=� () 48 ,.⁄ , where i can be conservatively estimated as the moment of inertia of the beam. authors in [13] suggested a prismatic beam with one rectangular opening in which i can be calculated at a section through the opening based on gross concrete section. while this suggestion contradicts the definition of δw in (1) (mid-span deflection in the absence of openings), the service stage deals with cracked transformed sections, so that using gross section gives high values of i which in turn leads to a very small value of deflection which is far from the real value. for above reasons, it may be suggested that i for service load can be calculated based on the cracked transformed section for the beam in the absence of openings. to calculate i for a nonprismatic beam, the section that reflects the uniform change in dimension (height) with length must be determined. after several trials it was found that the cracked transformed section at the quarter length of the gable beam can be used to calculate iaverage and converge to the experimental results of the gable beam without openings. the height at any distance (hx) can be calculated from the following equation (figure 1): 01 � 0� 21 3 1 45 6 � 145 0� (3) fig. 1. schematic layout of a gable beam b. direct stiffness method another way to calculate maximum beam deflections beside the deflections under each opening corner at the assumed service loads is the one where the beam is treated as a structural member with several segments constituting the portions with solid sections and those with sections crossed by the openings. an equivalent stiffness is adopted for the latter segments and the beam can be analyzed using methods such as the direct stiffness method [3]. the equivalent flexural stiffness (ei)eq of the continuous medium is based on the net section through the opening, assuming that the two chords act as one unit and that the section is cracked in flexure, the moment of inertia i is calculated using the transformed area method (figure 2). fig. 2. equivalent segmented beam the beam is divided into sections of different crosssectional properties: the solid section and the equivalent opening section as shown in figure 2(b), and the flexural stiffness is based on the cracked transformed section. the case of analyzing a simply supported beam with symmetrical multiple openings can be deduced due to this symmetry as shown in figure 2. the typical equation used in the analysis is: 789 � :;< 7�9 (4) engineering, technology & applied science research vol. 9, no. 5, 2019, 4813-4817 4815 www.etasr.com hassan & izzet: serviceability of reinforced concrete gable roof beams with openings under … where the stiffness matrix [k] for any element with length l is: 3 2 3 2 2 2 3 2 3 2 2 2 12 6 12 6 6 4 6 2 [ ] 12 6 12 6 6 2 6 4 l l l l l ll l k l l l l l ll l   −     −   =    − − −      −    (5) iii. comparison with test data (summary of beam details) the experimental data were acquired from the testing of 13 reinforced concrete gable roof beams, including the reference beam without openings (solid) and 12 beams with openings. the variables used in this work include the size and number of the openings, the inclination of the posts, and the configuration of the openings, as shown in table i. all beams had the same length, width, height, reinforcement details, and were subjected to one mid-point concentrated load. precautions were made to avoid local failure at the loading point and support was provided by steel plates. figures 3 to 7 show the details of the tested beams. the beams were tested with an overall clear span of 2800mm. the tested beams were divided into four main groups (a, b, c, and d). these groups were classified according to the variables that have been used in this study (table i). fig. 3. details of reinforcement for beam gb (all dimensions are in mm) fig. 4. details of reinforcement for beam gt6 fig. 5. details of reinforcement for beam gth6 fig. 6. details of reinforcement for beam gp6 fig. 7. details of reinforcement for beam gc1 table i. details of tested beams height of lower chord (mm) height of upper chord (mm) width of openings (mm) number of openings shape of openings beam mark group -------------------------gb ref. beam 100 100 200 6 trapezoidal gt6 a 100 100 150 8 trapezoidal gt8 100 100 100 10 trapezoidal gt10 75 75 200 6 trapezoidal gth6 b 75 75 150 8 trapezoidal gth8 75 75 100 10 trapezoidal gth10 100 100 200 6 trapezoidal with inclined posts gp6 c 100 100 150 8 trapezoidal with inclined posts gp8 100 100 100 10 trapezoidal with inclined posts gp10 75 75 d 8 circular gc1 d 100 100 0.83d 8 circular gc2 120 120 0.67d 8 circular gc3 since many approximations are involved in modeling reinforced concrete for the calculation of deflection, accuracy within ±20% usually is considered satisfactory for all design purposes. the predicted value of the maximum deflections at the assumed service load calculated by both the equation method from (1) and direct stiffness method from (4) are presented together with the corresponding experimental values in table ii and figure 8. in equations method the ratios of experimental to predicted deflections for beams with quadratic openings (nine beams) range from 1.04 to 1.21, with an average of 1.15 and a coefficient of variation of 5%, while the beams with circular openings (three beams) have ratios of experimental to predicted deflections ranging from 1.1 to 1.18 with an average of 1.14 and a coefficient of variation of 3.32%. engineering, technology & applied science research vol. 9, no. 5, 2019, 4813-4817 4816 www.etasr.com hassan & izzet: serviceability of reinforced concrete gable roof beams with openings under … note that for the total of 12 beams only one beam violated the acceptable accuracy of ±20% by a negligible margin. in direct stiffness method, the ratios of experimental to predicted deflections for beams with quadratic openings (nine beams) range from 0.95 to 1.15, with an average of 1.07 and a coefficient of variation of 6.21%, while the beams with circular openings (three beams) have ratios of experimental to predicted deflections ranging from 0.99 to 1.12 with an average of 1.06 and a coefficient of variation of 6%. all 12 beams were within the acceptable accuracy of ±20%. table ii. comparison between predicted and experimental deflections at calculated service loads deflection calculated by direct stiffness method deflection calculated by equation method load (kn) beam mark c.o.v mean => =? δe (mm) δp (mm) c.o.v mean => =? δe (mm) δp (mm) ----1.05 8.18 7.81 -----1.04 8.18 7.86 52.94 gb 6.21 1.07 1.06 9.11 8.61 5.00 1.15 1.21 9.11 7.52 45.76 gt6 1.14 9.02 7.88 1.20 9.02 7.52 47.17 gt8 1.15 8.78 7.65 1.18 8.78 7.44 48.24 gt10 1.05 9.31 8.89 1.15 9.31 8.09 43.48 gth6 1.06 9.11 8.56 1.16 9.11 7.87 45.19 gth8 1.13 9.05 8.02 1.18 9.05 7.67 47.35 gth10 0.99 8.58 8.64 1.08 8.58 7.97 48.51 gp6 1.08 9.14 8.44 1.16 9.14 7.86 49.30 gp8 0.95 7.94 8.32 1.04 7.94 7.66 49.65 gp10 6 1.06 1.12 8.89 7.92 3.32 1.14 1.18 8.89 7.54 47.94 gc1 1.08 8.74 8.11 1.14 8.74 7.65 50.59 gc2 0.99 8.53 8.56 1.10 8.53 7.73 51.71 gc3 service load is taken as the experimental ultimate load/1 7, δp =predicted deflection in mm, δ e =experimental deflection in mm, mean=average of δe/δp, c.o.v=coefficient of variation of δe/δp= @ab�cbdc c ��ba��� e b� ∗ 100 fig. 8. comparison of deflections at calculated service loads iv. maximum crack width the flexural crack width at service stage can be calculated according to control requirements in aci 318m-1995 code [5], using the following form: ghb1 � 0.011i j" klmn� ∗ 10o) pp (6) where i � �0 3 q�/�l 3 q� is the ratio of the distance between the neutral axis and extreme tension face to the distance between the neutral axis and the centroid of reinforcing steel, β=1.20 in beams may be used to compare the crack widths obtained in flexure and axial tension, j_t � u ∗ �v w�/. is the stress in the tension reinforcement calculated on the basis of a cracked section (n/mm 2 ), n=modular ratio=es/ec, dc is the distance measured from the centroid of tensile steel to the extreme tensioned fiber, m_x � �2 l_w y�/u_y is the area of concrete surrounding each reinforcing bar, and nb is the number of tension reinforcing bars. in the present study the width of flexural cracks is measured using a microscope during loading stages. table iii shows the maximum crack widths at the service loads, taken as the experimental ultimate loads divided by a load factor of 1.7. according to (6), the predicted maximum flexural crack width at service load for the reference beam (gb) is equal to 0.33mm, while the experimental value according to table iii is equal to 0.32mm and the mean of the maximum crack width for the beams with openings is 0.36mm, so that it can be concluded that the insertion of opening in a solid beam increases the maximum flexural crack width by 12.5%, therefore the equation of maximum crack width for beam with opening can be written as: gz[\ �$ bh ��a& � ��� � � 1.125 ∗ gz[\�"���c $ bh� �mm� (7) when using (7) to calculate the crack width of the tested beams under service loads as illustrated in table iii, it shows that for a total of 12 beams, the ratios of experimental to predicted maximum crack width range from 0.82 to 1.39, with an average of 1.06 and a coefficient of variation of 15.6%. only two beams violated the acceptable accuracy of ±20% (beam gth6 and gth8), where the maximum crack width for these two beams already marginally exceeded 0.4mm (max. crack width=0.43mm for beam gth6 and 0.41mm for beam gth8). the reason for this may be the reduction in depth of the upper and lower chords. on average, the proposed formula gives conservative predictions of maximum flexural crack width for beams with openings at service load. it is obvious from table iii that the provision of opening increases the maximum flexural crack width at service stage, in addition the increasing size of opening increases the maximum crack width at all load levels. despite that the serviceability criterion of maximum crack width is satisfied by all beams, except for beams gth6 and gth8 as mentioned above. engineering, technology & applied science research vol. 9, no. 5, 2019, 4813-4817 4817 www.etasr.com hassan & izzet: serviceability of reinforced concrete gable roof beams with openings under … table iii. maximum crack width under service load c.o.v mean _` _a wp (mm) we (mm) calculated services load (kn) beam mark group -----0.97 0.33 * 0.32 52.94 gb ref. beam 15.6 1.06 1.18 0.33 0.39 45.76 gt6 a 1.12 0.33 0.37 47.17 gt8 0.97 0.34 0.33 48.24 gt10 1.39 0.31 0.43 43.48 gth6 b 1.28 0.32 0.41 45.19 gth8 1.03 0.34 0.35 47.35 gth10 0.97 0.34 0.33 48.51 gp6 c 0.91 0.35 0.32 49.30 gp8 0.82 0.35 0.29 49.65 gp10 1.09 0.34 0.37 47.94 gc1 d 1 0.35 0.35 50.59 gc2 0.92 0.37 0.34 51.71 gc3 * predicted crack width according to (6) in mm v. conclusion for the calculation of deflection and crack width of reinforced concrete gable beams, two methods have been developed, the first method uses a general cumulative equation and the second is the direct stiffness method. the direct stiffness method is long and needs careful calculations for the flexural stiffness based on the cracked transformed section for each section. for crack width calculation, the equation of aci 318m-1995 code was used with magnification factor equal to 1.125 to predict crack width for beams with openings. the analytical results were compared with the experimental ones and on average the suggested methods to determine deflection and crack width for gable beams with openings at service loads give good predictions and satisfy design requirements. references [1] s. p. timoshenko, d. h. young, theory of structures, mcgraw-hill, 1965 [2] g. b. barney, w. g. corley, j. m. hanson, r. a. parmelee, “behavior and design of prestressed concrete beams with large web openings”, pci journal, vol. 22, no. 6, pp. 1977 [3] m. a. mansur, l. m. huang, k. h. tan, s. l. lee, “deflections of reinforced concrete beams with web openings”, aci structural journal, v. 89, no. 4, 1992 [4] n. j. carino, j. r. clifton, prediction of cracking in reinforced concrete structures, building and fire research laboratory, national institute of standards and technology, 1995 [5] aci standard: commentary on building code requirements for structural concrete (aci 318r-95), 1995 [6] j. v. amiri, m. h. alibygie, “effect of small circular opening on the shear and flexural behavior and ultimate strength of reinforced concrete beams using normal and high strength concrete”, 13th world conference on earthquake engineering, vancouver, canada, august 1-6, 2004 [7] a. s. al-shaarbaf, n. a-m. j. al-bayati, d. i. a. al-kaisy, “nonlinear finite element analysis of reinforced concrete beams with large opening under flexure”, engineering & technology, vol. 25, no. 2, pp. 210-228, 2007 [8] n. k. oukaili, a. h. shammari, “response of reinforced concrete beams with multiple web openings to static load”, fourth asiapacific conference on frp in structures, melbourne, australia, december 11-13, 2013 [9] b. aykac, i. kalkan, s. aykac, y. e. egriboz, “flexural behavior of rc beams with regular square or circular web openings”, engineering structures, vol. 56, pp. 2165-2174, 2013 [10] s. a. al-sheikh, “flexural behavior of rc beams with opening”, concrete research letters, vol. 5, no. 2, pp. 812-824, 2014 [11] m. b. dawood, r. a. a. nabbat, “flexural and shear strength of nonprismatic reinforced high strength concrete beams with openings and strengthened with nsm-cfpr bars”, international journal of civil engineering and technology, vol. 6, no. 9, pp. 93-103, 2015 [12] k. h. tan, ultimate strength of reinforced concrete beams with rectangular openings under bending and shear, msc thesis, national university of singapore, 1982 [13] m. a. mansur, k. h. tan, concrete beams with openings: analysis and design, crc press, 1999 microsoft word 30-2687_s1 engineering, technology & applied science research vol. 9, no. 2, 2019, 4030-4036 4030 www.etasr.com labidi et al.: a systematic controller design for a photovoltaic generator with boost converter using … a systematic controller design for a photovoltaic generator with boost converter using integral state feedback control zeineb rania labidi laboratory of application of energy, efficiency and renewable energies, faculty of sciences of tunis, tunis el manar university, tunis, tunisia zeinebrania.labidi@fst.utm.tn horst schulte department of engineering, university of applied sciences for engineering and economics, berlin, germany horst.schulte@htw-berlin.de abdelkader mami laboratory of application of energy, efficiency and renewable energies, faculty of sciences of tunis, tunis el manar university, tunis, tunisia abdelkader.mami@fst.utm.tn abstract—in this paper, a systematic controller design for a photovoltaic generator with boost converter using integral state feedback control is proposed. it is demonstrated that the state– space feedback enables the extraction of maximum available power under variable loads. for this purpose, a control-oriented state-space model of a photovoltaic array connected to a dc load by a boost converter is derived. this model is then linearized by one working point, but no further simplifications are made. the design-oriented model contains the dynamics of pv generator, boost converter, and the load. the controller design is based on the augmented model with an integral component. the controller is validated by a detailed plant model implemented in simscape. the robustness of the controller with variable solar irradiation and dc load changes is demonstrated. keywords-feedback control; boost converter; maximum power point tracking (mppt); state–space modeling; photovoltaic generator i. introduction the increasing need for energy, the high cost of generating electricity, and the sunlight availability made necessary the exploitation of the advantages of power electronics and control techniques which improve the efficiency of solar systems [1]. the evolution and development of the solar generator is a challenge for researchers as an optimal solution to the production of low-cost power [2]. studying photovoltaic generators using state-space systems for mathematical modeling allows not only better understanding but also a modern, straightforward approach that will be based on a state feedback controller or an observer-based feedback controller. authors in [3-6] did not consider the dynamic behavior and the non-linearity of the photovoltaic system, especially the interaction with the converters, which transmit power to the load, nor did they deal with the reliability and stability of the closed-loop control system. hence, the impact of pv generators on power devices has been neglected [7]. in our case, we considered this effect because the non-linearity of the pv cell can affect the stability and robustness of the system. authors in [8-10] used classic maximum power point tracking (mppt) algorithms, such as perturb and observe (p&o) and incremental conductance (ic), as a way to control the converter [11]. instead of p&o mppt heuristics, a state feedback controller approach to achieve optimal operation was proposed, where the reference voltage of the pv systems is calculated by the p/u curve of the pv cells. in this approach, the maximum power point tracking is a set point controlled by regulating the output voltage of the pv array. furthermore, the dynamics of the system could be better tuned by pole-placement based on the knowledge of the system matrix, the input matrix of the plant, and the desired poles in the closed-loop system. authors in [12] adapted a state–space feedback approach to a dc-dc converter in pv systems. they used a linear model to represent the pv generator in the system matrix. in the model, the single diode equivalent circuit of the pv array was limited to the distribution level of the voltage source and equivalent resistance, so the behavior of the diode was neglected. authors in [13] also dealt with the pv array block using an equivalent linearized model of a voltage source, so the non-linearity of the generator was neglected, and the influence of the sun was not included in the control strategy. furthermore, the study did not consider load change scenarios and the influence of fluctuating sun irradiation on the closed-loop dynamics. the main contribution of the current work is a systematic state feedback controller design based on a proposed holistic state space model of the pv system that contains the model of the pv array as the current source, the averaging model of the boost converter, and the dc load. the state–space model has three state variables: the output voltage of the pv array, the current through the induction of the booster, and the voltage at the capacitor. the input variables are the controllable duty cycle and the incontrollable input of the sun irradiation. the controller validation is carried out using a detailed simscape model of the plant. the results are discussed and compared with well-established methods, such as power optimization by the mppt algorithm. ii. pv panel modeling in this section we will describe two modeling topologies for the single diode equivalent circuit of the pv array: one includes corresponding author: zeineb rania labidi engineering, technology & applied science research vol. 9, no. 2, 2019, 4030-4036 4031 www.etasr.com labidi et al.: a systematic controller design for a photovoltaic generator with boost converter using … the devices presented in simscape (block set/tool box in simulink/matlab) and the other includes the mathematical equations describing the component of the pv array using the state-space model approach. the state–space model is validated by comparing it with the simscape model. a. simscape model the pv array block presented in matlab/simulink is modeled according to system advisor model (sam) from the national renewable energy laboratory (nrel) to perform depending on the type and module defined [14-16]. the panel model defined in this work is kaneka gsa 060, the pv array contains 5 parallel strings, each string containing 5 modules connected in series to produce maximum power of 1.5kw at 1000w/m 2 . the characterizing i/u and p/u curves of the pv array are shown in figure 1. fig. 1. parameter curves of the pv generator b. state-space model the state–space model is illustrated by the state equations that contain the derivatives of the state variable that stores the energy as inductors and capacitances [17]. thus, by adopting kirchoff’s laws on the electrical circuit (figure 2) that represents the system, the state space equations are: ������ � � �� � �� � ��� � �� � �� ��� � � � � ��� (1) i�� � i� � i� (2) i� = i� �exp� � �! "–1% & � '() & � '() s+, (3) i� � ../01 2i�+,& α456 t6,88,: � t+,-,:�; (4) v= � > =? na n6,88 n5,+ (5) v� � vcd & r5icd (6) c. validation of the state-space model of the pv generator authors in [8, 12, 13, 17] did not take into account the pv panel as a non-linear independent system that could negatively influence the results of the approach used to control the boost converter for maximum power, especially in state-space modeling. hence, a separate modeling and study of the pv system is very important. shunt resistance and diode compensation elements must not be neglected when building the state space model because they strongly influence the dynamics of the system, and without them the results are not accurate and do not reflect the real behavior of the system (i.e. the pv cells). as shown in figure 3, we validated the state space model because pv voltage and current are identical to those extracted by the simscape model. fig. 2. singe diode equivalent electric circuit of the pv generator fig. 3. power under different values of irradiation and load power under different values of irradiation and load is power for the same values of irradiation (i.e. it never reaches maximum power). the direct connection between the pv array and the load does not give maximum power independently from sunlight or load. the direct installation is useful only if we have constant light irradiation and constant load [18]. then we need to choose the appropriate load for the available light, which is not practical, especially in an irregular system. iii. boost converter modeling in this section we will present the characteristics of the boost converter and the state–space model using averaging technique to extract the system and its input matrix. a. boost converter the boost converter shown in figure 4 is a switched-mode supply which can increase the input voltage to the desired output voltage [19]. its fundamental function is to cut the input voltage by switching it on and off very quickly, in which the transistor serves as the switch. the cutting consists of accumulating energy and transferring it to the load through interrupting the current cyclically. when the transistor is closed, the inductance l stores the energy in a magnetic form, so when the igbt is opened, the energy goes to the capacitor c to aliment the load while the inductance receives more energy from the source. the timing in switching on and off the 0 100 200 300 400 500 voltage (v) 0 2 4 6 array type: kaneka g-sa060; 5 series modules; 5 parallel strings 1 kw/m 2 0.8 kw/m 2 0.5 kw/m 2 0 100 200 300 400 500 voltage (v) 0 500 1000 1500 1 kw/m 2 0.8 kw/m 2 0.5 kw/m 2 engineering, technology & applied science research vol. 9, no. 2, 2019, 4030-4036 4032 www.etasr.com labidi et al.: a systematic controller design for a photovoltaic generator with boost converter using … transistor is very important because it allows a stable voltage for the load, which is called duty cycle. as described in [20], some design rules must be followed and verified for the boost converter to operate well: the load (r>r_pv) must always be superior to the resistance of the pv defined in (9) because the duty cycle must be between 0 and 1. equations (7) and (8) describe two other important properties of the boost converter: the input voltage must be less or equal (i.e. the case when the duty cycle is equal to 0) to the voltage output and the input current must be greater or equal to the current output. f � 1 � ����gh (7) f � 1 � ighi�� (8) j�� � ���i�� (9) fig. 4. circuit of the boost converter b. state space modeling of the boost converter in the first step, we validated the state–space model of the pv array connected to a simple load, as previously mentioned. this step is very important for the dynamic interactions between the pv block, the boost converter, and the load. the irradiation input strongly influences the system response, which is precisely the function of the controller. the next step is to add the boost converter, but without the feedback controller. we need to validate and compare this model with the simscape model so that we can work on the controller. in this stage, the control input of the boost is a pwm simscape device provided by simulink/matlab, in which the duty cycle is equal to 0.5. fig. 5. equivalent electrical circuit of the system the state equations of the system in on and off modes will be extracted according to the equivalent electrical circuit of the pv generator (figure 2) connected to the load through the boost converter presented in figure 4. using the averaging technique, a generalized model for both modes with three states is derived. the on mode of the system is illustrated in figure 6, where input is controllable. according to (2), the input �� , which represents the photogenerated current proportional to the sun light, is uncontrollable and can be considered a disturbance. equations (10)-(12) describe the state–space mathematic modeling of the on mode. ��kl�� � m�� � � � � �n� � m�� � & � �� � � � � ��� (10) �o�� = m� �n� � �p � �q�� � (11) ��gh�� � � m� ���r� �s� (12) fig. 6. on mode of the system equations (13)-(15) represent the dynamic state–space modeling of the off stage illustrated in figure 7. we note that (10) and (13) are equal, which is obvious because the dynamics of the system on the photovoltaic generator side do not change in the on and off modes. ��kl�� � � m�� � � � � �n� � m�� � & � �� � � � � ��� (13) �o�� � m� �n� � � � �r��p �r� � �p� �r��� " � � �� �r��� �s� � m� �t (14) ��gh�� � �� ���r� � � m� ���r� �s� (15) fig. 7. off mode of the system the differential equations of on and off modes can be summarized according to (16). the state space averaging system [21], which combines both time switches, is presented in (20) by using (17): uv w� � x u w� & y u� z w� & [ (16) uv w� � uv\] z & uv\^^ 1 � z� (17) where the input z is related to the switch mode: s=_ `a ; c`defg `a`ee; c`defg `ee with dhi z� � z , dhjj z� � 1 � z , u ∈ l0,1n . engineering, technology & applied science research vol. 9, no. 2, 2019, 4030-4036 4033 www.etasr.com labidi et al.: a systematic controller design for a photovoltaic generator with boost converter using … u= o�n���s�p � o umuqurp (18) z= �stopt" = �susv" (19) c. validation of the state–space model the state–space model is implemented in simulink/matlab and compared to the simscape model. figure 8 shows the simulation results under variable irradiation and load. the results demonstrate that the dynamic behavior of the state– space model is equivalent to the simscape model, which confirms the validation of the modeling. in addition, the design rules of the boost introduced above are verified. therefore, ���<�s� and ���>�s�is fulfilled according to (9) ,and j w jn�. (a) (b) (c) (d) fig. 8. comparison between simscape and state space (a), (b) for r=100 and (c), (d) for r=150 iv. state space feedback ontroller in this section, we will describe the steps used to build the integral state feedback controller. first, the system (20) around an operating point using the taylor series is linearized without neglecting the parts of the system. this step is important in dealing with the dynamic matching between the pv panel and the load impedance in the control design. uv � xy yy z� m�� � �� � � m �� 0m� � � � �r��p �r� � �p� �r��� " � �� �r��� 0 �� ���r� � m� ���r� {| || }~umuqur� +� � �� � �� �00 �zq+xy yz 0�r�� �q�r��q �� �r��� �q & �� �r��� �r & m� �t – �� ���r� �q {| |}zm &� 0� m�0 ��t (20) a. linearization of the state space equations the first step in building the controller is to linearize the state equation (20) around a stationary operating point (u�,z�), which is characterized as uv � � u�,z�� � 0 , where z� � �susv" and u� � oum�uq�ur�p , see (18) and (19). then: a u� & b u� �0.5 � 0 → x1 u� & y1 � 0 (21) by setting zm � 0.5 and zq � 1 (19) the matrices (20) in consideration of (21) are given as follows: x1= xy yy z� m�� � �� � � m �� 0m� ��� �r��p �r� � �p� �.�∗ �r�� �q�r��q ���� �r��� " – �.��� �r��� 0 �.��� ���r� � m� ���r� {| || } (22) y1 � � � �� � �� � �.�� �t0 � (23) then according to (21) the equilibrium value of u� is: u� � � ��� x1�y1 � ~21.15840.862443.1183� (24) after calculating the equilibrium point by imposing uv � 0, we linearize the system around that operating point by using taylor series. uv � � u�,z�� � 0 → ∆uv � x� ∆u & y� ∆z (25) where x� � � ���� ��su��� � � x & �� ���� zm" (26) and y� � � ���� ��su��su � y u��� (27) ∆u � u � u� ; ∆z � z � z� (28) from the state matrix of the system (20) we extract (29) and (30): engineering, technology & applied science research vol. 9, no. 2, 2019, 4030-4036 4034 www.etasr.com labidi et al.: a systematic controller design for a photovoltaic generator with boost converter using … x � xy yy z� m�� � �� � � m �� 0m� � � � �r��p �r� � �p� �r��� " � �� �r��� 0 �� ���r� � m� ���r� {| || } (29) y u� � xy yz 0�r�� �q�r��q �� �r��� �q & �� �r��� �r & m� �t � �� ���r� �q {| |} (30) by using (30), the derivate �� ���� is given: �� ���� � xy yz0 0 00 �r�� �q�r��q �� �r��� �� �r��� 0 � �� ���r� 0 {| |} (31) by adopting (29) and (31) we obtain x�, and by employing the operation point calculated in (24) and in (30) we obtain y� . x� and y� are the linearized state space matrices that we will use to calculate the gains for the state feedback controller. b. calculation of the gain first, we need to find the control law [22] of the linear state variables in (32). then we define the location of the desired closed loop poles by computing the eigenvalues of the open loop system. the poles are adjusted by moving them to the left. z � �� u (32) uv � x u & y z (33) uv � x u & y ��u� � x � y��u (34) � � eig a� (35) it is well known that by using (34), there will be a steady state error in the closed loop system. to compensate, an integral state is added [22]. in addition, u is set, which represents the duty cycle and not the output voltage of the pv generator. to achieve this, an augmented vector and matrices are added [27], taking into account the voltage to be set. figure 9 shows the state feedback loop of the controller according to (36). fig. 9. integral state feedback controller the control law of the feedback controller with an integrated control is presented below: z � ��� u & �i ¡ ¢ £w�� (36) uiv � ¤ u � ¥¦§^ � ¢ (37) with: ¢ � ¥ � ¥¦§^ ¨�£ ui � ¡ ¢ £w�� (38) using (33) and (37), the augmented state matrix becomes: ©uvuiv ª � �x 0¤ 0% u & �y0% z & � 0�1% ¥¦§^ (39) which results in the following feedback law: z � �l �« �in �uui% (40) where ¥ � l ¤ 0n �uui% and ¤ � l1 0 0 n. (41) the column vector x contains the state variables of the system presented in (18). after choosing the appropriate poles: p = [-150 -55+250i -55-250i -110] (42) the gain matrix k is determined by using ackerman’s formula implemented in matlab: k = acker(a,b,p) with k= l �« �in (43) which gives the following: �« � l0.0175 0.8236 � 0.0072n, �i � l3.2482n (44) c. choosing vref vref denotes the reference voltage and is adjusted so that the pv array can provide maximum power extraction. the reference voltage depends on the sun irradiation and the load. the design rules of the boost converter and the dynamic behavior of the system must be taken into consideration. let’s consider the case of ir=1000w/m 2 . five panels in series give: ����­nn® � 335 � (45) and five panels in parallel are equal to: ¯���­nn® � 4.5 x (46) (see table i), so by using (9): j�� ≅ 75 ω , and considering section iii, the load must be in this case equal to or greater than 75ω . ����­nn® � 5 ∗ ��±]§²�­nn® (47) ¯���­nn® � 5 ∗ ¯�±]§²�­nn® (48) ����­nn® � ����­nn® ∗ ¯���­nn® (49) we know that: � � j � (50) ¨�£ ����­nn® � �s� � � � (51) so by (50) and (51) we get: �s� � j �q → �s� � ´ngh� (52) r=100ω is chosen. then by using (49) and (52), idc=3.8826a. ipv-mppt=4.5a is calculated by (48). hence, by adopting (8), the duty cycle is equal to 0.1372, which matches the value given by the simulation shown in figure 11. engineering, technology & applied science research vol. 9, no. 2, 2019, 4030-4036 4035 www.etasr.com labidi et al.: a systematic controller design for a photovoltaic generator with boost converter using … according to (7) and (50) vref≅335v, which results in vref=vpvmppt. v. simulation and validation of the control approach figure10 shows the simulation results with the designed and implemented controller. it demonstrates the response of the system according to different values of irradiation (500, 1000, and 800), and it shows that the desired maximum power is reached for ir = [1000 800]. furthermore, the rules of the boost are verified, where ��� µ �s� , ��� w �s�, and the duty cycle is equal to the theoretical value given by (8). in addition, the pv voltage follows the reference value, whereby the state feedback controller is verified under variable irradiation. however, theoretically, the maximum power for ir=500w/m 2 must be 750w and not 500w. how can this be explained? let us take (52) with r=100ω and pdc=750w. we obtain idc=2.74a or in this case ipu=2.245. according to the rule of the boost, the photovoltaic current must be greater than the output current, which is impossible when r=100 ω. therefore, by using (52), r must be greater than 150ω. therefore, the maximum power that can be reached in this case is 500w. then by using r=160ω, and the correspondingly calculated voltage value vref the maximum power point is reached (figure 11). therefore, the system is robust because it will work under variable values of sunlight and load. fig. 10. curve of the states of the model with power and duty cycle for r=100 fig. 11. curve of the states of the model with power and duty cycle for r=160 vi. discussion and outlook based on the simulation results shown in figure 11, the predefined control objectives were achieved. for each considered irradiation, maximum power was reached under various loads. the boost was limited by some rules, which were discussed. because of the load change, the reference value needs to be recalculated to obtain desired maximum power. in some cases, the load will be less than rpv. to achieve maximum performance in such cases, a buck converter instead of a boost converter is required. as shown, boost or buck converter alone is not sufficient to operate a solar system autonomously in the optimal state at different loads. a buckboost converter is the solution for variable load. the value of the reference will not be changed because it will be generated automatically by the feedback loop of the controller. the behavior of the pv generator connected to a boost converter was demonstrated. a reliable and efficient method for controlling the boost converter was presented. the robustness of the control system was tested in load changes, and the influence of fluctuating solar radiation on the dynamics of the closed control loop was investigated. the next step in future research is to build a control design for a buck-boost converter and combine it with a wind turbine that operates a hybrid generator. appendix parameters of kaneka gsa 060 maximum power 60.3w voltage in mpp 67v current in mpp 0.9a open-circuit voltage 91.8v short-circuit current 1.19a engineering, technology & applied science research vol. 9, no. 2, 2019, 4030-4036 4036 www.etasr.com labidi et al.: a systematic controller design for a photovoltaic generator with boost converter using … references [1] v. khare, s. nema, p. baredar, “solar–wind hybrid renewable energy system: a review”, renewable and sustainable energy reviews, vol. 58, pp. 23-33, 2016 [2] irena, renewable energy technologies: cost analysis series. solar photovoltaics, vol. 1: power sector, no. 4/5, irena, 2012 [3] q. liand, p. wolfs, “a review of the single-phase photovoltaic module integrated converter topologies with three different dc link configurations”, ieee transactions on power electronics, vol. 23, no. 3, pp. 1320-1333, 2008 [4] r. ingudam, r. nayak, “modelling and performance analysis of dc-dc converters for pv grid connected system”, international journal of science, engineering and technology research, vol. 4, no. 5, pp. 13781390, 2015 [5] r. faranda, s. leva, “energy comparison of mppt techniques for pv systems”, wseas transactions on power systems, vol. 3, no. 6, pp. 446-455, 2008 [6] g. vijay, d. k. palwalia, “a novel analysis and modeling of boost and buck converter”, international journal of electronics, electrical and computational system, vol. 6, no. 3, 2017 [7] i. anand, s. senthilkumar, d. biswas, m. kaliamoorthy, “dynamic power management system employing single stage power converter for standalone solar pv applications”, ieee transactions on power electronics, vol. 33, no. 12, pp. 10352-10362, 2018 [8] m. s. jamri, t. c. wei, “modeling and control of a photovoltaic energy system using the state-space averaging technique”, american journal of applied sciences, vol. 7, no. 5, pp. 682–691, 2010 [9] s. jain, v. agarwal, “a new algorithm for rapid tracking of approximate maximum power point in photovoltaic systems”, ieee power electronics letters, vol. 2, no. 1, pp. 16-19, 2004 [10] s. s. kondawar, u. b. vaidya, “a comparison of two mppt techniques for pv system in matlab simulink”, international journal of engineering research and development, vol. 2, no. 7, pp. 73-79, 2012 [11] m. g. villalva, e. rupert f., “analysis and simulation of the p&o mppt algorithm using a linearized pv array model”, 35th annual conference of ieee industrial electronics, porto, portugal, november 3-5, 2009 [12] d. a. fernandes, m. k. vieira, m. a. vitorina, f. f. costa, p. c. ribeiro, “modeling and state-space feedback control of a dc-dc converter for photovoltaic systems”, 2014 ieee energy conversion congress and exposition (ecce), pittsburgh, usa, september 14-18, 2014 [13] m. c. mira, a. knott, o. c. thomsen, m. a. e. andersen, “boost converter with combined control loop for a stand-alone photovoltaic battery charge system”, 14th workshop on control and modeling for power electronics, salt lake city, usa, june 23-26, 2013 [14] n. blaire, a. p. dobos, j. freeman, t. neises, m. wagner, t. ferguson, p. gilman, s. janzou, system advisor model, sam 2014.1.14: general description, national renewable energy laboratory, 2014 [15] https://sam.nrel.gov/ [16] https://de.mathworks.com/help/physmod/sps/powersys/ref/pvarray.html [17] a. r. m. sahab, m. t. mirzaee, k. ghorbany, “the state space average model of boost switching regulator including all of the system uncertainties”, advanced materials research, vol. 403-408, pp. 3476– 3483, 2012 [18] c. cabal, optimisation energetique de l'etage d'adaptation electronique dedie a la conversion photovoltaique, phd thesis, universite toulouse iii paul sabatier, 2008 (in french) [19] i. batarseh, a. harb, power electronics: circuit analysis and design, springer, 2018 [20] k. kassmi, m. hamdaoui, f. olivie, “conception et modélisation d’un systeme photovoltaique adapte par une commande mppt analogique”, revue des energies renouvelables, vol. 10, no. 4, pp. 451-462, 2007 (in french) [21] y. chen, b. zhang, equivalent-small-parameter analysis of dc/dc switched-mode converter, springer, 2018 [22] g. f. franklin, j. d. powell, a. emami-naeini, feedback control of dynamic systems, addison-wesley publishing company, 2005 microsoft word etasr_v11_n4_pp7381-7385 engineering, technology & applied science research vol. 11, no. 4, 2021, 7381-7385 7381 www.etasr.com loumi & redjem: integration of gis and hierarchical multi-criteria analysis for mapping flood … integration of gis and hierarchical multi-criteria analysis for mapping flood vulnerability the case study of m'sila, algeria kahina loumi city, environment, society, and sustainable development laboratory university of m'sila, algeria kahina.loumi@univ-msila.dz ali redjem city, environment, society, and sustainable development laboratory university of m'sila, algeria ali.redjem@univ-msila.dz abstract-this paper proposes the integration of gis (geographic information system ) and hma (hierarchical multi-criterion analysis) offering a low-cost methodology to produce vulnerability maps. the quintessential role the rivers play in urban development has long been asserted and accepted. however, one of the subsequent consequences of these urban development activities is the increased frequency of floods. the case in point is the city of m’sila, algeria. the subject city was settled along the banks of a river known as oued el ksob, which undoubtedly had a significant influence on its development. in the last 50 years, m’sila has experienced significant spatial growth, especially in its north and northwest sides. as such, the work presented in this article aims to assess the vulnerability of the city to the risks of flooding. the approach used is based on the combined use of the hma method coupled with the gis. the process allowed the graphical representation of the resulting analysis of complex data of the territory, i.e. the mapping of its vulnerability to flooding. the map has four vulnerability categories ranging from low to very strong. the proposed system serves as an essential decision-making tool for local government officials. keywords-flood risk; vulnerability; gis; hierarchical multicriteria analysis; m'sila city i. introduction floods in urban arrears constitute a severe risk and have become more frequent and severe along with the rapid urban development [1]. the urbanization along the river banks has contributed to the increased risk, severity, and frequency of floods. this is one of the most common and destructive risks of natural disasters. the city of m’sila is a good case in point. m’sila is the capital of the m’sila province and is located on the plains of hodna, along oued el ksob river, between the saline lake chott el-hodna and a range of the tell atlas mountains. known as a farming and trading center, the city of m'sila derives its true geographical personality from its relative wealth of water [2]. the city it has been a site of numerous catastrophic floods, such as the one of september 23rd, 2007. although flooding is a natural phenomenon, the urban explosion that the city has experienced creates these risks. as such, our research focused on analyzing and assessing the city vulnerability to flooding through integrated risk management. this study also intended to provide a decision-making tool to minimize the frequency and the impact of flooding on m’sila and its inhabitants. to address the issue of urban growth impact on flooding risks requires a multi-criteria approach concerning several and different elements, conditions, and factors. such an approach, when associated with the geographic information system (gis), has been widely used in different contextual areas including flood management. it also plays a major role in developing reference maps for damage prevention and charting, the integration of any type of information, a better presentation of ideas and a better understanding of the scope of possible solutions [3]. the method has also been used successfully to assess a territory's vulnerability to flood risks [4-7]. ii. study area m’sila is a city in the north-central part of algeria. it is seated between 35°66’ and 36°75’ north latitude and between 4°47’ and 4°57’ east longitude. the land of the city used to be primarily agricultural. under the effect of human pressure, this situation has changed. this change is marked by the extension of artificial land and the decrease in agricultural areas as it is given in table i and figures 1-2. iii. methodology to conduct this study, the hierarchical multi-criteria analysis (hma) method [8] was adopted. this approach is ideal for quantifying and prioritizing complex problems into an orderly hierarchical structure of criteria and sub-criteria [9]. the approach in our case study is to assess the risk of flooding in the city of m’sila by applying gis features that take into account interpolation and recovery, based on multi-criterion analysis, in order to develop a vulnerability map. in addition, gis coupled with a multi-criterion analysis offers opportunities to study the risks of flooding incorporating all the relevant conditions and parameters. it also identifies and prioritizes impact factors [10]. the method as used herein is based on the steps described below. a. phase 1: evaluation criteria identification the evaluation criteria were identified in relation to the factors that have the greatest impact on the vulnerability or proneness of the city to flooding. judgments were, therefore, corresponding author: kahina loumi engineering, technology & applied science research vol. 11, no. 4, 2021, 7381-7385 7382 www.etasr.com loumi & redjem: integration of gis and hierarchical multi-criteria analysis for mapping flood … exercised between the following four parameters: (1) proximity to a water stream, (2) population density, (3) land use, and (4) terrain slope. each parameter or criterion was consequently linked to several categories. these categories were established in relation to the data from the study area. each evaluation resulted in a map representing, for all elementary surfaces, their suitability to the considered criterion [11]. these maps were obtained from digital aerial images taken based on satellite images dating as of 2020 from algeria's national institute of mapping and remote sensing. fig. 1. evolusion of population. (a) (b) (c) fig. 2. land use in (a) 1960, (b) 1990, (c) 2020. table i. evolution of land use in m'sila year 1960 1990 2020 artificial 19.26% 42.75% 81.09% farm 37.18% 29.08% 9.00% brush 12.09% 8.55% 19.62% naked 31.47% 19.62% 9.85% population 35,377 113,683 238,689 b. phase 2 : weighting criteria the process of calculating the relative importance of each criterion is known as the standardization of the criteria [12]. the comparative weight scale as used in this study is given in table ii. table ii. comparative scale scale description 1 equal importance of two elements. 3 one element is a little more important than the other. 5 one element is more important than the other. 7 one element is much more important than the other. 9 one element is much more important than the other. 2, 4, 6, 8 intermediate values between two judgments. c. consistance verification in order to check that the transitivity of our judgment was respected, the author in [13] proposes the following mathematical formula: ic � ����� �� �� � (1) where ic is the consistency index, n is the number of elements compared, λmax is the average saaty matrix values of own vectors that indicates the order of priority or hierarchy of the studied characteristics. the consistency ratio (rc) is calculated by: rc � �� �� (2) where ia is defined as the random index of a matrix of the same size presented in table iii. table iii. random index n 1 2 3 4 5 6 7 ia 0 0 0.58 0.9 1.12 1.24 1.32 d. phase 4: aggregation of criteria this operation consisted of multiplying each factor layer by its respective weighting as confirmed in the hierarchical structure [14]. then, the ahp method is used, in combination with the integration of the criteria cards in accordance with their weight on the gis software, through a linear combination method of weighting in order to obtain a summary map. iv. results and discussion the results of the pairwise comparison of the sub-criteria relatively to the criteria considered for our case study are summarized in table iv (the comparison matrix is standardized so that the sum of all weights is equal to 1). engineering, technology & applied science research vol. 11, no. 4, 2021, 7381-7385 7383 www.etasr.com loumi & redjem: integration of gis and hierarchical multi-criteria analysis for mapping flood … regarding the results, we have rc = 0.095, so the consistency ratio is less than 0.1 which allows us to state that the judgments for the assessment of the criteria have been consistent. table iv. pairwise comparison results criterion categories rank weight terrain slope 0-3 3-6 6-9 9-12 12 > 7 6 4 2 1 0.511 0.262 0.118 0.067 0.041 proximity to a water stream 0-50 50-200 200-500 500-800 800> 9 7 5 3 1 0.518 0.263 0.129 0.063 0.032 population density 0-60 60-600 600> 1 3 7 0.087 0.444 0.467 land usage building industrial bare soil vegetation 9 7 1 3 0.628 0.254 0.399 0.771 the evaluated criteria are mapped in the figures 3-6 using the spatial analysis functionalities of gis. the layers with a common, registered map base are joined on the basis of their occupation of space. these outputs can reflect simple operations such as laying a road map over a map of local wetlands to determine averages and co-occurrences [15]. the result of the sum of the different criteria maps according to their weight under the arc gis software allowed obtaining the decision-making spatial reference map shown in figure 7. the interpretation of the resulting map allowed us to discuss the relationship between the urban growth and the risk of flooding. the map shows flood potential areas. the level of risk varies from one residential area to another. this level of risk is higher primarily in the northern and northwestern districts of the city, which have experienced significant urban extensions. these areas of greater flood concern include the two colonial and historical quarters, el-kouch and el argoub that are considered as the central nucleus of the city which were built at the edges of oued el ksob. large land areas have been used for urbanization purposes resulting in significant increase in population density. this accelerated rate of urbanization has generated multiple challenges and environmental issues. the growth of the city of m'sila constitutes a form of urbanization that has become widespread encroaching onto agricultural lands. the diachronic analysis of land use has shown an increase in built-up areas. this urbanization is intensifying at the expense of agricultural land because the areas open to urbanization do not always meet the increasing needs of the population. moreover, these changes in land use, associated with urban development, affect flooding risk. in urbanized areas, much of the permeable soil is replaced by impermeable infrastructure such as roads and buildings, minimizing its capacity to store rainfall and water. after the construction of any dam, the fluvial regime of the river is subjected to consequential change and its system or pattern of erosion may undergo metamorphosis. fig. 3. population density mapping. fig. 4. terrain slop mapping. dam construction alters the amount of sediment production, retention and transportation of the sediments in the system [16]. as a result, rain, which used to penetrate the ground, now flows directly into streams, increasing their flow. furthermore, buildings on floodplains can interfere with the passage of flood waters. the entropic risks are driven by the strong demographic engineering, technology & applied science research vol. 11, no. 4, 2021, 7381-7385 7384 www.etasr.com loumi & redjem: integration of gis and hierarchical multi-criteria analysis for mapping flood … changes coupled with the creation of new residential areas in the northern territory of the city. fig. 5. proximity to a water slop mapping. fig. 6. land used mapping. fig. 7. overall vulnerability mapping. v. conclusion the city of m’sila is built on the banks of the oued elksob between the mountain ranges that make it a natural water collector. due to this reason the subject land was initially and mainly agricultural. the villages used to be established in elevated areas in order to minimize flood risk. but under the influence of human pressure, the situation has changed. this change is marked by the extension of artificialized land to agricultural spaces, which has aggravated, or even created hazardous conditions. this growth of building has also resulted in a dense concentration of populations over restricted spaces, which mechanically increases risk exposure. the city is increasingly spreading in areas of flat reliefs and around several water points where flood overflows can spread out. the inadequate work on waterways promotes flooding possibility in urban areas and increases the vulnerability of exposed areas, or, for the most localized events, a worsening of flows. the hma method used in our research allowed us to study the risk of flooding, integrating all the parameters relating to the studied area. it also enabled us to determine the extent of flooded areas at the intra-urban level of the city as well as the water height at all points of these areas. this technique can play an important role, not only in terms of specific applications for urban risk management, but also in timely disseminating information to public and private stakeholders involved in the prevention and management of this risk. references [1] t. l. dammalage and n. t. jayasinghe, "land-use change and its impact on urban flooding: a case study on colombo district flood on may 2016," engineering, technology & applied science research, vol. 9, no. 2, pp. 3887–3891, apr. 2019, https://doi.org/10.48084/etasr.2578. engineering, technology & applied science research vol. 11, no. 4, 2021, 7381-7385 7385 www.etasr.com loumi & redjem: integration of gis and hierarchical multi-criteria analysis for mapping flood … [2] p. veyret, "le hodna (algérie)," revue de géographie alpine, vol. 42, no. 2, pp. 411–413, 1954. [3] a. ghosh and s. k. kar, "application of analytical hierarchy process (ahp) for flood risk assessment: a case study in malda district of west bengal, india," natural hazards, vol. 94, no. 1, pp. 349–368, oct. 2018, https://doi.org/10.1007/s11069-018-3392-y. [4] f. aibout, m. chouieb, d. baghadi, a. benaradj, and s. miloud, "contribution des sig à la gestion des risques naturels. détermination des milieux vulnérables au risque inondation dans le nord-ouest algérien," revue internationale de géomatique, vol. 24, no. 4, pp. 431– 450, dec. 2014, https://doi.org/10.3166/rig.24.431-450. [5] s. das, "geographic information system and ahp-based flood hazard zonation of vaitarna basin, maharashtra, india," arabian journal of geosciences, vol. 11, no. 19, sep. 2018, art. no. 576, https://doi.org/ 10.1007/s12517-018-3933-4. [6] e. s. mokhtar, b. pradhan, a. h. ghazali, and h. z. m. shafri, "assessing flood inundation mapping through estimated discharge using gis and hec-ras model," arabian journal of geosciences, vol. 11, no. 21, p. 682, nov. 2018, https://doi.org/10.1007/s12517-018-4040-2. [7] y. o. ouma and r. tateishi, "urban flood vulnerability and risk mapping using integrated multi-parametric ahp and gis: methodological overview and case study assessment," water, vol. 6, no. 6, pp. 1515–1545, jun. 2014, https://doi.org/10.3390/w6061515. [8] b. roy, méthodologie multicritère d’aide à la décision. paris, france: economica, 1985. [9] m. s. tehrany, m.-j. lee, b. pradhan, m. n. jebur, and s. lee, "flood susceptibility mapping using integrated bivariate and multivariate statistical models," environmental earth sciences, vol. 72, no. 10, pp. 4001–4015, nov. 2014, https://doi.org/10.1007/s12665-014-3289-3. [10] a. c. le gall, "panorama des méthodes d’analyse multicritère comme outils d’aide à la décision," onema-ineris, paris, france, study report, 2009. [11] f. joerin, "méthodes multicritères d’aide à la décision et sig pour la recherche d’un site.," revue internationale de géomatique, vol. 5, no. 1, 1995, art. no. 15. [12] t. l. saaty, the analytic hierarchy process. new york, ny, us: mcgraw-hill, 1980. [13] t. l. saaty, método de análise hierárquica. sao paolo, brazil: mcgraw-hill, 1991. [14] k. p. yoon and c.-l. hwang, multiple attribute decision making: an introduction, 1st ed. thousand oaks, ca, usa: sage publications, inc, 1995. [15] k. clarke, getting started with geographic information systems, 5th ed. upper saddle river, nj, usa: pearson, 2010. [16] a. liaghat, a. adib, and h. r. gafouri, "evaluating the effects of dam construction on the morphological changes of downstream meandering rivers (case study: karkheh river)," engineering, technology & applied science research, vol. 7, no. 2, pp. 1515–1522, apr. 2017, https://doi.org/10.48084/etasr.969. microsoft word 43-2949_s_etasr_v9_n4_pp4543-4547 engineering, technology & applied science research vol. 9, no. 4, 2019, 4543-4547 4543 www.etasr.com pirzadeh & aminlari: effects on the physiochemical properties of stored pomegranate seeds by the … effects on the physiochemical properties of stored pomegranate seeds by the application of aloe vera gel as coating agent maryam pirzadeh department of food science and technology, faculty of agriculture, sarvestan branch, islamic azad university, sarvestan, iran mahmoud aminlari department of biochemistry, school of veterinary medicine, shiraz university, shiraz, iran abstract—pomegranate has drawn the attention of dieticians and medicinal chemists due to its bioactive components. natural coatings increase the shelf life of such agriculture products and reduce the risks associated with the use of chemical preservatives. hence, we examined the effects of aloe vera coating on the pomegranate fruit. aloe vera gel coating was utilized in three proportions of 25%, 33%, and 50%, and its effects on the pomegranate seeds were compared with a control sample. experiments including moisture reduction, weight loss, sugar content, sensory properties, antioxidant capacity, and microbial analysis were performed over a period of 4 weeks. results revealed that the percentage of moisture reduction in 50% aloe vera coated sample was lower than in other groups, and the mildew and yeast in these samples were less than in the other groups. however, the 50% aloe vera gel showed the highest level of contamination, over time. furthermore, the 50% aloe vera gel showed higher sugar content, and over time the amount of sugar reduction in the 50% aloe vera was lower. additionally, the percentage of weight loss in samples coated with aloe vera was lower than the control group, and in the 50% aloe vera group it was less than in the other groups. keywords-pomegranate; aloe vera; edible coating; shelf life; physiochemical properties i. introduction pomegranate (punica granatum) is assigned to punicaceace family, punica genus and granatum species. the fruit is characterized with red or yellow skin, composed of clustered seeds, and consists of 82% water, 0.4% protein and 83kcal energy per 100g [1, 2]. it contains minerals like potassium and magnesium, which have effective impact on blood clearance, and the presence of phenolic compounds bestows anti-tumor properties [3]. long-term storage and edible coatings are by far the most common preservation techniques for pomegranate seeds. in edible coating, pomegranate seeds are embedded using plant-derived materials [4]. natural derivative components should be neutral, transparent, clear, colorless and flavorless in order to be applicable as layering agents [5]. postharvest quality maintenance of fruits and vegetables kept by edible coated process, extensively depends on inhibiting moisture content reduction, being less intense of biological activity associated with ripening stages, and, in particular, to turn down microbial activities. therefore, coatings are mainly performed to postpone moisture loss, inhibit microbial growth, diminish respiratory rate, prevent the occurrence of nonenzymatic browning, and reduce appearance defects such as ofnotes and bad color [4, 6]. the main types of coating materials that can be discerned are waxes and paraffin [7], polishing resins [8], gelatin, corn zein [4], gluten-based [7], soy proteinbased [4], edible chitosan [7] and aloe vera gel coatings [4]. aloe vera is extensively cultivated due to its high agricultural and medical advantages [8, 9]. derived compounds from aloe vera leaves and gel are considered medicinal agents. the gel is often yellow due to the presence of anthraquinones existing in the forms of free and glycosylated [9]. the aloe vera gel contains over 200 active ingredients such as essential minerals and vitamins, folic acid, polysaccharides, fats, proteins, and 18 amino acids [9-10]. bio-technically, the gel coated fruits or vegetables are protected against mechanical damaged cells through reduction of the activity of methyl ester pectin, polygalacturonase and beta-galactosidase. other than that, aloe vera gel can act against pathogens. in combination with gel, it can be integrated with antimicrobial agents. additionally, the gel can prevent loss of fruit juice, surround stoma in a coating layer and therefore alleviate the rate of gas flows through fruit skin. the gel modifies the inner atmospheric composition of a packaged food e.g. increasing co2 and decreasing o2, which results in less production of ethylene in climacteric fruits [4]. it helps maintain the content of soluble solids and organic acids of the fruit. it prevents weight loss and preserves the color of the fruit, as well as increases its longevity [11]. this study aims to study the impact of pomegranate coated by aloe vera gel on quality and shelf life. ii. materials and methods pomegranate fruits were selected on the basis of shape, size, uniformity, color and damage. any fruits with injuries and disease were discarded, and the selected ones were washed and grinded in the strainer. mature aloe vera leaves were harvested and washed, then gel matrix containing section was extracted and ground in a mixer, and the final produced gel was stored in the refrigerator [12]. the pomegranate seeds were distributed into 4 groups (5kg each), so a total of 20kg of seeds was used. corresponding author: maryam pirzadeh (pirzadeh224@yahoo.com) engineering, technology & applied science research vol. 9, no. 4, 2019, 4543-4547 4544 www.etasr.com pirzadeh & aminlari: effects on the physiochemical properties of stored pomegranate seeds by the … a. treatments the aloe vera gel was dissolved in distilled water in a 5000ml container. sample group a was selected as the control (untreated pomegranate seeds, and b, c, d group samples of pomegranate seeds were dipped in 50%, 33% and 25% aloe vera gel solution respectively (figure 1) [12-15]. the treated and non-treated samples were filtered using filter papers, widespread on several trays and were allowed to be dried at 50°c for 1.5h. the dried seeds were distributed in 12 separate sections (380g each) and were put in dishes and kept in refrigerator at 4°c for one month. consequently, the samples of each treatment were evaluated at 7-day intervals [6, 11]. fig. 1. provided pomegranate treatments b. moisture content to assess weight loss, samples of each treatment were selected, prepared in accordance with [11], and evaluated in 7day time intervals. weight loss is determined by: weight loss (%)=(m1-m2)/m1×100 (1) where m1 indicates fruit weight before drying, and m2 indicates fruit weight loss after storage time interval. c. microbial analysis the microbiological shelf life was determined using ygc1 medium following the method used in [14]. to assess the microbial part, 3 replicates were used for each treatment in 7day intervals. d. antioxidant activity antioxidant activity was measured using dpph method, where free radicals are being scavenged by 2-diphenyl-1hydrazilicircin (dpph) as a lipophilic radical with a maximum absorption of 517nm wavelength. the dpph solution was prepared on the basis of the method described in [16]. briefly, 0.0035g ddph were dissolved in 150ml methanol, and the solution was stored at 4°c in the dark [16]. an equal proportion of dpph solution (4cc) and samples (4cc) were transferred to 16 test tubes and stored in the dark (group b). in addition, equal ratio of dpph solution (4cc) and water (4cc) were transferred to the test tube and stored in the dark as group a. the absorbance was measured at 517nm and the activity expressed using following equation: rsa=(acontrol-asample)/acontrol ×100 (2) where rsa is radical scavenging activity, acontrol represents the absorbance amount of control, asample represents the absorbance amount of sample. e. reducing sugar content the reducing sugar content of the samples was measured using the fehling method. to prepare sample, 25g of pomegranate seeds were weighed and grounded, the obtained juice was transferred to a 100ml balloon and 2ml of saturated led acetate were added and distilled water was added until the total volume reached 100ml. aliquot of 10ml was titrated on the bases of fehling method. sugars were determined as the percentage of glucose by the following equation: � � ��������� ��� )3( the consumed volume of the solution was recorded and the regenerative sugars were calculated using (3), where f=fehling factor, v=the dissolved volume in mm and n=pre-hydrolysis reducing sugars in grams per 100g. f. weight loss samples were selected from the 4 treatments and their weight was measured as initial weight. then, consequently, their weight was measured in 7-day intervals during the total storage time of 1 month. weight loss was expressed using (4): ( ) % 100 initial weight secondary weight initial weight weight loss − = × (4) g. sensory evaluation to assess sensory characteristics, friedman test was used to express the impacts of coating on sensorial properties including color, taste and water content during the experiment. ten nontrained participants were asked to evaluate the above characteristics based on scale ranging from extremely like to extremely dislike [14]. h. statistical analysis the obtained results were subjected to anova test. to analyze data, spss software (version 22) and microsoft excell (version 2015) were used. iii. results and discussion loss of moisture content was significant during the storage of coated seeds. in general, reduction of moisture might occur due to dehydration, transpiration and metabolic activity. our results revealed that as gel concentration increases, it acts as a polysaccharide barrier, leading to less reduction of moisture owing to the hygroscopic gel nature which prevented water evaporation. the results were in accordance with similar studies on strawberries and peach saffron [12, 15] (table i). table ii represents the obtained results for weight loss of treatments during the experiment period. studies on apples and grapes exhibited that non-coated samples had more weight loss compared to the coated ones [14, 17]. these results are in accordance with the results on the application of aloe vera gel (2%) to extend the shelf life of green tomato [18]. the obtained results revealed that non-coated samples had the most weight loss. furthermore, the control samples exhibited the least uniformity of membrane among all samples. our results also found that weight loss increased during the experimental period (4 weeks) while the rate of weight loss increased in the control samples. engineering, technology & applied science research vol. 9, no. 4, 2019, 4543-4547 4545 www.etasr.com pirzadeh & aminlari: effects on the physiochemical properties of stored pomegranate seeds by the … table i. moisture content d urin g storage treatments a b c d 1 st week frequency 3 3 3 3 average 62.63 67.20 64.73 62.54 f value 14.39** 2 nd week frequency 3 3 3 3 average 59.41 66.42 62.30 60.03 f value 15.96** 3 rd week frequency 3 3 3 3 average 57.14 66.03 60.47 59.21 f value 43.61** 4 th week frequency 3 3 3 3 average 55.63 64.30 58.74 57.96 f value 34.85 table ii. lo st weight during storage treatments a b c d 1 st week frequency 3 3 3 3 average 0.29 0.17 0.17 0.19 f value 0.99** 2 nd week frequency 3 3 3 3 average 0.84 0.51 0.54 0.58 f value 161.33** 3 rd week frequency 3 3 3 3 average 1.03 0.69 0.84 0.96 f value 511.19** 4 th week frequency 3 3 3 3 average 2.22 0.96 1 10.04 f value 860.76** aloe vera gel acted as a hygroscopic polysaccharide barrier inhibiting moisture loss, similar to the findings in [19] where authors studied sapota fruit with aloe vera gel coating. aloe vera gel creates a protecting layer preventing moisture loss and at the same time inhibits ethylene production. the results summarized in table iii depict that after the first week of storage, the minimum decay was in sample b (containing 50% aloe vera) followed by treated seeds with 33% and 25% gel, whereas seed sample group a (control) had the utmost decay after the 4th week of storage. table iii. micro bial an alysis d urin g sto rage treatments a b c d 1 st week frequency 3 3 3 3 average 53.66 5.66 8.33 33 f value 35.13** 2 nd week frequency 3 3 3 3 average 63 46.33 54 63.33 f value 4.53** 3 rd week frequency 3 3 3 3 average 80.66 70.33 54 63.33 f value 9.62** 4 th week frequency 3 3 3 3 average 97.33 246.66 11.33 73 f value 27.05** the switch to culmination of decay in the 4th week of experiments could be detailed due to the contamination of aloe vera gel. as the gel proportion increased, in particular in the sample containing 50% gel, more deterioration was exhibited. authors in [14] reported that coated grapes by aloe vera gel faced significant microbial reduction, while non-coated samples exhibited increasing amount of yeast and mold. in addition, aloe vera gel harnessed the growth of mycelium. similar results were reported in [20]. indonesian fruit (1.5%) and aloe vera gel (20%) mitigated the microbial population. aloe vera gel causes reduction of microbial problems and prevents ascorbic acid reduction in matured fruits. additionally, it can be suggested to substitute conventional layers in fresh-cut fruits [21]. a. antioxidant level reduction of ethylene production and aging rate along with lower respiratory rate are possible reasons associated with the higher level of antioxidants in the last week of the experiment. some ingredients found in aloe vera such as vitamins and ascorbic acid could be regarded as other possible reasons (table iv). authors in [19] found that the combination of salisylic acid and 33% aloe vera gel can protect the antioxidant capacity of grape. similarly, a protecting effect was shown on strawberry due to the antioxidant capacity of aloe vera [15]. table iv. amount of scaven ging dpph exposed to seed juices treatments a b c d 1 st week frequency 3 3 3 3 average 88.09 76.18 73.80 73.80 f value 1.50 ns 2 nd week frequency 3 3 3 3 average 90.47 80.95 78.7 80.95 f value 6.55** 3 rd week frequency 3 3 3 3 average 90.47 85.71 83.33 83.33 f value 2.66 ns 4 th week frequency 3 3 3 3 average 92.85 85.71 88.09 90.47 f value 0.83 ns ns: no significant differences b. reducing sugar the amount of reducing sugar followed a reducing trend during the experiment period. the samples containing the higher percentage of gel showed the least reduction due to better surrounding seeds during coating (table v). the sugar content exhibited increase compared to control in the initial stages of the experiment. upon storage, sugar components degraded to smaller units, producing carbon dioxide. table v. percentage of reducing sugar durin g storage treatments a b c d 1 st week frequency 3 3 3 3 average 14.28 16.57 15.58 14.95 f value 18.53** 2 nd week frequency 3 3 3 3 average 12.56 15.92 14.68 13.33 f value 7.78 3 rd week frequency 3 3 3 3 average 11.05 14.95 13.18 11.60 f value 123.74** 4 th week frequency 3 3 3 3 average 10.05 13.56 11.13 10.05 f value 7** c. sensory evaluation the friedman test was used to evaluate sensorial property assessment on juice, color, and taste on the basis of dedicated engineering, technology & applied science research vol. 9, no. 4, 2019, 4543-4547 4546 www.etasr.com pirzadeh & aminlari: effects on the physiochemical properties of stored pomegranate seeds by the … scoring. in coated samples, no improved properties were found at the final time interval (tables vi-viii). some recent studies report increase in the quality of aloe vera coated food [22-24]. table vi. friedman test: mo isture treatment moisture frequency average x 2 sig a 1 st week 10 3.60 27.22 0.000 2 nd week 10 3.30 3 rd week 10 1.65 4 th week 10 1.45 b 1 st week 10 3.65 26.92 0.000 2 nd week 10 3.25 3 rd week 10 1.75 4 th week 10 1.35 c 1 st week 10 3.65 25.53 0.000 2 nd week 10 3.15 3 rd week 10 1.85 4 th week 10 1.35 d 1 st week 10 4 27 0.000 2 nd week 10 2.20 3 rd week 10 2.05 4 th week 10 1.75 table vii. friedman test: taste treatment taste frequency average x 2 sig a 1 st week 10 3.55 29.09 0.000 2 nd week 10 3.45 3 rd week 10 1.60 4 th week 10 1.40 b 1 st week 10 3.60 28.69 0.000 2 nd week 10 3.40 3 rd week 10 1.65 4 th week 10 1.35 c 1 st week 10 3.10 28.71 0.000 2 nd week 10 2.95 3 rd week 10 2.95 4 th week 10 1 d 1 st week 10 3.50 29.41 0.0000 2 nd week 10 3.50 3 rd week 10 1.60 4 th week 10 1.40 table viii. friedman test: color treatment color frequency average x 2 sig a 1 st week 10 3.65 28.92 0.000 2 nd week 10 3.35 3 rd week 10 1.55 4 th week 10 1.45 b 1 st week 10 3.60 28.69 0.000 2 nd week 10 3.40 3 rd week 10 1.65 4 th week 10 1.35 c 1 st week 10 3.20 27.81 0.000 2 nd week 10 2.90 3 rd week 10 2.90 4 th week 10 1 d 1 st week 10 3.60 28.60 0.000 2 nd week 10 3.40 3 rd week 10 1.70 4 th week 10 1,30 iv. conclusion in conclusion, the application of aloe vera gel coating on pomegranate seeds had beneficial effects in delaying the loss of physiochemical and microbial quality. this treatment acts as barrier against the loss of moisture content. additionally, as the concentration of the aloe vera gel increases, the percentage of decomposing sugar is mitigated. decay was observed to follow a growingly trend up to the end of experiment, in particular in sample b, that contained 50% aloe vera gel in coating treatment. regarding the sensory evaluatin, the obtained results revealed no significant impact the coated pomegranate seeds during the experiment. references [1] https://iranfreshfruit.biz/pomegranate/ [2] n. ahmadi, r. nourbakhsh, m. faraji, g. h. fadavi, “survey on the some specifications for 8 major varieties of iranian pomegranate”, iranian journal of nutrition sciences & food technology, vol. 5, no. 5, pp. 77-82, 2013 (in persian) [3] a. tehranifar, m. zarei, z. nemati, b. esfandiyari, m. r. vazifeshenas, “investigation of physico-chemical properties and antioxidant activity of twenty iranian pomegranate cultivars”, scientia horticulturae, vol. 126, no. 2, pp. 180-185, 2010 [4] p. k. raghav, n. agarwal, m. saini, “edible coating of fruits and vegetables: a reiview”, international journal of scientific research and modern education, vol. 1, no. 1, pp. 188-204, 2016 [5] s. mirnezami-ziabari, the principles of food packaging, aeeij publication, 2002 (in persian) [6] a. mortazavian, m. azizi, s. sohrabvandi, “edible films: qualitative markers and production methods”, food science and technology, vol. 7, no. 27, pp.107-117, 2001 (in persian) [7] t. bourtoom, “edible films and coating: characteristics and properties”, international food research journal, vol. 15, no. 3, 2008 [8] f. mousavi, m. steaki, aloe vera plant for a thousand treatments, nasouh publication, 2002 (in persian) [9] m. abdolalian, aloe vera, hormozgan jehad keshavarzi publication, 2002 [10] c. t. ramachandra, p. srinivasa rao, “processing of aloe vera leaf gel: a review”, american journal of agricultural and biological sciences, vol. 3, no. 2, pp. 502-510, 2008 [11] j. misir, f. h. brishti, m. m. hoque, “aloe vera gel as a novel edible coating for fresh fruits: a review”, american journal of food science and technology, vol. 4, no. 3, pp. 93-97, 2014 [12] s. r. karimi akandi, s. minaee, t. tavakoli hashjin, g. najafi, s. s. ghodsi, “mechanical properties of (aloe vera l.) leaf for designing gel extraction machines”, journal of agricultural science and technology, vol. 19, no. 4, pp. 809-820, 2017 (in persian) [13] s. l. marpudi, l. s. s. abirami, r. pushkala, n. srividya, “enhancement of storage life and quality maintenance of papaya fruits using aloe vera based antimicrobial coating”, indian journal of biotechnology, vol. 10, pp. 83-89, 2011 [14] g. m. valverde, d. valero, d. m. romero, f. guillen, s. castilo, m. serrano, “novel edible coating based on aloe vera jel to maintain table grape quality and safety”, journal of agricultural and food chemistry, vol. 53, no. 20, pp. 7807-7813, 2005 [15] s. h. vahdat, r. f. ghazvini, m. ghasemnejad, “effect of aloe vera gel on maintenance of strawberry fruits quality”, agris, vol. 877, no. 2, pp. 919-923, 2010 [16] m. s. shiban, m. m. al-otaibi, n. s. al-zoreky, “antioxidant activity of pomegranate (punica granatum l.) fruit peels”, food and nutrition sciences, vol. 3, no. 7, pp. 991-996, 2012 [17] m. ergun, f. satici, “use of aloe vera jel as biopreservative for ‘granny smith’ and ‘red chief’ apples”, journal of animal and plant sciences, vol. 22, no. 2, pp. 363-368, 2012 engineering, technology & applied science research vol. 9, no. 4, 2019, 4543-4547 4547 www.etasr.com pirzadeh & aminlari: effects on the physiochemical properties of stored pomegranate seeds by the … [18] t. t. chandran, c. mini, “aloe vera gel as a bio preservative for shelf life extension of mature green tomato”, international journal of food science and nutrition, vol. 3, no. 5, pp. 44-46, 2018 [19] a. macwan, b. joshi, a. macwan, “edible coating and irradiation of sapota fruit: a concise review”, international journal of chemical studies, vol. 6, no. 3, pp. 1908-1910, 2018 [20] t. w. augustini, s. a. eko, m. a. ismail, m. r. shafiur, “effect of alloe vera (alloe vera) and crown of god fruit (phaleria macrocarpa) on sensory, chemical, and microbiological attributes of indian mackerel (restrelliger neglectus) during ice storage”, international food research journal, vol. 19, no. 1, pp. 119-125, 2018 [21] s. benitez, i. achaerandio, f. sepulcre, m. pujola, “aloe vera based edible coatings improve the quality of minimally processed ‘hayward’ kiwi fruit”, postharvest biology and technology, vol. 81, pp. 29-36, 2013 [22] b. ozturk, o. karakaya, k. yildiz, o. saracoglu, “effects of aloe vera gel and map on bioactive compounds and quality attributes of cherry laurel fruit during cold storage”, scientia horticulturae, vol. 249, pp. 31-37, 2019 [23] t. k. mendy, a. misran,t. m. m. mahmud, s. i. ismail, “application of aloe vera coating delays ripening and extend the shelf life of papaya fruit”, scientia horticulturae, vol. 246, pp. 769-776, 2019 [24] s. sharifimehr, n. soltanizadeh, s. a. h. goli, “physicochemical properties of fried shrimp coated with bio-nano-coating containing eugenol and aloe vera”, lwt, vol. 109, pp. 33-39, 2019 microsoft word 08-3348_s_etasr_v10_n2_pp5387-5391 engineering, technology & applied science research vol. 10, no. 2, 2020, 5387-5391 5387 www.etasr.com khaskheli et al.: emission and noise characteristics of a diesel engine fuelled with diesel-chicken … emission and noise characteristics of a diesel engine fuelled with diesel-chicken oil biodiesel blends abid ali khaskheli department of mechanical engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan abidali_lifeskill@yahoo.com haris jawad arain department of energy & environmental engineering, quaid-e-awam university of engineering, science and technology nawabshah, pakistan harisjawad@quest.edu.pk imdad ali memon department of mechanical engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan engineerimdad@yahoo.com umair ahmed rajput department of mechanical engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan engineer.umair@quest.edu.pk muhammad junaid ahsan department of energy & environmental engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan mjunaidahsan@quest.edu.pk abstract—biodiesel is a renewable, safe, environmentally friendly, and significant source of energy which produces a lesser amount of greenhouse effect gasses. the biodiesel source is local chicken frying oil, synthesized by the trans-esterification process. in this research, the particulate matter (pm) exhaust gas emissions and sound emissions are examined. emissions such as pm (pm1.0, pm2.5, pm7.0, and pm10), nitric oxides (i.e. no and no2), co, co2, and noise were investigated at variable loads with constant engine speed. fuel samples, i.e. pure diesel (d100) and 20% biodiesel (b20) and 30%biodiesel (b30) blends were tested. conventional diesel was found to emit more particulate and sound emissions, while b30 had lower emissions than b20 and conventional diesel. the lowest average values regarding exhaust gas emissions was 0.00690ppm for pm1.0, 7.44ppm for no2, and 190.727ppm for co, presented in b30. however, emissions from the engine decreased with increase in the blending ratio of biodiesel. furthermore, the lowest average value of co2 was found in b30 and was about 1.457%. keywords-chicken frying oil; b20; b30; emissions; noise; engine i. introduction vehicles are almost entirely fuelled by internal combustion engines which burn fossil fuels such as liquefied petroleum gas (lpg) and oil. but global fossil fuel reserves are limited and in the not so distant future will become depleted. the most prominent alternative to the classic internal combustion engine is undoubtedly electric vehicles (evs). in recent years, interest in electric cars has been growing, and over the past decade, ev production has increased dramatically by 1500% [1]. nowadays, millions of people suffer from severe illnesses and even die from causes such as cancer, respiratory diseases, cardiovascular diseases, vision loss, etc. which are affiliated with hazardous exhaust gases produced by fossil fuel engines. besides, many countries, which have signed the kyoto protocol, fail to comply with their obligation to lower their level of greenhouse gases. the addition of nanoparticles to diesel is one of the most effective ways of converting diesel to a cleaner source of energy [2]. biodiesel is considered as an improved, renewable, and non-hazardous fuel substitute. it is obtained from animal fats or vegetable oils, and it is commonly manufactured by the trans-esterification process. biodiesel has more oxygen content than oil diesel [3-7]. cooking waste is an alternative option for the production of economically and environmentally friendly biodiesel. while waste cooking oil has high free fatty acids and cannot be used directly into the engine, but it can convert into biodiesel by trans-esterification. the blends of biodiesel with various sources of oil affect more the performance and the emissions of the engine. authors in [810] investigated bio-diesel from waste edible oil, coconut oil, and castor oil obtained by trans-esterification in blends with conventional diesel fuel. methanol, methyl esters, ethanol, and deposit oils formed from biomass are known as biofuels [11]. trans-esterification is the process in which alcohol and esters (triglyceride) react together and form methyl esters (biodiesel) and glycerol. it is the most common method to make biodiesel from edible oils, waste food oil, animal fats, and waste eating greases (yellow grease). those oils are considered possible candidates to complete the vacuum created by the reduction of conventional diesel fuels [12]. waste edible oils produce excellent results, are environmentally friendly, have reduced cost, and decreased corresponding author: abid ali khaskheli engineering, technology & applied science research vol. 10, no. 2, 2020, 5387-5391 5388 www.etasr.com khaskheli et al.: emission and noise characteristics of a diesel engine fuelled with diesel-chicken … exhaust gas emissions. biodiesel with blends has successful performance and reduces pm, co2, and co emissions as compared to diesel fuel [13-15]. in this study, wasted frying chicken oil was collected from the local city of nawabshah, pakistan. that oil was converted into biodiesel by trans-esterification [23]. the current research investigated the emissions of a diesel engine using different oil blends and conventional diesel. pm, nox, co2, co and sound emissions were measured for the performance comparison of biodiesel and conventional diesel fuel. ii. experimental method the working principle of the compression-ignition (ci) diesel engine consists of four strokes with a single, horizontal type, water-cooled cylinder used for changing performance parameters. the model name/serial number of the testbed diesel engine was dwe-6/10-js-dv. the testbed, fully equipped with instruments such as thermometer, dynamometer, tachometer, flow meter, and flue gas analyser, is shown in figure 1. fig. 1. diesel engine test bed diagram two fuel tanks were added to the diesel motor with ground and normal pipelines. the fuel tanks were linked with normal lines, and the fuel supply could be controlled with two different valves. one fuel tank was filled with diesel fuel and the other with biodiesel. in this work, three fuel types were tested: d100 (diesel 100%), b20 (biodiesel 20% + diesel 80%) and b30 (biodiesel 30% + diesel 70%). all samples were investigated for pm and exhaust gas emissions on varying load under constant motor speed. the specifications of the diesel engine are shown in table i [23]. a. fuel parameters fuel parameters can affect engine emissions. biodiesel produced specific almost identical parameters when it was blended in diesel fuel in different ratios. in this research, blends were arranged by volume percentage. the settings of all samples on astm standards are shown in table ii [23]. table i. engine specifications number of cylinders 1 cooling system water-cooled type horizontal piston size (bore) 80mm displacement of the piston (strokes) 95mm (477cc) compression ratio 23:1 starting method manual output/rotational speed 8.5ps/2200rpm(max) table ii. fuel parameters of alla samples physical property unit d100 b20 b30 astm standard testing limits total acid number mgkoh/g 0.24 0.27 0.28 d-664 0.80 max specific gravity at 15.6 0 c 0.83 0.85 0.84 d-891 0.8-0.9 kinematic viscosity at 40°c mm 2 /s 1.98 2.78 2.43 d-445 1.9-6.0 density at 40°c g/cm 3 0.85 0.86 0.86 d-1298 0.86– 0.90 cetane-index (calculated) 56.9 54.4 53.5 d-976 47 min flash point 0 c 103 123 115 d-93 130 min pour point 0 c 0 +1.5 +1.8 d-97 -15 +5 0 c calorific value mj/kg 44.8 43.2 43.8 d-240 37.5 45 oxygen content wt. % 0 2.53 3.71 b. pm and exhaust gas measurements the pm emissions depend on load, speed, and fuel characteristics of the engine. in this study, pm emissions of four distinct particle sizes, pm1.0, pm2.5, pm7.0, and pm10 along with exhaust gas emissions (co2, co, no, and no2 were measured from the diesel engine. a pm hand held device was used for particulate emissions and a flue gas analyser model no. test 350-xl was used for exhaust gas emissions (figure 2). the measurements of the gas analyser are shown in table iii. fig. 2. hand held pm measuring device and gas analyzer table iii. gas analyzer measurements gas measuring range unit accuracy no 0 to +300 ppm ±2ppm (0 to +39.9 ppm) no2 0 to +500 ppm ±5ppm (0 to +99.9 ppm) co2 0 to +50 vol.% ±0.3vol.% + 1% of mv (0 to 25vol.%) co 0 to 500 ppm ±5% of mv (+40 to +500ppm) ±2ppm (0 to +39.9ppm) c. engine noise level measurements the noise level was determined by a sound pressure level meter (figure 3). the three different fuels were measured for noise level on varying load conditions at a constant speed. all fuel samples were measured for varying load on the engine from 0 to 20n.m. three different directions, front, left, and engineering, technology & applied science research vol. 10, no. 2, 2020, 5387-5391 5389 www.etasr.com khaskheli et al.: emission and noise characteristics of a diesel engine fuelled with diesel-chicken … back, were selected for measuring. the microphone was set up at 1m away from the engine cylinder at the above mentioned three locations. the specifications of the microphone are given in table iv. fig. 3. held hand noise level meter table iv. hand held noise meter specifications type electric condenser microphone range of db level 35db to 150db determination 0.1db accuracy ±1.5db microphone diameter ½ ″ dynamic range 55db iii. results and discussion a. engine emissions the engine emissions depend on operating conditions, engine type, fuel, lubricating oil, and the control of the emission systems. in general, the exhaust contains pm, nitric oxides, co, and co2. pm, and co emissions decreased when the ratio of biodiesel blended in the diesel increased [16-18]. the average emissions values are shown in table v. table v. average engine emissions of all samples fuel pm1.0 (ppm) no (ppm) no2 (ppm) co2 (%) co (ppm) d100 0.0269 65.909 11.845 1.832 361.272 b20 0.0123 73.090 15.318 1.542 287.727 b30 0.00690 53 7.44 1.457 190.727 fig. 4. comparison results for pm1.0 emissions b. particulate matter (pm) emissions pm is an air-suspended mix of active and liquid particles of varying size, shape, surface region, number and compound arrangement, solvency, and source [19]. diesel fuel is a major pm source. both b20 and b30 samples had less pm emissions than pure diesel, with b30 having the least emissions. the pm emission results are shown in figures 4-6. fig. 5. comparison results for pm2.5 emissions fig. 6. comparison results for pm7.0 emissions fig. 7. comparison results for pm10 emissions c. nitric oxides (nox) emissions biodiesel has a shorter deferred start, nox outflow reduction, and a high cetane profile. in any case, high burning temperatures came to the ignition because of more upper ignition timing and more extended staying period and nox discharges were increased. biodiesel diminishes the nox discharges by enhancing fuel properties [20]. fig. 8. comparison results for no emissions consequently, no emissions reduced by increasing loads. in this comparative study, nox emissions increased in b20 as engineering, technology & applied science research vol. 10, no. 2, 2020, 5387-5391 5390 www.etasr.com khaskheli et al.: emission and noise characteristics of a diesel engine fuelled with diesel-chicken … compared to d100 at different loading conditions of the engine. the b30 had lower nox emissions due to the decreasing exhaust gas temperature with quick combustion from the engine [23]. the nox emissions of b30 increased at middle engine load, while they reduced with increasing load. the results of nox emissions are shown in figures 8-9. fig. 9. comparison results for no2 emissions d. carbon dioxide (co2) emissions co2 is a colorless and non-combustion gas released when fuels with carbon content burn entirely. consequently, co2 is a significant parameter in engine exhaust emissions. the co2 emissions increase when engine’s speed and loading increase. the exhaust emissions of co2 were determined for varying loads at a constant engine speed [21]. in this study, the percentage of co2 emissions decreased when the ratio of blends in biodiesel increased. therefore, the average value of co2 emissions from b30 was 0.373%. the co2 emissions for all samples are shown in figure 10. fig. 10. comparison results for co2 emissions e. carbon monoxide (co) emissions co emissions depend on the speed of the engine. they occur when the combustion is insufficient, and therefore, fuel cannot oxidize [25]. oxygen content in ethanol is high, which allows lower co emissions and increased burning quality [26]. co production results from oxidation of fuel, including carbon and hydrogen, with oxygen. in this work, three different fuels were studied for co emissions on variable load and at a constant speed. co emissions reduced when the blending ratio of biodiesel in diesel increased. the comparison results of carbon monoxide emissions are shown in figure 11. f. noise characteristics usually noise level decrement is accompanied with biodiesel practice. noise is fundamentally influenced by motor speed because of upward and descending cylinder development in the motor chamber [22]. diesel fuel has a lesser amount of aromatic compounds than biodiesel. the aromatic compounds increase the ignition delay by decreasing the noise level. in this research, the noise levels were measured for different loading conditions of the engine. therefore, three locations (i.e. front, left, and back) were designated for noise level study. all corresponding positions were 1m away from the piston head cylinder. the noise level depends on the load and the blending ratios of biodiesel [24]. the noise level decreased slightly after increasing the middle brake load of the engine. the results showed that diesel produced higher noise level than b20 and b30. the b30 sample exhibited the least noise level due to its improved oxygen content. the results are shown in figures 1214. fig. 11. comparison results for co emissions fig. 12. comparison results of engine’s noise level (front position) fig. 13. comparison results of engine’s noise level (left position) fig. 14. comparison results of engine’s noise level (back position) engineering, technology & applied science research vol. 10, no. 2, 2020, 5387-5391 5391 www.etasr.com khaskheli et al.: emission and noise characteristics of a diesel engine fuelled with diesel-chicken … iv. conclusions pm1.0 was the higher emitted pm component. b20 produced less pm emissions than d100, while b30 produced even less on variable loadings. nitric oxide emissions increased for b20 as compared to d100 at different loading conditions, while for b30 they were less than diesel and b20 due to the lower exhaust gas temperature and quick combustion. co2 emissions increased when the speed and loading conditions of the engine increased. lower average value of co2 emissions in the engine was observed when using b30. co emissions moreover deceased with increasing blending ratio of biodiesel due to the high oxygen content of the blends. the noise level was reduced when the b30 was used due to the improved combustion process because the addition of biodiesel provided more oxygen atoms in the combustion chamber. acknowledgment this research work was conducted in the thermodynamics engineering laboratory at the department of mechanical engineering, quaid-e-awam university of engineering, science & technology nawabshah, pakistan. references [1] u. agbulut, h. bakir, “the investigation on economic and ecological impacts of tendency to electric vehicles instead of internal combustion engines”, duzce universitesi bilim ve teknoloji dergisi, vol. 7, no. 1, pp. 25-36, 2019 [2] u. agbulut, s. saridemir, “a general view to converting fossil fuels to cleaner energy source by adding nanoparticles”, international journal of ambient energy, available at: www.tandfonline.com/doi/ abs/10.1080/01430750.2018.1563822?journalcode=taen20 2019 [3] s. sadaf, j. iqbal, i. ullah, h. n. bhatti, s. nouren, h. u. rehman, j. nisar, m. 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waste cooking based biodiesel as fuel in a diesel engine”, energy, vol. 139, pp. 883-894, 2017 [9] h. liu, x. ma, b. li, l. chen, z. wang, j. wang, “combustion and emission characteristics of a direct injection diesel engine fueled with biodiesel and pode/biodiesel fuel blends”, fuel, vol. 209, pp. 62-68, 2017 [10] t. sukjit, v. punsuvon, “process optimization of crude palm oil biodiesel production by response surface methodology”, european international journal of science and technology, vol. 2, no. 7, pp. 4956, 2017 [11] k. manivannan, p. aggarwal, v. devabhaktuni, a. kumar, d. nims, p. bhattacharya, “particulate matter characterization by gray level cooccurrence matrix based support vector machines”, journal of hazardous materials, vol. 223-224, pp. 94-103, 2012 [12] t. wiesenthal, b. schade, g. leduc, l. govaerts, l. pelkmans, p. georgopoulos, p. christidis, “biofuel support policies in europe: lessons learnt for the long way ahead”, renewable and sustainable energy reviews, vol. 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and emissions of karanja oil and its blends in a single cylinder agricultural diesel engine”, applied energy, vol. 86, no. 1, pp. 106-112, 2009 [18] o. can, “combustion characteristics, performance and exhaust emissions of a diesel engine fueled with a waste cooking oil biodiesel mixture”, energy conversion and management, vol. 87, pp. 676-686, 2014 [19] p. geng, h. mao, y. zhang, l. wei, k. you, j. ju, t. chen, “combustion characteristics and nox emissions of a waste cooking oil biodiesel blend in a marine auxiliary diesel engine”, applied thermal engineering, vol. 115, pp. 947-954, 2017 [20] k. manivannan, p. aggarwal, v. devabhaktuni, a. kumar, d. nims, p. bhattacharya, “particulate matter characterization by gray level cooccurrence matrix based support vector machines”, journal of hazardous materials, vol. 223-224, pp. 94-103, 2012 [21] s. m. palash, m. a. kalam, h. h. masjuki, b. m. masum, i. m. r. fattah, m. mofijur, “impacts of biodiesel combustion on nox emissions and their 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diesel–biodiesel–alcohol blends”, journal of the brazilian society of mechanical sciences and engineering, vol. 41, article id 389, 2019 [26] u. agbulut, s. saridemir, g. durucan, “the impacts of ethanol-gasoline blended fuels on the pollutant emissions and performance of a sparkignition engine: an empirical study”, international journal of analytical, experimental and finite element analysis, vol. 5, no. 4, pp. 50-59, 2018 engineering, technology & applied science research vol. 9, no. 2, 2019, 3939-3944 3939 www.etasr.com matlani & shrivastava: an efficient algorithm proposed for smoke detection in video using hybrid … an efficient algorithm proposed for smoke detection in video using hybrid feature selection techniques princy matlani department of computer science & engineering guru ghasidas university bilaspur, india princy.matlani@gmail.com manish shrivastava department of computer science & engineering guru ghasidas university bilaspur, india manbsp@gmail.com abstract—as an emerging development in the digital technology era, video processing is useful in a wide range of applications. in the current paper, an algorithm is proposed which is useful for smoke detection in video processing. the algorithm quickly detects fire by eliminating common interruptions like noise, overlapping due to the collision, etc. the proposed algorithm is composed of several techniques such as haar feature, bhattacharya distance method, sift descriptors, gabor wavelets approach and svm classifier to identify the smoke by video processing. foreground object is identified using a moving object algorithm by predicting the movement of smoke in stable images. the implementation has been carried out in matlab. keywords-smoke detection; bhattacharya distance; video processing; bounding box technique; sift; gabor wavelet approach; hybrid algorithm; hill climbing algorithm; moving object algorithm i. introduction fire and smoke are needed to get detected at a very early stage in order to minimize the damage they cause. as we know, smoke is considered to be an initial indication of fire, thus, a smoke detecting technique is proposed for early detection and to avoid uncontrolled fires. conventional point based sensors work by ionization or photometry techniques for detecting the existence of smoke particles whereas, video based smoke detection system uses a newly developed technique based on pattern recognition [1]. compared to this conventional sensor based technology, video-based fire detection has the advantage of being applicable to large areas, having early response, and long distance of detection. although researchers have expanded the field of video based smoke detection, most of current methods for video based smoke detection have high rates of false alarms, and low accuracy. the change in transparency of smoke is considered as main feature in [2]. the research is based on edge analysis of background objects, i.e. if edges of background objects are appeared to lose sharpness and become blurred, the object may be considered to be smoke. despite the significant research done in video-based fire detection algorithms, these methods were found difficult in comparison due to insufficient common evaluation schemes and datasets [3, 4]. thus, there is a huge need of such a comparison to take place among several fire detection methods to prove their effectiveness. the effectiveness of detection strongly depends on both the distance of the fire source from the point of detection and the dimension of the monitored areas [5]. in this context, several methods have been developed for automatic smoke detection in videos [6, 7]. primarily, they consider several features of smoke such as its color, motion, and shape. a fire detection system should be designed in such a manner that it can successfully detect smoke with complex shapes [8]. the model proposed in [8] uses dark channel priori based early smoke detection algorithm. a group of pixels is not considered as smoke until they satisfy all considered factors. to achieve an efficient smoke detection in video processing, a hybrid algorithm was proposed. recursive algorithms are used in real world applications, hybrid algorithms are used especially in the implementation of the divide or conquer algorithms, whereas the size of the data declines as recursion moves deeper [9, 10]. hybrid algorithms have better results as compared to that of applying individual algorithms because they involve a combination of the desired features of each algorithm. several methods of automatic smoke detection in video have been developed. but, existing smoke detection methods have high false detection rates. existing methods require close proximity to the smoke and do not provide information about the type and amount of smoke. it is difficult to exactly detect smoke in video because of reasons such as:(i) smoke color differs largely and several non-smoke substances share the same color with smoke, (ii) smoke textures and shapes often alter erratically, (iii) smoke often blurs images, and causes unreliable features extracted from these blurred images and (iv) foreground objects hide smoke. in this paper, we propose a robust video smoke detection system. this paper has various contributions to video smoke detection. first, we combine extended haar-like features and statistical measures together, and these features are extracted from both intensity and saturation components of original rgb images. the proposed method then aims to design a novel smoke detection technique employing sift feature detection corresponding author: princy matlani engineering, technology & applied science research vol. 9, no. 2, 2019, 3939-3944 3940 www.etasr.com matlani & shrivastava: an efficient algorithm proposed for smoke detection in video using hybrid … technique along with svm classifier in order to decide the correct location of smoke within the image frame as well as the instance of the incident. it also aims to provide a better performance in terms of classification accuracy. ii. literature review authors in [11] proposed the h-lds descriptor, based on the higher order decomposition of the multidimensional image data and enabled the study of dynamic textures using information from various image elements. compared with standard lds descriptor, the particle swarm optimization approach is used by a combination of multidimensional texture analysis with the spatiotemporal modeling of smoke to analyze dynamic texture information. in [4], authors proposed a new idea with semi-transparent properties based algorithm of video smoke detection. the marginal area of smoke is semitransparent. authors in [2] focused on the verification of detection of smoke in video sequences by spatiotemporal local binary patterns. the following contributions were made: at first, numerous types of 2d and 3d variants in local binary patterns (lbps) were investigated according to changing properties of smoke, and then, brightness map, laplacian map and edge map were focused during the study of spatio-temporal lbp. authors in [8] proposed a tactic based on dark channel priority for early stage smoke detection in video. smoke indicates proof of fewer chrominance parts and chromaticity examination consumed to distinguish motion behaviors in video arrangements. motion history image (mhi) strategy is used to distinguish the motion attributes of smoke. in [12], two kinds of histogram are proposed by varying luminance/chrominance texture and its shape. linear interpolated luminance/chrominance subtraction picture is entered for periodical examination after the threshold position. authors in [13] propose an efficient smoke detection technique for intelligent video surveillance algorithm having both dynamic and static features of smoke which exhibit contrast, color, texture features, and motion. they are using detection color image segmentation, temporal and spatial wavelet for flame detection. a flame region is also extracted. authors in [5] proposed a high-speed and early smoke detection method that tracks the local fractal feature of smoke areas based on discrete cosine transform (dct) coefficients computed at the compression step. authors in [14] made improvements in yuan’s video based smoke detection and used made experiments of the accumulative motion orientation. optimal thresholds for motion, chrominance recognition and noisy blocks were eradicated. the experiment in [15] describes an adaptive log algorithm for smoke detection by energy difference. once the smoke region is identified, dynamic accumulation, separating and extricating smoke leakage position would be accomplished. authors in [16] made the utilization of optimal mass transport (omt) optical flow. the process of detection is encapsulated as an administered bayesian classification. feature vectors are embodied of omt velocities and red, green, blue color channels. the classifier is used as a specific hidden layer neural network. authors in [17] proposed a technique, composed of the subsequent basic steps: the initial step is selecting whether the camera is stationary or dynamic. the next step is finding the regions of motion occurred in the present input frame over the background frame of the image. and finally, regions of interest (rois) are pointed out through associated in-component testing. the block-based approach should be enforced for the first two steps. in the last step, the patterned roi is confirmed as smoke by utilizing the k-temporal representation of its shape and color separated from the roi. authors in [18] proposed turbulent smoke phenomena over the relationship of area and perimeter. authors in [19] gave a target-tracking established fire/smoke detection technique for an early fire alarming system in broad or wide spaces. brightness consistency, motion accumulation, and spread were effectively studied through improved gaussian mixture model positioning algorithm. it also gave three efficient static and dynamic visual features of smoke. authors in [20] investigated the approach of smoke pixel judgment made out of two decision principles: chromaticity-based static decision rule and diffusion-based dynamic characteristic decision rule. the chromatic rule assumes that the smoke has grayish color. the scattering properties of smoke were used as dynamic characteristics. iii. research methodology the flow chart of the proposed smoke detection method is shown in figure 1. block based implementation is used to ensure efficiency and robustness. flowchart of the proposed method. a. converingt video into frames the given input video has been converted into 693 frames using a standard matlab code. in our code, for converting the video frames, many functions were used. for example, video reader class was used to determine the starting time of the video. then we used read() function to extract a frame from the video at an exact particular time. also, imwrite function engineering, technology & applied science research vol. 9, no. 2, 2019, 3939-3944 3941 www.etasr.com matlani & shrivastava: an efficient algorithm proposed for smoke detection in video using hybrid … was used to store the images in a folder. in this manner, 693 frames have been converted from the given input video. b. background subtraction the converted video frames were further processed by background subtraction methods for object localization. moving pixels in the smoke image are calculated by deducting the current image of background image based on the threshold value. background subtraction, also termed as foreground detection, is a procedure in which the center of the image is extricated for further processing. background subtraction is an extensively utilized process to detect moving objects in a video captured on a static camera. the basic idea in this approach is to identify the moving objects by the change that occurs in the present frame and a reference frame referred as “background image”. the reference background and threshold is dynamically updated with incoming frames. smoke detected output after background subtraction is shown in figure 2. according to background subtraction method, the background frame is set as: , when current frame is the first frame (((1 ) ( )), otherwise   =   −  +   bframe bframe r tframe r bframe where bframe is the background frame, tframe is the current frame and r is a real and positive constant close to one. moving objects detected using background subtraction (white: no smoke, black: smoke) the algorithmic steps are: • select the background frame and current frame from the given video. • convert into grayscale those selected frames. • for calculation of pixel value, assume the frame dimension. • find the difference in pixels of the selected two frames which should be match with a defined threshold value. • update the threshold value according to the changes in frames. the algorithm is detecting the moving regions from deducting the current image pixel-by-pixel from a reference background image which is poised by averaging image. c. bounding box technique in the bounding box technique, the major work is to read the image and convert it into a gray image. further, it changes to a binary image using certain techniques. after converting the given image into a binary image, it is necessary to fill the acquired holes in the image. this work is done by using the bounding box technique. the region properties of the image have been considered in a regular manner for improving the performance of the algorithm. the bounding box will provide the properties of the given frame and the minimum or least bounding or enclose box for a point set (s) in n dimensions. this is the exact box with the fundamental measure (area, volume or hyper volume in greater dimensions) within which the entire points lie (figure 3). bounding box output d. bhattacharya distance technique we prepared the averaged histogram hs and hn from manually selected smoke and non-smoke image blocks. the bhattacharyya coefficient represents the similarity of two histograms from 0 to 1. the bhattacharya distance measure is mainly used for comparing the similarity among two histograms for the background subtracted resultant image as follows: let ri be the frequency coded quantity for the first histogram and si be the similar quantity for the second histogram. for probability distributions m and n over the particular domain i, the bhattacharya distance is described as: (1) where, ( , ) ( ) ( ) i i bc m n m i n i  =  (2) in (1)-(2), bc is the bhattacharya coefficient for distance probability distribution. for continuous probability distributions, the bhattacharya coefficient has been defined as: ( , ) ( ) ( )bc m n m i n i di=  (3) ( , ) ln( ( , )) b d m n bc m n= − engineering, technology & applied science research vol. 9, no. 2, 2019, 3939-3944 3942 www.etasr.com matlani & shrivastava: an efficient algorithm proposed for smoke detection in video using hybrid … in either case, 0 1 bc and 0    b d . db doesn't adhere to the triangle inequality, yet the hellinger distance 1− bc is observed to the triangle inequality. the bhattacharya distance is applied to all frames and the result is saved. in our research, bhattacharya distance will be calculated after the video-toframe conversion and background subtraction. the similarity between two consecutive frames and distance variation is computed by bhattacharya algorithm. then the sift technique will be applied to calculate the features of bhattacharya distance. e. sift method sift (scale-invariant feature transform) method is applied to extract the features of the smoke obtained from the bhattacharya distance method. the implementation of sift technique contains two steps. the first step extracts the characteristics of a smoke image and then determines its descriptors, which include detection of the characteristics that are most likely to represent smoke. the second step performs the mapping procedure from the obtained results. the features obtained by this method are called as its key points. in our work, we quantized the extracted features and combined the descriptors of the objects which belong to the same category. the relating k-means on these particular features were calculated. the features of k-means were applied to all possible categories for getting extra memory space in matlab implementation. the computed values of sift descriptors for each image are obtained using the bounding box method. after the similarity distance calculation, sift was applied. this technique is employed for locating the features of a particular object in an image consisting of many different objects. there are various examinations in methods of acquiring these features and how to conduct them. sift image features produce a set of local features of an object that are not affected by operations like object scaling and rotation. for image feature extraction method, it takes an image as input and converts it into a “large group of local feature vectors”. all these vectors remain constant for any rotation, scaling or image translation. sift process includes the following steps: • scale-space extremes detection. • localization of key point. • coordination assignment. • key point descriptor. sift analysis is combined with detecting salient locations in a given image and extracting descriptors that are distinctive yet invariant to changes in viewpoint, illumination, etc. both standard sift point detector and histogram-of-gradients descriptors can be used. the location of the features can be extracted by sift. by using sift, each key point descriptor extracted from the object image is matched independently to the selected database of descriptors extracted from all collected training images. it will find the best match from each descriptor from all training images. a subsequent threshold will be used for rejecting the key points, if there are not any good matches. some of the possible matches are: • the whole of an image matches with the whole of another selected image. • a single part of an image matches with the whole of another image. • one image part matches with a part of another image. f. gabor wavelet approach gabor wavelet transform analyzes the local structure based on spatial frequency, spatial localization and orientation selectivity for the extracted feature of the image from sift. among various wavelets, the gabor function provides the optimal resolution for the extracted smoke region in both time and frequency domain. the computation process involves two variables: frequency and orientations. to evaluate the magnitude of local frequencies of that estimated wavelength and coordination in the image, it is then convolved with the image. the gabor wavelets are measured as a class of selfsimilar functions. the equation of gabor wavelet is: (4) 1 4     t f among all types of functions, the gabor function is found to attain the minor bound and it also executes the finest analytical resolution in the joint domain. the characteristics of image texture can be obtained by convolving the image by gabor filters. gabor filters with different frequencies and orientations are selected to obtain the texture features of the smoke regions. in order to optimally sense and localize features at various scales, filters with varying parameters are used rather than a fixed one. this approach is used for certain applications like gabor networks for face reconstruction, facial expression classification, iris recognition, and fingerprint recognition. gabor features are approximated by using many gray values. the region is equivalent to the object which is usually segmented correctly in all images. the different set of gabor features is typically related with the segment containing the object of interest. iv. results and discussion in our research, we focused on detecting smoke in video processing. hence, moving object algorithm is developed to predict moving objects. in a video stream, the objects acquire a stability phase while the others remain the same. hence, it has an ability to detect moving objects and they are represented as smoke. this result has been implemented in matlab. in our experiments, initially we considered two videos prerecorded from youtube.com for smoke detection (figures 4-5 and 6-8). our program is implemented using matlab 2015. figure 9 shows the hybrid algorithm technique which degrades the clarity and reality of the original video. hence, it should be predicted using a suitable technique. figure 8 shows an exact output regarding smoke detection of the previous images. 2222 2 2 2 2 ( )( ) , ( ) ( ) t f f p f dft p t dt p t dt p f df    = =    engineering, technology & applied science research vol. 9, no. 2, 2019, 3939-3944 3943 www.etasr.com matlani & shrivastava: an efficient algorithm proposed for smoke detection in video using hybrid … blob detection of smoke in video1 taken at t1 blob detection of smoke in video1 taken at t2 blob detection of smoke in video2 at time t1 blob detection of smoke in video2 at t2 input video of smoke detection process with detected smoke area output image of predicted smoke table i displays a comparison of the proposed system with [21] and [22]. three smoke containing videos and three nonsmoke videos were considered and compared: 1) black smoke from a standing car, 2) white smoke from a vehicle, 3) black smoke from a car. the proposed method is detecting the smoke’s exact shape in less time. with the proposed method, the time consumption for the overall setup was minimized. table i. performance analysis videos movie 1 movie 2 movie 3 time/frame (msec) 117.334462/187 64.304860/142 /243 alarm at frame number proposed 91 89 82 [21] 164 216 68 [22] 89 94 99 description black smoke from standing car white smoke from vehicle black smoke from car v. conclusion this paper proposes a new smoke recognition system. many techniques and algorithms have been used for resolving issues like noise reduction, reliability, and cost-effectiveness. this research concentrates on the detection of: transparent smoke, dense smoke and non-smoke regions using various approaches like bounding box technique for the comparison of different frames, bhattacharya distance for the comparison of engineering, technology & applied science research vol. 9, no. 2, 2019, 3939-3944 3944 www.etasr.com matlani & shrivastava: an efficient algorithm proposed for smoke detection in video using hybrid … similarities between two histograms, sift technique for the extraction of original images from different frames, and gabor wavelet approach for the application of smoke detection approach. finally, moving object algorithm has been used for the detection of smoke as the only moving object. the experimental results show that the discussed method can be used for the accurate detection of smoke at a very fine rate. 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“real-time video-based fire smoke detection system”, 2009 ieee/asme international conference on advanced intelligent mechatronics, singapore, july 14-17, 2009 [19] z. wei, x. wang, w. an, j. che, “target-tracking based early fire smoke detection in video”, fifth international conference on image and graphics, xi'an, china, september 20-23, 2009 [20] t. h. chen, y. h. yin, s. f. huang, y. t. ye, “the smoke detection for early fire-alarming system base on video processing”, 2006 international conference on intelligent information hiding and multimedia, pasadena, usa, december 18-20, 2006 [21] b. u. toreyin, y. dedeoglu, u. gudukbay, a. e. cetin, “computer vision based method for real-time fire and flame detection”, pattern recognition letters, vol. 27, no. 1, pp. 49-58, 2006 [22] f. yuan, “video-based smoke detection with histogram sequence of lbp and lbpv pyramids”, fire safety journal, vol. 46, no. 3, pp. 132139, 2011 authors profile princy matlani (orchid id: https://orcid.org/0000-00027421-8366), was born in bilaspur, india, in 1990. she received the be degree in computer science & engineering from government engineering college, bilaspur, india, in 2011, and the mtech. degree from the national institute of technology (nit), raipur, india, in 2013. she is an active member of ieee, and pursuing her phd from guru ghasidas university, bilaspur, india. she is experienced in working in image processing field, and currently works on computer vision based surveillance systems. dr. manish shrivastava (orchid id: https://orcid.org/0000-0002-1346-968x), assistant professor, department of computer science & engineering, institute of technology, guru ghasidas university, bilaspur. he obtained his mtech degree from davv, indore, and phd from guru ghasidas university, bilaspur. he has about fifteen years of teaching and research experience, and a number of papers in various national and international journals to his credit. his field of interest is network security and image processing. a life member of the indian society for technical education, sr. member of iacsit, and a life member of the cryptology research society of india. https://orcid.org/0000-0002-7421-8366 https://orcid.org/0000-0002-7421-8366 https://orcid.org/0000-0002-1346-968x microsoft word 27-3694_s engineering, technology & applied science research vol. 10, no. 4, 2020, 6041-6046 6041 www.etasr.com villareal & tongco: remote sensing techniques for classification and mapping of sugarcane growth remote sensing techniques for classification and mapping of sugarcane growth marife kung villareal school of engineering, university of san carlos, cebu city, philippines and college of engineering and design, silliman university, dumaguete city, philippines mkvillareal27@gmail.com alejandro fernandez tongco school of engineering university of san carlos cebu city, philippines aftongco@usc.edu.ph abstract-this study aimed to apply remote sensing technologies in delineating sugarcane (saccharum officinarum) plantations and in identifying its growth stages. considering the growing demand for sugarcane in the local and global markets, the need for a science-based resource inventory emerges. in this sense, remote sensing techniques’ unique ability is vital to monitor crop growth and estimate crop yield. object-based image analysis (obia) concept was employed by utilizing orthophotos and light detection and ranging (lidar) datasets. specifically, the study applied the support vector machine (svm) algorithm to generate the resource map, validated by a handheld global positioning system (gps). the classification result showed an accuracy of 98.4%, delineating a total of 13.93 hectares of sugarcane plantation in the study area. the height information from lidar datasets aided in developing the rule-set that can further classify the sugarcane according to its growth stages. results showed that the area distribution of sugarcane at establishment, tillering, yield formation, and ripening stage were 6.65%, 11.61%, 13.89%, and 17.90% respectively. gps validation points of the growth stages verified the accuracy of svm. the accuracy results for growth stages, i.e. establishment, tillering, yield formation, and ripening are 88%, 94.4%, 96.3%, and 91.7% respectively. the results proved the usefulness of svm as a remote sensing classification technique which led to an exact mapping of the sugarcane areas as well as the practical use of lidar height information in estimating the growth stages of the mapped resource, both of which can provide valuable aid in estimating the potential sugarcane yield in the future. keywords-remote-sensing technologies; crop growth; remote images i. introduction accurate understanding and precise monitoring of land cover is essential for decision makers and producers in order to manage and improve crop production [1]. high value crops in asia are divided into two types, the principal crops which are rice, wheat, soybeans, barley, corn and the cash crops which are tea, rubber, palm oil, coconut, and sugarcane [2]. in the philippines, sugarcane is considered a high value crop, thus not surprisingly it is the fourth largest crop cultivated in the country yielding three major products: sugar, bio-ethanol, and power. the sugarcane is a plantation crop which requires big areas, greater than 10 hectares. the total area allocated to sugarcane planting nationwide totals to 422,384 hectares (3.36% of the country’s arable land). the sugarcane industry provides employment to around 700,000 workers [3]. the country is the ninth largest sugar producer in the world and the second largest among the association of south east asian nations (asean) [4]. sugarcane is an important perennial crop planted in tropical regions of many countries like brazil, india, china, and the philippines. increased attention on sugarcane plantation in recent years is attributed to both the diminishing global sugar supply and on the growing demand for biomass energy as alternative to the fossil fuels commonly utilized today. in this case, sugarcane is an important resource of alcohol for biofuel. the sugarcane industry’s potential impact on the philippine economy and environmental aspects, calls for effective methods that can provide timely and accurate information on sugarcane growing areas as well as growth conditions at both regional and global scales [5]. remote sensing (rs) and geographic information system (gis) provide useful tools for sustainable cultivation in developed countries’ agriculture [5, 6]. rs techniques have been widely used in agriculture surveys in the past decades because of the unique ability of rs in monitoring crop growth and estimating crop yield with certain accuracy [7]. for instance, rs techniques give up-to-date and relatively right information for sugarcane crops management [8]. studies have focused on various rs images to map sugarcane fields through automatic classification of landsat images [9], through a rule-based classifier applied to spot image time series [10] or through an obia approach on high resolution remote sensing images time series [11] to categorize sugarcane fields into similar age units. on the other hand, gps and gis technologies are suitable for better management of land and other resources for sustainable crop production. imagery could be integrated with other layers of spatial or geographical data in a gis, with the use of gps receivers to find positions of interest [12, 13]. the method employed in this study uses obia and the use of ideal features from lidar and orthophoto data. the obia workflows are highly customizable allowing the integration of human semantics and hierarchical networks [14]. generally, there are two main processes in obia, segmentation and classification. segmentation is the process wherein adjacent pixels group together based on their homogeneity thereby corresponding author: marife kung villareal engineering, technology & applied science research vol. 10, no. 4, 2020, 6041-6046 6042 www.etasr.com villareal & tongco: remote sensing techniques for classification and mapping of sugarcane growth creating meaningful “objects”. these objects are then subjected to classification. both segmentation and classification use different algorithms in ecognition with ease since much of the work referred to as obia originated from ecognition software [15-17]. object-based classification is through user-defined rule-sets. the study also uses support vector machine (svm) which is a machine learning algorithm. svm techniques can produce high classification accuracy and generate a neat image output [18]. its most important characteristic is its ability to generalize well from a limited amount and/or quality of training data. compared to other methods like artificial neural networks (anns), svm can yield comparable accuracy using a much smaller training sample size. this is due to the “support vector” concept that relies only on a few data points to define the hyper-plane that best separates the classes [19]. the advances in lidar technologies and the use of highresolution satellite images provide opportunities for detailed mapping and modelling of crops. in order to aid the precise inventory of sugarcane, this study utilizes lidar data, remote sensing techniques, and object-based image analysis to delineate sugarcane growth stages in the study area [20]. the lidar approach has emerged as a powerful active remote sensing method for direct measurement of 3d plant structure in precision agriculture [21, 22]. lidar is valuable in the effort to improve identification and delineation of remotely-sensed data making it one of the better rs tools and techniques used in resource mapping. numerous studies such as [23, 24] have proven that height features derived from lidar data can differentiate much between high and low vegetation. the highresolution aerial orthophotos and lidar data in the aforementioned studies address the problem of classification confusion caused by spectral mixing in areas with heterogeneous classes [1]. the lidar approach is an active rs technique like radar but uses laser light pulses to get elevation data [25]. the handheld gps is also used for classification routine and for ground truthing and accuracy assessment of the growth stages and location of sugarcane crops. gps technology has been adopted for better management of land and other resources for sustainable crop production [12]. these rs tools have been all utilized in this study. the sugar industry requires spatially explicit tools to provide reliable and precise information on the crops area and the field location to improve the accuracy in monitoring sugarcane production and yield estimates [26]. this study explores the application of rs techniques to map and monitor the sugarcane growth stages utilizing the classification algorithm coupled with lidar data and gps technology for ground truth survey. ii. methodology a. study area tuburan is located 10°43'38.7" north and 123° 49'55.4" east in the province of cebu, philippines. it has a total land area of 29,316 hectares. the study area for this mapping is barangay manga, tuburan, cebu. manga is one of the villages in the town of tuburan within the province of cebu. the municipality has 7,329 hectares of land devoted to agriculture. the main sources of income in tuburan are agriculture and fishing. sugarcane is among the cultivated crops. b. sugarcane growth stages mapping of sugarcane growth stages helps finding the locations of the newly planted, growing, and harvestable sugarcanes. sugarcane crops that are ready for harvesting are properly monitored and yield production can be estimated. rs images have been used to map sugarcane fields [9] through an obia approach on high-resolution images and to categorize sugarcane fields into similar age units [11]. sugarcane growth stages start from the establishment and tillering or germination phase. establishment stage begins when two leaves appear on the stem. tillering growth stage on the other hand, commences when the secondary sprouts forms from underground buds. this stage lasts for 4 to 6 months. the second stage is known as the vegetative and yield formation stage or the grand phase that will last for 5 to 8 months. sugarcane vegetates during these months if properly supplied with heat and moisture, hence, this is also called the vegetative stage. the first two stages of sugarcane growth show the sugarcane in its young phase. lastly, the ripening and maturation phases last for about three months. this growth stage is the harvestable sugarcane [27]. the use of technology like rs is necessary in the classification and identification of sugarcane growth, for instance authors in [28] suggested the need for automated methods to map sugarcane fields and other land uses. c. process workflow lidar data, gps, orthophotos, and software like ecognition and qgis were utilized for the classification map identifying the growth stages area of sugarcane crops. the lidar data show a high spatial resolution imagery which is effective in accurately mapping crop species by obia and for crop species classification [29-31]. the lidar derivatives and orthophotos have gone through a merging process and layer mixing to come up with a classified image (figure 1). fig. 1. process workflow. lidar derivative ndsm and orthophotos are required for crop classification. these lidar data give a z or height information. the ndsm is the lidar height data normalized with respect to the ground surface. all ground points in ndsm are normalized to 0. the lidar derivative produces ndsm by subtracting the digital terrain model (dtm) from the canopy surface model or the digital surface model (dsm). an orthophoto is an aerial rgb photo. using the rgb alone, one engineering, technology & applied science research vol. 10, no. 4, 2020, 6041-6046 6043 www.etasr.com villareal & tongco: remote sensing techniques for classification and mapping of sugarcane growth can perform obia (segmentation and classification). the best feature in rgb is texture information by visual inspection. using rgb orthophoto, estimation of classification accuracy and reliability is visually shown [32]. the ndsm and the merged orthophotos are now the raster data set collection needed for image segmentation and rule-set development in ecognition to produce the classified image. d. segmentation this study uses obia for classification. using obia, analysis and classifying of any raster image are possible. segmentation uses ecognition software. segmentation is the first step in obia. this is done so that instead of directly classifying pixels to produce a land cover or land classification result, classification is done by “segments” or groups of pixels (“object” based classification). object-based image analysis uses four image layers. these four layers are: ndsm from lidar and red, green, blue (rgb orthophoto) for presegmentation process. figure 2 shows an orthophoto and an ndsm images of barangay mangga. these data are courtesy of phil-lidar research center at the university of san carlos talamban campus. (a) (b) fig. 2. (a) orthophoto and (b) ndsm of barangay manga, courtesy of phil-lidar research center at the university of san carlos, philippines. fig. 3. pre-segmentation process classifying high, medium, and low elevation objects using ecognition software. the pre-segmentation process is done by using the ecognition software. the first segmentation process is quad tree-based segmentation using ndsm and having a scale parameter of 2.0m. next is the spectral difference segmentation with most spectral difference of 2.0m. after the preclassification, follows the segmentation process where objects are assigned in high, medium or low elevation. high elevation objects have a mean threshold condition of mean ndsm greater than 2.0 (ndsm>2.0). medium elevation objects have a mean threshold condition of mean ndsm less than or equal to 2.0 and greater than or equal to 0.25 (0.25<=ndsm<=2.0). the remaining are considered as low elevation objects. figure 3 shows the classification result. e. ground survey verification of the sugarcane crops and identification of the crops’ growth stages was conducted by ground survey using a handheld gps. in collecting data as points, it is advisable to collect multiple positions. the logging interval to select for collecting the positions can have an impact on accuracy. collecting data at the point site for a longer time and then averaging positions, yields better results than collecting data at the point site for a shorter time. the summary of the validation points and the growth stages of sugarcane are shown in table i. table i. area distribution of validated sugarcane plantations per growth stage. no. of validation points stages 8 establishment 12 tillering 19 yield formation 20 ripening f. image segmentation of sugarcane and growth stages after pre-classification, the next step is the segmentation to capture the target subclasses which are the sugarcane and the shrub. svm was employed to collect samples of sugarcane and shrub. sugarcane is a medium elevation object. segmentation setting for medium elevation and low elevation object is in a scale parameter of 40, 0.5 compactness, and 0.2 shape. the image layer weights are rgb. the threshold condition used for medium elevation objects is with a height of less than or equal to 2.0 and greater than or equal to 0.25. sugarcane and shrub were identified at this level: sugarcane crops lie in the range of height of less than or equal to 2.0 (<=2.0) and shrub and other species have a height that is greater than or equal to 0.25. in figure 4 the orthophoto and the classified output of sugarcane crops are shown. fig. 4. orthophoto and classified sugarcane crops. data are courtesy of phil-lidar research center at the university of san carlos, philippines. the validation points taken per area of the growth stages of sugarcane by field survey are the basis to apply the rule-set for the segmentation process. in figure 5 the orthophoto and the ndsm of the sugarcane growth stages can be seen. g. supervised learning algorithm sugarcane and shrub sample objects were extracted from the images. extracted features from the collected samples were used for classification and for creating class definitions. objects were subjected to a supervised learning algorithm to engineering, technology & applied science research vol. 10, no. 4, 2020, 6041-6046 6044 www.etasr.com villareal & tongco: remote sensing techniques for classification and mapping of sugarcane growth linearly separate classes and objects. classification process utilized the svm algorithm, whose most important characteristic is its ability to generalize from a limited amount and or quality of training data [19, 33]. svm is employed to classify land features in the images. the classified objects are acquired from the segmentation procedure. the lidar derivative (ndsm) is a feature for developing the svm model. (a) (b) (c) (d) fig. 5. growth stages of sugarcane: (a) establishment, (b) tillering, (c) yield formation, (d) ripening. (a) and (b) are courtesy of phil-lidar research center at the university of san carlos, philippines. iii. results and discussion a. classified image in figure 6 we can see the classified image of sugarcane while table ii shows the accuracy assessment result. fig. 6. result of the svm process using ecognition software. data are courtesy of phil-lidar research center at the university of san carlos, philippines. table ii. svm’s accuracy assessment for sugarcane confusion matrix user class/sample sugarcane shrub sum sugarcane 134 497 631 shrub 30 109771 111083 sum 1446 110268 accuracy producer 0.09266943292 0.9954928 user 0.2123613 0.9881890 hellden 0.129 0.9918275 short 0.06896551724 0.9837874 kia per class 0.08751539866 0.202 totals overall accuracy 0.9838069 kia 0.1221280 identification of the growth stages was conducted by gps field survey. the best features used in rgb are texture information by visual inspection. according to [32] the classification accuracy and reliability are visually estimated using rgb orthomosaic. with the validation points of the gps, the classification process using svm parameters was applied to these areas. the high accurate results in growth stages classification can then be used for mapping and monitoring sugarcane growth stages in philippines and in other sugarproducing countries in the world. the classified images of each growth stage are shown in figure 7. table iii shows the accuracy assessment result of each stage. (a) (b) (c) (d) fig. 7. classified images of the growth stages of sugarcane, processed with ecognition software. (a) establishment stage, (b) tillering stage, (c) yield formation stage, and (d) ripening stage. data is courtesy of phil-lidar research center at the university of san carlos, philippines. table iii. accuracy assessment after svm growth stages accuracy assessment (%) kia (%) establishment 87.5 75 tillering 94.4 83.9 yield formation 96.3 88.6 ripening 91.7 82.3 the land classification map of the growth stages of sugarcane is exhibited in figure 8. the points were overlaid and merged with the shape file of barangay manga using qgis to find the growth stages of sugarcane. utilization of qgis allowed the feature selection of the specific image map of the area. b. comparison the research in [34] on monitoring sugarcane growth phases based on satellite images is more or less similar to the current study, though the data employed in [34] come from landsat 8, and the vegetation indices of normalized difference vegetation index (ndvi) and enhanced normalized difference vegetation index (endvi) are employed to analyze the growing phases. field survey was also conducted. the engineering, technology & applied science research vol. 10, no. 4, 2020, 6041-6046 6045 www.etasr.com villareal & tongco: remote sensing techniques for classification and mapping of sugarcane growth ndvi and endvi results confirm the field data verification [34]. in the current study, the rs technologies used were lidar data, orthophoto images, and handheld gps for field survey. the results proved that they are also useful in the classification and identification of sugarcane growth stages. both studies use rs approaches in analyzing the growing phases of sugarcane and the harvest of sugarcane crops. fig. 8. land cover map of the growth stages of sugarcane processed with qgis software. data are courtesy of phil-lidar research center at the university of san carlos, philippines. iv. conclusion this study was able to test remote sensing technology and techniques in classifying sugarcane crop growth stages. ecognition and qgis software, lidar data, orthophotos, field work, and ground survey, all contributed to the making of the classification map, an output that locates the area of sugarcane plants and the specific growth stages of the crops in the study area. sugarcane plant classification revealed a high accuracy result of 98.4% while the ripening stage classification had an accuracy of 91.7%. the other growth stages, namely establishment, tillering, and yield formation yielded accuracy rates of 88%, 94.4%, and 96.3% respectively. with this highly satisfactory accuracy assessment, the rule set developed in mapping and identifying of the growth stages of sugarcane crops in this study could be the basis in mapping and checking other areas of sugarcane plantation and their growth stages in other parts of the country. acknowledgement this research was supported by phil-lidar research center at the university of san carlos, talamban campus through its project leader dr. roland emerito otadoy, research associate engr. beethoven arellano, and mr. james earl cabillas of phil-lidar 2. we would also wish to thank silliman university for providing the financial support. references [1] r. candare, m. japitana, j. e. cubillas, and c. b. ramirez, “mapping of high value crops through an object-based svm model using lidar data and orthophoto in agusan del norte, philippines,” isprs annals of photogrammetry, remote sensing and spatial information sciences, vol. iii–7, pp. 165–172, jun. 2016, doi: 10.5194/isprs-annals-iii-7-1652016. 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[34] m. v. japitana and m. e. c. burce, “a satellite-based remote sensing technique for surface water quality estimation,” engineering, technology & applied science research, vol. 9, no. 2, pp. 3965–3970, apr. 2019. microsoft word 12-822-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1269-1273 1269 www.etasr.com el-sinawi: production of hydrogen from poly ethylene terephthalate (pet) using ct 434 zsm-5... production of hydrogen from poly ethylene terephthalate (pet) using ct 434 zsm-5 catalyst at considerably low temperatures abdulaziz h. el-sinawi college of engineering king faisal university saudi arabia aelsinawi@kfu.edu.sa abstract—the production of hydrogen from poly ethylene terephthalate (pet) using ct 434 zsm-5 is investigated in this research study. gas chromatography equipped with a thermal conductivity detector is used to detect the amount of hydrogen produced at different temperatures. the chromatograph spectrum of pure hydrogen as well as the spectra of evolved gases at 250oc, 280oc, 310oc and 340oc are obtained to validate the presence of hydrogen. the spectra of percentage of hydrogen and peak area to height ratio with increasing temperature shows a similar trend except at the temperature of 340oc. maximum hydrogen percentage of 20.11% is found in the evolved gases collected at temperature of 250oc. the retention time of sample collected at 340oc is very close to reference retention time 2.014 min observed for a pure hydrogen sample. keywords-hydrogen; poly ethylene terephthalate (pet); gas chromatograph (gc); thermal conductivity detector (tcd) i. introduction the production of hydrogen has recently attracted the attention of scientists and researchers due to the increase in energy consumption to commensurate the rapidly growing technology and the dramatically increase in population. among different energy sources, the most popular and widely used energy source is fossil fuels. considering the over consumption, the decrease in the available stock and the high emissions of carbon dioxide, hydrogen may be an ideal candidate to be used as a greener energy. the production, storage and transport of hydrogen in an economical and safer way are major challenges for hydrogen to replace other sources of energy. today’s generation of hydrogen from hydrocarbon based compounds and derivatives are very popular [1-6]. hydrogen can also be produced by a steam reforming process. presently, a famous industrial process for the production of hydrogen is steam reforming of natural gas using methanol and ethanol as raw materials [7-9]. gases may be produced from the solid wastes first and then a steam-reforming process can be employed for hydrogen production [10]. recently a process to produce hydrogen from polyethylene (pe) milled with nickel hydroxide and calcium hydroxide was reported [11]. nickel hydroxide was dispersed completely among the samples converted to nickel metal during the heating process that act as catalyst to enable the conversion. calcium hydroxide fixed the carbon dioxide and allowed the production of hydrogen in high purity. production of hydrogen from pet (c10h8o4) using a ct 434 zsm-5 catalyst may provide an easy and sophisticated procedure to get hydrogen that can be used as green energy in the future. in this paper the production of hydrogen gas from pet using a ct 434 zsm-5 catalyst at various temperatures is studied. a perkinelmer clarus 580 gas chromatograph with a built-in auto-sampler equipped with a thermal conductivity detector had been used to detect the evolved hydrogen as a result of reaction. ii. experimental set-up a. materials a list of the materials used is given below:  polyethylene terephthalate (pet) square shape pieces (1cm×1cm): 20gm  ct 434 zsm-5 catalyst powder: 10gm  electric heater  five air tight glass vials with rubber lids for hydrogen samples collection  three necked (flanges) round bottom flask  an ebro tcl 730 infrared thermometer with readings up to 350oc  plastic tubes of 20 cm length with external diameter 3mm and internal 2mm having syringe needles on one end  a gas tight glass syringe for sample collection  hydrogen (h2): purity>99.99%  nitrogen (n2): purity >99.99% engineering, technology & applied science research vol. 6, no. 6, 2016, 1269-1273 1270 www.etasr.com el-sinawi: production of hydrogen from poly ethylene terephthalate (pet) using ct 434 zsm-5... b. instrument a perkinelmer clarus 580 gas chromatograph with thermal conductivity detector with a built in auto-sampler and a data acquisition system was used. a typical schematic diagram of the gas chromatograph (gc) system is shown in figure 1. fig. 1. a typical schematic diagram of a gas chromatograph with a thermal conductivity detector. c. methodsample collection small pieces of polyethylene terephthalate (pet) are obtained by cutting empty nestle mineral water plastic bottles in square shapes of 1×1 cm. these pieces are washed with boiling water and dried using an air drier. the round bottom flask with three flanges is used as a reactor. a sample of 20 gm of those pieces are placed in the reactor. ct 434 zsm-5 catalyst powder 10 gm is dispersed almost uniformly among the plastic pieces. an ebro tcl 730 infrared thermometer is fixed into the central flange of the reactor to record the temperature of the reactor. the thermometer is adjusted very carefully to read the temperature easily at different instants of time during the experiment. a glass capillary tube with a valve is open into the reactor through one of its flanges. a plastic tube with an internal diameter of 5 mm and external diameter of 7 mm having a syringe needle on its one end is fixed on the open end of glass capillary tube. the syringe needle is inserted into the glass vial. this vial is equipped with a purging valve. the third flange also has a valve to purge out the residual gases in the reactor before collecting the hydrogen gas sample. the reactor with above said arrangements is placed on an electric heater as shown in figure 2. electric power is turned on to start the heating process. it takes nearly 10 minutes to start the reaction between the pet pieces and the ct434 zsm-5. gases are evolved as a result of reaction with heating. these evolved gases can easily be observed. after few minutes, pressure is developed by the evolved gases and the air already present in the reactor. to minimize the presence of air in the reactor, the purging valve of third flange of reactor is opened and gases are released out freely. gases were purged out of the reactor several times using the purging valve to minimize the presence of air in the reactor. when the temperature rises up to 230oc, the valve of the capillary tube is opened and gas is allowed to rush to the vial. after some time, when a sufficient amount of evolved gases is accumulated, the vial is purged and evacuated several times to ensure that no air or any other gases are accumulated before collecting the actual hydrogen samples. when temperature reaches 250oc the first evolved gases sample was collected by closing the purging valve. this sample of evolved gas is considered to be taken at 250oc for the convenience of analysis purpose. similarly another vial is evacuated several times and then filled with evolved gases at 280oc. the same procedure was followed to collect two other samples at 310oc and 340oc respectively. the schematic diagram of experimental arrangements of the rector for hydrogen production and collection is shown in figure 2. fig. 2. a schematic diagram of experimental arrangements of the reactor for hydrogen production and collection d. gas chromatography  experiment is conducted with injector temperature of 150oc.  volume of 1ml produced hydrogen was collected from each sample at 250oc, 280oc, 310oc and 340oc .  each sample was manually injected through a septum with a gas tight syringe.  approximately 99.99% pure commercially available nitrogen is used as carrier gas with flow rate of 8.0ml/min. the gas chromatograph system was calibrated using pure hydrogen, hence 1ml volume was injected manually into the injector port through septum using the gas tight syringe. the spectrum of pure hydrogen was obtained for reference, then 1 ml of the collected gas samples from the reactor were analyzed at different temperatures (250oc, 280oc, 310oc and 340oc) respectively. spectra for gas samples collected at 250oc, 280oc, 310oc and 340oc was obtained for analysis. the sampling syringe had been purged several time to remove any residual gas from the previous runs. engineering, technology & applied science research vol. 6, no. 6, 2016, 1269-1273 1271 www.etasr.com el-sinawi: production of hydrogen from poly ethylene terephthalate (pet) using ct 434 zsm-5... iii. results and discussion the statistical data for the calibration curve is shown in table i. table i shows the experimental results of the mean hydrogen peak areas for injected volume of 0.5-2.5 ml pure hydrogen. figure 3 shows the linear fit of the peak points versus volume of injected hydrogen. it is clearly observed that the thermal conductivity response to the increasing volume of the injected hydrogen is approximately linear. table i. statistical data of injected hydrogen and peak area no injected volume (ml) peak area (µvs) 1 0.5 43739.4 2 1 87613 3 1.5 133864.8 4 2 201141.12 5 2.5 295130.14 fig. 3. linear fit of the peak area versus volume of pure hydrogen the reference spectra of pure hydrogen and the other spectra of collected samples of evolved gases at different temperatures, 250oc, 280oc, 310oc and 340oc are shown in figure 4. the retention time of pure hydrogen is observed at 2.014 min. the appearance of hydrogen spectra of evolved gas samples at nearly the same retention time indicates the production of hydrogen as a result of pyrolysis reaction of pet1 in the presence of the ct434 zsm-5 catalyst. the variation in retention time (peak position) versus the temperature of the reactor during the process is described in figure 5. the retention time for a sample taken at 250oc is 2.025 min and reached to the maximum of 2.029 min at 275oc whereas the retention time of hydrogen gas did not stay at the maximum for a long time, hence it decreased slightly to 2.027 min at 310oc. this deceasing trend continues to a minimum value of 2.015 min at 340oc, which is very close to the reference retention time of pure hydrogen (i.e. 2.014 min). it was observed that at higher temperature than 310oc, the collected hydrogen has similar trend as that of pure hydrogen with retention time of 2.014 min. fig. 4. pure and evolved hydrogen spectra at 250, 280, 310 and 340� fig. 5. retention time of evolved hydrogen versus temperature of reactor the variation of hydrogen percentage with temperature of the reactor is shown in figure 6. at temperature of 250oc, the hydrogen percentage is found to be around 20.11%. it decreases to 16.66% when the temperature rises up to 280oc and then increases slightly to 17.13% at 310oc. further slight increase in hydrogen percentage (i.e. 17.70%) was observed when the temperature increases up to 340oc. the maximum hydrogen percentage (20.11%) was obtained at 250oc while at high temperature (340oc) the maximum percent of hydrogen was still below that of 250oc. the variation of peak height of other evolved gases with the temperature is plotted in figure 7. the peek height starts from 18447.79 µv at 250oc then exponentially decreases to 17133.28 µv at 310oc where it increases rapidly at 340oc to reach the same peak level (i.e.18447.79µv) as that of 250oc. figure 8 depicts the impacts of temperature variations on the peak area to peak height ratio of hydrogen. it has been noticed that this ratio decreases rapidly from 2.68s at 250oc to 2.08s at 280oc, and then increases to a value of 2.38s at 310oc where it slightly engineering, technology & applied science research vol. 6, no. 6, 2016, 1269-1273 1272 www.etasr.com el-sinawi: production of hydrogen from poly ethylene terephthalate (pet) using ct 434 zsm-5... decreases again to 2.34s at 340oc. although there is little decrease in the peak height (i.e. 2.37s) at 310oc , but still it is very close to the originally obtained value (i.e. 2.38s); thus, the curve follows approximately a similar trend as that of hydrogen among the collected evolved gases except a minor decrease in peak area to height ratio at temperature of 340oc. fig. 6. variation of hydrogen percentage of the evolved gases with increasing temperature fig. 7. variation of peak height with the temperature of the evolved gases fig. 8. peak area/height ratio with increasing reactor temperature. iv. conclusion the production of hydrogen from poly ethylene terephthalate (pet) using ct 434 zsm-5 as a catalyst was experimentally investigated. hydrogen samples of the gases evolved from the reactor at different reactor temperatures were collected and analyzed. a gas chromatography machine with a thermal conductivity detector was used to detect hydrogen in the collected gas samples. hydrogen is observed in the spectra of gas samples at temperatures of 250oc, 280oc, 310oc and 340oc respectively. the presence of hydrogen is confirmed by comparing the spectra of evolved gas samples with the reference spectrum of pure hydrogen. the peak height values at 18430 µv and 18447.79 µv were noticeably very close to the values of the gas samples taken at 250oc and 340oc respectively. a similar trend is observed for peak area/height ratio and hydrogen percentage with increasing temperature of the evolved gases except a minor decrease in peak area/height ratio at the temperature of 340oc. maximum hydrogen percentage, around 20.11%, was found in the evolved gases at temperature of 250oc. the recorded retention time (i.e. 2.015 min) for the collected sample at 340oc was very close to the reference retention time (i.e. 2.014 min) of pure hydrogen. this process can be developed and utilized for the production of hydrogen from solid wastes to be used as a source of green energy. acknowledgment the author would like to thank king abdulaziz city for science and technology (kacst) for funding this ongoing strategic research project under the number ‘10-env1149-06’. the author would also gratefully acknowledge king faisal university (kfu) for furnishing the necessary research labs with cut of the edge technology and support to accomplish this work. references [1] p. d. vaidya, a. e. rodrigues, “insight into steam reforming of ethanol to produce hydrogen for fuel cells”, chem. eng. j., vol. 117, pp. 39-49, 2006 engineering, technology & applied science research vol. 6, no. 6, 2016, 1269-1273 1273 www.etasr.com el-sinawi: production of hydrogen from poly ethylene terephthalate (pet) using ct 434 zsm-5... [2] s. ahmed, m. krumpelt, “hydrogen from hydrocarbon fuels for fuel cells”, int. j. hydrogen energy, vol. 26, pp. 291-301, 2001 [3] a. n. fatsikostas, d. i. kondarides, x. e. verykios, “production of hydrogen for fuel cells by reforming of biomass-derived ethanol”, catal. today, vol. 75, no. 1-4, pp. 145-155, 2002 [4] f. melo, n. morlanes, “naphtha steam reforming for hydrogen production”, catal. today, vol. 107-108, pp. 458-466, 2005 [5] j. w. c. liberatori, r. ribeiro, d. zanchet, f. b. noronha, j. m. c. bueno, “steam reforming of ethanol on supported nickel catalysts”, appl. catal., a gen., vol. 327, pp. 197-204, 2007 [6] a. j. vizcaíno, a. carrero, j. a. calles, “hydrogen production by ethanol steam reforming over cu–ni supported catalysis”, inter. j. hydrogen energy, vol. 32, pp. 1450-1461, 2007 [7] j. g. seo, m. h. youn, j. c. jung, i. k. song, “hydrogen production by steam reforming of liquefied natural gas (lng) over mesoporous nickelalumina aerogel catalyst”, int. j. hydrogen energy, vol. 35, pp. 67386746, 2010 [8] r. padilla, m. benito, l. rodriguez, a. serrano, g. munoz, l. daza, “nickel and cobalt as active phase on supported zirconia catalysts for bio-ethanol reforming: influence of the reaction mechanism on catalysts performance”, int. j. hydrogen energy, vol. 35, pp. 8921-8928, 2010 [9] s. sa, h. silva, l. brandao, j. m. sousa, a. mendes, “catalysts for methanol steam reformingea review”, appl. catal. b environ., vol. 99, pp. 43-57, 2010 [10] a. v. maciel, a. e. job, w. da nova mussel, w. de brito, v. m. d. pasa, “bio-hydrogen production based on catalytic reforming of volatiles generated by cellulose pyrolysis: an integrated process for zno reduction and zinc nanostructures fabrication”, biomass and bioenergy, vol. 35, no. 3, pp. 1121–1129, 2011 [11] w. tongamp, q. zhang, f. saito, “hydrogen generation from polyethylene by milling and heating with ca(oh)2 and ni(oh)2”, int. j. hydrogen energy, vol. 33, pp. 4097-4103, 2008 microsoft word 37-3318_s_etasr_v10_n1_pp5301-5306 engineering, technology & applied science research vol. 10, no. 1, 2020, 5301-5306 5301 www.etasr.com shahami et al.: steady state stability analysis and improvement using eigenvalues and pss: a case … steady state stability analysis and improvement using eigenvalues and pss a case study of a thermal power plant in jamshoro, pakistan zulfiqar ali shahani department of electrical engineering mehran university of engineering and technology jamshoro, pakistan zulfiqar.shahani57@gmail.com ashfaque ahmed hashmani department of electrical engineering mehran university of engineering and technology jamshoro, pakistan ashfaquehashmani1@gmail.com muhammad mujtaba shaikh department of basic sciences and related studies, mehran university of engineering and technology jamshoro, pakistan mujtaba.shaikh@faculty.muet.edu.pk abstract—the efficient handling and distribution of electrical power consist one of the most complex and appealing research problems. due to the interconnection of different power plants and intensity of load, which gradually changes due to continuous change in load on generating units, careful treatment of the small disturbances in a power system which may lead to severe disturbance is necessary. stability is an essential part in electrical power system operation and control. the stability problem is related with the behavior of synchronous machine after the power system is subjected to trouble. this work presents steady state stability (sss) analysis of a jamshoro thermal power plant (jtpp) by using eigenvalue analysis of the different cases by varying load at three different positions. a mathematical model has been used for the jtpp with real data in order to examine the behavior of the system and to find the eigenvalues. a simulink model of the jttp for waveform analysis in matlab/simulink has been used without and with power system stabilizer (pss). numerical quantification of the eigenvalues under the examined cases categorizes the stability of the system. the waveforms of the system are analyzed, and in cases of instability, the proposed procedure utilizing pss helps in maintaining the system’s usual working conditions. the eigenvalue analysis and simulation results show the behavior of synchronous machines when loading changes gradually. the existing system becomes stable after more swings, whereas by using pss in the existing system, stable regimes are attained in less time. the obtained results demonstrate the effectiveness of the proposed solution for sss examination and securing of the disturbances of the jtpp. keywords-steady state stability; power plant; eigenvalues; power system stabilizer; matlab i. introduction in an electrical power system, it is essential to transmit reliable, secure and free from disturbances power, but load and external faults are independent which may affect voltage and frequency values, or even cause loss of synchronism [1]. the ability of a power system to remain stable after facing a small or large disturbance, which occurs in the existing system, is called power system stability. stability problems are divided into two categories: transient stability (ts) and steady state stability (sss) [2]. in ts, the power system remains in normal condition when a large disturbance occurs such as a loss of excitation, fault on the system, a sudden outage of line, removal of large load, etc. [3]. on the other hand, in sss, the power system remains in normal condition when small disturbances occur, such as gradual variation in electrical load [4]. nowadays, electrical power systems grow day by day, with increase of interconnection, installation of very large units, and extra high voltage (ehv) tie-lines [5]. ts is usually analyzed through euler method, modified euler method, and rungekutta (rk) methods whereas sss of the power system is usually examined using eigenvalues [6]. eigenvalues and wave-forms of synchronous machines were analyzed in [7]. the examination was carried out by varying faults at three different locations: generating point, middle of transmission line, and an infinite position. the fault near the machine appeared to be most severe. in [8], by varying instantaneous power disturbance, eigenvalues and wave forms were analyzed in power system generating units, disturbance of waveforms dependence on the amplitude and location of disturbance. according to [9] the sss of power systems by increasing loads is complementary to the usual ts investigations. to study the sss of a complex power system, eigenvalue analysis was used. in [10], analysis of sss on the near connection between the already-connected luzon-visayas grid with the isolated mindanao power grid was investigated in free and open-source software. there are not publicly available studies regarding this inter-connection. in [11], small signal stability analysis for a hybrid renewable energy system was conducted and an integrated hybrid system was analyzed with the help of lyapurav’s stability criteria and small signal stability disturbance with power system stabilizer (pss) through matlab/simulink. power flow and sss of interconnected three isolated philippine power grids was studied in [12]. eigenvalues analysis was employed to find the sss of the main power grid and a model was developed in matlab/simulink. according to [13], if the quantity of perturbation is very small, in the initial stage when there is small perturbation in the load, the system remains in stable condition (sss). under small perturbation if the eigenvalues of the mathematical model have corresponding author: muhammad mujtaba shaikh engineering, technology & applied science research vol. 10, no. 1, 2020, 5301-5306 5302 www.etasr.com shahami et al.: steady state stability analysis and improvement using eigenvalues and pss: a case … negative real parts, the system is under stable condition. in case the system becomes unstable, this means that the eigenvalues have positive real parts, while complex eigenvalues, produce oscillations in the system. in [14], the ts of a power system was verified by using time domain (td) analysis, and eigenvalues analysis when the system was brought under small disturbances. the use of facts devices for ts was investigated in [15]. other approaches like the use of fuzzy logic controllers [16] and harmonic function [17] have also been used to improve pss under different conditions [18]. in this paper, stable and efficient operation of a jtpp have been considered. stable operation, voltage stability, frequency stability, and rotor angle stability were studied. voltage stability considered voltage control through an automatic voltage regulator (avr) for frequency stability. focus was given on primary frequency control (pfc) through governor, and rotor angle stability focus is on the deviation of rotor speed. this work analyzes small signal stability which can be modified by using pss. in that way, the system becomes stable and will remain in stable condition for a long period of time. the proposed procedure assures the secure and reliable operation of the jtpp even in conditions when disturbance, either small or large, occurs in the system, by changing different loads. the objective of the current work is to analyze the stability of a power system under varying load at alternator side. by varying load at alternator side, it has been shown that the system has more swings when large load is connected on a power system. so, in order to remove more swings a pss was used. by using pss, the system became stable in less time. the main contribution of this work lies on the use of eigenvalues as indicators of the small signal stability in usual operation so that the unstable regimen may be analyzed and taken care of in order to retain stability. the use of pss on usual operation has also been tested and found to improve the stability regimen. ii. materials and methods the jtpp has four units, one with 16.5kv rated voltage and three with 15.75kv rated voltage. two transformers are used which step up from the rated voltage to 220kv transmission line voltage. a generating unit was developed in the mathematical model, at alternator side, at excitation side and at prime mover governing system side. the eigenvalues were found and the analyzed system’s stability was improved by pss. a. plant overview the plant was visited and all the necessary data, parameters, and specifications mentioned in tables i-ii were collected. b. small signal stability analysis the ability of the running power system to maintain synchronism after the occurrence of small interruption is known as steady state stability [1]. as variations occur in the system, they cause small unbalances. a dynamic equation model of the system will be developed and will be linearized to understand sss. table i. system parameters and specifications type units 1 synchronous machine fthri 562/68-2 2-4 synchronous machines qfsn-210-2 connections 3-phase star 3-phase star power in mw 250 210 rated current 10.294ka 9.056ka rated voltage 16.5kv 15.75kv visual power 294200kva 247000kva power factor 0.85 0.85 speed 3000rpm 3000rpm critical speed second order 3590rpm 3494rpm critical speed first order 1200rpm 1263rpm rated excitation voltage 370v 489v rated excitation current 2020a 1867a efficiency 99.02% 98.66% pressure of h2 3kg/cm 2 0.3mpa water flow for stator winding ---35m 3 /h insulation class f f table ii. power transformer properties and specifications model units 1 ad69030t1 2-4 sfp7250000/220ta rated power 294.2mva 250000kva rated current 772/10294a 656.1/9164.3a rated voltage 220/16.5kv 220±4x2.5%/15.75kv cooling type oil immersed, (odaf) cooled oil immersed, (odaf) cooled frequency 50hz 50hz poles 3 3 temperature class a a connection of symbol yn. d1 yn. d1 noise level 90db (a) 75db load loss <500kw 609.9kw no load loss <520kw 613.6kw no load current 0.2% 0.12% impedance voltage 15% 13.5% under balanced condition, we may define the system as: ∆ẋ = a∆x (1) it is defined as the rate of change of each state variable with the linear composition of all thee states available in the system. to inscribe the small signal analysis problem, the modified state vector z is described in equation (2): ∆x = ϕ� (2) the variable matrix φ is the right modal matrix of vector a. a is consisting of n right eigenvectors φᵢ;i∈n . equation (3) is developed by combining (1) and (2): ϕż = aϕ� (3) by rearranging (3), we get: ż = φ¯�aφz = ⋀z (4) λ represents a matrix having diagonal elements of eigenvalues where λ=i belongs to n, so (5) represents n engineering, technology & applied science research vol. 10, no. 1, 2020, 5301-5306 5303 www.etasr.com shahami et al.: steady state stability analysis and improvement using eigenvalues and pss: a case … decoupled first order: żᵢ = λᵢz i (5) the resolved form of (5) is: zᵢ�t� = zᵢ�0���ᵢ� (6) to obtain zi(0), (7), can be written as: z�t� = φ¯�∆x�t� = ѱ∆x�t� (7) where ψ is the left matrix of vector a, which consist of n left eigenvectors ψi, hence every variable of state and its starting condition are given as: zᵢ�t� = ѱᵢ∆x�t� ;zᵢ�0� = ѱᵢ∆x�0� (8) in accordance with (6), the actual state vector ∆x(t) is written as: ∆x�t� = ∑ ѱᵢcᵢ��ᵢ��� � (9) with cᵢ as zᵢ(0). the actual state variable ∆xᵢ(0) can be extracted from (2) and (9): ∆xᵢ�t� = ѱᵢ₁c₁��"� + ѱᵢ₂c₂��%� +⋯+ѱ'(c(�� ) � (10) free motion quickness of the power system is determined by the linear composition of eigenvalues, dynamic modes and left/right eigenvectors. the frequency behavior of the system can be successfully examined and evaluated by using the ssa in terms of the time-domain simulation (tds). linear analysis can be obtained by using digsilent software and the nonlinear tds of the dynamic system, which makes it easy by software. the major benefits of the linear model are that it gives the opportunity for using the eigenvalues to adjust the frequency handling controllers and the use of eigenvectors to trace the contents of the frequency regulation mode. generators’ frequency shows the condition of the systems which may be scripted in the forms of entire eigenvalues and conditions of the system by using (10)[19]: ωᵢ�t� = ѱᵢ�c�+, "+ ѱᵢ.c.+, %+⋯+ѱᵢ(c(��)� (11) c. general mathematical model the electrical system exists on synchronous machines connected to an infinite bus bar. there are four conditions to sink the alternator with the infinite bus. it must have the same value of voltage, frequency, phase sequence, and phase angle difference. every alternator has two main controllers, one for speed, called governor and another for voltage, the avr. by varying load gradually at the alternator side through matlab/simulink, we analyzed the small disturbances without pss and with pss. in the two axis model, the synchronous alternator consists of the transient and sub transient effect. the transient effects are taken into consideration and sub transient effects are considered as negligible, so the effects of transients are overcome with the rotor circuit which is the field circuit in the d-axis and q-axis formed by solid rotor [1]. 1) swing equation ω/ = �01 �p3 −d6ω− p7� (12) 2) rotor angle equation ∂/ = �ω−ω9� (13) 3) excitation system every alternator has an avr. through the avr we can control the terminal voltage of an alternator by varying field current and maintain the terminal voltage as per our needs. usually loop gain ka must be as per command of avr, if the loop gain is very high the system will be unstable, if it is very low the system performance of avr step response will be unsatisfactory. therefore, to enhance the related stability and steady state behavior, the transformer is used for stabilizing. ė;< = � => ?−e;< +�ab7c − a� −ad�kfg (14) v/d = � =i ?−vd +e;<g (15) the transient voltage of armature on d and q-axes may be indicated like: ėdk = � =klm n−edk +�op −oqk�ips (16) ėdp = � =ktm ?u;< −edk + �ok −oqk �ikg (17) 4) governor system when the load on alternator increases suddenly, it causes rapid change in the governor intake. the deficient power is delivered by the kinetic energy of the rotary system. so, the depletion in kinetic energy decreases the alternator speed, hence change in new operating speed is identified by the governor which will act to adjust the intake valve to generate the mechanical power output which will counterbalance the normal operating position. the equations that express the prime-mover governing system are: ṗw = � =xy n−pw + k6�ωb7c −ω�s (18) ṗz = � =x[ ?−pz +pwg (19) ṗ\z = � =][ ?−p\z +pz +p39 g (20) ṗ3 = � =y[ ^−p3 +ṗ\z + _y[=y[ =][ �−p\z +pz +p39 �` (21) the standard action for small faults is basically that the disturbed system may be linearized near quiescent operating point. m6∆ω/ = ∆p3 − d6∆ω−idk9∆edk − idp9∆edp − edk9∆ik −edp9∆ip (22) ∆∂/ = ω9∆ω (23) tf∆/e;< = −∆e;< + kf�−∆ad −c�∆uqk − c.∆uqp +cd∆ek +cf∆ep� (24) −k;∆/u;< + t;∆v/d = −∆vd (25) tdp9∆/edk = −∆edk − �op − ok�ip (26) tdp9∆/edp = ∆e;< − ∆edp +�ok −oqk�∆ik (27) engineering, technology & applied science research vol. 10, no. 1, 2020, 5301-5306 5304 www.etasr.com shahami et al.: steady state stability analysis and improvement using eigenvalues and pss: a case … tdb∆ /pw � 4∆pw 4 g6∆ω (28) td3∆ /pz � 4∆pz # ∆pw (29) t\z∆ /p\ � 4∆p\ # ∆pz (30) 4kbzt3∆ /ph # t3∆ /p3 � 4∆p3 # ∆p\ (31) where f� � jtm j-m , f. � jlm j-m , fd � f.xdk 4 f�rn , and ff � 4f�xdk 4 f.rn. we consider vb7c � 1p.u ω9 � 1p.u and vd � 0. d. proposed stability snalysis of the jtpp the flowchart given in figure 1 represents the work division in two parts. one part consists of the mathematical model, in which stability is analyzed through eigenvalues. if the eigenvalues are negative, the system is in stable state. if the obtained eigenvalues are positive, the system is in state of instability, and it will be stabilized by the pss. in the other part, the developed matlab/simulink model, stability is analyzed through waveforms, and is also improved by pss. fig. 1. flow chart of the proposed identification by eigenvalues and pss the equation for a system under an instability state can be given in matrix form as follows, here we can determine eigenvalues. ?fg?xg/ � ?bg?xg # ?dg?ikpg (32) ikp � lgx . ./ fx �/ �b # dgl�x . ./ x/ � �fy��b # dgl�x/ ) (33) . ./ x/ � ax (34) the values of a matrix are known. finally, the eigenvalues are obtained with matlab r2017a. eigenvalues play an important part in determining power system stability. two real separate eigenvalues have the same symbols. both may be positive or negative. positive values will show that the system is unstable and negative will show that the system is stable. nodal real eigenvalues with two eigenvectors are unstable if these are positive and the opposite if they are negative. saddle points with two distinct real eigenvalues of opposite signs are always unstable [6]. on the spiral chart, there are complex eigenvalues with non-zero and real parts. the system is unstable if the real part is positive and stable if the real part is negative. on the other hand, improper node represents unstable condition if it is positive and asymptotically stable if it is negative [19]. figure 2 shows an existing electrical power system with generating unit, circuit breakers, transformer, and infinite bus. three different loads are applied at generating stations and the waveforms are monitored. severe disturbance occurs when more loads are applied. figure 3, similarly, shows the developed matlab/simulink model modified by pss. stability is analyzed by changing load after modification. it has been concluded that the system becomes stable in a very short time after the modification when compared to the system of figure 2. fig. 2. matlab/simulink model without pss fig. 3. matlab/simulink model with pss the data regarding the parameters of the simulation model defined in (11)-(20) were obtained from the jtpp and are given in p.u. in table iii. iii. results and discussion by varying reheat system prime mover gain krh=0.3, 2, 2.5, and 10, we find that at krh=10 the system is unstable. figures 4-7 represent the system’s eigenvalues. in normal condition, the system is stable with constant speed (no deviation), constant output voltage, and constant output power. when load changes, small disturbances occur. engineering, technology & applied science research vol. 10, no. 1, 2020, 5301-5306 5305 www.etasr.com shahami et al.: steady state stability analysis and improvement using eigenvalues and pss: a case … table iii. data obtained from jtpp parameters symbols values symbols values mg 8 tdqo 0.3 dg 0 xq 1.58 iddo 0.39 xdd 0.32 idqo 0.6329 xd 1.67 eddo 0.1248 tsr 0.1 edqo 0.9999 kg 4 wo 1 tsm 0.2 ta 0.05s tch 0.2 to 0.5s ka 50 krh 0.3,2,2.4 and 15 f1 0.9523 tm 0.93 f2 0.9523 po 0.8 f3 0.2322 vdo 1 f4 0.2344 vto 1.05 kf 0.11 vqo 0.999 tf 0.7 ra 0.0023 fig. 4. stable condition at krh=0.3 fig. 5. stable condition at krh=2 fig. 6. stable condition at krh=2.5 fig. 7. unstable condition at krh=10 fig. 8. without pss when 240mw load is connected fig. 9. with pss when 240mw load is connected fig. 10. without pss when 300mw load is connected the behavior of a synchronous machine with small disturbances has been analyzed with the help of maltab/simulink, when 240mw, 300mw, and 175mw load changes. the respective waveforms are shown in figures 8, 10, and 12 with pss and in figures. 9, 11, and 13 without pss. the instabilities were identified using eigenvalues, as shown in figures 4-7, they have been overcome and quickly minimized with the help of pss. engineering, technology & applied science research vol. 10, no. 1, 2020, 5301-5306 5306 www.etasr.com shahami et al.: steady state stability analysis and improvement using eigenvalues and pss: a case … fig. 11. with pss when 300mw load is connected fig. 12. without pss when 175mw load is connected fig. 13. without pss when 175mw load is connected iv. conclusion nowadays, electrical power systems are more complex in nature and widely interconnected. continuous changes in load cause deviation in frequency and voltage. these changes result in small disturbances in the power system posing instability problems. hence, steady state stability is important for generating stations. this work proposes a mathematical model and a matlab/simulink model. eigenvalues are found and employed for finding whether the system is stable or unstable. when they are negative the system stable and vice versa. matlab/simulink model demonstrates the variations in the waveform by varying load, and then improves by applying pss. this work promotes fast recovery in stable condition when unstable conditions occur in a system when the load gradually changes. this method is helpful for improving the reliability and stability of the system and small disturbances can be rectified without further isolation. acknowledgment the authors would like express their gratitude to the mehran university of engineering and technology authorities for their support. references [1] n. balu, t. bertram, a. bose, v. brandwajn, g. cauley d. curtice, a. fouad, l. fink, m. g. lauby, b. f. wollenberg, j. n. wrubel, “on-line power system security analysis”, proceedings of the ieee, vol. 80, no. 2, pp. 262-282, 1992 [2] b. singh, “applications of facts controllers in power systems for enhance the power system stability: a state-of-the-art”, international journal of reviews in computing, vol. 6, 2011 [3] t. s. sidhu, d. a. tziouvaras, a. p. apostolov, c. h. castro, s. r. chano, s. h. horowitz, w. o. kennedy, s. kim, r. j. martilla, p. g. mclaren, g. l. michel, “protection issues during system restoration”, ieee transactions on power delivery, vol. 20, no. 1, pp. 47-56, 2005 [4] y. song, b. wang, “survey on reliability of power electronic systems”, ieee transactions on power electronics, vol. 28, no. 1, pp. 591-604, 2012 [5] e. mariani, s. s. murthy, advanced load dispatch for power systems: principles, practices and economies, 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and power system stabilizer design for grid-connected photovoltaic generation system, phd thesis, carleton university, 2015 [12] k. himaja, t. s. surendra, s. t. kalyani, “steady state stability analysis of a single machine power system by using matlab”, international journal of engineering research & technology, vol. 1, no. 7, 2012 [13] y. c. choo, m. a. kashem, m. negnevitsky, “assessment of small disturbance stability of a power system”, australasian universities power engineering conference, victoria, australia, december 10-13, 2006 [14] w. yang, hydropower plants and power systems: dynamic processes and control for stable and efficient operation, springer; 2019 [15] n. e. akpeke, c. m. muriithi, c. mwaniki, “contribution of facts devices to the transient stability improvement of a power system integrated with a pmsg-based wind turbine”, engineering, technology & applied science research, vol. 9, no. 6, pp. 4893-4900, 2019 [16] o. kahouli, b. ashammari, k. sebaa, m. djebali, h. h. abdallah, “type-2 fuzzy logic controller based pss for large scale power systems stability”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3380-3386, 2018 [17] g. shahgholian, a. fattollahi, “improving power system stability using transfer function: a comparative analysis”, engineering, technology & applied science research, vol. 7, no. 5, pp. 1946-1952, 2017 [18] d. v. ngo, k. v. pham, d. d. le, k. h. le, k. v. huynh, “assessing power system stability following load changes and considering uncertainty”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2758-2763, 2018 [19] r. azizipanah-abarghooee, m. malekpour, m. s. ayaz, m. karimi, v. terzija, “small signal based frequency response analysis for power systems”, 2018 ieee pes innovative smart grid technologies conference europe, sarajevo, bosnia-herzegovina, october 21-25, 2018 microsoft word 23-3406_s__etasr_v10_n2_pp5470-5476 engineering, technology & applied science research vol. 10, no. 2, 2020, 5470-5476 5470 www.etasr.com tellala et al.: α modified emd-acwa denoising scheme using a noise-only model α modified emd-acwa denoising scheme using a noise-only model ihssene tellala lis laboratory department of electronics ferhat abbas setif university 1 setif, algeria ihcene-electro@hotmail.fr nourredine amardjia lis laboratory department of electronics ferhat abbas setif university 1 setif, algeria amardjianour@univ-setif.dz abderrezzak kesmia lccnc laboratory department of electronics ferhat abbas setif university 1 setif, algeria arz.kesmia@gmail.com abstract—this paper describes a modified denoising approach combining empirical mode decomposition (emd) and adaptive center-weighted average (acwa) filter. the intrinsic mode functions (imfs), resulting from the emd decomposition of a noisy signal, are filtered by the acwa filter, according to the noise level estimated in each imf via a noise-only model. the noise levels of imfs are estimated by the characteristics of fractional gaussian noise through emd. it is found that this model provides a better estimation of noise compared to the absolute median deviation of the signal used in the conventional method. the proposed emd-acwa scheme is tested on simulation and real data with different white gaussian noise levels and the results are compared with those obtained by the conventional emd-acwa, emd interval thresholding (emdit) and wavelet methods. test results show that the proposed approach has a superior performance over the other methods considered for comparison. keywords-empirical mode decomposition; adaptive center weighted average; noise-only model; signal denoising i. introduction signal denoising is a key process in speech, image, and other signal processing applications. it enables noise removal to its maximum extent in order to restore the original signal [13]. linear methods, such as wiener filtering [4] are among the simplest and commonly used methods to suppress noise from a signal, yet they remain not effective for nonlinear and nonstationary signals which are usually the case of real signals. noise reduction methods based on wavelets [5-8] have been the dominant techniques for several years. in wavelet domain, the signal enhancement is based on applying a thresholding to wavelet coefficients of the noisy signal. wavelet based methods are relatively more suitable for non-stationary signal analysis. however, the main drawback of these techniques is that the basic functions are predetermined, which results in mismatching with the varying nature of signals. empirical mode decomposition (emd) [9] has been extensively used as an alternative approach to analyze non-stationary and nonlinear signals. unlike wavelet methods, the basic functions of emd methods are derived directly from the signal itself. the emd principle is to decompose adaptively a given signal into a finite number of components, called intrinsic mode functions (imfs) through an iterative process known as “sifting”. in [10-13], the statistical characteristics of white fractional gaussian noise have been extensively studied by emd. it was proved that the emd acts as a dyadic filter bank when applied to various types of noise and therefore is a powerful tool for removing noise from observed data [14-16]. among the most important methods of emd-based denoising, is the denoising by reconstructing the signal with previously thresholded imfs [16, 17]. in [18], a denoising approach, called emd interval thresholding (emd-it), was developed by applying the wavelet thresholding principle to the imfs resulting from the emd decomposition. the threshold was obtained by using the statistical characteristics of the white gaussian noise through emd. authors in [1, 19] proposed a novel emd-based denoising method by applying the adaptive center weighted average (acwa) filter to the imfs and provided the term emd-acwa. however, their study is limited to only speech signals. the acwa is a simple filter which has been used largely in white noise suppression in image enhancement applications [20, 21]. stationarity of the signal is not necessary for the implementation of acwa filter because it operates in the time domain. in the current study, a modified emd-acwa method for signal denoising is proposed by adding an improvement to the strategy developed in [1]. the improvement is achieved by estimating the noise contained in each imf using a noise-only model [11], thus enhancing the accuracy of noise estimation. the proposed emd-acwa denoising scheme is tested on real speech signals of corpora database [22], real ecg records from the mit-bih arrhythmia database [23], and different simulation signals. ii. empirical mode decomposition the emd method was developed from the assumption that any non-stationary and nonlinear time series consists of different simple imfs. each imf has a distinct time scale and acts as a basis function which must meet the following two conditions: corresponding author: ihssene tellala engineering, technology & applied science research vol. 10, no. 2, 2020, 5470-5476 5471 www.etasr.com tellala et al.: α modified emd-acwa denoising scheme using a noise-only model • in the whole signal, the number of local extrema must be equal with the number of zero crossings or differ at most by one. • the average value of the local maxima envelope and the local minima envelope is zero. the sifting algorithm to obtain imfs of a signal ( )x t could be described as [9]: 1. find the local extrema (maxima and minima) of the signal ( )x t . 2. construct the upper and lower envelopes max ( )e t and min ( )e t , respectively, using cubic spline interpolation. 3. determine the local mean as: [ ]1 max min( ) ( ) ( ) 2m t e t e t= + 4. subtract 1 ( )m t from the original signal to form the details 1 1 ( ) ( ) (t)h t x t m= − . 5. decide whether 1 ( )h t is an imf or not by checking the two basic conditions mentioned above. 6. regarding 1 ( )h t as the new data and repeating steps 1 to 5 until the first imf 1 1 ( ) ( )c t h t= , is obtained. 7. compute the residual 1 1 ( ) ( ) ( )r t x t c t= − . 8. the residual is treated as the new data and the steps 1 to 7 are repeated until all the imfs are obtained. at the end of the algorithm, the emd decomposition of ( )x t is given by: ( ) ( ) 1 ( ) n j n j x t c t r t = = +∑ (1) where n is the number of imfs, ( ) j c t is the th j imf and ( ) n r t is the residue. iii. proposed method a. conventional emd-acwa approach the conventional emd-acwa denoising is based on filtering the imfs resulting from emd decomposition by the acwa [1]: ( ) ( )( ) 2, , mean j j mean var j j mean f k c t f if f c t f otherwise σ + − ≥ =   � (2) with: 2 1 j j var k f σ = − (3) where mean f and var f are the average and the variance of the noisy imfs computed over an (l) sized window respectively, and �� � is the variance of the noise contained in the thj noisy imf. the absolute median deviation of imfs is used to estimate the noise variance in this method as follows [16]: ( ) ( )( )( ) 2 2 0.6745 j j j meadian c t median c t σ  −   =       (4) the denoised signal is the sum of all filtered imfs. b. proposed emd-acwa denoising an improved emd-acwa denoising scheme is proposed by estimating the noise energies of all imfs using an energy model, called noise-only model, introduced in [24] and which gives a better estimate of the noise contained in each imf. based on emd studies, it turns out that emd acts on fractional gaussian noise as a dyadic filter bank. the noise energy contained in the thj imf can be parameterized by a function of the first imf energy as [24]: ( )1 ˆ ˆ , 2, 3..., j j h h e e j nρ β − = = (5) where 1ê is the noise energy of the first imf estimated by (4), hβ and hρ are experimentally estimated for white gaussian noise (h=0.5) as 0.719hβ = , and 2.01hρ = . on the basis of this model, a new formulation of the conventional method is developed to improve its denoising efficiency. the proposed emd-acwa denoising scheme is summarized in the following steps: 1. perform an emd decomposition of the noisy signal x(t). 2. calculate the noise energy contained in the first imf using (4). 3. compute the noise energies contained in the rest of imfs using the noise-only model, as in (5). 4. filter all imfs by the acwa filter over a window of size (l) based on noise energy estimated in each imf as follows : ( ) ( )( ) ˆ, , mean j j mean var j j mean kn c t f if f e cn t otherwise f f  + − ≥ =   � (6) with: ˆ 1 j j var e kn f = − (7) 5. reconstruct the denoised signal : ( ) 1 ( ) ( ) n j n j x t cn t r t = = +∑ �� (8) figure 1 shows a comparison between the estimated noise energies of imfs calculated by the median method using (4), and the noise-only model using (5). the signal is contaminated engineering, technology & applied science research vol. 10, no. 2, 2020, 5470-5476 5472 www.etasr.com tellala et al.: α modified emd-acwa denoising scheme using a noise-only model by white gaussian noise with an input signal to noise ratio (snr) of 4db. from this figure, we can see that the noise-only model follows the noise level much better than the median estimation. the median method diverges significantly from the actual energy of noise in the last imfs (from 6 to 10) that enclose high energy concentration. in addition of a piecewiseregular signal, two other types of test signals and their noisy versions shown in figure 2 have been used in this section to study the proposed emd-acwa denoising approach. figure 2(a) is a speech signal from corpora database [22] and figure 2(b) is an ecg record of 2048 length chosen from the mitbih database [23].they are corrupted by white gaussian noise corresponding to 4db of input snr. figure 3 shows the results, together with the achieved snrs, when the proposed emdacwa denoising are applied on the noisy signals shown in figure 1(a), figure 2(c) and figure 2(d). fig. 1. (a) a piecewise regular signal and its corresponding noisy signal with input snr of 4 db. (b) comparison of noise estimation obtained by median method and noise-only model in this example, the size (l) of the acwa filter window for the proposed emd-acwa approach is fixed to 161, 201 and 41 for the piecewise-regular, speech, and ecg signals respectively. the black line is the clean signal, and the red one is the denoised signal. as it’s shown, the denoised version of noisy signals tracks the clean one closely, producing significant snr improvements where the output snrs have increased to 15.49db, 12.18db and 14.60db in the cases of the piecewiseregular signal, speech signal and ecg signal respectively. fig. 2. (a), (b) clean versions of a speech signal and ecg record 100. (c), (d) their noisy versions (input snr=4 db) figure 4 illustrates the results of denoising when the proposed emd-acwa, conventional emd-acwa, emd-it and wavelet methods are applied to the noisy piecewise regular signal of figure 1(a). the daubechies 8 wavelet (db8) with a hard threshold as a tool of comparison was used because it gives good results compared to the other wavelets. the black line is the clean signal and the red one is the denoised signal. clearly, the proposed approach performs better than the other emd-based methods and the wavelet one. the proposed scheme provides an improvement of about 2.85db compared to the conventional emd-acwa. iv. results and discussion in order to study further the efficiency of the proposed method, tests were applied on different simulation and real signals. besides the piecewise regular signal, “doppler”, “blocks” and “bumps” signals are considered in this section (figure 5). they were generated by the matlab function wnoise(fun, n) which returns ( )x t values of the test signal “fun” (eg. fun=1 for blocks signal) evaluated at 2 n linearly spaced points. experiments have also been conducted on thirty real speech signals from corpora database [22] and thirty real ecg records from the mit-bih arrhythmia database [23]. ecg and simulation signals are sampled with a sampling frequency that results in 2048 samples. the speech signals are sampled at 16khz with 16-bit resolution. (a) (b) (b) (c) (d) (a) engineering, technology & applied science research vol. 10, no. 2, 2020, 5470-5476 5473 www.etasr.com tellala et al.: α modified emd-acwa denoising scheme using a noise-only model fig. 3. results of the proposed emd-acwa denoising. (a) piecewiseregular, (b) speech signal, (c) ecg signal fig. 4. results of the piecewise regular signal denoising. (a) proposed, (b) conventional emd-acwa, (c) emd-it, (d) daubechies 8 wavelet figure 6 shows the variation of the output snr versus the size (l) of the acwa filter window for different values of input snr, when the proposed method is applied on the simulation and real signals. the best choice of the window size for simulation signals is l=161. in the case of real signals, the best choice of parameter l is 201 for speech signals and 41 for ecg signals. as an evaluation criterion of different methods, we use the snr after denoising in case of simulation and ecg signals. in case of speech signals, the evaluation is based on snr and the weighted-slope spectral distance (wss). all the results presented in this section for the real signals correspond to the average of the ensemble of the results obtained by the different 30 test signals. noisy versions of the different signals are generated by adding white gaussian noise to the clean signals with different input snrs varying from -10 to 8db. the best parameters of the size of the acwa filter window are taken into account when applying the conventional emdacwa denoising and the proposed method on the different noisy signals. the performance evaluation of the proposed emd-acwa, conventional emd-acwa, emd-it and wavelet methods when applied on simulated signals is shown in figure 7. the curves correspond to the output snr versus the input snr of different signals: piecewise regular, doppler signal, blocks signal and bumps signal. the reported results show the effectiveness of the proposed emd-acwa method in denoising as it gives a higher enhancement in snr compared to the other three methods in all cases, especially for low values of input snr. for relatively high values of input snr (>6db), the conventional emd-acwa method gives the worst denoising results. when applied to the simulated signals, the proposed approach leads to gains between 1 to 4db compared to the conventional emd-acwa method, 0.55 to 1.84db compared to emd-it one and 1.45 to 7.2db compared to the wavelet one. from these results, we can say then that the proposed denoising method gives the best results. fig. 5. test signals. (a) doppler, (b) blocks and (c) bumps figure 8 depicts the denoising results of the proposed method and the other methods considered for comparison when applied on speech and ecg real signals. (c) (b) (b) (b) (a) (a) (c) (d) (c) (a) engineering, technology & applied science research vol. 10, no. 2, 2020, 5470-5476 5474 www.etasr.com tellala et al.: α modified emd-acwa denoising scheme using a noise-only model fig. 6. effect of the size (l) of the acwa filter window on the performance of the proposed method when it is applied on simulation and real signals. (a) piecewise regular, (b) doppler signal, (c) blocks signal, (d) bumps signal, (e) speech signals, (f) ecg signals fig. 7. performance evaluation of the denoising methods applied on simulated signals. (a) piecewise regular, (b) doppler, (c) blocks, (d) bumps (b) (a) (c) (d) (e) (f) (a) (b) (c) (d) engineering, technology & applied science research vol. 10, no. 2, 2020, 5470-5476 5475 www.etasr.com tellala et al.: α modified emd-acwa denoising scheme using a noise-only model with respect to the real speech signals (figure 8(a)), the proposed method outperforms the others for almost all snr levels, especially in range of -6 to 6 db. the proposed approach offers improvements in output snr up to 2.85db when compared to the conventional one, 2.45db compared to emd-it, and 1.07db when compared to the wavelet method. in regards with the real ecg signals (figure 8(b)), the conventional emd-acwa method gives a very low performance in all cases of input snr. in contrast, the proposed approach exhibits a significant performance improvement compared to other methods and especially the conventional one. it leads to improvements in output snr up to 6.95db compared to the conventional emd-acwa, 2db compared to the emd-it, and 1.86db compared to the wavelet method. fig. 8. performance evaluation of the denoising methods applied on real data. (a) speech signals, (b) ecg signals table i. compparison of the wss distance input snr proposed emd-acwa emd-it wavelet -10 57.737 63.953 141.346 202.353 -6 52.459 58.484 107.869 166.487 -2 45.064 53.532 75.014 115.603 0 41.311 50.806 65.267 92.924 2 38.745 48.684 58.019 84.236 6 32.323 43.822 41.319 59.214 10 26.123 37.584 33.200 39.720 another measure that characterizes the performance of speech denoising methods is the weighted-slope spectral (wss) distance [25], which is shown in table i for different values of input snr. the proposed emd-acwa approach gives the lowest wss distance which indicates a less distortion degree for all snr levels. although the wavelet method gives good results of snr, it gives inferior quality results of wss. v. conclusion in this paper, the acwa filter was combined with the noise-only model obtained by means of emd decomposition to improve the denoising performance of the conventional emdacwa method. the proposed method shows important enhancement in denoising when using the noise only model along with the acwa filter and choosing the appropriate size of the filter window. to illustrate the effectiveness of the proposed approach, numerous simulations were carried out with different input snrs, ecg and speech signals. this improved approach exhibits a superior performance compared with emd-it, conventional emd-acwa, and wavelet methods for all test signals whatever the value of the input snr. the results were confirmed by the wss measure in the case of speech signals. references [1] k. khaldi, m. t. h. alouane, a. o. boudraa, “speech denoising by adaptive weighted average filtering in the emd framework”, 2nd international conference on signals, circuits and systems, monastir, tunisia, november 7-9, 2008 [2] m. rakshit, s. das, “an efficient ecg denoising methodology using empirical mode decomposition and adaptive switching mean filter”, biomedical signal processing and control, vol. 40, pp. 140-148, 2018 [3] m. v. sarode, p. r. 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//www.physionet.org/physiobank/database/nstdb [24] p. flandrin, g. rilling, p. goncalves, “emd equivalent filter banks, from interpretation to applications”, in: hilbert-huang transform and its applications, world scientific, pp. 57-74, 2005 [25] d. klatt, “prediction of perceived phonetic distance from critical-band spectra: a first step”, ieee international conference on acoustics, speech, and signal processing, paris, france, may 3-5, 1982 engineering, technology & applied science research vol. 8, no. 3, 2018, 2869-2874 2869 www.etasr.com nguyen et al.: forecast on 2030 vietnam electricity consumption forecast on 2030 vietnam electricity consumption vu h. m. nguyen faculty of electrical and electronics engineering hcmc university of technology and education ho chi minh city, vietnam vuminh.1974@gmail.com cuong v. vo faculty of electrical and electronics engineering hcmc university of technology and education ho chi minh city, vietnam cuongvv@hcmute.edu.vn khanh t. p. nguyen department of research and development global electrical technology corporation ho chi minh city, vietnam phuckhanh180388@gmail.com binh t. t. phan faculty of electrical and electronics engineering hcmc university of technology ho chi minh city, vietnam thanhbinh055@yahoo.com abstract—the first but very significant step in electricity system planning is to make an accurate long-term forecast on electricity consumption. this article aims to forecast the consumption for the vietnam electricity system (gwh) up to 2030. an econometric model with the cobb douglas production function is used. the five variables proposed in the forecasting function are gdp, income, population, proportion of industry and service in gdp, and number of households. the forecasting equation is tested in terms of stationary and co-integration to choose meaningful variables and to eliminate the minor ones which account for none or small impacts on the forecast. the results show that: (1) the qualified forecasting equation only includes 3 major variables: the per capita income, the population, and the number of households, (2) with the medium income scenario, the forecasting consumptions in 2020, 2025, 2030 are 230,195 gwh, 349,949 gwh, 511,268 gwh respectively. (3) the gdp and the proportion of industry and service in gdp do not make major impacts on this forecasting in vietnam. the method and the result of this article are likely a typical example of forecasting electricity consumption in developing countries which have a transforming economy similar to that in vietnam. keywords-long-term; forecasting; electricity; consumption; econometric; model; cobb douglas; production; function; vietnam i. introduction one of the most important requirements in national electricity system planning is to forecast the long-term electricity consumption for more than 5 or 10 years. the accuracy of the forecast makes a significant contribution to building up an economically optimal scenario for electricity system planning. in fact, it is very challenging to accurately estimate the long-term electricity consumption for the reason that the far-future (more than 5 years) consumption is dependent on some factors such as the gdp growth rate, the population, the transforming of economy structure, the electricity price, the level of applying scientific and technological advances in efficiently using energy, the electricity consumers’ behavior and the climate change. vietnam is one of the few countries which experienced gdp growth rate more than 6% per year over the last 20 years. as a result, the electricity consumption increases by 15% annually. in 2010 the electricity consumption for more than 5 years ahead was simply predicted by using the value of the elasticity coefficient between the electricity growth rate and the gdp, whose value is 2. however, there have been some considerable gaps between forecasting and actual consumption from 2010 to 2015 [1]. the purpose of this article is to forecast vietnam’s electricity consumption up to 2030 with high reliability by applying the scientific forecasting method which is popular in other developing countries. to make a forecast on long-term electricity consumption, developing countries usually focus on 2 main methods: (1) to predict by using time-series models (tsms), and (2) to predict by using artificial neutral networks (anns). recently, in [2], authors utilized the mean absolute percentage error (mape) and the coefficient of determination (r2) to point out that the tsm method brings more accurate predictions in comparison with anns method. a new prediction method named newton was also introduced with promisingly higher accuracy. it should take more time to verify this new method. this article uses econometric model the econometric approach combines economic theory and statistical techniques for forecasting electricity consumption. the approach estimates the relationship between electricity consumption and factors influencing the consumption. the relationships are estimated by the tsm method. the most frequently used model is that of cobb douglas production function. it is widely utilized in researches from malaysia [3], pakistan [4], and china [5]. the common method shared by these researches is to investigate the influential factors or variables impacting the forecast result. in other words, it means to find the independent variables of the equation. then, the past time-series data of variables are utilized to verify the proposed forecasting equation with major variables. features of a transforming economy in developing countries which are taken into account as variables in this article are: (1) gdp, (2) income, (3) population, (4) proportion engineering, technology & applied science research vol. 8, no. 3, 2018, 2869-2874 2870 www.etasr.com nguyen et al.: forecast on 2030 vietnam electricity consumption of industry and service in gdp, and (5) number of households. the input data are collected from 1990 to 2015. ii. method and data a. applying cobb douglas production function non-linear form of cobb douglas production function is given below:  3 51 2 4t t t t t tec g p i x h       where ect is electricity consumption in year t. gt, pt, it, xt and ht denote gdp, population, income, proportion of industry and service in gdp, and number of households, in the year t, respectively. the technological parameter is indicated by φ. βi are returns to scale linked with the five above variables. by logarithmizing the two sides of (1), a linear function emerges:  0 1 2 3 4 5ln ln ln ln ln lnt t t t t tec g p i x h            b. testing there are many methods to test econometric models with the same purpose – to establish a prediction equation with the highest accuracy. for researches proving the causality between variables, the date in time series should be stationary tested (augmented dickey fuller (adf) or phillips-perron (p-p)) to avoid the spurious regression. after stationary test, the causality between variables is proven by using granger causality test. for forecasting purpose, stationary test only is enough. 1) stationary test in order to ensure the sustainability of the forecasting function, the stationary tests by using adf unit root test and pp unit root test are conducted. if there are any non-stationary series, the first difference of the series is calculated and eliminating inappropriate variables is done. if all series are non-stationary, calculating the first difference of all variables, then removing the primary features of the series leads to low r2 in regressing. the low r2 means low prediction accuracy. therefore, the co-integration test is conducted to avoid low r2. 2) cointegration test authors in [6] supposed the linear combination between non-stationary time series can be a stationary series and these non-stationary time series are co-integrated. the non-stationary linear combination is called co-integration equation and can be explained as the balance relationship between variables in longterm. therefore, if variables co-integrate, regression can be conducted. in this article, johansen trace test is utilized to test the co-integration. in the trace test (t-test), there are some hypotheses h0 listed as follows: “none”, means there is no cointegration; “at most 1; 2; 3…”, means there are 1, or 2, 3 … co-integrations. to decide if we should reject or accept hypothesis h0, trace statistic value and critical value of 5% are compared. if trace statistic<critical value, then h0 is accepted. if trace statistic>critical value, then h0 is rejected. 3) r2 test in addition to stationary and co-integration tests, the research also tests the possibility and eliminates inappropriate variables of prediction equation on the base of two values of r2. the high value of r2 is a signal for intensive relationship. 4) eliminating inappropriate variables p-value is used to eliminate inappropriate variables. p-value is the lowest value of α through which the test result is statistically meaningful. the use of p-value to test the hypothesis is: reject h0 if p-value<α (α=0.05). after testing and eliminating inappropriate variables, a qualified forecasting equation to be proposed. c. data 1) gdp vietnam is one country that has experienced annual gdp growth rate of about 6.5% for the last 20 years. there are 3 scenarios of gdp growth rate of vietnam up to 2030 [1]. because of low gdp growth rate archived in recent years, the low scenario of gdp growth rate is taken into account in this article. it is likely that the consumption for electricity continues to increase sharply. it is shown that there is partly relationship between the gdp and the electricity consumption. the gdp in vietnam is extracted from the world bank data [7]. 2) income per capital income and the electricity consumption tend to be positively correlated. as the income increases, families have a tendency to purchase more electrical devices to satisfy their needs. for instances, at a certain level of income, they do not buy air conditioners and heaters. however, when the income reaches a higher level, after considering if they afford paying the electricity consumption, they purchase these devices to make their life more comfortable. as a result, the electricity consumption in that households rises [9]. therefore, the per capital income is taken into account in this research. data is extracted from the world bank data (atlas method) [7]. 3) population the population growth rate in vietnam is around 1.08% [7]. if there is a variable impacting on the electricity consumption, it is the population. the population increases, which enlarges power consumption. the population data are provided by the general statistics office of vietnam [8]. 4) number of households the household separation leads to the increasing consumption for home electric appliances. it creates not only increase of electricity consumption in human livelihood but also that in the industry sector for manufacturing these engineering, technology & applied science research vol. 8, no. 3, 2018, 2869-2874 2871 www.etasr.com nguyen et al.: forecast on 2030 vietnam electricity consumption appliances. authors in [10] mention “households energy consumption accounts for a large share of total energy consumption”. however, there is a problem in data collecting that vietnam and other developing countries encounter. it is the fact that the household data in vietnam is not fully recorded. this requires establishing a method of calculating the number of households in vietnam. the household data in vietnam is scanty and un-intensive. in the years 1999, 2004 and 2009, the accurate numbers of households are 16.66, 19.01 and 22.44 million, respectively. recognized as the official figures by vietnam and the united nations, these numbers are the results from the investigation on population and housing [8, 9]. moreover, the increasing and decreasing rates of number of households are also important parameters to calculate the numbers of households in the upcoming years. according to [8], the number of households in vietnam 2014 is 24.27 million, two times that of 25 years ago (1/4/1989), one-and-ahalf time that of 15 years ago (1/4/1999), and nearly 2 million households higher than that in 1st april 2009. during the 20092014 period, the average increasing rate of households is 1.6% per year period. recorded by helgi library, the number of households in vietnam reached 26.9 million in 2016, increasing by 2.43 % compared with that of the previous year [11]. table i shows the number of households in vietnam. the comparison between vietnam and other countries should be made to figure out the similarities in the average size of a household. the average size of vietnam households in 1999 was 4.6 people/household, equivalent to that of thailand in 1990 (4.62 people). according to the thailand development research institute, the size of thailand’s households changed throughout the years as follows: 1985: 4.98, 1990: 4.62, 1995: 4.27, 2000: 3.96, and 2005: 3.7. according to the national statistical office of thailand, the number of households in thailand reached 20.6 million in 2016. this increase accounts for 0.205%, compared with that of the previous year. the number 20.6 million in 2016 is the highest, while the lowest is 0.6 million in 1960. in comparison with thailand, those figures of cambodia and malaysia respectively are 3.34 million and 7.30 million [11]. according to the department of statistics in malaysia, in 2016, the number of households in malaysia reached 7.30 million, a rise of 1.74 %, compared with the previous year. this figure is the highest, while the lowest was 1.50 million in 1960. compared with other neighbor countries of malaysia, the numbers of households in 2016 were respectively 3.34 million in cambodia, 1.26 million in singapore, 20.6 million in thailand, and 26.9 million in vietnam [11]. it is easily recognized that there are geographic and socioeconomic similarities between vietnam, thailand and malaysia. even in japan, a developed country, the number of households keeps increasing at nearly 1%/year, while, population has been decreasing [11]. the statistical charts of the household growth in these countries tend to have exponential shapes. based on the data in table i, the trend line has the exponential shape shown in figure 1. the trend line equation is:  2.71 0.24.85 23 e xy e e     table i. number of households [8, 9] (millions) year 1999 2004 2009 2014 2016 16.66 19.01 22.44 24.27 26.9 fig. 1. the trend line of the number of households. the household data from 1990 to 2015 are shown in table ii. using the trend line, the prediction on the number of households in the future is shown in table iii. table ii. the number of households calculated by the article (millions) year 1990 1991 1992 1993 1994 1995 1996 12.79 13.14 13.50 13.87 14.25 14.64 15.05 year 1997 1998 1999 2000 2001 2002 2003 15.46 15.88 16.66 16.77 17.23 17.70 18.19 year 2004 2005 2006 2007 2008 2009 2010 19.01 19.20 19.73 20.27 20.83 22.44 21.99 year 2011 2012 2013 2014 2015 22.59 23.21 23.85 24.27 25.18 table iii. the number of households in the future (millions) year 2020 2025 2030 forecast number of households 28.83 33.02 37.81 5) proportion of industry and service in gdp in addition to the human livelihood, the proportion of industry and service in gdp are also sectors accounting for a large share of electricity consumption. a feature of a transforming economic in a developing country like vietnam is that this proportion increases. relevand data are shown in table iv [1]. 6) collecting data in time series of 1990-2015 after analyzing factors likely to influence the electricity consumption in vietnam, the past data of the factors are collected. with full, accurate data and long enough time series, the equation predictions are more exact. according to [12, 13], if n the data in time series and k the independent variables in the model, then: n–k>20. as mentioned above, the chosen variables include the gdp, the income, the population, the number of households, the proportion of industry and service. therefore, the forecasting equation contains 5 independent variables and: n>20+5. this study selects the time series from engineering, technology & applied science research vol. 8, no. 3, 2018, 2869-2874 2872 www.etasr.com nguyen et al.: forecast on 2030 vietnam electricity consumption 1990 to 2015. the time series is relatively long enough variable including 26 values (equivalent to 26 years) to conduct testing. in addition to the domestic statistical data, the country has the chance to assess those data from international organizations. table iv presents the relevant data. table iv. summary of input data year e le ct ri ci ty c o n su m p ti o n (g w h ) g d p (b il li o n $ ) p o p u la ti o n (x 1 0 3 ) in co m e ($ /p er so n ) in d u st ry & s er v ic e (% ) n u m b er o f h o u se h o ld s (m il li o n s) 1990 8,678 6.47 66,017 130 61.3 12.79 1991 9,152 9.61 67,242 110 59.5 13.14 1992 9,654 9.87 68,450 130 66.1 13.50 1993 10,665 13.18 69,645 170 70.1 13.87 1994 12,284 16.29 70,825 200 72.6 14.25 1995 14,636 20.74 71,996 260 72.8 14.64 1996 16,946 24.66 73,157 310 72.2 15.05 1997 19,151 26.84 74,307 350 74.2 15.46 1998 21,665 27.21 75,456 360 74.2 15.88 1999 23,739 28.68 76,597 370 74.6 16.66 2000 26,745 33.64 77,631 400 77.3 16.77 2001 30,187 35.29 78,621 430 78.5 17.23 2002 34,073 37.95 79,538 460 78.7 17.70 2003 38,461 42.72 80,467 510 79.1 18.19 2004 43,414 49.42 81,436 590 80.0 19.01 2005 49,008 57.63 82,392 680 80.7 19.20 2006 53,845 66.37 83,311 760 81.3 19.73 2007 59,159 77.41 84,219 850 81.3 20.27 2008 64,998 99.13 85,119 1,000 79.6 20.83 2009 71,415 106.01 86,025 1,120 80.8 22.44 2010 78,466 115.93 86,933 1,270 69.1 21.99 2011 94,658 135.54 87,860 1,390 69.0 22.59 2012 105,474 155.82 88,809 1,550 70.8 23.21 2013 115,069 171.22 89,760 1,740 71.9 23.85 2014 128,435 186.20 90,729 1,900 72.3 24.27 2015 141,800 193.60 91,704 1,990 73.0 25.18 iii. results a. converting independent variables the series of input data are converted into natural logarithms listed in table v. b. testing 1) stationary test the stationary test results are shown in table vi. it is shown that all p-values are larger than α (α=0.05), except for the population variable (lnpt) when p-p test is conducted. in other words, all variables are not stationary. therefore, the cointegration test is to be conducted instead of calculating the first difference. 2) co-integration test the co-integration test results are shown in table vii. after the test, we accept the hypothesis h0. there are three cointegrations with trace statistic method. 3) testing r2 and p-value after the co-integration test, the coefficients of (2) are calculated and the results are shown in table viii. the condition for choosing the coefficients of equation is that the r2 almost equals to 1 and pvalues of all variables are less than 0.05. in table viii, r squared (r2 testing)=0.997953. it means that 99.8% of dependent variables have impacts on independent variables. however, due to the fact that the p-value is above 0.05, then, lngt is removed. table v. converting independent variables into natural logarithms year ln(ect) ln(gt) ln(pt) ln(it) ln(xt) ln(ht) 1990 9.07 1.87 11.10 4.87 4.12 2.55 1991 9.12 2.26 11.12 4.70 4.09 2.58 1992 9.18 2.29 11.13 4.87 4.19 2.60 1993 9.27 2.58 11.15 5.14 4.25 2.63 1994 9.42 2.79 11.17 5.30 4.28 2.66 1995 9.59 3.03 11.18 5.56 4.29 2.68 1996 9.74 3.21 11.20 5.74 4.28 2.71 1997 9.86 3.29 11.22 5.86 4.31 2.74 1998 9.98 3.30 11.23 5.89 4.31 2.77 1999 10.07 3.36 11.25 5.91 4.31 2.81 2000 10.19 3.52 11.26 5.99 4.35 2.82 2001 10.32 3.56 11.27 6.06 4.36 2.85 2002 10.44 3.64 11.28 6.13 4.37 2.87 2003 10.56 3.75 11.30 6.23 4.37 2.90 2004 10.68 3.90 11.31 6.38 4.38 2.94 2005 10.80 4.05 11.32 6.52 4.39 2.96 2006 10.89 4.20 11.33 6.63 4.40 2.98 2007 10.99 4.35 11.34 6.75 4.40 3.01 2008 11.08 4.60 11.35 6.91 4.38 3.04 2009 11.18 4.66 11.36 7.02 4.39 3.11 2010 11.27 4.75 11.37 7.15 4.24 3.09 2011 11.46 4.91 11.38 7.24 4.23 3.12 2012 11.57 5.05 11.39 7.35 4.26 3.14 2013 11.65 5.14 11.40 7.46 4.28 3.17 2014 11.76 5.23 11.42 7.55 4.28 3.19 2015 11.86 5.27 11.43 7.60 4.29 3.23 table vi. stationary testing of the forecasting equation variable adf test p-p test t. statistic prob.value t. statistic prob.value lnect 0.000867 * -0.026761 * lngt -2.287395 * -2.232903 * lnht 0.632598 * 0.721125 * lnit -1.210096 * -0.475247 * lnpt -0.641799 * -9.851650 *** lnxt -2.457299 * -2.457299 * * variables with p-value > 0.05 ** variables with 0.02 < p-value < 0.05 *** variables with p-value < 0.02 table vii. co-integration test hypothesized no. of ce(s) trace statistic critical value prob. none * 179.6550 95.75366 0.0000 at most 1 * 109.0413 69.81889 0.0000 at most 2 * 52.81937 47.85613 0.0159 at most 3 27.25295 29.79707 0.0956 at most 4 9.796955 15.49471 0.2967 at most 5 0.530471 3.841466 0.4664 * denotes rejection of the hypothesis at the 0.05 level engineering, technology & applied science research vol. 8, no. 3, 2018, 2869-2874 2873 www.etasr.com nguyen et al.: forecast on 2030 vietnam electricity consumption the recalculation of the equation coefficients is shown in table ix. similarly, lnxt is removed and the equation coefficients are again re-calculated. the result is shown in table x, in which all p-values of variables in the equation reach *** level. in other words, all p-values are less than 0.02 (very qualified). table viii. calculation of the coefficients of (2) variable coefficient std. error t-statistic prob. c -69.19764 8.675347 -7.976353 *** lngt -0.110864 0.083668 -1.325048 * lnht 0.682145 0.164572 4.144974 *** lnit 0.220460 0.087524 2.518847 ** lnpt 6.937385 0.861815 8.049738 *** lnxt -0.357666 0.151796 -2.356232 ** r-squared 0.998899 f-statistic 3628.116 prob (f-statistic) 0.000000 aic -3.800512 table ix. calculation of the coefficients (second time) variable coefficient std. error t-statistic prob. c -62.79885 7.335583 -8.560853 *** lnht 0.756167 0.157561 4.799209 *** lnit 0.145212 0.067787 2.142167 ** lnpt 6.327205 0.741462 8.533421 *** lnxt -0.283445 0.143599 -1.973864 * r-squared 0.998802 f-statistic 4377.180 prob (f-statistic) 0.000000 aic -3.793289 table x. calculation of the coefficients (third time) variable coefficient std. error t-statistic prob. c -53.82916 6.125857 -8.787205 *** lnht 0.974249 0.119498 8.152860 *** lnit 0.197233 0.066438 2.968668 *** lnpt 5.338763 0.581688 9.178048 *** r-squared 0.998580 f-statistic 5156.169 prob (f-statistic) 0.000000 aic -3.700022 c. eliminating inappropriate variables after the eliminating of lngt and lnxt, (2) becomes:  0 1 2 3ln ln ln lnt t t tec p i h         where β0, β1, β2, and β3 are -53.829, 5.339, 0.197, and 0.974, respectively (see table x). equation (4) becomes:  ln 5.339ln 0.197ln 0.974ln 53.829t t t tec p i h      equation (5) is the qualified forecasting equation. d. forecast on electricity consumption to 2030 future values of population, income, and number of households are predicted and shown in table xi. using this data, the natural logarithms, and (5), vietnam electricity consumption in the future can be forecasted. the results are shown in table xii. table xi. forecast on population, number of households and income variable note 2020 2025 2030 population (thousands) [14] 96,302 99,929 102,886 income ($/year) [1] low scenario 3,307 4,939 7,205 medium scenario 3,370 5,111 7,836 high scenario 3,485 5,450 8,450 number of households (millions) 29.89 34.49 39.79 table xii. forecast on electricity consumption to 2030 (gwh) electricity consumption 2020 2025 2030 low income scenario 229,341 347,597 502,882 medium income scenario 230,195 349,949 511,268 high income scenario 231,722 354,404 518,923 the results show that in the low income scenario, the electricity consumption in 2020 is around 229,241 gwh, in 2025 is around 347,597 gwh and that in 2030 is 502,882 gwh. in the medium scenario, the electricity consumption in 2020 reaches 230,195 gwh, in 2025 is around 349,949 gwh and that in 2030 is 511,268 gwh. finally, in the high scenario, the electricity consumptions in 2020, 2025, and 2030 are 231,722 gwh, 354,404 gwh, and 518,923 gwh, respectively. with the income increase from about 2% in case of medium and low scenario in 2020 to about 9% in case of medium and low scenario in 2030, electricity consumptions increases from about 0.4% to about 1.7%, respectively. iv. conclusion by using the econometric model with the cobb douglas production function, the proposed forecasting equation (1) is made with five variables: gdp, income, population, proportion of industry and service in gdp and number of households. after adf, co-integration and r2 and p-value tests, the qualified forecasting equation (5) has only three variables: income, population, and number of households. this means that gdp, and the proportion of industry and service in gdp do not make a major impact on this forecasting in vietnam. this is quite a surprising result. the explanation for this can be that income increase is also followed by gdp increase and that the data set of gdp (1990-2015) may not be aligned with the proportion of industry and service in the gdp. the equation of the number of households for vietnam is proposed by exponential function (3) which is the one of thailand, malaysia, and japan. electricity consumption in 2030 will be more than two times that of 2020, and more than 3 times that of 2016 (159,450 gwh). this means that billions of us dollars per year will need to be invested to the power system of vietnam. in details, in case of the medium income scenario, electricity consumption increase about 10%/year in 2017-2020, 8.4%/year in 2021-2025 and 6.8%/year in 2026-2030. this is engineering, technology & applied science research vol. 8, no. 3, 2018, 2869-2874 2874 www.etasr.com nguyen et al.: forecast on 2030 vietnam electricity consumption quite a good trend, because the increasing is slowing down gradually compared with that of the previous period (20102015) which was 10%-15%/year. the method and the results of this research likely are a typical example for the forecasting of electricity consumption of those developing countries which have the same transforming economy with vietnam. references [1] institute of energy, evn, revised version of master plan no. vii for power system in vietnam, 2015 [2] p. ozoh, s. abd-rahman, j. labadin, m. apperley, “a comparative analysis of techniques for forecasting electricity consumption”, international journal of computer applications (0975 – 8887), vol. 88, no. 15, pp. 8-12, 2014 [3] a. k. imtiaz, n. b mariun, m. m. r. amran, m. saleem, n. i. a. wahab, mohibullah, “evaluation and forecasting of long term electricity consumption for malaysia by statistical analysis”, ieee international power and energy conference (pecon 2006), putrajaya, malaysia, pp. 257-261, november 28-29, 2006 [4] m. shahbaz, h. h. lean, “the dynamics of electricity consumption and economic growth: a revisit study of their causality in pakistan”, energy, vol. 39, no. 1, pp. 146-153, 2012 [5] j. yuan, c. zhao, s. yu, z. hu, “electricity consumption and economic growth in china: co-integration and co-feature analysis”, energy economics, vol. 29, no. 6, pp. 1179–1191, 2007 [6] r. f. engle, c. w. j. granger, “co-integration and error correction: representation, estimation, and testing”, econometrica, vol. 55, no. 2, pp. 251-276, 1987 [7] world bank data, available at: http://data.worldbank.org/country/ vietnam [8] general statistics office of vietnam, master investigation on population and households 2009 – vietnam, 2009 [9] general statistics office of vietnam, master investigation on populayion and households 2014 – vietnam, 2014 [10] r. raudjarv, l. kuskova, “energy consumption in households”, , quarterly bulletin of statistics estonia, vol. 2010, no. 1, pp. 21-28, 2010 [11] helgi library, “number of households in vietnam”, available at: http://www.helgilibrary.com/indicators/number-of-households/vietnam/, last access: 03/2018 [12] s. b. green, “how many subjects does it take to do a regression analysis?”, multivariate behavioral research, vol. 26, no. 3, pp. 499510, 1991 [13] b. g. tabachnick, l. s. fidell, using multivariate statistics, california state university northridge, pearson education. inc., 2007 [14] general statistics office of vietnam, united nations fund for population activities (unfpa), “vietnam population projection 20142049”, 2016 engineering, technology & applied science research vol. 8, no. 5, 2018, 3456-3462 3456 www.etasr.com aygun & aktas: a novel dtc method with efficiency improvement of im for ev applications a novel dtc method with efficiency improvement of im for ev applications hilmi aygun electrical-electronics engineering department karabuk university karabuk, turkey hilmiaygun@karabuk.edu.tr mustafa aktas department of electrical and electronics engineering ondokuz mayıs university samsun, turkey mustafa.aktas@omu.edu.tr abstract—induction motor (im) stator flux optimization is very important in order to get increasing running distance per battery charge of electric vehicles (evs). this study introduces a new direct torque control (dtc) method for efficiency improvement of im in ev applications. also, it is proposed to decrease the torque ripple of dtc based im. generally, loss minimization algorithms can be simplified by neglecting the core loss or the effect of leakage inductance in the motor model. however, neglecting the core loss causes an error in torque control of dtc. beside this, exact loss minimization cannot be achieved since a large voltage drop across leakage inductance occurs especially in high-speed region. in the proposed method, the motor model is simplified by neglecting the current in the core loss resistance branch instead of neglecting the core loss and the effect of leakage inductance. the proposed method is simulated in matlab for variable speeds and loads. results show that it provides a significant reduction of losses and decreases the torque ripple of im drives. keywords-efficiency improvement; electric vehicle; induction motor; model-based controller; direct torque control i. introduction the popularity of evs has been growing up due to their quiet operation and harmless emissions. evs can be improved by regenerative braking systems which convert kinetic energy back into stored electricity. generally, ev applications are of great industrial interest [1, 2], however, the charging time of the batteries is very long. therefore, electrical energy must be used optimally for increasing running distance for every battery charge. as a result, the losses of electric motors must be reduced for efficiency optimization [3-5]. squirrel cage induction motor (im) is widely accepted as the best candidate for evs thanks to its reliability, ruggedness, low maintenance and cost. ims are particularly well suited for traction drive environments [6]. they have good efficiency at rated load when operating at steady state. however, their efficiency is low at light loads due to increased core losses [7]. dtc method appears as a suitable way to improve dynamic performance of ims as it provides a fast torque response and robustness to motor parameter variations. however, dtc has some serious problems such as variable switching frequency and a high amount of torque ripple caused by hysteresis controller [8-9]. if the hysteresis band range is selected narrow, the thermal limits of the power switches are enforced due to the switching frequency. otherwise, if the hysteresis band range is selected in wide range, the torque ripple increases due to decreased switching frequency [10]. the torque ripple can be decreased by stator flux optimizing that improves the efficiency of im. generally, two kinds of methods are used for increasing im efficiency. one of them is a search controller is based on measurements of parameters like the input power of the motor. the other method, called loss model-based controller, needs the mathematical model of the motor. the aim of these methods is to find optimum flux which will provide maximum efficiency, especially at light loads [11, 12]. in loss model-based controller, the term of total losses, consisting of copper and core losses, is determined as a function of flux, torque and speed. in this method, the model must include the core loss resistance which is usually ignored. generally, optimal flux value can be obtained at different load torque and speed conditions by setting the derivative of total loss with respect to the flux to zero. therefore, the convergence speed of loss model-based controller is fast, and as a result, this method is suitable for ev applications [13]. in search control algorithm, the flux is decreased step by step, and at the same time the input power of motor is measured until the maximum efficiency point is obtained. the biggest advantage of this method is that it does not require prior knowledge of motor parameters which might change by temperature. since this method does not need a mathematical model, it is not affected by saturation. in this method, the step range of flux must be as small as possible to obtain a low flux ripple. however, if the step range of flux is chosen very small, convergence problem can occur [14]. many different optimal control methods to improve energy efficiency of im have been proposed, e.g. loss minimization algorithms, including search controller presented in [15-17]. convergence time of a search controller is longer than a loss model-based controller. since the speed and load torque of evs change frequently, search control algorithm is not sufficient for ev applications because of its low convergence speed. a loss model-based control method was proposed in [18] for reducing the losses of im. according to this method, when two axis power loss components are equal in the stator-fixed d-q frame, maximum efficiency is obtained for a given load and speed. in engineering, technology & applied science research vol. 8, no. 5, 2018, 3456-3462 3457 www.etasr.com aygun & aktas: a novel dtc method with efficiency improvement of im for ev applications this loss minimization method, a pi controller is used to produce the reference stator flux. however, power loss components have harmonic pollution caused by current distortion. therefore, tuning the mentioned pi controller is very difficult. another type of loss model-based method of im for high operating life of the battery in the evs was presented in [3]. in this method, the losses are quantified in the synchronous rotating d-q frame. the effect of leakage inductances is neglected to find optimal rotor flux value. however, the maximum efficiency point cannot be determined as a high voltage drop across the leakage inductances is ignored, especially in high speed region. for the efficiency optimization of vector control-based ims, maximum efficiency operating point is obtained without neglecting leakage inductances thanks to the reference frame fixed to the rotor magnetizing current in [19, 20]. these studies require an additional controller to obtain optimal reference flux component. however, the additional controller increases the method complexity. in [21-22], a loss model-based approach neglecting core loss is presented for im drives. however, neglecting the core losses for simplifying the model causes an error in the torque control of dtc. as ev motors have low inductance, the current ripple causes a significant amount of core losses, especially in high speed region. in this paper, dtc method combined with an online loss model-based controller is proposed to minimize the losses of ev induction motors at variable load and speed conditions. also, it is proposed to decrease the torque ripple which is a problem of classical dtc method based on variable switching frequency. in this method, a simplification for modeling of losses is made by neglecting the current in the core loss resistance branch of the equivalent circuit of im in the synchronous reference frame. also, the proposed method does not neglect the core losses and effect of the leakage inductances. optimal stator flux value of im is obtained by setting the derivative of total loss with respect to the stator flux to zero. ii. direct torque control direct torque control (dtc) method consists of estimators and hysteresis comparators for electromagnetic torque and stator flux, and an optimal switching table. in a three-phase induction motor, torque and stator flux are given by [23]: 3 2 e s s t p i=  (1) ( )s s s sv r i dt = − (2) where p is the pole pair, �̅�𝑆 is the stator flux linkage vector, 𝐼�̅� is the stator current vector, �̅�𝑠 is the stator voltage vector, and rs is the stator resistance. torque and flux references are compared with the estimated values to determine the error signals. flux and torque hysteresis comparators produce control signals. according to the control signals and stator flux position, the appropriate stator voltage from optimum switching table (table i) is applied to the inverter circuit. therefore, the required torque can be obtained effectively thanks to the rotating stator flux vector as fast as required [24]. figure 1 is given as an example for the stator flux control. the stator voltage vectors are moved in a rotating counterclockwise direction with staying between the hysteresis bands. stator flux amplitude can be increased or decreased by selecting different stator voltage vectors. the block scheme of dtc based on im drives is given in figure 2. pi controller produces the torque reference value according to the error between reference and measured speeds. this way torque and speed can be controlled. fig. 1. stator flux trajectory by suitable voltage vector selection. table i. optimum switching table for dtc based im dψ dte sect. 1 sect. 2 sect. 3 sect. 4 sect. 5 sect. 6 1 1 v6 v2 v3 v1 v5 v4 0 v7 v0 v7 v0 v7 v0 -1 v5 v4 v6 v2 v3 v1 0 1 v2 v3 v1 v5 v4 v6 0 v0 v7 v0 v7 v0 v7 -1 v1 v5 v4 v6 v2 v3 fig. 2. block scheme of the dtc based im drives. iii. induction motor model considering core losses in order to determine the required optimal stator flux for increasing the efficiency of the im, the losses must be modelled. in im modeling, the core loss is usually neglected [21, 22]. however, the core loss must not be neglected for energy optimization and is taken into account in the dynamic model of induction motor through the core loss resistance rfe as shown in figure 3. the core loss of im includes eddy current loss component 𝑃𝐹𝑒 𝑒 and hysteresis loss component 𝑃𝐹𝑒 ℎ . these losses are given in (3) and (4): e 2 2 fe e s p = k ω φ (3) h 2 fe h s p = k ω φ (4) engineering, technology & applied science research vol. 8, no. 5, 2018, 3456-3462 3458 www.etasr.com aygun & aktas: a novel dtc method with efficiency improvement of im for ev applications where ωs is electrical angular speed, φ is flux level, ke and kh are coefficients related to eddy current and hysteresis losses, respectively. vs jωalσsis rs lσs is lm jωalmim rfe ife im lσr rr jωalσrir jωrψr fig. 3. equivalent circuit of im at a general rotating reference frame. while the hysteresis loss is proportional to ωs, eddy current loss is proportional to 𝜔𝑠 2 . therefore, eddy current loss is dominant over hysteresis loss in a high frequency region. the stator core loss 𝑃𝐹𝑒 𝑠 and rotor core loss 𝑃𝐹𝑒 𝑟 in an im can be calculated approximately by the following equations: 2 2 2 2 s 2 2 s m s m fe e s h s m e fe ω φ ω φ p = k ω +k ω φ = 1 / k r     (5) 2 2 r 2 2 sl m fe e sl h sl m e 2 2 2 2 2 s m s m 2 e fe ω φ p = k ω +k ω φ 1 / k s ω φ ω φ = = 1 / k r / s     (6) where rfe is the core loss resistance, s is the slip, ωsl is the slip angular speed, ωr is the rotor angular speed, 𝜔𝑠𝑙 = 𝜔𝑠 − 𝜔𝑟 = 𝑠𝜔𝑠 and 𝜙𝑚 is the airgap flux. 𝜔𝑠𝜙𝑚 represents the airgap voltage. notice, that the rotor core loss is much smaller than the stator core loss, since |𝑠𝜔𝑠| ≤ |𝜔𝑠|. according to figure 4 we write the current and voltage equations related to the stator and rotor in the synchronous reference frame: ( )ds dmds s ds σs m s σs qs m qm di di v = r i + l + l ω l i +l i dt dt (7) ( ) qs qm qs s qs σs m s σs ds m dm di di v = r i + l + l +ω l i +l i dt dt (8) ( )dr dmr dr σr m sl σr qr m qm di di 0 = r i + l + l ω l i +l i dt dt (9) ( ) qr qm r qr σr m sl σr dr m dm di di 0 = r i + l + l +ω l i +l i dt dt (10) 2 dm ds dr dm m s m qm fe dis + 1 i + i = i + l ω l i r dt       (11) 2 qm qs qr qm m s m dm fe dis +1 i + i = i + l +ω l i r dt       (12) (a) (b) fig. 4. equivalent circuit of im in the synchronous reference frame. where vds and vqs are the stator voltage components, ids and iqs are the stator current components, idr and iqr are the rotor current components, idm and iqm are the magnetizing current components, rr is rotor resistance, lm is the magnetizing inductance, and lσs, lσr are the stator and rotor leakage inductances, respectively. a. loss model simplification im losses consist of copper and core losses. the converter losses have no significant effect to determine the optimal flux value for medium-sized im drives [22]. therefore, the converter losses are not taken into account in this study. it should be kept in mind that since optimal flux value is usually smaller than the rated flux for the ev applications, there is no magnetic saturation [18], and, as a result, magnetic saturation is neglected. to prevent loss model complexity, simplification methods are applied. one of them is to neglect the effect of leakage inductances [3], which can be effective in the low speed region. however, the voltage drop over the leakage inductances becomes significant in high frequency operations. therefore, due to neglecting leakage inductance over the base speed, a significant error will be in losses calculation. to design a controller without taking into account the effects of the leakage inductances is impractical, especially in high frequency operations [26]. in the proposed method, the simplification without ignoring leakage inductances is based on the fact that magnetizing currents idm and iqm are much bigger than core loss currents idfe and iqfe. |𝑖𝑑𝑚| ≫ |𝑖𝑑𝐹𝑒| (13) |𝑖𝑞𝑚| ≫ |𝑖𝑞𝐹𝑒| (14) where 𝑖𝑑𝐹𝑒 = 𝑠2+1 𝑅𝐹𝑒 (𝐿𝑚 𝑑𝑖𝑑𝑚 𝑑𝑡 − 𝜔𝑠𝐿𝑚𝑖𝑞𝑚) and 𝑖𝑞𝐹𝑒 = 𝑠2+1 𝑅𝐹𝑒 (𝐿𝑚 𝑑𝑖𝑞𝑚 𝑑𝑡 + 𝜔𝑠𝐿𝑚𝑖𝑑𝑚). then the magnetizing current components are approximated by: engineering, technology & applied science research vol. 8, no. 5, 2018, 3456-3462 3459 www.etasr.com aygun & aktas: a novel dtc method with efficiency improvement of im for ev applications dm ds dr i i i + (15) qm qs qr i i i + (16) the magnetizing voltage components are approximated by: ( ) ( )ds drdm m s m qs qr d i +i v = l ω l i +i dt (17) ( ) ( ) qs qr qm m s m ds dr d i +i v = l +ω l i +i dt (18) in (7)-(12) after substituting idm and iqm by ids+idr and iqs+iqr, respectively, a simplified model is obtained as follows: ds ds s ds σs s σs qs dm di v = r i + l ω l i v dt + (19) qs qs s qs σs s σs ds qm di v = r i + l +ω l i v dt + (20) ( )drr dr σr r r qr m qm s r qr dm di 0 = r i + l +ω l i +l i dt ω l i +v   (21) ( ) qr r qr σr r σr dr m dm s σr dr qm di 0 = r i + l ω l i +l i dt ω l i v+ + (22) 2 ds dr dm dm fe s + 1 i + i = i +v r (23) 2 qs qr qm qm fe s + 1 i + i = i +v r (24) iv. loss minimazation algorithm the rotor flux-oriented reference frame is utilized for calculating losses and finding optimal stator flux, since it provides greater simplification. this frame is obtained by aligning the reference frame on the rotor flux axis. as a result, 𝜆𝑞𝑟 = 𝜆𝑞𝑟 ′ = 0 . we define the rotor flux components as follows: dr r dr m ds λ = l i +l i (25) 0 qr r qr m qs λ = l i +l i = (26) where lr is the rotor inductance. the rotor current components are calculated from (25)-(26). dr m ds dr r λ l i i = l (27) m qs qr r l i i = l (28) replacing idr and iqr in (17) and (18) we have: m r ds m dr m r dm s qs r r r l l di l dλ l l v = + ω i l dt l dt l   (29) ( ) qsm r m qm s r ds dr r r dil l l v = +ω l i +λ l dt l   (30) in the steady state, 𝑑𝑖𝑑𝑠 𝑑𝑡 = 𝑑𝑖𝑞𝑠 𝑑𝑡 = 𝑑𝜆𝑑𝑟 𝑑𝑡 = 0 and 𝑖𝑑𝑟 = 0 , since 𝜆𝑑𝑟 = 𝐿𝑚𝑖𝑑𝑠. therefore, in the steady state we have: m r dm s qs r l l v = -ω i l  (31) ( )mqm s r ds dr s m ds r l v = ω l i +λ ω l i l  = (32) since slip is low (𝑠 ≪ 1) in normal operation of im, the rotor core loss is neglected, hereafter. the core loss and copper loss are expressed by the following equations: ( )3 3 2 2 2 2 2 2 2 2 2r s m qs s m ds2 2 rdm qm fe fe fe l ω l i +ω l i lv +v p = = r r            (33) ( ) ( ) ( ) 2 2 2 2 2 2 2 2 3 2 3 2 cu s ds qs r dr qr m s ds qs r qs r p = r i i r i i l r i i r i l  + + +       = + +       (34) also, the total loss is expressed as a function of electrical angular speed ωs, torque te and d axis component of rotor flux λdr: ( ) 22 2 2dr e total s s r r m m p m dr 22 2 2 p s dr r m e s r r fe fe dr 3 λ 2 t p = r + r l + r l 2 l 3 n l λ n ω λ3 l + l 2 t ω l + + 2 l r 3r λ                               (35) where np is the pole number. a. proposed dtc based on loss minimization the torque of im at steady state is given by: 2 m e p dr qs r l3 t = n λ i l (36) when the total loss term is examined, it is seen that it is closely related to the rotor flux level. in order to reduce core losses, the rotor flux, or in other words, d axis stator current ids, must be decreased. if the rotor flux is decreased, q axis stator current iqs must be increased very much in order to obtain the necessary torque causing a lot of copper loss. therefore, optimal flux must be determined in order to provide balance between core loss and copper loss. optimal rotor flux value is obtained by following equations: total dr dp = 0 dλ (37) engineering, technology & applied science research vol. 8, no. 5, 2018, 3456-3462 3460 www.etasr.com aygun & aktas: a novel dtc method with efficiency improvement of im for ev applications 1/ 4 opt ref dr e 2 a λ = t 3 b       (38) where a and b are equal to 2 2 2 2 s r r m s r 2 2 2 p m p fe r l + r l ω l a = + n l n r  (39) ( )2 2 2 2s fe r s m m σr 2 2 m fe r r r l +ω l l +l b = l r l (40) however, in dtc control of im, since stator flux control is required, optimal rotor flux is converted to optimal stator flux by the following equations: m s m sd s sd rd rd rd r m r l l l ψ =σl i + ψ =σ ψ + ψ l l l (41) e r sq s sq s p m rd 2 t l ψ = σl i = σl 3 n l ψ (42) 2 2 s sd sq ψ = ψ ψ+ (43) ( ) 2 2 ref 2 opt ref opts r e s s dr opt m p dr l 2 σl t ψ =ψ = ψ + l 3 n ψ             (44) where 𝜎 = 1 − 𝐿𝑚 2 𝐿𝑠𝐿𝑟 , is the leakage factor and ls is the stator inductance. the block scheme of the proposed dtc method for evs is shown in figure 5. the difference between the proposed dtc and conventional dtc methods is the usage of optimal stator flux block obtained by (44). fig. 5. proposed dtc block scheme for evs. v. simulation results the proposed method is simulated by matlab. an im with capacity of 3kw fed by a voltage source inverter is used in the simulation. the im parameters are given in table ii. the applications aim to investigate the efficiency and dynamic performance of the proposed method, and compare it with the conventional dtc method. in this application, reference electrical angular speed is 250rad/s and load torque is 2nm. in the conventional dtc, the reference stator flux is 1wb (rated conditions) while in the proposed dtc that is applied for t>2.5s, the reference stator flux is determined by the loss minimization algorithm. the results are shown in figure 6. table ii. induction motor parameters parameters values power 3kw rs 1.795ω rr 1.52ω rfe 1340ω ls= lr 0.2405h lm 0.2323h j 0.0044kgm2 np 1 (a) (b) fig. 6. (a) total loss of im, (b) efficiency of im. (a) (b) fig. 7. (a) reference stator flux, (b) circular trajectory of stator flux. as shown in figure 6(a), the proposed method provides a significant losses reduction for t>2.5s. therefore, the efficiency is improved at the same rate as shown in figure 6(b). the comparison of both dtc methods is given in table iii. figure engineering, technology & applied science research vol. 8, no. 5, 2018, 3456-3462 3461 www.etasr.com aygun & aktas: a novel dtc method with efficiency improvement of im for ev applications 7(a) shows the variation of the reference stator flux. as shown in figure 7(b), firstly the rated flux value is applied until im reaches its steady state and then the stator flux reaches its optimal value apart from a small transient. figure 8 shows the dynamic performance of the proposed dtc method. speed control capability of the proposed approach is good in figure 8(a) and the torque ripple is comparatively decreased using the proposed dtc, figure 8 (b). (a) (b) fig. 8. (a) speed of im, (b) torque of im. (a) (b) (c) fig. 9. the performance of the proposed method at variable speeds. (a) speed of im, (b) total loss of im, (c) efficiency of im. table iii. comparison of conventional and proposed dtc mean value conventional dtc proposed dtc total loss (w) 231.1961 166.2806 efficiency (%) 77.1 82.4 reference stator flux (wb) 1 0.7539 figure 9 shows the performance of the proposed method at variable speeds. loss minimization algorithm starts for t>2.5s. the reference electrical angular speed is reduced to 150rad/s from 250rad/s for t>4 s. the total losses decrease due to the reduced output power as seen in figure 9(b). the efficiency decreases due to the reduced rotor speed as seen in figure 9(c). figure 10 shows the performance of the proposed method at the variable loads. the loss minimization algorithm starts for t>2.5 s. the load torque is decreased to 1 nm from 2 nm for t>4 s. the total losses decrease due to the reduced output power as shown in figure 10 (b). although the motor operates at the lower load, the efficiency is almost the same as shown in figure 10 (c). (a) (b) (c) fig. 10. the performance of the proposed method at variable loads. (a) torque of im, (b) total loss of im, (c) efficiency of im vi. conclusions in this paper, energy efficiency improvement of dtc based on im drives is proposed for ev applications. results show that the dtc method can be successfully combined with the proposed loss minimization algorithm, while maintaining a good dynamic response. also, the proposed method decreases engineering, technology & applied science research vol. 8, no. 5, 2018, 3456-3462 3462 www.etasr.com aygun & aktas: a novel dtc method with efficiency improvement of im for ev applications the torque ripple of dtc based im. to eliminate disadvantages of neglecting core loss and the effect of leakage inductance, both are included in the motor model and a simplification is made by ignoring the current in the core loss resistance branch of the equivalent circuit of im in the synchronous frame. therefore, the proposed dtc method can be used effectively in ev applications to improve the efficiency and decrease the torque ripple by optimizing the stator flux. references [1] d. ziane, s. aissou, a. azib, t. rekioua, “performance test of the control strategy applied to the electric vehicle, in the case of fwd and 4wd”, international journal of hdyrogen energy, vol. 39, no. 36, pp. 21259-21264, 2014 [2] z. mokrani, d. rekioua, t. rekioua, “modeling, control and power management of hybrid photovoltaic fuel cells with battery bank supplying electric vehicle”, international journal of hdyrogen energy, vol. 39, no. 27, pp. 15178-15187, 2014 [3] f. tazerart, z. mokrani, d. rekioua, t. rekioua, “direct torque control implementation with losses minimization of induction motor for electric vehicle applications with high operating life of the battery”, international journal of hdyrogen energy, vol. 40, no. 39, pp. 13827-13838, 2015 [4] j. o. estima, a. j. m. cardoso, “efficiency analysis of drive train topologies applied to electric/hybrid vehicles”, ieee transactions on vehicular technology, vol. 61, no. 3, pp. 1021-1031, 2012 [5] f. sun, r. xiong, h. he, “a systematic state-of-charge estimation framework for multi-cell battery pack in electric vehicles using bias correction technique”, applied energy, vol. 162, pp. 1399-1409, 2016 [6] m. zeraouila, m. e. h. benbouzid, d. diallo, “electric motor drive selection issues for hev propulsion systems: a comparative study”, ieee transactions on vehicular technology, vol. 55, no. 6, pp. 17561764, 2006 [7] n. kumar, t. r. chelliah, s. p. srivastava, “adaptive control schemes for improving dynamic performance of efficiency-optimized induction motor drives”, isa transactions, vol. 57, pp. 301-310, 2015 [8] v. ambrozic, g. buja, r. menis, “band-constrained technique for direct torque control of induction motor”, ieee transactions on industrial electronics, vol. 51, no. 4, pp. 776-784, 2004 [9] s. kaboli, e. v. khajeh, m. r. zolghadri, “probabilistic voltage harmonic analysis of direct torque controlled induction motor drives”, ieee transactions on power electronics, vol. 21, no. 4, pp. 1041-1052, 2006 [10] t. sutikno, n. r. n. idris, a. jidin, “a review of direct torque control of induction motors for sustainable reliability and energy efficient drives”, renewable and sustainable energy reviews, vol. 32, pp. 548-558, 2014 [11] m. c. d. piazza, m. pucci, “techniques for efficiency improvement in pwm motor drives”, electric power systems research, vol. 136, pp. 270-280, 2016 [12] o. s. ebrahim, m. a. badr, a. s. elgendy, p. k. jain, “ann-based optimal energy control of induction motor drive in pumping applications”, ieee transactions on energy conversion, vol. 25, no. 3, pp. 652-660, 2010 [13] a. m. bazzi, p. t. krein, “review of methods for real-time loss minimization techniques in induction machines”, ieee transactions on industry applications, vol. 46, no. 6, pp. 2319-2328, 2010 [14] s. sridharan, p. t. krein, “minimization of system-level losses in vsibased induction motor drives: offline strategies”, ieee transactions on industry applications, vol. 53, no. 2, pp. 1096-1105, 2017 [15] m. hajian, g. r. arab markadeh, j. soltani, s. hoseinnia, “energy optimized sliding-mode control of sensorless induction motor drives”, energy conversion and management, vol. 50, no. 9, pp. 2296-2306, 2009 [16] f. farhani, c. b. regaya, a. zaafouri, a. chaari, “real time pibackstepping induction machine drive with efficiency optimization”, isa transactions, vol. 70, pp. 348-356, 2017 [17] f. farhani, a. zaafouri, a. chaari, “real time induction motor efficiency optimization”, journal of the franklin institute, vol. 354, no. 8, pp. 3289-3304, 2017 [18] a. haddoun, m. e. h. benbouzid, d. diallo, r. abdessemed, j. ghouili, k. srairi, “a loss-minimization dtc scheme for ev induction motors”, ieee transactions on vehicular technology, vol. 56, no. 1, pp. 81-88, 2007 [19] m. n. uddin, s. w. nam, “new online loss-minimization-based control of an induction motor drive”, ieee transactions on power electronics, vol. 23, no. 2, pp. 926-933, 2008 [20] m. n. uddin, s. w. nam, “development of a nonlinear and model-based online loss minimization control of an im drive”, ieee transactions on energy conversion, vol. 23, no. 4, pp. 1015-1024, 2008 [21] a. borisevich, g. schullerus, “energy efficient control of an induction machine under torque step changes”, ieee transactions on energy conversion, vol. 31, no. 4, pp. 1295-1303, 2016 [22] a. ammar, a. benakcha, a. bourek, “closed loop torque svm-dtc based on robust super twisting speed controller for induction motor drive with efficiency optimization”, international journal of hdyrogen energy, vol. 42, no. 28, pp. 17940-17952, 2017 [23] m. aktas, h. i. okumus, “stator resistance estimation using ann in dtc im drives”, turkish journal of electrical engineering and computer sciences, vol. 18, no. 2, pp. 197-210, 2010 [24] h. i. okumus, m. aktas, “direct torque control of induction machine drives using adaptive hysteresis band for constant switching frequency”, ieee international electric machines and drives conference, antalya, turkey, may 3-5, 2007 [25] f. abrahamsen, f. blaabjerg, j. k. pedersen, p. b. thoegersen, “efficiency-optimized control of medium-size induction motor drives”, ieee transactions on industry applications, vol. 37, no. 6, pp. 17611767, 2001 [26] s. lim, k. nam, “loss-minimising control scheme for induction motors”, iee proceedings-electric power applications, vol. 151, no. 4, pp. 385-397, 2004 microsoft word 23-3008_s_etasr_v9_n5_pp4702-4705 engineering, technology & applied science research vol. 9, no. 5, 2019, 4702-4705 4702 www.etasr.com mudiyono & sudarno: the influence of coconut coir fiber on compressive and flexural strength of … the influence of coconut fiber on the compressive and flexural strength of paving blocks rachmat mudiyono department of civil engineering, universitas islam sultan agung, semarang, indonesia rachmat@unissula.ac.id s. sudarno department of civil engineering universitas tidar, indonesia sudarno@untidar.ac.id abstract—the aim of this study is to determine the influence of coconut coir fiber on the compressive and flexural strength of paving blocks. the research was carried out using paving blocks with dimensions of 20cm×10cm×6cm, mixed with coir fiber by 0%, 0.1%, 0.2%, and 0.3% by weight. the results showed that no addition of coconut coir fiber resulted in compressive strength of 24.49mpa, while the addition of 0.1% coconut coir fiber resulted in compressive strength of 25.39mpa after 7 days. a mixture with no coconut coir fiber resulted in flexural strength of 31.5mpa while the addition of 0.1% coconut coir fiber gave a flexural strength of 33mpa in the age of 14 days. the conclusion of this study is that the addition of 0.1% coconut coir fiber in a paving block mixture can increase its compressive and flexural strength. keywords-coconut coir fiber; paving block; compressive strength; flexural strength i. introduction coconut fiber use in a reinforced concrete mixture to increase its strength is widely researched. in this study, we used coconut coir fiber for a mixture of paving blocks. nowadays the technology development in the field of construction has been increased, especially for highway pavement. paving block pavements start to be widely used for pavement construction on roads [1]. this can be seen from the use of paving blocks which are increasingly used as asphalt replacement because they are easy to install, do not require heavy equipment, can be mass produced, and are easy to maintain and reinstalled. the quality of paving blocks can be measured by their strength in compressive loads and resistance [2]. paving can withstand small earthquakes, freeze and melt [3]. the contribution of this research is the utilization of coconut fiber as a substitute for steel to paving blocks, making it cheaper. ii. materials and methods a. materials 1) fiber the fiber is a material that has a diameter ranging from 0.00015 to 0.008m. there are short fibers, continuous fibers and bundle fibers. fibers have been used to mix concrete for a long time to increase its strength (e.g. asbestos fibers) and for this reason the research of sustainable composite concrete is necessary [4]. 2) effect of coconut coir fiber traditionally coconut fiber is used for household products. coconut fiber is used in mixes with construction materials to increase their strength [5]. coconut fiber is divided into two types of colors, namely white from young coconut and brown from old coconut, both with low thermal conductivity [6]. the stress and strain produced by coconut coir fibers have a higher value than other natural fibers [7, 8] coconut coir fibers can be used in concrete mixtures, because the properties of coconut fiber can bind the concrete material well. addition of coconut fiber increases the compressive and tensile strength of concrete with the optimal mixture consisting of fibers with 1%, 2%, 3% of the weight of cement [9]. concrete mixed with coconut fiber has compressive strength which always increases with curing age. the maximum compressive strength of a concrete mix with coconut fiber increases for fiber concentrations up to 0.5% and gradually declines from 0.75% to 1.0%. the flexural strength of concrete increases in mixtures with coconut coir fiber 0.25%, 0.5% and 1.0%, tested at the age of 28 days[10]. 3) paving blocks in general, there are several types of paving blocks such as rectangle, u-norm, tri hex, hexagonal, etc. paving blocks are made from a mixture of portland cement or other hydraulic adhesives, water and aggregates with or without other additives that do not reduce the quality of the concrete. this paper will discuss the effect of the addition of coconut fiber to the flexural strength of rectangular paving blocks [11]. b. methods coir or coconut fiber is a natural fiber extracted from the husk of the coconut, used in products such as floor mats, doormats, brushes and mattresses. coir is the fibrous material found between the hard, internal shell and the outer coat of a coconut. other uses of brown coir are in upholstery padding, sacking and horticulture. white coir, harvested from unripe coconuts, is used for making finer brushes, string, rope and fishing nets. it has the advantage of not sinking, so it can be corresponding author: s. sudarno engineering, technology & applied science research vol. 9, no. 5, 2019, 4702-4705 4703 www.etasr.com mudiyono & sudarno: the influence of coconut coir fiber on compressive and flexural strength of … used in long lengths in deep waters [12]. its chemical composition consists of cellulose, lignin, pyroligneous acid, gasoline, charcoal, tannin and potassium. the primer products from coir are fibers, bristle (smooth and short fibers) and shell fibers [13]. to obtain the water content of coir fiber the steps are cut ±3cm of the coir fiber to prevent agglutination. before conducting tests the coir fibers should be drained first and the old ones should be picked, so the water content will be low [14, 15]. fig. 1. coconut coir fiber table i. composition of coconut coir fiber [13] parameter coir fiber coir fiber shell ash 4.49 5.62 sio 0.74 0.57 extract 6.62 6.7 lignin 37.80 43.04 c&b cellulose 49.62 alfa cellulose 33.74 pentosan 15.63 11.51 dissolve in warm water 12.51 22.16 dissolve in cold water 10.29 17.22 dissolve in naoh 1% 34.78 45.57 table ii. coconut coir fiber water content no crucible weight (g) crucible and aggregate weight before ovening (g) crucible and aggregate weight after ovening (g) water content (%) average water content (%) i 20 70 65 11 7 ii 45 200 195 3 1) sludge content sludge content test allows us to know the sludge percentage in aggregate. if the sludge content is too much it is not allowed because the material and cement will not combine and will reduce the compressive strength of the paving block [16]. the formula of sludge content is: 1 1 2 v w v v = + (1) where v1 is the sand volume and v2 the sludge volume in grams. table iii. sludge content of fine aggregates no v1 (ml) v2 (ml) w (%) avg. sludge content (%) i 350 10 2.7 2.8 ii 500 15 2.9 2) procedure of the making the paving blocks the mixture compositition paving block used the ratio of 1:2: 2 which is 1kg cement, 2kg sand, and 2kg ash with the addition of 1200ml of water (not too much water should be added in order to get maximum water-cement ratio). coir fibers by 0%, 0.1%, 0.2%, and 0.3% of cement’s weight were added. the mixture compositions were mould. the mould was hit 6 times in order to even up the mixture so there were no air voids. the finished mixture was taken out from the mould into plywood. 3) curing and setting time the paving samples were kept away from the elements. during curing time, the paving block was submerged for about one minute every day and covered by gunny sack for 7 and 14 days. fig. 2. paving block curing iii. results and discussion c. compressive strength test results table iv. coconut coir fober paving block at 7 days no parameter weight (kg) maximum weight (kn) surface area (mm²) 1 ccf 0.0% 2.31 490 19.680 2 ccf 0.1% 2.35 510 19.680 3 ccf 0.2% 2.36 460 19.680 4 ccf 0.3% 2.28 430 19.680 table v. compressive strength test at 7 days no parameter compressive strength (mpa) (kg/cm²) 1 ccf 0.0% 24.9 249 2 ccf 0.1% 25.9 259 3 ccf 0.2% 23.4 234 4 ccf 0.3% 21.8 218 fig. 3. coir fiber paving block compressive strength graph at the age of 7 days engineering, technology & applied science research vol. 9, no. 5, 2019, 4702-4705 4704 www.etasr.com mudiyono & sudarno: the influence of coconut coir fiber on compressive and flexural strength of … from the result of paving blocks’ compressive strength at the age of 7 days (figure 3) we can see that there is an increase from the addition of 0.1% coir fiber which was 259kg/cm² (4% increase as compared with the normal paving block). this is in accordance with the results of [17]. figure 4 shows that a mixture with 0.1% coconut fiber produces a paving block compressive strength of 330kg/cm 2 which then decreases. this is in accordance with the results reported in [18], namely that concrete mixed with coconut coir fiber will be lighter but in a certain amount will decrease its compressive strength. table vi. coconut coir fiber paving block at 14 days no parameter weight (kg) maximum weight (kn) surface area (mm²) 1 ccf 0.0% 2.41 620 19.680 2 ccf 0.1% 2.44 650 19.680 3 ccf 0.2% 2.4 620 19.680 4 ccf 0.3% 2.38 540 19.680 table vii. compressive strength test at 14 days no parameter compressive strength (mpa) (kg/cm²) 1 ccf 0.0% 315 315 2 ccf 0.1% 33.0 330 3 ccf 0.2% 31.5 315 4 ccf 0.3% 27.4 274 fig. 4. coir fiber paving block compressive strength graph at the age of 14 days c. flexural strength test results table viii. flexural strength test at 7 days no parameter flexural strength result (p) flexural strength (kn) (mpa) (kg/cm²) 1 ccf 0.0% 5 2.78 27.8 2 ccf 0.1% 5 2.78 27.8 3 ccf 0.2% 7 3.89 38.9 4 ccf 0.3% 6 3.33 33.3 table ix. flexural strength test at 14 days no parameter flexural strength result (p) flexural strength (kn) (mpa) (kg/cm²) 1 ccf 0.0% 6 3.33 33.3 2 ccf 0.1% 6 3.33 33.3 3 ccf 0.2% 7 3.89 38.9 4 ccf 0.3% 8 4.44 44.4 figures 5-6 show that paving blocks mixed with 0.2% coconut coir fibers produce flexural strength that at first rises and then decreases with increasing amount of coconut fibers [19-21]. fig. 5. coir fiber paving block flexural strength graph at the age of 7 days fig. 6. coir fiber paving block flexural strength graph at the age of 14 days iv. conclusion the results showed that with no coconut coir fiber addition, the paving blocks resulted having compressive strength of 24.49mpa. the addition of 0.1% coconut coir fiber resulted in compressive strength of 25.39mpa in the age of 7 days. for a mixture of 0% coconut coir fiber the result was a flexural strength of 31.5mpa, while the addition of 0.1% coconut coir fiber gave a flexural strength of 33mpa in 14 days. the conclusion of this study is that the addition of 0.1% coconut coir fiber can make a paving block mixture increase its compressive and flexural strength. references [1] m. qomaruddin, s. sudarno, “influence of bottom-ash mixed with gypsum as concrete bricks for wall construction material”, journal of applied environmental and biological sciences, vol. 8, no. 4, pp. 109114, 2018 [2] i. p. hastuty, i. s. s. nursyamsi, “comparison of compressive strength of pavingblock with a mixture of sinabung ash and pavingblock with a mixture of lime”, iop conference series: materials science and engineering, vol. 309, article id 012011, 2018 [3] s. i. zia, “use of coconut fiber concrete”, international research journal of engineering and technology, vol. 2, no. 6, pp. 235-237, 2015 [4] a. abdullah, s. b. jamaludin, m. m. noor, k. hussin, “composite cement reinforced coconut fiber: physical and mechanical properties and fracture behaviour”, australian journal of basic and applied sciences, vol. 5, no. 7, pp. 1228-1240, 2011 [5] a. n. ede, a. o. ige, “optimal polypropylene fiber content for improved compressive and flexural strength of concrete”, iosr journal of mechanical and civil engineering, vol. 11, no. 3, pp. 129-135, 2014 engineering, technology & applied science research vol. 9, no. 5, 2019, 4702-4705 4705 www.etasr.com mudiyono & sudarno: the influence of coconut coir fiber on compressive and flexural strength of … [6] n. m. s. hasan, h. r. sobuz, m. s. sayed, m. s. islam, “the use of coconut fibre in the production of structural lightweight concrete”, journal of applied sciences, vol. 12, no. 9, pp. 831-839, 2012 [7] m. a. aziz, p. paramasivam, s. l. lee, “concrete reinforced with natural fibres”, in: concrete technology and design vol. 2: new reinforced concretes, pp. 107-140, surrey university press, 1984 [8] c. asasutjarit, j. hirrunlabh, j. khedari, m. paguenet, d. quenard, “coconut coir cement board”, 10th international conference on the durability of building materials and components, lyon, france, april 17-20, 2005 [9] p. paramasivam, g. k. nathan, n. c. d. gupta, “coconut fibre reinforced corrugated slabs”, international journal cement composites lightweight concrete, vol. 6, no. 1, pp. 19-27, 1984 [10] m. brahmakumar, c. pavithran, r. m. pillai, “coconut fibre reinforced polyethylene composites: effect of natural waxy surface layer of the fibre on fibre/matrix interfacial bonding and strength of composites”, composites science and technology, vol. 65, no. 3-4, pp. 563-569, 2005 [11] a. h. chkheiwer, “improvement of concrete paving blocks properties by mineral additions”, journal of babylon university/engineering sciences, vol. 25, no. 1, pp. 157-164, 2017 [12] o. owolabi, t. czvikovszky, i. kovacs, “coconut fibre reinforced thermosetting plastics”, journal of applied polymer science, vol. 30, no. 5, pp. 1827–1836, 1985 [13] d. verma, p. c. gope, “the use of coir/coconut fibers as reinforcements in composites”, in biofiber reinforcements in composite materials, woodhead publishing, pp. 285-319, 2014 [14] e. a. olanipekun, k. o. olusola, o. ata, “a comparative study of concrete properties using coconut shell and palm kernel shell as coarse aggregates”, building and environment, vol. 41, no. 3, pp. 297-301, 2006 [15] v. anggraini, a. asadi, b. b. k. huat, h. nahazanan, “effects of coir fibers on tensile and compressive strength of lime treated soft soil”, measurement, vol. 59, pp. 372-381, 2015 [16] a. y. adeyemi, “an investigation into the suitability of coconut shells as aggregates in concrete production”, journal of environment design and management, vol. 1, pp. 17-26, 1998 [17] k. g. satyanarayana, c. k. s. pillai, k. sukumaran, s. g. k. pillai, p. k. rohatgi, k. vijayan, “structure property studies of fibres from various parts of the coconut tree”, journal of materials science, vol. 17, no. 8, pp. 2453–2462, 1982 [18] k. gunasekaran, p. s. kumar, “lightweight concrete using coconut shells as aggregate”, international conference on advances in concrete and construction, hyderabad, india, february 7-9, 2008 [19] a. n. ede, j. o. agbede, “use of coconut husk fiber for improved compressive and flexural strength of con-crete”, international journal of scientific and engineering research, vol. 6, no. 2, pp. 968-974, 2015 [20] s. s. munawar, k. umemura, s. kawai, “characterization of the morphological, physical, and mechanical properties of seven nonwood plant fibre bundles”, journal of wood science, vol. 53, no. 2, pp. 108113, 2007 [21] r. shikha, a. k. saxena, a. k. jha, “evaluation of compressive strength of concrete using coconut coir fibre”, international journal for research in applied science & engineering technology, vol. 3, no. 9, pp. 313317, 2015 authors profile rachmat mudiyono graduated and obtained a phd in engineering from the universiti teknologi malaysia in 2001. he is the dean of the faculty of engineering, universitas islam sultan agung semarang, indonesia. his main research interest is pavement structures using paving blocks. s. sudarno finished his phd in environmental engineering from the universitas diponegoro semarang, indonesia in 2015. his main research interest is pavements using environmentally friendly materials. he works as a lecturer at the department of civil engineering, universtas tidar, indonesia. microsoft word 25-3532_s_etasr_v10_n3_pp5724-5727 engineering, technology & applied science research vol. 10, no. 3, 2020, 5724-5727 5724 www.etasr.com akinyi et al.: road safety in kenya: a case study of nairobi southern bypass (uca-2) road road safety in kenya: a case study of nairobi southern bypass (uca-2) road mercyberyl akinyi sustainable materials research & technology centre jomo kenyatta university of agriculture and technology nairobi, kenya mercyberylakinyi@gmail.com charles kabubo sustainable materials research & technology centre jomo kenyatta university of agriculture and technology nairobi, kenya kabcha@jkuat.ac.ke mathew m. o. winja department of civil, construction and environmental engineering jomo kenyatta university of agriculture and technology nairobi, kenya winjamathew@gmail.com abstract—the fundamental objective of transportation is to ensure that people and goods are safely and effectively moved from one place to another. analyzing the design consistency is one of the ways in which the road’s safety can be maintained or enhanced. in order to obtain a balance in highway design, all the geometric components should, along with being economical functional, be designed to provide safety at speeds likely to occur under ordinary conditions. distinguishing and treating any geometric inconsistency on an expressway can altogether enhance its safety outcome. keywords-geometric consistency; accidents; road safety i. introduction road accidents are associated not only with injuries and fatalities but with existent or potential financial damage. by the year 2020, the global road traffic fatalities will increase to 1.9 million from the 1.3 million that were recorded in 2014 [1]. according to world health organization (who), 1.25 million people are killed and 50 million are injured around the world each year in road traffic accidents [2]. in 2011, statistics from who approximated kenya’s loss to be at least us$ 4 billion as a result of road accidents which is about the 11% of the country’s gdp [3]. forecasts for 2020 raise road accidents to be the third leading cause of death [3]. every year in kenya, about 3,000 individuals are killed on road related accidents, which means roughly 68 deaths for every 1,000 enrolled vehicles, which is 30-40 times more than similar ratios in highly motorized countries [4]. records from ntsa stated that one in each seven street crashes in nairobi occurs on the three bypass roads (eastern, southern and northern bypasses), and a total of 133 individuals died on those bypasses since the opening of the first one in 2014. between january and november 2014, 37, 31 and 15 individuals were killed on the eastern bypass, northern and southern bypass roads respectively [5]. it has been established that the nairobi southern bypass (uca-2) is an accident-prone road. the causes of these accidents have not yet been studied systematically, therefore there is a need to carry out a research on road safety on this road. the current study involves the use of linear regression models to investigate the connection between road geometric design consistency and road accidents on the nairobi southern bypass (uca-2) road and to come up with suggestions that will mitigate the problem. ii. literature review a road accident is characterized as an irregular occasion which comes after a circumstance in which at least one road user has failed to adapt to the immediate environment [6]. road safety includes three noteworthy segments: the road system, the human factor, and the vehicle. the way these three segments exist and interact affects the possibility of accidents [4]. according to [7] accidents tend to happen at specific points on the road or among specific types of road users. this infers that there is likely to be a non-random component in the occurrence of most accidents and it should be possible to prevent some incidences from occurring. in this perspective, the nairobi southern bypass road has indeed specific areas where accidents tend to happen, consequently the need to analyze the primary causes of car accidents on this bypass road emerges. the first 11 months of 2018, one of every seven road crash deaths in nairobi occurred on bypass roads [5]. since the opening of the first bypass in 2014, about 133 people died on the three bypasses and the trend increases [4]. accidents may be caused by haziness, road surface wetness, flawed headlamps, darkened visibility, or driver’s reflectance [1]. drivers, pedestrians, and vehicle defects fundamentally affect the possibility of an accident, while travelers and road defects did not essentially cause accidents. human mistakes, particularly with respect to drivers and pedestrians, is the main accident cause in kenyan roads, while drivers have been blamed for careless or even drunken driving, pedestrians have been known to spurn traffic rules by crossing the streets at non-assigned points and disrespecting the traffic lights [5]. a road traffic system is intended to be a safe and practical utility. road traffic related fatalities and injuries are mostly preventable. this is because the danger of an incurring injury in an accident is to a great extent predictable and there are numerous effective countermeasures. the provision of safe, supportable and moderate methods for transport is a key goal in the planning and design of road traffic systems. wherever such plans and corresponding author: mercyberyl akinyi engineering, technology & applied science research vol. 10, no. 3, 2020, 5724-5727 5725 www.etasr.com akinyi et al.: road safety in kenya: a case study of nairobi southern bypass (uca-2) road strategies are made, they result in a decrease in the number of road accident related deaths and injuries [1]. iii. research objectives the main research objective was to determine the relationship between geometric design consistency and road safety on nairobi southern bypass (uca-2) road in nairobi county. the specific research objective was to determine the frequency, type and severity of accidents on nairobi southern bypass (uca-2) road in nairobi county. iv. research methodology this used a questionnaire survey along with analyzing the consolidated traffic accident data acquired from the police stations that recorded accidents that occurred along uca-2. the study period involved accidents that occurred along nairobi southern bypass between the years 2016 and 2019. a. consolidation of traffic accident data the traffic accident data of southern bypass road from karen, langata and industrial area police stations collected from the year 2016 to 2018 were consolidated. the raw data were fed in microsoft excel and classification of the accidents was done in terms of location, frequency, and severity. a distribution map showing the location, frequency and severity of road accidents from the year 2016 to 2018 was plotted. b. data collection by the use of questionnaires data were collected using structured questionnaires which were filled by the main people who frequently used the nairobi southern bypass, namely the police, drivers, and pedestrians. these data were collected from four locations, namely kibera, kikuyu, ngong and olesereni. qualitative data were acquired from the police and were further analyzed. the sample size was determined using the table published in [9], which provides the necessary sample sizes for given combinations of confidence levels, precision, and variability. the nairobi southern bypass stretches across nairobi and kiambu counties. according to the kenya bureau of statistics, the total population in these counties lies at 6,814,808 [10]. using this population as the population size of this study, a confidence level of 95% and a precision of 10% the required sample size was found to be 100. based on this, 100 questionnaires were distributed to police officers, drivers, and pedestrians. the questionnaires composed of openand close-ended questions to examine how much the users of nairobi southern bypass knew regarding road safety. the acquired data were the frequency of accident incidences along nairobi southern bypass, the causes of the accidents, and possible solutions, if any. out of the distributed questionnaires, 48 were returned. ten of the returned questionnaires were from police officers and the remaining 38 were from drivers and pedestrians. v. results and discussion a. occurrence of traffic accidents along uca-2 from the secondary data, a total of 87 accidents had occurred between june 2016 and april 2019 (figure 1). the data indicated that 26% of the accidents occurred in 2016, 20% occurred in 2017, 36% occurred in 2018 while 18% occurred in 2019. this situation is comparable to accident occurrence in india, where traffic crashes increased by about 5% per year from 2009 to 2010 [11] .one of the reasons for this increase in traffic accidents was the increased number of vehicles on the road. it is suggested that having a properly coordinated official policy to control how vehicles move along a road can minimize accident occurrence [1]. fig. 1. accident occurence b. the victims the main victims of the traffic accidents are passengers, pedestrians, drivers, motor cyclists and pedal cyclists. the secondary data categorized the accident victims according to the severity of the accidents (fatal, seriously injurious or slightly injurious). a fatal accident is defined as an accident resulting in the death of one or more individuals. the definition of a seriously injurious accident covers injuries resulting in a person being detained in hospital and all injuries causing fractures, concussion, crushing, burns (excluding friction burns), severe cuts, internal injuries, severe general shock which require medical treatment even if this does not result in a stay in hospital as an in-patient. a slightly injurious accident is one that leads to a person acquiring a sprain that is not severe (including neck whiplash injury, cuts or bruises). such victims can also suffer a slight shock requiring first aid [12]. from the acquired secondary data, 39% of the total recorded accidents were fatal, 47% were seriously injurious while the remaining 14% were slightly injurious (figure 2). fig. 2. accident severity a total of 131 victims were reported by the traffic accidents that occurred along the nairobi southern bypass. it was discovered that passengers were the most affected traffic engineering, technology & applied science research vol. 10, no. 3, 2020, 5724-5727 5726 www.etasr.com akinyi et al.: road safety in kenya: a case study of nairobi southern bypass (uca-2) road accident victims, composing 35% of all the victims while pedal cyclists were the least affected victims, covering 4% of the total number of victims. c. factors contributing to traffic accidents according to the field data (table i), the most common causes of accidents included over speeding, improper overtaking, and driver ignorance of traffic rules. the factors contributing to the traffic accidents occurring along nairobi southern bypass were recorded by the police in terms of cause codes. each cause code represented a certain cause of traffic accident. the cause codes include the following: code 7driver proceeding with high speed code 8driver failing to keep to the proper lane code 10driver improperly overtaking code 26driver losing control of the vehicle code 29driver misjudging clearance, distance or speed code 30driver’s error of judgment or negligence code 68pedestrian’s error of judgment or negligence code 98cause not traced the traffic accident data indicated that the cause code of 5% of the accidents that occurred along the nairobi southern bypass could not be traced. most of the accidents occurred as a result of the driver losing control of the vehicle (code 26). this factor caused 29% of the total accidents. another 11% of the accidents were caused by speeding while 10% of the accidents were caused by pedestrians’ error of judgment or negligence. some of the other causes of recorded accidents were driver swerving, skidding, failing to comply with the traffic signs or signals, improperly changing of lanes, sudden stopping, speeding cyclists, etc. it was seen that drivers, pedestrians, and vehicle defects fundamentally cause accidents while travelers and road defects did not essentially do. human error, particularly of drivers and pedestrians is the main accident cause in kenyan roads. drivers have often been blamed for careless driving, while pedestrians have been known to spurn traffic rules by crossing the streets at non-assigned points and disrespecting traffic lights among others [8]. table i. accident causes according to the respondents measures 5 strongly agree 4 agree 3 undecided 2 disagree 1 strongly disagree average over speeding 16 13 1 4.5 improper overtaking 17 10 1 2 4.4 driver’s failure to obey/ignorance of traffic rules 8 16 4 0 2 3.9 poor roadway maintenance 1 1 4 13 10 1.9 poor road marking 1 4 3 8 14 1.9 defective motor vehicles 5 8 4 11 1 3.2 lack of roadway identification signs 4 4 6 14 2 2.7 lack of speed bumps, raised medians, zebra crossings 8 8 4 8 4 3.3 bad weather 3 5 1 10 10 2.4 this case is similar to what was experienced in the united states of america, where 92.6% of investigated accidents cases were caused by human factors. environmental factors probably caused 33.8% of the accident cases while 12.6% of accident cases may have been caused by vehicular factors [14, 15]. the research findings further indicated that the main human direct causes of the traffic accidents were speeding and internal distraction. in saudi arabia, between the years 1971 and 1997, 3.5% of the total population was involved in traffic accidents [13]. excessive speeding and/or drivers’ disobedience to traffic signals caused 65% of the accidents. according to [1, 16] most of the accident occurrences could be avoided or minimized through the following measures: • ensuring that traffic safety is one of the main objectives in the planning and implementation of transport networks. • better land use practices to reduce traffic volume. • setting appropriate speed limits depending on the road function and design. • encouraging good road use by improving road layout and design. • ensuring that all motor vehicles met the safety standards set for high income countries, including providing safety belts. • encouraging the manufacture of vehicles with safer fronts and intelligent systems. vi. summary and conclusions this paper involved a field study and the analysis of secondary data acquired from the kenya police covering the period between 2016 and 2019 regarding road safety on the nairobi southern bypass. the following are the key study results: • a total of 87 traffic accidents had occurred along nairobi southern bypass during the period between june 2016 and april 2019 with 26% of the occurring in 2016, 20% in 2017, 36% in 2018, and 18% in 2019. • from the total accident incidences, 39% of them were fatal, 47% seriously injurious and 14% slightly injurious. • the victims were drivers, passengers, pedestrians, pedal cyclists, and motor cyclists. out of the 131 victims recorded, passengers led with 35%. • the major cause of the traffic accidents was over speeding. while bad weather was considered as the least contributor. traffic accidents are predictable and can be prevented, or at least minimized. in high income countries, adoption of new engineering, technology & applied science research vol. 10, no. 3, 2020, 5724-5727 5727 www.etasr.com akinyi et al.: road safety in kenya: a case study of nairobi southern bypass (uca-2) road technology and proper implementation of traffic safety policies to improve traffic safety minimized the number of such incidences. references [1] p. deshpamde, “road safety and accident prevention in india: a review”, international journal of advanced engineering technology, vol. 5, no. 2, pp. 64-68, 2014 [2] m. touahmia, “identification of risk factors influencing road traffic accidents”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2417-2421, 2018 [3] c. g. manyara, “combating road accidents in kenya. a challemge for an emerging economy”, in: kenya after 50: reconfiguring education, gender and policy, springer, 2016 [4] b. obwocha, “why bypasses have pushed up road accident toll”, nairobi news, march 20, 2020 [5] w. odero, m. khayesa, p. heda, “road traffic injuries in kenya, magnitude causes and status”, injury control and safety promotion, vol. 10, no. 1-2, pp. 53-61, 2003 [6] c. castro, human factors of visual and cognitive performance in driving, taylor & francis, 2009 [7] s. rajalin, h. summala, “what surviving drivers learn from a fatal accident”, accident annalysis and prevention, vol 29, no. 3, pp. 277283, 1997 [8] l. k. muchene, “road accidents in kenya, a case of poor network or human error”, 59 th isi world statistics congress, hong kong, china, august 25-30, 2013 [9] i. d. glenn, “determining sample size”, university of florida, available at: https://www.tarleton.edu/academicassessment/documents/samplesize .pdf ,1992 [10] kenya national bureau of statistics, 2019 kenya population and housing census, volume 1, population by county and sub-county, knbs, 2019 [11] ministry of affairs, accidental deaths and suicides, government of india, 2008 [12] l. harms-ringdahl, guide to safety analysis for accident prevention, irs riskhantering ab, 2013 [13] s. ansari, f. akhdar, m. mandoorah, k. moutaery, “causes and effects of road traffic accidents in saudi arabia”, public health, vol. 114, no. 1, pp. 37-39, 2000 [14] c. w. ndung’u, r. m. bonface, l. k. mwai, “analysis of causes & response strategies of road traffic accidents in kenya”, journal of business and management, vol. 17, no. 4, pp. 58-77, 2015 [15] national highway traffic safety administration, tri-level study of the causes of traffic accidents, u.s. department of transportation, national highway traffic safety administration, 1979 [16] m. z. hasanpour, m. r. ahadi, a. s. moghadam, g. a. behzadi, “variable speed limits: strategies to improve safety and traffic parameters for a bottleneck”, engineering, technology & applied science research, vol. 7, no. 2, pp. 1535-1539, 2017 engineering, technology & applied science research vol. 9, no. 2, 2019, 3990-3997 3990 www.etasr.com touileb et al.: mixing design for atig morphology and microstructure study of 316l stainless steel mixing design for atig morphology and microstructure study of 316l stainless steel kamel touileb mechanical engineering department, college of engineering, prince sattam bin abdulaziz university, al kharj, saudi arabia k.touileb@psau.edu.sa abdejlil hedhibi mechanical engineering department, college of engineering, prince sattam bin abdulaziz university, al kharj, saudi arabia a.hedhibi@psau.edu rachid djoudjou mechanical engineering department, college of engineering, prince sattam bin abdulaziz university, al kharj, saudi arabia r.djoudjou@psau.edu.sa abousoufiane ouis mechanical engineering department, college of engineering, prince sattam bin abdulaziz university, al kharj, saudi arabia a.ouis@psau.edu.sa mohamed lamjed bouazizi mechanical engineering department, college of engineering, prince sattam bin abdulaziz university, al kharj, saudi arabia my.bouazizi@psau.edu.sa abstract—this work is a study of the effects of oxides combination on the morphology of 316l stainless steel welds. a series of thirteen weld lines were carried out using thirteen different oxides. based on the depth and ratio d/w results, three candidate oxides were selected: ti2o, mn2o3, and sio2. mixing method available in minitab 17 software is the most appropriate method to find the optimal combinations to get the best depth and d/w ratio. according to simplex lattice degree four, nineteen combinations of these oxides were prepared. the results show that the optimal composition of flux was: 66%sio2-34% mn2o3. the depth and d/w ratio increased to 8.85mm and 0.98 respectively for optimal atig, whereas for the conventional tig welding, the depth and the ratio d/w didn't exceed 1.65mm and 0.17 respectively. for tig weld joint the hardness is about 47 hra and it increases to 77 hra for the optimal atig weld joint. the absorbed energies in charpy impact test are 146 and 138kj in the weld zone and in the heat affected zone respectively for the tig welding and they dropped to 111 and 74kj for the optimal atig welding. the fracture surface examined by scanning electron microscope (sem) shows a ductile fracture for tig weld with small dimples but ductile-brittle fracture for atig weld. energy dispersive spectroscopy (eds/sem) analysis shows the formation of fes2 and sio2 in the weld zone causing low absorbed energy for atig weld. keywords-atig; 316l austenitic stainless steel; atig welding mixing method; ternary flux i. introduction tig welding process is quite widespread. however, weld penetration varies from cast to cast and the maximum weld depth in a single pass does not exceed 3mm. activated tig (atig) welding proposed by paton institute-kiev [1, 2] seems an appropriate process to overcome these weaknesses. atig welding uses the same equipment as tig except a prior weld operation layer of activated flux paste is deposited on the workpiece. hypotheses have been made to explain the phenomenon favoring a high weld depth. authors in [3-6] proposed that the marangoni convection is the most important factor in determining weld shape. surfactant elements as s, se, te, o in weld pool affect the convection of molten metal leading to centripetal circulation of weld metal getting a depth of weld. authors in [7, 8] applied the principle of electron absorption [9], electronegative elements as halides (fluorine) migrate to arc weld and capture outer arc electrons which contribute to contract the arc welding. this phenomenon increases the density of arc welding and the heat provided to weld pool. authors in [10-12] proposed that high electrical resistance of flux components contributes to arc constriction. many works were subsequently carried out using oxides like sio2, tio2, cr2o3, fe2o3, cao, zro2, mgo [13-24], chlorides [25-27], and fluorides [28, 29] to improve weld depth. these studies showed an increasing in the weld depth without affecting the mechanical properties of the specimens [30, 31]. other studies were dedicated to microstructure and mechanical properties [32-33]. in this work, 13 oxides were investigated on 316l austenitic stainless steel. design of experiments was used to predict the best combination of the tested oxides. mixing method based on a simplex lattice degree four was the key tool to optimize the flux combination in order to enhance the depth and d/w ratio. ii. experimental procedure a. materials the material used was the 316l stainless steel whose chemical composition is shown in table i. experiments consisted of welding a 20cm line on a rectangular plate of 6mm thickness. before welding, the plates were cleaned with acetone. flux powders were dried in furnace to eliminate humidity, and then mixed with methanol in 1:1 ratio. a flux corresponding author: kamel touileb engineering, technology & applied science research vol. 9, no. 2, 2019, 3990-3997 3991 www.etasr.com touileb et al.: mixing design for atig morphology and microstructure study of 316l stainless steel layer less than 0.2mm thick was deposited on the surface to be welded. table i. 316l chemical composistion element percentage (%) c 0.018 mn 1.30 si 0.43 p 0.034 s 0.0029 cr 16.78 ni 10.00 mo 2005 ti 0.0042 cu 0.2082 co 0.226 n (ppm) 321 b. welding procedure a tungsten inert gas welding machine was used. a watercooled torch with a standard 2% thoriated tungsten electrode rod having diameter of 3.2mm has been used for the experiments. the torch was mounted on a motorized carriage as shown in figure 1. a series of tests were carried out with 150a welding current and 15cm/min welding speed leading to a provided energy of 540kj/m. the welding parameters for the tig welding are listed in table ii. fig. 1. experimental setup of tig welding with flux paste (a motorized carriage, torch–workpiece). table ii. welding parameters welding speed 15cm/min welding current 150a arc length 2mm electrode tip angle 45 ͦ shield gas on work piece argon with flow rate 12l/min shield gas back side argon with flow rate 5l/min welding mode direct current electrode negative c. mechanical testing after welding, the samples were cut as shown in figure 2 to acquire test samples for mechanical testing and weld morphology. the rockwell hardness measurement was performed with a digital hardness tester model hrs-150. the hardness tests were conducted in the bulk of weld bead, and the results were the average of four indentations as shown in figure 3. fig. 2. different test specimens on welded tig and atig plate fig. 3. hardness test locations on weld bead impact tests were carried out with the impact testing machine model jbs-500. the specimens were cut according to astm e23 and the impact tests were conducted in the weld bead and in the haz as shown in figure 4. (a) (b) fig. 4. test specimen for impact test (a) weld zone, (b) haz d. experiment by mixing method design (doe) for the doe, mixing method in mini tab 17 was applied and consequently the number of experiments to be conducted was reduced. in order to compare the effect of the flux on the tensile strength, 13 oxides (sio2, tio2, fe2o3, cr2o3, zno, zro2, cao, mn2o3, v2o5, moo3, sro2, coo3, and mgo) were engineering, technology & applied science research vol. 9, no. 2, 2019, 3990-3997 3992 www.etasr.com touileb et al.: mixing design for atig morphology and microstructure study of 316l stainless steel tested. among these oxides, 3 gave the best depth and d/w ratio and were selected to be used in the mixing design method. based on the simplex lattice degree four designs, 19 combinations have been selected. nineteen weld lines were executed and samples for morphology, hardness and impact tests were cut. the optimizer module available in mini tab 17 was used to get the optimal formulation of flux which is expected to give the best depth and d/w ratio of weld. finally, using the optimal formulation, atig weld line has been carried out along with another weld line without flux (tig). iii. results and discussion a. depth d and d/w ratio figure 5 shows the weld depth results of atig weldment of the tested preliminary 14 oxides. the highest value of depth is 6.04mm which is obtained for the sample welded with mn2o3 flux, followed by the sample welded with sio2 flux (5.29mm), and then by the sample welded with tio2 (4.81mm). so the oxides mn2o3, sio2, and tio2 were selected. the results of the depth and d/w ratio for different proportions of the 3 selected oxides are shown in table iii. fig. 5. depth of atig welds. table iii. different compositions of fluxes, depth and d/w exp. no. sio2 % tio2 % mn2o3 % depth (mm) d/w 1 75 25 0 4.23 0.54 2 75 0 25 6.72 0.92 3 0 75 25 4.47 0.58 4 25 75 0 4.61 0.61 5 25 0 75 3.77 0.49 6 0 25 75 3.95 0.53 7 0 50 50 5.66 0.77 8 50 0 50 6.63 0.90 9 50 50 0 6.36 0.83 10 50 25 25 6.66 0.86 11 25 50 25 4.85 0.63 12 25 25 50 3.48 0.43 13 33.3 33.3 33.3 4.93 0.66 14 66.67 16.67 16.67 5.01 0.72 15 16.67 66.67 16.67 5.27 0.72 16 16.67 16.67 66.67 4.70 0.64 17 100 0 0 5.29 0.74 18 0 100 0 4.81 0.66 19 0 0 100 6.04 0.82 b. mixture contour plot mixture contour plots for depth d and d/w were generated using minitab software and are shown in figure 6. the isocontour lines and the regions confined between them indicate different levels of depth or d/w. different colors represent the different levels of the two properties. the interesting zone lies where the values of depth and d/w were higher. optimizer module available in minitab was used to predict the responses of depth and d/w ratio. the composite desirability is equal to 1 (100%). it indicates that the parameters achieve favorable results for all responses, which means that both responses are within acceptable limits, as shown in figure7. the predicted values are listed in table iv. the optimal combination of flux is represented in table v. (a) (b) fig. 6. mixture contour of plot for (a) depth and (b) d/w ratio. fig. 7. optimization plot table iv. predicted responses (uts, hra) of weld executed with optimal flux responses predicted responses desirability depth(mm) 7.01 100% d/w 0.96 100% table v. optimal composition of flux. variables sio2 tio2 mn2o3 percentage (%)s 66 0 34 100 c. confirmation test the confirmation test is the last step in the experimental process. confirmation tests were conducted based on the optimum flux composition obtained in the mixing design method of minitab. the experimental values of depth and d/w ratio of the optimal flux atig weld are reported in table vi. engineering, technology & applied science research vol. 9, no. 2, 2019, 3990-3997 3993 www.etasr.com touileb et al.: mixing design for atig morphology and microstructure study of 316l stainless steel the results show the depth of optimized flux is greater than tig weld by 5 times. the ratio d/w improved 6 times. the experimental values obtained for depth in atig and tig welds are shown in figure 8. the penetration weld of optimized flux (8.85mm) is greater than the maximum value predicted by the software (7.01mm). furthermore, the d/w value obtained for atig weld (0.98) is very close to the maximum predicted value of 0.96 as shown in figure 9. tig molten metal behaves as pure metal with centrifugal convection leading to wide and sallow weld bead contrariwise. atig weld metal has a centripetal movement related to oxygen liberated from oxides during welding operation. the quantity of liquid melted in atig (51.51mm2) is higher than in tig weld bead (14.2mm2) as shown in figures10-11. table vi. morphology of tig and atig welds. atig(with optimal flux) tig depth(mm) 8.85 1.65 w(mm) 9.04 9.92 d/w 0.98 0.17 fig. 8. depths of atig and tig welds fig. 9. d/w of atig and tig welds fig. 10. areas of atig and tig welds d. hardness test the experimental values obtained for hardness are shown in figure 12. atig hardness number of hra=77 is greater than tig hardness number of hra=47. (a) (b) fig. 11. morphology of (a) atig and (b) tig welds fig. 12. hardness hra in weld zone for atig and tig welds. e. impact test the experimental values obtained from the impact test are shown in figures 13-14. fig. 13. absorbed energy in weld zone for tig and atig welds. fig. 14. absorbed energy in haz for tig and atig welds. the energies absorbed either in the weld zones or in haz of tig welds are higher than the ones of atig welds. figure 15 shows the images of fractograph of the “v” notch charpy engineering, technology & applied science research vol. 9, no. 2, 2019, 3990-3997 3994 www.etasr.com touileb et al.: mixing design for atig morphology and microstructure study of 316l stainless steel impact test conducted on scanning electronic microscope (sem). the images show the formation of micro-voids, with multiple dimples which demonstrate that the fracture is in ductile mode in the cases of tig weld zone (a) and in tig heat affected zone (c). combined ductile (small colonies with finer dimples) and brittle fracture mode formation characterizes the atig weld zone (b) and the atig affected zone (d). the combined ductile and brittle fracture mode leads to poor resistance to sudden impact loads. (a) tig welded zone (500x ) (b) atig welded zone (500x ) (c) tig heat affected zone (500x) (d) atig heat affected zone (500x) fig. 15. fractograph of ss 316l impact charpy “v” notch f. microstructure study microstructure study was performed in order to view the material properties after the welding in both tig and atig weldings. 1) eds/sem analysis the results of eds/sem analysis in figures 16 and 17 show the presence of silicon, sulphur and oxygen in atig weld bead and in the heat affected zone, that lead to formations of inclusions as fes2. moreover, oxygen initiates microvoids and propagates by micro void coalescence, which facilitate the fracture phenomenon. these results can explain the low impact resistance in atig weld. the results of eds/sem analysis in figures 18 and 19 show the presence of silicon in tig weld zone in quantities close to the quantity in the received plate. the weld zone and the haz are free from oxygen and sulphur which can explain the withstanding of tig weld to sudden impact. the results obtained with eds/sem regarding tig weld may explain the high resistance to impact test. fig. 16. eds/sem spectrum analysis of fracture face of atig welded zone fig. 17. eds/sem spectrum analysis of fracture face of atig haz engineering, technology & applied science research vol. 9, no. 2, 2019, 3990-3997 3995 www.etasr.com touileb et al.: mixing design for atig morphology and microstructure study of 316l stainless steel table vii. elements present in fracture face of atig welded zone element c si cr mn fe ni o s weight% 20.50 0.51 14.43 1.98 53.44 6.41 2.29 0.43 table viii. elements present in fracture face of atig haz element c si cr mn fe ni o s weight % 21.17 0.56 14.57 1.43 52.93 6.57 2.36 0.42 the results of eds/sem analysis in figures 18 and 19 show the presence of silicon in tig weld zone. the weld zone and the haz are free from oxygen and sulphur which can explain the widstand of tig weld to sudden impact. the results obtained with eds/sem regarding tig weld may explain the high resistance to impact test. fig. 18. eds/sem spectrum analysis of fracture face of tig welded zone table ix. elements present in fracture face of tig welded zone element c si cr fe ni weight% 21.23 0.48 14.52 56.32 7.44 fig. 19. eds/sem spectrum analysis of fracture face of tig haz table x. elements present in fracture face of tig haz element c cr fe ni weight% 44.04 7.06 36.10 12.81 2) ferrite proportions the measurement of ferrite content in the austenite matrix was conducted using area image processing software of microvision instruments. the weld zone appearance of atig and tig was examined by sem. the measurements were taken in 4 different locations in the weld zone and the results were the average of these measurements. delta ferrite morphology has a vermicular network structure in both atig and tig welds as shown in figure 20. results show ferrite content equal to 10.4% for atig. instead, there is a decrease in ferrite content to 6.8% for tig. this can be explained by the fact that in the case of atig operation, the weld bead is fully penetrated with a large weld bead area up to 55mm2. during atig weld operation, the activated flux has a beneficial effect in increasing the heat provided to weld pool and consequently the peak temperature in atig weld is greater comparatively to tig weld leading to increase the proportion of delta ferrite retained in austenite matrix. on the other hand, in tig welding, the bead is wide and shallow so the cooling rate is high. as the cooling rate is fast the transformation of delta ferrite to austenite is not completed, resulting on the presence of delta ferrite in the weld bead. (a) delta ferrite in atig weld zone (fn=10.4%) (b) delta ferrite in tig weld zone (fn=6.8%) fig. 20. sem micrograph of (a) atig weld zone and (b) tig weld zone. magnification 250x the ferrite content in heat affected zone is up to 4.6% in atig welding and decreases at 1.4% in tig heat affected zone. in tig, the delta ferrite is randomly distributed in globular form or in small slats as shown in figure 21(b). however, in atig heat affected zone, delta ferrite looks-like elongated inclined stringers as shown in figure 21(a). engineering, technology & applied science research vol. 9, no. 2, 2019, 3990-3997 3996 www.etasr.com touileb et al.: mixing design for atig morphology and microstructure study of 316l stainless steel (a) delta ferrite in atig haz (fn=4.6%) (b) delta ferrite in tig haz (fn=1.4%) fig. 21. sem micrograph of (a) atig haz and (b) tig haz. magnification 1000x iv. conclusion this study was conducted on atig welding of austenitic 316l. the results are summarized as follows: • among 13 oxides tested, sio2, tio2 and mn2o3 present the highest depth penetration. • the optimal flux is composed of 66% sio2 and 34% mn2o3. • the size of atig weld bead is bigger than the one of tig weld bead. the activated flux enhances the heat provided to the weld pool leading to high proportion of retained delta ferrite (10.4%). however, tig weld is wider and shallower so the molten metal cools rapidly in comparison with atig molten metal. in the case of tig weld the transformation of delta ferrite to austenite is stopped earlier due to the fast cooling giving delta ferrite proportions up to 6.8%. • the hardness hra property of atig weld is improved comparatively to tig weld. this result is related with the high delta ferrite content in atig weld zone. • eds/sem analysis reveals the presence of fes2, silicon, and oxygen in atig welded zone which could be the reason of the decrease of sudden impact load in comparison with tig weld. • mixing design method is the more appropriate tool to get optimal flux composition when depth and d/w ratio improvements are desirable. based on experiments’ results, one can say that minitab software can predict accurately the responses. acknowledgements this work is supported by the deanship of scientific research in prince sattam bin abdulaziz university, saudi arabia under the research project number 2017/01/7373. authors acknowledge and thank dr. nabeel alharthi, director, centre of excellence for research in engineering materials for his help in performing sem/eds analysis. references [1] s. gurevitch, v. zamkov, n. kushnirenko, “improving the penetration of titanium alloys when they are welded by argon tungsten arc process”, automat weld, vol. 18. no. 9, pp. 1-5, 1965 [2] b. paton, v. zamkov, v. p. prilouski, “le soudage a-tig du titane et de ses alliages”, soudage et techniques connexes, vol. 52, no. 11-12, pp. 23-26, 1998 (in french) [3] c. heiple, j. roper, “mechanism for minor element effect on gta fusion zone 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journal of science and technology, vol. 2 no. 2, pp. 163-168, 2013 microsoft word 15-889-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1288-1293 1288 www.etasr.com yildirim et al.: computation of the speed of the four in-wheel motors of an electric vehicle using… computation of the speed of four in-wheel motors of an electric vehicle using a radial basis neural network merve yildirim department of electrical and electronics engineering university of firat, elazig, turkey merveyildirim@firat.edu.tr mehmet cem catalbas department of electrical and electronics engineering university of firat, elazig, turkey catalbas@firat.edu.tr arif gulten department of electrical and electronics engineering university of firat, elazig, turkey agulten@firat.edu.tr hasan kurum department of electrical and electronics engineering university of firat, elazig, turkey hkurum@firat.edu.tr abstract—this paper presents design and speed estimation for an electric vehicle (ev) with four in-wheel motors using radial basis neural network (rbnn). according to the steering angle and the speed of ev, the speeds of all wheels are calculated by equations derived from the ackermann-jeantand model using codesys software package. the electronic differential system (eds) is also simulated by matlab/simulink using the mathematical equations. rbnn is used for the estimation of the wheel speeds based on the steering angle and ev speed. further, different levels of noise are added to the steering angle and the ev speed. the speeds of front wheels calculated by codesys are sent to two induction motor (im) drives via a controller area network-bus (can-bus). these speed values are measured experimentally by a tachometer changing the steering angle and ev speed. rbnn results are verified by codesys, simulink, and experimental results. as a result, it is observed that rbnn is a good estimator for eds of an ev with in-wheel motor due to its robustness to different levels of sensor noise. keywords-electric vehicle; electronic differential system; inwheel motor; radial basis neural network; speed estimation i. introduction electric vehicles (evs) are increasingly being used due to their reduced pollution emissions and fuel consumption [1, 2]. further, recent efficient electric motors and developments in drive and battery technology have resulted to an increase in the popularity of evs [3]. ev motors having a differential gear are fitted into the wheels of the vehicle to reduce the mass caused from the batteries and drive-trains [4]. in traditional vehicles, mechanical differentials are utilized in slippery and sloping roads to distribute power and torque equally to the traction wheels [1]. on the contrary, the electronic differential system (eds) is used in evs to eliminate mechanical losses, maintenance, and repair costs of gears caused by the powertrains. according to the curve of the road, the outer wheel speed of the ev must be higher than the inner wheel speed for safe driving [5]. an eds for ev is modelled by nn based on the vehicle speed and steering angle in [1]. using a fuzzy logic control method to estimate the slip rate of each wheel, a new electronic differential (ed) control for two in-wheel motors of ev is investigated in [4]. the designed ed control is validated by matlab/simulink results. in [6], authors estimate the speeds of four wheels for ev by using the ackermann-jeantand model [6]. the estimated speeds are also verified by matlab/simulink and experimental results. in [7], the speeds of the four wheels are calculated by nn pid ed based on the steering angle and speed of ev. an eds for rear wheels of an ev used in brushless dc motors is investigated by fuzzy logic speed controller using the ackermann-jeantand model [8]. the proposed eds is verified by matlab/simulink results. in [9], authors proposed an eds for the rear wheels of ev driven by fault tolerant permanent magnet motors. the speeds of the wheels are calculated by ackermann-jeantand model. authors in [10] design an eds for the rear wheels of an ev using dc motors based on the steering angle and vehicle speed. the results of the designed eds are verified by experimental results. nn control is used for estimating the rear wheels of an ev in [11]. the simulation results are tested by two 37-kw ims. in another paper [12], an eds for two rear wheels of ev is presented and analyzed versus the speed and torque observed for the dc motor. in this paper, an eds for all four wheels of an ev is modeled and the speeds of all wheels are calculated by the codesys software package using mathematical equations derived from the ackermann-jeantand model. then, the eds simulation is also conducted in matlab/simulink using these equations. the speeds of the wheels are estimated by an radial basis neural network (rbnn) based on the steering angle and the ev speed. further, white noise at specified amplitudes is added to the ev speed and the steering angle in order to investigate the behavior under sensor noise. according to the this work is supported by tubitak (the scientific and technological research council of turkey) with the project, 113m090. engineering, technology & applied science research vol. 6, no. 6, 2016, 1288-1293 1289 www.etasr.com yildirim et al.: computation of the speed of the four in-wheel motors of an electric vehicle using… noise levels, the speeds estimated by the rbnn are compared with simulink results. furthermore, the speeds of the front wheels calculated by codesys are sent to two im drives and measured by a tachometer experimentally. rbnn results are also verified by codesys, simulink, and experimental results. ii. electronic differential system for ev the ackermann-jeantand model is employed for eds design which is generally preferred at low speeds due to the effect of centrifugal force and centripetal forces is utilized [4]. a position encoder is used for the steering angle ( ). once  is zero, ev drives on a straight road. if  is different from zero, it means that ev drives on the curved road. according to the turning direction, the speed of the outer wheel has to be higher than that of the inner wheel [4, 6, 13]. in this situation, the eds is activated. the equations derived from this model are as follows: the inner and outer steering angles of the front wheel are respectively given by:        ))tan()2/(( )tan( arctan2,1    kl l (1) where k is the distance between the left and right kingpin, l is the distance between the front and rear wheel. to estimate the speeds, the turning radii of the front inner and outer wheels and rear inner and outer wheels can be respectively defined by: )sin( 2,1 2,1  l r  (2) 2)tan( 4,3 rdlr   (3) where dr is the distance between rear wheels. the gravity centre radius of the ev is: 2)(2))2/(( 3 rr ldr cg r  (4) where lr is the distance between the rear wheel and gravity centre. the angular speeds of the front inner and outer wheels, and the rear inner and outer wheels can be respectively expressed by: rr rv w cg    )( 2,1 2,1 (5) rr rv w cg    )( 4,3 4,3 (6) where r is the radius of the wheel and v is speed of ev. the equations derived from ackermann-jeantand geometry are given into codesys software package. l, lr, dr, r, and k parameters taken from a vehicle model are shown in table i. these parameters are used as the constant values in the codesys programmer. table i. eds model parameters parameters l lr dr r k values (m) 2.285 0.835 1.35 0.395 1.219 iii. modelling of eds via rbnn the implementation of rbnn is similar to performing exact interpolation of various data points in a multidimensional space [14]. the rbnns are rather popular due to their simple structure, fast training, and implementation time. the network architecture of an rbnn is similar to that of a classical nn [15]. the structure of rbnn includes the input layer, hidden layer and output layer [16, 17]. the input vector x is used as an input in all radial basis functions. µj is the vector determining the center of basic function ϕj and has elements µji. the weight parameter is represented by wkj and bias term is equal to wk0. the hidden layer includes nonlinear radial basis activation function and the output layer is linear combination of hidden layer. each node in the hidden layer uses an rbf as a nonlinear activation function. ϕ0(x)=1 corresponds to the bias in the output layer. the rbf network can give an optimal solution to the adjustable weights in the minimum mean squared error (mse) sense by linear optimization method [18]. the smoothness level of interpolation function is controlled by the parameter of spread (σ). the relationship between input, output, and nonlinear transfer function is given by :               22 exp)( j jx xj    (7)    m j k wx jkj wx k y 1 0 )()(  (8) rbnns are generally utilized for classification and curve fitting. our test system has two inputs: the steering angle and the speed of ev and the outputs are the speeds of front and rear wheels. the overall scheme is shown in figure 1. fig. 1. overall scheme engineering, technology & applied science research vol. 6, no. 6, 2016, 1288-1293 1290 www.etasr.com yildirim et al.: computation of the speed of the four in-wheel motors of an electric vehicle using… the signal-to-noise ratio is given by          noise a signal a db snr 10 log20 (9) where asignal and anoise are rms amplitudes of the signal and noise as decibel, respectively. gaussian white noise (gwn) is added to nn systems for performance analysis. gwn in this case represents sensor interference in steering angle and ev speed [19]. different levels of gwn are used to obtain the optimal solution. mse gives an idea about the behavior of the rbnn training process. low mse means a successful data fitting. therefore, the number of epochs is selected at nearly fixed value of mse. in this study, the number of epochs is taken as 400. the mse versus number of epochs is shown in figure 2. 0 50 100 150 200 250 300 350 400 10 -15 10 -10 10 -5 10 0 10 5 number of epochs m ea n s qu ar e e rr or fig. 2. mse versus number of epochs. iv. matlab/simulink model of eds eds is simulated by matlab/simulink using the equations derived from the ackermann jeantand model. the simulation model and subsystem of the model are shown in figures 3 and 4, respectively. fig. 3. matlab/simulink model of eds. fig. 4. subsystem of eds model. the maximum speed of an ev having 21-inch wheel size is 50.806 km/h. therefore, this speed is used as maximum value in the simulation. maximum manoeuvrability can be calculated by minimum circle radius of outer wheel trace at 10 km/h vehicle speed. turning radius is given by ϛ )sin( 21    l (10) turning radius changes between 7 m and 9 m in passenger cars. since the movement area where is placed in the wheels is another factor limited the steering of the wheel, the steering angle is taken as maximum value (15˚). the speeds of four wheels are calculated by simulink changing the steering angle from 1° to 10° and ev speed from 0 to 40 km/h. then, the relationship between input parameters (δ,v) and four wheel speeds are trained to nn model. the speeds are estimated by changing the steering angle from 10° to 15° and the ev speed from 40 to 50 km/h. the rbnn results are verified by simulink results for all wheel speeds as shown in table ii, iii, iv, and v. table ii. comparison of simulink and rbnn results for front inner wheel. δ (°) 13 14 15 v (km/h) simulink results rbnn results simulink results rbnn results simulink results rbnn results 45 43.334 43.300 43.300 43.253 43.282 43.210 46 44.297 44.226 44.263 44.171 44.244 44.117 47 45.260 45.119 45.225 45.052 45.205 44.985 48 46.223 45.961 46.187 45.879 46.167 45.792 49 47.186 46.729 47.149 46.626 47.129 46.514 50 48.149 47.393 48.112 47.264 48.091 47.122 table iii. comparison of simulink and rbnn results for front outer wheel. δ (°) 13 14 15 v (km/h) simulink results rbnn results simulink results rbnn results simulink results rbnn results 45 48.715 48.671 49.083 49.018 49.465 49.359 46 49.797 49.706 50.174 50.050 50.564 50.385 47 50.880 50.702 51.265 51.039 51.663 51.361 48 51.962 51.636 52.356 51.958 52.762 52.261 49 53.045 52.478 53.446 52.779 53.861 53.053 50 54.128 53.195 54.537 53.465 54.961 53.701 table iv. comparison of simulink and rbnn results for rear inner wheel δ (°) 13 14 15 v (km/h) simulink results rbnn results simulink results rbnn results simulink results rbnn results 45 41.783 41.752 41.514 41.474 41.241 41.184 46 42.711 42.645 42.436 42.355 42.157 42.052 47 43.640 43.507 43.359 43.203 43.074 42.883 48 44.568 44.320 44.281 43.997 43.990 43.657 49 45.497 45.059 45.204 44.715 44.907 44.350 50 46.425 45.697 46.126 45.327 45.823 44.933 engineering, technology & applied science research vol. 6, no. 6, 2016, 1288-1293 1291 www.etasr.com yildirim et al.: computation of the speed of the four in-wheel motors of an electric vehicle using… table v. comparison of simulink and rbnn results for rear outer wheel. δ (°) 13 14 15 v (km/h) simulink results rbnn results simulink results rbnn results simulink results rbnn results 45 47.899 47.856 48.115 48.053 48.331 48.233 46 48.963 48.874 49.184 49.066 49.405 49.237 47 50.028 49.853 50.254 50.035 50.479 50.192 48 51.092 50.769 51.323 50.935 51.553 51.071 49 52.156 51.595 52.392 51.738 52.627 51.845 50 53.221 52.294 53.461 52.405 53.701 52.475 v. experimental results the experimental setup is established to obtain the results of designed eds as shown in figure 5. the speeds of the front wheels calculated by codesys are sent to three-phase im drives (vfd c2000) via can-bus. an encoder is used for the steering angle. three-phase im drives, hy-ttc 60 and encoder which are fed from 24 v power supply communicate with each other on can-bus. hy-ttc 60 processor which is an advanced model of 16-bit controller family produced by ttcontrol company and consists of power and control cards is a master unit on can-bus line. two drives connected to im motors and encoder are slave units on the can-bus line. characteristic line impedances are used in beginning and end of the line. by changing the steering angle from 0° to 15° degree and taking the ev speed which is fixed as 50.806 km/h, the speeds of front wheels calculated by codesys using the ackermann-jeantand model are sent to im drives. the speeds of front wheels are measured by a tachometer experimentally. codesys results are verified by simulink, experimental, and rbnn results as given in table vi. according to the difference of the comparison, mse of all wheel speeds estimated by rbnn are shown in table vii based on the noise level and function spread. once examining the table vii, the large number of the spread is preferred to estimate the speeds due to having less error based on different noise levels. hence, the spread value and noise level are selected as 10 and 40 db, respectively. rbnn results of the front inner and outer, rear inner and outer wheel speeds are illustrated based on the noise level in figures 6-9, respectively. table vi. comparison of codesys, simulink, experimental, and rbnn results for front wheel speeds δ(°) codesys results (km/h) simulink results (km/h) exp. results (km/h) rbnn results (km/h) n1 n2 n1 n2 n1 n2 n1 n2 0 50.807 50.807 50.803 50.803 50.803 50.803 50.805 50.805 1 50.577 51.050 50.582 51.054 50.562 51.054 50.575 51.048 2 50.360 51.306 50.361 51.305 50.351 51.285 50.359 51.305 3 50.158 51.576 50.160 51.577 50.139 51.536 50.157 51.575 4 49.969 51.859 49.969 51.858 49.959 51.848 49.968 51.858 5 49.794 52.155 49.798 52.160 49.778 52.149 49.793 52.154 6 49.633 52.465 49.637 52.461 49.607 52.431 49.632 52.463 7 49.487 52.787 49.486 52.783 49.496 52.742 49.486 52.786 8 49.355 53.123 49.356 53.124 49.346 53.084 49.354 53.122 9 49.239 53.471 49.235 53.476 49.225 53.446 49.238 53.470 10 49.137 53.834 49.134 53.838 49.134 53.828 49.136 53.832 11 49.051 54.209 49.054 54.210 49.044 54.159 49.049 54.207 12 48.980 54.598 48.984 54.602 48.954 54.572 48.978 54.596 13 48.926 55.001 48.923 55.004 48.903 54.963 48.922 54.997 14 48.888 55.417 48.883 55.416 48.873 55.386 48.882 55.412 15 48.867 55.847 48.863 55.848 48.843 55.808 48.858 55.839 table vii. mean square errors of four wheel speeds noise (db) 30 db spread (σ) n1 n2 n3 n4 0.5 12.004 15.369 10.822 14.685 1 31.400 36.197 30.987 35.445 5 5.627 6.663 5.340 6.480 10 0.741 0.848 0.757 0.815 spread (σ) 40 db 0.5 11.987 15.346 10.807 14.662 1 30.909 35.763 30.484 35.006 5 5.397 6.369 5.094 6.205 10 0.323 0.368 0.320 0.364 fig. 5. the experimental setup estimation results of rbnn for the front and rear wheel speeds are compared with simulink results. differences between simulink and rbnn results are illustrated for the front inner and outer wheel speeds based on the noise levels in fig. 10-11, respectively. as shown in the figures, the errors of all wheel speeds increase with rising of steering angle and ev speed. engineering, technology & applied science research vol. 6, no. 6, 2016, 1288-1293 1292 www.etasr.com yildirim et al.: computation of the speed of the four in-wheel motors of an electric vehicle using… fig. 6. rbnn results of front inner wheel (40 db). fig. 7. rbnn results of front outer wheel (40 db). fig. 8. rbnn results of rear inner wheel (40 db). fig. 9. rbnn results of rear outer wheel (40 db). fig. 10. difference between simulink and rbnn results of front inner wheel. fig. 11. difference between simulink and rbnn results of front outer wheel. vi. conclusion in this paper, eds modelling and estimation parameters for front and rear wheels of an ev are realized. according to the steering angle and speed of the ev, the speeds of the four wheels are calculated by mathematical equations derived from the ackermann-jeantand model using the codesys software package. matlab/simulink modeling of eds is also realized by using the equations obtained from the ackermann-jeantand model. the speeds of the all wheels are calculated by simulink changing the steering angle from 1˚ to 15˚ and the ev speed from 0 km/h to 50 km/h. different levels of white noise are added to the steering angle and ev speed as sensor noise. rbnn is used to estimate the speeds changing the steering angle from 10˚ to 15˚ and the ev speed from 40 km/h to 50 km/h. the steering angle is taken by an encoder. the calculated front wheel speeds are sent to im drives via can-bus for taking experimental results by a tachometer. rbnn results are verified by comparing with simulink, experimental and codesys results. furthermore, rbnn results are compared with simulink results based on noise and function of spread at different levels. to conclude, rbnn is show to be appropriate for the estimation of eds parameters due to its minor error and its robustness to different levels of sensor noise. vii. references [1] j. s. lee, y. j. ryoo, y. c. lim, p. freere, t. g. kim, s. j. son, e. s. kim, “a neural network model of electric differential system for electric vehicle”, ieee 26th annual conference of the industrial electronics society (iecon), vol. 1, pp. 83-88, 2000 [2] t. ma, a. m. osama, “optimal charging of plug-in electric vehicles for a car-park infrastructure”, ieee transactions on industry applications, vol. 50, no. 4, pp. 2323-2330. 2014 [3] m. yildirim, m. polat, h. kurum, “a survey on comparison of electric motor types and drives used for electric vehicles”, ieee 16th international power electronics and motion control conference and exposition (pemc), pp. 218-223, 2014 [4] y. e. zhao, j. w. zhang, x. q. guan, “modelling and simulation of the electronic differential system for an electric vehicle with two-motorwheel drive”, international journal of vehicle systems modelling and testing, vol. 4, no. 1-2, pp. 1209-1214, 2009 [5] j. l. febin daya, p. sanjeevikumar, f. blaabjerg, p. w. wheeler, j. o. ojo, “implementation of wavelet-based robust differential control for electric vehicle application”, ieee transactions on power electronics, vol. 30, no. 12, pp. 6510-6513, 2015 [6] y. zhou, s. li, x. zhou, z. fang, “the control strategy of electronic differential for ev with four in-wheel motors”, ieee control and decision conference (ccdc), pp. 4190-4195, 2010 engineering, technology & applied science research vol. 6, no. 6, 2016, 1288-1293 1293 www.etasr.com yildirim et al.: computation of the speed of the four in-wheel motors of an electric vehicle using… [7] l. zhai, s. dong, “electronic differential speed steering control for four in-wheel motors independent drive vehicle”, 9th world congress on intelligent control and automation (wcica), pp. 780-783, june 2011 [8] h. kahveci, h. i. okumus, m. ekici, “an electronic differential system using fuzzy logic speed controlled in-wheel brushless dc motors”, ieee fourth international conference on power engineering, energy and electrical drives (powereng), pp. 881-885, may 2013 [9] r. wan, g. liu, d. zhang, w. gong, “a fault-tolerant electronic differential system of electric vehicles”, in ieee vehicle power and propulsion conference (vppc), pp. 1-5, oct. 2013 [10] s. sharma, r. pegu, p. barman, “electronic differential for electric vehicle with single wheel reference”, ieee 1st conference on power, dielectric and energy management at nerist (icpden), pp. 1-5, jan. 2015 [11] a. haddoun, m. e. h. benbouzid, d. diallo, r. abdessemed, j. ghouili, k. srairi, “modeling, analysis, and neural network control of an ev electrical differential”, ieee transactions on industrial electronics, vol. 55, no. 6, pp. 2286-2294, 2008 [12] d. foito, g. manuel, v. f. pires, “road motion control electric vehicle with speed and torque observer”, ieee international conference on new concepts in smart cities: fostering public and private alliances (smartmile), pp. 1-6, 2013 [13] m. yildirim, e. oksuztepe, b. tanyeri, h. kurum, “electronic differential system for an electric vehicle with in-wheel motor”, in 9th international conference on electrical and electronics engineering (eleco), pp. 1048-1052, 26-28 nov. 2015 [14] m. j. l. orr, introduction to radial basis function networks, technical report, center for cognitive science, university of edinburgh, 1996. [15] t. bow, pattern recognition and image preprocessing, crc press, sing, 2002. [16] c. m. bishop, neural networks for pattern recognition, oxford university press, 1995. [17] a. rubaai, m. d. kankam, “adaptive tracking controller for induction motor drives using online training of neural networks”, ieee transactions on industry applications, vol. 36, no. 5, pp. 1285-1294, 2000 [18] k. du, ns madisetti, neural networks in a softcomputing framework, springer science & business media, 2006 [19] s. stergiopoulos, advanced signal processing: theory and implementation for sonar, radar, and non-invasive medical diagnostic systems, crc press, 2009 [20] m. yildirim, e. oksuztepe, b. tanyeri, h. kurum, design of electronic differential system for an electric vehicle with in-wheel motor, ieee power and energy conference at illinois (peci), pp. 1-5, 2016 microsoft word 22-3171_setasr_v9_n6_pp4990-4995 engineering, technology & applied science research vol. 9, no. 6, 2019, 4990-4995 4990 www.etasr.com ghaly & khan: design, simulation, modeling, and implementation of a square helmholtz coil … design, simulation, modeling, and implementation of a square helmholtz coil in contrast with a circular coil for mri applications sidi m. ahmed ghaly electrical engineering department, college of engineering al imam mohammad ibn saud islamic university riyadh, saudi arabia smghaly@imamu.edu.sa mohammad obaidullah khan electrical engineering department, college of engineering al imam mohammad ibn saud islamic university riyadh, saudi arabia dearkhan@gmail.com abstract—this paper focuses on helmholtz-type coils that can produce a second-order homogeneity field to be used for magnetic resonance imaging (mri) applications. a helmholtz coil is a device used for producing a region of a nearly uniform magnetic field. it consists of two identical magnetic coils that are placed symmetrically along a common axis, one on either side of the experimental area, separated by a distance equal to the radius of the circular coil and half-length of the side of the square coils. each coil carries an equal electrical current flowing in the same direction. the main objective of this article is to calculate the magnetic field provided by the coils at any point in space and to show and compare the uniform magnetic field induced by the square and circular helmholtz coils. with the aid of matlab simulation tool, mathematical equations are simulated to demonstrate the axial magnetic field produced by one and two loops. also, the design and simulation of electrical modeling for square and circular helmholtz coils are performed using pspice. finally, these coils are realized and tested experimentally, and the results for square and circular helmholtz coils are compared. keywords-square and circular helmholtz coil; radiofrequency coils; modeling; simulation; matlab; pspice; electromagnetic field measurement; impedance measurements; mri i. introduction a helmholtz coil is a device used for producing a region of nearly uniform magnetic field [1-2]. it consists of two identical circular magnetic coils that are placed symmetrically, one on either side of the experimental area along a common axis, and separated by a distance d equal to the radius r of the coil. the currents in the coils are equal and flowing in the same direction. several variations exist in the coil topology, including the use of rectangular coils, and different number of coils. however, a two-coil helmholtz pair is the standard model, with coils that are circular in shape and flat on the sides. in such a device, an electric current is passed through the coils to create a very uniform magnetic field. helmholtz coils are used for a variety of purposes. they were used in an argon tube experiment to measure the charge to mass ratio of electrons [3]. they are often used to measure the strength and fields of permanent magnets [4-5]. to do this, the coil pair is connected to a flux meter, a device which contains measuring coils and electronics that evaluate the change of voltage in the measuring coils to calculate the overall magnetic flux. in some applications, a helmholtz coil is used to cancel out earth’s magnetic field, producing a region with magnetic field intensity close to zero. this can be used to see how electrical charges and magnetic fields operate when not affected by the gravitational pull of the earth or other celestial bodies [6-7]. this work is focused on radiofrequency helmholtz type coils that can be used for mri applications. in particular, the design, modeling, and comparison of circular and square helmholtz coils for magnetic resonance imaging render certain simplicity of implementation besides generating good homogeneity of the radiofrequency electromagnetic field. ii. magnetic field calculation and electrical modeling a. circular helmholtz coil consider a circular helmholtz coil of radius r, separated by a distance l as illustrated in figure 1. there is a steady current flow i in the same direction through each coil. let the magnetic field b1 be calculated on the axis at a distance z from the center of one coil. (a) (b) fig. 1. helmholtz circular coil arrangement: (a) 3d, (b) 2d corresponding author: sidi m. ahmed ghaly engineering, technology & applied science research vol. 9, no. 6, 2019, 4990-4995 4991 www.etasr.com ghaly & khan: design, simulation, modeling, and implementation of a square helmholtz coil … ����� � �� � � � �� ��� � ����� ��������� �⁄ � � ���� ������� � � �⁄ � (1) the magnetic field strength at z=0 and l=r is given by: �� �0� � � � ���� �⁄ �� �⁄ � (2) b. double square coil (square helmholtz coil) fig. 2. (a) square helmholtz coil, (b) a current-carrying vertical eire consider two square coils arranged as a helmholtz coil, as illustrated in figure 2(a). the magnetic field produced by the side 3a can be obtained by the same rotation on that by the side 2a. similarly, the rotation on the field by the side 3a gives the field by the side 4a. the field by the other coil (coil b) can then be obtained by simply replacing every d in the equation by -d. the total field can be obtained by superposition of all the contributions of the wire segments. the separation between the two square coils is critical in the construction of the helmholtz coil. consider the field along the z-axis, which points along the z-direction only [8-10]. by taylor expansion around z=0, we have: ���� � ��0� � ! !� �0�� � �� !� !�� �0�� � � "��#� (3) for small z (0<z<1), the higher the order of the term is, the smaller the contribution this term has to the field at that point. by symmetry, b(z) is symmetric about the z=0. therefore, b(z) is an even function, and (0) 0 db dz = . the term that follows immediately after b(0) should be the second order term. in order to have a uniform field around the center of the helmholtz coil, the contribution by this second order is suppressed to zero. this means that the condition for uniformity is: !� !� � �0� � 0 (4) along the z-axis, the magnetic field is given by: ���� � � � $�% � �&$�����! �⁄ ��'(�$�����! �⁄ �� ��&$ �����! �⁄ �� '(�$�����! �⁄ �� � (5) the mutual inductance for the circular and square helmholtz’s loops are calculated based on the electrical modeling illustrated below: ) � � * �+ ���, (6) where µo is the permeability of free space (4π×10 -7 ), µr is the relative permeability of the soft iron core, n is in the number of coil turns, a is in the cross-sectional area in m 2 , and l is the length of the coil in meters. the design values for the typical parameters used in the square and circular helmholtz coil setups are shown in table i. table i. typical design values for circular and square helmholtz coils parameter circular square mutual inductance : ) � -. -/ 0� 0� 12 8.0046h 6.2836h coupling coefficient for l1=l2: ) � :(;� . ;� 0.023 0.016 resonant frequency f0 f0=99mhz f0=102mhz self frequency 107 mhz 107 mhz resistance: = � >,� 2.64μω 3.36μω inductance: ; � -. a� ln d8a�= e 1.75h 0.3529μh 0.3863μh capacitance:k � ���%l ��m 7.323pf 6.899pf iii. field calculation and pattern plot to calculate the electromagnetic field (b1) produced by the proposed square and circular helmholtz structures which consist of two symmetrical elements and have small dimensions compared to the wavelength, the superposition principle can be applied to obtain the total field as indicated in (2) and (5) for circular and square patterns [11-13]. fig. 3. uniform magnetic field pattern between square coils the simulation code for the double square coil is programmed in matlab for a typical input data of i=1a, d=2.77cm, a=5cm, n=1, and µ0=4π×10 -7 mkgs -2 a -2 . the simulation result is shown in figure 3, where each coil has a magnetic field pattern indicated by red and green color patterns engineering, technology & applied science research vol. 9, no. 6, 2019, 4990-4995 4992 www.etasr.com ghaly & khan: design, simulation, modeling, and implementation of a square helmholtz coil … and the summation of these patterns is shown with blue color. it was noted that the best distance between the two coils separation was equal to 2.7cm, giving the maximum uniform magnetic field pattern corresponding to this input data. and it was also noted that a few (5) points that appear on constant magnetic field region as depicted in figure 3 were obtained. similarly, the simulation code for the double circular coil is developed in matlab for a typical input data of i=1a, d=2.56cm, r=5cm, n=1, and µ0=4π×10 -7 mkgs -2 a -2 . the simulation result is shown in figure 4 where each coil has a magnetic field pattern indicated by red and green color and the summation of these patterns is shown with blue color. it was noted that the best distance between the two coils separation was equal 2.56cm, for which it gives the maximum uniform magnetic field pattern corresponding to this input data. and it was also noted that there are 3 points obtained that appear on constant magnetic field pattern. figure 5 illustrates the normalized axial profiles of the b1 field for the proposed square and circular structures where y is along the coil axis in the same reference. the magnetic field is calculated by the biot–savart law and normalized to its maximum value. fig. 4. uniform magnetic field pattern between circular coils fig. 5. normalized magnetic field pattern for square and circular coils iv. simulations in this part, the electrical response of the system is investigated for the proposed structures (circular and square). the system consists of two coaxial wire loops whose coupling mode is inductive coupling between all loops and capacitive coupling between adjacent left or right loops. each one consists of identical tuned circuits resonating at the same frequency. the proposed coil is matched using an inductive coupling [14]. this kind of matching uses an attack loop with the same dimensions with the first loop of the proposed coil, and this attack loop is tuned to f1, as shown in figure 6. the attack coil is inductively coupled with the two loops of the structure. the matching of the coil at 50ω is performed by optimizing the coupling loop position. the simulation of the matching at 50ω gives the corresponding distance between the attack loop and the circulator of the square helmholtz coils [16-18]. the typical distances measured for circular and square coils are equal to 2.56cm and 2.77cm respectively. figure 7 illustrates the simulation result of pspice for matching to 50ω for the circular single and double mode coil at f0=99mhz. the inductive coupling results in an impedance inversion, the series resonance modes become parallel, and the simulation allows the user to check the design values for the circuit elements in the structure thoroughly. similarly, for square helmholtz coil pspice simulation is carried out, and the results are noted graphically. fig. 6. spice model for matching of the square and circular helmholtz coils with inductive coupling fig. 7. simulation of the matching to 50ω for the circular and square single mode coils at resonant frequencies: x-axis represents the frequencies, and y-axis represents the magnitude of the input impedance v. experimental results in this section, the experimental results obtained with the implemented circular and square helmholtz coils are demonstrated. the specimen tests conducted in this experiment are out-of-field tests (in the air) using a network analyzer. these tests were facilitated to carry out relative measurements of the radiofrequency electromagnetic field (b1) along the main axis of the coils and to compare them with the theoretical results [15]. engineering, technology & applied science research vol. 9, no. 6, 2019, 4990-4995 4993 www.etasr.com ghaly & khan: design, simulation, modeling, and implementation of a square helmholtz coil … a. prototype dimensions to facilitate comparisons, both the circular and the square helmholtz coils have the typical precise dimensions reported in table ii. photographs of the developed coils can be seen in figure 8. table ii. precise dimensions of circular and square helmholtz coils coil structure parameters distance between loops circular r=5cm 2.56cm square l=5cm, b=5cm 2.77cm (a) (b) fig. 8. (a) square, (b) helmholtz coils b. matching and tuning of the coils it is possible to proceed directly to the tuning of the coils, but this requires a certain control of the various influential parameters (stepwise adjustment of the tuning capacitors). the tuning of each loop at f0 is performed individually by shorting the other loops and bringing it closer to a test loop. by predetermination of f0, a vacuum presetting of the coil is carried out. figure 9 shows a photograph of the tuning of the circular coil obtained with impedance measurements using a network analyzer. the variations of the module and phase of the input impedance are seen by the source as a function of the frequency. the same is repeated for the square coil. fig. 9. typical screen shot illustrating the resonance frequency for the circular helmholtz coil in the network analyzer two parallel resonance frequencies were observed for the square and circular coils. table iii gives the comparison between the values of the measured resonant frequencies with losses (experimental measures) and those calculated theoretically (case without losses) for both coils. table iii. theoritical and experimental frequency comparison parameter square helmholtz coil circular helmholtz coil theoretical experimental theoretical experimental resonant frequency f0=102mhz f0=102mhz f0=99mhz f0=99mhz it can be noted that the same value of the frequency f0 is observed theoretically and experimentally. impedance matching allows optimal energy transfer between the coils and the transmission and reception system. for an optimal transfer in the coaxial transmission cable during excitation, the impedance of the system should be 50ω [14]. the matching of the coil is achieved by optimizing the position of the attack loop with the coils. thus, the distance to have an impedance of 50ω is equal to 2.77cm and 2.56cm for square and circular coils theoretically and practically. c. test results comparative tests were conducted for both circular and square helmholtz coils. in the air, in the absence of a sample, relative field measurements along the axis of the coils were conducted using a small test loop connected to the network analyzer as shown in figure 10. a similar scheme was employed for the square coil with loops, as shown in figure 11. fig. 10. the mmasurement bench of the circular coil fig. 11. typical experimental setup for the square helmholtz coil the electromagnetic field along the axis of the coils (o-y) is measured with respect to the distance by facilitating to and fro motion arrangement as depicted in figure 11. the curves of engineering, technology & applied science research vol. 9, no. 6, 2019, 4990-4995 4994 www.etasr.com ghaly & khan: design, simulation, modeling, and implementation of a square helmholtz coil … this normalized field produced by both coils are shown in figure 12. this practical pattern can be compared with the simulation result depicted in figure 5. table iv illustrates the measurements of field intensity in terms of voltage with respect to the distance for a circular and a square helmholtz coil. this practical result is plotted in figure 12. table iv. measurement of field intensity in terms of voltage with respect to distance distance (mm) circular coil square coil voltage (db) voltage (v) voltage (db) voltage (v) 24 -5.04 0.313 -4.86 0.327 22 -4.86 0.327 -4.82 0.329 20 -4.62 0.345 -4.78 0.332 18 -4.38 0.365 -4.72 0.337 16 -4.16 0.384 -4.66 0.342 14 -4.01 0.397 -4.62 0.345 12 -3.76 0.421 -4.57 0.349 10 -3.55 0.442 -4.48 0.356 8 -3.38 0.459 -4.42 0.361 6 -3.26 0.472 -4.37 0.366 4 -3.23 0.474 -4.32 0.369 2 -3.22 0.477 -4.32 0.369 0 -3.22 0.477 -4.32 0.369 -2 -3.22 0.477 -4.33 0.369 -4 -3.24 0.474 -4.35 0.367 -6 -3.28 0.471 -4.39 0.364 -8 -3.34 0.463 -4.46 0.358 -10 -3.58 0.439 -4.55 0.351 -12 -3.78 0.419 -4.62 0.345 -14 -3.98 0.399 -4.68 0.341 -16 -4.22 0.378 -4.74 0.336 -18 -4.45 0.359 -4.77 0.333 -20 -4.68 0.341 -4.83 0.329 -22 -4.82 0.329 -4.89 0.324 -24 -5.11 0.308 -4.91 0.323 fig. 12. measurement results for the circular and square coils d. results with loaded test for circular and square coils the loaded tests for the developed coils were performed using bruker-biospec-avance on mri images which are in the form of a large open on the sides cylinder (dimensions: 1.40m diameter and 1.2m length). a cylindrical free region (15cm diameter) is used to receive the coil by the two lateral accesses. the static magnetic field produced had an intensity of 2.4t and was directed along the horizontal axis, corresponding to the irradiation of the sample (water) at the larmor frequency (ν0 (proton)=100.240mhz). an electrostatic or magnetic shielding was employed to prevent the coupling gradient coils and to improve the system’s efficiency [19-20]. in the beginning, the coil was placed horizontally in the transverse plane of the spectrometer. the tuning of the coil with load was checked and refined. in the second step, after the verification of obtaining an nmr signal, a calibration of the homogeneity of the field was done by means of the shim coils provided for the purpose. in the last step, sections were made in imaging. thus figures 13-14 represent the axial sectional images obtained by the developed circular and square coils respectively. fig. 13. axial sectional image (1mm) produced by the circular coil fig. 14. axial sectional image (1mm) produced by the square coil these images were utilized (1mm slices) to extract relative profiles of the intensity of the images (figure 13). furthermore, the widths of the lobes noted for the developed coils are in proportions substantially identical to those found in the air without sample. vi. conclusion in this work, the operation of standard square and circular helmholtz coils, which can be used for magnetic resonance imaging, is investigated and demonstrated. the coil assembly comprises of two coaxial loops separated by a distance equal to their radius for the circular coil and half the length of the side for the square coil, and carrying the same current (co-current mode), in a symmetric arrangement. the developed helmholtztype coils produce a second-order homogeneous field. comparative study of simulation using matlab & pspice along with the experimental implementation was conducted to check the magnetic field uniformity of the circular and square helmholtz coils. the magnetic field value for which the coil was designed was attained successfully. helmholtz coil is an excellent source of uniform magnetic field, and it was built within a very economic budget range. it was observed that if the radius of the circular coil is equal to the side of the square, and the distance between the loops is less than 50% of the radius for the circular loop and less than 55.4% of the side for the square loop, then the sensitivity of the magnetic field for the circular coil is more than for the square coil. but the pair of engineering, technology & applied science research vol. 9, no. 6, 2019, 4990-4995 4995 www.etasr.com ghaly & khan: design, simulation, modeling, and implementation of a square helmholtz coil … square coils exhibit greater homogeneity of magnetic field than the pair of circular coils. it was also observed that the distance between the loops must be approximately equal to 50% of the radius for the circular coil and 27.7% of the length of the side for the square helmholtz coil. the pair of square helmholtz coils exhibited more filed homogeneity than the circular helmholtz coils, which is desired for mri applications. the sensitivity (magnitude) of the magnetic field in the pair of the circular helmholtz coils is found to be more than the one of the square coils. acknowledgement the authors would like to thank mohammad al aqal for his participation throughout this work references [1] f. romeo, d. i. hoult, “magnet field profiling: analysis and correcting coil design”, magnetic resonance in medicine, vol. 1, no. 1, pp. 44-65, 1984 [2] c. e. hayes, w. a. edelstein, j. f. schenck, o. m. mueller, m. eash, “an efficient, highly homogeneous radiofrequency coil for whole-body nmr imaging at 1.5 t”, journal of magnetic resonance, vol. 63, pp. 622-628, 1985 [3] l. guendouz, s. m. a. ghaly, a. hedjiedj, j. m. escanye, d. canet, “improved helmholtz-type magnetic resonance imaging coils with highb1 homogeneity-spherical and ellipsoidal four-coil systems”, concepts in magnetic resonance, vol. 33b, no. 1, pp. 9-20, 2008 [4] k. asher, n. k. bangerter, r. d. watkins, g. e. gold, “radiofrequency coils for musculoskeletal mri”, topics in magnetic resonance imaging, vol. 21, no. 5, pp. 315–323, 2010 [5] s. m. a. ghaly, l. guendouz, a. hedjiedj, j. m. escanye, d. canet, “improved helmholtz-type coils with high b1 homogeneity-spherical and ellipsoidal configurations”, 24th iasted international multiconference on biomedical engineering, innsbruck, austria, february 15-17, 2006 [6] s. li, q. x. yang, m. b. smith, “rf coil optimization: evaluation of b1 field homogeneity using field histograms and finite element calculations”, magnetic resonance imaging, vol. 12, no. 7, pp. 10791087, 1994 [7] b. gruber, m. froeling, t. leiner, d. w. j. klomp, “rf coils: a practical guide for nonphysicists”, journal of magnetic resonance, vol. 48, no. 3, pp. 590–604, 2018 [8] j. mispelter, m. lupu, a. briguet, nmr probeheads for biophysical and biomedical experiments, theoretical principles & practical guidelines, 1st edition, imperial college press, 2006 [9] b. j. dardzinski, s. li, c. m. collins, g. d. williams, m. b. smith, “a birdcage coil tuned by rf shielding for application at 9.4 t”, journal of magnetic resonance, vol. 131, no. 1, pp. 32-38, 1998 [10] s. m. a. ghaly, s. a. sowayan, “a high b1 field homogeneity generation using free element elliptical four-coil system”, american journal of applied sciences, vol. 11, no. 4, pp. 534-540, 2014 [11] s. m. a. ghaly, k. a. a. snaie, s. s. a. sowayan, “design and testing of radiofrequency spherical four coils”, modern applied science, vol. 10, no. 5, pp. 186-193, 2016 [12] s. m. a. ghaly, k. a. a. snaie, o. k. mohammad, “spherical and improved helmholtz coil with high b1 homogeneity for magnetic resonance imaging”, american journal of applied sciences, vol. 13, no. 12, pp. 1413-1418, 2016 [13] s. m. a. ghaly, k. a. a. snaie, a. m. ali, “design and modeling of a radiofrequency coil derived from a helmholtz structure”, engineering, technology & applied science research, vol. 9, no. 2, pp. 4037-4040, 2019 [14] m. decorps, p. blondet, h. reutenauer, j. p. albrand, c. remy, “an inductively coupled, series-tuned nmr probe”, journal of magnetic resonance, vol. 65, no. 1, pp. 100-109, 1985 [15] j. m. boesch, a. p. koretsky, “an in vivo nmr probe circuit for improved sensitivity”, journal of magnetic resonance, vol. 54, no. 3, pp. 526-532, 2003 [16] f. alorifi, s. m. a. ghaly, m. shalaby, m. a. ali, m. o. khan, “analysis and detection of a target gas system based on tdlas & labview”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4196-4199, 2019 [17] s. m. a. ghaly, “labview based implementation of resistive temperature detector linearization techniques”, engineering, technology & applied science research, vol. 9, no. 4, pp. 4530-4533, 2019 [18] s. m. a. ghaly, m. o. khan, s. o. e. mehdi, m. a. awad, μ. a. ali, k. a. a. snaie, “implementation of a broad range smart temperature measurement system using auto-selected multi-sensor core in labview environment”, engineering, technology & applied science research, vol. 9, no. 4, pp. 4511-4515, 2019 [19] d. m. ginsberg, m. j. melchner, “optimum geometry of saddle shaped coils for generating a uniform magnetic field”, review of scientific instruments, vol. 41, no. 1, pp. 122-123, 2010 [20] h. fujita, t. zheng, x. yang, m. j. finnerty, s. handa, “rf surface receive array coils: the art of an lc circuit”, journal of magnetic resonance imaging, vol. 38, no. 1, pp. 12–25, 2013 microsoft word 2-andoulidakis.doc etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 30-35 30 www.etasr.com androulidakis and kandus: mobile phone brand categorization vs users’ security practices mobile phone brand categorization vs. users’ security practices iosif androulidakis jožef stefan international postgraduate school jamova 39, ljubljana si-1000, slovenia sandro@noc.uoi.gr gorazd kandus department of communication systems jožef stefan institute jamova 39, ljubljana si-1000, slovenia gorazd.kandus@ijs.si abstract— in the present paper, we correlated the brand of mobile phone to users’ security practices, statistically processing a large pool of the responses of 7172 students in 17 universities of 10 eastern and southern europe countries. users show different behavior in an array of characteristics, according to the brand of the mobile phone they are using. as such, there is a categorization of areas, different for each brand, where users are clearly lacking security mind, possibly due to lack of awareness. such a categorization can help phone manufacturers enhance their mobile phones in regards to security, preferably transparently for the user. it can also allow mobile phone resellers to implement specific security awareness programs for their clients. keywords-mobile phone security; brand profiling, security practices; survey; i. introduction mobile devices are becoming a critical component of the digital economy, a style statement and useful communication device, a vital part of daily life for billions of people around the world. there exist dozens of different brands, overlapping in public’s coverage of communication needs. given their ubiquitous presence, mobile phones are used from both experienced and security savvy users as well as from people that do not pay that much attention to security issues. all of them must be protected from unauthorized third party access to their data and from economic frauds. since users’ alone can’t cope with this task, operators and handset manufacturers have to take extra security measures. starting from manufacturers, they must provide better designed and more security hardened phones. operators, on the other hand must effectively protect their networks. both can further educate users. as this paper reveals, users exhibit different levels of knowledge in regards to security depending on the brand of the phone they are using. this can possibly be explained because certain brands are more appealing to different classes of users (i.e. depending on age, sex, financial status etc). as such, the mere knowledge of the brand alone (which is possible for the operator to know without users’ intervention), can provide valuable information. this diversity in security knowledge is apparent not only in subjective answers but also in the specific answers they provide to questions testing their practices. certain brand users need proper training and education more than others in order to mitigate the increased security risks they face due to their ignorance. thanks to the statistical process concluded in this work, these specific user categories can easily be pinpointed. in the rest of the paper, in section ii, related literature is examined. the methodology used for the survey is described in section iii. results are presented in section iv, closing with conclusion and future work in section v. ii. related work although there have been quite many theoretical studies concerning mobile services and mobile phones, a significant means for investigating and understanding users’ preferences is asking their opinion via specific questioning techniques. the vast majority of these surveys indicate the growing importance of mobile phones in everyday life and the increased popularity of new features [1]. in any case, the security of mobile phones is proven not to be adequate in many research papers [2][3]. modern smart phones, specifically, are vulnerable to more security risks [4]. there also exist several survey studies in this direction. some of these surveys studies focus on mobile phone’s security issues [5][6] while others on mobile phone services, touching also security issues [7]. a survey [8] published in november 2008 focused on mobile phones security issues and in which degree these issues concern the users. the conclusion was that a major part of the participants are extremely concerned about security and don’t want any of their private data to be available to 3rd party unauthorized users. furthermore, users are interested in mobile services adoption only if the prices are low and the security framework tight enough [9]. despite the importance of security in the given field, cyber security and safety education is left out from the educational system [10]. users, in turn, do not know if their phones are secure or not [11]. etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 30-35 31 www.etasr.com androulidakis and kandus: mobile phone brand categorization vs users’ security practices iii. methodology a very useful evaluation method for surveying user’s practices is the use of multiple-choice questionnaires (i.e. in person delivery or e-mail questionnaires) [12][13]. our survey was conducted using in-person delivery technique, with a total of 7172 respondents participating in this survey. this method was selected from other alternatives because is more accurate and has a bigger degree of participation from the respondents (e-mail questionnaires usually are treated as spam mail from the respondents plus there is the risk of misunderstand some questions). data entry took place using custom software [14]. the target group of the survey was university students from ages mostly 18-26, incorporating both younger and older youth segments because these ages are more receptive to new technologies. since they are still studying, it would be easier to participate in security education programs, possibly implemented in universities. as stated in the introduction, we correlated students’ answers to the brand they are using. since there was a bias in the demographics (mainly in age and in less extent to age) we normalized the values for the investigation of their correlation to the brand. this was accomplished by using weights according to the participation of these groups in the whole sample iv. results the questionnaire was divided in two parts. in the first part participants were asked demographic questions including gender, age and field of studies. in the second part we introduced security knowledge and practice questions. in the following sections we present the results of the brand categorization in regards to the security knowledge and practices of respective users. all of the findings presented are statistically significantly (pearson’s chi-square). a. demographics and hardware 53% of the participants were females and 47% were males. weighting the sample’s responses to overcome this minor bias, we noticed that samsung and lg have a greater penetration in women (figure 1). fig. 1. brand vs. sex. fig. 2. brand distribution most of the respondents, in turn, were aged 18-26 (75%). normalizing again, in order to overcome the bias in ages, we got the distribution of figure 3. nokia, sony-ericsson and samsung have almost uniform distribution among ages, with the first two being slightly more preferred by younger segments. motorola and iphone were mainly preferred by older youth segments. fig. 3. brand vs age. b. security specific questions our fundamental research questions were whether students are informed about how the options and the technical characteristics of their mobile phones affect their security and, secondly, how safe they consider communication using mobile phones. students answered subjectively those two questions. we further used some objective questions in regards to security practices (noting imei-international mobile equipment identity, using pin-personal identification number, using password protected screen saver, using antivirus, taking backups). this way, we were able to conclude whether their subjective answers are actually in pace with the objective facts. etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 30-35 32 www.etasr.com androulidakis and kandus: mobile phone brand categorization vs users’ security practices answering the question “are you informed about how the options and technical characteristics of your mobile phone affect its security?”, the majority of students (30.8%) states that they are “moderately” informed about security options and characteristics while a large 15.8% believes that they are “not at all“ informed. the specific brand distribution is shown in figure 4. we proceeded to weighting the responses with the following weights: very much: 4, much: 3, moderately: 2, not much: 1, not at all: 0 and then divided by the number of occurrences, in order to get an arithmetic value to better compare the results (figure 5). that proved that lg and samsung users are mostly in need of security education since they scored the least in the 0-4 scale (1.74 and 1.73). nokia (1.85) is around the total mean (1.86). iphone and ericsson users are the most informed ones (1.97 and 1.95). continuing with a general question about how “safe” users feel the mobile phone communication is, the majority (36.9%) replied “moderately” followed by 28.6% “much”. on the other hand, some 21.36% felt not too much or not at all sure they are safe. the specific brand distribution is shown in figure 6. fig. 4. brand vs. security knowledge fig. 5. brand vs. security knowledge. weighting with the same scale (0-4), we got the results of figure 7. we can see that iphone users are the ones that are most ‘suspicious’ in regards to how safe they consider mobile phone communication. sharp users are the more relaxed ones. leaving aside the subjective answers of the previous two questions, we moved into more objective questions, to test the security practices of students. in figure 8, we can see that contrary to other users, sharp users are more aware of their phone’s imei. at the same time, half of lg and nokia users do not even know what it is. focusing on the subset of users that are aware of imei, we plotted the ratio of users that have written it down to users that have not written it down vs. the brand. sharp was the only brand that had a ratio of more than one (more yes than no). fig. 6. how safe do you consider communication through mobile phones? fig. 7. how safe do you consider communication through mobile phones? fig. 8. brand vs. written down imei etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 30-35 33 www.etasr.com androulidakis and kandus: mobile phone brand categorization vs users’ security practices fig. 9. brand vs. yes/no ratio of noted imei imei is very significant because if the phone is ever stolen, using this serial number the provider can (in theory, not always implemented in practice) block access to the stolen phone effectively mitigating stealing risks. knowledge of this feature would possibly help 51.3% of the whole sample who unfortunately had their phone stolen once or more. similarly high percentages are noted by other studies too [15][16]. it is well interesting to note that sharp users that are most actively noting down their imei, were indeed the ones that had mostly their phone lost or stolen in the past (figure 10). proceeding to pin code, users, as expected, are actively (67.2%) using it. it is rather surprising however that sharp users, that had the most incidents of lost/stolen phone are the ones least using it (figure 11), despite the fact that they had the best behaviour in noting down imeis. only a small percentage of 14.7% uses screen-saver password. 26.3% of them do not even know if their phone has such an option. that leaves 85.3% of users without a screen saver password protection, and their phones ready to be manipulated by “malicious” hands. an attack can take place in a few minutes by downloading specific software to the phone; this is why it is not enough to protect the phone only by pin but also by a screen saver password. sorting by ignorance (figure 12) we see that motorola and sharp users are the least informed regarding this feature. as expected, iphone users are downloading far more than other users and mostly applications (figure 13). given the rising downloading trends, a mobile phone antivirus will soon be needed. for the moment (figure 14), 20% of iphone owners are using such a product, while for all brands the dominant answer is that users do not know if such a product exists for their phone. it was not possible to test what kind of antivirus users mentioned, since for iphone there is no specific antivirus available, but rather applications that can help the security but not actually “scan” the phone for viruses. so the 20% percentage is probably lower. this finding should anyway lead manufacturers to collaborate with software vendors in order to incorporate antivirus in the phones without users’ intervention. luckily, organizations, in contrast to home users, show an increase in mobile phone antivirus tools usage [17]. closing our survey, the issue of backup was examined (figure 15). iphone users are again the most cautious ones. nokia users exhibit a very high percentage (almost 60%) in the category that never performs a backup. it is clear that for such a category of users automated tools should undertake the process of backup. fig. 10. brand vs. lost phone fig. 11. brand vs. pin usage fig. 12. brand vs. screen saver etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 30-35 34 www.etasr.com androulidakis and kandus: mobile phone brand categorization vs users’ security practices fig. 13. brand vs. downloading fig. 14. brand vs. antivirus fig. 15. brand vs. backup v. conclusion and future work as this survey proved (using pearson’s chi square), users can be grouped in well defined categories according to the brand of the mobile phone they are using, correlated to an array of demographic and security practices characteristics. among the findings of this survey we focus on the most interesting ones: • samsung and lg have a greater penetration in women • motorola and iphone were mainly preferred by older youth segments • lg and samsung feel least informed with iphone and ericsson users at the other end • iphone users have the least feeling of security in mobile phone communications. sharp users are the more relaxed ones • sharp users are the ones that had mostly had their phone lost or stolen in the past • probably in connection to the previous point, sharp users are most actively noting down their imei. at the same time, half of lg and nokia users do not even know what it is. • motorola and sharp users are the least informed in regards to password protected screen savers. • iphone users are downloading far more than other users and mostly applications • 20% of iphone users have installed an antivirus in their phone (although not clear what kind of antivirus since there aren’t “classical” antiviruses for iphone but rather different applications increasing the security level). ignorance levels are in the level of 50% for all other brands. • nokia users are the ones that are least taking backups. it seems that iphone users represent a well informed part of the sample. unfortunately given their small number, the image from the general user behaviour is not that positive. using the results provided, manufacturers can immediately take advantage of this categorization, enhancing the security features of their phones. there is also arguably need for better software and better designed user interfaces. enhancing users’ security knowledge would lower their fear of communication insecurity, leading to increased mobile phone usage. references [1] synovate, “global mobile phone survey shows the mobile is a 'remote control' for life”, synovate survey, http://www.synovate.com, 2009 [accessed: 09/10/2010] [2] m. rahman, h. imai, “security in wireless communication”, wireless personal communications, vol. 22, no. 2, pp. 218-228, 2002 [3] i. androulidakis, “intercepting mobile phones”, it security professional magazine, no. 8, pp. 42-28, 2009 [4] comscore m:metrics, “smarter phones bring security risks: study”, http://www.comscore.com, 2008 [accessed 09/10/2010] [5] trend micro, “smartphone users oblivious to security”, trend micro survey, http://www.esecurityplanet.com, 2009, [accessed: 09/10/2010] [6] goode intelligence, “mobile security the next battleground”, http://www.goodeintelligence, 2009, [accessed: 09/10/2010] [7] a.p. vrechopoulos, i.d. constantiou, i. sideris, “strategic marketing planning for mobile commerce diffusion and consumer adoption”, proceedings of the first international conference on mobile business: evolution scenarios for emerging mobile commerce services, mbusiness, 2002 [8] i. androulidakis, c. basios, and n. androulidakis, “surveying users' opinions and trends towards mobile payment issues”, frontiers in etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 30-35 35 www.etasr.com androulidakis and kandus: mobile phone brand categorization vs users’ security practices artificial intelligence and applications, vol. 169, (techniques and applications for mobile commerce proceedings of tamoco 2008), pp. 9-19, 2008 [9] i. androulidakis, d. papapetros, “survey findings towards awareness of mobile phones’ security issues, recent advances in data networks, communications, computers”, proceedings of 7th wseas international conference on data networks, communications, computers (dncoco '08), pp 130-135, nov. 2008 [10] national cyber security alliance (ncsa), “schools lacking cyber security and safety education”, http://www. staysafeonline.org, 2009 [accessed: 09/10/2010] [11] mcafee, “most mobile users don't know if they have security”, mcafeesponsored research, http://www. esecurityplanet.com, 2008 [accessed: 09/10/2010] [12] d.a. dillman, “mail and internet surveys: the tailored design method”, john wiley & sons, 2nd edition, 1999 [13] s.l. pfleeger, b.a. kitchenham, “principles of survey research part 1: turning lemons into lemonade”, acm sigsoft software engineering notes, vol. 26, no. 6, pp 16-18, 2001 [14] i. androulidakis, n. androulidakis, “on a versatile and costless omr system”, wseas transactions on computers, vol. 4, no. 2, pp. 160165, 2005 [15] cpp, “mobile phone theft hotspots”, cpp survey, http://www.cpp.co.uk, 2010 [accessed: 09/10/2010] [16] itwire, “one-third of aussies lose mobile phones: survey”, itwire article, http://www.itwire.com, 2010 [accessed: 09/10/2010] [17] darkreading, “survey: 54 percent of organizations plan to add smartphone antivirus this year”, darkreading article, http://www.darkreading.com, 2010[accessed: 09/10/2010] appendix the questionnaire used 1) male (a) or female (b)? 2) age? (a < 18, b 18-20 , c 21-23, d 24-26 , e >26) 3) are you studying: (a: humanities-philology, b medicine, c law, d engineering-computer science, e maths-natural sciences, f economics-business administration, g other 4) how many mobile phones do you use (daily)? α) 1 β) 2 c) >2 d) none 5) are you a contract subscriber or a prepaid subscriber? α) pre-paid (card) β) post-paid (contract) c) both 6) your average monthly phone bill? (a up to 10 euros, b 11-20 euros, c 21-30 euros, d 31-40 euros, e >40 euros) 7) brand of the phone you are mostly using now? (a nokia, b sony-ericsson, c samsung, d sharp, e apple i-phone, f motorola, g lg, h other) 8) does it have an advanced operating system (eg symbian, windows mobile, android)? (a i don’t know, b yes, c no,) 9) have you noted somewhere your mobile phone’s imei? (a, i don’t know what it is, b yes, c no,) 10) was your mobile phone ever lost or stolen? (a never, b once, c more than once) 11) are you aware of the existence of a special icon in your telephone which informs you for the encryption's deactivation? (a yes, b no) 12) do you have sim card’s pin activated? (a yes, b no) 13) do you use password in your phone's screen-saver? (a i don’t know if it has such a feature, b, doesn’t have such feature, c, yes, d no) 14) do you have bluetooth: (a switched on and visible, b switched on and invisible, c switched off, d don’t know the difference between visible and invisible, e my phone doesn’t have bluetooth, 15) do you lend it to others? (a never, b only for a while and if i am present, c yes) 16) do you "download" software to your phone? (a i don’t know if my mobile phone can download, b no, c mostly ringtones/logos, d mostly games, e mostly applications) 17) do you use antivirus software in your phone? (a doesn’t have the ability, b don’t know if there is such product for my phone, c i know there is but i don’t use d yes) 18) do you store important passwords in your phone (eg credit cards passwords, atm passwords)? (a no, b yes and "encrypted", c yes, without encryption) 19) how often do you create backup copies of your phone's data? (a never, b >3 times per month, b 2-3 times per month, c once per month, d less often) 20) do you keep sensitive personal data into your phone (photos/videos/discussion recordings)? (a yes, b no) 21) how safe do you consider communication through mobile phones? (a very much, b much, c moderately, d not too much, e not at all) 22) are you informed about how the options and technical characteristics of your mobile phone affect its security? (a very much, b much, c moderately, d not too much, e not at all) microsoft word 48-3061_s_etasr_v9_n5_pp4846-4850 engineering, technology & applied science research vol. 9, no. 5, 2019, 4846-4850 4846 www.etasr.com ksisi et al.: a graphene based frequency reconfigurable square patch antenna for … a graphene based frequency reconfigurable square patch antenna for telecommunication systems mohamed amine ksisi department of physics, university of tunis el manar, tunis, tunisia ksiksimedamin@gmail.com hosni ajlani department of physics, university of tunis el manar, tunis, tunisia hosni.ajlani@gmail.com mohamed karim azizi department of physics, university of tunis el manar, tunis, tunisia medkarim.azizi@gmail.com ali gharsallah department of physics, university of tunis el manar, tunis, tunisia ali.gharsallah@gmail.com abstract-current research on tunable patch antennas for wireless applications has mostly focused on the dimensional variations of patch elements, such as geometry and substrate materials, using different techniques to achieve the reconfiguration. the use of different mixing materials to ensure reconfiguration and improvement of antenna performance in microwave frequencies has not yet been studied thoroughly. in this article, we consider graphene as a patch material, due to its unique chemical, mechanical, electronic, thermal and optical features, which assist in providing a highly flexible and adaptive antenna. the proposed antenna is a square plate excited by a coaxial probe, operating at a 2.45ghz spectrum. adding graphene to the antenna structure and tuning its chemical potential, a frequency reconfiguration from 2.36ghz to 1.26ghz is obtained. this antenna can be deployed in many communication systems. results demonstrate the importance of this material in the development of nanoelectronics in the future. keywords-patch antenna; graphene; reconfiguration i. introduction reconfigurable antennas have attracted the attention of many researchers due to their ability to operate at different frequencies, standards and applications, replacing the use of multiple antennas [1]. such a multifunctional antenna that is weight-, sizeand cost-saving has innovative applications [2]. the reconfiguration of an antenna is usually accomplished by readjusting its current or reconfiguring its radiating edges [3-5]. the antenna’s functionality is changed by redistributing some of its properties using a variety of techniques. the techniques that have been used since the rise of reconfigurable antennas are grouped into four categories, namely electrical, mechanical, optical, and smart material [6]. the techniques based on pin diodes [7-8], varactors [9-10] and micro electromechanical systems (rf-mems) [11-12] represent the electrical reconfiguration techniques, which are based on the connection and disconnection of switches that redistribute the antenna current. on the contrary, the mechanical reconfiguration technique studied in [13] is based on the antenna’s structure alteration. the optical reconfiguration technique presented in [14], introduces photoconductive switch elements. moreover, there are reconfiguration techniques based on smart materials such as ferrites, graphene [15] and liquid crystals [16-17]. frequency reconfigurable antennas can alter their resonant frequency and several proposals have been described in [1820]. the radiation pattern reconfigurable antennas presented in [9] can change their radiation pattern while keeping the same resonant frequency. moreover, polarization reconfigurable antennas are able to change their polarization while keeping the resonant frequency unchanged [21]. due to the design complexity of reconfigurable antennas, many researchers are studying new techniques to enhance their performance, such as gain, stability, impedance and limit their cost, losses, weight and length. one of these rising techniques is the utilization of graphene. thanks to its chemical, mechanical, electronic, thermal, and optical properties [22], graphene is the ideal candidate to elaborate frequency reconfigurable antennas. this 2-d material is made of carbon atoms, arranged in honeycombs. its thickness is of the same order as that of a carbon atom, i.e. 0.345nm and it is flexible, transparent and more resistant than steel. moreover, graphene’s massless-dirac-fermions and ultra-high electron mobility [2324] allows the development of high-speed devices [25], optical devices [26], field effect transistors [27], and frequency multipliers [28]. its optical conductivity can be modulated by applying an external grid voltage between the graphene layer and a ground plane. varying the applied voltage allows modifying the behavior of the graphene layer, which can pass from a dielectric behavior to a metallic behavior or vice versa [29]. in this paper, we present a graphene based frequency reconfigurable square patch antenna for multiple communication systems. a comparison between the performance of a standard antenna using a varicap diode and corresponding author: mohamed amine ksiksi engineering, technology & applied science research vol. 9, no. 5, 2019, 4846-4850 4847 www.etasr.com ksisi et al.: a graphene based frequency reconfigurable square patch antenna for … the proposed graphene-based one shows that the latter can save space and cost and also switch between different communication frequencies through the adjustment of the applied gate bias. ii. graphene behavior graphene is a flat mono-atomic layer of carbon atoms distributed along a two-dimensional honeycomb lattice which can be modeled by a surface conductivity σ [30]. the control of electromagnetic wave propagation has attracted research interest in various applications in microwave [31] and thz domains [32, 33], due to its remarkable performance. compared with metallic materials, graphene could be more efficient for use in antennas [34]. the surface conductivity of graphene is expressed by the kubo formula as a function of frequency f, temperature t, and chemical potential �� as [35]: ���� � ��� � ������� � � � �� � �� ������ �� � ������� �� � � !� � � ������������� � �����"�#$�� � !�% (1) where ω is the radian frequency, ε is the energy, &' is the charge of an electron, h is planck’s constant and () is the fermi-dirac distribution described as (2): () � *+ #�,./0 1 13 �� (2) where �4 is the chemical potential of graphene and 56 is the boltzmann’s constant. iii. antenna design a. antenna structure the geometry of the proposed patch antenna is shown in figure 1. it consists of a square patch antenna printed on a cuclad substrate 1.6mm thick with relative permittivity of εr=2.2. a 39.2×39.2mm² patch is fed by an underneath located sma connector and an 80×80mm² ground plane. the proposed antenna is optimized to operate at 2.45ghz. fig. 1. geometry of the proposed patch antenna b. results the antenna structure is simulated and investigated using cst microwave studio. the patch antenna’s behavior operating at 2.45ghz is studied without any additional components. the magnitude of the antenna’s reflection coefficient has to be below -10db in order to reach suitable matching impedance and is determined by cuclad substrate. figure 2 shows the magnitude of the antenna’s reflection coefficient, with a maximum peak value of -29.02db for the desired frequency of 2.45ghz. fig. 2. magnitude of the reflection coefficient of the initial antenna we notice that the impedance bandwidth attained for the proposed antenna goes from 2.434 to 2.469ghz for -10db. for this study’s simple configuration, the -10db bandwidth is achieved with a frequency of 350mhz. the voltage standing wave ratio (vswr) of the antenna shown in figure 3 describes how well the antenna gets its impedance matched, which should be less than 2 for a well efficient antenna. the proposed antenna achieves a valuable impedance matching of -29, with 2db in the desired frequency with an ideal value of approximately 1 for the vswr at the corresponding resonant frequency of 2.45ghz. fig. 3. vswr iv. the reconfigurable antenna using graphene as a conducting material in the antenna is anticipated to enhance both gain and bandwidth. the simulation results of the graphene antenna compared to a similar copper and varicap diode one are shown in figure 4, indicating much better impedance matching. engineering, technology & applied science research vol. 9, no. 5, 2019, 4846-4850 4848 www.etasr.com ksisi et al.: a graphene based frequency reconfigurable square patch antenna for … fig. 4. comparison between antennas with varicap diode and graphene the antenna resonates at 1.87ghz for -34db and for a chemical potential �4 =0.3ev. it is noticed that varying the chemical potential of the graphene antenna, a remarkable amplitude improvement is established. moreover the graphene patch antenna achieves better impedance matching in comparison to the metallic one. figure 5 shows the improved gain, as the graphene antenna attained 5.43db compared to the varicap diode one which attained 2db. fig. 5. simulated 3-d gain given at 1.87ghz with 0.3ev comparing the reconfiguration behavior of the graphene patch antenna to the metallic one using varicap diode, a simulation was carried out without any modification on the antenna’s geometric dimensions [29]. figure 6 shows better impedance matching for the graphene antenna, around -22.14db at 1.42ghz, which is a promising result for further practical applications. when the chemical potential is altered to �4 =0.13ev, another resonant peak appears with a maximum value of -22.14db at 1.42ghz, as shown in figure 6. embedding the patch antenna with graphene leads to an improvement of -10db in the reflection factors compared to the varicap diode one. altering the chemical potential improves its gain, reaching about 3.76db compared to the 2db for the varicap diode one, as shown in figure 7. the use of graphene has considerably affected the impedance properties and thus the resonant frequency of the antenna. fig. 6. the magnitude of the reflection coefficient at 1.42ghz fig. 7. simulated 3-d gain given at 1.42ghz figure 8 shows the results of using graphene instead of other techniques usually used to achieve the frequency reconfiguration of the antenna. the integration of graphene, by replacing the copper substrate used for the patch by a graphene layer, has allowed efficient control of antenna’s resonant frequency. by altering the chemical potential of the graphene antenna, the resonant frequency changes, achieving frequency reconfiguration. figure 8 exhibits the potential of using graphene to realize tunability. the antenna was perfectly adapted for different chemical potentials. due to the use of graphene instead of varicap diode, the antenna resonates at 2.36ghz with a chemical potential µc=2ev. by altering the graphene chemical potential from 0 to 2ev, the antenna operates at a frequency from 1.26ghz to 2.36ghz. graphene’s conductivity changes when we change its chemical potential. therefore, a dynamic tuning of the resonant frequency of the patch antenna can be accomplished. an impedance bandwidth in the range of 300-375mhz is obtained for the proposed graphene patch antenna at those different resonant frequencies. engineering, technology & applied science research vol. 9, no. 5, 2019, 4846-4850 4849 www.etasr.com ksisi et al.: a graphene based frequency reconfigurable square patch antenna for … fig. 8. simulated s11 of the graphene antenna for different chemical potential: using hfss and cst simulators (a) (b) fig. 9. simulated (a) epatterns (y-z plane) and (b) hpatterns (x-z plane) of the patch antenna the eand h-plane radiation patterns of the reconfigurable antenna presented in figure 9 are obtained for different chemical potentials of 0ev, 0.4ev and 2ev. it is clearly noted that similar broadside radiation characteristics are obtained at all eplane patterns. table i presents the performance comparison of this frequency reconfigurable patch antenna based on graphene with previous works [36-37]. it is clearly noted that the proposed design has widest continuous tuning range compared to these works and the highest gain value. v. conclusion this paper investigated a frequency reconfigurable square patch antenna based on graphene for communication systems. the tunable resonant properties of the graphene patch antenna have been investigated in the microwave spectrum. by replacing copper in a metallic antenna with graphene, a frequency reconfiguration can be achieved with better impedance matching and remarkable gain improvement. these results show the importance of graphene as a reconfigurable rigid semi-metallic material in amplifying the antenna’s gain and lowering its energy consumption. also, graphene’s particular properties proved to favor the tunability of the antenna, which is attained through an interaction between the graphene’s chemical potentials. recent research has focused on graphene as a promising material to achieve reconfiguration without any active components and to create nano-antennas through the process of miniaturization. table i. performan ce comparison antenna type fmax/fmin (ghz) gain (dbi) slot loo antenna with ferroelectric varactors [36] 1.38 3.1 patch antenna with diode varactors [37] 1.09 2 this work 1.87 3.7 references [1] x. s. yang, s. q. xiao, b. z. wang, “reconfigurable antennas”, in: compact multifunctional antennas for wireless systems, pp. 85–116, john wiley & sons, 2012 [2] j. kiriazi, h. ghali, h. ragaie, h. haddara, “reconfigurable dual-band dipole antenna on silicon using series mems switches”, ieee antennas and propagation society international symposium, columbus, usa, june 22-27, 2003 [3] j. t. bernhard, reconfigurable antennas, morgan and claypool, 2007 [4] c. a. balanis, modern antenna handbook, john wiley and sons, 2011 [5] j. costantine, y. tawk, c. g. christodoulou, design of reconfigurable antennas using graph models, morgan and 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setif university 1, setif, algeria kharchouche.electro@yahoo.fr abstract—the dielectric properties of barium titanate as functions of the mgo addition in various rates are investigated in this paper. the ceramics were prepared by conventional methods. x-ray diffraction, scanning electron microscopy and energy dispersive spectrometry, were applied to determine the structure and microstructure of the studied material. phases mgo, tio and tio2, have been detected. decrease of the grain size with increasing mgo content was observed. measurements of εr, tgδ and resistance have been performed at temperatures ranging from 300c to 4000c. the electric permittivity (εr) showed a considerable decrease with increasing mgo concentration. additionally, for low mgo concentration (10≤≤≤≤mol.% mgo) a shift of the dielectric loss peak (tgδm) towards low temperatures was observed. when the mgo content was ≥15mol.% mgo the tgδm moved into higher temperatures. the obtained results indicate that the substitution of mg2+ ions in b-site ions (ti4+) had a significant influence on the values of εr, tgδ and the resistance increase of the ceramics. keywords-batio3; mgo-doped batio3; thermistors ptc; dielectric properties; electric permittivity i. introduction barium titanate (batio3) is considered one of the most promising systems for applications in electro-optic devices, memory devices, temperature sensors, time delay circuits, current limiters, current stabilizers and capacitors [1]. batio3 is used as doping in other electrical engineering applications such as varistors [2] and in polymer composites like cable insulation sheaths [3, 4]. the dielectric and ferroelectric properties of batio3 can be efficiently controlled by dopant addition. batio3 is used in electric devices manufactured to work at temperatures less than its curie temperature (tc=120°c). in devices functioning at a temperature other than 120°c, it is mixed with other materials such as mg, pbtio3 (pt), zr oxide, and other oxides, in order to shift tc, above or under 120°c [5-11]. pure batio3 exhibits very high electric permittivity, since it has positive -temperature-coefficient resistivity (ptcr) above the curie temperature [12, 13]. this phenomenon was considered as a consequence of the double schottky barrier, formed at the grain boundaries and of the strong temperature dependence [14]. the ptcr phenomenon of doped batio3, has been explained in [13, 15]. it has been concluded that the ptcr effect is caused by defect distribution in the samples. the effects of sintering conditions have been investigated in [11, 13, 16-19]. batio3, as additive in a varistor based zno, reduced the grain growth of zno as a function of the content of batio3. it is found that an excess of 9.6wt% batio3 leads to the batio3 phase segregation on the surface of the sample [2]. mgo-doped batio3 has been less studied. mgo is very often added at small amounts, less than 3mol.%. this mgo ratio is generally used in multi-component batio3-based ceramics, as high temperature capacitor in order to improve their temperature stability. mgo as an aliovalent in batio3 plays a decisive role in achieving ultra-broad temperature stability [20-23]. the effect of the aliovalent dopant on the bulk electrical conductivity is strongly dependent on its substitution site in the batio3 perovskite structure. site replacement in the crystal lattice mainly depends on the dopant’s ionic radius [8, 10, 13]. for small ions, with ionic radius r≤0.09nm, dopants preferentially occupy the ti site. for intermediate ions, with 0.09nm<r<0.099nm, dopants can substitute either ti or ba depending on dopant concentration, sintering conditions and ba/ti molar ratio. for larger ions, with r≥0.099nm, dopants preferentially occupy the ba sites. in [21-22], the solid solution between mgo (content <1.5%) and batio3 presents a xrd pattern, characteristic only of a single phase structure (bto).this implies that mg2+ ions have entered the unit cell maintaining the perovskite structure of solid solution. mgo phase in addition to the bto phase, is detected for mg contents, greater than 1.5% [21]. electro-conductive composite ceramics are composed of an independent phase, of conglomerates and a continuous phase connecting mutually the independent phase of conglomerates. they are composed of an independent phase of conglomerates (50%-98% by weight) and of a continuous phase (2%-50% by weight) [24]. these ceramics can exhibit stable electro conductivity-temperature characteristics. they can be excellent in thermal shock resistance, in mechanical strength, and in chemical resistance. concerning mgo-doped batio3 composite, only a few studies have been made [25]. in this paper, 5mol.%, 10mol.%, 15mol.%, 20mol.%, 30mol.%, and 50mol.% mgo-doped batio3 have been studied. the study aims to modify the bt-based materials characteristics such as tc, electric permittivity and broaden the maxima peak. sintering effect, microstructural evolution and incorporation degree of mg into lattices (batio3) have been discussed as functions of the mgo content. electric permittivity and resistance have been measured in temperatures ranging from 20°c to 400°c. corresponding author: samira boumous engineering, technology & applied science research vol. 9, no. 3, 2019, 4092-4099 4093 www.etasr.com boumous et al: mgo effect on the dielectric properties of batio3 ii. experimental procedure high-purity commercial powder batio3 (code 01-0812200), obtained from alfa aesar, was used as starting material with 70nm grain size. using a conventional ceramic procedure, batio3 based varistor samples, doped with various contents of mgo (0, 5, 10, 15, 20, 30, 50mol.%.) were prepared. these samples are termed as btm0, btm5, btm10, btm15, btm20, btm30 and btm50 respectively. reagent grade oxides were mixed and homogenized in absolute ethanol media for 2 hours by planetary high-energy ball milling in a polyethylene bowl with zirconia balls. the slurry has been dried and sieved through a 200 mesh screen to produce granules without binder. the obtained powder was calcined at 1150°c for two hours in air at heating and cooling rates of 5°c/min. after drying and granulating with polyvinyl alcohol (pva 4wt%) granules were uniaxially pressed into pellets under 20mpa and then ciped at 200mpa. the pellets were placed in an alumina crucible and sintered at 1250°c for 2h in air at heating and cooling rates of 5°c/min, and silvered on both sides for electrical measurements. silver electrodes were deposited by screen printing on each face. the sintered samples were all lapped and polished to be 1.0mm thick. the final samples had about 8mm i diameter and 1.0mm thickness. the samples were characterized by x-ray diffraction (xrd) using an automated diffractometer, phillips pw-1710 type, coupled to a copper anode x-ray tube. the microstructure of the samples was characterized by scanning electron microscopy (sem type hitachi-s2150) equipped with energy dispersive xray (edx) spectrometer for elemental analysis. dielectric measurements were carried out with the use of an impedance analyzer rlc (wayne kerr 6420). the measurements have been performed from room temperature up to 400°c, at a heating rate of 3°c/min. εr, tgδ and resistance were measured. under an alternate electric field, the electric permittivity of the material can be expressed by a complex permittivity such ε=ε΄(ω)–jε΄΄(ω). the dielectric loss tangent is defined as tgδ=ε΄΄/ε΄. in the following, we use the simplified notation εr and we will speak simply of permittivity to denote the real part of relative permittivity ε΄(ω). fig. 1. sem image of the commercial batio3 powder iii. results and discussion commercial powder (batio3) was used. it is composed of a very small agglomeration, whereas the grains were very fine, of the order of 70nm. figure 1 shows a sem image of the commercial batio3 powder. we can see grain sizes smaller than one micrometer. in order to analyze the effect of mgo content on the microstructure and grain sizes, the samples have been characterized by sem and xrd. figure 2 shows the sem images and edx spectra of samples btm0, btm5 and btm10 sintered at 1250°c. we can see in figure 2(a) that the grain sizes of batio3, are larger in comparison with the ones of the same sample before sintering (figure 1). they are larger than 1µm, while some are even larger than 10µm. the bimodal microstructure of fine and large matrix grains can be attributed to the temperature effect, as in the case of zno [2] and to presence of titanium oxide. the edx spectrum characteristic of btm0 (figure 3(a)) indicates that, there are 60.30atom% of oxygen, 20.77atom% of ti and 18.84atom% of ba. (a) (b) (c) fig. 2. sem image of mgo-doped batio3 after sintering at 1250°c (a) btm0, (b) btm5, (c) btm10 the grain size of btm0 (pure) has increased under the temperature effect. figures 2(b) and 3(b) show the morphology engineering, technology & applied science research vol. 9, no. 3, 2019, 4092-4099 4094 www.etasr.com boumous et al: mgo effect on the dielectric properties of batio3 and edx spectrum of the sample btm5. we can see that the grains are smaller. the surface morphology revealed some clear grain shapes. figure 2(b) is brighter than figure 2(a). we can see some bright domains, characteristics of mgo. the incorporation of mgo particles into the matrix is confirmed by edx spectrum (figure 3(b)). au peak artifacts of sample preparation and support grid are noticed. in figure 2(c), of the sample btm10, the brightness domains are greater, the grain sizes are smaller and the brightness is stronger than that of figure 2(b), since mgo content is greater than that of the samples btm0 and btm5. (a) (b) (c) fig. 3. edx spectrum of mgo-batio3 compared with pure batio3. (a) btm0, (b) btm5, (c) btm10 we can see the effect of mgo on the microstructure of the sample. the doping with mgo led to a consequent decrease in the grain size. the samples sintered at 1250°c show that grain sizes are smaller, whereas, undoped batio3 exhibits larger grain sizes (greater than 1µm). the most large grain size was estimated to be 10µm. for the sample btm10, the grain size was in the order of 300nm. the result is in agreement with the findings in [21]. incorporation of mgo particles in batio3 led to the grain growth inhibition of the composite. even in other system such as (ba1-xcax)mtio3–mgo–sio2, mgo has been detected in the grain boundary region where mgo acts as a grain growth inhibitor [8, 26]. it is thus confirmed that in a mgo–batio3 system the grain growth is inhibited by the secondary phase which can be due to excess of mgo, existing in the grain boundary. edx mapping of elemental distribution of ba, ti, mg and o has shown that mgo is highly dispersed in the batio3 matrix. we can see that the density of mg in the btm10 sample is greater than that of the sample btm5. the distribution of the chemical elements is homogenous except for mg in btm10 probably near the grain boundaries where the solid solutions can be located. the non-homogeneity is characterized by a strong concentration in these regions. these are the dark regions in the sem image representing the morphology of the sample. the sem image and mapping of elemental distribution shows that batio3 seems to be covered with mgo particles. a. x-ray diffraction the diffraction pattern of x-ray (xrd) of these powders was performed for 45min at angle of 2θ, in temperatures ranging from 20°c to 80°c. the xrd spectra of the samples, btm0, btm5 and btm10 sintered at 1250°c, are shown in figure 4. the pure batio3 spectrum has been used as a reference. (a) (b) (c) fig. 4. xrd spectra of (a) btm10, (b) btm5 and (c) btm0 sintered at 1250°c 1) btm0 a representative xrd spectrum of the sample btm0 is shown in figure 4(c). the xrd study confirms the formation of the cubic system. all diffraction peaks coincide to that one of reference code 01-074-1964 where lattice parameter was equal to 4.0060å. the obtained diffraction pattern is characteristic of a single perovskite phase. engineering, technology & applied science research vol. 9, no. 3, 2019, 4092-4099 4095 www.etasr.com boumous et al: mgo effect on the dielectric properties of batio3 2) btm5 the xrd spectrum of the sample btm5 (figure 4(b)), reveals that the microstructure consists of three phases: batio3 grain (primary phase) characterized by a peak appearing at an angle of 2θ=31.559° and corresponding to (110) reflection plane. the other phases, mgo and tio2 are characterized by peaks appearing, at angles 2θ=42.917° and 2θ=28.527° and correspond to (200) and (421) refection planes respectively. the peak corresponding to the reflection plane is smaller (421). the parameters of these phases are given in the table i. the increase in lattice constant of mgo-doped batio3, supports that mg2+ ions occupy ti sites and expand the cell size, which is compatible with the acceptor doped behavior of mgo-doped batio3. three phases are detected in btm5. the result suggests that the solubility limit of mgo in batio3 has been exceeded whereas authors in [21] evaluate it between 1 and 1.5 at.%. they found only a second phase (mgo) from 2 at.% of mgo. in [22] where mgo content was only 1.0 vol%, the secondary phase (mgo) has not been detected. however, our samples contain more than 5 mol% mgo. the solid solution between mgo and bto occurred by dissolution of a low amount of mgo (<1.5 at.% mgo) into batio3 and mg 2+ replaces ti4+, since the ionic radius of mg2+ is larger than that of ti4+. this result is in agreement with [8, 16, 21, 22]. as our samples contain more than 1.5 at.% mgo, other phases of mgo and tio2 have been detected. mgo phase is the non-dissolved excess which is located in the grain boundaries. furthermore, tio2 phase was formed via the reaction of mgo with batio3. the ti atoms seem also segregated in the grain boundaries under oxide form. the segregation phenomenon is explained below using the energies of oxides formation. otherwise, in the multi-component batio3-based ceramics, the ti-rich phase forms via the reaction of excess tio2 with batio3 but mgo addition suppresses the ti-rich phase as reported in [20]. our bi-component sample (btm5) seems to be insufficient to suppress the ti-rich phase. table i. parameters of characteristic phases – btm5 phase reference code crystal system a (å): b (å): c (å): density [g/cm3] batio3 01-075-0461 cubic 4.0119 4.0119 4.0119 6.00 mgo 01-078-0430 cubic 4.2112 4.2112 4.2112 3.56 tio2 01-088-1175 tetragonal 4.5172 4.5172 2.9400 4.42 3) btm10 the xrd spectrum of the sample btm10 (figure 4(a)) reveals that the microstructure consisted mainly of four phases: i) a primary phase (batio3 grains) characterized by a peak appearing at an angle 2θ=31.559° and corresponds to (110) reflection plane, ii) the mgo phase characterized by a peak appearing at an angle 2θ=42.906° and corresponds to (200) reflection plane, iii) the tio2 phase characterized by a peak appearing at an angle 2θ=27.911° and corresponding to (110) reflection plane, and finally iv) the tio phase characterized by a peak appearing at an angle 2θ=43.671° and corresponding to (240) reflection plane. the detection of tio phase indicates that 10 mol.%, as ratio of mgo, begins to reduce a part of tio2 phase into tio phase. the parameters of these phases are given in table ii. we can see that mgo density has increased in comparison with the density of btm5 (table i), while those of batio3 and tio2 have kept the same values. the result is in agreement with [27], and indicates that the amount of intergranular pores is decreasing with increasing mgo. consequently, the hardness of the batio3-mgo composite increased with increase in the mgo content. table ii. parameters of characteristic phases – btm10 phase reference code crystal system a (å): b (å): c (å): density [g/cm3] batio3 01-075-0461 cubic 4.0119 4.0119 4.0119 6.00 mgo 01-078-0430 cubic 4.2123 4.2123 4.2123 4.21 tio2 01-088-1175 tetragonal 4.5170 4.5170 2.9400 4.42 tio 01-072-0020 monoclinic 5.8550 9.3400 4.1420 4.91 the models of diffusion and segregation, based on the sublimation enthalpies (bond energy) and the bond-breaking theory, are detailed in [28-30]. a preferential interaction coefficient (β) between the various atoms has been used to explain the evolution of the segregation. concerning batio3, β= ∆g���� � − g �� � , g����, �� � are the enthalpies of mixing of the intermetallic compound. if β>0 there is interaction between ba and oxygen. the segregation energy of ba increases with the superficial concentration of o. if β<0, the interaction between ba and oxygen is of repulsive type. the element with the stronger tendency to segregate will push the other elements towards the bulk. the obtained results concerning the sample btm10 can be explained as follows. taking account of mixing enthalpies of components bao (-609.4kj/mol), mgo (-603.6kj/mol), tio2 (-940kj/mol), mg 2+ (-4.66.85kj/mol), ti (468kj/mol), the component having the lowest heat, of sublimation, segregates to grain boundaries (or to the surface) and the element that has the stronger tendency to segregate, pushes the other elements towards the bulk. the calculation method of segregation energy is developed in [2830] the tio2 enthalpy is the smaller (β=-331). this one segregates to grain boundaries and pushes mgo to the bulk, therefore mg2+ substitutes for ti4+, since ti4+and mg2+ ions have respectively, 0.605 and 0.720å radius. mg2+ ion is more likely to replace the ti4+ions instead of substituting for ba2+ (1.61å) [16]. also, as the mixing enthalpies of components bao and mgo are very close, the dissolution of mgo into batio3 was easier. thus, when mgo content is greater than 1.5% (as carried out in [21]), the exceed is located in the grain boundaries or adsorbed at the surface [16, 23]. concerning the fourth phase (tio), it is known that beyond the oxygen solubility limit into titanium, different oxides can be formed such as ti6o, ti3o and tio. however, stability of tio has been obtained for an oxygen content between 34.5 at.% and 55.6 at.% [31]. the ratio of measured oxygen (60.25 at.%) is beyond this limit confirming the stability of the tio phase. however, the driving force for the formation of the tiox originates from the respective energies of formation [32]. segregation and ti oxide formation depend on temperature, oxygen pressure and exposition time. tio phase has been engineering, technology & applied science research vol. 9, no. 3, 2019, 4092-4099 4096 www.etasr.com boumous et al: mgo effect on the dielectric properties of batio3 detected only in btm10 which contains 60.25 at.% oxygen. the energy of tio formation is greater than that of tio2, therefore, it is expected to detect, especially tio2 but the result indicates reduction of tio2 into tio if one considers that the titanium segregates, under tio2 form. in this case, the chemical reaction of tio2 reduction can be considered. as the energy of tio formation (-517.9kj/mol) is greater than that of bao, β will be greater than 0, since it is equal to 91.5 kj/mol. thus, tio cannot segregate from grains towards grain boundaries. it is formed in the grain boundaries after the reduction of tio2 into tio. the chemical reaction can be explained by using ellingham diagram which shows the stability of the oxide as a function of temperature. a given metal can reduce the oxides of all metals whose lines lie above its own on the diagram. for mg, 2mg � o� ↔ 2mgo line lies below the ti � o� ↔ tio� line and so mg can reduce tio2 into ti. for higher content of mgo (greater than 5 mol%.) a part of tio2 is dissolved in the matrix, another part is reduced into tio if the partial oxygen pressure in the matrix is lower than the equilibrium pressure value with the metal oxide at a given temperature. the remainder of tio2 is located in the grain boundaries. the result is in agreement with [20-22] since mgo was detected in the grain boundary regions of the system. tio2 reduction into tio, can be explained in the following way. ti atoms, or a portion of them, can segregate in the grain boundaries under metallic form, instead of oxide form, and mg atoms (under metallic form) diffuse into the matrix. oxidations of ti and mg occur respectively in the grain boundaries and in the matrix. the formed oxides will depend of the oxygen amount in the matrix. if the oxygen amount located in the grains boundaries is low, tio oxide can be formed, in addition to tio2 oxide. finally, from the results of the microstructure, density data and xrd analysis as reported in [22] suggest that a quantity of mgo did not dissolve into the batio3 and remains present under the form of phase inclusion in the batio3 matrix and is located in the batio3 grain boundaries. some mg2+ ions have dissolved into the lattice to substitute ti4+ ions on the b site of batio3 maintaining the perovskite structure of solid solution with additional phases such as tio2 and tio when mgo content is greater than 5 mol%. the results confirm the ones carried out in [21]. concerning the microstructure of this system, abnormal grain growth was found in pure batio3 with a 10µm average grain size. after addition of mgo particles into the system, the grain size decreased to less than 1µm for btm5 and continuously decreased, with increasing mgo content (sample btm10). mgo incorporation in the grain boundaries might be the grain growth inhibitor as reported in [8, 20-22]. high and stable electric permittivity, over a broad temperature range is significant for batio3-based ceramics due to their use in multi-layer ceramic capacitors [20, 23]. mgo is an important additive in batio3-based ceramics, because of its interesting electric properties. it has low electric permittivity (9 to 10.1), high dielectric strength (10 to 35kv/mm), apparent porosity null (%), tgδ around 9.10-3 and high use temperature (1800°c) [33-35]. the presence of mgo in batio3 matrix decreases the intergranular pores and increases the hardness of the mgo-batio3 composite [27]. the four samples (bmt15, bmt20, bmt30 and bmt50), have been processed to achieve ultra-broad-temperature stability. b. temperature dependence of dielectric loss energy losses in ferroelectric materials are one of the most critical issues of high power devices. ferroelectrics combined with mgo as a function of intrinsic and extrinsic defects should have other behavior regarding dielectric loss. the tgδ of a dielectric material is a useful indicator of dielectric loss. the samples with uniform microstructure, narrow grain size distribution, and less defects, exhibits low dielectric loss properties. figure 5 shows the tgδ of the btm0, btm5, btm10 samples over a temperature ranging from 25 to 300°c. fig. 5. tgδ versus temperature of all samples btm0 exhibits broad peak between 270°c and 290°c. the dielectric loss increases with increasing mgo content. the maximum values of tgδ for the three samples are ∼ 0.15, 0.25 and 1.15 and correspond to temperatures 285°c, 270°c and 270°c respectively. for btm5 and btm10 the maximum is shifted to 270°c. the moving of loss peaks towards low temperature with increasing mg content has been reported in [19]. in higher temperature range (200-500°c), the high dielectric loss peak may be induced by the polarization of free space charge associated with a thermally active relaxation process. the results are in agreement with [19-21, 36]. authors in [21] attribute the result to the increase in the oxygen vacancies. in our case the oxygen vacancy concentration increases with increasing mgo content, since mg2+ is an acceptor for batio3 and a double ionized oxygen vacancy (v0 ++) is formed in addition to the reduction of tio2 into tio phase. however, mgo addition with multi-component batio3based ceramics, for example batio3 co-doped with y, ga and si [8], reduces dielectric loss, because of y3+doping. when the amount of mgo increases, (btm15 and btm20), the maxima of the loss curves shifted towards lower temperatures. these curves are characterized by oscillations around 200°c. at this temperature, the losses are greater than that of btm5 and btm10. the curve of the sample btm20 presents a peak well resolved at 200°c. however, for the samples btm30 and btm50, the losses increase in comparison with that of btm15 and btm20, to reach respectively maxima at 9 and 12. these peaks are shifted towards higher temperatures (300°c) in comparison with that of btm15 and btm20. the increase of the losses can be so attributed to the increase of the oxygen engineering, technology & applied science research vol. 9, no. 3, 2019, 4092-4099 4097 www.etasr.com boumous et al: mgo effect on the dielectric properties of batio3 vacancies with the increase of mgo such as previously explained for btm5 and btm10. c. temperature dependence of electrical resistance figure 6 shows the resistance versus temperature, in the temperature range from 25°c to 400°c, of all samples. it is a typical resistance-temperature characteristic of a batio3 based ptcr material. impurities and lattice imperfections play an important role in the exhibition of the ptc effect, in the doped samples, since the losses are in connection with these imperfections [21]. their conductivities are influenced by intrinsic defects such as oxygen vacancies and cation vacancies, and the extrinsic defects produced by dopant addition. here, divalent mg ions (under oxide form) are added to substitute ti ions in the batio3. the conductivity seems to be influenced by oxygen vacancies generated by ti, and the lattice deformation of the composite (4.0119å) is larger than that of pure batio3 (4.0060) (see tables ii and iii), proving that mg substitutes ti. tio phase has been detected in btm10, contributing to cation vacancy generation. the evolution of resistance versus temperature in figure 6 shows the influence of these imperfections on the resistance. we can see that as the mgo content increases, the resistance is increasing along. however, the switching temperatures of the samples btm0 and btm5 are around 270°c, whereas that of btm10 is located at 225°. the characteristic of btm10 presents oscillations below the switching temperature (225°c). authors in [17] attribute the temperature stability of the resistance, below the switching temperature (of ptcr ceramics), to the uniform grain size. fig. 6. resistance versus temperature of all samples looking to the sem image in figure 2(a)-(b) corresponding to the samples btm0 and btm5, the grain sizes are lightly different, whereas the grain size, in the two samples, is in the order of µm. the switching temperature of the two samples is remains equal to 270°c. only the amplitude of btm5 is enhanced beyond 105ω because of mgo doping. however the grain size of btm10 (figure 2(c)) is smaller than that of the two precedent samples, in the order of a few hundred nanometers. we can see also that the resistance of this sample evolves differently. this one presents a broad peak where its maximum (smaller than that of btm5) begins at 225°c and ends by oscillations until 350°c. the resistance, at room temperature, increases with mgo content increasing but, that of btm10 decreases at 100°c, becomes smaller than that of btm5, and afterwards increases again. however, the curves of the samples btm15, btm20 are close in point of view form, and evolve in the same way with the sample btm10. the maxima are less broad than that of btm10 and their maxima are shifted towards 175°c. the minima are higher than the ones of the bm10. the sample btm30 has a broad maximum which begins at 175°c and ends at 270°c. its minimum is higher than the ones of btm15 and btm20. however, the curve of the sample btm50 begins by a minimum, around 10000, greater than that of all other samples, and afterwards it increases to reach a maximum (around 30000), greater than that of all other samples. it is inferred that more mgo content reduces more tio2 into tio or even into ti, more cation vacancies are generated and the resistance is rising. this maximum appears at the curie temperature (125°c) and ends with oscillations with a minimum well resolved at 300°c. these results confirm that, as mgo content increases, the dielectric loss of mgo-doped batio3 increases and curie temperature shifts lower. consequently, the resistance of the system increases. the result is in agreement with the findings in [21]. d. electric permittivity figure 7 shows the electric permittivity of mgo-doped batio3, for various mgo contents, in a temperature range from 20°c to 300°c. a sharp dielectric peak is recorded at curie temperature (120°c) for btm0. this tc value has been found equal to the one reported in [20] for multicomponent batio3based ceramics without mgo. electric permittivity of btmo reaches almost 6000 while in [20], it is only 1700. however, mgo effect on batio3 begins to appear on btm5 by an enlargement of εr peak. εr maximum (5000) is located at 50°c. this enlargement of εr peak, has been indicated in [20] for samples containing 1.0wt%, 1.5wt% and 2wt% mgo, where maxima (around 2000) was located at 250°c. however, εr of btm10 and bmt15, corresponding to the maximum and tc=80°c, has been evaluated to 4500 and 4250 respectively. the minima are located around 240°c. a broaden peak has been recorded for btm5. mg plays a role, in curie peak depression [8]. the εr peak is shifted towards lower temperatures. authors in [21] attribute this result to the diffuseness of the phase transition. the electric permittivity decreases with increasing mgo content. this is in agreement with [8, 16, 21-23]. our samples contain mgo, tio2 and tio phases in the grain boundaries and even perhaps ti in btm30 and btm50. btm30 and btm50 can be even two phase materials, with mgo as continuous phase. the grain boundary is a non-ferroelectric phase, therefore its electric permittivity is lower. otherwise, the permittivity at room temperature can be explained by the ionic polarization. this one can be calculated using the clausisus-mossotti equation [8]. εr decreases with increasing mg, because of the decrease in ionic polarizability (α) of the dipole as shown in [8]. the more the mgo content is, the smaller is the grain size, and the lower the εr. this justifies that εr changes as a function of mgo content over the studied temperature range (from ambient temperature to 250°c). at 250°c and beyond, the curves of εr (btm0 and btm10) present a minimum and increase again. however, for btm5, the minimum appears at 350°c from which εr begins to increase slowly but remains smaller than that of btm0 and btm10. concerning the samples btm20 and btm 30, the engineering, technology & applied science research vol. 9, no. 3, 2019, 4092-4099 4098 www.etasr.com boumous et al: mgo effect on the dielectric properties of batio3 curve evolution of εr kept the same form but their maxima, evaluated respectively to 4250 and less than 4000, are shifted towards 100°c. with 20 mol.% of mgo and more (30 mol.%.) as dopant, tc shifts slightly again towards higher temperatures. after the minimum located at 300°c, as we can see in figure 7, the εr of btm30 decreases in comparison with that of btm20. this part of the curve is comparable with that of btm10. the εr of btm50 is equal to 500. it is 10 times smaller than that of btm5 and 12 times smaller than that of btm0. its curve is characterized by small maxima at 120°c and 200°c and ends by an increase towards 1000 at 400°c. the εr of the sample btm50 is close to the value found in [25] where batio3 and mgo were both in the ratios 50% in volume. the εr, of the two phase material depends not only on the electric permittivity of the two phases (mgo and btio3), but it is highly affected by the structure (phase distribution and grain size) and the stress level between the phases as a result of the differences in their thermal expansion result [25]. the two phases, are promising for the development of high electric permittivity and high dielectric strength capacitors, therefore, the breakdown voltage is expected to be high, since the paraelectric (mgo) phase is continuous at this concentration [25]. our results confirm the findings in [25] since tio2 and tio phases have vanished in btm50. sample btm50 is a two phase material which is promising to have excellent thermal shock resistance, mechanical strength, and chemical resistance preperties. fig. 7. temperature dependence of electric permittivity iv. conclusion the effects of mgo additions on the microstructure and the dielectric properties of batio3, have been studied. oxides mgo and tio2 have been detected in the sample btm5. mgo, tio2 and tio were detected in the sample btm10. mgo addition at 10 mol.%. and more, reduces the tio2 phase into tio phase and can be even reduced into ti phase. the grain size strongly depends on the mgo content. the average grain size of pure batio3 was near 10µm, whereas that of doped samples was about 1µm for btm5 and some hundred nanometers for btm10. the bimodal microstructure of fine and large matrix grains in btm0 has been attributed to the temperature effect and to the presence of titanium oxide. εr decreases with increasing mgo content, while grain size and εr decrease. the electric permittivity of btm50 was 12 times smaller than that of btm0.the maximum peak was broader for increased mgo content. the tc, of btm10 and btm15 has been evaluated to 80°c, and to 100°c for btm20 and btm30. beyond 15mol.% mgo, tc is shifted again towards higher temperatures. the curie temperature of btm50 was equal to that of btm0 (120°c). the conductivity is influenced by intrinsic defects, oxygen vacancies, and cation vacancies. the extrinsic defects were produced by dopant addition. divalent ions (mg) substitute ti ions. consequently, the conductivity was influenced by oxygen vacancies generated by ti and the lattice deformation of the composite. the dielectric loss increases strongly with increasing mgo content. the loss peak, shifts towards low temperatures with increasing mgo content, whereas it may be induced by the polarization of free space charge associated with a thermally active relaxation process. the highest loss (tgδ=12) has been measured on the btm50, whereas that of btm30 was equal to 9. the lowest loss has been measured on btm0 (tgδ=0.2) and btm5 (tgδ=0.3). tio2 and tio phases have probably vanished in btm30 and btm50 samples. these samples, particularly btm50, can be considered as two-phase materials, which is promising regarding shock resistance, mechanical strength and chemical 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incorporating fly ash muneeb ayoub memon department of civil engineering quaid-e-awam university of engineering, science & technology pakistan engr.muneebmemon@gmail.com noor ahmed memon department of civil engineering quaid-e-awam university of engineering, science & technology pakistan nahmedmemon@gmail.com aftab hameed memon department of civil engineering quaid-e-awam university of engineering science & technology pakistan aftabm78@hotmail.com riaz bhanbhro department of civil engineering quaid-e-awam university of engineering, science & technology pakistan riaz@quest.edu.pk mujahid hussain lashari department of civil engineering quaid-e-awam university of engineering, science & technology pakistan emhlashari@gmail.com abstract—flow ability is one of the prime characteristics of good concrete and plays a key role in self compacting concrete (scc). this study assesses flow ability of scc in which cement content was reduced and replaced by fly ash. several mixes were prepared by using 5% to 30% fly ash. from the experimental work it was realized that by adjusting a suitable percentage of super plasticizer (sp), fly ash dosage can be increased with satisfactory fresh properties of concrete in accordance with the guidelines of efnarc. at t50cm time the optimum amount of sp was 2%. it was noted that with increase in dosage of fly ash the slump flow increased but t50cm and v-funnel time were reduced. j-ring height value varied from 9 to 10 for all the mixes. keywords-self compacting concrete; flow ability; fly ash; slump flow i. introduction self compacting concrete (scc) is popular because it is a workable concrete with a satisfactory level of strength. it is very useful for narrow sections with ignorable level of segregation and higher flexibility [1, 2]. scc is also proved to be very useful when reinforcement is very congested. scc offers ease in pouring compared to ordinary concrete and hence has more commercial benefits [2, 3]. although compared to ordinary concrete, scc is a little more expensive but this can be compensated by replacing cement content with supplementary cementitious materials [4-6]. the incorporation of cementitious materials such as metakaolin ash in scc not only enhances its properties at fresh and hardened state but also decreases the cost of materials and the amount of produced co2 [7–12]. fly ash (fa) is one of the commonly used cementitious materials used in producing economical and ecofriendly scc with a satisfactory level of performance [13, 14]. it is also useful in reducing the necessary quantity of super plastisizer (sp) for maintaining the required slump flow [15]. the overall performance of scc can be further improved by using mixtures of different fillers of fa with lime stone and/or any other natural pozzolanic materials [16, 17]. the benefits of incorporating cement replacement materials depend on their type, dosage, and physical and chemical composition [18]. the use of fa is very helpful in decreasing the requirement of water in the manufacturing of scc with a liquefied consistency [19]. on the other hand, when palm oil fuel ash (pofa) was used instead of ordinary portland concrete (opc), it increased its initial and final setting time but reduced passing ability. this has gained high importance in concrete technology [21-25]. pofa and fa have been used in [26] in scc individually and combined. it was observed that fa shows better performance than pofa in all measured characteristics of scc mixes. furthermore, it was also reported that the use of higher quantity of pofa and fa has a momentous possibility for medium strength concrete. authors in [25] used blends of fa, ggbs and sf for assessing scc and found that fa is the major material in decreasing the compressive strength of the concrete, whereas authors in [21] used fa, marble powder (m) and limestone filler (lf) in scc and found that the compressive strength of scc with binary concrete samples was better than of concrete with fs at an early age but there was no difference at a later age. ii. experimental procedure figure 1 shows the flowchart of the current research, which starts from literature review, goes to the selection of materials, physical and chemical analysis of materials, and mix design by ennarc [1], and evaluates the fresh properties of concrete reaching the final conclusions. opc conforming astmc150m-18 and class f fly ash (fla) as per astm c 618-17 were used. corresponding author: muneeb ayoub memon engineering, technology & applied science research vol. 10, no. 2, 2020, 5392-5395 5393 www.etasr.com memon et al.: flow assessment of self-compacted concrete incorporating fly ash fig. 1. flowchart showing the work methodology figures 2-3 demonstrate the chemical compositions of opc and fla respectively. table i shows the values of physical and chemical analysis. fine aggregates (fa) passed from #4 sieves and coarse aggregates (ca) with 13mm maximum size were used throughout the study. the gradation of aggregates presented in table ii. a poly-carboxylate based sp was used to maintain the required workability. in order to investigate the flow characteristics of scc, seven different mixtures were produced in total with varying percentage replacement of cement by fla with one being the control mixture as shown in table iii. the fresh properties checked were filling ability, passing ability and segregation resistance. the filling ability was evaluated by slump flow time t50sec, slump flow diameter, and v-funnel time. the passing ability was measured with jring height, and l-box height ratio. v-funnel time at 5 minutes was recorded as a segregation resistance test. fig. 2. chemical composition of opc fig. 3. chemical composition of fla table i. materials required for 1m3 of scc mix id mix description opc kg/m 3 fla kg/m 3 binder kg/m 3 fa kg/m 3 ca kg/m 3 w/b water kg/m 3 sp kg/m 3 m1 pc 550 0 550 870 880 0.34 187 11 m2 5% fla 522.5 27.5 550 870 880 0.34 187 11 m3 10% fla 495 55 550 870 880 0.34 187 11 m4 15% fla 467.5 82.5 550 870 880 0.34 187 11 m5 20% fla 440 110 550 870 880 0.34 187 11 m6 25% fla 412.5 137.5 550 870 880 0.34 187 8.25 m7 30% fla 385 165 550 870 880 0.34 187 5.5 table ii. opc and fla physical and chemical properties opc (%) fla (%) sio2 15.1 47.98 al2o3 6.27 30.4 mgo 2.089 0.945 cao 59.35 2.994 fe2o3 4.003 4.07 k2o 1.421 1.84 so3 3.495 tio2 2.185 loss of ignition 2.64 1.32 specific gravity 3.25 2.13 table iii. sieve analysis of fine and coarse aggregates sieve size (mm) fine aggregates coarse aggregates passing (% ) passing (% ) 13.2 100 95.43 9.5 100 46.1 4.75 99.8 0.35 2.36 83.96 0 1.18 66.42 0 0.6 54.1 0 0.3 38.1 0 1.15 9.1 0 pan 0 0 iii. results and discussion a. sp dosage optimization it is well recognized that sp is added in scc to achieve the required workability. therefore, it was necessary to acquire the optimized dosage of sp in the selected mixes. for this purpose, slump flow time t50cm tests were conducted to get the optimized dosage of sp from the trial batches of each mix. t50cm time should be within the range of 2-6s. the workability of scc increases with increase in the dosage of sp as can be seen in table iv. table v shows the observed results of fresh characteristics during various lab tests. table iv. variation of slump flow time with sp dosage sp dosage 1 1.5 2 2.5 3 mixes t50cm slump flow time (sec) control 12 9.3 4.6 -- 5% --4.4 3.9 2.6 10% --4.3 3.3 3 15% --4.2 4 2.3 20% --4.1 3.1 2 25% -4.2 3.2 2.5 2.1 30% 3.9 3.6 3 2.1 - engineering, technology & applied science research vol. 10, no. 2, 2020, 5392-5395 5394 www.etasr.com memon et al.: flow assessment of self-compacted concrete incorporating fly ash b. filling ability the filling ability was assessed through (t50cm), slump flow diameter and v-funnel tests. figures 4-6 show the variation of slump flow time, slump flow diameter, and v-funnel flow time respectively, for the tested mixes including control. it can be seen from these figures that t50cm and v-funnel time decrease with increasing in fly ash percentage. likewise, slump flow diameter is slightly increasing for increased replacement levels of fly ash due to the viscosity modifying properties of fly ash. the filling ability values of all mixes with the optimised dosages of sp were within the required range [1]. fig. 4. variation in t50cm with fly ash dosage fig. 5. variation in slump flow diameter with fly ash dosage fig. 6. variation in v-funnel flow time with fly ash dosage c. passing ability passing ability is a major characteristic of scc in maintaining concrete flow. when structural components are very narrow or highly reinforced with small spaces between them, passing ability is more important than the uniformity of concrete. at laboratory level, this can be performed through the j-ring and l-box tests. the height of j-ring and l-box height ratio (h2/h1) are given in table v which depicts the passing ability of prepared mixes confirming the desired level as suggested by efnarc. fig. 7. variations in j-ring height with fly ash dosage fig. 8. variations in l-box height ratio with fly ash dosage d. segregation resistance the consistency of the mixes was inspected through the vfunnel test at 5min. it is observed from figure 9 that for all the mixes the v-funnel flow time was in the required range (8-25s) according to the efnarc guidelines. fig. 9. variation in v-funnel flow time at (5min) with fly ash dosage iv. conclusions the fresh properties assessed by the workability tests of scc depend upon the dosage of fly ash in the mix which can be adjusted by a suitable percentage of sp. t50cm is the key test for the fresh properties of scc, while t50cm time between 4 and 5s is considered optimum. on the basis of t50cm time, the optimized dosage of sp for mixes are (cm 2%), (5fa 2%), 4.6 4.4 4.3 4.2 4.1 4.2 3.9 0.0 1.0 2.0 3.0 4.0 5.0 6.0 cm 5% fly ash 10% fly ash 15% fly ash 20% fly ash 25% fly ash 30% fly ash t 5 0 s lu m p f lo w t im e : se c mix id 74.6 74.8 75.3 76.0 76.8 75.3 74.9 65.0 66.0 67.0 68.0 69.0 70.0 71.0 72.0 73.0 74.0 75.0 76.0 77.0 78.0 79.0 80.0 cm 5% fly ash 10% fly ash 15% fly ash 20% fly ash 25% fly ash 30% fly ash s lu m p f lo w d ia m e te r : c m mix id 16.3 13.5 12.6 9.7 9.7 12.6 11.3 5.0 7.0 9.0 11.0 13.0 15.0 17.0 19.0 21.0 23.0 25.0 cm 5% fly ash 10% fly ash 15% fly ash 20% fly ash 25% fly ash 30% fly ash v -f u n n e l f lo w t im e : se c mix id 9.6 9.8 9.7 10.1 9.4 10.0 10.3 5.0 6.0 7.0 8.0 9.0 10.0 11.0 cm 5% fly ash 10% fly ash 15% fly ash 20% fly ash 25% fly ash 30% fly ash j -r in g h e ig h t: m m mix id 0.90 0.86 0.88 0.84 0.88 0.86 0.87 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 cm 5% fly ash 10% fly ash 15% fly ash 20% fly ash 25% fly ash 30% fly ash l -b o x h e ig h t r a ti o mix id 22.5 20.5 19.5 19.5 18.4 18.0 14.8 5.0 7.0 9.0 11.0 13.0 15.0 17.0 19.0 21.0 23.0 25.0 cm 5% fly ash 10% fly ash 15% fly ash 20% fly ash 25% fly ash 30% fly ash v -f u n n e l f lo w t im e a t 5 m in : se c mix id engineering, technology & applied science research vol. 10, no. 2, 2020, 5392-5395 5395 www.etasr.com memon et al.: flow assessment of self-compacted concrete incorporating fly ash (10fa 2%), (15fa 2%), (20fa 2%), (25fa 1.5%) and (30fa 1%). slump flow diameter increases and t50cm and v-funnel time decrease with increase in the percentage of fly ash. j-ring height for all the mixes ranged from 9 to 10mm. the values of l-box height ratio for all mixes are between 0.8 and 1.0. it was observed that filling ability, passing ability and segregation resistance for all the mixes with the optimised sp dosage were within the required range as per efnarc. table v. scc fresh properties filling ability passing ability segregation resistance mix slump flow time (s) limits [2-5] sec slump flow diameter (cm) limits [65-80] cm v-funnel time (s) limits [6-25] s jing height (mm) limits [0-10] mm l-box height ra io limits [0.8-1 v-funnel time at 5min (s) limits [8-25] s pc 4.6 74.6 16.3 9.6 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science research vol. 9, no. 4, 2019, 4423-4427 4423 www.etasr.com khan et al.: towards achieving machine comprehension using deep learning on non-gpu machines towards achieving machine comprehension using deep learning on non-gpu machines uzair khan college of computing and information sciences, paf karachi institute of economics and technology, karachi, pakistan ukhan@eemaan.com khalid khan college of computing and information sciences, paf karachi institute of economics and technology, karachi, pakistan khalid.khan@pafkiet.edu.pk fadzil hasssan department of computer and information sciences, universiti teknologi petronas, perak, malaysia mfadzil_hassan@utp.edu.my anam siddiqui department of computer sciences, sir syed university of engineering and technology, karachi, pakistan sidd.anam@ssuet.edu.pk muhammad afaq college of computing and information sciences, paf karachi institute of economics and technology, karachi, pakistan sanaraba@gmail.com abstract—long efforts have been made to enable machines to understand human language. nowadays such activities fall under the broad umbrella of machine comprehension. the results are optimistic due to the recent advancements in the field of machine learning. deep learning promises to bring even better results but requires expensive and resource hungry hardware. in this paper, we demonstrate the use of deep learning in the context of machine comprehension by using non-gpu machines. our results suggest that the good algorithm insight and detailed understanding of the dataset can help in getting meaningful results through deep learning even on non-gpu machines. keywords-natural language processing; machine comprehension; deep learning; non-gpu machines; squad i. introduction automated question answering has been a point of discussion in the field of computer science for more than 50 years and can easily be the most awaited task in the domain of natural language processing. still it is considered as an open problem and research is still conducted on its various aspects. the early work in this area was domain specific in which ai was used as a building block [1]. with the advancement of enabling technologies, researchers found various ways/methods to come out of the domain restriction and focus on open domain systems and applications such as chat bots, personal assistants, medical assistants, etc. today, automated question answering has become a part of the more holistic concept of machine comprehension which enables machines to analyze a context and answer general questions against it by utilizing new and evolving machine learning models. the goal is to achieve human-like accuracy on the said task. with the ever increasing processing capabilities and hardware capacity, advance machine learning techniques and deep learning algorithms, available knowledge bases and generalized data sets such as squad [2, 3], it is expected that machine comprehension will soon achieve human like accuracy. question answering can be broken down into three basic parts: understanding the question, searching for answer and answer generation. understanding factoid questions is the simplest task and machines can usually carry one or two word answers, e.g. answering a question regarding the distance of moon from earth. for simple questions like this, we can use pattern matching techniques to find answers from the given text and the answer generation is also simple. various open source libraries are available for this purpose [4]. taming generally means to extract only the information which contains some meaning. this includes stemming, i.e. breaking down verbs in their first tense, and the ability to extract these factors with increasing amount of text. ii. conventional and modern techniques automated question answering has two common approaches, answer matching and machine learning. in answer matching, one needs to do information extraction. in a question like “how many white tigers are left in the world in 2018?”, the keywords are white, tigers, left, world, 2018. the term “how many” determines that a quantity is asked, which is the askingpoint of this question. as a first step, the question is tokenized by using a tokenization technique [5]. the second step is do token matching with corpus keywords that may result in the selection of a few sentences where the matching remains positive and there is a chance to find potential answers. the intersection of question and sentences gives a score which determines how likely it is to get the answer in any sentence. machine learning on the other hand is a branch of artificial intelligence (ai) that gives computers the ability to automatically learn from the data and improve their efficiency without being explicitly programmed [6]. mostly, machine learning models use supervised learning in which the system corresponding author: khalid khan engineering, technology & applied science research vol. 9, no. 4, 2019, 4423-4427 4424 www.etasr.com khan et al.: towards achieving machine comprehension using deep learning on non-gpu machines learns from given examples, so it has both input and output variables and use algorithms to derive mapping functions from input to output. so we can say that the data is labeled [7]. whereas, in unsupervised learning, the algorithms themselves find relevant structures in the context, so there are no output variables. in unsupervised learning there are no correct answers and the machine has to draw inferences from datasets to describe hidden structures from data. basically, the data is unlabeled. there is another approach which is known as semisupervised learning falling right between supervised and unsupervised learning. it typically uses a small amount of labeled data and a large amount of unlabeled data to improve learning accuracy. deep learning accomplishes results that were unrealistic earlier [8]. deep learning models can accomplish intricate perfection sometimes even more accurate than human performance. deep learning systems are instructed by utilizing large arrangements of labeled data and neural network architectures that learn features from the information without the requirement of manual feature extraction. a standout amongst the most prominent kinds of deep neural networks is known as convolutional neural networks (cnn or convnet). a cnn convolves learned features with fed data, and utilizes 2d convolutional layers, making this design appropriate to preparing 2d content, for example, pictures. there are three ways in order to categorize objects using deep learning: a. training from scratch to create a network architecture which learns the features we need to gather a very large dataset. this is a less common approach because it is good for the applications that have a large number of output categories or generally new applications. the problem is that with a large amount of data we typically need a few days or even weeks to train the model. b. transfer learning the transfer learning method is used by the majority of deep learning apps. this method includes the fine-tuning of an already trained model. one starts with an already existing network like alexnet or googlenet, and adds some new data in it which contain previously unknown classes. this also comes with an advantage of needing less data (operating thousands of pictures instead of millions), so the operating time reduces. c. feature extraction a less used, more concentrated way of deep learning is to utilize the network as a feature extractor. since every one of the layers is instructed with learning specific features from pictures, we can extract these features from the network whenever amid the training procedure. most of the researches on this task are performed on a cluster of computers. however we are trying to achieve it on mid-range computers, contrary to the fact that deep learning models require heavy computational power. to achieve this, we gave more time and smaller chunks of data as per the computational power we are providing to this task. we test results by partitioning the data differently until they provide us with the best possible results. this might be a new step towards deep learning with conventional computing power. iii. related work automated question and answer using wikipedia as a source has been discussed in [3]. wikipedia is used as the knowledge base, bigram hashing and tf-idf matching are performed with a multi-layer recurrent neural network model to detect answers in wikipedia’s paragraphs. authors in [9] performed a similar task, matching potential answers on semantic similarity with the question and concluded that a bigram model performs better than the unigram model and the addition of the idf-weighted word count features improves performance for both models by 10%–15%. its efficiency can be further improved using a sentence model with higher order n-grams. authors focused on answer sentence selection, the task that selects the correct sentence, answering a factual question from a set of candidate sentences. the relevance of an answer sentence to a question is typically determined by measuring the semantic similarity between question and answer, but in this paper authors shown that a neural networkbased sentence model can be applied to the task of answer sentence selection that can be applied to any language and does not require feature-engineering and hand-coded resources beyond some large corpus on which to train the initial word embeddings [9]. the answer selection problem can be formulated as follows [10]: given a question q and an answer candidate pool {a1,a2,•••,as} for this question, we aim to search for the best answer candidate by using bidirectional long short-term memory (bilstm) models on both questions and answers respectively. in order to better distinguish candidate answers according to the question, authors in [10] introduced a simple but efficient attention model to this framework for the answer embedding generation according to the question context. in [11], grounded text and question-answer pairs are simultaneously generated with the hope that the analysis of performance on these tasks will help expose the frailty of current models and help motivate new algorithm designs that alleviate these frailties. authors in [12] proposed a new end-toend neural architecture to address the machine comprehension problem as defined in the squad dataset [12]. they used the pointer net model that allows the predictions of tokens from the input sequence only, rather than from a larger fixed vocabulary and thus allows them to generate answers that consist of multiple tokens from the original text. in [13], authors built a reading comprehension dataset containing 500 fictional stories, with 4 multiple choice questions per story. the stories were chosen to be fictional to focus work on finding the answer in the story itself, rather than in knowledge repositories such as wikipedia. the goal is to build technology that actually understands stories and paragraphs on a deep level such as opposed to using information retrieval methods and the redundancy of the web to find the answers. authors in [14] addressed the issue of unavailability of real natural language training data by introducing a novel approach for building a supervised reading comprehension data set. supervised machine learning approaches have largely been absent from this space due to both the lack of large-scale training datasets, and the difficulty in structuring statistical models flexible enough to learn to exploit document structure. engineering, technology & applied science research vol. 9, no. 4, 2019, 4423-4427 4425 www.etasr.com khan et al.: towards achieving machine comprehension using deep learning on non-gpu machines authors compared these neural models to a range of baselines and heuristic benchmarks based upon a traditional frame semantic analysis provided by a state-of-the-art natural language processing. in [15], authors introduced the bidirectional attention flow (bidaf) network, a hierarchical multi-stage architecture for modeling the representations of the context paragraph at different levels of granularity. the computed attention weights were used to extract the most relevant information from the context for answering the question by summarizing the context into a fixed-size vector. this allowed the attention at each time step to be unaffected from previous incorrect attendances [15]. in [3], the authors addressed the need for a large and high-quality reading comprehension dataset by presenting stanford question answering dataset v1.0 (squad) [2], consisting of questions posed by crowd workers on a set of wikipedia articles, where the answer to every question is a segment of text, or span, from the corresponding reading passage. the authors also found that the model performance worsens with increasing complexity of (i) answer types and (ii) syntactic divergence between the question and the sentence containing the answer. another solution to the problem on machine comprehension is long short-term memory (lstm) architecture for recurrent neural networks (rnn) which is used to find complex answers using semantics [16]. machine reading, text extraction and word embedding is used to improve the understanding the text along with lstm and rnn [17]. almost all the discussed models were trained using gpu machines to ensure accuracy, although machine learning models can work on a moderate non-gpu machine as well. in this paper, we have shown that a deep learning model using the same dataset of wikipedia can be trained over ordinary cpu based machines, if the data-set does not contain images or large data entities. squad [2] is comparatively a mid-size data-set containing 100,000+ question-answer pairs on 500+ articles. we used a 3 rd generation intel powered machine with 8gb ram for this testing (no graphics memory). iv. methodology we used deep learning methods on a non-gpu machine to create a model that predicts answers from a given context. as mentioned previously, squad is a new generation dataset which contains questions by a number of people on wikipedia articles. the answer of each question is always a part of a given context and about three-quarters of the answers are four words long. there is a fast progress in this dataset where some models achieve the same accuracy as humans in the task of question answering. a. embedding glove (global vectors) [18] embedding is an unsupervised learning algorithm to obtain vector representation of words and the resulting representations showcase interesting linear substructures of the word vector space. for this problem there were used 100 glove word embeddings. b. encoding we used bi-directional lstm to add a rnn based encoding layer, because we wanted each word to be aware of words before and after it. the output is a series of vectors in the forward and backward direction which were we concatenated. c. attention layer since we got the hidden context vector and the hidden question vector, for answer generation we have to look at them together. that’s where the attention layer comes in. it is the primary component of the question answering task. d. dot production attention for each context vector ci we multiply each question vector qj to get vector ei (attention scores). then we take a softmax over ei to get αi (attention distribution). softmax ensures that the sum of all ei is 1. finally we calculate αi as the product of the attention distribution αi and the corresponding question vector. dot product attention is described below: � � = [�� ���, … , �� ���] � � (1) � � = �������(�� ) �� (2) �� = ∑ �� ������� ∈ � �� (3) we run squad with basic attention layer as mentioned, but results were not as promising. for better results we needed to add more complexity. as mentioned above, bi-directional attention flow can improve the results i.e. computing the similarity matrix, which contains a similarity score sij for each pair (ci, qj) of context and question hidden states, as shown in (4): �� = !"�# � $��;��;�� ∘ ��' � (4) where, ci ◦ qj is an element-wise product and wsim is a weight vector. similar to the dot product attention above, we performed context to question attention using softmax of s to get attention αi , which is used later to get c2q attention outputs αi , from the weighted sums of question hidden states qj. � � = �������( �,) * � � ∀, {1,… , /} (5) �� = ∑ �� ��� � ��� ��� ∀, {1,…, /} (6) for question to context attention, for each context location {1,…,n}, we take the max of the corresponding row of similarity matrix, mi= max j sij ∈ r. then the softmax over the resulting vector m ∈ rn  gives the attention distribution β ∈ rn of context locations. then, β is used to get the weighted sum of context hidden states ci. this is the question to context attention prime output. �� = �� ∈ � ∀, {1,… , /} (7) 1 = ���������� �2 (8) �3 = ∑ 1��� 2 ��� � �� (9) eventually, to get context position ci, we combine both outputs i.e. context to question and question to context as: 4� = [�� ; ��; �� ∘ �� ; �� ∘ � 3] �5� ∀, {1,… ,/} (10) e. output layer using the results of the context hidden states and the attention vector from the previous layer we can decide the start engineering, technology & applied science research vol. 9, no. 4, 2019, 4423-4427 4426 www.etasr.com khan et al.: towards achieving machine comprehension using deep learning on non-gpu machines and end index of the answer. so we created blended reps, these reps become the input to a fully connected soft-max layer to create a start vector with a probability of start index, and an end vector with a probability of end index. loss function is calculated using cross-entropy loss for start index, summed with cross-entropy loss for end index. the results were evaluated using f1 score and em score. f1 score is the weighted average of precision and recall. precision is the ratio of correctly predicted positive answers to total predicted positive observations, whereas recall is the ratio of correctly predicted positive answers to total observations. em score is the exact match score, the total number of predictions that match the actual answer. v. results the test results were quite appealing, but we could not run more than 3 epochs due to exhaustion of resources. it took more than 24 hours to complete 1000 iterations or 1 epoch which provided us with the following results. our average f1 score turned out to be 0.77, with average em score of 0.64. the average loss was 3.2. the results of 12 iterations are shown in figures 1 and 2. figure 1 shows the outcome of 12 iterations, blue color shows the f1 score and orange shows the em score, grap range is from 0 to1, 1 being the best case. figure 2 shows the loss in each of the 12 iterations. loss is inversely proportional to the correctness of the model. the more the loss, the less accurate is the model. observed values were around 3.2 which means that the model performs accurately. fig. 1. f1 and em score fig. 2. loss vi. conclusion machine learning research aims to produce methods that can reason with natural language. deep learning is playing an important role in this field improving the results. we have demonstrated the use of deep learning in the context of machine comprehension by using non-gpu machines. our results suggest that the good insight of the algorithm and the detailed understanding of the dataset can help in getting meaningful results through deep learning even on non-gpu machines. we believe existing learning systems cannot solve many issues in this field, whereas our proposed method has produced results with reasonable improvements. our results show that, the performance of the model is quite appealing, however for a moderate sized dataset like squad, these models need more processing power. the results are not bad in one epoch, but ultimately, to train these data sets, more powerful computers are needed to train deep learning models. there might be a follow up in the future in this direction which may provide us with even better results. references [1] d. karunakaran, “entity extraction using deep learning based on guillaume genthial work on ner”, available at: https:// medium.com/intro-to-artificial-intelligence/entity-extraction-using-deeplearning-8014acac6bb8, 2017 [2] https://rajpurkar.github.io/squad-explorer/ [3] p. rajpurkar, j. zhang, k. lopyrev, p. liang, “squad: 100,000+ questions for machine comprehension of text”, available at: https://arxiv.org/abs/1606.05250, 2016 [4] d. chen, a. fisch, j. weston, a. bordes, “reading wikipedia to answer open-domain questions”, 55th annual meeting of the association for computational linguistics, vancouver, canada, july 30august 4, 2017 [5] e. loper, s. bird, “nltk: the natural language toolkit”, acl-02 workshop on effective tools and methodologies for teaching natural language processing and computational linguistics, philadelphia, usa, july 7, 2002 [6] m. richardson, c. j. c. burges, e. renshaw, “mctest: a challenge dataset for the open-domain machine comprehension of text”, conference on empirical methods in natural language processing, washington, usa, october 18-21, 2013 [7] j. weston, a. bordes, s. chopra, a. m. rush, b. v. merrienboer, a. joulin, t. mikolov, “towards ai-complete question answering: a set of prerequisite toy tasks”, 4rth international conference on learning representations, new york, usa, may 2-4, 2016 [8] k. m. hermann, t. kocisky, e. grefenstette, l. espeholt, w. kay, m. suleyman, p. blunsom, “teaching machines to read and comprehend”, international conference on neural information processing systems, montreal, canada, december 7-12, 2015 [9] s. b. kotsiantis, “supervised machine learning: a review of classification techniques”, informatica, vol. 31, pp. 249-268, 2007 [10] j. schmidhuber, “deep learning in neural networks: an overview”, neural networks, vol. 61, pp. 85-117, 2015 [11] b. f. green jr, a. k. wolf, c. chomsky, k. laughery, “baseball: an automatic question-answerer”, western joint ire-aiee-acm computer conference , los angeles, california, may 9-11, 1961 [12] m. seo, a. kembhavi, a. farhadi, h. hajishirzi, “bidirectional attention flow for machine comprehension”, 5th international conference on learning representations, toulon, france, april 24-26, 2017 [13] y. lecun, y. bengio, g. hinton, “deep learning”, nature, vol. 521, article id 7553, 2015 [14] k. greff, r. k. srivastava, j. koutnik, b. r. steunebrink, j. schmidhuber, “lstm: a search space odyssey”, transactions on neural networks and learning systems, vol. 28, no. 10, pp. 2222-2232, 2017 [15] l. yu, k. m. hermann, p. blundom, s. pulman, “deep learning for answer sentence selection”, available at: https://arxiv.org/pdf/ 1412.1632.pdf, 2014 engineering, technology & applied science research vol. 9, no. 4, 2019, 4423-4427 4427 www.etasr.com khan et al.: towards achieving machine comprehension using deep learning on non-gpu machines [16] a. finch, y. s. hwang, e. sumita, “using machine translation evaluation techniques to determine sentence-level semantic equivalence”, third international workshop on paraphrasing, jeju island, korea october 14, 2005 [17] k. cho, b. v. merrienboer, c. gulcehre, d. bahdanau, f. bougares, h. schwenk, y. bengio, “learning phrase representations using rnn encoder-decoder for statistical machine translation”, conference on empirical methods in natural language processing, doha, qatar, october 25-29, 2014 [18] j, pennington, r. socher, c. d. manning, “glove: global vectors for word representation”, conference on empirical methods in natural language processing doha, qatar, october 25-29, 2014 microsoft word 02-3608_s_etasr_v10_n4_pp5875-5881 engineering, technology & applied science research vol. 10, no. 4, 2020, 5875-5881 5875 www.etasr.com chaoui et al.: effect of starch nanocrystals on the properties of low density polyethylene/thermoplastic... effect of starch nanocrystals on the properties of low density polyethylene/thermoplastic starch blends saliha chaoui department of chemical engineering university ferhat abbas of setif 1 setif, algeria salihachaoui@yahoo.fr abdelhak hellati faculty of science and technology med bachir el ibrahimi university bordj bou arreridj, algeria hellati_abdelhak@yahoo.fr dalila smail department of chemical engineering university ferhat abbas of setif 1 setif, algeria dalila.smail@yahoo.fr djafer benachour department of ehemical engineering university ferhat abbas of setif 1 setif, algeria bendjafer@univ-setif.dz abstract-in this study, low density polyethylene (ldpe) and thermoplastic starch (tps) reinforced with different amounts of starch nanocrystals (sncs) with and without dicumyl peroxide (dcp) were blended in an internal mixer. the xrd results showed that crystallinity decreases with increasing snc content with and without dcp. tensile test results showed that elongation at breaking, tensile strength, and elastic modulus are lower than that of neat ldpe, whereas, the elastic modulus for the ldpe/tps/snc5%/dcp is higher than that of ldpe. afm showed a decrease in the roughness of the surface after the addition of snc and the surface become less rough after dcp addition. keywords-nanocomposites; thermoplastic starch; ldpe; starch nanocrystals; dcp i. introduction environmental pollution from consumed polymers has become a serious global concern. this type of pollution comes mainly from plastic waste, particularly from packaging materials, offset plastic bags, bottles, cups, etc. [1]. considerable efforts are being directed towards developing biodegradable composites using renewable resources in an attempt to replace petroleum-based plastics with more sustainable materials [2, 3]. starch is one of the most promising materials that can remedy these problems and improve the properties of plastic packaging materials. experience has shown that it is possible to transform native starch into thermoplastic resin products under deformation and plasticization conditions. unfortunately, thermoplastic starch (tps) is a very hydrophilic material with limited performance. to overcome this difficulty and maintain its biodegradability, one strategy is to combine plasticized starch with another biodegradable polymer [4]. to decrease the brittleness of biodegradable plastics, another approach is to blend thermoplastic starch with synthetic materials such as lldpe, hdpe, pp and others. synthetic materials have advantages such as high mechanical properties. polyethylene (pe) is one of the most widely produced non-biodegradable polymers, and different types of pe are commonly used in many fields. the main sectors are food packaging products and garbage bags [5]. biodegradable plastics made from blends of tps/synthetic materials have little compatibility with hydrophilic starch and hydrophobic synthetic polymers. in order to achieve compatibility between these two fractions, compatibilizers can be added to reduce the interfacial energy and homogenize the polar starch with the synthetic polymer. compatibilizers can act by reactive process, for example grafting techniques or hydrogen bonding based on the polarity of the material. among these, maleic anhydride, succinic anhydride and acid acrylate are the most widely used compatibilizers [6]. with the development of biodegradable materials, polysaccharides and nanocrystals/nanoparticles in particular, are attracting more scientific interest. these materials are among the more promising sources for the production of nanoparticles mainly due to their semi-crystalline structure. starch is a promising candidate for the production of nanoparticles because it has a semi-crystalline structure that confers some interesting properties [2]. over the last decade, starch nanocrystals (sncs) have attracted a growing interest due to not only their nano-scaled size but also their renewable and biodegradable nature. the availability of reactive hydroxyl groups on the surface of the freeze-dried powders was essential for the chemical modification of the sncs. most studies have only focused on the use of sncs as reinforcing agents for polar polymers. sncs have been used as filler for latex of natural rubbers (nrs). it is shown that up to a content of 20wt % this new filler presents the advantage to reinforce nrs without corresponding author: saliha chaoui engineering, technology & applied science research vol. 10, no. 4, 2020, 5875-5881 5876 www.etasr.com chaoui et al.: effect of starch nanocrystals on the properties of low density polyethylene/thermoplastic... decreasing significantly the elongation at break of the material [7]. sncs prepared by acid hydrolysis of native granules were used as a reinforcing agent in a thermoplastic waxy maize starch matrix plasticized with glycerol. sncs have showed a reinforcing effect which can be attributed to strong filler/filler and filler/matrix interactions due to the establishment of hydrogen bonding. the presence of sncs slows down the recrystallization of the matrix during aging in humid atmosphere [8]. poly(îµ-caprolactone) (pcl) was grafted to the surface of sncs via microwave-assisted ring-opening. the resultant nanoparticles were then incorporated into a poly(lactic acid) matrix to produce fully-biodegradable nanocomposites. a loading level of 5wt% snc-g-pcl resulted in simultaneous enhancements of strength and elongation. the snc-g-pcl self-aggregated as rubbery microparticles to enhance elongation. meanwhile, the grafted pcl chains were miscible with pla and formed a stress-transferring interface to the sncs, providing a reinforcing function [9]. thermoplastic starch (tps) films were prepared with normal maize starch matrix using glycerol, d-isosorbide and 1,3-propanediol as plasticizers. tps nanocomposite films were prepared using normal maize starch matrix plasticized with glycerol filled by waxy starch nanocrystals (wsncs) and cellulose nanocrystals (cncs). the results suggested that effective interfacial hydrogen bonding interactions were achieved by extrusion/compression processing, obtaining tensile strength, strain at break and young’s modulus increments higher than 100% for nanocomposites reinforced by only 1wt% of polysaccharide nanocrystals, either with only wsnc or with combinations of wsncs/cncs in different ratios [10]. there are only a few studies available on the use of sncs as reinforcing agents for nonpolar polymers, especially for polyolefins. three types of starch were converted into nanoparticles for the purpose of modifying the matrix of lowdensity polyethylene (ldpe) in order to enhance its biodegradability. authors in [11] outline the process of the synthesis and characterization of starch nanoparticles from three different starch sources. the utilized kinds of starch were: zea mays (corn), ipomoea batatas (potato), and manihot esculenta (cassava). in [12], starch nanoparticles (snps) were synthesized and used as fillers to prepare high density polyethylene (pe) composites by in situ polymerization. the effect of these particles on thermal degradation, isothermal and nonisothermal crystallization, and photodegradation of pe has been studied. snps decreased the thermal degradation temperature of pe and increased the relative crystallinity and crystallization rate under isothermal conditions. the composite pe/snp showed the nucleating effect of snps. this nucleating agent effect was confirmed by nonisothermal crystallizations as composites presented higher crystallization temperatures than neat pe. the photodegradation tests showed that nps promoted the polymer degradation by forming cavities at the np/pe interface. based in [12], where pe/snps in situ polymerization was investigated, we aim to determine the influence of various amounts of snc incorporation in ldpe/tps blends in the presence of a low amount of dcp. ldpe/tps blend has mediocre mechanical properties, the dcp is added to create some crosslinking in the ldpe matrix and therefore to overcome the weakness of ldpe/tps composites. the structural, morphological, and tensile properties of different samples were examined using ftir analysis, x-ray diffraction (xrd), tensile properties, and afm imaging. until now, no scientifics work has been focused on the study of the ldpe/tps/snc/dcp system. ii. materials and methods a. materials the materials studied were ldpe supplied by sabic society (saudia arabia), with a melt flow index (mfi) of 0.8g/10min at 190°c and a density of 0.92g/cm3. corn starch (supplied by roquette firm, with a density of 1.46g/cm3 and 13µm average size) initially composed of 23% amylose and 77% amylopectine, was used as degradable component. glycerol (with a density of 1.25g/cm3) was used as plastizer for starch. the peroxide used is dcp provided by acros, belgium. it is a white powder, and its decomposition temperature is 140°c. b. preparation of thermoplastic starch (tps) plastized starch (pls) was prepared according to the following experimental protocol [13]: pls formulation used was composed of 23wt % of glycerol, 23wt% of distilled water and 54wt% of starch. first, the starch was introduced into a turbo mixer, and then water was gradually added during stirring. in the second step, glycerol was gradually added during stirring. after the complete addition of glycerol, the mixture was mixed at high speed to obtain a homogeneous dispersion. the resulting mixture was placed in an oven at 170°c for 40 minutes in order to evaporate water and to facilitate plasticizer diffusion into starch grains. tps was prepared by melting processing in an internal mixer at 140°c. c. preparation of starch nanocrystals sncs were prepared by acid hydrolysis. native starch (147g) was dispersed in a 1l sulfuric acid (h2so4) solution (3.16m) at 300rpm and 40°c. after three days of hydrolysis, the process was finished. the insoluble residue was washed by successive centrifugations with distilled water for 10 min at 10000rpm until neutral ph was obtained. the precipitate containing starch crystals was dried and crushed [14]. d. sample preparation ldpe, tps, sncs and dcp were mixed together as dry mixtures. they were melt blended in one step in an internal mixer (plasti-corder) at 140°c with rotor speed of 50rpm for 10min. tps and dcp contents were fixed at 30% and 0.2% (wt%) respectively for all formulations. snc amount varied from 1, to 3 and 5wt%. the ldpe/tps/snc nanocomposites were prepared with different concentrations of sncs with and without dcp. the various studied formulations are summarized in table i. e. films preparation concerning the different characterizations, after preheating and degassing, the samples are compressed at 140°c for 5min using a polylab hydraulic press. the obtained films were engineering, technology & applied science research vol. 10, no. 4, 2020, 5875-5881 5877 www.etasr.com chaoui et al.: effect of starch nanocrystals on the properties of low density polyethylene/thermoplastic... cooled to ambient temperature. the thickness of the films was ~0.2mm. table i. sample codes and compositions sample code ldpe (wt%) tps (wt%) snc (wt%) dcp (wt%) ldpe 100 0 0 0 ldpe/tps 70 30 0 0 ldpe /tps/snc% 69 30 1 0 ldpe/tps/snc3% 67 30 3 0 ldpe/tps/snc5% 65 30 5 0 ldpe/tps/snc1%/dcp 68.8 30 1 0.2 ldpe/tps/snc3%/dcp 66.8 30 3 0.2 ldpe/tps/snc5%/dcp 64.8 30 5 0.2 f. characterization 1) ftir analysis the absorbance spectrums (ftir) of prepared films were recorded in a perkin-elmer fourier transform infrared spectrometer working in transmission and reflection. the spectra were obtained with a resolution of 4cm-1 for field study from 4000 to 450cm-1. 2) water absorption water uptake was carried out on specimens using square films (1cm×1cm) with around 0.2mm thickness. after being weighed, the samples were immersed in distilled water. at different times, they were removed from water, their surface was dried on paper, and the amount of the absorbed water by the samples was determined by weighting them periodically, until equilibrium of a constant weight was obtained. the water uptake (w%) was given by: ��%� � ��� � �� � � 100 (1) where, wt is the weight of the sample at time (t) after immersion, and w0 its initial weight before immersion. 3) xrd analysis all the film samples were analyzed by xrd using a philips diffractometer. the following conditions were employed: cu k radiation, angular range (2θ) 2°–43°, and scan rate 0.05°/s. crystallinity was calculated by dividing the area of crystalline phase with the total area of the xrd diffractograms of the sample. 4) mechanical properties the samples were prepared for tensile tests according to astm 638-72. tensile strength, young’s modulus, and elongation at break were measured. the tests were performed at a cross-head speed of 20mm/min using an mts model lps.504 machine. 5) atomic force microscopy imaging atomic force microscopy (afm) was also used to explore the surface state of the resulting samples by imaging their morphologies. this characterization was carried out using a pacific nanotechnology type atomic force microscope in noncontact mode. iii. results and discussion a. ftir analysis figures 1 and 2 show the ftir spectra of pure ldpe, ldpe/tps blend and ldpe/tps/snc nanocomposites at different snc contents with and without dcp. ldpe spectra show characteristic bands at 2980 cm−1 and 2830 cm−1 which correspond to asymmetric and symmetric c-h stretching vibrations respectively (figure 1). the sharp peak at 1462cm-1 and the peak at 720cm-1 also indicate the c-h bending and c-c rocking deformation vibrations [15]. ldpe/tps spectra show characteristic bands of saccharides localized between 950 and 1200cm-1. they are characterized by stretching vibrations of cc and c-o bands present in amylose and amylopectin [16]. a wide band can be seen between 3100 and 3600cm-1 corresponding to the vibration of o-h group [16]. a peak localized around 1650cm-1 is attributed to stretching vibrations of the o-h bond of absorbed water. in the ftir spectra of ldpe/tps/snc nanocomposites at different contents of snc without dcp, all characteristic peaks of ldpe and starch were observed (figure1). the intensities of characteristic peaks of the ldpe were decreased by increasing snc content in the nanocomposites without dcp. in figure 2(a), a decrease in the intensities of ldpe peaks was observed. the characteristic peaks of dcp (1700-1740cm-1) did not appear on the nanocomposite spectra, maybe due to the low concentration of dcp (0.2wt%). no displacement of the peaks was observed for all nanocomposites. fig. 1. ftir spectra of ldpe, ldpe/tps blend and ldpe/tps/snc nanocomposites without dcp. fig. 2. ftir spectra of ldpe, ldpe/starch blend and ldpe/tps/snc nanocomposites with dcp. engineering, technology & applied science research vol. 10, no. 4, 2020, 5875-5881 5878 www.etasr.com chaoui et al.: effect of starch nanocrystals on the properties of low density polyethylene/thermoplastic... b. water abortion figure 3 shows the evolution of swelling ratio (w%) for the ldpe/tps blend and ldpe/tps/snc nanocomposites at 1, 3 and 5wt% of sncs with and without dcp. fig. 3. water uptake ratio of the ldpe/tps blend, ldpe/tps/snc nanocomposites with and without dcp. the kinetics of water uptake for all samples increased linearly with time in the initial step until the equilibrium was reached at about 20min after the immersion in distilled water. ldpe/tps blend showed the lower water uptake compared to the other samples. this behavior is due to the hydrophilic nature of tps, which is responsible for the water absorption in the blend. water molecules interacted with the hydroxyl groups of starch and saturated the surface through voids at a short swelling time [17]. the water uptake of the ldpe/tps/snc nanocomposites increased at equilibrium state compared to the ldpe/tps blend with increasing snc content. this was probably caused by the increasing starch content, since the sncs are starch-based. the percentage of water uptake for the ldpe/tps/snc/dcp nanocomposites increased more than those without dcp. this can be explained by the increasing of the voids caused by dcp after chains scission and crosslinking. c. xrd analysis figure 4 shows the diffractograms of native starch sncs. native starch showed crystalline pattern a with three strong peaks (2θ) at 15.4°, 17.1°, and 23.3°. after acid hydrolysis treatment, there were significant changes in the diffraction pattern of sncs [1]. the results showed that snc peaks have higher intensity than those of native starch with a new peak appearing at 26.8°. the higher intensity of diffraction peak indicates that snc crystallinity has been increased by acid hydrolysis [18]. the crystallinity values (determined from the xrd patterns) were estimated as 56% and 62% for native starch and sncs respectively [19]. figure 5 shows the x-ray diffractograms of neat ldpe, ldpe/tps blend and the ldpe/tps/snc nanocomposites at 1, 3 and 5wt% of sncs without dcp. the x-ray diffractogram of the ldpe reveals a crystal lattice showing the diffraction characteristic peaks at the 2θ equal to 21.56° and 23.87°. the superposition of the ldpe spectrum with those of ldpe/tps blend and the nanocomposites containing 1, 3, and 5wt% of snc, showed a diminution in the intensity of characteristics peaks of ldpe with increased amounts of sncs. table ii shows a decrease in the degree of crystallinity for ldpe/tps /snc by increasing snc content indicating that snc particles do not act as nucleating agents. in contrast to our result, an increase in crystallinity of ldpe was observed for ldpe/snc composite after snc addition using in situ polymerization[12]. fig. 4. x-ray diffractograms of native starch and its sncs. fig. 5. x-ray diffractograms of ldpe/tps blend and ldpe/tps/snc nanocomposites at various snc contents without dcp. fig. 6. x-ray diffractograms of ldpe/tps blend and ldpe/tps/snc nanocomposites at various snc content with dcp. engineering, technology & applied science research vol. 10, no. 4, 2020, 5875-5881 5879 www.etasr.com chaoui et al.: effect of starch nanocrystals on the properties of low density polyethylene/thermoplastic... figure 6 shows the x-ray diffractograms of ldpe/tps/snc/dcp nanocomposites at different snc levels in presence of dcp. a decrease in the intensity of characteristics peaks of ldpe is observed after the dcp addition. a diminution in the degree of crystallinity is also observed after the dcp addition (table ii). this is probably due to some crosslinking of ldpe by dcp, which can be considered as deficiencies center and hindered folding of macromolecular chains [17, 18]. this behavior led to a decrease in crystallinity. this behavior is also observed in [2022]. table ii. crystallinity sample code crystallinity ldpe 54 ldpe/tps 50 ldpe/tps/snc1% 50 pebd/tps/snc3% 40 pebd/tps/snc5% 48 pebd/tps/snc1%/dcp 45 pebd/tps/snc3%/dcp 43 pebd/tps/snc5%/dcp 34 d. tensile properties figures 7 and 8 show the evolution of elongation at break and of the tensile strength of the ldpe/tps blend and ldpe/tps/snc nanocomposites as a function of snc amount with and without dcp. ldpe/tps blend exhibited a decrease in tensile properties compared to neat ldpe. this can be explained by the incompatibility between ldpe and tps caused by the difference in their hydrophobic and hydrophilic character respectively. a significant decrease in tensile strength and elongation at break was observed for ldpe/tps/snc nanocomposites at 1, 3, and 5wt% snc with and without dcp compared to pure ldpe (figures 7-8). this result (summarized in table ii) suggests that snc did not act as nanocomposite reinforcing agent. according to [12], snc can create cavities in the ldpe due to the difference in the results in the deterioration of mechanical properties. this result confirmed the crystallinity decrease (measured by drx). the addition of dcp for the ldpe/tps/snc/dcp nanocomposites at different amounts of snc (figures 7-8) added more cavities which are attributed to some crosslinking provoked by dcp. these cavities lead to the diminution of crystallinity and therefore to the decrease of tensile properties [23]. figure 9 shows the effect of snc content on the elastic modulus of ldpe/tps/snc nanocomposites at different snc amounts, with and without dcp. it could be noted that the elastic modulus decreases at 1wt% of snc and increases at 3wt%, but remained lower than ldpe modulus, whereas at 5wt% of snc it is slightly superior to that of pure ldpe. the values of elastic modulus for all nanocomposites with dcp are slightly superior to those without dcp. this increase in the elastic modulus for the ldpe/tps/snc5%/dcp nanocomposite can be related to the snc agglomeration [24] (because of the high amount of snc (5wt%) ). filler-filler interactions become more significant than the filler–matrix interactions [25] or the reduction in polymer chains mobility in the presence of the filler [26]. fig. 7. elongation at break evolution of ldpe and ldpe/tps/snc nanocomposites at different snc contents with and without dcp. fig. 8. tensile strength evolutions of ldpe and and ldpe/tps/snc nanocomposites at different snc content with and without dcp. fig. 9. elastic modulus evolution of ldpe and ldpe/tps/snc nanocomposites at different snc content with and without dcp. e. afm imaging the morphological aspect was evaluated by afm. figure 10 shows the surface images of neat ldpe, ldpe/tps/snc5 engineering, technology & applied science research vol. 10, no. 4, 2020, 5875-5881 5880 www.etasr.com chaoui et al.: effect of starch nanocrystals on the properties of low density polyethylene/thermoplastic... nanocomposite of 5wt% snc without dcp and ldpe/tps/snc5/dcp nanocomposites of 5wt% snc with dcp. the film surface of ldpe is rigorous and dense which appeared well on the surface (figure 10(a)). as the tps and sncs were added to ldpe for the nanocomposite ldpe/tps/snc5% (figure 10(b)) the density of roughness decreased. since the sncs present a platelet -likeshape, a packet of sticks is observed on the film surface. the presence of dcp in the nanocomposite ldpe/tps/snc5/dcp (figure 10(c)) makes the surface smooth. the decrease in the film surface roughness in the presence of snc and dcp may be caused by the decrease of density and crystallinity (measured by xrd) and was confirmed by the decrease in the tensile properties. fig. 10. afm images of the surface of (a) neat ldpe, (b) ldpe/tps/snc5 nanocomposite with 5% of snc, and (c) ldpe/tps/snc5/dcp nanocomposite with 5% of snc in the presence f dcp. iv. conclusion in this work, ldpe/tps/snc nanocomposites reinforced with various amounts of snc with and without dcp were prepared with an internal mixer. structural tests showed that the crystallinity of ldpe/tps/snc nanocomposites decreased with increasing snc content and decreased even more after dcp addition. water uptake test showed an increase in water absorption by increasing snc amount, whereas the dcp addition provoked more increasing of this property. ftir analysis showed a decrease in the intensity peaks of ldpe/tps/snc with increasing snc content with and without dcp. the afm showed that the snc and dcp decreased the roughness of the nanocomposite surface. tensile results showed that the elongation at break of the nanocomposites decreases sharply with increasing snc content. the same behavior was noted in tensile strength and elastic modulus, whereas young's modulus of the ldpe/tps/snc5%/dcp was slightly higher than that of the pure ldpe. afm imaging showed a decrease in roughness and surface density after the addition of snc and dcp. references [1] k. piyada, s. waranyou, and w. thawien, “mechanical, thermal and structural properties of rice starch films reinforced with rice starch nanocrystals,” 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[26] j. gu, h. xu, and c. wu, “the effect of pp and peroxide on the properties and morphology of hdpe and hdpe/pp blends,” advances in polymer technology, vol. 32, no. 1, 2013, doi: 10.1002/adv.21326. microsoft word 88-263-1-proofed-2.doc etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 162-166 162 www.etasr.com tripathy and panigrahi – simulation studies on switching table based dtc and fuzzy rule based dtc… simulation studies on switching table based dtc and fuzzy rule based dtc for three-phase squirrel cage induction motor pradeep ranjan tripathy department of electrical engineering kalinga polytechnic, kiit bhubaneswar, india pradeeptripathy_10@yahoo.co.in bibhu prasad panigrahi department of electrical engineering indira gandhi institute of technology, sarang dhenkanal, odisha-759146, india bibhu89@yahoo.com abstract—this paper describes a study of switching table direct torque control (st-dtc) and fuzzy rule based direct torque control (fr-dtc) in case of a three phase induction motor. the hysteresis band and the switching table used in the st-dtc scheme have been replaced by a fuzzy rule based controller in the fr-dtc. results show that the fr-dtc method provides better transient performance compared to the st-dtc method. keywordsst-dtc; vsi; hysterisis band; three level control signal; fuzzy controller; gaussian; sigmoid; d-sigmoid; membership functions i. introduction induction motors with conventional control used in common industrial drives are not capable of providing fast and smooth torque variation, due to the inherent characteristics of the induction motor, including complex, non-linear, time varying dynamics and inaccessibility of some states and outputs. safety concerns regarding dc motors helped induction motors to gain industrial acceptance, especially after the introduction of field oriented control (foc) in the 1970s. this scheme decouples the stator current into the torque producing and flux producing components. these components are controlled like a separately excited dc motor. the method is complex, due to the reference frame transformation and the dependence on machine parameters. the torque control was simplified with the introduction of the dtc scheme in the 1980s. the dtc method does not require transformation, as the foc method did, and stator resistance is sufficient to estimate the stator flux and torque. to increase or decrease the output torque, the torque angle is required to be increased or decreased respectively, while stator linked flux is kept intact at desired magnitude [1-9]. the change in the torque angle is performed by acceleration or deceleration of the angular speed of the stator linked flux vector by selecting the optimum voltage vector, which is selected from the switching table based on the flux and torque errors. however, implementing this method using high speed processors with multiple a/d converters is rather costly, especially in case of small scale industries [10, 11]. in such cases, the low cost analog st-dtc control for single quadrant operation [11, 12] is considered much more cost effective. the speed and torque can also be controlled for forward and reverse motoring operation, as previously reported by the authors [12]. the present simulation study aims to compare the torque response and ripple content of st-dtc and fr-dtc. the proposed scheme replaces the flux and torque hysteresis bands and the switching table of the st-dtc scheme with a fuzzy rule based controller and, as shown, provides better results. it should be noted that both methods can be implemented using low cost discrete electronic components. ii. principle of st-dtc the three phase motor terminal voltages and line currents are sensed and transformed to d-q stationary frame as shown in figure 1. induced emfs are calculated after compensating the resistance drop from line voltage. the stator flux components ψds and ψqs are calculated by integrating the induced emfs. the torque is calculated using the flux and current components. the absolute flux and calculated torque are compared with the reference or command signal to generate the flux error and the torque error signals. the instantaneous angular position of the stator flux in space, is determined digitally using a switching table as depicted in table i. since the air gap space is divided into six sectors each spreading 60 0 , the absolute value of ψqs/ψds is compared with tan60 0 . signal a equals 1 when absolute value of the ratio (ψqs/ψds) is greater than or equal to tan60 0 , otherwise it equals 0. digit ‘0’ denotes the negative sign and digit ‘1’ denotes the positive sign. thus the sector is determined and the third controlled signal sθ is generated. the torque error and flux error signals are compared in terms of their respective hysteresis bands, a three level control signal st is obtained for torque and a two logic control signal sλ is obtained for flux. the three control signals are used as inputs to a look-up table, as shown in table ii, which decides the switching pattern of the voltage source inverter (vsi). etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 162-166 163 www.etasr.com tripathy and panigrahi – simulation studies on switching table based dtc and fuzzy rule based dtc… fig. 1 block diagram for st-dtc control of 3 phase im table i. sector determination ψds ψqs a sθ 0 0 0 <5> 0 0 1 <4> 0 1 0 <6> 0 1 1 <1> 1 0 0 <3> 1 0 1 <4> 1 1 0 <2> 1 1 1 <1> table ii dtc switching table sψ st sθ <1> <2> <3> <4> <5> <6> 1 1 110 100 101 001 011 010 1 0 111 000 111 000 111 000 1 -1 101 001 011 010 110 100 0 1 010 110 100 101 001 011 0 0 000 111 000 111 000 111 0 -1 001 011 010 110 100 101 iii. principle of fr-dtc in the fr-dtc scheme, the hysteresis bands creating the torque and flux control logic signals are replaced by a fuzzy rule based controller as shown in figure 2. the switching look up table is realized using fuzzy rules. the fuzzy controller proposed here has been designed so as to use three fuzzy state variables as inputs and three control outputs to achieve the switching pattern for the vsi. the three fuzzy state variables inputs are flux error, torque error and the angular position of the stator flux. the absolute flux is compared with the rated flux of the three-phase induction motor (0.5606 wb) to obtain the flux error. the six voltage vectors (differential stator flux) for any specific positioned stator flux indicate either increase or decrease of the stator flux for flux control. thus, flux errors are identified by three state variables chosen as membership functions. the membership function n intends to decrease the flux, p intends to increase it and z denotes no change in stator flux. the membership functions used are gaussian, sigmoid and d-sigmoid functions as shown in figure 3. fig. 2 fuzzy dtc controlled 3 phase induction motor fig. 3 membership functions for flux error fig. 4 membership functions for torque error fig. 5 membership function for 12 angular dwelling instants of flux the torque error is calculated by comparing the calculated electromagnetic torque with the desired command torque. considering the stator flux to dwell in the first 60 0 in the air gap space and assuming the torque and flux errors to be positive, the demanding voltage phasor will tend to increase the torque. the voltage demand can be satisfied with voltage phasor in sector i or vi. if the flux is in first 30 0 of sector i, then any of the above voltage vectors can meet the purpose. etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 162-166 164 www.etasr.com tripathy and panigrahi – simulation studies on switching table based dtc and fuzzy rule based dtc… when it is in the second 30 0 , the voltage phasor corresponding to sector vi of sextant provides the advancement of the flux vector. the torque error state-variable is chosen in five states as rapid increase, increase, no action, decrease and rapid decrease. the membership functions are a combination of gaussian, sigmoid and d-sigmoid membership functions as shown in figure 4. the angular dwelling position of stator flux is defined in twelve zones, spreading for π/6 radian each in the sextant. the angular position θ is defined as d q1 ψ ψ tan − . the range has been chosen from –π/2 to 3π/2 in twelve equal sub sectors for selecting the membership functions for stator flux position. each sextant has been divided into two sub sectors to yield accurate judgments regarding the call of appropriate voltage phasor in direct torque control as shown in figure 5. the controlled output of the fuzzy controller gives the inverter switching states. in the three phase voltage source inverter eight switching vectors are possible. the controller uses three input state variables and three crisp outputs using a proposed 180 rule table. mamdani method is used for defuzzification. iv. simulation study the st-dtc and fr-dtc schemes were simulated using the matlab simulink environment, employing a 3-phase induction motor with the following parameters: 3hp, 220v, 50hz, rs=0.435ω, lls=2mh, rr ’ =0.816ω, llr ’ =2mh, lm=69.31mh, moment of inertia j=0.00089 kg·m 2 , friction constant f=0.0001 and number of poles per phase p=4. in each case the line voltage and line current supplied to the stator are sensed and transformed to d-q components. the emf is calculated after compensating for the resistance drop, then d-q flux is derived which helps to calculate the electromagnetic torque and the stator flux position. the calculated torque and the absolute flux are compared with their respective command values in order to obtain the error. the simulation has been performed for two quadrant operation. the torque command for the first 0.1 second is 100% of the base value, then it changes to -30% till the 0.15 second, and then returns back to the base value. the errors are processed with respective hysteresis bands in order to obtain two control signals with the third signal being the position of flux, which in st-dtc are judged by a look up table to decide the switching vectors of vsi. in fr-dtc each of the two errors and the flux position is represented with three input membership functions of a fuzzy rule based controller. the controller uses 180 newly defined rules. mamdani method has been used here to obtain the crisp output to be used as a switching vector for the vsi. v. results and discussion the x-y plots for d-q flux for both schemes are depicted in figures 6a and 6b which shows that the circular shape and the magnitude matches the base flux value of the machine. the d-q flux loci plotted against time as depicted in figures 7a and 7b for st-dtc and fr-dtc are shown for two quadrant operation. the q-axis flux lags the d-axis flux in forward motoring mode, while its reverse takes place in reverse motoring. a b fig. 6 a. d-q flux in st-dt b. d-q flux in fuzzy dtc a b fig. 7 a. ψq , ψd vs time in st-dtc b. ψq , ψd vs time in fuzzy dtc etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 162-166 165 www.etasr.com tripathy and panigrahi – simulation studies on switching table based dtc and fuzzy rule based dtc… absolute flux and angular position of stator flux versus time for both schemes are shown in figures 8a and 8b. the upper plotting in each figure shows the absolute flux. the flux in both cases attains its steady value (0.56 wb). in comparison to the st-dtc scheme the flux reaches its steady value much quicker in the fr-dtc scheme. in the first scheme the time taken is 0.0175 sec, where in the latter it is only 0.004 sec. as observed in the angular position of stator flux shown in figure 8b, instant rotation of flux is obtained while the motor is commanded from forward motoring to reverse motoring in frdtc. it is further found that fr-dtc responds faster to changes in torque command. figures 9a and b depict the change in forward motoring to reverse motoring for both schemes. the graph plotted is the superimposed graph of torque command and resulting torque in falling mode. the time taken to respond to the command in the st-dtc scheme is 0.00004 seconds whereas in the fr-dtc scheme is 0.000025 seconds. the rising mode is depicted in figures 10a and b. the resulting rising torque attains the command value in 0.00005 seconds for the st-dtc scheme and in 0.000033 seconds for the fr-dtc scheme. vi. conclusion a simulation study was performed for st-dtc scheme and the proposed fr-dtc scheme. the basic objective of the dtc scheme is to obtain fast response to changes in torque command. it is shown that the fr-dtc scheme offers faster transient response to torque changes. the ripple content in the resulting torque in the fr-dtc can be minimized by further refining the tuning of the input membership functions. a b fig. 8 a. |ψ| and stator flux position vs time in st-dtc b. |ψ| and stator flux position vs time in fr-dtc a b fig. 9 a. falling mode t* and te superimposed in st-dtc b. falling mode t* and te superimposed in fr-dtc a b fig. 10 a. rising mode t* and te superimposed in st-dtc b. rising mode t* and te superimposed in fuzzy-dtc references [1] f. blaschke, “the principle of field-orientation as applied to the trans vector closed-loop control system for rotating-field machines”, siemens review, vol. 34, pp. 217-220, 1972 [2] m. depenbrock, “direct self-control (dsc) of inverter – fed induction machine”, ieee transactions on power electronics, vol. 3, no. 4, pp. 420-429, 1988 [3] i. takahashi, y. ohmori, “high performance direct torque control of an induction motor”, ieee transactions on industry applications, vol. 25, no. 2, pp. 257-264, 1989. [4] t. g. habetler, f. profumo, m. pastorelli, l. m. tolbert, “direct torque control of induction machines using space vector modulation”, ieee transactions on industry applications, vol. 28, no. 5, pp. 1045–1053, 1992 [5] u. baader, m. depenbrock, g. gierse, “direct self control (dsc) of inverter fed induction machine: a basis for speed control without speed etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 162-166 166 www.etasr.com tripathy and panigrahi – simulation studies on switching table based dtc and fuzzy rule based dtc… measurement”, ieee transactions on industry applications, vol. 28, no. 3, pp. 581-588, 1992 [6] d. casadei, g. serra, a. tani, “implementation of a direct torque control algorithm for induction motors based on discrete space vector modulation”, ieee transactions on power electronics, vol. 15, no. 4, pp. 769–777, 2000 [7] f. zidani, r. nait said, “direct torque control of induction motor with fuzzy minimization torque ripple”, journal of electrical engineering, vol. 56, no. 7-8, pp. 183–188, 2005 [8] f. zidani, d. diallo, m. e. h. benbouzid, r. nait said, “direct torque control of induction motor with fuzzy stator resistance adaptation”, ieee transaction on energy conversion, vol. 21, no. 2, pp. 619-621, 2006 [9] m. vasudevan, r. arumugam, “high performance adaptive intelligent direct torque control schemes for induction motor drives”, kmitl science and technology journal. vol. 5. no. 3, pp. 559-576, 2005 [10] b. p. panigrahi, d. prasad, s. sengupta, “digital simulation and pc based implementation of switching table based direct torque control of induction motor drive”, iit conference, kharagpur, pp. 1–6, 2005 [11] b. p. panigrahi, d. prasad, s. sengupta, “a simple hardware realization of switching table based direct torque control of induction motor”, electric power systems research, vol. 77, no. 2, pp. 181–190, 2007 [12] p. r. tripathy, b. p. panigrahi, “simulation study on dtc based induction motor drives using matlab”, ieee proceedings of indicon, india, vol. 1, pp. 65-68, 2008 microsoft word 26-2866_s_etasr_v9_n4_pp4457-4462 engineering, technology & applied science research vol. 9, no. 4, 2019, 4457-4462 4457 www.etasr.com bhatti et al.: active contours using harmonic global division function active contours using harmonic global division function muhammad tarique bhatti department of mechanical engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan trqbhatti@quest.edu.pk ahsin murtaza bughio department of electronics engineering, quaid-e-awam university of engineering science & technology, nawabshah, pakistan ahsan.murtaza@quest.edu.pk ali anwar department of electronics engineering, quaid-e-awam university of engineering science & technology, nawabshah, pakistan alianwer@quest.edu.pk toufique ahmed soomro department of electronics engineering, quaid-e-awam university of engineering science & technology, nawabshah, pakistan etoufique@yahoo.com muhammad afzal soomro department of mathematics and statistics, quaid-e-awam university of engineering science & technology, nawabshah, pakistan m.a.soomro@quest.edu.pk shafiullah soomro department of basic science and related studies, quaid-e-awam university of engineering science & technology, nawabshah, pakistan s.soomro@quest.edu.pk abstract—this paper presents the region-based active contours method based on the harmonic global signed pressure force (hgspf) function. the proposed formulation improves the performance of the level set method by utilizing intensity information based on the global division function, which has the ability to segment out regions with higher intensity differences. the new energy utilizes harmonic intensity, which can better preserve the low contrast details and can segment complicated areas easily. a gaussian kernel is adjusted to regularize level set and to escape an expensive reinitialization. finally, a set of real and synthetic images are used for validation of the proposed method. results demonstrate the performance of the proposed method, the accuracy values are compared to previous state-ofthe-art methods. keywords-image segmentation; active contours; hgspf function i. introduction segmentation is a technique to isolate particular image regions having a variety of uses in image processing and computer vision [1]. images with feeble edges, noise, and obscured boundaries have some regarding this aspect. in manual segmentation, human mistakes can deliver more false results, so, a computer-based system is required, which can bolster experts and radiologists to partition accurate tumor muscles or true regions [2]. a few techniques have been proposed regarging the image segmentation issue. authors in [3] proposed an underlying contour based procedure for separating objects in an image. active contour image segmentation is a strategy, in which an implicit curve is deformed using some minimization procedure until it achieves the ideal boundary. there are two significant groupings of active contour techniques, which are edge based strategies [46] and region based techniques [7-14]. edge based procedures set up an edge force by using the edge data of an image, which turn towards the required boundaries. these models do not accomplish right segmentation on images with weak and obscured boundaries. region based methods use image pixel information and develop region based force terms, which divide the pixels inside an image. the work in [9] is viewed as the most utilized model for global region based segmentation. this strategy is not suitable for unclear boundaries and images which have intense pixel contrast and complicated background variations. to minimize such problems, authors in [8] proposed an altered global region based technique, which utilizes four intensity means for pixel regions across the image. due to the impact of global division algorithim, this technique enhances segmentation. authors in [7] proposed a strategy which utilizes global pixel data from [9] and builds up a spf (signed pressure force) function. also, it utilizes a gaussian kernel to regularize a level set function in each cycle. a modified spf method was formulated in [15] using harmonic means instead of arithmetic. this method reduces the approximation error of the previous methods. motivated by [7, 8, 15], we propose a novel harmonic global signed pressure force (hgspf) function. hgspf function utilizes global division and harmonic intensity information in its design. it yields better results over images having complicated intensity information and/or low contrast. moreover, a gaussian filter has been induced to regularize level set and to overcome the need of level set reinitialization. the proposed strategy is validated over synthetic and real images. the results are compared in terms of accuracy, which indicates the effectiveness of the proposed method compared to previous state of the art methods. ii. related work authors in [9] proposed a mainstream global intensity technique in the light of [16]. this technique relies upon corresponding author: shafiullah soomro engineering, technology & applied science research vol. 9, no. 4, 2019, 4457-4462 4458 www.etasr.com bhatti et al.: active contours using harmonic global division function gradient based segmentation techniques. lets suppose an image :i rω ⊂ with a level set : rφ ω ⊂ and c is a curve for level set: the following formulations are proposed: 2 2 1 1 2 2 2 1 2 ( , , ) | ( ) | | ( ) | length( ) area( ( )) cv e c c i x u i x u m dx c v in c u m dxλ λ µ ω ω = − + − + + ∫ ∫ (1) where µ, v, λ1 and λ2 > 0 are constants. length term regularizes the contour c. m1 and m2 are defined as: 1 ( ( ))m h xφ= ε (2) 2 (1 ( ( )))m h xφ= − ε (3) where hε(ϕ) is a heaviside function is defined as: 1 2 ( ) 1 arctan 2 hε φ φ π ε = +          (4) ε accomplishes the smoothness of the heaviside function. u1 and u2 are statistical means of an image inside and outside of curve c respectively, which are explained as: 1 1 1 ( )i x m dx u m dx ω ω = ∫ ∫ (5) 2 2 2 ( )i x m dx u m dx ω ω = ∫ ∫ (6) minimizing (1) by gradient descent [17], we achieve the following variational formulation: ( 2 21 1 2 2( ) ( ) div ( ) | | i u i u v t ε φ φ λ λ µ δ φ φ ∂ ∇ = − − + − + − ∂ ∇        (7) where δε(ϕ) is a dirac function defined as: 2 2 ( ) ( ) ε ε δ φ π φ ε = + (8) where µ controls the smoothness of the level set function, v is utilized to pace contour evolution and λ1, λ2 are constants for the inner and outer force of the contour. it is considered as a sound technique for segmenting images with noisy and obscured regions. however, this strategy is not fit for images which have higher intensity distinction or images with convoluted intensity information in the background. to overcome this obstacle, authors in [8] proposed an enhanced global division intensity term, which can segment complex intensity regions inside homogenous images. global division function is joined in their energy definition in a new region based term. this strategy can segment objects with enormous distinction of intensity regions. they proposed the following formulations: 1 2 11 12 21 22 2 1 11 2 1 12 2 2 12 2 2 22 2 2 1 1 ( , , , , , , ) ( ( ) )( ( ) ) (1 ( ( ) ))( ( ) ) ( ( ) )( ( ) ) (1 ( ( ) ))( ( ) ) min e u u w w w w h i x u i x w dx h i x u i x w dx h i x u i x w dx h i x u i x w m dx m m m φ ω ω ω ω = − − + − − − + − − + − − − ∫ ∫ ∫ ∫ (9) where ( ( ) ),( 1,2))ih i x u i− = is a global division intensity function. instead of considering two intensity terms, this procedure considers four intensity terms, two inside and two outside the contour. the technique developed in [9] cannot authentically capture an object with bigger intensity distinction. figure 1 displays the segmentation of one complex image for both methods. (a) (b) fig. 1. image segmentation on images having intensity difference (a) chan-vese [9], (b) [8] an active contour strategy with respect to acslg (active contour with selective local and global) technique was proposed in [7] as a blend of gac [18] and [9] methods. in this model, a region based spf term was proposed, which can perfectly stop the curve at weak or fuzzy edges. this model can capture outside regions if initialized inside and capture inside regions if initilzed outside the object. in addition, this model uses the gaussian kernel to regularize the level set dimension set. they propose the energy term as: ( )( ( )) | | div | | ( ( )) spf i x t spf i x φ φ φ α φ φ ∂ ∇ = ∇ + ∂ ∇ + ∇ ∇             (10) a novel spf force term is introduced: ( ) 1 2 1 2 ( ) ( ) / 2 ( ( )) max | ( ) ( ) / 2 | i x u u spf i x i x u u = − + − + (11) where u1 and u2 are global intensities computed from the given image defined in (5) and (6) correspondingly. more recently, authors in [15], summed up the chan-vese [9] energy formulation and proposed another exceptional case. engineering, technology & applied science research vol. 9, no. 4, 2019, 4457-4462 4459 www.etasr.com bhatti et al.: active contours using harmonic global division function the new energy in this method reduces the estimate error and can more effectively safeguard the regions with minute difference between rois and background, hence this method can viably segment images, particularly with low contrast. authors came up with a two-phase harmonic approximation in their energy formulation instead of the traditional arithmetic intensity approximations in [9]. they proposed the following general form of energy function: 2 1 1 2 2 2 1 2 ( , ) | f( ( )) ( | | f( ( )) ( | length( ) area( ( )) ) ) e c i x f u i x f u m dx c v in c u m dxλ λ µ ω ω = − + − + + ∫ ∫ (12) where f is reciprocal harmonic mean average i.e., f(x)=1/x. the harmonic mean intensities are usually less than one, while the traditional means u1 and u2 in (1) are greater than one. so, in this case, this method penalizes the approximation error in a lighter way than chan-vese method, which does this in a stronger way. for low contrast images u1 and u2 remain close to each other, which makes the contour stationary and does not capture the required boundaries. therefore, this method can get image boundaries in low contrast images. iii. proposed method the following harmonic energy function is proposed: 1 2 11 12 21 22 2 1 11 2 1 12 2 2 22 2 2 12 1 1 2 2 ( , , , , , , ) ( ( ( )) ( )( ( ( )) (( ))) (1 ( ( )) ( ))( ( ( )) ( )) (1 ( ( ( )) ( )))( ( ( )) ( )) ( ( )) ( )( ( ( )) ( )) ) ) ) ( ( min e u u w w w w h f i x f u f i x f w dx h i x f u f i x f w dx h f i x f u f i x f w h i x f u f i x f w dx d m f m m f m x φ ω ω ω ω = − − + − − − + − − − + − − ∫ ∫ ∫ ∫ (13) where ( ( ( )) ( )),( 1,2)ih f i x f u i− = is a harmonic global division function. in (13), we take four harmonic means, two for each side of the contour. after minimizing the above problem, we get the following new harmonic solutions: 1 1 11 1 1 ( ( ( ( )) ( )) ( ( ( ( ))) ( )) ( ) ( ))) h f i x f u m dx w h f i x f u f i x m dx ω ω − = − ∫ ∫ (14) 1 1 12 1 1 (1 (( ( )) ( ))) (1 ( (( ( ))) ( ))) ( ( )) hf i x f u m dx w h f i x f u f i x m dx ω ω − − = − − ∫ ∫ (15) 2 2 21 2 2 ) )( (( ( )) ( )) ( ( (( ( )) ( )) ( ( )) ) hf i x f u m dx w h f i x f u f i x m dx ω ω − = − ∫ ∫ (16) 2 2 22 2 2 (1 ( (( ( )) ( ))) (1 ( (( ( ) ) ) ) ( ) ( ( ))) h f i x f u m dx w h f i x f u f i x m dx ω ω − − = − − ∫ ∫ (17) lets take an image :i rω ⊂ , a level set : rφ ω ⊂ , and a closed contour c equivalent to a zero-level set: c = {x ϵ ω|ϕ(x) = 0}. the following energy term is proposed: ( ) ( ) ( ) ( ) hgspf hgspf hgspf e l va pφ λ φ φ α φ= + + (18) where lhspf (ϕ) is the length and ahspf (ϕ) is the area terms respectively. these terms are calculated as: ( ) ( ) ( ) | | hgspf l hgspf i dx ε φ δ φ φ ω = ∇∫ (19) ( ) ( ) ( ) hgspf a hgspf i h dxεφ φ ω = −∫ (20) where hgspf (i) is a hgspf function which is defined as: ( ( ) ) ( ) max(| ( ) |) i x hg hgspf i i x hg − = − (21) where hg is a newly developed two-phase harmonic global fitted image model which is characterized as: 11 12 21 22 12 21 22 11 21 22 11 12 22 11 12 21 4w w w w hg w w w w w w w w w w w w = + + + (22) where w11, w12, w21 and w22 are the intensity means described in (14)-(17). by the calculus of variations [17], the final level set of an energy functional ehgspf in (27) can be defined as: .div ( ) ( ) ( ) ( ) | | hgspf i vhgspf i t ε ε φ φ λ δ φ δ φ φ ∂ ∇ = + ∂ ∇       (23) the hgspf term has the incentive to modulate its sign within the [-1,1] region depending on the initialization of the curve. if it is placed outside of an object, the curve deforms inwards and if placed inside, the curve expands in the outward direction. traditional level set methods use some initialization techniques to maintain the level set ϕ as signed distance function (sdf). the proposed method totally discards the costly re-initialization strategy by utilizing the penalization term from lsewr method [9]. the initialization function for our method is defined as: 0 0 0 0 ( , 0) 0 x x t x x ρ φ ρ − ∈ ω − ∂ω = = ∈∂ω ∈ω − ω      (24) where ρ>0 is constant. the steps of the proposed method are: 1. initialize ϕ by ϕ0 using (24) at t=0. 2. compute w11(ϕ), w12(ϕ), w21(ϕ) and w22(ϕ) using (14), (15), (16) and (17) respectively. 3. compute hgspf(i) from (21). 4. solve the pde of ϕ using (23). engineering, technology & applied science research vol. 9, no. 4, 2019, 4457-4462 4460 www.etasr.com bhatti et al.: active contours using harmonic global division function 5. if the result does not change then terminate, otherwise, move to step 2 and repeat. iv. experimental results the experiments were performed on matlab 8.0 installed in a pc running windows 10, with quad core cpu 2.4ghz and 8gb ram. in this paper, these parameters were selected manually: λ=1, µ=200/2552, v=15, α=0.2/∆t, ∆t=1.0, k=5, ρ=4, ε=1.5 and s=1.5. initially, the method was tested on some simple images, which are demonstrated in figure 2. figure 3 delineates segmentation utilizing the proposed method and some previous methods. results demonstrate that the proposed technique accomplishes the required segmentation results correctly. chan-vese [9] had also segmented some noise, while lbf neglected to accomplish the ideal segmentation results. figures 4-5 exhibit the results of the chan-vese [9], lbf [21, 22] and the proposed strategy on mammograms taken from the mini mias database [20]. the results demonstrate that tumor segmentation has been efficiently segmented by the proposed technique while the other methods delivered inadmissible outcomes. fig. 2. proposed method segmentation results and their initialization (a) (b) (c) (d) (e) fig. 3. noisy image segmentation results: (a) images and initial contours, (b) chan–vese, (c) lbf, (d) lcv and (e) proposed (a) (b) (c) (d) (e) fig. 4. segmentations result on a real set of images, (a): original images, (b) ground truth (c) chan-vese, (d) lbf, (e) proposed engineering, technology & applied science research vol. 9, no. 4, 2019, 4457-4462 4461 www.etasr.com bhatti et al.: active contours using harmonic global division function (a) (b) (c) (d) (e) (f) fig. 5. quantitative comparison on mammogram images: (a) original images, (b) ground truth. (c) [9], (d) [7], (e) [19], (f) proposed v. quantitative comparison for quantitative results, we used images taken from a publically accessible dataset [20] (figure 5). the results exhibit that the proposed strategy improved the results of previous methods. we have utilized an accuracy metric to validate nature of our outcomes. the formulation of the metric is defined as: tp tn accuracy tp tn fp fn + = + + + (34) where tp (true positive) stands for the segmented region, tn (true negative) for the accurately unsegmented regions, fp (false positive) stands for regions erroneously considered as true and fn (false negative) are the undetected tumor areas. table i demonstrates the accuracy metric study of proposed technique and previous methods. we can see that the accuracy of the proposed methodology is essentially improved in comparison with the previous methods. table i. accuracy comparison method image [9] [7] [19] proposed row 1 0.5368 0.9587 0.7247 0.9628 row 2 0.6856 0.7456 0.7124 0.9698 row 3 0.5789 0.8321 0.2354 0.9321 vi. conclusion a novel hgspf (harmonic global signed pressure force function) was presented in this paper. a global division function was used to approximate intensity means inside image regions. with the incursion of global intensity means and harmonic function, the proposed technique brought better outcomes in terms of accuracy, than the previous methods. gaussian filter was adapted to eliminate an expensive reinitialization and to regularize level set. finally, quantitative analysis demonstrated the effectiveness of the proposed method. references [1] s. soomro, k. n. choi, “active contours based on an anisotropic diffusion”, digital image computing: techniques and applications, canberra, australia, december 10-13, 2018 [2] b. w. hong, b. s. sohn, “segmentation of regions of interest in mammograms in a topographic approach”, ieee transactions on information technology in biomedicine, vol. 14, no. 1, pp. 129-139, 2010 [3] m. kass, a. witkin, d. terzopoulos, “snakes: active contour models”, international journal of computer vision, vol. 1, no. 4, pp. 321-331, 1988 [4] c. li, c. xu, c. gui, m. d. fox, “level set evolution without reinitialization: a new variational formulation”, ieee computer society conference on computer vision and pattern recognition, san diego, usa, june 20-25, 2005 [5] v. caselles, r. kimmel, g. sapiro, “geodesic active contours”, international conference on computer vision, cambridge, usa, june 20-23, 1995 [6] y. liu, g. captur, j. c. moon, s. guo, x. yang, s. zhang, c. li, “distance regularized two level sets for segmentation of left and right ventricles from cine-mri”, magnetic resonance imaging, vol. 34, no. 5, pp. 699-706, 2016 [7] k. zhang, l. zhang, h. song, w. zhou, “active contours with selective local or global segmentation: a new formulation and level set method”, image and vision computing, vol. 28, no. 4, pp. 668-676, 2010 [8] h. min, w. jia, x. f. wang, y. zhao, r. x. hu, y. t. luo, f. xue, j. t. lu, “an intensity-texture model based level set method for image segmentation”, pattern recognition, vol. 48, no. 4, pp. 1547-1562, 2015 [9] t. f. chan, l. a. vese, “active contours without edges”, ieee transactions on image processing, vol. 10, no. 2, pp. 266-277, 2001 [10] x. f. wang, d. s. huang, h. xu, “an efficient local chan-vese model for image segmentation”, pattern recognition, vol. 43, no. 3, pp. 603618, 2010 [11] c. li, c. y. kao, j. c. gore, z. ding, “minimization of region-scalable fitting energy for image segmentation”, ieee transactions on image processing, vol. 17, no. 10, pp. 1940-1949, 2008 [12] s. lankton, a. tannenbaum, “localizing region-based active contours”, ieee transactions on image processing, vol. 17, no. 11, pp. 20292039, 2008 [13] s. soomro, f. akram, a. munir, c. h. lee, k. n. choi, “segmentation of left and right ventricles in cardiac mri using active contours”, computational and mathematical methods in medicine, vol. 2017, article id 8350680, 2017 [14] s. soomro, f. akram, j. h. kim, t. a. soomro, k. n. choi, “active contours using additive local and global intensity fitting models for intensity inhomogeneous image segmentation”, vol. 2016, 2016 engineering, technology & applied science research vol. 9, no. 4, 2019, 4457-4462 4462 www.etasr.com bhatti et al.: active contours using harmonic global division function [15] a. razi, w. w. wang, x. c. feng, “an active contour method using harmonic mean”, ieee international conference on signal and image processing, beijing, china, august 13-15, 2016 [16] d. mumford, j. shah, “optimal approximations by piecewise smooth functions and associated variational problems”, communications on pure and applied mathematics, vol. 42, no. 5, pp. 577-685, 1989 [17] g. aubert, p. kornprobst, mathematical problems in image processing: partial differential equations and the calculus of variations, springer, 2006 [18] b. appleton, h. talbot, “globally optimal geodesic active contours”, journal of mathematical imaging and vision, vol. 23, no. 1, pp. 67-86, 2005 [19] s. soomro, k. n. choi, “robust active contours for mammogram image segmentation”, international conference on image processing, beijing, china, september 17-20, 2017 [20] the mini-mias database of mammograms, available at: http://peipa.essex.ac.uk/info/mias.html [21] c. m. li, c. kao, j. gore, z. ding, “implicit active contours driven by local binary fitting energy”, 2007 ieee conference on computer vision and pattern recognition, minneapolis, usa, june 17-22, 2007 [22] c. m. li, c. kao, j. gore, z. ding, “minimization of region-scalable fitting energy for image segmentation”, ieee transactions on image processing, vol. 17, no. 10, pp. 1940–1949, 2008 microsoft word 36-3443_s_etasr_v10_n2_pp5538-5546 engineering, technology & applied science research vol. 10, no. 2, 2020, 5538-5546 5538 www.etasr.com irmak: structural and electrical properties of ca 2+ doped lafeo3: the effect of a-site cation size … structural and electrical properties of ca2+ doped lafeo3: the effect of a-site cation size mismatch ali ekber irmak physics department faculty of science mugla sitki kocman university mugla, turkey ekberirmak@gmail.com abstract—in this study, nanosized la1-xcaxfeo3 (0.00≤≤≤≤x≤≤≤≤0.40) compounds prepared via sol-gel method followed by heat treatment at 1100oc for 24 hours are studied. crystal structure, microstructure, surface morphology and temperature-dependent resistivity of the samples are investigated. tem investigation reveals nanoparticles with an average size of 35nm produced from the sol-gel process. the crystal structure of the compounds belongs to an orthorhombically distorted perovskite structure with pbnm space group. lattice distortion and cation size mismatch increase with an increase in ca and particle and grain growth are suppressed by ca doping. electrical conduction is explained via thermally activated hopping of small polarons. unit cell volume, charge ordering temperature, and activation energy for small polarons decrease linearly with an increase in cation size mismatch. room temperature resistivity decreases with ca doping and gets its minimum value for 30% ca at which the orthorhombic distortion is maximum. keywords-cation size mismatch; lattice distortion; particle size; grain size; charge order i. introduction rare-earth (re) transition metal perovskite oxides attract attention due to their electronic and magnetic properties, such as insulator to metal and paramagnetic to ferromagnetic phase transitions, magnetoresistance, electroresistance, magnetocaloric effect and charge order properties. lafeo3 is a semiconductor/insulator perovskite oxide and its derived compounds by replacement of some of la atoms by other re or alkaline earth (ae) elements give rise to significant physical and chemical properties with promising applications in advanced technologies as in electronics, magnetics, fuel cells, gas sensors, and catalysts [1]. by partially exchanging la in the parent compound with other re or ae (la1-xaxfeo3, a: re or ae) lead to structurally distorted compounds, and induce different lattice parameters and unit cell volumes [2-4]. in addition, ae doping has an influence on particle size (ps) and grain size (rg). the former is calculated using xrd data and the later is calculated using surface images taken by scanning electron microscope (sem) or atomic force microscope (afm). ps has an effect on electronic, magnetic and chemical properties and is an important parameter in determining the performance of the material. lack of holes or a trace of holes due to nonstoichiometric oxygen undoped compound has high resistivity at room temperature. ae doping increases the number of holes in the compound and the polyvalent nature of the fe compensates the created charge imbalance by oxidation. ae with a valance state of + oxidizes two fe+3 to two fe+4 and ae with a valance state of 2+ oxidizes one fe+3 to fe+4. therefore, the charge imbalance created by ae doping is removed, and this process also increases holes in the compound leading to lower resistivity. besides, oxygen content plays an important role in charge compensation. oxygen deficiency leads to decrease the number of fe4+, and excess oxygen leads to increase the number of fe4+. furthermore, doping at la site and o vacancy, have a direct impact on the local environment of fe ions [4] and thereby resistivity. in addition, the difference of ionic radii of la-site ions in the compound and the difference of ionic radii of fe+3 and fe+4 have an influence on lattice and electrical properties. the measure of distortion due to la-site ionic radius difference is the cation size mismatch, �� = ∑ �����−〈� 〉�� , where xi and ri are the concentration and ionic radius of the i th a-site ion and 〈� 〉 is the average a-site ionic radius. the electrical transport in doped lfo compounds usually takes place by the “polaron hopping”. an electron or a hole is trapped by a potential well resulting from the ionic displacements it created. moreover, oxygen vacancy, which is a defect site, traps an extra electron and leads to polaron like bound states [5]. charge order (co) is another property in some of these compounds which takes place in a material by a localization of charge carriers below a certain temperature, tco, giving rise to long-range order throughout the crystal structure leading a sudden increase in resistivity. the electrical transport and the structural properties of la1xaxfeo3 have been studied extensively. in refeo3 oxides having an orthorhombic perovskite structure with pbnm space group, the structural distortion increases with decrease in re3+ ionic radii [6]. it was shown that a decrease in ionic radii of re3+ leads to decrease in lattice parameters and unit cell volume. authors in [7] reported that doping the lfo with li+ destroys the perfection of crystallinity and lead to decrease of ps. authors in [8], contrary to other studies, reported that hightemperature synthesis of k+ doped lfo doping with an ion having larger ionic radii than that of la, leads to a decrease of corresponding author: ali ekber irmak engineering, technology & applied science research vol. 10, no. 2, 2020, 5538-5546 5539 www.etasr.com irmak: structural and electrical properties of ca 2+ doped lafeo3: the effect of a-site cation size … unit cell volume. an increase in mg2+ doping in lfo leads to lowered ps and doping with mg2+ prevents ps from growing up during high temperature treatment [2]. however, despite the smaller ionic size of mg2+ there was no considerable change in unit cell volume up to 70% doping. a study on ba2+ doped lfo revealed that an increase in doping decreased the ps and contrary to the larger ionic size of ba2+ the unit cell volume decreased and appropriate ba-doping restrained the growth of grains [9]. moreover, the effect of pb2+ doping on the structural properties of lfo was conducted in [10] with no change in the unit cell volume and a decrease in the ps with an increase in pb2+ content [10]. an increase in ca2+ in lfo leads to decrease in ps [11, 12] and in grain size [13]. structural and electrical properties of simultaneously doping lfo with ca2+ and pb2+ [14] showed that doping with larger pb2+ ions up to 20% did not change the principal phase, but lattice parameters, unit cell volume and ps increased. however, another study reported that pb2+ doping lead ps to decrease [15]. electrical transport properties of lfo can be tuned by alkaline ion substitution. the incorporation of ca2+ ions into the la sub-lattice decreased the lanthanum ferrite’s electrical resistivity [16, 17]. moreover, doping the parent compound lfo with another divalent ion, mg2+, led to increase the resistance of lfo due to secondary phases and nonstoichiometric oxygen in the structure [2]. although there are studies involving the effect of divalent ion doping on the structural properties of the lafeo3 compound, a detailed and combined study on the effect of divalent ion doping on structural parameters, microstructure, and electrical properties is required. therefore, in this study, the effect of cation size mismatch on the unit cell volume, charge order temperature, compound activation energy, microstructure, particle size, and grain size evaluation are discussed in detail. using divalent ca2+ as a dopant ion, crystal structure, microstructure, and the electrical properties of laxca1-xfeo3 (x=0.10, 0.20, 0.30, 0.40,) perovskites prepared by standard sol-gel route are considered. ii. experimenatal procedure la1-xcaxfeo3 (0.0≤x≤0.4) samples have been prepared by standard sol-gel method, using appropriate amounts of la(no3)3.6h2o, ca(no3)2.4h2o, fe(no3)3.9h2o with the desired stoichiometry. pellets pressed using the fine powders were sintered at 1100oc for 24h and cooled down to room temperature in the furnace. close cycle cryostat was used to perform temperature dependent resistivity measurement using four-point probe from 320k down to 140k. details of the experimental procedure can be found in [18]. iii. results and discussion a. crystal structure analysis the room temperature structures of the la1-xcaxfeo3 (0.0≤x≤0.4) samples were investigated using their respective x-ray diffraction profiles. to explore the effect of ca doping in detail, the structural parameters of all the samples were refined by rietveld’s profile-fitting using freely available fullprof suit software [19]. the given structural model was refined with the peak shapes of the experimental patterns were assumed to be a thompson-cox-hastings (tch) pseudo-voigt profile functions. lattice parameters, particle size and lattice strain were refined to fit the peak shifting and broadening of the experimental data. the values of goodness of fit (gof) for all of the refinement lie between 0.87 and 1.3. gof was calculated by the ratio re/rwp, where re and rwp are the expected weighted and weighted profile factors. the experimental and calculated profiles with their differences were figured out along with bragg positions (see figure 1). rietveld refinement reveals that the samples crystallize in orthorhombically distorted perovskite structure with pbnm space group. inspecting on main peak, in figure 1 (xrd pattern of lcfo40) and in figure 2, there emerges another peak (marked with a ∗) in the pattern of lcfo40. fig. 1. the experimental and calculated xrd patterns of all samples. open circles indicate the experimental data and the calculated data are shown in the continuous line overlapping them. the curve (at the bottom) shows the difference between the experimental and calculated patterns. the vertical bars indicate the expected reflection positions for the main (blue-upperbars) and fe2o3 impurity (red-lower bars) phases. further investigation revealed that this peak was due to the trace of the rhombohedrally distorted perovskite fe2o3 (hematite) with �3�� space group (crystallographic open data (cod) base card # 96-901-0140). refined lattice parameters, unit cell volumes, average a-site radii, 〈� 〉, average distortion ratio (d), cation size disorder (σ2), and rietveld refinement parameters are summarized in table i. inspection on the xrd patterns of the samples makes clear that following ca doping, main-peak of parent compound lfo at 32.17o (figure 2) is rendered broader and shifted to higher angles. it is known that the former is due to decrease in particle size and the latter is a change of the lattice constants. engineering, technology & applied science research vol. 10, no. 2, 2020, 5538-5546 5540 www.etasr.com irmak: structural and electrical properties of ca 2+ doped lafeo3: the effect of a-site cation size … fig. 2. main peaks of lcf, lcfo10, lcfo20, lcfo30, and lcfo40 samples with * indicating the main peak of the fe2o3 phase calculated unit cell volumes for all samples after reitveld refinement are given in table i. unit cell volume calculated for the parent compound lfo is 242.72å3. a 10% increase in ca, results to smaller unit cell with volume 239.85å3. further increase in ca leads to decreased unit cell volumes: 238,04å3, 235.26å3, and 235.12å3 for 20%, 30%, and 40% ca respectively. therefore, an increase in ca amount decreases the unit cell volume which agrees with the replacement of la3+ having 12 coordinated ionic radii of 1.36å with the smaller ca+2 ion with 12 coordinated ionic radii of 1.34å. doping the parent compound with smaller ion decreased 〈� 〉 thus unit cell volume decreases. moreover, there is another contribution on shrinkage of the unit cell which can be explained by parent compound doping, lfo, with ca2+ ion resulting to oxidation of fe3+ to fe4+. an increase in doping leads to a decrease in concentration of fe3+ (0.645å) with larger ionic radii, and an increase of concentration of fe4+ (0.585å) with smaller ionic radii. hereby, there is a decrease in size around fe-site which may also contribute to a decrease of unit cell volume [20]. table i. lattice parameters x (%) a (å) b (å) c (å) v (å3) 〈��〉 (å) d (%) σσσσ2 (10-4åååå2) rp (%) rwp (%) χχχχ2 gof 0.00 5.5598 5.5565 7.8569 242.72 1.360 0.06 0.000 24.2 13.4 1.66 1.3 0.10 5.5399 5.5353 7.8216 239.85 1.358 0.11 0.360 34.5 18.4 1.45 1.2 0.20 5.5075 5.5162 7.8024 238.04 1.356 0.15 0.640 22.4 13.5 1.13 1.1 0.30 5.5063 5.4973 7.7721 235.26 1.354 0.16 0.840 34.7 17.4 1.02 1.0 0.40 5.5045 5.4935 7.7755 235.12 1.352 0.14 0.960 23.9 14.1 0.75 0.87 fig. 3. change of unit cell volume with respect to cation size mismatch. the line represents the fitting result. even expressing the decrease in unit cell volume with ca doping, it will be better to express the change in the unit cell volume with respect to a-site cation size mismatch (σ2) which is an inherent parameter for doped perovskite structures and it measures the size disorder of the structure [21]. to represent the change of unit cell volume, v is plotted with respect to �� which is given in figure 3. it is clear from the figure that as the cation size mismatch increases the unit cell volume decreases linearly. therefore, fitting the data with following linear equation in σ2 was performed: ����� = �� − ��� (1) where v0 represents the volume of the sample at which �� is zero (namely v0 is the volume of the parent compound, lfo) and m is the slope of the line. fitting results to χ2=0.98, v0 and m, 242.81±0.41å3 and -82373±6268 å respectively. the calculated unit cell volume for the parent compound using linear fitting is almost equal to the value (242.72å3) from rietveld refinement. it is seen from table i and figure 3 that there is no considerable change in the volume of lcfo40 as it is expected due to 10% more ca with respect to lcfo30. for lcfo40, the amount of ca in the structure may be lower than the expected. this can be explained with the appearance of fe2o3 as an impurity phase in lcfo40 (figure 1). if some fe atoms are not in the main phase, then there should be the compounds or the oxides of ca and/or la. however, there is no trace of the compound or the oxide of la and/or ca in the xrd pattern. an amount of impurity phase which should be dispersed in the main perovskite phase and the precipitates with low concentration usually exhibit particle sizes in the range of a few nm, invisible to the xrd [22]. doping an orthorhombic perovskite component at the asite with an element having different ionic radii results to deviation from the cubic symmetry. the measure of deviation is an average distortion ratio, d, which is defined as [23]: � = �� ∑ � ����〈�〉� �� ����� (2) where 〈 〉 = ! "� √2⁄ & � �⁄ , � = , � = ", � = � √2⁄ , and a, b, and c are calculated lattice parameters. the calculated values of d for all of the compounds are given in table i. the average distortion ratio d, exhibits a drastic increase from 0.6% to 0.11% for 10% and 20% ca respectively which implies a larger orthorhombic distortion from sample lcfo10 to lcfo20 and it increases monotonically with increase in ca. however, there is a distortion decrease for the sample doped with 40% ca compared to the 30% sample. one can argue that this is compatible with fe2o3 as an impurity in the structure, which engineering, technology & applied science research vol. 10, no. 2, 2020, 5538-5546 5541 www.etasr.com irmak: structural and electrical properties of ca 2+ doped lafeo3: the effect of a-site cation size … may indicate that the ca amount in the compound is less than 40%. b. microstructural analysis: particle size and strain particle size and lattice strain (s) are parameters which can be extracted from the peak width analysis. particle size generally has been calculated using scherrer equation and williamson-hall (w-h) method. the full width at half maximum of the most intense peak for a given pattern is used in scherrer’s equation (� = )* +�,-./ 0. without correction for the lattice strain, this gives a rough particle size. one can say that, scherrer’s equation gives only an approximate estimate of the mean particle size. but, the peak broadening due to size and strain is expressed in williamson-hall method as: +123�,-. = 45 6 7 49-:;. (3) where +123 is the full with at half maximum of the corresponding reflections in xrd pattern, k is the shape factor, λ is the x-ray wavelength, d is particle size and ε is strain. plotting βhklcosθ values with respect to 4sinθ is called a williamson-hall plot. fitting the data with a linear equation gives the strain and particle size from the slope and y-intercept of the fitted line respectively [24]. the fullprof suite program was used to calculate the microstructural parameters of the sample. the microstructural effects were handled using the voigt approximation: both instrumental and sample intrinsic profile are supposed to be described approximately by a convolution of lorentzian and gaussian components [19]. table ii. average particle size, and average grain size ca (%) 〈<=〉(nm) s rg (nm) 0 77.18±0.08 1.95±0.02 940 10 56.43±0.01 18.25±0.03 670 20 51.43±0.05 25.17±0.01 620 30 33.12±0.05 17.39±0.00 450 40 24.06±0.02 6.48±0.01 540 the parent compound lfo has the largest particles with average size of 77.18±0.08nm. the doping parent compound with 10% ca, had an average ps decrease to 56.43±0.01nm. ps gets its minimum value for lcfo40 at 24.06±0.02nm. as doping increases, the average ps decreases. the average strain for the parent compound is 1.95 which is the smallest, while 10% ca doping increased strain to 18.25. further increase in ca with 10% leads strain to attain its maximum for lcfo20. doping more ca decreases strain. the average strain is calculated as 6.48 for the lcfo40 sample with 40% ca. the calculated particle size and strain for the samples are given in table ii, and the plot representing the change in these parameters with respect to ca is given in figure 4. it is clear from the plot that as ca doping increases, ps size decreases. the particle size of the doped oxide becomes smaller than the pure host oxide, as a consequence of the restriction of the motion of particles at the boundaries between host and dopant particles [25]. the results obtained in this study are consistent with findings in [2, 8-12, 26], even if these studies have concluded to a decrease in average ps with an increase in doping. the method used in these studies to calculate average ps is only taking the contribution of the main peak in the xrd pattern. it is well established that, as the particle size decreases, surface and interface between the particles increase. and, surfaces are the place of broken bonds and oxygen vacancies which increase stress and strain on the surface and interface of the particles [27]. c. atomic force microscopy analyss surface scanning of the samples was performed by afm in non-contact mode with a resolution of 5µm×5µm. scanned images of all samples are given in figure 5. these images reveal that larger grains are surrounded by smaller ones and they are tightly connected with each other. this introduces that the grain growth process is not finalized yet. the average grain size calculated for the undoped sample is 940nm. grain size decreases from 940nm, as nominal ca increases in the samples up to 30% ca for which grain size is 450nm. the grain size of the doped sample becomes smaller than the pure host sample [9, 13, 28], and the sample with 40% ca has an average grain size of 540nm. a decreasing trend in grain size up to 40% ca is consistent with the decreasing trend of particle size with ca content. however, the average grain size of the sample lcfo40 was calculated to be 540nm. this increase in grain size (from 450nm to 540nm) may result from a ca deficiency in the sample lcfo40 and impurity phase la2feo3. the change in rg with ca content is given in figure 4. the largest particles calculated for the parent compound are 77.18±0.08nm. the sample with the largest average ps has the largest average grain size (940nm). average ps is smaller than the average grain size calculated from afm images (table ii). fig. 4. variation of particle and grain size as a function of nominal ca. inset represents the change of strain with nominal ca. this suggests that, the grains viewed by afm images are agglomerates of almost a few thousands (>? @a 0 � of particles [29]. grain size calculated using the afm image is a local average over tens of grains, but particle size calculated using xrd data is an average namely over 1010 particles. one can say that particle size calculated using xrd pattern with w-h analysis is a more accurate method. the change of microstructural strain with respect to ca is given in figure 4 as an inset. since the sign of the strain is positive, it stands for compressive strain. generally, there is a trend of increasing and decreasing strain with ca. the samples undergo increasing compressive strain up to 20% ca and then decrease up to 40% ca. engineering, technology & applied science research vol. 10, no. 2, 2020, 5538-5546 5542 www.etasr.com irmak: structural and electrical properties of ca 2+ doped lafeo3: the effect of a-site cation size … fig. 5. 5µm×5µm afm images of the samples, (a) lfo, (b) lcfo10, (c) lcfo20, (d) lcfo30, (e) lcfo40 d. high-resolution tem analysis surface morphology, particle size distribution and structure of the nanoparticles were studied by high-resolution transmission electron microscopy (hrtem) using a jeoljem 2010 operated at 200kv. powder specimens were dispersed into acetone and underwent an ultrasonic bath for 20 minutes. a drop of solution was taken on a carbon grid to carry out hrtem analysis. tem investigation was performed to clarify the nanosized particle distribution and perfect crystallinity of lcfo20 precursor after calcination of the solgel route for 12hs at 600oc. a general view of the particle distribution of lcfo20 precursor is given in figure 6(a). it is clear from the image that nanoparticle distribution with size between 20nm and 50nm was produced from the sol-gel process. though tem images are not necessarily representative of the whole sample, the average value of particle size calculated from xrd analysis (table ii) was closely represented by them. for further structural investigation one of the nanoparticle’s surface was focused (figure 6(b)) and hrtem technique was applied. inverse fast fourier transform (ifft) of the real image indicated by a square in figure 6(b) was taken in order to filter the unwanted noise (figure 6(c)). the perfect crystalline structure of lcfo20 precursor before heat treatment is clear. fft diffraction pattern extracted by applying a rectangular region of interest (r-roi) is given in the upper left inset of figure 7(a). ifft of the r-roi of real image is given in the upper right inset of figure 7(a). five spots were identified which correspond to the distance between different lattice planes as 0.5929, 0.4122, 0.3124, and 0.2048nm. these planes, having plane distances of 0.2601, 0.3124 and 0.2048nm, labeled as 1, 2 and 3 respectively, were indexed using lattice parameters of lcfo20 calculated from xrd data. the planes were indexed as follows: plane 1 was indexed as (0 2 0), (1 1 2), (2 0 0), plane 2 was indexed as (1 1 1) and plane 3 was indexed as (0 0 4) and (2 2 0). theoretical calculation using lattice parameters of the sample lcfo20 gives an angle of 5.86o between the planes (2 2 0) and (1 1 1), and 50.89o between the planes (2 0 0) and (1 1 1). the two planes shown in figure 7(a) form an angle of 50.06o which was calculated by ifft analysis. this result suggests that high-quality crystalline structure was obtained in this study. the line profile is given in figure 7(b) to emphasize interatomic distances. the average distance between the atoms was found to be 5.1å which closely represents the lattice parameters a and/or b of the lcfo20 (table i). fig. 6. (a) tem image of the prepared lcfo20 taken after burning the dried jel at 600oc, (b) hrtem image of the particles with size 20nm, (c) iffft of the image in (b). fig. 7. high resolution tem image (hrtem) of lcfo20 after heath treatment at 1100 oc. (a) fft diffraction pattern extracted by applying rectangular r-roi left inset, ifft of the r-roi of real image is given in the upper right inset. (b) the intensity profile of the atomic layers. engineering, technology & applied science research vol. 10, no. 2, 2020, 5538-5546 5543 www.etasr.com irmak: structural and electrical properties of ca 2+ doped lafeo3: the effect of a-site cation size … e. electrical properties temperature dependence of the samples’ resistance is given in figure 8. the change of the resistance of the samples shows the same trend with temperature which exhibits insulating properties for the studied temperature range (140-320k). moreover, all samples exhibit strong insulating behavior at low temperatures. due to the compliance limit of the measuring device, the resistance of the parent compound lfo could not be measured. at high temperature, the resistance of the sample changes slightly and increases as the temperature decreases. however, at low temperatures, resistance increases abruptly. this abrupt increase in resistivity may indicate that the samples are charge ordered (co) insulators. this phenomenon is another property of mixed valence perovskite oxide. the onset of co phase can be triggered by temperature and causes a sudden increase in the transport properties of the perovskite and lattice degrees of freedom [30]. the charge order temperature, tco, is a temperature at which the onset of co is observed. tco can be calculated by taking the derivative of ln(ρ/t) against the 1/t curve (d(lnρ)/d(1/t)) and plotting the derivative as a function of temperature (figure 9). the temperature at which a sharp peak within the derivative plot observed is the tco. the calculated values of tco for all the samples are shown in table iii and the plot of the variation of tco with σ 2 is given in figure 9. for the samples lcfo10, lcfo20, lcfo30, and lcfo40 the calculated values are 197k, 177k, 161k, and 164k. there is a decreasing trend in tco with increase in ca except for lcfo40. ca deficiency and fe2o3 as an impurity phase in lcfo40 may lead to an increase of tco for this sample. fig. 8. plot of ln(ρ/t) vs 1/t. the continuous lines represent the linear fitting. the temperature dependent resistances of the samples are given in the inset. table iii. debye temperature, activation energy and ρ300k ca (%) θθθθd (k) ea (mev) ρρρρ0 (µωcm) ρ300κ (ωcm) 10 400 332.57±0.36 3.59±0.06 405.16 20 368 312.45±0.41 1.14±0.02 52.12 30 332 287.65±0.54 0.49±0.04 10.47 40 320 276.57±0.46 2.11±0.05 29.37 the resistivity of all samples increased rapidly after co took place, due to the localization of electronic states which characterize the co state. changing the number of charge carriers by hole doping (ca2+ amount in the sample) has an effect on tco, but hole doping alone cannot describe the change of co temperature. the structural factors including structural distortion or cation size disorder influence the electrical transport properties of these compounds. electrical properties can be modified by changing the type and the concentration of trivalent re, divalent or monovalent ae cations, which led distorted crystal structure due to ionic size differences [31]. in our study, la3+ and ca2+ have different ionic radii coordinated by 12 nearest o ions in the perovskite structure (〈rcd〉=1.36å and 〈red〉=1.34 å). fig. 9. plot of tco vs σ 2. the line represents the fitting result. inset, the plot of the derivative of ln(ρ/t) curve with respect to t. the concentration of the cations and their ionic radii differences determine the distortions of crystal structure [31, 32]. the plot of tco with σ 2 is used to express the influence of a measure of this distortion at the a−site on tco (figure 9). a linear decrease of tco with σ 2 is clear. linear variation of tco versus σ2 was analyzed with [33]: fgh���� = fgh�0� − ��� (4) where fgh�0� represents the estimated value of the tco of a parent compound in the given series and m is the proportionality factor which was obtained from the slope of the corresponding figure. fitting gives fgh�0�=224.20±1.53k, and slope m=-18.69×10−4k/å2 with reduced chi-square of 0.97. due to the compliance of the measurement devices ρ(t) for the parent compound, lfo was not performed. but, for the parent compound, tco was estimated to be 224.20k with the help of (4) and fitting results. 224.20k is the estimated highest possible co temperature of the parent compound with no mismatch, which is consistent with the results of [34]. with a linear decrease in tco with σ 2 we may conclude that upon increasing a-site disorder, i.e. an increase in σ2 from 0.0 to 1.0×10-4å2, the co is gradually suppressed. since ionic radii of ca2+ are close to ionic radii of la3+ (〈rcd〉=1.36å and 〈red〉=1.34å, the change of σ2 even at high doping with ca2+ will be small. however, using dopant elements with larger ionic size may give high disorder at a-site, which may lead to collapse of charge order for a given composition. typical plots of temperature variations of electrical resistivity for all samples are shown in figure 8. the resistivity axis is represented with engineering, technology & applied science research vol. 10, no. 2, 2020, 5538-5546 5544 www.etasr.com irmak: structural and electrical properties of ca 2+ doped lafeo3: the effect of a-site cation size … ln(ρ/t) and temperature axes with 1/t scale. all samples exhibit insulating behavior. thermally activated hopping of small polarons is a model which describes the resistivity of perovskite oxides [35, 36]. therefore, the resistivity was analyzed with the use of the small polaron hopping (sph) model [37]. according to the sph model, the expression for the temperature dependence of the electrical resistivity is given by [38]: k = klfm�n( opqrs0 (5) where ρ0 is a pre-exponential factor, t is the absolute temperature, kb is the boltzmann constant and ea represents the activation energy for small polarons. calculated debye temperatures are given in table iii (the temperature at which resistivity deviates from linearity is θd/2). in the high temperature region, linear increase of ln(ρ/t) with 1/t is clear for all samples (figure 8). therefore, resistivity data in the given temperature range, (temperatures higher than θd/2) fit to a linear equation. from the fitting results of the best fitted lines, the slope gives ea/kb and the intercept gives ρ0. the results of ea for all samples are given in table iii. an increase in ca leads to a decrease in ea from 332.57±0.36mev, to 312.45±0.41mev for samples lcfo10 and lcfo20 respectively. the calculated activation energies for samples lcfo30 and lcfo40 are 287.65±0.54mev and 276.57±0.46mev. as the doping increases, ea decreases for all the samples, in accordance to [2, 16, 17]. the perovskite oxides are classified in terms of their conduction mechanism based on the values of ea. if ea>1ev then that material is oxide ion conductor [39, 40]. whereas, it is p-type polaronic insulator if 900mev>ea>200mev and it is an n-type polaronic insulator if ea≤200mev [41, 42]. therefore, the activation energies calculated for samples in this study reveal that they are p-type polaronic insulators. to explore the effect of cation size mismatch on activation energy, ea is plotted against cation size mismatch (figure 10). from the plot, the inverse linear relation with ea and σ 2 is clear. the highest value of ea occurs at the lowest σ 2 and vice versa. as the cation size mismatch increases, activation energy decreases. it is well known that the electronic properties of perovskite oxides are often crucially connected with structural distortions around the re site and/or transition metal sites [43, 44]. linear fitting was performed to represent the variation of ea with σ 2 and the following relation was written from the fitting result: t����� = t��0� − ��� (6) where ea(0) represents the activation energy at which σ 2=0, or the activation energy of the parent compound lfo which was not calculated in this study due to the compliance limit of the measuring devices, and m is the slope of the best fitted line. fitting results are: ea(0)=367.87±5.49mev and m=934502.54k/å2. ea(0) is the activation energy of the undoped sample lfo which was estimated with the use of (6) and the fitting results. it is clearly evident (figure 10) that room temperature resistivity decreases with increasing ca and gets its minimum value at 10.47ωcm for sample lcfo30. as ca2+ increases, the p-type carriers in a doped compound increase. this results to an increase in conductivity or equivalently a decrease in resistivity. moreover, increasing p-type carriers causes ea to decrease, leading to a decrease in the energy gap of the doped compound. furthermore, the decrease in resistivity possibly suggests that the fermi level shifts to the nearer edge of the conduction band [45]. fig. 10. variation of ea as a function of σ2. chance of r0 at 300k with nominal ca (inset) the room temperature resistivity of lcfo40 increased to a value of 29.47ωcm. this may be the result of oxygen vacancy and appearance of impurity phases in that compound. oxygen vacancies can provide electrons which compensate some of the holes created with ca doping. this results to filling the d band of fe4+ ions and transforming them to fe3+. in addition, ca deficiency and impurity phase la2feo3 in lcfo40 leads to decrease of the fe4+ ions. as a result, the number of holes contributing to conduction decreases and therefore resistivity increases. iv. conclusion the structural and electrical properties of nanosized la1xcaxfeo3 compounds prepared via sol-gel method have been studied. rietveld refinement of the xrd pattern of the samples indicates that all the samples have distorted orthorhombic structure with pbnm space group, except the sample doped with 40% ca which is single phase. increase of ca doping leads to increase of the average distortion ratio. there is a drastic increase of average distortion ratio from parent compound lfo to lcfo10 and to lcfo20. moreover, particle and grain growth are suppressed with ca. there is an inverse linear relation between unit cell volume and σ2. it was shown that electrical conduction in these compounds is thermally hooping of small polarons. the studied compounds are p-type polaronic insulators considering the conduction mechanism based on the values of ea. as the ca amount increases, ea and room temperature resistivity of the samples decreases. inverse linear relation between ea with σ 2 and tco with σ2 were introduced. moreover, charge ordering temperature, tco, decreases with increasing cation size mismatch. engineering, technology & applied science research vol. 10, no. 2, 2020, 5538-5546 5545 www.etasr.com irmak: structural and electrical properties of ca 2+ doped lafeo3: the effect of a-site cation size … acknowledgment the author gratefully acknowledges the support of the mugla sitki kocman university scientific research projects coordination office (grant no: 14/027). references [1] k. mukhopadhyay, a. s. mahapatra, p. k. chakrabarti, “multiferroic behavior, enhanced magnetization and 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mechanism in fe doped lamno3”, the journal of chemical physics, vol. 135, article id 054501, 2011 [45] y. liu, x. y. qin, “temperature dependence of electrical resistivity for ca-doped perovskite-type y1−xcaxcoo3 prepared by sol–gel process”, journal of physical chemistry of solids, vol. 67, no. 8, pp. 1893-1898, 2006 microsoft word 28-2768_s_etasr_v9_n3_pp4218-4224-converted engineering, technology & applied science research vol. 9, no. 3, 2019, 4218-4224 4218 www.etasr.com chouaba & barakat: controlled brushless de-excitation structure for synchronous generators controlled brushless de-excitation structure for synchronous generators seif eddine chouaba dac-hr laboratory, ferhat abbas setif university 1, setif, algeria seif.chouaba@univ-setif.dz abdallah barakat electrical & computer engineering department, beirut arab university, beirut, lebanon a.barakat@bau.edu.lb abstract—the main weakness of the brushless excitation system in a synchronous generator (sg) is the slow de-excitation response obtained during a load rejection. that is why voltage overshoots may be observed on the generator terminals. this behavior is mainly due to the exciter machine response time and the rotating diode bridge which is not able to quickly de-excite the generator by negative excitation voltages. this paper presents a new brushless de-excitation structure able to perform a quick de-excitation of the generator by providing controlled negative excitation voltage to the generator main field winding. the proposed structure is based on a new brushless de-excitation machine, called a control machine, and mounted on the same shaft of the generator and the brushless exciter. the brushless control machine is a low power one and used to transfer the orders from the voltage regulator to the discharge system located on the rotor side of the main generator. the dynamic performance of the proposed de-excitation system is evaluated in terms of system stability, voltage regulation response times and voltage overshoots during different load rejection tests. the proposed system is compared to the conventional brushless excitation system without the proposed de-excitation structure. in addition, a comparison is done with the static excitation system. the simulation tests are realized on an experimentally validated model of 11kva synchronous generator developed in matlab/simulink. keywords-excitation system; synchronous generator; brushless excitation; static excitation; voltage regulation; feedback control systems i. introduction synchronous generators (sgs) are the most used machines in power generation. they are used in hydro, gas, steam and nuclear power plants. they are also used in diesel generators for hospitals, islands, electrical ships, etc. [1-4]. a good dynamic performance of the voltage regulation is required during small and large disturbances as full load rejection. stability and performance of the voltage regulation depend mainly on the excitation system associated with the sg. the static excitation (se) system presented in figure 1 is commonly used in power plants. its main advantage is the ability to control directly the field winding of the sg by positive and negative excitation voltages. thus, static excitation system achieves high dynamic performances [5]. however, it is necessary to use a ring-brush system to transfer the power from the thyristor bridge located in the stationary part to the rotating part. in addition, the static excitation system includes heavy and bulky equipment with high current capability as the field current of generators is generally between 1000a and 8000a. the conventional brushless excitation (cbe) system presented in figure 2 is widely used. it includes an exciter machine (em) connected to an uncontrolled rotating diode bridge that excites the rotating field winding of the sg. consequently, the cbe system does not need the ring-brush system used in static excitation systems to supply the sg field winding. the maintenance costs are then reduced. in addition, the power of the excitation equipment in the cbe system is small compared to the static excitation system as the excitation current of the exciter machine is generally less than 50a. fig. 1. schematic of the se system. fig. 2. schematic of the cbe system corresponding author: seif eddine chouaba engineering, technology & applied science research vol. 9, no. 3, 2019, 4218-4224 4219 www.etasr.com chouaba & barakat: controlled brushless de-excitation structure for synchronous generators nevertheless, the main disadvantage of the cbe system is the impossibility to supply the field winding of the generator by negative excitation voltages which causes high voltage overshoot in the generator terminal during a full load rejection. negative excitation voltages are needed to perform a fast deexcitation of the sg during a load rejection and stop orders (e.g. after a fault detection) [6-9]. considerable efforts have been placed on the cbe system to improve the dynamic performances of sg. voltage regulation with advanced digital controllers, sliding mode control, fuzzy logic controllers, h∞ controllers, and neural network controllers achieves good performance and improves the transient stability of the closed loop system [10-14]. however, these advanced controllers have a minor effect in reducing the voltage overshoot and the response time during a load rejection. this is due to the rotating diode bridge which only provides positive excitation voltages to the sg field winding. recently, many studies have been carried out on the optimization of the cbe power structure in order to provide negative excitation voltages. in [15], the negative excitation capability is obtained by self actuating deexcitation impedance located on the shaft. in other words, a fast demagnetization is obtained by short-circuiting the generator field winding with a discharge resistor mounted in parallel. however, the de-excitation system proposed in these researches cannot be controlled in a closed loop control strategy to improve the dynamics of the voltage regulation. authors in [16, 17] proposed an excitation structure based on a rotating thyristor bridge. this solution allows controlling the generator field winding by negative and positive excitation voltages. the thyristor bridge control signal is transmitted from the stationary part to the rotating part by using wireless transmission techniques. this solution requires a robust transmission mode with respect to internal and external noises and perturbations. in this paper, a new brushless de-excitation structure which can be controlled in a closed loop is studied. the proposed structure associated with the conventional brushless excitation system is presented in figure 3. fig. 3. schematic of the abe system this advanced brushless excitation (abe) can be used in new or refurbishment excitation projects. the de-excitation structure is based on a rotating igbt mounted in parallel to a discharge resistor and controlled by a dedicated negative excitation controller via a rotating control machine. the openings of the rotating igbt induce negative excitation voltages in the field winding and quickly de-excite the generator. in this paper, we will evaluate the performance of the new de-excitation structure with a pid negative excitation controller which is able to control continuously the rotating igbt in steady and transient states. the influence of the resistance of the discharge resistor is also analyzed and presented. using a realistic simulator, the cbe and abe systems are tested and compared under a variety of operating conditions. in addition, a comparison is made with the static excitation system. ii. de-excitation system as presented in figure 3, the proposed de-excitation structure includes the following: • an igbt located in the rotating part and mounted in series with the main field winding. the igbt is sized to support the rated generator field current and the over-excitation current. in addition, during the opening of the igbt, the voltage across the igbt will be equal to the voltage across the discharge resistor. consequently, the igbt should support this induced voltage. • a linear discharge resistor connected in parallel with the igbt. the opening of the igbt introduces the rotational discharge resistance rd and a negative excitation voltage across the field winding of the generator will then be applied. this helps in quickly demagnetizing the synchronous generator and allows the machine to react rapidly to over-voltage cases. the influence of the discharge resistance value, rd, on the system stability and performances is studied in section iii. • a control machine which is an inverted small power synchronous generator. this machine is used to transfer the order coming from the pid negative excitation to the rotating igbt. the apparent power of the machine is very small because the connected load is only the driver of the igbt. • a small power dc chopper used to control the excitation current of the control machine current. it represents a converter from the pid orders to excitation voltage of the control machine. • a negative excitation controller used to control the igbt via the control machine. the controller selected is a pid one based on the supervision of the generator terminal voltage [18]. the cbe system with the main voltage regulator (positive excitation controller) is maintained to regulate the generator terminal voltage by controlling the generator field winding with positive voltages. the rotating igbt can be controlled by two ways: • via a pwm signal controlled by the voltage output of the rectifier supplied by the control machine. • directly via the output voltage of the rotating rectifier connected to the control machine. engineering, technology & applied science research vol. 9, no. 3, 2019, 4218-4224 4220 www.etasr.com chouaba & barakat: controlled brushless de-excitation structure for synchronous generators a. negative excitation control strategy the igbt is controlled by a negative excitation controller based on the measured terminal voltage. the control strategy of the rotating igbt is done by means of a proportional-integralderivative (pid) type regulator. its control strategy is discussed below. in order to improve the transient performance in the presence of a voltage overshoot on the generator terminals, a negative excitation pid based controller for the rotating igbt opening and closing control is set up. the pid regulator is widely used in industries and it does not require exact or precise modeling of the system as it is adjustable according to the application [19]. the pid law is given by: pid 1 n s u (s) = p( 1+i( )+d( ) ) s s+n (1) where s is the laplace operator. the pid regulator is described by four parameters. p (proportional), i (integral), d (differential), and n (filter coefficient). the derivative term d improves the dynamic performance by anticipating the opening of the rotating igbt. the regulator input is the difference between the voltage reference value (u2ref) and the measured generator voltage (umes). the pid parameters are adjusted to give a trade-off between the overvoltage overshoots and the response times. in this work, proportional and derivative constants are p=100 and d=0.9 respectively, and n=700. the voltage reference value of the pid is set equal to 105% of the generator rated voltage. during normal operation, the sg voltage is generally regulated to the rated value by the positive voltage regulator. consequently, the pid output will saturate to “1” and the igbt will be always ordered to close [18]. the igbt is controlled to open during transient states when the terminal voltage tends to be higher than 105%. the pid control scheme of the rotating igbt is presented in figure 4. fig. 4. negative excitation control based on the pid regulator. in this paper we make use of a low pass filter to simulate the system that transmits the orders from the pid regulator to the rotating igbt. we present the closed loop system response during loads impact and shedding by considering the time constant of the low pass filter τ=2.5ms. b. positive excitation control strategy the positive excitation control strategy is the main control loop in cbe and abe systems. the voltage reference of the controller is generally equal to the generator rated voltage. this controller operates during steady and transient states (loads impact and loads rejection). the pid regulator is widely used in industries [20]. researchers validated the performances of advanced controllers (fuzzy logic, h∞, [21, 22]). based on the h∞ control research done in [17], we designed an h∞ regulator for the positive excitation in the abe and the cbe systems. the system parameters and the reduced state space representation of the h∞ regulator are given in the appendix. the h∞ regulator considers the parameters of the sg and the excitation structure. the mathematical model of the system is given by the following equations: 2 3 ( ) fexc exc e exc e se didi v r i l k k m dt dt = + − (2) 1 1 1 dp d dp ep qp dv i i c v c dt ω= + − (3) 1 1 1 qp q qp ep dp dv i i c v c dt ω= − − (4) 0 dp dp s dp q ep qp sq ep q d f d sf sd di v r i l i m i l dt di di m m dt dt ω ω= − − + − − + + (5) 0 qp s qp d ep dp sf ep f sd ep d qp q q sq v r i l i m i m i di di l m dt dt ω ω ω= − − − + + − + (6) 1 0 ω= − + + − + f se ee exc f f dp d sf fd di k m i ai l dt di di m m dt dt (7) 0 f dpd d d d fd sd di didi r i l m m dt dt dt = + + − (8) 0 q qp q q q sq di di r i l m dt dt = + − (9) this model has several parameters: re and le denote the resistance and the inductance respectively of the em field winding, rs, lf and rf are the sg stator resistance, field winding inductance and field winding resistance respectively, ld and lq are the direct and the transverse stator inductance, rd, rq, ld and lq are the direct and transverse dampers resistances, and the direct and transverse dampers inductances respectively, msf and mfd are the mutual inductance between the direct stator winding and field winding and the mutual inductance between the field winding and the direct damper winding, msq and msd are the mutual inductance between the direct stator winding and the transverse damper winding and the mutual inductance between the stator and the direct damper, ep ω and ee ω are the electrical angular speed of the sg and the em, and c1 represents a virtual three-phase capacitor added at the terminal of the sg to model the load current as a perturbation to be engineering, technology & applied science research vol. 9, no. 3, 2019, 4218-4224 4221 www.etasr.com chouaba & barakat: controlled brushless de-excitation structure for synchronous generators rejected by the voltage regulator. in addition, 4 3 ω= + de ee f a k k l r , where k1, k4 and k3 are constants that depend on the em parameters (leakage inductances, main inductance) and the operating mode of the rectifier. k2 is a correction factor [17]. id1 and iq1 are the load currents in dq frame. vexc and iexc are the excitation voltage and the excitation current of the em. the variables vdp, vqp, idp and iqp are the generator voltages and currents in dq fram, id and iq represent the direct and transverse dampers currents respectively, and if denotes the current of the sg main field winding. iii. validation and performances analysis a realistic simulator, based on matlab/simulink, of the exciter machine, rotating diodes, and the synchronous generator was used [17]. the parameters of the sg and the em are given in the appendix. this section shows the validation of the abe dynamic performance. cbe, se, and abe structures were tested. in addition, the influence of the discharge resistance value rd on the abe system performances in closed loop will be shown. the performance of each system is evaluated during sudden load impact and shedding tests. a. sudden load impact and shedding tests during the impact test, a load is suddenly connected to the unloaded sg. when the generator reaches its steady state, the shedding test is performed by removing the load. the active and reactive powers of the used loads are given in table i. pa denotes the load active power, s the apparent power, q the reactive power, and pf the power factor. the value of the discharge resistor rd=3rf is chosen so that it does not stress the closed-loop behavior. rf is the resistance of the generator field winding. table i. used load during impact/shedding tests. tests pa (kw) s (kva) q (kvar) pf 1000.8 8.96 11.2 6.72 0.8 1000.3 6.72 11.2 8.96 0.3 1000.6 3.36 11.2 10.6 0.6 1500.8 13.4 16.8 10 0.8 in order to present clearly the systems responses, we will present the r.m.s. value of the terminal voltage (per unit). figures 5-8 show the responses of the three systems (cbe, se and abe) during load impact and shedding tests. the black curves refer to the system response using the cbe system, the red curves refer to the abe system, and the blue dashed ones correspond to the se structure. during load impact tests, the generator voltage drops due to the armature reaction of the generator. the positive voltage regulator increases the excitation currents to regulate the voltage at its rated value (1p.u.). the cbe and abe systems give approximately the same results in terms of stability, voltage drop and response time. this is expected as the negative excitation controller presented in the abe systems will not order the opening of the igbt. the rotating igbt is still closed during this transient. in the se system, the voltage drop and the response time decrease. this expected result is related to the ability of the static excitation to control directly the generator field winding by positive and negative voltages. during load shedding tests and with the cbe system, the minimum excitation voltage that can be delivered to the generator field winding is zero. in addition, we should consider the response time of the exciter machine which reduces the dynamic of the system. this will increase the generator voltage overshoot and the system response time. however, in the abe system, the opening of the rotating igbt will directly introduce negative excitation voltages to the generator field winding. we can see that the abe performance in terms of voltage overshoot and response time is better than the cbe’s. this improvement is mainly related to the negative excitation system which de-excites fast the generator field winding. during the load shedding tests, we also see the good behavior of the static excitation in quickly stabilizing and regulating the sg voltage. the high negative ceiling voltage provided by the abe system allows minimizing the peak voltage obtained on the sg terminals. (a) (b) fig. 5. generator voltage (r.m.s.) during the (a) impact and (b) shedding test (1000.8) table ii shows a quantitative comparison between the results. ∆ts (ms) and ∆us (%) are the response time and the voltage overshoot during load shedding tests. note that the response time is measured at 0.5% of the set-point value. according to the different tests, the abe system gives the overall better results. there is a minimization of the response time and the voltage overshoot during load shedding tests. for example, during the 1000.3 test, the voltage overshoot is about 10% using the abe system and 15.1% using the cbe system. regarding the response time, thanks to the abe system, it is reduced from 350ms to 146ms (i.e. a ratio of 2.4). 1 1.05 1.1 1.15 1.2 1.25 1.3 0.8 0.85 0.9 0.95 1 1.05 cbe abe se engineering, technology & applied science research vol. 9, no. 3, 2019, 4218-4224 4222 www.etasr.com chouaba & barakat: controlled brushless de-excitation structure for synchronous generators (a) (b) fig. 6. generator voltage (r.m.s.) during the (a) impact and (b) shedding test (1000.3) (a) (b) fig. 7. generator voltage (r.m.s.) during the (a) impact and (b) shedding test (1000.6) (a) (b) fig. 8. generator voltage (r.m.s.) during the (a) impact and (b) shedding test (1500.8). table ii. results for load shedding tests. shedding tests 1000.8 1000.3 1000.6 1500.8 ∆ts ∆us ∆ts ∆us ∆ts ∆us ∆ts ∆us cbe 226 12.5 350 15.1 316 13.3 340 17.8 abe 130 10.8 146 10 130.3 11.4 160 15.6 se 85 12.8 175 14 172 13.4 171 17.6 figure 9 shows the evolution of the generator field voltage (i.e. excitation voltage of the sg field winding). in the cbe system, only positive excitation voltages can be provided. in the abe system, when the igbt opens, the negative forcing voltage quickly dissipates the sg field winding stored energy via the discharge resistor rd. in the se system, the thyristor bridge is able to deliver negative excitation voltages by controlling the firing angle to be around 155°. figure 10 shows the field winding current evolution during de-excitation. it can be observed that the field current decay is much faster in the case of the abe system. b. influence of the discharge resistance value by using the abe system, it is possible to increase the speed of the de-excitation by increasing the discharge resistance rd. however, very high negative voltages can stress the generator field windings. in this case, we must respect the maximum permissible insulation voltage of the generator field winding which is generally very high. figures 11-14 illustrate the responses the abe system for different values of rd (rd=rf, rd=3rf and rd=6rf) and for different load impact and shedding tests (1000.8, 1000.3, 1000.6 and 1500.8). 1 1.05 1.1 1.15 1.2 1.25 1.3 0.82 0.84 0.86 0.88 0.9 0.92 0.94 0.96 0.98 1 1.02 cbe abe se 1 1.05 1.1 1.15 1.2 1.25 1.3 0.8 0.85 0.9 0.95 1 1.05 cbe abe se 1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.95 2 2.05 2.1 0.98 1 1.02 1.04 1.06 1.08 1.1 1.12 1.14 cbe abe se 1 1.05 1.1 1.15 1.2 1.25 1.3 0.7 0.75 0.8 0.85 0.9 0.95 1 1.05 cbe abe se 1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.95 2 2.05 2.1 0.98 1 1.02 1.04 1.06 1.08 1.1 1.12 1.14 1.16 1.18 cbe abe se engineering, technology & applied science research vol. 9, no. 3, 2019, 4218-4224 4223 www.etasr.com chouaba & barakat: controlled brushless de-excitation structure for synchronous generators fig. 9. rotor voltage of the main generator (field voltage) of a load that consumes the 100% of the generator apparent power with a 0.3 pf. fig. 10. rotor current of the main generator (field current) of a load that consumes the 100% of the generator apparent power with a 0.3 pf. fig. 11. rd influence during the shedding of the load (1000.8) with the pid negative excitation controller. high discharge resistance values rd will reduce voltage overshoots during the load shedding tests because of the high negative voltage introduced in the generator field winding. however, a very high resistance value increases the dynamic of the system and may increase the oscillation amplitude in the generator voltage. during load impact tests, all structures give almost the same response. so, the value of the discharge resistor does not influence the closed-loop behavior because the rotating igbt still closed during load impact tests. fig. 12. rd influence during the shedding of the load (1000.3) with pid negative excitation controller. fig. 13. rd influence during the shedding of the load (1000.6) with pid negative excitation controller. fig. 14. rd influence during the shedding of the load (1500.8) with pid negative excitation controller. iv. conclusion this work presents a brushless de-excitation structure for brushless synchronous generators. the de-excitation structure can be controlled in static and transient states. in this paper, we compared the advanced brushless excitation system with conventional brushless and static excitation systems. the performance of each structure is presented by performing a sudden variation of the load connected to the main sg. the obtained results show that the proposed de-excitation structure maintains the system stability and improves the dynamic 1.6 1.65 1.7 1.75 1.8 -6 -5 -4 -3 -2 -1 0 1 2 3 cbe abe (r d =6r f ) se 1.6 1.65 1.7 1.75 1.8 0 0.2 0.4 0.6 0.8 1 1.2 cbe abe (r d =6r f ) se 1.6 1.7 1.8 1.9 2 2.1 2.2 0.98 1 1.02 1.04 1.06 1.08 1.1 1.12 abe (rd=rf) abe (rd=3rf) abe (rd=6rf) 1.6 1.7 1.8 1.9 2 2.1 2.2 0.98 1 1.02 1.04 1.06 1.08 1.1 1.12 1.14 abe (rd=rf) abe (rd=3rf) abe (rd=6rf) 1.6 1.7 1.8 1.9 2 2.1 2.2 0.98 1 1.02 1.04 1.06 1.08 1.1 1.12 1.14 1.16 1.18 abe (rd=rf) abe (rd=3rf) abe (rd=6rf) engineering, technology & applied science research vol. 9, no. 3, 2019, 4218-4224 4224 www.etasr.com chouaba & barakat: controlled brushless de-excitation structure for synchronous generators performance of the generator voltage regulation during load rejection tests. the quick dynamic de-excitation of the generator field winding reduces the terminal voltage overshoot and the response time. for example, during the shedding 1000.6 test, a considerable improvement in the response time and overshoot of the system response was observed. the response time for this test with abe structure is 130ms whereas it takes 316ms with the cbe structure or 2.4 times longer than the abe structure. finally, the obtained results demonstrate the effectiveness of the proposed techniques and show good performance of the negative excitation pid controller in terms of system stability, voltage overshoot and response time. appendix sg and em parameters (resistances in ω, inductances in mh) characteristics of the sg poles sr fr fl dl sfm ql 4 0.71 2.06 695 63.6 200.5 38.6 d l q l fd m sd m sq m d r q r 0.0685 0.0236 6.7 2 0.9 8.6e-4 9.9e-4 characteristics of the em poles ser er el del sem qel 8 0.26 24.5 1750 5.8 89 3.1 references [1] m. mirosevic, z. maljkovic, “effect of sudden change load on isolated electrical grid”, international conference on electrical systems for aircraft, railway, ship propulsion and road vehicles, aachen, germany, march 3-5, 2015 [2] i. boldea, “electric generators and motors: an overview”, ces transactions on electrical machines and systems, vol. 1, no. 1, pp. 314, 2017 [3] g. g. gutierrez, d. m. romero, m. r. cabello, e. pascual-gil, l. d. angulo, d. g. gomez, s. g. garcia, “on the design of aircraft electrical structure networks”, ieee transactions on electromagnetic compatibility, vol. 58, no. 2, pp. 401–408, 2016 [4] b. stevens, a. dubey, s. santoso, “on improving reliability of shipboard power system”, ieee transactions power systems, vol. 30, no. 4, pp. 1905–1912, 2015 [5] j. k. noland, m. giset, f. alves, “continuous evolution and modern approaches of excitation systems for synchronous machines”, xiii international conference on electrical machines, alexandroupoli, greece, september 3-6, 2018 [6] r. c. schaefer, “applying static excitation systems”, ieee industry applications magazine, vol. 4, no. 6, pp. 41-49, 1998 [7] j. taborda, “modern technical aspects of field discharge equipment for excitation systems”, ieee power and energy society general meeting-conversion and delivery of electrical energy in the 21st centuty, pittsburgh, usa, july 20-24, 2008 [8] c. a. platero, m. redondo, f. blazquez, p. frias, “high-speed deexcitation system for brushless synchronous machines”, iet electric power application, vol. 6, no. 3, pp. 156-161, 2012 [9] a. barakat, s. tnani, g. champenois, e. mouni, “output voltage control of synchronous generator using diode and thyristor excitation structures combined with multivariable h∞ controllers”, iet electric power applications, vol. 6, no. 4, pp. 203-213, 2012 [10] d. m. sajnekar, s. b. deshpande, r. m. moharil, “efficient pid controller tuning method selection to be used in excitation system of brushless synchronous generator”, international conference on computation of power, energy information and communication, chennai, india, april 20-21, 2016 [11] n. m. guan, w. pan, j. zhang, q. hao, j. cheng, x. zheng, “synchronous generator emulation control strategy for voltage source converter (vsc) stations”, ieee transactions on power systems, vol. 30, no. 6, pp. 3093–3101, 2015 [12] h. zhang, f. shi, y. liu, “enhancing optimal excitation control by adaptive fuzzy logic rules”, international journal of electrical power and energy systems, vol. 63, pp. 226-235, 2014 [13] e. swidenbank, s. mcloone, d. flynn, g. w. irwin, m. d. brown, b. w. hogg, “neural network based control for synchronous generators”, ieee transactions on energy conversion, vol. 14, no. 4, pp. 16731678, 1999 [14] r. l. a. ribeiro, c. m. s. neto, f. b. costa, t. o. a. rocha, r. l. barreto, “a sliding-mode voltage regulator for salient pole synchronous generator”, electric power systems research, vol. 129, pp. 178-184, 2015 [15] e. rebollo, c. a. platero, f. blazquez, r. granizo, “internal sudden short-circuit response of a new hsbds for brushless synchronous machines tested on a 15 mva generator”, iet electric power applications, vol. 11, no. 4, pp. 495–503, 2017 [16] f. bensmaine, a. barakat, s. tnani, g. champenois, e. mouni, “dual control of synchronous generator for terminal voltage regulationcomparison with a single control”, electric power system research, vol. 91, no. 1, pp. 78-86, 2012 [17] a. barakat, s. tnani, g. champenois, e. mouni, “monovariable and multivariable voltage regulator design for a synchronous generator modeled with fixed and variable loads”, ieee transactions on energy conversion, vol. 26, no. 3, pp. 811-821, 2011 [18] a. barakat, s. chouaba, “performance improvement of brushless generator voltage regulation by using a controlled non linear discharge resistor”, xxiii international conference on electrical machines, alexandroupoli, greece, september 3-6, 2018 [19] k. j. astrom, t. hagglund, pid controllers: theory, design, and tuning, instrument society of america, 1995 [20] k. kim, r. c. schaefer, “tuning a pid controller for a digital excitation control system”, ieee transactions on industry applications, vol. 41, no. 2, pp. 485-492, 2005 [21] m. gunes, n. dogru, “fuzzy control of brushless excitation system for steam turbogenerators”, ieee transactions on energy conversion, vol. 25, no. 3, pp. 844-852, 2010 [22] e. mouni, s. tnani, g. champenois, “synchronous generator output voltage real-time feedback control via h∞ strategy”, ieee transactions on energy conversion, vol. 24, no. 2, pp. 329-337, 2009 authors profile seif eddine chouaba received his phd degree in automatic control from the university of poitiers, france, in 2012. he is an assistant professor at ferhat abbas university, setif, algeria. his main research interests include linear parameter-varying systems identification and modeling of heat exchangers. his current activities focus on modeling and control of electrical machines and static converters. abdallah barakat received his phd in 2011 from the university of poitiers (france). he is an assistant professor at beirut arab university in lebanon. he worked at general electric as principal engineer for 6 years in control of hydropower plants. his major research interests include modeling and control of electrical machines, power systems and static converters. microsoft word etasr_7-1_1329-1333.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1329-1333 1329 www.etasr.com bayati et al.: optimal placement and sizing of fault current limiters in distributed generation systems... optimal placement and sizing of fault current limiters in distributed generation systems using a hybrid genetic algorithm navid bayati department of electrical engineering amirkabir university of technology tehran, iran n-bayati@aut.ac.ir seyed hossein h. sadeghi department of electrical engineering amirkabir university of technology tehran, iran sadeghi@aut.ac.ir amir hosseini department of electrical engineering amirkabir university of technology tehran, iran hosseini.amir@aut.ac.ir abstract—distributed generation (dg) connection in a power system tends to increase the short circuit level in the entire system which, in turn, could eliminate the protection coordination between the existing relays. fault current limiters (fcls) are often used to reduce the short-circuit level of the network to a desirable level, provided that they are dully placed and appropriately sized. in this paper, a method is proposed for optimal placement of fcls and optimal determination of their impedance values by which the relay operation time, the number and size of the fcl are minimized while maintaining the relay coordination before and after dg connection. the proposed method adopts the removal of low-impact fcls and uses a hybrid genetic algorithm (ga) optimization scheme to determine the optimal placement of fcls and the values of their impedances. the suitability of the proposed method is demonstrated by examining the results of relay coordination in a typical dg network before and after dg connection. keywordshybrid ga; fcl; placement; dg; relay i. introduction in power systems, the short-circuit current will be examined by a directional over-current relay (docr) and, if necessary, break command be given to a circuit breaker (cb). each docr defines a certain breaking time based on the shortcircuit current which passes through it. if this performance fails, the backup docr will be activated after a minimum time interval. the coordination among docrs is very important in power system protection. coordination between docrs is usually adjusted using pickup current (ip) and the time multiplier setting (tms). the adjustment of tms in docr is a linear problem and the adjustment of ip is a non-linear problem. for the optimal adjustment of coordination between docrs, the optimal adjustment of tms and ip in [1-2] has been performed using ga and particle swarm optimization (pso) methods. in [3], relay adjustment is done by changing the network's topology. power network’s structure and short-circuit level in power systems change when connecting the distributed generation (dgs). in fact, after connecting dg, the increase in short circuit level causes a change in the coordination of docrs and may result in a protection miscoordination. there are several ways to reduce the short circuit level in the presence of dg. in [4] it has been stated that when there is a fault in the short circuit connection, dg connection should be interrupted; this method would cut off access to the dg after handling the fault which creates operational problems. one of the best ways to reduce the short circuit level is to use fault current limiters (fcls), which reduce the shortcircuit current with an increased impedance during faults. although using fcl is very costly, it offers many advantages such as reducing short-circuit current, reducing the voltage sag during fault and increasing the stability and reliability of the network. since fcl connection is costly, proper placement of the device and reducing the number of fcls are very important. in [5], the sensitivity factor method is used to determine the optimal placement of fcls. in [6], gas are used for optimal fcl placement. in addition, in order to reduce costs, optimum values of fcl's impedances should be considered. in [7-8] various methods have been used to optimize the amount of fcls. in this article, hybrid ga is implemented which uses a combination of ga and linear programming (lp) to optimize the amount of fcl. also, a new method is presented for proper placement of fcls that minimizes the number of fcls. here, the aim of placing the fcl is to restore the coordination of docr in the presence of dgs which reduces the operating time of docrs as well. the advantages of this method have been assessed in a network under several scenarios. finally the proposed method is compared with conventional algorithms such as gas. ii. relay coordination the aim of coordination of docrs is to adjust the tms and ip for each docr in a way that the time difference between the main docr and a backup docr of a specific coordination time interval (cti) is more. moreover, this means that if the main docr is not operated, the backup docr will be operated after cti. if the time difference of the operation between the main relay and the backup relay is less than cti, miscoordination will occur. also the main relay's engineering, technology & applied science research vol. 7, no. 1, 2017, 1329-1333 1330 www.etasr.com bayati et al.: optimal placement and sizing of fault current limiters in distributed generation systems... operating time should be minimized. in other words, the optimization of the objective function is defined as follows [9]: 1 n i i of t   (1) in the above equation, n is the number of relays and ti is the operating time of the main relay. according to iec standard, this time performance is defined as follows: 0.02 0.14 ( ) 1 p i i i i sc t tms i i   (2) in the above equation, tmsi and ipi are the settings of ith relay and isci is the short-circuit current passing through the main relay. in the optimization of docr’s coordination, a problem is stated where its constraints are as follows: j it t cti  (3) in the above equation, tj is the operating time of the backup relay and ti is the main relay operating time. cti is usually considered as 0.3 second. maxmin i tms tms tms  (4) a maximum and a minimum value are defined for tms and the value of tms for each relay should be considered in this range. maxminp p p i i i  (5) in the above equation, ipmin must be more than the maximum load current and ipmax should be less than shortcircuit current. using the constraints mentioned in (2) to (5) and using the fitness function which was defined in (1), we can adjust the docrs with the help of optimization algorithms such as ga. iii. optimizing fcl impedance the purpose of this article is to optimize the impedance value of fcl in a way that it restores the coordination of docrs, and optimizes their performance time; also due to economic reasons, the impedance value of fcls should be considered optimally. in this article, a resistive type fcl is used because its cost is lower compared to other types of fcl. the fitness function used in this paper is applied to determine the importance of the optimizing the weighting. the fitness function is composed of two parts, part one is related to the reducing time of the docrs’ performance and part two is related to optimization of the fcl's resistance. fitness function is as follows: 1 1 n l i i i j f t r      (6) in the above equation, 1 n i i t   represents the sum of the operating time of the main relay, 1 l i j r   indicates the total fcl's resistance used in the network, and  is the weight factor for the resistance. in this article,  is considered as 10. also the optimization constraints are as follows: maxmin r r r  (7-a) j it t cti  (7-b) in the above equation, r represents the resistance value of fcl that should be considered between the minimum and maximum values. also the second constraint represents the difference between the operating time of the backup and the primary relays which should be more than cti. because of the constraints, we can consider a penalty factor for the fitness function. by considering the penalty factor, the objective function is defined as follows[5]: 1 2 1 1 1 1 n l n l i i i j i j f t r k k            (8) in the above equation, k1 and k2 are considered as penalty factors. if the constraint which is shown in (7-a) is applied, the amount of k1 will be equal to zero and if the constraint is not applied, the amount of k1 will be equal to 500. the same consideration is applied for 7-b. iv. optimal fcl placement for optimum fcl utilization in power systems, restoration of protective miscoordination of docr caused by dg and the reducing the cost of fcl installations, proposed method must first determine and optimize the number and placement of fcls and then determine the amount of each fcl. for this purpose, at this stage, a method is proposed for the optimal placement of fcl. after the installation of dg in the power systems, the protection coordination of docr is eliminated due to changes of short-circuit level. again, it is necessary to use fcl to restore protection coordination. but the increase in the number of fcls and installation of additional fcls is very expensive. for this reason, it is necessary to optimize the number of fcls. for this purpose, after the optimization of fcls by optimization algorithms, the value of the fcl resistance is determined. first, it is assumed that all lines are candidates for fcl placement. then, after optimizing and determining the resistance of the fcls, the candidate locations having the least effects on eliminating miscoordination would be specified fcls at these places have the least resistanceso the places whose resistance is less than a certain amount can be determined and removed from the candidates. then the optimization can be applied again. the difference is that the optimization of the second low-impact places has been removed from the fcl candidates’ site. in this method, the number of fcls is reduced as much as possible and thus the cost is reduced. engineering, technology & applied science research vol. 7, no. 1, 2017, 1329-1333 1331 www.etasr.com bayati et al.: optimal placement and sizing of fault current limiters in distributed generation systems... v. hybrid ga optimization problems are defined both in linear and nonlinear parts. the linear problems can be optimized by lp algorithms and the nonlinear problems can be optimized with evolutionary algorithms such as the ga. in hybrid ga which has arisen from the combination of ga and lp, the linear parts of optimization problem are optimized by lp method and the non-linear parts of optimization problem are optimized by ga. [3] the advantages of this method are reducing simulation time and achieving better fitness function. also, this method improves optimized solutions due to reduction of ga variables. in this paper, hybrid ga is used for optimizing coordination between docrs and optimizing the resistance value of fcls. in the problem of coordination of docrs, the linear part determines the tms and the non-linear parts determine ip. in the optimization problem of fcl’s resistance, the linear parts determine the optimization of the fcl’s resistance and the non-linear parts determine the optimization of the time performance of the relays. hybrid ga flowchart is used to optimize fcl's resistance which is shown in figure 1. fig. 1. hybrid ga for optimize fcl resistance ga is composed of multiple parts: initialization, crossover, evaluation and mutation. these are further explained below: • initialization: at this stage, the need to optimize the initial population is conducted randomly and this initial population is used to build the next generation by evaluation. • evaluation: in ga, the value of each generation or string is determined by the fitness function and it becomes clear at this stage which parts of the population are to be used in the next step. in this paper, the used fitness function has been shown in (8). • crossover: this stage is usually probabilistic, the population which has a more desirable fitness function is more likely to be selected to participate in the next generations. • mutation: at this stage, a new population is created to participate in the ga which was not present in the previous population. this step makes it possible to increase the search in all cases of the problem. in the hybrid ga, the lp is described as a sub-problem being applied to the fitness function, in other words, the lp first specifies the linear values and then these values are given to ga and the ga optimizes the values of non-linear problem. vi. simulation and results the proposed method is applied on an 8-bus system with 14 docrs which is shown in figure 2 [10]. the dg has a capacity of 50mva, which is connected to bus 2 in the first scenario and they are connected to the buses 2 and 5 in the second scenario. the optimization method is conducted in a way that it first optimizes the coordination between docr regardless of dg. at this stage, (1) is the fitness function of the docr coordination. after docr’s coordination, with the addition of dg to the network, the short-circuit levels of the power network are changed and this change may cause protection miscoordination. then, in the next stage, by inserting the fcls to the network and measuring the shortcircuit currents and investigating the protection coordination, optimization is performed using hybrid ga, equation 7 and 8 have considered the fitness function and constraints, respectively. fig. 2. 8-bus system table i shows the docr settings without the presence of dg. to have a better protection coordination the following constraint is used; if the value of the constraint is positive, the protection coordination will be established: constraint= primarybackupt t cti  (9) in the first scenario, dg has only been connected to bus (2). as it is shown in table ii, a number of miscoordinations has arisen in docrs when dg is connected to bus 2. in other engineering, technology & applied science research vol. 7, no. 1, 2017, 1329-1333 1332 www.etasr.com bayati et al.: optimal placement and sizing of fault current limiters in distributed generation systems... words, the difference between the main and the backup relay’s operation time is less than the cti. for this reason, the fcl has been used to restore the protection coordination and its resistance value has been determined using the proposed method. as indicated in table ii, 15 pairs of docrs have been miscoordinated after installing the dg. as it has been shown in table ii at the first stage, all lines are candidates for the placement of fcls. after determining the fcl’s resistance by hybrid ga, all fcls with a resistance less than 0.2pu which is determined considering economic issues, are regarded as low impact fcls. so these fcls are removed and optimization is done again. as indicated in table iv, by removing the specified fcls, the protection coordination of docrs is restored and consequently, the costs of installing fcls are reduced. table i. docr settings without the presence of dg tms ip relay no. 0.058 596 1 0.573 120 2 0.297 338 3 0.332 123 4 0.228 120 5 0.262 120 6 0.571 80 7 0.488 120 8 0.050 353 9 0.198 120 10 0.330 120 11 0.482 120 12 0.354 120 13 0.501 80 14 table ii. relay pairs constraints primary relay no. backup relay no. constraint (without dg) constraint (with dg) 1 6 0.00 0.086 2 1 0.00 -0.919 2 7 0.00 -0.052 3 2 0.00 -0.017 4 3 0.00 -0.058 5 4 0.00 -0.024 6 5 0.49 0.272 6 14 0.37 0.291 7 5 0.00 -0.164 7 13 0.00 -0.362 8 7 0.12 0.035 8 9 0.91 -0.407 9 10 0.00 -0.012 10 11 0.00 -0.019 11 12 0.00 -0.017 12 13 0.11 -0.256 12 14 0.00 -0.038 13 8 0.00 0.144 14 1 0.14 -0.768 14 9 0.95 -0.343 also as it is shown in table iv, all protection coordination of docrs are restored after the installing the fcls. also optimization is performed using hybrid ga and ga. in hybrid ga, the value of the fitness function is less than that of ga and this reflects the strength of the proposed method. in the second scenario, dgs are connected to buses number 2 and 5. as indicated in table v, 15 pairs of docr s have miscoordinated after installing two dgs. after installing the fcls on the lines and the optimizing the values of the fcls, as shown in table vi, all coordination of docrs are restored. the amount and the location of the fcl have been shown in table vii. table iii. fcl resistance and placement line no. resistance (first stage) resistance ( second stage using hybrid ga) resistance ( second stage using ga) 1 0.6699 0.6553 0.7281 2 0.4066 0.3666 0.3496 3 0.0465 0.0000 0.0000 4 0.1924 0.0000 0.0000 5 0.2539 0.4883 0.8321 6 0.6994 0.7675 0.7087 7 0.3164 0.2057 0.8326 table iv. relay pairs constraints with fcl primary relay no. backup relay no. constraint (hybrid ga) constraint (ga) 1 6 0.4125 0.3778 2 1 0.0181 0.4470 2 7 0.0190 0.4649 3 2 0.0206 0.0346 4 3 0.2731 0.2644 5 4 0.0143 0.0120 6 5 0.4837 0.3814 6 14 0.3246 0.8334 7 5 0.0208 0.1050 7 13 0.0679 0.0004 8 7 0.0630 0.6060 8 9 0.9746 0.3135 9 10 0.0088 0.0638 10 11 0.1250 0.2287 11 12 0.1804 0.2889 12 13 0.2028 0.0686 12 14 0.0249 0.4151 13 8 0.6341 0.7164 14 1 0.1728 0.6842 14 9 0.9973 0.4096 fitness function 40.4 52.1 vii. conclusion this paper proposes an efficient method to determine the optimal resistance values and optimal placement of fault current limiters (fcls) in a distributed generation (dg) network to ensure protection coordination of directional overcurrent relays (docrs) both before and after dg connection. the proposed method adopts the removal of lowimpact fcls and uses a hybrid genetic algorithm (ga) optimization scheme to determine the optimal placement of fcls and the values of their resistances. the implementation of the proposed method on a typical dg network has shown that that the existence of fcls reduces the operating times of docrs while restoring their protection coordination in the presence of dg. it has also been shown that the proposed method minimizes the required number of fcls, thus reducing the installation costs. engineering, technology & applied science research vol. 7, no. 1, 2017, 1329-1333 1333 www.etasr.com bayati et al.: optimal placement and sizing of fault current limiters in distributed generation systems... table v. relay pairs constraints with 2 dgs primary relay no. backup relay no. constraint (without dg) constraint (with dg) 1 6 0.00 0.0287 2 1 0.00 -0.9331 2 7 0.00 -0.1457 3 2 0.00 -0.0168 4 3 0.00 -0.2068 5 4 0.00 0.0000 6 5 0.49 -0.2336 6 14 0.37 0.2143 7 5 0.00 -0.6487 7 13 0.00 -0.3608 8 7 0.12 -0.0438 8 9 0.91 -0.9382 9 10 0.00 -0.0359 10 11 0.00 -0.0586 11 12 0.00 0.0235 12 13 0.11 -0.2987 12 14 0.00 -0.1387 13 8 0.00 0.0281 14 1 0.14 -0.7835 14 9 0.95 -0.8905 table vi. relay pairs constraints with 2 dgs and fcl primary relay no. backup relay no. constraint (hybrid ga) constraint (ga) 1 6 0.4175 1.0427 2 1 0.0030 0.0085 2 7 0.2244 0.4860 3 2 0.0679 0.0153 4 3 0.2554 0.1536 5 4 1.0404 0.9189 6 5 0.6701 0.5322 6 14 0.6146 0.8668 7 5 0.1591 0.0058 7 13 0.0317 0.8896 8 7 0.3596 0.6248 8 9 0.5350 0.0000 9 10 0.0910 0.0084 10 11 0.2849 0.2604 11 12 2.1610 1.8342 12 13 0.1270 0.9622 12 14 0.1990 0.4129 13 8 0.6621 0.6842 14 1 0.2204 0.2512 14 9 0.6172 0.1040 fitness function 71.25 81.00 table vii. fcl resistance and placement line no. resistance (first stage) resistance ( second stage using hybrid ga) resistance ( second stage using ga) 1 0.6800 0.6625 0.6636 2 0.1687 0.3350 0.2568 3 0.7600 0.0000 0 .0000 4 0.2400 0.9783 0.9416 5 1.2600 1.6860 1.5008 6 0.9600 0.7635 1.6103 7 0.3600 0.6314 0.9259 references [1] f. razavi, h. a. abyaneh, m. al-dabbagh, r. mohammadi, h. torkaman, “a new comprehensive genetic algorithm method for optimal overcurrent relays coordination”, electric power systems research, vol. 78, no. 4, pp. 713-720, 2008 [2] j. b. ekanayake, “a systematic approach for phase-fault over-current protection coordination of complex networks”, international journal of electrical engineering education, vol. 45, no. 3, pp. 229-238, 2008 [3] a. s. noghabi, h. r. mashhadi, j. sadeh, “optimal coordination of directional overcurrent relays considering different network topologies using interval linear programming”, ieee transactions on power delivery, vol. 25, no. 3, pp. 1348-1354, 2010 [4] w. k. a. najy, h. h. zeineldin, w. l. woon, “optimal protection coordination for microgrids with grid-connected and islanded capability”, ieee transactions on industrial electronics, vol. 60, no. 4, pp. 1668-1677, 2013 [5] j. –h. teng, c. –n. lu, “optimum fault current limiter placement with search space reduction technique”, iet generation, transmission & distribution, vol. 4, no. 4, pp. 485-494, 2010 [6] s. a. hosseini, h. a. abyaneh, s. h. h. sadeghi, f. razavi, “merging the retrieval of the protection coordination of distribution networks equipped with dgs in the process of their siting and sizing”, journal of renewable and sustainable energy, vol. 8, no. 3, 2016 [7] h. –c. jo, s. –k. joo, k. lee. “optimal placement of superconducting fault current limiters (sfcls) for protection of an electric power system with distributed generations (dgs)”, ieee transactions on applied superconductivity, vol. 23, no. 3, article sequence number: 5600304, 2013 [8] w. el-khattam, t. s. sidhu, “restoration of directional overcurrent relay coordination in distributed generation systems utilizing fault current limiter”, ieee transactions on power delivery, vol. 23, no. 2, pp. 576-585, 2008 [9] a. s. noghabi, j. sadeh, h. r. mashhadi, “considering different network topologies in optimal overcurrent relay coordination using a hybrid ga”, ieee transactions on power delivery, vol. 24, no. 4, pp. 1857-1863, 2009 [10] h. h. zeineldin, e. f. el-saadany, m. m. a. salama, “optimal coordination of overcurrent relays using a modified particle swarm optimization”, electric power systems research, vol. 76, no. 11, pp. 988-995, 2006 microsoft word 07-823-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1245-1248 1245 www.etasr.com kurt et al.: important non-wood forest products in turkey: an econometric analysis important non-wood forest products in turkey: an econometric analysis rifat kurt bartin university, faculty of forestry bartin, turkey rkurt@bartin.edu.tr selman karayilmazlar bartin university, faculty of forestry bartin, turkey selman@bartin.edu.tr yildiz cabuk bartin university, faculty of forestry bartin, turkey ycabuk@bartin.edu.tr abstract—wood resources obtained from forest and non-wood forest products (nwfp) have gained great importance recently as their economic values keeps increasing by the day. in this study, forecasting of turkish non-wood forest products such as thyme, bay leaves, salvia and pine nut export amounts was carried out using a linear regression analysis method for the next fifteen years based on the data for the years between 1990 and 2009. moreover, estimated import values and actual import values from the last years were compered and analyzed. finally, predictions on future trends were made. keywords-regression; export; thyme; bay leaves; salvia; pine nut i. introduction an important potential of forests is the non-wood forest products (nwfp). since most of the non-wood forest products in turkey are subject to traditional small scale utilizations and are called secondary forest products. even in forests where wood is produced, non-wood forest products are seen as “auxiliary” or “secondary” products. forests where wood is not produced are considered as low-value or unvaluable forests [1]. non-wood forest products are defined as all kinds of plant or animal products which grow inside or around a forest, and from which human beings and other living things benefit to meet their needs or to generate income [2]. according to the world health organization (who) the number of plants used for various purposes around the world is 20,000. and of these plants, whilst 4,000 are widely used as herbal medicine, approximately 10% is traded [3]. as in all around the world, non-wood herbal forest products (nwhfp) make up the most important part of non-wood forest products in turkey. it is estimated that the number of nwhfp significant in world foreign trade is 150 and the annual foreign trade volume is around 1.1 billion dollars [4]. today, nwhfp can be used in a wide range of industries such as medical, spices, food, tea, dyes, perfumery and textiles and the marketing of these products could provide significant benefits [5]. bay leaves, thyme, salvia, pine nut, flower bulbs are among the main byproducts for which turkey has an export potential. apart from these products, different faculties continue their research on the species that could be grown in forest bedding [6]. ways are sought for increasing the contribution of nwfp to the economy, as their contribution is far below their potential. our country’s revenue from nwfp export in the past years is a lot higher than its revenue from wood products. in other words, nwfp make up the 98% of export revenue from wood products [7]. in the current study, based on the export data of thyme, bay leaves, salvia and pine nut, which have economic precedence, compared to other non-wood forest products in turkey, for 1990-2009 years, the export numbers for 15 years covering the period between 2010-2024 are estimated with regression analysis. ii. materials and methods a. materials the material in this study is the export data of thyme, bay leaves, salvia and pine nut between 1990-2009 (figure 1). the data for the aforementioned products were taken from the turkish statistical institute (turkstat) and the possible export numbers for 2010-2024 were calculated. the optimal regression models were formed using the spss statistical package. b. methods the main econometric method used in this study is simple linear regression analysis. regression analysis is a statistical procedure which uses the least squares approach in estimating the relationship between independent variable (s) and dependent variable in developing the estimation model [10]. if the regression analysis involves one dependent and one independent variable, then it is a simple linear regression. simple linear regression model is solved with the following equation: iii xy   where αi and βi represent the unknown parameters of the model, εi represents the error term, y represents dependent and x represents independent variables [11]. in this study, the export numbers of thyme, bay leaves, salvia and pine nut, which are the dependent variables of the study, for 15 years were found based on time series (years) and projection values were calculated using this collected data. calculation results given in the variance table of the regression model were compared with the coefficients of regression equation, statistical values f and t and table values of f and t statistical values at the significance level of α=0.05 and test was engineering, technology & applied science research vol. 6, no. 6, 2016, 1245-1248 1246 www.etasr.com kurt et al.: important non-wood forest products in turkey: an econometric analysis performed to find out whether the model is valid and the selected independent variable may be used satisfactorily or not. iii. findings a. regression analysis results and projection values relating to thyme, bay leaves, salvia and pine nut exports the results of regression analysis on thyme, bay leaves, salvia and pine nut exports indicated that the r square in the regression model is relatively high in non-wood forest products except pine nut. it was also seen that the f statistical values were valid for all the models or that the relationship between dependent and independent variables was significant at α=0.05 significance level (table i). it should be noted that r2=0.929 value for thyme export is a high certainty coefficient. this number indicates that the independent variable explains thyme export almost around 93% and that the structure of the linear model is appropriate. similarly, the certainty coefficient of the model set for bay leaves and salvia export (bay leaves: 0.920, salvia: 0.875) are high and provided the required explanation. and for pine nut, r2 =0.49 value is an acceptable certainty coefficient. because, coefficient of correlation, 0.70 (r), linear relationship between the variables, is about the level 0.60-0.70 recognized in the literature. the results of t and f statistical tests of the hypotheses obtained from anova and coefficient tables are given in table ii. the regression models built with thyme, bay leaves, salvia, pine nut are valid and significant. table iii shows the export projection values for thyme, bay leaves, salvia and pine nut. these values are found by putting the independent variable (year) in the regression equation (table i) formed for each product. in the table, it is estimated that the thyme export which was 11474 tons in 2009 is expected to be 17735 in 2024 with an increase of 54.5% (1.54 times). and similarly the bay leaves export is expected to see a 38.7% increase (1.38 times) and reach 12570 tons and salvia exports which was 1544.7 tons is expected to see 100.4% increase (2 times) and reach 3096 tons. also, pine nut export is estimated to have a 4% increase compared to 2009 and realize as 2300 tons in 2024. fig. 1. export amounts of thyme, bay leaves, salvia and pine nut (in tonnes). table i. the regression analysis results of non-wood forest products products r r2 regression model regression equation significance thyme 0.964 0.929 linear y = -806834.211+407.396x p<0.05 bay leaves 0.959 0.920 linear y= -649413.2+327.067x p<0.05 salvia 0.936 0.875 linear y= -160560.158+80.858x p<0.05 pine nut 0.70 0.49 linear y= -123531.883+62.170x p<0.05 table ii. t and f test results of non-wood forest products. products t calculation t table result h0 f calculation f table result h0 significance thyme 15.313 2.101 t calculation > t table reject 234.492 4.41 f calculation > f table reject significant bay leaves 14.414 2.101 t calculation > t table reject 207.758 4.41 f calculation > f table reject significant salvia 11.243 2.101 t calculation > t table reject 126.401 4.41 f calculation > f table reject significant pine nut 4.187 2.101 t calculation > t table reject 17.534 4.41 f calculation > f table reject significant engineering, technology & applied science research vol. 6, no. 6, 2016, 1245-1248 1247 www.etasr.com kurt et al.: important non-wood forest products in turkey: an econometric analysis table 3. export projecti̇ons for thyme, bay leaves, salvi̇a and pi̇ne nut (i̇n tons). years thyme bay leaves salvia pine nut 2010 12031.749 7991.47 1964.422 1429.817 2011 12439.145 8318.537 2045.28 1491.987 2012 12846.541 8645.604 2126.138 1554.157 2013 13253.937 8972.671 2206.996 1616.327 2014 13661.333 9299.738 2287.854 1678.497 2015 14068.729 9626.805 2368.712 1740.667 2016 14476.125 9953.872 2449.57 1802.837 2017 14883.521 10280.94 2530.428 1865.007 2018 15290.917 10608.01 2611.286 1927.177 2019 15698.313 10935.07 2692.144 1989.347 2020 16105.709 11262.14 2773.002 2051.517 2021 16513.105 11589.21 2853.86 2113.687 2022 16920.501 11916.27 2934.718 2175.857 2023 17327.897 12243.34 3015.576 2238.027 2024 17735.293 12570.41 3096.434 2300.197 b. comparison of projection values and actual values figure 2 shows the comparison of projected and actual export values of non-wood forest products between 2010-2014. in the figure, it is seen that the projected thyme and bay leaves numbers are very close to the projected numbers. it is also seen that the projected salvia values are within acceptable limits. however, it is seen that the actual pine nut numbers are far from the projections and that the export has shown significant decrease. the main factor behind this is the huge crop fall in bergama district of i̇zmir province particularly as of 2009 which provides 80% of turkey’s pine nut production [12]. a disease that occurred in pine nut trees as of 2009 caused to a significant decrease in production and as a result of that, the pines dried out and pine nut crop fell by a significant ratio of 60%. as a result of this, the amount of product exported and the inflow of currency decreased significantly [13-14]. fig. 1. projected and actual export numbers between 2010-2014 iv. results and conclusion when the 15-year export projections (covering 2010-2024) for thyme, bay leaves, salvia and pine nut, which have a significant share in turkey’s non-wood forest product export, was examined, it was seen that the certainty coefficient of the regression model set for thyme, bay leaves and salvia export (r2) had such high values as 0.929-0.920-0.875, respectively and that the linear model set for the projections was appropriate. and certainty coefficient of the model set for pine nut (0.49) had an acceptable correlation based on the literature (0.60-0.70). in general, it was projected that thyme export which was 11474 tons in 2009 is expected to increase 1.54 times, whilst bay leaves export which was 9063 tons in 2009 is expected to increase 1.38 times and salvia exports which was 1544.7 tons is expected to increase 2 times. also, pine nut export is expected to have a small increase of 1.04 times compared to 2009 and reach 2300 tons in 2024. when the last 5 years comparison for projected and actual export numbers are analysed, it is seen that the projections for thyme and bay leaves are very close to actual numbers. also, the projections for salvia could be considered acceptable. however, the projections and actual numbers for pine nut have significant differences. when the reasons of this is examined, it is seen that the reason behind it is not the structure of the model but the huge crop fall in bergama district of i̇zmir province which provides 80% of turkey’s pine nut production. due to a disease seen in pines in this area as of 2009, there has been a significant fall in productivity and a 60% fall in pine nut crops. in addition to their contribution to development and economy, the use of non-wood forest products in medicine and pharmaceutical industry in today’s world in which gm (genetically modified organism) foods are discussed, are highly important in terms of food safety due to their organic structure and their small interaction with chemicals. and these nwfps are becoming more and more prominent. turkey ranks the 21st in the export of non-wood forest products, however, the country ranks at the top of the list in the export of some nwfps. still it is obvious that non-wood forest products, which have a rich source in terms of plant diversity, wild life resources and endemic species, are not given due consideration and do not deserve its current condition. in order to increase the export of non-wood forest products in turkey the inventory and expansion of prominent products should be determined and the best time to harvest those products should be determined to ensure maximum engineering, technology & applied science research vol. 6, no. 6, 2016, 1245-1248 1248 www.etasr.com kurt et al.: important non-wood forest products in turkey: an econometric analysis productivity. considering that although there has been an increase in the export numbers of thyme and bay leaves in recent years, the fact that their unit prices fell necessitates that pricing decisions during the marketing phase should be taken in a healthier manner as soon as possible. in addition, during secondary wood raw material production and forestation, necessary measures shall be taken in order not to damage these resources. besides, in order to harvest these products in the following years, they should be harvested without damaging and the factories where they are processed should be equipped with the necessary technology. as stated in earlier research, by attaching the deserved importance to non-wood forest products, more contribution will be provided by these products to the economy of the country compared to the wood raw material and with efficient management, damage to the forests in the country will be prevented. references [1] r. kurt, y. cabuk, s. karayilmazlar, “türkiye ve dünya yuvarlak odun ve odun dışı orman ürünlerinin üretim, dış ticaret ve ekonomik potansiyel analizi” bartın üniversitesi, orman fakültesi dergisi, cilt: 13, sayı: 20, s.1-9, 2011a [2] u. geray, ulusal çevre eylem planı, orman kaynakları yönetimi, dpt yayınları, isbn:975-19-1917-7, ankara, 115 s, 1998 [3] o. balci, “odun dışı bitkisel ürünler”, bitkisel ürünler şube müdürlüğü, uluslararası orman yılı, www.ogm.gov.tr [4] dpt “viii beş yıllık kalkınma planı ormancılık özel i̇htisas komisyon raporu”, ankara, 2001 [5] r. kurt, y. cabuk, s. karayilmazlar, “foreign trade analysis of spices and spices derivates as non-wood forest products of turkey”, 2nd international non-wood products symposium, isparta, turkey, pp. 23-31, 8-10 september 2011, [6] b. ors, “orman ürünlerimiz ve orman köylüsüne katkıları”, kozalak, tc orman bakanlığı gazetesi, yıl:2, sayı:14, ekim 1999 [7] m. konukcu, “ormanlar ve ormancılığımız, faydaları”, i̇statistiki gerçekler, dpt yayın no: 2630, eylül, 2001 [8] turkstat, “turkish statistical institute (turkstat)”, ankara, www.tuik.gov.tr [9] r. kurt, türkiye odun dışı orman ürünlerinin mevcut durumu ve dış ticaret analizi, yüksek lisans tezi, bartın üniversitesi, bartın, 2011 [10] y. cabuk. s. karayilmazlar, r. kurt, s. m. onat, “estimating future development of the turkish plywood sector by the use of models affecting this forest i̇ndustry sector”, international journal of the physical sciences, vol. 6, no. 4, pp. 808-818, 2011 [11] o. unver, h. gamgam, uygulamalı i̇statistik yöntemler. i̇kinci baskı, siyasal kitabevi, ankara, 1996  [12] a. alp, “çam fıstığında düşen rekolte kozak üzümünü öne çıkardı”, ekonomi,http://www.dunya.com/ekonomi/ekonomi-diger/cam-istigindadusen-rekolte-kozak-uzumunu-one-cikardi-199122h.htm, [13] e. seyirden, “çam fıstığı rekoltesi üreticiyi de i̇hracatçıyı da üzdü”, http://ticaretgazetesi.com.tr/haberler_cam_fistigi_rekoltesi_ureticiyi_de_ ihracatciyi_da_uzdu-l-1-sayfa_id-666-id-103440, 2016 [14] url-1 “çam fıstığı verimini düşüren böcek bulundu”, http://www.yeniasir.com.tr/kenthaberleri/2015/01/13/cam-fistigiverimini-dusuren-bocek-bulundu , 2016 microsoft word 41-3615_s_etasr_v10_n3_pp5832-5836 engineering, technology & applied science research vol. 10, no. 3, 2020, 5832-5836 5832 www.etasr.com quoc: robust correction procedure for accurate thin shell models via a perturbation technique robust correction procedure for accurate thin shell models via a perturbation technique vuong dang quoc school of electrical engineering hanoi university of science and technology hanoi, vietnam vuong.dangquoc@hust.edu.vn abstract—this research proposes a robust correction procedure to improve inaccuracies around edges and corners inherent to thin shell electromagnetic problems by means of perturbation technique. this proposal is developed with three processes: a classical thin shell approximation replaced with an impedancetype interface condition across a surface is first considered and then a volume correction is introduced to overcome the thin shell approximation. however, the volume correction is quite sensitive to cancellation errors, with dramatic effects in the calculation of the local fields near edges and corners. therefore, a robust correction procedure is added to improve cancellation errors of the volume correction. each step of the developed method is validated on the practical problem. keywords-thin shell approximation; magnetic field; eddy current; joule power loss; perturbation method; subproblem method i. introduction thin sell (ts) models [1-3] are approximated by a priori known 1-d analytical distributions to avoid meshing the thin regions and lighten the mesh of surrounding regions with interface conditions (ics). however, these ics generally neglect end and border effects, which lead to inaccuracies in the calculation of local and global fields in the vicinity of geometrical discontinuities near borders and corners, increasing with thickness. in order to scope with this difficulty, a sub problem technique has been implemented for correcting errors surrounding the corners and edges appearing from the ts [4-5, 11]. but in this development, the volume correction is quite sensitive to cancellation errors, with the calculation of local fields (magnetic fields, eddy current losses, and joule power losses) near edges and corners. in this study, a robust correction procedure is embedded in the subproblem technique to guarantee the obtained solutions from volume corrections without cancellation errors in magnetic materials. the method is extended in the hearth of the sub problem method (spm), allowing a complete solution to express as a sum of sub problems (sps) solutions, already to applied numerous corrections and problem splitting [4-5]. the extensions are herein implemented for the magnetic vector potential finite element (fe) magnetodynamic formulation, paying special attention to the proper discretization of the constraints involved in each sp. ii. sequence of the perturbation technique a. definition of coupled sub problems based on the spm strategy [3-5], the scenario of the perturbation method is herein considered in two steps: a problem attending with the stranded inductor and ts model is first solved on a simplified mesh. the inaccuracy on ts solution is then improved by the volume correction taken by a robust correction procedure in order to overcome the cancellation error [4-7]. the relationship between sps is constrained by surface sources (sss) or volume sources (vss), where sss show changes of ics across surfaces from previous sps, and vss point out changes of material properties of volume thin regions. each sp is directly performed on its own mesh without depending on other meshes or solving again a new full problem for each new set of parameters as a traditional finite element method [7, 8, 10]. b. canonical magnetodynamic problem in the sp scenario, a canonical magnetodynamic problem p is defined in a domain ω� , with boundary �ω� = γ� = γ�,� ∪ γ ,�. it should be noted that the subscript p refers to the associated sp p. the eddy current conducting part of ω� is denoted ω�,� and the non-conducting one ω�,�� , with ω� = ω�,� ∪ ω�,�� . stranded inductors belong to ω�,�� . the equations, material relations, and boundary conditions (bcs) of the sp p are [4-7]: curl �� = ��, div�� = 0, curl�� = −����, (1a-b-c) �� = ������ + � ,�, �� = !��� + � ,� (2a-b) [# × ��]&',( = )*,�, # × ��|&',( = 0 (3a-b) where �� is the magnetic field, �� is the magnetic flux density, �� is the electric field, � ,� is the electric current density, �� is the magnetic permeability, !� is the electric conductivity and n is the unit normal exterior to ω�. the source fields � ,� and � ,� in (2 a-b) are vss. in the frame of spm, the field � ,� is usually considered as a remnant field in magnetic materials and expressed changes of permeability. the field � ,� is an imposed electric current corresponding author: vuong dang quoc engineering, technology & applied science research vol. 10, no. 3, 2020, 5832-5836 5833 www.etasr.com quoc: robust correction procedure for accurate thin shell models via a perturbation technique density in inductors and presented changes of conductivity. for that, the changes from sp u (�, and !, to sp p (�� and !�), � ,� and � ,�) are defined [4-7]: � ,� = (���� − �,��)�,, � ,� = (!� − !,)�, (4a-b) the total fields to be related by the uploaded relations � = ����(�� + �,) and � = !�/�� + �,0 [3, 4]. the source field )*,� in (3a) is sss. in general, these sss are defined as zero for classical homogeneous bcs. ics can define their discontinuities through any interface 1� (with sides 1�2 and 1��) in ω�, with the notation [∙]4( = |4(5 − |4(6. on the other hand, they can be considered as sss for particular phenomena appearing at the both sides (1�2 and 1��) of the thin regions [3, 4]. c. thin shell finite element model the constraints between the ts model and volume corrections are expressed via vss and sss. for the magnetic vector potential formulation (b-conformal formulation) in the ts model [3], these sources are defined via the bcs and ics of impedance-type boundary conditions (ibc) associated with solutions from previous sp which can be a stranded inductor alone or the inductors with the ts model. therefore, the constraint from the ts model to the volume correction problems, or from the volume corection to the robust correction procedure, can be obtained from [3], i.e.: [# × ��]4( = −!7��/29�,� + 9:,�0 (5) # × ��|4(5 = � ; <!7��/29�,� + 9:,�0 + � => 9:,�? − # × �,|4(5 = � ; <!7��/29�,� + 9:,�0 + � => 9:? − )*,� (6) where 9:,� and @�,� are respectively the discontinuous and continuous components of the field 9�. it should be noted that 9:,� is considered as zero on the negative side γ� ,�� of the ts, which cancels the magnetic flux entering there [3]. a (the thickness of the ts), b (the skin depth) and 7 are also given [3]. the discontinuity [−# × �,|4(5 in (6) is really an ss for the volume correction. iii. sequence of weak formulations a. b-conformal formulation the weak �� -conformal formulation for problem p is achieved from the weak form of the ampere’s law (1a), i.e. [47]: (����curl 9�, curl 9�c )de + (!���9�, 9�c )f + (!�grad i�, 9�c )dj,( + (� ,�, curl 9�c )dj,( +(� ,�, curl 9�c )dj,( + 〈# × ��, 9�c 〉&',(�m( + 〈# × ��, 9�c 〉&n,( + 〈−[# × ��]4( , 9� c 〉m( = (� , 9� c )do,( (7) ∀9�c ∈ r��/ω�0 where r��/ω�0 is a gauged curl-conform function space presented in ω�, containing the basis functions for 9� and for the test function 9�c . factors (. , . )de and 〈. , . 〉&e are respectively notations of a volume intergal in ω� and a surface intergal on γ� of the product of their vector field arguments. the surface integral term on γ�,� accounts for natural bcs of type (3 b), which is usually zero. the term 〈−[# × ��]4(, 9�c 〉m( in (9) is the ts model and can be expressed as [3]: 〈[# × ��]4(, 9�c 〉m( = 〈[# × ��]4(, 9�,�c 〉m( + 〈# × ��|m(5, 9:,� c 〉m(5 + 〈# × ��|m(6, 9:,� c 〉m(6 (8) where 9:,�c and 9�,�c are the test functions and 9:,�c is equal to zero on the negative side γ�,�� = γ�,�� of the ts [3]. the terms 〈[# × ��]4(, 9�,�c 〉m( and 〈# × ��|m(5, 9:,� c 〉m(5 are already defined in (5) and (6). thus, (8) becomes: 〈[# × �]4(, 9�c 〉m( = −〈!7��/29�,� + 9:,�0,9�,�c 〉m( + � ; 〈<!7��/29�,� + 9:,�0 + � => 9:? , 9�,�c 〉m( − )*,� (9) b. volume correction and robust correction procedure replacing ts representation the ts solution is obtained by combining (7), (8) and (9). the solution is now improved by the volume correction (e.g. problem k) via vss (� ,�,curl 9�c )dj,( (� ,�,curl 9�c )dj,( given by (4a) and (4b). this means that these fields need to be transferred from the mesh of the ts problem p to the mesh of next problem k (volume correction k) via a projection method [9]. for that, the weak form for the problem k is written as (�u��curl 9u, curl 9uc )dv + (!u��9u, 9u c )dj,v +(!ugrad iu, 9uc )dj,v + ((�u �� − ����)(curl 9�, curl 9uc )dv +〈[# × �u]4w,v, 9u c 〉mw,v + (!u��9�, 9u c )dj,v = 0, ∀9uc ∈ ru�(ωu) (10) at the same time to the vss in (10), the sss related to ics [4-5] have to extract the ts discontinuities. thus, the trace # × �u]4w,v in (10) is strongly fixed as: 〈[# × �u]4w,v, 9u c 〉mw,v = −〈[# × ��]4w,v,9u ′ 〉γw,v (11) at the discrete level, the source field 9� solved in the mesh of the ts problem p is projected to the mesh of problem k in (10), with ω�,u limited to the volume correction, which thus reduces the computational effort of the process of projection. the volume correction in (10) is really sensitive to cancellation errors, with dramatic effects on the calculation of the field 9� (see figure 5 in [6]). in order to avoid the cancellation error, we need to combine a problem k-a with: �u�x = �u�x�� �u�x + (�u�x�� − ����)�� (12) considering a perfect magnetic region in ω�,u (�u�x = ∞, �u�x�� = 0), and a problem k-b with: �u�z = �u�z�� �u�z + (�u�z�� − �u�x�� )(�u�x + ��) (13) presenting a change to the actual permeability ( �u�z = �x�,�x[ = �u). the problem k-a uses a ss only contributing on the positive side of γ�,u2 of γ�,u, that is: engineering, technology & applied science research vol. 10, no. 3, 2020, 5832-5836 5834 www.etasr.com quoc: robust correction procedure for accurate thin shell models via a perturbation technique [# × �u�x]&j,v= # × �u�x|&j,v5 = −# × ��|&j,v5 = � ,\,u�x (14) with � ,u�x = 0 and �u�x ≠ 0. the trace # × ��|&j,v5 is originally presented in (18) for the problem p limited to γ�,u = = γ�,�. it maybe also naturally presented via the volume in (10), that is: 〈[# × �u�x]&j,v,9u c 〉&j,v = − 〈# × ��|&j,v5 , 9u c 〉&j,v = (����curl 9�,curl 9uc |&j,v5 )d^_ (15) where ω`a is limited to one single layer of fes touching γ�,u2 , because it involves only the associated trace # × 9uc |&j,v5 [5] ( 9u�xc = 9u�zc = 9uc because of the same property on the mesh). for the problem k-b, the vs has: � ,u�z = (�u�z�� − �u�x�� )(�u�x + ��) (16) with �u�z = �x�,�x[ = �u and �u�x�� = 0. both problems k-a and k_b are being solved at the same time, with the ss �*,u = # × ��|&j,v5 = �*,u�x and the resulting relation is: �u = �u�x + �u�z = −������ + �u�z�� �u�z + �u�z�� /�u�x + ��0 = = �u��/�u�x + ��0 + (�u�� − ����)�� (17) this procedure needs the projection of the source field in the added magnetic region (for vss) as well as in the layer of fes surrounding this region (for sss). c. projections of solutions between meshes in the spm strategy, the ts is considered as an ss in a submodel ω�,u which is a subset of ωu. at the discrete level, the source field from the previous problem (e.g. 9� in the previous mesh problem p) is projected in the mesh of the current (new) problem (e.g. problem k). this can be done via a projection method [8] of its curl limited to ω�,u, i.e.: /curl 9�,u��\bc, curl 9uc 0dj,v = /curl 9�, curl 9u c 0 dj,v , ∀9uc ∈ du�(curl, ωu) (18) where du�/curl, ω�,u0 is a gauged curl-conform function space for the k-projected source 9�,u��\bc and the test function 9uc . iv. numberical test the numerical test is an actual problem including an inductor located below a shielding thin plate (figure 1). fig. 1. flux geometry of inductor and thin plate (dimensions in mm) the inductor carries a fixed current density (excitation current i =1a, frequency f = 50 hz, number of turns n = 1000). the test problem is solved in three steps: • step 1: the stranded inductors with the ts model approximations (sp p) are first solved • step 2: the volume correction (sp k) is given to overcome the ts approximations at step 1 • step 3: the robust correction procedure is considered to improve cancelation errors at step 2 the ts solution sp p on the magnetic vector potential at step 1 considered with the thin plate and the stranded inductor is shown in figure 2(a). next, a volume correction sp k then replaces the ts approximation with an actual volume covering the plates and their surroundings without including the stranded inductor anymore (figure 2(b)). as presented, this volume correction is very sensitive to cancellation errors, with dramatic effects on the calculation, thus it is improved by a robust correction procedure (figure 2(c)). (a) (b) (c) fig. 2. flux lines (real part) on the magnetic vector potential for (a) the ts solution, (b) volume correction with cancellation errors, and (c) robust correction procedures (c) (d=10mm, f=50hz, �\=100 and !=59ms/m). engineering, technology & applied science research vol. 10, no. 3, 2020, 5832-5836 5835 www.etasr.com quoc: robust correction procedure for accurate thin shell models via a perturbation technique the relative robust correction procedure of the longitudinal magnetic flux along the thin plate increases with the different thicknesses (f= 50 hz, �\ = 100 and ! = 59 ms/m), as shown in figure 3. for thickness d = 10 mm, it can reach several tens percent in the vicinity near edges and corners of the plate, i.e. 70 %, with f = 50 hz, �\ = 100, ! = 59 ms/m and b = 1.977 mm. for the lower thickness d = 2.5 mm, the error is lower than 15% from the middle to the end. fig. 3. relative robust correction procedure of the longitudinal magnetic flux along the thin plate, with different thicknesses (f=50hz, �\ =100 and !=59ms/m). (a) (b) (c) fig. 4. distribution of eddy current densities with (a) the ts solution, (b) cancellation error, and (c) the robust procedure (d=10mm, f=50hz, �\=100and !=59ms/m). fig. 5. joule power loss densities with ts solution, volume correction with cancellation error, and the robust procedure along the thin plate (d=10mm, f=50hz, �\=100 and !=59ms/m). the eddy current density of the ts sp p (figure 4(a)) is corrected by the volume correction sp k (figure 4(b)) without taking the cancellation error into account. the robust correction procedure (figure 4(c)) is proposed to improve the cancellation errors to overcome the volume correction at step 2. the error obtained is 32% at the plate end. the inaccuracy on the joule power loss density along the half plate of the ts solution approximation sp p, the volume correction sp k and the robust correction procedure are pointed out in figure 5, with d = 10 mm, f = 50 hz, �\ = 100, ! = 59 ms/m. the significant errors approximately reach 58% between the ts solution sp p and the volume correction sp k, or nearly 20% between the volume correction sp k and the robust correction procedure. the robust correction procedure is then compared with the reference solution computed from the traditional finite element method (fem) [7, 8, 10]. this is an agreement to illustrate a very suitable validation of the robust correction procedure developed in the perturbation technique. v. discussion and conclusions robust correction procedure with the magnetic vector potential formulation has been sucessfully developed via a perturbation technique in order to improve the cancellation errors on the local fields of magnetic vector potential, magnetic flux, eddy current loss, and joule power loss density inherent to the ts approximation and the volume correction. the computed results of the extend method are close to the reference fem calculation solution [7, 8, 10], which is a very good validation of the studied technique. the development has been successfully done with the linear case in the frequency domain. extension of the method could be further performed in two-way coupling [12]. all the steps of the technique have been validated and applied to the practical problem. references [1] h. tsuboi, t. asahara, f. kobaysashi, t. misaki, “eddy current analysis on thin conducting plate by an integral equation method using edge elements”, ieee transactions on magnetics, vol. 33, no. 2, pp. 13461349, 1997 [2] c. geuzaine, p. dular, w. legros, “dual formulations for the modeling of thin electromagnetic shells using edge elements”, ieee transactions on magnetics, vol. 36, no. 4, pp. 799-802, 2000 [3] p. dular, v. q. dang, r. v. sabariego, l. krahenbuhl, c. geuzaine, “correction of thin shell finite element magnetic models via a 0 10 20 30 40 50 60 70 80 0 0.02 0.04 0.06 0.08 0.1 0.12 r o b u st p ro c e d u re o f fl u x ( % ) position along half-plate, from the middle to the end (m) d = 10 mm d = 7.5 mm d = 5 mm d = 2.5 mm engineering, technology & applied science research vol. 10, no. 3, 2020, 5832-5836 5836 www.etasr.com quoc: robust correction procedure for accurate thin shell models via a perturbation technique subproblem method”, ieee transactions on magnetics, vol. 47, no. 5, pp. 1158--1161, 2011. [4] v. q. dang, p. dular, r. v. sabariego, l. krahenbuhl, c. geuzaine, “subproblem approach for thin shell dual finite element formulations”, ieee transactions on magnetics, vol. 48, no. 2, pp. 407-410, 2012 [5] p. dular, r. v. sabariego, “a perturbation method for computing field distortions due to conductive regions with h-conform magnetodynamic finite element formulations”, ieee transactions on magnetics, vol. 43, no. 4, pp. 1293-1296, 2007 [6] p. dular, r. v. sabariego, c. geuzaine, m. v. ferreira da luz, p. kuopeng, l. krahenbuhl, “finite element magnetic models via a coupling of subproblem of lower dimensions”, ieee transactions on magnetics, vol. 46, no. 8, pp. 2827-2380, 2010. [7] s. koruglu, p. sergeant, r.v. sabarieqo, v. q. dang, m. de wulf “influence of contact resistance on shielding efficiency of shielding gutters for high-voltage cables”, iet electric power applications, vol. 5, no.9, pp. 715-720, 2011 [8] g. meunier, the finite element method for electromagnetic modeling, john wiley & sons, 2008 [9] c. geuzaine, b. meys, f. hernotte, p. dular, w. legros, “a galerkin projection method for mixed finite elements”, ieee transactions on magnetics, vol. 35, no. 3, pp. 1483-1441, 1999 [10] k. abubakri, h. veladi, “investigation of the behavior of steel shear walls using finite elements analysis”, engineering, technology & applied science research, vol. 6, no. 5, pp. 1155-1157, 2016 [11] f. g. kizilcay abdulla, r. abdulla, “a comparative application for evaluating composite fabrics used in electromagnetic shielding”, engineering, technology & applied science research, vol. 7, no. 6, pp. 2156-2159, 2017 [12] v. d. quoc, c. geuzaine, “two-way coupling of thin shell finite element magnetic models via an iterative subproblem method”, compel the international journal for computation and mathematics in electrical and electronic engineering, ahead-of-print, doi: 10.1108/compel-01-2020-0035, 2020 author profile vuong dang quoc received his phd degree in 2013 from the faculty of applied sciences at the university of liege in belgium. after that he came back to the hanoi university of science and technology in september 2013, where he is currently working as the director of the training center of electrical engineering, school of electrical engineering, hanoi university of science and technology. dr. vuong dang quoc’s research domain encompasses modeling of electromagnetic systems by coupling of subproblem method with application to thin shell models. . microsoft word 07-3350_s engineering, technology & applied science research vol. 10, no. 2, 2020, 5382-5386 5382 www.etasr.com sahhal & gunay: effect of severe plastic deformation on the mechanical properties of welded … effects of severe plastic deformation on the mechanical properties of welded st37-2 steel abubaker sahhal mechanical engineering department karabuk university karabuk, turkey abubaker_ahmad@yahoo.de mustafa gunay mechanical engineering department karabuk university karabuk, turkey mgunay@karabuk.edu.tr abstract—cold treatment techniques are used to enhance the mechanical properties of metal alloys, whose most important characteristics are strength, roughness, and microstructure. the aim of this research is to test the effect of conventional shot peening (csp) and severe shot peening (ssp) on the mechanical properties of st37-2 steel. the results of the experiments showed enhancements in surface roughness and tensile strength. however, shot peening decreased the ductility of the metal and caused changes in its microstructure that are indicated in the xrf and xrd tests. results’ data are provided as an original contribution to the literature while they are compared with the existing data. keywords-st37-2; shot peening; severe plastic deformation i. introduction surface treatment using cold techniques is widely used to enhance the mechanical properties of metal alloys [1]. shot peening is one of these processes that has an impact on surface roughness, residual stresses, microstructure, and folding of the metal [2]. the effects of plastic deformations resulting from welding or shot peening can be beneficial or have adverse effects on its strength and ductility [3]. severe plastic deformation (spd) is formed in metals through processes such as hydrostatic extrusion which deform the metal at low temperatures. spd results into a fine crystalline structure that differs from the crystallographic structure of the original metal or alloy, through forming micrometric and submicrometric subgrains in the coarse grain of the original material [4]. the advantages of spd on the performance and mechanical properties derive from its ability to achieve deformations in the microstructure through fine grains, which reflects on the performance results of hardness and yield stress to saturation levels [5]. the disadvantages of spd are embodied mainly in the decreased ductility and decreased metal ability to undergo plastic deformation under stress [6]. ii. research aim and methods a. research aim the main aim of the current research is to test the effects of spd through electric arc welding and shot peening on the mechanical properties and microstructure of st37-2. it is expected for these processes to affect the microstructure and the homogeneity of the specimens, thus altering their mechanical properties. b. material and sample preparation the alloy used in this experiment is st37-2 (metal content percentages are shown in table i). the alloy has 0.2% carbon and 0.011% nitrogen maximum content. the tensile strength of the alloy ranges between 360 and 460mpa while it yields at 235mpa with a minimum elongation of 25% [7]. table i. chemical composition of st37-2 (%) [8] fe mn si al cr cu ni p s 98.7012 1.0916 0.0641 0.0408 0.0285 0.0253 0.0235 0.0158 0.0091 after cleaning the steel plates, the samples were initially prepared with dimensions of 400mm length, 200mm width, and 10mm thickness. plate pairs were welded with an arc welding device with a 10mm welding to form a single plate, as shown in figure 1. the welding slag was removed with an electric grinding machine. using a plasma cut, the welded plates were cut into six samples, as shown in figure 2. three specimens were prepared for tensile testing and three for fatigue testing. the sample dimensions followed the astm specifications of the testing specimens. figure 3 shows the specimens for tensile and fatigue testing. fig. 1. arc welding of steel plates fig. 2. testing specimens schematic corresponding author: abubaker sahhal engineering, technology & applied science research vol. 10, no. 2, 2020, 5382-5386 5383 www.etasr.com sahhal & gunay: effect of severe plastic deformation on the mechanical properties of welded … (a) (b) fig. 3. samples for (a) tensile testing and (b) fatigue testing four out of the six specimens were shot peened with two almen intensities, a12-14 (csp) and a28-30 (ssp). the shot peening conditions are shown in table ii. table ii. conditions of shot peening for csp (conventional) and ssp (severe) almen intensity shot size coverage duration (sec) air pressure (psi) arc height (mm) a12-14 (csp) s230 200% 10 30 0.13 a28-30 (ssp) s230 200% 15 60 0.29 the process of shot peening involves striking the samples with tiny particles with a specific pressure that acts as a hammer on a small area of the surface in order to create indentations or dimples [9]. the process energizes the particles with kinetic energy which is absorbed by the metal surface [10], which then attempts to restore its original condition [11]. the main target of using shot peening is to increase the hardness and fatigue resistance of the samples, while reducing tension [12]. figures 4-5 show the metal surfaces after using the two types of shot peening. the top picture shows shot peening with a12-14 almen, while the bottom picture shows shot peening with a28-30 almen. fig. 4. surface of st37-2 after shot peening, a12-14 fig. 5. surface of st37-2 after shot peening, a28-30 iii. results and discussion a. surface roughness three samples were tested for surface roughness: untreated, type a12-14 shot peening, and type a28-30 shot peening. average roughness (ra), root mean square roughness (rq) and average maximum height of roughness profile (rz) were obtained. figures 6-8 show the plots of the testing outputs. the results show a significant increase in roughness between the untreated metal and the csp cases, while more increase in roughness can be observed in the ssp cases. these results are in accordance with the literature. authors in [13] increased hardness and roughness for engine bladed with shot peening, while authors in [14] showed that the increase in shot peening severity increased surface roughness in zk60 alloy. table iii. surface roughness values material almen intensity ra rq rz st37-2 steel a12-14 (csp) 6.568 8.174 32.267 st37-2 steel a28-30 (ssp) 7.466 8.907 34.432 st37-2 steel as received 0.198 0.253 1.432 fig. 6. roughness test profiles (untreated) fig. 7. roughness test profiles (a12-14) fig. 8. roughness test profiles (a28-30) b. tensile test the force required to break a specimen and its elongation were measured through a tensile strength test according to astm d-638, astm d-3039, and astm c-297 standards. as shown in table iv, the first sample treated with type a2830 shot peening retained the yield strength of 360mpa, while the ultimate tensile strength was enhanced by less than 5%. the engineering, technology & applied science research vol. 10, no. 2, 2020, 5382-5386 5384 www.etasr.com sahhal & gunay: effect of severe plastic deformation on the mechanical properties of welded … elongation of the first sample decreased by around 5%. the changes are considered insignificant for the first sample. however, the second sample treated with type a28-30 shot peening showed more significant results as yield strength increased by 19.7%, ultimate tensile strength increased by 22.8%, and elongation decreased by at least 46.8%. the results indicate increased tensile strength accompanied with decreased ductility of the sample. samples treated with shot peening type a12-14 and those that were not treated with shot peening showed insignificant changes in yield strength and ultimate tensile strength. figures 9-11 show the plots of the tensile test results. elongations have decreased at least by 1.2% to 27.2%, confirming the effect of shot peening on the ductility of the alloy. these results are based on standard range values of st37-2. however, other studies of the alloy showed yield strength and ultimate tensile strength values of 235mpa and 436.8mpa respectively for untreated samples. therefore, the results of the current study are considered significant in comparison to such results [15]. the results also show that ssp with type a28-30 showed enhanced tensile strength in comparison with csp which confirms the results of the literature in this aspect [16]. generally, shot peening showed enhanced strength in comparison with untreated samples [13]. table iv. results of tensile strength t testing material almen intensity ys (mpa) uts (mpa) elongation (%) st37-2 steel a28-30 360 482 23.7 a28-30 431 565 13.3 a12-14 352 478 24.7 a12-14 357 472 20.7 as received 349 469 18.2 as received 348 469 23.2 fig. 9. tensile test plots for a12-14 c. microhardness test vickers microhardness test was conducted by applying a load of 1kg for 15s by a ball indicator. measurements were taken by a calibrated optical microscope for the stress in mpa, as shown in table v. shot peening increased microhardness from its original value of 150 for st37-2 by averagely 21.1% to 47.6% [17]. authors in [18] showed that microhardness for low carbon steel has an average value of 92, which proves that the obtained hardness values in the current study are a huge enhancement. fig. 10. tensile test plot for a28-30 fig. 11. tensile plots for the untreated samples table v. vickers microhardness test values almen intensity value (1) value (2) value (3) average a28-30 222 224 218 221.33 a12-14 189 192 188 189.67 as received 183 181 181 181.67 d. xrf analysis x-ray fluorescence (xrf) is a microscopy method that is used to measure the concentration of metals in a specific area. the method depends on the interaction between the x-ray arrays with the matter by dislodging electrons from atoms, measuring the resulting energy and correlating it with a specific element [19]. as seen from the results of the xrf (table vi), the mass percentage of each metal component has been changed through shot peening, while the analysis depth ranged between 0.0009 and 0.0355mm. 0 100 200 300 400 500 600 -0,5 4,5 9,5 14,5 19,5 24,5 29,5 s ta n d a r d f o r c e [ m p a ] strain [%] 0 100 200 300 400 500 -0,5 4,5 9,5 14,5 19,5 s ta n d a r d f o r c e [ m p a ] strain [%] 0 100 200 300 400 500 600 -0,5 4,5 9,5 14,5 19,5 24,5 29,5 s ta n d a r d f o r c e [ m p a ] strain [%] 0 50 100 150 200 250 300 350 400 450 500 -0,5 4,5 9,5 14,5 19,5 24,5 s ta n d a r d f o r c e [ m p a ] strain [%] 0 100 200 300 400 500 -0,5 4,5 9,5 14,5 19,5 24,5 29,5 s ta n d a r d f o r c e [ m p a ] strain [%] engineering, technology & applied science research vol. 10, no. 2, 2020, 5382-5386 5385 www.etasr.com sahhal & gunay: effect of severe plastic deformation on the mechanical properties of welded … table vi. xrf analysis of st37-2 component result unit ei line det. limit intensity w/o normal analyzing depth (mm) al 0.0408 mass% 0.00204 al-ka 0.3807 0.0418 0.0009 si 0.0641 mass% 0.00205 si-ka 0.6215 0.0656 0.0013 p 0.0158 mass% 0.00103 p-ka 0.4290 0.0161 0.0018 s 0.0091 mass% 0.00072 s-ka 0.2240 0.0093 0.0025 cr 0.0285 mass% 000432 cr-ka 0.6336 0.0292 0.0230 mn 1.0916 mass% 0.00870 mn-ka 20.4876 1.1177 0.0265 fe 98.7012 mass% 0.02378 fe-ka 2319.6146 101.0629 0.0355 ni 0.0235 mass% 0.00802 ni-ka 0.2879 0.0241 0.0066 cu 0.0253 mass% 0.00556 cu-ka 0.3890 0.0259 0.0104 e. xrd analysis in order to identify crystalline material in the samples that were treated with shot peening, x-ray powder diffraction (xrd) analysis was used. figure 12 shows the peaks of three samples, which are identical in phase pattern and position, while differing in intensity. the matching patterns and positions are signs of error absence in positioning during the experiment. the slightly higher broadening at 64.85 and 82.27 degrees indicates minor nanocrystalline ceria. the three peaks shown in the figure show that changes in the micro-strains have occurred with shot peening and their intensities decreased with the increase of the severity of the deformation through shot peening in the metal. fig. 12. diffractogram of xrd analysis f. optical microscope two specimens were investigated with an optical microscope (figure 13) to study the microstructure and mechanical changes of the shot peening treatment. shot peening with csp a12-14 almen intensity affected a thin layer with minimum influence, while shot peening with ssp a28-30 almen intensity had a higher intensive influence to a thicker layer. in the ssp case, an intrinsic structure is observed. the ferrite and perlite phases are clear with ssp a28-30 [20]. g. scanning electron microscopy (sem) as shown in figure 14, the specimens treated with shot peening were tested with sem. both a12-18 and a28-30 almen intensities yielded plastic deformations. disturbances were increased in the ssp case, while it created more intense bumps and pits. layer thickness was increased by 24.4% in the ssp case in comparison with the csp case. the homogeneity of the alloy did not seem to be affected in both samples by shot peening, however the increase in hardness as confirmed by the hardness test is reflected by the formation of connected deformed structures [21]. (a) (b) fig. 13. optical microscope images for shot peened samples: (a) csp a1214, (b) ssp a28-30 (bottom) (a) (b) fig. 14. fesem images of plastic deformed layer of shot peened specimens: (a) csp a12-14 (top-layer thickness=7.8µm), (b) ssp a28-30 (bottom-layer thickness=9.7µm) engineering, technology & applied science research vol. 10, no. 2, 2020, 5382-5386 5386 www.etasr.com sahhal & gunay: effect of severe plastic deformation on the mechanical properties of welded … iv. conclusion the enhancement of alloy properties can be achieved through cold techniques such as shot peening, targeting improvements in strength, roughness, and microstructure. the current research aims to investigate the effects of conventional (csp) and severe (ssp) shot peening on the mechanical properties of st37-2 steel through their comparison with untreated specimens, and performing an arc weld as severe plastic deformation (spd). two almen intensities were used, a12-14 and a28-30. the surface roughness values showed substantial increases in ra, rq and rz values between a12-14 and untreated st37-2 samples, while a higher increase in roughness was achieved with a-23-30 shot peening. the tensile strength results show enhancements in yield strength and ultimate tensile strength values reaching up to 19.7% and 22.8% with ssp, while elongation decreased up to 27.2% confirming the decrease in ductility with shot peening. the hardness of the alloy increased in treated samples and the changes in microstructure were exhibited by xrf and xrd analyses. deformation intensities were investigated with optical microscopy and were found to have increased while a layer thickness increase in the ssp case (in comparison with the csp case) was observed. some data confirm the past literature findings, while the research contributes to the relevant literature with original data. references [1] l. singh, r. a. khan, m. l. aggarwal, “effect of shot peening on hardening and surface roughness of nitrogen austenitic stainless steel”, international journal of engineering science and technology, vol. 2, no. 5, pp. 818-826, 2010 [2] a. kubit, m. bucior, w. zielecki, f. stachowicz, “the impact of heat treatment and shot peening on the fatigue strength of 51crv4 steel”, procedia structural integrity, vol. 2, pp. 3330-3336, 2016 [3] y. ma, m. yang, f. yuan, x. wu, “a review on heterogeneous nanostructures: a strategy for superior mechanical properties in metals”, metals, vol. 9, article id 598, 2019 [4] m. umemoto, y. todaka, k. tsuchiya, “formation of nanocrystalline structure in steels by air blast shot peening”, materials transactions, vol. 44, no. 7, pp. 1488-1493, 2003 [5] o. unal, e. maleki, “shot peening optimization with complex decisionmaking tool: multi criteria decision-making”, measurement, vol. 125, pp. 133-141, 2018 [6] d. kumar, s. idapalapati, w. wang, s. narasimalu, “effect of surface mechanical treatments on the microstructure-property-performance of engineering alloys”, materials (basel), vol. 12, no. 16, article id 2503, 2019 [7] a. ampaiboon, o. u. lasunon, b. bubphachot, “optimization and prediction of ultimate tensile strength in metal active gas welding”, the scientific world journal, vol. 2015, article id 831912, 2015 [8] r. ranji, a. h. zakeri, “mechanical properties and corrosion resistance of normal strength and high strength steels in chloride solution”, journal of naval architecture and marine engineering, vol. 7, pp. 93-100, 2010 [9] i. karademir, o. unal, s. ates, h. gokce, m. gok, “effect of severe plastic deformation on wear properties of aluminum matrix composites”, acta physica polonica a, vol. 131, no. 3, pp. 487-489, 2017 [10] o. unal, i. zulcic, r. varol, i. karademir, s. ates, “novel type shot peening applications on railway axle steel”, journal of mineral metal and material engineering, vol. 2, pp. 1-5, 2016 [11] o. unal, r. varol, “surface nanostructuring of aisi 1017 by severe shot peening”, research and reports on metals, vol. 1, pp. 1-4, 2017 [12] o. unal, a. c. karaoglanli, y. ozgurluk, k. m. doleker, e. maleki, r. varol, “wear behavior of severe shot peened and thermally oxidized commercially pure titanium”, engineering design applications, vol. 5, pp. 461-470, 2019 [13] m. a. omari, h. m. mousa, f. m. al-oqla, m. aljarrah, “enhancing the surface hardness and roughness of engine blades using the shot peening process”, international journal of minerals, metallurgy and materials, vol. 26, no. 8, pp. 999-1004, 2019 [14] w. liu, j. ding, p. zhang, c. zhai, w. ding, “effect of shot peening on surface characteristics and fatigue properties of t5-treated zk60 alloy”, materials transactions, vol. 50, no. 4, pp. 791-798, 2009 [15] a. thakur, g. aregawi, “effect of heat treatment on mechanical properties and microstructure of st 37-2 rear trailing arm”, international journal of current engineering and technology, vol. 9, no. 1, pp. 8091, 2019 [16] e. maleki, g. h. farrahi, “modelling of conventional and severe shot peening influence on properties of high carbon steel via artificial neural network”, international journal of engineering, vol. 30, no. 11, pp. 382-393, 2017 [17] m. yazdani, m. r. toroghinejad, s. m. hashemi, “investigation of microstructure and mechanical properties of st37 steel-ck60 steel joints by explosive cladding”, journal of materials engineering and performance, vol. 24, no. 10, pp. 4032-4043, 2015 [18] f. o. sonmez, a. demir, “analytical relations between hardness and strain for cold formed parts”, journal of materials processing technology, vol. 186, pp. 163-173, 2007 [19] a. b. m. helaluddin, r. s. khalid, m. alaama, s. a. abbas, “main analytical techniques used for elemental analysis in various matrices”, tropical journal of pharmaceutical research, vol. 15, no. 2, pp. 427434, 2016 [20] m. i. mohamed, “studies of the properties and microstructure of heat treated 0.27% c and 0.84% mn steel”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3484-3487, 2018 [21] s. h. abro, a. chandio, a. r. jamali, s. a. shah, “influence of austenite phase transformation on existing microstructure of low c-mn steel”, engineering, technology & applied science research, vol. 8, no. 6, pp. 3525-3529, 2018 microsoft word 21-2689_s1_etasr_v9_n3_pp4182-4187 engineering, technology & applied science research vol. 9, no. 3, 2019, 4182-4187 4182 www.etasr.com belarbi et al.: implementation of a new geometrical qualification (dq) method for an open access … implementation of a new geometrical qualification (dq) method for an open access fused filament fabrication 3d printer boumediene belarbi electrical engineering department, university of abu bekr belkaid, tlemcen, algeria belarbi_boumediene@yahoo.fr mohamed el amine ghernaout mechanical engineering department, university of abu bekr belkaid, tlemcen, algeria mea_ghernaout@mail.univ-tlemcen.dz tawfik benabdallah mechanical engineering department, national polytechnic school (enp), algiers, algeria tawfikbenabdallah@yahoo.fr abstract—this work presents geometric qualification on rapid prototyping process in the case of open access 3d printers where a working model is proposed and a prototype measurement is presented. the problem, which is to develop a methodological approach for the realization of five test pieces of equal dimensions based on complete process knowledge of the downstream material deposit movement according to xml standards, is addressed after a state of the art review. the result allows confirming the quality of the machine recommended by the manufacturer. basically, the adopted methodology was used to fill the vacuum in the 3d fdm (open source) 3d geometric qualification (dq) as well as to pave the way for the 3d printing processes standardization [1]. keywords-qualification; 3d; part test, quality; insurance; rapid prototyping; geometry i. introduction often small and medium-sized enterprises (smes) use lowcost, open access printers, which make the cost of research and development low. it is difficult to check if the designer's data conform to the manufacturer's specifications. therefore, it is necessary to develop a machine qualification methodology and product test. the prototype model is inevitable in the development phase, that’s why the research problem lies in the fact of how to qualify 3d printing processes realized in open source (figure 1) [1]. manufacturing consists of an iterative ratio of material (point by point and layer by layer) according to the different forms of the parts, whereas in the machining techniques we proceed by removing material (subtractive process).this work is concerned with the qualification of rapid prototyping processes (figure 2) [1]. therefore, a real industrial need was met, following a qualification procedure and standards adapted to 3d printers (figure 3). fig. 1. the flux of rapid prototyping process fig. 2. (a) process of xxx3d printer, (b) deposition of molten wire (fdm) fig. 3. cycle of product development (xxx3d) ii. problem statement qualification process is crucial to quantify influences of each factor and is achieved with checking the data of the designer with the manufacturer’s specifications. in this study, only the additive processes fdm, laser polymerization, stereo lithography (stl), manufacturing by point-by-point/layer by layer, and material projection are tackled. it is noted that metrology is interested in the quality of measurements by various methods that complete qualification. moreover, the control of the surface state and all its complex shapes obtained by 3d printing must constitute in the third level of the qualification action where the product conformity and its quality improvement are allowed by geometric metrology. corresponding author: boumediene belarbi engineering, technology & applied science research vol. 9, no. 3, 2019, 4182-4187 4183 www.etasr.com belarbi et al.: implementation of a new geometrical qualification (dq) method for an open access … iii. state of the art review the basic approach to rapid prototyping can be described by a model or a component modeled on a cad/cam system, the assembly is represented according to a 3d model [2] in figure 4. this work aims at laying the foundations of a qualification methodology that fills the gap since there are no references related to the qualification of low-cost open access (lcoa) 3d printers, with the exception of two contributions of the authors of this paper [1]. fig. 4. basis for rapid prototyping (std. part: motorcycle housing) iv. methodology one should refer to the three approaches forming the verification triangle (figure 5). fig. 5. three methods for the verification triangle [3] • study of the machine geometry, probe behavior and different analytical approaches with precise experiments to integrate the uncertainties calculation. • performing an estimate to separate the input of all fixed errors. the approach for thermal phenomena embodied in the removal and pile-up of the raw material. • a comparison between the value of the measurements taken and those given by the manufacturer (true values or standard measurements) [4]. metrology allows us to analyze and verify the results obtained by carrying out an analysis between the specifications and the obtained results, as it is shown in the procedural flowchart in figure 6. a. application (implementation) the qualification procedure consists of taking measurements on the test pieces (prototypes) and analyzing the results. computer-aided construction (cad) generates an stl file that represents its digital definition, hence the boundaries of the quality process. besides, the qualification procedure must set the parameters of the production conditions, while considering the imposed post-processing (finalization, polymerization), the movement of the machine according to the xy plane (2d) by stepper motors, servo-control and measuring system and the 3rd z-axis (3d). moreover, this study evaluates the layer’s thickness and smoothness of the device (displacement perpendicular to x and y), the speed of movement which is either straight or cylindrical confronted to the material behavior (deposition, connection of the preceding layer and cooling rate with shrinkage). fig. 6. theoretical description of the qualifying process b. qualification of the printer process however, quality is not considered the maximum performance, but the respect of the performance specified by the contract of realization. in order to qualify the process (fdm) and the printer, tests were carried out on measurements of certain functional ribs of the prototype v. qualification task procedure data collection was conducted through the following procedure: • data catalog: the qualification relates to a series printer taken randomly from a batch manufactured on a given date. the data will be collected directly from the catalogue, accompanying the machine in paper or electronic form. • quality insurance [5]: quality assurance requires the mastery of the fdm process, hence the need to guide the development of the procedure for rapid prototyping qualification by the verification of conformity with an existing adapted standard. the most used iso models in qualification are: 9000, 9001, 9002, 9003, 9004 and 14001. after evaluation of this conformity, a decision has been made on the recognition of the process suitability of a production line, a supplier, a component, etc. • working model: measurements should be made in the laboratory with means that should be adapted to the characteristics covered by the qualification procedure. the ambient conditions (temperature of reference 20°±1°c, relative humidity 55% and pressure 101325pa) must be monitored. variations affect the expansion of certain plastic materials which may affect the dimensions of the part. • test piece: the test piece is described with its design and material. it is a protective chain cover of a sport bike, made on a 3d printer based on abs. it does not require posttreatment or manual intervention or supports to facilitate its control and to deduce the origin of its defects. engineering, technology & applied science research vol. 9, no. 3, 2019, 4182-4187 4184 www.etasr.com belarbi et al.: implementation of a new geometrical qualification (dq) method for an open access … • measurement: measurements were carried out on all dimensions, verifying the compliances contained in the designer (manufacturer) specification book. metrology is an integral part of the early stages of designing the production process and verifying alternatives to product solutions. considering the importance of the measurement errors’ influence on the precision of the parts and their valued measurements, a three-dimensional measuring device was used. • treatment of results: the determination of the statistical uncertainty of the quantities is performed by measuring the test piece deviations with the three-dimensional measuring machine (tmm). the 3d printer’s deviations and the errors were measured, the part’s statistical series and arithmetic averages were calculated. after verification, the deviation of these values became very small compared to the conditions recommended by the designer. finally, it has been concluded that these values were within the tolerance interval imposed by the designer. • comparison and validation: it is required to make a comparison between theory and the results of the different points of the qualification process. a validation of these results is provided below. determination of uncertainty requires that a series of measurements are made on the same part from which a full-scale statistics is drawn. • report (end): once the qualification procedure is done, a final report should be released which must decide on the acceptance of the fdm printer qualification. the product is accepted for printing multiple plastic prototypes. therefore, the obtained results lead in the acceptance of the 3d printer qualification, after verification. a. environment it should be noted that the geometrical measurements and those of the metrology laboratory must be adapted to the characteristics of the concerned means. the ambient conditions must be monitored. variations affect the expansion of certain plastic materials and affect the part’s shape. b. test piece description a motorcycle chain cover was chosen, made on the open source lcoa 3d abs-based printer, based on simple geometric shapes allowing differentiation of the origin of the defect on the part upon which the test is conducted. it does not require post treatment, manual intervention or media. moreover, a synthesis of the shapes which are to be joined makes it possible to define it completely (figure 7). (a) (b) fig. 7. (a) test piece defined by cao, (b) piece obtained by xxx3d c. test piece positioning (tpp) the positioning of the test piece on the 3d measuring machine (tmm) requires the following specifications on the software (cad) [6]: the minimum number of points to position is 3 (flat support) (figure 8), the functional dimensions are selected and their probing system is defined [2]. then, they are decomposed with simple geometric elements (figure 9). the 3d printer specifications given by the manufacturer are illustrated in table i before the start of the measurements. fig. 8. position of the test piece relative to the mmt probe fig. 9. the test piece control operation on the mmt. table i. the xxx3d printer characteristics [7] measures and dimensions width 480mm length 455mm including height 455mm weight 14kg temperature extruded 270°c (s/type of filament) print volume 230mm×210mm×190mm maximum print speed 15mm 3 /s and 50mm/min movement x-y 50microns, minimum print thickness (z) 100microns materials pla, abs, nylon, lay wd &brick nozzle diameter 0.4mm filament diameter 3mm steering and connectivity usb and carte sd system compatibility windows, mac, linux alimentation 110-220v, 50-60hz d. running a measuring range the correlation matrix indicates the link between measures and the influence factor with analysis of interactions. the geometric control considered is explained by the researchers’ contribution with the study of the product “cache carter”. table ii lists the different test pieces obtained, referring to the conditions imposed on the definition drawing by the design office. this work showed more accuracy and conformity with the definition drawing. e. verification of the geometric specifications the parts must respect a minimum geometric tolerance. there are several types of apparatus, such as those used to characterize straightness, flatness, circularity, parallelism and engineering, technology & applied science research vol. 9, no. 3, 2019, 4182-4187 4185 www.etasr.com belarbi et al.: implementation of a new geometrical qualification (dq) method for an open access … perpendicularity. the tolerance interval imposed is 0.1mm for all cases of this study. to do this, the computer tool cad was chosen for the design of the decision support program. the treatment was performed by comparing the theoretical and measured results. some measurements allow quantification of single defect, but analysis made it possible to determine more generally the defects of machine or material origin. thus, the exploitation of all the collected information enabled identifying the sources of the defects influencing factors on the matrix. the use of the test pieces ensures the implementation of a correlation matrix. this, with the analysis of the interactions, helps list the measurements to be made and link between observations. the parameters related to the final prototype are taken into account [9]. the aim was to complement the correlation matrix for the geometric control of the test piece (realized on the 3d printer, by fdm=fff). table i. correlation matrix reduced for dimensional inspection [8] parameter process observation mode l issa g e s tr a ig h / c y lin d r . x t a n g . y t a n g . x r o ll y r o ll z r o ll d e fo r m . p e r p . z /x y p e r p x /y w ith d r a w a l parall.plan perp.to x measure according z ⊗ parall.plan perp.to y measure according z ⊗ straightness xz according x ⊗ ⊗ ⊗ straightness yz according y ⊗ ⊗ ⊗ straightness xy according y ⊗ ⊗ ⊗ ⊗ straightness xy according x ⊗ ⊗ ⊗ ⊗ flatness: thin xy ⊗ ⊗ ⊗ ⊗ ⊗ ⊗ flatness: thick xy ⊗ ⊗ ⊗ ⊗ ⊗ ⊗ ⊗ angles/x, angles/y ⊗ homogeneity material ⊗ ⊗ f. data and results of straightness and flatness: for the first two following control cases, the diagonal line is the straightness direction/nominal ideal geometric element. 1) according to xz the x axis represents the nominal geometric element and carries the abscissa xi points palpated from 0 to 100mm. the maximum and minimum value of the measurement deviation is 0.035mm (right above the x axis) and -0.03mm (right below the x axis). they intercept the default of the nominal form (dfn). the z axis carries the ordinates zi (the measurement deviation), with it=0.1mm (between the extreme lines). 0 0002 0 01 0 0187758775. . .y ax b x= + = + + (1) the values chosen according to xz are the two extremes of the distance considered (100mm): 100΄-9΄-70΄=21+1=22mm and 22+70=92mm . fig. 10. values and plot of the geometric control, test piece. 2) according to yz the y axis represents the nominal geometric element and carries the abscissa yi points palpated from 0mm to 110mm. the max and min value of the measurement deviation are 0.05mm (right above the x-axis) and -0.015mm (right below the x-axis). 0 000110511055454 0 022608511. .y ax b x= + = + (2) the values chosen according to yz are the two extremes of the distance considered (110mm): the first is: 15+2=17mm and the second is: 15+84=108mm. fig. 11. values and plot of graphs of the geometric control test piece 3) according to xy the diagonal line is the direction of straightness (associated line)/nominal ideal geometric element and is of the form: 0 00191 0 0057852 0 1050. . .y ax by c x y= + + = + + (3) the coordinates of the palpated points are projected onto the xy plane. the max and min values of the measurement deviation are the line above the x axis=0.05mm and below the x axis=-0.015mm. intercepting the (dfn), for it, diff.sup=+0.0680 and diff.sup=-0.32. following the control process, the test piece is taken on a marble and calibrated the dial gauge in the “zero” position on the two end points of the dimensions to be checked. g. the flatness data flatness measurements include devices to determine the surface state of a plane (the surface of the cover with the motor). it is to be noted that concerning the verification of the circularity, a work for a forthcoming, extended publication given the range of shapes and different diameters is underway. engineering, technology & applied science research vol. 9, no. 3, 2019, 4182-4187 4186 www.etasr.com belarbi et al.: implementation of a new geometrical qualification (dq) method for an open access … fig. 12. values and plot of the geometric control, test piece h. processing results the theoretical results (cad plan) and the geometrically measured defects were compared for influencing factor definition. there is a correspondence with the correlation matrix by indicating the link (s) between measurements and influencing factor (s). some measurements tend to provide a quantification of a single defect, but the analysis helped to determine the defects of machine and material origin. vi. results interpretation the evolution of the ranges with the differences of measurements 'e' are less dispersed and their distribution confirmed. their concentration is within a tolerance range which can be characterized by two limits between 10 and 15µm. the lack of straightness is defined by the minimum distance between two parallel straight lines that envelop this line (figure 13). fig. 13. straightness defects on the contact surface following the recommendations of the standard [7], the straightness of a product is controlled by direct (tensile wire, ruler, marble, cylinder or optical beam) or indirect (level indicator etc.) measurement. finally, shrinkage is identical to the settlement in the two dimensions of the xy plane, with a difference of the mean deviations on the two axes (figure 14). therefore, because of the uncertainty effect of the measurement deviations, it can be concluded that the test piece is accepted because it lies within the compliance zone (figure 15). a. conformity and optimization of measurements after selecting the measuring equipment, the question of the conformity of the measured dimensions is to be tackled. the uncertainty represents the space in which the part’s dimension must lie relative to the value given by the instrument. when it is at the center of the tolerance interval and the uncertainty is low, no problems are encountered. on the other hand, if it is at the limit of the tolerance interval, there is a risk for the acceptance of non-conforming parts. if the measurement uncertainty is low, i.e. less than or equal to one quarter of the tolerance interval, the part is accepted. the method is advantageous when you have a good command of metrology and its investment will be valued because the elimination of parts will be scarce. figure 16 illustrates the percentage between the measurement uncertainty and the tolerance interval. fig. 14. graph giving away the withdrawal of matter fig. 15. area of doubt and confirmation of the tolerance interval fig. 16. statistical representation by sector it seemed essential to carry out a preliminary analysis in order to collect the necessary forms, knowing that this part will have to be fast and economical to manufacture. conceiving it as a test makes possible to identify the origins of the defects. the approach that seems to be appropriate is the establishment of a correlation matrix, making possible to make the link between possible observations on the part (in metrology) and on the parameters related to the process and to the employed material. its design makes possible to identify the origin of the deviations and to remove multiple interactions between the measurements and the parameters. vii. conclusion this work is a response to a real industrial need: setting up a qualification procedure adapted to fast prototyping machines (3d printers). measurements of the same dimensions were conducted for five realized pieces. this study will be completed with the use of more test pieces. during measurements, effort was done to limit the influence of the environment, workforce, and method. the r & d needs in this field are expressed by the implementation of a qualification approach by taking into account integrated geometric engineering, technology & applied science research vol. 9, no. 3, 2019, 4182-4187 4187 www.etasr.com belarbi et al.: implementation of a new geometrical qualification (dq) method for an open access … correctors. quality is an essential variable for any company. the quality approach has become an indispensable management practice to achieve the objectives set. the adopted experimental procedure confirmed that all measurements are included in the interval of tolerance given by the designer. in perspective, other quality measurements (circularity, straightness, flatness, etc.) will be submitted in following articles to complete the qualification dimension. this study proposes a better product quality procedure that opens the way for a low-cost open access guarantee. references [1] b. belarbi, qualification des drocessus de prototypage rapide ‘cas d’imprimante 3d’, msc thesis, ecole nationale polytechnique d'oran maurice audin, 2013 (in french) [2] h. bonnefoy, “du prototypage rapidea la fabrication rapide”, technologie, vol. 124, pp. 37-45, 2003 (in french) [3] f. hennebelle, determination des incertitudes de mesures sur machines a mesurer tridimensionnelles: application aux engrenages, phd thesis, arts et metiers paristech, 2007 (in french) [4] b. rylands, t. bohme, r. a. gorkin iii, j. p. fan, t. birtchnell, “3d printing to print or not to print? aspects to consider before adoption a supply chain perspective”, 22nd euroma conference, neuchatel, switzerland, june 28–july1, 2015 [5] g. cortes robles, management de l’innovation technologique et des connaissances: synergie entre la theorie triz et le raisonnement a partir de cas, phd thesis, institut national polytechnique de toulouse, 2006 (in french) [6] https://www.heidenhain.com/en_us/products/cnc-controls/ [7] http://fr.wikipedia.org/wiki/reprap (in french) [8] d. scaravetti, p. dubois, r. duchamp, “qualification of rapid prototyping tools: proposition of a procedure and a test part”, the international journal of advanced manufacturing technology, vol. 38, no. 7-8, 2008 [9] b. belarbi, t. benabdallah, g. abdi, “implementation of a new dimensional qualification (dq) method for an open access fused deposition modeling 3d printer”, ireme, vol. 10, no. 2, pp. 73-80, 2016 authors profile boumediene belarbi, was born in 1958, is a researcher and member in the industrial products and systems innovation laboratory (ipsil) at the national polytechnic school in oran (enpo-algeria) and a lecturer at the department of electrical engineering and electronics and industrial engineering at the faculty of technology at the abu bekr belkaid-tlemcen university. also he works on rapid prototyping, in the qualification of 3d printers (fdm), and in innovation systems. m. el amine ghernaout, was born in 1959, is a professor and a phd holder in thermal machines and the head of etap laboratory at the faculty of technology at the abou bekr belkaid-tlemcen university. he is currently a lecturer at the mechanical engineering department. he is involved in several research projects. tawfik benabdallah, was born in 1960, is a professor and phd holder in thermal machines and the head of the industrial products and systems innovation laboratory (ipsil) at the national polytechnic school of oran (enpo-algeria). he is currently a lecturer at the mechanical engineering department. he is involved in several research projects and international cooperations in innovation and prototyping. also he is a member of many international scientific comities, and works in the field of energetic systems. microsoft word 14-2577_s engineering, technology & applied science research vol. 9, no. 2, 2019, 3945-3948 3945 www.etasr.com momade & hainin: identifying motivational and demotivational productivity factors in … identifying motivational and demotivational productivity factors in qatar construction projects mohammed hamza momade school of civil engineering, universiti teknologi malaysia, johor bahru, johor, malaysia hmmohammed2@live.utm.my mohd rosli hainin school of civil engineering, universiti teknologi malaysia, johor bahru, johor, malaysia mrosli@utm.my abstract—motivation is one of the factors that influence productivity. project management plays a vital role in the success of projects in qatar construction industry (qci). it relies profoundly on the team’s active participation and effective performance. hence it is important to assess the impact of motivation and demotivation on performance. the main objective of this paper is to identify the key factors that cause motivation and de-motivation in qci. literature review, surveys with experts and semi-structured interviews were conducted to identify these factors. using these factors to conduct specific motivational programs will help improve productivity in qci. research on motivational factors impacting productivity has not been conducted in qatar before, so this work will provide insight on how to deal with productivity issues that qci faces ahead of a major world event that qatar will host in 2022. keywords-motivation; qatar; project management; productivity i. introduction projects have been around for ages [1]. the definition of a project is that it is a methodized task headed for a predefined target which depends upon resources and effort, a unique and risky venture containing a schedule and budget. project management has been in practice for thousands of years, though it has been evolving in the 20th century. the concept of project management has been more critical during the industrial revolution and the introduction of the classical management theories paved the way in the most extensive and exclusive ways of development of projects. the evolution has been tougher and complex with the emergence of globalization. the virtual and current modernization in the middle east construction and built environment has evidenced a greater recognition and growth in the management of projects. qatar is considered a developing country although the country’s gdp is $143,788. the reason for being an exception to the rule is that the majority of the citizens may enjoy the luxuries of the developed world and their lifestyles but the gap between the extreme poverty and extreme richness, which had led to hdi of 0.85, pushes it to the category of the developing country. one of the reasons behind this low index is its excess expenditure on infrastructure projects. thus, brings the significance of the project management in the country along with the recent announcement of fifa 2022 world cup hosting rights. therefore, the objective of this research is to identify motivational and demotivational factors in qatar construction project management practices. as a host of fifa world cup 2022, it is highly vital to identify the motivational and demotivational factors in construction industry in order to mark the success of the country. with given time constraints and the short time burden, it becomes an increasing burden to the host to mark for quality projects. research on motivational factors impacting productivity has not been conducted in qatar before, so the current work shall provide new insight on how to deal with productivity issues in qci. ii. research methodology the research was carried out in two phases: a) investigation and b) survey. based on literature survey and experts’ opinions, a list of factors influencing motivation and demotivation was prepared. expert opinions were sought from senior engineers with 10 years of field and administrative experience and the faculty guiding research studies in human resource management. subsequently, semi-structured interviews were conducted to narrow down the list and identify the key motivating and demotivating factors. • literature review: in order to determine the major published research outputs for the chosen topics, we adopted similar methodology to those employed in [2-9]. • identification of productivity factors: a questionnaire was made considering the factors impairing productivity. the factors were listed and categorized by respective researchers and inserted into the questionnaire for data collection [10-12]. • pilot testing: some questionnaires were given in a small scale survey in order to ensure the questionnaire’s readability, accuracy, and comprehensiveness [10-12]. • data collection: questionnaire survey was used as the medium for data collection [13]. • data analysis: the data collected were analyzed using the relative importance index (rii) technique [14]. • conclusions were derived from the highest ranked factors. corresponding author: mohammed hamza momade engineering, technology & applied science research vol. 9, no. 2, 2019, 3945-3948 3946 www.etasr.com momade & hainin: identifying motivational and demotivational productivity factors in … iii. data analysis a total of 77 questionnaires were distributed, to 6 project managers, pmp certified and carrying more than 15 years of experience in the field of project management, 17 project managers with a master’s degree and an experience of more than 5 years, 22 from consultants and site supervisors who work closely with project managers, and 32 respondents were owners, contractors, and design engineers who are directly linked to construction projects. all questionnaires were answered and none was excluded. in order to conduct a reliable factor analysis the sample size needs to be big enough [15, 16]. a common rule of thumb is that a researcher at least needs 1015 participants per item. since the sample size in this study is 77 instead of the required 60, we have acceptable sample size. table i. factor analysis motivational factors rii rank i. achievement 0.854 1 ii. proper recognition and rewards 0.813 2 iii. interesting work 0.755 3 iv. involvement in decision making 0.723 4 v. adequate training and development 0.678 5 demotivational factors rii rank i. poor work conditions 0.846 1 ii. poor administration policy 0.830 2 iii. poor work relationship 0.764 3 iv. lack of communication (english) 0.718 4 v. lack of appreciation 0.653 5 generally, a questionnaire with an α of 0.8 is considered reliable [16]. this questionnaire certainly is certainly reliable, since its α is 0.919. the resulted α should yet be interpreted with caution. since the amount of items in a questionnaire is taken into account in the equation, a high amount of variables can rise the α. for example, if we do a reliability analysis for just the items making up the first factor in our research, we get the same α, but the average correlation is 0.49 instead of 0.43. how high the alpha should be for a dataset with a particular amount of items is still a point of discussion. authors in [17] recommend determining the adequacy of a measure on the level of precision needed. iv. productivity factors several researchers have conducted studies on productivity in neighboring middle eastern countries. authors in [18] conducted a study on productivity factors in gaza and found material shortage, lack of experience, poor supervision, and misunderstanding and change in orders as the top 5 factors. authors in [19] conducted a similar study in uae and found the following as top 5 factors: proper work timings, leadership skills of supervisors, salaries paid on time, technical qualified and reasonably well payed job. authors in [20] conducted a similar study in turkey and found the following as top 5 factors: quality of site management, material management, and systematic flow of work, supervision, and site layout. authors in [4] conducted a similar study in kuwait and found the following as top 5 factors: payment delay, rework, lack of financial incentives, changes in orders and incompetent supervisors. authors in [21] conducted a similar study in iran and found construction methods, site manager experience, lack of proper tools, inexperienced operatives, and site managers’ ability as the top regarded factors. authors in [22] carried out a similar study in oman and found drawing errors, change in orders, instruction delay, poor supervision and clarity of project specifications as top 5 factors. authors in [23] carried out a similar study in jordan and found the following factors as the most influential: feeling of achievement, experience, use of foreign workers, scheduling and use of machinery. authors in [24] carried out a similar study in saudi arabia and found the following factors as the most influential: skilled labor, education and experience, better communication, budget, and safety. v. discussion on results five key motivational factors were identified: achievement, proper recognition and awards, interesting work, involvement in decision making, and adequate training and development. out of these, the four factors ‘achievement’, ‘interesting work’ ‘proper recognition and awards’ and ‘advancement’ were selected from the herzberg’s two factor theory [34]. according to the experts’ suggestions, ‘growth’, ‘responsibility’ and ‘advancement’ were combined as a single factor ‘advancement’. the other two factors, ‘participation in decision making’ and ‘adequate training and development’ were taken from literature and ratified by the experts and field engineers. five key demotivational factors were identified: poor work conditions, poor administration policy, poor work relationship, lack of communication (english), and lack of appreciation. ‘poor work conditions’, ‘poor administrative policy’ and ‘poor work relationship’ were selected from [34]. in context to the demotivational factors, english language played a significant aspect in project management. with regard to the arguments concerning qatar, the multinational task force has faced a severe communication problem, as communication can play a major threat towards the success of a project and its delay in construction. the core input to produce optimum output in a construction industry is its labor, as labor is considered to be the most efficient and valuedriven output in a construction industry [25]. authors in [26] identified inappropriate recommendations and specific strategies are demotivational factors in project management. however, there were still arguments that with the advanced technological factors, construction industry still remains as labor intensive [27] as before. according to a survey in qatar, 82% of the engineers were of the opinion that poor labor productivity is one of the prime reasons behind the failure of the projects and budget excess [28]. poor management of the workforce would result in less productivity. the construction engineers should definitely focus on the strategies to improve labor productivity which has several related factors including long working hours, job satisfaction, leadership, commitment to organization, and work engagement. in order to organize the fifa world cup, qatar has a long way to address the issues and identify the demotivational factors in project management. lack of materials is an interlinking factor that causes low labor productivity influencing all demotivation factors in project management in construction industry. lack of materials at the site delays the work and leads to many idle working hours [29]. there are engineering, technology & applied science research vol. 9, no. 2, 2019, 3945-3948 3947 www.etasr.com momade & hainin: identifying motivational and demotivational productivity factors in … multiple factors that remain as obstacles for the timely delivery of materials in the construction area, including shortage of materials, political triggers and supply monopolies. lack of materials is one of the common obstacles in construction companies which affect their competitiveness. shortage of raw materials has been the main factor leading to project failure and delay [30]. frequent change in orders and rework from the clients also cause delay in the productivity of a project. revised drawings in the design and layout plan might lead to project delays and low productivity leading to project demotivation. this leads to a variation of order in contracts. authors in [31] argued that temperature and weather conditions are significant issues that influence labor productivity. an increase in temperature has negative effect on the productivity in the construction industry. determination of leadership style is a very challenging aspect concerned with the project management, conversely influencing productivity. in project management, the determination of leadership can be task oriented or relations-oriented. however, it is very difficult to determine the best leadership style in a project. it is very difficult to determine the strategies. there should be positive and motivative management to lead the team with a high sense of ethics and morality. authors in [32] report that relationships between project manager, client and worker are very crucial to project success. the following are stated as key advantages of project management: • improved efficiency in carrying out the project. • customer increased satisfaction. a customer is always glad and satisfied whenever a project is carried out on time and within the available budget. intelligent project management provides the guidelines and tools that enable the customer and project manager relationship to flourish. • improved effectiveness in delivering of services: the steps are approximately the same for every project, just the working environment and the situation are altered. • project success brings in confidence, growth and development within the team. • competitive edge in the business hub: a successful and excellent performance is always required to gain a fair share of the construction market. • chances to grow the company: successful projects always lead to new chances to grow in the market. • more elasticity in approach is available: project management has a wide scope and a lot of approaches can be taken depending on the situation. • risk assessment increases. • quality is raised and therefore there is increase in quantity. project management is a modern-day tool which has perfected the projects in construction industry bringing in more organization and discipline and a smoother flow of work [33]. vi. conclusion this study identified the key factors that motivate and demotivate the construction industry in qatar. the study shows the findings of herzberg’s theory to be relevant to the engineers in qatar construction industry. intrinsic motivators comparatively play a vital role for many workers in any project. the interesting nature of the construction work has to be properly utilized by the organization along with providing achievable goals to improve the motivation level. similarly, the organization has to address the poor administrative policies and the poor work conditions to reduce de-motivation. further study about the key factors will help in identifying the underlying reason for more detailed analysis. these reasons should be used to evaluate the root cause of the problem. thus, companies can plan their motivational programs based on these details with periodical assessment to induce motivation and reduce de-motivation. vii. further study further research shall be conducted into clp and its factors: workers opinion in identification of clp for construction projects, research on the clp models impact on construction labor productivity, and study on what skills are essential in upgrading worker productivity levels. references [1] s. e. portny, project management for dummies, john wiley & sons, 2013 [2] f. al-sharif,. a. kaka, “pfi/ppp topic coverage in construction journals”, 20th annual arcom conference, heriot-watt university, uk, september 1-3, 2004 [3] y. hong, d. w. m. chan, m. asce, a. p. c. chan, j. f. y. yeung, “critical analysis of partnering research trend in construction journals”, journal of management in engineering, vol. 28, no. 2, pp. 82-95, 2012 [4] a. m. jarkas, m. radosavljevic, “motivational factors impacting the productivity of 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construction management, vol. 13, no. 4, pp. 103-125, 2013 [9] c. c. tsai, m. l. wen, “research and trends in science education from 1998 to 2002: a content analysis of publication in selected journals”, international journal of science education, vol. 27, no. 1, pp. 3-14, 2005 [10] m. r. abdul kadir, w. p. lee, m. s. jaafar, s. m. sapuan, a. a. a. ali, “factors affecting construction labour productivity for malaysian residential projects”, structural survey, vol. 23, no. 1, pp. 42-54, 2005 [11] h. m. alinaitwe, j. a. mwaka, b. hansson, “factors affecting the productivity of building craftsmen‐studies of uganda”, journal of civil engineering and management, vol. 13, no. 3, pp. 169-176, 2007 [12] k. shashank, s. hazra, k. n. pal, “analysis of key factors affecting the variation of labour productivity in construction projects”, international journal of emerging technology and advanced engineering, vol. 4, no. 5, pp. 152-160, 2014 engineering, technology & applied science research vol. 9, no. 2, 2019, 3945-3948 3948 www.etasr.com momade & hainin: identifying motivational and demotivational productivity factors in … [13] o. j. ameh, e. e. osegbo, “study of relationship between time overrun and productivity on construction sites”, international journal of construction supply chain management, vol. 1, pp. 56-67, 2011 [14] g. a. bekr, “study of significant factors affecting labor productivity at construction sites in jordan: site survey”, journal of engineering technology, vol. 4, no. 1, pp. 92-97, 2017 [15] a. b. costello, j. w. osborne, “best practices in exploratory factor analysis: four recommendations for getting the most from your analysis”, practical assessment, research & evaluation, vol. 10, no. 7, pp. 1-9, 2005 [16] a. field, discovering statistics using spss, sage publications, 2009 [17] j. m. cortina, “what is coefficient alpha? an examination of theory and applications”, journal of applied psychology, vol. 78, no. 1, pp. 98, 1993 [18] a. enshassi, s. mohamed, z. a. mustafa, p. e. mayer, “factors affecting labour productivity in building projects in the gaza strip”, journal of civil engineering and management, vol. 13, no. 4, pp. 245254, 2007 [19] n. ailabouni, k. gidado, n. painting, “factors affecting employee productivity in the uae construction industry”, 25th annual arcom conference, nottingham, uk, september 7-9, 2009 [20] a. kazaz, e. manisali, s. ulubeyli, “effect of basic motivational factors on construction workforce productivity in turkey”, journal of civil engineering and management, vol. 14, no. 2, pp. 95-106, 2008 [21] p. ghoddousi, m. r. hosseini, “a survey of the factors affecting the productivity of construction projects in iran”, technological and economic development of economy, vol. 18, no. 1, pp. 99-116, 2012 [22] a. m. jarkas, r. a. al balushi, p. k. raveendranath, “determinants of construction labour productivity in oman”, international journal of construction management, vol. 15, no. 4, pp. 332-344, 2015 [23] m. a. 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vol. 63, no. 8, pp. 1070-1090, 2014 [28] a. m. jarkas, t. c. haupt, “major construction risk factors considered by general contractors in qatar”, journal of engineering, design and technology, vol. 13, no. 1, pp. 165-194, 2015 [29] i. mahamid, “contractors perspective toward factors affecting labor productivity in building construction”, engineering, construction and architectural management, vol. 20, no. 5, pp. 446-460, 2013 [30] k. m. el-gohary, r. f. aziz, “factors influencing construction labor productivity in egypt”, journal of management in engineering, vol. 30, no. 1, pp. 1-9, 2014 [31] j. chinnadurai, v. vengugopal, p. kumaravel, r. paramesh, “influence of occupational heat stress on labour productivity – a case study from chennai, india”, international journal of productivity and performance, vol. 65, no. 2, pp. 245-255, 2016 [32] k. berezina, c. cobanoglu, b. l. miller, f. a. kwansa, “the impact of information security breach on hotel guest perception of service quality, satisfaction, revisit intentions and word-of-mouth”, international journal of contemporary hospitality management, vol. 24, no. 7, pp. 991-1010 [33] d. s. barrie, b. c. paulson, “professional construction management”, journal of the construction division, vol. 102, no. 3, pp. 425-436, 1976 [34] f. herzberg, “one more time: how do you motivate employees?”, harvard business review, vol. 40, no. 1, pp. 53-62, 1968 microsoft word 03-3696_s_etasr_v10_n5_pp6172-6175 engineering, technology & applied science research vol. 10, no. 5, 2020, 6172-6175 6172 www.etasr.com phan: evaluation of some rheological properties of xanthan gum evaluation of some rheological properties of xanthan gum van tien phan faculty of construction vinh university vinh city, viet nam vantienkxd@vinhuni.edu.vn abstract−the squeeze flow behavior of a shear thinning fluid was studied in this paper using squeeze tack technique. the test material was firstly squeezed out between two parallel circular plates, then it was relaxed for 1.5min and finally was separated at a predefined pulling velocity. from the flow curves obtained in the squeeze tack experiments, the rheological parameters, including yield stress in tension and in squeeze, have been calculated. the results show that the squeeze-tack test can be used for the analysis and evaluation of shear thinning fluids. although the experimental results may not be considered complete, it can be seen that the stresses and tensile stresses have a linear relationship witch goes through the origin. keywords-squeeze flow technique; xanthan; yield stress; shear thinning fluid i. introduction xanthan gum (also called xanthan) is a naturally occurring powdered polysaccharide, created through the fermentation of sugars (glucose or sucrose) by the bacteria xanthomonas campestris. it is often used as an additive in foods and as a thickener and emulsifier in cosmetics. xanthan has been studied for use in construction materials as a binder for soil stabilization when constructing roads in sri lanka [1], but these studies have not fully evaluated the applicability of xanthan in construction, especially its rheological properties. xanthan additives have been used in food and cosmetics, as thickeners, emulsifiers, etc. in construction, xanthan has been studied and applied in bridge construction materials as adhesive binder to stabilize the ground when constructing roads in sri lanka [1], viscosity control additives in self-compacting concrete [2], etc.. in general building material technology, xanthan is used as viscosity control admixture, thickener, etc. in concrete. however, in order to master the application of xanthan additives in construction, the study of xanthan’s rheology and the proposition of specific application directions for construction is very necessary and highly practical. ii. experimental setup squeeze test has been widely used to determine the flow properties of highly viscous pastes [3-5], as it overcomes some of the common problems of conventional rheometry such as slip, disruption of plastic materials, and the difficulty to load very thick and fiber-containing fluids in rotational devices [6]. squeezing technique can characterize cementitious materials by compressing a cylindrical specimen between two parallel surfaces with controlled force or displacement rate. this method has been used by various researchers for characterizing the rheological behavior of cement pastes [4], herschel bulkley fluid [5], bingham plastic [7], etc.. the typical load vs. displacement profile of a constant velocity squeeze flow experiment was determined in [8]. it can be used to obtain the rheological parameters of testing materials, including yield stress and viscosity. direct measurements of yield stress are uniquely performed by stress-controlled rheometry [9-11]. squeeze flow tests carried out with constant displacement velocity do not allow such direct measurements [6, 11] since the material flow occurs regardless of the existence of the materials’ yield stress, unless the force required to overcome this value exceeds the load limit of the testing device. in this work, the testing material (figure 1) is firstly compressed/squeezed between two parallel surfaces until a predefined thickness. then a relaxation period of 1.5min follows and it is finally separated with a predefined tack velocity. a typical curve of squeeze-tack experiment is presented in figure 2, in which three periods can be observed, including squeeze, relaxation and tack. (a) (b) fig. 1. xanthan in (a) powder and (b) gel form. it is possible to conduct indirect yield stress determination by the extrapolation of the flow curves in the squeeze stage of the experiment. the yield stress is calculated by dividing the maximum force recorded by the area at that time: �� � �� max � (1) corresponding author: van tien phan engineering, technology & applied science research vol. 10, no. 5, 2020, 6172-6175 6173 www.etasr.com phan: evaluation of some rheological properties of xanthan gum where as is the average area of the testing sample at the moment that the recorded load is max and: as= � � = � � � � � (2) where h is the predefine thickness of the test mortar, r is the radius of the sample and �� is the mortar’s thickness at the moment of the maximum squeeze force. similar calculations with the yield stress at tensile stage can be performed in order to investigate the variation of the material’s resistance in tack measurement. fig. 2. a typical curve obtained in a squeeze tack test. iii. results and discussion firstly, a controlled stress experiment was performed in order to plot the relationship between shear rate and shear stress. the applied stress was gradually increased until the appearance of material flow inside the vane. the result of this part of the experiment is the loading curve as can be seen in figure 4. (a) (b) fig. 3. stress controlled experiment. fig. 4. flow curves experimental results determine the testing material is shear thinning. then the applied stress was gradually decreased until the recorded shear rates approach 0. the result of this part is the unloading curve in figure 4. the test procedure may be seen in figure 3. the result in figure 4 indicates that the test material is shear thinning, a non-newtonian behavior of fluids whose viscosity decreases under shear strain. the flow curves obtained in the squeeze step can be seen in figure 5. the subfigures correspond to initial material thicknesses of 1mm, 2mm, 3.5mm, and 5mm. during the squeeze step, the test material was squeezed to the previous set-up thickness and the normal forces were recorded as a function of displacement/time. the squeeze stress was then calculated. from the obtained graphs, it is possible to evaluate the role of the sample thickness to the rheological properties of the material by displaying the force relational graphs over time on the same general chart. from each of the graphs, the maximum tensile force value, corresponding to the yield tensile stress, can be calculated. fig. 5. flow curves obtained in the squeeze experiments. at the gap of 1mm, we can see a big difference between the recorded squeeze forces at different squeeze velocities. the recorded values are much higher in the case of high squeeze velocity (200mm/s) compared with those of the case of low squeeze velocity (20mm/s). these two sets of recorded forces come close as the predefined thickness of the material increases. it can be easily seen in figure 5 that at the gaps of 3.5mm and 5mm, the squeeze speed does not affect to the squeeze forces. figures 6 and 7 show the variation of normal force values over time for different sample thicknesses. it can be noticed that these measured force values fluctuate greatly around certain equilibrium values. the amplitude of oscillation is increasing at the end of the tensile test. -25 -20 -15 -10 -5 0 5 10 0 50 100 150 200 250 300 350 5mm_s20_t20 compression relaxation traction f o rc e ( n ) time (sec) 0 20 40 60 80 100 120 140 0 100 200 300 400 500 xanthane 5% loading unloading s tr e s s ( p a ) shear rate -15 -10 -5 0 5 10 0 5 10 15 20 25 30 squeeze_1mm squeeze 20 mm/min squeeze 200 mm/min f o rc e ( n ) time (sec) -15 -10 -5 0 5 10 0 5 10 15 20 25 30 35 squeeze_2mm squeeze 20 mm/min squeeze 200 mm/min f o rc e ( n ) time (sec) -8 -6 -4 -2 0 2 4 6 0 5 10 15 20 25 30 squeeze_3.5mm squeeze 20 mm/min squeeze 200 mm/min f o rc e ( n ) time (sec) -8 -6 -4 -2 0 2 4 6 0 5 10 15 20 25 30 35 squeeze_5mm squeeze 20 mm/min squeeze 200 mm/min f o rc e ( n ) time (sec) engineering, technology & applied science research vol. 10, no. 5, 2020, 6172-6175 6174 www.etasr.com phan: evaluation of some rheological properties of xanthan gum fig. 6. flow curves obtained in the tack measurements, for material thickness h=1mm. fig. 7. flow curves obtained in the tack measurements, for material thickness h=3.5mm. it can be seen that the obtained magnified graphs in figures 6 and 7 are almost similar to the typical graph in figure 2, especially at low material thickness. the maximum force value recorded will be used to calculate the tensile stress of the test material. the fluctuation with large amplitudes of recorded normal forces also shows that later calculated stress values will also fluctuate. this should be noted when commenting or giving future trends. figure 8 shows a visual image after the end of the experiment. as it can be seen, xanthan gel is almost concentrated in the center of the lower plate. almost no gel remains stick on the upper plate and the rest of the lower plate. this shows that the force obtained is mainly the adhesive force between the gel and the surface. xanthan gum can be used in self-consolidating concrete. this result is consistent with xanthan applied research in road construction [1], in which xanthan was used as soilstabilization binder. furthermore, this proves that xanthan gel can be used in concrete to increase the possibility of mold peeling. figure 9 represents the relationship between tack stress and squeeze stress of the xanthan gel. individual areas that are related to each sample thickness value can be easily distinguished. this proves that the smaller the sample thickness, the greater the squeeze stress. also, the tack stress obtained in the tack measurement significantly increases. as the thickness increases, these individual zones come closer to each other and progress toward the origin. this result can be explained by the arrangement of material particles when the thickness of the layer is high. fig. 8. the rest of materials after tack measurement. the photos were taken after the end of the tack process. the fluid was concentrated in the middle zone of the plate. fig. 9. tack stress in ralations with squeeze stress. considering the relationship between the two types of stresses when fixing squeeze and tack speed (figure 10), one can see a messy behavior when observing figure 10(a). this can be explained as follows: in the compression and tensile tests, from the recorded force value, shown in figures 5-7, these values are unstable and fluctuate around an average value. this oscillation is large and noticeable. thus, the calculated stress also oscillates, leading to the seemingly unordered picture in figure 10. because of the chaos of the data in figure 10(a), especially when the material thickness is high (3.5mm and 5mm), splitting into two parts was attempted, each part corresponding to a different squeeze engineering, technology & applied science research vol. 10, no. 5, 2020, 6172-6175 6175 www.etasr.com phan: evaluation of some rheological properties of xanthan gum speed as in figure 10(b). with the data fluctuations as analyzed above, it is difficult to comment on the relationship between the two types of stresses. however, in most cases it can be seen that the stresses and tensile stresses have a linear relationship and go through the origin. (a) (b) fig. 10. tack stress versus squeeze stress at constant test speeds. furthermore, the recorded yield stresses in both cases are relatively small, as can be easily seen in figure 10. that proves that the squeeze-tack experiment is not sufficient to assess the change in stress of xanthan under squeezing and tacking deformation. the obtained stress value is very small, showing the ability to apply xanthan in construction to adjust the ability of formwork peeling. iv. conclusions squeeze flow behavior of a shear thinning fluid was studied using the squeeze tack technique. the test material was firstly squeezed between two parallel and circular plates, then it was relaxed for 1.5 minutes, and finally it was separated at a predefined pulling velocity. from the flow curves obtained in the squeeze tack experiments, the rheological parameters, including yield stress in tension and in squeeze, have been calculated. the results show that the squeeze-tack test can be used for the analysis and evaluation of shear thinning fluids. although the experimental results are far from complete, in most cases it can be seen that stress and tensile stress have a linear relationship and go through the origin. the recorded normal forces also indicate that the squeeze flow experiment is not really suitable to study large sample thicknesses. when the thickness is greater than 2mm, the recorded force values fluctuate vividly around a certain equilibrium value. therefore, the results of stress calculation are for reference and forecast only. references [1] s. lee, m. chung, h. m. park, k.-i. song, and i. chang, “xanthan gum biopolymer as soil-stabilization binder for road construction using local soil in sri lanka,” journal of materials in civil engineering, vol. 31, no. 11, p. 06019012, nov. 2019, doi: 10.1061/(asce)mt.19435533.0002909. 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[11] k. kardjilova, v. vozarova, and m. valah, “influence of temperature on energetic and rheological characteristics of plantohyd bio lubricants – a study in the laboratory,” engineering, technology & applied science research, vol. 3, no. 3, pp. 424–428, jun. 2013. engineering, technology & applied science research vol. 8, no. 4, 2018, 3213-3217 3213 www.etasr.com laghari et al.: analysis of mapping techniques for mountain precipitation: a case study … analysis of mapping techniques for mountain precipitation: a case study of alpine region, austria abdul nasir laghari department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan a.n.laghari@quest.edu.pk gordhan das walasai department of mechanical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan valasai@quest.edu.pk daddan khan bangwar department of civil engineering, quaide-awam university of engineering, science and technology, nawabshah, pakistan skb_khan2000@yahoo.com aftab hameed memon department of civil engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan aftabm78@hotmail.com abdul hannan shaikh department of mathematics, quaid e awam university of engineering, science, and technology, nawabshah, pakistan hanangul12@yahoo.co.uk abstract—truly representative precipitation map generation of mountain regions is a difficult task. due to poor gauge representativity, complex topography and uneven density factors make the generation of representative precipitation maps a very difficult task. to generate representative precipitation maps, this study focused on analyzing four different mapping techniques: ordinary kriging, spline technique (sp), inverse distance weighting (idw) and regression kriging (rk). the generated maps are assessed through cross-validation statistics, spatial cross-consistency test and by water balance approach. the largest prediction error is produced by techniques missing information on co-variables. the me and rmse values show that idw and sp are the most biased techniques. the rk technique produced the best model results with 1.38mm and 72.36mm me and rmse values respectively. the comparative analysis proves that rk model can produce reasonably accurate values at poorly gauged areas, where geographical information compensated the poor availability of local data. keywords-mountain regions; poor gauge representativity; spatial interpolation techniques i. introduction scientists generally agree that the earth is undergoing critical climate changes [1-5]. climatic changes based on the hydrology, development and management of water resources have been under major attention over the years. the distributed hydrological models are gaining huge standing in analyzing and investigating the overall impacts on mountain regions and their environment [6-8]. distributed hydrological models require input variables like estimates of climatic variables at regular and continuous intervals as pre-requisites for their proper functioning [5, 6, 9, 10]. the amount of rainfall is the most vital parameter for any distributed hydrological model. nevertheless, the amount of rainfall is a matter of various uncertainties like measurement errors, systematic errors during applying interpolation and stochastic errors resulting from the random nature of rainfall. the performance of the models depends heavily upon the accurate estimation of precipitation over specific area and time. the results can be highly compromised [11]. this challenge of reliable and accurate rainfall estimates increases in mountain regions where the geography is complex and measuring stations are scattered over vast areas and concentrated in the valleys [12-14]. the measurement of accurate data for the mountainous range is a very difficult task, resulting in poor representation in the model that analyzes the various rainfall patterns. resultantly, in these types of situations, when no single method is optimal nor the accuracy of a specific interpolation technique is proven, the performance relies on the variable under study, spatial configuration, and the assumptions used in the estimation [1517]. the accuracy of measured data under a certain technique can be verified by comparing and analyzing by applying different techniques to the same data. in order to achieve this objective, the current study analyzes the range of stochastic and deterministic mapping techniques to estimate the values at ungauged locations. ii. data and models a. study area the study was carried out at the alpine area of kitzbühl ache region situated in the austrian eastern province of tyrol with an area of about 2000km2. complete details about the study region are given in [18]. the available 30 year time series (1960-1990) of mean annual precipitation of 14 gauge stations are taken into consideration for spatial interpolation. the catchment topography is highly rugged with elevation that ranges from 400m to 2400m above m.s.l as shown in figure 1. the catchment shows strong seasonal precipitation behaviors. b. sto dis pre kri spa is [17 [20 wh c. cli of est dis wh ob loc po sig ass inf far d. dim tec of cur the cal cur ten engineerin www.etasr spatial inter mapping tec ochastic appro stance weighin ecipitation, w iging [19-21]. atial correlatio able to remov 7, 26]. this a 0, 26-28]. th hereas the deta fig. 1. s idw techni it is form o matic data by each unknown timated have d stance from kn ˆ( ) i t x   1 ( , ) i pd x x   i xd s ,( 1 here )(ˆ xt = in served values cation, d(x, xi) int, and p= gnificantly inf signs more w formation, wh raway samples sp techniqu it is a de mensional cu chnique assign neighboring rvature. this p e sample point lculated samp rvature. the te nsion. the firs ng, technology r.com rpolation tech chniques are c oaches. the fo ng and spline whereas, the la the regressio on of the differ ve the drifts w approach has hese techniqu ailed discussio study area with lo ique of a determin y averaging sa n point [31-33 decreasing inf nown locations * ( )i it x .p s p ix ) 1 , follows nterpolated val at the ith locat i)= distance f weighting po fluence the in weightage to c hile lower po s with little inf ue eterministic te urves on 3-d ns the mathem points that produces an ev ts. this is alik ple points whi echniques com st one generat y & applied sci hniques categorized int ormer techniq and is used ater technique on is carried rent variables with validated been used fo ues are brief n is referred to ocations of 14 rain nistic techniqu ample values i 3]. it’s assume fluence or wei s. the formula 1i i  . lue at location tion, t(xi)= ob from known p ower. the cho nterpolation re loser points a ower assigns m formation. echnique, wh dimensional s matical function t decrease t ven surface w ke to fit a rubb ilst decreasing mmonly used tes the uniform ience research laghari et al.: to deterministi que includes in for interpolati e includes ord out on the ba [22-25]. the m intrinsic hypo or climatic ma fly presented o [20, 29, 30]. n gauge stations ue that interp in the neighbo ed that the var ight with incre a is given as: (1) (2) n x, λi= the wei bserved value point to interp oice of powe esults. high p and results in more weighta hich represen surfaces [34]. ns to certain nu the whole su while passing a ber piece acro g the entire su are regularize m changing su h v : analysis of m ic and nverse ion of dinary asis of model othesis apping here, polates orhood riables easing ight of s at ith preted er can power more age to nts 2. the umber urface around oss the urface d, and urface with whi valu insp regu foll f whe unk solu kno fun coe e. and neig bas of k for by d whe obs valu the loca arou esti kno wei by: for sem sele (t̂ equ vol. 8, no. 4, 20 mapping techniq h values that ile the other o ues confined pection and r ularized splin lowing formul ˆ( ) ( ,it x f x { 21 ( ) 2 4 2 0 r r r r k              f(xi, yi)=a1+a2 ere )(ˆ xt = in known smooth ution of a syst own point to nction, c= the efficients found ok techniqu this techniqu d works the s ghboring mea ed on distance known points. kriging, after d.l. krige: 0 1 ˆ( ) n i t x    ere )(ˆ 0xt = th served value a ues at the ith l number of ation and spat und the pre imator varianc own as “best ights sum to u 1 ( , n i i j i x x    all j, where φ mivariogram a ected as a bes )( 0x , and t uation: bac .1 , 018, 3213-3217 ques for mount may remain one influences by the sam results through e method was a is used for su 1 , ) ( n i i i y r r   } 2 ln 2 ln 2 r c r c                   2x+a3y nterpolated spl h function, λ tem of linear interpreted p e constant eq d by a solution ue ue uses a semi ame way as i asured values. es but also dep . author in [3 a first use of t . ( )i it x he interpolated at ith location, location. the measured poi tial relationsh ediction locat ce and ensure t linear unbi unity [36]. est ) ( ,j jx   φ=lagrangian analysιs, the st-fit model fr the weights λi c 7 tain precipitati outside the s s the rigidity o mple data ra h cross-valida s selected from urface interpo )ir } 1   line value at lo i= the coeffic equations, ri= point, k0= the qual to 0.577 n of a system o ivariogram for idw works, however, we pend on total s 35] developed the theory in t d value at loc and λi= the w λi depends on ints, distance hips among th tions. krigin es the unbiase iased estimato timator varianc 0, )x n multiplicator gaussian va from all other i are calculate        i  3214 ion: a case stu sample data r of the surface ange. after v ation statistics m both types lation: (3) (4) (5) ocation x, f(xi, cients found = the distance e modified b 7215, and αi= of linear equat r spatial predi which weight eights are not spatial arrange d a general for the mining ind (6) cation x, t(xi) weight of obse n: fitting mod to the predi he measured v ng minimizes ed estimation or (blue)” ce can be ach (7) r. after perfor ariogram mod models to pr ed from the m (8) udy … range, with visual s, the . the , yi)= by a from bessel = the tions. iction ts the only ement rmula dustry = the erved del to iction values s the often with ieved rming del is redict matrix engineering, technology & applied science research vol. 8, no. 4, 2018, 3213-3217 3215 www.etasr.com laghari et al.: analysis of mapping techniques for mountain precipitation: a case study … where matrix a contains the semivariances of all data point pairs, b is a vector containing semivariances between the location of interest and observed point. λi is the weight to be calculated [20, 37-41]. f. rk technique authors in [17] conclude that ordinary kriging does not produce representative precipitation values in mountain regions all the time. alternative techniques might fully utilize the relationship between predicted variable and co-variables for variability analysis. two of these techniques are cokriging and regression kriging. due to poor cross-covariance between precipitation and any topographical variable, the former application did not produce good results. however, in such situations regression kriging seemed the natural choice, which is commonly used in hydro-sciences [42, 43]. the technique defines the relationship between target and co-variables in order to predict the values at grid nodes through linear regression. the auxiliary variables are easy to measure, they provide an alternative to target variable at the under sampled locations to model and quantify the existing patterns. to quantify the existing trend of the variable and its variability in a regression model, we preferred to use multiple linear regressions the further extension of straightforward linear regression with the variety of descriptive variables. as altitude alone flopped to signify the variation of precipitation sufficiently, we tested other variables like slope, topographic index, aspect, hill shade, curvature etc. these extra explanatory variables were obtained from the elevation model, in order to make better predictions of the target variables at grid nodes of the dem. we adopted stepwise procedures to select the most crucial variables and the subsequent regression equation to predict the target variable at un-sampled locations. the regression led to a three parameter equation, significant at 5% level, explaining 62% of variability of precipitation.      1 ˆ : 1075.94 42.59 * 0.26 * 3.98 * r hill shade dem slope t      (9) the resulting regression residuals (ε) are further kriged at grid nodes by fitting variogram models, and then finally both values are summed up to predict the target variable values. ˆ ˆ ˆ( ) ( ) ( )rk r okt x t x x  (10) where rkt̂ = combined predicted values of target variable, rt̂ = regression predicted values of target variable, ok̂ = kriged values of regression residuals. iii. validation methods the mapping techniques performance was assessed by following three steps: a. cross-validation statistics the cross validation method depends on eliminating one sample location (measurement station) from the data set at a time and calculating the value of the removed sample with the remaining data points. this routine was followed for each measurement station. the comparative indices were then used as a measure of prediction quality by the me and the rmse, which are defined as follows: 1 1 ˆ( ) n i i i me t t n    (11) 0.5 2 1 1 ˆ( ) n i i i rmse t t n          (12) where n is the number of validation points, and ˆ &t ti i are the predicted and observed values at location i. the me criterion is used to check the conditional bias property, while the rmse criterion assesses the precision quality. a smaller value of rmse indicates higher accuracy and vice versa. cross validation statistics can be used to find the optimal mapping technique, however, the presence of short range correlations in data may raise questions regarding the reliability of its statistical results [35]. b. cross-consistency a second step to analyze reliability and consistency of predictions, spatial cross-consistency approach was adopted [44]. all statistical parameters of different calculated precipitation mapping estimates were compared with a referenced precipitation map (rpm). this rpm was carefully produced during a 4 year project (www.waterpool.org) in which different experts from different institutes were involved, and results were consistent with water balance estimates. c. water balance approach finally all calculated precipitation maps including the rpm were evaluated by means of a general water balance approach.        – – q discharge p precipitation et evapotranspiration s storage changes   (13) gridded discharges were calculated for each mapping technique as a result of subtraction of actual evapotranspiration grid estimates from interpolated mapping precipitation grid estimates. the actual evapotranspiration values are obtained from the hydrological atlas of austria. storage changes can be ignored, as for long-range mean annual water balances; it was assumed that there is no sensible change in the water contents of different reservoirs, e.g. groundwater, snow cover [44, 45]. the difference between the calculated discharges with observed discharges gives a measure for the reliability and consistency of the precipitation. iv. results and discussion the me values clearly indicate the superiority of rk technique over the other techniques, showing almost 42% less bias than ok. whereas idw and sp techniques produce higher bias, almost 2 to 5 times higher than ok technique. the rmse results also reveal the primacy of rk technique over the other ones. however, all techniques yield high uncertainty in calculated values. thus, considering co-variables into account certainly improves the performance by decreasing rmse values from 111 to 72. the spatial cross-consistency tests are also conducted by computing precipitation maps with ref ado fig stud dif pro inc per ref the ele po sta of cov zon fig com reg map fig com neg valu ann engineerin www.etasr ferenced preci opted in [46]. g. 2. cross va dy region are the the statisti fferences. ho omising resul corporation o rcentile varia ferenced map. eir performanc evation zones sition of gaug ations are locat basin area. zo vering 39% a ne-4 possesses g. 3. summary mputed precipitat gion. negative val p value, while po g. 4. compara mputed precipitati gative values ind ues indicate the o the basin le nual values in ng, technology r.com ipitation raster the comparis alidation statistics me and rmse ical paramete owever, the r lts except in of topographi ation in rk to further an ces, first at 4 c of the whol ge stations are ted below 100 ones 2 and 3 c and 26% of a s only 3% area y statistics of p tion estimates by lues indicate a lo ositive values indi ative statistics of ion estimates by dicate the less val opposite. evel values fo n the region. y & applied sci r. the same s on results are s of four mappin ers clearly rk technique n maximum v ical informati map is clos nalyze all tech catchment leve e basin (figu e highly biase 00m (zone-1), ontain only on area respectiv a without any percent differenc idw, spline, ok ower value with r cate the opposite. f percent differen idw, spline, ok lue from the refer ollow the sam rk method ience research laghari et al.: strategy was e given in figur ng techniques app show the v e yields the values due t ion. similarly sely matched hniques we ana els and then th ures 3 and 4) ed, more than covering only ne station each vely. the top gauge station. ces between rp k and rk for th respect to the refe . nces between rp k and rk at four renced map and p me pattern of is found to p h v : analysis of m earlier re 2. plied in visible most to the y the d with alyzed hrough ). the n 80% y 32% h, with most pm and e entire ferenced pm and basins. positive mean present bett othe tech just con altit ok altit how not and high perf dep zon com the imp map was ord esti atla map gau with the tech fig. com elev map pro valu at h uno pro leve [1] [2] vol. 8, no. 4, 20 mapping techniq ter result in th er techniques hniques like tifies the co nclusions are s tude. without k techniques p tude which co wever, at the be effective, d 33% at zon her sparse dat formance of pendence resul nes 2 and 3 mparatively, al e better resu portance of g pping at highe s adopted for der to validate imates of the w as of austria. ps and evapotr uged runoff an h rpm, 2.7% ese outcomes hnique in the h 5. comparati mputed precipitati vation zones. neg p and positive valu comprehensiv duces reason ues. the prim high altitude sp obtainable. ho duce good re el height with b. klove, p. a kværner, t. m velasco, m. groundwater an 518b, pp. 250-2 h.-m. fussel, a a. bigano, s. c 018, 3213-3217 ques for mount hree basins, w have better es idw, spline onclusions of strengthened b t elevation in performed com ontains 86% o higher altitud where the con e-4 resulting ta zones. duri ok at high lted to be hig 3. for analy ll stations wer ults from rk geographical er sparse data z the four inte e the rpm. m whole region w total runoff w ranspiration es nd computed ru % with rk and s validate th higher altitude ive statistics of ion estimates by gative values indi ues indicate vthe v. co ve analysis c nably accurate macy of this te parse data zon owever, the sp esults over ge a wide networ refer ala-aho, g. bertr muotka, h. mykr pulido-velazqu nd dependent eco 266, 2014 a. jol, a. marx, m castellari, m. erh 7 tain precipitati whereas in kit stimates. the s over geosta f many othe y further analy nformation the mparatively w of the total sta des these three nsistency rang in relegation ing semivariog zone was po gher at zone 1 yzing the ma re included in k at higher information zones. a wate erpolation pre mean annual were taken fro was computed stimates. the unoff found o d 13-20% with he overall su e region with sp percent differenc y idw, spline, icate the less val opposite. onclusion learly indicat e average an echnique is pa nes where map line and idw eostatistical te rk of gauge sta rences rand, j. j. gurdak ra, e. preda, p. uez, “climate osystems”, journ m. hilden, a. apa ard, b. georgi, c 3216 ion: a case stu tzbüleher ach superiority of atistical techn er studies. t ysis on the ba e idw, spline well below 10 ations under s e techniques c ges at 8% at zo of their abili gram modelin oor, as the sp 1 and weaken apping techn the final map zones prove in estimating er balance appr ecipitation ma evapotranspir om the hydrolo d from precipit difference bet out to be only h other techni uperiority of parse data. ces between rpm ok and rk a lue from the refe es that rk m nnual precipit articularly obse pping variable w model results 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electric and electronic engineering mersin university, mersin, turkey alkanalkaya@mersin.edu.tr abstract—accurate state of charge estimation and robust cell equalization are vital in optimizing the battery management system and improving energy management in electric vehicles. in this paper, the passive balance control based equalization scheme is proposed using a combined dynamic battery model and the unscented kalman filter based state of charge estimation. the lithium-ion battery is modeled with a 2nd order thevenin equivalent circuit. the combined dynamic model of the lithiumion battery, where the model parameters are estimated depending on the state of charge, and the unscented kalman filter based state of charge, are used to improve the performance of the passive balance control based equalization. the experimental results verified the superiority of the combined dynamic battery model and the unscented kalman filter algorithm with very tight error bounds. furthermore, these results showed that the presented passive balance control based equalization scheme is suitable for the equalization of seriesconnected lithium-ion batteries. keywords-combined dynamic modelling; li-ion battery; passive balance control; soc based equalization; soc estimation; unscented kalman filter i. introduction conventional fossil fuel vehicles are emitting a considerable amount of co2. in response to the concern for the protection of environment, automotive industries proposed electrical vehicles (evs) as a solution for conventional fossil fuel vehicles [1-3]. rechargeable battery technologies which have become an alternative power are used in the evs. batteries with different chemicals such as ni-based batteries, li-based batteries, na-based batteries and lead acid batteries are used in evs. li-ion batteries are more preferred in electric vehicles due to their significant advantages such as high energy density and nominal cell voltage, long life and having no memory effect [4, 5]. the high performance and safe use of liion batteries depends on the efficiency of their battery management system (bms). the state of charge (soc) of the li-ion battery, defined as the ratio of the remaining capacity and maximum available capacity of a battery, is a key component of the bms for the equalization of battery packs on evs. soc cannot be measured directly from the battery. therefore, soc should be estimated by using an accurate battery model and measured signals such as current and voltage [6-8]. modeling of li-ion battery in evs applications can be mainly divided into three categories: electrochemical models, mathematical models and electrical equivalent circuit (eec) models [9]. the complexity of the electrochemical models and the low accuracy of mathematical models led to the investigation of the eec models. eec models can be classified based on the different circuit topology used. partnership for a new generation of vehicles (pngv), randles, national renewable energy laboratory (nrel) and thevenin models are the most used electrical circuit models in ev applications [10, 11]. soc estimation is more powerful with an accurate battery model. there are many methods to estimate the soc of a li-ion battery, methods such as coulomb counting (cc), open circuit voltage (ocv), neural network (nn), fuzzy logic, and kalman filter based algorithms [12-16]. cc method is the basic approach which is widely used for soc estimation, but it accumulates error problems. in addition, the initial soc must be known in order to use this method [17, 18]. ocv method is another basic technique which can be used to determine soc directly, but this method suffers from long resting time [19, 20]. nn and fuzzy logic methods define the battery as a blackbox system and can achieve accurate soc results. however, these methods are in need of a large and of good quality training data set. the model performance strongly depends on the data set used [21, 22]. kalman filter (kf) which can solve initial soc and cumulative error problems is widely used as an accurate soc estimator, but it is only suitable for linear systems [23, 24]. extended kalman filter (ekf) known as the nonlinear extension of the conventional kf, is the most commonly used filter to estimate soc. ekf linearizes the battery model using taylor series expansion and jacobian matrix [25]. ekf ensures accurate estimation of the soc of the battery using the measured load current and terminal voltage. the accuracy of ekf based soc estimation depends on the precision of the battery model and information of the system noise and covariance matrix [26-28]. however, the ekf has drawbacks. the linearization process using jacobian matrices could have high computation cost. unscented kalman filter (ukf) uses an unscented transformation with a set of sigma points to estimate corresponding author: alkan alkaya engineering, technology & applied science research vol. 9, no. 6, 2019, 4876-4882 4877 www.etasr.com muratoglu & alkaya: unscented kalman filter based state of charge estimation for the equalization … soc without linearization [29]. due to this transformation, ukf has more robust accuracy than ekf in estimating posterior mean and covariance of the state distribution [30-33]. changes in internal impedance or capacity reduction due to cell aging cause deviations in cell behavior. therefore, equalization of the cells in the battery pack is essentially required. cell equalization can be mainly categorized into soc based and voltage-based methods [34-36]. in the voltage-based method, the voltage is measured directly on the battery and is easily used in cell equalization. voltage, which is the external characteristics of the battery cannot reflect the capacity or the internal resistance. therefore, the voltage-based method is unsuitable for determining the battery imbalance. on the other hand, soc is affected by both internal and external characteristics of the battery such as battery voltage/current, temperature, internal resistance, and capacity. to improve the cell equalization, the soc based method is more suitable because soc represents a comprehensive performance of the battery characteristic [37]. in this study, the second order thevenin equivalent circuit method is chosen considering optimum model accuracy and complexity. equivalent circuit parameters are associated with soc to reflect the dynamic characteristics of the li-ion battery. the combined dynamic battery model (a combination of thevenin equivalent circuit model, ocv method and cc method) is used to better represent the dynamical behavior of the li-ion battery. according to the combined dynamic battery model, ukf based soc estimation is used to implement the equalization of li-ion battery packs. in order to protect seriesconnected li-ion cells from cell inconsistencies, passive balance control (pbc) is used with soc based equalization. ii. combined dynamic modeling of li-ion batteries the dynamic model of the li-ion battery was formed by combining different methods. the combined dynamic battery model is constructed using second order thevenin model, ocv method, and cc method. the schematic diagram of the combined dynamic battery model is shown in figure 1. fig. 1 the schematic diagram of the combined dynamic battery model soc is obtained from the load current by using the cc method. the definition of the cc method is: 0 , 0 1 t t l b soc soc i d c τη τ= − ∫ (1) where ���� is the present soc, ���� is the initial soc, �� is the maximum available capacity, � is the charge-discharge efficiency, and � ,� is the load current. the relationship between ocv and soc is determined by the ocv method. ocv is defined as electrical potential difference between the two terminals of the battery when it is disconnected from the electrical load. ocv has a non-linear relationship with soc which is obtained by the curve fitting method using the rest points of the ocv of the test data. second order thevenin equivalent circuit model, given in figure 2, is chosen as the cell characteristic of li-ion battery due to its high precision and low complexity. the equivalent circuit parameters can be changed dynamically depending on soc. fig. 2 second order thevenin equivalent circuit model the state-space representation of the combined dynamic battery model is: [ ]1 2 t x soc u u= (2) ( ) ( ) ( ) ( ) ( ) ( ) 1 1 2 2 1 2 1 0 0 0 1 , , 0 0 0 1 , , 1 , 1 , b l x f r soc f c soc x f r soc f c soc c f c soc i f c soc η     = −   −  −    +     � (3) ( ) ( )0, 1 1 , ly f ocv soc x f r soc i = − − + −     (4) where � ��,���� is the ohmic resistance, � ��,���� and � ��,���� are polarization resistances, � ��, ���� and � ��,���� are polarization capacitances, and �� and �� are the polarization voltages crossing on �� and ��. iii. ukf algorithm ukf is a widely used state estimator for nonlinear systems. the ukf uses the unscented transformation principle rather than linearizing the nonlinear functions as in the ekf. the ukf consists of four major steps: initialization, sigma point calculation, state prediction and measurement update. in the initialization step, mean of initial state �̅� � and covariance p� � are estimated as gaussian random vectors: 0 0 s s x e x =   (5) ( )( )0 0 0 0 0 t s s s s s p e x x x x  = − −    (6) then, � set of sigma points are selected by using unscented transformation principle in sigma point calculation step: engineering, technology & applied science research vol. 9, no. 6, 2019, 4876-4882 4878 www.etasr.com muratoglu & alkaya: unscented kalman filter based state of charge estimation for the equalization … ( )2 n nλ α κ= + − (7) ( ) ( ) 1 , 1 1 1 1 1 0 1,..., 1,...,2 s n s s s k n n n s s n n x k x x n p k n k n n x n p λ λ − − − − − −  =  = + + =  = +  − + (8) each sigma point passes through the non-linear functions � .� and � . � . priori state estimate ���|��� , priori error covariance matrix ��|��� and measurement of system output vector ���� are calculated in state prediction step: ( ), 1 1 1 1, ,x x vk n n n nx f x x u− − − −= (9) ( )| 1 | 1 1, ,x wn n n n n ny h x x u− − −= (10) ( ) 2 ( ) | 1 , | 1 0 ˆ n k x n n m k n n k x w x− − = = ∑ (11) ( )( ) 2 ( ) | 1 , | 1 1 , | 1 1 0 ˆ ˆ n t k x x n n c k n n n k n n n k p w x x x x− − − − − = = − −∑ (12) ( ) 2 ( ) 1 , | 1 0 n k n m k n n k y w y− − = = ∑ � (13) where the weights of the sigma points are !" #� $ % &'% and !( #� $ % &'% ) 1 + ,� ) β� for . $ 0 , !" #� $ !( #� $ � � &'%� for . $ 1,…,22. finally, the measurement covariance �3� and the crosscorrelation covariance �4�,3� are calculated. kalman gain 5� is calculated based on measurement covariance and crosscorrelation covariance. posteriori state estimate ���|� and posteriori error covariance matrix ��|� are calculated in the measurement update step: ( )( ) 2 ( ) , | 1 1 , | 1 1 0 n tk yn c k n n n k n n n k p w y y y y− − − − = = − −∑ � � (14) ( )( ) 2 ( ) , , | 1 1 , | 1 1 0 ˆ n tk x xn yn c k n n n k n n n k p w x x y y− − − − = = − −∑ � (15) 1 ,n xn yn ynk p p −= (16) ( )| | 1ˆ ˆn n n n n n nx x k y y−= + − � (17) | | 1 t n n n n n yn n p p k p k−= − (18) iv. passive balancing control for soc based equalization battery packs used in evs, contain many cells. these cells interact with each other. inconsistencies that may occur in these interacted cells can lead to reduced capacity, overcharge and over-discharge. cell equalization is essentially required to prevent cell inconsistencies in the battery pack. traditionally, pbc is used to protect li-ion cells from cell inconsistencies with soc based equalization. the fixed shunting resistor method shown in figure 3 is one of the most common used in pbc. this method is accomplished by using a switch and drain resistor in parallel with each battery cell. fig. 3 schematic diagram of fixed shunting resistor method v. experimental validation in order to validate the ukf based balancing performance of li-ion battery packs, an experimental test bench was set up. this test bench consisted of a programmable dc power supply (gwinstek psh-3620a), a programmable dc load (gwinstek pel-2002/2040), a real-time controller (dspace ds1104), a liion battery (panasonic ncr18650b), a balancing circuit and a pc as shown in figure 4. the balancing circuit shown in figure 5 is developed to perform soc based equalization for battery packs by using pbc. the soc of each cell is compared with the average soc in the cell balancing circuit. when the difference is over a predetermined threshold of inconsistency, the equalization begins. otherwise the equalization process stops. fig. 4 experimental test bench a. determinaton of ocv impulse discharge test was performed to determine ocv in the experimental test bench. in this test, the li-ion battery was discharged for 5 minutes and rested for 2 hours. this process continued until the battery was fully discharged. the ocv was obtained using the resting points of the discharge process with the curve fitting method. engineering, technology & applied science research vol. 9, no. 6, 2019, 4876-4882 4879 www.etasr.com muratoglu & alkaya: unscented kalman filter based state of charge estimation for the equalization … fig. 5 the balancing circuit fig. 6 ocv-soc non-linear relationship the ocv curve, given in figure 6, can be represented with a sixth degree polynomial as: ( ) 6 5 4 3 2 , 16.07 43.57 37.89 5.85 7.59 4.41 2.8 ocv f u soc soc soc soc soc soc soc = × − × + × − × − × + × + (19) b. ukf based soc estimation ukf algorithm has been tested on the combined dynamic battery model to estimate soc. the initial parameters of the ukf were defined as: state variable �� $ 6���� 0 07 8 , covariance matrix � $ 9:,; 1,1,1� , weight matrix < $ 9:,; 10���,10���,10���� and � $ 10. q and r weight matrices were determined by trial and error. the ���� was set to 0.8 (80%), in order to better interpret the sensitivity to the initial state of ukf algorithm. soc estimation performance based on ukf is shown in figure 7. fig. 7 ukf based soc estimation it can be seen that the ukf algorithm can quickly eliminate the initial soc error and accurately track the soc after the elimination of the initial error. the calculated estimation error signals are shown in figure 8 with the initial soc error. in order to verify the performance of the ukf algorithm, detailed calculations were carried out by using the comparison of the estimation results. it is clear that the ukf algorithm with the combined dynamic battery model provide robust performance in detailed calculations (table i). table i. detailed calculations for ukf results mean error mean square error error variance ukf results 1.91% 1.6380 ×10-4 1.0133×10-4 fig. 8 error signal of ukf based soc estimation c. real-time user interface the interfaces of the battery equalization, shown in figure 9 and figure 10 are built in matlab/simulink and ds1104 controldesk respectively. the architecture consists of a measurement block, a li-ion battery block and a cell balancing block. the measurement block captures battery voltages, battery currents and initial socs of the individual li-ion cells. battery voltage and battery current data of li-ion battery cells were measured online by using the ds1104 r&d controller board. the initial soc was determined by the use of these data and cc method. the obtained data were given as input to the li-ion battery block. the li-ion battery block estimates soc by using ukf for the cell balancing block. in the li-ion battery block, the soc was estimated with the combined dynamic battery model based on the ukf algorithm. the combined dynamic battery model consists of a second order thevenin equivalent circuit, ocv, and cc. the cell balancing block keeps the soc of the cells at the same level with the pbc. the algorithm of the equalization process is given in figure 11. voltage and current of the li-ion cells were obtained. the initial soc of each li-ion cell was determined by the ocv method. the soc of each li-ion cell was estimated and compared with the average soc. when the soc difference of each li-ion cells was over the predetermined threshold of inconsistency, the balancing switch turned on, otherwise it stayed off. engineering, technology & applied science research vol. 9, no. 6, 2019, 4876-4882 4880 www.etasr.com muratoglu & alkaya: unscented kalman filter based state of charge estimation for the equalization … fig. 9 matlab interface of the equalization process fig. 10 graphical user interface of the equalization process fig. 11 algorithm of the equalization process d. validation of pbc the pbc is applied to four series of li-ion cells to test and verify the presented equalization scheme. in the first experiment, the battery pack is discharged at the load current which is randomly varied between 0,65a and 1a. to examine the performance of the balancing process, the pbc is turned off after 180min. the result of the first experiment is shown in figure 12. in the second experiment, the balanced battery cells are charged for 180s. afterwards, only the pbc of b1 cell (first battery cell) is turned off during the charging process. unbalanced battery cells are charged for 320s and afterwards the pbc of the b1 cell is turned on for balancing in the discharge process. when the cells are equalized, the pbc of the b1 cell is turned off again during the charging process for 600s. then the pbc of b1 cell is turned on for balancing in the charge process until the cells are equalized. the result of the second experiment is shown in figure 13. as shown in figure 12, cell inconsistencies were successfully prevented during discharge process until the pbc was off. on the other hand, engineering, technology & applied science research vol. 9, no. 6, 2019, 4876-4882 4881 www.etasr.com muratoglu & alkaya: unscented kalman filter based state of charge estimation for the equalization … cell inconsistencies were quickly observed when the pbc was turned off. likewise, it was seen that the unbalanced cells equalize rapidly during both charging and discharging processes as shown in figure 13. experimental results validate that pbc can equalize the li-ion cells accurately and rapidly by using ukf-based estimation with combined dynamic battery model. fig. 12 soc vs time, first experiment fig. 13 soc vs time, second experiment vi. conclusion this paper presented a soc based equalization scheme based on pbc. a combined dynamic model of the li-ion battery was proposed by using a second order thevenin model, ocv, and cc method. in the combined dynamic model, the parameters of the equivalent circuit vary depending on soc. accurate soc estimation of each li-ion cell was implemented by ukf. the soc based equalization utilizing pbc was applied to equalization of the unbalanced of series-connected li-ion batteries. the simulation architecture utilizing pbc was designed in matlab/simulink. real-time experimental verification was performed with a real-time controller dspace ds1104. two different experiments were performed to validate the effect of the designed pcb unit. in the first experiment, the battery pack was discharged under variable loads and cell imbalance was successfully prevented by the pcb unit during the discharge process. in the second experiment, the battery pack was tested under the charge/discharge conditions at different times and unbalanced cells equalized rapidly during charging and discharging process. the experimental results show that the presented pcb based equalization scheme and ukf based soc estimation can perform well in real-time applications. acknowledgment the authors would like to thank the scientific and technological research council of turkey (tübi̇tak-3501, 114e515) for the financial support. references [1] m. a. hannan, m. s. h. lipu, a. hussain, a. mohamed, “a review of lithium-ion battery state of charge estimation and management system in electric vehicle applications: 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abra.oek@gmail.com abdelhadi raihani ssdia laboratory enset mohammedia hassan 2 university casablanca, morocco abraihani@yahoo.fr ouafae serrar grief team regional center for education and training professions marrakech, morocco serrar.ouafae@gmail.com lhoucine bahatti ssdia laboratory enset mohammedia hassan 2 university casablanca, morocco lbahatti@gmail.com abstract—the construction of a wind power generation center starts by the selection of a suitable wind farm location. the selection includes six factors, namely wind speed, slope, land use, distance from the power lines, distance from the roads, and distance from populated areas which have been integrated into qgis by weights calculated using the analytical hierarchy process (ahp) approach. as a result of this study, the areas having very high wind potentiality have been identified and a best wind farm location map has been prepared. the map, using the overlay function in gis, exhibits the most and least suitable areas for the location of wind farms in morocco. the approach could help identify suitable wind farm locations in other areas using their geographic information. keywords—analytical hierarchy process (ahp); multicriteria decision making (mcdm); geographic information system (gis); wind farms; renewable energy i. introduction electric energy production is an important factor for the economic growth of any country. globally, fossil fuels are the main resource for electric energy production, but there are not unlimited, they pollute the environment, and their prices vary. the use of renewable energy, especially wind power, to generate electricity is a relevant solution because it has advantages such as low pollution and very low prices [1-3]. morocco has great resources for renewable energy exploitation. due to its geographical position, it has a good potential of wind energy development to cover the increasing energy demand. morocco has a goal of exploiting renewable energy by increasing wind energy production to satisfy the increasing demand. the research of a suitable location for wind farm setting [4] is crucial because it encloses different criteria such as wind speed, land cover, slope, distance to urban places and roads around the candidate area. in order to have an optimal location, site selection analysis [5] is the best solution to find these sites. as a result, the suitability of a wind farm location is subject to multiple decision criteria [6]. for this purpose, two decision tools, geographic information systems (gis) and multiple criteria decision analysis (mcda) [7] were utilized to identify suitable sites for wind farms [5]. applying gis-based analytic hierarchy process (ahp) approach is meant to specify and classify the criteria, to identify the suitable and unsuitable locations for each layer in a gis, and calculate the weights using ahp [8] to create the final map of wind farm suitability in morocco. the aim of this work is to provide decision makers with a tool for the implementation projects of new turbines [9]. ii. study area the kingdom of morocco is located in the north-west of the african continent. it is bordered by the atlantic ocean on the west, the mediterranean sea on the north, algeria on the east, and mauritania on the south. its total area is 710850km 2 , the lowest point is −55m (sebkha tah) and the highest is 4144m (toubkal summit). morocco has an estimated population of 34 million people, mostly concentrated in the northwest. the north of the country is covered mostly by forests. in the south, bare areas are the dominant land cover. morocco has good climatic conditions for the installation of wind farms. morocco has a large surface where wind speed can reach up to 8m/s. the methodology developed in this section is applied to evaluate the suitability of wind farms in morocco. iii. mcdm and gis methodology a. identification of decision criteria and constraints the wind farm planning process [10] often incorporates complexity, uncertainty, multiple management objectives, and various spatial data attributes. moreover, in order to assess the degree of suitability for a certain potential location, most corresponding author: fatma elmahmoudi engineering, technology & applied science research vol. 10, no. 4, 2020, 6068-6075 6069 www.etasr.com elmahmoudi et al.: elaboration of a wind energy potential map in morocco using gis and analytic … decision-making processes generally consider multiple criteria. in this study, decision criteria consist of constraints representing quantifiable attributes to assist the decisionmaking process. moreover, the overall objective of the decision criteria identified in this study is to evaluate wind farm site suitability based on different types of criteria (figure 1). the criteria were established based on previous scientific publications and the current legislative framework in morocco as described below. fig. 1. hierarchy structure. 1) data collection in order to reach an accurate and reliable estimation of the wind power potential in of morocco, proper data should be collected, modified and analyzed. several data sources have been utilized, not only for wind speed, but also for land cover, slope, urban areas, power lines, and road proximity. to determine the different classification potential for wind energy in morocco, several satellite images and traditional data sets have been garnered from irena global map atlas [11]. the shuttle rader topographic mission (srtm) digital elevation model (dem) of 30m 2 resolution has been processed in qgis 2.18.3 software for the preparation of the slope map [12]. the roads and the power lines have been developed by using open street map tools in qgis [13]. by using the buffer tools, distances from urban areas, roads, and power lines have been assessed. landsat 8 satellite images of morocco have been obtained from its official website [14]. all the layers have been converted into raster format, reclassified and the weight of each layer was calculated with the ahp method [15]. table i shows the information about wind farm suitability criteria. table i. data sources criteria data sources original data structure wind speed irena global map atlas raster land cover landsat 8 satellite images raster slope digital elevation model (dem) raster urban area open street map vector distance to power lines open street map vector distance to roads open street map vector 2) decision criteria choosing the best wind farm location depends on several factors [16]. the combined assessment of those factors using modern techniques can provide a detailed picture of this location. the selection of criteria began with a literature review to reduce the criteria deemed relevant and critical for the adequacy of a wind farm facility. in this paper, a total of 6 criteria are considered for modeling the suitability of wind farm locations in morocco. a) wind speed in the field of selecting the best location of wind energy, according to the experts’ opinion, wind speed is the most important criterion to consider when building a wind energy plant site. authors in [17] applied the wind speed data at various heights through various probability distribution functions and got as a result that the rayleigh distribution function is the best for finding site selection. regions with higher wind speed generally have higher potentiality for wind farm installation. the wind speed in morocco varies depending on location (figure 2 )[11]. b) land cover land cover or land use is one of the most important criteria for energy investments. wind farms should be installed outside protected areas, wetlands, aquatic and forest areas. the study area is classified into five categories of land use practices (figure 3) [14]. c) slope slope has a direct relationship with construction and maintenance costs. as the gradient becomes higher, the costs of construction and maintenance also become higher. as a result, areas with higher slopes are generally considered less suitable (figure 4) [12]. d) distance from urban places this is a very important criterion in wind farm siting. distance from populated areas is an important geomorphic factor that should be considered. as a result, regions far from urban places are having higher index of suitability [18]. in this paper, the distance from populated areas is prepared in qgis by using the buffer tool multiple times, from residential areas to avoid noise and nuisance, and later, a single vector has been created and converted to the raster image (figure 5) [13]. e) distance from power lines when choosing a favorable location for a wind farm, it is necessary to take into account the availability of transmission lines between the wind farms and the electricity grid to reduce the cost related to cabling and electricity losses [19]. wind farms should be sited in the close vicinity of the electricity grid (figure 6) [13]. f) distance from roads to minimize cost, it is important that the wind farm should be near the road for the easier transmission of the installation and maintenance equipment (figure 7). in most wind farm siting assessments, the areas closer to roads are considered more suitable. however, there is not an exact optimum value of distance from the wind turbines to the road. in our study, we considered different buffer distances (table ii). 3) decision constraints in this study, each criterion has a number of constraints which are identified, discussed, and summarized in table ii. a) wind speed wind turbines start producing electricity at around 4m/s. in this study, the wind speed was reclassified into 5 classes: 03m/s, 3-5m/s, 5-6m/s, 6-7m/s, and above 7m/s. the areas with engineering, technology & applied science research vol. 10, no. 4, 2020, 6068-6075 6070 www.etasr.com elmahmoudi et al.: elaboration of a wind energy potential map in morocco using gis and analytic … a wind speed lower than 4m/s were considered unfeasible for wind farm development. in figure 2 the wind speed map is exhibited. the data used are from [11]. fig. 2. wind map. data taken from [11]. b) land use in this study, the land cover was reclassified into 5 classes: water area, forest, shrub land, tree land, and bare area. in these cases the first class represented unsuitable areas for location of wind farms due to environmental reasons and the remaining classes represented increasing suitability. fig. 3. land cover map. data taken from [14]. c) slope for economic reasons, wind farms should be located in flat areas. in this study the slope was reclassified into 5 classes: <25m, 25–650m, 650–1250m, 1250–2000m and >2000m. the class representing flat areas (<25m) has been judged as the most suitable and the other areas as the least suitable. d) distance from urban areas previous scientific publications detail various distances from urban areas. for this study, we create new feature classes from the dataset representing populated areas that included multiple buffer zones: 0–10km, 10–15km, 15-20km, 20-25km and >25km around these areas. in these cases the first buffer zone represented unsuitable areas for wind farm positioning according to safety reasons and the other buffer zones represented decreasing suitability. fig. 4. slope constraints map. data taken from [12]. fig. 5. distance from urban areas. data from [13]. e) distance from power lines for economic reasons, wind farms should be located in close proximity to power lines. as a result in our study we create new feature classes of the distance from power lines that included multiple buffer zones: 0–5km, 5-10km, 10-15km, 1520km and >20km around these areas. the first buffer zone represents the most suitable areas for wind farm positioning according to economic reasons and the other buffer zones represented increasing unsuitability. f) distance from roads for the purpose of this study, we created new feature classes that included multiple buffer zones: 0–5km, 5-10km, 10-15km, 15-20km and >20km around these areas. the first engineering, technology & applied science research vol. 10, no. 4, 2020, 6068-6075 6071 www.etasr.com elmahmoudi et al.: elaboration of a wind energy potential map in morocco using gis and analytic … buffer zone represents the most suitable areas for wind farm positioning due to economic and accessibility reasons and the remaining buffer zones represented increasing unsuitability. fig. 6. distance from power lines. data from [13]. fig. 7. distance from roads. data from [13] b. reclassification of criteria 1) simple reclassification of criteria decision constraints are based on a scale rating aim to exclude areas deemed ‘unfeasible’ for wind farm development. therefore, unfeasible areas are denoted a value equal to 0 whilst feasible areas are denoted a value ranging from 1 to 4. the complete classification is presented in table ii, where ��,��,��,��,��,�� are wind speed (m/s), land cover, slope (m), distance from urban places (km), distance from power lines (km) and distance from roads (km) respectively. 2) ahp reclassification of criteria the ahp model has been applied to determine weights and ranks of all the subcategories of different parameters for the purpose of finding suitable wind farm locations. the complete classification is presented in table iii. the selection of the best location of wind farm can be expressed as: � ∑ � � ��� � �� (1) where sl is the suitable location index, wi is the weight of each parameter, and ri is the rating of the classified values under a parameter. using the sl model, we can classify the final map into five classes of very low, low, moderate, high and very high potentiality. table ii. rating scheme for multiple modeling criteria ri a1 a2 a3 a4 a5 a6 very high (4) >7 bare area <25 >25 (0,5) (0,5) high (3) (6,7) tree land (25,650) (20,25) (5,10) (5,10) moderate (2) (5,6) shrub land (650,1250) (15,20) (10,15) (10,15) low (1) (3,5) forest (1250,2000) (10,15) (15,20) (15,20) very low (0) (0,3) water area >2000 (0,10) >20 >20 c. gis analysis and mcda spatial decision making is often a process characterized by complexity, uncertainty, multiple and sometimes conflicting management goals, and the integration of different types of data. a decision is an assessment of suitability of a location. in this research, a number of siting criteria are used to apply an integrated approach of two decision tools, the geographic information systems (gis) and the multiple criteria decision analysis (mcda) [20]. the suitability analysis aims to identify the most appropriate sites for wind power development. the overall procedure uses spatially referenced data to create a decision map of suitable locations in qgis. all map layers have been converted to grid data. this section explains our analysis step-by-step. 1) integration of gis analysis and mcda the solution of spatial decision problems is the combination between geographic and decision data to get a decision. gis is the analysis and modelling of geographic data to solve complex decision problems. open source software quantum geographic information system (qgis) is our tool of implementation, analysis, and incorporation of different types of data. mcda is a famous decision making instrument. it is used to make decisions in a multi-criteria situation [21]. it computes the weights of the criteria and the position of alternatives. the integration of gis-mcda means to use gis to prepare layers for the multi-criteria method by calculating the contribution of each layer in the final map to be viewed in gis. a variety of mcda methods exists that can be used for various purposes such as choosing, ranking, or sorting. the decision maker usually decides which method to be used by taking the nature of the problem into consideration. authors in [22] calculated the potential for biodiesel production from plant sources, in this region using gis software. authors in [23] applied gis and ahp methods in order to provide suitable sites for the construction of sanitary landfills in johor bahru, malaysia and authors in [24] utilized ahp to provide an accurate result for flood mapping. engineering, technology & applied science research vol. 10, no. 4, 2020, 6068-6075 6072 www.etasr.com elmahmoudi et al.: elaboration of a wind energy potential map in morocco using gis and analytic … table iii. sub-criteria of each parameter and their weights criteria sub-criteria sub-criteria weight criteria weight a1 >7 (6,7) (5,6) (3,5) (0,3) ri wi >7 1 2 4 6 8 0.459 0.427 (6,7) 1 2 4 6 0.261 (5,6) 1 2 5 0.146 (3,5) 1 4 0.097 (0,3) 1 0.037 a2 bare area tree land shrub land forest water area ri wi bare area 1 3 5 7 9 0.508 0.089 tree land 1 2 5 7 0.241 shrub land 1 3 5 0.142 forest 1 4 0.075 water area 1 0.034 a3 <25 (25,650) (650,1250) (1250,2000) >2000 ri wi <25 1 3 5 7 8 0.489 0.207 (25,650) 1 4 5 7 0.276 (650,1250) 1 3 5 0.13 (1250,2000) 1 3 0.068 >2000 1 0.036 a4 >25 (20,25) (15,20) (10,15) (0,10) ri wi >25 1 3 5 7 9 0.491 0.033 (20,25) 1 3 7 9 0.287 (15,20) 1 3 4 0.12 (10,15) 1 4 0.07 (0,10) 1 0.033 a5 (0,5) (5,10) (10,15) (15,20) >20 ri wi (0,5) 1 2 4 6 8 0.452 0.175 (5,10) 1 3 4 6 0.281 (10,15) 1 3 5 0.151 (15,20) 1 3 0.078 >20 1 0.039 a6 (0,5) (5,10) (10,15) (15,20) >20 ri wi (0,5) 1 2 4 6 8 0.453 0.068 (5,10) 1 2 5 7 0.278 (10,15) 1 3 5 0.158 (15,20) 1 3 0.074 >20 1 0.038 in the current study gis and ahp methods were applied. the detailed steps are described in our previous paper [25]. 2) ahp model. as mentioned in the previous sections, 6 layers of data which are related to the construction of wind power stations were considered. all the layers are classified using a rating scale (table ii) and ahp scale (table iii) in the qgis. once the map layers were generated, a pairwise comparison matrix has been built in which the diagonal elements are equal to 1 (table iv). for instance, the first row represents the significance of wind speed when compared to the other six parameters positioned in the column. in the pairwise comparison matrix, the rows follow the inverse value of each factor and its significance with other (e.g. the wind speed is little more important than the land use and slope, hence, the value of wind speed is 1 and other two factors are 5 and 4, thus in the next row land use and slope in having a value of 1/5 and 1/4 respectively and so on). after the preparation of all the thematic layers, the analytical hierarchy process model has been applied to give different weights (table v) to the considered parameters [26]. the factors controlling the wind farm selection of our area are wind speed, slope, distance from the power line, distance from roads, and distance from urban areas. table iv. pairwise matrix a1 a2 a3 a4 a5 a6 a1 1 5 4 8 3 6 a2 1 1/4 4 1/3 2 a3 1 4 3 2 a4 1 1/6 1/3 a5 1 4 a6 1 table v. weight of criteria a1 a2 a3 a4 a5 a6 wi 0.427 0.089 0.207 0.033 0.175 0.068 multiplication of the classified layers with their associated weights was carried out during the ahp method. all the weighted grid layers were added together in the easy ahp tool in qgis to get the final suitability map. the final grid layer has been classified into five classes: very low, low, moderate, high, and very high suitability for wind farm development in morocco based on the criteria and their calculated weights (figures 8, 9). engineering, technology & applied science research vol. 10, no. 4, 2020, 6068-6075 6073 www.etasr.com elmahmoudi et al.: elaboration of a wind energy potential map in morocco using gis and analytic … iv. results a. decision constraints analysis this study’s objective was to determine suitable wind farm locations in morocco. the criteria were selected from different sources reflecting different considerations. the impact of each criterion in the suitability of wind farms was identified. most data were available in vector format and were converted into grid. the vector layers needed more complex operations such as distance calculations for the factors using calculator raster. fig. 8. ahp suitability for rating scale map. fig. 9. ahp suitability for ahp scale map. b. ahp results a weight for each criterion has been calculated using ahp methods to get information about the relative importance of each factor in modeling wind farm locations (table v). wind speed potential was rated as the most important criterion affecting wind energy development, so it was assigned a weight of 0.427. slope, land use, distance from transmission lines, distance from roads and population density were assigned weight values of 0.207, 0.089, 0.175, 0.068, and 0.033 respectively. fig. 10. spatial patterns of suitability scores for each criterion. engineering, technology & applied science research vol. 10, no. 4, 2020, 6068-6075 6074 www.etasr.com elmahmoudi et al.: elaboration of a wind energy potential map in morocco using gis and analytic … fig. 11. spatial patterns of ahp-suitability scores for each criterion. all data layers were combined using ahp and were classified using a rating scale (figure 10) and ahp scale (figure 11) in qgis. the final wind farm suitability map for the rating scale is shown in figure 8 and for ahp scale is shown in figure 9. v. discussion by comparing the ahp result, it was shown that wind speed and slope are the most important attributes with values of 0.43 and 0.21, and land use, distance from urban places, distance from roads and distance from power lines followed with values of 0.09, 0.03, 0.07, and 0.18 respectively. it was noted that the locations of existing wind farms in morocco and the very high suitability locations for installing wind farms coincide. vi. conclusion considering the growing demand for energy in morocco and the global conspicuous attention on renewable energy sources, careful selection of energy investment projects and efficient use of resources is important. multi-criteria decision making methods can be utilized to select an appropriate location for renewable energy generation. in this paper, the ahp method was employed. the weight of each of the six criteria was determined and was assigned to different map layers in gis, with each layer representing one of the criteria. wind speed and slope were found to be the most important criteria for wind farms positioning. distances to transmission lines and roads are associated with wind energy development cost, whereas land use and proximal population density are associated with the environmental consequences. the objective of this study was to design a cartography of the wind potential of the moroccan territory. to our knowledge, it is the first geographical study carried out in this sense, on the whole map of morocco. the approach developed in this study will help stakeholders in the decision-making to discover the different classified areas in morocco. furthermore, it can be used to evaluate the suitability of operating projects. as future work, pertinent wind farm site suitability analysis can be 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[26] t. l. saaty, decision making for leaders: the analytic hierarchy process for decisions in a complex world, new edition 2001, 3rd revised edition. pittsburgh, pa: rws publications, 2012. microsoft word 20-2667_s engineering, technology & applied science research vol. 9, no. 2, 2019, 3978-3980 3978 www.etasr.com chakravorty & saraswat : deciding optimal location of dpfc in transmission line unsing artificial … deciding optimal location of dpfc in transmission line using artificial algae algorithm jaydeep chakravorty electrical engineering department, indus university ahmedabad, india jyoti saraswat alpla india pvt. ltd. dadra & nagar haveli, india abstract—in this paper, the application of artificial algae algorithm (aaa) in optimal placement distributed power flow controller (dpfc) with mcfc in transmission networks has been proposed the proposed method is tested on ieee 14bus system and the results are discussed. the biggest advantage of dpfc is that it can control the active and reactive power flow and bus voltages, simultaneously. in this paper, the optimal placement of one dpfc in ieee-14 bus system and then optimal placement of two dpfcs in ieee-14 bus system has been proposed. optimal placement of dpfc in power system by aaa leads to increased stability and capacity of the power transmission in lines. the proposed model has been simulated in matlab/simulink and the performance results are tabulated. keywords-artifical algae algorithm; dpfc; mcfc i. introduction increase in power demand has led modern power system networks to operate under stressed conditions. load increase in the system is tolerable up to a particular limit but if it is increased further it may lead to voltage drop which may result to system instability and line overloading. facts devices help maintain system stability and maintain the system to normal condition. many researchers proposed different methods to install facts devices in the system [1-5]. optimal location of various facts devices in different test systems was done by multi-objective generalized approach [6], genetic algorithm and de [7], pso and harmony search algorithm [8] and several hybridized methods [9-12]. the major role of facts is to control the flow of real and reactive power by injecting a voltage in series with the transmission line. real and reactive power flow control allow power flow in the specified routes. a new dpfc model with mcfc and ultra-capacitor is proposed in [13]. in this paper, aaa has been used to determine the optimal location of the dpfc proposed in [13]. ii. artificial algae algorithm it is a bio inspired meta-heuristic algorithm [14]. this algorithm has three main basic parts called evolutionary process, adaptation, and helical movement [15]. a. evolutionary process in this process, the algae receive sufficient nutrients and enough sunlight to grow and reproduce. but if the circumstances are not supportive, for example if the sunlight is not enough, then the algae may die. this process can be mathematically expressed by: 1 ( ) ( ) jt t j j j f x g g k f x +    = ×  +  for j=1,2,3,….n (1) where, g is the size of the jth algal in time t and n is the colony in the system. of all n colonies, the colonies that provide better solutions grow bigger because they get enough sunlight to grow. the colonies which do not give good solutions become smaller. the smallest colony dies. d is the problem dimension. max( ) big t j colony g= for j=1,2,3,….n (2) ( )minsmall tjcolony g= for j=1,2,3,….n (3) small big m m colony colony= for m=1,2,3,….d (4) b. adaptation in this process the insufficiently grown algal colony tries to adapt to the environment. the insufficiently grown algal colony tries to resemble itself to the biggest algal colony: ( )maxt tjstarv a= for j=1,2,3,….n (5) ( )1t t big tstarv starv colony starv rand+ = + − × (6) the initial starvation value is assumed to be zero for each algal and it is increased with time t. the starvation value of the jth algal colony in time t is t j a . the algal colony with the highest starvation value in time t is starv t . ap is a constant in the interval [0,1] called adaptation constant which determines whether adaptation process will be applied or not in time t. if rand>ap then the adaptation will be applied. c. helical movement the algal cells generally swim helically to stay close to the water surface. movement restriction due to gravity is displayed as 0 and viscous drag is displayed as shear force which is proportional to the size of the algal cell. 2 3 3 2 4 / ( ) j j g t x π π    =       (7) corresponding author: jaydeep chakravorty (jaydeepchak@yahoo.co.in) engineering, technology & applied science research vol. 9, no. 2, 2019, 3978-3980 3979 www.etasr.com chakravorty & saraswat : deciding optimal location of dpfc in transmission line unsing artificial … ( ) ( )( )1t t t tjm jm im jm jx x x x t x p+ = + − × ∆ − × (8) ( ) ( )( )1 cost t t tjk jk ik jk jx x x x t x α+ = + − × ∆ − × (9) ( ) ( )( )1 sint t t tjl jl il jl jx x x x t x β+ = + − × ∆ − × (10) iii. application of artificial algae algorithm the algorithmic steps of the application of aaa in optimal placement of dpfc with pem are: 1. randomly select dpfc parameters vse and vsh. 2. perform load flow analysis of the system. 3. from the obtained result of step 2, calculate the value of the objective function. 4. select the minimum value of the objective function as the best algae solution. 5. update the algae colony using helical movement. 6. perform the operation of reproduction and adaptation. 7. repeat steps 2-4. 8. compare the two outputs. if the stopping condition is achieved then stop, else repeat the same process again. iv. problem formation the proposed algorithm has been tested with standard ieee 14 bus system. numerical data and parameters were taken from [16]. in ieee 14 bus system, load flow analysis is performed using the newton raphson method and the ranking is obtained from contingency analysis. the transformer ratio varies from its nominal value during the calculation process. first, the process assumes one dpfc is required to be placed in the system then the process is repeated for two dpfcs. v. simulation and results ranking and performance parameter (pp) of the system based on contingency analysis is given in table i. in table i, only transmission lines whose pp is greater than or equal to 1 are shown. table ii, represents the optimized values of the transformer tap ratio. when one dpfc is considered, the application of aaa gives the location of dpfc between bus 4 and bus 10 as shown in table iii. when two dpfcs are considered, the application of aaa gives the location of dpfcs between bus 4 and bus 5 and between bus 6 and bus 9 as shown in table iv. the final bus voltages after the simulation is over are given in table v. table i. ranking line no. from bus to bus no. of overload lines no. of voltage violations pp rank 1 1 2 5 7 12 1 3 2 3 4 5 9 2 2 1 5 2 6 8 3 10 5 6 1 5 6 4 4 2 4 2 3 5 5 14 7 8 0 3 3 6 15 7 9 1 2 3 7 13 6 13 1 2 3 8 5 2 5 0 1 1 9 7 5 4 0 1 1 10 9 4 9 0 1 1 11 20 13 14 0 1 1 12 table ii. transformer tap ratio from to ratio 3 4 1.064 4 6 1.062 6 8 1.042 9 11 1.081 12 13 1.109 14 15 1.084 16 17 1.038 18 19 1.074 10 21 1.052 table iii. result with only one dpfc bus no. pi qi 4 -200 -150 10 -45 -20 table iv. result with two dpfcs bus no. pi qi 4 -130 -100 5 -200 -145 6 -10 -3 9 -30 -90 table v. bus voltages bus no. without dpfc with 1 dpfc with 2 dpfcs 1 1.05 1.05 1.05 2 1.05 1.05 1.05 3 1.03 1.01 1.01 4 0.98 1.02 1.00 5 1.00 1.03 1.01 6 1.05 1.05 1.06 7 0.05 0.98 1.00 8 1.05 1.05 1.06 9 0.90 1.05 1.06 10 0.88 0.97 0.80 11 0.95 1.00 1.00 12 0.94 1.01 0.90 13 0.95 1.00 1.00 14 0.84 0.98 0.90 vi. conclusion in this paper, optimal dpfc placement on an unstable power system because of contingency has been discussed. the optimal location of dpfc in ieee 14 bus system using aaa has been tested. the proposed algorithm was executed for a maximum of 100 iterations and the results were tabulated. the case study of the ieee 14-bus system confirmed that the developed algorithm is correct and effective. the losses are reduced and voltage profile is enhanced by placing dpfc(s) at optimal locations. the acquired solutions prove that the aaa has advanced specifications with accurate, balance characteristics, excellent quality of solution and best computation efficiency. references [1] s. v. ravi kumar, s. s. n. raju, “loss minimization by incorporation of upfc in load flow studies”, international journal of electrical and power engineering, vol. 1, no. 3, pp. 321-327, 2007 engineering, technology & applied science research vol. 9, no. 2, 2019, 3978-3980 3980 www.etasr.com chakravorty & saraswat : deciding optimal location of dpfc in transmission line unsing artificial … [2] a. m. vural, m. tumay, “mathematical modelling and analysis of a unified power flow controller: a comparison of two approaches in power flow studies and effects of upfc location”, electrical power and energy systems, vol. 29, pp. 617-629, 2007 [3] b. v. rao, g. v. n. kumar, m. r. priya, p. v. s. sobhan, “implementation of static var compensator for improvement of power system stability”, 2009 international conference on advances in computing, control, and telecommunication technologies, trivandrum, india, december 28-29, 2009 [4] m. d. reddy, k. d. babu, “optimal placement of svc using fuzzy and pso algorithm”, international journal of engineering research and applications, vol. 3, no. 1, pp. 485-490, 2013 [5] v. k. shende, p. jagtap, “optimal location and sizing of svc by pso technique for voltage stability enhancement and power loss minimization”, international journal of engineering trends and technology, vol. 4, no. 6, pp. 2278-2282, 2013 [6] r. s. rao, v. s. rao, “a generalized approach for determination of optimal location and performance analysis of facts devices”, international journal of electrical power & energy systems, vol. 73, pp. 711-724, 2015 [7] b. bhattacharyya, v. k. gupta, s. kumar, “upfc with series and shunt facts controllers for the economic operation of a power system”, ain shams engineering journal, vo. 5, no. 3, pp. 775-787, 2014 [8] n. karuppiah, v. malathi, g. selvalakshmi, “optimal placement and sizing of multi-type facts devices using pso and hsa”, in: lecture notes in computer science, vol. 8947, springer, 2014 [9] s. frank i. steponavice, s. rebennack, “optimal power flow: a bibliographic survey ii nondeterministic and hybrid methods”, energy systems, vol. 3, no. 3, pp. 259-289, 2012 [10] s. akumalla, s. peddakotla, s. r. a. kuppa, “a modified cuckoo search algorithm for improving voltage profile and to diminish power losses by locating multi-type facts devices”, journal of control, automation and electrical systems, vol. 27, no. 1, pp. 93-104, 2016 [11] s. dutta, p. k. roy, d. nandi, “optimal location of upfc controller in transmission network using hybrid chemical reaction optimization algorithm”, international journal of electrical power & energy systems, vol. 64, pp. 194-211, 2015 [12] s. a. taher, m. k. amooshahi, “new approach for optimal upfc placement using hybrid immune algorithm in electric power systems”, international journal of electrical power & energy systems, vol. 43, no. 1, pp. 899-909, 2012 [13] j. chakravorty, j. saraswat, v. bhatia, “modeling a distributed power flow controller with a pem fuel cell for power quality improvement”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2585-2589, 2018 [14] s. ali, g. tezel, e. yel, “artificial algae algorithm (aaa) for nonlinear global optimization”, applied soft computing, vol. 31, pp. 153-171, 2015 [15] s. a. uymaz, g. tezel, e. yel, “artificial algae algorithm with multilight source for numerical optimization and application”, biosystems, vol. 138, pp. 25-38, 2015 [16] m. p. aghababa, m. e. akbari, a. m. shotorbani, “an efficient modified shuffled frog leaping optimization algorithm”, international journal of computer applications, vol. 32, pp. 26-30, 2011 engineering, technology & applied science research vol. 8, no. 3, 2018, 3013-3017 3013 www.etasr.com saadi and chaker: a numerical simulation approach for sunspot area calculation a numerical simulation approach for sunspot area calculation souad saadi energy physics laboratory department of physics university of constantine 1 constantine, algeria saadi.acwa@yahoo.fr abla chaker energy physics laboratory department of physics university of constantine 1 constantine, algeria chakamine@yahoo.fr abstract—the aim of this paper is the numerical simulation of the sunspot area (ssa) and its location on the walls and on the floor of a room with a single window facing south. the input parameters of the calculation code are the geometry of the cell located in the site of ksar challala (35.1 n, 2.19 e, 800 m) in algeria for the 21st of march, june and december. the ssa is a function of the window’s area, the date and time, the orientation of the room, the altitude and the azimuth of the sun. the obtained results show that the western wall is affected by the sun in the morning, the eastern wall in the afternoon, the floor and the north wall in the middle of the day. by increasing the window area from 1 m2 to 2 m2 we found that the ssa increases considerably. keywords-window; sunspot; residence; time-direct gains i. introduction a window is an essential element of the passive approach of bioclimatic design as it has a significant influence on the energy efficiency of buildings [1]. from a thermal point of view, it is one of the most sensitive elements standing between the indoor and the outdoor environment. it may be integrated in the building envelope but, unlike the other parts of the envelope, it allows the light to pass and often offers a lower resistance to heat transmission. on the other hand, it can capture solar energy to heat the indoor environment when the solar energy is high and the outside temperature is low [2-4]. authors in [4-5] showed, by the use of derob-lth software in order to simulate the thermal behaviour of passive houses, that using high-performance windows would be better than having windowless insulated walls. the dimensions of the most appropriate windows depend on the orientation of the building and its thermal mass. french thermal regulation proposes a reference value of 16.5% (percentage of glazed area in relation to living space), but this value can be as high as 22%. higher values would increase the risks of overheating during the summer period [4]. the need to use precise simulation models for the distribution of solar energy in buildings has become an essential subject of research in recent decades [6-7]. the calculation and distribution of incident solar energy in closed spaces can be accomplished through a number of approaches of several levels of complexity of effect and accuracy [6]. therefore, taking into account the sunspot (ss) in the thermal modelling of buildings has the advantage of improving the precision of the model and its performances for the calculation of the temperatures of the air and the walls as well as the accurate estimation of heating and cooling requirements. most existing building thermal models do not take into account the impact of the evolution of ss in a room with glazing which is a rough approximation [8]. other models take into account the modelling of short-wavelength radiation (swl) exchanges inside the building assuming that all radiation is projected onto the floor uniformly throughout the year [7]. this hypothesis is very debatable because during the winter, the sun is quite low and can touch all the vertical surfaces [8]. another hypothesis, yet not precise and commonly used, assumes that 60% of the swl radiation is distributed on the floor and the rest is distributed, in proportion, to the other surfaces [9]. in other software, the percentage of flux reaching each wall is kept constant throughout the simulation period [9]. authors in [9-11] simulated the thermal behaviour of a room with a large glass surface using four different software programs (derob-lth, sunrep (trnsys), fres and tsbi3). they concluded that heating requirements in heavily glazed areas were underestimated in most software due to poor consideration of sunspot. there are other more efficient methods that calculate the ssa on each wall and at each time step. authors in [8, 12] calculated and localized the ssa using the delaunay triangularization method [13]. author in [9] proposed a geometric calculation approach to determine the surface and the position of the ss. depending on the positions of the window and the sun, there are 20 cases of figures and each of them has an explicit and distinct equation. authors in [14-20] modelled and counted the ssa for a cell oriented to the west and located in paris. the localization is verified by the application of a membership test whose principle is to verify the inclusion or not of the projections of the centers of the meshes on a plane perpendicular to the rays of the sun in the polygon resulting from the projection of the window on the same plan. to verify the validity of the obtained numerical results, authors carried out a series of tests on different periods of the year. in our work, the model proposed in [21] is chosen to calculate and locate the ssa on the walls and on the floor of a engineering, technology & applied science research vol. 8, no. 3, 2018, 3013-3017 3014 www.etasr.com saadi and chaker: a numerical simulation approach for sunspot area calculation room (3×3×3 m) with a window (1×1 m) facing south. the choice of the model is based on its simplicity and its modest calculation time. this study is carried out for the 21st of march, june and december at the ksar challala site in algeria. ii. description and mathematical modeling to calculate locate the ssa, we must first calculate the solar time, hour angle, inclination angle and azimuth. consider a room with a square window. the orientation of the room is identified by the azimuth (ab) relative to the southern direction (figure 1) [21]. the components of the unit vector in the frame ( , ) are a function of the altitude (h) and the azimuth (az) of the sun [21]: = − cos(ℎ) cos( ) (1) = − cos(ℎ) sin( ) (2) = − sin( ) (3) in the orthonormal system ( , ′ ′ ′ ) relative to the orientation of the test cell, these components become [21]: ′ = cos( ) + sin( ) (4) ′ = sin( ) + cos( ) (5) c′ = c (6) fig. 1. the principleof the method. to find the irradiated parts of each face of the cell, each wall is subdivided into a set of small facets (figure 1). from the barycenter of each facet, a vector is projected whose direction is opposite to the sun. if this vector intercepts the surface of the window, the elementary surface is irradiated otherwise it is in the shadow [21]. if g ( , , ) the barycenter of the square m in the landmark ( , ′ ′ ′), the projection of g will be g’( ′ , ′ , ′ ). as the sun is supposed in the infinity, we can write [21]: ′ ′ − ′ − ′ − ⋀ = 0 (7) where: ′ = + ′′( ′ − ) (8) yg′ = xg + ′′(xg′ − xg) (9) zg′ = xg + ′′(yg′ − yg) (10) by comparing these coordinates with the window’s dimensions we can judge if the square m is irradiated. the ssa of each wall is calculated by the sum of the irradiated elementary surfaces [21]. iii. results and discussion the simulation of the ssa was done using the predescribed model by establishing a calculation code in fortran 90 language. the obtained results are given every one minute. a. temporal evolution of the ssa the temporal evolution of the ssa on the walls affected by solar radiation according to the window’s area variation between 1m2 and 2m2 for the 21st of march, june and december is examined. the analysis of the curves regarding the 21st of march (figure 2) shows that the western wall is affected by the sun during the morning, the east wall in the afternoon and the floor in the middle of the day. the north wall is not affected during the studied days. it also appears that the ssa records its greatest values when the window area is 2m2, meaning that the ss grows with the enlargement of the dimensions of the window. indeed, the maximum ssa on the floor is 2.89 m2 and 0.73m2 for a window area (sw) of 2m2 (figure 2(b)) and 1 m2 (figure 2(a)) respectively. furthermore, it is clear that the ssa on the floor is significantly higher than those calculated for the other walls even if the dimensions of the window are increased. (a) (b) fig. 2. temporal evolution of the ssa according to the window area (21 march) with window area (a) 1 m2 and (b) 2 m2 7 8 9 10 11 12 13 14 15 16 17 18 19 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 sw=1 m2 east wall north wall west wall floor s s a (m 2 ) time (h) 7 8 9 10 11 12 13 14 15 16 17 18 19 0,0 0,5 1,0 1,5 2,0 2,5 3,0 sw=2 m2 s s a (m 2 ) time (h) east wall north wall west wall floor engineering, technology & applied science research vol. 8, no. 3, 2018, 3013-3017 3015 www.etasr.com saadi and chaker: a numerical simulation approach for sunspot area calculation for the summer solstice, the ssa is smaller than that obtained on the 21st of march resulting from the height of the sun which is maximum during the summer. the ss is visible on the walls only between 9:30 and 16:20. nevertheless, it grows significantly with the increase of the glazed surface as it is clear in figures 3(a) and 3(b). on the other hand, we can observe that the north wall is not affected by the radiation through the window. for the chosen orientation and the site study, it appears that the ss on the east wall is slightly larger than that on the west wall. the ss on the floor is clearly superior to those obtained on the vertical walls even if the glazed surface is increased. (a) (b) fig. 3. temporal evolution of the ssa according to the window area (21 june) with window area (a) 1 m2 and (b) 2 m2 for the 21st of december (figure 4), ssa is greater than those obtained for the 21st of march and the 21st of june. it is also noted that the maximum values of the ssa on the east wall, west wall and on the floor are close opposed to the ss on the north wall which has considerably lower maximum values. it can be seen in figures 4(a) and 4(b) that the north wall is affected by solar radiation with maximum surfaces of ss of 0.306m2 and 1.5075m2 for a sw of 1m2 and 2m2 respectively. b. localisation of the ssa we have located in figures 5, 6 and 7 the ss on each wall and on the floor for the 21 of march, june and december respectively. in figure 5, it is noted that at 10:00, the ss is located on the west wall and forms a trapezoidal whose base is located on the axis (oy) between -69 cm and -141 cm. the heights of the left and right sides of the trapezoidal are respectively 104 cm and 9.8 cm (see figure 5(a)). (a) (b) fig. 4. temporal evolution of the ssa according to the window’s area (21 december) with window area (a) 1 m2 and (b) 2 m2 at 12:00 (figure 5(c)), the ss is located on the floor and forms a parallelogram whose base parallel to the axis (ox) varies between 77cm and 177cm. its two sides are parallel and equal and vary according to the axis (oy) between -72 cm and -146 cm. on the east wall at 15:00, the ss forms a triangular surface whose right angle is on the left, its base is on the axis (oy) and varies between 74.6 cm and 143.6 cm. the height of the triangle reaches 97 cm (figure 5(b)). for the summer solstice, the ss on the west and east walls occupy small surfaces as illustrated in figures 6(a) and 6(b) respectively. indeed, the ss is placed in the morning at 10:00 on the west wall forming a surface of 0.0261 m2 on the extreme left side of this wall (figure 6(a)). at 15:00, we see in figure 6(b) that the ss is located on the bottom of the left side of the wall where it occupies an area of 0.0099 m2. as for the ss on the floor, it appears clearly in figure 6(c) that it forms a parallelogram surface whose base varies between 75 cm and 174 cm, while the two sides vary between -19cm and -40cm. the relatively small ssa is due to the higher solar altitude values during the summer. for the 21st of december, at 10:00, it is noted in figures 7(a) and 7(b) that the ss is located on the west wall and on the floor simultaneously forming a parallelogram whose lower right side is located on the floor thus forming a triangular surface. examining figures 7(c) and 7(d), we notice that at 12:00 the ss is located on the floor and the north wall at the same time. on the floor, the ss forms a parallelogram while on the north wall it forms a rectangular surface. at 15:00, the ss is 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 0,00 0,03 0,06 0,09 0,12 0,15 0,18 0,21 0,24 sw=1 m2 s s a (m 2 ) time (h) east wall north wall west wall floor 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 sw=2 m2 s s a (m 2 ) time (h) east wall north wall west wall floor 7 8 9 10 11 12 13 14 15 16 17 18 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 sw=1 m2 east wall north wall west wall floor s s a (m 2 ) time (h) 7 8 9 10 11 12 13 14 15 16 17 18 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 sw=2 m2 east wall north wall west wall floor s s a (m 2 ) time (h) engineering, technology & applied science research vol. 8, no. 3, 2018, 3013-3017 3016 www.etasr.com saadi and chaker: a numerical simulation approach for sunspot area calculation located simultaneously on the floor and the east wall forming a parallelogram whose bottom left side is on the floor (figures 7(e) and 7(f)). fig. 5. ss location on the walls and on the floor for glazed surface of 1 m2 fig. 6. ss location on the walls and on the floor for glazed surface of 1 m2 c. ss residence time on the walls and on the floor the effect of the variation of the dimensions of the window on the residence time of the ss on each wall and on the floor is demonstrated in the histograms represented in figure 8. for march 21 (figure 8(a)), we note that the ss residence time on the floor and the walls increases with increasing window size. for the floor, the residence time increases further, it grows from 7.64 h to 10.03 h for glazed surfaces from 1 m2 to 2 m2 respectively. on june 21st, the residence time of the ss on the floor remains unchanged, while those of the ss on the east and west walls increase with increasing dimensions of the window (figure 8(b)). as for the 21st of december, it is clear that the residence time of the ss on all the walls increases. in particular the residence time on the floor which increases by about 2 hours when the glazing surface increases from 1 m2 to 2 m2 (figure 8(c)). fig. 7. location of the ss on the walls and on the floor for a glazed surface of 1 m2 iv. conclusion current research concerns the accounting and localization of the ssa on the walls and on the floor of a room (3×3×3 m) equipped with a window (1×1 m) on its southern wall, located in the site of ksar challala. in order to demonstrate the effect of the variation of the glass surface on the ssa, we varied the window area between 11.1% and 33.3% of the surface of the south wall for the 21st of march, june and december. the analysis of the results obtained leads to the following conclusions:  the western wall is affected by the sun in the morning, the eastern wall in the afternoon, the floor and the north wall in the middle of the day.  the north wall is affected by solar radiation only on the 21st of december because of the relative low values of the solar height.  by increasing the window’s area from 1 m2 to 2 m2, we found that the ssa increases considerably. (a) (b) (c) (a) (b) (c) (a) (b) (c) (d) (e) (f) engineering, technology & applied science research vol. 8, no. 3, 2018, 3013-3017 3017 www.etasr.com saadi and chaker: a numerical simulation approach for sunspot area calculation  the residence time of the ss on the walls and on the floor rises with the increase of the ssa except the residence time of the ss on the floor for the 21st of june which remains unchanged. (a) (b) (c) fig. 8. variation of the residence time of the ss on the walls and on the floor according to the dimensions of the window references [1] c. tian, t. chen, h. yang, t. chung, “a generalized window energy rating system for typical office buildings”, solar energy, vol. 84, no. 7, pp. 1232–1243, 2010 [2] f. gloriant, p. tittelein, a. joulin, s. lassue, “comparaison de deux modèles numériques d’une fenêtre pariéto-dynamique de type paziaud® en vue d’une simulation en thermique du bâtiment”, xxxe rencontres augc-ibpsa chambéry, savoie, june 6-8, 2012 (in french) [3] f. gloriant, p. tittelein, a. joulin, s. lassue, “modeling a triple-glazed supply-air window”, building and environment, vol. 84, pp. 1-9, 2015 [4] t. catalina, j. virgone, j. roux, e. blanco, “effet de l'inertie thermique, de la surface vitrée et du coefficient de forme sur les besoins en chauffage d'une habitation”, congrés ibpsa, lyon, france, november, 2008 (in french) [5] m. persson, a. roos , m. wall, “influence of window size on the energy balance of low energy houses”, energy and buildings, vol. 38, no. 3, pp. 181–188, 2006 [6] k. chatziangelidis, d. bouris, “calculation of the distribution of incoming solar radiation in enclosures”, applied thermal engineering, vol. 29, no. 5-6, pp. 1096–1105, 2009 [7] y. g. yohanis, b. norton, “useful solar heat gains in multi-zone nondomestic buildings as a function of orientation and thermal time constant”, renewable energy, vol. 27, no. 1, pp. 87–95, 2002 [8] h. bouia, j. roux, c. teodosui, “modélisation de la tache solaire dans une pièce équipée d’un vitrage utilisant un maillage en surface de delaunay”, france, november, 2002 (in french) [9] p. tittelein, environnements de simulation adaptés à l'étude du comportement énergétique des bâtiments basse consommation, phd thesis, université de savoie, 2008 [10] m. wall, “distribution of solar radiation in glazed spaces and adjacent buildings. a comparison of simulation programs”, energy and buildings, vol. 26, no. 2, pp. 129-135, 1997 [11] m. h. benzaama, m. lachi, c. maalouf, a. m. mokhtari, g. polidori, m. makhlouf, “study of the effect of sun patch on the transient thermal behaviour of a heating floor in algeria”, energy and buildings, vol. 133, pp. 257–270, 2016 [12] h. bouia, j-j. roux, “application de la triangulation de delaunay au calcul des facteurs de forme entre deux surfaces planes quelconques”, congrès français de thermique, sft2002, vittel, june 3-6, 2002 (in french) [13] j. jan, rayonnement solaire: aspects géométriques et astronomiques, collection cours et manuels, ministère des transports, direction de la météorologie, 1983 (in french) [14] a. rodler1, j. virgone, j. j. roux, “impact of sun patch and threedimensional heat transfer descriptions on the accuracy of a building’s thermal behavior prediction”, building simulation, vol. 9, no. 3, pp. 269-279, 2016 [15] a. rodler, j. j. roux, j. virgone, e. j. kim, j. l. hubert, “are 3d heat transfer formulations with short time sted and sun patch evolution nececessary for building simulation?”, building simulation conférence, aix-les-bains, france, pp. 3737-3744, 2013 [16] a. rodler, j. virgone, j. j. roux, j. l. hubert, “development and validation of a three dimensional thermal transientnumerical model with sun patch: application to a low energy cell”, energy and buildings, vol. 87, pp. 425–435, 2014 [17] a. rodler, j. virgone, j. j. roux, e. j. kim, j. l. hubert, “impact de la tache solaire sur un modéle thermique tri-dimensionnel de bâtiment : application à une cellule fortement isolée”, xième colloque interuniversitaire franco-québécois sur la thermique des systèmes, reims, france, june 3-5, 2013 (in french) [18] a. rodler, j. virgone1, j. j.roux1, h. castet, r. le berre, m. baranzini, j. l. hubert, “expérimentation in situ sur la cellule bestlab pour la validation d'un modèle prenant en compte la tache solaire”, conférence ibpsa france-arras, 2014 (in french) [19] a. rodler, j. virgone, j. j. roux, “impact of the sun patch on heating and cooling power evaluation for a low energy cell”, cisbat 2013, lausanne, switzerland, 2013 [20] a. rodler, j. virgone, j. j. roux, “sun patch impact for the evaluation of operative temperatures distributions”, study of civil engineering and architecture, vol. 3, pp. 130-134, 2014 [21] y. boukhris, l. gharbi, n. ghrab-morcos, “coupling the building simulation tool zaer with a sunspot model. case study in tunis”, energy and buildings, vol. 70, pp. 1–14, 2014 0 2 4 6 8 10 12 floor east wall west wall north wall sw=1 m2 sw=1.5 m2 sw=2 m2 21 march 2015 0 1 2 3 4 5 6 7 8 floor east wall west wall north wall sw=1 m2 sw=1.5 m2 sw=2 m2 21 june 2015 0 1 2 3 4 5 6 7 8 9 floor east wall west wall north wall sw=1 m2 sw=1.5 m2 sw=2 m2 21 december 2015 microsoft word 32-2314_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3479-3483 3479 www.etasr.com shastri et al.: coplanar stripline loaded reconfigurable loop antenna for wlan and … coplanar stripline loaded reconfigurable loop antenna for wlan and wimax applications s. p. r. shastri pacific institute of technology, pacific university, rajasthan, india shailendra.shastri@thakureducation.org r. r. singh thakur educational trust, mumbai, india ravishrsingh@yahoo.com k. v. ajetrao k. j. somaiya college of engineering, mumbai, india kiranjetrao@somaiya.edu abstract—in this paper, a loop antenna loaded with coplanar strip (cps) line is proposed as a multiband antenna. the cps line is added with two switches to vary the antenna perimeter to cover seven different bands. the cps line introduced into the loop is not only useful in reconfiguring antenna dimensions but also provides stationary radiation patterns for the all the covered bands. the proposed antenna works in single and dual-band modes. when the proposed antenna works as a single band antenna, it produces a band from 4.2ghz to 5.7ghz. under dualband operation, it produces bands from 3.75ghz to 4.7ghz and from 6.4ghz to 7.8ghz. the other dual-band mode ranges from 3.5ghz to 3.8ghz and from 5.58ghz to 7.4 ghz. the simulated and measured results are in good agreement and the proposed antenna can be used satisfactorily for w-lan and wimax applications. the proposed technique can also be used for size reduction of loop antennas. keywords-coplanar stripline; loop antenna; multiband; wideband; wavelength i. introduction uwb band allocation ranges from 3.1ghz to 10.6ghz. there are 12 different bands, each 528mhz wide [1]. the center frequency of each band from [1] is used as reference below. the electrical behavior of the wire loop antenna is examined in [2]. for a fixed radius of the loop, the impedance of the antenna depends on the wire thickness. the relation between the wire thickness and loop radius is referred to as thickness factor (ω). the thickness factor is defined in (1): ω = 2ln (2� ⁄ ) (1) where ω is the thickness factor, is the radius of the loop in meters and is the wire radius in meters, used to construct the loop antenna. the impedance variation of the loop as a function of the thickness factor and the loop circumference can also be seen in [2]. as the thickness factor decreases, antenna impedance also decreases. therefore by varying thickness of the loop antenna, the impedance of the antenna can be varied easily. the loop antenna is categorized as thin or thick loop. the thin antenna has ω>9 and resonates at more than one frequencies [2]. the thick antenna is capacitive in nature with the advantage of almost uniform resistance. the loop antenna is also categorized as small or large loop antenna. when the circumference of the loop is equal to or larger than the operating wavelength, the loop is called a large loop and small otherwise. in general, the small loop antenna has a circumference less than λ/10, where λ is the wavelength at which the antenna is designed. the small loop is a poor radiator while the large loop antenna is a good radiator as shown in [2]. the loop antenna resonates at a wavelength equal to the circumference of the loop. the circumference of the loop is calculated using (2) and (3): = 2� = � (2) � = � �⁄ (3) where c is the circumference of the loop antenna (m), r is the radius of the loop (m), � is the speed of light in free space (m/s), � is the design frequency of the loop (hz). a multiband antenna should operate at different frequencies with stable radiation patterns. since a thin and large loop antenna resonates at different frequencies [2], it can be used to operate at different frequencies. it is observed that the pattern at a smaller wavelength is different from the pattern at a larger wavelength for the specified band of operation. this happens due to the variation in the current distribution along the loop due to variation in the operating wavelength. a thin loop with ω=12 resonates at c/λ=1.1 i.e. c=1.1λ or c=2.2λ. the second resonant wavelength is twice the first. therefore we can design a loop to have the two desired bands using (2). but this technique suffers from poor stability in radiation patterns. figure 1 explains this very well. a simple wire loop whose circumference is c=λ radiates normal to its plane as shown in figure 1(a). when the same loop is excited at a wavelength double to that of the previous case, then the pattern does not remain the same (figure 1(b)). the radiation pattern at 2λ is too random. such an antenna cannot be claimed as a multiband antenna. a simple solution to this problem is that the circumference of the loop should vary in accordance with the desired wavelength. this arrangement will keep the circumference c=λ or near to λ. ii. research method since mechanical changes in the entire structure of the antenna are not possible to hold c=λ true for different wavelengths, the loop structure in figure 2 is proposed. the proposed loop is square in shape and a coplanar strip (cps) engineering, technology & applied science research vol. 8, no. 5, 2018, 3479-3483 3480 www.etasr.com shastri et al.: coplanar stripline loaded reconfigurable loop antenna for wlan and … line is added to it. the cps line is added with multiple electronic switches that can be turned on and off to change cps line length. the change in the cps line length finally changes the overall circumference of the loop. (a) (b) fig. 1. the loop antenna showing radiation patterns at (a) λ, (b) 2λ. fig. 2. proposed loop antenna with cps line along with the arrangement of switches. the total length of the loop is 4×l, l representing the arm length of the loop. when switch 1 is closed and the others are open, the length of the loop is 4×l+2d, where d is the length of the cps line. therefore, the loop length can be varied from 4×l to 4×l+2d. the loop length can be varied in small steps if the switches are placed close to each other. it is known that the transmission line only carries electrical energy from one point to another but does not radiate significantly. therefore the four sides of the loop are the only radiating components of the proposed structure. the role of the cps line is to only vary the overall length of the structure and eventually the generation of multiple bands. this structure ensures that the current distribution along the radiating portion will remain the same, therefore uniform radiation pattern is expected. a square loop of 16mm outer length and 0.7mm and 1mm width is simulated using cst studio software in order to know the availability of possible bands with the corresponding antenna impedance as shown in figure 3. it can be observed in figure 4 that the antenna behaves differently for the two widths. there can be two bands available only after proper impedance matching. the larger width ensures larger bands since the antenna impedance is uniform. it can be observed in figure 5 that the width of the loop antenna affects its impedance. when antenna width is 0.7mm, the loop resonates at 4.55ghz. the resistance at this frequency is about 125ω. the resistance drops to about 96ω for 1mm width. the loop with 1mm width shows minimum reactance at 5.1ghz and the resistance at this frequency is about 176ω. the loop resistance is more than 270ω for the same frequency when the width is 0.7mm. the antenna impedance for these frequencies is larger than the reference impedance of 50ω, therefore there is poor reflection coefficient at these frequencies (figure 4). since the magnitude of the reflection coefficient is more than -8db at the lower frequency, the band availability cannot be ignored. another possible location for the availability of the band is at 7.6ghz and 7.9ghz for a loop with width 0.7mm and 1mm respectively. the reactance is larger at these frequencies. the loop with 1mm width has less variation in reactance than the loop with 0.7mm width. fig. 3. proposed loop antenna with cps line along with the arrangement of switches. fig. 4. frequency v/s reflection coefficient of the loop antenna for different widths. fig. 5. loop impedance as a function of width and frequency. in order to solve the impedance mismatch problem, a printed balun transformer can be used to feed the antenna. the inclusion of the balun increases antenna size and if possible should be avoided. here, we are providing a simple engineering, technology & applied science research vol. 8, no. 5, 2018, 3479-3483 3481 www.etasr.com shastri et al.: coplanar stripline loaded reconfigurable loop antenna for wlan and … solution to bring antenna impedance down to the reference impedance of 50ω. above, it was demonstrated that the loop impedance can be varied by varying the loop width. therefore, instead of having a uniform width the loop can be made to have non uniform width. the proposed loop antenna contains non uniform width which changes gradually from 1mm to 1.5mm and then to 2mm towards feed end. since there is no standard technique to introduce nonlinearity in the loop antenna, the dimension for the different arms of the loop is chosen only after multiple simulations. the different dimensions are given to the loop for reducing antenna impedance so that the loop can be directly fed with a 50ω source. the dimensional information of the loop is shown in figure 6. the feed is connected to the broader width of the antenna since it offers low impedance while the narrow width offers high impedance. here the broader width helps converting loop antenna to a thick antenna which has low resistance with high capacitive reactance. the narrow dimension of the loop is present at the opposite of the feed and is 1mm wide. the narrow dimension of the loop converts the loop to a thin antenna which has high resistance and inductive and capacitive reactance. therefore this combination brings overall antenna impedance to a uniform level. finally, a folded coplanar strip line (csp) feed is added to the loop. the folded cps feed not only helps in lowering antenna impedance to 50ω but also it saves the onboard space as most of the part of the folded cps is within the loop area as shown in [1]. the proposed feed can be useful in feeding the antenna directly with a coaxial feed. the dimensional details of the folded cps line are shown in figure 7. fig. 6. the proposed loop with dimensional details. fig. 7. the dimensional details of the feed. the cps line not only plays important role in the transformation of impedance but also converts an unbalanced coaxial cable to balanced feed [3]. the proposed loop is added with additional cps line of 10mm length exactly opposite to the feed as shown in figure 6. therefore the inclusion of the cps line can increase the length of the loop by 20mm. the cps length can be increased or decreased by turning on and off the switches and the overall length of the loop can be varied to obtain different frequencies. iii. loop response analysis in this section, the proposed reconfigurable loop is analyzed for different switching conditions of the switches along csp line. the on state of the switch is realized by the short circuit and the off state by the open circuit. the switch is operated from the left of the cps line towards the thin arm of the loop and the response of the loop is tabulated in table i. it can be observed from table i that there are two distinct modes of antenna operation: single and dual band modes. the antenna works as dual band antenna when the switch at locations 0mm and 3mm is on from the left end of the cps line. the bands covered are band-6, band-7, and band-2, band-8 respectively. only one switch is on at a time while the others are off. table i. bands generated under switch on state mode switch location f1-f2 10db bw (ghz) available band [1] center frequency (ghz) % bandwidth a 0mm 3.5-3.8 no band 3.65 8.2 5.6-6.85 band-6, 7 6.23 20 b 3mm 3.7-4.5 band-2 4.1 19.5 6.8-7.43 band-8 7.12 9 c 8mm 4.17-5.9 band-3, 4, 5 5 34.4 d all off 4.2-5.75 band-3, 4, 5 4.975 31.2 a, b = dual band and c, d = single band, f1 and f2 are the lower and upper cut –off frequency respectively. the switch location is measured from the left of the cps line shown in figure 6. it can be observed in table i that when the switch at 8mm (near to the thin arm of the loop), is on, the loop generates a wider band from 4.17ghz to 5.9ghz. the loop produces band-3, band-4 and band-5 for this particular position of the switch. the loop generates the same bandwidth when all the switches present along the cps line are off. therefore to get the maximum number of bands at the minimum expense of switches, switch at location 8mm can be discarded. if we operate the switch at 0mm, and 3mm, we can easily get 7 different bands. it is also observed that the loop antenna generates larger bandwidth when it is operated under single mode (mode c and mode d). the maximum % bandwidth under c mode is 34.4%. it is also important to note that under c mode, cps line is almost completely removed from the loop as the switch is closed. the lowest frequency observed under this mode of operation is 4.17ghz. when the switch at 0mm is on, complete cps line is added in series with the loop. the lowest frequency under this mode, i.e. mode a, is 3.5ghz. since the area occupied by the proposed antenna is the same for the two frequencies, this technique can also be used to reduce antenna size. the different bands under the influence of the operating switches are shown in figure 8, which gives a good idea of how well the proposed technique covers a wider band from 3.5ghz to 7.43ghz. in order to check the stability of the radiation pattern for claiming multiband operation, the radiation pattern at the center frequency of each band listed in table i is analyzed. the radiation patterns are orthogonal to the plane of the loop and are shown in figures 9(a) and 9(b). the patterns are plotted at the center frequencies of each obtained band listed in table i. the plane of the proposed loop is aligned with x-y plane for all radiation patterns. an antenna engineering, technology & applied science research vol. 8, no. 5, 2018, 3479-3483 3482 www.etasr.com shastri et al.: coplanar stripline loaded reconfigurable loop antenna for wlan and … having such a stable radiation pattern for different frequencies must have a uniform current distribution. fig. 8. the reflection coefficient v/s frequency for different switches. (a) (b) fig. 9. the simulated radiation patterns at the center frequency of the bands listed in table i. in order to verify this relation, current distribution for all the plotted radiation patterns is reproduced and analyzed in figure 10. the current distribution in the proposed antenna can be divided into two parts: a) current in vertical arms, parallel to y-axis and b) current in horizontal arms, parallel to x-axis. the variation in the magnitude of current along the antenna is shown with a dashed line and the direction of current is shown with a continuous line (figure 12(a)-(b)). it can be observed that the current distribution along y-arms is in phase, while out of phase along x-arms. x-arms radiations are mutually canceled. on the other hand, the current from y-arms contributes to radiation. the inclusion of the cps line is completely justified here.as it only helps in reconfiguring the antenna dimension and keeps the current distribution uniform along the loop for all the frequencies. a comparison of the proposed loop is done with other recent existing reconfigurable antennas. the summary of the comparison is shown in table ii. (a) (b) fig. 10. the current distribution along the loop for different center frequencies. (a) f=3.9ghz, (b) f=7.1ghz table ii. proposed antenna comparative analysis reference bands frequency (ghz) number of switches number of antennas [4] 2 1.8, 2.4 8 1 [5] 2 8.2, 10.4 1, mem capacitor 1 [6] 2 15.95, 17.1 1, mem capacitor 1 [7] 2 2.4, 5.8 motor 2 [8] 3 1.58, 2.38 2 1 5 1.51, 2.28 4 1 [9] 5 2.16-9 4 1 [10] 3 2.4, 3.5, 5.2 6 1 [11] 4 2.45, 3.49, 5.13, 5.81 2 1 proposed 7 3.9-7.4 2 1 the antenna given in [4] generates two distinct bands centered at 1.8ghz and 2.4ghz. these two bands are generated using eight different switches. the antennas proposed in [5, 6] are multiband antennas generating two bands at 8.2ghz, 10.4ghz and 15.95ghz, 17.1ghz respectively. both antennas use mem switch for reconfiguration. there are four antennas proposed in [7]. the two antennas are used to generate two different bands and the others are used to change pattern and polarization. the two antennas used to generate different bands are selected using a rotating mechanism so the reconfiguration is controlled mechanically. the antenna proposed in [8] is operated with two switches and depending on the on and off states of diodes, the antenna generates three different bands from 1.58ghz to 2.38ghz. when the same antenna is added with four diodes and is made on or off in a particular sequence then it generates five different bands from 1.51ghz to 2.28ghz. the antenna proposed in [9] uses 4 switches and depending on the on and off state of switches, it is operated as single, double and triple band antenna generating a total of 5 different bands. the antenna proposed in [10] uses 3 pairs of the diode and generates six different bands under single, dual and triple band modes. a single monopole antenna with two optical switches generates four different bands in [11]. the proposed antenna uses only two switches and can be operated as single and dual band antenna. when both switches are off, the loop works as a wideband antenna. the total bands generated by the proposed antenna are seven and is higher than all the antennas compared engineering, technology & applied science research vol. 8, no. 5, 2018, 3479-3483 3483 www.etasr.com shastri et al.: coplanar stripline loaded reconfigurable loop antenna for wlan and … in table ii. the proposed antenna uses a lesser number of switches. other than this the antenna profile is very compact. iv. results and analysis the proposed reconfigurable antenna is manufactured and tested using vector network analyzer n9926a. a photograph of the entire four proposed antennas is shown in figure 11. a comparison between the simulated and measured reflection coefficient is shown in figure 12. fig. 11. photograph of the reconfigurable square loops for (a) no switch, (b) switch at 0mm, and (c) switch at 3mm and (d) switch at 8mm. (a) (b) fig. 12. comparison between simulated and measured reflection coefficient. table iii. simulated and measured result comparison switch location simulated f1-f2 (ghz) measured f1-f2 (ghz) bands available center frequency (ghz) 0 mm 3.5-3.8 3.5-3.8 no band 3.65 5.6-6.85 5.58-7.4 band-6,-7 6.23 3 mm 3.7-4.5 3.75-4.7 band-2 4.1 6.8-7.43 6.4-7.8 band-8 7.12 all off 4.2-5.75 4.2-5.7 band -3, -4, -5 4.975 6.8-8.3 7.55 f1, f2 lower and upper cut off frequencies respectively the simulated and measured results are in good agreement and are summarized in table iii. measured results justify the importance of folded cps feed and the role of the non-uniform loop arms with inner cps line for frequency reconfigurablility. it also shows that the inclusion of two switches is sufficient to cover seven different bands. v. conclusion the proposed structure shows that a loop antenna can be designed to have multiple bands. the included cps line within the antenna ensures the reconfigurability in antenna structure to get multiple bands with uniform radiation pattern. since the cps line does not contribute to radiation, the patterns generated for different lengths of csp line have the same orientation. the proposed loop can be operated as single and dual band antenna and generates a total of seven bands using minimum number of switches. since the proposed antenna covers band-2, band-3, band-4, band-5 band-6, band-7 and band-8 ranging from 3.5ghz to 7.8ghz, it can be useful in wlan 802.11 a/n and wimax applications. the proposed structure has the smallest dimensional profile. the proposed technique can be used for size reduction of the loop antenna. references [1] s. p. shastri, r. r. singh, k. v. ajetrao, “multiband printed loop antenna for uwb applications”, helix, vol. 8, no. 4, pp. 3481-3490, 2018 [2] c. a. balanis, “small circular loop: loop antennas”, in: antenna theory: analysis and design, john wiley & sons, 2010 [3] k. wei, z. zhang, z. feng, “design of a wideband horizontally polarized omnidirectional printed loop antenna”, ieee antennas and wireless propagation letters, vol. 11, pp. 49-52, 2012 [4] p. tilanthe, p. c. sharma, “a new frequency reconfigurable antenna”, journal of active and passive electronic devices, vol. 9, pp. 133-140, 2014 [5] k. topalli, e. erdil, o. a. civi, s. demir, s. koc, t. akin, “tunable dual-frequency rf mems rectangular slot ring antenna”, sensors and actuators a: physical, vol. 156, no. 2, pp. 373-380, 2009 [6] k. topalli, e. erdil, o. a. civi,“reconfigurable antenna structures using mems technology”, ieee transactions on antennas and propagation, vol. 55, no. 4, pp. 392-395, 2007 [7] f. alsharif, s. safi, t. aboufoul, m. abu nasr, s. a. nasser, “mechanical reconfigurable microstrip antenna”, international journal of microwave and optical technology, vol. 11, no. 3, pp. 153-160, 2016 [8] s. sharma, c. c. tripathi, “frequency reconfigurable u-slot antenna for sdr application”, progress in electromagnetics research letters, vol. 55, pp. 129-136, 2015 [9] x. liu, x. yang, f. kong, “a frequency-reconfigurable monopole antenna with switchable stubbed ground structure”, radioengineering, vol. 24, no. 2, pp. 449-454, 2015 [10] h. i. idris, m. r. hamid, m. h. jamaluddin, m. k. a. rahim, j. r. kelly, h. a. majid, “single-, dualand triple-band frequency reconfigurable antenna”, radioengineering, vol. 23, no. 3, pp. 805811, 2014 [11] s. a. a. shah, m. f. khan, s. ullah, a. basir, u. ali, u. naeem, “design and measurement of planar monopole antennas for multiband wireless applications”, iete journal of research, vol. 63, no. 2, pp. 194-204, 2017 microsoft word etasr_7-1_1338-1344.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1338-1344 1338 www.etasr.com javanpour and zarfam: application of incremental dynamic analysis (ida) method for studying… application of incremental dynamic analysis (ida) method for studying the dynamic behavior of structures during earthquakes mohsen javanpour department of civil engineering, dezful branch, islamic azad university, dezful, iran panam zarfam department of civil engineering, science and research branch, islamic azad university, tehran, iran abstract—prediction of existing buildings’ vulnerability by future earthquakes is one of the most essential topics in structural engineering. modeling steel structures is a giant step in determining the damage caused by the earthquake, as such structures are increasingly being used in constructions. hence, two same-order steel structures with two types of structural systems were selected (coaxial moment frames and moment frame). in most cases, a specific structure needs to satisfy several functional levels. for this purpose, a method is required to determine the input request to the structures under possible earthquakes. therefore, the incremental dynamic analysis (ida) was preferred to the push-over non-linear static method for the analysis and design of the considered steel structures, due its accuracy and effect of higher modes at the same time intervals. opensees software was used to perform accurate nonlinear analysis of the steel structure. two parameters (spectral acceleration and maximum ground acceleration) were introduced to the modeled frames to compare the numerical correlations of seismic vulnerability obtained by two statistical methods based on the "log-normal distribution" and "logistics distribution", and finally, the parameters of displacement and drift were assessed after analysis. keywords-seismic vulnerability; nonlinear incremental dynamic; moment frames; coaxial braced frames i. introduction in order to obtain a proper instruction for decreasing the impact of earthquakes, prediction of potential vulnerability of existing buildings due to future earthquakes is one of the most essential affairs in structural engineering. the design and construction should be in a way that does not lead to human loss. common earthquakes of relatively low magnitude should not have an impact on building performance whereas a certain extent of compensated damage can be accepted in structures and equipment for earthquakes with greater magnitudes,. steel moment frames have thus been classified into 3 categories including special moment-resisting frame (smf), intermediate moment-resisting frame (imf) and ordinary moment-resisting frame (omf). these three types of systems do not have the same function. special moment-resisting frame has more ductility than intermediate moment-resisting frame and ordinary moment-resisting frame. hardness, ductility and strength are important parameters in seismic response of earthquake resistant structures. although moment frames offer a very high hardness, they possess a low ductility, as in these frames usually displacement controls become dominant. despite the moment frames, coaxial frames offer a high lateral strength and very low ductility, which brings about a very low coefficient of behavior for these frames. incremental dynamic analysis (ida) is a new method to have a proper evaluation of the seismic requirements of the structure. in this method, the structure is studied under a specific set of selective earthquakes at different seismic levels. then, usually about 16%, 50% and 84% of the capacity corresponding to the limiting conditions can be defined, based on the summarized curves of incremental dynamic analysis. one goal of this study is to use special features of incremental dynamic analysis for studying the dynamic behavior of structures during earthquakes. in nonlinear dynamic analysis, one or more accelerograms have been used in any analysis that each of them represents a structural response. usually, because of the high costs of this analysis and also the long period of time required for conducting the experiments, dynamic nonlinear methods that have been designed for control of structures are applied. the nonlinear static analysis method, in particular the nonlinear incremental dynamic analysis (pushover), has the capability of evaluation of the structure behavior form elastic to plastic and final failure conditions by taking advantage form scaling the forces in different loading patterns. considering the similarity of the transfer from the linear static analysis to nonlinear incremental dynamic analysis, we can obtain the linear dynamic analysis from nonlinear incremental dynamic analysis (ida), where the seismic loading is also scaled. this concept was first introduced by bertero in 1977 and then described in different templates [1-10]. in [11], authors prepared a detailed report about integration and the perfect introduction of nonlinear incremental dynamic analysis and cleared many of the previous ambiguous concepts. recently, ida method was coordinated with fema updated instructions, which is officially used as a method for determination of the engineering, technology & applied science research vol. 7, no. 1, 2017, 1338-1344 1339 www.etasr.com javanpour and zarfam: application of incremental dynamic analysis (ida) method for studying… general collapse capacity of the structure [12]. today, not mush studies have been conducted on the dm choices (an important parameter in the ida analysis).this problem occurred because the studied structures are all form conventional structural buildings, as the maximum relative displacement of stairs of the overall displacement of the structure usually has two proper values of dm. for several years pacific earthquake engineering research center (peer) concentrated on the development of a method to evaluate the seismic performance of buildings learning [13]. in earthquake engineering based on the performance, one of the important factors is to estimate the performance of the structure under seismic loading. thus the need for a method for estimating the parameters such as mean return period from a specific seismic requirement such a maximum displacement in stairs with one performance level such as instability caused the creation of ida method. in reality, this method was a set of non-linear incremental dynamic analysis under a set of earthquake records for a specific case. in this method, the records scaled incrementally, are applied on the studied structure as finally the structure affected by overall dynamic instability. in this method first the behavior of structural components must be modeled in nonlinear form and then the records were applied on the structure and extracted the response. in this condition, the ida curves can be described based on the response of structure to the damage in terms of intensity and vice versa. the curves, provide unique information about the nature of the structure response for several degrees of freedom. this analysis is specified for a variety of purposes, some of which include: creating a correct understanding of structural behavior under extreme and rare earthquakes, having a better perception of changes in the nature of structure response by increasing the magnitude of earthquake (change of maximum deformation patterns at the height of structure, trend of decrease of strength and resistivity by being sensitive to the model and magnitude), obtaining estimations of the overall system dynamic capacity, studying the trend of constant or variable condition of each of the above cases for each of the records involved in the ida analysis. ii. seismic vulnerability "vulnerability" is generally a term used to indicate the extent of the damage and losses that may probably occur as a result of accidents in buildings, services, geographies and in general applied to communities. according to the unesco’s definition, the sensitivity of the environment against the occurrence and severity of a natural disaster determines its vulnerability. in [14], authors designated a general index of softening damage. target index was based on change of the specific frequency of the first mode by reducing the hardness and resistance. by investigating the hysteresis behavior of the first modes they predicted the local and global damages. in [15], authors introduced a new way to study and measure and the concentration of damage in rc frames under the earthquake. in this method, at least one measured response was required in the case of structure and the ground acceleration. in addition, two of the lowest specific frequencies must be determined at different. classification of damages was compared both in physical inspections and statistical tests. it was concluded that, particularly in cases where the damage is concentrated at a certain level of seismic evaluation, an appropriate assessment of the damage is achieved by using the proposed method. seismic evaluation of a building existed in romania was conducted in [16, 17], under the influence of strong earthquakes, likely for the area. their purpose was to evaluate the appropriate modeling and analysis techniques to predict the inelastic behavior of damaged buildings vulnerable to consecutive earthquakes. the assessment was conducted using the damage indicator proposed in [18]. in [19], authors suggested a design approach based on the performance of the structure using some studies for designing against the earthquake. this means that before the designing phase, the behavior of the considered structure during the earthquake (objectives of study) were determined qualitatively and since then, some definitions were converted in quantitative form and applied as useful design information during the numerical phase. for this purpose, a method of using the concepts of energy and damage indicators was proposed. after the earthquake of rudbar-manjil in iran, evaluation of the vulnerability of buildings and studying the strengthening methods were followed strictly. for example preparation of the technical information of buildings at the iranian center of opposing the natural disasters provided in order to deal with vulnerability of buildings and strengthening techniques. in [20], authors conducted some studies about a theoretical empirical case named the model of iran seismic vulnerability and its sub-models besides the seismic vulnerability of ahwaz city. in [21], authors studied the seismic vulnerability of tehran rf bridges and the vulnerability of samples of constructed or under construction bridges and considered the qualitative aspects regarding the credit instructions of construction of bridges. in [22, 23], six reinforced concrete frames designed for gravity loads with lack of seismic resistance were studied. the results indicated that the structures showed severe weakness against the earthquake as high lateral displacement and damage of columns were observed in all of them and they were not able to tolerate the probable earthquakes in most of iranian cities. then, authors suggested to use cross braces to increase lateral hardness. iii. the intensity measure of the ground’s motion in order to determine the motion of the earth at different levels of severity, from mild to very strong, it is needed to scale the selected accelerogram. for this purpose, a simple and uniform conversion has been used by scale coefficients. scale factor (sf) in a scaled accelerogram is a non-negative numeric value (scalar) that has a range of zero to infinity which means λ [0, )î +¥ .this numerical value is multiplied in all values recorded from considered accelerogram and regarding being less, more or equal to 1, the intensity level is reduced or increased. 1λα λα= where, αλ is the scaled accelerogram vector and a1 is the non-scaled accelerogram vector. the intensity measure of the ground’s motion (im) is a scaling quantity of an accelerogram. this quantity is a function of the original accelerogram which varies according to the increase or decrease in the accelerogram: engineering, technology & applied science research vol. 7, no. 1, 2017, 1338-1344 1340 www.etasr.com javanpour and zarfam: application of incremental dynamic analysis (ida) method for studying… 1im ( ( ))f a  (1) examples of such quantity that can be scaled include: peak ground acceleration (pga), peak ground velocity (pgv), spectral acceleration (sa) in vibrating mode of structures taking into account the damage measure, sa(ti, ξ%). iv. damage measure or variability of structures damage measure or the variability of structure variability (dm) is a positive numeric value that describes the response properties of structural models against seismic loads or in other words, it is the excess reaction of structural model due to loading. this quantity is a non-negative numerical value (scalar) that has a range of zero to infinity, where dm [0, )î +¥ . v. curves of incremental non-linear dynamic analysis incremental non-linear dynamic analysis curves include of some (ida) curves, as each of them are obtained using several nonlinear dynamic analysis on a accelerogram scaled at some magnitude level. vi. the introduction of studied frameworks frameworks under consideration include the mean steel moment frames and steel coaxial braced frames (cross). both frames consist of 6 floors (including the roof, 7 stair levels) and 5 openings. floors heights were 3 meters and length of each opening was considered to be 4 meters. it is worth noting that the width of load-bearing of the roofs was also 4 meters. seismic loading was based on the fourth edition of iranian 2800 instruction and gravitational loading was also performed based on the sixth issue of national building regulations. the following characteristics have been used for determining the seismic parameters of frames: residential application (i = 1), tehran area with very high risk (a = 0.35), average steel moment frame (r1 = 7), coaxial braced steel frame (r2 = 6) and soil of zone iii. according to paragraph 3.2.2 of regulations of designing buildings against earthquakes (2800 instruction), fourth edition), equivalent static analysis can be applied in three-storey and shorter buildings, from the ground state or the following buildings:  regular buildings with a height of less than 50 meters from the base level.  irregular buildings with a height less than 50 meters from the base level that has: high and extreme torsional irregularity is not exited in the plan. no mass, soft and very soft irregulation was exited in the height. also in accordance with paragraph 3.2.3 of regulations of construction of buildings against earthquakes (2800 fourth edition), dynamic analysis method can be used for all buildings, but applying them for buildings not subject to clause 2.2.3, is essential. so considering all mentioned issues, the frames considered in this study were analyzed, designed and applied, as figures 1 and figure 2 show the geometry and sections used in these frames. a. vulnerability correlation no.1: annual frequency of exceeding demand – dm hazard here we want to derive a method based on displacement for calculating the probability of occurrence of limit conditions, as this issue is discussed in the following two sections:  the first part: we obtain the possibility that the demand exceeds the specified value of d.  the second part: the possibility that demand exceeds capacity. in reality the second part is to obtain probability of limit states. these correlations are as follows: 2 2 2 2 2 9 . . 4 1 . . 2 logistic : ( ) ( ). log-normal : ( ) ( ). d sa d sa k bd d sa k bd d sa h d h sa e h d h sa e                    (2) where:      model record count i=1 d 0 2 ( ) )(d -d = (count-1) k b d sa i i sa d h sa k a             (3) in these correlations βd׀sa is the logarithmic standard deviation of demand. this parameter is calculated in two ways, based on correlations 2 and 3. based on the figures and tables, the values of structural vulnerability in the logistics method is lower than that of the log-normal approach and this difference is more clear in braced structures. also in terms of numerical values, the braced structure showed more vulnerability, representing the higher vulnerability of the structure. in the case of showing the difference between the values obtained for structures, the correlations derived based on the sa, showed more realistic differences due to the dependence of these parameters to specifications and period of structure compared to pga-based values. b. vulnerability correlation (2): annual frequency of exceeding a limit state – the dm-based approach. so far, we obtained the possibility of passing a limiting case of a specified value. the next step is to calculate the probability of limit state variable from a certain threshold. the difference is that here, the threshold limit states can be a random variable. and now we want to obtain the probability occurrence of limit state, as the threshold of limit states is a variable, not a constant figure. these relationships are as follows:     2 22 2 2 2 2 2 2 9 1. . . .4 2 1 1. . . .2 2 logistic : ( ). . log-normal : ( ). . d sa c c d sa c c k kb b ls sa k kb b ls sa h h sa e e h h sa e e                        (4) where: engineering, technology & applied science research vol. 7, no. 1, 2017, 1338-1344 1341 www.etasr.com javanpour and zarfam: application of incremental dynamic analysis (ida) method for studying…       0( ) ( (t arget d m )) (t arget d m ) c k b c sa c c h sa k a l n m edian                (5) where βc is the logarithm of standard deviation of capacity based on the damage intensity of the structure and ηc is the mean of capacity based on the damage intensity of the structure. this parameter has been calculated in two ways, based on correlations 4 and 5, respectively. based on the figures and tables, the values of structural vulnerability in the logistics method was lower than that of log-normal and in the case of braced structures, the difference is more clear. fig. 1. the geometry and sections dedicated to mean steel moment frame fig. 2. geometric properties and sections dedicated coaxial braced frame steel (crossed) c. annual frequency of exceeding a limit state – the imbased approach in this section, we act completely similar to the previous section, except that in this section we want to calculate hls with im-based approach. these correlations are as follows: 2 2 ,2 2 2 , 9 . . 4 , 1 . . 2 , logistic: ( ). log-norm al: ( ). sa c sa c k ls sa sa c k ls sa sa c h h e h h e        (6) where:     , 0 , , , ( ) . ( (target im )) (target im ) k sa sa c sa c sa c sa c h k ln median         (7) in these correlations, βsa,c is the logarithm of standard deviation of capacity based on the ground motion intensity and ηsa,c is the mean of intensity based on the ground motion intensity. this parameter is calculated in two ways, based on correlations 6 and 7. according to the findings, quantities of structural vulnerability in the logistics method are lower than that of the log-normal approach and this difference is more obvious in the braced structures. also in terms of numerical engineering, technology & applied science research vol. 7, no. 1, 2017, 1338-1344 1342 www.etasr.com javanpour and zarfam: application of incremental dynamic analysis (ida) method for studying… values, braced structures represented more vulnerability that represents that the structure is more vulnerable. in the case of showing the difference of obtained values for the structures, due to the dependence of these parameters to the specifications and period of structures, the correlations obtained on the basis of sa showed more realistic values than pga-based ones in tables i-iv. d. vulnerability correlation (4). probability of exceeding a dm demand value – dm hazard in this section the possibility that demand exceeds a certain amount of structural damage intensity (threshold) is introduced as the risk of structural failure intensity. the correlations are as shown below:     22 2 2 2 2 2 22 2 2 9 1. . . .4 6 1 1. . . .2 2 logistic: ( ) ( ). . log-normal: ( ) ( ). . rd ud rd ud k k bd b d sa kk bd b d sa h d h sa e e h d h sa e e        (8) where:   2 2 6 0 2 0 logistic: ( ) . . log-normal: ( ) . . 0.5 uh uh k b d sa k b d sa rd d sa rd ud uh d h sa k e a d h sa k e a count                           (9) in these correlations, βuh is in danger of risk curve. this parameter is calculated in two ways, based on correlations 8 and 9. according to the figures and tables, the values of structural vulnerability of structures in the logistics approach is lower than that of the log-normal method and the braced structures it represents the clearest difference. also in terms of numerical values, braced structures represent more vulnerability of the structure. in the case of the difference between the values obtained for the structures, due to the dependence of this parameter to the specifications and period of the structures, the correlations derived on the basis of sa, pga-based values showed more realistic differences. e. vulnerability correlation (5). annual probability of exceeding a limit state in this section we want to determine the risk of probability where the damage of structure exceeds the limit state (or the probability or occurrence of limit state or frequency of limit states) while facing the uncertainty (due to lack of knowledge and data). at the final step, we introduced the demand exceeds the specific value of structure damage intensity as the term of risk of structure damage intensity. uncertainty was also considered for obtaining the risk of ground motion intensity and demand of structures damage intensity. now, we want to determine the possibility of pass from demand of structures damage intensity from the capacity of structures damage intensity (which itself is an uncertain quantity). similar to the previous section, capacity was considered as the random variable. the correlations are as shown below:           22 2 22 2 2 2 2 2 2 22 2 2 2 2 2 9 1 1. . . . . .4 2 6 1 1. . . . 2 2 logistic : ( ). . . log-normal: ( ). .               rd rc ud uc c rd ud rc uc c ls k k k b b b sa k k b b ls sa h h sa e e e h h sa e e (10) where:     0( ) . c k b csa rc c rc uc h sa k a count                 (11) this parameter has been calculated in two ways, based on correlations 10 and 11, respectively. based on the figures and tables, the values of structural vulnerability in the logistics method were lower than that of the log-normal approach, and in the case of braced structures, the difference is more clear. also in terms of numerical values, braced structures represented more vulnerability, representing that the structure is more vulnerable. in the case of showing the difference values obtained for the structures, due to the dependence of these parameters to the specifications and period of the structures, the correlations calculated on the basis of sa showed more realistic data than the pga-based data. f. vulnerability correlation (6). annual probability of exceeding a limit state the im-based approach the annual probability of passing the limiting state was obtained in previous sections by using im method. but there we only considered the uncertainties caused by changes of one record to another record for demand and capacity. in this section we want to apply the same method to obtain the probability of limit state by considering the uncertainties caused by lack of knowledge and data. these correlations are as follows :         2 2 2 2 ,2 , 2 2 2 , ,2 9 1. . . .4 6 1 . . 2 logistic: ( ). . log-normal: ( ). rsa c usa cc rsa c usa c c k k ls sa k b ls sa h h sa e e h h sa e         (12) where:     0 , , , , ( ) .c k b csa rsa c sa c rsa c usa c h sa k a count                 (13) this parameter has been calculated in two ways, based on correlations 12 and 13, respectively. based on the findings, the values of structural vulnerability in the logistics method were engineering, technology & applied science research vol. 7, no. 1, 2017, 1338-1344 1343 www.etasr.com javanpour and zarfam: application of incremental dynamic analysis (ida) method for studying… lower than that of the log-normal approach, and in the case of braced structures, the difference is clearer. also in the case of numerical, th braced structure showed more vulnerability, reflecting its more vulnerability to damage. in the case of showing the difference values obtained for the structures, due to the dependence of these parameters to the specifications and period of the structures, the correlations calculated on the basis of sa showed more realistic data than the pga-based data in tables v-viii. table i. vulnerability correlation (3), based on the dip.-pga for two studied frames lsh {disp.-pga} logistic-[mf] lsh {disp.-pga} logistic-[bf] lsh {disp.-pga} log normal-[mf] lsh {disp.-pga} log normal-[bf] 0.000285544 0.000904713 0.000409753 0.001152174 table ii. vulnerability correlation (3), based on the disp.-sa for two studied frames lsh {disp.-sa} logistic-[mf] lsh {disp.-sa} logistic-[bf] lsh {disp.-sa} log normal[mf] lsh {disp.-sa} log normal[bf] 0.000389395 0.000593656 0.000662878 0.000781767 table iii. vulnerability correlation (3), based on the drift-pga for two studied frames lsh {drift-pga} logistic-[mf] lsh {drift-pga} logistic-[bf] lsh {drift-pga} log normal[mf] lsh {drift-pga} log normal[bf] 0.000283478 0.001766809 0.000393283 0.002131271 table iv. vulnerability correlation (3), based on the drift-sa for two studied frames lsh {drift-sa} logistic-[mf] lsh {drift-sa} logistic-[bf] lsh {drift-sa} log normal[mf] lsh {drift-sa} log normal[bf] 0.000300858 0.000978815 0.000501526 0.001393139 table v. vulnerability correlation (6), based on the disp.-pga for two studied frames lsh {disp.-pga} logistic-[mf] lsh {disp.-pga} logistic-[bf] lsh {disp.-pga} log normal[mf] lsh {disp.-pga} log normal[bf] 0.000418844 0.000413495 0.000331439 0.00042035 table vi. vulnerability correlation (6), based on the disp.-sa for two studied frames lsh {disp.-sa} logistic-[mf] lsh {disp.-sa} logistic-[bf] lsh {disp.-sa} log normal[mf] lsh {disp.-sa} log normal[bf] 0.000404206 0.000565317 0.000296043 0.000482789 table vii. vulnerability correlation (6), based on the drift-pga for two studied frames lsh {drift-pga} logistic-[mf] lsh {drift-pga} logistic-[bf] lsh {drift-pga} log normal[mf] lsh {drift-pga} log normal[bf] 0.000409736 0.000650206 0.000331405 0.000658552 table viii. vulnerability correlation (6), based on the drift-sa for two studied frames lsh {drift-sa} logistic-[mf] lsh {drift-sa} logistic-[bf] lsh {drift-sa} log normal[mf] lsh {drift-sa} log normal[bf] 0.000362407 0.000715243 0.000268709 0.000584209 vii. conclusion by reviewing the figures and tables related to vulnerability, it can be concluded that the mean steel moment frame structures showed less vulnerability than steel coaxial braced frame structures (cross). in this way, depending on the type of im and dm parameters, between 20% to 90% of vulnerability values of steel moment frames were less than coaxial braced frame structures (cross). the greatest difference was observed when using displacement as a component of structural damage and peak of ground acceleration as the component of ground motion intensity. in the case of vulnerability correlations of logistic and log-normal methods, it is concluded that correlations of log-normal represented more conservative values than the logistics ones. in the same way, depending on the type of structure and parameters of im and dm, vulnerability values were about 5% to 20% lower than that of the logistic method. this means that the designs based on the logistics methods by assumption of loading and similar site and structurewould calculate lighter and more cost-effective sections than the lognormal method. in the coaxial braced frame, difference between logistic and log-normal methods are more evident than the moment frame. the most important reason for this case can be found in the risk curves. based on these curves, the higher period of the structure, the lower probability of exceeding a certain intensity. so the moment frame structures with higher period, provides lower risk values (k0 and k). since the majority of logistic and log-normal differences can be seen in the coefficients associated with these two parameters, thereby the moment frame structure with a less period (due to the lower effectiveness by these parameters), shows less difference between the two correlations. while examining the methods in which the ground motion parameters (im) is the type of peak of ground motion pga, difference of structures is less evident. the reason is that the values of the probability of the event obtained from the risk curve were related to the peak of ground motion independent of the structure period (pga is one of the seismic characteristics of the ground independent from type of structure and its period), as gives the constant value for both types of the structures. engineering, technology & applied science research vol. 7, no. 1, 2017, 1338-1344 1344 www.etasr.com javanpour and zarfam: application of incremental dynamic analysis (ida) method for studying… references [1] n. luco, c. cornell, “effects of connection fractures on smrf seismic drift demands”, asce journal of structural engineering, vol. 1, no. 1, pp. 127-136, 2000 [2] n. luco, c. cornell, “effects of random connection fractures on demands and reliability for a 3-story pre-northridge smrf structure”, proceedings of the 6th u.s. national conference on earthquake engineering, paper 244, vol. 1, no. 2, pp. 1-12, 1998 [3] p. bazzurro, c. cornell, “seismic hazard analysis for non-linear structures. i: methodology”, asce journal of structural engineering, vol. 1, no. 7, pp. 332-3344, 1994 [4] p. bazzurro, c. cornell, “seismic hazard analysis for non-linear structures. ii: applications”, asce journal of structural engineering, vol. 1, no. 7, pp. 3345–3365, 1994 [5] s. yun, r. hamburger, c. cornell, d. foutch, “seismic performance for steel moment frames”, asce journal of structural engineering, vol. 1, no. 8, pp. 20–25, 2002 [6] s. mehanny, g. deierlein, modeling and assessment of seismic performance of composite frames with reinforced concrete columns and steel beams, the john a. blume earthquake engineering center, stanford university, report no. 135, 2000 [7] d. dubina, a. ciutina, a. stratan, f. dinu, “ductility demand for semi-rigid joint frames”, moment resistant connections of steel frames in seismic areas, vol. 6, no. 7, pp. 371-408, 2000 [8] g. de matteis, r. landolfo, d. dubina, a. stratan, “influence of the structural typology on the seismic performance of steel framed buildings”, moment resistant connections of steel frames in seismic areas, vol. 1, no. 7, pp. 513-538, 2002 [9] a. nassar, h. krawinkler, “seismic demands for sdof and mdof systems”, the john a. blume earthquake engineering center, stanford university, stanford, vol. 8, no. 7. pp. 1991 [10] i. psycharis, d. papastamatiou, a. alexandris, “parametric investigation of the stability of classical comlumns under harmonic and earthquake excitations”, earthquake engineering and structural dynamics, vol. 8, no. 7, pp. 1093-1109, 2000 [11] c. a. cornell, d. vamvatsikos, f. jalayer, n. luco, “seismic reliability of steel frames”, proc., 9th ifip wg 7.5 working conf. on reliability and optimization of structural systems, vol. 8, no. 9, pp. 30-35, 2000 [12] fema, “350: recommended seismic design criteria for new steel moment-frame buildings”, federal emergency management agency, washington dc, vol. 5, no. 4, pp. 15-20, 2000 [13] g. g. deierlein, h. krawinkler, c. a. cornell, “a framework for performance-based earthquake engineering”, pacific conference on earthquake engineering, 2003 [14] h. u. koyluoglu, s. r. nielsen, j. abbott, a. s. cahmak, “local and modal damage indicators for rc frames subject to earthquakes”, journal of engineering mechanics, vol. 124, no. 12, pp. 1371-1379, 1998 [15] p. s. skjaerbaek, s. r. k. nielsen, a. s. cakma, “assessment of damage in seismically excited rc-structures from a single measured response”, proc. of the 14th international modal analysis conference, vol. 1, no. 2, pp. 133–139, 1996 [16] f. paulet-crainiceanu, active control approach for long span bridge responses to strong earthquakes, ph. d. thesis, yokohama national university, yokohama, 1997 [17] a. madan, a. m. reinhorn, j. b. mander, r. e. valles. “modeling of masonry infill panels for structural analysis”, journal of structural engineering, vol. 123, no. 10, pp. 1295-1302, 1997 [18] y. j. park, a. h. s. ang, “mechanistic seismic damage model for reinforced concrete”, journal of structural engineering, vol. 111, no. 4, pp. 722-739, 1985 [19] a. teran-gilmore, “energy concepts and damage indices”, proceedings of the symposium curee-eerc, vol. 1, no. 4, pp. 133140, 1997 [20] r. razani, k. l. lee, “the engineering aspects of the qir earthquake of 10 april 1972 in southern iran”, national academy of science, washington. vol. 1, no. 1, pp. 102-105, 1973 [21] f. hamedi, m. tehrani zadeh, amir kabir university magazine, vol. 50, vol. 1, no. 1, pp. 307, 2002 [22] m. a. shayanfar, m. angouti. “the study of seismic vulnerability of gravity load designed reinforced concrete frame”, journal of school of engineering, vol. 13, no. 2, pp. 45-58, 2001 [23] t. angotti, “playing politics with disaster”, international journal of urban and regional research, vol. 1, no. 4, pp. 327-331, 1977 microsoft word 01-galvin-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 381-386 381 www.etasr.com marin galvin and rodriguez mellado: quality improvement of a small water supply. a practical application… quality improvement of a small water supply a practical application of a full system of nanofiltration rafael marín galvín control de calidad, calidad y medio ambiente empresa municipal de aguas de córdoba, s.a. córdoba (spain) rmargal@emacsa.es josé miguel rodríguez mellado dept. química física y termodinámica aplicada universidad de córdoba e-14014-córdoba (spain) jmrodriguez@uco.es abstract: the thm level in the spanish drinking water is limited to less than 0.100 mg/l, due to its potential toxicological effect on humans. this paper investigates the comparison of the results obtained in a small supply of water that historically presented thm contents out of the spanish normative, versus the results there obtained when the treatment was modified with the inclusion of a nanofiltration system. so, the conventional treatment first applied was that of pre-oxidation with chlorine and/or kmno4, followed by coagulation with aluminum salts directly on closed sand filter, and disinfection final by chlorination: with this system, thm levels lower than 0.100 mg/l were not always secured. thus, to improve the water quality, a full system of nanofiltration was implemented, after the above treatment, consisting in: pre-filtration through cartridges, filtration over activated carbon, post-filtration for retaining impurities, and finally, nanofiltration and chlorination of water after nanofiltration. in this order, the new treatment scheme has usually produced water with maximum thm levels of 0.058 mg/l, and average values of 0.013 mg/l, 0.30 mg/l for organic matter concentrations, and water always microbiologically pure. also, the contents of fe, mn and al in the treated water were significantly reduced with respect to the previous situation without nanofiltration. keywords: nanofiltration; activated carbon; trihalometanes; water treatment plant (wtp); water supply i. introduction the current normative for drinking water in spain (rd 140/2003) establishes the content in trihalomethanes (thm) in water for public distribution as a parameter of special interest [1, 2]. so, by considering the potential toxic impact of this type of compounds on the health of consumers [3], the limitation of the total thm concentration to a maximum value of 100 µg/l was established from january 1, 2009. this value must be respected in all drinking water in spain in order to be qualified as safe and clean, i.e. as drinking water. the generation of trihalomethanes is linked, among other causes, to the presence in the water of their precursors, in general aromatic polyphenolic compounds originated from degradation of biological material (especially vegetable materials). chemical reactions between such precursors and the chlorine added to water for the treatments are the responsible for the formation of thm in waters subject to chlorination [1, 2, 4, 5]. in this way, the most important factors related with the thm generation in chlorinated waters are the following: • number and type of organic molecules present in the water. • type and amount of halogens other than chloride present in the water. so, the action of chlorine provokes the oxidation of these halogens different of chlorides and subsequently, the formation of bromine and iodine thm of high toxicological effect on humans. • chlorine applied dose: the higher the chlorine added, the higher the thm generation rate. • water temperature: higher temperatures increase the rate of thm formation. • ph: alkaline values of the water favor the formation of chloroform, especially. • presence of catalysts: fe and mainly mn are very abundant in the majority of raw waters intended for treatment, and they can increase the practical speed of thm formation. • contact time between chlorine and water: as the time is increasing the thm level also increase. in this way, the highest rate of thm formation is given during the first 24-25 hours of chlorine-water contact [6-8]. in this regard, the practical formation rate of thm in waters is investigated using the known thm formation potential test, which consists of raw water chlorination with given levels of chlorine and the subsequent measurement of thm compounds formed along the reaction time [6-8]. with this information one can assess the most effective strategy for each particular supply to minimize the content of thm in drinking water. summarizing, all available strategies may include the following [5, 9-11]: a. in the pre-oxidation step: • total or partial replacement of chlorine used in the treatment of raw water. when the applied chlorine is lower, the thm formation is also reduced. etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 381-386 382 www.etasr.com marin galvin and rodriguez mellado: quality improvement of a small water supply. a practical application… • use of alternative oxidants to chlorine, especially kmno4, clo2 and o3. it is sufficiently proved that substitution of chlorine by the above reactants forms sensibly lower thm levels [5-11]. • use of activated carbon (powdered or by filtration bed). in this case, the adsorbent capacity of carbon can remove organic matter and thm precursors of the raw water at the beginning of the treatment. moreover, when the water has already been chlorinated, activated carbon can also remove thm initially formed in the system. b. in the coagulation-flocculation-sedimentation step: • use of more active coagulants than those conventionally employed in water clarification, such as different types of aluminum polychlorides and other similar ones. thus, the reduction of organic matter amount in water could lead logically to lower thm formation with the same applied dose of chlorine. • by changing the hydraulic and the design of decanters. this effect can affect the reaction time between organic matter and chlorinated water. c. in the disinfection step: • by replacing conventional chlorination disinfection by chloramines or clo2. production of thm is sensibly lower compared to when disinfectants are used [6-8]. d. apllication of non-conventional steps: • use of membrane filtration techniques: nanofiltration and reverse osmosis, especially [12]. in this sense, it is known that the systems of nanofiltration or reverse osmosis have included units of ultrafiltration and adsorption with activated carbon prior nanofiltration and osmosis, to lead its correct function. in theses cases, the finished water can be finally chlorinated without any thm problem. according to the above, the valid strategy for each case is defined by the specific type of raw water, the previous design of each wtp or treatment available, the distribution network, and the technical and economic capacity of the supply. the aim of this paper is to present the yielding achieved with the implementation of a full nanofiltration system in a small water supply, which was troubled in meeting parametric levels of trihalomethanes, when the treatment was carried out by conventional pre-oxidation by chlorine and/or kmno4, coagulation-flocculation, filtration on sand and final disinfection by chlorination. ii. materials and methods dates here presented are referred to the water treatment system without nanofiltration and with nanofiltration. so, the studied period begins with the effective implementation of the nanofiltration system, from january 1st and ends on october 31st 2012, i.e. 10 months of continuous operation, during which sampling was carried out on a weekly basis. three types of samples were taken each week: the first one was raw water intended for treatment and emanating from the guadalmellato reservoir (córdoba) [13, 14]; the second one corresponded to water after the conventional treatment of preoxidation, coagulation-flocculation, filtration and final chlorination; and the third one was water after the full treatment, i.e., pre-oxidation, coagulation-flocculation, filtration, nanofiltration and final chlorination: this finished water was distributed to the public. determinations of the quality parameters in water were carried out according to the usual standard water quality control methods: • color and turbidity were investigated by colorimetry; ph and conductivity with the corresponding electrodes; • free chlorine, iron, manganese, nitrite and ammonium by visible spectrophotometry using, respectively, dpd, α,α’bipyridyl and ammonium thioglycolate, formaldoxime in basic medium, zambelli method, and nessler method (without distillation). • organic matter was quantified as potassium permanganate oxidizability; and hardness and bicarbonate levels were measured by volumetric titration [15, 16]. • the aluminum determination was made with the icp technique (inductively coupled plasma) without previous digestion of the sample and for the measurement of trihalomethanes (thm) gas chromatography with microautomatic solid phase extraction and subsequent detection by electron capture was used. thm data correspond to the sum of chloroform, bromoform, bromo-dichloromethane and dibromo-chloromethane [15, 16]. • finally, the determinations of escherichia coli and total coliform were made by filtration through a membrane of 0.45 µm pore size and incubation with chromogenic culture medium for 48 hours at 37°c to permit the development of colonies of potential microorganisms present in the water [15, 16]. iii. results and discussion water uptake for the small supply (<10 m3 of average daily consumption) comes from the guadalmellato reservoir (located about 25 km from cordoba, spain). table i presents the characteristics of water quality during our study. it should be noted that water has an acceptable organoleptic quality, conductivity and moderate saline contents, and middle hardness. its main problem is the microbiological content, which sometimes reaches very important recounts, especially during the rainy season and subsequent runoff water to the reservoir [13, 14]. in addition, ammonia and manganese concentrations can be elevated, while the concentration of organic matter is moderate. in this sense, without being specially high in absolute terms, it is true that the origin of water from a reservoir with a high rate of algal presence (middle degree of eutrophication) during very few months of the year, favors the generation of thm in water after chlorination, especially in spring and autumn. etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 381-386 383 www.etasr.com marin galvin and rodriguez mellado: quality improvement of a small water supply. a practical application… table i. untreated raw water characteristics (guadalmellato reservoir-córdoba, spain). parameter units max. min. mean color mg/l pt-co 19 6 10 turbidity unf 7.7 1.7 4.2 ph ph units 7.75 7.36 7.50 conductivity µs/cm 284 251 267 hardness mg/l caco3 125 50 104 bicarbonates mg/l hco3 – 141 116 126 manganese µg/l 995 52 293 iron µg/l 213 18 85 4itrites mg/l 0.084 0.006 <0.005 ammonia mg/l 0.383 <0.020 0.110 permanganate oxidability mg/l o2 4.8 2.8 3.5 total coliforms colonies/100 ml 5000 4 674 escherichia coli colonies/100 ml 600 0 70 figure 1 shows the tests carried out to investigate at laboratory scale the potential of thm generation in the raw water by chlorination, by using two variables: applied chlorine dose (from 1 mg/l to 8 mg/l) and contact time water-chlorine (up to 120 hours) maintaining a given chlorine dose (3 mg/l). fig. 1. thm formation from raw water as a function of: a) chlorine dose, contact time=2 h; b) water-chlorine contact time, chlorine dose=3mg/l. figure 1a indicates that the higher the dose of chlorine, the higher the thm formation. thus, an increase of four times in the chlorine dose is associated to an increase of the same level in the production of thm: so, dosages of 2 g/m3 of chlorine generated around 30 µg/l of thm, and dosages of 8 g/m3 of chlorine produced around 125 µg/l of thm. at the same time, figure 1b shows that thm formation increases quickly up to more than 150 µg/l after 24 hours of contact time water-chlorine while the production is much more slower after the first 24 hours, as it has been stated in the bibliography [6-8]. by observing figure 1 we can conclude that the dosage of about 5 mg/l chlorine (a quantity relatively frequent in the common water treatment) generated amounts of thm very close to 100 µg/l after only two hours of contact (figure 1a) while contact times of only 8 hours with 3 mg/l chlorine dose caused a similar effect (figure 1b). in addition, contact times of 24 hours were associated to production of thm levels higher than 150 µg/l. all these information is very valuable to establish the industrial treatment of raw water. on the other hand, the usual purification treatment of raw water before the implementation of nanofiltration was the following: • pre-oxidation with potassium permanganate (solid product previously dissolved in water). • pre-chlorination (naclo solution). • coagulation and subsequently filtration on sand filters by using commercial aluminium polyclhoride. • final disinfection before the distribution of water to the public, with commercial sodium hypochlorite solution. the doses of all reactants were always adjusted depending on the practical operative results obtained in each moment, which varied accordingly the quality of the incoming raw water received in plant [5-8]. in this way, the practical reactants doses used during our study were the following: • pre-oxidation: kmno4 solution with dosages ranging from 0 to 0.8 g/m3. • pre-chlorination: naclo solution with dosages expressed as chlorine ranging from 1.5 to 3.5 g/m3. • coagulation-flocculation on closed sand filter: aluminium polychloride commercial solution ranging from 45 to 60 g/m3, expressed as commercial product. • disinfection final: naclo solution with non-variant dosages expressed as chlorine of 1.5 g/m3. in the most past of the sampling carried out along the 10 months of the survey, the applied treatment achieved treated water of high quality, with modest levels of mn, fe, nitrites and ammonia, but showing occasionally problems of concentrations of manganese out of limits, light microbiological occurrence not specifically pathogenic, and especially, a total thm levels over-passing the limiting values. during these episodes of production of water out of normative, which can’t be distributed to the supply (as established the spanish normative –rd 140/2003-) the etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 381-386 384 www.etasr.com marin galvin and rodriguez mellado: quality improvement of a small water supply. a practical application… practical alternative was the use of cisterns. this implied additional difficulty and economical over. as a complementary data, table ii presents the chemical and microbiological characteristics of finished water subjected to conventional treatment, i.e. before nanofiltration, along our study. table ii. treated water characteristics after the treatment with filtration (whitout nanofiltration) parameter units limits a maximum minimum mean color mg/l pt-co 15 3.4 <0.2 0.7 turbidity unf 5 0.76 0.02 0.23 ph ph units 6.5–9.5 7.71 7.33 7.56 conductivity µs/cm 2500 319 132 274 residual free cl2 mg/l 0.2–1.0 1.75 <0.05 0.9 hardness mg/l caco3 (c) 118 49 99 bicarbonates mg/l hco3 – (c) 126 65 114 manganese µg/l 50 108 <10 21 iron µg/l 200 57 <5 12 nitrites mg/l 0.500 0.030 <0.005 0.009 ammonia mg/l 0.500 0.033 <0.020 <0.020 aluminum mg/l 0.200 0.10 0.02 0.05 oxidability to kmno4 mg/l o2 5.0 2.2 0.3 1.6 total thmb µg/l 100 282 30 131 total coliforms colonies/ 100 ml 0 25(d) 0 3(d) escherichia coli colonies/ 100 ml 0 5(d) 0 <1(d) a) from rd. 14/2003. b) after water chlorination. c) not contemplated in rd. d) total coliforms and escherichia coli were only detected in 2 sampling of all the carried out: thus, the mean values are affected by these two samplings. in this way, the maximum value column indicates manganese problems (more than 50 µg/l), occurrence of total coliforms and escherichia coli (more than 1 colony by filtering 100 ml of water –these positive results were tested in only 2 samplings of all the ones carried out-) and levels of total thm very much higher than the imperative parametric value of 100 µg/l (up to 282 µg/l). moreover, the mean value of total thm also over-passed the parametric limit. this previous situation became both a potential sanitary problem and a potential incidence of parametric nonobservance of the spanish normative (rd 140/2003) in this supply. raised the question, the empresa municipal de aguas de córdoba s.a. as responsible of above supply, and the córdoba university laboratory evaluated several options in order to have a full treatment to ensure, except eventualities, adequate quality in all times. in this regard, figure 2 shows the known ability of separation associated to the industrial filtration techniques available [5, 10, 12]. due to fact that we want to specially remove thm precursors (colloids), unspecific organic matter and microorganisms, implementation of a nanofiltration system could be found as a suitable solution. fig. 2. filtration spectrum and filtration capacity of the different techniques available. fig. 3. internal scheme of the full nanofiltration system. thus, a full nanofiltration system commercially available (supplied by kärchertm) [17] was installed to treat the water produced from the conventional treatment (pre-oxidation and coagulation in closed sand filter). in this sense, the water was subjected to the following inner line process, as reflected in figure 3: • pre-filtration through cartridges with particle retention capacity equal to or greater than 5 µm. • activated carbon filtration for the adsorption of varied organic compounds, including those associated with phenomena of occurrence of odor-taste in the treated water. • post-filtration, after the activated carbon filter, for retention of impurities which could be unfavorable to the nanofiltration membranes. • nanofiltration. in this sense, nanofiltration is the last phase in the removing of organic matter, colloids, thm precursors etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 381-386 385 www.etasr.com marin galvin and rodriguez mellado: quality improvement of a small water supply. a practical application… and formed thm, as well as microorganisms (bacteria and viruses) in the water [5, 6-9]. nanofiltration membranes have a pore size of <2 nm, and all the substances and molecules lower than the above size should be retained in the system. • final chlorination of treated water for distribution to consumers. the full system of integrated water treatment (i.e., prefiltering, adsorption by activated carbon, post-filtering and nanofiltration) has also a continuous residual chlorine analyzer to regulate the level of chlorination in treated water, considering the imperative value (0.2 to 1.0 mg/l of cl2). another complementary information is that treated water after nanofiltration could not be chlorinated to allow us some uses outside direct consumption, such as irrigation and gardening. finally, after the installation of nanofiltration was effective and optimization time was reached, data of quality treated water without and with nanofiltration were obtained to compare the two situations along the period studied. in order to the above said, tables ii and iii provide a comparative yield pattern obtained with the two available treatment processes. in this regard, the priority is the performance with respect to the removal of organic matter and the subsequent generation of thm in chlorinated water. table iii. treated water characteristics after nanofiltration parameter units limits a maximum minimum mean color mg/l pt-co 15 0.50 <0.02 0.03 turbidity unf 5 0.24 0.02 0.07 ph ph units 6.5 – 9.5 8.05 7.05 7.63 conductivity µs/cm 2500 281 108 177 residual free cl2 mg/l 0.2–1.0 0.26 <0.05 <0.05 hardness mg/l caco3 (c) 80 43 53 bicarbonates mg/l hco3 – (c) 98 58 72 manganese µg/l 50 45 <10 15 iron µg/l 200 56 <5 15 nitrites mg/l 0.500 0.049 <0.005 0.010 ammonia mg/l 0.500 0.075 <0.020 <0.020 aluminum mg/l 0.200 0.07 0.02 0.04 oxidability to kmno4 mg/l o2 5.0 1.0 <0.1 0.3 total thmb µg/l 100 58 <10 13 a) from rd. 14/2003. b) after water chlorination. c) not contemplated in rd. moreover, in figure 4a the extreme and mean values of organic matter in the raw, filtered and nanofiltered water are given. fig. 4. comparison of maxima, minima and mean values of: a) oxidability and b) thm content, in raw, filtered and nanofiltered water. as expected, the situation is significantly more favorable after nanofiltration. in this regard, the average content of organic matter in water after nanofiltration is only 19% compared to the filtered water (0.3 mg/l vs. 1.6 mg/l). furthermore, after nanofiltration the maximum does not exceed 45% of that corresponding to filtration (1.0 mg/l versus 2.2 mg/l). also, as a side effect, the incidence of odor-taste in treated water was zero during the period studied. in figure 4b the extreme values of thm in chlorinated water after nanofiltration and after filtration can be observed. again, and which involved the main objective pursued, the situation is very different in the two cases. thm generated in the water after nanofiltration do not exceed the parametric limit of 100 µg/l, nor in average value (13 µg/l) nor in the maximum value (<60 µg/l). finally, the generation of thm in chlorinated filtered water, even on average value, amply exceeded the imperative limit (100 µg/l). as supplementary information, figure 5 shows the weekly evolution of thm levels in the produced water after nanofiltration along the study. it is observed that after relatively high values at the beginning of the installation of the system (which coincided with a situation of poor quality of the raw water from the reservoir) its behavior exhibits a sustained maintenance of very low thm concentrations after the integrated treatment. thus, after the first five weeks of implementation of nanofiltration, the total thm levels were normally lower than 20 µg/l. etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 381-386 386 www.etasr.com marin galvin and rodriguez mellado: quality improvement of a small water supply. a practical application… fig. 5. evolution of the total thm after the full nanofiltration system is operating (weekly sampling). in summary, these results extensively justify the adopted system as the solution to the problem of inadequate thm levels. as a positive additional aspect of system performance, full nanofiltration system always guaranteed the absence of total coliforms and escherichia coli in water throughout the study. further, the full nanofiltration system led a significantly lowering in the salt content. thus, the average value of the conductivity of the filtered water was reduced to 65% (from 274 µs/cm to 177 µs/cm), while the hardness decreased by 54% (99 mg/l versus 53 mg/l of caco3) and bicarbonate in 63% (114 mg/l vs. 72 mg/l). finally, although the full nanofiltration system does not significantly reduce the average content of iron and manganese, a decrease in the obtained maximum values of these metals must be noted in the treated water. the maximum manganese concentration never exceeded the parametric value required, condition that was not satisfied only by filtration. similarly, no remarkable improvement was observed in relation to the contents of aluminum, nitrites or ammonium, although these parameters were not among the primary objectives pursued. iv. conclussions the application of a complementary system of nanofiltration to the water produced after pre-oxidation and closed sand filter coagulation in a small supply is able to maintain thm concentrations far below required, with mean values of 13 µg/l, and with tips, 58 µg/l, well below the maximum limited (100 µg/l). the full nanofiltration treatment installed is integrated by a pre-filtration system, an adsorption system, a post-filtration system, and finally, the nanofiltration system. nanofiltration system, apart from the production of water with lower salt content than the starting water, produced water with very low concentrations of organic matter (average value of 0.3 mg/l) and therefore with minimum odor-taste incidents. the production of water with levels of mn always according to that imperative in spanish normative (<50 µg/l), should also be noted. finally, the system is able to produce treated drinking water with an excellent microbiological quality in all situations which represents a relevant yielding for it. acknowledgment to juan sánchez bejarano, technician of the engineering and maintenance department of emacsa by the information provided. references [1] j. m. rodríguez mellado, r. marín galvín, fisicoquímica de aguas, díaz de santos, madrid, 1999 [2] r. marín galvín, fisicoquímica y microbiología de los medios acuáticos. tratamiento y control de calidad de aguas, díaz de santos, madrid, 2003 [3] world health organization, guidelines for drinking water qualityrecommendations, vol. 1, 3rd ed., genéve, 2006. 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[17] kärchertm. technical information supplied by the supplier of the industrial system kärchertm wpc 100 fw-a-ro. microsoft word 31-3320_s_etasr_v10_n1_pp5265-5269 engineering, technology & applied science research vol. 10, no. 1, 2020, 5265-5269 5265 www.etasr.com rehman & shaikh: critical factors influencing the behavioral intention of consumers towards … critical factors influencing the behavioral intention of consumers towards mobile banking in malaysia zahoor ur rehman faculty of technology management and business universiti tun hussein onn malaysia parit raja, malaysia zahoorrehman715@gmail.com fazal ali shaikh department of economics university of sindh jamshoro, pakistan fazal_110_shaikh@hotmail.com abstract—mobile banking services are widely adopted in developed and developing countries, while their adoption by malaysian consumers is relatively low. the effective adoption of mobile banking mostly depends on consumers. this study’s objective was to examine the factors that influence malaysian customers’ behavioral intention toward mobile banking. a detailed literature review was conducted in order to identify the critical factors that affect mobile banking users. the research model was based on the technology acceptance model, investigating additionally perceived risk. primary data were collected from 384 generation y bank customers. structure equation modeling through smart-pls was used for data analysis. results revealed that consumers’ behavioral intention was significantly and positively influenced by perceived usefulness and ease of use, while a significant negative relationship was found between consumers’ behavioral intention and perceived risk. the findings also revealed a mediating relationship of attitude between perceived usefulness, ease of use and risk, and behavioral intention to use mobile banking. the study provides appropriate guidelines to malaysian banks and mobile banking application developers for the effective implementation and design of mobile banking services. keywords-mobile banking adoption; technology acceptance model; perceived risk; generation y; malaysia i. introduction mobile banking is defined as any form of banking transaction that is carried out through a mobile device [1]. according to [2], mobile banking got underway at the end of the 1990s. mobile banking is widespread in developed and developing countries, such as the us [3], the uk [4], china [5], india [6], pakistan [7, 8], malaysia [9] and iran [10]. juniper research estimated that more than 2 billion mobile users would use their devices for banking by the end of 2021, compared to 1.2 billion people in 2016 [11]. malaysia is among the fastest growing mobile and telecommunications technology countries in asia, and the proportion of smartphone users continues to rise from 68.7% in 2016 to 75.9% in 2017, indicating a sharp increase in their penetration rate [12]. malaysian central bank officially permitted mobile banking services in 2005 [13], and 17 commercial banks announced mobile banking services [14]. developments in technology and mobile banking applications attracted gradually more users by time, but malaysian customers show less attention and enthusiasm towards mobile banking services [15, 16]. moreover, there is a lack in the awareness of malaysian customers’ acceptance, behavioral intention, and in the investigation of factors affecting their intention to adopt mobile banking. furthermore, people born between 1980 and 1994, called generation y [17, 18], are the majority of subscribers of mobile phones in malaysia. they are the first generation to have spent all their life in the digital environment and information technology fundamentally influences how they live and work [19]. the purpose of this study was to examine the malaysian generation y consumers’ behavioral intention towards mobile banking adoption. ii. literature review investigating customers’ intention and mobile banking adoption has attracted the focus of many researchers, while this issue has experienced a spectacular increase in the related literature of online and internet banking channels [20–22]. researchers used different methodologies to describe how consumers articulate their opinions, attitudes, intentions, and behaviors towards mobile banking [21, 23–25]. despite these studies provided a better understanding of the critical factors for predicting consumers’ intention and use of mobile banking, there are further essential aspects to study. a. technology acceptance model (tam) tam explains technology acceptance from the customer’s point of view. it is a model that covers almost all the constructs that determine customers’ intentions in adopting mobile banking, and it was selected as the theoretical basis of this study’s conceptual model. perceived usefulness (pu) and perceived ease of use (peou) were proposed as direct determinants of customers’ attitude, affecting indirectly the behavioral intention to adopt it. both factors, behavioral intention (bi) and attitude (att), have been identified as important predictors of adoption behavior in mobile banking [26]. many studies adapted tam to examine the influence of various factors to the adaptation of technology, concluding that tam itself is inadequate in explaining the user’s decision to adopt technologies [6, 7, 9, 12, 24, 27-31]. according to [9], perceived risk (pr) is a decisive factor for customers’ perceptions and their intentions in adopting such a technology. corresponding author: zahoor ur rehman engineering, technology & applied science research vol. 10, no. 1, 2020, 5265-5269 5266 www.etasr.com rehman & shaikh: critical factors influencing the behavioral intention of consumers towards … fig. 1. research framework b. perceived usefulness (pu) pu is the degree to which a person believes that using a particular system would enhance his job performance [26]. in general, individuals seem interested to adopt new technologies when they believe that technology is more beneficial and suitable for their daily lives [26, 32, 33]. consumers’ attitudes and their intentions to adopt mobile banking are predicted by pu [32, 34-37]. as a result, the following hypotheses were proposed: h1: pu has a significant relationship with the behavioral intention to use mobile banking h2: pu has a significant relationship with the attitude towards using mobile banking c. perceived ease of use (peou) peou is the degree to which a person believes that using a particular system would be free of effort [26]. although individuals may believe that an application is beneficial, they may also think that it is difficult to use [26]. the easier the use of a technology is, the more beneficial it could be, increasing its adoption and usage [38]. due to the mobile banking applications’ features, which require a certain amount of knowledge and skills, perceived ease of use plays an essential role in affecting individuals’ attitudes to accept such a system [39]. several empirical studies have shown that peou plays a crucial role in predicting consumers’ intentions to use mobile banking, confirming its impact on individuals’ attitudes [16, 26, 36, 37]. thus, the following hypothesis was developed: h3: peou has a significant relationship with the attitude towards using mobile banking. d. perceived risk (pr) pr is the uncertainty about the outcome of the use of the innovation or the level of uncertainty on its security [40]. authors in [18] stated that individuals were reluctant to accept mobile banking when the fear of insecurity existed, and increasing uncertainty increased the awareness of risk. pr is recognized as a dynamic factor in predicting an individual’s attitude and intention to use mobile banking [19, 21, 41]. in particular, perceived risk was negatively related to the consumers’ attitudes towards mobile banking in [6, 34, 42]. an increase in the perception level of risk would decrease consumers’ attitudes and intentions towards mobile banking. hence, the following hypothesis was proposed: h4: pr has a significant relationship with the attitude towards using mobile banking. e. mediating effect of attitude and behavioral intention to the use mobile banking attitude refers to an individual’s positive or negative evaluative effect about performing a particular behavior [9], whereas behavioral intention is the measure of the likelihood of a person employing the application [43]. in [44], it was hinted that individuals’ attitudes predicted their behavioral intention to use a technology, which sequentially predicted their actual usage behavior. previous studies examined the relation between individuals’ attitudes and their behavioral intentions [7, 16, 43-45]. this study assumes that mobile banking adoption can be predicted by the users’ attitudes to the adoption of mobile banking. furthermore, attitude was hypothesized as a mediator to the relation between pu, peou, pr and behavioral intention, as: h5: attitude has a significant relationship with the behavioral intention to use mobile banking. iii. methodology data were collected from 550 respondents, using selfadministered questionnaires that investigated their perceptions on the characteristics of their behavior towards mobile banking and usage acceptance. the questionnaire consisted of 38 scale items that measured the constructs of the conceptual model. pr covered nineteen items adapted from [26, 46, 47]. pu and peou were determined by nine items each, adapted from [35, 48]. a seven-point likert scale, from strongly disagree to strongly agree, was used to measure the respondents’ responses. partial least squares equation model (pls-sem) was utilized for the data analysis. pls-sem was chosen because of the type of the relationships, the data characteristics, and its convenience. iv. data analysis a. respondent’s profile and characteristics three hundred eighty-four (384) usable questionnaires were collected from generation y respondents, where 51.4% were male and 48.6% female. the age group of 24-34 years represented the largest part of the total valid samples (76%), the largest group of the respondents (38.2%) had a monthly income between 2000 and 3500 malaysian ringgit (myr), while their vast majority (88.3%) had more than ten years of experience on mobile phones and internet. moreover, 55.5% of the respondents had already adopted mobile banking services. b. construct reliability table i indicates the reliability of the constructs, displaying cronbach’s alpha, compound reliability (cr) and average extraction variance (ave). results show that cronbach's alpha for each one of the five variables exceeded the minimum 0.70 threshold [49]. cr values for all the variables are within the range of 0.70, as suggested by [50, 51]. the highest value of cr was 0.96 for pr and attitude, while its lowest was 0.83 for peou. as shown in table i, ave values for all the variables are above the suggested limit of 0.50 [49], while these values started from 0.52 for pu, reaching 0.86 for attitude. engineering, technology & applied science research vol. 10, no. 1, 2020, 5265-5269 5267 www.etasr.com rehman & shaikh: critical factors influencing the behavioral intention of consumers towards … table i. construct reliability and convergent validity constructs items factor loadings ave composite reliability cronbach’s alpha attitude (att) att1 0.944 0.863 0.969 0.960 att2 0.937 att3 0.904 att4 0.918 att5 0.941 behavioral intention (bi) bi1 0.907 0.792 0.950 0.934 bi2 0.897 bi3 0.862 bi4 0.900 bi5 0.885 perceived ease of use (peou) peou1 0.776 0.565 0.838 0.744 peou2 0.653 peou3 0.756 peou4 0.813 perceived risk (pr) fr1 0.808 0.628 0.966 0.963 fr2 0.817 fr3 0.837 fr4 0.831 fr5 0.811 perr2 0.594 perr3 0.809 pr1 0.847 pr2 0.850 pr3 0.841 pr4 0.892 sr1 0.803 sr3 0.766 sr4 0.805 tr1 0.661 tr2 0.536 tr3 0.867 perceived usefulness (pu) pu1 0.649 0.522 0.844 0.801 pu2 0.674 pu3 0.828 pu4 0.811 pu5 0.627 c. construct validity a discriminant validity test was used to indicate that all constructs have not any relationship. based on the suggested criterion, discriminant validity is acceptable when the square root of the ave of the variable of interest is higher than any correlation between this and the other variables in the model [52]. as shown in table ii, the diagonal values, which represent each variable’s square root, are higher than the intercorrelations between the model’s variables, satisfying the discriminant validity criterion. in addition, as shown in table i, all item loadings meet the recommended 0.5 threshold except of two: security risk (item2) and performance risk (item1), which were excluded. table ii. discriminant validity constructs att bi peou pr pu att 0.929 bi 0.767 0.890 peou 0.225 0.271 0.752 pr -0.135 -0.134 0.481 0.792 pu 0.173 0.434 0.123 0.042 0.723 d. structural model the path coefficient is the appraisal of the proposed hypotheses and the relationship between the dependent and the independent variables in the structural model. path coefficient close to 1 is considered as a strong positive correlation, while close to -1 represents a strong negative correlation [53, 54]. as the coefficient approaches zero, the relationship is weaker, while very low values close to zero are generally negligible. table iii. research model evaluation paths beta t-statistic p-value r 2 pu→bi 0.137 4.027 0.000 0.258 peou→att 0.310 6.104 0.000 pu→att 0.366 8.902 0.000 0.624 pr→att -0.269 3.912 0.000 att→bi 0.658 19.393 0.000 as shown in table iii, all path coefficients have significant relationships. the highest significant positive path relationship was found between att and bi (β=0.658, t=19.393, p=0.000). the second most significant positive relationship was found between pu and att (β=0.366, t=8.902, p=0.000). among significant positive relationships, the lower correlation was found between peou and att (β=0.310, t=6.104, p=0.000), while the least but significant positive relationship was between pu and bi (β=0.137, t=4.027, p=0.000). on the other hand, the most negative significant relationship was found between pr and att (β=-.269, t=3.912, p=0.000). in summary, all positive and negative paths show significant relationships. the results shown in table iii indicate that pu, peou, and pr have a direct relationship with the attitude towards the use of mobile banking (r 2 =0.258), explaining approximately 26% of its variance. moreover the combined influence of pu, peou, and pr have a moderate effect on behavioral intention (r 2 =0.624) explaining about 62% of the variance. e. mediating effect of attitude towards the use of mobile banking the variable “attitude towards using mobile banking” was hypothesized to mediate the relationship between pu, peou, pr, and behavioral intention to use mobile banking. results show that all hypotheses are supported, indicating a partial mediation, following the mediation criteria recommended by [51, 54]. v. discussion results showed that the proposed model was able to reach an acceptable level of predictive power for all factors, as all the criteria related to the measurement model, i.e. construct reliability and validity, were met. further, r 2 shows the combined effect of the exogenous latent constructs, explaining about 62% of the variance in the endogenous latent construct, suggesting that pu, peou, pr and attitude predict the consumers’ intention towards mobile banking. according to the path coefficient analysis, attitude was proved as key factor in predicting an individual’s intention to adopt mobile banking. results also made available significant evidence on the causal path between behavioral intention and pu, suggesting that malaysian consumers’ perception of usefulness is fundamental to their intention to adopt mobile banking. results also showed engineering, technology & applied science research vol. 10, no. 1, 2020, 5265-5269 5268 www.etasr.com rehman & shaikh: critical factors influencing the behavioral intention of consumers towards … the significant relationship between peou and attitude towards the use of mobile banking. this means that malaysians tend to worry about the degree of easiness, or struggle in the use of mobile banking. this relationship is traced back to the fact that clients need some basic knowledge and abilities, due to the special characteristics of mobile banking [10, 42]. in particular, when individuals realize that the use of a technology requires minimum effort, they realize that they can take advantage of it [26]. regarding the role of pr, results showed that it significantly influenced negatively the behavioral intention through attitude. it is deduced that pr plays a crucial role in shaping the individuals’ beliefs and perceptions, affecting their behavior and intention to use mobile banking. vi. research contribution this study examined the key factors that predict the malaysian customers’ intentions towards mobile banking adoption and its usage, contributing to the literature of online banking channels and technology acceptance in general. moreover, this study provides useful guidelines towards mobile banking, which has not been evaluated thoroughly in the context of malaysia. therefore, this study considerably expands the knowledge and literature in malaysia, by focusing more thoroughly on mobile banking as a new technology that requires greater understanding. it is also noteworthy that researchers [9, 23, 34, 55] have empirically investigated the validity of tam in explaining mobile internet services and other technology acceptance in developed and developing countries. accordingly, this study is amongst the studies that have extended tam by monitoring a new technology (mobile banking) in a modern context (banking sector) in malaysia. furthermore, as the adoption level of mobile banking in malaysia is considered low, banks should struggle in building trust with users, make mobile banking operating services easier, and customers more aware of mobile banking’s usefulness. banks should minimize the perceived risk factors as a core of their strategic objectives. vii. research limitations and future directions although this study was a successful attempt in exploring the area of mobile banking adoption, however, it has certain limits. data were collected from a convenient sample of generation y bank customers in a single state of malaysia (johor), which sequentially could negatively affect the generalization of results in other states of the country. this fact increases issues about the results’ applicability to other population groups with different demographic characteristics and experience in technology. moreover, findings were based on cross-sectional data. a future study can deliver more indepth insight into the mobile banking acceptance and usage in a different context, examining the degree to which the influential factors could stabilize or improve by time. viii. conclusion mobile banking is an 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technology & applied science research vol. 8, no. 5, 2018, 3321-3328 3321 www.etasr.com marouani et al.: a modified artificial bee colony for the non-smooth dynamic … a modified artificial bee colony for the nonsmooth dynamic economic/environmental dispatch i. marouani national school of engineering of sfax (enis), university of sfax, sfax, tunisia ismailmarouani@yahoo.fr a. boudjemline university of hail, hail, saudi arabia a.boudjemline@uoh.edu.sa t. guesmi college of engineering, university of hail, hail, saudi arabia tawfiq.guesmi@gmail.com h. h. abdallah national school of engineering of sfax (enis), university of sfax, sfax, tunisia hsan.hadj@enis.rnu.tn abstract—this paper presents an improved artificial bee colony (abc) technique for solving the dynamic economic emission dispatch (deed) problem. ramp rate limits, valve-point loading effects and prohibited operating zones (pozs) have been considered. the proposed technique integrates the grenade explosion method and cauchy operator in the original abc algorithm, to avoid random search mechanism. however, the deed is a multi-objective optimization problem with two conflicting criteria which need to be minimized simultaneously. thus, it is recommended to provide the best solution for the decision-makers. shannon’s entropy-based method is used for the first time within the context of the on-line planning of generator outputs to extract the best compromise solution among the pareto set. the robustness of the proposed technique is verified on sixunit and ten-unit system tests. results proved that the proposed algorithm gives better optimum solutions in comparison with more than ten metaheuristic techniques. keywords-evolutionary computation; power generation dispatch; optimal scheduling; decision making; cost function i. introduction emission dispatch aims at minimizing emission of harmful gases, caused by fossil-fueled thermal units, such as co, co2, nox and so2 [1-2]. the combination of the above problems is called the economic emission dispatch (eed) problem. however, due to the dynamic nature of today’s network loads, it is required to schedule the thermal unit outputs in real time according to the variation of power demands during a certain time period [3]. to solve this modified eed problem, known as dynamic economic emission dispatch (deed), several mathematical formulations have been suggested [3-6]. usually the deed problem is considered as a dynamic optimization problem having the same objectives as the eed over a timeperiod of one day, subdivided into definite time intervals of one hour with respect to the constraints imposed by the generator ramp-rate limits (rrl) [3]. therefore, the operational decision at an hour may be influenced by the one taken at a previous hour. other constraints such as prohibited operating zones (poz) and valve-point loading effects (vple) have been considered [7-8]. however, incorporating vple in the fuel cost function introduces ripples in the latter and the problem will be with multiple minima. on the other hand, poz constraints due to physical operation limitation like vibrations in the shaft bearing [9] create discontinuities in the objective functions. therefore, the deed becomes a highly nonlinear problem with non-convex and discontinuous fitness functions. classical methods like, dynamic programming [10] and linear programming [11], have been used to solve the static eed. however, these techniques are iterative and require an initialization step, which can cause the convergence of the search process into local optima. moreover, they may fail to solve the dynamic case including the above constraints. recently, metaheuristic search algorithms have demonstrated good performance and high efficiency when applied to complex optimization problems. these optimization procedures are classified into various groups in terms of the optimization methodology. swarm intelligence-based evolutionary algorithms are the most used algorithms. among metaheuristic-based optimization techniques, genetic algorithm [12], particle swarm optimization [13], simulated annealing [14], artificial bee colony (abc) [7], tabu search [15], differential evolution [4] and bacterial foraging [5] have been suggested for solving the eed problem. despite the fact that these techniques have been proven to have a clear edge over traditional methods, they have been criticized [16] because their efficiencies are sensitive to the form of problem constraints and number of units. most of the above-mentioned works have concentrated only on the static eed problem. only a few considered the multi-objective deed problem. in addition, rrl and poz constraints were not considered during the transition from the last hour of the current day to the first hour of the next day. abc algorithms attracted much attention for eed problems [9]. abc algorithm [17] simulates the foraging behavior of a real bee colony for maximizing the nectar amount stocked in the hive. compared to several population-based techniques like, pso and ga, the abc algorithm is simple in concept with a few setting parameters, easy for combination with other optimization approaches and more effective. unfortunately, like other evolutionary algorithms, the abc method has also been criticized for its poor convergence rate and premature convergence due to the unbalanced exploration-exploitation processes [16]. exploration corresponds to the capability to avoid convergence toward local optima by expanding the search into new areas, while exploitation is the capability to engineering, technology & applied science research vol. 8, no. 5, 2018, 3321-3328 3322 www.etasr.com marouani et al.: a modified artificial bee colony for the non-smooth dynamic … search the space to find interesting new solutions. thus, many improved techniques have been proposed to further enhance its performance [16-17]. in order to increase abc's exploitation ability, the classical employed bee and onlooker bees’ phases have been changed by incorporating the so-called grenade explosion method (gem) [18]. the gem is an optimization method proposed in [19] and, as the name suggests, it imitates the mechanism of a grenade explosion. the effectiveness of this modified version of abc, symbolized by gabc, was verified on a set of standard reference functions. in [16], the cauchy operator is embedded into the scout bees' phase of the abc in order to increase the exploration ability by generating a larger set of solutions instead of one random solution for each scout bee. a new method exploiting the advantages of gem and cauchy operator is proposed in the present work in order to solve the deed problem with respect to all the abovementioned constraints. this optimization, symbolized by gcabc, integrates the gem and cauchy operator into the abc technique. in addition, a new decision-making method based on shannon’s entropy, called extended entropy-weighted reference (eewr) approach, is developed and incorporated into the gcabc algorithm to select the most suitable solution among all non-dominated solutions provided by the optimization algorithm. unlike other techniques like those based on graph theory [20] and z-transformation [21], the eewr is characterized by uncomplicated mathematics [22]. the main contributions of the current work are:  a new optimization technique, called gcabc, for scheduling power production of thermal units according to the expected load variations is proposed. to the best of our knowledge, the present work is the first attempt to solve the eed problem by the use of gcabc algorithm. in addition, a modified ewr-based technique, called extended entropyweighted reference (eewr), is proposed for decision making. this technique has not been used in any field of power systems.  all aforementioned constraints are considered simultaneously in the deed problem.  the rrl constraints are taken into account during the transition from the last hour of the one day to the first hour of the next day. ii. problem formulation the deed problem is considered as a multi-objective optimization problem (mop). it aims to minimize simultaneously total fuel cost and total emission by finding the power production of thermal power plants according to the predicted load demands. the resolution of the deed problem can be accomplished by solving the static eed (seed) problem over a certain period of time subdivided into smaller time intervals. deed problem objectives and constraints are described below. a. objective functions thermal units with multi-steam admission valves that work sequentially to cover the demand, involves higher order nonlinearity to total fuel cost due to vple, as illustrated in figure 1. unfortunately, neglecting the vple, which is required when using classical methods, causes some inaccuracy in the solution of the deed problem. taking into account vple constraints, a sinusoidal form is included in the total non-smooth cost function expressed in $/h, as given in (1). the second objective corresponding to the total emission in ton/h is described by (2):      2 min 1 1 sin        t n t t t t i i i i i i i i i t i c a b p c p d e p p (1)    2 1 1 exp       t n t t t t i i i i i i i i t i e p p p     (2) where, ia , ib , ic , id and ie are the cost coefficients of the i-th unit. while, i , i , i , i and i are the emission coefficients. tip is the output power in mw at the t-th interval. t is the number of hours. in this study, 24t  . the bi-objective deed problem is converted into a monoobjective optimization problem in [23]. in this study, the price penalty factor (ppf)-based method is adopted. thus the combined economic-emission objective function ft can be described by (3):  1  t t tf c e   (3) where,  0,1rand  . for each generated value of , the function ft is minimized to obtain the optimum solution that can be a candidate solution to be in the pareto front. the parameter  is the average of the ppf of all thermal units. as shown in (4), the ppf of the i-th unit is the ratio between its fuel cost, maxi c , and its emission, maxi e , for maximum generation capacity. max max  i i i c ppf e (4) fig. 1. fuel cost function with five valves (a, b, c, d, e) b. problem constraints the deed problem is solved by minimizing the function ft defined in (3) with respect to the following constraints:  generation capacity the real power output of each unit i should be within its minimum and maximum limits minip and max ip : generation (mw) f u el c o st ( $ /h ) without vple with vple e c a b d engineering, technology & applied science research vol. 8, no. 5, 2018, 3321-3328 3323 www.etasr.com marouani et al.: a modified artificial bee colony for the non-smooth dynamic … min max , 1, ,   ti i ip p p i n (5)  power balance constraints at each time period t, the total power generation must cover the total demand power tdp plus the total transmission losses t lp . thus, the power balance constraints can be described by: 1 0, 1,...,      n t t t i d l i p p p t t (6) where tlp can be calculated using the constant-loss formula [3] given by (7): 1 1 1       n n n t t t t l i ij j oi i oo i j i p p b p b p b (7) where, ijb , oib , oob are the loss parameters also called bcoefficients.  generating unit rrl in practice, power generation of each unit i during two consecutive time periods is limited by its rrls defined by (8) and (9): 1  t t downi i ip p r (8) 1  upt ti i ip p r (9) where, 1tip  is the previous output real power of the i-th machine. downir and up ir are the down-ramp and up-ramp limits of the i-th unit in (mw/time period). as one of the contributions of the present work, the rrl constraints are taken into account during the transition from the last hour of the current day to the first hour of the next day. two constraints are embedded in the problem formulation and they are described by (10) and (11): 24 1  downi i ip p r (10) 1 24  upi i ip p r (11)  poz constraints the poz constraints are described as: min ,1 , 1 , max , , 2,...,              i t down i i i upt t down i i ii k i k up t i ii z p p p p p p p k z p p p (12) where, , down i kp and , up i kp are down and up bounds of poz number k, iz is the number of poz for the i-th unit due to the vibrations in the shaft or other machine faults. therefore, the machine has discontinuous input–output characteristics [19]. figure 2 shows the fuel cost function for a typical thermal unit with poz constraints. fig. 2. cost function for a thermal unit with poz constraints. by considering the generation capacity, rrl and poz constraints, the minimum and maximum limits of the power generation tip of the i-th unit for the period t are modified as:  min 1max , max 1 min , , ,1 min 1max , , , 1 max 1 min , , , min 1max , , , mi                               i t down tp p r pi i i i upt downp p r pi i i i upt down tp p r p pi i i ii k tpi upt downp p r pi i i i k upt down tp p r p pi i i ii z max 1n ,                      uptp p ri i i (13) where 2,..., ik z iii. original abc algorithm overview abc algorithm [17] is an efficient and robust technique for several optimization problems. as all swarm-based techniques, abc algorithm starts by generating randomly an initial population of sn solutions. each solution is considered as a food source and it corresponds to an employed bee. sn is half of the entire population size (pn). the onlooker bees constitute the second half. if d is the number of the decision variables, an i-th solution ix will be represented by 1 2 ...    i i i i dx x x x . the fitness function evaluated at the solution ix , signifies the nectar quantity of the corresponding food source estimated by an employed bee:           1 , 0 1 1 , 0        i i i i i f x f xfit x f x f x (14) where,  if x is the objective function estimated at ix . the probability ip to choose the candidate solution ix by an onlooker bee is expressed as follows. power output (mw) f u el c o st ( $ /h ) p i min p i,1 down p i,1 up p i,2 down p i,3 down p i,3 uppi,2 up p i max poz 3 poz 2 poz 1 engineering, technology & applied science research vol. 8, no. 5, 2018, 3321-3328 3324 www.etasr.com marouani et al.: a modified artificial bee colony for the non-smooth dynamic …     1   i i sn n n fit x p fit x (15) the onlooker bees update the selected food source ix to discover a new one. the new solution iv is generated by modifying only one parameter ijx of ix as:    i i i i kj j j j jv x x x (16) where, indices k and j are chosen randomly from  1, 2,..., sn and  1, 2,..., d , respectively. the index k must be different from i. the parameter ij is a real number   0,1 generated from the uniform distribution. during the onlooker phase, a greedy selection between food sources iv and ix will be done. if an employed bee’s food source cannot be improved through a pre-specified triggering threshold, called limit, it becomes a scout and its solution will be abandoned. if ix is an abandoned solution, the converted scout-bee starts to search for a new solution randomly according to (17):   min max min0,1  ij j j jx x rand x x (17) where, max jx and min jx are bounds of the food source in dimension j. iv. proposed optimization algorithm an enhanced version of the classical abc technique is presented to enhance its exploitation and exploration abilities related to the onlooker and scout bees respectively. in [18-19], the abc method was criticized for the random selection of the j-th dimension because it may slow the convergence of the algorithm and increase the risk of convergence of the search phase to a local optima. to ovoid these limitations, authors in [19] incorporated a new method, called grenade explosion based method (gem), into the employed bee and onlooker bee phases. the idea behind this technique is to mimic the grenade explosion principle where, the fitness function is the overall damage of the explosion. in each cycle of the proposed method, it is assumed that there is only one grenade with one piece of shrapnel for each decision parameter. a procedure guideline for tuning the parameters of gem is given in [19]. the shrapnel pieces are thrown in all dimensions to collect information about the area of the explosion which is considered as the old food source as given in (18). then, a set of new food sources is proposed by the onlooker bees based on the damageper-shrapnel degree. this allows reaching the global solution more quickly. as given in (19), the optimal search dimension (osd) of the new candidate iosdv corresponds to the maximum damage in all directions.    i i i i kt t t t tv x x x (18) where,  1, 2,...,k sn is a randomly chosen index and k i and  1, 2,...,t d .  0,1it  is a random number.     max | 1, 2,..., i iosd tfit v fit v t d (19) as explained above, a greedy selection between the new solution iv and the old one ix is applied. in order to improve the global and local exploration abilities of the optimization algorithm and ensure the convergence into the global solution within a short calculation time, the cauchy operator is embedded in the scout bee phase. the incorporation of a cauchy operator in optimization techniques has been employed in some algorithms to enhance the global search ability [16]. this enhancement is due to the long tail of cauchy distribution compared to other operators such as gaussian distribution. as given in figure 3, the standard gaussian function has a large probability within the interval [-3,3]. nevertheless, it is possible to make larger jumps in the search space using cauchy operator. fig. 3. standard cauchy and gaussian distributions in this study, the origin-centered cauchy distribution with unit scale parameter is used. thus, the new solution provided from an abandoned solution ix will be obtained using (20) instead of (17).  0,1i ij jx x cauchy (20) where,    2 1 0,1 1 ( )   ij cauchy x (21) based on the above explanation, the main steps of the modified abc algorithm are listed below.  step 1: initialization preset population size pn (sn ) initialize iteration: iter = 0 preset maximum cycle number (mcn) fix triggering threshold (limit) initialize food sources using (4)  step 2: population evaluation estimate fitness value of each source using (1) initialize failure counter of each source xi,   0fc i  step 3: cycle increment  step 4: employed bees’ phase for i= 1 to sn do produce new source iosdv from ix using (19); estimate the fitness value of iosdv using (19); -4 -2 0 2 4 0 0.1 0.2 0.3 0.4 x p ro b ab il it y d is tr ib u ti o n gaussian (0,1) cauchy (0,1) engineering, technology & applied science research vol. 8, no. 5, 2018, 3321-3328 3325 www.etasr.com marouani et al.: a modified artificial bee colony for the non-smooth dynamic … apply greedy selection between iosdv and ix ; end for  step 5: onlooker bees’ phase t = 0;i = 1; while (t<sn) ifrand<prob(i) 1 t t apply steps 1 to 2 of employed bee phase; end if apply greedy selection between iosdv and ix ; if solution does not improve     1 fc i fc i ; end if 1 i i ; end while  step 6: memorization of the best food source  step 7: conditional test 1: if cycle <mcn go to step 8, else go to step 10  step 8: conditional test 2: if   fc i limit go to step 3, else go to step 9  step 9: scout bee phase apply cauchy operator using (20) and (21) and go to step 3  step 10: end v. extended entropy-weighted reference approach the deed is a bi-objective optimization problem with contradictory functions. consequently, results with any optimization algorithm will be a set of non-dominated solutions called pareto front. providing an adequate candidate pareto-optimal solution for the decision makers (dm) is a persistent requirement. in the present study, a shannon’s entropy-based multi-attribute decision-making (madm) method is proposed to rank the obtained non-dominated solutions. the concept of shannon’s entropy is used in several scientific domains such as material selection [22] and singlesensor fault location [24]. this concept can be adopted for mops with n objective functions and m non-dominated solutions as:  step 1: construct the decision matrix     ij m n x x , where, ijx , called performance index, is the value of the j-th function for the i-th solution.  step 2: normalize matrix x in order to have performance indices comparable and dimensionless. * 2 1   ij ij m ij i x x x (22)  step 3: calculate entropy je as follows. * * 0 1 ln , 1,...,     m j ij ij i e e x x j n (23) where  0 1 ln e m  and *ln ijx is considered 0 for * 0ijx  .  step 4: compute the weight of each objective j.   1 1 1     j j n j j e w e (24) the decision maker can assign a degree of importance js for each objective function j called subjective weight. thus, weights should be modified as follows. * 1 j j j n j j j s w w s w    (25)  step 5: determine the i-th co-ordinate reference point (crp) per objective function. it is defined as the highest performance index for maximization and the lowest for minimization [22]. however the deed is a minimization problem. the crp can be found using (26): *minj ij i r x (26)  step 6: calculate the deviation of each performance index from the crp for each objective function. then, determine the maximum deviation for each alternative respecting all objective functions using (27). each non-dominated solution is considered as alternative. * * *maxi j j j ij j z w r w x  (27)  step 7: classify all alternatives according to their maximum deviations then, select the alternative with rank one as the optimal alternative. vi. implementation of the proposed algorithm having been applied for the first time to solve one of the main power system problems, which is the deed problem, the gcabc is to be tested in this section on two well-known benchmark power systems. in order to demonstrate the effectiveness of the proposed optimization technique, a comparison with abc algorithm and more than six metaheuristic-based techniques used for solving the power dispatch problem is presented. for fair comparison, gcabc and abc algorithms have been implemented with the same parameters. results were obtained using matlab r2009a installed on a 64-bit pc with i7-4510u cpu @ 2.60 ghz. a. case 1: six-unit system the six-unit system with quadratic cost and emission functions is used to test the gcabc algorithm in solving the engineering, technology & applied science research vol. 8, no. 5, 2018, 3321-3328 3326 www.etasr.com marouani et al.: a modified artificial bee colony for the non-smooth dynamic … seed problem. the system data are taken from [25]. the bloss matrix of this system is given below: 6 140 17 15 19 26 22 17 60 13 16 15 20 15 13 65 17 24 19 10 19 16 17 71 30 25 26 15 24 30 69 32 22 20 19 25 32 85                      b (28) power production cost and emission were optimized simultaneously by minimizing the combined objective function (3). the ppf of the six thermal units are given in figure 4, hence, the average of these factors is 51.3073 $ / ton  . fig. 4. ppf for the six-unit system to collect the required number of non-dominated solutions, the proposed optimization algorithm was performed several times. best, worst, mean solutions and standard deviation (std) of the 10 trials obtained by the proposed gcabc and the original abc algorithms, for total demand power about of 700mw and the convergence ratio cr that equals to the number of successful trials ns divided by the total number of trials nt, are shown in table i. s r t n c n  (29) table i. results for 10 trials total fuel cost ($/h) total emission (ton/h) gcabc abc gcabc abc best 36912.24 36918.56 434.1320 434.1331 worst 36912.63 36913.46 434.1568 434.3861 mean 36912.29 36913.03 434.1368 434.2349 std 0.1176 0.3658 0.7328e-02 8.3723e-02 cr (%) 90 70 90 60 table i shows the robustness of the convergence of the gcabc and its good stability compared to the original abc. pareto fronts for both gcabc and classical abc algorithms are given in figure 5. it can be seen that when the total cost in $/h is minimized, the total emission in ton/h is at its maximum value and vice versa. figure 5 shows that pareto solutions obtained using gcabc are well distributed when compared to those obtained using abc algorithm. in addition, gcabc gives the best solutions for production cost or emission. the best compromise solution, shown in figure 5, has been extracted from the pareto solutions using the eewr approach. the convergence of the proposed algorithm is depicted in figure 6. gcabc algorithm converges into optimum solution at iteration 80 for best cost (figure 6(a)) and at iteration number 54 for best emission (figure 6(b)). fig. 5. pareto solutions (a) (b) fig. 6. convergence of the proposed algorithm the optimum power generation of all units for minimum cost and minimum emission using gcabc, abc and other metaheuristic techniques [25] are summarized in tables ii and iii. these tables show that gcabc, fa (firefly algorithm), ba (bat algorithm) and hyb (hybrid algorithm) outperform the classical abc algorithm. the investigation of the equality constraint described by (7) for each method, shows that gcabc is more accurate than fa, ba and hyb techniques. this is clearly depicted in figure 7 where, an accuracy value of each method is given by calculating the difference between the total production and the sum of the total load and power losses as described in (29). in figure 7, the accuracy is calculated with 4 digits after the decimal point.   1    n i d l i accuracy p p p (29) b. case 2: deed problem for the ten-unit system with pozs the well-known benchmark test system, called the ten-unit system, was used to prove the feasibility of gcabc for solving the deed problem including all operating constraints 1 2 3 4 5 6 0 20 40 60 80 unit number p p f 3.65 3.7 3.75 3.8 3.85 x 10 4 420 440 460 480 500 520 total cost ($/h) e m is si o n ( to n /h ) with gcabc with abc compromise solution 0 20 40 60 80 100 3.69 3.695 3.7 3.705 3.71 x 10 4 iterations c o st ( $ /h ) 0 20 40 60 80 100 434 434.5 435 435.5 iterations e m is si o n ( to n /h ) engineering, technology & applied science research vol. 8, no. 5, 2018, 3321-3328 3327 www.etasr.com marouani et al.: a modified artificial bee colony for the non-smooth dynamic … such as, vple, rrl and poz. the rrls corresponding to the transition from the last hour of the current day to the first hour of the next day, given by (10) and (11) were taken into account. fig. 7. accuracy of gcabc, fa, ba and hyb for different load table ii. best solution for minimum cost (pd=700mw) method gcabc abc fa ba hyb p1 (mw) 281,562 318,442 283,151 282,862 282,491 p2 (mw) 100,000 100,000 100,000 100,000 100,000 p3 (mw) 1,192.695 1,270.720 1,188.216 1,189.333 1,188.833 p4 (mw) 1,193.578 1,201.647 1,188.329 1,186.760 1,185.778 p5 (mw) 2,294.322 2,269.768 2,309.801 2,307.614 2,305.090 p6 (mw) 2,132.045 2,030.748 2,124.811 2,127.731 2,132.178 losses (mw) 194.202 191.325 194.311 194.324 194.373 ct ($/h) 36912.24 36918.56 36912.19 36912.08 36912.19 et(ton/h) 500.53 494.25 501.02 501.02 501.08 table iii. best solution for minimum emission (pd=700mw) method gcabc abc fa ba hyb p1 (mw) 804.827 767.280 801.523 801.431 801.506 p2 (mw) 822.259 797.532 824.019 824.033 824.054 p3 (mw) 1,140.623 1,097.203 1,139.655 1,139.684 1,139.570 p4 (mw) 1,137.692 1,182.489 1,134.758 1,134.763 1,134.851 p5 (mw) 1,631.220 1,695.130 1,634.493 1,634.530 1,634.436 p6 (mw) 1,628.759 1,626.760 1,630.944 1,630.950 1,630.975 losses (mw) 165.378 166.394 165.398 165.397 165.397 ct ($/h) 38105.00 37987.80 38101.09 38100.95 38101.13 et(ton/h) 434.13 434.66 434.13 434.13 434.13 the problem becomes highly non-linear and more complicated. the b-loss matrix of the system is given as: 0.49 0.14 0.15 0.15 0.16 0.17 0.17 0.18 0.19 0.20 0.14 0.45 0.16 0.16 0.17 0.15 0.15 0.16 0.18 0.18 0.15 0.16 0.39 0.10 0.12 0.12 0.14 0.14 0.16 0.16 0.15 0.16 0.10 0.40 0.14 0.10 0.11 0.12 0.14 0.15 0.16 0.17 0.12 0.14 0.35 0.11 0.13 0.13 0. 10 4 b 15 0.16 0.17 0.15 0.12 0.10 0.11 0.36 0.12 0.12 0.14 0.15 0.17 0.15 0.14 0.11 0.13 0.12 0.38 0.16 0.16 0.18 0.18 0.16 0.14 0.12 0.13 0.12 0.16 0.40 0.15 0.16 0.19 0.18 0.16 0.14 0.15 0.14 0.16 0.15 0.42 0.19 0.20 0.18 0.16 0.15 0.16 0.15 0.18 0.16 0.19 0.44                                 (30) total cost and emission functions were minimized individually and simultaneously according to the variation of the power demand tdp in mw over a time-period of one day, subdivided into 24 time intervals of one hour (relevant data were taken from [12]). results obtained using gcabc were compared with other techniques used recently in this field such as ibfa [23] and nsgaii [12]. the comparison results, shown in table iv, confirm that the proposed gcabc outperforms the other optimization techniques in providing the optimum generation schedule for the deed problem. this good performance was obtained despite the constraints (10) and (11), which were considered in gcabc. table iv. meta-heuristic techniques comparison minimum total cost ($/h) minimum total emission (ton/h) method without pozs with pozs without pozs with pozs gcabc 2474472.8 2484750.6 293416.3 293651.3 ibfa 2481733.3 na 295833.0 na nsgaii 2.5168x106 na 3.1740x105 na vii. conclusion dynamic economic emission dispatch (deed) is a tricky optimization problem. the quality of its optimal solution is influenced by the operating constraints, such as valve-point loading effects, prohibited operating zones and ramp rate limits (rrls). within this context, the present study proposed a new artificial bee colony (abc)-based technique for solving the deed problem. moreover, power balance constraint was also considered. unlike previous works, the rrls were embedded in the solution procedure during the transition from one day to the next. the proposed optimization technique incorporates the grenade explosion method and cauchy operator in the classical abc algorithm to avoid the random search in the different abc phases. to provide adequate compromise solution for the decision makers, an approach based on extended entropyweighted reference was proposed. the validation of the proposed optimization algorithm was verified on ten-unit system test with pozs. comparison results with more than ten metaheuristic techniques show that the proposed algorithm gives the best optimum solutions. references [1] p. k. roy, s. a. bhui, “multi-objective hybrid evolutionary algorithm for dynamic economic emission load dispatch”, international transactions on electrical energy systems, vol. 26, no. 1, pp. 49-78, 2016 [2] r. 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58-64, 2014 [6] z. zhu, j. wang, m. h. baloch, “dynamic economic emission dispatch using modified nsga-ii”, international transactions on electrical energy systems, vol. 26, no. 12, pp. 2684-2698, 2016 engineering, technology & applied science research vol. 8, no. 5, 2018, 3321-3328 3328 www.etasr.com marouani et al.: a modified artificial bee colony for the non-smooth dynamic … [7] m. k. sharma, p. phonrattanasak, n. leeprechanon, “improved bees algorithm for dynamic economic dispatch considering prohibited operating zones”, ieee-innovative smart grid technologies-asia (isgt asia), bangkok, thailand, november 3-6, 2015 [8] m. i. behnam, r. abbas, s. alireza, “nonconvex dynamic economic power dispatch problems solution using hybrid immune-genetic algorithm”, ieee systems journal, vol. 7, no. 4, pp. 777-785, 2013 [9] t. sen, h. d. mathur, “a new approach to solve economic dispatch problem using a hybrid aco–abc–hs optimization algorithm”, international journal of electrical power & 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using max/max price penalty factor”, neural computing and applications, vol. 28 (suppl. 1), pp. 197-205, 2017 [15] w. m. lin, f. s. cheng, m. t. tsay, “an improved tabu search for economic dispatch with multiple minima”, ieee transactions on power systems, vol. 17, no. 1, pp. 108-112, 2002 [16] j. g. zheng, c. q. zhang, y. q. zhou, “artificial bee colony algorithm combined with grenade explosion method and cauchy operator for global optimization”, mathematical problems in engineering, vol. 2015, article id 739437, 2015 [17] d. karaboga, an idea based on honey bee swarm for numerical optimization, tech rep tr06, erciyes university, engineering faculty, computer engineering department, turkey, 2005 [18] c. zhang, j. zheng, y. zhou, “two modified artificial bee colony algorithms inspired by grenade explosion method”, neurocomputing, vol. 151, no. 3, pp. 1198-1207, 2015 [19] a. ahrari, a. a. atai, “grenade explosion method-a novel tool for optimization of multimodal functions”, applied soft computing, vol. 10, pp. 1132-1140, 2010 [20] r. venkata rao, “a material selection model using graph theory and matrix approach”, material science engineering: a, vol. 431, no. 1-2, pp. 248-255, 2006 [21] m. soleimani-damaneh, m. zarepisheh, “shannon’s entropy for combining the efficiency results of different dea models: method and application”, expert systems with applications, vol. 36, pp. 5146-5150, 2009 [22] a. hafezalkotob, a. hafezalkotob, “extended multimoora method based on shannon entropy weight for materials selection”, journal of industrial engineering international, vol. 12, no. 1, pp. 1-13, 2016 [23] n. pandit, a. tripathi, s. tapaswi, m. pandit, “an improved bacterial foraging algorithm for combined static/dynamic”, applied soft computing, vol. 12, no. 11, pp. 3500-3513, 2012 [24] a. hafezalkotob, a. hafezalkotob, “fuzzy entropy-weighted multimoora method for materials selection”, journal of intelligent & fuzzy systems, vol. 31, no. 3, pp. 1211-1226, 2016 [25] y. a. gherbi, h. bouzeboudja, f. z. gherbi, “the combined economic environmental dispatch using new hybrid metaheuristic”, energy, vol. 115, part 1, pp. 486-477, 2016 microsoft word 21-3172_s_etasr_v9_n6_pp4984-4989 engineering, technology & applied science research vol. 9, no. 6, 2019, 4984-4989 4984 www.etasr.com behih et al.: real-time investigation of an adaptive fuzzy synergetic controller for a dc-dc buck … real-time investigation of an adaptive fuzzy synergetic controller for a dc-dc buck converter khalissa behih department of electrical engineering ferhat abbas university setif i setif, algeria khalissabehih@univ-setif.dz ziyad bouchama department of sciences and technology bachir el ibrahimi university bordj bou arreridj, algeria bouchama_ziad@yahoo.fr khier benmahammed lsi laboratory ferhat abbas university setif i setif, algeria kierben@ieee.org mohamed naguib harmas quere laboratory ferhat abbas university setif i setif, algeria mharmas@yahoo.fr abstract—in this paper, an adaptive fuzzy synergetic controller (afsc) for a dc-dc converter is introduced. two robust control techniques, synergetic control combined with fuzzy logic control, are utilized to produce a reliable dc-dc power supply. this isrealized by an indirect adaptive control of a dc-dc buck converter. to further enhance robustness, a nonlinear constraint, the equivalent of the sliding surface, is used to guarantee performance and stability for any operating condition. to ensure overall strength, closed-loop signals are bounded and the stability is guaranteed using the lyapunov theory. control parameters are optimized using a pso algorithm to further enhance performances. the proposed controller (afsc) is designed through a dspace based experimental setup to provide robust dc-dc buck converter voltage control. keywords-adaptive; fuzzy control; synergetic control; dc–dc converter; pso algorithm; dspaceboard ds1104 i. introduction reliable power supply is indispensable in any energetic system and computing unit. dc-dc converters represent a dependable power source used in many computer-based industrial plants as well as in renewable energy systems control [1-3]. failure or chaotic behavior may occur in these subsystems, often resulting in catastrophic repercussions [4-5]. therefore dc-dc converter robust operation is essential for a wide operating range and for different loading conditions [6-7]. parameter variations and varying operating points require a robust modeling approach. fuzzy systems have been proven to adequately handle systems with partially known or unknown system models using the universal approximation theorem [811] and will be exploited to approximate nonlinear system dynamics. added robustness in controlling such systems has been achieved using sliding mode control despite unwanted chattering. many sound approaches have been elaborated to alleviate [12-13] this unsafe drawback or to eliminate it completely, often at the expense of robustness. synergetic control, providing a robust and continuous control law, has emerged recently [14-16] as a promising technique. it relies on the same principles with sliding mode control and provides similar robustness but without discontinuous components in its control signal, therefore eliminating chattering. buck converter is the name given to a step-down dc-dc converter producing a lower average voltage at the output than the input supply voltage. its control performance must be upheld despite load and parameter variations occurring in many applications starting from basic computers to space vehicles or nuclear submarines. many control methods have been used, such as pid [17], fuzzy control [18], feedback linearization [19], and many others schemes using a precise model and fixed control parameters which can be detrimental to system performance [20]. the principal contribution of this paper consists in combining fuzzy inference systems and synergetic control to provide a reliable and robust dc-dc converter voltage control despite operating point excursions and parameter uncertainties. the adaptive scheme ensures robustness despite system parameter fluctuations while synergetic approach permits imposing system designer chosen dynamics without incurring devastating chattering inherent to sliding mode methodology. controller parameters are obtained with the use of particle swarm optimization (pso) algorithm and closed-loop stability is insured utilizing lyapunov synthesis. results are given for dc-dc converter control for different operating conditions showing remarkable performance. ii. model of the dc-dc converter the basic buck dc-dc converter topology is shown in figure 1. when the converter works in conduction mode, the system can be described by: corresponding author: ziyad bouchama engineering, technology & applied science research vol. 9, no. 6, 2019, 4984-4989 4985 www.etasr.com behih et al.: real-time investigation of an adaptive fuzzy synergetic controller for a dc-dc buck … ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) 1 1 1 c l l l c c c d d in m l c l c c c rr r i t r i t u t l r r l r r v v v r i t d l l r u t i t u t c r r c r r    =− + −   + +   − + + +   = + + + � � (1) where l i is the average inductor current, c u is the average capacitor voltage and d is the control signal. the positive constants r, l, c and inv are the load resistance, inductance, capacitance and input voltage source while rl, rc, rm, and dv are parasitic elements. the output voltage ( )0v t can be determined from: ( ) ( ) ( ) ( )0 c l c c c rr r v t i t u t r r r r = + + + (2) the control law objective is to drive the circuit with a desired constant output voltage regardless of load and line input variations. tracking error and its derivative are defined as follows: ( ) ( ) ( ) ( ) 0 , , ref l c l c ref e t v v e t f i u g i u d v = −  = + −� � (3) where ref v is the desired output voltage, ( , )l cf i u and ( , )l cg i u are variable functions of state system and circuit components [21]. the adaptive fuzzy synergetic control applied to a buck dc-dc converter is developed in the next section. fig. 1. buck dc-dc converter schematics iii. dc-dc converter fuzzy synergetic control synergetic control synthesis of the system given in (1) begins by defining a designer chosen macro-variable given as in (4): e edtβψ = + ∫ (4) whereβ is a positive constant. let the desired dynamic evolution of the macro-variable be designer imposed as: + 0α ψ ψ =� (6) whereα is a positive constant. taking the first time derivative on the macro-variable function leads to: e eβψ = +� � (7) which can be rewritten as: ( ) ( ), ,l c l c reff i u g i u d e vβψ = + + −� � (8) combining (6) and (8) yields: ( ) ( ) 1 , , + l c l c ref f i u g i u d e vβ α + + − = − ψ� (9) solving for the synergetic control law leads to: ( ) ( ) 1 1 , , ref l c l c d e v f i u g i uβ α −  =− ψ+ − +    � (10) the control law in (10) assumes that ( ),l cf i u and ( ),l cg i u are perfectly known and that the system is operating in the controllability region, that is ( ) 1 , 0 l c g i u − ≠ . in the more realistic case where ( ),l cf i u and ( ),l cg i u are unknown, the control law (10) for dc-dc buck converter must be modified as: ( ) ( ) 11 ˆ ˆ/ / f ref f g d e v f x g xβ θ θ α −  =− ψ+ − +    � (11) where [ ] tl cx i u= is a vector of measurable states and the fuzzy estimates function ˆ( / ) f f x θ and ˆ( / ) g g x θ are defined as [8-9]: ( )ˆ( / ) tf ff x xθ θ ξ= (12) ( )ˆ( / ) tg gg x xθ θ ξ= (13) where ( )xξ is the fuzzy basis function defined as: ( ) ( ) ( ) 1 1 1 l i l i n if i l nm if l i x x x µ ξ µ = = = =         ∏ ∑ ∏ (14) ( )l i if xµ represents the membership function value of ix and engineering, technology & applied science research vol. 9, no. 6, 2019, 4984-4989 4986 www.etasr.com behih et al.: real-time investigation of an adaptive fuzzy synergetic controller for a dc-dc buck … l if are labels of fuzzy sets in 1i n n iu u r = = ∈∏ . fuzzy logic systems’ vectors f θ and g θ can be continuously updated as in [13, 22-23]: ( )f f xθ κ ξ= ψ� (15) ( )g g x dθ κ ξ= ψ� (16) where f κ and g κ represent adaptive positive learning rates. fuzzy system sets can provide up to the desired accuracy approximation as detailed in [8-9, 13, 22]. iv. stability and robustness analysis using the control action (11) in system (1), with f̂ and ĝ defined in (12) and (13), while parameters vectors f θ and g θ are adjusted by the adaptive laws (15) and (16) the closed loop system signals are bounded and the tracking voltage error converge asymptotically to zero. proof: the stability and robustness issue of the controller are addressed here by using lyapunov stability theory as follows: first, defining the optimal parameters of the fuzzy system: ( ) ( )ˆˆ arg min sup / nf f f f x r f x f x θ θ θ ∈ω ∈   = −   (17) ( ) ( )ˆ ˆarg min sup / ng g g g x r g x g x θ θ θ ∈ω ∈   = −   (18) where f ω and g ω are constraint sets for f θ and g θ , respectively, then (8) can be rewritten as: ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ˆ ˆˆ ˆ/ / 1ˆ ˆ g f g f t t t t f f g g f t e f x g x d g x d g x d x x d β θ θ ε θ θ ξ θ θ ξ α ψ = + + + − = + − + − − ψ � (19) where 0 ref v =� , and ε is the minimum approximation error defined by: ( )ˆ ˆ ˆˆ( ) ( / ) ( ) ( / )f f ff x f x g x g x dε θ θ= − + − (20) letting ( )ˆf f fϕ θ θ= − and ( )ˆg g gϕ θ θ= − one may rewrite (19) as: ( ) ( ) ( ) 1t t f g f x x x dε ϕ ξ ϕ ξ ξ α ψ = + + − ψ� (21) defining lyapunov function candidate: 21 1 1 2 t t f f g g f g v ϕ ϕ ϕ ϕ κ κ   = ψ +     (22) the time derivative of v leads to: ( ) ( ) ( )( ) ( )( ) 2 1 1 1 1 1 1 1 1 t t f f g g f g t t f g f t t f f g g f g t f f f f t g g f g g v x x d x x d ϕ ϕ ϕ ϕ κ κ ε ϕ ξ ϕ ξ α ϕ ϕ ϕ ϕ κ κ ϕ κ ξ ϕ α κ ϕ κ ξ ϕ ε κ =ψψ+ +   =ψ + + − ψ    + + ≤− ψ + ψ + + ψ + +ψ � � � � � � � � (23) where f f ϕ θ=− �� and g g ϕ θ=− �� . substituting (15) and (16) in (23), leads to: 21 v ε α ≤− ψ +ψ� (24) based on the universal approximation theorem [8-9], if 2 lε ∈ , then 2lψ∈ . from (17) and (18), one concludes that ψ is bounded as well as every term in (24). hence, , l∞ψ ψ∈ � , and using barbalat lemma [24-25] leads to: lim 0 t→∞ ψ = while the term εψ , in (24) is very small such that 0v ≤� . the error will asymptotically converge to zero. the stability of system (1) is therefore guaranteed. the control parameters used were selected on a trial-error basis thus not leading to optimum performance. this issue is addressed in the ensuing section using the pso algorithm. v. particle swarm optimization traditional optimization techniques among which linear programming, nonlinear programming, quadratic programming, and interior point methods are very sensitive to starting points and often diverge or converge to local optimums. more global nature-inspired optimization approaches have been developed [26-27]. pso, as evolutionary algorithm and genetic algorithm, is a heuristic and global search method which explores the search space to get to the global optimum, using a population-based algorithm modelled on swarm intelligence. seeking further enhancement of system control performance, optimization techniques have been used successfully in buck dc-dc converter [28]. in the present work, pso [29-32] is used to minimize an objective function thus obtaining optimum parameter settings of the proposed dc-dc converter fuzzy synergetic controller. the selected objective function to be minimized (itae) is defined by: 0 0 t reft v vitae dt= −∫ (25) where t is the time range of simulation and 0 refv v− the absolute value of the voltage error. engineering, technology & applied science research vol. 9, no. 6, 2019, 4984-4989 4987 www.etasr.com behih et al.: real-time investigation of an adaptive fuzzy synergetic controller for a dc-dc buck … a simplified schematic diagram of the proposed controller afsc and the interconnection of the techniques used is illustrated in figure 2. control parameters to be tuned through the optimization algorithm are a and β, with the aim to minimize the selected fitness objective function improving system response performance in terms of voltage tracking error. the objective function (25) evolution is shown in figure 3. fig. 2. overall scheme of the optimal afsc controller for a dc–dc buck converter fig. 3. objective function evolution vi. simulation results simulation results are given for a dc-dc converter with given parameters: vin=30v, l=50mh, c=470µf, r=25ω and vref=12v. optimized values for a and β are sought through pso and they were found to be: a=0.3210 and β=64.01 as shown in figures 4-5. performance and robustness of the proposed afsc for the dc-dc buck converter are investigated experimentally for different operating conditions through the use of a dspace board ds1104 and a dc-dc buck converter. the experimental results are shown in figures 6-8 with uncertainties on the system parameters. fig. 4. the parameter value trajectory α fig. 5. the parameter value trajectory β a load disturbance was considered in the first case, in which the system is subjected to strong perturbation as the load changes abruptly and periodically, the output voltage remains insensitive to fluctuations while inductor current follows its desired value with no steady-state error as shown in figure 6. considering the reference output voltage changes, from vref=12v to vref=5v the corresponding results are shown in figure 7. it can be easily concluded that the proposed controller achieves strong robustness and has satisfactory response under these types of disturbance and uncertainties. finally, further experimental test is carried out for a severe operating condition such as line variation from vin=45v to vin=24v. the system responses are shown in figure 8. from the results, one can see that afsc has remarkable performance despite the introduced perturbations. engineering, technology & applied science research vol. 9, no. 6, 2019, 4984-4989 4988 www.etasr.com behih et al.: real-time investigation of an adaptive fuzzy synergetic controller for a dc-dc buck … fig. 6. inductor current response (green line) and output voltage response (dark yellow line) fig. 7. inductor current response (green line) and output voltage response (dark yellow line) fig. 8. inductor current response (green line) and output voltage response (dark yellow line) vii. conclusion an adaptive fuzzy synergetic control scheme for a dc-dc buck converter has been presented. its stability has been provided through lyapunov synthesis with controller parameters optimized by pso algorithm. the real time implementation of the proposed approach overcame the necessity of a fully known mathematical model of the dc-dc converter even though the latter has been subjected to different operating conditions showing good overall performance, improved tracking, and faster response. references [1] s. mohamadian, m. h. khanzade, “a five-level current-source 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coimbatore – 641047, india kandavelkk@gmail.com b. nirmal kumar p.g. scholar anna university regional centre coimbatore coimbatore – 641047, india bnirmalkumar@live.com abstract— in pneumatic circuits, a solenoid valve is a key component for controlling and directing pneumatic energy. the solenoid valve functional performances are defined as response time parameters with respect to its actuations in terms of direction changing time. this paper aims to present response time parameters of solenoid valves under various working pressures. an experimental setup is employed in order to measure response time with reference to the input signals. the response time plays significant role for evaluating the valve performance in sensitive applications. the response time parameters includes the on delay, the off delay, the on time, the off time, the cycle time and the switching frequency. in this experimental investigation the influence of various input pressure conditions is recorded and tabulated. valves with varying orifice diameter are employed and the investigation reveals the influence of orifice diameter in response time variations. the newlyproposed six response time parameters can be used to rate and select the appropriate valve for various industrial applications. keywords-pneumatic 3/2 solenoid valve; response time; switching frequency i. introduction pneumatic control systems provide low cost automation to the industry with the added benefits of easy maintenance and greener environment. this technology aims to great flexibility in the energy used in intricate machine parts and complex manufacturing activities using a cheap power source [1]. pneumatic systems come with a good weight/power ratio, which makes them suitable for numerous applications in industries. in pneumatic applications, actuators are the resultant working element of transferring pneumatic energy into mechanical energy. the actuators’ movements are controlled by directional control solenoid valves. subsequently actuators are subjected to high friction forces which directly lead to a low output of the system. the actuator speed is the critical operation for controlling the subsequent machine activities. the servo-pneumatic switching valve has been widely used in the industry [2-4]. the valve response time has attracted considerable work to enhance its responsiveness based on various designs. pulse width modulation (pwm) has been proposed to control the velocity and the position of the pneumatic cylinder in [3]. the pneumatic actuators functionality has been presented as a linear time varying mathematical model in [5]. the static characteristics of pwm have been discussed with a mathematical model for calculating maximum operating modulation ratio in [6]. in continuation to this, modified pulse width modulation (mpwm) has been implemented to control hydraulic actuators in [7]. the servo system considered in [8] described the performance evaluation method, whereby the desired force can be controlled in steadystate working condition with speed disturbance. a pneumatic servo-system proposed in [9] was realized with digital on-off valves, instead of high cost proportional valves, to obtain a satisfactory dynamic performance by using modulation techniques. the mpwm techniques are linked with performance deterioration due to the abrupt change in external loads and have been further rectified in [10] with the use of learning vector quantization neural networks (lvqnn). the dynamic model was then implemented with a new solenoid valve to describe the switching characteristic in [11]. the switching type on-off valves (small in size, simple in construction, low cost, high flow rate gain) are preferred to for the control of pneumatic actuators. the evaluation method described in [12], investigated the performance of electropneumatic valves used in air-powered engines and analyzed the on delay time, the full opening/closing time along with the seating velocity of the valves. in [13], further investigation of the dynamic analysis of a pilot-operated two-stage solenoid valve used in pneumatic system was conducted. the development [14] of al-fe soft magnetic materials led to the redesign of the structure of magnetic circuits employed to achieve rapid response and strong magnetic force. a pwm-driven pneumatic fast switching valve was presented in [15] to identify spool position at various conditions. two types of electro-pneumatic valves are used for the control of the fluid flow of a pneumatic actuator. these are the continuously acting servo/proportional valves and the onoff switching valves [15]. the response of these valves is a etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 502-505 503 www.etasr.com venkataraman et al.: investigations of response time parameters of a pneumatic 3/2 direct acting… critical operation for the control of the subsequent actuator speeds. the servo/proportional valves are used to achieve high linear control accuracy in pneumatic actuators, but their complex structure leads to high cost. the other type of on-off type solenoid valves are subgrouped as direct acting solenoid valves and pilot operated. this work focuses on the establishment of a measuring kit for measuring both coil and valve response time parameters with testing procedures. investigation of response time behavior against various working pressures is presented. response time parameters such as: on delay, off delay, on time, off time, cycle time and switching frequency are investigated. valves with varying orifice diameters are employed and the investigation reveals the influence of nominal diameter in response time variations. ii. response time parameters the response time of a solenoid valve is measured as the lagging time or time delay between the input and output signals. the response time of the solenoid valve can be analyzed as the response of the solenoid coil and of the mechanical valve the response time parameter of coil is used to calculate the switching frequency for blowing applications. similarly, the response time of the mechanical valve is calculated based on the lagging time (or time delay) between the input (electrical signal) and the output (pressure). this valve uses as an input a dc supply to deliver the pressurized air. the air output response depends on the following factors namely: area of the air flow passages throughout the circuit, fitting/connector’s internal diameters, mounting positions and the distances from the cylinder, directional control, flow control and rapid relief valves’ nominal width for air flow, pipe/tube internal diameters and working element frictional force. the response time parameter and measurement methods are discussed in [10, 16] as characteristics of the on/off solenoid valve. these characteristics are focused on the control of the position of a pneumatic cylinder in the system. this includes dead-time, the rise time of valve and the maximum current. additional parameters are the: valve opening signal, on duty ratio of valve for one mpwm cycle, mpwm cycle time and continuous time. the parameters are analyzed in [11] considering the static and dynamic characteristics of the valve by solving equations, using mathematical models in matlab and simulink. the parameters of disc time delay, disc travel time and total opening time of the valve are presented. total closing time is defined as the sum of closing delay time and the disc travel time of the valve closing. the analysis in [15] illustrates plots and compared graphs for current consumption rates at 24 v and 15 v versus time to attain the maximum rated current, used to find out the spool position against duty cycle. the parameter discussion in existing works reveals that the integrated approach of input signals and final pressure output of valve responsive time needs further improvement. the valve response time parameters are investigated under the integrated conditions of signal input and output pressure. the response parameters are on delay (t1), on time (t2), off delay (t3), off time (t4), coil’s switching frequency (csf), valve’s working frequency (vwf).   fig. 1. response parameters diagram the response time parameters are illustrated in figure 1 for 24 v signal input and output pressure. the input signal curve shows the supply input time, pulse width and supply off time. the line pressure curve indicates the pressure on, maximum output pressure and pressure off. on delay (t1) is measured as the lagging time or time difference between the coil energizing and the pressure just starting to shoot-up. on time (t2) is measured as the maximum (100%) inlet air pressure that reached the outlet. off delay (t3) is measured as the lagging time or time difference between the coil de-energizing and the pressure just starting to decrease from the maximum. off time (t4) can be defined as the time taken to shut off the valve pressure completely. the response time is measured in milli seconds (ms) and coil’s switching frequency (csf) and valve’s working frequency (vwf) are calculated as:  coil’s switching frequency (csf) = 1000/(t1+t3) hz  valve’s working frequency (vwf) = 1000/ (t2+t4) hz iii. response time measuring kit a response time measuring experimental test kit includes the compressor unit, the air pressure reservoir with a capacity of 3000 mm3, the pressure regulator and the response time measuring unit. the response time measuring unit is presented in figure 2 with a of 3/2 normally closed solenoid valve as a test specimen, a pulse generator, a pressure transducer, a cathode ray oscilloscope (cro), a 24 v dc power supply and a relay unit. pressure transducer (4-20 ma) and pulse generator (24 v dc signals and pulse width ranging from 1 to 999 ms) are preferred in this unit to get more accuracy and a better least count value. the working principle of the measuring kit is represented in figure 3. the regulated input air pressure is supplied to the solenoid valve, which is fixed in the measuring unit. the pulse generator generates a 24 v dc input signal to the 8 watt coil, etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 502-505 504 www.etasr.com venkataraman et al.: investigations of response time parameters of a pneumatic 3/2 direct acting… which causes the plunger movement. the plunger movement permits the air flow from the upstream to the downstream side. fig. 2. response time measuring unit fig. 3. block diagram of measuring kit the pulse generation is predefined as 30 ms to ensure the maximum opening of plunger movement. the measurement procedure of the current in the solenoid valve applied, is the one proposed in [11] with the ‘on’ signal applied to the valve for 100 ms. the current was measured from the voltage drop across the resistance, which is serially connected to the solenoid valve. the measured current is captured as an input voltage signal graph in the cro unit. simultaneously the pressure transmitter senses and converts the downstream pressure to the corresponding output signal which is captured as an output pressure graph in the cro unit. fixed and movable cursors are available in the cro output for measuring the time lagging or time difference of input supply and output pressure. iv. results two types of 3/2 nc solenoid valves with different orifice diameters are employed to measure the four response parameters namely t1, t2, t3 and t4. further, csf and vwf are calculated. the response parameters of the solenoid valve of orifice diameter of 1.2 mm are presented in table i and for the one with orifice diameter of 2.5 mm are presented in table ii. seven tests are conducted with pressure ranging between 1 bar and 7 bar as shown in table i and ii. table i. solenoid valve of 1.2 mm orifice diameter. test no. input air pressure (bar) t1 (ms) t2 (ms) t3 (ms) t4 (ms) csf (hz) vwf (hz) 1 1 14 40 8 43 22 83 2 2 14 61 8 73 22 134 3 3 14 66 8 82 22 148 4 4 14 68 8 92 22 160 5 5 14 70 8 95 22 165 6 6 14 71 8 113 22 184 7 7 14 72 8 116 22 188 table ii. solenoid valve of 2.5 mm orifice diameter. test no. input air pressure (bar) t1 (ms) t2 (ms) t3 (ms) t4 (ms) csf (hz) vwf (hz) 1 1 11 20.0 10 18.4 21 38.4 2 2 11 21.0 10 25.6 21 46.6 3 3 11 23.6 10 32.8 21 56.4 4 4 11 24.8 10 38.4 21 63.2 5 5 11 25.6 10 42.0 21 67.8 6 6 11 25.7 10 46.4 21 72.1 7 7 11 27.1 10 55.6 21 82.7 v. discussions the above parameter data reveals that t1 for the 1.2 mm orifice is 14 ms and for the 2.5 orifice is 11 ms. similarly, t3 is 8 ms for the 1.2 mm orifice and 10 ms for the 2.5 mm orifice. the study reveals t1 and t3 to be constant for varying pressure conditions. the difference between t1 and t3 is 6 ms for the 1.2 mm valve and 1 ms for the 2.5 mm valve. this implies that an increase in nozzle diameter brings down the gap between t1 and t3. the increase in orifice diameter of the valve reduces t1 due to the increase of thrust to the plunger whereas t3 increases due to the time delay in exhausting. the input pressure correspondingly increases t2 and t4 in both valves. the double increment of orifice diameter (1.2 mm to 2.5 mm) causes a 50% reduction in the total cycle time (vwf). in figure 4, the valve working frequency for various pressure ranges is plotted for the 1.2 mm orifice and the 2.5 mm orifice valves. fig. 4. input air pressure vs. valve’s working frequency etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 502-505 505 www.etasr.com venkataraman et al.: investigations of response time parameters of a pneumatic 3/2 direct acting… the on delay time t1 reveals the behaviour of electromechanical component’s response with respect to the input signal during magnetisation whereas the off delay time t3 shows the behaviour during de-magnetisation. the response time parameter of coil i.e; t1 & t3 are the very important parameters required to calculate the switching frequency for blowing and sorting applications where the outlet pressure is opened to atmosphere. similarly the on time t2 and t4 can be used to calculate the working frequency of the valve at loaded conditions of any pneumatic system (valve’s outlet pressure is connected to any type of pneumatic actuator). vi. conclusions in this paper, the behavior of the response time parameters of pneumatic solenoid valves with various working pressures is investigated with the establishment of measurement methods and test results. four parameters are measured and the remaining 2 parameters are calculated for two types of valves. the importance and the usages of each and every response parameter are discussed. it is shown that the orifice diameters and input pressure influence the response parameter and the cycle time of the valve this work can be extended further in order to reduce the difference between on delay and off delay timings with increased orifice diameter. references [1] b. w. anderson, the analysis and design of pneumatic systems, john wiley & sons, 1967 [2] s. r. goldstein, h. h. richardson, “a differential pulse-length modulated pneumatic servo utilizing floating-flapper-disc switching valves”, journal of basic engineering, vol. 90, no. 2, pp. 143-151, 1968 [3] t. noritsugu, “development of pwm mode electro-pneumatic servomechanism, part i: speed control of a pneumatic cylinder”, journal of fluid control. vol. 17, no. 1, pp. 65-80, 1986 [4] t. noritsugu, “development of pwm mode electro-pneumatic servomechanism, part ii: position control of a pneumatic cylinder”, journal of fluid control, vol. 17, no. 2, pp. 7-28, 1987 [5] c. kunt, r. singh, “a linear time varying model for on-off valve controlled pneumatic actuators”, journal of dynamic systems, measurement, and control, vol. 112, no. 4, pp. 740-747, 1990 [6] n. ye, s. scavarda, m. betemps, a. jutard, “models of a pneumatic pwm solenoid valve for engineering applications”, journal of dynamic systems, measurement, and control, vol. 114, no. 4, pp. 680-688, 1992 [7] y. suematsu, h. yamada, t. tsukamoto, t. muto, “digital control of electrohydraulic servo system operated by differential pulse width modulation”, jsme international journal, series c, dynamics, control, robotics, design and manufacturing vol. 36, no. 1, pp. 61-68, 1993 [8] m. sorli, s. pastorelli, “performance of a pneumatic force controlling servosystem: influence of valves conductance”, robotics and autonomous systems, vol. 30, no. 3, pp. 283-300, 2000 [9] g. belforte, s. mauro, g. mattiazzo, “a method for increasing the dynamic performance of pneumatic servosystems with digital valves”, mechatronics, vol. 14, no. 10, pp. 1105-1120, 2004 [10] k. ahn, s. yokota, “intelligent switching control of pneumatic actuators using on/off solenoid valves”, mechatronics. vol. 15, no. 6, pp. 683702, 2005 [11] e. e. topcu, i. yuksel, z. kamis, “development of electro-pneumatic fast switching valve and investigation of its characteristics”, mechatronics, vol. 16, no. 6, pp. 365-378, 2006 [12] p. chen, x. yu, l. liu, “simulation and experimental study of electropneumatic valve used in air-powered engine”, journal of zhejiang university sicence a, vol. 10 no. 3, pp. 377-383. 2009 [13] q. ye, j. chen, “dynamic analysis of a pilot-operated two-stage solenoid valve used in pneumatic system”, simulation modelling practice and theory, vol. 17, no. 5, pp. 794-816, 2009 [14] q. wang, f. yang, q. yang, j. chen, h. guan, “experimental analysis of new high-speed powerful digital solenoid valves”, energy conversion and management, vol. 52, no. 5, pp. 2309-2313, 2011 [15] m. taghizadeh, a. ghaffari, f. najafi, “modeling and identification of a solenoid valve for pwm control application”, comptes rendus mécanique. vol. 337, no. 3, pp. 131-140, 2009 [16] e. gallasch, m. fend, d. rafolt, r. nardone, a. kunz, m. kronbichler, r. beisteiner, s. golaszewski, “cuff-type pneumatic stimulator for studying somatosensory evoked responses with fmri”, neuroimage, vol. 50, no. 3, pp. 1067-1073, 2010 microsoft word etasr_v13_n4_pp11157-11165_needs_update engineering, technology & applied science research vol. 13, no. 4, 2023, 11157-11165 11157 www.etasr.com srivastava & kumar: the impact of road side friction on the traffic flow of arterial roads in varanasi the impact of road side friction on the traffic flow of arterial roads in varanasi kartik srivastava department of architecture and planning, national institute of technology patna, india kartikshri128@gmail.com (corresponding author) ajay kumar department of architecture and planning, national institute of technology patna, india arajay@nitp.ac.in received: 1 april 2023 | revised: 19 april 2023 | accepted: 27 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5897 abstract varanasi's prominence as a cultural and historical center means it receives visitors from all over the world. the city's tourism industry is a boon to the local economy. better transportation infrastructure is crucial to attracting more tourists and increasing revenue. varanasi is currently experiencing terrible difficulties due to various roadside frictional activities. vehicle ownership grows in tandem with population growth. the increase in the number of vehicles on the road significantly impacts the reliability of the transportation network since land availability is fixed. the various roadside frictional activities usually found in the streets of varanasi are on-street parking, pedestrian crossing, and non-motorized vehicles (nmvs). there are not enough legal on-street parking and segregated lanes for nmvs/slow-moving vehicles or demarcation for pedestrian movements in the old city of varanasi. vehicles in varanasi are traditionally parked on the street due to the narrow carriageways. slow-moving vehicles are forced to move with fast-moving vehicles, and pedestrian crossings affect traffic flow. integrated movement of slowmoving vehicles and rapid-moving vehicles affects traffic speed, pedestrian crossings impact the level of service (los), and on-street parking results in the reduction of the effective carriageway width and, hence, road capacity. this paper aims to identify the impact of pedestrian crossings, nmvs, and on-street parking on the traffic flow, speed, capacity, and los of urban arterial roads in varanasi. to achieve this objective, two case studies were considered: the base section (with minimum side friction) and the friction section (with maximum side friction). the videography method was used for data collection. nine hours of data were collected from 9:30 am to 6:30 pm. the video was played on the screen for data extraction. the speed model was developed by using fundamental diagram methods. speed-density curve was drawn using greenshield’s model. the speed-flow curve was derived from the speed-density curve to estimate the capacity at the base and friction sections. reduction in capacity was determined by comparing friction section capacity with base section capacity. v/c ratio of a particular road compared with the v/c value provided by irc 106 to predict los. a correlation model was developed between the percentage reduction in capacity and road width. increase in parking, the proportion of nmvs, and pedestrian crossing frequency reduce the traffic flow. it was observed that a 34.10% capacity loss occurs at a 29.31% reduction in effective width, and a 40.54% loss occurs at a 40.98% reduction in effective width. roads with frictional activities affected its level of service up to los-e (for the bhelupur section). keywords-side friction; speed; capacity; level of service; non-motorized vehicles; on-street parking; pedestrian crossing; traffic flow; linear regression; correlation i. introduction side frictional activities take place on or along the road and disrupt traffic flow. varanasi, the cultural capital of india, attracts visitors from all over the globe. on-street parking, nonmotorized transportation, and pedestrian crossing are all activities that add friction to the streets of varanasi. these activities affect traffic flow characteristics in several ways: they result in road capacity reduction, impact speed, and affect the level of service (los). a vehicle requires parking space at the start and end of its journey. the significant growth in vehicular traffic has increased the need for parking in urban centers. scarce parking can interrupt traffic flow and produce congestion. in varanasi, on-street parking is a commonality, since there simply aren't enough legal on-street parking places, so people use to park their vehicles on the street, hence inducing a reduction in effective carriageway width. also, there is no segregated lane for non-motorized transport, which forces slowand fast-moving vehicles to flow in the same lane, which causes a reduction in traffic flow speed and los. pedestrian crossing is another common problem in varanasi. engineering, technology & applied science research vol. 13, no. 4, 2023, 11157-11165 11158 www.etasr.com srivastava & kumar: the impact of road side friction on the traffic flow of arterial roads in varanasi ii. literature review in [1], various side friction elements were considered, such as on-street parking, city buses stopping on the roadway, exit/entry vehicles, and vehicles about to turn. the study proposed a novel formula to update the indonesian highway capacity manual to estimate the speed and capacity of urban highways with significant side friction. in [2, 3], several forms of roadside frictional parameters were discussed along with their impact on urban road capacity, highlighting the relationship between side friction parameters, road capacity, and los. these studies showed that capacity reduction in urban streets depends on roadside activity and varies with side friction. loss of capacity on urban highways is caused by various factors, including roadside activity such as on-street parking, pedestrian movement, the presence of street vendors, the lack of lateral clearance and lane discipline, and diverse traffic, which is particularly prevalent in developing countries like india. in [4], a microscopic simulation model was developed to investigate the impact of bus stops on mixed traffic movement, focusing on reducing traffic flow rates. this study evaluated the impact of bus stops, which act as side friction on urban traffic. based on the collected data, several areas for further work were recommended, as very few studies examine mixed traffic situations [5, 6]. in [7], three different side friction factors were used in a survey (on-street parking, bus bay stops, and curbside bus stops) and their impact on traffic quality performance was examined. this study showed an average speed drop due to side friction, a reduction in stream speed of 49-57% due to bus stops and bays, and a loss of 45-67% in speed due to on-street parking. this study used dynamic and static pcu (passenger car unit) values. as a result of using these two different types of pcu values resulted in a 10-53% capacity reduction in bus bays and bus stops and about 28-63% due to on-street parking. authors in [8-10] investigated urban arterial roads, finding that parked and stopped vehicles act as frictional elements that impact traffic flow, los, speed, and delay. on-street parking has been highlighted as a substantial source of side friction in urban arterial roads, and there is a relationship between the presence of on-street parking and the reduction in stream speed. according to [11-13], the impact of on-street parking as a side friction element on urban arterial roads results in a slowdown in traffic flow ranging from 15 to 44% or 5.1 to 21 km/h. in [13], parking density was considered a side friction element. the survey results showed that parking density on urban arterial roads harms average traffic flow, with a decrease of around 13 km/h for every 100 vehicles/km increase in parking density. in [15], various types of side frictional activities were examined, using small simulation models to evaluate how bus stops impact mixed traffic movement and their relation to the reduction in travel speed. in [2, 8], parked and stopped automobiles were studied, along with various other factors. these studies showed that parked and stopped vehicles are critical side frictional elements, as they harm the regular traffic flow, speed, capacity, and los more than other side frictional factors, such as pedestrian movements. in [9, 14], t-junctions and bus stops were characterized as static features contributing to traffic congestion. on the other hand, static factors can be addressed by upgrading the geometric aspects of roadways to increase los. roadside friction elements found in urban roads in asian countries were pedestrians, stopped vehicles, parking, and access to roadside premises. based on the weights assigned to each side friction element, side friction classes were developed for urban and interurban roads. in [16], motorcycle taxis were found to add another degree of friction when parking or loading and unloading passengers. in [17], on-street parking produced a decrease in stream speed, ranging from 15 to 44% or 5.1 to 21 km/h. in [18], speed–flow diagrams at various flow levels were plotted to analyze the collective effect of all these factors. the capacity of urban motorways and four-lane two ways were found as 4600 pcu/ and 5700 pcu/h, which further matched with the capacity values recognized in the south korean manual and us hcm. the study concluded that indonesian roads function poorer than those in the usa and south korea. drivers' speed choices are expressively affected by crossing pedestrians, engaged curbside bus stops and confrontation with vehicles in the opposing direction [19]. the effect of crossing pedestrians on stream speed was analyzed using the networkbased speed–flow relationships by [20]. authors in [21] established a microscopic simulation model in vissim to simulate pedestrian flow properties by coding pedestrians as a vehicle that follows the pedestrian flow characteristics despite many issues related to pedestrian behavior, pedestrian route choice decisions, and multidirectional flow. authors in [22] demonstrated the effect of operating speed on the capacity of a midblock section of urban road using field data collected at 12 midblock sections in india. authors in [23] evaluated the effect of the pedestrian refuge island on the speed of vehicles and, accordingly, the effects on the probability variations of fatal accidents. authors in [24] used the simulation approach to study pedestrian crossing behaviors. they concluded that pedestrians show more tolerance in waiting time in developing countries as compared to developed countries. due to the high percentage of heavy vehicles, this study used dynamic and static pcu values. as a result, a 10-53% capacity reduction was observed in bus bays and bus stops and about 28-63% was attributed to on-street parking. authors in [25] included nmvs (non-motorized vehicles) as a source of side friction. he created a speed model for this purpose, which is based on the ratio of nmvs. a 10% rise in the nmv ratio, according to the model, would result in a 0.8 mile per hour (1.29 km/h) reduction in average traffic flow speed. the inclusion of nmvs in the traffic volume classification was suggested because cycle rickshaws generate greater side friction than bicycles. authors in [26, 27] identified the degree of correlation between nmvs and traffic performance. the side frictional element (nmvs) is further divided into various subcategories, such as the proportion of nmvs, the proportion of bicycles, the proportion of cycle rickshaws, the proportion of handcarts, and the percentage of nmvs that travel beyond 20% of the roadway width from the edge. the correlation values of n-3 and n-4 were the highest among all the subcategories. the literature review reveals that most researchers tried to find the impact of various side frictional activities on traffic characteristics individually. only some studies have been carried out on more than one and maximum two side friction parameters combined. to the best of our knowledge, no study engineering, technology & applied science research vol. 13, no. 4, 2023, 11157-11165 11159 www.etasr.com srivastava & kumar: the impact of road side friction on the traffic flow of arterial roads in varanasi related to the combined effect of on-street parking, nmv, and pedestrian crossing on traffic flow, speed, capacity, and los has been attempted for mixed traffic conditions. the present research attempts to identify the impact of these 3 side frictional parameters on various traffic characteristics like traffic flow, speed, capacity, and los. iii. research objectives the present work aims to study the impact of on-street parking, pedestrian crossing, and nmvs on traffic flow, traffic speed, road capacity, and los on the urban arterial roads of varanasi. iv. methodology study stretch selection: to achieve the objective of this research, firstly, two types of study stretches were chosen: base section (bs), with minimum side friction and friction section (fs), with maximum side friction. these sections are away from the intersection to avoid its effect. seven bss and seven fss were selected based on the similarity of road characteristics. planning phase: in this stage, two survey methods were prepared. the first one is a manual survey to collect geometric details of the road. the survey format (traffic volume count, parking, speed, and pedestrian movements) were prepared to observe data manually. the second is the videographic method. a 60 m stretch was marked to be captured in the video. the camera was mounted at a certain height and the time of survey was recorded. data collection: data were collected on both stretches for 9 hours per day, from 9:30 am to 6:30 pm. the data were collected from 14 mid-block sections (7 bss and 7 fss) of a 2lane urban arterial road. data regarding classified traffic volume count, peak hour volume, peak hour duration, number of on-street parking, parking duration, speed of traffic flow, traffic density, and to examine the los were extracted from the recorded videos. data extraction: the recorded videos were played on screen, individual vehicles were counted at an interval of 15 min. these data were used to calculate the classified traffic volume count, proportion of non-motorized vehicles, peak hour volume, peak hour factors, peak hour duration and heterogeneous traffic flow. to understand the on-street parking demand during peak hours, the parking vehicles were counted and the parking duration was noted. the pedestrian crossings during peak hours were counted. the video data were used for speed measurements. the entry and exit times of every vehicle over a 60 m trap length were observed. speed was calculated for the individual vehicles by dividing the 60 m trap length with the entry-exit time difference of a vehicle. data analysis: by using peak hour factor, traffic flows at bss and fss were calculated. the fs traffic flow rate was compared with bss' to determine the reduction in traffic flow rate. the video data were used for speed measurement. individual vehicles' entry and exit times over a 60 m trap length were observed. speed was calculated for individual vehicles by dividing the entry-exit time difference of a vehicle by 60 m trap length. the obtained space mean speed of the vehicles was used to calculate the traffic speed. the data set of speed and flow for all base and friction sections were pooled together and a speed prediction model was developed. by using the speedflow curve, the capacity for each parking number and nmv proportion was determined. all the observed capacities at the base and friction sections were compared, and the reduced capacity due to on-street parking and nmvs is calculated. after this, the parking numbers were correlated with the available effective width and a relationship between capacity reduction and available effective width was developed. finally, the volume/capacity (v/c) ratios were calculated for the fs. the value obtained from the v/c ratio was compared with the v/c ratio provided by the indian road congress (irc) to measure the los. v. data collection this study focuses on the impact of on-street parking on road capacity, speed, and los, the result of non-motorized transport on traffic flow speed and los, and the effect of pedestrian crossings on rate and los. to achieve the objective, seven midblock 2-lane arterial sections with minimum side frictions were selected. indiranagar, bisesarganj, sonia, salarpur, lahurabeer, dlw campus and bhu (a1, b1, c1, d1, e1, f1 and g1), were named as the bss. similarly, seven midblock 2-lane arterial sections, with side frictions, were selected with different levels of parking maneuvers, nmv, and pedestrian crossing. chitaipur, godowlia, benia, sarnath, sigra, dlw and bhelupur (a2, b2, c2, d2, e2, f2 and g2), respectively, were named as the fss. both manual and videographic methods were used for data collection. the data were collected for 9 hours, from 9:30 am to 6:30 pm, on both types of stretches (bs and fs) on weekdays only. a 60 m stretch was chosen for data collection. the global coordinates of each roads are: indira nagar (25°16'25.77" n, 82°58'7.34" e), bisesarganj (25°19'26.89" n, 82°59'30.05" e, sonia (25°21'14.49" n, 83°1'25.04" e), salarpur (25°21'12.07" n, 83°2'19.76" e), lahurabeer (25°19'8.44" n, 83°0'5.23" e), dlw campus (25°17'11.05" n, 82°58'9.21" e), bhu(25°16'3.79" n, 82°59'28.53" e), chitaipur (25°16'18.72" n, 82°58'3.47" e), godowlia (25°18'36.27" n, 83°0'34.74" e), benia (25°19'3.28" n, 83°0'15.89" e), sarnath (25°22'34.2" n, 83°1'21.76" e), sigra (25°18'39.89" n, 82°59'11.19" e), dlw (25°17'11.05" n, 82°58'9.21" e), and bhelupur (25°18'14.29" n, 82°59'24.03" e). from the inventory survey, geometric details of the road section, carriageway width, right of way, onstreet parking, road surface quality, street vendors etc., were obtained. the classified traffic volume count survey was conducted manually (survey format) and by videographic survey. the data were collected at 15 min intervals. from the traffic volume count survey, traffic composition, peak hour traffic, peak hour volume, directional split, peak hour factor, and proportion of motorized and non-motorized vehicles were all measured to learn more about the traffic characteristics of each place. for counting flow, a video is played, and each vehicle category is counted per min. the video data were used for speed measurements for a 60 m trap length entry and the exit time of vehicles was noted. in order to calculate the speed of individual vehicles, the 60 m trap length was divided by the interval exit time – entry time. the same procedure was applied engineering, technology & applied science research vol. 13, no. 4, 2023, 11157-11165 11160 www.etasr.com srivastava & kumar: the impact of road side friction on the traffic flow of arterial roads in varanasi for both bs and fs. from the parking survey, the number of parking maneuvers was calculated for the peak hours of the respective sections, the parking duration, the types of parked vehicles, the peak hour parking demand, the occupancy level, and the proportion of the road occupied by on-street parking were noted. from the pedestrian survey, the number of pedestrian crossings during peak hours was observed in 15 min intervals. tables i and ii represent the vehicular composition of the bss and fss chosen in this study. the percentages of motorized and nmvs are calculated from these data and are used in further analysis. as the traffic is heterogeneous, in order to convert the stream into homogenous traffic, the data were used with pcu to get homogenous traffic conditions. this process simplifies the analysis phase. tables iii and iv represent the traffic volume count at the bss and fss. the collected data were used to calculate peak hour (from 9:30 am to 11:30 am) volume, as shown in table xi. a parking survey was conducted at both sections by videographic survey from 9:30 am to 6:30 pm. it can be observed in table v that all roads have on-street parking issues. the parking location on each road shows all roads having an unauthorized type of parking. they determine the on-street parking demand during peak hours and identify its impact on speed, capacity, and los. the parking maneuvers during peak hours in various vehicle categories are shown in table vi. vi. results and discussion a. impact of on-street parking, nmv, and pedestrian crossing on traffic flow the peak time of the bs (the hour of the day with the highest traffic volume for that section) can be seen in tables iii-iv. the peak hour volumes of the bss and the fss are shown in tablevii. table i. vehicular composition at the base sections bs νame vehicular composition (in % age) car 2w 3w bus/truck sgv lgv cycle others a1 indira nagar 23.97 36.03 22.37 3.26 7.63 4.74 0.33 1.67 b1 bisesarganj 18.69 39.37 19.32 5.68 6.21 7.23 1.47 2.03 c1 sonia 18.36 41.12 20.87 4.96 5.26 6.66 1.33 1.98 d1 salarpur 24.32 39.67 19.46 5.32 4.21 4.66 1.20 1.16 e1 lahurabeer 22.96 40.48 17.56 5.03 4.52 5.72 1.60 2.09 f1 dlwcampus 28.66 42.39 15.23 2.01 5.62 0.92 3.37 1.83 g1 bhu 22.84 42.98 18.76 3.20 3.96 1.82 5.23 1.21 * sgv = small goods vehicle, lgv = large goods vehicle table ii. vehicular composition at the friction sectioνs fs name vehicular composition (in % age) car 2w 3w bus/truck sgv lgv cycle others a2 chitaipur 25.34 38.66 20.09 4.91 3.26 4.74 0.87 2.13 b2 godowlia 13.86 42.24 21.14 2.00 8.76 7.29 1.83 2.88 c2 benia 17.28 43.13 22.18 2.90 7.87 2.10 1.60 2.40 d2 sarnath 26.21 38.97 19.23 4.77 3.97 5.03 0.80 1.20 e2 sigra 23.07 37.93 20.91 6.09 3.26 5.74 1.76 1.24 f2 dlw 29.87 41.13 13.66 2.34 7.98 1.03 2.02 1.97 g2 bhelupur 21.07 44.93 19.02 2.79 4.21 1.90 4.98 1.10 table iii. traffic volume counts at the base section bs 9:30-9:45 9:46-10:00 10:01-10:15 10:16-10:30 10:31-10:45 10:46-11:00 11:01-11:15 11:16-11:30 a1 277 232 201 211 159 248 152 176 b1 348 346 350 337 232 221 388 279 c1 233 247 242 239 198 202 187 203 d1 339 347 350 344 336 297 252 289 e1 296 289 250 232 249 286 192 132 f1 342 375 326 266 298 287 232 198 g1 226 268 275 266 295 286 176 145 table iv. traffic volume count at the friction section fs 9:30-9:45 9:46-10:00 10:01-10:15 10:16-10:30 10:31-10:45 10:46-11:00 11:01-11:15 11:16-11:30 a2 154 146 186 183 198 181 163 159 b2 282 276 206 216 211 211 142 144 c2 186 158 142 153 182 182 127 113 d2 289 248 252 244 179 191 188 136 e2 141 137 143 141 139 127 132 138 f2 214 273 268 152 189 197 157 196 g2 108 113 137 109 111 88 98 108 engineering, technology & applied science research vol. 13, no. 4, 2023, 11157-11165 11161 www.etasr.com srivastava & kumar: the impact of road side friction on the traffic flow of arterial roads in varanasi table v. on-street parking locations bs place type fs place type lhs rhs lhs rhs a1 * un-authorized a2 * un-authorized b1 * un-authorized b2 * un-authorized c1 * un-authorized c2 * un-authorized d1 * un-authorized d2 * un-authorized e1 un-authorized e2 * un-authorized f1 * * un-authorized f2 * un-authorized g1 * un-authorized g2 * un-authorized * lhs = left hand side, rhs = right hand side table vi. parking manoeuvres bs parking manoeuvres (peak hours) car 2w auto lcv truck other total a1 1 2 2 2 7 b1 4 1 5 c1 1 1 1 3 d1 1 3 1 2 7 e1 1 1 f1 1 1 2 g1 1 1 2 a2 13 36 17 3 1 6 76 b2 18 27 17 7 4 73 c2 8 24 32 12 8 84 d2 12 32 16 9 2 6 80 e2 16 36 18 3 2 9 84 f2 18 32 21 7 11 89 g2 16 28 15 5 9 73 table vii. peak hour volume bs peak hour volume fs peak hour volume a1 921 a2 748 b1 1381 b2 980 c1 961 c2 639 d1 1380 d2 1033 e1 1067 e2 562 f1 1309 f2 907 g1 1122 g2 470 b. peak hour factor (phf) phf is the hourly volume during the analysis hour divided by the 4 × peak 15-minute flow rate within the analysis hour. the phf is also considered a measure to estimate traffic demand fluctuations and traffic flow rate within the peak hour. phf is used to calculate the base and friction section traffic flow rate during peak hours. as shown in table ix, the traffic flow rate can be calculated by peak hour volume with the phf. table x shows that due to side frictional activities, the reduction percentage in traffic flow ranged from 36.67% to 66.13%. bhelupur stretch is majorly impacted by side frictional activities as a reduction in traffic flow is 66.13%, while the chitaipur stretch is the least affected with a reduction in traffic flow of 36.67%. as shown in figure 1, due to various side frictional activities at the fs with respect to the bs (free from any side friction), the reduction in traffic flow can be observed due to on-street parking, nmvs and pedestrian crossing are directly proportional to the reduction percentage in traffic flow. the r 2 value of 0. 896 for the created model indicates high dependability. table viii. traffic flow rate bs phf at the bs traffic flow rate at the bs (veh/hr) a1 0.83 1110 b1 0.98 1410 c1 0.97 991 d1 0.98 1409 e1 0.90 1186 f1 0.87 1505 g1 0.95 1181 fs phf at the fs traffic flow rate at the fs (veh/hr) a2 0.94 703 b2 0.86 843 c2 0.85 543 d2 0.89 919 e2 0.98 551 f2 0.83 753 g2 0.85 400 table ix. reduction percentage in traffic flow due to frictional activities reduction in traffic flow (veh/h)r traffic flow reduction percentage (%) 407 36.67 567 40.21 448 45.20 490 34.78 635 53.54 750 49.83 781 66.13 fig. 1. flow-density relationship at fs c. speed-density relationship three fundamental parameters, traffic flow, speed and density, were used to develop the relationship between traffic speed and density of the 14 sections. space mean speed data extracted from videography were used to predict traffic speed. the speed of traffic flow in each section was determined using the 85 th percentile cumulative method as in (1). traffic volume data were converted into passenger car units to develop a speed-flow relationship. each vehicle type was found in mixed traffic conditions, so it was more challenging to predict the density and capacity of the road. to analyze the mixed scenario space, the mean speed used in this research. space mean speed (sms) of vehicles was noted in the presence of on-street parking and nmvs. the sms for the indiranagar section (a1) is shown in table xi. the values of the speed of traffic flow at the bs and the fs in the presence of on-street parking and nmvs are shown in table xii. table xiii and figure 2 show the reduction in speed in the fss. the r 2 value of 0.865 for the engineering, technology & applied science research vol. 13, no. 4, 2023, 11157-11165 11162 www.etasr.com srivastava & kumar: the impact of road side friction on the traffic flow of arterial roads in varanasi created model indicates high dependability. these speed data were further used in the prediction of road capacity. table x. traffic speed at base and friction section bs traffic speed at bs fs traffic speed at fs a1 29.081 km/hr a2 13.392 km/hr b1 32.173 km/hr b2 14.637 km/hr c1 32.112 km/hr c2 13.338 km/hr d1 30.694 km/hr d2 14.194 km/hr e1 29.963 km/hr e2 16.196 km/hr f1 27.252 km/hr f2 16.826 km/hr g1 29.246 km/hr g2 14.324 km/hr table xi. traffic flow speed parking manoeuvres at bs pedestrian crossing at bs nmv at bs parking manoeuvres at fs nmv at fs traffic speed (km/hr) bs fs 7 11 9 76 23 29.081 13.392 5 8 4 73 46 32.173 14.637 3 13 12 84 26 32.112 13.338 7 9 7 80 21 30.693 14.194 1 9 11 84 17 29.963 16.196 2 2 13 89 36 27.252 16.826 2 7 19 73 47 29.246 14.324 1 n sms vi   (1) where sms is the space mean speed, n is the number of vehicles, and vi is the speed of an individual vehicle. table xii. reduction in speed at the fs due to onstreet parking and nmvs fs speed reduction (kmph) speed reduction percentage a2 15.689 53.94 b2 17.536 54.50 c2 18.774 58.46 d2 16.499 53.75 e2 13.767 45.94 f2 10.426 38.25 g2 14.922 51.02 fig. 2. speed reduction percentage in traffic speed at the fss. d. impact of on-street parking and nmvs on road capacity two types of data were used to determine the road section capacity at both sections: sms and classified volume data. data were extracted by the videography method at intervals of 15 min. a 60 m trap length was chosen for all 14 sections to collect data regarding speed and classified traffic volume count. a video camera was fixed 5.2 m above the ground, and 9 hours of video were recorded. the fundamental diagram method was used to establish the speed-flow relationship. volume data (veh/h) were recorded in the video, which need to be converted into pcu as it was mixed traffic. highway capacity manual categorized vehicle types should be considered as motorized and nmvs (cycles, cycle rikshaws, and animal-drawn vehicles). the pcu factors for individual vehicle categories given by irc 106 (for urban streets) were used. using pcu factors, each 15 min traffic count (veh/h) was converted into pcu/h and was multiplied by 4 to get the hourly volume. the flow (pcu/hr) at the bss and fss is shown in table xiv. the density of each section was calculated by: � = �� (2) where � = �/�, q is the traffic flow (veh/hr), k is the traffic density (veh/km), and v is thee traffic speed (km/hr). by using the greenshield’s model (3), speed and density graphs were designed to estimate the section capacity. figure 3 shows the speed-density curve for the bss. table xiii. flow (pcu/h) bs/fs vehicular composition in percentage car 2w 3w bus/truck sgv lgv cycle others total a1 66 75 124 31.5 42 28.6 0.4 10 377.5 b1 65 103.5 136 38.5 44 55 2 14 458 c1 45 76.5 104 42 26 35.2 1.2 10 339.9 d1 85 104.25 136 49 46 33 0.4 8 461.65 e1 68 90 104 35 52 50.6 2.8 12 414.4 f1 96 119.25 82 45.5 38 46.2 2.4 16 445.35 g1 67 94.5 110 59.5 42 41.8 1.6 9 425.4 a2 48 57 78 10.5 26 15.4 0.4 2 237.3 b2 43 73.5 102 17.5 30 28.6 0.8 6 301.4 c2 26 57 78 24.5 18 24.2 0.4 4 232.1 d2 63 76.5 102 14 26 19.8 0.8 2 304.1 e2 49 64.5 66 7 24 26 2.4 6 244.9 f2 76 99 58 14 18 15.4 1.6 8 290 g2 52 72 70 21 16 17.6 0.4 4 253 engineering, technology & applied science research vol. 13, no. 4, 2023, 11157-11165 11163 www.etasr.com srivastava & kumar: the impact of road side friction on the traffic flow of arterial roads in varanasi table xiv. flow, speed, and density bs flow (pcu /h) stream speed (km/h) density (pcu/km) fs flow (pcu/h) stream speed (km/h) density (pcu/km) a1 1510 29.081 51.92 a2 950 13.392 70.93 b1 1832 32.173 56.94 b2 1206 14.637 82.39 c1 1360 32.112 43.71 c2 929 13.338 69.65 d1 1847 30.693 60.17 d2 1217 14.194 85.74 e1 1658 29.963 55.33 e2 980 16.196 65.50 f1 1782 27.252 65.38 f2 1160 16.826 68.94 g1 1702 29.246 58.19 g2 1012 14.324 70.65 greenshield's straight line can be seen in the graph, best fitted on the basis of the r 2 value. similarly, figure 4 shows the speed-density graph for the fss, while also the greenshield's straight line can be observed, which is best fitted on the basis of the r 2 value. � = � – ∗ � (3) fig. 3. speed-density relationship at the bs. fig. 4. speed-density relationship at the fs. table xv, shows the traffic flow, speed, and density at the bss and fss. to determine the capacity, the developed model (speed-density model) was used to generate the speed-flow curve shown in figure 5. the speed-flow curve will give the capacity of the respective sections. the generated capacity is shown in table xvi. the reduction percentage in the capacity due to on-street parking and nmv on the fs are shown in table xvii. the los of each section was calculated by dividing the road volume with the capacity. the volume/capacity ratio was compared with the values provided by irc 106. table xviii represents the impact of on-street parking, nmv, and pedestrian crossing on los at the fs. according to the irc guidelines for urban roads, a road will lie in los a if its v/c value lies in 0-0.60 (free flow), similarly for los b, it should be in 0.61-0.70 (reasonable free flow), for los c 0.71-0.80 (near free flow), for los d 0.810.90 (medium flow), for los e 0.91-1.00 (capacity flow), and los f values should be greater than 1 (congested flow). it can be observed from table xviii, that frictional activity affects the service level of sarnath road up to los-b, while the level of service of bhelupur road is impacted up to los-e. fig. 5. correlation between the reduction percentage, effective width, and capacity. table xv. capacity reduction percentage due to nmvs capacity at bs (pcu/hr/2lane) capacity at fs (pcu/hr/2lane) reduction in capacity (pcu/hr/2lane) reduction percentage (%) 1510 950 560 37.08 1832 1206 626 34.17 1360 929 431 31.69 1847 1217 630 34.10 1658 980 678 40.86 1782 1160 622 34.90 1702 1012 690 40.54 table xvi. capacity reduction percentage due to on-street parking parking manoeuvres/hr nmt reduction percentage (%) 76 23 37.08 73 46 34.17 84 26 31.69 80 21 34.10 84 17 40.86 89 36 34.90 73 47 40.54 table xvii. impact on los at fs fs v/c at fs los as per irc remarks a2 0.787 los c near free flow b2 0.812 los d medium flow c2 0.687 los d medium flow d2 0.848 los b reasonable free flow e2 0.873 los d medium flow f2 0.781 los c mear free flow g2 0.902 los e capacity flow engineering, technology & applied science research vol. 13, no. 4, 2023, 11157-11165 11164 www.etasr.com srivastava & kumar: the impact of road side friction on the traffic flow of arterial roads in varanasi e. correlation of capacity reduction with the effective width of the carriageway on-street parking along the roads led to a loss of carriageway width, resulting in loss of road capacity. a correlation model was developed between the effective carriageway width and the capacity of the fs. the available effective width is the width of the carriageway available at any instance for traffic movement. on-street parking reduces the available effective width, and the capacity of the friction section decreases, as shown in table xix. table xviii. relationship between parking maneuvers per hour, capacity reduction, and effective width fs parking manoeuvres per hour capacity reduction (pcu/hr) capacity reduction percentage flow at bs (veh./ 5 min.) a2 76 560 37.08% 126 b2 73 626 34.17% 153 c2 84 431 31.69% 113 d2 80 630 34.10% 154 e2 84 678 40.86% 138 f2 89 622 34.90% 149 g2 73 690 40.54% 142 for data extraction, the bs (ex: a1) with minimum (as possible) and the fs (ex: a2) with the maximum number of onstreet parking maneuver issues were selected. the flow ratio (veh / 5 min) at these two sections for each interval is determined with the corresponding number of parking maneuvers. the ratio of flow at section a1 to section a2 directly gives the effective width factor for each 5 min interval, as shown in (4). these effective width factors for various sections at different parking maneuvers were multiplied with the actual width of the road to get the available effective width, as shown in (5). the reduction in width can be calculated by deducting the available effective width for various parking maneuvers from the actual width of the road. 2 1 f(a ) ewf= f(a ) (4) aew=ewf×aw (5) where ewf is the effective width factor, f(a1) is the traffic flow at a1, f(a2) the traffic flow at a2, aew is the available effective width, and aw the actual width of the road. fig. 6. correlation between the reduction percentage, effective width, and capacity. as shown in figure 6, a linear relationship exists between width decreases and capacity reductions, with an r 2 value of 0.853. it is determined that a 34.10% capacity loss occurs at a 29.31% reduction in effective width, and a 40.54% loss occurs at a 40.98% reduction in effective width. reduced effective width and capacity are related, as demonstrated in (6). percentage reduction in width = 0.709 × percentage reduction in capacity + 0.109 (6) with r 2 = 0.853. vii. conclusion roadside frictional activities are prevalent in developing countries like india. this study focused on the urban arterial roads in varanasi. it is observed that the presence of side frictional activities such as on-street parking, nmvs, and pedestrian crossing reduces the traffic flow, speed, and road capacity and impacts los. in this study, two types of roads were considered: base section (with minimum side friction) and friction section (with maximum side friction). data were collected from 7 base and 7 friction sections to analyze the effects of the considered fractional activities on the friction section. a correlation model was developed at the friction section and was compared with the base section to understand the impact of on-street parking, nmv, and pedestrian crossing on traffic flow. the speed-density model was developed using three fundamental parameters, which were further used to develop the speed-flow model. the speed-flow curve is plotted using the model's speed at various flow levels. the speed-flow curve is used to estimate the capacities of respective roads. capacities at each parking maneuver and the proportion of nmv were determined and compared with the base section capacity. the capacity obtained for different roads was used to calculate the v/c ratio to understand the quality of the respective roads' service levels. the values obtained from the v/c ratio were compared with those suggested by irc 106 guidelines. the main conclusions of this study are:  traffic flow of two-lane divided friction urban arterial midblock sections decreases with the increase in the influence of on-street parking, nmv, and pedestrian crossing, compared to the base section. the r 2 value obtained from the developed model indicates high dependability.  the reduction percentage in traffic flow ranged from 34.78% to 66.13%. bhelupur stretch is majorly impacted by side frictional activity as the reduction in traffic flow is 66.13%, while the sarnath stretch is least affected with a reduction in traffic flow of 34.78%.  the r 2 value obtained from flow-density relationship at bs is 0.576, at fs it is 0.896, showing high dependability between traffic flow rate and side frictional parameters.  the reduction percentage in speed at friction section ranged from 38.25% to 58.46%. from the developed model between % age reduction in speed and parking maneuvers per hour, the value of r 2 (0.865) indicates high dependability. engineering, technology & applied science research vol. 13, no. 4, 2023, 11157-11165 11165 www.etasr.com srivastava & kumar: the impact of road side friction on the traffic flow of arterial roads in varanasi  a correlation is obtained between the available effective width and percentage reduction in capacity.  it is observed that a 34.10% capacity loss occurs at a 29.31% reduction in effective width, and a 40.54% loss occurs at a 40.98% reduction in effective width.  the capacity of indira nagar road (a1) is 1510 pcu/hr/2lane, while the capacity 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[20] b. r. kadali, t. chiranjeevi, and r. rajesh, "effect of pedestrians unsignalized mid-block crossing on vehicular speed," international journal for traffic and transport engineering, vol. 5, no. 2, pp. 170–183, 2015, https://doi.org/10.7708/ijtte.2015.5(2).07. [21] m. o. kuttan, s. babu, and g. asaithambi, "impact of pedestrian road crossing on capacity and level of service of urban undivided roads in indian traffic conditions," in transportation research board 96th annual meeting, washington, dc, usa, jan. 2017, pp. 1–17. [22] a. dhamaniya and s. chandra, "influence of undesignated pedestrian crossings on midblock capacity of urban roads," transportation research record, vol. 2461, no. 1, pp. 137–144, jan. 2014, https://doi.org/10.3141/2461-17. [23] m. angın and s. i. a. ali, "analysis of factors affecting road traffic accidents in north cyprus," engineering, technology & applied science research, vol. 11, no. 6, pp. 7938–7943, dec. 2021, https://doi.org/10.48084/etasr.4547. [24] s. ranjan and v. singh, "hec-hms based rainfall-runoff model for punpun river basin," water practice and technology, vol. 17, no. 5, pp. 986–1001, apr. 2022, https://doi.org/10.2166/wpt.2022.033. [25] s. ranjan and v. singh, "ann and grnn-based coupled model for flood inundation mapping of the punpun river basin," engineering, technology & applied science research, vol. 13, no. 1, pp. 9941–9946, feb. 2023, https://doi.org/10.48084/etasr.5483. [26] a. jawed, m. a. h. talpur, i. a. chandio, and p. n. mahesar, "impacts of in-accessible and poor public transportation system on urban enviroment: evidence from hyderabad, pakistan," engineering, technology & applied science research, vol. 9, no. 2, pp. 3896–3899, apr. 2019, https://doi.org/10.48084/etasr.2482. [27] k. srivastava and a. kumar, "critical analysis of road side friction on an urban arterial road," engineering, technology & applied science research, vol. 13, no. 2, pp. 10261–10269, apr. 2023, https://doi.org/ 10.48084/etasr.5603. microsoft word 21-3408_s_etasr_v10_n2_pp5459-5465 engineering, technology & applied science research vol. 10, no. 2, 2020, 5459-5465 5459 www.etasr.com hassan & yousif: ions motion optimization for cloud job scheduling cloud job scheduling with ions motion optimization algorithm mohammed elobied hassan faculty of mathematical science university of khartoum khartoum, sudan elbashier.mohd@gmail.com adil yousif college of sciences and arts najran university sharourah, saudi arabia ayalfaki@nu.edu.sa abstract—cloud computing technology success comes from its manner of delivering information technology services, how they are designed, propagated, maintained and scaled. job scheduling on cloud computing is a crucial research area and is known to be an np-complete problem. scheduling refers to assigning user requests to underlying resources effectively. this paper proposes a new job scheduling mechanism for cloud computing environment. the proposed mechanism is based on the ions motion optimization (imo) algorithm. imo has two phases, liquid, and crystal. these two phases balance the algorithm behavior between convergence and local optima avoidance. to evaluate the proposed mechanism, a simulation with different scenarios using the cloudsim simulator is conducted. the performance of the proposed algorithm is compared with two metaheuristic algorithms known as cat swarm optimization (cso) and glowworm swarm optimization (gso). furthermore, the proposed imo mechanism is compared with first come first served and random solution. the experimental results demonstrated that the proposed mechanism outperformed both cso and gso and produced the shortest execution time in all experimental scenarios. keywords-optimization; ions motion; cloud; job scheduling i. introduction cloud computing is a new technology based on transferring computation processes from local desktops to remote providers on the internet. cloud computing services are extensive and provide on-demand access to a pool of computational resources [1-3]. the consistency and stability of cloud services is based on several features such as the scheduling process of jobs. scheduling is categorized into three levels, namely job level, resource level, and workflow level. in job scheduling, users submit jobs to cloud providers and job scheduling distributes the jobs submitted by the cloud clients to the provider with suitable resources [4-6]. cloud job scheduling is a job and resource management process based on several factors to increase the overall cloud performance [7, 8]. cloud jobs may comprise key in data, processing, accessing software, or storage maintaining process. cloud providers classify jobs based on the service-level agreement (sla) and requested services. each user job is assigned to one of the available cloud resources. cloud providers execute the submitted jobs, and the results are transmitted back to cloud users [9-12]. job scheduling in cloud computing is an np complete problem due to the huge amount of tasks submitted by cloud users to cloud providers. the job scheduling process starts when cloud users submit their jobs to cloud providers. the job scheduler in cloud providers requests the resource information service in order to obtain the status of available resources and their features. then, the job scheduler assigns the jobs to suitable resources based on the job and resources information requirements. cloud job scheduler allocates several clients jobs to multiple cloud resources. job scheduling mechanism tries to allocate cloud resources in an optimal way [3, 13-16]. current job scheduling methods that use a variety of optimization criteria suffer from several issues. the cloud batch systems prefer turnaround time and throughput as job scheduling criteria. however, interactive cloud systems use response time and fairness [17-19]. different types of cloud job scheduling based on heuristic, metaheuristic and optimization techniques have been proposed [20-22]. heuristic cloud job scheduling presents an optimal solution based on knowledge theories for obtaining optimal scheduling solutions [23, 24]. metaheuristic methods are general methods used for job scheduling based on natural inspired optimization methods such as particle swarm optimization and ant colony optimization [25-27]. optimization techniques provide good solutions but still not the optimal solution. therefore, there is a need for new job scheduling methods that optimize cloud turnaround and execution times. this paper proposes a new job scheduling mechanism for cloud computing environment. the proposed mechanism is based on ions motion optimization (imo) algorithm. imo has two phases, liquid and crystal. these two phases balance the algorithm behavior between convergence and local optima avoidance. ii. related works glowworm swarm optimization (gso) for solving independent job scheduling and allocation problem of cloud computing resources is presented in [28]. the gso mechanism considers each glowworm as a job scheduling candidate solution. the mechanism starts with an initial random population containing a number of n solutions. after developing the initial random population, gso calculates the fitness value for each glowworm. the calculation of the fitness corresponding author: adil yousif engineering, technology & applied science research vol. 10, no. 2, 2020, 5459-5465 5460 www.etasr.com hassan & yousif: ions motion optimization for cloud job scheduling value starts with dividing each job length by the speed of the resource the job is assigned to. then, gso calculates the summation of the division results for each glowworm and finds the maximum fitness value. authors in [29] proposed cat swarm optimization (cso) for solving the independent job scheduling problem and job allocation to the resources. each cat represents a candidate solution. the cat population is divided into two modes, seeking mode (sm) and tracing mode (tm). a new job scheduling mechanism using firefly algorithm to minimize the execution time of jobs is presented in [30]. firefly algorithm is a nature-inspired metaheuristic algorithm based on the light attractiveness of fireflies. the mapping process considers each firefly as a job scheduling solution. the firefly with less brightness is attracted and moved towards the brighter one. this process continues for several iterations until the algorithm reaches a specified fitness value [30]. authors in [31] emphasize on the performance of infrastructure as a service (iaas) based on a meta-scheduling model to accomplish enhanced job scheduling in multiple clouds. they proposed a new inter-cloud task scheduling framework and employed policies to improve the performance of participating clouds. a modified particle swarm optimization (mpso) method was introduced for cloud job scheduling in [10]. mpso has two important parameters in cloud scheduling, namely average length and ratio of successful execution. in [32], a hybrid cloud job scheduling mechanism using shortest job first and priority based scheduling is introduced to enhance the scheduling process. in [33], a chemical reaction optimization method is presented as an optimization method for cloud job scheduling problem. the method maps the cloud job scheduling problem to chemical reaction behaviors. this method has shorter execution time compared to the firefly algorithm and gso according to the experimentation results. the cloud job scheduling problem is modeled using shark smell optimization problem in [34]. the results of the shark smell job scheduling method outperformed the firefly algorithms’. a cuckoo-inspired cloud job scheduling mechanism is proposed in [35]. iii. ions motion optimization imo algorithm [36] is a metaheuristic algorithm proposed for solving optimization problems. imo as its name suggests is inspired from ion properties in nature, it mimics the attraction and repulsion forces between ions. imo is population based, it divides the population into two sets of negative and positive charged ions. these ions move in the search space according to a simple rule (ions with the same charge tend to repel each other while ions with opposite charges attract each other) [37, 38]. ions in imo can be in two different phases, liquid phase and crystal phase. in liquid phase, ions move around in the search space more freely. the repulsion forces are ignored in this phase to reassure exploration. the only factor that affects the attraction force is the distance between ions, while force is inversely proportional to the distance between ions [38, 39]. as a result, search agents of imo eventually converge toward a solution in the search space, and the algorithm enters the crystal phase. crystal phase implies that ions have converged toward a point in the search space. though, this point could be a local minimum [40, 41] due to the unknown characteristics of the search space. therefore, crystal phase aims to solve this entrapment by randomly relocating ions in the search space in respect to the best ions. nevertheless, the mechanism used for transiting from liquid to crystal phases is to check if the average fitness of the worst ions is equal or smaller than the fitness of the best ions [42, 43]. imo has been applied to solve different computation problems such as tackling the short-term hydrothermal scheduling problem [40], optimum coverage in wireless sensor networks [44], and optimal robot path planning [42]. iv. the proposed imo-based scheduling mechanism a. proposed mechanism description imo starts by initializing a population of search agents (ions). each ��� is defined by a number of attributes: � �����, ℎ���� and �� ��� � from the opposite �� ����. ��� � ����� represents a feasible scheduling solution and is defined as a vector of integer values ���������� of � length (where � is the total number of tasks) and its values fall in the range [ 0 , � − 1 ] (where � is the total number of resources). imo then divides the population of ��� randomly into two groups (����� and ������), by assigning a value ∈ {0,1} to the ℎ���� attribute of each ��� . after ��� have been assigned a � ����� and a ℎ����, imo evaluates the fitness of each ��� using the objective function #(%) and determines �� � ����� and �� � ������. ions with similar charge repel each other while ions with opposite charge attract each other. the �� ��� � for every ��� from the �� � ����� with opposite charge is calculated using (1): �'(,) = +�(,) − ��� �)+ �'(,) = +�(,) − ��� �)+ (1) where �'(,) is the distance from �����(,) in the , − �ℎ job and the �� �������) in the same job, �'(,) is the distance from ������(,) in the , − �ℎ job and the �� ������) in the same job. after calculating the distance, we map the distance to the range [0, 1] by: -� ��'� �./,0 = .1/,02341(56 -� ��'� �7/,0 = 71/,02341(56 (2) where -�%'� � = �8�9��:#;� �8� � − 1. after that, the force can be calculated using the mapped distance by (3): �<(,) = == >?@a.c/efgghij/klm/,0 �<(,) = == >?@a.c/efgghij/klm/,0 (3) where �<(,) and �<(,) are the force for the � − �ℎ anion and cation in job , respectively. now, the new position of anion and cation are updated as in (4) and (5): �(,) = �(,) + �<(,) × pqrstuv − �(,)w (4) �(,) = �(,) + �<(,) × (xrstuv − �(,)) (5) where �(,) is the element of the � − �ℎ anion in , − �ℎ job engineering, technology & applied science research vol. 10, no. 2, 2020, 5459-5465 5461 www.etasr.com hassan & yousif: ions motion optimization for cloud job scheduling dimension and �(,) is the element of the � − �ℎ cation in , − �ℎ job dimension. b. the proposed imo pseudocode the pseudocode that describes the proposed imo cloud job scheduling mechanism follows. initialize parameters: popsize, cbestfit, abestfit, cworstfit, aworstfit, bestion let pop be the set of ions 1, 2, 3, ... , popsize assign random solution (position) to each ion assign a charge (anion or cation) to each ion while (stopping criteria not met) do for each ions do evaluate fitness using #(%) determine bestion, cbestfit, abestfit, cworstfit, aworstfit calculate distance form the best ion with opposite charge using: �'(,) = +�(,) − ��� �)+ and �'(,) = +�(,) − ��� �)+ calculate force by �<(,) = == >?@a.c/mj/,0 and �<(,) = == >?@a.c/yj/,0 end for if (cbestfit≥cworstfit/2 and abestfit≥aworstfit/2) then get ө[andө\ randomly in interval [-1, 1] get α randomly in interval [0, 1] if (α>0.5) then �( = �( + ө[ × (�9� � − 1) else �( = �( + ө[ × (�9� �) end if get α randomly in interval [0, 1] if (α>0.5) then c^ = c^ + ө_ × (abest− 1) else �( = �( + ө\ × (�9� �) end if get α randomly in interval [0, 1] if (α>0.05) then re-initialize �( and �( end if end if end while output the position of the best ion c. the proposed imo for cloud job scheduling in details assume we have a set of � jobs to be scheduled among a set of � resources where � > � as in table i. e = [ f=, f_, fg, fh,…, fj ], = [ ;=,;_,;g,;h,… ,;k ] let � = 6 ,�9 and � = 4 �� �8� � as in table ii. table i. example jobs length job j1 j2 j3 j4 j5 j6 cycle 4 8 10 6 12 3 table ii. example resources speed resource r1 r2 r3 r4 cycles per second 8 4 2 6 the solving procedure using imo algorithm to find an efficient scheduling solution follows. 1) parameter initialization the algorithm begins by defining the population size as n� o�p�=6 and initializing empty variables for best and worst ions of both types as well as a variable to store the best ion. 2) assign random solutions to each ion a solution in job scheduling is a mapping of jobs to resources where the dimension index represents the job index f( and the number corresponding indicate the resource ;( q rr s �=�_�g�h�t�uv ww x = q rr s 2 3 1 2 4 11 3 4 2 3 22 3 4 1 2 33 4 1 2 4 42 3 3 4 1 13 4 1 2 3 2v ww x 3) divide ions randomly to anions �( and cations �( q rr s �=�_�=�g�_�gv ww x = q rr s 2 3 1 2 4 11 3 4 2 3 22 3 4 1 2 33 4 1 2 4 42 3 3 4 1 13 4 1 2 3 2v ww x 4) evaluate the fitness of each ion using {(|) {(|) = q rr s �=�_�=�g�_�gv ww x = q rr s 121613111415v ww x 5) determine �9� �<��, �9� �<��, �~�� �<��, �~�� �<��,�� ���� assuming a minimization problem (without loss of generality), we determine the best anion and cation respectively by selecting the lowest fitness values among anions and cations: �9� �<�� = �= �9� �<�� = �g �~�� �<�� = �g �~�� �<�� = �_ �� ���� = �g 6) calculate distance for every ion from the best ion with opposite charge the distance is calculated using cartesian distance: distance from �= to �9� �<�� = +�=,) − �9� �) + = 7 distance from �_ to �9� �<�� = +�_,) − �9� �) + = 4 distance from �g to �9� �<�� = +�g,) − �9� �) + = 9 distance from �= to �9� �<�� = +�=,) − �9� �) + = 9 engineering, technology & applied science research vol. 10, no. 2, 2020, 5459-5465 5462 www.etasr.com hassan & yousif: ions motion optimization for cloud job scheduling distance from �_ to �9� �<�� = +�_,) − �9� �) + = 12 distance from �g to �9� �<�� = +�g,) − �9� �) + = 3 7) normalize the distance between ions to normalize the distance to the range [0, 1] we need to calculate the maximum distance between two ions using the following equation: -�%'� � = $�8�9��:#;� �8� � − 1& × �8�9��:#f�9 then we can map the distance between every two ions using the equation below: -� ��'� � = 1(563j�?2341(56 now we calculate the max distance according to our problem: -�%'� � = 18. then, max distance is evaluated to obtain the mapped distance to the range [0, 1] -� ��'� �(�= to �9� �<��) = 0.38 -� ��'� �(�_ to �9� �<��) = 0.22 -� ��'� �(�g to �9� �<��) = 0.50 -� ��'� �(�= to �9� �<��) = 0.50 -� ��'� �(�_ to �9� �<��) = 0.66 -� ��'� �(�g to �9� �<��) = 0.16 8) calculate the attraction force between ions note that, imo algorithm assumes that the only factor for computing the attraction force is the distance between ions. the mathematical model is: �<(,) = == >?@a.c/mj/,0 and �<(,) = == >?@a.c/yj/,0 where �<(,) and �<(,) is the resultant attraction force of anions and cations respectively, and �'(,) represents the resultant distance of � − �ℎ anion from the best cation, and �'(,) represents the resultant distance of � −�ℎ cation from the best anion. now, we calculate the attraction force for each ion using above equations: �<= = == >?@a.c/a.�� = 0.56 �<_ = == >�@a.c/a.�� = 0.61 �<g = == >�@a.c/a.�a = 0.55 �<= = == >�@a.c/a.�a = 0.55 �<_ = == >�@a.c/a.�� = 0.53 �<g = == >�@a.c/a.c� = 0.65 9) update the positions of anions and cations according to the force value the positions are updated according to the following equations: �(,) = �(,) + �<(,) × (�9� �) − �(,)) �(,) = �(,) + �<(,) × (�9� �) − �(,)) calculation of the new position of �=: �=,) = ��=,= �=,_ �=,g �=,h �=,t �=,u2 3 1 2 4 1 � �′=,= = �=,= + �<=,= × (�9� �= − �=,=) = 2 �′=,_ = �=,_ + �<=,_ × p�9� �_ − �=,_w = 3 �′=,g = �=,g + �<=,g × (�9� �g − �=,g) ≈ 3 �′=,h = �=,h + �<=,h × (�9� �h − �=,h) ≈ 1 �′=,t = �=,) + �<=,t × (�9� �t − �=,t) ≈ 3 �′=,u = �=,u + �<=,u × (�9� �u − �=,u) ≈ 2 the new position of a= is as follows: �= = $2 3 3 1 3 2& calculation of the new position of a_: �_,) = � �_,= �_,_ �_,g �_,h �_,t �_,u 1 3 4 2 3 2 � a′_,= ≈ 2 a′_,_ = 3 a′_,g = 4 a′_,h ≈ 1 a′_,t ≈ 2 a′_,u ≈ 3 the new position of a_ is as follows: �_ = $2 3 4 1 2 3& 10) entering a crystal phase if (cbestfit≥cworstfit/2 and abestfit≥aworstfit/2) then the algorithm will enter a crystal phase. the new position of ions will be updated according to the following pseudocode: get α randomly in interval [0, 1] ө= ,ө_ are a random numbers in interval [-1, 1] if (α>0.5) then a^ = a^ + ө= × (cbest − 1) else a^ = a^ + ө= × (cbest) end if get α randomly in interval [0, 1] if (α > 0.5) then c^ = c^ + ө_ × (abest− 1) else c^ = c^ + ө_ × (abest) endif get α randomly in interval [0, 1] if (α>0.05) then re-initialize c^ and a^ randomly engineering, technology & applied science research vol. 10, no. 2, 2020, 5459-5465 5463 www.etasr.com hassan & yousif: ions motion optimization for cloud job scheduling v. evaluation and experimentation this section covers the experimentation conducted to verify the applicability of the proposed mechanism and to confirm its advantages over other metaheuristic mechanisms. firstly, the proposed mechanism is compared with first come first served (fcfs) scheduling method and with a random solution using four different scenarios. secondly, a simulation comparison is conducted a between imo and cso under two different scenarios. finally, a comparison between imo, cso and gso is conducted. a. experimental settings the proposed mechanism is simulated using cloudsim simulation model. the population size of imo is set to 30 ions and the maximum number of iterations to 100. each scenario is conducted 10 times and the results are recorded. the processing powers of resources are generated randomly between 10 and 70, while the lengths of tasks are between 40 and 150. b. imo, fcfs and random solution experiment scenarios this section presents a comparison of the four experiment scenarios between the proposed imo scheduling algorithm, fcfs algorithm and a randomly generated scheduling solution. as seen in table iii and figure 1, imo algorithm performs better than the fcfs algorithm and the random solution. also, it has the best execution. table iii. imo fcfs and random solution comparison results scenario algorithm best fitness first fcfs 119.37 random 54.92 imo 30.596 second fcfs 155.1479 random 88.283 imo 64.2411 third fcfs 406.913 random 211.07 imo 90.405 forth fcfs 608.2968 random 383.8813 imo 232.6167 fig. 1. comparison between imo, fcfs and random solution c. imo and cso comparison result in this comparison, the processing speed of resources and the length of jobs were generated randomly in the intervals [0, 200] and [0, 400] respectively. both algorithms used the same jobs and resources specification and both performed 30 runs and the average execution time was calculated. 1) first scenario this scenario considers a number of 50 jobs and 20 resources. table iv. imo and cso 1st scenario fitness (execution time) iteration 1 20 40 60 80 100 imo fitness 181.54 131.50 105.12 80.51 80.51 76.98 cso fitness 149.93 110.34 107.39 107.39 102.71 100.51 fig. 2. comparison between imo, cso, first scenario as shown in table iv and figure 2, although cso starts with a better solution and imo starts with a slightly high fitness solution, both of them continue to improve the quality of their solutions. cso maintains its advantage in the first 30 iterations. but as the iterations continue, the imo found a better solution than cso in iteration 31, overcame cso and then continued to improve the performance by reducing execution time. 2) second scenario this scenario considers 100 jobs and 30 resources. table v. imo and cso 2nd scenario fitness (execution time) iteration 1 20 40 60 80 100 imo fitness 467.79 295.89 242.64 198.78 188.05 162.29 cso fitness 492.67 266.16 259.31 259.31 259.31 259.31 fig. 3. comparison between imo, cso, second scenario engineering, technology & applied science research vol. 10, no. 2, 2020, 5459-5465 5464 www.etasr.com hassan & yousif: ions motion optimization for cloud job scheduling as shown in table v and figure 3, imo starts with a slightly better solution than cso, but after the first iteration cso came up with a better solution. both algorithms continued to improve their solutions. imo found a solution better than cso’s after 30 iterations and continued to improve it. cso remained constant after 30 iterations d. imo, cso and gso comparison result this section presents a comparison between the proposed mechanism imo and two other metaheuristic algorithms, cso and gso, using 50 jobs and 20 resources generated randomly and used by all the three algorithms. fig. 4. comparison between imo, cso, and gso as shown in figure 5, imo started with a good solution but both gso and cso were better during the first 20 iterations. imo found a better solution in less than 30 iterations. both gso and cso did minor improvements to their solutions after 20 iterations and then remained constant while imo continued to improve its solution until the 96th iteration. e. discussion it was proved that the imo algorithm can produce promising solutions to scheduling problems. imo performed 100 iterations in the above scenarios, switching between liquid and crystal phases to overcome local minimum entrapment. liquid phases were 80% of the total number of iterations, evidencing the exploitation ability of imo. crystal iterations were about 20% of the total number of iterations. this proves that the ions do not trap in a local minimum. moreover, ions in imo move toward the best ion with opposite charge, thus increasing the number of ions will increase the exploitation of promising regions in the search space. to conclude, imo starts initializing ions (search agents) randomly, then it changes their location (scheduling solution) and moves them toward the best location found so far. while this will lead to local minimum stagnation, however, crystal phases relocate ions around the best ions found so far randomly. vi. conclusion this research proposed a scheduling mechanism for cloud computing jobs based on ions motion optimization. the proposed mechanism considers minimizing the execution time of jobs. this research started by finding an optimal analogy between imo algorithm and the problem of job scheduling in cloud. imo begins by initializing randomly a population of ions where each ion position represents a candidate scheduling solution. then the algorithm divides the population into two groups of anions and cations before evaluating the fitness of each ion using the objective function. the objective function calculates the execution time of each candidate solution. furthermore, ions move toward the best ions from the other group in the population. imo continually transits between liquid and crystal phases to maintain a ratio between exploitation and exploration of the search space. liquid phase guarantees convergence of ions toward the best found solutions and also guarantees exploiting the promising locations found so far. crystal phase relocates ions randomly around the best solutions found at this point. when compared with two metaheuristic algorithms using the same set of jobs and resources, imo outperformed them. imo starts the search with a solution that is slightly better or worse than gso and cso, but it overcomes both algorithms after about 30 iterations in all scenarios. imo also proved its advantage over traditional methods and produced highly competitive solutions having the less execution time when compared to fcfs. references [1] b. k. rani, b. p. rani, a. v. babu, “cloud computing and inter-clouds– types, 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engineering, technology & applied science research vol. 9, no. 4, 2019, 4516-4519 4516 www.etasr.com radwan & mangi: municipal solid waste management practices and opportunities in saudi arabia municipal solid waste management practices and opportunities in saudi arabia neyara radwan faculty of economics & administration, king abdulaziz university, jeddah, saudi arabia and mechanical department, faculty of engineering, suez canal university, ismailia, egypt nrhassan@kau.edu.sa sajjad ali mangi department of civil engineering, mehran university of engineering and technology, szab campus khairpur mir’s, sindh, pakistan sajjad.nec@muetkhp.edu.pk abstract—municipal solid waste management has been given serious attention by the authorities of saudi arabia (sa). this study focuses on municipal solid waste (msw) that predominantly contains food, paper, and plastic waste. however, improper handling of msw causes several environmental and human health issues. therefore, it is necessary to review the current practices and future opportunities that have been adopted for solid waste collection, handling, and disposal. considering the current scenario, this study proposed a reversal approach for msw management. this study considered that msw generated in sa has great potential to be converted into wealth. hence, considering the hostile environment anaerobic treatment and incineration for msw has been proposed in this study for future research. keywords-municipal solid waste; disposal practices; environmental issues i. introduction generation of municipal solid waste (msw) is a common issue and its production is being increased gradually as the commercial and industrial activities extend [1]. currently, msw in saudi arabia (sa) is considered as a significant issue, the annual generation of msw in sa is 14×10 6 tons [2], whereas most of msw is generated in the main cities: damman, hofuf and riyadh in the west and jeddah, medina and mecca in the east. the annual production of msw from only three of the main cities, namely jeddah, damman and riyadh is more than 6×10 6 tons [3]. this huge generation of msw creates serious environmental and public health issues. improver msw management affects all stakeholders and particularly the public. however, improper dumping of urban waste could affect the landscape and pose environmental and public health threats. particularly, domestic waste, which is organic in nature, poses a serious threat, since it creates conditions favorable to the survival and growth of microbial pathogens [4]. therefore, many studies have been conducted to overcome the solid waste (sw) issue, particularly the issue of managing msw. details of previous studies and their key findings are reported in table i. it was observed in earlier studies that there is a growing concern about the msw management in each part of the country. however, most studies highlighted that the msw of sa have great potential to generate electricity. it was stated that burning of sw can achieve high power generation [5]. msw generated in sa is mostly comprised of organic waste, which can be utilized to produce biogas for energy production [6]. it is important to promote waste to wealth strategies and research for possible opportunities for the future [7]. table i. previo us fin gings ref. objectives key findings [3] msw disposal optimization. combustion of msw can reduce the load of landfill and procure electricity preferable with eco-friendly combustion technology. [5] energy recovery from waste. incineration of sw can achieve high power generation. [6] energy recovery from waste. biogas can be produced through organic waste. [8] household waste management. quantity and quality of waste can be minimized by increasing awareness through education and media. [9] energy recovery from waste annually 1.03 and 1.55twh of electricity can be produced from waste. [10] msw practices. need to enhance awareness about waste sorting at source, separate bins to be introduced, and strong rules need to be implemented. [11] recycled plastic waste (rpw) to modified asphalt binder. rpw cannot meet the requirements of elastic recovery for polymer-modified asphalt. [12] renewable energy resource (rer). msw has great potential as rer. [13] msw management. msw in sa contains about 40% organic materials. therefore, it has great potential to produce energy through anaerobic digestion. previous studies [5, 6, 9, 12] indicated that msw is currently considered as a good source for energy production. however, the method of its handling is debatable. therefore, this study aims to identify the current practices and opportunities for the handling of msw around the globe and in sa. this study summarizes important information regarding msw management in sa and proposes potential opportunities considering environmental preservation and sustainable development. corresponding author: neyara radwan engineering, technology & applied science research vol. 9, no. 4, 2019, 4516-4519 4517 www.etasr.com radwan & mangi: municipal solid waste management practices and opportunities in saudi arabia ii. theoretical approach to minimize waste the current practices of msw handling in sa are presented in figure 1, which indicates that most of msw goes directly to landfills, and less consideration has been given on recycling, composting or source reduction. however, this approach creates environmental issues in terms of leachate generation from landfills and contaminated soil and underground water. the current practices are not environmentally acceptable but are intensively adopted due to the unavailability of advanced technologies and skilled professionals. the switching from one method to a more advanced one is very hard for the authorities [15], therefore this paper proposes the reversal approach as shown in figure 2, which demonstrates that first priority should be given to the source reduction or source minimization in order to produce less msw [16]. this requires continuous emphasis on the importance of waste minimization practices through education and electronic media and the promotion of the 3r (reduce, recycle and reuse) approach. however, 3r approach can also be applied at the source of waste generation. the government should make strong rules and increase awareness to alarm the public. successful msw management can be achieved by adopting reversal approaches as proposed in this study. fig. 1. current practice. fig. 2. reversal approach. iii. environmental issues msw has been considered as a valuable source for recycled materials and energy [17]. it could give numerous benefits in countries like sa. environmental issues associated to the msw handling in sa and other countries have been given serious attention [5]. the method of handling msw is challenging for the authorities [12]. it was previously well recognized that there are three methods, which are commonly in practice at sa as shown in figure 3: landfilling, anaerobic digestion and combustion/incineration. however, every method has some consequences on the environment. fig. 3. methods of handling msw a. landfilling landfilling is the most common method for the disposal of msw [18]. however, it occupies huge areas and creates environmental problems in terms of leachate and undesirable gas production. the leachate produced by the landfills can contaminate the soil and underground water. besides that, landfills also affect their surrounding environment, habitats, cultivation lands, commerce and recreational areas [2]. b. anaerobic digestion it was noticed that msw generated in sa mostly contains organic waste, which indicated its potentiality to produce energy through anaerobic digestion [19]. this method produces methane (ch4) gas [20], which could be used to produce electricity, but this process leaves a by-product known as sludge, which requires huge areas for drying. c. combustion/incineration the best practice is the combustion of msw to generate electricity. this is globally the most acceptable and widely used method. however, this process leaves a by-product known as msw ash. this ash can be used as cementitious material contributing to sustainable concrete production [21]. currently researchers are emphasizing on the utilization of msw to develop waste to energy practices with minimal environmental impact [22-24]. iv. msw ash utilization in concrete msw has been considered as hazardous and there is a dire need to reduce its volume [25]. incineration is a useful technique to reduce the quantity of waste up to 70% by weight and 90% by volume [26]. the incineration process of msw generates electricity but leaves a huge volume of ash known as msw ash. this ash is generally disposed in landfills, creating environmental problems and increasing landfill cost. researchers are looking for ways to manage this ash as alternatives to open dumping and landfills [21, 26]. based on its chemical properties, it was declared that msw ash has a good potential to be utilized as cementitious material in concrete production [27, 28]. msw ash is obtained from different locations, its chemical composition is evaluated and the possibility of posing pozzolanic characteristics comparable to class-c as per astm c618 [29] is identified. si, al and fe are the key indicators that represent the pozzolanic activity of ashes. if the combined sum of sio3, al2o3, and fe2o3 is greater than 50%, msw ash can be utilized in concrete to enhance its engineering, technology & applied science research vol. 9, no. 4, 2019, 4516-4519 4518 www.etasr.com radwan & mangi: municipal solid waste management practices and opportunities in saudi arabia strength and durability [26, 27]. the properties of msw ash indicate that it also contains high amounts of cao, which could be beneficial in the hydration process of the cement paste in concrete [30]. besides that, it contains around 5.27% so3 which is allowable for pozzolanic ashes. ash blending can provide a positive pozzolanic reaction. the chemical composition of the msw ash could vary according to its type [27], but in almost all cases it contains high amounts of silica dioxide. the comparison of the chemical properties of msw ash with ordinary portland cement (opc) as provided by [31] is shown in table ii. table ii. chemical properties of msw sample msw ash [27] opc [31] chemical content % % silica dioxide (sio2) 53.16 20.61 aluminium trioxide (al2o3) 3.98 3.95 ferric oxide (fe2o3) 1.40 3.46 calcium oxide (cao) 19.13 63.95 titanium dioxide (tio2) 0.18 0.20 potassium oxide (k2o) 0.94 magnesium oxide (mgo) 1.49 1.93 phosphorus pentoxide (p2o5) 5.00 sulfur trioxide (so3) 5.27 3.62 zirconium dioxide (zro2) 0.67 sodium superoxide (nao2) 6.67 v. conclusion and recommendations the main conclusions and recommendations regarding future research are: • msw generated in sa contains about 40% organic waste, which indicates its potentiality to produce energy through anaerobic digestion. • the abundant production of msw increases the demand for landfills, which occupy huge areas of land and create environmental problems. • considering the energy production through msw, incineration is the best solution, which can reduce the waste 70% by weight and 90% by volume. the by-product of incineration process known as msw ash can be utilized in concrete production. • msw ash is characterized as pozzolanic material, which could deliver positive influence on the properties of concrete. hence, a reversal approach has been proposed for the minimization of msw at the source. this approach could reduce the cost of segregation and transport. besides that, this study suggests the incineration process for safe handling of msw. however, the ashes produced through this process, can further be utilized in the production of sustainable and durable concrete. references [1] a. d. d. b. fernandez, j. e. s. aquilar, n. radwan, f. n. rivera, j. m. p. ortega, m. m. e. halwagi, “strategic planning for managing municipal solid wastes with consideration of multiple stakeholders”, acs sustainable chemistry & engineering, vol. 5, no. 11, pp. 1074410762, 2017 [2] o. k. m. ouda, h. m. cekirge, “roadmap for development of waste-to energy facility in saudi arabia”, 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annual review of environment and resources, vol. 37, no. 1, pp. 277-309, 2012 [24] i. budhiarta, c. siwar, h. basri, “current status of municipal solid waste generation in malaysia”, international journal on advanced science engineering information technology, vol. 2, no. 2, pp. 16-21, 2012 [25] m. sharholy, k. ahmad, g. mahmood, r. c. trivedi, “municipal solid waste management in indian cities-a review”, waste management, vol. 28, no. 2, pp. 459-467, 2008 [26] c. h. k. lam, a. w. m. ip, j. p. barford, g. mckay, “use of incineration msw ash: a review”, sustainability, vol. 2, pp. 1943-1968, 2010 [27] r. siddique, “use of municipal solid waste ash in concrete”, resources, conservation and recycling, vol. 55, no. 22, pp. 83-91, 2010 [28] r. siddique, j. khatib, i. kaur, “use of recycled plastic in concrete: a review”, waste management, vol. 28, no. 10, pp. 1835-1852, 2008 [29] astm, “astm c618-05 (2005): specification for coal fly ash and raw or calcined natural pozzolan for use in concrete”, in: annual book of astm, standard, section 04 construction, volume 04.02 concrete and aggregate, astm international, 2005 [30] s. a. mangi, n. jamaluddin, m. h. w. ibrahim., a. h. abdullah, a. s. m. a. awal, s. sohu, n. ali, “utilization of sugarcane bagasse ash in concrete as partial replacement of cement”, iop conference series: materials science and engineering, vol. 271, no. 1, pp. 1-8, 2017 [31] s. a. mangi, m. h. w. ibrahim, n. jamaluddin, m. f. arshad, s. a. memon, s. shahidan, “effects of grinding process on the properties of the coal bottom ash and cement paste”, journal of engineering and technological sciences, vol. 51, no. 1, pp. 1-13, 2019 author profiles neyara radwan is an assistant professor and the quality assurance officer for master programs for (amba) in king abdulaziz university, jeddah, saudi arabia. moreover, she is an assistant professor in the mechanical department, faculty of engineering, suez canal university, ismailia, egypt. she has been involved in many local and international research projects. also she has participated in many international conferences as a keynote speaker. she is in the editorial board of many international journals. her research interests lie in the field of waste management and optimization. sajjad ali mangi is an assistant professor in the department of civil engineering, mehran university of engineering & technology, szab campus khairpur mir's, sindh, pakistan. he has been involved in many local and international research projects. he has participated in national and international conferences and has been awarded as a lifetime member of the ewt for clear and green pakistan. his research interests lie in the field of utilization of waste materials in sustainable and durable concrete production. microsoft word 25-3444_s1_etasr_v10_n2_pp5483-5486 engineering, technology & applied science research vol. 10, no. 2, 2020, 5483-5486 5483 www.etasr.com daslim & mursadin: a control model for reinforced concrete work materials on the construction … a control model for reinforced concrete work materials on the construction of duta mall 2 sudiono daslim department of civil engineering faculty of engineering lambung mangkurat university banjarmasin, indonesia sudiono_daslim@yahoo.com aqli mursadin department of civil engineering faculty of engineering lambung mangkurat university banjarmasin, indonesia a.mursadin@ulm.ac.id abstract—controlling is a crucial stage in achieving a project target, covering aspects of cost, quality, and time. in the construction industry, the cost aspect is often the main focus. the project of duta mall 2 (dm 2) is the development of an existing building and the cost aspect is a major concern to the owner. dynamic internal and external factors of the dm 2 project cause the project control to be quite difficult, with the materials becoming the most dominant factor in construction cost. cost control starts from reinforced concrete work materials, consisting of ready mixed concrete, concrete steel, wire, plywood, timber, and nails. bad control of material purchasing can lead to cost escalation, degradation of material quality, and impact on the execution schedule of works. this research was conducted to obtain quantitative correlations between material components based on reinforced concrete works material supply data. from these data, some linear regression models can be designed to obtain a more accurate and effective prediction of material volume needs in the future. model equations can be applied to control material demand, measure waste, reference of material volume in arranging the project cost budget, in addition to the process in the control procedure of the request for goods (materials and equipment). keywords-reinforced concrete works; material control; linear regression; predictive capabilities; control procedure i. introduction on all construction projects, cost, quality and time are parameters that need to be optimized. cost is a very important project parameter. it stands as a single aspect and is also influenced by the quality and completion time of works. poor quality works will lead to complaints and can potentially create a construction claim or at least a demand of reworks/repairs which will lead to cost overrun. delay in project completion will cause cost overrun or even a fine. cost management is a completion of three constraints covering cost, schedules, and scope. each must be completed in order to complete the project on time and budget and meet all customer expectations. projects must be settled on an approved budget. it is therefore very clear that the quality problem and the work schedule will also affect the cost [1]. duta mall 2 (dm 2) is a building construction project. it is the expansion of duta mall 1 (dm 1) which is already in operation. in this dynamic dm 2 project, there are several factors that cause difficulty in material control. material management, especially for reinforced concrete works in the dm 2 project, is done by the contractor but its purchase system is controlled by a management team from the owner to minimize cost. besides the cost aspect, the material management system also touches integrated environmental and social aspects [2]. material control of reinforced concrete works is very important, because the material cost is a significant part of the overall cost of the project, representing anything from 40% to 60% of the final cost, so tight control is essential [3]. based on the historical data on material supply of reinforced concrete works in dm 2, there are some regression models of volume supply of the materials. material components of reinforced concrete works consist of ready mixed concrete, concrete steel, wire, plywood, timber and nails. the aims of the current research are: • to find the various causes of difficulty in material control of reinforced concrete works on the development of dm 2 based on the existing procedure. • to develop a relationship model of volume supply between materials on the construction of dm 2. • to improve material planning procedures and control on reinforced concrete works in dm 2 project. ii. theoritical basis a. project management and project control a project is defined as a temporary effort made to create unique products, services or results [4]. it is defined by pmbok (project management body of knowledge). project management aims to plan, to organize, to lead, and to control company resources to achieve a predetermined short-term goal [5]. control of construction project includes cost, quality, and time. the concept of controlling the project in the lean construction method has a principle in downsizing or reducing/eliminating waste. construction waste is anything generated as a result of construction and is then abandoned, regardless weather it has been processed or stockpiled [6]. b. material control on construction projects in the production system, especially in the construction corresponding author: sudiono daslim engineering, technology & applied science research vol. 10, no. 2, 2020, 5483-5486 5484 www.etasr.com daslim & mursadin: a control model for reinforced concrete work materials on the construction … industries related to supply chain management, there are two methods, i.e. push system and pull system. the dm 2 construction project utilizes a combination of both methods. controlling of reinforced concrete work materials to optimize construction project cost can be achieved by the following process: • fulfillment of demand or submission of materials. • estimation of inventory according to the job stage or work schedule that has been planned some time ahead. • supervision of material acceptance to fit the demand. • storage and protection of materials. • efficiency of material use in the project through appropriate supervision and working methods. • evaluation of progressive material usage. the ability to control reinforced concrete work materials certainly increases the effectiveness of the contractor. in addition to economic reasons, effective material control also reduces material waste. material cost, delay of material arrival and inaccurate estimates are examples of causes of cost overrun [7]. the objective is to assure that the right materials in the right quantities and at the right locations are provided at the right time to the construction crews on the project. most construction site layout planning for construction sites is based upon contractors’ prior experience and it is designed only once before construction starts without consideration of the dynamic nature of the supply problems, such as dynamic changes of requirements and available site information in consecutive construction project phases [8]. material procurements on several projects also have constraints on the availability of location in the field. adequate supply of materials in accordance with the planned job site will help the implementation of construction effectively and efficiently. however, in some projects the stages of construction activities may differ from the initial planning, due to the dynamic implementation of construction. consequently, there is a distortion between the material supplies previously proposed based on estimates and the new areas of the work. c. simple linear regression model in the construction industry, some problems have relationships that can be predicted through regression models. the relationship between a variable in a group and other groups is often very useful in statistical analysis. the relationship between the independent variable and the matched response is an equation of regression [9]. steps or stages that need to be conducted in order to obtain a good linear regression model consist of model identification, parameter estimation, parameter testing, and application of regression models [10]. iii. research method in this research, preliminary analysis is applied to the recapitulation acceptance data of reinforced concrete materials, i.e. ready mixed concrete, concrete steel, wire, plywood, timber, and nails with the scatter plot method. parameter estimation for linear regression models was conducted with the least squares method and validation followed [11]. the formed linear regression model was adopted into the pre-existing model of the dm 2 materials control procedure. the implementation steps of the research are: • preliminary study, in the form of observations in the field (project dm 2). • literature review. • primary and secondary data collection. • study of the causes of difficulty in controlling reinforced concrete work materials by observation of the work processes and materials used. • regression model construction based on the supply data. • validation of the linear regression models. • model of planning and material volume control. • conclusion. iv. data analysis a. initial data collection the materials of reinforced concrete works are exhibited in table i along with the periodic data which must be transformed in cumulative data. the cumulative data of each material have been tested for normality distribution as shown in table ii. b. developing of linear regression models 1) regression equations of reduction data constructed with the least squares method in developing linear regression models, the research uses the cumulative data, so the periodic data should be modified or transformed. table ii shows that models for plywood-timber and timber-nails do not pass the normality test. the p values for both data pairs are less than 0.05, which means that the data have non-normal distribution. therefore it is necessary to reduce outlier data. the data that should be eliminated for the above models are described below. • plywood-timber: data that should be eliminated are variable no. 12 (december 2017) and no. 15 (march 2018). • timber-nails: data that should be eliminated are only variable no. 12 (data on december 2017). after eliminating the outlier data, the normality tests for both models are fulfilled. next, the used data are normally distributed variables that generate the following equations: • ready mixed concrete and concrete steel: ��� = −109.92+ 0.1787 �� (1) • concrete steel-wire: ��� = 1,885.25 + 7.6577 �� (2) • ready mixed concrete-plywood: �� � = −358.95 + 0.4228 �� (3) engineering, technology & applied science research vol. 10, no. 2, 2020, 5483-5486 5485 www.etasr.com daslim & mursadin: a control model for reinforced concrete work materials on the construction … table i. supply of reinforced concrete work materials no. month ready mixed concrete (m 3 ) concrete steel (×1000kg) wire (kg) plywood (pcs) timber (m 3 ) nails (kg) 1 jan’17 1,653.5 182.513 2,780 546 56.11 1,125 2 feb’17 715.0 244.771 200 294 64.03 1,040 3 mar’17 890.5 44.746 1,500 104 20.01 695 4 apr’17 815.0 167.096 1,400 448 4.31 770 5 may’17 896.0 63.952 1,300 240 11.00 695 6 jun’17 355.5 190.131 800 6.11 270 7 jul’17 211.0 110 60 33.00 8 aug’17 1,067.0 145.029 1,830 583 84.50 860 9 sep’17 948.5 297.365 1,050 528 65.70 1,040 10 oct’17 509.5 455.435 1,800 150 42.30 520 11 nov’17 1,125.0 1,550 607 72.45 1,130 12 dec’17 952.5 112.619 600 304 184.18 510 13 jan’18 1,764.5 3,150 832 136.91 1,650 14 feb’18 1,587.5 218.068 1,100 900 85.81 1,550 15 mar’18 1,402.5 415.649 2,100 252 151.30 2,330 16 apr’18 1,579.5 2,150 1,202 101.06 1,205 17 may’18 827.5 177.642 1,500 165 33.11 827 18 jun’18 346.0 144.040 19 jul’18 599.5 135.359 2,100 150 38.14 1,706 20 aug’18 1,543.5 2,700 391 63.75 1,363 21 sep’18 969.5 567.687 600 510 12.54 1,200 22 oct’18 1,297.5 60.561 1,600 820 38.31 170 23 nov’18 973.0 313.245 1,200 300 19.28 814 24 dec’18 1,135.5 260.196 1,700 150 31.04 520 25 jan’19 1,062.5 270.529 1,250 1,118 55.94 955 26 feb’19 1,255.5 275.682 1,900 551 53.53 1,125 27 mar’19 2,009.0 75.035 2,100 625 82.49 1,030 28 apr’19 1,789.5 583.495 1,700 475 95.32 605 29 may’19 1,051.0 367.654 1,200 295 51.57 381 30 jun’19 247.0 215.986 500 150 6.52 690 31,579.5 5,984.485 43,470 12,750 1,700.32 26,776 table ii. value of normality test in saphiro wilk method no. model statistic p value remark 1 ready mixed concrete-concrete steel 0.974 0.641 normal distribution 2 concrete steel-wire 0.982 0.875 normal distribution 3 ready mix concrete-plywood 0.963 0.374 normal distribution 4 plywood-timber 0.891 0.005* non-normal distribution 5 timber-nails 0.874 0.002* non-normal distribution * p value < 0.05 • plywood-timber: �� � = 39.29 + 0.1095 �� (4) • timber-nails: �� � = 613.76+ 16.9934 �� (5) the result of normality retest to the regression of plywood and timber was p=0.369 and the regression of wood and nails was value p=0.145. 2) heteroscedasticity test the results of heteroscedasticity test with glejser method are shown in table iii. 3) modification of the regression equations model with mathematics substitution method shown (5-10) • ready mixed concrete and concrete steel: �� � = − 109.92 + 0.1787 �� (6) • ready mixed concrete-wire: �� � = −1,043.52 + 1.3684 �� (7) • ready mixed concrete-plywood: �� � = −358.95 + 0.4228 �� (8) • ready mixed concrete-timber: �� � = −2.97+ 0.0463 �� (9) • ready mixed concrete-nails: �� � = 563.29+ 0.7868 �� (10) table iii. heteroscedasticity test values no. model t value p value remark 1 ready mixed concrete concrete steel 1.862 0.073 homoscedasticity 2 concrete steel -wire 1.869 0.072 homoscedasticity 3 ready mixed concrete plywood 1.715 0.097 homoscedasticity 4 plywood-timber 0.179 0.859 homoscedasticity 5 timber-nails 0.917 0.368 homoscedasticity engineering, technology & applied science research vol. 10, no. 2, 2020, 5483-5486 5486 www.etasr.com daslim & mursadin: a control model for reinforced concrete work materials on the construction … note in (1)-(10): s: concrete steel, w: wire, p: plywood, t: timber, n: nails, c: ready mixed concrete c. development of the material planning and controlling procedure model the obtained regression model of reinforced concrete work materials will be absorbed by the existing procedure. the proposed revision procedure is a corrective plan that adds predictive capabilities based on historically valid information and thus improving the existing procedure. although there is a volume analysis check, the additional process is necessary in order to minimize the causes of material control difficulties based on research observation results. the model of the procedure of material request submission control can be seen in figure 1. the additional processes in this revised procedure include: • a controlling process of the material volume of reinforced concrete works by using the equation reference of regression models. this control uses the regression model of reinforced concrete works as an independent variable by relaying the predictive capability to the needs of various materials of reinforced concrete works. • an evaluation process of the submission of volume, inventory, and deviation of material waste. start acceptance of prf submission / purchase request form (materials & equipment) prf & materials analysis (limited) materials & equipment specification check materials/goods volume analysis check conform? returning of the prf to project for correction submission of prf to purchasing department project director approval approved? ordered by purchasing department to inform to project about prf refusing end list of materials & equipment specification materials calculation analysis no yes no yes controlling on materials of reinforced concrete work evaluation on materials quantities, available stock & level of materials waste materials regression model budgeting plan fig. 1. flowchart of the revised standard operating procedure v. conclusion various project problems that occur in the case of duta mall 2 project are caused by material controlling, especially regarding reinforced concrete works. the control of these materials becomes a critical point of the construction process of duta mall 2, and aside from its impact to cost it also has impact to the material quality and the schedule of work completion. effective material control methods are required for complex and dynamic projects such as the construction of duta mall 2. the proposed method considers linear regression equation models between various material components of reinforced concrete works based on available historical data. the model equations that are formed can be modified by referring to one independent variable, i.e. the volume of ready mixed concrete. other material components such as concrete steel, wire, plywood, timber, and nails can be planned more easily and according to its needs. the validated model of the equations can be an analysis tool in the control procedure model for material requests of reinforced concrete works. the evaluation of material waste that occurs can also be done during the works process. another benefit from the regression model is that it can be a reference of cost budget calculations. references [1] m. w. newell, preparing for the project management professional, american management association, 2002 [2] d. battini, m. calzavara, i. isolan, f. sgarbossa, f. zangaro, f. “sustainability in material purchasing: a multi-objective economic order quantity model under carbon trading”, sustainability, vol. 2018, no. 10, article id 4438, 2018 [3] c. march, operations management for construction, taylor and francis, 2009 [4] i. suharto, project management from conceptual to operational, erlangga, 2017 (in indonesian) [5] project management institute, inc., a guide to the project management body of knowledge, sixth edition, newtown square, 2017 [6] k. kupusamy, s. nagapan, a. h. abdullah, s. kaliannan, s. sohu, s. subramaniam, h. maniam, “construction waste estimation analysis in residential projects of malaysia”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4842-4845, 2019 [7] s. sohu, a. h. abdullah, s. nagapan, t. a. rind, a. a. jhatial, “controlling measures for cost overrun causes in highway projects of sindh province”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4276-4280, 2019 [8] q. yu, k. li, h. luo, “a bim-based dynamic model for site material supply”, procedia engineering, vol. 164, pp. 526-533, 2016 [9] r. e. walpole, r. h. myers, probability & statistics for engineers & scientists, 9th edition, prentice hall, 2012 [10] m. f. quadratullah, applied statistics: theory, examples of cases and applications with spss, andi offset, 2014 (in indonesian) [11] a. mursadin, module of applied statistical volume 4: measures of association, university of lambung mangkurat, 2019 (in indonesian) engineering, technology & applied science research vol. 8, no. 3, 2018, 2901-2906 2901 www.etasr.com le and nguyen: stochastic sizing of energy storage systems for wind integration stochastic sizing of energy storage systems for wind integration dinh duong le faculty of electrical engineering the university of danang—university of science and technology danang, vietnam ldduong@dut.udn.vn nhi thi ai nguyen faculty of electrical engineering the university of danang—university of science and technology danang, vietnam ntanhi@dut.udn.vn abstract—in this paper, we present an optimal capacity decision model for energy storage systems (esss) in combined operation with wind energy in power systems. we use a two-stage stochastic programming approach to take into account both wind and load uncertainties. the planning problem is formulated as an ac optimal power flow (opf) model with the objective of minimizing ess installation cost and system operation cost. stochastic wind and load inputs for the model are generated from historical data using clustering technique. the model is tested on the ieee 39bus system. keywords-energy storage system; ess; opf; sizing; stochastic; wind i. introduction renewable energy has been increasingly integrated into power systems as a result of the effort to reduce co2 emissions and build a future power grid economically feasible and environmentally sustainable. particularly, according to the blue map scenario for power supply, electricity generation from renewable energy will provide a share of 22% of global electricity generation in 2050, which grows almost threefold compared to the baseline scenario [1]. along with this growing share of renewable technologies, greater interest has been attracted to the use of esss due to the variable nature of most renewable energy sources. esss can accommodate renewable generation in time-shifting its energy to match demand and avoid power curtailment. they can also be used to mitigate transmission congestion and hedge forecast errors, etc. in this context, appropriate sizing of storage systems is of importance not only for power system operation but also for economic consideration. in recent years, there has been extensive study on optimal sizing of esss for different applications with wind generation [2-10]. analytical techniques are developed in [2, 3] to determine optimal ess capacity with wind integration. authors in [4] propose a methodology to size ess for power balancing of variable energy generation. they use discrete fourier transform to decompose the required balancing power into different time-varying periodic components, which can be used to quantify storage capacity for different types of energy storages. to deal with the variability and uncertainty of wind power, author in [5] decides optimal ess capacity by using chance-constrained programming. he uses ga combined with monte-carlo simulation to solve the optimization problem in order to minimize energy cost while ensuring the difference between wind/ess output and a predefined profile within a certain limit. in [6], a dynamic sizing based on statistical scenario forecasts and real market situation is presented to assess necessary ess capacity in each period for compensating deviations from proposed bids of wind power. in [7], a methodology is presented to optimize storage capacity for mitigating wind prediction errors. typical seven-scenario approximation of wind power forecast errors are modeled and used in the system tests. authors in [8] focus on storage sizing for voltage support in low voltage distribution networks. the model is formulated as a stochastic optimization problem and a scenario reduction procedure is proposed to reduce the size of the problem. a probabilistic sizing method is proposed in [9] to reduce wind forecast uncertainty. the sizing method is based on persistence-based forecast data and verified with real-world forecast data. authors in [10] apply two-stage stochastic optimization to optimally size esss while minimizing generation cost and maximizing the use of renewable generation. however, they do not incorporate transmission constraints and only focus on an intra-hourly economic dispatch. stochastic programming has been widely employed to handle uncertainties in some areas of power system planning such as power capacity expansion planning [11-13] and transmission planning [14-16]. thus, in this paper, we propose a two-stage stochastic model to determine the optimal capacity of esss in time-shifting wind generation considering wind and load variability. the planning problem is formulated as a nonlinear programming ac opf model, aiming to minimize ess installation cost and system operation cost. our contribution is providing a tool for long-term sizing of esss under the stochastic behavior of both wind generation and load. this planning tool allows to optimally size esss for time-shifting application considering investment costs, generation costs, taking into account network constraints. extensive tests are performed on ieee 39-bus system. the remaining of the paper is organized as follows: in section ii, the mathematical formulation of the model is introduced. in section iii, we engineering, technology & applied science research vol. 8, no. 3, 2018, 2901-2906 2902 www.etasr.com le and nguyen: stochastic sizing of energy storage systems for wind integration describe the stochastic wind and load inputs. in section iv, we discuss a case study and simulation results and section v concludes the paper. ii. mathematical formulation generally, a two-stage stochastic programming problem has the form [17]: min ( ) + ( , )   s.t. g(x) ≤ 0 ( , ) is the optimal value of the second-stage problem: min ( , )  s.t. g(y, ) ≤ 0 where, x are first-stage decision variables, y are secondstage decision variables, ξ is a vector of random parameters, and the expectation operator at the first-stage problem (1) is taken with respect to probability distribution of the random parameters ξ. for random parameters with discrete distribution, i.e., ξ has a finite number of realizations (scenarios) ξω with respective probabilities pω, ω = 1,...,nscen. then: ( , ) ∑ = 1 ( , )  where, nscen is total number of scenarios of the random parameters. in this paper, the two-stage stochastic programming model has the goal of minimizing ess installation cost in the first-stage and total generation cost in the second-stage; therefore, the objective function is formulated as: min, ∑ + + ∑ ∑ ∑ + , + , + =1 , + ℎ ℎ ,   in (4), and , which are respectively energy rating and power rating of the ess, are control variables of the first-stage. , , , , , are variables of the second-stage. they are respectively real generation power of generating unit at bus i in hour t and scenario ω, including power from both conventional and wind generators, and discharging and charging power of ess at bus i in hour t and scenario ω. , , are cost coefficients of the generating unit at bus i. and are discharging and charging cost of the ess at bus i. ns and ng are total number of esss to be installed and total number of generating units, respectively. t is the optimization period considered for the second-stage problem. in this model, the second-stage problem is based on a daily basis, and hence t=24 hours. c [$/kwh/day] and c [$/kw/day] are respectively ess daily energy-related and power-related capital cost. assuming a life time of n years, ess total capital cost is converted into daily capital cost by multiplying the energy-related cost and power-related cost by the daily capital recovery factor [18]: = ( )( ) (5)  = ( )( )  (6) where, cb[$/kwh] and cr[$/kw] are energy-related and power-related capital costs of esss, r is annual interest rate and nday is the number of days in a year, which is 365 days. the 3rd component in the objective function (4) is the implementation of complementary constraint to make sure an ess is not charged and discharged simultaneously. this constraint is incorporated by applying suitable values for charging and discharging costs (cch and cd) of the ess. since the operational cost of charging cch is the locational marginal price (lmp) at the ess bus, it is set to zero. to prevent simultaneous charging and discharging, the operational cost of discharging cd is set to a very small quantity, i.e., cd =10-2 [19]. this objective function has to fulfill both network constraints (7)-(13) and constraints for esss (14)-(20):  power balance equations include equations for real and reactive power at each node i in each time period t for each scenario ω: , − , + , − , = ∑ , , cos , −, + sin , − , (7) , − , + , − , = ∑ , , sin , −, − cos , − , (8) where, nb is the total number of buses in the system. , and , denotes real and reactive power of load at bus i in hour t and scenario ω. , defines reactive power of generating unit at bus i in hour t and scenario ω. , and , are reactive charging and discharging power of ess at bus i in hour t and scenario ω. , and , are voltage magnitudes of bus i and k in hour t and scenario ω. , and , are voltage angles of bus i and k in hour t and scenario ω. gik and bik are line conductance and line susceptance of branch ik.  upper and lower limits for voltage magnitudes: ≤ , ≤ (9) where, and are lower and upper limits of voltage magnitude at bus i.  bounds on real and reactive generation powers: engineering, technology & applied science research vol. 8, no. 3, 2018, 2901-2906 2903 www.etasr.com le and nguyen: stochastic sizing of energy storage systems for wind integration ≤ , ≤ (10)  ≤ , ≤   where, and are lower and upper limits of real power generation of generating unit at bus i. and are lower and upper limits of reactive power generation of generating unit at bus i.  branch current limits: 0 ≤ , ≤ (12) or 0 ≤ , ≤ (13) where, , and , are magnitude of currents flowing from bus i to bus j and from bus j to bus i in hour t and scenario , respectively. and are upper limits of currents flowing from bus i to bus j and from bus j to bus i, respectively.  ess energy balance equations include energy balance equation for each ess in each period, considering charging and discharging efficiencies: , = , + ( , + , ⁄ )∆ (14) where, , and , are energy levels of ess at bus i in hour t and t-1 in scenario . and are ess charging and discharging efficiencies, respectively.  ess energy continuity this constraint is added to make sure energy of ess i at the end of the day is equal to energy at the beginning of the day b0. , = , (15) where, , and , are respectively energy level at the beginning of the day and at hour 24 of ess at bus i in scenario .  ess charging/discharging power bounds: ≤ , ≤ (16)  ≤ , ≤    ≤ , ≤    ≤ , ≤   where, is lower limit of real charging/discharging power of ess at bus i. and are lower and upper limits of reactive charging/discharging power of ess at bus i.  ess energy limits: ≤ , ≤ (20) where, , is energy level of ess at bus i in hour t and scenario . is lower limit of energy of ess at bus i. the proposed two-stage stochastic model is a non-linear and non-convex problem. it is implemented in gams on a pc with intel core i7 – 3.4ghz cpu and 8.0gb of memory, using ipopt solver with optimality gap of 0.5%. iii. stochastic input data stochastic programming is a programming approach involving uncertain parameters which can be characterized by discrete distributions with a set of scenarios or realizations. in stochastic programming, deterministic mathematical formulation of any model is solved with this set of scenarios of uncertain parameters. therefore, a necessary step in applying stochastic programming approach is generating a set of scenarios that realistically represents parameter uncertainties. for planning problems, the long-term planning horizon may result in a very large number of scenarios, which leads to intractability of the problems. to attain tractability with reasonable computation time for such planning problems, there is a need to approximate the original scenario set into a smaller subset, which still preserves essential features of the original one by using different scenario reduction techniques. in this paper, we consider the stochastic nature of both wind and load. scenarios for these parameters are generated from historical hourly data using pca-guided k-means clustering technique [20]. daily wind and load data are clustered into distinct groups and the resulting representative wind and load profiles of each cluster along with their probabilities are obtained. k-means is known as one of the most popular and efficient clustering techniques in many applications because of its simple and efficient implementation. however, for high dimensional data set such as wind power and load, it is extremely difficult to identify their coherent patterns. therefore, applying directly k-means technique to these data may result in clusters with less accuracy. a possible solution to this problem is the use of a dimension reduction technique such as principle component analysis (pca) [21], which projects data to a lower dimensional subspace, where their patterns are more easily identified. in pca-guided k-means clustering technique, k-means is performed in the pca subspace to initialize centroids for clustering in the full data space. this pca-guided algorithm is proved to be effective in obtaining better solutions and computation time, especially for such high dimensional data as wind and load. to prepare stochastic inputs for the model, we use historical 5-minute data of wind power and load from 2007 to 2013 [22].these wind and load data are averaged to create hourly data and then scaled down to a suitable level for the test engineering, technology & applied science research vol. 8, no. 3, 2018, 2901-2906 2904 www.etasr.com le and nguyen: stochastic sizing of energy storage systems for wind integration system (figure 1). the pca-guided k-means clustering technique is applied to these data by first performing pca analysis on the set of wind and load data to create another set of the same size of linearly independent variables called principle components (pcs). the first few components, which contain the highest amount of information (up to more than 90%) of the original data, are selected. the original data set is thus reduced to another with smaller dimensionality called pca subspace. the selected pcs of the above wind and load data can be seen in figure 2. k-means clustering is then performed in the pca subspace to obtain initial cluster centroids and performed in the full space afterwards using the above initial cluster centroids. finally, the representative scenario of each cluster is determined by averaging the members of the cluster. a) wind data b) load data fig. 1. input data for ieee 39-bus case study. a) wind pcs b) load pcs fig. 2. pcs of the input data. after performing clustering on wind and load data, we obtain a set of wind scenarios and load scenarios as shown in figure 3, each of them associated with a probability. these wind and load scenarios are used to create sets of wind-load scenarios for the problem. each set of scenarios consists of one scenario of wind and another scenario of load. these sets are created by listing all possible combinations of wind scenarios and load scenarios. the probability of any combined wind-load scenario is obtained by convolving the two probabilities of wind and load scenarios. iv. case study and discussion we performed tests on a modified ieee 39-bus system (figure 4), which has 9 conventional generators with a total capacity of 2200mw and system load with peak value of 2007mw. wind farms were connected to buses 32 and 35. in order to test the model with different wind penetration levels, which is the ratio between wind farm installed capacity and the peak load, we assume the total installed capacity of both wind farms as 400mw, 600mw, and 800mw, accounting for 20%, 30%, and 40% of wind penetration respectively. an ess system, with capacity to be determined, is installed at a wind bus, for example, bus 32. three different ess technologies are considered, i.e., battery energy xtorage (bes), compressed air energy storage (caes) and pumped hydro storage (phs). parameters of these storage technologies are shown in table i, assuming ηch=ηd=η [23–25]. for the sake of simplicity, we assume a correlation coefficient of 1 for the wind farms. if the correlation coefficient is different from 1, wind power of each wind farm will be represented by each set of wind scenarios, which results in an increase in the total number of scenarios. this will only increase the computation time and does not affect the accuracy of the proposed model. the daily capital cost of each ess technology is calculated according to (5) and (6) is shown in table ii. a) wind scenarios b) load scenarios fig. 3. wind and load scenaios for ieee 39-bus case study. fig. 4. ieee 39-bus system. table i. parameters of the three ess technologies cb ($/kwh) cr ($/kw) n (years) η r (%) bes 330 400 15 0.85 5 caes 5 700 30 0.79 phs 14 1000 30 0.87 engineering, technology & applied science research vol. 8, no. 3, 2018, 2901-2906 2905 www.etasr.com le and nguyen: stochastic sizing of energy storage systems for wind integration table ii. daily capital cost of the three ess technologies cbd ($/kwh/day) crd ($/kw/day) bes 87.1 105.6 caes 0.89 124.7 phs 2.5 178.2 from the 6 wind scenarios and 5 load scenarios (each associated with a probability) shown in figure 3, we combines each wind scenario with the 5 load scenarios to create a set of 30 wind-load scenarios as system input. the probability of each scenario in this set is obtained by convolving probabilities of the corresponding wind and load scenarios. we run the model with this set of 30 wind-load scenarios at different wind penetration levels. the test is performed first with bes system, and then repeated for the remaining ess technologies considered, i.e., caes and phs. it turns out that due to the high investment cost of bes, the model does not choose to install this technology for any wind penetration level. in other words, installing bes in this case does not yield any benefit for the system since its capital cost overweighs the profit from the combined operation of wind and bes. the model, instead, chooses to install caes and phs. optimal capacities of the caes and phs are shown in table iii. ess of both technologies is installed at wind penetration level from 30% to 40%. at 20% wind penetration level, which is 400mw for both wind farms, since the amount of excess wind power to be timeshifted is also not enough to cover the investment cost of either caes or phs, the model does not install the storage device. at higher wind penetration levels (30% and 40%), the model decides to install either caes or phs system and capacity of the storage device is gradually increased with the wind penetration. capacity of caes is larger than that of phs. this capacity difference is higher at higher wind penetration levels. as noted from table i, even phs technology has higher efficiency than caes, its higher daily capital cost still results in smaller capacities of the storage device. table iii. optimal capacity of ess in 39-bus system wind 20% 30% 40% phs caes phs caes phs caes bmax (mwh) 0.0 0.0 74.4 83.1 109.3 162.8 rmax (mw) 0.0 0.0 12.2 15.0 18.3 29.5 we also performed tests for the case when there is no ess installed to compare the total yearly cost of the system in both cases, with and without the storage device (table iv). this cost includes the yearly capital cost of the ess and the expected value of the yearly generation cost. table iv. total cost of 39-bus system with and without ess wind 30% 40% no ess 4.6355e+8 4.4588e+8 caes 4.6329e+8 4.4526e+8 phs 4.6343e+8 4.4547e+8 as can be seen from table iv, the total yearly cost of the system is lower when ess is installed. moreover, the case of phs results in a slightly higher yearly cost compared to that of caes. the cost difference between these three cases is higher at higher wind penetration, when higher ess capacity is installed. that is, the caes gains a cost reduction of 0.06% at 30% wind penetration and 0.14% at 40% wind penetration while the phs yields 0.03% cost reduction at 30% wind penetration and 0.09% at 40% wind penetration. daily operation of the caes in all scenarios at 30% wind penetration level, can be seen in figure 5 as an example. basically, in many scenarios (corresponding to load scenarios with higher peaks in figure 3b), the caes is charged at off-peak periods (hours 1 to 5 and hours 13 to 16) and then discharged at peak periods (hours 7 to 12 and hours 18 to 20). in other scenarios (corresponding to load scenarios with lower peaks in figure 3b), it is charged at off-peak periods (hours 1 up to 7) and gradually discharged at high load periods (hours 9 to 11, 12 to 16, and 17 to 21). in other words, the storage has been fully employed to time-shift wind energy for matching the demand in all scenarios of wind and load. fig. 5. energy level of the caes in daily operation. we also performed tests on a reduced model by removing the constraints on branch current limit, i.e., constraints (12) (13), for branches with current flow less than 70% of the branch limit. the size of the model is thus reduced considerably and the computation time is also significantly less than that of the full model. in particular, computation time of the ieee 39-bus system is reduced from 17 minutes to only 2 minutes. v. conclusions in this paper, we propose a two-stage stochastic model to optimally size esss in power systems with high wind integration aiming to minimize ess capital cost and system generation cost. the model is incorporated into an ac opf problem, taking into account network constraints and ess constraints. stochastic input data of wind and load are generated from historical data using pca-guided k-means clustering technique. the model is extensively tested on ieee 39-bus with three ess technologies and different wind penetration levels. optimal sizes of the esss, energy rating and power rating, are explicitly determined. simulation results show that the esss are efficiently employed in time-shifting wind energy to meet the demand. the model is solved using direct method and tests on the case study give reasonable computation time. engineering, technology & applied science research vol. 8, no. 3, 2018, 2901-2906 2906 www.etasr.com le and nguyen: stochastic sizing of energy storage systems for wind integration acknowledgment this work was supported by the university of danang, university of science and technology, code number of project: t2017-02-95. references [1] p. taylor, energy technology perspectives 2010 -scenarios and strategies to 2050, international energy agency, paris, france, 2010 [2] h. t. le, t. q. nguyen, “sizing energy storage systems for wind power firming: an analytical approach and a cost-benefit analysis”, ieee power and energy society general meeting – conversionand delivery of electrical energy in the 21st century pittsburgh, usa, july 20-24, 2008 [3] z. y. gao, p. wang, l. bertling, j. h. wang, “sizing of energy storage for power systems with wind farms based on reliability cost and wroth analysis”, ieee power and energy society general meeting, san diego, usa, july 24-29, 2011 [4] y. v. makarov, p. du, m. c. w. kintner-meyer, c. jin, h. f. illian, “sizing energy storage to accommodate high penetrationof variable energy resources”, ieee transaction on sustainable energy, vol. 3, no. 1, pp. 34-40, 2012 [5] l. li; l. yang, “a chance-constrained programming based energystorage system sizing model considering uncertainty of wind power”, international conference on sustainable power generation and supply (supergen 2012), hangzhou, china, september 8-9, 2012 [6] p. pinson, g. papaefthymiou, b. klockl, j. verboomen, “dynamic sizing of energy storage for hedging wind power forecast uncertainty”, ieee power & energy society general meeting, pes 2009, calgary, ab, canada, july 26-30, 2009 [7] t. hou, y. cui, y. li, w. zhang, x. zhou, “sizing battery energy storage for wind farms based on wind power forecast 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uncertainty using benders decomposition”, international review of electrical engineering, vol. 4, no. 5, pp. 976-984, 2009 [17] a. shapiro, d. dentcheva, a. ruszczynski, lectures on stochastic programming: modeling and theory, society for industrial and applied mathematics and mathematical programming society, philadelphia, usa, 2009 [18] c. s. park, fundamentals of engineering economics, pearson education, inc., new jersey, 2004 [19] a. castillo, d. f. gayme, “profit maximizing storage allocation in power grids”, ieee 52nd annual conference on decision and control (cdc), pp. 429-435, 2013 [20] q. xu, c. ding, j. liu, b. luo, “pca-guided search for k-means”, pattern recognition letters, vol. 54, pp. 50-55, 2015 [21] d. d. le, g. gross, a. berizzi, “probabilistic modeling of multisite wind farm production for scenario-based applications”, ieee transactions on sustainable energy, vol. 6, no. 3, pp. 748-756, 2015 [22] bonneville power administration, wind generation &total load in the bpa balancing authority, available at: http://transmission.bpa.gov/ business/operations/wind/ (date of last access: february 21, 2018) [23] s. m. schoenungand, w. v. hassenzahl, longvs. short-term energy storage technologies analysis, sandia national laboratories, u.s. department of commerce, 2003 [24] s. m. schoenungand, characteristics and technologies for longvs. short-term energy storage, sandia national laboratories, u.s. department of commerce, 2003 [25] s. m. schoenungand, energy storage systems cost update, sandia national laboratories, 2011 microsoft word natarajan-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 387-390 387 www.etasr.com rajamohan and rajasimman: kinetic modeling of dye effluent biodegradation by pseudomonas stutzeri kinetic modeling of dye effluent biodegradation by pseudomonas stutzeri natarajan rajamohan dpt of chemical engineering, sohar university, sohar, sulatanate of oman natrajmohan@gmail.com manivasagan rajasimman dpt of chemical engineering, annamalai university, annamalai nagar, india simms@rediffmail.com abstract—dye industry waste water is difficult to treat because of the presence of dyes with complex aromatic structure. in this research study, the biodegradation studies of dye effluent were performed utilizing pseudomonas stutzeri in a controlled laboratory environment under anoxic conditions. the effects of operational parameters like initial ph of the effluent and initial chemical oxygen demand (cod) of the effluent on percentage cod removal were studied. a biokinetic model is established giving the dependence of percentage cod removal on biomass concentration and initial cod of the effluent. the biokinetics of the cod removal was found to be first order with respect to both the microbial concentration and initial cod of the effluent. the optimal ph for better bacterial degradation was found to be 8.the specific degradation rate was found to be 0.1417 l/g dry cell mass (dcm) h, at 320 c. keywordsdye effluent degradation; biokinetics; anaerobic. i. introduction over 7x10 5 metric tons of synthetic dyes are produced world wide every year for dyeing and printing. a very small amount of dye in water (10-50 mg/l) is highly visible and affects the aesthetic merit, water transparency and gas solubility of water bodies, dyeing units are found in most countries and their numbers have increased. these industries have shown a significant increase in the use of synthetic complex organic dyes as the coloring material. the annual world production of textiles is about 30 million tones requiring 700,000 tonnes of different dyes which causes considerable environmental pollution problems. dyes include a broad spectrum of different chemical structures, primarily based on substituted aromatic and heterocyclic groups such as aromatic amine (c6h5-nh2), which is a suspected carcinogen, phenyl (c6h5-ch2) and naphthyl (no2-oh), the only thing in common is their ability to absorb light in the visible region. the waste water from these industries are characterized by high alkalinity, biological oxygen demand, chemical oxygen demand, total dissolved solids and with dye concentrations usually less than 1 g/dm 3 [1]. color is the first contaminant to be recognized in wastewater and has to be removed before discharging in to water bodies or on land. the inefficiency in dyeing processes has resulted in 10-15% of unused dyestuff entering the wastewater directly. color present in dye effluent gives a straightforward indication of water being polluted and discharge of this highly colored effluent can damage directly the receiving water. furthermore, it is difficult to degrade the mixtures of the wastewater from the textile industry by conventional biological treatment processes, because their ratio of biochemical oxygen demand (bod)/chemical oxygen demand (cod) is less than 0.3 [2]. the discharges of dye house wastewater into the environment is aesthetically displeasing, impede light penetration, damage the quality of the receiving streams and may be toxic to treatment processes, to food chain organisms and to aquatic life. the degradation of molecules of dyes in the environments by microorganisms is likely to be slow, which means that it is possible for high levels of dye to persist, and potentially accumulate. due to the low biodegradability of dyes, conventional biological treatment processes are inefficient in treating dye wastewaters. in addition, numerous physical and chemical techniques such as flocculation combined with flotation, electro-flotation, flocculation with fe(ii), ca(oh)2, membrane filtration, precipitation, ionexchange, ozonation and katox treatment method involving the usage of activated carbon and air mixtures were also used [3]. even though some of the above mentioned methods are effective, most of them suffer from shortcomings such as excess usage of chemicals, sludge disposal, expensive operating cost, ineffective color reduction for sulfonated azo dyes and poor sensitivity towards shock load conditions. biological decolonization is employed under either aerobic or anaerobic environment. a number of reports discourage the azo dye decolonization by microorganism under anaerobic conditions as it leads to the formation of corresponding aromatic amines. even though their reductive cleavage is responsible for colour removal, the formation of aromatic amines is highly undesired as they are reported to be carcinogenic. in the presence of oxygen, aromatic amines can be degraded. degradation of azo dyes has been studied under aerobic conditions using both pure and mixed microbial cultures. the restrictive environmental legislation, the ecological problem and the high cost of conventional technologies for dye house effluent treatment have resulted in the search of economically viable and technologically suitable wastewater treatment plants. dye house effluents usually contain azodyes which are highly resistant to biological treatment and these dyes are considered to be recalcitrant xenobiotic compounds because of the presence of n=n bonds etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 387-390 388 www.etasr.com rajamohan and rajasimman: kinetic modeling of dye effluent biodegradation by pseudomonas stutzeri and other possible groups, like the sulphonic group, which are tough to be degraded. it was reported that some anaerobic bacteria could biodegrade dyestuffs by azoreductase activity. however the effluent from biodegradation of dyestuffs could be toxic. also, reverse coloration may take place when the degradation products are exposed to oxygen. [4]. because of these above-mentioned problems, full-scale application of bacterial degradation is limited. also, only few research works have been reported on the aerobic degradation of azo dyes. therefore, a need exists to develop a novel treatment technology for textile dye effluent treatment to ensure environmental protection from these harmful pollutants. the effectiveness of microbial decolorization depends on the adaptability and the activity of selected microorganisms. over the past decades, many microorganisms are capable of degrading azo dyes, including bacteria, fungi and yeast [5, 6]. however, the low ph requirement for an optimum activity of the enzymes and the long hydraulic retention time for complete decolorization are the disadvantages of using fungi. in addition, they may inhibit the growth of other useful microorganisms. thus, large-scale applications of fungal decolorization have been limited. with the aforesaid details in the background, this investigation was aimed to study the feasibility of biodegradation of the dye house effluent by employing the bacterial strain pseudomonas stutzeri under anoxic conditions. also, the biokinetic pattern of cod removal of the effluent was studied and the kinetic constants were determined. ii. materials and methods a. dye house effluent the dye house effluent was collected from a dyeing unit situated in tirupur region (tamilnadu, india). the characteristics of the dye house effluent were cod-3200 mg l1, bod-840 mg l-1 and ph 8.2±0.1 [7]. the colour of the effluent was dark red due to the presence of dyes. the effluent was refrigerated at 4ºc and used without any preliminary treatment. b. microorganism pure bacterial strain pseudomonas stutzeri (mtcc no: 101) was purchased from microbial type culture collection and gene bank, chandigarh, india. the strain was maintained in growth medium whose composition is agar-15g, beef extract1g, yeast extract-2g, peptone-5g, sodium chloride-5g in 1 liter of distilled water. the cultures were growth in a controlled environment in a working temperature of 32ºc. c. estimation of cell mass and cod of effluent with cell free supernatant samples were withdrawn from the conical flasks and centrifuged at 13,000 rpm for 5 minutes. with the clear supernatant obtained, cod was evaluated [7]. similar procedures were also followed to evaluate the degradation potential of strains incubated for specified period of time. the initial cod removal data were used to find the microbial activity based on per mg/l of cod removed per gram of dry cell mass (dcm) per unit time. the dcm in suspension was determined after dehydration at 80ºc to constant weight. control experiment was conducted in parallel with uninoculated flasks. the pseudomonas stutzeri strain was added in predetermined proportion (0.62 g dcm/l) to the effluent along with the growth medium. in order to find the maximum cod removal percentage of the dye house effluent by the bacterial strains, a test solution containing 0.62 g dcm per liter and the proportionate quantities of growth medium constituents, was incubated under static conditions at 32 ºc. the time courses of percentage cod reduction and effluent cod removal were observed and plotted. in order to find out the concentration of cell mass, a calibration curve was also prepared between the dry weight of cell mass and optical density of the broth at 540 nm. d. effect of ph stock culture of the selected bacterium, pseudomonas stutzeri was prepared by growing a single colony in 100 ml of growth medium in 500 ml conical flasks for 3 days at 32 ºc under static condition. an aliquot of 1 ml of each bacterium was inoculated into a 500 ml conical flask with 10 ml of growth medium plus 100 ml of dye house effluent. as ph is one of the controlling factors of bacterial activity, it is inevitable to study its influence on % cod removal. the ph of the medium was adjusted 4, 6, 8, 10, 12 with 1m hcl. iii. results and discussion a. effect of effluent ph among the various process variables, ph play a vital role for the optimal activity of bacterial cultures and ph is an influencing factor for nutrient transport across the bacterial cell membrane [8]. to determine the optimal ph for the bacterial activity, a set of batch tests were conducted at different ph. the highest cod removal percentage of 93% was achieved at ph=8. whereas acidic effluent environment (ph=4, ph=6) reduced the activity of, pseudomonas stutzeri producing 12% and 58% cod removal respectively. similar inhibitory effect on % cod removal was achieved when the ph moved towards a more basic region (i.e. ph=10, 12). the influence of ph on the percentage cod removal is illustrated in figure 1. fig. 1. effect of solution ph on degradation of dye house effluent by pseudomonas stutzeri (t=48 h; temp=32 o c; m=0.62 g dcm) the microbial action at the actual effluent ph, which was normally in the range of 8.2±0.1, was effective yielding cod removal of 77%. very similar results have been reported with the decolorization study on acid violet 7 by an isolated pseudomonas strain [9]. many researchers have studied the etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 387-390 389 www.etasr.com rajamohan and rajasimman: kinetic modeling of dye effluent biodegradation by pseudomonas stutzeri effect of ph on decolorization of different textile dyes [10, 11, 12, 13].the optimal value for better dye waste water treatment is reported to be often a neutral value or slightly alkaline value [8]. defale et al.[14] reported the optimal ph range 7.0-8.0 for the removal of remazol black b by pseudomonas aeruginosa. ponraj et al.[15] reported maximum decolorization efficiency (89.0 %) at ph 6.0 for pseudomonas sp. b. bio kinetic modeling in order to measure the minimum degradation rate of dye house effluent pseudomonas stutzeri, the static effluent and 0.62 g dcm/l and 10 ml of growth medium was incubated under anoxic condition at 32 o c for 48 hr. figure 2 shows the time course of cod remaining. fig. 2. the time course of degradation of dye house effluent by pseudomonas stutzeri (t=48 h; temp=32 o c; m=0.62 g dry cell mass) ][ ]][[ ][ ][][ 1 2 1 02 s k k k sek sk sv dt sd v m m ++ = + =−= − (1) the below mentioned equation 2 gives the convenience on analysis of effect of temperature m nds km s dt = − (2) where t is the incubation time (h), m is the biomass concentration (mg dcm/l), m is the partial reaction order with respect to biomass, s is the cod value of the effluent (mg/l) and n is its partial reaction order. here, k is the specific cod removal rate with units (mg (1–n) l (m+n–1) / mgdcm m h). it was reported that (2) could be considered as a modified model of michaelis menten rate equation (1), when the parameter km is not included. the relationship between the cod of the effluent and incubation time depending on the partial reaction order (n) is given by (1 ) (1 ) 0 0 (1 ) 1 , when (n 1) n m n s n km t s s − − − = − ≠       (3) 0 exp( ), when (n 1) ms km t s = − ≠       (4) when the plot between incubation time and the cod value was made, a high degree of linearity was observed (r 2 >0.99), as shown in figure 3. hence the order of the reaction with respect to effluent cod value was found to be 1.0. fig. 3. data fitting and estimation of bio kinetic parameters for this set of experiments, used to establish a relationship between biomass concentration and effluent cod removal rate, the incubation time was fixed as 12 h. as shown in figure 4, a linear relationship (r 2 >0.97) was obtained between biomass concentration m and km m that indicates m equals to unity. therefore, the cod removal was a first order reaction with respect to biomass concentration (m). fig. 4. effect of cell mass concentration on remaining cod of the effluent at 32 o c the kinetic model of cod removal by the pseudomonas stutzeri was given by ds kms dt = − (5) s = s0 exp (− kmt) (6) the value of specific cod removal rate, k, obtained from the slope of the line in figure 3 was 0.1417 l k gdcmh = at 32°c etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 387-390 390 www.etasr.com rajamohan and rajasimman: kinetic modeling of dye effluent biodegradation by pseudomonas stutzeri iv. conclusion 1. effective degradation of dye house effluent was achieved by the bacterial strain pseudomonas stutzeri under anoxic environment. 2. the optimal ph for better degradation of dye effluent was found to be 8.0. 3. the biokinetics of the cod removal was found to be first order with respect to both the microbial concentration and initial cod of the effluent with the rate equation 0.1417 ds ms dt = − 4. the specific cod removal rate (k) was found to be 0.1417 l gdcmh at 32°c. references [1] p. kaushik, a. malik, “fungal dye decolourization: recent advances and future potential”, environment international, vol. 35, no. 1, pp. 127141, 2009 [2] k. chen, j. wu, d. liu, s. j. hwang, “decolorization of the textile dyes by newly isolated bacterial strains”, journal of biotechnology, vol. 101, no. 1, pp. 57-68, 2003 [3] a. srinivasan, t. viraraghavan, “decolorization of dye waste waters by biosorbents: a review”, journal of environmental management, vol. 91, no. 10, pp. 1915-1929, 2010 [4] i. m. banat, p. nigam, d. singh, r. marchant, “microbial decolorization of textile dye containing effluents: a review”, bioresource technology, vol. 58, no. 3, pp. 217227,1996 [5] e. forgacs, t. cserhati, g. oros, “removal of synthetic dyes from wastewaters: a review”, environment international, vol. 30, no. 7, pp. 953-971, 2004 [6] j. s. knapp, p. s. newby, “the decolourisation of a chemical industry effluent by white rot fungi”, water research, vol. 33, no. 2, pp. 575577, 1999 [7] american public health association (apha), standard methods for the examination of water and wastewater, 20 th ed, american public health association, american water works association, water pollution control federation, washington dc, 1998 [8] s. k. garg, m. tripathi, s. k. singh, j. k. tiwari, “biodecolorization of textile dye effluent by pseudomonas putida skg-1 (mtcc 10510) under the conditions optimized for monoazo dye orange ii color removal in simulated minimal salt medium”, international biodeterioration & biodegradation, vol. 74, pp. 24-35, 2012 [9] j. yu, x. wang, p. l. yue, “optimal decolorization and kinetic modelling of synthetic dyes by pseudomonas strains”, water research vol. 35, no. 15, pp. 3579-3586, 2001 [10] o. d. olukanni, a. osuntoki, g. o. gbenle, “decolorisation of azo dyes by a strain of micrococcus isolated from a reuse dump soil”, biotechnology, vol. 8, pp. 442-448, 2009 [11] r. g. saratale, g. d. saratale, d. c. kalayani, j. s. chang, s. p. govindwar, “enhanced decolorization and biodegradation of textile azo dye scarlet r by using developed microbial consortium-gr”, bioresource technology, vol. 100, no. 9, pp. 2493-2500, 2009 [12] r. sawney, a. kumar, “congo red (azo dye) decolourization of local isolate vt-ii inhabiting dye-effluent exposed soil”, international journal of environmental sciences, vol. 1, no. 6, pp. 1261-1267, 2011 [13] h. wang, j. q. su, x. w. zheng, y. tian, x. j. xiong, t. l. zheng, “bacterial decolorization and degradation of the reactive dye reactive red 180 by citrobacter sp. ck3”, international biodeterioration & biodegradation, vol. 63, pp. 395-399, 2009 [14] n. dafale, s. wate, s. meshram, t. nandy, “kinetic study approach of remazol blackb for the development of two-stage anoxic reactor for decolorization/biodegradation of azo dyes by activated bacterial consortium”, journal of hazardous materials, vol. 159, no. 2-3, pp. 319-328, 2008 [15] m. ponraj, k. gokila, v. zambare, “bacterial decolorization of textile dye-orange 3r”, international journal of advanced biotechnology and research, vol. 2, no. 1, pp. 168-177, 2011 engineering, technology & applied science research vol. 9, no. 6, 2019, 4870-4875 4870 www.etasr.com danikas: bubbles in insulating liquids: a short review bubbles in insulating liquids: a short review michael g. danikas department of electrical & computer engineering democritus university of thrace, greece mdanikas@ee.duth.gr abstract—this paper deals with the influence of bubbles in insulating liquids (e.g. transformer oil) and their role in liquid breakdown. bubbles play a deleterious role in the dielectric strength of insulating liquids. depending on their shape and localized electric field, bubbles may significantly lower the dielectric strength of an insulating liquid. the present paper offers a short review –albeit incomplete– on the role of bubbles and tries to elucidate their relation to the total breakdown of dielectric liquids. it also proposes some further fields of research. keywords-bubbles; insulating liquids; low refractive index; dielectric strength; breakdown strength; bubbles; streamer i. introduction insulating liquids are widely used in high voltage equipment to easily fill a space needed to be insulated and since they can be circulated easily, they can also be used to dissipate any heat generated in the system. they exhibit, in general, a satisfactory dielectric strength [1]. their principal disadvantage is that they can be easily contaminated. of the various insulating liquids, transformer oil is the most widely used. previous research has investigated the physics of the breakdown mechanism in insulating liquids in detail [2-5]. statistical investigations have also been conducted and various statistical models have been proposed in [6, 7]. a special subject of interest when working with insulating liquids is the subject of bubbles, the presence of which may vastly increase the probability of breakdown. it is the aim of the present paper to approach the subject of bubbles in insulating liquids and to try to give an overall picture of the work done. needless to say that the present review is incomplete in terms of investigating the numerous factors affecting the dielectric strength of insulating liquids, as it is only focused in the effect of bubbles. ii. bubbles in insulating liquids the gas content of an insulating liquid is one of the most important factors affecting the conduction and breakdown processes. the gas can be traced either in solution or in suspension in the form of bubbles. the dielectric strength of a dielectric liquid is often no more than that of a gas at moderate pressure (5 to 10 bar), even though the density of the former is 100 time greater [8]. pohl studying the motion of suspensoids in divergent electric fields, made the clear distinction between dielectrophoresis (arising due to the tendency of conducting particles to become polarized and move into regions of highest field strength) and electrophoresis (arising from the electrostatic attraction of charged electrodes for charged particles) [9]. years later, the same researcher gave experimental evidence according to which the phenomenon of dielectrophoresis becomes large and noticeable when large suspensoids are subjected to non-uniform fields [10]. considering the field strength inside a spherical bubble kao calculated the change in stored energy due to the presence of the bubble in [11]. then, assuming that a spherical bubble may deform into a spheroidal shape, he calculated the change in stored energy. the difference between these two illustrates the energy for the bubble deformation. it is obvious that if this difference is positive, a spherical bubble will elongate in the direction of the field. however, despite his elaborate analysis, kao did not present any experimental data to support his theoretical calculations. later on, the same researcher experimenting with air bubbles and water drops in transformer oil and reached two interesting conclusions: (a) that gas bubbles and liquid drops tend to elongate in the direction of the applied field in a fluid dielectric, irrespective of whether the permittivity of the bubble (or drop) is larger or smaller than that of the surrounding liquid, and (b) that the greater the difference in permittivity between the bubble (or drop) and the liquid dielectric and the larger the original size of the bubble (or drop), the smaller the electric field required to cause elongation [12]. although kao’s work was criticized in [13] because of his criteria for energy relations, the latter also suggested that a gas bubble in a liquid, subjected to an electric field between parallel plane electrodes, assumes the shape of a prolate spheroid in the direction of the electric field, elongating until a critical shape is reached when the bubble becomes unstable. in a later publication, kao proposed that near breakdown there is only one filament in which the current density is large enough to cause vaporization of the liquid and consequently bubbles [14]. experimental data presented in [13] indicated that a conducting or a non-conducting bubble for which its permittivity is 20 times larger than the permittivity of the liquid, has a critical stable shape corresponding to a critical value of the ratio of the major to the minor semi-axis of the bubble. at low values of the above mentioned ratio, however, elongation requires much higher fields, although not greater than the required for breakdown in pure liquids. in a work reminiscent of the research done by pohl [9, 10], stuetzer performed studies by analyzing the flow of a bubblecontaining charged liquid in a rectangular channel, and drew the conclusion that gas bubbles in charged regions of an insulating liquid move away from high fields. they do not corresponding author: m. g. danikas engineering, technology & applied science research vol. 9, no. 6, 2019, 4870-4875 4871 www.etasr.com danikas: bubbles in insulating liquids: a short review acquire a net charge of their own but they are moved by electrical pressure gradients and polarization forces. the bubble motion is determined by electrical pressure gradients, superimposed on hydraulic pressure distribution and by dielectrophoretic forces [15]. a somehow complete picture of the behavior of a gas bubble in a liquid dielectric was given in [8], where an approximate condition for bubble stability was proposed, assuming that (a) a gas bubble has the shape of a hollow prolate ellipsoid the major axis of which is parallel to the applied electric field, (b) the field inside the bubble is uniform and very nearly equal to the applied electrical field, (c) the field outside (i.e. in the liquid) is nowhere larger than the field inside the bubble and (d) the pressure in the gas bubble is larger than the pressure in the liquid outside the stressed region. of the four main possible sequences (1-elongation/ignition/ instability/breakup, 2-no elongation/ignition/instability/breakup 3-no elongation/ignition/no instability, 4-elongation/without ignition), felici considered the sequences 3 and 4 rather rare. in fact, after ignition, strong instability and breakup of the bubble is likely to occur; very high field concentrations may develop and cause intrinsic breakdown of the liquid phase. gas bubble behavior was also the subject of [16], where it was shown that an electrically stressed bubble volume decreased by more than an order of magnitude in the naphthenic mineral oil, by over 50% in the blend of a naphthenic and a paraffinic oil (nh-ph) but it increased by 4 to 1 in the paraffinic mineral oil. such differences are possibly due to the gas-evolving properties of the paraffinic mineral oil. in [16], it was also indicated that various discharges related to an electrically stressed gas bubble were observed ranging over a 10 to 1 magnitude. this is because at times the whole bubble may discharge or just parts of it. obviously, the largest partial discharge magnitudes are related to the complete bubble volume. the observations of [16] were not at variance with those of [17], even though the latter used a completely different experimental setup. going back to older research, it was indicated quite early that bubbles are associated with the breakdown of insulating liquids, with bubbles on the electrode surfaces having a most important role [18]. in [18], it was pointed out that the main effect of bubbles is to cause enhanced emission of electrons from the underlying metal due to the local increase of the electric field. other researchers also associated the breakdown mechanism with the development of gas bubbles in an insulating liquid [19, 20]. bubble breakdown in liquids was also discussed in more recent publications, where it was stressed that bubbles may be formed because of (i) gas pockets on the surface of the electrodes, (ii) due to irregularities of electrode surfaces, where point charge concentrations may lead to corona discharge and thus vaporization of the liquid, (iii) changes in pressure and temperature, and (iv) dissociation of products by electron collisions giving rise to gaseous products [21, 22]. such ideas are intimately linked with earlier theories about breakdown in insulating liquids, namely that in [23, 24] which observed a strong dependence of the dielectric strength on pressure. since the dielectric strength increases with pressure, they suggested that such pressure dependence indicates that there is a change of phase (i.e. formation of a bubble) during some step in the breakdown process. a bubble may expand until it reaches a critical length or until it bridges the gap. they proposed a model according to which the local energy input equals the heat required to raise the temperature of m grams of liquid from ambient temperature to the boiling temperature and vaporize it. such a model shows a strong pressure dependence of the dielectric strength. the same authors in a later publication, however, although supporting the idea of a breakdown occurring in the gas phase, did not exclude the possibility of an electronic multiplication process taking place at elevated temperatures [25]. the instability of a bubble can either result in the continuous elongation of the bubble until it bridges the gap between the electrodes or there may well be some sharp points at the edges of the bubble which will result in its disintegration. such disintegration may also result in a total breakdown of the liquid [26]. bubble instability was studied in relation to streamer development in [27], where it was shown that the bubble can take different shapes, with the local electric field at the liquid-bubble interface having very high values. the work in [26, 27] is original in that it relates bubbles with streamer development and it is reminiscent of earlier work reported in [8, 13]. relatively recently, some researchers proposed a critical field value necessary to form a critical sized bubble [28]. the bubble is formed at the tip of an electrode as soon as the field is greater than this critical value [28]. such an approach helps in distinguishing between various insulating oils regarding the respective critical bubble formation fields, and consequently the respective dielectric strengths. the observation made in [29] that in highly divergent fields, breakdown is preceded by the formation of a region of very low refractive index at the cathode seems to support the thoughts in [28]. it has to be noted, however, that such a low refractive index region was attributed by some to a gas phase composed of microbubbles in the liquid [30-33] and by others to a plasma raising the temperature of the liquid [2]. the effect of pressure on bubble behavior in insulating liquids was early noticed in [34, 35], where it was pointed out that the dependence of dielectric strength on hydrostatic pressure implies that breakdown takes place in the gaseous phase. pressure effects disappear when the applied field rate of voltage rise is greater than 4 mv/cm/μsec, indicating that the bubble mechanism may not be operative beyond a certain value of rate rise [36]. a combination of the reported theories between [2] and [30-33] was tried in [37], where it was proposed that although the initial stage of breakdown in transformer oil is due to a gas bubble formed by vaporization of liquid by local heating in a strong field region of the electrode surface, during breakdown a plasma channel will be formed with a high initial resistance. such initial resistance changes from a few ohms to a few hundreds milliohms due to joule heating caused by the arc current flowing through the arc channel. pressure effects on bubble were analyzed in [38], where it was noted that a vapor bubble can be formed when a liquid is subjected to a highly localized heat pulse that rapidly raises the temperature of the liquid. the authors of [38] proposed that an increase in hydrostatic pressure decreases the maximum radius of a bubble by a certain factor derived from the value of the pressure far away from the bubble. they also remarked that there is no significant bubble expansion over 1 mpa. for slightly viscous liquids, the bigger the maximum engineering, technology & applied science research vol. 9, no. 6, 2019, 4870-4875 4872 www.etasr.com danikas: bubbles in insulating liquids: a short review bubble radius, the more violent is its collapse and, consequently, the higher the pressure wave amplitude emitted through the liquid and the higher the dissipated energy of the bubble [39]. viscosity is an important parameter in shaping the behavior of a bubble, although it is not the only one. moreover, as was reported in [40], the prediction of the deformed bubble shape is difficult since the stress distribution on its surface depends on localized field distribution. this is a general conclusion applied to gas bubbles, although the research in [40] was referring to a different type of bubbles from those investigated here. space charge, developed on the bubble surface, is of crucial importance determining the bubble behavior. the involvement of multiple parameters in calculating the space charge as well as the uncertainty of determining accurately the value of the applied electric field makes the calculation of space charge difficult [41]. in [42], some researchers attacked the problem of bubbles from another viewpoint, namely that of the different gases. they indicated that transformer oil having sulfur hexafluoride instead of air gives higher breakdown values and this disregarding chemical purity and humidity. this has to be expected given the electronegativity of the sulfur hexafluoride. in [43], it was indicated that a gas bubble may elongate and, in case of very high local field, charge can be injected into the liquid near the poles of the bubble. in case of a string of bubbles in the liquid, a breakdown in one bubble may lead to an increase of the field in the nearby bubbles, increasing thus the probability of a total breakdown. furthermore, instability in a gas bubble is a pre-condition for possible paths for initiation of streamers. the aforementioned work reminds of earlier research regarding bubble behavior [8]. the string of bubbles reminds also of similar phenomena in solid dielectrics, where a partial discharge in an enclosed cavity may trigger partial discharges in nearby cavities [44-46]. such parallels between liquid insulation and solid dielectrics [43-46] may point out to some common ground among the breakdown (or prebreakdown) phenomena in liquid dielectrics and solid insulating materials. besides pressure, temperature is also a factor to be reckoned with when we refer to bubbles in insulating liquids. an insulating liquid presents a reduced surface tension at elevated temperatures. consequently, a reduced surface tension will result in a reduction of pressure inside the bubble. thus, the electric field needed for the ignition of a bubble at elevated temperature will be less and initiation of breakdown may result [47, 48]. investigating composite (solid/liquid) insulating systems at both ambient and elevated temperatures, it was reported that a bubble –under some special circumstances– may burst by a partial discharge and partially dissolve in the liquid [48, 49]. this of course depends on the nature of the insulating liquid [16, 48, 50, 51]. however, and despite the fact that in some insulating liquids bubbles may disperse because of the partial discharges, it is still unclear the sort of damage such discharges may cause in the solid insulation. it must, however, be noted that the temperature effect is a complex phenomenon because of the possible changes in cathode emission, gas content and liquid viscosity [52]. as was pointed out in early papers [53], factors such as pressure and temperature affect bubble behavior. such effects may differ depending on the use of ac or dc voltages and also on whether the applied field is uniform or non-uniform. the research reported in [53] is reminiscent of earlier research, where it was suggested that with non-uniform field configurations, the initiation of breakdown can be divided into two parts: one including the formation of gas bubbles in the liquid at the cathode and the other being an adequate multiplication by a gaseous ionization in the bulk of the liquid [54]. relatively recent research [55] distinguished between the mechanisms of townsend and streamer in bubbles in liquids, considering some limiting cases regarding bubble dimensions and the minimum duration of applied field. the authors admitted, however, that such mechanisms are expressions of a more complex breakdown process phenomenon depending on both the duration of the applied field and the diameter of the bubble. the authors in [55] distinguish the aforementioned mechanisms in liquids, whereas most of other researchers pay attention mainly to the steamer mechanism [5, 56]. bubble conductivity as a factor was investigated in [57], where it was shown that for non-conductive bubbles the instability takes place with formation slender waist whereas with conductive bubbles the instability takes place at the tips of the bubble. the question of a bridge formed from bubbles in transformer oil under non-uniform electric fields was discussed in [58]. the authors showed that bridges can be formed from bubbles and consequently facilitate the final failure of the liquid. paper [58] elucidates some aspects of the breakdown in liquids and brings into the fore the question of the influence of electrode configuration [59] as well that of the effect of the oil flow velocity upon the breakdown strength [7, 52, 60, 61]. despite the fact that oil flow velocity refers more to particle removal from the liquid, [58] brings about a discussion as to the removal of bubbles. the question of bubble bridges was the subject of [62], where it was remarked that bubble bridges are more likely to affect the breakdown voltage in uniform electrode arrangements than in non-uniform electrode arrangements. similar observations, albeit in a different context, were also made in [48, 50, 51]. iii. thoughts about future research it is evident from the above that a considerable amount of work has been done on bubbles in insulating liquids during the past decades. models of bubble behavior have been proposed as well as experimental data have been presented. there is an intimate link between bubbles and liquid breakdown, although bubbles are not the sole cause of liquid breakdown. bubbles play a vital role both in conventional insulating liquids and also in liquids for superconducting applications [63-65]. although there are two main groups of theories put forward to explain electrical breakdown in dielectric liquids (i.e. (a) those which suggest that breakdown takes place in a gas or vapor phase before complete collapse occurs, and (b) those which propose an electron avalanche in the liquid which grows to a critical size [23, 24, 4, 66 70]), it would be interesting if we can explore the possibility of the two groups of theories to be intimately linked. in the past, significant amount of research has been performed on mineral oils with additives [71]. in [71], engineering, technology & applied science research vol. 9, no. 6, 2019, 4870-4875 4873 www.etasr.com danikas: bubbles in insulating liquids: a short review it was remarked that bubbles formed at lower stresses in a gassaturated liquid are likely to be expelled from the high field regions before the right conditions for a gaseous discharge arise. it would be highly interesting if further work can be done in this direction regarding bubbles, additives and –the recent trend of research– vegetable oils [72]. strings of bubbles have been researched in [43, 73] and a possible parallel was drawn above between this research and work done in solid dielectrics [44-46]. it would be challenging to see whether such micro-bubble interaction and behavior is also valid for vegetable oils. liquid flow and its effect upon the dissolution of bubbles is a subject needing further work. it is already known that circulating an insulating liquid offers higher breakdown strength than a stationary oil [7, 30, 60]. it is, however, questionable whether such a liquid flow effect is due simply to the liquid flow velocity or whether other parameters, such as liquid viscosity, liquid density and surface tension play an equally important role. it was also observed that the breakdown strength of a liquid cannot be raised indefinitely by increasing the liquid flow velocity because of turbulent flow and, consequently, cavitation [60, 74]. liquid flow velocity and the upper limits of it, as well as the aforementioned proposals, can be researched in the future, especially with regards to the advent of nanofluids [75]. iv. conclusions in the context of the present paper, some aspects of bubbles in insulating liquids were studied. this short review traces some important research with regard to insulating fluids back in the thirties of the last century. it points out that some problems regarding bubbles and their deteriorating role for liquid insulation stay with us even nowadays. bubble behavior depends on bubble shape, liquid permittivity, liquid viscosity, liquid density, applied electric field and localized electric field, among others. although significant steps were taken in elucidating various aspects of bubble behavior in conventional insulating liquids, a lot remains to be done with the advent of a new class of liquids, such as the nanofluids. references [1] d. f. binns, “breakdown in liquids”, in: electrical insulation, peter peregrinus ltd., london, uk, 1983 [2] r. n. allan, e. m. hizal, “prebreakdown phenomena in transformer oil subjected to non-uniform fields”, proceedings of the iee, vol. 121, pp. 227-231, 1974 [3] w. g. chadband, j. h. carderwood, “the propagation of discharges in dielectric liquids”, journal of electrostatics, vol. 7, pp. 75-91, 1979 [4] a. h. sharbough, j. c. devins, s. j. rzad, “progress in the field of electric breakdown in dielectric liquids”, ieee transactions on electrical insulation, vol. 13, pp. 249-276, 1978 [5] a. beroual, m. zahn, r. badent, k. kist, a. j. schwab, h. yamashita, k. yamazawa, m. danikas, w. g. chadband, y. torshin, “propagation and structure of streamers in liquid dielectrics”, ieee electrical insulation magazine, vol. 14, no. 2, pp. 6-17, 1998 [6] b. epstein, “statistical aspects of fracture problems”, journal of applied physics, vol. 19, pp. 140-147, 1948 [7] w. r. bell, “influence of specimen size on the dielectric strength of transformer oil”, ieee transactions on electrical insulation, vol. 12, no. 4, pp. 281-292, 1977 [8] n. j. felici, “bubbles, partial discharges and liquid breakdown”, electrostatics, vol. 79, institute of physics conference series vol. 48, pp. 181-190, 1979 [9] h. pohl, “the motion and precipitation of suspensoids in divergent electric fields”, journal of applied physics, vol. 22, no. 7, pp. 869-871, 1951 [10] h. pohl, “some effects of 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clouds for object-oriented source code visualization ra'fat al-msie'deen department of computer information systems, faculty of it mutah university, karak, jordan rafatalmsiedeen@mutah.edu.jo abstract—software visualization helps software engineers to understand and manage the size and complexity of the objectoriented source code. the tag cloud is a simple and popular visualization technique. the main idea of the tag cloud is to represent tags according to their frequency in an alphabetical order where the most important tags are highlighted via a suitable font size. this paper proposes an original approach to visualize software code using a tag cloud. the approach exploits all software identifier names to visualize software code as a tag cloud. experiments were conducted on several case studies. to validate the approach, it is applied on nanoxml and argouml. the results of this evaluation validate the relevance and the performance of the proposed approach as all tag names and their frequencies were correctly identified. the proposed tag cloud visualization technique is a helpful addition to the software visualization toolkit. the extracted tag cloud supports software engineers as they filter and browse data. keywords-software engineering; software visualization; objectoriented source code; tag clouds i. introduction object-oriented (oo) source code visualization helps software engineers understand and manage the complexity and size of software code [1]. this paper proposes an original approach called iconic to visualize oo software as a tag cloud [2] (the name of approach is inspired by icons, iconic is the feature of an icon). a tag cloud is a visual representation of textual content that uses color and size to point out word frequency [3]. the tag is generally a single word. the importance of each tag is displayed with font size or colour [4]. tag clouds can be categorized into two categories: static tag clouds and dynamic tag clouds [5]. most existing approaches are designed to extract tags from web pages and text documents [3, 5-7]. the current studies that identify tag clouds from software code exploit only software classes and methods [8-11]. moreover, these approaches add class and method names to the tag cloud without any pre-processing (i.e. as written in the software code). in the literature, there is no approach to identify tag clouds by using all software identifiers (i.e. packages, classes, attributes and methods). in this paper, tag cloud shows the most common tags across software identifiers. in the cloud some tags may appear more important than others, where the tag frequency determines the tag font size. the use of color is arbitrarily, it is used just for aesthetic purposes. tags are sorted alphabetically or according to their frequency (figure 2). iconic accepts the source code of software systems as input. then, based on static code analysis [12], iconic extracts all software identifier names. then, it splits the identifier names into their constituent words. then, it acquires the words’ roots. after that, it assigns weights to each tag based on its frequency across software code and stores the tags in a standard order. finally, iconic builds the tag cloud as output. ii. related work and comparison with iconic authors in [9] used tag cloud to visualize software classes. the extracted tag clouds exposed the most common tags used in software class names. iconic visualizes software package, class, attribute and method names as a tag cloud. the identified tag cloud has exposed the most frequently-used tags across software identifier names. authors in [10] proposed an approach to visualize software methods via tag cloud. the tag cloud visualizes names of methods, parameters and local variables. in a tag cloud, if a tag name is selected, then the related source code elements in the graph visualization will be highlighted. in iconic, there is no graph visualization of source code elements. iconic does not identify the link between tag in the cloud and the source code elements in the graph visualization. iconic visualizes software identifiers as a tag cloud. authors in [8, 11] used the tag cloud to visualize software methods. their tool allows the user to explore the tag cloud using different layouts. in a tag cloud if a tag is selected, then the related tags in the cloud will be highlighted. in their work, the tag cloud is customizable and the tool allows tag layouts to change. iconic uses a tag cloud to visualize all software identifiers. iconic allows the software developer to explore the tag cloud using a typewriter layout with tag names in alphabetical order. author in [13] presents an automatic approach to extract software code labels. the approach splits the name of an identifier into a set of keywords. then, it returns each keyword to its stem to generate the code labels. the approach creates labels with the same font size and colour. there is no indication about label importance in the extracted code labels. in iconic, the tag frequency determines the tag font size in the tag cloud. there are other approaches to visualize software code by using different techniques. in a previous work [1], this author has developed a tool named vsound to visualize the software corresponding author: ra'fat al-msie'deen engineering, technology & applied science research vol. 9, no. 3, 2019, 4243-4248 4244 www.etasr.com al-msie’deen: tag clouds for the object-oriented source code visualization source code and its main dependencies. vsound depends on software identifiers to visualize, understand and document the software code. vsound aims for a graphical representation of software code as a graphic-based document. authors in [14] suggested a feature naming technique by using the variclouds approach. variclouds is a method that uses word cloud visualization in order to assign names to identified blocks (i.e. features) based on the most frequent words in those blocks. variclouds is developed for helping software engineers in feature identification and naming. authors in [15] offered a feature naming method as part of their automatic feature model extraction technique (called revpline approach). they assigned names for features based on the most frequent tokens of the identified blocks. the most frequent tokens within the block represent the most frequent tags within a tag cloud. the word cloud can be used in [15, 16] in order to identify the name of the features extracted from the software code as atomic blocks based on the most frequent words in those blocks. in a software engineering domain, there are limited existing software engineering tools which use a tag cloud visualization technique. eclipse plugin sourcecloud [17] creates a tag cloud visualization of the text within a package, class or project with font size weighted by tag frequency and colors assigned arbitrarily. on the other hand, iconic uses all software identifiers to generate tag cloud, not the whole software document. a tag cloud is often used to show an overview of the contents of textual documents. wordle [18] made it easy to generate tag clouds from a specific text. wordle is a tag cloud generator for any text. wordle presents tags in the cloud without any pre-processing; as it appears in the text, while iconic uses wordnet [19] to do some simple pre-processing on the software identifiers such as stemming and removal of stop words. most existing approaches are designed to extract tag clouds from web pages and textual documents. in software systems, there are limited existing approaches which use a tag cloud to visualize software code. the current approaches use tag clouds to visualize software classes or methods. the concise overview of the existing approaches shows the need to propose an approach to extract tag cloud from software code using all software identifier names. iii. approach overview this section presents the main ideas used in iconic. it also gives an overview of the tag cloud process. finally, it shortly describes the example that illustrates the tag cloud process. the main objective of iconic is to visualize software identifiers as a tag cloud. the tag cloud displays the most frequently-used words across software identifiers. tag cloud builds an alternative representation of the software identifiers at a higher level of abstraction. figure 1 presents the tag clouds process and a sample execution of the iconic approach (i.e. drawingshapes). this process takes the software source code as its input. its first step aims to identify all software identifiers. then, iconic splits the identifier names into their constituent words. in the next step, iconic turns the identifier words into their word stems or roots. then, iconic assigns a weight for each tag based on its appearance frequency. after that, iconic stores all tags in a standard (e.g. alphabetical) order. finally, iconic generates the tag cloud. fig. 1. the tag cloud process, and a running example. as an illustrative example, iconic approach considers the drawing shapes software system [12, 13]. this software product allows the software developer to draw three types of shapes which are: lines, rectangles and ovals. in addition, drawing shapes software lets the user to select the shape color. iv. tag cloud process step by step iconic identifies the software tag cloud in six steps which are detailed below. a. extracting software identifiers iconic takes the software code as input. then, iconic parser generates an identifier file as output. identifier file contains the main oo elements (i.e. package, class, attribute and method). iconic uses the eclipse java development tools and the eclipse abstract syntax tree to access, modify and read the elements of the software [20]. the abstract syntax tree is widely used in numerous areas of software engineering as a representation of source code. b. splitting the identifiers into their constituent words iconic splits the software identifier names into a set of words. iconic uses the camel-case splitting algorithm [15], which splits words based on capital letters, underscores and numbers. each identifier name is split into words based on the camel-case syntax. for example: drawingshapes is split into drawing and shapes. camel-case method is a simple and broadly used method for identifier splitting algorithms [21] and the rules of splitting are largely based on camel-case convention. c. stemming words into their word stems stemming is a method of stripping affixes from words to form the word stem or base (e.g. performed to perform). in iconic approach, the stemming (e.g. removing word endings) was achieved via wordnet [19]. iconic uses wordnet [22] dictionary to replace english words with their stems. in iconic, stemming is a way of converting an identifier name (word) to engineering, technology & applied science research vol. 9, no. 3, 2019, 4243-4248 4245 www.etasr.com al-msie’deen: tag clouds for the object-oriented source code visualization its stem (tag). for instance, the words writing, wrote and written all have the same base/stem which is write. d. assigning weights to tags in iconic approach, the tag weight gives an indication about the tag frequency (or tag importance) across software identifiers. in this step, tag weight is assigned to each tag, based on its frequency of appearance in software identifiers. for example, in drawing shapes software the draw tag occurred ten times across software identifiers, so the given weight of this tag is ten (figure 4). e. storing tags in a standard order in iconic, the tags within a tag cloud are arranged from left to right, and top to bottom (i.e. typewriter style). iconic presents tags in a tag cloud in alphabetical order (figure 2). the software engineers seem more able to simply find tags in alphabetically ordered clouds [11]. authors in [8] indicated that alphabetical ordering is particularly effective for tasks involving searching for a specific tag or confirming its absence from the cloud. f. generating tag clouds iconic approach generates several clouds based on the software identifiers. iconic clouds cover all granularity levels of the software code. figure 2 shows the tag cloud extracted from drawing shapes code. this tag cloud contains all software identifier tags (i.e. package, class, attribute and method). the tag cloud in figure 2 shows that the most frequently-used words (tags) in software identifier names are draw and shape. the most frequent tags are shown in larger fonts. fig. 2. tag cloud generated from drawing shapes software. tag cloud helps software engineers to get the most common and rare tags. using iconic approach five tag clouds are generated: these are package, class, attribute, method, and all software identifiers. different software tag clouds are shown in figure 3. filtering the unwanted tags from tag clouds is a critical issue. many filters can be added to the tag cloud [23]. the cloud filters are very important for filtering the unwanted tags such as short tags. on the other hand, cloud filters can be added to present precise information about tags such as the number of tag frequency. filtering facilities are essential and very important to deal with enormous tag clouds. iconic uses two filters: short-tag and tag-frequency filters. the short-tag filter aims to filter out the tags which have less than four characters. while, the tag-frequency filter can be used as an indicator for the tag frequency across software identifiers. these two filters are very useful for software developers. for example, short-tag filter is very important when there are too many tag names to display in the cloud. by using this filter some of the smaller names will not be displayed in the cloud, while the tag-frequency filter determines the frequency of the tag name across software identifier names as a precise number between square brackets. figure 4 presents the generated tag cloud from all identifiers of drawing shapes software after applying these two filters (figure 2 shows the generated tag cloud from the same software without filters). fig. 3. different tag clouds extracted from drawing shapes software. in the current approach, the tags are produced stripped of information as they are simply word stems of split identifiers. the whole identifiers may carry some information (e.g. drawingshapes) but the split and stemmed tags do not carry the same information (e.g. draw and shape). figure 5 shows the identifiers tag cloud of the drawing shapes program without splitting and stemming the identifier names. white, black and red colours are used as a design choice of the cloud. the tag labels are shown in black, while the tag frequencies are presented in red color between square brackets. fig. 4. a tag cloud generated by using iconic filters. v. experimentation this section presents the experiments conducted in this study to show its soundness, and presents the argouml and nanoxml case studies. it also summarizes the obtained results engineering, technology & applied science research vol. 9, no. 3, 2019, 4243-4248 4246 www.etasr.com al-msie’deen: tag clouds for the object-oriented source code visualization for the case studies, presenting the threats to the validity of iconic approach. argouml [24] is a java-based software. argouml is used for designing software systems in uml. nanoxml software [25] is a java program for parsing xml files. iconic implementation [26] converts software code into a tag cloud. argouml software represents a large system [27]. iconic performed an evaluation of the execution time (in ms) of its algorithms. table i presents the execution time for each case study. in addition, software size and the number of software identifiers are presented. argouml software is considered as a large base code (i.e. 120,348 lines of code). the execution time of iconic on this case study is relatively little (approximately 45s). the different size and complexity levels show the capability of iconic to deal with such software systems. fig. 5. tag cloud visualization created by iconic. table i. information about tag clouds extracted from case studies. case study argouml nanoxml # of packages 103 3 # of classes 1745 24 # of attributes 3649 63 # of methods 10319 318 # of identifiers 15816 408 # of tags 1511 135 execution time 44836 1197 fig. 6. tag cloud extracted from nanoxml software. figure 6 shows the generated tag clouds from nanoxml software. the most frequent tag names in argouml are get and action, while in nanoxml are get, and attribute. figure 7 shows the tag cloud generated from the argouml after applying the short-tag and tag-frequency filter. fig. 7. tag cloud extracted from argouml software. the extracted tag clouds from argouml and nanoxml show that the developer can easily find tags in alphabetically ordered clouds [8]. software developers look able to more simply find tag names in alphabetically ordered clouds [28]. the evaluation of tag cloud is a vital, but challenging, aspect of visualization [8]. despite the abundance of visualization techniques proposed in the software engineering field, there remains a dearth of extensive use of the tag cloud technique. to evaluate the proposed filters, a simple case study with five java developers as participants was performed. upon starting the evaluation, each participant was asked to see the tag cloud of nanoxml software without filters (figure 6) and with filters (figure 8). then, each participant was asked to answer two questions with agree or disagree. table ii displays the study design in detail. table ii. the design of the user study. all participants see different clouds for the same software. kind of cloud question # users' ratings for each question without filters with filters s1: agree s2: disagree p1 p2 p3 p4 p5 × q1 s2 s2 s2 s2 s2 q2 s1 s2 s1 s2 s2 × q1 s1 s1 s1 s1 s1 q2 s1 s1 s1 s1 s1 questions asked: q1 the cloud is missing important tag names. q2 the cloud contains information that helps me understand the importance of tag names. the cloud without filters contains all tag names while, the tag cloud with filters does not contain all the tag names, because the smaller tag names are omitted. also, the tag cloud with filters shows the importance of tag names using tagfrequency in addition to tag font size. figure 8 shows the generated tag cloud from nanoxml software using iconic filters. the effectiveness of iconic approach is measured by their precision, recall and f-measure [20]. for a given tag name within the cloud, precision is the ratio of correctly retrieved tag frequencies to the total number of retrieved tag frequencies, while recall is the ratio of correctly retrieved tag frequencies to the total number of relevant tag frequencies. fmeasure is the harmonic mean between precision and recall engineering, technology & applied science research vol. 9, no. 3, 2019, 4243-4248 4247 www.etasr.com al-msie’deen: tag clouds for the object-oriented source code visualization [29]. f-measure gives a high value in cases where both precision and recall are high [30]. all metrics have values between zero and one. table iii summarizes the obtained results for some samples. fig. 8. a tag cloud generated from nanoxml software. table iii. tags mined from nanoxml and argouml case study tag name * ** evaluation metrics precision recall f-measure argouml apply 13 13 1 1 1 area 9 9 1 1 1 array 11 11 1 1 1 nanoxml exception 13 13 1 1 1 element 45 45 1 1 1 entity 25 25 1 1 1 * tag frequency within the cloud ( figure 7 and 8) **the number of identifiers that contain this tag results show that the precision value is one for all tag names and their frequencies. if precision equals one, all retrieved tag frequencies are relevant. this means that all generated tag names and their frequencies are correct. moreover, tag cloud does not miss any tag names. this accuracy in the result is due to the pre-processing steps, where the identifier names are split into multiple words based on the camel-case splitting algorithm. then, word stemming is applied to find the root of each word. considering the recall metric, recall value equals one for all tag names. if recall equals one, all relevant tag frequencies are retrieved. this means that all frequencies that measure the tag importance are counted. considering the f-measure metric, the f-measure value equals one for all tag names. if f-measure equals to one, all relevant tag frequencies are retrieved, and only relevant tag frequencies are retrieved. this means that all frequencies that display the importance of tag names via font size are extracted. the result shows the efficiency of iconic approach. the threat to the validity of iconic is that the current prototype considers only java software. furthermore, when a software developer uses mix words to name software identifiers (e.g. setsettings) the camel-case splitting algorithm can’t handle it. the wordnet may not be reliable in all cases to find the word stem. currently, the tag clouds are missing some filters for example, they do not filter tag names that are too long (e.g. filter the identifier names to only 5 characters). in addition, it would be much faster to be able to have a filtering search that the developer can type the tag to find it. vi. conclusion and perspectives this paper proposed an original approach to visualize all software identifiers as a tag cloud. iconic was implemented on numerous case studies. iconic has been applied on nanoxml and argouml software. results showed that all tag names and their frequencies were correctly identified. the extracted tag clouds have shown the most common and rare tags. tags are sorted alphabetically or according to their frequency. the most frequent tags are highlighted via appropriate font size and color. tags within the cloud are filtered according to their length or frequency. for future work, iconic is planned to support the current tag cloud with a set of user tasks [23], including tag searching, browsing, zooming and filtering. it is also planned to use other layouts for tag cloud such as spiral layout [31]. in addition, it is planned to build a tag cloud using software identifiers and code comments [32] and to identify the link between tag names and software identifiers. thus, in a tag cloud if a tag name is selected, then the related identifiers will be highlighted. therefore, the software developers could click a tag name and see where it is used in the source code. finally, the use of javadocs in iconic [33] to build the tag cloud is another future work aim. references [1] r. al-msie’deen, “visualizing object-oriented software for understanding and documentation”, international journal of computer science and information security, vol. 13, no. 5, pp. 18–27, 2015 [2] o. kaser, d. lemire, “tag-cloud drawing: algorithms for cloud visualization”, www2007, banff, canada ,may 8–12, 2007 [3] m. a. hearst, d. rosner, “tag clouds: data analysis tool or social signaller?”, 41st hawaii international conference on systems science, waikoloa, usa, january 7-10, 2008 [4] m. j. wilson, m. l. wilson, “tag clouds and keyword clouds: evaluating zero-interaction benefits”, international conference on human factors in computing systems, vancouver, canada, may 7-12, 2011 [5] w. cui, y. wu, s. liu, f. wei, m. zhou, h. qu, “context-preserving, dynamic word cloud visualization”, ieee computer graphics and applications, vol. 30, no. 6, pp. 42–53, 2010 [6] l. j. garcia-castro, m. hepp, a. garcia, “tags4tags: using tagging to consolidate tags”, in: lecture notes in computer science, vol. 5690, springer, 2009 [7] g. j. greene, b. fischer, “interactive tag cloud visualization of software version control repositories”, ieee 3rd working conference on software visualization, bremen, germany, september 27-28, 2015 [8] j. emerson, n. churcher, c. deaker, “from toy to tool: extending tag clouds for software and information visualisation”, 22nd australian software engineering conference, melbourne, australia, june 4-7, 2013 [9] c. anslow, j. noble, s. marshall, e. d. tempero, “visualizing the word structure of java class names”, in companion to the 23rd annual acm sigplan conference on object-oriented programming, systems, languages, and applications, nashville, usa, octomber 13-19, 2008 [10] r. cottrell, b. goyette, r. holmes, r. j. walker, j. denzinger, “compare and contrast: visual exploration of source code examples”, 5th ieee international workshop on visualizing software for understanding and analysis, edmonton, canada, september 25-26, 2009 [11] j. emerson, n. churcher, a. cockburn, “tag clouds for software and information visualisation”, 14th annual acm sigchi nz conference on computer-human interaction, christchurch, new zealand, november 15-16, 2013 [12] r. al-msie’deen, a. blasi, “the impact of the object-oriented software evolution on software metrics: the iris approach”, indian journal of science and technology, vol. 11, no. 8, pp. 1–8, 2018 engineering, technology & applied science research vol. 9, no. 3, 2019, 4243-4248 4248 www.etasr.com al-msie’deen: tag clouds for the object-oriented source code visualization [13] r. al-msie’deen, “automatic labeling of the object-oriented source code: the lotus approach”, science international-lahore, vol. 30, no. 1, pp. 45–48, 2018 [14] j. martinez, t. ziadi, t. f. bissyande, j. klein, y. l. traon, “name suggestions during feature identification: the variclouds approach”, 20th international systems and software product line conference, beijing, china, september 16-23, 2016 [15] r. al-msie’deen, m. huchard, a. seriai, c. urtado, s. vauttier, “automatic documentation of [mined] feature implementations from source code elements and use-case diagrams with the revpline approach”, international journal of software engineering and knowledge engineering, vol. 24, no. 10, pp. 1413–1438, 2014 [16] r. al-msie’deen, a. d. seriai, m. huchard, c. urtado, s. vauttier, “documenting the mined feature implementations from the objectoriented source code of a collection of software product variants”, 26th international conference on software engineering and knowledge engineering, knowledge systems, vancouver, canada, july 1-july 3, 2014 [17] https://misto.ch/2011/09/19/tag-cloud-visualization-for-source-code/ [18] www.wordle.net [19] g. a. miller, “wordnet: a lexical database for english”, communications of the acm, vol. 38, no. 11, pp. 39–41, 1995 [20] r. al-msie’deen, reverse engineering feature models from software variants to build software product lines: revpline approach, phd thesis, university montpellier 2, 2014 [21] b. dit, l. guerrouj, d. poshyvanyk, g. antoniol, “can better identifier splitting techniques help feature location?”, 19th international conference on program comprehension, kingston, canada, june 22-24, 2011 [22] https://wordnet.princeton.edu [23] j. emerson, tag clouds in software visualisation, msc thesis, university of canterbury, 2014 [24] http://argouml-downloads.tigris.org/argouml-0.28.1 [25] http://nanoxml.sourceforge.net/orig/index.html [26] https://sites.google.com/site/ralmsideen/tools [27] j. martinez, n. ordonez, x. ternava, t. ziadi, j. aponte, e. figueiredo, m. t. valente, “feature location benchmark with argouml spl”, 22nd international systems and software product line conference, gothenburg, sweden, september 10-14, 2007 [28] m. halvey, m. t. keane, “an assessment of tag presentation techniques”, 16th international conference on world wide web, alberta, canada, may 8-12, 2007 [29] t. f. bissyande, f. thung, s. wang, d. lo, l. jiang, l. reveillere, “empirical evaluation of bug linking”, 17th european conference on software maintenance and reengineering, genova, italy, march 5-8, 2013 [30] r. al-msie’deen, a. d. seriai, m. huchard, c. urtado, s. vauttier, “mining features from the object-oriented source code of software variants by combining lexical and structural similarity”, 14th international conference on information reuse & integration, san francisco, usa, august 14-16, 2013 [31] s. lohmann, j. ziegler, l. tetzlaff, “comparison of tag cloud layouts: task-related performance and visual exploration”, in: lecture notes in computer science, vol. 5726, springer, 2009 [32] r. al-msie’deen, a. blasi, “supporting software documentation with source code summarization”, international journal of advanced and applied sciences, vol. 6, no. 1, pp. 59–67, 2019 [33] p. w. mcburney, c. mcmillan, “automatic source code summarization of context for java methods”, ieee transactions on software engineering, vol. 42, no. 2, pp. 103–119, 2016 author profile ra'fat al-msie'deen is an assistant professor at mutah university since 2014. he received his phd in software engineering from the university of montpellier 2, montpellier – france, in 2014. he received his msc in information technology from the university utara malaysia, kedah – malaysia, in 2009. he got his bsc in computer science from al-hussein bin talal university, ma’an – jordan, in 2007. his research interests include software engineering, software product line engineering, and formal concept analysis. microsoft word 35-3063_s_etasr_v9_n5_pp4769-4774 engineering, technology & applied science research vol. 9, no. 5, 2019, 4769-4774 4769 www.etasr.com alanazi & soh: behavioral intention to use iot technology in healthcare settings behavioral intention to use iot technology in healthcare settings meshari alanazi department of computer science and information technology, la trobe university, melbourne, australia m.alanazi@latrobe.edu.au ben soh department of computer science and information technology, la trobe university, melbourne, australia m.soh@latrobe.edu.au abstract—rapid scaling of using the internet of things (iot) technology has been seen recently in numerous applications in healthcare to deliver proper services. this was motivated by the declining size and cost of the employed iot devices. developing such technology has been well investigated in the literature; however, few studies have explored the factors influencing its adaptation in the healthcare setting. in this study, we investigate the core factors that influence the acceptance of using iot for healthcare purposes in the kingdom of saudi arabia (ksa). accordingly, a theoretical framework, based on the technology acceptance model (tam), was developed and tested empirically. the modified model added variables that provide a better explanation of the acceptance of healthcare technology. to ground our conceptual idea, a survey was designed and performed on 407 patients (207 males, 200 females). the partial least square structural equation modeling (sem) technique was applied to analyze the effect of eight hypothesized predicting constructs on the collected data. results revealed that cost, privacy concerns, and perceived usefulness were the most significant predictors of behavioral intention to use. however, attitude and perceived connectedness were found to be irrelevant in predicting the intention to use iot. ultimately, results found that there is no correlation between gender and behavioral intention. keywords-internet of things; healthcare; technology acceptance model (tam); structural equation model i. introduction internet of things (iot) technology is a system of interrelated smart devices (computers, sensors, etc.) that are connected to the internet to develop new capabilities and services [1]. these services aim to improve system performance and quality of life, e.g. in healthcare, communication, education, etc. [2]. iot has many advantages to offer, for example, the internet of medical things (or the internet of healthy things). internet of medical things is an application of iot for medical and health-related purposes [3], where iot devices (devices for monitoring blood pressure, heart rate, or specialized implants, such as pacemakers, or advanced hearing aids) are used to enable remote health monitoring process [4]. this process can significantly improve the quality of life for patients, especially for chronic diseases, as they can be monitored in non-clinical environments such as their home. while iot delivers an impressive set of benefits, concern exists over the extent of iot technology use by patients. in other words, as any new technology proposed, it has the potential to enhance the provided services and achieve its goals when intended users understand it. but, if the technology meets resistance to use or acceptance, it will be underutilized or completely abandoned. the lack of user acceptance has been long identified as an obstacle to the success of new technologies [5]. therefore, it has become crucial for practitioners and decision-makers to better understand the factors that influence the adoption of iot, since it is considered an essential step toward the development of a successful healthcare system [6]. many models and theories have been proposed to examine and predict the acceptance of new technologies. one might consider the technology acceptance model (tam) [7], the unified theory of acceptance and use technology [8] and the theory of reasoned action [9]. the tam model is employed in this study to understand and estimate the users’ adoption behaviors toward modern technologies [7]. this is due to the fact that tam is the most common and cited model in the is research [10] and healthcare domain [11, 12], because of its adequate explanatory power and parsimonious structure [13]. being said that, tam has not been widely tested in developing countries [14]. consequently, the author of [15] emphasizes on the importance of examining tam in different cultures to ensure adequate reliability and validity. moreover, tam does not serve equally across cultures, and the inconsistency in previous studies’ results highlight the importance of conducting this research in the ksa context [16, 17]. ksa remains relatively unexplored in terms of technology acceptance, while investment in healthcare system technology is promised for future projects. hence, this study aims to examine the individual patients’ perceptions towards the adoption of iot technology in ksa by applying the tam model. ii. research model our purpose is to study the acceptance of using iot technology in the healthcare sector in ksa from a conceptual viewpoint. we propose a theoretical model that extends tam with its original four factors, perceived usefulness (pu), corresponding author: meshari alanazi engineering, technology & applied science research vol. 9, no. 5, 2019, 4769-4774 4770 www.etasr.com alanazi & soh: behavioral intention to use iot technology in healthcare settings perceived ease of use (peo), attitude (att), and behavioral intention to use (bi), including four new external factors: connectedness (pco), convenience (pcv), privacy (ppr), and cost (pc) (figure 1). fig. 1. the proposed research model a survey instrument was developed and distributed to 450 patients in order to test the research model [37]. collected data were analyzed using the structural equation model, based on the partial least square approach. this method shows relationships and the quality of connections among the factors in the proposed model. in particular, we want to assess the influence of the four original factors on the intention of using iot, by specifying the relationships between them and among the new factors that subsequently influence the usage intention. accordingly, a set of hypotheses were set to determine if there is a correlation between these factors. those hypotheses are listed in table i. table i. research hypotheses hypotheses h1 perceived convenience has direct effect on perceived usefulness h2 perceived connectedness has direct effect on perceived ease of use h3 perceived cost has direct effect on behavioral intention to use h4 privacy concern has direct effect on behavioral intention to use h5 perceived ease of use has direct effect on perceived usefulness h6 perceived usefulness has direct effect on attitude h7 perceived ease of use has direct effect on attitude h8 perceived usefulness has direct effect on behavioral intention to use h9 attitude has direct effect on behavioral intention to use before conducting the survey, two independent experts reviewed the instrument for ensuring its validity and relevance. the instrument was structured in two parts. the first part contained sociodemographic questions and a basic question on iot awareness, which was “do you have basic knowledge of iot?”, with response options ranging between “general idea”, “good idea,” and “already using some services”. the second part contained questions that measured the respondents’ intention to use iot for healthcare, utilizing a five-point likert scale (from 1=“strongly disagree” to 5=“strongly agree”). the interval scale was used because it allows specific mathematical operations on the data collected from respondents. in order to ensure that the survey will be distributed over a sufficient number of participants so as to generalize our model, the cochran’s sample size formula was utilized to calculate the minimum sample size, as it is proven reliable for use in large populations [18]. the current study targeted adult patients and according to the ksa general authority for statistics data in 2016 the proportion of the adult population of saudi arabia is 75.2%, which equals to 23,870,215 persons. the cochran’s sample size formula [18] is given as: �� � �� ��∗ � �� (1) where e is the desired level of perception (error margin), p is the estimated proportion of the population which has the attribute in question, q=1–p and z-value is found in the z table. in this study, we desired 95% confidence level, p=0.05 and at least 5%. a 95 % confidence level gives us z-value of 1.96, so, based on (1), the minimum sample size is 385. the instrument was distributed to 450 patients in ksa hospitals and 426 responses were obtained, out of which 19 were excluded because of missing values. hence, data from 407 respondents were processed for the final analysis. iii. testing results a. respondents demographic statistics descriptive statistics showing the respondents demography can be seen in table ii. there were 207 male and 200 female participants, where 27.5% of them were 55 years old or older, 21.1% were 45-54 years old, 20.1% were 35-44 years old, 16.5% were 25-34 years old, and the remainder 14.7% were 18-24 years old. 48.2% of our sample had basic knowledge of iot, while the rest either had a good idea or already used some iot services. regarding the income, 23.8% registered high income with more than 190k sr, 40.3% had income 120k190k sr, 20.4% had income 48k-120k sr, and 15.5% had less income than 48k sr. table ii. demograph ic in formation of the respondents characteristics frequency percent % age 18-24 60 14.7 25-34 67 16.5 35-44 82 20.1 45-54 86 21.1 55 or older 112 27.5 total 407 100.0 gender male 207 50.9 female 200 49.1 total 407 100.0 income (sr) <48k 63 15.5 48k-120k 83 20.4 120k-190k 164 40.3 190k or more 97 23.8 total 407 100.0 basic knowledge of iot general idea 196 48.2 good idea 144 35.4 already using iot 67 16.5 total 407 100.0 b. normality testing skewness and kurtosis have been calculated using the spss platform to test the normality of the used data set. normality tests are used to determine whether a dataset has normal distribution. in this study, skewness was used to measure the asymmetry of the probability distribution of a random variable about its mean, while kurtosis was utilized to tell the height engineering, technology & applied science research vol. 9, no. 5, 2019, 4769-4774 4771 www.etasr.com alanazi & soh: behavioral intention to use iot technology in healthcare settings and sharpness of the central peak, relative to the standard bell curve. skewness and kurtosis values can be positive or negative or even undefined. if skewness value is between -0.5 and 0.5, and if kurtosis value is between -2 and +2, they are acceptable and prove normal univariate distribution [19]. as shown in table iii, all factors have obtained values in the acceptable range, which reflects a high degree of normality. table iii. normality of the dataset factor skewness kurtosis behavioural intention to use (bi) bi1 0.453 -0.802 bi2 0.387 -1.128 bi3 0.197 -1.133 perceived usefulness (pu) pu1 -0.092 -0.084 pu2 0.136 -0.037 pu3 0.089 -0.133 pu4 0.042 -0.348 pu5 0.075 -0.058 pu6 -0.030 -0.201 perceived ease of use (peo) peo1 0.017 -0.705 peo2 0.099 -0.592 peo3 0.141 -0.581 peo4 0.244 -0.824 peo5 0.140 -0.442 peo6 0.087 -0.605 attitude (att) att1 -0.062 -0.535 att2 -0.132 -0.440 att3 0.030 -0.864 perceived connectedness (pco) pco1 0.328 -0.114 pco2 0.237 0.044 pco3 0.240 -0.268 perceived cost (pc) pc1 -0.262 -1.083 pc2 -1.035 -0.272 pc3 -0.533 -1.092 privacy concerns (ppr) ppr1 0.462 -0.842 ppr2 0.578 -0.825 ppr3 0.349 -1.174 perceived convenience (pcv) pcv1 0.474 -0.417 pcv2 0.500 -0.482 pcv3 0.477 -0.288 c. validity testing cronbach's alpha is calculated to measure the internal consistency for the reliability of the used questionnaire, measuring how a set of items is closely related as a group. table iv presents all the factors that are used, where the value of cronbach's alpha obtained is greater than 0.7, which reflects a high degree of internal reliability [20]. table iv. instrument’s in ternal consisten cy factor no. of questions cronbach's alpha bi 3 0.894 pu 6 0.929 peo 6 0.874 att 3 0.939 pco 3 0.863 pc 3 0.883 ppr 3 0.783 pcv 3 0.875 d. convergent validity in order to measure the convergent validity, the average variance extracted (ave) and the composite reliability have been calculated for every factor, as shown in tables v and vi. the corresponding factor loading for every construct exceeds the threshold value of 0.60, which is a minimum requirement criterion for the convergent validity test to pass [21]. also, for every construct, the value obtained for ave is higher than the recommended level of 0.5 [22]. table v. facto r loading pu peo att pcv pco pc ppr bi pu 0.793 0.761 0.820 0.829 0.898 0.863 peo 0.701 0.745 0.729 0.722 0.738 0.761 att 0.912 0.984 0.859 pcv 0.816 0.829 0.866 pco 0.806 0.955 0.718 pc 0.802 0.867 0.869 ppr 0.771 0.816 0.650 bi 0.822 0.861 0.887 table vi. convergen t validity factor no. of questions average variance extracted (> 0.50) composite reliability (> 0.70) bi 3 0.734591 0.892418 pu 6 0.686464 0.929071 peo 6 0.537153 0.874351 att 3 0.84596 0.942609 pco 3 0.692395 0.869442 pc 3 0.716685 0.883432 ppr 3 0.560932 0.791627 pcv 3 0.701018 0.87546 e. discriminant/divergent validity the discriminant/divergent validity was also tested. discriminant validity refers to the extent to which factors are distinct and uncorrelated. the rule is that variables should relate more strongly to their factor than to any other factor. the test was calculated using spss, and the result is shown in table vii. when examining discriminant validity, the square root of the ave for each construct should be greater than the correlational values between any two constructs. this is precisely our case: all diagonal elements have a higher correlation level between any two specific factors. thus, the discriminant validity test is sufficed for our model. engineering, technology & applied science research vol. 9, no. 5, 2019, 4769-4774 4772 www.etasr.com alanazi & soh: behavioral intention to use iot technology in healthcare settings iv. hypotheses results amos 23.0 has been used to test the proposed model and the corresponding hypotheses. figure 2 and table vii present the results of the research model. as shown, p-value is used to determine the significance of the results. in other words, our hypothesizes were tested by using the p-value to weigh the strength of the evidence. the p-value is a number between 0 and 1 and interpreted in the following way: a small p-value (≤0.05) indicates strong evidence against the null hypothesis, so the null hypothesis is rejected. a large p-value (>0.05) indicates weak evidence against the null hypothesis, the null hypothesis in not rejected. if p-values are very close to the cutoff (0.05), they are considered to be marginal [23]. accordingly, results in table viii show that hypotheses h1, h3, h4, h5, and h8 are supported and have a high level of statistical significance (p<0.05), while h2, h6, h7, and h9 are not supported (p>0.05). for additional analysis, we found that there is no significant correlation between age and behavioral intention (r=-0.043, p=0.560, p>0.05). fig. 2. summary of our proposed model table vii. discrimin ant valid ity pcv pco pc pco att bi peo pu perceived convenience (pcv) 0.837268 percieved connectedness (pco) 0.01145 0.832103 percieved cost (pc) 0.03312 0.04796 0.74895 privacy concerns (ppr) 0.03168 0.03764 0.70560 0.846573 attitude (att) 0.00208 0.00043 0.00488 0.01000 0.919761 behavioral intention to use (bi) 0.00725 0.02103 0.01061 0.01416 0.00090 0.85708 perceived ease of use (peo) 0.00001 0.00299 0.01277 0.00800 0.01877 0.00811 0.73291 percieved usefulness (pu) 0.01369 0.00531 0.00341 0.00152 0.01416 0.00543 0.01020 0.82853 table viii. hypothesis testin g hypothesis p status h1 perceived convenience → perceived usefulness 0.002 supported h2 perceived connectedness → perceived ease of use 0.204 not supported h3 perceived cost → behavioral intention to use 0.000 supported h4 privacy concerns → behavioral intention to use 0.021 supported h5 perceived ease of use → perceived usefulness 0.005 supported h6 perceived usefulness → attitude 0.838 not supported h7 perceived ease of use → attitude 0.140 not supported h8 perceived usefulness → behavioral intention to use 0.005 supported h9 attitude → behavioral intention to use 0.281 not supported v. discussion this study applied an extension to tam to determine the factors that influence the acceptance of iot technology for healthcare in ksa. empirical research was performed to test the study’s hypotheses. most of our findings are in line with findings from previous studies that applied tam in healthcare systems and e-health. the results offer various useful insights into the acceptance behavior on the iot technology for healthcare. we found that cost and privacy concerns are the most significant predictors of behavioral intention to use. moreover, results reveal that perceived usefulness is another important construct that affects the system usage, which in turn is strongly influenced by both perceived convenience and perceived ease of use. on the other hand, results show that perceived connectedness does not affect behavioral intention, neither directly nor indirectly. however, perceived ease of use affects it indirectly through perceived usefulness. authors in [24-27] found that perceived usefulness and perceived ease of use significantly influence behavioral intention, which is consistent with our results. this is due to the level of effort that goes into learning a new technology or service, which may far outweigh the perceived benefit of the proposed system for many people. authors in [28-29] found that perceived usefulness was a significant indicator, however, they contradict our findings in which perceived ease of use was an insignificant predictor. this is because their study targeted patients with chronic conditions who tend to rely a lot on the diagnosis and advice (e.g. remote patient monitoring devices) from experts to facilitate disease management and reduce engineering, technology & applied science research vol. 9, no. 5, 2019, 4769-4774 4773 www.etasr.com alanazi & soh: behavioral intention to use iot technology in healthcare settings medical costs. authors [30-32] revealed that perceived cost and privacy concerns have a significant impact on forming users’ intention. these findings are consistent with ours that show perceived cost as the most significant predictor affecting the behavioral intention. this implies that high cost of implementing this technology can impact the use of iot services. thus, inventors must consider cost when implementing this technology for healthcare purposes. moreover, privacy concerns is another important construct that affects the entire system usage, as patients are extremely concerned and sensitive about the privacy and security of the collected data. this important factor must be kept in mind by healthcare providers as they must be able to provide a technique to support customized data accessing. the results obtained in [26] are quite different from our findings. specifically, the authors in [26] found that perceived cost was not significantly associated with intention to use mhealth. this variation can be attributed to the availability of mobile services to the population studied in that research. authors in [33-34] found that perceived convenience has significant impact on forming behavioral intention, which is compatible with our findings. we attribute this to the fact that iot and the context of providing health support is a relatively new idea, while the underlying technologies are still evolving. consequently, patients are willing to proceed with this technology and services with little effort or difficulty. perceived connectedness has not been extensively considered in the literature. the effect of this construct was found to be non-significant in our study. this observation is in contrast with the findings of other researchers, where connectedness plays a significant role in determining the intention to use a system [35]. this means that patients do not bother about the devices’ connectedness. consequently, patients perceive this technology to be immature and in an early developmental state. ultimately, although many researchers have considered healthcare services [37, 38] and the use of tam in their studies [39], we believe that our study added more variables to the original tam model that could provide a better explanation of patients’ acceptance of iot technology. vi. conclusion and future work this study assesses empirically the intention of saudi patients to use iot technology from a healthcare perspective. to this end, an extended model based upon the tam was built with eight factors. the proposed model was validated using a instrument designed specifically for this research. in order to ensure that our model can be generalized, the survey was distributed to more than 450 participants, and the responses of 407 of them were considered valid and were further analyzed. spss v25.0 and amos v23.0 have been utilized to process the results, test the proposed model and the corresponding hypotheses. all test results met normality and validity requirements. the discriminant validity was also tested between factors, showing the sufficiency of our model. the pvalue was used to determine the significance during the hypotheses testing. results showed that perceived usefulness, cost, and privacy concerns were the leading predictors of behavioral intention to use. moreover, the perceived usefulness was strongly affected by both perceived convenience and perceived ease of use. however, attitude and perceived connectedness did not have any effect on behavioral intention, directly or indirectly. this research provides the groundwork to explore the process of the actual adoption of iot services for healthcare. however, as future work, more factors should be identified and added to the model, in order to gain more insights and ensure greater success of such service. moreover, the model could be extended to include a larger number of patients. in addition, we can extend our current findings by investigating the moderating effects of age, cultural background, and other factors. references [1] r. minerva, a. biru, d. rotondi, towards a definition of the internet of things (iot), ieee internet initiative, 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of connected objects in e-health: a mixed methods approach”, systemes d'information et management, vol. 23, no. 4, 2019 [34] h. emad, h. m. el-bakry, a. asem, “a modified technology acceptance model for health informatics”, international journal of artificial intelligence and mechatronics, vol. 4, no. 4, pp. 153-161, 2016 [35] s. dunnebeil, a. sunyaev, i. blohm, j. m. leimeister, h. krcmar, “determinants of physicians’ technology acceptance for e-health in ambulatory care”, international journal of medical informatics, vol. 81, no. 11, pp. 746-760, 2012 [36] m. alanazi, b. soh, “internet-of-things for healthcare purposes: extending the technology acceptance model for saudi arabia patients”, international journal of computer science and network security, vol. 19, no. 2, pp. 74-81, 2019 [37] f. e. idachaba, e. m. idachaba, “robust e-health communication architecture for rural communities in developing countries”, engineering, technology & applied science research, vol. 2, no. 3, pp. 237-240, 2012 [38] d. virmani, p. girdhar, p. jain, p. bamdev, “fdrenet: face detection and recognition pipeline”, engineering, technology & applied science research, vol. 9, no. 2, pp. 3933-3938, 2019 [39] p. shayan, e. iscioglu, “an assessment of students’ satisfaction level from learning management systems: case study of payamnoor and farhangian universities”, engineering, technology & applied science research, vol. 7, no. 4, pp. 1874-1878, 2017 authors profile meshari alanazi received his bsc degree in computer science from northern border university and his msc degree in computer science from western illinois university in usa 2016. during 2016-2018, he was a lecturer in northern border university, and in 2018 he started his phd. in la trobe university. ben soh obtained his phd in computer science & engineering from la trobe university in 1995. since then, he has successfully supervised to completion nine phd students and published more than 160 peer-reviewed research papers. he has made significant contributions in the following research areas: fault-tolerant and secure computing, cloud computing, information systems research, pervasive wireless network communications, and business process management. microsoft word etasr_7-1_1358-11362.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1358-1362 1358 www.etasr.com jooybari and rezaie: petrophysical evaluation of the sarvak formation based on well logs in dezful… petrophysical evaluation of the sarvak formation based on well logs in dezful embayment, zagros fold zone, south west of iran akram jooybari peiman rezaie geology department university of hormozgan bandar abbas, iran a91.jooybari@gmail.com geology department hormozgan university bandar abbas, iran peiman_rezaie@yahoo.com abstract—dezful embayment in the south west of iran is part of zagros fold zone which despite the small area includes almost all of iran oil production. sarvak formation with middle cretaceous (albin-turunin) is the second biggest reservoir of zagros basin, after the asmari formation. in this study, with well logging data of two wells, by geolog software, the petrophysical parameters of sarvak formation in the dezful embayment was studied using the contingent probabilistic method. petrophysical parameters such as determination of porosity, water saturation, shale volume and lithology were calculated using this data and common cross plots. based on this evaluation and utilizing cross plots result, the lithology of sarvak formation in this zone was determined to be limestone with traces of dolomite and shale. according to the calculated petrophysical properties of the reservoir, and for more accurate assessment, sarvak formation was divided to 6 sections. findings of this research show that sarvak formation includes good reservoir parameters only in half its sections (sections 4, 2 and 6). keywords-petrophysical evaluation; dezful embayment; sarvak formation; iran i. introduction the bangestan group of albian -campanian age contains some of the most prolific reservoirs of the arabian plate and zagros basin hydrocarbon provinces, predominantly within neritic carbonates of the sarvak formation and equivalent units (e.g., the mishrif formation in iraq). dezful embayment (southwest of iran) is one most important hydrocarbon states in world which located in northeast of arabian plate margin [1]. petrophysical evaluation is the science of insight and interpretation of obtained information from well logging for examination of the reservoir quality of different parts of formation and for determining the best zones for optimized exploitation of reservoirs and development of oil fields [2]. recognition of lithology, calculating the shale volume, porosity and water saturation are the most important parameters in petrophysical evaluation necessary to determine a reservoir’s quality [3]. the aim of this study is to specify the reservoir’s parameters and evaluate the quality of sarvak formation in the dezful embayment. in this study well logging data from two wells (a and b) in sarvak formation and geolog software have been used to determine petrophysical parameters. similar studies have been performed in different regions [4-7]. also, in [8], this approach has been combined with other techniques to study the mishrif formation in iraq, which is equivalent to the sarvak formation. ii. geological setting more than 65%of confirmed petroleum resources in the world and 34% of gas fields in the world are located in giant hydrocarbonic fields in the middle east [9]. the zagros fold and thrust belt is one of the most important active tectonics belts in the middle east, that is in south-west of iran between the arabian plate and the center of iran [10]. the belt is extended along the north-northwest boundary of arabian plate, i.e. from the southeast of turkey, syria and iraq to the minab’s fault in the south of iran [11]. this area includes enormous hydrocarbonic fields and consequently it is distinguished as one of the richest oil belts in the world [12]. dezfol embayment in zagros is surrounded by three important structural features which are: the flexural balarood zone in the northwest, the mountain bend front in the northeast and a complicated fault zone named qatar-kazerun in the east and southeast (figure 1). zagros mountains width consists of major anticlines, elevated and folded, which contain several reservoir inside [13]. more than 45 perineum fields have been discovered inside the dezfol embayment [14]. the dezful embayment zone despite the small area (about 40000 km2), includes almost all of iran’s oil production [14]. oil reservoirs in this zone include the khami group (fahlian and daraian formations) and the bangestan group (ilam and sarvak formations) and the asmari reservoir. thick sedimentary successions of cretaceous age in the arabian plate and zagros basin contain numerous economically important hydrocarbon accumulations [15-20]. the development of an epeiric platform occurred during the early cretaceous throughout the middle east [21, 22]. the engineering, technology & applied science research vol. 7, no. 1, 2017, 1358-1362 1359 www.etasr.com jooybari and rezaie: petrophysical evaluation of the sarvak formation based on well logs in dezful… stratigraphic record of the late albian, cenomanian and turonian (89-98.9 ma) in the arabian plate and zagros basin includes the mishrif, ahmadi and rumaila formations in saudi arabia, the natih formation in oman [23, 24], the derdere formation in south-east turkey, the mishrif formation in iraq and the sarvak formation (figure 2). the sarvak formation middle cretaceous (albin-turunin) is in the bangestan group. the upper boundary of the sarvak formation is discontinuous with part of ilam formation deposited on it whereas the lower boundary is transitional boundary with the kazhdumi formation (figure 2a). lithology of these formations are mainly limestone and dolomite in some parts. sarvak formation includes two facies, shallow and deep. the lower part of sarvak formation includes clay limestone and pelagic and the reservoir quality is lower than in the upper part of formation. the upper part of sarvak formation shows higher reservoir quality which can be attributed to effect of discontinuity between the two parts [25-28]. this formation is widely present in the dezful embayment and the persian gulf [29]. many studies have focused on the sarvak formation which, in a qualitative sense, has become known as the second biggest reservoir of iran [18, 25-27, 30-31]. iii. data and methodology in this study, well logging data from two well were used. raw and environmental data were provided. these data were digitized by surfer 9 software and conversed with a proper format (las) for geololg software. depth matching was performed before quantity processing. notron and density logs were used as the basis for matching logs. next, environment correction is performed by schlumberger standard charts on the whole logs. in the next stage the multimin method was used in geolog for calculations. finally, data is surveyed and evaluated, the necessary parameters are calculated and petrophical crossplots are acquired. fig. 1. dezful embayment location in the zagros fold belt fig. 2. a: sratigraphy of cretaceous in the zagros region (sw iran), kuwait and saudi arabia. b: stratigraphic location of sarvak formation in dezful embayment to better assess reservoir distances according to the shale volume, the sarvak formation was divided to separate sections. conventional petrophysical cross plots were used to determine the lithology. water saturation was calculated using the archie method and porosity by neutron graph, sonic and density. also neutron-gama and water saturation-effective porosity cross plots were used to separate quality reservoir samples from poor quality samples. the studied logs in this survey include notron (nphi), density (rhob), sonic (dt), gama ray (cgr, sgr), resistivity (lld, lls, ll3, mll), caliper (cal) and pef logs. iv. results and discussion petrophysical evaluation of a formation by well login can have an important role in quantitative and qualitative assessment of that formation. in the petrophysical evaluation of the sarvak formation using two wells (a and b), the following cases were studied: a. lithological interpretation with cross-plots identify the lithology is an important step on evaluation of reservoir properties and helps to separate reservoir zones from non-reservoir zones. in this study, formation lithology was identified using two methods. b. neutron-density cross plot in this cross plot three graph of limestone lithology, sand and dolomite are plotted (figure 3). for identifying lithology just a plot of density against neutron is needed. the location of plotted points considering point distances from matrix lines shows the lithology percent [32]. this method shows the best porosity recognition among cross plots. as showed in figure 3 major lithology of well a is limestone and little dolomite. well b has the same lithology but with a different ratio engineering, technology & applied science research vol. 7, no. 1, 2017, 1358-1362 1360 www.etasr.com jooybari and rezaie: petrophysical evaluation of the sarvak formation based on well logs in dezful… c. neutron-sonic cross plot in this cross plot, it is sufficient to plot dt (sonic) against neutron. location of plotted point considering to distances of point from matrix lines shows the percent of lithology. due to matrix effects on porosity, the individuation of curves is impressive [32]. obtained results from this cross plot approximately confirm the lithology and porosity obtained from the neutron-density cross plot (figure 4). d. effective porosity-gama cross plot (nphi-cgr) with this cross plot, reservoir intervals can be separated from shale intervals, at intervals of shale cgr and nphi response to shale presence and as a result, plotted points appear as a linear graph, considering to this point which cgr only response to the shale and nphi addition of response to shale presence, also response to saturated fluid. if clay percentage is low, plotted point are set out of the process of the linear graph [33]. the plotted points in the sarvak formation, in both a and b wells, show increased nphi that is not matched with increased cgr and in fact the cgr is approximately linear which shows the low amount of shale and nphi increase of porosity in this formation (figure 5). e. water saturation-effective porosity cross plot in this cross plot, water saturation plotted against effective porosity is performed. these two parameters are inversely with each other. so, a section with low saturation shows good reservoir quality. by using this cross plot, it was determined that when saturation decreases, the effective porosity increases and reservoir quality rises (figure 6). f. calculating shale volume one of the most important considerations in the evaluation of formation is the identification of shale percentage, as it is rather important to the correct calculate formation porosity and fluid saturation. several log are used, including gama, neutron and resistance, separately or combined [34]. the cgr log was used in this study. if the amount of shale is less than 10% then we have a “clear stone” whereas between 33-10 we have a “shaley” and over 33% a “shale” [34]. average calculated shale volume of this formation in wells a and b respectively is 2.9 and 7.04. thus, the sarvak formation is clean limestone without clay and shows increased shale volume in well b. g. calculating porosity stored, porosity is also an important parameter in petrophysical evaluation. porosity is calculable with neutron, sonic and density graphs. in well a, most porosity is related to section 6 whereas in well b most porosity is related to section 2. h. calculating water saturation fluid saturation is the ratio of fluid volume in rocks (into volume empty spaces). this parameter اhas no dimension and is expressed as a percentage. to calculate the water saturation in zone that is not impregnated to reservoir (to drilling mud), is performed with the archie formula [35]: sw = (a/phi^m*rw/rt)^1/n (1) fig. 3. neutron-density cross plot for wells a and b fig. 4. neutron-sonic cross plot for wells a and b fig. 5. effective porosity-gama cross plot for wells a and b fig. 6. water saturation-effective porosity cross plot for wells a and b where sw is the water saturation, a is the tortuosity coefficient, phi is the porosity, m is the cementation ability, rw is the engineering, technology & applied science research vol. 7, no. 1, 2017, 1358-1362 1361 www.etasr.com jooybari and rezaie: petrophysical evaluation of the sarvak formation based on well logs in dezful… resistance of water formation in formation temperature, rt is the true formation resistance and n is the saturation power that changes from 1.8 to 2.5, with 2 usually considered. in table i the average saturation of each zone is showed. the largest saturation for the sarvak formation is found in section 1 of well a (84.5%) and in section 1 of well b (77.5%). table i. results of petrophysical evaluation in wells a and b vsh sw phie net interval well api % % meters meters 2.28 84.5 1.2 50 1a a 2.21 55.4 3.2 210 2a a 6.26 67 3.8 120 3a a 2.12 28.3 9.2 132 4a a 2.49 53 5.2 48 5a a 2.41 52.6 9.4 150 6a a 13.91 77.5 3.2 45 1b b 4.96 58.5 5.5 210 2b b 7.76 62.8 1.3 110 3b b 4.15 19.5 13.8 130 4b b 6.52 76 1.6 60 5b b 4.98 25.7 12.2 105 6b b v. conclusion the key conclusions of this work are as follows:  petrophysical evaluation of well a: the sarvak formation in this well composes from mainly limestone and little dolomite and shale. mentioned formation in this well has 710 meters thickness and is divided into 6 sections. the average formation effective porosity in this well is 4.6%, the average shale volume 2.96 and the average water saturation is 56.8%. section 4 shows the best petrophysical parameters and it is the best section of this formation in terms of reservoir quality, followed by sections 6 and 2 respectively. section 1 has the weakest petrophysical parameters and is the weakest, in terms of reservoir quality, section of this formation.  petrophysical parameters of well b: the sarvak formation in this well composes mainly from limestone and little shale and dolomite. the thickness is 660 meters and is divided to 6 section. the average porosity is 6.2%, the average shale volume is 7.04 and the average water saturation is 53.2%. section 4 shows the best petrophysical parameters and reservoir quality and section 5 and 1 shows the weakest petrophysical parameters and thus a very low reservoir quality.  the comparison of wells a and b shows that the major lithology in both wells is limestone and traces of shale and dolomite. low shale volume is shown to be an important controlling factor regarding reservoir 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carbonates, officer basin, south australia”, apea journal, vol. 35, pp. 106-120,2003 [35] g. e. archie, “the electrical resistivity log as an aid in determining somereservoir characteristics”, petroleum technology, vol. 5, pp. 5462, 1942 microsoft word 20-3284_s_etasr_v10_n1_pp5205-5210 engineering, technology & applied science research vol. 10, no. 1, 2020, 5205-5010 5205 www.etasr.com alsuwaiket et al.: refining student marks based on enrolled modules’ assessment methods using data… refining student marks based on enrolled modules’ assessment methods using data mining techniques mohammed a. alsuwaiket department of computer science and engineering technology, hafar batin university, hafar batin, saudi arabia malsuwaiket@uhb.edu.sa anas h. blasi department of computer information systems, mutah university, karak, jordan ablasi1@mutah.edu.jo khawla altarawneh department of computer science, mutah university, karak, jordan khawla_t@mutah.edu.jo abstract—choosing the right and effective way to assess students is one of the most important tasks of higher education. many studies have shown that students tend to receive higher scores during their studies when assessed by different study methods which include units that are fully assessed by varying the duration of study or a combination of courses and exams than by exams alone. many educational data mining (edm) studies process data in advance through traditional data extraction, including the data preparation process. in this paper, we propose a different data preparation process by investigating more than 230,000 student records for the preparation of scores. the data have been processed through diverse stages in order to extract a categorical factor through which students’ module marks are refined during the data preparation stage. the results of this work show that students’ final marks should not be isolated from the nature of the enrolled module’s assessment methods. they must rather be investigated thoroughly and considered during edm’s data pre-processing stage. more generally, educational data should not be prepared in the same way normal data are due to the differences in data sources, applications, and error types. the effect of module assessment index (mai) on the prediction process using random forest and naive bayes classification techniques were investigated. it was shown that considering mai as attribute increases the accuracy of predicting students’ second year averages based on their first-year averages. keywords-edm; data mining; machine learning; naïve bayes; random forest; module assessment i. introduction during the last few decades the use of coursework-based module’s assessment has increased in the uk and other countries due to various educational arguments justifying it. the students prefer assessments based on coursework alone or a mix of both coursework and exams because these types of assessments tend to yield higher marks than exam based assessment alone [1]. the expanded use of coursework-based evaluation has added in the imprints of singular modules and has led in the extension of good degrees [2]. an expanding number of colleges moved from conventional test based to consistent appraisal all through the semester (for example coursework-based) [3]. coursework-based evaluation techniques differ from test based appraisal strategies where the learning or the ability is tried in a quite certain timeframe. in addition, it has been generally recognized that the picked appraisal strategy will decide the style and substance of understudy learning and ability procurement [3]. coursework imprints are a superior indicator of long haul learning than tests [4]. to the best of our knowledge, no studies have considered the increase in marks in the data pre-processing phase. this led to a conclusion that applying conventional dm processes on educational data may not produce accurate results. authors in [5] proposed a model that refines students’ marks based on enrolled modules’ assessment methods. the model represents a sub process through which module assessment methods are considered for further processing using a new attribute that reflects the ratio of coursework weightings. although educational data have been recorded and analyzed from educational software for long, only recently this process has been formed into the new field of educational data mining (edm) [6]. the edm process converts raw data from educational systems into useful information that could potentially have a greater impact on educational research and practice [6]. additionally, edm uses a wide range of methods to analyze data, including but not limited tosupervised and unsupervised model induction, parameter estimation, relationship mining, etc. [7, 8]. ii. assessment methods in higher education regardless of the inability to absolutely ensure student learning, assessment is still an essential tool through which teachers have to influence the ways students respond to courses. there are clear steers from uk government towards coursework-based assessment focused on employability [9]. however, not all assessment methods suit all programs or all courses [10]. thus, student assessment methods in higher education can be generally divided into two main categories: exam-based assessment, which includes different forms of exams such as closed and open book examination, essay-type exams, multiple-choice exams, etc. and coursework-based assessments, which include research projects, assignments, etc. different studies have proved that students tend to gain higher marks from coursework-based assignments than they do from examinations [11]. it was also found that combined exambased and coursework-based assessment methods produced up to 12% higher average marks than examinations. author in [10] conveyed an analysis of marks on more than 1,700 modules at oxford polytechnic. modules with 100% corresponding author: anas h. blasi engineering, technology & applied science research vol. 10, no. 1, 2020, 5205-5010 5206 www.etasr.com alsuwaiket et al.: refining student marks based on enrolled modules’ assessment methods using data… coursework had an average mark 3.5% higher than modules with 100% examination assessment. this paper solves the problem of a gap between coursework and exam based assessments and tries to normalize students’ marks based on the assessment method of the enrolled modules. iii. student transcript data in this paper, 4662 modules with different assessment methods were investigated. the basic average calculations of module marks in all departments showed that students who are assessed by coursework tend to get higher marks than those who are assessed by exams or a mixture of both coursework and exams, as shown in table i. table i. average module marks of students in each department and their assessment methods department number of students average module mark of students by assessment type exam-based coursework-based mixed business 54960 59.77 60.83 60.01 civil engineering 34892 58.78 63.74 60.70 computer science 19800 58.18 64.40 58.87 electrical and computer systems engineering 13740 59.55 63.26 57.00 mathematics 24152 61.59 66.00 61.17 mechanical engineering 31385 58.80 64.26 60.24 a simple t-test was applied to the data of table i in order to measure the difference between the means of each pair of variables. results show that there is a statistically significant difference between exam-based and coursework-based assessments (with 95% confidence level which equates to declaring statistical significance at the p<0.05 level), a t-value of -5.06 and a p-value of 0.001). applying the t-test to measure the significance of difference between each pair of variables (ex-cw, ex-both, and cw-both assessment methods) has the following results. • significance of difference between exam-based and coursework-based assessments: by applying the paired ttest on the above fields, with 95% confidence level (which equates to declaring statistical significance at p<0.05), a tvalue of -5.83 and a p-value of 0.002 were obtained. since the p-value is less than 0.05, it can be concluded that there is a statistically significant difference between the exambased and course-based assessments. • similarly, the p-value of the paired t-test between the coursework-based and mixed assessments (0.004) was also less than 0.05, which also indicates the statistically significant difference between these two assessment methods. on the other hand, it seems to be no statistically significant difference between the exam-based assessment and the mixture of both exam and coursework assessment methods, since the pvalue was 0.749 which is greater than 0.05. a. understanding student transcript data student transcript data were collected systematically. the data consisted of files with hundreds of thousands of records. the data in these files had first to be understood, then cleaned, and finally factors that have the most significance had to be highlighted in order to further process these data using edm techniques. therefore, prior to modeling the data in either dm or edm, the data types should be first identified and understood. normally, educational data are discrete, i.e. either numeric or categorical data, and noise-free. the lack of noise in educational data is due to the fact that they are not measured, they are either collected automatically or checked carefully [12]. on the other hand, missing data values exist, usually in the cases where students skip answering a given questionnaire or when teachers skip checking attendance data. humans normally do this type of errors, which are generally referenced as data entry errors [13]. the investigated data represent around 230,823 student records representing a total of six departments at a uk university. each one of these department data sheets contains a number of student records. for each record, a number of attributes that represent a student’s academic accomplishment are divided as follows: 1) student-related attributes these attributes highlight the status of the students, including: • module mark: student’s mark in a certain module. • exam mark: the mark achieved by a student on the exambased assessment part. • cswk mark: the mark achieved by a student on the coursework-based assessment part. 2) module-related attributes they describe a certain module and its characteristics. these attributes include: • module code: an alphanumerical sequence of digits as a short code for each module. • exam weighting (exw): based on the assessment method for each module, this attribute represents the total marks reserved for the exam-based assessment out of 100, i.e. it can be seen as the ratio of exam-based assessment to the total mark of a module. • coursework weighting (cww): alternatively, this attribute indicates the ratio of coursework-based assessment to the total mark of a module. for each module, the values of these two attributes complement each other to reach the maximum total mark (100). for each department, different ratios between exam weighting and coursework weighting will be described in detail. • module assessment method: this categorical attribute represents the ratio between exam and coursework based assessment for a given module. this attribute may take the value of “exam”, coursework”, or “both” where the “exam” indicates that the exam weighting is 100 while the coursework weighting is 0, “coursework” represents the engineering, technology & applied science research vol. 10, no. 1, 2020, 5205-5010 5207 www.etasr.com alsuwaiket et al.: refining student marks based on enrolled modules’ assessment methods using data… opposite, and finally “both” represents all ratios in between. 3) program-related attributes these attributes describe the program in which the student is registered, namely: program code, which represents the program in which a student is enrolled. b. causes of errors in educational data prior to storing data in databases, data normally are processed by human interaction, computation or both. the sources of errors in databases are categorized into four main types: data entry errors, measurement errors, distillation errors, and data integration errors [13]. as mentioned above, since educational data are usually not measured, the errors in them can be caused by humans (i.e. through data entry errors) so these data have minimum or zero noise compared to other, noneducational, data types. alternatively, the data we have are normally referred to as quantitative data, which are defined as a set of integers or floating point numbers that measure quantities of interest [13]. c. missing data fields as mentioned above, educational data are characterized by minimum noise, or sometimes they can be noise-free. the data we have are not noise-free because of the fact that some values are missing. the missing values most of the times are left empty because they are implicitly shown in other fields. for example, the module desc field is barely filled and this creates an obstacle if this field is used by any statistical or data mining tool. hence, a basic algorithm was developed that considers both the exam weighting and coursework weighting fields to fill the module desc categorical field as follows: for resit desc in records: if resit desc= exam or resit desc=blanks: if(exam weighting ==100) assessment method is through exam only else if resit desc= coursework or resit desc=blanks if(coursework weighting ==100) assessment method is through coursework only else if (resit desc=both or resit desc= blanks or resit desc =exam or resit desc= coursework) if (exam weighting !=0 and exam weighting !=100) assessment method is through both exam and coursework there are other records that were removed from our datasets for the fact that they represent an extremely low percentage of the data which were detected through the method of outliner detection (i.e. readings that are in some sense “far” from what one would expect based on the rest of the data) [13]. for example, in the department of mechanical engineering, the module mark of some students was not recorded because of the nature of the enrolled modules that either pass a student or not without including the pass or fail marks. the percentage of such students in the department of mechanical engineering is 0.000047%, which can be neglected without affecting the remaining data. d. most significant factors affecting students’ marks as mentioned upon investigating all the factors (attributes) mentioned above, some factors were immediately neglected as they were irrelevant to the issue at hand. on the other hand, some other factors are directly connected to the studied problem. those factors were considered for cleaning and then for further processing in order to understand the effect of the assessment method on student academic accomplishments and how to achieve more accurate marks. module mark, cww, exw, module code, regno, and module desc are the most significant factors that contribute in achieving more accurate marks. the choice of the above factors was based on observation and coefficient correlation. those chosen based on observation are the ones that are directly connected to the problem at hand, such as module mark, cw weighting, ex weighting, regno, and module code. in other words, the choice of the factors was based on the effect of those factors on the final outcome. for instance, a question to be asked is whether or not the cw weighting can play a role in determining the accuracy of a student’s mark based on the enrolled module’s assessment method. this question can be directly and positively answered using pearson correlation method. the method was applied on different factors to determine the correlation between them. table ii shows the coefficient correlation on selected factors where these values tend to be high for cw and ex to module mark and low to other factors: table ii. pearson correlation of data factors exw cww cw mark exam mark exw cww -1.00 cw mark 0.03 -0.030 exam mark 0..13 -0.013 0.461 module mark -0.126 0.126 0.690 0.966 by observing the correlation matrix, it can be noticed that exam mark has the biggest positive effect on module mark, followed directly by cw mark. on the other hand, some other factors have negative correlation to module mark, such as ex weighting. that is, the more the weight of the exam based assessment, the less the module mark will be. therefore, this research has considered the most significant factors whose correlations values are the highest in order to investigate the accuracy of students’ module marks under different assessment methods. the following section will present the pre-processed students’ transcript data in a different way in order to increase the data mining accuracy by extracting a new factor from the assessment method and use it to refine student marks to ensure more accuracy prior to processing them using edm. iv. module assessment index in order to reflect the module assessment method on students’ marks, the data have to be statistically investigated so that outliners can be identified, and information can be extracted and highlighted. the data have been processed through various steps, each of these steps either adds or removes data. the first step is to categorize the cw to ex ratios. in other words, to ease the processing of numerical ex and cw weighting fields, and combine their values into a categorical field that can later be a part of further processing, a combining and categorizing algorithm is proposed. the algorithm relies on the number of classes the ratio between cw engineering, technology & applied science research vol. 10, no. 1, 2020, 5205-5010 5208 www.etasr.com alsuwaiket et al.: refining student marks based on enrolled modules’ assessment methods using data… to ex weightings can have. namely, each department has its own classification of cw to ex weightings. table iii shows the different classes. by observing table iii, it is clear that no single department shares the same ratio classes with the other departments. thus, filling the table and therefore the data is not a solution since filling the empty cells in the table results to filling the data tables with extra fields, yielding adding empty records which should be cleaned (i.e. removed) again. the solution would be to consider the department with the most number of classes to start with, and then generalize the findings on other departments while bearing in mind the change of ratios. the table shows two departments that have 12 complete ratios (the cs and ecseng departments), in this paper, the cs department was chosen for further processing. table iii. classes of ex to cw weighting ratios model assessment method cw 0:100 25:75 30:70 34:66 35:65 40:60 45:55 50:50 55:45 60:40 65:35 70:30 75:25 80:20 85:15 90:10 100:0 business � � � � � � � � � � cs � � � � � � � � � � � � ceng � � � � � � � � � � � ecseng � � � � � � � � � � � � math � � � � � � � � � meng � � � � � � � � � � the algorithm first tries to ease the manipulation of ratio field by converting it into a categorical field. figure 1 shows a simple procedure which will convert the exw to categorical index values that can later be used in re-evaluating student marks. the output values are 0 to 11, representing the exw to cww ratio. for example, module assessment index (mai) value of 0 represents 0:100 exw to cww ratio, while mai of 11 represents the opposite. the cases in the flowchart can be changed to different ratios from other departments in order to generalize this method. fig. 1. exw to mai matching – department of cs v. re-evaluating students marks based on mai in order to uncover the relation between the student’s module marks and mai, simple quadratic regression was used. exw and cww were combined into one variable hence the simple quadratic regression is more suitable for one variable relation. the choice of quadratic over linear is based on the rsquared of the quadratic model (2.90%) which is higher than the one in the linear model (2.77%). by applying simple quadratic regression on the data with mai as a variable for module mark as a response, we achieved the following fitted regression line: y=mm+0.0035(mai) 0.05688(mai) 2 (1) where y is the re-evaluated module mark after fitting and mm is the current module mark. as a next step the the data of cs department are applied to (1) using the following pseudo code: input: current module mark (mm) for each student and mai output: re-evaluated module mark (rmm) for each mm: if mai=0 then rmm=mm else rmm=mm+0.0035(mai) 0.05688(mai)^2 by applying the above pseudo code on student transcript data of the cs department, an additional field will be added which contains the rmm for each student at the department. as a real example on applying the above, for the student with regno of x in the module “server side programming” which has 0:100 exw to cww ratio (i.e. mai=0), the rmm would be equal to mm, and since this student’s mm is equal to 60, his rmm would be also 60. however, for the same student in another module, social informatics that has a mai value of 5, the student’s mm of 55 is re-evaluated as 57.03 after applying the formula. the new values of rmm are self-explained. table i compares the average module marks for student attending modules with different assessment methods. that is, the more the percentage of cww (yields more mai), the more the added marks to mm, and vice versa. regardless of the fact that this increase on marks has been proved in literature, yet it appears to be that none of the previous studies have considered this engineering, technology & applied science research vol. 10, no. 1, 2020, 5205-5010 5209 www.etasr.com alsuwaiket et al.: refining student marks based on enrolled modules’ assessment methods using data… increase as a feedback to re-evaluate the marks. therefore, it is vital to consider this feedback generation for the educational data mining pre-processing phase. this means that the formulation of the relation between mai (which reflects the ration between exw and cww) and the current mm should be a part of the educational data mining processes. figure 2 shows the additional processes on raw students’ module marks. the goal is to take the differences of the assessment methods into account. fig. 2. re-evaluating students’ module marks vi. the effect of mai on dm’s prediction accuracy in order to verify the effect of the newly constructed variable, the prediction of a student’s second year average mark using only his first year’s average compared to the predicted second year’s average using first year’s average and the newly constructed variable, mai are compared. this comparison may highlight how accurate can the prediction process be by adding new attributes that reflect the nature of the module. two prediction techniques were investigated: orange data mining tool: naive bayes [15, 16] and random forest [17]. the random forest showed more accuracy in terms of classification accuracy (ca) as shown in table iv, hence it was used to evaluate the role of mai in increasing prediction accuracy. table iv. classification evaluation of prediction techniques method auc ca f1 precision recall random forest 0.827 0.942 0.194 0.273 0.15 naive bayes 0.876 0.924 0.330 0.281 0.40 therefore, random forest was used to investigate the effect of including mai as an attribute in prediction process. the data of 407 undergraduate students of the computer science department, including their first and second years’ average marks and their average mai for both years were considered. the comparison has been done with and without the existence of mai. tables v and vi show the confusion matrices of comparisons and how mai affected the accuracy of predicting the students’ second year average marks. table vi shows an enhancement on the prediction probabilities for each of the mark classes (fail, pass, third, lower second, upper second, and first) compared to the probabilities of prediction shown in table v. the random forest showed more accuracy in terms of ca when mai was considered as shown in figure 4 with an accuracy value 0.942, but when mai was excluded, as shown in figure 3, the accuracy was lower with a value of 0.874. table v. predicting second year’s average without mai fail first lower second pass third upper second ∑∑∑∑ fail 57.1% 2.9% 3.9% na 5.0% 2.2% 12 first 0.0% 87.1% 3.9% na 0.0% 6.6% 72 lower second 28.6% 1.4% 72.5% na 10.0% 7.3% 52 pass 0.0% 0.0% 0.0% na 0.0% 2.2% 3 third 14.3% 1.4% 2.0% na 80.0% 4.4% 25 upper second 0.0% 7.1% 17.6% na 5.0% 77.4% 121 ∑∑∑∑ 7 70 51 0 20 137 285 table vi. predicting second year’s average including mai as an attribute fail first lower second pass third upper second ∑∑∑∑ fail 100.0% 3.9% 7.1% 0.0% 10.3% 1.5% 15 first 0.0% 89.6% 0.0% 0.0% 3.4% 3.1% 74 lower second 0.0% 2.6% 85.7% 0.0% 0.0% 5.3% 45 pass 0.0% 0.0% 0.0% 100.0% 0.0% 0.0% 2 third 0.0% 0.0% 2.4% 0.0% 82.0% 2.3% 28 upper second 0.0% 3.9% 4.8% 0.0% 3.4% 87.8% 121 ∑∑∑∑ 4 77 42 2 29 131 285 vii. results and discussion by refining students’ marks, they either increase or decrease depending on the ration between exw to cww for each student during his study. for instance, considering the student x as an example, who was enrolled in 32 modules during this study at the cs department. out of 32 modules, 19 are 100% exam-based assessed modules, 7 are assessed by a mixture of coursework and examination, while only 6 modules are 100% assessed by coursework only. despite that the majority of the modules are assessed through examination only, which means that the student gets no extra marks compared to coursework-based modules, the rest of the modules give the student extra marks and hence add to his overall average. in numbers, 19 modules have 0 mai value, which means that rmm = mm. on the other hand, the rest of the modules have values of mai ranging from 1 to 11, which means that the rmm is always less than mm for those 13 courses. this decrement in the marks is due to the fact that students get higher marks in modules that are assessed by coursework or a mixture of coursework and examinations. therefore, to balance the module marks and the overall average, the formula decreases the module marks by varying percentage depending on the exw to cww ratios. table vii shows the differences in module marks and overall average for the example student. engineering, technology & applied science research vol. 10, no. 1, 2020, 5205-5010 5210 www.etasr.com alsuwaiket et al.: refining student marks based on enrolled modules’ assessment methods using data… table vii. refining example student’s marks based on enrolled modules’ assessment methods average mm average rmm 19 exam-based modules 48.6 48.6 6 coursework-based modules 60.3 53.5 7 mix of ex and cw modules 60.4 59.1 total of 32 modules 53.4 51.8 by following the procedure in figure 2 on a real student’s marks, table vii shows that the rmm remained unchanged for the student when the assessment method of the enrolled modules was purely exam-based. alternatively, when the assessment method of the enrolled modules was purely coursework-based, the rmm was refined down on an average mark of 6.8 compared to mm. finally, a mixture of ex and cw based modules yields less refinement of the rmm (1.3 marks) compared to mm for the same student. this means that the student in the example who is taking 32 modules of different types may have his average marks refined down by 1.6 by the proposed procedure. viii. conclusions and future work during the last few decades, there has been an increased interest in coursework-based assessment in the uk and some other countries due to its various educational and personal advantages such as its learning effectiveness and the lack of time limits and stress. this increased interest had led to discovering that students who are assessed by coursework tend to achieve higher marks than those who are assessed by examinations in the same modules. however, to the best of our knowledge, no studies have considered this increase in marks in the data pre-processing phase. more generally, this led to a conclusion that applying conventional dm processes on educational data may not produce accurate results. in this paper, a model that refines students’ marks based on enrolled modules’ assessment methods has been proposed. the key to refine students’ marks is to develop an index that categorizes ratios between exams to coursework weightings. this index – mai – has been extracted using simple quadratic regression on the module marks (mm) variable. based on mai values, the refined module marks (rmm) were calculated and compared to the original mm. the comparison showed that based on the percentage of pure exam-based assessed modules, the rmm may be less or more than the original mm. this study shows that the pre-processing phase of educational data should include additional sub-phases that deal not only with noise or missing data, but also with data refinement to cope with differences between various educational systems. the effect of mai on the prediction process was also investigated using random forest classification. it was shown that considering mai as attribute increases the accuracy of predicting students’ second year averages based on their first year averages. the findings of this paper will be generalized in different departments and universities that may have various assessment methods, in other words, the refinement procedure should be considered as a sub-process within edm data preprocessing phase when dealing with different assessed modules and their marks. references [1] j. t. e. richardson, “coursework versus examinations in end-of-module assessment: a literature review”, assessment & evaluation in higher education, vol. 40, no. 3, pp. 439-455, 2015 [2] 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wiley & sons, 2007 [15] b. k. bhardwaj, s. pal, “data mining: a prediction for performance improvement using classification”, available at: https://arxiv.org/ftp/ arxiv/papers/1201/1201.3418.pdf, 2012 [16] m. alghobiri, “a comparative analysis of classification algorithms on diverse datasets”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2790-2795, 2018 [17] s. kotsiantis, k. patriarcheas, m. xenos, “a combinational incremental ensemble of classifiers as a technique for predicting students’ performance in distance education”, knowledge-based systems, vol. 23, no. 6, pp. 529-535, 2010 engineering, technology & applied science research vol. 7, no. 5, 2017, 2026-2029 2026 www.etasr.com bahrami: design of a mobile agents based solution to distributional management of computer … design of a mobile agents based solution to distributional management of computer networks, taking into account the security mechanisms saeed bahrami department of science farhangian university qazvin, iran saeedbahrami13@chmail.ir abstract—mobile agents (mas) is one of the technologies considered in the recent years to perform management processes. this technology provides the ability to move code in distributed environments and to connect with other resources and agents locally which makes it an appropriate technology in the development of software applications of distributed network, especially management systems. for using mobile agent technology, an infrastructure for the management of mas is needed. in this project, an infrastructure called mct management is introduced for network management. in this infrastructure, some protocols like snmp are used to get management data for the network administrator. with respect to management ability, mas can dynamically access the database snmp (i.e. mib) and extract the data required by the managers. most well-known methods are characterized by being static relative to code and location in which components cannot modify their location or code in a lifetime. however, the mas method can dynamically increase communications, reduce costs and overcome certain limitations by changing location and components. keywords-design; mobile agent; security mechanisms; mct i. introduction for a long time the client-server (c/s) model has been applied for various network affairs. in this model, a computer, taken as the client, demands a request from another device as a server and returns the response. the relationship between the two is done in sync format and can be done in rpc and message passing [1]. this method is frequently used in network management systems including distributed systems. network management can be a process of controlling a network with complex data for maximizing its efficiency. given that network systems are constantly increasing their size, their management with modern styles is not efficient, because of the stability, synchronous operation, transfer of massive data and homogeneous acts. in order to overcome such limitations, various decentralized methods have been recommended. one of these methods is the use of mobile agents (mas). agents are actually codes moved from a network element to another and communicate with local resources and other agents, returning the data of one network element to the manager. because of their movement, agents are called mobile. due to their ability to move in distributed environments, mas are very suitable for the development of distributed software applications, especially in network management systems where the decentralization of management operations is one of the main characteristics. in this mode of operation, management duties are delegated to the agents and a number of them can be dynamically distributed between management entities in the network management system. using migration capacities, they can communicate locally using this protocol, and according to information already stored, use the hardware and software necessary for the operations management. in this paper, first the case of ma technology and its management is introduced and then the managing infrastructure called mct is presented and its connection with snmp is also expressed. then, in simulation mode, the communication of ma and mib, snmp for administrators is designed in order to monitor and control the network. ii. network management by the ma scheme one of the major problems in the c/s method occurs due to large data volumes that do not improve network’s efficiency. as noted earlier, client-server communication is synchronous in c/s model. although this method performs well in some aspects, higher applications in distributed systems will reduce the quality of connections and cause problems in applications due to the synchronous nature of communications. therefore, mas are proposed as a new method that instead of moving the data to the code, it moves code towards the data. the efficiency of the method depends on the code/data volume relation. this method basic function is that a code form agent is sent to the station(s). the code carries the operations defined on it and then returns the required information in two ways: directly or by assigning it to another agent [2]. according to the motion, this method is particularly suitable for distributed environments. with respect to their performance (mobility) mas have enormous potential. for example, they can stop their run at one point and resume execution at another location until engineering, technology & applied science research vol. 7, no. 5, 2017, 2026-2029 2027 www.etasr.com bahrami: design of a mobile agents based solution to distributional management of computer … the interruption point [3]. agents can also communicate with stations locally [4, 5]. these capabilities have advantages over the traditional method of c/s that include: overcoming network latency, reducing network load, working in heterogeneous environments, being adaptable to dynamic form and being fault-tolerant. this feature also makes this method capable of being used in various fields, one of them being the field of network management. snmp protocol is widely used for network management [6]. in this protocol, all properties of the system either software or hardware are stored in a table called mib. in reality, regarding the existence of different types of agents, they can be moved towards various stations, as the required data is extracted from mib table and report to the manager. therefore, agents can be used in different network management fields including fault management, configuration management, performance management and audit management applications. iii. the security mechanisms of mobile agents a. security threats agents provide great opportunity for misuse and improper use, widening the range of threats [7-9]. to discuss on security is enough for one to select a simple method that consists of two parts: agent and agent platform. an agent includes code and data that required performing calculations. mobility provides the possibility of movement and circulation of agent among the platforms. agent platform provides the necessary environment for the agent to perform calculations and computing affairs. a platform that an agent stems by is called a home platform, which is usually the safest environment for an agent. a host may contain one or more agent platforms and an agent platform may protect several computing environment and meeting places where agents are connected. four categories of threats have been detected including threats created by the attacks of an agent to an agent platform or an agent platform to the agent and an agent to another agent in the agent platform, or when other entities attack to system agent. the last classification covers the attack of an agent to another agent and attack of an agent platform to another platform because these attacks at first focused on platform communication capabilities and benefit from potential vulnerabilities. the last classification also includes conventional attacks against the operating system under agent platform. for more studies about security, readers can refer to [10-13]. b. security requirements users of networked computer systems, have four kinds of security requirements: the ability to be faithful, integrity, responsibility or accountability and accessibility. agent users and framework of ma also need the above requirements (confidentiality, integrity, responsibility or accountability, accessibility, and anonymity.) c. countermeasures many agent systems relied on a series of hypothetical demarcation lines with regard to the issue of safety. first, an agent relies on its home platform, where it has been established and its implementation begins. afterwards, home platforms and other agent platforms who rely in this case can be safely realized without defect or deficiency. third, coding or encryption which is in the beginning in the form of digital signage and used in the list of revoked or certificated, is supervised and managed by a specific and general infrastructure based on mobile agent. in order to create a system based on ma, a sub-structure is required. each infrastructure should be capable of running a defined agent and can move it in different machines, and even, if necessary, is able to establish communication between agents. also it provides the necessary security operations for the agent and infrastructure. unfortunately no infrastructure with the desired security could have been created so far. all mas based infrastructures work on the java virtual machine (jvm). so first the jvm is installed; then, the working infrastructure will be installed. of course there are a lot of infrastructures, but very few of them are standardized. there are two standards named masif and fipa for them, as we select one of them named grasshopper which is based on masif standard for simulation of one of the network management operations. in the simulation process, we created 3 locations where one of the agents starts to move on the other two virtual machines and reports on a management accounting in telecommunication networks. iv. simulation and results various experiments in the following manner were conducted to evaluate both types of network management, each one was individually investigated and the results were recorded. a. effect of the number of network managed elements (mne) first, we investigate the effect of managed network elements to assess the response time. assumptions: the request / response length was fixed (50 bytes), with 2 mbps rate of data communication, the delay of data connections was within milliseconds and initial number of the mas was five obtained as a result of the experiments. test: behavior of mas does not change according to the type of topology and is almost constant, but in snmp response times in different topologies increase faster by increasing the number of managed elements, because packets surveyed in snmp are dependent on the type of topology. this experiment shows that if the number of managed elements is low, snmp works better than ma because the snmp message is smaller than the initial value of ma. as managed elements increases, the response time for snmp shows a proportionate growth, while is faster for ma. result: between the two areas, by increasing managed elements, ma performs better than snmp. b. effect of initial value of ma in this section, we investigate the effect of initial value of ma on response time. assumptions: data communication rate was in mbps and connections delay was 4 ms. testing was started by different initial values of ma (1, 3, 5, 7, 9 kb) and engineering, technology & applied science research vol. 7, no. 5, 2017, 2026-2029 2028 www.etasr.com bahrami: design of a mobile agents based solution to distributional management of computer … other affairs are as noted before. experiment: conducted tests showed that for smaller number of elements less bites are used for ma. but when the number of mnes increases, ma is more suitable, according to the pdu getreguest, udp and ipheader. as the size of ma increases, the number of bytes depended on the management station also relatively increases. in the case of response time, as the number of mne increases the difference between the types of ma size increases faster. for example, ma with size of 5 k has a better performance than snmp in mne less than 200. but in more than 200, response time of snmp is less. results: the lower initial value of ma, the better it performs than the snmp. c. effect of task in this section, we examine the effect on response time regarding the kind of action. assumptions: first action is 5 bytes in length (like the previous sections), the second action has a request / response with a length of 400 bytes and the third action has a variable length of 150 bytes. ma size is 5 kb and topologies are like the previous section. experiment: according to test carried out on these three different size actions, it showed that when the ma or snmp are used for network management, different response times are obtained. in snmp type of operation does not have a high impact on response time (very small difference), because in fact the number of bytes exchanged between the management station and mnes is low, but in ma, because the number of exchanged bytes increases (for example, from the first to the third action) response time also increases because ma is transmitted with more problems. the result: by increasing the size of an action, response time increases in ma and is nearly constant in snmp. d. effect of unload strategies in this part, two strategies are considered for ma. first their performance is explained and then we examine which of them is better. assumptions: we consider the three different actions of previous section. the maximum number of visited elements is from 1 to 240. ma topologies and sizes are as the previous section and the number of visited elements in sweep is the same. test: in the previous sections was revealed that size of ma has a direct relationship with number of visited elements, which means that as the number of visited elements increase, ma size also increases and as a result migration is more difficult. now consider two strategies to evaluate this issue: • the first strategy (s1): ma is returned to the management station with the results. • strategy 2 (s2): ma only returns the results to the management station. (number of elements that ma passes during the sweep is fixed.) 1) strategy 1 (s1) experiments show the response time of strategy s1, when the number of managed elements in the path of movement visited by the agents is greatly reduced. if the visited nodes during movement are rising up to a specific point, the response time is decreased, and it increases if the number of agents raises and creates problems for motion. the optimum point for the number of nodes for this strategy is 16. the tests are shown in table i. table i. response time in s1 strategy with different operations taskt3(s) taskt2(s) taskt1(s) elements per trip numbers 32.73 32.63 32.54 1 1 19.63 19.53 19.44 2 2 10.25 10.02 9.80 8 3 9.16 8.75 8.34 16 4 10.03 9.29 8.54 30 5 11.75 10.28 8.82 60 6 15.83 12.93 10.03 120 7 24.35 18.56 12.78 240 8 11.30 10.75 10.21 snmp 9 based on the data of this table, the response time is up to 62% compared with optimal point (16 elements) of t1 and t2 operations, and is reduced by accumulation of all 240 variables in path. the strategy optimized for all operations works better than snmp. for a smaller number of elements in motion, size of operation has no effect when ma has a low size, but when number of elements in the movement is bigger, for example, 240, difference between practices is significant. therefore, increase of the size effect, makes this strategy better. 2) strategy 2 (s2) response time in s2 strategy has an optimum point. the following table shows the results of tests performed in accordance the results. based on table ii, the response time is up to 64% compared with optimal point of t1, t2 and t3 operations and is reduced with accumulation of all 240 variables in path. table ii. response time in s2 strategy with different operations taskt3(s) taskt2(s) taskt1(s) elements per trip numbers 21.86 21.54 21.22 1 1 14.51 14.19 13.86 2 2 9.48 9.03 8.58 8 3 8.86 8.45 7.84 16 4 9.87 9.13 8.38 30 5 11.67 10.20 8.74 60 6 15.79 12.89 9.99 120 7 24.33 18.54 12.76 240 8 11.30 10.75 10.21 snmp 9 comparison of both strategies for action, t1, indicates that s2 performs better when the number of managed elements in path is low, compared to the case where ma’s code is not sent to the management station. as the number of elements in path is increased, both methods act in the same way, because the size of the data collected by the agent becomes more than the size of ma code. in this experiment, the initial value of ma also has an effect. because the initial value of ma is lower response time is also less. the result: if the number of elements met in path is high (more than 16) and if results are returned to origin or ma is returned associated with ma, they act in similar ways. engineering, technology & applied science research vol. 7, no. 5, 2017, 2026-2029 2029 www.etasr.com bahrami: design of a mobile agents based solution to distributional management of computer … e. effect of the data rate of domain links in this section, we want to know how data rate affects the connections made between domain links. assumptions: each request / response possess 50 bytes data, data rates are of 1, 2 and 0.064 mbps, connections delays of 4 ms and the initial ma value of 5 kb. according to the operation performed on different data rates, the results show that in lower data rate (0.064), snmp and ma both have more response time (but response time of ma is more than snmp). but for other data rates, both have almost the same response time. results: when data rates are higher, ma and snmp have a better performance compared to the case where data rates are lower. v. conclusion considering their performance, mas have many capabilities. they can stop running in one point and continue running from that stop point in another location. they perform synchronously and they can communicate with stations locally. these capabilities offer them advantages over the traditional client-server scheme. snmp protocol is widely used for network administration. in this protocol, all traits and characteristics of the system are stored in a mib table. in fact, different existing agents can be moved to different stations to extract data required by administrator from mib table of each station and report to the administrator. in this study, an ma based solution was designed to manage distributed computer networks, taking into account security mechanisms. in this project, an infrastructure called mct is introduced for network management. results of simulation have revealed that between the two areas, by an increase of the managed elements, ma works better than snmp. if the initial ma value is lower, it performs better than snmp. increasing the size of an action leads to an increase of ma response time but it is almost constant at snmp when the number of visited elements in the path is large (more than 16). ma acts almost the same and in higher data rates, if the ma is returned by the result or the result only is returned to the source. ma and snmp work better in the conditions where data rates are lower. references [1] k. fall, k.varadhan, ns notes and documentation, vint project,2015 [2] a. campeau, managing networks with mobile code, tech. report sce-97-o9, carleton university, 1997 [3] s. green, l. hurst, b. nangle, p. cunningham, software agents: a review, trinity college dublin, 1997 [4] g. goldszmidt, y. yemini, “distributed management by delegation, distributed computing systems”, 15th ieee international conference on distributed computing systems, pp. 333-340, 1995 [5] t. white, a. bieszczad, b. pagurek, “distributed fault location in networks using mobile agents”, in: intelligent agents for telecommunication applications, springer berlin heidelberg, 1998 [6] a. bieszczad, b. pagurek, t. white, “mobile agents for network management”, communications surveys, vol. 1, no. 1, pp. 2-9, 1998 [7] a. fuggetta, g. p. picco, g. vigna, “understanding code mobility”, ieee transactions on software engineering, vol. 24, no. 5, pp. 342366, 1998 [8] w. a. arokiasami, p. vadakkepat, k. c. tan, d. srinivasan, “interoperable multi-agent framework for unmanned aerial/ground vehicles: towards robot autonomy”, complex & intelligent systems, vol. 2, no. 1, pp. 45-59, 2016 [9] p. d. o'brien, r. c. nicol, “fipa—towards a standard for software agents”, bt technology journal, vol. 16, no. 3, pp. 51-59, 1998 [10] s. javanmardi, m. shojafar, s. shariatmadari, s. s. ahrabi, “fr trust: a fuzzy reputation–based model for trust management in semantic p2p grids”, international journal of grid and utility computing, vol. 6, no. 1, pp. 57-66, 2014 [11] z. s. daliri, s. shamshirband, m. amiribesheli, “railway security through the use of wireless sensor networks based on fuzzy logic”, international journal of physical sciences, vol. 6, no. 3, pp. 448-458, 2011 [12] m. shojafar, s. javanmardi, s. abolfazli, n. cordeschi, “fuge: a joint meta-heuristic approach to cloud job scheduling algorithm using fuzzy theory and a genetic method”, cluster computing, vol. 18, no. 2, pp. 829-844, 2015 [13] s. shamshirband, s. kalantari, z. sam daliri, l. ng, “expert security system in wireless sensor networks based on fuzzy discussion multiagent systems”, scientific research and essays, vol. 5, no. 24, pp.38403849, 2010 microsoft word 19-2735_s_etasr_v9_n3_pp4169-4175 engineering, technology & applied science research vol. 9, no. 3, 2019, 4169-4175 4169 www.etasr.com kamala & thangaiah: a novel two-stage selection of feature subsets in machine learning a novel two-stage selection of feature subsets in machine learning f. rosita kamala department of computer science, bharathiar university, coimbatore, india rositakamala@gmail.com p. ranjit jeba thangaiah department of information technology, karunya institute of technology and sciences, coimbatore, india ranjit@karunya.edu abstract—in feature subset selection the variable selection procedure selects a subset of the most relevant features. filter and wrapper methods are categories of variable selection methods. feature subsets are similar to data pre-processing and are applied to reduce feature dimensions in a very large dataset. in this paper, in order to deal with this kind of problems, the selection of feature subset methods depending on the fitness evaluation of the classifier is introduced to alleviate the classification task and to progress the classification performance. to curtail the dimensions of the feature space, a novel approach for selecting optimal features on two-stage selection of feature subsets (tsfs) method is done, both theoretically and experimentally. the results of this method include improvements in the performance measures like efficiency, accuracy, and scalability of machine learning algorithms. comparison of the proposed method is made with known relevant methods using benchmark databases. the proposed method performs better than the earlier hybrid feature selection methodologies discussed in relevant works, regarding classifiers’ accuracy and error. keywords-dimensionality reduction; feature subset selection; filter method; hybrid method; variable selection; wrapper method i. introduction an extensive, high dimensionality problem is caused by the numerous volumes of feature dimensions [1]. to find a solution, feature subsets are applied to alleviate the features dimensions and to give better outcomes in performance by reducing the less significant features. these methods boost the classification accuracy and reduce the training time of the learning techniques. the methods which select features, namely filters and wrappers, are distinguished on the basis of classifier evaluation [2]. the filter method finds the weight of the attributes on the basis of relevance that is computed by using different measures like information, distance, consistency, and correlation. it is fast and simple computationally, not depending on any learning algorithm, and scalable to huge-dimensional datasets. the feature subset can undergo an evaluation by the classifier subsequently, once the feature selection (fs) is performed. the outcome of feature selected results in the worst classification performance because the dependency of features is mostly overlooked. wrapper methods depend on classifiers and work together between feature subset searches and model selection dependent on feature selection methods. the impediments in this method are the high risk of overfitting and that it is computationally intensive [3], particularly if the classifier is built. the embedded technique chooses features on the basis of filter methods and performs evaluation on the basis of the classifier of the wrapper method within the model. this method is less computationally intensive than wrappers. the selection of feature subsets is considered as an initial processing technique on the basis of an evaluation criterion for high dimensional data-sets. the four step process of selecting features stated in [1] is generating subsets, evaluating subsets, setting criteria to stop the process, and validating results. the first step produces a subset of features and performs an evaluation of features. the process goes on until the stopping criterion is reached. the feature subsets selected in the previous step are validated for performance analysis by the classification algorithm. a feature space of n features causes the subsets of 2 n to exist generally. the most important drawbacks are the point to start the search and the direction of search. the subset of features begins with a null set, and the features are added in the onward direction which satisfies the evaluation criteria, otherwise they are eliminated. a. objectives feature subset methods depend on parameters. the number of features in the final set is identified by the inputs and the threshold values. the issues of the above-mentioned filterwrapper techniques claim the improvement of innovative algorithms. the overall objectives of this paper are: • to eliminate irrelevant and redundant features. • to select the optimal features from a huge set. • to build up a multiple objective, filter-wrapper hybrid framework for continuous, categorical and hybrid data. • to conduct an extensive experiment with the hybrid framework for evaluating the proposed methodology. • to improve the classification accuracy and to minimize the error rate. a novel algorithm is proposed and compared with the state-of-the-art methods. the results of the proposed method, using a subset of features, are similar or superior with the ones of the existing methods. corresponding author: f. rosita kamala engineering, technology & applied science research vol. 9, no. 3, 2019, 4169-4175 4170 www.etasr.com kamala & thangaiah: a novel two-stage selection of feature subsets in machine learning ii. relevant work a lot of attribute selection methodologies have been proposed in recent studies for classification by machine learning. in high-dimensional feature sets, the choice of relevant features is indispensable, as a result of the large space of search of 2 n for n dimension variables. it is a challenging task to perform a comprehensive search to enhance the significant measures of the learning system [2]. a lot of filters, wrappers, and hybrid methodologies for feature selection have been adopted to accomplish a smaller set of features with relevance and significance [3]. to deal with this issue, a collection of techniques to perform a search in every feasible way for a solution, and explore an algorithm that is guaranteed to uncover a solution. the greedy algorithm always makes the choice that seems to be the best at that moment. heuristic search and arbitrary search have been adopted in [4]. particle swarm optimization (pso) is proposed in [5]. in comparison with different evolution algorithms such as genetic algorithms (gas) and genetic programming, pso is cost effective, and more swift convergence is possible. a combination of pso, and aco (ant colony optimization) hybrid method was initiated for classification in [6]. the demerit of pso was the requirement of conversion of nominal data to binary overcoming the need for preprocessing. a hybrid method of the filter wrapper methods on the basis of pso-ga which aimed to incorporate the merits of filter and wrapper techniques resulting in a smaller number of optimum features with better efficiency was proposed in [7]. a novel gini-index filter was proposed in [8]. it was formulated and adapted by the theory of gini-index for text classification in the selection of features, and produced better performance than the other methods. authors in [9] proposed a hybrid fs algorithm for gene data by combining mutual information maximization and adaptive ga (mimaga) to enhance the competence of mimaga algorithm. authors in [10] employed a hybrid technique for ga by considering the merits of filters to improve the crossover and mutation operators. hybrid fs approaches were created by subsets with features of different sizes and importance. authors in [11] proposed a hybrid method using filters and wrappers based on instance learning. in the wrapper approach, a classification algorithm is adopted in a cooperative subset search in [11]. authors in [3] proposed a hybrid fs method by combining the information gain ratio (igr) filter and backward elimination (be) wrapper in the first phase and pso in the second phase. the method performs better for continuous features than for categorical features [3]. the relevant study leads to a framework of hybrid methodology of feature selection. iii. materials and methods a. the proposed methodology in this paper, feature subsets are formulated from chi square, gini index, and pso algorithms to solve fs problems in machine learning. 1) chi square test statistic (chi) the characteristics of a categorical data were studied in various perspectives like data size, number of features, possible values of attributes, and values of frequency distribution for the attributes of a dataset. for categorical data the similarity measure chi was acknowledged as a goodness of fit test [12], with an estimated chi distribution. comparison of several classes can be assessed with the help of this test. it is considered as a test for independence and homogeneity [13, 14]. authors in [15] accounted a comparison study of these methods and found that information gain and chi are the best methods in feature selection. chi-square distance is computed between every attribute and class. it is a measure of an attribute weighting task, as a result of its capability in attributes ranking [16]. this test is applicable for categorical datasets, and it does not perform well for data of quantitative nature. frequency or count of data is needed for calculations with chi square test. no relationship of associativity between attributes is stated as null hypothesis. it creates a model by distributing data in different categories with an assumption that it follows the null hypothesis. thus, this test compares the given data values of distribution with the expected data values. the frequency outcomes observed for the cell cij are ��� . the frequency outcomes expected for the cell cij are ���. �2 = sum [(��� − ���)2 / ���,{i, 1,r},{j,1,c}] (1) where ���=ni*nj/n. chi square value is contributed by rows, having different actual and expected values. the maximum value indicates the related features. 2) gini index(gini) gini is the most suitable to classify attributes which have distributions clump together. during the evaluation process, gini uses the combination of feature condition probability with its previous probability to evade the unbalanced class effects [17]. the inequality of a distribution is measured by the gini coefficient [17]. the gini is explained as the inequality percent within a specified population. gini index is a correlation-based criterion. it approximates the features and discriminates among classes. it was first proposed as a rule for splitting in the generation of a decision tree [18]. it reveals the reduction of impurity, if features are chosen. the feature is represented by y. gini( ) = sum!"# $%, �&sum["#'() $) *,+& − sum["('() *, +] (2) where p( $) is the previous probability of the feature y has value $, p('(| $) is the probability of a random sample from the dataset, that feature y has value yj , appertain to class '(, and p( '( ) the previous probability of a random sample appertain to class '(. gini index, as a measure of inequality has some advantages. gini index has very low computation requirements in high-dimensional data analysis. analysis of increasing or decreasing inequality is possible. it can be used to compare feature distributions across different populations. it is sufficiently simple and easily interpreted. the weakness of gini index is that it is not able to detect redundant features, with inter-feature relationships. engineering, technology & applied science research vol. 9, no. 3, 2019, 4169-4175 4171 www.etasr.com kamala & thangaiah: a novel two-stage selection of feature subsets in machine learning 3) pso the wrapper method pso [4] is selected due to advantages such as simple implementation, sufficiently less parameters to fine-tune, it is more robust, it has fast convergence, less computing time, and finds global optima with high probability and efficiency. pso is inspired by the societal way of behaving birds in flocks. pso’s fundamental characteristic is the social interaction in the population that optimizes information. every result can be described as a particle in the swarm. every particle’s position in the search space is described by a vector si=(si1, si2, . . . , sid), where d is the dimensionality of the space for search. in order to achieve optimal solutions, the particles move in the space for search. as a result, every particle’s velocity is described as ci=(ci1, ci2, . . . , cid). every particle’s position and velocity can be revised with respect to the movement of its neighbors. pbest is the best preceding location and is depicted as the personal best of the particle, and gbest is the best location in the population. derived from pbest and gbest the optimal solution is searched by improving the velocity c and every particle’s position in space for search s in relation to the subsequent equations [5]: ,-(. + 1) = 0,-(.) + 1232#4567.(�, .) − 8-(.)% + 1*3*(9567.(.) − 8-(.)) (3) s: (t + 1) = s: (t) + c: (t + 1) (4) where t describes the number of repetitions in the evolution process, ω performs inertia weight, which controls the responses of the earlier velocities, a1 and a2 are acceleration constants, r1 and r2 are random numbers following a uniform distribution in [0, 1]. the algorithm stops after a predefined condition is attained, which might be the best suitable assessment or a specified count of iterations. b. the proposed algorithm the methods of the filter and wrapper undergo a combination in the proposed two staged method. the pseudocode of the proposed framework, named two-stage selection of feature subsets (tsfs), is presented in figure 1. figure 2 shows a flowchart of the tsfs algorithm. in figure 1, lines 1-5 account for the preprocessing step for the selection of relevant features of the algorithm tsfs. it is an introductory step to be performed for the datasets downloaded from uci (university of california, irvine). in the first phase of the algorithm, filter techniques, namely chi square and gini index, are applied separately to the datasets for the elimination of the superfluous or inappropriate features. the chi filter selects the feature subset f1 features and the gini filter selects the feature subset f2 features. the selected subsets of features f1 and f2 are calculated as the most relevant features associated with the class label. the methods which are described above, weigh up the significance of the features by computing the weight for each and every feature of the dataset, with the class label of the dataset. the outputs from the filter techniques undergo a combination of two feature subsets f1 and f2 in line 6 for better performance outcomes by removing the subset of features available in both subsets resulting in a feature subset with fewer features. fig. 1. the pseudocode of the suggested tsfs algorithm lines 7-11 correspond to the wrapper approach using pso to select the subset of optimal features in the feature space. the pso algorithm computes the two best values for each and every particle in each iteration. the selection for an optimal subset is achieved to diminish the dimension of features. lines 12-16 correspond to the resultant optimal subset by the wrapper approach pso. training and testing sets in the second phase undergo tenfold cross-validation (cv) for improvement in learning efficiency. this is the tuning step to remove redundancy for optimal subsets. c. k-nearest neighbour classification (knn) to classify data, their nature is most important. it can be either parametric or non-parametric. k-nearest neighbor classification is non-parametric. the instances of the data input: features set d ={ fi , i = 1.....n} c: class labels output: the subset p of d features 1. (initialize) let d ← "original set having d dimensions"; p ← { } 2. evaluate the significance of chi with the resultant class c. for each fd ∈ d find chi(c; fd) applying (1) 3. (possibility of the first dimensions) find a dimension f1 that improves chi(c, fd); let d ←d \{f1}; set p ← {f1} 4. evaluate the significance of gini with the output class c. for each fd ∈ d find gini(c; fd) applying (2). 5. (possibility of the next dimensions) find a dimension f2 that improves gini(c, fd); let d ←d \{f2} 6. (optimal output) output the set p ← p ∪ {f2} 7. split the feature set p into s for training dataset and testing dataset. for p generate particles p. 8. for each particle from 1 to n 9. initialize particle 9.1 initialization of particle’s position in the search space. 9.2. initialization of pbest and gbest. 9.3. initialization of velocity. 10. repetition until the termination condition is met. 10.1 update particle’s velocity using (3). 10.2 update particle’s position using (4). 10.3 t ←t +1 11. best found solution for the output gbest. 12. fitness evaluation through cv. 13. split the data into k equal sized folds. 14. for s = 1.....k 14.1 training a model with basis features on s th fold’s training set. 14.2 computation of testing error on this corresponding fold. 15. return values over all k folds with the lowest average of testing error. 16. learning results and significance of a predicted outcome for p as subset of selected features. engineering, technology & applied science research vol. 9, no. 3, 2019, 4169-4175 4172 www.etasr.com kamala & thangaiah: a novel two-stage selection of feature subsets in machine learning which are together in nearby proximity are self-reliant and distributed separately. those instances have similar classification results [19]. fig. 2. the flowchart of the suggested algorithm tsfs iv. results and discussion a. datasets the experimentation in java environment using rapidminer confirms the efficiency of the suggested algorithm. eight uci [20] datasets are shown in table i. the pso parameters pbest and gbest are assigned to 1. true value is set for dynamic inertia weight which makes the enhancement of inertia during its run. the upper limit for the generations to be performed is 30. the size of population is 100. the model is evaluated by the conduction of experiments on all sample instances by performing 10 cvs using knn classifier for better performance outcomes. table i. experimental dataset information datasets #samples #features #classes total numeric nominal type anneal 898 38 6 32 discrete+ continuous 6 vowel 990 13 10 3 discrete+ continuous 11 hypothyroid 3772 29 6 23 discrete+ continuous 4 sick 3772 29 7 22 discrete+ continuous 2 splice 3190 61 0 61 discrete 3 chess 3196 36 0 36 discrete 2 sonar 208 60 60 0 continuous 2 waveform 5000 40 40 0 continuous 3 b. performance metrics the most common measures for the evaluation of feature subset are precision and recall. precision is the ratio of instances of relevance among the instances of retrieved while recall is the ratio of instances of relevance that have been retrieved over the total number of instances of relevance. precision and recall are the estimates for finding relevance in terms of true positives, false positives, false negatives and true negatives [21]. figures 3 and 4 show the outcomes of precision and recall fitness functions on the efficiency of various variable selection techniques and the suggested tsfs. fig. 3. comparative study of the significance measure precision of the tsfs with other existing methods fig. 4. comparative study of the significance measure recall of the tsfs with other existing methods c. statistical analysis the proposed tsfs algorithm’s evaluation has been carried out by the knn classifier. the main objectives, i. e. the number of selected features, the selected feature subsets’ classification accuracy, and the computing time with the measures of performance like precision, sensitivity, and kappa have been documented. in figure 5 the accuracy of the suggested algorithm is compared with the traditional existing methods of features subsets in the literature. depending on the results obtained in figure 5, the proposed method tsfs is considered to be superior in terms of accuracy than the traditional methods. it can be seen that tsfs performs better for continuous datasets like sonar and waveform than for discrete datasets like splice and chess and hybrid datasets like sick, anneal, and hypothyroid. engineering, technology & applied science research vol. 9, no. 3, 2019, 4169-4175 4173 www.etasr.com kamala & thangaiah: a novel two-stage selection of feature subsets in machine learning fig. 5. accuracy comparison for each feature selection algorithm with the proposed algorithm. d. kappa statistic as performance measure the kappa statistic measures whether the instances are closely classified by the learning algorithm with the matching data label, controlling the accuracy of random classification. classifiers constructed and calculated with datasets of various distributions of learning can undergo comparison by kappa in association with expected accuracy. this shows a better indication of how the classification of instances occurred, because accuracy could be skewed, provided that class distribution is skewed. there is no identical representation of kappa. authors in [22] represent 0-0.20 as minor, 0.21-0.40 as light, 0.41-0.60 as reasonable, 0.61-0.80 as significant, and 0.81-1 as almost ideal, while author in [23] considers kappa>0.75 as outstanding, 0.40-0.75 as fine, and kappa<0.40 as deprived. it is commonly considered as a more vigorous estimate. the proposed tsfs’s kappa analysis is outlined in table ii. table ii. kappa coefficient of the framework tsfs dataset anneal vowel hypothyroid sick kappa 0.982 1.00 0.961 0.972 dataset splice chess waveform sonar kappa 0.980 0.914 0.937 0.928 e. mae and rmse analysis mean absolute error (mae) [18] is the average of the discrepancy between anticipated and actual data values, and is given by: mae = 2 b ∑ |e$ − b $f2 ŷ$| (5) mae ranges from zero to infinity and a perfect fit is obtained when mae=0. root mean squared error (rmse) [21] is one of the most commonly used measures for calculating the average amount of error in numerical prediction. it is the square root of the average of squared discrepancies between prediction and actual observation. its value is computed by: rmse � i2b ∑ e$ �b$f2 ŷ$�* (6) the smaller the rmse value, the better the model performance. table iii presents the results of mae and rmse. table iii. mae and rmse dataset anneal vowel hypothyroid sick mae 0.010 0.000 0.054 0.052 rmse 0.085 0.000 0.075 0.056 dataset splice chess waveform sonar mae 0.045 0.082 0.042 0.073 rmse 0.112 0.207 0.205 0.196 table iv. comparative analysis of the framework tsfs to relevant methods datasets tsfs % results obtained from the literature methodology & accuracy methodology & accuracy methodology & accuracy anneal 99.28 [24] rcrf 99.63 [24] crf 99.71 [24]rf 99.68 vowel 100 [25] iem 99.29 [25] em-1nn 98.88 [25]iga 98.18 hypothyroid 99.44 [24] rcrf 99.73 [24] ba-cdt 99.59 [24] ba-c4.5 99.62 sick 99.68 [24] ba-c4.5 98.97 [24] rcrf 98.64 [24]crf 98.59 splice 98.75 [24] rf 95.88 [24] rcrf 96.48 [24]crf 96.31 chess 95.71 [25] bpnn 99.28 [25] lr 97.43 [25]c4.5 97.90 sonar 96.17 [3] hfsm 97.13 [26] woasa 95.67 [26]megwo 94.81 waveform 95.78 [24] rcrf 85.01 [24] crf 85.15 [24] rf 85.2 best results are shown in bold table v. tsfs comparison on computing time with most relevant methods datasets tsfs (s) results obtained from the literature (in seconds) methodology & run time methodology & run time methodology & run time anneal 59 [27] a4 162.06 [27] efsh 59.39 [28] om 90.80 vowel 1 [27] a4 41.82 [27] efsh 4.66 [28] om 34.40 hypothyroid 732 [27] a4 1446.28 [27] efsh 148.09 [28] om 1362.80 sick 793 [27] a4 1516.71 [27] efsh 310.06 [28] om(wrapper) 540.70 splice 690 [29] fssmc 25.7 [29] relief 164 [29] relief-rs 18.4 chess 542 [30] ma+ svm optimized 176.3 [31] bf-mlp 302.13 ± 1.05 [31] bf-rbf 4347.9 ± 21.17 sonar 4 [32] issa 61.43 [32] alo 58.48 [33] psopg2 25.2 waveform 1201 [32] pso 290.37 [32] issa 293.45 [32] ga 288.50 best results are shown in bold engineering, technology & applied science research vol. 9, no. 3, 2019, 4169-4175 4174 www.etasr.com kamala & thangaiah: a novel two-stage selection of feature subsets in machine learning f. result analysis comparison of classification accuracy and computing time with existing methods in tables iv and v the accuracy and run time of tsfs is compared with other methods, available in the literature. regarding accuracy, the tsfs method shows appreciable improvement for all datasets except chess and sonar, when compared with the other existing methods. tsfs achieves the best accuracy values for vowel, sick, splice, and waveform datasets and the best run time for anneal, vowel and sonar datasets. v. conclusion and future work feature selection is an imperative method for dimensional reduction in machine learning. in this paper, a proficient methodology for selecting instructive features is being proposed for massive hybrid datasets. experimentation confirms that the methodology is effective and efficient, especially considering classification performance. it was shown that the proposed methodology provided better accuracy rates than the existing methods. additionally, the use of the proposed method decreased error rates regarding two error measures, mae and rmse. these results are important and show that the use of feature selection can provide better performance and higher efficiency for hybrid systems. the weakness of this work is that it fails to produce better computation time even though the accuracy outperforms other methodologies, under experimentation with uci repository datasets. it would be notable to use mutual information [34] for estimating and finding features that are minimal redundancy-maximal relevance (mrmr) in future research. these concepts could be integrated with the proposed method in order to get a quicker and improved method, which may be applied effectively to huge datasets. references [1] m. dash, h. liu, “feature selection for classification”, intelligent data analysis, vol. 1, no. 1-4, pp. 131–156, 1997 [2] r. kohavi, g. h. john, “wrappers for feature subset selection”, artificial intelligence, vol. 97, no. 1-2, pp. 273–324, 1997 [3] f. r. kamala, p. r. j. thangaiah, “a proposed two phase hybrid feature selection method using backward elimination and pso”, international journal of applied engineering research, vol. 11, no. 1, pp. 77–83, 2016 [4] m. dash, h. liu. “consistency-based search in feature selection”, artificial intelligence, vol. 151, no. 1-2, pp. 155–176, 2003 [5] j. kennedy, r. c. eberhart, “particle swarm optimization”, ieee international conference on neural networks, perth, australia, november27-december 1, 1995 [6] n. holden, a. a. freitas, “a hybrid pso/aco algorithm for discovering classification rules in data mining”, journal of artificial evolution and applications, vol. 2008, articleid 316145, pp. 1-11, 2008 [7] indriyani, w. gunawan, a. rakhmadi, “filter-wrapper approach to feature selection using pso-ga for arabic document classification with naive bayes multinomial”, iosr journal of computer engineering, vol. 17, no. 6, pp. 45-51, 2015 [8] w. shang, h. huang, h. zhu, y. lin, y. qu, z. wang, “a novel feature selection algorithm 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guide to chi-squared testing, john wiley & sons, 1996 [14] h. o. lancaster, the chi-squared distribution, john wiley & sons, 1969 [15] y. yang, j. o. pedersen, “a comparative study on feature selection in text categorization”, in: proceedings of the 14th international conference on machine learning(icml) san francisco, usa, pp. 412–420, morgan kaufmann publishers, 1997 [16] i. h. witten, e. frank, data mining practical machine learning tools and techniques with java implementations, morgan kaufmann, 2005 [17] a. jacobson, a. d. milman, d. m. kammen, “letting the (energy) gini out of the bottle: lorenz curves of cumulative electricity consumption and gini coefficients as metrics of energy distribution and equity”, energy policy, vol. 33, no. 14, pp. 1825-1832, 2005 [18] l. breiman, j. friedman, r. olshen, c. stone, classification and regression trees, chapman and hall, 1984 [19] d. wettschereck, d. aha, w. t. mohri, “a review and empirical evaluation of feature weighting methods for a class of lazy learning algorithms”, artificial intelligence review, vol. 11, no. 1-5, pp. 273314, 1997 [20] uci machine learning repository, university of california, available at: https://archive.ics.uci.edu/ml/index.php [21] v. s. stehman, “selecting and interpreting measures of thematic classification accuracy”, remote sensing of environment, vol. 62, no. 1, pp. 77–89, 1997 [22] j. r. landis, g. g. koch, “the measurement of observer agreement for categorical data”, biometrics, vol. 33, no. 1, pp. 159–174, 1977 [23] j. l. fleiss, statistical methods for rates and proportions, john wiley, 1981 [24] j. abellan, c. j. mantas, j. g. castellano, s. moral-garcia, “increasing diversity in random forest learning algorithm via imprecise probabilities”, expert systems with applications, vol. 97, pp. 228–243, 2018 [25] k. j. wang, a. m. adrian, k. h. chen, k. m. wang, “an improved electromagnetism-like mechanism algorithm and its application to the prediction of diabetes mellitus”, journal of biomedical informatics, vol. 54, pp. 220–229, 2015 [26] q. tu, x. chen, x. liu, “multi-strategy ensemble grey wolf optimizer and its application to feature selection”, applied soft computing, vol. 76, pp. 16–30, 2019 [27] f. wang, j. liang, “an efficient feature selection algorithm for hybrid data”, neurocomputing, vol. 193, pp. 33–41, 2016 [28] c. li, h. li. “a survey of distance metrics for nominal attributes”, journal of software, vol. 5, no. 11, pp. 1262-1269, 2010 [29] y. huang, p. j. mccullagh, n. d. black, “an optimization of relieff for classification in large datasets”, data & knowledge engineering, vol. 68, no. 11, pp. 1348-1356, 2009 [30] m. nekkaa, d. boughaci, “a memetic algorithm with support vector machine for feature selection and classification”, memetic computing. vol. 7, no. 1, pp. 59–73, 2015 [31] l. t. kueti, n. tsopze, c. mbiethieu, e. mephu-nguifo, l. p. fotso, “using boolean factors for the construction of an artificial neural network”, international journal of general systems, vol. 47, no. 8, pp. 849-868, 2018 engineering, technology & applied science research vol. 9, no. 3, 2019, 4169-4175 4175 www.etasr.com kamala & thangaiah: a novel two-stage selection of feature subsets in machine learning [32] a. e. hegazy, m. a. makhlouf, g. s. el-tawel, “improved salp swarm algorithm for feature selection”, journal of king saud university – computer and information sciences, 2018 [33] b. xue, particle swarm optimisation for feature selection in classification, phd thesis, victoria university of wellington, 2014 [34] c. pascoal, m. r. oliveira, a. pacheco, r. valadas, “theoretical evaluation of feature selection methods based on mutual information”, neurocomputing, vol. 226, pp. 168–181, 2017 authors profile f. rosita kamala got her masters in computer application (mca) from the bharathidasan university in 1999 and her master of engineering in systems engineering and operations research from anna university, chennai in 2008. she is currently an assistant professor in an affiliated college under visvesvaraya technological university, karnataka, and a doctoral student at bharathiar university, tamil nadu. her current research interests include data mining, data analytics, machine learning, and intelligent information processing. p. ranjit jeba thangaiah did his bsc (physics) at the p.s.g. college of arts and science, coimbatore, m.c.a. at karunya institute of technology, coimbatore, mphil at manaonmanian sundaranar university, tirunelveli, he did his full time phd at the bharathiar university, coimbatore. he is working in the karunya institute of technology and sciences, coimbatore in the last 15 years. he has published 25 papers on international journals and conferences. his areas of research include networking, data mining and machine learning. microsoft word 20-3116_s_etasr_v9_n6_pp4980-4983 engineering, technology & applied science research vol. 9, no. 6, 2019, 4980-4983 4980 www.etasr.com bousselmi et al.: design and implementation of a tri-band miniaturized planar inverted-f antenna … design and implementation of a tri-band miniaturized planar inverted-f antenna with double resonator for gps application amira bousselmi faculty of sciences of tunis tunis el manar university el manar, tunisia bousselmiamira@gmail.com ali gharsallah faculty of sciences of tunis tunis el manar university el manar, tunisia ali.gharsallah@fst.utm.tn tan phu vuong institute of microelectronics electromagnetism and photonics grenoble, france tanphu.vuong@gmail.com abstract—in this paper, a new planar inverted-f antenna is presented for gnss applications and the dcs band. the proposed antenna structure is based on capacitive slots that achieve multiband behavior. the antenna has two resonators of dimensions (31mm×17mm×0.35mm) and (20.5mm×17.5mm× 0.35mm), a ground plane (60mm×17.5mm×0.35mm) and 6.5mm height. a prototype was implemented and good agreement was noticed between the simulation and test results, indicating three resonant frequencies, namely 1.176ghz, 1.8ghz and 2.8ghz. radiation characteristics and diversity performance of the proposed structure is presented with detail. keywords-planar inverted-f antenna (pifa); multi-band; gnss; return loss; bandwidth i. introduction multi-band antennas have been widely used for new generation mobile communications, such as dcs1800, pcs1900, umts, wimax and bluetooth [1, 2]. global positioning system (gps) applications have become very popular due to the fast advances in electronic technology, while their addition to handheld devices increases their antenna versatility [3]. the design of novel components with compact size and multi band operation has attracted interest, for its outstanding advantages [4]. miniaturized components allow their integration in compact devices, resulting in small and lightweight portable terminals. moreover, the cost of electronic circuits is gradually decreasing, which is a requirement for new and accessible tools. finally, the integration of gps band along with other wireless communication bands is also required in order to avoid an additional antenna [5, 6]. the planar inverted-f antenna (pifa) could be a promising structure for new wireless communication systems and it has been widely used as an internal antenna in commercial applications [7-13]. in [10], a quad-band pifa antenna with two radiating elements has been proposed. the radiating elements consist of two pifa structures constituted by a meandered line and a folded patch connected with interdigitated capacitive strips. in [12], a compact dual-band pifa antenna working in both digital video broadcasting-terrestrial and wireless local area network ieee 802.11b/g frequency bands has been proposed. this structure was designed to be integrated on a monitorequipped device. on [8] a dual band platform-free antenna for the 5g mimo application of mobile devices was investigated [14]. the antenna was designed by adding a vertical metallic patch to the pifa and setting another pifa to feed the antenna by coupling. the pifa antenna proposed in this paper is designed to exhibit reduced size with respect to these works. the structure consists of nested pifas that initially operate at the dcs and gps bands. moreover, a juxtaposition technique was employed to add a second resonator between the ground plane and the patch loaded by the u-slot. therefore, a new resonance at 2.8ghz appeared and multi-band behavior was achieved. a parametric study was carried out allowing a significant reduction in the size of the antenna. the proposed design was implemented, tested and good agreement between the simulation and the prototype test results was obtained. ii. multi-band pifa antenna the geometry of the proposed multiband pifa structure is exhibited in figure 1. its components were built from 0.35mm thick copper substrate. the first design was composed of two layers. the first layer was a (60×17.5×0.35mm) rectangular ground plane, corresponding to the dimensions of a typical mobile device. the second layer consists of a (20.5×17.5×0.35mm) rectangular patch. the radiation is occurring through a graved by a radiating u-slot as shown in figure 1(b). a shorting sheet, 10.5mm wide, was placed between the resonator and the ground plane, in order to achieve the appropriate matching at the various operating bands of the antenna. this sheet was positioned 2mm away from the feeding probe and was optimally located at the edge of the structure. the dimensions of the u-slot are illustrated in table i. a coaxial cable was attached in position (x, y)=(10mm, 2mm) to excite the antenna. this location was selected in order to obtain good matching results. the proposed antenna was designed to operate at the l5-gps band, by optimizing the dimensions of the patch from (1) [6]: � = �/4(� + ) (1) corresponding author: amira bousselmi engineering, technology & applied science research vol. 9, no. 6, 2019, 4980-4983 4981 www.etasr.com bousselmi et al.: design and implementation of a tri-band miniaturized planar inverted-f antenna … the dimensions of the radiating u-slot were optimized to cover the dcs band. in (1), c is the speed of light, l and w are the length and width of the top plate respectively, and f is the center frequency of the antenna. (a) (b) fig. 1. (a) dual band antenna, (b) detailed dimensions of the u-slot table i. dimensions of u slot parameters values (mm) l1 31 l2 28 l3 26.7 l4 24.5 w1 17 w2 1.3 w3 2.3 in order to further improve the performance of the proposed design and minimize its size, the juxtaposition technique was used by adding a second resonator between the two layers that compose the structure as shown in figure 2. fig. 2. the proposed antenna with two resonators cst microwave studio simulation software was used in order to optimize all the geometrical parameters of the proposed antenna and obtain the far-field radiation patterns. in order to understand the effect of each resonator, the simulation s11 results for two prototypes were compared, as shown in figure 3. it can be noticed that the first antenna has two resonance frequencies. the first one is allocated at 1176mhz while the second is at 1800mhz. adding the second resonator, a third resonance appeared around the frequency of 2.8ghz. the radiation performance of the proposed dual band pifa antenna is determined by two important factors: the width and the height of the shape slot and the length and the width of the antenna. in order to understand the influence of each element in the performance of the new structure, a parametric study was conducted to optimize the distance h given between the new and the old resonator. figure 4 shows the variation of the frequency as a function of high h. it was noticed that with increasing h, the two resonance frequencies increase and the third one decreases. thus, parameter h has an important effect on the antenna resonance. the optimized dimensions, through the parametric study, are exhibited in table i. fig. 3. simulated return loss of the proposed antenna fig. 4. variation of the reflection coefficient with frequency of the proposed antenna for various h values iii. experimental validation a prototype of the multi-band pifa antenna was implemented in order to verify the simulation results. the top and bottom views of the prototype are exhibited in figure 5. the design has the disadvantage of being very difficult to manufacture and solder. another drawback resides in the sensitivity of the antenna with respect to mounting dimensions, hence the difficulty to be precise at inter-levels. the experimental part of this study was conducted at the institute of microelectronics electromagnetism and photonics (imeplahc). fig. 5. the prototype of the multi-band antenna engineering, technology & applied science research vol. 9, no. 6, 2019, 4980-4983 4982 www.etasr.com bousselmi et al.: design and implementation of a tri-band miniaturized planar inverted-f antenna … a. s-parameters the s-parameter testing of the prototype was carried out using a vector network analyzer as shown in figure 6. fig. 6. the antenna in s-parameter testing figure 7 displays the return loss results of both the prototype and the cst simulation tests, showing good agreement. it is noted that by adding the second resonator u slot, a third resonant frequency appeared. the first resonance frequency is located at 1.176ghz with -14.27db matching level and the second is located at 1.8ghz with matching level around -34.3db. the new resonance frequency is located at 2.8ghz and with -11db impedance matching. the bandwidth at -10db covers the bands: 1.164-1.18ghz, 1.78-1.82ghz and 2.79-2.81ghz. fig. 7. simulated and measured reflection coefficient: b. radiation patterns the radiation patterns of the prototype multi-band pifa antenna were tested in an anechoic chamber, within the antenna system operating bands, as shown in figure 8. the simulation results of the proposed antenna’s 3-d gain at the resonant frequencies are shown in figure 9. it is observed that the gain for the first resonance (1.176ghz) is 1.75db, for the second resonance (1.8ghz) is 1.92db, and finally for the last resonance (2.8ghz) the gain is maximized at 3.2db. it is clearly obvious that the test results reasonably correspond to the simulation. the radiation efficiency comparison between simulation and test results is shown in figure 10. results show that the antenna has good radiation efficiency, at all operating bands, with an average of 70%. more details about the simulation and the prototype results of the proposed triple band pifa antenna are presented in table ii. fig. 8. the proposed antenna prototype during testing in the anechoic chamber fig. 9. simulated 3-d far-field total radiation patterns at (a) 1.176ghz, (b) 1.8ghz, (c) 2.8ghz fig. 10. the results for the measured and simulated gain table iii compares the results of this work with others in the literature. the comparison takes into account the dimensions of the antenna, concluding that the proposed antenna is much smaller. engineering, technology & applied science research vol. 9, no. 6, 2019, 4980-4983 4983 www.etasr.com bousselmi et al.: design and implementation of a tri-band miniaturized planar inverted-f antenna … table ii. simulation and prototype results simulation prototype first band (galileo, gps) resonant frequency(ghz) bandwidth (ghz) matching level (db) gain (db) 1.176 0.16 -14.27 1.75 1.17 0.19 -22 1.65 second band (dcs) resonant frequency(ghz) bandwidth (ghz) matching level (db) gain (db) 1.8 0.40 -34.3 1.92 1.75 0.50 -35.1 1.8 third band (2.8ghz) resonant frequency (ghz) bandwidth (ghz) matching level (db) gain (db) 2.8 0.20 -12.02 3.2 2.77 0.20 -18.02 2.1 table iii. comparison of the proposed with other antennas ref band antenna dimensions volume [7] gsm band dcs band bluetooth wlan 100×60×8 48000 [8] 2.6ghz 5.0ghz 136×68×5 46240 [9] 1.9ghz 2.1ghz 140×60.5×10 84700 [10] 746–787mhz, 1850-1990mhz, 1920–2170mhz, 3600–3700mhz 60×100×5 30000 [11] 2ghz 2.6ghz 44×100×11.5 50600 [12] 470–862mhz 2400–2484mhz 217×12×8 20832 [13] gps l1 wi-fi/lte2500 wimax hiperlan1 25×10×5.8 2400 [8] wifi gps 20×15×8 2400 proposed 1.176ghz 1.8ghz 2.8ghz 20.5×17×6.5 2265.25 iv. conclusion this work presented a multiband miniaturized pifa antenna, consisting of three elements. the antenna operates at the frequency bands of 1.164-1.18ghz, 1.78-1.82ghz and 2.79-2.81ghz, covering gps and dcs applications. the proposed design is suitable for many portable devices, thanks to its low profile and small size and it can be used in handheld devices. a prototype of the proposed antenna was constructed and tested. the test results agree with those predicted by simulation. references [1] t. y. wu, k. l. wong, “on the impedance bandwidth of a planar inverted-f antenna for mobile handsets”, microwave and optical technology letters, vol. 32, pp. 249–251, 2002 [2] m. c. huynh, w. stutzman, “ground plane effects on planar inverted-f antenna (pifa) performance”, iee proceedings–microwaves, antennas and propagation, vol. 150, no. 4, pp. 209–213, 2003 [3] y. x. guo, s. tan, “new compact six-band internal antenna,” ieee antennas and wireless propagation letters, vol. 3, pp. 295–297, 2004 [4] a. a. serra, p. nepa, g. manara, r. massini, “a low-profile linearly polarized 3d pifa for handheld gps terminals”, ieee transactions on antennas and propagation, vol. 58, no. 4, pp. 1060–1066, 2010 [5] k. hirasawa, m. haneishi, analysis, design and measurement of small and low-profile antennas, artech house, 1992 [6] d. m. nashaat, h. a. elsadek, h. ghali, “single feed compact quadband pifa antenna for wireless communication applications”, ieee transactions on antennas and propagation, vol. 53, no. 8, pp. 26312635, 2005 [7] d. q. liu, m. zhang, h. j. luo, h. l. wen, j. wang, “dual-band platform-free pifa for 5g mimo application of mobile devices”, ieee transactions on antennas and propagation, vol. 66, no. 11, pp. 63286333, 2018 [8] b. r. jackson, s. j. boyes, “radiation pattern-agile dual planar invertedf antenna”, ieee antennas and wireless propagation letters, vol. 16, pp. 2090-2093, 2017 [9] m. k. meshram, r. k. animeh, a. t. pimpale, n. k. nikolova, “a novel quad-band diversity antenna for lte and wi-fi applications with high isolation”, ieee antennas and wireless propagation letters, vol. 60, no. 9, pp. 4360-4371, 2012 [10] s. vergerio, j. p. rossi, p. sabouroux, “a two-pifa antenna systems for mobule phone at 2 ghz with mimo applications”, 2006 first european conference on antennas and propagation, nice, france, november 610, 2006 [11] r. caso, a. d’alessandro, a. a. serra, p. nepa, g. manara, “a compact dual-band pifa for dvb-t and wlan applications”, ieee transactions on antennas and propagation, vol. 60, no. 4, pp. 20842087, 2012 [12] h. s. singh, m. agarwal, g. k. pandey, m. k. meshram, “a quad-band compact diversity antenna for gps l1/wifi/lte2500/wimax/hiperlan1 applications”, ieee antennas and wireless propagation letters, vol. 13, pp. 249-252, 2014 [13] a. bousselmi, a. gharsallah, t. vuong, “a novel high-gain quad-band antenna with amc metasurface for satellite positioning systems”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4581-4585, 2019 [14] e. s. ahmed, “conformal band-notch uwb monopole antenna on finite cylindrical substrates”, engineering, technology & applied science research, vol. 3, no. 3, pp. 440-445, 2013 microsoft word 38-3616_s1_etasr_v10_n3_pp5814-5818 engineering, technology & applied science research vol. 10, no. 3, 2020, 5814-5818 5814 www.etasr.com aichouni et al.: experimental evaluation of nano-enhanced phase change materials in a finned … experimental evaluation of nano-enhanced phase change materials in a finned storage unit mohamed ayoub aichouni mechanical engineering department university of hail hail, saudi arabia ayoubaichouni@outlook.com nidhal ben khedher mechanical engineering department university of hail hail, saudi arabia n.benkheder@uoh.edu.sa nayef farhan alshammari mechanical engineering department university of hail hail, saudi arabia naif2012fm@gmail.com mohamed aichouni industrial engineering department university of hail hail, saudi arabia m.aichouni@uoh.edu.sa abstract—the intermittent nature of renewable energy sources such as solar and wind necessitates integration with energystorage units to enable realistic applications. in this study, thermal performance enhancement of the finned cylindrical thermal energy storage (c-tes) with nano-enhanced phase change material (pcm) integrated with the water heating system under storage, charging and discharging (scd) conditions were investigated experimentally. the effects of the addition of copper oxide (cuo) and aluminum oxide (al2o3) nanoparticles in pcm on thermal conductivity, specific heat, and on charging and discharging performance rates were theoretically and experimentally investigated and studied in detail. the experimental apparatus utilized paraffin wax as pcm, which was filled in finned c-tes to conduct the experiments. the experimental results showed a positive improvement compared with the non-nano additive pcm. the significance and originality of this project lies within the evaluation and identification of preferable metal-oxides with higher potential for improving thermal performance. keywords-phase change material; thermal energy storage; latent heat; energy efficiency i. introduction the ongoing increase in world population and industrial infrastructures is accompanied by major energy consumption. on the other hand, the decreasing sources of conventional fossil fuels and the environmental issues linked with their use have created a series of issues and concerns such as energy security and global climate change. to overcome these issues, exploitation of renewable energies (e.g. solar energy, geothermal energy, wind energy, etc.) has been significantly considered by energy suppliers. however, due to the fluctuations and inability to control the renewable energy sources, it is more efficient for these systems to be used with energy storage systems. the finned cylindrical thermal storage unit (c-tes) with phase change materials (pcms) has been found to be a very efficient energy storage application for this purpose. however, the low thermal conductivity of pcms used makes them unable to give the desired response for storage and recovery. various techniques like the application of fins, metal foams, etc. have been explored to solve the problem and focus has been mainly given on energy storage and recovery separately, but in real life the systems operate mostly through simultaneous storage and recovery or charging and discharging (scd). pcms are materials that undertake a liquid-solid phase transformation (known as the fusion-solidification period) at a temperature within the limits of a chosen thermal application. the latent heat absorbed during the melting process is indicative of the latent heat of fusion. this is distinguished from the other type of latent heat – vaporization – which is characterized by a change in phase from a liquid to a gas. the heat of the material acts to raise the energy of the constituent molecules, and as a result their vibrational state increase. at melting temperature, the atomic bonds loosen and the material changes from solid to liquid. the inverse of this process is solidification, during which the material transmits energy to the area around it. latent heat storage is accomplished by changing a material’s physical state whereas sensible heat storage is accomplished by increasing a material’s temperature. materials that act as latent heat stores are termed as phase change materials. significantly less energy is required to change a material’s temperature than is required to change a material’s physical state, consequently latent heat storage can offer higher storage capacities and hence space savings over sensible heat storage. due to the effective use of pcms in improving latent heat thermal energy storage (lhtes) systems, more impetus has been provided by researchers to develop lhtes systems with pcms. utilizing pcms in lhtes systems has provided the advantages of high energy density and an almost constant corresponding author: nidhal ben khedher engineering, technology & applied science research vol. 10, no. 3, 2020, 5814-5818 5815 www.etasr.com aichouni et al.: experimental evaluation of nano-enhanced phase change materials in a finned … operating temperature. in these systems, thermal energy is stored during the melting process and released during the solidification process. a wide range of pcms with various melting temperatures including paraffin waxes, organic and non-organic compounds, and hydrated salts are available for use in lhtes systems. to select a proper pcm, different parameters including phase change temperature, stability, amount of latent heat, and thermal conductivity should be considered ii. literature review the energy density of the storage medium may be greatly enhanced if a material that undergoes a phase transition from solid to liquid is employed. the storage media used by these systems are the pcms which offer advantages such as much greater heat storage per unit volume. thermal energy storage using the latent heat of pcsm has received considerable attention in the past 3 decades. there have been many research efforts devoted to developing such novel materials for a variety of applications, such as buildings, textiles, and space heating. pcms are promising thermal storage materials for storing and discharging bulk amounts of latent heat throughout phase change process [1-4] with regulated time intervals associated as per energy demand. though, the criteria for the choice of a pcm for a specific application is its melting temperature, but other properties such as the latent heat of fusion, thermal conductivity, thermal stability, density, and lower volume change, also play significant role and therefore are essential to be considered [5, 6]. authors in [7] presented a detailed numerical investigation of a heat storage system’s inclination effect on the pcm melting process in order to comprehend the natural convection mechanism inside a shell and tube thermal energy storage (tes) unit. several unit positions were examined to interpret physically the thermal demeanor of the fusion process in terms of heat transfer modes estimation, pcm melting rate, and axial and radial temperatures distribution. the results showed that the tes unit inclination according to the range angle (0°-90°) makes an imbalance of the natural convection in the pcm liquid fraction which contributes in creating an instability and diminution of heat transfer during the melting process. as the increase of the heat transfer inside the pcm space could augment the efficiency of the storage unit, the method of including extended surfaces (fins) is used to ameliorate the heat transfer interchange inside the pcm. this method was experimented in a horizontal shell and tube tes unit [8] through testing the unit thermal performance in standard configuration, then in annular space embedded by circular and longitudinal fins. the test outcome elucidated a positive response of the natural convection activity in the longitudinal fins case, which made the melting process faster due to the swiftness of the heat transfer diffusion along the fins. the integration of a combined sensible and lhtes with a solar water heating system in [9] presented a detailed review on thermal energy storage using pcm focusing on three aspects: materials, heat transfers, and applications. authors in [10] developed a computer model based on the two-phase schumann model for the estimation of temperature profiles of the solid and the fluid along the length of the packed bed of eutectic al–si pcm encapsulated spherical capsules as functions of distance along the bed and time during a series of heat storage and utilization cycles[10]. iii. methodology a. experimental setup a schematic diagram of the experimental setup and its physical model are shown in figures 1 and 2 respectively. the setup consists of a water tank (1), the finned storage unit which goes inside the water tank, which is insulated from all sides except one for visualization, 2 electrical heaters, an 8-channel daq (data acquisition) system (2) connected to a computer (3) for data capture and processing, and thermocouples (4) connected to the daq system. fig. 1. schematic diagram of the setup used in the experiment fig. 2. the actual setup used in the experiment fig. 3. the physical model used in the experimental setup thermal conductivity was tested using kd2 pro thermal property analyzer, hotplate stirrer, thermostatic bath, heated ultrasonic cleaner, and a computer for data recording and analysis. engineering, technology & applied science research vol. 10, no. 3, 2020, 5814-5818 5816 www.etasr.com aichouni et al.: experimental evaluation of nano-enhanced phase change materials in a finned … b. materials pcms have high energy density that sets them at the forefront of energy storage materials. however, their power density is low due to their low thermal conductivity, which results in a decrease in the rate of heat transfer [11]. to solve this issue, the effect of performance increase of the system and latent heat stored will be investigated by adding nanoparticles to the pcm storage unit. paraffin wax (a51h) was chosen as a base pcm due to its average melting temperature range between 58 o c-58.5 o c. it provides dependable cycling, is noncorrosive and chemically inert when compared to non-paraffin organics, hydrated salts, and metallic pcms [12]. aluminum oxide (al2o3) and copper monoxide (cuo) nanoparticles were chosen to be studied, having average particle size of 50nm (max 100nm). before we begin to conduct the main experiment, we need to test the nanomaterial to make sure the thermal conductivity is within the acceptable range of the theoretical values. the experiment included filling test tubes with pcm and nanomaterials as shown in table i. table i. mass fraction [%] of the tested tubes test tube number contents pcm (%) nano particle type nano particle (%) 1 100 2 99 al2o3 1 3 98 al2o3 2 4 97 al2o3 3 5 99 cuo 1 6 98 cuo 2 7 97 cuo 3 c. volumetric fraction the volume fraction which is necessary to calculate the theoretical thermal conductivity and specific heat is: φ � ��� ��� ��� ��� � ���� ���� ∗ 100 (1) fig. 4. volume fraction versus mass fraction the equation of the line for volume fraction vs mass fraction can be applied to obtain any volume fraction value using mass fraction. from that equation, we determine the graph in figure 4. the line equation for pcm with al2o3 nanocomposites is: 2 0.0652 0.005, with of 0.998 y x r= + (2) the same can be said for pcm with cuo nano-composites: 2 0.0429 0.0027, with of 0.9993y x r= + (3) the line equation can be used to obtain any volume fraction value using mass fraction. the specific heat and thermal conductivity are calculated by (4) and (5) respectively: � .���� �� � ����������∗��.���������∗ ���� ������������ �� (4) !� � ! �� "#�$"����$%�"����"#�"&�$"����%�"'�(�!&� ) ���%�� $"'�( * $+ , -./��01 (5) the thermal conductivity due to the addition of nanoparticles (ko) was determined by the model of maxwell, however, it was modified in [13] and (5) was obtained. d. procedure the experiment consists of two parts: 1) charging phase during the charging process, the pcm storage unit is initially at ambient temperature of 20°c and is injected inside the hot water tank (70°c) and it starts melting once its temperature reaches the melting temperature (58°c). the duration of the charging/discharge process is an important factor considered in the design of latent tes systems. it reveals how the storage material is effective in responding with time for the energy storage/retrieval. this phase stops when the temperature of the water tank and tes system reaches thermal equilibrium. we repeat the charging procedure for all our experiments. 2) discharging phase in the discharging phase, the pcm storage unit is dropped inside a white cold-water tank (with ambient temperature of 21°c) while the data acquisition system records data. this phase stops when the temperature of the water tank and tes system reaches thermal equilibrium. iv. results and discussion the performance enhancement of the tes with nanoenhanced pcm under scd conditions was investigated experimentally. before we start with the main experiment, the correlation between thermal conductivity and temperature was determined experimentally for both pcms with cuo and al2o3 as shown in figures 6 and 7. a. specific heat and charging time improvement the results shown in figure 5 represent the relation between specific heat and thermal conductivity before and after adding nanoparticles to pure pcm. figure 5 shows that the specific heat of the nano-enhanced pcm decreases due to the lower specific heat capacity (cp) of both al2o3 and cuo nanoparticles associated with an increase in thermal conductivity (k). lower specific heat capacity ensures faster addition and release of energy which is desired in thermal storage applications. higher thermal conductivity is also engineering, technology & applied science research vol. 10, no. 3, 2020, 5814-5818 5817 www.etasr.com aichouni et al.: experimental evaluation of nano-enhanced phase change materials in a finned … desired because it guarantees faster heat conduction from the surrounding tank. fig. 5. the theoretical specific heat and thermal conductivity of pcm with and without nanoparticles b. correlation between thermal conductivity and temperature fig. 6. thermal conductivity of pcm with al2o3 fig. 7. thermal conductivity of pcm with cuo c. duration of the charging/discharging process the duration of the charging/discharging process is an important factor considered in the design of latent tes systems. it reveals how the storage material is effective in responding with time for energy storage/retrieval. for the present experiment, the results are shown in figures 7-8. these figures show that at the beginning of the solidification period the temperature of the pcm decreased rapidly by transferring the sensible heat stored to the cooling water. during this period, the temperature of the pcm is high, and the pcm is in liquid state. this is mainly because the heat transfer inside the molten pcm is conducted by natural convection and the temperature gap between pcm storage and the cooling water is large. then the pcm begins to freeze and discharge its latent heat. it was found that the pcm releases its sensible heat very rapidly while a longer time is needed to transfer the latent heat during the phase change. the experimental results show clearly that the charging duration was decreased with the addition of nanoparticles. the charging and discharging rates of base pcm were significantly enhanced with the inclusion of nanoparticles. the experimental results indicate that using al2o3 with 3% volumetric fraction ensures a rapid charging and discharging processes compared to cuo and pure pcm. moreover, it is clearly noticed that higher mass fractions engender short charging and discharging periods. but at the same time, the latent heat will slightly decrease. the percentage enhancement in charging rates of al2o3 based nano-pcm samples with 1%, 2% were 29.4% for both cases, and 41.04% for the al2o3 3% case. likewise, the discharging rates are improved by 21.09%, 29.45% and 30.08%. however, an increase in volume concentration reduces natural convection and overall thermal enthalpy and increases the total cost of the nano-pcm. fig. 8. charging times for all cases fig. 9. discharging times for all cases engineering, technology & applied science research vol. 10, no. 3, 2020, 5814-5818 5818 www.etasr.com aichouni et al.: experimental evaluation of nano-enhanced phase change materials in a finned … v. conclusion this study focused on the experimental analysis of al2o3 and cuo metal oxides-based nano-pcms of different concentrations to establish an approach for selecting nano additives for optimal thermal enhancement. charging and discharging processes, heat transfer, and energy storage characteristics of nano-pcms in a finned tube storage system were numerically and experimentally investigated. the finned tes system is either filled with al2o3 or cuo nanoparticles dispersed in a58h paraffin at different mass fractions of nanoparticles (1%, 2%, and 3%). the thermal conductivity of each nanofluid solution was measured by varying temperature from 60 o c to 83 o c. the obtained results demonstrate that the thermal conductivity of nanofluids increase with the increase of volume fraction. aluminum oxide showed the best results of charging and discharging times enhancement which are directly linked with the increase of thermal conductivity. the presented experimental investigation conclusions are: • the addition of metal-oxide nanoparticles significantly enhances the effective thermal conductivity and surface area for heat transfer. • in general, al2o3 nanoparticles exhibit by far greater enhancement of thermal conductivity in comparison to cuo. the enhancement in charging rates of al₂o₃ based nano-pcm with 3% was 30%. acknowledgment the authors would like to acknowledge the research deanship of the university of hail, for funding the project “rg-191225”. partial support provided by the innovation and creativity program, funded by the saudi ministry of education within the framework of the national initiative on creativity and innovation in saudi university is also acknowledged. nomenclature 4 = volumetric fraction (%) ( = mass (kg) 5 = density (kg/m3) � = specific heat (j/kg k) kg = thermal conductivity of nano-particles (w/m.k) bo = boltzmann’s constant = 1.381 *10 -23 j/k 67 = dynamic viscosity (pa.s) 8' = nano particles t = temperature (k) 9 = particle diameter (m) references [1] g. fang, h. li, f. yang, x. liu, s. wu, “preparation and characterization of nano-encapsulated n-tetradecane as phase change material for thermal energy storage”, chemical engineering journal, vol. 153, no. 1-3, pp. 217–221, 2009 [2] s. m. hasnain, “review on sustainable thermal energy storage technologies, part i: heat storage materials and techniques”, energy conversion and management, vol. 39, no. 11, pp. 1127–1138, 1998 [3] k. kant, a. shukla, a. sharma, “ternary mixture of fatty acids as phase change materials for thermal energy storage applications”, energy reports, vol. 2, pp. 274-279, 2016 [4] m. kenisarin, k. mahkamov, “solar energy storage using phase change materials”, renewable and sustainable energy reviews, vol. 11, no. 9, pp. 1913-1965, 2006 [5] t. c. ling, c. s. poon, “use of phase change materials for thermal energy storage in concrete: an overview”, construction and building materials, vol. 46, pp. 55-62, 2013 [6] h. mehling, l. cabeza, “phase change materials and their basic properties”, in: thermal energy storage for sustainable energy consumption se-17, nato science series. springer, pp. 257– 277, 2007 [7] a. elmeriah, d. nehari, a. mohamed, a. remlaoui, “natural convection mechanism evaluation inside a shell and tube thermal energy storage (tes) devise inclination”, revue des domposites et des materiaux avances, vol. 28, no. 2, pp. 257-276, 2018 [8] f. agyenim, p. eames, m. smyth, “a comparison of heat transfer enhancement in a medium temperature thermal energy storage heat exchanger using fins”, sol energy, vol. 83, no. 9, pp. 1509-1520, 2009 [9] b. zalba, j. m. marin, l. f. cabeza, h. mehling, “review on thermal energy storage with phase change: materials, heat transfer analysis and applications”, applied thermal engineering, vol. 23, no. 3, pp. 251– 283, 2003 [10] v. ananthanarayanan, y. sahai, c. e. mobley, r. a. rapp, “modeling of fixed bed heat storage units utilizing phase-change materials”, metallurgical transactions b, vol. 18, pp. 339–346, 1987 [11] n. ben khedher, “numerical study of the thermal behavior of a composite phase change material (pcm) room”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2663-2667, 2018 [12] h. a. fakhim, “an investigation of the effect of different nanofluids in a solar collector”, engineering, technology & applied science research, vol. 7, no. 4, pp. 1741-1745, 2017 [13] s. mentha, k. prashanth chauhan, s. kanagaraj, “modeling of thermal conductivity of nanofluids by modifying maxwell’s equation using cell model approach”, journal of nanoparticle research, vol. 13, pp. 27912798, 2010 etasr paper format engineering, technology & applied science research vol. 9, no. 2, 2019, 4048-4052 4048 www.etasr.com bhajana & drabek: development and evaluation of an isolated resonant converter for auxiliary … development and evaluation of an isolated resonant converter for auxiliary power supply in dc traction veera venkata subrahmanya kumar bhajana school of electronics engineering kalinga institute of industrial technology bhubaneswar, india bvvs.kumarfet@kiit.ac.in pavel drabek regional innovation centre for electrical engineering university of west bohemia pilsen, czech republic drabek@ieee.org abstract—this paper presents the implementation and evaluation of an isolated resonant converter and also compares the efficiencies of hard and soft switching isolated converter topologies using high-frequency transformer for auxiliary power supplies in dc traction. the half-bridge dc-dc converter with resonant network has been tested under zero voltage switching (zvs), zero current switching (zcs) operations, and also dead time variation of the power switches improving the overall system efficiency. this paper provides guidelines for a cost effective dcdc converter design based on discrete 1200v/40a igbts driven with high switching frequency. that would allow optimization of passive elements by reducing their mass making the converter suitable for traction application. simulations and test results of an experimental setup with output power up to 3kw are presented. the overall system efficiency of the zvs and zcs operations of half-bridge llc dc-dc converter were compared with a classic hard switching topology. keywords-zvs; zcs; half bridge resonant converter; llc; dc-dc; auxiliary power supply i. introduction typical light traction vehicles contain electrical equipment such as air brakes, cooling system, air pressures, fans etc. supplied from a standard 3×400vac on-board power grid. the grid is generated by a structure of dedicated converters which usually provide battery charging functionality. the design of such an auxiliary power supply has to respect the fact that the catenary voltage of nominal voltage 600vdc or 750vdc may vary in the range of 400vdc to 950vdc. also, the outputs, i.e. the power grid or the battery charger, must be isolated in order to maintain a high level of safety. the overall structure of an auxiliary power supply (without a battery charger branch) used in practice consists of the input voltage stabilizer (ivs), supplied from the catenary through, which stabilizes voltage to the catenary lower range level, and the half-bridge (hb) isolating converter. due to additional requirements from vehicle manufacturers concerning small size and low weight, high frequency operations with reduced losses allowing further savings in passive components mass and volume become key parameters of the converter in the auxiliary power supply. the resonant network topology suggested in [1] provided useful soft switching operations for the isolated dual bridge dc-dc converters. to obtain ultra-high input and better efficiency in a dc-dc converter [2], different combinations of type-4 series resonant networks were reported. a burst oscillation control [3] has been used to improve the efficiency of current resonant, full bridge and half bridge converters. these converters achieved the highest efficiency at low and high output power levels. for the applications of on-board charging, an llc resonant converter [4] operated under continuous conduction mode achieved zvs turn-on operation to their mosfets. a half bridge llc resonant converter is described in [5] for low power applications with higher switching frequency and digital control system developed for multi resonant network [6] for dc-dc converters. a half bridge converter has been developed with a simple resonant inductor, capacitor and an additional switch, and obtained zvs operation with 94.5% efficiency at 350w output power in [7]. a zvs full bridge resonant converter has been implemented in [8] by utilizing simple resonant elements and obtained 93.3% efficiency at 8kw output power. a low power full bridge converter [9] attained zvs operation by the additional resonant network. however, it had poor efficiency at low output power. a half bridge resonant converter with voltage rectifier attained soft-switching (zvs) operation to their mosfets and achieved 96% efficiency below 100w, was studied in [10]. this paper focuses on the high power dc/dc isolating converter which converts stabilized voltage 380vdc-390vdc (has to be lower or higher than input catenary voltage range) to a level suitable for the consequent appliances (standardly 560vdc to supply vsi to produce output power grid 3×400vac). half bridge topology was chosen for the study as it offers lower prices. in order to achieve maximum efficiency, a resonant network was utilized, allowing higher switching frequency at reasonable efficiency level. in this paper, a half bridge resonant converter was verified under two different operating modes, continuous conduction and discontinuous conduction. comparison was made between the effectiveness of this converter and the one of a conventional hard-switching converter. this article presents the operation principles, dc characteristics, simulation analysis, and laboratory tests conducted with the half bridge llc resonant dc-dc converter. corresponding author: veera venkata subrahmanya kumar bhajana engineering, technology & applied science research vol. 9, no. 2, 2019, 4048-4052 4049 www.etasr.com bhajana & drabek: development and evaluation of an isolated resonant converter for auxiliary … ii. operation principles figure 1 shows the schematic of a typical half bridge resonant dc–dc converter. the primary side contains four active igbts s1–s2, the resonant elements cs, ls, and the magnetizing inductance (lm). the turns ratio of the transformer is 1:1.5. the secondary side of the transformer includes rectifying diodes d1–d4, the filter capacitor (co) and the load resistance (rl). the primary-side active switches are controlled with 50% duty cycle. when s1 and s2 conduct simultaneously, the input power is transferred to the output load. the zero voltage switching (zvs) turn-on and zero current switching turn-off are achieved by the resonance of ls and cs. figure 2 shows the waveforms of half bridge llc resonant dc-dc converter. the first stage is resonant current in continuous conduction mode, the operating frequency is above the resonant frequency and the second stage is resonant current in discontinuous conduction mode, with the operating frequency below the resonant frequency. in these stages, during continuous conduction mode, all the power switches can turnon under zvs condition and in discontinuous conduction mode all the power semi-conductor switches can turn on/off under zcs. figure 2(a) shows the continuous conduction mode, resonant tank current (ilr), magnetizing inductance current (ilm), and switch current (is1) waveforms and similarly figure 2(b) shows the waveforms of the discontinuous conduction mode. fig. 1. isolated half bridge llc resonant converter fig. 2. key waveforms: (a) ccm mode, (b) dcm mode a. continuous conduction mode when the resonant frequency of the half bridge dc–dc converter is set below the switching frequency zero voltage, turning on of the converter power switches is possible. these conditions ensure that the resonant current ilr freewheels through the body diodes of the main switches prior to turn on, thus preventing turn on losses. figure 2(a) shows the key waveforms for continuous conduction mode (ccm) of resonant half bridge converter. at t=t0 the igbt s2 is turned off which forces the resonant tank current ilr to freewheel through the body diode of s1, resonant tank. the voltages on s1 basically the diode drop, become close to zero when the gate turn on pulse for s1 applied at t=t1. during the time from t1 to t2, s1 is turned on, the output rectifier diodes d1, d4 conduct and energy is transferred to the secondary through the transformer. after the time t2, the power switch (s1) is turned off, the body diode of s2 creates the path for freewheeling the primary resonant tank current ilr which makes zvs condition for the following s2 turn on. b. discontinuous conduction mode figure 2(b) shows the discontinuous conduction mode (dcm) waveforms, at t=t0 igbt s2 is turned off, the lm inductor current reaches maximum, and the resonant current drops to zero. the output rectifier diodes are also turned off. s1 is turned on under zcs at t=t1. the resonance of the inductors ls and cs creates ilr current in a sinusoid shape and the magnetizing inductor current decreases linearly. the switch s1 is turned off under conditions close to zcs at t=t2. the ilr value at this moment equals to the magnetizing current of the transformer. after that the output capacitances of s1 and s2 are recharged by ilr until s2 voltage reaches vdc when s2 body diode is forced to conduct. it provides zvs conditions for the subsequent s2 turn on at t=t3. iii. dc characteristics and design procedure a. dc characteristics the dc characteristics of the half bridge converter are obtained by experimental studies performed for steady state response. voltage gain characteristics curves are illustrated in figure 3, which shows that the resonance frequency is above the switching frequency. from the dc characteristics, it can be seen from peak gain changing by adjusting load. the peak gain measured values were taken at high load conditions. fig. 3. dc characteristics of zcs operating region. b. design procedure based on the theoretical analysis, the design procedure is presented in this section. it discusses that the resonant network can be suitable for traction applications. the equivalent circuit of the llc resonant tank is shown in figure 4. the load resistance (re) shown in the primary side is defined as: 2 2 8 e o n r r   (1) using the ac equivalent circuit of figure 4, the voltage gain is expressed with the following parameters and definitions: engineering, technology & applied science research vol. 9, no. 2, 2019, 4048-4052 4050 www.etasr.com bhajana & drabek: development and evaluation of an isolated resonant converter for auxiliary … resonant frequency: 1 2 r s s f l c  (2) characteristics impedance: 1 2 2 s r s s r s l z f l c f c      (3) quality factor: 2 2 2 2 8 o o o o e o o z z z p q r n r n v     (4) inductance ratio: s m l l   (5) normalized frequency: sw n r f f f  (6) voltage gain characteristics curves are shown in figure 5. they curves show the resonance frequency is 90khz when the switching frequency is 100khz, and the converter operates in zvs region. fig. 4. equivalent circuit of llc fig. 5. dc characteristics of zvs operating region fig. 6. simulated results: voltage and current through switches s1, s2 when the converter operates in zcs region. iv. simulation results simulation results were obtained separately for zvs and zcs by matlab/simulink. the simulation parameters used are mentioned in table i. figure 6 depicts switches’ (s1 and s2) voltage and currents, which show the zvs operating region of the converter. figure 8 illustrates switches’ voltage and currents, which represent the zcs operation of the converter. figure 9 shows the voltage and current through the transformer in zvs and zcs regions. fig. 7. simulated results: voltage and current through switches s1, s2 when the converter operates in zvs region. fig. 8. (a) measured waveforms of the primary side of the transformer: voltage (ch1), current (ch2). (b) measured waveforms of igbt s1: voltage (ch1) current, (ch2). hard switching. v. experimental results laboratory tests were conducted for the two case studies under steady state operation. zvs and zcs conditions were tested separately in order to show the efficiency of the zvs and zcs converters separately. the design specifications (table i) for this converter are vin=400v, vout=300v, pout=1kw to 3kw, switching frequency 100khz and the switching device we used was igbt ikw40n120h3. the resonant inductor ls=15µh, the transformer magnetizing inductance lm=17µh, and the resonant capacitor cs=130nf/200nf. the realization of dc-dc converter system is a low cost system to drive auxiliary systems in traction. figure 9(a) shows the transformer primary side voltage and current waveforms of hard-switched half bridge converter and figure 9(b) shows the device voltage and currents. figure 10 depicts igbt (s1) voltage and current engineering, technology & applied science research vol. 9, no. 2, 2019, 4048-4052 4051 www.etasr.com bhajana & drabek: development and evaluation of an isolated resonant converter for auxiliary … waveforms for the zvs operating region. figure 11 shows the experimental waveforms of the transformer primary side voltage(vp) and resonant tank current (ilr). fig. 9. measured waveforms of the primary side of the transformer: voltage (ch1), current (ch2). (b) measured waveforms of igbt s1: voltage (ch1), current(ch2). ccm mode. fig. 10. (a) measured waveforms of the primary side of the transformer: voltage (ch1), current (ch2). (b) measured waveforms of igbt s1: voltage (ch1), current (ch2). dcm mode. a. observations made by varying dead time by varying the dead time between each switch, laboratory tests were conducted in order to observe the optimum efficiency of the converter. during the resonant cycle, all the power switches will transfer the output power. two switches for a half of the resonant cycle and the other two for the next resonant cycle, maintaining the zcs, but a delay is introduced between each switch turning on. therefore the switch current transfers to the corresponding freewheel diode before returning to zero. the switch currents remain zero until the next switch turns on. results shown in figure 11 are obtained for dead time of 0.5µs. by changing the dead time between switches to 0.9µs, it is observed that all power switches are turned on under zvzcs. also, the efficiency of the converter has been increased from 0.5% to 1%, when comparing with zcs operating region with 0.5µs. figure 12(a)-(b) depicts the zcs turn on with 0.5 µs dead time interval, which is having large current spikes when switches are turn on/off. due to the large amount of spikes the efficiency is very poor. it is observed in figure 12(c)-(d), that with 0.9µs dead time, zvzcs turn on is achieved and the overall system efficiency is improved. figure 13 shows the collector-emitter voltage and current of the switch (s1), when it is operated in zvs and zcs regions. fig. 11. (a) measured waveforms of igbt s1 voltage and current of the switch with 0.5μs dead time. (b) measured waveforms of igbt s1 voltage and current of switch with 0.9μs dead time. fig. 12. (a) turn-on and (b)turn-off transitions of the switch. zvs. (c) turn-on and (d) turn-off transitions of the switch. zcs. table i. component and parameter values, simulation and experimental parameters symbol values input voltage vin 400v output voltage vo 300v output power po 3kw switching frequency fsw 100khz resonant inductor ls 15µh magnetizing inductance lm 217µh resonant capacitors cs 130nf/200nf output capacitors co 470µf main switches s1-2 ikw40h1203 diodes d1-4 aptdc20h1201g 8 transformer tr skyvftr15 input voltage vin 400v output voltage vo 300v b. efficiency comparison in this part, the efficiency of the dc-dc converter for auxiliary drives is discussed comparing two topologies of input engineering, technology & applied science research vol. 9, no. 2, 2019, 4048-4052 4052 www.etasr.com bhajana & drabek: development and evaluation of an isolated resonant converter for auxiliary … half bridge converter (resonant and hard switching). in figure 13, the comparison between hs (hard switching), zvs, zcs is shown while figure 14 shows the efficiency comparison between converter switches operated at 0.5µs dead time in zcs operating region with switching frequency 112khz, resonant frequency 118khz and 0.9µs delay used with 100khz switching frequency. the efficiency of hs full bridge topology at maximum output power 3kw is 92.1% and zvs half bridge resonant converter is 92.6%. there is an augmentation in 0.5% efficiency in comparison with hs. when the converter operates in the zcs region at maximum output power 3kw, there is 94.3% efficiency achieved. the overall system efficiency is about 2% more than when using hs converter. fig. 13. efficiency curves between hs and soft-switching. fig. 14. efficiency curves: zcs operating region. vi. conclusion this paper presents an efficiency comparative study of hs and soft switching dc-dc converter for auxiliary power supply in traction with maximum efficiency of 94.3%. the maximum output power of the resonant converter is 3kw with 100khz switching frequency. it has been simulated and laboratory tests investigated the zvs and zcs resonances separately in order to show the performance of the overall system efficiency. the output power levels can be increase up to 10kw by changing transformer turns ratio. the efficiency obtained for hard switched dc-dc converter is 92.1% at maximum output power of 3kw. when the resonant frequency operates below the switching frequency, the converter has maximum efficiency 92.6% and the zcs resonant converter has maximum efficiency of about 94.3%. by varying the dead time interval between power switches in the zcs operating region, the system efficiency was improved by 2% when compared to the conventional converter. the experiments were performed for steady state condition. acknowledgement this research has been supported by the ministry of education, youth and sports of the czech republic under the rice – new technologies and concepts for smart industrial systems, project no. lo1607 and by project sgs-2018-009 references [1] x. li, “a llc type dual bridge resonant converter: analysis, design, simulation and experimental results”, ieee transactions on power electronics, vol. 29, no. 8, pp. 4313–4321, 2014 [2] w. chen, z. lu, “investigation on topology for type-4 llc resonant dc-dc converter”, 39th annual ieee power electronics specialist conference, rhodes, greece, pp. 1421–1425, june 15-19, 2008 [3] h. kato, h. matsuo, t. ito, s. kawazu, d. kawahara, s. motomura, r. hamaguchie, “comparative analysis of full bridge and half bridge current resonant converter”, ieee 33rd international telecommunications energy conference, amsterdam, netherlands, october 9-13, 2011 [4] y. s. dow, h. i. son, h. d. lee, “a study on half bridge llc converter for battery charger on board”, 8th international conference on power electronics and ecce asia, jeju, korea, may 30-june 3, 2011 [5] b. yong, f. c. lee, a. j. zhang, g. huang, “llc resonant converter for front end dc-dc conversion”, apec. seventeenth annual ieee applied power electronics conference and exposition, dallas, usa, march 1014, 2002 [6] p. spanik, p. drgona, m. frivaldsky, a. prikopova, “design and application of full digital control system for llc multiresonant converter”, elektronikair elektrotechnika, vol. 106, no. 10, pp. 75-78, 2010 [7] j. b. lee, j. k. kim, j. i. baek, j. h. kim, g. w. moon, “resonant capacitor on/off control of half-bridge llc converter for highefficiency server power supply”, ieee transactions on industrial electronics, vol. 63, no. 9, pp. 5410-5415, 2016 [8] v. v. s. k. bhajana, p. drabek, m. jara, “performance evaluation of llc resonant full bridge dc-dc converter for auxiliary systems in traction”, revue roumaine des sciences techniques serie electrotechnique et energetique, vol. 60, no. 1, pp. 79-88, 2015 [9] j. i. z. chen, “a high efficiency full-bridge converter”, journal of electrical systems, vol. 8, no. 4, pp. 442-458, 2012 [10] j. w. kim, j. k. han, j. s. lai, “apwm adapted half-bridge llc converter with voltage doubler rectifier for improving light load efficiency”, electronics letters, vol. 53, no. 5, pp. 339-341, 2017 authors profile veera venkata subrahmanya kumar bhajana received his b.e in electronics and communication engineering from the sapthagiri college of engineering, dharmapuri, tamilnadu, india (university of madras), in 2000, m.e from the p.s.n.a college of engineering and technology, dindigul, tamilnadu, india in 2005 and his phd in electrical engineering from the bharath university, chennai, india in 2011. he has 11 years of teaching experience in various engineering institutes in india. he worked as a post-doc researcher at the university of west bohemia, czech republic from august 2013 to june 2015. since december 2011, he is working as associate professor in the school of electronics engineering at kalinga institute of industrial technology, india. he has presented papers in many reputed ieee international conferences. his main areas of interest are power electronics engineering, including soft switching dc to dc converters, ac‐ac converters, and multilevel converters. pavel drabek received his m.s. and ph.d. degrees in electrical engineering from the university of west bohemia (uwb), czech republic, in 2000 and 2004, respectively. from 2003 to 2005, he was a design engineer in alltronic, ltd., pilsen. in 2005, he joined the uwb as an assistant professor at the department of electromechanics and power electronics. his main research interests include soft‐switching inverters, ac‐ac converters, multilevel converters, and electromagnetic compatibility (particularly low‐ frequency interference) of power electronics converters. http://journal.esrgroups.org/jes/papers/8_4_7.pdf i. introduction ii. operation principles a. continuous conduction mode b. discontinuous conduction mode iii. dc characteristics and design procedure a. dc characteristics b. design procedure iv. simulation results v. experimental results a. observations made by varying dead time b. efficiency comparison vi. conclusion acknowledgement references microsoft word 01-karakalos-ed.doc etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 291-294 291 www.etasr.com s. karakalos: growth mode study of mgcl2 on ti (0001) and sio2 under ultra high vacuum by xps growth mode study of mgcl2 on ti (0001) and sio2 under ultra high vacuum by xps stavros karakalos 1, 2 1 forth/ice-ht, stadiou str., platani achaias, gr-26504, p.o. box, 1414, patras, greece 2 surface science laboratory, department of chemical engineering, university of patras, university campus, gr-26504, rion, patras, greece skaraka@hotmail.com abstract the growth mode of mgcl2 on ti (0001) and on sio2 grown on si (100) was investigated by x-ray photoelectron spectroscopy (xps) under uhv conditions. magnesium chloride grows on both ti (0001) single crystal and sio2 following the frank-van der merve, (fm) growth mode. keywordsgrowth mode; mgcl2; ti(0001); sio2; uhv; xps i. introduction the deposition of mgcl2 on a well characterized ti surface and sio2 is of special interest in studies related to ziegler-natta catalysts which are used for the heterogeneous polymerization of olefins. in the so called third or fourth generations of tibased ziegler-natta catalysts, ticl4 is chemisorbed on “activated” magnesium chloride, a defective form of mgcl2 with high miller index planes exposed at the surface [1]. many granular materials have been proposed as supports in modified ziegler-natta catalysts. porous silicas, magnesium halides and their combination are the most important. in order to extend the knowledge of such complex catalyst system at the atomic level, different scientific groups develop catalytic models compatible for study with surface sensitive techniques [2, 3]. the previous studies of our group, and in order to understand the nature of the catalytically active sites, were to simplify the model catalyst by depositing the catalyst components under uhv conditions. the first step in developing this ideal model catalyst, is the deposition of mgcl2 on foils, single crystals [4] and on sio2/si(100) well characterized substrates [5] which are studied by means of xps. the present work deals with the investigation of the growth mode of mgcl2 on ti (0001) and sio2 by x-ray photoelectron spectroscopy (xps). for the purposes of the present study, mgcl2 is applied on these supports by evaporation under uhv conditions. ii. experimental the experiments took place in the surface science laboratory of chemical engineering department of university of patras. for the xps measurements the non-monochromatic mgkα line was used with hν= 1253.6 ev. the hemispherical analyser (leybold ea-11) was working at constant pass energy ep=100 ev. the first substrate used in this study, was a ti (0001) disc (mateck), 10mm in diameter and 2mm thick, which was subjected to in-situ cleaning by repeated cycles of 1kev ar + sputtering and annealing at 450 o c in order to remove c, s, and o and h contamination. many cycles of this procedure produced a surface without impurities except for the small amount of hydrogen, the existence of which was eventually verified at the valence band spectra. the second substrate was a p-type si (100) single crystal. it was annealed in the atmosphere at 873 k for 60 min, in order to develop a thick sio2 layer on its surface. before introduction in the ultra high vacuum (uhv) system the sample was chemically cleaned by immersion in a 2o2/nh4oh/h2o (1:1:5) solution at 323 k for 10 min in order to remove organic contaminants. the crystal was then transferred into the uhv system and annealed at 973 k for 15 min. this procedure leads to desorption of the largest percentage of hydroxyl species from the sio2 surface, leaving about 1–3 oh/nm 2 [6]. this is a common treatment of silica supports during the industrial preparation of ziegler–natta catalysts [7, 8]. magnesium chloride was deposited under uhv conditions through a mgcl2 evaporation source, described elsewhere [4]. all depositions were carried out at a source temperature of 795 k, while the substrate was held at room temperature. the cl/mg atomic ratio was found to be ~2 indicating that the deposit consists essentially of stoichiometric mgcl2. iii. results and discussion after confirming the atomically clean ti (0001) surface, a stepwise deposition procedure of mgcl2 took place under uhv, at a constant source temperature of 795k, measuring the deposition time of each step in seconds. after each mgcl2 deposition, two photoelectron peaks were recorded (cl2p and ti2p) as well as one (x-ray induced) auger peak (mgkll). figure 1 shows the xps spectra of ti2p derived from the substrate and mgkll, cl2p originating from the deposit. etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 291-294 292 www.etasr.com s. karakalos: growth mode study of mgcl2 on ti (0001) and sio2 under ultra high vacuum by xps 466 464 462 460 458 456 454 452 450 448 ti2p after mgcl 2 dep. x p s p e a k i n te n s it y / a .u . binding energy /ev 1170 1173 1176 1179 1182 1185 1188 mgkll after mgcl 2 dep. on ti(0001) kinetic energy /ev x p s p e a k i n te n s it y / a .u . 206 204 202 200 198 196 cl2p after mgcl 2 dep. on ti(0001) binding energy /ev x p s p e a k i n te n s it y / a .u . fig. 1. xps peak intensity of ti2p, mgkll and cl2p spectrum after stepwise mgcl2 deposition on au foil at rt. the ti2p core level peak appears at binding energy (be) 454.0ev and shifts by +0.3ev (be) after mgcl2 deposition indicating chemical interaction between the support and the deposit. the mgkll auger photoelectron peak shifts -2.2ev to lower kinetic energy (ke) and the cl2p core level peak shifts +1.5ev to higher be after deposition of the maximum amount of mgcl2 on the ti single crystal. this is expected and has its origin to both interaction between the deposit and the substrate and to electrostatic charging of the deposited mgcl2 layer, as mgcl2 is an insulating material [4, 5, 9]. figure 2 shows the intensity ratios of each one of the peaks originating from the deposit, divided by the intensity of the ti2p of the substrate as a function of the deposition time. these graphs provide strong indication that mgcl2 follows a layer by layer deposition on ti(0001). the figure clearly shows a “break” of the lines slope after the completion of each monolayer pointing out a frank-van der merve, (fm) growth mode. the same procedure of mgcl2 deposition took place also on sio2/si(100) substrate. figure 3 shows the xps spectra of si2p derived from the substrate and mgkll, cl2p from the deposit. etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 291-294 293 www.etasr.com s. karakalos: growth mode study of mgcl2 on ti (0001) and sio2 under ultra high vacuum by xps fig. 2. graphical representations of the ratios cl2p/ti2p and mgkll/ti2p as a function of the mgcl2 deposition time. 108 106 104 102 100 98 96 binding energy /ev x p s p e a k i n te n s it y / a .u . sio 2 /si(100)si2p after mgcl 2 dep. 1170 1172 1174 1176 1178 1180 1182 1184 1186 kinetic energy /ev x p s p e a k i n te n s it y / a .u . sio 2 /si(100)mgkll after mgcl 2 dep. fig. 3. xps peak intensity of si2p, mgkll and cl2p spectrum after stepwise mgcl2 deposition on si (111) 7x7 at rt. the si2p core level peak appears at be= 99.5ev derived from the si(100) and there is another component which appears at 103.5ev be and derives from the oxide layer on top of the single crystal. the si2p peak does not shift after mgcl2 deposition indicating that in this case no chemical interaction between the support and the deposit takes place. the mgkll auger peak shifts again by -0.3ev to lower ke and the cl2p core level peak shifts +0.3ev to higher be after deposition of the maximum amount of mgcl2 on sio2. these shifts appear due to electrostatic charging of the deposited mgcl2 layer. figure 4 shows the intensity ratios of each one of the peaks originating from the deposit, divided by the intensity of the 0 200 400 600 800 1000 1200 1400 1600 1800 2000 3ml 2ml 1ml in te n s it y r a ti o c l2 p /t i2 p deposition time /sec 0 200 400 600 800 1000 1200 1400 1600 1800 2000 deposition time /sec in te n s it y r a ti o m g k l l /t i2 p 3ml 2ml 1ml etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 291-294 294 www.etasr.com s. karakalos: growth mode study of mgcl2 on ti (0001) and sio2 under ultra high vacuum by xps si2p of the substrate as a function of the deposition time. these graphs provide also in this case strong indication that mgcl2 follows a layer by layer deposition on ti(0001). the figure clearly shows a “break” of the lines slope after the completion of each monolayer pointing out a frank-van der merve, (fm) growth mode. 0 100 200 300 400 500 2m l 1ml deposition time /sec in te n s it y r a ti o c l2 p /s i2 p 0 100 200 300 400 500 2ml 1ml deposition time /sec in te n s it y r a ti o m g k l l /s i2 p fig. 4. graphical representations of the ratios cl2p/si2p and mgkll/si2p as a function of the mgcl2 deposition time. iv. conclusions the mgcl2 was deposited on the atomically clean surface of the ti (0001) single crystal. the deposition took place via a layer by layer growth mode. chemical interaction between the deposit and the substrate was observed while the energy shifts of the mgcl2 photoelectron peaks occurred due to this interaction and due to electrostatic charging. energy shifts were also observed after deposition of mgcl2 on sio2/si (100) due to the insulating nature of the deposit. the growth of mgcl2 on the sio2 surface follows also the frank-van der merve, (fm) mode. refernces [1] p. sobota, s. szafert, “ionization of ticl4 and mgcl2 during the formation of a high-activity α-olefin polymerization catalyst. crystal structure of [cis-{c2h4(co2et)2}2cl2ti][sbcl6]2×ch2cl2 and [mg{c2h4(co2et)2)3][mgcl4]×2ch2cl2”, inorg. chem., vol. 35, pp. 1778-1781, 1996 [2] e. magni, g. a. somorjai, “preparation and surface science characterization of model ziegler−natta catalysts. role of undercoordinated surface magnesium atoms in the chemisorption of ticl4on mgcl2 thin films”, j. phys. chem. b., vol. 102, no. 44, pp. 8788-8795, 1998. [3] a. andoni, j. c. chadwick, s. milani, h. j.w. niemantsverdriet, p. c. thüne, “introducing a new surface science model for ziegler–natta catalysts: preparation, basic characterization and testing”, journal of catalysis, vol. 247, no. 2, pp. 129-136, 2007. [4] s. karakalos, a. siokou, v. dracopoulos, f. sutara, t. skala, m. skoda, s. ladas, k. prince, v. matolin, v. chab, “the interfacial properties of mg cl2 thin films grown on si (111) 7×7”, journal of chemical physics, vol. 128, art. no. 104705, 2008 [5] s. karakalos, a. siokou, s. ladas, “the interfacial properties of mgcl2 films grown on a flat sio2/si substrate. an xps and iss study”, applied surface science, vol. 255, pp. 8941-8946, 2009 [6] r.k. iler, the chemistry of silica: solubility, polymerization, colloid and surface properties and biochemistry, wiley-interscience, chichester, 1979. [7] j. c. chadwick, “ziegler–natta catalysts”, encyclopedia polym. sci. technol., vol. 6, p. 517, 2003. [8] p. corradini, v. busico, g. guerra, comprehensive polymer science, vol. 4, pergamon press, p. 29, 1988 [9] s. karakalos, a. siokou, f. sutara, t. skala, f. vitaliy, s. ladas, k. prince, v. matolin, v. chab, “the interfacial properties of mgcl2 thin films grown on ti(0001)”, journal of chemical physics, vol. 133, art. no. 074701, 2010 authors profile stavros karakalos was born in athens in 1979. he received a b.s. in physics from the university of ioannina in 2003, an msc in material science and technology and a ph.d. in chemical engineering – surface science in 2009. he worked as a post doctoral researcher at the foundation for research and technology, institute of chemical engineering and high temperature chemical processes in patras and as a part time teacher in the technological educational institute of patras, greece. presently he is a postdoctoral employee in university of california riverside. his research interests include the use of a large variety of surface analysis and characterization techniques in order to determine the structure, composition and electronic properties of the outermost atomic layers of solid materials exposed to ultra-high-vacuum or controlled gaseous atmospheres and correlate them with the material behavior in various processes. his main research interests include surface science aspects of heterogeneous catalysis. microsoft word 3-2578_s engineering, technology & applied science research vol. 9, no. 2, 2019, 3887-3891 3887 www.etasr.com dammalage & jayasinghe: land-use change and its impact on urban flooding: a case study … land-use change and its impact on urban flooding: a case study on colombo district flood on may 2016 t. l. dammalage department of remote sensing and gis, faculty of geomatics, sabaragamuwa university of sri lanka, belihuloya, sri lanka thilantha@geo.sab.ac.lk n. t. jayasinghe department of remote sensing and gis, faculty of geomatics, sabaragamuwa university of sri lanka, belihuloya, sri lanka nishara.jayasinghe91@gmail.com abstract—colombo district has become an increasingly congested urban society. it has been reported that the frequent flooding in the colombo district occurs due to the shrinking of open spaces, illegal constructions, and lack of suitable waste disposal facilities. therefore, this study focuses on analyzing the impact of land-use change on the flood of colombo district in may 2016 in comparison to the land-use during the flood in 1989. accordingly, landsat images were utilized to identify the land-use by using ndvi, ndbi, and ndwi indices. out of the several techniques examined, svm classification was chosen, and change detection techniques in conjunction with remote sensing and gis environment were adopted. svm classification showed the highest accuracy for land-use classification, which was 99.0% in 1989 and 99.9% in 2016. the comparison of land-use changes of 1989 and 2016 with similar flood extent of the colombo district proved that the area of the kelani river watershed changed into urban area, having a significant impact on flood inundation. the kelani river watershed includes 23% of the total urban area of the colombo district. similarly, the entire area of land-use transformation covered 37.7% of the area within the watershed region of the colombo district. eventually, this research identified the significant impact of colombo district floods in may 2016 on land-use changes. keywords-ndvi; ndbi; ndwi; landsat satellite images; land-use classification; urban floods i. introduction floods in urban arrears constitute a severe risk and have become more frequent and severe along with rapid urban development. watersheds in and around urban areas become more developed and more hydrologically active, changing the flood volume, runoff components, and the origin of stream flow [1]. therefore, the transformation of the watersheds to urban or sub-urban land-uses creates frequent flooding more than before. hydrologic modeling with the assessment of the effects of land-use and land cover changes on water resources is becoming one of the leading research topics [2]. the influence of land-use on storm runoff generation is highly complicated. for instance, croplands and urban lands yield more flood volumes, higher peak discharges, and shorter flow travel times than grassland or woodland [3]. floods are identified as the most frequent natural disasters. authors in [4] reported that in between 1994-2004, asia accounted for onethird of 1,562 flood disasters where nearly 60,000 persons were killed. flood occurrences in sri lanka are occurring mainly because of excessive rainfall during the monsoon periods [5]. occasionally, the depressions over the bay of bengal bring in heavy rains causing floods [6]. according to the records, major floods have occurred in sri-lanka in 1913, 1940, 1947, 1957, 1967, 1968, 1978, 1989, 1992, 2003, 2016, and 2017 with severe losses of human lives, public and private property [7]. world meteorological organization has categorized floods as local/urban, riverine, coastal, and flash floods. out of those, riverine and urban floods are the most common types in sri lankan urban and suburban areas. in june 1989, the western part of sri lanka experienced a natural disaster bordering three major river basins, namely kelani ganga, kalu ganga, and gin ganga. high-intensity rainfall caused several earth slips in the upper catchment while lower catchment suffered from flash floods. it was reported that 300 lives were lost, 15,000 houses were damaged, and 225,000 people became homeless during this disaster. the total damage was estimated at rs.120 million [8]. the recent flood in may 2016 is the most severe hydrological hazard after the major flood in june 1989. rainfalls caused the onset of two floods that were similar in the magnitude (an 8-day total was around 560mm) but different in the spatial and temporal distribution pattern. in june 1989, the rainfall stations of norton, maussakele and laxapana experienced total rainfalls of 1222.9mm, 1694.2mm, and 1184.8mm respectively, while the highest rainfall in may 2016 was recorded as 898.8mm at deraniyagala (metrological department data). however, the damage of the 2016 flood was significantly higher due to the longer durations of inundations, and the irregular developments that took place in the floodplain [9]. united nations reported that these were the worst floods reported in 25 years, 5,037 houses have been estimated as destroyed, while 104 people are known to have died. sri lanka experienced the highest economic loss in south asia with total damages exceeding rs 82,650 million due to the floods in may 2016 [10]. author in [9] reported that frequent flooding in the colombo region was corresponding author: t. l. dammalage engineering, technology & applied science research vol. 9, no. 2, 2019, 3887-3891 3888 www.etasr.com dammalage & jayasinghe: land-use change and its impact on urban flooding: a case study … caused by the shrinking of open spaces, illegal constructions, and lack of suitable waste disposal means. therefore, the primary goal of this study is to identify the impacts of land-use change on colombo district on may 2016 flood by comparing with the flood and land-use situation in 1989. ii. study area colombo district is the largest and the most industrialized city in sri lanka. it is famous for its commercial, cultural, scientific, and technological activities. it lies between the parallels of 6°52"n and meridians of 80°01"e and has an area of 699km 2 the city of colombo is the capital of sri lanka, whereas sri jayewardenepura is the administrative capital. iii. methodology satellite remote sensing image processing algorithms and geographical information system (gis) approaches were implemented to accomplish the main objective of the study, i.e. to analyze the land-use change and its impact on the colombo district flood on may 2016. according to the workflow summaries in figure 1, a land-use change analysis was conducted to determine how much alterations have taken place in the colombo district between 1989 and 2016. further, a comparison between flood and rainfall of 2016 and 1989 was conducted to correlate the two flood conditions. the impact of land-use change on may 2016 flood was analyzed based on the findings of these investigations. a. study of land-use change three indexes were used to identify the land-use classes of kelani river watershed: normalized difference vegetation index (ndvi), normalized difference built-up index (ndbi), and normalized difference water index (ndwi). ndvi values were calculated based on (1) varying from -1 to +1. non-vegetated areas are generally indicated with negative values and vegetated areas with positive values [11]. ndvi � �nir � red /�nir � red (1) ndvi images were used to identify the green areas, agriculture, and low settlement areas for classification. ndbi values were calculated based on (2) and were used to extract built-up features. the ndbi indices range from -1 to 1, and the positive values correspond to built-up areas [12]. ndbi � �swir � nir /�swir � nir (2) ndwi images were derived from (3). the ndwi index was used to identify the water features of the classified image. positive data values are typically open-water areas while negative values are typically non-water features [13]. ndwi � �nir � green /�nir � green (3) land use classes obtained from the above indexes were used for classification. five supervised classification methods were tested, and out of that, svm (support vector machine) classifier showed higher accuracy. svm, also known as support vector networks, supervise learning models with associated learning algorithms that analyze the data used for classification and regression analysis [14]. medium resolution satellite images (landsat) of 1989 and 2016 were used to detect the land-use change by applying post-classification change detection techniques. the post-classification comparison approach involves independent production and subsequent comparison of spectral classification for the same area at two different time periods [15]. thematic change of the two classified images was analyzed by a facility given in envi software which determines the land-use differences between 1989 and 2016. land use change map was then created in arcgis environment using the resultant image. fig. 1. methodology flow chart. b. comparison of flood and rainfall between 1989 and 2016 watershed is an area of land “that drains all the streams and rainfall to a common outlet such as the outflow of a reservoir, mouth of a bay, or any point along a stream channel” [6]. therefore, the changes in the watershed of an area play a leading role in its flood situation. hence, the thiessen polygon for the kelani river watershed area was generated to calculate the total rainfall caught by the watershed during both floods in 1989 and 2016. accordingly, the kelani river watershed was created based on a 90m resolution srtm-dem in arcgis environment. eleven rainfall stations distributed along the watershed area were used to create the thiessen polygon, and the total rainfall impact on both floods was compared at each station. flood maps published by the irrigation department were used to extract the flooded area of colombo district, and the flooded area and rainfall were comparatively analyzed for 1989 and 2016 floods. c. the impact of land-use change on flood inundation the land-use change in the watershed area is expected to have a high impact on flood inundation and was the main focus of the current study. the colombo district was divided into three sections for detailed investigation of the flooded area and the corresponding land-use change of kelani river watershed. iv. results and discussion a. land-use classification and change detection the resulted overall accuracy and kappa coefficient for each classification technique are listed in table i for the tested 5 techniques of landsat satellite image classification. engineering, technology & applied science research vol. 9, no. 2, 2019, 3887-3891 3889 www.etasr.com dammalage & jayasinghe: land-use change and its impact on urban flooding: a case study … table i. classification techniques comparison classification method accuracy kappa coefficient 1989 2016 1989 2016 maximum likelihood classification 92.05 92.05 0.89 0.83 minimum distance classification 71.97 71.97 0.61 0.76 parallelepiped classification 57.41 57.41 0.47 0.51 mahalanobis distance classification 76.41 76.41 0.67 0.68 svm classification 99.04 99.04 0.96 0.98 out of the tested 5 methods, svm produced maximum overall accuracy of 99.04 for both years, and kappa coefficient of 0.96 and 0.98 for 1989 and 2016 respectively. therefore, the svm linear kernel type is used to classify the urban and suburban compositions of the colombo district. accordingly, classified maps for the 5 land-use classes of colombo district were prepared as presented in figure 2. fig. 2. land-use map of 1989 and 2016, derived using landsat images. according to the land-use classification, the distribution statistics of urban, agriculture, water, green, and low settlement areas of colombo district for both 1989 and 2016 were calculated. urban areas increased from 10% to 36% from 1989 to 2016, which was observed to be the most significant landuse change in the area. on the other hand, agricultural areas declined from 41% to 39%, green areas reduced from 11% to 7%, and the low settlement areas decreased by 20%. the urban expansion was highly significant in the western part of the district, compressing the greenery towards the center and the eastern parts of the district. post-classification change detection method was applied due to its direct information retrieval nature of land-use changes. the analysis helped to understand and identify the land-use classes which were turned into urban or built-up environments or other land classes. table ii lists a total of 11 class transformation statistics from 1989 to 2016. table ii. change detection statistics land-use classes area (km 2 ) total area percentage (%) 1989 2016 low settlement urban 124.7 18.2 agriculture urban 48.2 7.0 green urban 6.7 1.0 water urban 2.9 0.4 no change 295.8 43.3 low settlement other 88.5 12.9 agriculture other 64.8 9.5 green other 32.0 4.7 water other 1.9 0.3 urban other 1.9 0.3 cloud other 16.0 2.4 accordingly, a total of 182.5km 2 (26.6% of the total area in the district) changed to urban from 1989 to 2016.for the tested 5 land classes, 43.3% of land-use remained without any change from 1989 to 2016. besides, 27.7% of total area in the colombo district changed from the 5 tested land classes to other land-uses including only 0.3% of urban to other land-use. the highest change was observed for low settlement, which was 31.1% for both urban and other land-uses. the change detection revealed that a total of 113km 2 and 38.7km 2 of agriculture and green areas changed to other land-uses. however, 4.8km 2 in the district changed from water to both urban and other land class. this is about 0.7% of the total area in the district. these change statistics were further analyzed by comparing the rainfall and flooded areas of 1989 and 2016. b. rainfall comparison kelani river flows through the colombo district, and the sea outlet is located near the city. therefore, the overflow of the river has impacts as flooding in the colombo city. therefore, a comparative study of the rainfall effect on the kelani river watershed is essential to analyze the flooding scenarios of 1989 and 2016 of the district. a total of maximum 8-day rainfall during the floodings of 1989 and 2016 for the 11 rainfall stations distributed along the watershed is used, and the values are presented in table iii. table iii. rainfall data of the selected stations station 8 days rainfall (mm) 1989 2016 nagalagam street 558.9 557.5 angoda 152.4 370.6 hanwella 332.6 364.8 labugama 386.5 499.4 glen course 669.1 620.7 norwood 352.5 680.1 norton 1222.8 304.3 laxapana 1693.9 599.5 maliboda 754.0 561.8 maussakele 693.7 430.8 udugoda 714.2 876.3 three stations, i.e., nagalagam street, angoda, and hanwella are in the colombo district, and the rainfall recorded in these stations would have a direct influence on the flash flood in the district. however, during the two flood conditions in colombo, the rainfall at these stations was not significantly different except from angoda. however, a significant difference of rainfall in higher catchment areas, especially norton and laxapana were recorded in 1989. this reveals that the rainfall conditions on creating flash a flood scenario in colombo urban area is similar in 1989 and 2006. flooding in colombo district is not only affected by rainfall in the district area itself but also by the rainfall in the kelani river watershed. therefore, a “thiessen polygon” is generated using all 11 rainfall stations data. accordingly, the total rainfall of the watershed for both years is calculated by multiplying the rainfall data of the stations with the corresponding area relevant to that station. the resulted total rainfall was 1.424x10 9 m 3 and 1.350x10 9 m 3 for 1989 and 2006 respectively. in 1989, the total rainfall, which could make riverine floods in colombo is significantly higher than in 2006. therefore, the flood area in engineering, technology & applied science research vol. 9, no. 2, 2019, 3887-3891 3890 www.etasr.com dammalage & jayasinghe: land-use change and its impact on urban flooding: a case study … 1989 should be higher than 2006 if rainfall was the only considered factor. the flooded area was calculated based on the digitized flood maps obtained by the irrigation department. accordingly, in 1989 it was 63km 2 , and in 2016 it was 74.7km 2 . this indicates that the rainfall is not the only reason for the major flood in 2016. hence, the impact of land-use change on the flood of may 2016 is being investigated. c. impact of land-use change on the flood in may 2016 the change of land-use due to urbanization in colombo district, especially within the kelani river, poses a severe impact on flooding. a watershed is an area of land that feeds all the water running under it and draining it off into a water body. further analysis was conducted to understand the landuse change of the area of colombo district within the kelani river watershed. figure 3 presents the resulted land-use change map. red color indicates land-use area which is transformed to urban, and ‘no change’ denotes the area which is not affected by any change. the map outlines that most western parts and the eastern part of kelani river watershed have not undergone much land-use change compared to the middle section. the most significant land-use change was in the colombo city and its suburban areas situated in the western part of the kelani river watershed. fig. 3. land-use change map of kelani river watershed from 1989 to 2016 by 2016 the area of the urban land class of the district was 182.5km 2 , and 57.16% of it was concentrated within the area of kelani river watershed. the significant increases in built-up areas in the watershed created increased inundation. the area that has transformed to an urban land class in the watershed is 104.3km 2 and covers 23% of the total watershed area in the colombo district. agriculture and green areas that were transformed into other classes may also have influenced flood inundation since hydrological and erosion characteristics alter with the changes of land-use. thus, the total area of land-use transformation in the watershed is 171km 2 which covers 37.7% of the watershed area in the district. as discussed above, during the floods in 1989 and 2016 the total rainfall was 1.424x10 9 m 3 and 1.350x10 9 m 3 , and the total flood area was 63.0km 2 and 74.7km 2 respectively. increased land-use change in the watershed contributed to the higher floods in may 2016, even though the recorded rainfall was comparatively lower than that of 1989. for a detailed analysis of these changes, the watershed and corresponding flooded area are divided into three sections as illustrated in figure 4. section 1 includes the heart of colombo district including colombo city, section 2 consists of the suburbs and most rapidly urbanizing areas, and section 3 is the tail of colombo district with a comparatively lower urbanization rate than section 2. fig. 4. sections of kelani river watershed according to the flood extent and the land-use change of section 1, the total flooded area in 2016 was only 3.3km 2 greater than the 19.4km 2 flood area of 1989. the area marked with pink color (figure 4) indicates the flooded area only in 1989. this is the parliament area along with the diyawanna oya in section 1. comparative analysis of the two classified images of 1989 and 2016 revealed that this is due to the newlybuilt channel or stream in the year 2016 by land reclamation and development cooperation to prevent flood inundation of the parliament area. further, it was linked with a special flood mitigation project of development of water retention lakes done in 2012. however, the significant land-use change of 44.2km 2 in section 1 has created an additional flooded area in 2016, which is shown in blue color in figure 5. in addition, water level data from the irrigation department indicate 2.79m in 1989 and 2.33m in 2016 at the nagalagam street station. although the water level of the station in 1989 is higher than in 2016, the recorded flooded area of 2016 is larger than the area in 1989. hence, it is evident that the changes in land-use have an apparent influence on flooding. the suburban area of the colombo city is included in section 2, and a 68.2km 2 of land in this area were transformed into urban and other areas. this was the highest of the 3 sections. also, this is the section which had the highest flood inundation area increase of 8.1km 2 . this section of the colombo district was urbanized recently. these statistics confirm the relationship between flood area enhancement and land-use change due to urbanization. this section includes kaduwela and part of the homagama ds divisions where massive suburbanisation is underway. according to the analysis, 47.3km 2 area was urbanized while green and agriculture areas reduced by 20.9km 2 from 1989 to 2016. one of the best examples is the southern expressway opened in 2011 which runs through kaduwela area. due to the excessive demand for land for residential, commercial, and infrastructure use, the remaining agricultural, green, and low settlement lands are the only alternatives in both homagama and kaduwela areas. during the floods of 1989 and 2016, the water level reading at kaduwela station was 6.24m and 6.17m engineering, technology & applied science research vol. 9, no. 2, 2019, 3887-3891 3891 www.etasr.com dammalage & jayasinghe: land-use change and its impact on urban flooding: a case study … msl respectively. even though the recorded water level was lower in 2016, the flood inundation area changed from 17.5km 2 to 25.6km 2 from 1989 to 2016. therefore, the land-use change has a clear and significant impact on flood inundation. section 3 represents seethawaka, padukka, and part of the homagama ds divisions where only 0.3km 2 increase of flood area was observed from 1989 to 2016. the land-use change of this section of colombo district is different from the other two sections. the transformation of other land-use into urban was only 20km 2 , which is the minimum of the tested three sections of the district. however, the green and agriculture area that changed into other land-use increased significantly from 1989 to 2016. it was 1km 2 , 20.9km 2 , and 45km 2 for sections 1, 2, and 3 respectively. an increased flooded area was shown near the hanwella station in 2016 and a decrease in the proximity of the glen course station. this might be due to the significantly higher discharge of 16252.6m 3 s -1 observed at glen course station in 1989, which is almost the double of the recorded 8118.9m 3 s -1 in 2016. however, at hanwella station it was the opposite: only 5865m 3 s -1 in 1989 and 8394.8m 3 s -1 in 2016. this confirms that not only the changing into urban areas effected the inundation, but also the change into other land-uses. the reason for less flood inundation in this section as compared to the other two sections was the existence of considerably higher extent of green and agriculture lands, because agriculture and green lands absorb water, making fewer run-offs created by undisturbed grassland and woodland areas. v. conclusion colombo city and the metropolitan area are imperative to the economic growth of the country, and thus, rapid urbanization, as the city is currently facing, is not a strange experience. besides, the kelani river watershed of the district has a significant land-use change during 1989 to 2016. the higher percentage of the land-use change incident in the kelani river watershed was identified as the major impact on colombo district flood on may 2016. a sharp increase of built-up areas combined with the reduction of agriculture and green areas are the main causes of increased incidence of flood inundation. out of the entire urban area of the colombo district, 23% of it is within the kelani river watershed. similarly, the total area of land-use transformation that influences the flood inundation covered an area of 37.7% within the watershed area of the colombo district. eventually, this research identified the significant impact of land-use changes on colombo district flood in may 2016. references [1] c. g. berry, “multi-temporal land cover classification of the little wasillta watershed using the kauth-thomas greenness vegetation index”, phd thesis, oklahoma state university, 1998 [2] y. qin, h. liling, y. min, l. yi, “researches on the land-use change detection of mine area based on tm/etm images international archives of the photogrammetry”, remote sensing and spatial information sciences, vol. xl-7/w1, pp. 91-101, 2013 [3] s. idris, l. m. dharmasiri, “urban development and the increasing trend of flood risk in gombe metropolis, nigeria”, international journal of science and research, vol. 5, no. 8, pp. 500-504, 2015 [4] b. corley, s. bartelt-hunt, e. rogan, d. coulter, j. sparks, l. baccaglini, m. howell, s. liaquat, r. commack, a. s. kolok, “using watershed boundaries to map adverse health outcomes: examples from nebraska, usa”, environmental health insights, vol. 12, pp. 1-10, 2018 [5] r. g ariyawansa, “demographic characteristics and planning challenges: the case of colombo city”, sri lanka journal of population studies, vol. 11, pp. 93-106, 2009 [6] n. alahacoon, k. matheswaran, p. pani, g. amarnath, “a decadal historical satellite data and rainfall trend analysis (2001–2016) for flood hazard mapping in sri lanka”, remote sensing, vol. 10, no. 3, pp. 448-465, 2018 [7] n. m. s. i. arambepola, g. iglesias, “effective strategies for urban flood risk management”, expert group meeting on innovative strategies towards flood resilient cities in asia-pacific, bangkok, thailand, 2017 [8] m. a. c. niroshani, “adaptation to extreme floods under future climate change scenarios for colombo, sri lanka. isap-international forum for sustainable asia and the pacific”, international forum for sustainable asia and the pacific, pacifico yokohama, japan, july 24-25, 2012 [9] p. hettiarachchi, “hydrological report on kelani river flood in may 2016”, hydrological annual, irrigation department, 2016 [10] w. silva, “may floods – the highest economic loss in south asia”, the sunday leader, available at: http://www.thesundayleader.lk/2016/ 09/18/may-floods-the-highest-economic-loss-in-south-asia/, 2016 [11] n. pettorelli, j. o. vik, a. mysterud, j. m. gaillard, c. j. tucker, n. c. stenseth, “using the satellite-derived ndvi to assess ecological responses to environmental change”, trends in ecology & evolution, vol. 20, no. 9, pp. 503-510, 2005 [12] y. zha, j. gao, s. ni, “use of normalized difference built-up index in automatically mapping urban areas from tm imagery”, international journal of remote sensing, vol. 24, no. 3, pp. 583-585, 2003 [13] s. k. mcfeeters, “the use of the normalized difference water index (ndwi) in the delineation of open water features”, international journal of remote sensing, vol. 17, no. 7, pp. 1425-1432, 1996 [14] c. c. chang, c. j. lin, “libsvm: a library for support vector machines”, acm transactions on intelligent systems and technology, vol. 2, no. 3, articleno. 27, 2001 [15] x. yang, c. p. lo, “using a time series of satellite imagery to detect land use and land cover changes in the atlanta, georgia metropolitan area”, international journal of remote sensing, vol. 23, no. 9, pp. 1775-1798, 2002 engineering, technology & applied science research vol. 8, no. 4, 2018, 3260-3264 3260 www.etasr.com akhund et al.: risk attributes, influencing the time and cost overrun in joint venture construction … risk attributes, influencing the time and cost overrun in joint venture construction projects of pakistan muhammad akram akhund department of civil engineering isra university hyderabad, pakistan akhund42@gmail.com ali raza khoso department of civil engineering mehran university of engineering & technology, jamshoro, pakistan aliraza.khoso@faculty.muet.edu.pk ashfaque ahmed pathan department of civil engineering mehran university of engineering & technology, jamshoro, pakistan ashfaquepathan2003@gmail.com hafiz usama imad department of civil engineering isra university hyderabad, pakistan usama.imad@isra.edu.pk fida siddiqui department of civil engineering mehran university of engineering & technology jamshoro, pakistan fidasiddiqui2@gmail.com abstract—business collaborations formed by construction contractors to enhance their abilities and effectiveness in large construction projects are known as construction joint ventures (cjvs). it is widely used as a way of merging assets, capitals, funds, resources and expertise of different organizations. it helps business to grow faster, increase efficiency and generate greater profits without borrowing money. though it is useful and beneficent for the vendors, it may contain several types of risk. it is both beneficial and stimulating due to differing technical skills, economic and political atmospheres, and cultural and legal backgrounds. recent development and modernization in pakistan have led it towards a new construction phase, which involves national and multinational joint venture projects. global and local cjvs have become gradually prevalent to produce mega construction projects. current research aims to investigate and to identify the communal, ecological, political, legal, economic and other external risks associated with cjv projects in pakistan. the study was carried out by literature review and a few national and international guidelines. interviews were conducted with relevant professionals, experts, and owners of the organizations working on cjv projects. data was collected in the form of a questionnaire from relevant professionals. the descriptive analysis was performed through spss using average index (a.i) technique. this study is helpful for the government of pakistan, public and private construction firms working under jv to reduce the emerging risks of construction projects. keywords-joint venture; risk; construction; pakistan i. introduction developing countries usually prioritize to invest in construction and infrastructure development [1]. infrastructure development and mega construction projects need huge financial and human resources. building complex engineering projects requires prominent level of expertise, sophisticated machinery and well managed teams with sufficient monetary resources, which is often beyond the scope of a single contractor. a joint venture (jv) is a commercial alliance between two or more separate entities that offers a unique opportunity to combine the distinctive competencies, increase the capacity of advantages and the complementary resources to participating firms [2]. construction joint ventures (cjvs) have nowadays become more popular because of their importance as a strategic alternative in global competition and its vast advantages to the concern entities. in cjvs, two or more independent partners ally to achieve their goals [3]. all the terms and conditions of the alliance are pre-agreed between the parties, something that stipulates the conditions of partnership including work distribution, profit sharing, resource contribution and conflict resolution [4, 5]. for multinational and international projects, the alliance is made between local and foreign teams. this type of association is termed as international construction joint venture (icjv) [6]. it is extensively used to improve the capacities of partners and competitiveness of the cjv [7]. due to the change in the globalized and modern demands of construction many studies carried out regarding construction procurement methods have revealed that there needs to be a change of culture and attitude in the construction industry, moving away from traditional adversarial relationships to cooperative and collaborative relationships [8-11]. there are increasing concerns on improving the industry by alternative procurement methods, involving a movement away from traditional procurement systems [12]. jvs possess a lot of advantages, but they also offer a high level of uncertainty. de hig gen to th loc of bu ult fam [17 lac var con attr ide risk dif to lik inc am pro an [22 and env adv off con wo for con the and int ma sur thr ass res ado wit con qu qu th col un lite res occ con con wh th engineerin www.etasr espite the ben gh, higher tha nerally face g the complexi he variation in cal markets ha an icjv pro siness corpora timately have miliarized a 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a p p methodology and then disc ature review and to suppo onnaire comp hat participated participated in categories of collected from estionnaire an the probabilit or each risk. with experts factors were ndustry of pak nstruction ind h v butes, influenci rate is e ijvs ky due s [14]. n and mance ational which v has usual arriers, slative imatic es that d early r these it has ording is the gative as an verity, ards of ors in to jvs he risk lot of , so it ational ope of paid to ational hlights ational ed on e local nnaire alyzed risks proper y was cussed was ort the mprised d in it. n data f risks m the nd the ty of after and added kistan. dustry stak coll (sta fact con disc con met firs the pak jv and mea the imp was con cate hav vary wer com cov had fig pos resp tho wer pak info vol. 8, no. 4, 20 ing the time an keholders i.e. lecting the d atistical packag tors were sele nstruction ind cussed with th nstruction indu thodology. iii. the designed st part consist e second part kistan. respon firms which a d estimated co aning that the duration and pacts on durat s distributed nstruction fie egories, name ve a better und rying between re considered mmercial, pub vered for data d a wide rang gure 2, shows sitions are ass pondents at ke se on lower re used for i kistan constru ormation is sum 018, 3260-3264 nd cost overru owners, con data, the anal ges for social ected as main dustry of pak he relevant ex ustry. figure fig. 1. rese data colle d questionnaire ted of particip t contained th ndents were req are affecting t ost. the ranki mentioned fa d cost while 5 tion and cost o among 180 ld, mainly f ely clients, co derstanding of 5 million to d. all major blic amenities collection. re ge of experie s the responde ociated with t ey positions is positions. av identifying th uction indust mmarized in t fig. 2. posit n in joint vent nsultants, and lysis was do sciences). the causes of a ch kistan. these xperts in the c 1 shows the earch methodolog ection and an e was divided pant’s demogr he risk factors quested to rank the constructio ing scale rang actor is not sig means that t of the project. 0 professional from three m onsultants, and the issue, diff 3500 million r fields incl s, roads, and espondents inc ence, so the d ents’ range a their experien more worthy verage index t he risk factor try. [24-25]. table i. tion of responden 3261 ture constructi contractors. one through s en the most cr hanged order i causes were context of pak e detailed res gy nalysis into two parts raphic informa s in cjv firm k the risk facto on project dur ges from 1 to gnificantly affe the factor has . the question ls related to major stakeh d constructors ferent scale pro n pakistani ru luding reside d bridges etc luded in the su data were reli and position. ce. the opinio than the opini technique met rs in jv firm all demogr ts ion … after spss ritical in the then kistan earch s. the ation. ms of ors in ration o 5, 1 ecting high nnaire o the holder s. to ojects upees, ential, c. are urvey iable. their on of ion of thods ms of aphic engineering, technology & applied science research vol. 8, no. 4, 2018, 3260-3264 3262 www.etasr.com akhund et al.: risk attributes, influencing the time and cost overrun in joint venture construction … table i. demographic results frequency percentage (%) cumulative % organization type client 68 44.44 44.44 consultant 33 21.58 66.02 constructor 52 33.98 100.00 project size <20million 21 13.73 13.73 20–40million 46 30.06 43.79 50–150million 14 9.15 52.94 150–400million 12 7.84 60.78 400–800million 16 10.46 71.24 800–1800million 23 15.03 86.27 1800–3000million 10 6.53 92.80 >3000million 11 7.20 100.00 project type commercial 46 30.06 30.06 roads 30 19.60 49.66 residential 32 20.91 70.57 social amenities 21 13.72 84.27 bridges 24 15.73 100.00 working experience 0–5 years 62 40.52 40.52 6–10 years 23 15.03 55.55 11–15 years 33 21.57 77.12 16–20 years 13 8.50 85.62 more than 20 years 22 14.38 100.00 iv. results and discussion all influencing factors are categorized into six categories namely cultural, contractual, financial, managerial, legal and political. the average score of liker’s scale by each type of respondent is listed in tables ii-vii. average index and standard deviation of factors are also listed in front of each factor. it is observed that unidentified organizational goals are the highest ranked factor among the factors in the contractual category. the average score from clients is higher than the one of the other two types of respondents. it is clearly evidenced that regarding the opinion of clients this factor is responsible for the time and cost overrun of the project. for mega projects, where the team is large and consists of members having diverse cultural and lingual background, language barriers is of the highest concern and ranked 1st in the category of cultural attributes. the pattern of work and its difference with the difference in the background of the worker is the least concerning issue in this category. similarly, price escalation, distrust, lack of laws and political influence are top-ranking attributes in each category respectively. difference of opinion exists in clients, consultants and constructors, but on average the above-mentioned factors are identified as the most risky and most critical in their respective category. overall sudden policy change and other political issues are highlighted as crucial features which can cause delays and can raise other complexities in jv projects. v. conclusion jvs in construction are growing day by day due to their increased work capacity, so this study just highlights the points related to project risks. in future, the jvs would be more embraced in the field of construction. further work can be done in order to resolve the issues regarding the pakistan law, because new laws must be introduced for jvs. risks of being delayed and being the defaulter of the project become more crucial in jv projects. among 48 critical attributes responsible for causing undesired interruptions in the project, the most crucial factors are a change in policies, distrust between parties and non-enforcement of laws. irrespective of position and designation in the project, clients, consultants, and constructors have identified these factors in independent surveys. if jv projects in pakistan have to be strengthened, policymakers should mitigate these obstacles and remedy the risk causing factors. vi. suggestions and recommendations some suggestions by experts to alleviate risk in the jv projects follow:  organizational goals should be defined clearly with the scope of the project and in compliance with 3c principles.  10% of workers on site and at each specific task should have sufficient qualification and the multilingual background to overcome communication concerns.  sufficient inflation cost should be included at the time of bidding.  consultants should be bound to weigh the project activities as per legislation.  there should be weekly meetings among clients, consultants, and constructors. table ii. contractual risk attributes of cjv projects in pakistan 1 undefined organizational goals 4.78 4 3.63 4.13 0.48 2 violation of contract by project partner 3.16 4.41 4.73 4.1 0.68 3 lack of organizational commitment 3.8 4.01 4.29 4.03 0.20 5 contractual terms not clear (from partner side) 3.98 3.95 3.89 3.94 0.04 6 ownership problem in project partner 3.33 3.78 4.54 3.88 0.50 7 undefined degree of agreement 4.13 3.94 3.36 3.81 0.33 8 less availability of information to partners 3.98 3.88 3.03 3.63 0.43 9 quality assurance 2.89 3.19 4.42 3.5 0.66 10 payment distribution 3.19 2.89 4.06 3.38 0.50 11 profit/loss distribution among partners 2.94 3.18 3.81 3.31 0.37 12 variation in payments 2.77 3.47 3.69 3.31 0.39 13 risk allocation 3.16 2.93 3.48 3.19 0.23 14 extension in time 4.12 2.1 3.35 3.19 0.83 engineering, technology & applied science research vol. 8, no. 4, 2018, 3260-3264 3263 www.etasr.com akhund et al.: risk attributes, influencing the time and cost overrun in joint venture construction … table iii. cultural risk attributes of cjv projects in pakistan 1 language differences between parties 4.57 4.09 4.33 4.33 0.20 2 lack of communication between parties 4.13 4.18 4.56 4.29 0.19 3 cultural differences between partners 3.98 4.35 4.06 4.13 0.16 4 social differences between partners 2.76 3.33 3.9 3.33 0.47 5 unfamiliarity with local conditions 3.02 2.98 3.3 3.1 0.14 6 clashes of parties while doing same work with different patterns 2.24 2.1 2.65 2.33 0.23 table iv. financial risk attributes of cjv projects in pakistan 1 labor and material price escalation 4.11 4.02 4.56 4.23 0.24 2 budget over run 3.9 3.31 3.8 3.67 0.26 3 loss due to variation of currency exchange rate 4.1 3.13 3.78 3.67 0.40 4 loss due to variation in interest rate 3.74 3.07 3.69 3.5 0.30 5 financial management issues with firm itself 3.08 2.93 3.98 3.33 0.46 6 change in market conditions 3.13 3.36 3.5 3.33 0.15 7 bankruptcy of project partner 2.91 3.11 3.55 3.19 0.27 8 poor consideration for inflation 2.85 3.36 3.21 3.14 0.21 9 low credibility of shareholders and lenders 1.97 2.89 4.14 3 0.89 table v. managerial risk attributes of cjv projects in pakistan 1 distrust between partner employees 4.92 4.87 4.91 4.9 0.02 2 incompetence of project management team 4.88 4.37 4.91 4.72 0.25 3 disagreement between both parties about staff allocation 4.09 4.04 3.87 4 0.09 4 improper project planning and budgeting 4.11 3.31 4.07 3.83 0.37 5 improper project feasibility study 4.28 3.17 3.62 3.69 0.46 6 inadequate choice of partner 3.24 4.09 3.68 3.67 0.35 7 poor relations with government departments 3.28 3.34 3.37 3.33 0.04 8 relationship with government 4.01 2.42 3.56 3.33 0.67 9 relationship with power groups 2.88 3.12 3.99 3.33 0.48 10 inadequate project organization structure 4.02 2.68 3.29 3.33 0.55 11 involvement of more decision makers 3.11 2.86 3.54 3.17 0.28 12 poor relations and disputes with partners 3.33 2.27 3.4 3 0.52 table vi. legal risk attributes of cjv projects in pakistan 1 lack of enforcement of legal laws 4.52 4.47 4.9 4.63 0.19 2 no joint ventures laws 4.12 3.88 4.24 4.08 0.15 3 difference of laws between partners 3.13 3.33 4.16 3.54 0.45 table vii. policy and political risk attributes of cjv projects in pakistan 1 issues due to change in policies and political changes 4.98 4.96 4.94 4.96 0.02 2 lack of project performance due to the involvement of political stable partner 4.79 4.56 4.18 4.51 0.25 3 corruption and bribery 3.82 4.08 4.19 4.03 0.16 4 bureaucracy issues 3.42 2.88 3.69 3.33 0.34 references [1] a. prasitsom, v. likhitruangsilp, “effects of organization structures on international construction joint venture risks”, international journal of construction engineering and management, vol. 4, no. 4, pp. 128-148, 2015 [2] x. zhao, b. g. hwang, g. s. yu, “identifying the critical risk in underground rail international construction joint ventures: case study of singapore”, international journal of project management, vol. 31, no. 4, pp. 554-556, 2013 [3] y. t. roma, s. o. ogunlana, “chapter 3 culture and workplace behavior: a case study of joint venture construction projects in thailand”, in: joint ventures in construction, , pp. 30-40, thomas telford publishing, 2009 [4] v. bagdonavicius, j. kruopis, m. s. nikulin, non-parametric tests for complete data, john wiley & sons, 2011 [5] a. prasitsom, a life cycle risk management and prediction system for construction joint ventures, phd thesis, chulalongkorn university, bangkok, thailand, 2014 [6] a. gale, j. luo, “factors affecting construction joint ventures in china”, international journal of project management, vol. 22, no. 1, pp. 33-42, 2004 [7] k. kobayashi, joint ventures in construction, thomas telford publishing, 2009 [8] c. black, a. akintoye, e. fitzgerald, “an analysis of success factors and benefits of partnering in construction”, international journal of project management, vol. 18, no. 6, pp. 423-434, 2000 [9] f. y. k. cheung, “relationship management in the australian construction industry-a grounded study”, symposium on cib w92: sustainability and value through construction procurement, salford, uk, pp. 92-101, november 29-december 2, 2006 [10] j. egan, rethinking construction, construction task force report for the department of the environment, transport and the regions, hmso, 1998 [11] a. ashworth, s. perera, contractual procedures in the construction industry, routledge, 2018 [12] k. m. hmieleski, r. a. baron, “entrepreneurs' optimism and new venture performance: a social cognitive perspective”, academy of management journal, vol. 52, no. 3, pp. 473-488, 2009 engineering, technology & applied science research vol. 8, no. 4, 2018, 3260-3264 3264 www.etasr.com akhund et al.: risk attributes, influencing the time and cost overrun in joint venture construction … [13] b. g. hwang, x. zhao, e. w. y. chin, “international construction joint ventures between singapore and developing countries: risk assessment and allocation preferences”, engineering, construction and architectural management, vol. 24, no. 2, pp. 209-228, 2017 [14] b. g. hwang, x. zhao, l. p. toh, “risk management in small construction projects in singapore: status, barriers, and impact”, 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wiley & sons, 2003 [20] a. ardeshir, m. amiri, y. ghasemi, m. errington, “risk assessment of construction projects for water conveyance tunnels using fuzzy fault tree analysis”, international journal of civil engineering, vol. 12, no. 4, pp. 396-412, 2014 [21] f. nasirzadeh, h. mazandaranizadeh, m. rouhparvar, “quantitative risk allocation in construction projects using cooperative-bargaining game theory”, international journal of civil engineering, vol. 14, no. 3, pp. 161-170, 2016 [22] g. zhang, p. x. zou, “fuzzy analytical hierarchy process risk assessment approach for joint venture construction projects in china”, journal of construction engineering and management, vol. 133, no. 10, pp. 771-779, 2007 [23] m. abdelgawad, a. r. fayek, “risk management in the construction industry using combined fuzzy fmea and fuzzy ahp”, journal of construction engineering and management, vol. 136, no. 9, pp. 1028-1036, 2010 [24] f. siddiqui, a. r. khoso, a. a. pathan, m .a. akhund, s. h. khahro, “concept and willingness to adopt zero energy buildings”, indian journal of science and technology, vol. 11, no. 5, 2018 [25] m. a. akhund, a. r. khoso, u. memon, s. h. khahro, “time overrun in construction projects of developing countries”, imperial journal of interdisciplinary research, vol. 3, no. 5, pp. 124-129, 2017 microsoft word etasr_7-1_1334-1337.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1334-1337 1334 www.etasr.com do mobaraki et al.: a survey of health, safety and environment (hse) management and safety climate... a survey of health, safety and environment (hse) management and safety climate in construction sites ali mobaraki department of environment management (hse), faculty of engineering and technology, islamic azad university, zahedan branch, zahedan, iran ramazan mirzaei department of environmental and occupational health engineering, school of health, mashhad university of medical sciences, mashhad, iran hossein ansari health promotion research center, department of epidemiology and biostatistics, zahedan university of medical sciences, zahedan, iran abstract—the principles of health, safety and environment (hse) in different development activities, including construction, are constantly gaining in significance. this study aims to evaluate the condition of hse management and safety climate in construction sites. in this descriptive-analytic study, 111 male employees are randomly selected. to determine hse condition and management and safety climate condition, the nosacq questionnaire was used. the collected data are analyzed using spss. based on data analysis a significant relationship between the mean scores of safety climate, job groups and hse management system with job groups, education and experience (p<0.05) was found. the study results show that hse management and safety climate in sites are relatively acceptable, that the perception of safety had no special association with age, work experience, education and that the creation of a safety climate depends on the people high in the hierarchy. keywords-health; safety and environment (hse); safety climate; construction site. i. introduction with the development of technology and wide application of different harmful materials, the role of human resources in industrial environment is much emphasized [1]. this however has been a result of heavy human, economic and environmental damage [2]. besides the obvious benefits, industrialization may also lead to an increase of accidents and this is especially true in developing countries where for preventive safety principles, working hour standards and using suitable individual protection are often neglected in an attempt to further increase productivity [3]. iran has also followed the development and industrialization route [4, 5] and thus the significance of safety culture has increased. various definitions of safety culture have been presented (e.g. [3, 6]). as safety is a sub-set of safety culture, we investigate the perceptions of employees about the work place, interest of management to safety and measurements of safety and participation in risk control [7]. one of the present issues regarding human resources is the high rate of financial and life damage. work accidents are one of the most important health, social and economic factors in industrial and developing communities and are the third mortality cause in the world [8-10]. in recent decades, organizations have attempted to reduce these life and financial damages and these efforts mostly focus on safety culture, a term firstly employed with hse management in organizations, companies and big industries [10]. however, reaching an satisfying level of safety has not been easy [11, 12]. many researchers and scientists have defined safety climate and extended its concept. in [7], authors considered safety climate as an individual feature of combination of two factors of management commitment to safety and participation of employees in safety. in [11], safety climate is considered as the temporary image of culture reflecting in common perception of employees of organization at a certain time. regarding the construction industry, despite its progress and the use of new construction methods, health, safety and environment (hse) has not progressed considerably [11]. the managers of construction projects often view safety as a cost in contradiction with production and ignore it [13]. the evaluation of the relationship between safety climate factors and risk perception of risky situations among construction workers showed that there was a positive relationship between the attitude of workers in the construction sector and their perception of risk and safety rules [14, 15]. the mental climate has been shown to have a direct and indirect relationship with safety behavior, safety motivation and safety knowledge [16]. work place stress (working hours, job requirements, job control and ambiguity in job) has been associated directly with accidents and quasi-accidents [17-18]. in a study used to evaluate safety performance of employees in road construction companies, contradictory results were found as there was no relationship between safety climate and measured safety behavior [19]. this study attempts to evaluate the condition of health, safety and environment (hse) and safety climate and their relationship with age, work experience and marital status in construction sites and present some recommendations to improve each factor and reduce risks. ii. research methodology to determine safety, health and safety climate, the selected population in the study is personnel working in active construction sites of tehran city as managers, engineers, engineering, technology & applied science research vol. 7, no. 1, 2017, 1334-1337 1335 www.etasr.com do mobaraki et al.: a survey of health, safety and environment (hse) management and safety climate... technicians, workers. the samples are selected randomly among the workers of the construction sites of district 22 of tehran city. the nordic occupational safety climate questionnaire (nosacq) was employed. this questionnaire consists of 50 items by which people attitude to safety at work place is determined. these questions cover 7 dimensions (factors) of safety climate as ability and priority of safety management, power of safety management, justice of safety management, commitment of workers to safety, lack of risk acceptance and priority of safety by workers, communication of co-workers with each other and learning safety issues and trust of workers to the effectiveness of safety systems. the respondents to questionnaire stated their agreement to the questions in four-item likert scale. value 1 indicates “total disagree” and 4 as “totally agree”. the measure of data collection of safety management, health and environment was designed using hse questionnaire. this questionnaire consists of 63 items at five-item likert scale. value 1 indicates totally disagree and 5 indicates totally agree. seven parts of this questionnaire include leadership and commitment, strategy, organizing, risk assessment, planning, execution and monitoring and audit. the reliability of hse management questionnaire is secured by cronbach’s alpha coefficient. total cronbach’s alpha of questionnaire is 0.96 and shows good reliability of the hse management system questionnaire. the questionnaire results were processed in spss. descriptive statistics as central measures and dispersion, tables and statistical charts were used. for data analysis (to determine the relationship between quantitative and qualitative variables) chi-square test and one-way variance analysis (anova) test are used. iii. results in this study, 111 questionnaires were answered. in the present study, 100% of people are men, 44.1% have an education level above diploma and 72.1% are married. detailed results are shown in tables i-iv. anova test and lsd showed significant relationship between the groups {work experience less than 5 years} and {work experience more than 10 years}, with p-value=0.006 and the groups {work experience less than 5 years} and {work experience 5-10 years} with p-value as 0.04. however, between the scores of safety, health and environment and the number of hours worked per month, marital status, having a second job, working shift the incident was not statistically significant (p>0.05). based on data study of the mean and standard deviation of table ii, safety climate among construction workers was achieved in tables iii-iv. the one-way analysis of variance (anova) and lsd test showed that there was significant correlation between the safety condition scores, with groups of employees (p=0.02) and the second jobs of employees (p=0.04),. however, the mean total score of safety condition, education, age, work experience, hours worked per month, marital status, having a second job, an accident and work time staff was not statistically significant (p>0.05). pearson correlation coefficient between the average scores of hse with safety condition in employees of construction sites of tehran city was 0.335, (p=0.001). table i. frequency of quantitative and qualitative variables in workers of construction sites of tehran variable mean standard deviation minimum maximum age (year) 34.17 8.75 19 65 work experience (year) 7.64 6.42 1 30 work hour per month 214.65 51.56 80 400 mean safety climate 3.29 0.24 2.62 3.96 hse mean 3.64 0.51 2.52 5 total scores of safety climate 164.25 12.38 131 198 hse sum of squares 228.09 33.25 125 315 table ii. safety, health and environment sectors health, safety and environment management sectors mean standard deviation leadership 3.78 0.64 strategy 3.77 0.64 organization 3.64 0.58 risk management 3.8 0.71 planning 3.37 0.64 execution and monitoring 3.56 0.61 audit 3.67 0.55 table iii. safety climate dimensions of employees of construction sites of tehran city safety climate dimensions number of items mean standard deviation ability and priority of management 9 3.28 0.34 power of safety management 7 3.30 0.4 justice of safety management 6 3.26 0.35 commitment of workers to safety issues 6 3.14 0.37 lack of acceptance of risk and priority to safety by workers 7 3.56 0.5 communication of co-workers with each other and learning safety issues 8 2.89 0.27 trust of workers to effectiveness of safety systems 7 3.65 0.44 table iv. safety climate score in job groups of employees dimensions of safety climate engineering administrative servant, operator, technician ability and priority of management 3.22 3.27 3.32 power of safety management 3.15 3.35 3.38 justice of safety management 3.17 3.17 3.33 commitment of workers to safety issues 3.10 3.01 3.2 lack of acceptance of risk and priority of safety by workers 3.51 3.44 3.63 relationship of coworkers with each other and learning safety issues 2.84 2.93 2.91 trust of workers to effectiveness of safety systems 3.57 3.73 3.67 engineering, technology & applied science research vol. 7, no. 1, 2017, 1334-1337 1336 www.etasr.com do mobaraki et al.: a survey of health, safety and environment (hse) management and safety climate... iv. discussion in the present study, total people are men. the age mean of participants is 34.17 and people have relatively low work experience. 44.1% of people have an education level above diploma and 72.1% are married. the dimension of workers trust to effectiveness of safety systems had the highest score. thus, to improve safety system of site, improvement of safety systems and periodical evaluation are necessary. the results showed that the perception of personnel of safety of environment had no special association with age, work experience, education. the score of safety climate among age, work experience and education showed no significant difference. the study in [20] showed that education and work experience had no significant relationship with any of the dimensions of safety climate. the study showed that of safety climate dimensions, safety management power had significant relationship with job group and education and it showed that engineers with higher education based on different managerial positions and safety management had high power in creating safety climate. another dimension of safety climate is nonacceptance of risk and prioritization of safety as associated with age and work experience and based on the young participants and no high experience, safety issue is not considered well and prioritization of safety issues is considered not vital. the mean score of safety climate among job groups had significant difference. in [22], it was stated that planners of safety climate should consider that in some cases, improvement of safety climate in a special group needs intervention in another group. thus, in interventions on groups with low score of safety climate, considering important factors of such phenomenon should be considered. the results showed that the mean score of hse management was 3.65 and it is ranging from “no idea” to “agree”. the element of risk assessment of hse management system had the highest mean 3.8 which means that assessment of hse is performed regarding activity, services and development of useful measurements to reduce risk and events at work place. then leadership and strategy and audit with 3.78±0.7, 3.77±0.64, and 3.67±0.55 had the highest mean of hse management system elements. among hse management systems and age, marital status, there was no significant relationship found. hse management system had significant relationship between job groups, education and work experienced. v. conclusion this study focus on the aspects of health, safety and environment (hse) management and safety climate in construction sites. 111 male workers from construction companies active in tehran, iran were randomly selected to answer the nosacq questionnaire. the collected data are analyzed using spss. results are shown in detailed and further discussed. the study results show that hse management and safety climate in sites are relatively acceptable. further, the results showed that the safety perception of personnel had no special association with age, work experience, education. however, it was shown that the creation of a safety climate heavily depends on the people high in the hierarchy (engineers with higher education based on different managerial positions). references [1] m. macik-frey, j. c. quick, d. l. nelson, “advances in occupational health: from a stressful beginningto a positive future”, journal of management. ember 1, vol. 33, no. 6, pp. 809-840, 2007 [2] k. christion, “trends in accidents, disasters and risk sources in europe. journal of loss prevention in the process industries”, vol. 33, no. 1, pp. 7-17, 1999 [3] l. m. goldenhar, l. j. williams, n. g. swanson, “modelling relationships between job stressors and injury and near-miss outcomes for 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glascoe, c. martínez valdés, e. arellano garcía, “occupational risks and health: perceptions of indigenous female agricultural workers in northwestern mexico”, sci elo public health, vol. 9, no. 1, pp. 247-256, 2013 [10] c. a. ericson. a. clifton, “event tree analysis. hazard analysis techniques for system safety”, vol. 4, no. 1, pp. 223-234, 2005 [11] a. cheyne, s. cox, a. oliver, j. m. tomás, “modelling safety climate in the prediction of levels of safety activity”, work & stress, vol. 9, no. 3, pp. 255-271, 1998 [12] b. fernández-muñiz, j. m. montes-peón, c. j. vázquez-ordás, “safety management system: development and validation of a multidimensional scale”, journal of loss prevention in the process industries, vol. 20, no. 1, pp. 52–68, 2007 [13] j. turner, excavation systems planning, design, and safety. mcgraw hill professional, 2008. [14] s. mortazavi, h. asilian, m. ostakhan, “the relationship between safety climate factors and workers behavior working in potentially dangerous situations in height among construction workers”, iran occupational health, vol. 8, no. 1, pp. 51-60, 2011 [15] a. i. glendon, d. k. litherland, “safety climate factors, group differences and safety behaviour in road construction”, safety science, vol. 39, no. 3, pp. 157-188, 2001 [16] o, siu, d. r. phillips, t. w. leung, “safety climate and safety performance among construction workers in hong kong: the role of psychological strains as mediators”, accident analysis and prevention, vol. 36, no. 3, pp. 359-366, 2004 [17] m. findley, s. smith, j. gorski, m. o'neil, “safety climate differences among job positions in a nuclear decommissioning and demolition industry: employees' self-reported safety attitudes and perceptions”, safety science, vol. 45, no. 8, pp. 875-89, 2007 [18] s. azir, safety behavior in the malaysian petrochemical industry, phd thesis, universiti utara malaysia, 2010 [19] m. n. vinodkumar, m. bhasi, “safety management practices and safety behavior: assessing the mediating role of safety knowledge and motivation”, accident analysis and prevention, vol. 42, no. 1, pp. 2082-2093, 2010 engineering, technology & applied science research vol. 7, no. 1, 2017, 1334-1337 1337 www.etasr.com do mobaraki et al.: a survey of health, safety and environment (hse) management and safety climate... [20] j. adl, m. jahangiri, m. rismanchian, h. marioryad, a. karimi, m. r. ghaderi, “evaluation of safety climate in a steel-manufacturing plant. journal of school of public health and institute of public health research, vol. 9, no. 1, pp. 23-34, 2011 [21] m. findley, s. m. smith, t. kress, g. petty, k. enoch, “safety program elements in construction: which ones best prevent injuries and control related workers' compensation costs?”, professionals safety, vol. 49, no. 2, pp. 14–21, 2004 microsoft word 35-3352_s_etasr_v10_n3_pp5796-5802 engineering, technology & applied science research vol. 10, no. 3, 2020, 5796-5802 5796 www.etasr.com biberci & celik: dynamic modeling and simulation of a pem fuel cell (pemfc) during an ... dynamic modeling and simulation of a pem fuel cell (pemfc) during an automotive vehicle’s driving cycle mehmet ali biberci vocational school cankiri karatekin university cankiri, turkey m.alibiberci@karatekin.edu.tr mustafa bahattin celik faculty of engineering karabuk university karabuk, turkey mcelik@karabuk.edu.tr abstract—polymer electrolyte membrane fuel cells (pemfcs) are the most appropriate type of fuel cells for application in vehicles due to their low operational temperature and high-power density. in this paper, a zero-dimensional, steady state thermodynamic modeling for an automotive 90kw pemfc system has been built up in order to investigate the effects of operating parameters such as vehicle acceleration and operating pressure on the size of the system elements, heat and water system constitution, fuel consumption, and efficiency. a dynamic model was formed for the fuel cell power system in matlab. power output and power losses of the system were investigated at 3atm operation pressures. keywords-dynamic modeling; fuel cell system; pem; thermal analysis;matlab i. introduction pem (proton exchange membrane or polymer electrolyte membrane) fuel cells are considered candidates for automotive applications due to their low operational temperature and highpower density. even so, fuel cell systems face substantial barriers to commercialization due to their high price and short lifespan. pemfc durability is mainly compromised by the degradation of the membrane electrode assembly during longterm operation [1]. generally, the fuel of a pemfc is pure hydrogen. the basic electrochemical reaction cell consists of one anode and one cathode electrode where on their surface electrochemical reactions occur and conduct ions from the one to the other, and the external circuit between electrodes for current flow [2-4]. many research attempts for automotive applications focus on pemfcs due to their capacity of higher power density and faster start-up compared to other fuel cell types. water and heat management for pemfcs is one of the key technical issues that must be resolved in order to be used in automotive applications. proper water and thermal management is significant for optimizing the carrying out of a fuel cell stack. water and heat management in automotive fuel cell systems can be classified and analyzed at cell and system levels. the cell level fields investigate the effects of parameters such as pressure, rate of flow, temperature, humidity, and membrane heaviness on the performance of the fuel cell stack [5-9]. authors in [10] studied the pem fuel cell engine system which is used in transportation applications. this system consists of a compressor, humidifiers, pressure regulator, hydrogen storage tank, cooling system, heat exchanger and the fuel cell stack. the system performance was looked into by parametric studies of energy, exergy and work output values by changing operating conditions and system parameters. the results demonstrated that the system efficiency increases with the increase of temperature and pressure and that an increase in relative humidity of the system has a positive effect on the efficiency and power product values. in addition, the results showed that the efficiency increases with the decrease of membrane thickness, anode stoichiometry, and cathode stoichiometry. the model was developed in [11] in order to study the water and thermal management and balance of the fuel cell stack. the results showed that the decrease of air humidity increases the ionic resistance eventually and it causes a significant drop in the voltage. in addition, the air stoichiometric ratio must be greater than one to remove the produced water from the stack in order to prevent the cathode from flooding. furthermore, the operating temperature of the cell significantly affects the fuel cell performance. higher temperature increases the need for humification and water production cannot meet the corresponding demand. this work presents a general zero-dimensional pem fuel cell model for a vehicle application. the model was developed in order to study water and thermal management and the balance of the fuel cell stack of an automotive pem fuel cell system with a maximum power of 90kw. a model of the fuel cell power system was created to power a true automotive vehicle (weight=1880kg, air friction coefficient=0.65, front surface area=2.68, rolling resistance coefficient=0.012). dynamic modeling was carried out with all its components (auxiliary units, fuel cell, and aerodynamic structure of the vehicle). the analysis of the system was run on the matlab program and during the ece-15 driving cycle, the power required for the vehicle, the fuel cell current value, the fuel cell water and heat management, the required power amounts for auxiliary equipment, and the amount of hydrogen consumed etc. values were studied. corresponding author: mehmet ali biberci engineering, technology & applied science research vol. 10, no. 3, 2020, 5796-5802 5797 www.etasr.com biberci & celik: dynamic modeling and simulation of a pem fuel cell (pemfc) during an ... ii. system description a. overall pemfc system model in this chapter, a common zero-dimensional pemfc example is presented for automotive applications. the first step in the evolution of such a model is the innovation of the system layout including the fuel cell stack and auxiliary equipment. as explained below, as the operational pressure is increased the layout from the system changes due to the cooling system requirements of the compressed air. in this paper, system simulations were carried out at operating pressure of 3atm. figure 1 demonstrates the formal diagram of an automotive pemfc system proposed for 3atm operating pressure. this diagram is similar to the existing commercial pemfc automotive systems accessible in the market and consists of components necessary to add reactants, remove the generated heat, and manage the produced water. the fuel cell stack demands three flow systems that interact with each other: air supply system, hydrogen supply system, and water and thermal management systems. fig. 1. schematic view of a fuel cell power system the air provision system consists of a compressor, an air cooler (intercooler), a humidifier, and a heater. air supply at high pressure is provided by the compressor. the compression process causes a temperature rise in the supplied air. to lower the temperature of the entering air to the humidifier, the air transits from an intercooler. the air is moisturized by the humidifier before ingoing to the cathode side of the fuel cell stack to ensure a suitable hydration level of the membrane. the unused air leaving the stack can be heated by the heater and used to increase the hydrogen temperature through a heat exchanger in the hydrogen supply line. the hydrogen supply system consists of a hydrogen tank, a pressure regulator valve, a heat exchanger, a humidifier, and the unused hydrogen recycle line. the hydrogen is stored in a tank at high pressure. the pressure regulator valve is used to adjust the flow rate of the hydrogen. the heat exchanger helps warming the incoming hydrogen which is then fed to the humidifier. like air flow, hydrogen is moisturized by the humidifier prior to entering the anode side of the fuel cell stack. the recycling hydrogen system is used to accumulate the hydrogen that has not reacted in the stack and sends it back to mix with the entering anode flow after the humidifier. the water system and thermal management system consist of a radiator, a fan, pumps, and a water storage tank. the chief function of the radiator is to maintain the fuel cell stack at its operation temperature by dissipating heat to the coolant. the fan increases the potency of heat convection at lower vehicle speeds. the pumps recirculate the water and the coolant through the system and the water storage tank is used to reconstruct and save the generated water. the generated water is used to moisturize the reactant gases through the humidifier [2, 12]. b. vehicle force and torque parameters in general, the force and torque parameters of the ev (electrical vehicle) powertrain are borrowed from the wellestablished definitions used in icev (internal combustion engine vehicle) for powertrain. figure 2 shows the force components that the vehicle powertrain must provide for the vehicle to travel, which include the road load fload and the acceleration force faccel. this road load consists of three main components as described by (1): the aerodynamic drag force fdrag, the rolling resistance force fresist, and the climbing force fclimb [11]. fig. 2. vehicle powertrain force ����� � ���� ���� �� ��� �� (1) c. driving cycle in the european union, a vehicle is commonly tested using two kinds of driving cycles. the first one is the urban driving cycle known as the ece-15 which was introduced in 1999. it was devised to represent city driving conditions in paris or rome. as shown in figure 3, it simulates an urban trip of 4052m at an average speed of 18.7km/h and maximum speed of 50km/h. it is particularly useful for testing the urban driving performance of an ev [13]. fig. 3. ece-15 driving cycle d. simulation software a zero-dimensional and steady state pemfc model is developed and presented. this example was enforced in matlab which contains several types of heat exchangers, compressors, pumps, mixtures, separators, etc. that have been developed over the years. the users can add new elements to the library components, which is the case for the auxiliary equipment in this study. the equations used for modeling were either analytical or semi-empirical as engineering, technology & applied science research vol. 10, no. 3, 2020, 5796-5802 5798 www.etasr.com biberci & celik: dynamic modeling and simulation of a pem fuel cell (pemfc) during an ... described below. the accuracy of the theoretical results was validated by stack data and the ece-15 driving cycle produced by this model matches very well the corresponding stack data. the presented model can be used for all types of pemfc stacks by replacing the adjusting parameters explained in detail below [2, 14]. iii. pem model and basic equations to establish a general, zero-dimensional model of pemfc, a semi-empirical solution was applied for reproducing the experimental polarization curve of the fuel cell. the average cell voltage can be analytically expressed by the following expression: ����� � � − ���� − ���� � − ����� (2) where e is the open circuit voltage. ���� , ���� �, ����� are activation, ohmic, and concentration losses respectively. there are numerous equations proposed in the literature for predicting the aforementioned terms which are elaborated below [14]: ������ � �����.����� (3) where the stack voltage ������ is simply the cell voltage multiplied by the ����� number of cells [15], �� � �. �����.����� � �.������ (4) where �� is the power output of the fuel cell stack (w) [15]. a. activation loss the activation losses in fuel cell voltage can be calculated using the well-known butlervolmer equation [16]: ���� � � �!"#$%&' ()� �*����� � �!+",-$%&' ()� �*������� (5) where � is the current density, �. is the reaction exchange current density, n is the number of exchange protons per mole of reactant, f is faraday’s constant, and α is the charge transfer coefficient [17]. b. ohmic loss the total fuel cell ohmic losses can be written as [16]: ���� � � � / σ1 � �/ 23 4567�������8�� 3 4 567������� 3 4 567�����9 (6) where l is the thickness of the electrolyte layer, and σ is the conductivity, and a is the active area of the fuel cell. c. concentration loss the concentration losses can be calculated using (7) [17]: ����� � � �' ln < <=> (7) where �4 the limiting current density, which is the point where the current density becomes large and the reactant concentration falls to zero, so the fuel cell will not be able to produce a higher current density than its limiting current density. d. fuel cell thermal efficiency generally, the thermodynamic fuel cell efficiency is the relation between the electrical power produced and the total rate of fuel energy entering the fuel cell: ����� � ?.@+&aa.�+&aa�b cd,e#.ff@cd (8) e. hydration management of the membrane the water content in the polymer electrolyte plays a significant role in pemfc stack lifetime and the ionic resistance of the membrane. low humidification in the membrane causes a rapid increase of the ionic resistance and high humidification will cause too much liquid water to overflow into the reactant channels and fill the pores in the electrodes. in order to have high ionic conductivity in the membrane, it should be fully hydrated. hydration can be achieved by the humidification of gases, or by designing the fuel cell to allow the product water to hydrate the membrane [14, 18]. in this study both methods are applied. generally, diffusion of water in the polymer electrolyte is expressed in two terms: one is the electro osmotic drag phenomenon, which is representative of the number of water molecules associated with protons (h + ) while crossing the membrane. but when the water is generated in the cathode side this phenomenon is the other way round. water concentration gradient makes the water move from the cathode to the anode side, a phenomenon called water back diffusion [14]. water molar flux due to electroosmotic drag can be defined as: g��� b � hifdj .��. .6+&aa.�+&aa ' (9) where �� is the electro-osmotic drag coefficient in water molecules per proton. the electro-osmotic drag coefficient �� can be calculated from the membrane water content k� [2]: �� � 0.0029k�o 0.05 k� − 3.4.10=>t (10) the water content in the membrane, k� is defined as the ratio of water molecules to the number of sulfonic acid groups within the ionomer and is calculated from the water activity uv [2]: k� � 0.043 17.8 uv − 39.85uvo 36.uvz (11) water activity is defined as: uv � 8[\\]",( ) = rh (12) where p is the pressure of the anode or the cathode. the amount of water concentration across the membrane that is caused by back diffusion is assumed equal to 0.9 of water transfer by electro osmotic drag. f. mass balance mass balance equations are applied for each composition in the reactants separately. water mass balance can be written as: gb fd`abc,d� b gb fd`e&# −fgb ��� ./����.hfd` .10=zg � gb fd`aec,�h� (13) gb fd`ij&a,d� b gb fd`e&# − fgb ��� ./����. hfd`.10=zg engineering, technology & applied science research vol. 10, no. 3, 2020, 5796-5802 5799 www.etasr.com biberci & celik: dynamic modeling and simulation of a pem fuel cell (pemfc) during an ... � gb fd`ij&a,�h� (14) these equations represent the water mass balance on the cathode and anode sides respectively which can be liquid or vapor. acell is the active cell area and 2h o m represents the water molecular weight. gb fd` is the water mass flow rate and subscripts in, out and gen represent inlet, outlet and generated respectively [14]. g. heat transfer balance the energy released in the electrochemical reaction must be taken away from the stack in order to maintain the desired constant temperature. the thermodynamic steady state energy balance of the fuel cell is given as: ∑l , � � ∑l ,�h� i�� l���� l��m (15) where l , � is the rate of energy entering with the reactant gases, l ,�h� is the rate of energy leaving with the unused reactant gases, wel is the electrical power generated, l���� ̇is the rate of heat carried from the fuel cell to the coolant, and ̇l��m the rate of heat dissipated by the exposed stack surface to the environment. h. total system power and system thermal efficiency the efficiency of the fuel cell power system is the relation between the net electric power output and the total rate of fuel energy entering the fuel cell: ��8� � \e# \$j, (16) where the output electrical energy ��h� is: ��h� � �� � ��hn (17) � � � gfd, �.oo�fd (18) where the gross output power �� was calculated (4) and the parasitic loads by all the auxiliary system equipment ��hn is the sum of all parasitic loads, commonly: ��hn � ����p �ph�p �q�� ������� (19) where ����p is the power of the compressor, �ph�p is the power of hydrogen recirculation and cooling circuit pumps, �q�� is the power of cooling circuit fan, and ������� is the electrical power of the heater. iv. results and discussion the simulation model was implemented using the above formulation systems within the ece-15 driving cycle. in this section, an automotive pemfc system is simulated in matlab. the described aboce thermodynamic models for compressors, pumps, humidifiers, and heat exchangers are required to operate the pemfc system under the required conditions. figure 4 shows the required power output as a function of vehicle speed for 3atm working pressure. as can be seen, the change in speed values directly affects the required output power. figure 5 shows the dissipation of auxiliary power as a function of vehicle speed at 3atm operating pressure. the auxiliary components include a compressor, an electric heater, a coolant pump, an injection pump, a radiator fan, and an intercooler fan. in this way, it is possible to see that the electrical power consummation by the fan grows faster than the electrical power consumed by the other auxiliary components. it is further noted that the compressed air will need to be cooled before it enters the humidifier using the intercooler. it is stated that the temperature of the air coming to the humidifier drops in an air cooler. fig. 4. power output as a function of vehicle speed fig. 5. auxiliary equipment power requirement as a function of vehicle speed fig. 6. vehicle speed vs cumulative hydrogen fuel consumption the electrical energy generated by a fuel cell is directly proportional to the amount of fuel consumed, because each mole of fuel provides specific electron moles. figure 6 shows the consumption of hydrogen as a function of vehicle speed. when the vehicle speed increases, more energy is needed, so more fuel is consumed. figure 7 shows the efficiency value as a function of vehicle speed indicating fuel cell thermal engineering, technology & applied science research vol. 10, no. 3, 2020, 5796-5802 5800 www.etasr.com biberci & celik: dynamic modeling and simulation of a pem fuel cell (pemfc) during an ... efficiency and system thermal efficiency. the fuel cell thermal efficiency curves present the relationship between the generated electricity and the maximum usable operation for the vehicle drive. the curves of the fuel cell thermal efficiency are decreased when thespeed of the vehicle increases due to the increase in the fuel consumption of the vehicle. it is also seen that an increase in working pressure increases the fuel thermal efficiency due to an increase in power output at high pressure from the fuel cell. in the system thermal efficiency curves, it can be seen that the increase in vehicle speed from 0km/h to 50km/h reduces significantly the system’s thermal efficiency. this is mainly due to the electrical energy consumed by the compressor and other auxiliary components. by entering the appropriate operating parameters, the model produced in this study can perform system optimization and select the best operating condition for the system. fig. 7. system and thermal efficiency throughout the driving cycle figure 8 shows the water balance of the pemfc system, the amount of water entering the system in the ambient air, and the amount of water injected into the humidified gases. fig. 8. water management values during ece-15 driving cycle the water produced in the cathode due to the electrochemical reaction must be greater than or equal to the amount of water exiting the system. the water in the exhaust may be liquid or gaseous. the condition of the water depends on the operating conditions of the fuel cell (air stoichiometric ratio and operating pressure and temperature). liquid water is easily separated from the gas flow in the condenser. figure 8 shows the amount of water (liquid and vapor) at the outlet of the stack required for humidification as a function of vehicle speed for 3atm pressure. as a result it is concluded that the average value of water at the exit of the fuel cell stack consists of 60% liquid water and 40% water vapors. at high pressures, the vapor pressure of the water is high, so the boiling point of the water increases. therefore, the amount of liquid water increases with increasing working pressure. it also appears that the liquid water at the exit of the fuel cell is larger than the injected water and is sufficient to moisten the reagents before entering the fuel cell without using a condenser. thermal management is one of the most important features in the development of the fuel cell stack system because heat is produced in large quantities by an electrochemical reaction in a pem fuel cell. if the rate of generated heat is too high, the fuel cell overheats and may cause membrane dehydration. low temperatures reduce the speed of the chemical reaction, reduce efficiency, and can cause water condensation and electrodes to overflow. as noted above, proper thermal management is required to maintain the required performance and durability temperatures of the cells and to prevent the stack from heating up the fuel cell stack system. the heat balance of the fuel cell stack as a function of vehicle speed is shown in figure 9. the sum of the generated electrical energy, the rate of energy released by unused reactive gases and the rate of heat removal from the fuel cell should be equal to the rate of energy entering with the reactant gases. fig. 9. energy quantities during the ece-15 driving cycle the size of the heat exchanger (radiator) depends on the amount of heat to be extracted from the fuel cell stack and is influenced by the operating pressure. figure 10 shows that as the speed of the required heat exchanger area increases the power from the fuel cell stack increases and the effective area of the radiator is also increased in order to spread the waste heat to the environment. this means that the size of the radiator is the main factor affecting system thermal performance. figure 11 shows the effect of vehicle speed on the refrigerant flow. it is seen that if the vehicle speed increases, the required power from the fuel cell stack increases and the refrigerant flow rate must be increased to match the increased waste heat output. fossil fuels used in vehicles cause environmental pollution in many ways. at the same time, the fossil fuel reserves are engineering, technology & applied science research vol. 10, no. 3, 2020, 5796-5802 5801 www.etasr.com biberci & celik: dynamic modeling and simulation of a pem fuel cell (pemfc) during an ... running out [19]. in some studies, alcohol based bio fuels are used as alternative fuels reducing the environmental pollution to some, but not sufficient extent [20, 21]. since fuel cell vehicles use hydrogen as fuel, they emit only water vapors to the environment and cause zero environmental pollution. for this reason and because of the abundance of hydrogen in nature, they are seen as the technology of the future. some researchers have simulated only one fuel cell power system, [10, 22] while others have examined the power requirements of the auxiliary equipment (pump, compressor, fan, etc.) required to operate, fuel and power management, and a power generating engine of the fuel cell [10, 12, 14]. however, a fuel cell engine system for a passenger vehicle has not been studied within a driving cycle. in this paper, a detailed study was conducted by examining and simulating the fuel cell system and thermal efficiency, the power requirements of the auxiliary equipment, the engine cooling system, and the radiator area required for this system. real vehicle features were used. for this reason, this study eliminates the large experimental costs of the companies developing fuel cell vehicles and makes the development studies safer. from these perspectives, this paper paves the way on future studies that can be conducted in different real vehicles with different driving cycles. fig. 10. required radiator area according to speed values during the ece15 drive cycle fig. 11. cumulative coolant flow ratio during the ece-15 drive cycle v. conclusions this paper has attempted to integrate component models for an automotive pemfc system that includes fuel cell stack, air supply system, hydrogen supply system, and thermal circuit. increase of the operating pressure of the system increases the fuel cell thermal efficiency but has no effect on the system thermal efficiency. the system pressure has a significant positive impact on the power density and water balance characteristics of the fuel cell. increase of the vehicle speed has a negative impact on the system efficiency and stack efficiency. auxiliary components are necessary to operate the pemfc system but decrease its efficiency. water management is one of the problems in systems that operate at low pressure because they need a large amount of water for the humidification process and the sizes of the humidifier and the condenser increase. this parasitic power requirement increases due to the fan condenser. several improvements can be made to the pemfc system model. the existing model can investigate the effects of stack geometry and fuel cell material properties on the system’s performance. an improved model can be used to simulate the vehicle performance in different realistic driving cycles. acknowledgement the authors will like to thank the tubitak (scientific and technological research council of turkey) for supporting this research. references [1] y. wang, k. s. chen, j. mishler, s. c. cho, x. c. adroher, “a review of polymer electrolyte membrane fuel cells: technology, applications, and needs on fundamental research”, applied energy, vol. 88, no. 4, pp. 981-1007, 2011 [2] a. akroot, modelling of thermal and water management in automotive polymer electrolyte membrane fuel cell systems, hacettepe university, 2014 [3] j. chakravorty, j. saraswat, v. bhatia, “modeling a distributed power flow 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with multiple attribute decision analysis problems under risk and uncertainty md. zahid hasan department of computer science and engineering jahangirnagar university dhaka, bangladesh zahid.cse@diu.edu.bd mohammad shorif uddin department of computer science and engineering jahangirnagar university dhaka, bangladesh shorifuddin@gmail.com shakhawat hossain department of computer science and engineering international islamic university chittagong chattogram, bangladesh shakhawat.cse@outlook.com mohammad shahidul islam institute of information technology jahangirnagar university dhaka, bangladesh suva93@gmail.com abstract—this paper represents a generic feature extraction approach to handle multiple attribute decision analysis problems. for that purpose, available decision support frameworks are carefully studied and the basic types of attributes involved in the decision problems are identified. based on this analysis, a generic decision support scheme is proposed that can deal with all sorts of attributes in order to deduce the optimal solution for any decision problem. the proposed framework is capable of handling multiple attributes throughout the process of providing a flawless solution for the decision problem under both risk and uncertainty. this paper provides detailed information about the sources of uncertainty in the decision-making process and proposes a sophisticated approach for capturing all sorts of uncertainties. in the proposed approach, a cross assessment of every attribute against the corresponding attribute of the other alternatives is conducted to extract the significant features of an attribute. the relative importance of every attribute is considered as a supporting knowledge representation parameter in order to optimize the attribute-assessment process. the final decision is made based on the numerical scores seized by the alternatives. the paper also represents a numerical study to demonstrate the potential applications of the proposed methodology. keywords-multi-attribute; decision problem; feature extraction; knowledge base; uncertainty; risk; cross evaluation i. introduction dealing with multiple attributes for making the right decision is a key challenge for a business or an organization. both businesses and organizations need to analyze a huge number of data for solving decision problems during planning and operation. in the real world, a different type of attributes may need to be considered for making the right decision [1-6]. so, there is an extended demand for decision support frameworks for handling multiple attribute decision analysis problems [7-10]. though numerical attributes are comparatively easier to calculate during decision making, qualitative attributes require a different evaluation process. on the other hand, mapping boolean data with qualitative or quantitative data is not always easy. besides, existing frameworks can make decisions fall into either under uncertainty or at a risk which leads a decision maker to implement two separate decision support systems. moreover, considering all the attributes with equal importance may lead to an inappropriate decision. so, it is important to allocate weights to the decision attributes in order to find the best possible solution for a decision problem. unfortunately, there is no suitable decision framework that can evaluate qualitative, quantitative and boolean data with respect to their weights for finding the ultimate alternative for supporting a decision. it is significant for decision makers to comprehend the idea of uncertainty so as to improve their competence to take decisions and to make a balance of risk related to their decisions. in addition, their comprehension of the idea of uncertainty could bring down inconsistency rates and give an increasingly powerful and respectable illustration of the impact of uncertainty on the performance of a decision making model. in real-life decision-making problems, most people are just able to deal with a few attributes at the same time [11], but they can hardly handle multiple attributes in an effective way to find out a reasonable ultimate outcome. to solve the decision problem under uncertainty, the bayes-minimax algorithm was proposed as a decision support framework for the first time in 1951 [12]. unfortunately, this decision support framework could only handle a single attribute decision problem which raised an extended demand for a robust decision framework that would be capable of solving multi-attribute decision problems. in 1954, authors in [13] proposed the simple additive weighting method (sawm) for dealing with corresponding author: md. zahid hasan engineering, technology & applied science research vol. 10, no. 3, 2020, 5775-5783 5776 www.etasr.com hasan et al.: a generic feature extraction approach for dealing with multiple attribute decision … multiple attribute decision analysis (mada) problems [13] which could calculate the impact of a set of actions for a certain operation along with its importance for optimizing the decision-making process. in 1980, an analytical hierarchy process (ahp) was proposed [14-15] for handling different mada problems in various fields of engineering and management. it was stated that if the ratio of inconsistency is greater than 10%, the performance of decision-making process can be degraded [16]. ahp addresses complex decisions by making a pair wise comparison among the decision criteria. in addition, it captures both subjective and objective attributes of a decision problem. authors in [2] suggested the technique for order of preference by similarity to ideal solution (topsis) as the most suitable model for capturing multiple attributes in order to choose the most feasible alternative [14, 15, 17, 18]. although the topsis method provides an optimal solution for mada problem, many decision experts oppose using topsis because of its time complexity. on the other hand, a grey-based decision-making approach was used in [19] for the supplier selection problem. in the grey-based approach, the weights and attributes of all the alternatives are first defined by some linguistic variables and then some grey possibility degrees are used to rank the order of all the alternatives. at the same time, some researchers proposed the fuzzy set theory to solve multiple attribute decision problems [20-25] under uncertainty. some researchers suggested the dempster-shafer (d-s) theory [26] instead of using the traditional probability theory to improve the process of capturing uncertainty while developing the decision support systems. recently, the evidential reasoning (er) approach was proposed [27-28] for solving different decision problems. er approach is able of handling both qualitative and quantitative attributes to order the rank of a group of alternatives. authors in [6, 28, 29] used the evidential reasoning (er) approach for solving multiple attribute assessment problems. finally, rulebased inference methodology using evidential reasoning (rimer) [30] was proposed in 2006. the rimer approach is a hybrid mathematical framework, constructed with the combination of bayesian probability theory, dempster–shafer (d–s) theory of evidence, and fuzzy set theory for demonstrating and reasoning with uncertain knowledge. though many researchers appreciate rimer approach for solving decision problems under uncertainty, some find it complex and not a flawless process for capturing uncertainty. at the same time, some researchers concentrated on establishing decision support frameworks under risk. risk can be defined as uncertainties which can emerge a positive or negative impact on the solution of a decision problem. finding the optimal solution for a decision problem without the proper management of its risk is almost impossible. therefore, decision scientists have been trying to establish a suitable methodology in order to manage the risks involved in multiattribute decision analysis problems. for the first time, in 1944, von neumann & morgenstern proposed expected utility theory (eut) for solving decision-making problems under risk [31]. but, allais had a doubt about the accuracy of the expected utility theory and he mentioned how eut is unable to capture human problems [32]. to solve allais paradoxes and enhance decision support frameworks, a number of decision theories were proposed. authors in [33] proposed the prospect theory for helping people make the optimal decision by evaluating some potential values rather than depending on the final outcome. later in 1992, cumulative prospect theory was proposed as the improved version of the prospect theory, for handling both risky and uncertain information in order to acquire the optimal decision solution [34]. in 1974, the configural weight models [35] were suggested for solving decision problems with risky prospects. the authors implemented the transfer of attention exchange (tax) model to predict results from some previously estimated data [36]. in 2001, authors in [37] proposed minimax algorithm to solve decision problems under risk [37]. recently, the author in [38] developed the opportunity-threat theory for dealing with the new paradoxes in cumulative prospect theory which benefits the decision makers in selecting the optimal alternative. unfortunately, the opportunity-threat theory is not capable of analyzing all type of data for making the optimal decision for a certain type of mada problems. based on the above analysis, it becomes clear that some researchers focused on decision making under uncertainty while others concentrated on decision making under risk. so, there should be a decision framework able to provide an optimal solution for a decision problem under both risk and uncertainty. this paper proposes a new generic decision framework to handle all types of data for choosing the optimal alternative under both uncertainty and risk. the proposed framework is less complex and capable of handling all sorts of uncertainty and risks throughout the decision-making process. ii. feature extraction approach for multiple attribute decision problems a. decision attribute there are basically three types of attributes in a decision support system. 1) qualitative qualitative attributes are subjectively judgmental. for example, the performance of a computer can be evaluated as average, good or excellent. in the feature extraction approach, these subjective inputs are transformed into some numerical values. the domain experts set the numerical values against the subjective evaluation. for instance average can be transformed into 0.1, good can be transformed into 0.5 and excellent can be transformed into 1. the size and numerical evaluation of the subjective grades of an attribute can vary depending on experts’ opinions. 2) quantitative quantitative attributes describe numerical values. for example, the price of a computer is $100. 3) boolean the input for a boolean attribute can be either true or false. the proposed feature extraction approach considers ‘1' and '0' to address the 'true' and 'false' statements. engineering, technology & applied science research vol. 10, no. 3, 2020, 5775-5783 5777 www.etasr.com hasan et al.: a generic feature extraction approach for dealing with multiple attribute decision … b. additional knowledge representation parameter: attribute weight attribute weight states the relative importance of an attribute and is numerically described to address the impact of an attribute on the decision making process. a precise decisionmaking process mostly depends on its attributes’ weights. for example, suppose a school committee declares to appoint a math teacher. to select the best alternative, the committee sets two parameters as the basic quality measurement attributes: math score and music performance score. results for two alternatives are c1= (math, 0.6) and (music, 0.3) c2= (math, 0.4) and (music, 0.6) now, if both attributes are considered with equal importance, then c2 will be selected, though c1 scored higher in math test and should actually be selected. on the other hand, if the committee wanted to appoint a music teacher from these two alternatives then c2 would have been selected. so, it is necessary to set some importance for each attribute based on a certain decision-making aspect. attribute weights can be set by domain experts or by analyzing historical data. geometric mean method [39], geometric least squares method [39], and eigenvector method [40] provide very well-formed formulas to extract attribute weights from historical data. c. basics about decision making framework 1) representation schema feature extraction approach analyzes the attributes of all the provided alternatives to choose the best alternative for a possible operation. suppose there are n distinct alternatives ��(i=1,….., n )for a particular operation. so, the alternatives can be represented as: c= {��, �� , …, �� , …, ��} (1) suppose, there are l basic attributes �� (j=1,…..,l) associated with every alternative. the basic attributes can be stated as follows: e = {��, �� ,…, �� ,…, ��} (2) so, the basic attributes for �� (j=1,….., l) of an alternative can be mathematically represented as ��,� ; where, i (i=1,…,n) is the number of alternatives and j (j=1,….,l) is the number of attributes. ��,� denotes the j th attribute (��) of the i th alternative (�� ). for example, ��,� means the 2 nd attribute of the 1 st alternative where ��,� means the 1 st attribute of the 2 nd alternative. again, the attributes of an alternative can be represented using some belief degrees against a predefined evaluation grade. 2) attribute expression matrix the basic attributes of each alternative can be presented using an attribute expression matrix. the attribute expression matrix provides a transparent visualization of the attributes' input against their respective alternatives. in the case of qualitative attributes, the attribute expression matrix exhibits the attributes evaluation grade along with its belief degree. for example, the input for attribute a11 can be presented as (good, 0.5) meaning the user is 50% sure that the input for attribute a11 will be good. suppose, h = {h1, h2,……., hm} is a set of evaluation grades to which all the qualitative attributes for a decision support problem are measured. the degree of belief against the evaluation grade can be presented using some numerical values, bn (� ∈ ). the basic attributes expression matrix can be structured as shown in table i. table i. attribute expression matrix alternative attribute a1 a2 a3 … am a1 a11 a12 a13 … a1m a2 a21 a22 a23 … a2m a3 a31 a32 a33 … a3m .. . .. . .. . .. . .. . .. . an an1 an2 ... ... anm in table i, an �� (� ∈ )� is the number of alternatives, and ����� (� ∈ )� is the number of attributes representing the input of an alternative. if the input variables are qualitative, the representation of the input variables will hold its evaluation grade along with its belief degrees. in that case, ��� will be represented as (��� , ��� ). on the contrary, ��� will be replaced with a numerical value if the input type is quantitative. in case of boolean data, ��� will accept only a binary statement: yes or no. 3) handling uncertainty due to incomplete information one of the most important tasks for a decision support framework is to handle uncertainty during processing of the information of a decision problem. uncertainty may come from human ignorance in case of providing inputs or from the vulnerability of the utilized model. though it is expected that the input provider will provide complete data for each input in most of the cases the input provider fails to provide complete information. in that case, the system needs to infer the final result using some incomplete data. for instance, the input for the attribute, ‘quality of a teacher’ can be achieved as, (good, 0.8) which means, the input provider is 80% sure that the quality of the teacher is good. so, the remaining 20% is ignorance in this case. or, the input provider may fail to provide any information about the quality of the teacher. thus, information may come with partial or full ignorance. in case of full ignorance, obtained uncertainty can be handled with the help of a knowledge base. in the proposed methodology, knowledge base is constructed using some if-then rules. these if-then rules are set by a group of domain experts. the basic rules can be represented as follows: � � :if �(��,��)⋀(��,��)⋀……⋀(��,��)� then �( �,� ! �),( �,� ! �),…,( �,� ! �)� (3) where � � , {(k=(1,2,…, n) is the number of rules and l=(1,2,…, n) represents the number of attributes} represents the rule for the knowledge base. ��={��,��,..., ��} represents attributes’ evaluation grade and ��{i∈(1,..., n)} is the degree of belief in terms of ��. � (i=1,2,…, n) is the rule consequence and �!�" {(i=1,2,…, n), (k=1,2,…., n)} is the degree of belief in terms of ".here, ∑��" ≤ 1 and ∑�&"!!!! ≤ 1. engineering, technology & applied science research vol. 10, no. 3, 2020, 5775-5783 5778 www.etasr.com hasan et al.: a generic feature extraction approach for dealing with multiple attribute decision … the degree of belief ��" can be represented by a fuzzy membership function. in that case, (3) can be written as: � � :if'���",��"� to ��"� �∧ ���",��"� to ��"� �∧ ……⋀���" ,��"� to ��"� � + then �� �,�!�"�,� �,�!�"�,…,� �,�!�"�� (4) where n represents the minimum degree of belief in fuzzy membership function and m presents the maximum degree of belief in fuzzy scale, and ∑(��"� / ��"�) ≤ 1. for example: �� : if {(good, (0.2-0.4)} ⋀ {(fair(0.3-0.6)} then {(good,0.2), (average, 0.3) (fair,0.5)} the final input for attribute ��� can be measured as: ��� 0 ∑ �����1��12 (5) 4) decision modeling with non-obtainable data a decision problem becomes more complex when the user fails to provide any information about an attribute for an alternative. due to this type of ignorance, decision frameworks often fail to provide an optimal solution for a decision problem. this paper proposes a breakdown approach to process this type of non-obtainable information. for example, to decide whether an applicant is valid for a house loan or not, a bank needs to check the following criteria: credit score, affordability, property evaluation, monthly income, and expenses declaration. suppose the bank manages the necessary information about all the above attributes apart from the ‘property evaluation'. so, the input for the attribute ‘property evaluation’ is non-obtainable for the bank. to process this type of non-obtainable information, the attribute needs to be broken down into its sub-attributes. for instance, the property evaluation can be assessed by the following sub-attributes: • does the candidate own a house? • does the candidate own a car? • is the candidate in possession of land or property? • does the candidate have a private business? thus the total ignorance of an attribute can be completely handled by providing information about all of its sub-attributes. if the user fails to provide sufficient information about any of these sub-attributes, then the attribute information will be partially incomplete and can be handled by the process stated in section iii. 5) attribute analysis and feature extraction feature extraction approach (fea) analyzes the attributes of all the provided alternatives to choose the best alternative for a possible operation. to analyze the attributes precisely, fea makes a cross evaluation among the respective attributes of every given alternative. for that, fea finds the minimum value of a particular attribute from every alternative. the minimum value of the attribute j for the given alternatives is called floor value and can be expressed as: 3� = min (��,�) (6) where i is the number of alternatives, j is the number of attributes and 3� is the minimum value of the j th attribute. for example, for the 1 st iteration, 3�(j=1) expresses the minimum value of the 1 st attribute of all the alternatives. and for the 2 nd iteration, 3� (j=2) expresses the minimum value of the 2 nd attribute of all the alternatives. feature extraction is the easiest way to demonstrate the extent a certain attribute of an alternative differs from the same attribute of the other alternatives. the basic feature extraction is done by calculating the arithmetic difference between the minimum value of a certain attribute and the same attribute of all the alternatives: 4�,� = ��,� 3� (7) where β�,� determines the feature of the jth attribute of the ith alternative with respect to the j th minimum value (3�). 6) decision making using feature extraction approach suppose, the attributes’ weights are represented as wj; where j (j=1,….,l) is the number of attributes. 6� states the weight of the j th attribute (ej) with 0<6� ≤1. the weight of an attribute is always greater than 0 because if the weight of an attribute is considered to be 0 the attribute becomes useless for that operation. let mi,j be the basic probability mass for the j th attribute of the i th alternative. the probability mass of an attribute can be calculated by: ��,� = ∏ �4�,�,6� ��1�,�1��1�,�1� (8) where 6� is the relative importance of the jth attribute. fig. 1. feature extraction model finally, the utility or risk-severity of an alternative is calculated by aggregating its probability masses. the basic arithmetic summation formula is used to aggregate the probability masses: ��= ∑ ��,��1�,�1��12,�12 (9) where, �� (i=0,…., n) is the utility of ith alternative. to make the final decision or choose the best alternative for a certain operation, the utilities scored by the alternatives are engineering, technology & applied science research vol. 10, no. 3, 2020, 5775-5783 5779 www.etasr.com hasan et al.: a generic feature extraction approach for dealing with multiple attribute decision … analyzed. and then, based on the operation nature, the final decision is made. so, the best alternative can be chosen as: max( ) for benefit attributes min( ) for cost attributes i i c c c  =   (10) here, i (i=1,2,….., n) is the number of alternatives. the feature extraction model is shown in figure 1. the value for c in (10) will be determined by the nature of decision problems. for example, to choose the best machine based on its performance, the maximum utility should be considered. on the other hand, to invest in a new business based on minimum risk, the minimum utility will be considered. iii. numerical experiments a. decision making under uncertainty 1) problem illustration a numerical study is provided in this section to explain the practical implementation of the fea under uncertainty. this experiment is conducted on daffodil international university, dhaka, bangladesh to choose the best teacher by analyzing the key performance indicators (kpi) set by the university authorities. the considered teachers for this experiment can be defined as t1, t2, t3 and t4. the input variables considered for obtaining the best teachers are defined as follows: • x1: delivery of course outline with an adequate number of text and reference books. • x2: seriousness about class time. • x3: delivery of practical examples in the class. • x4: lecture quality in terms of making the class topic clear and specific to the students. • x5: response to the students’ questions in the classroom. • x6: consciousness about the arrangement and evaluation of required quizzes, assignments. • x7: coverage of course materials as per course outline. • x8: students' feedback. • x9: attendance in exam duty. • x10: punctuality about result submission time. • x11: activity in learning management system (lms) and course repository. • x12: mentoring and counseling. • x13: research and publications. • x14: interpersonal relationships with the other teachers and working teams. • x15: researchgate profile. • x16: attendance on conferences, seminars, and workshops. • x17: engagement in extracurricular activities. the attribute weights considered for this experiment are: w1=0.5, w2=0.7, w3=0.8, w4=1.0, w5=0.7, w6=0.7, w7=0.9, w8=0.8, w9=0.7, w10=0.7, w11=0.7, w12=0.85, w13=0.9, w14=0.65, w15=0.5, w16=0.5, w17=0.5. in this example, 17 variables are used to determine the best teacher, where x7 and x9 are quantitative, x15 is boolean and the rest are qualitative. the inputs for the qualitative attributes are normalized to make the calculation easy and universal. the subjective evaluation of qualitative attributes is determined in table ii. the inputs collected against each alternative can be expressed using the attribute expression matrix. in table iii, the provided input (e14, 1.0) for a11 describes that the input provider is 100% sure that the delivery of practical examples in the class is e14. table ii. transformation of evaluation grades into numerical values e1 e2 e3 e4 e5 e6 e7 e8 e9 e10 e11 e12 e13 e14 e15 e16 e17 e18 e19 e20 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1.0 table iii. system input acquisition x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x14 x15 x16 x17 t1 e14,1.0 e14,1.0 e16,1.0 e14,1.0 e14,1.0 e10,1.0 0.9 e8,1.0 0.9 e18,1.0 e14,1.0 e12,1.0 e14,1.0 e16,1.0 yes e16,1.0 e16,1.0 t2 e14,1.0 e16,1.0 e14,0.9 e16,1.0 e16,1.0 e16 0.6 0.9 e12,1.0 0.7 e14,1.0 e14,1.0 e14,1.0 e16,1.0 e14,1.0 no e12,1.0 e12,1.0 t3 e10,1.0 e12,1.0 e10,1.0 e14,1.0 e13,1.0 e12,1.0 0.8 e10,1.0 0.5 e6,1.0 e12,1.0 e12,1.0 e10,1.0 e12,1.0 yes e10,1.0 e8,1.0 t4 e14,1.0 e14,1.0 e16,1.0 e14,0.8 e14,1.0 e16,1.0 0.9 e10, 0.6 0.9 e17,1.0 e16,1.0 e16,1.0 e4,1.0 e14,1.0 no e15,1.0 e12,1.0 in other cases, the user provides 80% and 90% confidence about the input value for a23 (e14, 0.8) and a44 (e14, 0.9). here 20% and 10% of the information remains uncertain. 2) knowledgebase construction the basic knowledge base for this experiment is constructed with the help of 10 prominent university faculties and 7 experienced members of university trusty board as illustrated in table iv. 3) step by step illustration of utility assessment with fea a) data processing • transformation of complete information into quantitative format: to assess the performances of a teacher, first the inputs with complete information are transformed into numerical values according to the evaluation grades stated in table ii. the incomplete data are kept untransformed in this stage. • handling incomplete data: the proposed methodology suggests a way to capture the incomplete information provided by the user. the incomplete belief degrees are handled with the help of a belief rule-based knowledge base, e.g. in table iii, the input for attribute a23 is (e14, 0.9) engineering, technology & applied science research vol. 10, no. 3, 2020, 5775-5783 5780 www.etasr.com hasan et al.: a generic feature extraction approach for dealing with multiple attribute decision … where 0.1 is ignorance. this ignorance can be handled with the help of the system’s knowledge base (described in table iv). in that case, the final input for a23 will be: ( ) ( ) ( ) ( ) ( ) ( ) 13 14 15 *0.1 *0.85 *0.05 0.65*0.1 0.7*0.85 0.75*0.05 0.697 e e e+ + = + + = • transformation of complete information into quantitative format: after the incomplete information is properly handled, the inputs are finally transformed to numeric values. table vi shows the final input transformation. b) inference using feature extraction approach after successfully transforming attributes’ inputs into numeric values, the minimum value for every particular attribute of every alternative needs to be calculated. attributes floor value for the given alternative can be calculated using (6) and the result is shown in table vii. after obtaining the floor values, features are extracted for each attribute by (7). finally, the probability mass for every attribute is measured by (8). the aggregated probability mass of all the attributes of an alternative provides its utility. to choose the best teacher, the maximum utility is considered in this that states the best performance (figure 2). table iv. rules set up for knowledgebase construction rule no. antecedent consequence 1. if (e1,0.8) ⋀ (e2,0.1) then (e1, 0.7),( e2, 0.1),(e3, 0.2) 2. if (e14, 0.8) then (e13, 0.2 ),(e14, 0.7),(e15, 0.1) 3 if (e16, 0.6) then (e15, 0.25 ),(e16, 0.5),(e17, 0.25) 4. if (e1, 0.4) ⋀ (e2, 0.2) ⋀ (e3, 0.1) then (e1, 0.3, e2, 0.2, e3, 0.1, e4, 0.2, e5, 0.2) 5. if (e3, 0.4) ⋀ (e4, 0.4) then (e3, 0.3, e4, 0.3, e5, 0.3, e5, 0.1) 6. if (e3, 0.2) ⋀ (e4, 0.5) ⋀ (e5, 0.2) then (e3, 0.15, e4, 0.4, e5, 0.25, e5, 0.2) 7. if (e5, 0.3) ⋀ (e6, 0.3) ⋀ (e7, 0.2) then (e5, 0.25, e6, 0.2, e7, 0.2, e8, 0.2, e9, 0.15) 8. if (e5, 0.6) ⋀ (e6, 0.3) then (e5, 0.4, e6, 0.2, e7, 0.2, e8, 0.2) 9. if (e6, 0.5) ⋀ (e7, 0.3) then (e6, 0.4, e7, 0.25, e8, 0.25, e9, 0.1) 10. if (e14, 0.9) then (e13, 0.1 ),(e14, 0.85),(e15, 0.05) 11 if (e7, 0.5) ⋀ (e8, 0.3) then (e7, 0.4, e8, 0.25, e9, 0.25, e10, 0.1) 12 if (e8, 0.4) ⋀ (e9, 0.4) then (e7, 0.3, e8, 0.3, e9, 0.3, e10, 0.1) 13 if (e10, 0.2) ⋀ (e11, 0.7) then (e10, 0.2, e11, 0.6, e12, 0.2) 14 if (e10, 0.4) ⋀ (e11, 0.3) ⋀ (e12, 0.1) then (e10, 0.25, e11, 0.25, e12, 0.25, e13, 0.25) 15 if (e11, 0.4) ⋀ (e12, 0.3) then (e11, 0.35, e12, 0.25, e13, 0.25, e14, 0.15) 16 if (e13, 0.3) ⋀ (e14, 0.4) then (e13, 0.35, e14, 0.3, e15, 0.35) 17 if (e15, 0.3) ⋀ (e16, 0.2) then (e15, 0.35, e16, 0.25, e15, 0.25, e16, 0.15) 18 if (e17, 0.3) ⋀ (e16, 0.3) then (e17, 0.35, e16, 0.35, e15, 0.25, e14, 0.1) table v. initial input transformation with incomplete information x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x14 x15 x16 x17 t1 0.7 0.7 0.8 0.7 0.7 0.5 0.9 0.4 0.9 0.9 0.7 0.6 0.7 0.8 1 0.8 0.8 t2 0.7 0.8 e14, 0.9 0.8 0.8 e16, 0.6 0.9 0.6 0.7 0.7 0.7 0.7 0.8 0.7 0 0.6 0.6 t3 0.5 0.6 0.5 0.7 0.65 0.6 0.8 0.5 0.5 0.3 0.6 0.6 0.5 0.6 1 0.5 0.4 t4 0.7 0.7 0.8 e14, 0.8 0.7 0.8 0.9 0.5 0.9 0.85 0.8 0.8 0.2 0.7 0 0.75 0.6 table vi. final input transformation x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x14 x15 x16 x17 t1 0.7 0.7 0.8 0.7 0.7 0.5 0.9 0.4 0.9 0.9 0.7 0.6 0.7 0.8 1 0.8 0.8 t2 0.7 0.8 0.697 0.8 0.8 0.8 0.9 0.6 0.7 0.7 0.7 0.7 0.8 0.7 0 0.6 0.6 t3 0.5 0.6 0.5 0.7 0.65 0.6 0.8 0.5 0.5 0.3 0.6 0.6 0.5 0.6 1 0.5 0.4 t4 0.7 0.7 0.8 0.695 0.7 0.8 0.9 0.5 0.9 0.85 0.8 0.8 0.2 0.7 0 0.75 0.6 table vii. attributes’ minimum value calculation x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x14 x15 x16 x17 t1 0.7 0.7 0.8 0.7 0.7 0.5 0.9 0.4 0.9 0.9 0.7 0.6 0.7 0.8 1 0.8 0.8 t2 0.7 0.8 0.697 0.8 0.8 0.8 0.9 0.6 0.7 0.7 0.7 0.7 0.8 0.7 0 0.6 0.6 t3 0.5 0.6 0.5 0.7 0.65 0.6 0.8 0.5 0.5 0.3 0.6 0.6 0.5 0.6 1 0.5 0.4 t4 0.7 0.7 0.8 0.695 0.7 0.8 0.9 0.5 0.9 0.85 0.8 0.8 0.2 0.7 0 0.75 0.6 min 0.5 0.6 0.5 0.695 0.65 0.5 0.8 0.4 0.5 0.3 0.6 0.6 0.2 0.6 0 0.5 0.4 table viii. attributes’ feature extraction x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x14 x15 x16 x17 t1 0.2 0.1 0.3 0.005 0.05 0 0.1 0 0.4 0.6 0.1 0 0.5 0.2 1 0.3 0.4 t2 0.2 0.2 0.197 0.105 0.15 0.3 0.1 0.2 0.2 0.4 0.1 0.1 0.6 0.1 0 0.1 0.2 t3 0 0 0 0.005 0 0.1 0 0.1 0 0 0 0 0.3 0 1 0 0 t4 0.2 0.1 0.3 0 0.05 0.3 0.1 0.1 0.4 0.55 0.2 0.2 0 0.1 0 0.25 0.2 engineering, technology & applied science research vol. 10, no. 3, 2020, 5775-5783 5781 www.etasr.com hasan et al.: a generic feature extraction approach for dealing with multiple attribute decision … table ix. alternatives’ utility calculation x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x14 x15 x16 x17 utility t1 0.1 0.07 0.24 0.005 0.035 0 0.09 0 0.28 0.42 0.07 0 0.45 0.13 0.5 0.15 0.2 2.74 t2 0.1 0.14 0.197 0.105 0.105 0.3 0.09 0.16 0.14 0.28 0.07 0.085 0.54 0.065 0 0.05 0.1 2.632 t3 0 0 0 0.005 0 0.07 0 0.08 0 0 0 0 0.27 0 0.5 0 0 0.925 t4 0.1 0.07 0.24 0 0.035 0.21 0.09 0.08 0.28 0.385 0.14 0.17 0 0.065 0 0.125 0.1 2.09 from the graph in figure 2, it becomes clear that t1 performs better than the rest and so, t1 is selected as the best teacher. to visualize the accuracy of the proposed methodology, a comparative evaluation between the systemobtained results and established benchmark results is presented in table x and its graphical representation is shown in figure 3. the benchmark results are collected from the human resource (hr) department at daffodil international university (diu). fig. 2. teachers’ performance evaluation table x. cross-validation between experimental and benchmark results location system obtained results benchmark results system inference hr at diu inference t1 2.74 2.71 t1 t1 t2 2.632 2.5 t3 0.925 0.98 t4 2.09 1.96 fig. 3. graphical representation of cross-validation between the experimental results and the benchmark results b. decision making under risk 1) problem illustration this numerical study is presented to explain the practical implementation of fea under risk. this experiment is conducted to select the best location to rent a house from a course of alternatives based on four basic attributes. the input variables for this experiment have been determined by analyzing 10 years of historical data collected from gis (geographic information system) and rajuk (rajdhani unnayan kartripakkha).the probabilities of attributes are determined by analysing 10 years’ historical data. the locations considered for this experiment are defined as: l1=location a, l2=location b, l3=location c, and l4=location d. the input variables or the attributes considered for choosing the best location to rent a house can be defined as: • x1: probability of the area getting flooded during the rainy season. • x2: probability of load shedding occurrence in the area. • x3: probability of gas crisis occurrence in the area. • x4: probability of water crisis occurrence in the area. the input values for these four attributes have been determined as shown in table xi: table xi. attributes’ degree of probability x1 x2 x3 x4 l1 0.2 0.3 0.5 0.5 l2 0.5 0.4 0.4 0.6 l3 0.3 0.2 0.7 0.2 l4 0.7 0.3 0.3 0.6 the attribute weights, collected from the domain experts, considered for this experiment are w1=0.5, w2=0.85, w3=0.9, and w4= 0.95. 2) selecting an optimal location with fea to choose the best location to rent a house, the feature of every single attribute is extracted through a cross judgment of attributes against all the alternatives. to extract the feature of an attribute, at first the minimum value for every attribute is calculated as shown in table xii. table xii. attributes’ floor value calculation x1 x2 x3 x4 l1 0.2 0.3 0.5 0.5 l2 0.5 0.4 0.4 0.6 l3 0.3 0.2 0.7 0.2 l4 0.7 0.3 0.3 0.6 min 0.2 0.2 0.3 0.2 then, the feature of every attribute is extracted with the help of (7), as shown in table xiii. table xiii. attributes’ feature determination x1 x2 x3 x4 l1 0 0.1 0.2 0.3 l2 0.3 0.2 0.1 0.4 l3 0.1 0 0.4 0 l4 0.5 0.1 0 0.4 engineering, technology & applied science research vol. 10, no. 3, 2020, 5775-5783 5782 www.etasr.com hasan et al.: a generic feature extraction approach for dealing with multiple attribute decision … finally, the probability mass for every attribute is measured by (8). the aggregated probability mass of all the attributes of an alternative provides its risk severity. table xiv. attributes' risk-severity calculation x1 x2 x3 x4 risk severity l1 0 0.085 0.18 0.285 0.55 l2 0.15 0.17 0.09 0.38 0.79 l3 0.05 0 0.36 0 0.41 l4 0.25 0.085 0 0.38 0.715 to choose the best location in order to rent a house, the location with minimum score is considered in this experiment, as the minimum risk score ensures the maximum privilege (figure 4). from figure 4, it becomes clear that location c states lesser risk than all the rest alternatives and so, location c is selected as the best location to rent a house. to validate that the experimental results reflect the most accurate consequences, cross-validation between the experimental results and the benchmark results is exhibited in table xv and figure 5. fig. 4. risk severity assessment table xv. cross evaluation of experimental and benchmark results location system obtained results benchmark results system inference rajuk inference l1 0.55 (55%) 0.5 (50%) l3 l3 l2 0.74 (74%) 0.8 (80%) l3 0.41 (41%) 0.45 (45%) l4 0.715 (71.5%) 0.75 (75%) fig. 5. graphical representation of cross-validation iv. conclusion decision-makers may need to analyze various types of information to achieve the optimal solution for a decision problem. decision problems often come with multiple attributes and an individual may need to make decisions under risk and uncertainty. so, the decision-making approach must be optimized enough to conclude any type of decision problems into a rational, reliable, and transparent solution. the feature extraction approach proposed in this paper is competent enough to make decisions under risk and uncertainty. the system provides a rational means to capture qualitative and quantitative attributes along with boolean data to make a dynamic decision-making approach. for decision making under uncertainty, the proposed system extracts features from the inputs provided by the decision makers. so, decision making under uncertainty is normally triggered with providing some input variables and its associated weights against all the decision attributes to deduce the best solution. in the case of decision making under risk, decision-makers need to provide the probabilities of the attributes in terms of real event occurrences that impact the decision solutions. for that purpose, some previous data on those respective attributes need to be analyzed to measure each of its degree of probability. the numerical experiments presented in this paper provide the practical implementation of the feature extraction approach for deducing optimal solutions for decision-making problems under uncertainty and risk. in both experiments, relative attribute weights have been collected from domain experts. these experiments clearly state that the feature extraction approach can capture multiple attributes for providing the optimal solutions 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vol. 48, no. 12, pp. 1226– 1232, 1997 microsoft word 1-gamel_atta.doc etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 532-539 532 www.etasr.com gamal et al.: effect of iron additives on the microstructure of hydroxyapatite effect of iron additives on the microstructure of hydroxyapatite g. a. gamal college of engineering, alqassim, saudi arabia profdrgamal@qec.edu.sa f. a. al-mufadi college of engineering, alqassim, saudi arabia almufadi@qec.edu.sa a. h. said department of physics, south valley university, qena, egypt alaahassan2010@yahoo.com abstract— in this article, some fe (iii) doped hydroxyapatite samples (fehap) were prepared using the wet chemical method. the prepared samples were characterized via the use of x-ray diffraction (xrd) and scanning electron microscopy (sem). detailed structural analysis were done by scherrer and williamson–hall plot methods to detect the effect of iron on the structure of hydroxyapatite (hap). xrd patterns showed that all samples were single phased hap. relations between the fe content and the deformation of the lattice parameters, dislocation density, grain size, microstrain, crystallinity were investigated. the presence of iron in the hap lattice is found to decrease both the crystal size and the dislocation density. further results are presented and discussed. keywordshydroxyapatite; lattice parameters; dislocation density; crystallite size; microstrain i. introduction calcium hydroxyapatite (hap) appears now of high interest in the field of material science, since it represents the compatible inorganic component of natural bones and it can directly bond to bone in vivo. hap is usually used as bone substitution or bone filling material, but by introducing new ions into hap structure, new applications could be implemented. one of them is to use it as drug delivery material due to its biocompatibility, degradation, dissolution and nontoxic properties [1]. in recent years hap was also investigated as a magnetic material for cancer treatment. it is known that heating cells up to 42 to 45 oc results in the death of cancer cells. this is usually done by delivering magnetic nanoparticles to the tumor and irradiating the particles with an ac magnetic field. generally, hap has many applications in both medical and engineering sciences, but further modification is needed in order to satisfy the requirements of recent applications [2]. among the advantages of hap is that its crystal structure is flexible due to the substituting ions. the general chemical formula of the apatites is m5 (yo4)3x, where: m is monovalent cations (such as na+, k+), or divalent cations (such as ca2+, sr2+, ba2+, mg2+, cd2+, pb2+, etc.), or trivalent cations (such as na+, k+, al3+, fe3+, fe2+, la3+, etc.) , x=univalent anion (such as oh-, f-, cl-, br-, or co32-) and yo4 = (po4 3-, vo4 3, aso4 3-, sio4 4-, co3 2-) [3]. it is an established fact that substitution of iron ions in the crystal structure of hydroxyapatite affects its physical and biological properties. morrissey et al [4] studied the influence of fe (ii) ions on the structural properties of hap prepared by the wet chemical reaction with diammonium hydrogen phosphate, calcium nitrate and ferrous nitrate solution. filho et al [5] studied the effect of iron oxide concentration and the influence of heat treatment on the microhardness of hydroxyapatite. kuda et al [6] found that the addition of iron or magnetite to biogenic hydroxyapatite makes it possible to produce magnetic biocomposites. the magnetic properties of such materials depend on the type and amount of additives. yan li et al [7] reported that fe3+ doped hap showed paramagnetic properties and the magnetic susceptibility increased with the increase of fe3+ content. recently mirestean et al [8] prepared hydroxyapatite doped with different iron concentrations by the sol–gel method and stated that it can be used for hyperthermia treatment of bone tumors. nakahira et al [1] synthesized hydroxyapatite doped with iron for drug delivery system (dds). various papers have been recently published on the continuous improvement of hap, focusing on the limitations to low load bearing applications or on physical properties. this is evident from the work of li et al [9] for synthesis and cytocompatbility of manganese (ii) and iron (iii) substituted hap nanoparticles, kai et al [10] who studied the synthesis and magnetic property of iron ions–doped hap and the investigation of synthesis and ha nanoparticles with tailorable morphologies and carbonate substitutions using a wet precipitation method done by fei et al [11]. the present work aims to investigate the effect of iron additives on the structural properties of hydroxyapatite. ii. experimental procedure a. synthesis of pure hydroxyapatite and fe3+ doped hydroxyapatite five samples of hydroxyapatite were synthesized via the wet chemical method [12, 13]. the chemical reagent and starting materials concentrations for the precipitation are listed in table i. in order to avoid tedious details about sample preparations, figure 1 illustrates the preparation procedure. etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 532-539 533 www.etasr.com gamal et al.: effect of iron additives on the microstructure of hydroxyapatite table i. chemical reagent of the prepared samples. ca(no3)2.4h2o (nh4)2hpo4 fe(no3)3.9h2o sample code gm mol gm mol gm mol 1 hap 36.8 0.16 12.66 0.096 -------- 2 fehap1 36.8 0.16 12.66 0.096 2.02 0.005 3 fehap2 36.8 0.16 12.66 0.096 4.04 0.01 4 fehap3 36.8 0.16 12.66 0.096 8.08 0.02 5 fehap4 36.8 0.16 12.66 0.096 12.12 0.03 fig. 1. flow chart of the preparation technique b. scanning electron microscope (sem) the morphology of the prepared samples was examined using a jeol sem model jsm-5500-japan, with 10 kv accelerating voltage. c. x-ray diffraction x-ray diffraction (xrd) pattern data were obtained at room temperature for the prepared samples using the powder technique in an x’pert pro-pan analytical diffractometer (with cu-kα radiation, λ= 1.54056a˚ ) at 40 kv and 30 ma. intensity data were collected by the step-counting method (step 0.020 and a time per step of 0.4 s) between 10˚ and 80˚ for (2θ) as illustrated in figure 2 where θ is the angle between the incident ray and the scattering planes. the lattice parameters were calculated by the following formula [14]. where d is the interplanar spacing, hkl are miller's indices and a and c are lattice parameters. for determination of the unit cell volume, the following formula is used [14]: cav  2 2 3 (2)  1 3 41 2 2 2 22 2 c l a khkh d         etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 532-539 534 www.etasr.com gamal et al.: effect of iron additives on the microstructure of hydroxyapatite also the crystallinity of the studied samples is calculated with the aid of the following equation [15]: 300 300/1121 i v x c  (3) where xc is the percentage of crystallinity degree, v112/300 is the intensity of the hollow between (112) and (300) diffraction peaks, i300 is the intensity of (300) diffraction peak. the size of the crystallites responsible for the bragg reflection of the (002), (112), (211) and (300) planes were determined using the well-known scherrer relationship [16]:   cos 94.0 d  (4) where γ is the full width at half-maximum (fwhm) and d is the crystal size. williamson hall technique takes into account both size and strain effects. this method provides estimation for the crystal size d as well as for the micro-strain ε as follows [17]:    sin4 9.0 cos  d (5) the above formula between γcosθ and sinθ is a linear relationship as predicted. from the intercept of the line we can have the crystal size. the slope of the fitted line provides the micro-strain. the average dislocation density ρ can be determined from the following equation [18]: 2= (πab2/2) rec (6) where (b2/2) is the burgers vector, a is a constant defined by the effective outer cut-off radius of dislocations (re) and c is the contrast factor. iii. results and discussions a. scanning electron microscopy sem is used to examine the morphology of the studied samples and to show the effect of the substitution process on the structure of hap. two magnifications were used for all samples x 50 with magnification bar 500 µm and x 1000 with magnification bar 10 µm. red circles illustrate the hap particle agglomeration at different fe concentrations. the effect of substitutions on the structure of hap leads to a decrease in the grain size as the concentration of iron increase. this is attributed to the smaller ionic radius of iron compared with that of calcium as seen in figures [2(a), 3 (a), 4 (a), 5 (a), 6 (a)]. this is in complete agreement with the results obtained from xrd. the formation mode of hap particles appears as spherical particles agglomerated together as indicated in figures [2 (b), 3 (b), 4 (b), 5 (b), 6 (b)]. b. xrd phase identification was done via the xrd method. figure 7 shows the xrd patterns of all prepared samples. present peaks agree with icsd (inorganic crystal structure database) card no.76-694 [19] and none of the patterns displayed extra peaks indicating that all samples are single phased hap. also it is concluded that the grown phase is a hexagonal system with a space group p6/3m. the effect of substitutions in hap structure is appeared in the xrd chart as a change in the peak position, intensity and broadening. from xrd we can observe that there is a slight shift of the peak position in all iron doped hap samples compared with pure hap and also that the peak intensity of all samples is smaller than of that of purehap. this may be attributed to the smaller particle size and greater structural strain in the metal cations doped hap relative to pure hap. for more utilization of figure 2, we shall digress with an illustration of the width of the main peak in case of five samples. so, software and computational treatments yields the obtained histogram shown in figure 8. except for the case of fe3+ concentration of 0.3, it evident that the quantity (the full width at half maximum) rises as the fe3+ increases. the significance of this observation is that substitution of fe3+ causes some kind of defects in the crystal arrays i.e. with the increment of fe3+ substitution the obtained crystal becomes more defective. the obtained values of unit cell parameters (a, c) and unit cell volumes are listed in table ii. since the ionic radius of fe3+ (0.64 a˚) is smaller than that of ca2+ (0.99 a˚), therefore it is logical that the substitution of fe for ca causes a decrease in either or both lattice parameters. figure 9 shows the variation of both lattice parameters (a, c) and the unit cell volume with the concentration of the substituted iron. we can see a slight decrease in both lattice parameters and unit cell volume as the concentration of fe increases, for all iron doped hap samples in comparison to pure hap. this indicates that fe substituted for ca caused shrinking to the hap crystal. a similar behaviour was observed in a previous work with cations smaller than ca such as (mg2+, zn2+, in3+, y3+), while an expansion also observed with cations larger than ca such as (bi3+, la3+) [14]. in spite of the clear decrease in both lattice parameters he unit cell volume, one can't exclude the impression that there is an evident fluctuation in the recorded lattice parameter values. the fluctuation in the lattice parameter may be attributed to:  the substitution range of fe3+ as the probability of substitution changed from one sample to another.  the effect of carbonate substitution as the carbonate anion enters the hap lattice by substituting for either hydroxyl or phosphate anions. etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 532-539 535 www.etasr.com gamal et al.: effect of iron additives on the microstructure of hydroxyapatite fig. [2(a), 3(a), 4(a), 5(a), 6(a)] sem of hap, fehap1, fehap2, fehap3 and fehap4 samples with magnification bar 500 µm. fig. [2(b), 3(b), 4(b), 5(b), 6(b)] sem of hap, fehap1, fehap2, fehap3 and fehap4 samples with magnification bar 1000 µm etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 532-539 536 www.etasr.com gamal et al.: effect of iron additives on the microstructure of hydroxyapatite fig. 7. xrd patterns of pure hap and fe substituted hap fig. 8. the full width at half-maximum of the main peak as a function in fe content table ii. lattice parameter and unit cell volume of the prepared samples samples plane d (å) parameter (å) average (å) unit cell volume (å)3 300 2.718 9.416 a 211 2.810 9.405 9.410 002 3.443 6.887 h a p c 004 1.721 6.885 6.886 528.190 300 2.711 9.416 a 211 2.794 9.345 9.369 f eh a p 1 c 002 3.431 6.862 6.866 521.989 004 1.717 6.869 300 2.715 9.405 a 211 2.807 9.392 9.399 002 3.445 6.890 f eh a p 2 c 004 1.719 6.877 6.883 526.7005 300 2.706 9.376 a 211 2.804 9.384 9.380 002 3.433 6.866 f eh a p 3 c 004 1.717 6.869 6.868 523.411 300 2.716 9.409 a 211 2.808 9.400 9.404 002 3.438 6.876 f eh a p 4 c 004 1.721 6.886 6.881 527.138 depending on the deviations in the lattice constants, the position of the substitution can be determined. it is established that the substitution of carbonate anion for the phosphate anion, provokes an expansion in the unit cell length along the c-axis and a contraction along the a-axis. whereas, the substitution of carbonate for the hydroxyl group is induced and causes an expansion along the a-axis and a contraction on the c-axis [20]. in the prepared samples under study both types of carbonates are expected, which means that the two possibilities are expected too. for a detailed study about this point and in order to find out the influence of fe3+ substitution on the crystal size we applied (4). table iii shows the average crystal size of all samples calculated by (4) due to the peaks from (002), (112), (211), (300) reflection planes. the values of the crystal sizes for all samples ranged from 26.8 to 18 a˚. the effect of iron in the crystal size can be observed easily via the decrease of the crystal size of all iron doped samples compared to pure hap as indicated in table iii and figure 10. this may be attributed to the smaller ionic radius of iron that causes a shrinking to the hap. these results confirm the reduction observed in the cell parameters and volume values as seen in figure 9. fig. 9. lattice parameters (a) a axis, (b) c axis and (c) unit cell volume as a function of iron concentration. fig. 10. the calculated crystal size d from scherrer and willimson-hall equations as a function of fe content. etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 532-539 537 www.etasr.com gamal et al.: effect of iron additives on the microstructure of hydroxyapatite another method for finding d is the williamsonhall relation. figure 10 also shows the corresponding estimated values of crystal size d. regarding (5), it was utilized because it takes into account that the total width of the x-ray diffraction peak is due to both size and strain effects. for the separation, the different dependence is helpful: the size broadening is proportional to cos-1θ and the strain broadening is proportional to tanθ . accordingly plotting the relation between γcosθ and sinθ, we can get from the intercept the value of d and from the slope the value of ε (the microstrain). the crystallinity of the five samples is deduced with the aid of (3). variation of the crystallinity against the fe concentration is depicted in figure 11. the general mode of variation of fe content against the crystallinity is the decrease of the crystallinity and/or the increase in the lattice imperfections [21] as fe content increases. the degree of crystallinity of hap ceramics can be influenced by many factors such as preparation methods, heat treatment, crystal size and substitutions. presently we believe that the effect of decreasing the crystal size is the factor responsible for decreasing the crystallinity of the prepared samples. this is supported with the xrd spectra where a broadening of diffraction peaks is noticeable as the fe3+ increases. these results agree with the observations in [7, 22]. also one can’t exclude the role played by doping of iron ions which inhibited the c-axis growth and promoted the a-axis growth as concluded in [10]. the effect of substitutions can vary according to the amount and the type of the substituted ions. for example mg+2 can cause a decrease in the crystallinity of hap [15] while the substitutions of fluoride (ffor oh-) can cause an increase in the crystallinity [23]. also the substitution of carbonate in β position reduces the stability and crystallinity of hap, since vacancies in calcium site will be formed in order to re-equilibrate the change neutrality [24]. fig. 11. effect of iron content on the xc%in the studied samples. table iii. calculated crystal size of the prepared samples sample d (nm) scherrer d (nm) williamson hall  hap 26.8 20.5 9.75 e-4 fehap1 18.6 17.2 19.9 e-4 fehap2 18.5 13.1 12.2 e-4 fehap3 18.3 11.1 5.37e-4 fehap4 18 10.4 9.17e-4 now it is clear that d decreases as fe3+ is increased. this is true for d estimated by scherrer or even by williamsonhall relations. from the results of the crystal size and microstrain measurements of the prepared samples shown in table iii we can note that:  the average crystal size measured by scherrer equation is larger than that measured from williamsonhall plot. thus, apparently, the scherrer method overtimes the crystal size likely due to the fact that it does not separate broadening due to the strain in the lattice from that due to refined grain structure [25].  there are strains and lattice distortions in our samples, which mean that our samples may have dislocations [26]. for better understanding of the nature of the relation between d and ε and fe3+ concentration, figure 13 is constructed. this was done on the basis of (5). a set of straight lines (as expected) were obtained as illustrated in figure 12. from the intercepts we computed values of  as listed in table iii. so, figure 13 depicts the relation between  and fe3+ concentration. from figure 13 it is seen that the relation between  and fe3+ concentration is decreasing linearly. this reflects the fact that as the amount of fe substitution increases, the hap sample tends to be more mechanically stable. because of the availability of  values at different fe3+ concentrations and by using (6), dislocation densities can be obtained at that condition. accordingly, figure 14 is drawn. one sees the trend line for the dislocation density decreasing gradually as a function of fe3+ concentration. this conclusion is rather surprising since we concluded from figure 8 that the width of the x-ray main peak increases (indicating that more fe3+ yields more defects). also the crystallinity was decreased as fe3+ increased. here dislocations are decreasing as fe3+ concentration increases. in the mean time, it seems that the generation of another type of defects (point or line defects) as a result of fe3+ concentration increases. etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 532-539 538 www.etasr.com gamal et al.: effect of iron additives on the microstructure of hydroxyapatite 0.2 0.3 0.4 0.5 -0.04 -0.02 0.00 0.02 0.04 0.06 sin()  c o s ( ) (a ) hap 0.2 0.3 0.4 0.5 -0.04 -0.02 0.00 0.02 0.04 0.06  c o s ( ) sin() (b) fehap 1 0.20 0.25 0.30 0.35 0.40 0.45 0.50 -0.04 0.00 0.04 0.08 (c) fehap 2  c o s ( ) sin() 0.2 0.3 0.4 0.5 -0.04 -0.02 0.00 0.02 0.04 (d) fehap 3  c o s ( ) sin() 0.2 0.3 0.4 0.5 -0.04 -0.02 0.00 0.02 0.04 (e) fehap 4  c o s ( ) sin() fig. 12. the williamson hall plot of the prepared samples (a) hap, (b) fehap1, (c) fehap2, (d) fehap3 and (e) fehap4 respectively fig. 13. the calculated microstrian of the prepared samples as a function in fe content. fig. 14. the calculated dislocation density of the prepared samples as function in fe content. iv. conclusion some fe3+ doped hap samples were prepared by the wet chemical method. the influence of iron additives on the microstructure of the prepared samples was studied. detailed study was done using the x-ray and sem methods. scherrer and williamson–hall relations were employed to detect the effect of fe3+ introduction in hap structure. definite results were obtained as fe3+ concentration increase: 1. the width of the main x-ray peak was broadening indicating a generation of new defects inside the samples. 2. the crystallinity decreases as a result of doping of iron ions. 3. from scherrer and williamson–hall data it was found that crystal size d decreased. this was attributed to the smaller ionic radius of iron that causes shrinking of the unit cell volume. 4. the dislocation densities were decreased. 5. combining point 4 with the xray peaks broadening and the crystallinity decrease, we concluded a generation of other defects (point or line) as fe3+ is substituted in hap. appearance of the point defects instead of the dislocations opens up new possibilities for modern use of the iron substituted ha as a hard, strong and durable material. references [1] a nakahira, s nakamura, m. horimoto, “synthesis of modified hydroxyapatite (hap) substituted with fe ion for dds application”, ieee transactions on magnetics, vol. 43, no. 6, pp. 2465-2467, 2007 [2] c. hou, s. hou, y. hsueh, j. lin, h. wu, f. lin, “the in vivo performance of biomagnetic hydroxyapatite nanoparticles in cancer hyperthermia therapy”, biomaterials, vol. 30, no. 23-24, pp. 39563960, 2009 [3] w. pon-on, s. meejoo, i. tang, “incorporation of iron into nano hydroxyapatite particles synthesized by the microwave process”, international journal of nanoscience, vol. 6, no. 1, pp. 9-16, 2007 [4] r, morrissey, l. m. rodriguez-lorenzo, k. a. gross, “influence of ferrous iron incorporation on the structure of hydroxyapatite”, journal of materials science: materials in 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technology & applied science research vol. 6, no. 6, 2016, 1280-1287 1280 www.etasr.com rahat and riaz: enhancing transient stability in limited variable speed induction generator (optislip)… enhancing transient stability in limited variable speed induction generator (optislip) based wind turbine (case study: binalood wind farm) omid rahat department of electrical engineering ramhormoz branch, islamic azad university ramhormoz, iran rahat_omid@yahoo.com iman riazy department of electrical engineering ramhormoz branch, islamic azad university ramhormoz, iran imanriazy@gmail.com abstract-enormous penetration of wind power in power systems and its contribution in covering a major part of grid load demand, require higher stability during disturbances. the most important issue of wind generators is the early outage of several generating units when a sudden voltage drop occurs in the grid. voltage drops near wind generators are mainly due to abrupt load rises and integration of large-scale factories and industrial units into the grid. in this paper, the case study of binalood wind farm is studied, analyzed, and simulated. then, various proposed methods are investigated in terms of stability enhancement such that when a disturbance appears near the binalood wind farm, it can hold up its stability and connection to the grid. simulations are carried out using matlab and simulink. keywords-wind farm; transient stability enhancement; induction generators; optislip; matlab; simulink i. introduction binalood wind farm with a total capacity of 28.4 mw is comprised of 43 limited variable speed generating units (660 kw) with a voltage level of 600v. this wind farm is located 55 km away from mashhad city-nishaboor town road in the dizbad district which is one of the most appropriate regions for harvesting wind power in iran. various industrial parks and production firms are located near this wind farm, causing huge voltage drops when they are connected to the power grid. the major problem with this wind farm, since its establishment, is the early outage of some generating units when an abrupt voltage drop appears near it. in wind farms with induction generators, voltage reduction of generator terminals leads to reduced generated power and electromagnetic torque of the generator. the difference between electromagnetic and mechanical torques results in acceleration of the generator and slip rise which in turn increases reactive power extremely. reactive power rise in a weak grid decreases voltage more sharply. once a generator speed is out of control, reactive power consumption will increase and voltage reduction will be much more extreme. sharp voltage drop may increase generator speed dramatically and then result in operation of protection systems and wind farm outage. due to the importance of stability enhancement issue in wind farms, numerous works have been conducted. for instance, in [1-4], angle change of turbine blades is suggested in order to reduce the input mechanical power into the generator when a fault occurs. in addition, the effect of improving control ring performance on tuning the angle of blades is highly considered. conversely, authors in [3] had a completely different idea and assert that because this system is of mechanical type, delay in operation is unavoidable and it has no influence on stability improvement of the generating unit. rather, it is advantageous in preventing generator acceleration after isolating that unit from the grid. in [1], beside angle change of blades, the use of svc and rotor resistance rise are also suggested. this article considers a high capacity for svc to maintain transient stability. additionally, rotor resistance rise method specifies that this method is viable by inserting an external resistor in rotor circuit when a fault occurs. normally, this resistor is in short-circuiting condition by a switch. in [2, 3], the performance of capacitor banks and svc are compared. also, it is mentioned that svc not only increases stability, but also decreases dynamic voltage oscillations and, in turn, the quality of power delivered is improved. in this paper, binalood wind farm is simulated using realistic data. then, a disturbance with a close-to real world characteristic is employed on the location of the wind farm and its stability is analyzed. next, different methods are individually evaluated towards stability improvement and comparisons are made. ii. binalood wind farm binalood wind farm with a capacity of 28.4 mw is comprised of 43 generating units (660 kw). the power produced by the wind farm is delivered to the power grid engineering, technology & applied science research vol. 6, no. 6, 2016, 1280-1287 1281 www.etasr.com rahat and riaz: enhancing transient stability in limited variable speed induction generator (optislip)… through 132/20 kv binalooed substation and two transmission lines (shariati-binalood and attar-binalood). each generating units includes a turbine, gearbox, generator, step-up transformer, capacitor bank, rcc system, etc. figure 1 depicts one-line diagram of the mentioned wind farm. fig. 1. one-line diagram of binalood wind farm a. turbine model wind turbine produces eclectic energy by transforming wind power into mechanical torque through the operation of blades. the amount of transformed energy by the rotor depends upon air density, rotor area, wind speed, aerodynamic coefficient of turbine blades and is obtained by[ 5]: 31 ( , ) (1) 2 m pp pac vl b= cp(λ,β) is different for various turbines and provided by the manufacturer in curves and/or mathematical relationships. the following exponential relationship is more general [6]¨ 12.5 3 116 1 0.035 0.22( 0.4 5) , 1/ ( ) 0.08 1 i p i i c e               (2) the angle value is also determined by τηε control system of blades’ angle. in order to obtain the output torque of the turbine, the following relationship is employed: ( ) ( ) ( )pu m m r p pu t pu  (3) the value of parameters and characteristics of the turbine are provided in table ι. table i. binalood wind farm turbine characteristics r= 23.5 m cut in speed: 4 m/s ωr =28.5 rpm ρ= 1.225 kg/m3 cut out speed: 25 m/s b. drive-train model two-mass model is utilized in modeling rotor, shaft, and gearbox which are named so-called drive-train. the use of this accurate model, instead of one-mass model, allows us to consider mechanical mode oscillations in stability studies because of shaft non-rigidity condition. in this model, the set of turbine and gearbox are considered as one mass; while, generator rotor and its equipment are taken as a separate mass (figure 2). high speed shaft is also simulated as a nonrigidity object connecting the two mentioned masses. regarding figure 2, following relationships may be written [7]: engineering, technology & applied science research vol. 6, no. 6, 2016, 1280-1287 1282 www.etasr.com rahat and riaz: enhancing transient stability in limited variable speed induction generator (optislip)… fig. 2. mechanical model of wind turbine shaft ' ' ' ' ' ' ' ' ' ' ' ' ' ' 2' ' ' ' 2 2 ' ' 2 2 ( ) ( ) ( ) ( ) / 1 , , , / 1 1 , t t t m t g t t t g g g g e g t g g g t g g tt t g t t g t t t m m d t j d d k dt d t j d d k dt d k k nd k j j dt dt k k n n d d d d n n w w w w q q w w w w q q qq w w = + + + = + + + ´ = = = = + = = (4) where n denotes gearbox turn ratio, ' tt denotes wind turbine torque transferred to the generator shaft-side, τg denotes generator torque, ' tw denotes turbine rotor speed transferred to the generator shaft-side ' tj denotes turbine inertia moment transferred to the generator shaft-side, jg denotes generator rotor’s inertia moment, ' md denotes damping ratio of the shaft transferred to the generator shaft-side, ' td denotes damping ratio of the turbine transferred to the generator shaft-side, dg denotes damping ratio of the generator shaft, kt denotes spring ratio transferred to the generator shaftside, kg denotes spring ratio of generator shaft, 'k denotes total spring ratio (torsion spring ratio) that is obtained by equaling the spring ratio of generator shaft and turbine shaft. in these relationships, the quantities of low-speed shaft side (turbine shaft) are transferred to high-speed shaft side (generator shaft) (noted by “ ' ”). table ii provides parameters used in simulation. table ii. drive train characteristics ' tj =277000 kgm2 dm= 10 knms/rad n=52.65 k=4330000 nm/rad dt=1000 nms/rad jg=29 c. generator model in this research, the induction generator model available in matlab/simulink is used. the generator is modeled in 3-phase mode using the diagram shown in figure 3 considering rotor and stator transient behaviors [8-10]. the generator used in binalood wind farm is of winding type without brushes. the rotor resistor of this generator can be controlled by rcc system. the parameters used in the simulation are expressed in table iii. fig. 3. simplified diagram of induction machine table iii. induction generator characteristics [11] p=660 kw xs= 0.049 pu xr=0.0589 pu xm=2.88 pu np=2 v=690 v rs=0.0064 pu rr=0.006 pu j=29 kg/m2 pf =0.91 d. rcc system although there is no exact data about performance process of this system and its parameters, the control system illustrated in figure 4 can be implemented with regard to the aim and role of rcc system in induction generators. fig. 4. block diagram of rcc control system in [12], rotor current signal is used to tune rotor path resistor. here, the used control signal is the generator output power. this signal is compared with reference value (660 kw), i.e. generator rated power, and the error signal is obtained. the obtained error is employed on pi controller where the value of the resistor to be placed in rotor circuit is calculated. the value of external resistor of rotor in each phase is 1ohm. considering rotor/stator windings’ turning ratio and p.u. impedance, its final boundary is 0.1 controlled by control limiting block. e. pitch angle control system here, speed quantity is used as a control signal. the role of this controller is to limit turbine rotation speed and, in turn, maintain output power at nominal value. since the system is of mechanical type and blades’ inertia is high, the performance of this system is lower than that of rcc method. when an abrupt wind over-speed occurs, rcc system starts operation. then because of the thermal limit in resistors, the received power of wind is reduced by the increase in blades’ angle. in figure 5, the block diagram of the model can be seen [13]. the findings in [14] are used to calculate the parameters. the blocks of servo part are used here in order to model the performance of blades’ slow movement, resulting in changes of the angles of interest with a maximum rate of 5 deg/s. the parameters are shown in table iv. engineering, technology & applied science research vol. 6, no. 6, 2016, 1280-1287 1283 www.etasr.com rahat and riaz: enhancing transient stability in limited variable speed induction generator (optislip)… fig. 5. block diagram of blades angle control table iv. parameters of blades angle control p=100 beta_min=0 rate_op= 5 time constant =0.5 i= 20 beta_max=90 rate_cl= 5 f. capacitor bank in binalood wind farm, each unit is equipped with a capacitor bank of 250 kvar composed of two 50 kvar and two 75 kvar steps. thus, two capacitors are used for each unit for modeling purpose as shown in figure 1. the controller of each capacitor is regulated in a way that the minimum power factor in each unit is 0.95. delay time in operation of each step is 0.5 seconds. g. electrical grid the set of elements and devices in the grid are simulated by existing models in the software. electrical characteristics of these elements are shown in table v. table v. parameters of blades angle control transforme r 20 kv line power transformer load power grid s=800 kva uk= 6 % dyn5 wiretype: dog r=0.273 km/ x=0.346 km/ s=230 mva uk= 12 % ynd11 tap numb: 19 p=30 mw q=10 mvar ssc=1370 mva " 6ki k a x/r=4.3 iii. power angle in induction machine from the machine terminal, by the change of parameter s, the generator will act as variable impedance that is dependent on s. magnetizing current amplitude is approximately independent of the slip value and is negligible in comparison to the rotor current in normal operating condition. thus, the stator is obtained in permanent mode by the following relationship: ssr r sss ijxrijx s r jxrv )()(  (5) in order to calculate the power angle of the induction machine, the vector vs is taken as a reference vector. thus, the power angle is defined by: )(tan )re( )im( tan 11 r x i i s s         (6) since the slip is negative, the power angle will be positive. induction machine active power is obtained by (7) in permanent operating condition: 2 2 2 2 sin x v rip ss  (7) the above equation states the relationship between the machine active power and the power angle. by the use of power angle, one can obtain the generator stability range. the higher this angle the higher the possibility for the generator to approach the non-stability region. the maximum power angle for which the generator remains stable depends on the generator characteristic and its operating point. a typical curve is illustrated in figure 6. here, the generator is stable when power angle during disturbance does not go beyond φ2 . fig. 6. power-angle curve for induction generator iv. disturbance and wind farm behavior the behavior of the wind farm is examined when a voltage drop appears on 20 kv bus according to figure 7. the trend of changing output active and reactive power of the wind farm is shown in figure 8. by the reduction of voltage, the produced active power reduces and so does the consumed reactive power. for a moment, the wind farm acts as a reactive power producer due to capacitor banks. reactive power production leads to a reduction in voltage drop due to fault occurrence in initial time. this helps us to improve stability. nevertheless, the fault current also increases. once the voltage recovers, the output reactive power increases instantly, approaching to its initial value. meanwhile, the speed of the generator also decreases until it reaches its initial value. however, due to rotor inertia, the reduction amount will be negligible. figure 9 shows the changes of speed and angles of blades during fault appearance. fig. 7. the experienced voltage drop v. wind farm stability enhancement apprach a. rotor resistance increase according to (6), it can be found that if the rotor resistance is high, the power angle will be small. small power angle requires more time in order to reach its critical speed. thus, it can be asserted that the generator has higher stability. however, with rcc system, one can assert that until a fault engineering, technology & applied science research vol. 6, no. 6, 2016, 1280-1287 1284 www.etasr.com rahat and riaz: enhancing transient stability in limited variable speed induction generator (optislip)… remains, this system stops to operate because the output power is less than the nominal power. after voltage restoration, an external resistor is inserted into the circuit due to power oscillations when the output power is more than the nominal power. although the insertion of external resistor intensifies the speed oscillations, it alleviates the power oscillations. there is no necessity to have rcc system in order to increase rotor resistor; it is adequate to have the winding rotor type generator with available terminals. consequently, a constant external resistor should be inserted into the rotor circuit. the resistor is normally short-circuited by a switch. it is brought to the circuit by opening that switch. in order to evaluate the behavior of such system, simulation results of a wind generating unit without/with switching resistor are illustrated in figure 10 and 11. the mentioned resistor with a value of 0.1 p.u. is connected to the grid immediately after fault occurrence. here, faults with a long-time are ignored for the better comparisons to a system with an external resistor. figure 10 depicts unit response to a 400ms-fault without the external resistor. it can be observed that the generator becomes unstable and its speed growth continues. figure 11 shows the response with an external resistor without any reactive power compensation. this resistor should remain in the circuit at least 850ms to help increase generator stability. that is, the resistor should stay in the rotor circuit after fault clearance. in fact, the main contribution of the resistor is after the fault which can be justified from another perspective. with voltage restoration and rotor current rise, power loss increases in the mentioned resistor such that the sum of generator output power will be less than the input mechanical power and its stability is confirmed by generator speed reduction. based on the simulations, even if the resistor is inserted into the circuit after fault clearance, it will enhance the generator stability. thus, there will be no problem even though a delay exists in fault detection and rotor resistor insertion into the circuit. b. rotor inertia increasing according to the oscillation equation of electrical machines, speed changes due to the difference between mechanical and electrical torques depending on machine inertia. when a fault occurs, more time is required for heavier wind turbine to increase the rotor speed and for the generator to reach the non-stable region. accordingly, by increasing rotor mass and inertia, the unit stability will be increased. beside generator stability improvement, this will aid in decreasing sudden oscillations in turbine speed due to wind speed swings [16]. additionally, the reduction of oscillations leads to reduced generator output power changes, improving the delivered power quality. considering a fault time of 400ms, a 70% increase in inertia constant of generators leads to wind farm stability without reactive power compensation. as shown, with the increase in inertia, the units’ speed growth drops when a fault occurs and since reactive power of the induction generator is proportional to the speed, the absorbed reactive power from the grid reduces. however, inertia rise causes mechanical oscillations to be reduced. mechanical oscillation frequency, therefore, comes closer to the grid natural frequency. this not only decreasing the output power quality, but also leads to subsynchronous resonance (ssr) and swing instability. the result in the long-term is extreme damages to the turbine shaft. further, high inertia in mechanical parts of the system results in a difficulty of halting turbine operation in emergency conditions. fig. 8. the trend of changing output active and reactive power of the wind farm during a disturbance in 20 kv bus fig. 9. reaction of a unit during the fault in the main bus of the power plant engineering, technology & applied science research vol. 6, no. 6, 2016, 1280-1287 1285 www.etasr.com rahat and riaz: enhancing transient stability in limited variable speed induction generator (optislip)… fig. 10. power plant instability during the fault without an external resistor c. grid reactance decreasing another approach to increase stability is to reduce the available reactance between the grid and wind farm. based on (6), a reduction of reactance, (transformer, transmission line and generator reactance), will decrease the power angle and, thus, increase stability. it should also be noted that changing the reactance of transformers, transmission lines and generators is not always viable. by decreasing path reactance by 50%, the system will become stable without the need of any reactive power compensation. the increase in total resistance of the path, based on (6), can improve stability. the increase in shortcircuit level and harmonics pollution are among the main disadvantage of the method. d. reactive power injection during fault occurrence, capacitor banks are unable to produce adequate reactive power; specially, when the wind farm is connected to a weak grid. thus, the flux of stator and rotor decrease, leading to reduced electric power. this, in turn, results in acceleration of turbine and generator. reactive power injection at the instant of fault occurrence increases voltage level and, in turn, power transferred from generator to the power grid. so, generator acceleration and magnetic flux reduction are avoided. for exact and timely injection of reactive power, dynamic injector such as statcom and svc should be used. the amount of reactive power injected depends on voltage drop and grid reactance. the lower the voltage drop and the higher the grid reactance, the less reactive power is required to maintain generator stability. figure 14 shows simulation results for the least required capacity to keep generator stability. the capacity is 15 kvar which is huge compared to the wind farm generated power. if the generated reactive power is considered as a back-up for compensation of unit fault, the required capacity for this unit will again be high. fig. 11. the response of a unit of the wind farm during the fault (switching resistor in rotor) engineering, technology & applied science research vol. 6, no. 6, 2016, 1280-1287 1286 www.etasr.com rahat and riaz: enhancing transient stability in limited variable speed induction generator (optislip)… fig. 12. the response of a unit of the wind farm during the fault (70% increase in inertia constant). vi. discussion for binalood wind farm of v47 model and optislip design from danish company, vestas, and close-to-real world external grid, there is a need to use at least 15mvar reactive power compensation using facts devices. however, reactive power compensation unit capacity can be reduced by two ways: 1. optimization of electrical and mechanical characteristics of wind farm 1. operational improvement of wind farm controllers such as blades’ angle control system and generator’s electrical characteristics during a fault by improving wind farm characteristics, one can reduce the compensation unit capacity by a half. in addition, it was found that by taking some operational improvements in generators and grid, there may be no need to inject reactive power to provide wind farm stability. the use of facts devices not only maintain generator stability, but also compensate reactive power, eliminate flickers produced by generator, and enhance delivered power quality to the grid. however, there is a need for a high capacity of 15 mvar, imposing high cost to the system. fig. 13. the response of a unit of the wind farm during the fault (50% decreas in path reactance) in binalood wind farm, since the generating units have winding type rotors, the addition of a rotor resistor during fault occurrence is a viable option. in this paper, simulations have been completed based on the least required resistor. of course, simply by selecting a larger resistor not only stability margin is increased, stator and rotor currents are also reduced. moreover, the presence of a resistor leads to increased damping and, compared to the other methods, oscillations are damped fast. it was shown that grid reactance reduction is also an appropriate method. but, a reduction of grid reactance results to an increased short-circuit level. inertia growth method and change of generator’s other parameters are not always possible or at least is a burdensome task that can be done only by the manufacturer. in designing a generator and its parameters, all involving factors should be considered aiming at the type of engineering, technology & applied science research vol. 6, no. 6, 2016, 1280-1287 1287 www.etasr.com rahat and riaz: enhancing transient stability in limited variable speed induction generator (optislip)… usage. improving the operation of wind farm controllers can be very effective in maintaining stability. for example, power angle control systems in wind farms equipped with these systems, such as binalood wind farm, is merely used for optimization of wind farm output power versus input wind amount and they have no response when a fault occurs until the speed of wind generator reaches critical region. correction of this operation is very influencing on system stability. fig. 14. the response of a unit of the wind farm during the fault with reactive power injection via statcom vii. conclusion considering the increase in wind farms’ penetration to power systems, stability of a wind farm and its connectivity to the grid during fault occurrence and grid disturbances are vital issues. in this paper, several methods have been examined for the improvement of a wind farm’s stability. different methods are employed to enhance stability when a near-by disturbance occurs. simulations are carried out using matlab and simulink. results are investigated and discussed and the different approaches are compared. acknowledgment funding support of this research was provided by the ramhormoz branch, islamic azad university, ramhormoz, iran. moreover this paper was derived from a report named “specify the best transient stability support method in binalood wind farm with optislip wind turbine during disturbance”. references [1] v. akhmatov, h. knudsen, a. h. nielsen, j. k. pedesen, “modeling and transient stability of large wind farms”, electrical power energy system, vol. 25, pp. 123-144, 2003 [2] t. sun, z. chen, “voltage recovery of grid-connected wind turbine after a short-circuit fault”, ieee 35th annual power electronics specialists conference, vol. 3, pp. 1991-1997, 2004 [3] k. rajambal, b. umamaheswari, c. chellamuthu, “electrical braking of large wind turbines”, renewable energy, vol. 30, pp. 2235-2245, 2005 [4] m. g.kanabar, s. a. khaparde, “rotor speed stability analysis of constant speed wind turbine generators”, 2006 international conference on power electronic, drives and energy systems, pp. 1-5, 2006 [5] v. agarwal, r. k. aggarwal, p. patidar, c. patki, “a novel scheme for rapid tracking of maximum power point in wind energy generation systems”, ieee trans. energy convers., vol. 25, no. 1, pp. 228-236, 2010 [6] h. famesh, guidelines for design of wind turbines, wind energy department, risø national laboratory, 2002 [7] f. iov, a. d. hansen, p. sorensen, f. blaabjerg, wind turbine blockset in matlab/simulink, aalborg university, 2014 [8] i. boldea, electrical machines and transformers, ed. didactica si pedagogica, 1994 [9] p. c. krause, o. wasynczuk, s. d. sudhoff, analysis of electric machinery, ieee press, 1995 [10] p. pillay, v. levin, “mathematical models for induction machines”, ieee industry applications conference, thirtieth ias annual meeting, vol. 1, pp. 606-616, 1995 [11] m. barakat, s. elmasry, m. e. bahgat, a. a. sayed, “effect of rotor current control for wound rotor induction generator on the wind turbine performance”, international journal of power electronics and drive systems, vol.2, no. 2, pp. 117-126, 2012 [12] d. j. burnham, s. santoso, “variable rotor resistance control of wind turbine generators”, ieee power and energy society general meeting, pp. 1-6, 2009. [13] v. le , x. li, y. li, t. l. t. dong, c. le, “an innovative control strategy to improve the fault ride-through capability of dfigs based on wind energy conversion systems”, energies, vol. 9, no. 2, art. no. 69, pp. 1-23, 2016 [14] g. ofualagba, e. ubeku, “wind energy conversion system: wind turbine modeling”, ieee proceeding on power and energy society general meeting – conversion and delivery of electrical energy in the 21st century, pp. 1-8, 2008 [15] a. petersson, analysis, modeling and control of doubly-fed induction generators for wind turbines, chalmers university of technology, goteborg, sweden, 2005 [16] a. g. g rodriguez, m. b. payan, c. i. mitchell, “pscad based simulation of the connection of a wind generator to the network”, ieee power tech proceedings, porto, 10-13 sept. 2001 microsoft word 06-3322_s_etasr_v10_n2_pp5377-5381 engineering, technology & applied science research vol. 10, no. 2, 2020, 5377-5381 5377 www.etasr.com khaskheli et al.: tank drainage for electrically conducting newtonian fluid with the use of the bessel … tank drainage for an electrically conducting newtonian fluid with the use of the bessel function mansoor ali khaskheli faculty of bio-sciences sbbuvas sakrand, pakistan mansoor11ms21@gmail.com kamran nazir memon department of mathematics and statistics quest nawabshah, pakistan kamrannazirmemon@gmail.com abdul hanan sheikh department of mathematics and statistics quest nawabshah, pakistan hanangul12@yahoo.com abdul majeed siddiqui pennsylvania state university york campus usa ams5@psu.edu syed feroz shah department of basic science & related studies muet jamshoro, pakistan feroz.shah@faculty.muet.edu.pk abstract-in this work, an unsteady flow for drainage through a circular tank of an isothermal and incompressible newtonian magnetohydrodynamic (mhd) fluid has been investigated. the series solution method is employed, and an analytical solution is obtained. expressions for velocity field, average velocity, flow rate, depth of fluid at different times in the tank and time required for the wide-ranging drainage of the fluid (time of efflux) have been obtained. the newtonian solution is attained by assuming σβ0 2 =0. the effects of various developing parameters on velocity field υυυυzzzz and depth of fluid h(t) are presented graphically. the time needed to drain the entire fluid and its depth are related and such relations are obtained in close form. the effect of electromagnetic forces is analyzed. the fluid in the tank will drain gradually and it will take supplementary time for complete drainage. keywords-tank drainage; newtonian mhd fluid; analytical solution; series solution i. introduction tank seepage by gravity is an old, but still open issue. the tank might be exhausted through an opening (gap situation) or may be depleted through a connected pipe. the pipe may be flat or vertical or may include a full directing system with vertical drop and even enlargement with valve and fittings, etc. the tank has frequently a barrel shaped structure with a vertical divider. anyway the base level may be cone molded, hemispherical or of another shape. gravity depleting of liquid frameworks is utilized quite often in businesses, e.g. in condensate depleting, water division, recovery of synthetic concoctions from a homestead tank, etc. the outfitted model will precisely show the tank depleting conduct for all tanks with a similar arrangement. end impacts, exactness of time estimation, precision of stature estimations and grating misfortunes will be examined [1]. many real life applications are modeled by the tank drainage flow. considering the inevitable applications, this problem has attracted research of not only mathematical but also engineering background. authors in [2] have used the newtonian fluid principle for tank drainage flow and power law fluid has been considered in [3] in an attempt to solve the problem analytically. theoretical results of time drainage have been derived in [3, 4]. further, in [5], the study has been extended while considering different geometries for outflow. in [3, 6] the discharge velocity and flow rate of the fluid outflowing through a hole are discussed using torricelli’s equation. the relationship between the efflux time needed to drain and the depth of the turbulent fluid has been derived in [7, 8]. the unsteady tank drainage flows are discussed in [9, 10] in two and three dimensional tanks respectively. efflux time and the cylindrical flow are presented in [11]. the gravitational force has been considered in [12], acting on a fluid in a spherical tank. in some similar work regarding gravity driven flow [13], the polymer solutions have been considered for drag reduction. an exact solution of navier stokes equation modeling the tank drainage flow problem for an electrically conducting newtonian fluid has been derived in [14]. the exact solution for a tank with a newtonian fluid with slip condition has been solved in [16]. in [17], an analytical solution approach of the tank drainage problem for an electrically conducting power law fluid is presented. in [18-20], the ellis fluid has been studied regarding the tank drainage problem with the special cases of newtonian, power law and bingham plastic fluid. ii. basic equations the governing equations for the incompressible thick liquid stream, dismissing warm impacts are: � ⋅ � = 0 (1) � � = −�� + �� + � ⋅ � + (� × �) (2) corresponding author: abdul hanan sheikh engineering, technology & applied science research vol. 10, no. 2, 2020, 5377-5381 5378 www.etasr.com khaskheli et al.: tank drainage for electrically conducting newtonian fluid with the use of the bessel … where � represents the velocity vector, ρ represents density, � is the dynamic pressure, � the body force and � the extra stress tensor. the material derivative is denoted by d dt and the electric current density is denoted by � . also � = �∘ + � (where �, �∘ and � are the total magnetic field, the forced magnetic field, and the induced magnetic field respectively). the modified ohm’s law and maxwell’s equation [21-24] are: � = ��� + � × �� (3) ��� � = 0,  � � � � !" �,  #$%&� � � '(' (4) where e, µm and σ are the electric field, the magnetic permeability, and the electrical conductivity respectively. the magnetic flux � is derived by the magnetic induction equation which describes the motion of an electrically conducting fluid under the influence of a magnetic field. the magnetic field � is assumed to be perpendicular to the velocity field � . the magnetic reynolds number is very small, which means that the induced magnetic field � is negligible in comparison with �∘. meanwhile no outdoor electric field is considered, the outcome of polarization of the ionized fluid is insignificant, and the fluid flow area is supposed to be free of electric field. under these expectations [25], the mhd force in (2) can be placed into: � � � � ���∘*� (5) the extra stress tensor, essential in a newtonain fluid is specified by: � � !+, (6) where +, is the first rivlin-ericksen tensor defined as: +, � �� ���� (7) for the rivilin-ericksen tensor, in cylindrical co-ordinates, we have: .v � 01 11 2'3'4 ,4 5'3'6 � �7 '3'8'9 '4 , 4 5'9'6 $7 '9'8': '4 , 4 ': '6 ': '8 ;< << = (8) iii. tank drainage consider a cylinder-shaped tank containing an incompressible newtonian mhd fluid. the radius of the tank is >and its diameter is ?. the initial depth of the fluid is @a. the fluid in the tank is drained down through a pipe of radius > and length b. let @�c� be the depth of fluid in the tank at any time c. we plan to compute flow rate, velocity profile, shear stress, pressure profile, average velocity on the pipe, connection of how does the time vary with length, and the time required for the whole drainage. we use cylindrical coordinates �%, d, e� with e-axis end to end the midpoint of the pipe in vertical direction and % -axis normal to it. then the flow is only in the e-direction, and the % and d components of velocity field are zero: � � ��4 , �6 , �8 � � �0,0, �8 �%, c�� (9) by (9), the equation of continuity (1) is identically fulfilled and the momentum equation (2) after using (3), reduces toward: r-component of momentum: 'f '4 � 0 (10) θ-component of momentum: , 4 'f '6 � 0 (11) z-component of momentum: � 'gh' � � 'f'8 i4 ''4 j% 'gh'4 k �l � �� *a �8 �%� (12) fig. 1. geometry of the tank drainage flow through the pipe from (10)-(12) we can see that the equation of motion is simple, yielding that the pressure is only a function of z and t and the equation to be solved for vz(r,t) is: � 'gh' � � 'f'8 i4 ''4 j% 'gh'4 k �l � �� *a �8 �%� (13) equation (13) is a partial differential equation for p and �8. the velocity in the pipe flow remains almost constant in time due to the slow draining since we may neglect the time derivative '9h' . the flow in the pipe of radius r is caused by both gravity and hydrostatic pressure. the pressures at the pipe entry and exit are one-to-one: at z=0, � � �, � �l@�c ), at z=l, m � m* � 0, so that: 'f '8 � � nop � �q (14) the domain of the problem is bounded by the following equation (boundary conditions): , 4 ''4 j% '9h'4 k � r(s t i �u�%� � � noi 5p � �q 17 (15) at % � 0, '9h'4 � 0 (16) at % � >, �u � 0 (17) equation (15) can be written as: 't 9y '4t ,4 '9h'4 � r( ts i �u�%� � � noi 5p � �q 17 (18) with: �8 � nor(t s 5p� �q 17 � z�%� (19) by using (19) in (16)-(18), we obtain: 't [�4� '4t ,4 '[ �4�'4 � r( ts i z�% � � 0 (20) engineering, technology & applied science research vol. 10, no. 2, 2020, 5377-5381 5379 www.etasr.com khaskheli et al.: tank drainage for electrically conducting newtonian fluid with the use of the bessel … with related boundary conditions: at % � 0, '[ �4�'4 � 0 (21) at % � >, z�% � � nor( ts 5p � �q 17 (22) the general solution of (20) after using the bessel function is: z�%� � \, �a ]%�a^_ri ` \*aa ]�%�a ^_ri ` (23) where \, and \* are arbitrary constants and �a and aa are the bessel functions of first and second kind of order zero. for a particular solution using (21)-(22) in (23), we get: z�%� � no�p� �bq�csd4(s^ efg h qrcs di(s^efg h(ts (24) substituting (24) in (19) we get: �8 � no�p� �bq�rcs di(s^efg h(t s j�a d>�a^ _r i h � �a d%�a^_ri hk (25) a. finding flow rate (l) according to (26) we can find the flow rate: l � m 2πr vr�r, t�drta (26) by using the velocity profile from (25) in (26), we get: l � nouiv�p� �bq�awxyd;{;| tf}t svg h ~iq�s di(s ^fg h (27) where �a is the modified bessel function of the 1st kind of order 0 and here 0fx, j; 3; it �t~ k presents the hyper geometric 0�x, regularized function, which can be specified as: 0�x, j; 3; it r(t s~i k � ∑ ji tr(t s ~i k � , ��{b���!���a (28) b. finding average velocity we find the average velocity �� by: �� � luit (29) putting (27) in (29) we get: �� � ��tt�����b��a��yd;{;� t��t sv� h ~���sdt�s^��h (30) c. finding mass balance we find the mass balance by: � � ��>* @�c�� � � l�t� (31) the remaining mass in the tank (mass balance) can be computed by the following procedure: putting (27) in (31), and then separating variables on both sides of equation one obtains by taking t=0, @�c� � @a: 2 2 4 0 0 1 2 0 0 ;3; 4 4 0( ) ( ) t r b gr t f lr i rb n h t l e h l σ ρ η σ η   −            = − + + � (32) the relation of tank depth with respect to time is: _~iq it � �s di(s ^fg h no iv a��yd;{;�t��t sv� h &� jp� �bqpsbq k � c (33) the time of efflux is attained by taking h(t)=0 in (33): ~iq it � �sdi(s^fgh noiva��yd;{;�t ��tsv� h &� jpsq 1k � c (34) remark: by taking �� *a � 0 in (34), the newtonian arrangement without mhd is recovered, which remains complete through by bernoulli's equation [26]. fig. 2. effect of � on velocity profile , when �=0.78g/cm3, >=1cm, l=9.8m/s2, b=10cm, @(c)=20cm, �=0.1, �a=0.25 fig. 3. effect of h(t) on velocity profile , when �=0.6poise, �=0.78g/cm3, >=1cm, l=9.8m/s2, b=10cm, �=0.1, �a=0.25 fig. 4. effect of l on velocity profile, when �=0.6poise, �=0.78g/cm3, >=1cm, l=9.8m/s2, @(c)=20cm, �=0.1, �a=0.25 engineering, technology & applied science research vol. 10, no. 2, 2020, 5377-5381 5380 www.etasr.com khaskheli et al.: tank drainage for electrically conducting newtonian fluid with the use of the bessel … fig. 5. effect of b0 on velocity profile, when �=0.6poise, �=0.78g/cm3, r=1cm, l=9.8m/s2, b=10cm, h(c�=20cm, �=0.1 fig. 6. effect of σ on velocity profile, when �=0.6poise, �=0.78g/cm3, >=1cm, l=9.8m/s2, b=10cm, h(t)=20cm, �a=1 fig. 7. effect of ρ on velocity profile, when r=1cm, �=0.6poise, l=9.8m/s2, b=10cm, h(c)=20cm, �=0.1, �a=0.25 iv. results and discussion in this article, the unsteady drainage problem through a circular pipe which is attached at the center of the circular tank by applying an incompressible, isothermal electrically conducting newtonian fluid was addressed, through which analytical solutions of bessel's differential equation were obtained, which are certainly more accurate than the solutions obtained with existing methods like adm and perturbation methods. the analytical solution was obtained in a compact form, which helps in visualizing the fluid velocity profile, flow rate, average velocity, and time required for complete drainage. this can be utilized in many applications, for example waste management, industrial flow problems, etc. the effect of velocity profile �u and depth h(t) has been analyzed with regard to various parameters. on the velocity profile, the effects of different parameters were observed, i.e. the effect of the applied magnetic field �a, electrical conductivity σ, pipe radius r, depth h(t), density ρ, dynamic viscosity �, length of pipe l and the difference of the radius of the circular tank rt on the depth of tank h(t) versus the radius of the pipe r and time t. it was observed that the magnitude of the velocity of the fluid decreases when the applied magnetic field b0, length of the pipe l, electrical conductivity σ, dynamic viscosity � increase (figures 2-7) and increases when the depth h(t)and density ρ of the fluid increase figures (8-9). fig. 8. effect of rt on depth w.r.to r, when �=0.6 poise, �=1.38g/cm3, g=9.8m/s 2 , l=10cm, t=1, h0=20cm, �=0.1, �a=0.25 fig. 9. effect of rt on depth w.r.to t, when �=0.6poise, �=1.38g/cm3, g=9.8m/s 2 , l=10cm, r=1cm, h0=20cm, �=0.1, �a=0.25 v. conclusion the equation of isothermal, incompressible, unsteady tank drainage flow for an electrically conducting newtonian fluid is studied to obtain closed form expressions of velocity field, average velocity, flow rate, fluid depth in the tank, and time required for complete drainage of the fluid (time of efflux) by using bessel functions. a relationship between the fluid depth and time required to complete drainage in (32) was obtained. fluid depth variation with time was demonstrated. it was also noted that the applied field and electrical conductivity are inversely proportional to the velocity field and that as the electromagnetic forces increase the fluid in the tank drains slow and clearly complete drainage takes more time. the presented results are validated by assuming ��a * � 0 in (34). the results of this work are compatible with those presented in [27], where the bernoulli's equation was used. references [1] d. d. joye, b. c. barrett, “the tank drainage problem revisited: do these equations actually work?”, the canadian journal of chemical engineering, vol. 81, no. 5, pp. 1052–1057, 2003 [2] a. n. hrymak, “applied fluid mechanics by t. c. papanastasiou, prentice-hall, englewood cliffs, nj, 1994, 520 pp.”, aiche journal, vol. 41, no. 10, pp. 2342–2342, 1995 [3] r. b. bird, w. e. stewart, e. n. lightfoot, transport phenomena, john wiley and sons, 1961 [4] e. j. crosby, experiments in transport phenomena, wiley, 1961 engineering, technology & applied science research vol. 10, no. 2, 2020, 5377-5381 5381 www.etasr.com khaskheli et al.: tank drainage for electrically conducting newtonian fluid with the use of the bessel … [5] d. hanesian, a. perna, a laboratory manual for fundamentals of engineering design, chemical engineering module: measurements laboratory, new jersey institute of technology, 1995 [6] n. d. nevers, fluid mechanics for chemical engineers, mcgraw-hill education, 2005 [7] j. o. wilkes, fluid mechanics for chemical engineers with microfluidics and cfd, prentice hall, 2006 [8] s. channer, k. n. memon, a. a. ghoto, a. m. siddiqui, s. f. shah, “analytical solutionof lift for thin film flow for phan thien tanner fluid”, sindh university research journal, vol. 51, no. 2, pp. 215–222, 2019 [9] l. k. forbes, g. c. hocking, “unsteady draining flows from a rectangular tank”, physics of fluids, vol. 19, no. 8, article id 082104, 2007 [10] l. k. forbes, g. c. hocking, “unsteady draining of a fluid from a circular tank”, applied mathematical modelling, vol. 34, no. 12, pp. 3958–3975, 2010 [11] g. v. s. k. reddy, c. v. subbarao, “comparison of efflux times between cylindrical and spherical tank through an exit pipe”, international journal of engineering and applied sciences, vol. 3, no. 2, pp. 61–68, 2011 [12] c. v. subbarao, p. s. rao, g. m. j. raju, v. s. r. k. prasad, “slow draining of large spherical tank under gravity”, elixir international journal, vol. 50, pp. 10346-10348, 2012 [13] c. v. subbarao, y. p. yadav, p. king, “drag reduction by surfactant solutions in gravity driven flow systems”, iranian journal of chemistry and chemical engineering, vol. 32, no. 2, pp. 119–123, 2013 [14] c. y. wang, “on a class of exact solutions of the navier-stokes equations”, journal of applied mechanics, vol. 33, no. 3, pp. 696–698, 1966 [15] a. a. mahessar, a. l. qureshi, a. n. laghari, s. qureshi, s. f. shah, f. a. shaikh, “impact of hairdin, miro khan and shahdad kot drainage on hamal dhand, sindh”, engineering, technology & applied science research, vol. 8, no. 6, pp. 3652–3656, 2018 [16] k. n. memon, a. m. siddiqui, s. f. shah, “exact solution of tank drainage for newtonian fluid with slip condition”, sindh university research journal, vol. 49, no. 2, pp. 283–288, 2017 [17] s. islam, k. n. memon, a. m. siddiqui, s. f. shah, “analytical solution of tank drainage for electrically conducting power law fluid”, available at: https://www.preprints.org/manuscript/201802.0033/v1, 2018 [18] k. afanasiev, a. munch, b. wagner, “landau-levich problem for nonnewtonian liquids”, physical review e, vol. 76, no. 3, article id 036307, 2007 [19] n. ali, a. abbasi, i. ahmad, “channel flow of ellis fluid due to peristalsis”, aip advances, vol. 5, no. 9, article id 097214, 2015 [20] k. n. memon, s. f. shah, a. m. siddiqui, “exact solution of unsteady tank drainage for ellis fluid”, journal of applied fluid mechanics, vol. 11, no. 6, pp. 1629–1636, 2018 [21] m. r. mohyuddin, t. gotz, “resonance behaviour of viscoelastic fluid in poiseuille flow in the presence of a transversal magnetic field”, international journal for numerical methods in fluids, vol. 49, no. 8, pp. 837–847, 2005 [22] j. j. v. rossum, “viscous lifting and drainage of liquids”, applied scientific research, section a, vol. 7, pp. 121–144, 1958 [23] i. pop, m. kumari, g. nath, “conjugate mhd flow past a flat plate”, acta mechanica, vol. 106, pp. 215–220, 1994 [24] s. abel, p. h. veena, k. rajgopal, v. k. pravin, “non-newtonian magnetohydrodynamic flow over a stretching surface with heat and mass transfer”, international journal of non-linear mechanics, vol. 39, no. 7, pp. 1067–1078, 2004 [25] m. abdullah, n. saada, “free convection mhd couette flow with application of periodic temperature and constant heat flux on walls”, engineering, technology & applied science research, vol. 9, no. 2, pp. 4007–4011, 2019 [26] g. f. round, v. k. garg, applications of fluid dynamics, e. arnold, 1986 engineering, technology & applied science research vol. 9, no. 2, 2019, 4002-4006 4002 www.etasr.com ozhan et al.: effects of brick and aerated concrete infill walls on buildings effects of brick and aerated concrete infill walls on buildings hacer bilir ozhan department of civil engineering, bursa technical university, bursa, turkey hacer.ozhan@btu.edu.tr caner beklen department of civil engineering, cukurova university, adana, turkey cnr_beklen@hotmail.com ismail h. cagatay department of civil engineering, cukurova university, adana, turkey hcagatay@cu.edu.tr abstract—it has already been proved that infill walls have great impact on the behavior of the frame systems, especially under earthquake-like lateral loads. infill walls are generally considered as partition members between spaces in concrete frame systems. they are generally included into calculations as dead loads exerted on beams, but they have various impacts on the behavior of frame-wall systems. therefore, the well-known behavior of infill walls will have positive contributions. in the present study, a 10-story building was modeled with brick and aerated concrete infill walls. window and door spaces were taken into consideration. infill walls were modeled with the equivalent compression strut method. changes in building rigidity, period, lateral displacement, base shear force and building behavior were investigated with relevant analyses. keywords-infill wall; earthquake analysis; brick; aerated concrete; equivalent compression strut i. introduction along with increasing sheltering demands, construction industry is continuously growing. however, the available land for construction is not increasing at the same pace, thus highrise buildings have opted. in this sense, economy and utilization of concrete frame systems have become significant issues of construction industry. generally, light-weight materials are preferred in such frame systems especially for heat, noise and similar insulations and partition walls are constructed also with these materials to facilitate the utility of building space. infill walls have significant effects on the bearing-system of the building under lateral loads, therefore, the behavior of these walls under lateral loads, like earthquake loads, should be well elucidated. negative impacts of such walls are generally attributed to the diverse range of materials, the diversity in their strength, and insufficient inspections of present implementations. in practice, these walls are reflected in calculations as the members increasing only the dead loads of the building and their load-bearing behaviors are generally neglected. observations and investigations on earthquake damages of the buildings revealed that although infill walls were not considered in calculations made for earthquakes, they resisted to lateral earthquake loads like a shear wall until time of failure. post-failure behavior of these walls cannot be estimated accurately and they are considered as if they did not exist in calculations. then, great damages are experienced in practice. the literature on infill walls revealed that infill walls had significant contributions to rigidity, load-bearing capacity, period and damping-like dynamic attributes of the buildings. the structure altogether behaves like a composite material. therefore, the behavior of each and every single member of the structure should be known. in the present study, a ten-story building was modeled to investigate how effective the infill walls in increasing building resistance to vertical and especially to lateral loads. bricks and aerated concrete were used in building infill walls. in calculations, the behavior and effects of infill walls with two different materials were investigated. ii. methodology a. infill walls there are several studies about the behavior of frame systems with/without partition walls under earthquake and similar lateral loads. in [1], experiments were conducted to determine the behavior of infill walls under lateral loads and it was reported that the concrete frame with infill walls had greater load-bearing capacity than the frames without infill walls and infill walls significantly improved building elasticity and rigidity behavior. infill walls are not always formed in fully-filled fashion. there may be empty spaces on them left for different purposes. in cases where the infill wall was created as macro-void, the frame system with infill wall provided at least 40% greater contribution to lateral loadbearing capacity as compared to frame system without an infill wall [2]. similarly, a soft-story concrete building and a concrete building without infill walls exhibited similar behavior with regard to lateral load bearing capacity [3]. in turkey, ground floors are generally used for purposes other than housing. ground floor projects are thus generally altered (columns are cut, existing walls are removed etc.). therefore, partition walls generally do not exist in ground floors. in this case, the upper floors behave more rigid because of the partition walls in comparison with ground floors. such a case results in concentrated energy consumption on the ground floors. a soft-story is formed in such buildings and destructive damages and failures are experienced in this weaker floor of the building. in other cases, damages are generated over the columns of these floors without infill walls. since the earthquake energy is confronted in this floor, the rigidity of the corresponding author: hacer bilir ozhan engineering, technology & applied science research vol. 9, no. 2, 2019, 4002-4006 4003 www.etasr.com ozhan et al.: effects of brick and aerated concrete infill walls on buildings columns and shear walls of this floor should be improved as to bear inter-floor displacements. if the walls are constructed short and connected to frames, then the columns of the main frame cannot bend in between two stories they connect under lateral forces of an earthquake because of the rigidity of the walls along their own planes. then a soft-story is formed. in this case, columns are forced to bend over the section with the empty height left over the upper sections of the walls. then quite greater shear forces are generated over this section of the columns [4]. long windows extending along the both sides of the walls preferred in factory-like buildings generate a shortcolumn effect and reduce the effective length of the column. experimental works on frames with infill walls revealed that door and window spaces should be avoided on these members and thus building rigidity should be increased to reduce potential damages [5, 6] confinement of stirrup should be increased to bear resultant shear force. b. brick as infill wall material brick is one of the most commonly used and preferred materials for infill walls of concrete structures. since the use of two different materials in infill walls is compared in this study, horizontally perforated bricks with greater hallow ratios were used since they have low compression strength. specifications for horizontally perforated bricks are provided in table i. while modeling infill walls, 13.5 horizontally perforated bricks were used in exterior walls and 8.5 horizontally perforated bricks were used in interior walls. g2-class aerated concrete was also used as infill wall material. this material is generally used as exterior and interior infill wall material of concrete frame structures or used as load-bearing exterior and interior wall material of masonry structures. they are composed of 7080% less concrete, and are resistant to earthquake and fires. specifications for g2-class aerated concrete are provided in table ii. table i. horizontally perforated bricks specifications specification 8.5 horizontally perforated bricks 13.5 horizontally perforated bricks height×width×length (cm) 8.5×19×19 13.5×19×19 mean compressive strength (mpa) 4 5.2 single brick weight (kg) 2 3 bricks per m2 25 25 or 33 table ii. aerated concrete specifications specification for interior walls for exterior walls length×height×width (cm) 60×25×8.5 60×25×19 mean compressive strength (mpa) 2.5 2.5 weight of single aerated concrete (kg) 5.1 12 number of aerated concrete per m2 6.66 6.66 c. modulus of elasticity infill wall modulus of elasticity significantly influences wall rigidity of frame-wall systems. infill walls exhibit complex behavior since the modulus of elasticity values in different directions (horizontal, vertical, diagonal) are different. significant effects of compressive strength of the material, height, compressive strength of mortar layer on the modulus of elasticity are indicated in [7]. it was also indicated that the modulus of elasticity of infill walls was different for plastered and unplastered walls and varied with the thickness of the plaster layer. modulus of elasticity values of brick walls used in different studies are provided in table iii. in this table, ew and ec respectively express the modulus of elasticity of the wall and the concrete under compression. table iii. brick wall modulus of elasticity values reference ew (mpa) ec (mpa) ed / ec [8] 5200 30000 1/6 [9] 1240 30000 1/24 [10] 2850 28500 1/10 [11] 6000 12000 1/2 [12] 700 25310 1/36 [13] 17000 28500 1/1.7 [14] 3000 32000 1/10 [15] 1000 in a study carried to determine aerated concrete wall modulus of elasticity values [16], the modulus of elasticity of a wall constructed with a2 class aerated concrete and without plaster was reported as 1500mpa. the modulus of elasticity of a plastered wall was reported as 2091mpa, unit weight was reported as 400kg/m3 and compressive strength was reported as 2.5mpa. in [17], masonry aerated concrete blocks were cut into 10×10×10cm3 cubes and 10×10×40cm3 prisms and their modulus of elasticity values and poisson ratios were experimentally determined. resultant values are summarized in table iv. in [18], modulus of elasticity of aerated concrete of a wall panel was identified as 1750mpa. specifications of turkish aerated concrete producers association for aerated concrete of wall blocks are provided in table v [2]. table iv. physical attributes of aerated concrete wall specific gravity (n/m3) mean cube strength (mpa) mean prismatic strength (mpa) mean initial modulus of elasticity(mpa) mean poisson ratio 7500-8000 4.90 3.32 1620 0.21 9000 4.60 3.08 1570 0.20 8000-8500 3.60 2.64 1490 0.19 table v. aerated concrete wall blocks material strength class a2 a3 a4 unit mean compressive strength 2.5 3.5 5.0 mpa modulus of elasticity 1250 1750 2250 2750 mpa d. equivalent diagonal strut model previous studies conducted to determine and elucidate the linear behaviors of infill walls [19, 20] revealed diagonal cracks at the center of the modeled panel, voids between the frame and infill at opposite unloaded corners of the model, and a full contact at the other two loaded diagonal corners. to reflect such behaviors on actual infill walls and to facilitate the analysis of infill wall frame systems, infill walls were placed as equivalent compression struts (figure 1). the compressive load-bearing region was represented with an equivalent diagonal strut in static analysis of frame systems under external forces (figure 2). engineering, technology & applied science research vol. 9, no. 2, 2019, 4002-4006 4004 www.etasr.com ozhan et al.: effects of brick and aerated concrete infill walls on buildings fig. 1. representation of infill wall analysis model fig. 2. representation of infill wall frames with two end-hinged equivalent virtual diagonal bar different researchers used different assumptions in calculating the thickness of equivalent diagonal struts. authors in [19, 20] proposed (1) and (2) for strut width representing the infill wall: ( )0 175 0 4. . ' 'w h h l= − + (1) 4 2 4 sin ' m c c e t e i h   = (2) the compressive load-bearing region was represented with an equivalent virtual bar in static analysis of frame systems under external forces (figure 2). the value of θ used in (2) is calculated with the aid of (3): 1tan ( '/ ')h l −= (3) where w is the width of equivalent diagonal compression strut, λ is the rigidity parameter of the infill and frame, h the floor height, l the frame span, h΄ the infill wall height, l΄the infill wall width, em is the modulus of elasticity of equivalent virtual compression strut, t the infill wall thickness, θ the angle of equivalent virtual compression strut from the horizontal plane, ec the frame modulus of elasticity, and ic is the column moment of intertia. e. partially infilled frames infill walls are either constructed without openings or they may have window and door spaces. in such a case, equivalent compression strut width is multiplied with a reduction factor to include loss of strength due to these void spaces into calculations [21]. ( ) ( )1 2 reduction i iw w r r= (4) 2 1 0 6 1 6 1( ) . . gap gap i panel panel a a r a a        =  −  +         (5) where agap is the total area of void spaces over the infill wall, apanel is the full area of infill wall without voids, (r1)i the expression of reduction factor for infill walls with void spaces, and (r2)r the expression of reduction factor for existing infill damages. in cases where infill walls have window and door spaces, the reduction factor r1 is applied on the calculations made for the width of equivalent compression strut. in cases where there aren’t any damages on infill walls, then r2 is considered as 1. in cases where there are heavy damages, r2 can be taken as 0 since the wall will have slight contributions to building rigidity due to breakouts between the frame and the infill wall. in such cases, the wall will contribute only to the weight of the building and will not have any contributions to lateral rigidity. iii. building model a building was modeled with two different infill wall materials to investigate their effects on structural irregularities. total floor height (hn) was 15m and the elasticity level was high. earthquake analysis of a regular structure was performed with equivalent seismic load method. table vi. building information building information slab 12cm interior wall thickness (brick and aerated concrete) 10cm exterior wall thickness (brick and aerated concrete) 20cm beam dimensions 25×50 cm column dimensions 40×40cm concrete class c30 concrete modulus of elasticity (ec) 32000mpa brick wall modulus of elasticity (ew) 1000mpa aerated concrete wall modulus of elasticity (ew) 2091mpa number of floors 10 bearing system type r.c. frame floor height 3m earthquake zone 1 effective ground acceleration coefficient 0,4 local ground class z3 spectrum characteristic periods ta=0.15sn tb=0,60sn building ax along x direction are a, b, c, d, e and f and axle spacing was 5m (figure 3). the axles along y direction are 1, 2, 3 and 4 and ax spacing was 4m, 2m and 4m. except for the window in the hall, the size of all windows was 150×130cm2 and the door size was 90×220cm2. the size of the window at the hall was 100×200cm2. the building was considered as separated from a-axle with a joint to separate shear wall effect from the building, in this way, the effects of infill wall on the building were analyzed. fig. 3. building model https://www.sciencedirect.com/topics/engineering/struts https://www.sciencedirect.com/topics/engineering/struts engineering, technology & applied science research vol. 9, no. 2, 2019, 4002-4006 4005 www.etasr.com ozhan et al.: effects of brick and aerated concrete infill walls on buildings the abbreviations for the model are: bef: empty frame modeled though taking brick wall only as weight, bwf: the frame with brick wall, aef: empty frame modeled though taking aerated concrete wall only as weight, awf: the frame with aerated concrete wall. normal floor weight (n), roof-floor weight (r) and total building weight at an incidence of earthquake (w) are provided in table vii. table vii. building floor weights floor wi (t) bef bwf aef awf n 287.25 287.25 252.85 252.85 r 228.19 228.19 217.22 217.22 w 2813.44 2813.44 2492.87 2492.87 building total weight was reduced by 11.36% with the use of aerated concrete wall instead of brick wall. the first natural vibration period of 10-story building along the y-axis was calculated with the aid of rayleigh ratio. period values are provided in table viii. table viii. period values of the building period (s) bef bwf aef awf 1.38 1.17 1.28 1.01 period values decreased by 7.25% with decrease in building weight. weight and modulus of elasticity together decreased period values by 13.68%. period values decreased by 15.22% with the modeling of brick wall and 21.09% with the modeling of aerated concrete wall (table ix). total equivalent seismic load of 10-story building along the y-axis (base shear force) (vt) was calculated and provided in table x. base shear force values decreased by 6.91% with decrease in building weight. weight and modulus of elasticity together reduced base shear force values by 7.35%. base shear force values increased by 13.70% with the modeling of brick wall and by 13.155 with the modeling of aerated concrete wall (tables x-xi). table ix. % eductions in building period values bwf/bef awf/aef aef/bef awf/bwf 15.22 21.09 7.25 13.68 table x. base shear force values bef bwf aef awf 183.00 208.07 170.36 192.77 table xi. % changes in building base shear force bwf/bef awf/aef aef/bef awf/bwf (+)13.70 (+)13.15 6.91 7.35 equivalent seismic loads were affected on the displaced center of gravity considering +5% additional eccentricity at floor alignments (ey=0.5). eccentricity-induced displacement values for the 10th floor of the building are provided in table xii. reductions in displacement values were also calculated and are provided in table xiii. table xii. displacement values of 10th floor frames (di)min (m) (di)max (m) bef 0.0410 0.0579 bwf 0.0343 0.0470 aef 0.0382 0.0539 awf 0.0235 0.0318 table xiii. % reductions in building displacement values floor bwf/bef awf/aef aef/bef awf/bwf min. max. min. max. min. max. min. max. 10 16.37 18.80 38.49 41.07 6.87 6.88 31.50 32.42 9 16.75 19.06 39.03 41.46 6.87 6.88 31.79 32.65 8 17.07 19.24 39.51 41.88 6.89 6.90 32.09 32.99 7 17.32 19.35 39.95 41.96 6.86 6.89 32.36 32.99 6 17.58 19.42 40.29 42.11 6.90 6.90 32.55 33.12 5 17.72 19.37 40.60 42.16 6.88 6.91 32.78 33.21 4 17.71 19.17 40.77 42.05 6.92 6.90 32.99 33.26 3 17.50 18.67 40.63 41.65 6.96 6.87 33.04 33.19 2 16.57 17.50 39.93 40.52 6.90 6.90 32.97 32.88 1 13.73 14.23 36.94 37.03 6.72 6.82 31.82 31.59 maximum displacement graphs of the 10-story building for different column sizes were drawn for all floors. displacements increased with increasing number of floors (figure 4). fig. 4. maximum deflection graphs of the building earthquake analysis for all frame systems of the building revealed that torsion irregularity, rigidity irregularity, relative floor displacement and second-order indicator values were below the limit values specified in [23]. iv. conclusion and discussion in previous experimental studies, brick wall modulus of elasticity values were reported between 1000mpa–4272mpa and the taken value of 1000mpa, based on concrete class for hallow bricks used in construction of a hotel, was found to be suitable [14]. with the use of aerated concrete instead of brick in infill walls, the building’s total weight decreased by 11.36%, period values decreased by 7.25%, base shear force values decreased by 6.91% and displacements decreased by 6.72%6.96%. weight and modulus of elasticity together reduced period values by 13.68%, shear force values by 7.35% and displacements by between 31.50%-33.26%. with the model of brick wall, period values decreased by 15.22%, shear force values increased by 13.70% and displacements decreased by between 13.73-19.42%. with the modeling of aerated concrete, period values decreased by 21.09%, shear force values increased by 13.15% and displacements decreased by between 36.94%-42.16%. eventually, in turkey where frequent engineering, technology & applied science research vol. 9, no. 2, 2019, 4002-4006 4006 www.etasr.com ozhan et al.: effects of brick and aerated concrete infill walls on buildings earthquakes and heavy destructions are experienced, no concessions should be made on the quality and rigidity of the buildings. therefore, the behavior of any single constructional member should be well-known and calculations should be made accordingly. previous studies and present analysis reveal that infill walls have great contributions to building behavior under lateral loadings like earthquakes and negligence will bring about various negative outcomes. it is recommended that these existing structural members should definitely be included into calculations to improve positive impacts of infill walls on structure strength, elasticity and rigidity. acknowledgment this study was supported by the scientific research projects department of cukurova university (project no: mmf2008yl3). references [1] p. govindan, m. lakshmipaty a. r. santhakumar, “ductility of infilled frames”, journal proceedings, vol. 83, no. 4, pp. 567-576, 1986 [2] e. vintzeleou, “infilling of reinforced concrete frames as a strengthening intervention”, seminar on the assesment and redesign of reinforced concrete structures, izmir, turkey, 1989 [3] p. negro. g. verzeletti, “effect of infills on the global behaviour of r/c frames:energy considerations from pseudo-dynamic tests”, earthquake engineering and structural dynamics, vol. 25, no. 7, pp. 753-773, 1996 [4] i. h. cagatay, “binalarda kisa kolona etki eden parametrelerin incelenmesi”, altinci ulusal deprem muhendisligi konferansi (sixth national earthquake engineering conference), istanbul, turkey, october 16-20, 2007 (in turkish) [5] r. zarnic, “modelling of response of masonry infilled frame”, 10th europen conference on earthquake engineering, vienna, austria, august 28-september 2, 1995 [6] a. kocak, depreme, dayanikli yapi tasarimi ders notlari, yildiz teknik universitesi, 1998 (in turkish) [7] h. bilir ozhan, i. h. cagatay, “mechanical behavior of brick masonry panels under uniaxial compression”, journal of mechanics of materials and structures, vol. 9, no. 4, pp. 385-395, 2014 [8] i. o. demirel, e. canbay, b. binici, a. yakut, z. eryurtlu, “gazbeton dolgulu betonarme cercevelerin deprem performansi uzerine deneysel çalisma”, 3. turkiye deprem muhendisligi ve sismoloji konferansi (turkey earthquake engineering and seismology conference), izmir, turkey, october 14-16, 2015 (in turkish) [9] i. aydogdu, dolgu duvarli cercevelerin davranisi, msc thesis, yildiz teknik universitesi, 1995 (in turkish) [10] e. yalcin, dolgu duvarlari ve konumlarinin cok katli betonarme yapilarin deprem kuvvetleri altindaki davranisina etkileri, msc thesis, itu, 1999 (in turkish) [11] i. h. cagatay, s. ve guzeldag, yeni deprem yonetmeligi (tdy-98) sap2000n uygulamalari, birsen 2002 (in turkish) [12] o. oktem, betonarme cerceve sistemlerinin lineer olmayan hesabi ve dolgu duvarların modellenmesi, msc thesis, itu, 2003 (in turkish) [13] e. dundar, cok katli betonarme yapılarda bolme duvarlarının deprem davranisina etkisi, msc thesis, cukurova universitesi, 2007 (in turkish) [14] a. budak, dolgu duvarli cercevelerin sonlu elemanlar yontemi ile malzeme bakimindan dogrusal olmayan hesabi, phd thesis, karadeniz teknik universitesi, 1997 (in turkish) [15] s. donmez, deprem etkisinde betonarme binalarda hasarin olusmasinda dolgu duvarların modellenmesi ve tasiyici sisteme katkisi, msc thesis, itu, 2006 (in turkish) [16] b. yucesan, betonarme cercevelerin guclendirilmesinde yuksek dayanimli tugla duvarlar, msc thesis, itu, 2005 (in turkish) [17] a. karaduman, “dolgu duvarli cercevelerin yatay yukler altindaki davranislari uzerine deneysel bir calısma”, muhendislik fakultesi muhendislik bilimleri dergisi, (journal of engineering sciences), pamukkale university, vol. 11, no. 3, pp. 345-349, 2005 (in turkish) [18] z. babayev, c. eyyubov, i. murat, c. askerov, “kirec tasiyla yapilmis tasiyici duvarların dusey ve yatay yuklerin etkisi altindaki davranisinin arastirilmasi”, ace fifth international congress on advances in civil engineering, itu, istanbul, 2002 (in turkish) [19] h. sesigur, o. c. celik, f. cili, “deprem riski dusuk bolgelerde orta yukseklikteki donatili gazbeton binalarin uygulanabilirligi, altinci ulusal deprem muhendisligi konferansi (sixth national earthquake engineering conference), istanbul, turkey, october 16-20, 2007 (in turkish) [20] b. s. smith, c. a. carter, “method of anlaysis for infilled frames”, proceedings of the institution of civil engineers, vol. 44, no. 1, pp. 3148, 1969 [21] r. j. mainstone, “on the stiffness and strengths of infilled frames”, in: ice proceedings, suppl. iv, pp. 57-90, 1974 [22] e. caglayan, “betonarme cercevelerin yatay yuklere gore analizinde dolgu duvar etkisinin incelenmesi, msc thesis, fen bilimleri enstituss manisa celal bayar universitesi, 2006 (in turkish) [23] turk deprem yonetmeligi, deprem bolgelerinde yapilacak yapilar hakkinda yonetmelik, 26454 2007 (in turkish) engineering, technology & applied science research vol. 8, no. 3, 2018, 3044-3047 3044 www.etasr.com memon et al.: effect of prepackaged polymer on compressive, tensile and flexural strength of mortar effect of prepackaged polymer on compressive, tensile and flexural strength of mortar noor ahmed memon department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan nahmedmemon@gmail.com aijaz hussain larik department of civil engineering swedish college of engineering and technology rahim yar khan, pakistan engraijazlarik@gmail.com muhammad aslam bhutto department of civil engineering ned university of engineering & technology karachi, pakistan mabhutto@neduet.edu.pk nawab ali lakho department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan nawablakho@gmail.com muneeb ayoub memon department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan engr.muneebmemon@gmail.com ammaar noor memon department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan anmemon96@gmail.com abstract—synthetic materials, like various types of polymers, are introduced as having cementitious qualities, which improve the system of pores of mortars and concretes by the formations of polymer films and thereby enhancing their strength and durability. this experimental study focuses to use a water-based pre-packaged grout powder containing polymer as cementitious material available in the local market under the brand ‘hibond (universal)’ in mortar. the hi-bond is added in mortar as partial replacement of cement. the replacement levels were from 2.5% to 10% of cement by weight with an increment of 2.5%. in addition, same proportions mortar without hi-bond, was also tested to compare the hi-bond effectiveness in mortar. mortars of three proportions; 1:2, 1:3 and 1:4 were cast and tested. the water-binder ratio was fixed at 0.5. the specimens were cured in three curing conditions i.e., water, room temperature and natural environment (outside the room, open to sky). all specimens were tested after 28 days of curing. the mortar performance with and without hi-bond was investigated in terms of compressive strength, tensile strength and flexural strength. enhancements in almost all the strength properties of mortar with hi-bond were observed. a pronounced effect of curing condition and the mortar proportion is observed on the strength properties of the prepackaged polymer. keywords-prepackaged polymer mortar;compressive strength; tensile strength; flexural strength i. introduction cement mortars are a main component of construction industry, used in many applications over a structure such as finish and repair, concrete cover to reinforce concrete structures from environmental effects, manufacturing of ferrocement elements, mortar joints in brick masonry structures and protection layers to porous construction materials like light weight concrete elements or brick masonry walls [1-4]. various additives including synthetic (resins and other polymers) and non-synthetic materials (fly ash, slag, silica fume etc) owing cementitious properties are used not only to enhance the strength properties of concrete mortars and grouts but their durability characteristics also [5-8]. water based polymers are used in different ways in concrete and plain mortar. the polymers when used with cement and aggregates, the produced composite is known as polymer modified concrete (pmc) and polymer modified mortar (pmm). pmm consists of cement sand mixture, organic film-forming polymer latex in emulsion (liquid) form, and other related ingredients in appropriate ratios [10-11]. the other way is to mix polymer with the aggregate only without cement. the product is known as the polymer concrete (pc) and polymer mortar (pm). however the addition of polymers modifies many properties of concrete/mortar e.g. enhances strength properties, produces adhesion, reduces permeability, improves resistance against chemical attacks, exhibits high durability and is environmental friendly [12-15]. the above mentioned remarkable improvements in the properties of concrete with polymers encourage their use in many structural and non-structural applications in construction engineering [1619]. a wide variety of polymers is reported being used to modify the concrete and mortar. these may be in the forms of liquid resins, water based/water soluble latexes, redispersible powders etc. [20, 21]. since the polymer modified concretes and mortars are produced by adding polymers at the working place during the mixing of the other common ingredients of the concrete/mortar along with other admixtures, thus, control of the proportion of all the ingredients and the polymer dosage becomes very difficult causing a lot of variations in the final product from batch to batch [22-24]. this led to the engineering, technology & applied science research vol. 8, no. 3, 2018, 3044-3047 3045 www.etasr.com memon et al.: effect of prepackaged polymer on compressive, tensile and flexural strength of mortar development of prepackaged polymers which are produced from dispersible polymer powders. prepackaged product is often in the form of powder which may only be mixed with water at the work place, which makes work more efficient. this technique facilitates to achieve accuracy of the batching and mixing [25]. nowadays prepackaged polymer powders are produced by various manufacturers. in pakistan a prepackaged polymer with the brand name of hi-bond is available in the market. a substantial experimental work is reported by various researchers [26-30] regarding the efficient use of hi-bond (universal) in repair and rehabilitation and other applications of hi-bond in concrete and grout. since the pre-packaged polymers may also be used as an additive in the cement mortars their dosage and mortar proportion (cement: sand) shall affect the overall performance of the mortars. further, the exposing conditions (curing conditions) also influence the strength and durability characteristics of the mortar. therefore, this paper reports the results of the experimental study conducted to investigate the fundamental strength properties of mortars of different proportions with different dosage of hi-bond exposed to three different curing conditions i.e., water, room temperature and natural environment (ambient temperature open to sky). the strength properties studied are compressive strength, tensile strength and flexural strength. ii. materials and methodology ordinary portland cement (opc) and hi-bond (universal) were selected as binder for this study. three mix proportions of cement: sand were taken, 1:2, 1:3 and 1:4. hi-bond was added up to 10% following an increment of 2.5% (starting from 0%) by weight of cement. all five batches were cast and tested for each studied parameter (table i). iii. results and discussion a. compressive strength table ii presents the details of the results of the average mortar compressive strength. it can be that the compressive strength increases with increase in hi-bond dosage in every case of mortar proportion and every exposing condition. this increase ranges between 2.1% and 21.3% depending upon the mortar proportion, hi-bond dosage and exposing condition. the compressive strength of the mortar decreases when the proportion of sand in the mortar increases. an average reduction of 6% in compressive strength is recorded in the case of mortar 1:3 compared to the values of the mortar 1:2. this reduction in compressive strength reaches an average of 21% when compressive strength values of 1:4 mortar are compared to the corresponding values of 1:2 mortar. however, it is worth noting that the decrease in the compressive strength due to mortar proportion is independent of hi-bond dosage. it is worth noting that the curing condition significantly affects the mortar’s compressive strength. the mortar cured in water exhibited maximum values followed by the mortar cured in room temperature and natural temperature. the water cured mortars showed about 21% average increase in the compressive strength which reduced to 16% and 12% when cured in room temperature and natural temperature respectively. this inferred that likewise normal mortars the mortars with pre-packaged polymers are also curing conscious. figures 1-3 depict the sample graphical views of effect of hibond, mix proportion and curing condition on the compressive strength of mortar. table i. details of the batches cast and tested s. no. batch designation hi-bond dosage (%) batch description 01 cm 00 cement mortar without hi-bond 02 chbm2.5 2.5 cement mortar with 2.5% hi-bond 03 chbm5 5.0 cement mortar with 5% hi-bond 04 chbm7.5 7.5 cement mortar with 7.5% hi-bond 05 chbm10 10.0 cement mortar with 10% hi-bond table ii. details of cast and tested batches batch designation cm chbm hi-bond dosage (%) 0.0 2.5 5.0 7.5 10.0 curing condition mortar proportion average compressive strength (mpa) water 1:2 16.0 16.9 18.0 18.9 19.4 1:3 15.2 15.7 17.3 17.6 18.2 1:4 12.5 13.6 14.4 14.7 15.0 room temperature 1:2 14.2 15.1 16.0 16.4 16.7 1:3 13.1 13.5 14.3 14.7 14.7 1:4 9.7 10.3 10.9 11.2 11.2 natural temperature 1:2 14.0 14.3 14.8 15.0 15.2 1:3 12.0 12.5 13.0 13.3 13.5 1:4 9.5 10.1 10.3 10.7 11.0 fig. 1. hi-bond effect on compressive strength of mortars cured in water b. tensile strength tensile strength of mortar without and with different hibond dosages exposed to the three curing conditions is presented in table iii. in terms of the effect of hi-bond dosage and mix proportion, an identical trend to that of compressive strength is also observed in case of tensile strength. the tensile strength increases with the increase in hi-bond dosage. the average increase in the tensile strength of mortar due to hibond and cured in water is observed to be 28.7% followed by 19.9% and 19.6% when exposed to room temperature and natural temperature curing conditions respectively showing a little bit better mortar performance in terms of tensile strength. tensile strength of mortar with 1:2 mix proportion was maximum followed by the tensile strength of 1:3 and 1:4 mix proportions. however, mortars exposed to room temperature showed anomaly by giving slightly higher tensile strength engineering, technology & applied science research vol. 8, no. 3, 2018, 3044-3047 3046 www.etasr.com memon et al.: effect of prepackaged polymer on compressive, tensile and flexural strength of mortar results than the mortars of same batch cured in water and natural temperature/environment which is shown in figure 4. this infers that hi-bond mortars can be applied in room temperature and natural (higher) temperature with more confidence and less wet curing particularly as plasters etc. c. flexural strength the experimental results of flexural strength are presented in table iv. from the table values it can be observed that the effect of hi-bond in mortar is more pronounced in flexure strength than that observed in compressive and tensile strength. the maximum average increase in flexural strength is of the order of 74.4% and is obtained in the case of 1:2 mortar cured in water whereas, the minimum average increase in flexural strength is 32.9% in the case of 1:4 mortar cured in water. individually maximum flexural strength increase is 94.4% exhibited by 1:2 mortar with 10% hi-bond and cured in water while the minimum value is 12.8% in case of 1:4 mortar with 2.5% hi-bond dosage, again cured in water. this high impact of hi-bond on flexural strength may be attributed to the strong formation of the matrix between binder (cement and hi-bond combined) and sand particles due to the presence of hi-bond. this may be considered as a positive sign because the mortar is used mostly for plaster applications and the manufacture of ferrocement elements where the major parameters of consideration are the tensile and flexural strength along with the reduced shrinkage. it is expected that a stronger matrix is liable to exhibit low shrinkage value. it is important to mention here that likewise tensile strength in flexure, the mortar with hi-bond, exposed to room temperature, exhibited greater flexural strength than the ones cured in water and exposed to natural temperature which is visible in figure 5. fig. 2. mix proportions effect on compressive strength of mortars cured in water fig. 3. curing conditions effect on compressive strength of 1:3 mortars fig. 4. effect of curing conditions on tensile strength of 1:3 mortars fig. 5. effect of curing conditions on flexural strength of 1:3 mortars fig. 6. table iii. average tensile strength of mortar with prepackaged polymer details batch designation cm chbm hi-bond dosage (%) 0.0 2.5 5.0 7.5 10.0 curing condition mortar proportion average tensile strength (mpa) water 1:2 0.61 0.69 0.73 0.80 0.89 1:3 0.52 056 0.61 0.67 0.74 1:4 0.44 0.47 0.54 0.64 0.72 room temperature 1:2 0.66 0.69 0.77 0.81 0.84 1:3 0.57 0.64 0.68 0.69 0.71 1:4 0.45 0.49 0.52 0.57 0.61 natural temperature 1:2 0.63 0.69 0.73 0.75 0.79 1:3 0.47 0.56 0.60 0.62 0.66 1:4 0.39 0.43 0.47 0.52 0.54 table iv. average flexural strength of mortar with prepackaged polymer batch designation cm chbm hi-bond dosage (%) 0.0 2.5 5.0 7.5 10.0 curing condition mortar proportion average flexural strength (mpa) water 1:2 3.73 5.48 6.45 6.88 7.25 1:3 3.36 4.46 5.13 5.50 5.99 1:4 3.01 3.79 4.21 4.76 5.10 room temperature 1:2 5.16 6.08 6.66 7.59 9.23 1:3 4.09 5.14 5.61 6.51 7.23 1:4 3.12 4.13 4.53 5.07 5.72 natural temperature 1:2 4.71 5.37 6.16 6.84 7.42 1:3 3.71 4.52 5.03 5.49 6.20 1:4 2.53 3.70 4.15 4.67 5.25 engineering, technology & applied science research vol. 8, no. 3, 2018, 3044-3047 3047 www.etasr.com memon et al.: effect of prepackaged polymer on compressive, tensile and flexural strength of mortar iv. conclusions based on the experimental study’s obtained results it may be concluded that the hi-bond (a water based polymer) may be considered a promising material as cement replacement in the three tested mix proportions. it not only enhances the compressive strength but is more efficient in terms of tensile and flexural strength. hi-bond mortars are found to be curing condition friendly. hi-bond mortars may be considered less wet curing conscious, particularly in terms of tensile and flexural strength, with this aspect is suggested to be further studied in order to achieve a more concrete conclusion. acknowledgment authors are grateful to the quaid-e-awam university of engineering, science and 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highperformance concrete bridge decks”, construction and building materials, vol. 25, no. 1, pp.1-13, 2011 [27] aci committee e706, field guide to concrete repair application procedures: structural crack repair by epoxy injection (aci rap bulletin 1), aci, 2003 [28] c. a. issa, p. debs, “experimental study of epoxy repairing of cracks in concrete”, construction and building materials, vol. 21, no. 1, pp. 15763, 2007 [29] e. david, c. djelal, f. buyle–bodin, “repair and strengthening of reinforced concrete beams using composite materials”, in: 2nd international phd symposiumin civil engineering, budapest, pp. 23-34, 1998 [30] d. kachlakev, d. d. mccurry, “behavior of full-scale reinforced concrete beams retrofitted for shear and flexural with frp laminates”, composites part b: engineering, vol. 31, no. 6-7, pp.445-452, 2000 microsoft word rev_ed.doc etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 285-290 285 www.etasr.com ilhan et al: energy conversion loops for flux-switching pm machine analysis energy conversion loops for flux-switching pm machine analysis e. ilhan electromechanics and power electronics group (epe) electrical engineering eindhoven university of technology eindhoven, netherlands e.ilhan@tue.nl, esinilhan@hotmail.com t. e. motoasca electromechanics and power electronics group (epe) electrical engineering eindhoven university of technology eindhoven, netherlands j. j. h. paulides electromechanics and power electronics group (epe) electrical engineering eindhoven university of technology eindhoven, netherlands e. a. lomonova electromechanics and power electronics group (epe) electrical engineering eindhoven university of technology eindhoven, netherlands abstract— induction and synchronous machines have traditionally been the first choice of automotive manufacturers for electric/hybrid vehicles. however, these conventional machines are not able anymore to meet the increasing demands for a higher energy density due to space limitation in cars. fluxswitching pm (fspm) machines with their high energy density are very suitable to answer this demand. in this paper, the energy conversion loop technique is implemented on fspm for the first time. the energy conversion technique is a powerful tool for the visualization of machine characteristics, both linear and nonlinear. further, the technique provides insight into the torque production mechanism. a stepwise explanation is given on how to create these loops for fspm along with the machine operation. keywords-energy conversion loops; flux-switching pm machines; nonlinear magnetic analysis; pm motors i. introduction flux-switching pm (fspm) machines are suitable alternatives when it comes to e-mobility applications. what makes fspm appealing for the automotive industry, among its many advantages, is its high energy density in the airgap [1], which is caused by the operation near the saturation region. this operating point results in a nonlinear behavior of the softmagnetic material used in the machine. additionally, fspm has a rather unconventional structure, embodying all its energy sources in the stator frame, as illustrated in figure 1a. due to this arrangement of sources, the double salient machine structure is a must for its operation; however, this geometry results in a non-uniform airgap. with the flux focusing effect due to the alternating magnet polarity, the double salient structure of fspm is capable of a high torque density. it is a result of the parallel magnetic paths of the stator coils and magnets. the magnetic circuit also decreases the demagnetization probability, which is crucial for the vehicle safety. due to mentioned peculiarities, many researches in this area focus in modeling problems [2-7]. in these researches, analytical and numerical fspm models are explained along with their results. this paper brings the modeling issue one step further by discussing how these models can be used to create the energy conversion loops for the fspm. the phase flux linkage calculated by any of these methods can easily be used to create the energy conversion loops for the fspm by following the stepwise explanation provided in this paper. besides linear analysis also nonlinear analysis of the fspm, which is often neglected in analytical modeling techniques [3, 5, 7], is included in the paper. additionally, to give more insight into machine operation, the torque calculation mechanism is explained separately. the motor quantities used in this paper, such as flux linkage, are calculated by means of the numerical finite element method (fem). ii. energy conversion loops for fspm machine there are multiple methods to create the energy conversion loop of an electrical machine. for constructing the energy conversion loops of the fspm, flux linkage-current (λ-i) characteristic is chosen. the area of the loop is proportional to the change of magnetic energy inside the machine. one energy loop corresponds to one phase flux linkage variation over one electrical cycle and the corresponding change in the instantaneous current for the same rotor position. torque production in electrical machines mainly depends on the airgap flux density. distinctively, fspm does not have a rotating magnetic field in the airgap. because of the machine saliency, there is a change of the magnetic energy in the airgap. in the fspm, there are two separate energy sources, i.e. coils and magnets. to investigate the torque production mechanism, the sources are separately evaluated. therefore, the energy conversion loops are constructed for the following cases: with coils and with coils&magnets. also the magnetic material properties are included in this work, namely linear and nonlinear. etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 285-290 286 www.etasr.com ilhan et al: energy conversion loops for flux-switching pm machine analysis table i. fspm size and parameters number of phases, m 3 rotor pole pair number, p 10 stator pole number 12 frame size 90 mm frame length 25 mm rated power 90 w rated torque 2.2 nm rated current 10 a rated speed 400 rpm iii. constructing the loops for fspm in the considered fspm, with the parameters given in table i, phase a consists of 4 coils (a1 & a2) in 8 slots (figure 1b). due to the half machine periodicity, a1 and a2 coil pairs are shifted by 90 ◦ mechanical. flux linkages for one coil of phase a, for the a1-a2 pairs and for phase a are shown in figure 2. the resulting energy conversion loops of figure 2 are plotted in figure 3. because the supplied current and the magnetic flux linkage have a sinusoidal shape, the ideal loop shape is elliptic. if they have a trapezoidal form, e.g. brushless dc (bldc) machines, the loops ideal shape is rectangular [9]. the higher flux linkage values of figure 2b, compared to figure 2a, result in larger loops in figure 3b, compared to figure 3a. because the total area of these loops is proportional to the average electromagnetic torque, the loops with a larger area correspond to a higher torque [8, 10]. the enclosed areas in figure 3a show that the torque production in the presence of coils only is very weak compared the areas in figure 3b, which is due to coils & magnets. although structure-wise fspm resembles switched reluctance machine (srm), the reluctance torque from coils cannot drive any load including the rotors own mass. if i(t) is the time dependent current of phase a and λ(t) is the time dependent flux linkage of phase a, then for a certain time instant, i.e. at a certain rotor position, the energy function becomes: λ= ( ( )) c w f i (1) the energy converted into mechanical work is in fact the change in coenergy wc. the torque capability of an electrical machine can be calculated by computing the total area enclosed by the λ-i loop. although both i(t) and λ(t) are functions of time, the energy conversion loop itself is not dynamic. from this quasi-static loop, the torque capability of the machine can be determined by calculating the average torque tave using the following formula [11-12]: π = , 2 ave c m p t w  (2) with the phase number m and the pole pair number p. for the 12/10 fspm, m equals 3 and p equals 10. each rotor tooth in fspm acts like a magnet pair in bldc. for transient torque calculation as a function of rotation, additional information is required besides the obtained static energy conversion loop. the electromagnetic torque is proportional to the change in the magnetic energy ∆wc; the change from one rotor position to the next one is bound by magnetization curves. the curves show how the inductance changes, if current increases. each point of the magnetization curve corresponds to the same rotor position of different energy conversion loops, i.e. of different current levels. a b fig. 1. fspm with 10 rotor and 12 stator poles. a) 3d illustration b) phase a coil distribution figures 4a-b show the change of energy conversion loops with increasing stator current. in figure 4a, all loops have the same orientation and the loop with a higher current encircles completely the loop with a lower current. once magnets are included in the calculation, the orientation of the loops in figure 4b change with the increasing current and the increase in the loop area is significantly higher than in figure 4a. in the first and forth quadrants of figure 4b at the flux linkage upper and lower limit (0-2.5a interval), there exist very small areas where the lower current loop is not covered by the higher current loop. it is a result of the sudden change in the loop orientation with increasing current. due to magnets the flux linkage changes in this interval at a much faster rate compared to the case with only coils. visually, a certain rotor position in figure 4b occurs in a shifted position at a higher current level. therefore, physically the shift does not mean that the higher current loop does not cover an energy region which is covered by the lower current loop. a. magnetization curves magnetization curves, which are imperative to transient torque calculation, can be calculated by applying different current values at the same rotor position. along one magnetization curve, the rotor position stays constant. examples of magnetization curves are plotted in figure 4c, when only phase a coils and magnets are activated. the curves etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 285-290 287 www.etasr.com ilhan et al: energy conversion loops for flux-switching pm machine analysis are bound on the outer side by the energy conversion loop corresponding to the current value supplied to the machine. for the fspm with coils only, magnetization curves obtained with linear analysis (µiron=∞) are identical to the magnetization curves obtained from nonlinear analysis (figure 4d). on the other hand, these curves differ for the fspm with coils & magnets. a b fig. 2. flux linkage of different coils of phase a for 11a. a) with coils only b) with coils & magnets once magnets are included in the analysis, the magnetization curves become distinct as illustrated in figure 4d. for both linear and nonlinear analysis with coils & magnets, the curves have a shift at initial value i=0 corresponding to their pm-flux linkage values (λpm). since theoretically the iron is capable to store more magnetic flux in the linear case, λpm value is higher for the linear case compared to the nonlinear. due to saturation of the iron material, the magnetization curves in figure 4d deviate from each other while the current increases. unlike srm, in fspm current is not responsible for entering the nonlinear region in the λ-i characteristic. with the presence of magnets, fspm is pre-biased in the magnetization curve up to a point, where it can exchange more magnetic energy. eventually this high change in the energy storage increases the torque capability of the fspm significantly compared to a srm, which has a very similar iron structure compared to fspm. the use of magnetization curves plays an important role for making such useful comparisons, which provide more insight into the fspm operation. a b fig. 3. energy conversion loops of fspm for 11a a) with coils only b) with coils & magnets iv. transient torque calculations as stated before, torque production depends on the change in the stored magnetic energy ∆wc with an example given in figure 5. the energy conversion loop wc in figure 5a is exaggerated for illustrative purpose. the actual loop in figure 4a is much smaller than the illustrated loop in figure 5a. to calculate the transient torque t(θ) at constant current, the areas ∆wc in figure 5 have to be divided to the mechanical displacements ∆θm: θ θ = ∆ = ∆ . ( ) c m i const w t (3) using formula (3) gives torque only from one phase. since fspm is a three phase machine, the result is shifted electrically 120 ◦ for the remaining two phases. eventually, resulting torques from all three phases are added together. preliminary results show that by only using energy conversion loops, obtained transient torques have the right effective value and the correct shape, but not the correct torque ripple amplitude. the torque ripple of the fspm consists of the cogging torque and etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 285-290 288 www.etasr.com ilhan et al: energy conversion loops for flux-switching pm machine analysis reluctance torque. it is stated in [9], transient torque can be calculated by using the energy conversion loops. this statement is true but not complete. the transient torque consists of the average torque and the torque ripple. if torque ripple component is only reluctance torque due to the rotor saliency (in case of srm), the amplitude of transient torque can be calculated by the loop. however in fspm, cogging torque is the dominant torque ripple, which is a a result of not only the changing airgap permeance between the rotor and stator iron parts but also the changing magnet related permeances, i.e. inner permeance and leakages. the static energy conversion loop cannot visualize the dynamic change of the magnetic loading, therefore the loop is not able to calculate the ripple correctly. in the paper, energy conversion loops are used to calculate the instantaneous torque, to which cogging torque is added later. how to estimate the cogging torque is discussed in the next subsection more detailed. transient torques calculated by the fspm’s energy conversion loops are given in figures 6-7. the results match to fem results, where virtual work method is chosen. the magnetization curves for the fspm with coils only, do not differ for the linear and nonlinear analysis, therefore their transient torques in figure 6 are identical. the similarity in the results is due to the low energy output, when only coils are considered as the source. the results for the fspm with coils & magnets are presented in figure 7. in this case, the torque calculations for the linear and nonlinear case show a distinct difference both in magnitude and in ripple shape. the nonlinear iron cannot store as much magnetic energy in the linear case. therefore, the average torque decreases in the nonlinear case. the area in figure 5b, ∆wc in the nonlinear analysis, does not change as rapidly as in the linear analysis, which causes a decrease of torque ripple oscillations in the nonlinear case. the important part is the calculation of the load lines. in practice, these load lines are changing with nonlinear intervals depending on the magnetic circuit and on the magnetic load. even for steady-state analysis, it is not straight forward to estimate the load lines when the machine is rotating. these can be calculated using reluctance network models presented in [2, 7]. in fspm, since the whole structure is magnetically prebiased, due to the coupling of energy sources in stator, the magnetic change of load lines could be assumed to be linear. the calculation is done first for one magnet only. next, the calculations for the similarly oriented magnets is realized, which are labeled as n-poles and s-poles as shown in figure 8. finally, the result from two poles is superimposed to calculate one period of cogging torque. due to the assumption of linear load lines, the estimation of cogging torque is with an error of 25%. in fact, this error exactly corresponds to the ripple calculated by the λ-i loop. summarizing, the 25% error is the reluctance component of the torque ripple, which depends on the coil inductance. for all the transient torque calculations shown previously, this estimation is added to the dynamic torque calculated by using λ-i loop. this analysis also proves that the main torque ripple component of fspm is due to the magnet-iron interaction, i.e. 75% of the torque ripple. a b c d fig. 4. a-b) change of energy conversion loops of fspm with increasing current, c-d) magnetization curves. a) with coils only b) with coils & magnets c) magnetization curves 11a d) ideal magnetization curves etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 285-290 289 www.etasr.com ilhan et al: energy conversion loops for flux-switching pm machine analysis a b fig. 5. c w∆ between two consecutive rotor positions. a) with coils only (enlarged view) b) with coils & magnets (normal view) a b fig. 6. torque calculations with coils only. a) linear analysis b) nonlinear analysis a b fig. 7. torque calculations with coils and magnets. a) linear analysis b) nonlinear analysis fig. 8. cogging torque estimated from φ-mmf diagram. etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 285-290 290 www.etasr.com ilhan et al: energy conversion loops for flux-switching pm machine analysis v. conclusions all quality electromagnetic designs require an understanding of the system. in automotive, due to the interaction of various subsystems, i.e. electrical, electronic, mechanic, etc., it is sometimes hard to estimate the behavior of each element of these subsystems. energy management is very dedicated to the limited energy sources on the subsystem level. precisely at this point, energy conversion loop technique provides the required visual tools to understand the machine operation and estimation of the parameters, from which not only the academic researchers but also the design engineers can benefit. since novel flux-switching pm machines require a good understanding of the machine operation, in this work, the energy sources are evaluated separately, as coils & magnets. both the linear and nonlinear soft magnetic material properties are evaluated in this paper, of which the nonlinear aspects have often been neglected in the literature. for each defined case, energy conversion loops are created successfully by concluding the physical meaning for the machine operations. concisely, based on the findings the general concept of energy conversion loops has been extended to cover the fspm machine class for proper energy management system. references [1] t. heoung kim, "a study on the design of an inset-permanent-magnettype flux-reversal machine", ieee transactions on magnetics, vol. 45, no. 6, pp.2859-2862, 2009. [2] e. ilhan, b. l. j. gysen, j. j. h. paulides, e. a. lomonova, "analytical hybrid model for flux switching permanent magnet machines", ieee transactions on magnetics , vol. 46, no. 6, pp. 1762-1765, 2010. [3] e. ilhan, j. paulides, e. motoasca, e. lomonova, "conformal mapping: schwarz-christoffel method for flux-switching pm machines", compumag 2011, 18 th international conference on the computation of electromagnetic fields, australia, 2011. [4] z. zhu, j. t. chen, y. pang, d. howe, s. iwasaki, r. deodhar, "modeling of end-effect in flux-switching permanent magnet machines", icems 2007, international conference on electrical machines and systems, pp. 943-948, 2007. [5] b. l. j. gysen, e. ilhan, k. j. meessen, j .j. h. paulides, e .a. lomonova, "modeling of flux switching permanent magnet machines with fourier analysis", ieee transactions on magnetics, vol. 46, no. 6, pp. 1499-1502, 2010. [6] c. anyuan, r. nilssen, a. nysveen, "analytical design of a high-torque flux-switching permanent magnet machine by a simplified lumped parameter magnetic circuit model", icem 2010, xix international conference on electrical machines, vol., pp.1-6, france, 2010. [7] e. ilhan, j. paulides, l. encica, e. lomonova, "tooth contour method implementation for the flux-switching pm machines", icem 2010, xix international conference on electrical machines, pp.1-6, france, 2010. [8] t. j. e. miller, "optimal design of switched reluctance motors", ieee transactions on industrial electronics, vol. 49, no. 1, pp. 15-27, 2002. [9] d. staton, r. deodhar, w. soong, t. miller, "torque prediction using the flux-mmf diagram in ac, dc, and reluctance motors", ieee transactions on industry applications, vol. 32, no. 1, pp. 180-188, 1996. [10] m. cheng, k. chau, c. chan, “static characteristics of a new doubly salient permanent magnet motor”, ieee transactions on energy conversion, vol. 16, no. 1, pp. 20–25, 2001. [11] t. miller, m. mcgilp, “nonlinear theory of the switched reluctance motor for rapid computer-aided design”, ieee proceedings on electric power applications, vol. 137, no. 6, pp. 337–347, 1990. [12] d. staton, w. soong, t. miller, “unified theory of torque production in switched reluctance and synchronous reluctance motors”, ieee transactions on industry applications, vol. 31, no. 2, pp. 329–337, 1995. [13] r. deodhar, d. staton, t. jahns, t. miller, “prediction of cogging torque using the flux-mmf diagram technique”, ieee transactions on industry applications, vol. 32, no. 3, pp. 569–576, 1996. microsoft word 31-2950_s_etasr_v9_n4_pp4484-4489 engineering, technology & applied science research vol. 9, no. 4, 2019, 4484-4489 4484 www.etasr.com kuswanto et al.: clustering of precipitation pattern in indonesia using trmm satellite data clustering of precipitation pattern in indonesia using trmm satellite data heri kuswanto department of statistics, institut teknologi sepuluh nopember, surabaya, indonesia heri_k@statistika.its.ac.id dedi setiawan department of statistics, institut teknologi sepuluh nopember, surabaya, indonesia dedi1statistika@gmail.com ardhasena sopaheluwakan meteorology, climatology, and geophysical agency (bmkg), jakarta, indonesia ardhasena@bmkg.go.id abstract—this paper identifies the climatic regions in indonesia based on the rainfall pattern similarity using trmm data. indonesia is a tropical climate region with three main climate clusters, i.e. monsoonal, anti-monsoonal and semi-monsoonal. the clusters were formed by examining rainfall observation datasets recorded at a number of stations over indonesia with coarse spatial resolution. clustering based on higher resolution datasets is needed to characterize the rainfall pattern over remote areas with no stations. trmm provides a high resolution gridded dataset. a statistical test has been applied to evaluate the significance of trmm bias, and it indicated that the trmm based satellite precipitation product is a reasonable choice to be used as an input to cluster regions in indonesia based on the similarity of rainfall patterns. the clustering by euclidean distance revealed that indonesia can be grouped into three significantly different rainfall patterns. compared to the existing references, there have been regions where the rainfall pattern has been shifted. the results in this research thus update the previously defined climate regions in indonesia. keywords-cluster; monsoon; trmm; remote sensing; precipitation i. introduction indonesia is an archipelago located between 10 0 s to 6 0 n, and 95 0 e to 141 0 e, and hence, part of its regions lies on the equatorial line with a high degree of rainfall variability. the indonesian climate conditions are influenced by several factors such as asia-australia monsoon, el nino, la nina, east-west and north-south circulation and other local influences [1]. moreover, the latitude and longitude position, topography, the ocean, and the land also influence the climate variability. authors in [2] found that indonesia can be clustered into three rainfall patterns (hereafter referred to as climate regions), i.e. monsoon, anti-monsoon and semi-monsoon types. the semimonsoonal type has two monthly maximum rainfalls in a year and is called bimodal. the monsoon type is influenced by the big scale of ocean wind and this pattern clearly shows the difference between the dry and wet season in a year, and has only one maximum rainfall in a year. the anti-monsoonal pattern is shown by the unimodal rainfall pattern, opposite to the monsoonal rainfall type. due to the high degree of rainfall variability, the analysis of precipitation conditions in indonesia requires long historical series with adequate spatial coverage. rainfall observation in indonesia is managed by the meteorology, climatology, and geophysical agency (bmkg) through 116 meteorological stations spreaded out all over indonesia. moreover, the bmkg also uses satellite data to support the need for fast and continuous rainfall data. one of the obvious advantages of satellite data is their spatial coverage, while they are normally available in a highresolution grid covering all areas of the regions. one of the satelite products that is commonly used by the bmkg as reference is the tropical rainfall measuring mission (trmm). trmm is a collaborative space project between nasa and the japan aerospace exploration agency (jaxa) to monitor the precipitation over tropical regions as an effort to study earth as a global system and it was developed in 1997 [4]. the trmm satellite measures rainfall intensity in every region on various temporal scales. the spatial resolution varies from 0.25 to 5 degrees. the mission of this satellite is to better understand the precipitation structure in the tropical region of the earth [5]. among the studies which note the strong performance of trmm in specific regions compared to other satelite products are [6, 7] for the case of china and iran respectively. the bmkg uses trmm satellite data to observe the rainfall conditions over indonesia due to the limited number of meteorological stations. the trmm data has also been widely used in weather and climate studies in indonesia, e.g. to study extreme weather events [8]. authors in [9] studied the advantages of using trmm based precipitation to investigate the spatiotemporal pattern and rainfall characteristics over indonesia. author in [10] compared the monthly rainfall observed from meteorological stations with trmm and noaa surface models using simple mean testing and found that trmm has a potential to impute the missing spatiotemporal data in some areas with no data. moreover, authors in [11] verified the trmm satellite precipitation data and rainfall observation over makassar indonesia using a simple t-test and found that the monthly trmm precipitation can be used to estimate the rainfall in some areas without meteorological stations. trmm satellite data have also been verified in many other countries, e.g. authors in [12] used trmm to estimate the rainfall in topajo river in amazon using bias correction, while authors in [13] verified trmm 3b42 over china. trmm applications have also been corresponding author: heri kuswanto engineering, technology & applied science research vol. 9, no. 4, 2019, 4484-4489 4485 www.etasr.com kuswanto et al.: clustering of precipitation pattern in indonesia using trmm satellite data intensively investigated in singapore [14, 15] and malaysia [16, 17]. the purpose of this study is to use trmm data to update the clustering of climatic regions in indonesia based on precipitation pattern. moreover, the trmm data will be verified towards observation data prior to clustering process in order to justify that trmm is a reasonable choice to be used as a basis of clustering. this work differs from [2] in several significant ways. first, we use the trmm satellite data as the basis of clustering, instead of using the station observation data. therefore, the clustering result is more reliable to explain the climate variability among regions due to the high resolution data used in the clustering process. moreover, the trmm data provide rainfall information over regions without stations. also, this research uses a different clustering process in terms of the distance measure, i.e. standard (euclidean) distance measure, while authors in [2] used double correlation (dc) which treats the data as a cross-sectional series. another important difference is the period of the examined dataset: this study examines the average monthly rainfall over the last 18 years, while [2] used data spanning from 1961 to 1993. ii. study area and data indonesia is an archipelago with thousands of islands stretching along the equator from the southeast asia to australia. it is a tropical country where the temperature is stable throughout the year, with lows around 22°c to 25°c, and highs around 30°c to 32°c all over the year. moreover, the rainfall quantity and distribution vary due to the location humidity level and the monsoon regime. the availability of historical rainfall data recorded at meteorological stations is an important aspect to further study the rainfall variability. figure 1 depicts the location of the 116 meteorological stations over indonesia. fig. 1. locations of the meteorological stations in indonesia we can see that there are some areas without meteorological stations making difficult to characterize the climatic pattern. using high resolution gridded data from the trmm will allow the investigation of the climate pattern in a specific region precisely. the climate in indonesia, according to [2] is classified into three different regions. region 1 is the southern monsoonal region covering the southern and central part of indonesia. this region is significantly influenced by the australian monsoon. region 2 is the anti-monsoonal region, while region 3, covering most of the northwestern part of indonesia, is the semi monsoonal region with two precipitation peaks per year. the precipitation data used in this study are secondary data collected from two different sources, i.e. trmm satellite-based data and ground data collected from the meteorological stations over indonesia. a. trmm data daily precipitation dataset has been collected from the trmm website. the data are in a grid point basis with resolution of 0.25 0 ×0.25 0 over indonesia regions and hence, we have 12765 grids points. the verification is applied to the daily precipitation data spanning from january 1, 1998, to december 31, 2016, while the time series clustering uses monthly average precipitation series from january 1998 to december 2017. b. ground data this research uses the measured daily precipitation from a total of 161 meteorological stations over indonesia (see figure 1) from january 1, 1998, to december 31, 2016. note that the ground data are used only to verify trmm data, which for the period of 1998 to 2016 are already sufficient to describe the climatological conditions. the measured precipitation data are freely available from bmkg. the daily precipitation was collected from 7 am to 7 am indonesia local time and it has been pre-processed for missing value imputation, where the missing data were filled with the precipitation data from the nearest adjacent station. iii. methodology in order to verify the precipitation between trmm satellite products and ground-based observations, the mismatch in the spatial scales between those two data sources needs to be carefully considered. this is mainly because the trmm precipitation values used in this paper are available at grid scale, while measurements from meteorological stations represent precipitation at point scale. there are several ways to deal with this issue in order to carry out a direct comparison, such as spatial interpolation or simple averaging. in this study, the comparison will be conducted by upscaling the spatial position of the meteorological station with the closest grid. meanwhile, areas with no meteorological station coverage were excluded from the evaluation. the analysis starts with the evaluation of trmm precipitation with ground data through visual presentations, i.e. time series plot, boxplots and distribution plot. moreover, the skill of trmm precipitation data is verified by a simple t-test. the evaluation is focused on regional basis, instead of a global mean over indonesia. furthermore, clustering is done by examining the gridded scale dataset of trmm precipitation data. the optimum number of clusters is determined by two criterias, pseudo-f statistic [18] and silhouette statistic [19]. high pseudo-f represents the optimal number of clusters, the members within a cluster are as homogeneous as possible, and the members between clusters are as heterogeneous as possible. the pseudo-f statistic is defined as: ( ) ( ) ( ) 2 2 1 1 r c pseudo f r n c    − − =  −   −    (1) engineering, technology & applied science research vol. 9, no. 4, 2019, 4484-4489 4486 www.etasr.com kuswanto et al.: clustering of precipitation pattern in indonesia using trmm satellite data with 2 sst ssw r sst −  =    , ( ) 2 1 1 1 cn pc kijk i j k sst x x = = = = −∑∑∑ , ( ) 2 1 1 1 cn pc ikijk i j k ssw x x = = = = −∑∑∑ where n is the number of samples, c the number of clusters, nc the number of data in group c, p the number of variables, xijk the group-i on sample-j and k-th variable, �̅� the average of all samples on variable-k, and �̅�� the average of group-j on variable-k. according to [20], one of the measurements to evaluate the goodness of time series clustering is the silhouette coefficient defined as: ( ) ( ) ( ) { ( ) ( )} b i a i s i max a i ,b i = , where a(i) is the average of the distance between members within a cluster, b(i) is the minimum value of the average distance of object i with object lies in other cluster, while s(i) is the silhouette coefficient of object i. the silhouette coefficient is the average of s(i) for every object. table i provides the silhouette categories [21]. table i. silhouette coefficients criteria silhouette coefficients category 0.71–1.00 strong 0.51–0.70 good 0.26–0.50 weak 0.00–0.25 bad if a cluster is bad, this means that the observations within the cluster are not homogeneous, while the observations between clusters tend to be homogeneous. if the coefficient lies within the interval of 0.71 to 1, the cluster is said to be very good (strong) which means that the observations within clusters are very homogeneous, while observations between different clusters are very heterogeneous. in summary, the higher the silhouette coefficient, the better the clustering results. figure 2 summarizes the research methodology steps. iv. results and discussion a. precipitation characteristics in indonesia using trmm data in general, indonesia has been characterized as a tropical country with two seasons, the dry season from october to march and the rainy season from april to september. however, many researches have shown that there has been a shift on the seasonal periods. furthermore, the area can be clustered into three climate regions [2]. figure 3 depicts the daily mean precipitation from the trmm data over the last 17 years. the picture shows that the mean precipitation over indonesia varied in the range of 0 to 18mm/day. the bmkg defined three categories of mean precipitation in indonesia, i.e. low (0mm/day to 3.33mm/day), medium (3.33mm/day to 10mm/day) and high (above 13.33mm/day). bali and nusa tenggara regions usually have longer dry seasons compared to others. we see also that papua and west papua are two regions with very high precipitation rate. kalimantan and sumatra have high precipitation rates, while java’s and sulawesi’s tend to be medium. fig. 2. steps of the analysis fig. 3. average rainfall in indonesia (mm/day) the average daily precipitation per month can be seen in figure 4. the bar chart shows the mean precipitation over three climate regions as defined by [2]. region 1 (monsoon type) has a u-shape, consistent with the findings of [2]. in this case, the rainy and dry seasons can be differentiated clearly, i.e. novemberapril for the rainy season and may-october for the dry season. the time series plot shows that the precipitation rate did not change significantly over time with the average level of 7.25mm/day. anti-monsoon regions have a nearly similar pattern with the monsoonal type, however, the precipitation rate during the dry season is higher than in the monsoonal type. for the semi-monsoonal, the monthly precipitation pattern is very similar to the anti-monsoonal type during rainy seasons, and nearly similar to anti-monsoonal type during dry periods. this paper carries out re-clustering to identify whether the precipitation patterns are significantly different among those three regions. figure 5 depicts the distribution of the observed precipitations with the trmm generated precipitation. the graph provides a nice way to verify the efficiency of the trmm data. furthermore, the mean rainfall difference from both sources is tested by t-test. we see that the trmm precipitation is an under-estimate of the observed data over all regions showed by their lower mean engineering, technology & applied science research vol. 9, no. 4, 2019, 4484-4489 4487 www.etasr.com kuswanto et al.: clustering of precipitation pattern in indonesia using trmm satellite data value than the ground observation. the difference (bias) is around 0.864mm/day, while the t-test showed that the differences are not statistically significant over those three regions. this means that the trmm generated precipitation data are good enough to represent the observation data. as for clustering, the bias can be neglected because the clustering process concerns only on the pattern of trmm data. (a) (b) (c) fig. 4. rainfall patterns (mm/day) over: (a) region 1, (b) region 2, and (c) region 3 b. clustering of climatic regions in indonesia clustering by using the euclidean distance is done by specifying the number of clusters as 2 and 3. the euclidean distance measures the distance between two series without taking into account the autocorrelation properties of the series, and it is hereafter refereed as standard approach in clustering. the pseudo-f statistic for each number of clusters is 291.691 and 342.51, while the silhoutte coefficient is 0.136 and 0.145 respectively. based on these two criteria, the euclidean distance suggests that the optimum cluster number is 3. the clusters of the climatic regions can be seen in figure 6. the distribution of the climatic regions looks very similar with the findings of [2]. however, we observe that there are shifts over some areas. most regions belong to region 1 or region 3, while region 2 consists of only a few regions. region 3 covers mostly the west and nortwest part of indonesia, i.e. most of the areas in sumatra, west java, central java, jakarta, banten, yogyakarta and the northern part of kalimantan. region 1 covers east java, bali, nusa tenggara, parts of sulawesi, riau, south sumatra, aceh, the entire maluku, parts of east kalimantan and south kalimantan. region 2 includes sulawesi and papua areas. the rainfall pattern over each region can be seen in figure 7. (a) (b) (c) fig. 5. rainfall pattern distribution over regions. (a) region 1, (b) region 2, and (c) region 3 (blue = ground data, red=trmm data) fig. 6. clustering of climatic regions with euclidean distance the rainfall pattern in region 1 forms a monsoon type or u-shape. the areas in this region had rainy season at the beginning and the end of the year, while the dry season occurred in the middle of the year, from may to october. the peak of the rainy season occurred in january and december while the dry season’s peak was in august and september. engineering, technology & applied science research vol. 9, no. 4, 2019, 4484-4489 4488 www.etasr.com kuswanto et al.: clustering of precipitation pattern in indonesia using trmm satellite data (a) (b) (c) fig. 7. rainfall pattern over different regions: (a) region 1, (b) region 2, and (c) region 3 over region 2, the rainfall pattern shows an opposite type than that of region 1, so it corresponds to the term antimonsoon. over this region, the rainy season occurred in the middle of the year starting from march to july, while the lowest rainfall happened in the beginning and the end of the year. region 3 has 2 rainfall peaks in a year, indicating rainy season occurrence twice in a year, in the beginning and in the middle of the year. based on [3], this pattern is termed as monsoon spring zone or semi-monsoon. the summary of the average precipitation cycle of these three regions is presented in histogram in figure 8. fig. 8. histogram of the average precipitation over the 3 different regions. blue: region 1, red: region 2, green: region 3 it can be seen that region 1 is drier than the two other regions with lower deviation. this indicates that the rainfall intensity in region 1 tends to be more stable. region 3 seems to be the wettest region with the largest deviation indicating higher variability in the rainfall intensity, while region 2 has a normal rainfall intensity. v. conclusion this paper identified the climatic regions in indonesia using the satelite trmm data as input. it has been proven that the trmm has no significant bias towards the ground dataset, which means that the trmm data are a good way to overcome the weaknesses of groud data, especially in the case of data scarcity due to the limited number of meteorological stations. clustering by euclidean distance suggested three clusters in line with the findings in [2]. we concluded that the current indonesia climate can still can be clustered into 3 zones, i.e. monsoonal type, anti-monsoon type and semi-monsoonal type. we observed that the average monthly precipitation cycle in some areas shifted from one to another type within last the 24 years. this fact is supported by the findings of [22-25], among others, which proved that climate change shifted the rainfall pattern. the climate change impact on the rainfall pattern in indonesia has been well documented in [26, 27]. references [1] m. c. wheeler, j. l. mcbride, australian-indonesian monsoon, springer, 2015 [2] e. aldrian, r. d. susanto, 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[24] j. crossman, m. n. futter, p. g. whitehead, “the significance of shifts in precipitation patterns: modelling the impacts of climate change and glacier retreat on extreme flood events in denali national park, alaska”, plos one, vol. 8, no. 9, article id e74054, 2013 [25] j. d. miranda, c. armas, f. m. padila, f. i. pugnaire, “climatic change and rainfall patterns: effects on semi-arid plant communities of the iberian southeast”, journal of arid environment, vol. 75, no. 12, pp. 1302-1309, 2011 [26] m. case, f. ardiasyah, e. spector, climate change in indonesiaimplications for humans and nature, wwf, 2007 [27] m. measay, “indonesia: a vulnerable country in the face of climate change”, global majority e-journal, vol. 1, no. 1, pp. 31-45, 2010 microsoft word 24-3173_s_etasr_v9_n6_pp5001-5005 engineering, technology & applied science research vol. 9, no. 6, 2019, 5001-5005 5001 www.etasr.com rahamat basha et al: a novel summarization based approach for enhancing text classification … a novel summarization-based approach for feature reduction enhancing text classification accuracy s. rahamat basha department of computer science & technology sri krishnadevaraya university andhra pradesh, india j. keziya rani department of computer science & technology sri krishnadevaraya university andhra pradesh, india j. j. c. prasad yadav department of computer science and engineering, rajeev gandhi memorial college of engineering and technology andhra pradesh, india abstract—automatic summarization is the process of shortening one (in single document summarization) or multiple documents (in multi-document summarization). in this paper, a new feature selection method for the nearest neighbor classifier by summarizing the original training documents based on sentence importance measure is proposed. our approach for single document summarization uses two measures for sentence similarity: the frequency of the terms in one sentence and the similarity of that sentence to other sentences. all sentences were ranked accordingly and the sentences with top ranks (with a threshold constraint) were selected for summarization. the summary of every document in the corpus is taken into a new document used for the summarization evaluation process. keywords-summarization; dimension reduction; feature selection; feature extraction; feature clustering; text classification i. introduction in text classification, the dimensionality of the feature vector is usually huge because the input document set consists of big data and many terms [1, 2]. the major approaches for feature reduction are feature selection [3-10] and feature extraction [11, 12]. feature extraction approaches are computationally more extensive and more effective than feature selection methods. another feature reduction technique is feature or attribute clustering, in which similar attributes are grouped into a cluster and each cluster can be considered as an attribute. with clustering noisy data, the repetition of text remains leading to less data transfer rate [13, 14]. to reduce this in pre-processing, the unnecessary words which do not support the classification task (articles, verbs, etc.) are removed. document summarization is the process that extracts a few sets of sentences and conveys the original meaning of the base corpus. there are two major text summarization approaches: extractive and abstractive. in the extractive approach, sentences or parts of sentences are extracted from the text. in the abstractive method a summary of the text is generated by using some natural language processing techniques. the number of digital documents that are added to the world wide web is increasing rapidly, and providing the most relevant information to the user is a big problem. each digital document consists of many words, but only a few of them are informative. extracting proper sentence features from documents and categorizing the documents by those features is important and it reflects classification computational efficiency [23-27]. ii. related work as shown in figure 1, the document summarization can be mainly dividedt in the contexts extractive vs. abstractive, generic vs. query-based, and single vs. multiple. fig. 1. document summarization models a. extractive vs. abstractive in the extractive summarization process, the more important sentences are selected (according to weights or similarities or degrees) from the original document. in abstractive summarization, a summary of the corpus which reflects the main theme of the original document is generated. b. generic vs. query-based a generic summarization method does not need any queries and focuses on extractive summarization, while in query-based summarization, the summary related to the query is generated. c. single vs. multiple single document summarization is the process which summarizes the text of a document whereas multi-documents methods can summarize more than one document at a time. after selecting a suitable feature set, the test document has to be classified by a suitable classification method. rule-based classification is accurate if the rules are written by experts and easily controlled if the number of rules is small, but if it increases, or the rules conflict with each other, the processing becomes more difficult. if the target domain changes, the rules have to be reconstructed. the machine learning-based approach is domain-independent and gives high predictive performance but training data required [15]. 1) bag of words method corresponding author: s. rahamat basha (basha.ste@gmail.com ) engineering, technology & applied science research vol. 9, no. 6, 2019, 5001-5005 5002 www.etasr.com rahamat basha et al: a novel summarization based approach for enhancing text classification … the corpus of documents is generally represented in a bag of words model which is the collection of feature vectors. let d = {��, ��, … . . ��} represent the corpus or document set, where each element of belongs to one class of the set { �, �, … �} . if a document with only one class label is included in d, then it is used for binary or multiclass classification. if a document is included multiple times with multiple class labels in d, then it is used for multi-labeled classification. 2) feature reduction method – example illustration generally, the process of feature reduction can be carried out in two ways, i.e. by feature selection, and feature extraction. the feature selection approach is used to select the subset of original features as the feature set which will be used as input to classification. for example, information gain (ig) is better suited to select the most valuable features in many information retrievals. the weight of feature � calculated in ig is: ��� � = ∑ p�c�logp�c�� + p�� � ∑ p�c|� �logp�c|� �� (1) + p�� ̅� ∑ p�c|� ̅�logp�c|� ̅� � table i. sample bag with 10 words of 10 documents belonging to 2 classes office (w1) apartment (w2) floor (w3) line (w4) bedroom (w5) kitchen (w6) building (w7) internet (w8) wc (w9) fridge (w10) class d1 1 0 0 1 0 1 0 0 0 1 c1 d2 0 0 0 0 0 2 1 1 0 0 c1 d3 0 0 0 0 0 0 0 1 0 0 c1 d4 0 0 1 2 0 1 1 2 0 1 c1 d5 0 0 0 0 1 1 0 0 1 0 c2 d6 1 2 1 0 0 1 0 0 1 0 c2 d7 2 3 1 0 3 1 1 0 1 0 c2 d8 0 1 1 0 1 1 0 0 0 0 c2 d9 1 1 1 0 1 0 0 0 0 0 c2 d10 1 1 1 0 1 0 0 0 0 0 c2 3) feature extraction – example illustration the extracted features in feature extraction approaches are obtained by some processes through algebraic transformation. an incremental orthogonal centroid (ioc) algorithm extracts features as follows [8]: let some set of documents of a corpus be represented as an m×n matrix with � !"×�. here, m stands for the number of documents in the corpus and n for the dimensionality of the corpus. the ioc algorithm finds an optimal transformation matrix $∗ !"× , k≤n, where k is the number of features or dimensionality of the projected matrix. $∗ = arg max �*+ ,�$-./$� where $ !"∗ +0� $-$ = 1 and ./ = 23456375 − 79:: 6375;79::6 (2) with 75 being the mean vector of class 45 , <�45� being the prior probability for a pattern belonging to class 45 and mall being the mean vector of all patterns. 4) feature clustering – modeling illustration generally, clustering means grouping, and in feature clustering, similar features are grouped in one cluster which is treated as a single feature. in hard feature clusters [14, 16-18], the threshold considered for membership in clustering is generally small, which results in a smaller number of features in each cluster. in soft clustering, the threshold size is generally a little larger and it effectively reduces dimensionality, but unimportant features may fall into the clusters. the mixed or medium clustering lies between the above two. the new feature set => = {��,> ��,…….. > � > } corresponds to partition {��, �� … . �?} of the original feature set w, i.e. =@ ∩ =5 = φ, where 1 ≤ e, � ≤ f and � ≠ e. let h be the bag of words consisting of all original documents with m features and h> be the bag of words after projecting h with a new k feature where k is less than or equal to the number of features in h. �i@> = ∑ �ijklmkn (3) this is the linear sum of the feature values in =@. iii. proposed summarization method for each doument of every category our summarization method uses the concept of neighbor with the measures of statistical evaluation. figure 2 illustrates the framework of the proposed method. this approach consists of four steps. 1. each pair of sentence similarity is calculated. 2. the term frequency (tf) of each sentence is calculated. 3. the score for each sentence of a document is computed concerning all documents that belong to the same category. 4. ranks to each sentence of that document are assigned according to their computed scores. let d0 be the document input to be summarized. our system finds the documents near d0 from the same category collection. the nearest neighbor documents that are similar to the specified document are identified by using the nearest neighbor search technique. the standard cosine measure is used to find the similarity between two documents. let �i, �j be two documents. the similarity between them is calculated as follows: engineering, technology & applied science research vol. 9, no. 6, 2019, 5001-5005 5003 www.etasr.com rahamat basha et al: a novel summarization based approach for enhancing text classification … opqrs�3�i,�j6 � tu . vwxtlvx ytuvxy#ztlvxz (4) fig. 2. the proposed single document summarization architecture affinity graph construction method is used to show the relationship between sentences. let [ = �.,\� be an undirected graph where s represents a set of sentences, \ represents a set of edges, and all edges among sentences are associated with a weight. the edge between sentence p and sentence ] is represented as ,ij, and the corresponding weight of that edge is the similarity value of those sentences. the edges of the graph [ are divided into two categories as follows: h� is a document with h�.�,h�.�,h�.^,h�._ , and h� a document with h�.�,h�.�,h�.^,h�._. fig. 3. example diagram showing with-in document and cross-document sentence similarities a. with-in document link (wdl) and cross document link (cdl) the edge between h�.� and h�.� is an example of wdl while the edge between h�.^ and h�.� is an example of crossdocument links. y is the similarity between statements h�.� & h�.�. the link between two sentences from the same document is a wdl and provides local information. the link between two sentences which belong to two different documents is a cdl and provides global information. both these link kinds are incorporated in a global affinity graph g and are represented by an adjacency matrix m in which each entry is the weight of the sentences corresponding to the matrix row and column. the matrix is defined as follows: 7ij = ` a × opqbc�3oi,oj6, pdp g ]0, f�g,*�po, (5) the confidence value is denoted by λ, it is 1 if the link is wdl and opqrs��� ��� if it is otherwise. the matrix m is normalized as follows: ~ 7i,j � i7i,j ∑ 7i,j |b|jj�⁄ , pd ∑ 7i,j|b|jj� g 00, f�g,*�po, (6) b. term frequency computation it is important to calculate the importance of the sentences in summarization. the sentences with importance contain words that occur frequently. term frequency is noting how many times a term is present in a document. the similarity measure of each sentence with all the sentences in the document illustrates the importance of that sentence in the knowledge base, which is the collection of all the documents belonging to a category. term frequency is a good sentence extraction method because it gives the priority of the sentence in a document while it can be computed very easily. in a sentence, the tf of each term is calculated separately and the sum of all these term frequencies gives l�.i�), for the sentence �.i� is defined as follows: l�oi� = ∑ �d��i�ijm (7) where �d��i� is the term frequency of term �i, the p@n term in the sentence. c. sentence evaluation we used the global affinity graph g to calculate the scores for the sentences which are linked to it and denoted as ..4f*,�oi� where o.i represents sentence p as follows: ..4f*,�oi� = ∑ li,j~7i,j9::ioj where: li,j � p -�bu� q-�bu�;-�bl�q , pdql�oi�8 l�oj�q g 01, f�g,*�po, (8) d. document level redundancy removing the sentences which are highly overlapped with others are removed by applying a penalty on them to avoid redundant information in the summary. the redundancy removing algorithm is [3]: 1. initialize: set r = s, set t � �.i �g,*, p � 1,2,3,….2, and r!. f*,�.i� � .. f*,�.i�,p � 1,2,….2 2. the sentences in set b are to be sorted according to their affinity scores (i.e. in descending order). 3. the sentence si with high score in set b is to move to set a. engineering, technology & applied science research vol. 9, no. 6, 2019, 5001-5005 5004 www.etasr.com rahamat basha et al: a novel summarization based approach for enhancing text classification … 4. a penalty on the affinity rank scores is applied to the sentences that are in set b with respect to the similarity of the sentence that is recently moved to set a. 5. from step 2 repeat the process until set t = s. the algorithm outputs the final score for each sentence in the specified document and based on these scores the sentences were ranked. depending on the summary limit specified, the highest-ranked sentences were selected. we selected 5 and 10 lines from each document which are summarized and labeled as in the corpus in tcej (text categorization environmentimplemented in java) experiment both times [4]. we got 150 labeled summarized training documents and tested them with the reut2-003 test document. we assumed that the results would be better for mutual information (mi), than for information gain (ig) because each document is summarized for all documents belonging to that category. we got similar results for the mi, ig, df feature selection techniques for the summarized training corpus with the results obtained with the original training corpus. iv. results and analysis two document collections were used for the tcej experiment [4]. a self-made data set was used to train the classifiers and reuters 21578 corpus was used as the test data set [19-22]. generally, the training corpus should be very suitable for every category and should be small to reduce the needed running time. this self-made corpus was collected from standard categories business, science, sports, health, education, movies, travel and consisted of 150 documents. fig. 4. average precision comparison of mi, ig, and df techniques table ii. self-made document collection and categories category # of documents sports 30 health 30 science 27 business 23 education 24 travel 06 movies 10 table iii. result comparison of feature vector for normal training document set corpus stop words stemming # of processed terms # of unique terms self-made no no 105443 12819 self-made yes no 105443 12660 self-made no porter 105443 8878 self-made yes porter 105443 8697 self-made no lancaster 105443 7490 self-made yes lancaster 105443 7288 table iv. result comparison of feature vector for summarized training document set * corpus stop words stemming # of processed terms # of unique terms self-made no no 19332 5150 self-made yes no 19332 5025 self-made no porter 19332 3977 self-made yes porter 19332 3838 self-made no lancaster 19332 3510 self-made yes lancaster 19332 3353 * each document consists of 5 summarized sentences table v. results comparison of feature vector for summarized training document set * corpus stop words stemming # of processed terms # of unique terms self-made no no 37323 7497 self-made yes no 37323 7358 self-made no porter 37323 5479 self-made yes porter 37323 5330 self-made no lancaster 37323 4734 self-made yes lancaster 37323 4563 *each document consists of 10 summarized sentences fig. 5. micro and macro averaged accuracy of mi technique v. conclusion and future work our proposed single document summarization method by using all documents belonging to a category consists of two statistical measures, term frequency, and sentence similarity. we can conclude that the summary generated in this work is more efficient. the feature selection techniques mi, ig, df gave good results. mi and ig gave similar results for binary problems. regarding future work, we aim at implementing multi-document summarization, in which all documents belonging to one category are summarized at a time and one engineering, technology & applied science research vol. 9, no. 6, 2019, 5001-5005 5005 www.etasr.com rahamat basha et al: a novel summarization based approach for enhancing text classification … single summarized document is constructed for each category. another aim is to implement some hidden markov model methods for the unigram, bi-gram, n-gram features that are selected from the summarized documents which were generated by single document summarization and multidocument 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study of european alps abdul nasir laghari department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan a.n.laghari@quest.edu.pk gordhan das walasai department of mechanical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan valasai@quest.edu.pk abdul rehman jatoi department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan jatoi.ar@gmail.com daddan khan bangwar department of civil engineering, quaid -eawam university of engineering, science and technology, nawabshah, pakistan skb_khan2000@yahoo.com abdul hannan shaikh department of mathematics. quaid e awam university of engineering, science, and technology, nawabshah, pakistan hanangul12@yahoo.co.uk abstract—the alps play a vital role in the water supply of the region through the rivers danube, rhine, po and rhone while they are crucial to the ecosystem. over the past two centuries, we witnessed the temperature to increase by +2 degrees, which is approximately three times higher than the global average. under this study, the alps are analyzed using regional climatic models for possible projections in order to understand the climatic changes impact on the water cycle, particularly on runoff. the scenario is based on assumptions of future greenhouse gases emissions. the regional model results show the consistent warming trend in the last 30-year span: temperature in winter may increase by 3 to 4.5°c and summers by 4 to 5.5°c. the precipitation regime may also be altered: increasing about 1050% in winter and decreasing about 30-60% in summer. the changes in the amount of precipitation are not uninformed. differences are observed particularly between the north west and south east part of the alps. due to the projected changes in alpine rainfall and temperature patterns, the seasonality of alpine flow regime will also be altered: massive rise will occur in winter and a significant reduction in summer. the typical low flow period during winter will also be shifted to late summer and autumn. keywords-climate change; european alps; flow regime; impact assessment i. introduction the alps, spanning over the central part of europe, play a key role in the water supply of the region. the chain of this mountain region known as the “water towers” of europe are a mother to number of rivers, i.e., danube, rhine, po, and rhone. these rivers provide key services to the ecosystem both at upstream and the downstream regions. worryingly, mountain regions and the alps in particular are highly exposed to the climate change. the region has witnessed a remarkably rise in temperature of approximately +2°c during the last two hundred years against the global mean surface temperature increase of 0.74°c [1]. the alps are highly sensitive to climate change, even a slight variation in climatic parameters can significantly change the hydrological cycle. seasonal snow and ice factor have strong altitude sensitivity concerning temperature conditions, so the variation in temperature could result in sharp changes both to the alpine climate and hydrology [2]. the increased temperature rate has severely affected the alpine hydro-climate system, i.e., extensive glacier retreat, decline in snow cover duration, rise of snowline, variations in seasonal runoff regime etc. [3]. authors in [4-6] analyzed the precipitation in the region and reported a rise in rainfall in winter season by 20-30% and a reduction in autumn by 20-40%. the buildup of snow at higher elevations may form glaciers, and during summer, when precipitation and runoff are low, their melting provides water to low-lying areas. the rivers rhine, rhone, and inn, show stable and higher mean specific discharges of 28-33l/s per km2 in comparison with po, adige and mur which show lower and variable mean specific discharges of 17-24l/s per km2. however, due to the three times higher impact of global warming, any further temperature change shall result in change in the alps hydrological cycle. the two-third of this water volume were lost by 2000 and 10% of the volume was lost just in the hot summer of 2003 [7]. if this trend continues, the large glaciers will lose about 30-70% of their remaining volume by 2050 [8, 9]. it is projected that the changes in the hydro-climate system will be further intensified in the coming decades, resulting into increased number of summer droughts, winter floods and higher inter-mean annual variation in river runoff regimes [1012]. anticipated shortfall of water along with continual intense events and with the growth in water demand will have negative impact on the ecosystem. agriculture, energy use, forestry, winter-tourism, and river transportation are highly susceptible to water shortage. these changes in temperature have left dra cyc am in inc the dec tem cyc on sr evo can on em dev are em fut sce pat cen 20 th me sw slo ext mo ita sto reg ori bas im los wa is hig mo the wh pro ave da bas flo mo 34 dis res bet the flo engineerin www.etasr astic impacts o cle of alps. t mounts and ext alpine glacier creased flood ese impacts w cades [20, 22 mperature and cle depends he energy use a res scenarios olution under n used to analy the future mission scena velopment, de e the primary mission scenar ture water cy enario a2 an tterns, and flow the alpine ntral europe. i 0km in width he arc is elon editerranean witzerland. th ovenia [23-25 tends to the so ost of the alpin aly and france orage site its gion, i.e. rhin iginate from th sins originatin mportance due t the increase ss due to its lo ater availability snowfall at h gh altitudes ma ountain hydrol e total area o hen precipitat ovides importa erage yearly sh anube and po sin (around 10 ow, producing ountain parts o %, 41%, and sproportional spectively [27] tween seasons e po basin, th ow in winter an ng, technology r.com on the alpine this could 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regional cl nario a2. the anging precipi ses early snow 4 shows tha drastic effect . the variati ncrease in win me analysis con ivers, e.g. the so drawn earl in water availa th a potential r nced drought i asing trends e different de h v effects of clima age of w line ree of reased cover. out 4. this 0 and n. the flows me will d [33]. o 50% m, the little educed reased hand, h early ooding spatial een in n mean lm a2 rudence er the ges in limate e high itation wmelt at the t over on in nter to nfirms rhine lier in ability risk of in late in all emand stak crea fig. runo scen web exp and tren hig futu win sno is p van red flow a si [1] [2] [3] [4] [5] [6] vol. 8, no. 4, 20 ate change on m keholders with ated in adjacen 4. relative s off till the last 3 nario. rasters are bsite, http://pruden the alps are periencing high d global avera nd of changes her increase uristic precipi nter and fall in ow-cover span projected to nished, and th duction by the w regime will ignificant fall i ipcc, 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two-dimensional analysis of cracks propagation in structures of concrete two-dimensional analysis of cracks propagation in structures of concrete djamila benarbia dpt of engineering mechanics djillali liabes university of sidi bel abbes, algeria d_benarbia@yahoo.com mohamed benguediab dpt of engineering mechanics djillali liabes university of sidi bel abbes, algeria benguediabm@gmail.com soumia benguediab dpt of civil engineering djillali liabes university of sidi bel abbes, algeria benguediabs@yahoo.com abstract— in this article we present a numerical simulation that allows describing and studying the damage of concrete works subjected to various stress types. in this study, the propagation of cracks in the concrete is analyzed as of their appearance, which requires having a thorough knowledge of the mechanical behavior of the material. the mechanical approach which leads to better understanding of fracture phenomena and can give satisfactory results, is that of the elastic linear mechanics of failure. the interest in this study is focused in the development processes of the cracks from a phenomenological point of view. the analysis is carried out by using fracture criteria while being based on the determination of the critical stress intensity factors, for each case of the several elaborate tests of indirect tensile per bending and brazilian disc. the analysis is carried out in a twodimensional medium by the finite element method by using the abaqus software. the results obtained are compared with experimental data obtained analytically from other authors. keywordscrack propagation; stress intensity factor; threepoints bending beam test; brazilian disc; fractures mechanics; two-dimensional medium. i. introduction the analysis of the behavior of any structure under different loads until its fracture, is an essential component of structural design. the classic methods of collapse designing are based on the research of acceptable fracture diagrams, and on the calculation of ultimate balance in the critical sections. thus, dimensioning of concrete works is done considering ultimate constraints corresponding to the crushing of the concrete or the plasticization of reinforcement‘s steels. with the development of numerical calculation techniques and finite element methods, it is currently possible to analyze the details of state of equilibrium in various points of the structure. models using the criterion of crack propagation based on the going beyond of the maximum stress of traction have been developed but are not sufficient to give an account of the harmfulness of the defect [1, 2, 3]. other models have also been developed [2, 4-8] using the criterion of the breaking process that give a report on the modeling of the cracks by redefining the networks of the elements to each step of propagation. the elastic linear mechanics of the failure is applied to study the crack propagation in concrete not reinforced with massive structures. this approach is adapted to analyze large-sized structures focusing on the influence of structure’s dimension on its behavior [9, 10, 11]. the utilization of a criterion of crack propagation, based on linear mechanics of the failure, imposes the determination of the stress intensity factors. this paper studies crack propagation in concrete structures, using the criterion of failure based on the determination of the stress intensity factors. two approaches were proposed, an approach based on an analytical approach where the stress intensity factor is calculated starting from the functions weight [12] and a numerical approach where the stress intensity factor is calculated by the finite element method using the abaqus software. ii. model used a. hypothesis of bases the numerical model used within the framework of our study, combines a criterion of the linear elastic mechanics of the failure and a distributed model of cracking that leads to taking into account the singularity of the stress field at the peak of a crack and the influence of the geometrical parameters on the development of cracking and fracture behavior. this model adopts a certain number of basic assumptions: • the not fissured concrete is regarded as an isotropic homogeneous material with an elastic linear behavior describing its mechanics. • the micro crack zones and the nonlinear behavior of the material at the point of the cracks are neglected. b. analytical and numerical analyses it is a question of determining, for the load patterns considered in this work, the values of the stress intensity factor ki and kii and which are expressed [9] starting from the following relation: etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 429-432 430 www.etasr.com benarbia et al.: two-dimensional analysis of cracks propagation in structures of concrete i k fσ π α= ⋅ (1) ii k fτ π α= ⋅ (2) where: α is the length or half-length of the crack, σ and τ are respectively the normal and shear stresses applied to the structure, f is the geometrical functions. two types of tests are used: • three-points bending test: the geometrical data and the principle of the test are schematized in figure 1: fig. 1. three bending beam tests. the specimen subjected to the bending test is a not reinforced concrete beam where its length is 2l and its width is w, receiving a load p with an eccentricity d. the beam is supposed to have an initial crack of length α located in the middle of the beam. • brazilian disc test: the geometrical data are illustrated in figure 2. fig. 2. description of the brazilian disc. the specimen submitted for testing is not reinforced concrete, whose dimensions are shown in table ii. the surface of the disc is supposed to be notched (halflength of the crack α ). the crack forms an angle θ with the vertical axis of the disc. in the numerical study, the values of the stress intensity factors ki and kii are numerically given by finite element modeling in a two-dimensional medium by the abaqus software. the models used during the simulation are represented in figures 3 and 4. fig. 3. geometrical representation by abaqus of three points bending test . fig. 4. geometrical representation by abaqus of the brawilian disc. table i. summary of geometric data 3-pt bb l the length of the beam varies from 320 to 800 mm w beam width equal to 160 mm α length of the initial crack varies from 8 to 64 mm d eccentricity of load 0≤ d <l table ii. summary of geometric data brasilian disk d disc diameter d = 160 mm equal to 160 mm r radius of the disk equal to 80 mm α half length of the initial crack varies from 8 to 40 mm θθθθ angle of inclination of the initial crack varies from 0° to 90° iii. results and discussions a. mechanical properties of the material (concrete) the mechanical properties of the concrete are given in table iii [13]. table iii. summary of mechanical characteritics of concrete e elastic modulus 35982 mpa σσσσc compressive strength 35 mpa σσσσt tensile strength 2.7 mpa νννν poisson’s ratio 0.2 b. comparison of the results 1) mode i: three-points bending test etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 429-432 431 www.etasr.com benarbia et al.: two-dimensional analysis of cracks propagation in structures of concrete a) variation of the stress intensity factor ki according to the length of the crack figure 5 shows the variation of the stress intensity factor ki (calculated numerically and analytically) according to the length of the crack; it is observed that the values of ki increase when the reported a/w increases. b) influence of the load’s position on the stress intensity factor ki figure 6 represents the variation of the stress intensity factor ki according to the position of the load; it is noticed that the increase in d/w leads to a reduction of ki and that when d/w = 0 the values of ki are maximum. fig. 5. variation of the sif ki according to a/w. fig. 6. variation of the sif ki according to the position of the load. 2) mode i: brazilian disc test: a) influence of the crack’s size on the stress intensity factor ki figure 7 represents the variation of the stress intensity factor ki according to a/r (brazilian disc). it is noted that for angles of inclination of the crack lower than 30°, the value of ki increases when a/r increases. for inclination angles larger or equal to 30°, ki decreases and become negative. b) influence angle of inclination of the crack on the stress intensity factor ki figure 8 represents the variation of the stress intensity factor according to the crack inclination angle. it is noted that for values of inclination angle θ lower than 22°, the values of ki are positives and become maximum for θ = 0. for values of θ larger than 22°, ki becomes significant in absolute value, specimen is in compression and the crack remains closed [1417]. fig. 7. variation of the sif ki according to a/r. fig. 8. variation of ki according to crack inclination angle. 3) mode ii in three-points bending test, the beam is not subjected to shearing and the values of ii k are negligible. the study is limited only to the case of brazilian disc test. a) influence of the crack’s size on the stress intensity factor kii figure 9 represents the variation of kii according to the size of the crack; we can note that kii varies proportionally with a/r i.e. when the length of the crack in the disc increases, the values of kii increase. this means that there exist high shear stresses that facilitate the fracture in mode ii and the propagation of the cracks is carried out quickly. if the crack is not inclined or not formed at an angle of θ=0° or θ=90°, we can note that kii values are cancelled and the increase of the crack‘s size does not have any effect on the variation of kii because of the absence of shear stresses in these two cases. b) influence of the angle of inclination of the crack on the stress intensity factor kii figure 10 represents the variation of kii according to the crack inclination angle; it is shown that kii reaches its maximum value when the crack inclination angle θ is in the interval of 30° to 60°, because shear stresses are highest in this zone. on the other hand if the inclination angle θ tends towards 0° or 90°, kii decreases until it is cancelled. etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 429-432 432 www.etasr.com benarbia et al.: two-dimensional analysis of cracks propagation in structures of concrete fig. 9. variation of the sif kii according to a/r. fig. 10. variation of the sif kii according to crack inclination angle. iv. conclusion in actual position, the phenomenon of crack propagation in concrete structures can be described by the concept of the elastic linear mechanics of failure starting from the criterion of the critical stress intensity factor. this method makes it possible to quantify the effects of the presence of a crack and its influence on the fracture behavior of the structure. in this study, we compared two methods of calculating the stress intensity factor, and showed that the obtained results are comparable. references [1] p. droz, modèle numérique du comportement non-linéaire d’ouvrages massifs en béton non armé, thesis epfl no. 682, lausanne, 1987 [2] b. karihaloo, fracture mechanics and structural concrete, longman scientific & technical, new york, 1995 [3] j. wang, development and application of a micromechanics-based numerical approach for the study of crack propagation in concrete, thèse de doctorat de l’epfl no. 1233, lausanne, 1994 [4] j. m. berthelot, j. l. robert, “damage evaluation of concrete test specimens related to failure analysis”, journal of engineering mechanics, vol. 116, no. 3, pp. 587-604, 1990 [5] m. matallah, c. la borderie, “modélisation numérique de l’ouverture des fissures dans les structures en béton”, rencontres universitaires de génie civil, bordeaux, france, 2007 [6] g. bilbie, modélisation multi-échelle de l’endommagement et de la rupture dans les milieux (quasi-) fragiles (multiscale modelling of damage and fracture in (quasi-) brittle media), phd thesis, université joseph-fourier grenoble i, 2007 [7] m. jirasek, “non local damage mechanics with application in concrete”, revue européenne de génie civil, failure, degradation and instabilities, vol. 8, pp. 683-707, 2004 [8] j. mazard, application de la mécanique de l’endommagement au comportement non linéaire et à la rupture du béton de structure, thesis, université paris 6, france, 1984 [9] s. kumar, s. v. barai, “size-effect of fracture parameters for crack propagation in concrete: a comparative study”, computers and concrete, vol. 9, no. 1, pp. 1-19, 2012 [10] b. qi, influence de l’endommagement sur les propriétés d’élasticité de matériaux modèles: approche numérique et expérimentale (damage influence for elastic properties of model materials: numerical and experimental approaches), phd thesis, université de limoges, france, 2009 [11] v. e. saouma, interactive finite element analysis of reinforced concrete: a fracture mechanics approach, cornell university, 1981 [12] t. fett, d. munz, stress intensity factors and weight functions for special crack problems, computational mechanics publications, 1997 [13] bulletin officiel fascicule n° 62; titre i section i règles techniques de conception et de calcul des ouvrages et constructions en béton armé suivant la méthode des états limites bael 91 révisé 99 avril 1999 [14] a. krayani, “contributions a la modélisation non linéaire du comportement mécanique du béton et des ouvrages en béton armé et précontraint”, phd thesis, nantes, france, 2007 [15] r.c. yu, x. x. zhang, g. ruiz, “numerical modeling of dynamic crack propagation in reinforced concrete”, anales de la mecánica de fractura, vol 1, pp. 295-300, 2007 [16] a. hillerborg, m. modeer, p. e. petersson, “analysis of crack formation and crack growth in concrete by means of fracture mechanics and finite elements”, cement and concrete research, vol. 6, no. 6, pp. 773-781, 1976 [17] h. n. atahan, m. a. tasdemir, c. tasdemir, n. ozyurt, s. akyuz, “mode i and mixed mode fracture studies in brittle materials using the brazilian disc specimen”, materials and structures. vol. 38, no. 3, pp. 305-312, 2005 microsoft word etasr_v13_n3_pp10969-10972 engineering, technology & applied science research vol. 13, no. 3, 2023, 10969-10972 10969 www.etasr.com quy et al.: a non-destructive radar device for detecting additive materials in concrete a non-destructive radar device for detecting additive materials in concrete vu ngoc quy faculty of electrical-electronic engineering, university of transport and communications, vietnam quygtvt2014@utc.edu.vn toan thanh dao faculty of electrical-electronic engineering, university of transport and communications, vietnam daotoan@utc.edu.vn (corresponding author) ho thanh trung faculty of electrical-electronic engineering, university of transport and communications, vietnam trunght@utc.edu.vn received: 3 april 2023 | revised: 21 april 2023 | accepted: 4 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5900 abstract the use of electronic devices based on electromagnetic waves is promising for inspecting additives in structural concrete. however, the existing commercial devices are high-cost and do not publicly provide circuit design information. to overcome this issue, this study designed a low-cost nondestructive testing device with a radar sensor, using an hb-100 radar sensor module to generate and receive the radar wave. a suitable bandpass filter was used to suppress electrical noise in the received signal, an arduino board was used for signal processing, and the measured data were displayed on a computer. the output at the if pin of the sensor module presents the doppler frequency and absorbance of the target materials. the device was tested to detect additives inside the concrete. an additive material can be recognized by the fact that the obtained signal magnitudes are different with different additive materials. the findings in this study can contribute to making a low-cost nondestructive testing device based on radar technology for structural concrete inspection. keywords-hb 100 radar sensor; active bandpass filter; nondestructive testing; structural inspection i. introduction concrete is one of the most important components used in civil engineering infrastructures. unwanted additive materials in concrete can cause cracks over time due to dopants, corroding steel rods, or environmental factors [1-8]. ensuring the structural integrity of concrete is very important for the longevity and safety of infrastructures [9-10]. currently, infrared thermography, ultrasonic-echo, and radars are conventional technologies for detecting internal additive materials [1-8], with radar being widely used. in this method, when the waves are transmitted through concrete, they are partially attenuated and reflected depending on the dielectric properties of the concrete material. the comparison to the initial wave provides useful information about the materials inside the concrete [1]. on the other hand, existing commercial radar testing devices have high costs and limitations in the information of circuit design, which could be due to industrial secret policies [1-2]. the hb 100 doppler radar sensor is widely used for motion detection thanks to its low cost and high reliability [11-12]. recently, the hb 100 sensor was used for additional functions such as underground metal detection [13] or wooden pole inspection in forests [14]. unfortunately, up to now, there are very few studies on the use of the sensor for detecting additive materials in concrete. this study designed a nondestructive testing device with the hb-100 radar sensor. the output of the intermediate frequency (if) pin of the sensor module presents the doppler frequency and the absorbance of the target materials. the if signal was enhanced by a band-pass active filter before going to the microcontroller. the final measured signal on a computer can adequately distinguish the additives in the concrete. ii. system design of the nondestructive testing device the proposed system was based on the hb100 miniature microwave sensor, an x-band doppler transceiver module speed sensor radar commercially available by st engineering engineering, technology & applied science research vol. 13, no. 3, 2023, 10969-10972 10970 www.etasr.com quy et al.: a non-destructive radar device for detecting additive materials in concrete electronics ltd, singapore [15]. the module has the features of low current consumption and a long detection range of about 20m. an effective isotropic radiated power of 15dbm was transmitted at the frequency of 10.525ghz. table i presents the parameters of the sensor. table i. radar sensor's device parameters no specification parameters 1 working voltage 5v±0.25v 2 operating current 50ma max., 30ma typical 3 emission parameters 2-16m 4 helium emission frequency 10.525ghz 5 frequency setting accuracy 3mhz 6 output power 13dbm 7 harmonic emission <-10dbm 8 pulse width 5usec 9 sensitivity -86dbm 10 vertical 3db beam width 36 o figure 1 shows the structure of the nondestructive testing device system. the microwave motion detector continuously transmits the signal within its range, and when the signal hits the target object it receives the reflected signal. the reflected signal is mixed with the transmitted and then the if or doppler frequency fd signal can be given by [13]: �� � ����� � (1) where v, , f, and c are the target speed, the angle between the trajectory of the concrete target and the radial line joining the target and the radar, the transmitted frequency, and the speed of light, respectively. the fd is typically below 100hz [15]. the radiation patterns of the antenna and their half-power beam width can be seen in [15]. the antenna patches were mounted on the module facing the desired detection. when measuring, the orientation of the module can be directed to get the best coverage. fundamentally, the amplitude of the if signals is very low and it is easy to attach electrical noise. to overcome that issue, an instrument amplifier based on a texas instruments lm324 was designed, as shown in figure 2. the if signal was amplified in the first stage by a noninverting amplifier and then by an inverting active bandpass filter [16]. the low(fl) and high-cutoff (fh) frequencies were calculated to be 3.38 and 72.38hz, using the following equations: �� � ������ (2) �� � ������ (3) the amplified signal was connected to an analog pin on an arduino board. the microcontroller has a built-in adc that processes the signal, converts it to a digital value, and sends it to a computer via a usb cable with a serial communication protocol. the amplitude of the signal can be observed in computer software. figure 3 shows a photo of the completed non-destructive testing device with the hb100 radar sensor. for convenient use of the device, the radar sensor was separated from the pcb by a 50cm long cable. fig. 1. the design of the nondestructive testing device system. fig. 2. design of the active band-pass filter for the hb100 sensor. fig. 3. the hardware implementation of the non-destructive testing device. gnd +5 v r1 100k r2 100k r3 330k c1 100uf 1 2 3 j1 hb100 +5 gnd r5 12k 4.7uf/50v c2 gnd c5 2.2nf r7 1m r6 10k 4.7uf/50v c7 4.7uf/50v c3 r4 8.2k +5 gnd c6 2.2nf r8 1m rx1 8.2k 4 1 1 1 3 2 1 v cc v ee ic1a lm324 14 12 13 2 ic1d lm324 gnd to arm engineering, technology & applied science research vol. 13, no. 3, 2023, 10969-10972 10971 www.etasr.com quy et al.: a non-destructive radar device for detecting additive materials in concrete iii. results and discussion figure 4 shows the test procedure, where wooden, steel, and plastic bar objects were placed inside a hole in the concrete sample. the distance between the surface and the hole was approximately 5cm. in this experiment, the target was stationary, thus, to make hb 100 detect the doppler effect, the radar sensor needed to move toward the target. the radar sensor was manually controlled to gradually move at a constant speed of about 0.45m/s and then touched the surface of the concrete sample. that generates a constant frequency of a certain amplitude. the amplitude levels of the reflected beat frequency were recorded at room temperature by a computer. figure 4 also presents the data measured from the concrete sample with different additives. it can be noted, that while the frequency values were not significantly altered, the magnitude or data volume depended on the additive materials. sensed data were further analyzed. the maximum values of the data volume in nominal units extracted from the examples in figure 4 were 466, 468, 478, and 482 for solid concrete, wood inside the concrete, steel inside the concrete, and plastic inside the concrete, respectively. figure 4 demonstrates that the designed device system could clearly distinguish the different materials. fig. 4. obtained signals measured from solid concrete with different additive materials. the amplitude of the received signal can be expressed as [17]: � � ������ (4) where a0, α, and z are the initial amplitude, attenuation factor, and travel distance, respectively. the value of a can be given by [17]: � � 2�� �� � !"1 $ ! % �&'� ( 1') /� (5) where μ is the magnetic permeability of the material, ε is the dielectric permittivity of the material, and σ is the electric conductivity. table ii. materials' dielectric permittivity no tested material dielectric permittivity  1 concrete 4.5 2 wood 4.0 3 steel 3.5 4 plastic 3.1 table ii shows the dielectric permittivities of the tested materials [18-19]. the a in (5) strongly depends on the dielectric permittivity of the material. therefore, (4) implies that the amplitude of the received signal is decreased with increasing dielectric permittivity. figure 5 shows the relation between the maximum data volume of the received signal and dielectric permittivity. as can be noted, a material with higher dielectric permittivity results in a lower amplitude of the received signal, i.e. it absorbs more of the transmitted signal. that is consistent with the theoretical relationships (4) and (5). the amplitude levels in figure 5 also confirm that the additive materials in concrete can be clearly identified. in previous studies on non-destructive radar inspection devices [1, 7, 8, 1113], the measured data were visualized and could be exported in several aspects, such as additive materials, defects, and scanned mapping. however, these devices had a complicated structure with a special radar sensor and an elaborated signal processing system. this study used a simple design with a lowcost commercially available motion radar sensor and a popular microcontroller. although the device needs to be further improved, integrating data analysis or visual mapping, it can be realized that the advantages of the proposed design are its low cost and simplicity. fig. 5. dielectric permittivity and maximum data volume of the received signal obtained from different additive materials inside the concrete. m ax im u m d at a v o lu m e (n o m in al u n it s) dielectric permittivity concrete wood steel plastic 464 468 472 476 480 484 2.5 3 3.5 4 4.5 5 engineering, technology & applied science research vol. 13, no. 3, 2023, 10969-10972 10972 www.etasr.com quy et al.: a non-destructive radar device for detecting additive materials in concrete iv. conclusion this study demonstrated an electronic device based on electromagnetic waves to inspect additive materials in structural concrete, based on the hb-100 sensor module to generate and receive the radar wave. a band-pass active filter was designed to suppress electrical noise from the received signal. the output at the if pin of the sensor module presents the doppler frequency and absorbance of the target materials. an arduino microcontroller was used for signal processing and the measured values were displayed on a computer. the proposed device was used to detect additives inside a concrete sample, and the obtained signal magnitudes were different for different additive materials. this design used a low-cost commercially available motion radar sensor and a popular lowcost microcontroller. the results of this study show the feasibility of designing and implementing a low-cost nondestructive testing device based on radar technology for structural concrete inspection. acknowledgment the authors acknowledge moet for the grant b2022gha-09. this research was funded by the university of transport and communications under grant t2021-dt-004td. references [1] s. k. sharma, v. s. chauhan, and m. sinapius, "a review on deformation-induced electromagnetic radiation detection: history and current status of the technique," journal of materials 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[19] f. t. ulaby and r. p. jedlicka, "microwave dielectric properties of plant materials," ieee transactions on geoscience and remote sensing, vol. ge-22, no. 4, pp. 406–415, jul. 1984, https://doi.org/ 10.1109/tgrs.1984.350644. microsoft word 13-3445_s engineering, technology & applied science research vol. 10, no. 3, 2020, 5655-5659 5655 www.etasr.com mekki et al.: miniaturization of circularly polarized patch antenna for rfid reader applications miniaturization of circularly polarized patch antenna for rfid reader applications kawther mekki department of physics university of tunis el manar tunis, tunisia kawther.mekki@gmail.com chokri boussetta department of physics university of tunis el manar tunis, tunisia chokri.boussetta@gmail.com omrane necibi faculty of computer and information sciences al jouf university jouf, saudi arabia oncibi@edu.ju.sa ali gharsallah department of physics university of tunis el manar tunis, tunisia ali.gharsallah@fst.utm.tn abstract—this paper presents a circularly polarized microstrip patch antenna (cpmpa) miniaturization with parasitic elements, suitable for uhf rfid systems. the antenna consists of a half e-shaped patch with cuts. a truncated corner patch can generate an additional circular polarization (cp) radiation mode and further enhance the axial ratio. two symmetric cross shaped slots along the horizontal axis of the cpmpa have been embedded, and its dimension optimization has been based on parametric analysis. thanks to this slotted structure and reduced surface area, good cp quality has been obtained with a 25% overall size reduction. the proposed antenna is lightweight, low profile, simple, and easily produced. the structure’s simulation is made using cst studio suite 2014 to compute return loss (s11), gain, and the axial ratio of the antenna while the overall miniaturized antenna’s volume is 77mm×58mm×1.6mm operating at 915mhz. keywords-rfid; return loss; axial ratio; slots; gain i. introduction radio frequency identification (rfid) is widely used in many applications. uhf rfid must provide appropriate isolation for high reader sensitivity, which is a key to an extended reading range of the rfid reader. many applications require compact cpmas, where the overall size of the antenna is an important factor [1]. for rfid systems, the size of the antenna is very important, especially for low frequency bands, and so is its gain. moreover, the antenna must cover the desired frequency bands for intended wireless applications, such as ultra-high frequency (uhf) rfid for implanted antennas and circularly polarized patch antennas for rfid reader applications [2]. several antennas have been designed the last few years for rfid readers, such as the helical antenna [3], the loop antenna [4], the pifa antenna [5], the unipolar antenna [6], the yagi antenna printed with three elements [7], etc. the proposed antenna is designed to enable faster and more accurate communication of epc-compliant passive tag data to rfid readers, even in harsh rf environments. the aim is to achieve higher performance, due to its low reflection coefficient, good gain, inherent power, and circular polarization, while maintaining a simple architecture that would make the rfid reader suitable for bi-static operation. although this structure has simplicity as its main advantage, the drawbacks that might make its use not so favourable are its limitations, notably lesser gain, low bandwidth, and low efficiency [8]. many studies have been conducted in order to reduce these disadvantages by making a different approach regarding the mpa’s geometry, such as the use of slots and splits, like the e-shaped [9], u-shaped [10], l-shaped [11] structures. this led to the improvement of performance to a certain level that made them widely used in wireless applications such as military devices, gps, satellite communications, rfid, etc. in this work, a modified cpmpa is presented, designed on an fr4 substrate for an rfid reader. the modifications made on this structure are mainly two symmetrical cross slots that contribute to its miniaturization, and the improvement of its reflection coefficient. ii. cpmpa structure and design a. design the circular polarization can reduce the transmission loss affected by misalignment between two connected antennas and offers better system performance and better mobility compared to linear polarization. two sided corner truncation technique was implemented on both sides of the patch so that better impedance matching across the operating bands can be obtained [12-14]. corner truncation also ensures the circular polarization of the antenna. figure 1 shows a basic rectangular cpmpa, with truncated edge technique applied on its edges. the proposed antenna component has an antenna patch, placed on a fr4 substrate with dielectric constant (εr) of 4.7 and corresponding author: kawther mekki engineering, technology & applied science research vol. 10, no. 3, 2020, 5655-5659 5656 www.etasr.com mekki et al.: miniaturization of circularly polarized patch antenna for rfid reader applications thickness (h) of 1.6mm. pec material was used for ground and patch with standard thickness of 0.035mm. the mpa dimensions at the 915mhz frequency are listed in table i. fig. 1. proposed circularly polarized microstrip patch antenna (cpmpa) table i. microstrip antenna dimensions parameters values (mm) w 98 l 76 wg 107 lg 87 t 10 wg 2 the microstrip antenna dimensions are based on standard mathematical models inspired by the literature for the design of the mpa [15-16]. in order to analyze the performance of the antenna, certain parameters need to be taken into account, such as the return loss s11, gain, and directivity. the antenna’s response is tuned by adjusting the substrate width (wg), substrate length (lg), antenna width (w), antenna length (l), antenna feed length (lg), antenna feed width (wf), choosing substrate material, thickness and size of the truncated segment (t1 and t2). b. results and discussion the cpmpa has a return loss value of -17db at its resonance frequency of 915mhz (figure 2). the cpmpa’s resonant frequency is not the desired frequency but the structure overall radiates with a circular polarization. modifying the truncated segments (t1 and t2) results in maintaining the desired polarization while shifting the resonant frequency. these segments dimensions are chosen depending on obtaining desired results while maintaining satisfying matching and low vswr. the radiation property of most concern is the two or three-dimensional spatial distribution of radiated energy as a function of the observer’s position along a path or surface of constant radius. the simulated gain of the cpmpa structure is shown in figure 3. the simulated gain of the antenna in the normal direction to the patch is equal to 5.1db at 915mhz. the simulated axial bandwidths at 915mhz is less than -3db. figure 4 shows the simulated axial ratio of the antenna without the connected patch. fig. 2. simulated return loss s11 of cpmpa fig. 3. gain of simulated cpmpa fig. 4. simulated axial ratio iii. a miniaturized cpmpa there are many miniaturization concepts that are intended to artificially lengthen the dimensions of the resonant device. among these techniques, we find the electrical elongation of the path of the current by modifying the antenna structure, the addition of parasitic elements or the use of particular materials. in this paper we will discuss the first technique of modifying the geometry of the radiating element by inserting slots on the patch. this technique of miniaturization is the most widespread engineering, technology & applied science research vol. 10, no. 3, 2020, 5655-5659 5657 www.etasr.com mekki et al.: miniaturization of circularly polarized patch antenna for rfid reader applications today and concerns a panel of antennal forms. on the radiating elements, such as patch antennas, the use of slots in a radiating element allows, when properly positioned, increasing the distance traveled by the surface current. indeed, a current flowing from one end to the other of the metal part of the antenna will be blocked by the slots. to get around them, it will have to take a longer path than the one without the slots. the length traveled by the current is greater, the wavelength of the antenna is artificially elongated, and its operating frequency is lower. with this technique it is possible to reduce the size of an antenna up to 25%. however, the quality factor increases with the number of slots, which has the effect of degrading the bandwidth. depending on their shape and location, the slots may optionally introduce capacitive and inductive effects. if these effects are properly controlled, they can increase the bandwidth of the antenna. but before discussing this technique, it is necessary to see the distribution of the surface current on the antenna structure in order to find the hot zones of the structure where a great concentration of surface current occurs. the slots must be placed according to these positions. the current distribution on the patch allows finding the ideal location for creating slots, for the structure to be optimized. this distribution is shown in figure 5. fig. 5. surface current distribution at 915 mhz a concentration of surface current on both sides of the excitation line is noticed, so slots will be inserted in the middle of the structure in a symmetrical way. a. parametric study of cross slot cpmpa this work is directed to having a miniaturized antenna for the rfid reader. the modifications consist of creating two symmetric cross slots then change the dimensions of the cpmpa to meet miniaturization. the miniaturization process of the antenna is based on a parametric study, by using the parameter scanning function provided by cst. in order to highlight the effect of modifying certain parameters of the antenna on its response, only one parameter is modified at a time, while the others (the structure’s dimensions) remain constant. the structure shown in figure 6 is the geometry of a miniaturized microstrip patch antenna, created with the two engraved symmetric slots technique. as with every design of a new structure, optimization is always important for better performance. indeed, the parametric study allows us to define the effect of each parameter on the overall characteristics of the antenna. the method to achieve our goal is to embed symmetric slots on the cpmpa and reduce the size of the patch to get the desired resonance frequency by controlling the return loss parameters. by using the same dimensions, truncating the edges of the mpa causes a shifting in the resonant frequency from 894mhz (figure 7-1) up to 915mhz (figure 7-2), while changing the polarization to circular, and with the integration of slots, the resonance frequency decreases to around 840mhz (figure 73). (a) (b) fig. 6. geometry of the proposed two symmetrical cross-shaped slots cpmpa: (a) simulated structure, (b) fabricated structure, where w=77, l=58, wg=80, lg=67, ws=1.5, ls=12 (all dimensions in mm) fig. 7. the simulated return loss of a cross slotted cpmpa based on two symmetric slots b. the effects of cross shape slot length ls and width ws variation the return loss is greatly influenced by the length ls of the cross shape slot, as depicted in figure 8(a). the increase of this parameter from 11mm to 13mm leads to a decrease of the resonance frequency. the path of surface current on the patch is extended by the cross shape slot. as a result the operating frequency drops and thus the antenna size can be reduced. similarly, the return loss is influenced by the width ws of the cross shape slot, as shown in figure 8(b). the increase in ws from 1mm to 2mm leads to a slight decrease in the resonant frequency shifts compared to ls variations, while keeping the impedance and ar bandwidths hardly influenced. as before, the path of surface current on the patch is extended by the cross shape slot. as a result, the operating frequency decreases and thus size reduction can be obtained. engineering, technology & applied science research vol. 10, no. 3, 2020, 5655-5659 5658 www.etasr.com mekki et al.: miniaturization of circularly polarized patch antenna for rfid reader applications (a) (b) fig. 8. reflection coefficient for different values of (a) ls and (b) ws we can conclude from figure 8 that both ls and ws affect the operating frequency, with ls having most significant effects. the length ls of the cross shape slot has been parametrically studied in the range of [8mm (λ/40) – 16mm (λ/20)], from which 12mm (λ/25) gave the most satisfying result. so, 12mm and 1.5mm for ls and ws respectively are selected as the optimal values at 915mhz. c. results and discussion the simulated and measured performance of the proposed cross slot cpmpa was compared with some related published compact cpma structures [17]. the comparison between simulated and measured return loss values is shown in figure 9. we can see that the simulated and measured results are in a good agreement. the comparison between simulation results and those of [17] allows us to conclude that they are in agreement, with slight difference in resonance frequency (5mhz). in fact, the simulated bandwidth ranges from 892mhz–940mhz (48mhz) while the bandwidth found in [17] ranges from 886mhz to 930 mhz (44mhz). the two simulated resonance frequencies of the proposed antenna and the one in [17] are 915mhz and 910mhz respectively. the simulated resonance frequency and measured resonance frequency of the proposed antenna are 915mhz and 913mhz respectively. the simulated and measured -10db return-loss bandwidths of this antenna are 48mhz (893mhz–940mhz) and 30mhz (900mhz–930mhz) respectively. moreover, the desired operating frequencies slightly shift from 915mhz (simulation) to 913mhz (measured) with return-loss values shifting as well, from -40db (simulation) to -35db (measured). it can be concluded that the simulation results are in good agreement with the actual measurements. the small difference between the simulated and measured results may be due to the effect of sma connector soldering and tolerance levels during the fabrication process. overall, the extracted results from the studied structure are considered better than those of the structures proposed in [17]. this difference in simulated results can be caused by the use of the slots and the type of the chosen excitation. the presence of a single resonance is remitted for the cst simulation while for the measurements the presence of two adjective resonances is distinguished. this difference is essentially due to the choosing of the ws and ls parameters, because the return loss parameter s11 and the bandwidth are very sensitive to their variations. the fact of inserting two symmetric slots on the circular polarization microstrip antenna allows maintaining gain while ensuring a good matching at 915mhz. fig. 9. reflection coefficient s11 of the miniaturized antenna fig. 10. gain of the cpmpa with and without cross slots d. structure comparison overall, the obtained results are found to be better than those of the structures proposed in [17-20]. table ii shows a comparison between the proposed antenna and the structures mentioned previously showing a better bandwidth in terms of both return loss and gain. when it comes to miniaturization, surface reduction size of 40% is achieved and an overall size reduction of 25% compared to the basic mpa is obtained. engineering, technology & applied science research vol. 10, no. 3, 2020, 5655-5659 5659 www.etasr.com mekki et al.: miniaturization of circularly polarized patch antenna for rfid reader applications table ii. comparison of cp microstrip antenna antenna description return loss at fr (db) operating frequency fr of cp (mhz) overall antenna size (mm 2 ) gain (db) [17] slotted cpma for rfid -24 910 80 x 80 3.07 [18] asymmetrical circular slotted -38 900 90 x 90 3.7 [19] cp cross shaped slotted -24 910 90 x 90 3.8 [20] compact cpma for rfid -20 920 90 x 90 3.4 proposed cp cross shape symmetric slot -40 915 77x 58 5.09 iv. conclusion a compact circularly polarized symmetric cross slotted mpa has been studied, simulated, and manufactured. the prototype made has a reduced size and delivers an exceptional performance with enhanced return loss value of -40db and an unusual high gain peaking up to 5.09dbi. in addition, usability of the reader unit in terms of reading directions and orientations of tags was ensured by the gain of 5.09dbi while the beamwidth value was 103°. the small sized proposed antenna design can be easily manufactured for uhf rfid reader applications. acknowledgment the authors wish to thank the laboratory for research on microwave electronics department of physics, fst tunis university tunis el manar tunis, tunisia. 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with improved impedance bandwidth and axial ratio”, engineering, technology & applied science research, vol. 10, no. 1, pp. 5104-5107, 2020 [15] m. m. nahas, m. nahas, “bandwidth and efficiency enhancement of rectangular patch antenna for shf applications”, engineering, technology & applied science research, vol. 9, no. 6, pp. 4962-4967, 2019 [16] j. elluru, s varadarajan, “design of uhf-band microstrip patch antenna for wind profiler radar”, international journal of advance engineering and research development, vol. 4, no. 8, pp. 567-572, 2017 [17] s. kumar, r. k. vishwakarma, r. kumar, j. anguera, a. andujar, “slotted circularly polarized microstrip antenna for rfid application”, radioengineering, vol. 26, no. 4, pp. 1025-1032, 2017 [18] nasimuddin, z. n. chen, x. qing, “asymmetrical-circular shaped slotted microstrip antennas for circular polarization and rfid applications”, ieee transactions on antennas and propagation, vol. 58, no. 12, pp. 3821-3828, 2010 [19] nasimuddin, z. n. chen, x. qing, “a compact circularly polarized cross-shaped slotted microstrip antenna”, ieee transactions on antennas and propagation, vol. 60, no. 3, pp. 1584-1588, 2012 [20] nasimuddin, x. qing, z. n. chen, “compact circularly polarized microstrip antenna for rfid handheld reader applications”, asia pacific microwave conference, singapore, singapore, december 7-10, 2009 microsoft word 32-3070_s1_etasr_v9_n5_pp4750-4754 engineering, technology & applied science research vol. 9, no. 5, 2019, 4750-4754 4750 www.etasr.com bhutto et al.: post construction and long term settlement of an embankment dam computed with … post construction and long term settlement of an embankment dam computed with two constitutive models amjad hussain bhutto department of civil engineering, quaide-awam university of engineering science and technology, nawabshah, pakistan amjadbhutto62@gmail.com shahnawaz zardari department of civil engineering, quaide-awam university of engineering, science & technology, nawabshah, pakistan shahnawazzardari@gmail.com ghulam shabir bhurgri department of civil engineering, quaide-awam university of engineering science and technology, nawabshah, pakistan ghulamshabirbhurgri14@gmail.com muhammad auchar zardari department of civil engineering, quaide-awam university, of engineering, science & technology, nawabshah, pakistan muhammad.auchar@quest.edu.pk riaz bhanbhro department of civil engineering, quaide-awam university, of engineering science and technology, nawabshah, pakistan riaz@quest.edu.pk bashir ahmed memon department of civil engineering, quaide-awam university, of engineering science and technology, nawabshah, pakistan bashir_m@hotmail.com abstract— for the settlement computation of an embankment dam, the soil stiffness is of great importance. unfortunately, due to the lack of funds allocated for geotechnical investigation, stiffness parameters are commonly not evaluated as compared to strength properties. as a result, this may create hindrance in the use of advanced constitutive models such as hardening soil model (hsm). in this study, the settlement with respect to depth and long term settlement of an embankment dam computed with mohr-coulomb model (mcm) is compared with that of hsm applied to foundation soil only with limited data on stiffness. the results show that the mcm overestimated settlement in comparison with hsm. the settlement increment of mcm, in comparison with hsm, at the crest and at the depth of 120m was 53% and 82% respectively after the filling of the reservoir. the settlement computed with mcm and hsm were 2.9% and 1.35% of the dam height. it can be interpreted that the settlement predicted with mcm is unrealistically high due to the single constant value of modulus of elasticity (moe), while the predictions of hsm are in agreement with the literature. in addition, the long term settlement computed using mcm is about 59% higher than that of hsm for the condition after the filling of the reservoir. this paper shows that the settlement of an embankment dam could be predicted reliably by using hsm even when a limited number of stiffness data is available. keywords-long term settlement; embankment dam; settlement with respect to depth; stiffness; crest i. introduction in pakistan, the construction of embankment dams is being given top priority to meet the shortage of electricity and water for drinking and irrigation purposes. depending upon the requirements and geology of the site, an embankment dam may be designed to last for hundreds of years. in order to ensure the safety of the dam, stability during various operational stages [12] and possible settlement play an important role [3-5]. both stability and settlement of an embankment dam could be evaluated with the help of modern numerical tools based on finite element methods. in geotechnical engineering, there are various software programs, which require some soil properties as input to compute the stability and settlement of an embankment dam. normally, stability is given high priority as compared to settlement. as a result, more focus is given on the determination of soil material properties that are required for stability estimations during the geotechnical investigation process [6]. the stability of an embankment dam is assessed based on factor of safety by using the mohr-coulomb model (mcm) to represent stress strain soil behavior. however, the settlement of an embankment dam is also equally important. the use of mcm for the computation of settlement is not considered reliable [7-8], since it does not include stress dependent stiffness, therefore, the settlement predicted could be unrealistically higher with respect to the depth of an embankment dam. in such a situation, it might be advantageous [9] to adopt advanced material models like the hardening soil model (hsm) for settlement computations. such model types require more material parameters that may be determined through laboratory or field tests. due to the limited available funding for geotechnical investigation, it might not be possible to conduct more detailed tests that could help in settlement evaluation. this type of problem requires evaluating material properties of hsm from the available material parameters of corresponding author: amjad hussain bhutto engineering, technology & applied science research vol. 9, no. 5, 2019, 4750-4754 4751 www.etasr.com bhutto et al.: post construction and long term settlement of an embankment dam computed with … mcm. therefore, it is interesting to compare settlement with respect to depth, and long-term settlement computed with mcm and hsm. the focus of this paper is to understand how much reliable prediction of the settlement of an embankment could be made by using hsm even by utilizing a limited number of parameters obtained from laboratory tests. ii. materials and methods settlement with respect to depth and long term settlement werre computed for an embankment dam called nai gaj dam located in dadu district, sindh, pakistan. the calculations were carried out using the plaxis 2d software [10] which is widely used for analysis of various geotechnical problems. initially, the settlement was computed with mcm [10]. the predictions made with mcm showed more settlement as compared to the values of similar type of embankment dams mentioned in the literature [14]. afterwards, four main zones with respect to large volume were identified. these zones were sandy gravel, clay core, random fill, and sandy siltstone (figure1). hsm was applied to the above-mentioned four zones of the dam and the mcm was used for the remaining zones. fig. 1. cross section of the nai gaj dam since the focus of this paper is to predict the settlement of the dam, it is relevant to describe that the modulus of elasticity (moe) is of vital importance for settlement computations. real soils exhibit stress dependent stiffness, whereas mcm uses a single value of moe, which may result in overestimation of settlement for embankment dams. on the other hand, the hsm uses three different types of stiffness, which are stress dependent. the stiffness values used in mcm are mentioned as [10]: ��� � ������ � �� ������� ������������� (1) where ��� is the confining stress dependent stiffness modulus for primary loading, ������ is the secant stiffness in standard drained triaxial test, c is cohesion, φ is the friction angle of soil, p��� is the reference stress for stiffness (100kpa), σ'3 is minor effective principle stress, and m is the power for stress level dependency of stiffness. for norwegian sands and silts, the value of m is reported to be 0.5 [11]. however, for most soils the values of m are ranging from 0.5 to 1 [12]. ��� � ������ � �� ������� ������������� (2) ��� is the stress dependent stiffness modulus for unloading and reloading, ������ reference young’s modulus for unloading and reloading corresponding to the reference pressure ���� of 100kpa. � � � � � ��� ! �� "��#$%&���� �����������' � (3) � � is a tangent stiffness modulus that can be determined from an oedometer test, � � ��� is tangent stiffness at a vertical stress of reference pressure ����100=kpa, ( )* is ko value for normal consolidation. figure 2 presents the procedure for determination of ��� and ���. figure 3 illustrates the method of finding � � . fig. 2. procedure for evaluation of ��� and ��� from drained triaxial test fig. 3. method of finding the value of � � ��� from the oedometer test as mentioned above there is a lack of data regarding stiffness behavior of soils as compared to that of strength mainly due to the testing cost. in order to reduce this cost, the following relations regarding stiffness parameters are found to be valuable for computation of settlement [6, 10]: ������ = � � ��� and ������ = 3������ (4) in this paper, the above correlations have been utilized for computation of settlement of the dam by using hsm separately for four zones of the dam. the dam is 59 meter high with a designed maximum flood water level of 56.6 m. details regarding the rising of the dam and material properties are described in [13]. engineering, technology & applied science research vol. 9, no. 5, 2019, 4750-4754 4752 www.etasr.com bhutto et al.: post construction and long term settlement of an embankment dam computed with … iii. results and discussion a. comparison of dam settlement with respect to depth computed with mcm and hsm at first, settlement of the dam was computed by applying mcm to all zones. for sake of convenience this is referred to as condition 1. in the second case, hsm was applied separately to the four main zones (clay core, sandy gravel, random fill, sandy siltstone) and mcm was used for the remaining materials (condition 2). the settlements were determined along the central axis of the dam and were computed up to a depth of 120m with an interval of 20m as shown in figure 4. the settlement with respect to depth response of the dam when computed with mcm (condition 1) and hsm applied to clay core, sandy gravel, random fill (condition 2) for the end of construction (ec) and after the filling of reservoir (afr) are respectively given in figures 5 to 10. fig. 4. the settlement of the dam was computed on the central axis of the dam with respect to depth at 20m intervals fig. 5. comparison of settlement of the dam with respect to depth for ec computed with mcm and hsm applied to clay core only fig. 6. comparison of dam settlement with respect to depth computed for afr with mcm and hsm applied to clay core only fig. 7. comparison of settlement of the dam with respect to depth for ec computed with mcm and hsm applied to sandy gravel only fig. 8. comparison of dam settlement with respect to depth for afr computed with mcm and hsm applied to sandy gravel only fig. 9. comparison of settlement of the dam with respect to depth for ec computed with mcm and hsm applied to random fill only fig. 10. comparison of settlement of the dam with respect to depth for afr computed with mcm and hsm applied to random fill only engineering, technology & applied science research vol. 9, no. 5, 2019, 4750-4754 4753 www.etasr.com bhutto et al.: post construction and long term settlement of an embankment dam computed with … from the results it can be clearly observed that there is less variation in settlement with respect to depth when computed with mcm as compared to hsm computation for both ec and afr for the four material zones (clay core, sandy grave and random fill). figures 11 and 12 illustrate the dam settlement with respect to depth for ec and afr, for conditions 1 and 2. fig. 11. comparison of settlement of the dam with respect to depth for ec computed with mcm and hsm applied to sandy siltstone only fig. 12. comparison of settlement of the dam with respect to depth for afr computed with mcm and hsm applied to sandy siltstone only there is a clear variation in settlement both at the crest of the dam and at the depth of 120m, because in hsm, the soil’s moe increases with respect to depth, which is a realistic soil behavior. most of the dams exhibit settlement of about 1% of the total height of the dam [14]. the settlement of this dam computed with mcm and hsm for afr was found to be 2.9% and 1.35% of the dam height respectively. by utilizing the hsm parameters as mentioned in this study, the settlement of the dam is considered to be in agreement with the literature findings. from the above results, it is observed that sandy siltstone has more influence on settlement with respect to depth of the dam as compared to the other material zones (clay core, sandy gravel, random fill) when computed with mcm and hsm. therefore, the settlement response of sandy siltstone is further investigated in detail. for this purpose, the moe of sandy siltstone varied from 70000 to 125000kpa and settlement with respect to depth was calculated using both mcm and hsm. b. effect of sandy siltstone moe variation on the settlement with respect to depth using mcm and hsm the results of the comparison of the settlement of the dam at the crest and at the depth of 120m computed under condition 1 and 2 for ec and afr are presented in figures 13 and 14. the moe of sandy siltstone varied from 70000 to 125000kpa with increment of 10000kpa. the results indicate that the rate of increase of the settlement computed with mcm (compared with hsm) increased with the depth of the dam. at the surface of the dam, the rate of increase of the settlement calculated with mcm (when compared with hsm) slightly decreased with increase of moe. however, at the depth of 80m and beyond the rate of increase of settlement computed with mcm is almost the same irrespective of any change in the moe of sandy siltstone. fig. 13. increase of ec settlement with respect to depth calculated by mcm and compared to hsm (%) fig. 14. increase of afr settlement with respect to depth calculated by mcm and compared to hsm (%) c. mcm and hsm applied to sandy siltstone long-term settlement comparison long-term settlement of the dam was calculated even though the foundation is reported to be weak and fragile with open bedding planes, since it consists of sandy siltstone. the settlement of the dam was calculated for 50 years for both ec and afr conditions using mcm (condition 1) and hsm (condition 2). the results are shown in figures 15 and 16. the results suggest that long-term settlement of the dam is almost the same to the afr settlement, even though the magnitude of the settlement predicted with mcm is higher than that of hsm. however, both models predicted that long term settlement did not increase with time. the long-term settlements predicted with mcm for both ec and afr conditions was about 51% and 59% higher than the ones predicted with hsm. the engineering, technology & applied science research vol. 9, no. 5, 2019, 4750-4754 4754 www.etasr.com bhutto et al.: post construction and long term settlement of an embankment dam computed with … magnitude of the settlement is concentrated in clay core, sandy gravel, and random fill. the clay core is compacted during the construction process of the dam. however, clay is considered to be a compressible material, therefore the compression of the clay mostly occurred during construction and afr phases. therefore, further settlement of the clay did not occur during the long-term period of 50 years. fig. 15. comparison of long-term settlement with mcm and hsm applied to sandy siltstone when the moe is 125000kpa fig. 16. comparison of long term settlement with mcm and hsm applied to sandy siltstone when the moe is 70000kpa iv. conclusions settlement with respect to depth and long-term settlement of an embankment dam were computed with mcm and hsm. the unrealistic settlement response predicted by mcm is due to the constant value of stiffness at all depths which is against real soil behavior. the hsm shows a settlement range which is in agreement with the literature even there is a limited availability of stiffness parameters. it would be more advantageous to use hsm instead of mcm for foundation soils because the former takes into consideration stress dependent stiffness. references [1] v. gikas, m. sakellariou, “settlement analysis of the mornos earth dam”, (greece): evidence from numerical modeling and geodetic monitoring”, engineering structures, vol. 30, no. 11, pp. 3074-3081, 2008 [2] r. y. liang, b. o. nusier, a. h. malkawi, “a reliability based approach for evaluating the slope stability of embankment dams”, engineering geology, vol. 54, no. 3-4, pp. 271-285, 1999 [3] a. d. penman, “instrumentation monitoring and surveillance”, in: embankment dams, routledge, 2018 [4] r. m. roosta, a. alizadeh, ”simulation of collapse settlement in rock fill material due to saturation”, international journal of civil engineering, vol. 10, no. 2, pp. 93-99, 2012 [5] r. mahinroosta, a. alizadeh, b. gatmiri, “simulation of collapse settlement of first filling in a high rockfill dam”, engineering geology, vol. 187, pp. 32-44, 2015 [6] t. schanz, p. a. vermeer, p. g. bonnier, “the hardening soil model: formulation and verification”, in: beyond 2000 in computational geotechnics, pp. 281-296, crc press, 1999 [7] y. hejazi, d. dias, r. kastner, “impact of constitutive models on the numerical analysis of underground constructions”, acta geotechnica, vol. 3, no. 4, pp. 251-258, 2008 [8] r. b. brinkgreve, “selection of soil models and parameters for geotechnical engineering application”, geo-frontiers congress 2005, austin, usa, january 24-26, 2005 [9] r. f. obrzud, “on the use of the hardening soil small strain model in geotechnical practice”, numerics in geotechnics and structures, pp. 1532, elmepress international, 2010 [10] r. b. j. brinkgreve, s. kumarswamy, w. m. swolfs, plaxis reference manual, plaxis, 2017 [11] n. janbu, “soil compressibility as determined by oedometer and triaxial tests”, proceedings of the european conference on soil mechanics and foundation engineering (ecsmfe), vol. 1, pp. 19-25, 1963 [12] p. v. soos, “properties of soil and rock”, in: grundbau taschenbuch part 4, ernst & sohn, 1990 (in german) [13] a. h. bhutto, s. zardari, m. a. zardari, g. s. bhurgri, b. a. memon, r. bhanbhro, m. m. babar, “mohr-coulomb and hardening soil model comparison of the settlement of an embankment dam”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4654-4658, 2019 [14] g. hunter, r. fell, the deformation behaviour of embankment dams, the university of new south wales, 2003 [15] a. araei, “artificial neural networks for modeling drained monotonic behavior of rockfill materials”, international journal of geomechanics, vol. 14, no. 3, article id 04014005, 2013 [16] asce task committee on instrumentation and dam performance, guidelines for instrumentation and measurements for monitoring dam performance, asce, 2000 microsoft word 17-2871_s_etasr_v9_n4_pp4405-4410 engineering, technology & applied science research vol. 9, no. 4, 2019, 4405-4410 4405 www.etasr.com jomaa et al.: greenhouse modeling, validation and climate control based on fuzzy logic greenhouse modeling, validation and climate control based on fuzzy logic manel jomaa ur-laper, department of physics, faculty of sciences of tunis, university of tunis el manar, tunis, tunisia manel.jomaa@enit.utm.tn fernando tadeo departamento de ingenieria de sistemas y automatica, institute of sustainable processes, university of valladolid, valladolid, spain fernando.tadeo@uva.es mehdi abbes laboratoire analyse et commande des systemes, national engineering school of tunis, tunis, tunisia mehdi.abbes@enit.rnu.tn abdelkader mami ur-laper, department of physics, faculty of sciences of tunis, university of tunis el manar, tunis, tunisia abdelkader.mami@fst.utm.tn abstract—this paper deals with the modeling and control of the air temperature and humidity in greenhouses. a physical model of the greenhouse used in the simulink/matlab environment is elaborated to simulate both temperature and indoor humidity. as a solution to the non-linearity and complexity of the greenhouse system, a fuzzy logic method is developed to control the actuators that are installed inside the greenhouse for heating, ventilation, humidification and cooling to obtain a suitable microclimate. keywords-greenhouse; fuzzy logic controller; air temperature; humidity; simulink; matlab i. introduction agricultural production is a central economy field in many countries. tunisia is considered one of the best worldwide agricultural product exporters. nowadays, greenhouse is the main solution to climate change effects. its main purpose is to effectively control the environment and protect the plants by creating a favorable climate. among the conditions in a greenhouse, this paper focuses on indoor temperature and humidity. an optimal vegetation yield can be produced from the precise configuration of these conditions [1]. numerous methods of greenhouse control have been studied and developed. the regulations inside the greenhouse consist of evaporation, fogging and ventilation systems. this paper presents a control system useful for adaptation despite the nonlinearity and complexity of greenhouse dynamics [2, 3]. various types of climate control greenhouse systems have been previously mentioned. in [4, 5], a feedback controller approach has been discussed. the type of climate control mentioned in [6] has been developed to the optimal control method. neural networks were studied in [7-9]. authors in [10, 11] offer a regulation of temperature and humidity inside the greenhouse with a fuzzy logic regulator. in [12], the takagi-sugeno method of the air temperature control is described. in [13-15], model predictive control (mpc) was used. the proposed work starts with the simulation of the dynamic greenhouse model followed by its validation and its control via fuzzy logic. ii. greenhouse model the model of the proposed input-output system can be seen in [16]. the considered variables are: intt is the interior temperature and inth is the humidity variable. the adjustment of these variables will be obtained by αmv which is the ventilation system, wmv which is the heating system, and fogmv which is the fogging system. the measurable disturbances consist of wind speed, solar radiation, and outside humidity and temperature [16]. a. proposed model the first step of the proposed study is the development of the dynamic model of the greenhouse using the simulink/matlab. many physical models like the energy balance and mass balance have been suggested to describe the dynamics of the greenhouse climate [17, 18]. b. greenhouse model with simulink a derived simple model is required to design a control system that analyzes and guesses the correct variables of cooling, heating and ventilation systems. the model consists of conventional dynamic equations that correspond to the indoor air temperature it , soil temperature mt , and indoor humidity ix [17]. the differential equations are given by the heat and humidity balance. 1) heat balance the dynamic model of the air temperature and the thermal mass temperature inside the greenhouse are described by (1) corresponding author: manel jomaa engineering, technology & applied science research vol. 9, no. 4, 2019, 4405-4410 4406 www.etasr.com jomaa et al.: greenhouse modeling, validation and climate control based on fuzzy logic and (9) [17]: ( ) dti v c q q q c q q q wi p s cc m sat e n v dt ρ = − + − + − + (1) where: sq is the solar energy supplied to the air volume determined by (2): 0siasq τ= (2) ccq is the energy exchange by the conduction and the convection phenomena that are explained using (3): ( )otitcaiaccq −= (3) mq is the energy exchange between the thermal mass and the inside air determined by (4): ( )itmtmhiamq −= (4) eq is the energy loss due to the crop evapotranspiration: eq eλ= (5) nq is the energy loss by the nebulization: nq fogλ= (6) vq is the energy exchange due to the window ventilation: ( )v p i oq c g t tρ= − (7) w is the energy provided from the heating system: max 100 wmv w w= (8) the thermal mass temperature inside the greenhouse is described by (9): m i m sm m f dt a c q q q dt = − − (9) knowing that: sm m sq qα= (10) equation (10) is the energy stored by the thermal mass during the day and (11) is the energy loss through the ground: m ref f i a ref t t q a k z  − =       (11) 2) humidity balance the model of the relative humidity inside the greenhouse is determined by (12) [17]: ( )ii v sat dx v f c e fog dt ρ = + + (12) where: vf is the water rate in the air renewal flow: ( )v o if g x xρ= − (13) e is the crop evapotranspiration identified by (14): ( )2 1 i n p ia r l c d gwb e gwb gws ρ γ λ ∆ + =     ∆ + +        (14) fog is the water rate of the fogging system: max 100 fogmv fog fog   =     (15) the greenhouse that is used for the validation is situated at the c.r.t.en borj cedria park of science and technology in tunisia, in a semi-urban environment. the greenhouse axes are in the east-west direction. the dimensions are 12.5m length, 8m width and 3m height. the acquisition of both external weather conditions (wind speed, temperature, radiation, and humidity) and internal climate greenhouse data are connected to a campbell 21x data logger. the measurements of external and internal relative humidity are performed via hmp35c sensors with 3% precision and a range between 0% and 100%. the external and internal temperatures are measured in a range from -35°c to +50°c. the solar radiation is measured by a pyranometer with 5% precision [3]. figure 1 shows the solar radiation measured in the 29th, 30th and 31st of march, 2001 whereas figure 2 presents the wind speed, measured at the same dates. fig. 1. reached cover solar radiations, march, 29–31, 2001 fig. 2. wind speed march, 29–31, 2001 figures 3-5 present the simulation results, for the same time period, of internal air temperature (k), internal soil temperature (k) and relative humidity (%). engineering, technology & applied science research vol. 9, no. 4, 2019, 4405-4410 4407 www.etasr.com jomaa et al.: greenhouse modeling, validation and climate control based on fuzzy logic fig. 3. simulation results of the air temperature inside the greenhouse fig. 4. simulation results of the soil temperature inside the greenhouse fig. 5. simulation results of the relative humidity inside the greenhouse the simulated results obtained via simulink are compared with the detailed model discussed and described in [3]. the same parameters of the greenhouse are used in both cases. fig. 6. measured and simulated internal air temperatures fig. 7. measured and simulated results of internal air humidity figure 6 presents the simulated and measured indoor air temperature. figure 7 shows the simulated and measured results of the indoor relative humidity. it can be seen that a good agreement is obtained between the simulated and the measured results of both temperature and relative humidity. in order to activate the actuators, power should be supplied. in this case, a logic control is selected and its pseudo-code is briefly described in figure 8. figures 9-11 present the heating, ventilation and humidifying rates that are delivered by the control algorithm in figure 8. fig. 8. algorithm block diagram fig. 9. heating rate fig. 10. ventilation rate fig. 11. humidifying rate engineering, technology & applied science research vol. 9, no. 4, 2019, 4405-4410 4408 www.etasr.com jomaa et al.: greenhouse modeling, validation and climate control based on fuzzy logic iii. fuzzy logic controller fuzzy logic has been considered an attractive solution for various engineering problems due to features such as its robustness, simplicity and flexibility. three stages must be satisfied to design this type of control system: fuzzification, inference rules and defuzzification [20]. the main aim of this system is to control the climate inside the greenhouse and boost its effectiveness. a. the structure of the control system the input variables of temperature and humidity in the fuzzy logic controller are represented by t∆ with outside temperature and h∆ with outside humidity knowing that: ( ), , , ,t t t nb nm z pm pbdesired indoor∆ = − ∈ (16) where outside temperature ∈(pm, z, pg). ( ), , , ,h h h nb nm z pm pbdesired indoor∆ = − ∈ (17) and outside humidity ∈(pm, z, gp) where         bigpositivepb mediumpositivepm zeroz mediumnegativenm bignegativenb _: _: : _: _:      bigpositivepb zeroz mediumpositivepm _: : _: the methodology described in figure 8 was used to develop this command. during the control we took into account the external environmental conditions (outside temperature and outside humidity). the output variables are the heating rate (heating), the ventilation rate (ventilation) and the humidifying rate (humidifying). (heating, ventilation) ∈ (zero, medium, high) (humidifying) ∈ (zero, medium, high) the fuzzy inference method that is used in this work is the mamdani method and the defuzzification technique is based on the center of gravity method. b. decoupling fuzzy logic controller figure 12 presents the input variables of the temperature and outside temperature and figure 13 presents the input variables of the humidity and outside humidity. figure 15 presents the output variables of heating, ventilation and humidifying rates. iv. simulation results the main objective of control is to smoothly regulate air temperature and humidity inside the greenhouse to their desired values ( desiredt , desiredh ). we controlled the actuators by lowering their rates in order to reduce energy. the value of the desired temperature is 15°c at night and 28°c at day. the desired relative humidity is 70%. the tracking performance of temperature and humidity inside the greenhouse are illustrated in figures 15 and 16 during simulation time of one day. fig. 12. membership functions of temperature error (∆t) and outside temperature fig. 13. membership functions of humidity error (∆h) and outside humidity fig. 14. membership functions of heating, ventilation and humidifying rates engineering, technology & applied science research vol. 9, no. 4, 2019, 4405-4410 4409 www.etasr.com jomaa et al.: greenhouse modeling, validation and climate control based on fuzzy logic fig. 15. simulation results of the greenhouse temperature with fuzzy logic controller fig. 16. simulation results of the greenhouse humidity with fuzzy logic controller the provided heating and ventilation rates are displayed in figures 17 and figure 18. a regulator fuzzy logic controller is applied to control the humidifying system in order to regulate the relative humidity at its set point value, as presented in figure 19. fig. 17. heating rate fig. 18. ventilation rate fig. 19. humidifying rate v. conclusion in this article, a greenhouse model has been proposed and validated. a comparison between the simulated and measured results of the internal air temperature and the relative humidity has been made using the parameters proposed in [3]. a good agreement has been obtained between the calculated and measured data, which indicates the efficiency of the proposed model. based on this model, a fuzzy logic controller has been developed to satisfy the demands in terms of temperature and humidity, using the measured data. the results showed a stable behavior of both temperature and humidity with a low rate of heating, ventilation and humidification. this behavior has been achieved without using the dehumidifier system in order to reduce energy consumption. in the future, we will focus on developing an improved control model for the greenhouse climate and testing the stability and robustness of the fuzzy logic controller with more variables representing the complete state of the greenhouse. in addition, we will design a power system based on renewable energy sources in order to reduce the use of grid utilities. nomenclature a [m²] windows area [50m²] a constant for renewal volumetric flow ac loss coefficient of conduction and convection ai [m²] greenhouse surface area [100m²] cm thermal mass heat capacity cp [j kg -1 °c -1 ] air heat capacity [1003j·kg -1 °c -1 ] csat air saturation coefficient di [kpa] air water vapor deficit e [kgh2o s -1 ] crop evapotranspiration fog[kgh2o s -1 ] water rate of fogging system fv [kgh2o s -1 ] water rate in the air renewal flow g [m 3 s -1 ] renewal air flow gwb [m s -1 ] boundary-layer conductance gws [m s -1 ] stomatal conductance hm [w m -1 k -1 ] conductivity coefficient between air and thermal mass hi [%] inside relative humidity ho [%] outside relative humidity l leaves area index mvfog [%] fogging system manipulated variable mvw [%] heating system manipulated variable mvα [%] windows opening manipulated variable psat [kpa] saturation pressure p [kpa] atmospheric pressure [98.1kpa] qcc [w] energy exchange by conduction and convection phenomena qe [w] energy loss due to crop evapotranspiration qf [w] energy loss through ground qm [w] energy exchange with thermal mass qn [w] energy loss by nebulization qs [w] solar energy supplied to air volume qsm [w] energy stored by thermal mass during the day qv [w] energy exchange due to window ventilation rn [w m -2 ] solar radiation absorbed by the crop so [w m -2 ] solar radiation ti [°c] inside temperature tm [°c] thermal mass temperature to [°c] outside temperature tref [°c] ground temperature at reference depth vi [m 3 ] greenhouse volume [300m 3 ] v [ms -1 ] wind speed w [w] energy from the heating system wmax [w] maximum power of the heating system xi [kgh2o kgair -1 ] inside absolute humidity engineering, technology & applied science research vol. 9, no. 4, 2019, 4405-4410 4410 www.etasr.com jomaa et al.: greenhouse modeling, validation and climate control based on fuzzy logic xo [kgh2o kgair -1 ] outside absolute humidity xsat [kgh2o kgair -1 ] absolute saturation humidity zref [m] reference depth α [°] opening window angle ∆ [kpa °c -1 ] slope of water vapor saturation γ [kpa °c -1 ] psychometric constant λ [j kg -1 ] latent heat of vaporization ρ [kgair m -3 ] air density [1.25 kgair m -3 ] τ transmission coefficient of the greenhouse references [1] l. m. mortensen, “growth responses of some greenhouse plants to environment: iii. design and function of a growth chamber prototype”, scientia horticulturae, vol. 16, no. 1, pp. 57-63, 1982 [2] l. meihui, d. shangfeng, c. lijun, h. yaofeng, “greenhouse multivariables control by using feedback linearization decoupling method”, chinese automation congress, jinan, china, octomber 20-22, 2017 [3] m. abbes, a. farhat, a. mami, g. d. tanguy, “pseudo bond graph model of coupled heat and mass transfers in a plastic tunnel greenhouse”, simulation modelling practice and theory, vol. 18, no. 9, pp. 1327-1341, 2010 [4] g. d. pasgianos, k. g. arvanitis, p. polycarpou, n. sigrimis, “a nonlinear feedback technique for greenhouse environmental control”, computer and electronics agriculture, vol. 40, no. 1-3, pp. 153-177, 2003 [5] c. j. taylor, p. c. young, a. chotai, a. r. mcleod, a. r. glasock, “modelling and proportional-integral-plus control design for free air carbon dioxide enrichment systems”, journal of agricultural engineering research, vol. 75, no. 4, pp. 365-374, 2000 [6] e. j. v. henten, j. bontsema, “time-scale decomposition of an optimal control problem in greenhouse climate management”, control engineering practice, vol. 17, no. 1, pp. 88-96, 2009 [7] x. luan, p. shi, f. liu, “robust adaptive control for greenhouse climate using neural networks”, international journal of robust and nonlinear control, vol. 21, no. 7, pp. 815–826, 2011 [8] r. linker, i. seginer, p. o. gutman, “optimal co2 control in a greenhouse modeled with neural networks”, computers and electronics in agriculture, vol. 19, no. 3, pp. 289–310, 1998 [9] p. m. ferreira, e. a. faria, a. e. ruano, “neural network models in greenhouse air temperature prediction”, neurocomputing, vol. 43, no. 1-4, pp. 51-75, 2002 [10] m. azaza, k. echaieb, f. tadeo, e. fabrizio, a. iqbal, a. mami, “fuzzy decoupling control of greenhouse climate”, arabian journal for science and engineering, vol. 40, no. 9, pp. 2805-2812, 2015 [11] p. salgado, j. b. cunha, “greenhouse climate hierarchical fuzzy modelling”, control engineering practice, vol. 13, no. 5, pp. 613–628, 2005 [12] m. nachidi, f. rodriguez, f. tadeo, j. l. guzman, “takagi-sugeno control of nocturnal temperature in greenhouses using air heating”, isa transactions, vol. 50, no. 2, pp. 315-320, 2011 [13] m. y. e. ghoumari, h. j. tantau, j. serrano, “non-linear constrained mpc: real-time implementation of greenhouse air temperature control”, computers and electronics in agriculture, vol. 49, no. 3, pp. 345–356, 2005 [14] j. p. coelho, p. b. de moura oliveira, j. b. cunha, “greenhouse air temperature predictive control using the particle swarm optimisation algorithm”, computers and electronics in agriculture, vol. 49, no. 3, pp. 330–344, 2005 [15] q. zou, j. ji, s. zhang, m. shi, y. luo, “model predictive control based on particle swarm optimization of greenhouse climate for saving energy consumption”, world automation congress, kobe, japan, september 19-23, 2010 [16] m. jomaa, f. tadeo, a. mami, “modelling and control of greenhouses powered by a renewable energy system”, 18th international conference on sciences and techniques of automatic control and computer engineering, monastir, tunisia, december 21-23, 2017 [17] x. blasco, m. martinez, j. m. herrero, c. ramos, j. sanchis, “modelbased predictive control of greenhouse climate for reducing energy and water consumption”, computers and electronics in agriculture, vol. 55, no. 1, pp. 49-70, 2007 [18] k. a. joudi, a. a. farhan, “a dynamic model and an experimental study for the internal air soil temperatures in an innovative greenhouse”, energy conversion and management, vol. 91, pp. 76-82, 2015 [19] r. c. miranda, e. v. ramos, r. r. peniche-vera, g. herrera-ruiz, “fuzzy greenhouse climate control system based on a field programmable gate array”, biosystems engineering, vol. 94, no. 2, pp. 165-177, 2006 microsoft word 98-12-2707_s_etasr_v9_n5_pp4859-4862 engineering, technology & applied science research vol. 9, no. 5, 2019, 4859-4862 4859 www.etasr.com awokola et al.: perspectives of threat modeling of a secure cloud picture archiving and … perspectives perspectives of threat modeling of a secure cloud picture archiving and communication system jinmisayo a. awokola department of computer science and engineering, ladoke akintola university of technology, ogbomoso, nigeria rhgonline@gmail.com ozichi n. emuoyibofarhe department of computer science, bowen university, iwo, nigeria eozichi@yahoo.com adebayo omotosho landmark university, omu-aran, nigeria bayotosho@gmail.com justice o. emuoyibofarhe department of computer science and engineering, ladoke akintola university of technology, ogbomoso, nigeria eojustice@gmail.com jacob o. mebawondu department of computer science, the federal polytechnic, nasarawa, nigeria mebawondu1010@gmail.com abstract—the picture archiving and communication system (pacs) used in electronic health, is computationally enhanced by the migration into the cloud, which reduces the cost of storage space and equipment. however, cloud-pacs technology is susceptible to threats and vulnerabilities. this paper implements a threat modeling approach on a cloud-pacs framework, using microsoft threat modelling tools. security requirements and mitigation strategies were formulated for the implementation of the framework, in order to improve cloud pacs security. keywords-picture archiving and communication (pac); ehealth; modeling; threat; cloud i. introduction picture archiving and communication system (pacs) has been deployed in health informatics due to the need to retrieve, capture and archive images, from different image modalities [1]. however, the rapid increase in volume and required speed of medical images has necessitated the need for acquiring highperformance, grid-based hardware and software, increasing pacs’ management cost. cloud computing technology has been proposed to provide a cost-effective approach for storage [3]. however, this resulted in several security vulnerabilities and loopholes. this, therefore, motivated the need for studies focusing on the development and implementation of different cloud-based security frameworks, in order to bridge the gap [4]. threat modeling is a quintessential software engineering methodology for security-compromisable systems [5]. it integrates goal and risk modeling methodologies, for any technology of interest [6]. this makes it possible to specify threat requirements, prior to the development of a security framework. however, the majority of existing studies did not focus on this aspect during the security framework development of cloud pacs. therefore, there is a need to adapt threat modeling techniques, in order to ensure a secured cloud pacs. threat modeling parameters are based on different cyber-security indices. in the threat framework presented in [7], the essential parameters for simulation are strength, threat capability, contact frequency, and vulnerability. the strength of a hypothetical security-compromisable system describes the level at which it can resist a malicious attack, whereas the threat capability denotes the level of the hacking that can deplete the strength of the system. contact frequency describes the rate at which the hacker interfaces with the system, while vulnerability denotes the rate of successful attacks initiated by an alleged intruder. threat modeling has been applied in sensitive utility areas, such as the smart electricity metering system (sems), because of some inherent security issues [8]. sems is the current trend because it provides a cost-effective approach to billing and utilization of energy. however, different threat modeling methodologies, such as stride and dread, were employed for the essential threat requirement elicitation and identification. stride acronym represents spoofing, tampering, repudiation, information disclosure, denial of service and elevation of privilege, whereas dread denotes damage, reproducibility, exploitability, affected users and discoverability [9]. based on the identified threats, a security software imitating sems was developed, as a proof of concept. consequently, adoption of sems will be higher if security is guaranteed optimally. additionally, it has been shown that threat modeling is very applicable to mobile and desktop e-health systems, due to the confidentiality requirements [10]. however, there is a lack of threat modeling studies on cloud pacs, although similar confidentiality requirements also exist. corresponding author: adebayo omotosho engineering, technology & applied science research vol. 9, no. 5, 2019, 4859-4862 4860 www.etasr.com awokola et al.: perspectives of threat modeling of a secure cloud picture archiving and … ii. methodology a cloud-based pacs framework was designed, with features that allow images to be captured and stored in cloud storage platforms. the proposed framework is fully described in [11]. the framework, embedding security features, takes care of medical images and their transmission through internet, until they are finally rested in the cloud, allowing access to every authorized user. microsoft threat modelling tool was used in order to analyze the cloud-pacs framework and identify points of vulnerabilities that could compromise the system, in terms of entry and exit points. all possible external dependencies, such as trust levels as well as entry and exit points to the system were identified. possible threats were identified and analyzed using stride. also, threats were ranked using the dread model classifier, by scaling its individual components from 1 to 10, which were summed up and divided by 5 in order to obtain a final threat value. threat values were ranked as low (1–3), medium (4–6) and high (7– 10). threats ranked as high were given utmost attention. at the end, possible mitigation strategies were proposed towards the final implementation, so that the resulting system would be able to achieve an optimum security level. fig. 1. dataflow diagram for the cloud pacs framework table i. system's threat analysis based on the stride approach system’s threats identification id threat type susceptible asset(s) threats 1. spoofing administrator/technical lead/users' login details, technical lead's credentials, personal, meta and pixel data 1. attacker aims to log into the pacs or server-based components with valid user’s privileges 2. attacker aims to retrieve meta and pixel data from the cloud storage provider. 2. tampering the pac system users, administrator and technical lead credentials 3. attacker aims to tamper configuration files rendering the pac system unavailable. 4. attacker aims to alter pacs’ data in transit. 5. attacker aims to modify user credentials so as to make user’s authentication impossible. 3 repudiation meta and pixel data 6. attacker is a valid user who aims to perform unauthorized actions unnoticed. 7. attacker aims to gain access to the pacs and/or its database so as to make illicit changes. 4. information disclosure administrator/technical lead/users' login details, technical lead's credentials, personal, meta and pixel data 8. attacker aims to intercept user’s credentials and personal details, transmitted through internet. 9. attacker aims to intercept meta and pixel data as they travel through the cloud storage provider's infrastructure, the web server and the pacs. 5. denial of service the pac system the internet server-based database. the internet server-based broker. 10. attacker aims to tamper system’s files in order to reduce functionality. 11. attacker aims to tamper system’s database files in order to reduce functionality of the pac application, such as authentication. this can also lead to a failed interaction with the broker. 6. elevation of privileges the pac system 12. attacker aims to gain unauthorized privileges in order to compromise the pac system. attacker could be a valid user. engineering, technology & applied science research vol. 9, no. 5, 2019, 4859-4862 4861 www.etasr.com awokola et al.: perspectives of threat modeling of a secure cloud picture archiving and … table ii. system's threat ranking based on the dread approach identified threats d r e a d total threat rating attacker aims to log into the pacs or server-based components with valid users’ privileges. 6 6 4 9 9 6.8 medium attacker aims to retrieve meta and pixel data from the cloud storage provider. 10 3 9 10 9 8.2 high attacker aims to tamper configuration files making the system unavailable. 2 4 5 1 6 3.6 low attacker attempts to alter pacs’ data in transit. 7 2 9 3 4 5 medium attacker aims to modify user’s credentials so as to make user’s authentication impossible. 7 4 8 9 3 6.2 medium attacker is a valid user who aims to perform unauthorized actions unnoticed. 6 4 9 4 6 5.8 medium attacker aims to gain access to the pacs and/or its database so as to make illicit changes. 8 5 8 7 7 7 high attacker aims to intercept user’s credentials and personal details transmitted through internet. 6 3 8 6 7 6 medium attacker aims to intercept meta and pixel data as they travel through cloud storage provider's infrastructure, the web server and the pacs. 6 3 8 6 7 6 medium attacker aims to tamper system’s files in order to reduce pacs’ functionality, such as authentication. this can also lead to a failed interaction with the broker. 6 4 9 6 7 6.4 medium attacker aims to gain unauthorized privileges in order to compromise pacs. the attacker could be a valid user. 10 7 6 6 9 7.6 high table iii. system's threat mitigation strategies table identified threats threat mitigation strategies attacker aims to log into the secured pacs system or server-based components with valid user’s privileges. all system’s users are authenticated with internet database server for the validity of their credentials. an attacker aims to retrieve meta and pixel data from the cloud storage provider. 1. meta and pixel data are distributed, so they are not useful if found in parts. 2. retrieved metadata are obfuscated and can only be deobfuscated by valid users. attacker aims to tamper configuration files rendering the pac system unavailable directory of the configuration files is accessible and modifiable only by the system’s administrator. attacker attempts aims to alter pacs’ data in transit. communication is made through encrypted tlp/ssl internet protocol which is relatively tamper-resistant. attacker aims to modify user’s credentials, so as to make future authentication impossible. user’s authentication and authorization are checked before any changes can be made. attacker is a valid user who aims to perform unauthorized actions unnoticed. every action inside the system is logged. attacker aims to gain access to the pacs and/or its database so as to make illicit changes. user’s authentication and authorization is checked before any change occures. attacker aims to intercept users’s credentials and personal details transmitted through internet. communication is made through the encrypted tlp/ssl internet protocol which is relatively tamper-resistant. attacker aims to intercept meta and pixel data as they travel through the cloud storage provider's infrastructure, the web server and the pacs. communication is made through the encrypted tlp/ssl internet protocol which is relatively tamper-resistant. attacker aims to tamper system’s files in order to reduce pacs’ functionality, such as authentication. this can also lead to a failed interaction with the broker. 1. database is located in a firewall secured internet server. 2. parameters inserted into forms are validated before processing, so as to avoid vulnerabilities like sql injection. attacker aims to gain unauthorized privileges in order to compromise pacs. the attacker could be a valid user. authorization check before making privileges accessible to users. iii. results and discussion table i shows the identified threats for a typical cloudpacs system prototype using the stride approach. assets at risk such as pacs, database hosted on an internet server, broker, system user's details, meta, pixel, and personal data, in a cloud-pacs system, are the major concerns of interest during the threat modeling pipeline. table ii shows the threat ranking, performed by the dread classifier approach. threats identified by stride methodology, were inputs into the dread threat classifier. risks ranked as “high” were given the highest attention during the implementation of the cloudpacs security framework, followed by the “medium” and “low” respectively. table iii shows different threat mitigation strategies to deploy during the implementation of the proposed cloud-pacs framework. the proposed framework is designed based on a security manager middleware, which comprises of components such as the obfuscator, cloud service broker, firewall, gateway, account and preference manager. figure 1 shows the detailed data flow diagram of the proposed framework, showing interaction details within the system, based on the threat modeling approach. iv. conclusion security is an essential factor in modern computer systems used in banking, health, schools and so on. it ensures that only authenticated and authorized individuals can use a system and term generally encompasses authentication, confidentiality, and integrity [12-14]. cloud-based systems can easily be compromised by malicious insiders or users, if the system cannot maintain continuously a certain level of integrity. this work used a threat modelling approach to identify possible threats to a cloud pacs, as well as elicit threat mitigation strategies for identified and classified threat rankings using stride and dread approaches. results from this threat modeling study will improve cloud-pacs’ usability and security, and ultimately enhancing its adoption. engineering, technology & applied science research vol. 9, no. 5, 2019, 4859-4862 4862 www.etasr.com awokola et al.: perspectives of threat modeling of a secure cloud picture archiving and … references [1] k. a. kurlakose, infrastructure for secure medical image sharing between distributed pacs and di-r systems, msc thesis, university of ontario, 2013 [2] r. k. grace, r. manimegalai, s. s. kumar, “medical image retrieval system in grid using hadoop framework”, international conference on computational science and computational intelligence, las vegas, usa, march 9-12, 2014 [3] c. stergiou, k. e. psannis, b. g. kim, b. gupta, “secure integration of iot and cloud computing”, future generation computer systems, vol. 78, no. 3, pp. 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private keys in electronic health records using session-based hierarchical key encryption”, journal of applied security research, vol. 12, no. 4, pp. 463-477, 2017 engineering, technology & applied science research vol. 8, no. 4, 2018, 3157-3161 3157 www.etasr.com ramzan et al.: an analysis of issues for adoption of cloud computing in telecom industries an analysis of issues for adoption of cloud computing in telecom industries case study of pakistan muhammad ramzan department of computer science & it university of sargodha, sargodha, pakistan school of science and engineering university of management and technology, lahore, pakistan mramzansf@gmail.com muhammad shaoib farooq school of systems and technology university of management and technology, lahore, pakistan shoaib.farooq@umt.edu.pk ammara zamir department of computer science university of wah punjab, pakistan ammara.zameer@uow.edu.pk waseem akhtar department of computer science & it the university of lahore lahore, pakistan wassimalix@gmail.com mahwish ilyas department of computer science & it university of sargodha sargodha, pakistan mahwishilyas@gmail.com hikmat ullah khan department of computer science comsats institute of information technology, wah cantt, pakistan hikmat.ullah@ciitwah.edu.pk abstract—in the modern era companies seek the use of modern technologies in order to upgrade their infrastructure and enhance their business growth. the use of business intelligence, data science and cloud computing (cc) has become an integral part of business. different factors play important role in the adoption of cloud services. an organization willing to adopt cloud services should consider them. this paper explores the factors and addresses the issues in implementing and deploying cc in telecom companies. in addition, this study also shares the benefits of utilizing cc which is a novel technical pattern which can change the use of different associations of information technology as a service. cc concentrates on the idea of definition, security problems, service models and infrastructures of its development. the important point is to analyze how this paradigm should be adopted in telecom industries and its results. this research study presents a comparative analysis of adaptation of cc by various telecom industries. the results identify certain limitations which also play their role for adaptation of cc in telecom companies. keywords-cloud computing; telecom industry; iaas; saas; benefits of cloud computing i. introduction the continuous increase in the data volume captured by social media and multimedia has brought forth an intense flow of data in structured and unstructured format. this data production is referred to as big data. big data is seeking attention from government, academic institutions and industry. the progress in data storage gave rise to data mining technologies including classification methods [1, 2], social web analysis [3-6], sentiment analysis [7, 8], scientometrics [9, 10] and cloud computing (cc). cc is the big shift in technology and provides an effective platform for big data computation. cc is a paradigm of information technology that allows clients and companies to get the required quantity of computing resources. cc has many advantages that attract individuals and enterprises to store and process their data on cloud platforms. these advantages are virtualization, scalability, parallel processing and security. cc reduces the cost of automation and infrastructure [11]. small and large companies are moving towards cc due to its efficacy, automatic software update, capital-expenditure fee, document control, security and competitiveness. cc provides large data storage and computing services through huge data centers. cc is among the top 5 influential technologies on a global basis [12]. sixty percent of small and large business purchases are based on cloud services, and 30% of businesses purchased more than five cloud services [13]. cc provides service-based low cost it solutions. companies can globalize their operations. cc services provide scalability and elasticity which increase business flexibility [14]. cc has different limitations along with its advantages, especially related to security issues [15] such as data leakage, and unauthorized access. companies are interested in shifting their business on cloud. security risks, privacy threats, national, and internal regulations are preventing organizations from adopting cc and implement it to avail new opportunities. organizations need to take into account all factors which are acting as a barrier for cc adoption. this paper focuses on studying cc in telecom industry. two things are addressed in this paper: the study of the level of knowledge, which identifies the issues of cc and its performance and to show the results, which come from cc utilization in different companies. with help from this study it professionals and researchers can engineering, technology & applied science research vol. 8, no. 4, 2018, 3157-3161 3158 www.etasr.com ramzan et al.: an analysis of issues for adoption of cloud computing in telecom industries identify the barriers in adopting cc in telecom industry. the study has been carried out in pakistan telecom industry. ii. related work in this section cc benefits, challenges, risks and limitations in their adoption in the it field are discussed. national institute of standards and technology (nist), defined cc as a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.cloud computing is developed through hardware, virtualization, distributed computing and service delivery over the internet. using cc, business can utilize computing services on low-cost [16]. transferring business towards cloud reduces the cost of it resources [17]. cc eliminates traditional boundaries in business. cc provides services in three categories: infrastructure as a service (iaas), platform as a service (paas) and software as a service (saas). these models are used to match the computing demand, deploy and integrate applications, provide user access to applications using a client (web browser) respectively. different cc models exist for deployment. the public cloud is provided for all industries. private cloud is used by a particular organization. hybrid cloud uses the services of both public and private cloud [18, 19]. still, the concept of cc is not well known and misunderstood [20] while cc is not well established for deployment [21, 22]. nowadays emphasis is given on the advancement of knowledge related to it services [23]. there is a need to enhance the knowledge of it services including cc services [24]. cc services across different industries need to be explored in future. this involves the issues related to technical and organizational issues on adoption of cc services [24]. a business that needs to adopt cc should consider its risks, opportunities, and challenges [17, 25]. business challenges need to make a strategy to decide how to use different transformed services [26]. it managers must have comprehensive knowledge of organizational structure, interdependencies, processes and habits to make decisions about the choices of organizational structures [27]. iii. research methodology this section identifies and discusses the issues in the selection of cc and its benefits in telecom sector. in this study, quantitative and qualitative techniques are applied. the main purpose of the quantitative approach is to improve the knowledge about different types of cc applications in the field of telecom and also to improve the quantitative approach in different phases. in 2011 different telecom industry managers were requested, to participate in meetings regarding the improvement of different quantitative phases. 17 people responded in two meetings and two main ideas were presented: research and concepts of cc and their different applications in the telecom field. on these meetings, different applications of cc in the telecom field were identified and are still concerning different telecom companies:  how to measure the security of different companies in telecom industry.  how to measure the different result in cc environments.  how to improve the quantitative phase. in quantitative phase enough data were collected and analyzed regarding different cc applications and different tests were applied. on the basis of the test results, various issues were identified. fifteen questions about these issues emerged which belong to three categories: the first group of questions relates to the employees of the company, the total sales, and the years the company is active. the second group is about the company’s knowledge about cc in telecom field. the third group is related to all barriers that were faced. surveys were conducted in all telecom industries by using random sampling in october 2011 to december 2011. in these surveys the decision makers targeted the it managers. interviews were also conducted in companies with no it department. the data set obtained from the responses was composed of 83% it managers, 9.6% managing directors excluding the it managers, and 7.4% owners. to get better responses the sample was divided into two different categories: the 1st category includes the available it managers and the 2nd category includes the unavailable it managers. the mean of the factor scores of these two categories is compared by using the anova. the result obtained after using the anova showed no main difference. it was concluded that in any survey the respondents’ position did not matter. after getting 94 responses, the main features of both phases, quantitative and qualitative, were identified and are shown in table i. table i. features used in qualitative and quantitative phase by using spss the collected data were statistically processed and two aims were addressed. the first one was the degree of information on cc and the second was the result received from the use of cc. for computing the group differences, statistic methods were used. anova test is one approach which is used for the appropriateness of the test, and for the variance of the group. by using anova, assumptions of parameters were also checked. in the same type of samples the statistical evaluation is obtained by using the anova test, for industrial telecom with and without cc. for different dimensions dependent and independent variables were found. by using the dependent variables the consequences of the cc staff interval year/month rate n avg. 0-9 >18 16.5 35 10-50 >60 59 50-249 >19 18 sum 100% 94.5 sale periodic sale (mill. euro) %age rate n avg. 0-0.5 more than 12 11 1.8 mll 0.5-1 50% 48 more than 1 39% 37.5 sum 100% 94.5 years interval % rate n avg. 0-9 14.9% 14 24 10-20 51.1% 47.5 more than 20 34% 32 engineering, technology & applied science research vol. 8, no. 4, 2018, 3157-3161 3159 www.etasr.com ramzan et al.: an analysis of issues for adoption of cloud computing in telecom industries on telecom were identified. aforementioned literature shows the benefits of the utilization of cc, but there is unavailability of quantitative analyzed results. the results obtained by the implementation of the cc, are not to be used as financial and economic variables because there are some issues which affect the results that may or may not be related to cc. in the review of the literature the following points are noted:  the effort to reduce the cost of software and hardware.  the effort to access the improved it resources.  the concentration on the main business point of view. in different group meetings it was shown that the main barrier of adoption of cc is related to security. this part consists of how cloud computing improved security in different telecom industries. table ii. it cost reduction features range of values f1 costs of hardware have been reduced in the previous two years f2 costs of software have been reduced in the previous two years f3 costs of it people have been reduced in the previous two years alpha value : 0.829 table iii. level of it resources used and organizational issues characteristics the range of less value t1 scalability, flexibility, accessibility, enhanced in the previous two years t2 in the previous two years it resources increased t3 costs of it people have minimized in the previous two years t4 security issues are minimized in the last two years alpha value : 0.72 table iv. cc utilization identify implemented cc concept %age for yes %age for no %age for yes %age for no %age for yes 19.5 80.5 11.60 88.40 195 iv. results the results are divided into two sections. in the first section all elements regarding different barriers faced when implementing cc were identified, while in the second section all effects that occurred while using cc in telecom industry were identified. a. barriers to cc implementation in telecom industry companies and academic sector know the benefits of cc. there are two main concerns: the first is to understand cc in the context of usage in the organization and the attitude of telecom industry in adoption of cc and the second one regards the elements that should be contained in different telecom companies when utilizing cc. on the basis of the survey, a small ratio of companies is aware of the concepts of cc. only 18 different companies (19.15% of the total) are aware of cc. only 11 companies (11.70%) have implemented cc services. the survey results show that 80.85% of the companies do not know about the cc concept. the cc characteristics are explained, as shown in table vi. table v. organization launch of the cc concept the idea of cc interested or not for in applying it %age for yes %age for no 55.5 4.5 table vi. organizations not implementing cc used value significant and not significant avg. value the problem in data surety 6.37 data loses while transferring to some other party 6.48 cc advantages 6.14 how to use services with their value 6.08 lock-in data, not easy for the client to modify a new supplier 7.87 privacy of data, protection with the position of given data 5.46 a number of companies started to use cc in their organization: 55.26% of the companies utilized cc services. some factors were identified on the basis of which different companies rejected or did not show their interest to utilize cc. an important barrier to the utilization of cc in the organization is the unavailability of it managers. b. effects of cc use in the telecom industry table viii shows the association of the different used variables in which the highest level of significance is<0.01. secondly, as stated in the given methodology portion, the investigation of different models is anova, which was made to detect the presence of important statistics among the uses of cc for every attribute of the scales (for the variables that are dependent and independent on the test). c. effect of cc use in cost reduction table ix shows us that companies that use cc have improved behavior in all attributes. the test significance value is less than 0.01, proving the relationship between the usage of cc and it decreasing costs. d. effect of using cc on organizational problems and it resources table x shows that all companies that use cc acquire significantly better behavior. but the association is statistically better in the main three attributes: ease of access, scalability and augmented flexibility in the utilization of it. accessibility of resources related to it and problems that are related to security are reduced. v. discussion and future work cc is a novel technological it organizational model. the addition of technical progress can modernize the organization. cc analysis shows that the main things on which this topic concentrates are its concepts, its main attributes, different exploitation model, main issues related to security and different services from the technological view. however, there is a lack of cc research for use in companies, identifying different barriers to its use and the identification of the main factors used for the assessment of the effect by implementing cc. this is important for the telecom field which is important in the engineering, technology & applied science research vol. 8, no. 4, 2018, 3157-3161 3160 www.etasr.com ramzan et al.: an analysis of issues for adoption of cloud computing in telecom industries economic field for any company. empirical qualitative and quantitative research methodology is used to identify the obstacles faced for its implementation in telecom industries. the effects or benefits of using cc in telecom companies are investigated. in this regard it is shown that most of telecom companies have small knowledge about the usage of cc, but when these telecom companies acquire that knowledge, they have shown their interest on implementing cc. this shows that the ignorance of cc is the main cause of not implementing it. this study is beneficial for those who want to bring the telecom closer to cc because the obstacles companies face while adapting cc are identified. these obstacles are organized hierarchically, according to their importance in telecom industry. the telecom companies identified that the two most important barriers for using cc are security issues and transferring data to a third party. a third barrier is the unawareness of the managers on how to calculate the results produced by cc. another barrier is the benefit of cost by using cc. other barriers identified include quality, availability of services, and requirements for data protection. table vii. different production level for minimizing cost bilateral pearson association descriptive figures characteristics cl-t1 cl-t2 cl-t3 avg. std min max scalability & ease of use costs minimized in the previous two years 1 4.404 1.712 1 7 access to previously unavailable it improved the previous two years 0.6 0.791 1 4.476 1.521 1 7 increased resources 0.676 0.735 0.586 3.380 1.72 1 7 issues related to security minimized in the previous two years 0.535 3.678 1.663 1 7 table viii. level used for organizational problems bilateral pearson association descriptive figures characteristics rl-t1 rl-t2 rl-t3 rl-t4 avg. std min max scalability & ease of use costs minimized in the previous two years 1 4.450 1.3 1 7 access to previously unavailable it improved the previous two years 0.6 0.791 1 4.296 1.672 1 7 increased resources 0.676 0.735 0.586 1 3.487 1.420 1 7 issues related to security minimized in the previous two years 0.53 3.678 1.663 1 7 table ix. anova of minimization cost by using cc avg. r-it 1 c-it 2 c-it 3 y 5.45 5.93 5.5 n 3.36 2.82 3.23 value of f 9.15 13.37 13.37 implication 0.007 0.002 0.002 table x. anova of organizational problems while 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conceptualization and valuation from the perspective of real options”, decision sciences, vol. 40, no. 3, pp. 381-402, 2009 [27] s. schneider, a. sunyaev, “determinant factors of cloud-sourcing decisions: reflecting on the it outsourcing literature in the era of cloud computing”, journal of information technology, vol. 31, no. 1, pp. 131, 2016 . microsoft word 26-3285_s_etasr_v10_n2_pp5487-5491 engineering, technology & applied science research vol. 10, no. 2, 2020, 5487-5491 5487 www.etasr.com amara et al.: sliding mode observer and event triggering mechanism co-design sliding mode observer and event triggering mechanism co-design houssem eddine amara electrical engineering department university ferhat abbas setif 1 setif, algeria houssem_am@hotmail.fr mohamed amine sid electrical engineering department university ferhat abbas setif 1 setif, algeria amineatweb@yahoo.fr samia latreche electrical engineering department university ferhat abbas setif 1 setif, algeria ksamia2002@yahoo.fr mabrouk khemliche electrical engineering department university ferhat abbas setif 1 setif, algeria mabroukkhemliche@univ-setif.dz abstract—sliding mode observer and event triggering mechanism co-design is the subject of this paper. the synthesis of a sliding mode observer under any event triggering mechanism is given, where the proposed observer can be viewed as a special structure of the kalman filter. then, the event triggering condition is updated according to the coverage index value computed with the help of the reachability set representation. a numerical example illustrates the effectiveness of the proposed approach. keywords-sliding mode observer; event-based scheduling; codesign; estimation performance; communication design optimization i. introduction many estimator design methods have been developed under the assumption that the measurement vector is periodically available. however, sensors may not feed-back the estimator periodically, due to several reasons such as limited network bandwidth and high energy consumption of the radio unit for wireless sensors. in this case, the classic periodic sampling can be replaced by an event-based technique, which insures acceptable estimation performance with limited network resources. achieving a desired balance between network state estimator quality and sensor to estimator communication rate has led to the use of robust observer methods and in this context sliding mode observer is a very popular tool. the sliding mode observers are proposed with the idea to drive the dynamics of a system to an sliding manifold, that is an integral manifold with finite reaching time [1]. the first sliding mode has been discussed in [2-4]. in addition, some smo have attractive properties similar to those of the kalman filter (i.e. noise resilience) [5], but with a simpler implementation [6]. sometimes this design can be performed by applying an equivalent control method [7, 8], allowing the proposal of robust to noise observers, since the equivalent control is slightly affected by noisy measurements. a key feature in the utkin observer [9] is the introduction of a switching function in the observer to achieve a sliding mode and also stable error dynamics. for better utilization of shared communication and processing resources or reduction of hardware costs we deal with event-based designs. the area of event-based control and estimation has substantially grown during the last decades [1012]. in [13 ], an event-triggered approach was used to trigger the data transmission from a sensor to a remote observer. in [14], a sensor data scheduling problem was considered and a feedback policy to choose the transmission times which provides a trade-off between the communication rate and the estimation error was used. the objective in [15] was the development of predictive triggering mechanisms for eventbased state estimation. the main contribution of this paper is the introduction of an event-based technique and a communication design optimization with a corresponding estimation by adopting a sliding mode from which we obtain high estimation quality with low energy consumption by minimizing the number of sensors. ii. problem formulation the event-based sliding mode state estimation process is illustrated in figure 1. fig. 1. event-based sliding mode state estimation consider initially a nominal linear system as described in (1): corresponding author: mabrouk khemliche engineering, technology & applied science research vol. 10, no. 2, 2020, 5487-5491 5488 www.etasr.com amara et al.: sliding mode observer and event triggering mechanism co-design �x� � = ax� + bu� � = cx� (1) where: x ∈ ���, ∈ ��� ,u ∈ ��� , and the matrices a, b, c have the appropriate dimensions. without loss of generality, we assume that c ∈ ℛ��×�� has full row rank which means each of the measured outputs is independent. let ℰ� ≜ � − �� , where �� denotes the previous time instant when the measurement of sensor is transmitted defined as follows: �� = ��� � �� γ� = 0! �� γ� = 1 , $%& �' � = 0 (2) where ��� denotes the left hand limit of �( at the instant t. the main advantage of using the send-on-delta conditions is that feedback communication from the estimator is not needed as the conditions only depend on the sensor measurements. this fact reduces hardware and energy consumption cost and facilitates the implantation of event-triggering schemes. the objective is to obtain an estimate of the state x� based only on the knowledge of the quantities y��and u�. in the simplest form of the sliding mode observer, instead of feeding back the output error between the observer and the system in a linear fashion, the output error is fed back via a discontinuous switched signal. furthermore, we consider the following eb sensor data scheduler: γ� = �0, if‖ϵ�‖∞ ≤ ζ,1, otherwise (3) where ζ ≤ ∞ is a predefined threshold and ϵ� the output error. the objective of this article is to find or approximate an optimal state estimate of eb sensor data scheduler (3), which we call nonlinear eb state estimation or eb state estimation problem interchangeably. in the next section, a sliding mode framework of the eb state estimation problem is presented. iii. event based sliding mode observer a. similarity transformation consider the transformation x = t7�8x8 associated with the invertible matrix: t7 = 9n;<c = (4) where n7 ∈ ℛ��×( �����) is a full rank column matrix composed with the null space basis of c. by substitution we obtain: @x�8(t) = aax8(t) + bau(t) (t) = cbx8(t) (5) where: aa = t7at7�8,ba = t7b, and cb = ct7�8 = c0 ief (6) an observer for (1) was proposed as follows [9]: @xg� � = axg� + bu� + g�v jt = cxg� (7) where (xg, j) are the estimates of x, and v is a discontinuous injection term. e� = xg� − x� and eno(t) = jt − �� are defined as the state estimation and output estimation errors respectively. the term v is defined component-wise as: vp = ρsignset ,pu, i = 1,… . ,p (8) where ρ is a positive scalar and eto,p represents the ith component of et . the term v is designed to be discontinuous with respect to the sliding surface s = ze:ce = 0\ to force the trajectories of e(t) into s in finite time. assuming, without loss of generality, that the system is already in the coordinate associated with (6), then the gain g� has the following structure: g� = 9 l−ie= (9) where l ∈ ℛ(��e)×e represents the design freedom, following the definition of e(t) and (1). the error system is given by: é(t) = ae(t) + g�v (10) from the structure of the output distribution matrix c in (6) the state estimation error can be partitioned as e = col (e8, e ), where e8 ∈ ℛ��e. consequently the error system from (10) can be written in the form: é8(t) = a`8e8(t) + a8`e (t) + lv (11) é (t) = a`8e8(t) + a8`e (t) − v (12) furthermore, (12) can be written component-wise as: é ,p(t) = a`8,pe8(t) + a``,pe (t) − psign(et ,p) (13) where a`8,p and a``,p represent the ith rows of a`8 and a`` respectively. to develop the conditions under which the sliding will take place, the reachability condition will be tested. notice that e ,p = p − ap and et ,p = �,p − ap . then e ,p − et ,p = p − �,p and from (3) we get: be ,pb − ζ ≤ bet ,pb (14) from (13) and (14) we obtain: e ,pe� ,p = e ,psa`8,pe8 + a``,pe u − ρb(et ,p)b (15) ≤ e ,psa`8,pe8 + a``,pe u − ρbse ,pub + ρζ (16) < −bse ,pub(ρ − bsa`8,pe8 + a``,pe ub − deb(f ,g)b (17) provided that the scalar p is chosen such (large enough) that: p > bsa`8,pe8 + a` ,̀peoub − debsf ,gub + n (18) where the scalar n ∈ ℜj. then : e ,pe� ,p < −nbe ,pb (19) this is the eta-reachability condition and implies that e ,p will converge to zero in finite time. when every component of engineering, technology & applied science research vol. 10, no. 2, 2020, 5487-5491 5489 www.etasr.com amara et al.: sliding mode observer and event triggering mechanism co-design e >t? has converged to zero, a sliding motion takes place on the surface s. remark: note that this is not a global result. for any givenρ , there will be an initial condition of the observer (typically representing the very poor estimation of the initial conditions of the plant) so that (16) is not satisfied. during sliding mode e >t? � e� >t? � 0 , and the error system defined by (11) and (12) can be written in a collapsed form as: e�8>t? � sa88e8>t? � lvfku (20) 0 � sa`8e8>t? � vfku (21) where vfk is the so-called equivalent output error injection that is required to maintain the sliding motion. this is the natural analogue of the equivalent control. substituting vfk from (18) and (19) yields the following expression for the reduced-order sliding motion: e� 8>t? � >a88 � la`8?e8>t? (22) this represents the reduced-order motion of order n � p that governs the sliding mode dynamics. it can be shown that if (a, c) is observable then >a88a`8? is also observable, and a matrix l can always be chosen to ensure that the reduced-order motion in (20) is stable. b. communication rate and threshold design the average sensor communication rate is defined as: γ � lim sup<→j∞ n 8<j8op γ�dt < �q' (23) the average rate r gives a general description of the network utilization. below we consider the choice of the threshold s issue, given in (3), in order to achieve a desirable trade-off between communication rate and estimation quality. c. communication design optimization in this section, the tradeoff between the estimation quality and the network bandwidth use as a constrained optimization problem is described. for this aim, the following cost functions �8 and �̀ are defined: �8>ζ? � γ (24) this function is related to number of the transmitted sensor measurement packets. �̀ >ζ? � lim<→j∞ t 8<j8 p eo>t?`dt < �q' (25) where �̀ is an estimation error rms performance index. finally, both functions can be used to formulate a general performance index as following: �>ζ? � q�8>ζ? � r�̀ >ζ? (26) where, q and r are weighting matrices used to penalize the number of transmitted packets and the estimation quality respectively. thus the co-design problem can be formulated as follows: ζ∗ � argminf>ζ? (27) iv. simulation results in this section, the effectiveness of the proposed co-design approach is illustrated with a numerical example. for simulation purposes, let us consider a nominal linear system described by (1) and modeled by: a � x 0 1�2 0z,b � x 0 1z, c � {1 1| (28) which represents a simple harmonic oscillator. for simplicity, we assume u>t? � 0,d � 0, and ρ � 1, q � 5, r � 1. the system’s initial state is x' � {0.5 ; �0.8|< , and the observer has zero initial condition. figure 2 shows the simulation diagram using matlab/simulink version r15.a. using a variable step ode45, dormand prince solver with a processor intel(r) core(tm) i5-8250u cpu. fig. 2. simulation diagram in table i the simulation results for different arbitrary values of ζ are summarized along with the optimal one for giving priority to the minimisation of energy consumption. table i. optimization of energy consumption case no different values of � with priority to energy minimization � rms(ey) number of transmissions objective function 1 0.1 0.0801 115 0.0806 2 0.50 0.1059 22 0.1060 3 1.50 0.3139 3 0.3139 optimal 0.9409 0.2291 9 0.2586 figures 3-6 show the system output yt, the transmitted output y�� and the output estimation yestim for different values of ζ. figure 6 is the optimal case. excellent tracking of the output occurs after approximately 1.3s and the output estimation error ey after approximately 1.0s becomes zero, and the transmitted outputs are minimized. this is indicative of a high estimation quality with minimization of energy consumption. if we give priority to estimation rather than energy minimization, then q � 1,r � 5. table ii exhibits the results of simulation for different values of ζ. engineering, technology & applied science research vol. 10, no. 2, 2020, 5487-5491 5490 www.etasr.com amara et al.: sliding mode observer and event triggering mechanism co-design fig. 3. 1 st case: the output yt, the transmitted output y�� , the output estimation error ey, and the output estimation yestim fig. 4. 2 nd case: the output yt, the transmitted output y�� , the output estimation error ey, and the output estimation yestim fig. 5. 3 rd case: the output yt, the transmitted output y�� , the output estimation error ey, and the output estimation yestim fig. 6. optimal case: the output yt, the transmitted output y��, the output estimation error ey, and the output estimation yestim table ii. optimization of estimation quality case no different values of � with priority to estimation � rms(ey) number of transmissions objective function 1 0.20 0.0801 57 0.4004 2 1.00 0.2585 10 1.2926 3 1.50 0.3139 3 1.5693 optimal 0.70 0.1564 14 0.7821 figures 7-10 plot the system output yt, the transmitted output y��, and the output estimation yestim for different values of ζ . figure 10 shows the optimal case which clearly demonstrates a high estimation quality always with minimization of the transmitted output y��. fig. 7. 1 st case: the output yt, the transmitted output y�� , the output estimation error ey, and the output estimation yestim fig. 8. 2 nd case: the output yt, the transmitted output y�� , the output estimation error ey, and the output estimation yestim fig. 9. 3 rd case: the output yt, the transmitted output y�� , the output estimation error ey, and the output estimation yestim engineering, technology & applied science research vol. 10, no. 2, 2020, 5487-5491 5491 www.etasr.com amara et al.: sliding mode observer and event triggering mechanism co-design fig. 10. optimal case: the output yt, the transmitted output y��, the output estimation error ey, and the output estimation yestim v. conclusions because of the verified benefits in terms of reduced energy consumption and better resource utilization compared to traditional designs, event-triggered estimation methods can be widely adopted in industrial applications. for instance, in achieving optimal state estimation over a shared network we use a sliding mode observer associated with an event triggering mechanism. it was shown that by the introduction of an event based technique and the communication design optimization with a corresponding estimator by adopting sliding mode, reduction of the estimation error and of the sensor transmission can be achieved. the simulation results illustrate the effectiveness of the proposed sliding mode observer in terms of decreased estimation error and reduced sensor transmitted information. references [1] y. shtessel, c. edwards, l. fridman, a. levant, sliding mode control and observation, birkhauser basel, 2014 [2] s. hui, s. h. zak, “observer design for systems with unknown inputs”, international journal of applied mathematics and computer science, vol. 15, no. 4, pp. 431-446, 2005 [3] b. walcott, s. h. zak, “state observation of nonlinear uncertain dynamical systems”, ieee transactions on automatic control, vol. 32 no. 2, pp. 166-170, 1987 [4] b. w. edwards, s. k. spurgeon, r. j. patton,“sliding mode observers for fault detection and isolation”, automatica, vol. 36, pp. 541-553, 2000 [5] o. aydogdu, m. l. levent, “kalman state estimation and lqr assisted adaptive control of a variable loaded servo system”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4125-4130, 2019 [6] s. v. drakunov, “an adaptive quasi-optimal filter with discontinuous parameters”, automation and remote control, vol. 44, no. 9, pp. 11671175, 1983 [7] s. v. drakunov, “sliding mode observers based on equivalent control method”, 31st ieee conference on decision and control, tucson, usa, december 16-18, 1992 [8] s. v. drakunov, v. i. utkin, “sliding mode observers. tutorial”, in: proceedings of 34th ieee conference on decision and control, vol. 4, pp. 3376-3378, ieee, 1995 [9] v. i. utkin, “sliding modes in control and optimization”, in: communications and control engineering series, springer-verlag, 1992 [10] j. sijs, b. noack, m. lazar, u. d. hanebeck, “time-periodic state estimation with event-based measurement updates”, in: event-based control and signal processing. crc press, 2016 [11] d. shi, l. shi, t. chen, event-based state estimation, springer, 2016 [12] s. p. singh, s. c. sharma, “a novel energy efficient clustering algorithm for wireless sensor networks”, engineering, technology & applied science research, vol. 7, no. 4, pp. 1775-1780, 2017 [13] l. li, m. lemmon, x. wang, “event-triggered state estimation in vector linear processes”, 2010 american control conference, baltimore, usa, june 30-july 2, 2016 [14] r. cogill, s. lall, j. p. hespanha, “a constant factor approximation algorithm for event-based sampling”, in: perspectives in mathematical system theory, control, and signal processing, springer, 2010 [15] s. trimpe, “predictive and sell triggering for event-based state estimation”, ieee 55th conference on decision and control, las vegas, usa, december 12-14, 2016 microsoft word etasr_7-1_1353-1357.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1353-1357 1353 www.etasr.com bagheri et al.: modeling support loss in torsional mode vibrations of a micromechanical disk… modeling support loss in torsional mode vibrations of a micromechanical disk resonator with two l-shaped support beams majid bagheri department of mechanical engineering university of birjand birjand, iran m_bagheri_ub@yahoo.com abolfazl bijari department of electrical and computer engineering university of birjand birjand, iran a.bijari@birjand.ac.ir mohammad imanparast department of mechanical engineering university of sistan and balochestan zahedan, iran mohammad.ipt.61@gmail.com mehdi raghebi department of mechanical engineering university of birjand birjand, iran raghebi@birjand.ac.ir abstract—in this paper, a new micromechanical disc resonator with two l-shaped horizontal support beams in torsional mode vibrations has been proposed. the proposed micromechanical resonator has been studied in the field of natural frequencies and support loss. in order to verify the findings of natural frequencies, the analytical results are compared to the simulation results given by ansys software. a good agreement between analytical and simulation results is shown. in addition a closedform equation for support loss quality factor in torsional mode vibrations of the proposed micromechanical resonator is presented. the results show that using l-shaped support beams can improve the support loss quality factor up to two times. keywords-quality factor; support loss; torsional mode; micromechanical disk resonator i. introduction micromechanical resonators are small micromechanical devices which vibrate at high frequencies and are used in devices such as filters [1], sensors [2] and gyroscopes [3]. several loss mechanisms in the resonators exist, such as air damping, thermoelastic damping (ted) and support loss. the measured unloaded quality factor is mainly the combination of these loss mechanisms, which expressed as [4]: tedsupporttotal air 1 1 1 1 q q q q    (1) among the loss mechanisms in a micromechanical resonator, air damping can be eliminated by operating the resonator in vacuum. thermoelastic damping is the result of an irreversible heat flow due to the stress gradients in micromechanical resonators and usually is too low to limit the quality factor at high frequency [5-7]. at high frequencies, the main loss mechanism which determines the quality factor is the support loss which is caused by the propagation of the elastic waves through the substrate [4]. in micromechanical resonators, a high quality factor is desirable as it leads to improved performance in frequency selective applications. therefore, modeling support loss as dominant mechanism of energy loss is a matter of debate for improving the performance of the resonators. in [8], authors studied the support loss in square rocking mass resonator. they derived the support loss quality factor equation for the torsion mode, out of plane rocking mode and a combination of both. in [9], authors presented an analytical model for support loss in clamped-free and clamped-clamped beam resonator with in-plane flexural vibrations. in addition, in [10], the support loss in the center supported micromechanical disk resonator under radial bulk-mode vibrations was calculated. authors provide significant insights into the geometrical design and choice of materials in high-q center supported disk resonant structures. in [11], the thermoelastic damping in microand nano-electromechanical circular thin-plate resonators under contour-mode vibrations was investigated and it was demonstrated that the qted of the contour-mode vibrations of a circular thin-plate resonator is well above 106 when its resonant frequency is below 1 ghz. in [12], authors presented the analytical equation of the support loss quality factor in the plunging-mode vibrations of a micromechanical rectangular-plate resonator with two tshaped support beams. they obtained the closed-form expression for support loss quality factor in the plunging-mode vibrations of micromechanical rectangular-plate resonator with two support beams. findings demonstrated the support loss quality factor in the plunging-mode vibrations is enhanced about 1.5 times using t-shaped support beams instead of conventional orthogonal support beams. engineering, technology & applied science research vol. 7, no. 1, 2017, 1353-1357 1354 www.etasr.com bagheri et al.: modeling support loss in torsional mode vibrations of a micromechanical disk… the main contribution of this paper is introducing a new support beams scheme for torsional mode micromechanical disk resonators. this paper is organized as follows. the closedform equations of support loss quality factor and natural frequency for a micromechanical disc resonator with two horizontal support beams in torsional mode vibrations is first obtained. then, a new design for support beams is presented to improve support loss quality factor. finally, the closed-form equation of support loss for proposed design is calculated and discussed. ii. torsional mode vibrations of a conventional micromechanical disc resonator figure 1 shows a micromechanical disk resonator of radius r, beam length l, beam width w and thickness h, suspended from the substrate through two support beams. the torsional mode vibrations for the micromechanical disc resonator with two horizontal support beams are shown in figure 2. in figure 2, the resonator is rotated by θ0 around the x axis. figure 3 illustrates the side view of the torsional mode vibrations for the micromechanical disc resonator with two horizontal support beams and also the transformations of the resonator in this mode. figure 4 shows how the torsional moment is exerted to the substrate in a micromechanical disc resonator with two horizontal support beams in torsional mode vibrations. fig. 1. conventional micromechanical disc resonator fig. 2. torsional mode vibrations of a micromechanical disc resonator fig. 3. side view of the torsional mode vibration fig. 4. exerted torsional moment to the substrate the torsional moment is obtained from (2) [8]: 3 0 t g wh m l    (2) where, θ0 is the angular rotation of the resonator. g is the shear modulus. values of  in w/h for w h is represented in [13]. the support loss quality factor in torsional mode vibration is obtained from (3) [8]: support 1 q u   (3) in (3), u is the total energy obtained from a single vibration cycle of the resonator and the support beams,  is the natural frequency of the resonator,  is the net power of the resonator output energy flow. in order to calculate the vibrational energy and frequency, the effective inertia moment and the equivalent stiffness should be determined. the equivalent inertia moment is obtained from (4) [14]: 2 2 2 2 21 ( ) (3 ) 9 12eff j whl w h hr r h     (4) the equivalent stiffness in torsional mode of the micromechanical disc resonator with conventional support beams for w h is obtained from (5) [8]: 3 32 (1 )t g wh e whk l l       (5) the natural frequency is obtained from (6): 3 2 2 2 2 2 (1 ) 1 ( ) (3 ) 9 12 t eff e wh k l j whl w h hr r h            (6) and the vibrational energy is obtained from (7): engineering, technology & applied science research vol. 7, no. 1, 2017, 1353-1357 1355 www.etasr.com bagheri et al.: modeling support loss in torsional mode vibrations of a micromechanical disk… 2 0 3 2 (1 ) u e w h l      (7) iii. verification resonator structure, support beams and substrate are made from single-crystal silicon with material properties listed in table i. the calculated frequency from (6) was compared to the frequency obtained by ansys for the design specifications given in table ii. the results of this comparison are listed in table ii. table i. material properties of single-crystal silicon e (gpa) ρ (kg/m3)  131 2330 0.28 table ii. comparison between analytical and simulation results of natural frequency. parameters example 1 example 2 r (m) 150 80 l (m) 300 250 w (m) 30 20 h (m) 10 5 analytical (khz) 85.7 138.9 ansys (khz) 83.9 136.81 %error 2.1 1.5 table ii shows that the frequency obtained from (6) is in agreement with the frequency from ansys, which verifies the equivalent stiffness and the effective inertia moment of the micromechanical disc resonator with two horizontal support beams. iv. admittance matrix and power flow the power flow into the support structure is explained as (8) [15]: 1 re( ) 2   f.v (8) in order to form a relation between the velocity vector and the power vector at the junction of the beam to the substrate, an admittance matrix (y) is applied. expressions for power in terms of shear force fz, bending moment mb and torsional moment mt (the shear force and bending and torsional moments in the beams and anchor connection point) are presented as (9)-(15) [12]: 2 2 33 2 3(1 ) z p fz h y f e      (9)   2 2 22 3 6 1 b p m b h y m e    (10)   2 2 11 3 6 1 t p m t h y m e    (11) 3 2 4 23 1 5 3 4 2 4 (12(1 )) zb p m f m fz zb b m fy h e         (12) m m m mt tb b   (13) m f m fz zt t   (14) m f mz tb      (15) table iii. constants associated with admittance matrix for poisson’s ratio of 0.28 and 0.3 [4, 16] υ = 0.3 υ = 0.28 coefficients 0.216450.22172 re(y11) = re(y22) -0.29149 -0.28546 re(y23) = re(y32) 0.461980.45735 re(y33) substituting (6), (7) and (11) in (3) and using (2), the support loss quality factor in torsional mode of the micromechanical disc resonator with two horizontal support beams will be obtained from (16):  2 36 1 (1 ) 11 3 2 1 q u lsupport y whm t h p          (16) v. torsional mode vibrational of a micromechanical disk resonator with l-shaped support beams figure 5 shows the schematic view of micromechanical disc resonator with l-shaped support beams along with geometric characteristics. as shown, l1, w1, l2, w2 are the related parameters for l-shaped part of support beam. the torsional mode vibrational of the resonator and the torsional moments which are applied to the substrate are shown in figure 6. the torsion moment is obtained from (17): 3 0 1 2 g wh m t l    (17) a t-shaped part has been added at the end of the l-shaped beams to halve the torsional moment. according to [14] the equivalent stiffness depends on the equivalent torsional moment which applied to the resonator and therefore, the tshaped part has not significant effect on the equivalent torsional moment applied to the resonator. hence, the stiffness remains constant. table iv shows the effect of neglecting the inertia moment of the t shaped part on frequency. table iv shows that neglecting the inertia moment of the t-shaped part has little effect on natural frequency. therefore, the natural frequency and vibrational energy in torsional mode vibrations of a micromechanical disc resonator with two lshaped support beams are obtained from (6) and (7), engineering, technology & applied science research vol. 7, no. 1, 2017, 1353-1357 1356 www.etasr.com bagheri et al.: modeling support loss in torsional mode vibrations of a micromechanical disk… respectively. by substituting (6), (7), (11) and (17) in (3), the support loss quality factor is calculated as follows:  2 33 14 11 ( ) 31 1 q u lsup y port l whm t h p           (18) fig. 5. micromechanical disc resonator with l-shaped support beams fig. 6. torsional mode vibrational of a micromechanical disc resonator with l-shaped support beams figure 7 shows the support loss quality factor in torsional mode vibrations of a micromechanical disc resonator with two l-shaped support beams in terms of the changes in beam length for three different width thicknesses. figure 8 shows the support loss quality factor in torsional mode vibrations of a micromechanical disc resonator with two l-shaped support beams in terms of the changes in thickness of substrate for three different beam thicknesses. the values in table iv example 1 has been used for the charts. considering the geometric values in table v, the support loss quality factors of micromechanical disc resonator with two l-shaped support beams and the micromechanical disc resonator with conventional support beams in torsional mode vibrations have been compared. as shown in table v, support loss quality factor at the same resonant frequency is enhanced about 2 times by using the l-shaped beams. table iv. comparison between analytical and simulation results of natural frequency in torsional mode vibrations of a micromechanical disc resonator with two l-shaped support parameters example 1 example 2 r (m) 150 80 l (m) 300 250 w (m) 30 20 h (m) 10 5 l1 (m) 40 35 w1 (m) 35 30 l2 (m) 55 60 w2 (m) 20 25 analytical (khz) 85.7 138.9 ansys (khz) 80.3 129.64 % error 6.3 6.67 l (m) q ua lit y fa ct or 1 0 8 300 320 340 360 380 4000 0.2 0.4 0.6 0.8 1 1.2 1.4 w = 30(m) w = 40(m) w = 50(m) fig. 7. support loss quality factor in term of the changes in beam length for three different width thicknesses hp(m) q ua lit y fa ct or 1 0 8 500 520 540 560 580 6000 0.05 0.1 0.15 0.2 0.25 h = 10 (m) h = 15 (m) h = 20 (m) fig. 8. support loss quality factor in term of the changes in thickness of substrate for three different beam thicknesses engineering, technology & applied science research vol. 7, no. 1, 2017, 1353-1357 1357 www.etasr.com bagheri et al.: modeling support loss in torsional mode vibrations of a micromechanical disk… table v. comparison between the support loss quality factors in the torsional mode vibrations of micromechanical disc resonator with two l-shaped support beams and conventional support beams model 2: l-shaped beams model 2: conventional beams model 1: l-shaped beams model 1: conventional beams parameters 80 80 150 150 r (m) 250 250 300 300 l (m) 20 20 30 30 w (m) 5 5 10 10 h (m) 35 40 l1 (m) 30 35 w1 (m) 60 55 l2 (m) 25 20 w2 (m) 1000 1000 1000 1000 hp(m) 138.9 138.9 85.7 85.7 analytical frequency (khz) 7.43108 3.715108 7.94107 3.97107 quality factor vi. conclusion in this paper, the closed-form expressions were obtained for natural frequency and support loss quality factor in the torsional mode vibrations of micromechanical disk resonator with two support beams. to verify the obtained frequency, analytical frequency was compared with the frequency obtained from the ansys software and a good agreement between them has been observed. in addition, a new design was proposed to enhance the support loss quality factor. the conventional support beams were replaced with l-shaped ones. the findings show that using the new design caused the support loss quality factor to increase 2 times. moreover, it show that an increment in thickness and width of the support beams, decreases the quality factor and that by increasing the length of the beams and thickness of substrate, the quality factor increases. references [1] l. lin, r. t. howe, a. p. pisano, “microelectromechanical filters for signal processing”, journal of microelectromechanical systems, vol. 7, pp. 286-294, 1998 [2] a. gualdino, v. chu, j. p. conde, “multi-modal analysis of out-of-plane vibration modes of thin-film circular resonators for mass sensing applications”, procedia engineering, vol. 47, pp. 1121-1124, 2012 [3] j. li, j. fang, h. dong, y. tao, “structural design and fabrication of a novel dual-mass resonant output micromechanical gyroscope”, microsystem technology, vol. 16, pp. 543-552, 2010 [4] b. chouvion, vibration transmission and support loss in mems sensors, phd thesis, the university of nottingham, 2010 [5] y. b. yi, “geometric effects on thermoelastic damping in mems resonators”, journal of sound and vibration, vol. 309, no. 3-5, pp. 588599, 2008 [6] b. kim, m. a. hopcroft, r. a. candler, c. a. jha, m. agarwal, r. melamud, s. a. chandorkar, g. yama, t.w. kenny, “temperature dependence of quality factor in mems resonators”, journal of microelectromechanical systems, vol. 17, no. 3, pp. 755-766, 2008 [7] s. a. chandorkar, r. agarwal, m. melamud, r. n. candler, k. e. goodson, t. w. kenny, “limits of quality factor in bulk-mode micromechanical resonators”, the ieee 21th international conference on micro electro mechanical systems, tucson, usa, pp. 74-77, 2008 [8] x. wang, d. xiao, z. zhou, z. chen, x. wu, s. li, “support loss for beam undergoing coupled vibration of bending and torsion in rocking mass resonator”, sensors and actuators a, vol. 171, pp. 199-206, 2011 [9] z. hao, a. erbil, f. ayazi, “an analytical model for support loss in micromachined beam resonators with in-plane flexural vibrations”, sensors and actuators a, vol. 109, pp. 156-164, 2003 [10] z. hao, f. ayazi, “support loss in the radial bulk-mode vibrations of center-supported micromechanical disk resonators”, sensors and actuators a, vol. 134, pp. 582-593, 2007 [11] z. hao, “thermoelastic damping in the contour-mode vibrations of microand nano-electromechanical circular thin-plate resonators”, journal of sound and vibration, vol. 313, pp. 77-96, 2008 [12] m. bagheri, a. bijari, m. raghebi, “modeling and calculating the anchor loss quality factor in the plunging-mode vibrations of a micromechanical rectangular-plate resonator with two t-shaped support beams”, modares mechanical engineering, vol. 14, no. 12, pp. 75-84, 2014, (in persian) [13] b. min-hang, analysis and design principles of mems devices, elsevier b.v, pp. 60–62, 2005 [14] h. urey, c. kan, w.o. davis, “vibration mode frequency formulae for micromechanical scanners”, journal of micro-mechanics and microengineering, vol. 15, pp. 1713–1721, 2005 [15] j. a. judge, d. m. photiadis, j. f. vignola, b. h. houston, j. jarzynski, “attachment loss of micromechanical and nanomechanical resonators in the limits of thick and thin support structures”, journal of applied physics, vol. 101, pp. 1-11, 2007 [16] j. x. su, a. t. moorhouse, “closed form solution for the mobility of an edge excited, semi-infinite plate”, journal of acoustical society of america, vol. 115, pp. 2075-2082, 2004 microsoft word 2-10-2771_s_etasr_v9_n4_pp4322-4328 engineering, technology & applied science research vol. 9, no. 4, 2019, 4322-4328 4322 www.etasr.com allani et al.: fpga implementation of a robust mppt of a photovoltaic system using a fuzzy logic … fpga implementation of a robust mppt of a photovoltaic system using a fuzzy logic controller based on incremental and conductance algorithm mohamed yassine allani ur-laper, faculty of sciences of tunis, university of tunis elmanar, tunis, tunisia medyassine.allani@fst.utm.tn fernando tadeo department of systems and automation engineering, university of valladolid, valladolid, spain fernando.tadeo@uva.es dhafer mezghani ur-laper, faculty of sciences of tunis university of tunis elmanar, tunis, tunisia dhafer.mezghani@fst.utm.tn abdelkader mami ur-laper, faculty of sciences of tunis, university of tunis elmanar, tunis, tunisia abdelkader.mami@fst.utm.tn abstract—climate dependence requires robust control of the photovoltaic system. the current paper is divided in two main sections: the first part is dedicated to compare and evaluate the behaviors of three different maximum power point tracking (mppt) techniques applied to photovoltaic energy systems, which are: incremental and conductance (ic), perturb and observe (p&o) and fuzzy logic controller (flc) based on incremental and conductance. a model of a photovoltaic generator and dc/dc buck converter with different mppt techniques is simulated and compared using matlab/simulink software. the comparison results show that the fuzzy controller is more effective in terms of response time, power loss and disturbances around the operating point. ic and p&o methods are effective but sensitive to high-frequency noise, less stable and present more oscillations around the ppm. in the second section, the fpga platform is used to implement the proposed control. the flc architecture is implemented on an fpga spartan 3e using the ise design suite software. simulation results showed the effectiveness of the proposed fuzzy logic controller. keywords-fuzzy logic controller; p&o; ic; mppt; energy solar; buck converter; fpga i. introduction the electrical energy produced by photovoltaic systems is very interesting and a modern topic of power generation. however, the costs of pv arrays are relatively high, and the efficiency of the energy conversion is quite low. therefore, the electric power generated by the pv arrays should be efficiently used. in a direct coupled (with no battery storage) pv system, the solar cell arrays are directly connected to the motor load couple. these systems are relatively simple and inexpensive to operate. a direct coupled system may include a maximum power point tracker (mppt) to improve its performance at starting and at steady state operation whenever it is needed. many researches on photovoltaic techniques [1-3] have been carried out in order to increase the efficiency of these panels, and to extract their maximum energy while designing reliable and stable systems. there are different methods of ppm tracking such as ic [4-6], parasitic capacitance method [7], p&o method [8], etc. they are based on the regulation of the current or voltage of the photovoltaic generator according to climatic conditions. as a result, the uncertainties associated with these conditions have decreased the reliability of these techniques, especially as a result of changes in sunlight and temperature. artificial intelligence techniques such as neural networks [9] and fuzzy logic [10, 11] have the characteristics of adaptive and versatile mechanisms and are able to improve the performance of the control system in the presence of these uncertainties. in addition, a software implementation of the flc developed on general purpose cannot be regarded as a suitable solution for such applications, especially when it is used as an mppt controller for autonomous pv applications. in this case, flc was usually implemented in microcontrollers [12] and/or in digital signal processors (dsps) [13]. simulation and experimentation results showed the advantages of flc over conventional p&o. this proposed technique was able to reduce steady-state oscillations and improve the convergence speed of the operating point. these devices can provide considerable performance, but they do not offer the advantages that fpga (field-programmable gate array) devices can offer for the implementation of certain commands. with the progress in microelectronics, real time applications use intelligent techniques and new hardware design solutions such as fpga. they are suitable for the implementation of control algorithms such as fuzzy logic controllers. these circuits allowed the corresponding author: mohamed yassine allani engineering, technology & applied science research vol. 9, no. 4, 2019, 4322-4328 4323 www.etasr.com allani et al.: fpga implementation of a robust mppt of a photovoltaic system using a fuzzy logic … reduction of the execution time by adopting parallel processing, rapid design prototyping and improved mppt control of the photovoltaic panel quality by exploiting new digital system technologies [9, 15, 16]. from the results of these works, it can be deduced that the mppt is reached quickly, especially under rapidly changing climatic conditions, the response time is improved, the exceedance and the oscillations are extremely reduced and therefore the energy losses are reduced. all these advantages of real time implementation form a necessity for mppt control. ii. modelling of the pv conversion system a. modelling of the photovoltaic panel the pv module converts light into electricity. the electrical characteristics of the photovoltaic panel depend on the irradiation and the temperature. figure 1 shows the complete system simulated in matlab/simulink. the photovoltaic cell is modeled by (1)-(6) [16-18] that define the static behavior of the p-n junction of a conventional diode. the electrical model of the pv cells is shown in figure 2. � � �� � �� (1) �� � �� � �� � �� � �� � 1� (2) �� � ���� � �� �� � ������ ! (3) �� � ��� " ��#$%& '()* �+� ,-./� � " 0�#$% � 0 �&1 (4) ��� � �23�456 7 893) : ;#$%<=0 (5) � � �� � �� � �'� >�?�@ �2� � � * � 1� � '�?� �2�2a * (6) fig. 1. simulink model of the photovoltaic conversion system fig. 2. simulink model of the photovoltaic conversion system the pv parameters used in the model are summarized in table i. table i. parameters of the pv panel kaneka g-sa060 [16-18] parameters of pv values and units pmax 60.3w cells per module 61 vpv at pmax 67v ipv at pmax 0.9a vo (open circuit voltage) 91.8v is (short circuit current) 1.19a a 2.1922 rs (series resistance) 5.8ω rsh (shunt resistance) 254.8ω b. modelling of the buck converter buck converter is a dc-dc converter. it adjusts the energy transfer between the photovoltaic generator (pvg) and the dc load and allows the reduction of the voltage. the buck converter model is illustrated in figure 3. the output voltage and current of the buck converter are expressed in: bc � d ∗ bf (7) �c � >1/d@ ∗ �f (8) where α is the duty cycle of the buck converter, 0<α<1. fig. 3. electrical circuit model of the buck converter. the parameters of the buck converter connected to the pv generator are presented in table ii. table ii. buck converter parameters and values parameters of the buck converter values and units vin 61v vout 24v l (inductance) 10µh ce (input capacitor) 470µf co (otput capacitor) 470µf f (switching frequency) 30khz iii. mppt control three methods are studied and developed in this work: a. mppt based perturb and observe perturb and observe (p&o) is one of the most popular mppt techniques used in a photovoltaic power system. this method uses the current/voltage measurements delivered by the pvg to calculate maximum power. figure 4 describes the operation of the algorithm (p & o). b. mppt based on incremental and conductance the ic method is often applied in photovoltaic systems. it tracks the mpp by comparing the instantaneous and incremental conductance of the source under consideration. the question asked of the ic method is similar to that of p&o. engineering, technology & applied science research vol. 9, no. 4, 2019, 4322-4328 4324 www.etasr.com allani et al.: fpga implementation of a robust mppt of a photovoltaic system using a fuzzy logic … the fixed step size is generally adopted, which determines the accuracy and speed of the mppt response. figure 5 illustrates the algorithm of the ic method. fig. 4. methodology of p&o method fig. 5. algorithm of the incremental and conductance method c. mppt based fuzzy logic control (based on ic) recently, several methods have been used to extract maximum power of the pvg [4-11, 9, 14-24]. in order to design an mppt controller not only efficient, but also able to operate properly under all variations, we used fuzzy logic control which is one of the most known control techniques of the mppt [10, 11, 21-23]. in addition, the ic method is often applied in photovoltaic systems. it tracks the mpp by comparing the instantaneous and incremental conductance of the source under consideration. the issues of the ic method are similar to the ones of the p&o method. the fuzzy logic converges quickly, although it can operate with inaccurate inputs, and does not require a perfectly well-known mathematical model. therefore, we have combined the ic method into a fuzzy logic controller. the fuzzy controller inputs are modeled by (9) and (10), the result of the incremental and conductance algorithm is presented in (8) [46]. pv pv pv pv v i dv di −= (9) pv pv pv pv v i dv di ke +=)( (10) )1()()( −−= kekekde (11) the proposed control model simulated with the use of matlab/simulink is shown in figure 6. fig. 6. simulink model of the fuzzy logic controller triangular membership functions for the fuzzification process are employed. for inputs e, de and duty output, 5 belonging functions have been identified depending on the following linguistic variables: grand negative (gn), negative (n), zero (z), positive (p) and grand positive (gp). the range for the error is (0.02 to 0.2), for the error change is (-0.4 to 0.4) and for the duty cycle increment is (-0.1 to 0.1). the degree of membership function of the input and the output of the pv is described in figure 7. (a) (b) (c) fig. 7. the membership function of duty cycle (c) and the two inputs of the fuzzy logic controller: (a) e, (b) de. according to the choice carried out for the fuzzification of the input and the defuzzification of the output, there are 25 inference rules on the fuzzy controller database. we use the engineering, technology & applied science research vol. 9, no. 4, 2019, 4322-4328 4325 www.etasr.com allani et al.: fpga implementation of a robust mppt of a photovoltaic system using a fuzzy logic … mamdani method with max-min for the fuzzy combinations [11]. they are presented in table iii table iii. inference rules of the fuzzy controller e\de gn n z p gp gn z z gp gp gp n z z p p p z p z z z n p n n n z z gp gn gn gn z z iv. simulation of the solar conversion system the solar conversion system is composed of four photovoltaic panels connected in parallel, a buck converter and a dc load. to guarantee maximum power delivered by the photovoltaic generator, a control based on the fuzzy logic is implemented (based on ic). this has two inputs (the voltage and the current delivered by the gpv) and allows the estimation of the duty cycle used to control the chopper. the solar radiation varies between 600 and 1000w/m 2 , and the temperature is considered constant during the simulation. the radiation, the output power and the duty cycle are plotted in figure 8. it is worth noting that the duty cycle and the power vary according to the climatic conditions. we can notice the rapidity and the performance of the mppt against the variation of the radiation. the profiles of the output voltage, the current and the power are shown in figure 8. fig. 8. variation of duty cycle, power and radiation of the pv when the radiation changes from 600 to 800w/m 2 , our control increases the duty cycle from 0.31 to 0.38 and the power from 160 to 206w. when the radiation decreases from 1000 to 700w/m 2 , the power and the duty cycle also decrease. hence, they vary according to the radiation behavior. figure 9 describes the output power profiles of the photovoltaic generator and the dc-dc buck converter for a progressive variation of the radiation starting from 600 to 800, 1000, 700w/m 2 to the value of 900w/m 2 . we note that the tracking of the maximum power point is efficient and without oscillations. in addition, the efficiency is optimal and the performance of the photovoltaic generator is greater than 94%. the simulation results proved the robustness of the proposed mppt control against the variation of the solar radiation. in figure 10, the variations of the current and the voltage are proportional to the variation of the power. fig. 9. output power profiles of the photovoltaic generator and dc-dc buck converter. fig. 10. profile of the output current, voltage and power delivered by the pvg. figure 11 shows the simulation results of flc, ic, and p&o algorithms, where the flc is achieved with a fast response time and few oscillations. in terms of response time, the three algorithms gave the same rise time to optimal power during each sunshine variation. the oscillation around the mpp increased power losses and thus the efficiency of the pv system was reduced. the flc operates with fewer oscillations around the mpp. the power difference between the flc and the ic is about 3 and 6w compared to the p&o algorithm. v. simulation and implementation of the fuzzy logic controller on fpga researchers can increasingly optimize problems using suitable platforms. this work results from the need to investigate the fundamentals of electronic power control strategies, using fuzzy logic. in this section, we have to implement on the fpga a flc based on ic. it is applied to the photovoltaic conversion system. in some cases, the engineering, technology & applied science research vol. 9, no. 4, 2019, 4322-4328 4326 www.etasr.com allani et al.: fpga implementation of a robust mppt of a photovoltaic system using a fuzzy logic … characteristics and the performance of the real-time implementation unjustified and unsatisfied the calculation of some arithmetic operations. in addition, the wrong choice of values can sometimes exceed the overflow limits in the results and give incorrect values. for this, the fixed point representation was chosen. moreover, we must define by calculating the number of bits (m) which designate the integer part and the rest forms of the fractional part (n) [24]. fig. 11. profile of the output power delivered by the pvg with flc, ic, p&o and without mppt. for more precision and to have a synthesizable code able to be implemented in the fpga, it is necessary to change the data type to fixed point and to add the ieee-proposed library. table iv describes some functions used in the vhdl program. table iv. functions and data types used in the iee_proposed library library added to the ise functions and types of data ieee_proposed fixed_pkg_c.vhd fixed_float_types_c.vhd sfixed (m-1 downto n) ufixed (m-1 downto n) resize(fixed point resultat,m-1,-n) to_ufixed(std_logic_vector valeur, m-1,-n) to_sfixed(std_logic_vector valeur, m-1,-n) to_slv(fixed point value) a. architecture of the fuzzy logic controller mamdani’s implication is the most popular method dedicated for the flc [4-6]. the fuzzy rule of this method is expressed in (12): )]]2(),1(max[min[)( 21 xxy kk aac µµµ = (12) where k=1, 2… 25. the various processes of the fuzzy logic controller are described in the functional diagram presented in figure 12. the mamdani method facilitates the hardware implementation thanks to the simple min-max structure. an overview of the internal structure of the controller is given by the functional diagram in figure 12. indeed, the fuzzification of the two input variables provides the linguistic values and the corresponding membership functions (b1... b5) and (b11… b15). in fact, the connection of the pairs of antecedents in the rule structure is based on an operator logical and. then all the rules are associated with a max operation using the bloc max of the diagram. therefore, the weighted average method is considered as one of the defuzzification techniques, which is suitable for hardware implementation. considering that the output membership functions are usually symmetrical, the average of the fuzzy sets can be employed as weightings for the defuzzification process. in addition, this technique contains two arithmetic operations: multiplication processes with a constant and a single division process. fig. 12. functional diagram of the fuzzy logic control the inputs / outputs of the analog-to-digital converter adc and the analog-to-digital converter dac existing in the spartan 3e fpga board are represented by 12 bits. therefore, the size of the integer part and the decimal part of each input/output signal is chosen according to the actual value of the signal to be represented. for example, the input signals can be represented by a vector of 12 bits (m=7, n=5) because the value of the voltage cannot exceed the open circuit voltage which is equal to 92v. on the other hand, the output value varies between 0 and 1, thus, we have represented the duty cycle by 12 bits. for more precision, we chose to represent the decimal part by 10 bits. b. simulation results after having detailed our architecture, we have to simulate and implement it. the simulation results using the ise simulator are shown in figure 13. fig. 13. simulation results of the fuzzy logic controller after simulation, we notice that the output of the fuzzy logic controller d (duty cycle) tracked the variation of the input variables vpv (voltage) and ipv (current). in addition, the output pwm changes after any variation of the duty cycle d. the input variables vpv and ipv are represented by 12 bits: 7 bits for the integer number and 5 bits for the fractional number. thereby, the output variable d is designed by 12 bits: 2 bits of the integer number and 10 bits of the fractional one. table v shows the simulation results of flc inputs and outputs whose data are represented in real and hexadecimal numbers. engineering, technology & applied science research vol. 9, no. 4, 2019, 4322-4328 4327 www.etasr.com allani et al.: fpga implementation of a robust mppt of a photovoltaic system using a fuzzy logic … table v. simulation results of the inputs/outputs of the proposed controller ppv (w) vpv (v) ipv (a) d (real) d (hexa) 8,48 10.6 0.8 0.3339 156 92.46 40.2 2.3 0.3574 16e 195 60 3.25 0.3837 189 12.6 10.5 1.2 0.3466 163 241.2 67 3.6 0.373 17e c. rtl architecture of the proposed control the proposed architecture shown in figure 14 is a black box with inputs/outputs. the role of fuzzy logic is to process inputs and interpret them to give accurate outputs. this box is divided into different blocks that are interconnected with intermediate signals. the rtl architecture of the fuzzy logic controller obtained after the synthesis process by the xilinx synthesis technology (xst) is illustrated in figure 15. fig. 14. the behavioral description of the controller fig. 15. rtl architecture of the controller the flc's rtl architecture is divided into 7 blocks. the role of the first block (interface1_u) is the calculation of the controller inputs, the second block (fuzzify_u) plays the role of fuzzification. then, the (infer_u) block is dedicated to creating fuzzy rules. the (defuzz_u) block allows reconverting the fuzzy output to the crisp output. furthermore, the fpga board card generates a frequency of 50mhz whereas the duty cycle is generated at a frequency of 30khz. therefore, the (divider_cl) block acts as a frequency divider. indeed, the block (mux_d1) represents a flip-flop that puts the duty cycle to the controller output. the (mux_pwm) block is the intermediary between the control signal and the transistor component. d. synthesisrreport to verify the architecture of the proposed system, simulations were performed using the ise design suite, version 14.7. information about the device utilization, after the synthesis process are given in figure 16. the hardware resources used by the architecture of the proposed controller are negligible compared to the available ones on the chip. fig. 16. the synthesis report e. comparison and discussion having obtained the proposed controller simulation results in real time, it is important to verify and justify these results. thus, we compared the behavior of the fuzzy controller in both environments (matlab/simulink and ise) for the following values of input variables (solar radiation between 600 and 1000w/m 2 , temperature equal to 25°c) during 5s. we compared the results of simulation of the duty cycle presented in figure 8 and the values obtained in table v. figure 17 shows shows the coherent profile of the duty cycle carried out in both environments. fig. 17. comparison of the two simulation results. the duty cycle varied between 0.33 and 0.4 for the same variation of the solar radiation (from 600 to 1000w/m 2 ). it is optimally changed after the variation of the solar radiation to track a maximal power from the pv module. the effectiveness of this method is evaluated with different simulation studies under matlab/simulink and ise design suite. the proposed architecture of the mppt was proved to be effective. moreover, the output simulation by the ise design suite is approximately identical to the one carried out using matlab/simulink environment. this study shows that the fpga circuit can be used to develop a cost-effective and adaptable implementation of the mppt control. vi. conclusion the difficulties and the non-linearity of pv systems are influenced by the solar radiation and the temperature conditions, resulting in power losses and reduced efficiency. in the present paper, we developed a pvg controlled by a fuzzy logic control based on the incremental and the conductance using matlab/simulink environment. the proposed mppt algorithm was compared with the traditional methods for nonlinear systems (p&o and ic). the conventional p&o and ic algorithms work with accepted time responses, minimization of maximum power, and more oscillations, which reduce the overall efficiency of the pv system. the proposed flc has reduced these disadvantages according to different values of solar radiation. the simulation results indicated that engineering, technology & applied science research vol. 9, no. 4, 2019, 4322-4328 4328 www.etasr.com allani et al.: fpga implementation of a robust mppt of a photovoltaic system using a fuzzy logic … the control with flc is more efficient than the traditional methods. it has the advantage of reducing the disturbances when the pvg reaches its maximum power and as a result, the performance of the photovoltaic installation has been optimized. on the other hand, to reach a fast response time and to take into account the time constraints, we adopted a functional diagram to facilitate the vhdl programming and to make this control executable in real time. thereby, the fuzzy logic controller based on the incremental and the conductance was developed and simulated in vhdl. the comparison of both results showed that the output parameters (duty cycle) reach all variations of the input parameters (voltage and current) of the gpv. therefore, this study showed that the proposed architecture was an adequate solution for a real-time implementation. the implementation of flc on fpga increases the efficiency of mppt control systems. in future works, we aim to apply the proposed strategy to other energy applications. nomenclature pvg photovoltaic generator fpga vhsic hardware description language i output current of the pvg iph photocurrent of the solar panel io photovoltaic reserve saturation current diode a ideality factor k boltzmann constant ki temperature coefficient in current t temperature tref reference temperature q elementary charge in coulomb g irradiance gref reference irradiance egap the energy gap references [1] a. kane, v. verma, b. singh, “optimization of thermoelectric cooling technology for an active cooling of photovoltaic panel”, renewable and sustainable energy reviews , vol. 75, pp. 1295-1305, 2017 [2] s. s. chandel, t. agarwal, “review of cooling techniques using phase change materials for enhancing efficiency of photovoltaic power systems”, renewable and sustainable energy reviews, vol. 73, pp. 1342-1351, 2017 [3] s. selvan, p. nair, umayal, “a review on photo voltaic mppt algorithms”, international journal of electrical and computer engineering, vol. 6, no. 2, pp. 567-582, 2016 [4] l. w. chong, y. w. wong, k. r. rajkumar, k. r. rajkumar, d. isa, “hybrid energy storage systems and control strategies for stand-alone renewable energy power systems”, renewable and sustainable energy reviews, vol. 66, pp. 174-189, 2016 [5] a. h. fathima, k. palanisamy, “optimization in microgrids with hybrid energy systems–a review”, renewable and sustainable energy reviews, vol. 45, pp. 431-446, 2015 [6] a. loukriz, m. haddadi, s. messalti, “simulation and experimental design of a new advanced variable step size incremental conductance mppt algorithm for pv systems”, isa transactions, vol. 62, pp. 30-38, 2016 [7] f. baghdadi, k. mohammedi, s. diaf, o. behar, “feasibility study and energy conversion analysis of stand-alone hybrid renewable energy system”, energy conversion and management, vol. 105, pp. 471-479, 2015 [8] a. mahesh, k. s. sandhu, “hybrid wind/photovoltaic energy system developments: critical review and findings”, renewable and sustainable energy reviews, vol. 52, pp. 1135-1147, 2015 [9] s. messalti, a. harrag, a. loukriz, “a new variable step size neural networks mppt controller: review, simulation and hardware implementation”, renewable and sustainable energy reviews, vol. 68, no. 1, pp. 221-233, 2017 [10] a. jouda, f. elyes, a. rabhi, a. mami, “optimization of scaling factors of fuzzy–mppt controller for stand-alone photovoltaic system by particle swarm optimization”, energy procedia, vol. 111, pp. 954-963, 2016 [11] h. othmani, d. mezghani, a. belaid, a. mami, “new approach of incremental conductance algorithm for maximum power point tracking based on fuzzy logic”, international journal of grid and distributed computing, vol. 9, no. 7, pp. 121-132, 2016 [12] w. dengsheng, w. lidi, h. chuncheng, l. tong, z. chenglong, l. chenyang, “research and design of pv mppt based on stm32”, chinese control and decision conference, shenyang, china, june 9-11, 2018 [13] m. farhat, o. barambones, l. sbita, “efficiency optimization of a dspbased standalone pv system using a stable single input fuzzy logic controller”, renewable and sustainable energy reviews, vol. 49, pp. 907-920, 2015 [14] m. ricco, p. manganiello, e. monmasson, g. petrone, g. spagnuolo, “fpga-based implementation of dual kalman filter for pv mppt applications”, ieee transactions on industrial informatics, vol. 13, νο. 1, pp. 176-185, 2017 [15] m. f. n. zolkifli, m. s. robian, s. saon, a. k. mahamad, “fpga based maximum power point tracking of photovoltaic system using anfis controller”, arpn journal of engineering and applied sciences, vol. 11, no. 8, pp. 5094-5097, 2016 [16] m. jomaa, m. y. allani, f. tadeo, a. mami, “design and control of the hybrid system pv-wind connected to the dc load”, 9th international renewable energy congress, hammamet, tunisia, march 20-22, 2018 [17] m. y. allani, m. jomaa, d. mezghani, a. mami, “modelling and simulation of the hybrid system pv-wind with matlab/simulink”, 9th international renewable energy congress, hammamet, tunisia, march 20-22, 2018 [18] m. a. jaballah, d. mezghani, a. mami, “design and simulation of robust controllers for power electronic converters used in new energy architecture for a (pvg)/ (wtg) hybrid system”, international journal of advanced computer science and applications, vol. 8, no. 5, pp. 244-255, 2017 [19] z. asma, d. karim, d. tarak, “maximum power point tracking of photovoltaic systems based on fast terminal sliding mode controller”, international journal of renewable energy research, vol. 6, no. 4, pp. 1435-1445, 2016 [20] j. jana, h. samanta, k. d. bhattacharya, h. saha, “design and development of high efficiency five stage battery charge controller with improved mppt performance for solar pv systems”, international journal of renewable energy research, vol. 8, no. 2, pp. 941-953, 2018 [21] b. benlahbib, n. bouarroudj, s. mekhilef, t. abdelkrim, a. lakhdari, f. bouchafaa, “a fuzzy logic controller absed on maximum power point tracking algorithm for partially shaded pv array-experimental validation”, electronika ir electrotechnika, vol. 24, no. 4, pp. 38-44, 2018 [22] j. lee, y. s. kim, “sensorless fuzzy-logic-based maximum power point tracking control for a small-scale wind power generation systems with a switched-mode rectifier”, iet renewable power generation, vol. 10, no. 2, pp. 194-202, 2016 [23] a. g. a. gizi, s. a. chlaihawi, m. louzazni, a. craciunescu, “genetically optimization of an asymmetrical fuzzy logic based photovoltaic maximum power point tracking controller”, advances in electrical and computer engineering, vol. 17, no. 4, pp. 69-76, 2017 microsoft word 23-2736_s1_etasr_v9_n3_pp4196-4199 engineering, technology & applied science research vol. 9, no. 3, 2019, 4196-4199 4196 www.etasr.com alorifi et al.: the analysis and detection of a target gas system based on tdlas & labview analysis and detection of a target gas system based on tdlas & labview fawzi alorifi electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university (imsiu), riyadh, saudi arabia fsorifi@imamu.edu.sa sidi m. ahmed ghaly electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university (imsiu), riyadh, saudi arabia smghaly@imamu.edu.sa mohamed y. shalaby electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university (imsiu), riyadh, saudi arabia myshalaby@imamu.edu.sa mohamed asad ali electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university (imsiu), riyadh, saudi arabia asadali@imamu.edu.sa mohammad obaidullah khan electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university (imsiu), riyadh, saudi arabia okkhan@imamu.edu.sa abstract—this paper introduces detection techniques of target gas concentration based on infrared absorption spectrum method and the simulation of the gas detection system using labview. in this work, the harmonic detection is performed by wavelength modulation technique with a related frequency signal to cover the measured signal and get the gas absorption coefficient that can be analysed to give a gas concentration. a series of simulations are carried out to scan weak absorption lines and extract the second harmonic curve of the absorption spectrum of the target gas. the absorption and second harmonic curves are acquired by changing the parameters of the target gas concentration and line width. this work claims to be a contribution to the study and the comprehension of gas detection system based on tunable diode laser absorption spectroscopy and can serve as a basis for practical data acquisition. keywords-infrared absorption spectrum; simulation system; second harmonic; phase-locked amplifier; tdlas; labview i. introduction tunable diode laser absorption spectroscopy (tdlas) [1, 2] is used to trace atmospheric constituent gases even with small concentrations as low as sub parts per billion (ppbv). the tunable diode laser source emits laser in mid infrared spectral region and has wavelengths from 3µm to 30µm. by adjusting laser conditions, temperature or injection current, the output wavelength can be tuned even continuously in small intervals. many trace gases strongly absorb the infrared spectrum. tunable diode laser (tdl) has a line width of 10 -4 to 10 -5 cm -1 range. these conditions result in high resolution and have high selectivity. second harmonic detection [3] is employed by using a modulation waveform in khz frequency domain, this is simultaneously superimposed on the diode laser scanning current. a lock amplifier is used to detect the resultant frequency–modulated absorption. in this research the spectrum modulation method is chosen since the direct absorption method [4, 5] provides a very weak signal. the use of wavelength modulation spectroscopy (wms) can clearly diminish the noise produced by the laser control and highly improve snr. the injection current in the system is varied simultaneously with the output wavelength characteristic of tdl. the superimposition of the high-frequency sinusoidal current and the low-frequency sawtooth can drive the output wavelength scanning around the center wavelength of the laser. realizing the wavelength modulation spectroscopy, the second harmonic and the absorption curves can be detected by the phase locked amplifier. overall, this work which includes both theoretical aspects and simulations, claims to be a contribution to the study and understanding of gas detection in the infrared absorption spectrum ii. target gas detection based on lambert-beer law, the harmonic detection method has a high sensitivity, high resolution, and fastresponse trace gas detection [1, 5]. near-infrared distributed feedback (dfb) semiconductor laser light source has a narrow bandwidth and rapid tuning characteristics. the detection of the gas concentration is done by detecting an isolated absorption line of the target gas. the applied light source spectrum contains the wavelength range of one or more gas absorption lines, when the light passes through the gas, attenuation occurs. the lambert-beer law is expressed by (1): ( )0i i exp clα= − (1) where i is the transmission line intensity absorbed by the gas, iₒ is the incident light intensity, α is the gas absorption coefficient, c is the gas concentration, and l is the length of light through gas. corresponding author: sidi m. ahmed ghaly engineering, technology & applied science research vol. 9, no. 3, 2019, 4196-4199 4197 www.etasr.com alorifi et al.: the analysis and detection of a target gas system based on tdlas & labview at atmospheric pressure the molecular absorption line broadening is mainly pressure broadening, the linear absorption coefficient α can be approximated by the lorentz law: �� � �ₒ�� � �ₒ���ₒ ������ₒ� � � (2) where nₒ is the number of molecules per unit volume at 25° under atmospheric pressure. nₒ=2.6875 x 10 19 , σ(v)=cross section, =wave number, ₒ =wave number at maximum absorption intensity, and γ=half width at half maximum (hwhm). the detection system involves harmonic detection modeled and elaborated in the next section. iii. implementation and modeling a. labview based detection system the target gas detection system has been implemented and simulated using labview (laboratory virtual instrument engineering workbench) which is a system-design platform and development environment. it is a graphical programming language which uses graphical user interface. it is simple and user friendly, a user can select a block from its function library and define the parameters, inputs and outputs and model a system. subprograms can be defined as sub-vi, these sub-vi’s can be connected at any stage, added, removed, varied and adjusted or modified as per the system modeled tested and remodeled according to task parameters changes with time and requirement. labview integrates the creation of user interfaces (termed front panels) into the development cycle. labview programs-subroutines are termed as virtual instruments (vis). each vi has three components: a block diagram, a front panel, and a connector panel. the last is used to represent the vi in the block diagrams of other, calling vis. the front panel is built using controls and indicators. controls are inputs: they allow a user to supply information to the vi. indicators are outputs: they indicate, or display, the results based on the inputs given to the vi. the back panel, which is a block diagram, contains the graphical source code. all the objects placed on the front panel will appear on the back panel as terminals. the back panel also contains structures and functions which perform operations on controls and supply data to indicators. collectively controls, indicators, structures, and functions are referred to as nodes. nodes are connected to one another using wires, e.g. two controls and an indicator can be wired to the addition function so that the indicator displays the sum of the two controls. thus a virtual instrument can be run as either a program, with the front panel serving as a user interface, or, when dropped as a node onto the block diagram, the front panel defines the inputs and outputs for the node through the connector panel. this implies each vi can be easily tested before being embedded as a subroutine into a larger program. the labview apart from providing programming can easily be integrated to direct hardware without any interface programming or special requirement by using the dac (data acquiring and controlling) assistant to different interfacing boards [14,15]. a thorough analysis of gas chamber parameters can be done by labview while a change with other parameters for say concentration and target gases can get the results for second harmonic and absorption curves. an analysis for different ramp laser light range can be done to get different target gases. different modulation coefficients can be adjusted to get weak signals and a thorough analysis can be done. a typical frame of the model for detection of target gas using labview is illustrated in figure 1. fig. 1. a typical frame of a virtual system for target gas detection on labview platform this model works on harmonic detection technique. wavelength modulation and second harmonic signal detection (2f) are both used in harmonic detection [6] to achieve highly sensitive target gas detection. the wavelength modulation of absorption spectra can produce a harmonic signal which is directly proportional to the concentration of trace gases. this is called zero background spectrum detection technique [3, 4]. to produce the harmonic signal by wavelength modulation a cosine modulation of angular frequency ω is superimposed on laser (sawtoth) which results in time varying laser frequency that can be given by: ( )                               cv v acos tω= + (3) where v is the instantaneous frequency of the laser wavelength, vc is the center frequency of laser modulation, and a is the modulation depth. the wavelength of the laser output is a modulated cosine, then the signal generated by passing laser through the gas is a periodic even function which can be expanded in a cosine fourier series as expressed in (4): ! � ∑ #$�vc cos �$%& '()* (4) where hn is the nth harmonic component of the modulated absorption coefficient. if the absorption coefficient ⍺ is sufficiently small, hn can be approximated to hn ∝ iₒ⍺lc the above harmonic components are proportional to the gas concentration and the amplitude of each harmonic decreases when the number of harmonics increases. low harmonic is chosen to obtain higher snr and by using a lock in amplifier a harmonic component can be selected. b. typical principle model of harmonic detection a typical schematic block diagram of wavelength modulation is illustrated in figure 2. engineering, technology & applied science research vol. 9, no. 3, 2019, 4196-4199 4198 www.etasr.com alorifi et al.: the analysis and detection of a target gas system based on tdlas & labview fig. 2. schematic model of wavelength modulation spectroscopy in the gas concentration system, the received laser signal is not unlimited and the component of the harmonic signal is weak. the band pass filter method can filter out the white noise. this means that the width of the filter is very thin, which is not good because the quality factor q is generally less than 100. consequently, the curve of the amplitude-frequency characteristic is not smooth enough and varies nonlinearly in the pass-band [7]. lock-in amplifier method is used instead to remove the external noise and extract a high-precision harmonic signal. the basic principles of the lock-in amplifier are performed by wavelength modulation like sinusoidal modulation with a related frequency signal and the signal is scanned to cover the measured signal. the modulation frequency is taken as a reference signal to the input into the locked-in amplifier. the locked-in amplifier technique extracts the harmonics signals at the same frequency, gives good performance in terms of density signal extraction, and improves significantly the detection snr for weak signals [8]. as illustrated in figure 2, an analog locked-in amplifier is used in the detection of trace signals because the error of harmonic amplitude signal extracted is smaller [9]. with the new dsp technology [10-12], a digital lock-in amplifier is used which can convert analog to digital signals. the center frequency of light output is accurately locked on the gas absorption peak. that means v0=vc. the detected signal can be obtained as: i=i0-1 / $01$%& 2 ⍺*34 ��5�67(�58] (5) where % � �9 :� , i0 is the input signal amplitude, n is the light intensity coefficient, c is the measured gas concentration, l is the effective optical path, ; is the frequency modulation amplitude and < is hwhm. equation (5) can be expanded into a fourier series sequence, since the higher harmonics’ amplitude is too small to be ignored. the second harmonic coefficients are shown in (6): i2f=2 =-=�5�>=���5� ?.ab 5����5� ?.a ⍺ₒcdeₒ (6) from (6) it is inferred that the amplitude of the second harmonic signal intensity is related to the initial gas concentration. thus, by extracting the second harmonic signal, gas concentration information can be retrieved. the locked-in amplifier method has the advantages of minor measurement error, big dynamic range, and no temperature bias effects [11]. iv. simulation results and discussion the detection system is characterized by initial characteristics [16] such as the optical path with a length of l, the incident intensity i0, the width of line ∆v, and the target gas concentration c. the values of these parameters are: i0=100cd and c value is changed from 10% to 100%. the line width ∆v is changed from 0.01 to 0.09 and l=15m. figure 3 illustrates the simulation of the spectrum of gas absorption in terms of the scanning frequency. figure 4 shows the second harmonic wave of the emission output intensity in terms of scanning frequency. fig. 3. absorption curve vs concentration of the target gas specimen fig. 4. second harmonic wave vs concentration of the target gas specimen it can be observed that the target gas absorption amplitude and the second harmonic depend on gas concentration. figure 5 shows that the gas concentration is proportional to the absorption peak values. as the concentration of gas gets smaller, the output intensity of the laser beam gets higher and the degree of absorption of the optical chamber decreases. in figure 6 the concentration of the gas is exhibited as proportional to the peak values of the second harmonics. as the gas concentration gets higher, the value of the second harmonic peak gets higher also. as the concentration gets higher, the probability of detecting the gas increases. similarly, the values of the other initial detection system parameters can similarly affect the gas absorption curve and the second harmonic wave. figure 6 depicts that by varying the value of the modulation coefficient ∆v over an interval of 0.01 to 0.09, and as the line width increases the broadening coefficient collision ϒ gets larger and the peak curve becomes stout and the absorption peak height gets smaller. figure 7 shows that as the line width increases the broadening coefficient collision ϒ gets larger, this includes the peak curve becoming stout and then the i2f peak height gets smaller. as the line width increases the band width increases. due to this effect the curve becomes of less height (amplitude) in value and more wide (bandwidth increases with frequency range). this is an advantage when the target gas has narrow spectra. the line width can be increased, the frequency range will be broader and then the target gas spectra can be easily detected. engineering, technology & applied science research vol. 9, no. 3, 2019, 4196-4199 4199 www.etasr.com alorifi et al.: the analysis and detection of a target gas system based on tdlas & labview fig. 5. peaks of absorption and second harmonic curves vs concentration of the target gas specimen fig. 6. peaks of absorption curves vs line width fig. 7. peaks of bandwidth and second harmonic curves vs line width v. conclusion and future scope this paper provides a detection method of the target gas modulated weak signal, by which concentration levels can be determined for different gases. labview simulation and analysis illustrated that the superimposition of the high frequency sinusoidal current and the low frequency saw-tooth current can provide the tuning of output wavelength around the central frequency and then the second harmonic and the absorption curves are detected by the phase locked amplifier that is proportional to the gas concentration within a certain range. the developed model and analysis can be thought of as a basis for practical gas detection systems and can also be applied for magnetic resonance imaging systems or other areas of spectroscopy. acknowledgment the authors would like to thank the deanship of academic research at al imam mohammad ibn saud islamic university for the financial support of this project. references [1] l. shuqin, the analysis and detection system of co2 gas based on tdlas, harbin industrial university, 2013 (in chinese) [2] l. ning, w. fei, y. jianhua, m. zengyi, c. kefa, “gas concentration measuremen based on tunable semiconductor laser absorption spectrum technology”, proceedings of the csee, vol. 25, no. 15, pp. 121-126, 2005 [3] j. l. han, l. jianguo, y. b. he, j. f. he, l. yau, z. yu, j. ying, s. yuan, r. f. kan, “simulation and analysis of second harmonic signal of the tunable diode laser absorption spectroscopy”, spectroscopy and spectral analysis, vol. 33, no. 4, pp. 881-885, 2013 (in chinese) [4] g. lijun, research on methane detection based on the principle of near infrared absorption, hebei yanshan university, 2008 (in chinese) [5] s. hui, multi-component gas analyzer based on infrared absorption theory, harbin industrial university, 2009 (in chinese) [6] l. tongxing, l. yiqun, the principle and application of laser spectroscopy, anhui university of science and technology of china press, 2006 (in chinese) [7] x. f. nan, y. zhang, m. yu, “laser gas telemetry test system automation test software design”, optical instruments, vol. 37, no. 3, pp. 210-213, 2016 [8] m. l. cong, d. d. sun, y. d. wang, “application of logarithmic transformation-wavelength modulation spectroscopy in gas detection”, infrared and laser engineering, vol. 46, no. 2, pp. 1-6, 2017 [9] a. de marcellis, g. ferri, a. d’amico, c. di natale, e. martinelli, “a fully-analog lock-in amplifier with automatic phase alignment for accurate measurements of ppb gas concentrations”, ieee sensors journal, vol. 12, no. 5, pp. 1377-1383, 2012 [10] s. m. ahmed ghaly, s. s. al-sowayan, “a high b1 field homogeneity generation using free element elliptical four-coil system”, american journal of applied sciences, vol. 11, no. 4, pp. 534-540, 2014 [11] s. m. ahmed ghaly, k. a. al-snaie, s. s. al-sowayan, “design and testing of radiofrequency spherical four coils”, modern applied science jounal, vol. 10, no. 5, pp. 186-193, 2016 [12] s. m. ahmed ghaly, k. a. al-snaie, o. k. mohammad, “spherical and improved helmholtz coil with high b1 homogeneity for magnetic resonance imaging”, american journal of applied sciences, vol. 13, no. 12, pp. 1413-1418. 2016 [13] h. f. liu, b. li, q. x. he, j. m. dang, h. y. yu, z. t. zheng, y. d. wang, j. q. pan, “development of digital orthogonal lock-in amplifier and its application in methane detection”, acta photonica sinica, vol. 45, no. 4, pp. 0423004-1 0423004-6, 2016 (in chinese) [14] c. j. kalkman, “labview a software system for data acquisition, data analysis, and instrument control”, journal of clinical monitoring, vol. 11, no. 1, pp. 51-58, 1995 [15] a. gani, m. j. e. salami, “a labview based data acquisition system for vibration monitoring and analysis”, student conference on research and development, shah alam, malaysia, july 17, 2002 [16] y. huo, w. fan, “application of harmonic detection technology in methane telemetry”, journal of physics: conference series, vol. 887, articleid 012020, 2017 engineering, technology & applied science research vol. 7, no. 2, 2017, 1540-1545 1540 www.etasr.com daeipour et al.: evaluation of the acoustic properties of wood-plastic-chalk composites evaluation of the acoustic properties of woodplastic-chalk composites zahra daeipour wood and paper science dpt islamic azad university karaj karaj, iran vahid safdari wood and paper science dpt islamic azad university karaj karaj, iran amir nurbakhsh wood and paper science dpt research institute of forests and rangelands (rifr), tehran, iran abstract—wood-plastic composites are a new group of materials that can be used in construction instead of wood and plastic. they are used in various industries due to features such as sound and water absorption, among others. this article aims to study the acoustic properties of wood-plastic composites made of wood flour, low-density polyethylene, and chalk. in this study, 6 combinations were made with different material percentages. acoustic tests were performed for frequency ranges of 125, 250, 500, 1000, and 2000 hz. the results of this study showed that the maximum amount of sound absorption was observed at a frequency of 2000 onwards. at the frequency of 25 to 2000, no remarkable change in sound absorption was recorded. at the 2000 to upper frequencies, one of the samples displayed the maximum amount of sound absorption. in terms of water absorption, a significant variation was reported in three samples with passing time (2, 24, 48 and 72 hours). keywords-wood-plastic composites; low-density polyethylene; chalk, poplar wood; maleic anhydrite polyethylene; sound absorption. i. introduction to cope with noise pollution, materials such as rock wool, glass wool, and asbestos were used as sound-absorbers in past decades. these materials are harmful both for manufacturers and for consumers and could endanger human health [1, 2]. moreover, pure chalk panels, which are used a lot in construction, have a small sound absorption coefficient. in fact, the sound is reflected by them. researchers have recently suggested the use of natural lignocellulosic materials in the manufacture of sound absorbing composites. hemp is a lignocellulosic material whose wastes can be used in the construction of sound-absorbing panels [3-5]. such materials can be used in interior and exterior areas. in general, the main markets of this material include the automotive industry, military industry, urban furniture, and construction services. some of the products that are made with these compounds are internal components of cars, office and home furniture, kitchen cabinets, railings and flooring, acoustic insulation, window and door frames, skate boards, lumber and prefabricated roofing boards, boxes and pallets of cargo, containers, etc. the products have some nice features such as dimensional stability, resistance to water absorption, low thickness swelling, resistance to decay due to lack of water absorption, high thermal expansion coefficient, high elastic modulus, low combustion speed, very good thermal properties, high compressive strength, recyclability, etc. wide ranges of polymers such as polypropylene, polyethylene, polyvinyl chloride and so on are used in the manufacture of wood-plastic composites. composites made with natural fibers have grown increasingly in a variety of industrial applications due to high resistance to weight ratio, low volumetric mass, low cost, and easy processing as well as being inexpensive and biodegradable. lignocellulosic materials are used in the manufacture of wood-plastic composites as natural fillers and reinforcements in the form of powder or fibers [6]. environmental compatibility, recyclability, and low cost are factors that result to the growing application of natural fillers. the lack of good adhesion between the surfaces of fibers and polyme is one of the main disadvantages of using lignocellulosic fibers in wood-plastic composites because it reduces the final product features. poor adhesion of reinforcements with polymer causes weak distribution reinforcements in molten thermoplastic materials; it creates weak intermediate phase between the reinforcements and matrix. both factors have great impact on physical and mechanical characteristics of composites. reinforcements must make a strong connection with the polymer to be effective. the bonding agents are used to increase affinity of reinforcements with polymer. bonding agents are substances with one nonpolarized end and one polarized end. thus, they act as a bridge between polarized reinforcements and non-polarized polymers. isocyanates alkoxy silanes and anhydrides such as phthalic anhydride and maleic anhydride are important connector factors [7]. the main purpose of the production of composite products with minerals connector is the combination of organic particles such as wood and lignocellulosic materials with mineral connectors such as cement, chalk, magnesite, etc. other fibers such as fiberglass resistant to alkalis can be used in this process. in addition, other inorganic materials such as gravel, sand, and perlite can also be used. the main fibers in the composition of the panel may be on a regular basis (arrow) or random mode. woodchalk was produced for the first time in scandinavia by the semi-dry method. this method has advantages because it makes the use of industrial chalk possible in the production process; this chalk may be achieved engineering, technology & applied science research vol. 7, no. 2, 2017, 1540-1545 1541 www.etasr.com daeipour et al.: evaluation of the acoustic properties of wood-plastic-chalk composites by various chemical processes. in general, there are two main sources to obtain chalk: natural plants and industrial boilers’ flue gases. the chalk available in exhaust gasses is created from entering chalk into the combustion process to reduce the emissions of sulfur dioxide. the modulus of rupture of wood chalk is generally higher than chalk-reinforced fiber or woodplastic; it is also lower than wood-cement or boards that have been produced using synthetic adhesives. reinforced chalk panels, which are produced with a density of 1000 to 1200 kg/m3 and with smooth and adjustable surfaces, have suitable properties for structural purposes. the stability of these products and their resistance to fire and biological agents are high; they have high thermal and sound insulation features. for interior purposes while emissions of formaldehyde gas is of utmost importance, panels with mineral fasteners have wide application as they are used for flooring, inner lining walls, ceilings, and separating walls (partitions). in comparison to wood-base panels, wood-chalk has better linear stability and represents better performance than other composite boards when it is exposed to fire. ii. research background in [8], authors studied high-density polyethylene-based composites and rice husk flour with 4 loading levels 2, 2, 4, and 6 phr. the results showed that crystallization temperature, enthalpy of crystallization and crystallization level increase with increasing nanoclay to 2 phr; then, it reduces. composites will improve by with the addition of nano storage fillers and losing modulus. x-ray diffraction patterns revealed the formation of the central composite. moreover, morphological findings showed that samples containing 2-phr nanoclay have regular formation. it seems that a full morphological cutting can be made by increasing maleic anhydride polyethylene coupling agent. therefore, thermal and rheological properties of composites of rice husk with high-density polyethylene have been improved by increasing the amount of maleic anhydride polyethylene. in [9], authors investigated the impact of adding compatibilizers on mechanical properties of polypropylene and wood flour. they concluded that the weakness of mechanical properties of unmodified composites is due to weak connections between the polymeric matrix and wood fibers; tensile modulus, tensile strength, and impact resistance increase with addition of linked maleic anhydride with polypropylene. in [10], high-density polyethylene and polypropylene grafted with maleic anhydride was used to make composites containing wood chips. the results showed that the use of maleic anhydride leads to better fiber wetting by the matrix; it increases adhesion at the interface between matrix and fibers. in order to evaluate mechanical properties of polypropylene and poplar wood fibers, authors in [11] prepared a sample with 0, 30, 40, 50, 60 percent fiber weight, and 2 percent maleic ayndryd grafted with polypropylene. in [12], the humidity properties of wood-plastic composites made of poplarpolypropylene fiber were discussed. pure polypropylene is regarded as control samples; the produced samples were made of 4 variable level of 30, 40, 50, 60% fibers, 3% maleic anhydride, and zero maleic anhydride. in [13], authors reviewed the mechanical properties of composites made from recycled high-density polyethylene and laminated poplar. they concluded that tensile strength of these composites improves by increase in fiber. thus, development of composites containing natural fibers and recycled plastic is an opportunity to use an abundant natural substance and a new method for reducing the serious problem of plastic wastes. in [14], authors examined the dimensional stability and mechanical behavior of woodplastic composites made based on high-density recycling polyethylene. this research examined dimensional stability, mechanical properties, and microscopic structure of composites. with the addition of maleic anhydride polypropylene at levels 3 to 5 wt percentage to the composite, a significance improvement is observed in dimensional stability and mechanical properties of composites. microscopic analyses of the fracture surface of maleic anhydride-modified polypropylene composites confirm improvement in binding of the molecular chain. in [15], authors conducted a research about the dimensional stability of composites made of fiber of old papers and thermo-mechanical pulp and paper (pp). the results showed that alkylation of fiber and the use of coupling auxiliaries increases dimensional stability of the wood composites or wood pp fiber. iii. materials and methods a. materials and equipment raw materials used for the research are poplar wood, lowdensity polyethylene, chalk powder, and malic anhydride polyethylene. the list of devices and equipment used in the project are stated in table i. table i. devices and equipment used in the project, along with their properties general properties device name speed: 70 rpm temperature 140 to 165 °c made in germany 1990 brand: collin non-collimator 2-screw extruder choline made in germany 1989 brand: wieser semi-industrial mill temperature capability: 150, 155, 160, 170 ° c. load speed: 60 cooling temperature: ambient temperature made in iran 1997 brand: iman machine 125-grams injection machine has 2 jaw temperature capability: 200 ° c curing presses (blister) b. research variables and samples six samples were prepared in this research. the percentage of components is shown in table ii. 800 grams raw material has been used for each combination. six combinations were made of different percentages of wood, low-density polyethylene, and chalk. in the first three combinations, the fixed amount of low-density polyethylene was 50 percent, compatibilizer amount was 0 percent, and the amounts of poplar wood flour and chalk varied (with the decrease in the percentage of wood, application of chalk increases). the amount of chalk is zero in the control sample; then it reaches to 5 and 10 percent. in the next three combinations, the fixed amount of low-density polyethylene is 47 percent, engineering, technology & applied science research vol. 7, no. 2, 2017, 1540-1545 1542 www.etasr.com daeipour et al.: evaluation of the acoustic properties of wood-plastic-chalk composites compatibilizer amount is 3 percent, and the amounts of poplar wood flour and chalk varied (with the decrease in the percentage of wood, application of chalk increases). the amount of chalk is zero in the control sample; then it reaches to 5 and 10 percent. c. the process of mixing and preparing boards low-density polyethylene, maleic anhydride polyethylene coupling agent, poplar wood flour and, chalk 2 are mixed in 2screw extruder with a speed of 50 rpm for 10 minutes at 180 ° c. then, rod-shaped pasty mixture exits from the the mixer, kept in cool water, and converts to granule. granules are dried at 105 °c for 24 hours (figure 1). finally, boards are prepared from granules by molding at a temperature of 175 ° c and a pressure of 10 mpa. table ii. percentage of components chalk (wt %) variable value compatibilizer (wt %) fixed value lowdensity polyethylene, (wt %) fixed value wood flour (wt %) variable value sample 0% (-) 5% (40 grams) 10% (80 grams) 0% (-) 0% (-) 0% (-) 50% (400grams) 50% (400grams) 50% (400grams) 50% (400grams) 45% (360 grams) 40% (320 grams) 1 2 3 0% (-) 5% (40 grams) 10% (80 grams) 3% (25 grams) 3% (25 grams) 3% (25 grams) 47% (375 grams) 47% (375 grams) 47% (375 grams) 50% (400grams 45% (360 grams) 40% (320 grams) 4 5 6 iv. research findings a. measuring sound absorption coefficient of samples in order to test sound absorption, two discs of each sample (one with a diameter of 100 mm and another with a diameter of 30 mm) are prepared. the prepared samples are transferred to physics laboratory to measure sound absorption coefficients. standard iso-10534-1 is used to measure the adsorption coefficient of sound. absorption coefficients of the boards are measured using standing waves device (standing waves tube method) by software cool edit. moreover, acoustic test is performed with a frequency range of 125, 250, 500, 1000 and 2000 hz (figure 2). b. test measuring sound absorption coefficient of samples first, the sample is placed inside an impedance tube. one side of the tube is a loudspeaker that is connected to the signal generator. another side of the tube is stalemate; thus, a standing wave is formed inside the tube. there are an incident wave and a reflected wave in; indentations and protrusions were found on the standing wave. indentations represent decrease in the domain of signal and protrusions show increase in the domain of signal (figure 3). a microphone placed inside the tube to discover indentations and protrusions. in fact, microphone is moved inside the tube; the microphone shows maximum and minimum pressures. the maximum and minimum can be read from the analyzer; finding maximum and minimum, we can calculate absorption coefficient as follows: n=( a+b)/(a-b) α= 4n/(1+n)2 where a=energy radiated, b=reflected energy, a+b=protrusions, b=indentations, α=sound absorption coefficient. fig. 1. granules obtained from sample preparation fig. 2. samples used in acoustic testing (left) and press machine for constructing the acoustic samples (right) fig. 3. measuring instrument for sound absorption. engineering, technology & applied science research vol. 7, no. 2, 2017, 1540-1545 1543 www.etasr.com daeipour et al.: evaluation of the acoustic properties of wood-plastic-chalk composites c. statistical analysis analysis of the results is performed in a completely randomized design and factorial analysis using the two-factor anova by spss software. then, averages are compared by lsd post hoc test with 95% confidence level. 1) descriptive statistics of the amount of water absorption the results of this test showed that water absorption after 72 hours after testing samples is significant. moreover, the maximum amount of water absorption belongs to the sample 4 and minimum amount of water absorption belongs to sample 3 (table iii and figure 4). fig. 4. the results of water absorption table iii. statistical indices describing the amount of water absorbed by the sample time (hours) sample minimum (%) maximum (%) average (%) standard deviation 1 0.0026 0.0027 0.0026 0.0000 2 0.0025 0.0026 0.0025 0.0000 3 0.0025 0.0026 0.0025 0.0000 4 0.0026 0.0052 0.003 0.0014 5 0.0025 0.0025 0.0025 0.0000 2 6 0.0025 0.0049 0.0032 0.0013 1 0.0105 0.0107 0.0106 0.0000 2 0.0051 0.0079 0.0068 0.0015 3 0.0101 0.0129 0.0118 0.0015 4 0.0103 0.0207 0.0138 0.0059 5 0.0025 0.0102 0.0059 0.0038 24 6 0.0075 0.0149 0.0107 0.0037 1 0.0079 0.0107 0.0097 0.0015 2 0.0076 0.0132 0.0103 0.0028 3 0.0075 0.0151 0.0109 0.0038 4 0.0103 0.0105 0.0103 0.0001 5 0.0076 0.0127 0.0109 0.0029 48 6 0.0098 0.0100 0.0099 0.000 1 0.0160 0.0238 0.0185 0.0042 2 0.0127 0.0203 0.0171 0.0039 3 0.0075 0.0283 0.0152 0.0113 4 0.0205 0.159 0.0747 0.0744 5 0.0101 0.0152 0.0135 0.0029 72 6 0.0050 0.1163 0.0445 0.0622 2) statistical indices describing sound absorption of samples at different frequencies the results of this test showed that the highest sound absorption is observed at frequency 2000 onwards. at the frequency of 25 to 2000, there was not a remarkable change in sound absorption. at the 2000 to upper frequencies, the maximum amount of sound absorption can be seen in the sample no. 6 (table iv, figures 5-7). table iv. statistical indices describing sound absorption of samples at different frequencies en g th (n a n o m et er sample 1 (%) sample 2 (%) sample 3 (%) sample 4 (%) sample 5 (%) sample 6 (%) 250 0.0059 0.019 0.0268 0.0325 0.0195 0.038 315 0.0292 0.040 0.0103 0.0272 0.038 0.026 400 0.0438 0.039 0.0406 0.0428 0.039 0.050 500 0.090 0.031 0.0105 0.0304 0.019 0.032 800 0.0487 0.029 0.0343 0.0466 0.038 0.054 1000 0.050 0.031 0.040 0.0507 0.027 0.041 1250 0.037 0.032 0.041 0.0362 0.033 0.045 1600 0.135 0.080 0.148 0.133 0.078 0.123 2000 0.0140 0.037 0.123 0.138 0.137 0.130 2500 0.0178 0.149 0.167 0.171 0.164 0.149 3150 0.171 0.162 0.199 0.169 0.148 0.176 4000 0.204 0.281 0.195 0.204 0.281 0.332 5000 0.362 0.285 0.216 0.357 0.293 0.369 6300 0.040 0.181 0.234 0.344 0.255 0.371 fig. 5. sound absorption coefficient for samples 1 to 3 engineering, technology & applied science research vol. 7, no. 2, 2017, 1540-1545 1544 www.etasr.com daeipour et al.: evaluation of the acoustic properties of wood-plastic-chalk composites fig. 6. sound absorption coefficient for samples 4 to 6 fig. 7. overview of sound absorption d. analysis of variance of sound absorption test the results of analyzing variance of sound absorption test are presented in table v. as seen, there are differences among sound absorption of samples at different frequencies (250, 500, 1000, 2000, 4000, and 6300). there is no significant difference among frequencies of 250, 500, and 1000; but there are significant differences among frequencies 200, 4000, and 6300 (sig. <0.05). v. conclusion this research aims to study the acoustic properties of woodplastic composites made of poplar wood flour, low-density polyethylene, and chalk. in this study, 6 combinations were made of different percentages of wood, low-density polyethylene, and chalk. the results of this study showed that the maximum amount of sound absorption was observed at frequencies of 2000 onwards and that a certain mix (which had 3% compatibilizer and 10% chalk) presented the best results. regarding water absorption, it was shown that three mixes revealed significant difference at 2, 24, 48 and 72 hours. table v. va test for comparison of mean sound absorption in samples at different frequencies test type sum of squares degrees of freedom mean squares f significance between groups 0.010 5 0.005 within groups 0.022 12 0.012 frequency 250 total 0.011 17 22.26 0.70 between groups 0.001 5 0.000 within groups 0.021 12 0.000 frequency 500 total 0.020 17 17.32 0.22 between groups 0.021 5 0.010 within groups 0.010 12 0.005 frequency 1000 total 0.011 17 2.42 0.78 between groups 0.011 5 0.005 within groups 0.021 12 0.000 frequency 1000 total 0.011 17 2.34 0.002 between groups 0.010 5 0.005 within groups 0.020 12 0.010 frequency 4000 total 0.020 17 8.96 0.005 between groups 0.033 5 0.015 within groups 0.002 12 0.000 frequency 6300 total 0.001 17 1.06 0.002 references [1] j. lee, g. w. swenson, “compact sound absorbers for low frequencies”, noise control engineering journal, vol. 38, no. 1, pp. 109-117, 1992 [2] s. v. joshi, l. t. drzal, a. k. mohanty, s. arora, “are natural fiber composites environmentally superior to glass fiber reinforced composites”, composites part a: applied science manufacture, vol. 35, no. 1, pp. 371-376, 2004 [3] y. xue, y. du, s. elder, s. devin, m. horstemeyer, j. zhang, “statistical tensile properties of kenaf fibres and its composites”, 9th international conference on wood & biofiber plastic composite, mississippi state university, usa, 2007 engineering, technology & applied science research vol. 7, no. 2, 2017, 1540-1545 1545 www.etasr.com daeipour et al.: evaluation of the acoustic properties of wood-plastic-chalk composites [4] l. w. charles, k. b. venita, e. b. robert, kenaf harvesting and processing, ashs press, alexandria, va, 2002 [5] w. charles, v. k. bledsoe, “kenaf yield components and plant 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25, no. 5, pp. 32-41, 2004 [10] r. c. thompson, c. j. moore, f. s. vom saal, s. h. swan, “plastics, the environment and human health: current consensus and future trends”, philos trans r soc lond b biol sci., vol. 364, no. 1526, pp. 2153– 2166, 2009 [11] y. xue, d. veazie, c. glinsey, m. wright, r. m. rowell, “mechanical properties of wood fiber composites the influence of temperature and humidity”, 7th international conference on wood fiber plastics composites, madison , wisconsin , usa, 2003 [12] m. daniel, “wood plastic composites in europe vs. usa – processing and product trends”, wood plastic composites 2005, applied marketing information, vienna, 2005 [13] k. l. yam, b. k. gogoi, c. c. lai, s. e. selke, “composites from compounding wood fibers with recycled high density polyethylene”, polymer engineering & science, vol. 30, no. 11, pp. 693-699, 1990 [14] k. adhikary, s. s. pang, m. staiger, “dimensional stability and mechanical behaviour of wood-plastic composites based on recycled and virgin high-density polyethylene (hdpe)”, composites: part b, vol. 39, no. 11, pp. 807-815, 2008 [15] j. y. eom, j. w. park, h. s. kwon, s. rajendran, “electrochemical insertion of lithium into multiwalled carbon nanotube/silicon composites produced by ballmilling”, journal of the electrochemical society, vol. 153, no. 9, pp. 1678-1684, 2006 microsoft word 8-2693_s_etasr_v9_n3_pp4116-4119 engineering, technology & applied science research vol. 9, no. 3, 2019, 4116-4119 4116 www.etasr.com catat & celikkay: limits of number of motes at smart city scenarios for lorawan limits of number of motes at smart city scenarios for lorawan muammer catak college of engineering and technology, american university of the middle east, kuwait muammer.catak@aum.edu.kw burak celikkaya baylan measuring instruments izmir, turkey b.celikkaya@baylanwatermeter.com abstract— lorawan is an emerging technology as a solution to iot sensor networks. since it is still in the evolvement stage, academic and industrial researches and applications have to be conducted in order to analyze its limitations and possible improvements. in this paper, the number of motes that could transmit data to a gateway within a 95% confidence interval has been studied under a number of scenarios. according to the results, the most significant parameter regarding the number of motes is the period of the downlink signal. keywords-lora; lorawan; spreading factor; channel limitations i. introduction long range wide-area network (lorawan) has an increasing popularity in engineering applications as a lesscomplex wireless communication protocol using the unlicensed spectrum associated with long range (lora) modulation [1]. a typical lorawan, consists of a server, a number of gateways and actuators (such as measurement instruments, sensors). an actuator, also called a mote, is connected to a certain gateway via a wireless link while the gateways are connected to the server by ip network means. iot sensors mostly need to send small amounts of data (uplink) and less frequently receive any data (downlink). hence, lorawan technology has been employed to transmit data of metering, smart city applications, etc. the key point is to combine low data rate and communication range [2]. lorawan operates in the industrial, science, and medical (ism) radio bands, and it has to obey to some certain regulations. lora can operate in the 868mhz eu ism band (table i), including three compulsory channels at 868.1, 868.3, and 868.5mhz [3]. maximum transmission time is bounded by duty cycle percentage in a way that an individual node may only switch its transmitter on for up to 36 seconds in an hour with duty cycle of 1%. the connected nodes are classified into three groups, namely class a, b, and c. class a: the mote listens to the gateway during two short time windows after it has transmitted some data. therefore, it uses the least power which is ideal for such a battery powered system. class b: besides the basic operations of class a, the node can open scheduled windows in order to capture the signals transmitted from the gateway. class c: the mote listens at all times except from data transmission. hence, it has to be connected to the mains electricity. table i. eu ism band power and duty cycle restrictions frequency band (mhz) applications max. radiated power (mw-dbm) duty cycle 863.0-864.8 iot 25-14 0.1% 864.8-865.0 wireless audio applications 10-10 865.0-868.0 iot 25-14 0.1% 868.0-868.6 iot 25-14 1% 868.6-868.7 alarms 10-10 1% 868.7-869.2 iot 25-14 0.1% 869.2-869.25 social alarms 10-10 0.1% 869.25-869.3 alarms 10-10 0.1% 869.3-869.4 alarms 10-10 1% 869.4-869.65 iot 500-27 10% 869.65-869.7 alarms 25-14 10% 869.7-870.0 iot 25-14 1% after an uplink has been transmitted, there are two available receive windows, regarding the downlink messages of class a. lora modulation technique is based on a chirp signal having variable frequency in a well-defined band. the frequency bandwidth of the chirp signal is equivalent to the bandwidth of the data signal. the corresponding data signal is chipped at a higher data rate, and then it is modulated. the chirp signal can be considered as a carrier signal referring to the fundamental modulation theory. the modulation bit rate is defined as [4]: �� = ����� (1) where sf:=spreading factor, a number from 7 to 12, bw:=modulation bandwidth (125khz in this study). symbol period and symbol rate, which are reciprocal of the symbol period, are calculated as: �� = ���� �; �� = ��� = �� �� �������/� (2) the chip rate is defined as: �� = ��2�� = �� ℎ"#�/� (3) the nominal bit rate of the data signal is: �� = $% &&'()��� bits/s (4) corresponding author: muammer catak engineering, technology & applied science research vol. 9, no. 3, 2019, 4116-4119 4117 www.etasr.com catat & celikkay: limits of number of motes at smart city scenarios for lorawan where cr is the code rate, it can be an integer from 1 to 4. if (4=4+cr) is defined as rate code, then the nominal bit rate is: �� = $% *+,./0-��� bits/s (5) ii. materials and methods the main objective of this study is to estimate the expected number of motes subject to satisfy a given error band outlined by a described scenario with and without downlink. when the adaptive data rate (adr) is on, the spreading factor (sf) of a mote is dynamically reassigned by the gateway regarding to the power of the corresponding received signal. if the signal power is low, most likely the gateway assigns the sf as 12, if the signal power is moderately high enough the sf is most likely assigned as 7. there are 6 levels of sf. if the sf increases the rf sensitivity also increases, which allows signaling propagates longer ranges. on the other hand, the nominal bit rate decreases, which results in increment in time on air (toa). detailed information are given in table ii. in this study, the following channels are employed in order to operate the system: 867.1, 867.3, 867.5, 867.7, 867.9, 868.1, 868.3, and 868.5mhz. a class a uplink transmission is followed by two downlink receive windows, during which the motes can capture the data including information from the gateway. the channels are selected randomly and they are assumed to act as uniformly distributed random variables. since the selections of sf and channel frequencies are completely independent of each other, the joint distribution of sf (assigned as random variable of x) and channels (assigned as random variable of y) can be written as: #12(4, �) = #1(4)#2(�) (6) table ii. sf properties # sf bandwidth (khz) code rate rate code rb (bps) rf sensitivity (dbm) 0 12 125 1 4/5 293 -137 1 11 125 1 4/5 537 -136 2 10 125 1 4/5 977 -134 3 9 125 1 4/5 1758 -131 4 8 125 1 4/5 3125 -128 5 7 125 1 4/5 5469 -125 there are 48 options at an instant time, 6(sf)×8(channels), the uplink signals cannot be overlapped. therefore, the system can be modeled using 48 individual service stations since the time on air parameters varies at each path. the overlapping probability of two uplink signals can be defined as: #1|2(4|�) = 89|:(;|<)8:(<)89(;) (7) the transmission of uplink packages is a bernoulli process, since there are merely two possibilities as success or fail [5]. let the random variable z be an identically independent bernoulli distributed with parameter = ∈ (0,1). the probability of “success” in n trials can be calculated as; a(b|c trials) = (de)=e(1 − =)dge = d!(dge)!e! =e(1 − =)dge (8) it is also reported that, a poisson process can be used as a sufficiently good enough approximation of a bernoulli process if c > 100, = < 0.01, and l = c= [6]: mgn noe! ≅ (de)=e(1 − =)dge (9) where k=1,2,…..n. at the gateway side, the uplink data transmission can be organized as an m/d/c queuing system. the arrivals are governed by poisson process (denoted as m), the job service time is deterministic, that is the times on air are depending on sf levels (denoted as d). if the gateway is idle at a specific sf and channel combination, then it is assumed that the transmission is successful, otherwise it is considered failed. that means there is no “waiting time” at the gateway side. the vendor reported that if two simultaneous transmissions occur with the same sf and the same channel, the gateway can receive the more powerful signal in the case that the ratio of the powers of the signals is greater than 2. however, this case is not considered in this study. iii. results and discussion the proposed model has been employed in order to simulate the network with or without downlink signals, since the number of downlink signals has a significant effect on the time-window, during which uplink signals can be transmitted. table iii. time on air and corresponding failure probability of sfs sf toa (ms) qsf 12 1710 118.75x10 6 11 962.5 66.84x10 6 10 468.75 32.55x10 6 9 287.5 19.97x10 6 8 181.25 12.59x10 6 7 125 8.68x10 6 a. no downlink the following scenario is employed in order to estimate the number of motes per gateway in an urban residential area. the motes operate in 8 channels with 125khz bandwidth. the spreading factors are numbered from 0 (sf 12) to 5 (sf 7). three different scenarios were employed to assign the probabilities of being in a specific sf level. 1) scenario 1 (s#1) the locations of the motes are classified into three groups: near, middle, and faraway. the number of sf is treated as a random variable governed by poisson distribution as: #1(4) = q rsstt!∑ -rsstt!vtw , 4 = 0,1,2, … , c0, �yℎmz["�m (10) the summation term in (10) is necessary for normalization. the parameter is taken as 1/6, 2/8, and 4/8 for near, middle, and faraway motes respectively. the corresponding probabilities are calculated as #\ = 0.12, #� = 0.09, # =0.14, #_ = 0.16, #a = 0.16, #b = 0.33. engineering, technology & applied science research vol. 9, no. 3, 2019, 4116-4119 4118 www.etasr.com catat & celikkay: limits of number of motes at smart city scenarios for lorawan 2) scenario 2 (s#2) the probabilities being in a sf level are assigned as #\ = 0.23,#� � 0.11,# � 0.08,#_ � 0.09,#a � 0.10,#b � 0.39 as suggested by semtech. 3) scenario 3 (s#3) the probabilities being in a sf level are #\ � 0.28,#� � 0.20,# � 0.14,#_ � 0.10,#a � 0.08,#b � 0.20 as reported by [7]. all motes transmit 51-byte frames payload. the time on air of each sf levels and their corresponding failure probabilities are listed in table iii. the total probability of the failure rate up to k failures of n trials can be calculated as: ∑ ∑ -ref��3dg��6 o e! � ��hi d eh� (11) the results obtained from (11) are listed in table iv under the case of no downlink for the three different scenarios. note that the geographic properties of the place, building heights, locations of the meters are not taken into account as parameters of the developed model. hence, the results obtained from the simulations, can be considered as bounding estimates. table iv. maximum number of motes* uplink period (h) number of motes s#1 s#2 s#3 1 11679 9091 8164 4 46719 36364 32655 6 70072 54546 48983 8 93429 72728 65310 16 186858 145455 130619 24 280287 218183 195929 *within 95% confidence interval without downlink b. with downlink it assumed that at least 1 downlink occurs within a period of 48 hours per mote. a downlink can be sent by an uplink or it can be sent regardless of the presence of an uplink. there are two options to select the sf of the downlink: i) it could have the same sf if they are 7 or 8, ii) it is predetermined as sf 9. the expected time on air of a downlink has to be calculated in order to analyze the effects of the downlink signals on the network traffic. let z be a random variable representing the time on air of a downlink. according to the total expectation theorem, the unconditional expectation value can be calculated by averaging the conditional expectations: jklm � n jkl|opma3op6 q ph� (12) the probability of having the same sf with the prior uplink is assigned as µ, then 1-µ is the probability of using a predetermined sf. hence (12) turns into: jklm � μjkl|$% � 7 or 8m t 31 f μ6jkl|$% � 9m (13) the period of 48 hours has been divided into 6 equal 8-hour parts. the probability to have a downlink in the first part is 1/6, and consequently the probability to have no downlink is 5/6. if a downlink transmits, the same probabilities are valid for the second part. if no downlink occurred in the first part, then the probabilities are updated as 1/5, and 4/5 to have a downlink, and to have no downlink, respectively. the entire probability tree is shown in figure 1. fig. 1. possible outcomes of having downlink in 48h with 8h intervals the number of downlinks and the corresponding probabilities are given in table v. at almost 60%, one downlink occurs during the 48h period. the general definition for the probabilities can be summarized as: a3u � b|c � v6 � wqx� ex� y e qo'z ; (14) where n=6, k=1,…..,6 table v. downlink number and corresponding probabilities # of downlink probability 1 21/36 2 70/216 3 105/6 4 4 84/6 5 5 35/6 6 6 6/6 7 the number of motes with the case of at least one downlink transmitted during the 48h period at various scenarios is shown in table vi. comparing with the results shown in table iv, the downlink transmission dramatically affects the number of motes that a gateway can handle within an acceptable error band. table vi. maximum number of motes* uplink period (h) number of motes s#1 s#2 s#3 1 552 552 533 4 1108 1251 1074 6 1358 1489 1316 8 1569 1692 1521 16 2221 2327 2154 24 2721 2820 2640 *within 95% confidence interval with downlink engineering, technology & applied science research vol. 9, no. 3, 2019, 4116-4119 4119 www.etasr.com catat & celikkay: limits of number of motes at smart city scenarios for lorawan the expected number of downlink is calculated 1.5216 as: jk�m � n #�3[6{ (15) where [ and the corresponding probabilities #{3[6 are supplied in table vi. with the same manner, the expected toas are calculated for s#1, s#2, and s#3 as 252.27, 250.55, and 267.04ms, respectively. iv. conclusion the number of motes that can be handled by a gateway using lorawan technology within 95% confidence interval has been studied. various scenarios have been employed to a smart city application. under the condition of no downlink transmission, a gateway can easily company a huge number of motes. however, with downlink transmission, the number of motes transmitting data with 95% confidence interval decreases dramatically. the possible solutions to overcome this effect could be the increase of the period of uplink and/or downlink, or the increase of the number of gateways, but both solutions increase the application cost. in the future, appropriate location estimation of a gateway in order to increase the network quality will be carried out. references [1] k. mikhaylov, j. petajajarvi, j. janhunen, “on lorawan scalability: empirical evaluation of susceptibility to inter-network interference”, european conference on networking and communications, oulu, finland, june 12-15, 2017 [2] f. adelantado, x. vilajosana, p. tuset-peiro, b. martinez, j. meliasegui, t. watteyne, “understanding the limits of lorawan”, ieee communications magazine, vol. 55, no. 9, pp. 34-40, 2017 [3] d. p. bertsekas, j. n. tsitsiklis, introduction to probability, athena scientific, 2002 [4] semtech, lrra modulation basics, an1200.22, 2015 [5] b. vejlgaard, m. lauridsen, h. nguyen, i. z. kovacs, p. mogensen, m. sorensen, “interference impact on coverage and capacity for low power wide area iot networks”, ieee wireless communications and networking conference, san fransisco, usa, march 19-22, 2017 [6] etsi, etsi 300 220-1 (v2. 4.1), electromagnetic compatibility and radio spectrum matters (erm), 2012 [7] d. bankov, e. khorov, a. lyakhov, “on the limits of lorawan channel access”, international conference on engineering and telecommunication, moscow, russia, november 29-30, 2016 microsoft word 361-ce_r2.doc etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 497-501 497 www.etasr.com mostefa kara eta al.:contribution of particles size ranges to sand friction contribution of particles size ranges to sand friction esma mostefa kara djillali liabes university dept. civil engineering, fac.technology labo. civil engineering & environment (lgce) sidi bel abbes, algeria mkesma@univ-sba.dz mourad meghachou djillali liabes university dept. civil engineering, fac.technology labo. civil engineering & environment (lgce) sidi bel abbes, algeria mourad_meghachou@univ-sba.dz nabil aboubekr tlemcen university dept. civil engineering, fac.technology labo. water and structures in their environment (eole) tlemcen, algeria aboubekrnabil@yahoo.fr abstract — this work studies the correlation between certain physical properties of granular material such as the friction angle and the grain size distribution. in the laboratory, the determination of friction angle requires hard and expensive testing. prediction of this parameter from the grading curve proves to be very interesting. direct shear tests were performed on actual marine sand of tergha (algeria) and on seventeen different samples arranged from the same sand with various particle size ranges. results showed that the friction angle of sand is a result of contribution of various constituent granular classes. keywords-component; sand; peak friction angle; particle size range; shear test; grading curve. i. introduction the shear strength of sands was first introduced by coulomb. he simply assumed that frictional resistance increases with normal pressure. in fact, there are three components contributing to the strength of sand [1-4]. according to [4], these components are:  strength mobilized by frictional resistance  strength developed by energy required to cause expansion or dilation of materials  strength developed by energy required to rearrange and reorient materials the first component is usually described as sliding friction, the second as interlocking friction, and the third as rolling friction. yong explained that sliding friction is included by microscopic interlocking arising from surface roughness; interlocking friction is caused by the physical resistance to relative particle translation affected by adjacent particles. the third component, rolling friction, might be ignored [5]. the nature of contacts between particles of soil directly influences its frictional character. dense sand, loaded in shearing, presents at early stage tangle grains which mobilize more friction and therefore shear strength. it is accepted now that the critical state reached for the sand, when subjected to large deformations whatever its density, gives the material a quasi-constant friction angle [6, 7]. however, the maximum friction angle characterizing the beginning of rupture and before the establishment of the critical state can be correlated with many parameters, among others, grain size distribution [8-11]. according to studies [12-15] made on various sands with constant density, friction angle increases with the reduction of particle size with an insignificant variation. other researches, aiming at the variation of internal friction angle according to the gradation, have shown that the friction angle increases with the increase of the uniformity coefficient (uc) for sands consisting of feldspar and calcite [9, 10]. on the other hand, for sands consisting mainly of quartz, the studies did not show any bond between the two [1520]. and thus, with constant void ratio, the size of the particles does not seem to have significant influence on the friction angle. consequently, a fine sand and a coarse sand presenting the same mineralogical composition and the same void ratio will probably have the same value of friction angle. however, by carrying out direct shear tests on samples of sand with the same void ratio but with different size, one finds considerable variations of friction angle. in summary, the effect of particle size on friction angles of cohesionless materials is not clear through the literature. the study described in this paper answers the following question: what is the relationship between the peak friction angle and the grain size distribution of sand? ii. experimental program the experimental study follows three stages:  separation of the various particles size ranges constituting the studied sand  reconstitution of ten samples, with different percentages from the seven particles size ranges;  realization of direct shear tests on tergha sand and seventeen other samples derived from it. a. description of tergha sand the distribution of particle sizes is obtained by dry sieving sand of known weight through a stack of sieves of progressively finer mesh size with a respect to the norm nf p94-056. according to classification lcpc, our sand is gap graded (figure 1). figure 2 shows a photo of tergha sand and a microscopic view is shown in figure 3. etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 497-501 498 www.etasr.com mostefa kara eta al.:contribution of particles size ranges to sand friction the granular properties of tergha sand are:  diameter of the soil particles for which 10% of the particles are finer (d10) is 0,20mm  diameter of the soil particles for which 30% of the particles are finer (d30) is 0,24mm  diameter of the soil particles for which 60% of the particles are finer (d60) is 0,31mm  uniformity coefficient (uc) is: 1,53  coefficient of curvature (cc) is: 0,92  maximum void ratio (loosest condition) (emax): 0,8  minimum void ratio (densest condition) ( emin): 0,52 the density of the solid particles of tergha sand is given according to nf p94-054:  s= 2.65 g/cm 3. fig. 1. grading curve of tergha sand fig. 2. photography of tergha sand. fig. 3. microscopic view of tergha sand (zoom 220). b. particles size ranges seven particles size ranges are studied after separation: ([1, 0,8], [0.8, 0.63], [0.63, 0.5], [0. 5,0.315], [0.315, 0.2], [0.2, 0.160] and [0.160, 0.125]) [mm]. each one of these classes is represented in the study by the smallest diameter of the class (di). figure 4 represents photo of the various ranges. figure 5 represents a microscopic view (zoom 220) of two particle size ranges and table i gathers the various grain size properties of the various reconstituted samples. it should be noted that the tenth sample in table i (s10) is composed of 50% of the smallest class and 50% of the biggest class. [0.8, 0.63] mm [0.63, 0.5] mm [0.5, 0.315] mm [0.315, 0.2] mm [0.2, 0.160] mm [0.160, 0.125] mm fig. 4. photography of particles size ranges. [0.160, 0.125] mm [0. 5,0.315] mm fig. 5. microscopic view of two particles size ranges (zoom 220). table i. granular properties of samples. sample d10 mm d30 mm d60 mm uc cc emax emin s1 0,16 0,22 0,41 2,50 0,75 0,709 0,45 s2 0,21 0,24 0,30 1,42 0,93 0,811 0,535 s3 0,18 0,28 0,38 2,13 1,16 0,737 0,474 s4 0,15 0,34 0,54 3,66 1,43 0,64 0,393 s5 0,16 0,23 0,60 3,64 0,53 0,641 0,394 s6 0,14 0,17 0,31 2,28 0,63 0,725 0,464 s7 0,31 0,63 0,86 2,74 1,46 0,693 0,437 s8 0,17 0,2 0,31 1,88 0,76 0,76 0,493 s9 0,16 0,23 0,54 3,37 0,63 0,655 0,405 s10 c. reconstituted samples ten samples are reconstituted from the seven particles size ranges with a random choice of percentage. figure 6 represent the composition of the different samples. d. tests several direct shear tests are applied to the eighteen samples referred to above (one of actual tergha sand, seven samples with different particle size ranges and ten reconstituted samples with random percentages of particle size ranges). the tests are carried out in a dry and dense state. the line of rupture is obtained following the application of five normal stresses (100, 200,300,400 and 600 kpa) to obtain more precision for etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 497-501 499 www.etasr.com mostefa kara eta al.:contribution of particles size ranges to sand friction the statistical study. the dry gravities of the various sheared samples are listed in table ii. figure 7 shows that the state of density is almost identical for all studied samples. fig. 6. composition of the various reconstituted samples table ii. dry gravity of samples fig. 7. dry gravity of samples e. results 1) curves of shearing for each sample, three curves are drawn up. figure 8 shows an example of the curves of shearing results. table iii gathers the values of the friction angle, for all samples. 2) variation of peak friction angle p and critical state friction angle cs according to the smallest diameter of particle size range (di) according to figure 9, the points (smaller diameter of a grain size range di, peak friction angle  p and critical state friction angle cs), respectively, are gathered around the linear regression lines: 34 10p i i d   (1) 29 3cs i i d   (2) where: di [mm] : smallest diameter of particle size range [di+1, di]. p i  and csi [°] : represent the peak friction angle and critical state friction angle, respectively, for the particle size range [di+1, di]. the results show a direct relation between particles size and peak friction angle. it is noted that there is an increase in peak friction angle with the increase of particles size. so if we know the size of particles of marine sand we can deduce directly the value of peak friction angle. on the other hand the line of variation of internal friction angle, according to di is almost horizontal, which shows that there is no influence of the particles size on the internal friction angle. table iii. frictions angle of samples at peak and critical state sample p cs tergha sand 36,5 28,5 [1; 0,8] mm 40,7 30,8 [0,8; 0,63] mm 41,1 29,6 [0,63;0,5] mm 40,9 31,4 [0,5; 0,315] mm 38,5 29,9 [0,315; 0,2] mm 34,7 27,8 [0,2; 0,160] mm 35,4 27,7 [0,160; 0,125] mm 35,1 30,6 s1 38,1 29,1 s2 36,6 28,9 s3 36,7 28,8 s4 40,7 30,0 s5 38,4 31,5 s6 42,2 28,5 s7 37,5 31,2 s8 39,6 29,0 s9 36,1 26,8 s10 38,9 32,3 (kpa) sample 100 200 300 400 600 tergha sand 1,67 1,72 1,65 1,69 1,71 [1, 0.8] 1,52 1,49 1,51 1,49 1,44 [0.8, 0.63] 1,65 1,61 1,61 1,63 1,61 [0.63, 0.5] 1,69 1,65 1,63 1,65 1,65 [0.5, 0.315] 1,66 1,70 1,74 1,69 1,69 [0.315, 0.2] 1,67 1,67 1,67 1,67 1,67 [0.2, 0.160] 1,67 1,67 1,64 1,65 1,67 [0.160, 0.125] 1,65 1,65 1,63 1,65 1,64 s1 1,76 1,73 1,75 1,74 1,74 s2 1,68 1,69 1,69 1,66 1,67 s3 1,72 1,70 1,71 1,71 1,71 s4 1,80 1,75 1,80 1,75 1,76 s5 1,76 1,75 1,85 1,79 1,75 s6 1,75 1,76 1,77 1,76 1,76 s7 1,67 1,60 1,67 1,61 1,63 s8 1,74 1,72 1,75 1,72 1,75 s9 1,76 1,76 1,77 1,76 1,75 s10 1,86 1,86 1,84 1,84 1,84 etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 497-501 500 www.etasr.com mostefa kara eta al.:contribution of particles size ranges to sand friction fig. 8. results of direct shear test on tergha sand. fig. 9. variation of p i  and cs i  according to di. 3) contribution of particle size ranges of a sand to its peak friction angle the use of (1), allows the determination of peak friction angle for each particle size range constituting the studied sand but not the global friction angle of sand. so we will try to determine the global peak friction angle of various sands from peak friction angles of particle size ranges constituting the same sands. for this we will study tergha sand and the ten reconstituted samples. results show that the peak friction angle of each sample corresponds to the sum of the contribution of the various particles size ranges. the contribution of each class being equal to its peak friction angle balanced by its percentage in the grain-size distribution of the sample: p p i i i p   (3) where: p [°] corresponds to the peak friction angle of sand. pi: percentage of particle size range [di+1, di] in the composition of sand figure 10 presents the comparison between peak friction angles measured in the laboratory and those calculated from (3). the use of this relation provided a calculation of the friction angle nearly identical to the values found experimentally. fig. 10. comparison between measured peak friction angle in laboratory and those calculated using (3). statistical analysis of the obtained results shows that a good correlation exists:  the difference between the theoretical and experimental friction angle or absolute error is approximately, 1° for six samples out of eleven, 0.3° for three samples, 0.5° for a sample, and 0.1° for the last sample, which corresponds to an relative error of almost 2,5%;  coefficient of correlation is equal to 0.862.  absolute errors of friction angles, for calculated and measured values, are estimated at maximum  1°. etasr engineering, technology & applied science research vol. 3, no. 4, 2013, 497-501 501 www.etasr.com mostefa kara eta al.:contribution of particles size ranges to sand friction 4) variation of peak friction angle with the smallest diameter of particls size range if we incorporate (1) in (3), we obtain: 34 10p i i i p d    (4) where: p in [°]. di in [mm]. p in [%]. figure 11 shows the comparison between measured friction angle in laboratory and those calculated using (4). the correlation coefficient is 0.755. this last equation enables us to determine the peak friction angle of sand directly from particle size (di). thus, a simple grain size analysis of sand enables us to deduce his peak friction angle. fig. 11. comparison between measured peak friction angle in laboratory and those calculated from (4). iii. conclusion at the last of this study one arrives at the following conclusions:  peak friction angle increases when the size of particles increases  grains size does not have a significant influence on internal friction angle  results show a relation between the grain size and the peak friction angle  the peak fiction angle can be deduced by the sum of elementary peak friction angles, of particles size ranges constituting the sand, balanced by their percentages in grain-size distribution  the use of (3) allowed the calculation of the friction angle which was nearly identical to the values found experimentally, the coefficient of correlation is 0.862.  by using (4) we can calculate the peak friction angle from the sum of each smallest diameter of particle size ranges balanced by its percentage in the granular composition.  a simple grain size analysis of sand enables us to deduce his peak friction angle. references [1] r. d. holtz, w. d. kovacs, t. c. sheahan, an introduction to geotechnical engineering, prentice hall, 2010 [2] j. k. mitchell, k. soga, fundamentals of soil behavior, john wiley & sons, 2005 [3] k. terzaghi, r. b. peck, g. mesri, soil mechanics in engineering practice, wiley-interscience, 1996. [4] p. w. rowe, “the stress dilatancy relations for static equilibrium of an assembly of particles in contact”, proceedings royal society, london, series a, vol. 269, pp. 500-527, 1962 [5] r. w. yong, b. p. warkentin, “soil properties and behavior”, elsevier scientific, 1975 [6] j. c. santamarina, g. c. cho, “determination of critical state parameters in sandy soils-simple procedure”, geotechnical testing journal, vol. 24, no 2, pp. 185-192, 2001 [7] k. been, m. g. jefferies, j. hachey, “the critical state of sands”, geoteschnique, vol. 41, no. 3, pp. 365-381, 1991 [8] e. frossard, “effect of sand grain shape on interparticle friction; indirect measurements by rowe's stress dilatancy theory”, geotechnics, vol. 29, no 3, pp 341-350, 1979 [9] g. viggiani, m. kuntz, j. desrues, “an experimental investigation of the relationships between grain size distribution and shear banding in sand”, continuous and discontinuous modeling of cohesive frictional materials, lecture notes in physics, vol. 568, pp. 111-127, 2001 [10] w. b. whalley, “discussion on ‘effect of sand grain shape on interparticle friction’”, geotechnics, vol. 29, no. 3, pp 341-350, 1979 [11] n. salimi, v. yazdanjou, a hamidi, “shape and size effects of gravel grains on the shear behavior of sandy soils”, proceedings of the 10th international symposium on landslides and engineered slopes, pp. 469474, 2008 [12] a. w. bishop, “a large shear box for testing sands and gravels”, proceedings of the 2nd international conference of soil mechanics and foundation engineering, vol. 1, pp. 207-211, 1948 [13] w. m. kirkpatrick, ” effect of grain size and grading on shear behavior of granular materials”, proceedings of the sixth international conference of soil mechanics and foundation engineering, vol. 1, pp. 273-277, 1965 [14] r. m. koerner, “effect of particle characteristics on soil strength”, journal of soil mechanics & foundations division, vol. 96, no. sm4, pp. 1221-1234, 1970 [15] j. s. zelasko, r. j. krizek, t. b. edil, “shear behavior of sand as a function of grain characteristics”, istanbul conference on soil mechanics and foundation engineering, vol. 1, pp. 55-64, 1975 [16] a. w. bishop, “discussion to ‘messurement of the shear strength of soils’ by skempton and bishop”, geotechnique, vol. 2, no. 1, pp. 113116, 1950 [17] r. m. koerner, “behavior of single mineral soils in triaxial shear”, journal of the soil mechanics and foundations division, vol. 96, no. 4, pp. 1373-1390, 1970 [18] t. kokusho, t. hara, r. hiraoka, “undrained shear strength of granular soils with different particle gradations”, journal of geotechnical and geoenvironmental engineering, vol. 130, no. 6, pp. 621-629, 2004 [19] a. simoni, g. t. houlsby, “the direct shear strength and dilatancy of sand-gravel mixtures”, geotechnical & geological engineering, vol. 24, no. 3, pp. 523-549, 2006 [20] a. hamidi, v. yazdanjou, n. salimi, “shear strength characteristics of sand-gravel mixtures”, international journal of geotechnical engineering, vol. 3, no. 1, pp. 29-38, 2009 engineering, technology & applied science research vol. 8, no. 3, 2018, 2969-2974 2969 www.etasr.com memon et al.: a review on self compacting concrete with cementitious materials and fibers a review on self compacting concrete with cementitious materials and fibers noor ahmed memon department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan nahmedmemon@gmail.com muneeb ayoub memon department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan engr.muneebmemon@gmail.com nawab ali lakho department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan nawablakho@gmail.com fareed ahmed memon department of civil engineering mehran university of engineering & technology, jamshoro, pakistan fareed.memon@faculty.muet.edu.pk manthar ali keerio department of civil engineering quaid-e-awam university of engineering, science & technology larkana, pakistan mantharali99@quest.edu.pk ammaar noor memon department of civil engineering mehran university of engineering & technology, jamshoro, pakistan anmemon96@gmail.com abstract—self-compacted concrete (scc) is cast in the formwork without compaction and it fulfills the formwork due to its own weight. scc is considered to have many advantages in comparison with conventional concrete like improved construction quality, faster construction activity, reduced cost etc. scc is produced with the same ingredients of normal concrete. however, cementitious materials are also adopted to replace the cement content in scc in order to use waste materials from industries and agricultural products. to further enhance the performance of scc, different types of fibers are tried in order to produce fiber reinforced scc. the fibers in the concrete bridge the cracks and diffuse the crack propagation which improves mechanical properties. in developed countries scc has reasonable acceptance in construction industry but in developing countries like pakistan has not gained acceptance. this paper is focused on undertaking a review of scc with cement replacement and fiber reinforcement materials. the main objective of this paper is to compile the literature in order to understand the various properties of scc in fresh and hardened state when these cement replacement materials and fibers are used. keywords-self-compacting concrete; cement replacing materials; fiber reinforcement i. introduction self-compacting concrete (scc) is a type of concrete which is produced without compacting effort in form work. it settles by its own weight without any bleeding and segregation and behaves cohesive enough [1]. the use of scc is believed to provide various advantages like reduced construction time, labor cost and noise pollution, ease to fill the congested and thin sections. it also facilitates casting in congested areas of construction. in recent years, different types of filler as a partial cement replacement have been widely used in scc. with this replacement, scc can be a more sustainable material [2]. the high flow and resistance to segregation abilities of scc can be achieved by adding large quantities of super plasticizer and filler materials in it. though there are many filler materials that have been used in scc manufacturing, the commonly used fillers are silica fume, fly ash, iron slag etc. [3]. scc prepared with micro-fillers and mineral admixtures as a partial replacement of cement becomes economical [4]. normally scc is produced with smaller water cement ratio which results in high strength, low permeability and more durability when compared to normal concrete produced with compaction with the use of vibrators. these properties of scc are further improved by the addition of fibers. the fibers work as crackarresters which bridge the cracks and also resist crack propagation. however, the workability of scc reduces with the addition of fibers and this reduction is dependent upon the type, shape, size and dosage of fibers used [5]. ii. literature review a. cementitious materials literature reports wide use of cementitious materials. the effect of cementitious materials is investigated on various properties of scc in fresh and hardened state. authors in [6] investigated the fresh and hardened properties of scc experimentally by using furnace slag as partial replacement of cement. the w/b ratio was kept constant at 0.37. the slag was used from 0% to 30% by cement weight. the effect of slag was investigated in terms of slump flow, shrinkage and compressive strength by upv. it was observed that the slump flow varies engineering, technology & applied science research vol. 8, no. 3, 2018, 2969-2974 2970 www.etasr.com memon et al.: a review on self compacting concrete with cementitious materials and fibers with the dosage of slag and it was within the designed value of 550 mm to 700 mm when 15% of slag was used exhibiting maximum compressive strength. the drying shrinkage increased with an increase in slag dosage but scc with slag had not any sign of bleeding pores and segregation of aggregates. authors in [7] carried an experimental study to understand the influence of natural zeolite (nz) on different properties of scc. nz was used from 0 to 20% with an increment of 5% with different water binding ratios. the results revealed increase in passing ability and viscosity of scc with the addition of nz but loss in flow ability with hauling time. also the increase in nz dosage caused decrease in slump flow. the compressive and tensile strength of scc with nz were found to be dependent upon w/b ratio and the enhanced compressive strength was achieved with slump flow more than 550 mm. the upv values were independent of nz particularly at high compressive strength. water absorption of scc with nz was decreased with passage of time. authors in [8] used metakaolin (mk) as cement replacement material from (0 to 20%). three w/b ratios 0.32, 0.38 and 0.45 were adopted. the addition of mk resulted in increase in workability and rheological properties of scc, even without any use of vma. a remarkable enhancement of the order of 27% in compressive strength was observed at 14 days. a similar trend was observed in case of tensile strength. it was reported that the compressive strength can be predicted by regression model in terms of upv. the use of mk reduced water absorption of scc below 3%. overall 10% mk is proposed as optimum dosage as cement replacement in scc. authors in [9] used cement kiln dust (ckd) as partial cement replacement to develop high performance scc. cement was replaced by weight (0%, 10%, 20% and 30%) while keeping other constitutes constant. the results showed that flow ability and mechanical properties decrease with increasing ckd replacement. however, high strength scc could be produced with 20% ckd replacement while high performance scc could be produced with 30% ckd replacement. ckd in scc reduces the dynamic modulus of elasticity and increases the damping capacity. authors in [10] investigated the feasibility of the scc’s medium strength prepared with local filler material (i.e. ckd) theoretically and practically. ckd replacement was 0%, 20%, 30% with 0.38 and 0.42 water/binder ratios. results showed fluidizing effect in the mixtures due to ckd which allows the use of smaller amount of cement with same finer content. the scc having 35mpa strength can be produced with 30% of ckd and 0.42 of water/fines ratio. authors in [11] reported enhanced workability, compressive strength and flexural strength of scc with increased dosage of ckd. the optimum ckd dosage is suggested to be 10% in terms of strength properties. authors in [12] used silica fume (sf) in scc with 10%, 12.5% and 15% replacement. slump flow, v-funnel, j-ring, lbox, u-box tests were conducted in order to measure the fresh properties of scc. upv and compressive strength by using rebound hammer were conducted to measure mechanical characteristics of scc. the results revealed enhanced properties of scc both in wet and hardened state. maximum 6% sf dosage is suggested. authors in [13] studied the influence of high exposing temperature on the strength properties (compressive and tensile) and durability (porosity, loss of mass and permeability) of scc. cement was replaced by fly ash from 0% to 50% and exposing temperature was 20oc, 100oc, 200oc and 300oc. it was reported that the tensile strength was significantly reduced due to the increasing of the temperature and fly ash dosage, but compressive strength decreased marginally. literature not only reports the use of cementitious materials individually but also the studies conducted with two or more cementitious materials used together. authors in [14] used silica fume and fly ash as partial replacement of cement from 5% to 25% of fly ash with 5% increment and 2.5% to 12.5% of sf with 2.5% increment. silica fume showed increase in fresh and hardened properties. scc with fly ash exhibited lower compressive strength. authors in [15] investigated experimentally rheological properties with the addition of silica nano particles, silica fume and fly ash. the results revealed the improvement in rheological properties of scc with fly ash dosage. the mixture of sf and nano siliceous particles added together enhanced both mechanical and rheological state. authors in [16] performed sorptivity test to determine the surface water absorption of the scc obtained by mixing fly ash and silica fume. addition of 20% or more fly ash in scc resulted in significant reduction of water absorption. a noticeable reduction in sorpitivity is obtained, but in case of binary replacement of silica fume and fly ash the decrease in water absorption is not of such extent as observed in separate replacement. however, compressive strength increase is more significant in case of the addition of both fly ash and silica fume together. authors in [17] prepared a mix of scc blended with microwave incinerated rice husk ash (mirha) and 20% fly ash to investigate the effect of fire flame on it. fire flame temperatures of 200oc, 400oc, 600oc, 800oc, 1000oc and 1200oc for 1 hour exposure duration were maintained. the weight and compressive strength of scc reduced with enhanced flame temperature. also high temperatures caused improved spalling effect. authors in [18] investigated the effect of limestone powder (lp) and fly ash (fa) on micro-structural and hydration properties of scc. they conducted x-ray diffraction, scanning electron microscopy (sem) and mercury intrusion tests, in addition, image and thermo gravimetric analysis were carried out. the results revealed identical compressive strength in case of lp and fa ranging from 50 to 60mpa at 28 days. the microstructure of scc was different with lp and fa with same replacement while scc with fa was found to be more suitable than scc with lp. authors in [19] tested 33 mixes of scc containing 495 samples with sf and fa. the mixtures contained iron slag as replacement of fine aggregates were produced with superplasticizer (0.5 to 1.8% of cementitious weigh). compressive strengths at 3, 7, 14, 28 and 56 days were determined. it was found that concrete with 30% fly ash and 20% silica fume the exhibited highest compressive strength. authors in [20] optimized different compositions of scc by using “concrete labpro2” software followed by an experimental study by casting scc with waste of marble and tiles as mineral admixture. it was found that the concrete with engineering, technology & applied science research vol. 8, no. 3, 2018, 2969-2974 2971 www.etasr.com memon et al.: a review on self compacting concrete with cementitious materials and fibers these minerals exhibits satisfactory fluidity and resistance to segregation. upv compressive strength and spilt tensile strength tests were also carried at 3, 7, 14 and 28 days. these tests reflected the sufficient strength properties suitable to scc with these admixtures. however, in comparison, the scc with marble waste exhibited lower strength than the scc with lime stone. authors in [21] produced scc with high content of waste perlite powder (wpp), slag (blast furnace) and mk. the results identified a pronounced pozzolanic effect of wpp on concrete microstructure. this effect caused enhancement in compressive strength and durability performance of scc. authors in [22] used three mineral admixtures namely sf (5% to 25%, increment 5%), mk (5% to 20%, increment 5%) and ggbfs (25% to 100%, increment 25%).the results were compared with normal concrete of 60mpa. water-binder ratio was obtained as 0.4 with optimum dosages of sp and vma as 2.3% and 0.15% weight of cement respectively. it was reported that 50% ggbfs, 10% sf and 20% mk were found to be the optimum values as partial substitute to cement. authors in carried out tests to improve the properties of low cement scc (with 50% opc and 50% ggbfs and low calcium fly ash) by using dolomite powder (dp). they concluded that dp had not showed any effect on the setting properties of scc blended with slag and opc. however, significant effect was observed on the properties of scc blended with ternary mixture (i.e. slag, opc & fa). furthermore, a significant enhancement in flow ability and compressive strength was observed with dp adjustment in ternary blended mixes of scc. the maximum 7 days compressive strength of hardened mortars was achieved with addition of 30% (by weight) of dp. however, 50% dosage of dp provided satisfying properties required in concrete structures. authors in [24] focused on the durability of scc incorporating copper slag (cs) as fine aggregates and mk as substitute to fa. a total of seven concrete mixes with constant percentage of 60% opc and remaining 40% adjusted between combined replacement of fa and mk cs was used from 0 to 100%. results revealed that fresh properties declined with inclusion of mk although escalated with increment of cs content. all scc mixes exhibited higher compressive and splitting tensile strength than control concrete. the minimum carbonation depth was marked for 100% cs substitution with 10% mk as replacement to fa. the maximum electrical resistivity and resistance to sulfate attack were obtained for 20% cs substitution while upv values of all the mixes were under the excellent quality of concrete beyond 7 days of curing. on full replacement of sand by cs with 10% mk, initial surface absorption and sorptivity were significantly lower than control concrete at each curing period. this study suggested that cs together with mk can be a potential substitute to natural sand in the construction sector to overcome the scarcity of aggregates. author in [25] studied the effects of ternary system on corrosion behavior of scc which is formed using mk and selfcombusted ash of rice husk (scrha). to achieve the objective, ordinary portland cement (opc) was replaced by scrha while preparing different mixes. in binary system, the replacement was from 0 to 30% (with 5% increment). on the hand, for ternary the replacement was done from 0 to 40% (with 5% increment). the experimental results revealed that scc with the replacement of 15% scrha, 10% mk and 10%scrha+10%mk was found to be optimum dosage to achieve satisfactory performance for all the parameters investigated. authors in [26] investigated the fresh and mechanical properties of scc containing an agro-waste byproduct “palm oil fuel ash” (pofa) as partial cement replacement. in this study, a new method was introduced to prepare treated pofa, called modified treated pofa (mtpofa) with full usage of original pofa. it was then used as a cement replacement at 0%, 30%, 50%, and 70% to produce sustainable scc. test results showed that the fresh properties of all concretes containing mt-pofa were ranged within scc requirements. the mechanical properties exhibited a reduction at the early ages of mt-pofa concretes. however, with increased curing time, these properties were significantly improved. scc incorporating mt-pofa performed better than control scc in terms of rapid chloride permeability test and elevated temperature. in general, mt-pofa was proposed to be cement replacement in scc. authors in [27] investigated the engineering properties of scc with magnetic water and sf, mk, rice husk ash and fa. results indicated that magnetic water and pozzolanic materials in scc can improve the selfcompatibility criterion in terms of flow-ability and viscosity. furthermore, scc mixture containing magnetic water and 20% of sf can be considered as an optimum mix design at the age of 28 days. compressive strength and splitting tensile strength increased up to 49% and 41%, respectively and the value of water absorption decreased by 55%. moreover, magnetic water can reduce the amount of high range water reducer (hrwr) required for scc up to 45%. b. fiber reinforcement authors in [28] tested five concrete mixes of steel fiber reinforced high strength lightweight self-compacting concrete (shlscc). steel fibers were added from 0% to 1.25%. a remarkable influence of steel fibers is identified due to fiber dosage being 1% and beyond. the compressive and flexural strength increased by 37% and 110% respectively. the modulus of elasticity was independent of fiber effect. authors in [29] focused on the performance of self-compacting lightweight concrete (sclc) having fibers of steel. two types of sclc, one with coarse aggregates only and another with coarse and fine lightweight aggregates were cast and tested. steel fibers (0.5% volume fraction) were added. the slump flow of fiber sclc mixes was found within 600-700 mm without segregation. all the mixes yielded compressive strength above 30 mpa and density within 1700-1900 kg/m3 at 28 days. tensile and bending strength increased due to fibers and all the mixes exhibited sufficient thermal insulation in comparison to the normal concrete. the autogenous and drying shrinkage were around 150 micro strains. authors in [1] compared the properties of scc having steel fibers and class f fa with plain normal compacted concrete (ncc). overall ten scc and one ncc mixes with constant dosage of cementitious material (35%) and 0.31% w/b ratio were cast. the effect of different aspect ratio and volumetric fraction of steel fibers on strength properties of scc and ncc were studied. it was observed that the ductility of concrete increased significantly due to the addition of fibers but a marginal increase in the engineering, technology & applied science research vol. 8, no. 3, 2018, 2969-2974 2972 www.etasr.com memon et al.: a review on self compacting concrete with cementitious materials and fibers ultimate strength properties was obtained. authors proposed 1% as volumetric fraction and 25 as aspect ratio of fibers for adequate performance of scc in terms of strength. authors in [30] investigated the compressive, tensile and flexural strength properties of scc manufactured with recycled steel fibers and silica fume. results revealed enhancement in strength properties and impact resistance of scc due to the availability of sf. authors carried a regression analysis which showed a considerable correlation between strength properties and impact resistance. authors in [31] investigated the fresh and hardened properties of self-compacting concrete containing hybrid steel fibers. in this study straight and corrugated steel fibers with different lengths (6 mm and 35 mm) and crosssections with volume ratio 1.0% to 3.0% were used to ensure the compressive strength and flexural behavior of scc. it was found that the hybrid fiber did not influence the workability but pronouncedly decreased the passing ability. based on the mechanical properties, the results showed flexural parameters of hfr-scc enhanced with hybrid fiber addition and at low dosage rates (≤2%). however, using higher amount of fibers did not cause further increase in flexural parameters. authors in [5] tried fibrillated polypropylene fibers and straight steel fibers with different aspect ratios and volumetric friction to produce fiber reinforced self-compacting concrete (frscc). they reported that scc of sufficient self-compacting properties may be produced with fibers. it was also indicated that the fiber type and mix composition had significantly affected the flow properties of frscc. authors in [32] studied scc containing hybrid fibers (steel and polypropylene (pp) fibers). steel fibers were used with three different volume ratios (0.5%, 1.0%, and 1.5%) with two amounts (0.3%, 0.9%) of two types of polypropylene fibers. it was found that volume ratio higher than 1.4% does not satisfy the passing ability requirements for scc. the mixes containing 0.9% of 38 mm pp may be used in conventional concrete. enhancement in flexural and tensile strength and toughness with increase of steel fibers volume ratio were observed, while pp fibers reduced the flexural and tensile strength but on other hand caused a beneficial effect on toughness of (hfr-scc). author in [33] studied the effect of glass fiber and fly ash on scc of m20 and m30 grade. workability and strength properties were studied with 25% fly ash and 0.05 to 0.2% of gf (with 0.05% increment) by mix volume. results showed that the compressive strength increased up to 0.15% of fiber while adequate increase in flexural strength is obtained with 0.1% of glass fibers. authors in [34] used waste plastic fibers (wpf) by cutting beverage bottles in scc mixtures produced with 0.35w/b ratio and fly ash. wpf from 0 to 2% by volume with an increment of 0.25% was used. fly ash was used as replacement at 25% cement weight. workability of scc along with compressive and flexural strength was studied at 7, 14 and 28 days. the addition of wpf showed adverse effect on workability while the compressive and flexural strength increased. authors in [35] investigated the effect of inclusion of different steel and polymer fibers on the fresh properties of scc. for this purpose various commercial and widely available types of steel and polymer fibers were used. the volume of steel fibers ranged from 0% to 1.5% and polymer fibers ranged from 0% to 0.9%. it was concluded that l-box test provides useful information of filling and passing ability of fiber-reinforced scc. in addition, lesser segregation resistance of the scc was achieved. authors in [36] determined the bond strength between old concrete and new scc. they used latex and fibers to achieve the study objectives. the factors affecting slant shear bond strength between old concrete and new scc were discussed. slant shear test was carried out. they concluded that the inclusion of latex (5% and 10%) and pp fiber exhibited enhanced slant shear bond strength between old concrete and new scc. it was proposed that prism specimen may be considered more reliable than cylinder specimen to assess slant shear strength. authors in [37] studied the shrinkage and durability properties of scc incorporating granite sawing waste (gsw) and pp fibers along with fly ash. shrinkage and durability properties; water absorption, porosity, acid resistance, sulfate resistance and chloride penetration were studied. reduced scc shrinkage was observed when using gsw and pp fibers, while, resistance against acid attack, chloride penetration and sulfate was improved. reduction in water absorption was observed at 10% of gsw. authors in [38] studied the suitability of river gravel as substitute of crushed aggregate to produce high strength steel fiber-river gravel-self compacting concrete (sfrgscc). the results exhibited improved rheology, enhanced concrete flowing, reduced yield stress and entrapped air. scc became more fragile under compression, tension and bending due to less strain capacity. scc ductility improved with steel fibers (0.75% and 1% fiber dosage), moreover, the reinforcement significantly increases the rgscc toughness which was even more significant under direct tension and bending loads. c. replacement of fine aggregates conventionally the waste materials obtained from various resources are added in scc as partially cement replacement. however, their effect depend upon various factors particularly fineness and reactivity characteristics in presence of cement and water. thus, a trend is also observed to use these materials as fine aggregates in scc, such as, coal bottom ash [39], copper slag [40], plastic waste [41] and ggbfs [42 ]etc. since this paper is focused to review the use of these wastes as cement replacement materials, the detailed review about these materials used as fine aggregate replacement in scc is beyond the scope of paper. iii. conclusions based on the literature review conducted and highlighted in this paper it may be concluded that; • a wide variety of waste materials is used as cement replacement in scc. • most studies are carried out in order to investigate the effect of these materials on fresh properties (flow ability, passing ability and segregation resistance) and mechanical properties (compressive, tensile and flexural strength). in addition, durability characteristics also have been one of the studied parameters. • the fresh properties are significantly affected by the addition of cementitious materials. however, the effect engineering, technology & applied science research vol. 8, no. 3, 2018, 2969-2974 2973 www.etasr.com memon et al.: a review on self compacting concrete with cementitious materials and fibers depends upon the type, dosage and combination of adopted cementitious materials. • mechanical properties were also remarkably affected by the cementitious materials used. the effect is significant on certain types of waste materials such as silica fume and fly ash. • different fibers added as fiber reinforcement in scc were used. • fibers exhibit pronounced effect on both fresh and hardened properties of scc. • in most of the cases the fresh properties of concrete (flow ability, passing ability and segregation resistance etc) decrease with the addition of fibers but the mechanical properties increased significantly particularly when the specimen are tested in tension and bending. type and shape of fiber, aspect ratio and volumetric fraction are observed to be major factors governing the performance of scc. • the waste materials obtained from different resources are also used as replacement of fine aggregates but the discussion in this regard is beyond the scope of this paper. further, in pakistan the use of scc is not common particularly with the applications of cementitious materials and fiber reinforcement. this is because the properties of scc vary due to variations in dosage, type, compination and application of cementitious materials and fiber reinforcement. nonetheless, the local resources from where these materials are obtained is also another major issue to consider because the properties of cementitious materials depend upon the way these materials are generated as byproducts from the local industry, agricultural land or naturally available mineral sources. the availability of cementitious materials varies with the locality, e.g. sorah [43] is one of the promising cementitious materials locally available in pakistan which may be tried in scc. thus, it may be concluded that there is always need of understanding the behavior of scc with materials and fibers obtained from local resources. acknowlegment authors are grateful to the quaid-e-awam university of engineering, science and technology, nawabshah, pakistan for providing the research facilities. references [1] b. k. rao, v. ravindra, “steel fiber reinforced selfcompacting concrete incorporating class f fly ash”, international journal of engineering science and technology, vol. 2, no. 9, pp. 4936-4943, 2010 [2] l. coppola, t. cerulli, d. salvioni, “sustainable development and durability of self-compacting 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2019, 4783-4788 4783 www.etasr.com chung: voltage enhancement on dfig based wind farm terminal during grid faults voltage enhancement on dfig based wind farm terminal during grid faults phan dinh chung the university of danang university of science and technology danang, vietnam pdchung@dut.udn.vn abstract—this paper proposes a method of retaining high enough voltage on the terminal of dfig wind turbines during a fault interval on the connected grid. this method is developed by the ideal of dynamic voltage restorer equipment and was applied to a wind turbines group. the dc-link and the grid side converter of the first dfig wind turbine in this group are utilized to support the other wind turbines. the converter is connected to a transformer, which is in series with the wind turbine group and the connected line, during an external fault. at the dc-link of the back-to-back converter of each dfig wind turbine, a dc chopper is equipped to dissipate excessive active power during the fault interval. moreover, the controllers of all wind turbines are modified to support all wind turbines in the group. the method is verified by matlab/simulink. simulation results implied that the proposed method can retain a high enough voltage on the terminal of dfig while preventing overcurrent on the rotor side. keywords-dfig; dvr; fault-ride-through capability; voltage enhancement; wind turbine i. introduction wind industry develops rapidly in many countries and many wind farms have been deployed successfully. according to [1], china owns the world’s highest installed capacity with about 211gw (35.74%), followed by usa and germany with about 96gw (16.34%) and 60gw (10.07%) respectively. in general, there are three kinds of generators used widely in wind turbines. these are: squirrel cage induction generator (scig), doubly-fed induction generator (dfig) and permanent magnetic synchronous generator (pmsg) [2]. dfig and pmsg wind turbines are more popular as they offer better control abilities [3]. however, in case of a voltage sag in the grid, the dfig wind turbine’s response differs from the pmsg’s. in pmsg, the generator is isolated from the connected grid using a frequency converter and hence, the voltage sag does not have serious negative impact on generator [4, 5]. in contrast, the stator side of the dfig wind turbine is directly connected to the external grid and hence, a voltage sag on the external grid has a serious negative impact on the generator, causing overcurrent in the rotor winding [6]. therefore, supporting dfig wind turbine during a voltage sag becomes a critical issue. many methods have been proposed that support dfig wind turbines during a voltage sag [7-14]. conventionally, a crowbar was suggested to avoid the overcurrent in the rotor side [7, 8]. however, when the crowbar in the rotor side of dfig is activated, dfig becomes an scig wind turbine consuming a significant amount of reactive power from the external grid, reducing the generator’s terminal voltage. another suggestion was the installation of a chopper at the dc-link of the back-to-back converter [9], which still allows overvoltage on the dc-link and damages the converters of the dfig wind turbine. a combination of crowbar and chopper was studied in [10], but the problem of reactive power requirement for dfig has not been solved yet. series dynamic braking resistors (sdbr) were suggested to overcome the drawback of using crowbar and chopper, because a high enough voltage can remain at the generator terminal [11], but it requires two sdbr to be installed at both stator and rotor side. fault current limiter (fcl) [12] was used to limit fault current and improve the rotor side converter (rsc) controllability, but it increased cost significantly. facts devices were also introduced to enhance the dfig’s fault-ride through (frt) ability [13, 14]. the use of a static var compensation (svc) or statcom to support the dfig wind turbine’s frt capability could not obtain high efficiency because of low voltage at its terminal during an external short-circuit. dynamic voltage restorer (dvr) can eliminate transience in the windings of dfig and restore voltage quickly, and hence the back-to-back-converter’s controllability during an external fault becomes as good as in normal operation. however, dvr is quite expensive. in order to overcome the cost of dvr, many improvements have been proposed. in [15], dvr was employed but authors utilized the dc-link of dfig wind turbine to replace the dcsource of dvr, saving investment cost. in [16], authors utilized both the dc-link and the grid side converter (gsc) of the dfig wind turbine to operate as a dvr, replacing both the dc-source and the converter in dvr. while these improvements can save investment cost, the use of these configurations in a wind farm brings some disadvantages. firstly, it is quite expensive as dvr is used at each wind turbine. secondly a lot of space is required in each wind turbine for the installation of the converter, the series transformer and auxiliary equipment, requiring a bigger nacelle and stronger foundation. this paper considers the use of a dvr to support the frt capability of a wind turbine group, utilizing the dc link and the grid side converter of the first dfig wind turbine in the group to support the others. this converter is connected corresponding author: phan dinh chung engineering, technology & applied science research vol. 9, no. 5, 2019, 4783-4788 4784 www.etasr.com chung: voltage enhancement on dfig based wind farm terminal during grid faults to a series transformer between the wind turbine group and the connected line. moreover, a chopper is installed at the dc-link of the back-to-back converter of each dfig wind turbine, to consume active power during fault periods. the converter’s controller at each dfig wind turbine is modified to minimize active power supply to the series transformer. this idea is verified by simulation in matlab/simulink and the simulation results are compared to the conventional scheme that uses a crowbar and a chopper at each wind turbine. ii. proposal of frt method for wind turbine group we suppose that a wind farm consists of several groups of wind turbines. each group consists of 4 dfig-wind turbines and each wind turbine is connected to collector line through a step-up transformer. to support the frt capability of all wind turbines in a group during external fault interval, a dvr is used as shown in figure 1. the dc-link and gsc of the first dfig wind turbine replaces the dc-source and the converter of dvr respectively. during normal operation, gsc of the first wind turbine is connected to the collector line through the low-side of the step-up transformer by switching the sw1 switch to pole a and closing sw2. when an external fault is detected, the sw1 switch is automatically switched to pole b so that the grid side converter is connected to the series transformer and the sw2 switch is opened. in this case, the dc-link, the gsc of the first wind turbine and the series transformer play the role of dvr, injecting voltage, so that a high enough voltage can remain on the collector line. fig. 1. configuration of a wind turbine group iii. dfig wind turbine a dfig wind turbine consists of a variable speed turbine, a generator and a gearbox [17, 18]. the main objective of turbine is to convert wind power to mechanical power on its shaft. the relationship between mechanical power, ��, and rotor speed, ��, is described as [19]: �� � � �� ����,�� �� ���, (1) where , �, ��, �, and � are air density, blade’s length, power coefficient, tip-speed ratio, and pitch angle respectively. the relationship between �, ��, and wind speed �� is: � � ���� (2) when � is constant, ����) has a unique maximum point with respect to �. this means that �� has a unique maximum point. the locus of maximum ��!" versus �� is described as[20]: ��!" �#��� (3) where # � � �� ����$�%,�� �$�%� and �&�' is the optimal value of �. the mechanical power on the shaft is converted to electrical power output in the stator and rotor winding of dfig. in () frame, where ( axis is aligned with the stator flux vector, dfig can be described as [20]: *�+, � ��-�+, ./+-�01+' .23 45 46 7 �80:.�82/3-�+, (4) *�+, � 7;�+;�,:; -�+, �< =�+=�,> (5) / � ?� @ ab c ad ; 3� 7 0 @1 1 0 : (6) �8 �@4546 �8=�,; �� � 45 46 2�8=�, (7) where, ;,=,� and 2 are corresponding to voltage, current, active power and slip of dfig, � and ? correspond to resistance and inductance, g,2,h,( and ) stand for rotor side, stator side, multal, ( axis, and ) axis respectively, while �8 is the magnitude voltage of stator winding. motion equation in dfig wind turbine can be described as: i +��j +' � �� @�1@2��8 (8) where k is the inertia constant of the dfig wind turbine. the dfig’s grid side converter is connected to the connected grid through a filter, described in the () frame as [21]: *l+, ��m-l+, .?m +-n01+' .*o+, .�8?m3-l+, (9) *l+, � 7 ;l+;l,:; -l+, �< =l+ =l,>; *o+, � 7 ;o+;o,: (10) �l � ;l+=l+ .;l,=l, (11) where ;,=,� and 2 are corresponding to voltage, current, active power and slip of dfig and p,q and r stand for filter, grid side and converter, respectively. the dc link in the back-to-back converter is described by: engineering, technology & applied science research vol. 9, no. 5, 2019, 4783-4788 4785 www.etasr.com chung: voltage enhancement on dfig based wind farm terminal during grid faults � +�0sj +' � �� @�l (12) where, � is capacitance and �+o is dc voltage on the dc link. iv. controler modification of converters the ability of active power generation depends on the stator voltage and hence if normal voltage can be retained on the terminal of the generator during an external fault interval, the generator can generate active power as in normal operation. however, if a voltage sag happens at the point of common coupling (pcc), active power cannot be supplied to the connected grid. hence, the controllers of wind turbines should be modified in order to ensure the stable operation of wind turbine during and after an external fault. a. the first wind turbine in the group during normal operation, the wind turbine’s rotor side converter adjusts rotor speed to obtain the maximum power point tracking of the wind turbine and retain constant voltage at the stator winding terminal, while the grid side converter is controlled to keep dc voltage at the rated value and ) component grid side current at zero. during an external fault interval, gsc is connected to the series transformer so as to inject voltage into the collector line. hence, both the rsc controller and the gsc controller should be modified. the rsc controller aims to control dc and the stator’s side voltage, while gsc’s controller injects voltage in order to retain the collector line’s voltage at about the pre-fault value. in order for rsc to adjust rotor speed or dc voltage [22], =�, can be adjusted via ;�,, using (7) and (4). maintaining a constant voltage at the stator winding terminal is carried out by =�+ via ;�+ [23]. the control diagram is shown in figure 2(a), where control blocks including the rotor speed, dc voltage, rotor current and pi controls are used as in [22, 23]. in order for gsc to maintain a high enough voltage on the collector line, gsc should inject voltage into the collector line to compensate the error between pre-fault and actual value. the current in the collector line can occur with a negative component, and hence, gsc should reduce it. the control diagram for gsc is shown in figure 2(b). (a) (b) fig. 2. controller applying to the first wind turbine: (a) rotor side converter, (b) grid side converter reference values are determined by: �l,�t�um � v��!'u+ @||xy+,,�|| (13) ;y+,,� �z;y+,� ;y,,�[\ (14) �l+,,�t�um � �n,�]�^_||`a01,�|| ;y+,,� (15) bo,ct�um �z=o+,�t�um =o,,�t�um[\ � 0 (16) where dl,�t�um is the magnitude of the positive component of the gsc side voltage, d�!'u+ is the rated voltage in the collector line referring to the gsc side voltage, ||xy+,,�|| is the magnitude of the positive component voltage in the () frame of the connected line (or pcc), referring to the gsc side voltage, dl+,,�t�um is the reference voltage in the () frame of the positive component voltage, eo,ct�um is the reference negative component current in the () frame of the connected line, while eo,c represents the actual negative component current in the () frame of the connected line. the more detailed control diagram applying to gsc of the first dfig wind turbine is shown in figure 3, where: dl+,,� ��?mfel+,,� .xl+,,� (17) ∆dl+,,c � @�?mfel+,,c .xl+,,c (18) hy,�, and hy,c are phase angles for positive and negative component voltage, respectively. fig. 3. controller applied to the first wind turbine’s grid side converter b. other wind turbines in the group at normal operation, wind turbines are controlled to generate maximum power output and maintain a constant voltage at the stator winding terminal. however, when an external fault occurs, since the voltage at the collector line is retained at a high value by the first wind turbine, other wind turbines can generate high active power. this active power cannot be transferred to the connected grid, due to the low voltage on the connected line, so the wind turbine’s controller objective of is to minimize the power output during the external fault. therefore, rsc must control active power instead of the rotor speed as in normal operation, and gsc is controlled to engineering, technology & applied science research vol. 9, no. 5, 2019, 4783-4788 4786 www.etasr.com chung: voltage enhancement on dfig based wind farm terminal during grid faults receive all active power output in the stator side instead of dc voltage control. it is noted that rsc controller’s reference power is set at minimum value. (a) (b) fig. 4. controller for the second to last wind turbine: (a) ) component of rotor side converter and (b) ( component of grid side converter in order to control the rotor speed or the active power in the () frame, the ) component’s rotor current must be adjusted via ;�,, as shown in figure 4(a). it is possible to adjust the dc voltage on the dc link or the active power in the grid side converter, the ( component grid side current via ;l, , as in figure 4(b). here, pi control is used for rotor speed control, active power, rotor current, and grid side current control, as mentioned in [24, 25]. transferring from normal to abnormal operation mode is carried out when an external fault is detected. c. chopper a chopper is installed in parallel with the dc-link at all wind turbines to dissipate all active power output generated by dfig. a chopper and its controller are described in [26]. v. verification to verify the proposed model, matlab/simulink was utilized to simulate a group of wind turbines with two methods, the proposed and the conventional. the conventional method which uses a crowbar at the rotor side and a chopper at the dc link of each generator is described in [26]. the parameters of a 1mw dfig-wind turbine used in simulation are given in [27]. it is supposed that an external short-circuit occurs at 2s and is cleared at 2.3s on the feeder, as in figure 1. simulation results are shown in figures 5 to 9. figure 5 shows the voltage at the terminal of the wind turbines. as it can be seen from figure 5(a), by using the proposed method the voltage on the stator winding terminal of all generators remains at around normal value during the external fault interval, while using the conventional method it is reduced to around 30v. concerning the grid side’s voltage of the first wind turbine, as shown in figure 5(b), with the use of the proposed method quite significant fluctuations exist at the beginning and at the end of the external fault. on the other wind turbines, the grid side voltage is retained at the stator winding’s terminal. therefore using the proposed method, the voltage at the terminal of wind turbines is better than using the conventional method. since the stator winding terminal voltage is reduced insignificantly at the beginning of the fault, the rotor current of all wind turbines at this time is smaller than the one obtained by using the conventional method, as shown in figure 6. therefore, using the proposed method, the overcurrent in the rotor side is mitigated significantly when the fault occurs. (a) (b) fig. 5. voltage at terminal wind turbine system: (a) stator side of generator and (b) grid side converter of the first wind turbine (a) (b) fig. 6. rotor current: (a) the first wind turbine and (b) other wind turbines normally, during an external fault interval, as wind power is almost constant and the active power cannot be distributed to the grid, the rotor speed increases. this can be seen in figure 7 for both methods. however, using the proposed method, the voltage at both the stator and the grid side is retained at a high value and the active power generated by dfig is dissipated on the chopper at the dc-link. therefore, in the first wind turbine, the maximum value of the rotor speed during the fault interval is still smaller than using the conventional method, as shown in figure 7(a). this benefit can be seen more clearly in the other wind turbines (figure 7(b)). the rotor speed in these wind turbines when using the proposed method reaches only 1820rpm while using the conventional method reaches 1980rpm. engineering, technology & applied science research vol. 9, no. 5, 2019, 4783-4788 4787 www.etasr.com chung: voltage enhancement on dfig based wind farm terminal during grid faults (a) (b) fig. 7. rotor speed: (a) the first wind turbine and (b) other wind turbines as it can be seen from figure 8 the active power supply to the grid is almost zero during the fault, in both methods, due to the low voltage on the connection line. however, in the conventional method the wind turbines still receive a small reactive power from the grid, while in the proposed method it is almost zero. when the external fault is cleared, after a short interval, wind turbines can supply stable power to the grid. (a) (b) fig. 8. power output in total: (a) active power and (b) reactive power vi. conclusion in this research, the dc-link and the grid side converter of the first dfig wind turbine in a wind turbine group is utilized to support the others in the case of an external fault. they are connected with a series transformer to inject voltage into the collector line. each back-to-back converter of each dfig wind turbine is equipped with a dc-chopper to dissipate the excessive active power during the fault period. moreover, the controllers of wind turbines are modified to retain a minimal active power generation. simulation results in matlab/simulink indicated that by using the proposed method the wind turbine group has better performance than using the conventional method. acknowledgment this work is supported by the university of danang university of science and technology, code number of project: t2019-02-47. references [1] global wind energy council, global wind report 2018, available at: 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2020, 5590-5595 5590 www.etasr.com malelis & danikas: insulating materials at very low temperatures: a short review insulating materials at very low temperatures: a short review petros malelis democritus university of thrace department of electrical and computer engineering power systems laboratory xanthi, greece petrmale@ee.duth.gr michael g. danikas democritus university of thrace department of electrical and computer engineering power systems laboratory xanthi, greece mdanikas@ee.duth.gr abstract—in this paper, a short review is given on insulating materials at very low temperatures. various insulating materials are investigated in terms of phenomena such as partial discharges. some of the factors affecting the behavior of the insulating materials at very low temperatures, such as the quality of the electrode surface, the stressed insulation volume, and the existing bubbles, are also reported and commented upon. proposals for future research are also discussed. keywords-superconductors; high temperature superconductors (hts); cryogenic insulation; liquid nitrogen; partial discharges; streamers; aging of materials i. introduction since the discovery of superconduction in 1911, there were plans for the design of superconducting cables [1]. after several decades from this discovery, the development of superconducting cables seemed to be possible. since the mideighties of the last century, there is a drastic development in superconducting research because of the discovery of high temperature superconductors (hts) in the critical temperature tc>t of liquid nitrogen (77k) by georg bednorz and karl mueller of ibm, rueschlikon, switzerland. let us notice that the power needed at room temperature for the function of a refrigerator at 77k is lower than the one tenth of the power needed for the function of a refrigerator at 4 k. regarding superconductivity and its possible applications, it becomes apparent that electrical insulation is pivotal to the development of reliable energy systems. a breakdown of the electrical insulation may have catastrophic consequences for a superconducting energy system. a hts superconducting cable offers reduced losses, it is more environment-friendly, it increases the reliability of the system and, it is more flexible than most traditional cables. there is a hope that hts superconducting cables may give the solution for large urban centers in the future, as the global population increases and the demand for electricity becomes more acute. to be sure, the new technology has to prove that its reliability is at least as good – if not superior as that of the conventional systems. such superconducting cables must withstand probable pressure variations as well as some electrical overstressing. in the context of this paper, some aspects of the electrical insulation for superconducting applications will be mentioned and analyzed. moreover, some proposals for future research will be made. ii. some general comments electrical insulation is crucial to the good performance of very low temperature energy systems or for any energy system for that matter. typical applications of superconducting systems are the superconducting faults current limiter (sfcl) and the superconducting magnetic energy storage system (smes). hts transformers are also a possible alternative to conventional transformers since they reduce the losses by 60% or even more. they are more environment-friendly and they use liquid nitrogen instead of mineral oil as insulation and coolant. they are more reliable than the conventional transformers. their possible applicability has been demonstrated in countries such as japan, the usa, germany, south korea and new zealand [3]. hts cables have been built in the past few decades. such cables use as insulation either non-polar polymer films with liquid helium or nitrogen, or polymer films such as cross-linked polyethylene xlpe. in the case of underground cables, insulating materials that have been used for conventional applications, have been adapted to hts applications. consequently, materials such as polypropylene laminated paper (pplp) [4], ethylene propylene rubber (epr), xlpe, low-density polyethylene (ldpe) and ptfe have been investigated accordingly [4-6]. however, with the requirements for higher voltages (e.g. 275kv), superconducting cables had considerable dielectric losses [7]. in such voltages, in order to reduce dielectric losses, other insulating materials were used (e.g. tyvek – a polyethylene nonwoven fabric – as opposed to conventional pplp, or the ultra high molecular weight polyethylene (uhmwpe)) [8-10]. iii. on superconductivity superconductors transfer practically current with zero losses when their temperature falls below a certain value, which is called “critical temperature”. superconductors preserve their properties in a region which is defined by three quantities, namely the critical current density jc, the critical temperature tc (the temperature at which the resistance becomes zero) and the critical magnetic field hc (as the magnetic field increases the superconductivity of the material is corresponding author: michael g. danikas engineering, technology & applied science research vol. 10, no. 3, 2020, 5590-5595 5591 www.etasr.com malelis & danikas: insulating materials at very low temperatures: a short review reduced). the higher the values of all three aforementioned quantities, the easier becomes the application of the superconductors. increase of one of the aforementioned quantities may return the material to its previous (nonsuperconducting) state. when a superconductor loses its superconducting state, it needs a considerable amount of time in order to revert to superconduction, whereas when a superconductor has an excessive current, the consequences may be deleterious because of the released heat [11, 12]. hts superconductors are more efficient than common superconductors which function at lower critical temperature. hts superconductors are in superconducting state at temperatures higher than 77k in applications with weak magnetic fields. on the contrary, materials of lower critical temperatures, such as nb-ti and nb3sn, must be cooled at 4k in order to have superconducting properties. however, in this way, their cost rises [13]. regarding high voltage cables, there are two main categories of cables, the cables of warm dielectric (wd) and the cables of cold dielectric (cd). cables of wd have liquid nitrogen whereas the solid insulation can be at room temperature. their insulation can be xlpe, pplp or ethylene propylene rubber (epr). the insulation is applied on the outer wall of the cryostat. this type of cables presents higher losses, which in turn cause higher released amounts of heat [14]. in the cd cables, the insulating material is on the inner wall of the cryostat. in this case, the liquid nitrogen functions both as coolant and as dielectric. this type of cables has an increased cost but, on the other hand, has lower losses and a higher conduction in higher currents [13, 15]. in the triax cables, all three phases are in a single cable. such a construction reduces the electric losses and requires half of the superconducting material compared with the cd cables. triax cables occupy less space than the aforementioned wd and cd cables [13]. iv. insulating materials for superconducting applications, partial discharges, and electrical trees as far as cables at very low temperatures are concerned, there are four types of insulations: 1) vacuum insulation with solid insulators, 2) liquid insulation with solid insulators, 3) tape insulation impregnated with liquid helium or liquid nitrogen, and 4) liquid helium with solid insulation [4, 16]. it goes without saying that in the above cases, the solid insulation must be compatible with the liquid or the vacuum, that the thermal expansion or contraction must be within certain limits and that the cost of construction must be reasonable [17]. generally speaking, an insulation is affected by factors which tend to reduce its molecular structure, such as high temperatures (which influence the conductivity and the generation of partial discharges), mechanical stressing (which reduces the distance between the electrodes), affecting thus the breakdown strength [18]. partial discharges are very dangerous in very low temperatures since they produce significant amounts of heat, leading in this way to the total failure of the insulation [1, 16]. in the case of superconducting insulation, partial discharges (pd) may contribute to the increase of dielectric losses. a way to reduce such effects is to increase the pressure, preventing therefore the creation of bubbles. in this way, pd activity is reduced and the inception voltage increases. pd measurements are considered crucial for cryogenic applications because pd are the main source of aging and breakdown of insulations in such low temperatures. various techniques have been proposed in relation to such measurements. phase-resolved partial discharge (prpd) measurements as well as the current pulse waveform analysis (cpwa) measurements have been proposed for a consequent study of pd in very low temperatures insulating systems. whereas the first has the advantage of offering an overall picture of the state of the insulation, the latter method can obtain detailed individual pd currents pulses together with the time transition from pd inception to breakdown with the pd detection sensitivity of 0.1pc [4, 19–22]. it has to be noted that during the past few years, a new technique was developed [23]. the latter technique is named chaotic analysis of pd (capd) and is based on three normalized parameters obtained from two consecutive pd pulses, i.e. amplitude difference (pt ), occurring time difference (tt ) and correlation between pt and tt. authors in [23] claim that besides prpd, their proposed method is suitable for hts applications. electrical treeing in polymers at cryogenic temperatures may also be noted. electrical trees may be the result of pd and/or some mechanical stressing. inception voltages for treeing are in general higher than the inception voltages at room temperature, and even if the electrical trees start, their development is much slower [17, 24]. in [24], a significant point is made, namely that, if a polymer is defect-free, it contracts heavily at very low temperatures and inadvertently introduced voids are squeezed out. however, if pd occur in a void at cryogenic temperatures, deterioration may proceed more rapidly and malignantly than in the case encountered at room temperature. v. hts insulation insulation is crucial to the successful performance of supeconducting apparatus [25]. the characteristics of liquid nitrogen (ln2) are fundamental to many hts applications. moreover, the role of composite insulating systems (from ln2 and solid insulating materials, such as paper and epoxy) is also very important, as well as the gaseous nitrogen (gn2) and the vacuum [21]. for the correct, reliable and practical design of an hts insulation is necessary to examine factors that are crucial for the cryogenic liquids, such as the state of the electrode surfaces, and their effect on the breakdown strength [26]. as critical factors influencing the pd behavior and the breakdown strength of ln2 are the quality of electrode surfaces, the volume of insulation, the presence of bubbles and foreign matter [27, 28]. vi. infuence of electrode surface, stressed volume and bubbles it is well known that the breakdown strength of conventional insulating materials is affected by the electrode surface (quality of the surface as well as size of the electrodes) and the stressed volume [29, 30]. relatively recently, it was shown that the breakdown strength decreases with the increase of the gap spacing and the electrode area for sub-cooled nitrogen (sln2). such phenomena were observed because the amount of impurities and bubbles increases with the gap engineering, technology & applied science research vol. 10, no. 3, 2020, 5590-5595 5592 www.etasr.com malelis & danikas: insulating materials at very low temperatures: a short review spacing and the electrode diameter [31]. in the same publication, it was reported that the number and size of bubbles as the weak points to cause breakdown can be reduced by high pressures in sln2. similarly the low temperatures contribute to reduce the number and size of bubbles. the question as to whether the size effect is due more to the electrode area or to the stressed volume in sln2, was treated in [21, 32]. experimental results revealed that the breakdown mechanism changed from an area dominant to volume effective region at larger electrode configurations in sln2 [32]. such behavior was also noted in conventional insulating liquids [29, 30, 33, 34], i.e. that the influence of the stressed volume is more crucial with larger electrodes. in the presence of bubbles, breakdown strength is reduced. in such a case, the breakdown voltage depends on the bubble volume. relatively recent research indicated the dependence of the breakdown strength of sln2 on the bubble presence. on the other hand, in such a case, an increase of pressure may have a beneficial effect on the breakdown strength since higher pressures suppress vapor bridge formation avoiding thus a precipitous drop in breakdown strength [35]. bubbles represent the weak link in sln2 since the discharge activity starts from them. in fact, paschen’s law is also valid at cryogenic temperatures making thus easier the calculation of inception voltages [36, 37]. furthermore, as was reported in [38], the development of discharges in bubbles is a process of ionizations and hence an increase in pressure affects the quantity of micro-bubbles. increasing pressure and reducing temperature may therefore offer an effective means to reduce the probability of inception of pre-breakdown streamer activity since the aforementioned quantities may influence streamer behavior and thus reduce the number of pd events from an anode tip [38]. reducing temperature has as a result the condensation of existing bubbles, which in turn leads to a decrease of the electrically weak links [39]. a sudden increase of temperature may cause – in combination with the electric stress – the so-called bubble disturbance. the latter may reduce the voltage breakdown from 165kvpeak to 80kvpeak for a gap spacing of 8mm with a sphere-plane electrode arrangement [31, 40]. vii. infuence of uniform and non-uniform electric fields the applied electric field has a preponderant role in determining the breakdown strength of insulating materials and/or of the insulation in electrical apparatus [16]. insulating materials at very low temperatures could not be an exception to the rule. earlier work indicated that the breakdown voltage of liquid helium (he) and liquid nitrogen (ln2) is higher with uniform fields than with non-uniform fields [27]. the initial increase of breakdown voltage with the gap spacing for both the aforementioned liquids, even with a point-plane electrode arrangement, and the subsequent leveling-off may be due to the low latent heat of cryogenic liquids, which may lead to the creation of vapor around the point electrode [27]. similar data to [27] were collected in [41], where authors observed that the impulse breakdown voltage is higher than the ac breakdown voltage for both sphere-plane and point-plane electrodes, with the former giving a much more distinct difference than the latter. agreeing qualitatively with [27], the leveling-off of the breakdown voltage with increasing the gap spacing – in a sphere-plane arrangement was also reported in [42], where the leveling-off was interpreted with the stabilization of the maximum electric field at larger gaps. the importance of bubbles on breakdown strength with various electrode arrangements was pointed out in [42]. more generated bubbles lower significantly the ac breakdown strength with both sphere-sphere and with tape electrodes, their effect being more emphatic with the latter [42]. the applied electric field has a vital influence on streamer propagation. streamer propagation is to a significant extent determined by the macroscopic electric field [17, 27]. experimenting with sphere-plane electrodes and with pressures of 500kpa, it was shown that positive streamers have a higher velocity than negative streamers and thus, positive streamers result in lower breakdown strength [17, 27]. such data were confirmed in yet another publication, where it was indicated that a transition from slow to fast positive streamer was observed at a threshold voltage below the breakdown voltage [43]. in [43], it was pointed out that at very low temperatures, with sphere-plane electrodes, and with impulse voltages there is a remarkable polarity effect [44], namely that at positive polarity a faster streamer was noticed whereas with negative polarity the phenomenon was slower. in this respect there is agreement between [45] and [17, 27]. viii. on the degradation of composite insulating systems pd consist one of the major sources of degradation of insulating materials [46, 47]. in an non-uniform electrode system containing a disc of ptfe in ln2, an increase of the applied voltage led to an increase of the cumulative number of pd as well as of their maximum values [38]. an increase of pressure in such an insulating system from 100kpa to 400kpa, reduces the pd number, whereas a reduction of temperature does not have any remarkable effect on the slow negative streamers. on the contrary, a reduction in temperature causes a reduction of the fast positive streamers [38]. further studies regarding the effect of pressure on the inception stress of a composite insulating system consisting of ln2 /polypropylene, indicated a decrease of inception stress by about 13% 40% when the pressure was reduced from 200kpa to 100kpa [48]. in a system consisting of ln2/polypropylene laminated paper (pplp) with butt gaps, it was noted that the inception stress depended on the butt gap thickness and that thicker butt gaps resulted in a larger inception stress drop. this is probably due to the existing probability of weak points of the electrical insulation at butt gaps [49]. regarding the role of butt gaps and their related parameters, there is a striking similarity between the observations of the above publication and those reported using conventional insulating systems [50, 51], i.e. that the butt gaps – if not well impregnated – may be the weak point of a composite insulation. pd current pulses recorded at pressures of 0.1mpa, 0.12mpa, 0.15mpa, and 0.2mpa, confirmed – in a more recent publication the above observations, namely that with increasing pressure, the pd current pulses become smaller and smaller [21]. solid insulators are used in combination with ln2 for some hts applications. various solid insulating materials have been engineering, technology & applied science research vol. 10, no. 3, 2020, 5590-5595 5593 www.etasr.com malelis & danikas: insulating materials at very low temperatures: a short review tried, such as pplp, tyvek, nomex, kapton, pva, pmma, pvb and pa66. the breakdown strength of pplp, kapton and pa66 was shown to be superior to the breakdown strength of other materials [52]. in yet another study by the same group of authors, it was indicated that the breakdown strength of kapton/ln2, polycarbonate/ln2, g10/ln2 (g10 being fiberglass reinforced plastic) and polyetherimide/ln2 depends on the frequency, and it indeed decreases with frequency [53]. such a decrease is possibly due to the dissipation of space charge in the dielectric. according to earlier works, charge dissipation from charge traps depends on the frequency of the applied voltage leading to reduced partial discharge at low frequency [54, 55]. the properties of solid insulation at very low temperatures depend also on the additives as well as on the particular experimental conditions. for example, the hdpe presents a small increase of tanδ at 4.2k in comparison with the tanδ at 77k. mechanical properties, such as the modulus of elasticity, are also most important since a combination of electrical and mechanical stresses may cause cracks [56-60]. ix. discussion and proposals for future resdearch regarding hts applications, it can be said that liquid nitrogen is an excellent medium for high voltage apparatus. it acts as both insulating and cooling medium for many hts applications. it also has the advantage of low cost. it is chemically inert and thus the risk of fire is considerably reduced. one of the problems facing the hts cables is that they must have high currents in order to have beneficial economic advantages for the companies and the end users. in the case of interruption of the superconducting state there may be a sudden failure, the latter may provoke a chain reaction which in turn may cause a generalized instability of the whole network. in such a case, the temperature of the cable may increase dramatically. that may have as a consequence that a considerable time interval will be required in order for the cable to reach its usual superconducting state. the remedy of a larger number of lapped tapes is not feasible since that would require increasing costs. consequently, the possible solution will be in improving the materials of such a cable. improved hts cable designs based on ybco as well as a reduction of the cost of cooling systems are proposed [61, 62]. during the last decade, the cost of superconducting materials has been reduced by about 10% per annum [62] and it is hoped that this trend will continue. furthermore although the cost of a superconducting apparatus is still high in comparison with the cost of a conventional apparatus – a factor that has to be taken into account is that much lesser space is required to accommodate superconducting equipment [63, 64]. with respect to materials research, further work has to be performed regarding the surface discharges in ln2 /polymeric insulation uniform electrode arrangements [65]. moreover, very low frequency (vlf) measurements regarding the insulation at cryogenic temperatures may offer an effective diagnostic technique to assess early insulation degradation [6668]. partial discharges due to defects must be further explored with insulating systems at very low temperatures both w.r.t their mechanisms and classification, as was done with conventional polymers at normal temperature with isolated as well as multiple defects [69, 70]. it is needless to say that with the advent of polymer nanocomposites, a new prospect opens in the field of the applications at very low temperatures [7174]. research in this direction has already been performed and the prospects of employing polymer nanocomposites has been discussed, although one gets the impression that more effort was put into clarifying their mechanical 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967-976, 2012 [77] n. manoharan, v. selvakumar, “cryogenic mechanical properties of pp/mmt polymer nanocomposites”, indian journal of science and technology, vol. 7, no. s7, pp. 16-23, 2014 [78] s. fu, z. sun, p. huang, y. li, n. hu, “some basic aspects of polymer nanocomposites: a critical review”, nano materials science, vol. 1, no. 1, pp. 2-30, 2019 [79] m. o. pace, i. sauers, d. r. james, a. r. ellis, “aging of lapped tape insulated model cables at cryogenic temperature”, annual report conference on electrical insulation and dielectric phenomena, cancun, mexico, october 20-24, 2002 microsoft word 7-2324_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3525-3529 3525 www.etasr.com abro et al.: influence of austenite phase transformation on existing microstructure of low c-mn steel influence of austenite phase transformation on existing microstructure of low c-mn steel shahid hussain abro department of materials engineering ned university of engineering & technology karachi, pakistan engrabro@neduet.edu.pk alidad chandio department of metallurgical engineering ned university of engineering and technology karachi, pakistan alidad@neduet.edu.pk abdul rauf jamali department of materials engineering ned university of engineering & technology karachi, pakistan engrabdulrauf@neduet.edu.pk syed aqeel shah department of metallurgical engineering ned university of engineering and technology karachi, pakistan aqeelshah@neduet.edu.pk abstract—cold heading quality chq steel is widely used for making small components due to its excellent cold heading response. austenite nucleation and growth morphology of a commercial chq steel has been studied by continuous heating experiments using lead-bath up-quenching at different heating temperatures. modern optical microscope olympus gx51, scanning electron microscopy techniques have been deployed to reveal and interpret the microstructure. it was found that at 740°c the microstructure shows lack of homogeneity, hence the cold-head-ability of chq steel is anisotropic. at high temperatures, in austenite domain, at 60sec, the resultant austenite is highly homogenous. then the cold-head-ability properties of chq steel turned to be isotropic. keywords-chq steel; up-quenching; phase transformation; microstructure; heating rate; austenite i. introduction chq steel components have been widely used in automotive, ship and aerospace engineering, thermal plants, etc. parts such as fasteners, pinions, connecting rods etc. are being manufactured by cold heading. in cold heading operations, the mechanical properties of such components are directly or indirectly controlled by metallurgical aspects like heat treatment. therefore it is unavoidable to design such parameters in thermal treatment which refines grain size, increases hardness and mechanically stabilize the microstructure by phase transformation. rapid austenitizing (up-quenching) refines the microstructure, eliminates distortion and provides uniform dispersion of carbide particles in the martensite matrix. in [1], authors worked on chq steel and microstructures, compositions and mechanical properties. they proved that good quality of feed stock of chq steel wires for increasing tool life should have a uniformly distributed microstructure. authors in [2] worked on microstructural consequences on chq steel grade 1036m. they emphasized their experiments on six microstructures obtained by individual heat treatment analysis. they gave attention to calculate pearlite volume fraction in each sample. the reduction in the pearlite phase can improve the ductility of chq steel [2, 3]. authors in [4] studied the deformation and thermodynamic behavior of en 10263 chq steel. they developed a model which can be imposed to a certain chq steel to conduct the elasto-viscoplastic response of that steel. they dealt with ferrite and pearlite microstructural steel. authors in [5] studied the parameters of rolling and cooling and their impact on microstructure and mechanical properties on different chq steels. they observed that the mechanical properties can be enhanced by refinement of ferrite-pearlite grains. they applied fast cooling rate to their steel samples and concluded that fast cooling could prevent the development of gamma-alpha phase transformation. the ferrite fraction manipulates the ductility and the martensite enhances the strength of steels. the combination of both microstructural constitutes can tailor the overall mechanical properties of steels [6]. to the best of our knowledge no previous study on chq steel dealt with the austenite phase transformation using upquenching technique. precise attention has been given in this work to study the austenite formation in chq steel. this technique can be employed to other grades. furthermore, soaking at high temperature in austenitic domain, the heterogeneously formed structure becomes anisotropic in nature, therefore the degree of non-homogeneous anisotropic nature of that steel is proportional to the formation and initiation of austenite phase volume percentage. the distribution of uniform volume percentage of austenite in this steel is mechanically stabilized. due to uniform distribution of microstructural constituents there will be a minute probability of abnormal grain growth during or after cold heading operations. as a result the steel becomes more favorable for cold heading process [7]. engineering, technology & applied science research vol. 8, no. 6, 2018, 3525-3529 3526 www.etasr.com abro et al.: influence of austenite phase transformation on existing microstructure of low c-mn steel ii. experimental procedure the chemical composition of the experimental steel is shown in table i. table i. chemical composition c si mn n cr 0.463 0.241 0.872 0.0049 0.25 the steel was heated up to 1200°c and was held at that temperature for 120 minutes for solution treatment purposes. after the solution process, the steel was engaged in hot rolling to reduce its thickness. a reduction of 80% was achieved in four passes. steel plates were then cut at 800°c and after cutting the plates were air-cooled. specimen cutting was performed to reduce the size of the plates. lead-bath furnace connected with thermocouple was used (figure 1). fig. 1. rapid heating cycle in lead bath up-quenching. austenitizing temperature for up-quenching heat treatment was selected by asm metals hand book [8]. after austenization the samples were water quenched, then were cut perpendicular to rolling plane direction, mounted and polished according to standard metallographic methods followed by polishing in 1µm and 0.5µm diamond paste as the last step for observing the structural features under optical photomicroscope. the samples were then ultrasonically cleaned in order to remove stubborn contaminants, chemical residuals, dirt or any finger print formed on the surface of the sample during polishing. two step etching technique, 2% nital and 4% picric acid was used to reveal the microstructure. the continuous heating experiments were performed in a lead bath as shown in table ii. table ii. continuous heating experiments. no temperature (°c) time (sec) 1 740 10, 15, 30, 60 2 770 10, 15, 30, 60 3 800 10, 15, 30, 60 iii. results and discussion a. microstructure evolution microstructure, as shown in figure 2, was carried out by using a solution of 2% nitric acid diluted in 100ml ethanol, which is a common etchant used to reveal the ferrite and pearlite grain boundaries. this etchant successfully revealed the grain boundaries and its only drawback was that it was difficult to distinguish eutectoid-ferrite from martensite because both appeared white. to differentiate between transformations such as martensite phase and ferrite phase, 2step etching, 2% nital followed by 4% picric acid was introduced. examination of this microstructure under light microscopy was not again satisfying because the distinction of the three phases (ferrite, pearlite and martensite) was still unclear. color etching technique using lepera solution then was implied to steel samples as described in [9]. a detailed inspection under polarized light in the microscopy successfully disclosed the three phases individually. then it was easy to determine the volume fraction of austenite with respect to increasing time and temperature. blue, brown off-white and white colors appeared as ferrite, bainite, martensite and retained austenite respectively. further details about this tint etching technique of lepera can be found in [9]. the volume fractions of displacive phase of martensite was calculated by using the point counting method described in [10]. fig. 2. microstructure using 2% nital fig. 3. micro structure using lepera etchant. b. microstructural features t0 the as rolled microstructure shown in figure 4 is a reconstructive phase having ferrite and pearlite only. the territory of pearlite is decorated with allotromorphic ferrite ring commonly termed as pro-eutectoid ferrite. the interface between this ring and pearlite colony acts as the austenite grain engineering, technology & applied science research vol. 8, no. 6, 2018, 3525-3529 3527 www.etasr.com abro et al.: influence of austenite phase transformation on existing microstructure of low c-mn steel boundary during transformation. the formation of martensite can take place within this territory because the coordinated motion of military transformation is weak against this ring and cannot cross this grain boundary barrier which behaves as a strong defect. the microstructure obtained at 710°c, and 10s, 30s, 300s holding time during up-quenching is slightly lower than eutectoid temperature which shows formation of larger fraction of “new” ferrite phase volume with respect to increasing holding time. fig. 4. reconstructive phase. at holding time of 300s, it can be noticed that deformed grains which are relatively enlarged are replaced by a freshly formed bunch of un-deformed ferrite grains which are nearly equiaxed, will nucleate and can grow above the eutectoid temperature which can be named as lower critical temperature or ac1. this recrystallization can take place until the original ferrite grains have been absolutely ingested at 300s holding time. whenever recrystallization of ferrite grains reaches a higher volume, it is an indication of decreasing hardness and strength but on the other hand ductility may increase. spheroidizing provides the needed ductility for cold heading [11]. during cold heading operations there is a strong driving force for these soft metals to become hard by cold working phenomenon. consequently they may lose their softening property and there is a strong driving force of abnormal grain growth and hence microstructure becomes un-identical. in order to decrease the degree of this non-uniformity, steel samples were up-quenched at different austenitic domains in lead bath. c. microstructural features at t1 (740°c, 10, 15, 30, 60sec) after heating at 740°c for scheduled soaking time, the stable recrystallized ferrite become unstable and starts to initiate the nucleation of austenite which moves heterogeneously upon cooling and the civilian transformation turns into military transformation. the extent of which recrystallization completes before the austenite begins to form influences the kinetics of austenite formation and the spread of austenite nuclei in pearlite domain [12]. the insoluble and discarded carbon by austenite and ferrite was not observed, possibly because of the high heating rates in the up-quenching bath, so the majority of austenite formation in this steel was obtained only in pearlite territory. because of the shorter path it was easy for cementite plate to supply carbon to neighboring ferrite. evidence of phase transformation can be seen at 30s and 60s holding time. in the microstructure obtained after 15s and 30s holding, the identification of austenite phase was not easy. d. microstructural features at t2 (770°c, 10, 15, 30, 60sec). the captured microstructure at 770°c can be seen in figure 5. austenite nucleation and growth were observed during the entire process but at 10s and 15s a low volume fraction of austenite was observed. the most possible reason behind this delayed transformation was that up to 10s holding time there was an incubation period of austenite nucleation. however, with extension of soaking time to 30s and 60s, austenite growth was rapid by consuming pearlite phase. ferrite packet size has declined in comparison with the 740°c microstructure. at 770°c, the mobility of atoms and the diffusion co-efficient of carbon might have increased. at this temperature it was noticed that a high fraction of pearlite was consumed for austenite mass production, but a very fine and dark trace of the boundary wall had still remained between pro-eutectoid ferrite and pearlite territory which acted as the prior-austenite grain borderline. fig. 5. austenite nucleation and growth. e. microstructural features at t3 (800°c, 10, 15, 30, 60sec) micrographs at 800°c reveal that the spiral of allotromorhic ferrite which was tightly surrounded at lower temperatures has been broken and the allotromorph slowly decreased and almost disappeared after 60s. the stability of austenite growth becomes stronger thus the degree of isotropy and homogeneity increases. the response during the forming of austenite is much different both at low and high temperatures. at elevated temperature and into the austenite region, the degree of transformation first increased and then decreased because at high temperatures the difference in free energy of the parent phase and product phase drastically declined, however the diffusion coefficient raised at higher level, meaning that minor phase had become major phase and austenite phase has been stabilized. to oversee this logical phase difference at low (740°c), and high (800°c) temperature, sem micrograph has been obtained (figure 6). austenite forming increases hardness engineering, technology & applied science research vol. 8, no. 6, 2018, 3525-3529 3528 www.etasr.com abro et al.: influence of austenite phase transformation on existing microstructure of low c-mn steel while the subsequent tempering can reduce hardness and improve toughness so both processes simultaneously can be achieved through up-quenching in lead bath. ausforming results in instantaneous increases in hardness, but this effect is substantially reduced after tempering under conditions which are suitable for fasteners [13]. fig. 6. sem micrographs f. mechanical stabilization and glissile transformation to stabilize the austenite thermodynamically, some alloying elements like nickel and manganese are added in steel. shape deformation on the other hand mechanically stabilizes the structure. this shape deformation involves the movement of glissile interface [14]. to ensure that this movement becomes phase change (displacive) and not just reorientation of the lattice (reconstructive), sem micrographs at early (740°c, 60s) and final stage (800°c, 60s) have been obtained. it is observed that the displacive transformation grows to a limited size at 740°c in which ferrite plate transforms slowly. at final stage the transformation propagates rapidly by forming a martensite plate which has very high strain energy against the dislocations formed during the shape deformation of austenite in invariant plane strain. the mechanical stabilization occurs when the strain required to initiate the stabilization is higher than the opposing dislocation which has a glissile interface that has to cross the dislocation barrier. to calculate this critical strain, (1) can be used: 1/2 3/21 8 (1 s b g gb b l ε  ∆ = + τ  π −ν)   (1) where b is the burger vector, ∆g is free energy, v is poisson’s ratio, g is the shear modulus, and l is the average distance moved by dislocation [15]. interface is the set of dislocations which allow the two crystals to connect to each other during transformation. this sort of interface is known as glissile interface, must exist between parent and product phase allowing rapid transformation without any diffusion involving in the system. displacive transformation is only possible when such an interface can be created between two crystals. it can also be observed that an invariant line is left behind between the product and parent phase, meaning there is not any distortion or rotation along this line and hence the atomic arrangement of austenite and martensite match perfectly at that line and the transformation that changes the parent phase (austenite) into the product phase (martensite) leaves at least one line undistorted and unrotated as evidence that the transformation is displacive rather than reconstructive. a detailed investigation of microstructural features at each temperature indicates that all pearlite is digested on the forming of austenite but a small trace of the boundary line is still left behind which is nothing but the p-austenite grain boundary so the gliding of glissile interface is possible within this protected area since the glide of atoms cannot be endorsed across these austenite grain boundaries. hence, it can be concluded that grain boundaries in the microstructure, presence of dislocations, available interstitial atoms, stacking faults and vacant lattice sites are normally not essential to describe an equilibrium state of phases, however if they are present they can be promoted to the process of phase transformation [16]. iv. conclusions three stages during austenite formation in up-quenching of a plastically deformed chq steel of 80% reduced thickness have been studied at different holding temperatures (710°c, 740°c, 770°c and 800°c). it has been found that microstructural features and mechanical stabilization of plastically deformed steel specimens can be restored to their normal pre-deformed states using up-quenching treatment. during this process recovery, recrystallization and grain growth phenomena occurred and there is a reduction in dislocation density. during the recrystallization formation of new and fresh ferrite, grains free from strain and grain growth increase the average grain size and austenite volume fraction. austenite formation is possible in pearlite phase and there is no evidence found about the nucleation of austenite at ferrite-ferrite grain interface. up-quenching refines the grain size so there is a strong tendency to achieve finer microstructure in conventional chq steels without additional alloying and heat treatments. uniform distribution of microstructure can increase the rate of elongation thus chq steel coldheability can be enhanced. the rate of nucleation and the rate of growth increases at higher temperatures to form austenite phases in bulk. rapid heating (up-quenching) is the main cause which could not permit carbides at ferrite-ferrite interface. with increasing holding time and temperature, pearlite packet size decreases and consecutively is turned into martensite upon cooling. proeutectoid α network first breaks and then slowly disappears at higher heating temperatures. finger type growth morphology was observed at 800°c. this sort of growth morphology is observed on pearlite laths perpendicular to the ferrite/pearlite grain boundary and is not observed if the laths are parallel to it. in the parallel case, there is strong tendency for bainite structure to be formed. the identicality and consistence of microstructural features is best executed by continuous heating in the high heating zone which is best suited to study these microstructural features at lowest possible time period to save the other parameters. references [1] t. das j. y. li m. painter e. summerville, “evaluation of two aisi 4037 cold heading quality steel wires for improved tool life and product engineering, technology & applied science research vol. 8, no. 6, 2018, 3525-3529 3529 www.etasr.com abro et al.: influence of austenite phase transformation on existing microstructure of low c-mn steel quality”, journal of materials engineering and performance, vol. 11, no. 1, pp. 86-91, 2002 [2] m. a. xiaoyu,“effect of microstructure on the cold headability of a medium carbon steel”, isij international, vol. 44 no. 5, pp. 905-913, 2004 [3] r. hill, “annealing: the first step in cold forming”, wire journal international, vol. 17, no. 7, pp. 95-97, 1984 [4] j. ramo, v. t. kuokkala, t. vuoristo, “influence of strain rate and adiabatic heating on the deformation behavior of cold heading steels”, journal of materials processing technology, vol. 209, no. 11, pp. 51865194, 2009 [5] y. h. lee, j. s. kwon, d. l. lee, “study on the formation of ferritecementite microstructure by strain induced dynamic transformation in medium carbon steels”, materials science forum, vol. 539-543, pp 4267-4271, 2006 [6] j. huang, w. j. poole, m. militzer, “austenite formation during intercritical annealing”, metallurgical and materials transactions a, vol. 35, no. 11, pp. 3363-3375, 2004 [7] a. sabih, j. a. nemes, “internal ductile failure mechanisms in steel cold heading process”, journal of materials processing technology, vol. 209, no. 9, pp. 4292-4311, 2009 [8] s. tajik, m. ahmad, i. ahmad, j. khan, “the effect of heat treatment on microstructure and mechanical properties of steels”, journal of engineering and applied sciences, vol. 17, no. 2, pp. 206-211, 1998 [9] e. girault, p. jacques, p. harlet, k. mols, j. van humbeeck, e. aernoudt, f. delannay, “metallographic methods for revealing the multiphase microstructure of trip-assisted steels”, materials characterization, vol. 40, no. 2, pp. 111-118, 1998 [10] r. l. higginson, c. m. sellars, worked examples in quantitative metallography, maney, 2003 [11] j. w. christian, theory of transformations in metals and alloys, pergamon, 2002 [12] v. i. savran, y. van leeuwen, d. n. hanlon, c. kwakernaak, w. g. sloof, j. sietsma, “microstructural features of austenite formation in c35 and c45 alloys”, metallurgical and materials transactions a, vol. 38, no. 5, pp. 946-955, 2007 [13] s. lee, s. j. lee, b. c. de cooman, “austenite stability of ultrafinegrained transformation-induced plasticity steel with mn partitioning”, scripta materialia, vol. 65, no. 3, pp. 225-228, 2011 [14] s. chatterjee, h. s. wang, j. r. yang, h. k. d. h. bhadeshia, “mechanical stabilisation of austenite”, materials science and technology, vol. 22, no. 6, pp. 641-644, 2006 [15] s. j. tajik, j. z. khan, m. pervaz, i. ahmad, “effect of cooling rate and austenite temperature on the mechanical properties of commercial steels”, journal of engineering and applied sciences, vol. 15, pp. 6168, 1996 [16] s. q. yuan, g. l. liang, “dissolving behaviour of second phase particles in nb–ti microalloyed steel”, materials letters, vol. 63, no. 27, pp. 2324-2326, 2009 [17] y. z. zhu, z. zhu, j. p. xu, “grain boundary segregation of minor arsenic and nitrogen at elevated temperatures in a microalloyed steel”, international journal of minerals, metallurgy, and materials, vol. 19, no. 5, pp. 399-403, 2012 engineering, technology & applied science research vol. 9, no. 2, 2019, 3981-3984 3981 www.etasr.com zurnaci et al.: three-point bending response of corrugated core metallic sandwich panels having … three-point bending response of corrugated core metallic sandwich panels having different core configurations – an experimental study erman zurnaci dr. engin pak cumayeri vocational school, duzce university, duzce, turkey ermanzurnaci@duzce.edu.tr muammer nalbant faculty of technology, gazi university, ankara, turkey nalbant@gazi.edu.tr hasan gokkaya mechanical engineering department, karabuk university, karabuk, turkey hgokkaya@karabuk.edu.tr gokhan sur mechanical engineering department, karabuk university, karabuk, turkey gokhansur@karabuk.edu.tr abstract—bending response of corrugated core metallic sandwich panels was studied experimentally under three-point bending loading. two different core configurations were used: the corrugated monolithic core and the corrugated sliced core. the trapezoidal corrugated cores were manufactured from aluminum sheets via a sheet metal bending mould. after the sandwich panel samples were prepared, they were subjected to three-point bending tests. the load and displacement responses of the sandwich panels having different core configurations were obtained from the experimental testing. the influence of the core configuration on the three-point bending response and failure modes was then investigated. the experimental results revealed that the corrugated sliced core configuration exhibited an improved bending performance compared to the corrugated monolithic core configuration. keywords-bending response; failure modes; three-point bending; metallic sandwich panel; corrugated core configurations i. introduction sandwich panels consist of thin, stiff surface plates and a lightweight core. the core and surface plates of the sandwich panels are made from different materials including metal, polymer, fiber reinforced polymer, and balsa [1]. sandwich panel cores are produced in different forms such as corrugated, lattice truss, honeycomb and foam cores. the surface plates show resistance to in-plane and lateral loads, whereas the sandwich panel core increases strength and contributes to important structural properties such as durability [2]. metallic sandwich panels having corrugated cores exhibit a high bending strength and stiffness-to-weight ratio and for this reason they are used as structural components in a number of industries including defence, transportation, and space [3-6]. the bending strength of sandwich panels is related to the core form [7]. the corrugated core form is composed of continuously repeating unit cells. the corrugated core form has a low specific weight and increases the resistance and moment of inertia without greatly increasing the weight of the sandwich panel [8] in addition to preventing shear and bending. in recent years, the bending performance and failure mechanism of corrugated sandwich panels has been researched extensively. for example, authors in [9] conducted an analysis of the bending behavior of a corrugated core sandwich panel with various boundary conditions using the mindlin–reissner plate theory. moreover, they investigated the effects of several geometric parameters on the rigidity and state of the sandwich panel, observing some new phenomena in their experimental studies. authors in [10] proposed a bi-directionally corrugated core design to reduce anisotropic behaviors of sandwich panels under bending load. they carried out three-point bending tests for different core orientations. test results revealed that sandwich panels having bi-directionally corrugated cores showed quasi-isotopic bending behaviors and structural performances. authors in [8] analytically and experimentally studied the tensile and bending characteristics of composite corrugated core sandwich panels and compared the experimental test results with the analytical ones. loaddisplacement curves were obtained as a result of the three point bending test applied to the sandwich panels. the resulting curves revealed two different types of deformation: pure bending and combined bending. in addition, the results showed that core thickness affects the mechanical behavior of the core in the tension state. authors in [11] studied the behavior of mild steel structural beams having a corrugated web under a three-point bending test. they investigated the semi-circular web corrugation in different directions of the beam experimentally and numerically. the results showed that the vertical-corrugated web-beam could be moved between higher moments. they also found that increasing the radius of the corrugation curvature of the groove caused higher bending stiffness. authors in [12] investigated the quasi-static threepoint bending response and deformation modes of metallic corresponding author: erman zurnaci engineering, technology & applied science research vol. 9, no. 2, 2019, 3981-3984 3982 www.etasr.com zurnaci et al.: three-point bending response of corrugated core metallic sandwich panels having … sandwich panels having a y-frame and a corrugated core. they investigated the indentation strength of the sandwich beams having a y-frame core. the experimental and numerical studies revealed that the initial collapse strength of the beams was directed by the indentation of the cores’ geometry. the present study aims to explore the effect of different core configurations on the bending response of metallic sandwich panels under three-point bending loading. metallic sandwich panel samples having corrugated monolithic core and corrugated sliced core configurations were produced. three-point bending tests were conducted experimentally. finally, the bending responses and failure modes of the sandwich panels having different core configurations were examined. ii. experimental work a. experimental samples in this study, two types of sandwich panel samples, one type with corrugated monolithic core (cmc) and another with corrugated sliced core (csc) configurations were used. an isometric view of the core configurations is given in figure 1. the corrugated sliced core was produced by slicing the corrugated monolithic core and placing it on the surface plate of the panel in different directions and angles. trapezoidal geometry was determined as the core form. the geometrical parameters of a core unit cell are given in figure 2. fig. 1. isometric view of the core configurations: (a) cmc and (b) csc fig. 2. geometrical parameters of the core unit cell aluminum 1050 h14 sheets were used as the core and surface plate material of the sandwich panel samples. the thickness of the core and surface plates were respectively 0.2mm and 1mm. the material properties of the aluminum 1050 h14 sheet are listed in table i. table i. aluminum 1050 h14 properties density (kg/m3) elastic modulus (gpa) poisson ratio yield stress (mpa) ultimate stress (mpa) 2634 40 0.33 108 100 the aluminum sheets were cut in widths of 64mm and 6.8mm to form the configurations of the cmc and csc, respectively (figure 3(a)). the sandwich panel corrugated cores were then manufactured from cut aluminum sheets using a custom-made bending mould (figure 3(b)). fig. 3. corrugated core production: (a) cutting the aluminum sheets and (b) moulding the corrugated cores each sandwich panel sample was made of three and twelve unit cells in the transverse and in the longitudinal direction respectively. the core and surface plates were assembled using araldite 2015 two-component epoxy adhesive. the prepared samples were kept for more than 24h under a specified press force at room temperature in order to ensure that the adhesive was completely cured. for evaluating the bending response of the sandwich panel, a total of six samples were prepared, three for each core configuration. the samples size was 244mm in length, 64mm in width and 12mm thick. average weights (w) of the samples were 97.640g and 100.760g respectively for the sequentially corrugated monolithic core and corrugated sliced core sandwich panel samples. the prepared samples having different core configurations are displayed in figure 4. fig. 4. experimental samples of metallic sandwich panels: (a) cmc and (b) csc b. three-point bending test the three-point bending tests were conducted on shimadzu autograph ags-x testing machine with a capacity of 100kn at loading rate of 2mm/min (figure 5). the tests were carried out in accordance with astm c393/c393m-16 standard [13]. an impact roller with a diameter of 10mm and a support roller with a diameter of 30mm with span length of 150mm were used for the bending tests. the experimental setup for the engineering, technology & applied science research vol. 9, no. 2, 2019, 3981-3984 3983 www.etasr.com zurnaci et al.: three-point bending response of corrugated core metallic sandwich panels having … three-point bending testing of the sandwich panel samples is shown in figure 6. the tests were ended when the deformation value reached 12mm. at least three tests were conducted for each core configuration, and the averages of the measurements were calculated to ensure the accuracy and reproducibility of the test results. load-displacement curves were recorded from the experimental tests. fig. 5. three-point bending test machine fig. 6. experimental setup of the three-point bending test iii. results and discussion a. bending responses the load-displacement curves represent the bending responses of the sandwich panels under the influence of bending load. the load-displacement curves are given in figure 7. bending strength and specific bending strength values were calculated for the evaluation of the bending responses of the sandwich panels having different core configurations. the bending strength value 𝜎 was calculated using (1): 𝜎 = 3𝐹𝑙 2𝑏ℎ2 (1) where 𝐹 is the peak load obtained from the load-displacement curve, 𝑙 is the span length, 𝑏 is the width of the sample and ℎ the thickness of the sample. the specific bending strength value 𝜎𝑆 is the ratio of the bending strength to the weight ( 𝑤 ) of the sandwich panel samples: 𝜎𝑆 = 𝜎 𝑤⁄ (2) examination of the curves shows that the sandwich panel having csc configuration exhibited higher bending strength. in addition, fluctuations occurred in the load-displacement curve of the sandwich panel having cmc configuration. the bending response values of the samples are given in table ii. the sandwich panels having cmc configuration began to bend after a peak load of 169.11kn, whereas the csc configuration increased the bending strength of the sandwich panels by 117% and the panels began to bend under a load of 368.18kn. performance values showed that the special bending strength increased by about 111% and the csc configuration increased the weight of the sandwich panel by only 3%. fig. 7. load-displacement curves of sandwich panels having (a) cmc and (b) csc configurations table ii. bending response values core configuration f (n) w (gr) σ (mpa) σs (mpa) cmc 169.11 97.64 4.12 0.04 csc 368.18 100.76 8.98 0.08 percentage of change (%) 117.66 3.19 117.73 111.90 b. failure modes in this section failure modes of the sandwich panels having different core configurations are presented. the loaddisplacement curves of the sandwich panel samples fluctuated. these fluctuations were caused by failures in sandwich panel samples [14]. upon examining the failures in the sandwich panel samples, it was determined that mainly two different failure modes occurred: buckling of the core wall and debonding of the surface. debonding of the surface occurred predominantly in the cmc sandwich panels. buckling of the core wall had not occurred as the core acted as a whole in the bending process. buckling of the core wall and debonding of surface occurred in the sandwich csc panels. this was due to the fact that the core was sliced. the dominant failure modes occurring in the sandwich panels are given in figure 8. the load fluctuations occurring in the load-displacement curves of the sandwich panels consisted of failure modes. in the cmc sandwich panels, debonding between the core and the surface plates was more noticeable because the adhesion proceeded linearly across the panel (figure 9(a)). this debonding of the surface decreased the strength of the panels. since the adhesion area of the csc configuration is small, the debonding of the engineering, technology & applied science research vol. 9, no. 2, 2019, 3981-3984 3984 www.etasr.com zurnaci et al.: three-point bending response of corrugated core metallic sandwich panels having … surface was limited and did not proceed through the panel (figure 9(b)). therefore, force fluctuations were much lower. the csc configuration, while maintaining the integrity of the panel, also increased the bending strength of the panel. fig. 8. dominant failure modes of sandwich panels having different core configurations: (a) cmc and (b) csc fig. 9. load fluctuations in the load-displacement curves of sandwich panels having (a) cmc and (b) csc configurations iv. conclusion in this study the production of metallic sandwich panel samples having different core configurations was accomplished. the samples were studied experimentally under three-point bending load testing. the test results were examined and compared. the effect of different core configurations on the bending responses of the metallic sandwich panels was determined. the main findings in this study are summarized as: • the corrugated sliced core configuration increased the bending strength of the sandwich panels. • the corrugated monolithic core configuration caused the bending load to fluctuate and this reduced the bending strength resistance of the panels. • the sliced core configuration prevented fluctuations in the load-displacement curve and contributed to the integrity of the panels. • as the adhesion surface of the corrugated sliced core to the surface plates was small, the debonding of the surface was limited and did not significantly affect the bending strength of the panel. acknowledgment this work was supported by the karabuk university coordinatorship of scientific research projects, karabuk, turkey (no. kbubap-17-dr-458). references [1] r. mohmmed, a. ahmed, a. e. mohamed, h. ali, “low velocity impact properties of foam sandwich composites: a brief review”, international journal of engineering science and innovative technology, vol. 3, no. 2, pp. 579-591, 2014 [2] j. r. vinson, the behavior of sandwich structures of isotropic and composite materials, thechnomic publishing co. inc., 1999 [3] s. hou, c. shu, s. zhao, t. liu, x. han, q. li, “experimental and numerical studies on multi-layered corrugated sandwich panels under crushing load”, composite structures, vol. 126, pp. 371-385, 2015 [4] j. w. hutchinson, z. xue, “metal sandwich plates optimized for pressure impulses”, international journal of mechanical sciences, vol. 47, pp. 545-569, 2005 [5] s. kazemahvazi, d. zenkert, “corrugated all-composite sandwich structures. part 1: modeling”, composites science and technology, vol. 69, no. 7-8, pp. 913-919, 2009 [6] g. lu, t. x. yu, energy absorption of structures and materials, woodhead publishing ltd., 2003 [7] s. hou, s. zhao, l. ren, x. han, q. li, “crashworthiness optimization of corrugated sandwich panels”, materials and design, vol. 51, pp. 1071-1084, 2013 [8] i. dayyani, s. ziaei-rad, h. salehi, “numerical and experimental investigations on mechanical behavior of composite corrugated core”, applied composite materials, vol. 19, no. 3-4, pp. 705-721, 2012 [9] w. s. chang, e. ventsel, t. krauthammer, j. john, “bending behavior of corrugated-core sandwich plates”, composite structures, vol. 70, no. 1, pp. 81-89, 2005 [10] d. y. seong, c. g. jung, d. y. yang, k. j. moon, d. g. ahn, “quasiisotropic bending responses of metallic sandwich plates with bidirectionally corrugated cores”, materials and design, vol. 31, no. 6, pp. 2804-2812, 2010 [11] y. a. khalid, c. l. chan, b. b. sahari, a. m. s. hamouda, “bending behaviour of corrugated web beams”, journal of materials processing technology, vol. 150, no. 3, pp. 242-254, 2004 [12] v. rubino, v. deshpande, n. a. fleck, “the three-point bending of yframe and corrugated core sandwich beams”, international journal of mechanical sciences, vol. 52, pp. 485-494, 2010 [13] astm c393/c393m-16:2016standard test method for core shear properties of sandwich constructions by beam flexure, astm international, 2016 [14] j. xiong, l. ma, a. stocchi, j. yang, l. wu, s. pan, “bending response of carbon fiber composite sandwich beams with three dimensional honeycomb cores”, composite structures, vol. 108, pp. 234-242, 2014 microsoft word 12-2584_s_etasr_v9_n3_pp4136-4139 engineering, technology & applied science research vol. 9, no. 3, 2019, 4136-4139 4136 www.etasr.com kori et al.: study of flow characteristics over a rounded edge drop structure in open channel study of flow characteristics over a rounded edge drop structure in open channel shafi muhammad kori department of civil engineering, mehran university of engineering and technology, jamshoro, pakistan shafi.kori@faculty.muet.edu.pk ali asghar mahessar sindh barrages improvement project, sindh irrigation department, sindh, pakistan amahessar@yahoo.com madeeha channa uspcas-w, mehran university of engineering and technology, jamshoro, pakistan madehachanna.uspcasw@admin.muet.edu.pk ashfaque ahmed memon department of civil engineering, mehran university of engineering and technology, jamshoro, pakistan ashfaque.memon@faculty.muet.edu.pk abdul rehman kori mehran university of engineering and technology, jamshoro, pakistan rehmankori57@gmail.com abstract-flow over a drop structure is a form of free overfall called hydraulic drop. hydraulic drop changes the nature of flow abruptly from sub-critical to super-critical condition. rapidly varied flow analysis is a complex phenomenon and involves remarkable characteristics. some of the drop structures constructed in sindh and punjab provinces of pakistan had gone through diverse failures, consequential in interruption of water supply to irrigation fields encountering substantial economic loss. in the present study experiments were carried out in the hydraulic laboratory of mehran university of engineering and technology on round edged drop structure fitted in a horizontal rectangular flume (channel model). data regarding hydraulic drop and hydraulic jump characteristics were collected during the experiment. the observed data included: flow discharge (q), radius of rounded edge drop structure (r), height of the structure (h), hydraulic drop length (ld), hydraulic jump length (lj), depth of flow at toe of the jump (y1) and tailwater depth (y2). applying dimensional analysis, the non-dimensional parameters of the observed data were calculated. using statistical analysis, empirical relationships among the non-dimensional parameters were established for the appropriate design of the drop structure. the research results showed that the length and depth indices are functions of d=q 2 gh 3 and r/h values. it was also found that for rounded-edge drop structure, the length of the stilling basin (lsb) reduces as r/h ratio increases. keywords-flow characteristics; hydraulic drop; hydraulic jump; length of stilling basin; rectangular channel i. introduction enormous water resource engineering projects have been built up all over the world. such man-made interventions, like weirs, barrages, dams, regulators, drops, etc. are key structures for supplying water to agriculture fields and other purposes at safe velocity through conveyance infrastructure. drop structures take the water flow abruptly from a higher section of the canal to a lower section [1]. water flowing over a drop structure has tremendous velocity because of its high hydraulic gradient [2]. the structure allows the canal to be constructed as a relatively flat series of sections of different heights. since the flow passing over the drop structure causes a change in the curvature of the water surface, the flow profile may be broken effectively in a sudden manner. as a result, the formation of the hydraulic jump on downstream apron of the structure due to the free fall after hydraulic drop occurs. also, water load on downstream apron increases, thereby counteracting the uplift in case of structure laid on permeable foundation. authors in [2-7] worked on flow parameters passing over drop structures on horizontal and sloping bed for empirical relationships of horizontal bed channel. hydraulic engineering systems help in planning and designing the most efficient and economic utilization of water through construction of various storage, diversion, regulation and conveyance structures. the conveyance structures consist of a network of canals with/without fall structure [8-9]. experimental and analytical research has been carried out on the hydraulic drop and jump in horizontal and sloping bed channel. hence, empirical relationships of various hydraulic characteristics have been developed [10-12]. author in [5] derived the set of equations (1)-(4) concerning the hydraulic characteristics due to flow in the horizontal channel passing over square edge drop structure: �� � = 0.54 .�� (1) �� � = 1.66 .�� (2) �� � = 4.30 .�� (3) �� � = 1.00 .�� (4) where, y1 is the initial depth of the flow or depth at toe of the jump, y2 is the sequent depth or tail water depth, yp is the pool depth, ld is the length of the hydraulic drop, lj is the length of the hydraulic jump, d (=q 2 /gh 3 ) is the drop number corresponding author: ali asghar mahessar engineering, technology & applied science research vol. 9, no. 3, 2019, 4136-4139 4137 www.etasr.com kori et al.: study of flow characteristics over a rounded edge drop structure in open channel (dimensionless), h is the height of drop structure, q (=q/b) is the discharge intensity (l 2 /t), q is the flow discharge in the channel (l 3 /t), b is the channel width and g is the acceleration due to gravity (l/t 2 ). author in [13] conducted research on the characteristics of flow through a rounded edge drop structure in a rectangular sloping bed channel. he did not take into account the radius of rounded edge of structure, and considered the cumulative bed slope of the channel during the analysis. he developed depth and length indices relationship of hydraulic drop and hydraulic jump with drop number (d) as: �� � = 0.389 .��� (5) �� � = 1.344 .��� (6) �� � = 4.30 .�� (7) �� � = 6.021 .��� (8) authors in [14] extended the work of [5] and developed a series of empirical formulas concerning the hydraulic characteristics of flow over straight drop structure on the cumulative bed slope in the rectangular channel: �� �� = 13.40 � .�� (9) �� �� = 4.30 � . �� (10) �� � = 8.50 .�� (11) �� �� = 0.44 .�� (12) �� � = 1.80 .� (13) �� � = 0.58 . (14) �� � = 1.65 .��� (15) �� � = 2.00 .�� (16) where, additionally, lc is the length of critical section of the flow and yc (= q 2 /g) 1/3 is the critical depth. authors in [2] worked on the flow characteristics of a round drop structure in a rectangular sloping bed channel and developed empirical formulas for the proper design of drop structures as: �� � = .��� 0.403 − 0.0191"# (17) �� � = .��� 1.346 + 6.389"# (18) �� � = .� 2.609 + 20.623"# (19) �� � = .�� 3.156 + 12.56"# (20) �� �� = � .�%� 8.102 + 149.594"# (21) �� �� = � . �� 2.356 − 3.737"# (22) where, additionally, s is bed slope of the channel. in the present study, the experiments were conducted in a rectangular horizontal bed channel (flume) at the hydraulic laboratory of mehran university of engineering and technology, jamshoro, pakistan. data for basic flow parameters/characteristics of hydraulic drop and hydraulic jump were collected for various flow rates over the rounded edge drop structure. the collected basic flow data were further evaluated through non-dimensional and dimensional analysis using buckingham π-theorem. using non-dimensional parameters, empirical relationships of length and depth indices were developed in terms of d and r/h for appropriate structure design. ii. application of hydraulic jump formation in order to design the length of stilling basin (lsb) within the range of hydraulic jump formation downstream of the drop structure, it is essential to calculate the length and depth indices of hydraulic drop and hydraulic jump. there are various practical applications of hydraulic jump formation on downstream apron of the drop structure. some of them are: to dissipate energy in case of free over falls, barrages, dams, regulators, etc, to decrease flow velocity (super critical to subcritical velocity) in order to avoid the erosion and scouring on downstream side, or to counteract the uplift pressure on the downstream pavement of the hydraulic structure constructed over permeable soil. iii. experimental work extensive study of free fall over a rounded edge drop structure in a horizontal rectangular channel has been conducted. different values of r/h and flow rate were used so that a reliable relationship of various flow characteristics of hydraulic drop and hydraulic jump could be developed for the required design parameters. a. equipment setup and data collection to study the basic characteristics of flow over a rounded edge drop structure, the experiments were conducted in a rectangular tilting flume at the main hydraulic laboratory of mehran university of engineering & technology. the flume comprises of a glass sided and steel floor working section having breadth, depth and length of 7.6cm, 25cm and 600cm respectively. it contains water tanks in connection with both u/s and d/s of the section. an adjustable tail gate was used to control downstream flow depth. water was discharged through a control valve connected to the centrifugal pump and the discharge was measured with a discharge gauge-meter connected by the pump. water depth data were measured with a sliding pointer gauge attached to the working section of the waterway. sixteen values for each hydraulic parameter were totally collected using four different heights of the droplet structure with the same rounded radius of 5cm. flow geometry and flow characteristics of the structure are shown in figure 1. engineering, technology & applied science research vol. 9, no. 3, 2019, 4136-4139 4138 www.etasr.com kori et al.: study of flow characteristics over a rounded edge drop structure in open channel fig. 1. flow characteristics during the formation of hydraulic jump, as a result of hydraulic drop iv. results and discussion the hydraulic data collected regarding flow parameters (passing through rounded edge drop structure) during experimentation in the laboratory and computed nondimensional parameters are represented in table i. by statistical analysis, using multiple regression, the respective relationships of y1/h, y2/h, ld/h, lj/h, lsb/h and y1/y2 in terms of d (=q 2 /gh 3 ) and r/h were obtained. the developed equations with correlation coefficient (r 2 ) are expressed in (23)-(28): �� � = 0.710d$ 0.151 rh $ 0.067 (r 2 = 0.973) (23) �� � � 0.395d$1.070 r h $ 0.243 (r 2 = 0.949) (24) �� � � 0.741d $2.423 r h $ 0.105 (r 2 = 0.928) (25) �� � � 8.615d $ 0.307 r h $ 4.455 (r 2 = 0.752) (26) �+, � � 9.357d $ 1.370 r h $ 4.560 (r 2 = 0.786) (27) �� �� � 0.401d 0.013 rh $ 0.2071 (r 2 = 0.946) (28) table i. collected experimental data for flow parameters and corresponding non-dimensional parameters s. no. h (cm) q (cm 3 /sec) q=q/b (cm 2 /sec) y1 (cm) y2 (cm) ld (cm) lj (cm) lsb (cm) r/h d=q 2 /gh 3 y1/h y2/h ld/h lj/h lsb/h y1/y2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 13 1675.54 220.47 1.85 8.70 13.1 65.0 73.1 0.38 0.02 0.14 0.67 1.01 5.00 5.62 0.21 2 13 1654.82 217.74 1.85 8.50 12.8 57.3 65.1 0.38 0.02 0.14 0.65 0.99 4.41 5.01 0.22 3 13 1520.00 200.00 1.65 8.20 12.5 57.0 64.5 0.38 0.02 0.13 0.63 0.96 4.39 4.96 0.20 4 13 1435.16 188.84 1.50 7.30 12.0 52.0 59.0 0.38 0.02 0.12 0.56 0.92 4.00 4.54 0.21 5 8.9 1675.54 220.47 2.00 8.90 15.0 53.5 63.5 0.56 0.07 0.23 1.00 1.69 6.01 7.14 0.23 6 8.9 1654.82 217.74 1.90 8.20 14.5 50.0 59.5 0.56 0.07 0.21 0.92 1.63 5.62 6.69 0.23 7 8.9 1520.00 200.00 1.80 8.00 13.5 48.5 57.0 0.56 0.06 0.20 0.90 1.52 5.45 6.40 0.23 8 8.9 1435.16 188.84 1.60 7.60 13.0 46.0 54.0 0.56 0.05 0.18 0.85 1.46 5.17 6.07 0.21 9 7.3 1675.53 220.47 2.10 7.90 15.0 45.0 55.0 0.68 0.13 0.29 1.08 2.06 6.16 7.53 0.27 10 7.3 1654.82 217.74 1.90 7.60 14.5 43.5 53.0 0.68 0.12 0.26 1.04 1.99 5.96 7.26 0.25 11 7.3 1520.00 200.00 1.80 7.30 14.0 42.0 51.0 0.68 0.11 0.25 1.00 1.92 5.75 6.99 0.25 12 7.3 1435.16 188.84 1.60 7.10 13.7 37.0 45.7 0.68 0.09 0.22 0.97 1.88 5.07 6.26 0.23 13 5.7 1675.53 220.47 2.30 7.50 14.8 42.7 52.5 0.88 0.27 0.40 1.32 2.60 7.49 9.21 0.31 14 5.7 1654.82 217.74 2.10 7.30 13.6 39.0 47.6 0.88 0.26 0.37 1.28 2.39 6.84 8.35 0.29 15 5.7 1520.00 200.00 2.00 7.00 12.8 35.7 43.5 0.88 0.22 0.35 1.23 2.25 6.26 7.63 0.29 16 5.7 1435.16 188.84 1.85 6.80 11.6 32.0 38.6 0.88 0.20 0.33 1.19 2.04 5.61 6.77 0.27 bed width b=7.6, radius of rounded edge r=5 cm table ii. observed data vs calculated values in terms of mape for hydraulic drop and jump characteristics s. no. y1 y2 ld lj lsb obs (23) ape (28) ape obs (24) ape obs (25) ape obs (26) ape obs (27) ape 1 1.85 1.84 0.76 1.84 0.78 8.7 8.62 0.87 13.1 13.70 4.55 65 61.97 4.65 73.1 70.7 3.3 2 1.85 1.83 1.04 1.79 3.16 8.5 8.62 1.43 12.8 13.69 6.96 57.3 61.91 8.05 65.1 70.6 8.4 3 1.65 1.80 9.03 1.72 4.06 8.2 8.60 4.92 12.5 13.66 9.26 57 61.53 7.94 64.5 70.2 8.8 4 1.5 1.78 18.70 1.52 1.51 7.3 8.59 17.72 12 13.64 13.65 52 61.30 17.89 59 69.9 18.5 5 2 1.80 10.13 2.03 1.34 8.9 7.76 12.82 15 13.51 9.92 53.5 46.57 12.95 63.5 55.1 13.3 6 1.9 1.79 5.98 1.86 2.01 8.2 7.75 5.45 14.5 13.50 6.89 50 46.44 7.12 59.5 54.9 7.7 7 1.8 1.72 4.52 1.78 1.00 8 7.72 3.56 13.5 13.43 0.52 48.5 45.62 5.94 57 54.0 5.2 8 1.6 1.68 4.93 1.67 4.61 7.6 7.69 1.22 13 13.39 2.99 46 45.14 1.88 54 53.5 0.9 9 2.1 1.91 9.23 1.97 6.35 7.9 7.49 5.19 15 13.57 9.53 45 42.07 6.52 55 50.6 7.9 10 1.9 1.89 0.53 1.88 0.92 7.6 7.48 1.56 14.5 13.55 6.53 43.5 41.87 3.75 53 50.4 4.9 11 1.8 1.79 0.59 1.75 2.70 7.3 7.43 1.71 14 13.45 3.94 42 40.65 3.22 51 49.1 3.7 12 1.6 1.73 8.15 1.67 4.44 7.1 7.39 4.12 13.7 13.39 2.29 37 39.93 7.92 45.7 48.3 5.7 13 2.3 2.22 3.40 2.27 1.35 7.5 7.34 2.18 14.8 13.84 6.46 42.7 40.07 6.17 52.5 48.9 6.8 14 2.1 2.20 4.54 2.19 4.25 7.3 7.32 0.29 13.6 13.82 1.59 39 39.74 1.90 47.6 48.6 2.0 15 2 2.03 1.50 1.98 0.76 7 7.23 3.28 12.8 13.64 6.59 35.7 37.74 5.71 43.5 46.4 6.6 16 1.85 1.93 4.51 1.86 0.71 6.8 7.18 5.53 11.6 13.54 16.74 32 36.57 14.27 38.6 45.1 16.9 mape 5.47 2.50 4.49 6.78 7.24 7.54 engineering, technology & applied science research vol. 9, no. 3, 2019, 4136-4139 4139 www.etasr.com kori et al.: study of flow characteristics over a rounded edge drop structure in open channel in order to check the accuracy of the developed equations, measures of the goodness of fit were used for comparison between observed and calculated parameters. the mean absolute percentage error (mape) was calculated using the following equation: mape � � %3 4 5 (67�87) 67 5 3 9:� (29) where oi is the actual/observed value and ci is the predicted/calculated value. the computed results of mape are shown in table ii, which varies between 2.50 and 7.54% (i.e. less than 10%). a good agreement between calculated and observed values is obtained, which verifies the developed models/equations. v. conclusions the following conclusions can be drawn from the present study: • the developed equations (23)-(28) show that the length and depth indices are functions of d=q 2 /gh 3 and r/h. • it was also found that if the ratio r/h of rounded-edge drop structure will increase, the length of stilling basin (lsb) reduces. acknowledgment the authors are thankful to the institute of water resources engineering and management, mehran university of engineering & technology, jamshoro, pakistan for providing the facilities to conduct laboratory experiments. references [1] fao, corporate document repository, irrigation water management: introduction to irrigation, produced by natural resources management and environmental department, ashgate publishing, 1979 [2] s. m. kori, n. a. memon, m. t. shaikh, “flow characteristics of round-edged drop structure in rectangular sloping bed channel”, pakistan journal of agriculture, agricultural engineering and veterinary sciences, vol. 24, no. 1, pp. 68-73, 2008 [3] h. b. bhutto, hydraulic jump control and energy dissipation, phd thesis, mehran university of engineering and technology, 1987 [4] m. y. shoro, hydraulic jump as an energy dissipater, msc thesis, mehran university of engineering and technology, 1991 [5] w. rand, “flow geometry at straight drop spillways”, in: proceedings of the american society of civil engineers, vol. 81, no. 9, pp. 1-13, asce, 1955 [6] a. h. shaikh, s. m. kori, a. l. qureshi, “characteristics of flow for different shapes of drop structure in rectangular horizontal chanel”, pakistan journal of agriculture, agricultural engineering and veterinary sciences, vol. 23, no. 2, pp. 35-43, 2007 [7] a. h. shaikh, s. m. kori, a. l. qureshi, “analysis of hydraulic jump formed below a straight drop in horizontal rectangular channel”, mehran universcity research journal of engineering and technology, vol. 27, no. 2, pp. 153-156, 2008 [8] b. s. thandaveswara, “hydraulics course material”, section 29.5, 2017, acceced january 8, 2017 from nptel.ac.in/courses/105106114/pdfs/ unit29/29_5.pdf [9] k. safranez, “researches relating to the hydraulic jump. basinginieur”, (english translation by d. p. barnes), no. 27, 38, bureau of reclamation files, denver, colarado, usa, 1934 [10] s. m. kori, m. t. shaikh, a. l. qureshi, “flow over sharped edge drops structures in rectangular sloping bed chanel”, mehran universcity research journal of engineering and technology, vol. 18, no. 3, pp. 167-176, 1999 [11] b. a. bakhmateff, a. e. matzke, “the hydraulic jump in terms of dynamic similarity”, transactions of the american society of civil engineers, vol. 101, no. 1, pp. 630-647, 1936 [12] h. rouse, s. m. woodward, r. e. kennedy, l. s. hall, m. p. o’brien, f. v. a. e. engel, b. m. woods, j. c. stevens, n. page, a. i. ivanchenko, f. t. mavis, a. luksch, i. m. nelidov, “discussion of ‘the hydraulic jump in terms dynamic similarity by boris a. bakhmeteff and arthur e. matzke’ ”, transactions of the american society of civil engineers, vol. 101, no. 1, pp. 648-672, 1936 [13] m. t. shaikh, laboratory study on basic characteristics of hydraulic drop structures, msc thesis, mehran university of engineering and technology, 1996 [14] s. m. kori, m. a. shaikh, a. m. phul, “hydraulic characteristics of straight drop structures”, mehran university research journal of engineering and technology, vol. 16, no. 1, pp. 33-39, 1997 microsoft word 2-2171_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3505-3507 3505 www.etasr.com laghari et al.: assessment of climate driven changes in flow series of alpine basin: a case study … assessment of climate driven changes in flow series of alpine basin: a case study of danube river basin abdul nasir laghari department of energy and environment, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan a.n.laghari@quest.edu.pk a. rajper department of mechanical engineering, quaid -eawam university of engineering, science and technology, nawabshah, pakistan altafrajpar@yahoo.com gordhan das walasai department of mechanical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan valasai@quest.edu.pk abdul rehman jatoi department of energy and environment, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan arjatoi@quest.edu.pk nabi bux jalbani department of chemical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan n.bux@quest.edu.pk hira soomro department of basic sciences and related studies, mehran university of engineering and technology, jamshoro, pakistan hirasoomro47@gmail.com abstract—this study was carried out in order to analyze the climate change driven influence on mean monthly flow series of danube river and its tributaries during the last century. the study confirms some signs of climate driven alterations in monthly river flow series along with change in flow seasonality during the last century. in spite of this, man-made interference in the basin like i.e. groundwater extraction, irrigation, river regulation, land use alteration and urbanization, has significantly changed danube flow regime in most areas of the catchment. the analysis of achleiten station demonstrates that average annual flow regime is a little bit increased. major increase is observed in winter and autumn months and decrease in summer months. these seasonal alterations clearly signal a future glimpse of reduced water availability in alpine basins. this will mainly occur due to the change in the form of precipitation in winter, from snow to rain and the consequent less snow accumulation, and the early melt of snow storage, less precipitation and high evaporation rate in summer. keywords-climate change; man-made abstraction; seasonal flow regime; alpine river i. introduction earth’s atmosphere has experienced an extraordinary warming over the 20th century. the average atmospheric temperature has risen by approximately 0.8°c during the last 200 years, and since the ‘80s, earth has witnessed the warmest years over the last 1400 years. the rise in average global temperature has caused a major change in weather patterns and properties of earth’s atmosphere [1]. the temperature increase over the last century emerged in two phases, during 1910-1940 and at higher rate since 1980. the increase in the average surface temperature has been caused by perturbations in the radiation system of earth’s atmosphere. perturbations might happen due to volcanic eruptions resulting in release of gases, changes in solar irradiation or greenhouse gas emissions. ipcc relates the increase in the average earth surface temperature to human activities [2]. ipcc reported that many river basins in mountain regions would suffer a massive decrease in water resources due to climate change. due to increased precipitation and decreased evapotranspiration with altitude, mountain regions are characterized by high discharge values [3]. their contribution in total water supply to global population is far greater than their areas [4]. their future global water resource role would likely be altered from the anticipated climate change. therefore, climate change impacts on the hydrological cycle of mountain watersheds and subsequent water availability which is critical for sustainable future water resource planning and management. ipcc reported that the change level is higher in mountain regions-approximately 300% more than the average global temperature [5-7]. the warming rate in the lower-troposphere rises with elevation. this makes mountainous regions very vulnerable [8]. therefore, any change in climatic parameters, i.e. temperature and precipitation patterns, will change significantly the snow storage and subsequently alter both timing and volume of the discharge regime of mountain rivers [8-18] and accordingly the water availability in downstream regions [19-20]. this may have severe implications on freshwater systems and their management [21]. under this study, flow series of danube river major tributaries originated from european alps have been investigated to check out the climate change driven signs. this would help water resource planning and development engineering, technology & applied science research vol. 8, no. 6, 2018, 3505-3507 3506 www.etasr.com laghari et al.: assessment of climate driven changes in flow series of alpine basin: a case study … managers to understand future changes in alpine region. ii. study area description danube river is the second largest in european region. it originates from black forest mountains of germany and cascades into black sea. it flows through germany, austria, slovak republic, hungary and croatia, passes through serbia, romania and bulgaria, ukraine and moldova (figure 1). approximately around 81 million people inhabit within its proximity. the basin is approximately 2900km long. it possesses drainage area of about 817000km 2 . plain and hilly areas are around the two thirds of the total basin area, while the remaining one third consists of mountains. its average flow is approximately 6500m 3 /sec. its elevation ranges from a few hundred meters at lowlands to over 3000m a.s.l with a mean height of about 475m a.s.l. fig. 1. geographical map of danube with both up and downstream gauge stations achleiten and ceatal izmail. the basin climate varies considerably from mountainous to plain areas due to diverse relief and surface area: mediterranean climate dominates sava and drava catchments, whereas in the western part, high precipitation is the main characteristic of the upper basin due to atlantic climate while low precipitation and cold winters are the main features of continental climate. the precipitation amount also varies from high altitude to low altitude: the upper part receives around 2000mm per year, while the lower basin receives around 500mm. similarly, temperature varies from 5-6°c at upper danube to 11-12°c at middle to lower part. snow cover is the dominant feature above 1500m a.s.l from november to march. the seasonal variation rises from western to eastern part [7, 10]. iii. results and discussion the surface runoff and discharge levels of the main river and its tributaries are highly influenced by seasonal and spatial variations. the tributaries morava, tisza, sava, drava and inn are the most vital ones. overall, danube river consists of 26 main tributaries. sava tributary is considered the leading one by average annual discharge volume (approx. 50km 3 ) and the second one by drainage area (approx. 95400km 2 ). whereas, inn river is the third main tributary regarding volume with approx. 23km 3 and the seventh by drainage area with 26128km 2 . the hydrological characteristics of several danube tributaries have been analyzed in [22]. authors in [22] monitored the alpine gauging stations (i.e. hofkirchen, passau, wien), found higher specific discharges compared to low land streams monitored at gauging stations (i.e. tisza, silistra, ceatal izmail). alpine tributaries, e.g. inn, originate at the upper basin and possess high runoff per unit area, whereas lower to middle region of danube basin produces small values. the mean annual specific value reduces from head waters of alpine part towards tributaries of the eastern region of carpathians i.e. 25 to 30l/s/km 2 for alpine headwaters to 14.59l/s/km 2 for drava, towards 6.03l/s/km 2 for tisza. the contribution of alpine tributaries is more than 25% of the total mean annual flow and particularly in summer months its average contribution is around 40-45%, and may even reach to 80% in dry years like in the hot summer of 2003. the austrian part of alpine region mostly lies with danube basin and adds up approximately 20% of total basin flow volume with mean flow of 1448m 3 /s [22]. the assessment of monthly flow series of achleiten station demonstrates that the average annual flow volume is marginally increased [22], however the main effect has been noticed over seasonal flows, i.e. flow volume is increased in winter and autumn and significantly decreased in summer. the increase in volume is most probably due to the increased precipitation rates in winter and recent general temperature increase. similarly, reduced precipitation rates in summer and early onset of snow melt including high summer evaporation rates are the main cause of reduced summer flows (figure 2). fig. 2. the linear trends of mean seasonal flow series of danube at high alpine gauging station achleiten over 1900-2008. linear trends indicate a significant shift in seasonality: increase in winter and decrease in summer. station flow data was provided by grdc, germany. these seasonal tendencies point the future, when the water availability might be affected during summer months like it did in the summer draught of 2003. the situation clearly demonstrates the importance of alpine contribution. the region fairly offsets the water scarcity through enlarged glacial melt. in a nutshell, there is little indication that climate change has altered seasonal or annual flow volume during the last century. however man-made interferences i.e. groundwater extraction, irrigation demand, urbanizations have remarkably changed river flow regime in most parts of catchment. iv. conclusion this study has been carried out to assess the climate change effect on mean annual and seasonal flow series of danube river and its tributaries during the 20th century. the study reveals the variations driven by climate change in mean annual and seasonal flow series. the analysis of achleiten station demonstrates that the average annual flow regime is a little bit increased. major increase is observed during winter and autumn months and while decrease is observed during summer months. this points out that in future, climate driven changes engineering, technology & applied science research vol. 8, no. 6, 2018, 3505-3507 3507 www.etasr.com laghari et al.: assessment of climate driven changes in flow series of alpine basin: a case study … may have a significant effect over snow storage and subsequently alter both timing and volume of the flow regime of mountain rivers and accordingly water availability in downstream regions. severe implications may emerge on fresh water management and development. however, currently manmade inventions have possibly been the main reason behind danube flow series alterations. references [1] d. l. hartmann, a. m. k. tank, m. rusticucci, l. v. alexander, s. bronnimann, y. a. r. charabi, f. j. dentener, e. j. dlugokencky, d. r. easterling, a. kaplan, “observations: atmosphere and surface”, in: climate change 2013 the physical science basis: working group i contribution to the fifth assessment report of the intergovernmental panel on climate change, cambridge university press, 2013 [2] ipcc, the fourth assessment report of the intergovernmental panel on climate change, geneva, switzerland, 2007 [3] r. weingartner, d. viviroli, b. schadler, “water resources in mountain regions: a methodological approach to assess the water balance in a highland‐lowland‐system”, hydrological processes, vol. 21, no. 5, pp. 578-585, 2007 [4] b. messerli, d. viviroli, r. weingartner, “mountains of the world: vulnerable water towers for the 21st century”, ambio, vol. 2004, pp. 2934, 2004 [5] d. nogues-bravo, m. b. araujo, m. errea, j. martinez-rica, “exposure of global mountain systems to climate warming during the 21st century”, global environmental change, vol. 17, no. 3-4, pp. 420-428, 2007 [6] m. beniston, “impacts of climatic change on water and associated economic activities in the swiss alps”, journal of hydrology, vol. 412413, pp. 291-296, 2012 [7] m. beniston, “is snow in the alps receding or disappearing?”, wires: climate change, vol. 3, no. 4, pp. 349-358, 2012 [8] s. u. islam, s. j. dery, “evaluating uncertainties in modelling the snow hydrology of the fraser river basin, british columbia, canada”, hydrology and earth system sciences, vol. 21, no. 3, pp. 1827-1847, 2017 [9] b. c. bates, z. kundzewicz, s. wu, climate change and water, ipcc, geneva, 2008 [10] d. vanham, e. fleischhacker, w. rauch, “impact of an extreme dry and hot summer on water supply security in an alpine region”, water science and technology, vol. 59, no. 3, pp. 469-477, 2009 [11] m. m. elsner, l. cuo, n. voisin, j. s. deems, a. f. hamlet, j. a. vano, k. e. mickelson, s. y. lee, d. p. lettenmaier, “implications of 21st century climate change for the hydrology of washington state”, climatic change, vol. 102, no. 1-2, pp. 225-260, 2010 [12] e. kerkhoven, t. y. gan, “differences and sensitivities in potential hydrologic impact of climate change to regional-scale athabasca and fraser river basins of the leeward and windward sides of the canadian rocky mountains respectively”, climatic change, vol. 106, no. 4, pp. 583-607, 2011 [13] s. j. dery, m. a. hernandez-henriquez, p. n. owens, m. w. parkes, e. l. petticrew, “a century of hydrological variability and trends in the fraser river basin”, environmental research letters, vol. 7, no. 2, pp. 024019-024028, 2012 [14] f. strauss, h. formayer, e. schmid, “high resolution climate data for austria in the period 2008–2040 from a statistical climate change model”, international journal of climatology, vol. 33, no. 2, pp. 430443, 2013 [15] a. laghari, d. vanham, w. rauch, “the indus basin in the framework of current and future water resources management”, hydrology and earth system sciences, vol. 16, no. 4, pp. 1063-1083, 2012 [16] a. laghari, d. vanham, w. rauch, “to what extent does climate change result in a shift in alpine hydrology? a case study in the austrian alps”, hydrological sciences journal, vol. 57, no. 1, pp. 103-117 [17] t. kohler, a. wehrli, m. jurek, mountains and climate chance: a global concern, cde, sdc and geographica bernensia, 2014 [18] d. h. kang, h. gao, x. shi, s. ul islam, s. j. dery, “impacts of a rapidly declining mountain snowpack on streamflow timing in canada’s fraser river basin”, scientific reports, vol. 6, article number 19299, 2016 [19] d. viviroli, d. r. archer, w. buytaert, h. j. fowler, g. greenwood, a. f. hamlet, y. huang, g. koboltschnig, i. litaor, j. i. lopez-moreno, “climate change and mountain water resources: overview and recommendations for research, management and policy”, hydrology and earth system sciences, vol. 15, no. 2, pp. 471-504, 2011 [20] m. beniston, m. stoffel, “assessing the impacts of climatic change on mountain water resources”, science of the total environment, vol. 493, pp. 1129-1137, 2014 [21] z. kundzewicz, l. j. mata, n. w. arnell, p. doll, b. jimenez, k. miller, t. oki, z. sen, i. shiklomanov, “the implications of projected climate change for freshwater resources and their management”, hydrological sciences journal, vol. 53, no. 1, pp. 3-10, 2008 [22] k. tockner, s. e. bunn, c. gordon, r. j. naiman, g. p. quinn, j. a. stanford, “4 a flood plains: critically threatened ecosystems”, in: aquatic ecosystems: trends and global prospects, pp. 45-61, cambridge university press, 2008 engineering, technology & applied science research vol. 8, no. 4, 2018, 3209-3212 3209 www.etasr.com laghari et al.: performance analysis of water filtration units for reduction of ph, turbidity, solids … performance analysis of water filtration units for reduction of ph, turbidity, solids and electricity conductivity abdul nasir laghari department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan a.n.laghari@quest.edu.pk gordhan das walasai department of mechanical engineering quaid-e-awam university of engineering, science and technology, nawabshah, pakistan valasai@quest.edu.pk abdul rehman jatoi department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan jatoi.ar@gmail.com faheem akhtar shaikh department of chemical engineering quaid-e awam university of engineering, science and technology, nawabshah, pakistan faheemakhtar86@yahoo.com zafar ali siyal department of energy and environment engineering quaid-e-awam university of engineering, science and technology, nawabshah, pakistan zafarsiyal@yahoo.com abstract—the main objective of this study was to analyze the performance of different filtration units that reduce turbidity, ph, total dissolved solids (tds) and electrical conductivity (ec) of canal water. for that, three different types of filtration units, namely, slow sand, rapid sand and dual media were fabricated. typical parameters of canal and filtered water, like ph, turbidity, tds and ec were examined, and then the filtered water quality was compared with world health organizations (who) standards. maximum ph reduction was noted with dual media and less by the rapid system, while more turbidity was reduced with the slow sand and less with the dual media filtration system. in contrary to the ph and turbidity results, increment in both tds and ec values were noted in filtered samples compared to that of raw water samples due to the transfer of dissolved minerals present in the sand into the filtered water during the contact period with media in the bed. however, all examined parameters of filtered water were within who standards. keywords-water filtration; ph; turbidity; water quality i. introduction water covers about 71.4% of the surface of the planet. pure water has no smell, taste, or color. potable (drinking) water is safe to drink or to use for other purpose like food preparation etc. [1]. clean water is a crucial requirement for a healthy life but, globally, almost more than 1.1 billion people can’t reach safe water sources. today, the worst victims of the water crisis are the populations of low and middle income countries [2, 3]. globally, each day, women and children spend almost 200 million hours on collecting often polluted water from distant water sources [2, 4]. the impact of unsafe drinking water not only has devastating effects to individuals and families, but over the society as a whole [2]. the primary sources of drinking water in pakistan include groundwater, rivers, lakes and canals. the canals are the most important source for the nearby population [5, 6]. the causes behind the degradation of water quality are mainly anthropogenic activities. however, an improved management system and implementation of different physical, chemical or biological techniques could help significantly to control the degradation [7, 8]. authors in [9] reported that the major reason behind almost 80% of ailments and more than 33% of deaths in developing countries is polluted water. among 122 nations with poor drinking water quality, pakistan ranks at number 80 [10, 11]. moreover, due to the absence of water treatment systems, the survival of a substantial portion of pakistan’s rural population relies on ground water sources. according to the reports, around 40% of the deaths in pakistan are a result of water borne diseases [12]. in the surface water bodies of pakistan 2000 million gallons of sewage are dissolved per day [13]. it has been reported that the percentage of people having access to safe drinking water in pakistan is just 60% [14]. by 2015, according to government’s set target, 93% of the population should be having access to safe drinking water, where by 2025, the entire population will have such provision [15, 16]. however, the target is not so easy to achieve and is challenging due to many economic, technical and political problems. the use of sand filters for domestic purposes has increased around the world for understanding the mechanisms for microbial control [17, 18]. color and turbidity (darkness of water due to suspended particles) are major properties therefore turbidity removal from canal water is important [19, 20]. locally developed sand filters have been proved to be a cost engineering, technology & applied science research vol. 8, no. 4, 2018, 3209-3212 3210 www.etasr.com laghari et al.: performance analysis of water filtration units for reduction of ph, turbidity, solids … effective and efficient solution towards removal of solids from the raw water [18]. therefore, the main goal of this study was to develop less expensive water treatment filters for ph, turbidity and solids and electricity conductivity reduction using locally available materials to remove the suspended particles from canal water. ii. materials and methods this study’s aim was to design and develop cheap water treatment systems from locally available materials in order to remove the pollutants/suspended particulates from canal waters. therefore, a slow, rapid and dual media filtration system was designed and fabricated for removing the pollutants/suspended particulates and turbidity from canal water and make it fit for human consumption in remote areas of the country where the conventional treatment plants are not available. a. water sampling the water samples were collected from rohri canal using plastic drums with a capacity of approximately 1800 liters. sampling was carried out in the morning time around 08:00 am pakistan standard time (pst). b. development of slow, rapid sand bed filtration and dual media filtration system fundamentally, all water treatment technologies focus on removing turbidity along with chemical and pathogenic contaminants from water with the most efficient and affordable way possible. natural settling using sand filtration is the most common type of natural filtration used today. such a filtration method has proved to be an excellent method and therefore is being used since nineteenth century [21]. therefore, in this study, three different filtration systems (slow sand bed, rapid sand bed and dual media filtration systems) were adopted and utilized in order to remove pollutants from canal water. the filters were prepared from local materials (plastic drums). each filtration system unit comprised of water reservoir, top cover, diffuser plate, main treatment unit and riser pipe. additionally, a plastic drum with a capacity of 1800 liters was used to hold the huge amount of canal water initially. the filtration system was designed and fabricated in mechanical engineering department, and it was tested in energy and environment engineering department of quest nawabshah. c. analyzing of water quality parameters the ph level of sampled water (before and after) was examined through a lovibond senso direct ph 110 meter. ele microprocessor turbidity meter was used to analyze the turbidity level, electrical conductivity was measured with ele international conductivity meter and total dissolved solids (tds) were measured by tds meter model hi98302 by hanna in the laboratory of energy and environment engineering department, quaid -eawam university of engineering, science and technology (quest), nawabshah. iii. results and discussion a total of four parameters, namely, turbidity, ph, tds and ec of rohri canal water were examined. as shown in table i, ph of the raw water was 8.4, whereas, ph of filtered water by rapid sand was 8.3, slow sand 7.8 and dual media 7.6. the who guideline value of ph is 6.5-8.5. it was found that dual media percentage of ph reduction was greater than that of slow sand and rapid sand bed filtration systems. the average turbidity values of raw canal water and filtered water are also shown in table i. turbidity level of raw water was 522.5ftu, whereas, its level was 55.1, 25.3 and 4.8ftu with dual media, rapid sand and slow sand filtration system respectively). slow sand bed filtration unit was found more effective in reducing turbidity level (the who guideline value of turbidity is 5ftu). tds level in raw canal water was 47mg/l as shown in table i. tds value in filtered water was 155mg/l with dual media, 145mg/l with slow sand and 68mg/l with rapid sand filtration system, whereas the acceptable who guideline for tds is 1000mg/l. dual media filtration system was found less effective and rapid sand more effective in reducing tds. the ec results of raw as well as filtered water samples are shown in table i. the values of ec of raw water were 78.6μs/cm. the ec of filtered samples were more than that of raw water. ec values were found increased by 230% with dual media, 204% with slow sand and 45% with rapid sand method compared to raw water. it is noted that rapid sand filtration system is more effective in reducing ec from raw water than other examined systems. it is deduced from the results that both tds and ec showed increasing behavior in filtered water. the increase of tds resulted in rise of ec and vice versa, therefore both are interrelated. table i. rohri canal water parameters treatment system ph turbidity (ftu) tds (mg/l) ec (µs/cm) slow sand filter 7.8 4.85 145 239 rapid sand filter 8.3 25.29 68.5 114.1 dual media filter 7.6 55.1 155 259 feed water 8.4 522.5 47.2 78.6 an economic analysis of the filtration unit development, materials used, and the quantity of water filtered is carried out under the current study. table ii details the economic analysis of the materials used in the water filtration units. the total cost amounts to rs. 3700. this includes water drum, sand, gravel, charcoal, and piping system. the cost of sand filter is given in table iii. the quantity of liters filtered in a single day is 2, this makes it to 720 liters per year, as shown in table iv. on the basis of water filtered using this unit, the payback period calculated for the sand filter is 1.9, approximately 2 years. the replacement cost of sand, used as a filter, is 140 rs. per month, the layer value of sand is 60 rs., whereas the cost of the course and fine gravel is 40 rs. each. table ii. economic analysis of the filtration unit items quantity cost/item total cost drum 3 800 2400 sand 5-tin 30 150 corse gravel 3-tin 40 120 fine gravel 3-tin 40 120 charcoal 5 kg 20 100 pipe (0.75") 10 feet 20 200 tape wall 3 50 150 miscellaneous items 10 -500 3740 1 tin = 15kg engineering, technology & applied science research vol. 8, no. 4, 2018, 3209-3212 3211 www.etasr.com laghari et al.: performance analysis of water filtration units for reduction of ph, turbidity, solids … the cost of the whole process of water filtration per liter is estimated to be 2.33 rs. (see appendix for details), therefore the cost per year is estimated to be 1677 rs.. comparatively, the price of water purchased from the local market costs 30 rs. per liter, whereas the annual consumption/annual filtration of water is 720 liters, therefore the total price of water becomes 21600 rs. per year. on comparing the cost of water purchased from the local market and the water filtered using the filtration unit developed under this research study, it is estimated that 20230 rs. per year can be saved, which is the difference between yearly expenditure on the filtration unit and the cost of the purchased water. table iii. capital cost of one filter (slow sand) items quantity cost/item total cost drum 1 800 800 sand 2-tin 30 60 corse gravel 1-tin 40 40 fine gravel 1-tin 40 40 pipe (0.75") 4 feet 20 80 tape wall 1 50 50 miscellaneous items 5 0 300 1370 table iv. quantity of filtered water parameter daily (ltr) monthly (ltr) yearly (ltr) treated water/ distilled water 2 60 720 on the basis of the above results it was found that the slow sand filter was significantly better that the other filter systems. however, there is still some gap to further improve the performance of slow sand filter, e.g. of layers of different materials can be used in the construction. this shall help control the performance enhancement of slow sand filters. iv. conclusions dual media filtration system was found more suitable for raw water ph reduction. in addition, slow sand bed filtration unit was found more effective in reducing turbidity. in contrary to the ph and turbidity of raw water, the level of tds and ec showed increasing behavior in filtered water comparing with raw water samples. it was observed that 108mg/l, 98mg/l and 21mg/l more tds was noted in filtered water by application of dual media, slow sand and rapid sand bed filtration system respectively. similarly, ec of filtered water was increased approximately by two and a half times with dual media, two times with slow sand and only half time by rapid sand method. tds and ec are found interrelated as the increase of tds results to increase of ec and vice versa. it was discovered that dual media filtration system was found less effective and rapid sand more effective in reducing tds and ec among the examined methods. appendix replacement cost of sand and gravel layer value of sand 60 rs. for ssf (slow sand filter) course gravel 40 rs. for ssf (slow sand filter) fine gravel 40 rs. the replacement cost of sand and gravel 140 rs./month cost per ltr (140/60) 2.33 rs./ltr cost per month (2.33*60) 140 rs./month cost per year (2.33*720) 1677.6 rs./year water price in local market water per liter in local market 30 rs. monthly water price (30*60) 1800 rs./month yearly water price (30*720) 21600 rs./year comparison of filtered water vs purchased water profit = (yearly expenditure of purchased wateryearly expenditure of ssf water) profit = (21600-1370) profit 20230 rs references [1] s. haydar, m. arshad, j. 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based copolymer poly(am-4vp) and a engineering, technology & applied science research vol. 8, no. 4, 2018, 3209-3212 3212 www.etasr.com laghari et al.: performance analysis of water filtration units for reduction of ph, turbidity, solids … cationic commercial flocculant: application in turbidity removal on semi-industrial pilot”, journal of polymers and the environment, vol. 26, no. 4, pp. 1550-1558, 2017 [18] m. w. jenkins, s. k. tiwari, j. darby, “bacterial, viral and turbidity removal by intermittent slow sand filtration for household use in developing countries: experimental investigation and modeling”, water research, vol. 45, no. 18, pp. 6227-6239, 2011 [19] s. yang, n. okada, m. nagatsu, “the highly effective removal of cs(+) by low turbidity chitosan-grafted magnetic bentonite”, journal of hazardous materials, vol. 301, pp. 8-16, 2016 [20] k. s. nitzsche, p. weigold, t. losekann-behrens, a. kappler, s. behrens, “microbial community composition of a household sand filter used for arsenic, iron, and manganese removal from groundwater in vietnam”, chemosphere, vol. 138, pp. 47-59, 2015 [21] c. ray, r. jain, drinking water treatment: focusing on appropriate technology and sustainability, springer, 2011 microsoft word 22-3357_s_etasr_v10_n2_pp5466-5469 engineering, technology & applied science research vol. 10, no. 2, 2020, 5466-5469 5466 www.etasr.com truong: a low-cost artificial neural network model for raspberry pi a low-cost artificial neural network model for raspberry pi son ngoc truong faculty of electrical and electronics engineering hcmc university of technology and education hcm city, vietnam sontn@hcmute.edu.vn abstract—in this paper, a ternary neural network with complementary binary arrays is proposed for representing the signed synaptic weights. the proposed ternary neural network is deployed on a low-cost raspberry pi board embedded system for the application of speech and image recognition. in conventional neural networks, the signed synaptic weights of –1, 0, and 1 are represented by 8-bit integers. to reduce the amount of required memory for signed synaptic weights, the signed values were represented by a complementary binary array. for the binary inputs, the multiplication of two binary numbers is replaced by the bit-wise and operation to speed up the performance of the neural network. regarding image recognition, the minst dataset was used for training and testing of the proposed neural network. the recognition rate was as high as 94%. the proposed ternary neural network was applied to real-time object recognition. the recognition rate for recognizing 10 simple objects captured from the camera was 89%. the proposed ternary neural network with the complementary binary array for representing the signed synaptic weights can reduce the required memory for storing the model’s parameters and internal parameters by 75%. the proposed ternary neural network is 4.2, 2.7, and 2.4 times faster than the conventional ternary neural network for mnist image recognition, speech commands recognition, and real-time object recognition respectively. keywords-artificial neural network; deep learning; speech recognition; image recognition; ternary neural networks i. introduction artificial neural networks (anns) and deep learning have achieved impressive successes in fields such as image recognition, speech recognition, and prediction [1-6]. anns are computationally expensive because they are composed of a huge number of computational tasks and internal parameters. anns are often implemented on high-performance cpus (central processing units) and gpus (graphics processing units) rather than low-cost embedded systems [7]. various models of anns have been proposed for low-cost embedded systems such as binary neural networks and ternary neural networks [8-14]. binary neural networks are the optimized models of neural networks that constraint the synaptic weights to the binary space {–1, 1} [8-11]. in a binary neural network, the conventional 32-bit floating-point multipliers are replaced by the logical xnor operation to speed up performance. however, their accuracy is lower than full-precision neural networks because only one bit is used to represent the synaptic weight and activation function. to increase speed and accuracy, ternary neural networks that constraint the synaptic weights to the ternary space {–1, 0, 1} have been proposed [1215]. the accuracy of the ternary and binary neural networks is slightly lower than the one of full-precision neural networks. however, the required memory is reduced significantly. ternary neural networks are suitable to be implemented on low-cost embedded systems [14]. for a ternary neural network, the signed values of –1, 0, and 1 require 8-bit width memories and the 8-bit multipliers. in this paper, a method for representing the signed ternary synaptic weights by using the binary numbers 0 and 1 is proposed. the multipliers are replaced by the logical and operations to reduce the required storage space and speed up the performance of the network. the proposed ternary neural network is deployed on a raspberry pi board for a mobile robot for object recognition and speech command recognition. fig. 1. block diagram of the control unit for a mobile robot using the raspberry pi board figure 1 shows a conceptual diagram of a control unit for a mobile robot. the control unit is implemented on a low-cost raspberry pi board. the system performs the tasks of pattern recognition including image recognition, speech command recognition, and real-time object recognition. ii. the proposed method for representing the signed ternary synaptic weights a. ternary neural networks a ternary neural network is an optimized model of anns with the weights constrained to –1, 0, and +1 to reduce the amount of required memory for storing the model’s parameters [12-15]. the synaptic weights are quantized by 2 bits. it should be noted that the negative synaptic weights are necessary because the synapses are either excitatory or inhibitory [16-18]. corresponding author: son ngoc truong engineering, technology & applied science research vol. 10, no. 2, 2020, 5466-5469 5467 www.etasr.com truong: a low-cost artificial neural network model for raspberry pi fig. 2. the conceptual diagram of a ternary neural network, where the synaptic weights are -1, 0, or +1 figure 2 shows a conceptual ternary neural network, where the synaptic weights are –1, 0, or +1. to represent the signed values of –1, 0, or +1, an 8-bit width memory can be used instead of the 32-bit width memory used in full-precision neural networks, so the amount of required memory for the model parameters of ternary neural networks is less than the full-precision neural networks. though the amount of required memory is reduced, the ternary neural network is still far from the capability of a low-cost embedded system such as the raspberry pi board. the huge number of computation tasks (additions and multiplications) makes ternary neural networks too much complicated to be deployed on a low-cost embedded system. in this work, a complementary binary array is proposed to represent the signed synaptic weights. the multiplication is replaced by the bitwise and operation to speed up the performance of the network. b. proposed method a complementary binary array to represent the signed synaptic weights is proposed. for the binary inputs, the output of the j th neuron in the hidden layer can be calculated by (1) [19]: , 1 ( )j j n j i i j i h f a a x w = = =∑ (1) where f is an activation function, xi is the i th input, wi,j is the synaptic weight representing the connection strength between the i th input neuron and the j th neuron in the hidden layer. equation (1) can be rewritten as: ( ), , , 1 1 , , 1 1 , , , ( ) where j j n n j i i j i i j i j i i n n j i i j i i j i i i j i j i j h f a a x w x w w a x w x w w w w + − = = + − = = + − = = = − = − = − ∑ ∑ ∑ ∑ (2) in (2), the signed values of –1, 0, and +1 can be represented by the binary numbers 0 and 1. for example, wi,j=–1 can be represented by w + i,j=0 and w – i,j=1. similarly, wi,j=+1 can be represented by w + i,j=1 and w – i,j=0. by doing this, two binary numbers are used to store a signed value instead of using an 8bit number. as a result, the amount of required memory is reduced dramatically. furthermore, for the binary input, the multiplication of two binary numbers can be performed by the bit-wise and operation to reduce the computational task. the concept of the proposed complementary binary array for representing the signed ternary weights is shown in figure 3. fig. 3. (a) the output of a neuron with signed ternary synapses. here multiplications are used to weight the inputs. (b) the concept of the proposed complementary binary array for computing the output of a ternary neuron, where the bitwise and operation is used to calculate the neuron’s output. figure 3(a) shows the performance of calculating the output of a conventional ternary neural network. the multiplications are used to perform the synaptic weighting. it requires a huge number of computational tasks. figure 3(b) presents the proposed method for storing the signed parameters and perform synaptic weighting. the signed values of –1, 0, and 1 are stored in two complementary binary arrays. if the weight is 1, the value of w + and w – are respectively 1 and 0. if the weight is –1, the value of w + and w – are respectively 0 and 1. by doing this, we need only two 1-bit memory cells for representing the signed value of –1, 0, or +1. furthermore, the multiplication of two binary numbers can be replaced by the bit-wise and operation, as shown in figure 3(b). the multiplications are omitted. the proposed ternary neural network can be deployed on low-cost embedded systems effectively. in figure 3(b), the summation of weighted inputs is performed by counting the “1” bits (population counting) in the result of the bit-wise and operation. employing two 1-bit memory cells to represent the signed synaptic weights can reduce the amount of memory dramatically. the proposed ternary neural network is effective for low-cost embedded systems used for mobile robots. iii. experimental results the proposed ternary neural network with the complementary binary array representing the signed synaptic weights is deployed on the raspberry pi board for the applications of speech recognition, image recognition, and realtime object recognition. for image recognition, a three-layer x1 xi xn h1 h2 +1 -1 -1 hj hm y1 yk+1 +1 0 0 -1 +1 +1 -1 x1 x2 x4 +1 -1 hj +1 x3 x5 -1 0 1 1 0 1 1 aj f 11011xi 1-1-101wi,j 1-1001 1, =∑ jiiwx (a)11011 10001w+i,j 10001xi and 11011 01100w-i,j 01000xi and 2, =∑ + jiiwx 1, =∑ − jiiwx 1,, =−∑∑ −+ jiijii wxwx (b) engineering, technology & applied science research vol. 10, no. 2, 2020, 5466-5469 5468 www.etasr.com truong: a low-cost artificial neural network model for raspberry pi neural network is deployed on the raspberry pi. the network is trained and tested on the mnist dataset for recognizing images of handwritten digits [20]. the input layer has 784 nodes corresponding to 784 pixels of images. the inputs are binary. the hidden layer has 512 neurons and the output layer has 10 neurons for recognizing 10 digits. the recognition rate is as high as 94% for 10,000 testing images. for speech recognition, an optimized convolutional neural network (cnn) is deployed on the raspberry pi board. the performance of the ternary cnn is evaluated using the google speech commands dataset [21] which contains 65,000 samples of 30 words. to deploy it on the raspberry pi board, a convolution neural network is designed with 4 convolutional layers, a fully-connected layer with 1024 neurons, and a softmax layer of 30 neurons for the outputs. mfcc (melfrequency cepstral coefficient) is used for feature extraction. the coefficients of mfccs are quantized by 8 bits. the recognition rate for speech commands recognition is 91%. this is the first test of the proposed ternary neural network for the application of image recognition and speech recognition for a mobile robot. the ternary neural network with the proposed method for representing the ternary synaptic weights is also deployed for the application of real-time object recognition. in this experiment, 10 simple objects, shown in figure 4, are used to evaluate the performance of the proposed neural network. fig. 4. simple objects used to evaluate the performance of the proposed ternary neural network for each object, 200 images were captured and converted to grayscale images for the training process. all images were captured with white background. then, a ternary convolutional neural network was deployed on the raspberry pi board. there were 64 3×3 kernels in each convolutional layer, followed by a max pooling layer. the fully-connected layer was composed of two hidden layers of 1024 hidden nodes. the output layer had 10 neurons for recognizing 10 objects. the convolutional neural network constraints the synaptic weights to the ternary space {–1, 0, 1}. the evaluated recognition rate for recognizing the 10 simple objects shown in figure 4 is 89%. to compare the required memory and speed of a ternary neural network with the conventional method and the proposed technique for representing the signed synaptic weights, we deploy the two models on a raspberry pi board. table i shows the comparison of the required memory of the conventional ternary neural network, and the proposed ternary neural network with a complementary binary array representing the signed synaptic weights. in table i, we evaluate the memory that is required for storing the model and internal parameters. for a multilayer neural network, the conventional ternary neural network requires a memory of 398.2754kb, whereas the proposed ternary neural network with a complementary binary array representing the signed synaptic weights requires a memory of 99.5688kb, i.e. the proposed ternary neural network requires 75% less memory than the conventional ternary neural network. by using the bitwise and operation and population counting instead of multiplication, the proposed ternary neural network is 4.2 times faster than the conventional ternary neural network for mnist image recognition. for the speech recognition and real-time object recognition, the proposed ternary neural network can reduce the required memory by 75%, compared to the conventional ternary neural network. for speech recognition, the proposed ternary neural network is 2.7 times faster than the conventional neural network. for real-time object recognition, the ternary convolutional neural network with the proposed technique for ternary synaptic weight representation is 2.4×times faster than the ternary convolutional neural network using 8-bit ternary synaptic weights. table i. required memory (kb) and internal paramaters applications (model) conventional proposed image recognition (multilayer nn) 398.2754 99.5688 speech recognition (cnn) 396.1543 99.0386 real-time object recognition (cnn) 2,573.5 643.38 iv. conclusion ternary neural networks have been proposed for reducing the required storage capacity and enhancing the speed of anns. however, the implementation of signed ternary weights still consumes high power and requires large computational resources. many ternary neural network models have been deployed on high-performance processors such as gpus for the application of image recognition [12-15]. in this work, the signed ternary synaptic weights are represented by two complementary binary synaptic weights. by doing this, the ternary neural networks are treated as binary neural networks. power-hungry computational tasks such as multiplications are replaced by the bitwise and operations to enhance the speed of the anns. the proposed technique is useful for deploying anns on low-cost embedded systems for mobile robots. the proposed ternary neural network is deployed on a raspberry pi board suitable for a mobile robot. for reducing the amount of required memory, the signed values of ternary synaptic weights are represented by complementary binary arrays. regarding image recognition, the proposed ternary neural network is tested in the mnist dataset and achieves a recognition rate as high as 94%. for speech recognition, the proposed ternary neural network is evaluated using the google speech commands and its accuracy is 91%. the proposed ternary neural network was also applied to real-time object recognition for a mobile robot. the proposed technique of representing singed synaptic weights reduces the required memory by 75% when compared to the conventional method. overall, the proposed ternary neural network is 4.2, 2.7, and 2.4 times faster than the conventional ternary neural networks for image recognition, speech commands recognition, and realtime object recognition respectively. engineering, technology & applied science research vol. 10, no. 2, 2020, 5466-5469 5469 www.etasr.com truong: a low-cost artificial neural network model for raspberry pi acknowledgment this work is financially supported by the ministry of education and training (grant number b2019-spk-05, 2019). references [1] a. krizhevsky, i. sutskever, g. e. hinton, “imagenet classification with deep convolutional neural networks”, advances in neural information processing systems, lake tahoe, usa, december 3-8, 2012 [2] k. he, x. zhang, s. ren, j. sun, “deep residual learning for image recognition”, in: the ieee conference on computer vision and pattern recognition, pp. 770-778, ieee, 2016 [3] a. graves, n. jaitly, “towards end-to-end speech recognition with recurrent neural networks”, international conference on machine learning, beijing, china, june 21-26, 2014 [4] p. b. patil, “multilayered network for lpc based speech recognition”, ieee transactions on consumer electronic, vol. 44, no. 2, pp. 435438, 1998 [5] b. m .zahran, “using neural networks to predict the hardness of aluminum alloys”, engineering, technology & applied science research, vol. 5, no. 1, pp. 757-759, 2015 [6] g. s. fesghandis, a. pooya, m. kazemi, z. n. azimi, “comparison of multilayer perceptron and radial basis function neural networks in predicting the success of new product development”, engineering, technology & applied science research, vol. 7, no. 1, pp. 1425-1428, 2015 [7] h. jang, a. park, k. jung, “neural network implementation using cuda and open mp”, in: proceedings digital image computing: techniques and applications, pp. 155-161, ieee, 2008 [8] y. wang, j. lin, z. wang, “an energy-efficient architecture for binary weights convolution neural networks”, ieee transactions on very large scale integration (vlsi) systems, vol. 26, no. 2, pp. 280-293, 2017 [9] t. simons, d. j. lee, “a review of binarized neural networks”, electronics, vol. 8, no. 6, pp. 1-25, 2019 [10] m. courbariaux, i. hubara, d. soudry, r. el-yaniv, y. bengio, “binarynet: training deep neural networks with weights and activations constrained to +1 or −1”, available at: https://arxiv.org/abs/1602.02830, 2016 [11] c. baldassi, a. braunstein, n. brunel, r. zecchina, “efficient supervised learning in networks with binary synapses”, proceedings of the national academy of science of the usa, vol. 104, no. 26, pp. 11079-11084, 2007 [12] k. hwang, w. sung, “fixed-point feedforward deep neural network design using weights +1, 0, and −1”, 2014 ieee workshop on signal processing systems, belfast, uk, october 20–22, 2014 [13] h. yonekawa, s. sato, h. nakahara, “a ternary weight binary input convolutional neural network: realization on the embedded processor”, ieee 48th international symposium on multiple-valued logic, linz, austria, may 16-18, 2018 [14] s. yin, p. ouyang, j. yang, t. lu, x. li, l. liu, s. wei, “an energyefficient reconfigurable processor for binary-and ternary-weight neural networks with flexible data bit width”, ieee journal of solid-state circuits, vol. 54, no. 4, pp. 1120-1136, 2018 [15] l. deng, p. jiao, j. pei, z. wu, g. li “gxnor-net: training deep neural networks with ternary weights and activations without fullprecision memory under a unified discretization framework”, neural networks, vol. 100, pp. 49-58, 2018 [16] l. f. abbott, w. g. regehr, “synaptic computation”, nature, vol. 431, pp. 796-803, 2004 [17] r. s. zucker, w. g. regehr, “short-term synaptic plasticity”, annual review of physiology, vol. 64, pp. 355–405, 2002 [18] r. lamprecht, j. ledoux, “structural plasticity and memory”, nature reviews, neuroscience, vol. 5, no. 1, pp. 45-54, 2004 [19] t. mitchell, machine learning, mcgraw-hill, 1997 [20] l. deng, “the mnist database of handwritten digit images for machine learning research [best of the web]”, ieee signal processing magazine, vol. 29, no. 6, pp. 141-142, 2012 [21] p. warden, “speech commands: a dataset for limited-vocabulary speech recognition”, available at: https://arxiv.org/abs/1804.03209, 2018 authors profile son ngoc truong received his bsc and msc degrees in electronic engineering from ho chi minh city university of technology and education, vietnam, in 2006 and 2011 respectively, and a phd degree in electronic engineering from kookmin university, seoul, korea, in 2016. he was a postdoctoral researcher fellow at kookmin university, seoul, korea in 20162017. he is currently a lecturer at ho chi minh city university of technology and education, vietnam. his research interests include circuits and systems for neuromorphic computing systems, artificial intelligence, and deep learning. microsoft word 40-3326_s1_etasr_v10_n1_pp5320-5324 engineering, technology & applied science research vol. 10, no. 1, 2020, 5320-5324 5320 www.etasr.com alenezi: effects of heat treatment on the corrosion behavior of astm a-36 steel effects of heat treatment on the corrosion behavior of astm a-36 steel ibrahim alenezi northern border university arar, saudi arabia i.alenezi@nbu.edu.sa abstract—the effects of different tempering temperatures and heat treatment times on the corrosion resistance of rolled astm a-36 steel in various concentrations of hydrochloric acid (hcl) and sodium chloride (nacl) were studied in this work, using the conventional weight loss measurement. rolled and heat-treated specimens were placed in the acidic media for five days and for seven days in nacl, respectively, and the corrosion rates were evaluated. the microstructure of steel before and after heat treatment was studied. corrosion resistance revealed remarkable changes from the effect of tempering after water or oil quenching of steel. generally, the corrosion rate increases from the effect of steel hardening. tempering of water-quenched steel at 450c o for one hour highly improves the corrosion resistance of 0.27% carbon steel. keywords-corrosion; hcl; nacl, a-36 steel i. introduction the high cost of the corrosion effects of industry, domestic applications, and public sector worldwide highlights the need for improved corrosion measures. effective corrosion inhibition has a high economic value, as the annual corrosion cost is estimated to reach 3–4% of the gdp in developed countries [1-4]. in the oil, gas, and chemical industries, corrosion is one of the most challenging tasks, and it is assumed that it costs $170 billion per year. it is not only the high cost of corrosion, but also the health and environmental risks associated with potential failures of the oil and gas industry that drive the developments of corrosion-resistant materials and improved corrosion mitigation strategies worldwide [5-9]. low-cost carbon steels are used as the preferred construction material across industries and are considered a more economical option than the costly corrosionresistant alloys. carbon steels typically contain less than 1.5% carbon content along with the minute presence of mn, si, p and s. based on the percentage of carbon (c), the classification is further divided into three forms, namely low-carbon steels (<0.25% c), medium-carbon steels (0.25–0.70% c) and highcarbon steels (0.70–1.05% c). carbon steels are used in a wide range of applications, such as structural components, industrial pipes, and kitchen appliances. with regard to applications in the oil and gas industry, the carbon dioxide (co2) corrosion could be considered as one of the major forms of corrosion [1013]. in this study, we discuss carbon steel as the most employable material for the construction of gas and oil pipelines, desalination plants, and water treatment construction and equipment. most of the corrosion issues occurring in the oil and gas and water treatment industries are related to pipelines and the conditions of exposure of the carbon steel that deem the selection of the suitable type of carbon steel. ii. experimental work steel astm a-36 (chemical composition shown in table i) was heated to the austenitizing temperature of 870 ° c for one hour followed by water quenching (wq), oil quenching (oq), air-cooling (ac) and furnace cooling (fc). representative samples of wq and oq medium-carbon steel were subjected to tempering at temperatures of 250 ° c, 350 ° c, 450 ° c and 550 ° c (t1, t1, t3 and t4, respectively). corrosion tests were carried out for as-rolled (ar) and heat-treated (ht) steels in various concentrations of hcl and nacl, as shown in table ii. specimens were placed for five days in the acidic media and for seven days in nacl. corrosion rates were calculated using the weight loss method in mils per year (mpy1mil=10 -3 inch). an optical micrograph was investigated for the ar and ht steels. the effect of tempering temperatures on the corrosion rate of water-quenched steel has been investigated according to table iii. table i. chemical composition of ar astm a-36 steel in wt.% c mn si cu al 0.27 0.84 0.24 0.095 0.003 p s zn v ta 0.02 0.02 0.05 0.006 0.06 table ii. concentrations of used hcl and nacl for corrosion tests concentration (%) hcl 0.1 0.15 0.2 0.25 0.3 nacl 0.4 0.45 0.5 0.55 0.6 table iii. heat treatments for astm a-36 steel ac fc wq/870 o c wqt1 wqt2 wqt3 wqt4 870°c 870°c 250°c 350°c 450°c 550°c ac fc wq/870 o c oqt1 oqt2 oqt3 oqt4 870°c 870°c 250°c 350°c 450°c 550°c corresponding author: ibrahim alenezi engineering, technology & applied science research vol. 10, no. 1, 2020, 5320-5324 5321 www.etasr.com alenezi: effects of heat treatment on the corrosion behavior of astm a-36 steel iii. results and discussion a. corrosion rate of astm a-36 steel in hcl figure 1 shows the effect of the cooling rate from the austenitizing temperature on the corrosion rate of astm a-36 steel using hcl with different concentrations for 5 days. the corrosion rate slightly decreased with a decreasing cooling rate at 0.1% hcl. by increasing the cooling rate, the corrosion rate increased to the maximum of 0.25% hcl. with a further increase in the hcl concentration to 0.3%, the corrosion rate decreased. in general, ar steel revealed a lower corrosion rate compared to ht steel. the corrosion rate increases for the ac and fc specimens after heating to 870 ° c to about twice the corrosion rate of the ar steel. the corrosion rate for the oilquenched steel shows a maximum corrosion rate of up to 0.2% hcl. with a further increase of hcl, the water-quenched steel reveled a higher corrosion rate. this could be explained by the effect of the martensite phase produced after wq. the effect of the tempering temperature after wq revealed a remarkable effect on the corrosion rate of the used steel in hcl. as shown in figure 2, the corrosion rate reaches its maximum after tempering at 350 ° c (wqt2) and 250 ° c (wqt1) respectively. tempering at 450 ° c (wqt3) revealed remarkable improvement in the corrosion rate for the water-quenched steel. a further increase in the tempering temperature up to 550 ° c (wqt4) leads to an increase in corrosion resistance. it can be summarized that tempering at 450 ° c is the best for the corrosion resistance of wq astm a-36 steel. fig. 1. effect of the cooling rate after austenitizing treatment on the corrosion rate of astm a-36 steel (using hcl) fig. 2. effect of tempering temperature after wq on the corrosion rate of astm a-36 steel (using hcl) the effect of the tempering temperature of the oq steel on the corrosion rate in hcl is summarized in figure 3. the maximum corrosion was measured after tempering at 250 ° c (oqt1). by increasing the tempering temperature, the corrosion rate gradually decreased. generally, the corrosion rate of astm a-36 steel after oq and tempering is higher than the one after wq and tempering. thus, if the mechanical properties of this steel need to be increased, tempering of oq steel is not recommended if this steel will be subjected to hcl. fig. 3. effect of tempering temperature after oq on the corrosion rate of astm a-36 steel (using hcl) b. corrosion rate of astm a-36 steel in nacl the corrosion rates of the heat-treated specimens in a marine medium (nacl) are low when compared to the ar steel, as shown in figure 4. this is because the ar steel consists mainly of a pearlitic-ferritic structure in which each crystal consists of alternate layers of ferrite and cementite. it was observed that ferrite is anodic to cementite and this corrodes with moisture as the electrolyte. this was confirmed from the microstructure of the ar steel shown in figures 7-9. figure 4 shows the effect of the cooling rate from the austenitizing temperature on the corrosion rate of this steel using nacl with different concentrations for 7 days. fig. 4. effect of heat treatment on the corrosion rate of astm a-36 steel (using nacl) the ac steel shows a little increase in the corrosion rate compared to the ar steel. on the other hand, the fc steel recorded a slight decrease in the corrosion rate. a further increase in the cooling rate from the austenitizing temperature of astm a-36 steel revealed a higher increase in the corrosion rate, which reaches its maximum after wq and oq. it was engineering, technology & applied science research vol. 10, no. 1, 2020, 5320-5324 5322 www.etasr.com alenezi: effects of heat treatment on the corrosion behavior of astm a-36 steel noticed that the corrosion rate of astm a-36 steel in hcl is much higher compared with the corrosion rate in nacl, as shown in figures 1 and 4. the corrosion resistance of this steel is good when using nacl even without heat treatment. it is recommended to avoid using wq or oq treatments if heat treatment is required for this steel. the tempering temperature after wq revealed a remarkable effect on the corrosion rate of the used steel in nacl, as shown in figure 5. the corrosion rate sharply decreases after tempering at different temperatures, with a minimum corrosion rate after tempering at 450 ° c (wqt3). fig. 5. effect of tempering temperature after wq on the corrosion rate of astm a-36 steel (using nacl) the effect of the tempering temperature of the oq steel on the corrosion rate in nacl is summarized in figure 6. the corrosion rate highly increased to double after tempering at 250 ° c (oqt1). by increasing the tempering temperature, the corrosion rate sharply decreased, revealing minimum values after tempering at 450 ° c (oqt3). generally, the corrosion rate of astm a-36 steel after oq and tempering is much lower than wq and tempered steel. thus, if the mechanical properties of this steel need to be increased, tempering of wq or oq steel at 450 ° c is the best heat treatment if this steel will be subjected to nacl. fig. 6. effect of tempering temperature after oq on the corrosion rate of astm a-36 steel (using nacl) c. microscopic observation of astm a-36 steel the microstructures obtained are shown in figures 7-9. the microstructure produced by the ar steel consists of a pearliticferritic structure, while the microstructures produced by the processes consist of a duplex ferrite martensite microstructure. the strong deformable second phase consists predominantly of martensite, with some bainite and retained austenite. martensite provides the strength in the steel whereas the ferrite provides the ductility. the strong second phase is dispersed in a soft ductile ferrite matrix. the effect of different cooling rates from solution treatment temperatures are shown in figure 7. this revealed mainly a pearlite in ferrite matrix. a martensite phase was clearly revealed after a high cooling rate. this could explain the higher increase in the corrosion rate of the wq and oq steel in hcl and nacl. (a) (b) (c) (d) fig. 7. effect of different cooling rates on the microstructure of astm a36 steel: (a) ar, (b) ac, (c) oq and (d) wq, x200 the effect of the tempering temperature on the microstructure of astm a-36 steel is summarized in figures 8 and 9. figure 8 shows the optical micrograph of the wq steel after tempering at different temperatures. remarkable changes in the microstructure and different phases have been revealed. engineering, technology & applied science research vol. 10, no. 1, 2020, 5320-5324 5323 www.etasr.com alenezi: effects of heat treatment on the corrosion behavior of astm a-36 steel the shape of the martensite phase obtained by rapid quenching changed and became courser after tempering. in addition, after tempering, wq steel shows changes in the microstructure as shown in figure 9. in contrast with the corrosion results, these changes in microstructure after heat treatment could be the reasons for the change in corrosion rate. (a) (b) (c) (d) fig. 8. effect of tempering temperature on the wq astm a-36 steel: (a) 250 o c, (b) 350 o c, (c) 450 o c and (d) 550 o c, x200 iv. conclusion the research results have shown that the corrosion rate changes as an effect of heat treatment and tempering conditions. also, the results revealed that the corrosion resistance of the rolled astm a-36 steel can be improved by carrying out heat treatment on this steel. this is because better corrosion properties were obtained from the heat-treated steel samples compared with the as-rolled medium-carbon steel. (a) (b) (c) (d) fig. 9. effect of tempering temperature on the oq astm a-36 steel: (a) 250 o c, (b) 350 o c, (c) 450 o c and (d) 550 o c, x200 thus, this steel can be used safely in oil and gas industries and water treatment fields. generally, the corrosion rate increases due to the effect of hardening of the steel. tempering of water-quenched steel at 450c o for one hour improves highly the corrosion resistance of astm a-36 steel. references [1] d. dwivedi, k. lepkova, t. becker, “carbon steel corrosion: a review of key surface properties and characterization methods”, rsc advances, vol. 7, pp. 4580–4610, 2017 [2] d. o. oluyemi, o. i. oluwole, b. o. adewuyi, “studies of the properties of heat treated rolled medium carbon steel”, materials research, vol. 14, no. 2, pp. 135-141, 2011 [3] o. o. daramola, b. adewuyi, i. o. oladele, “effects of heat treatment on the mechanical properties of rolled medium carbon steel”, journal of minerals & materials characterization & engineering, vol. 9, no. 8, pp. 693-708, 2010 engineering, technology & applied science research vol. 10, no. 1, 2020, 5320-5324 5324 www.etasr.com alenezi: effects of heat treatment on the corrosion behavior of astm a-36 steel [4] b. s. motagi, r. bhosle, “effect of heat treatment on microstructure and mechanical properties of medium carbon steel”, international journal of engineering research and development, vol. 2, no. 1, pp. 7-13, 2012 [5] o. o. joseph, r. o. leramo, o. s. ojudun, “effect of heat treatment on microstructure and mechanical properties of sae 1025 steel: analysis by one-way anova”, journal of materials and environmental science, vol. 6, no. 1, pp. 101-106, 2015 [6] j. k. odusote, t. k. ajiboye, a. b. rabiu, “evaluation of mechanical properties of medium carbon steel quenched in water and oil”, au journal of technology, vol. 15, no. 4, pp. 218-224, 2012 [7] v. k. murugan, p. k. mathews, “effect of tempering behavior on heat treated medium carbon (c 35 mn 75) steel”, international journal of innovative research in science, engineering and technology, vol. 2, no. 4, pp. 123-129, 2013 [8] s. a. tukur, m. m. usman, i. muhammad, n. a. sulaiman, “effect of tempering temperature on mechanical properties of medium carbon steel”, international journal of engineering trends and technology, vol. 9 no. 15, pp. 524-532, 2014 [9] a. k. tanwer, “effect of various heat treatment processes on mechanical properties of mild steel and stainless steel”, american international journal of research in science, technology, engineering & mathematics, vol. 8, no. 1, pp. 57-61, 2014 [10] a. calik, “effect of cooling rate on hardness and microstructure of aisi 1020, aisi 1040 and aisi 1060 steels”, international journal of physical sciences vol. 4, no. 9, pp. 514-518, 2009 [11] m. i. mohamed, “studies of the properties and microstructure of heat treated 0.27%c and 0.84%mn steel”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3484-3487, 2018 [12] j. a. al-jarrah, a. ibrahim, s. swalha, “effect of applied pressure on mechanical properties of 6061 aluminum alloy welded joints prepared by friction stir welding”, engineering, technology & applied science research, vol. 7, no. 3, pp. 1619-1622, 2017 [13] m. i. mohamed, “effects of cold rolling and aging treatment on the properties of cu-be alloy”, engineering, technology & applied science research, vol. 9, no. 4, pp. 4500-4503, 2019 engineering, technology & applied science research vol. 8, no. 3, 2018, 3023-3027 3023 www.etasr.com el badawi et al.: application of failure mode effect and criticality analysis (fmeca) to a computer … application of failure mode effect and criticality analysis (fmeca) to a computer integrated manufacturing (cim) conveyor belt isam a.q. elbadawi industrial engineering department university of hail hail, saudi arabia i.elbadawi@uoh.edu.sa mohamed arafat ashmawy mechanical engineering department university of hail, saudi arabia and suez university, suez, egypt arafat_696@yahoo.com wan ahmad yusmawiza industrial engineering department university of hail hail, saudi arabia yusmawiza@iium.edu.my imran ali chaudhry industrial engineering department university of hail hail, saudi arabia i.chaudhry@uoh.edu.sa naim ben ali industrial engineering department university of hail hail, saudi arabia naimgi2@yahoo.fr ayyaz ahmad industrial engineering department university of hail hail, saudi arabia ay.ahmad@uoh.edu.sa abstract—fault finding and failure predicting techniques in manufacturing and production systems often involve forecasting failures, their effects, and occurrences. the majority of these techniques predict failures that may appear during the regular system production time. however, they do not estimate the failure modes and they require extensive source code instrumentation. in this study, we suggest an approach for predicting failure occurrences and modes during system production time intervals at the university of hail (uoh). the aim of this project is to implement failure mode effect and criticality analysis (fmeca) on computer integrated manufacturing (cim) conveyors to determine the effect of various failures on the cim conveyor belt by ranking and prioritizing each failure according to its risk priority number (rpn). we incorporated the results of fmeca in the development of formal specifications of fail-safe cim conveyor belt systems. the results show that the highest rpn values are for motor over current failure (450), conveyor chase of vibration (400), belt run off at the head pulley (200), accumulated dirt (180), and bowed belt (150). the study concludes that performing fmeca is highly effective in improving cim conveyor belt reliability and safety in the mechanical engineering workshop at uoh. keywords-reliability; failure mode effect criticality analysis; maintenance i. introduction anticipating potential failure occurrences during conveyor productive time is important to achieve system pliability and to overcome unexpected and dangerous failure consequences. as machining tool systems become increasingly more complicated, the further development of system scale and functions, increases the probability of system failure. this paper starts with a brief historical overview of fmeca and the current international standards followed by a discussion of the core concept and implementation procedures of fmeca. finally, the paper illustrates the application of fmeca on the cim conveyor in the mechanical engineering workshop at uoh. a significant number of studies on the reliability and the related risks of manufacturing plants have been conducted. consequently policies for risk management, maintenance policies, and suggestions for improving the production process have been developed. a number of these studies aimed at minimizing the downtime rate and improving the equipment’s availability and reliability. furthermore, in order to improve the system efficiency with an optimized resource amount and to minimize the probability of system failure, several maintenance strategies were implemented, various approaches and maintenance planning models were developed, and many technical manufacturing specifications were listed. however, a comprehensive approach which tackles the potential causes and effects is yet to be developed [1]. ii. failure mode effect analysis (fmea) a. fmea every machine or system used in the manufacturing industry might fail to work properly. the failure may be caused by machines, materials, measurements, manpower, methods, and/or environmental factors. failure prediction methods have been used by leading production and manufacturing firms to control and minimize the impacts of failures on the cost of the product defect and the operational risk of manufacturing processes. a significant number of industrial firms and research organizations dedicated considerable efforts to analyze failure modes and their effects on manufacturing and engineering, technology & applied science research vol. 8, no. 3, 2018, 3023-3027 3024 www.etasr.com el badawi et al.: application of failure mode effect and criticality analysis (fmeca) to a computer … production systems. an important model was developed by the national aeronautics and space administration (nasa) in which they used a number of reliability practices in several space programs such as viking, galileo, apollo, and voyager to analyze the failure mode behavior of their systems [2]. according to nasa, fmea is a proactive quality tool for evaluating potential failure modes and their causes. fmea helps in prioritizing the failure modes, recommending corrective measures for the avoidance of catastrophic failures and, therefore, improving the quality of the manufacturing and production processes. the objectives of fmea include understanding the criticalities and dependencies of all types of systems as well as facilitating the evaluation of process manipulation options to achieve high level of system reliability. b. failure modes effects and criticality analysis (fmeca) fmeca methodology is an advanced level of fmea designed to assess the risk associated with all failure modes. the objective of fmeca is to design maintenance procedures required to eliminate points of failures as well as any catastrophic or critical consequence of such failures. the fundamental purpose is to initiate actions that reduce the likelihood of failure in the process. in 1965, the american aerospace manufacturer, grumman, developed fmeca to identify the potential failures of the manipulation system of the flight vehicles powered by jet engine. the severity (s), occurrence (o) and detectability (d) of the failure effect can be analyzed and quantified to evaluate the risk associated with the potential problems identified through the analysis.  severity. a value of 1 stands for an extremely low severity while a value of 10 stands for an extremely high severity as shown in table i.  occurrence is related to number of the preventive actions taken for the respective potential failure causes. the assessment of the probability for the occurrence of a potential failure cause is carried out while considering all listed preventive actions. a value of 10 is assigned, if it is likely that the potential failure cause will occur. a value of 1 is assigned for a very improbable potential failure cause. thus, the o assessment makes a statement concerning the quantity of defective components remaining in an entire batch of a certain product [3] (see table i).  detection is correlated to the actions taken to detect the respective potential failure causes. a value of 10 is assigned if no detection actions are mentioned whatsoever. a value of 1 is assigned, if the probability for the detection of the failure before the delivery to the customer is very high. thus, the d assessment makes a statement concerning the quantity of undetected, defect components in an entire batch of a certain product as shown in table i. in fmeca, risk is assessed with a value called risk priority number (rpn). rpn value is the quantitative measure in fmeca and is used to compare, analyze, and prioritize failures. these are important in order to suggest proper solutions and corrective maintenance procedures. rpn is calculated by multiplying severity, occurrence, and detectability as shown in (1). rpn=s×o×d (1) as shown in table i, the highest rpn value is 1000 which indicates the most dangerous failure and the lowest rpn value is 1 which indicates an unnoticeable failure, a failure that would be solved before the customer notices. table i. rpn scale how severe would the impact be? how likely is it to happen? how detectable is the problem? what is the rpn? st ra te gy reduce the severity of failure effects reduce the failure rate increase the detection rate of failure during the failure process severity risk(s) occurrence (o) detectability (d) rpn=s×o×d 10 serious safety hazards without warning more than 1 in 2 very high: failure evitable absolute uncertainty: cannot detect the problem 1000 most dangerous 9 hazard with warning 1 in 3 very high very remote 729 8 very high 1 in 8 high remote 512 7 high 1 in 20 high very low 343 6 moderate 1 in 80 moderate low 216 5 low 1 in 400 moderate moderate 125 4 very low 1 in 2000 moderate highly moderate 64 3 minor 1 in 15000 low high 27 2 very minor 1 in 150000 low very high 8 1 noneno effect: customer might not notice it 1 in 1500000 remote: rare event, no data of such failure in the past almost certain: (automation), current system certainly detects the failure 1 no one would notice: failure would be solved before the customer notices c. fmeca standards there is a number of published guidelines and standards for the requirements and recommended reporting format of fmeas and fmecas [4]. some of the main published standards for this type of analysis include sae j1739and milstd-1629a. in addition, many industries and companies have developed their own procedures to meet the specific requirements of their products or processes [5].  mil-std 1629 procedures for performing failure mode and effect analysis.  iec 60812 procedures for failure mode and effect analysis (fmea).  bs 5760-5 guide to failure modes, effects and criticality analysis (fmea and fmeca). engineering, technology & applied science research vol. 8, no. 3, 2018, 3023-3027 3025 www.etasr.com el badawi et al.: application of failure mode effect and criticality analysis (fmeca) to a computer …  sae arp 5580 recommended failure modes and effects analysis (fmea) practices for non-automobile applications [6].  sae j1739 potential failure mode and effects analysis in design (design fmea) and potential failure mode and effects analysis in manufacturing and assembly processes (process fmea) and effects analysis for machinery (machinery fmea) [7]. d. benefits of fmeca fmeca allows:  high degree of complexity.  uniform quantification of risk.  results to be correlated directly with actual risks.  easy modeling of the effect of various methods of mitigation/detection on risk.  implementation of a well-documented record of improvements from corrective actions.  acquiring information useful in developing test programs and in-line monitoring criteria.  obtaining historical information useful in analyzing potential product failures during the manufacturing process.  obtaining new ideas for improvements in similar designs or processes. e. types of fmeca fmeca can be classified into three main types as shown in figure 1. fig. 1. fmeca types iii. study objectives this study employed fmeca techniques to minimize the failure mode of the cim conveyor in the mechanical engineering workshop at the uoh. the study aims at providing cim users with a general background about the techniques available for failure effects analysis and their maintainability analysis, reliability prediction and safety analysis. this paper proposes a risk based maintenance method, which relies on regular and automatic update of risk analyses of the equipment including the equipment failure history. the method provides up-to-date information about the equipment’s risks. iv. previous work authors in [8], presented risk in early design phase (red) as a new method to introduce information about dysfunction during design phase of functionalities based on the following points:  the storage of breakdown events, (system breakdown database)  matrix linking parts and functions, (system components function and relationship)  translation of parts breakdown into risks of functional failure and database update. risk pooling of system breakdown and system components failure. later, they added an inspection module to improve maintenance operations schedule and to minimize failure risk by developing an optimal inspection strategy. they also pointed out the impact of the risk formalism on the assessment of occurrence, consequences and then the judgment of risk level. these results highlight the need for improving the quality of risk analyses. in [9], authors made a synthesis of 25 risk based maintenance (rbm) methods, presented their steps and described their main drawbacks. in particular they presented khan and haddara’s rbm process. they provided detailed description of each step as well as the factors affecting the quality of risk analysis evaluations. three major factors and their related contributors were highlighted. authors in [10] used the fmea method to study the reliability of a wind turbine (wt) system, using a proprietary software reliability analysis tool. they compared the quantitative results of an fmea and reliability field data from real wind turbine systems and their assemblies. their results may be useful for future wt designs. authors in [11] argue that a proper use of process failure modes and effects analysis (pfmea) could be of a great importance for the automotive industry. authors in [12] described the application of fmeca in toshiba bulb factory in monfiya, egypt. they found that fmeca is an efficient technique for reducing the chances of catastrophic failures. the application of fmeca also helped to increase the reliability and availability of the machines in the factory. authors in [13] devised an effective tool for solving the problems related to the quality of the manufacturing process through the application of fmeca. they identified and eliminated the problems they encountered during the manufacturing process of a cylinder head in an internal engineering, technology & applied science research vol. 8, no. 3, 2018, 3023-3027 3026 www.etasr.com el badawi et al.: application of failure mode effect and criticality analysis (fmeca) to a computer … combustion engine. however, the value of introducing fmeca to evaluate the reliability and to improve the maintenance process of the cim conveyor belt in an academic setting is still under-researched. thus, this study fills an important gap in this field. v. research methodology a. conveyor belt the conveyor system is part of the learning production system used in the workshops of the mechanical engineering department at the university of hail. the conveyor consists of a feed belt and a rotary table. when students practice hands-on processing, the feed belt transports objects placed on its left end from the cim robot to the right side of the assembly station. the belt has a bar code reader and photo-electric cells, which signal when an object arrives at its ends. controlling the motion of conveyor belt is synchronized with a cim robot and may be switched on and off: it has to be on while waiting for a new object and has to be switched off when an object is at the end of the belt. the conveyor belt is used as a means to transport material from one station to another. a description of the conveyor belt is illustrated in figure 2, and a brief of list of the specifications is provided in table ii. the conveyor belt either runs empty (while waiting for an object to be placed on it) or transports an object. table ii. conveyor belt specifications parameter value unit motor drive 2.5 hp belt width 40 cm assembly line length 6.4 m belt speed 29 cm/s assembly line height 87 cm control pad height 130 cm distance between each work station 1.5 m fig. 2. conveyor belt diagram and dimensions b. utilizing fmeca the methodology of this study utilizes fmeca according to the following sequence: fmeca scope, fmeca analysis, fmeca ranking, fmeca rpn calculations, fmeca verification, fmeca report . a detailed framework is illustrated in figure 3. data were collected and organized in a fishbone diagram as shown in figure 4.the failure modes and their causes were identified for the conveyor belt. the three key indices (severity, occurrence and detection) we reassessed and their analysis was carried out with the help of fmeca worksheet. finally, the necessary corrective actions were recommended. c. ishakawa fishbone analysis the cim conveyor belt was monitored for a total of 45 hours (3 hours a week over the period of 15 weeks). 100 failures were detected and categorized through ishakawa fishbone analysis. the study found that the material type and property have the highest effect on the conveyor belt failures, while the method has the lowest. we investigated the list of conveyor belt failures in the ishakawa fishbone and categorized them into a technical classification list as shown in figure 5. we found that 45% of failures were caused by the belt of the conveyor and 2 percent by the robot alignments as shown in figure 5. fig. 3. fmeca framework fig. 4. conveyor belt failures ishakawa fishbone fig. 5. failures distribution. engineering, technology & applied science research vol. 8, no. 3, 2018, 3023-3027 3027 www.etasr.com el badawi et al.: application of failure mode effect and criticality analysis (fmeca) to a computer … d. risk priority number (rpn) the failure modes and their causes were identified for each of the three key indices (severity, occurrence and detection). we investigated 150 failures of the conveyor, and then categorized them into two groups: 1) belt failures the results summarized in fmeca worksheet in table iii revealed that the rpn was the highest (rpn=200) for belt runs off at the head pulley, mainly owing to the degree of severity of the failure in disrupting the entire conveyor belt motion. hence, extra attention should be given to the corrective measures for the belt runs off at the head pulley to eliminate the failure. the next priority should be given to the bowed belt (rpn=150), mainly because of its criticality affecting belt efficiency. for the excessive belt stretch (rpn=64) and belt slip (rpn=30) their effect is less than the previous two failures, but found to be the correlated to the head pulley alignments. 2) motor failures from table iv it can be seen that the severity and occurrence of the motor over current and motor vibration are very high. the data revealed that both failures are critically affecting the cim conveyor belt efficiency. figure 6 shows that the motor over current rpn is 450 and it is the highest value, and the motor vibration rpn is 400. table iii. rpn conveyor belt results failure mode s (1-10) o (1-10) d (1-10) rpn belt slip 10 1 3 30 belt runs off at the head pulley 10 4 5 200 excessive belt stretch 8 4 2 64 bowed belt 6 5 5 150 table iv. rpn motor failure results motor failures s o d rpn (1-10) (1-10) (1-10) over-current 9 10 5 450 low resistance 8 3 1 24 over heating 6 1 9 54 dirt 9 4 5 180 moisture 6 5 1 30 vibration 10 10 4 400 fig. 6. rpn motor failures distribution vi. conclusion in this study the researchers designed a potential fmeca framework for the cim conveyor belt as an analytical technique utilized primarily to ensure that the mechanisms of potential failure modes and their associated causes and effects have been considered and addressed. the researchers demonstrated that fmeca is sufficient to derive a reliable conveyor belt safely failure mode system by reducing the risk of failures. they proposed a fmeca framework to facilitate the ability to build and a plan for a preventive maintenance and corrective action. this increased the belt’s efficiency and reliability. the study developed a list of potential failure modes and ranked them according to their effect on the conveyor belt. acknowledgment this research is supported by the deanship of academic research at university of hail by a grant for project number (0150191). references [1] r. k. mobley, maintenance engineering handbook, mcgraw-hill professional, 2001 [2] nasa, apollo gray team lunar landing design final report, 2007 [3] reliability analysis center, failure mode effects and criticality analysis (fmeca), reliability analysis center, rome, ny, 1993 [4] mil-std-1929a, procedure for performing a failure mode effects and criticality analysis (fmeca), washington, dc, 1980 [5] sae international, j1739, potential failure mode and effects analysis in design (design fmea), potential failure mode and effects analysis in manufacturing and assembly processes (process fmea), sae international, 2009 [6] u.s. department of defence, mil-hdbk-217f, reliability prediction of electronic equipment, 1991 [7] naval surface warfare center, handbook of reliability prediction procedures for mechanical equipment, naval surface warfare center, carderock division, w. bethesda, maryland, 2011 [8] i. y. tumer, r. b. stone, “mapping function to failure mode during component development”; research in engineering design, vol. 14, no. 1, pp. 25-33, 2003 [9] n. s. arunraj, j. maiti, “risk-based maintenance techniques and applications”, journal of hazardous materials, vol. 142, no. 3, pp. 653661, 2007 [10] h arabian-hoseynabadi, h. oraee, p. j. tavner “failure modes and effects analysis (fmea) for wind turbines”, international journal of electrical power & energy systems, vol. 32, no. 7, pp. 817-824, 2010 [11] h. c. liu, l. liu, n. liu, “risk evaluation approaches in failure mode and effects analysis: a literature review”, expert systems with applications, vol. 40, no. 2, pp. 828-838, 2013 [12] t. m. el-dogdog, a. m. el-assal, i. h. abdel-aziz, a. a. el-betar, “implementation of fmeca and fishbone techniques in reliability centered maintenance planning”, international journal of innovative research in science, engineering and technology, vol. 5, no. 11, pp. 18801-18811, 2016 [13] t. s. parsana, m. t. patel, “a case study: a process fmea tool to enhance quality and efficiency of manufacturing industry”, international journal of industrial engineering and management science, vol. 4, no. 3, pp. 145-152, 2014 microsoft word 21-3700_setasr_v10_n4_pp6004-6008 engineering, technology & applied science research vol. 10, no. 4, 2020, 6004-6008 6004 www.etasr.com ibrahim et al.: literature review and a conceptual research framework of adaptive road lighting … literature review and a conceptual research framework of adaptive street lighting criteria anwar hassan ibrahim department of electrical engineering college of engineering qassim university almulaidah campus, saudi arabia dr.anwar@qec.edu.sa meshal ibrahim almoshaogeh department of civil engineering college of engineering qassim university almulaidah campus, saudi arabia m.moshaogeh@qec.edu.sa fawaz ali alharbi department of civil engineering college of engineering qassim university almulaidah campus, saudi arabia f.a@qec.edu.sa abd elaziz mohamed elmadina department of optometry college of applied medical science qassim university almulaidah campus, saudi arabia a.alkhalil@qu.edu.sa abstract-street lighting (sl) aims to improve security for street users during the night by expanding perceivability level by guaranteeing a certain luminance level. this paper introduces a brief investigation of previous researches on sl criteria and applications. the main objectives were to assess and indicate further research required in sl criteria, and explore additional aspects to improve their efficiency, with the buraidah, qassim region in kingdom of saudi arabia used as a case study. this paper proposes additional limitations, alternative criteria, and their associated benefits. keywords-street lighting (sl); street lighting criteria; lighting environment and standardization; buraidah-qassim region i. introduction the primary purpose of street lighting (sl) is to protect people from road traffic accidents [1, 2]. many efforts and technological developments attempted to attain this goal and curb the economic toll that traffic accidents cause on national resources, as the reduction of accident cost justifies every investment in the optimization of street lighting [3]. the drivers’ ability to react in varying road conditions and traffic tends to deteriorate at night hours, as the adaptation in scotopic vision takes time, affecting contrast sensitivity and visual acuity [2]. perceptive reaction and color perception influence safety in road traffic. therefore, studying sl is extremely important, as studies pointed that a relatively, high percentage of serious traffic accidents occur in darkness. the term life of an electric lamp has two meanings: the time after which the lamp ceases its operation and the time after which the light output is reduced and potentially is less costly to replace it [4]. a few light sources are utilized in electric road lights. the most used types since l940s within the us are: radiant, fluorescent, low-pressure sodium, and highly concentrated release lamps [5]. the main disadvantages of utilizing low-pressure sodium (lps) lights incorporate color rendering. when the light is on, everything around it looks either orange-yellow, dark, or shades in between them. moreover, as the light ages it employs more wattage, and this increment results in small or no lumen deterioration, meaning that the light yield remains decently consistent over its life [6]. the spectral emission is concentrated at 589-589.6nm, which is close to the peak of the photopic curve. they are average in foggy or misty conditions, and water droplets do not disperse their monochromatic yellow light [4]. street lighting is an important issue, especially for big cities, in order to increase the safety of driving and security, improving the quality of life by giving people the opportunity to continue their activity at nighttime [7]. choosing the appropriate road lighting could offer a cash reduction rate by 30% in urban areas [8], and social aid to the public by counting the ability of smooth traffic flows. while this feature is usually accessible in evolved countries, many deficiencies exist in numerous territories in developing countries. the shortage of decent light quality at night can cause quality of life related problems [9]. street lighting is additionally an intriguing security point, as it is one of the most popular themes among individuals and a basic action of local authorities. the quantity of lights and power prerequisites remain generally consistent over the daily working period [10]. the main variable is the amount of operation hours at night, as dictated by light perception, visual adaptation, varying climate, pavement type, etc.[11]. ii. background sl helps creating a safe environment for residents and business owners to live, work, play, and travel [12]. however, corresponding author: anwar hassan ibrahim engineering, technology & applied science research vol. 10, no. 4, 2020, 6004-6008 6005 www.etasr.com ibrahim et al.: literature review and a conceptual research framework of adaptive road lighting … this essential need consumes a significant amount of energy, and is often tethered to substantial operation costs. outdoor lighting can represent more than half of the municipal energy budget, depending on the size of the municipality, the scope of the offered services, and the efficiency of the public lighting. states and counties are also responsible for roadway lighting, including freeway, interstate, bridge, and tunnel lighting [13]. roadway lighting reduced fatal accidents and injuries by 60% and property damage by 15% in [14]. however, as the electricity consumption of street lighting is considered high for the municipal authorities representing 10-40% of total consumption, many cities adopt new technologies in lighting systems [14]. in the last five years, a number of municipalities switched to new lighting technologies (e.g. induction and led), in order to reduce energy costs by approximately 50% over conventional technologies, getting additional savings through lower operation and maintenance costs. while several options could be considered for adapting outdoor lighting to more efficient technologies, this paper largely refers to led conversion, as it represents the majority of full-scale conversions by local governments and states [15, 16]. iii. adaptive lighting innovation design a. color properties color properties are related to the spectral composition of the emission, including color rendering and appearance. color rendering portrays the appearance of the color beneath a given light compared with the appearance beneath a reference source. however, the color appearance of a light does not guide its color properties, as it is possible for the lights from two sources to be apparently identical in appearance, but have different color rendering properties. cie has developed a method for indicating the color rendering properties of a light source. the color rendering index ranges from 0 to 100, where 100 represents no color distribution [4]. color appearance is the color of the light source or the color appearance of a white surface seen by its light, described in general as warm, intermediate or cold. [17] cold colors have a bluish tinge, while warm colors are close to the red end of the visible spectrum. filament lamps have warm colors, while highpressure mercury lamps have a cool appearance. the color appearance of a light source is classified according to cct. the color temperature of a radiator is the absolute temperature (k) of an ideal black-body radiator producing radiation of the similar chromaticity. b. lamp lifetime as mentioned above, the lifetime of an electric lamp has two meanings: the time after which the lamp ceases to operate, e.g. filament lamps failing due to filament breakage, or the time after which the light output is reduced so that it is more costeffective to replace the lamp [4]. c. luminaires luminaires are designed to perform a number of functions. they provide electric connection, adapting and isolating the lamp from the environment, even if it is wet, corrosive, or hazardous, and most importantly they provide physical appearance and a light distribution pattern suitable for the application. due to the variety of needs for lighting equipment, many different luminaire types exist on the market [18]. planning for luminaires requires considering many perspectives such as aesthetics, ergonomics, and useful aspects in order to attain high efficiency. the american national standard practice for roadway lighting, sponsored and published by the illumination engineering society of north america (ies) [4], defines the criteria for the classification of roadway, area, and high-mast luminaires. all classifications used in photometric data are based on lighting a strip running perpendicular to the cross arm of the luminaire, as a roadway would. iv. research gap modern demands and innovative technologies on street lighting constitute one of the hottest current research topics, but lighting criteria and standardization factors need to address all urban and suburban areas. so, there is a difficulty on the pertinence of alleged hypotheses, research, and their application on most common areas with the same lighting criteria. thus, most researchers tried to advance the current comprehension in the area of lighting standards and application, by either hypothesis testing or a hypothesis augmentation approach. this paper investigates crucial lacking points and issues in street lighting, studying the buriadah region, in qassim, saudi arabia. v. study area and population the study area was buraidah, qassim in saudi arabia, an area which, among qassim regions, is most affected by accidents. the study examined the existing lighting technology for deficiencies in order to propose ways to improve security and quality of light. the research targeted residents of the area aged from 20 to 70. the sample size was determined by using the data obtained from the traffic police surveillance manual, in order to estimate the frequency of accidents at night due to street lighting deficiencies and their risk factors. fig. 1. satellite map of buraidah, © google, terrametrics. vi. research framework many studies have considered lighting criteria and the standardization process, providing adequate indications on effective cost and environmental factors, whereas the energy monitoring system could be utilized easily [29, 30]. an improvement of multi-attribute techniques of street lighting technologies was elaborated to develop a conceptual framework for understanding the technologies and the importance of lighting criteria. figure 2 signifies the conceptual research hypotheses testing. engineering, technology & applied science research vol. 10, no. 4, 2020, 6004-6008 6006 www.etasr.com ibrahim et al.: literature review and a conceptual research framework of adaptive road lighting … table i. background summary ref. what how results and conclusion lacking points area for improvement [19] decision support system for assessing street lighting based on environmental criteria. based on energy saving and environmental benefits for led light sources indicators. expanded energy investment funds may be accomplished with natural benefits. expanded energy investment funds may be accomplished besides natural benefits. light visibility, roadway lighting, pedestrian discomfort, and glare at urban led lighting must be considered. [20] a pilot study of road and cycle lighting, and obstacle detection. data measurement based on rising detected obstacles. the diminishment in location was balanced when diminishing street lighting from 2.0 to 0.2 lux. decreasing road lighting is not a permanent solution. changing the angle of the light following the standard criteria. [21] led road lighting in practice: an evaluation of compliance with regulations and improvements for further energy savings. energy saving investments were considered. street lighting for vehicular activity satisfied most necessities, while for pedestrians and bikes it did not meet the constitutional necessities for uo and ui. the measurement should also target older people. further energy saving may miss the target of international standardization. [22] assesment of pedestrian discomfort glare from urban led lighting investigations were conducted on a test track. findings supported past work which prescribed optics to constrain most extreme and vertical luminance. a comparative study of the existing systems. investigation of glare rating during a walk. [23] comparative study of road lighting efficiency in the context of cen/tr 13201 2004 and 2014 standards and dynamic control. energy utilization. one year of activity concetrated information were utilized. results confirm the reduced cost due to the impact of dynamic control. the consideration brought the essentially augmented energy utilization due to extra lighting necessities. repeat measurements on additional lighting requirements. [24] comments on empirical evidence for the design of public lighting. light security was measured through an on-street query of pedestrians. an elective strategy such as daydark appraisals may be more informative. light range does not influence face-based interpersonal evaluations. actual measurements should be compined with the questionnaire. [25] literature study about visual clarity and spatial brightness. spatial brightness and visual clarity. differentiated definitions for spatial brightness and clarity. the category rating procedure depends on the area of deployment. experimenters ought to take advanced exertion to characterize the nature of users’ rating items. [26] design of led street lighting adapted for freeform roads. led lamps that deliver a roadway-shape light pattern. simulation and measurement results show the focal points of versatile luminaires over conventional approaches. led street lights installed in urban areas are sacrificing illumination to achieve energy saving. required several optical components that are prone to alignment issues while used in roads with curves. [27] drivers’ assesments on the risks of distraction, poor visibility at night, and safety-related behaviors. drivers surveyed on their undestanding of dangers related to driver diversion, low perceivability at night, and common safety-related behaviors. most drivers were completely mindful of dangers related with diversions from smartphones, in spite of the fact that more young drivers concede utilizing them. different people have different speed limits for driving at day and night. it is recommended to choose a group of people with the same or similar ages. [28] model calibration methodology to assess the actual lighting conditions of a road infrastructure. modeling recreation and calibration of lighting scenes for road lamps with genopt software. error as low as 13% for the calculation of illuminance shows its potential to survey the genuine lighting conditions of a road. software can only give a visualization concept rather than actual perception. light visibility and roadway lighting criteria need actual field study. fig. 2. research hypotheses testing. the lighting criteria in the study area typically affect the purchase decisions based on security council policy and cost factors. these factors are market attributes, lightening standardization, lightening technologies and environmental issues such as pavement, street width, pole height, etc. vii. data collection the overall research aimed to study the performance and efficiency of the existing sl in buraidah city, and calculate its impact on the drivers according to the international standards of lighting technology, the surrounding buildings, and the road designing strategies. the study was based on laboratory experiments to calculate the efficiency of lighting and its impact on the human eye. moreover, a questionnaire was utilized to compare the perceptions of drivers when they drive on different of street lighting conditions. the targeted population was the people in buraidah. figure 3 describes the conceptual research plan and depicts the elaboration of two approaches to achieve the potential objectives and answer the research questions. most of the research in the area of sl has significant safety concerns. clear street lighting offers a number of significant benefits, as it may improve safety for drivers and pedestrians, engineering, technology & applied science research vol. 10, no. 4, 2020, 6004-6008 6007 www.etasr.com ibrahim et al.: literature review and a conceptual research framework of adaptive road lighting … especially at urban areas. streetlights installed at various locations throughout the city needed to be categorized. the initial research phase, presented in this paper, targeted the highest capacity intersections. street and road lighting criteria were targeted considering that a satisfactory lighting structure is essential according to the standard criteria in buraidah city. fig. 3. conceptual research plan. viii. discussion streetlight is a raised source of light on the edge of a street or road. numerous lights have light-delicate photocells that actuate the light when required, for example at sunset or at the beginning of dull climate conditions. in most established lighting frameworks, a sunlight-based dial controls this feature. in this paper, municipal street lighting technologies were categorized according to power demand, lumens source (lpw) and life time per month as shown in figure 4. fig. 4. overview of street lighting source technologies. ix. conclusion worldwide growth of lighting intensity with standard distribution comes with variations in the spectral density of lighting. as technology grows, led high brightness streetlights replace old-fashioned ones such as high-pressure sodium (hps) and low-pressure sodium (lps). this paper presented various studies examining their street lighting criteria and applications. the study showed that the design and application of street lighting depends on environmental factors, market attributes, light technology, and standardization. considering the specific qualities and significant measures for that application in the study area, will conform the importance of street light at buraidah region. acknoledgement the authors gratefully acknowledge qassim university, represented by the deanship of scientific research, on the financial support for this research under the number (5584-qec2o19-2-2-1) during the academic year 1440 ah /2019 ad. references [1] p. marchant, j. d. hale, and j. p. sadler, “does changing to brighter road lighting improve road safety? multilevel longitudinal analysis of road traffic collision frequency during the relighting of a uk city,” journal of epidimiology & community health, vol. 74, no. 5, pp. 467– 472, may 2020, doi: 10.1136/jech-2019-212208. 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[30] r. pereira, j. figueiredo, r. melicio, v. m. f. mendes, j. martins, and j. c. quadrado, “consumer energy management system with integration of smart meters,” energy reports, vol. 1, pp. 22–29, nov. 2015, doi: 10.1016/j.egyr.2014.10.001. microsoft word 15-3140_s_etasr_v10_n1_pp5180-5185 engineering, technology & applied science research vol. 10, no. 1, 2020, 5180-5185 5180 www.etasr.com khalid & ahsan: computational fluid dynamics analysis of compressible flow through a converging… computational fluid dynamics analysis of compressible flow through a converging-diverging nozzle using the k-ε turbulence model muhammad waqas khalid school of chemical and materials engineering national university of sciences & technology islamabad, pakistan mkhalid.eme12@scme.nust.edu.pk muhammad ahsan school of chemical and materials engineering national university of sciences & technology islamabad, pakistan ahsan@scme.nust.edu.pk abstract—the thrust produced by a rocket motor is mainly dependent upon the expansion of the product gases through a nozzle. the nozzle is used to accelerate the gases produced in the combustion chamber and convert the chemical-potential energy into kinetic energy so that the gases exit the nozzle at very high velocity. it converts the high pressure, high temperature, and low-velocity gas in the combustion chamber into high-velocity gas of lower pressure and low temperature. the design of a nozzle has particular importance in determining the thrust and performance of a rocket. in recent years, it has received considerable attention as it directly impacts the overall performance of the rocket. this paper aims to analyze the variation of flow parameters like pressure, mach number, and velocity using finite volume method (fvm) solver with the standard k-ε turbulence model in computational fluid dynamics (cfd). the simulation of shockwave inside the divergent nozzle section through cfd is also investigated. in this regard, a nozzle has been designed using design modeler, and cfd analysis of flow through the nozzle has been carried out using ansys fluent. the model results are compared with theoretically calculated results, and the difference is negligible. keywords-converging-diverging (c-d) nozzle; cfd; ansys fluent; shockwave; k-ε turbulence model i. introduction the nozzle is widely used in various areas, from rocket propulsion to fuel sprayer. it has been applied in industrial, aerospace, automobile, and other sectors. the nozzle is a major part of any high-performance engine or rocket motor. it is used to control the velocity, direction, and required parameters of the flow. nozzles are designed to operate in all flow regions like subsonic, sonic, supersonic, and hypersonic. the design of the supersonic nozzle remains a challenging task in fluid mechanics. in a supersonic nozzle, not only the physical parameters of the nozzle play an essential role, but the thermodynamic parameters of the flow also play a crucial role in defining the design of a nozzle. the converging-diverging nozzle known as de laval nozzle is the most common and efficient design in rocketry. the chemical potential energy produced in the combustion chamber (rocket motor) is converted into kinetic energy by the nozzle. the nozzle converts high pressure, high temperature, and low velocity (subsonic) gases into low pressure, low temperature, and high velocity (supersonic) gases, hence producing high thrust [1]. to achieve the desired objectives, de laval found that the most efficient conversion occurred when the nozzle area converges until the throat area, where the flow travels at sonic velocity, followed by a divergent section of the nozzle which accelerates the gases to supersonic or hypersonic velocities based on the design [2]. the exit velocity achieved in a convergingdiverging nozzle is governed by the area ratios and pressure ratios [3]. the parameters which affect the performance or design of the nozzle include area ratios, pressure ratios, ratio specific heat constants, divergence nozzle angle, and nozzle length. studies have been carried out by keeping the mach number constant and varying the divergence angle to observe its effect on various parameters like velocity, temperature, and pressure [4, 5]. authors in [6] designed a nozzle by varying the exit mach number and observed its effect on the length of the nozzle, variation in pressure and velocity while keeping the throat area constant in all cases. authors in [7, 8] varied the divergence angles and observed their effect on mach number, pressure, and exit velocity. it was shown that the divergence angles up to a specific limit provide better results. in supersonic nozzles, the sudden expansion of gases can produce shock inside the nozzle due to flow separation. a good nozzle design must be optimized to achieve maximum thrust without producing shock due to flow separation [9]. hence, various simulations have been carried out to choose the best nozzle design for maximum thrust based on the same input conditions [10-12]. ii. cfd modeling a. basic equations the primary governing equations are the equation of conservation of mass or continuity equation and the equation of conservation of momentum. the continuity equation or mass conservation equation in differential form is: corresponding author: muhammad ahsan engineering, technology & applied science research vol. 10, no. 1, 2020, 5180-5185 5181 www.etasr.com khalid & ahsan: computational fluid dynamics analysis of compressible flow through a converging… �� �� � �.�� � � � (1) conservation of momentum equation is: � �� �� � � �.�� � � ��� � �. ��̿� � �� � � (2) b. standard k-ε (ske) model the standard k-ε turbulence model in ansys fluent has become the workhorse of practical engineering flow calculations [13, 14]. the standard k-ε model is a model based on model transport equations for the turbulence kinetic energy (k) and its dissipation rate (ε). in this model, it is assumed that the flow is turbulent, and other effects like molecular viscosity are negligible. therefore, it is only valid for turbulent flows. c. transport equations for the standard k-ε model � �� ���� � � ��ᵢ ����ᵢ� � � ��� ��μ � � !"# $� $%& ' �() � (* � �+ � ,� ) (3) � �� ��+� � � ��ᵢ ��+�ᵢ� � � ��. ��μ � � ! # �/ ��. ' �01/ /) �() � 02/(*� � 03/� /4 ) � / (4) d. modeling the turbulent viscosity μ� � �0� ) 4 / (5) where c1ε, c2ε, cµ, σk, and σε are the constants in the abovementioned equations and their default values are [15]: c1ε=1.44, c2ε=1.92, cµ=0.09, σk=1.0, σε=1.3 e. nozzle parameters there are few parameters which affect the nozzle performance regardless of the type of fuel used inside the combustion chamber. the throat area and performance parameters like pressure, temperature, and velocity at the throat are the most significant among them. the following are the basic formulas to calculate the values of pressure, temperature, and velocity at the throat: 5� � 516 3�)71� 8 " "9: (6) ;� � 3<:�)71� (7) � � = 3))71 >;1 (8) f. nozzle dimensions designing, modeling, and mesh generation of the convergent-divergent nozzle were carried out in design modeler and ansys mesh. the basic nozzle dimensions are given in table i. table i. nozzle dimensions parameter dimensions (m) nozzle length (l) 0.6 nozzle exit radius (?3) 0.12 nozzle inlet radius (?1) 0.1 area ratio 0.5625 g. simulation setup the design modeler application provides a persistent and parametric feature-based modeling environment that is a perfect tool for design optimization. its modeling standard is to outline a 2d sketched profiles and use them to generate features. the advantages of design modeler over other modeling tools are that it is easy to use, has user-friendly interface, and it has a function to divide a model into small separate surfaces during meshing for improved mesh generation. the geometry of the nozzle is shown in figure 1. the flow of high-pressure gases enters a nozzle from a combustion chamber with relatively low velocity. the total length of nozzle is 0.6m with variable diameter along the axis. the pressure of fluid flow at the inlet is varied from 300kpa to 240kpa (the pressure produced inside the chamber is dependent upon the type, size, and configuration of the propellant). at the outlet of the nozzle, the boundary condition was set to pressure outlet to observe the expansion of gases at sea level conditions. fig. 1. sketch of the proposed nozzle a design modeler has the provision of producing finer mesh at the desired area. therefore the mesh grid adjacent to the wall is finer as compared to the center region. the purpose is for the fine mesh is to capture the small gradients near the walls efficiently (figure 2). cfd is widely used for analyzing the fluid flow by solving the governing equations of fluid dynamics. cfd can be used to explain and analyze complex numerical problems involving multiphase flow and interaction. it has excellent potential in simulating in order to obtain a better design and optimize it rather than wasting time and cost on prototypes [16]. cfd is widely used in engineering, and it gives better understanding and visualization of the problem. it is involved with physical laws in the form of partial differential equations called navier-stroke equations [17]. cfd analysis consists of three steps called pre-processing, solving, and postprocessing. here, ansys fluent is used for computational analysis of the fluid flow inside the nozzle. this analysis includes various performance factors like inlet pressure, inlet temperature, inlet velocity/mach number, outlet pressure outlet temperature, and outlet velocity/mach number [18]. after designing and meshing the nozzle, the ansys fluent was launched. 2d, double precision options were selected. the case file was imported from an appropriate directory to pre-process the nozzle design (figure 3). pre-processing involves the transformation of physical problem statements into software. the type of material, fluid, and boundary conditions are defined as shown in table ii. the desired energy and flow models are selected, and assumptions were made concerning the nature of the flow, whether it’s viscous or inviscid, compressible or non-compressible, steady, or non-steady [19]. engineering, technology & applied science research vol. 10, no. 1, 2020, 5180-5185 5182 www.etasr.com khalid & ahsan: computational fluid dynamics analysis of compressible flow through a converging… fig. 2. simulation procedure for cfd model fig. 3. mesh imported in ansys fluent table ii. general setup setup solver type pressure-based 2d space axisymmetric time steady boundary conditions for case 1 pressure at inlet 300 kpa temperature at inlet 300k pressure at outlet 100 kpa temperature at iutlet 300k boundary conditions for case 2 pressure at inlet 240 kpa temperature at inlet 300k pressure at outlet 100 kpa temperature at outlet 300k boundary conditions for case 3 (inviscid flow) pressure at inlet 240 kpa temperature at inlet 300k pressure at iutlet 100 kpa temperature at iutlet 300k iii. results and analysis the nozzle plays a vital role in producing thrust and controlling the speed and direction in different applications like aerospace and rocketry. in this study, simulations were performed to carry out an analysis of fluid flow inside the nozzle, shock simulation inside the nozzle using the k-ε model, and then comparing it with the inviscid flow. a. case 1: fluid flow in converging-diverging nozzle (ske model) in figure 4, the red color shows the highest value of pressure, and blue is showing the lowest. the pressure at the inlet is close to 280kpa, and it is decreasing along the axis. the decrease in pressure is steady. the pressure at the outlet is close to 15kpa. the temperature inside the chamber is generally around 3000k, but we are studying the flow properties under the k-ε turbulence model and then flow properties of inviscid flow, therefore, the temperature at the inlet is kept at 300k, which is reduced during the expansion of gases in the divergent section of a nozzle to 125k, as shown in figure 5. in figure 6, the velocity of flow at the inlet is low as the pressure of the gases is higher. as the pressure decreases, the velocity increases along the axis of the nozzle and attains its highest value of close to 600m/s at the exit of the nozzle. the mach number is a key parameter used for the calculation of thrust of the nozzle and it segregates whether a nozzle is subsonic, sonic, or supersonic. the mach number is close to 1 at the throat of the nozzle, and the maximum achieved is at the exit, i.e., 2.64, as shown in figure 7. fig. 4. pressure contours fig. 5. temperature contours fig. 6. velocity vectors engineering, technology & applied science research vol. 10, no. 1, 2020, 5180-5185 5183 www.etasr.com khalid & ahsan: computational fluid dynamics analysis of compressible flow through a converging… fig. 7. mach number contours b. case 2: shockwave of converging diverging nozzle (ske model) there is a phenomenon called over-expanded nozzle, in which the exhaust pressure of the product gases falls below the atmospheric pressure, and expansion of the gases occurs very rapidly inside the nozzle producing a discontinuity in the flow. this sudden discontinuity is called a shockwave. this type of shockwave generally occurs where the area ratio gradient is higher, and pressure drops rapidly, often close to the exhaust end of the supersonic nozzle. the speed of the flow just before the shock has a significant impact on the shock. the higher the mach number just before the shock, the more significant would be the effect of shock on the nozzle. this can cause a reduction in thrust and sometimes physical damage to the nozzle. the second case is simulating a shock inside the nozzle in viscous flow using the standard k-ε model. the pressure at the inlet is close to 222kpa, as can be seen in figure 8. as flow passes through the throat, the expansion of the gases happens suddenly, unlike in case 1 where this expansion was steady, hence, producing a shock inside the nozzle. at that point, the pressure is measured close to 22kpa, much lesser than the atmospheric pressure. fig. 8. pressure contours fig. 9. temperature contours similar with case 1, the inlet temperature is kept at 300k. as soon as flow passes through the throat of the nozzle, a sudden decrease in temperature is observed to 152k with the sudden expansion of gases, shown in figure 9. in figure 10, the velocity vectors of flow show a rapid increase in the velocity of the divergent section of the nozzle. figure 10 also shows the formation of a vortex close to the wall of the nozzle just after the shock because the flow separation has occurred close to the outlet of the nozzle, and backpressure is generated. in figure 11, the mach number is approximately one at the throat and highest at the shock front, i.e. 2.20. the walls’ frictions are higher close to the wall of the nozzle and lesser at the center. hence, velocity is lower close to the wall, thus producing shock earlier close to the wall than it takes place in the main flow. it makes the shock shape as curved. fig. 10. velocity vectors fig. 11. mach number contours c. case 3: shockwave of converging diverging nozzle (inviscid flow) inviscid flow analysis assumes the flow to be laminar and disregards the effect of viscosity on the flow. it is only applicable for high reynolds number applications where inertial forces dominate the viscous forces. the inviscid theory predicts a simple shock structure consisting of a normal shock followed by a smooth recovery to exit pressure in the divergent part. but, viscous effects like wall boundary layer and flow separation alter drastically the flow in a converging-diverging nozzle. the velocity of the flow is high in this simulation. therefore, we can assume the flow to be inviscid so that we can have a comparison of shock and flow characteristics with the viscous flow simulations. the third case is simulating the shock inside the nozzle in an inviscid flow. the pressure at the inlet is 222kpa. in this case, the pressure decreases in the divergent section more steadily as compared to case 2. the wall frictions and viscosity of the flow are assumed to be zero. in this case, the shock location is shifted close to the nozzle exit, shown in figure 12. as in cases 1 and 2, the inlet temperature is kept at 300k. as soon as the flow passes through the throat of the nozzle, a gradual decrease in temperature is observed up to 120k where the shock is formed engineering, technology & applied science research vol. 10, no. 1, 2020, 5180-5185 5184 www.etasr.com khalid & ahsan: computational fluid dynamics analysis of compressible flow through a converging… as shown in figure 13. in figure 14, the velocity vectors of flow showing increase in the velocity of the divergent section of the nozzle. there is no flow separation at the outlet. hence, no vortex is formed, and no backflow is observed. fig. 12. pressure contours fig. 13. temperature contours fig. 14. velocity vectors fig. 15. mach number contours in figure 15, it is shown that the mach number is approximately one at the throat and highest at the shock front, i.e. 2.74. the viscosity causes a reduction in the momentum of the flow, as this loss is not considered in inviscid simulations. therefore, the achieved mach number is higher as compared to the standard k-ε turbulence model simulations with the same boundary conditions in both cases. the shock shape is straight in this case, as there are no wall frictions. d. comparison with analytical results table iii shows the comparison of values of pressure, temperature, and velocity at the throat obtained from these simulations and the analytical results calculated by using (6), (7), and (8). the simulation results obtained from this model showed good agreement with the analytical results. table iii. analytical and simulated results comparison chamber pressure (kpa) pressure at throat (kpa) % difference analytical this model 300 164.15 168.10 2.35 240 131.30 132.80 1.13 temperature at throat (k) 300 260.87 252.50 3.20 240 260.87 249.23 4.46 velocity at throat (m/s) 300 342.05 335.60 1.88 240 342.05 328.75 3.88 iv. conclusion a detailed study was conducted on the effect of inlet pressure variation on the mach number and shock produced inside the nozzle using the standard k-ε turbulence model. the pressure values were varied to check the position of the shock and the expansion of the product gases in the divergent portion of the nozzle. the outlet pressure was kept constant to 100kpa, which is close to the atmospheric pressure at sea level. the initial inlet pressure was set to 300kpa, and simulation was performed. no shock was observed inside the nozzle, and the expansion of the gases was steady inside the nozzle. the initial inlet pressure was gradually reduced. simulations were carried out to study and analyze the behavior of exhaust flow inside the nozzle. in the second case, the inlet pressure value was set to 240kpa and shock was observed inside the nozzle. in this case, the expansion of the gasses was sudden, shock was produced, and over-expanded nozzle behavior was observed. in the third case, the flow was assumed to be inviscid. a shock was observed inside the nozzle but close to the exit. it is evident that there are no wall frictions as the shape of shock is straight. hence, the simulations using the standard k-ε turbulence model give more realistic values than the simulation carried out using inviscid flow conditions. references [1] v. jayakumar, s. madhu, a. muniappan, a. h. ansari, s. n. kumar, “investigation of thermal characteristics in solid rocket nozzle with insulate using cad/cae”, international journal of pure and applied mathematics, vol. 119, no. 7, pp. 443-456, 2018 [2] s. sofyan, v. wuwung, “rx-320 rocket static pressure combustion chamber prediction and validation by using inverse method”, jurnal teknologi dirgantara, vol. 16, no. 1, pp. 45-58, 2018 [3] n. d. deshpande, s. s. vidwans, p. r. mahale, r. s. joshi, k. jagtap, “theoretical and cfd analysis of de-laval nozzle”, international journal of mechanical and production engineering, vol. 2, no. 4, pp. 33-36, 2014 [4] p. natta, v. r. kumar, y. h. rao, “flow analysis of rocket nozzle using computational fluid dynamics (cfd)”, international journal of engineering research and applications, vol. 2, no. 5, pp. 1226-1235, 2012 engineering, technology & applied science research vol. 10, no. 1, 2020, 5180-5185 5185 www.etasr.com khalid & ahsan: computational fluid dynamics analysis of compressible flow through a converging… [5] k. m. pandey, a. p. singh, “cfd analysis of conical nozzle for mach 3 at various angles of divergence with fluent software”, international journal of chemical engineering and applications, vol. 1, no. 2, pp. 179-185, 2010 [6] v. ramji, r. mukesh, i. hasan, “design and numerical simulation of convergent divergent nozzle”, applied mechanics and materials, vol. 852, pp. 617-624, 2016 [7] m. s. hossain, m. f. raiyan, n. h. jony, “comparative study of supersonic nozzles”, international journal of research in engineering and technology, vol. 3, no. 10, pp. 351-357, 2014 [8] p. biju kuttan, m. sajesh, “optimization of divergent angle of a rocket engine nozzle using computational fluid dynamics”, the international journal of engineering and science, vol. 2, no. 2, pp. 196-207, 2013 [9] g. mohan kumar, d. x. fernando, r. m. kumar, “design and optimization of de lavel nozzle to prevent shock induced flow separation”, advances in aerospace science and applications, vol. 3, no. 2, pp. 119-124, 2013 [10] g. satyanarayana, c. varun, s. naidu, “cfd analysis of convergentdivergent nozzle”, acta technica corviniensis-bulletin of engineering, vol. 6, no. 3, pp. 139, 2013 [11] b. v. v. naga sudhakar, b. p. c. sekhar, p. n. mohan, m. d. touseef ahmad, “modeling and simulation of convergent-divergent nozzle using computational fluid dynamics”, international research journal of engineering and technology, vol. 3, no. 8, pp. 346-350, 2016 [12] a. s. swaroopini, m. g. kumar, t. n. kumar, “numerical simulation and optimization of high-performance supersonic nozzle at different conical angles”, international journal of research in engineering and technology, vol. 4, no. 9, pp. 268-273, 2015 [13] m. ahsan, “numerical analysis of friction factor for a fully developed turbulent flow using k–ε turbulence model with enhanced wall treatment”, beni-suef university journal of basic and applied sciences, vol. 3, no. 4, pp. 269-277, 2014 [14] n. a. najar, d. dandotiya, f. a. najar, “comparative analysis of k-ε and spalart-allmaras turbulence models for compressible flow through a convergent-divergent nozzle”, the international journal of engineering and science, vol. 2, no. 8, pp. 8-17, 2013 [15] n. rolander, j. rambo, y. joshi, j. k. allen, f. mistree, “an approach to robust design of turbulent convective systems”, journal of mechanical design, vol. 128, no. 4, pp. 844-855, 2006 [16] m. elashmawy, “3d-cfd simulation of confined cross-flow injection process using single piston pump”, engineering, technology & applied science research, vol. 7, no. 6, pp. 2308-2312, 2017 [17] k. pansari, s. a. k. jilani, “numerical investigation of the performance of convergent divergent nozzle”, international journal of modern engineering research, vol. 3, no. 5, pp. 2662-2666, 2013 [18] a. k. reji, g. kumaresan, a. s. menon, j. parappadi, a. p. harikrishna, a. mukundan, “simulation and validation of supersonic flow through a convergent-divergent nozzle”, international journal of pure and applied mathematics, vol. 119, no. 12, pp. 2135-2142, 2018 [19] m. elashmawy, a. alghamdi, i. badawi, “investigation of the effect of pipeline size on the cross flow injection process”, engineering, technology & applied science research, vol. 6, no. 3, pp. 1023-1028, 2016 [20] a. a. khan, t. r. shembharkar, “viscous flow analysis in a convergentdivergent nozzle”, international journal of computational engineering research, vol. 3, no. 5, pp. 5-15, 2008 microsoft word 19-3447_s_d_etasr_v10_n3_pp5689-5693 engineering, technology & applied science research vol. 10, no. 3, 2020, 5689-5693 5689 www.etasr.com noaime et al.: a short review of influencing factors of islamic architecture in aleppo, syria a short review of influencing factors of islamic architecture in aleppo, syria emad noaime architectural engineering department college of engineering university of hail saudi arabia e.noaime@uoh.edu.sa ahmed osman architectural engineering department college of engineering university of hail saudi arabia ah.ibrahim@uoh.edu.sa mohamed ahmed said architectural engineering department college of engineering university of hail saudi arabia masnmas2@yahoo.com ghazy abdullah architectural engineering department college of engineering university of hail saudi arabia g.albaqawy@uoh.edu.sa mabrouk touahmia civil engineering department college of engineering university of hail saudi arabia m.touahmia@uoh.edu.sa yahya nasser architectural engineering department college of engineering university of hail saudi arabia y.alfraidi@uoh.edu.sa khaled salah architectural engineering department college of engineering university of hail saudi arabia k.elkhayat@uoh.edu.sa mohamed hassan architectural engineering department college of engineering university of hail saudi arabia mo.abdelhafez@uoh.edu.sa abstract—this research aims to examine aleppo’s distinctive architectural design profiles, most precisely those of residential buildings, and to highlight factors that indicate how the islamic culture influenced the architectural structure in the pre-civil war era. descriptive research, observation, and documentation of architectural elements that determine the general characteristics of housing in the city of aleppo were used. the study focused on wakil and zamriah houses as case studies because of their accessibility and excellent exemplary style. the current study sheds light on the history of aleppo’s urban development and its influence by the islamic civilization during the late ottoman era up to the syrian civil war in 2011. it is shown how islamic civilization influenced aleppo's residential buildings in terms of simplicity, respect for human scale, equality, and privacy. keywords-influence; islamic architecture; aleppo; residential buildings i. introduction architects not just design buildings but also shape the very definitions used in design, including the definition of space relationships and different design styles [1]. the main aim of architectural design is to create beautiful places that are environmentally appropriate with minimal negative impact [2]. a main concern is to achieve the best approach in evolving spatial and formal solutions [3]. modern architecture however has paid little attention to the concept of privacy. this is initiated by the increasing needs of advanced industrial countries, with most arab countries gradually following [4]. traditional islamic architecture has thus been gradually abandoned in residential areas and is now mostly used on the folklore of heritage [5]. aleppo is a historic multi-cultural city with a complex mix of syrians, kurds, iranians, turkmen, and armenian [6]. in 2011, it was syria's largest city with a population of 2.5 million people, a unesco world heritage site that has been described as syria's commercial capital. aleppo is one of the oldest cities in the world, maintaining its continuity as an inhabited city for more than 5000 years. it is characterized by the plateau in its center, which dates back to the third or the fourth millennium bc [7]. aleppo, known in the roman, hellenistic and the byzantine era as beroea, is characterized by the straight street, which extends from the western gate of the city (the gate of antioch) to the east, at the bottom of the castle. this axis in the middle linked with the rectangular shaped agora, which forms the site of the now great mosque. aleppo and damascus are characterized as islamic cities built on roman planning bases. the city is still changing according to the needs of its inhabitants, without losing however the elements of different civilizations, especially in the historic center of the city within its walls. the golden period of aleppo was in the 12 th and 13 th centuries during the reign of the zengids and the ayyubids, when the city played an important role in the conflict between islam and the crusaders, and due to its geographical location it became a commercial link between the east and the west [8]. there are sites that still give a great example of stone architecture that lasted until the 18 th and 19 th centuries. most of the buildings of the city of aleppo today, with its old and modern parts, are built of stone. after the fall of the ottoman empire, damascus began to overtake aleppo’s economic and political role in syria [8, 9]. however, old aleppo remains relatively conservative in terms of architectural elements compared to other historical centers in the islamic world. along with fez and sana'a, aleppo represents some of the corresponding author: mohamed ahmed said engineering, technology & applied science research vol. 10, no. 3, 2020, 5689-5693 5690 www.etasr.com noaime et al.: a short review of influencing factors of islamic architecture in aleppo, syria most complete and important examples of traditional islamic cities in the islamic world. today, aleppo is the home of around two million people and is the second most populated city in syria after damascus, although the exact number fluctuates heavily due to the civil war [10]. aleppo is also considered the economic center of the northern syria. the ancient city lies inside and outside the walls, and its population reached 120,000 in an area of 350 acres [11], mostly living in two story traditional houses with inward courts. ii. factors affecting the architectural profile islamic architecture is the result of the interaction between muslims and the social directives originating from islamic law. the surrounding islamic environment with its climatic, spatial and cultural elements in its broad sense also weighs in. the general profile of islamic architecture reflects these influences through organic and spontaneous architectural profiles that illustrate a simplicity and purity of architectural thought [1214]. these factors and their influence are further discussed in the following sections. a. social factors one of the most important things that characterize islamic architecture in general and housing in particular, is its distinction in privacy, which is rather important within arab traditions [15]. the house represents a large part of social life style formulated by the islamic culture. this was further organized by the legislation of the hijab which stipulates the separation of men from women and provides a detailed system for the distinction of family members and others [16-18]. the legislation is of two types: permission to enter the house from outside and permission within the same house to enter rooms. b. the security-political factor as a result of the often acts of aggression and warfare from outsiders, as well as internal safety issues, buildings were clustered and formed facades extending on both sides of the streets [19]. this reflected the demand to minimize the number and size of entrances. the external facades were also modest and not that representative of the interior, leading to a great contradiction between the inside and outside of richer houses [12, 13]. on the other hand, this created an obvious psychological need that led to excessive attention in the decoration and beauty of interior spaces [20]. c. the economic factor the wealth of the residents have a direct effect on architecture design of houses, evident mostly in the multiple courtyards found in wealthier houses, each one often designated for a certain activity. there could be a courtyard for “salamlek” (for men and guests), another courtyard for “haremlek” (especially for women), and sometimes a third courtyard “khadamlek” (for the servants, especially for guests served by servants as a sign of wealth and richness) [21]. the entrance of the house is generally the point at which its inhabitants and visitors move between the “salamlek” and the “haremlek”. the entrance also connects the exterior and the interior and thus received a great attention in design. most entrances offer indirect access with minimum or no visibility of the interior and the refraction, according to the living standards of the family, can be either simple or complex [12-14]. the houses are generally lacking openings or external windows that overlook the road. if such openings exist, they are placed on the top of the wall, often in the second floor and covered with “mashrabiyas” or similar elements, to ensure the privacy of the residents. it is believed that the creation of “mashrabiyas” [22] emerged for this purpose, and later on they were employed for ventilation and other purposes [23]. examples can be found in morocco [24], saudi arabia [25], and kuwait [26]. d. environmental and physical factors a) the surrounding environment the environment surrounding any urban setup has a clear impact on its formation. architecture is usually influenced and in accordance with the surrounding environment [27]. the desert environment and its impact on the formation of islamic architecture are vividly visible [27]. b) local building materials and their impact on the formation of islamic architecture the employment of raw building materials such as wood palm, stone, marble, gypsum, and treated mud is a common feature in islamic architecture [12, 13, 27, 28]. local construction materials were largely used with building techniques creating vivid differences in architectural expression [12, 13, 29]. 2) the aesthetic factor the urban environment is rich, interesting and in constant development [3]. the aesthetic factor is also considered, usually combined with other factors. an obvious example is the mashrabiyas which are designed in distinctive artistic styles. an additional factor is height restrictions usually present in islamic architecture as a result of respect for other residents and also as a mean to suppress material competition between residents [30, 31]. thus, an islamic urban environment is characterized by uniformity that often makes the facades of different houses look as one facade abiding with technical and aesthetic rules. iii. methodology descriptive research was used in carrying out this study as it describes the characteristics of the population or the phenomenon under study without influencing it in any way [32, 33]. this paper uses observation and documentation combined with literature review in order to further portray the general housing characteristics in the city of aleppo. the wakil and zamriah houses are used as case studies because of their accessibility and their excellent exemplary style. iv. case studies a. wakil house bayt wakil [34] is situated in the jdeide quarter on sissi street. it was built in the 18 th century, and is considered an ideal example of wealthier houses of that period. it is full of decorations and wooden claddings, including two attached houses that are best known for their intricate wooden paneling. carved in 1603, the depictions show biblical scenes featuring virgin mary, christ, and his disciples. the panels are now engineering, technology & applied science research vol. 10, no. 3, 2020, 5689-5693 5691 www.etasr.com noaime et al.: a short review of influencing factors of islamic architecture in aleppo, syria displayed in the aleppian hall in the islamic section of the pergamon museum in berlin, germany. wakil house has been renovated many times, adapting multiple functions throughout the previous century. it currently functions as a restaurant and a small inn [35]. figures 1-3 are examples of its vault-like style while the supporting structure is decorated with arches with wooden pattern. figure 4 shows the facade of the northern part. the allocation of an important main room facing the north, overlooking the inner courtyard, considered a key element in the design, can be seen in [35]. fig. 1. interior part fig. 2. a wooden column fig. 3. column detail after renovation fig. 4. north facade of wakil house fig. 5. south facade of wakil house the continuity of the simple rhythm at the horizontal and at the vertical level should be noted as well as the complex rhythm in the northern facade. the southern facade similarly shows balance and rhythm (figure 5). figures 6-8 are examples of the vault-like style adopted in this building showing details of the arches. fig. 6. typical arch engineering, technology & applied science research vol. 10, no. 3, 2020, 5689-5693 5692 www.etasr.com noaime et al.: a short review of influencing factors of islamic architecture in aleppo, syria fig. 7. arch resting on a square column fig. 8. arch resting on a round column b. zamriah house zamriah or zamaria [36] house was one of the finest boutique hotels in aleppo, lovingly restored from a magnificent ottoman home. an asymmetrical pattern can be seen in west and east sides. similarly to the wakil house, a simple rhythm can be observed at the horizontal and at the vertical levels. views and drawings of the house are shown in figures 9-13. fig. 9. interior part zamriah house (a) (b) fig. 10. east facade zamriah house (a) (b) fig. 11. west facade zamriah house v. conclusion the doctrine and philosophy of islam has a special effect in islamic architecture, not only in terms of increased privacy and engineering, technology & applied science research vol. 10, no. 3, 2020, 5689-5693 5693 www.etasr.com noaime et al.: a short review of influencing factors of islamic architecture in aleppo, syria social separation but also in terms of mutual respect between neighbors and suppression of exhibitionism. this paper offers a short review on the factors that have influenced islamic architecture in aleppo, syria. two case studies are briefly discussed as examples. some common characteristics are the presence of a main room which faces north and overlooks the inner courtyard, the small size and elevated position of outward facing openings in contrast with the inner facing ones, the use of decorations in the interior facades, the plainer design of exterior facades, the simplicity in form, and the respect of human scale. acknowledgment the authors would like to acknowledge the architectural engineering department, college of engineering, university of hail, saudi arabia for their support. references [1] d. e. hepler, p. r. wallach, d. hepler, drafting and design for architecture & construction, cengage learning 2012 [2] j. hill, actions of architecture: architects and creative users, psychology press, 2003 [3] s. odin, tragic beauty in whitehead and japanese aesthetics, lexington books, 2016 [4] t. a. soomro, m. a. soomro, a. n. laghari, d. k. bhangwar, m. a. soomro, “fading legacy of the architectural heritage of the historic core of 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rim international journal of nursing research, vol. 16, no. 4, pp. 255-256, 2012 [34] archnet, “courtyard houses of aleppo”, available at: https://archnet.org/collections/1210/sites/2860 [35] a. hadjar, historical monuments of aleppo, automobile and touring club of syria, 200 [36] syr-res, “the arab house in aleppo: the house of wakil, one of the most famous arab houses in aleppo”, available at: http://www.syrres.com/article/13403.html (in arabic) microsoft word 11-3013_s_etasr_v9_n5_pp4631-4635 engineering, technology & applied science research vol. 9, no. 5, 2019, 4631-4635 4631 www.etasr.com oad et al.: flexural behavior of rc beams made with recycled aggregates under 12-month long … flexural behavior of rc beams made with recycled aggregates under 12-month long term loading mahboob oad department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan engrmahboob04@gmail.com abdul hafeez buller department.of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan engrabdulhafeezbuller@gmail.com bashir ahmed memon department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan bashir_m@hotmail.com noor ahmed memon department.of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan nahmedmemon@gmail.com abstract—in the present era of infrastructure development, demolishing waste management poses serious problems, particularly in urban centers. vast development requires huge amounts of conventional concrete aggregates resulting in serious environmental problems. therefore, efforts are carried out in utilizing demolishing waste, particularly demolishing concrete as coarse aggregates used in new concrete. this article presents laboratory investigations of flexural behavior of reinforced concrete beams made with partial replacement of natural coarse aggregates with coarse aggregates from demolished concrete under 12-month long-term loading. two batches of beams were cast and cured for 28 days. in the first batch three rc beams with partial replacement of natural coarse aggregates were cast, while in the second batch 6 rc beams with all-natural coarse aggregates were prepared. out of these six beams three beams were tested under short-term loading to determine maximum load. 50% of this load was used as sustained load on the remaining all beams. the beams were mounted on purpose made frames and deflection, strain, and cracking were recorded on daily basis. after the elapse of the defined time the beams were tested under central point load until failure. result comparison shows a 4.96% increase in deflection and 2.33% reduction in peak load. based on the results of this study it is concluded that demolished concrete as coarse aggregates in new concrete shows reasonably good performance under 12-month long-term loading. keywords-recyclable aggregates; reinforced concrete beam; demolishing waste; flexural behavior; long-term loading; green concrete i. introduction concrete has proved itself as the best material for general construction. but there are several issues related with the production of its ingredients, since they pose problems to the environment. on the other hand, demolishing waste generated from demolishing of old structures, add up to the environmental issues. one way of dealing with both of these problems, at least to some extent, is using the waste in new concrete. the resulting product will be eco-friendly, help in waste management, and help in preserving the natural resources of the ingredients of conventional concrete. the concrete using waste material is termed as green concrete. the use of demolished old concrete as coarse aggregates in new concrete is an active area of research. the study of any aspect of a material requires comprehensive review of the literature related to it. author in [1] checked the recent developments about the use of demolished concrete as coarse aggregates in new concrete. the author highlighted different aspects of the material with respect to its use and problems associated with it. he concludes that the material has promising effects, particularly on the strength of concrete. concrete testing under short-term loading is routine practice to determine its various properties. in this connection authors in [2-5] used 50% replacement of natural coarse aggregates with coarse aggregates from demolished concrete to study flexural stress-strain behavior of rc beams. from the experimental observation, they observed 8.8% and 11.68% reduction in flexural capacity of 28-day cured normal and rich mix beams respectively. flexural strength, shear strength and bonding of green concrete beams have also been studied by authors in [6]. they used waste from the testing of cylinders as coarse aggregates in 40% and 100% dosages. the comparison of obtained results with control specimens, aci provisions and findings from literature showed good agreement. in real structures, the loads mostly are of sustained nature. therefore, evaluation of material properties and behavior under sustained/long-term loading is essential. to this end authors in [7] used 0%, 50% and 100% dosage of recyclable aggregates from demolished concrete to replace natural coarse aggregates in casting of reinforced concrete beams. the authors tested the beams with sustained load for 1200 days. using the obtained results, the authors developed a numerical expression for the corresponding author: mahboob oad engineering, technology & applied science research vol. 9, no. 5, 2019, 4631-4635 4632 www.etasr.com oad et al.: flexural behavior of rc beams made with recycled aggregates under 12-month long … evaluation of long-term deflection by introducing the creep coefficient of recycled aggregates. the analysis of the results revealed that the size of the aggregates has also influence on the final deflection, therefore the authors also introduced the regeneration coefficient to deal with this issue. using the above two coefficients and laboratory data, they introduced the deflection increase coefficient which simplifies the computation of long-term deflection. long-term loading effects, creep, and shrinkage of concrete made with old concrete as coarse aggregates under 365 days sustained loading were compared with aci provisions in [8]. after data analysis, the authors suggested modification in aci provisions. testing of the resulting equation showed good agreement between the two sets of the results. long-term behavior of concrete under different conditions has been quite studied, i.e. service conditions (cracking and induced stress) of fiber reinforced concrete [9], effect of compressive strength and reinforcement ratio on glass-fiber reinforced concrete [10], and a numerical expression for the effect of bending moment on long-term behavior [11]. from the above discussion it may be observed that there is still a need of research regarding the use of the material. therefore, this article presents a laboratory investigation on the effect of 12-month long-term loading on reinforced concrete beams. the 50% replacement [8, 12] of natural coarse aggregates with coarse aggregates from demolished concrete was used in casting. it is hoped that the outcome of the research will provide detailed understanding of the long-term behavior of the beams for the proposed duration and will not only improve the confidence about the material but also set a landmark for future research in the field. ii. materials and testing the demolished concrete used in this research work was collected in the shape of large blocks from the demolishing waste of a 45 year old, single story, school building. these blocks were processed manually to reduce to a maximum size of 25mm (figure 1). natural coarse aggregates of the same size were also used. the remaining ingredients of concrete used in this investigation are ordinary portland cement, hill sand, and potable water (ph=6.87). although good care is exercised in the hammering of the large blocks of the demolished concrete, yet some of the cracked particles were present. these particles if used in concrete will definitely affect its final strength, therefore, cracked particles, organic impurities, etc. have been removed manually, followed by washing of the aggregates. the use of well graded aggregates in concrete ensures proper functionality and strength. therefore, both natural and recyclable aggregates were sieved as per the relevant procedure and specifications of astm. figure 2 shows the gradation curve of both types of aggregates. it may be observed from the figure that both curves follow the same trend which ensures that the aggregates are well graded. in addition to sieve analysis, physical and basic properties, i.e. water absorption, specific gravity, and abrasion resistance of the recycled aggregates were examined. due to the mortar attached with the aggregates, the surface texture of the aggregates was rough and the color was dull in comparison to conventional coarse aggregates. water absorption of the aggregates was higher than of natural coarse aggregates, while the specific gravity of the recyclable aggregates was less than that of the conventional aggregates. it was also noted that the abrasion resistance of the aggregates was less compared to the abrasion resistance of conventional aggregates. this was primarily due to the old mortar attached with the aggregates and the age of the concrete. fig. 1. demolished concrete fig. 2. sieve analysis of coarse aggregates the natural and recycled aggregates were used in equal proportion (50%) to cast the reinforced concrete beams. concrete mix ratio of 1:2:4 with 0.5 water-cement ratio were used. to reinforce the beams, grade 60 deformed steel bars were used. the beams were cast in two batches. in the first batch, three beams were cast with both natural and recycled aggregates, whereas in the second batch six beams were cast with all-natural coarse aggregates. out of these six beams three beams were used to determine peak load under short-term gradually increasing load. the half of the average of this load was used as sustained load for long-term testing of the beams. the remaining three beams of this batch were treated as control specimen to check and compare the results of the proposed beams. the size of the beams was kept the same and equal to 1875mm×150 mm×300mm. to reinforce the beams four #4 bars were used as longitudinal reinforcement (2 bars in tension and 2 bars in compression zones). shear reinforcement in the form of stirrup #3 bars was provided at 150mm center to center along the length of the beams. deformed bars were used for both longitudinal and shear reinforcement. for the batching of the ingredients, weight batching method was adopted. the engineering, technology & applied science research vol. 9, no. 5, 2019, 4631-4635 4633 www.etasr.com oad et al.: flexural behavior of rc beams made with recycled aggregates under 12-month long … ingredients were mixed in concrete mixer and placed in moulds following the standard procedure of filling the moulds and to compact the concrete. in all beams, top and bottom concrete cover was kept equal to 25mm. after demoulding, all the specimens were cured for 28 days in water (figure 3). after curing, the beams were allowed to air dry for 24 hours. to determine the maximum load sustained by the rc beams, three beams made with all-natural coarse aggregates were tested in utm under central point load (figure 4). the load was applied gradually at the rate of 0.5kn/s. the peak load of the three beams was recorded and averaged. 50% of this load was used as sustained load during the long-term testing of the proposed beams. fig. 3. curing of specimens fig. 4. short term testing of rc beams demic pads were applied on all beams along the depth at center with 25mm center to center distance for strain measurement. all beams were then mounted on purpose made steel frames (figure 5). the load evaluated earlier was applied on the center with the help of load cell and screw jack system. this load was kept constant and maintained during the testing time. the beams were monitored for deflection, strain and cracking on a daily basis for 12 months. at the end of the required time, the beams were removed from the loading frames and were tested for peak load in utm in the same fashion that was done to determine the peak load before starting the long-term testing of the beams. the obtained results are discussed in the following section. (a) (b) fig. 5. beams under sustained loading iii. results and discussion during the long-term testing of the beams, deflection, strain, and cracking were monitored on a daily basis. deflection and strain recorded at eleven locations along the depth of beams at center were averaged. the weekly results of deflection of both beam groups are shown in figures 6 and 7. similarly, figures 8 and 9 show the weekly strain of beams cast with all-natural and recycled aggregates. the average values of both parameters for all beams are listed in table i. it may be noted that the deflection in beams cast with recyclable aggregates exhibited 5.6% increase when compared to the deflection exhibited by control specimens. the comparison of average strain results shows that the proposed beams exhibited 5.64% increase when compared to control specimens. the observed deflection was found within the limits of the approximate maximum deflection allowed by aci 318. fig. 6. weekly deflection (natural aggregate beams) engineering, technology & applied science research vol. 9, no. 5, 2019, 4631-4635 4634 www.etasr.com oad et al.: flexural behavior of rc beams made with recycled aggregates under 12-month long … fig. 7. weekly deflection (recycled aggregate beams) fig. 8. weekly strain (natural aggregate beams) fig. 9. weekly strain (recycled aggregate beams) table i. average deflection and strain aggregate type deflection (mm) strain natural 2.408 0.002606 recycled 2.543 0.002753 after 12-month observation under sustained loading, beams were un-mounted from the loading frames and tested in utm under central point load following the specification provided by astm for the purpose. both load and deflection were monitored in each beam until failure. the average weekly deflections versus time are plotted in figure 11. it may be observed that up to deflection of 1.5mm, the stiffness of both materials remained the same. beyond this value, the beams cast with recyclable aggregates exhibited more deflection than control specimens. it may be observed that all the beams exhibited similar pattern except for peak values. the average ultimate load observed by beams made with all-natural aggregates was recorded equal to 83.38kn. at ultimate load, the average deflection in all three beams of the group was recorded equal to 14.72mm. the average of both parameters for beams cast with recyclable aggregates was recorded equal to 81.44kn and 15.45mm respectively. it may be observed that recycled aggregate beams showed 2.33% reduction in load and 4.96% increase in deflection than control specimens. almost similar trend and behavior was observed for strain. the deflection and strain observed during the 12-month period of the proposed beams is compared with the results presented in [12]. the authors used the same material and configuration to study deflection and strain for 6-month sustained loading. the deflection of recyclable concrete beams under 12-month sustained loading exhibited 17.73% more deflection than the beams under 6-month sustained loading. similarly, an increase of 12.83% was observed in strain. fig. 10. average deflection vs time fig. 11. load vs deflection cracking due to sustained loading was monitored. the progression of cracks was marked and recorded. figures 12 and 13 show a beam from each group. it may be observed that the crack pattern of the proposed beams (figure 13) is almost similar to that of beams cast with all-natural aggregates. also, it is recorded that the crack width at the end of the 12-month observations was less than 1mm. further, the crack pattern at failure in the beams was also recorded and is displayed in engineering, technology & applied science research vol. 9, no. 5, 2019, 4631-4635 4635 www.etasr.com oad et al.: flexural behavior of rc beams made with recycled aggregates under 12-month long … figures 14 and 15 for a beam from each group. from the results it can be observed that the response of the proposed beams under 12-month loading matches well with the control specimens’. hence, 50% replacement of natural coarse aggregates with aggregates from demolished concrete may be used in new concrete. fig. 12. cracking of natural aggregate beam (12-month loading) fig. 13. cracking of recycled aggregate beam (12-month loading) fig. 14. cracking of natural aggregate beam (at failure) fig. 15. cracking ofrecycled aggregate beam (at failure) iv. conclusion in this article, the effect of 12-month sustained loading on reinforced concrete beams made with 50% replacement of natural coarse aggregates with aggregates from demolished concrete is presented. deflection and strain measured on a daily basis show a good agreement with control specimens with a deviation under 10%. also, the crack pattern of the proposed beams showed good agreement with the control specimens’. the maximum crack width after 12-month sustained loading was recorded less than 1mm. therefore, it is concluded that the use of demolished concrete as coarse aggregates in new concrete is a promising area of research. references [1] b. a. memon, “recent development on use of demolished concrete as coarse aggregates”, international journal of emerging technology and innovative engineering, vol. 2, no. 1, pp. 1-11, 2016 [2] m. oad, a. h. buller, b. a. memon, n. a. memon, s. sohu, “flexural stress-strain behavior of rc beams made with partial replacement of recyclable concrete aggregates, part-2: rich mix”, engineering technology and applied science research, vol. 8, no. 5, pp. 33383343, 2018 [3] m. oad, a. h. buller, b. a. memon, n. a. memon, “flexural stressstrain behavior of rc beams made with partial replacement of coarse aggregates with coarse aggregates from old concrete part-1(124 ratio)”, engineering technology and applied science research, vol. 8, no. 3, pp. 3048-3053, 2018 [4] s. laserna, j. montero, “influence of natural aggregates typology on recycled concrete strength properties”, construction and building materials, vol. 115, pp. 78-86, 2016 [5] n. k. bairagi, k. ravande, v. k. pareek, “behavior of concrete with different proportions of natural and recycled aggregates”, resources, conservation and recycling, vol. 9, pp. 109-126, 1993 [6] b. s. hamad, a. h. dawi, a. daou, g. r. chehab, “studies of the effect of recycled aggregates on flexural, shear and bond splitting beam structural behavior”, case studies in construction materials, vol. 9, article id e00186, 2018 [7] c. liu, z. y. lv, c. zhu, g. l. bai, y. zhang, “study on calculation method of long term deformation of rac beam based on creep adjustment coefficient”, ksce journal of civil engineering, vol. 23, no. 1, pp. 260-267, 2019 [8] m. oad, b. a. memon, “compressive strength of concrete cylinders using coarse aggregates from old concrete”, 1st national conference on civil engineering (ncce 2013-14)-(modern trends and advancements), nawabshah, pakistan, april 28–29, 2014 [9] d. h. moneti, l. torres, m. c. torrijos, r. giaccio, r. marti-vargas, p. serna, “long-term behavior of cracked fiber reinforced concrete under service conditions”, construction and building materials, vol. 196, pp. 649-658, 2019 [10] c. mias, torres, a. turon, i. a. sharaky, “effect of material properties on long-term deflections of gfrp reinforced concrete beams”, construction and building materials, vol. 41, pp. 99-108, 2013 [11] d. bacinskas, g. kaklauskas, v. gribniak, w. p. sung, m. h. shih, “layer model for long-term deflection analysis of cracked reinforced concrete bending members”, mechanics of timedependent materials, vol. 16, no. 2, pp. 117-127, 2012 [12] m. oad, a. h. buller, b. a. memon, n. a. memon, “impact of longterm loading on reinforced concrete beams made with partial replacement of coarse aggregates with recyclable aggregates from old concrete”, engineering, technology & applied science research, vol. 9, no. 1, pp. 3818-3821, 2019 microsoft word 30-3174_s_etasr_v9_n6_pp5033-5036 engineering, technology & applied science research vol. 9, no. 6, 2019, 5033-5036 5033 www.etasr.com abbasi & mohd hashim: evaluating pressure in deepwater gas pipeline for the prediction of natural … evaluating pressure in deepwater gas pipeline for the prediction of natural gas hydrate formation aijaz abbasi department of mechanical engineering universiti teknologi petronas bandar seri iskandar, malaysia aijazz.abbasi@gmail.com fakhruldin mohd hashim department of mechanical engineering universiti teknologi petronas bandar seri iskandar, malaysia fakhruldn_mhashim@utp.edu.my abstract—this paper proposes the prediction of hydrate formation pressure in deepwater pipeline with an approach of intelligent optimization. the proposed novel correlation of hydrate formation is using the function of ordinary differential equation. the developed optimization prediction model was founded on the constant coefficients which were examined by a multiple set of experimental data of methane (ch4), ethane (c2h6), propane (c3h8), iso-butane (ic4), nitrogen (n), carbon dioxide (co2) and hydrogen sulfide (h2s) hydrates. the consequences of this research are highly optimistic for the natural gas production industry. keywords-intelligent optimization techniques; hydrate formation conditions; natural gases; ordinary differential equation i. introduction a primary challenge for the deepwater hydrocarbon transmission pipeline is the formation of gas hydrate. thermodynamic properties play an important role in this forming. the natural gas hydrate formation is clogging the deepwater hydrocarbon pipeline on normal thermodynamic conditions [1-3]. a model was developed in [4] to predict the three phases of vapor, liquid and hydrate temperatures from 34 to 60f, pressure from 65 to 1500psi, and gas gravity 0.552 to 0.9 [4]. an intelligent computational method was used to find the best correlation function for hydrate formation temperature in [5, 6] which can be applied to estimate the temperature of gas hydrate formation. an improvement to that model is to predict the temperature and pressure conditions at where hydrate can form in the pipeline. under this scenario, this research paper suggests intelligent optimization algorithms (ga, pso and gwo) to be applied with the ordinary differential equation (ode) model for searching the unknown parameters for the proposed prediction model of hydrate formation pressure. the research objective of this paper is to develop a hydrate formation prediction model for pressure in deepwater pipelines. to achieve this objective, the suggested framework will be incorporated into the development of a correlation model at various gravities and thermodynamic conditions of hydrate formation. the hydrocarbon transmission pipeline is symbolized in a very complex process [7-10], hence making several assumptions of the problem is essential to delimit according to the scope of the study. the study is based on the natural gas hydrate formation in transmission pipeline systems. this refers completely to a network with large diameter pipelines that operate at high pressures. the natural gas transportation process is defined by inherent transient processes, because the problem is assumed as being in steady state. a mathematical model is required to determine the pipeline flow operation for a relatively large amount of flow, since the assumption of the system is to be in steady-state and the flow variables are independent of time. this is describing the flow behavior of natural gas in transmission lines. the governing equations will be described when gas flow, velocity, density, pressure, and temperature are considered as functions of time [11]. the pipeline transportation of natural gas is characterized by a complex process, hence, making demarcate assumptions of the problem is essential to the scope of the study. the modeling of the pipeline resistance is done in such a way that the variability of temperature and pressure is considered for the hydrate formation prediction model. ii. results and discussion intelligent optimization methods provide predictions of hydrate formation in deepwater pipelines. the unknown variables of the developed correlation model were optimized by an optimization algorithm. the unknown variables were used to enable the correlation-based approach for binary composition of pure water and natural gas hydrate formation thermodynamic conditions. the data will be modeled as a function of the ordinary differential equation (ode) (1) by applying the optimization algorithm to figure out the relation of thermodynamic properties for hydrate formation pressure. the optimization concept in the development of a hydrate formation prediction model can be expressed as an entity of three main parts: input, process, and output, which were analyzed quantitatively and qualitatively. the optimization method as a mathematical programming formally encompasses several stages [10, 12-15]. this perception is suggesting the idea that the exponential function would be the best function of a prediction model of hydrate formation. the first approach of model equation is a fractional exponent function [1], the model in [4] was an exponential function, and the model in [16] was a polynomial based equation. according to the above observation, the novelty of this model is that the proposed model in (1) is based on an ordinary differential equation (ode) which is used in the prediction of hydrate formation corresponding author: aijaz abbasi engineering, technology & applied science research vol. 9, no. 6, 2019, 5033-5036 5034 www.etasr.com abbasi & mohd hashim: evaluating pressure in deepwater gas pipeline for the prediction of natural … pressure as a thermodynamic property through an intelligent optimization algorithm: ( ) bt a f p e c b = + (1) where a, b and c are constant coefficient as shown in table i, t is the flowing temperature, and p is the pressure. table i. constant coefficients coefficients a b c ch4 pso 0.413 0.096 -3.50 ga 0.387 0.097 -2.16 gwo 0.366 0.099 -1 c2h6 pso 0.0511 0.152 0.161 ga 0.044 0.16 0.271 gwo 0.0514 0.152 0.162 c3h8 pso 0.041 0.181 -0.062 ga 0.034 0.233 0.0241 gwo 0.040 0.181 -0.062 ic4 pso 0.0176 0.206 0.031 ga 0.017 0.197 0.025 gwo 0.017 0.206 0.031 co2 pso 0.123 0.169 0.528 ga 0.122 0.169 0.5311 gwo 0.123 0.169 0.528 n pso 1.9605 0.082767 -8.438 ga 1.7372 0.088284 -1.99 gwo 1.74 0.08821 -2 h2s pso 0.0119 0.101 -0.044 ga 0.015 0.0887 -0.152 gwo 0.0118 0.101 -0.043 the challenge of using the ode function is to develop a prediction model with constant coefficients as shown in table i. the correctness or correlation and analysis of prediction model results were examined by the mean square error equation: ( ) 2 exp 1 1 n pre i mse x x n = = −∑ (2) where, n is total number of data points or numbers of points on i, xexp is the existing value, and xpre is the predicted value. mse is applied among the result of model and existing data sets with respect to i iterations [17-22]. the precise computational approach of methanol loss to the vapour phase within hydrate inhibition and right injection rate are calculated in (2) [23]. the neuro-fuzzy method is using (2) to find the growth rate of error [24] and in the statistical package for the social sciences (spss) static model of hydrate formation correlation (2) is also applied to determine its error [25]. the optimum number of hidden neurones is calculated by engaging mse and regression r-value as an evaluation of ann-mlp [26]. the relations between temperature, pressure and inhibitor were studied through the experimental data of [27]. these data present significant effects of temperature and pressure on hydrate-formation. the experimental data used give some interesting observations. at a certain temperature, hydrocarbons flow in the pipeline without inhibitors and no hydrate formation, but in the same conditions with lighter specific gravity of gas, hydrate is mostly formed at higher pressures. however, this condition is not always followed by the hydrocarbons. the propane and isobutene mixture of gasses will reduce the hydrate formation pressure notably and nitrogen is acting as an inhibitor. these generate an intelligent optimized result for hydrate formation conditions which are shown in table ii. hydrate formation prediction conditions for the composition of methane (ch4), ethane (c2h6), propane (c3h8), isobutane, nitrogen (n), carbon dioxide (co2) and hydrogen sulfide (h2s), gases in the deepwater pipeline were predicted on the data of [27] and are given in figures 1-7. the results show that the developed model provides the best prediction results with minimum error as shown in table ii. it is specified that pso and gwo give the best prediction results with fewer error points. the overall results of the developed model are validated through the [1, 4, 16] model equations and their comparison is given in table ii. this intelligent optimization correlation model is developed on the base of the ode with 3 constant coefficients which are illustrated in table i. the best minimum error difference was 2.3 in ch4 (figure 1). c2h6 gives 0.054187 with pso and gwo (figure 2), c3h8 gives 0.0161 in pso as shown in figure 3, isobutene gives 0.010441 with pso and gwo as shown in figure 4, co2 gives 0.093909 with pso and gwo as shown in figure 5, n has 2.2619 in pso as shown in figure 6, and h2s gives 0.09617 in pso as shown in figure 7. the developed model results are addressing the thermodynamic properties of hydrate formation for water and natural gas. table ii. error comparison gas algorithm error proposed [1] [4] [16] less than 23mol wt% more than 23mol wt% ch4 pso 2.39 7.74 18.93 12.227 12.259 ga 2.55 gwo 2.75 c2h6 pso 0.054 3.42 8.943 15.007 15.040 ga 0.05 gwo 0.054 c3h8 pso 0.016 4.22 3.443 15.131 15.160 ga 0.016 gwo 0.022 ic4 pso 0.010 4.83 1.074 15.155 15.185 ga 0.0104 gwo 0.0104 co2 pso 0.093 7.97 5.849 14.933 14.961 ga 0.093 gwo 0.093 n pso 2.26 19.8 13.21 9.515 9.542 ga 2.917 gwo 2.915 h2s pso 0.096 13.345 23.36 15.049 15.077 ga 0.1013 gwo 0.096 engineering, technology & applied science research vol. 9, no. 6, 2019, 5033-5036 5035 www.etasr.com abbasi & mohd hashim: evaluating pressure in deepwater gas pipeline for the prediction of natural … fig. 1. methane gas hydrate formation prediction on ode model fig. 2. ethane gas hydrate formation prediction on ode model fig. 3. propane gas hydrate formation prediction on ode model fig. 4. iso-butane gas hydrate formation prediction on ode model fig. 5. carbon dioxide gas hydrate formation prediction on ode model fig. 6. nitrogen gas hydrate formation prediction on ode model 0 200 400 600 800 1000 0 0.02 0.04 0.06 0.08 0.1 0.12 iteration e rr o r % 0 1 2 3 4 5 6 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 temperature c p re s s u re m p a gwo prediction data pso prediction data ga prediction data experimental data gwo pso ga 0 200 400 600 800 1000 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 iteration e rr o r % -2 -1 0 1 2 3 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 temperature c p re s s u re m p a gwo prediction data pso prediction data ga prediction data experimental data gwo pso ga 0 200 400 600 800 1000 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 iteration e rr o r % -5 0 5 10 15 1 1.5 2 2.5 3 3.5 4 4.5 5 temperature c p re s s u re m p a gwo prediction data pso prediction data ga prediction data experimental data gwo pso ga 0 200 400 600 800 1000 0 5 10 15 20 25 30 35 iteration e rr o r % -10 0 10 20 30 40 0 50 100 150 200 250 300 350 400 temperature c p re s s u re m p a gwo pso ga gwo prediction data pso prediction data ga prediction data experimental data engineering, technology & applied science research vol. 9, no. 6, 2019, 5033-5036 5036 www.etasr.com abbasi & mohd hashim: evaluating pressure in deepwater gas pipeline for the prediction of natural … fig. 7. hydrogen sulfide gas hydrate formation prediction on ode model iii. conclussion the developed model for the prediction of hydrate formation thermodynamic conditions was obtained by ordinary differential equation and optimization algorithms. results are presenting that ga, pso and gwo algorithms are effectively discovering the value of constant coefficients. pso and gwo algorithms are giving overall minimum error. however, there are some limitations in this prediction model which require further research, to enhance its accuracy and functionality. the accuracy of the proposed model can be enhanced by optimizing the phase behavior chart by having more accurate information of natural gas components, water composition and optimize operating conditions of natural gas hydrates formation during production, transportation and processing of natural gas hydrates. references [1] e. g. hammerschmidt, “formation of gas hydrates in natural gas transmission lines”, industrial & engineering chemistry, vol. 26, no. 8, pp. 851-855, 1934 [2] j. carroll, natural gas hydrate: a guide for engineers, gulf professional publishing, 2003 [3] a. abbasi, f. m. hashim, “hydrate formation prediction model for binary gases of methane+ethane and methane+propane by using optimization algorithm”, petroleum science and technology, available at: www.tandfonline.com/doi/abs/10.1080/10916466.2019.1655447, pp. 1-7, 2019 [4] r. g. kobayashi, k. y. song, e. d. sloan, “phase behavior of water/hydrocarbon systems”, in: petroleum engineering handbook, pp. 25-28, society of petroleum engineers, 1987 [5] a. abbasi, f. m. hashim, “a prediction model for the natural gas hydrate formation pressure into transmission line”, petroleum science and technology, vol. 34, no. 9, pp. 824-831, 2016 [6] a. abbasi, f. m. hashim, “development of a hydrate formation prediction model for sub-sea pipeline”, petroleum science and technology, vol. 35, no. 5, pp. 443-450, 2017 [7] d. mahlke, a. martin, s. moritz, “a simulated annealing algorithm for transient optimization in gas networks”, mathematical methods of operations research, vol. 66, no. 1, pp. 99-115, 2007 [8] e. d. fatnes, numerical simulations of the flow and plugging behaviour of hydrate particles, university of bergen, 2010 [9] w. duch, j. korczak, optimization and global minimization methods suitable for neural networks, neural computing surveys, 1998 [10] z. cui, x. gu, “an improved discrete artificial bee colony algorithm to minimize the makespan on hybrid flow shop problems”, neurocomputing, vol. 148, pp. 248-259, 2015 [11] r. z. r. mercado, c. b. sanchez, “optimization problems in natural gas transportation systems: a state-of-the-art review”, applied energy, vol. 147, pp. 536-555, 2015 [12] c. b. sanchez, optimization methods for pipeline transportation of natural gas, university of bergen, 2010 [13] h. kang, f. chen, y. li, j. deng, z. yang, “knot calculation for spline fitting via sparse optimization”, computer-aided design, vol. 58, pp. 179-188, 2015 [14] d. n. truong, v. t. bui, “hybrid pso-optimized anfis-based model to improve dynamic voltage stability”, engineering, technology & applied science research, vol. 9, no. 4, pp. 4384-4388, 2019 [15] k. soleimani, j. mazloum, “designing a ga-based robust controller for load frequency control (lfc)”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2633-2639, 2018 [16] a. bahadori, h. b. vuthaluru, “a novel correlation for estimation of hydrate forming condition of natural gases”, journal of natural gas chemistry, vol. 18, no. 4, pp. 453-457, 2009 [17] m. m. ghiasi, a. bahadori, s. zendehboudi, “estimation of triethylene glycol (teg) purity in natural gas dehydration units using fuzzy neural network”, journal of natural gas science and engineering, vol. 17, pp. 26-32, 2014 [18] s. rashid, a. fayazi, b. harimi, e. hamidpour, s. younesi, “evolving a robust approach for accurate prediction of methane hydrate formation temperature in the presence of salt inhibitor”, journal of natural gas science and engineering, vol. 18, pp. 194-204, 2014 [19] m. ghavipour, m. ghavipour, m. chitsazan, s. h. najibi, s. s. ghidary, “experimental study of natural gas hydrates and a novel use of neural network to predict hydrate formation conditions”, chemical engineering research and design, vol. 91, no. 2, pp. 264-273, 2013 [20] m. farzad, h. tahersima, h. khaloozadeh, “predicting the mackey glass chaotic time series using genetic algorithm”, sice-icase international joint conference, busan, south korea, october 18-21, 2006 [21] a. goshtasby, w. d. oneill, “curve fitting by a sum of gaussians”, cvgip: graphical models and image processing, vol. 56, no. 4, pp. 281-288, 1994 [22] d. c. montgomery, design and analysis of experiments, john wiley & sons, 2008 [23] m. m. ghiasi, a. bahadori, s. zendehboudi, a. jamili, s. r. gomari, “novel methods predict equilibrium vapor methanol content during gas hydrate inhibition”, journal of natural gas science and engineering, vol. 15, pp. 69-75, 2013 [24] j. foroozesh, a. khosravani, a. mohsenzadeh, a. h. mesbahi, “application of artificial intelligence (ai) in kinetic modeling of methane gas hydrate formation”, journal of the taiwan institute of chemical engineers, vol. 45, no. 5, pp. 2258-2264, 2014 [25] e. khamehchi, e. shamohammadi, h. yousefi, “predicting the hydrate formation temperature by a new correlation and neural network”, gas processing journal, vol. 1, no. 1, pp. 41-50, 2013 [26] m. m. ghiasi, a. bahadori, s. zendehboudi, “estimation of the water content of natural gas dried by solid calcium chloride dehydrator units”, fuel, vol. 117, part a, pp. 33-42, 2014 [27] e. d. sloan, c. a. koh, clathrate hydrates of natural gases, crc press, 2007 0 200 400 600 800 1000 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 iteration e rr o r % -10 0 10 20 30 0 0.5 1 1.5 2 2.5 temperature c p re s s u re m p a gwo prediction data pso prediction data ga prediction data experimental data gwo pso ga microsoft word etasr_v13_n4_pp11058-11063 engineering, technology & applied science research vol. 13, no. 4, 2023, 11058-11063 11058 www.etasr.com mamulaishvili et al.: a technological nanofluid for washing off oil deposits and increasing oil … a technological nanofluid for washing off oil deposits and increasing oil recovery nora mamulaishvili technical faculty, batumi shota rustaveli state university, georgia n.shvili@rambler.ru (corresponding author) gaioz partskhaladze technical faculty, batumi shota rustaveli state university, georgia gaioz partskhaladze@bsu.edu.ge gocha chavleshvili technical faculty, batumi shota rustaveli state university, georgia gocha.chavleshvili@bsu.edu.ge tea khitarishvili georgian technical university, georgia | department of petroleum chemistry, oil academy of azerbaijan, azerbaijan tea.khitarishvili@rambler.ru nigar salimova department of petroleum chemistry, oil academy of azerbaijan, azerbaijan nigarazizaga@mail.ru received: 3 april 2023 | revised: 30 april 2023 | accepted: 2 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5904 abstract the productivity of wells in the late stage of oil production is directly related to oil deposits, which gradually form blockages, fill the pipeline, and interfere with the free movement of the flow of produced oil. based on chemical composition, oil deposits are difficult to remove and require the selection of process fluids. an extractive method is proposed for the removal of oil deposits with the participation of process fluids, including nanofluids. the proposed nanofluid was prepared on the basis of low-viscosity petroleum oil with the addition of an organic solvent, a mixture of various classes of surface-active substances (surfactants), and alkali metal salts. the nanofluid contains a nanosolution based on alkali metal salts, with concentrations of na3po4=13700ppm, kcl=950ppm, and cacl2=241ppm, which were determined by the readings of an icpe-9820 spectrometer. it was found that the tested process fluid reduces the viscosity of deposits and interfacial tension and leads to an increase in fluid movement in the pipeline. the experiments were carried out in the direction of reducing the interfacial tension at the interface with the solvent. it was shown that the process of sediment reduction depends on the composition of the arpd, the surfactant, the composition of the solvent, and the salinity of the nanosolution. it is advisable to flush oil deposits from the surface of the tubing using the process fluid when creating a circular circulation in a closed annular space tubing – annulus circuit. keywords-nanofluid; oil deposits; solvent; surface tension; surfactant; tubing i. introduction in many countries, including georgia, at old mines (supsa, shromysubany, telety) most of the production wells work in a reduced format of their potential. which is connected with the deterioration of the filtration properties of rock collectors and the formation of heavy components of the final oil (asphalts, resins, and paraffins). productivity and rates of oil production are decreasing. increasing the output of such wells is possible with the help of innovative methods and effective technological fluids. inexpensive and non-toxic nanofluids can be used for the effective extraction of even heavy, highly viscous oil from formations. with the help of nanofluids. metallic sodium was engineering, technology & applied science research vol. 13, no. 4, 2023, 11058-11063 11059 www.etasr.com mamulaishvili et al.: a technological nanofluid for washing off oil deposits and increasing oil … used as a nanomaterial for effective oil extraction from heavy oil and oil sand layers. preliminary tests of the batch showed that when mixing 1g of heavy oil (2000 cp at 25 °с, density 12.5 °api) and 40 mg of sodium nanoparticles dispersed in 0.2 ml of silicone oil, and 1ml of physiological solution containing 5.66 wt.% nacl, as a result of the reaction of sodium with water, a sufficient amount of heat is released, preventing the formation of oil deposits [1-2]. authors in [7, 8] recognized the potential of low salinity waterflooding when they discovered that additional recovery of residual oil could be achieved using lsw flooding. the efficiency of lsw in oil recovery can be related to the presence of potential ions (mg 2+ and so4 2– ) in lsw. however, brine salinity is a major factor in oil recovery. additional oil recovery from lsw flooding is only possible if the salinity is in the range of 2000–5000 ppm [3]. recently, nanoparticles have been used for boosting oil recovery. nanoparticles can improve the performance of the injected water in the enhanced oil recovery (eor) process. a nanofluid consists of a liquid and nanoparticles dispersed in it. the properties and efficiency of nanofluids in eor depend on various parameters, such as the size and type of the dispersed nanoparticles. the behavior of the pressure drop in nanofluids differs from that in conventional fluids. nanoparticles dispersed in nanosuspensions usually have a size of 1 to 100nm. the small size of the nanomaterials increases their effective surface area, which will change some of the properties of fluids containing these particles, such as heat transfer, viscosity, and particle surface activity [4]. the main methods for removing deposits from tanks are mechanical cleaning or hot washing with the use of solvent removers. as removers, individual organic substances and their mixtures with the addition of surfactants, oil and its fractions, products of the petrochemical industry, and surfactant solutions are used. despite the widespread use of this method, there is the problem of the selecting effect [5]. the use of natural sas and bio additives in petroleum oils and fuels improves their performance. bio fuel for jet engines has been obtained with the addition of nettle seed oil. as a result, the operational properties of fuels are stabilized [9, 21]. authors in [19] propose the use of a combined method for cleaning small-diameter oil pipelines utilizing, as a flush solution, used engine oil with toluene added to dissolve arpd followed by the displacement of softened deposits by devices of various designs. a composition for the removal of paraffin deposits containing a mixture of hydrocarbons, in wt.%, is proposed: the spent cyclohexanefraction 70-80 and the spent tall oil or rapeseed oil -20-30 (rf patent 2185412, c 09 k 3/00, e 21 b 37/06, publ.20.07.02) [20]. ii. materials and methods the main goal of the current work is the development of new effective process fluids, the use of which will ensure the washing out of salt and paraffin deposits in the tubing of the well and intensify the flow of residual oil of the productive formation. the objects of study were asphalt-resin-paraffin deposits taken from different sites. their compositions are shown in table i. table i. composition of the studied arpd no compound 1 2 3 test 1 asphaltenes, % mass 4.7–7.74 6.5-25 10-15 gost 11851-85 2 resin, % mass 9.8-20.3 7-21.5 20-25 gost 11851-85 3 paraffin, % mass 3.2–3.9 3-4.5 45-60 gost 11851-85 4 mechanical ipurities, % mass 12-17 15-18 15-30 gost 6370-83 5 water, % mass 0.3-0.8 5-8 5-18 gost 2477-65 6 density, g/cm3 0.9–1.0 0.93-1.3 1.2–1.5 gost 3900-85 the chemical composition of petroleum residues of aspo is different: 1-reservoir oil, 2-transit oil from the tank, 3-from the main oil pipeline. the compositions are presented in table i. at this stage, the composition of the liquid was developed to remove petroleum deposits formed on the tubing (pumping equipment) of well no. 15 of the supsinsky field. the following instruments and reagents were used in the laboratory study:  plazma atomic emission spectrometer icpe-9820 japan, 2017, shimadzu [22].  biobasebk-r2sabbedigital refractometer, china [23].  stalagmometer, viscometer, density meter.  aromatic alcohols and their derivatives: isopropyl and isobutyl alcohol.  industrial solvent -646 (rf) [15], composition: 15% ethanol, 10% butanol, 50% toluene, 7% acetone, 10% butyl acetate and 8% cetate, industrial solvent, genc, turkey  used petroleum oil.  diluted solutions of surfactants.  nano-solutions alkali metal salts. the parameter calculation follows [12-14]: the solubility of the deposits is derived by: e = [(m1 − m2)/m1] × 100% (1) where m1 is the mass of the taken for the experiment (g) and m2 the mass of the residues in the basket after the experiment.  solvent liquid that prevents the rapid evaporation of the light fraction of solvents. it was revealed that the use of a mixture of solutions of an anionic and non-ionic surfactant composition regulates the uniform washing off of deposits of paraffin deposits and ensures the free movement of oil in the tubing and formation reservoirs. the kinematic viscosity (mm 2 /s) is: v = τ k (2) where τ is the expiration time (s) and k= 0.1006, viscometer capillary d= 0.99. engineering, technology & applied science research vol. 13, no. 4, 2023, 11058-11063 11060 www.etasr.com mamulaishvili et al.: a technological nanofluid for washing off oil deposits and increasing oil … interfacial tension at 20 0 c: � = �� ��� (3) liquid density: d20=dt+α(t-20) (4) where t is the temperature. iii. results and discussion the aspo dissolution process comprised the controlled gravimetric method and refractometry. the experiments were carried out in the educational laboratory of the batumi shota rustaveli state university. a. testing of solvents the following reagents were selected as arpd deposit removers:  waste and refined petroleum oil (om)  solvents 646 or 647 (rf) [15]  genc solvent  aromatic alcohols, isopropyl alcohol  ethyl acetate figure 1 shows the dynamics of the dissolution of the arpd sample depending on time with the reagents under study, in the ratio of arpd / solvent (1/30) at t = const. fig. 1. dynamics of the dissolution of thearpd sample vs time. table ii. change in solubility in time for different solvents contact time change in solubility used oil 646 solvent genc solvent ethyl acetate isopropyl alcohol 20 40 50 60 70 65 40 50 70 80 75 70 60 60 70 80 75 75 80 60 70 80 75 75 the obtained result shows that arpd deposits dissolve well in aromatic solvents, especially at the initial stage of dissolution within 60 min. asphaltenes dissolve well in aromatic hydrocarbons, paraffins in light hydrocarbons, and resins in both [14]. b. testing of used and enriched petroleum oil waste petroleum oils are concentrates of complex component compositions, fatty acids, heterocyclic compounds, additives, etc., forming a liquid with a density of 0.8862–0.920 g/cm 3 at 20°с. it should be noted that the waste oil, based on the degree of contamination, was purified with the use of extractive and adsorption methods. the results of technological research on the purification and regeneration of used engine oil are presented in [16] by the grant gnsf project 496-7-201 (georgia). fig. 2. refractive index of arpd deposits: 1. oil extract, 2. genc extract, 3. diesel extract. the obtained results confirm that the deposits are most dissolved in the egnk solvent. waste (and refined) petroleum oil contains an insufficient amount of fatty acids, so it was enriched with vegetable oils with a high content of fatty acids: ricinoleic, oleic, and linolenic [21]. when natural surfactants are added to used oil, its physicochemical parameters, such as cmc, ph, etc., improve. enriched oil was used to obtain oil extracts, which are oil-soluble surfactants and are actively involved in the process of dissolving deposits. all oil extracts and organic solvent extracts were tested on a biobase bk-r2 abbe digital refractometer to determine their refractive index. the test results are presented in table iii. table iii. index of refraction of sediment extracts sediment / solvent index of refraction of sediment extracts oil extract 646 extract genc extract diesel extract 1/10 1.4752 1.4355 1.3763 1.4578 1/20 1.4752 1.4323 1.3538 1.4528 1/30 1.4750 1.4323 1.3536 1.4528 1/40 1.4752 1.4355 1.3763 1.4578 engineering, technology & applied science research vol. 13, no. 4, 2023, 11058-11063 11061 www.etasr.com mamulaishvili et al.: a technological nanofluid for washing off oil deposits and increasing oil … c. testing of surfactants and nano fluid the main ability of surfactants is that their activity reduces surface tension at the interface. however, the surfactant has a cmc solubility limit (critical micelle concentration), with the achievement of which, with the further addition of a surfactant to the solution, its concentration at the interface remains constant. for this study, the decrease in interfacial tension and then the decrease in the viscosity of deposits of arpd is the most significant phenomenon. therefore, work was carried out in the direction of reducing the viscosity of arpd deposits [17] (table iv). the object of study was surfactants in concentrations ranging from 0.01% to 2.0 wt%. solutions of surfactants of various classes, such as washing, working reagents, anionic, and non-ionic surfactants and their mixtures, were chosen. the physical parameters, such as the coefficient of surface tension, of the reagents were determined. the sulfanol solution had the lowest coefficient of surface tension, so it was preferred as an additive to washing liquids [17-18]. table iv. surfactant test results surfactant concentration surface tension10 –3 n/m sulfanol alkane de 202 1.0 0.93 3.74 0.5 1.83 5.26 0.25 2.40 7.00 0.125 3.61 8.90 oil without sas 44 fig. 3. dependence of surface tension coefficient on the concentration of the investigated reagent: 1. sulfanol, 2. alkane de 2 02. authors in [6-8] propose the use of nanofluids containing nano-solutions for the effective flushing of oil deposits. researchers of the gubkina institute of oil and gas [10] offer process fluids, without nano-solutions, which include a solution of mineral salts and various surfactants (naphthols), which reduce interfacial tension at the interface with the solvent. we propose a composite composition of nano-liquid which contains waste petroleum oil, solvent, sulfanol surfactant, and nano-solution, which was prepared on the basis of alkali metal salts with the following composition:  na3po4 nanosolution with concentration of 13700 ppm  kcl nanosolution with concentration of 950 ppm  cacl2 nanosolution with concentration of 241 ppm in order to reveal the effect of nano solutions on the interfacial tension of a liquid, experiments were carried out at different salts and concentrations of nano solutions and at different surfactant concentrations. the results are shown in table v. the study was carried out at a temperature of 20 °c, and the best solvent (genc) was used as the hydrocarbon medium in all experiments. studies have shown that the interfacial tension reduction can be maximized when using a nano-solution of sodium salt, whereas in the case of calcium salt, the nano-solution did not work. the concentration spectra of nano-solutions obtained on the device plazma atomic emission spectrometers icpe-9820 are shown in figures 4-6. table v. nanosolution interfacial tension at the interface with the genc solvent at different surfactant concentrations # nanofluid composition interfacial tension(ift) 10 -3 n/m, 20°c 1 nanosolution na3po4 13700ppm 3.62 0.52 0.46 0.42 0.46 2 nanosolution kcl 950ppm 2.28 0.56 0.56 0.56 0.58 3 nanosolution cacl2 241ppm 1.98 1.98 1.94 1.94 1.94 4 surfactant, sas concentration % 0.01 0.25 0.5 1.0 1.5 fig. 4. nano solution # 1. wavelength 589nm. the field work that is planned to be carried out on wells, in relation to equipment and technology, is reduced to the existing methods of well treatment. of the existing technological schemes for well treatment, tubing and annular space are recognized as the best (figure 7). removal of deposits from the surface of tubing using process fluids is carried out on the basis of creating a circular circulation along a closed circuit: annular space tubing annulus [12-14]. 0 25 50 75 100 concentration (m g/l) 0 1 2 3 4 5 6 7 8 in te n s it y k 797.395 nm (1) r = 0.99985 equation: factor: b = 0.0000000 conc = a * i ̂3 + b * i ̂2 + c * i + d a = 0.0000000 c = 15.62108 d = -3.953421 weight: none origin: none detection lim it (3s) = 1.892222 lim it of quantity (10s) = 6.307406 0 100 200 300 in te n s it y k 766.490 cond 2 766.4 766.6 engineering, technology & applied science research vol. 13, no. 4, 2023, 11058-11063 11062 www.etasr.com mamulaishvili et al.: a technological nanofluid for washing off oil deposits and increasing oil … fig. 5. nano solution #2. wavelength 787nm. fig. 6. nano solution #3. wavelength 315nm. fig. 7. tubing flushing. 1. well 1 oilreservoir, 2. colons, 3. tubing, 4. pump, 5. οil deposits, 6. injection zone, 7. pumping unit, 8. volume for solvent, 9-10. volume for waste. iv. conclusions the effectiveness of the use of nanofluids for washing off oil deposits was revealed as a result of the current research. it is shown that when sodium phosphate, potassium chloride, and calcium chloride, in a combination of aqueous solutions of surfactants and a hydrocarbon medium, are introduced into the composition of the nanofluid, the arpd washing improves by 45%. this ensures the free movement of oil flow through the tubing and increases the productivity of the well. the dynamics of dissolution of arpd samples by individual reagents under statistical conditions was studied. the proposed nanofluid has a number of advantages. it is shown that arpd deposits are effectively dissolved at the initial stage of dissolution within 60 minutes. it was revealed that nano-solutions based on alkali metal salts using a mixture of solutions of anionic and non-ionic surfactant compositions are effectively involved in reducing interfacial tension, regulating uniform flushing of deposits in tubing, and ensuring free movement of oil flow through the well. in [13], the authors propose the elimination of the afs of the zhanaozen (ozen) oil field with a solvent mixture consisting of 50% gasoline and 50% kerosene. this paper shows that arpd deposits dissolve well in industrial solvents, especially at the initial stage of dissolution within 60 minutes. in [10], surfactants (naphthols) for dissolving arpd were proposed, which are much more expensive than sulfanol. petroleum oil in the composition of the nanofluid increases the density of the cleaning solution and prevents the rapid evaporation of the light fraction of solvents. it also ensures the safety of their storage in the conditions of downhole equipment. acknowledgement we would like to thank the rectoral and research service of batumi state university for their support and the funding of this publication. 0 25 50 75 100 concentration (mg/l) 0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 in te n s it y na 589.592 nm (2) r = 0.99868 equation: factor: b = 0.0000000 conc = a * i ̂3 + b * i ̂2 + c * i + d a = 0.0000000 c = 6.413349 d = -4.276356 weight: none origin: none detection limit (3s) = 2.110298 limit of quantity (10s) = 7.034328 0 1000 2000 3000 4000 in te n s it y na 589.592 bes t cond 2 589.5 589.6 589.7 0 25 50 75 100 concentration (mg/l) 0 100 200 300 400 500 in te n s it y ca 315.887 nm (2) r = 0.99824 equation: factor: b = 0.0000000 conc = a * i ̂3 + b * i ̂2 + c * i + d a = 0.0000000 c = 0.2132492 d = -1.015240 weight: none origin: none detection limit (3s ) = 0.0841290 limit of quantity (10s ) = 0.2804298 0 250000 500000 750000 in te n s it y ca 393.366 cond 2 393.3 393.4 engineering, technology & applied science research vol. 13, no. 4, 2023, 11058-11063 11063 www.etasr.com mamulaishvili et al.: a technological nanofluid for washing off oil deposits and increasing oil … references [1] d. zareei, d. luo, k. kostarelos, and z. ren, "sodium nanofluid for efficient oil recovery in heavy oil and oil sand reservoirs,"soft science, vol. 1, no. 2, sep. 2021, https://doi.org/10.20517/ss.2021.08. 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[23] "supply biobase bk-rzt bk-r2s abbe digital honey refractometer honey wholesale factory,"biobase group. https://www.biobase.com/product/biobase-bk-rzt-bk-r2s-abbe-digitalhoney-refractometer-honey. microsoft word 16-925-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1200-1206 1200 www.etasr.com khadra and el-morsy: prediction of springback in the air bending process using a kriging metamodel prediction of springback in the air bending process using a kriging metamodel fayiz abu khadra faculty of eng.-rabigh, king abdulaziz university saudi arabia fabukhadra@kau.edu.sa abdel-wahab el-morsy faculty of eng.-rabigh, king abdulaziz university, saudi arabia and faculty of eng.-helwan, helwan university, egypt aalmursi@kau.edu.sa abstract—this paper addresses the use of the kriging approach to predict the springback in the air bending process. the materials and the geometrical parameters, which significantly affect the springback, were considered as inputs, and the springback angle was considered as the response. a verified nonlinear finite element model was used to generate the training data required to create the kriging metamodel. the training examples were selected based on computer-generated d-optimal designs. a comparison between the kriging approaches and the response surface methodology is conducted and discussed. the results showed that kriging accurately predicts the finite element springback results. comparing the accuracy of kriging with a response surface methodology shows that kriging with a 2nd degree polynomial and exponential correlation function predicts the springback more accurately than the response surface methodology. keywords-metamodels; springback; kriging; response surface methodology; d-optimal designs i. introduction springback is a common phenomenon that occurs in sheet metal bending after unloading the static loads due to elastic recovery. in recent years, numerous investigations have been conducted on the springback phenomenon in sheet metal bending processes via experimental [1-5], analytical [6-9], and numerical [10-12] methods for different shapes, processes and material parameters. many types of geometries have been performed to predict the springback, including pure/air bending [4, 10, 13], v-bending [1, 14-15], u-bending [16-19], lbending [7, 20-21], draw-bending [2-3, 6], beams subjected to repeated bending [5], and tube bending [22]. a number of analytical models based on the geometry and the material characteristics have been conducted using the analytical methods for springback predictions. the recent approaches to analytical solutions include the prediction of springback considering young's modulus variation with a piecewise hardening function [23], friction modeling of high strength steels [24-25], semi-analytical modeling of springback [26], u-bending as a function of stress distribution in the thickness of sheet metal [27], springback prediction of an asymmetric thin-walled tube [28], and an analytical springback model for lightweight hexagonal close-packed sheet [29]. in general, most of the analytical models assume a simplified process and material properties due to the complexity of the problem. the finite element method is a powerful tool for analyzing sheet bending processes with various materials and test conditions [1, 11, 30-32]. because a large number of fems is required to develop an accurate approximation for springback prediction, it is not practical, relatively time-consuming, and computationally expensive to apply it for a complex process, such as metal forming. in addition, a direct link between finite element code and optimization routines can lead to inefficient results because a large number of iterative calls are required during the optimization. recently, there has been a great increase in the application of metamodels instead of the complex analytics models that are limited by assumptions [3334]. several metamodeling techniques with various degrees of complexity have been extensively applied, such as the response surface methodology [35-38], artificial neural network [39-42], radial basis function [43-45], and kriging [46-49]. some of these techniques are suitable for global approximations, i.e., can be used for representing the complete design space, while others are more suitable for local approximations of a part of the design space. the existing studies to predict springback in the air bending process mostly use training data from experiments with real-life systems. consequently, these studies considered only inadequate materials and tool geometry [37, 39-41, 50]. in this study, the kriging approach is developed to predict springback in the air bending process. the finite element simulation is employed to generate the training data required to train the kriging metamodel. the use of a finite element analysis permits the mapping of a large range of materials and geometrical tool dimensions. the kriging metamodel is compared with the traditional response surface methodology (rsm) to show the merits of the kriging metamodel to predict springback. ii. metamodel generation a metamodel [46] is a mathematical approximation of a computationally expensive numerical model. using a metamodel, one can study the behavior of the response engineering, technology & applied science research vol. 6, no. 5, 2016, 1200-1206 1201 www.etasr.com khadra and el-morsy: prediction of springback in the air bending process using a kriging metamodel function more efficiently and can perform an optimization very rapidly. the mathematical approximation can be written as:    xgxfy  (1) where f(x) is the simulation model function, and g(x) is the metamodel approximation to y, which maps the design variables x to the predicted response ŷ .the predicted response ŷ will differ from the observed response y from the simulation model.  yy  (2) where the error ε represents the approximation error. to build a metamodel, n runs of the simulation model with different variable settings  ni xxxx .......,,, 21 and the k design variables are required. a. response surface methodology rsm [35] is a set of mathematical methods for enhancing processes and products. the relationship between the response (y) and the vector independent factors (x) can be expressed by:  )(xfy (3) where ε is the random error, which is expected to be normally and independently distributed with a mean of zero and a standard deviation σ. the broadly used rsm functions are loworder polynomials and can be expressed as:   k i ii xy 10  (4) for considerable curvature, a second-order polynomial can be expressed as:     k i iiiji jiij k i ii xxxxy 1 2 10  (5) the parameters in (4) and (5) are typically determined by a least squares regression analysis. the least squares estimators of the regression coefficients b are denoted by b  . the regression model may be written as: y x b e= + (6) thus, y is a vector of n responses, x is an n × p design matrix consisting of variable settings, β is a vector of p regression variables and ε is a vector of the n errors. in the design matrix, each row corresponds to one design point, and each column corresponds to one regression coefficient. the fitted regression model becomes: y x b=  (7) assuming that β has a zero mean and a variance-covariance matrix given by ni 2 , the so-called ordinary least-squares estimator of β is [38]: ( ) 1t tx x x yb =  (8) the variance-covariance matrix of   is then of the form ( ) ( ) 12 tvar x xb s =  (9) b. kriging metamodel the kriging interpolation method [47], developed in the field of spatial statistics and geo-statistics, has been widely used in recent years to model deterministic simulations. kriging predicts the value of a new point using stochastic processes. kriging consists of a combination of a known polynomial plus fitting errors, as shown in 10: ( ) f ( ) ( )ty x x z xb= + (10) where y(x) is the unknown response of interest, 1 2 p f(x) [f (x),f (x),...,f (x)]t= is the (p×1) vector of regression functions, and t 1 2 p β [β ,β ,...,β ]= is the (p×1) vector of unknown coefficients. tf (x)β globally approximates the design space. in many cases, tf (x)β is assumed to be a constant (ordinary kriging), or it may be a first-order or second-order polynomial. “z(x)” is a stochastic process, which has a mean of zero, variance of σ2, and the following covariance matrix: 2cov ( ), ( ) ([ ( , ])i j i jz s z s r r s ss=é ùë û (11) z(x) performs localized deviations, so that the kriging model interpolates ns sampled data. the correlation matrix r is ns × ns is symmetric with ones along the diagonal. [r(s i, sj)] is a user-defined correlation function. the selection of the correlation function determines on how to fit the data. in this study, the most popular correlation function is gaussian, in which the exponent 2 is used in (12). 1 ( , ) exp ni j i j k k kk r s s s sq = = -é ùê úë ûå (12) the quantities j k i k ss and are the kth components of the sampled points si and sj, respectively. as part of the kriging approximation, the unknown θk terms are determined. the maximum likelihood estimation of θk can be calculated by maximizing the following expression: 2 ]ln)ln([ max 2 0 rns z      (13) 2 z s  is the estimated process variance and can be calculated by: 1 2 ( ) ( ) t z s y f r y f n b b s -=    (14) the kriging estimate at any untried point x is given by: ( )t t 1y(x) f (x)β r (x)r y fβ-= +   (15) engineering, technology & applied science research vol. 6, no. 5, 2016, 1200-1206 1202 www.etasr.com khadra and el-morsy: prediction of springback in the air bending process using a kriging metamodel ( ) 1t 1 t 1β f r f f r y --=  (16) sn1 2 tf [f(s ),f(s ),.....,f(s )]= (17) f is a column vector with ns components, which is filled with ones when p(x) is a constant. )],....yy,[yy ns21 sss is the column vector of length ns, which contains the response values at each sampled point. iii. methodology of springback prediction using a kriging metamodel the procedure to predict springback in the air bending process consists of the following phases. a schematic representation of the methodology for springback angle prediction using a kriging metamodel is shown in figure 1. fig. 1. flowchart of the methodology for springback prediction using kriging metamodel. a. identify the design space and select the design variables the first step is to select the design variables (e, σy, k, n, t, rp, rd, wd, θ1), which is a very important step for generating accurate models (table i). the method for selecting the sample points, which is dependent on the design variables, is called the design of experiments (doe). these sample points are used as the input variables for the next step. in this study, the doptimality experimental design criterion [51] was used to sample the design space. d-optimality is the most common criterion, which seeks to maximize |xt x|, the determinant of the information matrix (xt x) of the design. equation 18 shows the selection of xt out of all possible design matrices chosen from ξn. )(maxxx t xx t nn    (18) maximizing the determinant of the information matrix (xtx) is equivalent to minimizing the determinant of the dispersion matrix (xt x)−1. 1t t x)(x 1 xx   (19) table i. the design space considered in this study material parameters geometric parameters input parameter e gpa σy mpa k mpa n t mm rp mm rd mm wd mm θ1 (ο) maximum 210 525 1585.4 0.48 6 20 20 100 126.9 minimum 67.34 60 164.12 0.06 1 2 1 40 53.22 b. generate the training points using fe simulation the first step in generating the training points is to build an accurate fe model of the air bending process using the design space obtained from the previous stage. figure 2 shows a schematic of fe model.  fig. 2. schematic diagram of the finite element model. the material is assumed to be isotropic and homogeneous. the fe analysis is simplified to a 2d plane strain. a 4-node, iso-parametric, arbitrary quadrilateral plane-strain element is applied. this element uses bilinear interpolation functions by activation of the assumed strain formulation. the strain hardening is defined by swift’s eq. which is given by: nk )( 0   (20) the equivalent plastic stress s is described by swift’s exponential hardening law, based on the material’s consistency k, the equivalent plastic strain e , and the hardening exponent n. the input parameters influencing the amount of springback are the modulus of elasticity, the strain-hardening coefficient n, the yield strength σy, and the geometrical parameters. the geometrical parameters include engineering, technology & applied science research vol. 6, no. 5, 2016, 1200-1206 1203 www.etasr.com khadra and el-morsy: prediction of springback in the air bending process using a kriging metamodel the thickness of sheet t, radius of punch rp, radius of die rd, width of die wd, and bending angle θ1. the developed metamodel can be represented by: 1 ( , , , , , , , , ) y p d d e k n t r r wq s qd = (21) c. metamodel building in this study, two metamodel techniques were used, kmm and rsm. two training datasets were generated using the fe simulation stage. the first dataset is based on a linearinteractions (li) model. a model for two variables can be given by: 0 1 1 2 2 12 1 2 y b b x b x b x x= + + + (22) the second dataset is based on the full quadratic (fq) model. for example, a quadratic model for two variables is 2 2 0 1 1 2 2 12 1 2 11 1 22 2 y b b x b x b x x b x b x= + + + + + (23) for validation, the metamodels use a dataset, which is different from the above selected datasets to create the metamodels. the study was performed using a combination of selected datasets and different regression functions for kriging to find the best metamodel for the prediction of the springback angle in the air bending process. the results are presented for the following kriging metamodels: • kriging metamodel with a constant and an exponential correlation function (p0exp) • kriging metamodel with a 1st-degree polynomial and an exponential correlation function (p1exp) • kriging metamodel with a 2nd-degree polynomial and an exponential correlation function (p2exp) d. metamodel validation the accuracy of the metamodel is influenced by the metamodel type as well as the quality and quantity of the training dataset. the metamodels should be validated before being used as substitute models by comparing the metamodel results. in this study, useful means to determine the accuracy and the predictive capability of the metamodels are the normalized root-mean-squared error (nrmse), the normalized maximum absolute error (nmax), and the statistical correlation (r2). ( ) ( ) 2 2 1 2 1 1 m i li m i li y y r y y = = = å å  (24) ( ) ( ) 2 11 2 1 m ii m ii y y nrmse y = = = å å  (25) ( )2 1 max 1 i m i li y y nmax y y m = = -å  (26) where y and y  are measured and predicted values. additionally, y  is the mean of the actual function values at m test points. the larger the r2, the more accurate the metamodel. the lower nrmse and nmax, the more accurate the metamodel. the r2 and the nrmse provide a measure of the overall accuracy, while the nmax is a measure of the local accuracy of the model. to provide a reliable accuracy, the validation set must be large enough and spread out over the design space. iv. discussion of the results figure 3 shows the training points that are space-filling for two factors, the yield strength and the bending angle before springback θ1. from the histogram figures, the improvement in the space filling capabilities can be observed when the fq model is used. the selected design points are closely and uniformly distributed through the design space. table ii summarizes the coefficient of determination (r2) for the full quadratic and linear interaction models 40 60 80 100 120 140 0 100 200 300 400 500 600 b en d in g a n g le ( ) yield strength (mpa) training points (fq) testing points 40 60 80 100 120 140 0 100 200 300 400 500 600 b en d in g an gl e ( ) yield strength (mpa) training points (li) testing points fig. 3. the datasets based on (a) fq and (b) li models. from the results in table ii, it can be observed that the model in which examples were selected based on the fq model shows a higher correlation coefficient when compared with the model in which examples were selected based on the li model. engineering, technology & applied science research vol. 6, no. 5, 2016, 1200-1206 1204 www.etasr.com khadra and el-morsy: prediction of springback in the air bending process using a kriging metamodel finally, the model with examples selected based on the fq model reached a significant level (0.0012 in the case of p2exp), which is more reliable than the model based on the li model (0.026 in the case of p2exp). therefore, the fq model shows a better fit when compared to the li model, and the r2 values for the full quadratic models are satisfactory. table ii. coefficient of determination r2 model li fq rsm 0.9165 0.9945 p0exp 0.9694 0.9852 p1exp 0.9696 0.9879 p2exp 0.9740 0.9988 figure 4 shows the relationship between the normalized error and the metamodel type for both the fitted li (fig. 4a) and fq (fig. 4b) models. fig. 4a refers to the nmax and fig. 4b refers to the nrmse. the accuracy of all of the kriging metamodels and the rsm model is greater in the case of selecting examples based on the fq model than on the li model. there are large differences in the normalized error between the fq model and the li model. from fig. 4a, it can be observed that when selecting examples based on the fq model the best model with the minimum nmax is the p2exp followed by the rsm. 0 0.2 0.4 0.6 0.8 n m a x li fq p0exp p1exp p2exp rsm metamodel 0 0.03 0.06 0.09 0.12 0.15 n r m s e li fq p0exp p1exp p2exp rsm metamodel fig. 4. the relationship between normalized error and metamodel type for both trained models. figure 5 shows the result of the metamodel-predicted springback angle versus the actual fem. fig. 5a, 5b and 5c refer to the kmm of p0exp, p1exp and p2exp, respectively. fig. 5d refers to the rsm model. for accurate prediction, all of the points should lie on the 45° line. in the case of p0exp and p1exp, the prediction of the kriging metamodel is not accurate compared with p2exp and rsm, as shown in figs. 5c and 5d. in the case of rsm and p2exp, all of the points are close to the 45° line. the lines representing ± 5% accuracy are drawn to show the percentage error in the prediction. from fig. 5c, it can be observed that all of the predictions are within ±5% accuracy. the maximum absolute error in the prediction of springback is 2.8%. fig. 5d shows the best rsm predicted springback versus the simulated fem prediction. it can be observed that out of 50 predictions, most of the predictions are within ± 5% accuracy; seven predictions are within ± 10% and one prediction is outside the ±10% accuracy. 0 5 10 15 20 25 0 5 10 15 20 25 r s m p re d ic ti on fem prediction 10% 5%(a) p0exp 0 5 10 15 20 25 0 5 10 15 20 25 r s m p re d ic ti o n fem prediction 10% 5%(b) p1exp 0 5 10 15 20 25 0 5 10 15 20 25 r s m p re d ic ti o n fem prediction 10% 5%(c) p2exp 0 5 10 15 20 25 0 5 10 15 20 25 r s m p re d ic ti on fem prediction 10% 5%(d) rsm fig. 5. the metamodel predicted springback angle versus simulated fem results. the straight lines are confidence intervals (cis). v. conclusions in this study, the kriging metamodeling approach was implemented to predict the springback angle for the sheet metal air bending process. a comparative analysis of different metamodel schemes based on the kriging predictions has been conducted. on the basis of the computational results, the metamodels proposed avoid a great number of time-consuming evaluation processes and have significant merit in the aspect of accuracy. the kriging metamodels selected using a d-optimal design based on the full quadratic model are able to provide more accurate prediction of the springback than the metamodels based on the linear-interactions model. the kriging metamodel with a 2nd-order polynomial trend function and an exponential correlation function provides a minimal normalized error compared with alternative metamodels investigated in this paper; this error compares the prediction of the springback angle by the metamodels and the finite element simulation outputs. the springback angle of sheet-metal engineering, technology & applied science research vol. 6, no. 5, 2016, 1200-1206 1205 www.etasr.com khadra and el-morsy: prediction of springback in the air bending process using a kriging metamodel forming can be efficiently predicted using the kriging 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properties of al 6061-t6 alloy shatha m. rajaa institute of technology baghdad, iraq hassan a. abdulhadi institute of technology baghdad, iraq khairallah s. jabur institute of technology baghdad, iraq ghusoon r. mohammed institute of technology baghdad, iraq abstract—this work investigates the influence of artificial aging and solution heat treatment on the hardness and tensile strength (mechanical properties) of al 6061-t6 alloy. for this investigation, several aluminum 6061-t6 alloy specimens were prepared following the astm 176000 recommendations. the prepared specimens were heated for 1 hour at 500ºc before being water-quenched. the procedure for artificial aging was performed for 1, 2, 3, and 4 hours at 190ºc before being slowly cooled in air. several mechanical and characterization studies were performed on the treated specimens, including an investigation on their microstructure, tensile strength, hardness, and x-ray diffraction pattern. from the results, the strength and hardness properties of the specimens were found to be generally improved, even as the best features were obtained after 2 hours of artificial aging. keywords-heat treatment; al alloy 6061 t6; mechanical properties i. introduction the 6xxx group of al alloys has received much research attention due to their great technological potential, as well as their exceptional strength enhancement following precipitation hardening. these alloys are commonly employed in the construction and automotive sector. the metastable precursors of the equilibrium phase are precipitated in a process that involves one or more complex sequences. their chemical content, heat treatment parameters, and casting conditions greatly influence their extrudability and determine their microstructure. this implies that the properties of several aluminum alloys can be manipulated through specific heat treatment processes. the heat treatment can be executed either through solution heating (sh) or through artificial aging (aa). in the sh process, the alloy is heated to a temperature range of 400 ºc-530ºc, before water quenching at ambient temperature, while aa or simply “hardening” is performed at about 200ºc (in case of the group 6xxx of al alloys). the temperature for age hardening usually ranges from 160°c to 200°c [1-3]. aluminum alloys subjected to sh treatment are believed to have varying mechanical properties which account for their varying machinability. the stability and corrosion resistance of these materials can be improved by the addition of magnesium and silicon. several mechanical properties exhibited by the 6xxx group of aluminum alloys are attributed to the type of treatment (solution, aging time and temperature) they are exposed to [4, 5]. the impact of heat treatment on the mechanical and microstructural features of alloys has been extensively studied. authors in [1] investigated and reported the influence of precipitation hardening on the microstructural and mechanical attributes of 6xxx-group, 6061, 6063 and 6082 al alloys. the alloys were subjected to a 12-h heating in a furnace at a temperature of 565°c before being water quenched. the heated and cooled specimens were further exposed to aa for 98h at 175°c. the microstructural and mechanical properties of the studied samples were noted to be unaffected during aa as a result of the prior precipitation strengthening process. in [6], authors investigated the effect of combining different specified cold working and precipitation hardening procedures on the tensile strength of 6061 al alloy. the results showed that the application of a single aa process at 180°c for 4h improved the strength of the studied specimens, while a double aging process had no influence on the mechanical features of the specimens. additionally, the pre-aging process had a counteractive effect on the subsequent precipitation process on the material. these changes in the mechanical features of the specimens were attributed to the microstructural developments due to the conflicting influence of hardening by precipitation, work softening, and strain hardening processes on the samples. authors in [7] studied the mechanical properties of the 6061t6 al alloy at ambient temperature under various pre-thermal histories that represent an electron beam welding process. during the study, a fast-heating device was fabricated to deliver a controlled application of thermal loadings on the tensile samples. from the tensile tests conducted, it was observed that the yield stress decreased at rt when the optimum temperature limit was reached and when there was decrease in the heating rate. these differences in the mechanical properties were attributed to the microstructural changes that were evidenced by transmission electron microscopy. furthermore, authors in [8] studied the quench sensitivity of the mechanical properties of 6061 and 6069 al alloys by determining the relationship between quench delay time and the mechanical properties at varying temperatures in the range of 200°c to 500°c. from the study, it was reported that the quench sensitivity of 6069-t6 was higher compared to that of 6061, and this was attributed to the differences in their composition. the study also provided more information on the quench sensitivity of the conventional 6061 alloys. in the present study, our aim is to investigate the influence of aa time on the mechanical properties of al 6061 t6 alloy. ten rec all sev sel ma 50 bef in spe gri 80 al on dis aci the val wh dia engineerin www.etasr a. specim several spec nsile strength commendation b. specim the chemica oy was studied c. catego the specime veral groups a tabl specimen cate a b c d e d. heat tr solution hea lected for th aterial was in 0°c before b fore re-heating e. micros an optical m the microstruc ecimens for inding using s 0. the sample 2o3 solution. f the specimen stilled water + id + 1ml of h f. hardne a vickers ha e hardness pr lues (hv) were 1.854hv   here p is the ameter (mm). ng, technology r.com ii. exper en preparatio cimens of the test as show n of astm.17 fig. 1. ten en characteri al content of d using an ar rization of spe ens were cat s presented in le i. categ egory b s s s s not reatment at treatments he al-6061 a n t6 condition being water q g to for 1, 2, 3 tructure exam microscope wa cture of the ba microstructur sic emery pap es were later p furthermore, a ns using kelle + 2.5ml of nit hf). ess test ardness testing roperty of the e calculated us 2( ) p d  eexerted load y & applied sci rimental wor on al-6061 alloy wn in figure 76000. nsile test specime ization f the studied rl spectromete ecimens tegorized afte table 1. gorization of sp condition of s base metal witho sht for 500°c an sht for 500 °c an sht for 500°c an sht for 500°c an te: sht = solution heat t6 and art alloy. the as n. it was hea quenched at , and 4h at 190 mination as utilized to o ase metal after ral analysis per of grades olished with a an etching pro er’s reagent c tric acid + 1.5 g machine was e specimens, sing the follow (kg) and d ience research raj rk y were prepare 1 according t en aluminum al er. er preparation pecimens specimen out treatment nd aa for 1h nd aa for 2h nd aa for 3h nd aa for 4h t treatment, aa = artifi tificial aging s-received al at-treated for room temper 0°c. observe the ch heat-treatmen were prepare 120, 350, 500 a cloth soaked ocess was perfo containing 95m 5ml of hydroc s used to inves while the har wing equation: (1) is the penet h v jaa et al.: aging ed for to the l-6061 n into icial aging were l-6061 1h at rature, hanges nt. the ed by 0, and in the ormed ml of chloric stigate rdness tration amb mac 2m nan pre 606 an i u vol. 8, no. 4, 20 g time effects g. tensile the tensile s bient temperat chine. a load mm per minute. h. x-ray d the xrd pa no-lab of the a. specime the chemica sented in tabl table ii elements w si fe cu mn mg cr zn al b. microst the microstru (a) (d) fig. 2 c. hardnes table iii pres 61 alloy. d. tensile the tensile st instron 11 table iii. catego ultimate tensile s yield stress elongatio hv hardness ( 018, 3113-3115 on the mechan test strength of the ture with the a of 20kn was . diffraction (xr attern of the sp university of iii. en compositio al content of le ii. . chemical w% observe 0. 0. 0. 0.1 1.0 0. 0.1 re tructural exam ucture of the sa ( 2. specimen’ ss test sents the obse test trength of the 25 tension ma mechanical ry stress (mpa) s (mpa) on % (kg/mm2) 5 nical properties e specimens w aid of an inst s applied at a d rd) pecimens was technology, b results on f the studied l content of aled value stan 60 40 30 0 120 m 010 20 0 180 m em. mination amples is pres (b) s microstructure erved hardness specimens, as achine is presen l properties of t a b 332 387 285 309 10 8 95 118 3114 s of al 6061-t6 was determin tron 1125 ten deformation ra s determined a baghdad, iraq al-6061 allo -6061 (% wt.) ndard value 0.40-0.80 max 0.70 0.150-0.40 max 0.150 0.80-1.20 0.04-0.350 max 0.250 rem. sented in figur (c) (e) at 100x s values of th s determined u nted in table i the specimens c d 432 342 315 304 6 8.2 121 117 alloy ned at nsion ate of at the . oy is re 2. he alusing iii. e 336 292 8.5 110 fig t6 fea thr tho gav cre mg pat un tw res sam fin on str engineerin www.etasr e. xrd te the xrd pa gure 3. fi the effect of 6 al alloy wa atures of the rough the arti ose of the base ve the best s eated by the g6si7) which tterns (figure iformly distrib o hours, whil sulted in a r mples compar nding agreed w e hour (spec rengthening of ng, technology r.com est attern of the e ig. 3. x-ray p iv. d f aa time on t as investigated examined allo ificial aging p e metal. it was strengthening magnesium a appeared cl e 3). the p buted in the le their coarse reduction in red to those with previous r cimen b) rev f the specime y & applied sci examined spec (a) (b) (c) (d) phases of the spec discussion the mechanica d in this repo oys were foun process (tabl s observed tha likely due t and silicon el learly in the particles of t microstructure ening after th the mechanic after 2 hour reports [9, 10] vealed less im en compared t ience research raj cimens is sho imens al properties of ort. the mech nd to be imp e iii) compar at time of two to the hard p lements (mgs x-ray diffr those phases e of the alloy hree and four cal features o rs (figure 2). ]. artificial ag mprovement o to those treate h v jaa et al.: aging own in f 6061 hanical proved red to hours phases si and action were y after hours of the . this ging at on the ed for two pha gen obv har attr hin the this pro har be arti stre [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] vol. 8, no. 4, 20 g time effects o hours likely ases. the β p nerally harder vious from ta rdness of the ributed to the dered the disl presence of s s study are con aluminum 6 ocess of artific rdness value o achieved thr ificial aging ti ength and hard g. mrówka-no and heat treatm alloys”, archiv pp. 98-107, 201 n. r. prabhu s treatment on s composites”, b 2010 m. n. hawas, “ aa6061-t6”, j 152, 2013 c. f. tan, m. r aluminum alloy 3, pp. 276-286, h. demir, s. g aluminum alloy 2009 m. mansourine working and ag alloy”, transac no. 9, pp. 2072 d. maisonnette heat treatments 6061 aluminum no. 6, pp. 2718 m. kassner, p. 6061-t6 and 6 2011, article id c. ravi, c. wo stability of al14, pp. 4213-42 ] v. massardier microstructural its thermoelectr 2924, 2000 ] m. murayama, processes in a 1537-1548, 199 ] g. edwards, k sequence in al 3893-3904, 199 ] r. ahmad, m. mechanical and the gas metal design, vol. 32 018, 3113-3115 on the mechan y due to the phase in the and less duc able i that the e alloy. the precipitation location glide. maller precipi nsistent with p v. co 6061 alloys c ial aging with f the 6061alum rough a 2-hou ime of more t dness of the ma refer owotnik, “influen ment on microstruc ves of materials s 10 swamy, c. s. ram strength and abra bulletin of materi “effect of ageing journal of kerba r. said, “effect of y 6061-t6”, chian 2009 gunduz, “the eff y”, materials & d ejad, b. mirzak ging treatment on ctions of nonferr 2-2079, 2012 e, m. suery, d. n s on the microstr m alloy”, material 8-2724, 2011 geantil, x. li, 069-t6 aluminu d 747198, 2011 olverton, “first-p -mg-si–(cu) prec 227, 2004 r, t. epicier, evolution of a 60 ric power”, acta , k. hono, “pre al-mg–si alloys” 99 . stiller, g. l. d l-mg–si alloys”, 98 a. bakar, “effe d microstructure p arc welding cold 2, no. 10, pp. 512 5 nical properties microstructur internal stru ctile than the ere was an im e experienced inherent in t . hardening is itates. the obs revious report onclusion can be streng hin two hours. minum alloy o ur artificial a than two hour aterial. rences nce of chemical cture and mechan science and engin mesh, t. chandra asive wear beha ials science, vol g time on adhes ala university, vo f hardness test on ng mai journal o fects of aging on design, vol. 30, khani, “influence mechanical beha rous metals soci nelias, p. chaudet ructure and mech s science and en “a study of the um alloys”, journ principles study o cipitate”, acta m p. merle, “cor 061 aluminum all materialia, vol. e-precipitate clus , acta materialia unlop, m. j. cou acta materialia ct of a post-weld properties of aa d metal transfer 20-5126, 2011 3115 s of al 6061-t6 re of the α a ucture of allo α phase [1]. mprovement in d hardening the material w s most effecti served behavio ts [11-13]. gthened throu an increase i of about 27.4% aging process rs can decreas composition va nical properties o neering, vol. 46, ashekar, “effect o avior of al6061. 33, no. 1, pp. sive wear of al ol. 11, no. 4, pp precipitation hard of science, vol. 3 n machinability of no. 5, pp. 1480 of sequence o avior of 6061 alum iety of china, vo , t. epicier, “eff hanical propertie ngineering: a, vo e quench sensitiv nal of metallurgy of crystal structu materialia, vol. 5 rrelation betwee loy and the evolu 48, no. 11, pp. sters and precip a, vol. 47, no. uper, “the precip a, vol. 46, no. 1 d heat treatment a6061 joints weld method”, mater alloy and β ys is it is n the was which ive in ors in ugh a in the % can s. an se the ariation f 6xxx no. 2, of heat -sic p 49-54, l alloy p. 145dening 36, no. f 6061 0-1483, f cold minum ol. 22, fects of es of a ol. 528, vity of y, vol. ure and 2, no. en the tion of 2911pitation 5, pp. pitation 11, pp. on the ded by rials & microsoft word 3-2872_s2_etasr_v9_n5_pp4591-4595 engineering, technology & applied science research vol. 9, no. 5, 2019, 4591-4595 4591 www.etasr.com khoso et al.: investigation of building failure indicators identification of building failure indicators ali raza khoso department of civil engineering, mehran university of engineering & technology, jamshoro, pakistan aliraza.khoso@faculty.muet.edu.pk jam shahzaib khan department of civil engineering, quaide-awam university of engineering, science & technology, pakistan jam_shazaib@hotmail.com rizwan ullah faiz school of civil engineering, faculty of engineering, universiti teknologi malaysia, malaysia rizwantn16@gmail.com muhammad akram akhund department of civil engineering, isra university, hyderabad, pakistan akhund@42gmail.com aftab ahmed department of civil engineering, isra university, hyderabad, pakistan aftab.sohail19@gmail.com faizullah memon public health engineering department, government of sindh, mirpurkhas, pakistan fiaz.memon.1996@gmail.com abstract—a most frequent problem in the construction industry of pakistan is the failure of structures, especially buildings, before their expected design life. structural failure in buildings at the time of construction or after completion may result in human casualties, waste of money, social disturbance, and clashes, and claims between stakeholders. many researches have already been conducted about key causes which lead a structure to fail at later stages. this research is pursuing to analyze early building failure indicators (bfis) in pakistan. indicators and causes emerged from a thorough literature review, past projects, and site visits of various projects in pakistan. the causes were grouped in sets of bfis with the consent of structural experts. the collected data were analyzed in spss using mean value. critical reasoning and conceivable recommendations are suggested by the opinion of experienced stakeholders having worked at various projects in pakistan. the identification of these indicators is a key interest research topic for the country, as it would possibly reduce the failures of buildings in the future, saving lives, money, time, and conflicts among stakeholders. keywords-building failure indicators (bfi); construction projects; pakistan; structural failure i. introduction a structure may be a building, bridge, dam, retaining wall, sluice gate, etc. constructed from individual, interconnected, interrelated elements that are formed together with a system that can resist applied external load. this definition applies to much of what is seen in nature such as a fern leaf, an oak tree, shrub with ribbed branches, spider webs, etc. [1]. structures are used for a wide variety of purposes, such as residential, institutional, commercial, industrial, and transportation. if any of the operational activities goes wrong or out of schedule, then it will lead to failure of the project [2] resulting in human casualties, delay, cost overrun, environmental disturbances, etc. [3]. building failure is defined as a human act, or omission of occurrence or performance, lack of success, nonperformance, insufficiency, loss of strength, and cessation of proper functioning or performance [1, 4, 5]. obviously, a building must be structurally safe, and the floors must be capable of resisting any normally imposed loads [4, 6]. defects can be the results of design errors, manufacturing flaws, defective materials, improper use or installation of materials, lack of adherence to the design, or any combinations among the above mentioned causes [6]. initially, the causes reported on the uncertainties associated with structural failure during construction or after competition were divided into two groups: natural and man-made hazards [7]. since no location is safe from natural disasters, efforts can be made to improve human errors up to a certain extend in order to avoid failures. in the past, many structural failures caused numerous human casualties, cost overrun, delays, contractor bankruptcies, etc. [3, 8]. authors in [9] investigated the projects’ failure in the perspective of cost escalation in pakistan. similarly, regarding road projects, authors in [10, 11] studied cost related problems in pakistan. authors in [12] investigated the projects structural issues in different countries including pakistan and found that cost overrun and relevant failures are major problems. several studies have been conducted to examine the events that precipitated such failures [7, 8, 10]. structure failure is still a challenge for the construction industry, especially in developing countries, since the adaptation of sustainable construction through sustainable practices is very stagnant [13]. construction in western countries concerns code practice compared to the pakistani construction industry. during 20052006 a large amount of snow was accumulated in roofs in central europe, and more than 50 cases of roof failure were reported in germany, austria, and poland [14]. but these failures could be avoided if structures were designed to sustain extreme snow loads, as regulated in codes of constructions and build on sustainability grounds [8, 16]. authors in [1] report that the most common causes which lead a structure to failure are climate conditions, structure location, construction materials, building type, change in use, poor building maintenance, faulty design, corruption in construction, and lack of supervision. failure in structure may occur at three stages of the building’s life: construction, operation, and rebuilding, thus every stage failure may result in potentially dangerous unexpected accidents [17]. there is a stage wise failure of 58% corresponding author: ali raza khoso engineering, technology & applied science research vol. 9, no. 5, 2019, 4591-4595 4592 www.etasr.com khoso et al.: investigation of building failure indicators at construction, 39% at operation and 3% at rebuilding, hence the risk of accidents is about 65%-70% more during the construction stage [1, 18]. the impact of failure can be reduced in structures by providing good quality materials, sufficient manpower, good design and other favorable conditions that may increase the life of the structure [19]. the current research attempts to find those critical causes which lead to failure in structure within their designed life of the structure, in the local construction industry of pakistan. in this regard, this study is a novel investigation, especially in local construction projects, since a limited number studies are done in this matter. the examined critical causes responsible for structural failures in building construction of pakistan are thus confined in the set of building failure indicators (bfis). the identification of such indicators is helpful for concerned stakeholders to reduce any kind of failures in the future. the significance of these causes was analyzed by the statistical software package spss using the mean method of the average index (ai). the data were collected on a five-point likert scale. the mean values of critical causes were found with the help of spss as mentioned in table ii. ii. research methodology the aim of this research is to investigate the causes of structure failures in pakistan and to identify and study bfis. initially, an extensive literature review was carried out to determine the causative factors leading to building failure. the secondary data were gathered from published sources. to gather the primary data various construction sites in pakistan were visited. comprehensive sessions were conducted with experienced structural engineers and practitioners, construction managers, and site engineers to investigate the causative factors leading a structure to failure. structured interviews with experts were carried out and finally 28 causative factors were identified. those were grouped into seven bfis. the questionnaire was developed and distributed to gather responses from technical personnel working in the construction industry. the results were then analyzed in spss, using the ai technique [15-20]. the grouping of significant causes was merged into bfis and their causes and recommendations were examined at the second stage. iii. data collection and analysis a total of 115 questionnaires were distributed amongst professionals and experts. the response rate of the questionnaire survey is illustrated in table i. figures 1-2 show the demographics of the respondents. figure 1 shows that clients, contractors, and consultants were targeted to gather the opinion of professionals. figure 2 exhibits their experience level. table i. questionnaire statistics questionnaires distributed 115 questionnaires received 71 positive questionnaires for analysis 65 response rate 56.5% fig. 1. respondents’ status fig. 2. respondents experience table ii. critical causes of building failure in pakistan indicators for building failure code material ai mi 1 low-quality construction materials 4.68 mi 2 erroneous quality control of materials 4.04 mi 3 outlying material quarry from the construction site 2.59 quality control qci 1 inadequate quality assurance by officials 3.81 qci 2 erroneous soil testing 3.77 qci 3 inadequate quality assurance system of construction 3.77 qci 4 deterioration of structural components due to delay in construction 3.09 design code dci 1 contravening with standards codes of constructions 4.04 dci 2 indistinctive specifications 3.54 dci 3 construction of debile structures 3.50 dci 4 on-site alterations 3.04 structural inadequacy sii 1 precluding soil in contact 4.04 sii 2 inadequate connections 4.00 sii 3 uneven soil settlement 3.95 sii 4 miscalculating loads 3.86 sii 5 inappropriate installation of structural members 3.81 project management pmi 1 ineffective functioning of machinery 3.68 pmi 2 incompetent project manager 3.54 pmi 3 frivolity of consultancy staff 3.54 pmi 4 inadequate communication among structural team and contractors 2.90 pmi 5 indecisive to suggest remedial measures for unanticipated problems 2.86 man power mpi 1 inefficient project team 3.50 mpi 2 absence of key members 3.50 mpi 3 unproductive labor 3.45 mpi 4 untrained field inspector 3.14 mpi 5 unqualified staff for modern technology 2.36 risk ri 1 monetary turmoil 3.77 ri 2 natural disasters 2.86 engineering, technology & applied science research vol. 9, no. 5, 2019, 4591-4595 4593 www.etasr.com khoso et al.: investigation of building failure indicators iv. results and discussion the present study explores the critical causes of building failure in pakistan construction projects. the examined causes were grouped into seven major classifications called bfis. the mean sum of each category is calculated to prioritize the indicator. the analysis reveals that structural inadequacy indicator (sii) is the utmost cause in pakistan with the highest mean sum of 3.93, followed by material (mi) and quality control (qci) indicators with 3.77 and 3.61 mean sum respectively. the other major indicators responsible for building failures in pakistan are exhibited in table iii. table iii. most critical bfis in pakistan building failure indicators ai structural inadequacy (sii) 3.93 material (mi) 3.77 quality control (qci) 3.61 design code (dci) 3.53 risk (ri) 3.32 project management (pmi) 3.30 man power (mpi) 3.19 a. structural inadequacy indicator (sii) every civil engineering structure is constructed on the ground, withstanding several loads. for this structure, the consideration of soil and its properties are essential to investigate. the purpose of soil is to withstand the load of the structure coming from the structural skeleton through the foundation. the soil requires sophisticated tests and experiments before constructing any structure over it. the bearing capacity of the soil and the chemistry of its layer must be investigated in the form of deep soil investigation. the load coming over the structure transpires the settlement in soil. unequal settling of piers or footings of a foundation is an undesirable situation called uneven settlement which should be avoided. it occurs when the soil beneath the structure, contracts, expands or shifts away. uneven settlement can be caused by drought conditions, vibration in nearby areas, improper load distribution, type of soil, etc. unfortunately in pakistan no such detailed investigations are made on projects. the concept of deep soil investigation and several preliminary important parameters of structures are ignored. the interviews conducted with structural engineers and soil experts unfold that the owners of most of the projects or even government agencies are not fully aware of structural basic parameters and deep soil investigations. another problem is the allocation of limited funds. for large projects, the client always hires, directly or indirectly, geotechnical consultants. but when the funds are limited, these investigations are fully omitted or narrowed down. the experts suggested that deep soil investigation is very essential and no design should be allowed to execute without it by a competent authority. moreover, there is a strong need for social awareness regarding the importance of structure design and soil investigation. therefore, an awareness program must be organized by the government. finally, sufficient funds must be allocated for this important part of every project. b. material indicator (mi) it is a major issue in pakistan construction projects. no doubt, specifications are provided to contractors during the contract, but it is mostly observed that the strictness towards quality control is poor. during the visit of a few projects, the engineers agree that the specifications are provided, but due to poor consultancy at the site, contractors are free to use poor materials. although poor quality materials are cheaper, the durability of the building is reduced. there is no benefit of good design if the prime part of construction, i.e. materials, is of poor quality. so, proper material selection, handling and carrying out work as per standards will only lead towards safe implementation. in this regard, engineers interviewed at the site suggested that the client should follow a strict monitoring process. the client should not fully trust the consultants and should make routine visits at the site and call frequent meetings with consultants. c. quality control indicator (qci) improper quality control system will put no benefits to the project. defects and failure in constructed projects can result in very large costs. even for minor defects, reconstruction may be required, which directly results in delay and augmented cost. construction projects are composed of numerous interconnected activities, therefore it is not possible to construct a project lacking in terms of quality. to minimize quality control defects, certain teams and groups should be assigned with this task. it has been observed that quality is one of the leading issues in construction and results in poor-quality structures that fail before their design life. generally, this is the sole responsibility of consultants on behalf of clients to look after. but, as discussed above, several times this part is ignored. a qualified engineer must be always available during the construction. but unfortunately, the sites are often handed to labor and engineers and other technical staff is not available even during the major execution part. experts suggested that the clients themselves should visit the site on a regular basis and take timely progress reports from consultants to avoid this problem. more serious attitude from the client side could only open the direction of improvements. d. design code indicator (dci) small carelessness could lead to serious problems and failure. a good team of workers, good quality materials, and advanced machinery, are useless if, work is not carried out according to standardized codes and specifications. this indicator is one of the most neglected parameters in most projects in pakistan except the majority of mega projects. the contractors are not thorough in acquiring the true meaning of codes and specification resulting in feeble structures. it was revealed from the interviews that at construction site almost no one is aware of the standard codes. even the engineers who are qualified experts don’t take this part seriously. they follow their own traditional methodology just to save time and effort. the survey highlighted that many serious issues have occurred because of this cause. the experts reported that unfortunately, pakistan has no proper codes for construction. the pakistan building code is found to be not effective or trustworthy while mostly bs and aci codes are followed by the industry. even engineering, technology & applied science research vol. 9, no. 5, 2019, 4591-4595 4594 www.etasr.com khoso et al.: investigation of building failure indicators the proper use of such codes is not being followed in the construction leading to serious structure failures. this study suggests that the contractors need to train workers to operate as per specifications, and managers need to describe the complete tasks with clear concepts, before the start of any work. this will improve the skills of labor and put structure towards a safe site of construction. e. risk indicator (ri) the problem of the budget is one of the most common causes in every project. however, this is one of the leading and most common factors in almost every project in pakistan. several projects are found incomplete in major cities waiting for funds to be delivered. in some cases, even when the funds are released, the constructors are not getting their due payment at the right time due to other problems. these issues were found in most of the visited projects. the experts highlighted several funding problems that may become top risks for the constructors. the experts suggest that detailed planning must be conducted before executing the projects on these important monetary issues and certain rigid clauses must be added in the contractual agreement between parties. apart from monetary risk, natural disasters are very common in different forms. a natural disaster can happen everywhere, but the severity of its effects can be reduced. large buildings and other structures can survive powerful earthquakes if they are built with some level of flexibility. pakistan is exposed to several potential disasters including floods, earthquakes, landslides, etc. the experts during the interviews explained that pakistan is not working on natural disaster prevention effectively. in addition, during the design, no one is taking this part seriously. there is a need for detailed study on natural disaster management. if studies of this kind are implemented in pakistan construction industry, the effect of natural disasters can be reduced considerably. the experts further pointed out that there is no check and balance for the structures against safety in such severe conditions. proper construction methodology is not being followed and this may cause collapsing of structure even under small scale disasters. thus, due care is required to avoid large scale disasters in pakistan. f. project management indicator (pmi) the management is of utmost important in every project. the management of stakeholders, the correct and rightly communication and machinery and its proper usage and suitability are equally important for a project. it is noticed that suitable machinery is often not being installed on the sites. the success of any project depends on the shoulders of the project manager, but unfortunately, incapable and inexperienced managers are common. due to this, many project parameters are overlooked and cause many problems at a later stage. the right communications and relationships with stakeholders and especially with the consultants are most highlighted by experts. they suggest that the overall importance of project management and its core purpose is still not well understood to many construction stakeholders. therefore, it was suggested that the project owner must be careful in this phase and ask from the constructors to provide detailed planning. g. man power indicator (mpi) man power plays a key role in a successful project. one cannot expect a positive and successful project from an imbalanced team. the stable combination of man power in terms of key personnel and other technical staff is highly demanding for a project. it was observed in the interviews that the hired labor on most of the projects is not well trained and the shifting of the technical staff and labors is a common issue. it was reported from the experts that the continuous changes of the project team are an issue. the absence of qualified professionals is a common problem. the hiring of unskilled filed inspectors and labors further hits the project negatively. therefore, the latest use of technology is not seen on most of the projects. workers feel more comfortable with traditional methods. the professionals recommend the constructors must train teams for different projects thus suitable training sessions must be ensured for all personnel. in order to avoid the problem of brain drain sufficient incentives other than their salary must be ensured and certain contractual agreements can further help to reduce this issue’s impact. v. conclusion the present study investigates the core causes of structural failures in pakistan. after a literature review, structural experts in pakistan were interviewed. the detailed analysis from the collected data presented the critical causes of structural building failure in pakistan. the investigated causes were then grouped into a set of bfis. structural inadequacy (sii), material (mi), quality control (qci), design code (dci), risk (ri), project management (pmi), and man power (mpi) are the major indicators responsible for several failures in building projects in pakistan. it has been concluded that the building sector of pakistan is not following proper construction standards. quality is a major issue in every project in pakistan. soil testing and deep soil investigation are being neglected, proper structural design is not followed and implemented, and loads over the structure are not assessed properly. moreover, sometimes natural disasters also damage the structures due to improper risk mitigating approaches. the second important aim of this research was to consider recommendations on such failure cause. through detailed interviews with experts, possible solutions were provided and explained. the research findings can assist a client in executing future projects. the investigated bfis of this study have gone some way towards contributing to the level of understanding and further avoiding any miss happens in the future. acknowledgment authors would like to express their gratitude to the mehran university of engineering & technology, jamshoro, pakistan. references [1] m. k. parfitt, “why buildings fail: are we learning from our mistakes?”, buildings, vol. 2, pp. 326–331, 2012 [2] k. wardhana, f. c. hadipriono, “study of recent building failures in the united states”, journal of performance of constructed facilities, vol. 17, no. 3, pp. 151–158, 2003 engineering, technology & applied science research vol. 9, no. 5, 2019, 4591-4595 4595 www.etasr.com khoso et al.: investigation of building failure indicators [3] m. 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cross-event survey of survivors”, 14th world conferecne earthquake engineering, bejing, china, october 12-17, 2008 [18] m. buitrago, j. sagaseta, j. m. adam, “effects of sudden failure of shoring elements in concrete building structures under construction”, engineering structures, vol. 172, pp. 508-522, 2018 [19] un, global sustainable development report, 2015 edition, advance unedited version, un, 2015 [20] a. r. khoso, a. h. memon, a. a. pathan, m. a. akhund, “solid waste management issues in hyderabad city”, mehran university research journal of engineering and technology, vol. 37, no. 3, pp. 653-662, 2018 microsoft word 34-3547_s_etasr_v10_n3_pp5790-5795 engineering, technology & applied science research vol. 10, no. 3, 2020, 5790-5795 5790 www.etasr.com yatnalli et al.: review of inpainting algorithms for wireless communication application review of inpainting algorithms for wireless communication application veeramma yatnalli electronics and communication engineering department jss academy of technical education bengaluru, karnataka, india b. g. shivaleelavathi electronics and communication engineering department jss academy of technical education bengaluru, karnataka, india k. l. sudha department of electronics and communication engineering dayananda sagar college of engineering bengaluru, karnataka, india abstract—digital image inpainting is a technique of restoring large removed /damaged regions of an image with the data from the surrounding pixels of the removed region. the issue of image restoration with inpainting techniques occurs commonly in computer vision/image processing when unwanted objects have to be removed from images, for filling cracks in photographs, etc. digital image inpainting approach is an active field of research in two significant applications of wireless communication: image compression and image recovery from a damaged image due to errors in a wireless channel. this work presents a brief survey of different image inpainting techniques and their contributions to different wireless communication applications. keywords-inpainting; image compression; multipath fading; median filter; rs code i. introduction inpainting is a method of manually reconstituting paintings in a manner that the repaired region is imperceptible to the observer who is not acquainted with the image before damage. the term inpainting is lent from the arts, to describe a damaged picture recovery method. in this context, the inpainting paradigm may be considered from the following perspectives: • inpainting for image processing solutions: the main goal is to restore removed or damaged regions propagating information from undamaged areas, e.g. restoring cracks in photographs, removing overlaid text on advertisements, occlusion recovery, etc. • inpainting based image coding: signal processing solutions in which the main objective in exploiting digital inpainting techniques is to increase significantly the compression performance in comparison with standard coding solutions, e.g. jpeg and jpeg 2000 for images, and h.264/avc (advanced video coding) for video. hybrid inpainting methods are those which include both inpainting and compression standards (e.g. jpeg). • restoration of an image received through fading channels: the intention of applying inpainting algorithms for image enhancement and restoration (which are important) is to interpret pictures received through fading channels more easily. a literature study is presented in this paper, presenting inpainting algorithms for image restoration, image compression, and image recovery at the decoder side on images received through a multipath fading channel. ii. inpainting algorithms a. partial differential equation (pde) image inpainting the first digital inpainting was based on diffusion inpainting technique, in which the missing information in an image region was completed by diffusing image data into the missing region after identifying the surrounding region. the aim was to design an automatic digital inpainting in order to reproduce the basic techniques employed by professional restorators. basically, inpainting algorithms are based on the variational method and partial differential equations (pdes). image inpainting algorithms built on pdes use a mathematical model to treat image problems. by numerical representation, a pde is iteratively solved to propagate the information smoothly from surrounding areas to the areas that are to be inpainted along isophotes. isophotes are traces on which gray values are equal. the process of inpainting is terminated until the gray values in the region reach a steady state. some early work related to inpainting, based on level lines, was carried out in [1]. the problem was considered as a disocclusion problem. t-junctions were defined in an edge map which they intersect the occluding objects. digital image inpainting concept in completely digital sense was initiated in [2]. in this work, the interpolation method based on laplacian was discussed. the propagated information along the isophotes’ directions were estimated by the rotated image gradient by 90 degrees. authors in [3] extended the work of [2] and proposed a variational method of inpainting based on pdes. the pdes were devised and the solutions obtained were based on level sets of the intensity function. a method based on the outlines of the navier-stokes was introduced in [4]. the major drawback of [2-4] was that their inability to reconstruct regions containing textures. inpainting methods like those require complex energy functionals and solutions were found from the assumptions of bounded variation (bv) model. for non-texture images, theoretical image models popularly known as the tv (total variation) model were adopted in [5], in which the tv algorithm was extended to the curvature-driven diffusion (cdd) model. every pde-based inpainting model is more corresponding author: veeramma yatnalli engineering, technology & applied science research vol. 10, no. 3, 2020, 5790-5795 5791 www.etasr.com yatnalli et al.: review of inpainting algorithms for wireless communication application appropriate for carrying out small, non-textured target regions. the limitation of the diffusion process is that the blurring becomes obvious when filling larger image regions. the above methods have limitations in recovering large damaged regions. b. texture synthesis and exemplar based image inpainting anisotropic diffusion is related with the inpainting field [6] and keeps the boundaries intact across the inpainted region to avoid the edges getting blurred. when focusing on small regions, simpler models can be considered instead of specific mathematical geometrical theories. one such method [7] performs convolution using a simple 3×3 coefficient filter on the missing region to diffuse valid/known information to the missing domain pixels. to solve this problem, a diffusion barrier must be considered to stop the algorithm, where the changes in contrast are more significant. to remove film scratches in a video, the method based on spacio-temporal inpainting and proposed in [8] restores the image pixels in scratch areas by considering image pixels of a undamaged region in the same image frame and also considering the frames which are adjacent to it. texture synthesis is a technique related to inpainting. basically it deals with selecting and synthesizing the texture into the domain of inpainting. the texture’s most inherent property is its regularness. a regular (deterministic, periodic, structured) texture is characterized by a basic element (texel or texeton) which is regularly placed on lattice or a grid. examples of regular textures are floor tiles, brick walls, and sand while smoke is non-regular. every texture contains some deterministic and stochastic properties. texture synthesis algorithms test a variety of textures from periodic to most random types. in 1999, authors in [9] found a different approach to handle texture synthesis. they adopted a nonparametric way of developing texture from an initial seed. this was the first kind of image-based texture synthesis. they copied pixels of the image itself in the synthesis process. in [10], a specific algorithm was proposed to synthesize natural textures. in raster manner, every pixel has four previously synthesized neighbor pixels. the algorithm reduces the search space of every pixel to only four neighbors. if the left neighbor pixel is synthesized from (x; y) on the sample, its candidate pixel is (x+1; y). these methods favored copying neighbor pixels to preserve larger texture structures. it was considered as an intermediate step just before the development of patch based synthesis. they gave better and faster results for structure related problems. the first patchbased texture synthesis algorithm developed was image quilting [11], in which the sample of the image is treated as grid with a block size of 32×32, with 4 to 8 pixels overlapping each other by adjacent blocks. the blocks are picked up from the image sample texture to fit in a raster scan. in the search process, regions that are overlapping on left and top of a new block are matched. authors in [12] sought for better quality in reducing errors by finding boundaries between patches. graphcut synthesis procedure is not fast, but it provides very good results. variational inpainting and texture synthesis algorithms are separate fields of research, though their intention is to solve related problems. inpainting aims at filling an inpainting region by preserving image smoothness, texture synthesis generates new texture from a sample. authors in [13] carried out image completion by applying structure inpainting and texture synthesis simultaneously to fill image holes. in their work, image decomposition divides the image into structured regions and texture parts. inpainting is performed on the structure image and texture synthesis on the texture image. the two images are recombined to get the final result. the methods in [2, 9] are appropriately applied for damaged regions, and the final result is obtained by adding both. the algorithm is a bit slow, gives blurry results due to diffusion, and is limited to small gaps. however, it is the first pioneered work that combines the strengths of both structural inpainting and texture synthesis. similar efforts were made in [14], based on adaptive nd tensor voting. it provides good results, and large damaged areas can be repaired, but the technique requires the implementation of image segmentation. the most exquisite contribution in this field is a work popularly known as exemplar-based image inpainting [15] in which an sampling patch-based inpainting method for region filling and object removal method which is simpler and faster was proposed. inspired by [9], it selects locations at boundary gaps, then image blocks are matched with the copies searched from known regions to complete the gap. the method performs the synthesis task through a best-first filling strategy that depends entirely on the priority values assigned to each patch. after finding the patch with the maximum priority, the most similar patch is chosen from the intact region to replace it, and then the priority values are updated to continue the above steps repeatedly. except from exemplar-based methods, the following methodologies were applied to image inpainting and satisfactory results were obtained. authors in [16] applied discrete global optimization technique which was timeconsuming. an image inpainting based on context-aware patch-based was presented in [17]. the image was divided into patches with variable sizes. this encoding method maintained the consistency of neighboring patches. to complete the large gaps surrounded by varieties of structure and texture, authors in [18] achieved both significant speed and performance. to limit patch selection, a method on patch subspace learning which was sensitive to the initial values was proposed in [19]. to enhance the similarity between matching patches, runtime is reduced by the coherent direction-aware patch alignment scheme [20]. a patch-based image completion [21] with patch transformation guides the filling process. from the works available on inpainting, pde based interpolation inpainting technique provides a simple and appropriate solution for filling the missing region’s information while texture information can be used to grow the lost texture data. a state-of-the-art method which uses dense multi-scale fusion network with self-guided regression loss and geometrical alignment constraint for image fine-grained inpainting which highly improves the quality of produced images is proposed in [22]. iii. inpainting algorithms for image compression inpainting techniques exploit the redundancy which is inherent in images and achieve lossy compression. they aim at finding very compact representations in such a way that the results approximate the original image. some prominent characteristics extracted from the images are skipped at the engineering, technology & applied science research vol. 10, no. 3, 2020, 5790-5795 5792 www.etasr.com yatnalli et al.: review of inpainting algorithms for wireless communication application transmitter side. at the receiving end, they are recovered after using assisted inpainting techniques. the scheme in [23] is based on the framework of image patches for compression. from the compression point of view, a huge set of image patches can be represented with different shapes, sizes, and orientations. however, the restricted patches must be regular ones, e.g. squares with a fixed size. this idea stems from the texture synthesis technique, in which the texture is synthesized by sampling the best match patch from the known region. the reconstruction is only required for the removed regions by virtue of the preserved ones, which is virtually the inpainting problem carried out at a patch level to complete the image. several pde-based and texture synthesis image inpainting techniques in achieving image compression are discussed in [24-28]. pde-based methods are alternatives to transformbased methods such as the jpeg standard [29] which employs discrete cosine transform (dct), or its successor jpeg 2000 [30] that uses wavelet transform. in [31], implementing inpainting for compression is explained. in this approach, image regions dropped at the encoder intentionally describe the concise image. it also elaborates the transmission of image over multipath fading channels and reconstruction details about filling of the damaged or missing blocks in the propagation of compressed images (jpeg). since it is difficult for inpainting methods to recover large regions that were dropped, edgebased inpainting techniques were developed for image compression [32, 33]. edge information is extracted from dropped regions and later is converted into a compressed form which assists the inpainting process at the decoder. by recovering more edge regions, the edge-based inpainting achieves higher compression ratio. authors in [34] address an adaptive patch-based inpainting algorithm for recovering image blocks in block-based image coding. in order to achieve compression, a generic parameter assistant inpainting (pai) method exploits different distributions of an image region in [35]. a sparse representation of these parameters assists reliable inpainting at the decoder side to recover large dropped regions. the inpainting techniques proposed in [36, 37] have the ability to reproduce the lost information faithfully. this enables the user to intentionally or voluntarily remove some regions in an image, i.e. by providing the user the ability to select the regions that he wishes to remove. large dropped regions are restored utilizing the correlations between image blocks. to continue to achieve high cr and the required level of visual quality, a hybrid image compression method which embeds inpainting schemes into current transform based compression standards is considered to get the benefits of both algorithms. in [37], large dropped areas are recovered by filling various incomplete image regions, which consists of completely different descriptions of structures and surrounding backgrounds. this method achieves compression ratio up to 50%. a recent work on image compression with image inpainting based on pde approach concentrated on spatial and tonal data optimization has been published in [38]. this paper also includes a comprehensive survey on pde-based image compression. although pde-based methods are an alternative solution to transform-based methods such as the jpeg standard, from the earlier research publications, the conclusion can be drawn that combination of pde based inpainting and jpeg provides better solutions and wider range of compression ratios. the pde approach concentrated on spatial and transform-based compressions provides better results in terms of compression ratio without any need of assistant parameters. multi-scale convolutions that sample content at multiple scales to assist with inpainting are introduced in [39]. the proposed inpainting and compression models are jointly trained to show that inpainting reduces the amount of information. iv. image transmission over multipath fading channels and reconstruction in digital wireless communication systems, the multipath channel reflects signal at multiple places. consequently, the signal traverses to reach the receiver along several paths in addition to the direct signal. the channel impairments influence the transmission phenomenon in such a manner that errors occur in bursts and the damaged pixels become inconsistent with their adjacent pixels which are received correctly. from the reports in literature, the average loss rate of packets in propagation environment is 3.6% and they occur in a bursty manner. critically, we might lose an entire line of an image. when image or video data are transmitted over noisy channels, some data are either missing or incorrect due to channel transmission errors or channel impairments. images are prone to impulse (stuck-pixel) noise and other interference noises. based on the impulse noise pixel’s value, it can be either categorized into fixed valued impulsive noise (salt and pepper noise spn) or random valued impulsive noise (rvin). in suppressing impulse noise, filters designed with median, minimum, and maximum are special types of orderstatistics which are non-stationary (shift-variant) and nonlinear. the contribution of inpainting algorithms based on variants of median filter deals with the removal of two types of impulse noise. these filter structures (adaptive median filter and directional weighted median) are capable of restoring images that are affected by both rvin and spn under extreme conditions and provide adequate results in the regions containing both slow variations in gray and high contrast edges. many algorithms have been proposed in the past to remove impulse noise. authors in [40] deal with the basics of median filter, the development of a weighted median filter and the theory of optimal weighted median filter for speech processing, weighted medians as robust predictors in dep coding and quincunx coding for image sequence restoration. the technique reported in [41] efficiently restores images which are corrupted due to mixed impulse and gaussian noise. in [42], the median based filters are widely used because of their effective noise suppression capability and high computational efficiency. the technique uniformly replaces the gray-level value of every pixel by the median of its neighbors in the sliding window. consequently, some desirable details are also removed, in particular, when the window size is large. for the removal of random-valued impulse noise, the directional weighted median (dwm) filter [43] and the multi-stage directional median (msdwm) filter [44] provide better solutions. the filter presented in [45] attempts to eliminate spn effectively. the filter in [46] uses a new impulse detector, which is based on the difference between the current pixel and its neighbors aligned with four main directions. the impulse engineering, technology & applied science research vol. 10, no. 3, 2020, 5790-5795 5793 www.etasr.com yatnalli et al.: review of inpainting algorithms for wireless communication application detector addresses the challenge of detecting noisy samples and the output of noise removal technique is applied only to the affected image pixels. the algorithm is fast and provides good results in both edges and smooth regions. it is also understood from [47] that different kinds of errors such as spn and rvin can be removed from the variants of median filters such as amf and dwmf by employing the surrounding information of the lost data. by diffusing the median information of pixels from the outside to the inside of the inpainted region, the important properties of edges are preserved. bilateral filtering, produces unsatisfactory results. to process edge pixels and image pixels separately, rank ordered absolute differences (road) technique is incorporated by adding a third component to the weighting function and the resulting filter is a trilateral filter. the filter in [48] preserves the edge details. an inpainting algorithm based on directional weighted median (dwm) filter/ adaptive median filter [49] de-noises the affected pixels (rvin or spn) when applied on images received through multipath fading channels (rayleigh and rician). the algorithm diffuses the median value of pixels from the exterior area into the inner area to be inpainted and thus preserves edges and fine details. a unique noise removal algorithm is proposed in [50] which detects up to 75% noise density using region based detection and filters. progressive image transmission is difficult in the presence of a noisy channel, mainly due to the propagation of errors during the decoding of a progressive bit stream. excellent results for this problem can be obtained through combined source channel coding techniques [51-53]. in [54, 55], the authors discuss the image transmission approach and demonstrate the performance of the scheme when implemented over mobile fading channels. a two-stage strategy is described. the first stage comprises of error control coding (ecc) and the second of an inpainting tool for image reconstruction. visually plausible images are obtained from the combination of these two stages over a range of doppler frequencies. in [56], an inpainting algorithm applied to recover the errors from compressed data transmission through wireless sensor networks (wsns) has been proposed. the algorithm’s efficacy to restore the missing information of lossy received images has been experimentally proven. authors in [57] propose a method for completing lost blocks in h.264 compressed image transmission. the losses can be recovered from inpainting and the synthesis of textures combination provided that the features are not completely lost in the received image. in [58], copy-and-paste network, based on deep neural network framework, video inpainting is performed by utilizing the additional information from other video frames. the network is trained in such a way that it copies the contents in reference frames and pastes them to fill the gaps/holes in the target frame. the material available in [59] is helpful for channel implementation and in creating various multipath fading channel models. to compare ecc, details related to forward error correcting code such as reed solomon code are referred from [60]. v. modelling multipath fading wireless channels two kinds of mobile fading effects describe the channel characteristics: large and small scale fading [60, 62]. rayleigh or rician fading are examples of small-scale fading. when multiple reflective paths are encountered, the received signal envelope is expressed through a probability density function (pdf) related to a rayleigh or a rician distribution [62]. author in [63] summarized eight descriptions regarding rayleigh fading channel simulations consisting of one deterministic model and seven statistical models. to model the rayleigh fading channel, the models in [64, 65] have been widely used. the software simulations to model multiple path fading channels are important components of wireless systems simulations. authors in [66] discuss various ways of modeling fading channels (flat) in matlab. the details are helpful in modeling many of the fading channel effects with different test conditions. vi. conclusion in this paper, the contributions of pure inpainting are reviewed. a detailed review of pde-based image compression methods which constitute a challenging application of inpainting algorithms is conducted. several variants of filtering techniques are studied for impulsive noise removal. error control coding technique was selected for 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9, no. 4, 2019, 4338-4341 4338 www.etasr.com vidal-silva et al.: jpiaspectz: a formal requirement specification language for joint point interface … jpiaspectz: a formal requirement specification language for joint point interface aop applications cristian vidal-silva faculty of economics and administration, catholic university of the north, antofagasta, chile cristian.vidal@ucn.cl trung pham faculty of economics and business, university of talca, talca, chile tpham@utalca.cl luis alberto urzua faculty of health, santo tomas university, chile talca, chile lurzua@santotomas.cl erika madariaga faculty of engineering, bernardo o’higgins university, santiago, chile erika.madariaga@ubo.cl franklin johnson computing and information department, university of playa ancha, valparaiso, chile franklin.johnson@upla.cl luis carter ingenieria civil industrial, facultad de ingenieria, universidad autonoma de chile, chile luis.carter@uautonoma.cl abstract—aspect-oriented software development (aosd) solves a few issues of the object-oriented software development (oosd) approach and adds a few more concerning modules and their relationships. join point interface (jpi) is an aosd methodology that by the definition of the interface between advised artifacts and aspects solves associated aosd issues to get software with a high modularity level. looking for a jpi software development approach, this article proposes and exemplifies the use of jpiaspectz, an extension of the formal aspect-oriented language aspectz for the software jpi requirement specifications. mainly, jpiaspectz looks for a concept and model consistency in a jpi software development process. since the main jpi characteristics are the joining point interfaces definitions, i. e. explicit associations definition between aspects and advised modules, thus, by jpi, classes are no longer oblivious of possible interaction with aspects, and aspects, for their action effectiveness, do not depend anymore on signatures of advisable module components. jpiaspectz fully supports these jpi principles. as jpi application examples, this article shows the formal requirements specification for classic aspect-oriented and jpi examples, along with describing the advantages and disadvantages of this language. keywords-jpiaspectz; jpi; aspectz; aspects; join point interface i. introduction aosd permits modularizing crosscutting concerns in oosd stages [1]. because aosd was born at the objectoriented (oo) programming stage, to reach a complete transparency of concepts and design in the aosd process seems a complex task. looking for a transparency in the aosd process, different proposals of modeling language extensions already exist to support aosd such as aspectoriented uml use case diagrams [2] and aspect-oriented uml class diagram [3]. authors in [4] present a survey of aspectoriented uml language proposals. nevertheless, only a few articles about formal aspect-oriented languages for requirement specification exist so far. authors in [5, 6] describe and apply aspectz, authors in [7, 8] describe ooaspectz, and authors in [9] illustrate the use of an aspect-oriented alloy version. authors in [10] report that a double-dependency between base modules and aspects exists in traditional aosd solutions. to solve this issue, the works of [10-12] propose and apply join point interface (jpi) instances between classes and aspects. thus, with the purpose of obtaining jpi solutions and getting transparency of concepts in stages of the aosd-jpi process, this article proposes and applies jpiaspectz, an extension of ooaspectz [7, 8], for requirements specification of jpi software applications. ii. aspect oriented programming and jpi authors in [1] proposed aspect-oriented programming (aop) to modularize crosscutting concerns as aspects in oop. aspects advise classes like events, i.e. aspects introduce behavior and structural elements such as methods and attributes into classes. nevertheless, as authors in [10] indicate, aop presents implicit dependencies between advised classes and corresponding author: cristian vidal-silva engineering, technology & applied science research vol. 9, no. 4, 2019, 4338-4341 4339 www.etasr.com vidal-silva et al.: jpiaspectz: a formal requirement specification language for joint point interface … aspects. first, aspects define pointcut rules (pcs) for advisable class behavior, and, as a result, instances of those classes are entirely oblivious of possible changes in their components, methods, and attributes. second, aspects can be ineffective or spurious for signature changes on advised methods of target classes. as authors in [10, 11] mention, the last issue is known as the fragile pointcut problem. authors in [10] indicate that traditional aop like aspect-j solutions compromise the independent development of base code and aspect modules since developers of base code, and aspects must obtain a global knowledge about all program components and their associations, i.e. they must know all the details about aspects, classes, and their relations. to isolate crosscutting concerns and get modular aop programs without the mentioned implicit dependencies, authors in [10] describe the jpi programming methodology. jpi introduces the idea of join point interface on classic aop. like classic aop [10, 11], for jpi applications, aspects represent crosscutting functionalities, but without pcs. aspects in jpi only present their implementation of join point interfaces. besides, in jpi, non-oblivious advised classes exhibit explicit join point interfaces, that is, classes know about potential changes on their methods. figures 1 and 2 [10] illustrate dependencies between aspects and classes in classic aop and jpi applications, respectively. fig. 1. base and aspects modules association in classic aop. fig. 2. base and aspect modules association in jpi. iii. jpiaspectz principles z [13] and object-z [14] are formal languages for software requirement specification. specifically, z is the classic formal specification language without the direct support of objectoriented abstractions like classes and inheritance, and object-z is an extension of z to support oosd principles. likewise, aspectz [5, 6] and ooaspectz [7, 8] represent z extensions for requirements specification of aop applications and their integration with z and object-z, respectively. considering jpi ideas, this article describes jpiaspectz, an ooaspectz extension to model jpi applications and its integration with object-z. the main elements of a jpiaspectz formal specification are: base modules: unlike aspectz and ooaspectz which present oblivious base modules, jpiaspectz base modules are specified as object-z class modules which include an exhibit rule concerning advisable operations of advised class instances. figure 5 shows the structure of a jpiaspectz class schema, jpi schema, and aspect schema. since the declaration part of an object-z operation schema permits defining operation parameters, when looking for a transparency of concepts and design for jpi applications, an exhibit rule is definable in two sections: first, exhibits jpi for the join point interface instances which the class exhibits, and second, a set of conditions for the join point event. so far, jpiaspectz considers basic aop and jpi conditions for dynamic and static crosscuts, i.e. call operation, execution operation, logic connectors &&, ||, !; args (arguments list) to identify catchable method arguments, this(object) to determine the object on which the advisable method operates, and target(object) to identify the object owner of the advisable method. join point interface: in jpiaspectz, operation schemas starting with the jpi initials represent join point interfaces (jpi schemas) for a system specification. for example, figure 6 shows jpiupdatex and jpiupdatey. furthermore, jpi schemas only present a declaration section to indicate their list of parameters. aspects: jpiaspectz aspects-schemas are like objectz class diagrams labeled with the phrase aspect. aspect-schemas include state schemas to define attributes and invariants and operation schemas for the schema advice operations. as a distinction regarding class schemas, aspect-schemas can indicate the occurrence time for operations (before, after, and around) to specify the kind of advice. semantically, aspectschemas advise operation schemas, usually for inserting new methods in the advised classes, for adding behavior at the beginning, around, and end on advised operations schemas. from advised method schemas and associated aspect schemas, jpiaspectz permits obtaining woven schemas. it is relevant to highlight the modular evolution from aspectz, ooaspectz, and jpiaspectz schemas as figure 3 [5], figure 4 [7, 8], and figure 5 respectively present. note that for the first two, base schema, z operation schema and objectz class schema, aspectz aspects operate over oblivious advised elements. nevertheless, for the jpi philosophy, in jpiaspectz, the aspects and classes know about interfaces to implement and exhibit, respectively. fig. 3. classic aspectz aspect schema as figure 5 describes, jpiaspectz considers advisable classes which exhibit advisable operations in their state schema (figure 5(a)), join point interface (jpi) schemas as a link between advisable classes and aspects adviser, and aspects who engineering, technology & applied science research vol. 9, no. 4, 2019, 4338-4341 4340 www.etasr.com vidal-silva et al.: jpiaspectz: a formal requirement specification language for joint point interface … will advise those classes in the ocurrence of join points in objects of the class (figure 5(b)). fig. 4. ooaspectz aspect schema. (a) (b) fig. 5. base and aspect modules association in jpiaspectz: (a) advised class schema, (b) jpi and aspect-schemas iv. application examples the painting system [7] is a classic ao example that presents classes point and line which are shapes, and each line instance is composed of a few point instances. the main idea is to illustrate the updating screen process as an external behavior. an illustration of the uml class diagram can be seen in [7], which presents an interface shape to enclose point and line classes, and each line instance is composed of two point instances, p1 and p2. note that for classic ao, both classes obliviously wait for advices from the aspect updatesignaling concerning the pointcut rules definition outside the classes. a jpi uml class diagram that includes the main jpi elements for the painting system, that is, non-oblivious classes which exhibit jpi instances and aspect that implements those interfaces can be seen in [15]. clearly, for exhibits and implements rules, classes are not more oblivious, and aspect does not directly refer to classes: classes exhibit jpi and aspects implement those interfaces. we recommend reviewing [15] for more details about jpi. as a jpi example, [10, 12] show a shopping session ‘running example’ of an e-commerce system (shoppingsession system). this example presents a join point interface checkingout, a class shoppingsession that exhibits checkingout and an aspect discount that implements checkingout for around kind of advice. (a) (b) (c) (d) fig. 6. painting system jpiaspectz formal specification (a) advised class schema, (b) advisable class point, (c) advised class line, (d) jpi instances and aspect-schema v. experiments and results figure 6 presents the jpiaspectz specification for the painting system: a shape interface, point and line classes, jpi instances jpiupdatex, jpiupdatey, and jpimove, and aspect aspect1painting. point and line classes exhibit jpi instances, class point exhibit jpiupdatex and jpiupdatey, and class line exhibit jpimove, whereas aspect1painting implements these jpi instances. figure 6 presents the model’s consistency. engineering, technology & applied science research vol. 9, no. 4, 2019, 4338-4341 4341 www.etasr.com vidal-silva et al.: jpiaspectz: a formal requirement specification language for joint point interface … vi. conclusions after reviewing jpiaspectz examples for the painting and shop-pingsession systems, we can argue a clear consistency exists between jpi models and jpi code. furthermore, jpiaspectz includes jpi practical details such as exhibits and association among jpi components, that i.e., aspects, jpi, and classes to represent complete jpi applications using called external advises is possible. thus, jpiaspectz permits formal models of jpi applications without closure join points [16]. this article presented jpiaspectz that permits specifying formal requirements for jpi applications, i.e. nondependent classes and aspects according to the jpi central principle. besides, this extended jpi abstraction demonstrates that consistency and transparency of models and concepts for a jpi software development process is attainable, specifically, a consistency between requirements and structural models, and requirements and code. to achieve real consistency between structural models and jpi solutions code modules seems direct. a formal proof of this consistency represents a future work scope for the authors. furthermore, considering future work, authors want to continue proposing extensions on jpiaspectz to model closure join points as well as more advanced dynamic crosscuts [16]. besides, we propose the developing of a jpiaspectz specification validation tool for automatic validation of jpiaspectz specifications. references [1] g. kiczales, “aspect-oriented programming”, acm computing surveys, vol. 28, no. 4, 1996 [2] i. jacobson, p. w. ng, aspect-oriented software development with use cases, addison wesley professional, 2004 [3] f. wedyan, s. ghosh, l. r. vijayasarathy, “an approach and tool for measurement of state variable based data-flow test coverage for aspectoriented programs”, information and software technology, vol. 59, pp. 233–254, 2015 [4] m. wimmer, a. schauerhuber, g. kappel, w. retschitzegger, w. schwinger, e. kapsammer, “a survey on uml based aspect-oriented design modeling”, acm computing surveys, vol. 43, no. 4, pp. 28:1– 28:59, 2011 [5] y. huiqun, l. dongmei, y. li, h. xudong, “formal aspect-oriented modeling and analysis by aspect-z”, 17th international conference on software engineering and knowledge engineering, taipei, taiwan, july 14-16, 2005 [6] c. v. silva, r. saens, c. del rio, r. villarroel, “aspect-oriented modeling: applying aspect-oriented uml use cases and extending aspect-z”, computing and informatics, vol. 32, no. 3, pp. 573–593, 2013 [7] c. v. silva, r. saens, c. del rio, r. villarroel, “ooaspectz y diagramas de clase orientados a los aspectos para la modelacion orientada a aspectos (msoa)”, ingenieria e investigacion , vol. 33, no. 3, pp. 66–71, 2013 (in spanish) [8] c. v. silva, r. villarroel, r. s. simon, r. saens, t. tigero, c. del rio, “aspect-oriented formal modeling: (aspectz + object-z) = ooaspectz”, computing and informatics, vol. 34, no. 5, pp. 996– 1016, 2015 [9] f. mostefaoui, j. vachon, “verification of aspect-uml models using alloy”, 10th international workshop on aspect-oriented modeling, vancouver, canada, march 12-12, 2007 [10] e. bodden, e. tanter, m. inostroza, “join point interfaces for safe and flexible decoupling of aspects”, acm transactions on software engineering and methodology, vol. 23, no. 1, pp. a:1–a:42, 2014 [11] e. bodden, “closure join points: block join points without surprises”, tenth international conference on aspect-oriented software development, porto de galinhas, brazil, march 21-25, 2011 [12] m. inostroza, e. tanter, e. bodden, “join point interfaces for modular reasoning in aspect-oriented programs”, 19th acm sigsoft symposium and the 13th european conference on foundations of software engineering, szeged, hungary, september 5-9, 2011 [13] j. woodcock, j. davies, using z: specification, refinement, and proof, prentice-hall, 1996 [14] g. smith, the object-z specification language, kluwer academic publishers, 2000 [15] c. v. silva, r. villarroel, “jpi uml: uml class and sequence diagrams proposal for aspect-oriented jpi applications”, 33rd international conference of the chilean computer science society, talca, chile, november 8-14, 2014 [16] s. apel, d. batory, c. kastner, g. saake, feature-oriented software product lines: concepts and implementation, springer, 2016 engineering, technology & applied science research vol. 8, no. 4, 2018, 3276-3281 3276 www.etasr.com kebbab et al.: frequency speed control of rotary travelling wave ultrasonic motor using … frequency speed control of rotary travelling wave ultrasonic motor using fuzzy controller fatima zohra kebbab department of electrical engineering laboratory dac hr ferhat abbas university setif i, algeria fatimazohra.kebbab@univ-setif.dz dalel jabri department of electrical engineering laboratory dac hr ferhat abbas university setif i, algeria dalel.jabri@yahoo.fr djamel eddine chouaib belkhiat department of physics laboratory dac hr ferhat abbas university setif i, algeria djamel.belkhiat@univ-setif.dz saâd belkhiat department of electrical engineering laboratory dac hr ferhat abbas university setif i, algeria belsa_set@yahoo.fr abstract—this paper proposes frequency speed control of rotary travelling wave ultrasonic motor (twusm), type daimler benz awm90-x motor. the control characteristics of twusm are complicated, highly nonlinear and varying in time. this can lead to deterioration of the performance of conventional controller such as proportional integral (pi). in order to achieve high control performance of the twusm, fuzzy logic controller (flc) has been designed and compared to the conventional pi controller. to validate the performance of the proposed flc, simulation of the speed response has been performed and analyzed for a varying load. the simulation results show that the flc has smaller settling time, smaller rising time and minimum error in steady state. furthermore, the fuzzy controller provides good results for large load variations. the frequency output of the controller has been validated with experimental measurements of awm90-x. keywords-nonlinear control; fuzzy logic controller; travelling wave ultrasonic motor type daimler–benz; awm90-x i. introduction twusms have structural and operational advantages compared to conventional electromagnetic motors, such as compact size, lighter weight, very low speed operation, high torque, nonmagnetic operation, freedom of constructional design, very low inertia, high speed response, possibility of electromagnetic noise reduction and miniaturization [1]. moreover, the settling time in ultrasonic motors is very short, fast response is one of the most important twusm advantages, which makes it suitable for applications with fast response demands such as robot actuators and auto-focus cameras. several types of ultrasonic motors have been suggested and designed in the last 25 years [2]. their operating principle is based on piezoelectric vibrations that convert electric energy to mechanical energy in the form of elastic vibrations [3]. it consists of two basic parts: the stator with piezoelectric ceramics, and the driven part (rotor). apart from the advantages of twusm, deriving mathematical model for twusms is a difficult task due to their complicated and highly nonlinear characteristics. in addition, the dynamic speed characteristics of twusm are time-varying due to the increase in temperature and depend on operating conditions such as driving frequency, source voltage and load torque [4, 5]. the speed control of twusms is one of the important issues under consideration [5-7]. three kinds of speed control strategies exist in the literature. the twusm speed can be controlled by the driving frequency, the phase difference or the voltage amplitude of the two excitation sinusoidal voltage of twusm. however, aimed at these problems, several researchers have opted for the driving frequency of the sinusoidal voltage as control variable [6–8]. there is no perfect control scheme for twusms. the ultrasonic motor speed controllers belong to several conventional and numeric controller types. a speed tracking control system using both neuro-fuzzy control and direct pulse width modulation for twusm has been developed in [8]. in the same way, authors in [9] used also a fuzzy neural network controller. authors in [4, 10, 11] studied a servo speed control system for travelingwave ultrasonic motor [4] and a servo position control for twusm [10] where fuzzy neural network was the control tool [11]. authors in [12] proposed a position control scheme for twusms. authors in [13] used h∞ strategy to control rotary travelling wave ultrasonic motor twusm while authors in [14] proposed an intelligent pid speed controller of twusm. in a nutshell, most of developed works for ultrasonic motors control focused on a motor of usr60 type. however, the speed control for daimler–benz awm90-x motor has rarely been explored so far, which motivated us to make this study as a continuation of our previous works [15-17]. the main contribution of this work consists to the design of a fuzzy logic controller to drive the speed of the daimler–benz awm90-x motor. the robustness of the proposed controller against load var com fl per has aw a. spe and ord ass      b. 1. ma cer c. ult sta sup sta not pre illu exc engineerin www.etasr riation is ve mparative stu lc and those rformed in thi s been valid wm90-x. basic assump the structur ecial. they in d the whole der to simpl sumptions mus the rotor is a the friction neglecting th the surface neglecting th coulomb fri between stato the friction system indep model struct the model o the model o ain modules: ramic, stator-r fig. 1. func model of the stator is the trasonic motor ator generates perposition of ator ensures a te that the sta esented as a ustrated in f citation system fig. 2. equations (1 ng, technology r.com erified in th udy, between obtained by is paper. fina dated with ii. mathe mptions re and drivin nclude many drive course ify the mod st be made: a rigid body, it material is vi he influence of of stator teeth he influence of iction law is or and 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ification. eve vailable, the mo uires less comp s study are def eans negative ero, pm mean he control str f fuzzy logic con 8 4.85 4.9 equency [hz] 3278 sonic motor usi ral gains in th iod. pi gain v r different load to controller. values. kt 100 gic controlle controller. f general behavi ing if-then inputs, output mbership func am [21] can be p function, we nce. the trian se they are ea computation be improved therwise, the f i.e. crisp outpu en though m ost preferred o putation time fined as {nb, e big, nm m ns positive me ategy of the m ntroller. 4.95 5 x 10 4 t= 0nm t= 2nm t=1.5nm ing … he pi values orques. er fuzzy ior of rules t and ctions e seen e can ngular asy to time. d by fuzzy ut by many one is [22]. nm, means edium motor con set and res eff mo are shi mo re equ a. are con res fro and tw tha val tes engineerin www.etasr fig. 6. fig. 7. sp v. s speed respo nsidered twu ttling time, ste d compared t sults of speed fectiveness of otor condition e: 570v is exc ift between th 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controller. the is equal to 3 e case of the c e proposed fl 2.5ms . speed without l 2 2.5 3 3.5 time [s] fuz re pi ience research kebbab et al.: f d from fuzzy gic fuzzy controlle discussion s analyzed fo parameters su re obtained fo ntroller. simu order to valida no load and l piezoelectric e and π/2 rad ameter values esented in tab the reference motor without ollers (fuzzy a nalysis of the s given in tab has better rise e settling time .5ms [23], we controlled mot lc, the moto load 5 4 4.5 x 10 -3 zzy ference speed h v frequency spee er or the uch as r flc ulation ate the loaded motor is the of the ble ii. speed t load and pi speed ble iii. e time of the e note or. to or was d c b. part trac resu co c. pro sim that abil var vol. 8, no. 4, 20 ed control of r ta resistances o ceramics ca capacity of rotor ine radiu effective mass of r rotor rig rotor atten friction coe distance between points of s number of wa frequency of r wavelen wave num contact zone antiresonance modal mass o transfer stator rig disturbance damping r table iii. ontroller ris pi fuzzy the first loa from the resp t 3.3 3.8ms m ck the referen umed in the ta table iv. ontroller rise pi fuzzy the second l at this stage oposed flc ag mulation result t the pi contro lity and only iation. 018, 3276-3281 rotary travellin able ii. sim of entries apacity f stator ertia us mass rotor gidity nuation efficient n the surface stator ave crests resonance ngth mbers e rigidity frequency of stator ratio a a gidity e factor ratios comparison p e time (ms) p 1.000 0.73 ad, 1.5nm. ponse plots sh ms , the propo nce speed. th able iv. comparison paramet e time (ms) pe 1.000 0.73 load,1.6nm. e of study, w gainst a load ts are illustrat oller lose its p the flc h∞ 1 ng wave ultras mulation param rp1=r cp1= cp2=7 cps1=0 cps2=0 jr=3.3436 rw=4 meff=113 mr=(meff+22 cr=30 dr=50 μ= α=4 n= 1 2 2res res   2   k= cn=850 1 2 2 ant ant    0m    21 1 1anta mcp    22 2 2anta mcp  1s resc   2s resc   ε1=ε2 ds1=ds2= of control sys parameters peak time (ms) 4.5 0.893 hown in figur osed flc driv he controller’s n of control sys ters (loaded mo eak time (ms) 4.5 0.893 we check the condition equ ed in figure performance in can be resisti 3279 sonic motor usi meters [17] rp2=5ω =7.8e-9f 7.87e-9f 0.42e-9f 0.428.e-9f 67e-0.004kgm2 0.5e-3m 3.93·10-3kg 2.8+3)·1e-3kg 00e3n/m 0e3ns/m =0.21 .5e-3m =11 32 43.365 e hz  w r m n  =2π/λ 00e6n/m2 3 2 43.425 e hz  .082kg     1/22 2 1res kgfs       1/22 2 2res kgfs   21s m n m 22es m n m 2=0.02 =10ns/m stems performa settling time ( 2.500 1.200 re 9(a), in zoo ve the twus s performance stems performa otor) settling time ( 2.700 1.100 robustness o ual to 1.6nm. 9(b). we can n terms of trac ing this param ing … 1/2 1/2 ance (ms) omed m to es are ance (ms) of the . the n note cking metric engineering, technology & applied science research vol. 8, no. 4, 2018, 3276-3281 3280 www.etasr.com kebbab et al.: frequency speed control of rotary travelling wave ultrasonic motor using … d. the third load 3.3nm the motor has been loaded with a big load larger than the torque that can be supported by the pi controller. from the results given in the figure 9(c), we note that the flc can drive, similar to the previous cases, the twusm to track the reference speed. in the range 2.5 3t ms ms  , the motor speed decreases under the load effect and then it increases to reach the reference speed. noting that for a large load, greater than 3.3nm, the twusm under flc diverges. this phenomenon, called pull out phenomenon, has been signaled in the literature [24]. it is due especially to the variation of the resonance frequency. finally, flc is more robust than the pi controller and it presents low error. therefore, it is well suited to this actuator type which can be employed for varying loads. fig. 9. rotor speed, loaded motor a) 1.5nm, b) 1.6nm, c) 3.3nm vi. simulation results and experimental data validation to ensure the good operation of the twusm, the motor should be driven with the antiresonance frequency to reach the maximum of its efficiency [25]. to determine the antiresonance frequency of the twusm awm90-x, the stator parameters were calculated with finite elemet method (fem), obtained from the recorded admittance curve of the stator. the admittance curve of the free-vibrating stator was recorded with the impedance analyzer with a step size of 10hz. figure 10 shows the resulting measured curve. from figure 10, the antiresonance frequency is equal to 43.425khz [25]. fig. 10. recorded admittance curve of awm90-x stator regarding the proposed twusm model, we can note that it was validated in our previous work [17] without control speed. in fact, the simulation frequency of the proposed model was equal to 43.425khz which is the same with the one obtained in experimental validation [25]. moreover, to validate the proposed controller, the frequency output of the flc is illustrated in figure 11. hence, the simulation frequency has been found equal to 44.6khz, which is closer to the experimental antiresonance frequency (43.425khz). this result validates the efficiency of the flc. fig. 11. frequency output of the flc vii. conclusion in this paper, the frequency speed control of the twusm, type daimler benz awm90-x, has been studied. the design of flc and pi controllers has been presented and discussed. to illustrate the efficiency of the proposed controllers to drive the twusm to track perfectly the reference speed, thorough simulations were performed. the obtained results have revealed that the flc controller performs better than the pi controller with very good tracking performance, namely low rise time, low settling time and high steady state accuracy. likewise, the flc controller seems more robust that the pi controller against load variations. finally, the frequency output of the flc has been validated with experimental measurements of the twusm awm90-x. references [1] d. zhang, s. wang, j. xiu, “piezoelectric parametric effects on wave vibration and contact mechanics of traveling wave ultrasonic motor”, ultrasonics, vol. 81, pp. 11-126 ,2017 [2] y. wang, w. huang, “a piezoelectric motor with two projections using two orthogonal flexural vibration modes”, sensors and actuators a: physical, vol. 250, pp. 170-176, 2016 [3] f. r. m. romlay, w. a. w. yusoff, k. a. m. piah, “increasing the efficiency of traveling wave ultrasonic motor by modifying the stator geometry”, ultrasonics, vol. 64, pp. 177-185, 2016 [4] g. bal, e. bekiroglu, “servo speed control of traveling –wave ultrasonic motor using digital signal processor”, sensor and actuators a: physical, vol. 109, no. 3, pp. 212-219, 2004 [5] a. gencer, “a comparative speed/position control technique based fuzzy logic control for travelling wave ultrasonic motor”, 7th international conference on electronics, computers and artificial intelligence (ecai), bucharest, romania, june 25-27, 2015 [6] t. senjyu, m. nakamura, u. urasaki, h. sekine, t. funabashi, “mathematical model of ultrasonic motors for speed control”, electric power components and systems, vol. 36, no. 6, pp. 637-648, 2008 [7] j. shi, b. liu, “optimum efficiency control of traveling-wave ultrasonic motor system”, ieee transaction on industrial electronics, vol. 58, no. 10, pp. 4822-4829, 2011 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 x 10 -3 0 50 time [s] (a ) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 x 10 -3 0 50 time [s] (b ) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 x 10 -3 0 20 40 time [s] (c ) reference speed fuzzy pi 3.4 3.6 x 10 -3 44 45 46 35 40 45 50 55 -30 -25 -20 -15 -10 -5 0 5 frequency[khz] a d m it ta n ce -[ db ] 0 1 2 3 4 5 x 10 -3 4.45 4.46 4.47 4.48 4.49 4.5 x 10 4 time[s] f re q ue nc y [h z ] engineering, technology & applied science research vol. 8, no. 4, 2018, 3276-3281 3281 www.etasr.com kebbab et al.: frequency speed control of rotary travelling wave ultrasonic motor using … [8] k. t. chau, s. w. chung, c. c. chan, “neuro-fuzzy speed tracking control of traveling-wave ultrasonic motor drives using direct pulsewidth modulation”, ieee transactions on industry applications, vol. 39, no. 4, pp. 1061-1069, 2003 [9] k. t. chau, s. w. chung, “servo position control of ultrasonic motors using fuzzy neural network”, electric power components and systems, vol. 29, no. 3, pp. 229-246, 2001 [10] g. bal, e. bekiroglu, s. demirbas, i. colak, “fuzzy logic based dsp controlled servo position control for ultrasonic motor”, energy conversion and management, vol. 45, no. 20, pp. 3139-3153, 2004 [11] t. senjyu, s. yokoda, k. uezato, “speed control of ultrasonic motors using fuzzy neural network”, journal of intelligent and fuzzy systems, vol. 8, no. 2, pp. 135-146, 2000 [12] t. senjyu, t. yoshida, k. uezato, t. funabashi, “position control of ultrasonic motors using adaptive backstepping control and dead-zone compensation with fuzzy inference”, ieee international conference on industrial technology, bankok, thailand, pp. 560–565, december 1114, 2002 [13] m. brahim, i. bahri, y. bernard, “real time implementation of hinfinity and rst motion control of rotary traveling wave ultrasonic motor”, mechatronics, vol. 44, pp. 14-23, 2017 [14] s. jingzhuon, l. yu, h. jingtao, x. meiyu, z. juwei, z. lei, “novel intelligent pid control of travelling wave ultrasonic motor”, isa transactions, vol. 53, no. 5, pp. 1670-1679, 2014 [15] f. z. kebbab, z. boumous, s. belkhiat, “traveling wave ultrasonic motor type daimler-ben awm90–x: modeling and simulation mechanical characteristics”, journal of electrical systems, vol. 1, pp. 24-29, 2009 [16] f. z. kebbab, z. boumous, s. belkhiat, “rotary ultrasonic motors: daimler-benz awm 90–x twusm motor, experimental and simulation mechanical characteristics”, journal of electrical systems, vol. 5, no. 4, 2009 [17] z. boumous, s. belkhiat, f. z. kebbab, “effect of shearing deformation on the transient response of a traveling wave ultrasonic motor”, sensors and actuators a: physical, vol. 150, no. 2, pp. 243-250, 2009 [18] k. premkumar, b. v. manikandan, “adaptive neuro-fuzzy inference system based speed controller for brushless dc motor”, neurocomputing, vol. 138, pp. 260–270, 2014 [19] a. prabaharan. e. balamurugan, “speed control of switched reluctance motor using anfis and ga”, international journal of advanced research in electrical, electronics and instrumentation engineering, vol. 5, no. 7, pp. 152-158, 2016 [20] v. m. varatharaju, b. l. mathur, “adaptive neuro-fuzzy speed controller for husteresis curent controlled pmbldc motor derive”, international journal of advances in engineering & technology, vol. 1, no. 4, pp. 212-223, 2011 [21] h. chaudhary, s. khatoon, r. singh, “anfis based speed control of dc motor”, 2nd international innovative applications of computational intelligence on power, energy and controls with their impact on humanity (cipech), ghaziabad, india, november 18-19, 2016 [22] n. muruganantam, s. palani, “adaptive neuro-fuzzy inference system based controller for high performance bldc motor using soft switching inverter”, journal of theoretical and applied information technology, vol. 49, no. 3, 2013 [23] e. bekiroglu, “microcontroller-based full control of ultrasonic motor with frequency and voltage adjusting”, sensors and actuators a: physical, vol. 141, no. 1, pp. 151-159, 2008 [24] b. matteo, modelisation et commande du moteur piezoelectrique a onde progressive, phd thesis, ecole polytechnique federale de lausanne, 2005 (in french) [25] g. kandare, j. wallaschek, “derivation and validation of a mathematical model for travelling wave ultrasonic motors”, smart materials and structures, vol. 11, no. 4, pp. 565-574, 2002 authors profile fatima zohra kebbab was born in algeria in 1982. she received an electrical engineering degree and a master's degree from the electrical engineering department, ferhat abbas university, setif 1, algeria, in 2003 and 2007, respectively. she is an assistant professor in the electrical engineering department, ferhat abbas university, setif 1, algeria. she works on the traveling wave motor. djamel eddine chouaib belkhiat was born in algeria. he is an associate professor in the department of physics at the ferhat abbas university, setif 1, algeria, where he is also a member of dac hr laboratory. he earned his bachelor of engineering degree in electrical engineering at ferhat abbas university, setif 1, algeria, master's degree in automatic control from the university of poitiers, france, and phd degree in automatic control from the university of reims champagne ardenne, france, in 2007, 2008, and 2011, respectively. his research interests lie in the area of monitoring and diagnosis of dynamic systems. he has published several research papers in scientific journals, international conferences, and book chapters. dalel jabri was born in tunisia. she is an associate professor in the electrical engineering department at the ferhat abbas university, setif 1, algeria, where she is also a member of dac hr laboratory. she earned her bachelor of engineering degree in electrical engineering in 2006, her master's degree in automatic control in 2007 at national engineering school of gabes, tunisia, and her phd degree in automatic control at the university of reims champagne ardenne, france and the university of gabes at 2011. her research interests lie in the area of robust control of nonlinear systems. she has published several research papers in scientific journals, international conferences, and book chapters. saad belkhiat was born in algeria. he received an electronic engineering degree from polytechnic school of algiers, algeria, in 1979. he has worked as an engineer in the control and automatic departments in the production industry and as an engineering professor in the department of electronics, setif, algeria. he received an mph degree from the electronics department, and phd degree in physics, from university of setif in 2001. he is fullprofessor in the electrical engineering department at the ferhat abbas university, setif 1, algeria. his research interests include electrical engineering materials and their applications such as piezoelectric materials, dielectric and surface science. microsoft word 10-2708_s_etasr_v9_n3_pp4125-4130 engineering, technology & applied science research vol. 9, no. 3, 2019, 4125-4130 4125 www.etasr.com aydogdu & levent: kalman state estimation and lqr assisted adaptive control of a variable loaded … kalman state estimation and lqr assisted adaptive control of a variable loaded servo system omer aydogdu eee department konya technical university konya, turkey oaydogdu@ktun.edu.tr mehmet latif levent eee department faculty of engineering, hakkari university hakkari, turkey. mehmetlatiflevent@hakkari.edu.tr abstract—this study actualized a new hybrid adaptive controller design to increase the control performance of a variable loaded time-varying system. a structure in which lqr and adaptive control work together is proposed. at first, a kalman filter was designed to estimate the states of the system and used with the lqr control method which is one of the optimal control servo system techniques in constant initial load. then, for the variable loaded servo (vls) system, the lyapunov based adaptive control was added to the lqr control method which was inadequate due to the constant gain parameters. thus, it was aimed to eliminate the variable load effects and increase the stability of the system. in order to show the effectiveness of the proposed method, a quanser servo module was used in matlab-simulink environment. it is seen from the experimental results and performance measurements that the proposed method increases the system performance and stability by minimizing noise, variable load effect and steady-state error. keywords-adaptive control; lyapunov method; lqr; kalman filter; vls system i. introduction estimating the state variables in state feedback control systems at trust values is very important in terms of system performance and efficiently working of the system. immeasurable state variables are generally obtained by the state observers. if the system is stable, the observer used is called a deterministic observer. otherwise, it becomes a random observer. luenberger and kalman type observers are widely used. luenberger observer (lo) belongs to the deterministic observer class and kalman filter (kf) to the random observer class. basic kfs can only be applied to linear random systems [1]. accordingly, kfs are expressed as a mathematical method that can minimize the disruptive effects and estimate the states by reducing the root-mean-square error. this filter’s structure is especially used in space and military technology, robotics and trajectory control applications, artificial neural networks and different hybrid controller designs [2-5]. lqr that aims to minimize the errors that occur in state output value can also be called as linear optimal state feedback control in time-invariant systems. this is a technique that increases system performance and stability [6]. at the same time, the optimal control input is produced by using controller gain coefficients computed by the lqr method. and so, a response curve close to the desired reference value is obtained [7, 8]. lqr control is used with a kf that estimates the real states of the system in noisy environments in state feedback servo control systems [9, 10]. lyapunov stability criteria and mit rule are frequently used methods in designing traditional adaptive control systems to increase the system stability in time varying systems. this method organizes the parameter values based on a reference model output value and aims to increase the system performance against destructive effects [11]. lyapunov based adaptive control method is generally more effective on system performance and is preferred in various fields and control mechanisms, e.g. position control of permanent magnet synchronous motor [12], x-y table experimental platforms control [13, 14], and dc motor speed control [15]. ii. modelling of the vls system a rotary servo system that can change the load in time was used in the experiments. in industrial applications, permanent magnet dc (pmdc) motors are widely used as actuators for electromechanical energy conversion [16]. they directly provide rotary motion or moment and, coupled with wheels or drums and cables, can provide transitional motion or force. vls plant and pmdc motor parameters are given in table i. the differential equations based on newton's law combined with kirchhoff's law regarding the system are: ( ) ( ) ( ) ( ) a a b di t u t r i t l e t dt = + + (1) ( ) ( ) ( ) ( )mm m m m l dw t t j b w t t dt τ τ= + + (2) ( ) ( ) mm d t w t dt θ = (3) where ( )i t is the armature current, ( )be t is the back emf voltage, ( )m tτ is the produced motor torque, ( )l tτ is the load torque, ( )m tθ is the angle of the armature, ( )mw t is the angular velocity of the armature [17]. the produced motor torque ( )m tτ is related to the armature current ( )i t by a constant factor tk , and the back emf ( )be t corresponding author: omer aydogdu engineering, technology & applied science research vol. 9, no. 3, 2019, 4125-4130 4126 www.etasr.com aydogdu & levent: kalman state estimation and lqr assisted adaptive control of a variable loaded … is related to the rotational velocity of the armature ( )mw t by a constant factor mk as given by (4)-(5): ( ) ( ) m t t k i tτ = (4) ( ) ( )b m me t k tω= (5) table i. vls system and load parameters symbol definition value u(t) pmdc motor voltage 6volt ra motor armature resistance 2.6ohm la motor armature inductance 0.18mh kt motor torque constant 0.00767n.m/a kb motor back-emf constant 0.00767volt/(r/s) n total gear ratio (n1/n2) 70 g η gearbox efficiency 0.90 jm motor inertia 4.6x10 -7 kg.m 2 bm motor viscous coefficient ≅0 (negligible) jl_in initial load and gearbox moment of inertia 4.83x10 -7 kg.m 2 jl_sub subsequent load and gearbox moment of inertia 3.41x10 -3 kg.m 2 bl_in initial load viscous damping coefficient 4.41x10 -6 n.m/(r/s) bl_sub subsequent load viscous damping coefficient 4x10 -2 n.m/(r/s) in the vls system, angular velocity of the load, ( )lw t , transmitted by the gear box from armature velocity, ( )mw t and equivalent armature load torque ( )l tτ , may be expressed as: 1 ( ) ( ) l m w t w t n = (6) 2 ( )1 ( ) ( ( )) m l l l m g dw t t j b w t dtn τ η = + (7) where η is the total gear ratio and ηg is the gearbox efficiency. if (7) is substituted in (2), the general moment expression for the motor is obtained as: 2 2 ( ) ( ) ( ) ( ) ( ) l m l m m m m g g j dw t b t j b w t dtn n τ η η = + + + (8) the following equations are obtained for the state space expression of the system by using (1), (3), (4), (5) and (8): ( ) 1 ( ) ( ) ( ) a b m a a a r kdi t i t w t u t dt l l l = − − + (9) ( ) ( ) eqm t m eq eq bdw t k i t w dt j j = − (10) ( ) ( )m m d t w t dt θ = (11) where 2η = + leq m g j j j n and 2η = + leq m g b b b n . if (9)-(11) are arranged in the state space model and the armature angle is accepted as the output, the state space expression of the servo system is obtained as (12) and (13): ( ) ( ) ( )x t ax t bu t= +� (12) ( ) ( )y t cx t= (13) where state variables are defined as: 1 1 2 3 ( ) ( ) ( ) ( ) ( ) ( ) ( ) m m x t i t x t x t w t x t tθ        = =           and the state, input and output matrices are obtained as; [ ] 0 1 0 , 0 , 0 0 1 . 0 0 1 0 a b a a a eqt eq eq r k l l l bk a b c j j   − −           = − = =                iii. state estimation with kalman filter kalman filter is a method that estimates the states and the desired output of the system by using the control input signal u(t) and the noisy system output signal y(t). figure 1 shows the basic block diagram of this method, where ˆ( )x t represents the estimation state output, ˆ( )y t shows the estimation position (trajectory) output, ( )w t shows the process noise stemming from the deviations occur in the system model and ( )v t indicates the measurement noise stemming from the problems in measurements. fig. 1. block diagram of the state estimation with kalman filter linear difference equations (14) and (15) were used to estimate the states of the discrete-time kalman filter [18]: 1 1 1k k k kx ax bu w− − −= + + (14) k k kz hx v= + (15) where kz refers the real measurement value, kw shows the process noise and kv represents the measurement noise. kalman filter has two different equation groups. one of them consists of the time update equations that perform estimations of current situations and available error covariance. the other type of equations is the measurement update equations that perform the estimations of states to be used for the feedback. time update equations are known as “estimating equations” and the measurement update equations are known as the “corrector equations”. time and measurement updating systems of the cycle belonging to the kalman filter are given in engineering, technology & applied science research vol. 9, no. 3, 2019, 4125-4130 4127 www.etasr.com aydogdu & levent: kalman state estimation and lqr assisted adaptive control of a variable loaded … summary in figure 2, where ˆkx shows the estimated states and ˆ− khx indicates the measurement value estimated. kk matrix known as the gain value, with n×m dimensions, minimizes the next error covariance equality. in addition, noise covariance matrix q and measurement noise covariance matrix r should be defined for the estimation. fig. 2. kalman filter cycle iv. lqr assisted, lyapunov based, adaptive control of a vls system the block diagram of the system performed in this study is given in figure 3. the system consists of kalman state estimation, lqr control and adaptive control sub-blocks. as the figure shows, adaptive control is added to the lqr controlled system. in this way, the control signal (u) is the sum of the adaptive control signal u1 and the lqr signal u2. in the system, servo system’s states that are purified from the noise are estimated by the kf and the state space feedback of the system is actualized by the optimal k value computed by lqr for initial load [10]. in addition, adaptive control was added to eliminate the effects of the changing load parameters. proper selection of the parameter values that affect the system response is crucial for the system stability and performance in lyapunov’s stability theory. the transfer function of the servo system by taking the laplace transformation of (1), (3), (8) is obtained as (16). la is neglected because it is very small [19]. ( ) ( ) ( ) = + y s b u s s s a (16) where b and a coefficients are obtained as: t a eq k b r j = , . a eq t b a eq r b k k a r j + = fig. 3. state estimation with kf and lqr assisted adaptive control system accordingly, there is a need to know a quadratic system, a quadratic reference model, and the mathematical definitions belonging to the control input based on the controller parameters. let’s assume that these are defined as reference model in (17), plant model in (18) and adaptive control signal in (19) [20]: 2 2 m m m m d y dy a b r dtdt = − + (17) 2 12 d y dy a bu dtdt = − + (18) 1 1 2 dy u r dt θ θ= − (19) where, θ1 and θ2 refer the control parameters, y is the plant output, ym is the reference model output, and r is the reference input signal. the tracking error of the control system is given in (20): me y y= − (20) by subtracting the (17) from (18), we get: 2 12 ( ) m m m dyd e dy a bu a b r dt dtdt = − + − − + (21) equation (22) is obtained as below if (19) is written instead of u1 statement in (21): 2 1 22 m m m dyd e dy dy a b r a b r dt dt dtdt θ θ   = − + − + −    (22) if we add and subtract m dy a dt statement to both sides of equilibrium in (22) and necessary mathematical operations are performed, the derivative equation of the error is found in (23): ( ) ( )2 1m m m de a e b a a y b b r dt θ θ= − − + − + − (23) in (23), the required conditions need to be found for trajectory error to converge to zero. those conditions are provided by 2 mb a aθ = − and 1 mb bθ = equations. control parameters should be well organized to increase system performance. lyapunov function that is given in (24) is used to obtain the desired parameter values: ( ) ( ) ( ) 22 1 2 2 1 2 1 2 1 1 , , ( 2 1 ) θ θ θ γ θ γ = + + − + + − m m v e e b a a b b b b (24) in (24), lyapunov adaptation gain values are defined by γ1 and γ2. because they are greater than zero, 1bγ and 2bγ values are greater than zero. in this case, (25) can be written: ( ) ( ) ( )22 12 1 2 1 2 1 , , 2 2 2 m mb a a b b v e e b b θ θ θ θ γ γ + − − = + + (25) according to lyapunov stability theory, the lyapunov function needs to be bigger than zero for the system to be stable engineering, technology & applied science research vol. 9, no. 3, 2019, 4125-4130 4128 www.etasr.com aydogdu & levent: kalman state estimation and lqr assisted adaptive control of a variable loaded … [11]. moreover, the derivative of the same function needs to be smaller than zero. the following equations can be obtained when the derivative of this function is taken: ( ) ( ) 2 2 1 1 1 2 1 1 θ θ γ θ θ γ = + + − + − m m ddv de e b a a dt dt dt d b b dt (26) ( ) ( ) 2 2 2 1 1 1 2 2 1 θ θ γ θ θ γ γ   = − − + − − +      + − +    m m m ddv a e b a a ye dt dt d b b re dt (27) by reference to (27), the derivative expression of the function becomes smaller than zero if the parameter values are obtained. accordingly, the stability condition of the system is ensured, if the parameters are updated as follows: 1 2 θ γ= − d re dt (28) 2 1 θ γ= d ye dt (29) 2 1 γ θ = re s (30) 1 2 γ θ = ye s (32) where θ1 and θ2 are the control parameters with adjustable gains γ1 and γ2. in conclusion, the system becomes stable if a proper controller design is provided in (30) and (31). adaptation gain parameters should be selected according to the adaptation rate of the system [21]. linear quadratic regulator (lqr) provides an optimal control law for a linear system with a quadratic performance index. the lqr gain value (k), that provides optimal state feedback in the system is found in the solution of the riccati equation given by (32) [22]: 1 0 t t pa a p q pbr b p −+ + − = (32) the matrix p obtained from the solution of the riccati equation is replaced by (33) and the lqr gain value k is calculated. then using this k value, the u2 control signal is calculated as given in (34). 1 t k r b p −= (33) 2 ˆ( ) ( )u r t kx t= − (34) where ˆ( )x t is the estimation state vector, q is the state weighting matrix and r is the input weighting matrix as in kf. v. simulation results the block diagram of the kalman state estimation and the lqr assisted adaptive control system is given in figure 3. as seen from the figure, the control signals (u) is the sum of the adaptive controller output signal (u1) and lqr output signal (u2) given by (19) and (34). lqr and adaptive controllers are designed for initial load (jl_in, bl_in) in the experimental system. the load was kept constant at the first experiment, and the system output responses were obtained separately for lqr (not included adaptive control) and proposed lqr assisted adaptive control. in the second experiment, the system load was changed to jl_sub and bl_sub at 110 seconds and the response curve was obtained for the lqr assisted adaptive control system. the initial load values are given as 7 2 _ 4.83 10 −=l inj x kgm and 6 _ 4.41 10 / ( / s) −=l inb x nm r in table i. in this case the vls system parameters a, b, c are obtained as: [ ] 4 14444, 44 42.61 0 5555.56 16670 21.73 10 0 , 0 0 1 0 0 0 0 1 . a x b c − − −       = − =          = also, if we choose the r and q parameters for the kalman filter and lqr control as follows, the lqr gain is found as [ ]1.1036 0.9926 1=k . 3 0 0 0 3 0 , 3. 0 0 3 q r    = =     in the design of the lyapunov based adaptive control system, a 2 nd order system given in (35) is used as a reference model. 2 60 ( ) 15 60 mg s s s = + + (35) in the first experiment, while the load was kept constant at the initial value, performance measurements of the lqr control and lqr assisted adaptive control were obtained as given in table ii. it is seen that the proposed lqr assisted adaptive control system gives better performance values than the pure lqr control. the effects of the lqr and lqr assisted adaptive control on the system are shown in figure 4 and a zoom area of figure 4 is shown in figure 5. error change is shown in figure 6 and parameter changes are given in figure 7 for the lqr assisted lyapunov based adaptive control method. fig. 4. results obtained from the lqr and lqr assisted adaptive control method in a time-unvarying system engineering, technology & applied science research vol. 9, no. 3, 2019, 4125-4130 4129 www.etasr.com aydogdu & levent: kalman state estimation and lqr assisted adaptive control of a variable loaded … fig. 5. a magnified area of figure 4 fig. 6. error change in lqr assisted adaptive control system fig. 7. parameter changes in lqr assisted adaptive control system in the second experiment, the load values are changed to 3 2 _ 3.41 10 −= l sub j x kgm and 2 _ 4 10 / ( / s) −=l subb x nm r in the 110 th second to generate variable load. adaptation gains were taken the same as 1 30.5γ = and 2 21.2γ = (table ii). the response of the lqr assisted adaptive control system is given in figure 8. the effect of the variable load occurring at the 110 th second is clearly seen. the effect of variable load on parameter changes is shown in figure 9 and the error change is given in figure 10 for the lqr assisted lyapunov based adaptive control method. fig. 8. result obtained from the lqr assisted adaptive control method in variable load at the 110 th second fig. 9. effect of variable load on parameter changes in the 110 th second fig. 10. error change in lqr assisted adaptive control system for varying load at the 110 th second table ii. performace measurements method γ1 γ2 ise iae itae lqr control 3,058 7.802 885.5 lqr adaptive control 30.5 21.2 1,2 3.029 294.2 vi. conclusions this research designed a new control system with lqr assisted, lyapunov based, adaptive control that compensates disruptive effects like noise and variable load and increases system performance. this controller structure has been successfully used in the trajectory control of a servo system that can change the load over time. the system can estimate the states of the time-varying servo system, so, the disruptive effects can be minimized. a stable system design that can comply with the environmental conditions was prepared. it is seen by the experimental results that the proposed method gives very good results in controlling systems that are exposed to the adverse effects like variable load. actually, the proposed system compensates well in time-varying systems, so, the system is beneficial in optimal controlling of the system. the error between the system output response and the reference input signal is minimized in time as shown in figure 10. it is understood from the results that the system control parameters can adapt in time. references [1] g. bishop, g. welch, an introduction to the kalman filter, acm, 2001 [2] b. o. teixeira, m. a. santillo, r. s. erwin, d. s. bernstein, “spacecraft tracking using sampled-data kalman filter”, ieee control systems magazine, vol. 28, no. 4, pp. 78-94, 2008 [3] m. e. hough, “precise orbit determination using satellite radar ranging”, journal of guidance, control, and dynamics, vol. 35, no. 4, pp. 10481058, 2012 engineering, technology & applied science research vol. 9, no. 3, 2019, 4125-4130 4130 www.etasr.com aydogdu & levent: kalman state estimation and lqr assisted adaptive control of a variable loaded … [4] j. r. vetter, “fifty years of orbit determination”, johns hopkins apl technical digest, vol. 27, no. 3, pp. 239-252, 2007 [5] h. chen, g. chen, e. blasch, k. pham, “comparison of several space target tracking filters”, in: sensors and systems for space applications iii, vol. 7330, pp. 73300i-1 73300i-12, spie, 2009 [6] h. h. bilgic, m. a. sen, a. yapici, m. kalyoncu, “dofrusal ters sarkacin denge kontrolu icin yapay sinir agi tabanli bulanik mantik & lqr kontrolcu tasarimi”, otomatik kontrol ulusal toplantisi bildiriler kitabi, kocaeli, turkey, july 11-13, 2014 (in turkish) [7] j. arslan, g. muhurcu, “speed control of direct current motor with linear quadratic gaussian control”, elektrik – elektronik – bilgisayar ve biyomedikal muhendisligi sempozyumu–(eleco 2014), bursa, turkey, november 27-29, 2014 [8] d. grewal, “kalman filtering”, in: international encyclopedia of statistical science, springer, 2011 [9] s. tunyasrirut, v. kinnares, j. ngamwiwit, “performance improvement of a slip energy recovery drive system by a voltage-controlled technique”, renewable energy, vol. 35, no. 10, pp. 2235-2242, 2010 [10] y. zhi, g. li, q. song, k. yu, j. zhang, “flight control law of unmanned aerial vehicles based on robust servo linear quadratic regulator and kalman filtering”, international journal of advanced robotic systems, vol. 14, no. 1, 2017 [11] s. pankaj, j. s. kumar, r. k. nema, “comparative analysis of mit rule and lyapunov rule in model reference adaptive control scheme”, innovative systems design and engineering, vol. 2, no. 4, pp. 154-162, 2011 [12] f. j. lin, s. g. chen, i. f. sun, “adaptive backstepping control of six‐ phase pmsm using functional link radial basis function network uncertainty observer”, asian journal of control, vol. 19, no. 6, pp. 2255-2269, 2017 [13] h. wang, x. zhao, y. tian, “trajectory tracking control of xy table using sliding mode adaptive control based on fast double power reaching law”, asian journal of control, vol. 18, no. 6, pp. 2263-2271, 2016 [14] w. l. mao, c. w. hung, s. suprapto, “adaptive fuzzy trajectory control for biaxial motion stage system”, advances in mechanical engineering, vol. 8, no. 4, 2016 [15] b. rashidi, m. esmaeilpour, m. r. homaeinezhad, “precise angular speed control of permanent magnet dc motors in presence of high modeling uncertainties via sliding mode observer-based model reference adaptive algorithm”, mechatronics, vol. 28, pp. 79-95, 2015 [16] o. aydogdu, o. alkan, “adaptive control of a time-varying rotary servo system using a fuzzy model reference learning controller with variable adaptation gain”, turkish journal of electrical engineering & computer sciences, vol. 21, no. 2, pp. 2168-2180, 2013 [17] c. kasnakoglu, “modeling and control of flow problems by adaptationbased linear parameter varying models”, turkish journal of electrical engineering & computer sciences, vol. 18, no. 5, pp. 819-852, 2010 [18] f. l. lewis, l. xie, d. popa, optimal and robust estimation, crc press, 2007 [19] e. flores, r. e. castro, l. f. chaves, “conventional compensators design using newton's method”, 11th world congress on intelligent control and automation, shenyang, china, june 29-july 4, 2014 [20] m. pal, g. sarkar, r. k. barai, t. roy, “design of different reference model based model reference adaptive controller for inversed model non-minimum phase system”, mathematical modelling of engineering problems, vol. 4, no. 2, pp. 75-79, 2017 [21] p. swarnkar, s. jain, r. k. nema, “effect of adaptation gain in model reference adaptive controlled second order system”, engineering, technology & applied science research, vol. 1, no. 3, pp. 70-75, 2011 [22] s. b. roland, advanced control engineering, burterworth-heinemann, 2001 authors profile o. aydogdu received his be from the department of electrical and electronics engineering, selcuk university, konya, turkey, in 1995, and his msc and phd degrees from graduate school of natural sciences, selcuk university, konya, turkey, in 1999 and 2006, respectively. currently he is an associate professor in the faculty of engineering and natural sciences at konya technical university. he has many publications in different areas of control engineering. m. l. levent received his bsc degree from the department of electronics and communication engineering, kocaeli university, kocaeli, turkey, in 2011, and his msc degree from the graduate school of natural sciences, selcuk university, konya, turkey, in 2016. he continues his phd. studies at the institute of graduate education, konya technical university, konya, turkey. currently he is an research assistant in hakkari university, hakkari, turkey. his fields of interest are learning control, adaptive control and optimal state feedback control. microsoft word 45-2952_s1_etasr_v9_n4_pp4554-4560 engineering, technology & applied science research vol. 9, no. 4, 2019, 4554-4560 4554 www.etasr.com ng et al.: automated activity recognition with gait positions using machine learning algorithms automated activity recognition with gait positions using machine learning algorithms yeuk lam ng faculty of arts & science, university of toronto, canada xilin jiang grainger college of engineering, university of illinois at urbanachampaign, usa yinghui zhang college of letters and science, university of california, berkeley, usa seung bin shin hankuk academy of foreign studies, korea ruoci ning austin preparatory school, usa abstract—exoskeletons are wearable devices for enhancing human physical performance and for studying actions and movements. they are worn on the body for additional power and load-carrying capacity. exoskeletons can be controlled using signals from the muscles. in recent years, gait analysis has attracted increasing attention from fields such as animation, athletic performance analysis, and robotics. gait patterns are unique, and each individual has his or her own distinct gait pattern characteristics. gait analysis can monitor activity in sensitive areas. this paper uses various machine learning algorithms to predict the activity of subjects using exoskeletons. here, localization data from the uic machine learning repository are used to recognize activities with gait positions. the study also compares five machine learning methods and examines their efficiency and accuracy in activity prediction for three different subjects. the results for the various machine learning methods along with efficiency and accuracy results are discussed. keywords-exoskeletons; gait analysis; activity recognition; machine learning algorithms i. introduction exoskeletons are wearable devices for enhancing human performance. they can supplement or increase the wearer’s speed, strength, and endurance. the wearer applies some force that acts to send control signals to the robotic system. this signal is sensed and amplified by the exoskeleton to exert the requisite force for the desired movement [1]. exoskeletons have gained increasing attention in recent years when the u.s. defense department allotted funds for exoskeletons for human performance augmentation. there is a wide range of applications for exoskeletons, including walking assistance for physically impaired people. a. importance of wearable exoskeletons one important application of exoskeletons is walking assistance [2, 4]. walking or movement assistance is achieved when exoskeletons are used for the augmentation of a healthy individual’s physical ability such as running or in the rehabilitation of physically disabled individuals. in rough terrain or staircases, moving heavy things is difficult using wheeled vehicles. the use of automated or semi-automated human-like legs can be an alternative option since legs can adapt to a wide range of extreme surfaces. the berkeley lower extremity exoskeleton (bleex) allows its wearer to carry large loads on his or her back with minimal effort over various kinds of terrain [3]. the exoskeleton market’ worth was about $200 million in 2017 [5], and is estimated to reach $1.3 billion by 2024 [6]. this necessitates reliable and accurate methods for predicting human movement. b. movement prediction in exoskeleton robots the synchronization of the exoskeleton system with the wearer in motion and the application of force are of intense research interest. the ultimate objective is to actively support the wearer’s desired movement. the inherent periodicity of movement hassled to oscillator-based approaches for modeling and motion. an oscillator model is used for coordinated periodic trajectories of exoskeletons, where the wearer’s movement signals act as references to the robotic controller [6]. therefore, accuracy in predicting human motion from exoskeleton movement is crucial for estimating exoskeleton and human motion using sensors for effective human-robot interface. by being independent of any external measurement, this approach can provide precise measurement in real-world situations [7]. a precursor to proper exoskeleton operation is the ability to correctly estimate the wearer’s intended movement such as walking and running. the ability of the exoskeleton to recognize intended movement is crucial since controlling muscles and joints in walking is different from that in running or climbing. therefore, the device should predict the operator’s trajectory. finally, it is crucial to generate correct actuator signals for intended trajectories in real time [8]. ii. literature review authors in [9] proposed a control scheme based on machine movement synchronization where a neural oscillator model is used for motion assistance. authors in [10] developed an oscillator-based motion assistance protocol for medical therapy corresponding author: y. l. ng (jingwensun321@gmail.com) engineering, technology & applied science research vol. 9, no. 4, 2019, 4554-4560 4555 www.etasr.com ng et al.: automated activity recognition with gait positions using machine learning algorithms for exoskeleton use. the protocol was experimentally evaluated for a gait rehabilitation robot [11]. in [12-14], authors considered the adaptation of a mechatronic device to human movement. they segregated human gait patterns into spatial and temporal. the former represents personal movement style, whereas the latter is for any movement cycle. style and phase were separated from observed walking behaviors [12] to control exoskeletons [13-14]. the proposed style-phase separation approach was adapted to multi-user movement based on rapid online calibration mechanisms for predicting the wearer’s movement [6]. in [15], authors developed a method for obtaining joint angles, angular velocity, and force/torque from exoskeleton sensors and used them to distinguish different movements including standing, walking and sitting. in [16], they developed a model for predicting joint trajectories of the wearer and in [17] they evaluated leg dynamics for gait trajectory references for any movements. authors in [8] considered a class of unsupervised machine learning algorithms for intended movements and future trajectories for a lower limb exoskeleton. they considered the conditional restricted boltzmann machine, which can predict intended movements and trajectories on a real-time basis. authors in [18] used a multi-layer perceptron neural network to predict natural gait parameters and used age, gender, height, and weight, among others, as training input. the output included desired walking speed and cadence. two neural networks were trained to analyze efficiency and accuracy in the prediction of gait patterns involving slow speeds and then both slow and normal speeds [18]. in [19], three supervised machine learning techniques for predicting activation patterns for muscles and sensory data from time series for human movement for an exoskeleton for assisted walking were presented. authors considered a multilayer perceptron with modified backpropagation learning algorithm, an adaptive neuro-fuzzy inference system, and an entropy-based inductive learning model. training and testing data were used for the assisted controller. the minimal and most comprehensible rules were obtained through the adaptive neuro-fuzzy inference system. the il-rbf network provided the best generalization. in [20], authors used elman’s recurrent neural network (ernn) to automatically identify healthy and pathological gait. they considered stance, swing and double support intervals and developed two schemes to classify healthy individuals from patients with some disease, reporting an average performance value of 85%. iii. machine learning algorithms machine learning employs artificial intelligence with data mining to learn from experience without the need for explicit programming. this learning is performed either directly or by observing patterns, and its main objective is to make computers learn on their own without human intervention. the two most common forms of machine learning are supervised and unsupervised, followed by semi-supervised learning and reinforcement learning. supervised learning employs training using positive and negative examples, where the algorithm receives inputs and class labels as positive or negative. some examples of supervised learning include classification, regression, recommendation, and prediction systems. this type of learning anticipates future occurrences using previous (historical) data. unsupervised learning learns through historical data but with no historical labels. there is no class label for determining positive or negative examples. clusters or segments are formed with similarities in existing data. popular unsupervised learning methods include k-means clustering, nearest neighbor, and self-organizing maps. semi-supervised learning employs labeled or unlabeled historical data and it is used with supervised learning methods including classification, regression, and prediction. this type of learning is useful when it is difficult or costly to obtain class labels for all given data. in this case, some datasets contain class labels, while others do not. the final category of learning is reinforcement learning. here, the algorithm learns by trial and error. reinforcement learning is the most common in ai problems. its algorithm has three main components: agents, environment and actions. in exoskeletons, material heterogeneity, morphological incongruities, or dynamically asynchronous movements cause some relative motion between the exoskeleton and the wearer’s body. this must be minimized for efficient power transmission, effective limb control, and low pain from movement [7]. accurate and rapid prediction of gait patterns enables synchronous movement by reducing this human-machine relative motion. iv. methodology this study employs both supervised and unsupervised machine learning algorithms to classify human activity using a dataset of activity recordings using 4 tags from the uci machine learning repository. the experiments were conducted using weka with various algorithms. accordingly, 7 different machine learning algorithms were used in this study, namely naive bayes, knn, support vector machine, j48decision tree, radial basis function network classifier, multi-layer perceptron neural network, and random forest. the localization data for person activity dataset were downloaded from the uci machine learning repository [21]. the dataset contained 164,860 instances with 8 attributes for each instance. the dataset was univariate, sequential and in time series. this dataset was suitable for classification tasks in machine learning and provided recordings for 5 individuals who wore 4 tags at left ankle, right ankle, belt and chest. each instance was a localization data point for one tag. the tag attribute has 4 different labels with corresponding equivalent value in the dataset. localization data for tags were collected at 3 coordinates, x, y, and z. the class label for the dataset was activity containing 11 types of activities. the dataset contained 2 additional attributes: time stamp and date. since the study did not consider time series activities, these 2 attributes were removed in the data preprocessing stage. the resulting data were stored in the database in weka data format. the experiments involved 3 individuals for the performance of various machine learning classification algorithms, so the data were further processed to separate the datasets for each person’s activity. then the localization datasets for these 3 individuals were loaded to weka to build various machine learning models by passing through machine learning algorithms. the models were tested using 10-fold cross engineering, technology & applied science research vol. 9, no. 4, 2019, 4554-4560 4556 www.etasr.com ng et al.: automated activity recognition with gait positions using machine learning algorithms validation testing for a better performance evaluation. the experimental setup was run for 3 individuals and 7 algorithms. fig. 1. process flow diagram v. experiments gait pattern prediction is an important challenge in robotic gait rehabilitation. the key parameters are gait pattern, walking speed, cadence and stride length and require careful analysis. gait parameters in natural walking must be accurately predicted, and accurate gait pattern recognition can be implemented using various machine learning algorithms and proper datasets. we conducted experiments on 7 popular data mining algorithms and the results are tabulated for each algorithm. the results are analyzed and the performances are compared below. the following classes are used for the class attributes in the used dataset: a=walking, b=sitting down, c=sitting, d=standing up from sitting, e=falling, f=lying, g=standing up from lying, h=lying down, i=sitting on the ground, j=standing up from sitting on the ground, k=on all fours. considering the above class labels, experiments were conducted with 7 different data mining algorithms. for each algorithm the tp rate, fp rate, precision, recall, f-measure, roc curve are tabulated for all class labels. also, for each algorithm the number of correctly classified instances, incorrectly classified instances, kappa statistic and 3 different error measures, namely root mean squared error, relative absolute error and root relative squared error are tabulated. the detailed accuracies by class variable and the run information of the seven data mining algorithms are presented in tables i to vii and the final comparison of the 7 algorithms is exhibited in table viii. table i. naive bayes algorithm class tp rate fp rate precision recall f-measure mcc roc area prc area summary a 0.299 0.032 0.585 0.299 0.396 0.360 0.855 0.512 correctly classified instances 12804 46.6058% b 0.000 0.000 ? 0.000 ? ? 0.819 0.037 incorrectly classified instances 14669 53.3942% c 0.493 0.136 0.449 0.493 0.470 0.344 0.834 0.556 kappa statistic 0.2784 d 0.000 0.000 ? 0.000 ? ? 0.853 0.019 mean absolute error 0.1181 e 0.000 0.000 0.000 0.000 0.000 0.001 0.838 0.145 root mean squared error 0.2428 f 0.694 0.394 0.525 0.694 0.598 0.292 0.772 0.689 relative absolute error 83.2151% g 0.014 0.004 0.257 0.014 0.027 0.041 0.607 0.140 root relative squared error 91.1429% h 0.002 0.002 0.037 0.002 0.005 0.002 0.818 0.082 total number of instances 27473 i 0.597 0.137 0.291 0.597 0.391 0.338 0.842 0.249 j 0.000 0.000 ? 0.000 ? ? 0.870 0.095 k 0.355 0.023 0.413 0.355 0.382 0.357 0.951 0.400 l 0.466 0.195 ? 0.466 ? ? 0.798 0.494 table ii. k-nearest neighbour class tp rate fp rate precision recall fmeasure mcc roc area prc area summary a 0.720 0.040 0.736 0.720 0.728 0.687 0.840 0.577 correctly classified instances 21799 79.347% b 0.221 0.007 0.237 0.221 0.228 0.221 0.612 0.061 incorrectly classified instances 5674 20.653% c 0.898 0.029 0.874 0.898 0.886 0.860 0.935 0.811 kappa statistic 0.7347 d 0.272 0.004 0.276 0.272 0.274 0.270 0.634 0.079 mean absolute error 0.0376 e 0.253 0.010 0.298 0.253 0.274 0.264 0.625 0.091 root mean squared error 0.1937 f 0.906 0.068 0.893 0.906 0.900 0.836 0.920 0.852 relative absolute error 26.4912% g 0.506 0.044 0.532 0.506 0.518 0.472 0.728 0.323 root relative squared error 72.7205% h 0.296 0.019 0.323 0.296 0.309 0.289 0.634 0.119 total number of instances 27473 i 0.949 0.007 0.931 0.949 0.940 0.934 0.972 0.890 j 0.576 0.007 0.582 0.576 0.579 0.572 0.778 0.374 k 0.679 0.015 0.669 0.679 0.674 0.659 0.834 0.478 l 0.793 0.043 0.788 0.793 0.791 0.750 0.875 0.693 engineering, technology & applied science research vol. 9, no. 4, 2019, 4554-4560 4557 www.etasr.com ng et al.: automated activity recognition with gait positions using machine learning algorithms table iii. support vector machine class tp rate fp rate precision recall fmeasure mcc roc area prc area summary a 0.474 0.034 0.678 0.474 0.558 0.514 0.720 0.391 correctly classified instances 18662 67.9285% b 0.000 0.000 ? 0.000 ? ? 0.500 0.010 incorrectlyclassified instances 8811 32.0715% c 0.749 0.075 0.692 0.749 0.719 0.654 0.837 0.564 kappa statistic 0.5623 d 0.000 0.000 ? 0.000 ? ? 0.500 0.550 mean absolute error 0.0583 e 0.002 0.000 1.000 0.002 0.004 0.047 0.501 0.018 root mean squared error 0.2415 f 0.937 0.280 0.678 0.937 0.786 0.641 0.828 0.659 relative absolute error 41.0753% g 0.102 0.008 0.569 0.102 0.173 0.215 0.547 0.140 root relative squared error 90.6403% h 0.002 0.000 0.222 0.002 0.005 0.021 0.501 0.030 total number of instances 27473 i 0.937 0.025 0.770 0.901 0.830 0.816 0.938 0.702 j 0.006 0.000 0.300 0.006 0.012 0.042 0.503 0.019 k 0.702 0.028 0.528 0.702 0.603 0.589 0.837 0.384 l 0.679 0.130 ? 0.679 ? ? 0.774 0.501 table iv. rbf classifier class tp rate fp rate precision recall fmeasure mcc roc area prc area summary a 0.041 0.003 0.683 0.041 0.077 0.145 0.669 0.260 correctly classified instances 12521 45.5757% b 0.000 0.000 ? 0.000 ? ? 0.493 0.010 incorrectly classified instances 14952 54.4243% c 0.638 0.260 0.356 0.638 0.457 0.311 0.784 0.503 kappa statistic 0.2032 d 0.000 0.000 ? 0.000 ? ? 0.495 0.005 mean absolute error 0.1303 e 0.000 0.000 ? 0.000 ? ? 0.513 0.022 root mean squared error 0.2515 f 0.863 0.536 0.503 0.863 0.635 0.336 0.798 0.704 relative absolute error 91.7506% g 0.000 0.000 ? 0.000 ? ? 0.579 0.112 root relative squared error 94.4148% h 0.000 0.000 ? 0.000 ? ? 0.591 0.045 total number of instances 27473 i 0.000 0.000 ? 0.000 ? ? 0.709 0.200 j 0.000 0.000 ? 0.000 ? ? 0.554 0.022 k 0.008 0.000 0.015 0.008 0.015 0.06 0.641 0.097 l 0.456 0.255 ? 0.456 ? ? 0.724 0.432 table v. multi layer perceptron class tp rate fp rate precision recall fmeasure mcc roc area prc area summary a 0.563 0.062 0.583 0.563 0.573 0.509 0.892 0.591 correctly classified instances 19084 69.4646% b 0.000 0.000 0.000 0.000 0.000 -0.002 0.789 0.029 incorrectly classified instances 8389 30.5354% c 0.792 0.085 0.677 0.792 0.730 0.666 0.908 0.768 kappa statistic 0.5965 d 0.000 0.000 0.000 0.000 0.000 -0.001 0.834 0.024 mean absolute error 0.076 e 0.117 0.003 0.394 0.117 0.180 0.208 0.786 0.138 root mean squared error 0.2012 f 0.899 0.160 0.780 0.899 0.835 0.725 0.929 0.872 relative absolute error 53.5013% g 0.220 0.029 0.435 0.220 0.292 0.263 0.704 0.282 root relative squared error 75.5171% h 0.017 0.001 0.500 0.017 0.033 0.089 0.834 0.134 total number of instances 27473 i 0.882 0.018 0.822 0.882 0.851 0.837 0.962 0.843 j 0.072 0.004 0.264 0.072 0.113 0.130 0.868 0.159 k 0.644 0.036 0.443 0.644 0.525 0.509 0.942 0.447 l 0.695 0.091 0.658 0.695 0.661 0.596 0.895 0.683 table vi. j48 decision tree class tp rate fp rate precision recall fmeasure mcc roc area prc area summary a 0.709 0.049 0.689 0.709 0.699 0.652 0.877 0.631 correctly classified instances 21517 78.3205 b 0.118 0.005 0.195 0.118 0.147 0.145 0.724 0.089 incorrectly classified instances 5956 21.6795 c 0.895 0.036 0.850 0.895 0.872 0.842 0.953 0.848 kappa statistic 0.7182 d 0.143 0.002 0.280 0.143 0.189 0.197 0.730 0.098 mean absolute error 0.048 e 0.157 0.007 0.267 0.157 0.198 0.195 0.702 0.112 root mean squared error 0.1818 f 0.929 0.091 0.865 0.929 0.896 0.828 0.942 0.868 relative absolute error 33.7819 g 0.428 0.038 0.527 0.428 0.472 0.428 0.777 0.382 root relative squared error 68.2489 h 0.206 0.013 0.330 0.206 0.254 0.243 0.772 0.179 total number of instances 27473 i 0.930 0.008 0.918 0.930 0.924 0.917 0.973 0.880 j 0.436 0.006 0.541 0.436 0.483 0.478 0.812 0.329 k 0.677 0.016 0.657 0.677 0.667 0.652 0.908 0.570 l 0.783 0.054 0.763 0.783 0.771 0.728 0.907 0.723 engineering, technology & applied science research vol. 9, no. 4, 2019, 4554-4560 4558 www.etasr.com ng et al.: automated activity recognition with gait positions using machine learning algorithms table vii. random forest class tp rate fp rate precision recall fmeasure mcc roc area prc area summary a 0.816 0.063 0.772 0.816 0.793 0.738 0.964 0.882 correctly classified instances 25241 79.8943% b 0.202 0.003 0.401 0.202 0.268 0.279 0.881 0.227 incorrectly classified instances 6352 20.1057% c 0.917 0.030 0.862 0.917 0.889 0.866 0.989 0.954 kappa statistic 0.7482 d 0.366 0.003 0.556 0.366 0.442 0.447 0.949 0.389 mean absolute error 0.0506 e 0.218 0.004 0.444 0.218 0.293 0.304 0.908 0.296 root mean squared error 0.1607 f 0.933 0.063 0.873 0.933 0.902 0.855 0.983 0.960 relative absolute error 34.4957% g 0.557 0.042 0.643 0.557 0.597 0.548 0.916 0.652 root relative squared error 59.3177% h 0.414 0.013 0.574 0.414 0.482 0.470 0.934 0.505 total number of instances 31593 i 0.949 0.006 0.911 0.949 0.930 0.925 0.998 0.972 j 0.529 0.006 0.628 0.529 0.575 0.569 0.965 0.622 k 0.581 0.012 0.585 0.581 0.583 0.571 0.976 0.617 l 0.799 0.044 0.785 0.799 0.789 0.753 0.968 0.848 table viii. comparison of the 7 machine learning algorithms algorithm experiment – i experiment – ii experiment –iii rms error performance rms error performance rms error performance naive bayes 0.2428 46.60% 0.2483 46.64% 0.2471 46.60% k-nearest neighbor 0.1937 79.34% 0.1933 79.43% 0.2012 77.74% svm 0.2415 67.92% 0.2568 63.71% 0.2645 61.51% rbf classifier 0.2515 45.57% 0.2581 42.82% 0.2601 40.56% multi layer perceptron 0.2012 69.46% 0.2103 65.62% 0.2144 64.06% j48 classifier 0.1818 78.32% 0.1848 77.59% 0.1902 76.24% random forest 0.1536 81.82% 0.1556 81.43% 0.1607 79.89% a. naive bayes in machine learning models, the classifiers are used to discriminate different objects based on certain features in the datasets. naive bayes classifier is a probabilistic machine learning model used for classification problems using the bayes theorem. in that way, we can find the probability of event a happening, given that b has occurred. here, b is the evidence and a is the hypothesis. the assumption made here is that the predictors/features are independent. the presence of one particular feature does not affect the other. hence it is called naive. b. lazy ibk lazy learning algorithms in machine learning try to generalize the training data and the results are delayed until a query is made to the system, as opposed to eager learning, where the system tries to generalize the training data before receiving queries. generally, for employing lazy learning, knearest neighbor algorithm is implemented. the advantage in employing a lazy learning method is that the target function will be approximated locally as in the k-nearest neighbor algorithm. the disadvantages with lazy learning include the large space requirement to store the complete training dataset. mostly noisy training data increase the case support unnecessarily, because no concept is made during the training phase. another disadvantage is that lazy learning methods are usually slower to evaluate, though this is accompanied with a faster training phase. c. svm a support vector machine (svm) performs classification by finding the hyperplane that maximizes the margin between two classes. svms are perhaps one of the most popular and talked about machine learning algorithms. they were extremely popular around the time they were developed in the ‘90s and continue to be the go-to method for high-performing algorithms with little tuning. the learning of the hyperplane in linear svm is done by transforming the problem using linear algebra. d. multi layer perceptron a multilayer perceptron (mlp) is a class of feed forward artificial neural networks (anns). an mlp consists of at least three layers of nodes. except for the input nodes, each node is a neuron that uses a nonlinear activation function. mlp utilizes a supervised learning technique called back propagation for training. an ann has several advantages, but one of the most recognized ones is the fact that it can actually learn from observing data sets. in this way, the ann is used as a random function approximation tool. these types of tools help estimate the most cost-effective methods for arriving at solutions while defining computing functions or distributions. ann takes data samples rather than entire data sets to arrive at solutions, which saves both time and money. anns are considered fairly simple mathematical models to enhance existing data analysis technologies. e. random forest random forest is one of the most popular and most powerful machine learning algorithms. it is a type of ensemble machine learning algorithm called bootstrap aggregation or bagging. ensembled algorithms are those which combine more than one algorithms of the same or different kind for classifying objects. random forest classifier creates a set of decision trees from randomly selected subsets of the training set. it then aggregates the votes from different decision trees to decide the final class of the test object. engineering, technology & applied science research vol. 9, no. 4, 2019, 4554-4560 4559 www.etasr.com ng et al.: automated activity recognition with gait positions using machine learning algorithms f. j48 j48 is the java implementation of c4.5 which is a successor of id3. it is used for classification in which new data are labeled according to already existing observations (training data set). decision tree induction begins with a dataset (training set) which is partitioned at every node resulting in smaller partitions, thus following a recursive divide and conquer strategy. in addition to a data set, which is a collection of objects, a set of attributes is also passed. objects can be an event or an activity and the attributes are the information related to that object. every tuple in the data set is associated with a class label which identifies whether an object belongs to a particular class or not. splitting can further be performed only if the tuples fall in different classes. g. rbf classifier a radial basis function network (rbfn) is a particular type of neural network. rbfn performs classification by measuring the input’s similarity to examples from the training set. each rbfn neuron stores a “prototype”, which is just one of the examples from the training set. when we want to classify a new input, each neuron computes the euclidean distance between the input and its prototype. it consists of an input vector, a layer of rbf neurons, and an output layer with one node per category or class of data. each rbf neuron stores a “prototype” vector which is just one of the vectors from the training set. vi. results and discussion the study used the localization data for person activity dataset from the uci machine learning repository. the dataset contained 164,860 instances with 8 attributes. the dataset consisted of recorded data by 5 people who wore 4 tags (exoskeletons) on left ankle, right ankle, belt and chest. each instance was a localization data point for one exoskeleton. each data instance contained sequence number, tag identifier, timestamp, date format, x-coordinate, y-coordinate, zcoordinate, and activity. activity values were walking, falling, lying down, lying, sitting down, sitting, standing up from lying, on all fours, sitting on the ground, standing up from sitting, standing up from sitting on the ground. a total of 7 machine learning models were built using 3 different datasets. tables i to vii provide the detailed accuracy and run information of 7 ml algorithms and table viii provides their comparison. according to the results the k-nearest neighbor algorithm outperformed rbf and multi-layer perceptron, but random forest outperformed all other algorithms in all three experiments. vii. conclusion this study compares 7 machine learning algorithms using weka for the classification of action using a dataset on a person’s exoskeleton activity. the results show that the random forest algorithm provided good classification performance, whereas the radial basis function and naive bayes provided poor performance. further, the results of three experiments for different datasets show that the random forest algorithm outperformed the multilayer perceptron neural network in activity recognition. acknowledgement the authors acknowledge the assistance of seokwoo chung (shanghai american school) in literature review. references [1] i. s. dhindsa, r. agarwal, h. s. ryait, “a novel algorithm to predict knee angle from emg signals for controlling a lower limb exoskeleton”, information technology and nanotechnology, samara, russia, may, 2016 [2] j. o. brinker, t. matsubara, t. teramae, t. noda, t. ogasawarsa, t. afour, j. morimoto, “walking pattern prediction with partial observation for partial walking assistance by using an exoskeleton system”, ieee international conference on rehabilitation robotics, singapore, august 11-14, 2015 [3] a. zoss, h. kazerooni, a. chu, “on the mechanical design of the berkeley lower extremity exoskeleton (bleex)”, ieee/rsj international conference on intelligent robots and systems, edmonton, canada, august 2-6, 2005 [4] a. m. dollar, h. herr, “lower extremity exoskeletons and active orthoses: challenges and state-of-the-art”, ieee transactions on robotics, vol. 24, no. 1, pp. 144–158, 2008 [5] m. j. coren, “robot exoskeletons are finally here, and they’re nothing like the suits from iron man”, available at: https://qz.com/971741/robotexoskeletons-are-finally-here-and-theyre-nothing-like-the-suits-fromiron-man/, 2017 (accessed 27 june 2018) [6] v. verma, a. agarwal, “exoskeleton market size, by product (stationary, mobile), type (full body, upper body, lower body), by application (industrial, military, healthcare) industry analysis report, regional outlook (u.s., canada, germany, france, uk, russia, china, japan, south korea, brazil, mexico, mea), application development, competitive landscape & forecast, 2017 – 2024”, available at: https://www.gminsights.com/industry-analysis/exoskeleton-market , 2017 (accessed 27 june 2018). [7] d. torricelli, c. cortes, n. lete, a. bertelsen, j. e. gonzalez-vargas, a. j. del-ama, i. dimbwadyo, j. c. moreno, j. florez, j. l. pons, “a subject-specific kinematic model to predict human motion in exoskeleton-assisted gait”, frontiers in neurorobotics, vol. 12, 2018 [8] e. chong, f. c. park, “movement prediction for a lower limb exoskeleton using a conditional restricted boltzmann machine”, robotica, vol. 35, no. 11 pp. 2177-2200, 2017 [9] x. zhang, m. hashimoto, “sbc for motion assist using neural oscillator”, ieee international conference on robotics and automation, kobe, japan, may 12-17, 2009 [10] r. ronsse, n. vitiello, t. lenzi, j. van den kieboom, m. c. carrozza, a. j. ijspeert, “human-robot synchrony: flexible assistance using adaptive oscillators”, ieee transactions on biomedical engineering, vol. 58, no. 4, pp. 1001–1012, 2011 [11] r. ronsse, b. koopman, n. vitiello, t. lenzi, d. rossi, s. m. maria, j. van den kieboom, e. van asseldonk, m. c. carrozza, h. van der kooij, a. j. ijspeert, “oscillator-based walking assistance: a model-free approach”, ieee international conference on rehabilitation robotics, zurich, switzerland, june 29-july 1, 2011 [12] t. matsubara, s. h. hyon, j. morimoto, “real-time stylistic prediction for whole-body human motions”, neural networks, vol. 25, pp. 191– 199, 2012 [13] t. matsubara, a. uchikata, j. morimoto, “full-body exoskeleton robot control for walking assistance by style-phase adaptive pattern generation”, ieee/rsj international conference on intelligent robots and systems, vilamoura, portugal, october 7-12, 2012 [14] t. matsubara, d. uto, t. noda, t. teramae, j. morimoto, “style-phase adaptation of human and humanoid biped walking patterns in real systems”, ieee-ras international conference on humanoid robots (humanoids), madrid, spain, november 18-20, 2014 [15] h. a. varol, f. sup, m. goldfarb, “multiclass real-time intent recognition of a powered lower limb prosthesis”, ieee transactions on biomedical engineering, vol. 57, no. 3, pp. 542–551, 2010 engineering, technology & applied science research vol. 9, no. 4, 2019, 4554-4560 4560 www.etasr.com ng et al.: automated activity recognition with gait positions using machine learning algorithms [16] l. wang, e. h. van asseldonk, h. van der kooij, “model predictive control-based gait pattern generation for wearable exoskeletons”, ieee international conference on rehabilitation robotics, singapore, august 11-14, 2011 [17] j. f. veneman, r. kruidhof, e. e. hekman, r. ekkelenkamp, e. h. van asseldonk, h. van der kooij, “design and evaluation of the lopes exoskeleton robot for interactive gait rehabilitation”, ieee transactions on neural systems and rehabilitation engineering, vol. 15, no. 3, pp. 379–386, 2007 [18] h. b. lim, t. p. luu, k. h. hoon, k. h. low, “natural gait parameters prediction for gait rehabilitation via artificial neural network ieee/rsj international conference on intelligent robots and systems, taipei, taiwan, october 18-22, 2010 [19] s. jonic, t. jankovic, v. gajic, d. popovic, “three machine learning techniques for automatic determination of rules to control locomotion”, ieee transactions on biomedical engineering, vol. 46, no. 3, pp. 300310, 1999 [20] s. dutta, a. chatterjee, s. munshi, “an automated hierarchical gait pattern identification tool employing cross‐correlation‐based feature extraction and recurrent neural network based classification”, expert systems, vol. 26, no. 2, pp. 202-217, 2009 [21] https://archive.ics.uci.edu/ml/datasets/localization+data+for+person+a ctivity engineering, technology & applied science research vol. 8, no. 5, 2018, 3329-3331 3329 www.etasr.com oguntunde et al.: crude oil importantion and exportation in nigeria: an exploratory and … crude oil importation and exportation in nigeria: an exploratory and comparative study pelumi e. oguntunde department of mathematics covenant university ota, ogun state, nigeria pelumi.oguntunde@covenantuniversity.edu.ng omoleye a. oguntunde department of business management covenant university ota, ogun state, nigeria omoleye.oguntunde@covenantuniversity.edu.ng oluwadare o. ojo department of statistics federal university of technology, akure akure, nigeria daruu208075@yahoo.com hilary i. okagbue department of mathematics covenant university ota, ogun state, nigeria hilary.okagbue@covenantuniversity.edu.ng abstract—nigeria is an oil producing country and crude oil is an important asset to its economy. this research focuses on the analysis of importation and exportation of crude oil products (measured in million barrels). comparisons between the total importation and exportation were made and descriptive analysis was performed on the crude oil components. poisson regression was used to establish the relationship between total importation and the importation of the petroleum products under consideration. the results show that nigeria makes more importation than exportation of these products. keywords-crude oil; exploratory data analysis; exportation; importation; nigeria i. introduction crude oil, often called unrefined petroleum, is a natural product. just like other mineral resources, petroleum is found through drilling. crude oil is processed through distillation and produces several other components. table i shows the various components of petroleum and their boiling point [1]. these components are useful as transportation fuel, road tarring materials, paints, cosmetics and so on. various works on crude oil production especially in nigeria are contained in [2-4]. table i. crude oil components [1] components boiling point fuel gas, lpg, refinery gas below 250c gasoline-petrol 250c-750c naphtha 750c-1900c paraffin, kerosene 1900c-2500c diesel oil, gas oil 2500c-3500c residue (fuel oil, lubricating oil, waxes) >3500c bitumen 5000c-7000c this research makes comparison between the importation and exportation of these products in nigeria. crude oil is found in several countries, but nigeria is one of the countries that extract light and sweet oil, otherwise known as brent crude oil. ii. materials and methdos the data presented in this article represent the amount of imports and exports of crude oil products in nigeria from 1986 to 2010. total importation and exportation of crude oil, importation and exportation of kerosene, motor gas, jet fuel, distillate fuel and liquefied petroleum gasses were taken into consideration. the data was obtained from [5]. descriptive analysis was performed and poisson regression model was fitted to the importation datasets. total importation was the dependent variable while importation of kerosene, motor gasoline, jet fuel, distillate fuel oil and liquefied petroleum gasses were the independent variables. the software used in dataset analyzing was minitab 17. the poisson regression model is of the form:    0 1 1 2 2exp ...     k ke y t x x x    (1) where β0 is a constant and β1, β2,...,βk are the regression coefficients. for the present study, y is the total importation, x1, x2, x3, x4 and x5 are the importation of kerosene, motor gasoline, jet fuel, distillate fuel oil and liquefied petroleum gasses respectively. analysis contained in [6-8] can be used to analyze the dataset. iii. results the summary of the data used is provided in tables ii and iii. it is clear that nigeria imports more than what it exports. specifically, the highest importation regards motor gasoline while the highest exportation is for distillate fuel oil (among the considered variables). the lowest importation is for liquefied petroleum gasses while the lowest exportation is for kerosene. engineering, technology & applied science research vol. 8, no. 5, 2018, 3329-3331 3330 www.etasr.com oguntunde et al.: crude oil importantion and exportation in nigeria: an exploratory and … table ii. crude oil importation, 1986-2010 (million barrels) variable sum mean standard deviation skewness kurtosis total importation 2190.4 87.6 66.0 0.27 -1.50 kerosene 243.60 9.74 8.74 1.14 0.92 motor gasoline 1588.9 63.6 51.7 0.27 -1.69 jet fuel 101.630 4.065 4.951 1.01 0.11 distillate fuel oil 153.51 6.14 8.66 1.44 0.64 liquefied petroleum gasses 5.60 0.224 0.2886 1.05 0.01 table iii. crude oil exportation, 1986-2010 (million barrels) variable sum mean standard deviation skewness kurtosis total exportation 591.66 23.67 17.79 0.64 0.13 kerosene 9.841 0.394 1.145 4.76 23.28 motor gasoline 14.192 0.568 1.413 4.01 17.33 jet fuel 15.309 0.612 1.832 4.31 19.75 distillate fuel oil 99.00 3.96 5.80 2.92 10.66 liquefied petroleum gasses 23.429 0.937 1.669 1.95 3.11 the comparison between total importation and total exportation between 1986 and 2010 is provided in figure 1. the comparisons between importation and exportation of kerosene, motor gasoline, jet fuel, distillate fuel oil, and liquefied petroleum gasses for the period under study are presented in figures 2, 3, 4, 5, and 6 respectively. fig. 1. comparison between total importation and exportation of crude oil fig. 2. comparison between importation and exportation of kerosene fig. 3. comparison between importation and exportation of motor gasoline fig. 4. comparison between importation and exportation of jet fuel fig. 5. comparison between importation and exportation of distillate fuel oil fig. 6. comparison between importation and exportation of liquefied petroleum gasses 24222018161412108642 200 150 100 50 0 index d at a total importation total exportation variable time series plot of total importation, total exportation 24222018161412108642 35 30 25 20 15 10 5 0 index d at a importation of kerosene exportation of kerosene variable time series plot of importation of kerosene, exportation of kerosene 24222018161412108642 140 120 100 80 60 40 20 0 index d at a importation of motor gasoline exportation of motor gasoline variable time series plot of importation of motor gas, exportation of motor gas 24222018161412108642 18 16 14 12 10 8 6 4 2 0 index d at a importation of jet fuel exportation of jet fuel variable time series plot of importation of jet fuel, exportation of jet fuel 24222018161412108642 30 25 20 15 10 5 0 index d at a import of distillate fuel oil export of distillate fuel oil variable time series plot of import of distillate fue, export of distillate fue 24222018161412108642 6 5 4 3 2 1 0 index d at a import of liquefied pet. gasses export of liquefied pet. gasses variable time series plot of import of liquefied pet., export of liquefied pet. engineering, technology & applied science research vol. 8, no. 5, 2018, 3329-3331 3331 www.etasr.com oguntunde et al.: crude oil importantion and exportation in nigeria: an exploratory and …  poisson regression analysis the poisson regression equation is obtained as: ' 1 2 3 4 5 1.124 0.02239 0.01535 0.0214 0.0044 0.067       y x x x x x (2) where, total importation equals  'ye . the coefficients with the associated standard errors are presented in table iv. the result for the deviance is provided in table v and the model summary for the deviance is provided in table vi. the results for the goodness of fit test are provided in table vii. table iv. regression coefficients terms coefficient standard error vif constant 1.124 0.225 importation of kerosene 0.02239 0.00381 13.15 importation of motor gasoline -0.01535 0.00605 17.98 importation of jet fuel -0.0214 0.0169 1.40 importation of distillate fuel oil -0.0044 0.0100 2.50 importation of liquefied pet. gasses 0.067 0.347 2.22 table v. deviance table source df adj. deviation adj. mean chisquare pvalue regression 5 136.049 27.2099 136.05 0.000 importation of kerosene 1 34.209 34.2095 34.21 0.000 importation of motor gasoline 1 6.589 6.5888 6.59 0.010 importation of jet fuel 1 1.643 1.6430 1.64 0.200 importation of distillate fuel oil 1 0.189 0.1889 0.19 0.664 importation of liquefied pet. gasses 1 0.038 0.0375 0.04 0.846 error 19 56.831 2.9911 total 24 192.881 table vi. model summary for deviance r-square adj. r-square aic 70.54% 67.94% 155.17 table vii. goodness of fit test df estimate mean chi-square p-value deviance 19 56.83119 2.99112 56.83 0.000 pearson 19 50.22589 2.64347 50.23 0.000 iv. conclusions datasets on importation and exportation of petroleum products have been studied in this paper. the conclusion was that the amount of total importation was greater than the respective amount of total exportation in nigeria. the bulk of the importation is on motor gasoline while the bulk of the exportation is on distillate fuel oil. there is a negative linear relationship between total importation and variables x2, x3, and x4 (importation of motor gasoline, importation of jet fuel and importation of distillate fuel oil respectively). the results of the poisson regression provided regarded only importation of petroleum products, further research can include analysis on the exportation of these products. acknowledgment the research was supported by the covenant university. references [1] finelib.com, crude oil mineral resources in nigeria and the states deposits, available at: https://www.finelib.com/about/nigeria-naturalresources/crude-oil-mineral-resources-in-nigeria-and-the-states-deposits/ 81 [2] t. a. adedosu, o. o. sonibare, “characterization of niger delta crude oil by infrared spectroscopy”, journal of applied sciences, vol. 5, pp. 906-909, 2005 [3] a. e. ite, u. j. ibok, m. u. ite, s. w. peters, “petroleum exploration and production: past and present environmental issues in the nigeria’s niger delta”, american journal of environmental protection, vo. 1, no. 4, pp. 78-90, 2013 [4] a. a. akinlo, “how important is oil in nigeria’s economic growth?”, journal of sustainable development, vol. 5, no. 4, pp. 165-179, 2012 [5] opendata for the national bureau of statistics, nigeria crude oil and petroleum products import and export 1986-2010, available at: http://nso.nigeria.opendataforafrica.org/hcqhlcf/nigeria-crude-oil-and-pet roleum-products-import-and-export-1986-2010, 2015 [6] p. e. oguntunde, a. o. adebowale, h. i. okagbue, “breast cancer patients in nigeria: data exploration approach”, data in brief, vol. 15, pp. 47-57, 2017 [7] p. e. oguntunde, o. a. adejumo, o. a. odetunmibi, h. i. okagbue, a. o. adejumo, “data analysis on physical and mechanical properties of cassava pellets”, data in brief, vol. 16 , pp. 286-302, 2018 [8] p. e. oguntunde, h. i. okagbue, p. i. adamu, o. a. oguntunde, s. j. oluwatunde, a. a. opanuga, “statistical analysis of bank deposits dataset”, data in brief, vol. 18, pp. 864-872, 2018 microsoft word 41-2738_s_etasr_v9_n3_pp4292-4297 engineering, technology & applied science research vol. 9, no. 3, 2019, 4292-4297 4292 www.etasr.com latif & ismail: towards multi-objective optimization of automatic design space exploration for … towards multi-objective optimization of automatic design space exploration for computer architecture through hyper-heuristic mustafa latif department of software engineering, ned university of engineering & technology, karachi, pakistan mustafalatif@neduet.edu.pk muhammad ali ismail department of computer and information systems engineering, ned university of engineering & technology, karachi, pakistan maismail@neduet.edu.pk abstract—multi-objective optimization is an np-hard problem. adse (automatic design space exploration) using heuristics has been proved to be an appropriate method in resolving this problem. this paper presents a hyper-heuristic technique to solve the dse issue in computer architecture. two algorithms are proposed. a hyper-heuristic layer has been added to the fadse (framework for automatic design space exploration) and relevant algorithms have been implemented. the benefits of already existing multi-objective algorithms have been joined in order to strengthen the proposed algorithms. the proposed algorithms, namely rrsns (round-robin scheduling nsga-ii and spea2) and rsns (random scheduling nsga-ii and spea2) have been evaluated for the adse problem. the results have been compared with nsga-ii and spea2 algorithms. results show that the proposed methodologies give competitive outcomes in comparison with nsga-ii and spea2. keywords-hyper-heuristic; multi-objective optimization; design space exploration; x86 processor i. introduction computer architectures are getting more complex day by day. as a result, the optimization of multiple objectives becomes harder too. this occurs because usually the objectives are contradictory to each other. it has been recognized that automatic design space exploration (adse) is a good solution to the stated issue. in this work, selection hyper-heuristics have been applied in conjunction with all moves as acceptance criteria. simple random selection hyper-heuristic method has been used. this hyper-heuristic method is quite dominant in the field because of its execution according to the circumstances. this heuristic type uses existing heuristic methods [1]. numerous low level heuristics can be combined depending on the problem. commonly, there are two modules of the traditional selection hyper-heuristic model [2]. these include low level heuristics selection and acceptance. selection hyperheuristic has been extensively used in different optimization issues, some of them discussed below. but, to the best of our knowledge, the literature is relatively poor in the application of selection hyper-heuristics in the adse field using the fadse tool. in [3], a meta optimization function that uses various metaheuristics simultaneously to obtain better results in appropriate time has been introduced. the difference in our approach and in [3] is the use of round-robin and the random hyper-heuristic introduction in fadse to optimize the process of dse. in this work, several meta-heuristic approaches in random and roundrobin have been used to acquire the optimized solution in appropriate time. our scheme has been improving the convergence speed. additionally, it also provides diversified multi-objective optimizations of computer architecture dse problem. an additional layer has been added to fadse. the modified hyper-heuristic algorithms rrsns (round robin scheduling nsga-ii [16] and spea2 [11]) and rsns (random scheduling nsga-ii and spea2) are presented in this paper. ii. related work this section contains details about the methods and approaches used in this work. the use of the related variants in previous works is also discussed. the tools and simulators used for implementation and the algorithms used are presented in this section. a. selection hyper-heuristic selection hyper-heuristic implementation is one of the focusing areas of this paper. in [12], authors analyzed multiple methodologies of hyper-heuristics for the scheduling problem. they claim that hyper-heuristics yield better results than metaheuristics in some scenarios. however, the authors have not revealed the details of their introduced hyper-heuristic methods. in [4], a selection hyper-heuristic-based method has been introduced. authors combined the two components of hyper-heuristic in a fashion that combines late acceptance with random selection criteria. the results have been compared with exiting approaches to evaluate the performance. it has been concluded that this combination provides remarkable results. in [13], a methodology has been introduced that uses selection hyper-heuristic. in addition, acceptance criteria used were stimulated. these acceptance criteria will help in providing feedback for future selections. corresponding author: mustafa latif engineering, technology & applied science research vol. 9, no. 3, 2019, 4292-4297 4293 www.etasr.com latif & ismail: towards multi-objective optimization of automatic design space exploration for … in [14], selection hyper-heuristic has been applied to dynamic optimization problems. authors reported the sustainability of selection hyper-heuristic in dynamic environments. classical choice function heuristics selection method and modified choice function heuristics selection method are variants of each other. in [5], it has been argued that modified choice function gives good results when low level heuristics are absent. authors analyzed the results of modified choice function after the addition of crossover low level heuristics. b. fadse tool in this paper, the tool used for design exploration is fadse (framework for automatic design space exploration). fadse is the most commonly used tool for adse (automatic design space exploration) in computer architecture [6]. authors incorporated jmetal library with fadse to take benefit of a huge number of multi-objective algorithms. different tools have been found which worked on heuristics before the development of fadse, e.g. a statistical exploration algorithm based tool archexplorer [7] which requires design of the system to perform optimization. another similar tool is m3explorer [8] which is relatively more close to fadse in its working. nasa [9] is also a popular tool for dse. it has provided a simple interface for simulators to integrate. there are many other tools for dse [6] but fadse is more generalized and capable of solving complex computational problems. c. sniper simulator in this work, sniper simulator has been used. it is a high speed simulator for x86 architecture. sniper has been developed for calculating the performance of a processor, the energy consumed by the processor and the integration area [15]. sniper has been extensively exploited for obtaining results. d. multi-objective algorithms in this work, two evolutionary multi-objective algorithms of jmetal library have been exploited. the term multi-objective is used because in these problems, multiple contradictory goals need to be achieved. nsga-ii and spea2 used in this work are the most widely accepted algorithms to obtain the desired goals in this field [10]. in case of several objectives, the stated two algorithms perform better than other multi-objective algorithms [11]. table i. notations used in algorithms po initial randomly generated population psize population size emax maximum evaluation count ecurrent current evaluation count psolnew population generated by low level heuristics psol problem solution iii. research methodology this section presents the hyper-heuristic methodology used to accelerate the dse process of a multi core processor. it has been done by using multiple meta-heuristics in random and round-robin fashion to obtain quasi-optimal solution. the objective is to obtain better results in appropriate time. this strategy improves convergence speed. moreover, it also provides diversity of multi-objective optimization of dse problem of computer architecture. fadse framework [6] has been modified by adding a hyper-heuristic layer as shown in figure 1. two selection hyper-heuristic models (rrsns and rsns) have been introduced in fadse. in rrsns, roundrobin fashion scheme [17] has been used to run two state-ofthe-art multi-objective optimization algorithms (nsga-ii and spea2) as llh (low level heuristic). there are two variations of rrsns. rrsns1 schedules nsga-ii first and then spea2 and in rrsns2, spea2 has been scheduled first then nsgaii. in rsns, simple random [12] hyper heuristic selection mechanism has been used to find the quasi-optimal solution. in both rrsns and rsns models all moves [5] move acceptance method has been used. fig. 1. fadse with hyper-heuristic layer table i displays the notations used in this study. the pseudo codes of rrsns and rsns are shown in figures 2 and 3 respectively. in rrsns, fadse is configured by using its configuration file in which the number of objectives, parameters of processor architecture to be tuned, and the database configuration to reused already simulated results have been defined. also, the number of fadse clients and configuration parameters of nsga-ii and spea2 metaheuristic algorithms and their order of scheduling have been defined. after initialization, a random solution of the problem is produced and passes as a parent population to the first one in the round-robin order of llh. llh then applies the evolutionary operation (crossover, mutation) and generate offspring population. the generated individuals are evaluated using sniper simulator. sniper simulator is used as the objective function of the adse process. when the first one produces the solution of the problem, it is passed to the next order llh and so on. the last one gives its solution to the first on the llh list. the iterative process continues until the termination condition is reached i.e. when the evaluation count reached its maximum engineering, technology & applied science research vol. 9, no. 3, 2019, 4292-4297 4294 www.etasr.com latif & ismail: towards multi-objective optimization of automatic design space exploration for … limit defined in the initialization phase. in rsns, the initialization stage is similar to the rrsns except that the order of llh is not defined. instead, the order is generated randomly. all the generated solutions are accepted as parent population of the next iteration. the iteration is finished when the current evaluation count equals to the maximum evaluation count. 1 procedure rrsns() begin 2 initilization() /* initilize nsga-ii and spea2 algorithum, initial random population po, psize, emax ecurrent=0*/ 3 selected_order_list_of_llh=list_perturbative_llh() 4 psol=po/* assign randomly generated solution as a problem solution*/ 5 while ecurrent < emax do 6 for i=1 to selected_order_list_of_llh.length 7 psolnew=generate_population_through_llh(psol) 8 psol=psolnew /*update the problem solution with newly generated solution*/ 9 end loop 10 end while 11 return psol 12 end fig. 2. rrsns algorithm 1 procedure rsns() begin 2 initilization() /* initilize nsga-ii and spea2 algorithum, initial random population po, psize, emax ecurrent=0*/ 3 psol=po/* assign randomly generated solution as a problem solution*/ 4 while ecurrent < emax do 5 selected_llh=randomly_select_llh(list_of_perturbative_llh() 6 psolnew=generate_population_through_llh(psol) 7 psol=psolnew /*update the problem solution with newly generated solution*/ 8 end while 9 return psol 10 end fig. 3. rsns algorithm table ii. hardware parameters to tune microarchitecture parameter range of values min max individual number of cores 1 4 3 dram interleaving controllers 1 64 7 l1 data cache associativity 8 16 2 l1 data cache size [kb] 32 256 4 l2 cache associativity 8 16 2 l2 cache size [kb] 32 2048 7 l3 cache associativity 8 16 2 l3 cache size [kb] 128 32768 9 l3 cache shared cores 1 16 5 the dse process of 211,680 configurations of the x86 multi-core processor has been used. the list of parameters and their possible values are shown in table ii. the possible values of each parameter are exponents of 2 i.e. in case of the number of cores, the possible values are {1, 2, 4}. the dse process was done 5 times with 2 objectives and 6 x86 architectural parameters. seven splash-2 [18] benchmarks (fmm, lu.cont, ocean.cont, radix, water.sp, volrend, fft) were used to apply on each individual in the dse process. intel quad core i7, 3.2ghz processor with 4gb ram has been used to implement the dse process. two fadse clients were used, running in distributed environment with one fadse server. fifty individuals per generation and a total of 50 generations were used. the configuration parameters of the multi-objective optimization algorithms used in the study are shown in table iii. table iii. configuration parameters parameters value crossover operator single point crossover probability 0.90 mutation operator bit-flip mutation probability 0.16 selection operator binary tournament population size 50 archive size 50 teremination condition after 50 generations iv. results comparison of the proposed algorithms (rrsns and rsns) has been done with already presented state-of-the-art multi-objective evolutionary algorithms (nsga-ii and spea2). initially the two variations of rrsns (rrsns1 and rrsns2 were compared. the main difference between these variations is that in rrsns1, nsga-ii is scheduled first and in rrsns2, spea2 is scheduled first using the coverage quality metric [19]. the coverage metric can be used to compare two different multi-objective algorithms. it gives quantitative results regarding the percent of an algorithms’ individuals are non-dominated by the individuals of another algorithm. figure 4 shows that the coverage of rrsns1 is better than rrsns2’s. the results are mostly equal in the first 15 generations and then rrsns1 gives better results. figure 5 illustrates that both rrsns1 and rsns are competing each other after the 27th generation but overall the rsns gives better results. fig. 4. coverage comparison between rrsns1 and rrsns2 fig. 5. coverage comparison between rrsns1 and rsns engineering, technology & applied science research vol. 9, no. 3, 2019, 4292-4297 4295 www.etasr.com latif & ismail: towards multi-objective optimization of automatic design space exploration for … figures 6 and 7 show that rrsns and rsns give better results than nsga-ii. figures 8 and 9 show that rrsns and rsns give better coverage than spea2. in figure 8 it can be seen that in the initial generation spea2 gives good readings but after the 17th generation rrsns1 gives better results. fig. 6. coverage comparison between nsga-ii and rrsns1 fig. 7. coverage comparison between nsga-ii and rsns fig. 8. coverage comparison between rrsns1 and spea2 fig. 9. coverage comparison between rsns and spea2 in figure 10, the mentioned algorithms using hyper-volume metric [19] are compared. it can be seen that rrsns1 convergences faster than all the other algorithms. spea2 reaches its maximum at the very beginning but stucks in local minima due to the archiving mechanism and density computation method (duplicate solution) [11]. rsns is fast and reaches its maximum hyper-volume at the 16th generation as compared to the rrsns1, who reached its maximum at 37th the generation. both rrsns1 and rsns give better hypervolume than nsga-ii and spea2 because they both use the strengths of both nsga-ii and spea2. the two set hypervolume (tshd) metric [20] shown in figure 11 shows that ~94% of the hyper-volume is common to both the rrsns1 and rsns at the initial stage. after that the common hypervolume percentage increases up to ~99.5%. initially rsns contribution in the non-dominated hyper-volume is good up to the 21th generation, then rrsns1 contribution is greater than rsns up to the final generation. fig. 10. hypervolume comparison fig. 11. two set hypervolume difference (rrsns1 vs rsns) fig. 12. two set hypervolume difference (nsga-ii vs rrsns1) engineering, technology & applied science research vol. 9, no. 3, 2019, 4292-4297 4296 www.etasr.com latif & ismail: towards multi-objective optimization of automatic design space exploration for … figures 12 and 13 show the tshd between nsga-ii vs rrsns1 and nsga-ii vs rsns. figure 12 illustrates that nsga-ii non-dominated hyper-volume is good before the 17th generation. after that, rrsns1 produces greater nondominated hyper-volume, although all the time ~97% of the total hyper-volume is common among these two. it can be interpreted form figure 13, that most of the time rsns gives all non-dominated hyper-volume, but it can also be seen that the difference is only 2% and 98% non-dominated hypervolume is common. similarly, in figures 14 and 15 the comparison of tshd between rrsns1 vs spea2 and rsns vs spea2 is shown. it can be observed in both figures that initially spea2 gives better solution, but later on rrsns1 and rsns produce superior hyper-volume than spea2. in figure 16, the pareto front approximation of all compared algorithms is shown. fig. 13. two set hypervolume difference (nsga-ii vs rsns) fig. 14. two set hypervolume difference (rrsns1 vs spea2) fig. 15. two set hypervolume difference (rsns vs spea2) fig. 16. pareto front approximation rrsns, rsns, nsga-ii ans spea2 from figure 16, it can be seen that rrsns gives a unique solution which no other algorithm discovered during the adse process. also, rsns gives a more dominated solution as compared to nsga-ii and spea2. v. conclusion hyper-heuristic is a heuristic that runs on top of the existing or new low level heuristics to get the advantages of a wide range of existing or new heuristics to solve complex multiobjective optimization problems. in this paper, two hyperheuristic selection algorithms have been proposed to solve the dse process of an x86 multi core processor. a new hyperheuristic layer has been added in fadse and two algorithms were proposed are implemented. the biggest advantage of our proposed algorithms (rrsns, rsns) is that they use the combined advantages of existing multi-objective algorithms to solve the dse problem. the proposed rrsns and rsns algorithms have been evaluated for adse problem and compared with two state-of-the-art multi-objective algorithms, nsga-ii and spea2. results indicate that the proposed approaches give competitive results compared to nsga-ii and spea2. in the future, more existing multi-objective algorithms can be added in rrsns and rsns so that they produce more diversified and prominent solutions for the dse process of computer architecture. references [1] e. k. burke, m. r. hyde, g. kendall, g. ochoa, e. ozcan, j. r. woodward, “a classification of hyper-heuristic approaches: revisited”, in: handbook of metaheuristics, pp. 453-477, springer, 2019 [2] s. s. choong, l. p. wong, c. p. lim, “automatic design of hyperheuristic based on reinforcement learning”, information sciences, vol. 436-437, pp. 89-107, 2018 [3] l. vintan, r. chis, m. a. ismail, c. cotofana, “improving computing systems automatic multiobjective optimization through metaoptimization”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 35, no. 7, pp. 1125-1129, 2016 [4] w. g. jackson, e. ozcan, j. h. drake, “late acceptance-based selection hyper-heuristics for cross-domain heuristic search”, 13th uk workshop on computational intelligence, guildford, uk, september 9-11, 2013 [5] j. h. drake, e. ozcan, e. k. burke, “a modified choice function hyper-heuristic controlling unary and binary operators”, ieee congress on evolutionary computation, sendai, japan, may 25-28, 2015 engineering, technology & applied science research vol. 9, no. 3, 2019, 4292-4297 4297 www.etasr.com latif & ismail: towards multi-objective optimization of automatic design space exploration for … [6] h. a. calborean, multi-objective optimization of advanced computer architectures using domain-knowledge, phd thesis, university of sibiu, 2011 [7] v. zaccaria, g. palermo, f. castro, c. silvano, g. mariani, “multicube explorer: an open source framework for design space exploration of chip multi-processors”, 23th international conference on architecture of computing systems 2010, hannover, germany, february 22-23, 2010 [8] c. silvano, w. fornaciari, g. palermo, v. zaccaria, f. castro, m. martinez, s. bocchio, r. zafalon, p. avasare, g. vanmeerbeeck, c. ykman-couvreur, m. wouters, c. kavka, l. onesti, a. turco, u. bondik, g. mariani, h. posadas, e. villar, c. wu, f. dongrui, z. hao, t. shibin, “multicube: multi-objective design space exploration of multi-core architectures”, ieee computer society annual symposium on vlsi, kefalonia, greece, july 5-7, 2010 [9] z. j. jia, a. d. pimentel, m. thompson, t. bautista, a. nunez, “nasa: a generic infrastructure for system-level mp-soc design space exploration”, 8th ieee workshop on embedded systems for real-time multimedia, scottsdale, usa, october 28-29, 2010 [10] j. j. durillo, a. j. nebro, “jmetal: a java framework for multi-objective optimization”, advances in engineering software, vol. 42, no. 10, pp. 760-771, 2011 [11] e. zitzler, m. laumanns, l. thiele, spea2: improving the strength pareto evolutionary algorithm, tik-report, vol. 103, swiss federal institute of technology, 2001 [12] p. cowling, g. kendall, e. soubeiga, “a hyperheuristic approach to scheduling a sales summit”, in: lecture notes in computer science, vol. 2079, springer, 2001 [13] r. bai, j. blazewicz, e. k. burke, g. kendall, b. mccollum, “a simulated annealing hyper-heuristic methodology for flexible decision support”, 4or, vol. 10, no. 1, pp. 43-66, 2012 [14] b. kiraz, a. s. etaner-uyar, e. ozcan, “selection hyper-heuristics in dynamic environments”, journal of the operational research society, vol. 64, no. 12, pp. 1753-1769, 2013 [15] r. chis, a. florea, c. buduleci, l. vintan, “multi-objective optimization for an enhanced multi-core sniper simulator”, proceedings of the romanian academy-series a, vol. 19, no. 1, pp. 8593, 2018 [16] k. deb, a. pratap, s. agarwal, t. meyarivan, “a fast and elitist multiobjective genetic algorithm: nsga-ii”, ieee transactions on evolutionary computation, vol. 6, no. 2, pp. 182-197, 2002 [17] a. kheiri, e. ozcan, “a hyper-heuristic with a round robin neighbourhood selection”, in: lecture notes in computer science, vol. 7832, springer, 2013 [18] s. c. woo, m. ohara, e. torrie, j. p. singh, a. gupta, “the splash-2 programs: characterization and methodological considerations”, 22nd annual international symposium on computer architecture, santa margherita ligure, italy, june 22-24, 1995 [19] c. a. c. coello, g. b. lamont, d. a. van veldhuizen, evolutionary algorithms for solving multi-objective problems, springer, 2007 [20] e. zitzler, l. thiele, “multiobjective evolutionary algorithms: a comparative case study and the strength pareto approach”, ieee transactions on evolutionary computation, vol. 3, no. 4, pp. 257-271, 1999 engineering, technology & applied science research vol. 7, no. 2, 2017, 1535-1539 1535 www.etasr.com hasanpour et al.: variable speed limits: strategies to improve safety and traffic parameters… variable speed limits: strategies to improve safety and traffic parameters for a bottleneck m. z. hasanpour m. r. ahadi a. s. moghadam g. a. behzadi transportation research institute, road, housing & urban development research center tehran, iran transportation research institute, road, housing & urban development research center tehran, iran transportation planning shomal university iran transportation research institute, road, housing & urban development research center tehran, iran abstract—the primary purpose of the speed limit system is to enforce reasonable and safe speed. to reduce secondary problems such as accidents and queuing, variable speed limits (vsl) has been suggested. in this paper vsl is used to better safety and traffic parameters. traffic parameters including speed, queue length and stopping time have been pondering. for vls, an optimization decision tree algorithm with the function of microscopic simulation was used. the results in case of sub saturated, saturated and supersaturated at a bottleneck are examined and compared with the allaby logic tree. the results show that the proposed decision tree shows an improved performance in terms of safety and comfort along the highway. the vsl pilot project is part of the road safety improvement program included in iran’s road safety action plan that is in the research process in the bhrc research institute, road and housing & urban development research that is planned for next 10-year transportation safety view plan. keywords-variable speed limits; decision trees; safety, transportation; highway; traffic i. introduction worldwide, an estimated 1.2 million people are killed in road crashes each year and as many as 50 million are injured [1]. current strategies recognize that speed management should be central and have refocused attention on road and vehicle design and related protective features. the “blame the victim” culture is superseded by blaming the traffic system which throws illegal speed on the shared responsibility and accountability for a safe system [2]. international research has shown that the variable speed limits (vsl) system is a successful traffic engineering application used to manage traffic conditions during congestion, incidents, road building, and inclement weather [3]. vsl could be implemented in appropriate areas to disappear off the potential for driver error, excessive speeds, and the velocity differential between cars and to enhance safety [4]. also, very different studies have been performed that quantify the predicted benefits of implementing comprehensive vsl control strategies on state highways. in [5, 6] authors used microscopic simulation to examine the impacts of vsl responses to real-time traffic safety standards. in [5], it was found that that, for highly congested areas, vsl provided a reduction in crash potential of 25%, but increased travel time. in contrast, in [6] it was found that vsl provided a large reduction in crash potential during low traffic (higher speed) conditions, but had little impact for peak period conditions. authors in [6], likewise comprise a uniform decrease in travel time for the low traffic conditions using vsl, although the relative change in travel time from the non-vsl is controlling the condition to vsl controlling condition was very depressed. in [7] , authors evaluated the impact of vsl in an urban freeway in toronto, canada. the study was conducted using the microscopic simulator paramics combined with a categorical crash model developed in [5]. the vsl algorithm used was based on a logic tree that uses threshold values for a traffic flow, occupancy, and average travel speed. each vsl sign was associated to an adjacent loop detector, and each sign operated individually. the outcomes of the simulation indicated that the implementation of vsl signs could significantly improve safety, however the authors concluded that the use of vsl signs increased the travel time for all traffic scenarios considered. in [8], authors applied a method to explore the parallels between ramp metering and applying vsl upstream of a potential bottleneck or high volume merging situation. the metanet second order macroscopic model was modified to allow the vsls to be integrated.the study showed that when applied upstream, the vsl can act similarly to ramp metering where the current is brought back on the mainstream sooner than along the incline. the traffic arriving at the bottleneck is temporarily cut down and the system delays propagation of the congestion. four scenarios were evaluated: no-control, vsl control, ramp metering, and integrated instruction. the vsl case decreased total time spent in the system (tts) by 15.3%, and when vsls and ramp metering are used in conjunction the tts were reduced by as much as 19.5%. the survey concluded that traffic flow and mental ability can be improved through vsl use by boiling down the capacity drop at bottlenecks. nevertheless, if the vsl is applied at under-critical conditions without the potential for bottleneck mitigation, mean speed is turned down and flow efficiency is diminished. regarding these results and the limitations of empirical studies, the expected overall benefit of implementing vsls is still unclear [9]. engineering, technology & applied science research vol. 7, no. 2, 2017, 1535-1539 1536 www.etasr.com hasanpour et al.: variable speed limits: strategies to improve safety and traffic parameters… the purpose of this survey concentrates on fine tuning the algorithm of vsls algorithms for improve safety and traffic parameters. traffic parameters includes speed changes, queue length and time period. to optimize the vsl algorithm, a decision tree algorithm was used. in the following, the vsl performance in the three following conditions, including the sub saturated, the saturated and supersaturated at a bottleneck examined and compared with the results of an allaby logic tree. ii. description of study network to set a proper authorized speed and examine its effect on safety and terrific parameters, a specific part of the haraz road in iran was selected. a system of traffic, pavement and visibility sensors will be set up to observe conditions and provide operations staff with recommended speeds. iran’s road weather or traffic road conditions are shifting rapidly, particularly in high altitude mountain passes; operations staff will continuously monitor the conditions information and set the digital variable speed signs accordingly. overhead message signs will let travelers know when they’re entering a variable speed zone, and warn drivers to be aware of changing weather and traffic conditions. variable speed limits will be enforced by the police. the reason of choosing this part of the road is the change in the number of lanes and the bottleneck at this location. the study path is approximately 4 kilometers long. information and data required for the research are obtained from cameras installed in the studied area. the set-up is shown in figure 1. traffic volume, vehicle types, density per 20 seconds and rate of 10 vehicles per one minute are the first obtained information. the vehicles are considered as 3 types of personal vehicles, vans and buses. authorized speed was 100 kilometers per hour in the twolane section and 60 kilometers per hour in the one-lane section and the peak hour of traffic was 3:00 pm till 6:00 pm. fig. 1. exposure intervals cameras iii. simulation development: base model in [7], authors used simulation software paramics, to simulate vsl which speed was determined based on the decision tree. figure 2 shows a cross-sectional region of the study and figure 3 summarizes the logic used in the algorithm. each vsl sign connects to the adjacent sensor. for low volume (less than 1,600 vehicles per hour), “occupancy”, has been practiced as a constituent of the variables for reducing speed. for high volume (more than 1600 vehicles per hour) “occupancy” is not counted. finally, according to the average speed, the speed is determined and displayed. simulation results showed that vsl singes can improve safety by reducing speed, but increase the travel time for all considered traffic conditions. figure 4 shows, speed changes before and after implementation of vsl at study region [10]. in this method the highway is divided into specific sections, which each section has a sensor and vsl sign and acts as a unit. then by using of statistical information of traffic of each department (average current rate, and the rate of occupancy) thresholds and decision parameter sets and a tree structure for reaching conclusions about traffic speed limits in the different conditions forms. a. new model for the analysis and simulation of the network, aimsun simulation software is used. aimsun is one of the best microscopic simulation software and the ability to compound static and dynamic approaches in a single environment is its unique characteristic. before the simulation, aimsun should be calibrated to create a network same as the real one to observe the changes after creating a new management system. to do this, at first, path practical density was estimated according to following equations and finally compared with the aimsun output. j w hv pc=c nf f f (1) i w hv d v sf =2800* f f f c æ ö÷ç ÷ç ÷çè ø (2) fig. 2. the plan of implementation of vsl signs and sensors engineering, technology & applied science research vol. 7, no. 2, 2017, 1535-1539 1537 www.etasr.com hasanpour et al.: variable speed limits: strategies to improve safety and traffic parameters… fig. 3. decision tree to determine the new speed sent from vsl fig. 4. speed changes after vsl implementation the studied network was drawn in aimsun software and the primary simulation was performed after calculating the practical capacity of a path. ultimately, the main turnout was achieved from aimsun to calibrate the desired network; the answers indicated that volume, speed and travel time obtained from studying the region, were almost equal with the simulation results that indicated that the path is correctly calibrated in aimsun. rules and the simulation results are shown in table i. regarding to gathered information, the practical capacity and the average speed of the studied region was 1900 vehicles per hour and 70 kilometers per hour, respectively. table i. results of empirical and practical output practical results simulation results variable volume 1959 veh/hr 1830 veh/hr average speed 70 km/hr 68 km/hr travel time 47.5 sec/km 53 sec/km iv. the optimal decision trees weka software is used for designing the decision tree. weka provides a slightly complete collection of the latest machine learning algorithms and data pre-processing tools for data mining. this software is designed so that different algorithms can be examined on new data collections and includes the algorithms for all standard problems of data mining such as regression, classification, clustering, mining the association rules, choosing the features and predicting their class based on primary data. the weka software package contains the execution of the latest general version of c4.5 decision tree learning or the j48 and decision trees are created automatically through adjusting defined parameters and are displayed as an ascii statement [11]. three grades were designed for data: • e class; which is for speed ranges or same behavior in los e. • d class; which is for speed ranges or same behavior in los d • b class; which is for speed ranges or same behavior in los b. weka software needs training data to forecast the track of instruction of the main data and construct the decision trees. for this purpose, the data obtained from the first week of observation were used as the training data. after each data class was placed on the original data, re-analysis was performed and the ultimate decision tree in weka was achieved. two different input groups were used: (1) mean speed, speed variance and volume (2) mean speed, speed variance, density and volume. the decision tree outputs based on group (1) showed less validity whereas the outputs based on group (2) had higher validity in terms of classification and accuracy. high validity of the tree is mainly attributed to the density variable. the constructed decision tree and the statistics are depicted in figure 5 and table 2, respectively. fig. 5. decision tree design by weka software for: mean speed, speed variance, density and volume table ii. the results of the decision tree in different modes group (2): mean speed, speed variance, density and volume group (1): mean speed, speed variance and volume 91.1 % 86.6 % correctly classified instances 8.8 % 13.3 % incorrectly classified instances 0.83 0.7 kappa statistic 0.875 0.615 b 0.667 0.538 d 0.945 0.984 e tp rate 0.91 0.865 f-measure v. vsl design network to investigate the created path in three density conditions of sub saturation, saturation, super-saturation, a simulation volume of 1300 to 2700 vehicles per hour is applied to network and the simulation is performed for two conditions (without control and controlled by the decision tree). to implement the decision tree and utilize variable speeds in aimsun, three parameters should be fixed. at the beginning, the sensors were placed on simulation regarding to the site of cameras which is engineering, technology & applied science research vol. 7, no. 2, 2017, 1535-1539 1538 www.etasr.com hasanpour et al.: variable speed limits: strategies to improve safety and traffic parameters… shown in figure 6. then, two parameters of tree constructing were created by producing different policies and triggers and were applied on sensors of the primary tree. triggers are responsible for the activation and non-activation time. the insurance was based on speed change in this simulation and three types of 60, 80 and 100 speed was produced according to the number of modifications to cope during the itinerary. selecting 60, 80, 100 authorized speeds is because of the fact that the selected speed should be more eminent than the speed change threshold (50 and 70) so that sensors are able to change over from one active branch to non-active branch and the speed changes are brought near. eventually, through correct parameter setting, five simulation repetitions were performed for each volume. results are shown in table iii. fig. 6. positioning of sensors and vsl signs vi. vsl impact results for analyzing the variation of variables, the proposed decision tree is compared with an allaby logic tree at three traffic conditions: sub saturated, saturated and supersaturated with and without controlling the vsl signs. influential variables such as queue length, intermediate speed of travel, the amount of delay, numbers and stops time are examined. a. vsl traffic impacts the results regarding queue length are shown in figure 7. as shown, the vsl helps in reducing the queue length. the biggest reduction happened when the highway reached its capacity. a reduction of about 20% was reached with the new decision tree, compared to the results of the allaby logic tree. b. vsl safety impact 1) harmonic speed as shown in figure 8 the graph of average speed at the saturation capacity condition without any vsl is a sharp slope which shows that there is a sudden change in the speed and this an increased possibility for accidents. this improved the application of vsl and it is more improved with the proposed decision tree compared to the allaby logic tree and a higher average velocity is also achieved. 2) delay time, stop time, number of stop time as shown in figure 9, when the speed limit is controlled by the new decision tree algorithm, the delay, in small volumes increased, but in saturated volume did not interchange. but according to figures 10 and 11, which shows the vehicles stop time and the number of stops, when the study region has no variable speed limit control vehicles stop time and numbers of vehicle stops is larger. this means that safety is actually increased through the use of vsl as a more smooth movement is achieved. fig. 7. vsl effect on queue length fig. 8. vsl effect on harmonic speed fig. 9. vsl effect on delay time engineering, technology & applied science research vol. 7, no. 2, 2017, 1535-1539 1539 www.etasr.com hasanpour et al.: variable speed limits: strategies to improve safety and traffic parameters… fig. 10. vsl effect on stop time fig. 11. vsl effect on number of stops table iii. aimsun simulation results volume delay time vehicle density vehicle flow vehicle harmonic speed vehicle standard deviation mean queue vehicle number of stops vehicle stop time vehicle 1300 1.518 3.78 1272.66 90.034 5.3 0 0.028 0.018 1400 1.68 4.09 1365.20 90.642 5.3 0 0.03 0.026 1500 2.002 4.42 1465.73 90.886 5.4 0.002 0.038 0.052 1600 2.13 4.734 1565.2 87.602 6.5 0.028 0.048 0.108 1700 6.666 5.602 1653.60 81.54 7.9 0.576 0.11 0.644 1800 10.446 6.432 1744.13 75.422 8.6 1.878 0.202 1.548 1900 19.488 8.07 1809.19 63.456 11.5 8.986 0.51 5.2 2000 42.58 11.904 1827.86 45.694 13.6 40.69 1.436 18.17 2100 66.772 16.276 1829.33 35.762 15.2 86.486 2.378 34.53 2200 85.856 20.224 1838.66 29.874 14.8 131.11 3.21 48.14 2300 110.27 25.242 1837.20 25.43 13.4 183.11 4.252 66.64 2400 130.31 29.95 1833.46 21.458 12.9 251.45 5.138 81.75 2500 150.91 34.654 1832.93 19.128 11.9 312.46 5.648 97.62 2600 167.39 38.13 1831.46 17.582 11.4 355.65 6.332 110.4 2700 183.63 40.85 1832.53 16.298 10.8 391.51 6.944 123.7 vii. conclusion vsl is a promising highway traffic management tool for improving traffic safety by offering drivers more realistic speed limits when the driving environments are compromised by traffic congestion, incidents or adverse weather. the present work concentrates on fine tuning the vsl algorithm. traffic parameters considered includes speed changes, waiting line, time stop. a decision tree algorithm was used for optimization. the vsl performance during a heavy congestion for a bottleneck was considered. results show 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transactions on intelligent transportation systems, vol. 8, no. 4, pp. 671-680, 2007 [8] r. carlson, i. papamichail, m. papageorgiou, a. messmer, “variable speed limits as a mainline metering device for freeways”, transportation research board annual meeting, washington, dc, paper #10-1529, 2010 [9] m. abdel-aty, r. cunningham, v. gayah, l. hsia, “dynamic variable speed limit strategies for real-time crash risk reduction on freeways”, transportation research record no. 2078, transportation research board of the national academies, washington, dc, vol. 1, no. 1, pp. 108-116, 2008 [10] fhwa-sa-12-022, “guidelines for the use of variable speed limit systems in wet weather”, us department of tranportation, 2012 [11] f. rahmani, f. ghahari , weka software guide, 2010 microsoft word etasr_theofilatos-ed.doc etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 269-272 269 www.etasr.com theofilatos et al: modeling and trading the eur/usd exchange rate using machine learning techniques modeling and trading the eur/usd exchange rate using machine learning techniques konstantinos theofilatos dpt of computer engineering and informatics university of patras patras, greece theofilk@ceid.upatras.gr spiros likothanassis dpt of computer engineering and informatics university of patras patras, greece likothan@ceid.upatras.gr andreas karathanasopoulos london metropolitan business school london, united kingdom a.karathanasopoulos@londonmet.ac.uk abstract— the present paper aims in investigating the performance of state-of-the-art machine learning techniques in trading with the eur/usd exchange rate at the ecb fixing. for this purpose, five supervised learning classification techniques (k-nearest neighbors algorithm, naïve bayesian classifier, artificial neural networks, support vector machines and random forests) were applied in the problem of the one day ahead movement prediction of the eur/usd exchange rate with only autoregressive terms as inputs. for comparison reasons, the performance of all machine learning techniques was benchmarked by two traditional techniques (naïve strategy and moving average convergence/divergence model). trading strategies produced by the machine learning techniques of support vector machines and random forests clearly outperformed all other strategies in terms of annualized return and sharp ratio. to the best of our knowledge, this is the first application of random forests in the problem of trading with the eur/usd exchange rate providing extremely satisfactory results. keywordseur/usd exchange rate; future direction prediction; naïve strategy; macd strategy; naïve bayesian classifier; knearest neighbors classifier; svm; random forests; leverage; transaction costs i. introduction the application of machine learning techniques for market predictions has been widely established in the scientific community. this paper deals with the application of a variety of state-of-the-art machine learning techniques in the problem of predicting the one day ahead movement direction of the euro-usd exchange rates. developing high accuracy techniques for predicting financial time series is a very crucial problem for economists, investigators and analysts. the traditional statistical methods, used by economists in the past years, seem to fail to capture the discontinuities, the nonlinearities and the high complexity of financial time series. complex machine learning techniques like artificial neural networks, support vector machines (svm) and random forests provide enough learning capacity and are more likely to capture the complex non-linear models which are dominant in the financial markets. some approaches examining the performance of machine learning techniques in trading with the euro-usd exchange rate have already been developed. in [1], dunis and williams demonstrated the ability of multi layer perceptron (mlp) artificial neural networks in modeling and trading with the eur/usd exchange rate. their empirical results showed that the mlp outperformed all other benchmark models used. next, in [2], ullrich et al. used svms to trade with a variety of foreign exchange rates including eur/usd. their results indicated that svms outperformed artificial neural networks and all other traditional techniques used in this paper for comparative reasons. finally, in [3], dunis et al. compared higher order neural networks, psi sigma networks, recurrent networks and mlp in the task of trading with the euro/usd exchange rate. mlp was proved to outperform all other neural networks variation. the rest of the paper is organized as follows: in section ii, the dataset of euro-usd exchange rates is presented. in section iii, all the traditional and machine learning techniques used in the present paper are briefly described. in section iv the comparative results are presented and in section v they are discussed and some future research directions are proposed. ii. the eur/usd exchange rates and related financial data the european central bank (ecb) publishes a daily fixing for selected eur exchange rates: these reference mid-rates are based on a daily concentration procedure between central banks within and outside the european system of central banks, which normally takes place at 2.15 p.m. ecb time. the reference exchange rates are published both by electronic market information providers and on the ecb’s website shortly after the concentration procedure has been completed. although only a reference rate, many financial institutions are ready to trade at the eur fixing and it is therefore possible to leave orders with a bank for business to be transacted at this level. the ecb daily fixing of the eur/usd is therefore a tradable level which makes using of a more realistic alternative to, say, london closing prices and this is the series that we etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 269-272 270 www.etasr.com theofilatos et al: modeling and trading the eur/usd exchange rate using machine learning techniques investigate in the present paper. eur/usd is quoted as the number of usd per euro. specifically, the data which are used for our problem were downloaded from [4], and they were split as shown in table 1 in order to train and evaluate our models. table i. euro/ysd datasets. name of period trading days beginning end total dataset 2294 17 january 2002 30 december 2010 training dataset 1363 17 january 2002 16 may 2007 validation dataset 459 17 may 2007 2 march 2009 testing dataset [out of sample dataset] 471 3 march 2009 30 december 2010 the graph in figure 1 shows the total dataset for the eur/usd. as inputs to our models we selected a set of autoregressive terms of the eur/usd exchange rate returns presented in table 2. fig. 1. euro/usd daily fixing prices (total dataset) table ii. explanatory variables. number input variable lag 1 eur/usd exchange rate return 1 2 eur/usd exchange rate return 2 3 eur/usd exchange rate return 3 4 eur/usd exchange rate return 4 5 eur/usd exchange rate return 5 6 eur/usd exchange rate return 6 7 eur/usd exchange rate return 7 8 eur/usd exchange rate return 8 9 eur/usd exchange rate return 9 10 eur/usd exchange rate return 10 iii. forecasting models a. benchmark models in the present paper, the machine learning methods presented in section 3.2 were benchmarked with 2 traditional strategies, namely naïve strategy [3] and a moving average convergence/divergence technical model (macd) [3]. the naïve strategy takes the most recent period change as the best prediction of the future change. the macd strategy used is quite simple. two moving average series are created with different moving average lengths. the decision rule for taking positions in the market is straightforward. positions are taken if the moving averages intersect. if the short-term moving average intersects the long term moving average from below a ‘long’ position is taken. conversely, if the long-term moving average is intersected from above a ‘short’ position is taken. b. machine learning models some of the state-of-the-art machines learning classification techniques were applied in the problem of the one day ahead prediction of the direction movement of the eur/usd exchange rate. these machine learning techniques are: k-nearest neighbor classifier (knn), naïve bayesian classifier, support vector machines (svm) and random forests. in order to find the optimal parameters for each machine learning technique we used only the training and validation datasets leaving the test set for the final evaluation of the algorithms. doing this we avoid specializing in our dataset and getting misleading results. the parameters were optimized using genetic algorithms [5]. all implementations were done using matlab r2009a edition. k-nearest neighbors [6] is a method for classifying objects based on closest training examples in the feature space. the knn method is considered one of the simplest machine learning techniques. an object is classified by a majority vote of its neighbors. if k=1, then the object is assigned to the class of its nearest neighbor. in our case study the optimal k found was 8. the naïve bayesian classifier [7] is a simple probabilistic classifier with strong assumptions of independence among input variable. it is the classifier derived from the use of bayes’ theorem. bayes’ theorem expresses the conditional probability, or “posterior probability”, of a hypothesis h, (i.e. its probability after evidence e is observed) in terms of the “prior probability” of h, the prior probability of e and the conditional probability of e given h. in implies that evidence has a stronger confirming effect if it was more likely before being observed. bayes’ theorem is valid in all common interpretations of probabilities, and it is commonly applied in science and engineering. the main disadvantages of naïve bayesian classifiers are their assumptions about the independency of the input variables, which is not usually the case in real problems. neural networks [8] exist in several forms in the literature. the most popular architecture is the multi-layer perceptron (mlp). a mlp consists of at least three layers of nodes. the network processes information as follows: the input nodes etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 269-272 271 www.etasr.com theofilatos et al: modeling and trading the eur/usd exchange rate using machine learning techniques contain the value of the explanatory variables. each node of the hidden layers passes incoming information through a nonlinear activation function and passes it to the output layer if the calculated value is above a threshold. each node of one layer has weighted connections to all other nodes of the next layer. the training of the network (which is the adjustment of its weights in the way that the network maps the input value of the training data to the corresponding output value) starts with randomly chosen weights and proceeds by applying a supervised learning algorithm, called back propagation of errors. since networks with sufficient hidden nodes are able to learn the training data (as well as their outliers and their noise) by heart, it is crucial to stop the training procedure at the right time to prevent overfitting (this is called ‘early stopping’). in the present paper the best network’s architecture found was the one using one hidden layer with 19 hidden neurons. support vector machines (svm) are a group of supervised learning methods that can be applied in classification and regression problems. svms represent an extension to non linear models of the generalized algorithm developed by vapnik [9]. they have already been applied in many scientific problems. specifically, svm have already been used in many prediction and classification problems in finance and economics although they are still far from mainstream. the few financial applications so far have only been published in statistical learning and artificial intelligence journals. svm models were originally defined for the classification of linearly separable classes of objects. for any original separable set of two-class objects svm are able to find the optimal hyperplanes that separates them providing the bigger margin area between the two hyperplanes. furthermore they can also be used to separate classes that cannot be separated with a linear classifier. in such cases, the coordinates of the objects are mapped into a feature space using nonlinear functions. the feature space in which every object is projected is a high dimensional space in which the two classes can be separated with the linear classifier. in the present work we used the radial basis function (rbf) as kernel function for the svm models because of its efficiency in providing very high performance classification results. the optimal rbf parameters c and gamma were found to be 64 and 2 respectively re-assuring that the model does not over fit. another sophisticated machine learning method, such as the support vector machines (svm), is the random forest method. random forests [10] are ensemble classifiers that "grow" many decision trees simultaneously where each node uses a random subset of the features considered. specifically, random forests are a combination of tree predictors such that each tree depends on the values of a random vector sampled independently and with the same distribution for all trees in the forest. the idea of growing an ensemble of trees and letting them vote for the most popular class has led to significant improvements in classification accuracy. the generalization error for the forest converges to a limit as the number of trees in the forest becomes large. the generalization error for the forest of tree classifiers depends on the strength of the individual trees in the forest and the correlation between them. the optimal number of classification trees found for our case study was 51 which seem to be enough for achieving a very good generalization performance. the applications of random forests in predicting the movement direction of financial time series remains nowadays quit limited despite of their high classification performance and their ability to generalize in data that have not been used to train their classifiers [11]. iv. empirical trading simulation results the trading performance of all models considered in the validation subset is presented in table 3. due to the stochastic nature of the machine learning techniques, every method was executed 10 times and the results presented in table 3 present the mean performance of these executions. the trading strategy derived for all the machine learning classification techniques used in the present paper is simple and identical for all of them: go or stay long if the classification model forecasts a positive movement and go or stay short if the classification model forecasts a negative movement. since some of our models trade quite often, taking transaction costs into account might change the whole picture. the transaction costs for a tradable amount, say usd 5-10 million, are about 1 pip (0.0001 eur/usd) per trade (one way) between market makers. but since we consider the eur/usd time series as a series of bid rates, we have to pay the costs only one and not two times per position taken. with an average rate of eur/usd of 1.332 for the testing period, a cost of 1 pip is equivalent to an average cost of 0.008% per position. table iii. trading performance results. naïve strategy macd knn naïve bayes information ratio (excluded costs) -0.48 0.27 -0.12 -0.21 annualized volatility (excluded costs) 11.44% 11.46% 11.46% 11.46% annualized return (excluding costs) -5.51% 3.08% -1.36% -2.46% maximum drawdown (excluding costs) -26.54% -16.96% -13.98% -15.14% correct directional prediction 49.24% 50.11% 48.83% transaction costs 1.04% 0.28% 0.90% 0.62 annualized return (including costs) -6.59% 2.80% -2.26% -3.08 artificial neural networks (mlp) svm random forests information ratio (excluded costs) 0.22 0.43 0.72 annualized volatility (excluded costs) 11.46% 11.46% 11.45% annualized return (excluding costs) 2.51% 4.90% 8.29% maximum drawdown (excluding costs) -18.89% -14.74% -9.94% correct directional prediction 50.12% 52.65% 53.50% transaction costs 0.92 0.92% 1.01% annualized return (including costs) 1.59% 3.98% 7.28 etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 269-272 272 www.etasr.com theofilatos et al: modeling and trading the eur/usd exchange rate using machine learning techniques as observed in table 3, svm and random forests outperform all models in terms of annualized return and information ratio even when transaction costs are considered. random forests are the dominant model presenting the higher minimum drawdown and thus reducing the trading risk. furthermore, as a classifier random forests demonstrated the highest correct directional prediction in the out of sample period and thus being the most accurate one. v. conclusions in the present work, we applied a variety of machine learning techniques in the problem of modeling and trading with the euro/usd exchange rate. from all the applied machine learning techniques, random forests has not been applied in this problem again while being one of the most accurate classifiers. the machine learning techniques were benchmarked with two traditional trading strategies: naïve strategy and macd strategy. except from the simple methods of knn and naïve bayesian classifiers all other machine learning techniques outperformed the traditional strategies that are even until now used by economists. thus, our empirical results encourage future research in applying machine learning techniques in trading with financial time series. from all the machine learning techniques applied in the present paper, random forests indicated the best trading performance in terms of annualized return and information ration even when the transaction costs were considered. as a future direction we propose the application of random forests and other machine learning techniques in trading with other financial time series in order to test their performance and establish them as reliable quantitative trading tools. references [1] c. dunis, m. williams, “modeling and trading the euro/us dollar exchange rate: do neural networks perform better?”, derivatives use, trading and regulation, vol. 8, no. 3, pp. 211-240, 2002. [2] c. ullrich, d. seese, s. chalup, “foreign exchange trading with support vector machines”, advances in data analysis: studies in classification, data analysis and knowledge organization, part vii, pp. 539-546, 2007. [3] c. dunis, j. laws, g. sermpinis, “modelling and trading the eur/usd exchange rate at the ecb fixing”, the european journal of finance, vol. 16, no. 6, pp. 641-561, 2010. [4] thomson reuters datastream: http://online.thomsonreuters.com/ datastream/ . [5] j. holland, adaptation in natural and artificial systems: an introductory analysis with applications to biology, control, and artificial intelligence, cambridge: mass, mit press, 1995. [6] t. cover, p. hart, “nearest neighbor pattern classification”, ieee trans. inform. theory, vol. 13, no. 1, pp. 21-27, 1967. [7] c. howson, p. urbach, scientific reasoning: the bayesian approach, third edition, open course publishing company, 1993. [8] s. haykin, neural networks: a comprehensive foundation, prentice hall, 1998. [9] v. vapnik, the nature of statistical learning theory, springer 2000. [10] l. breiman, “random forests”, machine learning, vol. 45, no. 1, pp. 5-32 2001. [11] k. manish, m. thenmozhi, “forecasting stock index movement: a comparison of support vector machines and random forest”. in proceedings of ninth indian institute of capital markets conference, mumbai, india, 2005. authors profile konstantinos theofilatos is a phd candidate in the department of computer engineering and informatics of the university of patras, greece. in 2009, he received a master's degree from the department of computer engineering and informatics of the university of patras. his research interests include computational and artificial intelligence, evolutionary computation, time series modeling and forecasting, bioinformatics, data mining and web technologies. spiros likothanassis is an electrical engineer with a ph.d. in computer engineering and informatics. he currently is a professor in the department of computer engineering and informatics of the university of patras. he is a reviewer in many scientific journals and conferences including ieee neural networks, journal of knowledge and information systems, information sciences journal and journal of computational and applied mathematics. he has a very good knowledge on adaptive signal processing, adaptive control, computational and artificial intelligence, intelligent agents and bioinformatics. he has also experience in designing information systems, ecommerce applications, distance learning systems and teleworking applications andreas karathanasopoulos is a senior lecturer in london metropolitan business school. in 2008 he received the master of science in international banking and finance from the department of banking and finance of liverpool john moore’s university. his research interests include financial forecasting, trading strategies, time series prediction, artificial and computational intelligence and neural networks. microsoft word 26-3286_s engineering, technology & applied science research vol. 10, no. 1, 2020, 5237-5241 5237 www.etasr.com nguyen & nguyen: risk management in engineering and construction: a case study in design-build … risk management in engineering and construction a case study in design-build projects in vietnam phong thanh nguyen department of project management ho chi minh city open university ho chi minh city, vietnam phong.nt@ou.edu.vn phu-cuong nguyen faculty of civil engineering ho chi minh city open university ho chi minh city, vietnam cuong.pn@ou.edu.vn abstract—the constant demand for construction in developing countries like vietnam causes more and more challenges and difficulties to project management units (pmus) in carrying projects to completion on schedule, with quality assurance and fewer costs. in order to do this, pmus need to have better and tighter management tools and forms. however, in order to minimize risks during project implementation, the binding terms in contracts are also becoming stricter with more and more new forms of contracts. one of them is the design-build (db) contract form. this paper presents the critical risk factors for designbuild projects in the construction industry. good identification and management of these risk factors will help projects succeed and will increase the confidence of owners and contractors who seek to use the design-build form. keywords-design-build (db); risk management; project manager; construction management; vietnam i. introduction vietnam’s construction industry conducts projects are mainly based on the traditional design-bid-build (dbb) method [1]. in particular, a project is broken down into packages which are assigned to independent units that coordinate with the owner for implementation. preparation of investment reports, surveys and construction designs, and bidding to select construction contractors and/or equipment suppliers is carried out. work is assigned by the owner to individual contractors. accordingly, the risks during the process of project implementation from the commencement to the construction, acceptance, and delivery of the work will be shared equally by the parties involved in the project [2-5]. the owner, who is responsible for the quality, progress, and the costs of the project is the focal point [6, 7]. however, the fact that individual contractors deploy at the construction site only after research of design and cost estimate increases project duration [8]. in addition, the construction units spend too much time studying designs, and work at the site requires cooperation between owners, construction units, and design consultants which may affect the overall progress of the project. the fact that independent contractors are only in charge of their tasks fails to promote their initiative, flexibility, and creativity and makes them become dependent on the consultant. recently, many owners from different economic sectors have chosen the design-build (db) general contractor form for their projects, which has helped domestic construction enterprises, while consultants have access to a new form of project management with high professionalism because of their ownership in all aspects of consultancy and construction services. this paper presents an overview of db approach and also points out the critical risk factors for db projects in the construction industry. ii. research background normally, the db approach is often compared to the traditional dbb project implementation method, in which the owner hires two separate units to perform the design and construction activities [9, 10]. in other words, for dbb approach, owners employ independent contractors to carry out the design and construction of a work. in this form, design, bid, and construction activities are conducted sequentially so the design must be completed before bidding and contractor selection. after construction contractors are selected, the construction of the work begins. in dbb form, the relationship between the design contractor and the construction contractor is completely independent. however, the contractors must always exchange information and coordinate with each other during the process of project implementation through the owner, the focal point. in db there is participation of subcontractors to assist the contractors in project implementation (figure 1) [11]. meanwhile, the design and construction tasks are assigned to the same contractor. fig. 1. db project management model the db contractor may hire consultancy subcontractors and/or construction subcontractors to share part of the workload. however, the main contractor is still responsible for all design and construction activities of the db project including the work done by subcontractors. this helps the owner to simplify management interface throughout the project corresponding author: phong thanh nguyen engineering, technology & applied science research vol. 10, no. 1, 2020, 5237-5241 5238 www.etasr.com nguyen & nguyen: risk management in engineering and construction: a case study in design-build … life cycle [12]. as a result, the possibility of design changes, delayed completion time, and risks caused to owners will be limited. in addition, the construction design is implemented by a single unit, therefore, the construction contractor will be aware of the designs in an earlier stage. accordingly, the contractor can deploy the construction even if the design is not completed which makes possible to shorten the implementation time so that owner can sooner put the project into operation [13, 14]. moreover, this limits incrimination and complaints between the design and construction contractors or between two or more subcontractors. thanks to the continuity from design to construction, errors in the project implementation process are reduced significantly. due to being in the same organization, the design and construction units coordinate better and make design adjustments more easily even during the construction process. iii. risk factors basically, risk factors can be classified into groups including risks related to politics and laws, economics and finance, design, contracts and bidding, construction, and owners and contractors [15]. among those, common risks are divided into two groups, namely politics and laws, economics and finance. project risks are specifically divided into four main factor groups, including design, contract and bidding, construction, and owners and contractors. a. group 1: politics and laws political risks affect all actions at the central, provincial, and local levels by state agencies. political risks affect the attraction of project investment and include risks related to the advance of the project investment wihout being stopped by trade wars or protests [1, 16]. more specifically, political risks include corruption, government intervention, delays in approval, and differences in regulations due to regional differences. bureaucracy and harassment of local authorities also cause trouble for project owners and contractors. legal risks arise from deficiencies in the legal and institutional framework, namely incomplete legal and supervisory system, conflicts between laws, decrees, and circulars, changes in laws and decrees, risks due to tax policy changes [17, 18]. if the policies and laws of the state are altered too much from the time of project planning to the time of construction, the owners often have to change the design to fit the new policies or adjust the initially set goals. b. group 2: economics and finance the assessment of the financial feasibility of a project is the most common method of measuring the ability to achieve the financial goals set by stakeholders [19-23]. financial market risks and exchange rate fluctuations are unfavorable factors that have been identified in previous projects. moreover, inflation and interest rates are quite common risk variables. indeed, the fluctuation of inflation and interest rates affect the uncertainty in the construction industry. unfortunately, these risk factors are related to macroeconomics and are unavoidable. inflation can have a strong impact on the price of materials, equipment, and labor costs in a project [24]. the project must have appropriate solutions and the ability to change materials, equipment, labor costs, and machine shifts which are more relevant than the actual time of construction deployment. unstable interest rates are undesirable for most project participants as they lead to concerns about profitability and return on equity [25]. another possible barrier is whether private investors are able to access the projects’ capital through loans from financial institutions. they will also have to pay additional interest in case they are unable to pay on time. when an economy is not stable, investment capital mobilization for projects faces many difficulties and investors may have to suspend projects because of the lack of investment capital. c. group 3: design the design risks of db projects often stem from the roles (main or indirect) of the project participants [26]. design experts will face design risks, of course, but those involved in the projects such as owners or contractors will also face general design risks depending on their roles and their responsibility. this is because in db projects, design units no longer work exclusively for the owner but work in the same team with the construction units, resulting in less communication with the owner. the likely result is that there will be misunderstandings or untimely adjustments with the owner. the main design risks are changes or deficiencies in a design, inadequate designs, and difficulties in following instructions (standards). since a project’s objectives and scale are not clear, it may be necessary to adjust them during the project implementation process. this results in changes in design and the prolonging of document preparation and submission leads to project delays and excess costs. further, construction contractors may have to change or adjust construction methods, machinery, and types of materials [17, 27]. the db form is usually applied to projects with large scale and complex technical properties. therefore, few companies in vietnam can meet the project requirements, and thus, the cooperation of foreign contractors is very common. however, foreign contractors face many difficulties in organizing project implementation because they do not clearly understand climate, hydrogeology, customs, vietnam’s regulations, standards, and legal provisions because the applicable standards are outdated and inappropriate. therefore, using foreign standards or converting from foreign standards to vietnamese standards is often difficult and takes time, which further slows down the implementation progress. d. group 4: contracts and bidding this group of issues includes the lack of transparency in bidding (breakdown of packages, projects not yet approved but with proceeded bidding), conflicting or incomplete contracts, improper contracts signing, unfair allocation of responsibilities and risks, inappropriate contract quotes related to the bidding process and project evaluation. the lack of transparency and fraud in bidding leads to the selection of incompetent and inexperienced contractors who cannot ensure the design and construction work in accordance with specified requirements, causing problems during construction. in addition, a negative situation in bidding and collusion in bidding increases total investment cost. in addition, a db contract is a lump-sum contract [28]. therefore the contractor is the only one responsible to the owner for the whole project. thus, it is necessary to clearly indicate in the contract criteria such as ensuring work quality, specifying the scope of work, the engineering, technology & applied science research vol. 10, no. 1, 2020, 5237-5241 5239 www.etasr.com nguyen & nguyen: risk management in engineering and construction: a case study in design-build … standard system applicable to the work, identify specific timelines, and penalties, control of expenses incurred during the implementation process, bind responsibility upon the parties for risks occurring to the project, etc. in the contract’s terms. accordingly, the lack of experience in contract drafting or loose terms in the contract can cause controversies during project implementation. especially if potential risks (fluctuation, global instability, etc.) are not anticipated and are tightly bound into the contract the project’s progress will be prolonged and will often excess contract estimates. e. group 5: construction construction risks are adverse factors in the construction phase of a db project. these include unavailable labor/ materials/ equipment or delays, owners’ requirements on special or monopoly equipment, limited supply in the market, exorbitant requirements on the quality of the work, force majeure risks (abnormal events such as earthquakes, storms, floods, etc.), and accidents [29-31]. during the construction process, the contractor will face many difficulties if the project’s quality is not guaranteed [32]. therefore to minimize risks, the management and the inspection of the rationality of the design documents compared to geological documents, quality of supervision, control and assurance, and the construction method proposed by the contractor, are critical [33]. the schedule prepared by the contractor and approved by the owner is the basis for project implementation. however, during the implementation process, it may be overlapped due to weak coordination between the main contractor, subcontractors, and suppliers [34]. some contractors must wait for other contractors in order to be able to do their duties, causing problems for the contractors themselves and delaying the overall progress of the project. the management of project progress by the owner and the contractor must ensure the overall progress of the project [35, 36]. unforeseen force majeure risks often have a great impact on the construction project and may cause damage to the work or lead to designs arising out of the original design proposed by the contractor. this is costly and can impact an enterprise’s prestige and brand. the contractor for a db project is not only responsible for construction techniques, means, and methods, but also for the design, accuracy, and performance. the owners’ responsibility is also partially reduced while they can still follow the project quickly. as a result, contractors not only are responsible for their own specialties, but they also take more responsibilities [37]. contractors being not familiar with this situation can cause problems, including accuracy in assessing the feasibility of the project, investor’s incompetent supervisors, changes in project scope, contractors chasing maximum profit and ignoring project specifications, using inferior materials or using replacement materials to get profit because of a fixed price contract, insufficient capacity and experience of the staff on the db project, lack of reliable support from subcontractors, unsuitable allocation of resources to the project, and ineffective communication between owner and stakeholders in the project implementation process. iv. research methodology to determine risk, we need to know two dimensions, occurring probability and consequence levels. risk is often expressed in terms of a combination of the consequences of an event and its associated likelihood of occurrence. in short, a risk factor (rf) in this study is calculated by [17, 29, 35]: rf = c + l – c.l (1) where rf is the risk factor or level of risk, c is the consequence measure on a scale 0 to 1 = the average of consequence factors, and l is the likelihood measure, on a scale 0 to 1 = the average of likelihood factors mathematically, (1) derives from the probability calculation for disjunctive events: prob(a or b) = prob(a) + prob(b) − prob(a) × prob(b) (2) the risk factor value from 0 (low) to 1 (high), reflects the likelihood of a risk arising in the element and the severity of its consequences. the risk factor will be high if the likelihood l is high, or the consequence c is high, or both. it is important to remember that risk analysis rates consequences first, and then likelihoods, not the other way round. events may have many kinds of outcomes that could range from quite small to quite large, so the sequence of rating likelihood before a consequence is difficult: which of the many consequences should be selected when rating a risk? in practice, people who use this approach often select the likelihood of an event occurring irrespective of the level of consequence, and then select a conservative or worst-case consequence. this generated likelihood-consequence pairs that could never arise in practice and levels of risk that are far too high. we now rate the consequence first, usually a ‘most-likely’ or characteristic consequence, and then the likelihood of that level of consequence is arising. this ensures that likelihoodconsequence pairs are coherent, can actually occur, and describe the risk in a meaningful way [38]. v. results and discussion based on the results of the literature review and of the indepth interviews with experts, a total of 28 risk factors were identified in db projects in vietnam. after using (1), we can conclude that the top three most important risk factors have been identified. these leading risks are analyzed as follows: a. delays in project approval and licensing in vietnam, project approvals are often delayed and sometimes even a previous approval is canceled. the project approval process is prolonged for several reasons, including the lack of capacity and professionalism of the approval departments and complex project approval procedures. different departments often have different laws and regulations of their own with which contractors must comply. environmental agencies, land offices, electricity, water and irrigation authorities often cause delays in db projects. in addition, the amendment of some applicable laws and regulations in a short time forces contractors always to face changing regulations, which also takes a lot of time at the beginning of the project. moreover, complex legal hoops, prolonged submission procedures, and changes in the legal policies of the government also cause difficulties for owners, and contractors in the project implementation process as well as in payment and final settlement. engineering, technology & applied science research vol. 10, no. 1, 2020, 5237-5241 5240 www.etasr.com nguyen & nguyen: risk management in engineering and construction: a case study in design-build … b. interest rate fluctuation interest rate fluctuation can have a positive or negative effect on both owners and contractors [39, 40]. normally, owners and contractors borrow more than 50% of the capital from banks, with the interest rate depending greatly on the policies of the state bank. low interest rates will attract investors and motivate them to pay more attention to the construction market. on the other hand, when interest rates are volatile, there are problems with potential profit or return on equity. moreover, getting access to loans from financial institutions in the private sector is also difficult. c. design or technical specifications deficiency and change design or technical specification deficiency and change risks are unavoidable, particularly in large-scale db projects, because most of the design elements are not completed during the contracting period, resulting in disputes between owners and contractors. bigger inaccuracy creates higher risks for the contractors because they bear the cost [41-43]. in db projects, the investors regularly bring only an original idea about the project that they wish to build, but it is the contractors that prepare the proposals including the preliminary design and the estimated costs for the project based on the owner’s requirements. the bid price from the contractors is often fixed. therefore, if the db project contractors have incurred further costs for shortcomings in design or construction, they cannot have a claim against the owner. however, if an owner changes the requirements for the design or the project specifications, the contractors commonly do require an additional amount from the owner [44, 45]. one of the major reasons there are omissions in the design is due to unconditional surveying and measuring by the contractors [5], e.g. if the contractor conducts an improper geologic survey on the construction site it may result in inconsistency in the course of construction and augmented cost in the design. this can also cause serious problems in the quality of the structure if the problem is not detected quickly. the contractors may need a long time to carry out resurveying and design revisions. besides, the costs for troubleshooting during construction caused by unsatisfactory geologic survey works will be very high. thus, surveying and measuring are terribly significant for ensuring the project do not encounter difficulties. vi. conclusion this paper investigates the risk factors affecting the implementation of db projects in construction industry in vietnam. the results showed that the top three critical risk factors in descending order of importance are: delays in project approval and licensing, interest rate fluctuations, and design or technical specifications deficiency and change.we expect that the research results will support researchers and project managers in the db contract approach in project management. acknowledgment the authors acknowledge the help of ho chi minh city open university, vietnam in this research. references [1] f. y. y. ling, v. t. p. hoang, “political, economic, and legal risks faced in international projects: case study of vietnam”, journal of professional issues in engineering education and practice, vol. 136, no. 3, pp. 156-164, 2009 [2] l. h. pham, h. hadikusumo, 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impacts of construction change orders”, construction research congress, new orleans, usa, april 2– 4, 2018 [45] t. n. handayani, v. likhitruangsilp, n. yabuki, “a building information modeling (bim)-integrated system for evaluating the impact of change orders”, engineering journal, vol. 23, no. 4, pp. 67-90, 2019 microsoft word emad_ahmed-ce.doc etasr engineering, technology & applied science research vol. 3, no. 3, 2013, 440-445 440 www.etasr.com ahmed: conformal band-notch uwb monopole antenna on finite cylindrical substrates conformal band-notch uwb monopole antenna on finite cylindrical substrates emad s. ahmed department of electrical engineering university of technology baghdad, iraq dr_emad_sa@uotechnology.edu.iq abstract—a microstrip-fed new uwb monopole antenna with a band-notch characteristic mounted on the finite cylindrical surface is presented. the proposed antenna consists of a rectangular metal radiation patch fed by a 50 ohm microstrip line and a rectangular ground plane. to achieve ultra-wideband, three modifications are introduced. the first one is to blend the upper and lower corners of the radiating plates. the second one is to remove a circular section from the radiating metal. the third one is to blend the upper corners of the ground plane. the antenna is designed on a substrate with dielectric constant εr=3 and 1.6 mm height. the proposed antenna is conformed on finite cylindrical substrates of radiuses 4, 5 and 6 cm. the cylindrical structures were simulated through cst microwave studio finite element package. the simulation results, obtained via cst package on the return losses, vswr and radiation pattern of the antenna are presented. for both planar and conformal antennas, results show that the impedance bandwidth of the designed antenna is from 2-18 ghz with a return loss less than -10 db (vswr<2) and a band rejection of 5-6 ghz for wireless lan (wlan), that includes the band 5.15-5.825 ghz limited by ieee 802.11.a and hiperlan/2 with return loss greater than -10db. the proposed simple shaped conformal antenna provides a good radiation pattern and gain between 3.84 and 5.96 dbi over the entire frequency band excluding the rejected band. keywordsconformal microstrip antennas; ultra-wideband (uwb); band-notched, cylindrical substrate; monopole antenna. i. introduction monopole antennas, which feature broad bandwidth and small size, have received intensive attention in ultra-wideband uwb applications, due to the merits of wide impedance bandwidth and omnidirectional radiation pattern [1]. according to the federal communication commission (fcc), uwb systems have been collocated to the bandwidth from 3.1 to 10.6 ghz [2]. however, over the designated uwb frequency band, there are existing wireless local area network (wlan) operating bands such as the 5.2 ghz (5.150-5.350 ghz) and 5.8 ghz (5.725-5.825 ghz) bands which may cause interference with uwb [3]. to avoid any electromagnetic interference on wireless lan systems, many uwb antenna structures and techniques have been studied. also, broadband antennas of various types with stop-band notch have been reported [4, 5]. the use of cylindrical substrates for microwave design is generally driven by the physical attributes of the system rather than by choice, since the analysis and fabrication are more complicated than for a comparable planar implementation. however the cylindrical geometry can offer certain desirable antenna characteristics that are not provided by planar elements [6]. due to their conformability with the hosting structure, microstrip antennas find many applications related to curved structures such as cylindrical structures, high speed aircrafts and spacecrafts [7]. antennas mounted on small radius cylinders are increasingly more needed for the development of equipment for communication and industrial applications. the range of applications spans from sensors, goes through wireless access nodes and then up to modern miniaturized spacecrafts [8]. in this paper the design was subdivided into two parts. the first part describes the proposed planar monopole uwb antenna with a notch band characteristic. in the second part, the proposed antenna is conformed on a finite cylindrical substrate with three different radii. the cylindrical structure is simulated using the cst microwave studio package. results obtained on return loss, vswr and radiation pattern are presented and discussed. ii. antenna design and confguration a. the proposed plannar antenna design the configuration of the proposed planar ultra-wideband monopole antenna with a band-notch feature is shown in figure 1. the antenna uses a substrate having 1.6 mm thickness and relative dielectric constant of 3. the antenna is formed by two rectangles. on the backside of the substrate, the ground plane is printed to cover only the 50 ohm microstrip feed line. the detailed dimensions of the antenna are shown in table i. three modifications are introduced in this patch to improve its operating bandwidth. the first one is to blend each of the upper etasr engineering, technology & applied science research vol. 3, no. 3, 2013, 440-445 441 www.etasr.com ahmed: conformal band-notch uwb monopole antenna on finite cylindrical substrates and lower corner edges of the rectangles into an arc with radius of 20mm. the second modification is to cut a cylindrical section of radius 9.5 mm centered on the line between the rectangles. the third modification is made on a ground plane; it is designed not to have rectangular but tapered upper corners with 10 mm radius. the arc shaped patch and tapered ground plane make the best broadband impedance matching of antenna possible [9, 10, 11]. fig. 1. the geometry of the proposed planar antenna table i. antenna dimensions by inserting a slot of 20 mm length and 0.2 mm width on the radiating patch, a notched frequency band from 5-6 ghz is created. the slot length contributes to both the notch center frequency and notch bandwidth, while the slot width contributes mainly on the notch bandwidth. it is easy to design a specific notch-band range by adjusting the slot size [12,13]. by selecting the optimal parameters mentioned in table i, the proposed antenna can be tuned to operate within the uwb band. figure 2 shows the return loss characteristic of the proposed antenna as well as the effect of the modifications in the range of 2-18 ghz. from figure 2, it can be clearly indicated that when the rectangular angles of the patch are blended into arcs, the return loss is decreased below -10 db in the range of 4-18 ghz. the third and fourth lines in figure 2, regarding the second and third modifications, indicate that the bandwidth is further expanded to the range of 2-18 ghz. the fifth line reveals that by cutting a slot in the radiating patch, a stop-band has been created. b. the proposed conformal antenna structure the conformal antenna configuration is shown in fig. 3, where a modified planar monopole antenna is conformed on a cylindrical sector substrate of radius (r) mm. the thickness and dielectric constant of the substrate is 1.6mm and 3 respectively. this structure example is of practical interest, since the shape of the most airborne vehicle can be approximately described by a cylindrical sector. in addition, such antennas can be deployed in a special environment, e.g. in the corner of a building. fig. 2. return losses for all modifications of the proposed antenna fig. 3. 3d veiw of the proposed antenna conforming on cylindrical substrate, with front and back views antenna parameter dimension in mm w 57 w1 47 wf 4 l 45 l1 22.5 l2 12.5 l3 10 l4 1 r 9.5 h 1.6 etasr engineering, technology & applied science research vol. 3, no. 3, 2013, 440-445 442 www.etasr.com ahmed: conformal band-notch uwb monopole antenna on finite cylindrical substrates iii. simulation results and discussion the cylindrical structures of figure 3 were simulated through a finite element package, the cst microwave studiotm. cylinders with radiuses 40, 50, and 60 mm were analyzed while keeping the rest of the antenna parameters fixed. figure 4 show the simulated return loss curves for the proposed antenna. as shown in figure 4, the proposed antenna satisfies the 10db return loss requirements for the frequency range from 2 ghz to18 ghz. for comparison purposes, the return loss of the planar antenna with slot is also shown in figure 4. it is found that the impedance bandwidth slightly improves at lower frequencies, up to 5 ghz, for all cylinders used in the simulation. figure 5 shows the simulated return loss for the proposed antenna structure of the reference planar monopole antenna with slot width dimension of 0.1, 0.2, and 0.3 mm respectively. it obviously indicates that an uwb bandwidth defined by 10db return loss covering 3.1-10.6 ghz is achieved for all proposed slot width dimension. for all structures, a band rejection of 5-6 ghz with return loss greater than -10 db are obtained. figure 6 presents the simulated group delay of the proposed antenna. group delay variation is generally smooth, except around the notched band and around 8 ghz. figure 6 shows that the proposed antenna has good time/frequency characteristics and a small pulse distortion over the uwb operated band. figures 7-8 illustrate the simulated radiation patterns at 3, 4.5, 7.5, 8.5 and 10.5 ghz for a cylindrical structure with 4 cm and 5cm radii. the proposed antenna is characterized by an omnidirectional pattern in the h-plane (xz-plane) while it is a quasi-omnidirectional pattern in the e-plane (yzplane). it is obvious from these results that the radiation patterns are acceptable over the uwb bandwidth. the gain varies from 3.84 to 5.96 dbi over the operating frequency range while at the notched band, the antenna gain is sharply reduced to a frequency rejected function as shown in figure 9. iv. conclusions this paper proposes and simulates a new simple shape band-notched ultra-wideband antenna. to obtain sufficient matching bandwidth, two modifications are introduced to the radiating patch and one to the ground plane. the modified microstrip fed band-notched monopole antenna is conformed on a cylindrical substrate. the proposed conformal antenna exhibits uwb characteristics and provides a good impedance matching, good radiation patterns and relatively flat gain over the entire frequency band excluding the rejected band. these features of the proposed conformal antenna demonstrate that this antenna is suitable for uwb communication applications, especially for airborne vehicles and at corners of a frames. fig. 4. return losses of proposed antenaa conformed on cylindrical substrates of radiuses; 40, 50 and 60 mm. fig. 5. return losses of proposed antenna with slot width dimension of 0.1, 0.2, and 0.3mm respectively fig. 6. group delay of the proposed antenna etasr engineering, technology & applied science research vol. 3, no. 3, 2013, 440-445 443 www.etasr.com ahmed: conformal band-notch uwb monopole antenna on finite cylindrical substrates (a) xzplane field pattern (b) xyplane field pattern fig. 7. polar plot of far field pattern for cylindrical radius r=40mm, (a) xz-plane and (b) xy-plane. etasr engineering, technology & applied science research vol. 3, no. 3, 2013, 440-445 444 www.etasr.com ahmed: conformal band-notch uwb monopole antenna on finite cylindrical substrates (a) xz-plane far field pattern (b) xy-plane far field pattern fig. 8. polar plot of far field pattern for cylindrical radius r=50mm, (a) xz-plane and (b) xy-plane. etasr engineering, technology & applied science research vol. 3, no. 3, 2013, 440-445 445 www.etasr.com ahmed: conformal band-notch uwb monopole antenna on finite cylindrical substrates fig. 9. gain against uwb frequency band references [1] i. oppermann, m. hamalainen, j. iinatti (eds), uwb theory and applications, chichester, u.k., wiley, 2004 [2] federal communications commission, first report and order in the matter of revision of part 15 of the commission’s rules regarding ultra-wideband transmission systems, et docket 98-153, fcc 02-48, apr. 22, 2002 [3] k. h. kim, s. o. park, “analysis of the small band-rejected antenna with the parasitic strip for uwb”, ieee transactions on antennas and propagation, vol. 54, no. 6, pp. 1688-1692, 2006 [4] s. w. su, k. l. wong, c. l. tang, “band-notched ultra-wideband planar monopole antenna”, microwave and optical technology letters, vol. 44, no. 3, pp. 217-219, 2005 [5] h. k. yoon, h. r. kim, k. h. chang, y. j. yoon, , y. h. kim, “a study on the uwb antenna with band rejection characteristic”, ieee antennas and propagation society international symposium, vol. 2, pp. 17841787, 2004 [6] m. c. seardelletti, n. dib, t. weller, j. culver, b. king, “coplanar waveguide-fed slot antennas on cylindrical substrates”, international journal of electronics and communications, vol. 59, pp. 25-30, 2005 [7] m. pirai, h. r. hassani, “l-probe fed circular polarized wideband planar patch antenna on cylindrical structure”, progress in electromagnetics research c, vol. 3, pp.161-167, 2008 [8] p. kabacik, p. opalka, p. hornik, “ttc patch antennas made in a conformal form with small radius”, eucap 2006, first european conference on antennas and propagation, pp. 1-6, nice, france, 2006 [9] f. yu, c. wang, “a cpw-fed novel planar ultra-wideband antenna with a band-notch characteristic”, radioengineering, vol. 18, no. 4, pp. 551555, 2009 [10] k. yin, j. xu, “compact ultra-wideband monopole antenna with bandstop characteristic”, icmmt 2008, international conference on microwave and millimeter wave technology, vol. 3, pp. 1174-1176, nanjing, china, 2008 [11] k. j. hung, y. c. lin, “open-slot loaded monopole antennas for wlan and uwb applications”, ieee antennas and propagation society international symposium, albuquerque, usa, pp. 4653-4656, 2006 [12] c. y. huang, w. c. hsia, j. s. kuo, “planar ultra-wideband antenna with band-notched characteristic”, microwave and optical technology letters, vol. 48, no. 1, pp. 99-101, 2006 [13] c. qiu, t. yuan, y. zheng, l. li, q. zhang, “hybrid shaped bandnotched ultra-wideband patch antenna”, isap 2007, international symposium on antennas and propagation, pp. 282-285, niigata, japan, 2007 [14] n. yuan, t. s. yeo, x. c. nie, y. b. gan, l. w. li, “analysis of probefed conformal microstrip antennas on finite grounded substrate”, ieee transactions on antennas and propagation, vol. 54, no. 2, pp. 554-563, 2006 authors profile emad s. ahmed was born in mosul, iraq, in 1960. he received the b.sc. degree in electrical engineering from mosul university, mosul, iraq, in 1982, the m.sc. degree and ph.d. degree from al-rasheed college for engineering and science, baghdad, iraq, in 1990 and 2002 respectively. he is currently an associate professor for the communication engineering,university of technology, baghdad, iraq. his research interests include wireless communication, microwave circuits design, antennas and wave propagation. dr. emad is an ieee and ap-society member. microsoft word 08-3621_s engineering, technology & applied science research vol. 10, no. 4, 2020, 5921-5924 5921 www.etasr.com phan & nguyen: influence of squeezing rate on yield stress and viscosity of fresh mortar influence of squeezing rate on yield stress and viscosity of fresh mortar van tien phan faculty of construction vinh university vinh city, vietnam vantienkxd@vinhuni.edu.vn duy duan nguyen faculty of construction vinh university vinh city, vietnam duyduankxd@vinhuni.edu.vn abstract-in the present work, squeeze flow techniques were used to investigate the influence of squeezing rates on the yield stress of mortars in fresh state. the tested samples were prepared under similar conditions of room temperature and atmospheric pressure. the fresh mortars were tested at three squeezing rates (20 and 200mm/s) 15 minutes after mixing. the results show that the material’s yield stress increases with the increasing of the squeeze velocity. this increase is evident at low tensile speeds and is not obvious at high tack velocity. elongational viscosity values increased as a result of the gap reduction for all the tested samples. however, when the squeeze speed was high, the strain rate increased because of the high displacement rates, a significant reduction in the mortar’s elongational viscosity was observed compared with those obtained when the squeeze speed was low. despite that this behavior is associated with fluid-solid phase separation, which occurs for low displacement rates, these viscosity values actually represent the behavior of the material in practical situations when submitted to different velocities. the increase in the displacement rate of one order of magnitude caused a reduction in the viscosity of one order of magnitude. keywords-squeeze flow technique; fresh mortar; yield stress; viscosity i. introduction the fresh state of a cement-based material, including mortar, corresponds to only a minor part of its lifetime, nevertheless, the behavior of the material within this frame has major consequences on its hardened properties. the currently applied methods for testing this kind of materials during the fresh state are simple but limited. the flow table (astmc1437, en-1015-3) and dropping ball (bs-4551) methods investigate fresh mortar by using single point measurements [1]. these methods are unable to dissociate the contributions of the yield stress or of the viscosity on the resulting measurements. the material’s behavior is also undetermined, since at least two points are needed to describe simple rheological behavior [1, 2]. in order to overcome the limitations of the traditional methods, rotational rheometers have been used, in which the mortar’s rheological behavior and parameters such as yield stress and viscosity were determined in either shear stress or shear rate-controlled procedures [3, 4]. the technique is an important tool for controlling and developing cementitious material formulations, including mortar, especially for the simulation of mixing and pumping situations. however, during applications, the mortar is spread over a substrate and then squeezed between bricks (masonry and tile adhesive mortar) or projected and spread over a surface for internal and external rendering purposes. the mortar fraction of a concrete mix is also squeezed locally between coarse aggregates during fresh concrete flow [5]. therefore, the rotational rheometers are not suitable in these cases. the behavior of the material under different squeezing rates provides important information for controlling its rheological performance. considering this scenario, the main objective of this research is to investigate the influence of the squeezing rates on the yield value and the viscosity of fresh mortar. ii. squeeze test the squeeze test has been widely used to determine the flow properties of highly viscous pastes (food, cosmetic, polymers, composites, ceramic pastes and others) [6-10], as it overcomes some of the common problems of conventional rheometers such as slip, disruption of plastic materials and the difficulty to load very thick and fiber-containing fluids in rotational devices [5]. squeezing technique can characterize cementitious materials by compressing a cylindrical specimen between parallel surfaces by controlled force or displacement rate. this method has been previously used for characterizing the rheological behavior of cement pastes [11], herschel bulkley fluid [12], bingham plastic [13], etc. the typical load vs. displacement profile of a constant velocity squeeze flow experiment was determined in [11] and it is used to determine the rheological parameters of testing materials, including yield stress and viscosity. direct measurements of yield stress are uniquely performed by stress-controlled rheometers [3, 4]. squeeze flow tests carried out with constant displacement velocity do not allow such direct measurement [5] since the material flow occurs regardless of the existence of the material’s yield stress, unless the force required to overcome this value exceeds the load limit of the testing device. in this study, the testing material is firstly compressed/squeezed between two parallel surfaces continuously with relaxation periods of 1.5min until reaching the predefined thickness and is finally separated with predefined tack velocity (figure 1). a typical curve of squeeze-tack experiment is presented in figure 2, in which three periods can be observed, including compression, relaxation and traction. corresponding author: van tien phan engineering, technology & applied science research vol. 10, no. 4, 2020, 5921-5924 5922 www.etasr.com phan & nguyen: influence of squeezing rate on yield stress and viscosity of fresh mortar fig. 1. a squeezing experiment of mortar in process. it is possible to conduct indirect yield stress determination by the extrapolation of the flow curves in the squeeze stage of the experiment. the yield stress is calculated by dividing the maximum force recorded by the area at that time. the formula is as follows: �� � �� max �� (1) in which as is the average area of the testing sample at the moment that the recorded load is max: at= � � = ��� � (2) where h is the predefine thickness of the test mortar, r is the radius of the sample and � is the mortar’s thickness at the moment of the maximum squeeze force. fig. 2. a typical curve obtaines in a squeeze tack test. during the squeeze flow experiments conducted with a constant downward velocity of the upper plate, the sample height decreased linearly, as: h=h0 – vt, where h is the momentary height of the sample, h0 is the initial sample height, v is the displacement velocity of the upper plate and t is the time elapsed after the beginning of the test [6]. the biaxial extensional strain rate or elongational strain rate is equal to half the vertical hencky strain rate [6]: ��� = ��� � = � ���� (3) the extensional viscosity (ηb) is defined as the ratio between the biaxial extensional stress (σb), which is the squeezing load divided by the top plate area, and the extensional strain rate: ƞ�= �� ��� = 2�� ������ � �� ] (4) where l is the load and r is the radius of the sample [6]. iii. experimental procedure the mortar used in this investigation was referenced from the research of dr. rafael pileggi from the university of sao paolo, brazil [5, 14] and dr. mohend chaouche at lmt, ens cachan, france [15]. the detailed composition of the mortar is presented in table i. in order to minimize the effect of sand grading on the rheological properties of concrete, strict grading component control commercial normalized cen 1961 sand, was used. this is european standard sand (iso 679), which is very clean, with round shaped particles of the same size. it is dried, screened and prepared in a modern factory, ensuring quality and consistency, packed in bags containing 1350±5g (figure 3). table i. mortar composition constituents % wt. of dry mixture white cement 30 normalized sand 70 mkx 70000 pp01 0.5 water 25 walocel mkx 70000 pp01 hydroxyethyl methyl cellulose has been added in the composition of mortar with fixed percentage of dry mixture (0.5%). it imparts well-balanced properties, including open time, adhesion and shear strength, adds good workability and enhances water retention. the selected particle size distribution provides quick, lump-free dissolution. it is compatible with all conventional mineral and organic binders. fig. 3. normalized sand used in the experiments. for evaluating the influence of the squeezing rates to the yield stress of the mortar, testing samples were squeezed at 20 and 200mm/s squeezing speeds. after relaxation, the testing samples were pulled out at different speeds, including 2, 20 and 200mm/s. the variation of the yield stress of the testing material was studied by analyzing the recorded flow curves during the experiments. additionally, the height of the sample should be at least 10 times greater than the maximum particle size to avoid wall effects [5]. hence, the predefined thickness of the testing material was taken as 3.5mm. iv. results and discussion a typical flow curve obtained in the squeeze tack experiment is presented in figure 4. the maximum calculated stress is considered as the yield value of the material. from the flow curves, the value fmax is recorded and given in table ii. the yield stress of the material is calculated by (1) and is presented in table iii. -25 -20 -15 -10 -5 0 5 10 0 50 100 150 200 250 300 350 5mm_s20_t20 compression relaxation traction f o rc e ( n ) time (sec) engineering, technology & applied science research vol. 10, no. 4, 2020, 5921-5924 5923 www.etasr.com phan & nguyen: influence of squeezing rate on yield stress and viscosity of fresh mortar fig. 4. a typical curve obtained in the squeeze period of squeeze flow test. table ii. recorded maximum lo ad in a squeeze period vt = 2 mm/s vt = 20 mm/s vt = 200 mm/s vs = 20 mm/s 40.788 38.102 48.173 vs = 200 mm/s 59.084 60.427 47.838 table iii. yield stress under d ifferent squeezin g rates squeeze – tack velocity yield stress (n/mm 2 ) s20 t2 0.017168 s20 t20 0.016037 s20 t200 0.020276 s200 t2 0.024869 s200 t20 0.025434 s200 t200 0.020135 the variation of material’s yield stress versus the squeeze rate is plotted in figure 5. as it can be easily seen from the figure, at a constant pulling velocity the materials’ yield stress increases with increasing squeeze velocity. this increase is evident at low tensile speeds (2mm/s) and fast pulling speeds (200mm/s). at an average speed of 20mm/s, this increase is not obvious. the above results show that the pressing speed in phase i (construction phase) has a significant impact on the ability to remove the mortar and the upper surface (masonry bricks, tiles adhesive, etc.). high squeezing speed will increase the ability to resist peeling of materials when sticking to mortar. the extensional viscosity (ηb) is calculated by (4) and the results are shown in table iv. fig. 5. material yield stress versus squeeze rate at different tack velocities. table iv. extensional viscosity of testin g materials under different sq ueezin g rates squeeze – tack velocity extensional viscosity (pa.s) s20 t2 6,034.17 s20 t20 6,733.67 s20 t200 7,187.94 s200 t2 879.11 s200 t20 890.55 s200 t200 705.68 the evolution of material‘s extensional viscosity versus the squeeze rate is shown in figures 6 and 7. the interpretation of the viscosity results obtained by squeeze flow must consider that, although the downward velocity remains constant (20 and 200mm/s), the elongational strain rate is constantly increasing as the gap height decreases (within a single test). similar observations were recorded at different experiments with tack speeds of 2mm/s, 20mm/s and 200mm/s. elongational viscosity values increased as a result of gap reduction for all the tested samples. furthermore, unlike rotational rheometry, where the gap is constant and the increase of viscosity with the strain rate in fact represents dilatancy, the reduction of the gap during squeezing stimulates different units (grains getting closer to each other) causing the observed increase of the mortar’s elongational viscosity. this finding is similar to another case of cementitious materials, which has been reported in [5]. fig. 6. calculated material extensional viscosity at squeeze velocity of vs=20mm/s. fig. 7. calculated material extensional viscosity at squeeze velocity of vs=200mm/s. -60 -50 -40 -30 -20 -10 0 10 0 5 10 15 20 25 30 gap 3.5 mm squeeze 20 squeeze 200 f o rc e ( n ) time (sec) engineering, technology & applied science research vol. 10, no. 4, 2020, 5921-5924 5924 www.etasr.com phan & nguyen: influence of squeezing rate on yield stress and viscosity of fresh mortar however, when the squeeze speed was high (200mm/s) and the strain rate increased due to the high displacement rates, a significantly reduction in the mortar’s elongational viscosity was observed in comparison with those obtained when the squeeze speed was low (20mm/s). it can be easily seen that the average elongational viscosity is about 50007000pa.s in the case of high squeeze speed, compared with about 600-900pa.s in the case of low squeeze speed. despite the fact that this behavior is associated to fluid–solid phase separation which occurs for low displacement rates, these viscosity values actually represent the behavior of the material in practical situations when submitted to different velocities. the increase in the displacement rate of one order of magnitude from 20 to 200mm/s caused a reduction in the viscosity of one order of magnitude. v. conclusions the squeeze flow is a simple and versatile method for the rheological characterization of mortars in a wide range of consistencies, providing much important information of the rheological behavior of materials in practical applications. from the flow curves obtained by the squeeze tack experiments, the rheological parameters, including yield stress and elongational viscosity, have been investigated. the results show that the material’s yield stress increases with the increase of squeeze velocity. this increase is evident at low tensile speeds and is not obvious at high tack velocities. elongational viscosity values increased as a result of gap reduction for all the tested samples. however, when the squeeze speed was high and the strain rate was increased because of the high displacement rates, a significantly reduction in the mortar’s elongational viscosity was observed compared with those obtained when the squeeze speed was low. despite that this behavior is associated to fluid–solid phase separation, which occurs for low displacement rates, these viscosity values actually represent the behavior of the material in practical situations when submitted to different velocities. the increase in the displacement rate of one order of magnitude caused a reduction in the viscosity of one order of magnitude. references [1] p. f. g. banfill, “use of the viscocorder to study the rheology of fresh mortar,” magazine of concrete research, vol. 42, no. 153, pp. 213–221, dec. 1990, doi: 10.1680/macr.1990.42.153.213. [2] r. g. pileggi, “novel tools for the study and development of refractory castables,” (in portugese), ph.d. dissertation, federal university of sao carlos, sao carlos, brazil, 2001. [3] b. belahcene, a. mansri, and a. benmoussat, “investigation on the rheological behavior of multigrade oil under the effect of organic and inorganic impurities,” engineering, technology & applied science research, vol. 4, no. 6, pp. 711–713, dec. 2014. [4] v. t. phan, “influence of re-dispersible powder on the properties of mortars,” journal of materials and engineering structures, vol. 1, no. 1, pp. 2–10, jan. 2014. [5] f. a. cardoso, v. m. john, and r. g. pileggi, “rheological behavior of mortars under different squeezing rates,” cement and concrete research, vol. 39, no. 9, pp. 748–753, sep. 2009, doi: 10.1016/j.cemconres.2009.05.014. [6] k. kardjilova, v. vozarova, and m. valah, “influence of temperature on energetic and rheological characteristics of plantohyd bio lubricants – a study in the laboratory,” engineering, technology & applied science research, vol. 3, no. 3, pp. 424–428, jun. 2013. [7] g. h. meeten, “yield stress of structured fluids measured by squeeze flow,” rheologica acta, vol. 39, no. 4, pp. 399–408, aug. 2000, doi: 10.1007/s003970000071. [8] n. ozkan, c. oysu, b. j. briscoe, and i. aydin, “rheological analysis of ceramic pastes,” journal of the european ceramic society, vol. 19, no. 16, pp. 2883–2891, dec. 1999, doi: 10.1016/s0955-2219(99)00054-0. [9] j. engmann, c. servais, and a. s. burbidge, “squeeze flow theory and applications to rheometry: a review,” journal of non-newtonian fluid mechanics, vol. 132, no. 1, pp. 1–27, dec. 2005, doi: 10.1016/j.jnnfm.2005.08.007. [10] o. h. campanella and m. peleg, “squeezing flow viscosimetry of peanut butter,” journal of food science, vol. 52, no. 1, pp. 180–184, jan. 1987, doi: 10.1111/j.1365-2621.1987.tb14000.x. [11] b. h. min, l. erwin, and h. m. jennings, “rheological behaviour of fresh cement paste as measured by squeeze flow,” journal of materials science, vol. 29, no. 5, pp. 1374–1381, mar. 1994, doi: 10.1007/bf00975091. [12] j. d. sherwood and d. durban, “squeeze-flow of a herschel–bulkley fluid,” journal of non-newtonian fluid mechanics, vol. 77, no. 1, pp. 115–121, may 1998, doi: 10.1016/s0377-0257(97)00099-2. [13] d. n. smyrnaios and j. a. tsamopoulos, “squeeze flow of bingham plastics,” journal of non-newtonian fluid mechanics, vol. 100, no. 1, pp. 165–189, sep. 2001, doi: 10.1016/s0377-0257(01)00141-0. [14] f. a. cardoso, a. k. agopyan, c. carbone, r. g. pileggi, and v. m. john, “squeeze flow as a tool for developing optimized gypsum plasters,” construction and building materials, vol. 23, no. 3, pp. 1349– 1353, mar. 2009, doi: 10.1016/j.conbuildmat.2008.07.017. [15] n. delhaye, a. poitou, and m. chaouche, “squeeze flow of highly concentrated suspensions of spheres,” journal of non-newtonian fluid mechanics, vol. 94, no. 1, pp. 67–74, nov. 2000, doi: 10.1016/s03770257(00)00130-0. autho rs profile van tien phan was born in nghe an, vietnam, in 1984. he received the degree of civil engineering in the university of communication and transport, hanoi in 2007, master degree in advanced modelling of materials and structures from the ens cachan, france in 2008, and a phd degree in mechanical engineering from lmt, ens cachan, france, in 2012. he is the author of one book and more than 50 articles, and the principle investigator of more than 10 research projects. his research interests include material sciences and mechanical engineering. duy duan nguyen received a bsc degree of civil engineering at vinh university, vietnam in 2008, a msc degree of structural engineering at the national university of civil engineering, vietnam in 2012, and the phd degree of civil engineering at konkuk university, korea in 2019. his research interests are focused on structural and earthquake engineering and high-performance materials for civil engineering structures. he has published more than 30 papers in high-qualified journals and conferences proceedings. microsoft word 11-3363_s_etasr_v10_n2_pp5402-5405 engineering, technology & applied science research vol. 10, no. 2, 2020, 5402-5405 5402 www.etasr.com bheel et al.: rice husk ash and fly ash effects on the mechanical properties of concrete rice husk ash and fly ash effects on the mechanical properties of concrete naraindas bheel civil engineering department hyderabad college of science & technology sindh, pakistan naraindas04@gmail.com muneer ali jokhio civil engineering department hyderabad college of science & technology sindh, pakistan jokhiomuneer08@gmail.com javed ahmed abbasi hyderabad college of science & technology sindh, pakistan javikalhoro77@gmail.com hyder bux lashari hyderabad college of science & technology sindh, pakistan nbprinces12@gmail.com muhammad imran qureshi hyderabad college of science & technology sindh, pakistan muhammadimranqureshi276@gmail.com abdul salam qureshi hyderabad college of science & technology sindh, pakistan qureshi.salam@gmail.com abstract—cement production involves high amounts of energy consumption and carbon dioxide emissions. pakistan is facing a serious energy crisis and cement’s cost is increasing. in addition, landfilling of potential concrete components can lead to environmental degradation. the use of waste as cement replacement not only reduces cement production cost by reducing energy consumption, but it is also environmentally friendly. the purpose of this study is to analyze the characteristics of concrete by partially replacing cement with rice husk ash (rha) and fly ash (fa). this study is mainly focused on the performance of concrete conducting a slump test, and investigating indirect tensile and compressive strength. cement was replaced with rha and fa by 5% (2.5% rha + 2.5% fa), 10% (5% rha + 5% fa), 15% (7.5% rha + 7.5% fa) and 20% (10% rha+10% fa) by weight. ninety concrete samples were cast with mix proportions of 1:2:4 and 0.55 water/cement ratio. cube and cylindrical samples were used for measuring compressive and split tensile strength respectively, after 7 and 28 days. the results showed that after 28 days, the 5% rha+5% fa sample’s compressive strength was enhanced by 16.14% and its indirect tensile strength was improved by 15.20% compared to the conventional sample. moreover, the sample’s slump value dropped as the content of rha and fa increased. keywords-rice husk ash; fly ash; cement replacement; increased strength; reduced environmental pollution i. introduction concrete is extensively used in artificial materials. due to its adaptability and relative profitability, it is considered as a competitive building material [1]. concrete consists of cement, aggregates, and water. aggregates comprise about 75-80% of the total volume of concrete, affecting the properties of fresh and hardened concrete and its performance [2-3]. cement manufacturing has some disadvantages, such as high production cost and energy requirements. cement production also leads to mass emissions of co2 and other greenhouse gases. the production of one tone of cement emits 1-1.25 tons of co2 [4-6], requires about 1.60mwh of energy, and thus it is considered as an expensive and non-environment friendly process [7]. according to [8], human activity produces more than 5,000 tons of solid waste per year, which include ingredients such as silica fumes, rha [9, 10], fa, and corncob ash. considerable savings in cost and energy consumption could be achieved by utilizing these by-products as partial cement replacements [11]. the utilization of agricultural waste such as rha, sugarcane bagasse ash [12], waste glass powder, fa, and millet husk ash [13], in order to reduce cost, waste and co2 emissions, was investigated in [14, 15]. routine treatments of agricultural and industrial waste are a major concern. rha and fa are agricultural by-products [16-18], and they are considered hazardous as they are usually burnt [19, 20]. rha and fa are highly pozzolanic in nature, and they could be utilized as portland cement replacements. due to their high silica content and low cost, these materials have a high potential in the production of secondary cementing material [21]. the annual production of rice husk is about 120 million tons [22]. rha has a silica content of 85%, called amorphous silica, and it could be utilized as a cementitious material in concrete [23, 24]. under industrial conditions, fa is generated by burning coal. nowadays, with the use of pollution control equipment such as electrostatic precipitators or other filtering equipment, fa is captured before flue gases enter the chimney of a coalfired power plant. about 43% of fa from coal-fired power plants in usa is collected and utilized as a cementitious material in the making of concrete [25]. the main goal of this research is to evaluate the properties of fresh, physical and hardened concrete using rha and fa as cement replacements. corresponding author: naraindas bheel engineering, technology & applied science research vol. 10, no. 2, 2020, 5402-5405 5403 www.etasr.com bheel et al.: rice husk ash and fly ash effects on the mechanical properties of concrete ii. research methodology the properties of fresh and hardened concrete were studied for five concrete mixtures: 0%rha+0%fa, 2.5%rha+2.5%fa, 5%rha+5%fa, 7.5%rha+7.5%fa, and 10%rha+10%fa. ninety concrete samples were prepared, in 60 cylinders and 30 prisms, with 1:2:4 mix proportions, 0.55 water/cement ratio and were cured for 7 and 28 days. in order to determine the characteristic strength of concrete samples, they were tested on an universal testin machine (utm), and the astm c192 standard was met. concrete cubes (100×100×100mm) were used to measure compressive strength, and cylinder samples (200×100mm) were used for determining indirect tensile strength. similarly, the density and the water absorption of the samples were measured after 28 days. three concrete samples were cast for each ratio, and the final result was determined as the mean of the three samples. the study was conducted in the laboratory of concrete technology, h.c.s.t hyderabad, sindh, pakistan [26]. iii. materials used a. cement locally available ordinary portland cement, under the brand name “pakland”, was utilized as a binding material. its experimental physical properties are shown in table i. table i. physical properties of cement b. fine and coarse aggregates the aggregates used are locally available in the region of hyderabad. hill sand passing through #4 sieve was used as fine aggregates, and 20mm crushed stone was used as coarse aggregates. the properties of the laboratory test results of aggregates are shown in table ii. table ii. physical properties of aggregates s.n. properties fine aggregates coarse aggregates 01 fineness modulus 2.26 -- 02 sieve analysis zone-ii -- 03 water absorption 1.80% 1.20% 04 specific gravity 2.67 2.63 05 bulk density 123lb/ft 3 102lb/ft 3 c. rice husk ash the husk of rice was collected from the region of hyderabad. after its collection, the rice husk was burnt under uncontrolled burning temperature to produce ash. this ash was sieved through #30 sieves. d. fly ash the fa, generated in the form of very fine powder passing from #30 sieves, was collected from the lakhra coal power plant. the lakhra coal power plant generates about 2 million tons of fa annually, which are dumped in a landfill. utilizing the fa produced in the power plant as a cement replacement could reduce this. e. water: potable water was used. iv. results and discussion a. workability of fresh concrete the highest slump value measured was 42mm for the 0%rha+0%fa samples, while the lowest was 20mm for the 10%rha+10%fa mixture. the slump value reduced with the rise of rha and fa content, as shown in figure 1. fig. 1. workability of fresh concrete b. density of concrete the density of the samples was measured on the 28 th day. the conventional (0%rha+0%fa) sample had the highest density (2392kg/m 3 ), while the 10%rha+10%fa had the lowest (2288kg/m 3 ). the density of the concrete reduced as the rha and fa increased, as shown in figure 2. fig. 2. density of concrete c. water absorption the water absorption of the concrete samples was analyzed on the 28 th day. the highest water absorption was found to be 4.65% for the 10%rha+10%fa sample, while the lowest was s.n. tests results 01 normal consistency 33% 02 initial setting time 50 min 03 final setting time 260 min engineering, technology & applied science research vol. 10, no. 2, 2020, 5402-5405 5404 www.etasr.com bheel et al.: rice husk ash and fly ash effects on the mechanical properties of concrete 2.89% for the conventional sample. the water absorption of concrete augmented with the rise of rha and fa as shown in figure 3. fig. 3. water absorption of concrete d. compressive strength the cubical samples (100×100×100mm) were used for investigating the compressive strength of concrete. compressive strength was enhanced by 14.5% and 16.14% in comparison with the conventional mix when cement was replaced by 5%rha+5%fa, while it was reduced by 13.7% and 12.90% for the 10%rha+10%fa sample, on the 7 th and the 28 th day respectively as shown in figure 4. fig. 4. compressive strength of concrete e. indirect tensile strength of concrete the cylindrical samples (100×200mm) were used for determining split tensile strength. the indirect tensile strength improved by 11.4% and 15.20% in comparison with the conventional concrete for the 5%rha+5%fa sample, while it reduced by 19.6% and 9.30% for the 10%rha+10%fa sample, on the 7th and 28th day respectively, as shown in figure 5. fig. 5. split tensile strength of concrete v. conclusion based on the experimental results obtained, it is concluded that the highest measured slump value was 42mm for the conventional sample, while the lowest was 20mm for the 10%rha+10%fa. the highest density measured after 28 days was 2392kg/m 3 for the conventional sample, while the lowest was 2288kg/m 3 for the 10%rha+10%fa. the optimum water absorption measured after 28 days was 4.65% for the 10%rha+10%fa sample, while the lowest was 2.89% for the conventional sample. compressive strength improved by 14.5% and 16.14% compared to the conventional mix when cement was replaced by 5%rha and 5%fa, while it was reduced by 13.7% and 12.90% in the 10%rha+10%fa sample, measured on the 7 th and the 28 th day respectively. indirect tensile strength was enhanced by 11.4% and 15.20% compared to the conventional sample when cement was replaced by 5% rha and 5% fa, while it reduced by 19.6% and 9.30% for the 10%rha+10%fa sample on the 7 th and the 28 th day respectively. in conclusion, optimum hardened properties were obtained by using 5% rha and 5% fa as cement replacement material in concrete. references [1] s. ghosal, s.c. moulik, “use of rice husk ash as partial replacement with cement in concrete-a review”, international journal of engineering research, vol. 4, no. 9, pp. 506-509, 2015 [2] a. m. neville, j. j. brooks, concrete technology, pearson education asia pte ltd, 2008 [3] m. alexander, s. mindness, aggregates in concrete, taylor and francis, 2005 [4] p. v. naidu, p. k. pandey, “replacement of cement in concrete”, international journal of environmental research and development, vol. 4, no. 1, pp. 91-98, 2014 [5] z. h., shaikh, a. kumar, m. a., kerio, n. bheel, a. a., dayo, a. w. abro, “investigation on selected properties of concrete blended with maize cob ash”, 10 th international civil engineering conference, karachi, pakistan, february 23-24, 2019 [6] n. bheel, r. a. abbasi, s. sohu, s. a. abbasi, a. w. abro, z. h. shaikh, “effect of tile powder used as a cementitious material on the mechanical properties of concrete”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4596-4599, 2019 [7] a. m. neville, properties of concrete, pearson education asia pte ltd, 2000 engineering, technology & applied science research vol. 10, no. 2, 2020, 5402-5405 5405 www.etasr.com bheel et al.: rice husk ash and fly ash effects on the mechanical properties of concrete [8] v. w. ramasamy, “compressive strength and durability properties of rice husk ash concrete”, ksce journal of civil engineering, vol. 16, no. 1, pp. 93-102, 2012 [9] n. bheel, a. w. abro, i. a. shar, a. a. dayo, s. shaikh, z. h. shaikh, “use of rice husk ash as cementitious material in concrete”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4209-4212, 2019 [10] n. bheel, s. l. meghwar, s. a. abbasi, l. c. marwari, j. a. mugeri, r. a. abbasi, “effect of rice husk ash and water-cement ratio on strength of concrete”, civil engineering journal, vol. 4, no. 10, pp. 2373-2382, 2018 [11] j. p. broomfield, corrosion of steel in concrete: understanding, investigation and repair, crc press, 2006 [12] a. a. dayo, a. kumar, a. raja, n. bheel, z. h. shaikh, “use of sugarcane bagasse ash as a fine aggregate in cement concrete”, engineering science and technology international research journal, vol. 3, no. 3, pp. 8-11, 2019 [13] n. d. bheela, f. a. memon, s. l. meghwar, a. w. abro, i. a. shar, “millet husk ash as environmental friendly material in cement concrete”, 5 th international conference on energy, environment and sustainable development, mehran uet jamshoro, pakistan, november 14-16, 2018 [14] r. r. hussain, t. ishida, “critical carbonation depth for initiation of steel corrosion in fully carbonated concrete and development of electrochemical carbonation induced corrosion model”, international journal of electrochemical science,vol. 4, no. 8, pp. 1178-1195, 2009 [15] n. kad, m. vinod, “review research paper on influence of rice husk ash on the properties of concrete”, international journal of research, vol. 2, no. 5, pp. 873-877, 2015 [16] m. anwar, t. miyagawa, m. gaweesh, “using rice husk ash as a cement replacement material in concrete”, waste management series, vol. 1, pp. 671-684, 2000 [17] s. d. nagrale, h. hajare, p. r. modak, “utilization of rice husk ash”, international journal of engineering research and applications, vol. 2, no. 6, pp. 1-5, 2012 [18] i. b. ologunagba, a. s. daramola, a.o. aliu, “feasibility of using rice husk ash as partial replacement for concrete”, international journal of engineering trends and technology, vol. 30, no. 5, pp. 267-269, 2015 [19] a. n. givi, s. a. rashid, f. n. a. aziz, m. a. m. salleh, “contribution of rice husk ash to the properties of mortar and concrete: a review”, journal of american science, vol. 6, no. 3, pp. 157-165, 2010 [20] n. bheel, s. l. meghwar, s. sohu, a. r. khoso, a. kumar, z. h. shaikh, “experimental study on recycled concrete aggregates with rice husk ash as partial cement replacement”, civil engineering journal, vol. 4, no. 10, pp. 2305-2314, 2018 [21] h. b. mahmud, n. a. a. hamid, k. y. chin, “production of high strength concrete incorporating an agricultural waste-rice husk ash”, 2nd international conference on chemical, biological and environmental engineering, cairo, egypt, november 2-4, 2010 [22] h. t. le, k. siewert, h. m. ludwig, “alkali silica reaction in mortar formulated from self-compacting high performance concrete containing rice husk ash”, construction and building materials, vol. 88, pp. 10-19, 2015 [23] n. p. hasparyk, p. j. monteiro, h. carasek, “effect of silica fume and rice husk ash on alkali-silica reaction”, materials journal, vol. 97, no. 4, pp. 486-492, 2000 [24] k. sakr, “effects of silica fume and rice husk ash on the properties of heavy weight concrete”, journal of materials in civil engineering, vol. 18, no. 3, pp. 367-376, 2006 [25] v. goud, n. soni, g. varma, k. kushwah, s. chaurasia, v. sharma, “partial replacement of cement with fly ash in concrete and its effect”, iosr journal of engineering, vol. 6, no. 10, pp. 69-75, 2016 [26] n. d. bheel, s. a. abbasi, s. l. meghwar, f. a. shaikh, “effect of human hair as fibers in cement concrete”, international conference on sustainable development in civil engineering, jamshoro, pakistan, november 23-25, 2017 microsoft word 6-2587_s engineering, technology & applied science research vol. 9, no. 2, 2019, 3900-3904 3900 www.etasr.com khan et al.: power flow control by unified power flow controller power flow control by unified power flow controller muhammad yousaf ali khan department of electrical engineering, gomal university, d. i. khan, pakistan myousafak@gu.edu.pk umair khalil department of electrical engineering, gomal university, d. i. khan, pakistan engr.umairkhalil71@gmail.com hamayun khan department of electrical engineering, gomal university, d. i. khan, pakistan hamayunkhan@gu.edu.pk amad uddin department of electronic engineering, fatima jinnah women university, rawalpindi, pakistan ammad@fjwu.edu.pk sheeraz ahmed school of computer science, iqra national university, peshawar, pakistan sheerazahmed306@gmail.com abstract—the demand for electricity is increasing day by day and we have to produce more electrical energy to meet the load demands. most of the experts prefer to extend the existing electrical networks over building the new network with greater costs. in this paper, the implementation of the flexible ac transmission systems (facts) devices in a simple electrical network is described. facts devices enhance power transfer capacity of the line without laying out new transmission line. these devices also protect the system from overloading in case of any contingency in the electrical network. moreover, this paper describes the impacts of facts devices on improving the voltage stability and power handling capability of a transmission line. the proposed methods for the controllable flow of active and reactive power in a transmission line are also elaborated. a simple electrical system is examined to explain the improvement in the constraints of power system using facts devices. keywords-flexible ac transmission systems (facts); genetic algorithm (ga); phase shifting transformer (pst); static var compensator (svc); static compensator (statcom) i. introduction modern-day power systems are heavily stressed because of the growing demand for electricity and the competition in the electricity market [1]. nowadays, there is a huge difference between the supply and demand for electricity. power shortages occur due to the increasing population and improved living standards. a solution in these problems is to increase power generation and decrease power losses. any increase in power generation demands new transmission lines which require high capital investments. although the existing transmission networks operate near their rated capacity, yet there is some flexibility in increasing the power handling capacity of the existing transmissions lines. flexible ac transmission systems (facts) are power electronic based semiconductor devices used to enhance the power handling capability of the transmission lines [2]. the main capabilities of facts devices are to control power flow, reactive power compensation and voltage control. the installation of a new electrical network or extending the existing one requires a high capital cost. facts controllers save this capital by improving the constraints of the power system [3]. facts controllers utilize the existing electrical network to its maximum capacity. in the past, var generators were connected to improve the voltage profiles of the electrical networks thus improving the performance of the network. reliability and quality of the supplied power to the customers are improved by using var compensators [2]. in different contingency conditions, facts devices can be used to improve the static voltage stability margin of the system. the loading margin of the transmission line can be increased to its maximum capacity by the use of unified power flow controller upfc [4]. svcs and statcoms show better performance in terms of improving voltage profile and reducing line transmission losses [5]. although shunt capacitors serve the same purpose and are less expensive, they are rarely used because of their operation time. a substation is used to transport the electric energy from a producer a to a load center b located at a specific distance. the consumer can be supplied through a number of transmission lines. the problem of uncontrolled power flows between the transmission lines occurs in these types of systems. moreover, the transmission lines are loaded unevenly under these conditions. active power can be regulated in the power system through phase shifting transformers (psts) [6]. the voltage instability in a power system is caused by the imbalance of reactive power. when an electrical system tends to approach its operating limits the loss of real and reactive power increases rapidly. thus, in order to obtain voltage stability, reactive power must have to be supplied locally and adequately. the application of facts controllers enhances voltage stability and the loading margin of the system. the addition of upfc at corresponding author: muhammad yousaf ali khan engineering, technology & applied science research vol. 9, no. 2, 2019, 3900-3904 3901 www.etasr.com khan et al.: power flow control by unified power flow controller the weakest bus of the power system improves voltage stability and loading margin [7]. facts controllers have a strong effect on static voltage stability in power systems. the voltage stability and loading margin of an electrical network can be increased by the application of facts controllers [8]. the selection of the most suitable facts device to control the flow of active and reactive power depends upon the performance analysis of different facts devices. the application of facts controllers for congestion management and voltage support improves the stable operation of the power system. the voltage level can be maintained at its reference value (1pu) by the use of devices like statcom and upfc [9]. the installation of facts controllers solves the problems of uneven power flow and transient and dynamic voltage instability. the application of these devices locally is limited by their systematic control and capital cost. the abovementioned problems can be solved locally and economically by using a combination of energy storage systems (ess) and facts devices [10]. the transient stability control ensures the stable operation of the power system in the event of large disturbances. the transient stability of the power system can be improved by applying facts controllers [11]. the advancements in the field of facts technology introduced many different configurations to control power flow. upfc can improve the power quality of a system [12]. in order to improve power quality, the performance of upfc with pi controller and with conventional system has been investigated. the upfc with pi controller improves the power quality of the power system. active and reactive power can be controlled effectively by the use of upfc. the benefits of applying facts controllers in ac networks are power flow control, stability and loading margin. power system performance characteristics can be improved by using several facts controllers [13]. as mentioned above, the high initial cost of facts controllers limits their applications. however, facts devices had provided the most reliable and efficient solutions [14]. the benefits of facts controllers in electrical utilities are important but the problems of high losses by using advanced facts controllers must also be considered. flexible and dynamic control of electrical networks is made possible through facts devices [15]. the effectiveness of facts devices can be examined by applying them to the system in different scenarios. the semiconductor technology can be summarized in the development of these devices. in addition, major real-world installations and utility experiences with and without facts controllers can be also examined in order to know the importance of these devices. power flow in electrical systems can be optimized through facts controllers. ii. proposed model most loads of a power system are inductive in nature and draw reactive power along with active power from the supply source. so, in order to obtain better system results we have to maintain adequate supply of both active and reactive power. the modern electrical power system comprises of a number of generators, transmission lines, transformers and loads. some transmission systems are more loaded than their rated capacity because of increased power demand. power transmission lines operate at different voltage levels varying from 110kv to 800kv (66kv to 500kv in pakistan). the voltages of the power transmission lines are kept high to reduce the losses in transmission lines, while the distribution systems operate below 100kv for security and convenience reasons associated with the supply of electric power to domestic and industrial loads. the power transmission lines are highly interconnected because of the following economic advantages: • a tie line control is used to share the generating reserves for interconnected electric power transmission lines. • the transformers increase or decrease voltage levels according to the required conditions and power transmission lines can operate at different voltages. ac lines have inherent power flow control as the power flow is determined by the power at the sending end or receiving end. let us assume a lossless transmission line with negligible line charging. the transmission line equation can be given as: � = ���� � sin �� − ��� (1) where �� and �� are the sending end and receiving end voltages, �� and �� are the voltage angles while x is the reactance of the line. in case of disturbances such as line outage, line trip, generator outage or sudden increase in load, power flow is changed to ensure system reliability and security under these dynamic conditions. the flow of power is changed by the facts devices used in the system. moreover, the flow of power in ac transmission line is controlled to enhance power system transmission capacity. as the load increases, bus voltage drops and may cross the minimum allowable limit. so the buses operating closer to the limits have a tendency to drop their voltage below 0.95pu which is a limiting standard. we have to cope with this problem by using facts devices which can set and maintain a reference voltage level. moreover, in case of the contingency of one line, others can become overloaded. the voltage at the buses change and line currents are redistributed throughout the network when a transmission line is switched on or off through circuit breakers. in order to predict a new steady-state, bus voltages and line currents technique of contingency analysis is used. the system planners and operators are more concerned about overloads and under voltages rather than finding the exact values of voltage and current. due to this reason, largescale network models used for contingency evaluation are not required to be exactly like the models used for fault calculations. in this case, various contingency conditions, their effect on bus voltages and currents and the application of devices are checked. we can maintain power flow across lines by fixing these devices [10]. they will only allow reference power to flow, diverting the remaining power to flow from under-loaded lines. the proposed model shows that these problems come in our selected network and facts devices help to solve these problems. upfc can be used to control the flow of active and reactive power in a transmission system connected to the high voltage side of the network and control the amount of reactive power supplied to the line at the installation point. when a line is switched on or off, line currents are redistributed throughout the network and bus voltages change. the new steady-state bus voltages and line currents can be predicted by what is called the contingency engineering, technology & applied science research vol. 9, no. 2, 2019, 3900-3904 3902 www.etasr.com khan et al.: power flow control by unified power flow controller analysis program. although matlab has some disadvantages, most of the electrical systems can easily be examined through this software. in our case, some options are not available in matlab for load flow analysis as they are available in other professional software. for example, there is no bus bar available in matlab. we used three-phase measurement block as a bus bar. in pws we have the facility to add fields (voltages, angle, etc.) around the bus but in matlab this facility is not available. moreover, in order to calculate the line power flows, we have to adopt a lengthy procedure. however, some important features which are quite helpful in load flow analysis are provided in later versions of matlab. large-scale network models used for contingency evaluation, like those used for fault calculations, do not have to be exact because the system planners and operators are more concerned with knowing if overload levels of current and out-of-limit voltages exist than with finding the exact values of those quantities. the simulation of the whole electrical network is carried on matlab, but in matlab, load flow analysis does not work with facts devices, so to cope with this problem one can develop his own load flow tool for more accuracy. we implemented upfc from facts family on a four bus network. the data obtained from the network including line impedances, transformer parameters, load demand and generation are shown below. upfc can provide reactive power to the system because it consists of statcom which has the ability to generate reactive power according to the network demands. the power grid consists of two power generation substations and one major load centre at bus b3. the first power generation substation (m1) has a rating of 2100mva (l3). upfc is connected between bus number one and two. without upfc, active power of bus number two was 663mw and reactive power was -122.3mvar. the generation substation m2 is also connected to the load by a 50km line by setting the reference of the active and reactive power of m1 connected to this load by two transmission lines l1 and l2. l1 is 280km long and l2 is split into two segments where the active and reactive power are absorbed by the load. the total length of the line l1 is 280km, line l2 is 300km long and line l3 is 50km. the upfc measurement block has the set parameters of active power, reactive power and the phase and magnitudes of the voltage values. both generators are also connected with transformers. the network diagram on simulink is shown in figure 1. iii. results and discussion the generation substations m1 and m2 representing 4 and 6 machines of 350mva respectively have a rating of 1400mva. the load center of approximately 2200mw is modeled using a dynamic load only transfer’s active power from one line to the other according to the reference which is set for active power in order to simulate the effect of upfc. it should be noted that the upfc does not produce active power on bus two, it sets the active power to 763mw and maintains reactive power to -122.3mvar. however, the shunt compensation devices in the upfc supply the reactive power to the system. the upfc basically controls the active power flow. in overload conditions, it allows the flow of active power according to a set reference power, thereby minimizing the contingency. the results with and without upfc are shown in tables i-iv and in figures 2-5. fig. 1. network diagram on simulink table i. simulation results without upfc bus active power (mw) reactive power (mvar) voltages (v) b1 1337 -233 1.006 b2 663.5 -122.3 1.006 b3 988.9 -29.25 1.002 b4 563.2 -40.67 1.014 table ii. simulation results with upfc bus active power (mw) reactive power (mvar) voltages (v) b1 1331 -294.2 1.01 b2 762.4 -122 0.9925 b3 987 -10.71 0.9988 b4 460.3 -15.92 1.017 table iii. comparison of active power results bus without upfc (mw) with upfc (mw) b1 1337 1331 b2 663.5 762.4 b3 988.9 987 b4 563.2 460.3 table iv. comparison of reactive power results bus without upfc (mvar) with upfc (mvar) b1 -233 -294.2 b2 -122.3 -122 b3 -29.25 --10.71 b4 -40.67 -15.92 active power is set at 763mw and the other parameters are changed simultaneously. the active power has a relationship with the voltage angles and the reactive power is changed by changing the voltages of the lines. it can be seen from the figures that the active power of the bus 1 was 1337mw without upfc and it is changed to 1331mw by incorporating the upfc between the lines. the reactive power of the bus 1 without upfc was -233mvar which has been changed to -294mw and the simultaneous changes in the bus voltages with and without upfc can be seen. engineering, technology & applied science research vol. 9, no. 2, 2019, 3900-3904 3903 www.etasr.com khan et al.: power flow control by unified power flow controller fig. 2. active power without upfc fig. 3. active power with upfc fig. 4. reactive power without upfc fig. 5. reactive power with upfc the increase in the active power of the bus 2 from 663mw to 763mw can be seen from the graphs. it should been noted that the reactive power at bus 2 is the same with and without upfc. this shows that employing upfc doesn’t change the reactive power of the concerned bus. however, reactive power is transformed from a bus to another bus to change the active powers of the buses. the bus voltages in the system have a dynamic range of 10%. if the voltage drops below 0.90pu or increase above 1.10pu the system operation will be disturbed. shunt compensating facts devices maintain the voltage range by supplying or absorbing reactive power. moreover, the active powers are changed at the expense of voltage angles by controlling of voltage angles at the sending and receiving end of the transmission lines. iv. conclusion the flow of power can be controlled in a network through facts devices. basic parameters of a power system like active power, reactive power and voltages can be controlled and adjusted simultaneously by the use of a upfc. the incorporation of facts devices improves the stability of the power system. in pakistan’s wapda system, the rapid increase in load and no generation to cope the load has increased load shedding and supply problems through the country. the government has planned to increase the generation capacity but the supply companies faced the problems of line load-ability, environmental constraints, power limits etc. the series controlled compensation provided by facts can provide an efficient solution to this problem. with the use of tcsc we can enhance the power transfer capability of the existing lines and hence we can mitigate the problem line load-ability issues. with the application of facts, we also provide an additional feature of stability even in post contingency conditions for both transient and steady-state stability issues. so pakistan transmission companies should install facts devices because they will be proved to be beneficial in terms of cost and environmental concern. references [1] p. s. georgilakis, p. g. vernados, “flexible ac transmission system controllers: an evaluation”, in materials science forum, vol. 670, pp. 399-406, 2011 [2] j. dixon, l. moran, j. rodriguez, r. domke, “reactive power compensation technologies: state-of-the-art review”, proceedings of the ieee, vol. 93, no. 12, pp. 2144-2164, 2005 [3] a. sode-yome, n. mithulananthan, k. y. lee, “a comprehensive comparison of facts devices for enhancing static voltage stability”, ieee power engineering society general meeting, tampa, usa, june 24-28, 2007 [4] a. sode-yome, n. mithulananthan, “comparison of shunt capacitor, svc and statcom in static voltage stability margin enhancement”, international journal of electrical engineering & education, vol 41, no. 2, pp. 158-171, 2004 [5] d. van hertem, j. verboomen, r. belmans, w. l. kling, “power flow controlling devices: an overview of their working principles and their application range”, ieee international conference on future power systems, amsterdam, netherlands, november 18, 2005 [6] p. bresesti, m. sforna, v. allegranza, d. canever, r. vailati, “application of phase shifting transformers for a secure and efficient operation of the interconnection corridors”, ieee power engineering society general meeting, denver, usa, june 6-10, 2004 [7] n. s. do, m. m. gouvea jr, “voltage stability enhancement in power systems with automatic facts device allocation”, energy procedia, vol. 107, pp. 60-67, 2017 [8] b. bhattacharyya, v. k. gupta, s. kumar, “upfc with series and shunt facts controllers for the economic operation of a power system”, ain shams engineering journal, vol. 5, no. 3, pp. 775-787, 2014 [9] m. a. kamarposhti, h. lesani, “effects of statcom, tcsc, sssc and upfc on static voltage stability”, electrical engineering, vol. 93, no. 1, pp. 33-42, 2011 engineering, technology & applied science research vol. 9, no. 2, 2019, 3900-3904 3904 www.etasr.com khan et al.: power flow control by unified power flow controller [10] z. yang, c. shen, l. zhang, m. l. crow, s. atcitty, “integration of a statcom and battery energy storage”, ieee transactions on power systems, vol. 16, no. 2, pp. 254-260, 2001 [11] d. murali, m. rajaram, n. reka, “comparison of facts devices for power system stability enhancement”, international journal of computer applications, vol. 8, no. 4, pp. 30-35, 2010 [12] s. e. mubeen, r. k. nema, gayatri agnihotri, “power flow control with upfc in power transmission system”, international journal of electrical and computer engineering, vol. 2, no. 11, pp. 2507-2511, 2008 [13] j. j. paserba, “how facts controllers benefit ac transmission systems”, ieee power engineering society general meeting, denver, usa, june 6-10, 2004 [14] n. acharya, a. sode-yome, n. mithulananthan, “facts about flexible ac transmission systems (facts) controllers: practical installations and benefits”, australasian universities power engineering conference (aupec), hobart, tasmania, australia, september 25-28, 2005 [15] a. k. mohanty, a. k. barik, “power system stability improvement using facts devices”, international journal of modern engineering research, vol. 1, no. 2, pp. 666-672, 2011 microsoft word 32-3121_s1_etasr_v9_n6_pp5041-5046 engineering, technology & applied science research vol. 9, no. 6, 2019, 5041-5046 5041 www.etasr.com dhaked et al.: battery charging optimization of solar energy based telecom sites in india battery charging optimization of solar energy based telecom sites in india dheeraj kumar dhaked department of electrical engineering rajasthan technical university kota, rajasthan, india ddhakar9@gmail.com yatindra gopal department of electrical engineering rajasthan technical university kota, rajasthan, india ygopal.phd@rtu.ac.in dinesh birla department of electrical engineering rajasthan technical university kota, rajasthan, india birlartu2@gmail.com abstract—telecom sites get the power normally from the grid. at the occurrence of power outages power need to be supplied for telecom sites. the battery bank is a good option for telecom sites to fulfil power demand. this paper discusses a smooth battery bank charging and discharging system with solar power as the input supply source. the system requires a large capital investment, but it provides uninterrupted emergency power when needed. maintaining battery banks is essential for getting optimum performance. this paper also discusses the power requirements for telecom sites backup and various parameter impacts on battery life. methods are derived to optimize charging management of batteries in order to get maximum lifespan in addition to better battery performance throughout its useful life. keywords-telecom site; battery bank; charging-discharging; maximum power point tracking (mppt) i. introduction the telecom industry of india is growing at a very fast pace. telecom sites require uninterrupted power supply [1]. the main problem of the telecom sites is that rural areas have only 6 to 10 hours of power supply from the grid. to fulfil this demand, two ways are possible, either by grid or by some other renewable source, i.e. solar, biomass, wind, etc. [2]. also, there are other issues which make this solution worthy: • the dismal state of rural electrification • non-availability of grid power in rural areas • the grid might be away from the site • poor grid power quality • unreliable & erratic power behavior the use of renewable power sources also reduces environmental deteriorating agents, as carbon emission for power generation, thus rural sites will get reliable power for operation. solar energy is one of the best options as it is totally free of cost and can be harvested easily with available means like solar plates, inverters, and converters. the power harvested from the sunlight during the day can also be used during the night hours if stored in battery banks [3-4]. the power demand for a single telecom site ranges from 1 to 4kw for 24×7 hour operation. for back-up, it requires a 15-20kva diesel generator set (dg) which has 4l/h diesel consumption. the running time of the dg set is 6-10 hours per day in grid-connected areas but for about 14-16 hours in rural areas the grid is not available. the burning of diesel causes the emission of greenhouse gases (ghg) (carbon dioxide, methane, nitrous oxide etc.). solar energy can fulfil telecom sites’ load in day-time, while during night hours charged batteries can supply the system. the battery banks set-up will be placed at the telecom site and as an economical solution for back-up [5]. lead-acid battery model for simulation with solar system via a dc-dc converter with battery set-up was used in [6-7]. in this paper, particle swarm optimization (pso) algorithm is used for battery charging. this paper also describes an equivalent circuit model for battery and solar cell, and a battery model is made to match the model from the datasheet of the manufacturer. the performance of the battery cell, while being charged by solar array cell is also simulated. multiple modes of operation and scenarios which cause early battery failure are described in [8-11] and are taken into consideration while proceeding to develop the most suitable battery charging method. a. study objectives • to introduce the reader to current energy-efficient technologies which are environment supportive. • to study the solar fed battery bank system with model implementation in matlab. • to study the behavior of the model for battery charging and discharging and analyze its characteristics. b. problem statement • energy consumption from telecom network is an increasing contributor to ghg emission. • limiting carbon dioxide emissions will be more difficult for most of the countries where electric generation comes primarily from coal such as india. • the carbon emission footprint of the telecom sector has risen significantly and will rise despite the development of energy-efficient technologies. corresponding author: dheeraj kumar dhaked engineering, technology & applied science research vol. 9, no. 6, 2019, 5041-5046 5042 www.etasr.com dhaked et al.: battery charging optimization of solar energy based telecom sites in india ii. methodology of battery charging optimization as the scope of this manuscript is to develop modified charging algorithms for batteries, one has to reach to the exact traditional charging profile before using the suggested algorithms, according to battery chemistries and strict do’s and don’ts which must be kept in the algorithms. while varying parameters of batteries and changing operating conditions, critical parameters, like thermal dissipation which causes gassing and ageing of batteries, have to be observed and improved [6]. input varying conditions, like solar charging current, have to be simulated in most real-time scenarios to see the impact and sizing of solar panels to be optimized [4]. in most cases, the power input from solar panels is insufficient to keep the batteries full charged, especially during sunless days. in such conditions, the battery remains in partial state of charge (psoc) and deep cycling. solar systems are installed in conditions where battery temperatures remain usually high [78]. normal lead-acid batteries fail in such conditions due to sulphating, corrosion, and active material shedding. water topup in remote sites is difficult also. hence, the best option is gel batteries with vrla technology. for solar applications, charging hours are limited by sunlight availability. boost charge can be given every day since charging current and ambient temperature during the evening are already decreased to a certain level [9-11]. it would not lead to any heat generation or any other negative effect, but will help keep sulphation away because higher voltage kills sulphation and hence plates remain fresh and battery cycle life increases. in order to achieve the implementation of the above, a nominal charging algorithm has been modified to give everyday equalization charge keeping close monitoring of cell temperature avoiding any ill effect of heat to cycle life [12]. by removing sulphation, lead plates remain fresh and hence battery lasts longer as lead plate sulphation is a significant part in determining the battery life [13-15]. iii. mppt and battery charging optimization optimization is the mechanism which finds the maximum or minimum value of a function or process. it is used in fields such as physics, chemistry, economics, and engineering where the goal is to maximize efficiency, production, or some other measure. to gain the maximum power output, an mppt technique is used in the form of an electronic system that operates with the pv system. the maximal power point (mpp) doesn’t reach an exact end or point but it gets moving around the pv curve that depends on light intensity of irradiation and the temperature. the pso mppt is used and the flowchart of this algorithm is given in figure 1. the pso algorithm finds the best possible resolution of swarm particles through the particle’s progress in the investigation space with its optimized velocity and position. it finds the optimum solution by obtaining the minimum value of the given objective function [16]. the outline of the pso algorithm is presented below. step i: initialize the particles with random numbers having a consistent distribution: y=vrand (plowerlim, pupperlim). assign this position to the best known position array: r=y. initialize particle velocity: v=y. if the number of particles is nump then, y is the size of the array of particle positions. similarly, r is an array of pbest positions, and v is a nump-size array of particle velocities. step ii: calculate the fitness function: ey=f(y), er=f(r), and eg=f(gbest), where ey and er are the fitness evaluation arrays for y and r, respectively, and eg is the function evaluation at gbest. step iii: update pbest value for each particle of the population: if ey(i)<er(i) then r(i)=y(i), where i= 1, 2, . . . nump. step iv: update gbest value for the entire population: if er(i)<eg then gbest=r(i). step v: update the velocity and position of the particles: ( ) ( ) ( ) ( ) ( )( ) ( ) ( )( ) ( ) ( ) ( ) 1 2 1 , , 1 0,1 0 1 1 v i wv i c rrand r i y i c rrand gbest y i y i y i v i + = + − + − + = + + where w is the initial weight, c1 is the cognitive parameter, and c2 is the social parameter. step vi: exit criterion is generally a fitness threshold or a highest number of iterations. if the criterion is met, then exit or else, go to step ii. the pso works by simultaneously maintaining several candidate solutions in the search space [6]. during each iteration, each candidate solution is evaluated by the objective function to be optimized, determining the fitness of that solution. each candidate solution can be thought of as a particle “flying” through the fitness landscape finding the maximum or minimum of the objective function. iv. modeling and simulation the equivalent circuit model of a lead-acid battery is a voltage source connecting with the internal resistance. state of charge (soc), temperature and other elements of the battery parameters of circuit are related by the relationship between the resistance and voltage of capacitor. each cell of the lead-acid battery produces 2v. total terminal voltage will vary according to the working conditions. the concentration of the acid will change during charge and discharge [10]. the experiment has the following steps. • study of the battery used in the experiment and research data from various sources. • design of the battery circuit and the block diagram of a mathematical model using simulink. • simulations at different temperatures from 25 to 60 o c have to be conducted and recording for current and voltage graph has to be done. in this section, modeling of lead acid battery is done using the simscape language in order to implement nonlinear equations of the component of equivalent circuit as shown in figure 2. in this way, defining physical equations and the connection between model components described. the study in [13] is referred for defining equations and their validation. engineering, technology & applied science research vol. 9, no. 6, 2019, 5041-5046 5043 www.etasr.com dhaked et al.: battery charging optimization of solar energy based telecom sites in india start set default values of pwm initialize controller drivers initialize adc drivers get battery capacity from user set battery current limit threshold to capacity/5 i.e. c/5 set battery lvd, lv, ovd, ovr thresholds read battery voltage, battery current & temperature calculate battery soc calculate battery voltage and current threshold based on temperature set battery charging mode-boost or float is battery voltage <lvd is battery voltage >lvr is battery voltage>hvd is battery voltage <hvr is charging threshold reached load charging profile from memory, raise the pwm store the report in memory and regulate the current and voltage turn off load port reconnect the load disable charging port enable charging port yes yes yes yes yes no no no no no fig. 1. pso algorithm flowchart for digital control loop for battery charging initially, the battery is discharged at a load current of 10a in the simulation and then further recharged at a current of 10a to return to the initial state of charge. a simple thermal model is used to model battery temperature. it is considered that cooling is done primarily via convection method and that heating is mainly from the internal battery resistance r2. a standard 12v lead-acid battery is modelled by connecting six 2v battery cell blocks in series, or for telecom applications of 48v, more 2v cells should be used in series [10-11]. once the battery model is developed, then to simulate the application, a simulation profile is created where both charging and discharging parameters using controlled current sources and controlled load sources are programmed to simulate the actual conditions of solar panel and grid-based battery charging [1415]. fig. 2. battery simscape model fig. 3. simulink model for lead acid battery capacity=100ah, battery nominal voltage=52v, response time=30s, initial soc=100% v. description of simulation circuit the simulation circuit components of figure 3 are: • energy source: a solar panel providing 35v voltage and 10a current. • battery: a battery model with 48v nominal voltage and respective internal resistance as per battery model. • load: one controlled resistance is used in the simulation circuit which represents the telecom load for which the entire system has to be made. • voltage conversion module: a dc-dc boost converter to change the solar panel voltage to battery charging voltage in a controlled manner. engineering, technology & applied science research vol. 9, no. 6, 2019, 5041-5046 5044 www.etasr.com dhaked et al.: battery charging optimization of solar energy based telecom sites in india • monitoring modules: the necessary voltage and current measurement devices are used in the simulation circuit. • simulation: the dc-dc boost converter is used to boost the voltage to battery voltage and the whole circuit acts as a current limited source to charge the battery up to the desired voltage using the current source. using the pwm controller in the boost converter, the desired charging current can be set when charging the battery in bulk charging mode. it depends on the profile which is based on the charging and discharging time status of the battery voltage, current, solar module voltage and power output w.r.t. sunlight. once the battery voltage reaches full charge, it can be controlled to enter in constant voltage-based charging. in this case, the battery voltage reaches a constant value of 56v and the battery current starts decreasing slowly with time. with different charging current limits the battery voltage and soc can be plotted with charging current. with different charging voltage settings in constant charging voltage mode, the charging performance can be optimized [17-19]. with this practical simulation model, any permutation and combination of charging voltage versus charging current and battery soc can be developed and tested. the pso algorithm is loaded in the pwm controller in the simulation model. different charging and discharging curves are below simulating different battery sizes, charging voltages and charging current to confirm the system’s functionality. fig. 4. discharge characteristics of lead-acid battery: capacity=100ah, nominal voltage=52v, response time=30s, initial soc=100% the discharge characteristic of lead-acid battery for 100ah capacity, 52v battery voltage and 100% soc is shown in figure 4. the discharge characteristic of lead-acid battery for 50ah capacity, 13.5v battery voltage, and 90% soc, is shown in figure 5. the discharge characteristic of lead-acid battery for capacity of 100ah, 26.5v battery voltage and 80% soc is shown in figure 6. fig. 5. discharge characteristics of lead-acid battery: nominal voltage=13.5v, rated capacity=50ah, initial soc=90%, battery response time=30s fig. 6. discharge characteristics of lead-acid battery: initial soc=80%, capacity=100ah, nominal voltage=26.5v, response time=20s vi. simulation results the results of the above mentioned simulations are: • battery temperature rise is controlled by maximum battery charging current. current control is done through measuring the battery internal temperature by mounting the temperature sensor on the negative terminal of the battery. • when battery temperature control is done, the cycle life of batteries can be determined directly by the exclusive data provided by the manufacturer. this is usually at 25 o c as a function of depth of discharge in the cycle and the number of cycles. engineering, technology & applied science research vol. 9, no. 6, 2019, 5041-5046 5045 www.etasr.com dhaked et al.: battery charging optimization of solar energy based telecom sites in india • the charging profile is matched to the ideal charging profile given by the battery manufacturer. gassing can be controlled in simulations and the desired battery performance will be achievable when the system's operational needs are very close to the ideal conditions. • when the battery is charged and discharged using properly rated charging power, daily soc are at the higher sides of the soc scale. minimum battery soc after overnight discharge is 80% and 100% during charging time at around 3 pm. this results in highest cycle life as given in the depth of discharge (dod) vs cycle life chart provided by the battery manufacturer. • when the battery capacity selected for required load is as mentioned above, batteries are usually sized as per standard discharge current and capacity. usually, all batteries are rated as c/20 or c/10. • in telecom conditions, more than 25 hours back-up is needed for the batteries to operate to c/40 or greater (up to c/100) rating. this provides a very high cycle life but it requires increasing the low voltage disconnect threshold level depending on discharging current rating. vii. practical results after applying the pso algorithm, it has been observed that the daily soc battery level stayed from 80% to 100% and the voltage level ranged between 65% and 85%, hence the cycle life is certainly expected to increase. figure 7 shows the soc variation before applying pso mppt algorithm. the soc stayed between 65% and 80% throughout the week. fig. 7. soc variation before applying pso algorithm. soc stays between 65% and 80% fig. 8. soc variations after applying pso. soc stays above 80% battery’s life cycle was around 4000 cycles, as shown in figure 9. figure 8 shows the soc variation after applying the pso mppt algorithm. it can be seen from figure 9 that soc stayed above 80% throughout the week. the battery cycle life became around 5500 cycles (figure 9). it is observed that battery life increased by 30% with the suggested optimization. fig. 9. battery cycle life with respect to depth of discharge viii. conclusion in this paper, various parameters of charging battery and their respective impact on the battery cycle life were studied. while carefully considering all of them, an optimized charging method was driven which also takes proper sizing of battery bank and solar pv array into consideration. a lead-acid battery model was programmed in matlab and its characteristics were studied. dc-dc boost converter-based current source and constant-voltage source equations were programmed in matlab and their characteristics were studied. advance battery charging method was driven and the performance impact on batteries was studied while operating with solar panels. solar pv power system performance for 24x7 operating loads, such as telecom loads, is satisfactory when batteries perform for a long time and give better revenues to operators with less maintenance expenses. optimum calculations of system sizing for solar pv array and battery banks capacity were also derived. with the help of the developed algorithm, 30% more cycle life was achieved. references [1] intelligent energy, the true cost of providing energy to telecom towers in india, available at: https://www.gsma.com/membership/wpcontent/uploads/2013/01/true-cost-providing-energy-telecom-towersindia.pdf, 2012 [2] r. dabkeya, d. k. dhaked, m. lalwani, “an overview of gasifier and its application in indian context”, 3rd international conference on emerging trends in electrical, communication and information technologies, ananthapuramu, india, december 20-22, 2018 [3] n. bashir, h. s. sardar, m. nasir, n. u. hassan, h. a. khan, “lifetime maximization of lead-acid batteries in small scale ups and distributed generation systems”, 2017 ieee manchester powertech, manchester, uk, november 5-8, 2017 [4] f. chermat, m. khemliche, a. badoud, s. latreche, “techno-economic feasibility study of investigation of renewable energy system for rural electrification in southern algeria”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3421–3426, 2018 engineering, technology & applied science research vol. 9, no. 6, 2019, 5041-5046 5046 www.etasr.com dhaked et al.: battery charging optimization of solar energy based telecom sites in india [5] m. garba, m. a. tankari, g. lefebvre, “using of distributed energy resources for microgrid resilience achieving”, ieee 6th international conference on renewable energy research and applications, san diego, usa, december 5-8, 2017 [6] s. chen, c. kang, z. zhang, h. zhu, “a method for soc estimation for lead-acid battery based on multi-model adaptive extended kalman filtering estimation”, iecon 42nd annual conference of the ieee industrial electronics society, florence, italy, october 23-26, 2016 [7] k. dhaked, s. saini, p. sharma, “analysis of different converters for reduced total harmonic distortion and improved power factor”, ieee fifth international conference on signal processing and integrated networks, noida, india, february 22-23,2018 [8] c. c. freitas, m. b. ketzer, m. r. a. morais, a. m. n. lima, “lifetime estimation technique for lead-acid batteries”, iecon 42nd annual conference of the ieee industrial electronics society, florence, italy, october 23-26, 2016 [9] j. f. a. leao, l. v. hartmann, m. b. r. correa, a. m. n. lima, “leadacid battery modeling and state of charge monitoring”, 2010 twentyfifth annual ieee applied power electronics conference and exposition, palm springs, usa, february 21-25, 2010 [10] z. m. salameh, m. a. casacca, w. a. lynch, “a mathematical model for lead-acid batteries”, ieee transactions on energy conversion, vol. 7, no. 1, pp. 93-98, 1992 [11] m. y. chen, m. f. tsai, c. s. tseng, s. y. yen, “a novel control strategy for multiphase battery chargers without hall-effect current sensors”, international power electronics conference, sapporo, japan, june 21-24, 2010 [12] p. k. manoharan, r. mohan kumar, k. karthick, r. sowmya, “soc estimation and mmnitoring of li-ion cell using kalman-rilter algorithm”, international journal on electrical engineering and informatics, vol. 6, no. 4, pp. 418-427, 2018 [13] r. a. jackey, “a simple, effective lead-acid battery modelling process for electrical system component selection”, sae world congress & exhibition, april 2007 [14] j. jana, h. samanta, k. d. bhattacharya, h. saha, “design and development of high efficiency five stage battery charge controller with improved mppt performance for solar pv systems”, international journal of renewable energy research, vol. 8, no. 2, pp. 941-953, 2018 [15] a. hassoune, m. khafallah, a. mesbahi, t. bouragba, “power management procedures of electric vehicle charging station based grid tied pv-battery system”, international journal of renewable energy research, vol. 8, no. 2, pp. 851-860, 2018 [16] m. m. hoque, m. a. hannan, a. mohamed, “charging and discharging model of lithium-ion battery for charge equalization control using particle swarm optimization algorithm”, journal of renewable and sustainable energy, vol. 8, no. 6, article id 065701, 2016 [17] m. s. hossain lipu, m. a. hannan, a. hussain, m. m. hoque, p. j. ker, m. h. m. saad, a. ayob, “a review of state of health and remaining useful life estimation methods for lithium-ion battery in electric vehicles: challenges and recommendations”, journal of cleaner production, vol. 205, no. 1, pp. 115-133, 2018 [18] u. b. tayab, m. a. al humayun, “modeling and analysis of a cascaded battery-boost multilevel inverter using different switching angle arrangement techniques”, engineering, technology & applied science research, vol. 7, no. 2, pp. 1450-1454, 2017 [19] y. gopal, k. kumar, d. birla, m. lalwani, “banes and boons of perturb & observe, incremental conductance and modified regula falsi methods for sustainable pv energy generation“, journal of power technologies, vol. 97, no. 1, pp. 35-43, 2017 microsoft word 22-3072_setasr_v9_n5_pp4695-4701 engineering, technology & applied science research vol. 9, no. 5, 2019, 4695-4701 4695 www.etasr.com ben nasrallah et al.: temperature effect on al/p-cuins2/sno2(f) schottky diodes temperature effect on al/p-cuins2/sno2(f) schottky diodes tarek ben nasrallah physics department, university of hail, hail, saudi arabia and fst, upds, university of tunis el-manar, tunis, tunisia tarek.bennasrallah@fst.utm.tn mohcen jemai physics department, fst, lmapq, university of tunis el-manar, tunis, tunisia mohcen.jemai@gmail.com djelloul mahboub physics department, university of hail, hail, saudi arabia djmahboub@gmail.com said belgacem physics department, fst, upds, university of tunis el-manar, tunis, tunisia saidbelgacem55@gmail.com abstract—in this paper, schottky diodes (sds) obtained by evaporated thin films of aluminum on pulverized pcuins2/sno2:f have been studied using j-v-t characteristics in a temperature range of 200-340k. these characteristics show that aluminum acts as a rectifier metal-semiconductor contact. characteristic variables of the al/p-cuins2/sno2:f junctions, such as the current density, the serial resistance, the parallel conductance, the schottky barrier height (sbh), and the ideality factor of the sd were obtained by fitting the j-v-t data using the lambert function. data analysis was conducted with the use of matlab. results showed that n is greater than 1, which could be explained by the existence of inhomogeneities due to the grain boundaries in cuins2. through this analysis, one can see a good agreement between experimental and modeled data. the study has shown that the main contribution in the current conduction in such heterostructures is the thermionic emission (te) supported by the recombination of the carriers. the last phenomenon appears mainly in the grain boundaries, which contain both intrinsic and extrinsic defects (secondary phases, segregated oxygen). an investigation of the j-v-t characteristics according to te theory has demonstrated that the current density and the sbh increase while serial resistance, parallel conductance decrease with an increase in temperature. after an sbh inhomogeneity correction, the modified richardson constant and the mean barrier height were found to be 120ak -2 cm -2 and 1.29ev respectively. this kind of behavior has been observed in many metal-semiconductor contacts. keywords-cuins2; thin films; spray pyrolysis; schottky diodes; lambert function introduction i. the ternary semiconductors with the chemical formula of abncm (a=cu, ag, zn, cd, b=ga, in, c=s, se, te, n, m: integers) have aroused considerable interest [1-3]. their physicochemical properties allow them to be used in many applications in fields such as solar cells [3-5], photocatalysis [6], non-linear optics [7], lasers [8], solar cells, optronic devices [9], etc. a particular type of the ternary chalcogenides has emerged, which has proven the ability of these semiconductors to be used as an absorber in terrestrial photovoltaic applications. one of the main i-iii-vi2 types of semiconductors, namely cuins2 (cis) crystallize in the chalcopyrite structure, has a high absorbance in the visible and near-infrared region [4], a direct bandgap of 1.5ev, and nontoxic environmental constituents. all these properties allow the cis to be an excellent candidate for several applications in the field of optoelectronics in general [10-14]. on the other hand, the metal-semiconductor contacts (ms) are at the base of all electronic devices, whether ohmic type or rectifiers (schottky diode (sd)). nevertheless, it should be emphasized that the efficiency and reliability of an sd are highly influenced by the quality of the interface between the two (metal and semiconductor) surfaces [15-17]. therefore, special attention should be given to the state of the ms interface when analyzing the j-v-t characteristics of the sd with respect to the ideal thermionic emission (te) actual model [18-23]. recent studies have demonstrated a temperature dependence of the schottky barrier parameters [24-34]. throughout these studies and according to the te theory, the sbh decreases when the temperature increases whereas the ideality factor n increases with a decrease in temperature. the standard te theory seems to be unsuccessful in explaining these experimental results [35], since the barrier height (bh) does not depend on temperature, as the bandgap of the semiconductor [24]. the most used devices with schottky contacts and operating at cryogenic temperatures, as the infrared detectors in thermal imaging [34, 36-38], use low bh schottky diodes. this factor makes the analysis of j-v-t characteristics of the schottky barrier diodes at ambient temperature unable to provide us the transport phenomena of charge carriers as well as the nature of barrier formation. moreover, an in-depth study corresponding author: tarek ben nasrallah engineering, technology & applied science research vol. 9, no. 5, 2019, 4695-4701 4696 www.etasr.com ben nasrallah et al.: temperature effect on al/p-cuins2/sno2(f) schottky diodes of the j-v-t characteristics of schottky contacts allows determining the aspects of their conduction mechanisms. the conduction mechanisms and therefore the bh of ms contacts, whether they are ohmic or rectifiers, depends on intrinsic or extrinsic defects such as the atomic structure, the doping, and thickness inhomogeneities at the metal-semiconductor interface, the grain boundaries secondary phases as shown in [39-47]. these defects should introduce and develop substantial inhomogeneities in the schottky barrier height (sbh) [34, 48]. to the best of our knowledge, the electrical transport characteristics of a�/p-cis/sno2:f schottky contacts at low temperatures have not been reported yet. however, we have to cite [49] concerning the elaboration of a�/zno/cds/cuins2/mo/glass solar cells, were the j-v characteristic of a�/cuins2 was carried out at room temperature. therefore, the primary goal of the present paper is the study of the current-voltage characteristics of a�/p-cis/sno₂:f schottky diodes in the temperature range of 200-340k and therefore extract the five parameters (js, n, rs, gp and φ�) of the elaborated schottky diodes. the influence of the temperature on the ideality factor n and the barrier height φ� will also be presented. experimental procedure ii. cuins2 (p) thin films have been deposited using spray pyrolysis technique on sno2:f/pyrex substrates. the sprayed thin films were carried out at the optimized substrate temperature of 600k, and the concentration elements ratios in the spray solution were: �cu��/�in���=1.1 and �s���/�in���=4 with constant indium concentration �in���=3.3 10-2mol.l-1 [50, 51]. finally, a thin film of high purity (99.999%) aluminum (a�) with a thickness of 700å has been evaporated, under vacuum (10-6torr) onto cuins2 sprayed film to complete the sd development process (figure 1). fig. 1. structure of a�/cuins2 schottky diodes the sno2 doped with fluorine (f), prepared with the same spray technique [52] is used as a back ohmic contact. figure 2 shows that the j–v characteristic of the au/cuins2/sno2 contact is symmetric and rectilinear. the specific contact resistance rc=6.25ωcm 2 is independent of the applied voltage’s value or polarity, proving that the structure au/cuins2/sno2 is an excellent ohmic contact. the current density-voltage (j-v) characteristics at low temperatures (200k≤t≤340k) using liquid nitrogen have been carried out using a programmable voltage source (keithley 230) and a lock-in amplifier (sr 830). data acquisition was done using labview. fig. 2. i-v characteristic of au/cuins2/sno2 contact results and discussion iii. a. forward-bias j-v-t characteristics of a�/p-cis/sno2:f the determination with reasonable accuracy of the schottky diode parameters ideality factor n, barrier height ���, series resistance rs, shunt conductance gp, and saturation current js is fundamental to determine the charge carrier’s transport mechanisms and to optimize the electrical performance of these devices. several numerical analysis methods have been developed to extract these parameters [16, 53-59]. the method used in this work is based on the analytical solution of (1), while taking into account (2). a similar problem was shown in [58], but only with three parameters and straightforward relation between voltage and current, as shown in [59]. the lambert w-function method has been used to determine rs, gp, n, φb0, and js. the lambert w-function is the solution to the implicit equation w(x)exp[w(x)]=x. the problem is to be solved with the evaluation of a set of five parameters to fit a given experimental j–v-t characteristic. to understand if an sd has an ideal diode behavior, an analysis of its j-v-t characteristics must be analyzed using the te model [15, 16]: ���� � �� �exp � ���� !�"# $ % 1' ( )* �� % ,��� (1) with: �� � -∗/� exp�% 012 �"# $ (2) where js is the saturation current, v is the forward bias voltage, �34 � 56 7 is the thermal voltage, rs the serial resistance, gp the parallel conductance. a* is the effective richardson constant, t the absolute temperature, φb0 the zero bias effective barrier height, k is the boltzmann constant and q is the elementary charge. for an ideal diode where the conduction mechanism is governed only by the te process, the ideality factor has a value of n=1. this ideality factor n can be greater than 1 in the case of recombination of charge carrier in the depletion zone and/or if a tunneling effect through the barrier has been occurred for such diodes. typical forward bias j-v characteristics of a�/p-cuins2/sno2:f schottky contacts as a function of temperature in the range 200-340k are shown in figures 3-4. as expected, these characteristics deviate from ideality at low temperatures (200–265k), 8 ≳ 3, in this case, the conduction is due to the recombination of charge carriers in the depletion region [15, 16] also to the carriers tunneling through the barrier. at temperatures above 265k, the te process becomes dominant. engineering, technology & applied science research vol. 9, no. 5, 2019, 4695-4701 4697 www.etasr.com ben nasrallah et al.: temperature effect on al/p-cuins2/sno2(f) schottky diodes matlab was used to fit the data using (1) and (2) to extract the experimental values of rs, gp, n, φ;� and js as described above. experimental and fitted data are given in figures 3-4 for the temperature range of 200k≤t≤340k. it can be seen that the fitted data correspond to the experimental data. the electrical parameters obtained by this approach are summarized in table i. fig. 3. j-v curve of a�/cis/sno2 schottky diode for t=340k and t=300k. the fit using the lambert function is also shown. table i. temperature dependence of electrical parameters t (k) js (na.cm -2 ) n rs (ωωωω) gp (µωµωµωµω −1−1−1−1 ) φφφφb0 (ev) 340 60 1.5 1.36 1.13 1.122 300 2.96 2 30.55 6.71 1.098 280 0.99 2.49 43.68 7.56 1.032 265 0.4 2.85 179.5 7.56×102 0.950 250 7×10-2 3.5 207.3 7.85×103 0.888 230 1.43×10-2 4.25 294.71 4.97×104 0.830 200 1.25×10-3 7.51 473.22 13.74×105 0.750 figure 5 shows the plots of φb0 and n respectively vs. temperature for a�/p-cis/sno2:f. decrease in the ideality factors and increase in the barrier heights with an increase in temperature are observed. during the elaboration of the different thin films, especially the sprayed one, inhomogeneities in the structure of the interface of the ms contacts are induced which could explain the strong dependence of these parameters (φb0 and n) on temperature [60]. one can deduce that the transport of charge carriers through the metal-semiconductor interface is temperatureactivated, the sbh could contain inhomogeneities, and the current transport will be dominated by current flow through small interfacial regions with a weaker sbh that the electrons can overcome at low temperatures [17, 42]. due to these inhomogeneities, charge transport over the interface is never again commanded by te. moreover, numerous models have been put forward to clarify the inhomogeneity in the barrier [17, 42, 46]. authors in [17, 42] proposed a potential fluctuation model to describe bhs, which shows a more significant deviation from the classical thermionic theory at low temperature. according to the potential fluctuation model, at adequately low temperatures, a nonnegligible current is flowing through discontinuities at the ms interface, which probably presents a lower barrier height, when the temperature increases, electrons gain more thermal energy to cross the threshold of the higher barrier [60,61]. as a result, both parameters (φb0 and n) exhibited temperature-dependent j-v-t characteristics (figure 5) consistent with sbh inhomogeneity. fig. 4. temperature dependence of a�/cis/sno2 j-v curves and their fitting curves fig. 5. temperature dependence of ideality factor and bh for a�/p-cuins2/sno2:f schottky contact in the temperature range 200-340k the ideality factor is merely a manifestation of barrier uniformity. bh inhomogeneities, potentially begin from structural defects in semiconductors, inhomogeneous doping, contamination on semiconductor surfaces during the deposition process (chemical solution), thickness nonuniformity, roughness of thin films, and the presence of an insulating layer (a�2o3) at the ms interface [50, 51]. authors in [48, 62] claim that the bh obtained under the flat band condition must be considered as a reference value of φb0 for which one can assume that the electric potential is zero. in this case, the effect of image force lowering the bh should be compensated, and accordingly, the influence of inhomogeneity would be removed [62]. to describe the disparity with respect to te theory, authors in [60] proposed a gaussian distribution <��= � for the engineering, technology & applied science research vol. 9, no. 5, 2019, 4695-4701 4698 www.etasr.com ben nasrallah et al.: temperature effect on al/p-cuins2/sno2(f) schottky diodes spatial dispersion of the barrier height at the ms interface with a standard deviation (>? ) around an average value �@=. the barrier height can be determined by using (2) as follows: ln � �6b� � ln �∗� % c12�"# (3) the plot of ln � �6b$ versus (q/kt) should yield a straight-line if the sbh ����) is independent of temperature t. however, the richardson plot of the experimental data (figure 6) described by (3) deviates from linearity for low temperatures t≤265k. this nonlinearity can be justified by the fact that the ideality factor n and the sbh �;� depend on temperature as described for many types of materials [27, 48, 61-67]. the richardson constant �-∗� extrapolated from the y-axis intercept has a value of 22.68 -hi��j��. this value of �-∗� is much lower than the theoretical value which is ** -2 -2 0 120 156acm k th ma m = = , where m*=1.3m0 is the hole effective mass in cis [62, 65, 68] and m0 is the electron mass. likewise, an sbh value of 0.83ev deduced from the slope of the linear part of this richardson plot was found for t≥265k. fig. 6. classical and modified richardson plot for a�/p-cuins2/sno2:f schottky contact the discrepancy in the richardson plot is most likely due to the inhomogeneities of the bh and applied potential fluctuation at the ms interface. these morphological and structural inhomogeneities incorporate a low and high barrier along with the ms interface. at low temperature the current through the lower barriers lies in the applied potential distribution [60, 69, 70]. authors in [64] showed that the richardson constant calculated from the j-v-t characteristics depends strictly on the barrier inhomogeneities. b. analysis of the schottky bh inhomogeneities (sbhi) authors in [60, 61] introduced a gaussian distribution to describe the potential fluctuation of the sbh to explain its abnormal behaviors. in this approach, the bh φb0 and the ideality factor n are replaced in (1) and (2) by the apparent bh φap at zero bias and apparent ideality factor nap as follows: �kl � �@���/ � 0� % 7nob �56 (4) p !qr % 1 � s� ( 7tu �56 (5) where �@�� and >? are the mean value and standard deviation of φb0 respectively. the temperature-dependent coefficients s� and s� quantify the voltage deformation of the bh distribution. furthermore, one can consider that >? is independent on temperature [33, 61, 65]. the barrier inhomogeneities affect the current flow of electrons through the schottky barrier. at low temperatures (t<265k), tunneling of electrons is the dominant process, given the electrons do not have enough energy to overcome the bh, but the existence of low barrier areas facilitate to the charge carries further tunneling through the bh. a linear fit for 8kl, which obeys to (5) has been obtained as shown in figure 7. the voltage coefficients values of ρ2=−0.68 and ρ3=−7.59×10 -4v from the intercept and slope respectively have been deduced. otherwise, the linear fit of the experimental data using (3) gives the value of the apparent bh, which should obey to (4). the values of �@��=0.953ev and >?=0.139v from the intercept and slope respectively have been obtained. the lower the value of >?, the better is the quality of the barrier height and the diode rectifying performance. c. the modified richardson plots the richardson plots can be adjusted using (3) and (4) simultaneously: ln � � 6b � % 7 bnob ��56�b � ln �-∗∗� % cqr �"# (6) where -∗∗ is the modified richardson constant. the fitting of the new richardson plot using (6) generates a straight line. �@�� and -∗∗ are deduced from the slope and intercept respectively as shown in figure 6. the graph has been plotted for the 200k–340k temperature range. the modified richardson constant was -∗∗ � 120 ak�� cm�� and mean bh of 1.29ev. authors in [70] used the same method for al/pcuinalse2 sd and obtained a modified richardson constant of -∗∗ � 26 ak�� cm�� and a mean barrier height of 1.02ev. fig. 7. zero-bias apparent barrier and apparent ideality factor versus q/(2kt) curves of a�/p-cuins2/sno2:f schottky contact conclusion iv. the j-v-t characteristics of a�/p-cuins2/sno2:f schottky contacts elaborated with the use of the physical vapor engineering, technology & applied science research vol. 9, no. 5, 2019, 4695-4701 4699 www.etasr.com ben nasrallah et al.: temperature effect on al/p-cuins2/sno2(f) schottky diodes deposition system and spray pyrolysis were measured in the 200k-340k temperature range. it was noted that the ideality factors increase whereas barrier heights decrease when temperature decreases. these results have been attributed to the fluctuations in the barrier height due to the metalsemiconductor interface morphological and structural inhomogeneities. barrier height inhomogeneities can be related to the composition of the interface such as secondary phase, surface roughness, defects, presence of insulating layer (a�2o3) and non-stoichiometry, etc. the ideality factors and the barrier heights were obtained from the j-v-t characteristics of the schottky diodes. it has been shown that the ideality factors and therefore, the barrier heights varied from diode to diode even though they were identically made-up. the homogeneous barrier height values were obtained for the metals cis schottky contacts from the linear relationship between the j-v-t apparent barrier heights and ideality factors, which can be explained by the presence of many kinds of inhomogeneities as described above. the experimental data and the theoretical predictions for a�/p-cuins2/sno2:f schottky diodes are in good agreement for the temperature range of 200k-340k. the p-cis schottky contacts exhibited a significant dependence on temperature. the current transport mechanism is predominately thermionic emission at high temperatures (280-340k) whereas, the schottky contacts exhibited the dominance of the recombination and/or tunneling current at low temperatures. from the j-v-t measurements, the ideality factors were seen to increase and barrier heights to decrease with decrease in temperature. this has been related to the presence of low sbh areas at the metal-cis interface, overriding to the flow of excess current at low voltages and temperatures. from the modified richardson plot, the modified richardson constant for cis is -∗∗ = 120 ak�� cm�� with a mean barrier height of 1.29ev. -∗∗ has shown a strong dependence on the metal– semiconductor contact quality, saturation current, and probably temperature as shown in [62, 68, 70]. in determining -∗∗ 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and electromagnetic-plugging. the plugging process is implemented by disconnecting one of the stator phases and connecting it with an electromagnetic brake while interchanging the other two phases. the dynamic process is executed by inserting high resistance in the rotor circuit of the motor. the performance of the torque-speed characteristics of the induction motor will be studied and analyzed through the dynamic process. mathematical models have been developed and simulated. results show that the braking process time is greatly reduced. keywords-electromagnetic brake; plugging-dynamic brake; starting; torque-speed characteristics i. introduction induction motors (ims) are commonly used in a wide variety of industrial applications, because of their high robustness, reliability, easy maintenance, low cost, high efficiency and good self-starting [1-12]. the most important control parameters in a motor drive system are starting, speed control and braking processes. therefore, there is a need to deploy a fast braking system that brings the drive to a standstill after the completion of an operation. electrical braking for the three-phase im can be carried out by various methods. these include: regenerative braking, plugging braking, dynamic braking, dc dynamic braking, zero sequence braking etc. [6-8, 9-11]. the braking system technique of an electric motor is basically the removal of the stored kinetic energy from the mechanical part of the system via the speed reduction of the rotating system and the transforming of the stored kinetic energy into another energy which dissipates through heat due to joule effect losses in the rotor bars. this paper presents a new braking method for ims that integrates two conventional braking methods [6-13] mixing the plugging braking system with the electromagnetic braking system, or with the dynamic braking system. these methods are effective and efficient and employed in many industrial applications. the plugging braking system is achieved by the disconnection of one of the three phases which feed the motor and then connecting it to an electromagnetic braking coil, while, at the same time, the other two supply lines are interchanged. the switching processes are done in proper sequence and the time delays between the successive stages of switching are precise. for proper switching and proper time delay a microcontroller may be used. the plugging process leads to the development of a negative slip that is larger than one and acting on the opposite direction of the torque with respect to the motor rotation [1011]. this new method is effective in a variety of industrial applications for immediate motor stopping. braking can be achieved by the use of the dynamic braking method by inserting a high resistance in the rotor circuit of the motor, with the plugging braking. the braking methods, namely: electromagnetic-plugging or plugging-dynamic of the 3-phase induction motor have been implemented analytically in a systematic manner. the aim of this contribution is to study and examine new methods of braking for this type of motor drive. ii. analysis of the rotating magnetic field in this paper we will study the effect of the magnetic field on the behavior of the motor during braking process, especially when separating one phase from the power supply. assume the stator of an im is supplied by equal magnitude three phase currents with phase difference of 120 o between them: ���� = �� � �� � ���� = �� � �� − 120������ = �� � �� − 240�� � a (1) where ���� ,���� , ���� are the instantaneous stator currents. these currents produce a constant magnitude rotating magnetic field (rmf), which will produce a rotating circular motion that rotates at an angular velocity ω [2, 4, 5]. the magnitude of the generated magnetic field (bnet(t)), at any instant of time (t) is: ������� = 0.5� !�� [� �� �ẋ#$��� �ŷ]= = 0.5� !�� % ̶ '( + � *, ,-�. (2) where nph=2, 3, 4, 5 …, the number of phases. engineering, technology & applied science research vol. 8, no. 6, 2018, 3585-3591 3586 www.etasr.com al-barbarawi: improving performance of the braking process, and analysis torque-speed … this equation is the final expression for the total magnetic flux density (bnet) produced in the stator. the magnetic field will have a magnitude equal to 0.5nph.bm. the result of these waves is a sinusoidal wave distributed in the gap of the motor that continues to rotate in a circular motion at an angular velocity (ω) in clockwise or in counterclockwise direction depending on the phase sequence, and it starts rotating at angle ∠±900 as shown in figure 1. if one of the three phases in the stator of an induction motor is disconnected, the other two phases’ currents will produce a magnetic field with variable magnitude. supposing that a phase of a (0aa′) current from (1) has been disconnected, the other two phases’ currents will produce the following magnetic flux density : ������� = ������� + ������� = 0.5�� � �� � ) 1.5�� #$��� � ∟ ̶ 2 23 , �4 5(3 �3� where ���� , ���� , ���� are the instantaneous values of the magnetic field intensities for the different phases. this equation determines the total magnetic flux density presented in the stator, with total value distributed in a sinusoidal wave in the gap. this field begins to rotate in an elliptical form by an angle of -90 0 . the outcome of the field is distributed as a sinusoidal wave in the gap of the motor. the field lines are concentrated in a long axis of the phase aa′ on the vertices of the elliptic, and we can notice that the field value changes from 0.5bm in the middle of the elliptic up to 1.5bm on the vertices of the elliptic as shown in figure 2. figure 3 shows the results of the simulation aiming to illustrate torque-speed characteristics of a 3-phase im. in both, motoring and braking regions when one of the three phases in the im stator is separated from the power supply and a variable external resistance is inserted to the rotor circuit then decrease in motor speed and torque occurs. fig. 1. the sine, cosine and net waves of the magnetic density iii. breaking systems from the above analysis of the rotating magnetic field, it can be noticed that if any phase is disconnected, the total magnetic flux density presented in the stator, will consist of two parts that are changing in sine and cosine waves as shown in figure 2. the total value of the flux is distributed in a sinusoidal wave, and it rotates clockwise or counterclockwise in an elliptical form. the total value of the flux density in these cases will vary from 0.5bm at middle zone of the ellipse up to 1.5bm as shown in figure 2. the field lines are concentrated on the vertices zone of the ellipse and are weakened in the middle zone of the same ellipse [2-4]. this causes a high magnetic attraction on the vertices (between the stator and rotor), which consequently decreases the speed of the motor. integrating the two conventional braking systems [5], the electromagnetic braking and plugging braking, is an effective and efficient way to turn off the induction motor causing it to stop. during the braking process of the electromagnetic brake shown in figure 4, a knife switch as shown in figure 5 separates one phase from the motor supply and directly connects to the coil of the electromagnetic brake [6-7]. fig. 2. the net sinusoidal wave field, and space vector of the rotating field when phase current 0aa fails fig. 3. torque-speed characteristic for a phase failure, in both motoring and braking fig. 4. electromagnetic brake while the other two phases have been interchanged using the plugging process, this will energize the coil of the electromagnetic brake which will cause brake shoes to press on the brake drum that is installed on the motor shaft as shown in figure 5. the attraction force (fatt) between the cores (shoes) of the electromagnetic brake coil can be defined by (4): 78�� = 9: .�( � 9( (4) where k1 depends on the number of turns of the brake coils, the air gap length, the effective area and the reluctance of the engineering, technology & applied science research vol. 8, no. 6, 2018, 3585-3591 3587 www.etasr.com al-barbarawi: improving performance of the braking process, and analysis torque-speed … armature. k2 is the restraining force usually produced by a spring, while i is the rms current of the armature coil. fig. 5. torque-speed characteristic for a phase failure, in both motoring, braking and generating once one phase of the motor is disconnected from the motor supply, and connected to the electromagnetic brake coils, a strong magnetic attraction will be created between the coil cores (brake shoes). at the same time the plugging brake of the motor will be used by changing the direction of the rmf to oppose the direction of the former magnetic field by interchanging the connections of the other two phase currents of stator with respect to the supply terminals [9]. this leads to a decrease of the maximum torque, by 33.3% of its original value, as shown in figure 3 and as a result, the motor decelerates to zero before reversing. the resulting slip during plugging is (2-s), and the original slip of the running motor is (s). then (s) can be given in the following equation: ; = <=> <=?=> (5) where ns is the synchronous speed and nm the mechanical speed. as a result the two supply lines are interchanged, the motor speed will decelerate to zero before starting to rotate in the opposite direction, and the braking torque is not zero at zero speed [8, 9]. a speed sensor can be used to provide a signal to circuit breaker to disconnect the two phases from the power supply when the speed reaches zero. as a result of activating the electromagnetic brake, the motor will stop automatically and immediately in a very short time. braking process will work automatically with the appropriate arrangement of the switching circuit and a giving appropriate delay time [5]. for the proper switching procedure and proper time delay, a microcontroller can be used so that switching and time delay are easy and reliable. the combined braking system can stop the motor in less than 1s, safely, without any over voltage, over current or overheating in the motor windings. the illustration of the natural torque-speed characteristic for 3-phase, and 2phase (when one phase is separated from the motor feed), in three regions, motoring, generating and braking is shown in figure 5. the opposite direction of the torque characteristic and plugging curve are shown in figure 7, while figure 6 illustrates the control circuit. iv. simulink implementation of the induction motor a simple block diagram is simulated to show how to drive an im and how to use plugging and dynamic braking [10, 11]. the simulation is used to study the effects of variation of the im’s parameters and to determine the behavior of any im at plugging process. the simulation model is built up systematically by selecting a 3-phase 5hp im (table i). fig. 6. control circuit of the electromagnetic-plugging brake (a) (b) fig. 7. (a) natural torque-speed and (b) opposite direction torque-speed characteristics and plugging process the mathematical model used to calculate and simulate these models has been implemented with the use of matlab/simulink. the construction of the basic block diagram and the mathematical model for the plugging and dynamic braking process are based on the ratio between the conventional electromagnetic torque equation (tem) and the maximum electromagnetic torque equation (tmax). equation (9) is the critical slip equation [5]. the effect of various parameters such as the variation of the rotor resistance and the variable voltage were also used. @�� = a bcde . f�g.�hgij� �klm∗op [�gqh�g.�hgij� � /klm�.h�s>t �.u (6) engineering, technology & applied science research vol. 8, no. 6, 2018, 3585-3591 3588 www.etasr.com al-barbarawi: improving performance of the braking process, and analysis torque-speed … @�8v = a bcde .(op [ agqhwgq.hs>t. u (7) x��x?iy = (zlm∗ktklm. hkt. = @∗�[\� (8) ;� = �](� + ]8^� � _]:( + k̀�(⁄ (9) where vph is the voltage, sfl, sc are full load slip and critical slip, bc the angular velocity, r1, ](� are the stator and rotor resistances while k̀� = :̀ + (̀� are the stator and rotor inductances. ]8^� is the external resistance. table i. 3-phase induction motor parameters p-power (watt) 5×746 voltage (v) 380 frequency (hz) 50 r1-stator resistance (ω) 1115 l1s-stator inductance (h) 0.005974 r2-rotor resistance (ω) 1083 l2r-rotor inductance (h) 0.005974 lm-mutual inductance (h) 0.2037 inertia, friction factor (kg) 0.02-0.005752 pole pairs 2 v. plugging-elecrtomagnetic braking simulation equations (6)-(9) were simulated in matlab/simulink. figure 8 shows the block diagram model used to implement how the three phase im can be driven at normal operation and the simulation of the normal plugging and plugging brake. (a) (b) fig. 8. block diagrams of (a) normal operation and (b) plugging dynamic braking process figures 9-11 show the obtained results of the dynamic behavior of the motor, the oscillating torques as a function of speed, the oscillatory stator currents as a function of time during startup at normal operation and normal plugging with load, without brakes, without phase failure, and its effect upon the speed as a function of time and voltage. (a) (b) (c) fig. 9. simulation results during normal operation, and its effect upon current, torque and speed. (a) (b) fig. 10. simulation results during normal plugging operation, and its effects upon current and torque figures 12 and 13 show the results of the stopping process of the motor by using plugging brake, in matlab/simulink. the source will be disconnected when the speed reaches zero to satisfy the plugging braking. it is needed to set the breaker parameters on the stator side, to activate the braking when the speed reaches zero by using a speed sensor to provide a signal to the breaker to automatically and immediately stop it. vi. dynamic-plugging braking the moment that one of the three phases is separated, the plugging brake and dynamic brake of the motor are used engineering, technology & applied science research vol. 8, no. 6, 2018, 3585-3591 3589 www.etasr.com al-barbarawi: improving performance of the braking process, and analysis torque-speed … instantly while the separate phase is connected to the contactor coil in the control circuit in order to insert high resistance with the rotor circuit as shown in figure 1. (a) (b) fig. 11. the simulation results during the plugging operation, and its effects upon speed and voltage (a) (b) (c) fig. 12. simulation results during plugging brake, and its effects upon current, torque and speed dynamic braking which has been integrated with the plugging brakes is a process in which the kinetic energy of the rotor is dissipated in the internal and external resistor as heat energy after the main supply separation [9-13]. dynamic braking process is implemented when the motor operates at the other two phases, which makes the motor act as a single phase motor supplied in the opposite direction as a result of the plugging process, which leads to reduction of the braking torque. in this case, the motor operation as shown in figure 6. the resistance inserted in the rotor circuit to decelerate the motor speed can be obtained by (10): ]�d8e� = _]:( + � :̀ − (̀��( − ](� (10) figure 14 illustrates the control circuit diagram of the plugging and dynamic braking process. (a) (b) fig. 13. simulation results during plugging brake, and its effects upon voltage and torque when one phase fails fig. 14. control circuit of the dynamic-plugging braking with external resistances as a result of the single phase separation from the motor feed, this leads to maximum torque reduction. when the plugging brake is used, the magnetic field from the other two phases’ currents rotates in an elliptical form on the opposite direction. as a result of the plugging and the dynamic process, inserting a high external resistance in the rotor circuit makes the critical slip increase to one. at this case the speed of the motor decreases to reach zero, while the torque is not zero at zero speed. near zero speed, we can use a speed sensor to provide a signal to the breaker to automatically operate with the appropriate arrangement of the switching circuit and a giving appropriate delay time by using the microcontroller switch. the engineering, technology & applied science research vol. 8, no. 6, 2018, 3585-3591 3590 www.etasr.com al-barbarawi: improving performance of the braking process, and analysis torque-speed … combined braking system can stop the motor very quickly (in less than 1s) and safely. vii. simulation of the dynamic braking a matlab/simulik implementation approach similar to the model discussed above has been used to model the dynamicplugging braking for the induction motor by using (6)-(9). figure 15 shows the block diagram model used to implement and simulate the motor drive and the dynamic-plugging brake using matlab/simulink for a three phase im, to illustrate the performance dynamicplugging brake on the braking process of the motor at load, when inserting an external resistance in the rotor circuit, with and without disconnection of any phase from the motor feed. (a) (b) fig. 15. block diagrams of the im model as highlighted above, when one of the three phases is disconnected from the motor feed and simultaneously a resistance is added to the rotor circuit, as a result the motor speed decelerates to zero. at this instant, a speed sensor is activated and provides a signal to breaker to stop the motor automatically and to disconnect all current phases. figure 16 shows the matlab/simulink simulation results regarding oscillatory currents during start-up at normal operation, at load and at dynamic-plugging brake with and without added resistance. figure 17 shows the matlab/simulink simulation results regarding the effects of the dynamic-plugging brake on the braking process of the motor during start-up at normal operation at load and at dynamic plugging braking process, when inserting external resistance in the rotor circuit, with and without disconnection of a phase. another advantage of the added external resistances is that it decreases the high oscillatory currents in starting and braking process. the mathematical model used is described by (6) and (7) or (8) and (9). figure 18 shows the effect of inserting variable external resistance in the rotor circuit, on the torquespeed characteristics, in motoring and braking regions. (a) (b) fig. 16. simulation results of the oscillatory currents with and without added external resistance (a) (b) fig. 17. simulation results of the oscillatory currents with and without added external resistance viii. conclusions experimental and analytic results show that a most reliable induction motor fast braking system can be designed through the integration of two or more different traditional braking methods with utilization of all their properties. we can use a microcontroller switch to provide suitable arrangements of the switching circuit and to give appropriate time delay between stages, which makes the braking system stop safely and quickly. this paper shows the experimental and analytic results done by the integration of two pairs of conventional braking techniques, plugging brake with electromagnetic brake, and engineering, technology & applied science research vol. 8, no. 6, 2018, 3585-3591 3591 www.etasr.com al-barbarawi: improving performance of the braking process, and analysis torque-speed … plugging brake with dynamic brake. plugging-electromagnetic brake can be done by disconnecting any phase from the power supply, and connecting it with an electromagnetic brake which will press on the brake disk of the motor. (a) (b) fig. 18. programming results illustrating the effect of the added external resistance on the torque-speed characteristics, in both regions at the same time the connections of the other two phase currents of the stator will interchange with respect to supply terminals (plugging brake). the plugging braking will develop braking torque in the opposite direction of the rotating motor, which leads to deceleration to zero, while the braking torque is not zero at zero speed. the speed sensor provides a signal to circuit breaker to disconnect the two phases from the power supply, to make the motor stop automatically and in very short time. after that all the phases will disconnect from the voltage source before the motor starts to rotate in the reverse direction. this braking method provides simple and fast braking action but with high braking current and losses during the plugging process. dynamic-plugging braking is done by disconnecting one phase from the power supply, and connecting it with a control circuit that energizes the contactor coil which inserts an external resistance in the rotor circuit. this procedure leads to increase the braking torque to maximum and the critical slip to reach one, which leads to motor speed deceleration to zero. the plugging brake procedure is done as above. as a result of inserting a resistance in the rotor circuit, the plugging process becomes very slow, which activates the speed sensor to provide a signal to circuit breaker to disconnect the two phases from the power supply in order to stop the motor automatically and immediately. then, all the phases which feed the motor are disconnected. the presented braking methods are improving the power factor by reducing braking current and losses. these methods are quicker, more effective and efficient than the conventional ones. in the same reasoning, we also can implement a braking system by integrating three conventional braking systems, plugging braking, dynamic braking and electromagnetic braking, which also is effective and efficient. references [1] m. s. alshamasin, “control of zero sequence braking for a three-phase induction motor operating from single-phase supply with a controlled capacitor”, journal of applied sciences, vol. 12, no. 24, pp. 26162620, 2012 [2] o. m. al-barbarawi, “enhancing the braking process, starting and electromagnetic torques of the induction motor”, international journal on engineering applications, vol. 5,no. 4, pp. 108-114, 2017 [3] o. m. al-barbarawi, “analysis of the rotating magnetic field of an ac machines in the transient cases”, magnt research, vol. 4, no. 2, pp. 91-98, 2017 [4] s. j. chapman electric machinery fundamentals, mcgraw-hill inc, avenue of the americas, new york, 2005 [5] j. hindmarsh, a. renfrew, electrical machines and drive systems, alasdair renfrew, 1997 [6] p. l. rongmei, s. l. shimi, s. chatterji, v. k. sharma, “a novel fast braking system for induction motor”, international journal of engineering and innovative technology, vol. 1, no. 6, pp. 65-69, 2012 [7] d. sarkar, p. k. mukherjee, s. k. sen, “temperature rise of an induction motor during plugging”, ieee transactions on energy conversion, vol. 7, no. 1, pp. 116-124, 1992 [8] y. yasa, e. sincar, b. t. ertugrul, e. mese, “design considerations of electromagnetic brakes for servo applications”, 2014 ieee 23rd international symposium on industrial electronics, istanbul, turkey june 1-4, 2014 [9] c. b. rajanathan, z. w. shi, d. s. thompson, “electromechanical transients in a three-phase induction motor during phase failure and plugging”, ieee transactions on magnets, vol. 33, no. 2, pp. 12191222, 1997 [10] h. a. hairik, r. h. thejel, w. a. kadhem, “proposed scheme for plugging three-phase induction motor”, 15th ieee mediterranean electrotechnical conference, valletta, malta, april 26-28, 2010 [11] m. covino, m. l. grassi, e. pagano, “analysis of braking operations in present-day electric drives with asynchronous motors”, ieee international electric machines and drives conference record, milwaukee, usa, may 18-21, 1997 [12] r. singh, s. umashankar, d. vijaykumar, d. p. kothari, “dynamic braking of induction motor analysis of conventional methods and an efficient multistage braking model”, 2013 international conference on energy efficient technologies for sustainability, nagercoil, india, april 10-12, 2013 [13] t. sukmadi, s. c. buana, t. andromeda, m. facta, “a prototype of multistage dynamic braking of three phase squirrel cage induction motor”, 2016 3rd international conference on information technology computer and electrical engineering, semarang, indonesia, october 1920, 2016 microsoft word etasr_7-1_1369-1376.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1369-1376 1369 www.etasr.com pati et al.: design of a 2-dof control and disturbance estimator for a magnetic levitation system design of a 2-dof control and disturbance estimator for a magnetic levitation system avadh pati dept. of electrical engineering m. n. n. i. t. allahabad, india er.avadhmnnit@gmail.com vipin chandra pal dept. of electrical engineering m. n. n. i. t. allahabad, india vipin.vchandra@gmail.com richa negi dept. of electrical engineering m. n. n. i. t. allahabad, india richa@mnnit.ac.in abstract—this work proposes a systematic two-degree freedom control scheme to improve the reference input tracking and load disturbance rejection for an unstable magnetic levitation system. the proposed control strategy is a two-step design process. firstly, a proportional derivative controller is introduced purposely to get the desired set-point response of the magnetic levitation system and then, an integral square error (ise) performance specification is used for designing a set-point tracking controller. secondly, a disturbance estimator is designed using the desired closed loop complimentary sensitivity function for the rejection of load disturbances. this leads to the decoupling of the nominal set-point response from the load disturbance response similar to an open loop control manner. thus, it is convenient to optimize both controllers simultaneously as well as separately. the effectiveness of the proposed control strategy is validated through simulation. keywords—maglev system; pid; maclaurin series; disturbance estimator i. introduction magnetic levitation (maglev) systems have found wide applicability in various fields such as transportation (high speed maglev train), magnetic bearing system (contactless bearing), medical science (artificial heart pump), defense etc [1-8]. magnetic levitation systems are nonlinear and unstable in nature. designing a simple and efficient controller for a maglev system is a challenging task [9-31]. for stable and desired operation, various control strategies are reported in the literature. these controllers are generally applied either on the linearized model of magnetic levitation system or implemented in nonlinear environment [9-11]. in general, the proportional integral derivative (pid) controller is the most common controller used in industrial applications and apart from this an extended version of pids, the fractional order proportional integral derivative (fopid) controller that provides more flexibility in design, has also been reported in [12-13]. the problem of disturbance and parameter uncertainty in conventional pid controllers has been tackled using expert knowledge based fuzzy pid control scheme [14]. the two degree freedom based pid control strategy using pole placement technique is discussed in [15] for the stabilization and improvement of the transient behavior of magnetic levitation systems. apart from this, many nonlinear control algorithms [16-18] are also reported for the said system. a feedback linearization based control technique and differential geometry based control strategy is implemented in [16] and [17] respectively. a nonlinear control algorithm is successfully applied on a maglev train system in [18]. the problem of disturbance and parameter uncertainty associated with maglev system has also been addressed through various nonlinear control schemes as discussed in [19-29]. the classical and sliding mode control (smc) scheme for maglev system is reported in [19-20]. smc based integral variable structure grey control has been implemented on maglev system to avoid the chattering effect associated in the scheme [21]. in [22], an smc based fuzzy controller is described for reducing the effects of parameter uncertainty and disturbance in maglev system and a recurrent elman neural network (renn) estimator based robust dynamic sliding mode control has been used to estimate the nonlinear term [23-24]. the problem of uncertainty for maglev system has been stated in [25] where integral backstepping sliding mode control strategy is used and in [26-27] an adaptive backstepping algorithm has also been reported. the problem of noise associated with sensor output is tackled using robust output feedback technique in [28]. an h-infinity based control scheme is highlighted in [29-30]. an intelligent based adaptive pid fuzzy compensation technique is successfully implemented for the stabilization of a maglev system in [31]. these control methods have the ability to overwhelm the uncertainties and external disturbance in the system and improve the characteristics such as disturbance rejection and robustness to some extent. but all these methods are very complex in structure and tedious in adjusting the controller parameters. to overcome all these problems, an internal model control (imc) scheme is found to be effective especially if system has some disturbance such as internal change in system parameters or external disturbances on system. imc was initially proposed in [32]. the parameters of imc are directly related to system performance and are used for adjusting characteristics like tracking, disturbance rejection and robustness in a completely independent way. recently, a few engineering, technology & applied science research vol. 7, no. 1, 2017, 1369-1376 1370 www.etasr.com pati et al.: design of a 2-dof control and disturbance estimator for a magnetic levitation system publications [33-35] based on the imc scheme have been reported for controlling magnetic levitation system. a feedback linearization based imc technique is discussed in [33] and simulation based results are stated in [34] for controlling the speed of two mass maglev systems. a single degree of freedom imc based pid control technique is applied in [35] for controlling the rotor of wind generator. the structure of imc is very simple and easy to realize for stable systems but with the constraint that this scheme cannot be applied directly on unstable system due to the problem of internal instability [36]. thus, some modification is needed for the control of unstable systems based on the two degrees of freedom imc [37-40]. smith predictor based 2-dof control schemes are designed for unstable process for obtaining set-point response without overshoot [41-42]. but un-modeled dynamics uncertainty still raise problem in all existing 2-dof control schemes and also failed online tuning of controller parameters in presence of process uncertainty. in the proposed work, an analytical two degree of freedom control methodology based on [43-44] of analytical virtue is proposed for tackling the reference input tracking and load disturbance/process uncertainty for maglev systems. the proposed control strategy is a two-step design process. firstly, a proportional derivative controller is introduced purposely to get the desired set-point response of the magnetic levitation system and then, for designing set-point tracking controller, an integral square error (ise) performance specification is used. secondly, a disturbance estimator is designed using the desired closed loop complimentary sensitivity function for the rejection of load disturbances. ii. mathematical modeling of maglev systems the electrical equivalent circuit and schematic block diagram of a magnetic levitation system is shown in figure 1(a) and figure 1(b). this experimental setup is developed by feedback instrument ltd [45].    (s) (s) h i  1 c 2c 0h0i hiiv fig. 1. (a) electrical circuit model of maglev system (b) schematic block diagram of maglev system. table i. parameters of physical maglev system [15, 45] description parameters value unit mass of the steel ball m 0.02 kg acceleration due to gravity g 9.81 m/s2 equilibrium value of current 0i 0.8 a equilibrium value of position h0 0.009 m control voltage to coil current gain c1 0.951.05 a/v ir sensor gain c2 143.48 v/m offset 2.8 v control input voltage level v -5 to 5 v sensor output voltage level hv -3.75 to 1.25 v the major components of maglev system are suspended steel ball, position infra-red (ir) sensors, actuator (including electro magnet and power amplifier). the steel ball is controlled through current i, as seen in figure 1(a). the magnetic force acting on the steel ball depends on two parameters, firstly, the current i flowing in the coil and the second one is the distance h between coil and the steel ball. the non-linear model of magnetic levitation system [15, 45] which relates to the current i flowing in the coil and the position h of the steel ball is expressed as 2 2 ( ) i mh mg c h mg f i,h      (1) where 2 2 ( ) ci f i,h h  , c is a constant value which depends on the parameters of coil, m is mass of the steel ball and g is acceleration due to gravity. the magnetic levitation system expressed by (1) is nonlinear. for easy analysis and design of controller, the system is linearized about the equilibrium point ( 0 0.8 ai  & 0h 0.009 m ). at the equilibrium point, the dynamical equation is taken as 0h  and at this point the simplified expression is obtained as 2 0 2 0 mgh c= i (2) the linearization is carried out with the following assumptions that position of ball is considered as 0h=h + h and current in the coil is taken as 0i=i + i , where h is small deviation in position of ball with equilibrium position and i is the deviation in coil current from equilibrium current 0i . by calculating the partial derivative of (1), the linearized model of maglev system is obtained as 0 , 0 0 , 0 ( , ) ( , ) (3) i h i h f i h f i h h i h i i ¶ ¶ d = d + d ¶ ¶ æ ö÷ç ÷ç ÷ç ÷çè ø  (a) (b) engineering, technology & applied science research vol. 7, no. 1, 2017, 1369-1376 1371 www.etasr.com pati et al.: design of a 2-dof control and disturbance estimator for a magnetic levitation system taking laplace transform on both sides of (3), we get the transfer function as 2 i h ch i s c     (4) where 0 0 2 2g i h g c i c h        (5) in the electrical equivalent circuit of maglev system given in figure 1(b), the current i flows in the coil and is proportional to the control voltage v, expressed as 1 i c v (6) using (4) and (6), the transfer function of maglev system is obtained as 1 2 i h c ch v s c     (7) where v is small incremental control voltage around its mean value. by considering 2c , the gain of ir sensor, (7) is written as 1 2 2 v i h h c c c v s c      (8) using values of table i in (8), the transfer function of the linearized model of magnetic levitation system (plant) can be expressed as p 2 3518.85 ( ) 2180 g s s    (9) further, the generalized form of transfer function of p ( )g s is given by 1 p 1 2 ( ) ( 1)( 1) k g s τ s τ s    (10) where 1 1.6142k   and 1 2 0.0214τ τ  the maglev system (10) has two poles at  46.69 and it could be seen that it is unstable as one of its pole lies in right half of complex s-plane. hence, the main objective is to design a suitable controller that stabilizes this unstable magnetic levitation system. iii. proposed control strategy the proposed 2-dof control strategies consist of three major control components, stabilizing controller gc(s), setpoint tracking controller c(s) and disturbance estimator f for magnetic levitation system as shown in figure 2. in the above suggested control scheme as given in figure 2, the gp is the unstable maglev system and gm is the minimum phase part of gp. the two main controllers are c(s), the set point controller which is responsible for set-point tracking and gc(s), the stabilizing controller which ensures the closed loop stability of magnetic levitation system. the parameters of stabilizing controller and set-point tracking controller and their bounds are calculated using routh’s stability criterion. the disturbance estimator f [44] is designed using the desired closed loop complimentary sensitivity function for rejection of load disturbances. maclaurin series expansion method is used for calculation of pid structure of disturbance estimator f. fig. 2. block diagram of 2-dof control strategy the design steps of all the three controllers gc(s), c(s) and f(s) are described in section iii from a to c. the control efforts of gc(s), c(s) and f are specified as us, ut and f respectively. a. stabilizing controller from figure 2, using stabilizing controller (gc) the minimum phase model (gm) of maglev plant (gp) is augmented as * mm c m ( ) ( ) 1 ( ) ( ) g s g s g s g s   (11) the set-point transfer function of the overall system is obtained as p m c m p ( ) ( ) 1 ( ) ( ) ( ) . 1 ( ) ( ) 1 ( ) ( ) c s g s f s g s h s g s g s f s g s     (12) in special case when, m ( )g s is the perfect model of p ( )g s then the set-point transfer function is written as p c m ( ) ( ) ( ) 1 ( ) ( ) c s g s h s g s g s   (13) from (13), it is clear that, if uncertainty like dead time or any parametric variation is present in the magnetic levitation system, the set point transfer function will definitely achieve smooth set-point response. to avoid stability problem for the unstable magnetic levitation system (10), a proportional engineering, technology & applied science research vol. 7, no. 1, 2017, 1369-1376 1372 www.etasr.com pati et al.: design of a 2-dof control and disturbance estimator for a magnetic levitation system derivative (pd) form of stabilizing controller c ( )g s is proposed and for simplicity it can be chosen as c ( ) c dg s k k s  (14) now, the characteristic equation of set-point transfer function (13) is written as 2 1 2 1 1 2 1( ) 1 0d cτ τ s k k τ τ s k k      (15) with the help of routh’s stability criterion, the tuning parameters of stabilizing controller gc(s) is computed as 1 2 1 1 ( ) / 1 / d c k τ τ k k k       (16) for satisfying (16), when 1 1.6142 k (for maglev system (10)), the bounds on parameters of gc(s) are obtained as 0 0.62      d c k k (17) from (17), an effective gc(s) can be chosen as c ( ) 0.2 4g s s   (18a) as c ( )g s is not physically realizable, therefore a low pass filter is added, given by 1 ( ) ( 1)   j s λs (18b) where  is time constant and could be chosen between  0.01 0.1 dk . the final realizable form of c ( )g s with low pass filter of time constant 0.01  , and is given as c 0.2 4 ( ) (0.01 1) s g s s     (19) b. set-point tracking controller the set-point tracking controller is designed with the help of ise performance minimization. the main objective of proposed set-point of tracking controller c(s) is to improve the system performance satisfying the criteria of norm bound as 2 2 min ( )(1 ( ))w s h s (20) where w is the set-point weight function and could be taken as 1 / s for the strict step change of the set point input and the load disturbance. the set-point tracking controller c(s) is obtained analytically by substituting (10) and (13) into (20) as 2 2 2 1 2 1 2 1 1 2 1 2 min ( )(1 ( )) ( )1 (1 ( ) 1        d c w s h s k c s s τ τ s k k τ τ s k k (21) using orthogonality property of 2h norm, (21) is further simplified as 2 2 22 2 1 2 1 1 2 1 1 2 2 1 2 1 1 2 1 2 min ( )(1 ( )) ( ( ) 1) ( )1 ( ( ) 1)                 d c d c w s h s τ τ s k k τ τ s k k k c s s s s k k τ τ s k k (22) the optimal set-point tracking controller c(s) is obtained by minimizing the right hand side of (22). the simplified expression of c(s) is obtained by considering the second term zero as 2 1 2 1 1 2 1 1 ( ) 1 ( ) d c τ τ s k k τ τ s k k c s k       (23a) again, c(s) given by (23a) is not proper and realizable in practice. therefore, a second order low pass filter is added as c 2 c 1 ( ) ( 1) j s λ s   (23b) where cλ is time constant. the filter (23b) is added with (23a) for practically realizable form. the time constant of second order low pass filter can be chosen between (0.01 0.1) dk . hence, c(s) can be written as 2 1 2 1 1 2 1 2 1 c s ( ) 1 ( ) ( 1) d cτ τ k k τ τ s k kc s k λ s        (24) it can be seen from (19), 0.2 and 4   d ck k using (17), considering the same of values as in (19) and for c 0.01λ , the set-point tracking controller c(s) for system (10) is obtained as -4 2 -4 2 4.579 10 0.322 5.456 ( ) 1.6142 10 0.0323 1.6142 s s c s s s           (25) c. disturbance estimator the disturbance estimator is basically designed for improving the system performance when disturbance is encountered in the system in the form of internal parameter variation or external load disturbances. with the proposed disturbance estimator as shown in figure 2, the load disturbance transfer functions are realized as p p p ( ) 1 ( ) ( ) 1 1 ( ) ( ) i i o o d d i d d 0 y g s h d f s g s y h d f s g s            (26) the complementary sensitivity function of the closed loop between the system input and output for the load disturbance rejection is derived as p p ( ) ( ) 1 ( ) ( ) d i f s g sf t d f s g s    (27) engineering, technology & applied science research vol. 7, no. 1, 2017, 1369-1376 1373 www.etasr.com pati et al.: design of a 2-dof control and disturbance estimator for a magnetic levitation system the desired complementary sensitivity function should be equal to unity in an ideal case. the disturbance estimator f(s) should detect the resultant system output whenever the input disturbance id enters into the system input and then it should obtain an inversely equivalent signal f to counteract it (figure 2). however, the actual asymptotic tracking constraints are as follows lim ( ) 0, 1, 2,..., o k d s p h s k m    (28) 0 lim ( ) 0 ods h s   (29) where kp is the process model right hand side pole (rhp) and m is the number of these rhp poles. to ensure the internal stability of closed loop system for the load disturbance rejection, the constraints (28) and (29) are required to be fulfilled. hence based on the h2 optimal performance objective of the imc theory [36], the practically desired closed loop complementary sensitivity function is formulated as =1 + s +1 ( ) = ( +1) m k k k d m f a t s λ s   (30) where fλ is the adjustable parameter,  is the relative degree of the maglev model, m is the number of rhp poles in the maglev model and ka is calculated by the asymptotic constraints of (28)-(29). hence the desired disturbance estimator can be inversely calculated by (27), as p ( ) 1 ( ) . 1 ( ) ( ) d d t s f s t s g s   (31) for the system (10), closed loop complementary sensitivity function (30) for the load disturbance rejection is written as 1 3 1 ( ) ( 1) d f a s t s λ s    (32) now, substituting (10) and (32) in (31), the desired disturbance estimator is realized as 1 2 1 3 1 1 ( 1)( 1)( 1) ( ) [( 1) ( 1)]f τ s τ s a s f s k λ s a s        (33) where 3 1 1 1 1 1 fλ a τ τ            (34) however it is not difficult to find out that there exist a rhp zero-pole cancelling at 11 /s τ in (32), which tends the desired disturbance estimator to work unstably. the maclaurin series expansion is used to calculate the disturbance estimator of (33). let, f(s)=m(s)/s (35) using the maclaurin series expansion, we get ( ) 21 ( )( ) (0) (0) ... ... 2! ! k km s mf s m m s s s s k            (36) on application of maclaurin series expansion on (33), the first three terms can be used to constitute a standard pid controller structure as pid 1 ( ) s p d i f s k t s t         (37) where (0), 1 / (0), (0) / 2p i dk m t m τ m    remark: it should be noted that the pure derivative term in (37) can be physically realizable by cascading it with a first order low-pass filter whose time constant can be chosen between d(0.01 0.1) t . as for the design aspects of the disturbance estimator for magnetic levitation system (10), disturbance terms such as input disturbance 1 ( )  id h s s is applied at 3 second and output disturbance 0.5 ( ) od h s s  is applied at t 20 second. taking the above disturbances condition ( ) id h s and ( ) od h s on maglev system (10), the disturbance estimator (33) is obtained in pid structure whose parameters are obtained using (36) and (37) as (0) 38.23 (0) 2.47 (0) 0.0307 m m m            (38) for the practical realization of pid controller, a low pass filter whose time constant ft is chosen between  0.010.1 dt . by incorporating the parameters of pid obtained in (38) and low pass filter with time constant 0.005ft  second, the disturbance estimator for maglev system (10) is calculated as 20.0307 2.47 38.23 ( ) (0.005 1) s s f s s s        (39) the final control effort applied to maglev system (10) is sum of responses of all three control efforts us, ut and f obtained for (19), (25) and (39) respectively and is expressed as t su u u f   (40) the detailed discussion of simulation results of proposed control strategy is presented below in section iv. engineering, technology & applied science research vol. 7, no. 1, 2017, 1369-1376 1374 www.etasr.com pati et al.: design of a 2-dof control and disturbance estimator for a magnetic levitation system iv. simulation results and discussion the simulation result is carried out for the unstable magnetic levitation system (10) and various results are plotted to show the effectiveness of proposed control strategy. figure 3 gives the tracking response when system is associated with external disturbance. the external disturbances are given at 3 second and 20 second. 0 5 10 15 20 25 30 -2 -1.5 -1 time (second) d es ir ed & b al l p o si ti o n (v ol t) ball position desired fig. 3. desired & ball position (with proposed) from the simulation results shown in figure 3, it is clear that the proposed control scheme could stabilize the maglev system (10) and track the desired reference trajectory (square wave). it is also seen that when the system is subjected to input and output disturbances at 3 second and 20 second, the designed controller forces the disturbed plant to track the desired reference input trajectory and eliminate the effect of disturbances. the control parameters such as stabilizing controller gc(s), set-point tracking controller c(s) disturbance estimator f(s) and final control effort as us, ut ,f and u respectively are plotted in figure 4. 0 5 10 15 20 25 30 -2 0 2 4 6 8 10 12 14 time (sec) c o n tr o l ef fo rt ( v o lt ) final control effort (u(s)) control effort of disturbance estimator (f(s)) control effort of stablizing controller (gc(s)) control effort of set-point tracking contoller (c(s)) fig. 4. control efforts from figure 4, it is clearly noticed that the designed control scheme has ability to track the desired set-point input reference trajectory and remove the effect of external disturbances. the disturbance estimator works only when the system is subjected to external disturbances, as clearly seen at time 3 second and 20 second. the overall control effort is always maintained in a desirable voltage range ( 5 volt) as necessary for stable operation. to show the effectiveness of the proposed scheme, it has been compared with conventional pid control [45] and their comparative results are plotted in figure 5 for similar condition as considered in figure 3. 0 5 10 15 20 25 30 -2.2 -2 -1.8 -1.6 -1.4 -1.2 -1 -0.8 -0.6 time (sec) d e s ir e d & b a ll p o s it io n ( v o lt ) proposed strategy desired conventional pid fig. 5. desired & ball position (comparative) figure 5 depicts that the designed control strategy has better adaptability to avoid the effect of disturbance compared to conventional pid control. the conventional pid control has spikes and shows poor tracking for the set-point reference trajectory when the system is subjected to external disturbance/parameter uncertainty whereas the proposed two dof control strategy stabilizes the maglev system and tracks the reference trajectory even if the system is subjected to external disturbance and also shows remarkable improvement in system performances (settling time and peak overshoot) over conventional pid control. v. conclusion in this work a systematic dof control scheme is presented to improve the reference input tracking and load disturbance rejection for an unstable magnetic levitation system. here, both set-point tracking response and load disturbance response can be tuned separately using the proposed scheme. the stabilizing and tracking controller are applied in such a way that the unstable magnetic levitation system gets stabilized and at the same time the set-point tracking controller also forces the system to track the desired trajectory. the disturbance estimator is designed using the desired closed loop complimentary sensitivity function for rejection of load disturbances and it is realized in pid form using maclaurin series expansion. the disturbance estimator comes into existence only when the system is subjected to internal/external disturbances. this technique leads to a remarkable improvement of regulatory capacity for reference input tracking as well as load disturbance rejection. the effectiveness of designed control strategy is shown by comparing it with conventional pid controller. engineering, technology & applied science research vol. 7, no. 1, 2017, 1369-1376 1375 www.etasr.com pati et al.: design of a 2-dof control and disturbance estimator for a magnetic levitation system references [1] d. rogg, “general survey of the possible applications and development tendencies of magnetic levitation technology”, ieee transactions on 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1651-1658, 2000 [43] w. d. zhang, d. gu, w. wang, x. xu, “quantitative performance design of a modified smith predictor for unstable processes with time delay”, ind. eng. chem. res., vol. 43, no. 1, pp. 56-62, 2004 [44] t. liu, w. zhang, d. gu, “analytical design of two-degree-offreedom control scheme for open-loop unstable processes with time delay”, journal of process control, vol. 15 no. 5, pp. 559-572, 2005 [45] feedback expermental manual, magnetic levitation control experiments, feedback instruments limited, uk, 2011 microsoft word 36-2673_s_etasr_v9_n3_pp4265-4270 engineering, technology & applied science research vol. 9, no. 3, 2019, 4265-4270 4265 www.etasr.com salih et al.: a study on the effects of cellular mobile networks on people in tikrit city based on power… a study on the effects of cellular mobile networks on people in tikrit city based on power density measurements and calculations al-hakam ayad salih college of arts, tikrit university, tikrit, iraq alhakam.ayad1987@gmail.com amer t. saeed control of petroleum systems dept., college of petroleum & minerals engineering, tikrit university, iraq amer.saeed@tu.edu.iq zaid raad saber control of petroleum systems dept., college of petroleum & minerals engineering, tikrit university, iraq zaid@tu.edu.iq abstract—in this paper, the emitted electromagnetic waves (emw) from different cellular mobile base stations (bss) have been measured and calculated in order to study their effects on public health. moreover, a comparison between the effect of radiated power from the bss on people who live near them and those who live away has been made by using opensignal software and calculated theoretically. the values of power density for different cells were also calculated to compare them with the maximum permissible exposure limit-the acceptable range values of power density. the measurements were done in tikrit city considering ten cells and various locations and distances. the results show that most of the power density and emv for the tested cells are within the acceptable range. however, power density and emv for two of tested cells have hurtful effects in the long term for people who live near the bss. keywords-mobile effect (me); electromagnetic waves (emw); radiation; power density (pd) i. introduction the percentage of people in iraq who use mobile phones has been increasing exponentially, and the communication between people via mobile phones has become a commodity [1]. since mobile devices or networks are considered essential means in the modern way of life, it is important to study the effects of mobile networks on humans. some reports submitted by world health organization (who) reported that the emissions from the cell phones and bss placed on house rooftops and in populated zones are causing some severe health risks [2] and the effects of emw emitted by mobile phones and bss depend on the time of mobile phone use. before studying the effect of transmitted power by telecommunication towers on humans, we should know the range of the used frequencies. in general, 800mhz, 900mhz, 1800mhz, and 2450mhz represent the frequencies of emw used for wireless mobile connections. the range of frequencies for global system for mobile communications (gsm) is between 890 and 960mhz, these frequencies are divided into two groups: the frequencies from 890mhz to 915mhz are used for uplink while the frequencies from 935mhz to 960mhz are used for downlink as shown in table i. there is also an extended gsm (egsm), the range of the uplink frequency for egsm technology is between 880 and 890mhz [2] while the downlink of this technology is between 925 and 935mhz). the bandwidth in gsm is 25mhz. three main wireless mobile telecommunication providers are available in iraq: asiacell, korek, and zain. in this research, we focused only on gsm technology used by asiacell in tikrit (a city in the north of iraq), and the test was done for towers of this company and in this city. the signals of telecommunication towers must spread on to cover the mobile devices. these towers, as a part of a wireless mobile communication network, are required to create a connection between phone devices and the network. therefore, the commutation towers are distributed in all areas of tikrit city to ensure providing services for all users as shown in figure 1. table i. frequency spectrum for telecommunication companies in iraq. system frequency bandwidth channel number uplink downlink egsm 880-890 925-935 10 mhz 50 gsm 890-915 935-960 25 mhz 125 gsm 1800 1710-1785 1805-1880 75 mhz 375 gsm 1900 1850-1910 1930-1990 60 mhz 300 korek 880.2-891.8 925.2-936.8 11.6 mhz 58 zen 891.8-903.4 936.8-948.4 11.6 mhz 58 asiacell 903.4 -915 948.4-960 11.6 mhz 58 fig. 1. asiacell’s communication towers in tikrit by open signal program corresponding author: amer t. saeed engineering, technology & applied science research vol. 9, no. 3, 2019, 4265-4270 4266 www.etasr.com salih et al.: a study on the effects of cellular mobile networks on people in tikrit city based on power… the increase in the number of towers (base stations, node b) leads to an increase in the population who are exposed to the emw that are radiated from these towers. the emw radiation is defined as a stream of photons in a given space, each photon having a quantity of energy, and this energy creates different types of radiation. these radiations produce the electromagnetic (em) spectrum. em radiation is divided into two types: • ionizing radiation: the wave is a container of high energy that is stronger than the energy of the bonding of the electrons within atoms/molecules and the formation of ions, such as cosmic rays and gamma. • non-ionizing radiation: these radiations do not have enough energy to form ions from atoms or particles of matter, such as radio waves and infrared radiation [3]. the density of em radiation effect depends on 5 factors: • the frequency/wavelength of radio frequency (rf) transferred signal. • rf power radiated from the tower. • time of intake of rf signal at a given space from the tower. time/ frequency of recurring exposure. • temperature degree, and level of wetness. radiation ratio changes from one place to another. it depends on the person's distance from the bs, the rate of mobile daily use, and the power of the received signal. tissues in the body are exposed to the emw radiation emitted from mobile phones or communications towers, especially if these frequencies are high. the intensity of this effect depends on the location of the person, and the characteristics of the cell’s physiology [4]. in order to study the impacts of rf radiation on humans, it is essential to define the specific absorption rate (sar). sar is the quantity of rf energy absorbed per mass and time. many governments and international agencies have been standardized the accepted range values of sar, so if the value goes beyond this range, it will be considered unhealthy. sar � �|� | (1) equation (1) is the main equation of sar. |� 2 | is the root mean square of the intensity of the electrical field, σ is conductivity, and ρ is the mass density of tissue. power density (pd), magnetic field strength b, and electric field strength e are the main factors of the em field. in this paper, pds for different bs cells have been studied and measured. then a comparison between those values with the maximum permissible exposure limit was conducted and discussed. ii. literature review emf radiation on the human body causes biological changes and health effects. the biological changes are divided into two types: thermic effects and non-thermic effects. thermic effects are caused by the absorption of emw transmitted from towers while non-thermic effects are those that occur within the cells of the body and are possibly harmful. health effects are any changes that take place in the cells of the body. whether in a long time or for a short time, every person reacts in a different way in different levels of em radiation. there are short-term and long-term effects from phone radiation. the earliest effects are snooze diseases, headaches, gloominess, etc., while long-time effects can be brain tumours, cancer, dna corruption, memory weakness, etc. (figure 2) [7]. cancer is one of the most common diseases in the world, with no specific treatment, so, often studies avoid dealing with it. in [3], the researchers found that the diagnosed cancer rate for persons who live in range of 500m from a mobile bs is three times higher than of the persons that live outside this range. breast, prostate, liver, stomach, and blood cancer also increase near bss [8]. since the radiation effects on the body are cumulative, a handheld broadband radiation monitor (frequency range of 800mhz-2500mhz) has been established to measure total received power. radiation measurements were carried out in a lady’s apartment, who had developed cancer within one year of the installation of a cell tower. the layout of the apartment and the measured readings are shown in figure 3. it may be noted that the emission level is very high and it is between -4 to -10dbm at 900mhz, when -10dbm received power is equivalent to 7,068µw/m 2 , which is higher than the accepted value in india, which is 4.7w/m 2 =4,700,000µw/m 2 [9]. hormones are affected by em emissions [10]. people from both genders were exposed to larger levels of em emissions for an evening in the lab. serum estrogen levels in women were grown. on the other hand, testosterone serum in men decreased. the increase in the levels of estrogen augmented the risk of cancer and the decreased level of testosterone has been correlated to the growth of prostate and testicular diseases [11]. fig. 2. emf radiation effects fig. 3. measured power at a cancer patient’s residence. as a direct response to public concern, some significant studies with multiple contributors and diverse expertise have been published recently on the health effects of low frequency em fields. the mobile phone frequencies have effects such as psychiatric, muscle weakness diseases, and others. in [12] engineering, technology & applied science research vol. 9, no. 3, 2019, 4265-4270 4267 www.etasr.com salih et al.: a study on the effects of cellular mobile networks on people in tikrit city based on power… some steps to avoid the effects of cell phone exposure are proposed: • using pstn phone when it is available. • reducing call times as much as possible. • stay away from a call in case of bad coverage. • switching off mobile when sleeping. • holding a cell phone away from the heart and head during charging. the authors in[12] found that low-level emf motivates the calcium to release ions from the cell wall. infiltrate of calcium ions in the cytosol seems as a metabolic stimulant. this effects growth and healing, but also it supports the emergence of tumors. loss of calcium ions makes leaks in the wall of lysosomes releasing dna thus generating dna corruption. another probability of dna corruption can be in growing free radical formation inside the cells, which further causes cellular damage in the mitochondria [13]. em radiation increases heartbeat rate, changes body temperature, rises blood pressure, and causes breathing difficulties. in [14], a study was done on 20 people (10 men and 10 women), aged between 20 and 60 years. when the mobile was working in calling mode, rapid and arrhythmic heartbeat rate and changing in breathing time was recorded in 5% of the men in a group of 20–40 years after 30 minutes of exposure, during which the handset was installed in the ear end to the brain. in [15], a study on the effects of em radiation on sperm movement in men was presented. the study was based on a test of 27 men. some of them were exposed to em radiation. samples were taken and then were classified into two groups. the first group was taken from people who were exposed to emr (900mhz) while the second group included samples of non-exposed people. the results showed that emr released by the antenna had effects on the sperm movement. in addition it lead to behavioral or architectural changes of the germ cell [16]. international commission on non-ionizing radiation protection (icnirp), world health organization (who), and other public interest organizations have not mentioned harmless radiation procedures [17]. there are many countries that accept radiation standards and guidelines, and define a limitation to the power released from towers and the time of healthy mobile use. on the other hand, the radiation limit is not strictly fixed, many countries are adopting their own radiation limits. federal communications commission (fcc) and many other international communication organizations such as ieee have published guidelines of acceptable power density range in a frequency range of 300mhz-1500mhz. based on the maximum permissible exposure limit, the value of safe health pd is 0.6w/m 2 for general (900mhz) while 0.1w/m 2 for frequencies more than 1500mhz (same as fcc guideline). however, some countries like australia are very much stricter in terms of maximum radiation density values with a limit of 0.000005w/m 2 [5, 6]. iii. power measurements and calculations the procedure was divided in two stages: the first stage was measuring the received power and finding the frequencies of asiacell company by using specific software, and the second was conducting mathematical calculations. a. software results two mobile software applications were used: cellmapper 5.1.7 and opensignal 5.37. the first was used to acquire the frequencies of the tested cell id and the received power, while the other one was used to show the bs towers’ location (figure 4). received power, frequencies, and the running protocol for tested cell ids were measured. in order to cover different environments, several cells with different protocols (gsm, umts, dcs 1800, etc.), frequencies, and distances were tested. the tested cell ids were 50828, 52295, and 51515 at a distance of 100m, 51515 at 1000m, 50826, 52297, and 51511 at 200m, and 51511 at 800m (figures 5-7). the summary of the test results is presented in table ii. fig. 4. locations and id of the tested cells by opensignal fig. 5. results of 5082 and 51511 cell ids fig. 6. results of 52295 and 51511 cells engineering, technology & applied science research vol. 9, no. 3, 2019, 4265-4270 4268 www.etasr.com salih et al.: a study on the effects of cellular mobile networks on people in tikrit city based on power… fig. 7. results of cell id 51515 table ii. test results summary cell id technique frequency (mhz) distance power (dbm) 50828 umts 2137.4 100 -59 52295 umts 2132.4 50 -55 51515 dcs 1800 1856.6 100 -55 51515 dcs 1800 1856.6 1000 -75 50826 dcs 1800 1853.8 100 -55 52297 dcs 1800 1853.4 50 -53 51511 umts 957.6 200 -53 51511 umts 957.6 800 -83 b. mathematical calculations in order to calculate the received signal (pr) transmitted from a specific antenna bs, we will depend on (2): � � � ∗ �� ∗ �� ∗ � ����� (2) where pt is the transmitted power, pr the received power, d represents the distance between the transmit power source and the receiver, �� is the transmit antenna gain, and �� the received antenna gain. equation (2) is usually written in dbm instead of watts in the below form: � � � � �� � �� � 20���� ! ��"�# the theoretical calculation is done based on (2) and (4), then a comparison of those values with the practical power values (measured power) is made. $ � %&∗�"'(∗�) (3) where pd is power density, gm the mobile gain, λ the wavelength which is equal to *+, c the speed of light=3×108m/s, and f is the frequency. therefore, (3) becomes: power density � %&∗��∗+)'(∗*) (4) for all cells, the below values are used to find the power: gt=0, gr=0, pt=30dbm for umts and 33 dbm for dcs 1800. 1) cell id 50828 at 100m distance, frequency of 2137.4mhz, umts. � � 30 $89, � � � � �� � �� � 20���� ! ��"�), : � *+ � � 30 � 0 � 0 � 20���� ! ;∗ <=>)<;?.a∗ <=b�"∗� ) = -49.05dbm =12.45×10 -9 w �cd� edfgh�i � � .�j∗� kl∗�"∗mnopq.r ∗� bs)�∗!t∗� >#) ��ju.tv ! �juw�vw.vu#∗� x∗� <b =0.793mw/m2 2) cell id 52295 at a distance of 50m, frequency=2132.4mhz, umts � � 30 $89, � � 30 � 0 � 0 � 20���� ! ;∗ <=>)<;).a∗ <=b�"∗j ) =-43dbm=50.119×10 -9 w $ � j .��x∗� kl∗�"∗m �t .�∗� bs)�∗!t∗� >#) � j .��x∗� kl∗�"∗�j�v� x.vu∗� <)x∗� <b �31.8µw/m2. 3) cell id 51515 frequency=1856.6mhz, dcs 1800, pt=33dbm • at 100m � � 33 � 0 � 0 � 20log� ! ;∗ <=><>[b.b∗ <=b��∗� )=-44.82 =32.961×10 -9 w $ � t .xu�∗� kl∗�"∗mo\]^.^ ∗� bs)�∗!t∗� >#) � t .xu�∗� kl∗��∗t��uxut.ju∗ � <)x∗� <b =15.853µw/m2 • at 1000 m � � 33 � 0 � 0 � 20���� ! ;∗ <=><>[b.b∗ <=b�"∗� )=-64.82dbm $=329.610x10-12w t x.u� ∗� k<)∗�"∗t��uxut.ju∗ � <)x∗� <b � 0.158 µw/m2 4) cell id 50826 at 100m, f=1853.8mhz, dcs1800, pt=33dbm � � 33 � 0 � 0 � 20���� b 3 ∗ 10 w1853.8 ∗ 10u4d ∗ 100 e � 44.81=33.037×10 -9 w $ � tt. tv∗� kl∗�"∗t�tujv�.��∗� <)x∗� <b � 15.843µw/m2 5) cell id 52297 at 50m, f=1853.4mhz, dcs1800, pt=33dbm � � 33 � 0 � 0 � 20���� ! ;∗ <=><>[;.a∗ <=b�"∗j ) = -38.79dbm =132.130×10 -9 w engineering, technology & applied science research vol. 9, no. 3, 2019, 4265-4270 4269 www.etasr.com salih et al.: a study on the effects of cellular mobile networks on people in tikrit city based on power… $ � �t .�t ∗� kl∗�"∗t�tujv�.��∗� <)x∗� <b �63.368µw/m2 6) cell id 51511 frequency=957.6mhz, umts, pt=30dbm. • at a distance of 200m � � 30 � 0 � 0 � 20���� f ;∗ <=>l[?.b∗ <=b�"∗ g=-45.09 =30.974×10 -9 w $ � t .xv�∗� kl∗�"∗x�uxxv.vu∗� <)x∗� <b � 3.963µw/m2 • at a distance of 800m � � 30 � 0 � 0 � 20���� ! ;∗ <=>l[?.b∗ <=b�"∗w )= -57.31=1.858×10 -9 w $ � �.wjw∗� kl∗�"∗x�uxxv.vu∗� <)x∗� <b � 0.2377µw/m2 iv. results and discussion figure 8 shows the comparison between the measured and the theoretical received power values. it is obvious that there is a difference between the measured and the theoretical values. for instance, the calculated power for cell id (50828) was -49.05dbm while the measured power for the same cell id was -59dbm. fig. 8. measured and theoretical power for tested cell it can be noticed from the chart that 10dbm is the average difference between the calculated and the measured power for almost all cell ids. this difference could have occurred due to neglecting the loss values in connectors and feeders when we calculated the power theoretically. table iii presents detailed information about the parameters of the tested cells and results in values of power. those parameters are cell ids, distance, amount of frequency for each cell, measured received power form each cell, theoretical calculation, and power density. it is clear that the received power depends on the distance from the transmitter, and the frequency. for cell id 51515, there were two values of power measured, the power reduced from -55 to -75 because the first one was measured at a distance of 100m while the second measurement was at a distance of 1000m. however, the values of power also change if the value of frequency is changed even in the same distance as shown in the table for cell id 50826 and 50828. table iii. cell id, power and power density values c e ll i d p r o to c o l f (m h z ) d is ta n c e m e a su r e d p o w e r (d b m ) t h e o r e tic a l p o w e r (d b m ) p o w e r d e n s ity (µ w /m 2) 50828 umts 2137.4 100 -59 -49.05 0.000793 52295 umts 2132.4 50 -55 -43.00 31.8 51515 dcs 1800 1856.6 100 -55 -44.82 15.853 51515 dcs 1800 1856.6 1000 -75 -64.82 0.158 50826 dcs 1800 1853.8 100 -55 -44.81 15.843 52297 dcs 1800 1853.4 50 -53 -38.79 63.368 51511 umts 957.6 200 -53 -45.09 3.963 51511 umts 957.6 800 -83 -57.31 0.2377 the range of power density values for the tested cells is between 0.000793 and 63.368µw/m 2 as shown in table iii. the highest power density value was 63.368µw/m 2 at a distance of 50m for cell id 52297 which used dcs 1800 and f=1853.4mhz while the value of power density for the same cell reduced to 15.843µw/m 2 when the test was done at a distance of 100m. this means that the value of power density reduced by 75% when the distance changed from 50m to 100m whereas the lowest value of power density was 0.000793µw/m 2 at 100m distance for cell id 50828 which used umts protocol and 2137.4mhz frequency. the reason for that was that the telecommunication company uses lower power to transmit the signal in case of umts since it is rather designed to provide data than calls. so, when the transmitted power reduced, the power density decreased. the results also show the range of power density values for the tested cells is within the acceptable limits according to the maximum permissible exposure limit issued by the fcc and the ieee. the values were below 0.6w/m 2 for the general frequency 900mhz and 0.1w/m 2 for frequencies more than 1500mhz. however, some power density values for the tested cells such as 31.8, 15.853, 15.843, and 63.368µw/m 2 for cell ids 52295, 51515, 50826, and 52297 are considered unacceptable and harmful according to government agencies in australia because they are higher than the australian acceptable value of 0.000005w/m 2 [6]. v. conclusion in this research, the received power for eight cells has been theoretically calculated and practically measured. a comparison between the theoretical and the measured received power was conducted. power density values were calculated in order to decide if they are harmful or not based on safe range values issued by fcc, ieee, and australian agencies. the results demonstrate that the distance between the tower (bts/node b) and the receiver, and the used frequency have a major impact on power density. pd was reduced by 75% when the distance between the transmitter and the receiver doubled. the highest pd value was 63.368µw/m 2 at a distance of 50m for dcs 1800 protocol, and frequency of 1853.4mhz while it reduced to 15.843µw/m 2 when the test was done at a distance of 100m. the results show the range of power density values for the tested cells is within acceptable limits according to the guidelines and reports issued by fcc and ieee. however, engineering, technology & applied science research vol. 9, no. 3, 2019, 4265-4270 4270 www.etasr.com salih et al.: a study on the effects of cellular mobile networks on people in tikrit city based on power… some power density values are considered unacceptable and harmful according to the australian government agencies. references [1] l. m. salih, “performance study of the radio frequency radiation power density of mobile base station”, international journal of scientific & engineering research, vol. 8, no. 10, pp. 1729-1732, 2017 [2] k. sukhdeep, k. jaipreet, s. manjit, “effects of mobile radiations and its prevention”, international journal of computer science and mobile computing, vol. 5, no. 2, pp. 298–304, 2016 [3] m. d. bhawan, j. l. n. marg, effects of electromagnetic field radiation from mobile towers and handsets, telecom regulatory authority of india, 2014 [4] b. b. levitt, h. lai, “biological effects from exposure to electromagnetic radiation emitted by cell tower base stations and other antenna arrays”, environmental reviews, vol. 18, pp. 369-395, 2010 [5] d. thapa, b. r. shah, r. b. sahu, p. parajuli, “study of power density transmitted from cellular base station towers of nepal telecom in biratnagar sub-metropolitan city”, international journal of applied science and biotechnology, vol. 4, no. 3, pp. 338-345, 2016 [6] g. kumar, t. banerjee, n. kapoor, n. surolia, a. surolia, “sar and pharmacophore models for the rhodanine inhibitors of plasmodium falciparum enoyl-acyl carrier protein reductase”, international union of biochemistry and molecular biology, vol. 62, no. 3, pp. 204-213, 2010 [7] j. l. phillips, n. p. singh, h. lai, “electromagnetic fields and dna damage”, pathophysiology, vol. 16, no. 2-3, pp. 79-88, 2009 [8] c. graham, m. r. cook, m. m. gerkovich, a. sastre, “examination of the melatonin hypothesis in women exposed at night to emf or bright light”, environmental health perspectives, vol. 109, no. 5, pp. 501-507, 2001 [9] p. g. kumar, report on cell tower radiation submitted to secretary, dot, delhi, iit bombay, 2010 [10] a. tyagi, m. duhan, d. bhatia, “effect of mobile phone radiation on brain activity-gsmvscdma”, international journal of science, technology, and management, vol. 2, no. 2, pp. 1-5, 2011 [11] c. graham, m. r. cook, m. m. gerkovich, a. sastre, “examination of the melatonin hypothesis in women exposed at night to emr or bright light”, environmental health perspectives, vol. 109, no. 5, pp. 501-507, 2001 [12] m. shrestha, cell phone use and the associated health risks among adults, bn thesis, arcada , new delhi, 2018 [13] a. a. khaki, a. khaki, s. s. ahmadi, “the effect of nonionizing electromagnetic field with a frequency of 50 hz in rat ovary: a transmission electron microscopy study”, international journal of reproductive biomedicine, vol. 14, no. 2, pp. 125-132, 2016 [14] m. rajdeep, m. milan, p. koushik, j. subasish, “a study on the effect of mobile phone radiation on human health”, exploratory animal and medical research, vol. 4, no. 2, pp. 246-252, 2014 [15] a. agarwal, n. r. desai, k. makker, a. varghese, r. mouradi, e. sabanegh, r. sharma, “effects of radiofrequency electromagnetic waves (rf-emw) from cellular phones on human ejaculated semen: an in vitro pilot study”, fertility and sterility, vol. 92, no. 4, pp. 1318-1325, 2009 [16] o. erogul, e. oztas, i. yildirim, t. kir, e. aydur, g. komesli, a. f. peker, h. c. irkilata, m. k. irmak, a. f. peker, “effects of electromagnetic radiation from a cellular phone on human sperm motility: an in vitro study”, archives of medical research, vol. 37, no. 7, pp. 840-843, 2006 [17] k. h. ng, “non-ionizing radiations–sources, biological effects, emissions and exposures”, international conference on non-ionizing radiation at uniten, kuala lumpur, malaysia, october 20-22, 2003 microsoft word 33-2694_s1_etasr_v9_n3_pp4249-4254 engineering, technology & applied science research vol. 9, no. 3, 2019, 4249-4254 4249 www.etasr.com alanezi & sellami: an unified framework for measuring e-service quality an unified framework for measuring e-service quality mohammed ateeq alanezi college of computing and it, shaqra university, saudi arabia alanezi.mohd@su.edu.sa ali sellami college of computing and it, shaqra university, saudi arabia sellami2003@hotmail.com abstract—companies continually seek efficiency by utilizing the rapid advances in technology to improve their electronic services (e-services). a perusal of the literature shows varying approaches for measuring e-service quality; these approaches have found little consent among reviewers. therefore, this study attempts to provide a new framework, a roadmap, as a useful model for researchers to measure user perception of e-service quality. for this model, an extensive study is carried and these study findings indicate that system functionality, procedure, content, user support, and manageability should be included in an empirical research model for measuring eservice quality. keywords-electronic service; e-service quality; framework introduction i. indoduction electronic services through the internet have been adopted globally to reduce the cost of operations and improve customer service. however, acceptance of any service is predominantly due to its quality and without comprehensive attention to user acceptability, new services may fail [1]. quality e-services can provide competitive advantages for online companies by improving performance, increasing productivity, and improving client relationships and thus customer satisfaction and trust [2]. a literature review of the extant e-service quality scales results in a variety of measure dimensions. unfortunately, these dimensions are conceptualised differently, and there is little consensus for the basics of e-service acceptance [1, 3], possibly because the literature is currently inadequate in providing a conceptual framework of e-service quality [4-6]. as a result, many e-service quality researches developed models which may have omitted the user’s interaction with the website [4, 7]. the procedures necessary to navigate through a website for an e-service have become more important as a part of a quality approach. this paper assists such an approach by developing a framework that includes key factors for e-service assessment. this framework provides a useful roadmap to measure users’ perceptions of e-service quality. ii. literature review this brief survey of recent research findings on e-service quality is presented in two parts. the first one considers conceptualisation of e-service quality and its components, and the second explores theory in the form of technology acceptance models that are applicable in the field. a. e-service the e-service concept is increasingly used as an important determinant of a successful online environment [4]. before considering e-service quality, a definition of the term e-service is useful to ground the discussion. again, there is little agreement regarding the parameters of e-service, as the field has not yet matured [8]. e-service can be simply defined as providing service to users electronically [9]. more elaborately, e-service is defined as “deeds, efforts or performances whose delivery is mediated by information technology. e-service includes the service element of e-tailing, customer support, and service delivery” [8]. for a company, authors in [10] defined eservice as service that takes place from lunching the main page until the requested service has been completed or received, while in public sector, authors in [9] defined e-service as those public services, including information, interaction, communication and transaction services, that are delivered by electronic media to citizens and people who work with or in the e-government sector. by analysing the e-service literature [8], it is found that researchers conceptualized e-services as selfservice or information services, and that e-services are viewed as information services because information is the key value for the user. authors in [11] distinguished the quality between e-services and self-service. for self-service, a user has to visit a location (e.g. an atm) to receive the required service, whilst eservice is universally available from the internet. however, in [4], the author disagreed with this difference, claiming all eservices are inherently self-services. e-service, as a concept, has many applications and is located in a number of fields, especially in the forms of e-commerce and e-government. despite the varying definitions, the researchers agree on the role of technology in facilitating the provision of services to an end user with the objective of improving performance. b. e-service quality the study of e-service quality is increasingly recognized and management has directed more attention to the issue in the last few years [1, 9]. e-service quality [55] is defined in [12] as the overall consumer evaluations and opinions about the excellence of received e-service in the virtual marketplace. authors in [13] agreed with this definition, stating that it corresponding author: mohammed ateeq alanezi engineering, technology & applied science research vol. 9, no. 3, 2019, 4249-4254 4250 www.etasr.com alanezi & sellami: an unified framework for measuring e-service quality constituted “a customer’s experience with the service provider through a given electronic channel without human intervention”. however, there are no well-accepted conceptual definitions or models for measuring e-service quality [9], although, as noted, e-service quality is a determinant of successful or failure for online organizations [2, 5, 7, 14]. many online initiatives have failed due to insufficient attention to e-service quality [5, 7, 12]. as noted, e-service quality studies have increased, and the majority of the research adopted traditional service quality dimensions [15]. the servqual scale, which was developed for traditional market services, is a popular choice for researchers in the online environment [1, 16]. in [17], it is stated that the servqual dimensions can be used in an online environment through the addition of technical factors. some examples of studies that have adopted and extended the servqual scale are given in [5, 7, 18-20]. electronic service quality studies are found in banking, libraries, travel agencies, business portals and online shopping fields [1]. in online banking, four factors influence e-banking service quality: personal needs, site organisation, userfriendliness and efficiency [21]. authors in [22] suggested four factors relating to online shopping service quality: responsiveness, reliability, process, functionality, enjoyment. timely response, reliability, and courtesy are three factors proposed in [23] to influence the quality of academic library portals, and regarding online travel, authors in [11] posited four factors: presentation, information quality, trust, and responsiveness. in [6], similarly found factors were usability, usefulness of content, adequacy of information, accessibility, and interaction for business portals, while authors in [1] proposed seven dimensions for measuring e-government service quality: website design, reliability, responsiveness, security/privacy, personalisation, information, and ease of use. in the context of online retailers, [24] designated process quality, outcome quality, and recovery quality. process quality was deconstructed to identify aspects of functionality, information accuracy, design, privacy, and ease of use, whereas outcome quality was determined by order accuracy, order condition, and timeliness, and recovery quality by interactive fairness, procedural fairness, and outcome fairness. c. theories of acceptance of new technology researchers use a number of theories to study user acceptance of new technology in information technology and information systems (it/is) research. widely used theories in the it/is area are the theory of reasoned action and the technology acceptance model. the theory of reasoned action is a well-accepted model based on factors of intended behaviour [25]. this theory has a conceptual framework that separates beliefs, attitudes, intention and behaviour [26]. an individual’s behavior in the reasoned action theory is predicted by behavioral intention which is determined by attitudes and subject norms. authors in [25] defined the three components of the theory reasoned action as: • attitudes: “an individual’s positive or negative feeling about performing the target behavior”. • subjective norms: “the person’s perception that most people who are important to him think he should or should not perform the behavior”. • behavioral intention: “the strength of one’s intention to perform the specified behavior”. the assumption that individual behavior is under volitional control is a limitation for the theory of reasoned action, according to [28], as this was not always the case. thus, the theory of reasoned action was extended into the theory of planned behavior by adding one major predictor, perceived behavioral control and customer satisfaction [28, 44]. authors in [29] did not entirely accept the theory of reasoned action and suggested certain exceptions by saying “a behavioral intention measure will predict the performance of any voluntary act, unless intent changes prior to performance or unless the intention measure does not correspond to the behavioral criterion in terms of action, target, context, time-frame and/or specificity [29]. the technology acceptance model, developed in 1989, is the most practicable model for explaining the underlying factors that motivate users to accept and use the new technology in information system research [30]. in a literature analysis in [31], it is claimed that the technology acceptance model is central to it/is. this model was originally derived from the theory of reasoned action [25, 32]. the theory of reasoned action is extended replacing many of its attitude measures with two technology acceptance factors, namely perceived ease of use, and perceived usefulness, as these two factors will influence the user’s decision to use the technology [30]. perceived usefulness is defined in [31] as “the degree to which a person believes that using a particular system would enhance his or her job performance” and perceived ease-of-use is “the degree to which a person believes that using a particular system would be free from effort” [30]. the goal of the developed technology acceptance model was to provide the factors that explained user behavior regarding the use of new technology. the original model, tam1, extended to tam2 to explain usage intention by integrating social and cognitive factors such as experience, image, job relevance and voluntariness [33]. in [34], tam2 was extended to tam3 by adding factors that assist decision makers regarding interventions that can lead to acceptance and use of technology. researchers in different domains have used various forms of the acceptance model to evaluate the user acceptance of new technology, including e-commerce [35], e-learning [36], internet banking [24, 37], and e-government [38]. however, the main limitation of the initial model is that it does not include social factors that influence the acceptance the new technology [39]. author in [40] claimed that the conceptual model lacks sufficient rigour and relevance for it to constitute theory in the information system domain. in addition, the technology acceptance model debate has distracted research attention from other significant issues in the field [41]. d. methodology and analysis the relevant literature was reviewed to identify raised issues regarding the relevant models and theories of previous research [1, 2, 42]. the relevant studies were conducted in various contexts, including e-service, online banking, online travel agency, online public library, online retailing, web portal, and online shopping. table i shows the e-service quality dimensions used in the online environment, the contexts in which they appeared and the frequency of citation. engineering, technology & applied science research vol. 9, no. 3, 2019, 4249-4254 4251 www.etasr.com alanezi & sellami: an unified framework for measuring e-service quality table i. a review of e-service quality dimensions dimension research context references website designs/ web site appears/ aesthetic design e-service [10, 29] online retailing [25, 32] online shopping [9, 52] online banking [4, 7, 11, 24, 27, 33] reliability e-service [3, 18, 27, 52] online retailing [9, 33, 48, 53] online banking [8, 17, 24, 25] academic and public libraries [12, 20, 23] delivery e-service [8, 51] ease of use e-service [3, 10, 27, 52] online retailing [8, 17, 48, 53] online banking [12] efficiency online retailing [7, 17, 18, 32] e-service [12, 19] fulfillment online retailing [7, 17, 18, 51] e-service [19, 32] privacy online retailing [7, 17, 18, 32] e-service [19] responsiveness online retailing [4, 18, 27, 48] online banking [17, 19, 33, 53] e-service [7, 20, 24, 25] online travel [50-52] compensation online retailing [7, 17-19] contact online retailing [18, 19] e-service [7, 17] processing speed online retailing [10, 32] security online retailing [10, 12, 52, 55] e-service [17, 20, 25, 27, 48, 51] communication online retailing [30, 52] e-service [8, 32] online financial services [7, 12, 34, 51] accessibility online retailing [6, 20, 27, 29, 33, 51-53] credibility online retailing [27, 29, 33, 52, 53] understanding online retailing [27, 29] availability online retailing [19, 29, 32, 51] information online banking [7, 27, 50, 53] online retailing [6, 7, 17, 32] online travel [4, 51] web portal [33] courtesy online banking [27, 33] academic & public libraries [23, 52] customer service online shopping [9, 11] e-service [12] performance e-service [25] features e-service [25] service ability e-service [25] system integrity e-service [25, 51] trust e-service [8, 25, 32] online retailing [4, 18, 24, 50] service differentiation e-service [25] customisation e-service [8, 20, 25, 51] online financial services [7, 51] web store police e-service [25] reputation e-service [25] assurance e-service [25, 55] empathy e-service [25] response time online retailing [4, 32] intuitiveness online retailing [32] flow online retailing [32] innovativeness online retailing [32] substitutability online retailing [32] interactivity online retailing [32, 51] web portal [6, 48, 51] structure e-service [12] content e-service [2, 3, 6, 8, 12, 27] linkage e-service [3, 12] incentive e-service [2, 12] convenience online retailing [52] competence online retailing [33, 52] online shopping [48] personalisation online retailing [24, 50-52] collaboration online retailing [27, 52] product portfolio online retailing [48] entertainment online retailing [4] transaction capability online retailing [4] system availability e-service [7] graphic style e-service [7] order management e-service [11] functionality online financial service [8, 51] usability web portal [6, 17, 51] the review of the literature produced more than 50 dimensions relating to e-service and its quality. to analyze these dimensions, a content analysis technique was used. a form of data analysis was proposed by authors in [43] as appropriate to analyze written, verbal or visual communication messages. part of the set of empirical analysis methods for social research, content analysis is recognised for its validity for text analysis [45]. qualitative content analysis attends to specific topics that explain the meanings of the phenomenon, rather than counting words or identifying objective content from texts [45]. content analysis is described as “a research method for the subjective interpretation of the content of text data through the systematic classification process of coding and identifying themes or patterns” [46]. using suggestions for content analysis processes from [45, 47], themes that emerged from these dimensions, were identified and categorized. based on original definitions, each dimension and its constituent items were first described and prepared for data analysis. each dimension was identified in relation to the others. each description was read to note any interesting or relevant information, and this was recorded as a brief note on the page. from these notes, themes emerged, and the themes were sorted and categorised by topic. these were again analyzed and compared with the original description to ensure that the dimension was appropriately themed. several iterations of this process were undertaken to clarify complicated description of dimensions. when this part of the analysis was complete, the theme groups were then perused to find trends or relationships that could be linked as higher themes and these themes were then modeled. iii. results and discussion the factors relating to e-service quality can be assigned to five themes as shown in figure 1. these are defined as system functionality, content, manageability, customer support and procedures. a. system functionality this theme categorizes the technical functions of egovernment websites such as ease of use, system availability, engineering, technology & applied science research vol. 9, no. 3, 2019, 4249-4254 4252 www.etasr.com alanezi & sellami: an unified framework for measuring e-service quality privacy and security. system functionality is crucial to provide citizens with a reliable service they are willing to use. several researchers developed their e-service quality models by using factors within the system functionality theme dimensions in this regard [5, 7, 11, 19, 32]. certainly, the complexity of system feature and the difficulty to use the services weaken the e-service quality as supported in [7], which claims that problems related to technical functioning of the site lead to frustration and possible user exit. author in [12] also confirmed that problems related to technical functions influence e-service quality directly and negatively. fig. 1. conceptual eservice quality framework b. content this category includes all elements related to the content of the site, presentation, format and information. this category includes text, images, audio and video. these dimensions receive considerable attention [5, 7, 48]. there is a considerable body of evidence showing that better information quality influences e-service quality positively [11, 49-51], while inadequate web design influences e-service quality negatively [7]. authors in [52] found that content is an important factor in measuring e-service quality. c. manageability manageability [11, 22, 48] relates to efficiency factors of websites, such as processing time and other matters that streamline the website experience. as efficiency underpins the website’s usefulness, this theme is interwoven with all other categories. manageability includes improving processes and improving the user’s experience. failure to deliver a high quality service, failure to deliver service on time and on budget affects project quality [53]. in [53], it is claimed that quality of management provides benchmarking capabilities and comparative assessment of e-services and assists managers to improve the quality of service. d. procedures this theme includes all dimensions for e-service quality of work and activities such as credibility, interactivity, and personalization. procedure was defined as the quality of planning, execution and maintenance of the system work and activities done by e-service’s staff behind the system in order to complete the excellent delivery of e-service. many studies used a dimension that covers the activities under e-service system in order to consider the area of procedure [5, 13, 51]. failure to perform the promised service and failure to interact with the user affect the quality of e-service. authors in [51] confirmed that visitors and users are more attracted to interactive than static web sites. activities built into the website are a service to the end user, so ensuring the quality of operation and content leads to a quality experience. in the e-commerce domain, [48] declared that inaccurate order fulfilment and laxity in keeping service promises are primary elements that negatively influence customer satisfaction. e. customer support this category covers all dimensions that envelop user assistance such as responsiveness and contact. the importance of this category is that it helps the users to perform their eservice smoothly by giving them assistance and providing them the needed information. many studies include some dimension in their models to cover this area in order to measure e-service quality [5, 7, 11, 54]. users expect to be able to complete their request or actions properly, to receive personalized attention, to know how their request is proceeding, to have their enquiries answered quickly, to have contact details and to be able to contact an organization representative directly [11]. website administrators should ensure these expectations are met [11]. f. summary there is some crossover with these themes, and elements can be classified in more than one category. for example, processing time can be classified as procedure quality as well as manageability quality. this framework was developed to assist researchers and managers in their decision making by using a classification system for the range of elements that may affect e-service quality. iv. conclusion this model can be used as a roadmap for researchers who wish to measure user perception of e-service quality in eservice domains, and for e-service managers and website administrators in assessing the effects of changes to improve their service performance. this novel framework has been produced after reviewing the literature and considering the identified issues. this framework will assist in bringing order to the large number of elements identified as influencing eservice quality, as it takes the user-e-service interface as the nexus for analysis. in addition, this framework will assist developers to understand and evaluate the standards of eservice quality. future research could consider the relationship between the framework’s categories. in addition, researchers can examine these themes in different contexts in order to validate this model. acknowledgement authors would like to thank the shaqra university for supporting this research. this work had been financed from the deanship of scientific research at shaqra university, grant nr. d180326/g01/n002. references [1] m. a. alanezi, a. kamil, s. basri, “a proposed instrument dimensions for measuring e-government service quality”, international journal of ue-service, science and technology, vol. 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electrical engineering mahshahr branch, islamic azad university mahshahr, iran abstract—in this paper, gaas and ge solar cells have been studied and simulated separately and the inner characteristics of each have been calculated including the energy band structure, the internal field, carrier density distribution in the equilibrium condition (dark condition) and the voltage-current curve in the sun exposure with the output power of each one. finally, the output power of these two mechanically stacked cells is achieved. drift-diffusion model have been used for simulation that solved with numerically method and gummel algorithm. in this simulation, the final cells exposed to sun light in a standard am 1.5 g conditions and temperatures are 300° k. the efficiency of the proposed structure is 9.47%. the analytical results are compared with results of numerical simulations and the accuracy of the method used is shown. keywords-gummel method; mechanically stacked solar cell; numerical simulation; gaas/ge; drift-diffusion method i. introduction photovoltaic (pv) cells convert solar energy to electrical energy and thus they represent an important aspect of clean energy. since the power of solar cells’ energy conversion efficiency using single junction is limited, the multi-junction structure is mostly used. iii-v multi-junction solar cells have achieved the highest efficiencies of any present photovoltaic technology [1-2]. these classes of photovoltaic cells are often grown directly on a single substrate, and connected in series by tunnel diodes. despite the advantages of this type of solar cells, they still have problems such as the requirements of current matching, lattice matching and use of tunnel junctions. it seems that a mechanical stack structure is a solution for these problems. therefore, in this article mechanically stacked multijunction solar cells are considered. the sub-junctions in a mechanical stack are fabricated separately on their individual substrates and then are combined into one single mechanically stacked multi-junction device (mostly by using a transparent adhesive) [3-5]. this cell could obtain 38.5% under x20 radiation [6]. as mentioned in [7], the optimum structure for these cells (by two separated cells) consists of supernatant cell with energy gap 1.4 ev and a cell with energy gap 0.7 ev so the supernatant cell made of gaas and the underlying cell made of ge have been selected. ii. diffusion-drift model and numerical solution there are various models which can be used. considering to the discussed cell’s dimensions and the amount of its layers inject, the diffusion-drift model has been selected. this model consists of three main [8]: . v     (1) 1 n n n j u t q      (2) 1 p p n j u t q       (3) n n n nj qn e qd    (4) p p p pj qn e qd    (5) in the above equations, (1), (2), (3) are poisson's equation, electron continuity equation, holes continuity equation as respectively and relations (4) and (5) as electron flow equation and holes flow equation. in these relations ε is the throughput coefficient semiconductor, ρ the space charge density, v the electrical potential, n, p are electrons and holes density, q the electron charge, jp and jn the hole and electron density, µn and µp the electron and hole mobility coefficient, e the electric field and dp and dn carries the diffusion coefficient. in this paper, three variables (v, n, p) are selected as independent variables, the equations are accordingly adjusted and solved by a numerical method, as described below. a. gummel method one of the common methods for solving the diffusion-drift equations is the gummel method [9]. in this algorithm, first poisson’s equation is solved by considering the primary conditions and a distribution for carries in piece length is obtained, and then continuity equations are obtained by this distribution, solved and result to a new value for potential distribution in the piece. this process continues until the intended accuracy is reached. engineering, technology & applied science research vol. 7, no. 3, 2017, 1611-1614 1612 www.etasr.com enayat taghavi moghaddam and mehrdad kankanani: numerical simulation of a mechanically… b. discretizing the equations for discretization diffusion-drift equations have been used from finite difference method [10]. but in discretization the equations related to semi-conductive simulation it should be considered to one point. discretization steps should not be larger than a certain limit, otherwise the numerical iterative method is to be divergent and the simulation is not valid. along with, there are three conditions:  the limitation related to location steps 2( ) ) btk d q n r l     the limitation related to time steps ( )drt t q n      .  the limitation in voltage steps applied to the intended piece ( ) btt k v v q    . in above relations, ∆r, ∆v and ∆t are discretization steps of local, time, and applied voltage to piece as respectively. also kb is the boltzmann constant, t the environment temperature, n the density of carriers mold, tdr the semi-conductive rest time and vt its heat potential. in addition to the expressed issues, it is necessary to say that since the equations are solved numerically with replication methods (gummel method), these equations should be written in a way to be suitable for iterative algorithms. hence, in addition to discretization, it should be rewritten appropriately. so we rewrite one by one the relations to diffusion-drift equations for one-dimension mode. in order to rewrite poisson's equation, first we discretize the equation (1) and replace the relation ρ=p-n+nd-na (nd and na are donor and acceptor impurity densities as respectively) in it in order to write the equation in terms of independent variables. then we replace vnew=vold+∆v in obtained equation to give a final form for poisson's equation (6 and 7). this frame can be used in the iterative algorithm. 1 1 new new new i i i i i i iav b v c v d    (6) 2 2 2 ' 1 ( ( )), ( )i ii i i x t i qn d n b e e e e e e a c v l n x                     (7) , , ' old i i d a t v qn l n n n v       (8) where ∆x is the local step in one-dimension and i is the discrete points number along with this dimension. for solving (9), the lu placement method is used (10). however, it has been stated that using (7) and (8) depends the simulation to the discretization step length [11] and if the voltage difference between two subsequently points is higher than 2vt into the piece, the simulation will diverge. hence, the gummelscharfetter flow relation ( (9) for electrons) is used [12]. 1 1/ 2 1/ 2 2 [ ( ) ( ) ( 1) ( )] n ni i i i t v v qd m j n i b m n i b m v x            (9) the aim of b(m) is that bernoulli function. by replacing (9) in (2) and its discretization, assuming the steady state ( ) 0 n t    we obtain: 1 1i i i i i i ian n bn n cn n rn    (10) 1/2 1/2 1/2 1/2 2 2 2 ( ) ( )1 , [ ( ) ( )] n n i in n nt i i i i d b m d b n c bn d b n d b m an x x x              1i i t v v n v  , i i irn un gn  (11) where uni and gni are the recombination rate and the rate of electrons production respectively. similarity, the same process is used for holes. iii. proposed solar cell structure as mentioned in the introduction part, as it is necessary to be the higher cell energy gap as equal ¼ ev (3), semiconductive gaas to eg=1.41 ev is the best option. the structure of this cell is provided in figure 1a. the shown cell in figure 1a is a one-link pn cell that has used the areas with high injection in order to reduce the ohmic effect of contacts. the top surface of the cell is covered by an anti-reflex covering layer to minimize the reflection losses. the thickness of the desired cell is 14µm that is enough for our aim [3]. the underlying cell should have an energy gap of 0.7 ev and semiconductors as ingaasm, gasb, and ge are the best options for this purpose with energy gaps of 0.67 ev, 0.72 ev, and 0.75 ev respectively. in this paper, ge has been used for the underlying cell. the structure of this cell is shown in figure 1b. (a) (b) fig. 1. cell structure in simulation: (a) upper cell (gaas) (b) underlying cell (ge) engineering, technology & applied science research vol. 7, no. 3, 2017, 1611-1614 1613 www.etasr.com enayat taghavi moghaddam and mehrdad kankanani: numerical simulation of a mechanically… iv. numerical simulation the numerical simulations are performed in matlab 2010a [13-14]. it is assumed that each absorbed photon provide an electron-hole pairs. each of the sub-cells is simulated in two states (in balance state (dark) and in light radiation state). final results are shown in figure 2. comparison of analytic and simulation data is shown in table i. it should be noted that if we connect sub-cells in mechanical layout as parallel to have a separated charge, maximum final cell power is equal to the sum of powers maximum of each cells [3]. according to the simulation, the output maximum power of the gaas is equal to 0.635 mw/cm2 and of the ge cell to 0.635 mw/cm2. hence the efficiency of changing the gaas/ge cell with this mechanical layout is 9.47%. table i. comparison of analytic and simulation data variable simulation results analytic results isc(gaas) 7.543 ma 7.666 ma voc(gaas) 0.9501 v 0.9505 v isc(ge) 9.192 ma 9.343 ma voc(ge) 0.1300 v 0.1304 fig. 2. simulation results: )a) conduction band diagram (b) electrical field variations (c) carrier concentration (d) density of electric charge in balance state (dark) (e) i-v characteristics in light radiation state v. conclusion in this article, a gaas/ge solar cell by mechanical layout was simulated in two states, dark and light radiation, with standard conditions am1.5 g at 300o k temperature. for this work we used the diffusion-drift equations that were solved, using numerical methods, in matlab. the simulated results are shown and discussed and their values are compared to those from analytical computations. acknowledgment the author would like to acknowledge the islamic azad university, mahshahr branch, iran, for funding the research project entitled “simulation of hetero-junction gaas/ge solar cell” out of which this paper is derived. the authors also acknowledge mr. jabar ganji for his contribution. references [1] r. aguinaldo, modeling soluiton and simulation for advanced iii-v photovoltaics based on nanostructures, m.s. thesis, dept. material (c) d e (a) (b) (d) (e) engineering, technology & applied science research vol. 7, no. 3, 2017, 1611-1614 1614 www.etasr.com enayat taghavi moghaddam and mehrdad kankanani: numerical simulation of a mechanically… science & engineering, rochester institute of technology, new york, united states, 2008 [2] f. dimroth, m. grave, p. beutel, u. fiedeler, c. karcher, t. n. tibbits, a. w. bett, “wafer bonded four-junction gainp/gaas/gainasp/gainas concentrator solar cells with 44.7% efficiency”, prog. photovolt: res. appl., vol. 22, no. 3, pp. 277–282, 2014 [3] l. d. partain, m. s. kuryla, r. e. weiss, r. a. ransom, p. s. mcleod, l. m. fraas, j. a. cape, “26.1% solar cell efficiency for ge mechanically stacked under gaas”, journal of applied physics, vol. 62, no. 7, pp. 3010-3015, 1987 [4] s. yoshidomi, j. furukawa, m. hasumi, t. sameshima, “mechanical stacking multi junction solar cells using transparent conductive adhesive”, advanced materials and characterization techniques for solar cells ii, vol. 60, pp. 116-122, 2014 [5] k. makita, “highly efficient and reliable mechanically stacked multijunction solar cells using advanced bonding method with conductive nanoparticle alignments”, ieee 40th photovoltaic specialist conference (pvsc), pp. 0495-0498, 2014 [6] j. d. mc cambridge, m. a. steiner, b. l. unger, k. a. emery, e. l. christensen, m. w. wanlass, j. w. ashmead, “compact spectrum splitting photovoltaic module with high efficiency”, progress in photovoltaics: research and applications, vol. 19, no. 3, pp. 352-360, 2011 [7] i. mathews, w. yu, d. gordon, “mechanically stacked solar cells for concentrator photovoltaics”, international conference on renewable energy and power quality. spain, vol. 19, no. 1, pp. 627-628, 2011. [8] a. jungel, transport equations for semiconductors, springer, 2009 [9] h. k. gummel, “a self-consistent iterative scheme for one-dimensional steady state transistor calculations”, ieee transactions on electron devices, vol. 11, no. 10, pp. 455-465, 1964 [10] m. n. o. sadiku, “monte carlo methods for electromagnetics”, crc press, boca raton, 2009 [11] d. vasileska, s. m. goodnick, g. klimeck, “computational electronics: semiclassical and quantum device modeling and simulation”, crc press, boca raton, 2010 [12] d. l. scharfetter, d. l. gummel, “large signal analysis of a silicon read diode oscillator”, ieee transactions on electron devices, vol. 16, no. 1, pp. 64-77, 1969 [13] s. l. chuang, physics of optoelectronic devices, wiley, 1995 [14] s. m. kankanan, “numerical simulation of multijuction gaas solar cell”, msc. thesis, electrical engineering, faculty of engineering, shahid chamran universitu of ahwaz, 2015 microsoft word 06-3487_s1_etasr_v10_n3_pp5613-5618 engineering, technology & applied science research vol. 10, no. 3, 2020, 5613-5618 5613 www.etasr.com sicakova et al.: perlite application and performance comparison with conventional additives in … perlite application and performance comparison to conventional additives in blended cement alena sicakova institute of environmental engineering technical university of kosice kosice, slovakia alena.sicakova@tuke.sk erika kardosova institute of environmental engineering technical university of kosice kosice, slovakia erika.kardosova@tuke.sk matej spak dpt. of construction technology & management, technical university of kosice, kosice, slovakia matej.spak@tuke.sk abstract—this study compares the performance of perlite with that of conventional additives in blended cements. the results of the application of perlite powder (pp) as a component of blended cements in two different proportions (30% and 50%) are presented and compared with standard additives of fly ash (fa) and ground granulated blast furnace slag (ggbfs). moreover, perlite is tested as a component of ternary cement (70% cement, 15% p and 15% fa and ggbfs alternatively). blended cements are tested in terms of flexural strength, compressive strength, bulk density, water absorption, and frost resistance. the results show that although perlite blended cements achieve lower strengths and higher absorptivity compared to conventional additives, they have significant potential for freezing and thawing durability, especially in ternary combination with ggbfs. for practical applications, the intrinsic values of the parameters of the individual binders with perlite (e.g. flexural strength of 4.1– 6.2mpa or compressive strength of 18.8–38.5mpa) are sufficient for many practical applications. perlite, when suitably combined with other pozzolanic materials, can be a suitable component of blended binders. keywords-blended cements; perlite; slag; fly ash; compressive strength; water absorption; frost resistance i. introduction cement is a material consisting not only of ordinary concrete, but also of various types of cement composites. some by-product materials, including ground granulated blast furnace slag (ggbfs), fly ash (fa) and silica fume, are used as supplementary cementitious materials (scms) in a standard way to produce blended cements. nowadays, when sustainability principles, including the co2 footprint, have to be taken into account, other scms should be researched. these include raw materials, like micro-powder limestone, metakaolin [1], zeolite [2], rice husk ash [3], tile powder [4], perlite, etc. each of these materials has to undergo preproduction testing before being used as an scm in concrete. the technical properties (mechanical, rheology, durability and thermo-insulation) and the economic and environmental parameters of these scms must also be assessed [5]. perlite is a highly siliceous and amorphous hydrated volcanic glass containing crystalline impurities, such as quartz, biotite and alkali feldspars and falls in the category of unaltered volcanic alternatives. perlite is defined as a hydrated natural rhyolite, which is a glass formed from highly siliceous volcanic lava [2]. perlite varies from other hydrated volcanic glasses (e.g. obsidian or pumice) due to its high water content (typically ranging from 2–5%) [7]. perlite contains ~70–75% sio2 and ~12–18% al2o3. due to its glassy structure and high sio2 and al2o3 contents, perlite can be classified as a pozzolan [8, 9]. in [9], it is shown that the reaction between the lime, silica and alumina of perlite leads to several hydrates, such as calcium silicate hydrate, hydrated calcium aluminates, and hydrated gehlenite. however, as shown in [10], the nature of perlite powder (pp) is crucial: if expanded perlite is a source material, due to its cellular microstructure and high porosity, it cannot be used as an effective pozzolanic scm ‘‘as received”. grinding to a suitable grain size is necessary for achieving pozzolanic character. then, as the fineness of the powder increases, the pozzolanic activity increases. pp is a natural lowprice and commonly available (depending on the region) pozzolan, with the ability to reduce the hydration heat and control the shrinkage of concrete mixtures. nevertheless, its influence on the properties of concrete, including reactivity (specifically in the early ages), strength, durability, etc. is always a concern [11]. perlite has been declared as a satisfactory pozzolan with the ability of reducing co2 emissions and the overall cost of composites [9]. although the partial cement replacement with perlite significantly reduces the initial strength of mortars during the period from 7 to 28 days, with higher age, the compressive strength differences between the samples containing pp and cement become lower. authors in [9] reported that the optimal cement replacement ratio of pp ranges from 10% to 20%. in addition, densification of the transfer matrix of mortars and good resistance to carbonation were exhibited. similar results were presented in [12], where it is stated that the pozzolanic activity of pp is slow in the early age and develops with time, resulting in a decrease of absorbability and porosity and an increase in strength. the lower compressive strength of perlite mortars, compared with cement mortars, was highlighted in [8]. however, due to pozzolanic reactions, these differences are considered to be removed in later ages. the higher amount of perlite in the cement mortar led to a higher demand for water with the same consistency, longer setting time and lower strength. in contrast, the permeability for chloride and autoclave scattering decrease with an increasing percentage of corresponding author: alena sicakova engineering, technology & applied science research vol. 10, no. 3, 2020, 5613-5618 5614 www.etasr.com sicakova et al.: perlite application and performance comparison with conventional additives in … perlite [8]. somewhat different results are presented in [13], where the authors reported that the main parts of the pozzolanic reaction of pp occur after 28 days, but the effect on compressive strength was expressed as insignificant. according to the authors, replacing a part of ordinary portland cement with pp leads to an insignificant reduction in the compressive strength of the concrete. this reduction is between 8% and 12% for concrete with a 30% replacement. this study presents the results of the application of perlite as a component of blended cement in two different proportions (representing cem ii/b and cem iv/b types of cement), and compares it with standard additives (fa and ggbfs) in the same amounts. moreover, perlite was tested as a component of ternary cement: cem i+p+fa and ggbfs alternatively. to see the effect of perlite, the ternary cement of cem i+fa+ggbfs was also studied. this represents the basic contribution of the paper, since, when testing the performance of pp, it is usually used alone as a partial replacement of cement/clinker. however, blended cements in terms of ternary composition are highlighted at present. this is due to the need to apply different scms mainly for environmental reasons, as well as for a lack of standard scms in some regions (like ggbfs due to the high demand and therefore difficulties in satisfying supplies, and fa due to the lack of one that meets standard requirements for concrete production). furthermore, some regions or countries may be rich in natural pozzolans but do not generate substantial amounts of artificial pozzolans [14]. the combinations of scms need to be tested and optimized to achieve satisfactory performance. in this paper, pp testing is presented by systematic variants of blended binders. the samples were tested in terms of flexural strength, compressive strength, bulk density, water absorption, and frost resistance of the hardened mortar. this study compares the performance of perlite and conventional additives, with 28-day values taken as the comparative level. ii. materials and methods to verify the effect of perlite on the properties of the blended binders, ten binder mixtures were designed in different compositions, including the reference one without any additive. pp was applied as a component of portland cement (cem) in three different percentage proportions: • cem/p = 70/30: the cement represents the cem ii/b-p type of cement according to en 197-1 [15] • cem/p = 50/50: the cement represents the cem iv/b type of cement according to en 197-1 [15] to compare, the same compositions were tested with the utilization of the standard additives fa and ggbfs. • ternary cements cem/p/fa and cem/p/ggbfs = 70/15/15. to see the effect of perlite, also the ternary cement of cem i+fa+ggbfs composition was tested. these compositions fall into the cem ii/b-m type of cement. for testing the properties, standard mortars according to en 196-1 [16] were prepared. a. material characterization the following materials were used. the powder materials are shown in table i, including the presence of main oxides and grain size characteristics. • sand (s): cen standard sand according to en 196-1 [16] • cement (c): cem i 42,5 r (crh turna nad bodvou, slovakia) • mixing water (w): tap water • mineral additives (ad): ground granulated blast furnace slag (s): us steel kosice, slovakia, fly ash (f): energy segment of steel making factory, us steel kosice, slovakia, and perlite (p): natural, finely ground perlite, lehotka pod brehmi, slovakia table i. properties o f cement, perlite, slag and fly ash sio2 al2o3 fe2o3 cao others d (0.5) d (0.9) [%] [µm] cem i 42.5 r 20.3 4.0 3.0 64.1 8.6 26.7 67.9 s 41.3 6.3 0.4 36.0 16.0 19.0 111.5 f 56.4 19.9 7.3 4.4 12.0 19.1 94.8 p 53.9 9.3 1.3 1.3 34.2 33.7 78.0 b. experimental part the tested mixtures are given in table ii. first, the binders were prepared according to the proposed percentage composition by dry mixing. the mortar samples were mixed, moulded, and cured in accordance with en 196-1 [16]. each batch for three test specimens consisted of (450±2)g of binder, (1350±5)g of cen standard sand and (225±1)g of water. table ii. composition of blended binders 28-day values were taken as the comparative level of the performance of perlite with conventional additives. after the curing days, the following parameters were tested: • flexural and compressive strength according to [16]. • density according to [17]. • water absorption according to [18]. the method represents a trivial gravimetric course. • two of the tested series that proved to be the most promising (70/30 and 70/15/15) were further tested for frost resistance (25 cycles) according to [19]. the cycles consisted of freezing under -20°c (2h of temperature drop samples components [%] cem i 42.5 r slag (s) fly ash (fa) perlite (p) ref 100 c70s30 70 30 c70f30 70 30 c70p30 70 30 c50s50 50 50 c50f50 50 50 c50p50 50 50 c70/s15/f15 70 15 15 c70/p15/f15 70 15 15 c70/p15/s15 70 15 15 engineering, technology & applied science research vol. 10, no. 3, 2020, 5613-5618 5615 www.etasr.com sicakova et al.: perlite application and performance comparison with conventional additives in … and 2h of temperature holding) and defrosting under +20°c (0.5h of temperature rise and 1.5h of temperature holding). one freezing-thawing cycle lasts for 6h. frost resistance was expressed as a percentage change in flexural and compressive strength after 25 cycles of freezing and thawing. iii. results and discussion the results are shown in figures 1–6. the values considered were the means of the three results obtained for each set. table iii shows the percentage changes in properties in comparison with the reference sample (ref). the evaluation of the results is mainly focused on samples with perlite, both against the reference sample and samples with conventional additives of ggbfs and fa. a. density the density of the samples with perlite was between 1960 and 2080kg.m -3 . compared to the ref, the density at the c50p50 ratio decreased the most, by 5.9%. the application of additives in principle reduces density, only a 50% ggbfs replacement increases slightly the value. the c50s50 sample has a 1.5% higher density compared to the ref sample. fig. 1. density table iii. differences in properties in comparison with the reference sample sample density flexural strength compressive strength absorptivity increase / decrease [%] c70s30 -1.4 -2.9 -23.9 4.9 c70f30 -1.0 -15.7 -28.4 6.2 c70p30 -2.6 -24.3 -43.1 8.6 c50s50 1.5 -18.6 -36.0 4.9 c50f50 -2.5 -28.6 -50.5 13.6 c50p50 -5.9 -41.4 -65.5 19.8 c70s15f15 0.6 -2.9 -18.4 7.4 c70p15f15 -0.1 -11.4 -29.4 11.1 c70p15s15 -0.6 -15.7 -30.3 11.1 compared to the ggbfs and fa samples, the samples containing p exhibit a lower density in each of the studied sample groups. perlite causes a decrease in density by 28.8kg.m -3 on average for the 70/30 combination (which represents ~1.4% of the average density of samples with ggbfs and fa), by 113.2kg.m -3 for the 50/50 combination (which represents ~5.5% of the average density of the ggbfs and fa samples) and by 20.7kg.m -3 on average for ternary combinations (which represents ~1.0% of the density of the ggbfs and fa samples). it can be stated that the use of perlite leads to a negligible decrease in density, either with respect to the reference sample or to the samples with conventional additives. b. flexural strength when comparing the effect of additives on flexural strength in the individual sample groups, consistent results were achieved confirming the expectations. the best efficiency (smallest decrease in strength) was caused by ggbfs, followed by fa and finally p. as the amount of additive increases, the strength decreases. all samples where p was used had reduced flexural strength, not only in comparison with the reference sample, but also with the s and fa samples. samples with p achieved a flexural strength of 4.1–6.2mpa. fig. 2. flexural strength compared to the reference sample, the strength of c50p50 decreased at most by 41.4%. perlite binders in the ternary combination of c70p15s15 and c70p15f15 had the least decrease in strength of 15.7% and 11.4%, respectively. compared to ggbfs and fa samples, perlite causes a greater reduction in the reference flexural strength by 1.3mpa on average for the 70/30 combination (representing ~20% of the average ggbfs and fa samples’ strength), by 1.3mpa for the 50/50 combination (representing ~25% of the average strength of the ggbfs and fa samples), and by 0.7mpa on average for the ternary combinations (representing ~10% of the strength of the samples with ggbfs and fa). application of perlite at 30% of cem i yields a slightly lower flexural strength than application at 15% along with ggbfs (5.3mpa versus 5.9mpa). c. compressive strength compressive strength follows the same trend with flexural strength. all samples where perlite was used exhibited reduced compressive strength in comparison with the reference sample and the s and fa samples. samples with p achieved a compressive strength of 18.8–38.5mpa. the results are principally in accordance with [8], where results of 20–30% engineering, technology & applied science research vol. 10, no. 3, 2020, 5613-5618 5616 www.etasr.com sicakova et al.: perlite application and performance comparison with conventional additives in … replacement of cement by perlite were reported. their 28-day compressive strength went from 34.7 to 42.7mpa. fig. 3. compressive strength compared with the ref, the strength of c50p50 decreased the most by 65.5%. binders with perlite in the ternary combinations c70p15s15 and c70p15f15 had the least decreases in strength of 30.3% and 29.4% respectively. compared to slag and fa samples, perlite causes a greater reduction in compressive strength of 9.3mpa on average in the 70/30 combination (representing ~23% of the average ggbfs and fa samples strength), by 12mpa on average for the 50/50 combination (representing ~39% of the average strength of the ggbfs and fa samples), and by 6.5mpa on average for ternary combinations (which is ~14% of the average strength of the ggbfs and fa samples). the application of 30% perlite yields 7mpa lower strength than the application of 15% along with 15% of ggbfs and fa, respectively (31mpa versus 38mpa, which represents on average one strength class). looking at the result of c50p50 (18.8mpa), it can be stated similarly to [8] that the higher amount of perlite leads to lower strength. according to [15], the strengths of cem 32.5 must be between 32.5 and 52.5mpa at 28 days. mixtures c70s30, c70f30, c50s50 and all ternary compositions meet this criterion, including both samples with perlite powder c70p15f15 and c70p15s15. d. water absorptivity the absorptivity results correspond (i.e. run in reverse order) to those of the density and strength parameters. with the presence of additives and with an increase in their amount, water absorptivity increases. all samples where perlite was used exhibited increased absorptivity over the reference sample, and the slag and fly ash samples. samples with perlite achieved an absorptivity of 8.8–9.7%. compared to the reference sample, the absorptivity increased to the smallest extent (4.93%) for samples c70s30 and c50s50. the binder with perlite has the smallest decrease in absorptivity in the c70p30 combination of 8.64%. compared to the s and fa samples, perlite causes an increase by 0.25% on average in the 70/30 combination (representing ~2.9% of the average absorption of ggbfs and fa samples), by 0.85% for the 50/50 combination (which represents ~9.6% of the average absorptivity of ggbfs and fa samples) and by 0.3% on average for ternary combinations (which represents ~3.4% of the average absorptivity of ggbfs and fa samples). it can be stated that the worse influence of perlite on the absorptivity of mortars compared to slag and fa is negligible in the cases of the 70/30 and ternary combinations. application of perlite at 30% of cem i yields even 0.2% lower absorptivity than application at 15% along with 15% of ggbfs and fa, respectively (8.8% vs. 8.0%). the results of both strengths are in accordance with the findings in [9], in which a decrease was also observed in the strengths of samples with perlite along with an increase in porosity, which would point to a weaker structure of mortar. as for our results, a weaker structure of perlite specimens is indicated by higher absorptivity, while the results are consistent with strengths: perlite specimens have higher absorptivity with lower strength. e. frost resistance the results are shown in figures 5 and 6. the mean of the three results obtained for each set of three was considered. table iv shows the percentage changes in properties after 25 cycles of freezing and thawing. table iv. percentage ch an ges in properties in comparison with the reference sample sample flexural strength compressive strength increase / decrease [%] ref 12.9 -7.3 c70 s30 0 -18.1 c70 f30 -76.3 -35.9 c70 p30 -5.7 8.1 c70 s15 f15 -67.7 -29.2 c70 p15 f15 -69.4 -33.8 c70 p15 s15 -5.1 -4.0 1) flexural strength a significant decrease in flexural strength after freezingthawing cycles was found for all fa samples, by up to 76% (c70f30). in contrast, samples with perlite, when used alone or in combination with slag, had only ~5% lowered strength. fig. 4. frost resistance – flexural strength with the exception of the reference sample, only three samples achieved good performance in terms of frost resistance limit (minimum 75% of initial strength): c70s30, c70p30 and c70 p15 s15. engineering, technology & applied science research vol. 10, no. 3, 2020, 5613-5618 5617 www.etasr.com sicakova et al.: perlite application and performance comparison with conventional additives in … 2) compressive strength: a significant decrease in compressive strength was found in all samples with fa up to almost 36% (c70f30). samples with perlite had a lower strength of only 4% when combined with slag (c70p15s15) and on a single application the compressive strength after freezing was higher (c70p30). the results are in line with [20, 21]. in [20], it is stated that samples containing ggbfs achieved better results than the ones containing fa, and the authors in [21] associate the positive effect of ggbfs with its influence on permeability. the good performance of perlite is also in accordance with the results in [22], in which authors showed that frost resistance improved when mixtures were prepared with higher perlite concentration. they suggest that this is partly attributed to the porous nature of perlite that helps reducing the disruptive expansive stresses caused by the freezing-thawing process. the frost resistance results are consistent. the individual binder compositions are basically in the same order in terms of flexural and compressive strength, as shown in table v, which is arranged to give a quick indication of the impact of the binder compositions by indicating their order in individual properties, starting from the best. samples with perlite are highlighted in bold. on the basis of this order, it can be quickly stated that although perlite achieved lower strength compared to conventional additives (ggbfs and fa), it has a promising potential for durability in terms of resistance to freezing and thawing, especially in combination with slag. in contrast, another parameter associated with the characterisation of durability, which is absorptivity, appears relatively unfavourable. fig. 5. frost resistance – compressive strength table i. sample perfo rmance order in each property order flexural strength compressive strength absorptivity frost resistance flexural strength compressive strength 1 ref c70s30 ref ref ref 2 c70s15f15 ref c70s30 c50s50 c70s30 c70p15s15 3 c70s30 c70s15f15 c70s30 c50s50 c70p15s15 c70s30 4 c70f30 c70p15f15 c70f30 c70p30 c70p30 5 c70p15f15 c70f30 c70s15f15 c70s15f15 c70s15f15 6 c70p15s15 c70p15s15 c70p30 c70p15f15 c70p15f15 7 c50s50 c50s50 c70p15s15 c70f30 c70f30 8 c70p30 c70p30 c70p15f15 9 c50f50 c50f50 c50f50 10 c50p50 c50p50 c50p50 iv. conclusion the aim of this work was to compare the performance of perlite with the performance of conventional additives (ggbfs and fa), with 28-day concrete properties taken as the comparative level. ten recipes of binder mixtures have been designed in different compositions, including the reference mixure with no additives. the following percentage ratios of cem i and additive (ad) were tested: cem i/ad = 70/30, 50/50, and cem i/ad1/ad2 = 70/15/15, while all possible combinations of three additives were applied. for testing the properties, standard mortars according to [16] were prepared. after 28 days of curing, the following parameters were tested: density, flexural and compressive strength, and water absorption capacity. two of the tested series were the most promising (70/30 and 70/15/15) and were further tested for frost resistance. the use of perlite additive results in a slight decrease in density, in relation to the reference sample or to samples with ggbfs and fa conventional additives. when compared to the average results of samples with ggbfs and fa, the use of perlite causes the following: • a reduction of flexural strength by 10% for ternary combinations, by 20% for 70/30 and by 25% for the 50/50 combination. • a reduction of compressive strength of 14% for ternary combinations, by 23% for 70/30, and by 39% for the 50/50 combination. • an increase in absorptivity by 2.9% for 70/30, by 3.4% for ternary combinations, and by 9.6% for the 50/50 combination. • significantly better frost resistance compared to the fa samples. • good frost resistance when used alone in 70/30 and when used with ggbfs in 70/15/15 as well. the flexural strength decrease after 25 cycles of freezing and thawing was only about 5%, the compressive strength decrease was about 4% in the 70/15/15 combination with ggbfs, and even an increase in strength was observed when used in the 70/30 combination. engineering, technology & applied science research vol. 10, no. 3, 2020, 5613-5618 5618 www.etasr.com sicakova et al.: perlite application and performance comparison with conventional additives in … overall, it can be concluded that although perlite blended binders achieve lower strengths and higher absorptivity compared to conventional additives, they have a promising potential for freezing and thawing durability, especially in ternary combination with slag. from an application point of view however, it should be noted that the values of the individual properties of perlite binders (e.g. flexural strength of 4.1–6.2mpa or compressive strength of 18.8–38.5mpa) are sufficient for a number of practical applications and are expected to meet the required limits. the results are even more promising, as they are 28-day values with the expectation of further improvement in later times, and also because the samples were mortars with fine aggregate, they show a perspective for coarse-grained concrete mixtures. acknowledgment this research has been carried out within the project of slovak scientific grant agency vega (grant no. 1/0524/18). references [1] a. saand, m. a. keerio, d. k. bangwar, “effect of soorh metakaolin on concrete compressive strength and durability”, engineering, technology & applied science research, vol. 7, no. 6, pp. 2210-2214, 2017 [2] m. m. ranjbar, r. madandoust, s. y. mousavi, s. yosefi, “effects of natural zeolite on the fresh and hardened properties of self-compacted concrete”, construction and building materials, vol. 47, pp. 806–813, 2013 [3] n. bheel, a. w. abro, i. a. shar, a. a. dayo, s. shaikh, z. h. shaikh, “use of rice husk ash as cementitious material in concrete”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4209-4212, 2019 [4] n. bheel, r. a. abbasi, s. sohu, s. a. abbasi, a. w. abro, z. h. shaikh, “effect of tile powder used as a cementitious material on the mechanical properties of concrete”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4596-4599, 2019 [5] m. juenger, j. l. provis, j. elsen, w. matthes, r. d. hooton, j. duchesne, l. courard, h. he, f. michel, r. snellings, n. de belie, “supplementary cementitious materials for concrete: characterization needs”, mrs online proceedings library archive, vol. 1488, 2012 [6] m. rotella, g. simandl, “marilla perlite – volcanic glass occurrence, british columbia, canada”, 37th annual forum on industrial minerals proceedings, industrial minerals with emphasis on western north america, victoria, canada, may 23-25, 2001 [7] f. bektas, l. turanli, p. j. m. monteiro, “use of perlite powder to suppress alkali-silica reaction”, cement & concrete research, vol. 35, pp. 2014-2017, 2005 [8] t. k. erdem, c. meral, m. tokyay, t. y. erdogan, “effect of ground perlite incorporation on the performance of blended cements”, in: sustainable construction materials and technologies, taylor and francis, 2007 [9] f. guenanou, h. khelafi, a. aattache, “behavior of perlite-based mortars on physicochemical characteristics, mechanical and carbonation: case of perlite of hammam boughrara”, journal of building engineering, vol. 24, article id 100734, 2019 [10] l. kotwica, w. pichor, w. nocun-wczelik, “study of pozzolanic action of ground waste expanded perlite by means of thermal methods”, journal of thermal analysis and calorimetry, vol. 123, no. 1, pp. 607613, 2016 [11] s. m. m. karein, a. joshaghani, a. a. ramezanianpour, s. isapour, m. karakouzian, “effects of the mechanical milling method on transport properties of self-compacting concrete containing perlite powder as a supplementary cementitious material”, construction and building materials, vol. 172, pp. 677-684, 2018 [12] j. esfandiari, p. loghmani, “effect of perlite powder and silica fume on the compressive strength and microstructural characterization of selfcompacting concrete with lime-cement binder”, measurement, vol. 147, article id 106846, 2019 [13] a. a. ramezanianpour, s. m. m. karein, a. r. pilvar, f. moodi, “effect of perlite powder on durability properties of concrete under chloride attack”, fourth international conference on sustainable construction materials and technologies, las vegas, usa, august 7-11, 2016 [14] s. t. erdogan, a. u saglik, “early-age activation of cement pastes and mortars containing ground perlite as a pozzolan”, cement and concrete composites, vol. 38, pp. 29-39, 2013 [15] en 197-1: cement. part 1: composition, specifications and conformity criteria for common cements, cen, 2000 [16] en 196-1: methods of testing cement. part 1: determination of strength, cen, 2016 [17] en 1015-10: methods of test for mortar for masonry. part 10: determination of dry bulk density of hardened mortar, sis, 2000 [18] stn 72 2448: testing of moisture content and absorptivity of mortar, 1968 [19] stn 73 1322: determination of frost resistance of concrete, 2016 [20] h. toutanji, n. delatte, s. aggoun, r. duval, a. danson, “effect of supplementary cementitious materials on the compressive strength and durability of short-term cured concrete”, cement and concrete research, vol. 34, no. 2, pp. 311-319, 2004 [21] k. ebrahimi, m. j. daiezadeh, m. zakertabrizi, f. zahmatkesh, a. h. korayem, “a review of the impact of micro-and nanoparticles on freezethaw durability of hardened concrete: mechanism perspective”, construction and building materials, vol. 186, pp. 1105-1113, 2018 [22] a. el mir, s. g. nehme, j. j. assaad, “durability of self-consolidating concrete containing natural waste perlite powders”, heliyon, vol. 6, no. 1, article id e03165, 2020 microsoft word 15-3411_s_etasr_v10_n4_pp5967-5973 engineering, technology & applied science research vol. 10, no. 4, 2020, 5967-5973 5967 www.etasr.com kayanda & machuve: a web-based data visualization tool regarding school dropouts and user … a web-based data visualization tool regarding school dropouts and user asssesment angelika mark kayanda the nelson mandela african institution of science and technology arusha, tanzania kayandaa@nm-aist.ac.tz dina machuve the nelson mandela african institution of science and technology arusha, tanzania dina.machuve@nm-aist.ac.tz abstract—data visualization is important for understanding the enormous amount of data generated daily. the education domain generates and owns huge amounts of data. presentation of these data in a way that gives users quick and meaningful insights is very important. one of the biggest challenges in education is school dropouts, which is observed from basic education levels to colleges and universities. this paper presents a web-based data visualization tool for school dropouts in tanzania targeting primary and secondary schools, together with the users’ feedback regarding the developed tool. we collected data from the united republic of tanzania government open data portal and the president’s office regional administration and local government (po-ralg). python was then used to preprocess the data, and finally, with javascript, a web-based tool was developed for data visualization. user acceptance testing was conducted and the majority agreed that data visualization is very helpful for quickly understanding data, reporting, and decision making. it was also noted that the developed tool could be useful not only in the education domain but it could also be adopted by other departments and organizations of the government. keywords-data visualization; school dropouts; primary schools; secondary schools i. introduction dropping out from school is a global education issue. student retention and completion remain a challenge in education sector, causing a significant loss in current and future intellect. the united republic of tanzania through the government open data portal estimated 56,573 primary school dropouts in the year 2013 and a significant increase to 85,985 in 2015 and 117,927 in 2016 [1]. secondary school dropouts were about 94,990 in 2012, 61,488 in 2015 and 65,700 in 2017 [2]. the numbers remain high even after tanzania started implementing the free basic education policy in 2016. though studies about school dropouts have been done, and data have been collected and published, the data have not yet been fully explored. a study on school dropouts in three regions of tanzania revealed that socio-economic and political factors, along with parents’ views and government contribute to school dropouts [3]. the study results were presented in percentages, tables and simple text. similarly, a study focused on the artisanal mining areas of the geita region in tanzania presented the data regarding the dropout causes in mostly text [4]. this kind of presentation provides limited interactivity and difficulty in interpreting the information or revealing trends which are helpful in decision making. a recent study used machine learning techniques to develop a predictive model for secondary school dropouts in tanzania to help identify students who are at risk of dropping out and embedded a visualization module. however, the module visualized school data from only five regions in tanzania [5]. recently, data visualization has gained significant attention, not only for its ability to draw meaningful insights from data and events occurring around us through visual displays [6], but also for its ability to take advantage of the human mind’s powerful visual processing capabilities [7, 8]. there are many works that underline the importance of data visualization showing its usefulness and providing insights into complex datasets, by communicating key aspects in a more intuitive and meaningful way [9-11]. the united republic of tanzania government open data portal has visualized maps of primary schools’ pupil-teacher ratio, final examination performance, pupil-classroom ratio, and form four examination performance for the year 2014, but it is missing visualizations for dropouts [1, 2]. the tanzania national bureau of statistics has presented the status regarding dropouts of population aged above 5 years, but no visualization can be found [12]. therefore, the present student dropout data, which have been lightly explored, can be made more useful by employing visualization to support reporting, decision making and ultimately benefit the overall education sector and other interested parties. in this paper, we divided the task into three objectives: data preparation, implementation, and testing. after the data were collected and preprocessed, rapid prototyping was used for the development, and finally feedback was gathered from the users through focus group discussion and questionnaires. herein we report the experimental results of a data visualization tool developed for school dropouts in tanzania. ii. related work a. visualization in education data visualization has been employed in various aspects within the education domain. a visualization tool was developed for dropout reasoning and prediction for the corresponding author: angelika mark kayanda engineering, technology & applied science research vol. 10, no. 4, 2020, 5967-5973 5968 www.etasr.com kayanda & machuve: a web-based data visualization tool regarding school dropouts and user … massive open online courses (moocs) [13]. the pearson’s learning curve provides dynamic, interactive and easy-to-use data visualization tools to enable researchers and policymakers to derive meaning from global education datasets [6]. furthermore, visualization was useful in unearthing interesting findings and more detailed depiction of learners’ behaviors in an adaptive learning environment, which would otherwise remain hidden [14]. for improved teaching and learning online, two interactive visualization tools were developed at the unitelma sapienza university and the iislab of tampere university of technology for the moodle lms as plug-ins. these tools assist students and teachers to monitor, evaluate and make decisions to improve the learning outcome [15]. discrete graphs have been used to visualize learning logs, a method that collected data from e-text and learning management systems. the graphs assisted in observing learning activities’ features for each grade by visualizing combinations of achievements and failures, thus helping discovering the learning activities that should be avoided by students [16]. a web platform named swatshare, designed to enable collaborative hydrology research and education online, makes use of visualization tools such as dynamic time-series plots and spatial maps, to help users understand the variability of various hydrological processes through time [17]. furthermore, one study showed that integrating teaching strategies with interactive visualization techniques could greatly benefit the education domain and enhance visualization literacy to children in early grades [18]. it is pointed out that even though visualizations have recently become common, the ability of youths and adults to interpret them is still relatively low, which can be a serious handicap to learning and making informed decisions. in education, data visualization has been shown to play a key part in identifying and analyzing key causes and their variations in various issues, thus assisting decision makers to enforce more effective schemes in teaching, monitoring learner’s behavior and improve learner’s understanding and the learning outcomes. moreover, the usefulness and success of interactive visualizations in online learning environments suggests that it could also be useful in non-online educational issues. b. visualization in other domains a study was conducted on the prevalence of visualization for electronic health records data from 1996 to 2013. the study found that although electronic health records are increasingly being visualized, not many techniques have been found to display these complex data effectively and efficiently [19]. a visualization plugin that equipped the translational research open data warehouse with dynamic visual analytical workflows by using modern web technologies such as angularjs and d3 was developed in [20]. according to haehn, visualizing connectomics which have massive datasets of brain tissue details, allows neuroscientists to focus on the insights provided by connectome data, rather than managing of these massive datasets. these dynamic and interactive data visualizations provide easier access to data and support post-processing exploration for easier hypothesis generation [21]. a web application called ngl viewer was developed for the visualization of macromolecular structures. embracing the modern web technologies, the viewer can assist scientists to easily access 3d structural data [22]. a direct-manipulation approach for non-programmers to understand neural networks has been illustrated through an interactive open source visualization called tensorflow playground. this visualization intuitively gives its users a hand-on feel of how neural nets work without any coding [23]. in medical physics, a 3d visualization technique named cinematic rendering has been used to show photorealistic representations of 3d images from traditional ct and mri data [24]. in software engineering, tag cloud has been used as a visualization technique to assist software engineers understand and manage software code [25]. in various studies, visualizations have been used to convey study results and their comparisons in a way that is easily understandable [26-28]. all these works bring to light the data visualization tools in other domains and the technologies employed to create them, whereby some of the technologies could also be applied in the current study. c. web-based visualizations in tanzania in tanzania, a number of visualization tools and interactive dashboards can be currently seen in many web-based systems and portals. the national bureau of statistics has a data visualization section with interactive visualizations for tanzania’s statistics on population, economy, health, environment, agriculture, and education. however, for the case of dropouts, only school dropout status of children with an age above 5 years is shown in numbers with no visualization [12]. the tanzania national health portal of the ministry of health community development gender elderly and children has a data statistics section which contains interactive graphs, charts, and maps for various health statistics [29]. furthermore, the government of tanzania and the world bank have developed dashboards for three sectors: health, water, and education, aiming to support reporting and decision making through interactive mechanisms. regarding the case of education, visualizations for school dropouts are missing [1, 2]. therefore, data visualization has been widely applied in many domains, but in the educational domain the present visualization tools are mostly for e-learning platforms and the moocs. moreover, most visualization tools for education either do not present student dropout data or present only primary school data, or secondary school data or girl dropout data [5, 28, 30]. this study extends the already done works on student dropouts, aiming to develop a visualization tool for presenting both primary and secondary school dropout data. the tool presents dropout data of the whole country at region and district level through maps, and various kind of charts. the tool further allows users to upload their own data and generate visualizations. this tool will help reporting and decision making in student retention issues in tanzania. iii. methods different approaches are widely used in software tool development, utilizing techniques such as, but not limited to, parallel development, prototyping and iterative development [31]. this study used the rapid prototyping approach to develop the web based tool, in which an initial prototype was engineering, technology & applied science research vol. 10, no. 4, 2020, 5967-5973 5969 www.etasr.com kayanda & machuve: a web-based data visualization tool regarding school dropouts and user … developed, evaluated and continuously improved through a number of iterations until the desired outcome was reached. figure 1 shows the stages followed during the development of the visualization tool. fig. 1. development stages of the visualization tool. for this study, secondary data were collected from the united republic of tanzania basic statistics portal and the po-ralg. the collected datasets were .csv files. during data collection, a short interview was conducted at the education department of po-ralg to understand their procedure of data collection, analysis, visualization, and publishing of student dropout statistics. python libraries including pandas, matplotlib, seaborn and bokeh were used to preprocess the data. the resulting datasets, after preprocessing, included two datasets compiled according to level (region-level and councillevel) and two datasets compiled according to category (primary schools and secondary schools). the selected features from the datasets included male enrollment, female enrollment, total enrollment, male dropouts, female dropouts, total dropouts, pupil-teacher ratio (ptr), pupil-qualified teacher ratio (pqtr), pupil-classroom ratio (pcr) and pupil-latrine ratio (plr). the overall design of the data flow and the interactions in the tool are presented in the visualization pipeline shown in figure 2, which is modified from [32, 33]. fig. 2. visualization pipeline. user interactions in the tool are further indicated in the use case diagram in figure 3. the users of the tool include decision makers in the education domain such as education officers, education statistics experts, heads of schools, along with teachers, parents, students, education researchers and any citizen interested in education information. through a web browser, the users can access and view the visualizations using various menus provided in the user interface. users can further upload data and view the resulting visualizations. fig. 3. use case diagram. during the development, a number of tools and technologies were employed including javascript as the development language, react.js for the front-end development and node.js along with express.js for handling the back-end. an online csv to json converter was used to change the preprocessed data to json format, which were further formatted and saved as javascript files inside the project directory. this allowed the data to be imported to the application components easily. focus group discussion was then used to solicit users’ feedback on the developed webbased visualizations from the participants. thirteen participants were selected for the focus group based on their role in basic education and education statistics. questionnaires were used to assess the users’ opinion on the developed visualization tool for the purpose of supplementing on the feedback from the focus group discussion as shown in table i. table i. focus group discussion participants and questionnaire respondents title focus group participants questionnaire respondents principal education officers (peo) 2 2 principal statisticians 1 1 heads of school 4 28 ict officers 4 4 statisticians 2 2 education researchers 4 total 13 41 iv. results and discussion a. results from the developed tool the developed web based tool allowed users to explore student dropout data in various levels and categories through different charts and maps. the first page of the developed tool displays visualizations for student dropout statistics in maps and donut charts. from this page, users can navigate through the tool using the tabs provided at the top of the page and selecting the category in which they want to see the visualizations. the tabs lead users into four main menus which engineering, technology & applied science research vol. 10, no. 4, 2020, 5967-5973 5970 www.etasr.com kayanda & machuve: a web-based data visualization tool regarding school dropouts and user … are home, secondary schools, primary schools and upload data. figures 4-10 show parts of the developed tool. fig. 4. maps showing dropouts in primary and secondary schools. users can move the slider to view dropouts for different years and hover over a specific region to see the exact number. the donut charts below the maps present the dropout reasons. fig. 5. grouped bar chart showing secondary school dropouts in each region by gender. in this case, the user has selected the secondary schools tab, then male/female dropouts and year 2016 from the dropdown list. the name and number of dropouts are displayed when a user hovers over a specific bar. fig. 6. a bubble chart showing primary school dropouts in each district of a selected region in relation to enrollment. the chart appears after a user selects a region and year from the dropdown lists. fig. 7. the upload data section allows a user to upolad data and view them in different visualizations. after uploading a data file, options for selecting chart type and year are provided. fig. 8. the select graph dropdown menu which appears after a file is uploaded. fig. 9. a select year dropdown menu appears after selecting the type of graph. fig. 10. a bar chart showing total dropout in regions after a user uploads data and selects the type of graph and year. in this case, user has selected a total dropout vs region graph and year 2016. b. focus group discussion results during the focus group discussion, all participants generally reported that the data visualization tool was useful for getting a quick impression of the student dropout data. the majority liked the way data were presented in different kinds of charts and in various levels for regions and districts, though the majority suggested that more features should be added to the tool, especially going deeper to school level and including other education data apart from dropouts. to gather more specific information on the developed tool, the discussion was engineering, technology & applied science research vol. 10, no. 4, 2020, 5967-5973 5971 www.etasr.com kayanda & machuve: a web-based data visualization tool regarding school dropouts and user … led by a number of questions. the participants were asked whether they have used a similar tool before, which features they liked or disliked the most, when and how they would use the tool, their suggestions for improvement and what they thought was the most important thing about the developed tool. a few participants stated that they have used a similar tool while the majority replied that they have not. some commented further that even though they have not used a tool like this before, they considered it very helpful in making student dropout data understandable. on the feature preference, the majority liked the way data were presented in bar, pie and bubble charts. one participant commented that “the use of bubble charts helps to quickly compare the dropout rates among districts”. on the contrary another participant commented: “why bubble charts? they are difficult to understand and they need someone to be familiar with them, unlike the other charts such as pie charts with numbers and percentages”. a few suggested the use of “bubbles over maps” instead of just bubble charts. this brings to light that, though data visualization has become inescapably important, some of the current visualization techniques are still unknown and that people prefer viewing data in visualizations that are familiar with. on using the tool, one participant commented: “the tool is very promising in visualization and can further be extended to present data about other situations apart from dropouts and be included in every system”. another noted that, “it is very useful especially when researching issues related to education”. a further comment was that “it can be used when dealing with challenges in education” and “in planning and budgeting” and “to intervene with dropouts and find a solution”. for the improvement of the tool for reporting and decision making, the participants suggested that the tool should incorporate other data, and present them down to school level. one participant noted that: “the tool needs to incorporate feedback to the actions taken, based on the data perceived in the presented visualizations”. the participants were also asked what was the most important thing regarding the visualization tool. apart from the majority that said that the tool was simple and useful, one specifically said that: “the most important issue that i have come up with is that, it is easy for one to get information or data easily if tools like this are made or discovered”. c. questionnaire results the questionnaires for this study were filled on a 5-point scale from strongly agree to strongly disagree. the responses were centered on the ease of use, the usefulness of the tool at respondents’ line of work and at other departments, whether they will recommend it to their colleagues and if they think features should be added or removed. r statistical software was used to analyze the collected data form the questionnaires. on the ease of use, the majority (83%) agreed that the web based tool was easy to use and the rest (17%) strongly agreed that the tool was easy to use. figure 11 shows these responses, describing also the position (title) of the respondents in a stacked bar chart. for the usefulness of the tool, 22% of the respondents strongly agreed that the tool was useful at their line of work, 56% agreed to it, while the rest 22% were neutral as shown in figure 8. this discloses that even though interactive visualizations have been less used in student dropout issues in the context of non-online studying environment, they can yet be applied in this area to inform not only the decision makers but also the society in general. moreover, 49% of the respondents strongly agreed that the tool would be useful to other domains and departments while 32% agreed and 19% were neutral as shown in figure 13. the responses show that, visualizations play an important role for informing all domains of operation. fig. 11. responses on the ease of use. fig. 12. the usefulness of the tool at respondents' line of work. fig. 13. the usefulness of the tool at other organs and departments. engineering, technology & applied science research vol. 10, no. 4, 2020, 5967-5973 5972 www.etasr.com kayanda & machuve: a web-based data visualization tool regarding school dropouts and user … in checking if the tool would be recommendable, 7% of respondents strongly agreed that they would recommend it to their colleagues, 88% agreed that it was recommendable and the remaining 5% were neutral as shown in figure 14. fig. 14. responses on recommending the tool. regarding feature addition, figure 15 shows that the majority (59%) strongly agreed that more features should be added to the tool, the 39%agreed, while 2% of the participants were neutral. fig. 15. responses on the need to add more features. d. further discussion of the results the results from focus group discussion and questionnaires confirm the usefulness of visualization for data presentation and informing decisions not only in school dropout issues but also in other areas of administration. however, the challenges encountered in data preprocessing due to the disparity of data enlightens the need for continuous and comprehensive data collection practices for the purposes of enabling good visualizations which will accurately inform the respective domain. moreover, the results apart from emphasizing on the importance of data visualization, also show that different users have different knowledge, understanding, and preferences on various kinds of visualization techniques, and that, in general, the visualization literacy is still low. therefore, in order to exploit the benefits of data visualization, not only the data are needed, but also awareness of the users on the visualization techniques. v. conclusion and future work the developed visualization tool was generally agreed to be a simple, user friendly, and recommendable way of presenting the large amounts of student dropout data. it was also agreed that it enhanced quick understanding and thus is useful for decision making and reporting. nevertheless, the tool focuses on school dropout data which are only a very small subset of all educational data and presents them only up to council/district level while it does only annual reporting. so, further improvement is required in order to include deeper and wider levels of data and users. moreover, information about other persistent global challenges in the education sector such as poor learning outcomes, equity issues, infrastructure and learning materials, quality of teaching, etc. could be included in the tool for making regional and global comparisons. this study sought to develop a web-based data visualization tool for student dropouts in tanzania, an area which has been less explored and despite the limitations, it stands as a promising tool for informing all areas in education domain. acknowledgment the authors would like to express their gratitude to the african development bank (afdb) for funding this study and the nelson mandela african institution of science and technology (nm-aist) in arusha tanzania. the authors would also like to thank the heads of schools and the poralg staff from the departments of education, statistics and it. references [1] “dropout in primary schools datasets basic statistics tanzania.” http://opendata.go.tz/dataset/wanafunzi-wa-shule-za-msingiwalioachishwa-au-kuacha-shule (accessed oct. 22, 2019). 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[33] j. l. r. tamayo, m. b. hernández, and h. g. gómez, “digital data visualization with interactive and virtual reality tools. review of current state of the art and proposal of a model,” revista icono14 revista científica de comunicación y tecnologías emergentes, vol. 16, no. 2, pp. 40–65, 2018, doi: 10.7195/ri14.v16i2.1174. microsoft word 40-2894_s1_etasr_v9_n4_pp4530-4533 engineering, technology & applied science research vol. 9, no. 4, 2019, 4530-4533 4530 www.etasr.com ghaly: labview based implementation of resistive temperature detector linearization techniques labview based implementation of resistive temperature detector linearization techniques sidi m. ahmed ghaly electrical engineering department college of engineering al imam mohammad ibn saud islamic university (imsiu) riyadh, saudi arabia smghaly@imamu.edu.sa abstract—resistance temperature detectors (rtds) are highquality temperature sensors used for accurate temperature measurements and ideally suited for industrial applications, but their non-linearity is a serious drawback in temperature monitoring in which precise measurement and control are crucial. in this paper, two linearization techniques are implemented in labview environment involving voltage divider and feedback compensation circuits. the presented techniques considerably decrease the effects of non-linearity and may accommodate temperature variations). keywords-rtd; labview; wheatstone bridge; instrumentation amplifier; simulation; sensor i. introduction resistance temperature detectors (rtds), as their name implies, are sensors that measure the temperature by correlating the resistance of the rtd element with it. most rtd elements consist of a certain length of very thin wire surrounded by a ceramic or glass core [1, 2]. the element is usually quite fragile, and it is often placed inside a sheathed probe for protection. the rtd element is made from a pure material, whose resistance to different temperatures has been attested [3, 4]. rtd is one of the most accurate temperature sensors. it offers a good level of accuracy and is extremely stable and reliable. rtds are also relatively insensitive to electrical noise and therefore well suited for temperature measurements in industrial environments, especially around motors, generators and other high voltage equipment. the resistance of an rtd sensor increases with the temperature by about 0.39%/°c, but they have a significant non-linearity of about 0.38% for an interval of 100°c [5]. this non-linearity is often numerically corrected, but there are many applications to correct it analogically. rtds can be used for many industrial applications because they are inexpensive. however, their nonlinear resistance characteristic makes accurate temperature conversion complex. to minimize this difficulty, the rtd’s resistance characteristic should be linearized by placing a thermistor within a resistor divider or with feedback compensation. this linearized response is simpler to convert to a temperature value than the thermistor’s raw response. to obtain an optimum level of linearity, a pair of formulas can be derived as will be explained below. these formulas are useful in determining component values for this common linearization circuit. when the rtd is excited with a voltage source, the resulting rtd voltage is directly proportional to the resistance, producing the same nonlinearity. however, with the use of a resistor divider, wheatstone bridge, or feedback compensation, the non-linearity can be significantly reduced, and this linearization technique can be applied to other resistive sensors, mainly with second-order non-linearity. the law of variation of the resistance with the temperature for the rtd sensors is given by the formula of approximate relation [6]: ���(�) = �� (1 + � � + �� +� (t − 100)��) (1) where a=3.908×10 -3 , b=-5.802×10 -7 and c=0 for t<0. to obtain an rtd resistance that varies almost linearly with temperature, two linearization methods are presented in this paper using the laboratory virtual instrument engineering workbench (labview) environment which allows developing a program for the design and analysis of the rtd linearization circuits [7-9]. firstly, a voltage divider can be used by placing a resistor r in series with the rtd. then, a wheatstone bridge with feedback compensation is implemented. the bridge output varies in a non-linear manner with a variation of temperature of the process parameter, and this non-linearity factor can be eliminated by incorporating feedback in the bridge amplifier or by software means [10]. but for both methods, the combination of resistance tolerance and temperature coefficient defines the resistance against the temperature characteristics for the rtd sensor. the greater the tolerance of the element, the more the sensor will spread a generalized curve, and the more variation it will be to the sensor. this is important for users who need to change or replace sensors and want to minimize systematic errors. this work may offer a beneficial base for engineers who are trying to reduce the cost and time of rtd-related circuits and can also be applied for high precision temperature sensing in mri system applications [11-14]. ii. linearization techniques a. linearization with voltage divider method to obtain an output voltage vo that varies almost linearly with temperature, a voltage divider can be made by placing a corresponding author: sidi m. ahmed ghaly engineering, technology & applied science research vol. 9, no. 4, 2019, 4530-4533 4531 www.etasr.com ghaly: labview based implementation of resistive temperature detector linearization techniques resistor r in series with the rtd [15]. however, the major problem is how to determine the optimal resistance value that will attain the expected linear range. the ratio between the output and the input voltage can be expressed as: �� �� = �(�) = ���� �(�) (2) where m is the ratio of ro to r, and x(t) is the ratio of rtd to ro the function g(t) is represented in figure 1 in terms of temperature for different values of m. the expected temperature range is from 0°c to 180°c. fig. 1. curves of g(t) for different values of m it is clear from figure 1 that as the factor m increases, the linear region decreases and gets limited. the appropriate value of m can be determined to increase the linear region using the second derivative of the function g(t) that can be solved as: ���(�) ��� = � !(") "(��# $(%))� (3) to get a straight-line response for g(t). the appropriate value of m can be found from the following expression: & = � '(��(%�)��)*((��)%)���'+ )4( b. rtd linearization with feedback compensation one of the methods to avoid the non-linearity problem is the use of bridge measurement. wheatstone bridge measurement is an indirect indication of the resistance of the rtd. the bridge requires four connecting wires, an external source, an amplifier, and three resistors that have a temperature coefficient of zero. to avoid subjecting the other three resistors of the bridge to the same temperature, the rtd is separated from the bridge by a pair of connecting wires. these wires recreate the problem of non-linearity: the impedance of the connecting wires affects the reading of the temperature. this effect can be minimized by choosing a large value for the ratio of r1 to r3. however, the sensitivity of the bridge should be decreased, resulting in low bridge output and hence, low resolution. the bridge output voltage vo can be expressed as: ,= � ,./ 01 2"32"3�2�4 −1 2�2��2�45 (5) where rtd is the resistance of the rtd at temperature t, vin is the input voltage, and a is the gain of the amplifier. rearranging (5), the output voltage is expressed in terms of the ratio r1 to r3 as: ,= � vin 91 2"32"3�2�4− 0 ���(:;:<)5= (6) thus, the simple wheatstone bridge creates a non-linear relationship between the resistance change and the bridge voltage change, which requires a feedback compensation scheme that can be used for the linearization of the bridge output. the proposed diagram is shown in figure 2. the bridge output vob is amplified by an instrumentation amplifier of gain a to generate the final output, vo. a part of the output is added to a reference voltage vr using a unity gain adder, and the output of the adder delivers the source excitation, vin [16]. fig. 2. feedback compensation configuration it is clear from the feedback compensation circuit that the output voltage v0 is expressed as: ,= � ,-> = � (,?+ ,�) 91 2"32"3�2�4 − 0 ���1:;:<45= (7) where vg=(r5/(r5+r4)) vo, and vr is the reference voltage. rearranging (7), the output voltage v0 is expressed as: ,= � 1,? + 2@2@�2a ,-491 2"32"3�2�4−0 ���1:;:<45= (8) if the factor of attenuation 5 5 6 r r r+ is chosen such that 5 5 6 ar r r+ equals to 1 1 3 r r + then (8) implies that the feedback scheme of figure 4 provides an amplified output, linearly proportional to the temperature expressed as: ,= � ,? :;:<1��(:;:<)4� (1 � b�� (9) figrue 3 shows the output voltage as a function of temperature for different values of the r1/r3 ratio. a series of simulations were carried out in labview to determine the efficacy of the proposed method and are detailed below. engineering, technology & applied science research vol. 9, no. 4, 2019, 4530-4533 4532 www.etasr.com ghaly: labview based implementation of resistive temperature detector linearization techniques fig. 3. output voltage curves for different values of r1/r3 iii. software development and simulation results the virtual instrument concept that gave labview its name is manifested by the permanence of a graphical interface for each module (function) of a program. the controls and indicators on the front panel are the interfaces through which the program interacts with the user (reading commands and parameters, displaying results). the control-command functions of cards or instruments are the interface through which the program interacts with the editing [7]. both presented linearization techniques were implemented and incorporated into a virtual instrument on the labview environment. figure 4 shows the block diagram of the implementation process. fig. 4. block diagram of the implementation process the implementation includes the specified and defined rtd character and the expected temperature range. also, by the other described conditions, an optimal linear region or solution for linearization can be obtained. finally, the “waveform graph” output on the front panel can display simulation results and temperature plots in the expected range. figures 5 and 6 show the block diagram and the front panel (temperature waveform graph) that follows the divider voltage model presented in figure 1. in this block diagram, three sub virtual instruments (subvis) are created to specify the rtd character and perform the required calculations (optimal value of r and excepted linear region). the program gives the optimal value of r is 50k for linearizing a rtd over the range of 0–180°c. figures 7 and 8 show the block diagram and the interactive user interface of the vi (front panel of the system) that follows the feedback compensation model presented in figure 3. fig. 5. block diagram: voltage divider method it is clear from figure 8 that we can get a straight-line curve of rtd. this linearity is good relatively to the one obtained with the divider voltage method. simulation results show that the non-linearity decreases when the value of amplifier gain increases up to a certain limit. after that limit, non-linearity increases and the change will be on the value of the output voltage since the amplifier gain is multiplied by it and then the relation between temperature and voltage will be changed as shown in figure 9. fig. 6. waveform graph of the output voltage in terms of temperature for divider voltage circuit fig. 7. block diagram: feedback compensation method engineering, technology & applied science research vol. 9, no. 4, 2019, 4530-4533 4533 www.etasr.com ghaly: labview based implementation of resistive temperature detector linearization techniques fig. 8. interactive user interface for feedback compensation method fig. 9. output voltage curves for two values of amplifier gain a with feedback compensation. iv. conclusion rtd linearization has been implemented in labview, using divider voltage and feedback compensation methods. a two-parameter model for rtd was studied and presented to simulate and implement linearization techniques within an expected temperature range from 0°c to 500°c. the linearization error was estimated to be less than 0.5°c. by comparison with a resistance rtd without linearization, this represents an improvement of around 25%, which is very important for industrial applications like thermal compensation and room temperature measurement. as a final conclusion, labview is an effective tool for analyzing rtd to define an optimal value for a resistor used in rtd linearization. references [1] b. e. noltingk, instrumentation reference book, butterworthheinemann, 1988 [2] s. k. sen, “an improved lead wire compensation technique for conventional two-wire resistance temperature detectors (rtds)”, measurement, vol. 39, no. 5, pp. 477–480, 2006 [3] f. n. trofimenkoff, a. e. nordquist, “single amplifier resistance bridges with feedback linearization”, ieee transactions on instrumentation and measurement, vol. 33, no. 1, pp. 60–63, 1984 [4] omega engineering, omega complete temperature measurement handbook and encyclopedia, omega engineering, 1988 [5] b. trump, “analog linearization of resistance temperature detectors”, analog application journal, vol. 4q, pp. 21-24, 2011 [6] s. pradhan, s. sen, “an improved lead compensation technique for three-wire resistance temperature detectors”, ieee transactions on instrumentation and measurement, vol. 48, no. 5, pp. 903-905, 1999 [7] c. j. kalkman, “labview: a software system for data acquisition, data analysis, and instrument control”, journal of clinical monitoring, vol. 11, no. 1, pp. 51-58, 1995 [8] a. gani, m. j. e. salami, “a labview based data acquisition system for vibration monitoring and analysis”, student conference on research and development, shah alam, malaysia, july 17, 2002 [9] f. alorifi, s. m. a. ghaly, m. y. shalaby, m. a. ali, m. o. khan, “analysis and detection of a target gas system based on tdlas & labview”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4196-4199, 2019 [10] s. m. a. ghaly, antennes radiofrequence pour lirm, theorie et application: etude de systemes multispire derives des bobines de helmholtz-application a lirm, editions universitaires europeennes, 2015 [11] s. m. a. ghaly, s. a. sowayan, “a high b1 field homogeneity generation using free element elliptical four-coil system”, american journal of applied sciences, vol. 11, no. 4, pp. 534-540, 2014 [12] s. m. a. ghaly, k. a. a. snaie, s. a. sowayan, “design and testing of radiofrequency spherical”, modern applied science, vol. 10, no. 5, pp. 186-193, 2016 [13] s. m. a. ghaly, k. a. a. snaie, o. k. mohammad, “spherical and improved helmholtz coil with high b1 homogeneity for magnetic resonance imaging”, american journal of applied sciences, vol. 13, no. 12, pp. 1413-1418, 2016 [14] s. m. a. ghaly, k. a. a. snaie, a. m. ali, “design and modeling of a radiofrequency coil derived from a helmholtz structure”, engineering, technology & applied science research, vol. 9, no. 2, pp. 4037-4043, 2019 [15] s. k. sen, t. k. pan, p. ghosal, “an improved lead wire compensation technique for conventional four-wire resistance temperature detectors (rtds)”, measurement, vol. 44, no. 5, pp. 842-846, 2011 [16] p. r. nagarajan, b. george, v. j. kumar, “a linearizing digitizer for wheatstone bridge based signal conditioning of resistive sensors”, ieee sensors journal, vol. 17, no. 6, pp. 1696-1705, 2017 microsoft word 17-3014_s_etasr_v9_n6_pp4962-4967 engineering, technology & applied science research vol. 9, no. 6, 2019, 4962-4967 4962 www.etasr.com nahas & nahas: bandwidth and efficiency enhancement of rectangular patch antenna for shf … bandwidth and efficiency enhancement of rectangular patch antenna for shf applications mousaab m. nahas department of electrical and electronic engineering faculty of engineering university of jeddah jeddah, saudi arabia mnahas1@uj.edu.sa mouaaz nahas department of electrical engineering college of engineering and islamic architecture umm al-qura university makkah, saudi arabia mmnahas@uqu.edu.sa abstract—the microstrip patch antenna is used in various communication applications including cellular phones, satellites, missiles, and radars, due to its several attractive features such as small size and weight, low cost, and easy fabrication. the microstrip patch antenna consists of a top radiating patch, a bottom ground plane, and a dielectric substrate in between. the patch can have different shapes, the rectangular patch being the most commonly used. in practice, the microstrip antenna suffers from narrow bandwidth and low gain efficiency. this paper aims to enhance the bandwidth and efficiency of a rectangular-patch antenna using the high-frequency structure simulator (hfss). initially different patch sizes and substrate materials are investigated and optimal antenna parameters are achieved. then, the antenna performance is further enhanced by inserting single and double slot designs into the patch. two cost-effective feeding methods are involved in the investigation. the antenna is designed to operate in the super high frequency (shf) band. keywords-microstrip patch antenna; microwave; shf; slot i. introduction among various antenna structures, the microstrip patch antenna is the most widely used nowadays because it can be easily installed (due to its low size, weight and cost) and fabricated on a printed circuit board [1, 2]. the microstrip patch antenna is simply a metallic patch placed on a dielectric material and supported by a ground plane. there are different shapes that can be used for the patch, including rectangular, square, circular, triangular, semicircular, elliptical, diamond, hexagonal and bowtie [3]. however, the rectangular patch is the most common antenna geometry which has been extensively investigated [4]. due to its simplicity and other advantages, the microstrip antenna is used for various applications including aircrafts, spacecrafts, satellites, missiles and mobile phones [5, 6]. typically, the antenna is fed by two methods: contacting and non-contacting. contacting method is more attractive because it is easy to model and fabricate and simple to match the impedance. it uses either inset or probe feeding techniques. the inset feeding uses a microstrip line connected to the patch directly, while the probe feeding involves a coaxial cable connected to the ground and extended up to the patch. however, the main disadvantage of the contacting method is that it yields a low frequency bandwidth. non-contacting method involves the coupling of an electromagnetic field between the patch and the microstrip line. although it results in better bandwidth, it is less attractive due to its high cost and difficulty of modeling and fabrication [7]. in effect, the microstrip patch antenna still suffers from narrow bandwidth and low gain efficiency especially in rectangular shape. the bandwidth is typically around 2-5% while the gain is 5-7db by single patch [8]. the reason is that electromagnetic fringing occurs from two sides of the patch only, thus the antenna radiates into half plane. such fringing must be increased to enhance the antenna performance. there are several possible techniques to achieve this, for example, increasing the height (thickness) of the dielectric substrate. however, the thickness must not exceed 0.05λ, above which the antenna stops to radiate due to delivering the power into surface waves instead of transverse waves. other options involve reducing of the dielectric constant or increasing the patch width from which the fringing takes place [8]. in fact, the patch width ultimately controls the radiation pattern as it is inversely proportional to the input impedance and directly proportional to the bandwidth. in contrast, the patch length has no significant contribution to the radiation and it is typically fixed at ~λ/2. however, its optimal value depends on the patch width and substrate parameters. since the patch design, in general, plays important role in the antenna radiation, different patch shapes have been considered to enhance the antenna bandwidth and efficiency [9, 10], though introducing a slot into a simple patch shape is much more practical as it is very easy and can enhance the antenna fringing significantly [3]. therefore, many studies have demonstrated slots in simple rectangular patch, but the maximum bandwidth achieved is still relatively low (< 5ghz) [11-18]. this paper intends to further enhance the bandwidth and gain of the rectangular patch antenna. various design options and their simulation results are demonstrated using the 130ghz frequency range to include the entire shf band. a parametric study is initially performed to introduce a preliminary design, which involves different feeding methods, patch sizes and substrate materials. then, the antenna performance is enhanced by cutting different slot designs into the patch using one and two slots. corresponding author: mousaab m. nahas engineering, technology & applied science research vol. 9, no. 6, 2019, 4962-4967 4963 www.etasr.com nahas & nahas: bandwidth and efficiency enhancement of rectangular patch antenna for shf … ii. preliminary design the preliminary design is based on a parametric study that commences by comparing the inset and coaxial feeding methods using the fr-4 epoxy substrate. then, it goes through a sequence of empirical investigations including patch thickness, patch width, patch length, feedline width, substrate dimensions, and substrate material. as a result, the inset feeding yields higher bandwidth than coaxial feeding (see, for example, figure 1 and figure 5). the patch thickness has a negligible effect on the performance, thus 0.035mm is decided to be used to ensure minimal antenna weight. however, the other parameters affect the radiation where the optimal empirical patch length and width are found to be 6mm and 9mm respectively. these values are in a very good agreement with the calculated ones using 10ghz operation frequency in the following equations [17, 18]: �������� � �� ����� (1) ��������� � ������� � 0.824�!"����#$.%&' () #$. *+,"����-$. ./&'() #$./,0 (2) where εr is the dielectric constant, h is the substrate height, fo is the operation frequency and εeff the effective permittivity that is given by: 12�� � ��#3 4 ��-3 5 3 3#3 ')(,6 (3) the best inset feedline width is empirically ~2.8mm and the optimal substrate dimensions are 35×35×1.5mm. finally, different common substrate materials are compared including bakelite and rt duroid. the detailed results of the comparison are shown in table i. since frequency bandwidth is the most important parameter to consider in our research, rt duroid is decided to be used. however, the minimum reflection coefficient is reasonably low with such a dielectric. table i. dielectric material results substrate material fl (ghz) fh (ghz) bandwidth (ghz) minimum reflection coefficient (db) minimum reflection frequency (ghz) fr-4 epoxy 3.7 10.1 6.4 -32.4 6 bakelite 3.68 10.1 6.42 -27 6.1 rt duroid 4.4 12 7.6 -30.2 6.2 figure 1 shows the top-view design and results of our preliminary antenna using the optimal parameters obtained above. the results are depicted through the s11 curve that shows the power reflection coefficient vs frequency. typically, the acceptable performance corresponds to ≤�10db reflection. it is obvious that the antenna is ultra-wideband (uwb) where the frequency bandwidth reaches 7.6ghz. according to the ieee radio band designations, this antenna is suitable for the c-band (4 to 8ghz) and x-band (7 to 11.2ghz) applications, which involve satellites, wi-fi, cordless telephones, surveillance, radar, and weather radar systems. it is most efficient for the next wi-fi generation [19] since the minimum reflection coefficient reaches −30.2db at around 6ghz frequency. fig. 1. design and results of preliminary rectangular patch antenna iii. enhanced designs and results in this part, slot(s) is (are) added to the patch for further bandwidth and efficiency enhancement. another parametric study is performed on each slot design, including size and position, such that the best design is empirically obtained. single and double slots of the same shape are investigated respectively. finally, the inset feedline is replaced by a coaxial cable for comparison. this is because coaxial feeding is the second easiest feeding method in fabrication after the inset method [7]. a. inset feeding this section presents several slotted designs and their s11 results using inset feeding. figure 2 shows the antenna design and results with a u-slot. the position of the slot center is (−2.5, 0) mm, given that x is the vertical axis, y is the horizontal axis, and negative x is towards the top in our view. the slot width and length are 0.25 and 8mm respectively, while each arm is 1.2mm long. as a result, the bandwidth is increased up to ~9.8ghz but the minimum reflection becomes −27.7db at 6.4ghz. this design is suitable for c-band, x-band and some ku-band (12 to 18ghz) applications where the higher frequency exceeds 14ghz. again, it is most efficient for the next wi-fi generation since the minimum reflection coefficient is still around 6ghz. figure 3 shows the antenna design and results with a rectangular slot. the position of the slot center is (−1, 0) mm, while the slot length is 5.5mm and its width is 0.25mm. obviously, the bandwidth is enhanced to 11.5ghz where the higher frequency reaches ~16.2ghz. this antenna can operate in the c-band, x-band and most of the ku-band which involves satellite broadcast services, space shuttle communication and engineering, technology & applied science research vol. 9, no. 6, 2019, 4962-4967 4964 www.etasr.com nahas & nahas: bandwidth and efficiency enhancement of rectangular patch antenna for shf … international space station (iss) communication. moreover, the minimum reflection of this design is reduced down to −41db at 7ghz, which allows excellent operation in the next wi-fi generation band. fig. 2. rectangular patch with u-slot. design and results fig. 3. rectangular patch with rectangular slot. design and results figure 4 shows the antenna design and results with double rectangular slots. the central position of slot 1 is (−1, 0) mm, the length is 5mm and the width is 0.25mm. the position of slot 2 is (−1.7, 0) mm, the length is 9mm and its width is 0.1mm. the resulting bandwidth is 10.2ghz since the higher frequency becomes less than 15ghz. the minimum reflection coefficient is −25.5db at 6.2ghz. again, this antenna has peak resonance at the next wi-fi generation band, and it is generally suitable for applications of the c-band, x-band and ku-band. fig. 4. rectangular patch with double rectangular slots. design and results in addition, the same procedure is repeated for a rectangular patch with double u-slots. the first slot has the same dimensions and position of the one shown in figure 2. the second slot is located around the origin and its width and length are 0.25mm and 2.5mm respectively. again, the arm length is 1.2mm. as a result, the bandwidth is reduced to 7.1ghz and the minimum reflection becomes −25db at 6ghz. these values are worse than those of the preliminary design although they cover frequencies in the x-, cand ku-bands. this degradation can be understood as some fringing field components cancel each other, resulting in significant reduction of the overall radiation. table ii summarizes the results achieved for the rectangular antenna using inset feeding. obviously, the best design is corresponding to the single rectangular slot where the bandwidth reaches 11.5ghz and the minimum reflection coefficient drops down to −41db at 7ghz. however, other successful designs are achieved with double rectangular slots and single u-slot antenna, where the bandwidth is 10.2 and 9.8ghz respectively. table ii. rectangular patch fed by inset feedline results slot design fl (ghz) fh (ghz) bandwidth (ghz) min. ref. coef. (db) min. ref. freq. (ghz) ieee radio bands without slot 4.4 12 7.6 -30.2 6.2 c, x u-slot 4.7 14.5 9.8 -27.7 6.4 c, x, ku double u-slots 6.3 13.4 7.1 -25 6 c, x, ku rectangular slot 4.7 16.2 11.5 -41 7 c, x, ku double rectangular slots 4.4 14.6 10.2 -25.5 6.2 c, x, ku b. coaxial feeding in this part, the simulation results of using coaxial cable instead of inset feedline are shown. for comparison purposes, the antenna parameters and slots position and size are the same as before. engineering, technology & applied science research vol. 9, no. 6, 2019, 4962-4967 4965 www.etasr.com nahas & nahas: bandwidth and efficiency enhancement of rectangular patch antenna for shf … fig. 5. coaxially-fed rectangular patch without slot. design and results figure 5 shows the design and results of the coaxially-fed antenna without slot. it is obvious that the antenna is no more uwb and becomes multiband, where peak resonance occurs discontinuously for a few specific frequencies at which reflection ≤�10db. the best resonance is at 19.3ghz where the reflection coefficient reaches −40.3db. however, other resonance peaks are observed around 13.7ghz and 25.2−27.3ghz with acceptable reflection coefficient values. this antenna is most efficient for applications operating around 19ghz which belongs in the k-band (18 to 27ghz), which involves satellite, radar, and astronomical applications. the antenna can also operate at other frequencies in the same band including 25.2−27.3ghz. it is also suitable for ku-band applications operating around 14ghz. fig. 6. coaxially-fed rectangular patch with u-slot. design and results figure 6 shows the design and results of the coaxially-fed antenna with u-slot. the best resonance is observed at 19.6ghz where the reflection is −31.4db. moreover, the acceptable reflection is also seen between 25.5 and 29.1ghz where a reflection valley of −20.6db is observed at 27.2ghz. again, this design is most efficient for applications operating around 19ghz in the k-band. however, the resonance is expanded to include frequencies in the ka-band (26.5 to 40ghz), which is used for satellite communications and is also considered as the future spectrum for nasa communications. figure 7 shows the design and results of a coaxial patch antenna with a rectangular slot. the best reflection in the results reaches −38db at 13ghz. other resonance peaks are obtained at 19.4 and 26.1ghz where the reflection is −26.8 and −29.8db respectively. however, the antenna has continuous low reflection (≤−10db) between 24.6 and 28ghz. obviously, the results are enhanced by this design as the antenna becomes efficient for applications operating around 13ghz in the kuband, 19ghz in the k-band and 26ghz in the ka-band. it is also suitable for operation between 24.6 and 28ghz. fig. 7. coaxially-fed rectangular patch with a rectangular slot. design and results figure 8 shows the design and results of a coaxial patch antenna with double rectangular slots. as a result, resonance peaks are observed at 19.7 and 26.6ghz whose reflections are �26.3 and −22.7db respectively. moreover, the antenna has an acceptable reflection in the 24.5−28.9ghz range. this antenna is efficient for applications at 19.7 and 26.6ghz which are in the kand ka-band respectively. it is also suitable for any application between 24.5 and 29ghz. the same procedure is repeated for a coaxially-fed patch with double u-slots. unfortunately, the reflection never drops below −10db, hence no resonance is observed. this is due to field opposition and cancellation that arises from the slots. table iii summarizes the results achieved for our coaxiallyfed antenna. the best multiband design is corresponding to the single rectangular slot where three reflection valleys are obtained at 13, 19.4 and 26.1ghz. an additional operating band is also seen between 24.6 and 28ghz. engineering, technology & applied science research vol. 9, no. 6, 2019, 4962-4967 4966 www.etasr.com nahas & nahas: bandwidth and efficiency enhancement of rectangular patch antenna for shf … fig. 8. coaxially-fed rectangular patch with double rectangular slots. design and results table iii. rectangular patch fed by coaxial cable results slot design min. ref. coef. (db) min. ref. freq. (ghz) 2nd res. (ghz) 3rd res. (ghz) additional resonance (ghz) ieee radio bands without slot -40.3 19.3 13.7, 25.2-27.3 ku, k u-slot -31.4 19.6 27.2 25.5-29.1 k, ka double u-slots rectangular slot -38 13 19.4 26.1 24.6-28 ku, k, ka double rectangular slots -26.3 19.7 26.6 24.5-28.9 k, ka iv. conclusions this paper explored ways for enhancing the bandwidth and efficiency of a simple rectangular patch antenna using hfss. at first, a preliminary design was introduced via optimizing the patch size and substrate material parameters. further improvement was obtained by inserting different shapes of single and double slots into the patch. a comparison of two feeding methods was also carried out using inset and coaxial feeding. the results showed that the inset feeding is a better option as far as the frequency bandwidth is concerned. however, it was also proven that inserting slot(s) would improve the overall antenna performance significantly. in specific, a uwb antenna was successfully designed for shf applications with 11.5ghz bandwidth using a single rectangular slot. other uwb designs were also obtained with 10.2 and 9.8ghz bandwidth using double rectangular slots and single u-slot respectively. these designs are suitable for applications in the c-, xand ku-band. in addition, successful designs of multiband antenna using coaxial feeding along with a slotted patch were shown. such antennas are efficient for operation at discrete frequencies, where the best design covers applications in the ku-, kand ka-bands operating around 13, 19 and 26ghz respectively. they are also suitable for applications between 24.6 and 28ghz. however, the uwb results achieved by inset feeding are the most attractive ones in this research. acknowledgment the authors would like to thank ali al-yahyaoui and madi al-hazmi for their valuable assistance during this research. references [1] n. singh, s. kumar, b. k. kanaujia, “a new trend to power up nextgeneration internet of things (iot) devices:‘rectenna’”, in: energy conservation for iot devices, pp. 331–356, springer, 2019 [2] a. joret, m. f. l. abdullah, m. s. sulong, “simulation of gpr system design using cst microwave and matlab”, yanbu journal of engineering and science, vol. 14, pp. 49–57, 2017 [3] v. p. patil, “enhancement of bandwidth of rectangular patch antenna using two square slots techniques”, international journal of engineering sciences & emerging technologies, vol. 3, no. 2, pp. 1–12, 2012 [4] s. chattopadhyay, m. biswas, j. y. siddiqui, d. guha, “cad of mechanically tunable rectangular microstrip patch with variable aspect ratio”, ieee applied electromagnetics conference, kolkata, india, december 19-20, 2007 [5] s. r. emadian, j. ahmadi-shokouh, “very small dual band-notched rectangular slot antenna with enhanced impedance bandwidth”, ieee transactions on antennas and propagation, vol. 63, no. 10, pp. 4529– 4534, 2015 [6] m. u. khan, m. s. sharawi, r. mittra, “microstrip patch antenna miniaturisation techniques: a review”, iet microwaves, antennas & propagation, vol. 9, no. 9, pp. 913–922, 2015 [7] a. kumar, j. kaur, r. singh, “performance analysis of different feeding techniques”, international journal of emerging technology and advanced engineering, vol. 3, no. 3, pp. 884–890, 2013 [8] a. chaudhary, d. c. dhukaiya, “analysis and bandwidth enhancement by cutting pi and rectangular slot in rectangular mictrostrip antenna for broadband applications”, international journal of enhanced research in science technology & engineering, vol. 3, no. 1, pp. 431-437, 2014 [9] k. n. lal, a. k. singh, “modified design of microstrip patch antenna for wimax communication system”, 2014 ieee students’ technology symposium, kharagpur, india, february 28-march 2, 2014 [10] s. mahmoud, w. swelam, m. hassan, “parametric study of slotted ground microstrip patch antenna”, iosr journal of electronics and communication engineering, vol. 11, no. 1, pp. 1–8, 2016 [11] h. f. abu tarboush, h. s. al-raweshidy, r. nilavalan, “bandwidth enhancement for microstrip patch antenna using stacked patch and slot”, 2009 ieee international workshop on antenna technology, santa monica, usa, march 2-4, 2009 [12] r. j. chitra, v. nagarajan, “double l-slot microstrip patch antenna array for wimax and wlan applications”, computers & electrical engineering, vol. 39, no. 3, pp. 1026–1041, 2013 [13] l. agarwal, s. gandhi, s. malik, s. vijay, t. s. chauhan, “design and analysis of rectangular patch with square slots”, international journal of scientific research and management studies, vol. 3, no. 1, pp. 15–20 [14] k. f. tong, k. m. luk, k. f. lee, r. q. lee, “a broad-band u-slot rectangular patch antenna on a microwave substrate”, ieee transactions on antennas and propagation, vol. 48, no. 6, pp. 954–960, 2000 [15] s. chatterjee, “compact microstrip patch antenna for microwave communication”, indian journal of pure & applied physics, vol. 51, no. 11, pp. 800–807, 2016 engineering, technology & applied science research vol. 9, no. 6, 2019, 4962-4967 4967 www.etasr.com nahas & nahas: bandwidth and efficiency enhancement of rectangular patch antenna for shf … [16] g. chaouki, n. omrane, g. said, g. ali, “an electrical model to u-slot patch antenna with circular polarization”, international journal of advanced computer science and applications, vol. 8, no. 3, pp. 62-66, 2017 [17] a. rani, r. k. dawre, “design and analysis of rectangular and u slotted patch for satellite communication”, international journal of computer applications, vol. 12, no. 7, pp. 36-40, 2010 [18] a. burcakbas, s. soylu, b. bektas, s. t. imeci, “square shape patch antenna with triangular slot”, 2017 international applied computational electromagnetics society symposium, firenze, italy, march 26-30, 2017 [19] m. s. afaqui, e. garcia-villegas, e. lopez-aguilera, “ieee 802.11ax: challenges and requirements for future high efficiency wifi”, ieee wireless communications, vol. 24, no. 3, pp. 130–137, 2017 microsoft word 44-2710_s1_etasr_v9_n3_pp4306-4309 engineering, technology & applied science research vol. 9, no. 3, 2019, 4306-4309 4306 www.etasr.com kazi et al.: development of vinyl ester and reed composite material with weight fraction of 10% … development of vinyl ester and reed composite material with weight fraction of 10% and reinforcement at different orientations qamar abbas kazi department of mechanical engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan qaziqamarabbas@yahoo.com qadir bakhsh jamali department of mechanical engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan jamali_sattar@quest.edu.pk m. t. bhatti department of mechanical engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan trqbhatti@quest.edu.pk umair ahmed rajput department of mechanical engineering, quaid-e-awam university college of engineering, science & technology, nawabshah, pakistan engr.umair@quest.edu.pk ishfaque ali kazi department of mechanical engineering, quaid-e-awam university of engineering, science & technology, larkana, pakistan ishfaquealiqazi@gmail.com shafquat hussain solangi department of mechanical engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan shafquat13me31@gmail.com abstract—composite materials have been used to resolve industrial problems. considerable attention from the industrial side started in the 1960s with the introduction of polymer-based composite materials. their advantages such as low weight (density), resistance to corrosion, high strength and low maintenance cost made composite materials an attractive substitute to conventional materials. a new composite material was developed with 10% natural fiber at 0 o , 90 o and 0/90 o orientations resulting in ample improvements in the mechanical properties as compared to previous studies. the sample at 0/90 o orientation gives the best results with tensile, tensile strength, tensile elongation and young’s modulus values of 2458.19n, 4594.5mpa, 4.7% and 23.0 respectively. keywords-composite material; natural fiber; vinyl ester; reed plant i. introduction composite materials have been used to resolve industrial problems. considerable attention from the industrial side started in the ‘60s with the introduction of polymer-based composite materials. since then composite materials have been used in the field of engineering. features like better formability, low cost, renewability and eco-friendliness can be achieved by natural fiber reinforced composites and these composites play an important role in commercial engineering sectors [1]. the maximum strength initially decreases until critical point and then increases with duration of treatment while conducting tensile behavioral study of the natural fiber reinforced polymer matrix base composites. ultimate and failure stresses decreased with increase in the weight percentage of cashew-nut shells resin [2]. the natural fiber reinforced composites satisfy the required specifications in tribological applications. the results reflect that these composites can be comparable with conventional fibers, having additionally fiber treatment and fiber orientation [3]. a vacuum assisted resin transfer molding (vartm) system was developed in [4] for testing the mechanical properties of a composite material. the results reflect that the developed composite material specimen acquired significant enhancement in mechanical properties by adding cotton fabric as a reinforcement agent. properties (tensile strength, young’s modulus, break elongation and shear modulus) were improved considerably. it was also observed that the developed material was of ductile nature and exhibited improved mechanical properties with closely related developed composite materials. corresponding author: qamar abbas kazi engineering, technology & applied science research vol. 9, no. 3, 2019, 4306-4309 4307 www.etasr.com kazi et al.: development of vinyl ester and reed composite material with weight fraction of 10% … authors in [5] conducted research on cotton fiber as reinforcing agent. cotton fibber reinforced composite specimens were examined with the help of hand layup process. samples possessed significant improvement in mechanical properties. in [6], cotton fabric (2/2 plain weave 0/90 o oriented) was used as reinforcement agent with matrix material to develop samples, which were tested to study its effect as reinforcing agent. the result showed the tensile strength improved as much as 11 times, modulus of elasticity (moe) was increased up to 5.7 times, and break elongation decreased by 0.6%. in [4], the development of one layer, two-layer and four-layer composite material specimen by using vartm showed that the increasing number of lamination (1l, 2l, and 4l) in developed composite specimen acquired major enhancement in tensile properties. reed family natural fiber is a green color long fiber grass which is cultivated naturally at the banks of indus river and in water storages like fish farms. it has no need of plantation or other fertilizer for its growth and after cutting it grows back quickly. reed family is plant shown in figure 1. fig. 1. reed family natural fiber grown on indus river the utilization of environment-friendly composites is due to their advantages like good specific strength, less cost, lower pollutant emissions, and fine energy recovery. in this connection researchers developed composites by using unidirectional compressed jute fiber sheets as reinforcement agent with matrix material (unsaturated polyester resin) and it was found that the composites made from raw jute have higher tensile and flexural properties compared to the composites made from jute sliver [7]. composites can be developed by using epoxy novolac resin [8]. the composite possesses the desired and preferred properties by coalescing dissimilar constituents in a cautious and judicious way. generally, they possess higher specific modulus and high specific strength enabling them as valuable material in a huge number of industrialized requests which require such features [9]. the composites possess the desired and preferred properties by coalescing dissimilar constituents in a cautious and judicious way. generally, they possess higher specific modulus and high specific strength enabling them as a valuable material in a huge number of industrialized requests which requires such features [10-11]. in this study a composite material was developed using natural fiber reinforcement in brass metal to improve its mechanical properties. ii. materials and methods brass was used as base metal with dimensions 177.8mm length, 50.8mm width. after machining process, the base metal was cut into a mold cavity with dimensions of 152.4mm length, 25.4mm width and 8mm depth at a distance of 12.7mm from all four edges with the help of vertical milling machine. furthermore, for setting natural fibers in the base metal, 5mm thick slots were made at 0 o , 90 o and 0/90 o orientations as shown in figure 2. after mold developing, vinyl ester resin as a matrix material was transferred in the mold for sampling with total weight 200g for pure ve specimen and 10% natural fiber as a reinforcing agent. after curing the specimens were de-molded properly and prepared for testing. fig. 2. mold’s design iii. results a. pure vinyl ester the pure vinyl ester resins were tested on an sstm 20 kn tensile testing machine for mechanical properties. tensile properties of pure vinyl ester resin samples were tested before adding reed fibers. table i shows the values of tensile characteristics of the matrix material. it was observed that at maximum tensile load of 2116.6n, the material shows maximum tensile strength of 3955.7mpa, modulus of elasticity has observed as 22.2mpa, and tensile elongation was 3.3%. b. 10% reinforced vinyl ester in this setup, the tested samples were reinforced by 10% reed natural fiber (pal) at 0 o , 90 o and 0/90 o orientations. tables ii-iv show the obtained tensile characteristics for 0 o , 90 o and 0/90 o orientations respectively. in table ii, the result reflects composite specimens reinforced with 10% reed family natural fiber (pal) at 0 0 orientation. standard parameters at maximum tensile load of 2394.1n were: maximum tensile strength of 4474.6mpa, modulus of elasticity 22.6mpa, and 4.2% tensile elongation. similarly, composite specimens engineering, technology & applied science research vol. 9, no. 3, 2019, 4306-4309 4308 www.etasr.com kazi et al.: development of vinyl ester and reed composite material with weight fraction of 10% … reinforced with 10% reed natural fiber (pal) at 90 o results are shown in table iii. it was observed that at tensile load of 1925.8n, the tensile strength was 3599.4mpa, moe was 19.1mpa, and tensile elongation was 4.4%. in the same way the composite specimens reinforced with 10% reed family natural fiber (pal) at 0/90 0 orientation can be seen in table iv. it was observed that at tensile load of 2458.2n, the tensile strength obtained was 4594.5mpa, moe was 23.0mpa, and tensile elongation was 4.7%. table i. characteristics of pure vinyl ester composites pure vinyl ester strip 1 strip 2 strip 3 mean yield (n) 1798.54 1800.29 1798.78 1799.2 yield strength (mpa) 2670.83 2672.58 2671.07 2671.5 tensile (n) 2115.93 2117.68 2116.17 2116.6 tensile strength (mpa) 3955.00 3956.75 3955.24 3955.7 moe (mpa) 21.33 23.83 21.52 22.2 break elongation (%) 3.46 2.87 3.43 3.3 yield elongation (%) 2.56 2.30 2.54 2.5 tensile elongation (%) 3.46 2.87 3.43 3.3 linear strain 0.03 0.03 0.03 0.03 lateral strain 0.03 0.02 0.03 0.02 poisson’s ratio 0.74 0.80 0.74 0.76 energy of material (u) (j) 216.92 194.49 194.74 202.05 table ii. results for 10% reinforced composite at 0o 10% at 0 o strip 1 strip 2 strip 3 mean yield strength (mpa) 3021.51 3022.26 3021.75 3021.8 tensile (n) 2393.75 2394.50 2393.99 2394.1 break elongation (%) 4.44 3.85 4.21 4.2 yield elongation (%) 2.86 2.66 2.72 2.7 yield (n) 2034.68 2035.43 2034.92 2035.0 linear strain 0.04 0.04 0.04 0.04 lateral strain 0.03 0.03 0.03 0.03 poisson’s ratio 0.65 0.69 0.65 0.66 energy of material (u) (j) 274.28 254.31 254.56 261.05 table iii. results for 10% reinforced composites at 90o 10% 90 0 strip 1 strip 2 strip 3 mean yield strength (mpa) 2430.45 2431.20 2430.69 2430.8 tensile (n) 1925.49 1926.24 1925.73 1925.8 break elongation (%) 3.99 4.35 4.71 4.4 yield elongation (%) 2.05 2.81 3.25 2.7 yield (n) 1636.67 1637.42 1636.91 1637.0 linear strain 0.04 0.04 0.05 0.043 lateral strain 0.02 0.03 0.03 0.03 poisson’s ratio 0.51 0.65 0.69 0.62 energy of material (u) (j) 157.59 216.24 216.49 196.77 the graphical presentation of the comparison of tensile tests of 10% reed family natural fiber reinforced between 0 0 , 90 0 and 0/90 0 orientations is shown in figure 3. tensile characteristics of composite specimens reinforced with 10% reed natural fibers (pal) at 0/90 o orientation in matrix material are greater than the specimens developed at 0 o and 90 o . the increments are 13.11%, 9.01% and 16.14% in tensile (n), 13.12%, 9.01% and 16.15% in tensile strength, while the enhancement seen in moe was 1.45%, 13.97% and 3.45%. variation of 28.07%, 33.71% and 45.70% was also observed in tensile elongation (%) at samples reinforced at 0 o , 90 o and 0/90 o orientations respectively against pure vinyl ester specimens. table iv. results for 10% reinforced composite at 0/90o 10% at 0/90 o strip 1 strip 2 strip 3 mean yield strength (mpa) 3102.43 3103.18 3102.67 3102.8 tensile (n) 2457.86 2458.61 2458.10 2458.2 break elongation (%) 4.78 4.54 4.90 4.7 yield elongation (%) 2.45 2.93 2.97 2.8 yield (n) 2089.18 2089.93 2089.42 2089.5 linear strain 0.05 0.05 0.05 0.05 lateral strain 0.02 0.03 0.03 0.03 poisson’s ratio 0.51 0.65 0.61 0.59 energy of material (u) (j) 241.00 288.05 288.30 272.45 (a) (b) (c) fig. 3. comparison of (a) tensile strength, (b) yield strength, and (c) modulus of elasticity iv. discussion natural fiber reinforced composite materials play a vital role in today’s competitive marketing ranking. a new material was developed with natural reed fibers at different orientations in vinyl ester polymer matrix and was checked through sstm20kn. the developed reinforced material is comparative to other natural fibers like abaca, bagasse, bamboo, etc. [12]. after the pure matrix was embedded with 10% reinforcing agent at 0 o , the tensile parameters increased gradually, while specimens at 90 o showed decreasing results. the specimen engineering, technology & applied science research vol. 9, no. 3, 2019, 4306-4309 4309 www.etasr.com kazi et al.: development of vinyl ester and reed composite material with weight fraction of 10% … developed in woven form oriented at 0/90 o was tested at the same machine and gave better results than the other specimens. (a) (b) (c) (d) fig. 4. comparison of pure ve with 10% reed family natural fiber (pal) reinforced at 0 o , 90 o and 0/90 o orientations v. conclusion the developed composite materials are capable of being utilized as a substitute of expensive materials like metal and ceramic, which have much more weight and require maximum processing technology. in order to provide better alternatives, the natural fiber reinforced composite material was developed and tested at 10% weight fraction with different orientations, 0 o , 90 o and 0/90 o and it was found that at 0/90 o the results of tensile force, tensile strength, moe, and tensile elongation are better when compared to other natural fibers or petroleum based composite materials like carbon and glass fibers. the results obtained during analysis for tensile load, tensile strength, tensile elongation and moe were 2458.19 n, 4594 mp, 4.7% and 23.0 respectively. acknowledgment the authors would like to thank the department of mechanical engineering, quaid-e-awam university of engineering, science and technology nawabshah for providing the experimental work facilities. references [1] m. r. sanjay, g. r. arpitha, l. l. naik, k. gopalakrishna, b. yogesha, “applications of natural fiber and its composites: an overview”, natural resources, vol. 7, pp. 108-114, 2016 [2] g. venkatachalam, s. c. renjith, n. s. patel, m. vasan, r. a. a. rajan, “investigations into tensile strength of banana fibre reinforced hybrid polymer matrix composites”, engineering review, vol. 36, no. 1, pp. 13-18, 2016 [3] e. omrani, p. l. menezes, p. k. rohatagi, “state of the art on tribological behavior of polymer matrix composites reinforced with natural fibers in the green material world”, engineering science and technology, vol. 19, no. 2, pp. 711-736, 2016 [4] m. a. lakho, a. h. rajpar, a. l. manganhar, “mechanical characterization of locally developed composite materials”, 1st national conference on modern trends & techniques in mechanical engineering & management, sindh, pakistan, february 12-13, 2015 [5] a. h. rajpar, a. l. manganhar, s. a. shah, “mechanical characterization of cotton/polyester composite materials”, mehran university research journal of engineering & technology, vol. 33, no. 2, pp. 227-238, 2014 [6] m. a. lakho, a. h. rajar, a. l. manganhar “laminate effect on tensile behaviour of locally developed composite materials”, 1st national conference on intelligent manufacturing & sustainable energy systems, khairpur mir’s, pakistan, october 6-7, 2015 [7] s. das, m. bhowmick, “mechanical properties of unidirectional jutepolyester composite”, journal of textile science and engineering, vol. 5, no. 4, pp. 1-6, 2015 [8] s. k. saw, k. akhtar, n. yadav, a. k. singh, “hybrid composites made from jute/coir fibbers water absorption thickness swelling density morphology and mechanical properties”, journal of natural fibbers, vol. 11, no. 1, pp. 39-53, 2014 [9] z. n. azwa, b. f. yousif, “characteristics of kenaf fibre/epoxy composites subjected to thermal degradation”, polymer degradation and stability, vol. 98, no. 12, pp. 2752-2759, 2013 [10] s. nunna, p. r. chandra, s. shrivastava, a. k. jalan, “a review on mechanical behaviour of natural fiber based hybrid composites”, journal of reinforced plastics and composites, vol. 31, no. 11, pp. 759-769, 2012 [11] s. ramakrishan, k. krishnamurthy, m. m. parsath, r. s. kumar, m. dharmaraj, k. gowthaman, p. s. kumar, r. rajasekar, “theoretical prediction on mechanical behavior of natural fiber reinforced vinyl ester composite”, applied science and advanced materials international, vol. 1, no. 3, pp. 85-92, 2015 microsoft word 40-3703l_s_etasr_v10_n4_pp6126-6130 engineering, technology & applied science research vol. 10, no. 4, 2020, 6126-6130 6126 www.etasr.com khalifa: simulation of dissolved oxygen and dissolved substrate for hasel river simulation of dissolved oxygen and dissolved substrate for hasel river walid m. a. khalifa civil engineering department hail university, saudi arabia and fayoum university, egypt khalifawalid@yahoo.com abstract—hasel is considered a moderately polluted river in germany. this study investigated its water quality, examining dissolved oxygen (do) and dissolved substrate (cod) with the use of aquasim. the calibration procedure used observed data from various locations along the river. the model’s calibration was used to study the response of hasel river to the effluents of wastewater treatment plants and sewer overflow emissions. results revealed that high emissions from sewerage systems may reduce the oxygen concentration to low levels. furthermore, joined sewer overflows may disrupt the oxygen levels for a long period. in addition, oxygen was over saturation in some periods of the calibration period. the proposed model can be utilized in future analyses, improving the functional understanding of ecological processes in rivers and the identification of ecological effective management strategies. keywords-water quality models; rivers; dissolved oxygen; eutrophication; impact assessment i. introduction most water quality models are flexible to several environments and subjected to proper definitions of boundary conditions, dimensional variation, and factor characterization. the basic goal of river water quality models (rwqms) is to simulate the spatial-temporal effect of organic pollution on oxygen level, because of its significance for aquatic life. the streeter-phelps model, which describes the balance between deoxygenation and reaeration, was presented in [1]. another important example of rwqm is the simulation of toxic substances, such as organic chemicals or heavy metals, via the wasp model package [2]. the aquatic simulation (aquasim) program [3] was designed for creating standardized and consistent river water quality models. besides the fundamentals of biochemical conversion processes, the structure of compartments of flowing water ecosystems was examined in [4], including the longitudinal, vertical, and lateral zonation patterns. this aspect has not gained much attention in river water quality modeling so far [5], while it should be examined in order to attain an ecologically convenient choice of model compartments and state variables [6, 7]. streaming waters are linked elements within the hydrological continuum [8-10]. as a result, the hydrological interactions between water compartments are important, as they influence the transport and storage of water, chemical compounds, and nutrients [11-13]. quantifying the prominence of the exchange processes is complex, due to high spatial and temporal variations of the hydrological system based on a set of factors such as river morphology and hydraulic gradients [14-17]. furthermore, rivers’ dynamics are shaped by a complicated temporal style, due to daily and seasonal changes in trophic and respiration activities [18-22]. this complexity may be narrowed by analyzing the relevance of temporal dynamics of water constituents in a eutrophic shallow river [5]. this case study considered the hasel river in germany. its main goal was to analyze the oxygen concentrations as one of the water quality parameters using an aquasim model [23], and discuss the future river water quality management. ii. materials and methods a. study site hasel river is a right-sided tributary in the middle reach of werra river, located in thuringia, germany between 10°28ʹ and 10°47ʹe longitude and 50°32ʹ and 50°38ʹn latitude. its total length is 25km, and it is divided into four reaches coming from four catchment areas of 321km 2 , having an average gradient of 2‰. the first reach has a length of 6.0km and an average discharge of 1.54m³/s. the second reach has a length of 9.25km, and the catchment area discharges 0.02m³/s in average. the third reach has 2.75km length, and its catchment area brings an average discharge of 3.01m³/s. the fourth reach has 7km length, and its catchment area has an average discharge of 0.01m³/s. this study selected five trapezoidal cross-sections in the boundaries of the four reaches, with surface width ranging from 0.70m at the spring to 11.00m at the mouth. hasel river is affected by the influx of the wastewater treatment plants at suhl and rohr, located at 19.3km and 6.1km upstream (us) its mouth, respectively. the suhl plant, serving 48,000 inhabitants, discharges directly us the first reach terminal, while the rohr plant, serving 300 inhabitants, discharges downstream (ds) the third reach terminal [24]. the temporal and spatial dynamics of flow and physico-chemical parameters were measured during 1990-2001 by thüringen landesamstadt für umwelt und geologie, tlug (national thuringia town of environment and geology, germany). the surface water body was measured nearly every month in monitoring stations at ellinghausen, diezhausen, and simon (2.99, 14.6, 17.9km upstream the mouth respectively) for ph, oxygen, cod, bod, on, nh4, no2, no3, op, opo4. temperature and light intensity were measured daily in 2001. corresponding author: walid m. a. khalifa engineering, technology & applied science research vol. 10, no. 4, 2020, 6126-6130 6127 www.etasr.com khalifa: simulation of dissolved oxygen and dissolved substrate for hasel river b. modeling approach one-dimensional river hydraulics can be described by a set of two partial differential equations representing mass and momentum balance. the two most important approximations to these equations, the kinematic and diffusive wave [25], are implemented in aquasim to describe river hydraulics. the equations for river hydraulics are coupled with advectiondiffusion equations to describe the transport of dissolved or suspended substances in the water, leading to the following set of differential equations. the first equation describes the water flow through the compartment as: �� �� � �� �� � � (1) the temporal change in the immersed cross-sectional area a, is determined by the spatial gradient of the discharge q and the lateral inflow q. the behavior of the substances transported with the water flow is described by: �� �� � � �� �� �� � �� ���� �� ������� (2) the concentration is affected by four terms: advection with the water flow, longitudinal dispersion, transformation processes, and lateral inflow or outflow. in order to combine the above system of differential equations, one boundary condition is necessary for (1), and two boundary conditions are required for (2). the boundary condition for (1) that describes the discharge through river’s sections at the start point xs is: ����� � ��� (3) the boundary conditions for (2) are given by the continuity of the substance mass flows entering the river section and a transmission boundary condition [26] at the compartment end: ����� �� � �� � ���, (4) �� ��� � 0 (5) where iin,c is the total mass input of substances, described by the concentration c per unit of time. equation (5) is omitted for dispersion-free transport. the longitudinal dispersion coefficient in (2) is estimated according to [27], as: � � �� �!� "∗$ (6) where cf is a non-dimensional dispersion coefficient, w is the surface width of the river, d is the mean river depth, and %∗ � &'(�� is the friction velocity. the empirical expression (7) is used to calculate the friction slope: �� � ) *+,� ) -./0 12 (7) where kst is the friction coefficient according to strickler, r is the hydraulic radius of the river, and v is the average crosssectional flow velocity. c. modeling of oxygen series the oxygen balance of hasel river is characterized by high daily and seasonal temporal dynamics triggered from radiation and intense production-respiration processes. according to (2), it can be modeled with a simple version of aquasim using: � � 32� �4� 52�� 67 $ $ 3$89 :� *:�; :� <= (8) where r is the net oxygen production rate, k2 is the reaeration rate constant, csat is the oxygen saturation concentration, co2 is the oxygen concentration, i is the light intensity, d is the mean river depth, p and r are production and respiration parameters respectively, kdeg is the degradation rate constant, ko2 is the half saturation concentration with respect to oxygen, and cod is the concentration of substrates. iii. results and discussion a. verification of hydraulic model the study of hasel river was modeled using cross-section profiles throughout river’s length, a constant slope, and an effective coefficient through every reach. all simulations were performed using an extended version of aquasim [3, 28-30]. the calibration of the effective strickler friction coefficient in the four reaches of hasel river (kst,i, kst,ii, kst,iii, and kst,iv) was performed according to the tlug estimated values. the non-dimensional dispersion coefficient cf had a constant value based on the tracer transients in a water column [5]. the estimated parameters are given in table i. figure 1 shows the water level profile of hasel river. hydraulic height gradients through the four reaches and the calculated longitudinal water surface profile were in acceptable agreement. table i. hydraulic parameters estimates parameter unit value kst,i m 1/3 s -1 40.0 kst,ii m 1/3 s -1 35.0 kst,iii m 1/3 s -1 30.0 kst,iv m 1/3 s -1 32.5 cf 0.006 fig. 1. profile of water levels of hasel river. b. verification of dissolved oxygen model estimates for physical reaeration were based on empirical assessments [31, 32], considering the given flow velocities and water depths for the investigated time periods. empirical formulas resulted in k2-values ranging between 17.0 and 29.0d -1 . a value of k2=20d -1 was selected for model calculations. the oxygen saturation concentration formula is given in [33]. based on these boundary conditions, production and respiration rate parameters were estimated from continuously measured oxygen time series (table ii). in [34], an approximate value of kdeg was reported ranging between 0.5 and 3.0d -1 . engineering, technology & applied science research vol. 10, no. 4, 2020, 6126-6130 6128 www.etasr.com khalifa: simulation of dissolved oxygen and dissolved substrate for hasel river table ii. parameter estimates from oxygen time series parameter unit value std. dev. p g/(wd) 0.10097 0.0006 r g/(m 2 d) 11.27 0.06 fig. 2. oxygen time series for hasel river. the effect of the effluents on oxygen concentration in the river is based on a degradation rate coefficient of 1.0d -1 . figure 2 shows the concentration of oxygen at five sections of hasel river at the boundaries of the river reaches. this method achieved a meaningful agreement between measured and calculated oxygen concentrations. despite the enhanced gas exchange with the atmosphere, due to low depth and turbulent flow, daily oxygen amplitudes highly exceeded saturation up to 6mg/l in may-august 2001, while oxygen deficits were almost equal pronounced. these patterns were still existent in the remaining period of 2001, but in a more narrow range of oxygen concentrations. in addition, the concentrations of oxygen were validated for the mouth with data from [35]. when considering the oxygen balance in shallow eutrophic rivers, one important concern is the over-saturation which leads to gas-blisters in fishes. according to the european classification of water quality in water bodies, table iii shows the trophic state of hasel river [36-38]. as it is evident, hasel river is moderately polluted except some locations such as near the waste water treatment plant at suhl. table iii. trophic status for hasel river cross-sectional locations* o2-saturation % trophic state 19.30km (suhl) 132.53 eutrophic 19.00km 120.37 mesotrophic 9.75km 116.74 mesotrophic 7.00km 119.08 mesotrophic 0.00km (mouth) 107.92 mesotrophic * the locations are measured us of the mouth. c. system response to inputs of organic matter the sewage treatment plant at suhl is at x=19300m, having a mean dry weather discharge of 0.07m 3 /s and a mean cod of 77.3mg/l. the sewage treatment plant at rohr is at x=6100m, having a mean dry weather discharge of 0.004m 3 /s and a mean cod of 50mg/l. in addition, there is a sewer overflow at x=20600m with a mean cod of 125mg/l. in order to examine the pollution load impact, oxygen concentrations were calculated at x=19200m, 100m ds the sewage treatment plant effluent at suhl, under the assumption of constant cod concentrations of 90mg/l (upper legislation limit) combined with a sewer overflow duration of 2.4h, a discharge of 2m 3 /s, and cod concentration of 125 mg/l (about the yearly average). figure 3 shows the actual and hypothetical load cases. the comparison shows that during a dry period cod effluent concentration leads to a slight decrease in do concentrations, with no significant differences between the actual and hypothetical loads of cod. the decrease is between 0.3 and 0.5mg/l while daily fluctuations do not change significantly. the effect of a sewer overflow in august 26, 2001 is shown in figure 3(b). the simulation is in agreement with the documented effects of immediate and delayed oxygen depletion in the surface flow of running waters [39]. figure 4 shows the time series for cod and oxygen at 100m ds suhl. the joined sewer overflow increased cod concentrations for more than 4 hours. meanwhile, the oxygen concentrations decreased below 4mg/l for several hours, followed by a slow recovery. therefore it is concluded that joined sewer overflows engineering, technology & applied science research vol. 10, no. 4, 2020, 6126-6130 6129 www.etasr.com khalifa: simulation of dissolved oxygen and dissolved substrate for hasel river have the potential to disrupt oxygen balances for extended time periods. those single events suggest a real endangerment for populations of macro-organisms and fishes [5]. (a) (b) fig. 3. oxygen time series at 100m ds suhl of hasel river: (a) actual, b) hypothetical. fig. 4. hypothetical time series for cod and oxygen at 100m ds suhl. iv. conclusion the proposed aquasim model was used to quantify the oxygen balance of a highly eutrophic shallow river, using a systematic procedure of river compartmentalization including identification of flows and a simplified description of biochemical conversion processes in hasel river. the modeling approach quantified the temporal dynamic of oxygen in surface flow for spatially averaged scales, with consideration of distinct patterns at the boundaries of the river reaches, using physico-chemical data of 2001. the proposed model opens new perspectives in the study of ecological system responses to anthropogenic impact. the model’s potential is demonstrated by simulations showing the effect of emissions from wastewater treatment plants operating according to emissions standards, which may disrupt oxygen concentrations. moreover, combined sewer overflows may cause severe oxygen depletion for extended time periods, endangering macro-invertebrate and fish populations. further research is needed in ecologically meaningful river water quality modeling. in these efforts, this aquasim model could be utilized during system analysis at several levels of intricacy and human impact, improving the functional understanding of ecological processes in rivers and the identification of ecological effective management strategies. acknowledgments measurements and data from the national thuringia town of environment and geology in germany were a key factor for this study. most of the work was performed during a research visit in 2004 at kassel university financed through the german research foundation (dfg). finally, the staff members at kassel university, especially prof. dr. borchardt, prof. dr. tönsmann, mr. funke, and mr. weiss offered valuable advice, support, and great hospitality. references [1] s. c. chapra, surface water quality modeling. new york, ny, usa: mcgraw-hill, 1997. 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[39] p. harremoës, “immediate and delayed oxygen depletion in rivers,” water research, vol. 16, no. 7, pp. 1093–1098, jan. 1982, doi: 10.1016/0043-1354(82)90124-5. authors profile walid m. a. khalifa is an assistant professor at hail university, saudi arabia, and fayoum university, egypt. he received his b.sc. in civil engineering and his ph.d. in water resources and environmental hydrology at cairo university. his research interests include water quality and hydrodynamics modeling, pressurized irrigation modeling, and design of rc water structures. microsoft word 30-3175_s1_etasr_v10_n1_pp5259-5264 engineering, technology & applied science research vol. 10, no. 1, 2020, 5259-5264 5259 www.etasr.com khan et al.: rotor angle and voltage stability analysis with fault location identification on the … rotor angle and voltage stability analysis with fault location identification on the ieee 9 bus system hafiz farhaj khan department of electrical engineering wah engineering college university of wah wah cantt, pakistan farhaj.khan@wecuw.edu.pk aamir hanif department of electrical engineering wah engineering college university of wah wah cantt, pakistan dr.aamirhanif@wecuw.edu.pk naveed anwar department of electrical engineering wah engineering college university of wah wah cantt, pakistan naveed.anwar@wecuw.edu.pk abstract—transient stability is very imperative in multi-machine interconnected power systems in order to scrutinize and analyze the system’s performance and response. rotor angle stability and voltage stability are studied in this paper. by applying threephase symmetrical faults, the transient stability of the ieee 9 bus system is studied. a characteristic double hump is analyzed in the response of the generator, which is nearer to the fault location. by analyzing the characteristic double hump, the fault location in a large interconnected power system can be determined. it is shown that, as the fault is cleared, the system takes some finite time to return to its prior state. ieee 9 bus system is chosen as a test system, which standard parameters. matlab simpower system toolbox is used for load flow and transient stability analysis. keywords-transient stability; steady state stability; characteristics hump; rotor angle; ieee 9 bus system i. introduction there are three stages in a power system, generation, transmission, and distribution [1]. in generation, electric power is generated mostly from synchronous machines, which are very sensitive to disturbances [2]. nowadays, power industries move towards deregulation and competition and electric power systems are becoming increasingly interconnected and sophisticated [3-4]. loads are tapped off from different locations. a fault at any location in the system can distress the system’s performance [5] and under this scenario, transient stability is very significant in designing the electric power system [6]. a power system is designed to maintain continuous power supply to consumers and voltage stability when unwanted events, like short circuits, lightening strokes, etc., occur [7]. due to these faults, one or many generators can be out of synchronism causing a disproportion between generation and demand [8]. system’s stability is the capability of the system to return to its original state when subjected to disturbance(s) [9]. there are three types of stability: steady state stability, transient stability and dynamic stability [10]. steady state stability is actually restricted to small change, i.e. bus voltage should be close to their nominal value. transient stability refers to large disturbance(s) after which a system returns to its original state, otherwise that system may get unstable [11]. if the changes are continuous and after each the system maintains synchronism, this is referred as dynamic stability, also called small signal stability [12]. steady state stability is a function of only an operating point whereas, transient stability is a function of both initial condition and the state when a disturbance occurs [13]. load is increasing day by day, but the generation and transmission system is old. to resolve this issue of overburdened transmission line and increasing load, increasing power generation and up gradation of transmission lines may be useful, but both methods are not informal and beneficial [15]. one important part that should be integrated during the electric power system’s design is transient stability analysis. transient stability is the ability of the system to maintain synchronism when subjected to transient disturbance(s) [16]. transient disturbances/faults in a power system occur due to following reasons: • large excursion of generator rotor angle • loss of load • loss of generator • short circuit fault on transmission line • large change in load • loss of transmission network from the system [17] transient analysis of the ieee 9 bus system was studied in [16], where the settling of the generator’s response is shown to be very short which is not practical. moreover there is no information of fault’s location in the response of generator’s rotor angle and one cannot judge the location of fault by merely seeing the response of the respective generator. matlab/simulink was used for the analysis of the ieee 9 bus system, where transfer function blocks were used for the formulation of the system, which is a very lengthy process. power flow analysis of weekly meshed distribution system was corresponding author: hafiz farhaj khan engineering, technology & applied science research vol. 10, no. 1, 2020, 5259-5264 5260 www.etasr.com khan et al.: rotor angle and voltage stability analysis with fault location identification on the … conducted in [18], but no conclusion is drawn from the response of the generators. in this work, matlab simpower system toolbox is used for the formulation of the ieee 9 bus system providing block representation of non-linear systems instead of the lengthy coding or transfer function. ii. methodology the ieee-9 bus system model was developed using matlab simpower toolbox and load flow analysis of the developed system was carried out. the system was tested under normal and abnormal operating conditions. the developed system was investigated/tested for deviations in rotor angle, speed, and terminal voltages of three generators with different locations of fault. a. mathematical equations of the developed system under normal operating condition, the relative position of rotor axis and the resultant magnetic is fi and the difference between them is zero. the angle between these two is called power angle or torque angle θm [19]. when a machine is subjected to a disturbance, the power angle is created and has positive or negative value and the rotor will accelerate or decelerate with respect to synchronously rotating air gap mmf [20]. in order to describe this phenomenon, swing equation is used. its graph between pe and δ is elaborated in [22]. if τe is the electrical output in the form of torque and τm is the mechanical input torque, then during normal operation, the difference between them is zero, i.e τe=τm. when the disturbance occurs, a difference is created between them and is denoted by τa. swing equation can be written as in [17]: 2 m 0 a e m2 d j dt θ = τ = τ −τ (1) where j0 is the total moment of inertia in kg/m 2 , θm is the angular displacement of rotor with respect to a stationary axis in mechanical radians, τa is the accelerating torque in n/m. if θm is rotating with respect to synchronously revolving frame then it can be written as: m sm m tθ = ω +δ (2) where ωsm is the synchronous speed of the machine in mechanical radians per sec and δm is the angular displacement of the rotor in mechanical radians from the synchronously rotating reference axis. electrical torque τe can be converted into electrical power by multiplying with ω and swing equation can be written as: 2 m a (p.u) e(p.u ) m(p.u )2 e d2h p p p dt δ = = − ω (3) where h is the inertia constant which is the ratio between the stored kinetic energy in mega joules at synchronous speed and machine rating in mva. electrical power transfer from one point to another is can be written as: e max m p p sin( )= δ (4) where pmax is the maximum power output in watts. graphically, we can represent swing equation (swing curve). we can write a swing equation for our test system which is the ieee 9 bus system. the generalized form of the multi machine swing equation can be written as [22]: m2 ' 'i mi i j ij ij i j2 j 10 mi ei dh p e e y cos( ) f dt p p = δ = − θ −δ −δ π = − ∑ (5) where ' i e is the internal voltage of generators, ' j e is the voltage behind transient reactance, δi is the angle of ' i e with respect to ' j e and δj is the angle of ' j e . ij y is the ybus matrix of the system. after the fault is cleared, the system returns to a new operating point and the new rotor angle at new operation point is written as [23]: ' m 0 max p sin p δ = (6) b. test system a single line diagram of the ieee 9 bus system can be seen in [16]. the test system is developed using matlab simpower system toolbox as shown in figure 1. ieee 9 bus system has standard parameters like bus voltages, angle, active and reactive power at all 9 buses. there are three generator buses 1, 2 and 3 and three load buses 5, 6 and 8. generator 1, which is larger in size, is connected to slack/swing bus and generators 2 and 3 are connected to the pv bus. the three generators are producing 567mva and the total load is 321. c. load flow analysis load flow analysis is necessary in order to investigate the transient stability of any system [24]. it is also necessary to determine pre-fault conditions like voltage, its angle, active power, reactive power, and other variables being specified on every bus in the system [25]. the practical method of load flow study is the newton raphson method [26]. in planning stages, power flow study is very important for new networks and additions to an existing network for in order to meet the increasing load demand. load flow of the developed system is carried out so that system should not operate close to their voltage static stability [27-28]. table i. bus classification [16] bus no. bus type 1 slack/swing bus 2 pv bus 3 pv bus 4 transformer 5 load (b) bus 6 load (c) bus 7 transformer 8 load (a) bus 9 transformer engineering, technology & applied science research vol. 10, no. 1, 2020, 5259-5264 5261 www.etasr.com khan et al.: rotor angle and voltage stability analysis with fault location identification on the … iii. simulation results and discussion tables i-ii show the load flow analysis of the ieee 9 bus system for predetermined values of voltage, phase, and active and reactive powers. bus 1 is a slack/swing bus, because generator 1 is the largest generator with a capacity of 247mw. buses 2 and 3 are pv buses because we are required to know the active and reactive power supplied by the respective generators. after load flow analysis, voltage at each bus, their angles, active and reactive power are shown in table ii. specification of fault can be seen in table iii. all simulations are completed in matlab simpower system toolbox, which is very informal to use because it contains block diagram representation of non-linear components. in order to study transient stability, a three phase fault is introduced at different locations and the response is observed. three phase balanced fault occurred at 5s and was cleared at 5.08s. fault clearing time was 0.08s and after that, the system was stable. with different locations of fault, rotor angle, speed and terminal voltages of three generators were investigated. when there was no fault at any bus as shown in figures 2-4, the rotor angle deviated first to a point -90 o for generator 1, -30 o for generator 2 and -35 o for generator 3. after that, the response was smooth and no deviation was observed until the end and the system remained stable. generator’s terminal voltage (vt) was at 1 p.u. when the system was stable. table ii. load flow analysis bus no. voltage (p.u.) vangle ( o ) p (mw) q (mvar) 1 1.0400 0.00 72.19 26.80 2 1.0250 9.17 163.00 6.69 3 1.0250 4.56 85.00 -10.78 4 1.0261 27.77 0.00 0.00 5 0.9962 26.00 125.00 50.00 6 1.0131 26.30 90.00 30.00 7 1.0259 33.63 0.00 0.00 8 1.0160 30.63 100.00 35.00 9 1.0324 31.87 0.00 0.00 table iii. fault specifications components value fault resistance (ohm) 5 ground resistance (ohm) 0.001 snubber resistance (ohm) 1×10 6 snubber capacitance (farad) inf fig. 1. simulation diagram of the test system a. response of generators without fault the response of deviation in rotor angle, speed and the terminal voltages of all generators without fault are shown in figures 2-4. b. fault at bus 1 (swing bus) the response of deviation in rotor angle, speed, and terminal voltages of all generators with fault at bus 1 are shown in figures 5-7. c. fault at generator 2 (pv bus 1) the response of deviation in rotor angle, speed, and terminal voltages of all generators with fault at bus 3 are shown in figures 8-10. d. fault at generator 3 (pv bus 2) the response of deviation in rotor angle, speed, and terminal voltages of all generators with fault at bus 3 are shown in figures 11-13. e. fault between buses 5 and 7 the response of deviation in rotor angle, speed, and terminal voltages of all generators with fault between buses 5 and 7 are shown in figures 14-16. engineering, technology & applied science research vol. 10, no. 1, 2020, 5259-5264 5262 www.etasr.com khan et al.: rotor angle and voltage stability analysis with fault location identification on the … fig. 2. deviation in rotor angle without fault fig. 3. generator speed of generators without fault fig. 4. terminal voltage without fault fig. 5. deviation in rotor angle with fault at bus 1 fig. 6. rotor speed with fault at bus 1 fig. 7. terminal voltage with fault at bus 1 fig. 8. deviation in rotor angle with fault at bus 2 fig. 9. rotor speed with fault at bus 2 fig. 10. terminal voltage with fault at bus 2 fig. 11. deviation in rotor angle with fault at bus 3 engineering, technology & applied science research vol. 10, no. 1, 2020, 5259-5264 5263 www.etasr.com khan et al.: rotor angle and voltage stability analysis with fault location identification on the … fig. 12. rotor speed with fault at bus 3 fig. 13. terminal voltage with fault at bus 3 fig. 14. deviation in rotor angle with fault between bus 5 and 7 fig. 15. rotor speed with fault between bus 5 and 7 fig. 16. terminal voltage with fault between bus 5 and 7 when a three phase fault is introduced at bus 1 or generator 1, distortion in the response of all generators can be seen in figures 5-7. at first the rotor angle is at equilibrium point, but when fault occurred, oscillations were formed and after some time, they were damped out and vanished. a characteristic double hump can be easily observed in the rotor angle of generator 1. because fault is nearest to the generator 1, a double hump was introduced in response of generator 1. in figures 6 and 7, generator’s speed and terminal voltage is exhibited. the largest distortion can be seen in the response of generator 1, because the fault is nearest to generator 1. generators 2 and 3 are less effective, because they are far away from the location of the fault. when a three phase fault was introduced at buses 2 and 3, the response can be seen in figures 8 and 11. it is observed that, after the fault is cleared, the system takes its own time to return to a new equilibrium point. in our case, after the clearance of fault, the system takes 16s to return to a new equilibrium point. transient stability analysis of ieee 9 bus system is done in [12] but nothing can be concluded from the response of generators. in this work, the location of fault can be predicted by looking at the response of the generator, because fault prediction in a large power system is difficult. sensitive components cannot bear too much time of oscillations, that’s why this settling time can be decreased by using fact devices like dstacom, power system stabilizers, etc. [29-31]. the response of introducing fault was between buses 5 and 7 is shown in figures 14-16. in this case, because the fault occurred between generators 2 and 3, oscillations and characteristic hump were noted in the response of generators 2 and 3, but more oscillations can be observed in the response of generator 1, because it is nearer to the location of the fault than generator 2. iv. conclusion a complete model for transient stability of a 9 bus ieee system with 3 generators was developed and tested using matlab/simulink simpower system toolbox. the behavior of a three phase balanced fault with different locations was investigated. it is concluded that, the system takes some time to stabilize, i.e. it reaches a peak value and after that it decays to its final or steady state value. a three phase fault was introduced at 5s, and the system took some time to get stable. it was also determined that fault location is also important in order to analyze the stability of the system. fault location can be deduced by looking at the response of the generator. further, fault clearing time must be very short. in order to reduce settling time, fact devices like power system stabilizers, dynamic voltage restorer (dvr), dstatcom, etc. can be used to increase the stability of the system and reduce the system’s settling time preventing damage to sensitive equipment. references [1] s. a. nasar, f. c. trutt, electric power systems, crc press, 1998 [2] y. zhong, s. huang, d. luo, “stabilization and speed control of a permanent magnet synchronous motor with dual-rotating rotors”, energies, vol. 11, no. 10, article id 2786, 2018 engineering, technology & applied science research vol. 10, no. 1, 2020, 5259-5264 5264 www.etasr.com khan et al.: rotor angle and voltage stability analysis with fault location 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2016 [28] c. l. wadhwa, electrical power systems, new age international, 5th ed., 2009 [29] p. p. panchbhai, p. s.vaidya, “transient stability improvement of ieee 9 bus system with shunt facts device statcom”, international research journal of engineering and technology, vol. 3, no. 3, pp. 128–132, 2016 [30] r. rangu, p. upadhyay, “study of transient stability improvement of ieee 9-bus system by using svc”, international journal of engineering trends and technology, vol. 27, no. 3, pp. 162–166, 2015 [31] g. shahgholian, e. mardani, a. fattollahi, “impact of pss and statcom devices to the dynamic performance of a multi-machine power system”, engineering, technology & applied science research, vol. 7, no. 6, pp. 2113-2117, 2017 microsoft word 19-3146_s_etasr_v9_n6_pp4974-4979 engineering, technology & applied science research vol. 9, no. 6, 2019, 4974-4979 4974 www.etasr.com rahamat basha & rani: a comparative approach of dimensionality reduction techniques in text … a comparative approach of dimensionality reduction techniques in text classification shaik rahamat basha department of computer science & technology sri krishnadevaraya university, india j. keziya rani department of computer science & technology sri krishnadevaraya university, india abstract—this work deals with document classification. it is a supervised learning method (it needs a labeled document set for training and a test set of documents to be classified). the procedure of document categorization includes a sequence of steps consisting of text preprocessing, feature extraction, and classification. in this work, a self-made data set was used to train the classifiers in every experiment. this work compares the accuracy, average precision, precision, and recall with or without combinations of some feature selection techniques and two classifiers (knn and naive bayes). the results concluded that the naive bayes classifier performed better in many situations. keywords-stop word removal; stemming; feature weighting and selection; knn; naive bayes i. introduction in text classification, usually the dimensionality of the feature vector is huge because the input document consists of vast data and many terms [1, 2]. the major approaches for feature reduction are feature selection [2-8] and feature extraction [9, 10]. feature extraction approaches are computationally more extensive and more effective than feature selection methods [9, 10]. feature clustering is one effective technique in feature reduction, where similar features are grouped into one cluster and each cluster is treated as a feature [11, 12]. to reduce dimensionality severity in preprocessing, the unnecessary words which do not support the classification task (i.e. articles, verbs, prepositions etc.) are removed. for text categorization (by supervised learning procedure) labels are assigned for some documents from predefined categories (e.g. business, health, movies, etc.). the number of digital documents in the web is increasing, the number of terms (i.e. features) in those documents is quite large but only a few are informative. it is a severe problem which degrades the efficiency of information retrieval (ir) procedures. the current work includes stemming process [13] which reduces the dimensionality of feature space and stochastic dependence between terms. a better feature selection procedure reflects the effectiveness on classification and computational efficiency. in this paper, feature weighting is presented along with the implementation procedure of different feature selection methods and knn and naïve bayes classifiers [14, 15, 26-30]. experiments are conducted and the results are analyzed. ii. related work in feature selection approach the redundant and irrelevant features are removed from the corpus, e.g. selecting a subset of features from the training set and using that set as feature set for text classification. some supervised feature selection approaches (ig, mi, or, chi, ngl, gss etc.) [16] were used in our task. to reduce the noise of data with respect to term frequency (tf) [16], document frequency (df) [16], is implemented by giving user input threshold and selecting the most probable features (by a threshold value k) and analyzing results with respect to dimensionality size. rule-based classification is accurate if the rules are written by experts and are easily controlled if their number is small but if it increases or the rules conflict each other, rule maintenance becomes difficult. if the target domain changes the rules must be reconstructed. machine learning-based approach is domain independent and gives high predictive performance, but training data are required [17]. iii. feature weightening in this process, each feature (a single word or term or token) is assigned with a score based on a score computing function and the higher scored (weighted) terms are selected. score computing functions include some mathematical definitions and probabilistic approaches which are estimated by some static information in the documents across different categories. some example notations based on probabilities are: • p(t): the probability of a document x containing the term t • p(ci): the probability of a document x belonging to the category ci • p(t, ci): the probability of a document x containing the term t and belonging to the category ci • p(ci/t): the probability of a document x belonging to the category ci under the condition that it contains term t • p(t/ci): the probability of a document x containing the term t under the condition that it belongs to the category ci a. document frequency (df) the number of documents in which a word occurs is df: �� = ∑ ����� (1) corresponding author: s. rahamat basha (basha.ste@gmail.com) engineering, technology & applied science research vol. 9, no. 6, 2019, 4974-4979 4975 www.etasr.com rahamat basha & rani: a comparative approach of dimensionality reduction techniques in text … where ai= document i where the word is present, m= number of documents, and i is an integer ranging from 1 to m. the df was computed for every unique term in the training corpus and the features with less df than the predefined threshold were removed. b. mutual information (mi) mi and ig give similar results for binary problems. the implemented multi class problem solving procedure was such that these two techniques give different results. c. chi square it is a statistical measure used to measure the independence of a feature or a class. in this context, the null hypothesis here is that the particular word and category are completely independent, i.e. that the word is useless for classifying documents. d. gss coefficient it is a simplified chi square function. e. odds ratio (or) this measure compares the odds of a word occurring in one class with the odds of occurring in another. or is positive if the feature more often occurs in one document than the other, negative for vice versa and zero if the feature’s presence is equal in both: ���, ��� = �� ���|���� ����|�����������|�������� ����|���� = �� ���,����� �� � ��,������ ������� � ���,������������� �� � ��,�� ��� � (2) f. ngl coefficient it is a variant of the chi square metric, also called as correlation coefficient. g. information gain (ig) this method is implemented on the constraints of class membership function (presence/absence) and by how much information is gained. the ig of a term t is given as: !�"� = #© − # &�'( where ) = {+,-.-�", /0.-�"} /�3 � = {4+, 4−} (3) h. relevancy score 6�"7,4�� = �89[�; �"7|4�� + 3�/� ; �"7|4�� + 3�] (4) i. multi-set of feature (msf) >?� = |�| ∑ ;�� "�|� (5) @�tb� = c �|d|� �efg ∑ �p�d tb|c� − mkb�l (6) j. knn and naive bayes classifiers the advantage of knn in this model is that by choosing different constraints in every level of classification task we may compare the results with respect to m (m is variable) most matched values. this classifier is implemented by computing the euclidean distance. the following is an illustration of the naive bayes classifier. let d be a document set with 6 documents 3 , 3l, … 3o. the documents 3 , 3l, … 3p are used to train the classifier and we are predicting the label of document 3o. the classifier is trained under the bag of words representation method. as shown in table i the total unique words in the corpus are 14. according to the bayes theorem [18, 19], table ii represents the likelihood/impact of each word of the test document to the classes sports and politics. table i. bag of words representation of d a game very election was clean close over but forgettable match it great the label 3 1 1 1 sports 3l 1 1 1 1 politics 3q 1 1 1 sports 3r 1 1 1 1 1 sports 3p 1 1 1 1 1 politics 3o 1 1 1 1 ? table ii. test document words and their likelihood/impact for the categories sports and politics words in d6 p (word | sports) p (word | politics) a 2 + 1 11 + 14 1 + 1 9 + 14 very 1 + 1 11 + 14 0 + 1 9 + 14 close 0 + 1 11 + 14 1 + 1 9 + 14 game 2 + 1 11 + 14 0 + 1 9 + 14 the multiplication of all individual probabilities concludes to the label of 3o: ;�/|x+8,".� × ;�z-,[|x+8,".�× ;�4�8.-|x+8,".�× ;�9/>-|x+8,".� × ;�x+8,".� = = 2.76 × 10�p = 0.0000276 (7) ;�/|m8"x+8,".� × ;�z-,[|m8"x+8,".� × ;�4�8.-|m8"x+8,".�× ;�9/>-|m8"x+8,".� × ;�m8"x+8,".� = 0.572 × 10�p = 0.00000572 (8) according to the above illustration (i.e. 0.00000572 > 0.0000276 ) we can say that the test document d6 more likely belongs to the class sports. iv. results and analysis two different datasets, described below, were used in the experiments. engineering, technology & applied science research vol. 9, no. 6, 2019, 4974-4979 4976 www.etasr.com rahamat basha & rani: a comparative approach of dimensionality reduction techniques in text … a. data set 1: self made data set to train the classifiers, we used a small (of size around 1.5mb) self-made corpus. this allows the needed running time for training to be as short as possible. the documents of the self-made corpus were collected online articles from cnn, washington post, and new york times. we collected 150 documents under the following categories: business (23), education (24), health (30), movies (10), science (27), sports (30), travel (6), with an average of 702 words per document. table iii. preprocessing results of self-made data set corpus stopwords stemming # of processed terms # of unique terms self-made no no 105443 12819 self-made yes no 105443 12660 self-made no porter 105443 8878 self-made yes porter 105443 8697 self-made no lancaster 105443 7490 self-made yes lancaster 105443 7288 b. data set 2: the reuters 21578 corpus we have used this corpus as test data. reuters 21578 corpus consists of a total of 108 categories. the corpus is freely available in many internet sources [20-23]. by using the freely available tool sx, the 22sgml documents were converted to xml documents. then some single characters were deleted which were rejected by the validating xml parser (e.g. decimal values below 30). the results shown below in the tables are generated under the constraints where classifier is knn, n=30, threshold=1, threshold step size=0.1, method of summation is sum and df=<1, tf=<1 for the test documents reut2-003.xml, reut2.004.xml, and reut2.005.xml. here tf stands for term frequency, i.e. the frequency of a term in a document. often, chi square and msf gave similar results and away from ig and df values. when feature space size increased the similarity between chi square and msf diminished. table iv. dimensionality of feature space=250 chi square msf ig df break-even-point 0.266 0.262 0.429 0.687 11 point-precision 0.390 0.390 0.748 0.755 average precision 0.345 0.335 0.777 0.774 table v. dimensionality of feature space=500 chi square msf ig df break-even-point 0 0 0.429 0.687 11 point-precision 0.143 0.143 0.831 0.837 average precision 0.159 0.159 0.869 0.869 table vi. dimensionality of feature space=750 chi square msf ig df break-even-point 0.0814 0 0.804 0.804 11 point-precision 0.225 0.154 0.857 0.857 average precision 0.1631 0.172 0.893 0.893 c. classifiers performance and results for most results we may conclude that naïve bayes classifier performed better even though the performance of the two classifiers is efficient. in figure 1 it can be seen that the knn classifier gives different results for each feature selection technique and from figure 2 that naive bayes classifier gives almost similar results for all feature selection techniques except for ig and mi. we observe that knn classifier gave similar results for msf and chi square at feature space size=250 and 750, and for ig and df at feature space size=500 and 750. the effectiveness of a classifier is not described by precision and recall, it is necessary to compute different evaluation metrics. the f-measure was computed, i.e. the harmonic mean of recall and precision. micro-average f1 or micro average accuracy of f1 is calculated regardless of topics but macro-average f1 scores on all the topics [17, 24]. average precision [25] is the average of the precisions at eleven evenly spaced recall levels. break-even-point is the precision at the point where precision and recall are equal. the averaged value of the precision at the point where the recall equals the 11 values 0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0 is the 11-point precision [7, 25]. fig. 1. knn classifier results for the test document reut.003.xml at constraints k=30, tf<1 and df<1 engineering, technology & applied science research vol. 9, no. 6, 2019, 4974-4979 4977 www.etasr.com rahamat basha & rani: a comparative approach of dimensionality reduction techniques in text … fig. 2. naive bayes classifier results for the test document reut.003.xml at constraints k=30, tf<1 and df<1 table vii. knn classifier results for the test document reut.003.xml at k=30, tf<1 and df<1 chi square mi orr ngl gss relevancy score ig df msf bep 0.266 0.515 0 0.170 0.170 0 0.729 0.687 0.262 tolerance 0.233 0.702 0 0.162 0.162 0 0.0045 0.004 0.237 11 point-precision 0.390 0.586 0.195 0.339 0.339 0.162 0.748 0.755 0.390 avg-precision 0.345 0.593 0.218 0.282 0.282 0.173 0.777 0.774 0.335 best category movies bus movies movies movies science bus bus movies table viii. naive bayesclassifier results for the test document reut.003.xml at k=30, tf<1 and df<1 chi square mi orr ngl gss relevancy score ig df msf bep 0.5791 0.335 0.5791 0.5791 0.5791 0.5791 0.190 0.221 0.5791 tolerance 0.420 0.0250 0.420 0.420 0.420 0.420 0.142 0.173 0.420 11 point-precision 0.540 0.385 0.540 0.540 0.540 0.540 0.339 0.387 0.540 avg-precision 0.579 0.366 0.579 0.579 0.579 0.579 0.296 0.352 0.579 best category science science science science science science science science science table vii and table viii describe the performance of knn and naive bayes classifiers for the test document reut.003.xml at dimension size=250. each feature reduction technique gave a best category result for which the test document belongs. table ix. knn result for reut.003.xml at d=250 precision recall micro macro micro macro chi square 1 1 0 0 mi 0.469 0.513 0.720 0.688 orr 1 1 0 0 ngl 1 1 0 0 gss 1 1 0 0 relevancy score 1 1 0 0 ig 0.308 0.349 0.936 0.905 df 0.309 0.310 0.936 0.905 msf 1 1 0 0 tables ix and xiv describe the precision and recall values (micro and macro) given by the knn and naive bayes classifiers respectively while using different feature reduction techniques. the performance of knn at k=30, threshold=1, threshold step size=0.1, method of summation = sum, df=<1, tf=<1 and naive bayes classifier at threshold= 0.006666666666666667, threshold step size= 0.0001, method of summation = sum, df=<1, tf=<1for the test document reut.003.xml at different dimension sizes while using different feature reduction techniques are given by tables x-xiii, and xv-xviii respectively. table x. knn result for reut.003.xml 11 point precision values 250 500 750 1000 1250 1500 1750 2000 chisquare 0.4 0.15 0.14 0.12 0.18 0.38 0.4 0.45 mi 0.6 0.73 0.78 0.82 0.81 0.83 0.86 0.87 orr 0.19 0.15 0.16 0.12 0.31 0.38 0.4 0.41 ngl 0.18 0.14 0.16 0.13 0.16 0.18 0.3 0.31 gss 0.34 0.37 0.2 0.12 0.16 0.18 0.29 0.32 relevancy score 0.18 0.14 0.28 0.35 0.4 0.51 0.5 0.54 ig 0.75 0.82 0.86 0.84 0.83 0.6 0.87 0.89 df 0.76 0.82 0.83 0.82 0.82 0.9 0.88 0.88 msf 0.4 0.14 0.15 0.42 0.18 0.37 0.42 0.43 engineering, technology & applied science research vol. 9, no. 6, 2019, 4974-4979 4978 www.etasr.com rahamat basha & rani: a comparative approach of dimensionality reduction techniques in text … table xi. knn result for eeut.003.xml break-even point values 250 500 750 1000 1250 1500 1750 2000 chi-square 0.28 0 0 0.1 0.2 0.25 0.32 0.42 mi 0.51 0.7 0.75 0.79 0.78 0.8 0.81 0.82 orr 0 0.1 0 0 0.19 0.29 0.33 0.41 ngl 0.18 0.2 0 0 0 0 0.22 0.28 gss 0.18 0.28 0 0 0 0 0.19 0.29 relevancy score 0 0 0.18 0.29 0.38 0.4 0.41 0.49 ig 0.72 0.78 0.8 0.79 0.8 0.61 0.63 0.84 df 0.7 0.77 0.6 0.69 0.8 0.82 0.84 0.81 msf 0.28 0 0 0.2 0 0.39 0.4 0.42 table xii. knn result for reut.003.xml micro precision and recall values 250 500 750 1000 1250 1500 1750 2000 mi(p) 0.42 0.62 0.65 0.7 0.8 0.82 0.83 0.84 ig(p) 0.25 0.42 0.5 0.45 0.61 1 0.63 0.65 df(p) 0.24 0.43 0.55 0.49 0.65 0.71 0.82 0.95 mi(r) 0.66 0.68 0.69 0.66 0.65 0.65 0.64 0.63 ig(r) 0.3 0.42 0.45 0.5 0.62 0.4 0.65 0.66 df(r) 0.87 0.89 0.87 0.88 0.86 0.85 0.84 0.84 table xiii. knn result for reut.003.xml macro precision and recall values 250 500 750 1000 1250 1500 1750 2000 mi(p) 0.51 0.72 0.8 0.84 0.9 0.91 0.92 0.97 ig(p) 0.28 0.45 0.58 0.6 0.65 1 0.65 0.66 df(p) 0.3 0.24 0.25 0.6 0.7 0.52 0.68 0.78 mi(r) 0.7 0.72 0.73 0.72 0.73 0.7 0.71 0.69 ig(r) 0.76 0.78 0.87 0.89 0.84 0.6 0.82 0.91 df(r) 0.86 0.9 0.96 0.87 0.83 0.93 0.84 0.81 table xiv. naive bayes for reut.003.xml at d=250 precision recall micro macro micro macro chi square 1 1 0 0 mi 0.345 0.62 0.048 0.042 orr 1 1 0 0 ngl 1 1 0 0 gss 1 1 0 0 relevancy score 1 1 0 0 ig 0.487 0.866 0.48 0.424 df 0.487 0.866 0.048 0.042 msf 1 1 0 0 table xv. naive bayes for reut.003.xml 11 point precision values 250 500 750 1000 1250 1500 1750 2000 chi-square 0.2 0.25 0.3 0.35 0.28 0.29 0.15 0.1 mi 0.39 0.38 0.32 0.33 0.42 0.43 0.5 0.5 orr 0.53 0.54 0.55 0.45 0.4 0.61 0.32 0.63 ngl 0.1 0.2 0.25 0.25 0.3 0.29 0.4 0.2 gss 0.51 0.52 0.53 0.43 0.45 0.47 0.52 0.53 relevancy score 0.54 0.55 0.6 0.61 0.61 0.62 0.63 0.48 ig 0.35 0.61 0.61 0.61 0.62 0.63 0.64 0.65 df 0.39 0.61 0.62 0.23 0.24 0.4 0.65 0.66 msf 0.54 0.55 0.35 0.31 0.25 0.61 0.5 0.6 table xvi. naive bayes for reut.003.xml break-even point values 250 500 750 1000 1250 1500 1750 2000 chi-square 0 0.1 0.18 0.2 0.29 0.3 0.37 0.4 mi 0.32 0.31 0.25 0.22 0.32 0.33 0.4 0.41 orr 0.35 0.34 0.35 0.36 0.57 0.58 0.68 0.68 ngl 0.2 0.28 0.3 0.32 0.36 0.37 0.35 0.35 gss 0.36 0.57 0.57 0.48 0.48 0.39 0.6 0.61 relevancy score 0.54 0.55 0.66 0.68 0.69 0.69 0.6 0.54 ig 0.28 0.45 0.46 0.48 0.47 0.48 0.49 0.62 df 0.22 0.56 0.57 0.58 0.59 0.6 0.61 0.63 msf 0.46 0.45 0.48 0.49 0.6 0.71 0.72 0.74 table xvii. naive bayes for reut.003.xml micro precision and recall values values 250 500 750 1000 1250 1500 1750 2000 mi(p) 0.3 0.62 0.63 0.38 0.6 0.51 1 0.98 ig(p) 0.85 0.87 0.85 0.87 0.87 0.98 1 1 df(p) 0.45 1 1 0.6 1.1 1.1 1.1 1.1 mi(r) 0.09 0.1 0.09 0.07 0.2 0.1 0.12 0.14 ig(r) 0.45 0.1 0.1 0.14 0.12 0.3 0.19 0.19 df(r) 0.2 0.4 0.3 0.3 0.4 0.2 0.2 0.1 table xviii. naive bayes for reut.003.xml macro precision and recall values 250 500 750 1000 1250 1500 1750 2000 mi(p) 0.61 0.81 0.89 0.82 0.86 0.83 1 1.1 ig(p) 0.82 0.95 0.95 1 0.95 0.99 1 1.2 df(p) 0.82 0.9 0.9 0.95 0.99 0.99 1 1.1 mi(r) 0.05 0.1 0.14 0.16 0.17 0.4 0.15 0.19 ig(r) 0.04 0.02 0.01 0.03 0.02 0.03 0.04 0.04 df(r) 0.3 0.32 0.34 0.4 0.45 0.02 0.02 0.03 v. conclusion the results shown in figures 1-2 clearly show that knn classifier performed well in classification with mi and df but when other feature reduction techniques were used, the average precision was low. the naive bayes classifier performed well with the feature reduction techniques except mi. the higher average precision reported by knn was with df. the results reported in tables x, xv, xi, and xvi reveal that naive bayes classifier worked well with respect to 11 point precision and breakeven point. the results reported in tables xii, xvii, xiii, and xviii reveal that knn classifier worked better than naive bayes with respect to micro and macro precision and recall. figure 3 shows that naive bayes classifier works better than knn with the measures micro f1 and macro f1. the number of categories, the size of the class/corpus, the used feature selection techniques etc. were the key factors of the experimental results. time complexity of the experiments was not considered/reported in this study. generally, knn classifier is simple to use and takes less time when compared with naive bayes but it is proved that naive bayes can work better in many cases. engineering, technology & applied science research vol. 9, no. 6, 2019, 4974-4979 4979 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of innovations in engineering and technology, vol. 2, no. 4, pp. 139-144, 2013 microsoft word 39-39-2739_s engineering, technology & applied science research vol. 9, no. 2, 2019, 4075-4078 4075 www.etasr.com ghannam et al.: perspectives of an enterprise integration plug-in system architecture for networked … perspectives perspectives of an enterprise integration plug-in system architecture for networked manufacturing systems adel n. ghannam faculty of management sciences msa university cairo, egypt mghanam@msa.eun.eg ali el-bastawissy computer science msa university cairo, egypt aelbastawissy@msa.eun.eg hesham mansour faculty of computer science msa university cairo, egypt hhmansour@msa.eun.eg mohamed hamed development dirac systems cairo, egypt mhamed3476@gmail.com abstract—this paper is a part of a research project funded by the science and technology development fund (stdf), to create a product serving the digital transformation of egyptian manufacturing companies. it allows a manufacturing company to be a member of a distributed manufacturing network. the resulting system can be plugged into any erp system. in this work, the limitation of a centralized integration entity to satisfy loosely coupling of distributed systems is overcome. the soa framework and the remote method invocation (rmi) are applied using soap-xml technology. enterprise integration patterns (eip) were used in the architecture design. keywords-enterprise integration; erp; soa; web service; enterprise integration pattern; p2p i. introduction distributed manufacturing [1] consists of enterprise networks supported by computer networks. it dynamically combines core resources and skills of different entities to flexibly respond to business opportunities. this new organizational structure, used in worldwide manufacturing systems, requires the integration of distributed production planning and control systems known as enterprise resource planning (erp) systems of the individual partners. with the modern distributed manufacturing networks, global coordination among partners is thus required to integrate the erp systems of those partners to synchronize production planning and control. in other words, a function of an application may be distributed to several companies requiring the cooperation of different parts to work properly. this feature is known as processes integration. this paper is a part of a research project funded by the stdf [2-4] to create a software system that can be plugged-in any erp system of a manufacturing company to form a distributed manufacturing system. it is a plug-in component, which means that a core feature of the developed software is loosely coupling. the following features are mandatory for loosely coupling: • services are invoked remotely independently of their technology, any third part centralized entity, and location. • the plug-in component does not impose any restrictions on the hosting erp system. • the software is easily configurable to fit the member platform easily. traditionally the process of integration is done between the member systems, with the architecture shown in figure 1: in the middle, the integration broker, is a centralized hub [5]. it uses a central logic that can receive messages from multiple destinations, determine the correct destination and route the message to the correct channel. however, this architecture violates the loosely coupled feature of distributed systems, because having a single hub may make the system easy to manage but scalability becomes a problem. at some point, as the number of members increases, the messages increase, scalability gets bigger, and central integration management becomes more sophisticated corresponding author adel n. ghannam engineering, technology & applied science research vol. 9, no. 2, 2019, 4075-4078 4076 www.etasr.com ghannam et al.: perspectives of an enterprise integration plug-in system architecture for networked … fig. 1. traditional central integration ii. the solution framework in this work, we overcome the centralized limitation by developing a system that can be pluggedin the erp system of the network members based on: • soa framework. • point-to-point messaging architecture. • the concept of enterprise service bus (esb). soa is an architectural pattern that involves decomposing applications into managed networks of inter-operating services. those services could be implemented in a variety of technologies. soa, the web services description language (wsdl) and web services solutions [6, 7] support two key roles: a service requester (client) and a service provider, which communicate via service requests. service requests are messages formatted according to the simple object access protocol (soap). soap is a light-weight protocol allowing remote procedure calls (rpcs) over the internet using a variety of transport protocols. in principle, soap provides a distributed processing model that assumes a soap message originates at an initial soap sender and is sent to an ultimate soap receiver. the soap specification establishes a standard message format that consists of an xml document. the soap request is received by a runtime service (an soap “listener”) that accepts the soap message, extracts the xml message body, and delegates the request to the actual function or business process within an enterprise. after processing the request, the provider typically sends a response to the client in the form of an soap envelope carrying an xml message. wsdl is a w3c specification providing the foremost language for the description of web service definitions. web services need to be defined in a consistent manner so that they can be discovered by and interfaced with other services and applications. a wsdl service description, describes the point of contact for a service, also known as the service endpoint or endpoint. it establishes the physical location of the service and provides a formal definition of the endpoint interface so that programs wishing to communicate with the service know exactly how to structure the required request messages. wsdl is often used in combination with soap and an xml schema to provide web services over the internet. a client program connecting to a web service can read the wsdl file to determine what operations are available on the server. the client can then use soap to actually call one of the operations listed in the wsdl file using for example xml over http point-to-point (p2p) messaging architecture [8] is adopted (figure 2). the architecture is developed using the eips [8], to benefit from the architects expertise encapsulated in the eip design patterns. fig. 2. scheme of p2p messaging the main issues to notice in p2p are: • components directly interact as peers by exchanging services, which is matching the business case of a distributed manufacturing network, where each member is communicating with other identified members. • a system with completely decentralized self-organization and resource usage. • each peer provides and consumes similar services. • peers have the same capabilities (ability to act in any role, can act as “clients” and “servers” at the same time). • high scalability (the system can grow to a very large number of peers). the third member employed in our base concepts is the esb [9] (figure 3). soa, eda, and web services are combined to implement the integration media. the esb provides messaging, routing and transformation capabilities that enable services to be easily integrated at development time or runtime. the esb acts as an intermediary layer to enable communication between different application processes. a service deployed onto an esb can be triggered by a consumer or an event. we have used the esb concept, but without having a centralized reference entity, to configure the plug-in component at installation time on a partner erp server. fig. 3. illustration of esb iii. the proposed architecture with eip the system should be able to respond to the following cases: • a company wants to join a particular manufacturing network. • a company creates a network for its end product. • a prime partner (the end product owner) wants delegating production orders to specific members. engineering, technology & applied science research vol. 9, no. 2, 2019, 4075-4078 4077 www.etasr.com ghannam et al.: perspectives of an enterprise integration plug-in system architecture for networked … • wip monitoring at different partners locations. the metamodel of the adopted architecture is given in figure 4. each member of the network is having a plug-in integration unit known as the end point logic. fig. 4. the role of the endpoint it is the messaging endpoint code that takes remote service call-command or data, turns them into a message, and sends it on a particular messaging channel using http. it is the endpoint that receives a message, extracts the contents, and gives them to the application in a meaningful way. the endpoint main function is orchestration of how services interact at the message level, including the business logic and execution order of interactions under control of a single endpoint. the detailed architecture of the endpoint logic, using eip components, is given in figure 5. fig. 5. endpoint architecture using eip components each endpoint contains two processors, the sender logic and the receiver logic. at any instance, every endpoint is managing two processing channels. a. on the sender side the owner identifies the partner, the end-product code and the component code to be assigned to the partner, using the configuration console. the configurator request, from the wsdl object, the xml of the end-product bom and the xml of the component are constructed. the wsdl object will then invoke the xsd editor to construct the xsd of both the end-product and the component of target partner. for a large xsd document we may need to divide the document into a sequence of segments, which is done by the message sequence object. segmentation is required when the data packet is larger than the maximum transmission unit supported by the network or when the network is unreliable and it is desirable to divide the information into smaller segments to maximize the probability that each one of them can be delivered correctly to the destination. a set of identifiers are used to designate the components of the segment, as illustrated in figure 6. fig. 6. hierarchy of the sequence identifiers this hierarchy indicates that each sequence is divided into segments using the sequencer in the sender logic. these segments are collected on the receiving logic. each item in the hierarchy has an id. it is the role of the message sequencer to generate the sequence. then the resulting sequence is passed to the soap wrapper and the wrapped messages are passed to the channel adapter which will assign a specific channel and then generate the http request for the remote partner. b. on the receiver side: the channel adapter captures the relevant htpp request to the receiver url, using the logic of “check selective consumer” component. after checking the receiver address, the sequence is passed to the resequencer. the resequencer secures reconstructing the send sequence into a correct ordered series using the identifiers of the sequence, the segment position, and the message id. each message coming out of the resequencer is passed to the “unwrap soap” component, to produce a plain xml/xsd message. the resulting message invokes the “service activator” interfacing with the ws hosted by the receiving erp. for each message, a reply message is generated. the reply message is carrying a “correlation identifier”, which is the sender message id. when the caller receives this correlation identifier, the caller can thus link the reply to the sender. iv. conclusion in this paper we presented the developed architecture of a plug-in integration unit with the following attributes: engineering, technology & applied science research vol. 9, no. 2, 2019, 4075-4078 4078 www.etasr.com ghannam et al.: perspectives of an enterprise integration plug-in system architecture for networked … • it integrates manufacturing planning processes of members in a distributed manufacturing network. • the unit is plug-in and easily configurable, working in p2p network and not needing a centralized integration system. therefore, it eliminates the difficulty of scalability with centralized integration logic. • it satisfies the mandatory loosely coupling of distributed systems. it works in the soa framework through web services ws. • it applies the concept of rmi using soap-xml messaging technology. • it uses eip to build the architecture based on the logical uml models developed prior to the presented architecture. the architecture is implemented using the spring development framework [10]. references [1] h. kuhnle, distributed manufacturing, paradigm, concepts, solutions and examples, springer-verlag, 2010 [2] a. ghannam, a. el-bastawisy, n. s. abdel nour, h. mansour, m. hamed, developing a national technology toolkit, integrating technologies of bpm, web services, and rfid to consolidate egyptian manufacturing into global value chain, technical report, 2017 [3] a. ghannam, a. el-bastawisy, n. sobhi, h. mansour, m. hamed, developing a national technology toolkit, integrating technologies of bpm, web services, and rfid to consolidate egyptian manufacturing into global value chain, technical report 2, 2017 [4] a. ghannam, a. el-bastawisy, n. sobhi, h. mansour, m. hamed, developing a national technology toolkit, integrating technologies of bpm, web services, and rfid to consolidate egyptian manufacturing into global value chain, technical report 3, 2018 [5] h. l. lee, s. whang, e-business and supply chain integration, stanford university, 2001 [6] d. georgakopoulos, m. p. papazoglou, service-oriented computing. mit press, 2009 [7] k. j. clark, integration architecture: comparing web apis with serviceoriented architecture and enterprise application integration, available at: https://www.ibm.com/developerworks/websphere/library/techarticles/15 03_clark/1305_clark.html, 2015 [8] g. hophe, b. woolf, enterprise integration patterns, addison-wesley, 2012 [9] d. a. chappell, enterprise service bus, o’reily media, 2004 [10] m. fisher, m. bogoevici, i. fuld, j. partner, o. zhurakousky, g. russell, d. syer, j. long, d. turanski, g. hillert, a. bilan, a. nayak, j. bryant, spring integration, available at: https://docs.spring.io/springintegration/reference/html/index.html . engineering, technology & applied science research vol. 8, no. 6, 2018, 3576-3579 3576 www.etasr.com jatoi et al.: study of physicochemical properties of commercial drinking bottled water brands study of physicochemical properties of commercial drinking bottled water brands abdul rehman jatoi department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, sindh, pakistan arjatoi@quest.edu.pk abdul qayoom jakhrani department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, sindh, pakistan aqunimas@hotmail.com kishan chand mukwana department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, sindh, pakistan kcmukwana@quest.edu.pk abdul nasir laghari department of energy and environment engineering, quaid-eawam university of engineering, science and technology, nawabshah, sindh, pakistan mashaalnasirlaghari@gmail.com muhammad mureed tunio department of energy and environment engineering, quaid-eawam university of engineering, science and technology, nawabshah, sindh, pakistan mureed.tunio@gmail.com abstract—drinking water quality is being affected by industrial effluents, pesticides and fertilizers, poor sanitation services and unhygienic practices. thus, upper and middle-class people used to prefer bottled water for drinking instead of tap water. increasing demand for bottled water leads to the presence of low quality branded waters in the market due to the high demand and improper quality checks. in this regard, this study is carried out to assess the physicochemical properties of various branded bottled waters. for that, ten different water brand samples, coded from s1 to s10, were collected from safoora goth, karachi. various physicochemical quality parameters of branded water samples were analyzed according to the set procedures of american society for testing and materials. it was discovered that the ph levels of s9 and s8 bottled water brands were slightly less than world health organization guideline values. the physical and chemical quality parameters of s1, s2, s4, s5, s7, and s10 branded bottled water samples were found within standards. keywords-drinking water; bottled water; physicochemical properties; contamination i. introduction sufficient quantity of clean and safe water is crucial to human health [1-3]. population growth, rapid urbanization, industrialization, changing lifestyles and economic development cause severe stress not only on the quantity of available water resources but also on its quality [4, 5]. water resources are being contaminated by different physical, chemical and biological agents. its quality control is essential for environment preservation and for public health protection [6]. increasing rate of pollution in fresh water resources amplified the demand for bottled water [7]. bottled water consumption has significantly increased the last three decades, particularly in food and beverage industries with an annual average of 12% in spite of its high cost [8]. its annual average consumption is more than 100 liters per person in fifteen countries, and over 200 liters per person in mexico, italy, and the united arab emirates [7]. it is reported that bottle water utilization has been increased enormously in pakistan, approximately from 6% to 10% from 2003 to 2007 [9-12]. karachi is the biggest urban center and city of pakistan having population of more than 16 million [13, 14]. upper and middle class people use to prefer bottled water for drinking purpose instead of using tap water as it is considered to be free from contaminants [1, 11, 12, 15, 16]. although it is prerequisite for bottled water brands to register for quality production in pakistan, nevertheless replicas and inferior brands are posing serious threat to the public health. its high demand leads to the existence of low quality brands in the market [17]. the present study is an attempt to investigate on the physicochemical quality parameters of different branded bottled waters, commonly consumed by the people of karachi. ii. materials and methods samples from ten local bottled water brands were taken from different shops and supermarkets of safoora goth during the september to october time period. five samples of each brand were examined in the laboratory. the sample brands were assigned codes from s1 to s10. these codes were assigned for recognition of water samples during and after analysis. thermo-set containers were used to preserve the samples at 25°c [18-20]. the drinking quality parameters examined in the laboratory were ph, tds, ec, salinity, alkalinity, chlorides, hardness, turbidity, color, nitrates and fluorides. ph meter, gravimetric method, floating glass hydrometer and hi98302 meter were used to analyze ph, tds, salinity and ec respectively. titration method was employed for alkalinity, total hardness and chloride measurements. turbidity was measured with the use of a nephelometer engineering, technology & applied science research vol. 8, no. 6, 2018, 3576-3579 3577 www.etasr.com jatoi et al.: study of physicochemical properties of commercial drinking bottled water brands (turbidimeter), color by platinum-cobalt method and nitrates with phenol disulphuric acid method. fluoride content in was tested with spectrometer. iii. results and discussion all samples were examined according to defined procedures of astm and were compared with who standards. a. turbidity, colour and ph turbidity level and color of all examined samples were found within permissible limits. the level of ph in examined water samples is shown in figure 1. maximum ph value of 8.21 was found in s3 and minimum in s9 with 6.1. b. tds and ec the values of total dissolved solids (tds) samples are given in figure 2. maximum tds of 383mg/l was found in s9 and minimum 156mg/l in s1 and s2. besides tds, the results of electrical conductivity (ec) are given in figure 3. the maximum electrical conductivity value was found in s5 with 490µs/cm and minimum from s1 with 333µs/cm. the ec of all samples was found within who allowable limit of 2500µs/cm. fig. 1 level of ph in local brand bottled water samples fig. 2 level of total dissolved solids in local brand bottled water samples c. salinity, alkalinity and hardness figure 4 displays the analyzed values of salinity. three brands, namely s5, s6 and s7 displayed maximum salinity of 0.3%. the minimum concentrations of salinity were found in s1, s2, s3, s4, s8, s9 and s10 with 0.2%. moreover, maximum alkalinity of 120mg/l was found in s2 and minimum 53mg/l in s8 as shown in figure 5. similarly, the maximum level of hardness with 103mg/l was found in s8 and minimum 33.25mg/l in s1 as shown in figure 6. the results of hardness in all water samples were within who guideline value of <500mg/l. fig. 3 level of electrical conductivity in local brand samples fig. 4 level of salinity in local brand bottled water samples fig. 5 level of alkalinity in local brand bottled water samples d. chloride, fluoride and nitrates the chloride results are displayed in figure 7. maximum chloride value of 130mg/l was found in s5 and minimum of engineering, technology & applied science research vol. 8, no. 6, 2018, 3576-3579 3578 www.etasr.com jatoi et al.: study of physicochemical properties of commercial drinking bottled water brands 42.54mg/l in s1. the level of fluoride in water samples is shown in figure 8. maximum fluoride value was 0.9mg/l in s3 and minimum in s1, s7 and s8 brands with 0.2mg/l. figure 9 demonstrates the values of nitrates in the samples. maximum of 21mg/l was found in s6 and minimum 0.6mg/l in s1. fig. 6 level of hardness in local brand bottled water samples fig. 7 level of chlorides in local brand bottled water samples fig. 8 level of fluoride in bottled water samples iv. conclusion in this study, water samples of bottled water from 10 local brands were assessed for physicochemical properties. it was found that the ph value of s9 and s8 bottled water samples were slightly less than who guideline values. the results of s1, s2, s4, s5, s7 and s10 water brands were found within guideline values. it is strongly recommended that environmental protection agencies organize seminars, workshops and training programs to create awareness about the adverse impacts of polluted water. fig. 9 level of nitrates in local brand bottled water samples references [1] a. khatoon, z. a. pirzada, “bacteriological quality of bottled water brands in karachi, pakistan”, biologia (pakistan), vol. 56, no. 1-2, pp. 137-143, 2010 [2] o. oyedeji, p. o. olutiola, m. a. moninuola, “microbiological quality of packaged drinking water brands marketed in ibadan metropolis and ile-ife city in south western nigeria”, african journal of microbiology research, vol. 4, no. 1, pp. 96-102, 2010 [3] z. peh, a. sorsa, j. halamic, “composition and variation of major and trace elements in croatian bottled waters”, journal of geochemical exploration, vol. 107, no. 3, pp. 227-237, 2010 [4] e. o. oyelude, s. ahenkorah, “quality of sachet water and bottled water in bolgatanga municipality of ghana”, research journal of applied sciences, engineering and technology, vol. 4, no. 9, pp. 1094-1098, 2012 [5] r. cidu, f. frau, p. tore, “drinking water quality: comparing inorganic components in bottled water and italian tap water”, journal of food composition and analysis, vol. 24, no. 2, pp. 184-193, 2011 [6] s. n. majid, z. h. g. ahmad, z. k. muhammad, “a study of some physicochemical parameters of plastic bottled drinking water from different sources (manufactured brands) in kurdistan region-iraq”, international journal of plant, animal and environmental sciences, vol. 5, no. 4, pp. 129-133, 2015 [7] m. diduch, z. polkowska, j. namiesnik, “factors affecting the quality of bottled water”, journal of exposure science and environmental epidemiology, vol. 23, no. 2, pp. 111-119, 2013 [8] e. i. brima, “physicochemical properties and the concentration of anions, major and trace elements in groundwater, treated drinking water and bottled drinking water in najran area, ksa”, applied water science, vol. 7, no. 1, pp. 401-410, 2017 [9] j. j. toma, n. s. hanna, b. a. mohammed, “effect of storage condition on some bottled water quality in erbil city, kurdistan region-iraq”, international journal of software and web sciences, vol. 3, no. 1, pp. 33-43, 2013 [10] l. w. mays, water resources engineering, john wiley & sons, 2010 [11] w.h.o., guidelines for drinking water quality, who, geneva, switzerland, 2004 [12] m. t. samadi, a. r. rahmani, m. sedehi, n. sonboli, “evaluation of chemical quality in 17 brands of iranian bottled drinking waters”, journal of research in health sciences, vol. 9, no. 2, pp. 25-31, 2009 [13] f. perveen, u. asghar, t. h. usmani, “evaluation of water quality of different colleges of karachi city”, journal of the chemical society of pakistan, vol. 29, no. 5, pp. 458-462, 2007 engineering, technology & applied science research vol. 8, no. 6, 2018, 3576-3579 3579 www.etasr.com jatoi et al.: study of physicochemical properties of commercial drinking bottled water brands [14] s. t. betelhem, development impacts of poor accessibility of potable water supply and basic sanitation in rural ethiopia: a case study of soddo district, msc thesis, university of agder, 2011 [15] s. d. raj, “bottled water: how safe is it?”, water environment research, vol. 77, no. 7, pp. 3013-3018, 2005 [16] i. z. mihayo, s. l. mkoma, “chemical water quality of bottled drinking water brands marketed in mwanza city, tanzania”, research journal of chemical sciences, vol. 2, no. 7, pp. 21-26, 2012 [17] n. rosemann, drinking water crisis in pakistan and the issue of bottled water: the case of nestlé’s ‘pure life, actionaid pakistan, 2005 [18] s. r. samo, a. r. jatoi, f. h. mangi, a. n. laghari, k. c. mukwana, “design of a slow sand bed filtration system for purification of canal water”, quaid-e-awam university research journal of engineering, science & technology, vol. 14, no. 1, pp. 14-18, 2015 [19] k. h. lashari, a. l. korai, g. a. sahato, t. g. kazi, “limnological studies of keenjhar lake, district, thatta, sindh, pakistan”, pakistan journal of analytical and environmental chemistry, vol. 10, no. 1-2, pp. 39-47, 2009 [20] m. f. alam, n. c. dafader, s. sultana, n. rahman, t. taheri, “physicochemical analysis of the bottled drinking water available in the dhaka city of bangladesh”, journal of materials and environmental science, vol. 8, no. 6, pp. 2076-2083, 2017 engineering, technology & applied science research vol. 8, no. 3, 2018, 3004-3008 3004 www.etasr.com munir and qurashie: a semi-hexagonal array (1×2) antenna using half mode substrate integrated … a semi-hexagonal array (1×2) antenna using half mode substrate integrated waveguide for short range communication devices mehr e. munir electrical engineering department iqra national university peshawar, pakistan mehre.munir@inu.edu.pk shahryar shafique qurashie electrical engineering department iqra national university peshawar, pakistan its_shahryar@hotmail.com abstract—in this paper, the authors propose a single element semi-hexagonal half mode substrate integrated waveguide (hmsiw) antenna split across the line joining the opposite edge center of a hexagonal cavity, such that the line of separation includes the radiating edge, while the other edges are lined with metallic vias. the antenna was designed and fabricated on arlon ad270 and the substrate has a gain of 5.8 db at 5.9 ghz. the proposed array element is then used to design a linear array (1×2) resonating at 5.95 ghz. antennas are useful applications in vehicular communication systems, serving as internal parts of dedicated short range communication devices with frequency of operation laying in the ieee 802.11p band. keywords—semi-hexagonal array; short range; vehicular communication i. introduction dedicated short range communication (dsrc) is popularized worldwide as the wireless communication protocol for vehicles following wi-fi architecture [1] and it was initially focused on low overhead operations following ieee 802.11a standards. however, with the advent of years and in compliance with development and modern needs to support high-speed moving vehicles and to further simplify the communication mechanisms, ieee working group amended ieee 802.11 standards to incorporate wireless access in vehicular environments (wave). wave formed the core of dsrc in supporting intelligent transportation systems’ (its) applications for short range communication. wave, following ieee 802.11p standards, provides real-time traffic information, improves transportation safety, minimizes traffic congestion and helps maintaining transport sustainability. it helps establishing communication between vehicles (v2v) or between vehicles and roadside information (v2i) in the 5.9 ghz band (5.85–5.925 ghz) [2-5]. with the involvement of several companies, car manufacturers and universities worldwide pursued extensive research to develop ieee 802.11p standard commercial products. researchers extended their contribution in developing printed antennas and arrays to be used in conjunction with other devices for short range communication to support its applications [6-9]. though hexagonal shaped substrate integrated waveguide (siw) based components are widely popular [10-14], yet little has been reported about the unexplored domain of hexagonal siw based antennas and arrays. as a result, in this paper, authors propose a novel semi-hexagonal hmsiw antenna operating at ieee 802.11p frequency of 5.9 ghz and subsequently developed linear and planar arrays using the former as array elements. the 1×2 semi-hexagonal hmsiw array operates at a resonating frequency of 5.9 ghz with a gain of 8.2 db. the antennas are designed and fabricated using arlon ad270 substrate and the necessary full wave simulation are all carried out in ansys hfss v15.0. the simulation obtained results are compared with experimentally obtained results. ii. antenna design the concept of hexagonal waveguide is further extended to a substrate integrated waveguide concept wherein the metallic walls lying along the direction of the propagation are replaced by metallic conducting vias and the whole waveguide is integrated into a dielectric filled pcb. due to the resemblance of the hexagonal waveguide with the circular/cylindrical one, the former has been modeled in terms of its circular counterpart. the first twenty one normal modes and corresponding cut-off frequencies are all obtained for the emodes of waveguides with regular hexagonal cross-section. the cut-off frequency of the first mode for a hexagonal waveguide is given as the designing of antenna is achieved level by level in a appropriate way. the basic shape is shown in figure 1[14-18]. = √ (1) where c is the speed of light in vacuum (≈3×1010cm×s-1), kcmn, is the cut-off wave number and s is the side length of the regular hexagon. the fundamental tm01 mode is chosen as the mode of operation as it provides maximum directional radiation from the antenna. the cut-off wave number of the tm01 mode obtained after putting m=0, n=1 and kc01=2.69 is re tr ac te d lea me num of lea the fre the cav fre wi len the cav the fab 5.9 oth a. ant cha pro b. pat fre c. pat wh and he res by of cen dia res engineerin www.etasr = . √ however a d ads to the va ethods have b mber of the h such a struct ads to the acce e designed pr equency of a f e tm01 mode = . √ initially a f vity with side equency of 5.9 ith the array in ngth reduced t eoretical cut o vity for tm01 e resonating bricated proto 9ghz are sho her dimensions substrate sel substrate sel tenna. due t aracteristics a oposed design patch width with the hel tch is calculate = here εr is equency and c patch length with the hel tch is calculate = here d = the hexago ence, preservin sonator, we ca bisecting the bisection lie nters and type agonal of the spectively. w ng, technology r.com direct approxim alue shown in been used for hexagonal wav ture modeled eptance of the rototypes. th full mode hex is given by full-mode siw e length s=15 9ghz exciting ncorporation a to 13.5mm. s off frequency 1 mode obtain frequency ob otype and the wn in figure s are shown in lectivity lectivity is the o its high p arlon ad270 [16]. lp of the follo ed [17]. the relative c is the rapidity h lp of the follo ed [17-18]. 2∆ = 1 nal cavity is ng the tm01 an obtain two t cavity in two s along the p e-2, in which t hexagon, as d we chose the y & applied sci munir and mation from a n [15]. the f r approximatin veguide, and a as a substrate e modified val hus the formu xagonal siw c w (fmsiw) 5mm was desi g the fundam along its perip ubstituting s= of a full mo ned is 5.9ghz btained throug e fundamenta 1 (b) and (c) n table i. first step whe erformance a is chosen a owing equatio e constant w y of light in va owing equation / s symmetrical 1 mode of the types of half m o ways: typeplane joining the line of bise depicted in fig type-1 hms ience research d qurashie: a s (2) circular wave fact that num ng the cutoff also, the appli e integrated c lue as applica ula for the cu cavity, operat (3) regular hexa igned at the mental tm01 m phery the actua =13.5mm in (3 ode hexagonal z which is eq gh simulation al tm01 mo ) respectively, en designing a and high relia as substrate fo on, the width (4) with f0 functi acuum. n, the length (5) (6) (7) l about two e parent hexa mode siw ant 1, in which th the opposite ection lies alon gures 2(a) and siw structure v semi-hexagona eguide merical wave cation cavity, able in ut off ting in agonal center mode. al side 3), the l siw qual to n. the ode at , their patch ability or the of the ioning of the axes. agonal tennas he line edge ng the d 2(b) e. the hm alon dev hex fig (tm loss mm con diam cen inse dist stru sup nec fig. distr of th fig. ante l 60 vol. 8, no. 3, 20 al array (1×2) a msiw based se ng the walls o void, lying al xagonal cavity gure 3. the an m) with 0.79 m s tangent tan m(l)×60 mm(w nsidering the c meter is 1 m nter) is 1.5 mm et feed of wid tance of l5=8 ucture to mat ppress reflect cessary dimens (b 1. (a) geom ribution for the pr he cavity. 2. design of enna table i. l 60 table i. l w h 60 0.78 018, 3004-3008 antenna using emi-hexagonal of the hexagon long the line y and excited ntenna is devel mm thickness nδ=0.002 wi w). the leng corrected edge mm while the m. to excite th dth l7=0.58 m 8.22 mm from tch with the tion inducing sions of the an b) metry of the fms rincipal tm01 m (a) f (a) type-1 and dimensions of w s 60 15 0 dimensions of i1 i2 15 30 8 half mode sub l antenna lined n with the rad of bisection d with inset f loped on arlo s, dielectric co ith its overa gth of each si e length, is s=1 inter-via sep he fundamenta mm is inserte m the base of t 100 ω impe g spurious b ntenna are enlis (a) siw hexagonal ca mode at 5.9ghz. ( (b d (b) type-2 hm f the fmsiw hex h i1 i2 0.78 15 15 the fmsiw hexa i3 i4 17 30 8. 3005 bstrate integrat d with metallic diating surface of the full m feed is depicte on ad270 sub onstant ɛr=2.7 all size being de of the ant 13.5 mm. the paration (cente al tm01 mode ed at an optim the semi-hexag dance in ord beams. the sted in table i (c) avity. (b) electri (c) fabricated pro ) msiw semi-hex xagonal cavity 2 g 5 15 agonal cavity ( i5 i6 .21 1.72 0 ted … c vias , vias mode ed in strate 7 and g 60 tenna, vias’ er-toe, the mized gonal der to other ii. c field ototype agonal (mm) (mm) i7 0.56 r et ra ct ed fig fab fig hex fig tm tm opt nar engineerin www.etasr (a) (b) g. 3. (a) geo bricated prototype g. 4. simulated xagonal antenna fo g. 5. electric m01 mode. the simulate m01 mode of timized return rrow impedan ng, technology r.com ometry of the e of the cavity. d and measured for tm01 mode. field distributio ed fundament the single arr n loss value (s nce bandwidth y & applied sci munir and hmsiw semi-h return loss value on of the array e tal resonating rray element i s11 parameter) of 80 mhz ( ience research d qurashie: a s hexagonal antenn e of the hmsiw element at 5.9 g g frequency fo is 5.9 ghz w ) of -28.4 db w (5.93-5.85 gh v semi-hexagona na. (b) w semighz for or the with an with a hz) i.e. 1.36 mea ther mea retu sem dist rad fig the mh figu is 5 sim 4.8 both the fig. ante sim var d. illu freq s21 sep fro elem occ our elem vol. 8, no. 3, 20 al array (1×2) a 6% fractiona asured throug reby reflecting asured values. urn loss (s11 v mi-hexagonal a tribution for iation pattern gure 6. the rad help of hittite hz–20 ghz) a ure it is eviden 5.8 dbi while mulated and me dbi and 4.7d h eand h-pl antenna is obs (a) (b) 6. 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(b) fabricate v. anten from the simu operate at 5.9 6db while the na is -26.6db tenna (1×2), dbi with the r the same ante arized gains ar provement of mparison to the fig. 9. re an hmsiw b signed at ieee n of 5.8 db. t 018, 3004-3008 antenna using 1 (1×2 array ele ed prototype nna designing ar ulated results, 1ghz. the ob e correspondin b at 5.86ghz the simulated corresponding enna, the simu re 8.1dbi and f 2.4dbi is ac e single eleme eturn loss (s11) p vi. co based semi-he e 802.11p fre this parent ant 8 half mode sub ements) (a) geo g and result rray the linear arra btained simula ng measure v z. in figure 1 d e-plane co g measured v ulated and me 7.9dbi respec chieved with ent antenna. arameters of ante onclusion exagonal anten quency of 5.9 tenna is used a 3007 bstrate integrat ometry of linear ts of 1×2 linea ays (1×2) are f ated return los value using an 11 we see tha o-polarized ga value being 8 asured h-plan ctively. thus a the 1×2 arra enna (1×2) array nna is proposed 9 ghz produc as an array ele ted … r array ar found ss is nritsu at for ain is .1db. ne coa gain ay in d and cing a ement re tr ac te d in 5.9 is o the to arr enh 1× enh fig mo fig sim un con [1] [2] [3] engineerin www.etasr designing and 9 ghz and the observed that e array elemen a greater exte rays with red hancement ha 2 the corres hancement by g. 10. electric f de g. 11. e-plane mulated results. m the authors niversity for p nstruction of t d. jiang, l. standard for vehicular tec 2036–2040, 20 s. eichler, “p communicatio (vtc-2007), b ieee standar vehicular envi ng, technology r.com d fabricating li eir various para the presence nts reduces th ent thereby fa duced sizes. as been succe sponding gai 2.4 and 5.4 db field distribution pattern of antenn m: measured resul acknow would like to providing the the hardware m refe delgrossi, “iee wireless acces chnology confere 008 performance eva on standard”, ie baltimore, usa, p rd committee, ie ironments (wav y & applied sci munir and inear and plan ameters are stu of pec walls he mutual coup acilitating the the primary essfully achiev in is 8.2 db b over the par of antenna-1 (1 na (1×2 antenna lts. wledgement o acknowledg means and e model. erences ee 802.11p: to ss in vehicular ence (vtc-2008) aluation of the eee vehicular t pp. 2199–2203, 2 eee standard f ve)-networking s ience research d qurashie: a s nar antenna arr udied extensiv on the two sid pling between design of co objective of ved. for the b indicating rent antenna. ×2 elements) for a array) at 5.91g ge the iqra na environment fo owards an intern environments”, ), calgary, cana ieee 802.11p technology con 007 for wireless acc services, ieee, 20 v semi-hexagona rays at vely. it des of n them mpact f gain linear gain r tm01 ghz. s: ational for the national , ieee ada, pp. wave nference cess in 007 [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] vol. 8, no. 3, 20 al array (1×2) a f. bai, h. communication transportation september 17–2 a. vinel, “3gp is able to supp wireless comm j. hirokawa, m for plane tem antennas and p h. uchimura, t waveguide”, ie vol. 46, pp. 243 d. deslandes, k circuits and w theory and tec f. xu, k. wu, integrated wave techniques, vo d deslandes, k considerations o on microwave 2006 l. yan, w. ho experiment on s components le d. deslandes, concept and des proceedings (a g. q. luo, z. f by substrate int propagation let j. c. bohorquez pena, h. f. gu backed antenna 8, pp. 1139-114 m. h. awida, cavity-backed 2 wireless propag h. wang, d. g. integrated wave on antennas an q. lai, c. fum propagation pro ieee transacti 8, pp. 1996-200 j. xu, w. ho integrated wav wave applicatio vol. 7, pp. 85-8 018, 3004-3008 antenna using krishnan, “reli n for vehicle s systems confe 20, 2006 pp lte versus ie port cooperative munication letters m. ando, “single-l wave excitation i pr opagation, vol. t. takenoshita, m eee transactions 38-2443, 1998 k. wu, “single-s waveguide filters chniques vol. 51, , “guided-wave a 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pp. 3 g, l. l. sun, “pla de cavity”, ieee 236-239, 2008 za, i. c. h. pinzo substrate integra as and wireless pr ubstrate integrate atch array antenn ol. 8, pp. 1054-10 , w. q. che, “die plane horn antenn vol. 58, no. 3, pp. r. vahldieck, “ lf-mode substrate ve theory and te z. kuai, k. wu, w) leaky-wave a nnas and wirele 3008 bstrate integrat of dsrc w ns”, ieee inte 06), toronto, c ave: which techn y applications?”, pp. 125–128, 2012 uide consisting o ”, ieee transacti 25-630, 1998 lopment of a lam theory and techn ion technique of actions on micr 96, 2003 racteristics of sub microwave theor mechanisms and de”, ieee transa no. 6, pp. 2516 j. cui,”simulatio microwave and w , 2004 e leaky wave an microwave conf 46-349, 2005 anar slot antenna b antennas and w on, j. a. castiblan ated waveguide c ropagation letter ed waveguide ku a”, ieee antenn 056, 2009 electric loaded sub nas”, ieee transa 640-647, 2010 “characterization integrated waveg echniques, vol. 5 “half-mode sub antenna for mill ss propagation l ted … wireless elligent canada, nology ieee 2 f posts ons on minated niques, planar rowave ubstrate ry and design actions 6-2526, on and wireless ntenna: ference backed wireless nco, n. cavityrs, vol. u-band nas and ubstrate actions of the guide”, 57, no. ubstrate limeter letters, re tr ac te d microsoft word etasr_v13_n4_pp11124-11129 engineering, technology & applied science research vol. 13, no. 4, 2023, 11124-11129 11124 www.etasr.com zerdoumi et al.: an improved recursive least square algorithm for adapting fuzzy channel equalizer an improved recursive least square algorithm for adapting fuzzy channel equalizer zohra zerdoumi lge laboratory, department of electronics, university mohamed boudiaf of m’sila, algeria zohra.zerdoumi@univ-msila.dz (corresponding author) latifa abdou li3cub laboratory, department of electrical engineering, university of mohamed khider, algeria l.abdou@univ-biskra.dz elkhanssa bdirina laadi laboratory, faculty of science and technologies, university of djelfa, algeria khansabdirina@yahoo.fr received: 3 april 2023 | revised: 2 may 2023 | accepted: 17 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5906 abstract adaptive filters have been thoroughly investigated in digital communication. they are especially exploited as equalizers, to compensate for channel distortions, although equalizers based on linear filters perform poorly in nonlinear distortion. in this paper, a nonlinear equalizer based on a fuzzy filter is proposed and a new algorithm for the adaptation parameters is presented. the followed approach is based on a regularization of the recursive least square (rls) algorithm and an incorporation of fuzzy rules in the adaptation process. the proposed approach, named improved fuzzy recursive least square (ifrls), enhances significantly the fuzzy equalizer performance through the acquisition of more convergence properties and lower steady-state mean square error (mse). the efficiency of the ifrls algorithm is confirmed through extensive simulations in a nonlinear environment, besides the conventional rls, in terms of convergence abilities, through mse, and the equalized signal behavior. the ifrls algorithm recovers the transmitted signal efficiently and leads to lower steady-state mse. an improvement in convergence abilities is noticed, besides the rls. keywords-channel equalization; digital communication; nonlinear channels; adaptive fuzzy filtering i. introduction channel equalization has attracted a great attention owing its success in achieving high-speed data transmissions. equalization technique can cancel linear and nonlinear distortions and therefore recover the transmitted data [1, 2]. linear distortion can be caused by inter-symbol, co-channel and adjacent channel interferences, in the presence of additive white gaussian noise (awgn). burst noise, amplifiers, converters, and the modulation process can produce nonlinear distortions. different signal processing techniques have been implemented to perform adaptive channel equalization [3-11]. conventional adaptive filtering techniques [2, 4] perform well on linear channels, nevertheless, they perform poorly on severe and nonlinear channels [3, 6-11]. a diversity of nature and human intelligence-inspired techniques for channel equalization have been proposed [3, 5-14], including artificial neural networks [5-11], particle swarm optimization [12], artificial bee colony [13], firefly [14], and fuzzy logic [15-19]. among them, fuzzy logic is considered as a natural manner to represent and process uncertain data [20]. the revealed benefits of fuzzy logic are the ability to reduce the system complexity and procuring more robustness [15, 17, 19]. fuzzy logic incorporates a simple "if-then" rule-based approach to solve a problem rather than modeling the system mathematically [15, 20-22]. several researches have reported that incorporating fuzzy logic in adaptive filter structures improves their performance [15, 16]. adaptive fuzzy filters have been widely used in nonlinear channel equalization [15, 17, 19, 23-26]. if-then fuzzy rules using input-output data pairs of the channel allow implementing adaptive equalizers to eliminate severe channel distortions [16, 17]. adaptive algorithms are applied to change parameters of the adaptive nonlinear fuzzy equalizers through membership functions such as least square and rls algorithms [15, 16, 19, 23-26]. engineering, technology & applied science research vol. 13, no. 4, 2023, 11124-11129 11125 www.etasr.com zerdoumi et al.: an improved recursive least square algorithm for adapting fuzzy channel equalizer in this context, a new approach to adapt the nonlinear fuzzy equalizer is proposed. the new adaptation algorithm uses fuzzy logic reasoning through nonlinear membership functions in addition to the improvement procured in the rls. the proposed approach, named improved fuzzy recursive least square (ifrls) algorithm, consists of a particular regularization of the rls algorithm that improves significantly the adaptive fuzzy equalizer and guarantees a great improvement in performance by acquiring more convergence abilities and lower steady-state mse. ii. fuzzy logic fundamentals fuzzy systems perform nonlinear relationships between the input and the output. they do not make assumptions concerning the process structure, or invoke any kind of probabilistic distribution model [15-18]. the basic structure of a general fuzzy logic system is illustrated in figure 1. fig. 1. structure of a fuzzy logic system. the principal form of a fuzzy logic system includes the fuzzy rule base, fuzzification process, inference engine, and the defuzzification process [15, 23, 26]. a. fuzzy rule base the fuzzy rule base is the main module of a fuzzy system and consists of expert knowledge formed of a set of linguistic rules such as "if a set of condition are satisfied, then, a set of consequence are inferred". the fuzzy rules are combined in the inference engine to produce a fuzzy output. b. inference engine the inference engine provides the relationship between the fuzzy input in terms of membership functions and the fuzzy output. c. fuzzification phase through the fuzzification step, the crisp input samples are converted into the fuzzy input described by the membership function, thus offering the degree to which the input scalar belongs to the fuzzy set, and are then mapped into the fuzzy output by means of the inference fuzzy rules. d. defuzzification phase the defuzzification stage is intended for mapping the fuzzy sets yielded by the inference engine and evaluates the fuzzy output to the crisp output in a weighted average way. iii. adaptive fuzzy equalizer the schematic of the adaptive fuzzy equalizer is depicted in figure 2. fig. 2. the fuzzy logic-based equalizer. a. design of the adaptive fuzzy equalizer the equalization problematic is to recover the transmitted unobserved data sequence �� with the highest reliability, through exploiting the information given by the noisy observation from a set of received samples �� [1, 2]. the samples �� are connected to the fuzzy equalizer inputs, then the fuzzy sets are defined over the input space, and the membership function is incorporated into the equalizer. an adaptive algorithm performs the adaptation process on the free parameters of the fuzzy equalizer [15, 16, 24, 26]. the design of the adaptive fuzzy equalizer starts through expressing the membership functions denoted as: � � � �� . � : rccu ii   ],[ . the intervals ],[  ii cc are labeled as � � , where = 1, � , �� = 1, � , and u and r are the input and the output spaces, respectively. for each � � ],[  ii cc , there is at least one �� � � � ≠ 0 . the most used membership function is of gaussian type [15, 24]:                         2 2 1 exp)( ji ji ii i ji f i i yy y σ μ (1) where ji iy and ji iσ are the center and spread parameter, respectively. afterward the fuzzy �� … ���� … rules (  ) are defined as following:  ��,..,� � : �� "� �# �� �� and $ " is � � , ���� $ is '��,…� (2) where '��,…� are the fuzzy sets labels in the output space, they correspond to the linguistic terms of the rules (1), d is the desired output of the adaptive fuzzy equalizer d=#�(∆, and k is the time index. engineering, technology & applied science research vol. 13, no. 4, 2023, 11124-11129 11126 www.etasr.com zerdoumi et al.: an improved recursive least square algorithm for adapting fuzzy channel equalizer b. the proposed fuzzy recursive least square algorithm the equalizer output xk is performed by (3). let ( ) [ ( ), ( 1),...., ( )]y k y k y k y k n   and ( 1.... )j jn be the points at which the '��,…� of the then parts have maximum membership values. ( 1.... )j jn are the free parameters of the adaptive fuzzy equalizer that are collected as in (4). θ is of 1 π n i im dimension. at this phase, the fuzzy basis function is expressed as in (5). the vector )(yq is of the dimension of the vector θ, and can be explicitly written as in (6).     1 1 1 1 ( 1..... ) 1 1 1 1 1 1 1 1 ( )... ( ) ( ) ( )... ( ) j jn n j jn n mi mn j jn nf f j jn k mi mn nf f j jn y y x y y y             (3)                 t mmmmmmmm mm nn          ,.,,.,,11.,1,,1,.,1,,1 1.,1,2,1.,1,2,11,.1,1,.,1,1 212212 11 ,.,;.;,., ;;,.,;,., θθθθ θθθθ ⋯ (4)                   1 11 1 1 1 1 1 1 1)( m j mn jn nff nff yy yy yq nj n j jn n j μμ μμ ⋯⋯ ⋯ (5)                 t mmmmmmmm mm yqyqyqyq yqyqyqyq yq nn           )(),.,();.;(),..( );..;(),.,();(),.,( )( ,.,,.,,11.,1,,1,.,1,,1 1...,1,2,1.,1,2,11,..1,1,.,1,1 212212 11 (6) equation (3) can be rewritten as:    .)( yqyx tk (7) the adaptive process accomplishes the minimization of the cost function between the adaptive fuzzy equalizer output *� �� and the desired output $� = #�(∆ as:   )())(()( 0 2 kk fiyxid k i ik kj    γλ (8) where + is the forgetting parameter, γ the lagrange multiplier ensuring regularization, and f: r n → r a general convex function. we developed a new approach to adapt the θ parameters. the proposed approach consists of an improvement of the rls algorithm [27, 28] conjointly to the incorporation of the fuzzy logic membership functions. the proposed adaptive ifrls algorithm is partially inspired from [27, 28] but our approach incorporates fuzzy logic reasoning through membership functions thus procuring more suppleness and effectiveness. the parameters adaptation process is performed explicitly as follows: ( ) ( ( ))k q y k  (9) 1 ( ) [ ( 1) ( ) ( ) ( 1)] tp k p k k k k p k      (10) 1 ( ) ( 1) ( )[ ( ) ( 1) ( )]k k p k k k p k k         (11) θ( ) θ( 1) ( ) ( ) (1 ) ( ) sgnθ( 1)) k k k k k p k k          (12) ( ) ( ) θ( 1) ( )k d k k k    (13) where ( 1) .p    , δ is a small positive number, q is defined by (5), .sgn is the sign function, and γ is the regularizing parameter set as in [27]. note that the third term in (12) materializes the regularization term performing the improvement of the rls algorithm. the updating principle of the above equations is similar to those obtained through the rls algorithm. nevertheless, the regularization parameter in addition to the fuzzy logic nonlinear membership functions procures more suppleness and nonlinear processing to the proposal. iv. simulation results and discussion we used matlab to carry out all simulations. the digital message applied to the channel is made of uniformly distributed bipolar random numbers {-1, 1}. the channel output is corrupted by zero mean awgn with a signal to noise ratio (snr) of 20 db. the forgetting parameter is set to + = 0.995 for all the algorithms. the regularization parameter for the ifrls is set to γ = 1.5 as in [27]. a. nonlinear channel model a nonlinear channel model composed of a discrete-time equivalent modelled as a finite impulse response (fir) filter, followed by polonium nonlinearity as depicted in figure 3 was considered. engineering, technology & applied science research vol. 13, no. 4, 2023, 11124-11129 11127 www.etasr.com zerdoumi et al.: an improved recursive least square algorithm for adapting fuzzy channel equalizer fig. 3. nonlinear channel model. channel nonlinearities can occur in data transmission from the saturation phenomena of the amplifiers when they operate in their high-gain limits [1, 17, 29]. channel nonlinearity spreads the signal spectrum and leads to nonlinear amplitude and phase distortions. we selected two challenging nonlinear channel equalization problems, designated by cn1 and cn2. the first nonlinear channel model output is expressed as [17, 26]: 3 1 3 ( ) ( ( )) ( ( )) ( )y k a v k a v k n k   (14) 1 2 3 ( ) ( ) ( 1) ( 2)v k h s k h s k h s k     (15) where s(k), y(k) are the channel input and output, respectively, [a1 a2 a3]=[1 0 -0.9] are coefficients that control the nonlinearity degree, n(k) is the gaussian noise, and [h1 h2 h3]= [1 0.5 0] are the fir channel coefficients [17]. the second nonlinear channel model is more challenging, as in [17]. the nonlinear part is described by (14), whereas the fir channel is chosen to be of non-minimum phase with coefficients set to [h1 h2 h3] = [0.3482 0.8704 0.3482]. such fir channels are widely used in the literature to assess the equalization task [10, 12]. b. equalizer output signals figures 4 and 5 show the equalized signals features for the linear equalizer and the nonlinear fuzzy equalizer trained respectively by the rls and the ifrls. the transmitted signal (trans-sig) is represented by a discontinued blue line, the received signal (receiv-sig) is symbolized by a solid black line, and the equalized signal (eq-sig) is represented by a red solid line for both rls and ifrls. for more convenience and visibility, the equalized signal is scaled down. as we can perceive, the received signal is distorted by isi and nonlinearity, while the additive noise some parts are amplified and some others are attenuated. the magnitude of the received signal is occasionally greater than the transmitted signal and sometimes-near zero, thus can cause error detection. channel attenuation increases when considering the nonlinear channel cn2. despite channel alterations, the ifrls exhibits the best performance. the ifrls-equalized signal is smoothed and typically close to the transmitted signal, therefore, the channel impairments are successfully cancelled. the conventional rls algorithm performs poorly. some residual distortion persists witch is noticeable on its behavior for both nonlinear channels cn1 and cn2. fig. 4. equalized signals of nonlinear channel cn1: (a) fuzzy equalizerifrls, (b) ;inear equalizer-rls. fig. 5. equalized signals nonlinear channel cn2: (a) fuzzy equalizerifrls, (b) linear equalizer-rls. c. equalizers' mean square error convergence the mean square error (mse) convergence is shown in figures 6 and 7, respectively for the nonlinear channels cn1 and cn2. 200 210 220 230 240 250 260 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 (a) number of iterations a m p li tu d e trans-sig reciev-sig eq-sigifrls 200 210 220 230 240 250 260 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 (b) number of iterations a m p li tu d e trans-sig reciev-sig eq-sig-rls 200 210 220 230 240 250 260 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 (a) number of iterations a m p li tu d e trans-sig reciev-sig eq-sigifrls 200 210 220 230 240 250 260 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 (b) number of iterations a m p li tu d e trans-sig reciev-sig eq-sig-rls engineering, technology & applied science research vol. 13, no. 4, 2023, 11124-11129 11128 www.etasr.com zerdoumi et al.: an improved recursive least square algorithm for adapting fuzzy channel equalizer fig. 6. equalizers convergence, nonlinear channel cn1. fig. 7. equalizers convergence, nonlinear channel cn2. to further highlight the improvement of our approach, the convergence mse of the ifrls is compared with the ones of the fuzzy recursive least square (frls) and the conventional rls. the ifrls shows a significant improvement in convergence and steady-state mse, when compared to the frls and the rls algorithms. when considering convergence, we can perceive that the ifrls reaches the mse level of -20 db at about 35 iterations for cn1 and 108 iterations for cn2. the frls attains the same mse level at about 255 iterations for cn1 and 525 iterations for cn2. moreover, the rls attains the 20 db mse level at about 198 iterations for cn1 and presents a mse behavior above 20 db for cn2. thus, the ifrls procures a gain in convergence of 220 and 163 iterations in comparison with frls and rls for cn1, and about 417 over the frls for cn2. when considering the steady-state mse, the ifrls reaches a steady-state of about 37 db and 34 db for cn1 and cn2, respectively, whereas the frls attains 31 db and 27 db for cn1 and cn2. the steady-state for the rls is -22 db and -18 db for cn1 and cn2, respectively. therefore, the ifrls exhibits an improvement in steady-state mse of about 6 db and 15 db against frls and rls for the nonlinear channel cn1. when considering the nonlinear channel cn2, a gain of 7 db is realized over the frls and 16 db over the rls. these improvements are summarized in tables i and ii. for more reliability, we situate our approach relatively to the results of [27]. the improvement obtained in the convergence through the proposed approach over the rls is about 163 iterations in comparison with the 155 iterations obtained in [27], whereas the gain in steady-state reached by our approach over rls is about 15 db in comparison with the 10 db obtained in [27]. that confirms the effectiveness of our approach in improving the convergence and steady-state mse. table i. mse performance algorithms convergence (iterations) steady-state (db) cn1 cn2 cn1 cn2 ifrls 35 108 -37 -34 frls 255 525 -31 -27 rls 198 -22 -18 table ii. mse improvement of the ifrls against frls and rls channels cn1 cn2 gain in convergence: ifrls over frls (iterations) 220 417 gain in convergence: ifrls over rls (iterations) 163 gain in steady-state: ifrls over frls (db) 6 7 gain in steady-state: ifrls over rls (db) 15 16 v. conclusion in this paper, a new approach for the channel equalization problem was presented, that is an improvement of the recursive least square algorithm. the proposed improvement involves conjointly a regularization for the rls and an incorporation of a fuzzy logic reasoning through membership functions. the performance of the improved fuzzy rls was compared with the ones of the fuzzy rls and the conventional rls. extensive simulations revealed that the ifrls surpasses both frls and rls. the ifrls improves considerably the convergence abilities of the adaptive fuzzy equalizer through mse by procuring lower steady-states never reached through the frls and the conventional rls. the proposed approach was also compared with [27]. the proposed ifrls realizes an improvement in convergence and steady-state over rls that surpasses the improvement realized in [27], confirming its effectiveness in 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[29] jake et al.: spectral re-growth suppression in the fbmc-oqam signal under the non-linear behavior of a power amplifier. engineering, technology & applied science research vol. 9, no. 5, 2019, 4801-4807. engineering, technology & applied science research vol. 8, no. 3, 2018, 3073-3078 3073 www.etasr.com alshehri et al.: multicriteria decision making (mcdm) methods for ranking estimation techniques … multicriteria decision making (mcdm) methods for ranking estimation techniques in extreme programming sultan alshehri computer science and information technology college majmaah university al majmmah, saudi arabia su.alshehri@mu.edu.sa abstract—it is essential to use multicriteria decision making (mcdm) methods to evaluate human judgments, for decision problems requiring the measuring of tangible and intangible criteria. among the mcdm techniques, the analytic hierarchical process (ahp) and its extended version, the analytic network process (anp) are the most powerful methodologies for ranking options and alternatives. they have been utilized by many scientists and researchers in numerous fields, especially for complex engineering problems. both tools allow leaders to structure their issues numerically utilizing individual judgments. in this article, it is suggested that the mcdm can be useful in agile processes where complicated decisions happen routinely. this paper shows the ranking of the extreme programming (xp) estimation methods using ahp and anp in educational and industrial environments. keywords-analytic hierarchy process; analytic network process; extreme programming; planning game; estimation techniques; user stories i. introduction developers face uncertainties when designing software projects. it is important to minimize these uncertainties. in extreme programming practices, there are certain activities that aid this process, one of them being the planning game practice. in this practice, xp team needs to discuss the system requirements, known in agile methodology as user stories. author in [1] characterizes user stories as “short descriptions of functionality told from the perspective of a user that are valuable to either a user of the software or the customer of the software”. these client stories are noteworthy in light of the fact that they make it simple to draw a general structure regarding the system. user stories contain different activities such as writing and breaking stories down into tasks. user stories can be prioritized based on the customer business value. moreover, one of the most important activities is estimating user story effort and cost. during iteration planning meetings, estimating processes are used to establish the iteration plan. this occurs by assigning stories to each iteration considering their priorities. story points are used to measure the effort required to implement a story. story points can determine the cost and many-sided qualities of the requirements. developers usually break down the user stories into small tasks to be able to estimate effort and time. in this paper, the researcher conducted two case studies in educational and industrial environments to introduce the analytic hierarchy process (ahp) and analytic network process (anp) to assist the xp team ranking the estimation methods. there are four common estimation methods have been evaluated in this paper: planning poker, expert opinion, analogy, and disaggregation. ii. estimation methods with extreme programming agile methodology is based on collaboration among team members and therefore, estimations are not obtained by individuals. all team members share estimations, and “estimates are best derived collaboratively by the team, which includes those who will do the work” [2]. it is important during estimations of user stories to appropriately manage stories so that they can be estimated clearly. for example, one could combine related stories into a group, which is called theme to clearly estimate them as one item. there are several methods that can be used to software estimation. some methods mathematically obtain estimations by concentrating on historical data [3]. other methods estimate effort by measuring the size of the task. expert opinion is one that works by asking an expert about each story. based on his/her experience, the expert gives an estimate. another technique that can be used to estimate user stories is analogy. this technique can involve a triangulation process, which depends on comparing the story that is being estimated with two other stories [4]. disaggregation is another method that is used to split large stories into smaller ones to ease the process of estimation. some studies suggest that the best technique that can be used to estimate stories is planning poker. this merges the three abovementioned techniques of expert opinion, analogy, and disaggregation. all team members are involved in planning poker to estimate stories and this involves several steps and stages, which are explained in more detail in [2]. authors in [5] introduced several areas that are useful to estimate using expert opinion. these areas are: 1) areas where it is difficult to find empirical data, and 2) when it is difficult to engineering, technology & applied science research vol. 8, no. 3, 2018, 3073-3078 3074 www.etasr.com alshehri et al.: multicriteria decision making (mcdm) methods for ranking estimation techniques … estimate because of the lack of problem understanding. these areas are considered reasons for widely applying of the expert opinion method in software estimation. authors conducted an industrial experiment to evaluate the reliability of using the expert opinion method in cost estimation. the study aimed to enhance cost estimation in a medium size software organization. “the intention of the organization in supporting this study was to assess its cost estimation capability in the bid phase of a project and, if required, to use the results as a catalyst for change of their estimation practices” [5]. in this study, an on-line survey was distributed among thirty employees. the response rate of the survey was 47%, and the average experience of the participants was 7.5 years. the questions focused on two areas, variability and calibration. the study contained questions asking about several issues, for example, authors asked about the possibility of having the same estimate from various groups of estimators. after presenting the results, the authors concluded that the expert opinion method obstacles are inconsistencies and overconfidence. this issue causes unreliable software estimation. however, they suggested that integrating the expert opinion method with other techniques like wideband-delphito makes it more reliable. author in [6] conducted a survey in 364 organizations and found that only 51 estimated efforts by the use of models. however, the model was not better than the non-model users in estimation. but when they relied on the expert opinion, they believed that was better than the use of estimation models. authors in [7] investigated effort estimation in 32 software projects in different iranian software companies. questionnaires were distributed to collect data from these companies’ employees and their project estimation. the study shows that most of these companies depend on small teams (of five people and less) because of the small scale of developed products, and the simplicity of managing small teams. also, the most used development processes in product development are rational unified process and xp. the distributed questionnaire included various parts such as the type of estimation method used in a project and the degree of differences between estimated and real data. on this study, expert opinion and analogy method were the most common estimation methods. among all these projects, the percentages of using analogy method and expert opinion were 29% and 25% respectively. the study concluded stating that these two methods are simple to be applied to similar projects and provide rapidly estimation. the major defect, however, is the dependence on expert judgment, which may be less reliable. authors in [8] conducted a study to evaluate the accuracy of planning poker estimation method. 13 students were formalized in teams to develop a web-based student records information system. all students received the same user stories, and asked to implement them in three sprints. by using planning poker method, students estimated the user stories and “the estimates provided by each team member during the first round were averaged to obtain the statistical combination for further comparison” [8]. in the same time, a few experts were given the same user stories to provide their estimations. the results of this study show that planning poker method lead the students to have over optimistic estimation, while the expert’s estimation was closer to the actual effort. the study addressed that planning poker method is less beneficial when it is applied by less experienced developers. authors in [9] investigated xp practice development in an ibm group. they concluded that the xp product has improved pre-release and post release quality. the xp team noted enhancements in their effort estimation, schedule and productivity. also, customer satisfaction was very high with the xp product since developers delivered more than what was planned. authors in [10] estimated effort by applying artificial neural network (ann) and case-based reasoning. they used data set from the australian software metrics association. ann estimated the development effort within 25% of the actual effort in more than 75% of the projects. in [11] authors emphasized several challenges in current estimation methods. time duration is one of the challenges due to the differences in the story points and the velocity of the team. iii. the analytical network and hierarchy process author in [12] defined anp as “a multi-criteria theory of measurement used to derive relative priority scales of absolute numbers from individual judgments (or from actual measurements normalized to a relative form) that also belong to a fundamental scale of absolute numbers”. similarly, ahp is defined as a systematic approach for problems that include the thought of different criteria in a hierarchical model. ahp reflects human thinking by grouping the elements of a problem requiring complex and multi-aspect decisions [13]. both concepts were developed in [14] as means of finding an effective and powerful methodology that can deal with complex decision-making problems. ahp comprises the following steps: (1) structure the hierarchy model for the problem by breaking it down into a hierarchy of interrelated decision elements. (2) define the criteria or factors and construct a pairwise comparison matrix for them. each criterion is compared with the other criteria of the same level in respect of their importance to the main goal. (3) construct a pairwise comparison matrix for alternatives with respect to each objective in separate matrices. (4) check the consistency of the judgment errors by calculating the consistency ratio. (5) calculate the weighted average rating for each decision alternative and choose the one with the highest score. in the anp method, dependencies among various criteria are considered making it different from the ahp. “in fact the anp uses a network without the need to specify levels. as in, the ahp, dominance or the relative importance of influence is a central concept. in the anp, one forms a judgment from the fundamental scale of the ahp by answering two kinds of questions regarding strength of dominance: (a) given a criterion, which of the two elements is more dominant with respect to that criterion, (b) which of the two elements influences a third element more, with respect to a criterion” [15]? in pairwise comparisons, entered values mirror the relative effect among elements with respect to a control criterion. these entered values are based on the importance of each criterion. the network structure consists of different clusters, and these clusters contain various nodes or elements. these clusters are connected to each other based on the relative influences among the nodes. in [16], author developed a engineering, technology & applied science research vol. 8, no. 3, 2018, 3073-3078 3075 www.etasr.com alshehri et al.: multicriteria decision making (mcdm) methods for ranking estimation techniques … numerical scale for assigning the weight for criteria or alternative by giving a value between 1 (equal importance) and 9 (extreme importance), see table i. table i. ahp numerical scale [14] scale numerical rating reciprocal equal importance 1 1 moderate importance of one over another 3 1/3 very strong or demonstrated importance 7 1/7 extreme importance 9 1/9 intermediate values 2,4,6,8 1/2, 1/4, 1/6, 1/8 iv. methodology the primary goal of this exploration paper is to examine how the ahp and the anp can help in selecting the most suitable estimation method. the case study analysis strategy, which is clarified in [17], is the examination methodology. the following research questions give more concentration to the exploration contextual analysis:  could the ahp and anp process support the xp team to select the appropriate estimation method to estimate each user story?  how can the ahp and anp impact the improvement group's correspondence and efficiency? from the previous questions, the units of examination for our investigation were inferred. the primary goal is to rank the most common estimation methods used in xp approach. a. data collection and sources toward the start of each utilization of ahp and anp in xp, we investigated their benefits and abilities by introducing the related criteria and xp areas. data is gathered from looking past examinations and other reviews. also, information triangulation is obtained to expand the legitimacy of the investigations. the major data source for the educational case study was a project conducted during the winter semester of 2016 at the university of regina, while the data source for the industrial case study collected from two development teams located in canada and saudi arabia. the data sources in this research are:  questionnaires given to the participants during their development activities.  comments received from the developers in both studies.  open-ended interviews with the participants. b. proposed criteria for selecting estimation methods to rank estimation methods, it is important to identify the criteria that influence the estimation process. these criteria are compared with each other (to show the interdependences), and with alternatives. the estimation methods are compared with respect to the criteria to show the feedback relation in the selection process. in this case study, four estimation criteria were proposed. these criteria are:  accuracy: which estimation technique gives the most accurate estimation?  simplicity: what is the simplest estimation method to understand and to apply?  collaboration: which estimation method has the highest degree of collaboration between the team members?  time: which estimation method saves more time when estimating the user stories? v. anp and ahp case studies anp and ahp methods were used to rank the various estimation techniques in xp. in the following sections, the anp and ahp evaluations, structures and process are detailed. a. anp in educational environment the educational case study was conducted at the university of regina, at 2016. it took around 12 weeks. the case study included 12 graduate participants with an additional participant as a client. these students had intermediate knowledge of xp process and practices, and different programming levels. the participants’ backgrounds included various programming languages like c++, java, and php. the participants were organized into two teams, the first team used the anp method to make their decisions in the mentioned areas, and the second team followed the traditional xp method. both teams were asked to develop a project called “professors' availability managing system” complete with a set of requirements. the project was developed in 5 iterations, allowing two weeks for each. at the end of the project, the two teams implemented all system requirements. assistance materials that focused on planning game practices were given to the participants to ensure their understanding [18]. these materials involved estimating user stories, writing user stories, and making programming commitments. the anp team was given white papers, several presentations, and other important materials about the anp to allow them to apply it in their development. team 1 practiced on several pairwise comparisons and increased their understandings of the anp structure. at the end, the researcher handed out a survey to the participants to collect more data about the participants' perspectives. b. ahp in industrial environment eight experts in it industry were quested to participate in the evaluation. the experts were in two companies in two countries, canada and saudi arabia. three of them were working in a governmental project in canada. the rest of the participants were working in different projects in saudi arabia. their experience in project development ranged from 10 to15 years. they have been through many projects involved in managing teams and projects. the participants also were familiar with the activities of tasks estimations process and a good understanding of scrum and agile methodologies vi. anp and ahp structures for selecting the estimation methods organizing the problem [19] is the initial phase in both anp and ahp. the anp network contains a criteria cluster, an alternative cluster and the goal. the main cluster is the “alternatives” cluster, which contains the four afore mentioned estimation methods to select the most preferable one. the engineering, technology & applied science research vol. 8, no. 3, 2018, 3073-3078 3076 www.etasr.com alshehri et al.: multicriteria decision making (mcdm) methods for ranking estimation techniques … “objective” cluster referrers to the “criteria” cluster which interacts with the “alternatives” cluster. in ahp, the problem is structured as a hierarchy that includes three levels. the top level is the main objective: selecting the estimation technique. the second level contains the criteria (accuracy, simplicity, collaboration, and time). the third level has the alternatives (planning poker, expert opinion, disaggregation and analogy). the appropriate anp and ahp tables were created and gotten by every one of the participants. they were requested to round out the pairwise comparisons in view of the scale of [14] depicted in table i. vii. process of the pairwise comparison in both studies, participants had an opportunity to experience the estimation methods through real projects to see the real impact on the team and the velocity of the development. then they were required to rank the most favorite estimation methods based on the four criteria. for this aim, ahp sheets containing tables were given to the participants in the industry and anp tables were given to the students in the educational case study. members were asked to analyze the criteria utilizing the saaty scale from 1-9. the members were asked these inquiries:  which is more imperative: simplicity or accuracy and by what amount?  which is more imperative: simplicity or time and by what amount?  which is more imperative: simplicity or collaboration and by what amount?  which is more imperative: accuracy or time and by what amount?  which is more imperative: accuracy or collaboration and by what amount?  which is more imperative: time or collaboration and by what amount? after the criteria evaluations finished, members needed to rank all the estimation strategies in view of every criterion every time. (example: focusing on the simplicity, which is more vital: taking the expert opinion or doing the planning poker and by how much?). additionally, all the accompanying correlations were directed in view of every criterion [example: (planning poker-expert opinion), (planning poker disaggregation), (planning poker-analogy). (expert opiniondisaggregation), (expert opinion-analogy), (disaggregationanalogy)]. similar comparisons rehashed until the point when the participants assessed all estimation techniques in light of every criterion. viii. amp and ahp evaluation results a. anp in educational case study the sorting of the estimation methods in view of all criteria, is outlined as follows: expert opinion was first (35.36%), followed by planning poker (33.64%). analogy was third (15.35%) and disaggregation (5.48%) was fourth. table ii shows the results. figure 1 demonstrates the significance of every measure: accuracy (40.86%), collaboration (32.49%), simplicity (15.29%), and time (11.34%). table ii. ranking of the estimation techniques by team 1 criteria score % expert opinion 35.36 % planning poker 33.64 % analogy 15.35 % disaggregation 5.48 % fig. 1. criteria importance by team 1. each participant in team 1 evaluated the estimation techniques using the anp pairwise comparisons. super decisions software was used to determine the aggregation judgements for team 1. team 2 took after the conventional technique in their decisions and in this manner they were requested to archive each progression in their procedure of settling on choices. team 1 results show that expert opinion method was given the highest rank among the four alternatives. planning poker came second followed by analogy, then disaggregation. table ii exhibits the relative weight of each one as a percentage. the accuracy criterion received the highest importance among the criteria, followed by collaboration, simplicity, and time. team 2 results show that the analogy method was given the highest rank among the other estimation methods. by asking team 2 which was the most important factor for selecting an estimation method, they gave accuracy the top score. remarks:  considering all criteria, the expert opinion method was the most preferable estimation technique by team 1. analogy was selected as the best estimation method by team 2.  both teams considered accuracy the most significant criterion.  team 1 ranked the estimation methods by considering each criterion individually. the findings were: the planning poker method was ranked the highest in terms of accuracy, expert opinion placed as the top selection when focusing on time and simplicity, while analogy was ranked the highest in terms of collaboration.  these outcomes indicate the alternatives made by each group. rankings were finished exclusively, notwithstanding, the group act was steady in the engineering, technology & applied science research vol. 8, no. 3, 2018, 3073-3078 3077 www.etasr.com alshehri et al.: multicriteria decision making (mcdm) methods for ranking estimation techniques … consistency rates. figures 2 and 3 demonstrate the distinctions in group velocity between the two groups. fig. 2. velocity measuring for team 1. fig. 3. velocity measuring for team 2. b. ahp in industrial case study sorting the estimation techniques by experts in industry outlined as follows: planning poker (33.76%) was first, expert opinion (29.03%) second, disaggregation (20.89%) ranked third and analogy (16.30%) was fourth. table iii shows the results. figure 4 demonstrates the significance of every criterion. table iii. ranking of the estimation techniques in industry criteria score % planning poker 33.76 % expert opinion 29.03 % disaggregation 20.89 % analogy 16.30 % remarks:  the planning poker technique was the first choose by all experts.  expert opinion ranked with the highest score when the time and the simplicity were the most important criteria.  disaggregation ranked in the second position after the planning poker when considering accuracy and collaboration.  expert opinion technique ranked last two times, for the accuracy and collaboration criteria. it is clearly that relying on one person means the team will lose the benefits of the collaboration, but the surprising result was regarding the accuracy criterion. the question if the experience can help to get an accurate result arises. it could be true sometimes. yet, the result in this case study indicates the companies are getting more afraid to follow the opinion of one person. nowadays, the trend in the it companies is to minimize the approach of “one person” and replace it with a “team” approach.  the analogy technique did not attract the experts, it ranked last with “simplicity” and “time” criteria and third with “accuracy” and “collaboration” criteria.  looking closer to the estimation techniques and considering every criterion separately as it is appeared in table iv, it is confirmed that the expert developers ranked the expert opinion in the top place regarding the simplicity and time. on the other hand, the planning poker sorted at the top in accuracy and collaboration attributes. fig. 4. importance of the criteria for estimation techniques by experts. table i. estimation methods based on each of the criteria method simplicity method accuracy method time method collaboration expert opinion 48.28 planning poker 38.34 expert opinion 68.33 planning poker 49.00 planning poker 31.06 disaggregation 27.31 planning poker 16.45 disaggregation 21.58 disaggregation 11.16 analogy 21.85 disaggregation 9.17 analogy 16.23 analogy 9.48 expert opinion 12.47 analogy 6.03 expert opinion 13.17 ix. conclusions this research paper assessed the application of two of the common methods of mcdm methods, ahp and anp, in order to benefit practitioners to choose a method for solving a specific problem. these methods are advantageous as they reduce the burden of the decision-maker. after conducting two case studies in two different environments with varying experience and development culture the mcdm methods were engineering, technology & applied science research vol. 8, no. 3, 2018, 3073-3078 3078 www.etasr.com alshehri et al.: multicriteria decision making (mcdm) methods for ranking estimation techniques … found as an appropriate and beneficial tool that gave the development team a good understanding for selecting a suitable estimation method. the results of using anp in educational study and ahp in industrial study showed that the expert opinion is the most preferable tool in the estimation process. the most experienced members could easily convince the other team members of their preferences. junior developers may fear to express their opinions, even though relying on individuals is not always recommended for building motivated and energetic xp teams. the cases studies also emphasized on the importance of approaching “accuracy” when the team is estimating any development activities. references [1] m. cohn, “advantages of user stories for requirements”, informit network, available at: http://www.informit.com/articles/ article.aspx?p=342885, 2004, (last accessed: 05/31/2018) [2] m. cohn, agile estimating and planning, pearson education, 2005 [3] k. beck, extreme programming explained: embrace change, addisonwesley, 2000 [4] j. shore, s. warden, the art of agile development, q’reilly media inc, 2007 [5] p. faria, e. miranda, “expert judgment in software estimation during the bid phase of a project--an exploratory survey”, in: 2012 joint conference of the 22nd international workshop on software measurement and the 2012 seventh international conference on software process and product measurement, assisi, italy, pp. 126-131, ieee, 2012 [6] f. j. heemstra, “software cost estimation”, information and software technology, vol. 34, no. 10, pp. 627-639, 1992 [7] y. yavari, h. bashiri, “effort estimation of software development: depth view on iran case”, american journal of software engineering, vol. 1, no. 1, pp. 5-11, 2013 [8] v. mahnic, t. hovelja, “on using planning poker for estimating user stories”, journal of systems and software, vol. 85, no. 9, pp. 20862095, 2012 [9] l. layman, l. williams, l. cunningham, “motivations and measurements in an agile case study”, journal of systems architecture, vol. 52, no. 11, pp. 654-667, 2006 [10] g. r. finnie, g. e. wittig, “ai tools for software development effort estimation”, in: international conference on software engineering: education and practice, dunedin, new zealand, pp. 346-353, ieee, 1996 [11] r. popli, n. chauhan, “research challenges of agile estimation”, journal of intelligent computing and applications, vol. 7, no. 1, pp. 108-111, 2013 [12] t. l. saaty, “fundamentals of the analytic network process— dependence and feedback in decision-making with a single network”, journal of systems science and systems engineering, vol. 13, no. 2, pp. 129-157, 2004 [13] n. tiwari, using the analytic hierarchy process (ahp) to identify performance scenarios for enterprise application, the computer measurement group, google scholar, 2006 [14] t. l. saaty, the analytic hierarchy process, mcgraw-hill, 1980 [15] t. l. saaty, theory and applications of the analytic network process: decision making with benefits, opportunities, costs, and risks, rws publications, 2005 [16] t. l. saaty, “how to make a decision: the analytic hierarchy process”, interfaces, vol. 24, no. 6, pp.19-43, 1994 [17] r. k. yin, case study research: design and methods, fourth edition, sage publications, 2009 [18] a. aljuhani, l. benedicenti, s. alshehri, “ranking xp estimation methods based on the anp”, international journal of advanced computer science and applications, vol. 8, no. 5, pp. 1-8, 2017 microsoft word 22-3449_s_etasr_v10_n4_pp6009-6015 engineering, technology & applied science research vol. 10, no. 4, 2020, 6009-6015 6009 www.etasr.com mrema & dida: a survey of road accident reporting and driver’s behavior awareness systems … a survey of road accident reporting and driver’s behavior awareness systems: the case of tanzania ikunda j. mrema nelson mandela african institution of science and technology arusha, tanzania mremai@nm-aist.ac.tz mussa a. dida nelson mandela african institution of science and technology arusha, tanzania mussa.ally@nm-aist.ac.tz abstract—road traffic accidents are a leading cause of death in developed and developing countries. it has been shown that road accident reporting systems could reduce their effects by minimizing response time and mapping road accident-prone areas. this paper provides an overview of the systems and applications for road accident reporting and drivers’ behavior awareness. a field survey, conducted in dar es salaam region in tanzania, investigated the current state of road traffic accident reporting. findings showed that the main means of reporting road accidents were physical reporting and police emergency phone calls. the absence of alternative means for reporting road accidents causes information delay and lack of precise accident location for the emergency first responders. this paper concludes by proposing a mobile application system for road accident reporting and drivers’ over-speed awareness, in order to improve road safety in developing countries. keywords-road traffic accidents; road accident reporting; smartphone sensors; road safety; driver’s behavior; awareness i. introduction road traffic accidents are the 8 th global leading cause of death, with 1.35 million deaths and up to 50 million injuries in 2016 [1] with the death and injury rates are higher in developing than in developed countries [2]. strong enforcement of road safety laws, public awareness campaigns, smart road design, and safer vehicles have been determined as ways of reducing road traffic accidents [1]. in tanzania, road traffic accidents have high rates of morbidity and mortality [3]. the country has high rates of road accidents, with a traffic fatality rate of 32.9 per 100,000 people, pointing out the necessity for further improvements in road safety measures [1]. the factors of road traffic accidents related deaths and injuries in tanzania have been categorized as human, mechanical, or road/infrastructure condition related. among human factors, overspeeding was found to be the major cause of road traffic accidents [4]. underreporting of road traffic accidents is a challenge, as it leads to untrustworthy data [5]. it is also pervasive in many parts of the world and results in giving lower priority to road safety compared to other public health challenges. moreover, tanzania lacks road accident reporting systems, apart from emergency call numbers which are mostly unreliable and sometimes unavailable [1]. various measures were imposed to prevent road traffic accidents and improve safety in tanzania, for instance road safety regulations such as speed-limit laws, obligatory seat-belt and helmet use, and strict laws regarding driving under the influence. road traffic accident victims’ chances of survival increase with the immediate availability of pre-hospital emergency services [6]. this implies that response time reduction is needed in order to improve healthcare delivery in road accident emergencies. the reporting of traffic accidents could also be utilized for mapping accident hotspot (black spot) areas, notifying drivers and other road users to be more careful when accessing them. in a post-crash situation, usually the bystanders/witnesses contribute to the initiation of the emergency care, by either providing first aid or calling for help. this study aims to reduce road accidents both passively, through enabling drivers to observe speed limits by enhancing their driving over-speed awareness, and actively by enabling timely reporting of road accidents to minimize rescue time response. as tanzania has 43.5 million mobile phones and 23.1 internet users [7], this paper proposes a mobile application system for road accident reporting and drivers’ over-speeding behavior awareness that will enable road users to report road accidents and overspeeding drivers to traffic police officers, using smartphones’ built-in sensors such as gps receivers and cameras. to achieve these objectives, a literature review was conducted on related studies for drivers’ behavior awareness and road traffic accident reporting. a field survey was also conducted in dar es salaam, using questionnaires, interviews, document reviews, and observation to evaluate the current state of reporting road traffic accidents and drivers’ over-speeding behavior awareness. ii. related work the review of related studies on systems and applications for drivers’ behavior awareness and road traffic accidents’ reporting showed that the existing systems are categorized as in-vehicle and smartphone sensor based systems. a. in-vehicle sensor-based systems many vehicle built-in systems have been implemented to increase road safety and reduce accidents’ occurrence. since 2018, all new cars sold in the european union embed the invehicle ecall system for the detection and reporting of accidents to emergency services [8]. its main disadvantage is corresponding author: ikunda j. mrema engineering, technology & applied science research vol. 10, no. 4, 2020, 6009-6015 6010 www.etasr.com mrema & dida: a survey of road accident reporting and driver’s behavior awareness systems … the difficulty to install it in older cars, which are widely used in developing countries. e-notify is a similar proposed system, using an on-board unit (obu) that utilizes in-vehicle sensors to automatically detect and report accidents to the nearest control unit and nearby vehicles [9]. obu device obtains information from in-vehicle sensors in order to transmit the accident’s information, utilizing vehicle-to-vehicle (v2v) and vehicle to infrastructure (v2i) communications. the main disadvantage of this system is its costly installation. authors in [10] proposed an android-based mobile application system that detects and reports vehicle accidents through an on-board diagnostic (obd ii) which collects vehicle information such as gps, accelerometer, airbag triggers, and vehicle speed data. obd ii is a second generation obd that diagnoses the vehicle electrical system to detect vehicle problems. the mobile application is able to detect an accident by calculating g-force estimates or detecting airbag triggers through a smartphone connected to an obd ii, using bluetooth to receive data from the vehicle’s internal bus. when an accident is detected, it is reported to emergency services through email or sms. authors in [11] implemented a driving styles platform, based on neural networks, to define the driving style of each user and the type of road the vehicle is moving. the developed android application utilized the obd-ii bluetooth connection to collect vehicle information such as speed, acceleration, engine revolution per minute, throttle position, and vehicle’s geographical location. onstar is another vehicle built-in system implemented by general motors that utilizes in-vehicle sensors to detect road accidents and inform emergency services [12]. this system is vehicle dependent as it can be installed only on general motors’ vehicles. b. smartphone sensor-based systems authors in [13] presented a context-based driver score (cds) model to score driver’s behavior based on a context including road quality, weather, and time of day. the study aimed to improve usage-based insurance (ubi) products by including the context of the driver, which was mostly ignored by insurance companies. data collected from smartphone sensors were used to model vehicle maneuvers and their interaction with the road. in [14], a system similar to ecall but using a mobile device was presented, which detected accidents and sent notifications to emergency services or contacts. wreckwatch, a client-server system proposed in [15], utilized smartphones in road accident detection to reduce traffic congestion and emergency responders’ notification time. moreover, this study discussed some major challenges for accident detection using smartphone sensors. authors in [16] developed a traffic management system using crowd-sourced smartphone gps sensor data and other parameters, such as traveling time and distance, recommending alternative route paths for shorter traveling time or less fuel consumption. the system utilized only the gps sensor, and only drivers were involved in collecting driving data. another study developed a smartphone-based platform collecting low-cost and long-term naturalistic data for vulnerable road users (vrus) [17]. the logyard smartphone application was developed for recording high-quality data from a large number of users for off-line analysis, addressing privacy and integrity issues of the participants. authors in [18] proposed a system using the internal accelerometer and gps of a smartphone to enhance the existing safety features on a road, in order to increase drivers’ awareness, classifying road condition types and drivers’ driving patterns. another study surveyed smartphone-based sensing in vehicles for intelligent transport system applications [19], identifying certain advantages of using smartphone-based instead of in-vehicle sensing. among the advantages, smartphone-based sensing links driving behavior to an individual driver rather than a vehicle of which the driver may be unknown. it also provides connectivity without any additional equipment and has low installation cost. authors in [20] proposed the use of smartphones to automatically detect road accidents in order to increase road safety and reduce the time to call for help, specifically for cyclists as they are among the most vrus. the study used accelerometer, gyroscope, and gps sensors logged data to develop an algorithm for accident detection, but the algorithm and data were proprietary. in [21], an accident detection and reporting system based on the internet of things (iot) was presented. an android application was developed to collect smartphone sensor data and process them on a cloud infrastructure to detect an accident. the study focused ways to reduce the significant false positive rates for automatic accident detection found in previous studies. waze is a crowd-sourcing mobile application providing real-time traffic information for road users. in addition, it provides other services such as reporting of various road incidents, and it also collects anonymous users’ speed and gps locations for its service improvements [22]. τhis mobile application does not send these road incident reports to authorities, the information are mainly used for informing drivers. rac is another mobile traffic application, based in the uk, enabling users to share and view various road incidents, route planner, shortest route, and traffic news services [23]. c. characteristics of road accident reporting systems road accident reporting systems and applications have the following characteristics: • accident report content: the report includes automatic user location retrieval through an embedded gps sensor. it also includes simple forms that collect road accident data in text, photo, video or audio, with more emphasis in the text format. most accident reporting systems embed the minimum set of data (msd) of the accident information in reports [24]. • usability: mobile applications and systems for road accident reporting need to be attractive and simple in design in order to be easy to use. • interaction: given the road accident situation, the user interaction with mobile application systems for reporting road accidents needs to be quick and intuitive [25]. iii. methodology a field survey was conducted in the region of dar es salaam, tanzania, to determine the overall situation regarding the reporting of road traffic accidents to the traffic police authorities. the survey involved two groups: traffic police officers and road users (citizens). engineering, technology & applied science research vol. 10, no. 4, 2020, 6009-6015 6011 www.etasr.com mrema & dida: a survey of road accident reporting and driver’s behavior awareness systems … a. study area dar es salaam is tanzania’s largest city with five districts: kinondoni, ilala, temeke, ubungo, and kigamboni. the region’s 2016 projected population was 5,465,420, based on the 2012 census [26]. dar es salaam was chosen as a study area because of its high population and its effect on the high usage of roads for land transportation. according to the national government report of 2015, dar es salaam also had the highest number of road traffic accidents [27]. b. sample size and sampling yamane’s simplified formula was used to obtain the sample sizes [28]. this formula is widely used in statistics for sample size calculations. the formula is expressed as: � = � ����� (1) where n is the sample size, n is the population size and e is the acceptance sample error. the acceptance sample error was defined as 0.1, and the population size for dar es salaam was 4,364,541. on the other hand, the population size for traffic police officers in dar es salaam was estimated to be 1300 [29]. through yamane formula, sample sizes of 93 and 100 for traffic police officers and road users (citizens) were used respectively. simple random sampling was used for data collection from responders who were willing to complete the survey. the survey was conducted in three traffic police stations: traffic police headquarters (hq), oysterbay station, and urafiki station in ilala, kinondoni and ubungo districts respectively. the survey aimed to determine means, challenges and information collected on road accident reporting. c. data collection methods this research collected both quantitative and qualitative data utilizing questionnaires, structured interviews, and observation methods. 1) questionnaires two different structured questionnaires were utilized and given to traffic police officers and road users. • the questionnaire for the traffic police officers consisted of demographic questions about age and gender, the means used to receive road accident reports, the challenges faced in responding to road accidents, and the kind of collected information during road accident reporting. • the questionnaires for the road users consisted of demographic information about age, gender, and level of education, the source of help provided at the accident scene, awareness of existing mobile applications for road accident reporting, and the attitude towards the use of mobile application systems for road accident reporting. 2) interviews interviews were used to obtain detailed answers and opinions from the responders. interviews were also taken from senior traffic police officers who failed to complete the questionnaires for various reasons. some road users were also interviewed in order to determine their attitude on road traffic accident reporting and the feasibility of using a mobile application system. 3) observation the survey also involved first hand observation of road traffic accidents on the roads of dar es salaam. one of the observed incidents was a motorcycle and car accident. this accident was not reported, as the victims of the accident were only slightly injured without needing help to visit hospital facilities, and there was not a simple mechanism for road accident reporting to traffic police apart from traditional methods, such as telephones and physical reporting. road accident observation obviously occurred only by chance and not by systematic monitoring. d. data analysis analysis on collected data was conducted using python programming language and spreadsheet software programs because of their simplicity and the availability of various data analysis libraries. iv. results and discussion a. causes of road traffic accidents in tanzania several studies found that human factors constitute the main reason of road traffic accidents, with over-speeding being the leading factor [30]. in tanzania, 74% of the accidents that happened in 2010 were caused by human factors [4]. other factors include vehicle/mechanical and road conditions. table i shows the causes of road accidents, where some of the human causes include excessive speed, overtaking, and driving while intoxicated (dwi). reckless driving, which is driving with excessive speed for a given road/traffic condition, consisted about 57% of all accident causes [4] b. speed limits for road safety the methods for enforcing speed limit laws in tanzania include the use of speed radar guns and the vehicle tracking system (vts) installed in public transport buses to limit driving speeds to the regulated 80km/h outside urban and 50km/h in urban areas [31]. table ii shows the road speed limits for different vehicle types. table i. major causes of road crashes (sumatra, 2017) causes of road crashes contributory percentage (%) 2000-2005 2010 human factors reckless driving 54 57 over-speeding 8 9 improper overtaking 7 8 dwi 3 0 overloading 5 n.a mechanical factors 16 12 road conditions 7 14 total 100 100 c. road traffic accident reporting road traffic accidents are mainly reported by bystanders/witnesses. the responsible authorities for post-crash response include traffic police, insurance companies, ministry of health and social welfare, and fire and rescue services [4].. the current approach to road accidents’ reporting engineering, technology & applied science research vol. 10, no. 4, 2020, 6009-6015 6012 www.etasr.com mrema & dida: a survey of road accident reporting and driver’s behavior awareness systems … in tanzania is through phone calls, physical reporting to the traffic police officers, and sharing of information through social media such as instagram and whatsapp. table ii. speed limits in tanzania vehicle type all cars buses and coaches(less than 12m in length), goods vehicles(less than 3.5tn in weight) built-up area 50km/h 50km/h urban area 50km/h 60km/h single carriageways not stated 80km/h dual carriageways not stated 80km/h source: road traffic act, 1973 [31] d. field survey results: traffic police officers’ response the results obtained from data analysis of the collected responses from traffic police officers are shown below, by section. 1) responders’ demographic characteristics as noted in table iii, 79% of traffic police officer responders were male and 21% were female. the high number of male responders was due to the fact that most of the traffic police officers are male. on the other hand, 63% of the responders aged between 31-40 years, 29% between 41-50 years, and 8% between 21-30 years. table iii. demographic characteristics of traffic police officer responders demographic characteristics responders percentage (%) gender male 73 79 female 20 21 age groups (years) 21-30 7 8 31-40 59 63 41-50 27 29 2) means used to receive road accident reports the study aimed to determine the time efficiency of the means used for reporting road accidents to traffic authorities. as noted in figure 1, most road accident reports were received through telephone calls (62%). bystanders’ physical reporting for road accidents was found to be 28% of all responses. physical reporting from victims had a frequency of 10%. these results show that there are still some challenges in reporting accidents to responsible authorities, such as dealing with increased response times and underreporting. therefore, there is a need for alternative road accident reporting tools that will aid road users in immediate and effective reporting. 3) challenges faced in responding to road accidents traffic police officers responding to road accidents identified several challenges in timely assisting road accident victims to avoid preventable injuries and deaths. as shown in figure 2, information delay was noted to be the most important challenge in responding to road accidents with 43%. other challenges included accident location accuracy (38%), false information (13%), and lack of transport (6%). these findings signify that road users may fail to report road accidents on time due to the limitations of the existing methods. an alternative mobile application tool could enable road accident witnesses to easily report the accident with its accurate location using a smartphone’s gps sensor. fig. 1. means for road accident reporting. fig. 2. challenges faced in responding to road accidents. 4) collected information traffic police officer responders were asked about the necessary information collected during road accident reporting. this question aimed to determine the road accident details that should be reported by a mobile application. figure 3 shows the obtained results. fig. 3. information collected during road accident reporting. engineering, technology & applied science research vol. 10, no. 4, 2020, 6009-6015 6013 www.etasr.com mrema & dida: a survey of road accident reporting and driver’s behavior awareness systems … victims’ details were addressed as the most frequently collected information (32%), followed by the vehicle types involved (25%), the location of the accident (19%), the road accident diagrams (18%), and the accident’s causes (6%). as the information about a road accident is mainly collected from the witnesses’ point of view, there are high chances for false information. road accident report systems providing information such as accident’s location using a gps sensor would help to face this challenge. e. field survey results: road user responses after analyzing the data collected using questionnaires from road users, the following results were obtained. 1) responders’ demographic characteristics the responder’s demographic characteristics can be seen in table iv. table iv. demography of community responders demographic characteristics responders percentage (%) gender male 64 64 female 36 36 age groups (years) 20 or younger 5 5 21-30 43 43 31-40 32 32 41-50 12 12 51 or older 8 8 education level completed sec school only 17 17 completed more than sec school 68 68 didn’t complete sec school 15 15 2) source of help provided in the accident scene as depicted in figure 4, the majority of the responders (75%) indicated that accident witnesses provide help in the accident scene, while 23% indicated the traffic police officers, and only 2% indicated the hospital facilities for medical assistance. fig. 4. sources of help provided in the accident scene. this indicates that if bystanders had alternative means, they could possibly request for help from additional sources. 3) awareness of existing mobile applications almost all responders were unaware of any existing mobile applications for reporting road accidents. only one responder was aware of such an application, but the mentioned application was used for road traffic monitoring and was no longer available. the lack of any other alternative means points out the need for a road accident reporting mobile application. 4) attitude towards a mobile application system the vast majority of the responders had a positive attitude on the advantages of a mobile application system for road accident reporting and drivers’ over-speeding behavior awareness as can be seen in figure 5. only 2% responded that such a mobile application will not help in notifying the responsible authorities on time. fig. 5. attitude toward a mobile application for reporting road accidents and driver’s over-speeding awareness. f. proposed solution to address the challenges faced by the current road accident reporting systems in tanzania, this study proposes a mobile application system, by which road users could report road traffic accidents to traffic police authorities. the proposed mobile application system would also let road users be aware of their driving over-speeding behavior by utilizing data retrieved from the gps sensor. the system would report road accidents to the nearest traffic police station with the assumption that the users (drivers, passengers or pedestrians) are witnesses. the system could also enable the continuous collection of smartphone sensor data, such as accelerometer, gyroscope, and gps for the development of more robust automatic road accident detection and reporting algorithms. the mobile application system should feature the necessary required information for reporting road accidents. images captured using smartphone cameras could be considered as a way to determine the type of vehicles involved, and provide some insight into the accident’s causes, while gps sensors would retrieve the location of the accident automatically. v. conclusion and future work a. conclusion smartphone-based road accident detection and reporting systems can provide innovative solutions to improve drivers’ awareness on road safety and save lives in road traffic accidents. despite being more portable and relatively inexpensive in comparison with in-vehicle sensor-based engineering, technology & applied science research vol. 10, no. 4, 2020, 6009-6015 6014 www.etasr.com mrema & dida: a survey of road accident reporting and driver’s behavior awareness systems … solutions, smartphone sensor-based solutions face various challenges, such as more false positive occasions very likely to happen with smartphone-based accident detection compared to systems implemented with in-vehicle sensors, the reliability of smartphone sensors, and the availability of wireless network links. since tanzania lacks alternatives, apart from the police emergency number, a mobile application for reporting road accidents could deal with the current challenges faced by the traffic police authorities in receiving accident reports, reducing the time needed to provide help to the victims. b. future work the short-term goal is to develop a mobile application system that would report road accidents to the nearest traffic police station through crowdsourcing road users (drivers, passengers, and pedestrians) to report accidents as witnesses. the mobile application system would also utilize smartphone’s gps sensor to increase road safety consciousness, by notifying both drivers and passengers when exceeding speed limits. in addition, the system would continuously collect smartphone accelerometer and gyroscope sensors’ data in order to develop robust automatic detection and reporting algorithms, as the long-term goal of the study. the collected data may help reducing the false positives of already developed systems. future research work should involve the design, development, and validation of the proposed system in order to evaluate if the proposed solution will aid and increase the reporting of road accidents to the authorities. acknowledgment the authors wish to thank the african development bank (afdb) scholarship program at the nelson mandela african institution of science and technology (nm-aist) for funding this research. references [1] who, “global status report on road safety 2018,” world health organization, geneva, switzerland, 2018. 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[31] “the road traffic act,” government of ̀tanzania, 1973, pp. 1–71. microsoft word 14-2955_s1_etasr_v9_n6_pp4942-4945 engineering, technology & applied science research vol. 9, no. 6, 2019, 4942-4945 4942 www.etasr.com hindi et al.: a novel technique for data steganography a novel technique for data steganography amjad y. hindi department of communication technology engineering, faculty of engineering technology, al-balqa applied university, amman-jordan amjadhindi@bau.edu.jo majed o. dwairi department of communication technology engineering, faculty of engineering technology, al-balqa applied university, amman-jordan majeddw@bau.edu.jo ziad a. alqadi department of computer &network engineering, faculty of engineering technology, al-balqa applied university, amman, jordan natalia_maw@yahoo.com abstract—in this paper, a novel stego-method will be introduced, which can be used to hide any secret message in any holding color image. the proposed method will be implemented and tested and the calculated parameters will be compared with the lsb method parameters. it will be shown that the proposed method provides a high-security level by using two keys to extract the secret message from the holding image, making it very difficult to hack. keywords-steganography; hiding time; extracting time; mse; psnr i. introduction steganography is a process of hiding data in covering data, such as a hidden text message in a color image [1, 2]. steganography is an important process and many applications utilize it. hiding a text message in color image can be performed as shown in figure 1 by selecting a stego-system encoder to hide the message and a stego-system decoder to extract the message from the holding color image [3]. fig. 1. steganography process one of the most popular methods of secret message hiding is the least significant bit (lsb), and many methods are based on it [4-6]. lsb reserves 8 bytes from the covering image to hide a character from the secret message, the first bit of the binary version of the character is stored in the least significant bit of the first selected byte of the image, the second bit in the least significant bit of the second byte of the image and so on [4]. table i shows how to hide the letter “a” (ascii a is equal to 65 in decimal and 01000001 in binary) in a sequence of 8 bytes in a color image. lsb is easy to implement, the changes to the image are not essential and cannot be observed with the naked eye, and it is easy to discover the text message and therefore it is not considered safe. table i. hidin g letter a remarks color value after hiding binary value after hiding binary value before hiding color value before hiding byte sequence changed 241 11110000 11110000 240 s1 changed 176 10110000 10110001 177 s2 no change 180 10110100 10110100 180 s3 no change 150 10010110 10010110 150 s4 no change 190 10111110 10111110 190 s5 no change 200 11001000 11001000 200 s6 changed 111 01101111 01101110 110 s7 changed 134 10000110 10000111 135 s8 so, in order to take the advantages and to discard the disadvantages of lsb data hiding method we modified it to improve the security level of data hiding [7]. lsb method provides a small mean square error (mse), and a high peak signal to noise ratio (psnr) between the original and the holding images, these parameters are very important for analysis purposes [4] and they are calculated by: mse = � �� ∑ ∑ ∥ �� , �� � �� , �� ∥����� ��� � �1� psnr = 20log � � !" √�$% � �2� where f represents the matrix data of the original image, g represents the matrix data of the holding image in question, m represents the number of pixel rows of the images and i represents the index of the current row, n represents the number of pixel columns of the image, j represents the index of the current column, and &'() is the maximum signal value that exists in our original “known to be good” image. ii. related work lsb steganography is widely used to hide secret messages into color images due to its simplicity [15]. in [4], a method based on lsb was proposed, which creates a key of random positions to hide the message. this method is very secure but the mse increases when the message length increases. in [10], a technique was introduced on hiding a secret image into a cover image, where both images should have the same size. the technique first compresses the secret message using the set partitioning in hierarchical trees (spiht) algorithm, then the output of this compression was hided into the covering image corresponding author: majed o. dwairi engineering, technology & applied science research vol. 9, no. 6, 2019, 4942-4945 4943 www.etasr.com hindi et al.: a novel technique for data steganography using the default lsb technique. the compression is made by wavelet transform and then by spiht coding. image quality is retained with high psnr values. in [11], the authors hided a secret message file into a covering image, the image should be colored and transformed into 3 matrices (r, g, and b). the message converts to binary, depending on the secret message bit using or operation or and operation, sequentially (rgb, bgr, rgb, bgr...). the results showed better performance in terms of quality of the obtained stego-image. authors in [9] used lsb and dct to perform steganography. the comparison gave a good result according to the psnr values when compared with previous works and the security was increased by using dct. in [8], the message was embedded by hiding each byte of the message in three pixels based on randomization in the cover image using pseudo random number generator (prng) of each pixel’s value. this method achieved a very high maximum hiding capacity and higher visual quality as indicated by psnr. in [16], the authors tried to overcome the disadvantage of the lsb method by appending the encrypted data in an image in place of plain textual data. to encrypt the data rsa and diffie hellman algorithms were used. to check the efficacy of their proposed method, they calculated the number of instructions executed at sender and receiver site since the number of instructions executed is a measure of the time complexity of the process. the result showed that the use of encryption in stego-analysis does not affect the time complexity if diffie hellman algorithm is used instead of the rsa algorithm. in [15], a method that hided a secret text message was proposed based on searching for identical bits between the secret message and image pixels values. the proposed method was compared with the lsb benchmarking method for hiding a secret message which hides the secret message directly in the least two significant bits of the image pixels. the proposed method was more efficient, simple, appropriate and accurate than the lsb method, the change in the image resolution was quite low and it made the secret message more secure. in [17], the authors used the pixelvalue differencing (pvd) method as an image steganography mechanism. they eliminated the overflow problem of pixel values in the stego image exceeding the range 0 ... 255. moreover, for providing more security, they used different number of bits in different pixel components. it was very difficult to trace how many bits are embedded in a pixel of the stego image. the obtained results provided better visual quality of the stego-image compared to the pvd method. iii. the proposed method the proposed method for data hiding can be implemented by applying the following steps: • select the original color image, and find the image size (n1:number of rows, n2: number of columns, and n3: number of colors). • select the message to be hidden in the image and find the message length (n4). • define an 8 digit number to be used as private key (key1). • divide key1 into 2 equal parts (part1 and part2, each of them is a 4 digit number. • reshape the original image from 2d matrix to 2d matrix with size n1*n3, n2. • calculate the row and column indexes (where to start the hiding message) using a defined hash function, in our case we used the following functions: row index = floor (rand (1)*(n1*n3-n4)); column index = floor (rand (1)*(n2-n4)); • apply lsb method to hide a message using the indexes. • reshape the holding image back to a 3d matrix. • generate the second key (key2) by using another hash function. we used the xor function with the indexes and the two parts. • save n4, key1 and key2 to be used to extract the message from the image. to extract the data, the proposed method requires the following steps to be implemented: • select the holding image. • reshape the image matrix from 3d to 2d matrix. • get n4, key1 and key2. • xor the first part of key1 with the first part of key2 to get the row index. • xor the second part of key1 with the second part of key2 to get the column index. • use the indexes to retrieve n4 characters from the image. figure 2 shows the block diagram of the proposed stegosystem, while figure 3 shows a simple example of how to perform some calculations using the proposed method. fig. 2. the proposed stego-system fig. 3. a calculation example of the proposed method (image size=384×512×3), n4=100 using this method will increase security level, because we have to know key1 and key2 and the way of their calculations. engineering, technology & applied science research vol. 9, no. 6, 2019, 4942-4945 4944 www.etasr.com hindi et al.: a novel technique for data steganography this method also decrease mse, which will be very small whatever the message length was. figures 4 and 5 show the original image and the holding image after hiding 100 characters, and here we can notice that there are no visible differences between the two images. fig. 4. original image fig. 5. holding image iv. implementation, results, and discussion the proposed method was implemented several times using various images and different size messages. the experimental results are exhibited and analyzed below. a. experiment 1: hiding a fixed length message the following message with length of 100 characters was hidden in different types and size images. steganography is the process of hiding of a secret message within an ordinary message and extracting at its destination [20]. from the results shown in table ii we can conclude the following which can be considered as the advantages of the proposed stego-method: • hiding and extracting times are significantly small. • hiding time slowly increases due to the increase in image size. in the experiment it fell in the range 0.0930002.506000. • extracting time slowly increases due to the increase in image size and in the experiment it fell in the range 0.442000-0.469000. • the proposed method provides a significantly small mse. • the proposed method provides a significantly high psnr. table ii. experiment 1 results image # type size (each color) hiding time (s) extracting time (s) mse psnr 1 bmp 268x337 0.140000 0.459000 0.008400 158.6776 2 bmp 225x225 0.113000 0.462000 0.016300 152.0137 3 bmp 128x128 0.093000 0.442000 0.049000 140.8332 4 bmp 469x800 0.204000 0.412000 0.002100 172.2939 5 bmp 300x600 0.169000 0.418000 0.004400 165.0364 6 tif 941x1203 0.515000 0.420000 0.000718 183.2172 7 tif 768x1024 0.845000 0.403000 0.001000 179.7110 8 tif 516x600 0.242000 0.420000 0.002600 170.1870 9 tif 320x450 0.155000 0.401000 0.005600 162.6265 10 tif 201x251 0.118000 0.436000 0.015600 152.4010 11 png 750x975 0.964000 0.467000 0.001100 178.9544 12 jpg 184x274 0.124000 0.487000 0.015700 152.3940 13 jpg 1655x2498 2.506000 0.469000 0.000196 196.1701 14 jpg 320x450 0.165000 0.449000 0.005500 162.7715 15 jpg 201x251 0.118000 0.440000 0.015400 152.5456 16 jpg 214x236 0.113000 0.511000 0.013400 153.9270 17 jpg 180x279 0.114000 0.520000 0.016400 151.9212 18 jpg 217x232 0.110000 0.481000 0.015900 152.2288 19 jpg 180x280 0.110000 0.508000 0.015500 152.4927 20 jpg 300x300 0.131000 0.476000 0.002000 172.9714 b. experiment 2: hiding various messages in a colored image a tiff color image with size 516×600×3 was taken, and several messages with different lengths were hidden in the image and extracted from the holding image using the proposed method. the results of this experiment are shown in table iii. table iii. experiment 2 results psnr mse extracting time (s) hiding time (s) message length (chars) 192.5202 0.00028316 0.379000 0.210000 10 185.7420 0.00055771 0.397000 0.226000 20 180.3295 0.00095823 0.397100 0.226300 30 178.6954 0.0011 0.402000 0.228000 40 176.5868 0.0014 0.403000 0.229000 50 162.0298 0.0060 0.463000 0.694000 200 c. experiment 3: lsb implementation the lsb method was implemented to compare the calculated lsb parameters with the proposed method’s parameters. tables iv and v show the results. we can see that the calculated values of the proposed stego-method parameters are very close to the lsb parameters values. v. conclusion the proposed stego-method was presented, implemented and tested. the obtained results were acceptable when compared with the results of the lsb method. lsb method suffers from low security level. the proposed stego-method engineering, technology & applied science research vol. 9, no. 6, 2019, 4942-4945 4945 www.etasr.com hindi et al.: a novel technique for data steganography provides a high security level, because it needs two keys to extract the secret message from the holding image, each of these keys consisting of eight decimal digits making the process of penetration very difficult. table iv. time comparison image # proposed lsb hiding time (s) extracting time (s) hiding time (s) extracting time (s) 1 0.140000 0.459000 0.129000 0.021000 2 0.113000 0.462000 0.109000 0.433000 3 0.093000 0.442000 0.090000 0.452000 4 0.204000 0.412000 0.229000 0.415000 5 0.169000 0.418000 0.155000 0.398000 6 0.515000 0.420000 0.573000 0.488000 7 0.845000 0.403000 0.865000 0.409000 8 0.242000 0.420000 0.212000 0.403000 9 0.155000 0.401000 0.149000 0.424000 10 0.118000 0.436000 0.112000 0.428000 table v. error comparison image # proposed lsb mse psnr mse psnr 1 0.008400 158.6776 0.007600 159.6321 2 0.016300 152.0137 0.014800 152.9688 3 0.049000 140.8332 0.049300 140.7710 4 0.002100 172.2939 0.001500 176.0419 5 0.004400 165.0364 0.004100 165.8746 6 0.000718 183.2172 0.000726 183.1030 7 0.001000 179.7110 0.000996 179.9380 8 0.002600 170.1870 0.002600 170.3018 9 0.005600 162.6265 0.005500 162.8848 10 0.015600 152.4010 0.016500 151.8625 references [1] e. zukerman, “review: openpuff steganography tool hides confidential data in plain sigh”, pc world, available at: www.pcworld.com/article/2026357/review-openpuff-steganographytool-hides-confidential-data-in-plain-sight.html [2] encryption and steganography, available at: http://www.cis.upenn.edu/ ~cis110/13fa/hw/hw04/steganography.html#steganography [3] s. channalli, a. jadhav, “steganography an art of hiding data’’, international journal on computer science and engineering, vol. 1, no. 3, pp. 137-141, 2009 [4] a. a. z. alqadi, m. k. a. zalata, g. m. 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international journal of novel research and development, vol. 2, no. 4, pp. 48-51, 2017 microsoft word 39-2778_s_etasr_v9_n3_pp4281-4286 engineering, technology & applied science research vol. 9, no. 3, 2019, 4281-4286 4281 www.etasr.com bishay-girges: an alternative system for eccentrically braced frames resisting lateral loads an alternative system for eccentrically braced frames resisting lateral loads nagui william bishay-girges department of civil engineering college of engineering, university of hail hail, saudi arabia n.bishay@uoh.edu.sa abstract—eccentrically braced steel frames are structures used to resist lateral loads as they combine the ductility that is characteristic of moment frames and the stiffness associated with braced frames. damper devices can be used as the main source of energy dissipation and have become more popular lately for the lateral control of structures. control devices generally reduce damage by increasing structural safety, serviceability and preventing the building from collapse during vibration. this study focused on improving the performance of the structures with a proposed damping system, which has more advantages than eccentrically braced frames (ebfs). it can accommodate many architectural features and make construction and complementarity in the structures easier. the purpose of this study is to evaluate the performance of the structure with the proposed damping system and its construction in the building. keywords-lateral forces; eccentrically braced frames; active link; collector beam; dampers i. introduction eccentrically braced frames (ebfs) are a lateral loadresistance system that can be considered a hybrid between conventional moment-resisting frames (mrfs) and concentrically braced frames (cbfs). ebfs have become an attractive lateral resistance structural system since they provide high levels of both elastic stiffness and ductility. the distinguishing characteristics of an ebf are that at least one of the braces is connected in such a way that the brace force is transmitted either to another brace or to a column through shear and bending in a beam segment. fig. 1. eccentrically braced frame the short segment of the frame generally designated by the length (e) is called link as shown in figure 1. in ebf systems, yielding is concentrated only at link segments and all other members of the frame (beams, columns and braces) are expected to behave elastically. therefore, links can be considered as structural fuses which will dissipate the lateral input energy through stable and controlled plastic deformations. it is evident that the ability to dissipate energy depends strictly on the plastic deformations essentially located in links, designed to plasticize before beams, braces and columns, designed to use the forces generated by yielded and hardened links in order to remain in the elastic field. the eccentric-braced frame, as a system, has features for resisting lateral forces: • the system can be designed for stiffness, or drift control. • the link beam is designed to yield in shear or flexure prior to initiation of buckling or yielding of bracing member. • yielding of the link beam is a ductile phenomenon that absorbs energy and reduces the dynamic structural response by increasing the damping and the natural period of the building. ii. energy dissipation mechanism in the design of a lateral resistant ebf, energy dissipation mechanism (also commonly called collapse mechanism), is constructed by assuming rigid plastic behavior of the members (figure 2). in figure 2� represents the overall frame drift. the links are cross-hatched to indicate they have yielded in shear and have formed a shear hinge. for the ebfs the rotation demand on the links is much larger than � and from the geometry of the mechanism, it can be determined as follows: γ = � � � (1) link rotation, particularly for short links, is typically denoted by the symbol � as a reminder of the importance of shear yielding in supplying link rotation. the relation between frame drift � and link rotation � depends on the configuration of the ebf and must be determined from the appropriate mechanism. one of the most significant collapse criteria for ebfs was obviously the failure of link elements due to the over passing of the plastic rotation limit. corresponding author: nagui william bishay-girges engineering, technology & applied science research vol. 9, no. 3, 2019, 4281-4286 4282 www.etasr.com bishay-girges: an alternative system for eccentrically braced frames resisting lateral loads fig. 2. energy dissipate in plastic mechanisms the plastic rotation is defined as the ratio between the relative vertical displacement � and the length e: � � � = � = ����� (2) where �� and �� are the vertical displacements in the ends of the links. iii. characteristics of links the length of a link segment e is one of the key parameters controlling stiffness, strength ductility, and overall behavior of an ebf system. the link length ratio ρ=e/(��/�� ), where �� and �� are the plastic moment and plastic shear capacities of the link, provides a convenient measure for the yield behavior. the theoretical limit between the behavior dominated by shear and flexure is based on simple plastic theory. for a link in equilibrium (figure 3), shear and flexural yielding occur simultaneously. from statics, the length ratio for theoretical balanced failure is 2.0. for ρ<2.0, the link will reach full plastic shear capacity before full plastic moment capacity and, therefore, yield in shear, and vice versa. however, links do not behave as the plastic theory suggests. links experience marginal interaction between shear and moment with and without axial loading, but strain hardening has significant effects. for that reason, there is a range of length ratios in which failure behavior changes from shear to flexural yielding for increasing length ratios. forces acting on an isolated link, and the relationship between shear and bending moment in the link based on static equilibrium are illustrated in figure 3. when ��=��= � the equation reduces to �.� = 2�. fig. 3. static equilibrium of link element. for this case, if one considers simple plastic theory, i.e. no strain hardening and no m-v interaction, it is simple to derive that a link of length � = 2��/�� is the theoretical dividing line between a link that yields in shear and one that yields in bending moment. in this equation, �� = �� is the fully plastic moment of the section and is the fully plastic shear capacity of the section. �� = 0.55 � .#.$% (3) where � is the yield strength of the steel, z the plastic modulus, d is the beam depth, and $% is the web thickness. thus, based on simple plastic theory, if e<2��/��, the link shear will reach �� before the end moments reach ��, and the link will yield in shear. in order to assure more desirable behavior of that yield in shear, it is recommended that the link length comply with: � & 1.6 )* +* (4) both top and bottom flanges of the active link must be prevented from laterally deflecting. the active links are not usually long enough to require resistance between supports, however lateral restraint at the supports is always required. the strength requirement that must be met by the restraints is 1.5% of the beam flange design capacity. the beam adjacent to the active link region has normally the same section size with the active link itself and must be designed for the capacity derived actions induced in the beam by yielding of the active link. the collector beams are subjected to high axial forces and bending moments and must be designed as beam-columns for combined actions. the design shear force is unlikely to be significant, and therefore no shear and bending interaction should be considered. the collector beam top and bottom flanges must be laterally braced at the ends of the active link. the position of maximum bending moment (yielding region) in the collector beam is always adjacent to the end of the active link region, so the lateral bracing provided for the active link provides a lateral brace for the collector beam yielding region. the length of the collector beam between the active link region and the column must be able to resist the design compression force n. the top flange of the collector beam is usually effectively connected to a concrete slab (e.g. with shear welded shear studs) in such a way that it restraints the beam against axial shortening and also laterally supports the top flange. iv. size of active links steel links are subjected to high levels of shear forces and bending moments in the active link regions. the link is a single continuous member, the beam segments outside the link must be designed for the maximum possible forces that can be developed in the link. consequently, oversized links are often designed, something that causes the other members and connections of the ebf to be proportionally large, increasing the overall cost of the structure. for most ebf configurations, the shear force in the active link �,-./,(at level i), can be related to the story shear force in the level above the link (level i+1): �����,� = ��1� 23 � (5) where ��1� is the story shear force at level i+1, 45 the inter story height for story i, and l is the ebf bay width (spacing between column center lines). in eccentrically braced frames, the vertical force components in the diagonal braces are transferred to the columns or the braces through shear and bending in the beams. in a sense, this makes eccentrically braced frames a compromise between a truss and a moment resisting frame. the truss-like characteristics endow the frame with high stiffness while the moment resisting frame-like characteristics provide the frame with large ductility capability. engineering, technology & applied science research vol. 9, no. 3, 2019, 4281-4286 4283 www.etasr.com bishay-girges: an alternative system for eccentrically braced frames resisting lateral loads fig. 4. collector beam and stiffener. v. replaceable links the repair of the link after a lateral damage event is difficult and costly. figure 5, shows the replacement of the ebf links which is a good solution for reducing overall costs in both initial construction and repair stages. fig. 5. replaceable link in ebf vi. supplementary damping to structures structural control is an alternative energy dissipation approach that can be achieved by supplementary damping systems. adding damping is controlling the structural deformation by using damper devices. supplemental damping by increasing the system damping primarily reduces the inertia loads induced in the structural system. this effect may provide: • increased protection of the structural system since member loads are reduced. • a reduction in inelastic deformation sustained by the structure since some of the input energy is dissipated. • a reduction in non-structural damage since the maximum response of the structure is reduced. many buildings constructed after the earthquakes in new zealand were built using a structural control system. an example is the opus house in christchurch which features fluid viscous dampers in conjunction with steel moment frames. the dampers are installed on the bracing system at each side of the building and are distributed through the height of the building. another example is a 14-level office building constructed in wellington in 2017. the modern design implements the international best practices in safety and resilience with base isolation and a diagrid structure. the idea of diagrid structure appears to be close to the proposed system adopted in this research. control of the structure response under lateral forces has been demonstrated in [21] using a passive control system. friction dampers are a typical representative of passive control systems, which are used to dissipate the input energy through solid friction. the passive control system operates without requiring an external power source, which is necessary for active and semi-active control systems. the study showed that a large amount of the total input energy was dissipated by friction dampers. authors in [22] compared the performance of steel frames with concentric steel bracing reinforced with improved frictional dampers and steel frames with concentric steel bracing without dampers. they showed that in the absence of dampers, the energy they would absorb may damage parts of the structure. vii. proposed damping system the proposed system can be used as an alternative to the ebf. it is based on the use of a damper attached to longitudinal bracing throughout the structure to produce the damping forces and transfer them to different levels of the structure as shown in figure 6. the proposed system has an advantage over ebfs. it can accommodate various architectural features and provides room for doors, windows and hallways allowing access through the frames while the braces in the typical eccentric configurations get in the way of such features. fig. 6. proposed alternative system for ebf. fig. 7. ebf gets in the way of various architectural features one benefit of using the damping-tendon system is that there is considerable flexibility regarding the placement of ebfs, resulting in less interference with the architectural features of the building. figure 8 shows the architectural benefits of the proposed system as compared to the typical ebf systems. fig. 8. architectural features with the proposed system engineering, technology & applied science research vol. 9, no. 3, 2019, 4281-4286 4284 www.etasr.com bishay-girges: an alternative system for eccentrically braced frames resisting lateral loads viii. installing the damping system the present study provides an alternative and potentially more economical solution that is based on the principles of passive control. the proposed lateral approach intends to protect structures by introducing a tendon system with an energy dissipation device at the end of the tendon. the proposed system can be used as a good alternative solution for ebf for lateral load resistance. it consists of a damper device installed at the ground load of the structure. supplementary dampers at the ground floor of the structure transfer the control forces provided by the devices through the rest of the structure using straight tendons that significantly reduce and control the response of the structure when exited by lateral forces. the main feature of the concept is using only one damper on one side or two dampers, one on each side of the structure, to produce the control forces needed, and transfer them to the rest of the building by using the tendon as shown in figure 11. with the damper-tendon system, it is not necessary to distribute dampers throughout the height of the structure. the damper device that is adopted in this research consists of ring spring dampers. ring springs are passive devices with no reliance on external energy sources. with ring-spring dampers, no maintenance is required, nor leakage can occur because they are constructed of steel. ring-spring dampers have a small length and diameter when compared to other types of dampers such as viscous fluid dampers. as shown in figure 9, damping forces are applied to the structures by the dampers placed at the lower end of the tendon (at ground floor). the damping forces have a horizontal component that must be resisted by the reinforced concrete slab action at the floor level. the damper is installed to the steel column using steel plates and is connected to the tendon on the other end. the connection between the damper and the diagonal tendon can be done by using welded steel plates connected to the damper by steel bolts. the tendon is fixed in the concrete slab at the floor level using four steel plates installed in the concrete slab using anchor bolts (figure 10). fig. 9. the proposed system is installed to the ground floor and connected to floor slabs. ix. effect of the proposed system in reducing the structures’ response to illustrate the effect of the proposed damping system in controlling the impact of lateral forces on structures, a nine story building was used. a sketch of a building’s typical floor is shown in figure 11. the spacings between grids are 8m and 5m in x and y direction respectively. (a) (b) fig. 10. connection of the tendon at (a) ground and (b) floor level fig. 11. plan of a typical floor the total area of each floor is 24m×25m and its height is 3.5m for the whole building. the dead load is estimated to be 5.0kn/m 2 and the live load of 2.0kn/m 2 is used assuming that the structure is a residential building. the load combination case is the ultimate dead load which equals to 1.2×dead load, plus the ultimate live load and wind load. universal steel isections are used for columns and a couple of shear walls are located at the y-direction of the structural boundary to resist the lateral forces in y-direction while the proposed system with dampers is used to resist the lateral forces in x-direction as shown in figure 11. nonlinear static analyses of the model structures designed without and with ring spring dampers at the ground of the structure are carried out to evaluate the lateral performance of the structure. microstran software [12] is used for the nonlinear analysis of the model structure. figure 12, engineering, technology & applied science research vol. 9, no. 3, 2019, 4281-4286 4285 www.etasr.com bishay-girges: an alternative system for eccentrically braced frames resisting lateral loads displays the distribution along the height of the frames including the location of the control system. the effect of lateral load on the structure was considered as wind load distributed on the height of the structure according to australian and new zealand standards which are adopted in this study. wind velocity was v=45m/sec, total pressure was p=1.0kpa, and the wind external and internal coefficients were equal to 0.7 and 0.3 respectively. �5�6� is to be calculated from: �5�6�=�7..�89�:,;�6.�5.�6< (6) where �7 =regional 3second gust wind speed, in m/s, �8 =wind directional multipliers, �:,;�6 =terrain height multiplier, �5=shielding multiplier, and �6=topographic multiplier. (a) (b) fig. 12. displacement of the structure (a) without control system, (b) with control system the design wind pressure (p) in pa, is determined for the structure as follows: p=(0.5 =��>) ?�8�5,@a �.bc�d.b8 � (7) where =��>=density of air, which is taken equal to 1.2kg/m 3 , �8�5,@ = building orthogonal design wind speed, bc�d=aerodynamic shape factor, and b8 � =dynamic response factor. the influence of the lateral forces is concentrated at the floor level and the values are distributed through the height of the structure as shown in figure 12. it can be seen that the maximum displacement at the top of the structure without the control system is 550mm, which is reduced to 55mm after adding the damping system. the percentage of the reduction was about 90% of the response of the structure. it should be mentioned that using the proposed supplemental system significantly reduces the displacement and inter-story drift of the structure by adding damping. no increases in the floor acceleration of the structure occurred, which is a real benefit of using ring spring dampers opposed to adding conventional diagonal bracings to the frame structure. x. conclusion this paper describes an alternative system for ebfs in reducing the response of structures under lateral forces. in ebfs, forces are transferred to the brace members through bending and shear forces developed in the ductile steel link. the link is designed to act as a fuse by yielding and dissipating energy while preventing buckling of the brace members. this study is focused on the validation of the effectiveness of using a damping system for lateral resistance of structures. the proposed damping system offers advantages such as: a) the ability to accommodate openings, b) minimal added weight to the structure, and c) the steel system has been constructed with minimum disruption to the function of the building. the main feature of the concept which is adopted in this research is using only one damper on one side or two dampers, one on each side of the structure, to produce the control forces needed, and transfer them to the rest of the building by using tendons. with the proposed system, it is not necessary to distribute dampers throughout the height of the structure. the connection details between the damping system and the floor concrete slab for the transfer of horizontal damping components to the building are described. in order to assess the behavior of the damping system in multi-story buildings, the model of a nine-story frame with and without the system, was created in microstran and analyzed under lateral loads. the structure behavior was evaluated and the results indicated that the lateral displacements of the multi-story building have been significantly reduced by the installation of this energy absorber and considerable energy has been dissipated by the damping system. acknowledgement this research was funded by the deanship of scientific research at hail university, hail, saudi arabia, under the contract no.160536. author wishes to express his deep gratitude to the deanship of scientific research and the college of engineering at hail university for providing the necessary support for conducting this research. references [1] as/nzs 1170.2:2002, structural design actions: part 2: wind actions, standards australia/standards new zealand, 2002 [2] e. p. popov, m. d. engelhardt, “seismic eccentrically braced frames”, journal of construction steel research, vol. 10, pp. 321-354, 1988 [3] m. badalassi, a. braconi, s. caprili, w. salvatore, “influence of steel mechanical properties on ebf seismic behavior”, bulletin earthquake engineering, vol. 11, no. 6, pp. 2249–2285, 2013 [4] m. bosco, p. p. rossi, “a design procedure for dual eccentrically braced system: analytical formulation”, journal of constructional steel research, vol. 80, pp. 440-452, 2013 [5] h. s. monir, k. zeynali, “a modified friction damper for diagonal bracing of structures”, journal of 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dubina, “design implementation of recentering dual eccentrically braced frames with removal links”, soil dynamics and earthquake engineering, vol. 112, pp. 174-184, 2018 [17] s. mirzabagheri, m. sanati, a. a. aghakouchak, s. e. khadem, “experimental and numerical investigation of rotational friction dampers with multi units in steel frames subjected to lateral excitation”, archives of civil and mechanical engineering, vol. 15, pp. 479-491, 2015 [18] j. shen, o. seker, b. akbad, p. seker, s. momenzadeh, m. faytarouni, “seismic performance of concentrically braced frames with and without brace buckling”, engineering structures, vol. 141, pp. 461-481, 2017 [19] j. ruiz-garcia, e. bojorquez, e. corona, “seismic behavior of steel eccentrically braced frames under soft-soil seismic sequence”, soil dynamics and earthquake engineering, vol. 115, pp. 119-128, 2018 [20] g. ince, h. h. ince, c. ocal, “seismic behavior of rc frames retrofitted by eccentrically braced frames with vertical link”, international journal of advances in mechanical and civil engineering, vol. 2, no. 4, 2015 [21] p. h. sarjou, n. shabakhty, “effect of the improved pall friction damper on the seismic response of steel frames”, engineering, technology & applied science research, vol. 7, no. 4, pp. 1833-1837, 2017 [22] g. xu, m. yamanari, “performance of steel frame with linkage system under earthquake excitation”, engineering, technology & applied science research, vol. 9, no. 1, pp. 3796-3802, 2019 microsoft word etasr_7-1_1377-1381.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1377-1381 1377 www.etasr.com ghazi et al.: risk assessment in the maritime industry risk assessment in the maritime industry majid mousavi department of disaster management shakhes pajouh research institute isfahan, iran majidmousavi73@gmail.com iran ghazi department of disaster management shakhes pajouh research institute isfahan, iran iranghazi20@gmail.com behrooz omaraee islamic azad university kharg branch kharg island, iran b.omaraee@gmail.com abstract—risk assessment is a well-developed field which many operators are currently applying to improve their operations and reduce their risk exposure. this paper is intended to provide an overview of the risk assessment for mariners in the maritime transportation. the risks addressed are primarily those affecting the safety of a vessel, facility or operation. the concept of risk is defined, and the methods available to assess the risks associated with an operation are described. regulatory requirements that have prompted the development of modern risk assessment practices are described, and future regulatory trends are discussed. there are many different analysis techniques and models that have been developed to aid in conducting risk assessments. a key to any successful risk analysis is choosing the right method (or combination of methods) for the situation at hand. this is achieved through critical analysis of the available data concerning marine crises. this paper provides a brief introduction to some of the analysis methods available and suggests risk analysis approaches to support different types of decision making within the maritime transportation to cope with crises. finally, as awareness of risk assessment increases, the benefits which can be realized through its application will continue to increase. organizations in both the public and the private sector are becoming more and more familiar with the benefits associated with risk-based approaches to managing safety and consequently reducing crisis in maritime transportation. keywords-risk assessment; maritime; crisis; vessel i. introduction risk assessment is typically applied as an aid to the decision-making process. as options are evaluated, it is critical to analyze the level of risk introduced with each option. the analysis can address financial risks, health risks, safety risks, environmental risks and other types of business risks. an appropriate analysis of these risks will provide information which is critical to good decision making, and will often clarify the decision to be made. the information generated through risk assessment can often be communicated to the organization to help impacted parties understand the factors which influenced the decision. risk assessment is the process of gathering data and synthesizing information to develop an understanding of the risk of a particular enterprise. a detailed step by step guide to risk assessment follows in the next section. the guide is written in a follow-though fashion to provide a clear guidance path. ii. steps of risk assessment the first obvious step would be to identify the risks involved (step 1). the risks should be grouped under appropriate risk headings. one should consider the effect on people (staff, students and other people), information, physical assets and finances, reputation. the next step is to determine the consequences and likelihood of each risk using a predetermined scale (e.g. table i) (step 2). one should also consider the consequences to evaluate the risk level (table ii) (step 3). next, further risk treatments and opportunities for improvement should be considered (step 4). in this step, one should consider the actions needed to bring risks to an acceptable level and whether these actions are incorporated into other planning processes and include responsibilities, resources and timelines. the improvement opportunities should be considered. communication, consulting, monitoring and reviewing should be incorporated throughout the process. the assessment should be reviewed on a regular basis. the final step (step 5) is filing the documentation. risk assessment approaches are increasingly commonly used for the assessment of major hazards and the demonstration that risks have been controlled to an as low as reasonably practicable (alarp) standard. attitudes have changed in the oil industry from an initial position of skepticism to good support for the simpler approaches, and for the clarity of focus this brings to controlling hazards, but with still some question as to the effectiveness of quantitative risk assessment health & safety at work etc act 1974 (qra). for example, the regulations applying to offshore operations in the uk, including health & safety at work etc act 1974(hswa), mhswr and offshore installations safety case regulations 1992(scr), require operators to undertake risk assessment in order to identify appropriate measures to protect people against crises, so far as is reasonably practicable. scr includes specific requirement for qra, but this does not apply to marine hazards, i.e. hazards connected with the interface between the installation and the marine environment. perhaps as a consequence, the risk assessments of marine hazards in the safety cases submitted to date have been less thorough than the treatment of hazards from fire and explosions [1]. the safety of offshore installations against marine hazards has traditionally relied on imo legislation and classification society rules. these rules have been developed by expert judgment, responding to previous crisis experience, and in general prescribe specific engineering, technology & applied science research vol. 7, no. 1, 2017, 1377-1381 1378 www.etasr.com ghazi et al.: risk assessment in the maritime industry design solutions. they are only rarely based on risk assessment, and do not by themselves satisfy the requirement to perform a risk assessment. modern risk management approaches make clear that risk assessment has an important role to play in many risk-related decisions, particularly for decisions involving uncertainty, deviation from standard practice and risk trade-offs, for which marine regulations are less appropriate. the united kingdom offshore operators association (ukooa) decision support framework provides a suitable basis for such decision-making. the hse tolerability of risk framework shows how risk assessment can contribute to such decisions [1]. table i. consequences and likelihood of each risk consequences likelihood level descriptor level descriptor 1 insignificant a almost certain 2 minor b likely 3 moderate c possible 4 major d unlikely 5 catastrophic e rare table ii. identifying the risk level consequences likelihood insignificant 1 minor 2 moderate 3 major 4 catastrophic 5 a-almost certain high high extreme extreme extreme b-likely moderate high high extreme extreme c-possible low moderate high extreme extreme dunlikely low low moderate high extreme e-rare low low moderate high high iii. hazard identification (hazid) technique hazid is a general term used to describe an exercise whose goal is to identify hazards and associated events that have the potential to result in a significant consequence. for example, a hazid of an offshore petroleum facility may be conducted to identify potential hazards which could result in consequences to personnel (e.g., injuries and fatalities), environmental (oil spills and pollution), and financial assets (e.g., production loss/delay). the hazid technique can be applied to all or part of facility or vessel or it can be applied to analyze operational procedures. depending upon the system being evaluated and the resources available, the process used to conduct a hazid can vary. typically, the system being evaluated is divided into manageable parts, and a team is led through a brainstorming session (often with the use of checklists) to identify potential hazards associated with each part of the system. this process is usually performed with a team experienced in the design and operation of the facility, and the hazards that are considered significant are prioritized for further evaluation [3]. iv. check list analysis checklist analysis is a systematic evaluation against preestablished criteria in the form of one or more checklists. it is applicable for high-level or detailed-level analysis and is used primarily to provide structure for interviews, documentation reviews and field inspections of the system being analyzed. the technique generates qualitative lists of conformance and nonconformance determinations with recommendations for correcting non-conformances. checklist analysis is frequently used as a supplement to or integral part of another method (especially what-if analysis) to address specific requirements [3]. v. hazard and operability (hazop) analysis the hazop analysis technique uses special guidewords to prompt an experienced group of individuals to identify potential hazards or operability concerns relating to pieces of equipment or systems. guidewords describing potential deviations from design intent are created by applying a predefined set of adjectives (i.e. high, low, no, etc.) to a predefined set of process parameters (flow, pressure, composition, etc.). the group then brainstorms potential consequences of these deviations and if a legitimate concern is identified, they ensure that appropriate safeguards are in place to help prevent the deviation from occurring. this type of analysis is generally used on a system level and generates primarily qualitative results, although some simple quantification is possible. the primary use of the hazop methodology is identification of safety hazards and operability problems of continuous process systems (especially fluid and thermal systems [3]. vi. contribution of “human factors” issues in any effort to identify hazards and assess their associated risks, there must be full consideration of the interface between the human operators and the systems they operate. human factors engineering (hfe) issues can be integrated into the methods used to identify hazards, assess risks, and determine the reliability of safety measures. for instance, hazard identification guidewords have been developed to prompt a review team to consider human factor design issues like access, control interfaces, etc [2]. an understanding of human psychology is essential in estimating the effectiveness of procedural controls and emergency response systems. persons performing risk assessments need to be aware of the human factors impact, and training for such persons can improve their ability to spot the potential for human contributions to risk. risk analysts can easily learn to spot the potential for human error any time human interaction is an explicit mode of risk control. however, it is equally important to recognize human contributions to risk when the human activity is implicit in the risk control measure. for example, a risk assessment of a boiler would soon identify “overpressure” as a hazard that can lead to risk of rupture and explosion. a checklist of common errors or an audit of the management system for operator training are examples of methods used to address the human error potential and ensure that it also is controlled [4]. the purpose of any tool would be to identify the potential for error and identify how the error is prevented.  does the operator know what the alarm means?  does he know how to shut down the boiler? engineering, technology & applied science research vol. 7, no. 1, 2017, 1377-1381 1379 www.etasr.com ghazi et al.: risk assessment in the maritime industry  what if the overpressure event is one of a series of events (e.g. what if the operator has five alarms sounding simultaneously)?  did the engineer properly size and specify the relief valve?  was it installed correctly?  has it been tested or maintained to ensure its function? a corollary to each of the above questions is required in the analysis: “how do you know?” the answer to that last question is most often found in the management system, thus “human factors” is the glue that ties risk assessment from a technology standpoint to risk assessment from an overall quality management standpoint [3]. vii. hazard identification during project development hazard identification is most effectively applied early in a project’s life-cycle. if hazards can be identified early, they can often be “designed out” or eliminated completely during the early design phases of a project. if the hazards are not recognized until the design is complete or the system is operational, they will be more costly to address, and the only feasible way to address the hazards may be to provide measures to mitigate the hazardous events they may cause [2]. it is best to integrate hazard identification activities into the project development process to assure these activities are conducted at optimal times. for instance, high level preliminary hazards analysis should be conducted as early as possible in the project life-cycle, while multiple project options are under consideration. this will enable risk assessment of the various options and help identify the major hazards which will need to be dealt with as the project goes forward. as the development process progresses, more and more detailed hazard analyses can be conducted. in the offshore oil and gas industry, hazard identification is typically performed on process systems during conceptual design(when process flow diagrams and layouts are available) and again at the detailed design phase (when p & id’s and equipment specifications are available) [3]. viii. evaluation of safeguards since the hazards relating to oil and gas production facilities are generally well understood, safeguards and preventive measures have become fairly standard across the industry. however, each project has its own unique requirements as a result of the types and amounts of fluids handled, the location, existing infrastructure, manning philosophy and other parameters. safeguards must be customized for each project to adequately protect the facility. in order to evaluate safeguards, specialized safety studies are often applied. companies designing major new offshore facilities typically conduct a suite of these studies, including [2]:  fire and explosion risk analysis.  equipment layout review and optimization.  evacuation, escape and rescue analysis.  emergency systems survivability analysis. ix. management of change after a system is in operation, hazard identification is sometimes required by regulatory authorities as a design and operational check or to assure that changes made subsequent to the initial design have not introduced new hazards [2]. x. root cause analysis despite efforts to safeguard against all hazards during the design and specification of a facility, systematic analyses and strong management systems cannot completely eliminate the possibility of reliability-related problems. when failures occur, root cause analysis can be used to identify the underlying reasons (hazards and pre-conditions) that problems occur and to correct the root causes so that the same problem or related problems with shared root causes do not occur in the future. the root causes of an event are the most basic causes of an event that (1) can be reasonably identified and (2) management has the control/influence to fix. typically, root causes are the absence, neglect, or deficiencies of management systems that control human actions and equipment performance [4]. xi. evaluating new operating modes over the years, standard approaches have been developed for operating oil and gas related equipment. many of these have been documented as industry standards and/or codified into regulation. for example, regulatory bodies such as the u.s.’s osha and coast guard require adherence to basic standards in the areas of hearing conservation, lock-out/tagout, fall protection, electrical safety, fire protection, emergency response, etc. in addition, most operators have developed internal requirements to address recognized operational hazards [4]. in efforts to continually improve business performance, successful operators continue to challenge the established ways of conducting their operations. opportunities for improved business performance are continually identified, and must be assessed for risk impact in addition to financial impact and feasibility. risk studies can be conducted to assess the relative risks associated with various modes of operation, including [4] :  simultaneous operations (concurrent production and/or drilling and/or construction operations)  construction activities: (hazard analysis of construction activities, risk impact of major marine activities at producing locations, etc.) .  automation of drilling activities.  production and maintenance activities (manned vs. unmanned platforms, platform-based maintenance crews vs. roving maintenance teams, etc.) [3]. engineering, technology & applied science research vol. 7, no. 1, 2017, 1377-1381 1380 www.etasr.com ghazi et al.: risk assessment in the maritime industry xii. estimating overall facility risks in the north sea, it has become an industry norm to use quantified risk assessment (qra) methods to estimate the individual risk rate (annual potential of loss of life for an individual working on the facility) for safety case submittals to demonstrate that the risk associated with a particular platform is alarp. due to the potential for data and modeling uncertainties, and the assumptions made, the accuracy of such explicit risk rate calculations is not considered to be very good, and may be off by over 100%. unless specifically required by regulation (north sea safety cases), the calculation of individual risk rates does not typically prove to be a useful way to devote risk assessment resources. many operators prefer instead to conduct focused relative risk studies of a smaller scope to aid in making decisions between two or more viable options. when comparing the relative risks of two or more options, the same methodology and assumptions can be used to evaluate each option, and the uncertainties associated with the absolute risk numbers calculated does not significantly impact the decision. often, high-level estimates of overall facility risks and the major risk contributors are made early in the project life to aid in selecting between various development options. this is a valuable exercise, because it is at this point that a project team has the most impact on the overall risks associated with the project. conducting hazard and risk assessments early in the project life also allows time for the development of mitigation solutions to address major risk contributors [3]. xiii. accident costs a. 1accident cost models accident cost information is important for estimating the benefits of risk control measures that reduce crisis probability, as required for the cost-benefit step of the formal safety assessment procedure [4]. a basic loss matrix for ship accidents, considering the crisis categories collision, contact and grounding, consequences can result in impacts on humans (crew, passengers, and third parties), ships, the environment, industry, and the waterways and their future use, ship owners, government services such as search and rescue providers, spill response agencies, fairway maintenance, and crisis investigation services may all incur direct costs as a result of crises (figure 1). if environmental damage occurs, there will be many indirect costs to other users of the resource, including tourism and recreational users [5-8]. fig. 1. simplified model of accident consequences origon by collision, contact, and grounding crises. engineering, technology & applied science research vol. 7, no. 1, 2017, 1377-1381 1381 www.etasr.com ghazi et al.: risk assessment in the maritime industry xiv. conclusion the primary goal of many risk assessments is to identify the hazards that are involved in a particular process or system and to develop adequate safeguards to prevent or reduce negative consequences from the related hazardous events. as previously discussed, the first step in performing a risk assessment is hazard identification. whether done in an explicit or implicit form, this step provides an understanding of the basic hazards. the hazard identification step is a key factor in developing an understanding of the contributors to the risk of operating a particular system or process. once these hazards are identified and the potential undesirable events involving these hazards are described, risk assessment techniques can allow personnel to identify the safeguards, or risk-reducing measures, that are currently in place and to make recommendations for additional safeguards that would further reduce the risk. these safeguards can either prevent an event from occurring, or reduce (mitigate) the consequences if an event does occur. risk assessment is a well-developed field which many operators are currently applying to improve their operations and reduce their risk exposure. in many areas of the offshore and marine industries there is a dichotomy: operators must still comply with prescriptive “old-style” regulations while being encouraged on other fronts to develop a risk-based approach to safety. risk assessment should be at the core of any safety-related rule-making or regulatory development process. since the underlying goal of these rules and regulations is to reduce the risk of losses resulting from hazards, risk assessment seems an imperative part of any rule-making process. as awareness of risk assessment increases, the benefits which can be realized through its application will continue to increase. references [1] det norske veritas, marine risk assessment, offshore technology report 2001/063, crown, 2002 [2] h. a. oltedal, safety culture and safety management within the norwegian-controlled shipping industry, phd thesis, faculty of social sciences, university of stavanger, 2011 [3] abs, abs guidance notes on risk assessment, 2000 [4] m. lundkvist, risk värdering avsjötrafik information, draft report, swedish maritime administration,vol. 1, no. 1, pp. 12-23, 2010 [5] r. f. oy, p. iikkanen, m. mukula, “fma, alusliikenteen onnettomuuksien kustannukset” merenkulkulaitoksen julkaisuja, helsinki, finland, 2008 [in finnish] [6] j. ylitalo, modelling marine accident frequency, msc thesis, aalto university, 2010. [7] f. goerlandt, j. montewka, “maritime transportation risk analysis: review and analysis in light of some foundational issues”, reliability engineering & system safety, vol. 138, no. 1, pp. 115-134, 2015 [8] a. lehikoinen, m. hänninen, j. storgård, e. luoma, s. mäntyniemi, s. kuikka, “a bayesian network for assessing the collision induced risk of an oil accident in the gulf of finland”, environmental science & technology, vol. 49, no. 9, pp. 5301-5309, 2015 engineering, technology & applied science research vol. 8, no. 4, 2018, 3121-3125 3121 www.etasr.com ajetrao & dhande: phi shape uwb antenna with band notch characteristics phi shape uwb antenna with band notch characteristics k. v. ajetrao department of electronics & telecommunication engineering dr. d. y. patil institute of technology pune, maharashtra, india kiran_ajetrao@rediffmail.com a. p. dhande department of electronics & telecommunication pune institute of computer technology pune, maharashtra, india apdhande@pict.edu abstract—in this paper a novel band notch antenna in uwb frequency range is designed using split rings. split rings are overlapped with designed monopole to give phi shape. the slit gap gives band-notch operation from 5.1ghz to 6.29ghz and from 4.94ghz to 5.91ghz for spssr and spscr antennas respectively. simulated and measured results are in good agreement. keywords-monopole; split ring resonator; band-notch; uwb antenna; vswr i. introduction for a wireless communication system, large bandwidth is an important requirement. although uwb antenna gives large bandwidth of 7.7ghz (3.1ghz to 10.6ghz), it faces many challenges of interference with existing systems in uwb range. to avoid this interference with existing systems like wlan, hipperlan, wimax, c-band satellite communication etc., band notch antennas are nowadays becoming popular and necessary for communication. in this paper a novel band notch antenna is designed by merging a monopole antenna with a square or circular split ring resonator. this proposed antenna shape looks like the greek letter phi (φ) hence is named as split phi shape square ring (spssr) antenna and split phi shape circular ring (spscr) antenna. both antennas give single band notch operation in uwb band. monopole is designed at 3ghz. the parameters for the spssr antenna are designed, optimized and applied to the spscr antenna. it is found that both antennas give the same response hence the same design can be extended to any other shape as well. in proposed antennas, by varying the split gap of rings, band notch frequency can be tuned to the desired band. the length and width of split ring resonator gives inductance, and the gap between two rings and the slit gap of the rings gives the capacitance. the gap between the rings and the slit gap is optimized to give uwb antenna with notch band characteristics. at slit gap of 1.1mm the uwb operation in with band notch at 5.87 and 5.47ghz is achieved for spssr and spscr respectively. many antennas with band-notch characteristics are reported. band-notch characteristics are achieved by inserting different slots in the radiating patch [1-3]. in [4, 5] antennas with etching slots shapes such as h, m, w etc. slots in the ground plane are reported. a band notch antenna by etching a narrowband dual resonance fractal binary tree in the radiation element of the conventional uwb antenna is reported in [6], but the antenna manufacturing and structure are complex. the band-notched characteristics are obtained by adding a stepped impedance resonator (sir) or a split ring resonator (srr) on the feed line or cutting slots in the ground plane [7, 8]. a bandnotch antenna is designed by etching a nested csrr inside the ground plane in [9]. another technique to obtain band-notch characteristics is by adding the parasitic elements in the form of printed strips placed in the radiating aperture of the planar antenna at the top and bottom layer. they are employed to suppress the radiation at certain frequencies within an ultra-wide frequency band [10, 11]. by inserting the u-shaped parasitic element on the bottom plane of the basic planar monopole antenna [12] or by using a pair of arc shaped parasitic elements around the patch, an excellent notched frequency band for rejecting the wlan band (5-6ghz) can be obtained [13]. the electromagnetic coupling of the srr with the cpw yields the frequency notch [14]. there are many more techniques used to obtain bandnotch operation in uwb range. the proposed antenna is simple to design and implement. by changing the slit gap of the antenna the desired band-notch frequency can be tuned. additional varactor diode can be implemented with the antenna as a future scope to give variable capacitance and the same antenna can be used to tune different frequency bands. the proposed antenna was carefully fabricated and measured. the return loss, vswr, and impedance are measured to certify the performance. results show acceptable discrepancy between simulation and measurement due to the influence of the sma connector for testing and the indoor measurement environment. ii. phi shape uwb antenna with band notch characteristics initially a monopole antenna at 3ghz frequency is designed. the height of monopole antenna will be λ/4. heights of monopole antenna and ground plane dimensions are fixed by optimization. designed square and circular shape split ring resonators are overlapped with monopole to form the proposed phi shape antennas. the proposed spssr and spscr antennas for band notch applications in uwb range are shown in figure 1. the length of the outer ring is 38mm and the ring width is 1.1 ant sho giv the cha cap re cap cir val fig and inn mo fre int cir as: engineerin www.etasr 1mm. outer a tennas have a own in table ves the inducta eir slit gap g anged by chan pacitance by esonance freq pacitance. hen rcular ring is g le and ce a lues of square fig. fig. 2 from the em gure 2, l1 is th d c2 are cap ner rings and c onopole on le equency of the to considerati rcuit is given b considering : ng, technology r.com and inner ring a split gap of e i. the lengt ance and the sp ives the capa nging the lengt changing the quency is a nce the resona given as in (1) are the equiva and circular s 1. spssr ant 2. empirical a mpirical equiv he total equiva acitance beca c3 and c4 are eft half and ri e proposed an on. the total by (2) [16] as c1=c2= an y & applied sci gs are separate 1.1mm. detai th of rings w pacing betwee acitance. the th and width o e spacing and a function o ance frequency [15] alent inductan split rings. tenna and spscr antenna equivalen valent circuit alent inductan ause of the sli capacitance b ight half of a ntenna is calcu l equivalent nd c3=c4= , ience research ed by 0.7mm. iled dimension with specified en the two ring inductance c of rings where d slit gap of of inductance y for the squar (1) nce and capac r antenna nt circuit. diagram show ce of the circu it gap in oute between the rin antenna. reso ulated by takin capacitance o (2) , (2) can be w h v ajetrao & dha . both ns are width gs and an be eas the rings. e and re and citance wn in uit, c1 er and ng and onance ng (1) of the written betw wri rect (mm sam of s uw is: whe sam circ con and ran to s by by vol. 8, no. 4, 20 ande: phi shap metal thickne ween rings is itten as for square c 4a for circula , equivalent tangular/circul m) and thickn me concept is u spssr and s wb range. the 0.0002 ere, ϒ is the co 8 the equivale me as in (7) bu cular geometry 2 using (2)-(9) ncept in [13, 1 d spscr ante nge. calculated simulate the pr parameter l1 l2 l m y1 w ring length t g1 g2 h i the performa parametric an measuring th 018, 3121-3125 pe uwb antenn ess of copper g1 and ε0=8. rings is giveng c ar rings is give and are cal inductance lar cross sect ness of ring t used to calcul pscr antenn e equivalent in 2.303 onstant for wir; ent inductance ut with differe y and: ; in (1) gives th 15-18] is used ennas for ban d dimensions w roposed antenn table i. spssr ant dimensio 72mm 23mm 19.5mm 3mm 7.9mm 6.5mm 38mm (ringx= 1.1mm 0.7mm 1.1mm 1.6mm ii. results ance of the pr nalysis and the he s-paramete na with band n is p=35µm, r 854187817×1 n by (5) [13, 16 en by (6) [15] lculated as in [ le c ion of wire w (mm) is prop late the equiva a for band no nductance le f re loop of squa ; 2. e le for spsc ent (ϒ) consta ; 2.45 he ring resona d to design the nd notch app with some opt na. antenna dimen tenna ons sp m m m m m =9.5mm) 38m m m m m s and discuss roposed anten e simulated re ers and vsw 3122 notch character (3) ring width is t 0−12f/m. ca (4) 6] as (5) as (6) [13, 15-17]. calculation with finite len posed in [18]. alent inductanc otch applicatio for spssr ant (7) are geometry, 853 (8) cr antenna i ant for wire lo 1 (9) ance. the prop e proposed sp plications in u timization are nsions pscr antenna dimensions 72mm 23mm 19.5mm 3mm 7.9 6.5mm mm(r1=6.05mm) 1.1mm 0.7mm 1.1mm 1.6mm sion nnas is investi esults are vali wr. the prop ristics t, gap an be for ngth l . the ce le ons in tenna is the op of posed pssr uwb used gated dated posed ant thi tan are sho sol giv inp ref ant opt mi ant to fre 3. ver go sho sp pat at 3 is c res ant pat rad at h n engineerin www.etasr tennas are fa ickness, 4.4 ngent. the dim e optimised a own in figure both antenn lver based on ve good impe put impedance flected in tabl tenna and is a timised dimen ismatch in inp tenna and resu o understand t equncy simulat table ii. fig. 3. sim from figure ry close to eac od agreement ows the simu pscr antenna tterns for the s 3.4ghz and 8 clear that both spective band tenna and h ttern gets dis diation pattern high frequenci band uwb range frequ ba notched band cente f notvh ng, technology r.com abricated usin dielectric con mensions of bo as shown in t 1. a designs are finite element edence charac e is quite clo le ii. initial an applied to sp nsions, becaus put imedence ults are not ex the antenna re ted curves are spssr and mulated and measu s 3 and 4 it is ch other. simu t with each ot ulated and me as. figure 5 specified band .ghz respecti h antennas are ds. e-plane h-plane pattern sturbed at hig n is caused by ies. parameters uency range (gh s11 in db vswr nd width in ghz impedance er frequency (gh vswr freuency band h-band bw in mh impedance y & applied sci ng an fr4 su nstant and 0 oth spssr an table i and t e simulated w t method. the cteristics for ose to 50ω fo ntenna design scr antenna se of this the of spscr co xactly matchin esponse in bet e ploted for bot spscr antenna ured s11 spssr a clear that bot ulated and me ther for both easured vsw shows the s ds of spssr an vely. from the behaving in s pattern resem n is omnidir gh frequencie the change in spssr antenn hz) 2.75-11 less than less tha 8.65 around 50 said ran hz) 5.874 6.27 5.1-6.2 hz 1190mh 140 ω ience research ubstrate of 1 0.02 dielectric nd spscr ant the antennas a with electroma simulated ant both designs or both antenn is done for s by using the ere may be a omapred to s ng with each tter way s11 v th designs in f simulated resu and spscr antenn th antennas res asured results antennas. fig wr for spssr simulated rad nd spscr ant e radiation pat similar ways in mbles with d rectional. rad es. this chan current distrib r na spsc anten 1.4 2.63-1 -10db less th 10d an 2 less th 8.8 0ω for nge around for said 4 5.4 4.7 29 4.94-5 hz 970m ω 117 h v ajetrao & dha .6mm c loss tennas are as gnetic tennas s. the nas as spssr same slight spssr other. verses figure ults na sonate show gure 4 r and diation tennas ttern it n their dipole diation nge in bution fro for the opp fig. givin fig. 8.4g freq cap freq freq con opt wl ante freq cr nna 11.42 han db han 2 8 d 50ω d range 47 7 5.91 mhz ω vol. 8, no. 4, 20 ande: phi shap figure 6 show om the current spssr and s current is d posite direction 4. simulated ng band-notch. 5. spssr a ghz figure 7 sho quency. as th pacitance decr quency is in quency tuning nnecting varac timised to 1.1 lan frequenc ennas. the ga quencies. figu 018, 3121-3125 pe uwb antenn ws the curren t distribution p spscr in figu distributed onl ns giving band d and measured v and spscr ante ows the effe he slit gap is reases and as ncreased in b g is possible ctor diode in b 1mm which cy band. figu ain for both sh ure 9 shows the na with band n nt distribution pattern at 5.47 ure 6(b) and 6 ly in one sid d-notch operat vswr for spssr enna radiation p ect of slit ga increased the an effect the both antennas by changing between slit g gives band n ure 8 shows hapes is consta e fabricated an 3123 notch character for both ante 7ghz and 5.87 6(c), it is clear de and flowin tion. r and spscr an pattern at 3.0gh ap on band n overall equiv notch-band c s. hence, de the slit gap o gap. the slit g notch operatio the gain for ant and equal ntennas. ristics ennas. 7ghz r that ng in ntennas hz and notch valent center esired or by gap is on in both at all fig rad freq engineerin www.etasr g. 6. current diating patch at quency 5.87ghz fig. 7. ng, technology r.com distribution for frequency of 3g and 5.47ghz for effect of slit g y & applied sci (a) (b) (c) spssr and sp ghz and (b) (c spscr and sps gap on notch-band ience research pscr antennas c)for notch-band sr respectively. d frequency. h v ajetrao & dha (a) for center inte ban wir sps sps giv patt the ban can des not ban 5.9 the and the bot agr [1] [2] [3] vol. 8, no. 4, 20 ande: phi shap fig. 8 applications erference with nd notch anten reless commun ssr antenna i scr antenna ing similar r tern and gain. equivalent cap nd-notch cente n be connecte sired frequency tch at wlan nds are from 5 1ghz for sps wlan and d wimax wil e theoretical d th antennas. s reement with e s. tu, y. c. jia antenna with b in electromagn k. chung, j. antenna havin and wireless co m. naghshvari transmission l 3, pp. 283–293, 018, 3121-3125 pe uwb antenn 8. gain of sps fig. 9. fab iv. co of uwb anten h existing syst nnas are playi nications in uw is designed an in uwb freq response in te . it is observe apacitance incr er frequency. a ed between th y. both anten and wimax .1ghz to 6.28 scr antenna. wimax sys ll be avoided design results simulated and each other. refer ao, y. song, z. z band notched fun netics research le kim, j. choi, ng frequency ba omponents letters ian-jahromi ,“co line fed”, progres , 2008 na with band n ssr and spscr bricated antennas. onclusions nnas find diffi tems like wl ing an import wb range. in nd the same d quency range. erms of s11, ed that by incr reases which in as future wor he slit gap in nnas are capab x system frequ 8ghz for spss both notch b stems. interfer by using the p s are verified d measured re rences. zhang, “a novel m nctions for uwb etters, vol. 10, pp “wideband mic and-notch functi s, vol. 15, no. 11 ompact uwb ba ss in electromagn 3124 notch character antenna . ficulties in avo lan and wim tant role in to this paper, a n design is appli . both design vswr, radi reasing the sli n turn increase rk, a varactor d order to tun ble of giving uencies. the n sr and 4.94gh bands are cov rence with w proposed ante by simulatio esults are in miniature strip-si applications”, pr p. 29-38, 2009 crostrip-fed mon ion”, ieee micr 1, pp. 766-768, 20 andnotch antenna netics research b ristics oiding max. day’s novel ied to ns are iation it gap es the diode ne the band notch hz to vering wlan ennas. n for good ine fed rogress nopole rowave 005 a with b, vol. engineering, technology & applied science research vol. 8, no. 4, 2018, 3121-3125 3125 www.etasr.com ajetrao & dhande: phi shape uwb antenna with band notch characteristics [4] j. q. sun, x. m. zhang, y. b. yang, r. guan, l. jin “dual band notched ultra-wideband planar monopole antenna with m and w slots”, progress in electromagnetics research letters, vol. 19, pp. 1-8, 2010 [5] a. falahati, m. naghshvarian-jahromi, r. m. edwards ,“dual bandnotch cpw-ground-fed uwb antenna by fractal binary tree slot”, fifth international conference on wireless and mobile communications, cannes, france, august 23-29, 2009 [6] z. a. zheng, q. x. chu, “compact cpw-fed uwb antenna with dual band notched characteristics”, progress in electromagnetics research letters, vol. 11, pp. 83-91, 2009 [7] y. zhang, w. hong, z. q. kuai, j. y. zhou, “a compact multiple bands notched uwb antenna by loading sir and srr on the feed line”, ieee international conference on microwave and millimeter wave technology, nanjing, china, june, 13, 2008 [8] x. li, l. yang, s. x. gong, y. j. yang, “ultra-wideband monopole antenna with four-band-notched characteristics”, progress in electromagnetics research letters, vol. 6, pp. 27–34, 2009 [9] k.-h. kim, y.-j. cho, s.-h. hwang, s.-o. park, “band-notched uwb planar monopole antenna withtwo parasitic patches”, electronics letters, vol. 41, no. 14, pp. 783-785, 2005 [10] a. m. abbosh, m. e. bialkowski, “design of uwb planar bandnotched antenna using parasitic elements”, ieee transactions on antennas and propagation, vol. 57, no. 3, pp. 796-799, 2009 [11] b. v. kadam, l. j. gudino, c. k. ramesha, s. nagaraju, “a bandnotched ultra-wideband compact planar monopole antenna with ushaped parasitic element”, procedia computer science, vol. 93, pp. 101–107, 2016 [12] m. yazdi, n. komjani, “a compact band-notched uwb planr monopole antenna with parasitic elements”, progress in electromagnetics research letters, vol. 24, pp. 129-138, 2011 [13] j. y. siddiqui, c. saha, y. m. m. antar, “compact srr loaded uwb circular monopole antenna with frequency notch characteristics”, ieee transactions on antennas and propagation, vol. 62, no. 8, pp. 4015–4020, 2014 [14] j. y. siddiqui, c. saha, y. m. m. antar, “compact dual-srr-loaded uwb monopole antenna with dual frequency and wideband notch characteristics”, ieee antenna and wireless propagation letters vol. 14, pp. 100-103, 2015 [15] c. saha, j. y. siddiqui, “versatile cad formulation for estimation of the resonant frequency and magnetic polarizability of circular split ring resonators”, international journal of rf and microwave computer‐aided engineering, vol. 21, no. 4, pp. 432-438, 2011 [16] c. saha, j. y. siddiqui, y. m. m. antar, “square split ring resonator backed coplanar waveguide for filter applications”, 2011 xxxth ursi general assembly and scientific symposium, istanbul, turkey, august 13-20, ieee, 2011 [17] i. bahl, p. bhartia, microwave solid state circuit design, 2nd edition, john wiley & sons, new york, 1998 [18] f. e. terman, radio engineers’ handbook, mcgraw-hill, new york, 1943 microsoft word 32-3287_s_etasr_v10_n1_pp5270-5275 engineering, technology & applied science research vol. 10, no. 1, 2020, 5270-5275 5270 www.etasr.com ghnimi et al.: study of a new design of the planar inverted-f antenna for mobile phone handset … study of a new design of the planar inverted-f antenna for mobile phone handset applications said ghnimi faculty of sciences of tunis university of tunis el manar tunis, tunisia said.ghnimi@fst.rnu.tn abdelkhalek nasri faculty of sciences of tunis university of tunis el manar tunis, tunisia abdelkhaleknasri@yahoo.fr ali gharsallah faculty of sciences of tunis university of tunis el manar tunis, tunisia ali.gharsallah@fst.utm.tn abstract—this paper suggests a new design of the pifa antenna for mobile phone handset applications. in this context, we are interested in the development of new techniques based on the creation of slot matching for the improvement and miniaturization of a dual-band pifa antenna operating at 900mhz and 1800mhz. analysis of antenna parameters such as return loss (s11), radiation pattern, voltage standing wave ratio (vswr), current distributions, gain, and the relation between them are performed in cst software. there is a good agreement between the results of simulation by cst and hfss and those of measurement for the proposed antenna. keywords-pifa antenna; dual-band antenna; slots radiating element; cst microwave studio i. introduction wireless communication technologies have become an essential part of everyday life. antennas are basic components of any telecommunication system and are connecting links between the transmitter or receiver and free space. the pifa antenna is a good candidate for these applications because it meets certain technical requirements. several researches have been focused on the diverse applications of the pifa antenna [1-7]. this antenna can be printed on dielectric blocks, so the dielectric properties of the block can be used to miniaturize or to improve the performance at the lower band edge [8]. in [9, 10], diversity mimo pifa antennas, for multi-mode satellite navigation applications, have been modeled and realized. in [11-12], the authors proposed compact pifas operating at 2.45ghz for body communications and multi-input mimo applications [13]. however, these techniques provide important information for the design of mobile antennas in the presence of the human body such as the reflection coefficient, the radiation pattern, the antenna impedance and the specific absorption rate. currently, several research groups around the world have undertaken the assessment of technical requirements to verify the conformity of antenna design for mobile communication. the resonance characteristics of implanted pifa antennas and their radiation signature inside and outside the body must be evaluated by numerical analysis and measurements. among them, the pifa [14] using a conductive plate, and carried out on a flexible dielectric substrate flexpifa to operate at 2.45ghz [15]. other techniques have been proposed in [16]. in that case, the slot is not printed on the ground plane but integrated on pifa geometry. this technique creates an additional mode which improves the bandwidth to the upper band covering of gsm900-1800 for original design at gsm900 and1800 for the design of the integrated slot. the multiband objectives of pifa antennas can be found in [17]. in [18-19], authors present other solutions employing a monopole antenna, based on a lowprofile multi-band handset designed only with slot antennas. the slots are not only useful for pifa antenna design, but also for damping unwanted modes for emc purposes. a major interest area is the study of the effects of radiation on the organs of the human body. therefore, it is important to realize a new pifa antenna for mobile phones with the highest quality performance, with reduced electromagnetic exposure. in this context, a new compact pifa antenna operating at different operational frequencies (900mhz and 1800mhz) is proposed. a parametric study was conducted on the antenna in order to ensure the required electrical and radiation performance. after the design and parameter defining and optimization, the simulation phase by using suitable software is a compulsory optimization step in order to save time and cost. it is also possible to take into account the dielectric parameters of the chosen low-cost materials. the chosen cst and hfss electromagnetic simulation tools study and simulate complex structures for mobile terminals. the motivation for choosing a pifa structure is that thus a larger band operation is achieved in the presence of a ground plane. in addition, antennas on a ground plane will be less affected by the presence of the human body. the antenna structures without a ground plane exhibit serious changes in the resonance frequency, depending on the distance of the body. thus, the pifa antenna is an attractive choice for many integration devices due to its low cost, simplicity of design and low profile. ii. antenna design and parametric study in this part, we are interested in the simulation of a twoband rectangular pifa antenna. we have added slots to the antenna at the top and bottom of the substrate to achieve the functioning for these bands for mobile phones. the proposed antenna elements were manufactured on the substrate fr4_epoxy of relative permittivity ԑr=4.4, tanδ=0.0013, thickness h=1.6mm, and the ground plane was made of fr4 (ԑr=4.4, tanδ=0.03). the shorting pins and the feeding pin were corresponding author: said ghnimi engineering, technology & applied science research vol. 10, no. 1, 2020, 5270-5275 5271 www.etasr.com ghnimi et al.: study of a new design of the planar inverted-f antenna for mobile phone handset … made of short rectangular profile wires. they are part of connectors and their dimensions are defined in table i. the coaxial probe was provided by a standard 50ω connector of the sma type. figure 1 shows the built antenna. fig. 1. geometry of the proposed pifa antenna table i. optimized parameters of the proposed antenna parameters (mm) w l lp s s1 s2 39.87 89.88 23.52 13 21.38 30 a m f r1 h hs 2.7 6.88 1.86 0.05 6 1.6 the main objective of this part is to guarantee the resonant frequency at 900mhz and 1800mhz with the best possible adaptation and a high gain. it also includes a study of the effects of the geometric parameters of the antenna on the electrical and radiation characteristics (reflection coefficient, resonance frequencies, gain, and visualization of the radiation pattern). we first present the variation of some geometrical parameters of the slit and their influence on these characteristics. then, the results of the simulations of the optimized structure are exhibited. fig. 2. simulated reflection coefficient as a function of frequency for different values of a figure 2 shows the variation of the reflection coefficient as a function of the frequency for different values of parameter a. we note that when the parameter a is changed, the resonance frequency of the first bandwidth at 900mhz changes slightly, while the second band of the antenna at 1800mhz does not. the value 2.5mm for the parameter a is favored since it ensures a better adapted resonance frequency of 900mhz, while respecting a level of reflection coefficient as much as possible above -10db. figure 3 illustrates the variation of the reflection coefficient s11 as a function of the frequency for different values of the parameter s2. from the curves of figure 3, it is obvious that the variation of s2 has a slight influence on the second resonant frequency of the antenna and also on its adaptation of the first band. when the value of this variable is equal to 27.45, the resonance frequency in the first band decreases and has a better adaptation. the same is true for the resonant frequency in the first band. figure 4 illustrates the variation of the reflection coefficient s11 as a function of the frequency for different values of parameter x. it can be seen that when x varies, the resonance frequency and the bandwidth vary as functions of the frequency for the two gsm bands. the choice of x=1.42mm gives us the best performance of the antenna. fig. 3. simulated reflection coefficient as a function of frequency for different values of s2 fig. 4. simulated reflection coefficient as a function of frequency for different values of x figure 5 illustrates the variation of the reflection coefficient s11 as a function of the frequency for different values of parameter h. from these results we can see that the variable h does not have any effect on the proposed antenna’s characteristic. figure 6 illustrates the variation of the reflection coefficient s11 as a function of the frequency for different values of parameter hs. it can be seen that the variation of the parameter hs influences the variation of the reflection coefficient. however, when hs decreases, the resonance frequency increases for both bands (900mhz and 1800mhz). figure 7 illustrates the variation of the reflection coefficient engineering, technology & applied science research vol. 10, no. 1, 2020, 5270-5275 5272 www.etasr.com ghnimi et al.: study of a new design of the planar inverted-f antenna for mobile phone handset … s11 as a function of the frequency for different values of parameter r1. unlike hs, when r1 increases the resonance frequency increases for the second band, as it is best suited especially for r1=0.4mm. fig. 5. simulated reflection coefficient as a function of frequency for different values of h fig. 6. simulated reflection coefficient as a function of frequency for different values of hs fig. 7. simulated reflection coefficient as a function of frequency for different values of r1 figure 8 illustrates the variation of the reflection coefficient s11 as a function of the frequency for different values of parameter f. it is noted that when f reaches the value of 1.8mm, the resonant frequency and the remain almost constant. also, the adaptation for the first band is improved when f increases. when f decreases to 1.5mm the resonant frequency changes for the first and the second band. fig. 8. simulated reflection coefficient as a function of frequency for different values of f the variation of the reflection coefficient s11 simulated by cst as a function of the reconfigurable slot antenna, gave an optimized antenna model intended in particular for gsm networks. it operates on two frequency bands of 900mhz and 1800mhz. iii. experimental results and discussion to confirm our study, we realized the proposed pifa antenna and the obtained measurement results were explained by a vector network analyzer. these measurements were focused on the reflection coefficient of the antenna in order to evaluate the actual performance of the designed antenna. photos of the realized pifa antenna, of dimensions 89.88×39.87×1.6mm³, are given in figure 9. the antenna is printed on the substrate fr4_epoxy of relative permittivity ԑr=4.4 and has a thickness h=1.6mm. (a) (b) fig. 9. photos of the realized pifa antenna: (a) before and (b) after assembly figure 10 shows the variation of the reflection coefficient s11 simulated with cst, hfss and measured as a function of frequency. according to figure 10, there is almost an agreement between the simulated and the measured values of the reflection coefficients of the realized antenna. the simulation result by cst is almost similar to the measurement result for the first band. also, the simulation result by hfss is in accordance with the measurement result for the second band. nevertheless, the adaptation of the reflection coefficient of the engineering, technology & applied science research vol. 10, no. 1, 2020, 5270-5275 5273 www.etasr.com ghnimi et al.: study of a new design of the planar inverted-f antenna for mobile phone handset … measurement result is somewhat reduced as compared to that of the simulation curves. this may be due to the losses in the line of excitation. the antenna has an adaptation of -35db at 0.9ghz and -34db at 1.8ghz respectively for the first and second band of operation with the cst simulator. fig. 10. simulated and measured reflection coefficient as a function of frequency current distribution on the pifa and electrical field on the slot has been computed using the cst simulator to give an extra physical insight into the behavior of this antenna. figures 11 and 12 show the current distribution of the proposed antenna at 900mhz and 1800mhz. fig. 11. current distributions at resonant frequency 900mhz it can be seen that the current distribution reaches maximum density mainly on the l shaped stub in the same phase as shown in figure 12. the resonance behavior of antennas can be better understood by considering the current distribution. from the figures, it can be concluded that the resonance at 1800mhz is due to the slit in the ground plane because it shows a maximum along the length of the slot. the resonance at 900mhz is due to the modified patch because it shows the current minimum on the patch. it should be also noted that that the pifa is highly excited at 1800mhz (larger branch at figure 12) whereas it is weakly excited at 900mhz (short branch at figure 11). the pifa modes for both resonances are the fundamental ones, the maximum of current distribution is at the feeding/short area and its minimum is at the open edge. fig. 12. current distributions at the resonant frequency of 1800mhz the vswr value determines the matching properties of the proposed antenna (figures 13-14). it indicates how efficiently the antenna is transmitting or receiving the electromagnetic waves over gsm900mhz-1800mhz band frequencies. it describes the amount of power reflected by this antenna. the vswr should be between 1 and 2 for little reflection losses. fig. 13. simulated vswr value vs frequency for the gsm900 band based on figures 13 and 14, we found that the vswr value is 2.15 and 1.65 respectively at 900mhz and 1800mhz. as an explanation we might say that that the gsm900mhz band of the proposed antenna during the phase of transmission and reception of the electromagnetic wave is more efficient than the gsm1800mhz band. the same thing stands for the amount of power reflected by this antenna. the vswr investigation shows that dual frequency operation at 900mhz and 1800mhz is obtained by the parasitic element effects. the dual-frequency operation is revealed as a function of slot position above a ground plane. as the height of slot decreases, the separation of resonance frequency is higher. it also shows a better impedance matching of load to the characteristic impedance of the transmission line carrying radio frequency signals. engineering, technology & applied science research vol. 10, no. 1, 2020, 5270-5275 5274 www.etasr.com ghnimi et al.: study of a new design of the planar inverted-f antenna for mobile phone handset … fig. 14. simulated vswr value vs frequency for the gsm1800 band. in figure 15 the radiation patterns of the proposed pifa antenna for two resonance frequencies of 0.9ghz and 1.8ghz in the case of phi=0deg and phi=90deg are presented. from figures 15 and 16, it is noted that the radiation of the antenna is concentrated in four different directions for each resonant frequency with the appearance of a certain level of undesirable radiations. these are negligible in comparison with the main radiation lobe which justifies the multi-directional aspect of this antenna. we note that this has a gain greater than 7db for each resonant frequency, which is an important value for a single element antenna. fig. 15. radiation pattern for frequencies 0.9ghz and 1.8ghz, phi=0deg in table ii, a comparison of various parameters to verify the performance of the antenna is carried out. the proposed antenna is resonant at two frequencies, 902mhz and 1800mhz. it has been analyzed using cst microwave studio in terms of return loss (s11) plot, current distributions, gain (dbi), radiation efficiency, radiation pattern, vswr, and bandwidth (mhz). from table ii, it can be seen that the proposed antenna is more compact, has a wider impedance bandwidth and an acceptable peak gain for gsm applications. fig. 16. radiation pattern for frequencies 0.9ghz and 1.8ghz, phi=90deg table ii. characteristics of the proposed antenna frequency (mhz) gain (dbi) radiation efficiency (%) frequency range (ghz) bandwidth (mhz) 902 7.32 67.5 0.889-0.928 39 1800 8.16 72.14 1.752-1.87 118 iv. conclusion in this work, a new dual-band pifa antenna that covers gsm bands at 900mhz and 1800mhz was designed. the technique of modifying the geometry of the radiating element, in particular the creation of the slots and the use of the localized elements was exploited. this antenna is characterized by a good adaptation of the reflection coefficient for its two resonant frequencies, multi-directional radiation and a gain greater than 7db for each resonant frequency. the results found a good compromise between all the parameters and there is a good agreement between the simulated and the measured results. so, this realized antenna is a good candidate for gsm applications. this study establishes the foundation of a new future project that could revise the effects between the gsm network and its associated equipment and the organs of the human body and propose practical solutions to reduce the effects of electromagnetic radiation on humans. references [1] h. d. chen, y. h. tsao, “low-profile pifa array antennas for uhf band rfid tags mountable on metallic objects”, ieee transactions on antennas and propagation, vol. 58, no. 4, pp. 1087-1093, 2010 [2] s. lee, y. sung, “reconfigurable pifa with a parasitic strip line for a hepta-band wwan/lte mobile handset”, iet microwave of antennas and propagation, vol. 9, no. 2, pp. 108–117, 2015 [3] a. bousselmi, a. gharsallah, t. p. vuong, “design and implementation of a tri-band miniaturized planar inverted-f antenna with double resonator for gps application”, engineering, 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john, m. ammann, “miniature ceramic dual-pifa antenna to support band group 1 uwb functionality in mobile handset”, ieee transactions on antennas and propagation, vol. 59, no. 1, pp. 336-339, 2011 [9] y. yao, x. wang, x. chen, j. yu, s. liu, “novel diversity/mimo pifa antenna with broadband circular polarization for multimode satellite navigation”, ieee microwave and wireless components letters, vol. 11, pp. 65-68, 2012 [10] h.chattha, y. huang, x. zhu, y. lu, “dual-feed pifa diversity antenna for wireless applications”, electronis letters, vol. 46, no. 3, pp. 189190, 2010 [11] c. lin, k. saito, m. takahashi, k. ito, “a compact planar inverted-f antenna for 2.45 ghz on-body communications”, ieee transactions on antennas and propagation, vol. 60, no. 9, pp. 4422-4426, 2012 [12] r. bhattacharya, r. garg, t. bhattacharyya, “design of a pifa-driven compact yagi-type pattern diversity antenna for handheld devices”, ieee antennas and wireless propagation letters, vol. 15, pp. 255-258, 2015 [13] s. ghosh, t. tran, t. ngoc, “miniaturized four-element diversity pifa”, ieee antennas and wireless propagation letters, vol. 12, pp. 396-400, 2013 [14] p. salonen, l. sydanheimo, m. keskilammi, m. kivikoski, “a small planar inverted-f antenna for wearable applications”, third international symposium on wearable computers, san francisco, usa, october 1819, 1999 [15] p. soh, g.vandenbosch, s. ooi, n. rais, “design of a broadband alltextile slotted pifa”, ieee transactions on antennas and propagation,vol. 60, no. 1, pp. 379-384, 2012 [16] c. nallo, a. faraone, “multiband internal antenna for mobile phones”, electronics letters, vol. 41, no. 9, pp. 514–515, 2005 [17] s. hong, w. kim, h. park, s. kahng, j. choi, “design of an internal multiresonant monopole antenna for gsm900/dcs1800/uspcs/sdmb operation”, ieee transactions on antennas and propagation, vol. 56, no. 5, pp. 1437–1443, 2008 [18] c. lin, k. wong, “printed monopole slot antenna for internal multiband mobile phone antenna”, ieee transactions on antennas and propagation, vol. 55, no. 2, pp. 3690–3697, 2007 [19] s. kahng, “the rectangular power-bus with slits ga-optimized to damp resonances”, ieee transactions on antennas and propagation, vol. 55, no. 6, pp. 1892–1895, 2007 [20] m. a. ksiksi, m. k. azizi, h. ajlani, a. gharsallah, “a graphene based frequency reconfigurable square patch antenna for telecommunication systems”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4846-4850, 2019 microsoft word 40-3548_s1_etasr_v10_n3_pp5824-5831 engineering, technology & applied science research vol. 10, no. 3, 2020, 5824-5831 5824 www.etasr.com benaouda & benaouda: a preventive multi-agent based policy for distributed hardware resource … a preventive multi-agent based policy for distributed hardware resource balancing abdelhafid benaouda departement of computer science ferhat abbas university setif i setif, algeria ahbenaouda@univ-setif.dz nacera benaouda departement of computer science ferhat abbas university setif i setif, algeria nacbenaouda@univ-setif.dz abstract—the success of a business, especially a multi-site extended enterprise, depends on the good management of all its distributed resources. it is difficult for a company to be successful if it does not have a reliable and optimal management of resources by avoiding overstocking of certain resources on a site sitem ∈∈∈∈ e, and at the same time, the sub-storing of the same resources on another site sitep ∈∈∈∈ e. in both cases, there is a lack of profit. in this paper, we will try to resolve this situation, by the proposal of an architecture based on the cooperative multi-agent systems paradigm combined with the contract-net protocol. we bring in an intelligent agent whose role is to warn in advance and for each item itemi ∈∈∈∈ sitem, the coming of breakdowns and stock excesses by balancing the level of inter-site availability by a flow of resources of the same itemi by calling on the other e sites whose levels are in over-storage or under-storage. keywords-resource-balancing; multi-agent; flux-resource management i. introduction in the management of distributed material resources in a multi-site enterprise, always non-optimization issues arise, which generate losses and waste of resources. in the past, this situation was tolerable because the use of the networks was not so vast and communication and interaction means were not in the level they are today. nowadays, the use of solutions on network platforms, that may optimize the management of these distributed resources, is more than necessary. in this sense the provision of an academic solution is proposed in this paper, based on the multi-agent systems (mass) paradigm. as an application, a mapping of this proposal on a concrete example of distributed hardware resources was made. this example can be applied to any type of resources [1]. in other words, this paper offers a software solution that can ensure the balancing of various resources of a multi-site enterprise e whose sites are linked by a computer network on which a solution based on middleware such as java-rmi, dcom, orb/corba or soap/webservices was deployed through web. thus, the optimal solution that can bring added value [1, 2] can be found. the sites share their resources according to a cooperation model, therefore, they must interact with each other, and consequently, the implementation of our solution must use one of the previously mentioned middleware. in the remainder of this article, the generic term item instead of resource is used. ii. the problem let’s suppose a company composed of several websites sitem, m=1, nbs. these sites are interconnected by a computer network that may be a lan, internet or a vpn. the software means providing the middleware can be corba, rmi, dcom or webservices if corporate sites are connected through the internet. let’s suppose further, that each site sitem has a set of n items locally managed. we consider the class c items (see iii-a) because they are very numerous. we must find a mas paradigm based solution which can ensure the balancing of items between the different company sites, in other words, a solution that avoids having items in overstocking or in substorage in order to prevent and avoid abnormal storage situations. figure 1 illustrates this situation. fig. 1. the problem on the site site1, quantitatively ��� is over-stocking, while on the site3, ��� is understaffed storage for the same item k. for another item j, there is an approximate balance between the two quantities of items ��� and ��� on the sites site1 and site3. we make the same observation between the situations of the two sites site2 and site4 concerning items j and k. by extending this corresponding author: abdelhafid benaouda engineering, technology & applied science research vol. 10, no. 3, 2020, 5824-5831 5825 www.etasr.com benaouda & benaouda: a preventive multi-agent based policy for distributed hardware resource … observation to the sites (sitek, k=1, nbs) with � on each site, the proposed solution consists of watching dynamically at every moment tc the stock levels of all items on all the system’s sites, to alert policymakers and managers of an overstocking or sub stocking situation, and provide a solution that helps correcting this imbalance. iii. resource management in multi-site environment in this paper, we discuss items that are storable in a multisite environment. these items exist within the company, and are intended to be sold or reserved for internal use, such as, for example, spare parts, pharmaceuticals, consumables (paper, cartridges, etc.). the modeling and automation of such items on a local site is currently a very easy task. many dedicated solutions, marketed and even free, have been currently proposed. however, solutions for multi-site companies are stock-keeping applications only, and not stock management applications, because item inventory management for a company whose sites are interconnected via a local network or internet, requires the study, modelling, and validation of other criteria (communication, interaction, cooperation, negotiation, etc.). the “zero inventory” is a wrong approach because stock is necessary but it should not exceed a limit, because it negatively affects the business by including unnecessary costs (insurance, local, security, aging, etc.). on the other hand, substorage too can lead to out of stock situations. stock shortage can, in some cases, cause the production chain alteration by stopping the production machine. good management means managing the stock of these items, in sufficient quantity, but above all in an optimal way, to meet the needs for the proper functioning of the company. this is equivalent to finding an optimal stock s * for the entire multi-site enterprise, in the sense of cost and availability over a period t, so as not to expose it to an abnormal situation. in order to correct this way of storing, locally and statically, the current trend is to make “an item flow management” between different sites and to ensure an intra-site and inter-site balancing of these items in order to avoid over or under-storages. a. item classification an item is specific to the class to which it belongs, and this strongly influences the adopted replenishment policy. on the basis of this classification we can answer to questions such as: • what to resupply? • when resupply? • how much to resupply? • and above all, what partner site to resupply, in the case of deficit. and, which site, surplus items must be passed on? we will adapt this classification to item management: • class a: is the class of slow-rotating or slow-moving items. • class b: is the class of medium-rotating items. • class c: is the class of fast-rotating or fast-moving items. b. the extended enterprise case cited replenishment policies show the strategy with regard to each item, after having previously studied the demand, the cost, the necessary time, etc., which they can be applied especially to an autonomous site. a multi-site enterprise’s replenishment policy depends on the needs of all the interconnected sites. the class c items, for instance, can be found in all sites, but items supposed to belong to b and a may be available in specific sites deemed important by the extended enterprise managers. the management principle in this case is to maintain a balancing: first, in terms of availability, and second, in terms of cost. this balancing must be between all sites and for all items that are needed by each of these sites. to achieve this, we must design and implement appropriate solutions, to prevent and eventually avoid an availability imbalance of these items in a distributed multi-site environment with the constraint that each site supplies and demands different items. we know that, each item follows different criteria of cost, importance in the case of failure, etc. c. distribution of items in this paper, focus is given on class c items, because even if they are not expensive, their lack can cause system shutdown. the item classification is dynamic, a classi item may end up in another class classj, lower or higher. this will depend on this item consumption rate, and its importance. iv. related works there are not many works dealing with this issue as a “balancing of material resources” in a distributed environment, but they exist, as “load balancing”. a load is the set of processes (unix process, threads), running on a processor, on a machine or on a server at a time t. many algorithms have been proposed and implemented on load balancing. but the projection of this work on the distributed management of material resources is limited. the problem came up with bigdata, high availability in cloud-computing [1, 4-8] and in distributed systems in general because disk quotas distributed in clusters hosting data can be considered as well and optimally managed hardware resources[9, 10]. the problem of material resource balancing was initiated in [2, 3], within the framework of the european project proteus, with application to the distributed management of the spare part in a multi-site environment, which can avoid over-storage in a � site, to the detriment of an under-storage at another �� site. in our opinion, the management of material resources in a multi-site platform is at the intersection of the following three issues : • the projection of algorithms developed in the load balancing field. • inventory management across an extended enterprise. • distributed management of information flows in a multisite cooperative platform. v. prevention policy a. mathematical formulation the consumption law of an ����� on a ∆� = �� − �� interval with �� = 0, on a ���� , is defined by : engineering, technology & applied science research vol. 10, no. 3, 2020, 5824-5831 5826 www.etasr.com benaouda & benaouda: a preventive multi-agent based policy for distributed hardware resource … �� = �����, � = 1, (1) where �� is the consumption of the ����� at time ��. the law (1) obeys many criteria, item types (a, b or c), etc. for our part, we recall that we focus on the class c items with very high consumption. this class of items obeys a consumption law, approximated by a least squares line. but if this consumption law changes, the conceptual proposition that we present in this paper will remain valid. we wish to approximate the real consumption, by a consumption law at the moment ��, in order to be able later to detect stock shortages, at the moment � !, before the next replenish at time �". �� = #��� $ �, � = 1, # % & = 1, � (2) this should be done automatically for all common and existing items on each site. (a) (b) fig. 2. storage balance between two sites for �����: (a) under storage, (b) over storage to do this, we use least squares to find the coefficients #� and �. it is sufficient then to solve the system: '( ∑ �*+,-./+01-� 2-34-35 (* = 0( ∑ �*+,-./+01-�2-34-35 (/ � 0 (3) for a single itemk, there are nbs systems of linear equations, with unknowns #� and � to be solved. by considering: 6�� � 7���89�8� , 6:� � 7���� �89 �8� , 6�� � 7���89�8� , 6;� � 7��: �89 �8� which give: < 6�� � 6��#� $ � 6:� � 6;�#� $ 6�� � (4) this is equivalent to solving = ∗ � systems, similar to the system in (4). note that the number of units n available by itemk can vary on the same sitem or on different sites. the solution for ����� on a ���� is therefore immediate: ' #� � ?5+?@+09?2+?@+209?a+ � � ?@+?a+0?a+?5+?@+209?a+ (5) knowing #� and �, the stock shift for the item k at the moment � ! on a sitem will occur at : �� � � �/#� applying the sm and sp sites, stock-outs will occur at: c� !+d � 0/+d*+d �ef ���� � !+g � 0/+g*+g �ef ����h (6) and < �� � � �ef ���� ��h � �h �ef ����h (7) if the condition (8) is satisfied: ' �� � !+d ≪ � !+g #� � ! # % �� ��h ≫ �� #� �� (8) a balancing for itemk between sites sm and sp is necessary, because there will be a stock shortage in the sitem and a useless stock in the sitep (see figure 1), which is a shortfall for the company. b. transfer mechanism the transfer mechanism (figure 3) that we are going to use is essentially based on the role of a software agent called prevention agent agpk (see vii1), associated with each site sitek. agpk allows controlling the items by managing their state before, concretely, making their transfer (figure 3). vi. mas modeling a. agent, mas and cooperation we consider that the agent paradigm and mas is known now. however, it should be remembered that there is no unified definition of the term “agent” in mas community. however, everyone agrees that the autonomy concept is central to the issue of agents. for our part, we consider the consistent engineering, technology & applied science research vol. 10, no. 3, 2020, 5824-5831 5827 www.etasr.com benaouda & benaouda: a preventive multi-agent based policy for distributed hardware resource … academic definition of this notion given in [11, 12]. for our case study, we define an agent as a software entity, located in an environment, with an autonomous behavior enabling it to reach, by interacting with this cooperative environment, the objectives assigned to it during its creation. cooperation is the form of coordination between non-antagonistic agents. conversely, negotiation corresponds to coordination in competitive universes or between “selfish” or competitive agents. typically, to successfully cooperate, each agent must maintain a model of other agents, and also develop a model of future interactions (planning). the fact that a sitem agrees to troubleshoot another sitek is a form of cooperation. this can be done, of course, after a negotiation phase between the sites while maintaining their respective interests. moreover, a mas is a set of agents that respond to the architecture of a system and its dynamics, based on an organizational model and on a model of interaction between the agents of this system. these agents are activated for the emergence of the desired solution. fig. 3. transfer mechanism in this paper, we take note of the keywords: organization, autonomy, interaction, cooperation, and objective which, in our view, constitute the principal characteristics that the agentmas pair must have, and which constitute the reason for the dynamics of the system in order to fulfil the desired objective. unlike the top-down approach, known as static conventional approach, modeling the functioning of a complex problem using mas is starting from simple distributed tasks with local objectives in order to bring out the overall solution of the posed problem. in our case, the local objective is the optimal availability of items in quantity (neither under-storage nor over-storage) and cost. the goal of the entire system is the balancing of these items across all the enterprise’s sites. using mas in modeling is also to look for an adequate organization model that must be associated with an interaction model in order to respond as much as possible to the proper functioning and dynamics of the system. we consider that there is not yet a generic model that can satisfy all the criteria of organization and functioning of any problem. b. agent-oriented architecture model the agent architecture is the product of the transition from the objective component to the projective component. indeed, in the case of oriented object programming, the object is essentially a passive component offering services and using other objects to realize its functionalities. the object architecture is therefore an extension of the architecture in calls and returns. the agent, on the other hand, intelligently uses other agents to achieve his objectives. it performs this by establishing dialogues, negotiating and exchanging information with them. we involve the following five agents (figure 4): • agi, information agent. • agp, prevention agent. • ags, agent site supervisor. • cag, coordinator of the group acquaintances. • cig, inter-group coordinator. fig. 4. agent-oriented architecture vii. deployment scenario before describing the roles and behaviors of the software agents deployed to make the balancing in quantity of our system different items, we first briefly describe the process of interaction between these agents (figure 4): • on each site (sitem,m=1, nbs), there is an agent agpm associated with it, which watches periodically. after evaluation of the state of each itemi, i=1, nbi it alerts agsm in case of under-storage or over-storage. • agsm informs the cag for items that are in under or over storage. • the cag launches a call for tenders to sites k which are in under storage for an item j which is overstocked at site m (m≠k). if the answer is negative, an alert is sent to the cig. • if there is a positive answer from the agsp, a negotiation starts between the agsm and the agsp on quantities, deadlines, etc. • if there is confirmation of the incoming or outgoing, the agsm, agsp orders respectively the agim, agip to update the respective items information systems. viii. roles of system agents the roles of the agents involved in our architecture are: a. prevention agent (agp) agp is an intelligent agent that has an intelligence capacity that allows it to take decisions based on its knowledge base (bc). it is based on algorithms that calculate previous consumption and other availability criteria. this agent has the ability to predict cases of sub or over-stock of item quantities, based on the tprev prevention times calculated for each item. it engineering, technology & applied science research vol. 10, no. 3, 2020, 5824-5831 5828 www.etasr.com benaouda & benaouda: a preventive multi-agent based policy for distributed hardware resource … sends emergency messages to the supervising agent indicating, for a type of item, whether there will be an over or understorage. this agent therefore consults the database in a continuous and periodic manner and looks for cases that may cause abnormal situations, in order to prevent and send alert messages to the supervisor. our study gives more importance to the prevention aspect, and thus to the script of the agent dedicated to this role, because it ensures an optimal management of the items in a cooperative framework between all the sites of the extended enterprise. our study gives more importance to the prevention aspect and consequently to the script of the agent dedicated to this role, because it ensures an optimal management of the items in a cooperative framework between all the sites of the extended enterprise. the script of this agent is presented in figure 5. fig. 5. script of agpm b. site supervisor agent (ags) ags is the supervising agent. it is the master agent associated with a site, its role is to manage and control the system operation. it describes the overall objectives of the system and observes its state. the supervising agent communicates the incoming and outgoing quantities of items. it also launches requests for item acquisition or offering. it receives/sends messages from/to other sites. with this approach, it acts as an interface relative to other sites. its script is can be seen in figure 6. c. information agent (agi) agi is a reactive agent that has no intelligence, its role is stock management, in the traditional sense, with actions such as creating, consulting, and updating item database. this agent receives the order from the ags before any operation. fig. 6. script of agsm d. coordinator of the group acquaintances agent (cag) cag’s role is associated with a group of sites sitek , k=1, gs and gs subset e on the basis of a criterion, e.g. the geographical one. the cag ensures the coordination and reception of the needs, in quantity of items, of the different sites of the group. it classifies the needs of the sites concerned by items that are under or over storaged, optimizes these costs, according to the auction algorithm and communicates these needs to the appropriate agsk, k=1, nbs. its behavior is described by the script in figure 7. fig. 7. script of cagx e. inter-group coordinator agent (cig) cig has the same prerogatives as the cag, but at the top level. it intervenes only in very exceptional cases, e.g. in the engineering, technology & applied science research vol. 10, no. 3, 2020, 5824-5831 5829 www.etasr.com benaouda & benaouda: a preventive multi-agent based policy for distributed hardware resource … case where an itemi belonging to sitem is in global state of under or over-storage. in this case, it is necessary to negotiate with a sitek outside the group. as a result, the behavior of the cig is identical to that of the cag but in intergroup coordination. we notice that the agent-oriented architecture we propose has cognitive agents and reactive agents. the prevention agent is a cognitive agent, having the ability to reason on the basis of its past, regarding past consumption and all other information in its knowledge base. agents belonging to the same agent group recognize each other through their intercommunicating supervisors. ix. organization model the problem as it stands does not obey an already existing organizational model. we have developed our own model, based on our needs, called agirat (figure 4, figure 8) which is based on the following: 1) the agent is the basic conceptual entity of our organization. each moment a site is represented, in its environment, by the supervising agent. and the site itself can have a mas or another internal structuring. as a result, an agent is : • autonomous. • in intra-site interaction with the prevention and inventory management agents and in extra-site interaction with the other supervisory agents of the system. knowing that the agents are cooperative, they must communicate in asynchronous connected mode with answer times ∆t which must be determined by this same supervisor. • distributed. • has a goal. • our prevention agent is a cognitive agent because it has a form of intelligence, which allows it to predict its future and act in the present on the basis of its past. 2) group: represents the organization of agents in a group according to a specific criterion. as a result, an agent can belong to several groups (figure 8). 3) interaction: the whole system is based on the interaction of one entity with the others. without interaction, the system is static. 4) role: each agent has a role in relation to its existence, but performs one or more tasks at the time tcurrent. 5) authority (or privilege): authority is the rules governing the organization and the interest of the group. on this basis, a holistic strategy can be applied. 6) the task which is the subdivision of the role into task sequences (sequentially or in parallel) is the atomic element in relation to the conceptual mass. at implementation, a task can represent a script running on one or more processes in the it sense (thread or unix process) fig. 8. organization model x. experimentation and results let pi(ti) be the consumption of nbum units of a itemkm in the site sm and nbup units of a itemkp in the site sp to consume before a replenishment time tr. let’s suppose the following initial conditions: • items are in class c • tr = 80 days • initial number of items nbum = nbup = 5000 units • current time = tc = 70 • delivery times are very small the results of itemkm and itemkp consumption, respectively on the sites sm and sp, yielded the following results: 1) itemkm consumption: �� � �65.30833�� $ 4869.7373 (9) with: <#� � �65.30833 � � 4869.7373 (10) with asymptotic standard error: < ∆�#� � � r 0.3437 �0.5263%�∆� � � � r 13.74 �0.2822%� (11) we deduce for itemkm: u �ev � 74.56534 w 75 �"x *�9yx" � 298.1543 w 298 �"x *�9yx" � w 5 %#zv (12) 2) itemkp consumption: ��h � �47.335766 ∗ ��h $ 4904.9697 (13) with < #�h � �47.335766 �h � 4904.9697 (14) with asymptotic standard error: [ ∆\#�h] � r 0.2306 �0.4872%�∆\ �h] � r 9.22 �0.188%� (15) we deduce for itemkp : engineering, technology & applied science research vol. 10, no. 3, 2020, 5824-5831 5830 www.etasr.com benaouda & benaouda: a preventive multi-agent based policy for distributed hardware resource … u �ev � 103.6208 w 104 �"x *�9yx" � 1591.46608 w 1591 �"x *�9yx" � w 34 %#zv 3) balancing between itemjm and itemkp: by comparing the results of (12) and (16), we notice that the tremainder relative to itemkm is very close, while tokp on itemkp is very far (figure 9). in addition, itemkm is in under-storage and itemkp is in over-storage, i.e. pkp >> pkm. these quantities of under and over-storage are easily evaluable before the next replenish at tr = 80: �� �80� � �354.9291 ��h�80� � 1118.10842 therefore, the sitep in over-storage, can offer the sitem which is in under-storage situation, at least the deficit that is in this case easily quantifiable. this will be done in the same way for itemj on sitem and sitep. the sitem can offer the sitep the quantity it needs (figure 10). xi. generalization to n sites by generalizing this process to other items and other sites, and using scripts in figures 5-7, we are able to perform decision-making followed by the transfer via the network platform, (figure 4) using a software middleware, a global balancing of the system emerges and is maintained over time by determining the successive differences, i.e. the scales at each time period balp at tos and balp at tr, between the same itemi between two different sites (figure 11). interactions between the system agents are done by the quoted middleware (figure 4). messages sent between these agents and generating these interactions are characterized by the requests send() and receive() such as in the scripts in figures 5 and 7. the subscript negociate() (figure 6) is in fact a succession of asynchronous bi-directional messages between each two interlocutors agsm and agsp, but these messages are synchronous with other system interlocutors. this must be done in order to agree on how to make this contract work. but the last word comes from human decision-makers that are helped by these two facilitating agents installed on sites sitem and sitep. the system is balanced because it is generalized for all the system item s(itemk , k=1, nbim) and on each site (sitem ,m=1, nbs). xii. comparison and discussion as noted above, resource management in a multi-site environment depends on many research axes (load-balancing, material resource management with all the supply chain issues, management of information flows in an e-environment, etc.). in this work, a material resource can be a spare part to be acquired at the right time for preventive maintenance purposes, or a quota on disk in a multi-user system or even a virtual disk in cloud-computing on a data-center, and particularly in iaas (infrastructure as a service). compared to the cited works, our contribution defines this notion of distributed material resources and provides a “quantifiable and preventive” solution to this situation in a distributed multi-site environment. this point was not taken into account in the related work. (a) (b) fig. 9. unbalancing of itemj on sitem and sitep: (a) under-storage of itemj on sitem, (b) over-storage of itemj on sitep (a) (b) fig. 10. unbalancing of itemk on sitem and sitep: under-storage of itemk on sitem, (b) over-storage of itemk on sitep engineering, technology & applied science research vol. 10, no. 3, 2020, 5824-5831 5831 www.etasr.com benaouda & benaouda: a preventive multi-agent based policy for distributed hardware resource … (a) (b) fig. 11. pbalance between two different items on two different sites: (a) pbalance between sitem and sitep for itemj, (b) pbalance between sitem and sitep for itemk xiii. conclusion in this paper, an interaction model, dedicated multi-agent system (mas) was proposed, which responds to an organizational model based on the agirat (agent, group, interaction, authority and task) principles, and was applied to the management of material resources in a cooperative framework. a mas architecture was established, which is internal to the site, and which provides, among other things, a dedicated cognitive agent, whose role is to guard, and even prevent, possible cases of under or over-storage of items, based on past consumption. the global mas architecture of all the sites composing the system interacts with the internal mas of a site via a facilitating agent, in this same cooperative framework, ensuring the emergence of a “resource balancing”, and allowing quantification the of the availability of items. this solution prevents sites from exceeding the storage threshold. the implementation of the proposed architecture, requires the use of a dedicated middleware software. our approach has been validated in a distributed environment and has yielded satisfactory results. references [1] k. v. kavitha, v. v. suthan, “dynamic load balancing in cloud based multimedia system with genetic algorithm”, 2016 international conference on inventive computation technologies, coimbatore, india, august 26-27, 2016 [2] a. benaouda, n. zerhouni, c. varnier, “spare part management for emaintenance platform”, in: ieee :mechatronics and robotics, vol. 3, pp 1152-1157, ieee, 2004 [3] a. benaouda, n. zerhouni, c. varnier, “une approche multi-agents coopératifs pour la gestion des ressources matérielles dans un contexte multi-sites de e-manufacturing”, 6e conference francophone de modelisation et simulation, rabat, morocco, april 3-5, 2006 (in french) [4] x. nan, y. he, l. guan, “optimal resource allocation for multimedia cloud based on queuing model”, 2011 ieee 13th international workshop on multimedia signal processing, hangzhou, china, october 17-19, 2011 [5] n. benmoussa, m. fakhouri amr, s. ahriz, k. mansouri, e. illoussamen, “outlining a model of an intelligent decision support system based on multiagents”, engineering, technology & applied science research, vol. 8, no. 3, pp. 2937–2942, 2018 [6] m. a. patel, r. mehta, “a comparative study of heuristicload balancing in cloud environment”, international journal of advance engineering and research development,vol. 2, no. 1, pp. 2348-4470, 2015 [7] p. naik, s. agrawal, s. murthy, “a survey on various task scheduling algorithms toward load balancing in public cloud”, american journal of applied mathematics, vol. 3, no. 1-2, pp. 14-17, 2014 [8] s. f. issawi, a. al halees, m. radi, “an efficient adaptive load balancing algorithm for cloud computing underbursty workloads”, engineering, technology & applied scienceresearch, vol. 5, no. 3, pp. 795–800, 2015 [9] l. t. yang, m. guo, high-performance computing: paradigm and infrastructure, john wiley and sons, 2006 [10] w. zhu, c. luo, j. wang, s. li, “multimedia cloud computing : an emerging technology for providing multimedia services and applications”, ieee signal processing magazine, vol. 28, no. 3, pp. 59– 69, 2011 [11] j. ferber, les systemes multi-agents: vers une intelligence collective, intereditions, 1995 (in french) [12] m. wooldridge, intelligent agents, a modern approach to distributed artficial intelligence, mit press, 2001 microsoft word 41-3372_s_etasr_v10_n1_pp5325-5329 engineering, technology & applied science research vol. 10, no. 1, 2020, 5325-5329 5325 www.etasr.com ton et al.: optimal location and size of distributed generators in an elecric distribution system …. optimal location and size of distributed generators in an electric distribution system based on a novel metaheuristic algorithm trieu ngoc ton faculty of electrical and electronics engineering hcmc university of technology and education ho chi minh city, vietnam trieutn.ncs@hcmute.edu.vn viet anh truong faculty of electrical and electronics engineering hcmc university of technology and education ho chi minh city, vietnam anhtv@hcmute.edu.vn thuan thanh nguyen faculty of electrical engineering technology industrial university of ho chi minh city ho chi minh city, vietnam nguyenthanhthuan@iuh.edu.vn tu phan vu postgraduate training committee vietnam national university-hcmc ho chi minh city, vietnam vptu@vnuhcm.edu.vn abstract—this paper proposes a method for optimizing the location and size of distributed generators (dgs) based on the coyote algorithm (coa), in order to minimize the power loss in an electric distribution system (eds). compared to other algorithms, coa does not need control parameters during its execution. the effectiveness of coa was evaluated in an eds with 33 nodes for two scenarios: the optimization of location and capacity of dgs in an initial radial configuration, and the best radial configuration for power loss reduction. results were compared with other methods, showing that the proposed coa is a reliable tool for optimizing the location and size of dgs in an eds. keywords-distributed generators; coyote algorithm; electric distribution system; power loss; radial configuration i. introduction distributed generators (dgs) are connected to an electric distribution system (eds) offering economic benefits and energy security, and their appearance has increased rapidly. an eds performs the task of supplying electric energy to consumers, ensuring power quality, reliability, and safety requirements within the permitted limits. meanwhile, it also brings many other benefits, such as reducing the load on the grid, improving voltage, reducing losses, and supporting the grid. some of the problems related to connecting dgs in an eds consist of the increasing penetration of renewable dgs, the maximization of emitted power and reliability, the minimization of investment, operating costs and total payments, the reduction of system losses, and the improvement of voltage configuration, maximizing social welfare and profit margin. depending on the goals, it is possible to combine dgs appropriately to reduce the line overload and increase the operating range of the system, in order to operate more flexibly. exploiting the maximum potential benefits of dgs with minimum cost must be satisfied with technical constraints and the optimization of economic objectives [1, 2]. when considering connecting dgs to an eds, it is necessary to consider their location and their allowable amount, in order to get their maximum size pumped into the grid, minimizing loss to attract investment, ensuring the reliability of electric supply, and gaining economic benefits. therefore, the problem of determining the location and capacity of dgs for power loss reduction is important [3, 4]. various methods have been employed in order to determine the location and capacity of dgs in an edss. some classical methods are linear and non-linear programming (nlp) [5], mixed integer nlp [6], dynamic programming [7], ordinal optimization [8], and optimal power flow (opf) [9]. the disadvantages of these methods are the slow convergence to optimal results, or the fall into local extremes. metaheuristic methods have been applied for solving this problem, such as genetic algorithm (ga) [10, 11], particle swarm optimization (pso) [11-13], symbiotic organisms search [14], artificial bee colony algorithm (abc) [15], invasive weed optimization [16], cuckoo search (csa) [17], fireworks algorithm (fwa) [18], stochastic fractal search (sfs) [19], harmony search algorithm (hsa) [20], and salp swarm algorithm (ssa) [21]. these methods have the advantage of handling conveniently problem’s constrains. in addition, the solutions obtained are usually better than these obtained by the classical methods. however, finding suitable, stable, and reliable methods for each specific problem is a complicated task. therefore, finding new methods to solve the problem of optimizing location and capacity of dgs in an eds is a desired task. the coyote algorithm (coa) is based on the social life of coyotes, and [22] validated its efficiency using forty benchmark functions. corresponding author: thuan thanh nguyen engineering, technology & applied science research vol. 10, no. 1, 2020, 5325-5329 5326 www.etasr.com ton et al.: optimal location and size of distributed generators in an elecric distribution system …. however, the application of coa on engineering problems, such as dgs placement in order to examine its effectiveness, is a worthy consideration. this paper describes the application of coa in optimizing the location and size of dgs for power loss reduction in an eds with 33 nodes, and the comparison of the obtained results with other metaheuristic methods. ii. problem of optimal placement of dgs the objective function of the dgs’ location and size optimization in an eds is the reduction of the active power loss, formulated as: � = ���(∑� ��) (1) where ∑� �� is the total power loss in the eds. the placement of dgs in the eds should satisfy the following constraints: • power balance: the sum of output power from the slack bus and the dgs must be equal to the sum of loads and power loss in the eds. • the limits of nodes’ voltage and branches’ current are: v��� �� ≤ �� ≤ v��� �� , � = 1,2,⋯,���� �� � ≤ �� ���,� �� , � = 1,2,⋯, ��!��"# (2) where lcf is the load carrying factor of the i th branch. • the power limits of dgs are: �$%,�,��� ≤ �$%,� ≤ �$%,�,��� , � = 1,2,⋯,�$% (3) iii. application of coyote algorithm a. the coyote algorithm (coa) unlike other metaheuristic methods, coa does not need control parameters, enhancing its performance stability on the dgs optimization procedure. in order to search the solution in the search space, coa uses a population of coyotes divided into groups, and the social condition of each coyote in its group is considered as a candidate solution. candidate solutions are generated based on the interaction among coyotes in each group and the interaction among groups of the population. the interactions are described as follows: 1) renewal of the social condition of coyotes in each group the behavior of each coyote depends on the leader of its group, while each group usually has its own characteristics. the process of finding new solutions is as follows: in the g th group, the coyote having the best adaptive function value is chosen as alpha (&'(). subsequently, the culture tendency ()*() of the group is determined by the median social condition of the group’s coyotes, and a new social condition of each coyote is generated as: �_,)"( = ,)"( + ./.1&'( − ,)/(3 + .4. 1)*( − ,)4(3 (4) where �_,)"( and ,)"( are new and current social conditions of the c th coyote in the g th group, sc/( and sc4( are the social conditions of two coyotes selected randomly in the g th group, and finally ./ and .4 are random numbers in the range of [0, 1]. 2) birth of a new coyote to replace an old one in each group the coyote having the worst social condition, in the group, will die, and a newborn puppy will replace it, as: 78�889,:( = ; 7/,:( , .<,: < >/ 74,:( , .<,: < >/ + >47!,:( , ?*ℎa.b�,a (5) where 78�889,:( (j=1, 2, …, d) is the jth variable of the puppy’s social condition vector solution, d is the dimension of the problem, 7/,:( and 74,:( are the variables of two solutions chosen randomly in the group, .<,: is a random number in the range of [0, 1], and 7!,:( is a random variable, and >/ and >4 are the probabilities of scatter and association, which guide the cultural diversity of the coyotes from the group, determined as: c>/ = 1/e >4 = (1 − >/)/2 (6) 3) interchange of coyotes between groups although coyotes are living in groups, sometimes some individuals leave their group in order to live alone or join another group. based on this feature, to expand the process of creating new solutions, coyotes are exchanged among groups of the population. the probability (� ) of a coyote leaving one group to join another and vice versa is determined as: � = 0.005 × �"4 (7) where �i is the number of coyotes in the group. b. coa in optimizing location and size of dgs this section presents the application of the coa in optimizing the location and size of dgs, in order to minimize the active power loss in an eds. the following steps describe the overall procedure: • step 1: select the parameters of coa, including group number (�j), group size (�i), and the maximum number of generations (klmn). • step 2: the initial population of coyotes is represented as sc"( = o �/,"( , …,�qrs,"( ,�/,"( , …,�qrs,"( t with u = 1,2,…,�( and ) = 1,2,…, �" . variables �v,"( and �v,"( represent location and power of the k th dg, initialized as: �v,"( = .?w�xy2 + rand(0,1).(���� − 2)^ (8) �v,"( = rand(0,1)× 1�v,���( − �v,���( 3 + �v,���( (9) where �v,���( and �v,���( are the maximum and minimum power of the k th dg. • step 3: the initialized population is evaluated based on a fitness function, determined as: ��* = � + _ × o�&71���� �� − ����,03 + �&7(���� −���� �� ,0) + �&7(�� ��� − �� ��� �� ,0)t (10) engineering, technology & applied science research vol. 10, no. 1, 2020, 5325-5329 5327 www.etasr.com ton et al.: optimal location and size of distributed generators in an elecric distribution system …. where k is a penalty factor set to 1000, ���� and ���� are the minimum and maximum voltages in the eds, and �� ��� is the maximum load carrying factor in the eds. • step 4: the main loop begins from this step until step 8, and it is repeated until the preset generation value is reached. the inner loop in steps 5-6 is repeated until the last group of the population is reached. • step 5: the social condition of the coyotes in each group is renewed. for each group, the alpha coyote is selected, and the median of all coyotes is determined. a new social condition is generated for each coyote using (4). the fitness value is calculated for the new social condition. if the social condition is better than the previous one, it will replace it. • step 6: a puppy coyote, generated by (5), replaces an old one. the fitness value of the puppy’s social condition is calculated. if the puppy’s social condition is better than the worst social condition in the group, it will replace it. if the current group is not the last group of the population, step 5 is repeated, otherwise, this inner loop ends, and step 7 is executed. • step 7: a coyote is interchanged between the groups. if .&�x (0,1� = � , two groups are randomly selected for exchanging coyotes. in the selected groups, two coyotes are randomly chosen, and they are interchanged between the two chosen groups. • step 8: in the proposed coa method, the stopping criterion is based on a maximum number of generations. the algorithm terminates when the generation reaches a maximum value. otherwise, a new generation starts from step 4. as the maximum number of generations is reached, the best social condition of all coyotes in the population is considered as the optimal solution for the dgs’ location and size optimization. iv. numerical results in order to demonstrate the efficiency of the coa on the dgs’ location and size optimization, the algorithm was implemented in matlab 2016a. its performance was evaluated in an eds with 33 nodes [23], considering two scenarios: • scenario 1: location and size of dgs are optimized in the eds with the initial radial configuration with open switches {33-34-35-36-37}. • scenario 2: location and size of dgs are optimized in the eds with the optimal radial configuration for power loss reduction with open switches {7-9-14-28-32}. coa, for both scenarios, employed 5 groups, with 6 coyotes in each group, and the number of maximum generations was set to 300. the obtained results were compared with other methods in the literature, such as ga [11], pso [11], csa [17], fwa [18], sfs [19], hsa [20], and ssa [21]. in order to obtain optimal results, coa was executed in independent runs, and the best result was considered as the optimal solution. the results of the dgs’ location and size optimization in scenario 1 are shown in table i. after placing dgs in the nodes 30, 14 and 24 with corresponding power 1.07144, 0.75396 and 1.09944mw, power loss reduced from 202.6863 to 71.4599kw, corresponding to 64.74% power loss reduction. the minimum voltage amplitude in the eds enhanced from 0.9131 to 0.9687p.u.. in comparison with other methods, the obtained results are better than the ones obtained by ga, pso, csa, fwa and hsa. power loss reduction from coa was 64.74%, being 17.19, 16.69, 1.38, 8.49 and 12.48% higher than ga, pso, csa, fwa and hsa. compared to sfs and ssa, power loss obtained from coa is nearly the same. fig. 1. the eds with 33 nodes table i. optimal dg placement for scenario 1 method dg size in mw (node) power loss (kw) loss reduction (%) vmin (node) initial 202.6863 0.9131 (18) coa 1.07144 (30) 0.75396 (14) 1.09944 (24) 71.4599 64.74 0.9687 (33) ga [11] 1.5 (11) 0.4228 (29) 1.0714 (30) 106.3 47.55 pso [11] 0.9816 (13) 0.8297 (32) 1.1768 (8) 105.3 48.05 csa [17] 0.7798 (14) 1.1251 (24) 1.3496 (30) 74.26 63.36 0.9778 fwa [18] 0.5897 (14) 0.1895 (18) 1.0146 (32) 88.68 56.25 0.9680 sfs [19] 0.7540/(14) 1.0994/(24) 1.0714/(30) 71.47 64.74 0.9687 hsa [20] 0.1070 (18) 0.5724 (17) 1.0462 (33) 96.76 52.26 0.9670 ssa [21] 0.7536 (33) 1.1004 (23) 1.0706 (29) 71.45 64.75 0.9686 (32) the results of the dgs’ location and size optimization in the system with scenario 2 are shown in table ii. using the radial configuration of {7-9-14-28-32} after placing dgs in nodes 16, 12 and 25 with corresponding power 0.50263, 0.53576 and 1.61605mw, power loss reduced to 56.2782kw, corresponding to 72.23% power loss reduction. the minimum voltage amplitude in the eds was enhanced to 0.9722p.u. at node 32. the obtained results from coa are better than these obtained from csa, sfs and ssa. power loss reduction from engineering, technology & applied science research vol. 10, no. 1, 2020, 5325-5329 5328 www.etasr.com ton et al.: optimal location and size of distributed generators in an elecric distribution system …. coa was 72.23%, being 1.24%, 1.28% and 1.27% higher than csa, sfs and ssa. comparing scenarios 1 and 2, power loss obtained in the former was 71.4599kw (64.74%), and 56.2782kw, (72.23%) in scenario 2. in addition, the minimum voltage amplitude in scenario 2 improved more than in scenario 1. the voltage profile of the system after optimizing the location and size of dgs using coa is shown in figure 2. the voltage of the nodes improved after installing dgs, while the installation of dgs according to scenario 2 gained better voltage profile than scenario 1. moreover the load carrying factor of the system, shown in figure 3, reduced after optimizing the location and size of dgs using coa, as its maximum, being 0.8250 in the initial configuration, reduced to 0.4475 and 0.4640 for scenarios 1 and 2, respectively. table ii. optimal dg placement for scenario 2 method dg size in mw (node) power loss (kw) loss reduction (%) vmin (node) coa 0.50263 (16) 0.53576 (12) 1.61605 (25) 56.2782 72.23 0.9722 (32) csa [17] 1.7536 (29) 0.5397 (12) 0.5045 (16) 58.79 70.99 0.9802 sfs [19] 1.0682/(24) 0.9503/(30) 0.9317/(8) 58.88 70.95 0.9741 ssa [21] 0.932 (8) 1.068 (24) 0.950 (30) 58.87 70.96 0.9741 (33) fig. 2. the voltage profile of the 33-node eds fig. 3. the load carrying factor of the 33-node eds the mean and minimum convergence curves in 50 independent runs for both scenarios are shown in figures 4 and 5. the figures show that the mean and minimum curves converge to nearly equal values. this shows the stability and reliability of the coa in each run for the dgs’ location and size optimization in the eds. fig. 4. the convergence curves of coa in scenario 1 fig. 5. the convergence curves of coa in scenario 2 v. conclusion this paper presented a method based on coa for optimizing the dgs location and size in an eds, in order to reduce power loss. the effectiveness of the coa was evaluated in an eds with 33 nodes. two scenarios of dgs’ radial configuration were considered: the initial radial configuration, and placement in the optimal radial configuration with minimum power loss. numerical results showed that coa is better than methods such as ga, pso, csa, fwa, has, sfs and ssa. in addition, there is no need for control parameters in the process of applying coa to the optimization problem. moreover, the numerical results in 50 independent runs showed that coa is a reliable method for the problem of optimizing the location and capacity of dgs in an eds to satisfy other goals. references [1] w. l. theo, j. s. lim, w. s. ho, h. hashim, c. t. lee, “review of distributed generation (dg) system planning and optimisation techniques: comparison of numerical and mathematical modelling methods”, renewable and sustainable energy reviews, vol. 67, pp. 531–573, 2017 [2] p. s. georgilakis, n. d. hatziargyriou, “optimal distributed generation placement in power distribution networks: models , methods, and future research”, ieee transactions on power systems, vol. 28, no. 3, pp. 3420–3428, 2013 [3] b. singh, j. sharma, “a review on distributed generation planning”, renewable and sustainable energy reviews, vol. 76, pp. 529-544, 2017 [4] r. p. payasi, a. k. singh, d. singh, “review of distributed generation planning: objectives, 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evolutionary computation (cec),rio de janeiro, brazil, july 8-13, 2018 [23] m. e. baran, f. f. wu, “network reconfiguration in distribution systems for loss reduction and load balancing”, ieee power engineering review, vol. 9, no. 4, 1989 microsoft word 13-2327_s engineering, technology & applied science research vol. 9, no. 1, 2019, 3739-3743 3739 www.etasr.com khlifi: explaining the d-q magnetic couplings theoretically in saturated smooth air-gap ac machines explaining the d-q magnetic couplings theoretically in saturated smooth air-gap ac machines mohamed arbi khlifi department of electrical engineering, university of hail, hail, saudi arabia and sime laboratory, ecole nationale superieure d' ingenieurs (ensit), university of tunis, tunisia mohamedarbi.khlifi@issatm.rnu.tn abstract—the current paper discusses the theoretically detailed physical analysis of the effects of main flux saturation in smooth air gap ac machines. for that purpose, three sections are presented. the first one deals for presenting equivalence saturation-air gap. the second presents the equivalence of inductances between saturation induction machines and a dismounted salient pole synchronous machine. the method analyzes the leakage inductances that properly represent the corresponding leakage fluxes. the third section treats the physical interpretation of the cross-saturation. it is possible to show that the equations and physical picture in a saturated smooth-air-gap machine are similar to the equations and physical picture in a non-saturated salient-pole machine, where mutual coupling exists between the direct and quadrature axes and the self-inductances are also different on the non-salient part of the machine due to the variation of the reluctance with the rotor angle. keywords-ac machines; physical interpretation; magnetic saturation i. introduction in conventional models used in electrical engineering to represent electrical machines, it is quite common to neglect the magnetic saturation phenomenon, allowing the making of the simplifying assumption that inductances depend on the value of the flux imposed by currents, thanks to the non-linear relation: ( ) ( ) m m m m i l iλ = , where ( ) m m iλ is a picture of the non-linear magnetization characteristic b(h) of the employed ferromagnetic material [1-3]. saturation is a phenomenon that becomes apparent when the current through an inductor exceeds a certain limit. in effect, saturation of an inductor occurs when the core of the inductor can no longer store magnetic energy [4]. an inductor is usually constructed using a ferromagnetic material such as iron or one of its alloys. a ferromagnetic material is composed of small domains whose dipole moments are randomly oriented. when the material is completely demagnetized, the net magnetic moment over the material is zero. as the current passes through the inductor, the domains in the material tend to align in the direction of the magnetic field intensity [5]. as more domains are aligned, the magnetic flux density increases. when all domains have aligned in the direction of the magnetic field intensity, the flux density reaches its saturation density and cannot increase further in the same fashion. as the magnetic field intensity increases beyond the saturation point, relatively small increases of the magnetic flux density occur. when a large number of magnetic domains align this way, the material is said to be in its saturation region [6]. saturation representation is critical in the correct modeling of synchronous machines. the main effect of saturation in a synchronous generator is the decrease of its mutual inductances depending on the operating level of the generator. such a decrease may be considerable as the generator is driven higher into saturation. therefore, it is imperative that the effect of saturation is modeled in the parameter estimation procedure [7-12]. the representation of saturation is rather cumbersome because it is not possible to represent all the nonlinearities in a generator and the interaction between all circuits within the stator and the rotor (including the fictitious windings) with any single model for all the operating conditions. therefore, a number of assumptions have to be made in order to enable satisfactory saturation modeling. ii. problem formulation the variation of the level of magnetic saturation sheets can be transformed and described by an air-gap with modulated thickness. let us deal with the essential component of any revolving electric machine, in this occasion, the iron core coil. the usual structure is the one shown in figure 1. fig. 1. torus without air-gap. the application of the law of ampere gives: f f h l ni= (1) in addition, the analysis between electric quantities and magnetic carries out (2): f f f r λ = (2) with corresponding author: mohamed arbi khlifi engineering, technology & applied science research vol. 9, no. 1, 2019, 3739-3743 3740 www.etasr.com khlifi: explaining the d-q magnetic couplings theoretically in saturated smooth air-gap ac machines f ni= (3) f f fb sλ = (4) 0f r fb hµ µ= (5) finally, the magnetic reluctance of the iron which crosses the flux is: 0 1 f f r f l r sµ µ = (6) in addition, one can admit that the same magnetizing force fcan produce the same flow λf in the not homogeneous circuit of figure 2 or iron is supposed to be perfect. the ring of the permanent magnet material and the air-gap are excited by a wire coil of n turns and current i. fig. 2. permanent magnet as a part of a magnetic circuit consisting of iron and an air gap, which is divided into an air-gap flux and leakage flux. the geometry shown in figure 2 is an excellent canonical problem to illustrate the salient features of permanent magnet circuits. assume a small cross-section and ignore all leakage flux. the first topic is to show the steps necessary to determine b in this problem, which is the same in the gap and the magnet because of the boundary condition. under these conditions, the reluctances r must be equal to their precedents rf described by (6). that is to say: f r r= (7) the new total reluctance is reduced, it is the one of the airgap rα: 0 1 f a a e r sµ = (8) since the thickness of the air-gap is usually low, the useful section in the air and iron is unchanged: f air s s s= = (9) the equivalence of (6) and (8) gives: ste f f r r l c e µ µ = = (10) thus, the thickness of the virtual air-gap ef is inversely proportional to the relative permeability of iron. when the magnetic medium is linear, ef corresponds with a minimal width. a rise in the level of saturation, by increase in current i revolves a fall of µr, synonymous with a widening of the airgap ef, as it is indicated in figure 3. fig. 3. magnetizing curve, λm, ef, µr. so for magnetic circuit containing a real air-gap, the resulting air-gap will be: e+ef. in the electric machines the excitation i and consequent induction vary sinusoidalement according to time (figure 4). fig. 4. relation sheep between λm, ef, µr. the main flux distribution around the air gap periphery is sinusoidal at any rate of saturation. also the mmfs and voltages are sinusoidally distributed around the periphery. this assumption is equivalent to the supposition that the permeance of the iron is modeled by a factious variation of the air gap clearance (width). since the real saturation effect caused by the iron core is to be replaced by supposition of a variable air gap clearance of the threshold of saturation the minimal permeability corresponds to maximum of the magnetomotrice force and the air-gap. iii. expressions of inductances in salient pole sychronous machines a. formulation of voltage equations in undamped three phase salient pole synchronous machines there are four mutually coupled coils: the three phase windings and the field. therefore, the flux linkage equations for these windings result in the following matrix form: engineering, technology & applied science research vol. 9, no. 1, 2019, 3739-3743 3741 www.etasr.com khlifi: explaining the d-q magnetic couplings theoretically in saturated smooth air-gap ac machines [ ] a ab ac af ba b bc bf ca cb c cf fa fb fc f l l l l l l l l l l l l l l l l l       =         (11) where ljk is a self-inductance when j=k and a mutual inductance when j k≠ .the stator inductances and the coupled inductances between the stator and the rotor are time varying, while the rotor inductances are constants. expressions for the inductances in (11) are given below. b. inductances of the stator circuits the inductances can be assimilated with those of a diphase salient pole machine. the inductance of a diphase salient pole synchronous machine is expressed as: ' cos cos(2 )sm svaa l l lβ θ β= − − (12) with max min max min 2 2 2 sm sv l l l l l l π β + =  − =   =  (13) c. stator self-inductances ( ) ( ) cos 2 cos 2 a sm sv b sm sv l l l l l l θ θ = − = + (14) sm l and sv l are constants and sm sv l l� . the double frequency term (2θ) occurs due to the rotor saliency and the fact that self-inductances are the same for both rotor poles. d. stator mutual inductances the stator to stator mutual inductances are a function of rotor position since they are influenced by rotor saliency. ( )' sin 2svaal l θ= − (15) it is observed that (11) has time-varying terms which will cause complication when their derivatives are taken. thus, it is convenient to refer all quantities to a rotor frame of reference through a park’s transformation. iv. interpretation and discussion a. interpretation inductances can be comparable with those of a revolving machine diphase with salient poles whose principal inductances are lmdy, according to the direct axis (weak air-gap, weak reluctance) and lm following the axis squaring. the standard mathematical model of an induction machine is given in terms of space vectors (underlined variables), in an arbitrary frame of reference ωα with the following set of equations: s s s s a s d v r i jw dt λ λ= + + (16) ( )rr r r a r d v r i j w dt λ ω λ= + + − (17) where v, i and λ denote voltage, current and flux linkage space vectors respectively, while indices s and r stand for stator and rotor, respectively. equation of mechanical motion is irrelevant here and is hence omitted. ω is the electrical speed of rotation. it is assumed that leakage flux saturation and main flux saturation can be treated independently. as only main flux saturation is discussed, leakage inductances are constants. stator and rotor flux linkages are: s s s ml iλ λ= + (18) r r r ml iλ λ= + (19) where index m denotes variables and parameters associated with magnetizing flux. the proposed common approach to introduce magnetic saturation in any d-q existing model, for induction machine, relies only on the knowledge of the winding currents saturated model. for that reason, it will be first shown how to obtain it. leakage inductances in flux equation of induction machine (16)-(17) are assumed to be constant, only the main flux mλ is subject to saturation. deriving stator and rotor linkage fluxes, in (16)-(18), lead to the time derivative of the magnetizing flux mλ . , , , s r s r m s r d di d l dt dt dt λ λ = + (20) therefore, md dt λ has to be described by means of winding currents: ( ) ( ) i im m m m d d e d d e dt dt dt dt α αλ λ λ αλ= = + (21) where α is the angular position of mλ with respect to the daxis. it also characterizes the position of the magnetizing current mi in the air gap, since the hysteresis angle is neglected. writing mi , α and md dt λ as: 2 2 m dm qmi i i= + (22) 1 tan qm dm i i α −= (23) m m m m mdy m d d di di l dt di dt dt λ λ = = (24) we get: engineering, technology & applied science research vol. 9, no. 1, 2019, 3739-3743 3742 www.etasr.com khlifi: explaining the d-q magnetic couplings theoretically in saturated smooth air-gap ac machines qmdm dm d dq did di l l dt dt dt λ = + (25) qm qmdm dq q d didi l l dt dt dt λ = + (26) m mdy m d l di λ = is called dynamic inductance by analogy with m m m l i λ = static inductance. both coefficients are given by the conventional nonlinear magnetization curve, determined experimentally. ( )cos sindq mdy ml l l α α= − (27) cotd m dql l l α= + (28) tanq m dql l l α= + (29) b. discussion between rotor and stator we choose an integration path as shown in figure 5. this path is defined by the angle θ and we can notice that due to symmetry, the flux density at the two airgap segments in the path is the same. if we assume the permeability of iron to be infinite, then 0 iron h = .this means that for a given current i in the coil, the flux density in the airgap varies sinusoidally with angle. fig. 5. representation of salient pole synchronous machines. fig. 6. a sinusoidal winding on the stator. if the induction machine is saturated mdy m l l≺ and the direct axis of the critical two phase machine coincides with the axis with maximum air gap width, that is the quadrature direction in conventional salient pole machines. ( )cos sin ( )sin2 2 mdy m dq mdy m l l l l l α α α − = − = (30) where α is the angle position of the rotating magnetizing flux or current. cot cos = ( ) sin 2 2 sin 1 cos2 ( )( ) 2 ( ) ( )cos2 2 2 d m dq mdy m m m mdy m mdy m mdy m l l l l l l l l l l l l l α α α α α α = + − + + = + − + − = − (31) tan sin ( ) sin 2 2 cos 1 cos2 ( )( ) 2 ( ) ( )cos2 2 2 q m dq mdy m m m mdy m mdy m mdy m l l l l l l l l l l l l l α α α α α α = + − = + − = + − + − = + (32) for the saturated asynchronous machine static inductance is higher than that dynamic. while posing max( )ml l= and min( )mdyl l= , these inductances can be comparable with those of a diphase salient pole machine whose inductances along the direct axis, have weak air-gap and reluctance and inductances along the axis in squaring have strong reluctance and maximum of air-gap. for the saturated machine, permeance also depends in the state of saturation. the effect of saturation in the parts of iron results in the introduction of an equivalent air-gap with the same reluctance as the saturated parts. in the asynchronous machine, the function of permeance due to saturation varies along the armature. in fact, a saturated asynchronous machine can be regarded as equivalent to a diphase unsaturated salient pole synchronous machine. we presented a concise method of determining transient phenomena in a capacitor-excited induction machine, which, of course, requires taking into account the main field saturation. the new feature in this paper is the incorporation of crossmagnetization effects in the analysis. by this, we added a useful application to a number of previous papers dealing with smooth-air-gap machines. the current applied model describes the induction machine quantities in d-q-components. an essential part of the model is the inductance matrix along with the definitions of its elements. it is true that recently some contradictory views on the phenomenon of cross-magnetization have been stated. therefore it might be useful to repeat the basic considerations under which the present model holds: the magnetizing current produces a sinusoidal mmf distribution which gives rise to a flux-density curve containing a fundamental and saturation harmonics. the winding distribution is such that only the fundamental flux induces a voltage. expressing the magnetizing current and the engineering, technology & applied science research vol. 9, no. 1, 2019, 3739-3743 3743 www.etasr.com khlifi: explaining the d-q magnetic couplings theoretically in saturated smooth air-gap ac machines fundamental flux linkage as space-phasors, their magnitudes are related by the saturation curve. note that there is a formal resemblance to the main inductances of a salient pole synchronous machine in stator frame representation, where the angular position of the pole axis is analog to the position α of the above mentioned magnetizing current space-phasor. in further consequence of this analogy, the (saturation dependent) (lmdy−lm) takes the place of the difference between direct and quadrature axis synchronous inductances. it has been shown that when the currents are used as statevariables, it is possible to show that the equations and physical picture in a saturated smooth-air-gap machine are similar to the equations and physical picture in a non-saturated salient-pole machine, where mutual coupling exists between the direct and quadrature axes and the self-inductances are different on the non-salient part of the machine due to the variation of the reluctance with the rotor angle. however, in contrast to this, in the saturated smooth-air-gap machine, the cross-saturation coupling and self-inductances vary with the angle of the magnetizing current. this is one of the reasons why a specific form of the inductance terms has been presented in [l, 2]. this physical fact is also evidenced by (30)-(33), in contrast to the forms before where the small change of the magnetizing inductance is expressed by utilizing the difference between dynamic and static inductances. we utilized the first derivative of the magnetizing inductance with respect to the magnetizing current. the same derivative has been utilized in the paper under discussion, where an alternative formulation of these inductances has been given. if it is the purpose to focus attention to the analogy described above, or to give a clear analytical representation of the modifications in the impedance matrix, then it is useful to have expressions containing the angle of the magnetizing current space vector. v. conclusion a linear analysis of the machine based on the coupled circuit theory and assuming sinusoidal distribution of both mmf and flux density is performed and the saturated model is derived by making some model parameters dependent on suitable saturation laws. in this paper, a comprehensive winding model of both induction motors and synchronous generators has been proposed where the effects of saturation are incorporated in the main flux path and sometimes attributed to the leakage reactance too. saturation of the magnetizing reactance must be driven by the main flux, whereas saturation of leakages is mainly dependent on the involved currents. in round rotor machines the influence of saturation only depends on the amplitude of the main flux, whereas in salient pole machines the flux angle may also be involved by considering, if known, different saturation characteristics as the flux moves from the direct to the quadrature axis. at steady state operation, only the main flux path is affected by saturation, whereas the leakages are usually maintained at their unsaturated values. according to the selected model, the saturated magnetizing reactance is defined as the slope of the chord corresponding to the operating point on the proper magnetizing characteristic. the effect of saturation at steady state is of main importance for a correct setting of the state variables before a transient analysis is started. for instance, the initial load angle of synchronous generators is closely related to the stability characteristic of the machines. appendix: list of symbols n number of spire of magnetic circuit i current in magnetic circuit ef length of the air-gap rf magnetic reluctance λf flux iron sf surface of iron hf magnetic excitation lf length of the field lines b magnetic induction µr relative permeability µ0 permeability of vacuum d, q indices for direct and quadrature axis i space vector winding current references [1] m. a. khlifi, h. rehaoulia, “general modeling of saturated ac machines for industrial drives”, compel: the international journal for computation and mathematics in electrical and electronic engineering, vol. 35, no. 1, pp. 44-63, 2016 [2] m. b. slimene, m. a. khlifi, m. b. fredj, h. rehaoulia, “analysis of saturated self-excited dual stator induction generator for wind energy generation”, journal of circuits, systems and computers, vol. 24, no. 9, p. 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journal of electrical engineering and technology, vol. 12, no. 1, pp. 145-150, 2017 microsoft word 05-3630_s_etasr_v10_n4_pp5896-5902 engineering, technology & applied science research vol. 10, no. 4, 2020, 5896-5902 5896 www.etasr.com rani & prabakaran: ann based dc link control of statcom in wind integrated distribution … ann based dc link control of statcom in wind integrated distribution system for power quality conditioning sugeelin kalai rani department of eee sri chandrasekharendra saraswathi viswa mahavidyalaya university kanchipuram, india sugeelin@rediffmail.com s. prabakaran department of eee sri chandrasekharendra saraswathi viswa mahavidyalaya university kanchipuram, india prabakaran110768@gmail.com abstract—the integration of renewable energy sources (res) brings along abnormalities that affect the grid, loads, and may degrade the performance of the system. these issues can be alleviated with the integration of res with the use of a distribution static synchronous compensator (statcom). renewable generation with statcom provides quality of power during disturbances created by the ac loads and intermittent power from the res. the statcom distribution of dc link plays a major role in the supply quality during abnormalities. in this work, an attempt has been made to provide supply quality in the distribution system with the integration of a renewable energy farm using artificial neural network (ann)based dc link statcom control of distribution. the wind farm is analyzed for a double fed induction generator (dfig) based wind turbine system and it is integrated into the distribution system. the system was simulated in matlab 2018a. keywords-double fed induction generator; distribution static synchronous compensator; artificial neural network; windfarm generation; power quality i. introduction wind generation plays a vital role in energy production these days due to its comparatively lower cost and environmentally friendly status as compared to conventional power generation. there is a worldwide rapid growth of wind generation plants due to the high demand for the usage of electrical energy. wind energy generation is the most desirable non-pollutant source, it is renewable, and available in abundance [1-3]. in the early twentieth century, the aviation technology advanced rapidly and the blade technology improved. this allowed the wind turbine development with two or more blades [4-5]. at present, the wind farm was considered more economical when compared to conventional sources [67]. wind turbines can have different sizes, depending on power requirements. the electrical generator, the rotor, speed control, and a tower are the basic components of the electrically generating wind turbines. the wind turbines may fail sometimes to safe shut down due to malfunctions [8]. wind farm generation is installed in rural and remote places, which are usually away from the grid. some areas have weak grid due to voltage fluctuation [9]. the supply from the induction generator is unbalanced and the torque developed by the induction generator (ig) varies. due to the unbalanced current drawn by the ig, periodic pulsation torque is developed at two times the grid frequency [10]. recent research made the wind turbines to be operated between fixed speeds to variable speed utilizing model predictive control (mpc) approach which captures maximum wind energy even though wind is intermittent in nature and cannot be predicted. mpc approach gives better results when compared with a conventional pid controller [11]. this produces noise and affects the rotor shaft, the blade assembly or the gear box, causing overcurrent. to avoid these problems and in order to capture maximum wind energy, variable speed wind turbines are employed in many new wind farms. one of the components of the variable speed wind turbine is the dfig [12-13]. the dfig has many advantages compared to the fixed speed generators [14]. recently, many researchers focused on the study of dfigbased wind turbine systems which are connected to the grid. the most prominent one is the vector control of dfig. in this case, the stator is directly integrated to the grid and the rotor is connected to magnetizing the machine. disturbances created in the ac loads due to the intermittent power generated from the renewable energy leads to various power quality issues [15-16]. therefore, the abnormalities related with grid and loads will affect the performance of the system considerably. these issues can be alleviated with the integration of res using distribution static synchronous devices. statcoms are much used at the distribution level and in the installation of the end-user. voltage regulation, power factor correction, load balancing and harmonic filtering are some of the functions that are supported by statcoms. application of intelligent controllers like to compensate reactive power absorption, improves the dynamic voltage stability of a grid-connected wind power system [17]. the major advantage of a statcom distribution as compared to svc’s is its reduced size [18]. corresponding author: sugeelin kalai rani engineering, technology & applied science research vol. 10, no. 4, 2020, 5896-5902 5897 www.etasr.com rani & prabakaran: ann based dc link control of statcom in wind integrated distribution … in order to improve the operational efficiency of the controller of statcom, various intelligent controllers have been designed to improve system stability and voltage quality. svc and statcom are reactive power compensating devices and support the maintain voltage profile, however statcom performs better. the intermittent wind firm energy generation and the dynamic switching of load creates voltage instability and reactive power mismatch. this effect can be reduced with the use of statcom. hence, the proposed work investigated the statcom distribution wind generation system. the main objective of the proposed system is maintaining the dc link voltage constant and maintain the voltage profile under dynamic variations in wind generation. the grid integrated wind generation under dynamic load performance improved with statcom control. the dc link voltage of the statcom is regulated using ann and it tries to maintain the necessary power to the load. in this paper, an attempt has been made to improve the performance of power quality in the distribution system connected with a renewable energy farm using statcom. the wind farm is analyzed for a dfigbased wind turbine system integrated in the distribution system. this is studied in three different scenarios, i.e. isolated, gridintegrated, and grid-integrated using statcom, and compares their dynamic and transient performances under different load conditions. ii. literature review authors in [19] discuss the impact of statcom and power system stabilizer (pss) on multi-machine power systems. they improved the damping oscillations of synchronous generators under normal and abnormal network conditions. applying intelligent controllers with statcom and pss leads to better performance than the conventional controllers’. authors in [20] presented a distribution statcom reactive power source based on the magnitude of the dc link and ac voltage control. it includes a transformer, a voltage source converter (vsc), and a dc link capacitor. the transformer secondary winding is connected in shunt with the grid. the vsc is constructed as an inverter. it has a capacitor bank to stabilize the dc link voltage in order to perform the converter operation. the converter also keeps the capacitor charged to the necessary voltage by maintaining the output voltage of vsc to lag the ac system voltage by a small phase angle. the phase angle is maintained at a smaller range in order to permit active power flow to compensate solid state switching and coupling transformer losses. the dynamics of the load was not taken into account. retaining voltage and preventing overcurrent on the rotor side at the dfig during a fault interval on the connected grid is done by using the ideal of dynamic voltage restorer (dvr) in [21]. here, the capacitor is not used intrinsically in the variable reactive source. the variable reactive source process is achieved using pwm control signals of the vsc to satisfy operational requirements. the active and reactive power dynamic exchange between the statcom and grid is maintained by regulating the vsc output [22]. the system dynamics was not considered. distribution statcoms do not depend on the voltage level at the pcc for compensating the current. hence, it is not reduced as the voltage drops [23]. this is an important feature in new grid codes. hence, reactive power is provided to the wind generators, steadily depending on the grid demand and actual voltage level. other significant features are the provision of controllable reactive current independently of the grid voltage, the improvement of the margin of transient stability, and the improvement of power quality. performance strategies of different controllers were compared with h∞ in [24]. disturbances created in the ac loads due to the intermittent nature of the generated power from the res lead to reactive power mismatch and other power quality issues. therefore, any abnormalities related with grid and loads will affect the performance of the system considerably. these issues can be alleviated with the use of distributied statcoms in the integration of res [25]. under faulty conditions, there will be fluctuations in the frequency and eventually speed differences between the grid and the interconnected wind generator creating the need for transient stability. critical clearing time (cct) with facts devices is longer than the one without them, which is an indication of ts improvement [26]. hybrid systems with statcom have been investigated in [27, 28] and the grid integrated wind generation with statcom under dynamic load performance was presented ther for the first time. hence, there is a need to investigate the performance under dynamic source and load conditions [29, 30]. both source and load dyamics are considered in the proposed system and the complete and description is detailed below. iii. proposed integrated wind farm system using distribution statcoms the wind farm integrated to the distribution system with distribution statcoms connected with multiple loads and grid is shown in figure 1. fig. 1. integrated windfarm using a distribution statcom. a vsc based distribution statcom is integrated to the distribution transmission system via a shunt connected transformer. it can generate or absorb the reactive power from the bus through a controller and it is used for maintaining the voltage in distribution transmission systems. the voltage source converter is normally placed between the dc link and point of common coupling (pcc). it converts the dc link power into ac power, and it supports the load and the grid during the load demand. a. distribution statcom the distribution statcom has a vsc connected to a dc link and its ac side is connected in parallel across the pcc as engineering, technology & applied science research vol. 10, no. 4, 2020, 5896-5902 5898 www.etasr.com rani & prabakaran: ann based dc link control of statcom in wind integrated distribution … shown in figure 2. the vsc uses pwm control, hence it requires filters to overcome switching ripples. it uses a control algorithm to generate gating signals for the igbt devices. the vsc is usually in pwm current control mode to inject the necessary current into the system. statcom also requires passive elements like a dc link capacitor, ac inductors, injection transformers and passive filters [31-32]. fig. 2. distribution statcom. iv. wind turbine dfig with statcom design the distribution statcom is designed according to the requirements of wind generator. the electrical specifications of the wind energy system (wes) are shown in table i. the statcom design includes the selection of dc link voltage, dc link capacitor, ac inductor, ripple filter values, voltage and current rating of the igbt switches. the interfacing inductors and a ripple filter are used to limit the ripple in the currents and voltages. table i. wind energy system electrical specification apparent power 2.71mva real power 2.5mw voltage 11kv frequency 50hz reactive power 1.023mvar the required rating of the distribution statcom depends on the reactive power demand in the system. an uncontrolled rectifier contributes to lower order harmonics particularly of the fifth and seventh order, is considered as a nonlinear load and is connected to the pcc. a three leg vsc is used in this design. this configuration contains igbts, inductors, and a dc capacitor. the required reactive power of 1.53mvar comes from an 11kv, 50hz three phase system with compensation from statcom. the compensation support from distribution statcom depends on the rating of the vsc components. the vsc is designed for compensating and it decides the rating of the vsc components. during grid drop, the reactive power demand may vary. similarly, nonlinear load connected to the pcc contributes harmonics and considerably increases reactive power requirement. considering both aspects leads to 50% variation in reactive power. hence, it is selected to 1.53mvar. v. ann-based dc link control of statcom anns are computing systems inspired by the biological neural networks that constitute animal brains. such systems progressively improve their performance on doing tasks. they have found most use in applications difficult to express in a traditional computer algorithm using rule-based programming. an ann is based on a collection of connected units called artificial neurons. each connection (synapse) between neurons can transmit a signal to another neuron. the receiving neuron can process the signal(s) and then signal the downstream neurons that are connected to it. neurons may have states, generally represented by real numbers, typically between 0 and 1. neurons and synapses may also have a weight that varies as learning proceeds, which can increase or decrease the strength of the signal that it sends downstream. further, they may have a threshold such that only if the aggregate signal is below (or above) that level the downstream signal is sent. typically, neurons are organized in layers. different layers may perform different kinds of transformations on their inputs. signals travel from the first (input), to the last (output) layer, possibly after traversing the layers multiple times. the original goal of the ann approach was to solve problems in the same way that a human brain would. over time, attention focused on matching specific mental abilities, leading to deviations from biology such as backpropagation. anns have been used on a variety of tasks, including computer vision, speech recognition, machine translation, social network filtering, playing board and video games, medical diagnosis, etc. the dc link with ann control of distribution statcom is shown in figure 3. the layout of the ann is shown in figure 4 and the simulink model of the proposed system is given in figure 5. fig. 3. distribution statcom control. fig. 4. ann control layout. engineering, technology & applied science research vol. 10, no. 4, 2020, 5896-5902 5899 www.etasr.com rani & prabakaran: ann based dc link control of statcom in wind integrated distribution … fig. 5. simulink model of the proposed system. fig. 6. performance of ann. fig. 7. training of ann. figures 6-8 represent the performance of ann which depends on the dc link voltage. the mean squared error of the training performance of the ann is 0.012605 and the gradient is 0.008762 at 500 epochs. fig. 8. regression of ann. vi. simulink results the performance of the proposed system under wind changing wind, sudden switching of inductive load, and voltage variation is investigated below. a. wind speed characteristics figures 9-10 show the wind profile of gennerators 1 and 2 respectively. generator-1 is considered as the base generation. generatore-2 is considered only for creating dynamic variations in generation. b. switching of loads the dynamic switching of the rl and inductive load has been presented in different intervals at t=0.3 to 0.5s and 0.5 to 0.9s respectively. the load voltages are shown in figure 11. dynamic switching of inductive load t=0.3s to t=0.9s is shown in figure 11. during this period the voltage profile improved with the use of statcom. engineering, technology & applied science research vol. 10, no. 4, 2020, 5896-5902 5900 www.etasr.com rani & prabakaran: ann based dc link control of statcom in wind integrated distribution … fig. 9. wind profile of generator-1. fig. 10. wind profile of generator-2. fig. 11. load voltage. c. grid active power, reactive power, and time characteristics grid power in isolated case-1 net power delivery is zero (pnet, qnet) = 0. the grid integrated mode active and reactive powers in cases 2 and 3 are shown in figure 12. active and reactive power delivery in case-2 is less than in case-3. in case-3 the reactive power was supported with the statcom and the burden on the grid was reduced. fig. 12. grid active and reactive power. d. load active power, reactive power and time characteristics the dynamic switching of the four loads reactive performance is shown in figure 13. load 1 and load 2 are restive loads, load 3 is r-l load and load 4 is the inductive load. the reactive performance according to the dynamic switching of the four loads is shown in figure 13. load 1 and load 2 reactive power is zero hence the loads are resistive loads. e. statcom reactive power – time characteristics in cases 1 and 2, the statcom is not integrated in the system. the reactive power exchange is shown in figure 14. initially, the reactive power support is more due to insufficient sharing power from wind generation.at t= 4s to t=12s the change in the inductive load requires the necessary reactive power and it is supported with statcom as shown in figure 14. in case-1 the voltage drop variations is more during the t=0.3s to t=0.9s interval. the power is insufficient to meet the increased load demand, resulting in a voltage drop at the bus. in case-2, the voltage profile is improved compared to case-1 due to grid support. but the voltage profile suffers due to switching of large inductive load including resistive loads. still, there is a need to improve the voltage profile further. in case-3, the distribution statcom supports the counter effect of reactive power generated by the inductive load on the grid. the results in case-3 show the better voltage profile improvement compared to cases 1 and 2. engineering, technology & applied science research vol. 10, no. 4, 2020, 5896-5902 5901 www.etasr.com rani & prabakaran: ann based dc link control of statcom in wind integrated distribution … fig. 13. loads active and reactive power performance. fig. 14. statcom reactive power. fig. 15. dc link voltage of statcom. the statcom dc link voltage with pi, ann controller is shown in figure 15. the performance of statcom under dynamic switching of loads affects the dc link voltage and it is stabilized with the ann controller. from the results it can be inferred that the ann controller performs satisfactorily. vii. conclusion the performance of a dfig based windfarm using distribution statcom is analyzed under different load dynamics. the distribution grid maintains constant voltage and the necessary active and reactive power of the proposed system in the third case compared to the other scenarios. the system is stabilized even during fluctuating wind speed and the occurrence of varying ac load. it was shown that the effective work of the statcom made the system more reliable. the results show that the obtained voltage profile is maintained with the distribution statcom, which is effectively control of the dc link voltage 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[32] c. kumar and m. k. mishra, “a voltage-controlled dstatcom for power-quality improvement,” ieee transactions on power delivery, vol. 29, no. 3, pp. 1499–1507, jun. 2014, doi: 10.1109/tpwrd.2014.2310234. engineering, technology & applied science research vol. 8, no. 4, 2018, 3270-3275 3270 www.etasr.com dammalage: the effect of multipath on single frequency c/a code based gps positioning the effect of multipath on single frequency c/a code based gps positioning thilantha lakmal dammalage department of remote sensing and gis faculty of geomatics sabaragamuwa university of sri lanka belihuloya, sri lanka thilantha@geo.sab.ac.lk abstract—the differential gps (dgps) technique is one of the most popular and comparatively accurate techniques available to enhance the positioning accuracy by minimizing most of the common errors. however, the ultimate accuracy of the user location depends on the remaining non-common errors (multipath, receiver clock, and noise), which occur at the points of observation and reference. out of these errors, multipath is the most dominant and challenging error to predict and minimize. single frequency c/a code based gps receivers are popular due to their comparatively low cost compared to dual frequency (l1/l2) gps receivers. this paper focuses on evaluating the effect of multipath error on single frequency c/a code based gps positioning. for the analysis, 72,000 continuous gps observations with one-second interval under four different multipath environments were conducted by utilizing three geodetic gps units. accordingly, the observations with more than 5cm on the 2d positional error, created by the effected multipath, were always less than 25%. here, an average of 16% of observations exceeded 20cm in 2d positional error. further, it was noted that the presence of multipath introduces significantly higher and comparatively lower 3d positional errors on dgps observations. this could be due to the compensation of negative and positive effects caused by the multipath and other remaining noncommon mode errors at the reference and user stations. in addition, c/a code based single frequency gps observations were significantly influenced by multipath, not only by the close-by reflectors but also by the ground surface. the effect of multipath was about 50% of the total 3d positional error for the four tested multipath environments. keywords-c/a code observations; dgps; multipath i. introduction global positioning system (gps) developed by the us department of defense, was first planned to have 24 satellites in operation. each of the satellites continuously transmitted two high-frequency carrier waves l1 and l2, with frequencies of 1575.42mhz and 1227.60mhz respectively [1]. c/a-code (coarse-acquisition) is for civilian users and p-code (precision) for u.s. military or authorized users. the code signals are superimposed on the l1 carrier, while l2 carries only the pcode [2]. both codes allow a gps receiver to measure the signal propagation time from satellites to the receiver instantaneously using the distance from satellites to the receiver, (pseudo-range). pseudo-ranges are then utilized for the estimation of gps receiver position [3]. basically, there are two forms of observations depending on the capability of the receivers to process c/a code and l1/l2 carriers, referred to as code and carrier range observations respectively [4]. therefore, gps based positioning accuracy directly depends on the accuracies of calculated ranges to at least four satellites [5]. most of the presently available gps receivers utilize almost all the state-of-the-art technical improvements in gps hardware and processing algorithms. however, still these gps receivers suffer from significant positioning errors due to signal propagation delays through ionosphere and troposphere, satellite and receiver clock errors, bias on ephemeris data, multipath, and receiver and measurement noises [6-8]. hence, the standard positioning service (sps) accuracy widely varies with time, place, and most importantly, gps receiver performance [2]. these measurement errors are generally classified as either common or non-common mode errors. the common errors (ionosphere delay, troposphere delay, satellite clock, and bias on ephemeris data) have similar effects on all receiver measurements operating in a limited geographic area [7]. non-common mode errors (multipath, receiver, and measurement noises) are distinctive and the amount of their influence depends on the surrounding obstructions at the observation site and the technical specification of receivers [9]. numerous techniques are available to minimize the abovelisted sources of errors from gps position estimation. a user equipped with a dual frequency (l1, l2) gps receiver can estimate the ionospheric group delay and phase advance from the measurements themselves, and virtually eliminate the ionosphere as a source of error [10, 11]. besides, many different models have been proposed to quantify the effect of ionospheric and tropospheric delay on gps measurements. the klobuchar model is one of the popular empirical models, which uses the satellite broadcast parameters to estimate the propagation zenith ionospheric delay [12]. there is no dearth of tropospheric models, in particular, the saastamoinen model, which was derived based on the gas laws and simplifying assumptions regarding changes in pressure, temperature, and humidity with altitude [13]. however, none of these models can mo loc dat em and po err ref uti wh the sta err ref the aff hig the the tw dg me tec dou dep sof dg the eff the bee mu sur nea tha ob hav ma tha of ele ins tre div its cum sig sur the sig l1 wh engineerin www.etasr n precisely es ost of them a cal metrologic ta-processing mployed to ove differential c d comparativ sitioning accu rors as a co ference station ilized to deter hich are then a ese errors by ations. the ex rors depends ference and us e assumption fect both rece ghly dependen e capability of e position solu o categories, gps, where t eter-level res chniques are a uble differenc pend on the ftware [16]. gps, the ultim e amount of re fect of non-co e point of obs en identified t ultiple receptio rrounding obje multipath is ar the gps an at follows th structions in ve higher pos any ways [18] at the ideal co the sky with evation and stance, due to ees, fences, an verse nature an mathematic mbersome [19 gnal is demons rface at distan e respective g ght carrier pha frequency canφ , co here a and d ng, technology r.com stimate the to always require cal data. som software offe ercome these d correction (dg vely accurate uracy by minim mbined opera n, the position rmine the mag applied to othe assuming they xtent to which on various fa ser gps receiv of common eivers. furthe nt on the gps f utilizing carri ution. dgps t namely carri the accuracies spectively [4 available. for ce, which are capability o whatever the mate accuracy esidual commo ommon mode ervation. of th to be the mul ons of one sat ects. ii. mul caused by gp ntenna, which he direct path the surroundi ssibility to dim ]. therefore, a nditions for g h no obstructio up. however earth’s surfac nd cables, free nd complex be al representa 9]. the effect strated only by nce d from the geometry [15]. ase measureme n be representos denote the amp y & applied sci otal effect on e additional p me gps rece ered at a price drawbacks. gps) is one o e techniques mizing most of ation [6]. in of which is a gnitude of com er gps observ y were equall h dgps redu actors; mainly vers [14, 15]. i environmenta ermore, dgps receiver type ier and/or cod technique has ier phase base s vary from 4]. several r instance, sin e very comm of the receiv e processing of the user lo on mode error errors at the r he latter, the d ltipath, which tellite signal d ltipath error ps signals refl h could be mis h from the s ing vicinity o minish the pos as a thumb-ru gps observatio ons at least f r, in practic ce (ground an e observation ehavior of mul ations extrem of multipath o y using a plana e gps antenna . accordingly ent (φ ) for sa ted as in (1): plitude (voltag ience research dammalage: measurement parameters su eiver-operation e, however, c of the most po to enhance f the common this techniq accurately know mmon mode e vations to min ly affected for uces common y the separati it, sometimes, al conditions w s accuracy is e, which varies de measuremen been classifie ed and code centimeter-lev dgps proce ngle differenc on in practic ver and proce technique us ocation depen rs and the com reference poin dominant mod is named aft due to reflectio r lected from su staken as the satellite [17]. of the gps an sitional accura ule, it is consi ons are a clear for about 5 de cal conditions nd water), buil sites are rare ltipath signals mely difficult on the carrier ar vertical refl a. figure 1 pr y, the direct lin atellite “s” bas (1) ge) and the ph h v the effect of m ts and uch as n and can be opular gps mode que, a wn, is errors, nimize r both mode ion of limits which s also s with nts for ed into based vel to essing ce and e, yet essing sed in nds on mbined nt and de has ter the ons by urfaces signal any ntenna acy in idered r view egrees s, for dings, e. the cause t and phase ection esents ne-ofsed on hase of the fig. sign whe fact the whe frac sum con the whe sign sign whe fun dela freq min carr in r c/a effe wer mu neg and vol. 8, no. 4, 20 multipath on si signal respect . 1. geometric the carrier ph nals of the samφ , c ere / tor) and ′ is t phase shift du∆ ere is the f ctional shift. with referenc m of distance nverting this d phase shift (cos ere, is the w nal at the ante nal: φ φ φ ere, r is the nction of , ay which is quency (l1, nimise the com by solving th rier phase mulψ , t however, the representation a-code as longδ furthermore, ect based on c re derived in ltipath and gligible compa d (9) respecti 018, 3270-3275 ingle frequency tively. cal representation hase measurem me satellite cancos , , is the at the amplitude ue to reflection frequency, ∆ ce to figure 1 ab and bc, distance into pϕ) can be calcs wavelength of t enna is then th φ cos ϕ e resultant carand and ψ a function o l2) and sat mplexity of rep he previously d ltipath delay ctan e pseudo-range as in (7), and g as the approp a derivation carrier phase a n [20], takin noise on ca ared to those ively represen 5 y c/a code bas n of multipath effe ment (φ ) bas n be written as 0 ttenuation (am of the reflecte n. is the time d , the total mu , which equal phase cycles an culated as the carrier sign he sum of the d ψ rrier phase vψ is the carrie of and . tellite id (s) presentation. derived (4) an an be verified e multipath er d it is valid fo priate chipping n for pseudo and pseudo-ra ng advantage arrier phase of pseudo-ran nt the pseud 3271 sed gps positi fect by a vertical s sed on the refl s: 1 (2) mplitude redu ed signal, and (3) delay, and i ultipath delay i ls to 2 cos nd then to rad (4) nal. the comp direct and refl (5) voltage which er phase mult the notation are neglecte nd (5), the resu as; (6) rror ( ) is si or both p-code g period is use (7) o-ranges mult ange measurem of the fact measurments nge. equation do-range mult ioning surface lected uction is is the is the . by dians, posite lected is a tipath ns for ed to ultant imple e and d. tipath ments that s are ns (8) tipath bas wh ph mu sig th per pse be rec zer cor cod del of pse env env ho me 5cm hig osc dif mu car gp bas cod car kil gp low co of inv cor sta me eff fre suc ran sta the mi thi sin ma cod engineerin www.etasr sed on l1 and here, k1 and ase and incl ultipath effect gnals and can herefore, k1 a riod of few ho eudo-range mu a reflected s censored aut ceiver, where ro for delays rresponds to a de and 50m fo layed by less delay and s eudo-range m vironment to vironment. in owever, the easurements is m [2]. it has b ghly variable cillations with fficulty in mod ultipath error rrier phase me ps receivers, sed dgps co de based dgp rrier phase dg lometers [25]. ps receivers a w cost com onsidering the a multipath er vestigated the rrections that ation. they easurements f fect ( ), whi equencies as r ccessful attem nge (c/a code ations. the ex e method pro itigation from is paper is to ngle frequency a field expe ade to analyze de based gps ng, technology r.com d l2 frequencieφφ k2 are funct lude the unk is considered n be averaged and k2 can b ours [21], and ultipath and re signal, delayed tomatically by the auto-corre s longer than about 500m of or p-code signa than 1.5 chips signal amplitu measurements o more than n some cases, correspondin s typically two been found tha in the time d h a period of s deling it [21, is almost ten easurements [2 from low-cos orrections. bes ps is several h gps operation in addition, s are common in mpared to du practical adva rror on c/a co mitigation o are generated used a car for the deriva ch was formul represented by mpt was made e) multipath e xperiment pres oposed in [8 observations. analyze the y c/a code bas iii. fiel eriment was d e the multipath s positioning. y & applied sci es. φ kφ tions of the m known integer to be a combi d out to zero e estimated b d the result is eceiver noise. d by more tha y the correlat elation for the n 1.5 chips [ f increased pat al. the effect s would depen ude. typical varies from n 5m in a it could reac g error in o orders of ma at the error cau domain showi several minute 23]. the mag n times greate 24]. neverthele st to very exp sides, the oper hundreds of k ns are limited single frequen n use due to ual frequency antages and th ode measurem f the multipat d by a perman rrier phase ation of pseu lated in [20], b y (8) and (9) to precisely e error at perman sented in this ] for multipa . however, th effect of the sed gps positi ld experimen designed, and h effect on sin three dual-f ience research dammalage: k (8)k (9) multipath on c r ambiguities ination of harm over a few h by averaging o the combinati an 1.5 chips, w tion process o c/a-code is n 22]. such a th length for a of a reflected nd upon the am multipath err 1m in a b a highly ref ch even 100m the carrier agnitude small used by multip ing quasi-sinu es creating ex gnitude of c/a er than that o ess, a wide ran pensive, offer rational distan kilometres whi d to several te ncy c/a code their compara y gps rece he significant ments, authors th effect on d nent gps refe and pseudoudo-range mul based on l1 a ). based on t estimate the ps nent gps refe paper also u ath estimation he primary foc multipath err ioning. nt d observations ngle frequency frequency geo h v the effect of m carrier . the monic hours. over a ion of would of the nearly delay a c/asignal mount ror in benign flected m [15]. phase ler (1path is usoidal xtreme a code of the nge of r code nce of ile the ens of based atively eivers. effect in [8] dgps erence -range ltipath and l2 this, a seudoerence utilizes n and cus of ror on were y c/a odetictyp gro illu 03, con leng an obs d3= use obt sele sate 360 flat bod pro ben mu mu obs obs gen refl gp obs con obs cha met loca thro due of how mai to obs con gp dist com obs coo vol. 8, no. 4, 20 multipath on si e gps receiv ound control ustrated in figu fig. 2. g a trimble 57 and the obs nducted using gths between electronic di served distanc =19.9590m. t ed as ground tained through ected had mini ellites at very 00 undisturbed t ground. the dies and concr oximity. hence nign multipath ltipath effect ltipath envir servation for t servations wi nerating additi lectors. the la s 01 station servations wi nstructed at th servations, and anged for day tal sheets at ation, size, a oughout day 1 e to the change day 4 were c wever, the gp intained uncha the contribut minimum to servations. the nducted by as s 01 and 02 a tances, this a mmon mode servations. he ordinates are th 018, 3270-3275 ingle frequency vers were mou points to ure 2. gps receiver confi 700 l1/l2 rec servations at two leica each ground c istance measu ces were, d1 these precise truth to valid hout this exp imum obstruct low elevation d open sky vie ere were no b rete, mettle, or e, this site co h environment analysis, thre ronments we three consecu ith 1-second ional multipath ast set was ob . figure 3 i ith reflectors. he outset for th d then the sur y 2 and 3 obs the direction and orientatio 1, 2, and 3 ob e of multipath conducted wi ps receiver an anged. iv. resu tion of commo analyze the erefore, c/a c suming gps as users/rovers accuracy anal errors rema ence, the possi the effect of n 5 y c/a code bas unted over thr accomplish figuration in the fi eiver was utili stations gps – system 500 control points urement (edm =20.0295m, d ely known m date the accur periment. th tions for satell ns (~100). th ew and was sit buildings, elec r wood surface onfiguration as t for gps obs ee different ar ere introduce utive days. fo interval we th by concrete bserved witho illustrates the . the concr he first set of rface of the s servations by of gps rece on were main bservations, to h environment. thout any ref ntenna height ult analysis on mode errors e effect of m code based dg 03 as the refe s. due to the v lysis assumed ain on differ ible inaccurac non-common m 3272 sed gps positi ree precisely the configur ield experiment ized at station s 01 and 02 0 instruments. were measure m) instrument. d2=19.8930m measurements racy of the re e experiment lite signals eve e selected site tuated on elev ctric cables, w es found at th ssumed to be servations. fo rtificially desi ed for gps our-sets of 20 ere conducted e, wood, and m out any reflect field set up ete reflector f 20-hours of d same reflector placing wood iver. the refl ntained uncha minimize the . last, observa flector at gps and location s s has to be red multipath on gps processing ference station very short bas d that no res rentially corr cies of the res mode errors, o ioning fixed ration n gps were . the ed by . the m and were esults t site en for e had vated, water he site as a or the igned s 01 -hour d by metal tor at p for was day 1 r was d and flector anged e bias ations s 01, were duced gps g was n, and seline sidual rected sulted out of engineering, technology & applied science research vol. 8, no. 4, 2018, 3270-3275 3273 www.etasr.com dammalage: the effect of multipath on single frequency c/a code based gps positioning which the multipath effect is the most significant. according to the arrangement of the observation site, the possible source of multipath error at gps01 was the reflector and/or the ground surface. fig. 3. reflector configuration at gps 01 station at gps02 and 03, the only possible source was the ground surface. a trimble 5700 receiver was used at gps03 with a zephyr geodetic l1/l2 antenna and trimble stealth ground plane technology, which could reduce most of the multipath created from the ground surface. therefore, the negative influence that could be introduced by multipath on dgps corrections generated at gps03 reference station is assumed to be minimum. to evaluate the effect of multipath on c/a code based gps positioning, 2d and 3d positioning accuracies at gps1 and gps2 were comparatively analyzed by utilizing the accurately measured baseline distances with gps3 reference station. a. effect on 2d positioning the multipath effect is analyzed by evaluating the 2d positional accuracy of 72,000 observations recorded for 20hours with a 1-second interval. table i presents the number of observations as a percentage of total records, within four different 2d positional error limits, less than or equal to 5cm, greater than 5cm, and greater than or equal to 20cm and 50cm (<5cm, >5cm, >20cm, and >50cm). the effect of multipath is calculated for both baselines, bl1 (gps 03 – gps 01) and bl2 (gps 03 – gps 02), as reported in table i. table i. observation percentage at 2d positional error caused by multipath observation 2d positional error due to multipath <5cm >5cm >20cm >50cm day1 bl1 78.4% 21.6% 16.0% 7.6% bl2 80.1% 19.9% 04.1% 1.8% day2 bl1 79.1% 20.9% 16.1% 6.8% bl2 89.9% 10.1% 03.6% 0.5% day3 bl1 75.4% 24.6% 17.3% 9.3% bl2 84.7% 15.3% 3.8% 1.5% day4 bl1 79.3% 20.7% 06.7% 0.4% bl2 84.4% 15.6% 02.6% 0.7% observations with the 2d positional error of less than or equal to 5cm could be considered as observations that are comparatively low affected by multipath. an average of about 78% and 85% were recorded with minimum multipath error for baselines bl1 and bl2 respectively. in addition, an average of about 22% and 15% observations were affected by higher multipath errors (more than 5cm of 2d positional errors for baselines bl1 and bl2 respectively). according to the condition of the observation site, the possible source of error for bl1 is the multipath at gps01 created by the reflector and/or the ground surface. for bl2 it is the multipath at gps02 created by the ground surface. therefore, the percentage difference between bl1 and bl2 represents the additional multipath introduced by the artificial reflector separately from the ground. accordingly, the artificial reflectors introduced both lower and higher than 5cm multipath errors on average of 7%. the highest difference percentage was observed for 2d positional error limit more than or equal to 20cm. when compared to the observations without reflector at gps 01, the artificially-generated multipath diminished. however, for 2d positional error limit of more than or equal to 20cm, the number of observations were improved by 9.3%, 9.4%, and 10.6% over the observations without a reflector for concrete, wood, and metal, reflectors respectively. this confirms that the amount of multipath effect changes with the material of the reflector and is significant for higher 2d positional errors of greater than 20cm on c/a code based gps observations. b. effect on 3d positioning further analysis was conducted to investigate the effect of the multipath error on 3d positioning with single frequency c/a eff po wit cal pse mu mi the po mu bl ref mu mi res pse sim ref of bl can non mi fig mit ver rec ho sho for rem mu cha non be th cal sig acc engineerin www.etasr a code based fect of multipa sitional error th a 1-second lculated befor eudo-range ob ultipath residu itigated from g e methodology sitional errors ultipath mitiga l2 (gps 03 – ference statio ultipath mitiga itigation. the spective day o eudo-range m milarity to eac flector. howev 3d positiona l1 and bl2 w n be conclude n-common m itigation were g. 4. 3d posit tigation the common ry short baseli ceiver at both owever, the t own any sign r both bl1 maining 3d po ultipath mitiga anging with t n-common mo the possible s he comparison lculated befo gnificant dev curacies. for ng, technology r.com d gps observ ath generated b was calculate d interval. al re and after bservations be uals were calc gps 01, 02, a y proposed in s are presented ation for baseli – gps 02), w on. the red ation and the b time-series o of observation multipath mit ch other, even ver, after mul l errors for ea were significan ed that the rem mode errors fo almost similar tional accuracy n reference st ine observation h user station time-series of nificant correla and bl2. th ositional errors ation are not time and day ode errors, bot sources of thes n of time-ser ore multipath viation betwe bl2, the erro y & applied sci vations. in or by the reflecto ed for 10 hou lso, the 3d p the multipat efore dgps b culated based and 03 observ [8]. the resu d in figure 4 ines bl1 (gps where, gps 0 lines present blue ones the e of 3d position ns between bl tigation have n for day 4 ob ltipath mitigat ach day of ob ntly correlated maining un-mo or bl1 and b r. comparison befo tation used for ns and the use ns could be f 3d position ation between his provided s even after d systematic, th . the un-mod th at the refere se remaining 3 ries of the 3d h mitigation een bl1 and or after multip ience research dammalage: rder to analyz ors at gps 01, urs of observ positional erro th mitigation baseline proce on (8) and (9 vations by ado ulted time-seri as before and s 03 – gps 01 03 was used a t the error b error after mul nal errors for l1 and bl2 b e not shown bservations w tion, the timebservations be d. based on t odeled commo bl2 after mul ore and after mu r both of thes e of the same ty the main rea nal errors hav n the different evidence tha dgps correctio hey are random deled common ence and user, 3d positional e d positional revealed an d bl2 posi path mitigation h v the effect of m ze the , a 3d vations or was from essing. 9) and opting es 3d d after 1) and as the before ltipath r each before n any ith no -series etween this, it on and ltipath ultipath se two ype of asons. ve not t days at the on and m and n and could errors. errors nother itional n was alw bl erro mu pre 3d gp com mu refe sou surf tech mu the refe assu mu calc mit mo sam mu of eve fig fig rev pos obs pos con has on g fig. code freq vol. 8, no. 4, 20 multipath on si ways lower tha 1. surprisingl or before mu ltipath mitiga sence of mult positional er s observatio mpensation of ltipath and oth erence and use according to urce of multip face. however hnology at th ltipath on its erefore, the erence station, umed to be mi ltipath error culated by sub tigation from deled commo me before and ltipath error e true multipath en after c/a c gure 5. the s gure 4 is utiliz ealed that mu sitional error servations. th sition solution ndition of the s a significant gps observati 5. multipath e based dgps ob this paper quency c/a c 018, 3270-3275 ingle frequency an that before, ly, for some t ultipath mitiga ation. therefor tipath not only rrors but also ns. this cou f negative an her remaining er stations. o the observa path at the re r, with the use he gps03 re dgps correct contribution , to the differe inimum. base on c/a code btracting the 3d the one bef on and non-co d after multipa effected the us h error conce code based d same 10 hour zed for the cal ultipath contrib of single fre he magnitude n varies with t multipath env influence on s ions even at fa h error as a percen bservations v. co presented th code based gp 5 y c/a code bas but this was n time intervals, ation was bet re, it can be y introduces s comparativel uld be caus nd positive e non-common ation setup, eference statio e of trimble st eference stati tions could be of multipath entially correct ed on which, th e based gps d positional e fore by assum ommon mode ath mitigation ser observation erning the tot dgps processi rs of observa lculations. co butes about 50 equency c/a of the multip the time of o vironment. in single frequen avorable multi ntage of total rem onclusion he multipath ps positioning 3274 sed gps positi not always tru , the 3d posit tter than that concluded tha significantly h ly lower error sed by the effects cause n mode errors a the only pos on was the gr tealth ground p ion, the effec e easily minim h effected at ted observatio he real effect o observations rror after mult ming that the errors remain . the resulted ns. the percen al error rema ing is present ations presente omparative ana 0% of the tota code based path effect on bservation an general, mult ncy c/a code b ipath environm maining error afte effect on s g by comparat ioning ue for tional after at the higher rs on error d by at the ssible round plane ct of mized. t the ons, is of the s was tipath e unn the d true ntage aining ted in ed in alysis al 3d gps n 3d nd the tipath based ment. er c/a single tively engineering, technology & applied science research vol. 8, no. 4, 2018, 3270-3275 3275 www.etasr.com dammalage: the effect of multipath on single frequency c/a code based gps positioning analyzing the 2d and 3d positioning accuracies after dgps processing. based on the analysis, averages of 22% and 15% of the tested 72,000 observations were recorded with higher multipath errors of more than 5cm on 2d positioning for all the tested multipath conditions of baselines bl1 and bl2 respectively. it has observed that the magnitude of multipath error changed with the material of the reflector and was significant for higher 2d positional errors, greater than 20cm on c/a code based gps observations. further, it was noted that the presence of multipath introduces not only significantly higher positional errors, but also comparatively lower errors on c/a code single frequency gps observations. compensation of negative and positive errors caused by the multipath and other remaining non-common mode of errors at the reference and user stations could be the main reason for the observed irregular variation. multipath has a significant influence on single frequency c/a code based gps observations, and for the tested observations, the contribution was about 50% of total 3d positional errors of single frequency c/a code based gps observations. references [1] i. a. getting, “the global positioning system”, ieee 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environments”, international congress of the international society for mine surveying, fremantle, australia, pp. 447-457, november 2-6, 1997 [21] l. ge, s. han, c. rizos, “gps multipath change detection in permanent gps stations”, survey review, vol. 36, no. 283, pp. 306322, 2002 [22] r. d. van nee, j. siereveld, p. c. fenton, b. r. townsend, “the multipath estimating delay lock loop: approaching theoretical accuracy limits”, ieee position location and navigation symposium, las vegas, usa, pp. 246-251, august 6, 1994 [23] k. k. fan, x. l. ding, “estimation of gps carrier phase multipath signals based on site environment”, journal of global positioning systems, vol. 5, no. 1-2, pp. 22-28, 2006 [24] a. mertins, signal analysis: wavelets, filter banks, time-frequency transforms and applications. john wiley, 1999 [25] t. l. dammalage, p. srinuandee, l. samarakoon, j. susaki, t. srisahakit, “potential accuracy and practical benefits of ntrip protocol over conventional rtk and dgps observation methods”, map asia, bangkok, thailand, august 29 – september 1, 2006 microsoft word etasr_7-1_1425-1428.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1425-1428 1425 www.etasr.com fesghandis et al.: comparison of multilayer perceptron and radial basis function neural networks… comparison of multilayer perceptron and radial basis function neural networks in predicting the success of new product development golamreza soltani fesghandis department of management ferdowsi university of mashhad mashhad, iran rsoltani359@gmail.com alireza pooya department of management ferdowsi university of mashhad mashhad, iran alirezapooya@um.ac.ir mostafa kazemi department of management ferdowsi university of mashhad mashhad, iran kazemi@um.ac.ir zahra naji azimi department of management ferdowsi university of mashhad mashhad, iran znajiazimi@um.ac.ir abstract—given that the new product failure in practice entails huge costs for organizations, the need for competitive planning has led organizations to apply appropriate approaches; one of these approaches is to predict new product success before market entry. accordingly, this study predicts npd success by comparing two techniques, the multilayer perceptron (mlp) and the radial basis function (rbf) in the clothing industry of tabriz. in order to collect data, a questionnaire with good validity and reliability was distributed among the population. mlp and rbf were used to analyze data. based on mse, rmse and r2, data analysis showed that mlp had lower error than rbf in predicting npd success. keywords-new product development; success prediction; artificial neural network. i. introduction rapid technological changes, intense competition, dynamic customer needs and low demand of outdated products available have led to shorter product life cycle [1]. ability of new product development (npd) is very important to succeed in the current turbulent environment [2]. contemporary management literature often stresses the need for innovation and npd to compete in changing markets [3]. among a variety of product development processes, npd has its own complexities, including lack of knowledge of developers and product designers, which necessarily increases only during development time [4]. npd is an opaque and complex process which involves almost all departments of an enterprise such as marketing, design and engineering, manufacturing and so on. when it comes to new product, a wide range of concepts, from a simple consumable product to a new very complex military system, comes to mind. there are as many npd models as the number of people who have addressed this field of research [5]. npd processes are the most challenging activities of an organization due to unforeseen or unknown obstacles in terms of technology and business risks. most of these are because of the fact that knowledge of organizations always evolves during npd projects and there is no deep understanding of what will happen in the future. therefore, planning for this process is inherently dynamic and needs to adapt to changes in product knowledge as well as other changes [6, 7]. despite many complexities developers and designers of new products face, unfortunately there are not enough tools for decision support in implementing npd processes. in [8], the authors noted this in a review of more than 30 studies published; therefore, proper tools need to be developed to predict npd success, as the prediction of npd success is very important for industry leaders and organizations due to the high failure rate of npd that reflects the complexity of npd processes. for system identification and modeling of complex processes, scientists have been always concerned with input and output data. soft computing techniques are used for modeling in these processes. neural networks are well known components of soft computing techniques that are highly capable of control and identification of nonlinear complex systems. several studies done in various fields using these techniques reflect the fact that they are both simple and highly capable [1,9-12]. with respect to simplicity and high capability of these techniques as well as absence of similar models in study and prediction of npd success, predictive modeling of npd success using artificial neural network and adoption of the best prediction technique will result in development of a practical model in this area. a. effective factors on npd success new products provide new ways and new opportunities for organizations to make a profit and hope to survive; however, important risks associated with npd projects should not be neglected. empirical studies show high failure rates for new products in consumer markets [13]. nevertheless, expression of successes and victories is not only sweet but also provides credit for successful organizations. obviously, successful managers are willing to discuss these factors as much as their strategic interests are not endangered and other managers tend to gain experience of successful organizations [14]. lester [13] presents sixteen factors effective on npd success, which can help managers to flee usual traps in npd process and succeed in development of new products. in [14], the authors noted top management support for innovation, long-term strategy with an engineering, technology & applied science research vol. 7, no. 1, 2017, 1425-1428 1426 www.etasr.com fesghandis et al.: comparison of multilayer perceptron and radial basis function neural networks… innovative focus, long-term commitment to larger projects, flexibility and responsiveness to change, risk taking by top management and support of an entrepreneurial culture as effective factors on npd. ten effective factors on npd were presented in [15] and 11 in [16]. in [17], authors classified the success factors of a npd project into four main categories and five sub-categories; they believed that main factors for success of a new product included a high quality npd process, a welldefined (certain) strategy for business, adequate resources, human resources and money spent on research and development for npd. b. artificial neural network artificial neural networks (anns) are mathematical models that are able to extract patterns in the observed data without the need for assumptions about the relationships between the various variables [18]. anns tend to present a mapping between the input space (input layer) and the optimal space (output layer) by understanding inherent relationships between data. hidden layer(s) processes information received from input layer and delivers it to output layer. each network is trained by receiving examples. training is a process which leads to learning. network learning occurs when communication weights between layers change, so that difference between predicted and calculated values is acceptable. learning process occurs when these conditions are met. these weights express memory and knowledge of the network. a trained ann can be used to predict outcomes proportional to a new set of data [19]. based on ann structure, its major features include fast processing, ability to learn the pattern by pattern will, ability to extend knowledge after learning, flexibility against unwanted errors and lack of significant disruption if a problem occurs in a part of connections due to weight distribution [20]. there are several types of anns; this study used multilayer perceptron (mlp) and radial basis function (rbf). c. multilayer perceptron (mlp) an mlp (multilayer perceptron) is formed of neurons grouped in an input layer, several hidden layers and an output layer. a neuron is connected from a layer to all neurons in the next layer; however, there is no connection between neurons in one layer. an ann can have a number of hidden layers; theoretical research undertaken in this field showed that any complex and non-linear function could be approximated by a hidden layer for these models [21, 22]. therefore, this study used a mlp with one hidden layer. d. radial basis function (rbf) rbf networks need a large number of neurons for training. these networks best perform with a high number of training vectors. unlike other networks, the entire input space of rbf is not responded similarly. here, input space center is first calculated; then, inputs which are close enough to this center are responded. as a result, these networks respond to inputs locally. rbf has two layers; the first layer is radial basis and the output layer is linear. training process is done by competitive learning or clustering. network parameters include spread number and goal number. network performance can be improved by changing these parameters. by applying inputs to the network, the distance between input vectors and weight vectors is calculated and vector product is obtained by multiplying the calculated values by bias values. then, these values generate as many neurons as inputs by corresponding functions; finally, output values are obtained by output layer [23]. ii. methods and materials this is an applied extensive research. data was collected by using two questionnaires from 185 clothing manufacturers. the first questionnaire, based on [14], assessed effective factors on npd success. the second questionnaire evaluated npd success using the variables described in [24]. input variables included effective factors on npd success; output was npd success. in order to evaluate potential ambiguities of questionnaires, four questionnaires were filled face to face with participation of researchers and some questions were modified. finally, the questionnaires were given to university professors in order to obtain feedback on modifications, through which validity of the questionnaires was confirmed. cronbach's alpha coefficient was used to determine reliability of the questionnaires. this test was performed on the original sample by separating constructs (table i). the results indicate good reliability of the questionnaires. table i. cronbach's alpha coefficient questionnaire cronbach's alpha effective factors on npd success 0.856 npd success 0.792 mlp and rbf were used to analyze data. in order to compare performance of each ann, r2, mse and rmse were calculated as follows. 2 , ,2 1 2 ,1 ( ) r 1 ( ) n a k p kk n a kk u u u        (1) n uunk kpka  1 2 ,, )( mse (2) n uunk kpka  1 2 ,, )( rmse (3) where, up,k represents the predicted value by each model, represents actual data and represents the number of observations. iii. results a. prediction of npd success using mlp considering six input variables (top management support for innovation, long-term strategy with innovative focus, longterm commitment to larger projects, flexibility and responsiveness to change, risk taking by top management, and support of an entrepreneurial culture) and an output variable as success of new product performance, ann structure was implemented with six input variables, a hidden layer and an engineering, technology & applied science research vol. 7, no. 1, 2017, 1425-1428 1427 www.etasr.com fesghandis et al.: comparison of multilayer perceptron and radial basis function neural networks… output variable in matlab software (figure 1). to evaluate the performance of the mlp, the number of neurons increased in hidden layer by trial and error. the best performance of mlp based on mse, rmse and r2 is shown in table ii. a comparison of each mlp based on above indexes shows that increase of neurons to eight in the hidden layer reduced error and increased r2. then, network error increased and r2 was reduced. therefore, the best mlp to predict npd success was the network with eight neurons in the hidden layer. the results are shown in figures 2 and 3. b. prediction of npd success using rbf given that maximum number of neurons was equal to the number of samples, rbf was designed and trained with six primary neurons. increase in the number of neurons reduced error and increased r2. table iii shows the results for rbf with different number of neurons. fig. 1. ann structure to predict npd success table ii. mlp performance with different number of neutrons in the hidden layer number of neurons type of data r2 rmse mse training 0.55083 0.58331 0.34025 6 test 0.24033 0.76516 0.58547 training 0.47138 0.58657 0.34441 7 test 0.43308 0.80611 0.64981 training 0.68277 0.47439 0.22505 8 test 0.49852 0.72450 0.52490 training 0.57937 0.54498 0.29701 9 test 0.38444 0.73256 0.53664 training 0.58866 0.53615 0.28746 10 test 0.41011 0.81013 0.65632 training 0.59666 0.59441 0.35332 20 test 0.152116 0.83396 0.69548 training 0.51264 0.87912 0.77285 50 test 0.00299 1.3843 1.9163 fig. 2. the calculated correlation between actual data and output data for the neural network with eight neurons fig. 3. results for mlp training data with eight neurons table iii. rbf performance with different number of neutrons number of neurons type of data r2 rmse mse training 0.10284 0.79981 0.63969 6 test 0.07782 0.84492 0.71388 training 0.12214 0.79226 0.62767 7 test 0.00088 0.83857 0.70320 training 0.14074 0.78883 0.62225 8 test .06088 0.80154 0.64247 training 0.15898 0.77519 0.60092 9 test 0.11976 0.84427 0.71278 training 0.17248 0.76483 0.58497 10 test 0.15954 0.86481 0.74790 training 0.34640 0.48824 0.34727 20 test 0.12060 0.88313 0.77993 training 0.60516 0.53735 0.28864 50 test 0.09820 0.94692 0.89667 training 0.80718 0.37397 0.13986 100 test 0.10586 1.0848 1.1768 training 1 0.00000 0.00000 225 test 0.67179 0.43164 0.18631 as shown in table iii, an increase in the number of neurons reduced mse and rmse and increased r2. according to the results, best network performance occurred in 225 neurons and the training error was zero. in other words, rbf with 225 neurons presented output data proportional to actual data (r2=1) and a full training took place as shown in figures 4 and 5. in order to choose the best ann, the best network in terms of mse, rmse and r2 was selected and the results were compared. the results of comparison are shown in table iv. table 4 shows that the best method to predict npd success is rbf. iv. conclusion due to the high failure rate of new products and the need for a technique to predict new product development (npd) success before spending high cost and wasting corporate resources, this study presented a model to predict npd success engineering, technology & applied science research vol. 7, no. 1, 2017, 1425-1428 1428 www.etasr.com fesghandis et al.: comparison of multilayer perceptron and radial basis function neural networks… using artificial neural networks. the networks were designed and implemented based on the multilayer perceptron and the radial basis function architecture. the comparison of two models showed that the radial basis function network provides a better prediction with lower error. therefore, corporate executives, particularly cloth manufacturers, are recommended to predict new products’ success beforehand. fig. 4. the calculated correlation between actual data and output data from the model for the best rbf fig. 5. results for rbf test data with 225 neurons table iv. selection of the best npd prediction method prediction method r2 rmse mse mlp 0.49852 0.72450 0.52490 rbf 0.67179 0.43164 0.18631 references [1] y. c. ho, y-c, c. t. tsai, “comparing anfis and sem in linear and nonlinear forecasting of new product development performance”, expert systems with applications, vol. 38, no. 1, pp. 6498–6507, 2011 [2] s. sheng, z. k. zheng zh, l. lessassy, l, “npd speed vs. innovativeness: the contingent impact of institutional and market environments”, journal of business research, vol. 66, no. 1, pp. 2355– 2362, 2013 [3] a. la rocca, p. moscatelli, a. perna, i. snehota, “customer involvement in new product development in b2b: the role of sales”, industrial marketing management, vol. 58, no. 1, pp. 45-57, 2016 [4] b. westfechtel, “models and tools for managing development processes”, springer, berlin, 1999 [5] m. crawford, a. di benedetto, new products management, irwinmcgraw hill, 9th edition, 2008 [6] e. fricke, b. gebhard, h. negele, e. isenberg’s, e, “coping with changes: causes, findings, and strategies”, systems engineering, vol. 3, no. 4, pp. 169-179, 2000 [7] k. otto, k. wood, k, “product design: techniques in reverse engineering, systematic design, and new product development”, prentice-hall, new jersey, 2001 [8] s. shane, k. ulrich, k.(2004), technological innovation, product development, and entrepreneurship in management science, management science, vol. 50, no. 2, pp.133144, 2004 [9] p. s. ghosal, a. k. gupta, “enhanced efficiency of ann using nonlinear regression for modeling adsorptive removal of fluoride by calcined ca-al-(no3)-ldh”, journal of molecular liquids, vol. 1, no. 222, pp. 564-570, 2016 [10] l. zjavka, “recognition of generalized patterns by a differential polynomial neural network”, engineering, technology & 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[16] r. cooper, “from experience: the invisible success factors in product innovation”, journal of product innovation and management, vol. 16, no. 2, pp. 115-133, 1999 [17] r. cooper, e. kleinschmidt, “what make a new product winner: success factors at the project level”, r&d management, vol. 17, no. 3, pp. 175189, 2007 [18] a. azadeh, m. saberi, r. tavakkoli moghaddam, l. javanmardi, “an integrated data envelopment analysis–artificial neural network– rough set algorithm for assessment of personnel efficiency”, expert systems with applications, vol. 38, no. 1, pp. 1364–1373, 2011 [19] j. e. dayhoff, neural network architectures: an introduction, van nostrand reinhold, new york, 1990 [20] t. khanna, “foundation of neural networks”, addison-wesley publishing, boston, 1990 [21] m. m. gupta, l. jin, l. homma, “static and dynamic neural networks”, john wiley & sons, new jersey, 2003 [22] z. f. liu, x. p. liu, s. w. wang, g. f. liu, “recycling strategy and a recyclability assessment model based on an artificial neural network”, journal of materials processing technology, vol. 129, no. 1, pp. 500506, 2002 [23] j. c. principe, artificial neural networks, crc lc press, university of florida, 2000 [24] x. huang, g. n. soutar, a. brown, “measuring new product success: an empirical investigation of australian smes”, industrial marketing management, vol. 33, no. 2, pp. 117-123, 2004 microsoft word 39-3130-dion_etasr_v9_n6_pp4795-4800 etasr engineering, technology & applied science research vol. 9, no. 5, 2019, 4795-4800 4795 www.etasr.com marin galvin: evaluating pollutants of emerging concern in aquatic media through e-prtr regulation evaluating pollutants of emerging concern in aquatic media through e-prtr regulation a case study: cordoba, spain, 2009-2018 rafael marin galvin control de calidad empresa municipal de aguas de córdoba, s.a. (emacsa) cordoba, spain rmargal@emacsa.es abstract-the eu e-prtr regulation can be followed for the evaluation of the level of pollutants of emerging concern in treated wastewater. this regulation is of regional responsibility in the ue, and establishes for the andalusian region of spain the following pollution parameters as mandatory to be controlled periodically in treated wastewater in waste water treatment plants (wwtps) with more than 100.000 equivalent inhabitants of treatment capacity: cod, kjeldahl n, total p, cl , f (conventional pollution); as, cd, cr, cu, hg, ni, zn and pb, as heavy metals; pahs (polycyclic aromatic hydrocarbons), adsorbed organic halides (aoxs), benzene and chloroform, as organic compounds. this paper shows results obtained in the application of the e-prtr regulation to the wastewater of cordoba during 2009-2018. as shown, average of cod, kjeldahl n an total p values, respectively, in urban and treated wastewater were 604 and 89 mg/l, 54.1 and 33.4 mg/l and 3.4 and 1.4 mg/l. with respect to heavy metals, the mean content in treated wastewater was 0.135 mg/l, starting from 0.226 mg/l in raw wastewater. the majority of these are cu and zn (0.043 mg/l and 0.107 mg/l, respectively, in raw wastewater). for pollutants of emerging concern, the mean content of pahs was 13 ng/l in treated water vs 31 ng/l in raw wastewater. moreover, concentration of aoxs in raw wastewater was of 20 ng/l while in treated wastewater decreased up to 16 ng/l. also, benzene content in raw wastewater and treated wastewater decreased from 40 ng/l to 11 ng/l. finally, the major organic compound was chloroform, with a level in raw wastewater of 5.6 µg/l that was reduced along the treatment up to 3.2 µg/l. the provided data indicated a low concentration of the compounds of emerging concern in the wastewater of cordoba and its minimal impact on the receiving aquatic environment (the guadalquivir river). keywords-pollutants; emerging concern; e-prtr regulation; heavy metals; haps; aoxs; benzene; chloroform. i. introduction control of conventional and emerging pollutants that could be present in treated wastewater [1-3] in spain, as well as the mandatory levels of compliance, are included in the discharge authorizations to environment, granted to the waste water treatment plant (wwtp) managers by the basin organizations (state or regional level) in compliance with the hydraulic public domain regulation (rd 509/1996). in this way, general limitations of 25 mg/l for bod5, 35 mg/l for suspended solids and 125 mg/l for cod, in addition to parametric values in n and p in sensitive aquatic media, are applicable for treated wastewater evacuated to aquatic environments [4-5]. on the other hand, the well-known eu e-prtr regulation applies a regional responsibility to basin organizations in each european country (according to the rd 508/2007 and law 5/2013 in spain), and it requires a yearly report of the emissions of several conventional and emerging pollutants present in treated wastewater discarded to aquatic media. however, the e-prtr, whose data are of public knowledge, does not mark restrictions on the pollutants nor economic or other penalty charges. in this sense, in the andalusian region, the following parameters were stablished as mandatory to be communicated periodically by the managers of the wwtps (with treatment capacity larger than 100.000 equivalent inhabitants) to the regional administration (junta de andalucia): • cod, kjeldahl n, p-total, cl , f as conventional pollutants; • as, cd, cr, cu, hg, ni, zn and pb, as heavy metals; • pahs (polycyclic aromatic hydrocarbons), adsorbed organic halides (aoxs), benzene and chloroform, as organic compounds. it must be indicated that heavy metals and organic compounds are clearly emerging pollutants (or pollutants of emerging concern) and they can serve indirectly to evaluate the presence of these substances in aquatic media. for this reason, this paper presents the result of the mandatory monitoring carried out in the municipal sanitation of cordoba in 20092018, considering the e-prtr, as an insight to the contribution of this city’s wastewater to the contamination of environment water (mainly the guadalquivir river). corresponding author: r. marin galvin etasr engineering, technology & applied science research vol. 9, no. 5, 2019, 4795-4800 4796 www.etasr.com marin galvin: evaluating pollutants of emerging concern in aquatic media through e-prtr regulation ii. materials and methods the data presented in this paper refers to treated wastewater in la golondrina´s wwtp (emacsa-cordoba) along the 2009-2018 period and corresponding to both, raw and treated urban wastewater. the urban wastewater studied is that of the sanitation of the city of cordoba (327,000 inhabitants) that includes 15% of industrial component. la golondrina´s wwtp (maximum treatment capacity=148,000 m 3 /d) is operated by aerobic activated sludge process being its average flow of treatment along 2009-2018 around 26 hm 3 . treated wastewater is after discarded to guadalquivir river (figure 1). fig. 1. location of cordoba and guadalquivir river at spain. screenshot from google maps, map data © 2015 google. the considered wwtp performs the following operations through its several components [4-5]: lifting wastewater by means of archimedean screws, thick and thin sieves, removing of sand and oil-greases, primary settling (not adding of chemical reactants), biological treatment with atmospheric air dossing (the plant has also installed anaerobic selectors by removing of filamentous microorganisms (24% of total surface of biological treatment)), secondary settling, discarding of treated wastewater to guadalquivir river, treatment and reuse for agricultural practices of sludge produced. for the study carried out, we have taken integrated samples of raw and treated wastewater, along periods of 24 h, with monthly frequency. all the applied techniques have been the usual in water analysis [5-6]. in this sense, organics compounds were analyzed by gass chromatography-mass spectrometry (gc-ms) while heavy metals, by induced coupling plasmamass spectrometry (icp-ms) and aoxs, finally, by combustion and coulometry. on the other hand, cod was obtained through sample digestion in sulphuric media by using the known method of potassium dichromate, kjeldahl n corresponded to n obtained after digesting samples in acidic medium with potassium sulphate (kjeldahl n method) and total p was obtained by means icp-ms. finally, chloride and fluoride were determined by means ionic chromatography. iii. results and discussion la golondrina ś wwtp is authorized to discharge in guadalquivir by the watershed agency (guadalquivir hydrographic confederation or chg) with the last renovation of this authorization given in 2014. the wwtp quite reach the purification criteria required, and during the period 2009-2018 it achieved mean annual average values of chemical oxygen demand (cod) of 89 mg/l, biochemical oxygen demand (bod5) of 12 mg/l, and suspended solids (ssusp) of 17 mg/l, being the initial levels of, respectively, 604 mg/l, 367 mg/l and 311 mg/l. the evolution of yearly flow of wastewater treated in the wwtp is shown in figure 2. the 2011 and 2013 years were that of higher treated flow, and 2015 and 2017 that of lower treated flow. fig. 2. evolution per year of flow of wastewater in la golondrina wwtp during 2009-2018. a. conventional pollution in this category we have included the following substances: cod, kjeldahl n and total p [5-6]. in this way, the mean average cod values in urban and treated wastewater (as indicated above) were 604 and 89 mg/l, respectively, as well as 54.1 and 33.4 mg/l for n-kjeldahl, and 3.4 and 1.4 mg/l for total p. on the other hand, the evolution for the above parameters in 2009-2018 is presented in figure 3. moreover, it must be taken into account that these parameters quantify different forms of organic matter present in raw and treated wastewater [4-6] and they are not equivalent. with relation to cod in raw wastewater the highest values were detected between 2009 and 2012, keeping since then reasonably stable; mean while, those of cod in treated water were always below 100 mg/l, except in 2009. in any case, the average cod removal rate in the plant was high, at 86%. regarding the kjeldahl n behavior, the correlation between raw and treated wastewater is very remarkable, with an average reduction rate in the plant of 38%, the highest values having been detected in 2012 and 2018 in raw wastewater, and in 2009 and 2018 in treated wastewater. in addition, there seems to be an upward trend in the kjeldahl n content from 2013 onwards, which can be explained both, by the decrease in treated flow (increase of concentration) and by the ascertainable increase in nitrogen compounds in household products. with respect to the total p, the average elimination in the plant was 60%, with higher values at the beginning of the study (2009-2010) and from 2015 onwards. in this sense, two periods are identified in the sequence obtained: since 2009 to 2013, with a tendency to decrease values; and from here until 2018 with a sustained etasr engineering, technology & applied science research vol. 9, no. 5, 2019, 4795-4800 4797 www.etasr.com marin galvin: evaluating pollutants of emerging concern in aquatic media through e-prtr regulation increase in total p levels in both, raw and treated wastewater, whose explanation can be shared with that already given for the case of nitrogen. fig. 3. evolution per year of: cod (up); kjeldahl n (middle); total p (down). raw wastewater (squares-striped line); treated wastewater (dotscontinuous line). the evolution of cl and f in both, raw and treated wastewater is shown in figure 4. it can be observed that the average cl content is higher in treated wastewater than in raw wastewater (96.8 mg/l vs. 109.1 mg/l, respectively). this circumstance is due to the use in the wwtp of ferric chloride in the treatment process carried out to treat a specific industrial discharge of high polluting load, which must be treated before its incorporation into the flow of total urban wastewater. this effluent, treated via anaerobic, requires the use of ferric salts that promote enrichment in cl of treated wastewater. on the other hand, the mean average f content of the raw and treated wastewater was practically the same (0.21 mg/l); in this way, this substance was weakly affected with biological treatment, as would be expected. it is also worth mentioning that the levels since 2011-2012 were significantly lower as result of the progressive cessation of activity of a glass industry in the city, and logically, with the non-existence of effluents rich in f to sanitation network. fig. 4. evolution per year of: cl (up); f (down). raw wastewater (squares-striped line); treated wastewater (dots-continuous line). b. heavy metals table i shows the mean average values of the eight heavy metals investigated during our study, both in raw urban wastewater and in the treated one. of all the heavy metals investigated, zn and cu were the majority: mean levels along our study were 0.107 mg/l and 0.071 mg/l for zn, and 0.043 mg/l and 0.018 mg/l for cu, raw and treated wastewater, respectively. on the other hand, the rest of metals did not exceed 0.010 mg/l in raw water (ni) or in treated water, except pb, with 0.011 mg/l in the final discharge to river (treated wastewater). table i. levels of heavy metals (2008-2019) heavy metal raw wastewater (mg/l) treated wastewater (mg/l) arsenic (as) 0.005 0.004 cadmium (cd) 0.004 0.006 chrome (cr) 0.009 0.007 copper (cu) 0.043 0.018 lead (pb) 0.009 0.011 mercury (hg) 0.002 0.003 níckel (ni) 0.010 0.008 zinc (zn) 0.107 0.071 the origin of the presence of cu and zn in wastewater is clearly industrial since in cordoba there are several industries of copper and brass processing; on the contrary, the rest of the metals have varied origins (table ii), both industrial, domestic and still diffuse [4-5, 7, 15-16]. the total content of heavy metals in urban wastewater was 0.226 mg/l while in treated etasr engineering, technology & applied science research vol. 9, no. 5, 2019, 4795-4800 4798 www.etasr.com marin galvin: evaluating pollutants of emerging concern in aquatic media through e-prtr regulation wastewater it was reduced to 0.135 mg/l, reaching a reduction of 40%. it should also be noted that, in the cases of cadmium, mercury and lead, a slight increase in treated wastewater was detected compared to those of the initial content, which could be due to light and slow desorption phenomena from biological sludge to wastewater in the wwtp. table ii. origin s of heavy metals in wastewater. heavy metal uses and applications observations arsenic (as) wood preservative, semiconductors and lasers, metallurgical industry, pigment and pyrotechnics, glass manufacturing, pesticides (very deprecated) cadmium (cd) batteries, special surface treatments, pigments, pvc stabilizers, alloys, electronic components, welding it appears as an impurity in phosphate fertilizers, detergents and refined petroleum products chrome (cr) manufacture of steels, dyes and paints, wood preservation, ammonia synthesis, manufacture of refractory and ceramic materials, and lasers, magnetic tapes, water analysis (cod) copper (cu) water installations, electrical installations car industry, coins, ceramics, algicide, pig farms lead (pb) batteries, car industry, jewelry, industrial paintings mercury (hg) thermometers, lamps, catalysts, alloys, amalgams, explosives, medical applications, switches it can be mobilized naturally from its deposits níckel (ni) alloys, surface treatments, pigments, batteries, jewelry, catalysts zinc (zn) batteries, pipes, glass flux, pigments, alloys, welding, sulfuric acid manufacturing, gasoline additive, ammunition, paints, insecticides c. organic compounds in this category we have included the following substances or group of substances: pahs, aoxs, benzene and chloroform [7-11, 13-15, 17]. the total of the five pahs investigated (benzo(a)pyrene, benzo(b) and (k)fluorantene, benzo(g,h,i,) perylene and indene(1,2,3-c, d)pyrene) was of 31 ng/l in raw wastewater decreasing to 13 ng/l in treated wastewater (58% reduction). the emission of pahs to wastewater is related to use of fossil fuels (fuel or diesel in boilers) and cars (gasoline). in the sequence studied, the years 2010, 2015, 2016 and 2018 presented the maximum values of those measured, with concentrations between 50 and 100 ng/l (figure 5) which did not really affected the concentration of pahs in treated wastewater. as for aoxs, the so-called adsorbed organic halides are organic substances that contain one or more atoms of a halogen element (generally cl, although there are also compounds formed with br and i). they can be simple and volatile substances (trichlorethylene, for example) or complex organic molecules such as dioxins and furans, which can have a wide variety of physical properties. dioxins and furans are toxic substances at very low levels, being solid and crystalline compounds, very little soluble in water, but easily soluble in organic solvents, fats and oils. the emission of dioxins and furans to the environment comes from incineration and combustion processes (garbage and other solid waste, medicines, biological remains and other dangerous elements). they also can be byproducts of metallurgical processes (high temperature steel production, recovery of metals in blast furnaces, combustion of coal, wood, used petroleum products and tires), chlorine production and organic chlorinated derivatives for different purposes (insecticides, herbicides, catalysts and intermediate products for the synthesis of other substances) and, finally, from paper production. finally, other minor sources of emission are the processes of disinfection with chlorine of drinking water, disinfection of swimming pool water, and those of process water in industrial laundries. fig. 5. evolution per year of: pahs (up); aoxs (µg/l) (down). raw wastewater (squares-striped line); treated wastewater (dots-continuous line). the average concentration of aoxs was reduced by 20% in the treatment, from 20 ng/l to 16 ng/l. these compounds emanates specially from a paper industry located in cordoba, in addition to the tap water itself and the discharges to the sanitation of public and private pool waters (very notable activity in the city due to its hot weather). figure 5 shows the evolution of aoxs in raw wastewater and treated one throughout the study: the years 2015 and 2016 exhibited the maximum detected near 100 ng/l in raw wastewater, and somewhat lower in the treated one. benzene is employed in the manufacture of other chemicals used for the manufacture of plastics, resins, nylon and synthetic fibers, as well in the manufacture of different types of rubber, lubricants, dyes, detergents, medicines and pesticides. benzene is usually the main compound of all the benzene compounds present in wastewaters (between they, naphthalene, phenanthrene, xylene) [13, 17]. likewise, fires in general and forest fires in particular represent the main natural sources of benzene emissions, although it is also a natural constituent of crude oil, gasoline and cigarette smoke. it is, therefore, a clear exponent of the diffuse contamination of our environment (also in cordoba). the evolution of benzene in wastewater and treated wastewater during 2009-2018 is shown in figure 6. this compound etasr engineering, technology & applied science research vol. 9, no. 5, 2019, 4795-4800 4799 www.etasr.com marin galvin: evaluating pollutants of emerging concern in aquatic media through e-prtr regulation evolved from 40 ng/l in raw wastewater to 11 ng/l in treated wastewater (a 72% reduction). to highlight, in the year 2013 with a maximum of 290 ng/l in raw wastewater no increase was detected in treated wastewater (39 ng/l was the mean value in that year). fig. 6. evolution per year of benzene. raw wastewater (squares-striped line); treated wastewater (dots-continuous line). finally, the majority organic compound of those investigated was chloroform. this compound is used primarily as a solvent for organic compounds and as a component of some fire extinguishers, although it is also involved in the manufacture of dyes, being almost a generic fumigant and insecticide. however, its main source for sanitation in urban wastewater is tap water: this one yet contains chloroform as a disinfection byproduct [13-15, 17]. figure 7 shows the evolution of chloroform content in raw and treated wastewater during our study: two periods of higher levels are years 2009 to 2011 and 2013-2014, with values higher than 5 µg/l, while in the rest of the years investigated the levels were below 2 µg/l in raw wastewater. otherwise, the highest values in treated wastewater corresponded to 2011, 2013 and 2014 with close levels and even slightly higher than 5 µg/l. computing the average concentrations during the period studied, the level in the treated effluent was 3.2 µg/l compared to the initial in urban wastewater of 5.6 µg/l (42% reduction in plant). as reference, the city's drinking water contains chloroform in the order of 10 µg/l, justifying clearly the origin of this substance in the wastewater. fig. 7. evolution per year of chloroform. raw wastewater (squares-striped line); treated wastewater (dots-continuous line). iv. conclusions the well-known eu e-prtr regulation shows a regional responsibility to basin organizations in each european country requiring a report of the content of several pollutants present in treated wastewater discarded to aquatic media. in this study, covering the time span of 2009 to 2018, analysis in the wastewater of cordoba, spain shows that the average cod values in urban and treated wastewater were 604 and 89 mg/l, respectively, for kjeldahl n was 54.1 and 33.4 mg/l respectively, and for total p was 3.4 and 1.4 mg/l respectively. their origin is both domestic and industrial. in relation to heavy metals, their average content in treated wastewater was 0.135 mg/l, 0.226 mg/l in raw wastewater, mostly of cu and zn. their presence is mostly due to copper and brass processing industries located in the city. regarding contaminants of emerging concern, the average content of pahs in treated wastewater was 13 ng/l with a 58% reduction from the content found in raw water. it is estimated that its majority origin is the use of fossil fuels in industries, homes and urban traffic. in relation to aoxs, the concentration in raw wastewater, 20 ng/l, was decreased by 20% along the treatment. its major source seems to be a paper industry located in the city. the benzene content in wastewater and treated wastewater was 40 ng/l and 11 ng/l respectively (reduction of 72%). finally, the major organic compound was chloroform, with a level in raw wastewater of 5.6 µg/l, which was reduced to 3.2 µg /l after treatment. the chloroform contained in tap water and pool renewal water was essentially the origin of the levels detected. the data verify the low concentrations of compounds of emerging concern in the wastewater of cordoba and their minimal impact on the aquatic environment. references [1] d. barcelo, m j. lopez, “contaminacion y calidad química del agua: el problema de los contaminantes emergentes”, panel científico-técnico de seguimiento de la política de aguas, instituto de investigaciones químicas y ambientales-csic, barcelona, 2007 (in spanish) [2] r. lopez, r. r. irusta, “tendencias en el tratamiento de contaminantes emergentes”, foro regional de sostenibilidad e i+d+i (junta de castilla y leon), 2010 (in spanish) [3] m. j. gil, a. m. soto, j. i. usma, o. d. gutierrez, “contaminantes emergentes en aguas, efectos y posibles efectos”, produccion+limpia, vol. 7, no. 2, pp. 52-73, 2012 (in spanish) [4] metcalf and eddy, wastewater engineering: treatment and reuse, 4th ed., mc graw hill, boston, 2003 [5] r. marín galvin. fisicoquimica y microbiologia de los medios acuáticos. tratamiento y control de calidad de aguas, 2ª ed. ed. diaz de santos, madrid, 2018 (in spanish) [6] american water works association, standard methods for the examination of water and wastewater, water environment federation, 23rd ed., new york, 2017 [7] r. marin galvin, “el estado de las aguas continentales espanolas y la contribucion de las edar en su consecucion”, virtualpro, no. 208, pp. 1-30, 2019 [8] m. petrovic, s. gonzalez, d. barcelo, “analysis and removal of emerging contaminants in wastewater and drinking water”, trends in analytical chemistry, vol. 22, no. 10, pp. 685-696, 2003 [9] t. reemtsma, s. weiss, j. mueller, m. petrovic, s. gonzalez, d. barcelo, f. ventura, t. p. knepper, “polar pollutants entry into the water cycle by municipal wastewater: a european perspective”, environmental science and technololgy, vol. 40, no. 17, pp. 54515458, 2006 etasr engineering, technology & applied science research vol. 9, no. 5, 2019, 4795-4800 4800 www.etasr.com marin galvin: evaluating pollutants of emerging concern in aquatic media through e-prtr regulation [10] a. musolff, s. leschik, m. moder, g. strauch, f. reinstorf, m. schirmer, “temporal and spatial patterns of micropollutants in urban receiving waters”, environmental pollution, vol. 157, no. 11, pp. 3069– 3077, 2009 [11] g. teijon, l. candela, k. tamoh, a. molina-diaz, a. r. fernandezalba, “occurrence of emerging contaminants, priority substances (2008/105/ce) and hevay metals in treated wastewater and groundwater at depurbaix facility (barcelona, spain)”, science of the total environment, vol. 408, no. 17, pp. 3584-3595, 2010 [12] p. j. simon andreu, c. lardin mifsut, r. gonzalez herrero, a.v. sanchez beltran, j. a. vicente gonzalez, “estudio de la presencia de contaminantes emergentes en las distintas etapas de las depuradoras”, retema, vol. 186, pp. 84-91, 2015 (in spanish) [13] s. sauve, m. desrosiers, “a review of what is an emerging contaminant”, chemistry central journal, vol. 8, no. 15, pp. 1-7, 2014 [14] c. c. montagner, c. vidal, r. d. acayaba, “contaminantes emergentes em matrizes aquáticas do brasil: cenário atual e aspectos analiticos, ecotoxicologicos e regulatorios”, quimica nova, vol. 40, no. 9, pp. 1094-1110, 2017 (in spanish) [15] r. marin galvin, “emerging pollutants and heavy metals into spanish sanitation: a case study”, scirea journal of enivronment, vol. 2, no. 1, pp. 1-11, 2017 [16] k. khaskhoussy, b. kahlaoui, b. messoudi nefzi, o. jozdan, a. dakhell, m. hachicha, “effect of treated wastewater irrigation on heavy metals distribution in a tunisian soil”, engineering, technology & applied science research, vol. 5, no. 3, pp. 805-810, 2015 [17] m. narasimha vara prasad, m. vithanage, a. kapley, pharmaceuticals and personal care products: waste management and treatment technology, butterworth-heinemann, 2019 microsoft word 1-2696-s_etasr_v9_n4_pp4315-4321 engineering, technology & applied science research vol. 9, no. 4, 2019, 4315-4321 4315 www.etasr.com verginadis et al.: study of the phenomena of surface discharges and flashover in nanocomposite … study of the phenomena of surface discharges and flashover in nanocomposite epoxy resin under the influence of homogeneous electric fields d. verginadis democritus university of thrace, department of electrical and computer engineering, xanthi, greece dimoverg2@ee.duth.gr m. g. danikas democritus university of thrace, department of electrical and computer engineering, xanthi, greece mdanikas@ee.duth.gr r. sarathi indian institute of technology madras department of electrical engineering chennai, india sarathi@ee.iitm.ac.in abstract—a new class of insulating materials is the class of polymer nanocomposites. in the past twenty-five years, a lot of attention was paid to the various electrical, thermal and mechanical properties of polymer nanocomposite materials. in the present work, epoxy resin samples without and with nanoparticles (0 wt%, 1 wt%, 3 wt%, 5 wt%, and 10 wt%) are investigated regarding the surface discharges and the flashover voltages. four different water droplet arrangements were used, with eight different water conductivities in order to see the effect of the nanoparticle content on the surface discharges and the flashover voltages. keywords-polymer nanocomposites; nanoparticles; surface discharges; flashover voltage i. introduction a nanocomposite is defined as a material having constituents, one of which has dimensions in the nanorange. intensive research in the field of nanocomposites started especially after the publication of [1]. numerous other publications followed explaining the workings of such materials [2, 3]. models have been proposed and commented upon regarding the behavior of the polymer nanocomposites [4, 5]. it was shown that polymer nanocomposites present improved electrical, thermal and mechanical properties compared with the respective conventional polymers. polymer nanocomposites have been applied in various industries, such as the automobile industry, the building industry and the food industry. although much research has been carried out on various aspects of polymer nanocomposites, relatively little is known w.r.t. their surface discharge and flashover behavior [6]. as reported before, surface phenomena in polymer nanocomposites are important because they determine to a significant extent their behavior in indoor as well as in outdoor high voltage applications [7]. surface discharges and consequently the flashover phenomenon are due, among other factors, to the presence of water droplets on the polymer nanocomposite surface. it is the aim of this paper to investigate the influence of various water droplet arrangements, with various water conductivities, under uniform electrical fields on epoxy resin nanocomposite surfaces. a sample with no nanoparticles at all was used as reference. the epoxy resin nanocomposites contained nanoparticles of percentages 1wt%, 3wt%, 5wt% and 10wt%. the present work continues previous work conducted with the same samples [7]. ii. water droplet behavior water droplets on an insulating surface under the influence of an electrical field tend to deform. surface discharges follow such deformation. dry zones may ensue, then local arcs and finally a flashover. such a sequence of events is more or less common in both indoor and outdoor high voltage applications, although there are some differences [8, 9]. when a droplet becomes unstable because of a deformation, tiny droplets may be rocketed from it. the initial droplet oscillates violently and the tiny droplets are highly charged. the main droplet becomes smaller in size as well as in electric charge. under an electric field this is an ongoing process which may lead to intense surface discharging, formation of dry zones and then local arcing. relevant research performed in the past revealed that, in the case of polymer nanocomposites, the contact angle of the water droplet increases with the increase of the nanoparticle content and that the positioning of the droplet w.r.t. the electrodes is also important [10, 11]. iii. experimental arrangement and insulating materials the experimental arrangement used is described in detail in earlier publications [7, 12] and only a brief mention will be given here. the voltage was supplied from a 20kv transformer. the electrodes were made of copper and had a half cylindrical shape with rounded edges. needless to say that care was taken so that their surfaces were very smooth. the water droplets are shown in figures 1-4, and they were positioned on the sample in four different arrangements. it must be emphasized that two of the droplet arrangements in the present paper (those of figures 3 and 4) are different from the ones described in [7]. eight different water conductivities were used, namely 1.4µs/cm, 100µs/cm, 200µs/cm, 500µs/cm, 1000µs/cm, 2000µs/cm, 5000µs/cm and 10000µs/cm. in figure 1, one droplet of volume 0.05ml (or 0.1ml) was put at a distance of corresponding author: m. g. danikas engineering, technology & applied science research vol. 9, no. 4, 2019, 4315-4321 4316 www.etasr.com verginadis et al.: study of the phenomena of surface discharges and flashover in nanocomposite … 1.25cm from the electrodes. in figure 2, two droplets (each of 0.05ml or 0.1ml) were positioned one next to the other at a distance of 0.8cm between them and 0.8cm from the electrodes. in figure 3, two droplets were positioned one on top of the other of 0.05ml (or of 0.1ml) at a distance of 1.25cm from the electrodes and at a distance of 1 cm from each other. in figure 4, three droplets were positioned, each of 0.05ml (or 0.1ml) at a distance of 1.25cm from the electrodes. fig. 1. one-droplet arrangement fig. 2. two-droplets arrangement fig. 3. two-droplets arrangement the polymer nanocomposite used was epoxy resin plates having nanoparticles with 1wt%, 3wt%, 5wt% and 10wt%. a reference sample with no nanoparticles at all was also used.the epoxy nanocomposite was synthesized by mechanical shear mixing of organo-clay in the resin bath at room temperature. the high speed shear mixer consists of an impeller which rotates at a high speed of 2000rpm.the clay mineral used was organophilic montmorillonite (mmt) procured from southern clay products inc. (gonzales, texas) with the trade name of garamite1958 (colour: off white, bulk density: 1.5-1.7g/cc, weight loss at 10000c: 37%, d spacing at d001: 17.2å). fig. 4. three-droplets arrangement after uniform mixing of mmt clay in epoxy resin (which was dgeba, cy205, ciba geigy inc.), 10 wt% of triethylenetetramine (teta) hardener was added and then casted in a mould of required dimension and then degassed. the mmt clay belongs to a family of 2:1 layered silicates. epoxy nanocomposites of 3mm thickness with different percentages (1–10%) of clay were prepared [7]. the surface roughness of the samples was measured with a perthen device (perthometer m4p) and it gave the following results (minimum-maximum roughness): for the 0wt% (reference) sample from 0.59µm to 0.69µm, for the 1wt% sample from 0.60µm to 0.79µm, for 3wt% sample from 0.49µm to 0.59µm, for the 5wt% sample from 0.60µm to 0.68µm and for the 10wt% sample from 0.22µm to 0.22µm. iv. experimental method the parameters investigated in this work were the water conductivity, the number of droplets, the droplet volume and the positioning of the droplets w.r.t. the electrodes. the experimental method followed was the same as in previous papers [7] and it will briefly be given here: the droplet(s) were put on the polymer surface. then the voltage was raised until flashover happened. after that, new droplet(s) of the same number, volume and positioning were put on the surface and the voltage was raised up to a voltage which was lower by 1.2kv from the previous flashover. at this voltage the whole arrangement would stay for 5 minutes. if no flashover occurred, the voltage was raised by further 0.4kv and kept for another 5 minutes and this went on until flashover occurred. that was the flashover that was recorded. the reason the voltage was allowed to stay for 5 minutes at each value was because we wanted to see whether the droplet (or droplets) were deforming and whether surface discharging was starting. as in the previous publication [7], we thought that 5 minutes was enough time in order to see the oscillation and eventual deformation of the droplet(s), the development of surface discharges and the actual flashover. needless to say that for every new experiment, the electrodes were meticulously cleaned. the distance between the electrodes in all experiments was set at 2.5cm. the droplets were put on the polymer surface with the aid of a syringe. different syringes were used for the different water conductivities. flashover occurred either through the air (figure 5) or through the droplets (figure 6). v. experimental results figure 7 shows the variation of flashover voltage with water conductivity for one droplet of 0.05 ml. figure 8 shows the engineering, technology & applied science research vol. 9, no. 4, 2019, 4315-4321 4317 www.etasr.com verginadis et al.: study of the phenomena of surface discharges and flashover in nanocomposite … variation of flashover voltage with water conductivity for two droplets next to each other, each having a volume of 0.05ml. fig. 5. flashover through the air fig. 6. flashover through the water droplets figure 9 shows the variation of flashover voltage with water conductivity for two droplets of 0.05 ml each and being one on top of the other. figure 10 shows the variation of flashover voltage with water conductivity for the three droplets, each having a volume of 0.05ml. figure 11 shows the variation of flashover voltage with water conductivity for one droplet of 0.1ml. figure 12 shows the variation of flashover voltage with water conductivity for two droplets next to each other, each having a volume of 0.1ml. figure 13 shows the variation of flashover voltage with water conductivity for two droplets of 0.1ml each and being one on top of the other. figure 14 shows the variation of flashover voltage with water conductivity for the three droplets, each having a volume of 0.1ml. it must be noted that in all figures the blue line indicates the sample with 0wt% nanoparticles, the red line indicates the sample with 1wt% nanoparticles, the yellowline indicates the sample with 3wt% nanoparticles, the purple line indicates the sample with 5wt% nanoparticles and the greenline indicates the sample with 10wt% nanoparticles. vi. discussion in most experiments there was an oscillation of the droplet(s), which eventually were breaking up. for the droplets arrangement of the three droplets, it was noticed that there was too often a deformation and eventual break-up of the middle droplet. in the case of the two droplets, with one next to the other, it was often observed an oscillation and eventual coming together of the two droplets. in all results, irrespective of the number and/or the volume of droplets, water conductivity seems to lower the flashover voltage. as the conductivity increases, the flashover voltage decreases. the volume of the droplets plays also an important role, i.e. the flashover voltage seems to be lower for the 0.1ml droplet(s) than for the 0.05ml droplet(s). the positioning of the droplets w.r.t. the electrodes plays also a vital role, i.e. as the distance of the droplet(s) from the electrodes becomes smaller, the flashover voltage decreases (compare for example, the results between figures 12-13). fig. 7. comparison of flashover voltages for one droplet of 0.05ml fig. 8. comparison of flashover voltages for two-droplets arrangement of 0.05ml each (one droplet next to the other) engineering, technology & applied science research vol. 9, no. 4, 2019, 4315-4321 4318 www.etasr.com verginadis et al.: study of the phenomena of surface discharges and flashover in nanocomposite … fig. 9. comparison of flashover voltages for two-droplets arrangement of 0.05ml each (one droplet on top of the other) fig. 10. comparison of three-droplets arrangement of 0.05ml each fig. 11. comparison of one-droplet arrangement of 0.1ml fig. 12. comparison of two-droplets arrangement of 0.1ml each (one droplet next to the other) engineering, technology & applied science research vol. 9, no. 4, 2019, 4315-4321 4319 www.etasr.com verginadis et al.: study of the phenomena of surface discharges and flashover in nanocomposite … fig. 13. comparison of two-droplets arrangement of 0.1ml each (one droplet on top of the other) fig. 14. comparison of three-droplets arrangement of 0.1ml each this reminds us of a similar effect with the partial discharges, where cavities next to electrodes give higher discharge magnitudes than cavities which are totally enclosed in the solid insulation [13-15]. certainly, the proximity with the electrodes seems to initiate more easily electron emission in either case. the polymer nanocomposite surface is of great importance for the flashover data. it seems that nanocomposites with 1wt% and 3wt% nanoparticles have higher flashover voltages than the pure epoxy resin (with 0wt%), whereas the sample with 5wt% nanoparticles has comparable flashover voltages with the pure epoxy resin. the polymer nanocomposite with 10wt% nanoparticles gives the lowest results, even lower than the pure epoxy resin. the fact that polymer nanocomposites have higher flashover voltages than pure epoxy resin seems to agree with previous published research [16], where it was pointed out that the depth of erosion in pure polymers is larger than the erosion depth of polymer nanocomposites. this was attributed to the coming onto the surface of the nanoparticles and this contributes to the lowering of the surface discharges. however, as noted, a big increase of nanoparticle content does not necessarily imply the increase of flashover voltage. the 10wt% nanocomposite in our experiments did not perform well, even in comparison with the pure epoxy resin. the results of the present work agree with those published before, albeit with somehow different droplet arrangements [7, 17]. it may be that, as the percentage of nanoparticles increases beyond a certain value, agglomerations of nanoparticles may appear which may be sites of further discharging and of eventual erosion of the nanocomposite surface. this explanation, however, has to be further investigated. an ever increasing percentage of nanoparticles in a polymer may not be advisable in the light of other experimental evidence, as was noted elsewhere [18, 19]. the problem of the negative effect of exceeding nanoparticle content in a polymer has to be further investigated. a lot of research has been done regarding the effect of nanoparticle agglomerations on partial discharge activity [20, 21]. it is established that nanoparticle agglomerations may hinder the electrical performance of a polymer nanocomposite and may lower its breakdown strength. however, when one comes to the surface discharge behavior of the polymer nanocomposites, relevant information is missing or it is rather scant. there are reports of improvement of flashover voltage with the addition of carbon black nanoparticles (1 wt%) in ethyl-vinyl acetate [22]. according to the authors of [22], the improvement is attributed to the introduction of deeper traps capturing the charges and thus increasing the flashover voltage. in yet another work [23], the authors claimed that low nanoparticle content (1wt%) increases the density of deep traps and helps in improving the flashover voltage. however, with higher nanoparticle content, distances between adjacent nanoparticles decrease. overlapped interaction zones of nanoparticles are quasi-conductive and they raise the energy level of traps. deep traps are replaced by shallow traps and the latter contribute to charge dissipation. this in turn increases the mobility of carriers and increases the conductivity of nanocomposites. consequently, charge carriers tend to move engineering, technology & applied science research vol. 9, no. 4, 2019, 4315-4321 4320 www.etasr.com verginadis et al.: study of the phenomena of surface discharges and flashover in nanocomposite … through connected interaction zones more freely and thus triggering of a surface flashover becomes more probable. the above may be an explanation as to why higher nanoparticle content lowers the flashover voltage, but it is advisable to perform further research on the subject. an interesting topic of further contemplation may be about the role of nanoparticle agglomerations, since these, although they play a negative role in internal discharges, at least according to some researchers may play a positive role for surface flashover [16]. according to [16], nanoparticles may come onto the surface after the occasional erosion, and thus may act as minute barriers against the development of either a surface discharge or a flashover. there is, however, another point of view offered in [24]. according to [24], nanoparticles coming onto the surface of the nanocomposite, may agglomerate and cause local asymmetrical fields because of their higher dielectric constant. further work is urgently needed in order to clarify the whole mechanism. needless to say that all the above have to be investigated in the light of the morphology of polymer matrix, of processing conditions, of lamellar thickening process, and of crystallinity [25]. the present experimental results give an idea as to the parameters affecting the water droplet behavior on conventional and nanocomposite polymeric surfaces. a better picture may emerge if there will be more experiments w.r.t. the evolution of droplets with time. it is hoped that with this kind of experiments, details of the break-up of droplets will emerge with the aid of ultra-fast photographic apparatus. even more interesting would be the clarification of the role of nanoparticles with surface ageing, since it was reported that nanoparticles affect decisively the surface roughness during the ageing process [26]. the results of the present work point out to the influence of water conductivity, number of droplets as well as of their positioning on the flashover voltage. relatively little influence has the surface roughness of the polymer nanocomposite, as is evident in the results presented here. the latter remark is at variance with previously published work [27] (it must, however, be noticed that in [27], different insulating materials from the ones used in this work were used). the 10wt% nanocomposite has the lowest roughness but it also has the worst performance from all samples. the conclusions of the present work, regarding the above mentioned factors, agree qualitatively with previously published research [28, 29]. vii. conclusions factors that affect the flashover voltage in polymer nanocomposites are the water droplet conductivity, the number of droplets on the polymer surface and the positioning of the droplets w.r.t. the electrodes. the highest flashover voltages were noted with samples having nanoparticles in the range of 1 wt% up to 3 wt%. such percentages agree qualitatively with experimental results of other researchers. higher nanoparticle content may cause a decrease of flashover voltage. whether this is due to nanoparticle agglomerations or whether it is due to some inner workings of interaction zones between the nanoparticles remains to be seen. acknowledgment the present work was carried out with samples of epoxy resin nanocomposites, which were built at the department of electrical engineering, indian institute of technology madras, india. references [1] t. j. lewis, “nanometric dielectrics”, ieee transactions on dielectrics and electrical insulation, vol. 1, pp. 812-825, 1994 [2] j. k. nelson, dielectric polymer nanocompsites, springer, 2010 [3] t. tanaka, “dielectric nanocomposites with insulating properties”, ieee transactions on dielectrics and electrical insulation, vol. 12, no. 5, pp. 914-928, 2005 [4] m. g. danikas, “on two nanocomposite models: differences, similarities and interpretational possibilities regarding tsagaropoulos’ model and tanaka’ s model”, journal of electrical engineering, vol. 61, no. 4, pp. 241-246, 2010 [5] g. melissinos, m. g. danikas, “on polymer nanocomposites: electrical treeing, breakdown models and related simulations”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2627-2632, 2018 [6] t. tanaka, t. imai, “advances in nanodielectric materials over the past 50 years”, ieee electrical insulation magazine, vol. 29, no. 1, pp. 1023, 2013 [7] s. c. kechagia, m. g. danikas, r. sarathi, “water droplets and breakdown phenomena on polymer nanocomposite surfaces under the influence of uniform electric fields”, malaysian polymer journal, vol. 8, no. 2, pp. 41-48, 2013 [8] r. gorur, “high voltage outdoor insulation technology”, control and dynamic systems, vol. 44, pp. 131-191, 1991 [9] m. g. danikas, “surface phenomena on resin-type insulators under different electrical and non-electrical stresses in the early stage of ageing”, facta universitatis, vol. 13, no. 3, pp. 335-352, 2000 [10] r. s. sahu, understanding the electrical, thermal and mechanical properties of epoxy nanocomposites, ph.d. thesis, indian institute of technology madras, department of electrical engineering, chennai, india, 2007 [11] r. sarathi, m. g. danikas, “understanding discharge activity due to water droplet in epoxy nanocomposites using acoustic emission technique”, journal of electrical engineering, vol. 59, no. 6, pp. 294301, 2008 [12] a. bairaktari, m. g. danikas, x. zhao, y. cheng, y. zhang, “behavior of water droplets under the influence of a uniform electric field in nanocomposite samples of epoxy resin/tio2”, engineering, technology & applied science research, vol. 3, no. 5, pp. 511-515, 2013 [13] j. h. mason, “discharges”, ieee transactions on electrical insulation, vol. 13, no. 4, pp. 211-238, 1978 [14] m. s. naidu, v. kamaraju, high voltage engineering, mcgraw-hill publishing, 2000 [15] a. a. hossam-eldin, s. s. dessouky, s. m. el-mekkawy, r. a. abd elaal, “internal discharge in cavities in solid dielectric materials”, journal of electrical engineering, vol. 9, no. 4, pp. 1-5, 2009 [16] m. kozako, r. kido, t. imai, t. ozaki, t. shmizu, t. tanaka, “surface roughness change of epoxy/tio2 nanocomposites due to partial discharges”, 2005 international symposium on electrical insulating materials, kitakyushu, japan, june 5-9, 2005 [17] s. k. kechagia, flashover phenomena on the surface of nanocomposite materials under the influence of uniform electric fields, msc thesis, democritus university of thrace, 2010 (in greek) [18] j. k. nelson, y. hu, “nanocomposite dielectrics – properties and implications”, journal of physics d: applied physics, vol. 38, pp. 213222, 2005 [19] c. kalaivananand, s. chandrasekar, “understanding inception and propagation of electrical tree discharge characteristics in xlpe nanocomposites”, the journal of cpri, vol. 13, no. 1, pp. 111-116, 2017 engineering, technology & applied science research vol. 9, no. 4, 2019, 4315-4321 4321 www.etasr.com verginadis et al.: study of the phenomena of surface discharges and flashover in nanocomposite … [20] m. g. danikas, t. tanaka, “nanocomposites – a review of electrical treeing and breakdown”, ieee electrical insulation magazine, vol. 25, no. 4, pp. 19-25, 2010 [21] e. david, m. frechette, “polymer nanocomposites – major conclusions and achievements reached so far”, ieee electrical insulation magazine, vol. 29, no. 6, pp. 29-36, 2013 [22] b. x. du, j. li, q. du, m. l. fu, “surface charge and flashover voltage of eva/cb nanocomposite under mechanical stresses”, ieee transactions on dielectrics and electrical insulation, vol. 23, no. 6, pp. 3734-3741, 2016 [23] s. yu, s. li, s. wang, y. huang, m. tariq nazir, b. t. phung, “surface flashover properties of epoxy based nanocomposites containing functionalized nano-tio2”, ieee transactions on dielectrics and electrical insulation, vol. 25, no. 4, pp. 1567-1576, 2018 [24] w. yan, nanocomposite dielectric materials for power system equipment, phd. thesis, university of new south wales, 2013 [25] p. a. sharad, k. s. kumer, “application of surface-modified xlpe nanocomposites for electrical insulation – partial discharge and morphological study”, nanocomposites, vol. 3, no. 1, pp. 30-41, 2017 [26] m. liang, long-term performance of nanocomposite in power transmission and distribution systems, phd thesis, rmit university, 2018 [27] s. maslougkas, m. g. danikas, “study of water droplets behavior on electrical machine insulation under the influence of uniform electric fields: the influence of some parameters on mica sheets”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2351-2355, 2018 [28] l. zevgolas, y. cheng, m. g. danikas, r. sarathi, “study of the behavior of water droplets under the influence of a uniform electric field in epoxy resin samples having different wt% percentages of nanoparticles and microparticles”, journal of cpri, vol. 13, no. 1, pp. 1-6, 2017 [29] r. sarathi, v. sri harsha, n. j. vasa, “water droplet initiated discharges on epoxy nanocomposites under dc cvoltages”, ieee transactions on dielectrics and electriocal insulation, vol. 23, no. 3, pp. 1743-1752, 2016 microsoft word 24-2714_s_etasr_v9_n3_pp4200-4202 engineering, technology & applied science research vol. 9, no. 3, 2019, 4200-4202 4200 www.etasr.com alsaif: compact hexagonal monopole antenna for lower 5g bands compact hexagonal monopole antenna for lower 5g bands haitham alsaif electrical engineering department, college of engineering, university of hail, hail, saudi arabia hal-saif@hotmail.com, h.alsaif@uoh.edu.sa abstract—this paper presents a compact planar antenna with extreme wide band. the antenna is designed to cover the entire lower 5th generation operating bands ranging from 2.32ghz to more than 12ghz. this band also covers the ieee 802.11 a/b/g/n/ac. the patch geometry has been simulated using an industrial standard simulation software called cst mws. the monopole is miniaturized with a total size of 23x24x1.2mm 3 . the radiator and the ground plane are printed on a substrate of rogers duriod rt 5880 with relative permittivity of 2.2 and loss tangent of 0.00009. the simulated reflection coefficient and radiation pattern results are presented. s11 parameter for the designed antenna is less that -10db over the operating band, with lowest value of -32.5db at 2.85ghz. the radiation pattern is presented at the two orthogonal planes, elevation (e plane) and azimuth (h plane). simulated results show that the antenna is appropriate of lower 5g bands application and several other wireless systems. keywords-5g; ultra-wide band; planar antenna i. introduction in the near future, the global mobile data traffic is expected to yearly increase by a rate of 160% [1]. this massive growth is mostly caused by the implementation of internet of things (iot) and mobile video streaming. there will be about 18 billion devices using the iot out of a total of 29 billion devices [2]. therefore, the next wireless generation networks will need to overcome enormous demands of wider bandwidth at high frequency bands. the crucial constraint to deploy 5g networks in two years from now is the availability of frequency spectrum. both lower and higher frequency bands are required for that. for early implementation of 5g, lower bands are perfect because of their properties such as wave propagation and spectrum availability. the major frequency bands located between 2ghz and 6ghz are from 3.3ghz to 4.2ghz and from 4.4ghz to 4.990ghz. those bands are currently being targeted for early trials of 5g systems in several countries. table i demonstrations the country regions and the lower 5g bands [3]. to overcome such challenges and the in progress needs, an ultra-wide band (uwb) antenna has been designed. the monopole operates over a frequency band ranging from 2.32ghz to more than 12ghz, which include all the frequency bands allocated for lower 5g systems. it is a model candidate for new generation devices such as tablets and mobile phones etc. additionally, this band also fulfills the regulations of the uwb technology set by the federal communication commission (fcc) [4]. moreover, the designed patch covers several spectrum bands such as the ieee 802.11 a/b/g/n/ac standards for wi-fi. different new ultra-wideband antennas with various designs (rectangular, circular, vivaldi, elliptical, etc.) have been designed [5-13]. the designs differ in terms of main parameters such as frequency bands, radiation, gain, and physical size. some of these designs have shortages in their operating frequencies which do not include uwb set by fcc (3.1 to 10.6ghz). the suggested planar antenna in this paper is competitive with many of the previously published designs and has reduced size. table i. regions with expected lower 5g spectrum bands region frequency bands (ghz) europe 3.4-3.8 china 3.6, 4.4-4.5, 4.8-4.99 japan 3.6-4.2, 4.4-4.9 korea 3.4-3.7 usa 3.1-3.55, 3.7-4.2 ii. antenna design configuration figure 1 reveals the geometric shape labeled with parameters of the proposed monopole antenna and its parameters after optimization are shown in table ii. the patch has a miniaturized size with 25mm width and 23.5mm length and printed on a thick 1.2mm substrate of rogers duroid rt5880lz that has relative permittivity εr=2.2 and loss tangent δ=0.0009. as shown in figure 1, the patch is consisting of a main hexagonal shape radiator attached to thirteen smaller two sizes hexagonal radiators at the edges. the radiator is fed using coplanar waveguide (cpw) through a characteristic impedance of 50ω. the microstrip line has 9.5mm length, 2.2mm width with 0.4mm as a separation gap from the ground plane at each side. the ground is containing two slots which improve the impedance matching. these slots are 5mm long and 0.5mm wide. corresponding author: haitham alsaif engineering, technology & applied science research vol. 9, no. 3, 2019, 4200-4202 4201 www.etasr.com alsaif: compact hexagonal monopole antenna for lower 5g bands fig. 1. design of monopole antenna configuration with labeled parameters table ii. designed antenna parameters after optimization variables l w h dimensions (mm) 23.5 25 1.2 variables wf lf w1 dimensions (mm) 2.2 9.5 6 variables wg lg l1 dimensions (mm) 11 7 5 fig. 2. the proposed antenna from simulation software cst microwave studio iii. results and discussion the optimized reflection coefficient (s11) in db as a function of frequency in ghz is plotted in figure 3. it displays the extreme-wide bandwidth by which the design is characterized, from 2.32ghz until more than 12ghz which covers the whole fcc uwb set for such wireless applications as well as all for lower 5g bands in regions like europe, china, korea, japan, and united states of america (table i). the reflection coefficient or s11 has three resonant frequencies which are 2.82ghz, 6.1ghz, and 9.3ghz. as part of the parametric study for the proposed monopole antenna, several substrate materials have been tested and studied such as rogers rt 5880 (εr=2.2), rogers rt 5880lz (εr=1.9), fr-4 (εr=4.3), and polymide (εr=3.5). the tested materials are popular for such types of antenna designs. all reflection coefficients which represent the impedance matching for these materials are plotted in figure 4. it can be observed that rogers duroid rt 5880, with 2.2 relative permittivity provides the best impedance matching and covers wider operating frequency. in addition, its reflection coefficient is lower than the common -10db standard along the entire bandwidth, from 3.1ghz to 10.6ghz. figure 5 reveals the monopole power gain over the operating frequency in ghz versus the gain in db. the design is characterized by high power gain that reaches more than 5dbi. figure 6 demonstrates the normalized radiation pattern at the two main orthogonal planes in polar form at 2.82ghz, 6.1ghz, and 9.3 ghz. generally, the radiation pattern has an omnidirectional shape with minor distortions at high frequencies due to the increase in power gain. thus, the proposed antenna design can be placed in a wireless system at any position. fig. 3. simulated reflection coefficient s11 vs operating frequency fig. 4. reflection coeffecients11 vs operating frequency for several substrate materials: rogers rt 5880 (εr=2.2), rogers rt 5880lz (εr=1.9), fr-4 (εr=4.3), and polymide (3.5) fig. 5. simulated power gain of the proposed antenna 3 4 5 6 7 8 9 10 11 12 0 1 2 3 4 5 6 frequency (ghz) p o w e r g a in ( d b ) engineering, technology & applied science research vol. 9, no. 3, 2019, 4200-4202 4202 www.etasr.com alsaif: compact hexagonal monopole antenna for lower 5g bands fig. 6. normalized radiation pattern for e and h planes in polar form at the resonant frequencies iv. conclusion a new compact extreme wide antenna has been presented in this paper. the patch has a very compact structure size, the overall volume is 23×24×1.2mm 3 printed on a substrate of rogers duroid rt5880 with 2.2 relative permittivity and 0.00009 loss tangent. the proposed monopole has the ability to operate over a bandwidth from 2.32ghz to more than 12ghz. the maximum obtained power gain is 5.89db with an omnidirectional radiation pattern which is the optimum possible pattern for such antenna type. thus, the design is appropriate for lower 5g wireless system applications at many countries. also, the design is appropriate for ultra wide band wireless systems since the bandwidth covers the entire fcc band allocated for such systems. design and simulation have been conducted using the industrial standard simulation software called cst microwave studio. more miniaturizing strategies can be applied for further structure size reduction in the future. in addition, the design can be fabricated and experimentally measured. acknowledgement the author would like to express his thanks to the deanship of scientific research at university of hail (uoh)l in saudi arabia for supporting this project (ba-1512). references [1] t. dateki, h. seki, m. minowa, “from lte-advanced to 5g: mobile access system in progress”, fujitsu scientific and technical journal, vol. 52, pp. 97-102, 2016 [2] ericsson mobility report. november 2016, ericsson, 2016 [3] gsma, 5g spectrum–public policy position, gsma, 2018 [4] fcc, third memorandum opinion and order and memorandum opinion and order, available at: https://www.fcc.gov/document/ revision-part-15-commissions-rules-regarding-ultra-wideband, 2010 [5] p. s. bakariya, s. dwari, m. sarkar, “triple band notch uwb printed monopole antenna with enhanced bandwidth”, aeu international journal of electronics and communications, vol. 69, no. 1, pp. 26–30, 2015 [6] m. c. tang, t. shi, r. w. ziolkowski, “planar ultrawideband antennas with improved realized gain performance”, ieee transactions on antennas and propagation, vol. 64, no. 1, pp. 6169, 2015 [7] y. j. ren, k. chang, “ultra-wideband planar elliptical ring antenna”, electronics letters, vol. 42, no. 8, pp. 447–449, 2006 [8] m. g. n. alsath, m. kanagasabai, “compact uwb monopole antenna for automotive communications”, ieee transactions on antennas and propagation, vol. 63, no. 9, pp. 4204–4208, 2015 [9] m. naser-moghadasi, h. rousta, b. s. virdee, “compact uwb planar monopole antenna”, ieee antennas and wireless propagation letters, vol. 8, pp. 1382–1385, 2009 [10] o. m. h. ahmed, a. r. sebak, t. denidni, “compact uwb printed monopole loaded with dielectric resonator antenna”, electronics letters, vol. 47, no. 1, pp. 7-8, 2011 [11] m. almalkawi, v. devabhaktuni, “ultrawideband antenna with triple band-notched characteristics using closed-loop ring resonators”, ieee antennas and wireless propagation letters, vol. 10, pp. 959–962, 2011 [12] m. n. moghadasi, h. rousta, b. s. virdee, “compact uwb planar monopole antenna”, ieee antennas and wireless propagation letters, vol. 8, no. 22, pp. 1382–1385, 2009 [13] f. zhu, s. gao, a. t. ho, c. h. see, r. a. abd-alhameed, j. li, j. xu, “compact-size linearly tapered slot antenna for portable ultrawideband imaging systems”, international journal of rf and microwave computer-aided engineering, vol. 23, no. 3, pp. 290– 299, 2013 microsoft word 43-3082_s_etasr_v9_n5_pp4818-4823 engineering, technology & applied science research vol. 9, no. 5, 2019, 4818-4823 4818 www.etasr.com munir et al.: problems and barriers affecting total productive maintenance implementation problems and barriers affecting total productive maintenance implementation muhammad adeel munir department of mechanical, manufacturing and mechatronics engineering, university of engineering & technology, lahore, pakistan adeelmunir158@gmail.com mansoor ali zaheer department of mechanical engineering, the university of sargodha, sargodha, pakistan mechengineer778@gmail.com mustafa haider department of mechanical engineering, faculty of engineering & technology, university of lahore, lahore, pakistan mustafah.haider@me.uol.edu.pk muhammad zeeshan rafique department of mechanical engineering, faculty of engineering & technology, university of lahore, lahore, pakistan muhammadzeeshanrafique@gmail.com muhammad anas rasool department of mechanical engineering, faculty of engineering & technology, university of lahore, lahore, pakistan muhammad.anas@me.uol.edu.pk muhammad saad amjad department of mechanical engineering, faculty of engineering & technology, university of lahore, lahore, pakistan saadamjad95@gmail.com abstract—total productive maintenance (tpm) is at the forefront of the maintenance strategies which brought about a paradigm shift from repair-maintenance strategy to proactive maintenance. the philosophy of tpm entails the facets of cost reduction and increased productivity. however, it has been observed that many manufacturing enterprises have made unsuccessful attempts at its adoption. in order to detect and overcome a qualitative research methodology has been employed and a survey has been carried out identifying the barriers and categorizing them to strategic, managerial, departmental, financial, and social regimes through rigorous data analysis. it was observed that strategic constraints are primarily detrimental to the success of tpm due to the lack of defined strategies for workers by management. moreover, the departmental constraints are present due to misalignment between tpm and departmental objectives, in addition to the lack of training for workers in the system for tpm implementation. moreover, there are managerial and financial constraints due to the lack of information visibility and finances, social constraints due to gap between top management authorization and worker mentality. finally, a proper strategy has been proposed to address the issues affecting tpm implementation. keywords-total productive maintenance; cronbach’s alpha; correlation analysis; one way anova i. introduction total productive maintenance (tpm) is a technique employed to improve the performance of a plant and its assets. for its successful implementation, organizations require unequivocal top management support and commitment, whereas employees should be highly motivated and empowered. also, there should be a common conception among top management that tpm is a gradual process that demands patience and determination to achieve positive results. due to the new production technology and techniques, the competition between different companies is increasing every day. the emphasis is not only to gain maximum production but also product quality. the main purpose of tpm technique is to develop coordination between maintenance and production departments for continuously improving the manufacturing process. the main philosophy of tpm is no breakdown of machines, which ultimately leads to minimization of the production loss, whilst efficiently using human resources. it is a common narrative that the best quality machines produce the best quality products. the production department should take responsibility of seemingly trivial tasks as lubrication of machines, cleaning of the work area and machines, followed by regular checkups. machine operators should be motivated and empowered for small tasks, while the maintenance department should give full attention to the improvement of machinery and all the tasks that require skilled human resources. tpm was incepted by a japanese organization nippondenso, a subsidiary of toyota motors that introduced the concept of autonomous maintenance which implies that performing daily maintenance tasks is a responsibility of the operators. this helped in saving a lot of time and reaping economic rewards. the maintenance department was mandated to improve the overall equipment effectiveness (oee) by using tpm. the common benefits of tpm include employee involvement, performance improvement and quality production. by making an operator the stakeholder of maintenance tasks, the skill level increases which results in positive social performance. there are several factors that play an important role in successful implementation of tpm. ground realities for each country should be taken into context while its implementation, keeping in mind that tpm is a gradual process. there should be a structured training for tpm coordinators and team members aided by financial resources. a system that measures performance and economic benefits should be developed. the corresponding author: muhammad zeeshan rafique engineering, technology & applied science research vol. 9, no. 5, 2019, 4818-4823 4819 www.etasr.com munir et al.: problems and barriers affecting total productive maintenance implementation involvement of top management and their communication with all levels of employees is an essential requirement for tpm implementation. firstly, managers have to establish a consolidated strategy for the effective utilization of all employees. there should be clear policies and plans for the implementation of tpm in a company. higher management should establish a separate department in which a dedicated manager could control the process and evaluate performance. the successful tpm implementation may include cultural change, alignment of company’s goals with tpm goals, provision of appropriate financial resources for tpm, high level of cooperation among production and maintenance department, proper training and skill improvement, and removal of the barriers for its implementation. the success of tpm is highly dependent on the effectiveness of employees, so multi-skilled employee training is of paramount importance, which should not be confined to developing technical expertise but stretches to character and behavior improvement. through proper training and effective utilization of employees, higher productivity and high quality standards can be met as the defects will be minimized and the breakdown frequency will be reduced by reducing the defects and breakdowns. rewards and compensation in salary should be provided based on the success in the implementation of tpm. the results of employee’s evaluation should be shared with them so they can be motivated. the performance should be improved by focus improvements and there should be a proper system to get feedback from the employees in order to be able to overall improve the system. ii. literature review many years ago, japanese companies revealed that the performance of machines can not only be improved by the system but also by the people working on that machine. the term tpm was first time used by nippondenso. they first time discussed getting more output by using the employees effectively. later, nakajima implemented tpm in japanese plants. the main idea was that the basic responsibilities of the maintenance team should be given to operators. operators have more knowledge about machines, and they can continuously improve them by extensive involvement and autonomy. the intensity of barriers in implementation of tpm was evaluated through graph theoretic approach [1]. the barriers for successful implementation of tpm were identified. barriers may differ from organization to organization. they were grouped into categories that were behavioral barriers, human and cultural barriers, strategic barriers, operational barriers and technical barriers. behavioral barriers were found to be the most effective and intense. this category includes top management failure, lack of vision, fear of job security, and poor cooperation between maintenance and production department. quality of products and program cannot be increased without the involvement of top management which involves operational barriers, including the lack of standard operating procedures, improper maintenance schedule, bad working conditions and lack of performance measurement. human and cultural barriers entail the lack of motivation, recognition and empowerment. technical barriers can be handled by providing quality training for all employees. tpm and how it is utilized in manufacturing sector was studied in [2]. industries were categorized based on their region and type and the tools used for the implementation of tpm were analyzed. maintenance is considered as the strategy for success [3]. there should be a reliable maintenance system and managers should consider the importance of equipment efficiency and reliability. the quality of products depends on the condition of the machines and quality leads the competition in a global scale. there is high competition, so the maintenance system should be considered as an integral part of the company. teamwork in maintenance leads to the success of the industry [4]. the tpm is a technology-oriented concept and its failures are due to organizational problems, the style of management, lack of coordination between production and maintenance, and the lack of autonomy of the team which implements the tpm. firm competitiveness depends upon how efficiently is managed in its resources and culture, and how its objectives are gained for better achievements [5]. due to globalization and open trade, the firms are working in a highly competitive environment. by using competitive maintenance techniques, medium and small sized industries reached global competition. business improvement occurs due to the implementation of tpm and total quality management (tqm) in manufacturing sector [6]. in [7], it was found that the success of maintenance techniques can be achieved by the involvement of employees, cultural change, and continuous improvement. tpm and tqm are basic maintenance techniques for improvement and growth in business. if companies adopt preventive maintenance approach, it will reduce the costs from 2% to 16%, but there is a prevalent culture of parts’ replacement after they are worn out. due to downtime of machines, the expenditure of companies’ increases but the losses due to human laziness are more than the losses due to downtime. this could be improved by effective use of human power, continuous training and change of culture. the factors which effect the successful implementation of tpm in indian manufacturing companies were examined in [8]. it was found that the basic problems in the implementation of tpm were insufficient management support and lack of training. companies implemented the program and did not give time for performance measurement. there were no properly defined objectives for the tpm. tpm objectives must be aligned with the business plan because tpm is holistic in nature, its objectives are not limited to production only. in indian manufacturing industry, maintenance is treated as needless and generally, no attention is paid to it. it is considered as a reactive problem which has expenses that cannot be minimized, since rework is considered a part of the manufacturing process. lack of motivation, rigid unions, inconsistency, and absence of planned maintenance are key factors for the failure of tpm. there was no recognition, no reward, and a lack of trust from the maintenance department to the production regarding their ability to take the responsibility of small maintenance tasks. an efficient tpm program can solve all the maintenance related problems. many companies achieved improvements in their business by using the tpm approach. the issues related to the maintenance which effect the improvements in organization and create barriers at the initial stage of tpm were recognized in [9]. it was observed engineering, technology & applied science research vol. 9, no. 5, 2019, 4818-4823 4820 www.etasr.com munir et al.: problems and barriers affecting total productive maintenance implementation that tpm implementation improved the system by increasing productivity and quality, and decreasing cost. tpm avoids the equipment related losses and continuously improves performance. when the performance of the equipment is optimized, there will be fewer breakdowns and better employee performance. tpm improves the relation between maintenance and other departments of the manufacturing industry, which improves the reliability and at the end oee. there are many challenges which are raised at the initial stage of tpm implementation [10]. the performance measurement system was divided into three stages. the first stage was the design to measure the performance, the second was its implementation and the third its analysis by using feedback. without the full commitment of employees, no issues can be solved. oee only cannot measure the performance and effects tpm because it measures the internal factors and ignores external performance. to measure the performance improvement, both internal and external factors should be considered. external factors include the satisfaction of customers, on time delivery, after sales service and quality of products. the maintenance performance measurement (mpm) model was devised which measured losses due to poor equipment performance. the health and safety system was also considered. the only support between the planning and execution of maintenance is the availability of spare parts, tools and manuals which increase performance. one of the most important facets is the trained personnel. unskilled personnel act as a demotivating factor. it was observed that when the problem in any maintenance system arises, the main issue is its reporting. there should be proper and planned structure for its reporting and how to solve it. mpm measures all the factors and provides proper estimation for the maintenance part in business. the philosophy of tpm was used in timber companies in the initiation and implementation of the maintenance of machines before breakdown occurs, by using quality training and improvement of the process [11]. problems and complexities are found when one tries to change the culture and employees’ involvement in the process. management should adopt a participative way and should keep in mind that tpm will take long time to bring its benefits. despite the difficulties in implementing the program, this program is necessary in the competitive market. all the departments including top management, maintenance, and production will have to participate and facilitate pm implementation. participation of all personnel is a key factor in the implementation of tpm. the commitment and involvement of workers is used to align the objectives of tpm with the organizational objectives. for any type of improvements, there should be a search for all the areas which require improvement. there should be a proper structured team which must be able to find all those areas and they should actively participate to identify the problems and their solutions. the employees should be given responsibilities of their own interest. when there is an implementation program in any company, researchers should observe the process and find the difference between the academic and the actual process. standard operating procedures may be created, keeping in mind the ground realities. the main reason for failure of tpm is the lack of coordination between production and maintenance [12]. in [12], industries were divided in three levels. the ones that claim to have implemented tpm and carry the structure to implement it, the ones that claim that they implemented tpm, but they have not the necessary structure, and the ones who have implemented it, but just to satisfy audits. managers and administration who do not understand the real philosophy of tpm are the main reasons for its failure. audits show that they have implemented everything positively but there is not actual improvement in the process and oee. there is a negative attitude by companies including the decrease of budget for tpm by considering it as waste of time, selection of incompetent personnel, unscheduled maintenance, lack of commitment, etc. there are two types of maintenance. time based maintenance (tbm) and condition based maintenance (cbm) [13]. cbm is more realistic than tbm but there is a need for improvement in cbm. the cbm uses the fact that the 99% of failures can be predicted by machine and equipment condition. iii. research methodology a questionnaire was designed with five possible answers for each statement: strongly agree, agree, neutral, disagree and strongly disagree. the questionnaire was distributed among the people with different work positions, e.g. managers, assistant managers, supervisors, and workers in 3 different companies. the questionnaire consisted of 27 questions which covered seven basic factors which cause the failure of tpm. the factors (strategically constraints, managerial constraints, departmental constraints, financial constraints, social constraints, insufficient training, and lack of workers’ commitment and lack of workers’ commitment) were given numbers from 1 to 7 respectively (table i). the questionnaire was distributed in three different companies labeled as companies “a”, “b”, “c”. a total of 93 responses were returned, 9 responses from managers, 26 from assistant managers, 18 from supervisors, and 39 responses from workers. they showed that the strategic issue is the most effective regarding the failure of tpm, followed by departmental, insufficient training, managerial, financial, and social and lack of workers commitment. table i. failure factor numbering factor number strategic constraints 1 managerial constraints 2 departmental constraints 3 financial constraints 4 social constraints 5 insufficient training 6 lack of workers’ commitment 7 iv. results in order to check the reliability of data, the statistical package for the social sciences (spss) was used to ensure that no falsification took place while filling the questionnaire, employing cronbach’s alpha. if the significance value is less than 0.05 then both factors have different means and their effect on tpm is different. if their value is more than 0.05 then they have the same mean and their effect on failure of tpm is the same. post hoc analysis was performed in spss. the value engineering, technology & applied science research vol. 9, no. 5, 2019, 4818-4823 4821 www.etasr.com munir et al.: problems and barriers affecting total productive maintenance implementation for company a, b, and c was found to be 0.713, 0.680, and 0.75 respectively. the overall value for cronbach’s alpha was 0.79 which shows that the data were reliable (table ii). the anova technique was performed in mathematical software to find the most effective factors that cause failure of tpm and the turkey test was performed. table iii shows the subsets. there are 3 subsets of factors and each subset has the same mean value and the same effect on tpm. in figure 1, we can see that the strategic issue is the most effective in failure of tpm. table ii. anova for all factors factors mean difference (i-j) std. error sig. 95% confidence interval i j lower bound upper bound 1 2 -0.416489362 * 0.090305867 0.000 -0.68357675 -0.14940198 3 -0.308510638 * 0.090305867 0.012 -0.57559802 -0.04142325 4 -0.422872340 * 0.090305867 0.000 -0.68995973 -0.15578495 5 -0.461879433 * 0.090305867 0.000 -0.72896682 -0.19479205 6 -0.331382979 * 0.090305867 0.005 -0.59847037 -0.06429559 7 -0.610815599 * 0.090305867 0.000 -0.87790299 -0.34372821 2 1 0.416489362 * 0.090305867 0.000 0.14940198 0.68357675 3 0.107978723 0.090305867 0.896 -0.15910866 0.37506611 4 -0.006382979 0.090305867 1.000 -0.27347037 0.26070441 5 -0.045390071 0.090305867 0.999 -0.31247746 0.22169732 6 0.085106383 0.090305867 0.965 -0.18198100 0.35219377 7 -0.194326238 0.090305867 0.324 -0.46141362 0.07276115 3 1 0.308510638 * 0.090305867 0.012 0.04142325 0.57559802 2 -0.107978723 0.090305867 0.896 -0.37506611 0.15910866 4 -0.114361702 0.090305867 0.867 -0.38144909 0.15272568 5 -0.153368794 0.090305867 0.617 -0.42045618 0.11371859 6 -0.022872340 0.090305867 1.000 -0.28995973 0.24421505 7 -0.302304961 * 0.090305867 0.015 -0.56939235 -0.03521757 4 1 0.422872340 * 0.090305867 0.000 0.15578495 0.68995973 2 0.006382979 0.090305867 1.000 -0.26070441 0.27347037 3 0.114361702 0.090305867 0.867 -0.15272568 0.38144909 5 -0.039007092 0.090305867 1.000 -0.30609448 0.22808029 6 0.091489362 0.090305867 0.951 -0.17559802 0.35857675 7 -0.187943259 0.090305867 0.365 -0.45503065 0.07914413 5 1 0.461879433 * 0.090305867 0.000 0.19479205 0.72896682 2 0.045390071 0.090305867 0.999 -0.22169732 0.31247746 3 0.153368794 0.090305867 0.617 -0.11371859 0.42045618 4 0.039007092 0.090305867 1.000 -0.22808029 0.30609448 6 0.130496454 0.090305867 0.777 -0.13659093 0.39758384 7 -0.148936167 0.090305867 0.650 -0.41602355 0.11815122 6 1 0.331382979 * 0.090305867 0.005 0.06429559 0.59847037 2 -0.085106383 0.090305867 0.965 -0.35219377 0.18198100 3 0.022872340 0.090305867 1.000 -0.24421505 0.28995973 4 -0.091489362 0.090305867 0.951 -0.35857675 0.17559802 5 -0.130496454 0.090305867 0.777 -0.39758384 0.13659093 7 -0.279432621 * 0.090305867 0.033 -0.54652001 -0.01234523 7 1 0.610815599 * 0.090305867 0.000 0.34372821 0.87790299 2 0.194326238 0.090305867 0.324 -0.07276115 0.46141362 3 0.302304961 * 0.090305867 0.015 0.03521757 0.56939235 4 0.187943259 0.090305867 0.365 -0.07914413 0.45503065 5 0.148936167 0.090305867 0.650 -0.11815122 0.41602355 6 0.279432621 * 0.090305867 0.033 0.01234523 0.54652001 * the mean difference is significant at the 0.05 level. a comparison was made between the people of different posts such as managers, assistant managers, supervisors and workers. we see from table iv that the significance value of insufficient training is greater than 0.05 so all people from all designations agree that insufficient training is a basic cause for the failure of tpm. the second factor on which all people agree is the financial factor, with a value of 0.05. moreover, correlation defines the effect of one variable on another. table v shows that the most effective relation is between the social issues and the lack of workers’ commitment, having a value of 0.616. table iii. post hoc analysis is spss factors n subset for alpha = 0.05 1 2 3 1 94 1.78989362 3 94 2.09840426 6 94 2.12127660 2 94 2.20638298 2.20638298 4 94 2.21276596 2.21276596 5 94 2.25177305 2.25177305 7 94 2.40070922 sig. 1.000 0.617 0.324 means for groups in homogeneous subsets are displayed. fig. 1. ordering of all factors table iv. comparison betweeen people of different designations sum of squares degree of mean square f sig. 1 between groups 4.456 3 1.485 7.703 0.000 within groups 17.162 89 0.193 total 21.618 92 2 between groups 12.634 3 4.211 35.079 0.000 within groups 10.685 89 0.120 total 23.320 92 3 between groups 4.071 3 1.357 7.605 0.000 within groups 15.881 89 0.178 total 19.952 92 4 between groups 8.489 3 2.830 4.637 0.005 within groups 54.307 89 0.610 total 62.796 92 5 between groups 13.817 3 4.606 10.187 0.000 within groups 40.236 89 0.452 total 54.053 92 6 between groups 1.253 3 0.418 1.851 0.144 within groups 20.076 89 0.226 total 21.329 92 7 between groups 8.836 3 2.945 7.519 0.000 within groups 34.865 89 0.392 total 43.701 92 it is a general perception that workers resist change. worker unions resist change as they think that tpm will give more burdens to the workers so there is a strong correlation between the workers and social issues, such as job security, engineering, technology & applied science research vol. 9, no. 5, 2019, 4818-4823 4822 www.etasr.com munir et al.: problems and barriers affecting total productive maintenance implementation difficulty in working, complicated working conditions, intricate processes, etc. table v shows the strong relationship between strategic and social issues. table v. correlation analysis factors 1 2 3 4 5 6 7 1 p 1 0.549** 0.441** 0.255* 0.572** 0.152 0.421** s 0.000 0.000 0.013 0.000 0.145 0.000 n 94 94 94 94 94 94 94 2 p 0.549** 1 0.380** 0.467** 0.501** 0.202 0.418** s 0.000 0.000 0.000 0.000 0.051 0.000 n 94 94 94 94 94 94 94 3 p 0.441** 0.380** 1 0.061 0.419** 0.035 0.296** s 0.000 0.000 0.561 0.000 0.739 0.004 n 94 94 94 94 94 94 94 4 p 0.255* 0.467** 0.061 1 0.361** 0.497** 0.391** s 0.013 0.000 0.561 0.000 0.000 0.000 n 94 94 94 94 94 94 94 5 p 0.572** 0.501** 0.419** 0.361** 1 0.310** 0.616** s 0.000 0.000 0.000 0.000 0.002 0.000 n 94 94 94 94 94 94 94 6 p 0.152 0.202 0.035 0.497** 0.310** 1 0.202 s 0.145 0.051 0.739 0.000 0.002 0.051 n 94 94 94 94 94 94 94 7 p 0.421** 0.418** 0.296** 0.391** 0.616** 0.202 1 s 0.000 0.000 0.004 0.000 0.000 0.051 n 94 94 94 94 94 94 94 p: pearson correlation, s: sig. (2-tailed) strategically operators and supervisors should be empowered but there is a lack of trust between the upper management and supervisors and there is no proper two-way communication between them, so we can conclude that due to social barriers, the strategy to implement tpm can fail. the correlation between strategic and managerial issues can be explained in that way for the implementation of tpm. its value is 0.549. there should be dedicated managers to implement policies, strategies, and goals. in the absence of dedicated managers, there will be a lack of strategy that will lead to failure of tpm implementation in the company. similarly, the value of correlation between managerial and social issues is 0.501. if the management is effective, they will develop a strategy that will decrease social barriers. moreover, they will work to form proper communication channels between workers and higher management which will build mutual understanding and trust between them. another relationship exists between the financial constraints and insufficient training. its value is 0.497. due to financial constraints, proper education and training including information technology and experienced work force are not available. v. discussion tpm is a gradual and continuous improvement process which involves all employees and departments and the entire upper, middle and lower level management. its main purpose is to increase machine productivity and administration efficiency. most organizations usually spend their resources in repairs of machinery and after breakdowns. tpm focuses on prescheduling maintenance and preventive measures to save time and money. top management is responsible to create favorable environment to implement tpm. they have to bring change in the mindset of employees. the machine operators should be empowered and they should do basic maintenance repairs. the responsibilities of operators should include cleaning and small maintenance tasks. financial resources are key factors for the successful implementation of tpm. the benefits of tpm are obtained after a long time, so top level management should be patient. if the production department takes the responsibility of simple maintenance tasks, then the maintenance team will find more time to improve the system. employees must be rewarded for their good performance. tpm includes higher productivity, low cost, high quality of products, safety in all factory areas, healthy relations between employees and their work. the training for all employees should be provided at an initial stage. new skills about tpm are an important part for its successful implementation. statistical techniques can boost up the process towards success. tpm coordinators will provide training to management and shop floor employees. support for tpm coordinators from the top management (including financial resources and involvement in process) will guarantee their success. a clear plan and strategy should be defined. an inside analysis of the company should be conducted including business details, financial condition, and strength. weak areas should be analyzed preferably via this procedure rather than to depend on external analysis of other companies. the first step is to form a highly skilled team which should be highly educated and would be responsible for the implementation of tpm. in order to increase the involvement of employees, there should be a structured communication system between management and employees. the most difficult step in tpm implementation is to bring change in workers’ mindset, as employees usually resist change. they are hesitant to take the responsibility but in the case of tpm, they play a vital role. by providing clear objectives and by empowering the employees by providing incentives, they may take part in the growth of company. vi. conclusion tpm is an effective strategy for process improvement but there are many constraints and barriers affecting its implementation. the first constrain that affects the system is the strategic constraint that plays the most important part in tpm failure, because there are no proper goals, guidelines and strategies defined by the management for workers due to which some workers get overloaded and some are not properly involved, which leads to resistance against tpm. the second constrain was the departmental constraint because the objectives of a department were not aligned with the objectives of tpm e.g. the department demands 24-hour operational machines to get maximum production without considering preventive maintenance and proper cleaning which are essential parts of tpm. tpm demands proper structure and a team that is usually not provided by the department. the third constraint is insufficient training, agreed upon by all respondents. management emphasizes on initial training but with the passage of time, they do not provide structured training, although tpm is a continuous process. ground reality must be considered while providing training. the use of customized information technology in a proper way will boost success. managerial constraint refers to the lack of communication between top management and employees. top engineering, technology & applied science research vol. 9, no. 5, 2019, 4818-4823 4823 www.etasr.com munir et al.: problems and barriers affecting total productive maintenance implementation management wants to get immediate benefits without considering that tpm is a very long process, and it is incumbent upon them to provide healthy working environment. financial constraints are another hurdle since the organization’s top management is unsure about the return on investment (roi) and cost-to-benefit ratio (cbr) in tpm implementation. it is a widespread narrative that tpm will exert financial burdens and the production quantity will be affected. last examined was the social constraint which is caused by the authoritarian behavior of management, due to which there is a gap between top management and workers. in the future, research can be conducted regarding the economic benefits of tpm and the related social impacts from worker’s, management and organizational points of view. references [1] r. attri, s. grover, n. dev, “a graph theoretic approach to evaluate the intensity of barriers in the implementation of total productive maintenance (tpm)”, international journal of production research, vol. 52, no. 10, pp. 3032-3051, 2014 [2] a. k. digalwar, p. v. nayagam, “implementation of total productive maintenance in manufacturing industries: a literature-based metadata analysis”, iup journal of operations management, vol. 13, no. 1, pp. 1-15, 2014 [3] i. s. ahuja, “exploring the impact of effectiveness of total productive maintenance strategies in manufacturing enterprise”, international journal of productivity and quality management, vol. 9, no. 4, pp. 486501, 2012 [4] m. rolfsen, c. langeland, “successful maintenance practice through team autonomy”, employee relations, vol. 34, no. 3, pp. 306-321, 2012 [5] g. sardana, s. sinha, “enhancing firm competitiveness in fast track through total productive maintenance”, international journal of indian culture and business management, vol. 4, no. 1, pp. 88-103, 2010 [6] m. kaur, k. singh, i. singh ahuja, “an evaluation of the synergic implementation of tqm and tpm paradigms on business performance”, international journal of productivity and performance management, vol. 62, no. 1, pp. 66-84, 2012 [7] m. c. eti, s. ogaji, s. probert, “reducing the cost of preventive maintenance (pm) through adopting a proactive reliability-focused culture”, applied energy, vol. 83, no. 11, pp. 1235-1248, 2006 [8] g. singh, i. s. ahuja, “strategies and success factors for overcoming challenges in jit implementation in indian manufacturing industry”, international journal of technology, policy and management, vol. 13, no. 1, pp. 15-33, 2013 [9] i. ahuja, j. khamba, “an evaluation of tpm implementation initiatives in an indian manufacturing enterprise”, journal of quality in maintenance engineering, vol. 13, no. 4, pp. 338-352, 2007 [10] a. parida, u. kumar, “maintenance performance measurement (mpm): issues and challenges”, journal of quality in maintenance engineering, vol. 12, no. 3, pp. 239-251, 2006 [11] j. garcia arca, j. carlos prado prado, “personnel participation as a key factor for success in maintenance program implementation: a case study”, international journal of productivity and performance management, vol. 57, no. 3, pp. 247-258, 2008 [12] m. rodrigues, k. hatakeyama, “analysis of the fall of tpm in companies”, journal of materials processing technology, vol. 179, no. 1-3, pp. 276-279, 2006 [13] r. ahmad, s. kamaruddin, “an overview of time-based and condition-based maintenance in industrial application”, computers & industrial engineering,vol. 63, no. 1, pp. 135-149, 2012 microsoft word 13-3016_s_etasr_v9_n5_pp4636-4639 engineering, technology & applied science research vol. 9, no. 5, 2019, 4636-4639 4636 www.etasr.com mainier et al.: corrosivity evaluation of copper-nickel alloy (90/10) in pumps used in offshore platforms corrosivity evaluation of copper-nickel alloy (90/10) in pumps used in offshore platforms for seawater pumping fernando b. mainier escola de engenharia, universidade federal fluminense, niteroi, rio de janeiro, brazil fmainier@uol.com.br alessandro martins coelho escola de engenharia, universidade federal fluminense, niteroi, rio de janeiro, brazil coelho.alessandro@ig.com.br edilson ferreira barros escola de engenharia, universidade federal fluminense, niteroi, rio de janeiro, brazil edbarros.rj0@gmail.com abstract—this work discusses the case of corrosion in a coppernickel alloy used in seawater, where chlorination is necessary to control microand macro-organism growth that can render inoperable the seawater supply system used in an offshore platform. studies developed in the last 30 years have shown copper-nickel’s adequateness in seawater, with a corrosion rate of about 0.001mm/year. however, annual equipment inspection showed localized corrosion in an internal chamber in a stand-by pump. such corrosion occurred due to high-concentration of sodium hypochlorite (naclo) injection into the operational system, even for pumps that were out of operation. to evaluate this corrosive process, gravimetric (mass loss) and electrochemical tests were developed in synthetic seawater with naclo at concentrations of 100, 500, 1000 and 5000mg/l. the results indicated that the corrosiveness varied from low to moderate. the presence of pitting and crevices observed in the laboratory tests derails or compromises material use in seawater. it was concluded that there is a need for continuous monitoring of the naclo injection in seawater pumps, and a method was proposed in order to minimize or avoid a high concentration of chlorine in standby pumps. keywords-localized corrosion; copper-nickel alloy; sodium hypochlorite; seawater i. introduction the seawater system used in maritime oil production facilities located on the coast of south america is designed to supply units and equipment with water injection. depending on the purpose of each maritime installation project, seawater can be independent from the utilities and injection wells, except for the fire ring main systems, where pressurization can be used for an extension of the seawater intake system. the depth of seawater intake and the efficiency and integrity of seawater pumps, should be set based on these factors: • improvement of the seawater to be injected in oil wells, • cooling system optimization, • improvement of seawater quality in the dehydration of the natural gas unit, • reduction of seawater flows involved, and • reduction of energy consumption. for many decades, copper-nickel alloys have been used as materials for pipes and equipment for seawater systems, mainly in shipbuilding, offshore oil production platforms, and desalination plants. the main features of this alloy are good corrosion resistance in salt water and greater resistance to erosion than other copper alloys or carbon steel. in addition, copper-nickel alloys are resistant to biofouling, providing multiple economic benefits. generally, to reduce, minimize and control the growth of biofouling, continuous chlorination using sodium hypochlorite (naclo) is used, in such a way that the residual free chlorine should be established in the range of 0.2 to 0.5mg/l. in tropical seawaters the development of microorganisms is very intense, requiring the injection of naclo. generally, these submersible pumps on the platforms are inspected every two years. the novelty of this paper is to alert marine equipment inspectors that high concentrations of naclo can damage the rotors and internal pumps made of copper-nickel alloy. operational failures of these seawater suction pumps can cause disruption of oil production. despite the appropriate properties of this alloy, some failures can occur and compromise the pumping of seawater [1-4]. in this particular case evaluation, the intake and transfer of sea water to different equipment and processes of the platform consists, essentially, of four submerged pumps to a depth of 20m protected by a screen to avoid the penetration of sea animals. as shown in figure 1, to prevent biofouling a solution of naclo is injected continuously into a dosing pump to maintain the level of free chlorine at 0.5mg/l in the intake of the four pumps. those pumps were designed to work at 100% capacity, and the casing and impeller were manufactured from a coppernickel alloy (90/10). the three pumps (1, 2, and 3) operated in scheduled alternation, while the fourth pump was in standby mode. in the annual equipment inspection, it was observed that the stopped pump had pitting and crevice corrosion located in the internal chamber and in the impeller. it was also observed that this stopped pump continued to receive, continuously, the naclo solution injected by the dosing pump. this fact resulted corresponding author: fernando b. mainier engineering, technology & applied science research vol. 9, no. 5, 2019, 4636-4639 4637 www.etasr.com mainier et al.: corrosivity evaluation of copper-nickel alloy (90/10) in pumps used in offshore platforms in a considerable increase of concentration of naclo in the inner chamber, while on the outside of the pump (casing), in contact with sea water and without the presence of naclo, localized corrosion or pitting were not observed. it is important to note that in the deposits removed inside this pump (in standby) no micro or macro organisms that could cause a microbiologically influenced corrosion (mic) were identified due to the high concentration of clorine due to naclo accumulated inside this pump. figures 2 and 3 present a view of the seawater suction pump and the dosing pump hypochlorite injection. fig. 1. diagram of pump intake and seawater transfer fig. 2. seawater suction pump fig. 3. hypochlorite injection dosing pump in order to evaluate the corrosion in the internal chambers of the seawater suction pumps, gravimetric and electrochemical tests were developed, with coupons made with copper-nickel alloy in synthetic seawater with additions of naclo. ii. materials and methods a. gravimetric tests the material evaluated in this work was a copper-nickel alloy sheet (87.43% cu, 9.05% ni, 2.20% fe and 0.98% mn) used for the manufacturing of coupons. the coupons used in the gravimetric tests (weight loss) had the following dimensions: 3.50cm×1.0cm×0.2cm. the metal surface was prepared with grade 100 to 500 sandpaper. the coupons were cleaned with acetone and ethanol and dried with hot air. the test coupons were weighed with a digital electronic balance. the solutions used in the experiments were characterized as saline water containing 3.5% (% mass) nacl, 800mg/l of mgcl2 and 600mg/l of cacl2, and the ph was set at 7.2–8.0. in the saline solutions were added, respectively, in each test, 100mg/l, 500mg/l, 1000mg/l and 5000mg/l 10% by mass naclo. gravimetric tests were performed in glass containers with a capacity of 400ml. the coupons were completely immersed in 250ml of saline solution. the glass containers were maintained at a temperature of 25°c with a thermostatically controlled bath. the times for testing were fixed at 15, 30 and 60 days of exposure. immediately after the completion of the test, each coupon was washed with water, pickled with clark solution for 40s according to astm g 3172 [5], cleaned with ethanol and dried with hot air. the corrosion rates (cr) are defined by: ( ) / . . (mm/year)o icr k w w s tρ= − (1) where k is a constant equal to 8.76×10 4 , wo and wi are the loss weight in the absence and presence of addition of naclo, s is the sample area (cm 2 ), ρ is its density (8.9g/cm 3 for coppernickel alloy),and t is the exposure time (h). b. electrochemical tests for the polarization measurements, samples of the coppernickel alloy were cut in order to obtain an electrode surface of 0.20cm 2 . the metal surface was then embedded in polyester resin and polished with no. 600 emery paper. then, the samples were degreased with acetone and washed in distilled water before being inserted in a conventional polarization cell, as shown in figure 4. fig. 4. conventional polarization cell engineering, technology & applied science research vol. 9, no. 5, 2019, 4636-4639 4638 www.etasr.com mainier et al.: corrosivity evaluation of copper-nickel alloy (90/10) in pumps used in offshore platforms the polarization curves were recorded with an autolab potentiostat, type iii, by varying the voltage at 60mv/min over a range of −250mv to +250mv with respect to open circuit voltage. all measurements were carried out at a constant temperature of 25°c and without agitation. a solution of saline water containing 3.5% (% mass) of nacl, 800mg/l of mgcl2 and 600mg/l of cacl2 with the ph set between 7.2 and 8.0 was used. into the saline solutions were added, in each test, 100, 500, 1000 and 5000mg/l of sodium hypochlorite, 10% by mass. iii. results and discussion a. weight loss measurements the test results of the weight loss of copper-nickel alloy coupons in the saline solutions with 100, 500, 1000 and 5000mg/l sodium hypochlorite, 10% (by mass) are presented in figure 5. fig. 5. mass loss of copper-nickel alloy in saline solution with naclo, average of three coupons table i presents the results of the corrosion rate (mm/year) of copper-nickel alloy coupons in saline solution with additions of naclo and exposure time of 60 days. table i. corrosion rate of copper-nickel alloy coupons in saline solution with additions of sodium hypochlorite naclo (mg/l) corrosion rate (mm/year) 100 0.007 500 0.010 1000 0.014 5000 0.045 the mass loss assays (figure 6 and table i) showed that the increase in naclo in the saline solution and the immersion time promoted the loss of mass copper-nickel alloy, meaning that the corrosion rate can be considered to be low to moderate, based on table ii as proposed by [6]. figure 6 shows the copper-nickel alloy coupons after immersion tests in saline solution with 5000mg/l naclo at 15, 30 and 60 days. in these coupons, localized corrosion can be observed after the removal of corrosion products. figures 7 and 8 show other aspects of the corrosion deposits, pitting and crevice corrosion, in coppernickel alloy coupons immersed in a saline solution with 5000mg/l sodium hypochlorite. table ii. average corrosion rate [6] corrosiveness average corrosion rate mm/year mm/year low <0.025 <1.0 moderate 0.025-0.12 1.0-4.9 high 0.13-0.25 5.0-10 severe >0.25 >10 fig. 6. copper-nickel alloy coupons in gravimetric testing in saline solution with 5000mg/l sodium hypochlorite fig. 7. corrosion product of copper-nickel alloy coupons with 5000mg/l of sodium hypochlorite x-ray diffraction analysis of the corrosion deposits on the surfaces of the coupons showed the predominance of copper chloride hydroxide (cu2(oh)3cl) and small amounts of copper chloride (cucl2 ) and nickel chloride (nicl2). according to [7], for copper in pure water during the primary corrosion reaction, engineering, technology & applied science research vol. 9, no. 5, 2019, 4636-4639 4639 www.etasr.com mainier et al.: corrosivity evaluation of copper-nickel alloy (90/10) in pumps used in offshore platforms a cuprous oxide film (cu2o) is produced that is predominately responsible for corrosion protection. fig. 8. pitting (a) and crevice (b) corrosion in copper-nickel alloy coupons with 5000mg/l of naclo authors in [8, 9] report that in salt solutions, with oxygenation and the addition of oxidizing substances, cuprous oxide can initially react to form multilayer structures, for example, basic copper chloride to cucl 2 , cu(oh) 2 or cu 2 (oh) 3 cl. these products do not adhere well to the surface and can be easily removed. according to [10], depending on the concentration of free chlorine in the form of naclo, the corrosion rates of copper-nickel alloys saline solution are in the range of 0.07 to 1.27 mm/year. b. electrochemical tests in figure 9, polarization curves were only placed for assays with and without 5000mg/l naclo. the curves for solutions with concentrations of 100, 500 and 1000mg/l were superimposed and were not significantly different from the curve for the solution without naclo. the anodic and cathodic reactions are affected by the addition of naclo. the intersection of the anodic and cathodic curves showed an increase in the intensity of current (log i, a/cm 2 ). fig. 9. current density-potential curves of copper-nickel alloy with and without addition of sodium hypochlorite iv. conclusion based on laboratory tests and inspection of seawater pumps, it is concluded that: • the corrosion in copper-nickel alloy coupons was caused by high concentration of naclo (5000mg/l), while the concentration of 0.2 to 0.5mg/l of naclo indicated from the uptake of seawater did not cause any corrosion problems and prevented the proliferation of microorganisms in seawater. • corrosion in the interior of the pumps was due to continuous naclo injection, even when the pump was completely stopped. • modification of the project with installation of pilot valves monitoring the injection of naclo could prevent corrosion of copper-nickel pumps. fig. 10. modification proposal for of seawater pumps references [1] c. kapsalis, g. schmitt, r. feser, b. sagebiel, s. wilmes, m. macziek, “new investigations on critical wall shear stresses of cuni alloys in natural and artificial seawater”, eurocorr 2011, stockholm, sweden, september 4-8, 2011 [2] w. schleich, “typical failures of cuni 90/10 seawater tubing systems and how to avoid them”, eurocorr 2004, nice, france, september 1216, 2004 [3] j. h. michel, i. richardson, c. powell, b. phull, “development of copper alloys for seawater service from traditional application to stateof-the art engineering”, corrosion 2017, new orleans, usa, march 2630, 2017 [4] a. l. ma, s. l. jiang, y. g. zheng, w. ke, “corrosion product film formed on the 90/10 copper–nickel tube in natural seawater: composition/structure and formation mechanism”, corrosion science, vol. 91, pp. 245-261, 2015 [5] astm, astm g31-72, standard practice for laboratory immersion corrosion testing of metals, astm international, 1999 [6] nace, nace-rp0775-2005, standard recommended practice: preparation, installation, analysis, and interpretation of corrosion coupons in oilfield operations, nace, 2005 [7] m. pourbaix, “licoes de corrosao eletroquimica”, in: brasileira de corrosao–abraco1, pp. 338-342, 1988 (in portuguese) [8] f. j. kievits, f. p. ijsseling, “research into the corrosion behavior of cuni10fe alloys in seawater”, materials and corrosion, vol. 23, no. 12, pp. 1084–1096, 1972 [9] a. h. tuthill, “guidelines for the use of copper alloys in seawater”, materials performance, vol. 26, no. 9, pp. 12-22, 1987 [10] h. h. uhlig, uhlig's corrosion handbook, john wiley & sons, 2011 microsoft word elmeguenni-ed3.doc etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 373-380 373 www.etasr.com selini et al: effect of the triaxiality in plane stress conditions. triaxiality effect in a pvc material effect of the triaxiality in plane stress conditions triaxiality effect in a pvc material najia selini djillali liabes university of sidi bel abbes bp89, cite ben m’hidi, sidi bel abbes, 22000, algeria wassiselin@yahoo.fr mohamed elmeguenni djillali liabes university of sidi bel abbes bp89, cite ben m’hidi, sidi bel abbes, 22000, algeria elmeguennimohamed@yahoo.fr mohamed benguediab djillali liabes university of sidi bel abbes bp89, cite ben m’hidi, sidi bel abbes, 22000, algeria benguediab_m@yahoo.fr abstract— polymer materials are gaining more and more importance in engineering applications. a new methodology of analysis is required in order to assess the capability of such material in withstanding complex loads. therefore, the behavior of these materials currently arouses a great research interest. the use of pvc plastic pipes in pressure vessels and pipelines has increased rapidly in the last decade. in order to determine the plastic behavior of pvc, an experimental method is presented. through the results obtained from experimental tests, in the first part of this paper, we investigate the use of a phenomenological model proposed by g’sell and jonas. the true stress-strain response under large plastic deformation was investigated in different stress triaxiality frameworks. particular attention was given to volumetric strain evolution, separation resulting from elastic volumetric strain, plastic volumetric strain and pure shear. the effect of stress triaxiality on plastic instability and fracture strain was also examined. the deformation process should be considered as explained, and the anisotropic plastic response induced by the deformation could be introduced in constitutive equations of g’sell. keywordsplane stress; triaxiality; plastic instability; pvc i. introduction in the plastics industry, technical polymers are widely used in engineering components which may experience complex mechanical loadings. the understanding of their intrinsic mechanical behavior is of prime importance in the design of components made of such. over recent years, considerable attention has been focused on the analysis of large plastic deformation of ductile materials and solid polymers. the deformation processes involved in the plastic deformation of the ductile materials have been widely investigated by several authors [1-17]. however, most studies conducted on solid polymers were based on the same criteria used for ductile materials [18–36]. the response of solid polymers is known to be sensitive to factors such as: temperature, strain rate, strain, plastic instability during the necking stage and the hardening, and the type of loading conditions, i.e. the stress triaxiality effect [21, 37-38]. however, the determination of these parameters and the characterization of materials are really difficult with traditional measuring equipment like the one used for ductile materials. therefore, some experimental devices have been developed and proposed [25, 39-40]. the aim of this paper is to investigate the plastic behavior of polyvinyl-chloride (pvc) in different triaxiality frameworks, under large deformation and in plane stress condition. the pvc material used in this work is for pipe irrigation applications. we focused on the experimental determination of the constitutive behavior in well controlled conditions. the triaxiality effects induced by the flat sample shape are studied in detail. in recent years, the study and modification of the relationships of the stress triaxiality in plane stress and strain conditions, its evolution, the behavior law in ductile materials and fracture has been the subject of various studies [15, 41-47]. this work is based on the same principle, i.e. to validate the relationship of triaxiality proposed by bai [43] for a polymer material in plane stress condition and in large deformation. the pvc material presents a complex nature of behavior resulting to a difficulty in fine physical analysis. therefore, the deformation and damage of ductile materials and polymers under different stresses has been investigated [11, 16, 47]. the use of a phenomenological law can provide a solution to the problem of predicting the behavior of such materials and also ductile fracture. several models have been proposed in the literature in order to predict the behavior of ductile materials and polymers. these include several constitutive laws proposed [7, 8, 18, 48-56]. in this paper, the law of g'sell and jonas [18], where the stress depends on deformation, speed and temperature, is selected. this law has successfully characterized the behavior of a great number of polymers either amorphous or semicrystalline, under different simple loading modes (traction or compression). in the present study, we introduce the use of this constitutive model to describe the mechanical behavior of pvc. in the last part of this paper, the large deformation behavior of pvc is examined. the relevant features which should be taken into account in the application of an accurate constitutive model (like the g'sell model [22]), are discussed with a particular attention paid on the volumetric strain and damage. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 373-380 374 www.etasr.com selini et al: effect of the triaxiality in plane stress conditions. triaxiality effect in a pvc material ii. material and experimental methods in this subsection, the investigated pvc material is described. then, the specimens’ geometry and the experimental procedure under different loading paths are presented. a. material the polymer investigated in this work (pvc) is one of the most widely used and relevantly economical plastic materials, used for a large variety of industrial applications, especially in the field of packaging and of housing environment. in houses, it is used for pipings, dressing of windows and floor covering. pvc is a thermoplastic polymer with good strength, toughness and resistance to acids as well as corrosion. in this study, the pvc material was provided by a piping company as pipes with outer and inner diameters of 200 mm and 212 mm, respectively. the physical properties of the material are: density: 1.38 g/cm³, melt mass flow: 1.2 g/10 min, molecular weight: 310000, glass transition temperature: 84 °c, melting point: 180 °c. b. specimens geometry in order to examine the sensitivity of true stress strain response on the behavior of the pvc material for various stress triaxiality, tensile tests were made on different geometries. for all tests, the samples were extracted from pvc pipes, and machined in the same extruded sheets in order to have a flat shape, with four different curvature radii on the ends of the width and in a symmetrical position (r= 2, 4, 10 and 80 mm). the specimens will be referred to as x r , where x is the value of curvature radius. the initial dimension of flat specimens is defined by: the curvature radius r0= 2; 4; 10; and 80 mm; the minimum width w0=8 mm, when w=2a; the gauge length l0; the thickness of the specimen t0=4 mm and the maximum width w=12mm. all flat specimens have the same minimum and maximum widths, as shown in figure 1(a). in this type of specimen (flat in plane stress) with two symmetric cutouts, we can easily control the initial stress triaxiality. the geometry of the specimen is shown in figure 1(b). (a) (b) fig. 1. flat grooved plane stress specimen: a) the cross section b) geometry of flat specimens. one parameter that will be referred to frequently in this paper is the stress triaxiality β [59]. it is defined as the ratio of the mean stress σm and the von mises equivalent stress σeq as: eq m σ σ β = (1) where σm is expressed as: ( ) zzyyxxm σσσσ ++= 3 1 (2) it can be expressed, using the geometric parameters in the undeformed state, as the expression for the initial triaxiality, derived by bai [43], is given by: 13 21 2 ++ + = aa a β (3) where [ ])2/(1ln 0 raa += (4) however, the stress triaxiality is not constant, but increases with plastic deformation, and the bai formula is not valid in the median cross-section in large scale deformation [43]. note that at the center of the median cross-section, the stress triaxiality ratio β reaches its maximum. iii. results and analysis a. characterization of the plastic behavior in this section, comparison will be made between the results of tensile tests carried out on flat specimens in plane stress conditions for different triaxiality. the objective of this analysis is to demonstrate the flat specimen applicability and also to investigate the effect of the triaxiality on the responses and fracture under large deformation. tests were conducted on an instron machine. an optical measurement system was used to control the strain rate and measure the local strain in the specimen section. the mechanical tests were achieved at a strain rate of 10 -3 s -1 and at room temperature (23 °c). figure 2 shows the evolution of the true axial stress and the volumetric evolution vs. true axial strain of the pvc material, and summarizes the stress triaxiality effect on the behavior and damage of this material. globally, figure 2(a) indicates that the response of this material is similar to other polymers investigated in the literature. in this response, the curve shows a proportional limit followed by a maximum at which necking takes place. it is common to term this maximum as the yield stress in polymer materials. finally, before the rupture, and like most polymers, a hardening phenomenon is observed. results show a strong influence of stress triaxiality on pvc behavior, more evident at large strains. the influence of stress triaxiality on the behavior is also evident in the evolution of volumetric strain, shown in figure 2(b). the cavitation phenomenon increases with the increase in stress triaxiality. indeed, it should be recalled that the multiaxial stress state in the median crosssection favors high positive hydrostatic stress that enhances etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 373-380 375 www.etasr.com selini et al: effect of the triaxiality in plane stress conditions. triaxiality effect in a pvc material cavitation damage, which itself induces a softening of the strain hardening rate. in order to understand the macroscopic behavior of the pvc material, we have chosen to separate the volumetric strain according to the criteria described in [58]. we considered that the various changes in the volumetric strain evolutions are caused by linear elasticity and void volume evolutions coupled to shear deformation. we recall that the decomposition of deformation is given by the following relationship: shvcavvel εεεε ++= (5) where ( )      −−= −= −= velvcavsh velvvcav elvel εεεε εεε νεε 21 (6) and              =++= σ = 0 321 ln v v e v el εεεε ε (7) the true strain rate is maintained constant in the necking using an optical measurement system. at the beginning of the necking, a difference between the two deformations (transversal and longitudinal) will be detected by the optical system; therefore it will slow the speed of the machine in order to stabilize the local strain rate. the evolution of true stressstrain curves of the pvc material under uniaxial tension at a constant local true strain rate of 10 -3 s -1 is presented in figure 3 at different states of triaxiality according to the radius of curvature (r2, r4, r10 and r80), respectively. a very ductile behavior in the pvc specimens whatever the triaxiality state, is shown. the true stress-strain behavior is characterized by four main stages: an initial elastic response, followed by a rollover to yield; a progressive plastic strain hardening (necking), and finally a significant plastic strain hardening at very large strains before final rupture. also, the evolution of the three components of the volumetric strain according to the relationship of [57] (5) is presented. we noticed a typical character of the plastic behavior of polymer materials, which is characterized by a high ductility, and the triaxiality effect. the elastic volumetric strain vel ε is caused by the elasticity and the poisson's ratio effect; then, the plastic volumetric strain vcav ε allows to characterize the onset of damage and its kinetics; the latter representing a significant proportion of the total deformation. finally, the deformation due to pure plastic shear sh ε allows us to appreciate the deformation involving no change in volume (figure 3). another important feature is the influence of stress triaxiality on the plastic volumetric strain and the deformation due to pure plastic shear. the most direct indicator of this phenomenon is shown in a form of a pie chart by percentages. b. plastic instability in order to characterize the degree of inhomogeneity of deformation and identify the microstructural processes of the damage of the pvc material, the previously reported results are further investigated. the true stress-strain curve shown in figure 2(a) shows a viscoelastic range up to the yield point for all triaxialities considered in this study. during this stage, deformation is nearly homogeneous. at yield, several shear bands are hardly observed in the center of the sample and in the geometric defect as shown in figure 4. after the yield point, we have observed a load drop with a decrease of true stress from 60 to 50 mpa. during this critical stage, the plastic yielding propagates across the entire width of the sample (in the center of the geometric defect). finally, the true stress is stabilized; it appears that the center of the neck is less stable than before. thus, a peculiar behavior for this polymer is documented: a necking phenomenon due to plastic instability (figure 4). 0 40 80 120 0 0,2 0,4 0,6 0,8 1 true strain tr u e s tr e s s ( m p a ) r=2mm r=4mm r=10mm r=80mm (a) 0 0,1 0,2 0,3 0 0,2 0,4 0,6 0,8 1 true strain v o lu m e tr ic s tr a in r=2mm r=4mm r=10mm r=80mm (b) fig. 2. effect of stress triaxiality on (a) stress-strain response and (b) volumetric strain evolution. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 373-380 376 www.etasr.com selini et al: effect of the triaxiality in plane stress conditions. triaxiality effect in a pvc material r = 2mm 0 20 40 60 0 0,1 0,2 0,3 0,4 0,5 true strain tr u e s tr e s s ( m p a ) 0 0,1 0,2 0,3 0,4 0,5 v o lu m e tric s tra in εvcav εsh εvel (a) r = 4mm 0 20 40 60 0 0,2 0,4 0,6 true strain tr u e s tr e s s ( m p a ) 0 0,1 0,2 0,3 0,4 0,5 v o lu m e tric s tra in εvcav εsh εvel (b) r = 10 mm 0 20 40 60 80 100 0 0,2 0,4 0,6 0,8 true strain tr u e s tr e s s ( m p a ) 0 0,2 0,4 0,6 0,8 v o lu m e tric s tra in εvcav εsh εvel (c) r = 80 mm 0 20 40 60 80 100 120 0 0,2 0,4 0,6 0,8 1 true strain tr u e s tr e s s ( m p a ) 0 0,2 0,4 0,6 0,8 1 v o lu m e tric s tra in εvcav εsh εvel (d) fig. 3. true stress and volumetric strain evolution vs true strain response. fig. 4. photographs of the stretching behavior under tensile testing. the polymerists have sought more specific laws capable of accounting the viscoplastic behavior of most polymers. several approaches have been proposed. as g’sell and jonas [18] have initially proposed, for pvc, a phenomenological model of behavior is given by (8) where σ is the equivalent stress, ε is the equivalent strain, m is the coefficient of sensitivity to strain rate and torque, h are two material constants: ( )2, exp m k hσ ε ε ε ε • •      = (8) the factors ( )2exp hε and m ε • respectively describe the hardening and viscous behavior. g'sell [22] has proposed to modify (8) by including others factors, describing the law of behavior of all polymers by a global relationship expressed as follows: ( ), . . (9)k f gσ ε ε ε ε • •            = where k is a material constant and ( )f ε and g ε •      represent the influence of the deformation and the strain rate respectively. the function ( )f ε can be written as: etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 373-380 377 www.etasr.com selini et al: effect of the triaxiality in plane stress conditions. triaxiality effect in a pvc material ( ) ( ) ( ) ( )εεεε hcvf ..= (10) where ( ) ( ) ( ) ( ) ( ) ( ) 1 exp . 1 .exp . exp . n v w c a b h h νε ε ε ε ε ε       = − − = + − = (11) ( )v ε describes the viscoelastic behavior law; ( )c ε represent the draw-hook and ( )h ε describes the gradual hardening in large deformations, where n is equal to 2 in most cases. after the verification of the rate sensitivity of the pvc material, we have observed that this material is not sensitive to strain rate; where this sensitivity is expressed by the function       •εg , and can be written in the following form: m g •• =      εε (12) in the context of this work, in order to understand and explain the mechanical behavior of the polymer studied, the g’sell models [18, 22] are compared with the obtained experimental results of tensile testing. the found results after the identification of the parameters of the two formulas are presented in figure 5. the curves show a good correlation between the experimental results and those from modeling. indeed, the g’sell law [22] gives the same evolution for the behavior of pvc and allows reproducing faithfully all phases of deformation for a constant strain rate. however, the g’selljonas law [18] does not reproduce the same experimental evolution and it does not consider the tensile hook that reflects the true response of the pvc. one thing very important on the g’sell-jonas model, is that it does not take into account the effect of stress triaxiality, this is why we documented some dispersion in the results between the extreme triaxialities of r2 and r80, as shown in figure 5. in this paper we use the models without any modification. the introduction of the triaxiality effect in the hardening evolution will be the object of a future work. another objective in this part of the paper is to verify the manifestations of plastic instability on pvc in tension with the effect of the triaxiality. under isothermal mechanical behavior and a constant strain rate we assume that the criterion of strain localization is: 0d f = (13) with d ds s σ σ = − (14) and v si= representing the current volume. we obtain: 11 22 33 22 330 0 0 (15) i s s e s e i ε ε ε ε ε+ + + = =    ( )22 33 0 22 33 (16)ds s e d d ε ε ε ε+= + ( )22 33 (17) d d d σ ε ε σ = − + where localized deformation conditions can also be expressed as follows: 3322 11 11 11 (18) ddd d d d εεσ σ σ ε ε ε   = − + =    the variations of the plastic instability versus the true strain are illustrated in figure 5 for all triaxialities according to r2, r4, r10 and r80, respectively. this evolution can be qualitatively related to the microstructural evolution involved in the plastic deformation of the pvc material. first, there is a stretching of chains, followed by rotation, plastic deformation, and finally the formation of a fibrillar microstructure and the significant strain hardening observed in the stress-strain response. it can be observed in figure 2 that stress triaxiality has an important effect on strain hardening. we recall that the critical value of the plastic instability is equal to 1, which means that a plastic instability less than 1 results to the development and propagation of necking, as observed experimentally (figure. 4). however, it should be noted that the necking initial evolution stabilizes, which mean that plastic instability is greater than 1. iv. conclusion the mechanical behavior under large plastic deformation of a pvc was studied experimentally under uniaxial tension by using a videotraction system. the plastic damage of this material was analyzed in different triaxiality frameworks. to this end, the material was tested in uniaxial tension on flat grooved specimens in order to set specific values of the stress triaxiality in the median cross-section in a plane stress conditions, and with an optical measurement system in order to control the strain rate and measure the strain in the local specimen section. in order to quantitatively describe the damage of pvc, the volumetric strain was determined, with a decomposition caused by a linear elasticity and void volume evolutions coupled to shear deformation. it was found, for all tests, that the material undergoes significant volume changes during deformation favored by high values of the stress triaxiality ratio. the experimental results obtained in this work served fruitful basis of experimental data for introducing the use of a robust and constitutive model [18, 22]. to illustrate the applicability of this model to the mechanical behavior of pvc, a comparison was conducted between the two formulas. the complex mechanical behavior of polymeric materials can not be described by a simple constitutive law. this is why many models in the literature have shown deficiencies to describe the behavior of these materials. indeed, the model of g'sell [22] was able to reproduce in a simple and satisfactory way all the experimental results, and allows the description and reproduction of all phases of plastic flow such as etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 373-380 378 www.etasr.com selini et al: effect of the triaxiality in plane stress conditions. triaxiality effect in a pvc material r = 2mm 0 20 40 60 0 0,1 0,2 0,3 0,4 0,5 true strain tr u e s tr e s s ( m p a ) 0 0,5 1 1,5 2 p la s tic in s ta b ility experimental g'sell-jonas (1979) g'sell (1988) (a) r = 4mm 0 20 40 60 80 100 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 true strain tr u e s tr e s s ( m p a ) 0 0,5 1 1,5 2 p la s tic in s ta b ility experimental g'sell-jonas (1979) g'sell (1988) (b) r = 10mm 0 20 40 60 80 100 0 0,2 0,4 0,6 0,8 true strain tr u e s tr e s s ( m p a ) 0 0,5 1 1,5 2 p la s tic in s ta b ility experimental g'sell-jonas (1979) g'sell (1988) (c) r = 80mm 0 20 40 60 80 100 120 0 0,2 0,4 0,6 0,8 1 true strain tr u e s tr e s s ( m p a ) 0 0,5 1 1,5 2 p la s tic in s ta b ility experimental g'sell-jonas (1979) g'sell (1988) (d) fig. 5. true stress and plastic instability vs true strain response. draw-hook and gradual hardening in large deformations. in the continuum mechanics framework, the description of ductile materials is based on the concept of the yield criterion and its evolution with deformation. since the studied material presents cavitation damage, this one is compressible. therefore, the yield criterion needs to involve the hydrostatic stress but also the volumetric strain. furthermore, the deformation process as explained in figures 4 and 5 must be considered and at least the anisotropic plastic response induced by the deformation should be introduced in constitutive equations. in order to express quantitatively the damage kinetics in this material, we introduced the notion of ‘plastic instability’ which represents the instantaneous evolution of the volume strain vs true axial strain. also it was found that plastic strain hardening increases gradually with the triaxiality. finally, in order to highlight the evolution of the observed phenomena in the deformation process, e.g. volumetric deformation and plastic instability, the finite element modeling can prove very important. all these features will be investigated again in another paper on the basis of detailed characterization of plastically. however, approximate analytical theories, as those we presented in this work, remain very useful to account for basic phenomena. references [1] a. a. benzerga, “micromechanics of coalescence in ductile fracture”, j. mech. phys. solids, vol. 50, no. 6, pp. 1331-1362, 2002 [2] a. 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deformation”, j. mater. sci., vol. 16, no. 2, 429-432, 1981 [59] p. w. bridgman, studies in large plastic flow and fracture, mcgraw hill, new york, 1952 microsoft word 45-3148_s_etasr_v9_n5_pp4830-4834 engineering, technology & applied science research vol. 9, no. 5, 2019, 4830-4834 4830 www.etasr.com rajhi: numerical damage simulation in warm deep drawing of car sump oil made with aluminum … numerical simulation of damage on warm deep drawing of al 6061-t6 aluminium alloy w. rajhi university of hail, college of engineering, hail, saudi arabia and laboratoire de mecanique, ecole nationale superieure d'ingenieurs de tunis, universite de tunis, tunisia wajdirajhi@gmail.com abstract—this work focuses on the numerical simulation of warm deep drawing operation of car sump oil made with al 6061-t6 aluminum alloy for the purpose of process optimization. the thermo visco-plastic behavior with damage effect of the material is described by the johnson-cook (jc) model. the jc model parameters for the al 6061-t6 aluminum alloy were exploited. numerical simulation of the deep drawing operation was performed with the use of the abaqus fe software thanks to the dynamic explicit temperature-displacement algorithm. the design of the different tools is obtained on the basis of the geometry of the finished product. designing of punch, die and blank holder is performed using catia 3d cad software. the warm forming method involves the heating of the blank holder and the die to a certain temperature, whereas, the punch is kept at room temperature. in this study, predefined temperatures of the die and blank holder and punch speed will be investigated among other stamping parameters. the computed damage evolution curves for a given set of the process parameters are retrieved at the end of the simulation to determine suitable forming conditions. it can be noted that the slower the damage evolution achieved within the blank, the more appropriate the process parameters. thus, by increasing strain rate, main cracks change location. the dynamic explicit temperature-displacement algorithm available in abaqus is used to solve the equilibrium problem with temperature effect in order to investigate the appropriateness of the process parameters on the basis of the computed damage-displacement curves. keywords-warm deep drawing; car sump oil; johnson-cook model; optimization; numerical simulation i. introduction aluminum alloy sheet metal is characterized by its good weight to strength ratio. however, one shortcoming of aluminum is its low malleability compared to mild steel which is widely used in sheet metal forming. thus, costly multi-step manufacture processes are required to obtain intricate product geometries with aluminum alloys [1]. one technique to prevent such difficulty is the deep drawing at high temperatures [2, 3]. accordingly, the sheet metal forming of aluminum alloys may be enhanced considerably, as the number of required production phases can be limited. regarding car sump oil application, certain conditions and obligations in relation to certain physical proprieties and mechanical characteristics of the component material have to be met. the material of the sump should provide better corrosion resistance. even if the oil sump is not intended for cooling, better material thermal conductivity improves further the performance of the component. moreover, it should offer a good ductility or toughness to avoid crack or damage formation due to contact with obstacles. in addition, low material density represents an excellent benefit, since it alleviates the weight of the sump. this study is devoted to the prediction of damage for the purpose of optimization of the warm deep drawing operation of car sump oil made with al 6061-t6 aluminum alloy which meets all the above requirements [4]. once the final geometry of the car sump oil is provided, catia 3d is used to design the finished product and thereby the corresponding tools set. thus, the different tool parts are imported from catia to abaqus wherein several numerical simulations of stamping are performed while varying operating process parameters, principally the blank holder, the die temperatures, and the punch speed. the thermo mechanical behavior with strain rate and damage effects of the al 6061-t6 aluminum alloy is described under deep drawing loading conditions by jc thermo visco-plastic model through a well-defined set of jc model parameters garnered from previous works [5, 6]. the dynamic explicit temperature-displacement algorithm available in abaqus is used to solve the equilibrium problem with temperature effect in order to investigate the basis of the computed damage-displacement curves and the appropriateness of the process parameters. ii. car sump oil design and the corresponding tools this section is devoted to a brief summary of the principal steps allowing the design under catia software of the car sump oil and the corresponding stamping tools. figure 1 illustrates the 2d detail drawing of the car sump. it provides the detailed description of the finished part geometry with all required dimensions which should be obtained at the end of the deep drawing operation. the finished part designed in catia is given in figure 2. three tools are required to achieve a deep drawing operation: the punch, the die and the blank holder. their geometries are obtained from the finished design of the car oil sump part (figure 2), defined as: • a recessed die corresponding to the outer form of the car sump. • a punch, in relief, conforming to the inner shape of the part while preserving the sheet thickness. therefore, a clearance between the die and the punch is required which should be corresponding author: w. rajhi engineering, technology & applied science research vol. 9, no. 5, 2019, 4830-4834 4831 www.etasr.com rajhi: numerical damage simulation in warm deep drawing of car sump oil made with aluminum … somewhat superior to the thickness of the stamped sheet. in this study, the clearance is a fixed process parameter, given by c=e+0.5 with e representing the thickness of the blank. • a blank holder encloses the punch which is placed against the border of the die allowing clamping the blank during the displacement of the punch. the geometry of the die, the punch, and the blank holder are given in figure 3. fig. 1. 2d detail drawing of the car sump fig. 2. design of the car sump (a) (b) (c) fig. 3. design under catia of (a) die, (b) punch, and (c) blank holder the design of the car oil sump and the corresponding tools shown in figures 2 and 3 requires several geometric operations on catia. for the removal and shaping of material, tools such as pocket and hole were used. tools such as symmetry and circular repetitions were utilized. the main geometrical modeling steps are: • generation of the casing shape by extrusion and revolution • using a pocket to empty the housing core • making the fixing holes (hole with circular repetition), despite they are not requested in this analysis iii. thermo-mechanical behavior of al 6061-t6 aluminum alloy in this study the temperature dependence of the elastic behavior of al 6061-t6 aluminum alloy is considered. moreover, the temperature dependence of the physical and thermal proprieties of the materiel such as density, thermal conductivity, heat capacity and thermal expansion were taken into consideration during the numerical simulation of the deep drawing operation. the evolution of the cited above physical, thermal and elastic material proprieties as temperature increases up to the melting point of the material are given in figure 4. (a) (b) (c) fig. 4. material properties with temperature dependance of 6061-t6 aluminum alloy. data were taken from [5] thus, the jc constitutive model with the damage effect is used in this work to describe the thermo plastic behavior with strain rate effect (viscosity) of the blank accounting for material softening and failure under deep drawing loading conditions. it is worth noting that constitutive models based on thermodynamic of irreversible process [7-9] result in a more accurately damage prediction once the strain rate effect is taken engineering, technology & applied science research vol. 9, no. 5, 2019, 4830-4834 4832 www.etasr.com rajhi: numerical damage simulation in warm deep drawing of car sump oil made with aluminum … into consideration [10]. the jc flow stress relation accounting for temperature and strain rate effect is given by: � � �� � ��� �� 1 � � �� ��� ��� ��� 1 � � ���� ���� ��� �� (1) equation (1) includes five materials constants: the yield stress a, the hardening modulus b, the strain-hardening coefficient n, the viscosity parameter c, and the thermal sensitivity m. constants b and n describe the flow stress with hardening effect. to and tmelt are respectively the room temperature and the melting temperature, while ��! is the reference strain rate. the a, b, c, n and m jc material parameters of the al 6061-t6 aluminum alloy used in the present study are reported in table i. table i. plastic parameters of jc constitutive model for al 6061-t6 aluminum alloy [5] a (mpa) b (mpa) n c m "� # melting point (°c) 324 114 0.42 0.0083 1.34 1 582 the jc failure criterion is used to describe ductile damage evolution within the al 6061-t6 aluminum alloy sheet metal under stamping conditions: �$ � %&' � &()*+ &, �-.��/ 1 � &0 �� � �� � �� ��� 1 � &1 � �������� ����� (2) the parameters of jc failure criterion for the al 6061-t6 aluminum alloy are reported in table ii. table ii. damage parameters of jc constitutive model for al 6061-t6 aluminum alloy [6] d1 d2 d3 d4 d5 -0.77 1.45 -0.47 0 1.6 iv. car sump oil deep drawing finite element model we are interested in the numerical simulation of the deep drawing operation of the crater using the dynamic explicit temperature-displacement algorithm available in abaqus fe software. therefore, the different tool parts given in figure 3 are imported to abaqus from catia. in this study, the tools are considered as discrete rigid parts and their meshing is carried out using r3d4 (4-node 3-d bilinear rigid quadrilateral) rigid element type (figure 5). thus, the same element size of about 8mm has been adopted to mesh the die, the punch, and the blank holder. the simulated al 6061-t6 aluminum alloy sheet metal with dimensions of 400×400×6mm 3 is shown in figure 5. the thermo-elastic behavior of the sheet metal under stamping conditions is described by the al 6061-t6 alloy data shown in figure 4. the plastic behavior is dependent to both temperature and strain rate effects and defined by jc constitutive model presented above including the model parameters reported in table i [5, 6]. the blank is meshed with 3d solid element type c3d8t using only one element through thickness (an 8-node thermally coupled brick, trilinear displacement and temperature), with minimum mean size of 2mm. the blank holder is placed over the blank, i.e. no operating forces are applied on the blank holder. a friction coefficient µ=0.05 is defined between the upper face of the blank and the down surface of the blank holder and each of down and side surfaces of the punch. the same friction coefficient value is adopted to define the contact between the lower surface of the blank and the inner surfaces of the die. fig. 5. 3d mesh of the the blank and the tool parts the punch velocity v is considered as one of the main setting parameters for the deep drawing operation, thereby its value is altered in order to investigate such parameter effect on damage evolution. the blank under stamping condition is subjected to a strain rate magnitude which may be defined as the ratio between the operating punch velocity and the total punch displacement during which the contact between the punch and the blank is maintained. since the total displacement of the punch is constant, the magnitude is none other than that the stamping depth sd=55mm, hence, according to a strain rate reference value of 1s -1 , a reference value of punch velocity vpr of about 55mm/s will be adopted. the warm deep drawing process involves that the different stamping tools are preheated and thermally insulated. in this work, the temperature of the punch is kept constant and close to room temperature throughout all stamping simulations. the preselected temperatures t0 of blank holder and die which represent the second setting parameter for this study are considered the same and altered from one calculation to another. therefore, various temperature levels are assigned to both the die and blank holder ranging between room temperature and 2/3 of melting temperature of the aluminum alloy under investigation. the settings of stumping parameters are illustrated in table iii. table iii. selected stamping conditions for numerical simulation "� (s-1) v (mm/s) t0room (°c) t01 (°c) t02 (°c) t03 (°c) 0.02 1.1 25 100 200 400 1 55 25 100 200 400 100 5500 25 100 200 400 blank engineering, technology & applied science research vol. 9, no. 5, 2019, 4830-4834 4833 www.etasr.com rajhi: numerical damage simulation in warm deep drawing of car sump oil made with aluminum … v. results several numerical simulations of car sump oil stamping operation were performed accounting for the process sittings reported in table iii. the distributions mapping of vom equivalent stress, damage and temperature for setting parameters (1s -1 , 25°c) are illustrated in figure 6. these distributions were retrieved before the end of the simulation while showing a wide region of meshing elements fully damaged (see figure 6(b)). thus, cracks within the blank having different sizes occurring in the neighborhood of the die shoulder were initially detected (figure 7). (a) (b) (c) fig. 6. distribution mapping of (a) vom equivalent stress, (b) damage, and (c) temperature obtained during stamping simulation for stamping conditions (1s -1 , 25°c) the computed damage-displacement evolution curves within the area of mesh elements of the blank located neighborhood to the die shoulder were obtained for the magnitude v1 of punch velocity for temperature of the die and the blank holder ranging from room temperature to 400°c (table iii) and are shown in figure 8. it can be noted that there is no significant effect of the die and blank holder temperature on the damage evolution neighborhood to the die shoulder during stamping operation. the same observations about the effect of the variation of the die and blank holder temperature regarding damage evolution are valid for punch velocities v2 and v3. fig. 7. crakcs initiation neighborhood to the die shoulder for stamping conditions (1s -1 , 100°c) fig. 8. effect of die and blank holder operating temperature on the damage evolution within the blank the effect of punch velocity on damage evolution for setting temperature 100°c is illustrated in figure 9. fig. 9. effect of punch velocity on damage evolution in deep drawing of al 6061-t6 for punch velocity settings v1 and v2, the damage evolution neighborhood to die shoulder can be considered the same. the damage decelerates for punch velocity v3. similar observations were made for operating temperatures 25, 200, 300 and 400°c. initial die shoulder cracks punch shoulder crack die shoulder crack engineering, technology & applied science research vol. 9, no. 5, 2019, 4830-4834 4834 www.etasr.com rajhi: numerical damage simulation in warm deep drawing of car sump oil made with aluminum … hence, it can be noted that for a given operating temperature, according to the plastic and damage jc parameters given in tables i and ii respectively, the higher the strain rate the slower the initial damage or main crack occurrence in the die shoulder neighborhood in the deep drawing of al 6061-t6. it can be also noted that for deep drawing at high strain rate, the main cracks change their location from the die shoulder zone to the punch shoulder zone, which explains why damage decelerates in the die shoulder neighborhood for punch speed v3. vi. conclusion in this work, jc visco-plastic model with damage effect is used to predict damage and crack formation in warm deep drawing of car sump oil made with aluminum alloy al 6061t6. several deep drawing numerical simulations were carried out altering die and blank holder operating temperature as well as punch velocity in order to investigate damage initiation in the blank for purpose of process optimization. it has been found that preheating the die and blank holder had not significant effect on damage evolution within the zone where the cracks initiate. however, punch velocity influences damage evolution within such critical zone, so that, an increase in strain rate results in a change in the cracks location. acknowledgment the author would like to acknowledge the research deanship of the university of hail for supporting this study under the project no. 0160641. references [1] m. packo, m. dukat, t. sleboda, m. hojny, “the analysis of multistage deep drawing of aa5754 aluminum alloy”, archives of metallurgy and materials, vol. 55, no. 4, pp. 1173-1184. 2010 [2] g. venkateswarlu, m. j. davidson, g. r. n. tagore, “finite element simulation of deep drawing of aluminium alloy sheets at elevated temperatures”, arpn journal of engineering and applied sciences, vol. 5, no. 7, pp. 93-98, 2010 [3] g. ambrogio, l. filice, g. palumbo, s. pinto, “enhancing ldr in deep drawing by superimposing thermal gradients”, 8th international conference on numerical methods in industrial forming processes, columbus, usa, june 13–17, 2004 [4] b. m. dariani, g. h. liaghat, m. gerdooei, “experimental investigation of sheet metal formability under various strain rates”, proceedings of the 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application to metal forming simulation”, international journal of damage mechanics, vol. 23, no. 8, pp. 1211-1256, 2014 [9] w. rajhi, b. ayadi, a. alghamdi, n. messaoudene, “an anisotropic elastic-plastic model for the optimization of a press machine’s auxiliary worktable plate thickness”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2764-2769, 2018 [10] k. saanouni, damage mechanics in metal forming: advanced modeling and numerical simulation, john wiley, 2012 microsoft word 14-2740_s_etasr_v9_n3_pp4144-4147 engineering, technology & applied science research vol. 9, no. 3, 2019, 4144-4147 4144 www.etasr.com sulieman & alfaraidy: influences of project management capabilities on the organizational … influences of project management capabilities on the organizational performance of the saudi construction industry hassan ahmed sulieman faculty of engineering, civil engineering department, northern border university, arar, saudi arabia hassan.abdualrahman @nbu.edu.sa faris abdulaziz alfaraidy faculty of engineering, civil engineering department, northern border university, arar, saudi arabia falfaraidy @nbu.edu.sa abstract—this paper aims to study the relations between construction enterprises’ project management capabilities and organizational performance. a questionnaire survey was administered to 89 saudi construction contracting organization administrative members. data were obtained from 32 projects that were held during the last two years and were analyzed using structural equation modeling (sem). it was hypothesized in this study that a construction organizational performance is influenced by project management capabilities within the enterprise. a structural equation model was set up to measure the above two latent variables through their constituent variables. this study introduced a method to measure performance both in qualitative and quantitative terms. the strong path coefficients between the constructs of the model are an indication that after decades in pursuit of finding ways to improve the performance of construction organizations, subjective dimensions of performance have proven to be as effective as the traditional objective dimensions. keywords-balanced scorecard; performance; sem i. introduction saudi arabia is the largest oil exporter in the world. as a result, the saudi economy is constantly on the rise and the construction sector’s activity is increasing. the construction industry plays a key role in the performance of all economic sectors. the saudi government has supported construction projects through substantial investments in infrastructure projects. the problem of poor performance in construction projects is a global phenomenon and the construction industry in saudi arabia is no exception [1]. performance measurement has new methods that can measure financial and non-financial aspects [2]. these frameworks vary according to the place of application, and whether they are for organizations, projects, or stakeholder performance [3]. it is known that project management through integrated and balanced indicators will achieve a significant improvement in the performance and future of an industry. performance measurement and management are still unused as a performance improvement tool in the saudi arabia construction industry. the objective of this research is to study the relations between construction organization's project capabilities and organizational performance based on strategic measures, not only financial which are traditionally used in most construction organizations. the essence of these measurements is modified and they are being pushed from accounting-based towards an economicoriented framework. considering nowadays business and the global economic impact of the construction industry, performance management and measurement in construction is important and critical. therefore, effective construction project management is crucial for higher performance levels [4, 5]. ii. literature review the proposed framework consists of an integrated and balanced system for measuring and managing the organization's project capabilities in term of its ability to address all performance management stages and balanced scorecard (bsc) elements. public and private enterprises are gradually moving towards the adoption of the performance management system (pms) as it provides an integrated and coherent range of human resources processes which can be supportive in terms of contributing to the overall improvement of organizational and individual performance [6]. the sophistication of strategic project management is a function of the organization's level of relevant resources, competencies, and capabilities. these influence the propensity for learning, the characteristics and context that impact required strategic implementation and strategic outcome realized through strategic project management [7]. a. project management capabilities project management capabilities include management capabilities regarding research and development, health and safety, schedule [8], cost, quality, knowledge, risk, supply chain, and human resources. research and development capability is a response to increased industry requirements that occurred as a result of globalization and competition. developments occur in all phases of the construction process and technologies that are deemed to have a positive impact on competitive advantage emerge. it is a major enabler of the project to complete on time by the use of a series of processes. these processes are activity definition, sequencing, resource estimating, duration estimating, schedule development and schedule control [9]. cost management activities include planning, estimating, budgeting, and controlling of the project [9]. quality management refers to the activities in an organization that determine quality policies, objectives, and corresponding author: hassan ahmed sulieman engineering, technology & applied science research vol. 9, no. 3, 2019, 4144-4147 4145 www.etasr.com sulieman & alfaraidy: influences of project management capabilities on the organizational … responsibilities and represents solutions in response to the complex and non-standardized nature of construction projects. even minor defects may require re-construction and may impair the facility’s operations parties [10]. it has a strong correlation with project performance. knowledge management is essential in accessing information relevant to best practices, lessons learned, historical and schedule data, and any other information necessary to run a project efficiently [11]. the capability of an organization to cope with sophisticated projects is the result of successful knowledge management [12]. health and safety management has a human dimension as accidents during the construction process can result in personal injuries and cause an increase in indirect costs such as the cost of insurance, inspection, and conformance to regulations [13]. b. organization performance the balanced scorecard (bsc) perspective was adopted in this study to measure organization performance because of its established status and its common use. it is a framework for measuring the strategic, operational and financial characteristics of an enterprise. it combines four perspectives to assess the performance of an organization. the financial perspective indicates the success of the enterprise measured in terms of indicators such as profitability. the financial performance measures indicate whether the enterprise’s strategy, implementation, and execution are contributing to the bottom-line improvement. the financial objectives reflect the financial performance expected from the strategy and also serve as the ultimate targets for objectives and measures of all the other scorecard perspectives. measures of financial performance of an organization are important in the reduction of risk but overemphasis on it leads to an unbalanced situation with regard to other perspectives [14]. organizations that really benefit from a scorecard process would inevitably move the focus of their attention to the non-financial scorecard metrics [15]. it is understandable that overemphasis on short-term financial results can cause enterprises to overinvest in shortterm fixes and to underinvest in long-term value creation [16]. the learning and growth perspective refers to the progress achieved by an enterprise and its growth potential. organizational learning capacity and the achievements of the enterprise in areas such as the enterprise’s image or various competencies are also taken into account in this perspective. the learning and growth perspective of the bsc identifies the infrastructure that the organization must build to create longterm growth and improvement. the predominant element within this perspective is whether the organization possesses the required capabilities to improve and create future value for its stakeholders [17]. the internal business perspective is an indicator of the success and efficiency of operational and managerial activities in the organization. through the use of bsc, the key processes in an organization are monitored to ensure that outcomes will be satisfactory and thus this perspective serves as a mechanism through which performance expectations of both customers and enterprise are achieved. it is further argued that this perspective reveals two fundamental differences between the traditional and bsc approaches to performance measurement. the traditional approaches attempt to monitor and improve existing business processes whereas the bsc approach identifies entirely new processes at which the organization must excel to meet customer and financial objectives [17]. the customer perspective considers the satisfaction of the different participants in the project such as clients and end users. how an organization is performing through the eyes of its customers has become a priority for business managers and this perspective captures the ability of the organization to provide quality goods and services and achieve overall customer satisfaction [17]. leaders in the service industry are good at meeting customer requirements and performance measurement [18]. the core outcome measures include customer satisfaction, customer retention, average customer duration, loyalty, repeated businesses, customer claims, complaints, customer profitability, annual income per customer, short lead times, new customer acquisition, delivery on time, and market and account share in targeted segments [19]. iii. research methodology hypothetical relationships with proposed measures and indicators were set based on literature, consultation of professionals and previous studies, consisting of two latent variables and 13 constituent variables. then a questionnaire consisting of performance measures and indicator related questions was designed in likert scale. data were collected from saudi arabia construction organizations through 89 respondents which were randomly selected from the top to medium level staff of the organizations. influences on organizational performance were analyzed using sem. all the stages of the research methodology are presented in figure 1. fig. 1. research methodology flowchart. iv. results and discussion a. validity of performance measures and indicators the data were obtained from 89 respondents in saudi arabia construction organizations regarding 32 projects over the last two years. then they were analyzed using a sem software package called eqs6.4. 1) content validity testing of performance measures content validity tests rate the extent to which a constituent variable belongs to its corresponding construct. since content engineering, technology & applied science research vol. 9, no. 3, 2019, 4144-4147 4146 www.etasr.com sulieman & alfaraidy: influences of project management capabilities on the organizational … validity cannot be tested by using statistical tools, an in-depth literature survey is necessary to keep the researcher’s judgment on the right track [20]. an extensive literature survey was conducted to specify the variables that define latent variables. 2) scale reliability testing of performance measures the scale reliability is the internal consistency of a latent variable and is measured most commonly with a coefficient called cronbach's alpha. the purpose of testing the reliability of a construct is to understand how each observed indicator represents its correspondent latent variable. according to the analysis results, as seen in table i, cronbach’s alpha values were 0.787 for project management capabilities and 0.846 for organization performance. these reliability values are satisfactory since the cronbach’s alpha coefficients are all above 0.70, which is the recommended value [21]. table i. cronbach's alpha latent variable cronbach’s alpha project management capabilities, ф 0.787 organization performance, γ 0.846 3) convergent validity testing of performance measures convergent validity is the extent to which the latent variable correlates to corresponding items designed to measure it. ideally, convergent validity is tested by determining whether the items in a scale converge or load together on a single construct in the measurement model. if the factor loadings are statistically significant, then convergent validity exists. since sample size and statistical power have a substantial effect on the significance test, this statement needs expanding [20]. the model parameters were assessed and all factor loadings were found to be significant at (α=0.05) as in tables ii-iii. table ii. factor loading of organization project management capabilities project management capabilities, ф factor loadings human resources management, β� 0.625 cost management, β� 0.934 quality management, β� 0.852 schedule management, β� 0.682 risk management, β 0.789 supply chain management, β 0.694 health & safety management, β� 0.199 knowledge management, β� 0.885 research & development, β 0.855 4) discriminant validity testing of performance measures discriminant validity is the extent to which the items representing a latent variable discriminate that construct from other items representing other latent variables. this is particularly important when constructs are highly correlated and similar in nature. in essence, items from one scale should not load or converge too closely with items from a different scale. table iii. factor loading of organization performance organization performance, � factor loadings financial perspective, μ� 0.485 internal business perspective, μ� 0.499 learning & growth perspective, μ� 0.769 customer perspective, μ� 0.686 b. structural model analysis the sem steps are: (1) specification of the model, (2) estimation and identification of the model, and (3) evaluation of the model fit. the analysis of the model performance is explained below. 1) specification of the model literature review and expert interviews were conducted to develop a conceptual model that shows how the latent variable “resources and capabilities” affects organizational performance. the model prepared for this purpose assumed that “resources and capabilities”, influences the “organization performance”. this model is specified by the direct path equation (1): γ=bф+c (1) where, γ=organization performance, ф =project capabilities, b=path coefficient, and c=error term. 2) estimation and identification of the model it means that it is theoretically possible for the computer to derive a unique estimate of every model parameter. different types of structural equation models must meet certain requirements in order to be identified. if a model fails to meet the relevant identification requirements, the attempts to estimate it may be unsuccessful. there are several methods of model estimation. some frequently utilized methods include maximum likelihood (ml), generalized least squares (gls), asymptotically distribution-free (adf) estimator and robust statistics. 3) evaluation of the model fit it means to determine how well the model as a whole explains the data. once it is determined that the fit of a structural equation model to the data is adequate, the performance measurement model is completed. however, it seems that the concern for overall model fit is sometimes so great that little attention is paid to whether estimates of its parameters are actually analyzed. the model fit indices for each construct were assessed through the non-normed fit index (nnfi), comparative fit index (cfi), the root mean square error of approximation (rmsea) and the ratio of χ2 per degree of freedom (dof). model fit indices analysis results for each construct can be seen in figure 2 and table iv. within the structural model illustrated in figure 2, for every unit “project management capabilities” that goes up, “organization performance” rises. moreover, the influence of measures and indicators of project management capabilities on organization performance indicators can also be analyzed mathematically as: β�×0.617×0.542=0.735×μ� (2) the perspective values in term of measures and indicators are listed in table v. engineering, technology & applied science research vol. 9, no. 3, 2019, 4144-4147 4147 www.etasr.com sulieman & alfaraidy: influences of project management capabilities on the organizational … fig. 2. influence of project management capabilities to organizational performance table iv. model fit indices for project management capabilities to organization performance fit indices allowable range overall nni 0 (no fit)–1 (perfect fit) 0.792 cfi 0 (no fit)–1 (perfect fit) 0.819 rmsea <0.1 0.094 χ2/dof <3 1.864 table v. values of perspectives in terms of measures μ� μ� μ� μ� 0.455×β� 0.500×β� 0.483×β� 0.518×β� 0.602×β� 0.661×β� 0.638×β� 0.685×β� 0.552×β� 0.607×β� 0.586×β� 0.629×β� 0.490×β� 0.538×β� 0.519×β� 0.557×β� 0.521×β 0.572×β 0.552×β 0.592×β 0.512×β 0.562×β 0.543×β 0.582×β 0.367×β� 0.403×β� 0.390×β� 0.418×β� 0.585×β� 0.642×β� 0.620×β� 0.665×β� 0.561×β 0.617×β 0.595×β 0.639×β v. conclusion globalization brought on construction enterprises augmented capacity, project management capabilities, expanded market areas, a variety of projects, and improved competitivity. performance management of organizations became an important subject of interest during the last decades. the proposed performance measurement tool extrapolates the project management capabilities that the organization will need to innovate and enhance its “learning & growth”, “financial issues”, and “internal business”, which lead to “customer satisfaction”. this study introduced a method to measure performance in qualitative and quantitative terms. the strong path coefficients between the constructs of the model are an indication that after decades in pursuit of finding ways to improve the performance of construction organizations, subjective dimensions of performance have proven to be as effective as the traditional objective dimensions. references [1] n. m. a. abbas, “the impact of construction contractsmodels on construction claims in the saudi arabia”, 14 th annual arcom conference, reading, uk, september 9-11, 1998 [2] a. neely, b. marr, g. roos, s. pike, o. gupta, “towards the third generation of performance measurement”, controlling, vol, 15, no. 34, pp. 129-136, 2003 [3] h. yang, j. f. yeung, a. p. chan, y. chiang, d. w. chan, “a critical review of performance measurement in construction”, journal of facilities management, vol. 8, no. 4, pp. 269-284, 2010 [4] z. jin, f. deng, h. li, m. skitmore, “practical framework for measuring performance of international construction firms”, journal of construction engineering and management, vol. 139, no. 9, pp. 11541167, 2013. [5] h. s. robinson, p. m. carrillo, c. j. anumba, a. m. a-ghassani, “review and implementation of performance management models in construction engineering organizations”, construction innovation, vol. 5, no. 4, pp. 203-217, 2005 [6] a. jugmohun, “factors that influence the effectiveness of performance management system adoption in organization”, global journal of human resources management, vol. 6, no.1, pp. 51-66, 2018 [7] j. brathwaite, “a contemporary twist on capability enhancement: how strategic project management influences capabilities requirements relationship with strategic outcomes”, the business and management review, vol. 9, no. 4, pp. 574-591, 2018 [8] c. hendrickson, t. au, project management for construction, prentice hall, 1989 [9] project management institute, a guide of project management body of knowledge (pmbok), project management institute, 2017 [10] g. k. kanji, a. wong, “quality culture in construction industry”, total quality management, vol. 9, no. 4, pp.133-140, 1998 [11] j. m. kamara, g. augenbroe, c. j. anumba, p. m. carrillo, “knowledge management in the architecture, engineering and construction industry”, construction innovation, vol. 2, no. 1, pp. 53-67, 2002 [12] a. warszawski, “strategic planning in construction companies”, journal of construction engineering and management, vol. 122, no. 2, pp. 133140, 1996 [13] k. ringen, j. seegal, a. englund, “safety and health in the construction industry”, annual review of public health, vol. 16, pp. 165-188, 1995 [14] j. liebowitz, c. y. suen, “developing knowledge management metrics for measuring intellectual capital”, journal of intellectual capital, vol. 1, no. 4, pp. 54-66, 2000 [15] a. m. schneiderman, “why balanced scorecards fail?”, journal of strategic performance measurement, special edition, pp. 6-11, 1999 [16] r. s. kaplan, d. p. norton, the balanced scorecard: translating strategy into action, harvard business review press, 1996 [17] d. amaratunga, d. baldry, m. sarshar, “assessment of facilities management performance what next?”, facilities, vol. 18, no. 1-2, pp. 66-75, 2000 [18] a. robson, v. b. prabhu, “what can we learn from leading service practitioners about business excellence?”, managing service quality, vol. 11, no. 4, pp. 249-261, 2001 [19] s. mccabe, benchmarking in construction, blackwell science, 2001 [20] s. c. dunn, r. f. seaker, m. a. waller, “latent variables in business logistics research: scale development and validation”, journal of business logistics, vol. 15, no. 2, pp. 145-172, 1994 [21] j. nunnally, psychometric theory, mcgraw-hill, 2010 engineering, technology & applied science research vol. 7, no. 3, 2017, 1725-1731 1725 www.etasr.com fashami and babaei: a behavioral maturity model to establish knowledge management in an … a behavioral maturity model to establish knowledge management in an organization camellia salehi fashami department of information technology management college of management and economics science and research branch, islamic azad university tehran, iran mohammadreza babaei department of industrial management college of management and accounting yadegar-e-imam khomeini (rah) shahrerey branch islamic azad university tehran, iran abstract—modern organizations need intangible assets such as organizational knowledge and human resources to gain competitive advantage in the market. organizations can provide opportunities for behavioral maturity of managers to establish knowledge management. this study tries to develop a behavioral maturity model for managements to examine effectiveness of knowledge management. the study is conducted in iran insurance company as an empirical case study. twenty academic and organizational experts are selected for the study. employees and managers of iran insurance company are used to measure and test conceptual model (behavioral maturity of managers to establish knowledge management). both interview and questionnaire tools are used to collect data. fuzzy ahp and pls methods are used to analyze the collected data. fuzzy ahp results show that transformational leadership, human and social skills, knowledge orientation, emotional intelligence, trustful climate are identified as highly effective priorities. keywords-behavioral maturity model; knowledge management; managers; organization i. introduction knowledge organization is considered one of the organizational capitals. organizational knowledge means choosing the right science in the appropriate time and conditions [1]. in fact, information and knowledge management has become a strong position to survive in dynamic and innovative organizations; even market and business competitiveness requires acquisition, development and updating of individual and organizational knowledge to the extent that knowledge is considered as an essential part of organizational capitals [2]. hence, intelligent management is to use knowledge to face and deal with uncertainty factors, maintain opportunities and innovate to expand competition [3]. this requires organizations to value and prioritize knowledge management and related steps as an essential requirement for pioneering in the competition [4]. organizations with a high degree of creativity and work performance manage their knowledge more effectively [5]. in current business environment which is characterized by market globalization, increased competition and high rate of technological changes, tangible assets (such as capital, land, raw materials, etc.) do not create sustainable competitive advantages for the organization. recognition of knowledge management as the spirit of organizational actions is essential for its implementation [6]. despite strong reasons for strategic use of knowledge management to improve organizational performance, there are various obstacles in implementing knowledge management in organizations [7]. these obstacles can be summarized as: 1) unfamiliarity of managers with knowledge management (senior and middle managers are not fully familiar with knowledge management and do not understand its advantages for the organization); 2) employees consider knowledge as a source of power (employees do not tend to share their knowledge) [7]. currently, managers realize that machinery, equipment and buildings are not the most important organizational assets and and that a proper management of organizational knowledge lead to a competitive advantage for the organization [8]. following significance of knowledge assets, organizations are increasingly required to manage their knowledge assets. organizations need to share organizational knowledge between different sectors to accelerate individual and organizational performance [9]. it seems essential that leadership establish knowledge in the organization properly. considering the essential role of knowledge management, numerous methods have been presented for deployment of knowledge management in the organization; this confuses managers who tend to implement knowledge management. the purpose of this study is to develop a behavioral maturity model of managers for effectiveness of knowledge management establishment in iran insurance company. ii. literature review in [10], authors identified the effective factors on establishment of knowledge management systems in taiwanese smes. they used lisrel to analyze the data gathered. factor analysis model showed that structural (organizational), infrastructural and human factors were very important and effective in establishing knowledge management systems. in [11], authors developed a model for effective factors on establishment of knowledge management. their findings showed that employee participation and organizational engineering, technology & applied science research vol. 7, no. 3, 2017, 1725-1731 1726 www.etasr.com fashami and babaei: a behavioral maturity model to establish knowledge management in an … factors including culture had the highest effect on successful establishment of knowledge management. in [12], authors experimentally evaluated knowledge sharing, knowledge leakage and innovative performance. their results indicated that knowledge sharing positively influenced innovative performance; however, high rate of knowledge leakage negatively moderated the relationship between knowledge sharing and innovative performance. in [13], authors examined the role of knowledge-based leadership on actions of knowledge management and innovation. they found that actions of knowledge management mediated the relationship between knowledge-based leadership and innovative performance. moreover, they found that actions of knowledge management were effective on innovative performance. in [14], authors addressed the barriers and solutions of knowledge management establishment in iranian public organizations. they noted that intellectual assets and knowledge are as important as other physical and financial assets. they considered human, technological and structural barriers as important barriers to establishment of knowledge management. moreover, their solutions included the increased leadership support, promoted learning and restructure of organizations. in [15], authors studied the infrastructures required for establishing knowledge management in universities. as they noted, knowledge management was considered as a strategic need of education and higher education institutions in the third millennium. in [16] the effect of knowledge management establishment on organizational excellence was determined. it was noted that proper knowledge management leads to competitive advantage and ultimately organizational excellence. the study was conducted in payam nour university of west azarbaijan using descriptive-survey approach. considering the great responsibility of payam nour university, it has established knowledge management in the organizational structure through a knowledge network including top and middle management, executives and employees. collaboration, learning culture and knowledge sharing has improved capabilities of employees; it is suggested to repeat this study in other organizations. in [17], authors concluded that knowledge management directly influenced organizational innovation in manufacturing firms. in [18], authors analyzed the effect knowledge management project and efqm for improving the key results of the business. in [19], authors defined a model to properly evaluate knowledge management value. iii. research methodology the participants in this study included 20 experts in knowledge management establishment and organizational behavior as well as 800 employees of iran insurance company. twenty experts were used to identify effective factors on the role of behavioral maturity model in establishing knowledge management in the iran insurance company. a series of criteria were determined for inclusion of experts; these criteria included practical and working experience, major and important positions in the company, enough experience in establishing knowledge management, and at least a bachelor's degree. based on cochran’s formula, at least 260 questionnaires should be handed out, however, in an effort to increase the validity of the study, a total of 280 questionnaires were distributed. a. fuzzy analytic hierarchy process (ahp) triangular fuzzy numbers are used to avoid ambiguity caused by uncertainty in decision-making. table i shows pairwise comparisons in ahp. a triangular fuzzy number denoted by ã=(l,m,u) has the following membership function. figure 1 shows the membership function selected for fuzzy numbers. two indexes are used for triangular fuzzy numbers: confidence and optimism. confidence index (α) indicates confidence of the decision maker in his prioritization and judgement. by defining α, triangular fuzzy number is defined as follows: 0 , 1 1 / 1, 1( ) / , 0 , f x x m x mx u x u m m x u x u               (1) [0,1] [ , ] [( 1) 1, ( ) ]m l u m u m u             (2) optimism index (μ) can be used to estimate success rate. optimism index as shown in the formula (3) is a linear convex combination. (1 ) , [0,1]ij iju ijua a a            (3) accordingly, the following matrix can be formed from pairwise comparisons. 12 1 21 2 1 2 1 1 1 n a n n n a a a aa a a                                  (4) by completing pairwise comparisons, weight vector of indexes is calculated by using the following formula where λmax is the largest eigenvalue of the matrix: maxaw w (5) once all matrices of pairwise comparisons are formed, consistency rate (cr) is calculated for each matrix using the following formula: c i c r r i  (6) ci indicates deviation from consistency and is calculated by: m a x 1 n c i n     (7) where, n denotes the size of pairwise comparisons matrix and ri represents random consistency index or average weights produced randomly, which can be extracted from the relevant table 1. cr<0.01 indicates acceptable comparisons; otherwise, engineering, technology & applied science research vol. 7, no. 3, 2017, 1725-1731 1727 www.etasr.com fashami and babaei: a behavioral maturity model to establish knowledge management in an … comparisons should be repeated with more accurate information by more experienced people. iv. measurement model evaluation convergent validity and discriminant validity are used to evaluate reliability of the measurement model using confirmatory factor analysis (cfa) and average variance extracted (ave). cfa is in fact an extension of ordinary factor analysis and an important aspect of structural equations in which certain hypotheses are tested on the structure of factor loadings. according to [20], factor loadings which are larger than 0.5 are acceptably valid. moreover, ave≥0.5 is acceptable. as shown in table i, all factor loadings are at least 0.5; thus, convergent validity of data is fully confirmed. moreover, t-values listed in the left column indicate effectiveness of this variable for its corresponding construct. tvalues≥1.96 indicate that the variable is effective for the considered construct at 95% confidence interval; otherwise, the variable is not effective. obviously, t-values are >1.96 for all variables, indicating their effectiveness on the corresponding construct. therefore, convergent validity of the constructs is confirmed. moreover, composite reliability and cronbach’s alpha obtained for all constructs indicate acceptable internal consistency of the measurement models. v. finding and results following criteria were extracted for the evaluation of behavioral maturity (table ii). these criteria were confirmed by experts and professors for their effect on behavioral maturity of managers for establishment of knowledge management. the second questionnaire developed as a matrix of these variables was distributed among experts. a. prioritization of criteria using fuzzy ahp since 20 experts were used in this study, there are 20 different matrixes for comparison of criteria. fuzzy ahp initially converts these matrixes to a single matrix. let ãkij be the element related to the k-th respondent for comparison of the criterion i with criterion j; geometric mean for corresponding elements is calculated by: 1 1 1 1 2 10 10 1 10 12 ( ) ((1,2,3) (1,1,1) (1.67,0.2,0.25) (4,5,6) (2,3,4) (0.2,0.33,0.5) (6,7,8) (2,3,4) (1,2,3) (2,3,4)) (1.23,1.73,2.26) n n k ij ij k ij ij ij ij a a a a a a a                                (8) b. calculation of fuzzy weights for behavioral maturity criteria considering fuzzy ahp, information of the integrated matrix of criteria is analyzed as follows. first, geometric mean of value of the j-th criterion is determined to other criteria: 1 13 1 11 12 13 14 15 16 17 18 19 110 111 112 113( )r a a a a a a a a a a a a a                          (9) for example, value of the first criterion is calculated as follows: table i. factor loadings of the observed variables constructs item factor loading tstatistic ave cr cronbach’s α personnel empowerment 2 0.862 26.348 0.665 0.855 0.747 3 0.833 17.926 1 0.749 13.226 training courses for managers 4 0.905 40.111 0.813 0.929 0.885 6 0.904 32.683 5 0.897 40.228 teamwork spirit 8 0.869 22.148 0.754 0.902 0.838 7 0.876 31.277 9 0.861 22.938 decision-making power 10 0.931 70.387 0.773 0.902 0.838 12 0.887 36.741 11 0.816 17.972 human and social skills 15 0.929 64.505 0.822 0.932 0.892 14 901 55.742 13 0.884 31.577 trustful climate 17 0.898 47.325 0.729 0.889 0.813 18 0.857 26.824 16 0.804 12.578 professional commitment and responsibility 21 0.871 13.004 0.633 0.837 0.714 20 0.798 8.814 19 0.711 10.524 knowledge orientation and organizational knowledge 22 0.897 28.144 0.775 0.912 0.856 23 0.879 29.775 24 0.867 28.803 quantitative management 26 0.948 85.920 0.820 0.932 0.890 27 0.885 27.977 25 0.884 28.201 supportive behavior 29 0.898 25.511 0.770 0.909 0.851 30 0.872 22.505 28 0.863 27.600 transformational leadership 31 0.867 15.689 0.737 0.893 0.824 32 0.855 21.862 33 0.854 25.956 emotional intelligence 34 0.890 26.452 0.740 0.895 0.825 36 866 30.496 35 0.825 18.827 motivation 38 0.840 14.796 0.571 0.798 0.814 37 0.760 7.659 39 0.657 6.128 table ii. effective criteria on behavioral maturity of managers extracted from literature and interviews symbol criteria c1 transformational leadership c2 emotional intelligence of managers c3 training courses for managers c4 knowledge orientation and organizational knowledge c5 quantitative management c6 supportive behavior c7 personnel empowerment c8 trustful climate c9 teamwork spirit c10 human and social skills c11 decision-making power c12 stimulating and motivating people in the organization c13 professional commitment and responsibility 1 (1,1,1) (1.23,1.73,2.26) (2.08,2.59,3.14) (1.23,1.66,2.08) (2.26,2.94,3.56) (3.65,4.47,5.81) (2.81,3.44,4.09)(1.89,2.51,3.2) (3.23,4.37,5.37) (1.15,1.58,2.05) (4.44,5.43,6.35) (5.85,6.69,7.47) (3.2 r             (2.272,2.876,3.456) 3,4.36,5.4)          (10) engineering, technology & applied science research vol. 7, no. 3, 2017, 1725-1731 1728 www.etasr.com fashami and babaei: a behavioral maturity model to establish knowledge management in an … where, the triangular fuzzy number (1.23, 1.73, 2.26) is fuzzy value of the first criterion versus the second criterion and the triangular fuzzy number (2.2727, 2.876, 3.456) is fuzzy value of the first criterion versus the other twelve criteria (table iii). then, fuzzy weights of criteria are determined as follows: 1 1 2 3 4 5 6 7 8 9 10 11 12 13( )i iw r r r r r r r r r r r r r r                             (11) value of each criterion is multiplied by the inverse fuzzy sum of values. for example, fuzzy weight of the first criterion is determined as follows: 1 1 1 1 2 3 4 5 6 7 8 9 10 11 12 13( ) (12)                           w r r r r r r r r r r r r r r fuzzy weight of the first criterion is (0.118, 0.185, 0.28). fuzzy weights are listed in table iv. table iii. fuzzy value of pairwise comparisons of behavioral maturity criteria ir ilr imr iur r 2.272 2.876 3.456 r 1.454 1.847 2.271 r 0.879 1.091 1.355 r 01.455 1.878 2.376 r 0.864 1.094 1.364 r 0.511 0.641 0.816 r 0.608 0.752 0.935 r 0.943 1.183 1.492 r 0.582 0.721 0.894 r 1.589 1.993 2.431 r 0.383 0.472 0.607 r 0.271 0.326 0.405 r 0.526 0.654 0.836 table iv. fuzzy weights of behavioral maturity criteria jw ~ j lw j mw j uw defuzzified weight rank 1 ~ w 0.118 0.185 0.28 0.189 1 2 ~ w 0.076 0.119 0.184 0.12.26 4 3 ~ w 0.046 0.07 0.11 0.072 6 4 ~ w 0.076 0.121 0.192 0.12.53 3 5 ~ w 0.045 0.07 0.11 0.071 7 6 ~ w 0.026 0.041 0.066 0.042 11 7 ~ w 0.032 0.048 0.076 0.049 8 8 ~ w 0.049 0.076 0.121 0.079 5 9 ~ w 0.03 0.046 0.072 0.047 9 10 ~ w 0.083 0.128 0.197 0.132 2 11 ~ w 0.02 0.03 0.049 0.028 12 12 ~ w 0.014 0.021 0.033 0.021 13 13 ~ w 0.027 0.042 0.068 0.043 10 as shown, the top five priorities include transformational leadership (0.189), human and social skills (0.132), knowledge orientation and organizational knowledge (0.12.53), emotional intelligence of managers (0.12.26) and trustful climate (0.079), respectively. c. conceptual model testing structural equation modeling (sem) was used to analyze the conceptual model using the software smart pls. the structural model is reported below. t-values were used to analyze significance of the relationships; the figures 1 and figure 2 report t-values for structural relationships and measurement. d. hypothesis testing this section tests hypotheses by β-values and t-values. tvalues>1.96 indicate significant path; thus, the hypothesis is accepted (α=0.05). table 5 reports t-test results. based on pls outputs, hypotheses are tested as follows:  hypothesis 1: personnel empowerment as an aspect of behavioral maturity is effective on km establishment. t=5.533 (>|1.96|) indicates that hypothesis 1 is confirmed at 0.99 confidence. thus, personnel empowerment as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.199 indicates direct and positive effect of personnel empowerment on km establishment.word “data”  hypothesis 2: training courses for managers as an aspect of behavioral maturity is effective on km establishment. t=4.155 (>|1.96|) indicates that hypothesis 2 is confirmed at 0.99 confidence. thus, training courses for managers as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.356 indicates direct and positive effect of training courses for managers on km establishment.  hypothesis 3: teamwork spirit as an aspect of behavioral maturity is effective on km establishment. t=3.181 (>|1.96|) indicates that hypothesis 3 is confirmed at 0.99 confidence. thus, teamwork spirit as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.194 indicates direct and positive effect of teamwork spirit on km establishment.  hypothesis 4: decision-making power as an aspect of behavioral maturity is effective on km establishment. t=2.009 (>|1.96|) indicates that hypothesis 4 is confirmed at 0.99 confidence. thus, decision-making power as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.122 indicates direct and positive effect of decision-making power on km establishment.  hypothesis 5: human and social skill as an aspect of behavioral maturity is effective on km establishment. t=5.390 (>|1.96|) indicates that hypothesis 5 is confirmed at 0.99 confidence. thus, human and social skill as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.288 indicates direct and positive effect of human and social skills on km establishment. engineering, technology & applied science research vol. 7, no. 3, 2017, 1725-1731 1729 www.etasr.com fashami and babaei: a behavioral maturity model to establish knowledge management in an … fig. 1. pls model for estimates of significance fig. 2. pls model for standardized estimates  hypothesis 6: trustful climate as an aspect of behavioral maturity is effective on km establishment. t=3.549 (>|1.96|) indicates that hypothesis 6 is confirmed at 0.99 confidence. thus, trustful climate as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.156 indicates direct and positive effect of trustful climate on km establishment.  hypothesis 7: professional commitment and responsibility as an aspect of behavioral maturity is effective on km establishment. t=4.309 (>|1.96|) indicates that hypothesis 7 is confirmed at 0.99 confidence. thus, professional commitment and responsibility as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.137 indicates direct and positive effect of professional commitment and responsibility on km establishment.  hypothesis 8: knowledge orientation and organizational knowledge as an aspect of behavioral maturity is effective on km establishment. t=4.827 (>|1.96|) indicates that hypothesis 8 is confirmed at 0.99 confidence. thus, knowledge orientation and organizational knowledge as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.231 indicates direct and positive effect of knowledge orientation and organizational knowledge on km establishment.  hypothesis 9: quantitative management as an aspect of behavioral maturity is effective on km establishment. t=2.407 (>|1.96|) indicates that hypothesis 9 is confirmed at 0.95 confidence. thus, quantitative management as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.158 indicates direct and positive effect of quantitative management on km establishment.  hypothesis 10: supportive behavior as an aspect of behavioral maturity is effective on km establishment. t=3.508 (>|1.96|) indicates that hypothesis 10 is confirmed at 0.99 confidence. thus, supportive behavior as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.189 indicates direct and positive effect of supportive behavior on km establishment.  hypothesis 11: transformational leadership as an aspect of behavioral maturity is effective on km establishment. t=6.770 (>|1.96|) indicates that hypothesis 11 is confirmed at 0.99 confidence. thus, transformational leadership as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.045 indicates direct and positive effect of transformational leadership on km establishment.  hypothesis 12: emotional intelligence as an aspect of behavioral maturity is effective on km establishment. t=2.613 (>|1.96|) indicates that hypothesis 12 is confirmed at 0.99 confidence. thus, emotional intelligence as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.166 indicates direct and positive effect of emotional intelligence on km establishment.  hypothesis 13: stimulation and motivation of organizational people as an aspect of behavioral maturity is effective on km establishment. t=4.607 (>|1.96|) indicates that hypothesis 13 is confirmed at 0.99 confidence. thus, stimulation and motivation of organizational people as an aspect of behavioral maturity is effective on km establishment. moreover, β=0.176 indicates direct and engineering, technology & applied science research vol. 7, no. 3, 2017, 1725-1731 1730 www.etasr.com fashami and babaei: a behavioral maturity model to establish knowledge management in an … positive effect of stimulation and motivation of organizational people on km establishment. table v. t-test results; hypothesis testing hypothesis variable value tvalue result independent dependent 1 personnel empowerment km establishment 0.199 5.533 accepted 2 training courses for managers km establishment 0.356 4.155 accepted 3 teamwork spirit km establishment 0.194 3.181 accepted 4 decision making power km establishment 0.122 2.009 accepted 5 human and social skills km establishment 0.288 5.390 accepted 6 trustful climate km establishment 0.156 3.549 accepted 7 commitment and responsibility km establishment 0.137 4.309 accepted 8 knowledge orientation km establishment 0.231 4.827 accepted 9 quantitative management km establishment 0.158 2.407 accepted 10 supportive environment km establishment 0.189 3.508 accepted 11 transformational leadership km establishment 0.045 6.77 accepted 12 emotional intelligence km establishment 0.166 2.613 accepted 13 stimulation and motivation km establishment 0.176 4.607 accepted these findings are consistent with [8, 21-26] who identified a part of effective variables on behavioral maturity. for example, in [21] authors identified feedback and participatory culture as effective factors on maturity of human resources. in [22], authors noted personnel attitude as an important factor in maturity of employees and managers in knowledge management, while they identified pessimism and organizational silence as destructive factors in km establishment; this study identified these factors in a wider framework. moreover, in [23], the author identified participatory culture, trustful climate, feedback, transformational leadership, organizational intelligence and spirituality as effective factors on behavioral maturity of employees and managers, which is partially consistent with the current study. in [26], the author identified objective trainings, performance evaluation and meritocracy as the most important measures in maturity of human resources in establishing knowledge management. vi. conclusion three steps were used to identify the effective factors on behavioral maturity of managers in establishing knowledge management. in the first step, the author identified a number of criteria based on theoretical background and literature review. then, the author used interviews with experts to identify some other factors effective on behavioral maturity of managers in establishing knowledge management. thirty-four criteria were identified in this step. the author used screening for consensus of experts. the identified criteria were weighted by 20 experts. according to the experts, the importance of 13 criteria was higher than average. fuzzy ahp was used to obtain importance of variables. by pairwise comparison of variables by insurance and academic experts, the author weighted the variables. according to the results, the top five priorities included transformational leadership (0.189), human and social skills (0.132), knowledge orientation and organizational knowledge (0.12.53), emotional intelligence of managers (0.12.26) and trustful climate (0.079), respectively. as the results showed, behavioral maturity of managers was higher than average for km establishment; this indicates good maturity of managers in km establishment. t-test results showed that the mean behavioral maturity was higher than 3 (3.415-3.882), indicating relatively high importance of behavioral maturity among managers of iran insurance company. this suggests that managers of iran insurance company are well aware of the importance of km establishment in their organization and support this effectively. as the results showed, training courses for managers, personnel empowerment and transformational leadership are highly important; thus, top management of iran insurance company is recommended to make efforts to improve behaviors, job awareness and career path of employees and managers to direct them in a predetermined framework and foster them based on specified factors. references [1] h. r. rezvani, strategic knowledge management, mazandaran university publication, mazandran, iran, 2012 [2] m. allegra, d. la guardia, s. ottaviano, v. dal grande, m. gentile, “a serious game to promote and facilitate entrepreneurship education for young students”, international conference on education and educational technologies, pp. 256-263, july 16, 2013 [3] n. dehghan, f. dehghan, s. fathi, “explanation and testing of interaction between learning capabilities”, innovation and sustainable competitive advantage, 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management perspective of foreign student’s adaptation in chinese … an intercultural management perspective of foreign student’s adaptation in chinese universities: a case study of china three gorges university liu ping universiti tun hussein onn malaysia, malaysia and college of international communications, three gorges university, china hw180042@siswa.uthm.edu.my xi jing college of international communications, three gorges university, china geanxi@ctgu.edu.cn bestoon othman dept. of business administration, koya technical institute, erbil polytechnic university, iraq and universiti tun hussein onn malaysia, malaysia bestoon2011@yahoo.com zulida binti abdul kadir dept. of english language & linguistics, center for language studies, universiti tun hussein onn malaysia, malaysia zulida@uthm.edu.my feng yuefei college of science and technology, three gorges university, china 3300298@qq.com xiao ping college of international communications, three gorges university, china xping1212@ctgu.edu.cn abstract—globalization, the desire to access quality education and better opportunities abroad as well as the need to develop one’s capacities and many other factors have caused increased migration of international students and teachers into chinese universities. china has recorded over a 67% increase in higher education enrolment between 2011 and 2017. this increased level of student migration in china has brought an unprecedented number of challenges especially in transitioning into the cultural settings in china. as a result, chinese universities, in addition to their various obligations and roles in ensuring quality teaching and learning, have to engage in intercultural management to help foreigners’ transition seamlessly into the cultural landscape of china. this study examines intercultural adaptation of sojourners from an intercultural management perspective. using a mixed method approach, specifically an explanatory mixed method design, a sample of 140 respondents was investigated regarding their cultural adaptation to a chinese university. the positive and negative aspects of intercultural management as it relates to the university used in the case study were also explored. findings from the study were discussed in depth and recommendations for a holistic intercultural management system were made. keywords-intercultural management; intercultural adaptation i. introduction globalization, the desire to access quality education and better opportunities abroad, and the need to develop one’s capacities to earn a better life are among the factors that led to global increased migration [1-3]. this is often translated into a higher number of students and workers migrating into nations with open access policies for migration and a friendly economic climate. in this context, students and workers living in countries other than their countries of citizenship are referred to as sojourners. the people’s republic of china is one of such nations with a booming and developing economy as well as growing opportunities for employment [4] which has attracted numerous sojourners. three decades ago, authors in [4] reported that the number of student sojourners coming to mainland china was comparatively low, but today china is recording an increasing number of enrolments of foreign students in higher education institutions. in fact, student sojourners in chinese universities had increased by over 67% between 2011 and 2017 and by 299% since 2004 [5]. this rapid increase in foreign student enrolment has placed china as asia’s top destination for international students and the fourth student destination in the world after the united states, the united kingdom and france [6]. these sojourners are often faced with the realities and difficulties of living in a new environment with different cultural practices. several studies have reported the experiences of international students from varying perspectives, including institutional perspectives of the challenges these students face, educator’s perspectives and perspectives of the local communities regarding these groups [2-4, 6]. however, it was shown in [6, 7] that intercultural adaptation and the challenges sojourners face have not been given much attention. especially an examination of the management and intercultural adaptation of sojourners from their own voices and perspectives in chinese institutions is absent. some studies, however, have corresponding author: xi jing engineering, technology & applied science research vol. 9, no. 2, 2019, 3971-3977 3972 www.etasr.com ping et al.: an intercultural management perspective of foreign student’s adaptation in chinese … examined the experiences of international students. for instance, authors in [8] report the experience of a group of american students on a two-week visit to china. although it would be misleading to delimit the findings from this study to the challenges experienced by student sojourners in china, they, however, shed light into some minute perspectives of intercultural adaption on a temporary basis for a group of students. similarly, authors in [9] studied the cross-cultural adaptations of foreign students in universities across beijing using a sample of 88 foreign students. they found that foreign students found the cultural values in china to be in conflict with their previous experiences in their home countries and this impacted their adaptation to chinese societies negatively. furthermore, in [10] daily life experiences of student sojourners in six universities across china were studied using a mixed methodology and a sample of 200 respondents. they found that student sojourners in these chinese universities experienced great difficulty in integrating into chinese society, especially in the areas of making new friends, and variations in cultural values and social styles. author in [10] further reports that the variations in cross-cultural adaptations were a result of factors such as gender, length of stay, and cultural background. sojourners are thus required to develop coping strategies and adaptation skills in order to assimilate and be well integrated into these new cultural settings. but a critical question of interest at this point becomes what chinese universities are doing to aid the adaptations of sojourners across china. therefore, it is crucial to explore and understand the experiences of these sojourners within chinese universities and their views on the positives and negatives of how they are being assisted in integrating and assimilating into chinese society. intercultural adaptation is traditionally seen as the responsibility of the sojourner [2, 11-13]. however, author in [14] argues that adaptations should constitute a two-way process where communication should be seen as involving mutual adaptation between sojourners and the host communities. the researcher believes that it is crucial to explore foreign student’s perspectives of intercultural adaptation and how they are managed by chinese universities, as well as the positives and negatives in intercultural management of foreign student’s adaptations in a chinese university. china three gorges university (ctgu) was used as a case study. the university is a provincial sub-center university, which has grown from only a few sojourners in the year 2000 to over seven hundred sojourners at the moment. this increase in foreign student population has been attributed to the encouraging university support and policies that have been put in place. therefore, it is only reasonable to examine if students feel the same way regarding intercultural management at the university. hence, this study sought to ascertain the following: • what are the experiences of sojourners regarding their intercultural adaptation at ctgu? • what are the positives and negatives in intercultural management of sojourners at ctgu? culture as an essential determinant of intercultural adaptation, the concepts of intercultural adaptation, intercultural management, and insights in the use of a pragmatic research approach in reporting the experiences of sojourners are discussed below. also, the paper discusses the findings in line with the above questions and their implications for ctgu and other chinese learning institutions. ii. literature review a. culture: a determinant of adaptation in cross-cultural settings the term culture was first defined in 1871 [15] as a complex comprising of knowledge, faith, arts, virtue, law, custom and all the abilities and practices an individual acquires in social life. although this definition only reflects an ideological perspective, the conceptualization of culture has since influenced several scholars to espouse the concept of culture by including the concept of materials. culture according to authors in [15] is a sort of traditional instrument, merchandise, technology, custom and value, including social organization. furthermore, culture is as the way of life of a group of people as well as the sum of their learned behavior patterns, attitudes and material things. author in [2] explains that culture is often regarded as the core concept in intercultural communication and adaptation. author further emphasizes that culture provides people with a system of knowledge that enables them to communicate effectively with others and to interpret their behavior. similarly, it was shown in [16] that the complex concept of culture is characterized by: • common knowledge and meaning shared with others. • something that people do. • is continually recreated and is constructed between people. • it is not homogenous but must be seen as being divided into spaces, each of which is characterized by different values. • individuals can participate in several social categories and should therefore not be portrayed as a national category but in categories such as gender, education, social background, age etc. authors in [17] stated that culture is characterized by four features: it is holistic, it can be learned, it is dynamic and pervasive. people in multi-cultural societies tend to adapt and change their behaviors and practices with which they were socialized and had been accustomed to. hence interpersonal relationships have to be renegotiated [2]. previous ways of communication begin to become a challenge in newer settings, hence people also have to learn and develop new ways of communication. differences in cultural dispositions do exist, and nowadays people have come to recognize that they exist and respect them, but the question emerges: how sojourners are supported in multi-cultural settings such as in chinese universities to adapt seamlessly into society? b. understanding intercultural communication and adaptation according to [15], intercultural communication is regarded as the interaction between or among people of distinct cultural backgrounds. furthermore, culture is described as engineering, technology & applied science research vol. 9, no. 2, 2019, 3971-3977 3973 www.etasr.com ping et al.: an intercultural management perspective of foreign student’s adaptation in chinese … communication, implying that culture is the creation of meaning when we communicate and our behavioral practices affect each other. author in [12] defines intercultural communication as the interaction of meanings being generated differently. author explains that there are “conceptual filters” which people have to be aware of during cross-cultural interactions, and that these filters help people in understanding and predicting behaviors accurately. without them, conflicts tend to occur and delayed intercultural adaptations. as a result of globalization, more and more people tend to go abroad for study or work purposes. when people experience an entirely different culture, they are engaged in a particular type of intercultural communication, i.e. intercultural adaptation. hence, living in a different culture means an alteration of lifestyle, thinking pattern and almost every aspect of life, which will undoubtedly become a pressure to sojourners. intercultural adaptation on the other hand as described in [2] is a long-term process, which varies with every individual. author in [18] defines intercultural adaptation as a process of increasing the level of fitness of an individual or a group of individuals to fulfill the demands of a new cultural environment. several researchers agree that cultural adaptation is similar to the transitional processes experienced in other facets of life such as a new job, living in a new place, studying in a new and big city etc. several models have been propounded to explain intercultural adaptation. one of such models is the dialectical model of intercultural adaptation. the dialectical model of intercultural adaptation argues that the intercultural adaptation process is characterized by a cyclical and recursive process whereby people try to solve issues and overcome challenges embedded in interaction with the host culture. hence, author in [2], concludes that how a person responds in the intercultural adaptation process, creates his or her own adjustment patterns. therefore adapting to a new culture can often lead to fundamental changes which may feel like “rebirth” [2, 14]. furthermore, intercultural adaptation is usually accompanied by culture shock [17]. culture shock refers to a feeling of loss, confusion, exclusion, or even fear that occurs when a person is entering into a new cultural environment while losing familiar symbols and means of social communication. furthermore, author in [19] explains that understanding and dealing with problems associated with sojourners intercultural adaptation in higher education is pertinent to the success of international education. c. understanding intercultural management author in [20] defines intercultural management as a process of effective management formed in global operations. in corporate settings, a parent organization, usually an international organization, adopts an inclusive and understanding approach in adapting and integrating the culture of the host country, where the sub-company is located. the purpose of intercultural management is to overcome the conflicts of cultural differences and to create a unique organizational culture in cross-cultural conditions. the aim of intercultural management is to design an executable organization structure and management mechanism, to search organizational goals beyond cultural conflict, to maintain a standard code of conduct for employees, and finally to maximize control and utilize the potential and value of the company or enterprise. intercultural management, also known as cross-cultural management, is the type of management involving people, products, and matters of different cultural background [21]. the purpose of intercultural management is to minimize cultural differences, maximize efficiency and realize the common goal of the specific intercultural group. iii. methodology this study adopted an explanatory mixed methodology. explanatory mixed-method research design is one in which the researcher first collects quantitative data and then collects qualitative data to explain or elaborate the results of the quantitative phase [22]. the rationale behind this design in conducting research studies is that quantitative data and results provide a general picture of the research problems. then, qualitative data is then collected to refine, extend or explain that picture. data was collected by means of a structured questionnaire and a follow-up interview. the respondents of the study were international students and teachers at ctgu. a total of 140 questionnaires were retrieved in the quantitative phase of the study, while 27 sojourners consisting of 19 students and 8 teachers participated in the qualitative phase of the study. the instrument for data collection was a structured questionnaire adapted from [23] reflecting students’ experiences of the various aspects of intercultural management at ctgu. the adapted instrument contained 36 items and was pilot-tested using a distinct sample from those selected for the study. a cronbach’s alpha value of 0.833 was obtained. data for the qualitative phase of the study were collected using a researcher-made interview protocol soliciting foreign students’ in-depth experiences of the various aspects of intercultural management at ctgu. data were analyzed using descriptive statistics via the statistical package for social sciences spss 22. frequency counts, percentages, mean and standard deviations were used. iv. results a. respondent’s demographics respondents for the quantitative phase of the study consisted of 140 international students of which 65% were male, and 35% were female. the countries represented in the sample of the study were india (25%), indonesia (2.9%), korea (0.7%), maldives (2.9%), nepal (63.6%), sri lanka (0.7) and usa (4.3%). respondents ranged from freshman (1 st year) to senior (4 th year) undergraduate. senior year students represented 42.9%, junior (3 rd year) represented 10%, sophomore (2 nd year) represented 25% while visiting students represented 5% of the total sample of the study. this indicates that more than 50% of foreign student at ctgu had been in the university for more than one year, indicating that they have experienced first-hand the intercultural adaptation process at ctgu and how sojourners are managed. hence their experiences regarding the intercultural adaptation at ctgu are considered significant for this study. b. sojourners’ experiences regarding their intercultural adaptation at ctgu section 2 of the questionnaire for this study sought sojourners’ perspectives regarding various aspects of their engineering, technology & applied science research vol. 9, no. 2, 2019, 3971-3977 3974 www.etasr.com ping et al.: an intercultural management perspective of foreign student’s adaptation in chinese … intercultural adaptation at ctgu and the areas they identified as challenging in terms of cultural adaptation in china. furthermore, sojourners were also asked to rate the extent to which they were satisfied with the services provided by ctgu to help them to adapt seamlessly into china. a five-point likert scale was used. the following sections report the results from the collected and analyzed data. c. sojourners’ perspectives of support programs provided at ctgu part a in section 2 of the questionnaire specifically sought sojourners’ perspectives regarding the support programs and services they received during the orientation period of their programs. a 5-point likert scale ranging from strongly disagree (1) to strongly agree (5) was used. table i shows the results. regarding the support services sojourners received at ctgu, a significant portion agreed that they received support in terms of airport pick up service upon arrival to china and the necessary information pertaining to school timetable, classroom location and so on before classes begun. similarly, a substantial proportion acknowledged that they participated in orientation programs organized by the university. furthermore, a moderate proportion affirmed that they received necessary information regarding the chinese examination and assessment system. findings from table i show that a significant proportion of respondents disagreed that they received a campus tour upon arrival at the university, neither were they offered guidance to organize their studies upon enrolment, nor did they receive guidance on course selection or the academic requirements of the courses. finally, respondents disagreed that they received the necessary survival information to access food markets, shops, first aid etc. upon arrival at the university. summarily, these findings indicate that although ctgu had implemented some basic support programs and services to enable international students to settle into the country upon arrival, a lot is still needed to be done to address issues relating to students not receiving adequate information regarding how they could access basic facilities as well as guidance on how they could plan and organize their studies. the university management needs to ensure that students are guided to plan their studies adequately by supplying them with the needed information required for course selection and the requirements for the courses provided. it is also important that the university management organizes campus tours for these students in order to get them acquainted with the university environment and facilities. part b in section 2 of the questionnaire sought sojourners’ perspectives regarding their general evaluation of the support services they received. specifically, they were asked to indicate their level of satisfaction for the support services and programs provided with a 5-point likert ranging from of very dissatisfied (1) to very satisfied (5). table ii shows the results. mean and standard deviation were used to analyze the data. mean values ≥3 were marked as satisfied, while mean values ≤3 were marked as dissatisfied. findings revealed that respondents were dissatisfied with the accommodation conditions provided at the institution (mean=2.76), the language ability of the management staff (mean=2.84), and the attitude of the management staff (mean=2.94). on the other hand, findings from the analysis revealed that respondents were satisfied with the scholarship opportunities provided at ctgu (mean=3.00), the language ability of the teaching staff (mean=3.04), the tuition fee (mean=3.15), the attitude of the teaching faculty (mean=3.32), and the academic support received from professors and advisors. findings indicate that sojourners were satisfied with a lot of the support services provided at the university, whereas they were dissatisfied with the conditions of accommodation services provided, the language ability of management staff as this impeded foreign student’s ability to communicate effectively with the management regarding issues and concerns that they had and the work attitude of management staff. table i. foreign students’ perspectives regarding support services and programs provided items sd % d % n % a % sa % i received support upon my arrival at the university like airport pick-up service. 4.3 4.3 2.9 25.0 63.6 i received a campus tour upon my arrival at the university. 46.4 16.4 7.1 17.1 12.9 i participated in an orientation program organized by the university. 12.9 20.0 10.7 38.6 17.9 i was offered guidance on how to organize my future studies on my arrival. 29.3 31.4 14.3 21.4 3.6 i was given guidance on course selection and academic requirements for the courses. 30.7 36.4 5.0 21.4 6.4 i received the necessary information regarding the chinese examination and assessment system. 13.6 26.4 7.1 37.9 15.0 i received necessary instructions regarding directions to the food market, shops, first aid, and so on, immediately on my arrival. 25.7 18.6 7.9 23.6 24.3 i received necessary information pertaining to school timetable, classroom location and so on before i started my classes. 5.0 9.3 8.6 31.4 45.7 table ii. foreign students’ general evaluation of the support services and programs at ctgu items mean std. remarks accommodation conditions 2.76 1.351 dissatisfied language ability of the management staff 2.84 1.360 dissatisfied work attitude of the management staff 2.94 1.216 dissatisfied scholarship opportunity 3.00 1.275 satisfied language ability of the teaching faculty 3.04 1.274 satisfied tuition fee 3.15 1.156 satisfied work attitude of the teaching faculty 3.32 1.195 satisfied academic support from professors and advisors 3.46 0.940 satisfied engineering, technology & applied science research vol. 9, no. 2, 2019, 3971-3977 3975 www.etasr.com ping et al.: an intercultural management perspective of foreign student’s adaptation in chinese … furthermore, respondents (sojourners) in the quantitative phase of the study were asked to rate the extent to which they experienced difficulty in adapting to various aspects of the university’s cultural landscape and environment. using a 5point likert scale of no difficulty (1) to extreme difficulty (5), respondents rated their perspectives of the most challenging aspects of their adaptation at the chinese university. the results shown in table iii show that respondents experienced difficulty in their intercultural adaptation in two aspects only, namely difficulty in dormitory life and difficulty in understanding chinese laws and university regulations. these may have been a result of the university not clearly communicating chinese laws and regulations to sojourners. sojourners may also have found it difficult to study these regulations themselves as a result of the language barrier. similarly, the difficulty experienced in dormitory life may be caused by the fact that sojourners are often paired with other students, with whom they share little or no cultural similarity, thus making some of these students unable to clearly understand their roommates. table iii. respondents perspectives regarding the difficulty in adapting to chinese cultural climate items mean std remarks i have difficulty with dormitory life. 3.11 1.608 difficulty i have difficulty understanding chinese laws and university regulations. 3.07 1.381 difficulty i have difficulty getting along with the management staff 2.98 1.629 no difficulty i have difficulty understanding the university management system. 2.94 1.174 no difficulty i have difficulty understanding chinese university admission policies 2.86 1.273 no difficulty i have difficulty in finding medical services. 2.84 1.282 no difficulty i have difficulty with the campus food services. 2.79 1.491 no difficulty i have difficulty financing my education. 2.61 1.355 no difficulty i have difficulty participating in students’ activities organized by the university. 2.54 1.266 no difficulty i have difficulty understanding the registration procedure. 2.42 1.113 no difficulty i have difficulty with the practice of my religion. 1.96 1.311 no difficulty i have difficulty with roommates. 1.54 1.153 no difficulty d. positives and negatives in the intercultural management at ctgu this study also sought to determine specifically through indepth interviews the positive and negative aspects of intercultural management as experienced by sojourners in the case study. qualitative interviews were conducted with sojourners from ctgu, namely international students and teachers. participants for the qualitative phase of the study were asked to share their experiences regarding the management system at ctgu, i.e. how the international relations office formerly known as the foreign affairs office (fao) catered for their needs. findings from the interview revealed some positive and satisfactory feedback. however, some notable negatives were also recorded. the following discuss the positive and negative experiences reported regarding the management of their cultural adaptation in the host university. 1) the positives a) satisfactory airport pickup system a significant number of sojourners tested that the airport pick-up service provided a very keen first impression about the university, as students were satisfied with the quality of the provided service. sojourners expressed that the prompt airport pick up service made them feel welcomed. b) friendly academic staff and comprehensive language tutoring participants also reported that the academic staff at the university was friendly and interacted well with students on various matters. similarly, a substantial number of sojourners expressed that the chinese language classes held were among the most successful programs at the university. 2) the negatives a) the use of a hierarchical management system the university which constituted the case study for this research operates on a hierarchical cultural norm and although this system of management has its pros, participants from the qualitative phase of the study believed that this management system impeded the ability of departments and colleges to communicate effectively. b) the responsive but inefficient management system some participants also expressed that the management system at the university was one that could be described as responsive but not efficient. some participants expressed that sometimes it was difficult for an issue that affected them within the university to be resolved. in some cases, identifying the unit responsible for resolving such an issue was particularly tricky as the fao was not able to resolve the issue in a timely and efficient manner. a participant described the foreign affairs office as inefficient because the staff was sometimes not available even in office hours. another participant reported that they are unhelpful and could not respond to an issue adequately. another described the intercultural management staff of the fao as incompetent in english and having unacceptable behavior. c) incomprehensive orientation programs/guidebooks for new students/expatriate teachers participants expressed that the orientation programs at the university are not self-sufficient as they do not entirely aid students in transitioning into the new cultural landscape they find themselves in. some participants also expressed that in the absence of these orientation programs, the university could produce comprehensive guidebooks written in english that they could easily refer to when they need help. sadly, participants expressed that such a guidebook does not exist. this, as a result limits the university’s intercultural management. engineering, technology & applied science research vol. 9, no. 2, 2019, 3971-3977 3976 www.etasr.com ping et al.: an intercultural management perspective of foreign student’s adaptation in chinese … d) issues with the dormitory quality some participants expressed that the quality of the dormitory at the university was not up to the western standards. also, it was reported by some participants that rooms in the dorm were not adequately prepared upon arrival. participants also expressed that the charged fee was not on par with the actual condition of the dorms. e) recruitment of non-qualified academic staff participants also expressed that with respect to teaching and learning, they found some academics not suitable in terms of being qualified to teach at the university. some participants also expressed that the selection of foreign teachers should be rigorously carried out in order to ensure that foreigners who could facilitate effective teaching and learning were recruited into the university. participants expressed that these issues were the negative aspects of their adaption experiences at the host university. it is essential that chinese universities develop an effective intercultural management system to help sojourners adapt effectively into chinese culture. e. recommendations for effective intercultural adaptation and management improvement intercultural management is a particular type of intercultural communication. it involves the dialogue between the management of host culture and sojourners, including more people than in interpersonal communication. the success or failure of intercultural management determines the success or failure of communication within a culturally diverse institution. therefore, for effective intercultural communication between people and units of diverse cultural backgrounds, a holistic intercultural management system is needed. this holistic intercultural management system should constitute a dynamic organism of assimilation. an ‘organism’ in this context refers to a body that is working altogether to realize the processes of an effective intercultural management system. dynamism, on the other hand, refers to the vigorousness and activeness of the management system. therefore, a holistic intercultural management system should be dynamic, and all its constituent parts should work harmonically to aid the intercultural adaptation of sojourners in host countries. the first step to establish a holistic intercultural management system that is both organic and dynamic is to revamp existing management structures. such a management system should foster unhinged communication and cooperation between subordinates and managers. as a result, every entity or element of the system is expected to fulfil its responsibility as stipulated and defined in the management structure. furthermore, every entity within the system is expected to support an internationalized spirit of operation. internationalization should not be a responsibility that is borne by only a few groups of people. preferably, it is a process that is hinged on maximizing the involvement of entities within the international landscape of institutions. the second step is for international relations units within institutions to adopt an open-minded innovation mechanism where the goal is to consistently listen to various recommendations and suggestions of the international community as well as give voice to the most pressing issues affecting sojourners welfare and wellbeing in the host country. the management system within the university should also focus on minimizing and abolishing the hierarchical management model which delimits effective communication across various units of the institution as well as between sojourners and the management. furthermore, there should be strict avoidance of uncertainty in responding to issues of foreign students’ welfare and wellbeing. spontaneity should be the core competency of the international relations office in assisting and serving the international community. success in these leads to building good reputation for the university which in turn leads to attracting more international students and teachers. using an updated management software system is of crucial importance in intercultural management. findings from the study revealed that international students found the management system to be responsive but not efficient. a lack of efficiency could result in the university using an ad-hoc managerial software system which is not particularly tailored to the needs of the management team. the management system should be one that is democratic and characterized as one for the people, by the people and of the people. therefore, consolidating sojourners’ perspectives regarding issues could help improve intercultural management in the university. the university should also recruit qualified teaching and management staff in the various areas of study and programs offered. similarly, the university should also facilitate easy and open access to intercultural training provided for not only management staff and sojourners, but also for the chinese faculty and students in order to establish intercultural consciousness in students and staff alike. the intercultural training for sojourners can comprise of basic chinese language courses, a brief introduction to china and the chinese culture, a specific introduction to the management structure of the university, and orientation programs. also access to information such as campus geography, the education system, and evaluation methods should also be provided. the intercultural training on chinese people may include the basic knowledge of english language (specific domain oriented if necessary), intercultural communication such as diplomatic etiquette, basic intercultural theories and practices, a brief introduction of different cultures and so on. furthermore, a comprehensive policy framework should be developed to address effective consultation between university management and sojourners as well as responsive information circulation. the policy framework should be established on a people-oriented basis, i.e. it should focus on the needs of the international students as well as the entire student body in the institution. whenever the university produces policies and decisions, the concerned people, not only staff and teachers, but also students should be consulted. the policies or decisions should not only be beneficial for the university, but also should accommodate international students and teachers. a worthy point of note in intercultural adaptation is that sojourners ought to be aware of the challenges in transitioning to a culture that is different from theirs and as a result, ought to prepare themselves for the differences that may occur when they engineering, technology & applied science research vol. 9, no. 2, 2019, 3971-3977 3977 www.etasr.com ping et al.: an intercultural management perspective of foreign student’s adaptation in chinese … migrate to other countries for study and employment purposes. preparing oneself for future challenges allows one to be successful when such challenges arise. authors in [17] proposed another approach to intercultural adaptation. they explained that sojourners could seek support and help from people with similar backgrounds in order to adapt effortlessly into the host country. furthermore, participating in campus activities and social activities with people of similar and diverse backgrounds can also help foster intercultural adaptation [9]. there is a positive correlation between social support and intercultural adaptation. social contact and communication between people from both diverse and similar backgrounds will encourage intercultural adaptation. v. conclusion through a mixed method approach, this study explored the experiences of sojourners regarding their cultural adaptation in a chinese university. more specifically, the positives and negatives in the intercultural management of sojourners were examined. using a sample of 140 respondents in the quantitative phase and 27 participants in the qualitative phase of the study, findings established that university had some notable successes that were held in high esteem by sojourners. however, there were more recorded negatives than positives. the use of a hierarchical and inefficient management system, incomprehensive orientation programs/guidebooks, issues with dormitory quality, and the recruitment of non-qualified academic and management staff were some of the issues expressed by participants. the researchers therefore recommend a holistic management system to be developed to facilitate effective and efficient intercultural management at the university. some recommendations for fostering intercultural communication and adaptation have also been proposed. references [1] i. a. novikova, a. l. novikov, “relation between communicative tolerance and intercultural adaptation in international students”, mediterranean journal of social sciences, vol. 6, no. 2, pp. 109-116, 2015 [2] i. pietila, “intercultural adaptation as a shared learning process in the life-course”, in: cross-cultural lifelong learning, tampere university press, 2010 [3] l. ye, v. edwards, “chinese overseas doctoral student narratives of intercultural adaptation”, journal of research in international education, vol. 14, no. 3, pp. 228-241, 2015 [4] p. yang, “journey to the east: intercultural adaptation of international students in china”, in: international students in china, springer, 2018 [5] ministry of education, p.r.c., inbound international students in china, 2018 [6] m. tian, j. a. lowe, “intercultural identity and intercultural experiences of american students in china”, journal of studies in international education, vol. 18, no. 3, pp. 281-297, 2014 [7] y. zhou, k. topping, d. jindal-snape, “intercultural adaptation of chinese postgraduate students and their uk tutors”, in: researching chinese learners, springer, 2011 [8] j. riggan, s. gwak, j. lesnick, k. jackson, s. olitsky, “meta-travel: a critical inquiry into a china study tour”, frontiers: the interdisciplinary journal of study abroad, vol. 21, pp. 236-253, 2015 [9] h. chen, “the research in behavioral psychology of foreign students' sociocultural adaptation in china”, journal of beijing normal university (social science edition), vol. 6, pp. 135-142, 2003 [10] j. j. yang, “laihua liuxuesheng kuawenhua shiying de wenti yanjiu [research on cross-cultural adaptation of international students in china], shanghai, china: shanghai academy of social sciences press, 2009 [11] a. furnham, s. bochner, culture shock. psychological reactions to unfamiliar environments, methuen, 1986 [12] w. b. gudykunst, “intercultural communication theories”, handbook of international and intercultural communication, vol. 2, pp. 179-182, 2002 [13] l. a samovar, intercultural communication: a reader, cengage learning, 2014 [14] l. e. anderson, “a new look at an old construct: cross-cultural adaptation”, international journal of intercultural relations, vol. 18, no. 3, pp. 293-328, 1994 [15] e. t. hall, the silent language, doubleday, 1959 [16] i. jensen, “professionalism in intercultural job interviews”, journal of intercultural communication, vol. 8, pp. 241-249, 2003 [17] g. m. chen, w. j. starosta, foundations of intercultural communication, allyn and bacon, 2007 [18] y. y. kim, becoming intercultural: an integrative theory of communication and cross-cultural adaptation, sage, 2001 [19] p. bodycott, “embedded culture and intercultural adaptation: implications for managing the needs of chinese students”, journal of higher education policy and management, vol. 34, no. 4 pp. 355-364, 2012 [20] h. guo, “comparative study of bilingual educational sociocultural environments between china and canada”, journal of qinghai normal university (philosophy and social sciences edition), vol. 5, p. 32, 2010 [21] f. meng, “individualism/collectivism and group travel behavior: a cross-cultural perspective”, international journal of culture, tourism and hospitality research, vol. 4, no. 4, pp. 340-351, 2010 [22] j. w. creswell, educational research: planning, conducting and evaluating quantitative and qualitative, pearson, 2012 [23] j. r. jenkins, f. galloway, “the adjustment problems faced by international and overseas chinese students studying in taiwan universities: a comparison of student and faculty/staff perceptions”, asia pacific education review, vol. 10, no. 2, pp. 159-168, 2009 microsoft word 09-3491_s_etasr_v10_n3_pp5632-5636 engineering, technology & applied science research vol. 10, no. 3, 2020, 5632-5636 5632 www.etasr.com gurkan aydin et al.: calculated optimized structure and geometric analysis of oxygenated fuel … calculated optimized structure and geometric analysis of oxygenated fuel additives: alcohols and ethers sinem gurkan aydin opticianry department vocational school of health services istanbul gelisim university istanbul, turkey sgurkan@gelisim.edu.tr arzu ozgen medical laboratory techniques department vocational school of health services istanbul gelisim university istanbul,turkey aozgen@gelisim.edu.tr oktay polat aircraft mechanic-engine department school of applied sciences istanbul gelisim university istanbul,turkey 190809911@ogr.gelisim.edu.tr emre turali aircraft mechanic-engine department school of applied sciences istanbul gelisim university istanbul,turkey 190809907@ogr.gelisim.edu.tr abstract—oxygenated fuel additives are added to gasoline in order to reduce the gases released from vehicle engines, to increase the octane number, and to expand the use of renewable resources. in this study, molecular and geometric analysis of oxygenated fuel additives was conducted theoretically and the energy values of optimized structures were calculated. the effect of molecular energy and the bond structure between c, h and o on the chemical and physical properties of some oxygen fuel additives were investigated. the obtained results will form the basis for future studies in obtaining more environmentally friendly fuels. keywords-oxygenated fuel additives; gasoline; octane booster; energy; molecular analysis; geometric analysis i. introduction energy plays an important role in our daily life and is important for the socio-economic development [1]. today, the dominant share of fossil fuels in energy consumption continues [2, 3]. in 2011, 33% of the energy consumed was supplied from oil, 28% from coal, 22% from natural gas, and 6% from nuclear energy while the remaining 11% was covered by other energy sources [4-7]. petroleum fuels are widely used in the transportation sector. in 2011, 54% of world oil consumption was in the transportation sector, 18% in the industrial sector, 11% in the domestic, commercial and agricultural areas, 10% in the petrochemical industry, and 7% was consumed in electricity production [8-10]. it is inevitable to start producing more environmentally friendly fuels by changing the properties of the existing additives. a detailed examination of the molecular structure of the substances added to fuels will shed light on further studies. oxygen fuel additives are organic substances that contain one or more oxygen atoms in their molecular structures. oxygenates consist of different alcohols, ethers, esters and carbonates, but primary alcohols (methanol, ethanol) and ethers are commercially used oxygenates [11]. alcohols and ethers have been used for a long time to increase the octane number of gasoline, reduce the vapor pressure and add oxygen content to the mix. alcohols, heavy molecular alcohols, and ethers like methanol, ethanol, isopropyl alcohol, tert-butyl alcohol (tba), tert-amyl alcohol (taa), propanol, butanol, pentanol, methyl tertiary butyl ether (mtbe), 2-methoxy-2-methylpropane (etbe), tert-butyl ethylether (tame), 2-ethoxy-2methylbutane (taee), 2-ethoxy-2-methybutane (dipe), and di-tertamyl ether (di-tae) can be used as fuel additives. in practice, alcohols such as methanol, ethanol, butanol, mtbe, and etbe are the most preferred oxygenated fuel additives. since the physical and chemical properties of each alcohol and ether are different, the type and amount of the additives used directly affects the physical and chemical properties of the gasoline. some alcohols such as ethanol and methanol can be used as both pure fuel and fuel additive [12]. there are advantages and disadvantages of using alcohol and ethers as a fuel additive [13]. the biggest advantage of alcohols is that their octane number is high. therefore, the efficiency of the engine can be increased without knocking by selecting high compression ratios [14] while reducing co, hc and pm emissions. due to the high hidden evaporation temperatures, they increase the density of the mixture or air taken into the cylinder, thus the volumetric efficiency of the engine [15]. alcohols are safer in terms of transportation and storage due to their auto-ignition and flash point compared to gasoline corresponding author: sinem gurkan aydin engineering, technology & applied science research vol. 10, no. 3, 2020, 5632-5636 5633 www.etasr.com gurkan aydin et al.: calculated optimized structure and geometric analysis of oxygenated fuel … [16]. different results are available from the literature regading the effect of alcohols on nox and co2 emissions [17]. however, if alcohols are produced from biomass, they do not increase the total carbon dioxide emission since the carbon dioxide (co2) formed as a result of combustion of alcohols will be used by plants again in photosynthesis. however, the production cost of alcohols is higher than gasoline. low heat values compared to gasoline cause lower engine power and increased fuel consumption. they have high water-solubility rates and are highly prone to absorbing moisture from the air [18]. therefore, phase separation occurs in the gasoline-alcohol mixture and the corrosion effect of the fuel increases [19]. the thermal value of the ethers is lower than the thermal value of gasoline, but higher than the thermal value of alcohols. the octane numbers are higher than the octane number of gasoline but lower than the octane number of alcohols. the ethers’ oxygen content is lower than alcohols’. however, ethers have some important advantages over alcohols. ethers have low reid vapor pressure and therefore do not increase volatile hydrocarbon emissions [20]. they mix with gasoline at any rate and phase separation does not occur. thanks to their oxygen content, they reduce co, hc and pm emissions. however, their production cost is high and they can contaminate underground drinking water by seeping through storage tanks [21]. ethers are produced by the reaction of alcohols and petroleum-based hydrocarbons accompanied by an acidic catalyst. mtbe is obtained by reacting methanol and isobuten, an oil-based hydrocarbon, with an acidic catalyst at high pressure and temperature [22]. when using ethanol instead of methanol with the same method, etbe is obtained, which is a partially renewable fuel additive since ethanol from biomass is used. at the end of the reaction, a mixture of etbe and ethanol azeotropic is formed. it is not possible to separate etbe from this mixture by simple distillation. for separation, first of all, the azeotropic molecules formed by adding water to the reaction medium must be broken down and then the isobutene, ethanol and water must be removed and the etbe must be purified [23], thus its production cost increases [20, 23]. it is obtained by reacting tame with isoamylene (c5 olefins), a hydrocarbon, in the presence of an acidic catalyst. taee is obtained if ethanol is used in this reaction instead of methanol. it is a partially renewable oxygen fuel additive since ethanol obtained by fermentation of biomass is used in taee production [24]. dipe production is different from the production of other ethers. alcohol is not used in dipe production. isopropyl alcohol is obtained by propylene. then, isopropyl alcohol reacts with propylene to obtain diisopropyl alcohol. the biggest disadvantage of dipe is that when it is mixed with gasoline, peroxides that can explode easily occur and therefore pose more risks than other ethers during transportation, storage and distribution [22]. di-tae is obtained by reacting isoamylene with isoamyl alcohol [24]. isoamyl alcohol is approximately the 60% of the fusel oil and appears as a by-product in ethanol production [25]. di-tae has the potential to be used as an oxygenated fuel due to its cheap raw material production and being partially renewable [26]. the basic state optimized structures of some oxygenic fuel additives were calculated at the level of 6-311 ++ g (d, p) with dft (density functional theory) (b3lyp) method in this study. methanol, ethanol, mtbe, etbe, taee, tame and dipe were used as fuel additives. in addition, the geometrical parameters of the fuel additives were determined and detailed and a comparison of their physical and chemical properties was made. the effects of molecular energy and bond structure between c, h and o on the chemical and physical properties of some oxygen fuel additives were investigated. ii. materials and methods optimized basic state conformations of all oxygenic fuel additives were calculated by using spin-unrestricted dft (b3lyp) method with 6-311++g (d, p) basis sets implemented in the polarizable continuum model (pcm). the reason for choosing this method is that it gives better results in molecular calculations of a similar structure [27, 28]. gaussian 03 [29] and gauss-view molecular visualization [30] were used in all calculations on a personal computer. potential energy surface (pes) scans of oxygen fuel additives showed one or more minimum-energy structures. these minimum structures were chosen to achieve even more stable ones and more accurate results. iii. results and discussion the structures of molecules can be determined in detail using molecular modeling methods. this will be a guide for new materials to be developed in the future or for new materials to be added. the calculated ground state optimized structures and energies of the all oxygenic fuel additives are shown in figure 1. at the same time, molecular energy calculations for all fuel additives were made in the basic set of 6-311 ++ g (d, p) with the dft (b3lyp) method. the atomic bonds and energy values of the fuel additives in the molecular structure vary as shown in figure 1. this difference reflects on many physical and chemical properties (fuel performance, engine octane number, flash point, boiling point, freezing point, viscosity, etc.). fig. 1. the calculated ground state optimized structures and energies of the all oxygenic fuel additives a. methanol methanol is a high extract fuel additive. the octane value of methanol is ranges from 105 to 110. evaporation heat and extract value play important roles in the characteristics of the internal combustion engine using this fuel. as seen in the engineering, technology & applied science research vol. 10, no. 3, 2020, 5632-5636 5634 www.etasr.com gurkan aydin et al.: calculated optimized structure and geometric analysis of oxygenated fuel … molecular structure of methanol, it is a fuel additive that contains oxygen. therefore, it is important to know the binding properties of oxygen in its molecular structure with other atoms. some geometric parameters and energy of methanol were calculated in this study. geometrical parameters such as bond length, bond angle, and torsion angle calculated at the b3lyp/6311++g(d, p) level of theory are given in table i. table i. selected geometrical parameters of methanol* dihedral angle(°) angle (°) bond (λ) 5(h)-6(o)-1(c)-3(h) 179.999 5(h)-6(o)-1(c) 108.833 6(o)-5(h) 0.961 5(h)-6(o)-1(c)-4(h) -61.475 6(o)-1(c)-3(h) 106.661 6(o)-1(c) 1.424 3(h)-1(c)-6(o)-5(h) 179.999 4(h)-1(c)-3(h) 108.431 4(h)-1(c) 1.096 4(h)-1(c)-6(o)-5(h) -61.475 3(h)-1(c)-4(h) 108.431 4(h)-1(c) 1.096 *computed at dft(b3lyp)/6311++g(d,p) level b. ethanol the octane value of ethanol was determined between about 92-108. ethanol is a non-toxic substance that dissolves in water and can quickly biodegrade and disappear. it also significantly reduces the carbon monoxide rate. ethanol is a two-carbon monoalcohol. geometric analysis of carbon atoms in the molecular structure was conducted, and the same geometrical parameters were calculated and are given in table ii. table ii. selected geometrical parameters of ethanol dihedral angle(°) angle bond 12(h)-11(o)6(c)-9(h) 59.433 12(h)-11(o)-6(c) 108.481 12(h)-11(o) 0.962 12(h)-11(o)6(c)-10(h) 175.032 10(h)-6(c)-11(o) 105.109 11(o)-6(c) 1.429 11(o)-6(c)-2(c)8(h) 61.470 11(o)-6(c)-10(h) 105.109 9(h)-6(c) 1.098 11(o)-6(c)-2(c)7(h) 176.102 6(c)-2(c)-8(h) 108.912 10)h)-6(c) 1.093 6(c)-2(c)-1(c)3(h) 178.227 8(h)-2(c)-7(h) 105.967 6(c)-2(c) 1.528 6(c)-2(c)-1(c)4(h) -61.869 2(c)-1(c)-3(h) 111.221 2(c)-1(c) 1.530 6(c)-2(c)-1(c)5(h) 57.727 6(c)-2(c)-1(c) 113.666 2(c)-8(h) 1.098 11(o)-6(c)-2(c)1(c) -61.469 3(h)-1(c)-4(h) 107.759 2c-7h 1.096 *computed at dft(b3lyp)/6311++g(d,p) level c. mtbe mtbe is a water-soluble, volatile, and colorless fuel additive, commonly used to increase octane number. it is also known to dilute fuel better by gasoline components. when mixed with soil, it can biodegrade under the influence of bacteria. mtbe has an octane number between 101-116. the oxygen content in its molecular structure is 16% by mass and its geometrical analysis can be seen in table iii. d. etbe etbe is produced from ethanol and isobutylene. although it improves the combustion properties of the fuel, it is more compatible than ethanol. it provides high air quality when added to fuel. although etbe has the highest octane number among the oxygenated fuel additives mentioned in this study, it was found to have the highest molecular energy in our calculations. etbe is an important fuel additive with superior properties and its geometric analysis is given in table iv. table iii. selected geometrical parameters of mtbe* dihedral angle(°) angle bond 18(h)-15(c)-14(o)2(c) -61.683 17(h)-15(c)14(o) 106.071 18(h)-15(c) 1.097 17(h)-15(c)-14(o)2(c) -179.985 15(c)-14(o)2(c) 118.169 15(c)-14(o) 1.415 15(c)-14(o)-2(c)7(c) 61.905 14(o)-2(c)7(c) 110.897 14(o)-2(c) 1.446 15(c)-14(o)-2(c)6(c) -61.821 14(o)-2(c)6(c) 110.903 2(c)-7(c) 1.536 15(c)-14(o)-2(c)1(c) -179.959 14(o)-2(c)1(c) 103.402 2(c)-6(c) 1.536 14(o)-2(c)-7(c)12(h) -67.712 12(h)-7(c)2(c) 112.021 2(c)-1(c) 1.530 14(o)-2(c)-6(c)9(h) -172.738 4(h)-1(c)2(c) 110.196 12(h)-7(c) 1.092 14(o)-2(c)-1(c)4(h) 59.671 9(h)-6(c)2(c) 110.184 9(h)-6(c) 1.093 12(h)-7(c)-2(c)1(c) 178.385 6(c)-2(h)1(c) 110.234 4(h)-1(c) 1.092 12(h)-7(c)-2(c)6(c) 55.996 2(c)-6(c)8(h) 112.024 7(c)-2(c)-1(c)4(h) 178.266 2(c)-1(c)3(h) 110.196 7(c)-2(c)-6(c)9(h) 63.555 *computed at dft(b3lyp)/6311++g(d,p) level table iv. selected geometrical parameters of etbe* dihedral angle(°) angle bond 21(h)-18(c)-15(c)14(o) 59.955 20(h)-18(c)15(c) 110.601 21(h)-18(c) 1.092 20(h)-18(c)-15(c)14(o) -59.959 18(c)-15(c)16(h) 109.928 18(c)-15(c) 1.520 19(h)-18(c)-15(c)14(o) 179.998 18(c)-15(c)17(h) 109.928 15(c)-16(h) 1.098 18(c)-15(c)-14(o)2(c) 179.980 18(c)-15(c)14(o) 107.687 15(c)-14(o) 1.421 16(h)-15(c)-14(o)2(c) -59.736 15(c)-14(o)2(c) 118.745 14(o)-2(c) 1.445 17(h)-15(c)-14(o)2(c) 59.696 14(o)-2(c)-1(c) 103.445 2(c)-1(c) 1.530 7(c)-2(c)-14(o)15(c) 61.865 14(o)-2(c)-7(c) 110.964 2(c)-7(c) 1.536 7(c)-2(c)-6(c)-9(h) 63.806 2(c)-7(c)-12(h) 112.046 7(c)-13(h) 1.093 7(c)-2(c)-1(c)-4(h) 178.315 2(c)-1(c)-4(h) 110.182 1(c)-3(h) 1.092 9(h)-6(c)-2(c)-14(o) -172.388 14(o)-2(c)-6(c) 110.962 6(c)-10(h) 1.093 6(c)-2(c)-14(o)15(c) -61.899 2(c)-6(c)-9(h) 110.179 2(c)-6(c) 1.536 2(c)-6(h)-10(h) 110.298 7(c)-13(h) 1.093 *computed at dft(b3lyp)/6311++g(d,p) level e. taee taee is a fuel additive belonging to the ether class and its molecular formula is c7h16o. the engine octane number of taee has been determined to be above 105. the calculated geometrical analysis results of taee are given in table v. f. tame it is a fuel additive produced from naphtha c4 distillation fractions. it is added to the fuels in order to increase their engineering, technology & applied science research vol. 10, no. 3, 2020, 5632-5636 5635 www.etasr.com gurkan aydin et al.: calculated optimized structure and geometric analysis of oxygenated fuel … octane level, change the tetraethyl lead and increase oxygen content. it has a high boiling point and a low freezing point. the geometrical analysis of tame is given in table vi. table v. selected geometrical parameters of taee* dihedral angle(°) angle bond 18(h)-17(c)14(o)-13(o) 178.613 18(h)-17(c)-14(c) 110.285 18(h)-17(c) 1.093 20(h)-17(c)14(c)-13(o) 58.628 17(c)-14(c)-13(o) 107.394 17(c)-14(c) 1.519 19(h)-17(c)14(c)-13(o) -61.228 16(h)-14(c)-13(o) 111.481 15(h)-14(c) 1.097 17(c)-14(c)13(o)-2(c) 174.778 14(c)-13(o)-2(c) 120.671 14(c)-13(o) 1.423 16(h)-14(c)13(o)-2(c) 54.219 13(o)-2(c)-7(c) 112.997 13(o)-2(c) 1.450 15(h)-14(c)13(o)-2(c) -65.338 13(o)-2(c)-6(c) 109.403 2(c)-1(c) 1.534 14(c)-13(o)2(c)-6(c) -98.065 13(o)-2(c)-1(c) 103.982 2(c)-7(c) 1.535 14(c)-13(o)2(c)-1(c) 145.939 7(c)-2(c)-1(c) 109.407 11(h)-7(c) 1.091 14(c)-13(o)2(c)-7(c) 27.405 7(c)-2(c)-6(c) 111.964 4(h)-1(c) 1.092 13(o)-2(c)6(c)-8(h) -174.488 1(c)-2(c)-6(c) 108.716 2(c)-6(c) 1.547 13(o)-2(c)6(c)-21(c) 61.924 2(c)-6(c)-21(c) 117.267 6(c)-21(c) 1.531 13(o)-2(c)1(c)-4(h) 54.874 2(c)-6(c)-9(h) 107.026 6(c)-8(h) 1.096 2(c)-6(c)21(c)-24(h) 58.806 24(h)-21(c)-6(c) 112.448 21(c)-24(h) 1.093 8(h)-6(c)-2(c)1(c) -61.545 9(h)-6(c)-21(c) 108.701 1(c)-5(h) 1.093 1(c)-2(c)-6(c)21(c) 174.867 4(h)-1(c)-2(c) 109.955 6(c)-9(h) 1.095 *computed at dft(b3lyp)/6311++g(d,p) level table vi. selected geometrical parameters of tame* dihedral angle(°) angle bond 12(h)-10(c)6(c)-2(c) -175.546 12(h)-10(c)-6(c) 110.441 12(h)-10(c) 1.093 10(c)-6(c)-2(c)18(c) 177.394 10(c)-6(c)-2(c) 115.513 10(c)-6(c) 1.531 10(c)-6(c)-2(c)9(o) 54.175 7(h)-6(c)-2(c) 107.567 8(h)-6(c) 1.095 10(c)-6(c)-2(c)1(c) -60.729 8(h)-6(c)-2(c) 108.756 6(c)-2(c) 1.547 8(h)-6(c)-2(c)9(o) -60.089 1(c)-2(c)-9(o) 103.411 1(c)-2(c) 1.531 7(h)-6(c)-2(c)1(c) 62.289 9(o)-14(c)-15(h) 106.103 1(c)-5(h) 1.093 1(c)-2(c)-9(o)14(c) -176.194 9(o)-2(c)-18(c) 110.962 2(c)-9(o) 1.446 6(c)-2(c)-1(c)5(h) -56.295 9(o)-2(c)-6(c) 111.161 2(c)-18(c) 1.536 6(c)-2(c)-18(c)20(h) -175.265 1(c)-2(c)-18(c) 109.660 18(c)-21(h) 1.092 15(h)-14(c)9(o)-2(c) -178.039 1(c)-2(c)-6(c) 111.621 9(o)-14(c) 1.415 6(c)-2(c)-18(c)20(h) -175.265 14(c)-16(h) 1.097 *computed at dft(b3lyp)/6311++g(d,p) level g. dipe it is a highly flammable fuel additive, with a serious risk of fire and explosion when kept in the air for a long time. the geometrical analysis of oxygen and carbon atoms is given in table vii. table vii. selected geometrical parameters of dipe* dihedral angle(°) angles bonds 15(h)-13(c)11(c)-17(c) 62.076 20(h)-17(c)-11(c) 110.708 18(h)-17(c) 1.093 15(h)-13(c)11(c)-10(o) -59.563 14(h)-13(c)-11(c) 110.781 17(c)-11(c) 1.530 13(c)-11(c)17(c)-20(h) 62.238 17(c)-11(c)-13(c) 112.218 11(c)-13(c) 1.523 13(c)-11(c)10(o)-2(c) -153.714 17(c)-11(c)-10(o) 110.804 13(c)-14(h) 1.093 11(c)-10(o)2(c)-21(h) -36.240 11(c)-10(o)-2(c) 116.255 11(c)-12(h) 1.099 11(c)-10(o)2(c)-1(c) -153.685 13(c)-11(c)-10(o) 106.548 11(c)-10(o) 1.433 11(c)-10(o)2(c)-6(c) 83.784 12(h)-11(c)-10(o) 109.138 10(o)-2(c) 1.433 10(o)-2(c)1(c)-5(h) -179.507 10(o)-2(c)-21(h) 109.142 2(c)-21(h) 1.099 10(o)-2(c)6(c)-9(h) 61.566 10(o)-2(c)-6(c) 110.804 6(c)-9(h) 1.093 10(o)-2(c)1(c)-4(h) 59.906 10(o)-2(c)-1(c) 106.853 2(c)-1(c) 1.523 11(c)-10(o)2(c)-1(c) -153.685 2(c)-1(c)-5(h) 110.778 1(c)-4(h) 1.092 *computed at dft(b3lyp)/6311++g(d,p) level iv. conclusion in this study, the basic state optimized structures of some oxygenic fuel additives were calculated at the level of 6-311 ++ g (d,p) with the dft (b3lyp) method. methanol, ethanol, mtbe, etbe, taee, tame, and dipe were used as fuel additives. the geometrical parameters of the fuel additives were determined and a detailed comparison of their physical and chemical properties was made. the effects of molecular energy and bond structure between c, h and o on the chemical and physical properties of some oxygen fuel additives were investigated. it has been determined that there is a relationship between the molecular energy values of the fuel additives and the known octane numbers. the octane numbers of all the studied additives are close and the highest is approximately 115 for mtbe. the basic energy levels of all studied fuel additives were calculated and reported. mtbe, etbe, taee, tame and dipe are often used as an additive for gasoline. in general, these additives have a common trend in reducing harmful emissions. it is not possible to give an exact value of emission reduction regarding the type and percentage of the additive in the fuel of co, nox and hc emissions, because operating conditions, engine geometry and many other parameters are involved. however, an addition of these additives always leads to reduced co emissions while there are no consistent results available about 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kudin, h. p. hratchian, g. a. voth, a. j. austin, m. c. strain, c. adamo, p. m. w. gill, m. a. robb, g. a. petersson, j. b. cross, j. l. torre, g. w. trucks, j. c. burant, d. j. fox, a. d. rabuck, c. huerta, m. akhras, j. r. cheeseman, s. s. iyengar, j. a. pople, j. e. knox, j. w. ochterski, b. a. johnson, gaussian 03. revision c.02, gaussian inc., 2004 [30] a. frish, a. b. nielsen, a. j. holder, gauss view user manual, gaussian inc., 2001 microsoft word 36-2896_s1_etasr_v9_n4_pp4511-4515 engineering, technology & applied science research vol. 9, no. 4, 2019, 4511-4515 4511 www.etasr.com ghaly et al.: implementation of a broad range smart temperature measurement system using … implementation of a broad range smart temperature measurement system using an auto-selecting multisensor core in labview sidi m. ahmed ghaly electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university (imsiu), riyadh, saudi arabia smghaly@imamu.edu.sa mohammad obaidullah khan electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university (imsiu), riyadh, saudi arabia okkhan@imamu.edu.sa souleimane ould el mehdi electrical engineering department, ecole normale superieure mauritanie, nouakchott, mauritania souleiman6@ens.mr mohammed al-awad electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university (imsiu), riyadh, saudi arabia maawaad@imamu.edu.sa mohammad asad ali electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university (imsiu), riyadh, saudi arabia asadali@imamu.edu.sa khalid al-snaie electrical engineering department, college of engineering, al imam mohammad ibn saud islamic university (imsiu), riyadh, saudi arabia kalsnaie@imamu.edu.sa abstract—a conventional temperature sensing system employs a single transducer to convert temperature into an electrical signal. such a system suffers from the limitation of the sensing range of the sensing device thereby affecting its accuracy and its capability. therefore to make an accurate measurement in a typically abrupt temperature varying environment, a broad range high precision sensor is required. in this paper, an attempt is made to implement a wide spectrum temperature measurement system using auto-selected multi-sensor core in labview. this multi-sensor core can be composed of a set of different sensors having different capabilities to measure different temperatures ranges. these sensors are auto-selected by the program depending on the environment. this concept may be useful for space applications or it can also be useful for the monitoring of temperature and pressure in an oil/gas transportation or supply by means of underground/sea pipeline system or in a refinery plant. further, this may also be applied for high precision temperature sensing in magnetic resonance imaging system applications. keywords-broad spectrum temperature range measurement; multi-sensor core; lm-35; thermister; rtd; auto-select sensor; linearization; labview i. introduction temperature measurement is carried out by various devices, each with its own limitations of operating temperature range and capabilities. the purpose of this paper is to develop an idea and technique by which temperature measurement can be achieved through a varying wide range system. for this intention, three different types of sensors having three different temperatures ranges were employed. the three sensors are thermistor, resistance temperature detector (rtd) and lm35 sensor [1-4]. these three sensors are connected to a logic circuit which selects one particular sensor at a time. a software simulation program is developed such that at the start of the measurement a reference temperature and corresponding reference sensor are chosen. as the temperature increases, the software simulation program checks the temperature and the sensors’ range, a suitable sensor is selected among the set, and the system measures the temperature from the selected sensor as long as the range provided by the program is met. once the range crosses the threshold value, the software simulation program will check for another suitable sensor and so on. by this design the instrument measures varying temperatures by changing sensors. a similar approach is employed for decreasing temperatures. the sensors which are not used at the time of measurement should be kept switched-off so that higher temperatures do not damage unused sensors. at the same time the system does not give erroneous readings when its output is taken by a summing amplifier. the selection of sensors can be achieved by using a switching logic circuit connected to the set of sensors. these sensors give output in terms of voltage that corresponds to the measured temperature. the developed concept can be useful for many industrial applications, especially in magnetic imaging systems [5-8]. ii. impementation of a multi-range sensing system a multi-range sensing system is established as illustrated in figure 1. to implement this idea, three linearized resistor sensors, namely thermistor, rtd, and an integrated circuit sensor lm-35 are used. based on the environmental temperature range, the sensor auto-selecting circuit selects one corresponding author: sidi m. ahmed ghaly engineering, technology & applied science research vol. 9, no. 4, 2019, 4511-4515 4512 www.etasr.com ghaly et al.: implementation of a broad range smart temperature measurement system using … of the three sensors to measure the sampled area temperature. the linearity [9] of these sensors is illustrated in the next section. fig. 1. block diagram of the multi-range sensing system individual data acquisition and formatting circuits convert the received temperature signal, and based on individual underlying principles of conversions defined in (1) to (6), the temperature is measured and displayed. the principle of working and the linearization of each of the sensors are discussed below. ideally, it is often desired that a strictly linear relationship exists between the input and output signals in these sensing devices. practical units, however, will always have some degree of nonlinearity. if an instrument block has constant gain for all input signal levels, then the relationship response graphing the input against the output will be a straight line and the relationship is linear. the broad spectrum temperature measurement system using auto-selected multisensor core has been implemented and simulated in labview. labview is a graphical programming language which uses a graphical user interface. it is simple and user friendly. a user can select a block from its vast function library and define parameters, inputs, and outputs to model a particular system. subprograms can be defined as sub-vis. these sub-vis can be connected, added, removed, adjusted or modified, modeled, tested, and re-modeled according to task parameter changes with time and requirements. labview, apart from providing programming, can easily be integrated to direct hardware without any interface programming or special requirements by using the dac (data acquiring and controlling) assistant to different interfacing boards of national instruments [10-11]. a. the thermistor thermistors are temperature sensitive passive semiconductors, whose resistance can increase and decrease with temperature. the resistances vary by a large amount for small temperature changes. there are two types of thermistors: positive temperature coefficient (ptc) thermistor for which the resistance increases with increase in temperature, and negative temperature coefficient (ntc) thermistor for which the resistance decreases with increase in temperature. an ntc thermistor is used in temperature measurement [12]. since the thermistor has non-linearity for temperature measurement versus measured resistance rt, there should be some sort of linearization. for linearization to be obtained for our required range in a simple form we used two resistors r1 and r2. r2 and rt are connected in parallel whereas r1 is connected in series with the combination of r2 and rt. if a voltage of vin is applied to the circuit as shown in figure 2, the voltage across rt is given by vout: �� � ������ � ���� ������ � (1) equation (1) gives the relation for the determination of rt from the applied input voltage vin, which is 1v, the output voltage measured which is 0.56v to 0.78v, r2 which is 15000ω and r1 which is 2350ω. � � � ��� � � � ln ������� � (2) the linearized ntc thermistor output voltage vout versus temperature plot is illustrated in figure 3. fig. 2. ntc thermistor with input voltage vin fig. 3. thermistor output voltage vout versus measured temperature equation (2) gives the relation between the measured absolute temperature t, reference absolute temperature tr which is 298k corresponding to the reference resistance rr which is 2252ω, obtained resistance rt from (1) and a parameter b which is 1800, corresponding to (2) and (1). this thermistor with a typically given range from 0°c to 60°c is used to measure temperature. however, it can be changed to any other range e.g. from -50°c to 100°c. b. resistance temperature detector (rtd) sensor rtds are devices whose resistance increases with increase in temperature. these devices exhibit linearity response for temperature to voltage (resistance) measurement. rtds are used to measure metal temperature with high melting points and are able to stand corrosion. rtds have high accuracy, but low change in resistance for temperature change [13, 14]. therefore, they can be used to sense certain big levels of engineering, technology & applied science research vol. 9, no. 4, 2019, 4511-4515 4513 www.etasr.com ghaly et al.: implementation of a broad range smart temperature measurement system using … changes. figure 4 shows an input voltage vin applied and an output (measured) voltage vout. fig. 4. rtd sensor �� � � ������ � �� (4) � � �� ���� � ! � �"# (5) equation (4) gives the measured resistance rt from the input voltage vin which is 1v, output voltage vout which ranges from 0.12v to 0.23v for a range of 100ω to 500ω and resistance r1 which is 1000ω. equation (5) gives the absolute temperature measured from rt by (4) and reference resistance rr which is 100ω for reference absolute temperature tr which is 273k and a parameter called alpha (α) which is 0.0385°c -1 . a typical labview frame to measure temperature with rtd sensor under linearization environment is shown in figure 5. the linearized output voltage curve with respect to temperature is shown in figure 6. figure 7 shows the comparative study of linear and non-linear output voltage with respect to measuring temperature for rtd in the range from 0°c to 850°c. fig. 5. labview frame for temperature measurement with rtd sensor under linearization c. the lm-35 sensor the lm35 is an integrated circuit sensor that can be used to measure temperature with an electrical output proportional to temperature (in °c). it can measure temperature more accurately than a thermistor. the sensor circuitry is sealed and not subject to oxidation. the lm35 generates a higher output voltage than thermocouples and may not require the output voltage to be amplified. the lm35 has an output voltage proportional to celsius temperature. the scale factor is 0.01v/°c. the lm35 does not require any external calibration or trimming. it maintains an accuracy of ±0.4°c at room temperature and ±0.8°c in the range of 0°c to +100°c. another important characteristic of the lm35 is that it draws only 60µa from the supply and possesses a low self-heating capability. fig. 6. rtd output voltage vout versus temperature fig. 7. illustration of output voltage response of rtd under linear and non-linear condition for temperature range of 0°c to 850°c the lm35 comes in many different packages and can be selected accordingly. this sensor allows the temperature between -55°c to 150°c [15]. there are two transistors q1 and q2 in the center of the circuit. q1 has ten times the emitter area of the other. this means it has one tenth of the current density, since the same current is going through both transistors. this causes a voltage across the resistor r1 that is proportional to the absolute temperature, and is almost linear across the range. the "almost" part is taken care of by a special circuit that straightens out the slightly curved response of voltage versus temperature. an amplifier ensures that the voltage at the base of transistor q1 is proportional to the absolute temperature by comparing the output of the two transistors. another amplifier converts absolute temperature (measured in kelvin) into either fahrenheit or celsius, depending on the model (lm34 or lm35). this works according to (6): $%&' � �()*("+'&"( ,°/ �00 (6) a typical linearity curve obtained from the temperature measurement system using lm-35 in labview environment is shown in figure 8. a typical labview front panel display showing the selected sensor and a typical virtual temperature scale for temperature measurement is depicted in figure 9. engineering, technology & applied science research vol. 9, no. 4, 2019, 4511-4515 4514 www.etasr.com ghaly et al.: implementation of a broad range smart temperature measurement system using … fig. 8. lm35 temperature sensor linearization curve fig. 9. labview front panel showing the selected sensor for temperature measurement. iii. labview simulations the individual labview frames were combined and worked as a single system based on a multi-range temperature measuring device in which each sensor is auto-selected by the underlying logic [16, 17]. figure 10 shows a combination of the three discussed above sensors with a logic circuit. the logic circuit has three inputs, one for each sensor and two selection switches (for manual selection) to select any sensor among the three. the signal output is obtained from the logic block, a software simulation program selects an initial sensor, the temperature is measured from that sensor and the software is programmed to select the sensor automatically as the temperature reaches the predefined sensor range. the software keeps the values of two previously measured temperatures in order to select upward or downward temperature measurement and then selects the appropriate sensor automatically. as the temperature increases or decreases and goes out of the range of the present sensor and reaches the range of another sensor, the other sensor is selected by the auto-selection switches of the logic circuit which are shown with their temperature ranges in the plot [18]. iv. results and discussion the range of each sensor is assigned and the simulation is conducted in labview. a combined result is plotted and illustrated by using different colors. typically lm-35 is assigned the temperature range of -50 o c to 100 o c, the thermistor is assigned the range of 101 o c to 650 o c, and the rtd sensor is assigned the range of 651 o c to 850 o c. simulation experiments are repeated by changing the range of each sensor and it was noted that for a broad temperature range the simulation setup exhibited satisfactory results and the different sensors were selected automatically to operate in their assigned ranges, as illustrated in figure 11. thus, using the proposed method, this devised instrument can measure the temperature from a range of -50°c to around 1000°c. a sufficient number of simulations were carried out by changing temperature ranges assigned to each sensor and the results were preserved. the combined results of this technique are illustrated in figure 11. fig. 10. labview frame of the block diagram of multi-range sensing fig. 11. color illustration of the total temperature range measured by individual sensors v. conclusion and future work the proposed mechanism was devised with the help of labview. for a broad temperature range, the technique of using a multi-sensor auto-selecting system with the help of a software program for increasing the range of temperature measurement was employed and simulated. the combination of sensors can be used to display various physical quantities like temperature, air pressure and humidity in weather prediction. the future scope of this mechanism is to be employed for the monitoring of temperature and pressure in oil or gas transportation or supply by means of underground/sea pipeline system or in a refinery plant. furthermore, this may also be applied for high precision temperature sensing in magnetic resonance imaging (mri) system applications. engineering, technology & applied science research vol. 9, no. 4, 2019, 4511-4515 4515 www.etasr.com ghaly et al.: implementation of a broad range smart temperature measurement system using … acknowledgement the authors would like to thank eng. waleed al bourihfor his participation throughout this work. references [1] 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a. gani, m. j. e. salami, “a labview based data acquisition system for vibration monitoring and analysis”, student conference on research and development, shah alam, malaysia, july 17, 2002 [17] f. alorifi, s. m. a. ghaly, m. y. shalaby, m. a. ali, m. o. khan, “analysis and detection of a target gas system based on tdlas & labview”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4196-4199, 2019 [18] c. j. kalkman, “labview: a software system for data acquisition, data analysis, and instrument control”, journal of clinical monitoring, vol. 11, no. 1, pp. 51-58, 1995 microsoft word etasr_v11_n4_pp7363-7369 engineering, technology & applied science research vol. 11, no. 4, 2021, 7363-7369 7363 www.etasr.com alzaidy & albayati: a comparison between static and repeated load test to predict asphalt concrete … a comparison between static and repeated load test to predict asphalt concrete rut depth farhan alzaidy department of civil engineering college of engineering university of baghdad baghdad, iraq f.alzaidy1901m@coeng.uobaghdad.edu.iq amjad hamad khalil albayati department of civil engineering college of engineering university of baghdad baghdad, iraq a.khalil@uobaghdad.edu.iq abstract-rutting has a significant impact on the pavements' performance. rutting depth is often used as a parameter to assess the quality of pavements. the asphalt institute (ai) design method prescribes a maximum allowable rutting depth of 13mm, whereas the aashto design method stipulates a critical serviceability index of 2.5 which is equivalent to an average rutting depth of 15mm. in this research, static and repeated compression tests were performed to evaluate the permanent strain based on (1) the relationship between mix properties (asphalt content and type), and (2) testing temperature. the results indicated that the accumulated plastic strain was higher during the repeated load test than that during the static load tests. notably, temperature played a major role. the power-law model was used to describe the relationship between the accumulated permanent strain and the number of load repetitions. furthermore, graphical analysis was performed using vesys 5w to predict the rut depth for the asphalt concrete layer. the α and µ parameters affected the predicted rut depth significantly. the results show a substantial difference between the two tests, indicating that the repeated load test is more adequate, useful, and accurate when compared with the static load test for the evaluation of the rut depth. keywords-asphalt concrete; rut depth; vesys i. introduction rutting is a distress mechanism in flexible pavements. recently, due to the increased truck tire pressures and the lack of maintenance that result in roadway deterioration [1], rutting has become the predominant mode of flexible pavement failures. rutting is primarily caused by the accumulation of permanent deformations in the pavement or its layers. furthermore, a major portion of rutting in the surface layer of flexible pavements is subjected to high tire pressures and heavy axle loads. high tire pressures decrease the contact area between the tire and the pavement, producing high stress, which aggravates deformation in flexible pavements. in addition, environmental conditions affect significantly the surface layer of the pavements [2]. the permanent deformation of the asphalt concrete (ac) mixture has been studied by several researchers for various materials using different testing procedures. furthermore, various parameters and prediction models have been developed to measure rutting resistance. in this study, creep and uniaxial cyclic compression results of ac mixtures were estimated and compared based on various asphalt contents, asphalt types, and temperatures. many studies have been performed to study the mechanism of rutting, and many methods have been proposed for predicting the rut depth (rd). some of these methods are based on limiting the values of subgrade strain to levels that prevent rutting at the pavement surface. these methods were based on the assumption that when the maximum vertical compressive strain at the top of the subgrade is less than a critical value, rutting will be limited to an acceptable level for a specified number of load applications. however, this methodology does not essentially preclude the occurrence of rutting that might occur in the asphalt layer. therefore, a layerstrain method was proposed to improve the above process by including additional analysis to evaluate the amount of rutting occurring in the asphalt layer [3]. it is reported [4] that excessive permanent deformation can lead to longitudinal depressions in wheel paths. this can be followed by longitudinal cracking. subsequently, water can penetrate these cracks and deteriorate the roadway, causing it to lose its loadcarrying capacity. furthermore, excessive permanent deformation can reduce the driving comfort and can lead to icing or hydroplaning because of water getting collected in wheel paths. aashto classified traffic control and environmental factors as the major causes of ac rutting. however, highway authorities have little control over these two factors. furthermore, there are some limitations that prevent the redressing of problems that are within the control of highway agencies [5]. several highway engineers focused on ascertaining the factors that can help address the problem of rutting to propose better mechanisms to reduce the rd. authors in [6] performed several creep tests to study the permanent deformation of ac and developed a rutting prediction model based on a statistical method which considered factors such as stress, temperature, asphalt viscosity, effective asphalt content, air voids, and load repetition. to evaluate the parameters that affect the ac mix, authors in [7] evaluated the influencing factors and suggested variables such as the asphalt content, binder viscosity, air voids, and test temperature that affect the ac mix. corresponding author: farhan alzaidy engineering, technology & applied science research vol. 11, no. 4, 2021, 7363-7369 7364 www.etasr.com alzaidy & albayati: a comparison between static and repeated load test to predict asphalt concrete … furthermore, additives were also used to improve the strength of asphalt materials, e.g. using rubber modified asphalt binder [8]. most of the existing permanent deformation models for asphalt mixes have been empirically determined based on laboratory test results. as a simple performance test [9], a uniaxial repeated load test is generally used to characterize the permanent deformation response of asphalt mixes. permanent deformation measured using repeated load tests, as depicted in figure 1, is generally composed of three stages [10], primary, secondary, and tertiary. in the primary stage, the rate of permanent deformation accumulates quickly and tends to decrease, reaching a constant value in the secondary stage. finally, the rate starts to increase rapidly and accumulates again in the tertiary stage [11]. the objective of these tests is to simulate the repeated load conditions that occur on the road. authors in [12] compared the responses of 3 mixes consisting of conventional and modified binders under both creep and repeated loading. for creep loading at 37°c and confining pressure of 207kpa, the difference among the mixes was not discernible. the results of repeated load testing suggest that the repeated loading test may be more applicable than the creep test to calculate the permanent deformation characteristics of asphalt mixes. the results of strategic highway research program (shrp) [13] also suggest that more deformation occurs in repeated loading than in creep loading for the same materials and other test conditions. apart from the two conventional procedures used for repeated load tests, i.e. termination of the test at 10,000 loading cycles or 5% accumulated strain, regression coefficients a (intercept) and b (slope) were also used to determine the rutting susceptibility of ac mixtures [14]. authors in [15] proposed a method based on repeated axial load tests to determine the flow number of bituminous mixtures. static and repeated load tests were used to evaluate the rutting potential of asphalt mixtures, and the results indicated that the specimens of mixtures experienced a tertiary flow state in the repeated load test. however, no specimen achieved a tertiary flow state in the static load test. this can be attributed to the static pattern of loading that induces less strain when compared with that of repeated loading [16]. fig. 1. typical permanent deformation behavior of asphalt mixture. ii. materials characterization a. asphalt cement to characterize the properties of the base bitumen, conventional tests such as the penetration test, softening point test, flash point test, and penetration and ductility after the thinfilm oven test were performed. these tests were performed in conformity with the relevant test parameters listed in table i. table i. properties of asphalt cement property astm design ation penetration grade 40–50 penetration grade 60-70 test results scrb specification test results scrb specific penetration at 25°c, 100gm, 5s (0.1mm) d-5 42 40-50 67 60-70 softening point (°c) d-36 51 …… 45 ….. ductility at 25°c, 5cm/min (cm) d-113 >100 >100 …. >100 flash point (°c) d-92 289 min. 232 292 min. 232 specific gravity d-70 1.041 …… 1.028 …… residue from thin-film oven test: d-1754 -retained penetration (% of original) d-5 59.5 55+ 64.1 52+ -ductility at 25°c, 5cm/min (cm) d-113 80 25+ 100+ 50+ b. aggregates coarse and fine aggregates were chosen and mixed in appropriate proportions to meet the wearing course gradation prescribed by the scrb specification (scrb, r/9 2003). the gradation curve of the aggregates is depicted in figure 2. to obtain the properties of the coarse and fine aggregates used in the mixture, conventional tests, such as the specific gravity test, los angeles abrasion resistance test, sodium sulfate soundness test, and sand equivalent test were performed. the results, along with the specification limits set by the scrb, are listed in table ii. fig. 2. aggregate gradation curve. c. mineral filler the filler is a non-plastic material that must pass through sieve no. 200 (0.075mm). the physical properties of the filler used in this study are listed in table iii. engineering, technology & applied science research vol. 11, no. 4, 2021, 7363-7369 7365 www.etasr.com alzaidy & albayati: a comparison between static and repeated load test to predict asphalt concrete … table ii. physical properties of aggregates property astm designation test results scrb specification coarse aggregates: 1. bulk specific gravity 2. apparent specific gravity 3. water absorption (%) 4. wear by los angeles abrasion (%) 5. soundness loss by sodium sulfate solution (%) 6. fractured pieces (%) c-127 c-131 c-88 2.611 2.689 0.443 18.7 3.1 96 ….. ….. ….. 30 max. 10 max. 95 min. fine aggregates: 1. bulk specific gravity 2. apparent specific gravity 3. water absorption (%) 4. sand equivalent (%) c-127 2419 2.663 2.697 0.727 55 45 min. table iii. physical properties of the mineral filler (limestone dust) property test results specific gravity 2.794 passing sieve no. 200 (0.075mm) 94 d. specimen preparation the cylindrical specimens used in this study were 101.6mm (4in) in diameter and 203.2mm (8in) in height. the fractions of the aggregates were separated into groups and the aggregates retained on the pan were discarded and replaced by the mineral filler (limestone dust). based on the graduation specifications depicted in figure 2, the aggregates were mixed into a batch of 3800g on the mixing bowl and heated to 150°c in a temperature-controlled oven. asphalt was also heated in a container to a temperature in the range of 135–140°c for 2min, and the contents of the bowel were thoroughly mixed manually on a hot plate. to ensure a uniform compaction temperature, the bowel with its contents was transferred to an oven and stored for 10min at 140°c. a preheated to 100°c compaction mold was prepared and a 4-in paper disk was inserted to cover the mold base plate. the interior edge of the mold was lubricated using a brush to facilitate the specimen extraction. the specimen was compacted by the double plunger method with a load of 65000lb (29491kg) applied using a hydraulic compression machine at the material laboratory of the civil engineering department of the university of baghdad. the load was applied to each end of the specimen for 1min. finally, 36 specimens were carefully transferred to a smooth, flat surface and allowed to cool overnight at 25ºc and then were removed from the mold using a hydraulic extractor. the specimens were then numbered and stored in a bag. iii. evaluation of permanent deformation and testing results permanent strain values were determined using a pneumatic repeated load system (prls) apparatus manufactured under the auspices of the civil engineering department of the university of baghdad [17] as depicted in figure 3. axial repeated and static load tests were performed. the cylindrical specimens, 101.6mm (4in) in diameter and 203.2mm (8in) in height, were subjected to conditioning in the prls test chamber at various testing temperatures (20°c, 40°c, and 60°c) for 2h. a linear variable differential transformer was used to monitor the deformation of the specimens under each load cycle. compressive loading was applied at 138kpa in the form of a rectangular wave with a constant loading frequency of 60cycles/min and loading sequence including 0.1s load duration and 0.9s rest duration. fig. 3. a photograph of the prls. a. permanent deformation characteristic properties for repeated load test the values of the permanent strain were obtained at the following load repetitions: 1, 2, 10, 100, 500, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, and 10000. permanent strain (��) was calculated using (1): �� � �� � �� (1) where �� is the axial permanent microstrain, �� is the axial permanent deformation, and h is the specimen's height. the accumulative axial permanent strain versus the number of loading repetitions (n) is depicted in figure 4. fig. 4. cumulative permanent strain vs loading cycles from the repeated load test (log-log scale). engineering, technology & applied science research vol. 11, no. 4, 2021, 7363-7369 7366 www.etasr.com alzaidy & albayati: a comparison between static and repeated load test to predict asphalt concrete … b. permanent deformation characteristic properties for static (creep) load test data for the following loadings were recorded at 1, 10, 30, 60, 100, 260, 360, 500, 1000, 2000, and 3000s. the values of the permanent strain were calculated at these loadings using the following expression: �� � � � �� (2) where �� is the axial creep deformation. the cumulative axial permanent strain versus the number of loading times is depicted in figure 5. fig. 5. cumulative permanent strain vs loading times from the creep load test (log-log scale). c. regression analysis several formulas have been proposed to describe the relationship between �� and n. authors in [18, 19] suggested a log-log relationship, as described in the following equation: �� � �� � (3) where n is the number of load repetitions, and a and b are positive regression constants, as depicted in figure 4. the parameter a is the intercept with the permanent strain axis, and b is the slope of the linear portion of the logarithmic relationship. the double-logarithmic-scaled relationship between �� and n can be approximated using a linear function. iv. vesys theory authors in [20] developed the vesys software using multilayer visco-elastic theory to predict the rd in flexible pavement layers. the basic assumption of vesys rutting models is that permanent strain is related to resilient strain as follows: ����� � ���� �� (4) where ����� is the vertical permanent strain at the n th load repetition, and � and � are material properties that are functions of the stress state and temperature respectively. the material parameters are defined as � � 1� � and � � �� ��⁄ . these two parameters govern the permanent deformation behavior of the model. in particular, � is the rate of decrease or increase in permanent deformation as the number of load applications increases, and � is the constant of proportionality between permanent and elastic strains (� 0). values greater than 1 indicate premature rutting. the most critical task in using this model is the prediction of � and � accurately for each pavement layer within the pavement system. the permanent deformation parameters could be predicted using laboratory or field data [21]. the comparative evaluation of the impact of repeated and creep stresses on permanent deformation parameters is listed in table iv. intercept a represents the deformation of the specimen after the first load repetition, whereas slope b refers to the rate of deformation throughout the fatigue life of asphalt concrete. furthermore, this comparison also includes the average values of permanent strain and parameters α and β. table iv. permanent deformation parameters temperature (°c) asphalt content (%) asphalt grade 20 40 60 4 4.6 5.2 40-50 60-70 repeated load test (rlt) εp 266 5840 30000 9458 16160 16700 11160 17040 a 55 150 430 230 210 190 160 260 b 0.184 0.40 0.58 0.348 0.4 0.43 0.394 0.398 α 0.816 0.60 0.42 0.652 0.6 0.57 0.606 0.602 µ 0.105 0.270 0.50 0.340 0.285 0.250 0.23 0.36 creep load test (clt) εp 532 1730 9295 3850 3480 4219 3680 4020 a 210 555 1430 798 660 730 690 770 b 0.119 0.144 0.264 0.165 0.176 0.187 0.175 0.177 α 0.881 0.856 0.736 0.835 0.824 0.813 0.825 0.823 µ 0.120 0.145 0.260 0.165 0.175 0.189 0.176 0.178 v. discussion the accumulated strain at the flow number increased for the repeated load test (rlt) and exhibited the opposite behavior for the static load test (slt). the significant difference in the values of �� at the failure load for both tests is illustrated in figure 6. table v lists the anova analysis that explains the impacts of the testing variables on the plastic strain. the table lists the degrees of freedom (the number of variables used minus one), the f-test results, and the p-value (significance) for each test. the results particularly indicate that temperature plays a major role affecting plastic deformation (f value >> fcrit.). the variables (intercept and slope) used in this model when plotted on a log scale can be useful indicators of rutting resistance. the minimal values of each provide a good indicator of rutting resistance. furthermore, the slope coefficient b is also used as a term of creep rate (fc) to an assessment of the asphalt performance in resistance to permanent deformation. the intercept values of rlt increased by 2.7 and 7.8 factors with an increase in temperature from 20°c to 40°c and 60°c respectively, whereas slt increased by 2.6 and 6.8 respectively. the content and grade of the asphalt had only a minor impact. the slope or fc values for rlt increased by 2.17 and 3.15 with an increase in temperature from 20°c to 40°c and 60°c respectively, whereas that of slt increased by 1.21 and 2.21 respectively. the content and grade of the asphalt did not affect the slope of the slt. the sensitivity analysis of the vesys 5w rutting model clearly indicated that α and µ had a considerable effect on the predicted rd. the values of both parameters were measured using rlt and slt. figures 7–9 illustrate the impact of temperature and mixture properties (asphalt content and grade) engineering, technology & applied science research vol. 11, no. 4, 2021, 7363-7369 7367 www.etasr.com alzaidy & albayati: a comparison between static and repeated load test to predict asphalt concrete … on the rd of the ac layer. as mentioned above, temperature is considered to be the main factor that affects rutting in the ac layer. the results indicated that rd increased with an increase in temperature for both tests, as depicted in figure 7. at 20°c, the rd increased slightly. however, at 40°c and 60°c, the rd value was larger for rlt than for slt by a factor of 6.8 and 4.02 respectively. the asphalt content and grade had no effect on the rd for the creep test, as depicted in figures 8 and 9. the higher value of α and lower value of µ coefficients indicate pavements with lower rutting. at a lower value of α, rutting will develop over the entire pavement life and the mainstream of the rutting will occur at the initial stage and taper off with the remaining life of the pavement when the ac layer is soft (higher initial strain) or the climatic region is hot (higher temperatures). (a) (b) (c) fig. 6. impact of testing temperature and asphalt mixture on the plastic strain. table v. impact of variables and test methods on plastic strain ( wo-way anova) source of variation df f p-value f crit. repeated load test (rlt) temperature (°c) 2.000 38.474 6.03e-06 3.885 asphalt grade 1.000 2.666 0.128 4.747 asphalt content (%) 2.000 1.381 0.310 3.326 static load test (slt) temperature (°c) 2.000 291.438 6.74e-11 3.885 asphalt grade 1.000 1.096 0.316 4.747 asphalt content (%) 2.000 1.149 0.396 3.326 fig. 7. temperature vs predicted rut depth on ac layer (vesys 5w analysis). fig. 8. asphalt content vs predicted rut depth on ac layer at 40°c (vesys 5w analysis). fig. 9. asphalt grade vs predicted rut depth on ac layer at 40°c (vesys 5w analysis). engineering, technology & applied science research vol. 11, no. 4, 2021, 7363-7369 7368 www.etasr.com alzaidy & albayati: a comparison between static and repeated load test to predict asphalt concrete … fig. 10. impact of esal on the prediction of rut depth in ac layer at 40°c (vesys 5w analysis). to compare the trend of variation in rd with equivalent single-axle load (esal), figure 10 depicts the application of various esals on the ac layer. the total rd for rlt is higher than that for slt by a factor of 8.4. therefore, it is significant that the rd at the first million repetitions is approximately the 44% of the total rd. moreover, we can compare the predicted rd for the ac layer evaluated using rlt with the measured rd estimated using (5): "� � �� �# (5) where "� is the rutting depth (mm), �� is the permanent strain (mm/mm), and # is the total thickness (mm) of the asphalt concrete layer. �� is evaluated based on the model developed in [17] as follows: $%& � �34.463+0.983log� ��.��1234 �.��5678� + 1.961log9 +1.812log; +0.656log= � 37.277log? � 4.951log@ �1.455loga� 1.93logb (6) where $%& is the log of accumulated permanent micro strain at the n th load repetition, t is the test temperature (°c), s is the stress level (psi), d is the applied stress duration (s), b is the percentage absorbed asphalt (by weight of aggregates), a is the percentage of air voids, m is the percentage of voids in mineral aggregates, and f is the voids filled with asphalt. similarly, using the trend of variation in rd with esal, as depicted in figure 11, the values of rd for both the predicted and the measured data are closed. therefore, the use of repeated load tests to predict rd is significantly accurate and reliable. fig. 11. comparison between the predicted and the measured rut depths for various esal repetitions. in general, to evaluate the rutting resistance properly the parameters from unconfined rlts in [9,14] can be used. vi. conclusion in this study, the power-law model was used to obtain parameters for simulating the permanent deformation of the asphalt layer under uniaxial repetitive and static compression loads. the results indicated that the accumulated plastic strain for the repeated load test was higher than that of the static load test for various mixture properties and climatic conditions (temperature). vesys 5w was used to predict the rut depth at the asphalt concrete layer subjected to equivalent single-axle loads. the α and µ parameters exhibited a considerable impact on the predicted rut depths. finally, the results of this study indicated a high difference between the above two tests. the predicted rut depth based on repeated load tests was in reasonable agreement with the actual rut depth. references [1] o. m. kunene and d. allopi, "comparison between conditions of major roads within and outside the port of durban," engineering, technology & applied science research, vol. 3, no. 1, pp. 363–367, feb. 2013, https://doi.org/10.48084/etasr.263. [2] r. garba, "permanent deformation properties of asphalt concrete mixtures," ph.d. dissertation, norwegian university of science and technology, trondheim, norway, 2002. [3] e. r. brown and s. a. cross, "a national study of rutting in hot mix asphalt (hma) pavements," ncat, auburn, al, usa, ncat report 92–05, feb. 1992. [4] j. morris, "the prediction of permanent deformation in asphalt concrete pavements," 1973. [5] aashto guide for design of pavement structures, 4th ed. washington dc, usa: aashto, 2002. [6] r. b. leahy, "permanent deformation characteristics of asphalt concrete," ph.d. dissertation, university of maryland, college park, md, usa, 1989. [7] k. e. kaloush, "simple performance test for permanent deformation of asphalt mixtures," ph.d. dissertation, arizona state university, tempe, az, usa, 2001. [8] k. jadidi, m. khalili, m. karakouzian, and s. amirkhanian, "toughness, tenacity and maximum initial strength of rubber modified asphalt binders," engineering, technology & applied science research, vol. 9, no. 1, pp. 3765–3769, feb. 2019, https://doi.org/10.48084/etasr.2526. [9] "simple performance tests: summary of recommended methods and database," transportation research board, nchrp report 547, jun. 2006. https://doi.org/10.17226/13949. [10] standard specifications for highway bridges: 2002, 17th ed. washington dc, usa: aashto, 2003. [11] m. w. witczak, "development of the 2002 guide for the design of new and rehabilitated pavements-flexible pavements overview," hot topics, 2001. [12] c. l. monismith and a. a. tayebali, "permanent deformation (rutting) considerations in asphalt concrete pavement sections (with discussion and closure)," in association of asphalt paving technologists, 1988, vol. 57, pp. 414–463. [13] c. l. monismith et al., permanent deformation response of asphalt aggregate mixes. strategic highway research program, 1994. [14] m. w. witczak, k. kaloush, t. pellinen, m. el-basyouny, and h. von quintus, "simple performance test for superpave mix design," transportation research board, nchrp report 465, 2002. [15] a. r. archilla, l. g. diaz, and s. h. carpenter, "proposed method to determine the flow number in bituminous mixtures from repeated axial load tests," journal of transportation engineering, vol. 133, no. engineering, technology & applied science research vol. 11, no. 4, 2021, 7363-7369 7369 www.etasr.com alzaidy & albayati: a comparison between static and repeated load test to predict asphalt concrete … 11, pp. 610–617, nov. 2007, https://doi.org/10.1061/(asce)0733-947x (2007)133:11(610). [16] m. irfan, y. ali, s. iqbal, s. ahmed, and i. hafeez, "rutting evaluation of asphalt mixtures using static, dynamic, and repeated creep load tests," arabian journal for science and engineering, vol. 43, no. 10, pp. 5143–5155, oct. 2018, https://doi.org/10.1007/s13369-017-2982-4. [17] a. h. albayati, permanent deformation prediction of asphalt concrete under repeated loading, vol. 129. baghdad, iraq: university of baghdad, 2006. [18] t. l. j. wasage, g. ong, t. f. fwa, and s. a. tan, "laboratory evaluation of rutting resistance of geosynthetics reinforced asphalt pavement," journal of the institution of engineers, vol. 44, no. 2, pp. 29–44, 2004. [19] c. l. monismith, n. ogawa, and c. r. freeme, "permanent deformation characteristics of subgrade soils due to repeated loading," presented at the 54th annual meeting of the transportation research board, washington dc, usa, 1975. [20] w. j. kenis, predictive design procedures, vesys users manual: an interim design method for flexible pavements using the vesys structural subsystem. national technical information service, 1978. [21] x. qi and m. w. witczak, "time-dependent permanent deformation models for asphaltic mixtures," transportation research record, vol. 1639, no. 1, pp. 83–93, jan. 1998, https://doi.org/10.3141/1639-09. microsoft word 30-3710_s1_etasr_v10_n4_pp6057-6061 engineering, technology & applied science research vol. 10, no. 4, 2020, 6057-6061 6057 www.etasr.com my et al.: a magneto-electric dipole antenna array for millimeter wave applications a magneto-electric dipole antenna array for millimeter wave applications dang thi tu my quy nhon university binh dinh, vietnam dangthitumy@qnu.edu.vn tran thi huong huong ban mai education company limited da nang, vietnam huonggnouh@gmail.com huynh nguyen bao phuong quy nhon university binh dinh, vietnam huynhnguyenbaophuong@qnu.edu.vn bui thi minh tu university of da nang, university of science and technology da nang, vietnam btmtu@dut.udn.vn abstract-in this paper, a low-profile broadband antenna is proposed for future 5g millimeter-wave cellular wireless networks. the proposed antenna is a modified magneto-electric (me) dipole, which consists of four metallic plates, grounded vias, an aperture fed, a ground plane, and a microstrip line feed. the antennas are built on rt/duroid 5880 substrates and have been realized by the printed circuit board technique. a singleelement with an overall of 10×10×1.04mm 3 (~1.26λo×1.26λo×0.13λo at 38ghz) exhibits an impedance matching of 27.9% (32.242.8ghz) for |s11|<–10db and a realized gain up to 7.5dbi over the frequency band. the usefulness of these antennas as beamforming radiators is demonstrated by a 1×4 element linear array. also, a wide-band excitation is applied for the linear me dipole array to realize a broadband array. the simulated results proved the proposed array can operate in a frequency band spreading from 31.4ghz to 42.1ghz with a gain of 12.5dbi and a side-lobe of -13db. keywords-magneto-electric dipole; millimeter wave; beamforming; antenna array i. introduction the fourth generation (4g) long term evolution (lte) of cellular communication has been successfully implemented in many countries and areas. with a carrier frequency spectrum ranging from 700mhz to 2.6ghz, today’s cellular providers attempt to deliver high quality, low latency video and multimedia applications for wireless devices. however, the rapid increase of mobile data and the use of smartphones is creating unprecedented challenges to the wireless service providers. to address this, there has been a growing interest in cellular systems for the so-called millimeter-wave (mmw) bands, between 30 and 300ghz, where the available bandwidths are much wider [1]. next generation of wireless cellular networks, which are known as fifth generation (5g), will make better use of the mmw bands [2, 3]. despite the absence of official standard for the 5g, antennas for 5g cellular wireless networks have received much attention from the research community. it is well known that the path loss at the mmw bands is significant as compared to microwave bands due to the higher frequencies of mmw transmissions and the atmospheric absorption at the mmw frequency range. to mitigate the path loss at the mmw frequency range, beamforming has been proposed as an enabling technology for the 5g cellular wireless networks [4, 5]. in general, an antenna for beamforming must be small, lightweight, low-cost, lowmutual-coupling in array environment, with pure polarization and high radiation efficiency, and easy to fabricate. on the other hand, magneto-electric (me) dipole antennas, exhibiting wide impedance bandwidth and stable gain, have been presented for base stations in mobile communications [6, 7]. the basic design of the me dipole consists of a magnetic dipole and an electric dipole, which are excited simultaneously to achieve a radiation having equal eand h-plane patterns and low back-radiation. recently, the me dipole antennas [8-11] have been scaled for 60ghz mmw communications. the mmw me dipole antennas are easily realized by using printed circuit board (pcb) technology. however, these antennas were not characterized in an array environment. in addition, their magnetic dipoles are performed by two vertical quarterwavelength shorted patch antennas, thus, the antenna height is large. this paper proposes a low-profile me dipole antenna for use in 38ghz future 5g cellular wireless networks. the antenna is fed by an aperture slot, which ensures the excitation of the me dipole antenna and achieves low-profile. also, with wide-band excitations, the arrays yielded a wide bandwidth and side-lobe level better than –13db. ii. single element design this part presents the configuration of the proposed me dipole antenna and analyzes its principles by investigating the current distribution. the optimization process is provided in detail to show the final design of the me antenna. corresponding author: bui thi minh tu engineering, technology & applied science research vol. 10, no. 4, 2020, 6057-6061 6058 www.etasr.com my et al.: a magneto-electric dipole antenna array for millimeter wave applications a. antenna geometry figure 1 shows the geometry of the antenna. the me dipole antenna was designed on a substrate #1, which is a wgnd×lgnd rt/duroid 5880 sheet with 2.2 relative permittivity 2.2, 0.0009 loss tangent, 0.7874mm thickness, and 17µm copper thickness. the antenna consists of 4 metallic plates, 8 metallic posts, and a ground plane. the metallic posts with a diameter of 0.1mm were realized by plated through-hole technology. the aperture slot was etched on the ground plane of the substrate #1. a 50ω microstrip line for feeding through the aperture was built on the substrate #2 that is a rt/duroid 5880 sheet with thickness of 0.254mm. (a) (b) (c) fig. 1. geometry of the proposed antenna: (a) perspective view, (b) crosssectional view, (c) top view. b. the me dipole antenna operation ansys academic research hf was used for all simulations of the proposed antenna. in order to realize an me dipole antenna, the electric dipole and magnetic dipole should be excited simultaneously [4]. the metallic plates acted as the half-wavelength electric dipole antennas (ld~λ/2). in general, the magnetic dipoles are performed by two vertical quarterwavelength shorted patch antenna [5–7]. in particular, due to the presence of the aperture slot fed, the magnetic dipoles are mainly performed by the slot edges between the shorted patch antennas. therefore, the excitation of the me dipole antenna can be obtained with a lower antenna height. this is demonstrated by the proposed antenna, which has a 0.7874mm (~0.15λeff at 38ghz) distance from the metallic plates to the ground plane. the me dipole antenna operation can be seen in figure 2, which shows the current distribution on the proposed antenna at 38ghz for different phase angles. at the phase angle of 0º, the currents on the slot edges between the shorted microstrip patches attain maximum strength, which means that the magnetic dipoles are excited. at the phase angle of 90º, the currents on the planar electric dipoles attain maximum strength at the surround edges, which means that the electric dipoles are excited. at the phase angle of 180º, the magnetic dipoles are excited again with opposite direction to the currents at the phase angle of 0º. at the phase angle of 270º, the electric dipoles are excited again with opposite direction to the currents at the phase angle of 90º. these indicate that the electric and magnetic dipoles are excited with 90 0 phase difference consequently, the antenna obtains good broadside pattern and low back radiation [12]. fig. 2. current distribution on the me dipole antenna at 38ghz for different phase angles. the resonant frequency of the proposed me antenna can be optimized by changing its dimensions. in this case, the gaps between the metallic patches (g1 and g2) are fixed at 0.3mm while changing the length of me dipole ld. figure 3 presents the s11 simulated with different values of ld. as can be observed from this figure, the resonant frequency of the me antenna decreases while its length ld increases. the antenna shows a resonance at the desired frequency of 38ghz when the length of the antenna (ld) is equivalent to 3.46mm. next, the input impedance of the antenna is verified to obtain the impedance matching. due to the aperture fed, the me dipole antenna’s impedance mainly belongs to the length of the aperture slot while the width of the slot almost does not affect the input impedance of the proposed antenna, therefore, it was necessary to modify the length for getting a desired impedance matching. the length of the aperture slot la is investigated when its width wa is fixed at 0.4mm. as can be seen in figure 4, the return loss of the antenna changed when the length la engineering, technology & applied science research vol. 10, no. 4, 2020, 6057-6061 6059 www.etasr.com my et al.: a magneto-electric dipole antenna array for millimeter wave applications changed. furthermore, the resonant frequency of the antenna was hardly unchanged. this means that the input impedance of the me antenna can be easily optimized for matching with the impedance of the microstrip line at the input. it is shown that the antenna yields a very good impedance matching as la=2.05mm. fig. 3. s11 simulated results with different me dipole length ld. fig. 4. impedance matching investigation with different values of la. fig. 5. simulated s11 of the proposed me antenna. figure 5 shows the optimized s11 of the me antenna. it can be observed that the antenna has a wide bandwidth ranging from 32.2ghz to 42.8ghz with a center frequency of 38ghz. the final design parameters of the antenna were: wgnd=10mm, lgnd=10mm, wd=3.46mm, ld=3.46mm, wms=0.733, lms=5.9mm, wa=0.4mm, la=2.05mm, g1=0.3mm, g2=0.3mm, and sp=0.6mm. the radiation pattern simulated result of proposed me antenna at 38ghz is given in figure 6. it can be seen that the antenna yielded a directional radiation in xz plane with a peak gain of 6.09dbi while posessing an omnidirectional radiation in the xy plane. fig. 6. simulated radiation pattern of the proposed me antenna at 38ghz. iii. antenna array in this section, the me antenna array design is divided into two parts. firstly, the feeding network using t-junction power dividers is designed. the gradual transformer was used to realize a wide-band excitation. then, 4 optimized me antennas were integrated in a designed feeding network to form a 4element antenna array. figure 7 presents the realized gain of the proposed me antenna in its frequency band. it can be seen that the me antenna has a realized gain up to 7.5dbi across the whole bands. fig. 7. simulated realized gain of the single me antenna. a. feeding network to realize the wide-band excitation, a feeding network composed of several equal t-junction power dividers was implemented, as shown in figure 8. the feeding network was built on an rt/duroid 5880 sheet with a thickness of 0.254mm. equal t-junction power dividers were implemented based on microstrip lines. to avoid the tiny width of the microstrip line with high characteristic impedance, each power divider contains a 50ω to 25ω transformer. the gradual transformer is inserted between the 50ω and 25ω microstrip lines to increase the impedance matching and reduce the losses at the corner of 25ω lines. all corners of the divider are cut with an angle of 45 0 in order to reduce reflection. furthermore, the v-shaped cuts are also etched at the middle points of tjunction dividers for decreasing the reflected power. figure 9 shows the simulated scattering parameters of the power divider. it can be seen that the divider shows a wide bandwidth spreading from 17ghz to 44ghz corresponding to all the 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 -60 -50 -40 -30 -20 -10 0 s 1 1 ( d b ) frequency (ghz) ld = 3.44 mm ld = 3.46 mm ld = 3.48 mm 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 -50 -40 -30 -20 -10 0 s 1 1 ( d b ) frequency (ghz) la = 1.9 mm la = 2.0 mm la = 2.05 mm la = 2.2 mm la = 2.3 mm 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 -60 -50 -40 -30 -20 -10 0 s 1 1 ( d b ) frequency (ghz) engineering, technology & applied science research vol. 10, no. 4, 2020, 6057-6061 6060 www.etasr.com my et al.: a magneto-electric dipole antenna array for millimeter wave applications transmission coefficients changing from 6.1 to 6.8db. thus, the proposed power divider is suitable for a wide-band array antenna design. fig. 8. feeding network of wide-band excitation (all dimensions in mm). fig. 9. simulated s-parameters of the proposed wide-band excitation using t-junction power dividers. b. four element array antenna in this work, four identical me dipole antennas were integrated with the feeding network to create a higher gain antenna, as presented in figure 10. fig. 10. geometry of the proposed 4-elment array antenna. the mutual couplings between two me dipole antennas were studied for different values of center-to-center spacing. the final design was optimized with 6mm spacing (0.75λo at 38ghz). besides, the length of the gradual transformer was also investigated for optimizing resonant frequency. for the best center frequency of the antenna, the length of gradual transformer was chosen as 2.8mm. the performance of the 4element array with equal-magnitude excitation at all elements is given in figures 11-13. it can be observed from figure 11 that the array can operate through the impedance bandwidth spreading from 31.4ghz to 42.1ghz with a center frequency of 38ghz. figure 12 shows the simulated results of the radiation patterns of the array at 38ghz. as can be seen from this figure, the array yielded a gain of 12.5dbi and a side-lobe of -13db at phi=90 0 , as shown in figure 13. fig. 11. simulated s11 of the 4-element array. fig. 12. simulated radiation patterns of the 4-element array at 38ghz. the simulated result of the realized gain of the array over the frequency band is depicted in figure 14. as can be seen in, the array antenna exhibits a stable realized gain from 10.8 to 12.5dbi in the operational frequency band. the comparison results between the proposed 4-element me array antenna with the related works can be seen shown in table i. the me dipole antenna reported in [11] has a wider bandwidth as well as maximum realized gain compared to proposed me dipole. however, the model in [11] has a complex structure since the mushroom-like ebg structures were used as a high impedance ground plane for increasing the bandwidth as well as the gain of the antenna. the 2×2 me array proposed in [13] yielded a high directivity. but this antenna also has a complex structure by using a layer corporate-feed network based on ridge gap waveguide. table i. comparison between the proposed and reported me dipole antennas ref. me antenna bandwidth (ghz) realized gain (dbi) structure [11] single 23.4 41.5 8.2 complex [13] array (2×2) 24 30 15.4 a complex proposed single 32.2 42.8 7.5 simple array (1×4) 31.4 41.2 12.5 simple a : directivity of the me antenna. 10 20 30 40 50 -50 -40 -30 -20 -10 0 s -p a ra m e te rs ( d b ) frequency (ghz) s11 s21 s31 s41 s51 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 -35 -30 -25 -20 -15 -10 -5 0 s 1 1 ( d b ) frequency (ghz) engineering, technology & applied science research vol. 10, no. 4, 2020, 6057-6061 6061 www.etasr.com my et al.: a magneto-electric dipole antenna array for millimeter wave applications fig. 13. simulated broadside realized gain of the 4-element array. iv. conclusion a modified magneto-electric (me) dipole antenna has been proposed for mmw use in this paper. the proposed antenna consists of four metallic plates which are connected to a ground plane via metallic posts. the antennas are fed by a microstrip line through an aperture slot to widen the bandwidth. the single-element shows a good impedance matching up to 27.9% and a maximum realized gain up to 7.5dbi. a 4-element array has been designed for beamforming. the simulation results show that the array can operate in a frequency band ranging from 31.4ghz to 42.1ghz and yielded a gain of 12.5dbi with -13db-side lobe. the proposed me antenna and its array can be a good candidate for applications in mmw systems. acknowledgement this work was conducted at the calculation and simulation laboratory of the faculty of engineering and technology, quy nhon university, vietnam. the authors wish to thank the technical staff of the laboratory for its support. references [1] s. rangan, t. s. rappaport, and e. erkip, “millimeter-wave cellular wireless networks: potentials and challenges,” proceedings of the ieee, vol. 102, no. 3, pp. 366–385, mar. 2014, doi: 10.1109/jproc.2014.2299397. 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[10] m. li and k.-m. luk, “wideband magneto-electric dipole antenna for 60-ghz millimeter-wave communications,” ieee transactions on antennas and propagation, vol. 63, no. 7, pp. 3276–3279, jul. 2015, doi: 10.1109/tap.2015.2425418. [11] j. sun and k.-m. luk, “wideband magneto-electric dipole antennas for millimeter-wave applications with microstrip line feed,” in 2018 international symposium on antennas and propagation (isap), busan, south korea, oct. 2018. [12] a. chlavin, “a new antenna feed having equal e -and h-plane patterns,” transactions of the ire professional group on antennas and propagation, vol. 2, no. 3, pp. 113–119, jul. 1954, doi: 10.1109/tap.1954.27983. [13] w. y. yong, t. emanuelsson, and a. a. glazunov, “5g wideband magneto-electric dipole antenna fed by a single-layer corporatefeed network based on ridge gap waveguide,” presented at the 14th european conference on antennnas and propagation, eucap 2020, mar. 2020, accessed: jul. 05, 2020. [online]. available: https://research.utwente.nl/en/publications/5g-wideband-magnetoelectric-dipole-antenna-fed-by-a-single-layer. author profiles dang thi tu my received her b.eng. and m.eng. degrees from hanoi university of science and technology in 2000 and 2004, respectively. from 2016 she is a ph.d. student at the department of electronic and telecommunication engineering, university of science and technology, the university of danang. from october 2000 to present, she is a lecturer at the department of technique and technology, quy nhon university. research interests: electronics and telecommunications, ultra-high frequency and antenna technology, and artificial networks. huynh nguyen bao phuong received the b.e, m.sc. and d.e degrees from hanoi university of science and technology, vietnam in in 2003, 2007 and 2014, respectively. now he is a senior lecturer of the faculty of engineering and technology, quy nhon university, vietnam. his research interests are high impedance surfaces (his), microstrip and metamaterial antennas, mimo antennas. tran thi huong received the b.s degree in electrical and electronics engineering from the utsunomiya university, japan in 2004 and m.e. and d.e degrees in electrical and electronics engineering from tokyo institute of technology, japan in 2006 and 2010 respectively. from 2010 to 2019, a lecturer at the department of electronic and telecommunication engineering, the university of da nang, university of science and technology. research interests: dielectric resonator, material measurements in mmw bands and high frequency planar antennas. bui thi minh tu received her ph.d. from the universite de technologie de compiegne (france) in 2010. she started teaching at the faculty of electronic and telecommunication engineering, the university of danang, university of science and technology in 2010. since 01/2015, she has been appointed as vice-dean of the faculty. her research interests include communication systems, signal processing, renewable energy, and sustainable development 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 0 2 4 6 8 10 12 14 16 18 20 frequency (ghz) r e a li z e d g a in ( d b i) microsoft word 08-3412_s_etasr_v10_n3_pp5627-5631 engineering, technology & applied science research vol. 10, no. 3, 2020, 5627-5631 5627 www.etasr.com asiimwe et al.: usability testing of a web portal for ornamental plants and flowers in arusha, tanzania usability testing of a web portal for ornamental plants and flowers in arusha, tanzania kenneth patrick asiimwe school of computational and communication sciences and engineering nelson mandela african institute of science and technology arusha, tanzania patricka@nm-aist.ac.tz dina machuve school of computational and communication sciences and engineering nelson mandela african institute of science and technology arusha, tanzania dina.machuve@nm-aist.ac.tz mussa ally dida school of computational and communication sciences and engineering nelson mandela african institute of science and technology arusha, tanzania mussa.ally@nm-aist.ac.tz abstract—the information and communication technology (ict) adoption has steadily advanced in the horticulture sector in tanzania. this study aims to test and give feedback regarding the usability of a developed web portal prototype for ornamental plants and flowers in arusha city. the stakeholders are botanists and researchers who search for plant and flower information (taxonomy), small scale farmers, herbalists, and the arusha city council. the assessments were organized and conducted in groups where each stakeholder was given access to the web portal for 2 days. questionnaires were distributed to get feedback from each participant (a total of 48 participants). multicriteria satisfaction analysis was chosen to measure user satisfaction measuring usability factors such as service quality, technical quality, information quality, and system quality. the overall obtained results had a mean score above 3.5 (70%) on a fivepoint scale likert scale analysis. keywords-usability testing; web portal; user requirement satisfaction i. introduction web portals are gateways for the exchange of services and information with the use of simple user interfaces, a significant role in recent advancement of information and communication technology (ict) [1]. these portals enable database access, new user’s registration and search capabilities. therefore, their performance is very significant [2]. in africa, ornamental production, a subsector of horticulture, has developed in the past decade with kenya ranking first, followed by tanzania, south africa, and uganda. this is attributed to the adoption of ict and technology in the ornamental sector in africa [3]. however, the adoption of ict in horticultural production is still a challenge [4]. the horticulture sector in arusha city is dominated mainly by small-scale farmers (vendors) selling ornamental plants and flowers mostly on road sides (streets) contributing to about 70% of the production in the sector, without being directly connected to the regional and international market [5]. furthermore, horticulture in tanzania is challenged with inadequate access to information by stakeholders, including researchers and buyers. also, there is a lack of awareness by stakeholders in tanzania and internationally about the economic and social potential of the horticulture sector [6]. the access to information on varying species of ornamental plants and flowers in tanzania is limited [5]. it is therefore important to test the usability of the developed web portal to ensure the user needs are met. with the advancement of ict in the 21st century, access to information at anytime, anyplace with little effort should be possible. poorly designed interfaces hinder the effectiveness of a system [7]. additionally, according to [8], they bring low financial returns as many clients will seek alternative web systems that are better designed and have good user experience. many horticulture institutions in tanzania specifically have attempted to adopt the use of web portals, especially third party portals such as brahms (botanical research and herbarium management system) to provide their services. such portals store and share information on a variety of species of plants in the country, in other words they provide a digitization of the biodiversity collection of various horticulture institutions in the country. since these services are offered mainly by third parties, it is required that the efforts to ensure the achievements of their purpose must satisfy all stakeholder expectations measured on the level of user satisfaction by all the end users of the system. the third party web portal used in tanzania (brahms) is designed specifically for botanical collections and uses the obsolete disk operating system (dos) [9] which is not easily understood by common users. it does not have a graphical user interface (gui) which challenges user experience. therefore, this study aims to test the usability of the developed prototype web portal for ornamental plants and flowers in arusha city, to gather the user requirements, to measure user satisfaction, and to give feedback for the continuous enhancement of the portal. a website that is not user friendly does not attract users, it rather drives them away, thus it is crucial that a user-centered approach is followed in order to ensure usability and thus attract more users [10]. the developed web portal has two parts, one is client side where the information on the variety species of ornamental plants and flowers can be accessed and vendor ads on various products are showcased, the second is the server side which corresponding author: kenneth patrick asiimwe engineering, technology & applied science research vol. 10, no. 3, 2020, 5627-5631 5628 www.etasr.com asiimwe et al.: usability testing of a web portal for ornamental plants and flowers in arusha, tanzania allows the administrator to register or add information on the species including: english name, botanical name, family name, origin, vernacular name, trade name, description by size, shape, color, genus, image, use (medicinal or herbal, edible or poisonous, and ornamental), and also a conservation in terms of quantity (extinct in the wild, extinct, critically endangered, endangered, least concern vulnerable, nearly threatened, data deficient, and not evaluated). ii. usability testing usability testing is a technique of getting feedback from stakeholders about a product in order to ensure it meets their requirements [11]. usability is the most significant feature or aspect of an application [7]. according to [12], human computer interaction (hci) does not only involve ease of use but also proved easy access to information and thus users today are much now interested in user interfaces that are effective and easy to learn. it is for developers to spend much time in developing user interface and the outcomes of [13] show that in today’s application development, an average of 50% of the total time is spent on implementing user interface. this study therefore focused on the usability testing of the developed web portal prototype to ensure that it meets user requirements. according to [14] and to a certain extent, usability is no more significant than user acceptability as people may not find the system acceptable even when it scores highly on effectiveness and efficiency. this study therefore focuses on measuring user acceptance to determine user acceptability. there are several methods for measuring usability [8]. according to [15], the most used methods are statistical: conjoint analysis, discriminant analysis, multiple regression analysis, and multicriteria satisfaction analysis (musa) which uses ordinal regression analysis among others. usability factors, namely: service quality, technical quality, information quality, and system quality are chosen to measure user satisfaction of the developed web portal. this study therefore aims to analyze ease of use, efficiency, interaction, navigation, learnability, responsiveness, and satisfaction (figure 1). musa is recommended as a model of measuring user satisfaction. according to [16] there is no clear consensus on how to measure usability but a mean score value that is significant and meaningful is recommended. for this study, a mean score on a five-point scale likert scale was used to determine user acceptance of the developed web portal for ornamental plants and flowers and musa was adopted to measure satisfaction. the main purpose of this usability test is to make sure that the user requirements are met and to get feedback from the users in order to redesign or make changes that will improve the web portal’s performance. a. implementation of the web portal prototype the developed web portal for ornamental plants and flowers provides various services, namely: mapping and digitization of the various species of ornamental plants and flowers in arusha city, connecting vendors of arusha city to the regional and international market, and providing baseline information on horticulture to the arusha city council. the developed web portal contains two parts, the user interface or client side which is interactive, and where the users can interact with the other side which is the database that contains the information. the stakeholders of the web portal include: • botanists and researchers who interact with the web portal to access information stored in the database. the botanists are able to find plants’ and flowers’ varieties information, images, and sale locations online. • vendors who are able to advertise their products on the portal and conduct business with their customers online. • the arusha city council representatives who access baseline information on the sector to make informed plans and decisions. fig. 1. usability factors and features in order to access the web portal, a user is required to be authenticated, i.e. the user needs login credentials. the web portal allows quick browsing of the various species of ornamental plants and flowers, quick navigation of vendors’ adverts on a variety of products along with the location of the ornamental plants and flowers they are selling. the web portal also provides the administrator with an interactive interface allowing adding information on the species to the database. this information is retrieved on the client side easily via a search engine that retrieves information from the database based on user keywords making information access fast and simple for the users. iii. methodology a. participants the test involved 5 groups, namely botanists and researchers, herbalists, the it staff, vendors, and arusha city council representatives. the participants were 48 in total. four were botanists and researchers employed at tpri, 1 was a herbalist at the tpri, 1 was an it officer in charge of the database for the collected species at tpri, 1 was staff from the arusha city council and the other 41 were arusha vendors, growing and selling these species as shown in table i. table i. participants distribution participants number botanists and researchers 4 it officers 1 arusha city council representatives 1 vendors 41 herbalsits 1 b. testing phases the participants were given access to the web portal (hosted online) through their smart devices, they were trained engineering, technology & applied science research vol. 10, no. 3, 2020, 5627-5631 5629 www.etasr.com asiimwe et al.: usability testing of a web portal for ornamental plants and flowers in arusha, tanzania on how to navigate, and were given 2 days to use the portal to conduct their respective activities. then, their comments and recommendations were asked. questionnaires were used to measure the usability of the web portal of ornamental plants and flowers in arusha city. the main objective of the first phase of the usability test was to follow up on user feedback and recommendation regarding access and usability. thorough testing was done based on several important user requirements and a more accessible and easy to use user interface. after pretraining on usage and navigation of the web portal, the users were expected to login with their credentials after registration and approval. if the user could not login, the user could still navigate through the portal to access information on the species of plants and flowers available for sale by vendors in arusha city. however, there are features that the users could access only after logging, e.g. advertising products, viewing and responding to orders, seeing summarized data on the sector, and the administrator could insert and process the ornamental plants and flowers and their images in the database. the assessment was done online using browsers on smart phones and personal computers after which comments and feedback were collected form the participants regarding usability and accessibility. the main purpose was to report any errors or faults of the web portal, so they could be addressed by the developer. during testing, the stakeholders were given access via their smart devices (smart phones, laptops and personal computers) to the web portal. however, due to different backgrounds in the use of technology, the users were first given training on how to use the web portal before commencing with the usability testing. different stages of usability testing where undertaken to achieve this objective as shown in figure 2. the diversity of participants meant that there was a difference in the usage of smart phones and personal computers thus the users were grouped based on their knowledge and skills. the first group had better skills and knowledge on the use of smartphones and personal computers therefore required little training and the other group required more training on the navigation of the web portal. the participants’ gender and age groups can be seen in figures 3 and 4 respectively. iv. results and discussion a. results from the first phase test all the 48 participants clearly understood how to navigate the developed web portal and they were satisfied with the web portal services for inventory, mapping, digitization, and its use as a marketing tool. the participants agreed that the web portal allowed easy access of information on the species of ornamental plants and flowers available for sale in arusha city. the test’s objective was to acquire feedback on several user requirements. the acquired recommendations were: the users requested for a more user-friendly interface and a switch of languages from english to swahili text, the scientific names of the variety species should appear in italic as it is the proper way, and the image quality of the species should be improved. from the questionnaire results, it was observed that none of the 48 participants was dissatisfied with the workability of the web portal and they recommended a few rather minor changes. fig. 2. usability test for the web portal fig. 3. gender of respondents b. results from the final phase test of the web portal the comments and recommendations from the first phase test were addressed and the final phase test was done with the same participants to ensure that their recommendations were properly addressed and the web portal fully met their requirements. the participants were able to analyze the workability of the web portal during the final phase test based on parameters or features, namely (service quality) ease of use of the portal, (technical quality) interaction and navigation by vendors in its use as a marketing tool, (information quality) learnability for stakeholders to be able to access important information on the species of ornamental plants and flowers, and finally (system quality) satisfaction, i.e. if they would recommend the tool. the participants were allowed to interact with the system’s functional units to assess their correctness engineering, technology & applied science research vol. 10, no. 3, 2020, 5627-5631 5630 www.etasr.com asiimwe et al.: usability testing of a web portal for ornamental plants and flowers in arusha, tanzania and other performance factors like speed, easiness and responsiveness [17]. questionnaires were distributed to different participants with the aim to find users’ perception and views on the developed system based on the above mentioned parameters. the responses’ mean score on a five-point scale likert scale, where by (5=strongly agree, 4=agree, 3=neutral, 2=disagree and 1=strongly disagree), was computed as shown in table ii. the final phase of the test was to analyze the data from the questionnaire. fig. 4. age group analysis of the respondents table ii. user acceptance results usability factors usability features usability feature mean standard deviation service quality ease-of-use 4.65 0.56 efficiency 4.69 0.55 technical quality interaction 4.50 0.58 navigation 4.60 0.57 information quality memorability 4.48 0.62 learnability 4.50 0.62 system quality responsiveness 4.46 0.58 satisfaction 4.63 0.53 c. user acceptance results during testing, user acceptance was measured with musa based on the 8 usability features that were arranged into 4 usability factors namely: service quality, technical quality, information quality, system quality. the results are shown in tables ii-iii. table iii. usability features factors attributes %measure service quality (30%) a1. ease-of-use 16 a2. efficiency 14 information quality (20%) a1. interaction 12 a2. navigation 8 technical quality (30%) a1. memorability 8 a2. learnability 22 system quality (20%) a1. response time 7 a2. users satisfaction 13 regression analysis was performed on the usability features to determine the relationship between the dependent variable which is the overall quality, y and independent variables representing service quality (seq), information quality (iq), technical quality (tq) and system quality (sq). the regression model was: � � �� � �. � � 0.647� 0.841� (1) � � 1.364� 0.707� (2) � � 1.13� 0.765� (3) � � 0.785� 0.834�� (4) the results of multiple regression carried out on all usability factors are given in (5): � � 3.147 � 0.841� � 0.707� � 0.765� � 0.834�� (5) d. discussion the mean score for each validated feature was quite high, and in any case above 3.5 which is 70% of the maximum score value as shown in table ii which indicates that the majority of the sampled respondents accepted the system and expressed their willingness to use it to conduct their business activities. table iv. system testing results on user requirements requirement description test score registration web portal shall allow registration and login for access of exceptional information and guidance customized for a specific type of users. the administrator can register vendors/users. vendors/users can register themselves and await approval from an administrator. pass manage user accounts the administrator may add or delete users and vendors. pass add (upload images), delete ornamentals the administrator can be able to upload images of the ornamentals and add information of ornamental plants and flowers. pass search users and administrator must have an advanced search option to ease information retrieval pass view ornamentals the system should be able to display the information of ornamental plants and flowers. pass visual data the administrator should be able to upload a csv file in the database for visualization. users should be able to select entries and perform visualization. pass chat the system should provide access to chat rooms for vendors, botanists, and other users, store messages in chat rooms, and display messages in group chat rooms pass the service quality factor parameters, ease of use (4.65 mean and 0.56 standard deviation, which indicates that the majority of participants strongly agreed that the web portal is easy to use) and efficiency (4.69 mean and 0.55 standard deviation which meant that the service quality of the web portal is good), had the highest score. technical quality also involved two parameters of which interaction got a mean score of 4.50 and a standard deviation of 0.58 and navigation with a mean score of 4.60 with 0.57 standard deviation which shows that participants responded positively. the third usability factor was information quality having also two parameters, namely memorability and learnability that scored 4.48, and 0.62, and 4.50 and 0.62 mean and standard deviation respectively. lastly, system quality parameters, namely responsiveness with 4.46 mean and 0.58 standard deviation and satisfaction with 4.63 engineering, technology & applied science research vol. 10, no. 3, 2020, 5627-5631 5631 www.etasr.com asiimwe et al.: usability testing of a web portal for ornamental plants and flowers in arusha, tanzania mean and 0.53 standard deviation got also a positive response from the participants. these indicate the success of the web portal and that it met user requirements. the web portal passed all tests done while running on a remote server based on user requirements as shown in table iv. system testing was done to verify if the developed system met the business requirements of the end users. it is the outcome of many integrated and tested functional units that have successfully passed through the integration process. it does not deal with structural features of source codes but the functional features which are visible to the end user [17]. the system passed all the integration tests done while running on a remote server. the information submitted into the database from the web-based system could be successful retrieved as seen in table iv. v. conclusion the study shows that the developed web portal for ornamental plants and flowers is a good alternative according to the results obtained from the first and final phase tests of user acceptance. the adoption of the web portal will pave the way for biodiversity institutions to digitize their collection of species of ornamental plants and flowers and will also connect small scale farmers to the regional and international market. the user acceptance indicates that stakeholders face several challenges in the horticulture sector that need to be addressed by solutions as this web portal. the developed web portal has facilitated the inventory, mapping and digitization of the variety of species of ornamental plants and flowers in arusha. it is accessible online by all stakeholders, it will help vendors conduct their businesses online, and will also provide the arusha city council representatives with baseline information from which informed plans and decisions can be made. in future work, other stakeholder groups could be added, such as representatives from the tourism industry that require other services in the horticulture sector such as using computer vision to identify the various species of ornamental plants and flowers 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s. angilella, s. corrente, s. greco, r. slowinski, “musa-int: multicriteria customer satisfaction analysis with interacting criteria”, omega (united kingdom), vol. 42, no. 1, pp. 189–200, 2014 [16] m. hub, m. zatloukal, “model of usability evaluation of web portals based on the fuzzy logic”, wseas transactions on information science and applications, vol. 7, no. 4, pp. 522–531, 2010 [17] s. nidhra, j. dondeti, “black box and white box testing techniques: a literature review”, international journal of embedded systems and applications, vol. 2, no. 2, pp. 29–50, 2012 microsoft word 16-3452_s_etasr_v10_n3_pp5674-5677 engineering, technology & applied science research vol. 10, no. 3, 2020, 5674-5677 5674 www.etasr.com sanga et al.: mobile-based deep learning models for banana disease detection mobile-based deep learning models for banana disease detection sophia l. sanga nelson mandela african institute of science and technology arusha, tanzania sophiasanga66@gmail.com dina machuve nelson mandela african institute of science and technology arusha, tanzania dina.machuve@nm-aist.ac.tz kennedy jomanga international institute of tropical agriculture arusha, tanzania k.jomanga@cgirr.org abstract—in tanzania, smallholder farmers contribute significantly to banana production and kagera, mbeya, and arusha are among the leading regions. however, pests and diseases are a threat to food security. early detection of banana diseases is important to identify the diseases before too much damage is done on the plants. in this paper, a tool for early detection of banana diseases by using a deep learning approach is proposed. five deep learning architectures, namely vgg16, resnet18, resnet50, resnet152 and inceptionv3 were used to develop models for banana disease detection, achieving all high accuracies, varying from 95.41% for inceptionv3 to 99.2% for resnet152. inceptionv3 was selected for mobile deployment because it demands much less memory. the developed tool was capable of detecting diseases with a confidence of 99% of the captured leaves from the real environment. this tool will help smallholder farmers conduct early detection of banana diseases and improve their productivity. keywords-deep learning; banana diseases; smartphones; early detection; android based application i. introduction deep learning is a method of training an artificial neural network in machine learning in which it performs a task by frequently testing its performance, and altering the internal parameters within the network between each test. deep convolutional neural networks (cnns) have been used in many fields such as computer vision, speech recognition, face recognition, and natural language processing [1]. in computer vision, deep learning was found to be more effective for image recognition, object recognition, self-driving automobiles, object detection, and image segmentation. deep learning has been introduced as a new method to ensure semantic interoperability in the case of concrete concepts such as images [3]. applications such as affordable home robots and more intelligent personal assistants on a mobile phone will come when deep learning technologies become ubiquitous in smartphones [4]. these applications have higher resolution display and extensive built-in sets of accessories, such as advanced hd cameras and computing power [5]. using deep learning for crop disease detection and smartphone applications is an active research area [4, 5]. deep learning has shown a successful way for smartphones to assist in disease detection based on leaf images. in order to improve banana yield, various efforts have been made to provide information regarding disease management and develop an early warning system to help smallholder farmers and extension officers around the arumeru district to make the right decisions regarding disease management and control [8]. deep learning techniques were used for the detection of cassava disease using images captured from the real environment in tanzania in [9]. in this study, a deep cnn was used to train the developed model for identifying two types of pest damage and three diseases. the best accuracy for the trained model was 98% for brown leaf spot (bls), 96% for cassava mosaic disease (cmd), 96% for red mite damage (rmd), 98% for cassava brown streak disease (cbsd), and 95% for green mite damage (gmd). the best model scored an accuracy of 93% for a dataset that was not used during the training process. moreover, the method was validated in the real field with a mobile phone embedded with tensorflow android inference interface. mobile penetration in tanzania had reached 90% by june 2019, with more than 8 million people using mobile phones. this massive use of smartphones is one of the advantages that will help smallholder farmers in early disease detection. our aim was to develop a tool that would help smallholder farmers and extension officers in real-time detection of banana diseases because the present tools that have been developed in tanzania are limited to the detection of only cassava. in order to have an optimal yield in harvest, disease control and management are necessary, hence the need for the application of artificial intelligent systems for disease detection, control, and management [10]. regarding the banana disease early detection, there is a need for a supportive tool which is less expensive, operates in real-time, it is automatic, user-friendly, and fast. this tool will be of great importance in banana production [11]. the developed system is simple to use and easily available through a simple mobile application. it is thus a valuable tool for smallholder farmers and extension officers in tanzania and elsewhere, who lack the proper tools for the detection of banana diseases. to train our model we evaluated the applicability of transfer learning from a deep cnn [12]. due to the model’s complexity, a cnn can take weeks to fully train the model with millions of image samples. to avoid this challenge, transfer learning techniques were used in which a model developed for a task was reused as the starting point for corresponding author: sophia l. sanga engineering, technology & applied science research vol. 10, no. 3, 2020, 5674-5677 5675 www.etasr.com sanga et al.: mobile-based deep learning models for banana disease detection a model on a second task [13, 14]. previous research has shown that transfer learning is effective for diverse applications and has much lower computational requirements than learning from scratch [15, 16]. so, inceptionv3 architecture was selected as a deep learning tool because it combines very good performance with a low computational cost [12]. the software proposed for mobile development was an android application. android is a mobile operating system based on linux kernel and initiated by google designed purposely for touchscreen mobile devices such as tablets, computers, and smartphones with specialized user interfaces for wrist watches (android wear), televisions (android tv) and cars (android automatic) [17]. ii. materials and methods a. deep convolutional neural network models deep cnns have been used in many fields such as computer vision, speech recognition, face recognition, and natural language processing [1]. in computer vision, various developed cnn architectures were effectively applied to complicated tasks of visual imagery [5]. five basic cnn architectures tested in the problem of early detection of banana diseases from images of banana leaves were used [12, 18]. to train our pre-trained models we used tensorflow as it allows users to train their models on both graphics processing units (gpus) and central processing units (cpus) [19]. to train vgg16, resnet18, resnet50, and resnet152 we used a laptop, with these specifications: windows 10 pro n 64 bit equipped with one processor intel(r) core(tm) i5-4300u cpu @1.90ghz 2.50ghz with 4gb ram. the language used during training was python. the implementation was carried out by using keras library which is good in handling neural network activities/models and in acquiring higher performance for numerical computations. during training, tensorflow was used as the backend part. the software library used to train the models was the google colab machine with the following specifications: python3 runtime type, gpu hardware accelerator, and 20mb notebook size. to train inceptionv3 the following computer lab specifications were used: device name cocselab, 251.8gb memory size, intel xeon(r) cpu e5-26200@2.00ghz*12 processor, nvd9 graphics, gnome 3.32.1, os type 64-bit and 1.0tb disk. b. dataset training and testing python script was used for augmenting our dataset to 3000 images from each class. the augmentation technique for image data generator was horizontal flipping, zoom range of 0.2, rotating–right-bottom, rotating-left-bottom, shear range of 0.1, cropping and rescaling each image with 1/255 ratio and finally 27,000 banana leaf images of three classes (black sigatoka, fusarium wilt race 1 and healthy leaves) were acquired (see figure 1) from images collected from arusha and mbeya regions in tanzania. these leaf images were taken in real conditions in the cultivation fields and were captured by a simple camera that also captured effects such as shades and different backgrounds. to avoid bias in our pre-trained models, the data were randomly shuffled before splitting. our image dataset was then split into three groups, 80% for training, 15% for validation, and 5% for testing. the training and validation sets were used during model selection while the test set was used to evaluate the generalization performance (performance verification stage) of the selected model. (a) (b) (c) fig. 1. dataset samples: (a) fusarium wilt race 1, (b) black sigatoka, (c) healthy plant iii. results a. model results the selected models were trained with the parameters presented in table i. after several trials, these values were selected because they showed the best results during training. table ii shows the successful classification results from validation, testing, and training of the three classes from our dataset. regarding the performance of our models on the test set, resnet152 achieved the highest accuracy of 99.8% while inceptionv3 achieved the lowest, which howerer was quite high. all models achieved equal or better performance when tested on the original banana leaf images. figure 2 shows that there were no overfitting problems during the training process. table i. parameters used parameter value optimizer sgd batch-size 4 learning rate 1e-3 weight decay 1e-9 model architecture resnet, inceptionv3 momentum 0.9 image size (resnet) 244×244 pixels images size (inceptionv3) 299×299 pixels table ii. model performance comparison models validation accuracy % test accuracy % epochs time (/epoch) loss vgg16 98.4 98.7 35 30min 13s 0.197 resnet18 98.8 98.8 50 8min 35s 0.256 resnet50 98.8 98.9 50 8min 35 s 0.180 resnet152 99.2 99.8 50 8min 35s 0.0539 inceptionv3 95.4 95.5 1500 2min 39s 0.1351 fig. 2. validation and training graph for the inceptionv3 model engineering, technology & applied science research vol. 10, no. 3, 2020, 5674-5677 5676 www.etasr.com sanga et al.: mobile-based deep learning models for banana disease detection b. mobile deployment we chose inceptionv3 for mobile deployment because it demands less memory and it has a lower computational cost when deployed to mobile apps as compared to the other tested deep learning models [12, 20], ever if they achieved higher accuracy, because these models require larger memory space for mobile deployment. anyhow, the performance of inceptionv3 was satisfactory for our needs, so it was chosen as the solution that combined less computational resources and a high accuracy of 95.5%. tensorflow was used as it is a deep learning framework that offers apis for mobile deployment in android and ios-based smartphones [21]. the tensorflow was used to train the inceptionv3 model for banana disease detection. figure 3 shows how different activities will be conducted by users in disease detection while figures 4 and 5 show screenshots that were taken during the validation of our model. the inceptionv3 model showed good results in early detection of banana diseases with an accuracy of 99% for the images captured on real environment as seen in figure 5, and accuracy of at least 71% for the uploaded images from the internet. when tested again on real environment, it achieved an accuracy of 95% as shown in figure 4. fig. 3. activity diagrams of users in disease detection (a) (b) fig. 4. screenshots of the mobile application for uploaded images and captured from real environment with confidence percentage (a) (b) fig. 5. screenshots of the mobile application only for images captured from real environment with confidence percentage iv. conclusion the capability of deep learning models, and transfer learning techniques was evaluated in deploying an offline mobile application for the early detection of banana diseases. the performance of the deployed tools in detecting banana diseases was assessed for three datasets that were our main target. a rule was set that the results must at least have detection confidence percentage larger than 70%, otherwise the app will recommend having a clearer image of the captured leaf. real-time early detection of banana fungal diseases is very important in improving banana yields, which are largely affected by such diseases. it was shown that with the use of machine learning techniques via a mobile phone application, these diseases can be easily detected. the developed mobile application is called fusi (fusarium sigatoka) scanner, it works under android technology, and detects the presence of the two most common banana fungal diseases. references [1] a. voulodimos, n. doulamis, a. doulamis, e. protopapadakis, “deep learning for computer vision : a brief review”, computational intelligence and neuroscience, vol. 2018, article id 7068349, 2018 [2] w. liu, z. wang, x. liu, n. zeng, y. liu, f. e. alsaadi, “a survey of deep neural network architectures and their applications”, neurocomputing, vol. 234, pp. 11-26, 2017 [3] n. e. a. amrani, o. e. k. abra, m. youssfi, o. bouattane, “a novel deep learning approach for semantic interoperability between heterogeneous multi-agent systems”, engineering, technology & applied science research, vol. 9, no. 4, pp. 4566–4573, 2019 [4] h. a. pierson, m. s. gashler, “deep learning in robotics: a review of recent research”, advanced robotics, vol. 31, no. 16, pp. 821–835, 2017 [5] s. p. mohanty, d. p. hughes, m. salathe, “using deep learning for image-based plant disease detection”, frontiers in 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frontiers in plant science, vol. 8, article id 1852, 2017 [10] n. c. eli-chukwu, “applications of artificial intelligence in agriculture : a review”, engineering, technology & applied science research, vol. 9, no. 4, pp. 4377-4383, 2019 [11] h. a. hiary, s. b. ahmad, m. reyalat, m. braik, z. alrahamneh, “fast and accurate detection and classification of plant diseases”, international journal of computer applications, vol. 17, no. 1, pp. 31–38, 2011 [12] c. szegedy, s. ioffe, v. vanhoucke, a. a. alemi, “inception-v4, inception-resnet and the impact of residual connections on learning”, thirty-first aaai conference on artificial intelligence, san francisco, usa, february 4-9, 2017 [13] c. tan, f. sun, t. kong, w. zhang, c. yang, c. liu, “a survey on deep transfer learning”, in: artificial neural networks and machine learningicann 2018, vol. 11141, springer, 2018 [14] k. gopalakrishnan, s. k. khaitan, a. choudhary, a. agrawal, “deep convolutional neural networks with transfer learning for computer vision-based data-driven pavement distress detection”, construction and building materials, vol. 157, pp. 322–330, 2017 [15] a. karpathy, g. toderici, s. shetty, t. leung, r. sukthankar, f. f. li, “large-scale video classification with convolutional neural networks”, ieee conference on computer vision and pattern recognition, columbus, usa, june 23-28, 2014 [16] j. shijie, j. peiyi, h. siping, s. haibo, “automatic detection of tomato diseases and pests based on leaf images”, chinese automation congress, jinan, china, october 20-22, 2017 [17] k. divya, s. v. krishnakumar, “comparative analysis of smart phone operating systems android, apple ios and windows”, international journal of scientific engineering and applied science, vol. 2, no. 2, pp. 432-438, 2016 [18] k. he, x. zhang, s. ren, j. sun, “deep residual learning for image recognition”, ieee conference on computer vision and pattern recognition, las vegas, usa, june 27-30, 2016 [19] m. abadi, p. barham, j. chen, z. chen, a. davis, j. dean, m. devin, s. ghemawat, g. irving, m. isard, m. kudlur, j. levenberg, r. monga, s. moore, d. g. murray, b. steiner, p. tucker, v. vasudevan, p. warden, m. wicke, y. yu, x. zheng, “tensorflow : a system for large-scale machine learning”, 12th usenix symposium on operating systems design and implementation, savannah, usa, november 2-4, 2016 [20] c. meng, m. sun, j. yang, m. qiu, y. gu, “training deeper models by gpu memory optimization on tensorflow”, 31st conference on neural information processing systems, long beach, usa, december 4-9, 2017 [21] m. abadi, a. agarwal, p. barham, e. brevdo, z. chen, c. citro, g. s. corrado, a. davis, j. dean, m. devin, s. ghemawat, i. goodfellow, a. harp, g. irving, m. isard, y. jia, r. jozefowicz, l. kaiser, m. kudlur, j. levenberg, d. mane, r. monga, s. moore, d. murray, c. olah, m. schuster, j. shlens, b. steiner, i. sutskever, k. talwar, p. tucker, v. vanhoucke, v. vasudevan, f. viegas, o. vinyals, p. warden, m. wattenberg, m. wicke, y. yu, x. zheng, “tensorflow: large-scale machine learning on heterogeneous distributed systems”, available at: https://arxiv.org/pdf/1603.04467.pdf, 2016 authors profile sophia sanga is an msc student in information and communication science and engineering at the nelson mandela african institute of science and technology (nm-aist). she completed her bsc of engineering in computer science and engineering in st. joseph university, tanzania. her focus is to help smallholder banana farmers. currently she is researching the development of early detection tools for banana diseases. dina machuve is a lecturer and researcher at the nelson mandela african institute of science and technology (nm-aist) in tanzania. she holds a phd in information and communication science and engineering from nm-aist (2016), msc in electrical engineering from tennessee technological university, usa (2008), and bsc in electrical engineering from the university of dar es salaam (2001). her research interests are data science, bioinformatics, agriculture informatics on food value chains and stem education in schools. kennedy elisha jomanga is a holder of msc degree in plant protection and of a bsc degree of science in agronomy. he is currently working with iita as plant pathologist and senior research associate. he worked as an assistant area manager and agriculture manager for 5 years. he is a former world vision food security coordinator for seven regions in tanzania. he also has been working as an assistant lecturer for more than 4 years at the st. johns university of tanzania. he is a founder and a tutor of certificate and diploma courses in general agriculture at the same university. he has attended several trainings related to management skills in the past with robert antonio sugarcane research institute of mauritius. he was involved in a survey of different plant diseases causing pathogens in kilimanjaro, arusha, and mbeya. engineering, technology & applied science research vol. 8, no. 4, 2018, 3189-3193 3189 www.etasr.com mangnejo et al.: a parametric study of effect on single pile integrity due to an adjacent … a parametric study of effect on single pile integrity due to an adjacent excavation induced stress release in soft clay dildar ali mangnejo department of civil engineering mehran university of engineering and technology sindh, pakistan dildarali72@gmail.com mukhtiar ali soomro department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan eng.soomro@gmail.com naeem mangi department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan naeem08ce30@gmail.com imtiaz ali halepoto department of computer systems engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan halepoto@quest.edu.pk israr ahmed dahri department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan isrardahri55@gmail.com abstract—to gain new insights into single pile responses to adjacent excavations in soft ground, numerical parametric studies are carried out. an advanced hypoplastic (clay) constitutive model which takes account of small-strain stiffness is adopted. the effects of excavation depths (i.e. formation level) relative to pile were investigated by simulating the excavation near the pile shaft (i.e., he/lp=0.67), next to (he/lp=1.00) and below the pile toe (he/lp=1.33). among the three cases, the excavation in case of he/lp=1.33 resulted in the largest pile settlement (i.e. 7.6%dp). on the other hand, the largest pile bending moment was induced in case of he/lp=0.67. keywords-parametric study; different excavation depths; soft clay; single pile i. introduction due to the rate of population increment, it is desirable to construct multi-storey buildings in congested cities. it is well recognised that the favourable foundation for tall building is piling. pile foundation not only carries vertical but also lateral loading. besides this, underground constructions (i.e. basements and tunnels) are preferred to minimise traffic congestions. hence, it is unavoidable to construct a basement or tunnel adjacent to pile foundations. it is well recognised that the capacity of a piled foundation depends on mobilised stresses in the ground while excavation is essentially a stress release process. excavation may induce unfavourable ground deformations that can affect adjacent structures. therefore, it is necessary to assess catastrophic effects on a piled foundation due to adjacent excavation. it is well recognised that superstructure load is transferred to surrounding soil through piled foundation. consequently, high-stress regime is generated surrounding of the pile [1]. on the other hand, the excavation in the ground inevitably results to ground movement due to induced-stress release [2]. to cope with transportation problems in congested cities, underground transportation systems (involving metro tunnels, metro station excavations and parking basements) have been developed. these excavations are sometimes inevitable to be constructed adjacent to existing piled foundations. this condition leads to a big challenge for a geotechnical engineer to assess and protect the integrity of the piled foundation. authors in [3, 4] reported case studies in granular soil and alluvium residual soil. in both reported case studies, the pile toe level was much deeper than the excavation level and authors reported only the lateral pile behaviour. this problem has also been investigated by means of centrifuge modelling [5] and pile group in soft kaolin clay [6]. they concluded that the distance between pile and diaphragm wall is an important parameter which plays a major role on induced bending moment in the pile. in the presence of initial applied load, soil surrounding the pile foundation experiences higher stress level before the commencement of adjacent excavation. the excavation induced stress release in the ground induced bending moment and settlement. authors in [7, 8] conducted centrifuge tests to investigate the effects of an un-propped excavation on the behavior of nearby single piles and pile groups in dry dense toyoura sand. they found that the distance from the pile to the retaining wall and pile head conditions had a large influence on the induced pile bending moment and lateral deflection. authors in [1] reported the results of three centrifuge tests carried out to study the effects of a multi-propped deep excavation in-flight on the engineering, technology & applied science research vol. 8, no. 4, 2018, 3189-3193 3190 www.etasr.com mangnejo et al.: a parametric study of effect on single pile integrity due to an adjacent … behavior of single piles in dry toyoura sand. piles were laterally restrained in terms of rotation and deflection right at or above ground surface in three different tests. it was concluded that lateral restraints imposed on the pile head have a significant influence on induced pile bending moment. induced bending moment due to excavation can exceed the pile bending capacity. authors in [9] investigated the lateral responses of a single pile to an adjacent excavation. they performed two staged analysis, considering plane strain conditions and linear elastic soil model. similar work was conducted in [10] using finite element method. in both these studies lateral response of single pile was investigated. the settlement behaviour of pile and development of excess pore water pressure and consolidation settlement were not investigated. in [11] an analytical method was proposed in order to investigate the reduction of capacity and increase in settlement of a nearby pile during excavation. it was reported that pile settlement due to excavation depends on the percentages of end bearing and shaft friction of the pile, the soil movement pattern and the distribution of the maximum shaft friction with depth. however, shaft resistance in these methods is calculated on the assumption that horizontal stress acting on the piles does not change during excavation. this assumption may not be valid and the pile settlement may be underestimated using the preceding methods, leading to a non-conservative prediction. most of the previous studies focused on the lateral response of the piled foundation to excavation. in addition, different formation levels with respect to pile have not been understood. the effects of excavation on the behaviour of piles (i.e. induced settlement and axial forces along the pile length) were rarely reported. the main objective of this parametric study is to understand the mechanism of the effects of excavation depth systems of different formation level on a loaded single floating pile. a 3d finite element analysis was conducted to investigate the above mentioned problem. settlement and load transfer mechanism were reported and discussed. ii. three-dimensional coupled consolidation analysis a 3d finite element analysis (i.e. coupled consolidation parametric study) was conducted to investigate the problem. in this parametric study, final excavation depths (he) were taken as 12m, 18m and 24m. the effects of these excavations were investigated on a loaded single pile of length embedded length (lp) of 18m with diameter (dp) of 0.8m. the pile can sustain maximum bending moment of 800knm. figure 1(a) shows the elevation view of the configuration of numerical simulation of a typical case of he/lp=0.67. the clear distance between diaphragm wall and the pile is 3.0m. the excavation was supported by a 0.6m thick diaphragm wall. the ratio of wall penetration depth to excavation depth is typically 0.5-2 [12] and a value of 0.5 is adopted in this study. the props are used to support the diaphragm wall with a vertical spacing of 3m. the props are modelled as soft with axial rigidity of 81×103knm [12]. horizontal spacing of props is 10m. figure 1(b) shows the configuration (plan view) of the numerical model in case of he/lp=0.67. the length of the excavation is 12m. as excavation possesses symmetry, therefore, half excavation (with length 6m) was modeled. in addition to these simulations, a pile load test (l) is proposed to be conducted numerically in “greenfield” conditions (i.e. no excavation) to obtain the ultimate capacity of the pile in silty clay. based on this, the working load will be obtained with a factor of safety of 3.0. the obtained working load will be applied to the pile in the parametric analysis simulating excavation. table i summarises the numerical simulations conducted in this study. a. constitutive model and model parameters used in finite element analysis the basic hypoplastic model was developed to capture the non-linear behavior (upon monotonic loading at medium to large-strain levels) of granular materials [19-20]. the basic model consists of five parameters (n, λ*, κ*, φc and r). the parameters n and λ* define the position and the slope of the isotropic normal compression line in the ln(1+e) versus lnp’ plane [10], e is the void ratio and p’ is the mean effective stress, κ* defines the slope of the isotropic unloading line in the same plane, φc is the critical state friction angle, and r controls the large strain shear modulus. ground water table working load (720 kn) existing single pile soft clay prop 1 (1.0 m) p la ne o f sy m m et ry embedded length = 18 m diameter = 0.8 m diaphragm wall thickness = 0.6 m depth = 18.0 m 3.0 m prop 2 (4.0 m) prop 3 (7.0 m) prop 4 (10.0 m) formation level (12.0 m) monitoring section 50m 20m p la ne o f sy m m et ry 0.6 m thick diaphragm wall existing single pile prop prop 10m 6m fig. 1. configuration of a numerical model in the case of he/lp=0.67. (a) elevation view, (b) plan view table i. numerical simulation plan simulation id excavation depth (m) diaphragm wall depth (m) remark l n/a n/a pile load test he/lp=0.67 12.0 18.0 formation level near pile shaft he/lp=1.00 18.0 24.0 formation level next to pile toe he/lp=1.33 24.0 36.0 formation level below pile toe (a) (b) engineering, technology & applied science research vol. 8, no. 4, 2018, 3189-3193 3191 www.etasr.com mangnejo et al.: a parametric study of effect on single pile integrity due to an adjacent … to account for the strain-dependency and path-dependency of the soil stiffness (at small strains), authors in [13] further improved the basic hypoplastic model by incorporating the concept of intergranular strain. the intergranular strain concept requires five additional parameters(r, βr, χ, mt, and mr): r controls the size of the elastic range, βr and χ control the rate of stiffness degradation while mt and mr control the initial shear modulus upon 180° and 90° strain path reversal, respectively. in this hypothesised study, the parameters from [14] for silty clay were adopted and are summarised in table ii. the coefficient of lateral earth pressure at rest, ko is estimated by (1) [15]:   sin '0 1 sin ' φ k φ ocr  ¨ (1) table ii. μodel parameters of silty clay adopted from [14] description value effective angle of shearing resistance at critical state: ’ 33o parameter controlling the slope of the isotropic normal compression line in the ln(1+e) versus lnp plane, * 0.103 parameter controlling the slope of the isotropic normal compression line in the ln(1+e) versus lnp plane, * 0.015 parameter controlling the position of the isotropic normal compression line in the ln(1+e) versus lnp plane, n 1.31 parameter controlling the shear stiffness at mediumto largestrain levels, r 0.3 parameter controlling initial shear modulus upon 180 strain path reversal, mr 12 parameter controlling initial shear modulus upon 90 strain path reversal, mt 12 size of elastic range, r 2×10-5 parameter controlling the rate of degradation of the stiffness with strain, r 0.09 parameter controlling degradation rate of stiffness with strain 0.7 initial void ratio, e 0.7 dry density (kn/m3) 1615 coefficient of permeability, k (m/s) 1×10-9 b. finite element mesh and boundary condition figure 2 shows a finite element mesh used in the case of he/lp=0.67 with size of 50m×20m×40m. solid elements were used to model soil, pile and the diaphragm wall. the props were modeled by using truss elements. to restrain the horizontal and vertical movement, roller supports were applied. the base of the mesh was restrained in every direction by applying pin supports on it. the ground water table level was taken at ground surface. at geostatic state, pore pressure distribution was taken as hydrostatic. the top of the mesh was considered drainage boundary. the frictional interface was taken between pile and soil and wall and soil. the coulomb law for capturing frictional behavior was used in the interface. the coulomb’s frictional law parameters μand limiting displacement was taken as 0.35mm and 5mm, respectively [16]. excavation was carried out by deactivating soil elements within the zone of excavation in each analysis. activation of truss elements procedure was adopted for prop installation on the wall. the concrete pile, the diaphragm wall and the props were taken as elastic material with e=35gpa and v=0.25these parameters are given in table iii. table iii. concrete parameters description parameter young's modulus, e 35gpa poisson's ratio,  0.3 density,  2400kg/m3 c. procedure of numerical modeling the following is the procedure adopted for numerical modeling for a typical case he/lp=0.67.  generate geostatic stresses under ko condition and apply the boundary conditions as discussed above.  activate pile elements with application of working load as discussed above.  activate the brick elements representing the diaphragm wall.  staged multi-propped excavation is simulated as described in section ii. after excavating to 3m depth, the first level of props is installed at 1m below the ground surface.  same steps were taken for the remaining stages of excavation and props installation. single p ile diaphragm wall props formation level 40 m 20 m fig. 2. the mesh and boundary conditions in the case where he/lp=0.67 iii. interpretation of computed results a. determination of working load for the pile the objective of this parameter is to investigate the loaded single pile responses to adjacent excavations with different formation level relative to the pile length in soft clay. a numerical pile load test was conducted to compute the pile load carrying capacity. load of 3mn (with increment of 0.27mn) was applied on the pile over a period of 24 hours. figure 3 shows the computed load-settlement curve. a displacementbased failure criterion (see [17]) was used to obtain the load carrying capacity of the pile. pp ph pph ea lp d 2 1 045.0max,  (2) engineering, technology & applied science research vol. 8, no. 4, 2018, 3189-3193 3192 www.etasr.com mangnejo et al.: a parametric study of effect on single pile integrity due to an adjacent … based on this, the obtained load carrying capacity of the pile was 2.15mn. the working load was found to be 0.72mn with a factor of safety (fos) equal to 3. the pile settled at 5.12mm (0.64% dp) due to application of the working load. b. excavation-induced pile settlement figure 4 illustrates the normalised incremental settlement of the pile (sp/dp) with different excavation depths in all three cases (i.e. he/lp=0.67, he/lp=1.00 and he/lp=1.33). excavation depths are indicated by h. the measured centrifuge modeling [1] single pile settlement due to excavation in dry sand is also included in the figure. excavation depth was 8m (in prototype scale) in the centrifuge test. it can be seen from the figure that bi-linear increment in sp was observed with increasing excavation depth in each case. the sp increased linearly with excavation depth, however, the rate of induced settlement increased during the last two excavation stages (i.e. 6-12m, 1218m and 18-24m for of he/lp=0.67, he/lp=1.00 and he/lp=1.33 respectively). this is because of the degradation of clay stiffness due to excavation-induced stress release and shear strain surrounding the pile. similar characteristics of excavation-induced settlement of single pile were observed from the centrifuge test reported in [1]. however, because of higher stiffness of sand, induced settlement of single pile in sand was smaller than that in clay. by comparing induced settlement of the pile for he/lp=0.67 and he/lp=1.00, it is observed that the sp during the last two excavation stages in the former case is larger than that during similar excavation stages in the latter case. to be more specific, with same stress release due to excavation stages (9-12m), larger settlement was induced in the case of he/lp=0.67 than that in the case of he/lp=1.00. fig. 3. load settlement curve obtained from simulation l. the additional amounts of induced-settlement at excavation depths of 9m and 12m are 1.55dp% and 2.1dp%, respectively. similarly, the sp induced during excavation stages (12-18m) for he/lp=1.00 is larger than the sp induced for he/lp=1.33 because of the different embedded depths of the wall in each case. this revealed that the induced-settlement highly depends on the wall stiffness. among the three cases discussed, the largest and smallest settlement induced in the pile are for he/lp=1.33 and he/lp=0.67 respectively. this settlement behavior can be attributed to two reasons: the pile is subjected to higher stress release due to excavation in case of he/lp=1.33 than that due to excavation in case of he/lp=0.67, and the entire pile is located within the zone of excavation-induced displacement in case of he/lp=1.33. the single pile experienced total settlements (due to working-load and excavation) of 39, 51.5 and 66mm (i.e. 4.9, 6.4 and 8.3% of pile diameter) for he/lp=0.67, he/lp=1.00 and he/lp=1.33 respectively. fig. 4. normalised pile head settlement during excavation c. excavation-induced bending moment in the pile figure 5 illustrates the bending moment profile in pile on completion of excavation for all three cases. the excavationinduced bending moment profile measured in centrifuge test (excavation depth 1.2m) in [5] is also included for comparison with induced bending moment in case of he/lp=0.67. a positive bending moment value indicates that the compressive stresses are induced along the face of the shaft towards the excavation. the induced-bending moment is taken as positive if compressive stress was induced along the pile shaft facing the excavation. no bending moment was computed at the pile head because the pile heads were not constraint in each case. on completion of excavation, with formation level at middepth of the pile (i.e. he/lp=0.67), positive bending moments were induced along the entire pile. the bending moment increased linearly along the pile length with the maximum magnitude of 127knm at z/lp=0.8 (i.e. above formation level). this is because the pile was subjected to lateral soil displacements towards the excavation due to stress release. as pile displaced lateral with soil as rigid body, no bending moment was induced at the pile toe. the measured bending moment profile in centrifuge in [5] shows the similar trend with the computed bending moment in this study. the maximum bending moment was also reported to be above formation level. this agreement between computed and measured results gives confidence that finite element analysis can predict accurately the behavior of a single pile due to excavation-induced stress release. in contrast to induced bending moment in case of he/lp=0.67, negative bending moment profile was established on completion of excavation engineering, technology & applied science research vol. 8, no. 4, 2018, 3189-3193 3193 www.etasr.com mangnejo et al.: a parametric study of effect on single pile integrity due to an adjacent … for he/lp=1.00 and he/lp=1.33. the reason for this bending profile can be attributed to the embedded depth of the wall which makes soil displacement milder than that of he/lp=0.67. the maximum bending moment of 42knm and 13knm at z/lp=0.7 were induced in the pile in case of he/lp=1.00 and 1.33, respectively. it can be seen that the maximum induced bending moment at the excavation end all the three cases is much less than the pile bending moment capacity (800knm). therefore, the most critical issue to be considered in the excavation-soil-pile problem is the relatively large settlement and the lateral pile displacement. fig. 5. induced bending moment due to excavation iv. conclusions  because of the different embedded depth of the wall in each of the three cases, the induced settlement (sp), lateral displacement and bending moment in the pile at the same stage of the excavation were different.  by comparing the induced settlement of the pile for he/lp=0.67 and he/lp=1.00, it is observed that the sp during last two excavation stages in the former case is larger than that of the latter case. similarly, the sp induced during excavation stages (12-18m) for he/lp=1.00 is higher than for he/lp=1.33. final induced settlement (due to working-load and on completion of the excavation respectively) of 39, 51.5 and 66mm (4.9, 6.4 and 8.3% of pile diameter) was computed for the cases he/lp=0.67, he/lp=1.00 and he/lp=1.33, respectively.  due to excavation induced stress release, the bending moment was induced along the pile length. at the end of excavation in each case, the maximum induced bending moment in all cases was much less than the pile bending moment capacity. therefore, the most critical issue to be considered in excavation-soil-pile in soft kaolin clay problem is the relatively large settlement and lateral displacement of the pile. this conclusion may not be applicable to scenarios in which the ground conditions or the stiffness of the excavation system are different from those adopted in this study. references [1] c. w. w. ng, j. wei, h. g. poulos, h. liu, “effects of multipropped excavation on an adjacent floating pile”, journal of geotechnical and geoenvironmental engineering, vol. 143, no. 7, pp. 04017021-1 04017021-14, 2017 [2] m. korff, r. j. mair, f. a. f. van tol, “pile-soil interaction and settlement effects induced by deep excavations”, journal of geotechnical and geoenvironmental engineering, vol. 142, no. 8, pp. 04016034-1 04016034-14, 2016 [3] r. j. finno, s. a. lawrence, n. f. allawh, i. s. harahap, “analysis of performance of pile groups adjacent to deep excavation”, journal of geotechnical and geoenvironmental engineering, vol. 117, no. 6, pp. 934-955, 1991 [4] a. goh, k. wong, c. teh, d. wen, “pile response adjacent to braced excavation”, journal of geotechnical and geoenvironmental engineering, vol. 129, no. 4, pp. 383–386, 2003 [5] d. ong, c. f. leung, y. chow, “pile behavior due to excavationinduced soil movement in clay. i: stable wall”, journal of geotechnical and geoenvironmental engineering, vol. 132, no. 1, pp. 36-44, 2006 [6] d. ong, c. f. leung, y. chow, “behavior of pile groups subject to excavation-induced soil movement in very soft clay”, journal of geotechnical and geoenvironmental engineering, vol. 135, no. 10, pp. 1462-1474, 2009 [7] c. f. leung, y. chow, r. f. shen, “behavior of pile subject to excavation-induced soil movement”, journal of geotechnical and geoenvironmental engineering, vol. 126, no. 11, pp. 947-954, 2000 [8] c. f. leung, j. k. lim, r. f. shen, y. k. chow, “behavior of pile groups subject to excavation-induced soil movement”, journal of geotechnical and geoenvironmental engineering, vol. 129, no. 1, pp. 58-65, 2003 [9] h. g. poulos, l. chen, “pile response due to excavation induced lateral soil movement”, journal of geotechnical and geoenvironmental engineering, vol. 123, no. 2, pp. 94-99, 1997 [10] r. butterfield, “a natural compression law for soils”, geotechnique, vol. 29, no. 4, pp. 469-480, 1979 [11] b. c. b. hsiung, “a case study on the behaviour of a deep excavation in sand”, computer and geotechnics, vol. 36, no. 4, pp. 665–675, 2009 [12] d. liyanapathirana, r. nishanthan, “influence of deep excavation induced ground movements on adjacent piles”, tunnelling and underground space technology, vol. 52, pp. 168-181, 2016 [13] a. niemunis, i. herle, “hypoplastic model for cohesionless soils with elastic strain range”, mechanics of cohesive-frictional materials, vol. 2, no. 4, pp. 279-299, 1997 [14] d. masin, j. bohac, p. tuma, “modelling of a deep excavation in a silty clay”, in: proceedings of the 15th european conference on soil mechanics and geotechnical engineering, athens, greece, vol. 3, pp. 1509-1514, 2011 [15] p. mayne, f. kulhawy, “k0-ocr relationships in soils”, journal of geotechnical engineering, vol. 108, no. 6, pp. 851-872, 1982 [16] n. loganathan, h. g. poulos, d. p. stewart, “centrifuge model testing of tunnelling-induced ground and pile deformations”, geotechnique, vol. 50, no. 3, pp. 283-294, 2000 [17] c. w. w. ng, t. l. y. yau, j. h. m. li, w. h. tang, “new failure load criterion for large diameter bored piles in weathered geomaterials”, journal of geotechnical and geoenvironmental engineering, vol. 127, no. 6, pp. 488-498, 2001 microsoft word 27-2674_s engineering, technology & applied science research vol. 9, no. 2, 2019, 4012-4018 4012 www.etasr.com memon et al.: recent eco-friendly developments in personal protective clothing materials for … recent eco-friendly developments in personal protective clothing materials for reducing plastic pollution: a review arshad hussain memon institute of environmental engineering and management, mehran university of engineering and technology, jamshoro, pakistan arshad.memon@hotmail.com mazhar hussain peerzada department of textile engineering, mehran university of engineering and technology, jamshoro, pakistan mazhar.peerzada@faculty.muet.edu.pk khan muhammad institute of environmental engineering and management, mehran university of engineering and technology, jamshoro, pakistan dean.foapand@admin.muet.edu.pk sheeraz ahmed memon institute of environmental engineering and management, mehran university of engineering and technology, jamshoro, pakistan sheerazahmed.memon@faculty.muet.edu.pk sajjad ali mangi department of civil engineering, mehran university of engineering and technology, szab campus, khairpur mir’s, pakistan sajjad.nec@gmail.com ghulam mujtaba energy and environment engineering departement, dawood university of engineering and technology, karachi, pakistan gmujtabaawan@gmail.com abstract—due to the industrialization increase in the 20th century, the level of hazards for public health and the demand for personnel protective clothing (ppc) have increased. the area of ppc has been steered to high tech equipment made from plastic-based materials, which are derived from non-renewable sources and have a long life cycle expanding from hundreds to thousands of years, after their end of useful life. this paper reviews the information related to conventional plastic-based fibers, their properties, advantages, disadvantages, and applications in the battlefield, industry, automobiles, etc. this paper provides a basis for the selection of natural fibers and the replacement of conventional plastic-based fibers to reduce the plastic content in protective clothing or other composites. a comparative analysis of technological, environmental, economic and legal aspects of plastic-based and environment-friendly natural fibers is presented. natural fiber-based composite protective clothing is found to be environment-friendly and considered to have prospects for the future due to its comparative technological, environmental, economic and legal advantages. keywords-eco-friendly fibers; conventional plastic fibers; protective clothing; plastic pollution; kevlar; uhmpe; jute and ramie i. introduction plastic waste is a major environmental issue, which if not dealt properly could be potentially hazardous [1]. it is estimated that 8,300 million metric tons (mt) of virgin/nonrecycled plastics have been produced. by 2015, almost 6,300mt of plastic waste were generated, out of which, around 9% have been recycled, 12% incinerated, and 79% added up in landfills or simply dumped in the environment. if current production and waste management rate continues, it is estimated that almost 12,000mt of plastic waste will be landfilled or dumped by 2050 [2, 3]. the late 20 th century saw an unmatched increase in the emphasis of protection from occupational hazards. increasingly complex legislation, regulation and environmental awareness in workplaces were the result of the new philosophy. the range of hazards and the means of combating them continue to grow and become even more complex. a consequence of this is the development of new textile fibres, structures, and clothing systems whose purpose is to provide improved protection, whilst maintaining comfort, efficiency, and well-being [4, 5]. high strength polymers are commonly used in protective clothing due to their favourable mechanical properties, such as cut, impact, and chemical resistance. high-performance fibers such as aramid fiber (aromatic polyamide), ultra-high molecular weight polyethylene (uhmwpe) fibers, and zylon® (p-phenylene-26 benzobisoxaazole) have excellent performance and are being used in ppc, marine industry, etc. [6]. having the characteristics of the plastic family, on the other hand, causes various environmental problems in disposal by incineration. in the case of incomplete incineration, emissions released in the atmosphere can cause hazards for public health or the environment. plastic-based fibers derived from the petroleum products are not eco-friendly and have a very long life spanning from hundreds to thousands of years, while they are toxic [6]. raw material sources of these fibers are nonrenewable and expensive when compared to natural fibers. thus, in order to address these issues, eco-friendly/renewable resources should be utilized in composite materials and natural fibres may be added as reinforcement fibres [7, 8]. corresponding author: arshad hussain memon engineering, technology & applied science research vol. 9, no. 2, 2019, 4012-4018 4013 www.etasr.com memon et al.: recent eco-friendly developments in personal protective clothing materials for … lack of biodegradability, closing of landfill sites, and the increase in water, air, and land pollution issues, led to reluctance towards the use of plastics materials [9, 10]. most of plastic is non-biodegradable and remains in the environment for years after its disposal. recycling has practically failed to provide an environmentally safe solution for the disposal of plastic waste. in the dearth of efficient techniques for safe disposal of plastic wastes, they are accumulated in the ecosystem and pose an ecological threat. with the passage of time, this plastic waste converts in microplastics which accumulate in the marine and terrestrial environment. these microplastics can be ingested by animals and fish, and penetrate the food chain, becoming potentially hazardous for human health [11]. due to the increase in the awareness that non-renewable sources are becoming meager, markets started to look at renewable sources of fibers, like natural fibers. various studies were carried out regarding the replacement of plastic fibers with natural fibees in the field of protective clothing. this era witnessed notable successes in green technology in the field of material science through the development of bio-composites. the development of highperformance materials made from natural resources is increasing worldwide. the greatest challenge in working with natural fiber reinforced plastic composites is their large variation in properties and characteristics [12]. this paper provides information related to conventional plastic-based fibers, which include high-strength, highmodulus, high-performance, and high-chemical and combustion resistant fibers, their properties, advantages, disadvantages and applications in battlefield, industry, automobiles etc. also, information for the selection of natural fibers and partial reduction options of conventional plastic based fibers, are provided. a comparative analysis of technological, environmental, economic and legal aspects of plastic-based and environment-friendly natural fibers is presented. this paper also provides properties, advantages, disadvantages, and applications of natural fibers in protective textile and other composites. ii. conventional plastic based fibers for pc protective clothing (pc) requires the combination of various properties, depending on its end use and the severity of hazard involved: cut, impact, bullet, heat, cold, chemical, and bacterial hazards. the increasing requirements of legislations related to the human health and environment protection have applied pressure on new technologies and researchers to produce fibers, fabrics, new designs, and chemicals finishes which can provide protection against a high level of hazards involved in different kinds of jobs varying from industry to industry. simultaneously, due to environmental protection requirements, pc must be environment-friendly. in primeval years, a wide variety of natural fibers including abaca, bamboo, ramie, jute, kenaf etc. were used for the protection of the human body from weather and battle hazards. in recent years, as the severity and lethal impacts of arms has been increasing, high-performance fibers aramid, carbon, and glass are used in various applications. from the literature review, it has been shown that plastic-based fibers are being used in protective clothing for different applications such as industrial tech, sports tech, defense, marine, and geotextiles. the physical properties of conventional plastic fibers are given in table i. table i. physical properties of conventional/plasticbased fibers fiber/material type p-aramid uhwmp carbon meta aramid (nomex/ conex) strength (mpa) 2900 4000 3600 specific gravity 1.4 1.0 1.8 1.38 modulus (mpa) 95 95 400 75 breaking elongation 3.5 4.0 1.7 2.5 density (g/cm 3 ) 1.44 0.97 1.8-2.1 1.38 melting point/heat resistance ( o c) 550 150 >2500 425 moisture regain % 5 0 0 4.5 limiting oxygen index 29 20 30 a. classification of conventional fibers conventional plastic fibers are classified in the following three major categories: 1) high strength -high modulus (organic fibres) • para-aramid fibers, kevlar, tawron. • ultra-high molecular weight polyethylene e.g., dynema (dsm) and spectra . 2) high performance (inorganic fibers) • carbon • ceramics • tungsten • alumina 3) high chemical and combustion-resistant • meta-aramid fibers, e.g. nomex and conex. • kermel. • kynol. • oxidized acrylic fibers, e.g. panox. this paper presents details of the major fibres like paramid, uhwmpe, carbon, and m-aramid used in protective clothing and other composites. b. high strength -high modulus (organic fibers) fibers under this category have high strength and modulus, making them suitable for protective applications. they are impact and cut through resistant. these inherent properties of fibers help them to retain their shape during and after impact. 1) p-aramid fibers p-aramid fibers are high-performance organic fibers having properties such as high strength, high stiffness, high toughness, damage tolerance, durability, and heat and impact resistance. aramid is an organic-based fiber classified as p-aramid and meta-aramid. p-aramid material class has various commercial brands available in the global market, kevlar is the first engineering, technology & applied science research vol. 9, no. 2, 2019, 4012-4018 4014 www.etasr.com memon et al.: recent eco-friendly developments in personal protective clothing materials for … commercial product introduced by dupont in early 70’s, and its chemistry is based on p-phenylene terephthalamide. kevlar represents the largest global volume product, followed by tawron of the same chemistry group [13]. p-aramid fibres compine high strength, non-flammability and high-temperature resistance which makes them fit for use in applications such as ballistic protection in bulletproof vests and helmets, cut through protection in arms, safety gloves, shoes in high-risk industries, and aprons [5] . 2) kevlar kevlar is the first commercial product based on pphenylene terephthalamide. kevlar is used as a reinforcement material and became popular due to its excellent mechanical properties, unique flexibility, lightweight and corrosion resistance when compared with other metallic materials used for human body protection [14]. kevlar has comparatively lower fiber elongation, high tensile strength, and modulus than other synthetic fibers. there are various product types of kevlar available in the market. these products have different applications and properties. kevlar® is used in tires of 4×4 vehicles. kevlar® 29 is a highly engineered material, lightweight and non-flammable, used in the manufacturing of body armor (panels) for military vehicles, body armor of bulletproof jackets and bombproof suits. kevlar® 49 is comparatively lightweight, like glass fibers and metals used in industry. this material found its application in aerospace industry (eurofighter), and boat hulls due to its low weight, resistance to torque, and high impact resistance [15]. kevlar textiles tend to absorb moisture, this can be overcome with the use of natural fibers having hydrophilic properties to protect the kevlar from degradation and to provide comfort when used in protective clothing. kevlar counters well under tensile force (stretching force). unfortunately, it fails in compression strength where load bearing is required, like buildings or bridges. it is difficult and requires special cutting tools and equipment to cut and shape due to its high strength. kevlar is sensitive to u.v. light unless covered from direct sunlight. it is also sensitive to chlorine bleaches [15]. kevlar fiber is non-biodegradable, upon burning or incineration generates hazardous gases similar to wool fiber, including mainly carbon dioxide, nitrogen oxide, and fractional amounts of hydrogen cyanide, ammonia, aldehydes, etc. [16]. extensive research was performed to augment the properties of kevlar hybridization between synthetic fibers like carbon, glass, aluminum, etc. studies focused on increasing the mechanical performance of the synthetic fiber. however, very little research was performed for the hybridization of kevlar and natural fibers [14]. a study was performed to decrease the static and fatigue strength through hybridization of kevlar/epoxy composites with the addition of natural fiber cork powder filler [17]. the static and fatigue strength of the composite due to the increase in the hygroscopic nature of hybrid composite was decreased. 3) ultra high weight molecular polyethylene (uhwmpe) the uhwmpe is a highly oriented and low density crystalline produced with specific gel spinning and drawing. this method decreases the molecular defect rate. uhwmpe is commercially available under the names of dyneema and spectra [5]. uhwmpe fiber has various advantages, including low specific gravity and high specific strength/tenacity as shown in table i. it has high impact resistance, weather resistance, high abrasion resistance, high flexural resistance, and vibration dampening coefficient [18]. on the other hand, uhwmpe has a very low melting point (150 0 c) compared to p-aramid and carbon fibers. uhwmpe has a wide range of applications in various products like bulletproof jackets, helmets, ropes, cut resistant gloves, sleeves, butcher gowns, sport nets, medical applications, and fishing lines [5, 19]. in [20], it is reported that when compared with natural fibers, uhmwpe has ultra-high strength and modulus, and good impact resistance. it is inserted as reinforcement in composites. the disadvantages of uhwmpe fiber are that it is a plastic based fiber, non-biodegradable, non-renewable, has low surface hardness, strength and stiffness, poor creep resistance, bad adhesive wear and fatigue wear resistance, poor flow behavior and consequently is difficulty in processing [21]. c. high performance (organic fibers) 1) carbon fiber carbon is a high-performance organic fiber, produced by spinning and thermally carbonizing the precursor material. properties and microstructure of produced carbon fiber can vary with the production method applied. about 90% of commercially produced carbon fiber is a pan-based precursor [13]. isotropic pitch method is used for low strength carbon fiber manufacturing and mesophase pitch for high strength fibers [6]. the advantages of carbon fiber are its high tensile strength, high modulus, low thermal expansion coefficient, high fatigue strength, good thermal electric stability and chemical resistance, gas absorption capability, and noncorrosive nature. carbon fiber has some disadvantages. it is non-biodegradable, and has high cost, poor bending rigidity, and poor compressive strength [22]. carbon fiber is difficult to recycle, generates a high quantity of waste during processing while recycled carbon has generally low strength. another major disadvantage is its lack of elasticity, abrasion resistance, and electrical conductivity [23]. due to its high-end properties, carbon fiber is highly desirable in various industrial applications such as gas purification, respiratory filters, water filters, automobiles, sports tech, aerospace, marine transport, and medical applications [24, 25]. d. high chemical and combustion-resistant fibers there are various high chemical and combustion resistant organic fibers, like meta-aramid, kernel, kynol, and oxidized acrylic fibers. most popular fibers are meta-aramid fibers (nomex and conex) used in protective textiles. 1) meta-aramid (nomex and conex) the first ever aramid to be commercialized was the metaaramid polymer [m-phenylene isophthalamide] nomex (dupont) in 1967 [6]. m-aramid is a highly heat resistant organic fiber [18]. meta-aramid has 100% aromatic content, due to which it offers high heat resistance up to 425 o c. the aromatic composition is responsible for excellent performance in flame, leads to swelled char, which also tips to additional thermal insulation. these fibers are now available in paper engineering, technology & applied science research vol. 9, no. 2, 2019, 4012-4018 4015 www.etasr.com memon et al.: recent eco-friendly developments in personal protective clothing materials for … form for easy structural applications. m-aramid fibers have vast functionalities, which include high stiffness, high strength, high toughness, damage tolerance, and flame resistance [13]. maramids are also chemical resistant to acid, alkalis and organic solvents. m-aramids are low tenacity and low modulus fibers, whereas they are sensitive to u.v. light and sunlight. they are not dyeable with conventional dyeing methods, however, they have some affinity with a few cationic dyes [23]. meta-aramid fiber nomex is used in firefighter’s suits, heat resistant gloves, hot gas filtration, automotive hoses, electrical insulation, aircraft parts, and sports tech. iii. environment-friendly fibers natural fibers reviewed for their application and suitability in protective clothing, are abaca, bamboo, coir, ramie, jute, flax, and kenaf. natural fibers are eco-friendly materials, which have good properties compared to conventional synthetic fibers. natural fibers have comparatively low weight, low cost, are relatively less damaging to processing equipment, and are environment-friendly. a comparison of natural and conventional plastic-based fibres is presented in table ii. table ii. comparison of natural and conventional fibers parameter characteristics eco friendly/ natural fiber conventional/ synthetic fiber technical/ technological mechanical properties moderate high moisture sensitivity high low thermal sensitivity high low-high weight low heavy abrasiveness low high machinery required low-tech high-tech environmental availability renewable non-renewable production low high method of disposal landfill incinerate & recycling biodegradability complete no energy consumption low high economical cost low high legal patents no patents patents the environmental characteristics of natural fibers are more favourable, however due to some properties like high strength, high abrasive strength, and high modulus, synthetic fibers are still preferred by end-users. iv. types of eco-friendly fibers there are six major types of natural fibres, classified upon their source of production: plants which produce cellulose are known as bast fibers such as jute, flax, ramie, hemp, and kenaf, while cotton, coir, and kapok are known as seed fibers. leaf fibers come from abaca, sisal, and pineapple [4, 11]. the mechanical properties of natural fibers are given in table iii. images of the plants, and views of the fibers can be seen in [28]. a. abaca abaca fiber, also known as manila hemp, is an herbaceous plant, belonging to the musaceae family, looks like a banana plant, but it is entirely different in characteristics and applications [26]. abaca fiber is a leaf-based fiber and has 15% lignin content. abaca has high mechanical strength, which is three times stronger than sisal, it is a bouncy resistant and long fiber with length up to 3.7m [27]. it is resistant to salt-water, which differentiates it from other vegetable fibers. it originates from philippines and is one major export product [4, 26]. tensile strength and e-modulus are important parameters of abaca fiber, specifically for aerospace and automotive applications. abaca fiber possesses higher tensile strength and low elongation in dry and wet conditions compared to synthetic fibers like rayon [27]. abaca has applications in pulp and paper currency paper, cigarette filters, toiletries, lens cleansing, tea bags, and other related products. its composites have uses for aerospace and automotive industries. geotextiles of abaca are used for environmental protection specifically for soil conservation and control of soil erosion. new applications of natural fibers are on the rise, e.g. the preparation of cellulose nanocrystals as composite components. however, threats and emerging issues are concerns in the sustainability of the abaca growing areas [26, 27]. table iii. natural fibers properties [12] fiber tensile strength (mpa) stiffness /young’s modulus (gpa) elongation at break (%) density (g/cm 3 ) abaca 400 12 3-10 1.5 bamboo 140-230 1-17 0.6-1.1 coir 175 4-6 30 1.2 flax 345-1035 27.6 2.7-3.2 1.5 hemp 690 70 1.6 1.48 jute 393-773 26.5 1.5-1.8 1.3 kenaf 930 53 1.6 sisal 511-635 9.4-22 2.0-2.5 1.5 ramie 560 24.5 2.5 1.5 oil palm 248 3.2 25 0.71.55 pineapple 400-627 1.44 14.5 0.8-1.6 b. coir coir fiber is considered as the most green fiber as it utilizes less energy. coir fiber is obtained from tissues around the seed of coconut palm positioned between the husk and the outer shell of the coconut [29]. it is cultivated mainly in india and sri lanka. there are two types of coir fibers, brown coarse fiber, and white fine fiber. the brown fiber is obtained from mature brown coconuts and the white fiber is obtained from the raw green coconuts. the length of coir is measured up to 35cm. among its group, it has one of the highest contents of lignin making it stronger than cotton, but less flexible [30]. coir fiber is natural and renewable, it has high water retention, it is moth and rot resistant, and it is a good insulator of heat and sound. coir fiber has low cost, low density and is biodegradable with zero carbon footprint. coir based geotextiles have been developed for application towards soil erosion control, ground improvement, etc. [29]. the traditional applications of coir fiber are ropes, carpets or mattress but nowadays it has wide applications in protective textiles like bulletproof vests and flame-resistant boards [31, 32]. it has also found application in construction industry, due to its higher strength, conventional cement tiles are replaced with coir hybrid tiles. coir fiber has some disadvantages, including hydrophilic behavior, dimensional unstability, and low thermal resistance. its properties vary with the area of production and climate [33]. engineering, technology & applied science research vol. 9, no. 2, 2019, 4012-4018 4016 www.etasr.com memon et al.: recent eco-friendly developments in personal protective clothing materials for … c. bamboo bamboo is a regenerated cellulose fiber and perennial plant considered as eco-friendly and sustainable [12]. bamboo is a fast-growing plant (1 meter/day for some species) having the ability to absorb greenhouse gases, with the rate of five times more co2 than an equivalent stand of trees and producing 35% more oxygen, while it can prevent soil erosion. according to nfi, bamboo is considered the second highest produced fiber after cotton. bamboo is cultivated in tropical and sub-tropical areas like china, japan, and other asian countries. out of 1250 species of bamboo, 400 are found and processed in china. bamboo fibers are similar in structure to ramie fiber but shorter and finer. the length of bamboo fiber is very small and varies from 1mm to 5mm (with an average of 2.8mm) and diameter of 14µm-27µm (average 20µm). it has antifungal and antimicrobial properties [34]. bamboo fiber has various other advantages like high strength with low density, and high specific strength to its weight due to the longitudinal alignment of fibers in its body. due to its high strength, bamboo is known as “natural glass fiber” [35]. bamboo fibers found usage in traditional textile as well as in modern composites textiles [38]. applications of bamboo fibers are reported in the construction industry, traditional clothing, protective clothing, and medical textiles. due to inherent antimicrobial and antifungal properties, bamboo fibers are used in wound bandages, hygienic and odour resistant cloths, sports tech clothing, and sun protection clothing [34-37]. other advantages of bamboo fiber include that it is renewable, its efficient space consumption, its low water requirements, and organic status. disadvantages of bamboo fiber are that during processing it requires a high amount of energy, hazardous chemicals for processing, and more water compared to synthetic fibres [37]. d. jute jute is named as “golden fiber”. it is separated from the bark of the white jute plant and to a lesser degree from tossa jute, which includes 100 species. it is an inexpensive natural fiber and abundantly available in bangladesh, china and india with humidity of 60% to 90%. jute is an environment-friendly fiber, a hectare of jute plants absorbs around 15 tons of co2 and releases 11 tons of oxygen. yields are around 2 tons of dry jute fiber per hectare [12, 39]. jute is long, delicate and shiny, with a length of 1m to 4m and a diameter from 17µm to 20µm. it is one of nature's toughest vegetable fibers and positions second just to cotton in production quantity. jute has high insulating and antistatic properties, moderate moisture regain of 13% and low thermal conductivity [40]. due to its versatile characteristics, jute fiber is used in various applications from clothing to industry. its main advantages are its high modulus, strength and dimension stability, moderate draping and stiffness, biodegradability/eco-friendliness, high moisture absorption and breathability, and low cost. it is annually renewable, while it is abundantly grown in bangladesh and india. jute yarn is traditionally used in twine and sacks for the storage of grains and other food-related products, curtains, chair covers, carpets, and rugs. jute traditionally is blended with other natural fibers used in wall hangings, toys, and lamp sheds. in addition to this, jute fiber is used in various sectors of technical textiles like agro tech, automobiles, geo-tech, industrial textile etc. products of jute fiber are biodegradable, flexible, absorb moisture, drain well, and are helpful to prevent soil erosion [39-41]. the major disadvantages of jute fiber, which restrict its uses, are its rough nature, harsh feel, surface fuzziness, prominent hairiness, and poor washability [42]. jute fiber enjoys favour in the market due to its environment friendly properties. it is reported that jute is more environmentfriendly and less expensive than conventional synthetic materials. life cycle assessment study of conventional and jute fiber shows that the disposal of conventional synthetic material is causing more damage to the environment than jute [41]. natural fibers are used as reinforcement replacing the expensive glass fibers in polymer composites [6]. plywood, medium density fiberboards, panel, and plush doors are developed from jute and coir based composites. the addition of jute fiber (12%–24%) in glass showed an increase in the mechanical properties of the composites. hence, jute fiber shows an effective and value-added application. other applications of jute-polyester composites are lampshades, suitcases, paperweights, helmets, bath units, electrical appliances, covers, pipes, post-boxes, roof tiles, grain storage silos, panels for partition and false ceilings, biogas containers, and low cost mobile and pre-fabricated buildings. e. ramie ramie fiber is a bast fiber and belongs to boehmeria nivea urticaseae, commonly known as “china grass” which includes over 100 species, mostly grown in china. barks of ramie fiber are used for the making of twine threads, and spun as grasscloth or chinese linen. ramie fiber is more like flax in absorbency and density but coarser with diameter of 25-30 microns. it is also one of the strongest natural fibers with a tensile strength of 560mpa, more than coir (175mpa) and abaca (400mpa) while it is denser than bamboo [12]. ramie as a natural fiber has various advantages, such as: it is environment-friendly, resistant to bacteria, mildew and insects, it is highly moisture absorbent, easily dyeable, and in wet condition it increases strength like cotton [26]. a major disadvantage of ramie is that its chemical characteristics vary with its area of production, which requires more pre-treatment process than any other natural fiber [12]. other disadvantages are its low elasticity and abrasion, it wrinkles easily, and it is stiff and brittle in nature [26]. rami is utilized as a part of body armor, it is lightweight and has low cost in comparison with conservative bulletproof panels. results of impact resistance tests reveal that vests produced using ramie fiber could oppose the infiltration of high impact shots up to level ii, and it could not avoid the impact resistance of level iv [12, 43]. ramie fiber is used in various applications such as in industrial sewing threads, packaging material, fishing net, filter cloths, and home furnishing cloths. short fibers of ramie are used in high-class papers such as bank notes and security papers [44]. f. flax flax is a bast fiber, belongs to linum usitatissimum l. family, and is one of the oldest fiber crops in the world [12]. flax grows in moist climates, like europe, china, and egypt. flax is an environment-friendly fiber used in high-end textile products. the flax plant has a life cycle of 90-125 days, which includes vegetation, blossoming and ripening periods [45]. flax fiber is breathable and provides comforts during wearing, engineering, technology & applied science research vol. 9, no. 2, 2019, 4012-4018 4017 www.etasr.com memon et al.: recent eco-friendly developments in personal protective clothing materials for … absorbs sweat and is a good heat exchanger, which reduces body temperature during summer. during winter, flex fiber does not attract electrostatic charges, provides psychophysical comfort [26]. flax fiber is a cellulose polymer just like other natural fibers such as cotton and ramie. the structure of flax is crystalline, which make it stronger but it easily gets wrinkles. flax fibers are very popular in linen knitted and woven clothing, flax fibers are used for home textile accessories like tablecloth, bed linen and curtains [26]. in [45], flax fiber was compared with conventional glass fiber. it was reported that the reason which makes flax fiber more appealing than glass fiber is that it is cheaper than glass fiber, less toxic and has a high strength to weight ratio [45]. flax fiber has various advantages: it is biodegradable, it has less carbon footprint than other natural fibers, it requires less water and pesticides for cultivation, it has excellent tensile strength, and good u.v protection [46]. this fiber has some limitations for application in composites. flax fiber degrades above 200 0 c and due to moisture retention it cannot be used in external applications. just like other fibers, flax has variations in properties and irregular shape [47]. g. kenaf kenaf fiber belongs to genus hibiscus cannabinus, k family malvaceae, there are over 300 species related to kenaf fiber. kenaf due to its environment-friendly properties is preferred in composite products [12]. kenaf plant can grow in a wide range of climatic conditions and it is one of the fastest growing plants. kenaf has appealing characteristics like lowdensity, it is non-abrasive during processing and has high specific mechanical properties. the plant absorbs nitrogen and phosphorus from the soil and co2 at a high rate [48]. kenaf is a well-known cellulosic fiber having ecological and economic advantages [7]. kenaf fiber is traditionally used in ropes, canvas, and stacking, and nowadays is being used in composites in automobiles, aeronautics etc. [49]. table iv. world production of natural fibers, producing countries, and applications in protective textiles and other composites name world production rate (000) country of origin application reference abaca 70 native to philippines and tropical countries automobile, and airplane, geo-textiles, bank notes, security paper, and tea bags [12, 27] bamboo 30000 china, japan, and other asian countries construction industry. cut resistance gloves, sun protection clothing, anti-bacterial clothing [12, 34-36] coir 100 sri lanka used in bulletproof vests, building boards, roofing sheets, insulation boards, building panels, coir fiber reinforced composites, cement boards, geo-textiles. [29-33] flax 830 russia poland, france, belgium, and the czech republic fire protection, medical textiles as surgical thread, clothing, insulation, filtration, light aviation use. [12, 45, 47] hemp 214 poland, romania, russia, slovenia, spain and switzerland military uniforms, special uniforms requiring antibacterial properties, insulations, waterproofing, windproof, sunscreen, anti-infrared flame resistance. [44, 50] jute 2300 bangladesh, india and china plywood, medium density fiberboards, panel and plush doors. [12, 39-42] kenaf 970 china and india composites, automobiles, paper industry, and fiber boards. [12, 49] ramie 100 china bulletproof vests, industrial sewing threads, packaging material, fishing nets, filter cloths, and home furnishing cloths. [12, 26, 43-44] v. future challenges limited research is conducted in the field of hybridization of conventional (plastic-based fiber) and natural fiber. ecofriendly, low weight, low-cost pc can be developed through hybridization of conventional fibers like kevlar, dynema, spectra and natural fibers like jute, ramie, sisal, coir and bamboo with the selection of suitable design and the appropriate ratio of fiber mix. abaca fiber due to its high mechanical strength properties is a potential candidate to use in protective clothing (research is required). bamboo fiber, due to its inherent antimicrobial and antifungal properties, could be hybridized with nomex fiber and other conventional fibers for application in firefighter suits and medical textiles as a biological protective application. for the improvement of properties like moisture barrier, antifungal and antibacterial abilities, more research is required in this field. ramie and coir are the strongest natural fibers and can be utilized in protective clothing. limited research has been made to utilize ramie fiber in bulletproof panels. more research is required for the utilization of ramie fiber in other applications of protective clothing like hand gloves, sleeves etc. vi. conclusion natural fiber-based composite protective clothing and other composites have developed significantly due to their environmental, economic, technological and legal benefits. these natural fiber based composites are finding applications in various fields including protective clothing. review and examination of various studies highlighted the importance of environmental issues which occur due to plastic pollution, which can overcome by reducing the plastic based conventional fibers with natural fiber composites. a very limited research has been carried out in this area, however, during the past decade, various researchers focused on the development of eco-friendly materials for different applications including protective clothing. 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shanghai, china jiandong wu department of electrical engineering shanghai jiao tong university shanghai, china m. g. danikas department of electrical and computer engineering, democritus university of thrace, xanthi, greece yi yin department of electrical engineering shanghai jiao tong university shanghai, china abstract— in a previous work, a typical case was studied, where a solid sheet insulation contained a void under dc or ac voltage. in the present paper, a more complex case is studied in order to study the charging phenomenon in hvdc valve windings and cables under a superposition of ac and dc voltages. real inception voltage is calculated, and it agrees with the experimental results previously reported. moreover, the location of the charging phenomenon is calculated, and it is correlated to the ratio between ac and dc voltage. keywords-partial discharges; charging phenomena below inception voltage; cavities; simulation i. introduction for long-distance transmission of electric power, high voltage direct current (hvdc) systems may prove to be less expensive and to suffer lower electrical losses. converters are the heart of an hvdc converter station, which converts electric power from alternating current (ac) to direct current (dc) or in reverse. multilevel converters have reached a certain level of maturity, given their industrial presence and successful practical application [1]. the growing market size and increasing technical requirements of mv high-power drives are also pointed out [2]. to achieve a greater capacity, a lower loss and a higher voltage, many researchers study topological structure of hvdc converters [3]. however, in all these topological structures, there is an inevitable problem that the electric field distribution gets more complicated compared to that in common power transformers. for instance, insulations of valve windings and cables are working under a superposition of ac and dc voltage. some simulation results can be found in [4-6]. the attention given today to hvdc cables appears to be all-time high [7]. it is important to study the electrical behavior under such complicated voltage combinations. partial discharges (pds) are one kind of early insulation faults. through a suitable detection of pd, the recording of partial discharge inception voltage (pdiv) and appropriate study of pd data, insulation –and consequently apparatuscondition monitoring can be carried out, its state can be evaluated and appropriate measures –if there is any need– can be taken. it is interesting that charging phenomena may happen below inception voltage (iv). due to background interference or the limitation of pd equipment sensitivity, it is possible that pd (or charging phenomena) may occur below the so-called iv [8 – 10]. in a previous work, this phenomenon under ac or dc voltage was discussed from a historical perspective [11]. simulation was conducted and results showed some differences between the charging phenomena under ac and dc voltage [12]. in the present paper, the aim is to study charging phenomena in hvdc valve windings and cables, which is a more complex case, where a superposition of ac and dc voltage is applied on the insulation sample. ii. modeling a. geometry the insulation sample used in the simulation is a solid sheet insulation that contains a cavity. cross section of the sheet is shown in figure 1. the insulation is a cylinder. its top surface is in contact with the high voltage electrode, whereas its bottom surface is in contact with the ground electrode. the cavity is a spheroid in the center of the sheet. the sheet diameter is 2r = 20 mm and the height is h=10 mm. the cavity width is 2a = 12 mm and the height is 2b=6 mm. the sample is exactly the same as that in [12]. in the context of this work the terms “void” and “cavity” are used interchangeably. these parallel plate electrodes are widely used in high voltage experiments to test conductivity, permittivity, dielectric loss, space charge and other electrical parameters or behaviors. such a cavity inside the sample is a typical internal insulation defect. in the case of a cavity containing gas with a lower permittivity than that of the solid, the discontinuity has the effect of increasing the engineering, technology & applied science research vol. 8, no. 4, 2018, 3088-3092 3089 www.etasr.com hu et al.: thoughts on the possibility of damage of high-voltage electrical insulation below … magnitude of the electric field within the cavity. partial discharges occur if the field exceeds the dielectric strength of the gas in the cavity [13]. fig. 1. cross section of the insulation with a void b. materials the materials used in this simulation are exactly the same as those in [12]. their electrical parameters are shown in table i. the insulation sheet is the cross-linked polyethylene (xlpe). in the theory of dielectric physics, the conductivity of xlpe and other polymer solid insulation are affected by electric field and temperature. two models, namely hopping conductivity [14, 15] and space-charge limited currents [16, 17], give some explanations. here, it is assume that the sample is in room temperature, so that the conductivity is determined by the electric field. the relationship is shown in figure 2, which is an experimental result in [18]. before ionization and breakdown, air is a good insulation with very low conductivity. here, a typical value of conductivity under standard atmospheric pressure is used for air. permittivity is an electric parameter to describe the relationship between electric displacement field and electric field. usually, it is affected by the frequency of the applied voltage. here, for xlpe and air, typical values under 50 hz are used. table i. electrical parameters used in the simulation material conductivity (s/m) relative permittivity insulation (xlpe) affected by electric field 2.3 void (air) 5×10-14 1 co nd uc tiv ity ( s /m ) fig. 2. electric field vs conductivity of xlpe (after [18]) c. equations the electric field under a superposition of ac and dc voltage can be calculated by (1)-(5). (1)e v  0 (2)j   (3)j se d t       (4)s s e 0 (5)rd e  where e is electric field, v is voltage, j is current density, d is electric displacement, t is time, s is conductivity, εr is relative permittivity and ε0is vacuum permittivity. equation (1) means electric field is an irrotational field in math. electric field is the negative gradient of voltage. equation (2) means current field, as the result of charge movement, is a passive field. eq.(3)divides current into two parts, namely the conduction current and the displacement current. equations (4) and (5) are constitutive equations. equation (4) shows that the conductivity is related to electric field, which is demonstrated in section iii.b and is used when calculating conduction current. equation (5) is used when calculating the displacement current. it should be pointed out that these equations can also be used when only ac or dc voltage is applied. when studying the ac cases, the conduction current is ignored. when studying the dc cases, the displacement current is ignored. in the present case, both parts should be considered, and thus the equations make up a time dependent problem. d. conditions and voltage here, two boundary conditions should be applied. one is the high voltage electrode the voltage of which is a superposition of ac and dc, as shown in (6).    sin 2 (6)dc acu t u u ft  where udc is the value of dc voltage. uac is the magnitude of ac voltage. f is frequency and here is set to 50 hz. the other boundary condition is the ground electrode the voltage of which is set to zero. since the equations make up a time dependent problem, an initial condition is needed. usually initial conditions can be set to zero. after a transient process, the solution will reach a steady state. however, it will take some amount of calculation. for the present simulation, the whole process can be accelerated. when we remove ac voltage, the problem becomes a time independent problem and the solving process needs only a little amount of calculation. then we can set initial conditions for the ac-dc problem to the solution of the dc problem. as a result, this process shortens the transient process. iii. solution the solving here is similar to that in [12]. a two loops algorithm is used, as shown in figure 3. in the outer loop, we set voltages udc and uac, and then adjust these values based on the electric field solution, until the maximum electric field in engineering, technology & applied science research vol. 8, no. 4, 2018, 3088-3092 3090 www.etasr.com hu et al.: thoughts on the possibility of damage of high-voltage electrical insulation below … the void equals the break down field strength. the breakdown electric field in the void is set to 3 kv/mm. that is the real iv, or the minimum voltage for charging phenomena. in the inner loop, a voltage distribution is assumed, the conductivity is calculated, the electric field is calculated, and we repeat the two calculation processes until the field distribution does not change. this iteration is a common method when coefficients (such as conductivity) in equations are affected by solutions (such as electric field). the process of calculating the electric field is the main process. it is a traditional finite element method (fem) problem, which contains geometry, materials, equations and conditions. here, we use comsol multiphysics software as a finite element analysis solver, and all the algorithms are programmed in it. fig. 3. process of the two loops algorithm a. real inception voltage a simulation result of the real iv is shown in figure 4. when the dc voltage is zero, the aciv is 23 kv. when ac voltage is zero, the dciv is 160 kv, as can be seen from figure 4. these results correspond to those reported in a previous work of ours [12]. under a simultaneous superposition of ac and dc voltage, the iv forms a curve. below the curve, it is assumed that there is a safe area, where charging phenomena do not occur, and the power system works well. on the curve, whether pd is detected or not, charging phenomena may occur, and the system is considered to be no more safe. fig. 4. simulation results of real iv the curve is very similar to the experimental result reported in [19], as shown in figure 5. the experimental arrangement used in [19] was similar to the one used in the present paper. it has to be pointed out, however, that the insulation used in [19] was a composite insulation of oil-paper.to a great extent, the simulation results of figure 4 show the correctness of the simulation in the presentpaper. it should be emphasized, however, that in this paper the influences of factors such as temperature, space charge, chemical changes were not considered. needless to say that the actual situation would be far more complicated in reality. fig. 5. experimental results of iv reported in [19] b. location of charging phenomenon and further discussion a typical electric field distribution in the void under a superposition of ac and dc voltage is shown in figure 6. in figure 6(a), we have less dc voltage, and the maximum electric field occurs in major axis of the elliptic cross section of thevoid. in figure 6(b), we have more dc voltage, and the maximum electric field occurs in minoraxis. such results are in agreement with those obtained in [12], where ac and dc voltages were separately investigated. it is evident that the location of a charging phenomenon is related to the ratio between the applied ac and dc voltages. in other words, the sort of decomposition of a void (either along the major or along the minor axis) may indicate the prevalence of a dc or of an ac component. as was pointed out in [12], under only dc conditions, a much higher high-voltage source is needed in order to have pd in an insulation than when we have an ac voltage applied. partial discharges are far easier to be recorded with ac voltages. with the advent to the high-voltage engineering applications of more and more of power electronics arrangements, it becomes apparent that superposition of ac and dc voltages may occur and, consequently, new conditions for pd onset may arise. it has been noted that pd or charging phenomena may or may not be registered, depending on the sensitivity of pd detecting equipment [20]. in this context, figure 4 of this paper indicates that although the dielectric strength of the air void may be reached, it is by no means certain that something will be recorded by a pd detector. in other words, it is speculated that, although simulation results give the real iv, the latter may be lower than the experimental iv which is recorded. strong indications and hints to this view already exist [21-24]. especially in [24], the authors mention that, with very small enclosed voids, pd pulse currents tend to have the lowest engineering, technology & applied science research vol. 8, no. 4, 2018, 3088-3092 3091 www.etasr.com hu et al.: thoughts on the possibility of damage of high-voltage electrical insulation below … values. whether such low values can be detected by pd equipment depends on the sensitivity of the equipment. it also points out to the fact that there may a need to rethink about our approach as to the pd phenomena in general, since – as discussed long ago – charging effects may take place below the so-called inception voltage, the consequence of which is not yet clear [25, 26]. what some people perceive as self-extinction of pd may well be the inability of a pd detecting device to detect pd of extremely small magnitude (or even charging phenomena) which may be of detrimental nature [27, 28]. certainly more work has to be done in this direction since, although the criterion for a streamer development in a cavity is that this has to be >0.4 mm, the criterion for a townsend discharge is that a void has only to be larger than 0.1 micron [29, 30]. fig. 6. electric field distribution in the void. (a) udc=40 kv and uac=22 kv (b) udc=80 kvand uac=20 kv iv. conclusion in this paper, based on previous work, the charging phenomenon in hvdc valve windings and cables was studied, where a superposition of ac and dc voltage is applied on the insulation sample. an iterative method with two loops algorithm is used to solve the time dependent problem. real iv is calculated, and the results qualitatively agree with experimental results reported in another paper. moreover, the location of charging phenomenon is calculated, and it is related to the ratio between ac and dc voltage. references [1] s. kouro, m. malinowski, k. gopakumar, j. pou, l. g. franquelo, b. wu, j. rodriguez, m. a. pérez, j. i. leon, “recent advances and industrial applications of multilevel converters”, ieee transactions on industrial electronics, vol. 57, no. 8, pp. 2553-2580, 2010 [2] j. rodriguez, s. bernet, b. wu, j. o. pontt, s. kouro, “multilevel voltage-source-converter topologies for industrial medium-voltage drives”, ieee transactions on industrial electronics, vol. 54, no. 6, pp. 2930-2945, 2007 [3] d. legrand mon-nzongo, p. g. ipoum-ngome, t. jin, j. songmanguelle, “an improved topology for multipulse ac/dc converters within hvdc and vfd systems: operation in degraded modes”, ieee transactions on industrial electronics, vol. 65, no. 5, pp. 3646-3656, 2018 [4] z. liang-xian, z. qi-min, c. mo-sheng, p. zong-ren, “research on transient electric field distribution of converter transformer valve side winding under polarity reversal”, annual report on conference of electrical insulation and dielectric phenomena (ceidp), shenzhen, china, pp. 307-310, october 20-23, 2013 [5] y. li, x. li, j. du, l. li, d. li, “the calculate of nonlinear and anisotropic electric field in valve side winding of converter transformer”, 2011 international conference on electrical machines and systems (icems), beijing, china, pp. 1-4, august 20-23, 2011 [6] j. li, l. zhang, x. han, x. yao, y. li, “pd detection and analysis of oil-pressboard insulation under pulsed dc voltage”, ieee transactions on dielectrics and electrical insulation, vol. 24, no. 1, pp. 324-330, 2017 [7] g. -c. montanari, p. seri, x. lei, h. ye, q. zhuang, p. morshuis, g. stevens, a. vaughan, “next generation polymeric high voltage direct current cables—a quantum leap needed?”, ieee electrical insulation magazine, vol. 34, no. 2, pp. 24-31, 2018 [8] a. m. bruning, d. g. kasture, f. j. campbell, n. h. turner, “effect of cavity current on polymerinulation life”, ieee transactions on electrical insulation, vol. 26, no. 4, pp. 826-836, 1991 [9] m. g. danikas, n. vrakotsolis, “experimental results with small air gaps: further thoughts and comments on the discharge (or charging phenomena) below the so-called inception voltage”, journal of electrical engineering, vol. 56, no. 9-10, pp. 246-251, 2005 [10] y. zhang, m. g. danikas, x. zhao, y. cheng, “preliminary experimental work on nanocomposite polymer: small partial discharges at inception voltage, the existence of possible charging mechanisms below inception voltage and the problem of definitions”, journal of electrical engineering, vol. 63, no. 2, pp. 109-114, 2012 [11] m. g. danikas, y. yin, j. hu, “thoughts on the possibility of damage of high-voltage electrical insulation below the so-called inception voltage: the historical background–part i”, funktechnikplus# journal, no. 7, pp. 7-18, 2015 [12] h. fan, j. hu, y. yin, m. g. danikas, “thoughts on the possibility of damage of high-voltage electrical insulation below the so-called inception voltage: a proposed solution and some further comments–part ii”, funktechnikplus# journal, no. 9, pp. 355-367, 2016 [13] a. g. sellars, o. farish, b. f. hampton, l. s. pritchard, “using the uhf technique to investigate pd produced by defects in solid insulation”, ieee transactions on dielectrics and electrical insulation, vol. 2, no. 3, pp. 448-459, 1995 [14] h. böttger, v. v. bryskin, hopping conduction in solids, akademieverlag, berlin, germany, 1985 [15] j. r. dennison, j. brunson, “temperature and electric field dependence of conduction in low-density polyethylene”, ieee transactions on plasma science, vol. 36, no. 5, pp. 2246-2252, 2008 [16] p. cooperman, “a theory for space-charge-limited currents with application to electrical precipitation”, transactions of the american institute of electrical engineers, part i: communication and electronics, vol. 79, no. 1, pp 47-50, 1960 [17] t. christen, “the effect of injection properties of contacts on the dynamics of unipolar space-charge limited currents”, ieee transactions on dielectrics and electrical insulation, vol. 23, no. 6, pp. 3712-3724, 2016 [18] l. lan l., j. wu, y. yin, x. li, z. li, “effect of temperature on space charge trapping and conduction in crosslinked polyethylene”, ieee transactions on dielectrics and electrical insulation, vol. 2, no. 4, pp. 1784-1791, 2014 (b) (a) engineering, technology & applied science research vol. 8, no. 4, 2018, 3088-3092 3092 www.etasr.com hu et al.: thoughts on the possibility of damage of high-voltage electrical insulation below … [19] y. sha, y. zhou, j. li, j. wang, “partial discharge characteristics in oilpaper insulation under combined ac-dc voltage”, ieee transactions on dielectrics and electrical insulation, vol. 21, no. 4, pp. 1529-1539, 2014 [20] a. -c. gjaerde, multifactor ageing of epoxy–the combined effect of temperature and partial discharge, phd thesis, norwegian institute of technology, trondheim, norway, 1994 [21] d. koenig, erfassung von teilentladungen in hohlraumen von epoxydharzplattenzur beurteilung des alterungsverhaltens bei wechselspannung, phd thesis, technische universitaet braunschweig, braunschweig, germany, 1968 [22] t. tanaka, “internal partial discharge and material degradation”, ieee transactions on electrucal insulation, vol. 21, no. 6, pp. 899-905, 1986 [23] m. g. danikas, f. k. prionistis, “detection and recording of partial discharges below the so-called inception voltage”, facta universitatis (ser. electronics and energetics), vol. 17, pp. 99-110, 2004 [24] a. a. ganjovi, n. gupta, g. r. govindaraju, “a kinetic model of a pd pulse within voids of sub-millimeter dimensions”, ieee transactions on dielectrics and electrical insulation, vol. 16, no. 6, pp. 1743-1754, 2009 [25] n. h. turner, f. j. campbell, a. m. bruning, d. g. kasture, “surface chemical changes of polymer cavities with currents above and below corona inception voltage”, annual report of conference on electrical insulation and dielectric phenomena (ceidp), pp. 687-693, canada, october 18-21, 1992 [26] t. tanaka, “aging of polymeric and composite insulating materials – aspects of interfacial performance in aging”, ieee transactions on dielectrics and electrical insulation, vol. 9, no. 5, pp. 704-716, 2002 [27] e. brancato, “insulation aging: a historical and critical review”, ieee transactions on electrical insulation, vol. 13, pp. 308-317, 1978 [28] e. brancato, “electrical aging–a new insight”, electrical insulation magazine, vol. 6, no. 5, pp. 50-51, 1990 [29] m. g. danikas, t. tanaka, “aging and related phenomena in modern electric power systems”, ieee transactions on dielectrics and electrical insulation, vol. 1, no. 3, pp. 548-549, 1994 [30] k. wu, c. pan, y. meng, y. cheng, “effect of void area on pd magnitude uniformity”, annual report of conference on electrical insulation and dielectric phenomena (ceidp), pp. 1165-1168, shenzhen, china, october 20-23, 2013 microsoft word 9-2779_s1_etasr_v9_n4_pp4361-4366 engineering, technology & applied science research vol. 9, no. 4, 2019, 4361-4366 4361 www.etasr.com abdullah et al.: effect of non-uniform heat source and radiation on transient mhd flow past a … effect of non-uniform heat source and radiation on transient mhd flow past a vertical moving plate with inclined magnetic field and periodic heat flux mustafa rashied abdullah faculty of engineering al-ahliyya amman university amman, jordan mrashied@ammanu.edu.jo omar k. alghazawi faculty of engineering al-ahliyya amman university amman, jordan o.ghazawi@ammanu.edu.jo muhammad al-ayyad faculty of engineering al-ahliyya amman university amman, jordan mayyad@ammanu.edu.jo abstract—an analysis is carried out in order to examine the effects of non-uniform heat source and thermal radiation on the transient free convective mhd flow past a vertical plate. in this model, an inclined magnetic field with periodic heat flux along the wall is included. the governing equations (in non-dimensional shape) are solved numerically by a fully implicit finite difference scheme. a parametric study is performed in order to illustrate the influences of the model dimensionless parameters, namely, the magnetic parameter, the heat source term, the grashof number, the prandtl number, and the radiation parameter. the velocity field and the temperature field are evaluated for several amounts of these parameters. the obtained numerical results are compared with the analytical solution in case of constant heat flux with no heat source, and a full agreement was found. keywords-free convection; heat source; inclined magnetic field; radiation; periodic heat flux i. introduction there are a lot of recent studies on the effect of magnetohydrodynamics (mhd) on systems of fluid dynamics due to their wide applications in industrial manufacturing processes and cooling systems. many of these studies were made to predict the velocity and thermal behavior of the boundary layer over a moving vertical plate under different conditions. the effect of heat generation on mhd flow over flat plates has been analyzed in many papers. the effect of temperature dependent heat source on natural convection flow past an accelerated infinite vertical plate of a viscous incompressible fluid under the action of a uniform magnetic field through a porous medium was studied analytically in [1], where the plate temperature was raised linearly with time. authors in [2] studied the effect of temperature dependent electrical conductivity on steady free convection flow of a viscous incompressible low prandtl ( pr 1� ) fluid past an isothermal vertical plate in the presence of magnetic field and exponentially decaying heat generation. the heat and mass transfer effects on mhd flow of viscous incompressible fluid through a nonhomogeneous porous medium in the presence of heat source, oscillatory suction velocity have been investigated in [3]. authors in [4] studied the free convection flow in the presence of heat generation and a convective boundary condition. authors in [5] examined the mhd fluid flow over a vertical porous plate in the presence of radiation and heat generation. authors in [6] studied the influence of variable viscosity and thermal conductivity on laminar mhd free convective boundary layer flow of a dusty fluid past a vertical porous plate with viscous dissipation, joule heating, and heat generation. authors in [7] studied the effect of heat source and chemical reaction on mhd flow along a moving vertical plate with variable temperature. authors in [8] studied a transient mhd free convective flow over a vertical plate with an impulsive motion in presence of heat generation in a rotating system. an exact solution of a nonlinear mhd flow with heat generation has been studied in [9] for an incompressible viscous fluid along a vertical plate. authors in [10] studied the transient mhd free convection in a boundary layer flow through a porous medium past a moving infinite vertical plate in presence of heat source and chemical reaction. the effects of heat flux have been studied extensively. authors in [11] presented a theoretical study of unsteady free convection flow along a vertical flat plate embedded in a porous medium. the unsteady behavior is computed after the generation of an impulsive heat flux step. the free convection flow of a viscous fluid over a vertical accelerated plate embedded in a porous medium with constant heat flux has been analyzed in [12]. authors in [13] studied the transient free convection flow of a fluid past an accelerated vertical plate with constant heat flux in the presence of heat generation. an analytical study of transient mhd free convective flow of a viscous incompressible fluid over an infinite vertical plate immersed in a porous medium with viscous dissipation effect and uniform heat flux in the presence of chemical reaction was carried out in [14]. authors in [15] studied the free convective mhd flow past a moving plate maintained at constant heat flux and embedded in a viscous fluid saturated porous medium. the employed model included the effects of thermal radiation, heat sink and chemical reaction the effect of inclined magnetic field on the flow and temperature profiles of mhd flow past a vertical plate has also corresponding author: mustafa rashied abdullah engineering, technology & applied science research vol. 9, no. 4, 2019, 4361-4366 4362 www.etasr.com abdullah et al.: effect of non-uniform heat source and radiation on transient mhd flow past a … been under study. authors in [16] studied the effects of inclined magnetic field and radiation on the free convective flow of dissipative fluid over a vertical plate through a porous medium in the presence of heat source. the effect of radiation on transient mhd free convection flow of a viscous incompressible fluid past an impulsively moving vertical plate by applying inclined magnetic field was studied in [17]. authors in [18] examined the effect of inclined magnetic field on the transient flow over a moving vertical plate with variable temperature. the unsteady mhd flow between two nonconducting mhd infinite vertical plates in the presence of uniform inclined magnetic field was considered in [19] where it was assumed that one of the plates was in motion with constant velocity and the other plate was considered to be adiabatic. authors in [20] studied a theoretical model of transient mhd free convection flow with heat transfer of a viscous, incompressible, radiating and chemically reactive fluid past an impulsively moving vertical plate with ramped heat flux in the presence of inclined magnetic field. in this paper, the effect of heat generation and thermal radiation on the mhd free convection flow and heat transfer past a vertical plate has been studied. here, the magnetic field is assumed to be inclined. the contribution of periodic heat flux in the energy equation has been included. the governing non-dimensional differential equations were solved numerically by a fully implicit finite difference scheme known as the crank-nicolson method. numerical computations have been carried out for temperature and velocity profiles. the effects of magnetic parameter, heat source term, grashof numer, prandtl number and radiation parameter on the flow behavior and heat transfer process are presented through graphs, and their features are discussed. ii. mathematical formulation the problem of laminar, two-dimensional mhd flow of an incompressible electrically conducting viscous fluid past a vertical plate is shown in figure 1. fig. 1. schematic diagram of the problem a conductive liquid with a density ρ, dynamic viscosity µ, and electrical conductivity σ is considered. assume the coordinate system to be such that the x * -axis is taken along the vertical plate and the y * -axis is perpendicular to the plate. the flow is assumed to be laminar and the fluid properties are assumed to be constant. the fluid is subjected to a uniform magnetic field which is assumed to be inclined with an angle relative to the x * -axis, and the induced electric and magnetic fields are ignored. at time t≤0, the plate and the fluid are assumed to be stationary and having the same temperature t∞. at time t>0, the plate starts moving with a constant velocity in the presence of a periodic heat flux. assuming a fully developed flow, the transient governing equations of the mhd flow that represent the fluid motion and temperature are: ��∗ ��∗ � � � ��∗ ��∗� �� ∗ � ∞� � ��� �������� � �∗ (1) ��∗ ��∗ � ���� � ��∗ ��∗� ����� � ∗ � ∞� � �� ��∗ (2) using the rosseland approximation for radiation as that given in [21], the radiative heat flux is: !" � #$�∗%�∗ �� ∗& ��∗ (3) using taylor series expansion for ∗$, we have: ��∗& ��∗ ≅ 4 ∞% �� ∗ ��∗ (4) and then: �� ��∗ � )*� ∗ %�∗ ∞% � ��∗ ��∗� (5) using (5), equation (2) becomes: ��∗ ��∗ � ���� +1 )*� ∗ %�∗� ∞%� ��∗ ��∗� ����� � ∗ � ∞� (6) where u * is the axial velocity, t * is the fluid temperature, υ is the kinemetic viscosity, k is the thermal conductivity, and cp is the speicific heat. with initial and boundary conditions: 0 0 0 for all y 0 at y 0 * * * ** * * * * * : , * : , cos� � , t u t t t qt u u tky ω ∞ ≤ = = ∂ > = = − = ∂ 0 , as * * *,u t t y ∞ → → = ∞ (7) to write the governing equations in dimensionless form, the following dimensionaless variables are introduced: : � �∗��; , < � � ∗��� ; , = � > ∗; ��� , � � � ∗ �� , ? � ���#�∞����; , @ � ��� �; ���� , ab � cd�; � ��� , eb � f��� g � )*� ∗�∞h %�∗� i � ���; ������ (8) the dimensionless equations become: �� �� � ��� ��� ab? � @�sin l� m� (9) �n �� � �)op� q" ��n ��� i? (10) the dimensionless boundary conditions can be written as: engineering, technology & applied science research vol. 9, no. 4, 2019, 4361-4366 4363 www.etasr.com abdullah et al.: effect of non-uniform heat source and radiation on transient mhd flow past a … 0 0 0 for all y 0 1 at y 0 *: , : , cos� � , t u t u ty θ θ ω ≤ = = ∂ > = = − = ∂ 0 0, as ,u yθ→ → = ∞ (11) iii. numerical analysis the dimensionless momentum and energy equations subject to the initial and boundary conditions are solved numerically by using a stable fully implicit finite difference technique. using the crank-nicolson method, the fluid region is divided into a grid in x and y directions and central finite divided difference equations are obtained at each time step. to determine the velocity and temperature distributions for different parameter values the thomas algorithm is used by solving the resulting finite difference equations with tridiagonal coeffecient matrix. iv. exact solution the numerical solution has been verified by comparison with the analytical solution in the case of constant heat flux without heat generation. the eigenfunction expansion method was used to solve the special form of the energy equation. the dimensionless time dependent energy equation can be written as: �n �� � �)op� q" ��n ��� (12) the boundary conditions for constant heat flux can be written as follows: 0 0 for all y 0 1 at y 0 : : , t t y θ θ ≤ = ∂ > = − = ∂ 0, as yθ → =∞ (13) since the above boundary conditions are non homogeneous, a new function is introduced to convert them to homogeneous : s�:,<� � ?�:, <� � �∞ � :� (14) applying (14), the energy equation becomes: �u �� � �)op�q" � �u ��� (15) and the boundary conditions can be written as: 0 for all y 0 0 at y 0 : � � : , t h y ht y ≤ = −∞ ∂ > = = ∂ 0, as h y→ = ∞ (16) let s�:,<� � ∅�:�x�<� and compute the derivatives and substitute into (15) to obtain the eigenvalue problem as: y�∅ y�� z∅ � 0 �\�� �0� � ∅�]� � 0 (17) where λ is the separation constant, and ] → ∞ . the above equation has the following solution: ∅_�:� � `abc√z:e (18) with eigenvalues: z_ � + �m_#)�f mg m (19) for each n, the solution for δ(t) is x_�<� � h #ij�klm�n� , hence the series solution for h(y,t) becomes: s�:, <� � ∑ p_q_r) `abc√z:eh#ij�klm�n� (20) which satisfies the non-homogeneous initial condition: s�:,0� � �: � ∞�. hence: p_ � kicst�c√uge#)e vw�oxyzc�√i {e&√i | where } � 1,2,… …,∞. the final form of solution becomes: ?�:,<� � �∑ kicst�c√uge#)e�w�oxyzc�√i {e&√i � q_r) `abc√z:eh#ij�klm�n� � �∞ � :�(21) v. results and discussion using the above numerical method, the governing equations of the problem are solved for various sets of values of the physical parameters. the numerical results obtained are presented for dimensionless velocity and dimensionless temperature in figures 1-12. the velocity profile u is presented for different values of dimensionless parameters. the following dimensionless variables are used to get the results: gr=5, pr=7, m=1, ω=π/4, r=2, s=0.5, α=π/3 and t=1. the dimensionless velocity u increases from 1 at the plate, reaching its maximum value near the plate and decreases to 0 at the free stream. figure 2 shows the dimensionless velocity u for various values of grashoff number gr. the velocity profiles show that the velocity increases with an increase in gr. it is also shown that the velocity increases nearby the plate for higher gr more than for lower gr. fig. 2. velocity profile for different grashof numbers (gr) figure 3 demonstrates the effect of magnetic number m on the velocity. it is observed that the increase in m decreases the velocity profile. this means that increasing the magnetic field tends to slow the fluid flow. it is also shown that retardation of the flow can be achieved by law values of magnetic number. the effect of prandtl number on velocity and temperature behavior is illustrated in figures 4 and 5. increasing pr means decreasing thermal conductivity, and therefore reducing heat transfer rate. hence the effect of pr is to decrease velocity and engineering, technology & applied science research vol. 9, no. 4, 2019, 4361-4366 4364 www.etasr.com abdullah et al.: effect of non-uniform heat source and radiation on transient mhd flow past a … temperature. the profiles were obtained for different liquids. it is clear that for high pr the velocity and temperature magnitudes will be reduced significantly. figure 6 shows the effect of angle of inclination of the magnetic field α. it is noticed that increasing α will increase the perpendicular component of magnetic field and hence decrease the velocity. fig. 3. velocity profile for different values of magnetic parameter (m) fig. 4. velocity profile for different prandtl numbers (pr) fig. 5. temperature profile for different prandtl numbers (pr) fig. 6. velocity profile for different magnetic field inclination angles (α) the effect of the heat source term s on the velocity and temperature profiles is illustrated in figures 7 and 8. the velocity will increase as the heat source increases especially in the area around the plate. it is noticed that increasing the heat source will increase the plate and fluid temperatures. the temperature profile for different values of radiation parameter r is expressed graphically in figure 9. increasing r enhances the fluid temperature. figures 10 and 11 depict the velocity and temperature profiles for different time values. it is proven that increasing time will increase the fluid velocity and temperature of the plate and fluid. fig. 7. velocity profile for different values of heat source term (s) fig. 8. temperature profile for different values of heat source term (s) fig. 9. temperature profile for different radiation parameters (r) fig. 10. velocity profile for different time values (t) engineering, technology & applied science research vol. 9, no. 4, 2019, 4361-4366 4365 www.etasr.com abdullah et al.: effect of non-uniform heat source and radiation on transient mhd flow past a … fig. 11. temperature profile for different time values (t) figure 12 illustrates the effect of the heat flux frequency on the transient plate temperature behavior where the time is taken up to t=5. it is observed that the fluctuating behavior of the heat flux is reflected on the temperature behavior. a comparison between the numerical implicit solution and the exact solution for the dimensionless temperature in case of constant heat flux and in the absence of heat generation is shown in figure 13. it is observed that the two solutions are in full agreement. fig. 12. transient temperature for different values of heat flux frequency fig. 13. comparison of temperature numerical and analytical results vi. conclusions in this paper, a fully implicit numerical solution to the problem of transient free convective laminar flow past a moving vertical plate in the presence of periodic heat flux and inclined magnetic field has been presented. the velocity and temperature behaviors were studied for different dimensionless parameters by applying the crank-niclson technique, which is verified by an eigenfunction expansion method for constant heat flux, were computed. the effect of different parameters such as magnetic parameter with inclination angle, grashof number, prandtl number, heat source parameter, radiation parameter and time were studied. some of the conclusions of this work are: • the effect of mhd on the fluid flow appears through the magnetic parameter effect. magnetic field exerts a retarding influence on the fluid velocity. • increasing the grashof number will cause an increase of the velocity. • increased heat source increases velocity and temperature. • increasing the prandtl number will decrease velocity and temperature. • thermal radiation tends to enhance the plate and fluid flow temperature. • inclination angle of magnetic field will influence the fluid flow. • the fluctuating behavior of the heat flux is reflected on the temperature behavior. nomenclature bo magnetic flux density cp specific heat gr grashof number k thermal conductivity k * mean absorption coefficient m magnetic parameter pr prandtl number q constant heat flux at the surface qr radiative heat flux q0 heat generation coefficient r radiation parameter s heat generation parameter t * time t dimensionless time t * temperature t∞ free stream temperature u * velocity component in the x direction u dimensionless velocity x * , y * cartesian coordinates y dimensionless coordinate ω * frequency of oscillation ω dimensionless frequency α inclination angle of the magnetic field β volumetric coefficient of thermal expansion φ, δ separation variables θ dimensionless temperature λ separation constant ν kinematic viscosity σ electrical conductivity σ * stefan-boltzmann constant ρ density µ dynamic viscosity references [1] v. rajesh, s. v. k. varma, “heat source effects on mhd flow past an exponentially accelerated vertical plate with variable temperature through a porous 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sugunamma, “radiation inclined magnetic field effects on unsteady hydromagnetic free convection flow past an impulsively moving vertical plate in a porous medium”, journal of applied fluid mechanics, vol. 7, no. 2, pp. 275-286, 2014 [18] n. k. singh, v. kumar, g. k. sharma, “the effect of inclined magnetic field on unsteady flow past on moving vertical plate with variable temperature”, international journal of latest technology in engineering, management & applied science, vol. 5, no. 2, pp. 34-37, 2016 [19] p. t. hemamalini, m. shanthi, “heat and mass transfer on unsteady mhd flow in tow non-conducting infinite vertical parallel plates with inclined magnetic field”, international journal of mechanical engineering and technology, vol. 9, no. 3, pp. 521-536, 2018 [20] g. s. setha, p. k. mandal, a. j. chamkha, “mhd free convective flow past an impulsively moving vertical plate with ramped heat flux through porous medium in the presence of inclined magnetic field”, frontiers in heat and mass transfer, vol. 7, no. 23, pp. 1-12, 2016 [21] e. m. sparrow, r. d. cess, radiation heat transfer, augmented edition, hemisphere publishing corporation, 1978 microsoft word 17-838-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1297-1302 1297 www.etasr.com elbadawi et al.: developing an innovative and creative hands-on lean six sigma manufacturing… developing an innovative and creative hands-on lean six sigma manufacturing experiments for engineering education isam elbadawi mohamed aichouni noor aite messaoudene industrial engineering university of hail hail, saudi arabia i.elbadawi@uoh.edu.sa, isam149@gmail.com industrial engineering university of hail hail, saudi arabia m_aichouni@yahoo.co.uk mechanical engineering university of hail hail, saudi arabia n.messaoudene@uoh.edu.sa abstract—the goal of this study was to develop an innovative and creative hands-on project based on lean six sigma experiments for engineering education at the college of engineering at the university of hail. the exercises were designed using junction box assembly to meet the following learning outcomes: 1-to provide students with solid experience on waste elimination and variation reduction and 2-to engage students in exercises related to assembly line mass production and motion study. to achieve these objectives, students were introduced to the principles of lean manufacturing and six sigma through various pedagogical activities such as classroom instruction, laboratory experiments, hands-on exercises, and interactive group work. in addition, minitab 17 statistical package and quality companion 3 software were used to facilitate the lean six sigma exercises. the software application and hands-on manufacturing assembly were found to be extremely valuable in giving students the chance to identify which variables to control in order to minimize variation and eliminate waste. this research was funded by a grant from the deanship of academic research at university of hail for project number e26-ic, and under the umbrella of ministry of education within the framework of the national initiative on creativity and innovation in saudi universities at university of hail. keywords-innovation; creativity; engineering; education; lean manufacturing; six sigma; hands-on i. introduction the power that six sigma holds to accelerate innovation is through its inherent focus on continuous improvement. by a disciplined approach to innovative six sigma methodologies, efforts can be focused on identifying the hands-on activities that require a small time investment but deliver high learning effect. projects can then be prioritized for maximum employee workload reduction. utilizing six sigma methodologies, organizations have the potential of reducing employee frustration while simultaneously increasing the employee energy available to focus on innovation. a. hands-on approach it is often argued that engineering education must integrate engineering theory and practice in order to become more relevant to the needs of both students and market place. such integration is particularly important not only because the world has changed tremendously and new challenges have surfaced over the last decade, but also because a considerable number of the students who join engineering schools have probably never had their hands on any practical engineering project. at the present, this integration has become an essential practice in most engineering schools worldwide. however, the number and complexity of the project-based courses significantly vary among institutions with some having a project-based component to almost every engineering course [1] and others that have only a few of such projects. this issue becomes even more challenging when considering how to integrate theoretical concepts with the necessary training required for the production and manufacturing in the real world [2]. when hands-on projects are appropriately combined with virtual manufacturing software in the engineering education system, they do not only add value to the education and training of students, but become an essential component of the educational process [3]. b. lean manufacturing in [6], a work based on a three-year mit study in the automotive industry was described. the study showed that toyota outperformed the major us car manufacturers by a factor of 2:1 on quality, cost and time to market. they coined the term “lean” to describe the way the toyota production system (tps) sought to continually identify and eliminate waste. they described “lean” as a fundamentally different system “of thinking about how humans work together to add value”[7]. the term “lean” focuses on solving simple and minor problems and on the removal of waste. indeed, an important assumption underlying the lean methodology is that waste is the main limitation on profitability and that numerous and rapid improvements are more beneficial than analytical study. c. lean six sigma lean manufacturing and six sigma are often viewed as today’s two most important initiatives. therefore, the combination of these two techniques is believed to greatly improve the manufacturing process and to eliminate waste in time and money through simultaneously reducing variation and engineering, technology & applied science research vol. 6, no. 6, 2016, 1297-1302 1298 www.etasr.com elbadawi et al.: developing an innovative and creative hands-on lean six sigma manufacturing… improving manufacturing bottom line [4]. six sigma is a metric refers to 3.4 defects per million opportunities (dpmo), where sigma is a statistical term representing the variation around the process mean. how do lean and six sigma complement each other? this was an important question raised. it has been argued that lean cannot bring a process under statistical control, and six sigma alone cannot dramatically accelerate the speed of the manufacturing process or reduce invested capital [5]. therefore, a combination of the two resulted in lean six sigma defined as “a methodology that maximizes shareholder value by achieving the fastest rate of improvement in customer satisfaction, cost, quality, process speed and invested capital” [5]. table i below summarizes some of the six sigma tools and techniques that are applicable to the exercise projects described in this study. table i. dmaic methodology objective: define the problem (i.e opportunity) objective: measure current performance objective: analyze the root causes of problems objective: improve the process to eliminate root causes objective: control the process to sustain the gains. key define tools: house of quality project charter as-is process sipoc key measure tools: (ctqs) capability analysis (fmea) key analyze tools: seven tools, hypothesis tests regression analysis key improve tools: solution selection matrix to-be process map(s) key control tools: control charts contingency and/or action plan(s) d. statement of problem the problem of this research project is to develop a feasible way to impart the lean six sigma knowledge, principles, and tools to the real production and processing manufacturing through hands-on exercises. e. research objectives the researchers embarked on this study with the purpose of developing and testing a hands-on project based on lean six sigma exercises. the target students were those majoring in industrial and mechanical engineering at the university of hail (uoh) and enrolled in the quality and manufacturing courses during the first semester of the academic year 2015-2016. the general objective of this study is twofold: 1. to provide students with a solid experience on waste elimination and variation reduction 1. to engage students in exercises related to the assembly line mass production and motion study for the most part, the designed exercises focused on providing students with a solid theoretical introduction to the fundamentals of lean six sigma and to the analytical skills necessary for manufacturing process improvement. conversely, the hands-on project was designed to provide students with the know-how procedures for translating hands-on scale exercises processes to the factory floor. the educational objectives of the “lean six sigma handson exercises” are to: 1. introduce students to manufacturing process improvement methodologies, including hands-on experience with statistical and quality software 2. familiarize students with analytical methods to characterize, assess, and qualify these manufacturing process improvement methodologies 3. introduce six sigma quality methods as applied to manufacturing process improvement methodologies 4. familiarize students with the principles of lean manufacturing in an exercise setting that simulates a small manufacturing enterprise performing lowvolume and mix production ii. research method the study adapted a design for manufacturing washers, bolts, and nuts (wbn) assembly junction box described in [3] as a hands-on tool for students of industrial engineering at the university of hail. the junction box assembly was designed with a thorough understanding of the downstream manufacturing process and the assembly procedures were modified by the assembly team based on the feedback provided by the manufacturing designer. the variation of the wbn in junction box assembly enabled the teams to conduct several hands-on exercises in multiple concepts related to lean six sigma such as: 1. manufacturing process flow, variation journal development, waste identification 2. visual control, 5s, waste elimination 3. pull production system 4. work standardization 5. dmaic the junction box assembly consists of the materials illustrated in figures 1. fig. 1. water proof plastic junction box a. design for assembly manufacturing procedures each junction box assembly consists of one plastic junction box with one piece of each size of the bolts, nuts, and washers. the following steps were used to manufacture the assembly [3]: engineering, technology & applied science research vol. 6, no. 6, 2016, 1297-1302 1299 www.etasr.com elbadawi et al.: developing an innovative and creative hands-on lean six sigma manufacturing… 1. marking the drilling points for each bolt using the12cm × 12cm marking square 2. drilling the corners of the marked square with the appropriate bits starting with 6mm continuing the drilling process clock wise ascending to 12mm hole size 3. basic assembly: attaching each bolt to the appropriate hole as shown in figure 4. installing the appropriate washer to each bolt 5. tightening each nut to the appropriate bolt 6. repeating the above steps to manufacture 24 units b. lean six sigma models the variables (y) and (x) are defined in each model based on the installed components in each exercise according to specific instructions and procedures. each model represents a real mimic of actual manufacturing processing and production paradigm such as push-pull system, lean manufacturing, visual workplace, inventory control, poke yoke, 5s, etc. the authors designed the lean six sigma models to achieve the following create: 1. a smooth flow of the assembly process model 2. a clear and clean visual control model 3. a pull system model 4. a standardization of the tasks for each model each model shows how the manufacturing assembly rate of washers, bolts, nuts was improved and stabilized along with the use of lean six sigma tools. also, it shows the variation among the completed junction box assembly as a critical to quality (ctq) to measure the performance indicator from lean six sigma principles. one of the main goals of lean and six sigma models was to measure the process capability index (cp). cp can be calculated using the following equation [8]: cp = (usllsl) / 6σ (1) if only usl and lsl are given, where: usl=upper specification given, lsl=lower specification given, σ=standard deviation of the data. in this research, cp is constructed to express more desirable capability with in junction box assembly rate. the authors have developed a set of models using the junction box assembly, and each model was abstracted as shown in figure 2. fig. 2. six sigma abstract model diagram c. lean six sigma exercise the lean six sigma exercises format described here is sufficiently generic that it can be adapted for many different types of manufacturing systems. most of the exercises, as originally developed, require one or two several-hour of handson sessions to complete, but the addition of six sigma tasks added several hours to each hands-on session. these exercises have well-documented procedures and protocols, including supplemental instructional detailing each step of the exercise. the students assembled different models aimed at generating quantitative data that provides instructive examples in applying lean six sigma techniques to the manufacturing processes. a lean six sigma exercise starts with a problem statement followed by defining the primary metric, which aids to focus on the problem area and measures the input (x) and output or resulting (y). the primary metric for this exercise was the ‘the count of washers, bolts, nuts’ in addition to the arrangement of each set. to illustrate the common cause and the special cause variation in a typical lean six sigma process, the critical x’s which are the input to the process are represented in figure 3. the lean process always starts with identifying the value which is represented with the completion of assembling the correct size of washers and nuts on each bolt starting from with the 6 mm to 12mm clockwise assembly sequence. the value stream mapping (vsm) is the second step to determine the potential xs. as shown in figure 3, it shall be noted that the output or resulting y may also be variable, due to variations in the inputs. in this case, the prime y is the completion rate of the junction box model. fig. 3. lean six sigma implementation model d. define phase after being introduced to the exercise procedures, students were divided into teams and each team had a champion. the champion had to select an appropriate black belt and formulate tasks that must be undertaken during the define phase. these tasks include: 1. refining feasible exercise scope 2. setting-up exercise goals 3. estimating exercise challenges because the time period of each lean six sigma exercise is limited to a single academic semester, each exercise must have a suitable scope if it is to be successfully completed on time. in this phase students learn how to define the problem (i.e the opportunity). this phase guides the team to specify the variables for the opportunity effectively and to justify the commitment of resources so as to achieve the exercise goals. engineering, technology & applied science research vol. 6, no. 6, 2016, 1297-1302 1300 www.etasr.com elbadawi et al.: developing an innovative and creative hands-on lean six sigma manufacturing… various tools are used during this phase to ensure that the scope of the exercise and the opportunity are adequately defined namely 5s, ctq, project charter, and vsm. data related to the opportunity formulation was based on first time students indulge in the lean six sigma exercise. e. formulating the opportunity the opportunity formulated by the team was as follows: the current assembly rate for the washers, nuts, and bolts for one junction box is 70 pieces in 700 seconds. the goal set was to increase the rate to 99 pieces in 700 seconds by the end of the exercise. f. project charter assembly starts as the conveyor begins to movement until the junction box assembly reaches the packaging spot. the 6mm nuts were identified as a critical bottleneck for efficient junction box production flow. the misplacement of any item translates into a reduction in effective assembly capability, process delays and unsatisfied customer. g. voice of the customer (voc) a number of brainstorming sessions were held to discuss students and instructors’ observations about the assembly process. the outcome of these sessions indicated that there were several opportunities for improving the structure and processes related to the quality of assembly coordination. also voc indicated that the assembly process took longer than necessary and therefore negatively impacting the assembly completion rate. however, there are many opportunities to minimize unnecessary changes by improving the interaction process among teams. therefore, the researchers applied lean six sigma approaches to the assembly process in order to exclusively focus on reducing the assembly time. h. measure phase at this stage, the collected data was evaluated and sigma was calculated. the process baseline was established and each process in this phase had the purpose of mapping the assembly process and establishing methodology that describes the study in order to narrow the problem to its major factors. a tool such as the measurement system analysis (msa) can be used in the measure phase to ensure accuracy. as table ii below show, students were able to measure standard time and count for each size of the washers, bolts, and nuts assembly in junction box. table ii. standard time and count 6mm 8mm 10mm 12mm total all standard time /sec 270 180 150 100 700 standard count 32 28 22 18 100 washers standard time /sec 2 2 2 2 2 standard count 16 14 11 9 50 nuts standard time /sec 1-18 1-16 1-12 1-10 4-56 standard count 17 15 11 9 50 bolts standard time /sec 20 17 12 8 57 standard count 1 1 1 1 4 the exercise procedures were traced until the completion of each phase of junction box assembly. a sample was randomly selected and used to calculate the sigma level and the current assembly rate. the assembly process produces (100 pieces × 4 junction box × 4 assemblers × 4 teams × 3 shifts)= 19200. five types of defects were detected. the number of occurrences of each defect type is listed in table iii below: table iii. types of defects and number of occurrences defect type number of occurrences missing washer 73 double washers 42 defective part 16 loose assembly 8 cracked junction box 2 total number of defects 141 i. define defects a defect is defined as delay of the assembly process at any stage leading to the increase in the assembly time of each set of the junction box. defect per million opportunity (dpmo) = total no. of defects × 1,000,000 total no. of pieces × opportunities dpmo = (141×1000,000)/(19200×5) = 1468.75 sigma level for the above value of dpmo is equal to = 4.47 j. analyze phase analysis was performed on variables for which data can be readily collected, and then statistical analysis was used to test whether these factors (xs) had an influence on the project’s index (y) or not. for the statistical analysis, one set of the junction box assembly was randomly sampled from each shift over two weeks. each assembly was re-assembled to evaluate whether or not it would improve the assembly count and time. figure 4 shows the main effects plot for each factor with regard to assembly count. figure 5 identified the root cause analysis as follows: 1. manpower: students were unfamiliar with the teambased project, and they were speeding up the assembly process without paying attention to the sequence of the assembly process. 2. method: the process sequence was designed to facilitate a smooth assembly flow, but most students were rushing to randomly assemble the junction box which resulted in over processing and inventory waste 3. materials: the mix-up of washers, nuts and bolts in containers was found to be the main cause of delay, and the absence of size identification marks on the used items was causing time loss. 4. machine: part of the exercise was performed using the conveyor belt. the speed of the conveyor enhanced the engineering, technology & applied science research vol. 6, no. 6, 2016, 1297-1302 1301 www.etasr.com elbadawi et al.: developing an innovative and creative hands-on lean six sigma manufacturing… assembly process by reducing the motion and waiting time. fig. 4. random sample re-assembled data count assembly rate material manpower washers and nuts size items duplication machine method junction box assembly cause and effect conveyor belt speed assembly sequence manufacturing defect students' experience bolts length fig. 5. junction box assembly cause and effect the pareto chart in figure (6) indicates the major reasons for the delay of the assembly process. k. improve phase: applying 5s tool in lean six sigma define phase the purpose of the 5s model is to improve the assembly process by organizing the workplace through the following steps in table iv. the model begins with a normal mode where the assembly process starts random. then, an evaluation session for the count and waste identification is established according to the eight types of wastes. the collected data from the pilot test show an incremental improvement in the assembly processing. the measurement during the pilot test focused on the cycle time of each assembly and counting the repetition of the non-value added activities (waste). l. control phase control phase was critical to sustain the improvements made during previous phase and to maintain the solution for the problem. visual control was a common quality tools to keep tracking and managing the assembly processing in order to continuously improve the process. count 2 2 1 1 1 percent 28.6 28.6 14.3 14.3 14.3 cum % 28.6 57.1 71.4 85.7 100.0 c2 555025105 7 6 5 4 3 2 1 0 100 80 60 40 20 0 c ou nt pe rc en t pareto chart of c2 fig. 6. reasons for the delay of assembly process table iv. 5s lean manufacturing tool 5s goal eliminate or correct sort keep only what you need sort out wbn in separate containers according to size set in order a place for everything and everything in its place arrange containers according to size from right to left starting with 6mm and unto12 mm shine cleaning, and looking for ways to keep clean and organized clean the assembly area surfaces, remove items not needed in the exercise activities standardize monitoring the first three categories. sticking to the rules start the assembly process clockwise starting from 6mm unto 12 mm, label the containers and the process sequence sustain to maintain lean six sigma process number of workers without 5s training; number of daily 5s inspections not performed; number of personal items not stored; number of times job aids not available or up-to-date fig. 7. lean six sigma mode: parts count iii. discussion the observation of the lean six sigma exercises revealed that lean six sigma tools were used to identify and improve some input variables (critical xs) in a process. in some cases one of the critical xs may be related to technical problems. in such case, the application of lean six sigma could be beneficial in solving and improving the critical x. however, it would be fair to say, that lean is best used to address engineering, technology & applied science research vol. 6, no. 6, 2016, 1297-1302 1302 www.etasr.com elbadawi et al.: developing an innovative and creative hands-on lean six sigma manufacturing… production (or physics) problems [9] where flow in the process is not optimal, whereas six sigma is useful in identifying defects. total productivity could be improved by taking care of the critical xs through the following activities: x1: enhancing flexibility of resources utilization to optimize the flow of process by: • using individual containers in each assembly area • adding a table behind the assembly area to allow simultaneous to work on multiple tables • using the belt conveyor • x2: eliminate waste through improved inventory control • reconfiguring the container-refill sequence • reducing the inventory level to a maximum of 50 per pin • using visual controls to display product status according to a color code • x3: pull system • initiating kanban inventory control • status inventory and develop electronic inventory logs to track storage • x4: standardize work • preparing a list of standardized activities with clear roles, responsibilities and accountabilities • conducting the assembly process clockwise starting from 6mm and unto12 mm. • labelling the containers and the process sequence and using colour codes iv. conclusion this study demonstrated the key steps in developing innovative and creative hands-on exercises which introduce students to lean six sigma and utilizes the assembly line concept for data collection. four modules have been ‘studenttested’ as exercises appropriate for quality in manufacturing courses: the normal, 5-s, stationary and motion modes. these modes can be disseminated to other engineering courses. there is considerable scope for developing more modules to broaden the incorporation of lean six sigma topics and the depth and extent of quality and manufacturing. waste elimination and variation reduction prove very useful in generating sufficientlylarge (statistically significant) data for lean six sigma analysis. in addition, the study has shown that design for manufacturing and assembly is a methodology that works well in facilitating lean six sigma through waste elimination and cycle time minimization. the washers, bolts, and nuts junction box assembly was found to be an efficient and easy to use in lean six sigma model to measure the level of improvement in the manufacturing process. overall, the study was rather enjoyable and beneficial for students and enhanced the quality of the engineering education process. it is recommended that each lean six sigma hands-on be visualized through computer graphics virtual manufacturing programs before hands-on practice. acknowledgment the current undertaken research is supported by funded by the ministry of education within the framework of the national initiative on creativity and innovation in saudi universities and the deanship of academic research at university of hail by a grant for project number (e-26-ic). this is gratefully acknowledged. v. references [1] l. carlson, j. sullivan, “first year engineering projects: an interdisciplinary, hands-on introduction to engineering”, asee annual conference, pp. 2039-2043, 1995 [2] i. elbadawi, d. mcwilliams, t. tetteh, “enhancing lean manufacturing: learning experience through hands-on simulation exercises”, simulation and gaming journal, vol. 41, no. 4, pp. 537– 552, 2010 [3] i. elbadawi, “3d design process for manufacturing and assembly table top tools for incremental continuous improvement (kaizen)”, technology interface international journal, vol. 15, no. 1, pp. 28-34, 2014 [4] a. k. verma, simulation tools and training programs in lean manufacturing, nsrp-ase report no.0301-11, norfolk, va: old dominion university, 2003 [5] m. l. george, lean six sigma: combining six sigma quality with lean speed, mcgraw-hill, new york, ny, 2002 [6] j. womack, d. roos, d. jones, the machine that changed the world : the story of lean production, harper perennial, 1991 [7] j. womack, d. jones, lean thinking, simon & schuster, new york, 1996 [8] d. montgomery, introduction to statistical quality control, john willey & sons, inc., new york, ny, 2004 [9] g. ballard, the last planner system of production control; ph.d. dissertation, the university of birmingham, u.k., 2000 engineering, technology & applied science research vol. 8, no. 4, 2018, 3228-3233 3228 www.etasr.com siddiqui et al.: reduced feature set for emotion based spoken utterances of normal and … reduced feature set for emotion based spoken utterances of normal and special children using multivariate analysis and decision trees maria andleeb siddiqui department of software engineering ned university of engineering and technology karachi, pakistan mandleeb@neduet.edu.pk syed abbas ali department of computer science & information technology ned university of engineering and technology, karachi, pakistan saaj@neduet.edu.pk najmi ghani haider department of software engineering ned university of engineering and technology karachi, pakistan najmi@neduet.edu.pk abstract—the current paper deals with the use of multivariate data analysis and decision tree methods in order to reduce the feature set for the normal and special children speech in four different emotions: anger, happiness, neutral and sadness. ten features were extracted, by an algorithm implemented in a previous study to classify the speech emotions of normal and special children. in the current study, the best features are selected using multivariate analysis: principal component analysis (pca), factor analysis and decision tree. step by step pca is applied to reduce the feature set according to the variables that are collinear. the obtained reduced feature sets are applicable to both normal and special children samples. experimental results revealed that pca yields the feature set comprising pitch, intensity, formant, lpcc and rate of acceleration. factor analysis provides three feature sets out of which the feature set comprising of rasta plp, mfcc, zcr and intensity provides the best result. decision tree yields a feature set comprising energy, pitch and lpcc. keywords-speech emotions; pca; factor analysis; decision tree; features i. introduction emotion recognition system identifies the emotional state from voice [1], therefore it is called speech emotion recognition (ser). there are four modules of ser: input, feature extraction, feature selection and classification of emotions [2]. prosodic features, particularly pitch, intensity and duration were used in early research studies. currently, lld’s features such as shimmer, jitter, harmonic to noise ratio (hnr) and cepstrum have been used extensively [3, 4]. lpcc and mfcc were also accompanied in the speech feature set [5]. in [6], 40 depressed patients and 40 control subjects were used in a study for speech feature analysis. characteristics of depressed patients were found using anova analysis and the results were linked to gaussian mixture model (gmm) and support vector machine (svm). autism spectrum disorder comorbid for children (asd-cc) psychometric properties were evaluated and developed in [7]. confirmatory factor analysis (cfa) is used for the factor structure of the korean version of asd-cc. in [8], ten features were extracted: frequency, pitch, intensity, rate of acceleration, formant frequencies, log power, log energy, rate of zero passages, mel frequency cepstrum coefficient (mfcc), linear prediction cepstrum coefficient (lpcc). the extraction of frequency starts with the speech signal loading and the conversion of analog signal into numeric data. after loading, maximum and minimum frequency were set and fast fourier transform (fft) of windowed signal was performed as shown in (1). followed by the cepstrum calculation the frequency is extracted as shown in (2).  (1 .* ( )) ms fft x hamming length x (1)  / 1 1 f fs ms fx   (2) where ms1=windowed signal, fft=fast fourier transform, f=frequency, x=input signal, fs=sampling frequency, fx=input frequency. for pitch extraction, signal acquisition and signal processing are the same as in frequency extraction. fft is applied on the processed signal. discrete fourier transform (dft) is taken of the fft signal as in (3). then the log of fft is calculated. after that the real cepstrum is calculated and it is the absolute value of filtered log of dft as shown in (4). then finally real cepstrum pitch is extracted given in (5).   dfty abs fft x (3)  10 dft log dfty (4)   _ 16 : _ rcp real ceps length real ceps (5) (dft=discrete fourier transform, rcp=real cepstrum pitch). the magnitude of the dft signal with log10 is filtered as in (6). the conversion of the magnitude into decibels and transpose result of decibel gives out intensity as shown in (7).     20 * 10 1 : m log abs y length x eps  (6) engineering, technology & applied science research vol. 8, no. 4, 2018, 3228-3233 3229 www.etasr.com siddiqui et al.: reduced feature set for emotion based spoken utterances of normal and …  2 i mag db m (7) where m=magnitude, y=filtered signal, x=input signal, i=intensity, mag2db=magnitude to decibels. processing of the signal involves the time instant calculation as given in (8). the derivative of speed gives the velocity in (9). the gradient of velocity by 0.01 yields the acceleration in (10). finally the average rate of acceleration is calculated by taking the mean of acceleration.         1 0.4 * . ^ 8 4 10.8 * . ^ 3 64.4 * . ^ 2 2 .2 * 4.4 x t t t t      (8) v=diff(x1) (9) acc=gradient(v,0.01) (10) where x1=speed, t=time instant, v=velocity, diff=derivative, acc= acceleration. for extracting the formant frequency, preprocessing involves setting the number of coefficients according to the rule of thumb for formant estimation given in (11). after that calculation of the linear prediction coefficients is carried out in (12). then the frequencies are calculated using (13). the imaginary part of the root gives out formant frequencies. 2 / 1000 ncoeff fs  (11)  a lpc ncoeff (12)   r roots a (13) where ncoeff=number of coefficients, fs=sampling frequency, lpc=linear prediction cepstrum, a=linear prediction cepstrum coefficient, r=roots. preprocessing involves the setting of the sampling rate and sampling window size for log power extraction. after that the frame size is calculated and windowing is applied. then the average energy is extracted. average power is yielded by dividing the average energy with window size as shown in (16). _ * windowsize sampling rate fs (14)  _ . ^ 2 average energy sum result (15) _ / lp average energy windowsize (16) where, fs=sampling frequency, sum=sum of frame size of windowed signal, lp=log power. preprocessing involves the same procedure as log power extraction. average energy is calculated by applying windowing on signal according to window size and frame size, given in (17).  _ . ^ 2 average energy sum result (17) signal acquisition and signal processing are the same as in pitch and frequency estimation given in (18).      1 2 / 2 / rzp sum abs sign y sign y windowsize  (18) where rzp=rate of zero passages, y1=maximum frequency, y2=minimum frequency. preprocessing involves setting and analysis of frame duration and frame shift. it is followed by the setting of the pre emphasis coefficient alpha=0.97, the number of filter bank channels m=20 and lower and upper frequency limits. then the hertz to melwrapping function is calculated. application of dct matrix routine and the magnitude of the spectrum are calculated in (19). the filter bank is applied to the unique part of the magnitude spectrum. finally the calculation of cepstral liftering gives mfcc (20).            ( * ( * ) @ , 2.0 / 0 : 1 .',1, * 1 : 0.5 / , ,1 dctm n m sqrt m cos repmat n m repmat pi m m n    (19)      @ , 1 0.5 * * * 0 : 1 /cl n l l sin pi n l   (20) where dctm=secrete cosine transform matrix, n=number of coefficients, m=number of filter bank channels, l=length of channel, cl= cepstrum lifter. preprocessing involves the estimation exponent of next high power according to signal size. then the number of prediction paths ‘p’ is set. calculation of the number of linear prediction of coefficients is carried out. fourier transform is applied on x-lpc according to the number of shifts n as given in (21). the logarithm of lpc is taken and then the lpc coefficients are converted back to spectra. the number of cepstra is then set and the first and second derivative of lpcc features are estimated to have the value of coefficients in (22).    _ , x lpc lpc x p (21)  _ , lpcc fft x lpc n (22) where, lpc=linear prediction coefficients, x=input signal, p= prediction paths, fft= fast fourier transform, lpcc=linear prediction cepstrum coefficients, n= number of shifts. after extracting these features, speech emotion recognition of normal and special children (sernsc) is implemented. to make the algorithm run efficiently, dimension reduction is a valuable approach. the advantage of dimensionality reduction is that it helps to discover the grouping of features that for sure run the algorithm with improved accuracy [9]. detection of projection subspace basis evaluation is suggested in [10]. for deduction it uses generalized hyperbolic mixture (hmmdr) fit. this method is well accepted along with discriminant analysis, model based classification and clustering analysis. two sdr techniques are demonstrated in [11]. the relationship between partial least square (pls) and principal component regression (pcr) is explained. dimensionality reduction by joining features is one of the best strategies proposed so far [12]. sparse partial least square regression (splsr) is investigated in depth in [13]. it is revealed that the recognition rate of splsr is up to 79.23% and it is superior when compared to other methods used for dimensionality reduction. in this paper, feature reduction is presented using mu dec con acc me cep per a. rec dat of th app loa nam th inf cat thr fun hyb cla sco as 1) 2) em cla est 3) em engineerin www.etasr ultivariate ana cision tree me seven featur nsideration fo celeration, zer el frequency c pstrum coeffi rceptual linear classificatio the classifi cognition for n ta set is the sa the extracted he process of plied for dec ading the sam me, file path c hen, the file na formation, fil tegories are resholding fea nction for deci features=all function [ca brid_decision the test s assification fun ore position. t follows step#1: if result of p set category categories_o else category categories_o step#2: after the ca motion is lab assification ac timated in (25)   ,rn cn find step#3: if result of p set emotion _output(1). else if resul set emotion _output(2). else if resul set emotio motions ng, technology r.com alysis that con ethod. ii. me res and three or analysis: p ro 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misclassified larity rate. en rate in true n all emotions s whereas the variate analysi xtracted featur ormal and sp and … n and . the zcr, eature elp of to the e tree duced lating hown cy of wn in with lumn. other d. the nergy, e and . the least s and res of pecial chi and fro and utt chi exp com fa pl fre com 3) com dev fea n [1] [2] [3] engineerin www.etasr ildren in four d sadness). th om two multiv d decision tr terances in u ildren. the periments are mprising of p actor analysis lp, zcr, inten equency) and mprising of ra decision tre mprising of en velop an exp ature sets in or node class 1 28.335 2 16.6665 3 45.00 4 91.65 5 83.15 6 71.5 7 55.00 fig. 7. c s. ramakrishn in: speech en applications, p s. pahune, n. speech and im recent and inn 3, no. 2, pp. 13 b. schuller, a devillers, l. relevance of f user states: low 2007, antwerp ng, technology r.com r different em he reduced fea variate techni ee is applied urdu language observations e: 1) pca p pitch, intensity provides thre nsity and mf (lpc, pitch a asta plp, zcr ee technique nergy, pitch an periment to a rder to analyze table iii. sification accura condition 5>accuracy>=28. 5>accuracy>=16. 0>accuracy>=45. 5>accuracy>=91. 5>accuracy>=83. 5>accuracy>=71. 0>accuracy>=55. confusion matrix refe nan, “recognition nhancement, mod pp. 121-138, inte mishra, “emotio mage processing novation trends 34-137, 2015 a. batliner, d. s vidrascu, n. a feature type for t w level descripto p, belgium, pp. 22 y & applied sci motions (anger, ature set and fe iques (pca a d on the emo e for both n obtained fr provides a re y, formant, l e sets of redu cc), (energy, and power) ou r and mfcc s provides a r nd lpcc. aut apply the red e the classifier decision tree r acy less t nod .335 nod .6665 mfc .00 pow .65 nod .15 nod .5 nod .00 ener for decision tree erences n of emotion fro deling and recog ech, 2012 on recognition t g: a review”, i in computing an seppi, s.steidl, t amir, l. kessous the automatic cla ors and functiona 253-2256, august ience research siddiqui et al.: , happiness, n eatures are obt and factor ana otion based sp normal and s rom demonst educed featur lpcc and ro uced features , roa and fo ut of which th shows better re reduced featur thors are focus duced feature ’s accuracy. results than de great than n de 2 node cc ener wer node de 5 ener de 6 pitc de 7 lpc rgy intens factor reduction om speech: a re gnitionalgorithm through combina nternational jour nd communicatio t. vogt, j. wag s, v. aharonson assification of em al”, in: intersp t 27-31, 2007 h v : reduced feat neutral tained alysis) poken special trative re set oa. 2) (rasta ormant he set esults. re set sing to s and ter node e 3 rgy e 4 rgy ch cc sity eview”, ms and ation of rnal on on, vol. gner, l. n, “the motional peech [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] vol. 8, no. 4, 20 ture set for em b. schuller, g. comparing b interspeech y. zhou, y. su speech emotion research chall 28-29, 2009 s. alghowinem breakspear, “c interspeech k. m.chung, d autism spectrum in autism spec m. a. siddiqui for features e children speec computer scien 2017 l. e. aik, l. c multivariate sta aip conferenc publishing, 201 ] k. morris, p. d analysis, and di computational ] y. w. lin, b equivalence of in the sufficien intelligent labo ] k. mallick, s. criterion: an classification”, ] y. jingjie, x. based on spars pp. 465–470, 20 018, 3228-3233 motion based sp rigoll, “recogn ag of frame h, brighton, uk, un, l. yang, y. n recognition”, enges in comput m, r. goecke, characterizing d h, florence, italy d. jung, “validity m disorders como trum disorders, v i, n. g. haider, s extraction towar ch emotions in u nce and network c kiang, z. b. m atistical methods e proceedings, p 17 d. mcnicholas, imension reductio statistics and dat b. c deng, q. s partial least squa nt dimension red oratory systems, v bhattacharyya, “ efficient dimen procedia techno wang, w. gu, se representation” 013 3 poken utteranc nizing interest in s and 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2012 h emotion recog coustics, vol. 38, and … peech– atures”, 2009 ures to nce on cember er, m. ation”, 013 sion of esearch proach special rnal of 88-195, on the es”, in: 1, aip minant xtures”, 2016 , “the ression cs and margin r text gnition no. 4, microsoft word 23-3549_s1_etasr_v10_n4_pp6016-6020 engineering, technology & applied science research vol. 10, no. 4, 2020, 6016-6020 6016 www.etasr.com kandhro et al.: performance analysis of hyperparameters on sentiment analysis (sa) model performance analysis of hyperparameters on a sentiment analysis model irfan ali kandhro department of computer science sindh madressatul islam university karachi, pakistan irfan@smiu.edu.pk sahar zafar jumani department of computer science sindh madressatul islam university karachi, pakistan sahar@smiu.edu.pk fayyaz ali department of software engineering sir syed university of engineering and technology, karachi, pakistan fayyaz.ali@ssuet.edu.pk zubair uddin shaikh department of software engineering sindh madressatul islam university karachi, pakistan zubair@smiu.edu.pk muhammad arshad arain department of software engineering sindh madressatul islam university karachi, pakistan m.arshad@smiu.edu.pk aftab ahmed shaikh department of software engineering sindh madressatul islam university karachi, pakistan aftab.shaikh@smiu.edu.pk abstract-this paper focuses on the performance analysis of hyperparameters of the sentiment analysis (sa) model of a course evaluation dataset. the performance was analyzed regarding hyperparameters such as activation, optimization, and regularization. in this paper, the activation functions used were adam, adagrad, nadam, adamax, and hard_sigmoid, the optimization functions were softmax, softplus, sigmoid, and relu, and the dropout values were 0.1, 0.2, 0.3, and 0.4. the results indicate that parameters adam and softmax with dropout value 2.0 are effective when compared to other combinations of the sa model. the experimental results reveal that the proposed model outperforms the state-of-the-art deep learning classifiers. keywords-student feedback; sentiment analysis; performance analysis; lstm i. introduction in an education management system (ems), assessing the performance of faculty members is becoming an important component. it’s not only helpful for improving the quality of course content and teaching style but it is also used by the faculty annual appraisal process. the course evaluation is typically collected at the end of the semester of each course and a set of questions are answered in likert scale, open-ended, and self-evaluation approach. the combined response is used as a metric to measure the quality of the teaching staff. the evaluation form also provides room for open feedback which is typically not entertained in the performance appraisal due to lack of automated methods [1-3]. the textual data may contain some important information about the subject understanding, comprehension, regularity, and presentation skills and may also provide clear suggestions for improving the quality of teaching. this kind of information may not get from the likert scalebased feedback [4]. and conversely, getting sense out and understanding the semantic of text from the textual feedback manually is a painstaking task and as a result, and textual feedback is not properly utilized [3]. the main aim of this paper is to analyze and understand the textual feedback automatically and develop qualitative and quantitative metrics that can estimate the performance of a teacher. this work comes under the promising and emerging area of opinion mining which has gained eminence since the uprising of the world wide web. a lot of relevant research has been reported recently. researchers have extracted sentiments from comments posted online in websites and forums [5], movie and other review sites [6-7], social networking sites [8-9], course and teacher evaluations [3, 10], and so on. the main focus of a sentiment analysis model is on extracting and determining the writer’s feelings form a piece of text. the feeling might be his or her opinion, emotion, and attitude. the most valuable step of this analysis is to classify the polarity of the given text as positive, neutral, and negative [5, 11]. similarly, the obtained work aims to categorize the polarity of student comments in terms of these three labels. this paper suggests suitable hyperparameters for training and testing a sentiment analysis (sa) model and provides a comprehensive strategy for investigating the effects of the hyperparameter tuning model with deep learning lstm approach. the experiment was carried out with different tuning strategies to induce and evaluate the relevance of hyperparameters using student feedback dataset. ii. related work table i shows some related work carried out using combined methods of machine learning, deep learning, and other conventional techniques. this part briefly summaries studies interrelated to the sentiment analysis of web contents regarding user emotions, opinions, and reviews towards different matters and products using deep learning approaches. the opinion mining task can be powered by various models such as deep learning models. these models include recurrent neural networks, recursive neural networks, convolutional neural networks, and deep neural networks. this section corresponding author: irfan ali kandhro engineering, technology & applied science research vol. 10, no. 4, 2020, 6016-6020 6017 www.etasr.com kandhro et al.: performance analysis of hyperparameters on sentiment analysis (sa) model depicts the efforts of different researchers towards applying machine and deep learning models for performing classification and opinion analysis in a variety of datasets [23]. authors in [24] proposed a novel convolutional neural network (cnn) framework for visual sentiment analysis to predict visual content. transfer learning and hyperparameters have been used with biases and their weights were utilized from pre-trained googlenet with 22 layers for sentiment analysis. it has been optimized by using sgd (stochastic gradient descent) algorithm. the authors have developed a deep learning-based system for twit text analysis and focused on the weight parameters tuning of the cnn [25]. the long short-term memory model [22] has been proposed to analyze the student’s sentiments from textual student feedback of course evaluation of 2018-2019. authors in [23] utilized multinomial naive bayes, stochastic gradient descent, support vector machine, random forest, and multilayer perception classifier to analyze the sentiments expressed by students through textual feedback. authors in [27] focused on the aspect-based opinion mining method for recognizing the sentiments of a social movies review dataset. authors in [28] used the k-means/svm approach for identifying the social issues in sa. table i. miscellaneous techniques ref. techniques dataset size limitation result [1] srs, nrc lexicon students comments (coursera dataset) 4000 it is good only when data are cleaned and formal overall 90%, same teacher (85% p and 15% n) [2] deep feed forward neural network twitter database 2000 limited sample 75% [3] svm sentiment classifier lsabased filtering internet blogs chinese movie reviews 8000 small display capability of cellular devices 85% [4] dcnn+lstm twitter data 3,813,173 it cannot process very long sequences if using tanh as its activation function better accuracy than svm and naive bayes and less maximum entropy [5] analyzing financial news using lexical approach newspapers (the star online, national news agency of malaysia) 200 word loss st 76.7% and non st 82.4% [6] svm, naive bayes, complement naive bayes students reviews at the university of portsmouth 1036 performance comprised when trained class in model highest accuracy at 94%, followed by cnb at 84% [7] lexicon based, machine-learning and hybrid approaches comments in spanish 1000 issue with long sentence analysis the accuracy through the hybrid approach (83.27%). [8] lexicon in thai, svm, id3 and naive bayes student reviews at loei raja hat university 175 only 10 attributes for positive and negative 97% highest accuracy of svm [9] lexicon with 167 positive and 108 negative keywords feedbacks by students, obtained from ratemyprofessors.com 1148 the small data set of students’ comments was utilized to teacher evaluation the student comment text corpus score should be 0.67 [10] latent dirichlet allocation, svm, naive bayes and maximum entropy. movie reviews dataset 75 missing values and incomplete data svm 82.90%, naive bayes 81.50%, maximum entropy 81%, lda 88.50% the adopted system analyzed sentiments from macro and microblogs. the core reason for this study was to get user opinions and attitudes about hot topics and events by implementing cnn. cnn prevails over the problem of explicit feature extraction and learns completely through the training data. to gather the data from the target, the input url and crawler have been implemented. one thousand micro-blog comments were collected and divided into three labels: 300 negative, 274 neutral, and 426 positive. this study was compared with previous studies which used svm, crf and additional methods to perform sa [26]. iii. methodology the presented methodology classifies the students’ sentiments as positive, neutral and negative. the model workflow is shown in figure 1 and is analyzed below. a. data preprocessing the collected dataset is not well organized and in order to extract the meaning and information from the text we need strong data preprocessing techniques. there are several steps applied for the removal of spelling errors, grammatical mistakes, and urls. the details are described below: • punctuation consists of the special symbols and numbers, which were removed from the text, as these symbols are useless and only create ambiguity in processing. • tokenization is the process of splitting a sentence into words. • after tokenization, case conversion is performed to convert the uppercase tokens into lower case i.e. (good, good). • in nlp, stop words are a set of commonly used words such as determiners, conjunctions, and prepositions. these words are worthless for sentiment analysis and classification, and they are removed before training the model. b. word embedding the word embedding presents a dense representation of words and their relative significance. it can be learned from text data and reused among various applications. the word embedding maintains the relations of words, and captures context and semantics of particular words in text documents. in this model we used a pre-trained word2vec model as input in our lstm network and that model produced 300-dimensional vectors for processing the millions of words and get support from the bag-of-words scheme. engineering, technology & applied science research vol. 10, no. 4, 2020, 6016-6020 6018 www.etasr.com kandhro et al.: performance analysis of hyperparameters on sentiment analysis (sa) model c. lstm the representation of sentence in a sequence form was conducted by using the lstm network. the first layer used was the embedded layer that contains 32 length vectors to represent every word. the next layer is the lstm which contains 100 memory units. the final layer is the classification stage, where the model used a dense layer as the output layer with a single neuron. the model used the activation function to give a value between 0 and 1 for the predications of two classes. the model adopted log or entropy loss to execute and process the binary classification problem, and dropout ratio with lstm to maintain the learning and convergence of the network. fig. 1. system architecture of the proposed lstm model. d. hyperparameters testing in the model, the single hidden layer has 300 nodes which are the dimensions of a word in a form of a vector. the outputs of neurons were shaped with the activation functions (adam, adagrad, nadam and adamax). they push the output results up and down in a nonlinear fashion depending on the magnitude. when the magnitude is high then signals disseminate, and take their part at shaping the final prediction of the network. with the use of the activation function, the overall demonstration of the lstm model is highly complex and nonlinear, therefore the softmax, softplus, sigmoid and relu optimization functions are used for minimizing the error of the model. besides, to avoid the risk of overfitting, the regularization or shrinking approach has been used by making coefficients zero (dropout used between 0.1 to 0.4). after testing various combinations, the dense layer has a sigmoid activation function deployed for binary sentiment classification. in the last layer, we implemented the softmax activation function for the multi-class sa problem. iv. results and disscusion the experiments were conducted on a course evaluation dataset containing 3000 students’ comments [23]. in the dataset each feedback record contains fields such as teacher’s id, course name, comment, label, and semester. the dataset is divided into three groups for training (70%), testing (20%), and validation (10%). the research was conducted on sa where labels were 0 for negative, 1 for positive, and 2 for neutral. the diverse and blend parameters were tested considering regularization, optimization, and activation, in order to achieve the highest accuracy of the model as shown in figures 2 to 4. the performance of the sa model was greatly feasible and effective as compared to conventional models, and lstm sa model does not require prior knowledge such as sentiment lexicon and syntactic parsing. moreover, the lstm network has a long term memory to the context of the comment, which makes up the cons of the traditional sa. in a similar manner, the model adopted parameters are regularization, optimization, learning rate, and decay. and all these play a large part in reducing overfitting. the model also integrates max pooling, dropout, and normalization approach to reduce overfitting. by reducing dimensionally, max pooling performs best at a size of 2. dropout layers were assessed at different locations in the network and they were found to be most helpful after max pooling and before normalization. the model implemented the cross-entropy loss function which basically computes the error between the true label and the predicated label. figure 2 shows the validation accuracy of the model with a dropout value 0.2, “adam” optimizer, and softmax, soft plus, sigmoid, and relu activation functions. the results indicate that the accuracy of the model is outstanding with soft plus. fig. 2. validation accuracy for 0.2 dropout and adam optimizer. figure 3 depicts the accuracy of the model with softmax activation, adam optimizer, and dropout values of 0.1, 0.2, 0.3, and 0.4. the results indicate that the accuracy of the model is outstanding with a dropout value of 0.1. in the same way figure 4 compares the accuracy of the model with softmax activation and 0.2 dropout for adam, adagrad, nadam, and adamax optimization functions. the results indicate that the engineering, technology & applied science research vol. 10, no. 4, 2020, 6016-6020 6019 www.etasr.com kandhro et al.: performance analysis of hyperparameters on sentiment analysis (sa) model accuracy of the model is better with a dropout value of 0.1. table ii shows the experimental results obtained by the model on the student feedback dataset. the study was tested on 80 different combinations of parameters with 64 batch size for 30 epochs. the activation functions used were adam, adagrad, nadam and adamax, and hard_sigmoid, the optimization function were softmax, softplus, sigmoid, and relu, and the dropout regularization ranged between 0.1 to 0.4. the accuracy of the model was found to be higher with softmax, adam, and dropout ratio between 0.1 and 0.2. it has been noted that when the dropout value was 0.1 the model exhibited 89% training and 96% validation accuracy. similarly, when the dropout value was set at 0.2 the model accuracy improved to 90% training and 97% validation accuracy. fig. 3. validation accuracy for softmax activation function and adam optimizer. fig. 4. validation accuracy for 0.2 dropout and softmax activation function. v. conclusion in this paper, the learning capability of three different techniques, namely activation, optimization, and regularization were investigated for student’s sa from textual feedback. the course evaluation dataset used contains 3000 comments with labels (0,1, and 2). the dataset was divided into training, testing, and validation subsets. the lstm based deep learning method has been used in the sa model. the unigram and bigram bag-of-words approach has been used for feature extraction. in order to improve the performance of the model, preprocessing and filtering have been adopted. it has been shown that, out of 80 tested models only two performed with outstanding accuracy in terms of training, testing, and validation as shown in table ii and could be used as preeminent parameters on real-time feedback sa analysis. future work will include multi-lingual and fine-grained analysis of students’ comments at the aspect level. table ii. hyperparameter comparison activation optimization dropout validation accuracy training accuracy softmax adam 0.1 0.89% 0.96% softmax adagrad 0.1 0.89% 0.92% softmax nadam 0.1 0.88% 0.93% softmax adamax 0.1 0.89% 0.94% softplus adam 0.1 0.86% 0.91% softplus adagrad 0.1 0.86% 0.92% softplus nadam 0.1 0.85% 0.90% softplus adamax 0.1 0.86% 0.91% sigmoid adam 0.1 0.89% 0.93% sigmoid adagrad 0.1 0.82% 0.87% sigmoid nadam 0.1 0.82% 0.87% sigmoid adamax 0.1 0.83% 0.89% relu adam 0.1 0.88% 0.93% relu adagrad 0.1 0.86% 0.91% relu nadam 0.1 0.87% 0.90% relu adamax 0.1 0.81% 0.91% hard_sigmoid adam 0.1 0.87% 0.89% hard_sigmoid adagrad 0.1 0.86% 0.89% hard_sigmoid nadam 0.1 0.88% 0.92% hard_sigmoid adamax 0.1 0.85% 0.91% softmax adam 0.2 0.90% 0.97% softmax adagrad 0.2 0.90% 0.95% softmax nadam 0.2 0.90% 0.96% softmax adamax 0.2 0.88% 0.95% ……… ……… ………. …….. ……… hard_sigmoid adamax 0.4 0.85% 0.91% epochs: 30, batch size: 64 references [1] s. m. kim and r. a. calvo, “sentiment analysis in student experiences of learning,” presented at the 3rd international conference on educational data mining, pittsburgh, pa, usa, jun. 2010, pp. 111–120. 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[28] m. madhukar and s. verma, “hybrid semantic analysis of tweets: a case study of tweets on girl-child in india,” engineering, technology and applied science research, vol. 7, no. 5, pp. 2014–2016, 2017. microsoft word 6-2333_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3521-3524 3521 www.etasr.com khaskheli et al.: performance evaluation of locally-produced waste cooking oil biodiesel … performance evaluation of locally-produced waste cooking oil biodiesel with conventional diesel fuel abid ali khaskheli department of mechanical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan abidali_lifeskill@yahoo.com gordhan das walasai department of mechanical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan valasai@quest.edu.pk abdul sattar jamali department of mechanical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan jamali_sattar@yahoo.com qadir bakhsh jamali department of mechanical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan qadirquest@gmail.com zafar ali siyal department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan zafarsiyal@yahoo.com abdullah mengal department of mechanical engineering, balochistan university of engineering and technology, khuzdar, pakistan ahmengal@yahoo.com abstract—increasing environmental concerns forced us to look for cheaper, reliable and secure sources of energy. fossil fuels like oil, coal, and natural gas are having limited supplies and are depleting fast. both energy security and environmental concerns have resulted in inclination towards renewable energy sources. biodiesel does not contain petroleum, but it can be blended with petro-diesel in various mix levels. this research investigated biodiesel produced by the use of cheap waste cooking oil, collected from the local market of nawabshah, pakistan. the collected waste oil was converted into biodiesel by transesterification process at pcsir laboratory, karachi. the fuel samples were tested in a diesel engine test bed unit at the thermodynamics laboratory of quaid-e-awam university. biodiesel blends were compared with the conventional diesel fuel. the comparative analysis of the performance parameters concluded that brake specific fuel consumption of b30 (biodiesel 30%+diesel 70%) mix was 6.9% higher than that of 100% diesel. the brake thermal efficiency of b30 decreased about 4.75% in comparison with conventional diesel. keywords-biodiesel; wco; bsfc; bte; engine i. introduction biodiesel can be produced with the use of waste cooking oil (wco) as raw material. four types of wco, sunflower, maize, olive and palm can be used for the production of biodiesel [1]. global petroleum production is decreased while the current reserves are limited [2]. b100 is generally known as fresh fiery alternate fuel and can be produced from domestic and renewable resources. it comprises no petroleum and can be blended by any ratio level with petroleum diesel to produce biodiesel blends. biodiesel is produced by the use of methanol and ethanol with alkali catalyst. biodiesel blends can be used with conventional diesel with or without any major modification. wco biodiesel has less ignition delay. the blend of 20% wco biodiesel + 80% diesel has good brake thermal efficiency and indicates slightly more specific fuel consumption [3]. it is used as an environmentally friendly fuel. it has decreased greenhouse gas emissions and particulate matter emissions and other air toxics. biodiesel reduces premature exhausting of fuel pumps and recovers lubricity [4]. ii. related studies wco biodiesel is renewable, biodegradable and nontoxic. physical parameters like methyl ester fatty acids which are produced by the esterification process are similar to those of diesel. blended biodiesel can be used in engines directly without any modification. other feed stocks have also been used in the synthesis of biodiesel [5-7]. the eu prefers raw materials such as rapeseed oil, sunflower oil and cotton-seed oil [8, 9]. the production of biodiesel from waste vegetable oil is cheaper than from other feed stocks. the benefits of using wco to produce biodiesel are its low cost and the decreased emitted greenhouse gasses [10]. the density of wco is about 10% greater and the kinematic viscosity of wco is 10 times greater than that of conventional diesel. some modifications are compulsory in the engine when wco is used in engines [9, engineering, technology & applied science research vol. 8, no. 6, 2018, 3521-3524 3522 www.etasr.com khaskheli et al.: performance evaluation of locally-produced waste cooking oil biodiesel … 11]. if the free fatty acids (ffas) of wco oil are greater than 2% then it needs esterification process before transesterifcation [12]. iii. experimental setup wco was collected from two different chicken frying shops in nawabshah. it was converted in biodiesel by transesterification on pcsir laboratory at karachi, by the algorithm shown in figure 1. fig. 1. algorithm for bio-diesel production filter/cotton cloth filtered the collected wco. the oil to methanol ratio was 1:8. 183ml of methanol were put in a beaker of 250ml, along with 13.5g of dissolved koh. 500g of wco were taken in a glass flask connected with a reflux condenser using tap water to condense methanol vapour. the mixture was agitated by the use of a magnetic stirrer, and heated to 55 0 c-60 0 c. when oil temperature increased to 55 0 c60 0 c, the prepared koh solution was poured into the oil with stirring at 150rpm. after one hour, the mixture was poured into a separating funnel. glycerol, additional methanol and unused products were in the lower layer and were separated. the upper layer of biodiesel (ester) was washed several times with warm water (40 0 c) until the washing was neutral. the final product (biodiesel) was then dried over anhydrous sodium sulphate and filtered. iv. performance evaluation diesel performance evaluation was carried out in the thermodynamics laboratory of the quaid-e-awam university of engineering, science and technology nawabshah, sindh, pakistan. the engine model was dwe-6/10-js-dv. the specification details of the engine are illustrated in table i. table i. diesel test engine specifications number of cylinders 1 cooling system water cooled type horizontal piston size (bore) 80mm displacement of piston (strokes) 95mm (477cc) compression ratio 23:1 starting method manual output/rotational speed 8.5ps/2200 rpm(max) two fuel tanks were attached to the diesel engine test bed. one common pipeline was used for supplying fuel to the engine. both fuel tanks were linked with the common line. the flow could be controlled by two separate valves as shown in figure 2. the first tank was filled with diesel fuel (d100), and the second one with the test selected fuel. under this study, three selected fuels were tested: diesel (d100), 20% biodiesel+80% diesel (b20) and 30% biodiesel+70% diesel (b30). their specifics are given in table iii. exhaust gas temperature (egt), brake specific fuel consumption (bsfc) and brake thermal efficiency (bte) were measured at constant engine speed and variable load ranged from 0kg to 2.0kg at 1300rpm. table ii. fuel composition by volume d100 pure diesel b100 100% biodiesel b20 20% biodiesel+80% diesel b30 30% biodiesel +70% diesel table iii. comparative physical properties of oil samples physical property unit d100 b20 b30 astm standard testing limits total acid number mgkoh/g 0.24 0.27 0.28 d-664 0.80 max specific gravity* 0.83 0.85 0.84 d-891 0.8-0.9 kinematic viscosity** mm 2 /s 1.98 2.78 2.43 d-445 1.9-6.0 density** g/cm 3 0.85 0.86 0.86 d-1298 0.86–0.90 cetane index (calculated) 56.9 54.4 53.5 d-976 47 min flash point 0 c 103 123 115 d-93 130 min pour point 0 c 0 +1.5 +1.8 d-97 -15 to +5 calorific value mj/kg 44.8 43.2 43.8 d-240 37.5-45 * at 15.6 0 c ** at 40°c blended fuel tank diesel fuel tank lube oil temperature exhaust gas temperature suction air temperature fuel consumption water tank dynamometer controller exhaust emission pipe diesel engine fig. 2. experimental setup of diesel engine fig. 3. d100 and biodiesel specimens engineering, technology & applied science research vol. 8, no. 6, 2018, 3521-3524 3523 www.etasr.com khaskheli et al.: performance evaluation of locally-produced waste cooking oil biodiesel … v. results and discussion performance analysis was determined on a single cylinder diesel engine. a dynamometer was directly joined to the engine and could control the varying load. a dynamometer controller was connected to the panel. a water tank for cooling, and two fuel tanks were attached to the diesel engine test bed. one common pipeline has been used to supply the fuel. three different fuel types were experimented with. the performance parameters were determined on varying load at 1300rpm. the load range was 0n.m-2n.m. in this comparative study, the performance parameters were egt, bsfc and bte with varying brake power (bp). a. exhaust gas temperature (egt) egt increases continuously with load increase. during high engine load considerable heat was rejected. biodiesel and its blends have decreased percentage of heat rejected by the cooling fluid due to their lower combustion temperature. the smaller burning gas temperature is responsible for biodiesels’ quick combustion for the period of premixed combustion. it was observed that at increasing brake load the engine using d100 exhausted more temperature than when using b20 and b30, whereas b30 had reduced exhaust temperature than b20. the comparative results of egt are shown in figure 4. fig. 4. comparative results of egt with bp b. brake specific fuel consumption (bsfc) biodiesel showed higher bsfc than diesel for each different brake power of the engine because biodiesel and its blends have lower density and calorific value. the spfc has been expressed by kg/kwh. bsfc increases at high loads having improved fuel smoke related with the high fuel-air mixture in the compression-ignition (ci) engine. at low loads bsfc increases due to decreased mechanical efficiency. it is observed that brake fuel consumption is increased with increase in the blending ratio of biodiesel due to biodiesel’s low viscosity and density. consequently, the bsfc of b30 was higher than the ones of d100 and b20. the bsfc of b30 was 6.9% higher than that of d100 and 2.9% than that of b20. the detailed of comparative results of bsfc are shown in figure 5. c. brake thermal efficiency (bte) the bte decreased when the blending ratio increased. the compression ratios of the blended biodiesel were compared with pure diesel d100. the air-fuel ratio and volumetric efficiency decreased with increase in the concentration of biodiesel in the fuel [13-15]. it was observed that vegetable oil blends with methanol and ethanol provide lower thermal efficiency than diesel fuel. the bte of diesel is higher than that of biodiesel fuel due its higher viscosity, lower heating value, poor spray quality and higher volatility [16, 17]. increase in blending percentage of biodiesel in the diesel fuel improves its combustion process due to biodiesel’s higher oxygen content. the average value of bte of b30 is decreased by 4.75% when compared to d100. the comparative results of bte are shown in figure 6. fig. 5. comparative results of bsfc with bp fig. 6. comparative results of bte with bp vi. conclusion this research and experimental work consisted in engine performance analysis. three fuels, d100, b20 and b30 were tested without any modification of the diesel engine. based on the obtained results, b30 showed reduced exhaust gas temperature due to its quick combustion and improved fuel characteristics. the bsfc of b30 was 6.9% higher than the one of d100 due to its higher combustion and large oxygen content. bte was lower for biodiesel as compared to d100. when the blending percentage of biodiesel in the diesel fuel increased, the average value of bte of b30 decreases 4.75% as compared to d100. references [1] v. cordero-ravelo, j. schallenberg-rodriguez, “biodiesel production as a solution to waste cooking oil (wco) disposal. will any type of wco do for a transesterification process? a quality assessment”, journal of environmental management, vol. 228, pp. 117-129, 2018 engineering, technology & applied science research vol. 8, no. 6, 2018, 3521-3524 3524 www.etasr.com khaskheli et al.: performance evaluation of locally-produced waste cooking oil biodiesel … [2] m. abe, s. hirata, h. komatsu, k. yamagiwa, h. tajima, “thermodynamic selection of effective additives to improve the cloud point of biodiesel fuels”, fuel vol. 171, pp. 94–100, 2016 [3] y. h. teoh, h. h. masjuki, m. a. kalam, m. a. amalina, h. g. how, “impact of waste cooking oil biodiesel on performance, exhaust emission and combustion characteristics in a light-duty diesel engine”, sae technical paper 2013-01-2679, 2013 [4] a. m. a. attia, a. e. hassaneen, “influence of diesel fuel blended with biodiesel produced from waster cooking oil on diesel engine performance”, fuel vol. 167, pp. 316-328, 2016 [5] a. e. atabani, a. s. silitonga, h. c. ong, t. m. i. mahlia, h. h. masjuki, i. a. badruddin, h. fayaz, “non-edible vegetable oils a critical evaluation of oil extraction, fatty acid compositions, biodiesel production, characteristics and engine performance and emissions production”, renewable and sustainable energy reviews, vol. 18, pp. 211-245, 2013 [6] s. h. dhawane, t. kumar, g. halder, “biodiesel synthesis from hevea brasiliensis oil employing carbon supported heterogeneous catalyst: optimization by taguchi method”, renewable energy, vol. 89, pp. 506514, 2016 [7] s. h. dhawane, a. p. bora, t. kumar, g. halder, “parametric optimization of biodiesel synthesis from rubber seed oil using iron doped carbon catalyst by taguchi approach”, renewable energy, vol. 105, pp. 616-624, 2017 [8] a. bokhari, l. f. chuah, s. yusup, j. j. klemes, r. n. m. kamil, “optimisation on pretreatment of rubber seed (hevea brasiliensis) oil via esterification reaction in a hydrodynamic cavitation reactor”, bioresource technology, vol. 199, pp. 414-422, 2016 [9] n. h. abdullah, s. h. hasan, n. r. m. yusoff, “biodiesel production based on waste cooking oil (wco)”, internationals journal of materials science and engineering, vol. 1, no. 2, pp. 94-99, 2013 [10] m. mofijur, a. e. atabani, h. h. masjuki, m. a. kalam, b. m. masum, “a study on the effects of promising edible and non-edible biodiesel feedstocks on engine performance and emissions production: a comparative evaluation”, renewable and sustainable energy reviews, vol. 23, pp. 391-404, 2013 [11] a. e. atabani, a. s. silitonga, i. a. badruddin, t. m. i. mahlia, h. h. masjuki, s. mekhilef, “a comprehensive review on biodiesel as an alternative energy resource and its characteristics”, renewable and sustainable energy reviews, vol. 16, no. 4, pp. 2070-2093, 2012 [12] e. m. shahid, y. jamal, a. n. shah, n. rumzan, m. munsha, “effect of used cooking oil methyl ester on compression ignition engine”, journal of quality and technology management, vol. 8, pp. 91-104, 2012 [13] v. g. gude, g. e. grant, “biodiesel from waste cooking oils via direct sonication”, applied energy, vol. 109, pp. 135-144, 2013 [14] s. photaworn, c. tongurai, s. kungsanunt, “process development of two-step esterification plus catalyst solution recycling on waste vegetable oil possessing high free fatty acid”, chemical engineering and processing: process intensification, vol. 118, pp. 1-8, 2017 [15] s. nandi, “performance of c.i engine by using biodiesel-mahua oil”, american journal of engineering research, vol. 2, no. 1, pp. 22-47, 2013 [16] m. vijay kumar, a. veeresh babu, p. ravi kumar, “the impacts on combustion, performance and emissions of biodiesel by using additives in direct injection diesel engine”, alexandria engineering journal, vol. 57, pp. 509-516, 2018 [17] n. h. abu-hamdeh, k. a. alnefaie, “a comparative study of almond biodiesel-diesel blends for diesel engine in terms of performance and emissions, biomed research international, vol. 2015, article id 529808, 2015 microsoft word 43-3288 _s_etasr_v10_n3_pp5845-5850 engineering, technology & applied science research vol. 10, no. 3, 2020, 5845-5850 5845 www.etasr.com uzbas & aydin: microstructural analysis of silica fume concrete with scanning electron microscopy … microstructural analysis of silica fume concrete with scanning electron microscopy and x-ray diffraction burhan uzbas department of civil engineering faculty of engineering, ataturk university erzurum, turkey burhanuzbas@gmail.com abdulkadir cuneyt aydin department of civil engineering faculty of engineering, ataturk university erzurum, turkey acaydin@atauni.edu.tr abstract—the effects of using different ratios of silica fume on the mechanical and microstructural properties of hardened cement paste and concrete were investigated in this study. portland cement was replaced with 5%, 10%, 15%, and 20% silica fume (sf) by weight. microstructural properties of obtained samples were investigated by x-ray diffraction (xrd) and scanning electron microscopy (sem). the xrd analysis showed that the ratio of calcium hydroxide (ch), which is produced by hydration, decreases depending on the concrete age and the amount of silica fume. the sem analysis showed that the use of silica fume decreases gaps and calcium silicate hydrate (cs-h) which is also a hydration production. silica fume content of up to 15% improved the observed mechanical and microstructural properties of concrete. at the optimum value of 15%, improvement in the paste was observed due to the filler effect and the reaction between the silica fume and calcium hydroxide, leading to a reduction in calcium hydroxide in the concrete. keywords-silica fume; microstructure of concrete; scanning electron microscopy; x-ray diffraction; calcium hydroxide i. introduction increasingly strong pressure has been placed on natural resources due to the rapid economic development and the growth of the global population. concrete production is common use of natural resources. incorporating natural resources in concrete leads to environmental, economic, and technological benefits. one of the most important constituents of concrete is cement, which plays a crucial role as a foundational material in terms of structural costs, however, the use of natural reserves that contain pozzolanic materials rather than cement has become increasingly important [1]. from the economic point of view, cement and fine aggregates contribute the bigger portion of cost in the production of concrete, thus to have them replaced by waste material of similar characteristics has a major economic gain, while being more environmentally friendly [2]. most of the increase in cement demand will be met by the use of supplementary cementing materials, in order to reduce the green gas emission. industrial waste, such as blast furnace slag, fly ash, and silica fume are being used as supplementary cement replacement materials and, recently, agricultural waste is also being used as pozzolanic material in concrete [3]. the size of silica fume is hundreds of times smaller than cement particles, causing decrease to the permeability of concrete. reduction in the permeability of concrete decreases the deterioration caused by several factors such as alkali-aggregate reaction, carbonation, chloride attack, freezing and thawing, sulfate attack, etc. [4]. silica is a very fine-grained powder obtained by the reduction of high-purity quartzite with coal and wood particles in electric arc furnaces used in the production of silicon metal or ferrosilicon (fesi) alloys. in the low-temperature upper section of the furnace, sio2 gas is rapidly oxidized upon contact with the air and condenses as amorphous sio2 to form silica smoke [5]. silica fume is a pozzolanic material that is a byproduct of the silicon smelting process. it is known to produce high-strength concrete and is thus typically used either as a direct replacement for a proportion of the cement in concrete (usually for economic reasons) or an additive to improve the properties of concrete in both its fresh and hardened states, including reducing shrinkage and creep, increasing compressive strength, tensile and flexural strength, and optimizing its elastic modulus. silica fume is used in the production of high-strength concrete, reducing the required amount of cement [6]. silica fume is typically used at replacement levels of 5%–10% in high-performance concrete to improve strength and durability. silica fume not only reacts with calcium hydroxide (ca(oh)2) to produce calcium silicate hydrate (csh) but also modifies the microstructure of cement paste due to its fine particle size [7, 8]. the replacement of 20% cement with silica fume and the addition of superplasticizer in the mortar create a thinner interface area compared to plain cement mortar. this is due to the ability of silica fume to act as a filler material and to provide additional hydration, with the cement and silica fume particles mixing to provide microstructure condensation and better packaging. the addition of 20% silica fume also increases significantly the amount of silicon dioxide (sio2) in the interface zone between the cylindrical aggregate and the mortar matrices [9]. a silica fume admixture provides additional csh gels such as other pozzolans, and the fine silica corresponding author: burhan uzbas engineering, technology & applied science research vol. 10, no. 3, 2020, 5845-5850 5846 www.etasr.com uzbas & aydin: microstructural analysis of silica fume concrete with scanning electron microscopy … fume particles fill the aggregate-dough interface area to enhance concrete strength [10]. when added to fresh concrete, the silica fume reacts chemically with ca(oh)2 to produce additional csh increasing concrete’s compressive strength and chemical resistance. this is because the silica fume fills the cavities in the hydrated cement paste to form a denser structure. the addition of silica smoke increases the cement hydration rate and accelerates c3s and c3a hydration within the first few hours [11]. microstructural studies have shown that, in mortars containing silica fume, the reduction in the number of gaps causes the reaction of silica fume with ca(oh)2 around sand particles. the addition of silica fume to concrete increases compressive strength, reduces shrinkage, increases wear resistance, increases adherence, and decreases permeability [12]. incorporating a silica fume blend as an additive to cement is potentially very useful, as it results in increased strength of concrete. in this study, the specific effects of silica fume on cement hydration are investigated. more specifically, x-ray diffraction (xrd) and scanning electron microscopy (sem) are used to identify the mechanical and physical properties of concrete produced using silica fume. silica fume is generally added to concrete at a lower rate, but in this study four different rates were used. in addition, the internal structure of concretes containing silica fume have been generally examined with a single device (sem or xrd). in this study, sem and xrd were used simultaneously and the internal structure was examined. ii. materials and methods in this study, cement (cem i 42.5) from the votarantim hasanoglan cement factory and silica fume produced as a byproduct of ferrosilicon steel production in egypt were used. the chemical composition of these materials is shown in table i. coarse aggregates with a maximum particle size of 16mm were used for the concrete specimens. table i. chemical composition of portland cement and silica fume type styles chemical composition oxide cement(%) silica fume (%) sio2 19.43 93.65 al2o3 5.31 0.28 fe2o3 3.79 0.58 cao 64.39 0.28 mgo 2.25 0.25 k2o 0.90 0.87 na2o 0.09 so3 2.47 0.38 loss on ignition 1.07 xrd and sem techniques were used to determine the microstructure of the concrete. further, a variety of mix proportions to form cement pastes both with and without silica fume were used. four cement pastes with varying proportions of silica fume based on weight were prepared: 5%, 10%, 15%, and 20% (referred to as sf5, sf10, sf15, and sf20, respectively). these were compared to concrete made from a cement-only paste (cs). the concrete was mixed with water to cement/silica fume ratio of 0.60. a rotary mixer was used to mix the specimens. for the cement pastes, the binders (i.e., cem i and silica fume) were first blended in the mixer for three minutes before adding water and mixing for another two minutes. the mixes were then poured into oiled molds of size 150×150×150mm 3 , compacted, and covered for 24 hours. the specimens were then removed from the molds and cured in water at a constant 20±2°c temperature. three specimens of each mix were used for compressive strength tests at 7, 28, and 90 days after curing. some of the specimens were selected for microstructure analysis using xrd and sem. the concrete mix designs are summarized in table ii. table ii. mix propoprtions of the concrete specimens mix (1 m3) cs sf5% sf10 sf15 sf20 water to cement ratio 0.60 0.60 0.60 0.60 0.60 cement (kg) 350.00 332.50 315.00 297.50 280.00 water (kg) 210.00 210.00 210.00 210.00 210.00 agg. (kg) 0-2 mm 689.00 682.00 676.00 670.00 664.00 2-4 mm 350.00 350.00 350.00 350.00 350.00 4-8 mm 280.00 280.00 280.00 280.00 280.00 8-16 mm 420.00 420.00 420.00 420.00 420.00 silica fume (kg) 0.00 17.50 35.00 52.50 70.00 iii. results and discussions a. compressive strength table iii presents the compressive strength of the mixes in comparison to the control mix. it can be observed that, after 7 days of curing, the compressive strength of concrete with silica fume was stronger than that of the control concrete and that the compressive strength increased as the rate of silica fume increased up until sf15, which had the highest compressive strength. however, when the silica fume content was 20%, the compressive strength fell moderately. for all mixtures, the compressive strength increased with curing time, with the comparative strengths between the mixtures exhibiting the same trend after both 28 and 90 days of curing as for 7 days (i.e., cs had the lowest compressive strength and sf15 the highest). table iii. compressive strength results mixes compressive strength (mpa) 7 days 28 days 90 days cs 32.49 38.34 40.28 sf5 32.52 41.71 42.43 sf10 33.62 42.10 43.28 sf15 34.42 43.13 44.59 sf20 33.70 41.41 43.37 this increase in compressive strength with increasing silica fume content up until 15% is because the particle size of the silica fume is smaller than that of cement, leading to an increase in the pozzolanic reaction between the sio2 in the silica fume and the ca(oh)2 from the hydration process. b. sem and xrd analysis when cement paste is viewed at higher magnifications, the hydration products and particles of unhydrated cement are visible. xrd microanalysis allows quantitative chemical composition analysis. in addition, sem allows the cement and engineering, technology & applied science research vol. 10, no. 3, 2020, 5845-5850 5847 www.etasr.com uzbas & aydin: microstructural analysis of silica fume concrete with scanning electron microscopy … concrete microstructure to be characterized [13]. sem is a commonly used analytical technique due to the ease of sample preparation, the diversity of information it can collect, its high resolution associated with a high-field depth, and its broad, continuous range of magnification [14]. the xrd patterns of the hydration products and sem images were analyzed for the control mix and the four silica fume specimens. the results are presented in figures 1-15. the presence of ca(oh)2 was attributed to the partial carbonation of portlandite. after 28 days of curing, the intensity of the main ettringite peaks reduced significantly in the cs. this can be explained by the transformation of calcium sulphoaluminate into a more stable form of calcium aluminate hydrate. figure 1 presents the xrd and sem results of the control mix (cs) after 7 days of curing. the young concrete had strong peaks due to calcium and silicon and weak peaks from impurities of aluminum and iron. in the sem image, hexagonal calcium hydroxide (ch), needle-like ettringite, and sheet-like csh can be observed. figures 2 and 3 present the xrd and sem results of sf5 and sf10 respectively after 7 days of curing. strong peaks were observed for calcium and silicon, but there was a considerable lower amount of calcium hydroxide compared to cs. fig. 1. xrd and sem analysis of the control mix (cs) after 7 days fig. 2. xrd and sem analysis of sf5 mix after 7 days fig. 3. xrd and sem analysis of sf10 mix after 7 days figure 4 presents the xrd and sem results of sf15 after 7 days of curing. strong peaks were observed due to calcium and silicon, but there was a significantly lower amount of calcium hydroxide rather than other sf. it can also be seen that the voids in the concrete microstructure were filled to a large extent by the addition of silica fume. figure 5 presents the xrd and sem results of sf20 after 7 days of curing. strong peaks were observed due to calcium and silicon, but, as with sf15, there was a considerable decrease in calcium hydroxide. the sem image shows the presence of hydrated phases such as csh and ettringite. fig. 4. xrd and sem analysis of sf15 mix after 7 days fig. 5. xrd and sem analysis of the sf20 mix after 7 days figure 6 presents the xrd and sem results of cs after 28 days of curing. strong peaks were again observed due to calcium and silicon. hexagonal calcium hydroxide, needle-like ettringite, and sheet-like csh can be observed in the sem image. figures 7-8 present the xrd and sem results of sf5 and sf10 respectively after 28 days of curing. similar to the results after 7 days, strong peaks were observed due to calcium and silicon, but there was a considerably lower amount of calcium hydroxide compared to the cs. fig. 6. xrd and sem analysis of the control mix (cs) after 28 days fig. 7. xrd and sem analysis of the sf5 mix after 28 days engineering, technology & applied science research vol. 10, no. 3, 2020, 5845-5850 5848 www.etasr.com uzbas & aydin: microstructural analysis of silica fume concrete with scanning electron microscopy … fig. 8. xrd and sem analysis of the sf10 mix after 28 days figure 9 presents the xrd and sem results of sf15 after 28 days of curing. strong peaks are visible due to calcium and silicon, and the sem image indicates an increasing amount of c2s and c3s. figure 10 presents the xrd and sem results of sf20 after 28 days of curing. strong peaks due to calcium and silicon were also observed, while ch exhibited its lowest value and c2s and c3s their highest. fig. 9. xrd and sem analysis of the sf15 mix after 28 days fig. 10. xrd and sem analysis of the sf20 mix after 28 days figure 11 presents the xrd and sem results of cs after 90 days of curing. only csh can be observed in the sem image. fig. 11. xrd and sem analysis of the control mix (cs) after 90 days fig. 12. xrd and sem analysis of the sf5 mix after 90 days figure 12 presents the xrd and sem results of sf5 after 90 days of curing. only csh can be observed in the sem image. there was a considerable decrease in the amount of calcium hydroxide rather than other sf. it can also be seen that the voids in the microstructure are filled by the addition of silica fume. figure 13 presents the xrd and sem results of sf10 after 90 days of curing. only csh can be observed. figure 14 presents the xrd and sem results for sf15 after 90 days of curing. a considerable decrease in the amount of calcium hydroxide can be seen. ch reached its lowest value and c2s and c3s their highest. figure 15 presents the xrd and sem results of sf20 after 90 days of curing. only csh can be observed in the sem image and the voids in the microstructure are filled to a large extent by the addition of silica fume. ch reached its lowest value and c2s and c3s their highest. fig. 13. xrd and sem analysis of the sf10 mix after 90 days fig. 14. xrd and sem analysis of the sf15 mix after 90 days fig. 15. xrd and sem analysis of the sf20 mix after 90 days a considerable increase in the amount of calcium hydroxide (ch) was also observed, primarily due to the increase in the formation of csh. for all concrete mixes, including cs, it was observed that, after 28 days of curing, the amount of crystalline ch was reduced compared to the 7-day samples, which is indicated by the shorter length of the ch peaks. these results are evidence of the reaction of silica fume with ch to form csh matrices. during the hydration of the cement mortars, ch formation fell with the addition of silica fume, therefore lower compressive strength was attained in the early stages compared to cs. over time, silica fume, with its pozzolanic structure, bound to ch, producing pozzolanic csh gel, and raising the strength of the concrete to reach that of cs. highly crystalline portlandite and amorphous csh are formed during the hydration of portland cement [15]. ch, which engineering, technology & applied science research vol. 10, no. 3, 2020, 5845-5850 5849 www.etasr.com uzbas & aydin: microstructural analysis of silica fume concrete with scanning electron microscopy … occurs as a result of chemical reactions, is soluble in water and has low strength. these properties affect negatively the quality of concrete. adding a mineral admixture to cement decreases the amount of ca(oh)2. cement paste containing silica fume produces amorphous csh gel with high density and a low ca/si ratio. during the chemical reaction period of portland cement, silicate reacts with free ca(oh)2, thus forming amorphous csh gel. therefore, the amount of ca(oh)2, which is harmful for concrete in terms of structural strength, decreases accordingly [15-18]. in examined concrete containing silica fume, all the peaks characterizing the portlandite phase disappear completely. ch released during cement hydration, was consumed as a result of interaction with active silica fume to form csh phases [19]. in the present study, an increase in the cement reaction after 7 days was observed due to the small size and high surface area of the silica fume, which increased csh nucleation. as the curing time increased, there was a diminution of values between the tobermorite and portlandite phases. this occurred between 7 and 28 days and between 28 and 90 days. this phenomenon can be explained by the fact that during the first 7 days of hydration, tobermorites originating in the alite are more predominant, and alite is present in larger amounts than belite, which is a source of portlandite that develops more slowly. as time passes, a larger amount of portlandite is produced, so that, after 7 days, the difference between tobermorite and portlandite narrows. after 28 days, the difference between the two compounds widened as the development of tobermorite increased substantially. while hydration continued, ettringite became more and more evident throughout [14]. the presence of the portlandite peaks seen in both the xrd and sem analysis of hardened samples after varying periods of hydration indicated the presence of silica fume. portlandite, which is formed by the hydration of c3s and c2s, combines with silica fume to form csh. the lack of portlandite peaks in the xrd results can be explained by the poor crystallization of portlandite [16]. adding silica fume to ordinary concrete leads to the reduction in the ca(oh)2 produced during cement hydration, because it reacts with the active silica fume to form csh [17]. silica reacts with ch to produce csh due to the acceleration of hydration of tricalcium and diacalcium, which makes the concrete denser and homogeneous [20]. sem analysis is characterized by easy sampling, variety of accessible knowledge, and good resolution. the xrd method can be used to determine the crystal structure of samples, to conduct quantitative and qualitative phase analysis, to investigate phase transformation, to study crystallographic configuration, and to study the size of crystals [21]. iv. conclusions in this paper, the effect of silica fume on the microstructure and mechanical properties of concrete was investigated. in addition, the effect of silica fume on the amount of ch and csh in concrete was studied. silica fume has been shown to improve the microstructure of cement paste in concrete by densifying the cement paste matrix and the porous paste aggregate interfacial zone. in this study, it was observed that the porosity of silica fume concrete decreased as the silica fume content increased up to 15%, after which the porosity increased as the silica fume content increased. silica fume reduced the amount of ch for all content levels after 7, 28, and 90 days. a linear relationship between the use of silica as a binder instead of cement and the decrease in ch was observed. after 7 days of curing, ch reduced to 10%, 13%, 31%, and 37% for silica fume levels of 5%, 10%, 15%, and 20%, respectively. after 28 days of curing, ch fell to 11%, 20%, 32%, and 46% and after 90 days of curing ch dropped to 33%, 34%, 65%, and 81% for the same silica fume levels respectively. silica fume also decreased the amount of csh at all content levels. after 7 days of curing, csh fell to 1%, 7%, 9%, and 12%, after 28 it fell to 1%, 7%, 18%, and 19%, and after 90 days to 2%, 18%, 28%, and 28% for silica fume levels of 5%, 10%, 15%, and 20% respectively. references [1] a. c. aydın, r. gul, “influence of volcanic originated natural materials as additives on the setting time and some mechanical properties of concrete”, construction and building materials, vol. 21, no. 6, pp. 1277-1281, 2007 [2] a. a. adekunle, k. r. abimbola, a. o. familusi, “utilization of construction waste tiles as a replacement for fine aggregates in concrete”, engineering, technology and applied science research, vol. 7, no. 5, pp. 1930-1933, 2017 [3] f. a. olutoge, h. a. quadri, o. s. olafusi, “investigation of the strength properties of palm kernel shell ash concrete”, engineering, technology and applied science research, vol. 2, no. 6, pp. 315-319, 2012 [4] a. g. khan, b. khan, “effect of partial replacement of cement by mixture of glass powder and silica fume upon concrete strength”, international journal of engineering works, vol. 4, no.7, pp. 124-135, 2017 [5] a. yeginobali, “silica fume and cement and its use in concrete”, turkish cement manufacturers’ association, 2009 (in turkish) [6] t. nochaiya, w. wongkeo, a. chaipanich, “utilization of fly ash with silica fume and properties of portland cement–fly ash-silica fume concrete”, fuel, vol. 89, no. 3, pp. 768-774, 2010 [7] a. c. a. muller, k. l. scrinever, j. skibsted, a. m. gajewicz, p. j. mcdonald, “influence of silica fume on the microstructure of cement paste: new insights from h nmr relaxometry”, cement and concrete research, vol. 74, pp. 116-125, 2015 [8] m. kurt, m. s. gul, r. gul, a. c. aydın, t. kotan, “the effect of pumice powder self-compactability of pumice aggregate lightweight concrete”, construction and building materials, vol. 103, pp. 36-46, 2016 [9] n. ranjbar, m. mehrali, a. behnia, u. j. alengaram, m. z. jumaat, “compressive strength and microstructural analysis of fly ash/palm oil fuel ash based geopolymer mortar”, materials and design, vol. 59, pp. 532-539, 2014 [10] i. demir, “aynı oranda ikame edilen silis dumani ve ucucu kulun betonun mekanik ozelliklerine etkisi”, international journal of engineering research and development, vol. 1, no. 2, pp. 1-7, 2009 (in turkish) [11] k. baltakys, r. jauberthie, r. siaucinas, r. kaminskas, “influence of modification of sio2 and the formation of calcium silicate hydrate”, materials science-poland, vol. 25, no. 3, pp. 663-670, 2007 [12] i. b. topcu, m. canbaz, “an investigation of the interfaces of silica fume concrete”, ecas2002 international symposium on structural and earthquake engineering, ankara, turkey, october 14, 2002 [13] p. e. stutzman, “scanning electron microscopy in concrete petrography”, calcium hydroxide in concrete (workshop on the role of calcium hydroxide in concrete), anna maria island, florida, usa, november 1-3, 2000 [14] j. elena, m. d. lucia, “application of x-ray diffraction (xrd) and scanning electron microscopy (sem) methods to the portland cement hydration processes”, journal of applied engineering sciences, vol. 2, no. 15, pp. 35-42, 2012 engineering, technology & applied science research vol. 10, no. 3, 2020, 5845-5850 5850 www.etasr.com uzbas & aydin: microstructural analysis of silica fume concrete with scanning electron microscopy … [15] e. temiz, a. y. karakeci, “an investigating on microstructure of cement paste containing fly ash and silica fume”, cement and concrete research, vol. 32, no. 7, pp. 1131-1132, 2002 [16] i. b, topcu, m. canbaz, “an investigation of the interfaces of silica fume concrete”, international symposium on structural and earthquake engineering, ankara, turkiye, 2002 [17] m. saad, s. a. a. e. enein, g. b. hanna, m. f. kotkata, “effect of silica fume on the phase composition and microstructure of thermally treated concrete”, cement and concrete research, vol. 26, no. 10, pp. 14791484, 1996 [18] a. c. aydin, m. b. karakoc, o. a. duzgun, m. s. bayraktutan, “effect of low quality aggregates on the mechanical properties of lightweight concrete”, scientific research and essays, vol. 5, no. 10, pp. 11331140, 2010 [19] b. uzbas, a. c. aydin, “xrd analysis of mechanical properties of containing fly ash and silica fume concrete”, sinop university journal of natural science, vol. 3, no. 2, pp. 1-22, 2018 [20] a. k. nanda, p. p. bansal, m. kumar, “effect of nano silica and silica fume on durability properties of high performance concrete”, international journal of civil engineering and technology, vol. 9, no. 2, pp. 115-129, 2018 [21] b. uzbas, a. c. aydin, “analysis of fly ash concrete with scanning electron microscopy and x-ray diffraction”, advances in science and technology research journal, vol. 13, no. 4, pp. 100–110, 2019 microsoft word 15-3177_s_etasr_v9_n6_pp4946-4955 engineering, technology & applied science research vol. 9, no. 6, 2019, 4946-4955 4946 www.etasr.com duong et al.: an effective method for maximizing social welfare in electricity market via optimal … an effective method for maximizing social welfare in electricity market via optimal tcsc installation thanh long duong faculty of electrical engineering technology industrial university of ho chi minh city ho chi minh city, vietnam duongthanhlong@iuh.edu.vn thuan thanh nguyen faculty of electrical engineering technology industrial university of ho chi minh city ho chi minh city, vietnam nguyenthanhthuan@iuh.edu.vn ngoc anh nguyen faculty of electrical engineering technology industrial university of ho chi minh city ho chi minh city, vietnam nguyenngocanh@iuh.edu.vn le anh tu nguyen faculty of electrical engineering technology industrial university of ho chi minh city ho chi minh city, vietnam lenguyenanhtu@iuh.edu.vn abstract—the evolving electricity market has increased power demand and has brought many social benefits. meanwhile, the transmission systems are not developed to the same extent because building new lines is difficult for environmental and political reasons. hence, the systems are driven close to their limits resulting in congestions and critical situations endangering the system’s security. due to this, the study of enhancing the transfer capability of existing power networks to satisfy the increased power demand, maximum social welfare, and ensure its secure operation has become one of the challenges the independent system operator faces in the electricity market. in order to solve this problem without building more transmission lines, the installation of facts devices can be a better alternative. among facts devices, thyristor-controlled series compensator (tcsc) is one that can redistribute power flow in the network to improve the transfer capability of the existing system effectively. however, it is very difficult to implement. this paper presents the implementation of the cuckoo optimization algorithm (coa) to solve the opf problem which is formulated as a nonlinear optimization problem with equality and inequality constraints in a power system for social welfare maximization via the optimal installation of tcsc devices. as cuckoo search algorithm (csa), the coa also starts with an initial populationbased metaheuristic optimization inspired by the nature of brood parasitism of some cuckoo species. however, unlike csa, coa uses the cuckoo’s style for egg-laying to optimize the local search instead of using lévy flights. this model is tested in ieee 14 and ieee 30 bus systems. simulations results are compared with ga and gwo and show that the coa is one useful method for tcsc installation to maximize social welfare. keywords-cuckoo optimization algorithm; facts; tcsc; social benefits; electricity market i. introduction due to the rapid technological progress, the consumption of electric energy increases continuously. for the last three decades, many electrical power utilities have been forced to change their way of operation from monopolistic structure to competitive market structure. in vietnam, pilot steps of the roadmap for the application of electricity market approved by the prime minister, are being applied and the country moves towards a competitive electricity market. the basic idea of deregulation is to make supply and demand competitive so that all participants, i.e. generator companies, distribution companies, and the customers maximize their individual welfare. the supply or cost bid provided by a generator company is the minimum asking price that it would accept for supplying a particular amount of power. similarly, the demand or benefit bid of a consumer is the maximum price that it would pay for consuming a particular amount of power. the independent system operator (iso) is responsible for the buying and selling of power between generator and distribution companies to the customers based on supply and demand bids, which are prepared in such a way as to maximize social welfare. in order to solve this problem, transmission improvement methods are applied to achieve minimum generation costs, subject to system security constraints. in contrast, social welfare maximizing is the objective of most studies in deregulated power systems. several studies have also been performed on congestion management to maximize social and individual welfare [1-2], as well as social welfare maximization considering reactive power and congestion management in the deregulated environment [3]. distributed generator locations for social welfare maximization are presented in [4]. these studies focused on a method for increasing social welfare under congestion probability in transmission networks. recently, flexible ac transmission systems (facts) [5] have also been utilized to solve the congestion problem and maximize social welfare. many studies have been proposed for the improvement of existing power networks via optimal location of facts [6-19]. interior point method was used for system expansion with upfc to maximize social welfare and corresponding author: thanh long duong engineering, technology & applied science research vol. 9, no. 6, 2019, 4946-4955 4947 www.etasr.com duong et al.: an effective method for maximizing social welfare in electricity market via optimal … to manage congestion [20]. in [21], mixed integer non-linear programming was used for optimal location of facts to maximize social welfare based on multiple time periods. but it ignored the impact of facts on the reactive power flow. in [22] facts device thyristor-controlled series compensator (tcsc) is optimally located for congestion management maximizing social welfare using genetic algorithm (ga) and gwo algorithm. an efficient ga was proposed for optimal size and location of tcsc in a deregulated market for congestion management with aim of maximizing the social welfare cost [23]. in [24], a new fuzzy-based genetic algorithm (fuzzy-ga) for alleviating congestion and maximizing social benefit in a double-sided auction market by locating and sizing of one tcsc unit. in [25], a ga for finding the optimal location and size of this device was proposed for congestion management with the aim of increasing social welfare. a novel efficient differential evolution and evolutionary programming technique for social welfare maximization by optimal location of various facts devices in pool electricity market based on contingency analysis was introduced in [26]. optimal location of facts devices is a complex combinatorial analysis, which is best studied using metaheuristic algorithms. many researchers have tested different optimization algorithms. a new meta-heuristic algorithm called cuckoo optimization algorithm (coa) was developed in [27]. coa is a nature-inspired meta heuristic algorithm which is inspired by the life of cuckoo bird family. the special lifestyle of these birds and their characteristics in egg-laying and breeding has been the basic motivation for development of this new evolutionary optimization algorithm. it is a novel evolutionary algorithm, suitable for the continuous nonlinear optimization problem. similar to other evolutionary methods, the initial population of coa is randomly generated within the control parameter limits. the effort to survive among cuckoos constitutes the basis coa. during the survival competition some of the cuckoos or their eggs may perish. the survived cuckoo societies migrate to a better environment and start reproducing and laying eggs. cuckoos survival effort hopefully converges to a state that there is only one cuckoo society, with all birds having the best profit values. application of the coa algorithm to some benchmark functions and a real problem has proven its capability in solving complex, nonlinear and non-convex optimization problems [27]. the key features of the coa are its faster convergence rate and the reduction in computational complexity. hence, it may become an effective tool in solving power system optimization problems. however, the coa is only introduced in the opf problem [28], and it still hasn’t been used to solve tcsc optimization problems. in this paper, coa has been implemented to solve the opf problem which is formulated as a nonlinear optimization problem with equality and inequality constraints in a power system for maximization of the social welfare via optimal installation of tcsc devices. the proposed approach has been tested on the ieee 14-bus and ieee 30-bus systems. simulation results are compared with the re results of ga and gwo and show that the coa is also one of useful algorithm in solving the power system optimization problem. ii. problem formulation a. modeling of tcsc the model of the network with tcsc is shown in figure 1. tcsc is integrated in the opf problem by modifying the line data. this device may have either inductive compensation or capacitive compensation by limiting 70% to 50% of the reactance of the uncompensated line where tcsc is located. let xij be the reactance of the transmission line and xtcsc the reactance of tcsc and xnew the new reactance of the line after placing tcsc between buses i and j: new ij tcscx x x= + (1) tcsc tcsc ijx k x= (2) 2 = ( cos sin ) ij i ij i j ij ij ij ij p v g vv g bδ δ− + (3) 2 = ( sin cos ) ij i ij i j ij ij ij ij q v b vv g bδ δ− − − (4) 2 = ( cos sin ) ji j ij i j ij ij ij ij p v g vv g bδ δ− − (5) 2 = ( sin cos ) ji j ij i j ij ij ij ij q v b v v g bδ δ− + + (6) where δij is the voltage angle difference between bus i and bus,; the conductance and susceptance of transmission line can be calculated respectively as: 2 2 new ij ij ij r g r x = + (7) new 2 2ij ij ij x b r x = + (8) jxr ijij+ jb sh jb sh jx tcsc fig. 1. modeling of transmission line with tcsc b. objective function market prices for a given amount of power can be determined by solving the optimization problem with the objective of maximizing social welfare to satisfy limited constraints. generally, bulk loads as well as retailers in deregulated electricity market are required to bid their maximum demand and price function. similarly, all generators are also required to bid their generation cost function along with their maximum generation. in electricity market, generation and distribution companies are allowed to offer and bid their prices to the iso [29]. social welfare optimization provides the demand and the generation of all the buses to be known. let the vector of pool real power demand (pdp) and engineering, technology & applied science research vol. 9, no. 6, 2019, 4946-4955 4948 www.etasr.com duong et al.: an effective method for maximizing social welfare in electricity market via optimal … vector of pool real power generation (pgp) be given in (9) and (10): { }; 1,2,3.....p pjpd pd j m= = (9) { }; 1,2,3.....p pipg pg i n= = (10) where, m is the number of dispatch able loads, and n is the number of generators. let the generation cost curve of the generator placed at bus i bidding to the pool be denoted by ( )p ii pgc . the benefit function for a load is ( )p jj pdb . it represents the load price which is willing to pay for the purchase of an amount of electric power p j pd . in electricity market, the social benefit for an elastic load is given by (11). the elastic load is sensitive to the energy price.         + ∑∑ ∈∈ )()( j ni ji ni i pdwpgwmax dg (11) where wj(pdj) is the consumers welfare function. optimal social welfare occurs when the total of all generator and consumer units’ welfare in the system are maximized. ( ) ( ) jjjjj pdpdbpdw λ−= (12) the bj in (12) indicates the i-th load utility function and λ is the amount of cost that should be paid for each mw of energy per unit. wi(pgi) is the welfare function of the generators: ( ) ( ) iiiii pgcpgpgw −= λ (13) ci is representing the cost function of the i-th generator. the λ is the cost each generator should be paid per mw of energy. from (11)-(13) the objective function can be written as: ( ) ( ) d g obj j j i i i n i n f max b pd c pg ∈ ∈    = −     ∑ ∑ (14) where, ( ) gigigigìgi p ii cpbpapgc ++= 2 is the cost function of the generator and ( ) djdjdjdjdj p jj cpbpapdb ++= 2 is the profit function of the customer. the social welfare is mathematically maximized subject to the following transmission network constraints: • power balance equation: ( , ) 0 1,...,i di gi bp v p p i nδ + − = = (15) ( , ) 0 1,..., i di gi b q v q q i nδ + − = = (16) • power generation limit : min max 1,.....,gi gi gi gp p p i n≤ ≤ = (17) min max 1,.....,gi gi gi gq q q i n≤ ≤ = (18) • bus voltage limits: min max 1,.....,i i i bv v v i n≤ ≤ = (19) • apparent line flow limit: ,max 1,.....,l l ls s l n≤ = (20) iii. introduction of coa coa is inspired by the special life style of cuckoo birds. no cuckoo bird nests its eggs. mature cuckoos have to find a host bird nest to safely place their eggs. after that, the feed responsibility belongs to the host bird. only a number of the cuckoo’s eggs have the chance to grow and become mature cuckoos. all mature cuckoos will move forward to the best habitat. after some iterations, the cuckoo populations will converge in a habitat with the best profit values [27]. like other evolutionary algorithms, the proposed algorithm starts with an initial population of cuckoos. these initial cuckoos lay some eggs in some host bird’s nests. some of these eggs which are more similar to the host bird’s eggs have the opportunity to grow and become mature cuckoos. other eggs are detected by the host birds and are destroyed. the grown eggs reveal the suitability of the nests in that area. the more eggs survive in an area, the more profit is gained in that area. so, the habitat in which more eggs survive will be the term that coa is going to optimize. a. generating the initial cuckoo habitat in order to solve an optimization problem, it is necessary the values of problem variables to be formed as an array. in coa, it is called habitat. in the nvar dimensional optimization problem, a habitat is an array of 1×nvar, representing the current living habitat of cuckoo. this array is defined as: habitat = [x1, x2, . . . , xnvar]t (21) each of the variable values (x1, x2, …, xnvar) is a floating point number and a habitat may represent a vector of control variables of the opf problem. the profit of a habitat is obtained by the evaluation of the profit function fp at a habitat. profit = fp(habitat) = fp(x1, x2, . . . , xnvar ) (22) coa is an algorithm that maximizes the profit function. in order to use coa in cost minimization problems such as minimizing the fitness function in the opf problem, (22) can be write as: profit = − cost(habitat) = − fp(x1, x2, . . . , xnvar )(23) b. cuckoo’s style for egg laying in the first iteration, a candidate habitat matrix of size npop×nvar is generated. then some random eggs are dedicated to each cuckoo and its elr (eggs laying radius) is calculated. the elr is defined as: elr = � ∗ � !"#$ %& ' $$#() * '+%%,#../%)01 ( !"#$ %& #..∗ (23456 − 234789) (24) where α is an integer to handle the maximum value for elr and varhi and varlow is the up and down limits of optimal variables. the aim of elr is to determine and limit the searching space in each iteration step. engineering, technology & applied science research vol. 9, no. 6, 2019, 4946-4955 4949 www.etasr.com duong et al.: an effective method for maximizing social welfare in electricity market via optimal … c. eliminating cuckoos in worst habitats due to the equilibrium in bird’s population, only a maximum number of cuckoos may live in the environment, termed as maxnumofcuckoos. a priority list may be created by evaluation and sorting of the profit value of the habitat of each newly grown cuckoo. so, there are maxnumofcuckoos cuckoos from the first of priority list alive, and the other cuckoos will die. this work will decrease computational time because there is a limited number of best solutions to be used in the next iteration. d. immigration of cuckoos the habitat in which cuckoos have the best conditions to live and grow or the best profit value will be considered as the goal point of the other cuckoos. they will immigrate as closer as they can towards the goal point. after a period of time, cuckoos grow to mature cuckoos and restart the process. this means that cuckoo population will find the best place to live after many iterations. this work will help the opf problem to find the best solutions. iv. application coa for solving the problem of social welfare maximization the flow chart of coa for the social welfare maximization problem is presented in figure 2. read data input set parameter of coa calculated egg laying radius (elr) for each cuckoo as (29-30) update egg’s positions after laying eggs as (31-32). create the initial population of coa as (25-27 ) sort value of all fitness functions as a priority list and stores the relevant each cuckoo keep a number of maxnumofcuckoos cuckoos and kill the others at the bottom of list evaluate fitness function for each cuckoo as (33) determine the best cost and the goal point update new values to each cuckoo as (34) iter < iter max output: the best cost and the goal point calculate the number of eggs for each cuckoo as (28) start end yes no fig. 2. the flowchart of coa for the social welfare maximization problem the steps of the maximizing social welfare problem using the proposed coa are presented below. step 1: prepare a system data base. system topology, line and load specifications, generation limits, line flow limits and cost coefficient parameters. step 2: set parameter for coa and social welfare problem: numcuckoos: the number of cuckoos in the first population, mineggs: the minimum number of eggs of each cuckoo, maxeggs: the maximum number of eggs of each cuckoo, maxiter: the maximum number of iterations, motioncoceff: the variable to control the towards to goal point process, maxcuckoos: the maximum number of cuckoos that can live at the same time, radiuscoceff: the control parameter of egg laying radius, npar is the number of optimal variables. it is set equal to the number of variables included in vector xid. kp, kq, kv, ks: the penalty factors. step 3: create the initial population: 2 2 1 .... , .... , .... , , id g gng d dnd g gng tcsc tcsc x p p p p v v n k =  (25) each habitat of cuckoos (xid) is created as follows: ( )min max min1*id id id idx x rand x x= + − (26) a random goal point is created as follow: ( )min max minint 1*id id idgoalpo x rand x x= + − (27) the habitat is a random matrix sized [1xnpar], and is representing the living environment of each cuckoo. step 4: calculate the number of eggs for each cuckoo as: ( ) ’ – 2 numbercuckoo s eggs maxeggs mineggs xrand mineggs = + (28) step 5: calculate the elr for each cuckoo. update egg’s positions after laying eggs. ( )max min max ' id id i numbercuckoo s eggs x x radiuscoeff elr total number of egg ∗ − ∗ = (29) max * 3i ielr elr rand= (30) where rand3 is a random matrix with size 1xnumber of current eggs, so elri is a matrix with number of eggs rows and npar columns. ( ) ( ) ( )( )41 cos sinrandi i iadd elr in angles elr angles= − ∗ ∗ + ∗ (31) ( )1 id id ix x add= + (32) where rand4 is a random value, it can be set to 1 or 2, and angles is a random line space represent for the flying angles of cuckoo. each row of matrix xid is a candidate for the vector habitat xid. then, the limit for each xid is checked and the egg laying process is done. step 6: solve power flow for each candidate xid. the fitness function is calculated by: lim 2 lim 2 1 1 lim 2 max 2 1 1 nb nb f obj p gi gi q gi gi i i nb nl v i i s li li i i f f k (p p ) k (q q ) k (v v ) k (s s ) = = = = = − − − − − − − − ∑ ∑ ∑ ∑ (33) engineering, technology & applied science research vol. 9, no. 6, 2019, 4946-4955 4950 www.etasr.com duong et al.: an effective method for maximizing social welfare in electricity market via optimal … step 7: evaluate the fitness function for each xid in step 6. sort the value of all fitness functions as a priority list and store the relevant xid. step 8: based on the priority list, keep a number of maxnumofcuckoos xid and kill the others at the bottom of the list. step 9: the first xid of the list is the best xid solution in this iteration. it is the best cost and will be the new goal point for the others. their new habitat is determined as: ( ) ( )( ) ( )2 1 1int* 5*id id idx goalpo x rand motioncoeff x= + (34) step 10: update new values to xid and save the best cost, which is the goal point. step 11: check the condition to stop the program. if iter < itermax, iter = iter + 1 and return to step 4. otherwise, stop. v. numerical results a. ieee 14-bus test system the ieee 14-bus system was used to investigate the effect of tcsc on social welfare. the ieee 14 bus system consists of 5 generators and 20 lines, as shown in figure 3. the marginal benefit function for generator and load are given in [12]. optimal power flow programs are executed by modifying the matpower [30] program implementation of coa in scheduling gencos and discos (table i). fig. 3. the ieee 14-bus system fig. 4. the bus voltage profile of ieee 14-bus system with and without tcsc fig. 5. power flow branch of ieee 14-bus system with and without tcsc the results of social benefit, scheduling of gencos and discos in the case of with and without tcsc for the ieee 14 bus system are presented in tables i-iv. from table i it can be seen that, the total real power of the generator and the total power consumption in the case of using the coa algorithm are higher than when using the ga and gwo algorithm [22]. moreover, the distribution of power consumption at the load buses of the coa algorithm compared to ga, gwo is also different, reflecting in better social benefit value for coa algorithm as shown in table iii. fig. 6. convergence characteristics of coa compared pso and boa for the ieee 14 bus system without tcsc fig. 7. convergence characteristics of coa compared pso and boa for the ieee 14 bus system with tcsc engineering, technology & applied science research vol. 9, no. 6, 2019, 4946-4955 4951 www.etasr.com duong et al.: an effective method for maximizing social welfare in electricity market via optimal … table i. comparison of ga and gwo scheduling of gencos and discos without tcsc for the ieee 14 bus system bus no ga [22] gwo [22] coa v (pu) p (mw) q (mvar) v (pu) p (mw) q (mvar) v (pu) p (mw) q (mvar) gen 1 1.1 94.97 45.43 1.1 97.55 43.51 1.1 97.675 39.895 2 1.089 100.0 56.58 1.089 100.0 54.57 1.091 100.00 59.818 3 1.095 100.0 29.86 1.095 100.04 29.18 1.100 100.00 34.050 6 1.035 52.08 7.22 1.035 50.31 15.29 1.027 52.176 10.825 8 1.09 0 25.28 1.09 0 25.21 1.086 0 24.995 total 347.0 164.67 347.9 167.76 349.8 169.58 dis 4 0.997 110.9 53.75 0.998 110.9 53.73 0.998 110.11 53.330 5 0.991 131.3 63.61 0.994 117.6 56.99 0.993 118.79 57.536 9 1.039 5.01 2.43 1.04 5.02 2.43 1.045 0 0 10 1.019 20.82 10.08 1.022 11.15 5.4 1.034 5.0015 2.4223 11 1.01 18.19 8.81 1.0 29.92 14.49 1.015 13.897 6.7306 12 0.998 18.51 8.97 0.978 31.35 15.18 0.993 28.420 13.764 13 1.01 14.42 6.98 1.01 5.63 2.73 0.970 31.485 15.249 14 1.009 12.07 5.85 0.998 19.51 9.45 1.002 5.0000 2.4216 total 331.3 160.49 331.16 160.39 332.83 161.20 table ii. comparison of ga and gwo scheduling of gencos and discos with tcsc for the ieee 14 bus system bus no ga [22] gwo [22] coa v (pu) p (mw) q (mvar) v (pu) p (mw) q (mvar) v (pu) p (mw) q (mvar) gen 1 1.1 98.37 53.65 1.1 93.83 44.26 1.1 94.903 32.391 2 1.089 100.1 53.66 1.089 101.1 52.95 1.093 100.03 59.480 3 1.095 100.0 30.1 1.095 101.1 28.42 1.099 100.00 28.517 6 1.035 64.25 7.92 1.035 49.8 15.42 1.051 49.492 19.235 8 1.09 0 25.49 1.09 0 26.0 1.092 0 24.987 total 362.8 170.82 344.8 344.87 344.43 164.61 dis 4 0.997 125.4 60.74 0.999 102.8 49.79 1.000 116.8 56.60 5 0.995 129.1 62.54 0.994 118.7 57.71 0.997 117.6 56.97 9 1.039 5.0 2.42 1.036 5.0 2.42 1.038 5.001 2.422 10 1.019 20.12 9.74 1.019 14.46 7.0 1.019 22.14 10.72 11 1.007 20.48 9.92 1.001 26.95 13.05 1.014 20.13 9.749 12 0.995 27.99 13.55 0.981 27.71 13.42 1.014 22.03 10.67 13 1.012 10.5 5.09 1.002 8.57 4.15 1.019 11.45 5.546 14 1.016 7.69 3.72 0.985 24.14 11.69 0.996 22.85 11.06 total 346.3 167.74 328.37 159.04 328.1 158.88 table iii. comparison of ga, gwo and coa for social welfare maximization for the ieee 14 bus system without tcsc with tcsc ga [22] gwo [22] coa ga [22] gwo [22] coa gencos 1408.93 1415.50 1424.87 1494.77 1401.62 1396.48 discos 2910.75 2966.62 2982.17 3014.85 2969.66 3022.30 social welfare 1501.81 1551.12 1557.30 1520.08 1568.03 1581.21 location of tcsc line 1-5 line 6-13 line 7-9 size of tcsc (pu) -0.2315 -0.49 -0.693 table iii shows that the social benefit of ga and gwo algorithms is 1501.81 ($/h) and 1551.12 ($/h) while for coa is 1557.30 ($/h). compared with ga and gwo, the social benefit of coa is 3.56% higher than the one for ga and 0.39% higher than the one for gwo. in addition, as can be seen from figures 4-5, the power on the branches and the voltage at the buses when using the coa algorithm are within the allowable limits. the scheduling of gencos and discos in the case with tcsc of coa are presented in table ii. the tcsc has redistributed the power flow on the lines, increasing social benefits. the optimal position of tcsc is at line 7-9 with xtcsc=-0.693pu when using the coa algorithm. from figures 3-4 it can be seen that the power flow on the branches in the system is redistributed with more balance, the voltage at the buses is also within limits after installing tcsc. social benefits of ga, gwo and coa algorithms with tcsc are presented in table iii. it can be seen that the social benefit in the case when using tcsc of coa algorithm is 3.86% higher than with ga algorithm with tcsc and 0.83% higher than with gwo algorithm with tcsc. the results of generator power and load power cases with and without tcsc using coa algorithm are presented in table iv. from this table, it can be seen that the total real power of generator and total power consumption in the case of tcsc is less than in the case without tcsc, but the social benefits in the case of tcsc are higher than without tcsc as shown in table iii. this shows that tcsc has engineering, technology & applied science research vol. 9, no. 6, 2019, 4946-4955 4952 www.etasr.com duong et al.: an effective method for maximizing social welfare in electricity market via optimal … improved social benefits. the tcsc has redistributed the power flow and improved the transmission capability. hence, load buses that have high benefit factor tend to increase the power consumption as seen in table iv (bus 10, bus 14), while load buses that have low benefit tend to reduce power consumption as seen in table iv (bus 11, bus 4), so customer benefits are increased and results of social benefits in the case with tcsc is 1.51% higher than when there is no tcsc. in addition, the convergence of the coa algorithm is compared to particle swarm optimization (pso) and butterfly optimization algorithm (boa). from figures 6-7 can be seen that coa has the ability to converge quickly when compared to pso and boa. this shows that the coa algorithm is able to find the suitable location and size of tcsc to improve social benefits in the electricity market. it also shows the ability of the proposed coa algorithm to converge. table iv. the results of scheduling of gencos and discos with and without tcsc for the ieee 14 bus system coa without tcsc with tcsc bus no voltage (pu) real power (mw) reactive power (mvar) voltage (pu) real power (mw) reactive power (mvar) gencos 1 1.1 97.6759 39.8956 1.1 94.9034 32.3914 2 1.0911 100.0001 59.8188 1.0935 100.0353 59.4800 3 1.1000 100.0003 34.0500 1.0999 100.0024 28.5171 6 1.0271 52.1765 10.8259 1.0511 49.4929 19.2359 8 1.0862 0 24.9951 1.0924 0 24.9875 total 349.8529 169.5854 344.4340 164.6120 discos 4 0.9983 110.1130 53.3301 1.0050 103.1062 49.9366 5 0.9932 118.7988 57.5369 1.0011 115.3352 55.8594 7 1.0456 0 0 1.0521 0 0 9 1.0343 5.0015 2.4223 1.0410 5.0037 2.4234 10 1.0151 13.8970 6.7306 1.0227 22.2554 10.7788 11 0.9939 28.4203 13.7646 1.0178 19.7659 9.5731 12 0.9700 31.4859 15.2493 0.9954 30.8817 14.9567 13 1.0027 5.0000 2.4216 1.0255 5.0174 2.4301 14 0.9905 20.1220 9.7455 1.0063 26.6867 12.9250 total 332.8384 161.2010 328.0524 158.8830 table v. comparison of ga and gwo scheduling of gencos and discos without tcsc for the ieee 30 bus system bus no ga [22] gwo [22] coa v (pu) p (mw) q (mvar) v (pu) p (mw) q (mvar) v (pu) p (mw) q (mvar) gen 1 1.0 180.0 40.2 1.0 178.0 -39.78 1.0 192.5 8.253 2 1.0 53.19 54.31 1.0 60.29 52.42 0.977 79.67 37.74 5 1.0 35.32 89.76 1.0 33.61 91.46 0.947 32.56 70.01 8 1.0 35.0 53.43 1.0 34.99 53.21 0.953 19.66 54.63 11 1.0 30.0 12.69 1.0 30.0 12.09 0.997 27.48 15.84 13 1.0 40.0 28.27 1.0 40.0 32.06 0.999 39.35 20.74 total 373.5 198.05 376.9 201.48 391.3 207.2 dis 2 1.000 50.0 24.22 1.000 50.0 24.22 0.977 49.98 24.20 3 0.984 8.82 4.27 0.984 9.7 4.7 0.956 3.647 1.766 4 0.982 8.51 4.12 0.982 2.02 0.98 0.946 9.927 4.807 5 1.000 100.0 48.43 1.000 100.0 48.43 0.947 99.94 48.40 7 0.974 46.31 22.43 0.972 49.14 23.80 0.925 50.00 24.21 8 1.000 34.12 16.52 1.000 33.39 16.46 0.953 50.00 24.21 10 0.959 9.36 4.53 0.961 4.25 2.06 0.950 8.390 4.063 12 0.962 33.91 16.42 0.957 49.96 24.2 0.972 19.20 9.303 14 0.941 8.31 4.02 0.942 3.6 1.74 0.942 10.00 4.843 15 0.942 5.72 2.77 0.935 9.89 4.79 0.937 9.885 4.787 16 0.949 9.10 4.41 0.955 2.41 1.17 0.954 6.738 3.263 17 0.953 4.76 2.31 0.958 3.18 1.54 0.950 2.894 1.401 18 0.927 6.5 3.15 0.929 7.91 3.83 0.918 6.122 2.965 19 0.928 8.37 4.05 0.936 2.34 1.13 0.915 9.854 4.772 20 0.934 2.96 1.44 0.941 2.02 0.98 0.921 5.526 2.676 21 0.953 6.06 2.91 0.952 11.61 5.62 0.943 6.340 3.070 23 0.936 4.91 2.38 0.926 8.08 3.91 0.921 9.830 4.760 24 0.943 3.45 1.67 0.935 6.55 3.17 0.927 5.408 2.619 26 0.938 2.01 0.87 0.936 2.09 1.01 0.913 3.266 1.581 29 0.931 3.45 1.67 0.940 2.06 1.000 0.913 3.001 1.453 30 0.922 6.57 3.18 0.932 5.59 2.71 0.901 7.499 3.632 total 363.1 175.87 366.38 177.45 377.4 182.8 engineering, technology & applied science research vol. 9, no. 6, 2019, 4946-4955 4953 www.etasr.com duong et al.: an effective method for maximizing social welfare in electricity market via optimal … b. ieee 30-bus test system the ieee 30 bus data are considered from [31]. the system has 6 gencos and 21 discos with 41 transmission lines, as shown in figure 8. the marginal benefit function for gencos and discos are given in [31]. the implementation of coa in scheduling gencos and discos in the case without tcsc is presented in table v. the table shows that the total real power of generator and total power consumption when using the coa algorithm are higher than when using ga and gwo algorithms [22]. fig. 8. the ieee 30-bus system fig. 9. the bus voltage profile of ieee 30-bus system without and with tcsc the scheduling is different reflecting in better social benefit, which is shown in table vi. using ga and gwo algorithm, the social benefit is 5098.72 ($/h), and 5116.56 ($/h), and that of coa is 5771.90 ($/h), which is 11.66% and 11.35% higher respectively. figures 9-10 show the power on the branches and the voltage at the buses in the case without and with tcsc when using the coa algorithm, and they meet the allowable limits. it can be seen that, the social benefit value of using coa with tcsc is 5828.29 ($/h) as shown in table vi, which is 12.28% higher than the social benefit of using ga with tcsc, and is 6.66% higher than the social benefit of using gwo with tcsc. from figures 11-12 it can be seen that in the case with tcsc, coa has the ability to converge quicker than pso and boa. this shows that the coa is one of the useful methods for tcsc installation to maximize social welfare. fig. 10. power flow branch of ieee 30-bus system without and with tcsc fig. 11. convergence characteristics of coa compared with pso and boa for the ieee 30 bus system without tcsc convergence characteristics of coa compared with pso and boa for the ieee 30 bus system with tcsc p o w e r f lo w i n b r a n c h [ m v a ] engineering, technology & applied science research vol. 9, no. 6, 2019, 4946-4955 4954 www.etasr.com duong et al.: an effective method for maximizing social welfare in electricity market via optimal … table vi. comparison of ga, gwo and coa for social welfare maximization for the ieee 30 bus system coa without tcsc with tcsc ga [22] gwo [22] coa ga [22] gwo [22] coa gencos 1133.95 1144.84 1392.7028 1123.76 1250.19 1404.7130 discos 6232.68 6261.40 7164.8892 6235.99 6689.80 7233.0322 social welfare 5098.72 5116.56 5771.9023 5112.22 5439.61 5828.2939 location of tcsc line 6-28 line 6-8 line 1-2 size of tcsc (pu) -0.4366 0.5 0.4999 vi. conclusions maximizing social welfare is one of the most important issues in today’s competitive electricity market and a difficult challenge for the operator system to implement. maximizing social welfare depends on the optimal rescheduling of generation, demand levels, and optimal placement of tcsc. in order to solve this problem, 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2003 microsoft word 7-2715 -s_etasr_v9_n3_pp4112-4115 engineering, technology & applied science research vol. 9, no. 3, 2019, 4112-4115 4112 www.etasr.com vidal-silva et al.: advantages of giraph over hadoop in graph processing advantages of giraph over hadoop in graph processing cristian l. vidal-silva faculty of economics and administration, catholic university of the north, antofagasta, chile cristian.vidal@ucn.cl erika madariaga faculty of engineering bernardo o’higgins university santiago, chile erika.madariaga@ubo.cl trung pham information technology research center, faculty of economics and business, university of talca, talca, chile tpham@utalca.cl jose miguel rubio academic area of it and telecommunications, technological university of chile inacap, santiago, chile jrubiol@inacap.cl luis alberto urzua school of kinesiology, faculty of health, santo tomas university, talca, chile lurzua@santotomas.cl luis carter industrial civil engineering department, school of engineering, autonomous university of chile, talca, chile luis.carter@uautonoma.cl franklin johnson computing and information department, engineering faculty, university of playa ancha, valparaiso, chile franklin.johnson@upla.cl abstract—this article presents a comparison of the computing performance of the mapreduce tool hadoop and giraph on large-scale graphs. the main ideas of mapreduce and bulk synchronous parallel (bsp) are reviewed as big data computing approaches to highlight their applicability in large-scale graph processing. this paper reviews the execution performance of hadoop and giraph on the pagerank algorithm to classify web pages according to their relevance, and on a few other algorithms to find the minimum spanning tree in a graph with the primary goal of finding the most efficient computing approach to work on large-scale graphs. experimental results show that the use of giraph for processing large-size graphs reduces the execution time by 25% in comparison with the results obtained using the hadoop for the same experiments. giraph represents the optimal option thanks to its in-memory computing approach that avoids secondary memory direct interaction. keywords-giraph; hadoop; graph; big data; big graph i. introduction daily, 2.5 quintillion bytes are created globally [1]. the size of the “digital universe” was 4.4 zettabytes in 2013 and a tenfold growth is forecasted by 2020 [2]. precisely, given this growth exponential of information, the term big data is popularized. according to [3], big data is defined as: “large volumes, high speed and a great variety of information that demand innovative and profitable forms of information processing to improve understanding and decision making”. although there is a tendency to increase the space for information storage, there is no equivalent increase in the speed of access and processing. a direct solution to this problem, to reduce access time and data processing, is the use of computer clusters [4]. in this context, several distributed systems exist which permit combining data from different sources, but with high analysis and development costs, mainly for the concurrency of tasks, their synchronization, access and data transfer [4]. hadoop, an open-source framework based on mapreduce [5, 6] appears as a solution for the mentioned issues. according to [7], big data processing closely associates with unstructured information, that is, directly unrelated data. however, in current social networks, such as facebook and twitter, there are links between the component nodes, so their direct representation as graphs is adequate. however, due to the structure and associations of graphs, mapreduce and hadoop are not optimal for processing, due to the high cost of input/output of information and the possibility of requiring many chained mapreduce phases. in this context, giraph [8, 9] emerges. giraph is an open-source counterpart of pregel [10], a graph processing system developed by google for the processing of large graphs. although the generation of data grows at a rate of 60% per year, the technologies related to big data such as hadoop and giraph are still under development in chile. “we still need to know what big data can do for national companies and how they could impact different business lines” [11]. only 17% of companies are implementing or planning to corresponding author: cristian vidal-silva engineering, technology & applied science research vol. 9, no. 3, 2019, 4112-4115 4113 www.etasr.com vidal-silva et al.: advantages of giraph over hadoop in graph processing apply big data in the short term in chile [11]. the primary objective of this work is to present a review of the application of hadoop and giraph for the processing of graphs, and thus highlight the practical advantages that giraph has over hadoop when solving problems considering relational data which usually support iterative algorithms, such as graph structures. for this, this article presents a comparison performance results of hadoop and giraph algorithmic solutions for a classic problem (minimum spanning tree) and a more modern problem (classification of web pages). this work extends the research of [11] mainly to confirm the previously obtained results and conclusions, and to show its applicability for the processing of big data in developing countries like chile. ii. big data hadoop [4, 12] is an open source framework created to achieve secure, scalable and distributed computing. hadoop is based on google documents for mapreduce [5, 6] and google file system (gfs) [13] and allows the distributed processing of large data sets using computer clusters using simple programming models. a. mapreduce hadoop implements a computational paradigm called mapreduce. algorithmically, the base of mapreduce is the “divide and conquer” approach, that is, it divides the problem into small pieces for processing in parallel and thus obtains solutions in a distributed environment [12]. the mapreduce programming model composes of a map function and a reduce function: map receives a key-value input pair and produces a set of intermediate key-value pairs. then mapreduce groups all intermediate values associated with the same intermediate key as the input of the reduce function. in this way, the reduce function accepts an intermediate key and a set of related values for that key to mix these values and thus form a new set of final output [6]. usually, a solution in mapreduce is performed in five stages: i) splitting: the data are divided into multiple parts and delivered to each mapper. ii) the mapper executes the map function in charge of processing the data. iii) the combiner works directly on the output of mappers for local aggregation. iv) shuffle: it is responsible for shuffling and ordering the key-value pairs for the function reduce. v) reducer: in the last step all the values with the same intermediate key are reduced to generate the final key-value pairs [6]. b. hadoop distributed file system (hdfs) hadoop includes a distributed file system (hdfs) that can handle large amounts of data. the most efficient pattern of data processing is to write once and read many times [4]. such as in a file system of a single disk, the files in hdfs are divided into blocks for their storage and representation as independent units. an hdfs cluster presents two types of nodes which operate in a master-worker pattern: a namenode (the master) and several datanodes (workers) [12]. the namenode stores and manages the metadata of the file system, and knows the datanodes in which all the real blocks for a given file are located. when the data are retrieved, the client contacts the namenode to obtain the list of the requested data locations and then directly contacts the datanode to extract the real data [12]. both, mapreduce and hdfs, manage errors automatically by the hadoop framework [4]. iii. big graphs, pregel and giraph solutions graphs are a finite abstract data type, which consists of a set of edges and nodes or vertex. an edge between two nodes x and y can be described mathematically by a function edge (x, y) [7]. in big data analysis, graph processing is considered computationally tricky due to its variable nature [7]. besides, graph processing is not adequate with general-purpose systems such as mapreduce [14]. for the processing of large graphs (big graphs), pregel and giraph are used, which are based on the bulk synchronous parallel (bsp) [15]. bsp is a parallel computing model, in which the calculations are divided into super passes (super-steps) separated by global barriers [16]. a. pregel in 2010 google announced pregel [10], a framework for distributed graph processing based on bsp. its objective was to provide a certain level of abstraction so that programmers do not have to deal with distributed memory management or synchronization [8, 17]. the paradigm used by pregel is “think as vertex”. pregel specifies each calculation regarding what each vertex should do, and edges are the communication channels for the transmission of the results from one vertex to another. in each super-step, a vertex can execute a user-defined function and change its status from active to inactive. an argue vertex can vote to stop a super-step (inactive) and awake when it receives a message (active) [16]. b. giraph apache giraph [8, 9] is an open-source alternative of pregel. in pregel, to support multithreading, each worker is assigned several partitions of the graph. during each super step, a pair of available workers calculates threads with noncalculated partitions. each worker maintains its own message store to store all incoming messages. to reduce the contention in the warehouse, and to efficiently use network resources, each computing thread has a cache buffer for all outgoing messages [18]. to implement the bsp model, the workers maintain two stores in each super-step, one for previous messages and another for current messages [18]. giraph supports different data structures for the list of adjacent vertices [16]. it is important to note that giraph solutions run as mapreduce tasks and they use zookeeper to coordinate global barriers [18]. a giraph solution is organized as a set of idealized iterative super-steps. in each super step, a vertex can send messages to the other vertices, can get its stored values or known information from its edges, and vote to stop. at the beginning of the computation (super-step 0), all vertices start with an active state. a vertex votes to stop because it decided, from its local point of view, that its work is done and the calculation can conclude. the delivery of a message changes the state of a vertex from inactive to active. giraph finishes the calculation when all the vertices are inactive, and there are no messages to send. iv. experiments and results for performance comparison of graph processing between hadoop and giraph, two algorithmic situations are considered: engineering, technology & applied science research vol. 9, no. 3, 2019, 4112-4115 4114 www.etasr.com vidal-silva et al.: advantages of giraph over hadoop in graph processing • classification of pages pagerank: pagerank is an algorithm created by google [14] to classify web pages, based on the idea that the most relevant web pages probably receive more links from other web pages [16]. the web conceptualizes as a directed graph in which all web pages are nodes, and there are arcs between pages if there are links between those pages. typically, pagerank iterates until reaching a convergence, that is, when the pagerank values for each node no longer change. therefore, at the end of each iteration, pagerank should check the convergence state. on the other hand, as authors in [19] highlight, pagerank can also fix a fixed number of iterations. • minimal spanning tree kruskal and boruvka algorithm: the algorithms of kruskal and prim [20, 21] are standard solutions to obtain a minimal spanning tree of a graph. this paper uses an implementation of the kruskal algorithm in hadoop, and one implementation of a giraph solution to find a minimal distributed spanning tree, boruvka algorithm [16]. hadoop 2.4.0 and giraph 1.1 in ubuntu 15.10 were used for both experiments. for the execution tests of both solutions, due to hardware limitations, we decided to use hadoop in “single node setup” mode [4] in a machine with two cpus and 8 gb of ram. for comparison, pagerank, kruskal and boruvka algorithms testing will be carried out with implementations in hadoop and giraph, respectively. besides, we used a representative data set consisting of a graph with 31 vertices and 82 edges of weight one for the case of pagerank. this data set corresponds to a set of cities of the region of valparaiso, chile and their connection, that is, if there is a direct road to connect these cities. although these data are small, regarding big data, we can extrapolate them for larger computing scenarios. a. results both pagerank in hadoop and giraph were defined with 30 iterations / super-steps respectively. the calculation times of each of these tests are shown in figures 1-2. fig. 1. results of the pagerank algorithm in hadoop. kruskal’s algorithm found the minimum spanning tree (mst) in around 3 seconds in hadoop (figure 3) in a single iteration, while its implementation in giraph found the solution in around 0.7 seconds in 2 super-steps (figure 4). fig. 2. results of the pagerank algorithm in giraph. fig. 3. results of the kruskal algorithm in hadoop. fig. 4. results of the kruskal and boruvka algorithm in giraph. to justify the obtained results, to process the entire graph, mapreduce performs many chained tasks to achieve its objective, and each task involves inputs and outputs to disk. ideally, an iteration in mapreduce represents a super-step in the giraph approach [7]. with that assumption, we can establish an average time per iteration between the total time and the number of iterations / number of super-steps, for each of the four tests. table i presents the mentioned results. figure 5 shows a comparison of the average times for the calculations made by hadoop and giraph with the kruskal and boruvka algorithms, respectively, to find the minimal spanning tree of a graph. when comparing the times associated with pagerank, the giraph solution is at least four times faster than hadoop. this difference increases to 8 times in the case of kruskal in hadoop and boruvka in giraph to find a tree of minimum expansion of a graph. engineering, technology & applied science research vol. 9, no. 3, 2019, 4112-4115 4115 www.etasr.com vidal-silva et al.: advantages of giraph over hadoop in graph processing table i. execution time in hadoop and giraph. test results total time (ms) super-steps avg. time (ms) pagerank hadoop 32.238 30 1.074,6 pagerank giraph 7.925 30 264,2 kruskal hadoop 3.096 1 3.096 boruvka giraph 718 2 359 fig. 5. a comparison between hadoop and giraph for the pagerank and mst algorithms. v. conclusions according to the results, giraph presents a four times higher efficiency on hadoop in computation time of the pagerank algorithm. this advantage increases to almost eight times when it comes to finding the minimum spanning tree, because of the advantage of giraph to maintain a global communication between each super-step without requiring inputs and outputs to disk since each node can exchange messages with others [19]. the previously described situation is not possible in hadoop, since mapreduce does not provide any tool for global and direct communication between the participants in each iteration. also, the nature of the graphs means that the computation of each node depends on its neighboring nodes, which implies that mapreduce solutions have to perform many chained iterations, which generates an excessive i/o traffic. it should be noted that giraph is not a tool that comes to replace hadoop, it should rather be a complementary solution for given problems. hadoop has a complete ecosystem [4], which expands day by day, and it is relevant to know the advantages of both technologies, in order to assimilate them correctly. an immaturity still exists regarding big data technology and available information about its use and support use of big data tools in developing countries such as chile [2, 11]. because the focus of this work is a practical comparison between hadoop and giraph for graph problems, a future work would be to make a comparison between giraph and current big data tools such as apache spark [22] and flink [23, 24], in real and research scenarios such as model processing. since giraph’s primary focus is graph processing, it is required to verify its potential performance advantages. references [1] i. yaqoob, i. a. t. hashem, a. gani, s. mokhtar, e. ahmed, n. b. anuar, a. v. vasilakos, “big data”, international journal of information management, vol. 36, no. 6, pp. 1231–1247, 2016 [2] a. k. wahi, v. ahuja, “the internet of things-new value streams for customers”, international journal of information technology and management, vol. 16, no. 4, pp. 360–375, 2017 [3] p. zikopoulos, c. eaton, understanding big data: analytics for enterprise class hadoop and streaming data, mcgrawhill osborne media, 2011 [4] t. white, hadoop: the definitive guide, o’reilly media, inc., 2015 [5] j. dean, s. ghemawat, “mapreduce: simplified data processing on large clusters”, 6th conference on symposium on operating systems design & implementation, san francisco, december 6-8, 2004 [6] j. dean, s. ghemawat, “mapreduce: simplified data processing on large clusters”, communications of the acm, vol. 51, no. 1, pp. 107–113, 2008 [7] m. aurelio, b. fagnani, g. lotz, dynamic graph computations using parallel distributed computing solutions, science without borders, 3months project report, queen mary, university of london, 2013 [8] r. shaposhnik, c. martella, d. logothetis, practical graph analytics with apache giraph, apress, 2015 [9] s. sakr, f. m. orakzai, i. abdelaziz, z. khayyat, large-scale graph processing using apache giraph, springer, 2017 [10] g. malewicz, m. h. austern, a. j. bik, j. c. dehnert, i. horn, n. leiser, g. czajkowski, “pregel: a system for large-scale graph processing”, 2010 acm sigmod international conference on management of data, indianapolis, usa, june 6-11, 2010 [11] s. valenzuela, c. vidal, “evaluacion de hadoop y giraph para el procesamiento de grafos”, jornadas chilenas de la computacin, xxvii encuentro chileno de computacin. santiago, chile, 2015 (in spanish) [12] s. karanth, mastering hadoop. packt publishing, 2015 [13] s. ghemawat, h. gobioff, s. t. leung, “the google file system”, nineteenth acm symposium on operating systems principles, bolton landing, usa, october 19-22, 2003 [14] s. brin, l. page, “the anatomy of a large-scale hypertextual web search engine”, computer networks and isdn systems, vol. 30, no. 1-7, pp. 107–117, 1998. [15] l. g. valiant, “a bridging model for parallel computation”, communications of the acm, vol. 33, no. 8, pp. 103–111, 1990 [16] m. han, k. daudjee, k. ammar, m. t. ozsu, x. wang, t. jin, “an experimental comparison of pregel-like graph processing systems”, proceedings of the vldb endowment, vol. 7, no. 12, pp. 1047–1058, 2014 [17] s. salihoglu, j. shin, v. khanna, b. q. truong, j. widom, “graft: a debugging tool for apache giraph”, 2015 acm sigmod international conference on management of data, melbourne, australia, may 31june 4, 2015 [18] m. han, k. daudjee, “giraph unchained: barrierless asynchronous parallel execution in pregel-like graph processing systems”, proceedings of the vldb endowment, vol. 8, no. 9, pp. 950–961, 2015 [19] j. lin, c. dyer, data-intensive text processing with mapreduce, morgan and claypool, 2010 [20] m. held, r. m. karp, “the traveling-salesman problem and minimum spanning trees: part ii”, mathematical programming, vol. 1, no. 1, pp. 6–25, 1971 [21] r. c. prim, “shortest connection networks and some generalizations”, bell system technical journal, vol. 36, no. 6, pp. 1389–1401, 1957 [22] m. zaharia, r. s. xin, p. wendell, t. das, m. armbrust, a. dave, x. meng, j. rosen, s. venkataraman, m. j. franklin, a. ghodsi, j. gonzalez, s. shenker, i. stoica, “apache spark: a unified engine for big data processing”, communications of the acm, vol. 59, no. 11, pp. 56– 65, 2016 [23] e. friedman, k. tzoumas, introduction to apache flink: stream processing for real time and beyond, o’reilly media, 2016 [24] s. papp, the definitive guide to apache flink: next generation data processing, apress, 2016 microsoft word 1-3663l_s_etasr_v10_n5_pp6161-6164 engineering, technology & applied science research vol. 10, no. 5, 2020, 6161-6164 6161 www.etasr.com ho: fabrication of cu4sns4 thin films: α review fabrication of cu4sns4 thin films: α review soon min ho center for american education inti international university putra nilai, negeri sembilan, malaysia soonmin.ho@newinti.edu.my abstract-ternary compounds such as cu4sns4 thin films can be deposited onto glass substrates by various deposition methods: electrodeposition, chemical bath deposition, successive ionic layer adsorption and reaction, and evaporation techniques. cu4sns4 films could be used in solar cell applications because of their suitable band gap and large absorption coefficient. this paper reviews previous researches on cu4sns4 thin films. x-ray diffraction showed that the obtained films are orthorhombic in structure and polycrystalline in nature. cu4sns4 films exhibited p-type electrical conductivity and indicated band gap values in the range of 0.93 to 1.84ev. keywords-copper tin sulfide; thin films; solar cells; band gap; semiconductor i. introduction the preparation and characterization of binary [1-6], ternary [7-10], quaternary [11-13] and pentanary thin films [1418] have been reported. in general, these films are produced using various physical and chemical deposition techniques [19], each having its own advantages and limitations. the choice of deposition method depends strongly on the desired product, material cost, operational cost, and material’s properties. in recent years, many scientists researched on new ternary semiconductor materials for their applications in supercapacitor [20], sensors, solar cell [21], and optoelectronic devices. the cu-sn-s compounds have attracted great attention due to their excellent morphological, electrical, and optical properties [22, 23]. these materials are non-toxic [24], cheap, and derive from earth abundant elements [25]. this paper examines various deposition techniques used on the production of cu4sns4 thin films, investigating their results. moreover, the photovoltaic parameters of cu4sns4 films used as absorber material in solar cell applications are presented. ii. literature review a. structural analysis of thin films the deposition rate and thickness of evaporated cu4sns4 films have been studied at the substrate temperature of 400°c using x-ray diffraction (xrd). the films with orthorhombic phase were observed showing polycrystalline structure. many xrd diffraction peaks were observed corresponding to the (311), (121), (102), (112), (411), (022), (511), (222), (502), (512), (403) and (503) planes [26]. xrd patterns confirmed that the major peak corresponded to the (311) plane, as its intensity increased when the film’s thickness increased from 0.25µm to 1µm. lattice parameters were measured as a=13.52å, b=7.67å and c=6.43å. debye-scherrer formula was used to calculate the crystallite size. smaller crystallites sized 39nm were observed in thinner films (0.25µm), because of the strong interaction between the substrate and the vapored atoms [26]. larger crystallites sized 76nm could be found in thicker films (1µm) due to columnar grain growth in the films. raman analysis was in aggreement with the xrd results. raman line was detected in 317cm-1, indicating the existence of cu4sns4 phase. other binary (such as sns, cus, sns2, cu2s) or ternary compounds (such as cu2sns3, cu3sns4) were not detected. thin films of cu4sns4 were synthesized through mechanochemical and doctor blade processes under different temperatures. xrd patterns showed that diffraction peaks were weak at 28.6°, 33.1°, 47.7° and 56.5° in as-deposited films. however, sharp diffraction peaks were detected in films annealed at 350–450°c. researchers found that cu2s peaks appeared at 500°c, indicating the evaporation of tin and sulfur atoms or decomposition of the cu-sn-s compounds [27]. the successive ionic layer adsorption and reaction (silar) method was used to produce cu4sns4 films. deposition was carried out in 60 cycles in sncl2, cucl2, and na2s solutions [28]. xrd patterns showed the presence of cu2s and sns2 in deposited films. the formation of orthorhombic phased cu4sns4 films was observed in annealed under h2s atmosphere procedure. raman spectrum showed a peak at 312cm-1 confirming the existence of cu4sns4 films. nanostructured cu4sns4 films were produced by annealing chemical bath deposited sns–cus stacks at 823k in a graphite box under various n2+s2 pressures [29]. orthorhombic phase and crystallize size increased (200nm to 260nm) as pressure increased. xrd data confirmed that a mixture of orthorhombic and a dominant monoclinic phase was observed when the films were prepared at 101.3kpa. raman spectrum analysis supported this finding. a single peak at 322cm-1, corresponding to cu4sns4, and three peaks at 290cm -1, 351cm-1 (corresponding to monoclinic), 318cm-1 (corresponding to cu4sns4) were found for films synthesized at 1.3-66.7kpa, and 101.3kpa, respectively. electrodeposition was used to prepare cu4sns4 thin films onto indium doped tin oxide glass substrate under various deposition potentials in [30]. this deposition method has many advantages such as cheap raw materials and equipment, while it can deposit a large area of thin film in low temperature. xrd patterns showed that reflecting planes are (221), (420), (312), corresponding author: soon min ho engineering, technology & applied science research vol. 10, no. 5, 2020, 6161-6164 6162 www.etasr.com ho: fabrication of cu4sns4 thin films: α review (512), and (711), while a deposition potential of -0.4 and -0.6v versus ag/agcl was observed. however, only four diffraction peaks were detected at -0.8v. the effect of temperature on electrodeposited cu4sns4 was studied in [31]. xrd analysis showed six diffraction peaks when the films were prepared at low temperatures such as 25 and 35°c. the major peak corresponded to (221) plane, and its intensity increased as bath temperature increased from 25°c to 50°c. b. morphology analysis of thin films the morphology of cu4sns4 thin films with various thicknesses produced using the evaporation method was also studied. scanning electron microscopy (sem) images indicated worm like grains uniformly distributed on the substrate surface in all samples. however, small grains with regular shapes and bigger grains with multiple structures were observed in thicknesses less than 0.5µm and more than 0.75µm, respectively [26]. the effect of annealing temperature was also reported. cu4sns4 films prepared at low annealing temperatures (350-450°c) are powder-like and densely packed compared to films prepared at 500°c. the morphology of silar deposited thin films in h2s atmosphere was studied in [28]. it was found that as-deposited films contained clusters in the size of hundreds of nanometers. however, annealed films under h2s atmosphere showed coarse surfaces and small amounts of holes. nanostructured cu4sns4 films were produced by annealing chemical bath deposited sns–cus stacks at 823k in a graphite box under various n2+s2 pressures [29]. field emission scanning electron microscope (fesem) results showed that n2+s2 pressure can control the morphology of films at 1.3kpa (large grains with 3-6µm and compact grains), 26.7 to 66.7kpa (grains’ size increased up to 6µm), and 101.3kpa (small 2µm grains, with a few voids). the influence of deposition potential on electrodeposited cu4sns4 films was studied in [30]. these films showed incomplete coverage substrate’s surface (at deposition potential of -0.4 versus ag/agcl), compact and smooth surface (at deposition potential of -0.6 versus ag/agcl), and not uniform surface (at deposition potential of -0.8 versus ag/agcl) based on atomic force microscopy (afm) images. the influence of the concentration of na2edta complexing agent on the chemical bath deposited cu4sns4 films was studied in [32]. afm images revealed that film’s thickness increased from 640nm to 981nm with increasing na2edta concentration from 0.01m to 0.05m. however, its thickness was 125nm when 0.1m of complexing agent was used. c. compositional analysis of thin films energy dispersive x-ray analysis (edax) has been utilized to study the composition of thin films. the evaporated 1µm thick cu4sns4 films indicated that the elemental composition was copper at 43.35%, tin at 15.56%, and sulfur at 41.09%, respectively [26]. nanostructured cu4sns4 films were produced by annealing chemical bath deposited sns–cus stacks at 823k in a graphite box under various n2+s2 pressures [29]. as n2+s2 pressure increased from 1.3kpa to 101.3kpa the atomic percentage of sulfur and tin increased from 44.2% and 12.1% to 51.6% and 15.7%, respectively, but copper decreased from 43.1% to 32.7%. chemical bath deposition has been used to prepare cu4sns4 films under experimental conditions such as: ph 1.5, bath temperature 50°c, for 120 minutes, and 0.05m of electrolyte concentration [33]. the edax analysis indicated the presence of only copper (49.1%), tin (12.6%) and sulfur (38.3%) in the sample. d. optical analysis of thin films the transmittance of the evaporated cu4sns4 films with various thicknesses has been also studied. the presence of direct optical transition was observed with a steep increase in the transmittance near the fundamental absorption [26]. experimental results revealed that absorption edge moved towards longer wavelength as the film thickness increased from 0.25µm to 1µm. the band gap decrease of thin films from 1.47ev to 1.21ev with the increase in film thickness was caused by the reduction of structural disorder and the increase in the crystalline size. the influence of annealing temperature on the cu4sns4 prepared by mechanochemical and doctor blade processes was studied in [27]. the uv-visible-ir spectra indicated that absorption intensity reduced at 935–1500nm, but, its intensity increased at wavelengths longer than 1500nm as annealing temperature increased from 350°c to 500°c. the optical properties of thin films highlighted that cu4sns4 could be very sensitive to the annealing temperature in terms of band gap measurement. cu4sns4 thin films synthesized by using silar method in [28] had band gap and optical absorption coefficients at 0.93ev and 104cm-1, respectively. deposition potential plays an important role during the preparation of thin films. the band gap values of electrodeposited cu4sns4 films at deposition potential of -0.4 to -0.8v versus ag/agcl were in the range of 1.58 to 1.84ev [30]. preparation of cu4sns4 thin films onto indium tin oxide (ito) coated glass via chemical bath deposition method in the presence and absence of complexing agent was described in [34]. the films produced by using complexing agent such as na2edta showed high absorption characteristics, as more materials were successfully deposited onto substrates. the presence of complexing agent during the deposition process produced better quality of films. e. electrical analysis of thin films evaporated cu4sns4 thin films show p-type electrical conductivity based on the hot probe test. the increase of film thickness decreased resistivity and mobility of the films from 5.8×102ωcm to 2.5×102ωcm and 12cm2v-1s-1to7cm2v-1s-1 respectively, while their carrier concentration increased from 9×1014cm-3 to 3.6×1015cm-3 [26]. on the other hand, electrical resistivity decreased as the temperature increased, showing their semiconducting properties [35]. the p-type behaviors in cu4sns4 films are supported by large positive seebeck coefficients, indicating that major carriers are predominantly holes possibly arising from copper deficiency [35]. seebeck coefficients increased as temperature increased during the experiment. electrical properties of silar deposited thin films were also investigated, and electrical conductivity increased as temperature increased from room temperature to 475k [28]. activation energy values were 0.009ev and 0.06ev in the temperature regions less and more than 343k, respectively. in nanostructured cu4sns4 films produced by annealing chemical bath deposited sns–cus stacks at 823k in a graphite box under various n2+s2 pressures, resistivity, mobility and carrier concentration were found to be in the range of 0.41 to engineering, technology & applied science research vol. 10, no. 5, 2020, 6161-6164 6163 www.etasr.com ho: fabrication of cu4sns4 thin films: α review 0.52ωcm, 69.5 to 150cm2/vs, and 1.96×1017 to 1.25×1018cm-3, respectively [29]. f. photovoltaic characteristics analysis of thin films solar cells have been fabricated by using mo/cu4sns4/in2s3/tio2/fluorine doped tin oxide glass in [27]. as temperature increased from 350°c to 375°c, short circuit current, open circuit voltage, and power conversion efficiency increased from 17.44 to 29.24ma/cm2, from 0.21 to 0.3v, and from 0.91% to 2.34% respectively. however, these values decreased as temperature increased to 500°c. at this annealing temperature, short circuit current, open circuit voltage, fill factor and power conversion efficiencies were 1.12ma/cm2, 0.03v, 0.26, and 0.009% respectively [27]. on the other hand, the photovoltaic performance of cu4sns4 thin films was studied in [36] achieving a power conversion efficiency of 2.4%. iii. conclusions cu4sns4 thin films have been prepared by various deposition methods under different experimental conditions. the physical properties of films have been characterized via xray diffraction, atomic force microscopy, scanning electron microscopy, uv-visible spectrophotometer, energy dispersive x-ray analyzer, and raman spectroscopy technique. the formation of cu4sns4 phase was confirmed by using x-ray diffraction. cu4sns4 thin films have achieved a power conversion efficiency of 2.34%. acknowledgement the author is grateful to the inti international university for providing the financial assistance to carry out this work. references [1] g. m. mikheev, v. ya. kogai, t. n. mogileva, k. g. mikheev, a. s. saushin, and y. p. svirko, “photon helicity driven surface photocurrent in cuse films,” applied physics letters, vol. 115, no. 6, aug. 2019, art. no. 061101, doi: 10.1063/1.5109069. 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[34] a. kassim, z. kuang, a. sharif, t. w. tee, h. s. min, and s. nagalingam, “preparation and studies of chemically deposited cu4sns4 thin films in the presence of complexing agent na2edta,” indian journal of engineering and materials sciences, vol. 17, no. 4, aug. 2010. [35] a. choudhury et al., “new insights into the structure, chemistry, and properties of cu4sns4,” journal of solid state chemistry, vol. 253, pp. 192–201, sep. 2017, doi: 10.1016/j.jssc.2017.05.033. [36] v. r. minnam reddy et al., “review on cu2sns3, cu3sns4, and cu4sns4 thin films and their photovoltaic performance,” journal of industrial and engineering chemistry, vol. 76, pp. 39–74, aug. 2019, doi: 10.1016/j.jiec.2019.03.035. authors profile soon min ho is a professor in inti international university in malaysia. he received his ph.d. in materials chemistry at university putra, malaysia. he has taught a variety of chemistry courses such as physical chemistry, organic chemistry, general chemistry, chemistry & society over the last ten years. his research areas include chalcogenide metals, activated carbon, green chemistry, semiconductors, nano materials, and thin film solar cells. he has authored or co-authored more than 140 articles in scopus/isi/international referred journals and successfully produced more than 43 book chapters. he has been appointed as a journal reviewer, editorial board member, and thesis external examiner. microsoft word 29-2595_s engineering, technology & applied science research vol. 9, no. 2, 2019, 4027-4029 4027 www.etasr.com soomro et al.: shrinkage of concrete panels made with recyclable concrete aggregates shrinkage of concrete panels made with recyclable concrete aggregates faheem ahmed soomro department of civil engineering, quaide-awam university of engineering, science & technology, pakistan fahim.as96@gmail.com bashir ahmed memon department of civil engineering, quaide-awam university of engineering, science & technology, pakistan basher_m@hotmail.com mahboob oad department of civil engineering, quaide-awam university of engineering, science & technology, pakistan mahbooboad04@gmail.com abdul hafeez buller department of civil engineering, quaid-e-awam university of engineering, science & technology, pakistan engrabdulhafeezbuller@gmail.com zaheer ahmed tunio department of civil engineering, quaid-e-awam university of engineering, science & technology, pakistan zaheerahmedtunio@gmail.com abstract—an experimental study on the shrinkage of recyclable aggregate concrete panels is presented in this paper. recyclable aggregates are used in 50%, 60%, 70% and 80% replacement of natural coarse aggregates. for each replacement percentage, 3 panels were cast using 1:2:4 mix with 0.54 water-cement ratio and were cured for 28 days. in addition, 3 panels with the same parameters but using all-natural coarse aggregates were also cast to compare the results. shrinkage in all panels was recorded for 3 months. comparison of results reveals that with a 50% replacement, 8.33% increase in shrinkage was recorded. along with shrinkage, cracks were also observed. at the end of the three month period, the widest crack had less width than 1mm, showing good resistance of the proposed material to shrinkage. concluding, 50% replacement can be used in new concrete. keywords-shrinkage; reinforced concrete panels; recyclable concrete aggregates; green concrete; concrete demolishing waste i. introduction global increased use of concrete has led to the excessive consumption of natural aggregates resulting in gradual depletion of their natural sources. on the other hand, demolishing of old concrete and raising of reinforced concrete structures have resulted in huge amounts of demolishing waste. the search of alternate aggregates to save natural sources of aggregates and proper dealing of demolishing waste led to the research on the reuse of demolishing waste in new concrete. various components of demolishing waste have been studied and successfully used in new constructions. as a big proportion of demolishing waste is concrete, its probable use as coarse aggregates in new concrete has been researched extensively in order to understand the behavior of the material, the optimum dosage and the resulting strength of concrete and reinforced concrete members. developments regarding the use of demolishing waste as coarse aggregates have been studied in [1-3]. authors in [4] provided a review of the use of this material with respect to construction industry. their study is concluded with several suggestions on the use of recycled aggregate concrete. among the attempts made to evaluate the properties of these aggregates, shrinkage is one of the most important properties causing concrete volume change. authors in [5] reviewed the research conducted for the determination of shrinkage in concrete made by using recycled concrete aggregates. the results revealed that present models overestimate the shrinkage in the proposed concrete. composite members were used in [6] (steel tubes filled with rac) to study the shrinkage in rac. if water loss occurs after the placement of concrete, plastic shrinkage will develop resulting in surface cracking, cracking around aggregates and reinforcements. to understand this phenomenon in rac, an experimental study was conducted in [7] using ring test and suggested remedial measures to minimize it, whereas, authors in [8] used varying percentages of recycled aggregates to estimate the plastic shrinkage of rac concrete. based on the results, they proposed 25% replacement of natural coarse aggregates as optimum replacement ratio. authors in [9] performed laboratory experiments for the evaluation of drying shrinkage with 100% replacement at different curing ages while utilizing fly ash. they measured 25% increase in shrinkage with rac which reduced to 7% if fly ash was used in the concrete. similar results for the use of fly ash in recycled aggregate concrete were reported in [10]. fly ash was also used by authors in [11] in addition to replacement of natural coarse aggregates with recycled aggregates to study drying shrinkage in bridge deck slabs. they observed no consistent effect on shrinkage but 32% reduction in cement weight after 365 days. drying shrinkage was studied in [12] by using construction demolishing waste as replacement of fine aggregates in 50% proportion resulting in higher values of shrinkage for the proposed concrete. authors in [13] used replacement of both fine and coarse aggregates with different water-cement ratios to corresponding author: mahboob oad engineering, technology & applied science research vol. 9, no. 2, 2019, 4027-4029 4028 www.etasr.com soomro et al.: shrinkage of concrete panels made with recyclable concrete aggregates study the shrinkage for durations up to 224 days. they observed prominent increase in shrinkage when fine aggregates were replaced with recycled aggregates but less effect when coarse aggregates were replaced. authors in [14] evaluated creep and shrinkage in concrete made with 20%, 50% and 100% replacement of natural coarse aggregates with recycled concrete aggregates at the age of 180 days. they observed 51% and 70% increase in creep and shrinkage respectively. the above review motivated the research work presented in this article, in which the shrinkage of concrete panels made with partial replacement of coarse aggregates with recycled concrete aggregates is presented. comparison of the results of the proposed panels with panels made using all-natural aggregates shows that 50% replacement is optimum at which only 8.33% increase in shrinkage is recorded. therefore, it may be concluded that recycled concrete aggregates have resistance to concrete shrinkage and can be used as 50% replacement of natural aggregates in new concrete. ii. methodology and material testing large blocks of old demolished concrete were collected from demolishing waste from about 45-year-old reinforced concrete buildings. screening of aggregates for cracked particles was done after reducing large blocks to maximum 20mm size. to make sure that the coarse aggregates were well graded sieve analysis of both recyclable aggregates and natural coarse aggregates of the same size was done (figure 1). basic properties, water absorption and specific gravity of both types of coarse aggregates were evaluated and it was observed that water absorption of recycled aggregates was 4.88 times higher than natural aggregates’ whereas, the specific gravity of recyclable aggregates was approximately 91% of that of natural coarse aggregates. to prepare the concrete panels, 1:2:4 mix with 0.54 water-cement ratio was used. the panels were prepared using 50%, 60%, 70% and 80% replacement of natural coarse aggregates. in each replacement percentage three panels were cast. in addition, 3 panels were prepared using allnatural coarse aggregates to compare the results. the dimensions of all panels were kept the same and equal to 900mm×150mm×100mm. concrete ingredients (ordinary portland cement, hill sand, natural coarse aggregates, recycled coarse aggregates and water) were batched using weight batching followed by casting of panels in standard fashion. all panels were cured for 28 days by immersing in water. fig. 1. gradation of nca and rca after the elapse of curing time, all panels where air dried for 24 hours, followed by installation of dial gauges on all panels in laboratory for testing shrinkage. a selected panel is shown in figure 2. readings were taken every other day for three months. cracking was monitored in the panels on a regular basis. fig. 2. a selected rc panel iii. results and discussion the higher water absorption of recycled aggregates is caused by the old mortar attached with the aggregates, whereas, lower specific gravity is due to their age. the values obtained for both parameters approximately confirm the results presented in [15]. as mentioned earlier, readings were recorded regularly followed by computation of the average values of the three panels in each replacement percentage. figure 3 shows the shrinkage results for all replacements. it is observed that with increasing dosage of recyclable aggregates, shrinkage strain increases. also, it is noted that the trend of increase of shrinkage strain is similar between different replacement percentage and between all-natural aggregates and recycled aggregates. fig. 3. shrinkage strain for all replacements. average and maximum values for all replacements are given in table i. although the differences in shrinkage strain between 50% and 60% replacements are not high, the percentile increase of shrinkage strain for 50% replacement is the minimum, being only 8.33%. therefore, 50% is the optimum replacement ratio of natural coarse aggregates with recycled concrete aggregates. this observation confirms the recommendations of [15]. with 50% replacement, the proposed concrete panels give better resistance to shrinkage strain. during testing time the panels were monitored for cracks. it was observed that first shrinkage crack appeared within 5 days of testing. however, at the end of testing time, it was recorded that the maximum crack width remained less than 1mm. engineering, technology & applied science research vol. 9, no. 2, 2019, 4027-4029 4029 www.etasr.com soomro et al.: shrinkage of concrete panels made with recyclable concrete aggregates table i. average and maximum shrinkage strain % replacement average strain maximum strain % difference 0% 23.39 53.33 50% 32.43 57.78 8.33 60% 30.87 64.44 20.83 70% 39.66 75.56 41.67 80% 50.61 100.00 87.50 iv. conclusion from the analysis of the obtained results it is concluded that the shrinkage in recycled aggregates concrete increases with increase in the dosage of recycled aggregates. beyond 50% dosage, shrinkage increases from 21% to 88%. therefore 50% ratio is proposed as optimum (8.33% shrinkage increase in comparison with control specimens) at which the proposed concrete panels show good resistance to shrinkage. monitoring of shrinkage cracks revealed less than 1mm crack widths at the end of the three month testing period. thus, recyclable aggregates can be used in new concrete. references [1] b. a. memon, “recent development on use of demolished concrete as coarse aggregates”, international journal of emerging technology and innovative engineering, vol. 2, no. 1, pp. 1-11, 2016 [2] m. oad, a. h. buller, b. a. memon, n. a. memon, “flexural stressstrain behavior of rc beams made with partial replacement of coarse aggregates with coarse aggregates from old concrete part-1, ratio 1:2:4”, engineering, technology & applied science research, vol. 8, no. 3, pp. 3048-3053, 2018 [3] m. oad, a. h. buller, b. a. memon, n. a. memon, “flexural stressstrain behavior of rc beams made with partial replacement of coarse aggregates with coarse aggregates from old concrete part-2: 1:2:4 ratio”, engineering, technology & applied science research engineering, technology & applied science research, vol. 8, no. 5, pp. 3338-3343, 2018 [4] r. singh, j. singh, “recycled aggregate concrete (rac) – a sustainable approach for construction industry”, international journal of research in engineering & applied sciences, vol. 5, no. 11, pp. 6065, 2015 [5] r. v. silva, j. de brito, r. k. dhir, “prediction of the shrinkage of recycled aggregate concrete”, construction and building materials, vol. 77, pp. 327-339, 2015 [6] y. f. yang, l. h. han, x. wu, “concrete shrinkage and creep in recycled aggregate concrete filled steel tubes”, advances in structural engineering, vol. 11, no. 4, pp. 383-396, 2016 [7] m. eckert, m. oliveira, “risk of plastic shrinkage cracking in recycled aggregate concrete”, international journal of civil and environmental engineering, vol. 9, no. 7, pp. 931-937, 2015 [8] m. a. salau, e. e. ikponmwosa, a. o. adeemo, “shrinkage deformation of concrete containing recycled coarse aggregate”, british journal of applied science & technology, vol. 4, no. 12, pp. 1791-1807, 2014 [9] b. a. whiting, t. j. mccarthy, e. lume, “drying shrinkage of concrete made from recycled concrete aggregate”, 22nd australasian conference on the mechanics of structures and materials, sydney, australia, december 11-14, 2012 [10] l. j. zhu, “the study on early drying shrinkage of recycled aggregate concrete”, 2nd international conference on waste engineering and management, shanghai, china, october 13-15, 2010 [11] m. west, d. darwin, j. a. browning, effect of materials and curing period on shrinkage of concrete, structural engineering and engineering materials, sm report no. 98, university of kansas, 2010 [12] p. r. l. lima, m. b. leite, “influence of cdw recycled aggregate on drying shrinkage of mortar”, open journal of civil engineering, vol. 2, no. 2, pp. 53-57, 2012 [13] a. b. e. cabral, v. schalch, d. c. c. dal-molin, j. l. d. riberio, r. s. ravindrarjah, “shrinkage modeling for recycled aggregate concretes”, ibracon structures and materials journal, vol. 3, no. 1, pp. 1-23, 2010 [14] a. domnigo-cabo, c. lazaro, f. lopez-gayarre, m. a. serrano-lopez, p. serna, j. o. catano-tabares, “creep and shrinkage of recycled aggregate concrete”, construction and building materials, vol. 23, no. 7, pp. 2545-2553, 2009 [15] m. oad, b. a. memon, “compressive strength of concrete cylinders using coarse aggregates from old concrete”, 1st national conference on civil engineering (modern trends and advancements), april 28-29, 2014 microsoft word 13-2697_s_etasr_v9_n3_pp4140-4143 engineering, technology & applied science research vol. 9, no. 3, 2019, 4140-4143 4140 www.etasr.com oad et al.: long term impact in reinforced recycled concrete beams under 9-month loading long term impact in reinforced recycled concrete beams under 9-month loading mahboob oad department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan engrmahboob04@gmail.com abdul hafeez buller department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan ah.buller@quest.edu.pk bashir ahmed memon department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan basher_m@hotmail.com noor ahmed memon department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan nahmedmemon@gmail.com samiullah sohu department of civil engineering, quaid-e-awam university college of engineering, science & technology, pakistan sohoosamiullah@gmail.com abstract—green concrete is an active area of research. structural demolishing waste is a global serious problem, particularly in urban areas. this research paper presents the experimental evaluation of the effect of long term loading on reinforced green concrete beams. three beams were cast with partial replacement of natural coarse aggregates with demolished old concrete. three beams were cast with all-natural coarse aggregates to compare the results. the beams were mounted on purpose made frames for 9 months. deflection, strain and cracking in beams were monitored on a daily basis. after 9 months, the beams were tested until failure in a universal load testing machine under central point load. it was observed that the proposed beams exhibited 3.55% reduction in maximum load caring capacity compared to control specimens. the obtained results show good performance of the proposed green concrete beams under 9-month long term loading. keywords-green concrete; demolished concrete; coarse aggregates; long-term loading flexural strength; deflection i. introduction the production of conventional concrete ingredients gave rise to several environmental issues. the rapid pace of development around the globe consumes these ingredients in large quantities. green concrete is the best solution to not only protect environment to some extent, but also to save natural resources for the future. the use of old, demolished concrete in new concrete, in full or partial replacement of coarse aggregates is an active area of research the last two decades. in this regard, author in [1] reviewed the recent trends regarding the use of demolished concrete as partial or full replacement of coarse aggregates in new concrete. under short term loading, authors in [2, 3] studied the flexural stress-strain behavior of reinforced recycled concrete beams using normal and rich mix concrete. from the obtained results they observed 8.8% and 11.68% reduction in flexural capacity of 28-day cured normal and rich mix beams respectively. in addition to short term loading, structures also have to face random jerks (wind and earthquake) and long-term/sustained loading during their service life. therefore, it is essential to check the performance of the proposed concrete under long-term loading to study the behavior of the material and improve the confidence in using it. to this end, shrinkage, creep and deflection under long-term loading using recycled aggregates and high volumes of fly ash were studied in [4]. authors reported that all studied parameters showed increase with increase in dosage of recycled aggregates. authors in [5] extended the study to concrete creep and shrinkage. they used four replacement levels of coarse aggregates, namely 0%, 20%, 50% and 100% and two different water-cement ratios, 0.5 and 0.65 for 1000 days in order to study the parameters. their observations were almost the same with the ones presented in [3]. they also recorded different behavior of the parameters when they used pre-saturated coarse aggregates. they also developed a numerical expression to predict the parameters of the study. authors in [6] also studied long-term deflection. authors in [10] studied the flexural capacity of recycled concrete beams under the combined effect of corroded steel and sustained loading. they observed reasonable performance of the proposed material under longterm loading. pore size and mechanical properties of concrete with recyclable aggregates from different sources were experimentally investigated in [8]. the authors used 5-year corresponding author: mahboob oad engineering, technology & applied science research vol. 9, no. 3, 2019, 4140-4143 4141 www.etasr.com oad et al.: long term impact in reinforced recycled concrete beams under 9-month loading cured samples of the proposed concrete. from the obtained results, they observed good correlation between porosity and strength of the concrete. comparison of experimental creep and shrinkage of recyclable concrete specimens under 1-year sustained loading with aci provisions was made in [7]. using their observations, the authors suggested modifications in the equation given by aci provisions. the modified equation was then used to check the experimental data of the parameters with good agreement. old concrete aggregates have old mortar attached with them. this not only increases the water demand of the concrete, but also has effect on its performance. the effect of mortar attached with old concrete aggregates has been studied in [9]. based on their study results, authors introduced residual-mortar-factor to existing aci and ceb methods used for computation of creep and drying shrinkage. comparison of the results using residual-mortar-factor and original formulation revealed better results with the proposed factor. authors in [11] used cylinders as coarse aggregates in production of reinforced recycled concrete beams to test for flexure, shear and bond. they used 40% and 100% replacement of natural coarse aggregates and control specimen with 0% recyclable aggregates. the comparison of test results with control specimen, aci provisions and similar results from the literature revealed minimal differences in peak load and loaddeflection. they also used finite element method to model the obtained results. the results of the numerical model were in good agreement with the experimental observations. authors in [12] designed a 1200-day long-term deformation test on reinforced concrete beams made with 0%, 50% and 100% replacement of natural coarse aggregates with recycled aggregates. they introduced creep coefficient of recycled aggregates in the computation of additional curvature of the beam section to develop formulas for the calculation of longterm deflection. they also introduced the regeneration coefficient based on the size of recycled aggregates. finally, they developed the deflection increase coefficient which simplifies the computation of long-term deflection and the results obtained by the use of the coefficient agree well with the experimental results. the above discussion of the available relevant literature shows that there still is room for more research to build confidence in the use of recyclable demolished concrete as coarse aggregates in new, green concrete. therefore, in this work, the long-term effect of 9-month loading on reinforced concrete beams was evaluated. the beams were cast with 50% dosage [13] of recyclable aggregates from demolished concrete. ii. materials and testing a. materials for casting of the proposed beams, ordinary portland cement under the brand name pak land, hill sand, natural coarse aggregates of size approximately equal to 25mm and demolished concrete as coarse aggregates were used. large blocks of demolished concrete were collected from demolishing waste of an about 45 years old building. these blocks were manually hammered to get aggregate size approximately equal to 25mm as of the natural coarse aggregates. after washing and drying the aggregates in open air, screening of the aggregates for cracked particles was done to avoid the use of weak material. sieve analysis of both natural and recyclable aggregates was done in accordance with relevant (astm c 136) procedure to have well graded aggregates in the concrete mix (table i). table i. coarse aggregates sieve analysis s.no sieve % passing mm in/# rca nca 1 31.5 1.25 100.00 100.00 2 25.0 1.00 93.60 94.11 3 19.0 0.75 47.21 48.26 4 12.5 0.50 18.25 17.82 5 9.5 0.38 5.74 5.41 6 4.8 #4 2.43 2.29 7 2.36 #8 1.13 2.23 8 pan both natural and recyclable aggregates were used in 50% proportion. 1:2:4 concrete mix with 0.5 water-cement ratio was used because it is commonly used in the construction industry. potable water from the city water supply system with ph value equal to 6.9 was used in the concrete mix. deformed bars of 60 grade strength were used as reinforcement. b. model a total of 9 reinforced concrete beams were cast. the dimensions of all the beams were kept equal to 1875mm×150mm×300mm. weight batching ingredients of concrete were adopted. to reinforce the beams four #4 bars were used as longitudinal reinforcement (2 bars in tension and 2 bars in compression zones). shear reinforcement in the form of stirrups was provided at 150mm center to center along the length of the beams. six beams were cast with all-natural coarse aggregates. out of these, three beams were used for the determination of peak load under short term loading, whereas the remaining three beams were used for long-term load testing. three beams were cast with 50% dosage of natural and recycled aggregates. in all beams, top and bottom concrete cover were kept equal to 25mm. concrete mixer was used for mixing the ingredients, followed by casting of the beams in standard fashion. all the beams were cured for 28 days by fully immersing in potable water. after curing, beams were allowed to air dry for 24 hours, followed by installation of dumec pads in 11 rows at equidistant from center line of the beams for strain measurement. c. testing before starting the long-term loading test of the beams, three beams made with all-natural aggregates were tested in universal load testing machine using central point load (astm c 193) for short term loading. the average peak load of the three beams was recorded to be 74.022kn, and 50% of this load was used as sustained load for long-term loading tests. out of the remaining six beams, three of all-natural aggregates (nb1, nb2, nb3) and three beams with 50% dosage of recyclable aggregates (rb1, rb2, rb3) from demolished engineering, technology & applied science research vol. 9, no. 3, 2019, 4140-4143 4142 www.etasr.com oad et al.: long term impact in reinforced recycled concrete beams under 9-month loading concrete were mounted on long-term load testing frame (figure 1). the load was applied on the center of the beams with the help of a load cell and screw jack system and was maintained for 9 months. during this period of time, load, deflection, strain and cracking were measured on daily basis. fig. 1. beams mounted on loading frame. after the elapse of the 9-month period, the load was removed. the beams were then tested in the universal load testing machine. during the testing, load, deflection and cracking were recorded at regular intervals. iii. results and discussion the parameters were recorded on a daily basis. the strain was recorded on eleven locations along the depth of the beams. the average of all strain values was computed. the deflection, its average and difference between both groups of the beams is given in table ii. the strain results are given in table iii. it may be observed that the proposed beams in comparison to control specimen under sustained load for 9 months exhibited 6.235% increase in deflection and 6.322% increase in strain. it was further observed that the maximum deflection in the proposed beams is within the allowable limits specified by aci 318. figure 2 shows the average deflection vs. time and figure 3 shows the average strain vs. time. it is clear from these figures that both deflection and strain were increased due to the introduction of recycled aggregates in concrete. the trend of deflection and strain gain is the same in both types of the beams. all the beams were also tested under central point load in accordance to astm c 293 specifications until failure. during the process, load and deflections were monitored at regular intervals. the maximum load sustained by the beams made with all-natural aggregate was recorded equal to 83.150kn with deflection equal to 13.2mm while in beams with recyclable aggregates was equal to 80.200kn and 13.78mm respectively. the load vs. deflection of all six beams is shown in figure 4. except some minor jerks, the deflection patterns of all the beams are similar, recycled aggregate beams are in good agreement with all-natural aggregate beams. the reduction in maximum attained load of beams with recyclable aggregates is recorded equal to 3.55% whereas the increase in deflection is equal to 4.39%, both less than 5%. during the sustained loading cracks were monitored and marked (figure 5). the widest crack at the end of testing was recorded to be less than 1mm. this shows the strength of the proposed beams under sustained loading. after sustained loading and during the testing of the beams, the crack pattern in almost all the beams is shear failure (figure 6). from the obtained results it is very clear that the reinforced concrete beams made with 50% replacement of natural coarse aggregates with recyclable aggregates perform well under 9-month sustained loading. table ii. average deflection in all beams b# deflection (mm) average difference % nb-1 2.2050 2.165 6.235 nb-2 2.1225 nb-3 2.1700 rb-1 2.2950 2.300 rb-2 2.3375 rb-3 2.2650 table iii. average strain in all beams b# strain average difference % nb-1 0.00244 0.002420 6.322 nb-2 0.00239 nb-3 0.00242 rb-1 0.00257 0.002573 rb-2 0.00261 rb-3 0.00254 fig. 2. average deflection vs time fig. 3. average strain vs time engineering, technology & applied science research vol. 9, no. 3, 2019, 4140-4143 4143 www.etasr.com oad et al.: long term impact in reinforced recycled concrete beams under 9-month loading fig. 4. load vs deflection fig. 5. cracking under sustained load fig. 6. failure pattern iv. conclusion this research aimed to evaluate the effect of 9-month sustained load on reinforced concrete beams made with 50% dosage of recycled aggregates from demolished concrete. the test results of the proposed beams tested in a purpose made frame for 9 months under central point load show that the maximum deflection attained by the beams is 2.3mm which is only 6.235% higher than the maximum deflection of control beams. similar increase in strain is recorded, equal to 6.322%. crack initiation and propagation was also recorded and was observed that at the end of the 9-month period, the maximum width was 0.52mm. after the removal of sustained load, the beams were tested in utm until failure. during testing, load and deflection pattern of the beams remained in good agreement to each other. it was also observed that almost all the beams failed in shear test. the observations demonstrate that reinforced concrete beams made with 50% recycled aggregates showed good performance under 9-month sustained loads. references [1] b. a. memon. , “recent development on use of demolished concrete as coarse aggregates”, international journal of emerging technology and innovative engineering, vol. 2. no. 1, pp. 1-11, 2016 [2] m. oad, a. h. buller, b. a. memon, n. a. memon. s. sohu, “flexural stress-strain behavior of rc beams made with partial replacement of recyclable concrete aggregates, part-2: rich mix”, engineering technology and applied science research, vol. 8, no. 5, pp. 33383343, 2018 [3] m. oad, a. h. buller, b. a. memon, n. a. memon, “flexural stressstrain behavior of rc beams made with partial replacement of coarse aggregates with coarse aggregates from old concrete: part-1 (1:2:4 ratio)”, engineering technology and applied science research, vol. 8, no. 3, pp. 3048-3053, 2018 [4] n. tosic, s. marinkovic, n. pecic, i. ignjatovic, j. dragas, “long-term behavior of reinforced beams made with natural or recycled aggregate concrete and high-volume fly ash concrete”, construction and building materials, vol. 176, pp. 344-358, 2018 [5] s. seara-paz, b. gonzalez-fonteboa, f. martinez-abella, i. gonzaleztaboada, “time-dependent behavior of structural concrete made with recycled coarse aggregates. creep and shrinkage”, construction and building materials, vol. 122, pp. 95-109, 2016 [6] s. seara-paz, b. gonzalez-fonteboa, f. martinez-abella, d. carrolopez, “long-term performance of reinforced concrete beams with recycled coarse aggregates”, construction and building materials, vol. 176, pp. 593-607, 2018 [7] w. c. choi, h. d. yun, “long-term deflection and flexural behavior of reinforced concrete beams with recycled aggregates”, materials and design, vol. 51, pp. 742-750, 2013 [8] s. c. kou, c. s. poon, m. etxeberria, “influence of recycled aggregates on long-term mechanical properties and pore size distribution of concrete”, cement and concrete composites, vol. 33, no. 2, pp. 286-291, 2011 [9] g. fathifazl, a. g. razaqpur, o. b. isgor, a. abbas, b. fournier, s. foo, “creep and drying shrinkage characteristics of concrete producedwith coarse recycled concrete aggregate”, cement & concrete composites, vol. 33, no. 10, pp. 1026-1037, 2011 [10] a. lapako, r. grygo, “long-term deformations of recycled aggregate concrete (rac) beams made of recycled aggregates”, 10th international conference on modern building materials, structures and techniques, vilnius lithuania, may 19-21, 2010 [11] b. s. hamad, a. h. dawi, a. daou, g. r. chehab, “studies of the effect of recycled aggregates on flexural, shear and bond splitting beam structural behavior”, case studies in construction materials, vol. 9, pp. e00186, 2018 [12] c. liu, z. y. lv z, c. zhu, g. l. bai, y. zhang, “study on calculation method of long-term deformation of rac beam based on creep adjustment coefficient”, ksce journal of civil engineering, vol. 23, no. 1, pp. 260–267, 2019 [13] m. oad, b. a. memon, “compressive strength of concrete cylinders using coarse aggregates from old concrete”, 1st national conference on civil engineering, pakistan, april 28–29, 2014 microsoft word 30-3086_s_etasr_v9_n5_pp4741-4744 engineering, technology & applied science research vol. 9, no. 5, 2019, 4741-4744 4741 www.etasr.com kareem et al.: surface and deep soil 222 rn gas exhalation comparison surface and deep soil 222 rn gas exhalation comparison a case study in tawke, duhok, northern iraq idrees m. kareem radiation department, duhok environment office, duhok, northern iraq idris.majeed@yahoo.com lokman a. abdulkareem department of petroleum engineering, university of zakho, zakho, northern iraq lokman.abdulkareem@uoz.edu.krd hanaa i. al-barudi department of physics, university of mosul, mosul, northern iraq hana_hh200012@yahoo.com abstract— in this study, 13 different surface locations and 20 mud samples were collected during drilling, from one of the oil wells in the kurdistan region of iraq. the samples were taken at different well depths. rad7 technique was used for finding the radon concentration. the smallest values in soil and surface were 14.12±8.59 and 16±4.24bq/m3 and the highest were 93.25+21.72 and 137±8.76bq/m3 respectively. the difference in the depth and surface formation shows the surface formation over depth ratio. the exhalation rate recorded value of the surface was generally higher than that of the depth formations. the exhalation results were finally compared with the recommended values of the international atomic energy agency (iaea) levels. the data show that it was less than the standards of iaea. keywords-norm; surface geological formation; oil well; 222 radon gas; exhalation rate; rad7 i. introduction natural radioactivity is more than the background radiation in oil drilling. since the ‘80s some regulatory agencies paid attention to the naturally occurring radioactive material (norm) issues related to hydrocarbon production [1]. gamma radiation that comes from waste has an extremely wide range [2, 3]. activities relative to uncontrolled releasing and enhanced norm levels cause environment contamination. these kinds of risks can be reduced by the adoption of checks to recognize the norm source, controlling norm waste and polluted equipment, and protecting workers. the 238 u and 232 th are radioactive materials situated into rock formations and soil. unstable radioactive chemical elements of this kind create other radionuclides, which bring on certain conditions (temperature, pressure, acidity, etc.) into the surface layer and subsurface environment. they are mobile with a probability of transmitting from the reservoir to the surface during the extraction of crude oil products. this research aims to study radon gas and its exhalation in terms of area and mass ratio, considering depth. more than one samples come from the same formation, although their distance is of the order of hundreds of meters. samples were collected from different locations that have a spatial geological formation. in saudi arabia, radon concentration in the soil ranges from 75 to 220bq/m 3 [3], with a reported mean value of 4561bq/m 3 [4]. in india, the radon gas in soil is 7.46±0.69kbq/m 3 [5]. the radon exhalation rate in syria was measured as 9bq.m -2 .s -1 [6]. the aim of the current study is to find the radon concentration by using the rad7 technique. a total of 13 formation samples and 20 mud samples were collected in the north of duhok governorate during drilling. sampling was conducted at different depths, the purpose was to calculate the surface and mass exhalation rate of radon and to compare them with the findings of other studies. ii. study area the study area is located in iraq, northwest and in the north of duhok governorate, about 60km from the center of the city, in 37.161985 latitude, 43.016341 longitude. it is one of the 51 well locations that extract crude oil. the depth to reach the layer of crude oil is 2200m, so during the excavation, we can find different geological formations. iii. experimental preparation twenty samples of drilling mud from assorted depths (assorted formations) were gathered from the t-49 well, located in the tawke oil field. the radon concentrations and relative depths from the collected samples are listed in table i and the surface formation measurements are shown in table ii. the collected samples were dried in an oven at 110 o c for one day for eliminating moisture, then milled to fine powder, and finally garbled with 0.2mm mesh. this study used active mod as a solid-state determination to find the activity concentration of radon gas. the setup of the experiment is shown in figure 1 as an active method to find radon concentration. it consisted of a plastic tube of about 1l volume made from polyvinyl chloride (pvc) as a chamber to accumulate radon. the pvc-tube was joined with a vinyl tube that contained desiccant (caso4) for drying the gas from humidity, and a radon monitor device. soil samples were put in the bottom of the tube as radon exposure source, with closing sides by the pvc cover. then the plastic-tube container was isolated via two valves adjusted at the sides of the container. the concentration was measured after putting corresponding author: idrees m. kareem engineering, technology & applied science research vol. 9, no. 5, 2019, 4741-4744 4742 www.etasr.com kareem et al.: surface and deep soil 222 rn gas exhalation comparison the samples and leaving them in room temperature for about one month. this time was sufficient for the samples to reach radium-radon, and radon decay equilibrium. when connected to the closed loop both valves were open. the device pooled air from the container, passing it through the desiccant to the inlet filter and then to the rad7 device into the measuring tube chamber. the air was discarded from the outlet of the rad7 device. the radioactive element decays in the interior of the chamber, creating detected alpha (α) particles that emit progeny, especially polonium isotopes. there is a high voltage of about 2218v on the chamber walls. the rad7 detector converts alpha radiation to electrical signal by utilizing the alpha technique and is able to separate the different electrical pulses produced from 214 po and 218 po with energies of 7mev and 6mev correspondingly. the humidity is between 4%-8%, in room temperature ranging from 20 o c to 31 o c. fig. 1. method of radon concentration measurement. at equilibrium state, the flux (exhalation) of radon from the sample inside the can in terms of area and mass can be measured by [7]: ea= ����.�.��/ ��� ������/� (1) em= ����.�.��/� ��� ������/� (2) where ea is the exhalation rate in terms of area (bq.m -2 .d -1 ) and em is the exhalation rate in terms of mass (bq.kg-1.h-1), crn is the radon concentration calculated by the rad7 detector in a bq/m 3 , �=7.56×10 -3 h -1 is the constant of radon decay, t is the exposure time in hours, v is the volume of the can, equal to 0.001192m 3 and s is the surface area of the sample in the can, equal to 0.003847m 2 . the rad7 works on a four-cycle mode, the data are stored in an internal memory via using the starting protocol of 2-days test. the saved value depends on the average gas concentration of radon during each break time. iv. results and discussion the statistics of the concentration of radon into different depths and formations of tawke area and the soil from different locations show that different depths have different concentrations of radioactive radon gas and the results are compared with the ones from the surface samples. the surface formation in general was recorded to have higher concentrations than the depth locations. the highest rate was recorded in the depth of 1100m (euphrates formation and khormala formation), and the lowest ratio was recorded in the depth of 1900m (kolosh formation and jurbi formation), with values of 93.25±19.72, 137±8.76 and 14.12±8.59, 16±4.24bq.m -3 respectively. the results of radon concentration vs formation and depth measurement are displayed in figure 2. there are many factors affecting radon release from soil and rocks, such as permeability, moisture, porosity, co2 soil concentration, temperature, and pressure. maybe each location includes specific distinctive soil and rock properties, so the evaluation must be held accordingly [3]. table i. radon concentrations and exhalation in different depths depth (m) layer name weight (g) rn std division (bq/m 3 ) radon area (mbq.m -2 .h -1 ) radon mass (mbq.kg -1 .h -1 ) surface surface area 126.34 62±15.25 177.8±43.73 5.41±1.33 400 upper faris 129.96 85.25±7.2 244.48±20.59 7.24±0.61 500 sandston-clayston-upper faris 136.02 66.25±3.8 189.99±10.81 5.37±0.31 600 sandston-clystonupper faris 132.5 40.75±21.7 116.86±62.29 3.39±1.81 700 sandston-clystonupper faris 145.12 52.25±10.17 149.84±29.17 3.97±0.77 800 lower faris clayston 136.34 57.5±10.87 164.9±31.17 4.65±0.88 900 euphrates 145.1 40±16.79 114.71±48.15 3.04±1.28 1000 euphrates 129 47±11.46 134.79±32.86 4.02±0.98 1100 euphrates 137.8 93.25±19.72 267.42±56.55 7.46±1.58 1200 pelaspi 126.8 69±8.98 197.88±25.75 6±0.78 1300 pelaspi 142.2 63.5±12.15 182.1±34.84 4.93±0.94 1400 jurkes 138 24±3.36 68.83±9.64 1.92±0.27 1500 jurkes 126.04 29±8.44 83.17±24.2 2.54±0.74 1600 jurkes 149.69 24.25±7.93 69.54±22.74 1.79±0.58 1700 jurkes 150.6 23.75±5.85 68.11±16.78 1.74±0.43 1800 kolosh 153.34 27.05±4.71 77.6±13.51 1.95±0.34 1900 kolosh 129 14.12±8.59 40.52±24.63 1.21±0.73 2000 kolosh 137.58 18.23±7.21 52.3±20.68 1.46±0.58 2100 kolosh 137.15 23.01±1.32 65.98±3.79 1.85±0.11 2200 kolosh 140.34 30.50±5 87.47±14.34 2.4±0.39 max 93.25±21.72 267.42±62.29 7.46±1.81 min 14.12±8.59 40.52±3.79 1.21±0.11 average 44.53±9.52 125.0±26.45 3.52±0.74 engineering, technology & applied science research vol. 9, no. 5, 2019, 4741-4744 4743 www.etasr.com kareem et al.: surface and deep soil 222 rn gas exhalation comparison in the underground, there is radon movement depending on compaction, brittle, lithology, porosity, etc. [8, 9]. the raises of radon gas emission were caused by soil moisture, but if there is a saturation of soil pores, the emission will be inhibited. the co2 behaves as a radon carrier gas into the soil, enhancing the 222 rn concentration into the soil atmosphere [10]. note that the studied samples’ maximum radon concentration level is acceptable [11]. table iii shows the comparison of this study results with the results of other works regarding radon concentration and exhalation. the present study shows that the radon rate was higher than the study done in iraq-kurdistan, egypt, pakistan and india, while it was lower than in iraq-baghdad and iraq-erbil. anyhow, this value is lower than the acceptable level which should be less than 300bq.m -3 [12]. comparing with the mass exhalation rate in india, osaka-japan and cataniaitaly, the value of the average exhalation rate of this study was lower. in general the results were less than the mean world value which is 57600mbq.m -2 .h -1 [13]. in term of mass, this study results were near to india and erbil-iraq. fig. 2. radon concentration in different depths and soil formations table ii. 222radon concentration and exhalation in different surface formations formation name weight (g) rn std division (bq/m 3 ) radon area (mbq.m -2 .h -1 ) radon mass (mbq.kg -1 .h -1 ) jurbi formation 156.15 16±4.24 45.88±12.16 1.13±0.3 sludge after treatment 165.85 16±5.66 45.88±16.23 1.06±0.37 soil before treatment 165.35 66.5±11.27 190.71±32.32 4.43±0.75 lower faris formation 100.89 33.25±2.06 95.35±5.91 3.63±0.22 khormala formation 170.56 137±8.76 392.88±25.12 8.86±0.57 avana formation 128.07 39.5±13.87 113.28±39.77 3.4±1.19 waste mud 130.25 80±13.44 229.42±38.54 6.77±1.14 pelaspi formation 160.1 47±4.24 134.78±12.16 3.24±0.29 bakhtyari formation 142 31±8.49 88.9±24.35 2.41±0.66 jurkes formation 134.27 55.5±6.81 159.16±19.53 4.56±0.56 upper faris formation 154 57.5±7.14 164.89±20.47 4.12±0.51 qamchqa formation 161.25 123.25±17.34 353.45±49.73 8.43±1.18 sheranish formation 133.21 59.35±18.11 170.2±51.93 4.91±1.5 max 137±8.76 392.88±25.12 8.86±0.57 min 16±4.24 45.88±12.16 1.13±0.3 average 58.60±9.34 168.06±26.78 4.38±0.71 table iii. radon exhalation rate in terms of area and mass location 222rn concentration (bq/m 3 ) 222rn (mbq.m -2 .h -1 ) 222rn (mbq.kg -1 .h -1 ) reference tawky-t49. various well depths and formations 44.53+9.52 58.60±9.34 125.08±26.45 168.06±26.78 3.52±0.74 4.38±0.7 present study india 7.46±0.69 246.63–1100 7.17–31.98 [5, 14] turkey 1476 [15] erbil-iraq 361.77±3.79 67.962-515.167 1.88212.630 [16] iraq-kurdistan 15.638±7.38 5670-14020 536.09-1324.12 [17] osaka-japan 10.8 [18] hawaii 9.0±226 [19] japan 1260 [20] germany 7200-63000 [21] catania-italy 43.1±6.7 [22] baghdad-iraq 1337.55 1059.5 61.25 [23] alexandria-egypt 7 464.4 [24] saudi-arabia 75–220 [3] pakistan 666±55 5860±1200 [25] bengaluru-india 497±173 78588±27576 [26] mean world value <300 57600 [12, 13] v. conclusion there are differences on the amount of radon gas and its exhalation rate, depending on the depth and the surface formation soil. the overall surface exhalation rate area and mass average was greater than the depth soil’s. the natural decay of uranium produces radon gas. rad7 was the easiest way to find the radon concentration in the soil. the results show that the rates are less than the mean world value. engineering, technology & applied science research vol. 9, no. 5, 2019, 4741-4744 4744 www.etasr.com kareem et al.: surface and deep soil 222 rn gas exhalation comparison references [1] k. p. smith, an overview of naturally occurring radioactive materials (norm) in the petroleum industry, argonne national lab., usa, environmental assessment and information sciences division, 1992 [2] m. a. hilal, m. f. attallah, g. y. mohamed, m. fayez-hassan, “evaluation of radiation hazard potential of tenorm waste from oil and natural gas production”, journal of environmental radioactivity, vol. 136, pp. 121–126, 2014 [3] w. r. alharbi, a. g. e. abbady, “measurement of radon concentrations in soil and the extent of their impact on the environment from al-qassim, saudi arabia”, natural science, vol. 5, no. 1, pp. 93–98, 2013 [4] s. mittal, a. rani, r. mehra, “estimation of radon concentration in soil and groundwater samples of northern rajasthan, india”, journal of radiation research and applied sciences, vol. 9, no. 2, pp. 125– 130, 2016 [5] g. prasad, y. prasad, g. s. gusain, r. c. ramola, “measurement of radon and thoron levels 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dogru, m. inceoz, e. aksoy, “measurements of radon emanation from soil samples in triple-junction of north and east anatolian active faults systems in turkey”, radiation measurements, vol. 39, no. 2, pp. 209–212, 2005 [16] h. h. azeez, a study of radon and thoron gases release from iraqikurdistan building materials using passive and active methods, msc thesis, salahaddin university, 2010 [17] a. h. ismail, m. s. jaafar, “hazards assessment of radon exhalation rate and radium content in the soil samples in iraqi kurdistan using passive and active detecting methods”, world academy of science, engineering and technology, international journal of environmental and ecological engineering, vol. 70, no. 10, pp. 473476, 2010 [18] k. megumi, t. mamuro, “radon and thoron exhalation from the ground”, journal of geophysical research, vol. 78, no. 11, pp. 1804–1808, 1973 [19] m. h. wilkening, “radon-222 from the island of hawaii: deep soils are more important than lava fields or volcanoes”, science, vol. 183, no. 4123, pp. 413–415, 1974 [20] n. m. hassan, m. hosoda, k. iwaoka, a. sorimachi, m. janik, c. kranrod, s. k. sahoo, t. ishikawa, h. yonehara, m. fukushi, s. tokonami, “simultaneous measurement of radon and thoron released from building materials used in japan”, progress in nuclear science and technology, vol. 1, pp. 404–407, 2011 [21] g. keller, m. schutz, “radon exhalation from the soil”, radiation protection dosimetry, vol. 24, no. 1–4, pp. 43-46, 1988 [22] g. imme, r. catalano, g. mangano, d. morelli, “radon exhalation measurements for environmental and geophysics study”, radiation physics and chemistry, vol. 95, pp. 349–351, 2014 [23] s. a. amin, a. h. al-obiady, a. alwan, “radon level measurements in soil and sediments at oil field area and its impact on the environment”, engineering and technology journal, vol. 35, no. 1, pp. 1–7, 2017 [24] a. f. hafez, a. s. hussein, n. m. rasheed, “a study of radon and thoron release from egyptian building materials using polymeric nuclear track detectors”, applied radiation and isotopes, vol. 54, no. 2, pp. 291–298, 2001 [25] n. ahmad, j. rehman, j. u. rehman, g. nasar, “assessments of 226ra and 222rn concentration in well and tap water from sik, malaysia, and consequent dose estimates”, human and ecological risk assessment: an international journal, 2019 [26] k. kumar, n. nagaiah, g. mathews, m. r. ambika, “study on influence of soil and atmospheric parameters on radon/thoron exhalation rate in the bangalore university campus, bengaluru”, radiation protection and environment, vol. 41 no. 1, pp. 8-11, 2018 engineering, technology & applied science research vol. 10, no. 3, 2020, 5581-5589 5581 www.etasr.com pylarinos: overhead transmission line easement and right-of-way cases in crete, greece … overhead transmission line easement and right-of-way cases in crete, greece a statistical analysis of 1220 cases from 1974 to 2019 d. pylarinos islands network operation department hellenic electricity distribution network operator s. a. greece d.pylarinos@deddie.gr abstract—overhead transmission lines (otls) are used to carry high voltage (hv) between hv substations, usually constructed at long distances from each other, thus spanning across numerous different properties. easements, a legal term for nonpossessory rights, are essential to the utilities in order to maintain a right-of-way (row) for construction and maintenance purposes in a corridor of land underneath the lines, and also to enforce certain restrictions within that corridor, in order to ensure the safety of both the otls and the public. the exact details of row corridors’ management vary between countries as the legislation and each utility’s approach may differ. this paper focuses on 1220 easements/row cases regarding the isolated hv transmission system of the greek island of crete from 1974 to 2019. the various related factors are discussed and a statistical analysis of the records is performed. keywords-overhead transmission line; easement; right of way; building; restriction; safety; management; legislation i. introduction electric power transmission between high voltage (hv) substations is widely performed through the use of hv conductors suspended at safe distances above the ground, using specially designed structures such as lattice towers and poles of various materials (metal, wood, concrete) [1]. the sum of all these components (supporting structures, conductors, overhead ground wires etc) constitutes what is generally known as an overhead transmission line (otl) [1]. apart from the various technical aspects related to the design, construction, operation and maintenance of otls, a fundamental obvious issue regards to the fact that otls inevitably have to span over numerous, private or public, pieces of land. this has an obvious, yet difficult to estimate precisely, impact on property values [1-3]. property devaluation combined with concerns regarding safety and the visual and environmental impact, has resulted to a mainly negative public perception towards otls, especially in the recent decades [1, 4-8]. thus, even if purchasing the land under otls was economically feasible, it is highly unlikely that such agreements could be established with all owners for the whole route of an otl. further, the actual need is for the power utility in charge to have the right to visit the properties just for short periods of time (e.g. during construction, inspection or maintenance) and to enforce restrictions related to safety issues, for example tree trimming and restricting groundworks in vicinity of otls (potential issues resulting from such cases are shown in figure 1) [1-4, 7]. for all these reasons, easements are usually preferred over actual purchases. an easement is a nonpossessory right to a property and although, legally, a right-of-way (row) is just an easement allowing the passage over a third-party’s property, the term is often generally used to describe all the easements granted to the power utility for a corridor of land under an otl. the width of the corridor, and the easement type, generally depends on the otl voltage value and the legislation in effect. the ultimate goals of these easements are to provide to the utility easy and safe access to the line when needed, as well as the legal means in order to restrict potential safety threat factors. such factors include: construction and building activities of any kind (including additions in existing buildings/structures), groundworks of any kind (including dwelling, drilling, quarrying, excavating, landscaping etc), use of heavy machinery, irrigation works and related activities (e.g. use of water cannons, sprinklers etc), accumulation of flammable materials or garbage, fencing, initiating fires of any kind, flying objects, vegetation (including trees), lake, ponds, swimming pools etc [1, 7]. information of the public regarding easement/row regulations seems to be a matter of importance for several utilities worldwide that have put out brochures and leaflets, keeping them publicly available at their websites (e.g. [9-21]). however, this is not the case in greece as the aspect is neglected even in general information documents regarding hv transmission (e.g. [22]) or its interaction with the environment (e.g. [23]). it should be noted that a thorough survey regarding the various factors related to easements/row among 27 different countries (again, not including greece) can be found in [7]. thus, this paper contributes by providing an insight on basic easement/row policies and regulations in greece for 66 kv and 150 kv otls along with a statistical analysis performed on 1220 easements/row cases regarding the hv transmission system in crete, greece. it should be noted that corresponding author: d. pylarinos engineering, technology & applied science research vol. 10, no. 3, 2020, 5581-5589 5582 www.etasr.com pylarinos: overhead transmission line easement and right-of-way cases in crete, greece … the investigated cases range from 1974 to 2019 and that, in these years, several factors have kept changing (e.g. utility organizational restructures, transmission system upgrades and expands, legislation alterations, mapping and topographic advancements etc) and thus a brief discussion of the background is presented in the following section. fig. 1. examples of potential safety issues. ii. case study data & background a. otl row/easemets in greece in general, in greece the construction of a power line is considered a work of public interest and the land and easements are acquired through expropriation [24]. the easements include the right of passage, the expropriation of land around each tower’s base, additional restrictions of certain type of activities in the row corridor and the enforcement of building restrictions within the corridor. the actual area of land that is expropriated around the base of each tower depends on the tower type. the row width is set to 40 m for 150 kv otls when they are supported by lattice towers and 25 m when they are supported by metal poles. in case of 66 kv otls, the row width is set to 20 or 24 m when the otl is supported by wooden structures and 40 m when it is supported by lattice towers. however, these values are not universally set by a single law or legislation act. instead, each expropriated part is specifically mentioned in an announcement at the official government gazette (ogg) [25]. in other words, essentially, a specific law is passed for each expropriation. this creates a rather puzzling image as otls may be gradually constructed, upgraded, partially merged, renamed etc [24]. it should be noted that the number of ogg issues related just to the otls in crete are close to one hundred. the building restrictions set within the row corridor also comprise a complicated result as there are two types of easements are enforced in row corridors in greece: a) type i that allows building constructions up to a certain height and b) type ii that fully prohibits any construction. parts of the same otl may fall under different easement types. to make matters worse, the ogg issues generally refer to km positions (which is a legal term and does not necessarily match the actual length of the line up to the position) and to drawings and maps that are not included in the announcements. the allowed building height mentioned above is also a complicated issue as some early ogg issues referred to a specific height from the ground. however, it soon became evident that this would cause risks in the future (as the landscape may be altered) and later expropriations use a phrasing that refer to a minimum distance from the conductors under certain environmental conditions (absence of wind and 50 οc temperature). this however ultimately means that the specific height has to be provided by the utility on a case by case basis. the expropriation compensation is another source of confusion. the absence of a national cadastre in greece combined with the usually remote routing of otls meant that the utility could not have precise information regarding the properties underneath the lines (owner, boundaries etc). thus, the drawings and tables used for expropriations, referred to “alleged owners”. then, the exact compensation amounts were decided in local courts and, after that, a new announcement in an ogg issue followed, informing the public that a deposition in each owner’s name is made by the utility in the national deposit and loans fund. however, the actual data (owners’ names, compensation amounts etc) were not provided in the ogg announcement and whoever interested had to refer to the hard copy court records, held in local court archives. it should be clarified that a single ogg issue contains several different announcements (on different subjects) and tons of issues are published each year. the contents of all ogg issues have been digitized lately and remote public access has been provided [25]. however, older issues have been scanned without the use of optical character recognition techniques, making it impossible for the user to search using keywords e.g. in order to find the issue containing the announcement for the expropriation related to a specific otl or to find a specific name of an alleged owner. further, even if the ogg issue is found, the owner would still have no particularly useful information regarding a specific property as the ogg issue does not include the documents that contain these information. to complete the general legal background, it should be stated that other laws may enforce general rules and restrictions on a property because of an otl, even outside a row corridor (e.g. in case of gas stations, quarries, use of explosives, construction sites etc). b. the crete-rhodes row office in greece, the power transmission system was historically constructed, maintained and operated by the public power corporation (ppc) through several different divisions, sections and subsection. the crete and rhodes transmission systems were historically considered as a single administrative unit and their operation and maintenance was assigned to the same division. the exact placement of this division/section within the organization has changed through the years. since the 2011 split up of ppc, it has been placed under the islands network operation department of the hellenic electricity distribution network operator (hedno). it should be noted that hedno manages the network but ppc maintains the ownership of the network’s infrastructure which means that e.g. all row cases in crete are handled by the hedno row office but ppc retains the ownership of the land and easements. adding to the confusion, after the split-up all central transmission system services (including the ones dealing with otl construction, record keeping, expropriations, row corridor management in the rest of greece etc) were moved to the independent power engineering, technology & applied science research vol. 10, no. 3, 2020, 5581-5589 5583 www.etasr.com pylarinos: overhead transmission line easement and right-of-way cases in crete, greece … transmission operator (ipto) which is today a third party company. several internal changes within the parent division of the row office have also occurred over the years. in general, the row office has always been a part of the transmission line operation and maintenance subsection but was never considered an isolated entity with devoted personnel. the situation gradually evolved, as personnel kept being reduced over the years, from row office people being occasionally, if not rarely, called for maintenance works, to the same handful of people performing all duties of the transmission line subsection (including the duties of the row office). c. transmission system alterations the transmission system of crete is currently operating at 150 kv and includes 20 high voltage substations [24] and the cumulative length of its otls is over 580 km [26]. however, back in 1974 there were only 5 substations and the otl cumulative length was just over 360 km and operated mostly at 66 kv. these changes certainly have had an impact on row cases. obviously as the network expanded, more properties were affected. the upgrading of otls meant that wider and higher towers were used which meant that additional expropriation of land for their bases was required and also that height restrictions would now be more favorable for the property owner (figure 2). fig. 2. part of a typical drawing (side view) of an otl before upgrading (dotted line) and after upgrading (solid line). system upgrade from 66 kv to 150 kv also meant that all old 66 kv lines supported usually by wooden structures were gradually removed as their routing was judged unsuitable for further use. the conductors were removed and the poles were cut up to a height that would be significant enough to mark ppc owned land and at the same time pose minimal inconvenience and safety hazard (figure 3). the removal of old 66 kv lines supported by wooden structures has had a huge impact in the city of heraklion as two of these lines passed over fully urban areas. another 66 kv otl in the area, which was supported by lattice towers, was upgraded and parts of it were used as parts of a new 150 kv otl. a part of this otl that crossed residential areas of heraklion was however taken off service and all conductors were removed whereas the lattice towers remained on the properties (figure 4). the routing of the 150 kv otls in heraklion is now kept away from residential areas as much as possible with the additional use of underground cables. an overview of heraklion along with cable and past and present otl routing is shown in figure 5. fig. 3. removal of an old 66 kv line supported by wooden poles. left image: the wooden support structure (screenshot from google earth, image © 2018 google, © 2019 google, © 2018 basarsoft). right image: the current state. fig. 4. view of three lattice towers of an out off service 66 kv otl which used to span over residential areas in heraklion. all conductors and the overhead ground wire have been removed. fig. 5. an overview of heraklion. the blue square denotes the step up substation of linoperamata whereas the yellow triangles denote the step down substations heraklion i, heraklion ii and heraklion iii. the yellow lines denote the routing of two old 66 kv otl supported by wooden poles (now fully removed). the green line denotes part of an old 66 kv otl supported by lattice towers that is now out of service (conductors removed). the brown line denotes the routing of 150 kv underground cables (screenshot from google earth, image © 2019 terrametrics. map data: data sio, noaa, u. s. navy, nga, gebco). d. topography and mapping issues the history behind the still under-development national cadastre in greece, and the overall registration system, is thoroughly described in [27-31]. in short, the basic system in greece has been unchanged since the early 19th century and operates as a paper-based public register of real property owners and the deeds that they have been involved in (basically, a registrations and mortgages system) [27-28]. various offices operated throughout the country without any uniform/coordinated operation or service standards [27]. it should be noted that it is estimated that there are about 7.4 million property owners in greece [29]. also, that it had been usual for owners in the past (especially in remote areas) to acquire and pass the ownership using unofficial private agreements (often enough, such agreements were just verbal). in addition, the rights of the state and usucaptions were also engineering, technology & applied science research vol. 10, no. 3, 2020, 5581-5589 5584 www.etasr.com pylarinos: overhead transmission line easement and right-of-way cases in crete, greece … not registered [27-28]. in short, such a system could not identify individual real properties or boundaries and did not allow the identification of the owners of a property observed in the field [27]. thus, there had been several attempts to develop a national cadastre over the years [28]. the latest attempt that initiated in 1996 [27-31] has resulted in registering less than 10% of the area and 30% of the rights up to 2018 [27-28]. in crete, just the urban areas of major cities were registered. however, the registration has picked up lately and a large part of crete was registered in 2019 (figure 6). during the otl construction however, it obviously was not possible for the utility to have any positive information regarding the properties within a row corridor, which explains the “alleged owner” issue discussed earlier. it should be noted that there had not been any entity or public service where a property owner could ask for the slightest information regarding the easements on their property (not even the existence of such easements), other than the row office. fig. 6. areas of crete (with bright solid color) registered in the national cadastre in 2019, including over 7,000 different easement cases and expropriated areas. solid black lines depict the axes or overhead transmission lines, blue rectangles denote step up substations and yellow triangles denote step down substations. (screenshot from google earth, data sio, noaa, u.s. navy, nga, gebco, image landsat / copernicus). it should also be noted that there have been several changes in the coordinate systems used in greece over the years [24]. similarly, changes regarding the registration rules and/or the data needed to be registered have also taken place. these changes also included the necessity of providing coordinates under a country-wide coordinate system during the registration or mapping of a property, which was relatively recently added. this means that even if an ownership had been registered or a property had been mapped in the past that does not mean that the available information/diagrams/maps included the necessary information to provide a geospatial representation. needless to add that the absence of such requirements was also depicted in the construction sheets of otls and thus a new project had to be initiated recently in order to provide a geospatial representation of otls in crete and rhodes [24]. in relation to the properties in row corridors, it was also usual for past row office documents to refer to the relative position of the property from a tower, using a custom naming system for towers (usually following an incremental numbering system from one substation to another) [24]. however, as the power system developed over the years, otls were merged, partially removed, expanded etc and towers may be added, moved or renamed and thus the relative position from a tower cannot be considered a trustworthy information for a correct geospatial representation of row cases[24]. iii. dataset information a. general information the analysis presented in this paper aims to provide an insight of the easement/row cases for the otls of the transmission system of crete from 1974 to 2019. the hard copy files considered are contained in 72 a4 large lever arch folders shown in figure 7. fig. 7. the 72 folders containing the hardcopy files some key remarks regarding the data set have to be noted however:  the official division’s records include all correspondence conducted via all the different sections of the division archived in a yearly basis. up until few years ago, these records were hard copy only. in general, for practical reasons, they do not include attached documents as yearly correspondence includes the transfer of large data (manuals, drawings, schematics, maps, topographic plans etc). this means that going through the official records to identify row cases would be a rather tedious task that would ultimately produce insufficient information.  thus, the files considered in this paper are the hard copies kept within the row office. these records are informal, include the attached drawings and schematics and were kept mostly with the purpose of case monitoring.  the mapping/topography issues along with the transmission system alterations discussed in previous sections, has led to cases being identified by the property owner’s name(s) in the files, which provided an easier to work with approach.  an effort to have all entries in the hard copy records digitally organized started in 2018, with an entry for each new case made upon initiation. the general approach for previous cases was to assign to them the year of last correspondence. however, the vast majority of cases initiated and concluded in the same year and thus the impact of non-consistent year assignment can be considered insignificant.  a number of 107 cases fell under two or more categories. these are considered as different cases in this analysis although they were not separated in the hard copy records. the actual number of the hard copy entries is 1107. they engineering, technology & applied science research vol. 10, no. 3, 2020, 5581-5589 5585 www.etasr.com pylarinos: overhead transmission line easement and right-of-way cases in crete, greece … include 102 cases that fall under a second category (which increases the sum by 102), 5 cases that fall under 3 categories (which increase the sum by 8) and 1 that falls under 4 (which increases the sum by 3). b. issues not included in the data set 1) vegetation management (including tree trimming) worldwide, tree trimming and vegetation management is considered an important aspect of otl row management, mainly aiming to ensure the safety of the otl (e.g. from falling tree/branches as shown in figure 1) and easy and safe access to the supporting structures [1, 7-21, 32-35]. the development of the transmission system in greece initiated in 1953 (1968 for crete) [22] and trimming instructions back from 1957 can be found in islands network operation department’s hard copy archives, [34]. tree trimming and vegetation management are matters of significant importance in greece mainly due to fire hazard laws and fire preventing measures [34-35] and thus both these issues are individually monitored. 2) cadastre registration, otls alterations, asset appraisal several issues of major significance are also individually monitored and thus not included in the considered records, such as the gradual registration of easements and expropriated tower base areas in the national cadastre (over 7,000 just for the areas registered in 2019, shown in figure 6), any system alterations regarding otls, periodical asset appraisal (including expropriated areas and easements) etc. 3) property damages, vandalisms, correspondence minor row corridor issues such as property damages (e.g. damages to crops/trees etc) due to the passage of utility crews, internal correspondence within the utility, internal or external correspondence regarding the progress of current works, cases of vandalisms/shootings etc are dealt with as part of the run-ofthe-mill work of the transmission line subsection and thus are not included in the records considered in this paper. iv. dataset analysis & results a. main categories and results a breakdown of the considered 1220 cases in different categories is shown in figure 8. a further discussion on each category is given in the following subsections. fig. 8. a breakdown of the 1220 cases 1) general information: 356 cases (29.18%) this category includes all queries about general information related to otls (transmission system information, row/easements legislation, specific easements enforced on specific properties etc). such cases cover about one third of the dataset. the vast majority of these cases (298 out of 356) are cases referring to the request of one (or more) pieces of basic information such as the existence (or not) of easements on a property, the nature of these easements, the exact ogg issues referring to these easements, the related maps/drawings, the expropriation and compensation procedure, the expropriated area on a specific property etc. the remaining 58 cases include requests for information further broken down in categories as shown in figure 9. most notably, there have been 33 cases that are related to city and urban plans under development. such cases usually regard a large area. details on the routing (and easements) of otls in this area are requested in order to be considered during the city/urban plan development. there have also been 15 cases of property owners requesting information regarding the state of easements enforced on properties in the row corridor after the removal of the otl. as shown, cases regarding information about gas stations, quarrying and drilling in proximity of otls are rather rare (4, 4 and 1 respectively) which can be attributed to the routing of the lines and the rarity of the latter two activities. fig. 9. general information cases 2) building height restrictions: 349 cases (28.60%) as explained in section ii-a, row legal statute in greece either fully prohibits any construction in the row corridor or enforces height restrictions. these height restrictions, for cases from all over greece, were historically issued by a ppc division stationed in athens which was moved to ipto after the ppc split-up in 2011. thus, the actual issuing of building height restrictions is a service now outsourced to ipto with hedno’s row office in crete maintaining its historical role as the on-site expert (handling requests, provide on-site measurements, background information regarding the otl and its legal background etc). the number of such cases per year is shown in figure 10, with a dotted line depicted the time of the split up, after which issuing height restrictions was outsourced to ipto. fig. 10. building height restrictions cases per year engineering, technology & applied science research vol. 10, no. 3, 2020, 5581-5589 5586 www.etasr.com pylarinos: overhead transmission line easement and right-of-way cases in crete, greece … 3) connections to the distribution grid: 298 cases (24.42%) as a part of standard procedure, when a property in proximity of an otl is requested to be connected to the distribution grid, the assent of the utility in charge of the otl is required. in crete, hedno handles both distribution and transmission through different departments that are further divided in sections and, in case of distribution, local offices. thus, when a property located near an otl in crete is requested to be connected to the low voltage grid, the hedno distribution section having the jurisdiction in the area contacts the islands network operation department and, ultimately, the row office which, after checking that all rules and regulations are followed, assents to the request (or asks for remedies if easement violations are spotted). occasionally, owners include additional requests along their request for connection to the distribution grid. thus, 50 of the 298 “connection to the distribution grid” cases also fall into another category, as shown in figure 11. fig. 11. a further breakdown of the connection to the distribution grid category 4) violations: 123 cases (10.08%) when easement violations are spotted, the row office contacts the property owner (as well as other services that may be involved) aiming to remedy the situation. a number of 123 violation cases are included in the considered data set (figure 8). a large percentage of these cases (54 out of 123 or 43.9%) regard properties located in the row corridors of now removed 66 kv otls which spanned through the city area of heraklion and were also elevated at low heights, mostly supported by wooden structures, as explained in section ii-c and shown in figures 3-5. the majority of the considered violation cases is in fact related to –now obsolete66 kv lines throughout crete (73 out of 123 or 59.34%), as shown in figure 12. this can be attributed to both the lower heights that 66 kv lines reached and to their route. fig. 12. a breakdown of the 123 violation cases 5) other: 72 cases (5.90%) this category includes 72 issues that are further broken down to subcategories (figure 13) such as: requests to remove easements from properties in the row corridor of obsolete (removed) lines (21 cases), requests for a change in easement type (6 cases), requests to remove an otl from a property (24 cases), lawsuits related to row/easements (14 cases) and groundworks and use of heavy machinery under an otl (7 cases). fig. 13. further breakdown of “other” category 6) arbitrary buildings (law 4495/2017): 22 cases (1.80%) the most recent law regarding the legalization of arbitrary buildings in greece (law 4495/2017, effective since november 3, 2017), demanded owners of arbitrary buildings within row corridors to acquire a certification of compliance to “all restrictions” in order to move forward the legalization procedure. it should be noted however that both law 4495/2017 and its predecessor (law 4178/2013) used some unfortunate phrasing that had an impact on the cases included to other categories. law 4495/2017 stated that the compliance certificate was to be issued by the independent power transmission operator (ipto), neglecting that the otls of crete and rhodes are ppc owned and under hedno jurisdiction and law 4178/2013 referred to “high voltage transmission lines of current over 150 kw”. thus, following the adoption of these laws, several queries have been submitted regarding e.g. the voltage used by the transmission system, the role of hedno (and/or ipto) in crete and even, in some rare cases, requests for a certification stating that the transmission system carries “current of 150 kw”. such queries could not be directly related to the legalization of arbitrary buildings and are thus classified in this paper under the general information category. b. further insight 1) temporal analysis a breakdown of the 1220 of cases per year, along with a 5year moving average, is shown in figure 14. as shown, the number of cases during the first years is relatively small (5 to 12 per year) a fact that can be attributed to the size of the network and to its recent construction at the time. by 1980, the number of cases per year exceeds 20 and it generally shows an increasing trend up to 2011. the maximum number of cases is recorded in 2002 (58 cases) with three more years having over 40 cases (1991: 45, 2003: 45, 2006: 48). it should be noted that, engineering, technology & applied science research vol. 10, no. 3, 2020, 5581-5589 5587 www.etasr.com pylarinos: overhead transmission line easement and right-of-way cases in crete, greece … there are several contradicting factors that may influence these results. for example, the expansion of the transmission system is a factor that is obviously expected to cause an increase. however, the removal of obsolete 66 kv lines counteracts that influence. although the decrease of overall otl length due to their removal is minor, their routing (in some cases through residential areas) results to a disproportional impact on the row office workload. thus, it is not easy to pinpoint the exact causes for the recorded fluctuations. fig. 14. a temporal breakdown of the cases in the considered data set. two turning points (2011 and 2018) should be further discussed however. as shown in figure 14, cases related to new constructions steadily represent a large part of the cases recorded each year up to 2011. however, their contribution is significantly decreased after 2011. this should be attributed to the 2011 financial crisis [36]. further, an overall increase of cases is recorded after 2015 and especially after 2016. these are the years that laws 4178/2013 and 4495/2017 were in effect. as mentioned earlier, the exact impact of law 4178/2013 can not be determined due to its phrasing. however, this is not the case with law 4495/2017. thus, the 2011-2019 and 20182019 periods are further discussed in the following subsections. 2) 2011-2019: financial crisis as shown in figure 14, there has been a general decrease of the number of cases related to new constructions (violations, issuing height restrictions, connections to the distribution grid) that can be largely attributed to the general decline of construction activity due to the financial crisis that hit greece in 2011 [36]. a closer examination of the dataset shows that the overall percentage of such cases for 1974 to 2010 is 73.92%, the percentage of such cases for the decade right before the crisis reaches 65.98% but it falls to 14.80% for 2011-2019 (figure 15). fig. 15. row cases related to new construction activity in crete: the impact of the 2011 finanical crisis. 3) 2018-2019: law 4495/2017 in 2018-2019, basically the time that law 4495/2017 has been in effect (adopted on november 3, 2017), the row office has already handled 22 such cases. this number is almost negligible if one considers the full 1974 to 2019 time span. however, if one considers just the 2018-2019 period, then the percentage of this category rises to 30.16% (19 out of 63). thus, a further insight of the cases recorded in the last two years is given along with a comparison to the 1974-2019 period is given in figure 16. as shown, the legalization of arbitrary buildings is the second most dominant category in 2018-2019, behind the general information category that remains the most dominant one with 22 out of 63 cases (34.92%). in fact, law 4495/2017 has also had an impact on the cases regarding requests to change the easement type on a property further discussed in the following subsection, as owners moving to legalize a building may have to ask for such a change first. fig. 16. row cases in crete: 1974-2019 and 2018-2019. 4) 2018-2019: other factors it should be noted that, as shown in figure 16, the “other” category ranks third in 2018-2019 (12 out of 63 or 19.05%). its respective percentage for 1974 to 2019 is 5.9% and for 1974 to 2017 is just 4.91% (60 out of 1220). a closer look to the 12 cases recorded in the last two years (2018-2019) shows that they include 5 requests to remove easements from properties in the row corridor of obsolete (removed) lines, 2 lawsuit cases, 3 groundworks/use of heavy machinery cases and 2 requests for a change in easement type. a comparison with 1974-2017 is shown in figure 16 through a per year calculation. fig. 17. a per year calculation of the “other” subcategories for 1974 to 2017 and 2018 to 2019. it should be noted that the increase recorded in cases regarding easement removal requests and lawsuits can be engineering, technology & applied science research vol. 10, no. 3, 2020, 5581-5589 5588 www.etasr.com pylarinos: overhead transmission line easement and right-of-way cases in crete, greece … attributed to the general gradual realization of the public regarding the role of the national cadastre. easements are now easily documented and thus owners are moving to have them removed from the cadastre record of properties. further, the procedure in greece calls for owners that do not agree with a property’s registration data in the national cadastre, to file lawsuits against all parties related to this property, including easement owners. finally, as stated in the previous subsection, the requests to change easement types are sometimes a prerequisite for the legalization of an arbitrary building. thus, an increased number of such cases is expected to keep being recorded in the following years. this is not however the case with other, purely coincidental, cases such as groundworks/use of heavy machinery or requests to remove otls. v. discussion this paper discuss a total of 1220 row cases regarding the isolated hv transmission system of the greek island of crete from 1974 to 2019, as found in the hard copy records of the row office. the hard copy records considered are informal files kept mainly for case monitoring. different employees and even different divisions have been involved in the handling of easement/row corridor cases through the years. it is thus possible that the records of some cases may be missing or be incomplete. however, the time span and the number of cases are sufficient to provide a representative image and to acquire some useful insights. some key points follow:  the most usual row cases in the considered files are related to queries for general information, building height restrictions, safety violations (e.g. clearance) and connections of properties within the row corridor to the low voltage grid.  more infrequent cases include queries related to city plans under development, obsolete otls, drilling, quarrying, gas stations, groundworks, use of heavy machinery and public opposition to otls.  the absence of a public information policy is clearly depicted in the results. queries for general information are the dominant category from 1974 to 2019, with a percentage over 29% (356 out of 1220 cases). queries for the most basic information, usually available through leaflets and the utility’s webpages in other countries, are responsible for almost one quarter of the recorded cases (24.42% or 298 out of 1220 cases).  this is also hinted by the fact that there have been 30 cases where owners of buildings within the row corridor requested to be connected to the low voltage grid and that request led to the utility spotting an easement violation, which means that the owners were either unaware of the existence of easements or of their exact nature.  cases related to construction activity (building height restrictions, violations, connections to the distribution grid) reduced tremendously in 2011-2019, a direct result of the financial crisis that initiated in 2011.  building height restrictions are outsourced to ipto since the ppc split-up in 2011, with the hedno row office in crete acting as the on-site expert. the number of such cases per year since 2011 however, hardly justifies hiring the extra personnel necessary to perform the now outsourced part of this task (2.5 such cases per year with a maximum of 5 in 2019). hiring additional personnel however, is an option that should be considered if there is a significant increasing trend for such cases in the future.  transmission line route planning and design has a huge impact on maintaining safety clearance throughout the life time of the line. almost 60% of the recorded clearance violation cases since 1974 are related to 66 kv lines (59.34% or 73 out of 123 cases) although it’s been decades since the last 66 kv was taken off service. almost half of all violations (43.9% or 54 out of 123 cases), are related to 66 kv lines that spanned through urban areas of heraklion city.  recent major changes in greek state’s policy such as the adoption of a law for the legalization of arbitrary buildings and the gradual implementation of a national cadastre has had a major impact on the nature of row related queries/cases. this is a trend expected to grow in the following years.  obsolete lines continue to be responsible for a good percentage of row workload even after their removal from properties, as utility easements remain after the removal of the line. the current policy for easements on routes of obsolete and removed otls is that each owner is expected to contact the utility individually and initiate the procedure to lift easements and buy back expropriated areas. it is doubtful that the potential financial gain from these purchases would cover the costs of geospatial mapping these lines, individual case handling and of registering rights in the national cadastre. abolishing easement rights in case of obsolete lines following unattractive routes that are not yet registered in the national cadastre may in fact be a cost-savvy approach that could also be considered as a corporate social responsibility action, improving the public perception towards the utility and otls.  projects such as vegetation management, national cadastre registration, otls alterations and asset appraisal are individually monitored and not included in the cases considered in this paper. further, issues such as property damages, vandalisms and all other types of correspondence are also not included as they are considered a part of everyday work of otl maintenance.  the considered files do not provide a full image of the workload of the row office, as they do not include the substantial amount of verbal and unofficial communications conducted for each recorded case. a large portion of the row office’s workload also not depicted in the files, is the handling of general information queries conducted in an unofficial manner (e.g. in person or via phone) that do not actually result to the submission of an official hard copy query. engineering, technology & applied science research vol. 10, no. 3, 2020, 5581-5589 5589 www.etasr.com pylarinos: overhead transmission line easement and right-of-way cases in crete, greece … vi. conclusion overhead transmission lines’ easements and right of way management is a key issue for every transmission system utility. each utility is expected to ensure safe operation and maintenance of transmission lines along with their hazardless adjacency to private properties and structures under or in their vicinity. the exact policies followed, as well as the legislation, vary from country to country. this paper focuses on the greek island of crete, providing an insight on 1220 recorded cases from 1974 to 2019, as retrieved from the hard copy records of the row office in charge. a statistical analysis is performed focusing on the breakdown in different categories, the temporal variation and the impact of specific key factors. the cretan system’s evolution, its current state and a variety of local factors and their effect on the data are further discussed in order to provide a better interpretation of the results. vii. references [1] k. o. papailiou, overhead lines, cigre green books, springer, 2017 [2] o. c. anderson, j. williamson, a. wohl, j. pitts, s. norwood, “the effects of high voltage electric transmission lines on commercial and industrial properties”, american real estate society annual meeting, 2012 [3] o. c. anderson, j. williamson, a. wohl, “the effect of high-voltage overhead transmission lines on property values: a review of the literature since 2010”, the appraisal journal, vol. 85, no. 3, pp. 179193, 2017 [4] european commission, guidance on energy transmission infrastructure and eu nature legislation, european commission, 2018 [5] l. furby, p. slovic, b. fischhoff, r. gregory, “public perception of electric power transmission lines”, journal of environmental psychology, vol. 8, pp. 19-43, 1988 [6] p. lienert, public acceptance of high-voltage power lines in the context of the swiss energy transition: the influence of information and affect, phd thesis, eth zurich, 2017 [7] cigre jwg c3/b1/b2.13, environmental issues of high voltage transmission lines in urban and rural areas, technical brochure 748, 2018 [8] cigre wg c3-08, externalities of overhead high voltage power lines, technical brochure 616, 2015 [9] ausnet, “a guide to living with transmission line easements”, https:// www.ausnetservices.com.au/-/media/files/ausnet/residential-electricit y/safety/a-guide-to-living-with-transmission-line-easements.ashx?la=en [10] government of south australia office of the technical regulator, “building safely near powerlines”, https://www.sa.gov.au/__data/assets/ pdf_file/0003/18606/150513-building-safely-near-powerlines-web.pdf [11] transpower new zealand ltd, “transmission line buffer corridor”, https://www.aucklandcouncil.govt.nz/plans-projects-policies-reports-byl aws/our-plans-strategies/unitary-plan/history-unitary-plan/documentssec tion32reportproposedaup/appendix-3-10-4.pdf [12] national grid, “information for landowners along our transmission lines”, https://www.nationalgridus.com/media/pdfs/safety/cm4729_ivm _brochure_10_15.pdf [13] national grid, “development near overhead lines. planning and amenity aspects of high voltage electricity transmission lines and substations”, https://www.nationalgrid.com/sites/default/files/documents/developmen t%20near%20overhead%20lines_0.pdf [14] national grid technical guidance note 287, “third-party guidance for working near national grid electricity transmission equipment”, https://www.nationalgridet.com/document/82926/download [15] transource, “encroachments on transmission rights-of-way”, https:// www.transourceenergyprojects.com/docs/encroachmentonrow.pdf [16] state of wisconsin public service commision, “right-of-way and easements for electric facility construction”, http://www.atc-projects. com/wp-content/uploads/2011/12/rightofwayandeasements.pdf [17] public utility district no. 1 of chelan county, “guidelines for use of transmission line right-of-way”, https://www.chelanpud.org/docs/def ault-source/default-document-library/guidelines-for-use-of-transmissionline-right-of-way.pdf [18] bc transmission corporation, “rights-of-way guidelines for compatible uses”, http://www.wcowma.com/wp-content/uploads/rights ofwayguidelines.pdf [19] velco, “electric transmission right-of-way usage 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international fig workshop on 3d cadastres, athens, greece, 18-20 october, 2016 [30] p. lolonis, “progress and status of the development of the core geospatial information infrastructure in greece”, tufe 2018, high-level international interdisciplinary conference, athens, november 7-9, 2018 [31] p. lolonis, “an assessment of the socio-economic benefits of the hellenic national cadaster”, world bank conference on sustainable real estate markets, athens, greece, sept. 19-20, 2016 [32] national grid, “transmission right-of-way management program”, http://documents.dps.ny.gov/public/common/viewdoc.aspx?docrefid= %7b92b47ce9-84d1-4139-bd1a-13e472dff4fb%7d [33] i. ituen, g. sohn, “the way forward: advances in maintaining rightof-way of transmission lines”, geomatica, vol. 64, no. 4, pp. 451462, 2010 [34] d. pylarinos, “vegetation rules for greek utilities”, transmission & distribution world, june 2020 global vegetation management, pp. 1822, june, 2020 [35] d. pylarinos, “overhead power transmission lines and forests: an illregulated relationship”, naturevolve, issue 5, pp. 8-10, 2020 [36] european construction sector observatory, country profile greece, june 2019, https://segm.gr/wp-content/uploads/2019/07/ecso_cfs_gr eece_2019.pdf microsoft word 27-3413_s_etasr_v10_n2_pp5492-5495 engineering, technology & applied science research vol. 10, no. 2, 2020, 5492-5495 5492 www.etasr.com alsaif: extreme wide band mimo antenna for fifth generation wireless systems extreme wide band mimo antenna system for fifth generation wireless systems haitham alsaif electrical engineering department college of engineering university of hail hail, saudi arabia hal-saif@hotmail.com, h.alsaif@uoh.edu.sa abstract—a new compact 2×2 multiple input multiple output (mimo) antenna is presented in this paper, suitable for the new wireless communications. the proposed design also covers the complete ultra-wideband for short wireless systems. the antenna system is characterized by a super wideband covering radio frequency (rf) band starting from 2.97ghz to 19.82ghz. the mimo system contains two ship-shaped monopoles with trimmed edges. these antennas are printed on a single layer of rogers duroid rt5880lz with relative permittivity εr=1.96 and loss tangent δ of 0.0009. the overall size of the mimo system is 20mm×47mm×1.6mm. the peak-achieved gain is 8.12db with nearly omni-directional isotropic far field patterns. the design and simulation has been performed via an industrial simulation code. keywords-5g; ultra-wide band; planar antenna i. introduction a dramatic increase in data rates is mandatory by the new generation wireless systems, which ga rise to challenges of the communication systems industry. long-term evolution (lte) in fourth generation commercial services is at the border of meeting these high data rate requests. presently, in order to overcome such problems, the industry is launching sub-6ghz for the 5th generation mobile devices. however, it is aimed to use the current networks and then shift to higher bands or millimeter bands from 28ghz to 85ghz by the end of 2020 [14]. the present spectrum bandwidth, which is lower than 6ghz is not enough to meet the future requirements. therefore, new spectrum allocations above 6ghz are essential in order to alleviate the existing spectrum lack which is the main motivation in introducing the 5g in wireless communications systems. in the last few years studies for the 5g have started to move up from ultra-high frequencies (uhf) (300mhz-3ghz) to new frequency bands in the microwave range, counting millimeter-wave spectrums. henceforth, the spectrum range above 6ghz and mm-wave bands are the chief bases in solving 5g challenges [5-9]. different new ultra-wideband antennas with variety designs (rectangular, circular, elliptical, etc.) have been designed [513]. the designs differ in terms of parameters such as frequency bands, radiation, gain, and physical size. some of these designs have shortages in their operating frequencies which do not include uwb set by fcc (3.1 to 10.6ghz). the suggested planar antenna in this paper is competitive with many of the previously published designs and has a reduced structure size. aiming to satisfy this new challenge of intensely increasing data rates, a 2×2 mimo antenna system is proposed. the system has been designed and simulated in order to evaluate and test its performance. mimo antenna systems are enormously employed in wireless devices to enrich the channel capability and multipath propagation and to improve high datarates [10-15]. ii. antenna design the geometrical arrangement of the proposed mimo antenna along with design parameters for two feeding ports uwb mimo are shown in figure 1. the microstrip antennas have a simple and reduced structure size, which is 24mm long and 20mm wide, printed on a rogers duroid rt5880lz substrate with 1.6mm thickness with relative permittivity εr=1.96 and loss tangent δ=0.0009. as shown in figure 1, the mimo consists of two shipshape radiators with truncated edges in order to enrich the impedance matching and to improve the bandwidth up to 17ghz [17]. table i illustrates he optimized values of the geometric variables. the ship-shape antennas cover a radio frequency band from 2.97ghz to 19.89ghz, which includes ieee 802.11 a/b/g/n/ac standards and sub-6ghz 5g bands as well. additionally, this compact super wide band mimo antenna system fulfills the frequency operating regulations of the federal communication commission (fcc) for uwb communication systems [16-17]. thus, the designed system is a model candidate for use in the uwb, wi-fi and sub-6ghz, i.e. 5g mobile due to its very compact design and characteristics. iii. parametric study and simulation results parameter investigation and optimization have been conducted in order to discover the key parameters and to enhance the mimo antenna’s performance in terms of bandwidth, isolation, power gain, and radiation pattern. figures 2 and 3 show the optimized reflection coefficients (s11) and (s22) in db versus the operating frequency in ghz. they display the super ultra-wide bandwidth that varies from 2.97ghz to 19.82ghz, which covers the whole bandwidth allocated for short wireless systems and the entire lower 5g corresponding author: haitham alsaif engineering, technology & applied science research vol. 10, no. 2, 2020, 5492-5495 5493 www.etasr.com alsaif: extreme wide band mimo antenna for fifth generation wireless systems bands. the covered bandwidth holds all bands in europe, japan, china, korea, and united states. the reflection coefficient has multiple resonant frequencies of 3.48ghz, 7.32ghz, 9.89ghz, and 17.62ghz. a part of the parametric optimization process for the proposed antenna system for different values of the feeding strip line width is demonstrated in figure 4. it is observed that the greatest impedance matching is attained at a line width of 2.7mm. fig. 1. geometry of the proposed mimo antenna table i. parameters of the designed 2×2 mimo antenna parameter w l wg lg wr lr wf wm value (mm) 45 20 8.3 4.5 13 17 2.7 4.5 multiple substrate materials such as fr-4 (εr=4.3), rogers rt 5880lz (εr=1.96), and polymide (εr=3.5) have been investigated for optimization purposes. the reflection coefficients s11 for these materials are plotted in figure 5. it can be clearly noticed that the antenna’s bandwidth has been optimized by using rogers duroid rt 5880lz as a substrate material and during this super wide bandwidth the reflection coefficient is lower than -10db. figure 7 displays the normalized radiation pattern at resonant frequencies 3.35ghz, 7.31ghz, and 9.89ghz for the main perpendicular planes (elevation (e) and azimuth (h)) in polar form. generally, the presented antenna has an omni-directional radiation pattern with minor distortion at a higher part of the bandwidth as a result of the high growth in the power gain. consequently, the proposed mimo antenna can be inserted inside wireless systems at any position due to its radiation feature. the antenna is characterized by its high gain, which exceeds 8.12dbi. figure 8 displays the proposed mimo system power gain in db versus the entire operating frequency in ghz. fig. 2. simulated reflection coefficient (s11) vs operating frequency the key factor in mimo performance and the major effort in designing mimo antennas is obtaining lower transmission coefficient (s12 and s21) values between the two ports. in figure 8 it can be observed that both antennas have well decoupled, which have s12 and s21 less than -16db as well as good mutual coupling between the monopoles elements in the entire bandwidth. fig. 3. simulated reflection coefficient (s22) vs operating frequency fig. 4. reflection coefficients for several values of feeding line width fig. 5. several substrate materials for the proposed mimo antenna fig. 6. reflection and transmission coefficients for the monopole system vs operating frequency a brief performance comparison between the proposed mimo antenna system with similar mimo antennas available in literature in terms of bandwidth, isolation, power gain, and structure size is presented in table ii. the table clarifies that the suggested antenna is compact in size with extremely wide bandwidth, high power gain and isolation in comparison with similar existing antennas. engineering, technology & applied science research vol. 10, no. 2, 2020, 5492-5495 5494 www.etasr.com alsaif: extreme wide band mimo antenna for fifth generation wireless systems fig. 7. simulated power radiation pattern in polar form (elevation and azimuth planes) of the proposed mimo antenna at 3.48ghz, 7.32ghz, 9.89ghz, and 17.62ghz fig. 8. simulated power gain during the operating frequency with maximum gain of 8.12db table ii. performance comparison between the proposed antenna and previously published designs reference size (mm 2 ) bandwidth (ghz) isolation (db) power gain (db) [18] 35×40 3.1-10.6 -16 [19] 50×30 2.5-14.5 -20 7.4 [20] 32×32 3.1-10.6 -15 [21] 27×28 3-10.6 -16 proposed 20×45 2.97-19.82 -16 8.12 iv. conclusion a new compact 2×2 mimo antenna system is proposed in this paper. the antenna system has been designed, simulated using an industrial standard simulation code, and optimized. the proposed ship-design mimo system has s bandwidth of 16.85ghz ranging from 2.97ghz to 19.82ghz with s12 parameter less than -16db. the design is simple single layer and compact with total structure size of 20×45×1.6mm 3 . the overall fractional bandwidth of the antenna was measured as 148.1%. also, the obtained peak gain value of the presented antenna system was measured as 8.12db with nearly omnidirectional radiation pattern. references [1] i. ndip, t. h. le, o. schwanitz, k. d. lang, “a comparative analysis of 5g mmwave antenna arrays on different substrate technologies”, 22nd international microwave and radar conference, poznan, poland, may 14-17, 2018 [2] g. r. maccartney, t. s. rappaport, s. sun, s. deng, “indoor office wideband millimeter-wave propagation measurements and channel models at 28 and 73ghz for ultra-dense 5g wireless networks”, ieee access, vol. 3, pp. 2388-2424, 2015 [3] c. x. mao, s. gao, y. wang, “broadband high-gain beam-scanning antenna array for millimeter-wave applications”, ieee transactions on antennas and propagation, vol. 65, no. 9, pp. 4864-4868, 2017 [4] h. al-saif, m. usman, m. t. chughtai, j. nasir, “compact ultra-wide band mimo antenna system for lower 5g bands”, wireless communications and mobile computing, vol. 2018, article id 2396873, 2018 [5] ofcom, spectrum above 6 ghz for future mobile communications, available at: https://www.ofcom.org.uk/__data/assets/pdf_file/0023/ 69422/spectrum_above_6_ghz_cfi.pdf, ofcom, 2015 [6] 5g americas, 5g americas spectrum recommendations for the u.s., available at: https://www.5gamericas.org/wp-content/uploads/2019/07/ 5g_americas_spectrum_recommendations_for_the_u.s_final.pdf, 5g americas, 2018 [7] 5g americas, spectrum landscape for mobile services, available at: https://www.5gamericas.org/wp-content/uploads/2019/07/5g_americas _whitepaper_spectrum_landscape_for_mobile_services_1.5.pdf, 5g americas, 2017 [8] itu-r, final acts wrc-15, world radiocommunication conference, geneva, itu, 2015 [9] h. alsaif, “compact hexagonal monopole antenna for lower 5g bands”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4200-4202, 2019 [10] m. usman, r. a. abd-alhameed, p. s. excell, “design considerations of mimo antennas for mobile phones”, piers online, vol. 4, no. 1, pp. 121-125, 2008 [11] m. dighriri, g. m. lee, t. baker, “measurement and classification of smart systems data traffic over 5g mobile networks”, in: technology for smart futures, springer, 2018 [12] s. li, l. d. xu, s. zhao, “5g internet of things: a survey”, journal of industrial information integration, vol. 10, pp. 1-9, 2018 [13] y. wu, k. ding, b. zhang, j. li, d. wu, k. wang, “design of a compact uwb mimo antenna without decoupling structure”, international journal of antennas and propagation, vol. 2018, article id 9685029, 2018 [14] f. wang, z. duan, s. li, z. l. wang, y. b. gong, “compact uwb mimo antenna with meta-material-inspired isolator”, progress in electromagnetics research c, vol. 84, pp. 61-74, 2018 [15] l. wu, y. xia, x. cao, z. xu, “a miniaturized uwb-mimo antenna with quadruple band-notched characteristics”, international journal of microwave and wireless technologies, vol. 10, no. 8, pp. 948-955, 2018 [16] m. matinmikko, m. latva-aho, p. ahokangas, v. seppanen, “on regulations for 5g: micro licensing for locally operated networks”, telecommunications policy, vol. 42, no. 8, pp. 622-635, 2018 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 frequency in ghz g a in i n d b engineering, technology & applied science research vol. 10, no. 2, 2020, 5492-5495 5495 www.etasr.com alsaif: extreme wide band mimo antenna for fifth generation wireless systems [17] r. marsden, h. m. ihle, “mechanisms to incentivise shared-use of spectrum”, telecommunications policy, vol. 42, no. 4, pp. 315-322, 2018 [18] s. zhang, z. ying, j. xiong, s. he, “ultrawideband mimo/diversity antennas with a tree-like structure to enhance wideband isolation,” ieee antennas and wireless propagation letters, vol. 8, pp. 1279-1282, 2009 [19] a. iqbal, o. a. saraereh, a. w. ahmad, s. bashir, “mutual coupling reduction using f-shaped stubs in uwb-mimo antenna”, ieee access, vol. 6, pp. 2755-2759, 2018 [20] j. ren, w. hu, y. yin, r. fan, “compact printed mimo antenna for uwb applications”, ieee antennas and wireless propagation letters, vol. 13, pp. 1517-1520, 2014 [21] g. srivastava, a. mohan, “compact dual-polarized uwb diversity antenna”, microwave and optical technology letters, vol. 57, pp. 2951-2955, 2015 microsoft word etasr_7-1_1382-1386.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1382-1386 1382 www.etasr.com hamasha: a mathematical approximation of the left-sided truncated normal distribution using the … a mathematical approximation of the left-sided truncated normal distribution using the cadwell approximation model mohammad m. hamasha department of engineering management prince sultan university riyadh, saudi arabia mhamash1@binghamton.edu abstract—in the case that life distribution of new devices follows the normal distribution, the life distribution of the same brand used devices follows left-sided truncated normal distribution. in spite of many mathematical models being available to approximate the normal distribution density functions, there is a few work available on modeling/approximating the density functions of left-sided truncated normal distribution. this article introduces a high accuracy mathematical model to approximate the cumulative density function of left-sided truncated standard normal distribution defined on the range of [truncation point (zl): ∞]. the introduced model is derived from the cadwell approximation of the normal cumulative density. the accuracy level change with z score is discussed in details. the maximum deviation of the model results, from the real results for the whole region of [-∞<zl<-2: ∞], is 0.006877. keywords-truncated normal distribution; normal distribution; mathematical approximation i. introduction if is a continuous random variable x having a normal distribution with mean of μ and standard deviation of σ, the normal curve can be graphed using (1) 2 2 ( ) 2 1 ( ) 2 x f x e m s s p = (1) the normal distribution can take any mean and any positive standard deviation. these two parameters determine the shape of the normal curve. the mean provides the location of middle of distribution, and the standard deviation defines how much the data are spread from the mean. normal distribution is used to model many sets of measurements in industry, business and nature. for instance, the human blood sugar level, the lifetime of radio sets, and even automobile costs are all normally distributed. a normal distribution has many unique properties including that 1) the value for mean, median, and mode are equal, 2) the distribution curve is bell shaped and symmetric about the mean, 3) the total area under the normal curve equals to 1 (all probability distributions have this property), 4) the normal curve approaches to zero with x going to -∞ or ∞, and finally, 5) around the center of the curve, the graph curves downward (concave). further, the graph curves upward at the right and the left sides. the inflection points are the points at which the curve changes from curving downward to upward. the normal distribution with σ equals to 1 and μ equals to 0 is called the standard normal distribution. the standard normal distribution function is shown in (2). 2 2 2 1 )( z ez     (2) the standard normal distribution horizontal scale is well known as z score. any not standard normal distribution can be transferred into z score with using of the following transformation formula: ( ) /z x m s= . there are many situation where the interest is to compute the probability that the observed value x is less than or equal to some real number x. therefore, the cumulative distribution function is defined as f(x) = p(x ≤ x). for every real number x, f(x) is defined, as shown in (3). f(x) = p(x x) ( ) x f t dt -¥ £ = ò (3) the cumulative distribution function for the normal distribution is denoted by φ(z) as addressed in the following equation: dtez z t     2 2 2 1 )(  (4) the solution of the above mentioned equation is complex and cannot be solved manually. therefore, the statisticians prepared table to estimate the cumulative distribution function values for the standard distribution. this table is called a ztable. the normal distribution can be truncated in various ways as needed. for example, if the distribution of the gre scores is engineering, technology & applied science research vol. 7, no. 1, 2017, 1382-1386 1383 www.etasr.com hamasha: a mathematical approximation of the left-sided truncated normal distribution using the … normally distributed and a graduate school has a minimum acceptable score, then the distribution of the admitted student scores is basically left-sided truncated normal distribution. this is because the left tail of the normal distribution (e.g., scores lower than minimum acceptable gre scores) is truncated. another example, if the life in years, of a television set is normally distributed, then the distribution of a two years used television set from the same brand is left-sided truncated normal distribution. the tail of distribution at p(x<2) is truncated. the following figure (figure 1) is an example on the left-sided truncated normal distribution. fig. 1. left-sided truncated normal distribution (e.g.,μ=21.1, σ= 5.3, truncation point (xl)=10 ). the left-sided truncated standard normal distribution is defined on the region (zl:∞). since the final area under the curve of truncated distribution must equal to 1, the new curve is stretched up to compensate the lost truncated area over the region (-∞: zl). the probability density function of the leftsided truncated normal distribution is addressed in (5) , )( )( )(   lz t dtt z z     zzl (5) the cumulative distribution function for the left-sided truncated normal distribution can be defined as the cumulative density function divided by the area under the original distribution function over the region (zl: ∞). equation (6) represents the cumulative distribution function of left-sided truncated standard normal distribution. dt dtt t z z z z t l l    )( )( )(   ,  zzl (6) equation (6) is a complex integration function, and need a numerical solution to be solved. therefore, engineers usually use sophisticated computer programs or specialized software package to handle this kind of equations. however, in the case that φ(z) is approximated with function that is able to be differentiated and integrated, then the truncated normal distribution can be estimated in a function. ii. review of prior research much research on mathematical approximation of normal distribution functions is available in the literature. at least 15 highly accurate models were introduced. cadwell (1949) [1-3] introduced a very nice approximating model, as shown in (7)                                                 0, 3 )3(22 exp(11 2 1 1 0, 3 )3(22 exp(11 2 1 )( 2 1 2 42 2 1 2 42 z zz z zz z       (7) the following 6 models are mentioned in [1, 2]: polya (1945), 2) hart (1963), 3) zelen and severo (1966), 4) schucany and gray (1968), 5) hoyt (1968), 6) hamaker (1978), 7) lin (1988), 8) lin (1989), and 9) lin (1990). further, there are few recent models such as vazquez-leal (2012) [4], choudhury (2014) [5] and luis (2015) [6]. many authors discussed in details many aspect about the truncated normal distribution. for example, ke et al. [7] used double-sided truncated normal distribution on action reliability for ammunuition swing device of large caliber gun. pender [8] provided an exact expression for the moments of the truncated normal distribution using stein’s lemma. his moment expressions provide insight into the steady state skewness and kurtosis dynamics of single server queues with impatient customers. sun et al. [9] worked on finite fault modelling for the wenchuan earthquake using hybrid slip model with truncated normal distributed source parameters. beucher and renard [10] described a stochastic model called truncated gaussian simulations (tgs), which distributes a collection of facies or lithotypes over an area of interest. this method is based on facies proportions, spatial distribution and relationships, which can be easily tuned to produce numerous different textures. mukerjee and ong [11] worked on variance and covariance inequalities for truncated joint normal distribution via monotone likelihood ratio and log-concavity. horrace [12] developed probability statements and ranking and selection rules for independent truncated normal populations. sharples and pezzey [13] presented results pertaining to truncated multivariate normal distributions, some of which already appear in the mathematical literature. they focused to make these types of results more accessible to the environmental science community and to this end, they included a conceptually simple alternative derivation of an important result. furthermore, they illustrated how the theory of truncated multivariate normal distributions is employed in the environmental sciences. we can conclude from the above discussion that there is a lot on work on mathematical aspects and applications of the normal cumulative distribution function. even so, mathematical approximations on the truncated normal distribution are not that frequent. in this paper, a mathematical approximation model of left-sided truncated normal cumulative engineering, technology & applied science research vol. 7, no. 1, 2017, 1382-1386 1384 www.etasr.com hamasha: a mathematical approximation of the left-sided truncated normal distribution using the … distribution function is proposed. the model is derived from cadwell’s model of approximating the normal cumulative distribution function. iii. proposed model since (7) is separated into two parts according to z value, the model will be divided on two parts. we are going to formulate a model for the left part (z<0) first. the left part is recalled, as extracted and simplified in (8). 0, 3 )3(22 exp(1 2 1 2 1 )( 2 1 2 42            z zz z    (8) the left-sided truncated standard normal distribution can be obtained through integration as explained in (6). remember that φ(z) =dφ(z)/dz. the following equation can be used to obtain the first part of our model, as addressed in (9).  )(zt dt dt tt dt d tt dt d z z z l l                                                               0 2 1 2 42 2 1 2 42 3 )3(22 exp(11 2 1 15.0 3 )3(22 exp(11 2 1 1       , z<0 (9) the solution of the equation will give the following formula (written in the simplest form).                                            2 1 2 42 2 1 2 42 3 )3(22 exp(11 3 )3(22 exp(11 1)(       ll t zz zz z z<0 (10) if z>0, then approximating փt(z) needs to extract the positive z part of (7) and substitute it in (6), exactly as we did in (9). the result is addressed in (11).                                             2 1 2 42 2 1 2 42 3 )3(22 exp(11 1 3 )3(22 exp(1 1)(       ll t zz zz z , z≥0 (11) iv. numerical examples example 1: if the life of a television set is normally distributed with a mean of 22 years and standard deviation of 7. the interest of this question is to find the 6 year reliability of 6 years used television from the same brand. in other words, what is the chance that the 6 years old television will be survived for another 6 years? solution: reliability is defined as the probability that a device, part or system will perform their function for a given period of time when operated under stated conditions [14]. the requirement can be written in statistics notation as p(x> 6+6). since this distribution is not standard, the transformation formula, z=(x-µ)/σ will be used to find zl and z that are corresponding to x=6 and x=12, respectively. 286.2 7 226   lz 249.1 7 2212   z the probability p(x>12) is corresponding to p(z>-1.249) or 1-փt(-1.249). by using (11), the result is 0.905713. the model result is very close to the actual result which is 0.904229. the deviation of the model result from the actual result (i.e., error) is only 0.00148 example 2: let’s assume that the distribution of scores of gre analytical part test out of 800 is normally distributed with a mean of 540 points and standard deviation of 40 points, and let’s assume that the acceptable score for some graduate school is 460. if an admitted student is selected randomly, what is the probability that his score is below 620? solution: since the value of probability density at any x greater than 800 (more than is 6.5 sigma) is very close to zero, we will not assume that the distribution is truncated from the right side at 800. the distribution of the admitted students is left-sided truncated normal distribution at the acceptable level (i.e., 460). zl = -2 is corresponding to xl = 460 by using the transformation formula (i.e., z=(x-µ)/σ). further, z=2 is corresponding to x=620. in statistic notation, the requirement is p(x<620) which is corresponding to p(z<2) or փ t(-1.249). by using (11), the result is 0.9826. the model result is very close to the actual result for this example. the actual result is 0.97672, and deviation of the model result from the actual result is only 0.00588. it is noticeable from both examples, that the error level is very low. indeed, this level of error is very ignorable for most applications of reliability engineering as well as other probability fields. v. accuracy analysis in this section, the accuracy of the model is presented in term of approximating the left-sided truncated normal distribution. mainly, the change of deviation of the model results from the real results (i.e., error) with z and zl is focused. to make sure that the introduced model is good at all value z and zl, we are concerning about the maximum error over the whole defining range, (zl:∞) at any zl (-∞:-1.5). figure 2 presents the error versus z at zl= -4, -3.5, -3, -2.5, -2, and -1.5. we can clearly note that there are two maximum peaks (i.e., maximum deviation or error) for every curve. the first peak is noticed at somewhere between z=-1.6 and z=-1.7, and the second peak is noticed at somewhere between z=1.6 and z=1.7 for all curves. the maximum error for each curve is as follows: for zl= -4, the maximum absolute error is about 0.006452, for zl= -3.5, the maximum absolute error is about 0.006456, for zl= -3, the maximum absolute error is about 0.0065, for zl= -2.5, the maximum absolute error is about engineering, technology & applied science research vol. 7, no. 1, 2017, 1382-1386 1385 www.etasr.com hamasha: a mathematical approximation of the left-sided truncated normal distribution using the … 0.00663, for zl= -2, the maximum absolute error is about 0.006887, and for zl= -1.5, the maximum absolute error is about 0.0071251. usually, the literature does not focus on any truncation point higher that zl=-2 as it is rarely needed in most applications. in this study, we took zl=-1.5 as the final truncation point. in figure 3, the error versus z is constructed for the original approximation of standard normal distribution that our model is based on (i.e., cadwell approximation). we can see that the maximum error is 0.006466 at z= -1.655 and at z=1.655. the accuracy of the cadwell model is close to the accuracy of the truncated cadwell model at any considered zl. the current model is more accurate than the logistic function-based truncated normal distribution which introduced in [1]. the current model leads to a maximum absolute error of about 0.0071, while the maximum absolute error in the logistic function-based model is close to 0.02 at the range of -∞<zl<1.5. furthermore, the current model is easier to implement using simple calculator. figure 4 refers to a comparison graph of the model and real results of zl=-2 left-sided truncated normal cumulative distribution function. we can notice that they are very close to each other. we can’t distinguish the difference between the two curves with the normal paper scale. vi. conclusions in this article, an approximation to the left-sided truncated cumulative distribution function is introduced. the model can be used by reliability and quality engineers in order to avoid the sophisticated computer programs or software when having such distributions in their work. the model was build based on cadwell approximation to the normal distribution. this study is unique because it provided model with a higher accuracy than any similar study in the literature. it provided a maximum error of 0.006877 for z (-2:∞) while logistic function-based approximation [1], for example, provides a maximum error 0.017 on the same range of z. fig. 2. error (i.e., different between model and real results) versus z at zl=-4, -3.5, -3, -2.5, -2, and -1.5. fig. 3. error versus z for cadwell approximation (i.e., untruncated standard normal distribution). fig. 4. truncated normal distribution approximation versus the real truncated normal distribution at zl= -2. references [1] m. m. hamasha, “practitioner advice: approximation of the cumulative density of left-sided truncated normal distribution using logistic function and its implementation in microsoft excel”, qual. eng., 2016 [2] s. r. bowling, m. t. khasawneh, s. kaewkuekool, b. r. cho, “a logistic approximation to the cumulative normal distribution”, j. ind. eng. manage., vol. 2, no. 1, pp. 114-127, 2009 [3] j. h. cadwell, “the bivariate normal integral”, biometrika, vol. 38, pp. 475-479, 1951 [4] h. vazquez-leal, r. castaneda-sheissa, u. filobello-nino, a. sarmiento-reyes, j. s. orea, “high accurate simple approximation of normal distribution integral”, math. prob. eng., vol. 2012, article id 124029, pp. 1-22, 2016 [5] a. choudhury, “a simple approximation to the area under standard normal curve”, math. stat., vol. 2, no. 3, pp. 147-149, 2014 [6] a. j. luis, “an approximation to the probability normal distribution and its inverse”, ingeniería, investigación y tecnología, vol. 16, no. 4, pp. 605-611, 2015 [7] x. ke, j. hou, t. chen, “notice of retraction research on action reliability for ammunition swing device of large caliber gun based on doubly truncated normal distribution”, international conference on quality, reliability, risk, maintenance, and safety engineering (qr2mse), july 15-18, 2013 [retracted] engineering, technology & applied science research vol. 7, no. 1, 2017, 1382-1386 1386 www.etasr.com hamasha: a mathematical approximation of the left-sided truncated normal distribution using the … [8] j. pender, the truncated normal distribution: applications to queues with impatient customers”, oper. res. lett., vol. 43 no. 1, pp. 40-45, 2015 [9] x. d. sun, x. x. tao, c. q. liu, “finite fault modelling for the wenchuan earthquake using hybrid slip model with truncated normal distributed source parameters”, appl. mech. mater., vol. 256-259, pp. 2161-2167, 2013 [10] h. beucher, d. renard, “truncated gaussian and derived methods”, in press, c. r. geosci., vol. 348, no. 7, pp. 510–519, 2016 [11] r. mukerjee, s. h. ong, “variance and covariance inequalities for truncated joint normal distribution via monotone likelihood ratio and log-concavity”, j. multi. var. anal., vol. 139, pp. 1-6, 2015 [12] w. c. horrace, “on ranking and selection from independent truncated normal distributions”, j. econometrics, vol. 126, pp. 335-354, 2005 [13] j. j. sharples, j. c. v. pezzey, expectations of linear functions with respect to truncated multinormal distributions–with applications for uncertainty analysis in environmental modelling”, environ. modell. software, vol. 22, no. 7, pp. 915-923, 2007 [14] c. e. ebeling, an introduction to reliability and maintainability, 2nd ed. waveland pr inc, usa. 2009 authors profile dr. mohammad m. hamasha received his phd in industrial and systems engineering from the state university of new york at binghamton, new york, usa, in december 2011. he also received his ms in industrial engineering and bs in biosystems engineering from jordan university of science and technology (just) in 2008 and 2005, respectively. he worked for two years from 2011 to 2013 as a postdoctoral associate and team leader with the center for autonomous solar power (casp) in binghamton ny doing a research related to reliability of solar materials and cell, and optimization of smart grid. up to august 2016, dr. hamasha has published about 45 publications. over the years, he has been involved in a variety of projects that range from experimental-based research to operations research, management, simulation, material science, thin films and photovoltaic research. his current research interests are in the areas of simulation, operational research, reliability engineering, design and analysis of production systems, stochastic and simulation optimization and lean six sigma. microsoft word 07-3152_s_etasr_v9_n6_pp4901-4904 engineering, technology & applied science research vol. 9, no. 6, 2019, 4901-4904 4901 www.etasr.com saand et al.: effect of metakaolin developed from local soorh on fresh properties and compressive … effect of metakaolin developed from local soorh on fresh properties and compressive strength of selfcompacted concrete abdullah saand department of civil engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan abdullah.saand@gmail.com karam ali jamali department of civil engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan tespublic@yahoo.com manthar ali keerio department of civil engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan mantharali99@quest.edu.pk tariq ali department of civil engineering quaid-e-awam university of engineering, science and technology, nawabshah, pakistan tariqdehraj@gmail.com nadeem-ul-karim bhatti department of civil engineering quaid-e-awam university of engineering, science and technology, nawabshah, pakistan knadeem_b@quest.edu.pk abstract—this paper presents the fresh properties of selfcompacting concrete (scc) containing metakaolin (mk) produced by calcination of the natural material soorh of district thatta sind in pakistan. five mixes were tested, including four mk mixes replacing 5-20% of cement, with 0.38 water/binder (w/b) ratio. the fresh properties of the sccs were evaluated using slump flow, t50, v-funnel, j ring, l-box and sieve segregation tests. compressive strength of the control and the mk scc was also investigated. the fresh concrete test results revealed that scc could be developed by substituting cement with local mk, using 2% superplasticizers and without using a viscosity-modifying amplifier. the scc with 15% replacement of cement with local mk showed maximum compressive strength, which was 10.39% higher than the control specimen’s without mk. keywords-metakaolin; self-compacting concrete; soorh i. introduction self-compacting concrete (scc) is a highly flowable concrete, which can be installed and compacted without any vibration in complex or dense reinforced formworks. in order to achieve such behavior, the main requirements of fresh scc are filling ability, passing ability and very high segregation resistance. the first two properties can be achieved by using a high-range water reducer (hrwr) admixture. to secure the stability/cohesion of the mix, a large quantity of powder materials and/or viscosity-modifying admixture (vma) is required. according to [1], the term powder is defined for materials of particle size smaller than 0.125mm, which include a fraction of aggregate additions and cement. portland cement is a high energy-intensive product. on the other hand, about 7% of total co2 emissions are produced by the cement industry [2]. in addition, some disadvantages in the properties of concrete have been reported as the cement content exceeded a specified value [3]. to minimize these negative effects, the requirement to increase powder content in scc is usually met by using additions. for this purpose, various studies have been conducted on the usage of different additions for partially replacing cement in scc or self-compacted mortar such as marble powder [4, 5], limestone powder [6], basalt powder [5, 6], fly ash [7–9], slag [10, 11], mk [12-16], and other materials[17-22]. today global warming and energy crisis are major issues. the manufacture of one ton of cement emits approximately 0.8 tons of co2 into the atmosphere, which accounts about the 5-8% of worldwide co2 emissions [23, 24]. moreover, cement production emissions include also so3 and nox [24, 25]. cement production requires huge energy, as it needs temperatures of 1600-1900ºc, adding up to the energy crisis in many countries, such as pakistan, where the cost of cement is rising resulting in an overall rise in the construction cost. this study proposes a method that increases the properties of scc and reduces the cement production, reducing consequently both co2 emissions and construction cost, by replacing cement with local mk. ii. materials used a. cement ordinary portland cement (opc) from a brand named lucky, has been used in this research. its chemical composition and physical properties are shown in table i. b. fine aggregates the aggregates used are composed of hill sand passing from 4.75mm, crushed stone passing from 12mm and retained on 4.75mm sieves. corresponding author: tariq ali engineering, technology & applied science research vol. 9, no. 6, 2019, 4901-4904 4902 www.etasr.com saand et al.: effect of metakaolin developed from local soorh on fresh properties and compressive … c. local metakaolin local metakaolin (mk) was produced from local natural material soorh available at district thatta sindh in pakistan, by calcination at 800ºc for 2 hours. the mk was used as cement replacement at various dosages, after sieving it from a sieve no 325. the chemical composition and physical properties comparison of opc, soorh and developed mk are presented in table i. table i. chemical composition of materials [26] constituents percentage by cement weight percentage by soorh weight percentage by mk weight sio2 20.78 55.89 62.18% al2o3 5.11 23.51 21.67 % cao 60.89 3.01% mgo 3 3.53 3.41% fe2o3 3.17 8.15 6.05% k2o 5.89 1.85% na2o3 1.89 1.03% tio2 1.14 1.03% in2o3 0.8% loi (%) 1.71 7.4 0.5 blaine specific surface area (cm 2 /g) 3008 2101 2339 iii. mixture proportion based on the w/b ratio of 0.38, scc mixtures were prepared following [1]. the reference concrete was prepared by only opc while in the other mixtures opc was partially replaced by mk at 5%, 10%, 15% and 20% of the cement’s weight. details of mix proportions are exhibited in table ii. table ii. mix proportions concrete mix cement (kg/m 3 ) mk (kg/m 3 ) total binder (kg/m 3 ) water (kg/m 3 ) fa (kg/m 3 ) ca (kg/m 3 ) sp (%) cm 500 500 190 900 650 2 mk5 475 25 500 190 900 650 2 mk10 450 50 500 190 900 650 1 mk15 425 75 500 190 900 650 3 mk20 400 100 500 190 900 650 3 m/b=0.38 iv. test procedure the fresh properties of scc have been studied out by using the method specified in [1]. the filling ability tests respected slump flow using v-funnel and t50 flow time test, while passing ability tests, such as j-ring and l-box, were also carried out. moreover, sieve segregation test was carried out. various trial mixes with and without superplasticizers were prepared to develop the scc. twenty eight days after the development of the control and the modified mk scc, the compressive strength of concrete was evaluated using bs en 12390-3. v. results and discussion a. slump flow slump flow test was used to assess the horizontal free flow of scc in the absence of obstructions. the diameter of the concrete circle is a measure of the filling ability of concrete [1]. the results of slump flow test for the mixtures are shown in figure 1. fig. 1. slump flow of control and metakaolin scc the recommended values of slump flow in [1] are 650850mm. without using superplasticizers and using only 1% superplastericizers, the observed slump flow of control and mk scc was less than the recommended. by using 2% superplasticizers the slump flow of control and mk scc was within the recommended range. as the quantity of mk increased the slump flow increased due to mk’s less specific surface area as compared to cement. b. v-funnel this test was developed in japan and used in [27]. the vfunnel test is used to determine the filling ability (flowability) of the concrete with a maximum aggregate size of 20mm.the results of the v-funnel test are shown in figure 2. fig. 2. v-funnel of control and metakaolin self compacted concrete the recommended values [1] of the v-funnel are 6-12sec [1]. without using superplasticizers and using 1% superplasticizers, the observed v-funnel flow of the control and the mk sccs exceeded the recommended range. by using 2% superplasticizers the v-funnel of the control and the mk scc were within the recommended range. as the quantity of mk increased, the v-funnel time decreased. c. t50 flow t50 flow test was used to assess the horizontal free flow of scc in the absence of obstructions. the results of the t50 flow tests are shown in figure 3. engineering, technology & applied science research vol. 9, no. 6, 2019, 4901-4904 4903 www.etasr.com saand et al.: effect of metakaolin developed from local soorh on fresh properties and compressive … fig. 3. t50 flow of control and metakaolin scc the recommended values of t50 flow time are 2-5sec [1]. without using superplasticizers and using 1% superplastericizers, the observed t50 flow time of the control and the mk scc exceeded the recommended. by using 2% superplasticizers, the t50 values of the control and the mk scc were observed within the recommended range. as the quantity of mk increased the t50 flow decreased. d. j-ring the j-ring test was developed at the university of paisley and it is used to determine the passing ability of the concrete. the results j-ring tests are shown in figure 4. fig. 4. j-ring of control and metakaolin self compacted concrete the recommended values of j ring test [1] are 0-10mm. without using superplasticizers and using 1% superplastericizers, the observed values of the control and the mk scc exceeded the recommended. by using 2% superplasticizers the observed j-ring values of the control and the mk scc were within the recommended range. as the quantity of mk increased, j-ring decreased. e. l-box l-box test is used to assess the flow of the concrete and the extent to which it is subject to blocking by reinforcement. the results of l-box tests are shown in figure 5. the recommended values for the l-box test are 0.8-1.0. without using superplasticizers and using 1% superplasticizer, the observed values of control and the mk scc exceed the recommended range. by using 2% superplasticizers the l-box value of control and the mk scc were observed within the recommended range. again, as the quantity of mk increased the l-box is decreased. fig. 5. l-box ratio of control and metakaolin self compacted concrete f. sieve segregation test the sieve segregation test was developed by gtm to assess segregation resistance (stability). the results of the sieve segregation tests are shown in figure 6. fig. 6. sieve segregation of control and metakaolin self compacted concrete the recommended range of sieve segregation is 0-12% [1]. without using superplasticizers and using 1% superplasticizers, the observed values of the control and the mk scc exceeded the recommended range. by using 2% superplasticizers, the jring values of control and mk scc were within the recommended range. as the quantity of mk increased the sieve segregation increased. g. compressive strength the results of compressive strength tests are shown in figure 7. the test results show that the compressive strength of 5-15% mk scc increased compared to the control or the other mk sccs. the 15% mk mixture exhibited maximum compressive strength , being 10.39% higher than the one of the control mix. vi. conclusion this study evaluated the fresh properties of scc containing local mk. results showed that all the fresh properties of scc containing local mk with 2% superplasticizers like passing ability, filling ability, and sieve segregation tests are within the recommended range. the fresh concrete test results revealed engineering, technology & applied science research vol. 9, no. 6, 2019, 4901-4904 4904 www.etasr.com saand et al.: effect of metakaolin developed from local soorh on fresh properties and compressive … that scc could be developed substituting cement with local mk up to 20%, by using 2% superplasticizers, without using any viscosity-modifying admixture. compressive strength of 515% mk mixtures was increased, while in higher mk mixtures the compressive strength decreased. the 15% mk scc had the maximum compressive strength, which was 10.39% higher than the control mix without mk. fig. 7. compressive strength of control and metakaolin self compacted concrete acknowledgement authors acknowledge the quaid-e-awam university for the provision of the necessary funds. references [1] efnarc, the european guidelines for self-compacting concrete; specification production and use, available at: http://www.efnarc.org/pdf/sccguidelinesmay2005.pdf, 2005 [2] r. zerbino, g. giaccio, g. c. isaia, “concrete incorporating rice-husk ash without processing”, construction and building materials, vol. 25, no. 1, pp. 371–378, 2011 [3] a. m. neville, properties of concrete, vol. 4, longman, 1995 [4] e. guneyisi, m. gesoglu, e. ozbay, “effects of marble powder and slag on the properties of self compacting 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the intention to continue using b2b e-commerce in manufacturing smes lubna a. hussein school of distance education universiti sains malaysia penang, malaysia lubnafatlawi@gmail.com shaian kiumarsi graduate school of business universiti sains malaysia penang, malaysia kiumarsi78@gmail.com ahmad suhaimi baharudin school of computer sciences universiti sains malaysia penang, malaysia asuhaimi@usm.my mohd faiz hilmi school of distance education universiti sains malaysia penang, malaysia faiz@usm.my abstract—business-to-business (b2b) electronic commerce plays a tremendous role in nurturing the growth of small and medium enterprises (smes) in developed and developing countries. however, the growth of b2b e-commerce in developing nations remains at the early adoption stage. the purpose of this paper is to examine the factors that influence b2b e-commerce adoption in smes in a developing country. the current study employs the questionnaire survey technique to gather information from 245 manufacturing smes in jordan. it uses structural equation modeling (sem) to investigate the different factors that affect the intention to adopt or continue using b2b e-commerce. the study reveals that compatibility and outsourcing it support have significant effects on the intention to continue using b2b ecommerce in jordanian manufacturing smes. the implications of the findings are discussed. keywords-toe framework; intention to continue using b2b e commerce; outsourcing it support i. introduction business-to-business (b2b) electronic commerce is defined as the internet-enabled technologies which allow businesses to buy and promote products and offerings electronically and share value chain facts [1, 2]. e-commerce gains attention as it helps in achieving better prices, improved quality, and customer satisfaction with lower costs. this attention is growing as more facilities are introduced in the field [3]. furthermore, communication within the business has become faster and managing has become more efficient with the implementation of e-commerce technology [4]. several studies have anticipated that b2b e-commerce will dominate the global economic system since it is considered as a significant determinant of the future increase of the economy [5]. hence, developed countries have aggressively implemented b2b ecommerce, where it has become an essential part of business activities [6]. smes play an invaluable role in national and global economy [7]. the smes in jordan play a vital role in boosting jordan’s economy through the provision of employment opportunities which account for 97% of all jobs. in jordan smes contain 98.5% from the aggregate sum of enlisted enterprises and 60% of formal occupations [8]. it has been asserted that the use of b2b e-commerce is critical to the establishment of an organization as well as the future exponential growth of a nation [9]. nevertheless, the b2b ecommerce expansion in the country is low, and some companies have stopped using b2b ecommerce for their businesses. several b2b e-commerce adoption studies in smes have been undertaken in developing countries as can be represented by [5, 10-12]. a key area of concern in the previous studies is the lack of detail on how b2b e-commerce adoption by smes is undertaken as most researchers have used exploratory research methods such as surveys that lack depth and theoretical foundation [13]. according to [5, 10, 13], organizations adopting b2b ecommerce in developing countries face challenges such as lack of it infrastructure, lack of qualified staff to develop and support b2b e-commerce sites, lack of stuff skills and, low bank account and credit card penetration. however, lack of technical knowledge is considered as one of the major barriers confronting the use of b2b e-commerce in developing countries [13, 14]. therefore, it is necessary for the smes to train their staff on b2b e-commerce technology. but this training requires a lot of effort, time and financial resources, hence the smes take an alternative action of outsourcing it support. therefore, this study examines the main factors that affect b2b e-commerce continuance in manufacturing smes in jordan. ii. conceptual research model the technological, organizational and environmental (toe) framework can be combined with diffusion of innovation (doi) theory in a way that the five factors of doi theory (relative advantage, compatibility, complexity, trialability, observability) are used in a technological context to corresponding author: mohd faiz hilmi engineering, technology & applied science research vol. 10, no. 2, 2020, 5528-5533 5529 www.etasr.com hussein et al.: factors influencing the intention to continue using b2b e-commerce in manufacturing … describe the way that the adoption depends on the technologies inside and outside the enterprises. toe has been used in studies related to b2b e-commerce adoption in business. for instance, the toe framework has been used to identify factors influencing b2b e-commerce adoption of 320 iranian manufacturing companies [11] and of 926 vietnamese smes [15]. the toe framework emphasizes the internal and external characteristics of a company. internal characteristics refer to the organizational context in the toe framework, whereas the external characteristics of the organization refer to the environmental context within the toe framework. the toe framework has been suggested as a useful starting point in studying b2b e-commerce adoption [2]. b2b e-commerce expansion in the jordan can be considered as low, some firms may have even discontinued using b2b e-commerce for their business. the main reasons are uncertainties regarding online payments, information intensity for the products and lack of it staff, because the majority of smes employ from 1 to 9 employees. the proposed research model depicted in figure 1 shows the important variables that affect b2b e-commerce in jordanian manufacturing smes. the technological context for this study refers to compatibility, organizational context (information intensity), and environmental context (outsourcing it support and security) that influence the dependent variable (intention to continue using b2b e-commerce) which is the main contribution of this study since the previous b2b ecommerce technology models do not address the issue of intention to continue using b2b e-commerce. therefore, the model in this study is to determine the factors that influence the intention to continue using b2b ecommerce. fig. 1. conceptual framework iii. hypothesis development a. intention to continue using b2b e-commerce the intention to continue using b2b e-commerce is considered as the enterprise’s intention to frequently use or proceed to the use of b2b e-commerce in the enterprise’s current and future practices [16, 17]. b. compatibility compatibility is defined as the consistent between b2b ecommerce and the organization existent values, preferred work practices and the way its suppliers and customers do their business [18]. the compatibility of b2b e-commerce to a company’s current system is very important. otherwise, it is very difficult to continue using b2b e-commerce since it may necessitate making major changes in the organization. the changes could lead to many difficulties that prevent its continuance. the use of b2b e-commerce requires considerable modifications to an organization’s work practices, structure, processes and routines [6], therefore the perceived compatibility of the smes towards e-commerce is considered as a significant factor in b2b e-commerce adoption [19]. this is fundamental because the adoption may not succeed if the prevailing infrastructures are not consistent with the b2b ecommerce technology. therefore, this study proposes that compatibility has a direct influence on the intention to continue using b2b e-commerce in manufacturing smes in jordan.: h1: compatibility has a positive impact on the intention to continue using b2b e-commerce. c. information intensity information intensity is defined as the complexity of the records required to understand the products or the services provided by an enterprise and the process of ordering them [20, 21]. many enterprises are unable to continue using b2b ecommerce because their products or services require lengthy explanations which seem complicated, and the information for their products are difficult to explain. information intensity may also be related to the enterprise’s reliance on gaining access to up-to-date, reliable, applicable and accurate information whenever they want it. the jordanian manufacturing smes have different information processing needs, and those smes with more information intensity are more likely to continue using b2b e-commerce. therefore, this study proposes that information intensity has a positive impact on the intention to continue using b2b e-commerce by jordanian manufacturing smes. h2: information intensity has a positive impact on the intention to continue using b2b e-commerce. d. security security is defined as the trust or confidence of the organization in using b2b e-commerce [13], hence it is a critical barrier to technology adoption. in malaysia for instance, it security is one of the fundamental factors that determine the adoption of b2b e-commerce [22]. besides, the fear of fraud discourages many organizations in jordan from making payments online. moreover, various factors have been identified to contribute to the slow development of e-commerce in arabic countries (including jordan). the crucial role of security in technology adoption has been indicated in [23, 24]. since jordanian smes have concerns about security, a more secure b2b e-commerce would encourage the continuation of using b2b e-commerce. thus, this study proposes that security has an effect on the intention to continue using b2b ecommerce in jordanian smes. h3: security has a positive impact on the intention to continue using b2b e-commerce. e. outsourcing it support outsourcing it support is defined as the availability and the effectiveness of the support from external sources with respect to the implementation and maintenance of b2b e-commerce engineering, technology & applied science research vol. 10, no. 2, 2020, 5528-5533 5530 www.etasr.com hussein et al.: factors influencing the intention to continue using b2b e-commerce in manufacturing … [5]. outsourcing it support is an important factor in it adoption as it can facilitate the adoption, implementation, and on-going success [25], probably because many enterprises are confronted with a shortage of internal it skilled personnel and difficulty in engaging external experts or consultants, hence the organizations can overcome the challenge via the development of their internal end-users’ computing skills or get assistance from external sources. therefore, this study proposes that outsourcing it support influences the intention to continue using b2b e-commerce in the jordanian smes. h4: outsourcing it supports has a positive impact on the intention to continue using b2b e-commerce. iv. methodology a. measurement development this study employs a quantitative survey, with a structured questionnaire, consisting of 22 items and divided into two sections, containing respondents’ basic information and organization information. besides basic information, the other items were measured using a seven-point likert scale ranging from ‘strongly disagree’ to ‘strongly agree’. the items capturing the theoretical constructs were developed in line with an extensive literature review. b. data collection the population of this study consists of the manufacturing smes in amman, the capital city of jordan. this study requires the respondents to possess certain knowledge of information technology [11] as well as general organizational infrastructure. the respondents are made up of department managers, assistant managers, executives and supervisors. the sample frame of this study consists of the manufacturing smes in the amman chamber of industry, which is the association of manufacturing smes in the hashemite kingdom of jordan. however, some studies have indicated that a sample size of 200 to 500 is adequate for multivariate data analysis [26], while other researchers asserted that a sample size large than 30 and less than 500 is appropriate for most researches [27]. c. analysis this study employs the partial least squares (pls) approach to determine the relationship between constructs using smart pls 3.0. the collected data were analyzed with sem, based on the pls approach. this method shows the relationships and the quality of connections among the factors in the proposed model. it uses the two-step technique [28] for data analysis. the first step consists of analyzing the model’s measurements while the second step examines the structural relationships that exist among the latent constructs. fundamentally, the two-step technique seeks to ascertain the measures’ reliability and validity prior to the assessment of the model’s structural relationships. v. results a. demographic variables the result for demographic variables is analyzed by using the spss version 22, as shown in table i. the data are collected through distributed questionnaires to the respondents in manufacturing smes. a total number of 245 usable questionnaires were obtained from smes that have email or website and who intend to advance the level of utilization of b2b e-commerce technology. table i. descriptive information variable description number % number of employees 1-9 147 60 10-49 82 33.5 50-249 16 6.5 years of operation less than 1 year 6 2.4 1 year to less than 5 years 77 31.4 5 years to less than 10 years 73 29.8 10 or above 89 36.3 industry type (manufacturing) therapeutic & medical 34 13.9 chemical & cosmetics 39 15.9 plastic & rubber products 14 5.7 engineering & electronics 34 13.9 furniture, kitchens & doors 32 13.1 paper, stationeries & office supplies 13 5.3 food & supply 49 20.0 leather & garments 21 8.6 other 9 3.7 capital less than usd 42,440 80 32.7 equal or more than usd 42,440 165 67.3 level of b2b ecommerce email with no website 111 45.3 website with communication between supplier and customers 52 21.2 website with just information about products 57 23.3 website with ordering online 16 6.5 website with online payment and online transactions 9 3.7 b. assessment of measurement model the measurement model evaluated the reliability and validity of the constructs (variables). composite reliability (cr) and average variance extracted (ave) were determined in the course of such evaluation [29]. for cr the recommended minimum threshold is 0.7 [30]. in this study, the cr values ranged from 0.874 to 0.958 which goes higher than the minimum value. all constructs have an ave above 0.5, which demonstrated a satisfactory degree of convergent validity as suggested in [31]. table ii and figure 2 show all the values were above the suggested value points, thus confirming the accomplishment of convergent validity. moreover, s3 and s4 were deleted due to ave which is less than 0.5. c. discriminant validity of the measurement model the current technique for assessing discriminant validity is the heterotrait-monotrait (htmt) ratio of correlations. according to [32] the fornell-larcker criterion and the examination of cross-loadings are the major methods to evaluate discriminant validity. however, the simulation study has showed that these techniques are not reliable in detecting the lack of discriminant validity in common research situations. consequently the htmt ratio of correlations was proposed as a new approach that has the functionality to assess discriminant validity in variance-based sem. previous studies [32] engineering, technology & applied science research vol. 10, no. 2, 2020, 5528-5533 5531 www.etasr.com hussein et al.: factors influencing the intention to continue using b2b e-commerce in manufacturing … suggested construct thresholds of 0.85 [33] and 0.9 [34] for htmt to confirm discriminant validity. hence, this study uses the htmt of 0.85 to set up discriminant validity. table iii, reports the results of the discriminant validity evaluation of the measurement model using htmt. table ii. measurement model assessment variable items loading ave cr ca compatibility comp1 0.890 0.783 0.947 0.930 comp2 0.909 comp3 0.908 comp4 0.910 comp5 0.801 information intensity ii1 0.857 0.703 0.902 0.865 ii2 0.920 ii3 0.940 ii4 0.588 outsourcing it support oits1 0.847 0.832 0.952 0.933 oits2 0.941 oits3 0.945 oits4 0.912 security s1 0.930 0.706 0.874 0.821 s2 0.954 s5 0.586 intention to continue using b2b e-commerce int.con1 0.918 0.852 0.958 0.942 int.con2 0.936 int.con3 0.935 int.con4 0.902 fig. 2. measurement model (n=245) table iii. discriminant validity-htmt comp ii int.con oits s comp ii 0.101 int.con 0.433 0.048 oits 0.459 0.065 0.373 s 0.290 0.168 0.154 0.161 d. assessment of the structural model the path coefficient of the structural model and bootstrap analysis with 5,000 re-samples was used to check the structural model of the significance of path coefficients. the significant effects specified by the model were evaluated and the results indicated that the effects of comp → int.con (h1) (β=0.298, t-value=4.445, p<0.001), oits → int.con (h4) (β=0.230, t-value=3.567, p<0.001) have positive relationship and are supported. thus, h1 and h4 are supported. table iv presents the significance of direct effects, the path coefficients, and the f2 values. according to [35], 0.02 signifies ‘small’ f2 effect, 0.15 signifies ‘medium’ effect, and more than 0.35 signifies ‘large’ effect. it could be noted that there is a small effect of dropping incentives from the model. authors in [32] stressed the importance of presenting the standardized root means square residual (srmr) as an approximation of model fit. the recommended srmr score of less than 0.08 is appropriate for a satisfactory pls path models fit. this study’s srmr score of 0.058 suggesting a satisfactory model fit. besides, the int.con’s r-square value of 21.2 fulfilled the rule of thumb recommended by [30]. figure 3 shows the path analysis of t-values results. table iv. results from hypothesis testing beta value se t-value p-value results f2 h1 0.298 0.067 4.445 0.000 supported 0.084 h2 0.035 0.068 0.523 0.300 not supported 0.002 h3 0.030 0.056 0.542 0.294 not supported 0.001 h4 0.230 0.064 3.567 0.000 supported 0.054 fig. 3. pls-path analysis of t-values (n=245) vi. discussion the findings of this study are discussed with consideration of three distinct categories namely organization, technology and environment. from the perspective of technological factors, this study reveals that compatibility is a significant factor that influences the intention to continue using b2b ecommerce technology. thus, the adoption of b2b e-commerce should be compatible with the prevailing system otherwise the adoption level is low and will have no effects. in the context of organizational factor, this study indicates that information intensity has no significant effect on the intention to continue using b2b e-commerce technology. the reason for this result is because most of the manufacturing smes in jordan are at a lower level of b2b e-commerce adoption. hence, it is possible that despite their high information intensity, they are already satisfied with the use of e-mail to disseminate information. in the environmental context, the study reveals that outsourcing it support has a significant effect on the intention to continue using b2b e-commerce in the jordanian manufacturing smes. basically, outsourcing it support includes support in the engineering, technology & applied science research vol. 10, no. 2, 2020, 5528-5533 5532 www.etasr.com hussein et al.: factors influencing the intention to continue using b2b e-commerce in manufacturing … implementation of b2b applications and the use of the applications where the support is obtained from the sources outside the business organization [36]. outsourcing it support functions as an agent of change in b2b e-commerce adoption assisting enterprises that lack in it infrastructure and knowledge necessary for b2b e-commerce adoption. in this study, the majority of the manufacturing smes have the 1-9 employees. therefore, this small number makes the smes not to have much technical support internally. having a limited number of employees with it knowledge could inhibit the intention to continue using b2b e-commerce. so, they depend on outsourcing it to help them to continue using b2b ecommerce technology. regarding security, this study shows that security has no significant effect on the intention to continue using b2b e-commerce in the jordanian manufacturing smes. this is consistent with the findings in [24] regarding security and its not significant effect on cloud computing adoption. for this study, since the majority of smes are at a low level of b2b e-commerce adoption without online transactions, there is no reason to be concerned about security. vii. implications of the study a. implications for agencies this study shows that the majority of the manufacturing smes in jordan are enterprises with a small number of employees. therefore, they lack the it staff to implement b2b e-commerce technology. the findings serve as guidelines for government agencies and non-profit organizations (e.g. jordan chamber of industry, amman chamber of industry, and jedco (jordan enterprise development corporation)) to evaluate the existing policies and design the strategy and plan to support b2b e-commerce technology in manufacturing smes in jordan. they could assist the manufacturing smes to understand the usefulness of b2b e-commerce adoption or encourage them to continue using it. ways should be provided to link smes and it consultants available in the country. such strategies would include holding courses and workshops by the local it companies where the it consultants can educate and train decision makers of the smes on b2b e-commerce usefulness through conferences, workshops and personal visits. they may also persuade and assist smes with a low level of b2b e-commerce technology adoption to implement a higher level of adoption. another strategy is that they may encourage the it providers to offer trial periods before full implementation of b2b e-commerce. also, ways should be provided to link smes and it consultants from abroad. strategies may include advertising the availability of offshore and virtual it consultants. like the local it support, policies may also involve the motivation for it organizations and smes to link. b. implications for it developers in high-level adoption of b2b e-commerce, the provision of online electronic payment is crucial to ensure that the business transactions with customers or suppliers are convenient and swift. but it is the responsibility of the firms to ensure the safety of the transactions and the confidentiality of the information disclosed during transactions. viii. future work this study focused on the factors that influence the intention to continue using b2b e-commerce among the manufacturing smes with varying levels of b2b e-commerce adoption. future studies could examine the factors that influence the intention to continue using b2b e-commerce at each level of b2b e-commerce adoption. this would provide complete insight into b2b e-commerce adoption by identifying the different factors associated with different b2b e-commerce adoption levels. appendix: quastionnaire items no construct items references 1 compatibility comp1 b2b e-commerce is compatible with our existing values [5, 18] comp2 b2b e-commerce is compatible with our supplier’s and customer’s ways of doing business. comp3 b2b e-commerce creates changes which are compatible with our current business operations. comp4 b2b e-commerce is compatible with our preferred work practice. comp5 b2b e-commerce is compatible with our organization’s traditional operating procedures 2 information intensity ii1 the product/services in our industry are complicated or complex to understand. [20, 21] ii2 the product/services in our industry generally require a lot of information before selling. ii3 ordering products in our industry by customers are generally a complex process. ii4 our firm is dependent on up-to-date information 3 outsourcing it support oits1 there are businesses in the community who provide technical support for the executive use of b2b ecommerce technology. [5, 38] oits2 there are agencies in the community who provide training sessions for adoption. oits3 outsourcing it support in the region are actively promoting b2b e-commerce technology and other technologies by providing incentives for adoption. oits4 we can easily obtain support from local it support as we implement b2b e-commerce. 4 security s1 our firm is concerned that the information involved in a transaction over the internet is not private. [13, 37] s2 our firm lacks confidence about the security of b2b e-commerce transactions. s3 our firm trusts that the internet can protect the confidential data that we enter on the websites. s4 our customers are worried about the security of the internet and will not use the internet to make payments s5 our firm does not have confidence in the payment system of b2b e-commerce. 5 intention to continue using b2b ecommerce int.con1 i intend to use b2b e-commerce in my organization frequently. 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acceptance, intechopen, 2012 engineering, technology & applied science research vol. 8, no. 4, 2018, 3249-3254 3249 www.etasr.com elsanousi & ozturk: performance analysis of ofdm and ofdm-mimo systems under fading channels performance analysis of ofdm and ofdm-mimo systems under fading channels abdulbagi elsanousi department of electronics and communication engineering kocaeli university, kocaeli, turkey alsnousi06037@hotmail.com sitki ozturk department of electronics and communication engineering kocaeli university, kocaeli, turkey sitki59@gmail.com abstract—fourth-generation (4g) wireless communication system is mainly based on mimo (multiple input and multiple output) and ofdm (orthogonal frequency division multiplexing). the combination of these two techniques leads to a better system, known as ofdm-mimo system, providing higher capacity and data rate. this paper demonstrates the ber (bit error rate) performance of ofdm and ofdm-mimo system using convolution code to encrypt the data stream that can be sent over communication channels. simulation is made on matlab using three different channels (awgn, rician and rayleigh). the simulation results show that the combined system has better performance compared to ofdm system. the practical part of this study was conducted by using two usrps b210 (universal software radio peripheral) for transmitting and receiving, two antennas were used during transmission for both sides. the transmitted signal is successfully recovered. keywords-ber; ofdm; ofdm-mimo; convolution code; racian; awgn; rayleigh; usrp i. introduction wireless communication systems these days have to provide higher data rates to fulfill the high demand. mimo is basically about improving the channel capacity by using multiple antennas. mimo offers enhancement to data rate and channel capacity. mimo-ofdm is an essential point of today’s broadband wireless systems. in fact mimo-ofdm technology has been being used in 4g, 4.5g and is going to be used in 5g. current generation wireless systems, such as 4g, support data rates up to 1gbps, which seems to be insufficient for high demand. in order to achieve this requested data rate, the near future generation 5g plans to use mimo for signal processing and ofdm for radio technologies [1]. upcoming mobile and wireless applications will need significantly higher data rates and cut-price cost per transmitted bit compared to 3g systems. systems using single antenna fail to meet the requirements on data rate, link quality, spectral efficiency etc. in mimo technology high gain is ensured for both channel capacity and reliability. the use of multiple antennas instead of a single antenna allows to enhance coverage, data transfer rate, security of the radio networks [2]. the ber of convolutional coded orthogonal frequency-division multiplexing system is analyzed in [3]. the ber is evaluated for different modulation schemes. this paper gives a generalized ber analysis of ofdm and mimo-ofdm systems. ii. principles of ofdm system ofdm is a way of encoding digital data on multiple carrier frequency and is essential to current generation wireless technology [4]. ofdm is a multicarrier transmission technique based on the theory of frequency division multiplexing. it was introduced for 3g networks to improve overall link capacity but later on it became a part of the current generation of wireless technology [5]. in this technique spaced subcarriers are used to carry data on several parallel data streams or channels, and that is why it is called a multicarrier frequency technique. this helps in minimizing the signal fading as much as possible and provides enhanced data rates [6]. the main idea behind ofdm is to divide carriers to subcarriers that are transmitted in parallel. in the ofdm system [7], the data are sent to the serial to parallel block where signal converts to a set of data blocks. then this set of parallel data blocks are sent to constellation mapper which can be of three or four types (bpsk, qpsk, qam) and then this data need to be modulated [4]. once it is modulated it is passed on through the ifft block whose prior and most important work is to orthogonalize the data [9]. it takes a number of symbols that are the total number of subcarriers which are basically multicarrier, and provides orthogonal sinusoidal. each of these outputs has different frequencies like a multi carrier frequency technique which has different orthogonal frequency onto it and once it comes out of ifft, it goes onto the parallel to serial conversion block, where it can get one total serial signal [10]. once it is ready to be sent to the channel, the channel sends it to the receiver, which receives it and the inverse process happens first by deleting the cyclic prefix and then reversing the ifft time domain back into the frequency domain [3]. once we get the frequency domain parallel signals we equalize them and send them back to the constellation demapper, where the entire demodulation work occurs. after demodulating the entire signal and getting the parallel data, the signal converts finally to serial to get the final data [11]. iii. mimo wireless technology overview an antenna system, called single input single output (siso), which is a transmitting and receiving antenna, is usually also known as conventional mobile radio communication system. greater network capacity, higher data rate and better quality are needed in modern telecommunication engineering, technology & applied science research vol. 8, no. 4, 2018, 3249-3254 3250 www.etasr.com elsanousi & ozturk: performance analysis of ofdm and ofdm-mimo systems under fading channels systems. both bandwidth and transmit power need to be increased, in order to improve the capacity of the siso system. mimo system is well known as a technique to increase the capacity without changing the transmitted power and original bandwidth requirements [12]. the basic idea is to improve channel capacity by using multiple antennas. mimo gives significant enhancement to data rate and channel capacity. mimo communication promises large gains for both channel capacity and reliability. using multiple antenna instead of a single one can enhance data transfer rate, coverage, security and overall performance of radio networks. mimo technology uses two main techniques known as spatial multiplexing and spatial diversity. in the spatial diversity form of mimo, the same data is sent over different transmitters and this leads to augmented reliability. while in the spatial multiplexing the bites stream to be transmitted are divided or demultiplexed into several data segments. these segments are then transmitted through different antennas simultaneously and this leads to increased data rate [13]. iv. multipath fading unlike a wired channel, which uses a fixed path, the signals in a wireless channel can reach a user using multiple paths. all these signals known as multipath components may have different channel gains and time delay. this combined effect causes what we know as multipath fading. fading, usually called small scale fading, is caused by multipath signal, when signal transmits from source to destination. this signal may be constructive or destructive [6]. the time delay between first signal at the receiver always (line of sight) and the last signal received from multipath is called delay spread [14]. a. rayleigh model the common distribution that is used to describe statistical time varying nature of received envelope of flat fading signal is the rayleigh distribution. the main idea of the rayleigh flat fading channel model is that there is no line of sight between transmitter and receiver [15]. the received signal is reflected or scattered by multipath. the probability density function of rayleigh distribution is given by: ( ) = −2 0 ≤ ≥ ∞ 0 < 0 (1) where σ and σ2 are received root-mean-square and a.c power of the received signal respectively [16]. the rayleigh channel coefficients computed according to (2). ℎ = (√ ) ∗ ( (0,1) + (0,1)) (2) b. rician distribution the rician fading occurs when there is a dominant non fading signal component like a line of sight propagation path. when the power in the dominant component decreases to zero, rician distribution can be seen as rayleigh distribution. the ratio between the line of sight and the other diffused components is known as rice factor, denoted by kr and expressed as follows =a2/(2σ2) [15]. ( ) = − ≥ 0, ≥ 0 0 < 0 (3) where a represents the peak amplitude of the dominant component while and (.) is the modified bessel function of the first kind and zero order [12]. the rician channel coefficients can be computed according to (4), where < 1. ℎ = + (0,1) + . (0,1) (4) c. the need for equalization equalization is used for compensating inter symbol interference. also, an equalizer within receiver compensates for the average range of expected channel amplitude and delay characteristic [17]. equalizers must be adaptive as the channel is generally unknown and time varying. in the current study we used minimum mean-squared error (mnse). basically the mnse equalizer for each subcarrier is defined as = ( ). ( )∗( ( )∗. ( )) (5) where e0 is noise power, ( ) is the received symbol, ( ) is the channel in frequency domain at subcarrier . v. ofdm-mimo system in the future broadband wireless techniques will provide big data rates and will improve channel performance. these channels may be time or frequency selective. we know that mimo system has the capability to enhance bandwidth and diversity. adding ofdm can help us decrease the effects due to multipath fading. the use of mimo ofdm is to send data over wireless communications and to overcome frequency selective channel effect [18]. the main idea behind the use of ofdm on each subcarrier is to deal with narrowband fading by transforming frequency-selective fading channels into flat channels. mimo algorithms can be implemented in broadband transmission with the help of the combined mimo and ofdm techniques [19]. at the transmitter, ofdm modulated data can be transmitted over multiple antennas simultaneously using a mimo ofdm system. at the receiver, ofdm demodulation is required then recovery of the signal is performed by decoding techniques on each of the sub-channels originated from all the transmitting antennas [18]. using mimo ofdm, suppliers will have the opportunity to apply a broadband wireless access (bwa) system which possesses non-line-of-sight (nlos) features. other advantages of mimo-ofdm are that it provides flexibility and big throughput, and also, in multiuser application, it facilitates a big number of users to access the base station or access point. by using ofdm modulator the signal is modulated, and then transmitted by the mimo system. the inverse process can be used to recover signals [12]: = . ̅ + (6) where and ̅ are received and transmitted vectors respectively, while h and are channel matrix and noise. vi. universal software radio peripheral software-defined radio is a technology that enables users to experiment with radio waves. the usrp b210 is a fully int a po 6g 3.0 ban the tra a. the the the (d of fre up th osc (lo ste ov b. am the loc con qu filt sig (a dig sig mo us tw for rec fre  engineerin www.etasr tegrated single host pc throu wered device ghz setting a 0 interface c ndwidth. the b e b210 suppo ansmitter and r fi transmit pat the host com e device throu e digital up co e signal to 61 dac) converts the band pa equency comp is converting he phase-locke cillator (vco o) can be freq ep the amplifi er the antenna receive path the incomin mplifier and dr e vco so tha cked to a refer nverting the adrature-phase ter decreases gnal. then the adc) which r gital down con gnal to a user-s oved to the ho sb 3.0 or usb o usrps for r each usr covered. the equency. algor algorithm usrp b210 begin 1 randi(x 2 conven ng, technology r.com e board softwa ugh a usb provides cont new standard can stream u b200 is capabl orts 2x2 mim receiver conne ig. 1. usrp t th mputer builds a ugh either usb onverter (duc .44ms/s. the the incoming ass filter is t onents in the g the signals t ed loop (pll ) so that the d quency-locked er amplifies t a. h ng signal is rive amplifier. at the device c rence signal. t signals to t e (q) compon noise and hig e signal enter responsible to nverter (ddc) specified rate. ost computer th b 2.0 connect transmitting a rp. the tran experiment i rithm 1 illustra 1: psuedo-co x) ← generate nc(x) ← convol y & applied sci elsanousi & o are-defined rad 3.0 interface. tinuous covera d for wideband up to 56mhz le full duplex mo [20]. figu ected with two transmitter and re and sends base b 3.0 or 2.0 c c) mixes, filte en the digitalg signal to ana to decrease th signal. the pu o a user-speci l) controls the device clocks d to a referenc the incoming amplified b . the phase-lo clocks and lo the idea from the baseband nents. after t gh frequency rs the analogdigitize the ) mixes, filters the down con hrough usb c tion. this stud and receiving nsmitted sign is set to mea ates the scenar ode of the o bits lutional encod ience research ozturk: perform dio that conne . this entire age from 70m d access. the z of instanta communicatio ure 1 shows u laptops. ceiver eband i/q sign connection and ers, and interp to-analog con alog. the main he noise and urpose of the ified rf frequ e voltage-cont and local osc ce signal. at th signal and se by both low ocked loop co o can be frequ m the mixer do in-phase (i) that the band components -to-digital con i and q data s, and decimat nverted sampl connection wh dy is done by with two ant nal is succes asure the gain rio of the code ofdm-mimo ding h v mance analysis ects to usb mhz to e usb aneous on and usrp nals to d then polates nverter n goal d high mixer uency. trolled cillator he last ends it -noise ontrols uencyown is ) and d pass in the nverter a. the tes the les are hich is using tennas ssfully n and e. with wit com cc outp 64q fig. with the of cha cc has vol. 8, no. 4, 20 s of ofdm and 3 reshape( 4 bi2de(x) 5 reshape( 6 sort(rand 7 qammod 8 if (fft(x) 9 x(cyclic 10 x ← par 11 (1/sqrt{2 12 reshape 13 x (cyclic 14 fft(x)← 15 r(k)conj 16 qamdem 17 find(x) 18 de2bi(x) 19 vitdec(x table i paramete subcarrie digital modu signal to nois size of fram number of fr number of p cyclic pre channel fad v bit error rate thout convolu mpared. figure c in awgn tperforms the qam. 2. ber vs. s hout convolutiona figure 3 illus same modula dm system annel. figure 4 c for qpsk, 16 s good perform 018, 3249-3254 d ofdm-mim (x) ← symbol ) (x) ← serial to d(x)) ← interle d(x) ← qam m )) ← ofdm m c prefix) ← ad rallel to serial 2})*n(0,1)+jn (x) ← serial t c prefix) ← r ofdm demo (h(k)/(n, p h( mod(x) ← qam← deinterleav ) ← parallel to x) ← convolut . simulati er ers ulation e ratio me rames pilots fix ding vii. experim of ofdm sys ution code i e 2 shows the b n channel. ber withou signal to noise r al code strates ber w ation. the two in awgn 4 shows ber 6qam and 64 mance compare 4 mo systems und s construction o parallel eaver modulation modulation dding cyclic pr n(0,1) ← chan o parallel emove cyclic odulation (k)conj(h(k)) m demodulati ver o serial ion decoder on parameters valu 64 qam mod (0-30) 256 100 4 (16) 2 rician, rayleigh mental resul stem using con n three diff ber of ofdm ber with ut cc for 2q ratio (snr) for o with snr in ra o figures reve channel outp of ofdm wi 4qam in rici e with other m 3251 der fading cha n refix nnel prefix ← equalizer ion of ofdm system ue dulation )db 6 0 5% h and awgn lts nvolution cod ferent channe m with and wi cc signific am, 16qam ofdm system wi ayleigh chann al that ber o performs ray ith cc and wi ian channel. q modulations. annels m e and els is ithout cantly m and ith and el for of the yleigh ithout qpsk engineering, technology & applied science research vol. 8, no. 4, 2018, 3249-3254 3252 www.etasr.com elsanousi & ozturk: performance analysis of ofdm and ofdm-mimo systems under fading channels fig. 3. ber vs. snr for ofdm system with and without convolutional code fig. 4. ber vs. snr for ofdm system with and without convolutional code figures 5-7 show ber of ofdm-mimo system with snr in the same three different channels with convolutional code and without convolutional code. overall, results show that ber decreases when the number of antennas increases. this is because mimo technology uses spatial multiplexing and spatial diversity. in case of spatial diversity the same data is sent over different transmitters and this leads to augmented reliability, while in the spatial multiplexing the bite stream to be transmitted is divided or de multiplexed into several data segments. these segments are then transmitted through different antennas simultaneously, and this leads to increased data rate. one of the drawbacks of this system is that the use of more antennas can lead to more power consumption. fig. 5. ber vs. snr for ofdm-mimo system with convolutional code fig. 6. ber vs. snr for ofdm-mimo system with convolutional code fig. 7. ber vs. snr for ofdm-mimo system with convolutional code fig. 8. ber vs. snr for ofdm-mimo system with convolutional code fig. 9. ber vs. snr for ofdm-mimo system with convolutional code lt bot div hig cor ant rec tra cha is s sys dig tim dat cod engineerin www.etasr figure 10 illu te signal. du th sides. mim versity. in the gh reliability. rrectly parame tennas should ceived signal ansmitted and annel (pdcch shown in the s fig. 10. ber perfor stems using gital modulati me-invariant f ta, viterbi, tra de-rate, interle ng, technology r.com ustrates the po uring transmis mo 2x2 is used simulation, di in order to eters such as g d be conside is shown to shown in figu h) demodulat same figure. power spectrum fig. 11. rece viii. c rmance of bo convolutional ion schemes frequency sele ace-back-length eaver and type y & applied sci elsanousi & o ower spectrum ssion two ant d to offer spati iversity techni recover the gain, frequency ered. spectrum be equivalent ure 11. physic tion of the qp m of the two-chann (a) (b) ived signal spectr conclusion oth ofdm a l channel cod has been sho ective channel h, hard or soft e of equalizer ience research ozturk: perform m of the two-ch ennas are use ial multiplexin ique is used to transmitted y and position m analysis o t to the one t cal downlink c psk received nel lte signal rum and ofdm-m ding and dif own in this , the way of c t decision deco were conside h v mance analysis hannel ed for ng and o offer signal of the of the that is control signal mimo fferent study. coding oding, red as par obt ante mu resu than per wor and suc [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] vol. 8, no. 4, 20 s of ofdm and rameters durin tained at the h ennas. the ch lti path chann ults show that n ofdm syst rformance than rk has been c d receiving wit ccessfully reco n. sethy, s. sw fading channel” engineering & s. k. borra, s. with rayleigh, innovative rese 5, no. 7, pp. 13 n. h. maruf b rate performa frequency-divi conference on university, rig h. g. ryu, t. p process in the system”, ieee pp. 1058-1064, r. p. kumar, convolutional foundation, vo g. b. umesha system for w international j system, vol. 6, n. h. maruf bh analysis of w international jo 3, no. 4, pp. 18 j. korhonen, i artech house, 2 s. gravano, in press, 2001 ] s. singh, s. si coded ofdm engineering re 2014 ] t. f. wong, t. florida, 2004 ] y. i. hammadi, over wireless c ] j. a. shoko limited/interfer waterloo, 2008 ] a. goldsmith, 2005 ] s. gaur, analys msc thesis, vi ] p. podder, t. “ber performa fading channe electronics and ] d. neumann, t estimator”, iee pp. 2905-2917, 018, 3249-3254 d ofdm-mim ng the simula highest numbe hannel order i nel fading wh ofdm-mim tem. regardin n rayleigh wh conducted usi th two antenna overed. refer wain, “ber analy ”, international j management, vo k. chaparala, “p rician and aw earch in compute 222-13227, 2017 bhuyan, m. ahme ance analysis ision multiplexin power and ele a, latvia, octobe p. hoa, n. t. hieu forward link transactions on 2004 , “improving th codes”, internat ol. 1, no. 2, pp. 4a, m. n. shanmu wireless commun journal of elect no. 1, pp. 21-26 huyan, j. uddin, wi-max:modulat ournal of electron 88-191, 2012 introduction to 2003 ntroduction to er ngh rathore, “si under awgn n esearch & techn m. lok, theory o , study and desig channel, msc th ouh, receives rence mimo c 8 wireless commu sis of advanced d irginia polytechni zaman khan, m ance analysis of el & awgn chan d electrical engine t. wiese, w. ut ee transactions 2018 4 mo systems und ation. the low er of transmit increases due hich increases mo system has ng channels, r hile awgn g ing two usrp as each. the tr rencees sis of mimo-of journal of applic ol. 2, no. 4, pp. 40 performance evalu wgn channels”, i er and communic 7 ed, m. faisal, m of convolutiona ng system”, 57th ectrical engineeri er 13-14, 2016 u, j. jianxue, “be of the ofdm-f n consumer elect he bit error r tional journal o -8, 2014 ukha swamy, “p nication through tronics, electrica , 2017 m. hoque, m. a tion scheme ve nics & communic 3g mobile com rror control cod imulation and an noisy channel”, i nology, vol. 3, n of digital commu gn of mimo-of hesis, cankaya un of antenna s channels, phd unications, camb diversity receive ic institute and st m. haque khan, f ofdm-bpsk, qps nnel,” internationa eering, vol. 2, no tschick, “learnin on signal proces 3253 der fading cha west ber ca tting and rece to the increa ber as well better perform racian shows b gives the best. ps for transm ransmitted sig fdm system in di cation or innovat 05-409, 2013 ution of ofdm s international jour cation engineering m. salauddin, “bit al coded ortho international sci ing of riga tec er analysis of cl fdma communi tronics, vol. 50, rate of ofdm of advanced re performance of o channel estima al and computa a. habib, “perfor ersus bit error cation technology mmunications, 2n des, oxford univ nalysis of convo international jour no. 8, pp. 1489– unication, univer fdm system ope niversity, 2013 selection for n thesis, univers bridge university ers for fading cha tate university, 20 m. muktadir ra sk, qam over ra al journal of ind o. 7, pp. 1–5, 201 ng the mmse ch ssing, vol. 66, n annels an be eiving ase of . the mance better this mitting nal is fferent tion in system rnal of g, vol. t error ogonal ientific chnical lipping ication no. 4, using esearch ofdm ation”, ational rmance rate”, y, vol. nd ed, versity lutionrnal of –1493, rsity of erating noiseity of press, annels, 003 ahman, ayleigh dustrial 7 hannel no. 11, engineering, technology & applied science research vol. 8, no. 4, 2018, 3249-3254 3254 www.etasr.com elsanousi & ozturk: performance analysis of ofdm and ofdm-mimo systems under fading channels [18] h. sampath, s. talwar, j. tellado, v. erceg, a. paulraj, “a fourthgeneration mimo-ofdm broadband wireless system: design, performance, and field trial results”, ieee communications magazine, vol. 40, no. 9, pp. 143–149, 2002 [19] j. jayakumari, “mimo-ofdm for 4g wireless systems”, international journal of engineering science and technology, vol. 2, no. 7, pp. 2886-2889, 2010 [20] national instruments, usrp-2901 block diagram, available at: http://www.ni.com/documentation/en/software-defined-radio-device/ latest/usrp-2901/block-diagram/ microsoft word 17-3020_s_etasr_v9_n5_pp4667-4672 engineering, technology & applied science research vol. 9, no. 5, 2019, 4667-4672 4667 www.etasr.com galabada et al.: identifying the impact of concrete specimens size and shape on compressive strength identifying the impact of concrete specimens size and shape on compressive strength a case study of mud concrete g. h. galabada department of civil engineering, university of moratuwa, moratuwa, sri lanka hyasasiri@yahoo.com f. r. arooz department of civil engineering, university of moratuwa, moratuwa, sri lanka rizznaz@yahoo.com malthi rajapaksha department of civil engineering, university of moratuwa, moratuwa, sri lanka malthidzn@gmail.com rangika halwatura department of civil engineering, university of moratuwa, moratuwa, sri lanka rangikauh@gmail.com abstract—mud is a versatile material with a prodigious interest for traditional wall construction such as wattle and daub or rammed earth, with and without reinforcements. mud concrete has been identified as a unique modern material, though more research is required for generalization. compressive strength, a measure of concrete quality usually depends on the specimen’s size and shape. specimen’s size and shape for mud concrete is yet to be identified and established. addressing this knowledge gap, this research aims at investigating the effect of specimen’s size and shape on the compressive strength of mud concrete. at first, the compressive strength’s variation was estimated by varying water content. then, the water content was kept constant and the variations of compressive strength were estimated by varying specimen size and shape. both experiments were conducted for different mixtures and percentages of cement. the initial results suggest that the compressive strength of mud concrete decreases with the increase of water content. the decrease indicated linear behavior with a constant gradient. less influence on compressive strength was observed by considering specimen size, while the shape showed more contribution. the effect of specimen size and shape was increased with the increase of compressive strength. keywords-mud concrete; compressive strength; specimen size and shape i. introduction mud concrete is a modern composite material made out of soil consisting of gravel (sieve size: 4.75mm≤gravel≤20mm), sand (0.425mm≤sand≤4.75mm) and fine particle (≤0.425mm) in different compositions, which is composed of elements that have various strengths for different applications such as walling material, paving blocks etc., with various cement percentages and types [1, 2]. only a small number of researches have been conducted and fewer standards have been set to evaluate the strength characteristics of mud as a construction material. to determine the compressive strength of concrete, usually 150mm×150mm×150mm standard cubes are used for compressive strength test [2]. previous studies can be found on the effect of size and shape for conventional cement concrete and cement concrete with several other constituents such as glass fiber, admixtures, etc. literature testifies that hardening mechanical properties of mud concrete in different proportions are dissimilar to cement concrete, different size and shape effects can be expected. therefore the effects of specimen’s shape and size on the compressive strength of mud concrete are, to the best of our knowledge, not yet studied. cross sectional shape of the specimen and mix proportions were considered mainly as the two effective factors for compressive strength of concrete. further, there are advantages of using smaller specimens, which affect the test results such as ease of handling, likelihood of accidental damage, cheaper moulds, lower capacity testing machine and type of machines used [3, 4]. according to authors in [5], the compressive strength of materials such as concrete, stone, etc. is a function of the test specimen’s dimension [5]. the size of the test specimens is prescribed in different standards, but occasionally more than one sizes are permitted. in the case of cement concrete, the compressive strength test specimens vary from one country to another. table i summarizes the standard specimens used in different countries. table ii summarizes some of the studies regarding the effect of shape and size of the specimens on the compressive strength of cement concrete. many researches concentrated on the size and shape effect of the specimens and most of them found that the strength decreases with increase of the specimen size [7-12]. authors in [10] established that the ratio of cube to cylinder compressive strengths decreases with an increase in the level of concrete strength [10]. corresponding author: g. h. galabada engineering, technology & applied science research vol. 9, no. 5, 2019, 4667-4672 4668 www.etasr.com galabada et al.: identifying the impact of concrete specimens size and shape on compressive strength table i. standard specimens used. specimen country source 150mm×300mm cylinders usa, france, australia, america, s. korea, canada, norway [6-9] 150mm cubes uk, europe [6, 7, 9] cylinders and cubes turkey [6] 200mm cube, 150mm×300mm cylinder old turkish standard 300mm cubes, 150mm×300mm cylinder new turkish standard 150mm×150mm×600mm prismatic specimen russia [8] table ii. relationship of compressive strength of specimen with standard relationship relationship between source (1) � �6 = 0.56 + 0.697 6ℎ� + ℎ � strength of cylindrical, cubical or prismatic specimen to strength of 150mm cube [11] (2) �� �′ = 0.8 + 0.4 �1 + ℎ − �50 strength of cylindrical specimen to strength of standard cylinder [12] (3) �� = 0.49 � ′ �1 + �2.6 + 0.81 �′ strength of cylindrical specimen to strength of standard cylinder [9] (4) �� = 1.17 � ′ �1 + �2.6 + 0.62 �′ strength of cube specimen to strength of standard cylinder [9] (5) �� = 1.02 � ′ �1 + �2.6 + 0.52 �′ strength of prisms specimen to strength of standard cylinder [9] (6) � ��15 = 1.317 − 0.1694 �15ℎ� + ℎ � strength of cylindrical, cubical, or prismatic specimen to strength of 150mm cube [13] nomenclature p compressive strength of cylindrical, cubical, or prismatic specimen p6, fcu15 compressive strength of a 150mm cube fc΄ compressive strength of standard cylinder fcy compressive strength of general cylinder fcu compressive strength of general cube fpr compressive strength of general prism b length of cubic specimen v volume of specimen h height b15 length of 150mm cube d lateral dimension in [20], the astm c39/c39m-03 is intended, cylindrical concrete specimens as the standard test specimen to determine the compressive strength. authors in [11] proposed (1) to show the relationship of compressive strength of a concrete specimen and its size and shape. authors in [12] suggested (2) to convert the compressive strength [12]. both considered the conversion factor as a function of the specimen’s volume (v), aspect ratio (d/h), height (h), maximum lateral dimension (d), which were considered the main parameters for compressive strength. the effect of the specimen’s size is stronger for low strength concrete and it was more notable for specimens with less slenderness ratio. the effect of the specimen’s size for cubes and prisms is stronger than for cylinders [6, 17]. equations (3)(5) were suggested by authors in [9], to obtain compressive strength relationship of general cubes with standard cubes, compressive strength of prisms with standard cubes and of general cylinder to standard cylinder respectively [9]. authors in [13] developed (6) to relate the compressive strength of general cylinder with the standard cylinder’s [13]. according to authors in [17], the effect of the shape is unimportant and the effect of the size is noticeable in static compressive strength, but it is insignificant in dynamic tests. further, they reported that the effect of the specimen’s size and shape on concrete static test is independent of concrete’s grade [17]. moreover, the variation of compressive strength of 100mm cubes and 150mm standard cubes were in the range of 5-6% and the strength of smaller cubes was higher than that of larger cubes [5, 6]. based on the above, experiments were carried out for mud concrete to identify the relationship between compressive strength on specimen’s size and shape. ii. materials and methods a. materials used the soil for mud concrete mixture was extracted and sieve analysis was performed for randomly selected samples to identify particle size distribution. three sieve analyses were done and the average was used. in these experiments, the extracted soil samples were developed by adding gravel and sand to make soil to be 35%, gravel (sieve size 4.75mm≤gravel≤20mm), 60% sand (0.425mm≤sand<4.75mm), and 5% fine particles (<0.425mm). the maximum gravel size used in all mixes was 20mm which was identified as the best proportion for mud concrete [1]. the samples were cast in different cement percentages varying from 10% up to 20% and type 1 ordinary portland cement was used in all mixtures. the mud concrete mix proportions used are provided in table iii. figure1 shows the materials used to prepare the mud concrete. b. casting procedure: mud concrete mixing and specimen preparation 1) step 1: identifying the compressive strength variation with moisture content when creating the mixture, the moisture percentage of dry mix can have slight differences, although the added water quantity during mixing is the same. therefore, before addressing the main objective, finding out the effect of specimen’s size and shape on compressive strength, the variation of strength of mud concrete with moisture content was investigated. in this step, five different water contents were added for each mix (m1-m5). water content increased by 250ml gradually, starting from 2000ml up to 3000ml, which is identified as the workable range for mud concrete [1, 2]. 150mm×150mm×150mm cubes were prepared using steel moulds for the test. three cubes (x1, x2, x3) were cast from each mix which was mixed with different amounts of water (wj for i=1,…,5). the preparation plan of these mud concrete specimens is indicated in figure 2. after 24h from casting, the specimens were taken out from the moulds and all were subjected to moist-curing under equal conditions until the time of test. a total of 75 cubes were cast. after 28 days of curing, all cubes were tested for dry compressive strength. in addition, engineering, technology & applied science research vol. 9, no. 5, 2019, 4667-4672 4669 www.etasr.com galabada et al.: identifying the impact of concrete specimens size and shape on compressive strength three samples from each mix were oven dried at constant temperature (105°c) for 24hrs to calculate the moisture content. table i. mud concrete mix proportions mixture code cement % gravel % sand % fines % m1 10 35 60 5 m2 14 35 60 5 m3 16 35 60 5 m4 18 35 60 5 m5 20 35 60 5 fig. 1. material used to prepare mud concrete fig. 2. the preparation plan of mud concrete specimens 2) step 2: finding the effect of specimen’s size and shape on compressive strength five different mud concrete mixes were made while keeping water content constant to investigate the relationship of compressive strength variation with the specimen’s size and shape. the dimension and the shape of the selected specimens are shown in table iv and figure 3. fig. 3. steel moulds used for casting all specimens (cubes, cylinders) were cast in three layers in steel moulds inside the laboratory and with no vibrations during compacting. after 24h from the casting, the specimens were taken out from the moulds and were subjected to moistcuring under equal conditions until the time of test. a total of 135 specimens (table v) were cast. after curing, the cubes were tested for dry compressive strength. in addition, three samples from each mix were oven dried at constant temperature (105°c) for 24h to calculate moisture content. the process of mixing and casting in the moulds is shown in figure 4. figure 5 shows the prepared cylindrical and cubical specimens. table ii. shape and size of specimens type shape dimension (mm) aspect ratio (h/d) lateral dimension d (mm) cube square 100×100×100 1 100 cube square 150×150×150 1 150 cylinder circle 150×300 2 150 fig. 4. mud concrete mixing and casting to different mould sizes and shapes table iii. specimen preparation details mix (mi=1,2,3,4,5) age of test (days) no. of specimens 150mm cube 100mm cube 150mm×300mm cylinder 7 3 3 3 14 3 3 3 28 3 3 3 9 9 9 total 27 total no of specimens × five mixes=27×5=135 fig. 5. prepared specimens for testing c. procedure of the compressive strength test to determine the compressive strength in both above mentioned steps, axial compressive strength tests were carried out. an axial compressive load was applied using a universal compressive strength testing machine with a capacity of 2000kn under a constant rate of 6.8kn/s until the failure of the engineering, technology & applied science research vol. 9, no. 5, 2019, 4667-4672 4670 www.etasr.com galabada et al.: identifying the impact of concrete specimens size and shape on compressive strength specimen. the tests were performed in accordance with the [18]. figure 6 shows a few photos of specimens’ testing. in step 1, the samples were tested for 28days, while in step 2 the samples were tested for 7, 14, and 28 days. the top surface of the cylinder was finished with a trowel, which was not really plane according to [14]. therefore, prior to the testing, the cylindrical specimens were ground to level the surface. fig. 6. testing for compressive strength iii. results and discussion a. step 1: identifying compressive strength variation with moisture content figure 7 shows the behavior of mud concrete against the compressive strength test, with different moisture contents. the results indicate that the increase in water content causes a linear decrease in compressive strength at a constant rate. according to the results, gradient (m) of each graph gives equal values with negligible difference. thus, (7) can be derived to determine the compressive strength for any mix, with any water content value. y mx c= + (7) where, y=compressive strength, x=water % from the dry mix, fig. 7. compressive strength behavior of the mud concrete with different moisture content b. step 2: finding the effect of specimen’s size and shape on compressive strength although the added water was content kept constant, the moisture percentages of dry mixes showed slight variations (table iv). since the compressive strength results obtained in this step included these slight moisture content variations, it was decided to take the compressive strength values of all the mixes to a common moisture content value, which is 19%. table iv. calculated moisture content mixture code moisture % m1 19.7 m2 19.2 m3 18.9 m4 18.3 m5 19.1 the compressive strength test results were recalculated to a common moisture content value, as the compressive strength shows a drastically change with the moisture content with the results obtained in step 1. compressive strength variations with age to different shapes and sizes for the selected mixes are shown in figure 8. the results show that the compressive strength increased with age, exhibiting a large increment for the first 7 days, and showing a slow increment with time. fig. 8. compressive strength variation with age for different mixtures. the variations of compressive strength with cement percentage regarding different shapes and sizes for the selected mixes are graphically represented in figure 9. these results indicate that the compressive strength is increased with the increment of cement percentage. however, the rate of this increment was higher for lower cement percentages (10% to 14%) and lower for higher cement percentages (14% to 20%). it can be concluded that the pattern of the compressive strength variation is uniform for all the tested specimen shapes and sizes. the cylinder specimens showed lower strength than the cubes in all mixes. moreover, the difference in compressive strength at 28 days for both 100mm and 150mm cubes was found negligible, regardless to the cement content. this fact is in accordance with the findings for cement concrete in [6]. engineering, technology & applied science research vol. 9, no. 5, 2019, 4667-4672 4671 www.etasr.com galabada et al.: identifying the impact of concrete specimens size and shape on compressive strength fig. 9. compressive strength variation with cement percentage c. relationship of compressive strength with different sizes and shapes of the specimens the 150mm cubical specimen’s compressive strength was taken as the standard to compare the relationship of compressive strength with different sizes and shapes of the specimens. in the analysis of the results, the ratio of 28 days compressive strength of cubes with size of 100mm×100mm×100mm to the cubes with size of 150mm×150mm×150mm was between 1.05 and 1.09, and the average of this ratio was 1.06. for 7 days and 14 days, the same ratio was found to be 1.13 and 1.10 respectively. these results indicate that the effect of specimens’ size for the above two cube sizes decreased with age. the ratio of 28 days compressive strength of 150mm×300mm cylinders to 150mm×150mm×150mm cubes was between 0.17 and 0.21, with an average of 0.2. for 7 days and 14 days specimens, the same ratio was 0.22 in average. these results indicate that the effect of specimen’s shape also decreased with age. figure 10 illustrates how the compressive strength of 100mm×100mm×100mm cubes and the compressive strength of 150mm×300mm cylinders behaved against the 150mm×150mm×150mm cube’s compressive strength. the solid and dashed lines of the graph in figure 10 indicate the best-fit lines obtained from the linear regression analysis and the lines of equality y=x respectively. the equations showed in figure10 are obtained from linear regression analysis of the test data points. in [3], the cube’s compressive strength of cement concrete is found as 1.25 times the compressive strength of the cylinder, but the actual strength relationship of the two shapes (cube and cylinder) depends on the strength level and the moisture content of the concrete during testing. in [10], the factor to convert the cylindrical specimen’s strength to cube’s strength in normal cement concrete was 1.2. however, the correction factor depends on the level of the concrete strength, while the high strength concrete is less affected than the low strength concrete [19]. fig. 10. compressive strength variation for 150mm×300mm cylinder and 100mm×100mm×100mm cubes versus 150mm×150mm×150mm cubes d. crack propagation and failure zone during the initial stage of loading, cracks were developed longitudinally, and when the applied load increased, the initial cracks were sharply propagated from top to bottom until the failure of the specimen (figure 11). when the load on the cubical specimens increased, the cracks were slowly propagated and decreased (due to the effect of shear) toward the center of the cube. the center core was relatively undamaged, following the ‘non explosive’ failure pattern [11, 15]. according to authors in [11], failure pattern of this cylindrical specimens can be defined as cone and split failure [11, 20] and not as shear or splitting and shear [3, 11], or explosive [3, 21]. iv. conclusions the findings of this research can be concluded as: • the 150mm mud concrete cube’s compressive strength is 0.94 times the compressive strength of the 100mm cubes. the 150 cube’s compressive strength of mud concrete is 5 times the compressive strength of the cylinder. therefore, a relationship between the size and shape of specimens with mud concrete’s compressive strength is identified, as it was found for cement concrete in literature. • the increase in water percentage exhibited a decrease in the compressive strength linearly at a constant rate with negligible difference. this finding can be used to determine the compressive strength for any mix, with any water content value. engineering, technology & applied science research vol. 9, no. 5, 2019, 4667-4672 4672 www.etasr.com galabada et al.: identifying the impact of concrete specimens size and shape on compressive strength • the pattern of the compressive strength variation was uniform for all the mud concrete specimen shapes and sizes which were tested, and the cylindrical shaped specimens showed lower strength than the cubes in all mixes. (a) (b) fig. 11. observed failure patterns of the specimens: (a) observed crack similar to cone and split crack, (b) observed crack similar to non explosive v. limitations and future work this experimental study was done for a limited range of cement content of mud concrete mixes (cement content 10%20%). the research was also limited to one moisture content value (19%) due to time and financial limitations for casting. moreover, the range of sizes and shapes which were tested during the research were limited to the selected number of types (100mm and150mm cubes, 150mm×300mm cylinders) due to resources limitations. the findings of this research can be taken as a basis for further research directions with improvement regarding more specimens’ sizes, shapes, cement, and water content percentages. thereby, further directions are open to develop a quantitative relationship between the size and shape of specimens with mud concrete’s compressive strength, as found for cement concrete in literature. acknowledgment this research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. authors would like to acknowledge the support given by h.t.r.m. thanthirige, d.m.n.l dissanayaka, and w.b.u. rukma, university of moratuwa, sri lanka. references [1] c. udawattha, h. galabada, r. halwatura, “mud concrete paving block for pedestrian pavements”, case studies in construction materials, vol. 7, pp. 249–262, 2017 [2] f. r. arooz, r. u. halwatura, “mud-concrete block (mcb): mix design & durability characteristics”, case studies in construction materials, vol. 8, pp. 39–50, 2018 [3] a. m. neville, j. j. brooks, concrete technology, pearson education ltd, 1987 [4] m. gul, “effect of cube size on the compressive strength of concrete”, international journal of engineering development and research, vol. 4, no. 4, pp. 956-959, 2016 [5] j. c. morel, a. pkla, p. walker, “compressive strength testing of compressed earth blocks”, construction and building materials, vol. 21, no. 2, pp. 303–309, 2007 [6] o. arioz, m. tuncan, k. ramyar, a. tuncan, b. karasu, k. kilinc, w. mortaja, “specimen size and shape effects on measured compressive strength of concrete”, international ceramic, glass porcelain enamel, glaze and pigment congress, eskisehir, turkey, october 12-14, 2009 [7] a. j. hamad, “size and shape effect of specimen on the compressive strength of hplwfc reinforced with glass fibres”, journal of king saud university-engineering sciences, vol. 26, no. 4, pp. 373–380, 2017 [8] e. a. sahawneh, “size effect and strength correction factors for normal weight concrete specimens under uniaxial compression stress”, contemporary engineering sciences, vol. 6, no. 1, pp. 57–68, 2013 [9] s. t. yi, e. i. yang, j. c. choi, “effect of specimen sizes, specimen shapes, and placement directions on compressive strength of concrete”, nuclear engineering and design, vol. 236, no. 2, pp. 115–127, 2006 [10] m. a. mansur, m. m. islam, “interpretation of concrete strength for nonstandard specimens”, journal of materials in civil engineering, vol. 14, no. 2, pp. 151–155, 2002 [11] a. m. neville, “a general relation for strengths of concrete specimens of different shapes and sizes”, journal proceedings, vol. 63, no. 10, pp. 1095–1110, 1966 [12] j. k. kim, s. t. yi, c. k. park, s. h. eo, “size effect on compressive strength of plain and spirally reinforced concrete cylinders”, aci structural journal, vol. 96, no. 1, pp. 88-94, 1999 [13] e. y. zhu, w. yang, j. h. wang, w. q. lin, “relationship of compressive strength of specimens with various shapes and sizes for c20 mpa grade concrete”, journal of northern jiaotong university, vol. 2005, no. 1, pp. 1-3, 2005 (in chinese) [14] astm c 617, standard practice for capping cylindrical concrete specimens, astm international, 2003 [15] m. dehestani, i. m. nikbin, s. asadollahi, “effects of specimen shape and size on the compressive strength of self-consolidating concrete (scc)”, construction and building materials, vol. 66, pp. 685–691, 2014 [16] j. k. kim, s. t. yi, “application of size effect to compressive strength of concrete members”, sadhana, vol. 27, pp. 467–484, 2002 [17] m. li, h. hao, y. shi, y. hao, “specimen shape and size effects on the concrete compressive strength under static and dynamic tests”, construction and building materials, vol. 161, pp. 84–93, 2018 [18] british standard, en 12390-3 (2009): compressive strength of test specimens, british standards, 2009 [19] j. k. murdock, “effect of length to diameter ratio of specimen on the apparent compressive strength of concrete”, astm bulletin, vol. 221, pp. 68–73, 1957 [20] astm c 39/c39m-03, standard test method for compressive strength of cylindrical concrete specimens, astm international, 2012 [21] british standards institution and g. cement aggregates and quarry products standards committee, testing concrete, british standards institution, 1983 authors profile r. u. halwathura is a professor in civil engineering, at the university of moratuwa, sri lanka and a commissioner for sri lanka inventors, ministry of science, technology and research, sri lanka g. h. galabada is a phd candidate at the faculty of engineering, university of moratuwa, sri lanka and a visiting lecturer at the general sir john kotelawala defence university, sri lanka. malthi pajapaksha is a phd candidate at the faculty of engineering, university of moratuwa, sri lanka and a lecturer at the general sir john kotelawala defence university. dr rizna arooz is a visiting instructor at the faculty of engineering, university of moratuwa, sri lanka and a visiting design tutor at the faculty of architecture, university of moratuwa, sri lanka. microsoft word 31-3031_s_etasr_v9_n5_pp4745-4749 engineering, technology & applied science research vol. 9, no. 5, 2019, 4745-4749 4745 www.etasr.com trstenjak et al.: a decision support system for the prediction of wastewater pumping station failures … a decision support system for the prediction of wastewater pumping station failures based on cbr continuous learning model bruno trstenjak department of computer engineering, polytechnic of medimurje in cakovec, cakovec, croatia btrstenjak@mev.hr bruno palasek technical department, medimurje vode d.o.o., cakovec, croatia bruno.palasek@medjimurske-vode.hr jurica trstenjak department of computer engineering, polytechnic of medimurje in cakovec, cakovec, croatia jtrstenjak@mev.hr abstract—nowadays the communities are facing the problem of waste and wastewater. while wastewater systems have become more complex, the need for development of sustainable solution for wastewater management emerged. therefore, the development of a decision support system (dss) for wastewater disposal management became necessary. this paper presents a new dss for predicting the failure of wastewater pumping stations, the system architecture and its implementation. the prediction model is based on the case based reasoning (cbr) classification method. the standard cbr classification technique has been upgraded with an algorithm for continuous learning. the paper describes the system structure, its connection to the wastewater system, the internal processes involved in the prediction process and the implemented algorithm for continuous learning. furthermore, the features used in the prediction are indicated along with the achieved results and the method of results evaluation. the test and obtained results indicate that the proposed dss is efficient and capable of providing very good results in the prediction process. keywords-case based reasoning; continuous learning; decision support system; prediction; wastewater pumping station i. introduction nowadays the problem of waste and wastewater is apparent, as it is finding a way of sufficient waste disposal. in order to achieve maximum reliability of the wastewater system, various decision support systems (dss) have been developed. a dss aims at supporting the functionality and optimization of the entire system or achieving individually reliability of the elements of the system. because of the complexity of the wastewater system, it has become increasingly difficult to find a sustainable solution for wastewater management. authors in [1] presented different approaches and methods used in the process of developing dsss. they explore a systematic approach of developing dsss, which includes analysis of the treatment problem(s), knowledge acquisition and representation, and the identification and evaluation of the criteria controlling the selection of optimal treatment systems. authors in [2] describe the development and operation of a dss for waste water disposal management. the systems uses concepts such as components, community context, and data structures. the authors presented two software modules, design generation module and decision aid module, which give different alternatives in system design process. in the development of advanced wastewater dss, modern it technology is often used. authors in [3] presented a new approach in dss design by using the machine learning technique of specifically supervised decision tree algorithm. this developed system provides the best decision for the reuse of wastewater after treatment. this system is deployed on cloud environment, which provides good manageability and fast computational service. besides the different solutions that are focused on the management of the entire wastewater system, a variety of dsss has been developed, focused on wastewater system elements. authors in [4] presented a data-driven model with a new neural network algorithm for scheduling pumps in a wastewater treatment process, an optimization model to optimize the maintenance and operational schedules. authors in [5] presented a study that aimed to help decision-makers by developing an intuitionistic fuzzy set (ifs) theory based group multi-attribute decision analysis method. ten criteria in environment, economy, and technology dimensions were employed to achieve sustainability measurement of wastewater treatment processes. the developed multi-criteria sustainability assessment method allows different experts to conduct sustainability measurement. the results reveal that this method can determine a sustainability sequence of different wastewater treatment processes. this paper presents a dss for predicting the failure of wastewater pumping stations, the system architecture and its implementation. the primary objective in this research is focused on assessing the correctness of a wastewater pumping station, to predict the correctness of a wastewater pump as its base elements. the system performs an assessment of the probability of malfunction of a wastewater pumping station for the period of the next week. such information provides timely intervention and failure prevention for a given wastewater system segment. the dss implementation is applicable to various types of wastewater pumps and allows easy building and expansion of the system. a universal character system, which can be easily adapted to any wastewater system regardless of their architecture, has been developed. corresponding author: bruno trstenjak engineering, technology & applied science research vol. 9, no. 5, 2019, 4745-4749 4746 www.etasr.com trstenjak et al.: a decision support system for the prediction of wastewater pumping station failures … ii. research methodology and proposed dss nowadays, many machine learning techniques can be used in the prediction process. perhaps the most widespread of them is the neural networks [6]. in the process of forming the architecture of the wastewater pumping decision support system (wpdss), cbr was selected as the base technique. a. case based reasoning (cbr) the hybrid prediction model is based on the cbr classifier. the principle of cbr is based on solving new problems by observing their similarity with previously solved problems. the cbr method uses a problem-solving approach analogous to the way of problem solving by humans when they recall from past experiences. each cbr system contains an embedded library of the cases that were resolved in the past. each case represents a description of the problem with its associated solution. cbr method with a built-in function of similarities tries to find the most similar case from the library. the retrieved cases from the library are used to suggest a solution. if the proposed solution is not satisfactory, the method tries to revise the selected cases and find a new solution. the method adds a new revised case to the case library and thereby expands the knowledge base. the whole execution cycle of the algorithm can be divided into four main steps: retrieve, reuse, revise, and retain [7]. cbr performs measurements of similarity on local and global level. local similarity refers to the measurement of similarity between pairs of features. global similarity refers to comparison of similarity between all the features that make up the object. measuring similarity can be shown by [8]: ( ) ∑ ∑ = = × = n i i n i iij w wstf stsimilarity 1 1 , ),( (1) where t indicates the target case, s is a source case, n is the number of features in each case, i the individual feature from 1 to n, f is the similarity function for features i in cases t and s and w presents the importance weighting of feature i. b. continuous learning continuous learning is focused on constantly improving the prediction model and achieving higher prediction accuracy [9, 10]. after the prediction of the next week is conducted, the results for the end of the working week of the wastewater system are kept. wpdss starts the process of comparing the recent results with the prediction results. the wpdss calculates the overall prediction accuracy and checks if it has fallen below the set threshold. if it is below the set threshold, the process of improving the cbr model starts automatically. in the process of improvement, the implemented algorithm calculates the corrective factor [11]. the corrective factor defines the degree of correction for the weight features values, as shown in (1). this weight change itself can be constant or it can decay as the learning proceeds. the corrective factor can be calculated, as shown in (2)-(3) [12]: addition, increase: ( 1) ( ) c i i c f w t w t i k + = + ∆ (2) addition, decrease: c c ii k f itwtw ∆−=+ )()1( (3) kc and fc indicate the number of times that a case has been correctly and incorrectly retrieved. the ratio fc/kc reduces the influence of the weight update as the number of successful retrievals increases. the value ∆i determines the initial weight change. the process of upgrading the classification model can be also started after each weekly period, regardless of the achieved prediction accuracy. this approach achieves finetuning of the system to any changes. c. system architecture to achieve the set goals, a web based dss has been developed. the architecture of the system enables the execution of parallel processes and connection to the existing wastewater system. implementation and testing of the dss was carried out on the wastewater system of the medimurje county, croatia. testing was performed on a sample of over forty wastewater pumping stations. the existing wastewater pumping system uses several types of pumps made by two manufacturers: wilo (emu fa10.94e 294, t20-4/27h,) and grundfos (sev.80.80.110.a.2.51d, seg.40.09.2.50b, seg.40.31.2.50b). the diversity of wastewater pumps is the result of their long-term development, due to the system expansion and various reconstructions of wastewater pumping stations. figure 1 shows the architecture of the new wpdss and its basic components. fig. 1. the wpdss architecture the system is linked to the wastewater system and its scada (supervisory control and data acquisition) management system. scada is an industrial computer-based control system employed to gather and analyse real-time data to keep track, monitor, and control industrial equipment in different types of industries [3]. the data collected by scada are daily sent to the wpdss through a specially defined procedure. the data sent by scada refer to the measured values during the operation of each wastewater pump. scada and wpdss are connected using an application programming interface (api). at the end of the week the wpdss generates weekly and two-week data cases from these data. the formed data cases are used in the prediction process for the next period. the central component in the wpdss is the cbr model. the model is based on cbr machine learning technique [13]. for engineering, technology & applied science research vol. 9, no. 5, 2019, 4745-4749 4747 www.etasr.com trstenjak et al.: a decision support system for the prediction of wastewater pumping station failures … the purpose of prediction, the standard cbr classification technique has been upgraded with the algorithm of continuous learning. the constant learning algorithm is responsible for the automatic improvement of the system and its cbr prediction model. the wpdss system uses its case database for its work. after the prediction has been made, the wpdss enables presentation and analysis. the prediction result informs the user about the likelihood of malfunction of some of the wastewater pumping stations in the period of the next week. at the end of every week, based on the actual state of the wastewater pumping station, the system performs a prediction accuracy analysis. if the system indicates lower prediction accuracy, the system starts redefining certain parameters of the cbr model. all these changes contribute to a better functioning of the prediction model. iii. overview of the work principle the work of the entire wpdss system can be represented by a series of internal processes. figure 2 shows the most important of them. these processes are divided into four groups. the first group (i) consists of internal processes that are responsible for data collection, data validation, case formation and storing data into the database. these processes run on a daily basis every time scada sends data. the received data are processed in several phases. at the beginning of the process, the system starts pre-processing to adapt input data to case format. data pre-processing includes data cleaning, normalization, transformation, feature extraction etc. this is a process of transforming raw data into a suitable format ready to be used by the prediction process. current day data are processed on a weekly basis, which is necessary for later calculation of maximum, minimum and mean values. the process collects input data and forms new daily cases for the case database. the procedure for formation of a weekly case starts on the last day of the current week. the entire prediction is based on the prediction of wastewater stations works for the next week. fig. 2. wpdss internal processes the second group (ii) represents the processes for preparing data, and forming the cases that will be used in prediction. the wpdss collects data during the working week and at the end of the week it forms a weekly case. the new prediction process includes the features of the last two weeks of the wastewater stations’ works. the internal process merges the data from the last two weeks and sends them to the prediction model. the determined prediction result refers to the next week period. the third group (iii) of internal processes are responsible for continuous learning. one of its novelties is the modification of cbr as a technique for continuous learning. the work philosophy of the modified cbr technique is very similar to the back propagation neural network. the network allows corrections of the neurons’ weight based on prediction errors. a similar, but not identical, philosophy has been used in this new approach to improve the prediction accuracy of the cbr model. based on the comparison of the prediction results and the real states of the wastewater stations, the system measures the prediction accuracy for the current week. if the prediction accuracy is lower than the allowable level, the system triggers the internal correction process for new weight values used in (1). after the weight values are corrected, a new cbr prediction starts. the correction of weight values will not start if the system achieves high prediction accuracy. at the beginning of the system operation, the weights of the features are set to initial neutral value. the last group (iv) of internal processes consists of the processes responsible for presenting the prediction results. at the end of the week, a new prediction process starts automatically. as the system is implemented in cloud environment via a communication protocol, the result of prediction for each wastewater station is sent to the scada system or a remote point. internal processes allow monitoring of the system performance, analysis of previous prediction results or the data of a new prediction. iv. experimental results and discussion a. dataset description the implementation and testing of the wpdss was carried out in cooperation with the water system in the medjimurje county, croatia. for the purposes of testing the wpdss, data from 40 wastewater pumping stations were used. the selected wastewater pumping stations are geographically distributed throughout the region. input prediction data were used in case engineering, technology & applied science research vol. 9, no. 5, 2019, 4745-4749 4748 www.etasr.com trstenjak et al.: a decision support system for the prediction of wastewater pumping station failures … format. each case format consisted of three components: static, dynamic, and environment. the static data refer to the characteristics of the wastewater pumps set by the manufacturer. dynamic data refer to the measurements of the wastewater pump operation obtained from the scada. to all these features, the system adds the environment features. these features describe the work environment of the wastewater pumping station. the flexibility of the wpdss allows easily changing the number of the features which are involved in the prediction process. table i shows the features used in the prediction process. table i. list of features used in the prediction process no static features dynamic features environment features 1 manufacturer weekly average current (a) location of pumping station 2 year of manufacture maximum daily current (a) installation depth (m) 3 rated current (a) weekly average flow (l/s) number of households 4 rated current at 3/4 load maximum daily flow (l/s) altitude of the pumping station 5 rated current at 1/2 load pump alarm was on weather conditions 6 max flow (l/s) weekly average number of starts 7 rated power (kw) maximum daily starts 8 max starts per hour (no) maximum daily starts per hour 9 maximum particle size (mm) weekly average working hours 10 rated speed (rpm) maximum daily working hours 11 maximum installation depth (m) maximum water-in-oil (%) 12 type of impeller service period (%) 13 maximum operating pressure (bar) 14 water-in-oil sensor (y/n) 15 temp. sensor (y/n) b. evaluation of prediction accuracy for several months before starting the weekly prediction, the wpdss was only collecting information from the wastewater pumping stations. in this way, the system formed the initial case dataset for the prediction process. when the wpdss launches a new prediction process, the prediction results indicate at which pumping station certain operation problems can be expected. at the beginning of the system formation, all features are assigned equal weights. during continuous learning, these values are changing. a feature assigned with a higher weight value has a more significant influence on the functioning of the pumping stations. during the test period, features that do not have any or very little influence on pumping station operation will be detected. these features will be excluded from the case data model or will be replaced with new features. in the created application, the user is presented with the prediction results in a table form as shown in table ii. the table contains the following information: the names of the wastewater pumping stations, their pump labels, and the failure risk level (low, moderate, high) for each pumping station from the list. this information indicates the probability of failure for the next period. the number of faults represents the information about the number of failures detected at the wastewater station in the previous period. finally, the table shows the recommendations to perform urgent services at any wastewater station for the next week. during the development and testing period, information about recommended activities was intensively used. the values of recommended activities were used as guidelines for the prevention of failure. on the wastewater pumping stations which wpdss labeled as “mandatory pump service”, weekly surveillance was carried out although according to maintenance schedule this was not planned. this approach resulted in a reduction of the total number of station failures in the wastewater system up to 40%. table ii. water stations list and their failure risk level station name/ type of pump failure risk level failures/ year recommended activity p1_mackovec emu fa10.94e low risk 0 maintenance by schedule p1_pp2mihaljevec sev.80.80.110.a. moderate risk 3 regular station service p1_pp4mihaljevec seg.40.12.2.50b low risk 1 maintenance by schedule p1_cs1lopatinec seg.40.31.2.50b high risk 2 mandatory pump service … … … … in order to obtain complete details about the characteristics of the cbr model, additional analysis of model performance using the receiver operating characteristic (roc) curve was performed [14]. figure 3 shows the roc curves of measurements of classification accuracy over a few datasets. fig. 3. roc curve of wpdss performance engineering, technology & applied science research vol. 9, no. 5, 2019, 4745-4749 4749 www.etasr.com trstenjak et al.: a decision support system for the prediction of wastewater pumping station failures … the shapes of the roc curves indicate a very good performance of the cbr model with prediction accuracy between 85% and 97%. the analysis of the structure of the recorded data in the case database indicated that the system is working with unbalanced data. the reason for this is the high quality of wastewater stations and their regular maintenance. certain studies have shown that unbalanced data may have a detrimental effect on the prediction accuracy, which has not been manifested in this research. parallel to the evaluation of the prediction model, we have conducted an evaluation of the complete system. the communication channel between scada and wpdss was tested and the reliability of various scripts for daily data transmission to the web platform was checked. v. conclusion this paper introduced a new approach for the prediction of correct functioning of wastewater pumping stations. a new wastewater pumping decision support system (wpdss) was presented along with its architecture, its internal processes, and the way of performing the prediction process. the wpdss works in web environment and uses a different machine learning method for the prediction process. the development and implementation of the wpdss system were carried out in cooperation with the wastewater system in the medimurje county, croatia. the preliminary evaluation results indicate that the architecture of the system is well-conceived. additional research will surely provide new guidance in developing and improving the overall system performance. references [1] m. a. hamouda, w. b. anderson, p. m huck, “decision support systems in water and wastewater treatment process selection and design: a review”, water science & technology, vol. 60, no. 7, pp. 1757-1770, 2009 [2] a. s. patil, n. j kulkarni, “decision support system for waste water management: a review”, international journal of innovative research in advanced engineering, vol. 1, no. 3, pp. 24-29, 2014 [3] a. k. bhavsar, j. s. shah, “cloud based decision support system for waste-water management using supervised decision tree algorithm”, international journal of computer sciences and engineering, vol. 5, no. 10, pp. 367-372, 2017 [4] z. zhang, x. he, a. kusiak, “data-driven minimization of pump operating and maintenance cost”, engineering applications of artificial intelligence, vol. 40, pp. 37–46, 2015 [5] j. z. ren, h. w. liang, “multi-criteria group decision-making based sustainability measurement of wastewater treatment processes”, environmental impact assessment review, vol. 65, pp. 91-99, 2017 [6] w. x. hu, “the application of artificial neural network in wastewater treatment”, ieee 3rd international conference on communication software and networks, xi'an, china, may 27-29, 2011 [7] y. guo, j. hu, y. peng, “research on cbr system based on data mining”, applied soft computing, vol. 11, no. 8, pp. 5006–5014, 2011 [8] m. m. richter, r. weber, “case-based reasoning: a textbook”, in: basic cbr elements, springer science & business media, 2013, pp. 1734 [9] h. huang, h. qin, z. hao, a. lim, “example-based learning particle swarm optimization for continuous optimization”, information sciences, vol. 182, no. 1, pp. 125-138, 2012 [10] f. p. a. lima, m. l. m. lopes, a. d. p. lotufo, c. r. minussi, “an artificial immune system with continuous-learning for voltage disturbance diagnosis in electrical distribution systems”, expert systems with applications, vol. 56, pp. 131-142, 2016 [11] e. f. vazquez, “updating weighting matrices by cross-entropy”, investigaciones regionales, vol. 21, pp. 5369, 2011 [12] a. bonzano, p. cunningham, b. smyth, “using introspective learning to improve retrieval in cbr: a case study in air traffic control”, in: casebased reasoning research and development, springer, 2005 [13] c. k. riesbeck, r. c. schank, inside case-based reasoning, psychology press, 2013 [14] s. bernard, c. chatelain, s. adama, r. sabourin, “the multiclass roc front method for cost-sensitive classification”, pattern recognition, vol. 52, pp. 46-60, 2015 engineering, technology & applied science research vol. 9, no. 5, 2019, 4659-4666 4659 www.etasr.com danikas and morsalin: foreign inclusions, enclosed cavities, partial discharge models and … foreign inclusions, enclosed cavities, partial discharge models and discharge energy: a short review regarding solid dielectrics and composite insulating systems m. g. danikas democritus university of thrace department of electrical and computer engineering power systems laboratory xanthi, greece mdanikas@ee.duth.gr s. morsalin university of new south wales school of electrical engineering and telecommunications high voltage laboratory sydney, australia sayidul.morsalin@unsw.edu.au abstract—partial discharges in cavities are one of the main reasons of breakdown of insulating materials and insulating systems in general. the present paper aims at commenting some aspects of the relation between partial discharges and insulation damage. some basic models explaining the workings and impacts of discharges in cavities are discussed. discussions about the possibility of damage in the presence of multiple cavities as well as of the risks of minute discharges and/or charging phenomena below the so-called inception voltage are conducted. it is remarked that the question of the relationship between discharge parameters and insulation damage is still an important one, especially for composite insulating systems. keywords-solid dielectrics; partial discharges; inception voltage; insulation damage; discharge magnitude; discharge energy; charging phenomena i. introduction partial discharge is the name given to an electrical discharge, which involves only a portion of the dielectric without fully bridging the electrodes [1]. partial discharges often happen in enclosed cavities of insulation and thus they are sometimes called internal partial discharges. they can be extremely harmful to solid insulating materials and they start appearing when a cavity is subjected to an ac stress greater than its breakdown value. they may occur regularly at each half period of an applied sinusoidal voltage [2]. partial discharges in a dielectric develop in enclosed cavities (or because of inclusions) of lower dielectric strength than the dielectric strength of the surrounding material. the insulation in the inclusion breaks down at a stress lower than the dielectric strength of the surrounding material. the voltage at which discharges start occurring regularly in an enclosed cavity is called inception voltage [3]. when the voltage is reduced under a certain limit, discharges stop occurring. this limit is thus called extinction voltage [3] (all the above under the assumption that ac voltage is applied). enclosed cavities may be found in extruded plastics, lapped impregnated paper and cast resins, they may be filled with oil (as in layers and in butt gaps of oil-impregnated paper insulation) or may consist – as inclusions of various foreign particles (like textile fibers or dirt). it is the aim of the present paper to give a review regarding the problems arising because of partial discharges and their injurious effects on the insulating materials. however, the present paper is by no means an exhaustive review of all of the aspects of partial discharges and their deleterious effects. ii. partial discharge models partial discharges in enclosed cavities may be represented with the well known a-b-c model (or capacitor model) [4, 5]. this model is based on the assumption that the enclosed cavity may be represented as capacitance, while the neighboring to the cavity healthy insulation may be represented by another capacitance and yet another capacitance may represent the rest of the insulating material. in such a case, the apparent charge q detected by a pd detector may be given as: q = cb·δvc (1) where, cb is the capacitance of the healthy insulation adjacent to the cavity and δvc the voltage change that is caused because of the discharge inside the cavity. this quantity, although not determined by the dimensions of the cavity alone, as cb is affected by the insulation thickness, is considered approximately a right measure of a discharge [6]. related to the abc model is also the energy of an individual discharge, which is given as: w = 0.7·q·vi (2) where, q is the apparent charge of an individual discharge and vi the discharge inception voltage [6]. such a model, although very useful for many decades, was subjected to criticism [7], where it was opined that the notion of capacitance is limited to metal electrodes and not to insulating surfaces facing each other. thus, another model was corresponding author: m. g. danikas engineering, technology & applied science research vol. 9, no. 5, 2019, 4659-4666 4660 www.etasr.com danikas and morsalin: foreign inclusions, enclosed cavities, partial discharge models and … proposed, named pedersen’s model [7], based on electromagnetic theory: q = k·ω·εr·ε0·(εi – εl)∇λ0 (3) where, q is the charge induced on the measuring electrode by the partial discharge in a cavity, k the cavity geometric factor, ω the cavity volume, εi the inception electric field for streamer inception, εl the limiting electric field for ionization, εr the relative permittivity of the surrounding solid insulating material, ε0 the permittivity of the free space and ∇λ0 the function which gives the ratio of the electric field at the position of the cavity (in the absence of the cavity) to the voltage between the electrodes. the quantity (εi–εl) is calculated in terms of the streamer criterion, i.e.: (εi/p) = (1+b/√2·a·p) εl/p (4) where, b is a constant characteristic for the gas in the cavity, a the radius of the cavity and p the pressure in the cavity. as discussed in [8], the merit of (3) is that the charge q is related to a variety of parameters. this model was referring to streamer type discharges. such a model was preceded by the model proposed in [9]. according to that model, the apparent charge q is given from the following equation: q=εr·ε0·e2·γ·v/la (5) where εr and ε0 as in (3), v is the volume of the cavity, γ is the λ0, e2 is the partial discharge inception voltage according to paschen’s law and la the geometry factor depending on the axis ratio of the cavity. it is evident from (5) that this model refers mainly to townsend type of discharges (since it considers the partial discharge inception stress from paschen’s law viewpoint). in actual fact, the models of [7] and [9] have a number of common parameters. criticism of pedersen’s model came from [8, 10], where it was pointed out that pedersen’s model is valid for initial experimental conditions and that (3), which is vital to the model, assumes a breakdown in a uniform gap (cavity breakdown, however, is not, strictly speaking breakdown, but it leads to redistribution of charges on the surface of the cavity). subsequent criticism came from [11], where it was indicated that a direct correlation between the space charges and the change of capacitance exists and that the criticism against the change of the capacitance of the system in relation to space charges has been opposed by utilizing pedersen’s equations. however, it must be mentioned that –as far as some experimental results with enclosed cavities in polymers are concerned– pedersen’s model fared quite well (in comparison to the capacitor model) and gave closer theoretical discharge values to the experimental ones [12-14]. on the other hand, one should point out that in these experiments [12-14], only partial discharges under initial experimental conditions were investigated. iii. consequences of partial discharges quite early, there were experiments with plane discs from clean polyethylene having small cylindrical cavities and a uniform electrode arrangement [15]. the author of [15] calculated that about 10-15 cm3 of polyethylene was eroded by each discharge having a magnitude of 10 pc. the deterioration was dramatically increased if the applied voltage was raised above the inception voltage. in yet another work [16], the same researcher pointed out that among the main factors affecting the rate of deterioration of an insulating material are the ratio of the applied voltage to the discharge inception voltage, the magnitude and energy of the discharges, the waveform and frequency of the applied voltage, the resistance of the material both to the discharge erosion and to chemical attack by the byproducts generated by the discharge and finally the electrical and chemical characteristics of the ambient medium. (resonance of the work – mentioned in [15, 16] on the effect of the waveform of the applied voltage can be found in [17] and also in a more recent work [18], where there was an investigation on partial discharges in rotating machine insulation). the energy of discharges affects the local temperature rise at the point of impact of the discharges, and subsequently the value of the local dielectric strength is attained [19]. differences in discharge characteristics and time to breakdown arise if the cavity is (a) sealed or ventilated, and (b) surrounded by the insulation or adjacent to a conductor. moreover, conditions of pressure and temperature used during the processing of polymers (molding, curing) may greatly affect their “molecular packing” and consequently their resistance to discharge channels [20]. investigation of the behavior of discharges in air gaps facing solid insulation indicated that an increase of discharge magnitude with increasing voltage, which was explained in terms of a continuous recombination and neutralization of deposited surface charges which will reduce the shielding effect [21]. such a phenomenon will keep the discharge going and will cause a fresh and greater generation of surface charge. testing artificial and natural cavities in insulating materials (polyethylene and polyethylene terephthalate), the author of [22] found that the inception voltage of natural cavities formed in polyethylene was two to four times the calculated inception voltage, assuming that the electric field is uniform in the cavity. oxalic acid crystals and water vapor, when present in the cavity, are factors of serious deterioration of the material. confirmation of the above can be seen in [23], where it was stated that chemical byproducts contribute to charge deposition on the cavity inner walls and, thus, to the modification of discharge magnitudes in subsequent discharges. internal cavities with discharges cause lesser damage compared to cavities undergoing discharges, which are adjacent to electrodes [24]. this has been observed also in [15]. discharges in cavities with a large diameter/depth ratio cannot extinguish as in cavities with a small diameter/depth ratio. the former type of cavity is likely to have the more injurious effect on the insulation. in [23], it was reported that for very small cavities, the inception voltage decreases as the cavity depth increases, following the paschen curve of breakdown, thus agreeing with [24]. the increase of the number of discharges per unit time with frequency, the increase of the number of discharges with increasing electric stress in the dielectric, the increase discharge magnitude with increasing depth of the cavity as well as with its area, all these were observed experimentally in [6]. recent research indicated that, although an increase in cavity diameter causes more discharges of large engineering, technology & applied science research vol. 9, no. 5, 2019, 4659-4666 4661 www.etasr.com danikas and morsalin: foreign inclusions, enclosed cavities, partial discharge models and … magnitude, an increase in cavity depth causes an increase in inception voltage [25]. this conclusion is at variance with [23]. the authors of [26], working with a non-uniform electrode system and polyethylene samples, observed that the main chemical change occurring in polyethylene when exposed to discharge activity are crosslinking, increase in unsaturation and hydrogen evolution. the rate of chemical change depends on the total discharge energy and concentration of end products. the total volume of hydrogen v (in ml) in a system at a time of t seconds is empirically given by: v=√2·k·t (6) where, k is the hydrogen evolution coefficient which is directly proportional to the total discharge energy per cycle. furthermore, in [26] it was pointed out that semiconducting surface films play a significant role in retarding the ultimate failure of the insulation, agreeing in this respect with [6]. the discharge rate rises almost linearly with the applied voltage irrespective of the gap setting and vapor pressure in a spark gap [27]. it was also reported that the discharge process in artificial cavities is more constant than that in natural cavities. the relation between discharge energy and insulation damage is a subject which was and is a vital one for the insulation community. in [28], it was thought preferable to measure continuously both discharge magnitudes and repetition rates in order to better correlate discharge damage with discharge activity rather than measure either the maximum discharge magnitude or the total discharge energy. later research by the same author [29] confirmed the above conclusions with a variety of insulating materials, such as epoxy resin, polyethylene and mica under ac conditions. research in internal discharges in artificial cavities in polyethylene [30], reported that discharges generally decrease in magnitude and repetition rate with time and that absorbed water can greatly influence the pattern of discharges. the decrease of repetition rate of discharges with time happens because of a voltage decrease on the side wall due to the decline of the side wall resistance in the cylindrical cavity. the apparent charge of maximum discharge (qa) in a cylindrical cavity is given by qa=ε0·ε *· (vgo·s)/(d–d) (7) where, ε* is the specific dielectric constant of the material, d is the thickness of the whole specimen and d the cavity depth, s being the area of the cavity and vgo the inception voltage of the cavity. qa decreases with time because the discharging area is narrowed by the development of low resistance to inner top and bottom surfaces. on the same line of research, it was reported that the impulse inception stress increases with decreasing cavity diameter at constant cavity depth as well as with decreasing depth at constant diameter [31]. the inner workings of discharges in enclosed cavities were the questions tackled in [32], where it was observed that the nature of internal discharges is greatly affected by the assembly of the electrode system and the adhesion of the films and that such discharges become unstable with time, resulting thus in extremely long lifetimes. such observations were confirmed in [33], where it was reported that the internal surface of the cavity is subjected to physical damage or erosion, or a change in surface electrical resistivity. pressure change may also occur, again affecting internal discharge activity. such factors are responsible for the apparent characteristics of discharges in cavities, i.e. their intermittency, cessation and resumption. furthermore, in [34] it was pointed out by the same authors that gas pressure plays a determining role for internal discharges and, moreover, the question of multiple cavities formed by thermal expansion in extruded cables was discussed. experimenting with different arrangements and liquid nitrogen impregnated taped cable insulation, some researchers [35] postulating that discharges occur within bubbles and indicated that the logarithm of the discharge magnitude increases linearly with stress. they proposed that the applied voltage va, the inception voltage vi, m the discharge magnitude and k a constant, are related through the following equation: va=vi+k·lnm (8) performing similar experiments, the authors of [36] indicated that the discharge inception voltage depends on the product of butt gap depth and helium density. discharges start from a point in a butt gap. the probability of the presence of such a point depends on the gap area. in yet another study with pressboard/oil insulation [37], it was shown that, whereas an increase in the magnitudes of discharges by increasing the applied voltage is possible, a decrease of discharge magnitudes is also possible owing to the volume of discharges taking place in gas bubbles in such an arrangement. discharges start always in the electrically weaker medium, agreeing in this respect with [36]. moreover, deterioration of the surface of the pressboard is in most cases a necessary condition in order that dangerous discharges will appear in its volume causing thus ultimate failure. the dependence of discharge inception voltage both on pressure inside the cavity and on cavity diameter was noted in [38]. in fact, it was noted that the discharge inception voltage decreased at low pressures and with increasing cavity diameter, whereas the extinction voltage depends on the conditions of charges trapped on the surface of the dielectric. similar observations were made some years later [39]. in [39], it was also reported that, under the assumption that the insulation is subjected to combined electrical and thermal stresses, a large cavity gas pressure reduction rate is accompanied by a short time-to-breakdown, whereas a small pressure reduction rate is typical for long times-to-breakdown. in other words, the cavity gas pressure does reflect the ageing rate of polymer specimens. some researchers noted also a dependence of both inception and extinction voltages on pressure [40]. electrode design and material processing play also a deciding role according to [40], something also noticed in [32]. a direct relationship between discharge intensity and the rate at which deterioration is taking place in an enclosed cavity was noted in [41]. this relationship was confirmed in yet another study by the same author [42], where it was also observed that discharges initially of large magnitudes decrease with time. such conclusions were in agreement with [43], that engineering, technology & applied science research vol. 9, no. 5, 2019, 4659-4666 4662 www.etasr.com danikas and morsalin: foreign inclusions, enclosed cavities, partial discharge models and … suggested that the area associated with each discharge decreases with time and this can happen if the discharges occur between sites where degradation products accumulate. as the degradation products spread over the surface of the cavity, smaller areas between them are available to discharges. further confirmation of the above was given in [44], where it was reported that the cavity area affected by a discharge is usually much smaller than the area of the whole cavity in which it occurs, and consequently the discharge site is not uniformly discharged. a study of gaseous degradation products of corona exposed low density polyethylene showed that two degenerative processes were in action [45]: a) crosslinking of polyethylene which may be due to ultraviolet radiation and electrons, crosslinking being evidenced by hydrogen evolution, and b) erosion of polyethylene, which may be due to ion bombardment resulting in organic gases being evolved (co, co2, ch4). higher temperatures evolve smaller amounts of organic gases since at higher temperatures molecules can dissipate more of the mechanical energy through segmental motion rather than by means of bond breaking processes (e.g. erosion). in [46], the effect of polarity for cylindrical cavities is remarkable only when the applied voltage is equal to the inception voltage, otherwise, as the applied voltage becomes three or four times larger than the inception voltage, the polarity effect almost disappears. this can be explained as at higher voltages, important secondary phenomena, such as photoionization and dissociation of negative ions formed by the preceding discharges, originate from the gas phase and not from the metal electrodes. the subject of the relation between discharge energy and insulation damage was treated in [47]. the authors found a relationship between the loss of weight and the dissipated power of discharges. they rejected the notion of the importance of isolated discharges and their relation with insulation damage. their work was in agreement with [29, 48]. in [49], discharge magnitudes were shown to decrease with the thickness of cavity, whereas they tend to increase with the cavity diameter. the experimental data of [49] are in accordance with those published in [24] but they were at variance with those published in [6]. an approach similar to the one adopted in [47] was also adopted in [50, 51], where, investigating a complex insulation system (consisted of uniaxially orientated polyethylene tapes (uope) and doecylbenzene oil, the total discharge energy was correlated quite well with the surface area damage of the uope tapes (in fact the correlation coefficient between the aforementioned two quantities was in the region of 0.71–0.97, which is considered to be quite satisfactory). it is true, however, that, in such complex insulating systems, besides the surface area damage in the aforementioned work, other deteriorating mechanisms may take place, such as evolution of gases [52]. moreover, different types of discharges may cause increase or decrease of the gaseous evolution [52]. a more recent publication [53], is in accordance with [52] (albeit using a different electrode arrangement and different insulating materials), pointing out that three types of internal discharges are identified during ageing tests, namely, the first stage of discharges is linked to the streamer-type, the second stage to the townsend-type and the third stage to the swarming pulsive micro-discharges (spmd). the questions of sample thickness, cavity size and partial discharges were treated in [54]. it was shown that with larger specimens, the probability of having bigger cavities increases, and hence a longer free path for the ionization products. thicker specimens have normally higher discharge activity than thinner ones, for the same value of applied electric field. relevant to the above, and confirming [54], is work performed some years earlier, where it was reported that thicker insulation needs more sensitive discharge detection equipment. moreover, the latter conclusion is valid independently of the sort of the enclosed cavity in the insulation, and independently of the discharge model used for the interpretation of the discharge events inside the cavity [55, 56]. deteriorating results because of discharge activity in enclosed cavities were noted in [57], where it was reported that the rate of deterioration increases with an increase in concentration of discharges. deep erosion may ensue with an instability in the dielectric-gas interface. such a phenomenon may have as a result subsequent discharges to the same site. the observations of [57] were confirmed in a very recent paper [58]. further confirmation of the above was offered in [59], where the authors carried out a micro-analysis of chemical byproducts regarding the local erosion in enclosed cavities. localized spots are determined by their chemical byproducts. oxidative degradation mechanisms are at work and as such they change the discharge patterns. important observations regarding the creation of cavities from enclosed conductive contaminants were given in [60]. the authors postulated that high electric stresses develop at the tip of such contaminants and therefore high-energy electrons are injected into the bulk at the negative polarity and trapped electrons are extracted towards the tip at the positive polarity. such a phenomenon, when repeated in each cycle of the ac voltage, causes a small degraded area at the tip of the contaminant and with the passage of time may render a cavity, which finally may lead to deterioration paths. it should be noted that the ideas about the injection and extraction of charge carriers in [60] could also be seen in earlier publications [30, 33, 34]. elaborating on the internal discharges, yet another researcher dealt with their two main mechanisms, namely townsend-like discharges and streamer-like discharges [61]. his research indicated that active species from one half cycle can generate initiating electrons on the next, in accordance with [30, 33-34]. the deteriorating effects of discharges depend on the insulating materials, as shown in [62], where it was observed that discharge activity may lead to depolymerization of silicone rubbers. indeed, discharge activity in rtv silicone rubber affected the propensity of macromolecular chains to crystallize at very low temperatures more than in htv silicone rubber. a relatively recent paper [63] indicated the relationship between applied voltage and discharge intensity and also the relationship between discharge intensity and discharge energy. the discharge energy increases almost linearly with discharge intensity, with the authors noting that even a small discharge whose magnitude is 15 pc, at an inception voltage of 0.8 kv, will release energy of 8.48 x 10-9 joules. there was, however, engineering, technology & applied science research vol. 9, no. 5, 2019, 4659-4666 4663 www.etasr.com danikas and morsalin: foreign inclusions, enclosed cavities, partial discharge models and … no relationship given between discharge energy and insulation damage. the relationship between cavity diameter and discharge magnitude for enclosed cavities was discussed in some recent publications [64, 65]. both of them indicated an increase of partial discharge magnitude with cavity diameter and also a decrease of discharge inception voltage with cavity diameter. such results, albeit with different insulating materials, were in agreement with previous work [24]. the series resistance in the hv circuit has as task to limit the current in the transformer secondary between the hv transformer and the test cell, especially when we are concerned with laboratory experiments. as was noted in [66], the resistance is usually calculated by considering the maximum voltage available and the maximum current allowed. this on one hand has as a result to limit the damage in case of breakdown, but on the other hand the choice of the series resistance also affects the partial discharge activity. the series resistance is an important parameter in determining the current flowing through the test cell as well as the waveforms induced on the test cell’s terminals. since the discharge magnitude or current induced at the terminals is dependent on the current flowing through the hv side, it follows that a smaller current on the hv side will result in a decrease of the individual discharge current pulses. iv. partial discharges and multiple cavities from the above –non exhaustivereview, it is evident that there is a number of factors affecting the discharge behavior inside enclosed cavities and, consequently, the insulation damage. it is also evident that –especially for laboratory experiments– numerous researchers are confined in the study of only one well defined enclosed cavity. this is logical since the primary aim is to understand the discharge activity in one cavity before one proceeds to the study of more complex insulating systems. in real life, however, multiple cavities may be present. earlier research in this direction revealed that in the case of adjacent enclosed cavities in an insulating sample, a triggering mechanism may be at work, i.e. an eventual breakdown in one cavity may trigger breakdown in a second one, and so on [67, 68]. as was noted earlier [69-71], although the waveform of the recorded discharge pulses may not differ greatly between an isolated cavity and two (or three) adjacent cavities, the apparent charge recorded is different. this precisely may suggest that a triggering mechanism may be at work. v. influence of very small partial discharges very small discharges may damage an insulation, as suggested earlier in [29] and also in [50, 51], where it was pointed out that such discharges may have a cumulative effect, which with time will produce more material degradation (polymer disruption, carbonization, release of gaseous byproducts etc.). such views were contested however in [6]. pioneering work done in [72] revealed that chemical changes observed in an antioxidant free high molecular weight polyethylene (aofhmw-pe) in cavities above inception voltage were very similar to those obtained with values of applied voltage below inception. in fact, it was found that the presence of byproducts on the surface of similar nitrogen species only when corona and sub-corona took place indicates that corona aging and sub-corona aging result in similar aging products. since corona currents and resulting species lead to failure of polymer insulations in relatively short times, their findings bore strong evidence that sub-corona aging could lead to serious damage as well, even though a conventional partial discharge detector could not detect any activity. subsequent work [13-14, 73-74] tends to confirm [72]. very small partial discharges and/or charging phenomena below inception voltage were observed not only in conventional polymers but also with polymer nanocomposites, albeit with lesser frequency [75, 76]. earlier research pointed out the importance of small partial discharges and their influence on possible damaging effects on solid insulation [77-82]. certainly, the question of the effect of very small partial discharges on insulation degradation is a complex one since it has to do with not only the means of discharge detection and their respective sensitivities but also with the exact terminologies of the various regimes of discharges. moreover, there is always the question of the thickness of the investigated insulation, the size of minute enclosed cavities as well as the limitations of the discharge detector available, as was noted before [55-56, 83-84]. it is without any doubt that the points raised in [72] merits more attention and research. it must, however, pointed out that, although there are indications that minute discharges (possibly undetected from conventional discharge equipment) and charging phenomena below inception voltage may exist, more work has to be performed with a variety of insulating materials before any definite conclusions can be reached. vi. further comments on insulation damage as noted in [23], the observable effects of partial discharges can be an increase in the loss component of the charging current taken by the capacitive sample, an increased dielectric power loss, radiation of energy in the form of sound, light or ultraviolet radiation, changes in pressure and chemical changes in the dielectric material. of these effects, the most important -regarding the relation of discharge energy to the material damage– is the last one, i.e. the chemical changes. however, such changes can manifest themselves in different ways, especially if the insulation is a composite one. if, for example, we have a composite insulation of solid/liquid, chemical changes can be gaseous byproducts, changes on the surface of the solid insulation, changes in the liquid itself. which one of these changes can be related to the discharge energy, or for that matter to any discharge parameter? any of them or all of them? such questions are in need of an answer. although there have been numerous publications on condition monitoring of insulating systems [85-88], there are relatively fewer papers on the actual relationship between discharge energy and material damage. this does not mean that such a relationship does not present some difficulties, especially with composite solid/liquid insulation, as was noted in older publications [89, 90]. in [89], for example, the authors failed to obtain a quantitative relationship between the partial discharge parameters and the gaseous byproducts at atmospheric pressure, explaining that in the course of a test, absorption and evolution of gases were not related to each other with a permanent relationship. it is, however, a better and more reasonable approach, than to try to engineering, technology & applied science research vol. 9, no. 5, 2019, 4659-4666 4664 www.etasr.com danikas and morsalin: foreign inclusions, enclosed cavities, partial discharge models and … correlate insulation damage with individual discharges, no matter how large their magnitudes are. recent efforts, however, indicated that for different equipment with defects of the same type, the percentage of gases has similar values. the development of defects in high voltage equipment is accompanied not only by the growth of gas concentrations but also stabilization of the percentage of contents of gases at strictly defined levels. this gives some hope regarding the use of the gas content of oils as an additional criterion for interpreting the results of analysis of gases dissolved in oil and thus to try to correlate them with discharge energy [91]. in this respect, important work performed relatively recently should be taken into account [92-94]. it is true that in the context of the present paper, particular attention was given to the total partial discharge energy. this is not only in agreement with earlier publications [29, 47] but also in accordance with much older ones [95], where it was suggested that the energy dissipation of the individual discharge in an enclosed cavity appears to be more important than the discharge magnitude and the significance of cumulative energy dissipation was stressed. vii. conclusions partial discharges in enclosed cavities consist a major danger for insulating materials. past research indicated that it is better to try to correlate discharge energy with insulation damage rather than individual discharge magnitudes with insulation damage. the role of sample thickness, the role of cavity dimensions, the role of series resistance in the hv circuit, the role of multiple cavities in the same insulation as well as the possible damaging role of small discharges and/or charging phenomena below inception voltage are reviewed. however, it should be noted that the notion of insulation damage is still an elusive one, especially if we consider composite insulating systems. rreferences [1] n. b. timpe, “partial discharge measurements in distributed parameter systems: cables”, engineering dielectrics, vol. i: corona 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iee, vol. 100 (iia), pp. 276-283, 1953 microsoft word 05-3132_s_etasr_v9_n6_pp4886-4892 engineering, technology & applied science research vol. 9, no. 6, 2019, 4886-4892 4886 www.etasr.com pranitha & anjaneyulu: performance evaluation of a mimo based underwater communication … performance evaluation of a mimo based underwater communication system under fading conditions boddu pranitha department of electronics and communication engineering national institute of technology warangal, telangana, india pranitha.boddu@nitw.ac.in l. anjaneyulu department of electronics and communication engineering national institute of technology warangal, telangana, india anjan@nitw.ac.in abstract—due to the intense importance of underwater applications in military and commercial purposes, underwater acoustic communication (uwac) is an attracting research area. very high propagation delay, path loss, and low bandwidth are the factors that challenged the acoustic waves in an underwater environment. multi-input multi-output (mimo) techniques are currently considered in uwac to surpass the bandwidth limitation of the undersea channel. in this paper, the accomplishment of a mimo in uwac system highlighting both line of sight (los), i.e. the rician fading and non-line of sight (nlos), i.e. the rayleigh fading signal propagation, is assessed. spatial modulation technique is used, which helps in increasing the data rate in uwac. it controls the spatial distribution of the energy caused by a signal in such a way that the single ocean channel sustains multiple parallel communication channels. the utilization of zero forcing (zf) equalizer, which estimates the transmitted data proves the success of removing inter symbol interference (isi). matlab simulations are done for the uwac system for values of los/nlos. because of various scattering effects in nlos propagation, the error rate is considerably high when compared to that of the los propagation. bit error rate (ber) values for the corresponding signal to noise ratio (snr) are calculated. keywords-underwater acoustic communications (uwac); multiple input multiple outputs (mimo); rayleigh fading; nonline of sight (n-los); rician fading; line of sight (los) i. introduction nowadays, underwater acoustic communications (uwac) is an open research, which includes the present day expansion of human activities in undersea environments, i.e. environmental monitoring and offshore oil field exploration. robotics in underwater environment is also becoming a major aspect of research in uwac in order to increase precision [1]. today, underwater remote sensing systems such as sonars are used extensively for detecting and tracking different targets using sound signals [2]. recently, significant attention has been given to the underwater wireless sensor networks (uwsns) because of their applications in commercial, scientific, environmental and military purposes [3-4]. the performance and reliability of the system have been improved due to the continuing research. because of underwater high attenuation and absorption effect, electromagnetic waves can travel only short distances [5]. some investigations have been made about utilizing optical signals for underwater applications. however, it was found that they can only pass through a limited range in a very clean water environment, making them useless for underwater long-distance transmissions [6]. thus, acoustic signals are found to be the only physical feasible way that works in an underwater environment reducing bandwidth limitations [7]. high propagation delay, heavy energy consumption, large path loss, and low bandwidth have posed challenges for applying acoustic waves in underwater environment [8]. three major factors that characterize acoustic wave propagation are attenuation, multipath propagation that varies along with time, and low sound speed. attenuation increases with the frequency of the signal [9]. fading, usually called small scale fading, is caused by multipath signals. the signal may be constructive or destructive [10]. generally, these factors limit system performance. three factors that characterize the channel in uwac are long multipath delay, high doppler spread, and time-varying doppler shift. this multipath delay is the main cause of inter-symbol interference (isi). doppler spread, and doppler shift are caused due to relative speed that is comparable with the speed of sound [11]. severely low bandwidth, large area multi-path spread, doppler shift, and background noise make the underwater environment much more complicated than a simple wireless channel. hence, the design and implementation of high data rate uwac are a major challenge. influence of interference in wireless communication has been studied in fading environment using outage probability calculation [12]. in low frequency (i.e.<1khz) sound propagation, the fading components, rayleigh and rician are related with saturated and partially saturated schemes respectively in which the multipath is completely or partially random. the propagation of acoustic waves requires a medium to transmit data. this medium can be either shallow or deep water. irrespective of the type of the medium, propagation loss and fading exists. propagation loss, also known as path loss is the value of the power of the receiver at the receiving end. corresponding author: b.pranitha engineering, technology & applied science research vol. 9, no. 6, 2019, 4886-4892 4887 www.etasr.com pranitha & anjaneyulu: performance evaluation of a mimo based underwater communication … distance in the propagation (considering los and nlos), water density, strong currents, waves, etc. are factors that impact path loss. because of the presence of living and nonliving objects underwater, a portion of the acoustic signal gets either reflected or diffracted and scattered. this is referred to as slow fading in uwac, while fast fading is caused due to multipath propagation loss. considering all these issues, the main focus of our research is to characterize all the mentioned properties in the uwac channel. estimating the transmitted signal in uwac is to be studied as well [13]. multiple input multiple output (mimo) is the advanced and sophisticated technology which is adapted from land wireless communication to underwater communication because of the increasing demand for high data rates. in this paper, this technique is used which helps in reducing the interference of uwac systems. also, spectral efficiency in multiple transmitters can be increased [14]. mimo techniques are applied to uwac with spatial modulations [15]. mimo approaches have taken advantage of available channel equalization algorithms that are used for single carrier transmissions [16]. the bandwidth of the transmitting and receiving means of mimo occupy the same frequency band, without the use of any further receiver transmitting power. this can increase the capacity of the channel and lessen the bit error rate (ber) of the system [17]. whenever the transfer functions between different transmitting and receiving antennas are identically and independently distributed (i.i.d.) and their significances are explained by the rayleigh distribution, then an ideal situation arises for a mimo system. this distribution describes the conditions for nlos signal propagation. however, it can be noted that uwac scenarios deviate from the given ideal conditions as they give signal propagation details of los and nlos which are expressed as rician distribution and rayleigh distribution respectively. to recover the data that is transmitted, zero forcing (zf) equalization technique is used. an equalizer is a digital filter used to mitigate the effects of isi introduced by a time dispersive channel. mimo linear equalizer is used to attain lowcomplexity equalization. it reduces the error propagation. zf equalizer is a linear equalization algorithm used in communications. it generally affixes the inverse of the frequency response of the channel matrix. this technique is used when isi is high compared to the noise in the system. this technique is generally ideal in the case of noiseless channels. a zf equalizer controls the isi and ici introduced by the transmission channel. this equalizer does not take enhancement of the noise into consideration [18]. in our previous work [19], a comparison for zf equalizer and lms equalization has been made in uwac for a 2×2 mimo in which zf equalization outperforms lms equalization technique. in this paper, the zf equalization technique at the receiver will be compared for rayleigh and rician fading uwac mimo channels. rician fading includes the los while the rayleigh fading has the n-los component considering multipath of uwac in it. all the losses included in uwac channels such as spherical loss and absorption loss were considered. the doppler effect and the relative motion that exists between the transmitter and receiver were also considered. los and n-los links consider that the wave reflections are not significant, i.e. the transmitter and receiver are neither near to water surface nor to the seabed. matlab simulations have been carried out for all these conditions, and the results were compared. ii. system modeling to reduce bandwidth limitation to the most extent of the undersea channel, mimo is considered in uwac. multiple antennas are used by mimo technology to acquire various gains namely multiplexing and beam forming. nonetheless, the complexity and cost of the receiver are increased because of these gains. spatial modulation (sm) is one good approach to overcome the problems mentioned above. in sm, the information bits are mapped into two different constellations: a signal constellation and a spatial constellation. signal constellation is based on the modulation scheme, while the spatial constellation is used to encode the index of the transmitter. at any point in time, one of the transmitters remains active, while the other transmitter radiates zero power. thus, sm avoids the inter channel interference (ichi) at the receiver and reduces the high requirement of synchronization among transmitters. moreover, unlike the regular mimo system, rf chains are not required in sm at the transmitter [20]. in this part, we start by giving an introduction to sm– mimo concept in uwac. this modulation scheme is applied to the transmitting or receiving antenna to send extra information, and so sm is used to find the index of the active antennas at any time instance. therefore, the information bits that are to be transmitted are branched into two different parts. in the first part, they are graphed to a symbol from the signaling constellation. here the type of modulation used finds the number of bits per symbol. from the set of receivers available for transmission or reception, the second part of the information bits regulate the index of the receiver that is selected from a set of receivers that are available for transmitting or receiving the data. receiver selection in any general mimo system depends on the state of the channel and the signal strength of the receiver. in sm-mimo it depends on the incoming user data stream [21]. fig. 1. spatial modulation the number of transmitters and receivers is nt and nr respectively. m is the number of entities of the signal constellation. here we are considering a 4-qam modulation because of its bandwidth efficient quality. by finding the index of the active transmitter in sm–mimo, one symbol s1 is transmitted directly, and the other symbol s2 indirectly in each channel use. for subjective nt and m, the rate of sm is: ��� = log� + log� � (1) engineering, technology & applied science research vol. 9, no. 6, 2019, 4886-4892 4888 www.etasr.com pranitha & anjaneyulu: performance evaluation of a mimo based underwater communication … hydrophones are used as transmitters as shown in figure 1. higher throughput, simpler receiver and transmitter design, and lower transmit power supply are the main advantages of smmimo. but the antenna has to be switched very quickly in this case. here, a basic 4 qam modulation is used. the received data for the 2 ×2 mimo is given by: ������ = � ℎ�� ℎ��ℎ�� ℎ���� ����� + � ����� (2) where y1, y2 are the received data from the two receivers, h11, h12, h21, and h22 are the channel coefficients explained below, x1 and x2 are the transmitted data and n1, and n2 represent the uwac noise. to detect the data at the receiver, a zf equalizer is used. detecting the information from the original noisy data being received is known as detection. mimo detectors/receivers include a merge of many algorithms carrying out many tasks like estimation, detection, equalization, decoding, etc. [22]. in this paper, the zf equalizer, which is based on channel matrix estimation, is put forward. the original system is divided into several subsystems allowing data estimation with practicable complexity. the inverse of the channel matrix is calculated and multiplied with the received data to obtain the transmitted data. the estimated/detected data is given by: �� = ���� (3) �� = ������ + �� (4) �� = � + ���� (5) zf technique is less complex. the number of receivers should be equal to or greater than the number of transmit antennas in the case of zf. however, it comes at the cost of increasing the power of noise that leads to power degradation [23]. when the doppler frequency is small, the received signal quality will be better than when it is large. consequently, it will influence the received signal quality. interference between terminals can be suppressed further by using the zf equalizer. iii. channel modeling the uwac channel is highly complex because of its nonhomogenous nature. water densities, temperature gradients, and non-homogeneities caused by the dropping particles of either solid or gaseous matter are the main reasons for most imperfections. the constant flow of water and the channel reflections that are caused at the sea surface and bottom increase the complexity further. this effect of the underwater channel is that it has strong multi-path propagation and the doppler spread. however, salinity, temperature, and pressure help in finding the propagation velocity, which makes the transmission medium highly refractive [24]. the received signal combines a large number of multipath arrivals, especially scatterers formed by ocean surface and bottom. such fading is known as a rayleigh fading channel. rayleigh fading channel is a shallow water channel commonly used, but when discrete arrivals are seen in the channel response, it imposes a challenge to make assumptions [25]. point-to-point communications in uwac are a major research area that has to be studied. this is known as los communications to underwater multicarrier modulation networks. because of the presence of multipath scattering in the uwac channel, the application of mimo is promising in this case. large fractional bandwidth is one of the main difficulties associated with uwac. the acoustic multipath propagation in rayleigh fading model follows an exponential distribution at the received power, while in a los propagation path, the rician fading model is adapted [12]. when the rayleigh fading model is used, the scatterers that are explained in figure 2 are considered. fig. 2. multipath scattering in uwac in this type of channel, no straight path exists between the transmitter and the receiver, but at the receiver, the sums of all the reflected and scattered waves are combined. scattering may be mainly caused due to reflections from the sea surface and the ocean bottom. at the receiver signals are received in four different ways. they are the direct los direction between the transmitter and the receiver, the reflected signal from the bottom of the ocean surface, and the reflected signal from both surface and bottom. however, each receiver receives multiple reflected and direct signals from each transmitter. figure 2 depicts the scattering scenario in uwac. rough sea surface or the seafloor causes attenuation of the acoustic field in an ocean waveguide. here, attenuation increases with increasing frequency. ambient noise is considered in the rayleigh fading uwac channel due to turbulence, shipping, ocean waves, and thermal noise [26]. the power spectral density (psd) of these noise components as a function of frequency in khz is expressed as: ���� � � = 1.7 − 3log (6) ����&� � = 4 + 2)* − ��+ + 2.6log − 6log � + 0.03� (7) ����.� � = 5 + 0.750� �1 + 2 log − 4log � + 0.4� (8) ���� 2� � = −1.5 + 2��� (9) the shipping coefficient s varies from 0 to 1, for low and high action respectively. w is the wind speed (m/s) [27]. the final psd of the background noise is given by: �� � = � � � + �&� � + �.� � + � 2� � (10) where � � � is the noise due to turbulence, �&� � the noise due to the shipping activity, �.� � is caused due to waves and � 2� � is the thermal noise. in a rician fading channel, the los component is mainly due to ocean currents, pressure and temperature gradients, and engineering, technology & applied science research vol. 9, no. 6, 2019, 4886-4892 4889 www.etasr.com pranitha & anjaneyulu: performance evaluation of a mimo based underwater communication … salinity variations. the channel coefficients of uwac in los are calculated as: ℎ = 3 45�645 7&�8�79�8�:;��<=> 6?>� (11) where @a is the rician factor, 7&�8� is the propagation loss coefficient due to spherical spreading, and 79�8� is the absorption loss. b gives the doppler frequency and cb represents the phase shift of this los component [28]. while evaluating the channel coefficients, all the factors involved in effecting the performance of the system are considered. due to the motion between the source, the receiver and the inhomogeneous ocean medium, sound waves are affected by doppler shift which results in frequency spread in the received signal [29].the doppler frequency b is expressed as: b = d9ecos �hb − hia� (12) where d9e is the maximum doppler frequency given by: d9e = ja 4/@& (13) where ja is the receiver’s speed, 4 gives the carrier frequency, and @& denotes the sounds speed, which is generally considered as 1500m/s. the factors α0 and αv r are considered when there is an angle of arrival between the transmitter and the receiver. different water properties such as temperature, salinity and pressure impact the speed of sound in water. the speed of sound in water near the surface is approximately 4 times faster than the speed in the air. the propagating signal phase shift can be calculated as: cl; = mno�< ∗ q (14) where i is the i th transmitter and j is the j th receiver. the wavelength q is given by q = 1500/ 4 (15) if the signal gets weakened because of the geometrical spreading of a wave propagating away from the source, then the created loss is known as spreading loss. different kinds of non-uniformities are present in the sea and within its boundaries. these inhomogeneities reradiate a portion of the acoustic energy that is incident upon them which is known as scattering. due to the presence of geometrical spreading and absorption spreading, as an acoustic wave propagates through the medium, its intensity is reduced. however, there is a drastic change in the attenuation of acoustic waves in water when compared to the rf waves in water. also there is a heavy loss of energy in water due to absorption. the loss that is caused by geometrical spreading can be either spherical or cylindrical. the loss due to spherical spreading is calculated by: 7&�8� = �m (16) where d is the distance between the transmitter and the receiver. during sound wave propagation, energy can be converted to many other modes, and the medium absorbs it. the propagating physical wave controls the absorptive energy loss. the absorption loss according to the schulkin-marsh model is calculated as: 79�8� = 10 rst u>>>> (17) the parameter v is given by: v = 8.68 ∗ 10x )�y=z=[u\=zu6=[u + ]=[u =z + ∗ �1 − 6.54 ∗ 10 �^_� (18) where a and b are constants, `9 stands for salinity, fc for carrier frequency and a is the relaxation frequency which is given by: a = 21.9 ∗ 10c�� deu> zfugh� (19) here t is the hydrostatic temperature given in °c, p denotes the hydrostatic pressure which depends on water depth ht, which is given by: _ = 1.01�1 + 0.1ℎ � (20) in figure 3, two transmitters are placed apart at a distance l1, while d11 is the distance between the transmitter and the receiver, and l2 is the distance between the two receivers. it is assumed that the transmitters and receivers are in parallel planes and l1>l2. for calculating the channel coefficients �ℎ�� ℎ��ℎ�� ℎ��� using (2), we consider distances d11, d12, d21, and d22 respectively. assuming that the distances d11, l1 and l2 are fixed, the remaining distances could be calculated. the signal phase shift θij can also be determined for various distances. fig. 3. mimo los uwac channel iv. simulation results simulations in matlab have been carried out for the channel model shown in figure 3. 4-qam spatial modulation is given at the transmitter which is a cost and complexity efficient, while at the receiver zf equalization is utilized to detect the transmitted data. for nlos, i.e. the rayleigh fading considers the multipath fading involved in uwac. the ambient noise which involves noise caused due to shipping, waves, turbulence, and thermal noise is also considered. while in los, rician fading factors such as absorption loss, spherical loss, temperature, pressure, salinity, doppler frequency, etc. are considered as shown in table i. simulations were carried out for both los and n-los uwac, i.e. for both rician and rayleigh fading channels. figure 4 depicts that rician fading outperforms the rayleigh fading channel. the snr to ber values are tabulated in table ii. engineering, technology & applied science research vol. 9, no. 6, 2019, 4886-4892 4890 www.etasr.com pranitha & anjaneyulu: performance evaluation of a mimo based underwater communication … table i. simulation parameters symbol parameter value nt number of transmitters 2 nr number of receivers 2 n number of transmitted bits 10000 m qam order 4 cr rice factor 0.56 d11 distance 1m – 100 m fc carrier frequency 10khz t temperature 10°c sa salinity 35 psu p pressure 11 kg/cm 2 cs speed of sound 1500 m/s l1 distance between transmitters 5 m l2 distance between receivers 2 m ᶹr speed of the receiver 9 m/s ht shallow water depth 90m fig. 4. snr vs. ber of rayleigh and rician fading uwac table ii. ber values snr in db ber rician distribution rayleigh distribution 1 0.830409 0.94646 5 0.782244 0.915555 10 0.731129 0.870501 15 0.658818 0.789072 20 0.474383 0.689473 25 0.020281 0.571698 30 0.00 0.447859 35 0.00 0.324006 39 0.00 0.191 from the above-tabulated values, we can observe that the error rate for rayleigh distribution is very high when compared to rician distribution. this is because the scattering effects are very less in the los component than in the n-los and also the presence of multipath fading affects the performance of the system. from table ii, we notice that the ber values of rician distribution are zero for snr values at 30db. however, the ber value of rayleigh distribution is 0.448 for snr at 30db. for rician distribution, the distance between the transmitters and the receivers can be varied because of the line of sight propagation. as they are in parallel planes, the channel coefficients can be calculated, and the respective received data can be detected by using the zf equalizer. from figure 5 we observe that the error rate increases as the distance from the transmitter to the receiver increases. as the link distance d11 increased from 1m to 100m, it is observed that the geometry of the channel model is varying, thereby introducing larger spherical and absorption losses, calculated by (16) and (17) respectively. note that as the distance d11 varies, all other link distances, which are used to calculate various channel coefficients (h11, h12, h21, and h22) also vary. the phase shifts of the signals propagating in longer paths are recalculated by (14). it is observed that the ber is proportional to the considered distance. fig. 5. snr vs. ber of zf equalization with different distances the main intention of using the 4-qam modulation scheme is its efficiency to use the bandwidth. generally, whenever the requirement of linearity of a modulation scheme like qam increases, the power efficiency of the current power amplifiers considerably reduces. so a simple 4-qam modulation is used in this case of transmission. in figure 6 we observe that the 4qam is the best utilized modulation scheme. though the higher modulation orders give higher data rates, they are very resilient to noise and interference. therefore, there is a small deterioration in the performance of 4-qam between 15 to 23db of snr. as snr decreases, errors will increase along with data retransmitting, thereby slowing throughput. by reverting to a lower order modulation scheme the link can be made more reliable with fewer data errors and retransmittions. so, the 4-qam is used for better efficiency and reduced complexity. fig. 6. snr vs. ber for different states of qam 5 10 15 20 25 30 35 40 10 -3 10 -2 10 -1 10 0 snr in db b e r rayleigh fading rician fading 5 10 15 20 25 30 35 40 10 -3 10 -2 10 -1 10 0 snr in db b e r d11=1m d11=10m d11=5m d11=30m d11=50m d11=100m 5 10 15 20 25 30 35 40 10 -3 10 -2 10 -1 10 0 snr in db b e r 4-qam 8-qam 16-qam 32-qam engineering, technology & applied science research vol. 9, no. 6, 2019, 4886-4892 4891 www.etasr.com pranitha & anjaneyulu: performance evaluation of a mimo based underwater communication … fig. 7. snr vs. ber for different carrier frequencies figure 7 gives the snr to ber curve for various carrier frequencies. we observe that the number of errors keeps on decreasing as the carrier frequency value increases. carrier frequency and the relative motion between the transmitter and the receiver depend upon the doppler effect. by optimizing the choice of these basis functions, the doppler shift is estimated. doppler effect plays an important role in the efficient design of high data rate acoustic communication systems. v. conclusions and future work simulation results prove that the los component of uwac outperforms the nlos component. all the scattering effects of the undersea channel characteristics are considered in this work. moreover, in los propagation, the performance on varying distances is calculated. results have been presented for various states of the qam modulation scheme and also for different carrier frequencies. the shallow water acoustic channel is highly time-varying and does not assuredly follow a rayleigh distribution. high data rates, high performance and optimum utilization of the bandwidth are the ultimate goals of the future generation uwac. many other equalization techniques, which further improve the 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5565-5569 5565 www.etasr.com azizi & alotaibi: photonic jet suitable for high precision contact laser surgery applications in water photonic jet suitable for high precision contact laser surgery applications in water mohamed karim azizi department of physics faculty of sciences of tunis university of tunis el manar tunis, tunisia medkarim.azizi@gmail.com abdullah alhumaidi alotaibi department of mathematics turabah university college taif university taif, saudi arabia a.alhumaidi@tu.edu.sa abstract—the use of contact probes in surgical laser technologies (slt) allows tissue contact without damage and enables tactile feedback during operations. among the materials suitable for the manufacturing of chirurgical contact probes, sapphire has been widely used. indeed, the optical properties of this material allow the formation of a high energy density localized region at the front of the contact probe, when used in air. however, in water, this focusing effect is very weak. in this work, the use of a cylindrical sapphire contact probe associated with a continuous (cw) nd: yag laser (at 1064nm) is proposed and studied, which provides, in water, a narrow and high-intensity beam (photonic jet). with the evolution of technology, this kind of surgery can be done remotely. based on 5g technology, medical experts can bring their skills to remote other practitioners around the world. the obtained results show a linear dependence of the focal length and a linear dependence of the beam intensity of the photonic jet to the cylinder radius while the full width at half maximum of the photonic jet beam shows exponential decay dependence. such a system could give rise to a new kind of optical scalpel to the ultraprecise laser surgery in water. keywords-photonic jet; sapphire; scalpel; surgery i. introduction the concept of photonic jet [1] was presented for the first time in 2004. when a micro cylinder is illuminated by a plane wave, a beam (photonic jet) with a waist smaller than the classical diffraction limit is formed on the shadow-side surface of the cylinder. another characteristic of the photonic jet is its low spatial distribution which leads to a high energy density localization and thus to a high intensity exceeding that of the incident wave. until now [2-3], various studies and applications on these systems were carried out in microscopy [4] to improve image resolution, in spectroscopy [5-6] for the sensing of nanoparticles, or in biology [7]. several works have treated the case of photonic nano-jets emerging from dielectric micro cylinders illuminated by plane waves. the intensity of the nano jet and its location depend on the diameter of the micro cylinder and the refraction of the index between the micro cylinder and the surrounding environment. to do this, one must first define the width and the spatial length of the nano jet. the interaction of an electromagnetic wave with a metallic or dielectric obstacle, allows having at well-defined dimensions a diffused light well localized in a space of rather small volume. this phenomenon is called a photonic jet [8, 9]. this beam of high intensity, propagates over a distance of a few wavelengths with a section less than the wavelength. this small section is one of the essential characteristics of the photonic jet, since it is not possible to obtain it with a conventional optical device. this allows us to exploit the photonic jet to obtain optical instruments with a resolution lower than λ/2. photonic jet applications have been carried out for the detection of molecules [10], optical imaging, data storage [11], and high-resolution microscopy [12, 13]. the majority of these studies and applications were based on obtaining a photonic jet from the interaction of an electromagnetic wave with spherical [14, 15], cylindrical [16] or elliptical [17] obstacles [18]. another area where the use of photonic jets is likely to make a significant contribution is the medical field and more precisely the field of surgery. in surgery, the need to make precise incisions without damaging or harming the tissue is the cause of the development of several types of scalpels [19-20]. indeed, cut with a conventional scalpel requires mostly to force on tissues (pressure and pull). also, for example, the use of a laser [21] can damage tissues at the edge of the cut (due to high temperature), which can result in longer and more painful healing. this is disadvantageous because we need a high-power density since the greater the power density, the more rapid the tissue response. thanks to 5g technology, this kind of intervention can be done remotely, since 5g offers an even shorter reaction time (latency) and much better image quality than previous networks, thus limiting the risks of mistake in bringing more information to medical teams. 5g enables specialists to work together from different places due to its ability to offer high resolution images, enabling also specialists to monitor the console screen of the radiological device. by using the terahertz band which currently is a band less used, we can go towards very high speeds and thanks to the integration of miniature and efficient antennas [22] in this frequency band. in this paper, the use of a cylindrical sapphire contact probe associated to a continuous (cw) nd: yag laser (at 1064nm) which provides in water a narrow and high intensity photonic corresponding author: mohamed karim azizi engineering, technology & applied science research vol. 10, no. 2, 2020, 5565-5569 5566 www.etasr.com azizi & alotaibi: photonic jet suitable for high precision contact laser surgery applications in water jet is theoretically demonstrated. such a system could give rise to a new kind of optical scalpel to the ultra-precise laser surgery. ii. theory the calculation model used is based on rigorous resolution of the maxwell equations and allows determining the expressions of the field inside the cylinder as well as that of the diffracted field by the cylinder. assuming that the fields are te with a temporal variation of the form exp(-iωt), where ω is the angular frequency and t the time, the incident, absorbed and diffracted fields are expressed in the form of fourier-bessel series. the expressions of the fields inside and outside the cylinder are then written in term of the bessel functions as: 𝐸 , (𝑟,𝜃) = ∑ 𝑐 𝐽 (𝑘 𝑟)𝑒∈ (1) and 𝐸 , (𝑟,𝜃) = ∑ 𝑎 𝐽 (𝑘 𝑟)𝑒∈ + ∑ 𝑏 𝐻 ( ) (𝑘 𝑟)𝑒∈ (2) where subscripts i and e indicate internal and external fields, ki and ke are wave vectors, r and θ are the polar coordinates and am, bm and cm are coefficients that are determined after consideration of the conditions of continuity of the tangential components of the field at r=r (radius of the cylinder). in the simulations the cylinder center is laid out in the x-y plane (at the intersection of the two axes) and the light propagation is along the x axis. the cylinder is made of sapphire crystal which is largely transparent to the nd:yag laser wavelengths. an incident plane wave with wavelength λ=1064nm is adopted. at this wavelength, the sapphire cylinder has a refractive index of nc=1.7545 while the surrounding medium (water) has a refractive index nw=1.33. fig. 1. schematic representation of the focal and the waist of a photonic jet as shown in figure 1, the photonic jet can be described essentially by three parameters: its focal length f, its width at half maximum w in the x-y plane and its intensity imax at the focal point. the focal length is considered as the distance from the surface of the cylinder to the point of maximum intensity along the x axis. considering a constant index contrast of 1.32, the cylinder radius is varied and we explore how this change affects the scattered field which forms the photonic jet. iii. results and discussion figure 2 shows the electric field intensity map obtained for a cylinder of r=2.5µm radius. from the shadow side surface of the illuminated cylinder, a photonic jet emerges with high intensity and a focal length f=1.1µm. this photonic jet is a result of the interference between the incoming plane wave and the scattered field from the cylinder. as depicted in figure 3, the distribution of the intensity of the electromagnetic field along the propagation axis x shows a maximum at x=3.6µm which represents the focus point (f in figure 2). from this focus point, the intensity decreases continuously and reaches the value imax/e2 for a distance of 5.45λ relative to the focal point f. this propagation of the electromagnetic beam over several wavelengths along the propagation axis with little divergence is a particularity of the photonic jets. fig. 2. electric field intensity map (r=2.5µm). the photonic jet shows a maximum intensity at f (focus). the transverse axis represents the axis that passes through f and is perpendicular to the x direction. fig. 3. intensity distribution of the electromagnetic field along the propagation axis x (r=2.5µm). the photonic jet shows a longitudinal waist of 5.45λ figure 4 shows the distribution of the beam intensity along the transverse axis. as shown in this figure, in the immediate vicinity of the focal point, this curve is symmetrical and welladjusted by a lorentzian profile. the full width at half maximum (fwhm) of the photonic jet is then represented by the fwhm of this lorentzian profile. the characteristic of this system is that the values of the fwhm are smaller than the engineering, technology & applied science research vol. 10, no. 2, 2020, 5565-5569 5567 www.etasr.com azizi & alotaibi: photonic jet suitable for high precision contact laser surgery applications in water wavelength. the photonic jet thus provides a good focusing with sub wavelength spot size. as depicted in figure 5, the focal length, the intensity enhancement at the focus point and the fwhm of the photonic jet at the focus point depend on the cylinder radius. it is therefore necessary to find the value of the radius r, which optimizes these three parameters. fig. 4. electromagnetic field intensity along the transverse axis (black dotted curve) with lorentzian profile fitting (red curve) fig. 5. electric field intensity map (r=2.5µm and r=7.5µm). the focal length, the intensity, and the fwhm at the focus point vary with r a. focal length variation the variation of the focal length of the photonic jet was studied by varying the radius of the cylinder from 1μm to 10µm. as shown in figure 6, this variation is linear and has a slope equal to 0.73. for larger values of the radius r, a problem of focus, which consists of the appearance of different points of equal intensity, appears (figure 7). fig. 6. linear variation of the focal length versus cylinder radius fig. 7. intensity distribution of the electromagnetic field along the propagation axis x (r>10µm). focusing problem appears taking into account the fact that the wavelengths in the spectral 0.6 to 1.2μm are poorly absorbed and penetrate deeply into the tissues, a large focal length is thus not necessary in our case. this penetration is however limited by optical scattering and thus depends on the width at half height of the photonic jet. b. intensity variation the intensity is a key parameter in the interaction of an optical scalpel with tissues. indeed, once the wavelength of the photonic jet and the tissues-optical coefficients are well chosen, evaporation of the tissue will depend on its thermal parameters as well as on the intensity of the photonic jet (energy density engineering, technology & applied science research vol. 10, no. 2, 2020, 5565-5569 5568 www.etasr.com azizi & alotaibi: photonic jet suitable for high precision contact laser surgery applications in water and duration of application). the simulations results show that as the focal length, the enhancement of the intensity of the photonic jet increases linearly with the radius (figure 8). fig. 8. enhancement of the intensity at the focal point c. fwhm variation as presented in figure 9, the fwhm of the photonic jet decreases exponentially with cylinder radius to sub-wavelength values of the order of λ/10. this allows maximum energy density over a very low area and then a rapid diffusion. d. choice of parameters the preceding results show that it would be appropriate to select a cylinder radius of between 6µm and 10µm because of the small change in fwhm in this interval. in this range, a sub wavelength spot size of about λ/10 is provided which allows ultra-precise manipulation. in addition, this low value of the spot size minimizes thermal injury to adjacent tissues, for the considered intensities. thus, choosing a radius value close to the lower bound of this interval seems the best choice. fig. 9. exponential decrease of the photonic jet fwhm vs cylinder radius iv. conclusion the use of a cylindrical sapphire contact probe associated to a continuous (cw) nd:yag laser (at 1064nm) was theoretically demonstrated which provides, in water, a narrow and high intensity photonic jet with spot size of about λ/10. such a system could give rise to a new kind of optical scalpel to the ultra-precise laser surgery. in the near future several applications will be able to be treated, such as detection of cancer in the health field, improvement of data storage in the digital field, engraving and welding in the industrial field. references [1] z. chen, a. taflove, v. backman, “photonic nanojet enhancement of backscattering of light by nanoparticles: a potential novel visible-light ultramicroscopy technique”, optics express, vol. 12, no. 7, pp. 1214– 1220, 2004 [2] c zaichun, z hengyu, h minghui, “ultra-long photonic jet by hemispherical micro-particles”, in: laser science, optical society of america, 2015 [3] h. mohseni, “photonic jet and its applications in nano-photonics”, in: frontiers in optics, optical society of america, 2015 [4] e. betzig, j. k. trautman, “near-field optics: microscopy, spectroscopy, and surface modification beyond the diffraction 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11, pp. 10206–10220, 2011 [10] z. wang w. guo, l. li, b. luk'yanchuk, a. khan, z. liu, z. chen, m. hong, “optical virtual imaging at 50 nm lateral resolution with a whitelight nanoscope”, nature communications, vol. 2, no. 1, pp. 1-6, 2011 [11] v. r. dantham, p. b. bisht, c. k. r. namboodiri, “enhancement of raman scattering by two orders of magnitude using photonic nanojet of a microsphere”, journal of applied physics, vol. 109, no. 10, article id 103103, 2011 [12] s. c. kong, a. sahakian, a. taflove, v. backman, “photonic nanojetenabled optical data storage”, optics express, vol. 16, no. 18, pp. 13713–13719, 2008 [13] a. heifetz, s. c. kong, a. v. sahakian, a. taflove, v. backman, “photonic nanojets”, journal of computational and theoritical nanoscience, vol. 6, no. 9, pp. 1979–1992, 2009 [14] z. chen, a. taflove, v. backman, “photonic nanojet enhancement of backscattering of light by nanoparticles: a potential novel visible-light ultramicroscopy technique”, optics express, no. 12, 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liu, “microliquid jet induced by tunable holmium laser: a potential microsurgery scalpel”, microfluidics and nanofluidics, vol. 20, no. 1, article id 10, 2016 [20] m. c. chiang, c. c. huang, “optically-guided scalpel with lightscattering module for carpal tunnel surgical procedure via minimally invasive surgery”, bio-medical materials and engineering, vol. 26, no. s1, pp. s173–s179, 2015 [21] s. m. a. ghaly, m. o. khan, “design, simulation, modeling, and implementation of a square helmholtz coil in contrast with a circular coil for mri applications”, engineering, technology & applied science research, vol 9, no. 6, pp. 4990-4995, 2019 [22] m. amine ksiksi, m. karim azizi, h. ajlani, a. gharsallah, ‘frequency reconfigurable square patch antenna based on graphene for telecommunication systems”, engineering technology & applied science research, vol. 9, no. 5, pp. 4846-4850, 2019 microsoft word 6-2677-s1 engineering, technology & applied science research vol. 9, no. 3, 2019, 4108-4111 4108 www.etasr.com arisar et al.: optimizing the production from multizone well by selecting appropriate completion for … optimizing the production from a multizone well by selecting appropriate completion for a well of tal block, pakistan muhammad rafique arisar institute of petroleum and natural gas engineering mehran university of engineering and technology jamshoro, pakistan rafique.arisar@gmail.com muhammad zubair hingoro institute of petroleum and natural gas engineering mehran university of engineering and technology jamshoro, pakistan 13pet04@student.muet.edu.pk faisla najam abro institute of petroleum and natural gas engineering mehran university of engineering and technology jamshoro, pakistan faisal.abro@hotmail.com sohail nawab institute of petroleum and natural gas engineering mehran university of engineering and technology jamshoro, pakistan. sohail.nawab@faculty.muet.edu.pk imran hullio institute of petroleum and natural gas engineering mehran university of engineering and technology jamshoro, pakistan. imran.hullio@faculty.muet.edu.pk abstract—well completion is the process of construction a well geared up for production or injection. this mainly involves preparing the bottom of the hole to the required conditions and running the production tubing and associated downhole tools. production from a multizone well can be obtained from a single tubing string as well as from dual tubing strings but it depends on pressure difference, depth and fluid present in the formation. this paper is based on the optimum well completions design for a multizone well of the tal block region which contains four reservoirs of different formations: lockhart (limestone), hangu and lumshiwal (sandstone), samanasuk (limestone) & datta (sandstone) having pressures of 7432psia, 7563psia, 7843psia, and 7982psia respectively. the well is producing four zones (multilayer well) and the generated numerical model for each completion (single string multizone completion and dual string multizone completion) shows better performance and economic feasibility. keywords-completion; multilayer; permeability; single string; dual string; flowrate; drawdown i. introduction tal block is an oil and gas field, located in kohat district, pakistan. the field accounts for 20% of pakistan's oil production, amounting to 17,000 barrels per day [1]. six discoveries have been made in this block, the first in 2002 and the most recent in 2011. there is a 55% success ratio of discovery in tal block, compared to 33% in other areas [2]. in tal block region, four reservoirs can be produced from one well due to low pressure, depth differences between the layers, and similar properties of the fluid present in the formations. formations are lockhart (limestone), hangu and lumshiwal (sandstone), samanasuk (limestone), and datta (sandstone). the purpose of well completion is to connect the reservoir to the surface so that fluid can be produced or injected securely. the best completion design must reduce the fluid losses due to friction and produce fluid efficiently. the initial study related to this topic comprises a discussion of a well completion design methodology to overcome reservoir challenges [3]. advanced well completion solutions were used to satisfy specific reservoir and production requisites. “intelligent well completion” contains inflow control devices and permanent downhole gauges [4]. hydraulic fracture design and performance optimization were used for tight oil reservoirs to improve the permeability of the reservoir and the designed well completion improved the performance in case of hydraulic fracture [5]. the general idea of the design method utilizes a tubular design, supported by software, which offered an analytical method for reviewing tubing loads, design reliability and buckling behavior under composite mechanical, fluid pressure and thermal loading condition [6]. in [7], it was concluded that single trip multizone completion utilized only one trip for gravel pack or frac pack operation in a multizone corresponding author: muhammad rafique arisar engineering, technology & applied science research vol. 9, no. 3, 2019, 4108-4111 4109 www.etasr.com arisar et al.: optimizing the production from multizone well by selecting appropriate completion for … well. the production from a multizone well can be either taken from single tubing string or dual tubing string, depending on the conditions. if the pressure difference is low and fluid compositions are similar, then production can be taken from a single tubing string. intelligent well completion also known as smart well completion, which contains inflow control devices and permanent gauges which control the zonal flow and permanent gauges exclude the need of conventional wireline gauges [9]. ii. research methodology research methodology defines the step by step work on designing the well completion for a multizone well. the initial step was to start based on previous studies. after the literature survey, fluid and reservoir data were collected from the reservoirs of tal block. table i presents pvt data including fluid properties, while table ii presents inflow performance relationship (ipr) related data which define reservoir properties. table i. pvt data parameters values solution gor (scf/stb) 3145 oil gravity (api) 39.4 specific gravity (60/60) 0.738 water salinity (ppm) 1000 co2 (%) 1.5 table ii. ipr data parameters layer 1 layer 3 layer 5 depth (feet) 12218 13940 16403 layer pressure (psig) 7417 7521 7967 layer flowing radius (ft) 0.354 0.354 0.354 layer gor (scf/stb) 2321 3009 2067 layer permeability (md) 11.7 0.94 5.55 skin factor 42.8 36 22 it was concluded that samanasuk formation is a very tight one, having low permeability. so, it was observed that this layer will not flow and the other three layers will be produced. glaso’s correlations were used for calculating gas solubility, formation volume factor, and bubble point pressure of volatile or light oil. glaso’s correlations offer the best accuracy for light oils when compared with other correlations [10]. • gas solubility: �� = �� �� �� .��� (�����) .���� (��∗)� .!!"" (1) ��∗ = 10% where: & = 2.8869 − ,14.1811 − 3.3093 /01 (2)3�." • formation volume factor: log(78 − 1) = −6.58511 + 2.913219 ∙ log(<) − 0.27683 ∙ /01(<)! (2) where: < = �� � > ?� �."!� + 0.968 (@ − 460) • bubble point pressure: log(�a) = 1.7669 + 1.7447 ∙ (&) − 0.30218 ∙ /01(&)!(3) where: �a = 10b8�(ca) and & = def >g �.h � � .��� �� .��� . beggs-robinson correlation was used to calculate viscosity because of its high accuracy. for volatile oil, begg’s correlation offers less error: i8a = ji8kl (4) where: j = 10.715(�� + 100)��." " and 7 = 5.44(�� + 150)��.mmh . the next step was to generate the ipr curves. the “multilayer-dp loss in wellbore” reservoir model was used to generate the ipr curves for the multizone well. equation (5) shows the total pressure drops in wellbore in the case of a multilayer well: ∆pt = ∆phh + ∆pf (5) where: ∆�oo = p� �� �q ℎ and ∆�s = !spt�u �� �qv . ∆phh represents hydrostatic pressure losses while ∆pf represents frictional losses. begg’s and bill’s correlation was used in this case to design the surface equipment, because it is the most accurate correlation to select optimum surface equipment to reduce losses at surface. after that, the vertical lift performance curves were generated based on different variables which showed well performance. petroleum experts 2 correlation method was applied to generate vertical lift performance curves. it includes the features of the petroleum experts correlation plus original work on predicting low-rate vertical lift performances (vlps) and well stability. this correlation has been tested for numerous high flow rate cases and found to provide a good estimate of pressure drops. iii. results and discussion the ipr curves were generated with the help of the prosper software, and show the performance of reservoirs of tal block and the production from multizone wells. well completion was designed and different tubing sizes were selected to check the production. it was concluded that samanasuk formation was tight and would not flow, so the other three formations are discussed. when an ipr curve meets the vlp curve, the operating point is indicated, which shows that the well will flow. hence, production rate will be achieved at different tube sizes. production from multizone wells can be taken from single and dual tubing strings. a. case: 1 single string multizone completion ipr curves were generated for three producing layers. the reservoir data in table ii were used to calculate ipr curves. figure 1 shows the three producing layers’ ipr curves and the ipr curve of the multilayer well. from the results it is observed that layers 1, 3, and 5 are perforated while intermediate layers are unperforated. production is possible from only these three layers. absolute open flow (aof) shows the maximum production from a well, which is not possible in real conditions, usually a well produces less than aof. in this case, the aof from layer 1 is 2936stb/d, from layer 3 is 179.8stb/d, and engineering, technology & applied science research vol. 9, no. 3, 2019, 4108-4111 4110 www.etasr.com arisar et al.: optimizing the production from multizone well by selecting appropriate completion for … from layer 5 is 6905stb/d. layer 3 is tight. it has low permeability and high skin value. it is needed to be hydraulic fracturing in future. the overall well ipr is 10021.4 which shows that the well is producing efficiently. noddle analysis is the combination of ipr and vlp curves while sensitivity analysis is based on different tubing sizes. figure 2 shows the system performance which is the combination ipr and vlp curves which define the production rate of a single tubing string. the system shows that the production rate from a single string multizone is 5327stb/d from a 2.875 inch tube, while using a tubing size of 3.5 inches the production rate is 6702stb/d. from noddle analysis it is observed that erosional velocity will be achieved at the earlier stage which will wear the downhole equipment in cases of 2.875” and 3.5” tubes, so mostly 4.5” and 5.5” tubing sizes are preferred and production rate is 8020stb/d and 8697stb/d respectively. fig. 1. ipr curves for the three layers and the multilayer well fig. 2. flowrates at different tubing sizes for single string multizone b. case: 2 dual string multizone completions in this case, the well is producing from two tubing strings. two zones are produced from one string and the rest are produced from the other. in this case, the ipr curve is generated separately for each tubing string production. 1) for tubing 1 in this case, the ipr curve is generated for two zones which are produced from one tubing string (figure 3). the aof from layer 1 is 2936.4stb/d, while layer 2 is producing 180stb/d. these two zones commingled show an aof of 3116.18stb/d. figure 4 shows two zones producing from one tubing string by utilizing sensitivity analysis. simulation results show production rates of 2281.9stb/d, 2568.5stb/d, 2777stb/d and 2868stb/d from tubing sizes of 2.375, 2.875, 3.5, and 4.5 inches respectively. 2) for tubing 2 the ipr curve in figure 5 shows the performance of one zone which is the deepest and occupies high pressure. the aof of zone is 6933.5stb/d which shows that it has high reservoir pressure and low skin. figure 6 shows the deepest zone, which is producing from the other tubing string. the observed production rates are 3416.6stb/d, 4437.6stb/d, 5283.2stb/d and 5697.5stb/d from tubing sizes of 2.375, 2.875, 3.5, and 4.5 inches respectively. fig. 3. ipr curves for two zones fig. 4. flowrates at different tubing sizes for dual string fig. 5. ipr curve for one zone -290.528 2287.45 4865.42 7443.4 10021.4 741.7 2599.37 4457.05 6314.72 8172.4 ipr plot multilayer dp loss in wellbore rate (stb/day) p re s s u re (p s ig ) aof : 10021.4 (stb/day) aof (layer 1) : 2936.0 (stb/day) aof (layer 3) : 179.8 (stb/day) aof (layer 5) : 6905.5 (stb/day) layer 1 layer 3 layer 5 10.0214 2510.85 5011.69 7512.52 10013.4 0 1854.19 3708.38 5562.57 7416.76 inflow (ipr) v outflow (vlp) plot liquid rate (stb/day) p re s s u re (p s ig ) 0 0 0 0 0 0 e e e e e e e e e 1 0 0 1 0 0 e e e e e 2 0 0 2 0 0 3 0 0 3 0 0 -18.5404 765.218 1548.98 2332.73 3116.49 741.701 2540.46 4339.22 6137.98 7936.73 ipr plot multilayer dp loss in wellbore rate (stb/day) p re s s u re (p s ig ) aof : 3116.5 (stb/day) aof (layer 1) : 2936.4 (stb/day) aof (layer 3) : 180.1 (stb/day) layer 1 layer 3 3.11649 780.837 1558.56 2336.28 3114 0 1829.13 3658.26 5487.39 7316.52 inflow (ipr) vs outflow (vlp) plot liquid rate (stb/day) p re s s u re (p s ig ) 0 0 0 0 0 0 1 0 0 1 0 0 2 0 0 2 0 0 3 0 0 3 0 0 0 1733.37 3466.73 5200.1 6933.46 1.14135 1992.61 3984.07 5975.53 7967 ipr plot vogel method rate (stb/day) p re s s u re (p s ig ) aof : 6933.5 (stb/day) formation pi : 1.57 (stb/day/psi) engineering, technology & applied science research vol. 9, no. 3, 2019, 4108-4111 4111 www.etasr.com arisar et al.: optimizing the production from multizone well by selecting appropriate completion for … fig. 6. flowrates at different tubing sizes for dual string iv. conclusion this study focuses on the comparison of single string multizone completion and dual string multizone completion for a tal block region well. from the simulation study it is observed that the production from a single tubing string is 8020.2stb/d from a 4.5 inch tubing size, which is quite good production in a cost-effective way. on the other hand, production from a dual string is observed to be 6724.5stb/d and 7010.4 stb/d from tubing size of 2.375 and 2.875 inches respectively. in the case of dual string multizone completion, the production is low from the 2.375 and 2.875 inch tubing size which is not suitable for comparison. it is shown that, in the case of dual string, production is good from two tubing strings of 2.875 inches. considering a comparison between single tubing string and dual tubing string, the production from the single string is 8020.2stb/d from a 4.5 inch tubing size which is quite good when compared to dual string which is 7010.4stb/d. for this multizone well of tal block region, single string completion is best and most efficient for production. acknowledgement authors wish to thank the institute of petroleum and natural gas engineering, mehran university of engineering and technology for providing its facilities. references [1] h. saad, “barrel along: after a decade, pakistan resumes crude oil export”, the express turbine, 2014 [2] h. saad, “fifth discovery of oil and gas at tal block”, the express turbine, 2010 [3] m. a. chavez, g. a. garcia, o. pogoson, y. li, a. h. cardona, r. n. nelson, “a comprehensive well completion design methodology to overcome reservoir challenges”, spe annual technical conference and exhibition held in new orleans, usa, september 30–october 2, 2013 [4] j. suresh, k. m. naimi, “advanced well completion designs to meet unique reservoir and production requirements”, spe saudi arabia section technical symposium and exhibition, al-khobar, saudi arabia, april 21-24, 2014 [5] l. saputelli, a. chacon, “optimum well completion strategies in tight oil reservoirs”, offshore technology conference asia, kuala lumpur, malaysia, march 25-28, 2014 [6] a. chakraborty, a. b. a. madzidah, “well completion design integrity evaluation including thermal and stress analysis for complex well completions offshore”, offshore technology conference asia, kuala lumpur, malaysia, march 22-25, 2016 [7] s. hamid, r. jannise, g. garrison, m. coffin, “new technology provides zonal pressure maintenance in single trip multizone completions”, spe annual technical conference and exhibition, san antonio, usa, october 9-11, 2017 [8] t. grigsby, r. jannise, a. goodman, b. techentien, m. schexnailder, g. navaira, “the successful development and installation of a new single-trip multizone completion system developed for the deepwater gulf of mexico lower tertiary formation”, offshore technology conference, houston, usa, may 2-5, 2016 [9] b. h. muryanto, w. fransiskus, r. wijaya, b. styward, y. ji, e. albertson, a. w. sudirgo, a. hutahaean, a. widyastuti, “applications of a multizone single-trip gravel-pack system in developing a shallow-gas field, indonesia: case history”, offshore technology conference asia, kuala lumpur, malaysia, march 20-23, 2018 [10] t. ahmed, reservoir engineering handbook, gulf professional publishing, 2010 6.93347 1737.18 3467.43 5197.67 6927.92 0 2736.88 5473.76 8210.63 10947.5 inflow (ipr) vs outflow (vlp) plot liquid rate (stb/day) p re s s u re (p s ig ) 0 0 0 0 0 0 e e e e e e e e e e 1 0 0 1 0 0 e e e e e e e 2 0 0 2 0 0 e e 3 0 0 3 0 0 microsoft word 26-3495_s_etasr_v10_n4_pp6034-6040 engineering, technology & applied science research vol. 10, no. 4, 2020, 6034-6040 6034 www.etasr.com mwawado et al.: robust edge detection method for the segmentation of diabetic foot ulcer images robust edge detection method for the segmentation of diabetic foot ulcer images rehema mwawado nelson mandela african institution of science and technology arusha, tanzania mwawador@nm-aist.ac.tz baraka maiseli department of electronics &telecommunication engineering, university of dar-es-salaam dar-es-salaam, tanzania barakaezra@udsm.ac.tz mussa dida nelson mandela african institution of science and technology arusha, tanzania mussa.ally@nm-aist.ac.tz abstract—segmentation is an open-ended research problem in various computer vision and image processing tasks. this preprocessing operation requires a robust edge detector to generate appealing results. however, the available approaches for edge detection underperform when applied to images corrupted by noise or impacted by poor imaging conditions. the problem becomes significant for images containing diabetic foot ulcers, which originate from people with varied skin color. comparative performance evaluation of the edge detectors facilitates the process of deciding an appropriate method for image segmentation of diabetic foot ulcers. our research discovered that the classical edge detectors cannot clearly locate ulcers in images with black-skin feet. in addition, these methods collapse for degraded input images. therefore, the current research proposes a robust edge detector that can address some limitations of the previous attempts. the proposed method incorporates a hybrid diffusion-steered functional derived from the total variation and the perona-malik diffusivities, which have been reported to can effectively capture semantic features in images. the empirical results show that our method generates clearer and stronger edge maps with higher perceptual and objective qualities. more importantly, the proposed method offers lower computational times—an advantage that gives more insights into the possible application of the method in time-sensitive tasks. keywords-edge detection; execution time; diabetic foot ulcers; mssim; psnr; image segmentation i. introduction statistics show that the number of people with diabetes has been exponentially increasing worldwide [1]. this disease causes major life-threatening complications, including cardiovascular diseases, kidney failures, blindness, and lowerlimb amputations, often preceded by diabetic foot ulcers [2]. among these complications, managing and diagnosing diabetic foot ulcers remains a major challenge in healthcare systems [3]. being a serious health concern for diabetic patients, early detection and effective preventive care of the disease can greatly reduce the risk of further complications. non-invasive vascular testing methods and imaging are crucial in improving the healing of diabetic foot ulcers, and, more importantly, to prevent early amputation referrals. because the preliminary diagnosis of diabetes is relatively challenging with the existing conventional dermatological methods, (non-invasive) image processing techniques have been recently proposed which have demonstrated promising results [4]. these non-contact imaging methods assist clinicians to follow the prognosis and the healing status of the ulcers without compromising the sterilization techniques required to manage such ulcers [5]. digital image processing has become an important field in analyzing medical images. more specifically, the introduction of digital image processing for the detection and evaluation of ulcers and wounds has become one of the most important methods in linking and optimizing the results of the diabetic foot ulcers [6]. for example, the accurate detection of the edges of the foot ulcers ensures better results for further processing of these images. the effectiveness of many image processing and computer vision tasks depends on the perfection of detecting meaningful features, including edges (local discontinuities or abrupt changes in image grey values and/or texture). edge detection is one of the fundamental steps in image analysis and is useful in finding key features in images [7]. in digital images, edges are used to depict local and significant intensity changes [8]. the purpose of edge detection is to minimize the image data to be processed. hence, edge detection has become an important part of the pre-processing stage before the segmentation or classification of medical images. therefore, this pre-processing step plays a vital role in medical image analysis. conventionally, edges are detected using sobel, prewitt, or the laplacian of gaussian operators. in theory, these operators belong to high-pass filtering, which is unsuitable for edge detection in most medical images because noise and edges belong to high frequencies [9]. most of these edge detectors are based on detecting points in the image with a high image gradient value. this detection strategy is susceptible to false edge points, which are undesirable in the final output—a corresponding author: rehema mwawado engineering, technology & applied science research vol. 10, no. 4, 2020, 6034-6040 6035 www.etasr.com mwawado et al.: robust edge detection method for the segmentation of diabetic foot ulcer images consequence that can affect the subsequent image processing stages. this paper proposes an image pre-processing edge detector for the accurate segmentation of diabetic foot ulcers in digital images. segmentation is an essential preprocessing step in many computer guided medical image analysis and diagnosis methods [10]. we employ the idea that most shape information of the ulcers is embedded in the edges. in this work, we first detect the diabetic foot ulcer edges from the images using the proposed method, which is based on the gradient-driven quadratic functional. then several morphological operations are performed to enhance the quality of edges in the target regions. our method integrates two shape-defining constants that can be tuned to highlight the local edges of the ulcers. with the careful selection of the constants, the proposed edge detector can robustly reveal clear edges in ulcer images contaminated with noise. the novelty of our work can be derived from the proposed edge-locating functional, which integrates total variation [11] and perona-malik [12] diffusion coefficients. the hybrid nature of this formulation provides an effective way of extracting meaningful image features, including edges, contours, and textures. we noted that our edge detector outperforms the classical edge detectors, and can robustly reject unwanted artifacts that may smudge edges. this work, in addition, has established a systematic approach to locate regions of foot with diabetic ulcers. these contributions advance our current understanding of treating patients with diabetic foot ulcers. using matlab and foot ulcer images from accredited sources, different edge detectors (canny, sobel, roberts, laplacian of gaussian, and prewitt) were tested and their performance was evaluated. the selected edge detectors are classical and have been widely used in other image processing and computer vision tasks. three quality metrics were used to evaluate the performance of the proposed method: peak-signalto-noise ratio (psnr), mean structural similarity (mssim), and execution time. the results show that our method outperforms the classical ones, signaling its possible applications in industrial settings. ii. related work diabetes mellitus is a metabolic chronic disease that is associated with abnormal glucose levels in the blood. the disease leads to life-threatening complications, including diabetic foot ulcers discussed in the current work, and is generally considered as a major global health problem [13]. diabetic foot ulcers may cause amputation of a lower limb or even death in severe cases. the current diagnostic practice of the problem involves clinicians and nurses to perform visual wound assessment to determine wound size and healing status. in essence, evaluation of diabetic foot ulcers comprises of various important tasks in early diagnosis: (1) evaluation of patients’ medical history, (2) thorough examination of the foot ulcer by a specialist, and (3) initiation of additional tests, such as computer tomography (ct) scan, magnetic resonance imaging (mri), and x-ray, if applicable [14]. the visual approach is subjective and inaccurate for wound area determination and tissue classification [15]. furthermore, the imaging modalities, such as x-ray and magnetic resonance induction, are expensive, and therefore, may not be easily accessible in most developing countries with limited healthcare facilities. these challenges call for a need to establish methods that can objectify and increase the accuracy of the traditional methods of analyzing diabetic foot ulcers [16]. this work uses image processing and morphological operations as potential solutions to address the issue of inaccuracy caused by visual assessment. the solution can minimize the frequency of patient visits to the clinic to receive treatments or medical examinations. authors in [17] employed the sobel operator to exclude the edges of the feet in the developed thermal imaging system for the foot ulcers. in their work, the main focus was to get the feet edges and not the particular ulcer area. as this method was fully dependent on the temperature gradient from the acquired thermal images, it tended to generate false positives around the ulcer area. to further improve the edge detection accuracy, authors in [18] used an edge detection method that is based on active contour models (acms) as an attempt to address the drawbacks of conventional methods. although the acms have superior sub-pixel accuracies as compared to the conventional methods, their outputs can be easily affected by the intrinsic disadvantages of the active contour algorithms, including contour’s initial position and the presence of noise in the images. the fundamental requirement of any edge detection method is its ability to accurately extract the edge lines while maintaining their good orientations. given this requirement, the performance of different edge detectors depends on the imaging conditions. comparative evaluation of edge detectors facilitates the process of deciding an appropriate method for image segmentation of diabetic foot ulcers. for this purpose, two main approaches have been proposed in the literature as shown in figure 1. the gradient-based approaches, which detect the edges by finding the maximum and minimum values of the image’s first derivative and the laplacian-based approaches which search for zero crossings in the image’s second derivative [19]. fig. 1. classification of edge detection techniques. a number of studies have been done to compare the edge detectors performance by conducting comprehensive analysis of the image edge detection techniques. these studies are all aimed at determining the best operator when analyzing different shapes in image processing applications [20]. table i gives a summary of the performance for both gradient based and laplacian based operators [21]. this summary highlights the benefits and the weaknesses of the detectors. the proposed method is derived in a way that it maintains the benefits of these detectors and remedies their weaknesses. engineering, technology & applied science research vol. 10, no. 4, 2020, 6034-6040 6036 www.etasr.com mwawado et al.: robust edge detection method for the segmentation of diabetic foot ulcer images table i. a summary of various edge detecto rs used in image pro cessin g application s edge detector type advantages disadvantages sobel, prewitt, roberts gradient based simplicity detection of edges and their orientations sensitive to noise inaccurate laplacian of gaussian (log) laplacian based finding the correct places of edges testing wider area around the pixel malfunctioning at the corners, curves and where the gray level intensity function varies not finding the orientation of edge because of using the laplacian filter canny laplacian based using probability for finding error rate, localization and response improved signal to noise ratio better detection specially in noise conditions complex computations false zero crossing time consuming iii. the proposed edge detection method a. computing the edges inspired by the weaknesses of the mentioned traditional methods, an alternative approach is proposed that can facilitate the segmentation of a diabetic foot ulcer from an image, � (figure 2). let �� and �� be the horizontal and vertical derivatives of � respectively. furthermore, because an edge denotes a significant local change in the image intensity, it is usually associated with a discontinuity in either the image intensity or in its first derivative. the change in the intensity level is measured by the gradient of the image. the diabetic foot ulcer image, ���, ��, is a two-dimensional function, hence, its gradient is a vector. the magnitude and the direction of the gradient may, respectively, be computed as: | �| � ��� � �� (1) ���, �� � tan�� ������ (2) the magnitude of the derivative provides a measure of the strength/contrast of the edge. several experiments were conducted to determine the most suitable functional for computing edges, and it was empirically found that a formulation containing the diffusion kernels of both total variation [11] and perona-malik [12] methods outperforms the classical methods. therefore, our functional becomes: ��| �|� � � ��| �|�� � | �| �! " ! (3) where #� $ 0 and # $ 0 denote the tuning constants that determine a tradeoff between clarity of edges and noise. considering the denominator of the proposed functional, the second and third terms from the left signify versions of the total variation and the perona-malik methods. the proposed functional ensures that a proper balance is established between weaknesses and strengths of the two formulations, as evidenced by clearer and stronger edges recovered by the proposed edge detector. b. mathematical morphology we employed several morphological operators to increase the accuracy of locating and connecting the edges of the ulcer area. the goal was to ensure the continuity of adjacent objects by filling “breaks” with pixels. in matlab, the function bwconncomp can be used to connect edges of the ulcer area from the edge maps of the input binary image. fig. 2. flowchart of the proposed method. next, applying the matlab function regionprops on the binary edge map, allows us to find individual properties, such as pixellist and pixelarea. the regionprops function returns measurements for the set of properties specified for each eightconnected object in the binary image of the edge map. using these region properties, we eliminated all areas below the pixel area of 150 pixels. the eliminated areas were due to small objects or textures in the image, and included short lines outside the region of interest. the tuning constants, #� and # , control the sensitivity to edges, hence to ensure that the engineering, technology & applied science research vol. 10, no. 4, 2020, 6034-6040 6037 www.etasr.com mwawado et al.: robust edge detection method for the segmentation of diabetic foot ulcer images resulting edge map is clearly defined, the matlab skeletonization function, bwskel, was used. this function reduces all objects in the two-dimensional binary image to onepixel curved lines, without changing the essential structure of the image. the process extracts the centerline while preserving the topology of the resulting foot ulcer edge map image and the euler number of the objects in the image. iv. performance evaluation to verify the performance of the proposed edge detection method, a range of experiments was performed using various diabetic foot ulcer images. the dataset was obtained from accredited sources including the arusha regional hospital (arusha, tanzania) where images were captured from diabetic patients that voluntarily participated in the study. for the selfcaptured images, we obtained ethical clearance from the northern tanzania health research ethics committee. a variety of images were used to accommodate different skin types, image-capturing angles, and the separation distance between the camera and the target scene. the performance evaluation of different edge detection algorithms was accomplished through four indices: visual appealingness (ability to detect true edges), psnr [22], mssim [23], and processing time. psnr measures the strength of a signal relative to noise and is defined by: psnr � 10log�. /! 012 " (4) where 3 denotes the maximum variation in the input image data, and mse denotes the mean squared error given by: mse = ∑ 7��8,9��:�8,9�; !<,= >? (5) where ��@, a� and b�@, a� are respectively the original and the output images, c and d denote the horizontal and the vertical dimensions of an image; and (@, a� define the pixel location in the image [24]. psnr however, disregards the human visual system and therefore may provide incomplete information on the quality of the images [25]. authors in [26] recommended an alternative metric called mean structural similarity (mssim) to address some of the weaknesses of psnr. this alternative metric is defined by: mssim = � f�fg�h��� i�g �h!� �f�!�fg!�h���i�!�ig!�h!� (6) where the variables, respectively defined for � and f, are as follows: j� and j: , mean; k� and k: , variance; k�: , covariance; and, l�and l are stabilizing constants. another performance evaluation metric is computational complexity, which, in the context of our research, refers to the time taken for the edge detector to output the corresponding edge map. for this purpose, we used the matlab stopwatch timer functions, tic and toc to compare the execution time of the different edge detectors. in addition, we adhered to three principles governing our decisions on the quality of the results. foremost, the edge detector should accurately find all real edges (and should ignore false edges), secondly, the edges should be found in the correct image locations, and, thirdly there should not be multiple edges found for a single edge [27]. v. results and discussion visual results demonstrate that the proposed method outperforms the classic ones in several cases of input images (figures 3-6). (a) (b) (c) (d) (e) (f) (g) (h) fig. 3. (a) original foot ulcer image (foot ulcer 1), (b) grayscale image of the ulcer (c) canny edge detector result, (d) sobel edge detector result, (e) roberts edge detector result, (f) prewitt edge detector result, (g) log edge detector result, and (f) proposed method result. more specifically, our method generates appealing images that clearly reveal the location of the foot ulcers. to highlight the performance in terms of visual appeal, the proposed method produced superior edge maps compared to the results of the authors in [28], who employed the sobel operator to determine the ulcer edges. the method has also increased pixel accuracy in locating the ulcer edges when compared to another recent study [17]. engineering, technology & applied science research vol. 10, no. 4, 2020, 6034-6040 6038 www.etasr.com mwawado et al.: robust edge detection method for the segmentation of diabetic foot ulcer images (a) (b) (c) (d) (e) (f) (g) (h) fig. 4. (a) original foot ulcer image (foot ulcer 2), (b) grayscale image of the ulcer, (c) canny edge detector result, (d) sobel edge detector result, (e) roberts edge detector result, (f) prewitt edge detector result, (g) log edge detector result, (f) proposed method result. quantitative results further demonstrate higher values of psnr and mssim depicted by our method compared with the classical methods (tables ii and iii). this objective evaluation confirms the effectiveness of the strategy used to formulate the edge detector. combining the diffusivity of total variation and the perona-malik mask may generate more plausible edges. however, the tuning constants must be carefully selected to ensure better results. on the other hand, the canny operator shows the least average psnr and the visual results suggest that this operator detects weak edges, a consequence that signals a possible generation of the unrequired false edges. furthermore, the proposed method is computationally efficient (table iv). therefore, we can implement the method into actual hardware to segment foot ulcer images in practical settings. given the promising results, an extension of our approach to such hardware may provide a revealing experience to the healthcare industry (a) (b) (c) (d) (e) (f) (g) (h) fig. 5. (a) original foot ulcer image (foot ulcer 3), (b) grayscale image of the ulcer, (c) canny edge detector result, (d) sobel edge detector result, (e) roberts edge detector result, (f) prewitt edge detector result, (g) log edge detector result, and (f) proposed method result engineering, technology & applied science research vol. 10, no. 4, 2020, 6034-6040 6039 www.etasr.com mwawado et al.: robust edge detection method for the segmentation of diabetic foot ulcer images (a) (b) (c) (d) (e) (f) (g) (h) fig. 6. (a) original foot ulcer image (foot ulcer 4), (b) grayscale image of the ulcer, (c) canny edge detector result, (d) sobel edge detector result, (e) roberts edge detector result, (f) prewitt edge detector result, (g) log edge detector result, and (f) proposed method result. table i. mean structural similarity values generated by different ed ge detectors applied on the foot ulcer images images canny sobel roberts prewitt log proposed foot ulcer 1 0.9899 0.9974 0.9983 0.9974 0.9983 0.9985 foot ulcer 2 0.9941 0.9979 0.9981 0.9981 0.9994 0.9989 foot ulcer 3 0.9953 0.9984 0.9993 0.9986 0.9996 0.9996 foot ulcer 4 0.9934 0.9971 0.9979 0.9971 0.9992 0.9995 foot ulcer 5 0.9904 0.9974 0.9989 0.9970 0.9981 0.9993 average 0.9926 0.9976 0.9985 0.9977 0.9989 0.9992 table ii. psn r gen erated by different edge detectors applied on the foot ulcer images images canny sobel roberts prewitt log proposed foot ulcer 1 53.84 59.36 61.04 59.30 60.44 63.28 foot ulcer 2 56.98 60.33 60.61 60.42 63.95 63.84 foot ulcer 3 55.34 59.01 61.19 59.19 62.76 65.98 foot ulcer 4 56.17 58.77 59.91 58.76 63.02 63.13 foot ulcer 5 54.25 59.54 62.30 59.10 60.00 66.97 average 55.32 59.40 61.01 59.35 62.04 64.64 * input images contain salt and pepper noise.) table iii. algorithmic comp utation al times (s) of different edge detecto rs images canny sobel roberts prewitt log proposed foot ulcer 1 0.249 0.176 0.167 0.155 0.194 0.176 foot ulcer 2 0.288 0.178 0.155 0.188 0.177 0.163 foot ulcer 3 0.184 0.161 0.157 0.157 0.160 0.157 foot ulcer 4 0.187 0.176 0.281 0.243 0.331 0.178 foot ulcer 5 0.178 0.150 0.158 0.150 0.146 0.144 average 0.217 0.168 0.184 0.179 0.202 0.163 vi. conclusion in this paper, a method has been proposed for detecting and locating diabetic foot ulcers in images and its performance was compared to the existing classical methods. the major contribution of this work is its ability to combine the edgepreserving models of perona malik and total variation to produce edge maps that are more accurate and can be used for further processing of the ulcer images especially in segmentation and documentation of their characteristics such as shape and size during diagnosis and prognosis. the method achieves higher values of psnr and structural similarity, even under noise and varying skin colors. also, the method offers a smaller computational load, implying that it may be useful in real-world tasks. despite these promising achievements, the tuning constants must be manually chosen for optimal segmentation results. future research may consider automating the process of edge detection by minimizing the dependence of the tuning constants. the method, also, underperforms for images with dimensions smaller than 107×154 pixels. another challenge that calls for further research involves a variation of the skin color: although our method can deal with the black skin (on which other methods collapse), the results cannot be generalized across all skin types. these limitations may be addressed using other sophisticated image pre-processing techniques, including deep learning. acknowledgment this work was supported by the african development bank (afdb), united republic of tanzania, through project no. p-z1-ia0-016 and grant no. 2100155032816. references [1] j. w. walsh, o. j. hoffstad, m. o. sullivan, and d. j. margolis, “association of diabetic foot ulcer and death in a population-based cohort from the united kingdom,” diabetic medicine, vol. 33, no. 11, pp. 1493–1498, 2016, doi: 10.1111/dme.13054. 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[28] k. n. rao, srinivasa r. p, a. a. rao, and g. r. sridhar, “sobel edge detection method to identify and quantify the risk factors for diabetic foot ulcers,” international journal of computer science and information technology, vol. 5, no. 1, pp. 39–46, feb. 2013, doi: 10.5121/ijcsit.2013.5103. microsoft word 04-937-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1227-1234 1227 www.etasr.com tajari siahmarzkooh et al.: a cluster-based approach towards detecting and modeling network… a cluster-based approach towards detecting and modeling network dictionary attacks aliakbar tajari siahmarzkooh department of computer science university of tabriz tabriz, iran tajari.a@tabrizu.ac.ir jaber karimpour department of computer science university of tabriz tabriz, iran karimpour@tabrizu.ac.ir shahriar lotfi department of computer science university of tabriz tabriz, iran shahriar_lotfi@tabrizu.ac.ir abstract—in this paper, we provide an approach to detect network dictionary attacks using a data set collected as flows based on which a clustered graph is resulted. these flows provide an aggregated view of the network traffic in which the exchanged packets in the network are considered so that more internally connected nodes would be clustered. we show that dictionary attacks could be detected through some parameters namely the number and the weight of clusters in time series and their evolution over the time. additionally, the markov model based on the average weight of clusters,will be also created. finally, by means of our suggested model, we demonstrate that artificial clusters of the flows are created for normal and malicious traffic. the results of the proposed approach on caida 2007 data set suggest a high accuracy for the model and, therefore, it provides a proper method for detecting the dictionary attack. keywords-intrusion detection; markov chain; grpah clustering; dictionary attack i. introduction detecting the intrusion in the flow-based networks as an interesting research is almost a new topic in secure communications. recently, due to the nature of light weight and scaling, researches have focused on the flow-based approaches. in [1] authors have done a detailed study in the area of intrusion detection for such networks. in the mentioned research, the flow is defined as a set of packets which has similar properties like the same source and destination. hence, the measurement of the flows indicates an aggregated view of traffic information which reduces the amount of information being analyzed [2]. furthermore, considering the internal dependency in the network data and relational nature of anomalies, graph-based methods are crucial to detect attacks. in fact, the nature of anomalies is represented in a relational form, and graphs are used to reveal these relations. graph-based idss employ the data dependency and detect attacks by means of some parameters of network traffic. in [5], authors have designed and developed a system for the flow-based intrusion detection which proved to be suitable for higher efficient networks and resistant against dos attacks. in [6] authors developed a framework to monitor the network and identify the computer worms and in [7] authors considered the effect of methods of flow-based smart sampling in recognizing the anomalies. statistical methods to detect intrusion in the network flows were applied in [8] whereas a more general mechanism and defined statistical characteristics of anomaly in the network flows was used in [9]. many idss have employed the communicative graph-based models. in general, the types of anomaly detection methods include the following categories [10]: anomaly detection in static graphs, anomalies in simple graphs (without labeling), anomalies in attributed graphs (with label on nodes or edges), anomaly detection in dynamic graphs, feature-based events, decomposition-based events, community or clustering-based events and window-based events. in the “anomaly detection in static graphs” methods the main task is to trap malicious entities in the network (like nodes, edges and sub-graphs). in the “anomalies in simple graphs (without labeling)” method, the only reachable information in a simple graph is its structure. therefore, these anomaly detection methods might be used for checking the structure of graph in order to find the patterns and explore the anomalies [11-16]. in the “anomalies in attributed graphs (with label on nodes or edges)” methods there is a rich presentation of the graph for some types of data which might display the nodes and edges as attributes. an example for such graphs includes social networks with the user’s interests. these anomaly detection in the attributed graphs use the mentioned structure as well as convergence of graph attributes to find the patterns [17-21]. the “anomaly detection in dynamic graphs” methods are another type of algorithm to detect anomalies focusing on the sequence of static graphs. more specific, the evolution of graphs has been studied by several research groups recognized as the detection of temporal anomaly pattern, event and point of change which is usually defined as considering a sequence (simple or attributed) of graphs in which the target is to find the timestamp. it is related to a change or event and, consequently, represents the k nodes, k edges or graph parts that contributes in more changes. in the “feature-based events” methods the key idea is that similar graphs probably share certain attributes such as distribution of degree, diameter and engineering, technology & applied science research vol. 6, no. 6, 2016, 1227-1234 1228 www.etasr.com tajari siahmarzkooh et al.: a cluster-based approach towards detecting and modeling network… eigenvalues [22]. the “decomposition-based events” methods detect such temporary anomalies through tensor decomposition or decomposition of graph tensors as well as interpretation of eigenvectors and singular values chosen appropriately [23]. these methods can fall into two categories based on graph display: matrix or tensors. in the “community or clusteringbased events” methods, clustering plays a vital role. the major idea is monitoring the communities or graph clusters over time [24-27]. the “window-based events” methods recognize the anomalies of evolution graphs employing methods that look for behaviors and anomaly patterns in the input graph in time intervals. particularly, a number of previous works have been used to model normal behavior. in these researches the input graph is compared with the created model in order to detect the behavior as either normal or malicious [28, 29]. in this paper, a combination of flow-based and graph-based approaches is used to detect the attack and to model the behavior of the network using graph clustering concepts and time series related to the associated parameters. the overview of the proposed approach is the following: 1-collect the packets of network traffic, 2-extract packet headers, 3-create flows based on the common properties of the packets, 4-calculate the number and weight of clusters in the normal and abnormal state, 6-detect the attack considering the previous parameters, 7-create the markov model based on the average weight of clusters, 8-calculate the detection rate of intrusion detection and the accuracy of the model. it should be stressed that in this paper, the graph clustering algorithm in the network flows is used in order to achieve some appropriate parameters to detect the attacks whereas the cluster-like behavior of the produced flows of attacks has not been considered in the above mentioned works. ii. proposed solution in this section, we propose a new strategy for attack detection. particularly, we create a markov model for normal state as well as dictionary attack mode in the network traffic. the proposed solution needs to assume the network and transmitted packets as a directed weighted graph. consequently, in this graph, nodes, edges and weights represent ips, flows transmitted between the nodes and number of flows transmitted in each connection, respectively. time series are shown to be appropriate tools for intrusion detection and then a discussion is made upon how the attacks could be detected based on the number of clusters and their weights. it should be pointed that the results introduced in this work are achieved by analyzing the behavior of packets of network graph. a. analysis strategy the presented analysis in this section expresses two key concepts of the proposed solution for intrusion detection: a) we believe that the attacks or, in more general, the anomalies can be detected with regard to the evolution of clusters obtained from implementation of genetic-based graph clustering algorithm and also consideration of their weights (the number of flows among nodes) over time. in addition, time series of network traffic are analyzed in a sequential mode to determine what has happened. here, graph clustering parameters such as the number of clusters and their weights could be utilized to create time series. it should be noted that in [30], a clustering method based on genetic algorithms was presented in which the software system is assumed as a directed graph and, then, the available graph turn out to be clustered by the genetic algorithm [30, 31]. b) we suggest an approach using graph clustering to detect the attack so that each edge of the graph represents a flow between two ip addresses in the network which carries some packets. here, we believe that separate analysis of parameters which are obtained from the clustering on multiple separate pieces of traffic can assist in intrusion detection, since each separated piece in individual does not reveal the real behavior of traffic, however, multiple separated pieces will prove to do. subsequently, the mentioned genetic-based algorithm consists of the following steps: 1. at first, a set of chromosomes are created in which the encoding is random number generation so that the length of a chromosome depends on the number of graph nodes encoded with the random numbers starting from 1 to the number of nodes (n). 2. the objective function which consists of two parts is calculated as follows: the internal communication of clusters indicates the number of connections between the nodes within a cluster as given by i 2 i i a = μ n where µi and ni represent the number of edges and nodes in i-th cluster, respectively and that 2 i n indicates the total number of edges in i-th cluster. the communications of clusters represents the number of connections among the clusters for which the low values lead to the low dependency among the clusters and, thus, an appropriate clustering is achieved and is given by: ijij i j 0, if i=j εe = , if i j 2n n ìïïïïí ï ¹ïïïî where, eij shows the dependency degree between i-th and jth cluster. the number of edges from i-th to j-th cluster is indicated by and 2ninj is the maximum number of edges between two clusters. the objective function is obtained from: kk iji i,j=1i=1 i ea , k>1mq= k k(k-1) 2 a , k=1 ìïïïïï í ïïïïïî åå where k is the number of clusters. the above equation is used for evaluation of unweight graphs in a way that if the graph is a weighted one, we change the parameters of objective function using some new definitions such that here µi would be the sum of weight of edges in i-th cluster and shows the total weight of edges between i-th and j-th cluster in normalized state. 3. using selection function, selection process is performed. engineering, technology & applied science research vol. 6, no. 6, 2016, 1227-1234 1229 www.etasr.com tajari siahmarzkooh et al.: a cluster-based approach towards detecting and modeling network… 4. crossover and mutation operations are performed. 5. utilizing replacement action, new population and thus next generation are created. furthermore, the introduced algorithm must run until a better clustering wouldn't be obtained. generally speaking, if the number of iterations doesn't exceed a maximum, the algorithm goes to step 2; else, the process must be stopped and the best founded answer should be displayed. the algorithm iterates a fixed number of times. then, because the upper bound of function (the maximum fitness value is possible) is often not found, we limit the number of generations in order to guarantee the termination of search process. b. data set we use the caida 2007 data set which is comprised of packet-based traffic [4]. now, flow-based data is needed to evaluate our approach and, therefore, we have to do the following steps to convert the packet-based data into flows: 1. each packet is read from the traffic. 2. common properties (source ip address, destination ip, protocol, sending time, source and destination port) are extracted from the packets. 3. according to the flow definition, extracted headers are classified into one second intervals. 4. packets with common properties are placed in the same flow, the number of packets is also calculated. finally, there are 1-second flows which can be utilized on different time series. c. network traffic in this section, we test the normal and malicious traffic that can be observed on graph level. we analyze the time series of clusters, their weights, and then highlight the changes which exist in the malicious network. c.1. graph the time series related to the number of clusters and their weights are shown in figures 1 and 2. in some parts of the diagram in figure 1, the peak of nearly 190 is observed that indicates a lot of exchanged packets in the network. by considering the time series of number of clusters in the graph (figure 1), we can see the peaks in the diagram that are observed in some periods of time. in other words, such peak points in the graph can represent some anomalies but not all of them. therefore, we have to derive a new parameter to detect and model the anomalies based on these two parameters. significantly, knowing that simultaneous observing of the number of clusters and their weights allow us to distinguish between the normal traffic and the malicious one. for example, a peak point in the time series of the weights of clusters can be created by both of the file transfer and a scan however, if the peak occurs in the time series of the number of clusters, we can say that an ip scan creates a peak point. since during a scan, the edges come into the more number of nodes, more separate clusters are generated and therefore, the number of clusters increases. 0 20 40 60 80 100 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 1 1 0 1 1 1 1 n u m b er  o f  c lu st er s time (min) fig. 1. time series of number of clusters in 120 minutes. 0 50 100 150 200 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 1 1 0 1 1 1 1 w ei g h t  o f  c lu st er s time (min) fig. 2. time series of weight of clusters in 120 minutes. c.2. normal traffic versus malicious the aim of the analysis in this section is to prove that the mentioned peaks really relates to an attack. in order to identify the network behavior in the attack time, it is needed to compare it with another time frame reflecting in a network without any attack. table i represents the number of active hosts in the normal and malicious time frames which represents that the number of sources and destinations are approximately equal values in a normal time frame. on the contrary, in the malicious time frame, a large number of destinations against the number of sources are observed leading to many clusters created based on the clustering algorithm. the number of destinations in malicious condition indicates that almost all of ip addresses in the network are scanned, while increasing the number of sources is related to scanning task because of some destinations responding to it. table ii indicates that the low percentage of number of ips is assigned to clusters from 1 to 3 and other percentages are assigned to other clusters. however, 77% of total weight of clusters is assigned to these three clusters. hence, the unbalanced allocation of weights to the clusters represents the malicious behavior of the network traffic. d. overview on intrusion detection method in previous sections, we observed that the cluster-based time series such as the number of clusters and their weights could be appropriate solution to detect intrusion. we saw that the time series allow one to analyze data and keep the relation engineering, technology & applied science research vol. 6, no. 6, 2016, 1227-1234 1230 www.etasr.com tajari siahmarzkooh et al.: a cluster-based approach towards detecting and modeling network… between events. the graphs are then appropriate to create time series based on the number of clusters and their weights in time intervals. in addition, the anomaly analysis provides us to consider two parameters: "number of clusters” and “weight of clusters" to detect the intrusion in general form. furthermore, our analysis indicates that the time series related to the number of clusters and their weights in the graph produce such information on the amount of data transferred in the network. table i. number of sources and destinations within normal and malicious time frame malicious normal source destination source destination number 5 83 46 54 table ii. percentage of resources associated with clusters number of ips weight of clusters cluster 1 4% 33% cluster 2 6% 22% cluster 3 6% 22% total 16% 77% other 84% 23% e. markov model creation in the previous sections, we indicated that the time series obtained from some parameters of graph clustering algorithm can be a powerful tool to detect attacks. our suggestion is to create a model for normal and anomaly conditions of the network based on the parameters mentioned in the graph clustering. as an example we model dictionary attack using markov chain. a markov chain is a sequence of random variables such that the probability of going to the next state depends only on the current state: pr(xn+1=x|x1=x1, x2=x2, …, xn=xn)=pr(xn+1=x|xn=xn) markov chains are explained by a sequence of nodes, such that the edges between nodes are labeled by the probabilities of going from one state at time n to another state at time n+1. also, transition matrix of time n through time n+1 is used to represent the same information. the proposed approach is based on the following factors: we use the models to describe the specific properties such as the number of clusters and their evolution over the time. to do this, we need a framework for modeling so that markov chains turn out to be proper tools for sequential data modeling. now, in order to obtain correct information about the network traffic, it is necessary to know whether the attack is progressing in time series or the network is secure. therefore, we model the attack traffic and normal traffic, separately. we note that it is supposed that the time series for a complete network are combination of normal and anomalous activities of the network. f. some graph properties of network traffic the introduced method models the time series of dictionary attack traffic and normal traffic. in order to proceed, the first step is to understand what the traffic is like in its extensive form. at first, in what follows, we will explain how a dictionary attack performs if there only exists information related to the number and weights of clusters. afterwards, an example of network time series will be presented that includes normal and attack traffic. f.1. dictionary attack dictionary attack is one of the most common attacks in cyberspace. in the mentioned data set a dictionary attack is observed. here, as an example of such an attack we investigate the traffic generated by a host that has performed dictionary attack against the network. figures 3 and 4 depict the clusters and their weight during five minutes, respectively. the available values represent the normal and anomalous network traffic. during the attack, the number and weights of clusters are varying. in time series related to the number of clusters, it can be seen that the number of clusters is increasing in the range of 90 to 250 seconds that reaches up to 50 clusters. then, the number of clusters per second drops suddenly and reaches to 15 clusters in normal state. finally, the attack activity stops, gradually. figure 5 shows the time evolution of average weight of clusters at resolution of 1 second. based on this criterion, three phases of dictionary attack are completely identifiable. the first one is the scanning phase which can be identified by low average weight of clusters (between approximately 0 and 10). these values are based on the fact that three-phase handling has started but only a few of them are completed. the second phase i.e., brute-force phase when begins, average weight of clusters remarkably grows (up to 83). during this phase, various user/passwords are tested against a victim. this explains why the average weight of clusters increases. finally, the third phase which is die-off phase indicates low average weight of clusters. in most cases, the average weight of clusters will be 10. such traffic might be due to the fact that the attacker has not been able to finish the sessions. moreover, variations in the average weight of clusters over the time seem to be a key feature of dictionary attack. at last, in fig. 6, it is observed that a deeper analysis indicates that the time series of activity pattern is not constant over the time, i.e. every second of activity brings about one or some seconds of inactivity. the importance of this fact will be clear during the attack modeling. f.2. network time series as we see in figures 1 and 2, the traffic includes transmission of normal and malicious data which illustrate the time series, the number of clusters, and their weights at resolution of 1 second which include a dictionary attack. observing of the peak points in the weight of clusters is typically created by the file transmission which does not create a remarkable variation in the time series of number of clusters. on the other hand, in the time series of normal state traffic, it cannot be concluded that there is a key criterion to describe the traffic evolution whereas the time series of average weight of clusters is suitable for the traffic of dictionary attack (figure 4). g. traffic modeling in this section, traffic models are described based on the previous section. as it was already mentioned, a dictionary engineering, technology & applied science research vol. 6, no. 6, 2016, 1227-1234 1231 www.etasr.com tajari siahmarzkooh et al.: a cluster-based approach towards detecting and modeling network… attack includes three phases: scanning phase, brute-force phase and die-off phase. in this regard, we use active and inactive characteristics of the time series of the number of clusters and their weights to describe a discrete time markov chain. our model of dictionary attack has seven states. in three states of s1, s2, and s3, the attacker is active and the traffic is generated and in three states of i1, i2, and i3 the attacker is temporarily inactive and there is a final state called “end”. states s1 and i1 model the scanning phase of the attack, s2 and i2 model the brute-force phase, s3 and i3 model the die-off phase and the end state finishes the traffic [1]. since, in every transition from a state to another one, the number and weight of clusters are generated according to the empirical distribution related to the current state. this is equivalent to this fact that in states s1, s2 and s3 of the proposed model, the following empirical states are assigned: a) an empirical distribution probability related to the number of clusters in every time interval (pn) and b) an empirical distribution probability related to the average weight of clusters (pave). to proceed, the modeling of normal traffic is easier than the modeling of attack traffic. in fact, a two-state markov chain is used to describe the normal traffic. similar to the dictionary attack traffic, the time series of normal traffic include active and inactive time intervals that are indicated with s (active) and i (inactive). the empirical distributions of this state will be similar to the attack state such that in each transition, random values of n (number of clusters) and ave (average weight of clusters) will be generated. for more illustration, the dictionary attack models and normal traffic are presented in figure 6. 0 20 40 60 1 2 3 4 5 6 7 8 9 1 1 1 1 3 3 1 5 5 1 7 7 1 9 9 2 2 1 2 4 3 2 6 5 2 8 7n u m b er  o f  c lu s te rs time (sec) fig. 3. number of clusters during 5 minutes. 0 200 400 600 1 2 5 4 9 7 3 9 7 1 2 1 1 4 5 1 6 9 1 9 3 2 1 7 2 4 1 2 6 5 2 8 9w e ig h t  o f  c lu s te rs time (sec) fig. 4. weight of clusters during 5 minutes fig. 5. average weight of clusters during 5 minutes fig. 6. markov models: a) markov chain for dictionary attack, b) markov chain for normal state as shown in figure 6a, the model of dictionary attack has two states for each phase which consists of active and inactive states that are represented by si and ii, respectively. additionally, all of transitions are labeled by the probabilities of moving from a state to another one. the normal model of traffic is represented in figure 6b that only two states are assumed for modeling the traffic in the normal case; s and i. in this figure the probabilities of labeled transitions represent the probabilities of moving between the states. in more details, there are several traces from the initial state of model to the end state with different probabilities. for example, in the dictionary attack model, one trace can be s1i1s1s2i2i3s3s3s3i3end. also, ssiiisisii can be a trace in the normal model. as we introduced before, in each trace, the transition probability from one state to another, distribution probability of number of clusters and weight of clusters are calculated. h. model validation to validate the proposed model, artificial time series are generated with statistical properties from the original data sets and they are compared to the original ones [3]. in this section, the testing methodology is described and related results are presented. we evaluate our model on the network traffic data a) b) engineering, technology & applied science research vol. 6, no. 6, 2016, 1227-1234 1232 www.etasr.com tajari siahmarzkooh et al.: a cluster-based approach towards detecting and modeling network… set collected by caida 2007 that has been previously investigated. table iii presents a review of the attacks in the data set in the form of number of clusters and weight of clusters per second. likewise, table iv indicates the main properties of traffic in the data set. as shown in tables iii and iv, the number of clusters per second in the attack case is more than one in the normal case of traffic. also, the weight of clusters are more than one in the normal state. consequently, we can say that these parameters are useful to differentiate between the attack and normal traffic, however, it is the combination of these parameters that can be essential to detect the attack (so, we suggested the average weight of clusters to detect the dictionary attack). table iii. average number and weight of clusters in dictionary attack number of clusters weight of clusters per second 7.2 43.12 table iv. average number and weight of clusters in normal data number of clusters weight of clusters per second 3.3 22.16 i. traffic modeling we describe the time series as a sequence of observations that are created as output by the models when a random path is selected. the paths begin from s1 in the attack state and s in the normal state. the generation process is as following (supposing the model is in si): a. at time t, the model jumps from current state si to next state sj with the probabilities extracted from the model (j=1,…, n). b. if sj is in end state, the trace will be finished. c. when sj is selected, the models randomly generate values of n (number of clusters) and w (total weight of clusters) that are obtained from the inverted empirical cumulative distribution function of output distributions of the state. d. the model delivers the doublet of (n, ave) as an output that is based on the random values generated in the previous step. e. when the observations finish, the process repeats from the first step. in each iteration, the model generates a doublet (n, ave) which is independent of the previous outputs and is only controlled by empirical distribution probability of n and w related to the current state. j. testing methodology and experiment results our testing methodology measures a set of artificial traces and compares them with the original data set. therefore, we consider the following conditions as statistical parameters: a. the average number and standard deviation of number of clusters (µn, δn) and the average of the average weight of clusters and standard deviation of the average weight of clusters (µave, δave) over the time. hence, these measurements separately describe the entire behavior of number of clusters and average weight of clusters in a trace. b. correlation coefficient: the correlation coefficient between the number of clusters and average weight of clusters (ρn,ave) is calculated which could describe the correlation between them in an identical trace. as we know, if the value of correlation is high the selected parameters are then proportional. moreover, for every measurement, the related error ‘m’ is calculated in percentage through the following equation: error = (|moriginal – martificial| / moriginal) * 100 . in fact, this error is derived from the difference between the original and artificial traces. here, we describes the results of our experiment summarized in tables v and vi. the columns of table v indicate the statistical values of original data set. likewise, the columns of table vi present the statistical values calculated for the artificial time series. as we see in tables va and via, the difference between the statistical parameters is very low and it represents the accuracy of attack traffic model. for more details, in tables va and via, we consider three phases for dictionary attack and ni (i=1, 2, 3) represents the number of clusters in each phase. also, avei (i=1, 2, 3) represents the average weight of clusters in each phase of dictionary attack. as we know, the average weight of clusters in the second phase of attack is more than other phases because of more transmission of packets for testing passwords to attack to the victim which is clear in tables va and via. thus, the difference between numerical results (min, max, average and standard deviation) of the original and artificial data is very low, so that we could conclude the accuracy of model is statistically high. tables vb and vib represent low difference between the parameters and high accuracy of the normal traffic modeling. for tables vb and vb, we assumed only two parameters (n and ave) and only one phase for the normal traffic state. hence, the parameters of all of the traffic are measured together. as it is clear, the values of mentioned parameters in the tables are approximately equal which confirm the statistical accuracy of model. table v. details of observed distribution of number and average weight of clusters in original data set a. details of each phase of dictionary attack min max average standard deviation n1 0 11 3.44 3.15 n2 0 6 1.93 0.97 n3 0 7 2.14 0.86 ave1 0 11.46 3.13 1.78 ave2 0 95.23 16.48 4.44 ave3 0 36.23 8.17 5.76 b. betails of normal state min max average standard deviation n 0 11 3.85 0.86 ave 0 316.14 14.36 2.56 engineering, technology & applied science research vol. 6, no. 6, 2016, 1227-1234 1233 www.etasr.com tajari siahmarzkooh et al.: a cluster-based approach towards detecting and modeling network… table vi. details of observed distribution of number and average weight of clusters in artificial data set a. details of each phase of dictionary attack min max average standard deviation n1 0 9 4.23 4.05 n2 0 6 2.06 1.16 n3 0 7 1.98 1.28 ave1 0 12.82 3.18 1.69 ave2 0 91.19 15.35 4.38 ave3 0 38.14 7.68 5.18 b. details of normal state min max average standard deviation n 0 10 4.04 0.98 ave 0 329.54 14.22 2.11 in tables vii and viii, the column “error” represents the relative error between the original and artificial values as percentage in the normal and attack cases. it is seen that the results represent high accuracy of proposed approach. as one can notice, the average, standard deviation and correlation coefficient are correctly estimated for the original data set of attack and normal states. in the average and standard deviation measurements, the relative errors are lower than nearly 5% for the artificial attack traffic and artificial normal traffic. finally, in the correlation coefficient measurement, the error is nearly 6% in the attack state and nearly 5% in the normal state. thus, all of these results show the accuracy of the proposed model. table ix shows that the artificial data is created in high level of accuracy such that the anomalies could be detected with a high accuracy. these values represent that high accuracy in artificial data is created by markov model and could prove that our model is somewhat exact. table vii. numerical results for dictionary attack model original data set artificial data set error (%) µn 4.18 4.24 1.43 µave 42.54 43.19 1.52 δn 2.10 1.96 6.66 δave 15.34 14.86 3.12 ρn,ave 0.78 0.82 5.12 table viii. numerical results for normal model original data set artificial data set error (%) µn 3.12 3.25 4.16 µave 23.87 23.06 3.39 δn 1.46 1.28 12.32 δave 38.55 36.84 4.43 ρn,ave 0.66 0.69 4.54 table ix. numerical results for detection rate in original and artificial data set tp tn fp fn dr (%) original data 0.91 0.89 0.11 0.09 90 artificial data 0.95 0.93 0.07 0.05 94 iii. conclusion and future work in this paper, we proposed a new approach to detect attacks using genetic-based graph clustering algorithm. the number and weight of clusters is calculated for the normal and malicious network traffic graph. then, the attack is detected using the differences of these parameters. the results represent that the approach detects the attack in the network flows in a high accuracy. also, the normal and dictionary attack traffic in network flows are modeled using markov chain. consequently, three phases are assigned for the behavior of dictionary attack: scanning phase, brute-force phase and die-off phase. the values of these parameters are precisely calculated using the caida data set. approximately, the artificial traces could be used for estimating the statistical parameters such as average, min, max and correlation coefficient. the model is appropriately capable for simulating the behavior of network traffic. 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[29] l. peel, a. clauset, detecting change points in the large-scale structure of evolving networks, corr, abs/1403.0989, pp. 38-53, 2014 [30] d. doval, s. mancoridis, b. s. mitchell, “automatic clustering of software systems using a genetic algorithm”, 1999 international conference on software tools and engineering practice (step 99), pp. 73-81, 1999 [31] j. karimpour, s. lotfi, a. tajari siahmarzkooh, "intrusion detection in network flows based on an optimized clustering criterion", turkish journal of electrical engineering & computer sciences, accepted for publication: 10.3906/elk-1601-105. authors profile aliakbar tajari siahmarzkooh received the b.sc. in software engineering from the ferdowsi university of mashhad, iran, the m.sc. degree in computer science from the university of tabriz, iran. he is a ph.d student at the university of tabriz. his research interests include network security, cryptography and intrusion detection systems. jaber karimpour received the b.sc. degree in computer science and applied mathematics from the university of tabriz (iran) in 1998, the m.sc. degree specializing in the computer systems are of applied mathematics from the university of tabriz in 2000, and the ph.d. degree in computer systems form the university of tabriz. he is currently an assistant professor in the department of computer sciences at the university of tabriz and has been the manager of information technology of the university since 2011. his current research interests include cryptography, network security, formal specification, and verification. shahriar lotfi received the b.sc. in software engineering from the university of isfahan, iran, the m.sc. degree in software engineering from the university of isfahan, iran, and the ph.d. degree in software engineering from the iran university of science and technology. he is assistant professor of computer science at the university of tabriz. his research interests include compilers, supercompilers, parallel processing, evolutionary computing and algorithms. microsoft word recognition-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 167-172 167 www.etasr.com zjavka: recognition of generalized patterns by a differential polynomial �eural �etwork recognition of generalized patterns by a differential polynomial neural network ladislav zjavka faculty of management science and informatics university of žilina žilina, slovakia lzjavka@gmail.com abstract — a lot of problems involve unknown data relations, identification of which can serve as a generalization of their qualities. relative values of variables are applied in this case, and not the absolute values, which can better make use of data properties in a wide range of the validity. this resembles more to the functionality of the brain, which seems to generalize relations of variables too, than a common pattern classification. differential polynomial neural network is a new type of neural network designed by the author, which constructs and approximates an unknown differential equation of dependent variables using special type of root multi-parametric polynomials. it creates fractional partial differential terms, describing mutual derivative changes of some variables, likewise the differential equation does. particular polynomials catch relations of given combinations of input variables. this type of identification is not based on a whole-pattern similarity, but only to the learned hidden generalized relations of variables. keywords polynomial neural network; dependence of variables identification; differential equation approximation; rational integral function i. introduction the principal disadvantage of the artificial neural network (ann) identification in general is the disability of input pattern generalization. anns can learn to classify any input patterns but utilize only the absolute values of variables. however, the latter may differ significantly while their relations may be the same. that is why anns are able to correctly recognize only similar or incomplete patterns compared to the train set. if the input considered is e.g. a shape moved or sized in the input matrix, the neural network identification will fail. an approach to look at the input vector of variables not as a “pattern” but as a dependent bound point set of n-dimensional space could be attempted. a neural network, which would be able to learn and identify any unknown data relations, is to contain a multiparametric polynomial functions to catch partial dependence of given inputs. its response would be the same to all patterns (sets) which variables are performed with the trained dependence, regardless of the actual values [9]. biological neural cell seems to apply a similar principle. its dendrites collect electrical signals coming from other neurons. but unlike the artificial neuron, some of the signals already interact in single branches (dendrites) of a neural cell (see figure 1), likewise the multiplied variables of a multi-parametric polynomial do. parameters of polynomial terms can represent the synopsis of the cell dendrites. these weighted combinations are summed in the body cell and transformed into relative values using time-delayed dynamic periodic activation functions (the activated neural cell generates series of time-delayed output pulses, in response to its input signals). axon passes electrical pulse signals on to dendrites of other neural or effector cells [1]. the period of this function depends on some input variables and seems to represent the derivative part of a partial term of a differential equation composition. differential polynomial neural network (d-pnn) constructs and tries to approximate an unknown differential equation describing relations of input variables that are not entirely patterns. it forms its output as a generalization of input patterns similar to the ones utilized by the human brain. it creates a structural model of any unknown relationships of input variables description. d-pnn is based on gmdh (group method of data handling) polynomial neural network, which was created by the ukrainian scientist aleksey ivakhnenko in 1968, when the back-propagation technique was not known yet. he attempted to decompose the complexity of a process into many simpler relationships each described by a low order 2-variable polynomial processing function of a single neuron [2]. fig. 1. a biological neural cell etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 167-172 168 www.etasr.com zjavka: recognition of generalized patterns by a differential polynomial �eural �etwork ii. differential polynomial neural network the basic idea of the d-pnn is to create and approximate a differential equation (de) (3), which is not known in advance [3], with a special type of root (power) fractional multiparametric polynomials (5). ∑∑∑∑ ∞ ==== ==+ ∂∂ ∂ + ∂ ∂ + 11 2 11 0... k k n j ji ij n i n i i i uu xx u c x u ba (3) u(x1, x2,, … , xn) searched function of all input variables a, b(b1, b2,, ..., bn), c(c11, c12, ,... ) parameters fourier’s method of partial de solution searches the solution in a form of the product of 2 functions, of which at least 1 depends only on 1 variable. a partial derivation of function z(x, y) of 2 input variables x, y can be expressed by (4) [4]. )()( ),( 21 zfxf x yxz ⋅= ∂ ∂ (4) elementary methods of a differential equation solution express the solution in special elementary functions – polynomials (e.g. bessel’s functions, fourier’s power series). numerical integration of differential equations is based on their approximation through: • rational integral functions • trigonometric series the 1st, and more simple way, has been selected, using the method of integral analogues, which replaces mathematical operators and symbols in de by the ratio of corresponding variables. derivatives are replaced by the integral analogues, i.e. derivative operators are removed and simultaneously all operators are replaced by similarly or proportion marks in equations, all vectors are replaced by their absolute values. dimensional terms are divided by some others, which results in searched non-dimensional likeness criterions [5]. ( ) ( ) m n m m n nnn i xxx xxxf xbb xxaxaxaxaa y ∂∂∂ ∂ = ++ ++++++ = + ... ),...,,( ... ...... 21 21 1 110 1 21122110 (5) n – combination degree of n-input variable polynomial of numerator m – combination degree of denominator (m<n) 0... ...... ......... .. ... ...... 110 0 110 210 10 =+ ++++ +++++ ++ ++ +++ += vur kjiqjip t k xxbxbb xxxaxxaa w xbb xxaa wwy (6) wt – weights of terms the fractional polynomials (5), which can describe a partial dependence of n-input variables of each neuron, are applied as terms of the de (6) composition. they partly create an unknown multi-parametric non-linear function, which codes relations of input variables. the numerator of (5) is a polynomial of complete n-input combination degree of a single neuron and realizes a new function z of formula (4). the denominator of (5) is a derivative part, which gives a partial mutual change of some neuron input variables and its polynomial combination degree m is less then n. it arose from the partial derivation of the complete n-variable polynomial by competent variable(s). fig. 2. a block of differential neurons each layer of the d-pnn consists of blocks, which contain derivative neurons, one for each fractional polynomial (5), defining the partial derivative dependent change of some input variables. a block also contains additional extended neurons (en), which form compound functions (15) applying previous layer block outputs. each block contains a single polynomial (without derivative part), which forms its output entrance into the next hidden layer (figure 2.). neurons don’t affect the block output but are applied only for the total output calculation (de composition). each neuron has 2 vectors of adjustable parameters a, b and each block contains 1 vector of adjustable parameters of the output polynomial. the root functions of denominators (5) are lower than n, according to the combination degree, which take the polynomials of neurons into competent power degree. they can be replaced by power functions of denominators. inputs of constant combination degree (n=2,3,…) forming particular combinations of variables, enter each block, where they are substituted into polynomials (figure 3.). it is necessary to adjust not only the polynomial parameters, but also the d-pnn‘s structure. this means some neurons in terms of role of the de are to be left out. fig. 3. differential polynomial neural network x1 x2 x3 block output polynomial � neurons (5) combination degree n=3 extended neurons / / π etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 167-172 169 www.etasr.com zjavka: recognition of generalized patterns by a differential polynomial �eural �etwork iii. identification of simple linear dependencies consider a very simple dependence of 2-input variables, which multiplicity is constant (e.g. =2). d-pnn will contain only 1 block of 2 polynomial neurons (7)(8) as terms of de (figure 4.). as the input variables don’t change constantly, it is necessary to add both terms (fractional polynomial of derivative variable x1 and x2) in the de (block). d-pnn will learn this relation easily according to samples of the training data set by means of genetic and evolution algorithm (ga) [7]. ( ) 110 2 1 21322110 11 xbb xxaxaxaa wy + +++ = (7) ( ) 210 2 1 21322110 22 xbb xxaxaxaa wy + +++ = (8) consider a more complicated linear dependence, where 2 variables depend on a 3rd. for example sum of the first 2 variables equals the 3rd variable (x1 + x2 = x3). the complete de (for derivatives 1 and 2-combinations of block) consists of 6 terms (neurons) but only 3 of them will be enough for derivative terms x3 (9), x1x3 (10), x2x3 (11). if other terms (neurons) are added, the d-pnn will work amiss (see figure 5). two-variable combination polynomials of numerators (7)(8) can be also applied, which could improve the d-pnn functionality and increase the number of the de terms. this 3variable dependence is described by more complicated exponential functions. the d-pnn as well is charged by the possible 2-sided dependent change of input variables. for example 1+9=10 is the same sum as 9+1=10. the principal phase of its adjustment resides in eliminating of some neurons (in terms of the de). fig. 4. identification of a constant quotient of 2 variables (x1 = 2x2 ) fig. 5. identification of the sum dependence ( ) 310 3 1 32172143322110 11 ... xbb xxxaxxaxaxaxaa wy + ++++++ = (9) ( ) ( ) 2131332110 3 1 32172143322110 22 ... xxbxbxbb xxxaxxaxaxaxaa wy +++ ++++++ = (10) ( ) ( ) 2132332210 3 1 32172143322110 33 ... xxbxbxbb xxxaxxaxaxaxaa wy +++ ++++++ = (11) multi-layered d-pnn creates compound polynomial functions. main exponential functions of higher layers “carry” some secondary functions of previous layers, describing the partial relations of its variables. from mathematical point of view the 1st hidden layer forms the inner functions, which substitute the input variables of 2nd hidden layer neuron and block polynomials the outer functions. provided this assumption we are able to calculate the partial derivatives of compound functions by variables of previous layers as de terms (14), from the inner functions (12) of an outer function (13). these compound de terms are formed as products of partial derivatives of main and inner functions (15) [6]. ),...,,()( 21 niii xxxxy ϕϕ === i=1, … , m (12) f(x1, x2, … , xn) = f(y1, y2, … , ym) = f(φ1(x), φ2(x),..., φm(x)) (13)           ∂ ∂ ⋅ ∂ ∂ ++ ∂ ∂ ⋅ ∂ ∂ + ∂ ∂ ⋅ ∂ ∂ = ∂ ∂ ∂ ∂ ⋅ ∂ ∂ ++ ∂ ∂ ⋅ ∂ ∂ + ∂ ∂ ⋅ ∂ ∂ = ∂ ∂ ∂ ∂ ⋅ ∂ ∂ ++ ∂ ∂ ⋅ ∂ ∂ + ∂ ∂ ⋅ ∂ ∂ = ∂ ∂ n m mnnn m m m m xy f xy f xy f x f xy f xy f xy f x f xy f xy f xy f x f ϕϕϕ ϕϕϕ ϕϕϕ ... .......... ... ... 2 2 1 1 22 2 22 1 12 11 2 21 1 11 (14) ∑ = ∂ ∂ ⋅ ∂ ∂ = ∂ ∂ m i k i i m k x x y yyyf x f 1 21 )(),...,,( φ k=1, … , n (15) fig. 6. identification of the 3-variable dependence with 2-combination blocks x1 / x2 = 2 block output w0 + + neuron 1 neuron 2 (7) (8) x1 + x2 = x3 block output w0 + + + neuron 1 neuron 2 neuron 3 (9) (10) (11) etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 167-172 170 www.etasr.com zjavka: recognition of generalized patterns by a differential polynomial �eural �etwork each block of the d-pnn forms partial de terms utilizing its basic and extended neurons. single adjustable polynomial (p in figure 6.) without derivative part creates the block output (applying in the next hidden layer) but the neurons are applied only for the total de composition. the blocks of the 2nd and the following hidden layers create compound terms (ct) of the de using their additional extended neurons, outputs and inputs of back connected blocks of previous layers. consider for instance the 1st block of the last hidden layer, which takes its own neurons as 2 basic terms (16) of the de (6). subsequently it creates 4 extended terms of the 2nd (previous) hidden layer variables, using reverse output polynomials and inputs of 2 bound blocks. it creates 4 fractional compound terms of the de for 4 derivative input variables of previous hidden layer using derivations of compound and inner functions (17). as couples of variables of the inner functions φ1 (x1, x2) and φ1 (x3, x4) differ from each other, their partial derivations are = 0 and so the sum (15) will consist only of 1 term. ( ) ( ) ( ) ( ),,110 1 1 1,, 110 ,, 2 ,, 13 ,, 22 ,, 110 1 1 1 22 2 1 2 1 xbb x w xbb xxaxaxaa wy +⋅ = +⋅ ++ = (16) ( ),110 ,, 1 ,, 2 ,,, 1 3 3 1 3 2 )()( 2 1 2 1 xcc x x x wy +⋅ ⋅= (17) ( )110 , 1 , 2 ,, 1 ,, 2 ,,, 1 7 7 1 7 2 )()()( 2 1 2 1 2 1 xdd x x x x x wy +⋅ ⋅⋅= (18) the previous layer block reverse outputs are used to create necessary partial derivations of the outer and inner functions (of polynomials) of differential neurons (17). likewise compound terms can be created for the 1st hidden layer (18). the 3 linked blocks forming 8 terms of the de were attached to the presently adjusted block. this can be performed well by a recursive algorithm. it was not every term that was used in the complete de; some of them were necessarily left out. this indicates “0” or “1” in the neurons of blocks and is ease to use them as genes of ga. parameters of polynomials are represented by real numbers. a chromosome is a sequence of their values, which can be easy mutated. the d-pnn’s total output y is the sum of all active partial de term values according to (19), which the present active amount a can be built in. a y y k i i∑ == 1 k = total amount of de terms (19) it can be seen, that the 3-variable d-pnn (figure 6.) substantially consists of 3 overlaying “wedge” networks (wn), each going back out from the blocks of the last hidden layer and gradually attaching to the derivative variables of previous layers. the d-pnn of the 4 dependent input variables using 2combination blocks will have totally 6 blocks of all input combination couples in the 1st hidden layer. the number of combinations for all variables increases enormously each next hidden layer. this could be solved by applying wns, as only some of the blocks are created and used. the total amount of d-pnn’s hidden layers could equal at least to the number of input variables (i.e. 4), as it must be able to create each combination of which and to reach back all derivative variables of the 1st layer. so wns of the 1st hidden layer will involve min. 4 random blocks, consequently in the 2nd layer will contain min. 3 blocks, etc. this way the number of all wn blocks decreases each next hidden layer until is reached just 1 block. d-pnn will have several overlaying wns partly in the layers again. some wn layers overlay each other and so the blocks can be used several times by different wns (figure 7.). the blocks of the 2nd and following hidden layers can be reconnected and this could compensate missing combination blocks. the connections of the complete 1st hidden layer blocks are fixed. likewise the previous 3-variable d-pnn type does, it can construct the partial fractional terms of the de from back-connected blocks of previous layers. all wn blocks attach back gradually the derivative variables of previous layers. the searching space contains a great amount of local error solutions, which ga can finish easily. this problem is caused by a lot of possible combinations of block inputs and composed de terms (only some of them may be employed), which selection is a critical phase of the d-pnn’s construction, besides the simultaneous parameter adjustment [10]. fig. 7. “wedge” networks of the 4-variable 2-combination d-pnn the d-pnn of the 6 dependent input variables using 2combination blocks will have totally 15 blocks of all input combination couples in the 1st hidden layer and 6 hidden layers. however in experiment with right triangles (figure 9 and figure 10.) it could be sufficient with 4 hidden layers again, because there is the maximum of 4-variable dependence to identify. iv. experiments 4-variable d-pnn is able to identify row/column or diagonal dependence of chess pieces (figure 8.). input vector is formed by their x, y positions (row, column). if the white rook checks the black bishop their x or y positions equal and this can d-pnn learn to identify. another relation occurs if the black bishop checks the white rook, the sum or difference of their x and y-positions are equal ax+ay=bx+by or ax–ay=bx–by. table 1 and table 2 show network responses to dependent and x1 + x2 = x3 + x4 � � � de �.. etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 167-172 171 www.etasr.com zjavka: recognition of generalized patterns by a differential polynomial �eural �etwork independent variables of input vectors. training data set can consist of following 5 data samples x and y-positions of the chess pieces (the chessboard was enlarged) [9]: {1+22=20+3}, {16+1=2+15}, {34+3=30+7}, {60+30=42+48}, {5+25=2+28}, {2+5=4+3} 1 2 3 4 5 6 fig. 8. relations of chess pieces table i. responses to random input vectors with 4 dependent variables input vector output 31 + 46 = 11 + 66 0.9654 18 + 57 = 24 + 51 1.0273 46 + 30 = 25 + 51 1.0018 58 + 44 = 17 + 85 1.0006 14 + 25 = 1 + 38 0.9882 4 + 23 = 8 + 19 1.0031 table ii. responses to random independent input vectors of 4 variables input vector output input vector output 46 + 55 = 3 + 108 (-10) 1.2041 25 + 45 = 51 + 9 (+10) 0.8461 11 + 55 < 27 + 49 1.1865 57 + 54 > 43 + 58 0.9564 56 + 49 < 5 + 110 1.1213 15 + 42 > 12 + 35 0.9179 8 + 29 < 21 + 26 1.1587 49 + 47 > 52 + 34 0.9162 45 + 34 < 2 + 87 1.1917 31 + 32 > 37 + 16 0.8704 3 + 39 < 26 + 26 1.4803 45 + 56 > 30 + 61 0.9515 35 + 9 < 18 + 36 1.2038 27 + 58 > 45 + 30 0.9228 29 + 6 < 37 + 8 1.1653 44 + 34 > 36 + 32 0.9267 60 + 43 < 41 + 72 1.0526 39 + 25 > 30 + 24 0.9174 5 + 40 < 40 + 15 1.2457 59 + 39 > 51 + 37 0.9414 a separating plane could be noticed, detached from the relative “classes”, which have the same characteristic (if the sum of the 1st couple is less then it should be, the output is less then the desired round and other hand round). d-pnn can be trained only with small input-output data samples (likewise the gmdh polynomial neural network does) to learn any dependence [8]. 6-variable d-pnn can learn to identify (generalize) a changeable shape (e.g. triangle) regardless of its size or position in the input matrix (figure 9.). input vector of the dpnn is formed by x, y (row, column) coordinates of the 3 triangle apexes a, b, c. the dependence of points a, c is diagonal, a, b vertical and b, c horizontal. as there are simultaneously occurred 3 types of point relations, it is necessary to increase the number of blocks of d-pnn’s hidden layers. training data set can consist of following 5 data samples – right equal-based triangles : {6,44,11,44,11,49}, {22,13,32,13,32,23}, {10,30,25,30,25,45}, {3,20,23,20,23,40}, {25,50,50,50,50,75} testing random right triangles must keep the apexes a, b, c dependent to be correctly recognized by d-pnn. table 3 shows responses of trained network to dependent right triangles. table 4. applies only vertical deformations (+ and –) of right triangles in c apexes (fig.10. down), to be shown a transparent separating plane, detaching the relative triangles. fig. 9. dependent right equal-sided triangle shapes fig. 10. independent deformed right triangles in apexes a and c 1 2 3 4 5 6 etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 167-172 172 www.etasr.com zjavka: recognition of generalized patterns by a differential polynomial �eural �etwork table iii. responses to random input vectors with 6 dependent variables (right triangles) input vector (ax,ay bx,by cx,cy) output 34,44 60,44 60,70 1.0142 18,5 35,5 35,22 0.9692 15,39 35,39 35,59 0.9932 16,51 58,51 58,93 1.0095 29,51 45,51 45,67 1.0227 21,5 29,5 29,13 1.067 table iv. responses to random independent input vectors of 6 variables (deformed right triangles in c apexes) input vector (a b c) output input vector (a b c) output 13,36 42,36 33,65 0.8750 24,15 34,15 37,25 1.0713 21,27 59,27 47,65 0.8803 4,11 40,11 52,47 1.2376 9,10 34,10 26,35 0.8605 48,40 56,40 58,48 1.1255 12,43 25,43 21,56 0.9096 32,22 57,22 65,47 1.0885 35,10 57,10 50,32 0.9523 18,28 25,28 27,35 1.0558 2,12 28,12 20,38 0.9037 5,19 51,19 53,25 1.1906 6,43 42,43 30,79 0.8806 6,6 36,6 46,36 1.1850 16,35 48,35 38,67 0.8766 20,13 34,13 38,27 1.0477 13,48 16,48 15,51 0.9835 18,45 30,45 34,57 1.0857 10,8 49,8 36,47 0.9372 18,38 62,38 76,82 1.1325 v. discussion only linear dependencies of variables have been assumed for simplicity in the examples presented. if there is an occurrence of a non linear dependence of the input data, the square power exponent variables would extend combination polynomials of neurons and applied also as competent derivative terms (20). the denominators of (20)(21) result from the partial derivatives of the complete de term polynomials of numerators. the root square (or power) functions are likely not involved into fractions (21), if the differences of values of input variables are not too big (in case a real data model) as occurred in presented examples. ( ) ( ) 21 21 2 2 1 21522110 4 1 2 2 2 18 2 2172 2 16215 2 24 2 1322110 ),( xx xxf xxbxbxbb xxaxxaxxaxxaxaxaxaxaa y i ∂∂ ∂ = +++ ++++++++ = (20) 2 1 21 2 2 22210 215 2 24 2 1322110 ),( x xxf xbxbb xxaxaxaxaxaa y j ∂ ∂ = ++ +++++ = (21) according to (12)-(15) it is possible to define higher degree partial derivations of 2-variable compound function f(x,y)=f(u,v) (22) [6]. as the variables of the d-pnn’s inner functions u=φ(x1,y1) and ψ=(x2,y2) are different the 2 nd , 3rd and 5th terms of eq. (23) are = 0 (as the partial derivation of ψ by x1 is = 0). likewise the terms of (24) and (25) do [6]. )],(),,([),(),( yxyxfvufyxf ψϕ== u=φ(x, y) v=ψ(x, y) (22) 2 2 2 22 2 222 2 2 2 2 2 xv f xu f xv f xxvu f xu f x f ∂ ∂ ⋅ ∂ ∂ + ∂ ∂ ⋅ ∂ ∂ +      ∂ ∂ ∂ ∂ + ∂ ∂ ⋅ ∂ ∂ ∂∂ ∂ +      ∂ ∂ ∂ ∂ = ∂ ∂ ψϕψψϕϕ (23) 2 2 2 22 2 222 2 2 2 2 2 yv f yu f yv f yyvu f yu f y f ∂ ∂ ⋅ ∂ ∂ + ∂ ∂ ⋅ ∂ ∂ +      ∂ ∂ ∂ ∂ + ∂ ∂ ⋅ ∂ ∂ ∂∂ ∂ +      ∂ ∂ ∂ ∂ = ∂ ∂ ψϕψψϕϕ (24) yxv f yxu f yxv f yxyxvu f yxu f yx f ∂∂ ∂ ⋅ ∂ ∂ + ∂∂ ∂ ⋅ ∂ ∂ + ∂ ∂ ⋅ ∂ ∂ ⋅ ∂ ∂ +       ∂ ∂ ∂ ∂ + ∂ ∂ ∂ ∂ ∂∂ ∂ + ∂ ∂ ⋅ ∂ ∂ ⋅ ∂ ∂ = ∂∂ ∂ ψϕψψ ψϕϕψϕϕ 22 2 2 2 2 22 (25) a real data example might solve the weather forecast based on some trained data relations, which are used for calculating the next state of a system. let’s take several types of variables (e.g. pressure, damp, temperature) partly describing states of this very complex system. the input vector of the d-pnn is formed by values of these variables in defined matrix coordinates of a meteorological map. the training data set includes definite states of a time interval and desired network outputs. the output could mark the weather forecast as “rainfalls”= 1, “cloudy” = 2, “sunshine” = 3. there can naturally arise possible transient states (e.g. 1.4). the output is computed for 1 locality of the map and could also predict the atmospheric pressure or another quantity. vi. conclusion artificial neural networks in general respond to related patterns with a similar output. they identify input patterns on the bases of their relationship. likewise, the identification of unknown dependencies of the data variables could also be considered. this could be regarded as a pattern of abstraction, similar to that utilized by the human brain, which applies the approximation with time-delayed periodic activation functions of biological neurons in high dynamic system of behavior. dpnn is a new type of neural network, which performs identification based on any unknown generalized relations of input variables. d-pnn forms its functional output as a composition of differential equation terms (which describe a system of dependent variables) from rational integral functions. the problem of the multi-layered d-pnn construction reside creates every partial combination term for a complete de in utilizing some fixed low combination degrees (2, 3), while the amount of variables is as a rule higher. references [1] ľ. beňušková, neuron and brain. cognitive sciences, calligram bratislava, 2002 (in slovak). [2] a.g. ivakhnenko, “polynomial theory of complex systems”, ieee transactions on systems, vol. smc-1, no. 4, pp. 364-378, 1971. [3] j. hronec, differential equations ii., sav bratislava, 1958 (in slovak). [4] r. rychnovský, j. výborná, partial differential equations and some of their solutions, publ. sntl praha, 1970 (in czech). [5] j. kuneš, o. vavroch, v. franta, principles of modelling, sntl praha, 1989 (in czech). [6] i. kluvánek, l. mišík, m. švec, matematics i., ii., sntl bratislava, 1966 (in slovak). [7] s. das, a. abraham, a. konar, “particle swarm ptimization and differential evolution algorithms: technical snalysis, applications and hybridization perspectives”, computer and information science, vol. 38, pp. 1-38, 2008. [8] b. b. misra, s. dehuri, p.k. dash, g. panda, “a reduced and comprehensible polynomial neural network for classification”, pattern recognition letters, vol. 29, no. 12, pp. 1705-1715, 2008. [9] l. zjavka, “generalization of patterns by identification with polynomial neural network”, journal of electrical engineering, vol. 61, no. 2, pp. 120-124, 2010 [10] l. zjavka, “construction and adjustment of differential polynomial neural network”, journal of engineering and computer innovations, vol. 2, no. 3, pp. 40-50, 2011 microsoft word etasr_v11_n4_pp7336-7342 engineering, technology & applied science research vol. 11, no. 4, 2021, 7336-7342 7336 www.etasr.com zaher et al.: in-silico study of the developed hydroxychloroquine-based ace2 inhibitor molecules … in-silico study of the developed hydroxychloroquine-based ace2 inhibitor molecules against covid-19: molecular modeling and docking k. zaher laboratory of preparation modification and application of multiphase polymeric materials (lmpmp) university ferhat abbas setif-1 setif, algeria zaherkarma@gmail.com n. e. masango laboratory of preparation modification and application of multiphase polymeric materials (lmpmp) university ferhat abbas setif-1 setif, algeria nyarieellen@gmail.com w. sobhi laboratory of applied biochemistry faculty of nature and life sciences university ferhat abbas setif-1 and research center of biotechnology constantine, algeria sobhiwidad@gmail.com k. e. kanouni laboratory of preparation modification and application of multiphase polymeric materials (lmpmp) university ferhat abbas setif-1 setif, algeria khalilkanouni@hotmail.com a. semmeq national center for scientific research and laboratory of theoretical physics and chemistry university of lorraine nancy, france abderrahmane.semmeq@univ-lorraine.fr y. benguerba laboratory of preparation modification and application of multiphase polymeric materials (lmpmp) university ferhat abbas setif-1 algeria benguerbayacine@yahoo.fr abstract-in the present study, we will verify the action of hydroxychloroquine-based derivatives on ace2 which is considered to be the main portal of entry of the sars-cov-2 virus and constitutes an exciting target given its relative genetic stability compared to viral proteins. thus, 81 molecules derived from hydroxychloroquine by substitutions at 4 different positions were generated in-silico and then studied for their affinity for ace2 by molecular docking. only 4 molecules were retained because of their affinity and bioavailability demonstrated by molecular dynamics and molecular docking calculations using cosmotherm and materials studio software. keywords-hydroxychloroquine; molecular modeling; covid-19; ace2; affinity i. introduction covid-19 is caused by sars-cov-2 [1] which is one of the emerging respiratory viruses, including mers (middle east respiratory syndrome) and sars-cov (severe acute respiratory syndrome), which all belong to the same family of coronaviridae [2]. the most common symptoms include fever, dry cough, muscle fatigue, headache, and diarrhea in some cases. discovered in wuhan in china in december 2019, this disease quickly spread throughout the world [3]. a few months after the start of the pandemic, more than 2,500,000 people have already died, and more than 100 million have been infected. to date, there is no effective cure against covid-19 [4] and it is necessary to wait several months before the use of vaccines reaches a satisfactory level. during this time, the treatment of the disease relies on drugs to relieve the severe symptoms of the disease. to this end, more than 200 drugs have already been the subject of clinical trials, including hydroxychloroquine [5]. by targeting the sars-cov2 virus, it has been shown that chloroquine and several of its derivatives can bind to several viral proteins [6, 7]. besides, chloroquine and its derivatives can also bind to ace2 [8, 9]. the choice of this target is based on two main facts: the first is that ace2 is the main entry point for the virus and the second is because of its genetic stability corresponding author: k. e. kanouni engineering, technology & applied science research vol. 11, no. 4, 2021, 7336-7342 7337 www.etasr.com zaher et al.: in-silico study of the developed hydroxychloroquine-based ace2 inhibitor molecules … [10, 11]. chloroquine and hydroxychloroquine have been the subjects of several studies to explain their effect on the sarscov2 virus proteins [12, 13] such as nsp3, main protease, rna dependent polymerase, spike glycoprotein, adp-ribose-1 monophosphatase, and nsp9 replicase protein [6] these interactions, determined in silico, mean that chloroquine and its derivatives are potential active molecules against sars-cov2 [14, 15]. it appears -in many studiesthat hydroxychloroquine interacts with ace2 (pbd code: 6m18) [8]. we performed the present work to study, in silico, the effect of a series of hydroxychloroquine-derived molecules on ace2. thus, 81 molecules were obtained by substitution of hydroxychloroquine on 4 different positions. the study aims to estimate the affinity of the selected molecules for ace2, the prediction of their bioactivity, molecular docking, and their electronic properties by cosmo-rs using cosmotherm software (version 15.0). the second part of this work is focused on the selection of the preferred molecules according to their physicochemical properties calculated by molecular modeling and molecular docking method using materials studio software (version 17.1). ii. materials and methods the chemical properties of hydroxychloroquine were calculated using swissadme (table i). four positions, 4, 11, 12, and 13, were chosen to undergo modifications by substituting the original chemical groups with others (table ii). table i. hydroxychloroquine properties calculated by swissadme properties values molecular weight 335.9g/mol xlogp 3.6 hydrogen acceptors 4 hydrogen donors 2 rotative bonds 9 exact mass 335.17644g/mol mono-isotopic mass 335.17644g/mol tpsa (topological polar surface area) 48.4a2 heavy atoms 23 table ii. chemical groups selected to create new molecules. position original first modification second modification 4 – r1 h ch3 f 11 – r2 ch3 ch2oh cho (aldehyde) 12 – r3 ch2 ch-nh2 ch-ch3 13 – r4 ch2 -och2oh it should be noted that only these 4 positions leave the interaction between the candidate molecules with the receptor site relatively stable. these substitutions made it possible to generate 81 new molecules, which were subjected to the study of their affinity for ace2 by examining two essential parameters: ligand efficiency (le) and lipophilic ligand efficiency (lle). molinspiration chemoinformatics software carried out the prediction of the bioactivity of the selected molecules. this step allows classifying the molecules according to their capacity to bind to the protein. the study on the protein ace2-ligand complexes was investigated using seesar software. in the last step, we studied the electronic properties of these molecules by cosmo-rs software. iii. results and discussion a. construction of a series of inhibitor molecules from hydroxychloroquine after having done the modifications mentioned above, we managed to formulate 81 different molecules from hydroxychloroquine with the help of the seesar [16]. the main objective was to obtain a candidate molecule closer to hydroxychloroquine but increase the receptor ace2 (table iii). table iii. results explaining the fixation probability of each molecule with the receptor molecule r1 r2 r3 r4 fixation probability to the receptor site molecule_01 h ch3 ch2 ch2 yes molecule_02 h ch3 ch2 o yes molecule_03 h ch3 ch2 ch-oh yes molecule_04 h ch3 ch-nh2 ch2 yes molecule_05 h ch3 ch-nh2 o yes molecule_06 h ch3 ch-nh2 ch-oh yes molecule_07 h ch3 ch-ch3 ch2 yes molecule-08 h ch3 ch-ch3 o yes molecule_09 h ch3 ch-ch3 ch-oh yes molecule_10 h ch2-oh ch2 ch2 yes molecule_11 h ch2-oh ch2 o no molecule_12 h ch2-oh ch2 ch-oh no molecule_13 h ch2-oh ch-nh2 ch2 yes molecule_14 h ch2-oh ch-nh2 o yes molecule_15 h ch2-oh ch-nh2 ch-oh no molecule_16 h ch2-oh ch-ch3 ch2 yes molecule_17 h ch2-oh ch-ch3 o yes molecule_18 h ch2-oh ch-ch3 ch-oh yes molecule_19 h cho ch2 ch2 no molecule_20 h cho ch2 o no molecule_21 h cho ch2 ch-oh no molecule_22 h cho ch-nh2 ch2 no molecule_23 h cho ch-nh2 o no molecule_24 h cho ch-nh2 ch-oh no molecule_25 h cho ch-ch3 ch2 no molecule_26 h cho ch-ch3 o no molecule_27 h cho ch-ch3 ch-oh no molecule_28 ch3 ch3 ch2 ch2 no molecule_29 ch3 ch3 ch2 o no molecule_30 ch3 ch3 ch2 ch-oh no molecule_31 ch3 ch3 ch-nh2 ch2 no molecule_32 ch3 ch3 ch-nh2 o no molecule_33 ch3 ch3 ch-nh2 ch-oh no engineering, technology & applied science research vol. 11, no. 4, 2021, 7336-7342 7338 www.etasr.com zaher et al.: in-silico study of the developed hydroxychloroquine-based ace2 inhibitor molecules … molecule_34 ch3 ch3 ch-ch3 ch2 no molecule_35 ch3 ch3 ch-ch3 o no molecule_36 ch3 ch3 ch-ch3 ch-oh no molecule_37 ch3 ch2-oh ch2 ch2 no molecule_38 ch3 ch2-oh ch2 o no molecule_39 ch3 ch2-oh ch2 ch-oh no molecule_40 ch3 ch2-oh ch-nh2 ch2 yes molecule_41 ch3 ch2-oh ch-nh2 o no molecule_42 ch3 ch2-oh ch-nh2 ch-oh no molecule_43 ch3 ch2-oh ch-ch3 ch2 no molecule_44 ch3 ch2-oh ch-ch3 o no molecule_45 ch3 ch2-oh ch-ch3 ch-oh no molecule_46 ch3 cho ch2 ch2 no molecule_47 ch3 cho ch2 o no molecule_48 ch3 cho ch2 ch-oh no molecule_49 ch3 cho ch-nh2 ch2 no molecule_50 ch3 cho ch-nh2 o no molecule_51 ch3 cho ch-nh2 ch-oh no molecule_52 ch3 cho ch-ch3 ch2 no molecule_53 ch3 cho ch-ch3 o no molecule_54 ch3 cho ch-ch3 ch-oh no molecule_55 f ch3 ch2 ch2 no molecule_56 f ch3 ch2 o no molecule_57 f ch3 ch2 ch-oh no molecule_58 f ch3 ch-nh2 ch2 no molecule_59 f ch3 ch-nh2 o no molecule_60 f ch3 ch-nh2 ch-oh no molecule_61 f ch3 ch-ch3 ch2 no molecule_62 f ch3 ch-ch3 o no molecule_63 f ch3 ch-ch3 ch-oh no molecule_64 f ch2-oh ch2 ch2 no molecule_65 f ch2-oh ch2 o no molecule_66 f ch2-oh ch2 ch-oh no molecule_67 f ch2-oh ch-nh2 ch2 no molecule_68 f ch2-oh ch-nh2 o yes molecule_69 f ch2-oh ch-nh2 ch-oh no molecule_70 f ch2-oh ch-ch3 ch2 no molecule_71 f ch2-oh ch-ch3 o no molecule_72 f ch2-oh ch-ch3 ch-oh no molecule_73 f cho ch2 ch2 yes molecule_74 f cho ch2 o no molecule_75 f cho ch2 ch-oh no molecule_76 f cho ch-nh2 ch2 no molecule_77 f cho ch-nh2 o yes molecule_78 f cho ch-nh2 ch-oh no molecule_79 f cho ch-ch3 ch2 no molecule_80 f cho ch-ch3 o no molecule_81 f cho ch-ch3 ch-oh no b. affinity study parameters that explain in detail the affinity of each molecule for the receptor site include: le: refers to each atom's bond energy in a molecule toward the receptor. in other words, it refers to the ratio between ∆g (gibbs energy) and the number of atoms other than hydrogen in a molecule. if the le value is greater than 0.3, the molecule in question will have a greater probability of fixing itself to the receptor [17]. the corresponding mathematical equation is given by: le = (1.37×plc50)/ha (1) plc50 corresponds to the ligand concentration occupying 50% of the receptor, and ha represents the number of atoms other than hydrogen (heavy atoms). lle: refers to a parameter used in the conception of drugs that permits evaluating the potential energy of a chemical bond and its lipophilicity to deduce its drug-likeness [18]. for the ligand-receptor interaction to be favorable, the lle value should be greater than or equal to 5 [19]. the corresponding mathematical equation is given by: lle = plc50 – log (p) (2) every molecule was docked with the receptor ace2 model to show the possibility of forming a stable complex. from 81 molecules, it was found that only 19 were proved to interact with the specified target favorably. a drug's capacity to interact with a receptor is directly linked to its affinity for the receptor [20]. the estimated affinity for the 19 candidate molecules was calculated, and the results are shown in table iv. the results show that only 8 molecules are having a good affinity when compared with molecule_01 (hydroxychloroquine). table iv. estimated affinity values for the candidate molecules molecules estimated affinity (nm) molecules estimated affinity (nm) molecule_01 6202803 molecule_13 48012075 molecule_02 10178356 molecule_14 238783948 molecule_03 21861750 molecule_16 4668615 molecule_04 47841687 molecule_17 3998199 molecule_05 61083910 molecule_18 645211 molecule_06 7882945 molecule_40 454448307 molecule_07 4408448 molecule_68 477694848 molecule_08 4351693 molecule_73 5716436 molecule_09 720512 molecule_77 1016590889 molecule_10 2407812 c. bioactivity prediction the selected 8 molecules were examined in molinspiration chemoinformatics software to know the preferred binding protein of each molecule [21]. the results of the bioactivity prediction are summarized in table v. the symbol "xxxx" means that the molecule can interact with 4 types of protein, one of them being an enzyme inhibitor, the symbol "xxxxx" means that the molecule can interact with 5 types of protein, one of them being an enzyme inhibitor, and symbol "0" means that there is no particular interaction with any protein. only 4 molecules can have the same activity as hydroxychloroquine. table v. bioactivity prediction of the candidate molecules molecules predicted bioactivity molecule _01 0 molecule _07 xxxx molecule _08 0 molecule _09 xxxxx molecule _10 0 molecule _16 0 molecule _17 0 molecule _18 xxxxx molecule _73 xxxxx d. study on the protein-ligand complexes following the analysis of the candidate molecules by molinspiration, bioactivity results and the molecules' properties proved that only 4 of the 19 molecules had the desired engineering, technology & applied science research vol. 11, no. 4, 2021, 7336-7342 7339 www.etasr.com zaher et al.: in-silico study of the developed hydroxychloroquine-based ace2 inhibitor molecules … properties (had the estimated affinity closer to that of hydroxychloroquine). these are molecule_07, molecule_09, molecule_18, and molecule_73. figure 1 shows the candidate molecules in interaction with the receptor ace2 and energy values in kj/mol calculated from desolvation and interaction energies. seesar was used to study these complexes. each sphere represents atoms in the molecule, and each atom interacts differently with the atoms of the receptor (figure 1). (a) (b) (c) (d) (e) fig. 1. interaction of the 4 potential candidate molecules with the protein ace2. each sphere represents an atom, and the greater the sphere's size, the greater the interaction with the receptor site. when the sphere is colored green, this signifies that the contribution of this atom is favorable. on the contrary, the sphere colored in red characterizes the unfavorable atom's interaction contribution. if the sphere is not colored, the value of ∆g is null or close to zero. therefore, the contribution of the corresponding atom is negligible. blue color represents polar regions, while yellow color represents hydrophobic regions [22]. the following points describe the interpretation of the results obtained in figure 1. • molecule 01: the hydroxychloroquine molecule shows a low affinity with its receptor site. most of its atoms colored with green have a low ∆g values, and it has an unfavorable contribution formed by the n17 (2.7kj/mol) and c2 (2.3kj/mol). • molecule 07: atoms n17 and n3 are colored in red, with ∆g values of 9.3 and 1.6 kj/mol, respectively. therefore, the interaction with the receptor site is unfavorable. however, most of the atoms have negative ∆g values c19 (-5.7kj/mol), o46 (-5.2kj/mol), c18 (-3.7kj/mol), c41 (-3.1kj/mol), c10 (-2.9kj/mol), and cl6 (-1.9kj/mol), signifying that their interaction with the receptor site is favorable. • molecule 09: c21 is the only atom colored in red (∆g = 6.4kj/mol), corresponding to unfavorable interaction. atoms c47 (-3.7kj/mol), c2 (-3.6kj/mol), c19 (engineering, technology & applied science research vol. 11, no. 4, 2021, 7336-7342 7340 www.etasr.com zaher et al.: in-silico study of the developed hydroxychloroquine-based ace2 inhibitor molecules … 3.4kj/mol), and o44 (-3.1kj/mol), have negative ∆g values corresponding to favorable interactions with the ace2 protein model. • molecule 18: likewise, o37 has a positive ∆g value (2.3kj/mol), so as a result, its interaction with the receptor site is unfavorable. for the atoms c2 (-4.2kj/mol), c9 (-2.3kj/mol), c11 (-2.0kj/mol), cl6 (-1.8kj/mol), c19 (-1.6kj/mol), and c18 (-1.2kj/mol) the interaction with the receptor site is favorable. • molecule 73: for this molecule, n3 (7.0kj/mol) and c14 (5.8kj/mol) corresponding to unfavorable interaction. atoms c35 (-4.1kj/mol), c19 (-3.3kj/mol), c16 (-3.2kj/mol), c2 (-2.5kj/mol), c1 (-2.3kj/mol), and n12 (-2.3kj/mol) have favorable interactions with ace2. after this analysis, we can conclude that molecules 09 and 18 have the most significant probability to form a sufficiently stable complex with the receptor compared to the other molecules. however, for the other two molecules, the number of atoms with a favorable interaction with the receptor is very high compared to those having a non-favorable contribution, meaning that they also have sufficient capacity to interact with the receptor site. the second step of docking is performed using seesar software to determine the distances between the atoms of each candidate molecule with the amino acids of the protein receptor site (6m18). all the data are resumed in table vi. table vi. distances between atoms of candidate molecules with amino acids of the receptor site (6m18) molecules atoms amino acids distances (a°) molecule-01 h48 glu300 1.84 o47 trp530 2.01 molecule-07 h47 ser307 1.93 molecule-09 h45 glu300 1.94 h53 2.05 o44 asn527 1.96 o51 trp530 1.88 molecule-18 o37 trp530 2.01 h47 glu300 2.25 molecule-73 h33 glu300 1.95 • molecule 1 (hydroxychloroquine) forms 2 hydrogen bonds with the receptor site, the first is between h48 and glu300 with a short distance and the second is between o47 and trp530 with a moderate distance. • molecule 7 forms a single hydrogen bond with the receptor site, between h47 and ser307 with a moderate distance. • molecule 9 forms 2 hydrogen bonds with glu300, the first with h45 (short) and the second with h53 (moderate), asn-527 forms another hydrogen bond (moderate) with o44. the littlest interaction was created between o51 and trp530. • molecule 73 forms a single hydrogen bond with the receptor site between h33 and glu300 with a moderate distance. from these results, it can be concluded that molecule 9 will have the best interaction with the receptor site. e. prediction of electronic properties by cosmo-rs conductor-like screening model for real solvents (cosmo-rs) is a quantum chemistry method based on thermodynamics, which helps to determine chemical potentials for solutions [23]. this method can predict sigma charge densities as well as chemical potentials for each species in the solution. the calculation is done in two main steps: firstly, geometrical optimization on the molecule was done with the module dmol3 [24] of the software biovia material studio 2017 [25]. secondly, the obtained cosmo-files were used to calculate sigma profiles and sigma potentials with the cosmotherm software [26]. the sigma profile is divided into 3 distinct regions: • hbd region: hydrogen bond donor region: the sigma values are less than -0.01eå-2. the negative sigma values mean positive polarities [27]. • non-polar region: σ values are given in the interval -0.01eå-2 to +0.01eå-2 [28]. • hba region: hydrogen bond acceptor region: the σ values are greater than 0.01eå-2. positive sigma values represent negative polarities [29]. figure 2 shows that the highest picks for all the selected molecules are found in the non-polar region. they are showing the tremendous non-polar character of the molecule surfaces. that said, the 5 molecules have net peaks in the hbd and hba regions, making hydrogen bonds as acceptors and donors with the ace2. the selected molecules meet the criteria that a candidate-molecule must possess to interact with the protein target: hba, hbd, and hydrophobic sites [30]. fig. 2. electronic charge densities of the candidate molecules. molecule 01 (hydroxychloroquine) possesses a small hbd and hba region. molecule 07 shows a small hbd region and also some hba regions. in molecule 09, there are 3 regions capable of accepting hydrogen atoms and a small hydrogen donor region. molecule 18 possesses a large enough hydrogen donor region as well as a hydrogen bond acceptor region. a tiny region in molecule 73, almost negligible, can donate a hydrogen atom (colored in blue) while a more significant part, engineering, technology & applied science research vol. 11, no. 4, 2021, 7336-7342 7341 www.etasr.com zaher et al.: in-silico study of the developed hydroxychloroquine-based ace2 inhibitor molecules … colored in red, represents the hydrogen acceptor region; the most prominent picks in the range -0.01eå-2<σ<+0.01eå-2 are due to the non-polar chemical groups such as ch3, ch2, ch, which are more abundant in the molecules. negatively charged atoms such as oconstitute hydrogen acceptors (region hba) [31]. the positively charged atoms or atoms with lone pairs of electrons are responsible for the picks in the region hbd (nh, nh2, and nh3). figure 3 proves the results obtained from the sigma profiles and the energies of desolvation and interaction. all candidate molecules have strong affinities hbd and hba well balanced. this demonstrates that they have sufficient solubility in water and blood after administration [28]. fig. 3. sigma potentials of the four candidate molecules. iv. conclusion taking hydroxychloroquine as the primary molecule, we built 81 new derivative molecules, of which only 4 molecules had improved affinity for ace2. the modifications of the hydroxychloroquine structure at critical positions enhance properties such as affinity for the receptor site, solubility, and permeability and allow reconsidering the hydroxychloroquine derivative molecules for therapeutic use as a ligand for ace2. nevertheless, in-vitro and in-vivo studies will help confirm the results obtained in this study. acknowledgment the authors would like to express their gratitude and acknowledge the support of ferhat abbas setif-1 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[31] w. m. a. w. ahmad, r. a. a. rohim, y. norhayati, n. a. aleng, and z. ali, "developing a new dimension of an applied exponential model: application in biological sciences," engineering, technology & applied science research, vol. 8, no. 4, pp. 3130–3134, aug. 2018, https://doi.org/10.48084/etasr.2124. microsoft word 17-2742_s_etasr_v9_n3_pp4159-4164 engineering, technology & applied science research vol. 9, no. 3, 2019, 4159-4164 4159 www.etasr.com abdulmula et al.: power consumption modeling based on real-time data traffic for balancing power … power consumption modeling based on real-time data traffic for balancing power supply and energy demand to develop green telecommunication tower: a case study ahmed abdulmula solar energy research institute national university of malaysia bangi, malaysia abdulmula@yahoo.com kamaruzzaman sopian solar energy research institute national university of malaysia bangi, malaysia kospian@ukm.edu.my lim chin haw solar energy research institute national university of malaysia bangi, malaysia chinhaw.lim@ukm.edu.my abstract—green telecommunication tower primarily depends on renewable energy and energy efficiency technologies. this study presents a power consumption model to estimate the load demand of a telecommunication tower (tt) to improve energy efficiency. the method is based on field measurements of realtime data traffic load of the entire operated macrocell telecommunication tower to balance power supply and energy demand. this advanced method is investigated using homer pro simulation and compared with a widely accepted technique called overall peak load method for a chosen case study. the comparison simulation results showed that by using the power consumption model method, the energy-saving efficiency at the tt is improved by 24.19% and the size of the overall system is decreased by 33.33%. consequently, the annualized cost is reduced by 25.7%. this optimum performance contributes to the effective development of green telecommunication towers. keywords-green telecommunication tower; solar energy technology; energy consumption modeling; data traffic load i. introduction the diversity of services provided by the mobile telecommunications industry has led to a significant increase in the capacity of data traffic and has thus increased energy consumption and co2 emission [1]. increasing the number of subscribers leads to a significant increase in data traffic transfer [2]. tts serve as terminal links between the subscribers and the data center, so cellular network operators (cnos) constantly need building tts to increase coverage areas and data transfer capacity for improving the quality of services. three significant problems are considered by cnos when building tts. at first, the locations are carefully selected without any coverage holes or unnecessary overlap. then, given that tts consume around 60% of the total cost of network operating expenditures, increasing the cost of running the network, it is necessary to reduce energy consumption as much as possible. also, the provision of electricity to tts in off-grid sites is an issue. in the past, in off-grid sites, diesel generators (dgs) were widely used for powering tts. however, they have become less favorable because of their close relation to increased operating and maintenance costs and harmful effects on the environment [37]. the challenge for cnos is to provide the reliable power required to run tts in an off-grid site where the electrical energy is unavailable without resorting to costly and environmentally unfriendly power systems. renewable energy sources of enormous potential availability have been developed and used globally to reduce the economic cost and the impact to the environment [8-13]. the recent enhancements in solar energy technology solutions have made adopting advanced green technology of an off-grid solar power generation for energy-efficient tt the optimal viable solution to attain green tts. such concept reliably generates power without interruption, thereby eliminating dependence on dgs. this advanced green technology can reduce carbon emissions and operating expenses [14]. regarding the use of green technology, its energy efficiency must be improved because the sizing of green power generation for tts depends not only on geo-location and weather [15], but also on the dynamics of energy consumption of tt. therefore, the load demand must be accurately estimated to sustain a balance between electricity supply and energy demand. based on that, appropriately sizing an off-grid solar power generation system requires accurate knowledge of the tt electricity demand including calculating total daily energy consumption and the peak load. this study aims to develop the concept of an off-grid green solar power system for macrocell tt by proposing an efficient method of estimating the tt load profile with high accuracy. the method is based on modeling the power consumption through actual real-time data traffic measurements that reflect the interdependence between energy consumption of tt and its data traffic load. the critical contribution of this study is the proposal of a powerful energy management technology method for shifting the energy efficiency of tts in the off-grid site by ensuring the balance between supply power and energy demand. the benefit of applying this method is energy-saving efficiency, i.e. avoiding extra costs due to increased power consumption. the technique also minimizes the sizing of corresponding author: kamaruzzaman sopian engineering, technology & applied science research vol. 9, no. 3, 2019, 4159-4164 4160 www.etasr.com abdulmula et al.: power consumption modeling based on real-time data traffic for balancing power … power system generation and thus reduces the initial cost with optimized performance. to demonstrate the benefits of the proposed method, techno-economic analysis comparison is conducted using homer pro for the proposed power consumption model and overall peak load method for a chosen case study of the power generation system. the effect of the two qualified methods on sizing responses, initial cost, cash flow, and energy cost produced by the power system is investigated. to the best of the authors’ knowledge, this comparison has never been performed before. ii. literature review various previous studies on the sizing of off-grid power systems for tts have been conducted to increase costeffectiveness and reliability. in [5,16-19], authors used the overall peak load method to estimate the hourly load profile of tts, which depends on the determined peak load. however, the hourly load profile changes depending on the hourly data traffic load of the radio equipment. the reason is that a close interconnection exists between the data traffic transfer capacity of the radio equipment and its power consumption. in other words, the power consumption of any tt depends on the hourly data traffic load, which is affected by the activeness of subscribers in the use of smartphones during night and day [2024]. also, the sizing of power generation systems depends on the hourly load profile needs of the tt. accordingly, the specific estimated load demand is significant for designing green power systems of energy-saving efficiency and optimized performance. iii. research methodology a. energy consumption modeling tts consume the highest proportion of energy among other units of the cellular network [2]. to balance power supply and energy consumption of tt, the energy consumption of tt per hour of the day and every day of the year must be determined. moreover, knowledge about the energy consumption of the radio equipment of tt and the effect of the capacity of data traffic load on the hourly power consumption are needed. regarding power consumption, the radio equipment of macrocell tt consists of two component types, loadindependent and load-dependent components. loadindependent components include the microwave link, rectifier, and air conditioner. the power consumption of these components are constant and not affected by the capacity of data transfer. load-dependent components include the transceiver, digital signal processing, and power amplifier. the power consumption of these components strongly varies depending on the data traffic transfer. the hourly energy consumption of the tt is estimated by the sum of the energy consumption of these components. with the variation in the activity of subscribers in the use of smartphones, the capacity of data traffic load by tt varies continuously. it gradually increases during the day when subscribers are active and then progressively decreases during the night until the early hours of the morning when most subscribers are asleep, and the data traffic is lower. tt energy consumption is directly proportional to the capacity of data traffic load, which increases in the day and decreases at night. thus, the overall peak load must be considered in power consumption modeling for balancing power supply and energy demand. the power consumption in watt (w) of a macrocell tt can be determined by (1): ���(�) = ��� (�) + ∑ � �(�)� × �� (1) where pind is the sum of power consumption for the components that have load independent (const) (w), pdp is the power consumption of the components that have load dependent (depend on data traffic load) (w), fi is a load factor which reflects the efficiency of electrical energy usage, equal to the average load divided in peak load, (i=0…..0≤fi≥1). the values of fi are determined through actual measurements. ��� (�) = ƞ_� × �_� (�) + �_� (�) + �_��� (�) (2) � �(�) = ƞ��ƞ�������(�) + �����(�)� + ��� (�)!(3) where ƞ� is the number of sectors, ƞ�� is the number of transmitting antennas per sector, pr is the power consumption of rectifier (w), pl is the power consumption of microwave link (w), pair is the power consumption of air condition (w), pamp is the power consumption of power amplifier (w), ptrns is the power consumption of the transceiver (w), ppro is the power consumption of digital signal processing in (w). the power consumption of load-independent components and some parameters of long-term evolution (lte) macrocell tt for the considered technologies are summarized in table i [25]. the power consumption of the power amplifier, digital signal processing, and transceiver (load-dependent components) vary during the time depending on the change in the capacity of data traffic load of the tt. 1) measurement setup to determine the power consumption of the tt, actual realtime data traffic measurements were performed at an operating lte macrocell tt in bangi, selangor, malaysia (figure 1). the tt is owned by celcom bhd, which is the oldest and one of the largest cnos in malaysia with coverage of over 99% throughout malaysia and over 12 million mobile subscribers. the tt components were fed with a constant dc voltage of approximately 54v. using (4), the power consumption in watt in a specific time was determined by actual real-time measurements of the current i in ampere (a) at any time. the current i was measured using the pel 103 data logger and e3n current clamp over three consecutive months. figure 2 shows a photograph of the measurement setup. �(") = # × $(") (4) 2) measurements and modeling results from the actual measurements shown in figure 3 and after the value of 1.25 was added as a safety factor, the hourly power consumption for three months was collected, averaged, and modeled. the result of the average full-day power consumption is plotted in figure 4. the results illustrate that energy consumption continually changes: it increases during the day and gradually decreases at night. this result is due to the disparity in the rate of the use of smartphones by subscribers between day and night. this condition confirms the existence of a close relationship between the tt energy consumption and the capacity rate of data traffic transfer. when the capacity of engineering, technology & applied science research vol. 9, no. 3, 2019, 4159-4164 4161 www.etasr.com abdulmula et al.: power consumption modeling based on real-time data traffic for balancing power … data traffic increases, the power consumption of the tt also increases, and vice versa. the minimum power consumed is 1.0kw at 6:00 am, whereas the maximum power consumed is 1.233kw at 7:00 pm. the average total daily energy consumption is 27.29kwh/day. the considered estimation load demand model completely improves the tt efficiency and guarantees the balance between power supply and energy demand without any shortage or waste of electricity. fig. 1. photograph of the macrocell tt fig. 2. measurement setup table i. power consumption of load-independent components and characteristics for lte macrocell tt components and parameters value rectifier pr 100w microwave link pl 80w air condition pair not including (passive ventilation) number of sectors ƞs 3 number of transmitting antennas per sector ƞtx 1 b. a case study description and homer pro simulation full autonomy stand-alone high-efficiency heterojunction intrinsic thin (hit) film solar modules coupled with state-ofthe-art dual-axis maximum light detection (mld) solar tracking system with a battery bank were established using the homer pro software as a case study. additional details of the system are available in [26, 27]. it is a most advanced green technological power system that has been designed in malaysia through collaboration among solar energy research institute (seri), universiti kebangsaan malaysia (ukm), and celcom bhd mobile telecommunication company in green innovation park, ukm, bangi. figure 5 shows the tt load profile of the case study that was estimated by the overall peak load estimation method based on the peak load of 1.5kw. the system involves the following components: (i) hit panasonic photovoltaic cells made of mono-crystalline and amorphous silicon layers. (ii) dual-axis tracking system with mld controller. (iii) twenty-four units of battery bank of cl 2000, valve-regulated lead acid (vrla) battery storage system with a capacity of 2,000ah/2v for each battery. (iv) three units of solar controllers with maximum power point tracking (mppt) of 48 v/64a. fig. 3. screenshot of observation logging for three months of a change in amperage under real-time data traffic load fig. 4. a 24-hour tt energy consumption based on real-time data traffic fig. 5. load profile estimation of tt based on overall peak load estimation method a techno-economic analysis was performed using homer pro to compare the two methods and determine their effect on the power generation system (our case study). homer pro is powerful in simulation and optimization, and has been used in many studies. the software displays all simulation and optimization results in charts and tables for comparison and evaluation in technical and economic terms [28-31]. homer pro determines the optimal power system depending on various values of tt load profile, technical and economic parameters of components, and solar radiation and temperature of the site. the estimated specific load profile of tt, the conventional overall peak load estimation method and the proposed power consumption model based on real-time data traffic were used. engineering, technology & applied science research vol. 9, no. 3, 2019, 4159-4164 4162 www.etasr.com abdulmula et al.: power consumption modeling based on real-time data traffic for balancing power … figures 6, 7 show the results of the load profile calculation of both methods. the values represent the electric load needed by the tt each hour of the day throughout the year. the total daily energy consumption and the peak load for the power consumption model based on real-time data traffic (first method) and the overall peak load estimation method (second method) are 27.29kwh/day and 1.233kw and 36kwh/day and 1.5kw respectively. the data of solar radiation and temperature of the site were downloaded from the national renewable energy lab database and nasa surface meteorology and solar energy database (table ii). the details of the technical and financial parameters for the homer simulation setup are shown in table iii. table ii. monthly average of horizontal irradiance, clearness index, and temperature of the site month daily radiation (kwh/m 2 /day) clearness index daily temperature ( o c) january 5.332 0.546 25.360 february 6.003 0.590 25.900 march 5.878 0.562 26.090 april 5.664 0.548 26.108 may 5.182 0.523 26.240 june 5.274 0.549 25.860 july 5.223 0.538 25.500 august 5.350 0.530 25.650 september 5.403 0.522 25.730 october 5.455 0.535 25.910 november 5.109 0.521 25.760 december 5.215 0.546 25.360 table iii. technical and financial component parameters components parameters value spv installation type dual-axis solar tracking system with maximum light detection (mld) controller. module size 240w sizes considered (kw) 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 efficiency 95% derating factor 93% lifetime 25 years ground reflectance 25% initial capital cost $ 2000/kw replacement cost $ 1000/kw operation & maintenance $ 25 per year mppt initial capital cost $ 250/kw replacement cost 1, 2, 3, 4, 5, 6, 7kw considered lifetime 15 years battery bank number of batteries 24 nominal voltage 2v nominal capacity 2000ah initial capital cost $ 300 replacement cost $ 300 maintenance cost free lifetime 5 years iv. results and discussion after entering all required input data, the homer pro 3.8.3 software was run for the case study, firstly using the power consumption model based on real-time data (first method), then using the overall peak load estimation (second method). the homer pro searched to obtain the best optimal sizing in order to cover all power needs at the lowest of the total present cost (npc) of each system component including costs in $ of capital, replacement, operation, and maintenance throughout the life of the project. also, the minimum of the levelized cost of energy (lcoe) and characteristic of annual energy production was obtained. a. estimated optimal sizing (first method) figure 6 shows the schematic of the modeled system. the estimated total daily energy consumption and peak load for load profile are 27.29kwh/day and 1.233kw, respectively. the technical and financial parameters of the system components and the solar and temperature site resources are the same as presented in tables ii and iii. the obtained results of the homer pro optimization sizing of the system, showed in figure 7, comprise 8kwp of the solar pv array, 24 units of cl 2000, vrla, agm battery bank, and 4kw of mppt. the levelized cost of energy (lcoe) of the system and the total npc were 0.229$/kwh and $29,524.46 respectively. figure 8 shows the npc summary of components. the graphics represent the npc costs for the dual-axis pv solar tracking system, mppt, battery bank respectively, and the total value of the system which are respectively $16,025.86, $1,344.46, $12,154.19, and $29,524.46. fig. 6. system architecture of the adaptive first method fig. 7. screenshot of homer optimization result of using the first method fig. 8. summary of npc of the system components using the first method the result of optimization indicated that the annual output of energy production was 12,897kwh/yr with 4kw of mppt. this value is higher than the yearly load consumption of 9,960.85kwh/yr. the variables indicate that the amount of energy produced by solar pv panels covers all energy consumed with a slight increase of 18.3%, which can be engineering, technology & applied science research vol. 9, no. 3, 2019, 4159-4164 4163 www.etasr.com abdulmula et al.: power consumption modeling based on real-time data traffic for balancing power … considered a safety factor. this result is due to the balance between the production and consumption of power. thus, the system works very efficiently without any shortage or high increase in capacity. b. estimated optimal sizing (second method) figure 9 depicts the power system architecture using the second method. the total daily energy consumption and peak load of the macrocell tt by using this method are 36kwh/day and 1.5kw respectively. figure 10 shows the result of the optimization system configuration suggested by homer pro, that was 12kwp of the solar pv array, 24 units of cl 2000, vrla, agm battery bank, and 6kw of mppt. by using this method, the size of components increases compared to the first method, which also increases the cost of the overall system. consequently, the optimization results of total npc and lceo of the system are $39,730.36 and 0.234 $/kwh, respectively. figure 11 illustrates the npc values of components for the second method. the costs for the dual-axis pv solar tracking system, mppt, and battery bank are $24,039, $2,017, and $13,675, respectively. fig. 9. power system architecture using the second method fig. 10. screenshot of the optimization result of the system configuration using the second method fig. 11. summary of npc of the system components using the second method by using the overall peak load estimation method, the annual output of energy production was 19,345kwh/yr. this amount of energy is considerably more than the estimated consumption need of 13,131kwh/yr. thus, the excess electricity is 5,449kwh/yr, equal to 28.2% of the total annual energy production. this value is high and thereby causing a waste of energy and higher cost. c. comparison of the two methods the graph in figure 12 shows the comparison result of the total npc between the two methods. by using the first method, the saving values of npc for the dual-axis solar tracking system, battery bank, and mppt are $8,012.9 (33.33%), $1,520.81 (11.12%), and $672.3 (33.33%) respectively compared with the second method. thus, the saving value of npc for the entire system is $10,206 (25.68%). table iv presents the results of the variation in spv sizing, lcoe, and annualized costs of both methods. using the power consumption model based on real-time data traffic (first method), the spv sizing, mppt sizing, lcoe, and annualized cost decrease by 33.33%, 33.33%, 2.13%, and 25.7%, respectively compared with the second method. thus, the proposed method makes a realistic estimation of the load profile because of its size efficiency and reduces economic cost during the lifetime of the project. fig. 12. comparative result of the npc summary of both methods table iv. detailed comparative analysis results description first method second method savings decrease % load profile estimited 27.29kwh/d 36kwh/d 8.71kwh/d 24.19 spv component size 8kwp 12kwp 4kwp 33.33 mppt size 4kw 6kw 2kw 33.33 annualized cost $2,284 $3,073 $789 25.7 levelized cost of energy $0.229/kwh $0.234/kwh $0.005/kwh 2.13 moreover, the first method obtained an energy-saving efficiency of up to 8.71kwh/day, and significantly improves the efficiency of tt by up to 24.19% compared with the second method. this improvement in energy efficiency is due to the fact that the first method depends on the balance between power supply and energy demand, which causes no waste of energy, while the second method is based on supplying electricity equal to the peak load all the time. v. conclusion green tts in off-grid sites evolved rapidly over the past decade because of their utilization of advanced technologies of solar power and energy-efficiency solutions. this study proposed a critical method to estimate the tt’s load profile to develop the concept of green macrocell tt. the proposed power consumption method, based on real-time data traffic, achieves balance between power supply and energy consumption needs. the optimization findings confirm that the engineering, technology & applied science research vol. 9, no. 3, 2019, 4159-4164 4164 www.etasr.com abdulmula et al.: power consumption modeling based on real-time data traffic for balancing power … proposed method has energy-saving efficiency and avoids extra costs caused by excessive power supply. additionally, it minimizes the size of the system, which reduces the space required to install pv 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system for rural electrification in southern algeria”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3421–3426, 2018 engineering, technology & applied science research vol. 8, no. 4, 2018, 3126-3129 3126 www.etasr.com oghonyon et al.: a dilated trigonometrically equipped algorithm to compute periodic vibrations … a dilated trigonometrically equipped algorithm to compute periodic vibrations through block milne’s implementation j. g. oghonyon department of mathematics covenant university ota, nigeria godwin.oghonyon@ covenantuniversity.edu.ng s. a. bishop department of mathematics covenant university ota, nigeria sheila.bishop@ covenantuniversity.edu.ng k. s. eke department of mathematics covenant university ota, nigeria kanayo.eke@ covenantuniversity.edu.ng abstract—this paper intends to investigate the use of a dilated trigonometrically equipped algorithm to compute periodic vibrations in block milne’s implementation. the block-milne implementation is established by developing a block variablestep-size predictor-corrector method of adam’s family using a dilated trigonometrically equipped algorithm. the execution is carried out using a block variable-step-size predictor-corrector method. this system has significant advantages that include the varying step-size and finding out the convergence-criteria and error control. convergence-criteria and operational mode are discussed to showcase the accuracy and effectuality of the proposed approach. keywords-dilated trigonometrically equipped algorithm; block milne’s device; convergence-criteria; max errors; principal-local truncation-error nomenclature bmd: errors in bmd for computing test problems 1, 2 and 3. memployed: approach employed. maxerrors: the magnitude of the max errors of bmd. : convergence-criteria. tsdm: errors in tsdm (trigonometrically-fitted second derivative method) for numerical tested problem 1, [12]. bhmtb: errors in bhmtb (block hybrid method with trigonometric basis) for numerical tested problem 1 [10]. bht: errors in bht (block hybrid trigonometrically fitted of = 10 ) for numerical tested problem 1, 2 and 3 [13]. bhtrknm: errors in bhtrknm (block hybrid trigonometrically fitted runge-kutta-nystrom method of = 10 ) for numerical tested problem 1, 2 and 3 [14]. bhtfm: errors in bhtfm (block hybrid trigonometrically fitted method) for numerical tested problem 2 [11] i. introduction the dilated trigonometrically equipped algorithm is virtually among the utilitarian procedures which constitute block-milne’s implementation for approximating solutions of periodic vibrations. a trigonometrically equipped algorithm is more effective compared to non-fitted methods especially when the outcome exhibits periodical vibrations [1, 2]. the block milne’s implementation is of significant importance for documneting block variable-step-size predictor-corrector methods, convergence-criteria and check errors [3-6]. this composition aims at approximating the solution of periodic vibrations of class: [1, 6] 0 0 0 0 0 '' ( , ), ( ) , '( ) ' for υ [ , ] g f g g g g g x         (1) where : × → , is the dimension of the physical system. presuming f  r equals to the differentiability to sufficient degree on u [ , ] and meets a worldwide lipchitz precondition, i.e., ≥ 0 ∋ | ( , ) − ( , ̅| ≤ | − ̅|,∀ , ̅ ∈ . underneath this presumption, (1) ascertains the universal and singularity place as ∈ [ , ] which is similarly considered to meet the weierstrass theorem [6-9]. in particular, periodic vibrations often spring up in areas of scientific knowledge like newtonian mechanics, uranology, quantum theory, control theory, electric circuits and biological science. various approximation methods have been established. clear cut methods instituted on trigonometrically equipped algorithms may be realized [1, 10-18]. their execution is carried out while adopting fixed step-size strategies [1, 10-22]. the motive governing a trigonometrically equipped algorithm is inherent in the fact that if the frequency is acknowledged in advance, this method turns more beneficial compared to the multinomial established methods [1, 10-18]. in addition, a block milne’s implementation is primarily employed for changing step-size, fixing convergence-criteria and check ciphered errors [3-6, 23-26]. the main target of this paper is to implement a dilated trigonometrically equipped algorithm for ciphering periodic vibrations where the frequency of the outcome is anticipated in advance. this approach possesses advantages like varying step-size, deciding the convergence criteria and error control [7-8, 24-25, 27-29]. the dilated trigonometrically equipped algorithm has extra advantages which includes reduced computation costs and engineering, technology & applied science research vol. 8, no. 4, 2018, 3126-3129 3127 www.etasr.com oghonyon et al.: a dilated trigonometrically equipped algorithm to compute periodic vibrations … improved accuracy. milne’s implementation is examined as a broad prospect of the predictor-corrector method on account of the computational benefits. this approach employs components like adams type class, block predictor-corrector pair of similar order and principal local truncation errors as mentioned in [7-8, 24-25, 27-29]. definition 1: − , − stage ℎ . whenever k refers to block size and h as pace size, then block size in time is ℎ. let = 0,1,2,… form the block number and let = , then the − , − method can be composed in the next class: = ∑ + ℎ∑ . (2) for = [ ,…, ,…, ] , = [ ,…, ,…, ] and are × constants matrices [6, 17, 30]. hence, taking off from the over account, a block method has computational benefits. for each practical real-life program, the terminate product is assessed to a greater extent at the same time. utilizing these methods can permit faster outcomes of the problem which can be handled to generate the sought after accuracy [10-12, 16-17]. ii. methods block-milne’s device is a combination of adams-bashforth − (predictor) method and adams-moulton − 1 − (corrector) method of the same order. this combination can be of the form: ( ) = ∑ + ℎ ∑ ( ) , (3) ( ) = ∑ + ℎ ∑ ∗( ) . (4) equations (3) and (4) represent the adams family of block milne’s device with = ℎ , ( ), = 0,1,2 comprising invariants that depend on the varying step-size and frequency. observing that is the numeric approximate of the analytical results ( ) i.e. ( ) ≈ , and ≈( , ) owning = 0,1,2. to arrive at (3) and (4), the trigonometrically fitted method is written as the dilated trigonometrically equipped algorithm in which runs by looking forward to approximate the analytical result ( ) on distinct time intervals of , through with the interpolating subprogram of (5): ( ) =∝ +∝ +∝ +∝ sin( ) +∝ cos ( ) (5) revising (4) produces the dilated trigonometrically equipped algorithm as: ( ) =∝ +∝ −ℎ +∝ −ℎ +∝ w υ −h − w6 υ −h + ∝ 1 − + , (6) where ∝ ,∝ ,∝ ,∝ and ∝ are invariants needed to be determineδ in a especial direction. presume the precondition that (6) matches with the accuracy output at definite length of time , to get the approximant of (7): ( ) ≈ , ( ) ≈ . (7) demanding that the interpolating function (6) conforms to (1) at the levels , = 0,1,2 we get the next approximates as ( ) ≈ , ( ) ≈ , = 0,1,2 (8) linking (7) and (8) will lead to a fivefold system of equations which gives birth to av=d. computing the systems of equation adopting mathematica 9 kernel 64 to obtain , = 0,1,2,3,4 and subbing the measures of ′ into (6) will yield the continuous block milne’s device. assessing the continuous block milne’s device at some preferred points of , = 1,2,3 will invent the milne’s device as ( ) = + + ℎ ( ( , ) + ( , ) + ( , ) ) (9) where is the frequency, and ( , ), ( , ), and ( , ) are uninterrupted invariants [5, 10-14]. a. forming convergence criteria for block milne’s device in launching operation of block-milne’s device, adamsbashforth − and adams-moulton − 1 − approaches are employed in a predictor-corrector approach [36, 23-25]. mixed block-milne’s device proves the feasibleness to determine principal-local-truncation-error in predictorcorrector approach in absence of finding higher differential coefficient, ( ). taking for granted that = , where and showcase the order of the predictor and corrector. right now, in approach of order , the investigation of the block-adamsbashforth − brings forth principal-local-truncation errors. ̅[ ] ℎ ( )( ̅ ) = ( ) − [ ] + (ℎ ), [ ] ℎ ( )( ) = ( ) − [ ] + (ℎ ) (10) [ ] ℎ ( )( ) = ( ) − [ ] + (ℎ ). a corresponding break down of block-adams-moulton − 1 − brings about principal-local-truncation-errors: [ ] ℎ ( )( ̅ ) = ( ) − [ ] + (ℎ ), [ ] ℎ ( )( ̅ ) = ( ) − [ ] + (ℎ ) (11) [ ] ℎ ( )( ̅ ) = ( ) − [ ] + (ℎ ), where [ ] , [ ] , [ ] , [ ] , [ ] and [ ] are existing as independent entities of the step-size h and ( ) behaves as the result to the differential coefficient fulfiliing the initial consideration ( ) ≈ [3-6, 23-25]. to move ahead, the precondition for small assesses of h is reached as ( )( ) ≈( )( ̅ ), and the dominance of block-milne’s device banks right away on this condition. further simplification of the principal local truncation errors of (10) and (11) while neglecting terms of (ℎ ) order, makes it easy to achieve computation of principallocal-truncation-errors of blockmilne’s device as: [ ] ℎ ( )( ̅ ) ≈ [ ][ ] [ ] [ ] − [ ] < , [ ] ℎ ( )( ̅ ) ≈ [ ][ ] [ ] [ ] − [ ] < , (12) engineering, technology & applied science research vol. 8, no. 4, 2018, 3126-3129 3128 www.etasr.com oghonyon et al.: a dilated trigonometrically equipped algorithm to compute periodic vibrations … [ ] ℎ ( )( ̅ ) ≈ [ ][ ] [ ] [ ] − [ ] < . mentioning the affirmations that [ ] ≠ [ ], [ ] ≠ [ ] and [ ] ≠ [ ] are the predicted and corrected approximates which are given by the block milne’s device of order p, while [ ] ℎ ( )( ̅ ), = 1,2,3 are the principal-localtruncation-errors. , and are the boundaries of the convergence-criteria of block-milne’s device. moreover, the estimates of the principal local truncation error (12) ar utilized to determine whether to go for the results of the current step or to reconstruct the step with a slighter variable-step-size. the step is established on a trial run as defined by (12) [3-6, 23-25]. the principal-local-truncation-error (12) is the convergencecriteria of block-milne’s, device distinctly seen as blockmilne’s device (estimate) for conforming to convergence. iii. numerical examples three selected numerical test problems were viewed and solved utilizing the proposed approach (denoted as bmd in this paper) at different convergence criteria of 10 , 10 , 10 , 10 and 10 [10-14]. programming codes on block milne’s are compiled employing mathematica 9 kernel 64. these codes are executed in a block by block mode together with the block milne’s device. numerical test problem 1. consider the inhomogeneous ivp: ( ) = −100y + 99sin ( ) , (0) = 1 , (0) = 11 , 0 ≤ ≤ 1000. solution: ( ) = cos(10 ) + sin(10 ) + sin ( ) numerical test problem 2. consider the nonlinear duffing equation: + + = (ω ), (0) = , (0) = 0. solution: ( ) = cos(ω ) + cos(3ω ) + cos(5ω ) +cos (7ω ) where ω=1.0, β=2x10-3, c0=0.200426728069, c1=0.20017947753, c2=0.246946143x10-3, c3=0.304016x10-6, c4=0.374x10-9. choose w=1.01 numerical test problem 3. consider the harmonic oscillator with frequency ω and small perturbation . + + ω = 0, (0) = 0, (0) = − , 0 ≤ ≤ 1000. solution: ( ) = ω − , where ω = 1 and = 10 . iv. results the numerical results of the implementation of the dilated trigonometrically equipped algorithm on block milne’s device for ciphering periodic vibrations are exhibited in table i. table i. milne’s implementation memployed maxerrors ccriteria tsdm 1.7e-03 10-3 bhtfm 1.2e-03 bht 1.9e-03 bhtrkknm 2.14e-03 bmd 9.15202e-04 10-3 bmd 2.79178e-04 bmd 1.83035e-04 tsdm 2.7e-05 10-5 bhtfm 1.4e-05 bhmtb 3.9e-05 bhtrkknm 5.98e-05 bhtrkknm 2.06e-05 bmd 1.05006e-07 10-5 bmd 3.75372e-08 bmd 3.34795e-06 tsdm 1.0e-07 10-7 bhtfm 1.5e-07 bhmtb 1.4e-07 bmd 1.05933e-10 10-7 bmd 3.76048e-11 bmd 3.4074e-09 tsdm 6.3e-09 10-9 bhtfm 8.7e-09 bhtfm 1.1e-09 bhtrkknm 4.67e-09 bmd 1.07025e-13 10-9 bmd 3.9968e-14 bmd 3.40017e-12 bht 9.7e-11 10-11 bht 6.7e-11 bmd 4.88498e-15 10-11 bmd 1.04361e-14 bmd 3.57492e-14 bht 4.3e-13 10-13 bmd 1.9984e-15 10-13 bmd 5.10703e-15 bmd 2.39808e-14 tsdm 3.3e-03 10-3 bhtfm 1.3e-03 bmd 3.60282e-06 10-3 bmd 7.81099e-06 bmd 1.31395e-04 tsdm 6.4e-05 10-5 bhtfm 5.6e-05 bht 7.7e-05 bhtrkknm 7.52e-05 bmd 3.11695e-10 10-5 bmd 7.32379e-10 bmd 1.20413e-08 tsdm 1.0e-07 10-7 bhtfm 1.4e-07 bhtrkknm 1.34e-07 bmd 3.14471e-14 10-7 bmd 7.38853e-14 bmd 1.20062e-12 bhtrkknm 8.11e-09 10-9 bmd 1.38778e-16 10-9 bmd 3.60822e-16 bmd 1.66533e-15 bht 1.23e-11 10-11 bhtrkknm 7.13e-11 bmd 4.06231e-13 10-11 bmd 9.65783e-13 bmd 4.14513e-12 engineering, technology & applied science research vol. 8, no. 4, 2018, 3126-3129 3129 www.etasr.com oghonyon et al.: a dilated trigonometrically equipped algorithm to compute periodic vibrations … v. conclusion computed results demonstrated that the bmd is attained with the aid of the convergence-criteria. these convergence criteria decide whether the result is accepted or the algorithm is repeated. the results also establish that the performance of the bmd allows improved maximum errors compared with the tsdm, bhmtm, bht, bhtrknm and bhtfm at all examined convergence criteria of 10 , 10 , 10 , 10 , 10 and 10 [10-14]. thus, it can be concluded that the devised method is suitable for working out periodic vibrations dealing with non-stiff and stiff odes. bmd performs better when compared to the existing methods for reasons pointed out above. further work will deal with carrying out the block milne’s device on dilated exponentially fitted algorithm. acknowledgment authors would like to thank the covenant university for providing the financial backing throughout the study time period. references [1] r. d’ambrosio, e. esposito, b. paternoster, “exponentially fitted twostep hybrid methods for y = f(x,y)”, journal of computational and applied mathematics, vol. 235, no. 16, pp. 4888-4897, 2011 [2] h. ramos, j. vigo-aguiar, “on the frequency choice in trigonometrically fitted methods”, applied mathematics letters, vol. 23, no. 11, pp. 1378-1381, 2010 [3] u. m. ascher, l. r. petzold, computer methods for ordinary differential equations and differential algebraic equations, siam, philadelphia, 1998 [4] j. r. dormand, numerical methods for differential equations, crc press, 1996 [5] j. d. faires, r. l. burden, initial-value problems for odes, dublin city university, 2012 [6] j. d. lambert, computational methods in mordinary differential equations, john wiley and sons, 1973 [7] e. hairer, g. wanner, solving ordinary differential equations ii, springer, 1996 [8] m. k. jain, s. r. k. iyengar, r. k. jain, numerical methods for scientific and engineering computation, new age international, 2003 [9] l. xie, h. tian, “continuous parallel block methods and their applications”, applied mathematics and computation, vol. 241, pp. 356370, 2014 [10] f. f. ngwane, s. n. jator, “block hybrid method using trigonometric basis for initial value problems with oscillating solutions”, numerical algorithms, vol. 63, no. 4, pp. 713-725, 2013 [11] f. f. ngwane, s. n. jator, “solving oscillatory problems using a block hybrid trigonometrically fitted method with two off-step points. electronic journal of differential equations”, 9th conference on differential equations and computational simulations, vol. 20, pp. 119132, 2013 [12] f. f. ngwane, s. n. jator, “trigonometrically-fitted second derivative method for oscillatory problems”, springer plus, vol. 3, no. 1, 2014 [13] f. f. ngwane, s. n. jator, “solving the telegraph and oscillatory differential equations by a block hybrid trigonometrically fitted algorithm”, international journal of differential equations, vol. 2015, article id 347864, 2015 [14] f. f. ngwane, s. n. jator, “a trigonometrically fitted block method for solving oscillatory second-order initial value problems and hamiltonian systems”, 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implementation on block predictor-corrector methods”, journal of applied sciences, vol. 16, no. 5, pp. 236-241, 2016 [25] j. g. oghonyon, s. a. okunuga, s. a. bishop, “a variable-step-size block predictor-corrector method for odes”, asian journal of applied sciences, vol. 10, pp. 96-101, 2017 [26] z. b. ibrahim, k. i. othman, m. suleiman, “variable step block backward differentiation formula for solving first-order stiff odes”, proceedings of the world congress on engineering, london, u.k, vol. 2, pp. 2-6, july 2-4, 2007 [27] z. b. ibrahim, k. i. othman, m. suleiman, “implicit r-point block backward differentiation formula for solving first-order stiff odes”, applied mathematics and computation, vol. 186, no. 1, pp. 558-565, 2007 [28] z. a. majid, m. suleiman, “parallel direct integration variable step block method for solving large system of higher order odes”, international journal of mathematical and computational sciences, vol. 2, no. 4, pp. 269-273, 2008 [29] s. mehrkanoon, z. a. majid, m. suleiman, “a variable step implicit block multistep method for solving first-order odes”, journal of computational and applied mathematics, vol. 233, no. 9, pp. 23872394, 2010 [30] z. a. majid, m. b. suleiman, “implementation of four-point fully implicit block method for solving ordinary differential equations”, applied mathematics and computation, vol. 184, no. 2, pp. 514-522, 2007 engineering, technology & applied science research vol. 8, no. 4, 2018, 3103-3107 3103 www.etasr.com odedairo & nwabuokie: framework for operational performance measurements in small and medium… framework for operational performance measurements in small and medium scale industries using discrete event simulation approach babatunde omoniyi odedairo department of industrial and production engineering university of ibadan ibadan, nigeria bo.odedairo@ui.edu.ng nnamdi nwabuokie department of industrial and production engineering university of ibadan ibadan, nigeria valiantnnamdi@yahoo.ca abstract—globally, production systems must cope with limitations arising from variabilities and complexities due to globalization and technological advancements. to survive in spite of these challenges, critical process measures need to be closely monitored to ensure improved system performance. for production managers, the availability of accurate measurements which depict the status of production activities in real time is desired. this study is designed to develop an operational data decision support tool (odata-dst) using discrete event simulation approach. the work-in-process and processing time of each workstation/buffer station in a bottled water production system were investigated. the status of each job as they move through the system was used to simulate a routing matrix. the production output data for 50cl and 75cl product from 2014-2016 were collected. a mathematical model for routing jobs from the point of arrival to the point of departure was developed using discrete event simulation. a graphical user interface (gui) was designed based on the factory’s performance measurement algorithm. simulating the factory’s work-in-process with respect to internal benchmarks yielded a cycle time of 4.4, 6.23, 5.04 and throughput of 0.645, 0.455, 0.637 for best case scenario, worst case scenario and practical worst case scenario respectively. the factory performed below the simulated benchmark at 26%, 28%, 28% for the 50cl and at 51%, 54%, 59% for 75cl regarding the year 2014, 2015 and 2017 respectively. performance measurement decision support tool has been developed to enhance the production manager’s decision making capability. the tool can improve production data analysis and performance predictions. keywords-performance measures; production system; discrete event simulation;decision support system i. introduction the need for continuous performance improvement in a production system despite the complexities arising from market fluctuations will continue to drive the desire for innovative research. performance measurement, a sub-division of performance evaluation involves the selection of appropriate quantitative measures to aid decision making in a system. these measures are vital input into any decision support tools (dst) [1, 2]. also, such measures are required to assist executives at different decision levels. ultimately, these decisions will contribute to the actualization of the strategic goals of the organization [3-7]. authors in [8] classified performance measures into: (1) measure focus, and (2) measure tense. the former comprises of financial (monetary) and operational (non-monetary) data, while measure tense entails studying the past to improve the present. diverse studies have been carried out on how to measure system performance using dst [6, 9-11]. this is necessary as the profitability, productivity, and survivability of any production system largely depend on the quality of the decisions obtained from such tools. dst in a production system can be deployed at operational, tactical and strategic levels. however, due to the ambiguities associated with most decision processes, the need to smoothen the complexities associated with choosing the best alternative cannot be ignored [12]. decision support tools relevant to the production system include the following: (1) thermodynamics and exergy analysis, (2) optimization, and (3) simulation [13-16]. on simulation, the aim is to imitate real-world process over time [17, 18]. also, in a simulation model, discrete mathematics can be employed in which events of various kinds are kept and governed in a queue for each object [19]. discrete event simulation (des) considers state changes at discrete points (points which an event occurs). it can be used to answer “what if” scenarios, diagnose the occurrence of certain phenomena and enhance system development over time [12, 17, 20-22]. despite the increase in the research work on using des as a dst, empirical studies have shown that it is minimally used in production systems [1, 12, 23-25]. in nigeria, one of several challenges limiting the performance of small and medium scale enterprises (smes) involved in production process is the lack of access to proprietary dst [7, 26, 27]. based on this reality, in this study the objective is to develop an operational data dst (odatadst) for a bottled water factory using des analytical approach. the rest of this paper is structured as follows: a brief discussion on dst and des is the focus of section ii. in section iii, odata-dst was developed using an illustrative example. results from the example and conclusion are the focus of sections iv and v respectively. pec lim loa bot qu pro im a ind exa mo inc ava lin vag dec ma (2) mo ma pro (2) pre ma di sim per to set ins res dis pro bas aut for aut sys opt eff per op beh a. pla pro ii. fol dis pro bec eve engineerin www.etasr in [18] auth culiar to most mited to, the fo ad resources, ttlenecks and euing and del ocess and (7 mprove efficien performance dustries usin amination. au odel to measur creasing comp ailable to org nguistic variab gueness and u cision making aking process ) documentatio odels are used any problems. ocesses in mo ) state estim ediction, (6) athematical im screte event mulation meth rformance of abstract the dy t of discrete stants of time sources and is screpancies in oduction syste sed real-time tomation syste r planning, pr thors utilized stem design. timization to ficiency indust the mathem rformance me erational perf havior of the p descriptive p the flow pro ant is describ oduction line the worksta llowing the screte event oduction line cause their ac ent, there is a ng, technology r.com ii. relat hors suggeste t production sy ollowing: (1) , (2) labor d choke poin lays caused by ) scheduling ncy of the supp measurement ng data ca uthor in [10] d re business pe plexity and h ganizations. h bles have the uncertainty nat g. authors in [ is driven by th on, (3) knowle d to demystify . authors in odeling as: (1) mation, (3) m hypothesis mage to a pro simulation hod universa a production ynamic and sto sequence of e [30]. also s useful in sol simulated env ems, authors decision ma em. authors i roduction and d des for c author in o improve d try. iii. me matical model p easurement wa formance mea production line problem defin ocess of a sma bed in figure with 9 workst ations are arr same process simulation will be limi ctivities are d change in the y & applied sci odedairo & n ted literatu ed some perf ystems, these throughput un and machin nts, (4) staff y material han effectiveness ply chain, auth t system for ategorization, developed a fu erformance as eterogeneous he concluded t ability to dea ture of produc [13] comment he following: edge and (4) m y the complex [28, 29] iden ) data assessm monitoring, ( generation, oblem, and (8 (des) mode ally suitable system. the m ochastic behav events by co , des dema lving statistica vironments. o in [31] deve aking tool fo in [32] presen d scheduling customer driv [19] combine decision supp ethodology proposed in [3 as adopted. in asures required e are defined. nition all scaled bottle e 1. the pro tations (a1-a ranged in ser sing sequence framework, t ited to works discrete events e state of the p ience research nwabuokie: fr ure formance mea include, but a nder mean and ne utilization f requirements ndling, (6) wo s. on the ne hor in [11] des r thai autom clustering, uzzy data ware a result of the nature of the that fuzzy set al with imprec ction data for ted that the de (1) communic model develop xity associated ntified some o ment and redu (4) diagnosis (7) creatio 8) decision ma el is a com for modeling method can be vior of a system onsidering eve ands less com al uncertaintie n the use of d eloped a simu or a manufac nted the use of decisions. in ven manufac ed simulation ort in an e 34, 35] on fac table i, the v d to understan ed water produ ocess consists a9) defined in ries with eac e. in design the study o stations a2 t s. for each di product as it m h v ramework for o asures are not d peak n, (3) s, (5) ork in eed to signed motive and ehouse e evere data ts and cision, better ecision cation, pment. d with of the uction, s, (5) on of aking. mputer g the e used m as a ent in mputer es and des in ulation cturing f des [33], cturing n and energy ctory’s arious nd the uction of a table ch job ing a of the to a9 iscrete moves from pro wor in f b.        t c. foll  vol. 8, no. 4, 20 operational perf m one workst oduct. each w rkstation. job figure 2. fig. 1. p model assum the bottled w finished good the cycle ti throughput tim been empty o processing ti varies from on buffer capaci the product exponential d blockage of a buffers are be the factory downtimes, n constantly in notation wip ct ctbest tapprox capprox. th ctworst pr w0 thbest ma n w to t thworst mathematica to model o lowing measur cycle time case 1: when 018, 3103-3107 rformance mea tation to anot workstation (a routing of the plant layout of the mptions water factory ds buffers. ime of the m me varies with r saturated). me in each w ne workstation ity between su tion line is distribution fail a station occu eyond its capac production no loss in pro operation. table i. w cycle tim time for a job to c cycle time criti aximum throughp n leve r ave throughput for l model odata-dst res were adopt n the productio 7 asurements in s ther until it b a2-a9) has e production s e bottled water pro is a serial pr machines is c h respect to it workstation is n to the other. uccessive work reliable with lure rate. urs if the jobs city. line model oduction due basic notation definition work–in–process cycle time me at best case per o go through an u capacity of the lin throughput for worst case pe production rate ical work–in–pro ut at best–case pe number of station el of work–in–pro raw process time erage processing t worst case perfor bottleneck rate t using des ted. on line is relati 3104 small and medi becomes a fin at least one system is pres oduction plant. roduction line constant while ts state (in term s deterministic k stations is fin h a steady at the downst has no ma to waste and ns s formance uncongested line ne erformance cess erformance scenar s ocess e time rmance scenario s framework, ively empty ium… nished subented with e the ms of c but nite. state tream chine d it is rio , the engineering, technology & applied science research vol. 8, no. 4, 2018, 3103-3107 3105 www.etasr.com odedairo & nwabuokie: framework for operational performance measurements in small and medium… = (1) case 2: when the production line is saturated = . , . (2)  machine capacity . = (3)  throughput = ∗ (4)  work-in-process (from little’s law) = × (5)  bottleneck rate = (6)  average time at a station = (7) table ii. plant naming convention conventions name description a1 belt conveyor belt conveyor a2 buffer station 1 buffer station 1 a3 workstation 1 automatic rinsing machine a4 buffer station 2 buffer station 2 a5 workstation 2 automatic filling machine a6 buffer station 3 buffer station 3 a7 workstation 3 automatic capping machine a8 buffer station 4 buffer station 4 a9 workstation 4 automatic packaging machine a10 warehouse warehouse d. odata-dst graphic user interface the computer implementation of odata-dst was achieved using visual basic application (vba) integrated development environment. the following motivated the use of vba: (1) compatibility, (2) availability across multiple platforms, (3) interactive nature, and (4) ease of numerical programming. a screenshot of odata is shown in figure 3. e. best-case scenario, worst-case scenario and pratical worstcase scenario of the production line analyzing the production line based on the best-case scenario, worst-case scenario and practical worst-case scenario is essential. these parameters are required to measure performance, determine the possible behavior, and areas requiring improvement at any time period. 1) best-case performance (bcp) this can be classified into minimum cycle time and maximum throughput. minimum cycle time for a given wip level (w) is given by: = ≤ _0 ℎ (8) maximum throughput for a wip level given by : = ≤ ℎ (9) start arrival and movement to workstation 1 workstation 1 idle buffer 2 process job in workstation 1 buffer next workstation no yes yes yes no yes yes fig. 2. flow chart of job routing. 2) worst-case performance (wcp) this involves the maximum cycle time and minimum throughput possible for a line with bottleneck rate and raw process time ( ). equation (10) is the worst-case cycle time for a given wip level w. = (10) equations (11)-(13) are the worst-case throughput for a given wip level w. = (11) = 1 + (12) = + (13) applying little’s law, the corresponding throughput will be: = (14) = (15) 3) practical worst-case (pwc) equation (16) is the cycle time for a pwc. = + (16) bot req tim 2.2 pro bes rel fo out no out rel and engineerin www.etasr the pwc thr= the results a ttleneck of 0 quired to achi me of 2.2 minu 2 minutes. th ocess time, as st-case, worst lation to cycle or 50cl bottled tput were 16 ovember respe tputs were 28 lationships bet d 75cl are show station nu buffer workstat buffer workstat buffer workstat buffer work sta av w (bottles) 10 20 30 40 60 70 ng, technology r.com roughput for a fig. 3. oda iv. are presented i 0.645jobs/minu ieve maximum utes is 1.419 c his is lower th proposed in [ t-case and pr e time and thro d water produ 6% and 40% ectively. for th % and 83% in tween work-in wn in figures umber numb r 1 tion 1 r 2 tion 2 r 3 tion 3 r 4 tion 4 verage processin bottleneck w (cartons) 0.8 1.7 2.5 3.3 5.0 5.8 y & applied sci odedairo & n a given wip le ata – dst scree results in table iii. w ute, the critic m throughput artons. the ra han the sum o 34]. the relati ractical worst oughput is pre uction, minim % and occurr he 75cl, minim n july and ma n-process and 4 and 5 respe ber of machines 4 4 4 4 4 3 4 1 ng time best c ctbest (mins 2.2 2.6 3.9 5.2 7.8 9.0 ience research nwabuokie: fr evel is given by (17 en workstation 4 cal work-in-pr at raw proce aw process tim of each works ionship betwe t case scenari esented in tab mum and max red in march mum and max ay respectively throughput fo ctively. table iii. process time 3 8 4 8 5 3 21 93 18.125 0.645 table iv. case scenario s) thbest (m 0.379 0.645 0.645 0.645 0.645 0.645 h v ramework for o y: 7) has a rocess essing me was station en the ios in ble iv. ximum h and ximum y. the or 50cl dev cap mac pro too per fig. fig. results fro es (secs) proce 5 5 internal ben w mins) ctwors 1.8 3.6 5.5 7.3 11. 12. vol. 8, no. 4, 20 operational perf a performan veloped to enh pability. perfor chine capacity ocess time we l is capable formance pred . 4. relations . 5. relations om odata-dst ess times (mins) 0.050 0.133 0.067 0.133 0.083 0.050 0.350 1.550 raw proces critical w nchmark output worst case scen st (mins) thw 83 67 50 33 .00 .83 018, 3103-3107 rformance mea v. co nce measurem hance product rmance measu y, work–in–pr re used to de of improving dictions. hip between throu hip between throu ) jobs/minute 80 30 60 30 48 60 11.428 0.645 ss time wip t nario worst (mins) 0.455 0.455 0.455 0.455 0.455 0.455 7 asurements in s onclusions ment suppor tion manager’ ures like cycle rocess, bottlen erive a suitabl g production ughput and work ughput and work e station cap 1.3 0.5 1.0 0.5 0. 1.0 0. 0.0 2 1 practical wors ctpwc (mins) 1.94 3.23 4.53 5.82 8.40 9.69 3106 small and medi rt tool has ’s decision ma e time, throug neck rate and le benchmark. data analysis in process (50cl b in process (75cl b pacity (job/sec) 3333 5000 0000 5000 8000 0000 1905 0108 2.20 .419 st case scenario thpwc (mins 0.619 0.632 0.636 0.638 0.641 0.641 ium… been aking ghput, d raw . the s and bottle) bottle) o s) engineering, technology & applied science research vol. 8, no. 4, 2018, 3103-3107 3107 www.etasr.com odedairo & nwabuokie: framework for operational performance measurements in small and medium… references [1] j. heilala, j. montonen, p. jarvinen, s. kivikunnas, “decision support using simulation for customer-driven manufacturing system design and operational planning”, in: advances in decision support systems, pp. 235-260, intechopen, 2010 [2] m. p. roessler, j. reimer, m. mueller, “decision support for choosing an appropriate simulation method for dynamic material flow analysis”, journal of industrial and intelligent information, vol. 3, no. 4, pp. 337-341, 2015 [3] w. j. hopp, m. l. spearman, factory physics, irwin mcgraw-hill, 2000 [4] m. wilcox, m. bourne, “predicting performance”, 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manufacturing systems, digital enterprise, production networks, budapest, hungary, pp. 444-448, 2004 [33] j. heilala, j. montonen, a. salmela, p. jarvenpaa, “modelling and simulation for customer driven manufacturing system design and operations planning”, ieee 2007 winter simulation conference, miami, usa, december 7-10, 2007 [34] w. j. hopp, m. l. spearman, factory physics: foundations of manufacturing management, waveland press, 2008 [35] g. l. curry, r. m feldman, manufacturing system modeling and analysis, springer, 2007 engineering, technology & applied science research vol. 8, no. 6, 2018, 3515-3520 3515 www.etasr.com tarhda et al.: implementation of an optimized steganography technique over tcp/ip and tests … implementation of an optimized steganography technique over tcp/ip and tests against wellknown security equipment mohamed tarhda laboratory of electrical engineering & energy systems, faculty of sciences, ibn tofail university kenitra, morocco tarhdamo@yahoo.fr rachid el gouri laboratory of electrical engineering and telecommunications systems, ensa ibn tofail university kenitra, morocco elgouri.rachid@yahoo.fr laamari hlou laboratory of electrical engineering & energy systems, faculty of sciences, ibn tofail university kenitra, morocco hloul@yahoo.com abstract—nowadays we are witnessing a total convergence towards a digital world where information is digitized, conveyed and processed using highly developed techniques and tools. the development of broadband networks, including the internet, has made easy the manipulation, transmission and sharing of information. however, new security issues arise and they are particularly related to integrity, confidentiality and traceability of data. facing this situation, network security has become very important and challenges related to the protection of exchanged data over the internet against unauthorized access and use have increased. in the current work, we propose to implement an optimized steganography technique over tcp/ip protocol [1]. we have also tested it against well-known security equipment using latest versions. we will see that they are inefficient to stop this kind of cover channels. our work is like an alarm to every it administrator to change their thinking about data lost prevention (dlp) and exfiltration of sensitive information. keywords-steganography; tcp/ip; cover channel; firewall; hidden channel i. introduction networks based on tcp and ip protocols are widespread and their uses are endless whether professional or personal. however, while computer security has increased, network security has only been slightly improved. many security issues are still present, especially in businesses and private networks. hidden channels remain for the most part a source of unknown risk, and are in fact totally ignored by the public, while they represent a real threat. a hidden channel is defined as a communication channel that can be exploited by a process to transfer information in a manner that violates the system's security policy. in general, hidden channel implementations try to leave no trace [2]. hidden channels pose problems for highly secure environments such as government and military agencies. in multi-tier security environments where users with high levels of security should not be able to deliver information to users with lower security levels, hidden channels can be used to bypass these policies. in a more traditional environment, hidden channels can be used by a malicious user to secretly communicate with a compromised machine, which makes attack detection difficult. ii. implementation of cover communication over tcp/ip a. basic idea the key idea for our implementation is to exploit the tcp sequence filed and the ip identification field in order to insert confidential data that we want to share using a specific encoding, said radix-50. this optimized encoding approach allowed us to send more data in less tcp/ ip packets. here we are considering ipv4 protocol only. b. proposed approach although headers are not intended for communication, a sender can encode information in them. once transmitted over the network, this information may be decoded by a receiver. the ipv4 packet header consists of 14 fields, of which 13 are required. the 14th (options) field is optional. the ipv4 packet header consists of 20 bytes (figure 1). we choose to exploit properties given by the “identification” field, which is primarily used for uniquely identifying fragments of an original ip datagram. this 16-bit field contains a random number, generated by the sender and used to identify fragments from the same ip packet. having this said, we exploit this randomness to hide our useful data into the ip header. to optimize the flow of the shared information, we can combine the tcp sequence field and the ip identification field to hold the confidential data that we want to share. we use radix-50 encoding. this allowed us to code three characters in a 16-bit word and so risen data transfer speed [1, 6]. the choice of tcp and ip fields was based on their random characteristic that can make it difficult to detect by an unauthorized person. c. the choice of method a tcp sender generates an initial sequence number (isn). this sequence number is used in the communication flow engineering, technology & applied science research vol. 8, no. 6, 2018, 3515-3520 3516 www.etasr.com tarhda et al.: implementation of an optimized steganography technique over tcp/ip and tests … between the sender and the receiver to keep track of each packet and to ensure that the conversation continues correctly (figure 2). fig. 1. ipv4 header fig. 2. tcp handshake the id field is 16 bit long and represents identification used to reconstitute different fragments. each fragment has the same id number. these numbers (id field) are randomly generated and depend on the platforms in which they are located. therefore, we focused on the concept of randomization, best suited for information dissimulation. d. encoding radix-50 message exchange over long distances is a very old need. claude chappe invented an optical communication system called the tower chappe. this was the first system using a communication standard with the control codes. the first computers (tx-0, tx-2 and the pdp series ced) used memory words of a multiple size of 6, 12, 18 and 36 bits. various encodings were invented, radix-50 being one of them. radix-50 is a method designed for rapid and efficient integer conversion. it converts an integer of any size to a radix-50 alphabet character and vice versa. this library was originally designed for id generation. chains are encoded with the first most significant character. for example, the string “abc” (codes 11, 12 and 13) is encoded as: ((11*40)+12)*40+13=18093 in a 16-bit word. possible values are in the range 0-63999. as a result more data are transmitted in less tcp/ip packets. this technique can be useful in the case of transmission of many strings. so, we could get reliably 3 characters in 2 bytes. however, the bad news is that radix-50 is limited to 40 characters (capital letters, numbers 0 to 9, “.”, “$”, “%” and space) that we could use. anyway, in a multitude of scenarios, this is not a big problem. e. software environment our program is c language based, as this language is a lowlevel language. it is powerful in the context of network and system programming. it allows manipulation and creation of packages. it works in different platforms: centos, debian, windows, etc. for our tests and experiments, we chose vmware virtual platform, which is a leader in virtualization of it infrastructure. vmware creates a closed environment in which we can create multiple virtual machines representing our test lab. we used vmware esx that allows a more accurate resource management of each virtual machine and better performance. our implementation was tested and experimented upon in ubuntu operating system. f. implementation our program is written in c, it works in client-server mode, it is executable on linux platforms, and it is based on sockets for the creation and manipulation of packets. it takes as argument a file containing the confidential message we want to share with the server. figure 3 shows a part of the code related to radix-50 encoding for the client mode. fig. 3. program c–radix-50 decoding part in the server mode engineering, technology & applied science research vol. 8, no. 6, 2018, 3515-3520 3517 www.etasr.com tarhda et al.: implementation of an optimized steganography technique over tcp/ip and tests … the program takes over a number of parameters that can be used for network communication between a client, who sends the data, and a server, the one who receives them. 1) client mode options for client mode are: • dest <ip address>: the destination ip address of the target server. • source <ip address>: the ip address of the client. • file <file.txt>: the text file containing data. • port_source : the source port. • port _dest : the destination port. the operations that the client mode performs are: • open the file passed as an argument. • extract characters of this file. • convert these characters in ascii code. • call the encoding function that takes as argument the ascii characters and provides a result radix-50 encoding number. • create a socket that will be as a point of communication with the server. • create a package and fill in the tcp and ip headers. • take the number and encode it in the fields of identification and sequence. • send the packet through the network. 2) server mode options for server mode are: • server: this option tells the program to run in server mode. • source <ip address>: the ip address of the server. • file <file.txt>: the file in which the received data will be saved. • port_source: the source port. the operations that a server can perform are: • get in listening phase on a given port of the machine. • receive the package and put it in a “buffer”. • extract the ip and tcp headers. • search identification fields and sequence. • retrieve values. • call the decoding function that takes numbers as argument and retrieves the letters. • put the letters in the file passed as an argument. g. communication flow figure 4 describes the communication flow between client and server. the main functions are: • socket () creates a socket for establishing a communication channel. • bind () provides a name for the socket descriptor returned by the socket () function. • send () and the recv () allow respectively to send and receive data through a socket. • close () releases the communication channel. fig. 4. client-server communication flow iii. tests and discussion a. test environment for our tests, we deployed a virtual environment containing all the information we need. in fact, virtualization of operating systems is a technique to run simultaneously multiple operating systems, as if they were working on separate computers, on a single physical computer. these operating systems are called virtual machines (vms) (figure 5). fig. 5. vmware architecture virtualization of operating systems has several advantages: • the use of a different operating system without restarting the computer. • testing under development products and systems without compromising a stable existing environment. • software testing in controlled environment, isolated and secure. • operating system migration from one computer to another, as virtual machines would work on any computer with a compatible hypervisor. having this said, in our case, virtualization allows us to perform simulations using a professional-network-like model. engineering, technology & applied science research vol. 8, no. 6, 2018, 3515-3520 3518 www.etasr.com tarhda et al.: implementation of an optimized steganography technique over tcp/ip and tests … it allows us also to test our approach of hidden communication via tcp/ip while providing usability and portability. our platform is based on the vmware environment using the following components: vmware esxi 6.0.0 build 3620759, vsphere client version 6.0.0 build 6855219 and vmware vcenter server version 6.0.0 build 5112529. vmware is one of the pioneers of virtualization in data centers. it provides customers with a highly available, resilient and flexible infrastructure. figure 6 shows the two main models used for this section. they include the following machines: • the two communicating parties: “ubuntu-vm1” and “ubuntu-vm2”. their operating systems is ubuntu 18.04.1 lts, updated on august 2018. they contain client and server instances. • virtual machine “monitoring-vm” for monitoring and network analysis tools like wireshark and others. • the firewall virtual appliance fortigate “fortigate-vm”. • the firewall virtual appliance “forcepoint-ngfw”. • the virtual appliance vcenter to manage the vmware environment in a more efficient way. • the virtual appliance “forcepoint-smc-appliance” to manage the firewall solution forcepoint. it is called forcepoint ngfw security management center fig. 6. models used first, we run successfully our program of cover channel over tcp/ip in the case of the following scenarios: • case 1: the client and server instances are running on the same machine, each program in a separate terminal. the adresses used are the loopback address 127.0.0.1. the client sends a string to the server, which displays the received message and puts it in the output file. • case 2: client and server instances are running on two different machines that are on the same subnet (without active material between them). in the previous two scenarios, we were able to transfer information to the server successfully. below we will consider a third scenario, closer to reality, where we put a firewall between the two communicating machines. for testing, we chose two of the best firewalls in the world, which are widely deployed in professional and secure environments. the topology of the deployed network is shown in figure 7. fig. 7. network topology for test purpose b. fortigate firewall 1) presentation fortinet is a leading network security editor [3]. its products such as utm fortigate are high performance solutions adapted to increasingly intensive bandwidth networks and the proliferation of complex and virulent computer threats. in this part of our tests, we used the fortigate-vm solution, which is a complete fortigate firewall, presented as a virtual appliance. the fortigate-vm virtual appliance is ideal for monitoring the virtual traffic on major virtualization platforms, including vmware vsphere, hyper-v, and xen. the firewall fortigatevm provides intrusion prevention, vpn management, antimalware protection and other consolidated security features. note that the appliance version fortigate-vm is used fortios build0163 v6.0.2 (ga), firmware june 5, 2018. 2) configuration for this test, fortigate-vm has three network interfaces, representing the three network segments: intranet, extranet and management. by default, the firewall blocks all connections and allows only connections that were explicitly permitted by the administrator. so far, in our setup we chose to allow https connections from the machine n°1 to machine n°2 (figure 8). we also applied all security profiles to their default values (antivirus, web filter, filter dns, application control, ips inspection and ssl inspection). https protocol was chosen because it is a common used rule and also to show that the parties wishing to communicate secretly could exploit the rules already used in the network. having said this, our test results are the same regardless of the authorization protocols. fig. 8. fortigate firewall policy setting 3) results figure 9 shows that the secret communication between the two machines has been successfully established and the text was sent from one machine to another. firewall was unable to block it or to log it as hidden channel. in other words, the text was transmitted without a trace. engineering, technology & applied science research vol. 8, no. 6, 2018, 3515-3520 3519 www.etasr.com tarhda et al.: implementation of an optimized steganography technique over tcp/ip and tests … fig. 9. illustation of successful secret communication between two virtual machines in a separate subnet c. stonesoft ngfw firewall 1) presentation forcepoint is a leading cybersecurity editor. one of its flagship products is forcepoint ngfw solution which is an award-winning new generation firewall that blocks malicious attacks and prevents data theft and intellectual property. this technology is increasingly adopted by security companies and organizations: • the community of gartner magic quadrant 2017 has appreciated the ngfw firewall. the performed analytical tests receive a rating of 95% [4]. • forcepoint ngfw received the best score among 10 tested editors in the nss labs report (june 2017), an independent cybersecurity recognized worldwide, evaluating the effectiveness of security firewalls. • it is deployed by more and more companies around the world to fight against threats and reduce operational complexity in security systems [5]. 2) configuration in this test scenario the fortigate-vm was replaced by the firewall forcepoint ngfw and simulations were testing hidden communications between the endpoints with the restrictive rules in place (figure 10). fig. 10. forcepoint ngfw firewall rules 3) results the communication between the two machines by exploiting the tcp and ip headers has been established, even with all the security and inspection profiles activated in the firewall rule (figure 11). fig. 11. forcepoint ngfw firewall rules with all inspection profiles applied d. discussion these tests show that the current firewall approach is powerless against the methods of covert channel through tcp/ip protocols. in our tests, we were able to transfer long texts like dozen-pages-meeting reports. note here that there are programs like matlab that are able in a few lines of code to convert an image into text and vice versa (figures 12 and 13). hence, we underline the critical danger that can cause the existence of such hidden channels over tcp/ip protocols. fig. 12. matlab code lines to convert image to text fig. 13. matlab code line to convert text into image according to our tests, as we can see, the detection of hidden channels is not always possible. detecting and stopping engineering, technology & applied science research vol. 8, no. 6, 2018, 3515-3520 3520 www.etasr.com tarhda et al.: implementation of an optimized steganography technique over tcp/ip and tests … covert channel before data exfiltration is even more difficult because we need exchanged data to detect the hidden channel, which would result in the loosing of some data. having this said, it should be noted that when legitimate users are not looking to establish covert channels themselves, the attacker would compromise communicating machines. therefore, increasing security in endpoint machines reduces the risk of covert channel, as hidden channels generally require administrator privileges. security of endpoint is a wide subject to be addressed exhaustively here, but we could give a minimum list of tips to apply in order to reduce the risk of attacks leading to hidden channel and exfiltration of data: • workstations should have at least one active antivirus and firewall. • we should not install nor run any software that it is not digitally signed and delivered from reliable sources. • cryptography can be used to encrypt important data and limit their exfiltration. • operating systems and software should be updated regularly. • implementation of dlp solutions against data leak. • implementation of security analysis solutions to monitor events, user behaviors and access to data. • users should be aware of security issues. • physical access to the machines and the network should be restricted to authorized users. • security policy should be defined and applied. the list is endless, but the application of these tips is already a good step to secure endpoints. an important step for securing machines is to apply the principle of least privilege. each application, service or user should have access to only what he needs to do his/its work. iv. conclusions our implementation is a concrete illustration of the vulnerability of tcp/ip protocols and the robustness of the covert channels over tcp/ip. furthermore, few applications exist to detect hidden channels and most companies do not try to identify if there is a hidden channel or not in their network. if the hidden channels are difficult to stop, we need to reduce their potential, especially in an environment with strong security requirements. the most effective method is to reduce the bandwidth or close the channel. for example, local area networks can be closed outside working hours. v. contribution summary although the flaws in tcp/ip protocols exist by design, professionals of network security and the research community do not seem to pay enough attention to them. thus, we believe that the present work on steganography over tcp/ip adds values as: • compared to existing research [1, 6], we have increased the flow of information sent over a tcp/ip packet (three characters instead of one character). • our secret communication testing through well-known firewalls and security equipment (with the latest versions and security updates) in professional network model scenarios shows their limitations in detecting hidden channels and in fighting data exfiltration. this is in itself very important because if taken seriously, it could lead to more research to counter this type of vulnerability. references [1] c. h. rowland, “covert channels in the tcp/ip protocol suite”, first monday, vol. 2, no. 5, 1997 [2] m. kouremetis, c. west, “private information retrieval”, 16th annual information security symposium, west lafayette, in, usa, march 2425, 2015 [3] fortinet, “customer reviews on gartner peer insights”, available at: https://www.fortinet.com/demand/gated/gartner-enterprise-firewall.html, 2018 [4] gartner peer insights, “forcepoint-fortinet comparison”, available at: https://www.gartner.com/reviews/market/enterprise-network-firewalls /compare/forcepoint-vs-fortinet, 2018 [5] v. satrom, “forcepoint positionné “visionnaire” par gartner dans la magic quadrant des firewalls réseau”, available at: https://www.forcepoint.com/fr/newsroom/2017/forcepoint-recognizedvisionary-gartner-magic-quadrant-enterprise-network-firewalls, 2017 (in french) [6] s. j. murdoch, s. lewis, “embedding covert channels into tcp/ip”, in: information hiding. ih 2005, lecture notes in computer science, vol. 3727, pp. 247-261, springer, berlin, heidelberg, 2005 authors profile mohamed tarhda works at the electrical engineering and energy systems laboratory, faculty of science, university ibn tofail, kenitra, morocco. rachid el gouri is professor at the electrical engineering and energy systems laboratory at faculty of science. he is also professor at the laboratory of electrical engineering and telecommunications systems, national school of applied sciences, university ibn tofail, kenitra, morocco. laamari hlou is the head of the physics department at the faculty of science, kenitra. he is also professor and director of the electrical engineering and energy systems laboratory, faculty of science, university ibn tofail, kenitra, morocco. https://www.forcepoint.com/fr/newsroom/2017/forcepoint-recognized-visionary-gartner-magic-quadrant-enterprise-network-firewalls https://www.forcepoint.com/fr/newsroom/2017/forcepoint-recognized-visionary-gartner-magic-quadrant-enterprise-network-firewalls microsoft word 7-2780_s_etasr_v9_n4_pp4349-4354 engineering, technology & applied science research vol. 9, no. 4, 2019, 4349-4354 4349 www.etasr.com kandamby: investigation and analysis of wall cracks in cement stabilized rammed earth technology investigation and analysis of wall cracks in cement stabilized rammed earth technology g. w. t. c. kandamby institute of technology, university of moratuwa, diyagama, homagama, sri lanka kndamby@yahoo.com abstract-cement stabilized rammed earth (csre) is one of the developed and affordable housing technologies, adopted in many countries, which has been used in sri lanka since 2004 for building single and two-floor houses. steel slip-form and timber formwork have been used for casting walls. information collected on wall cracks under these two methods is analyzed to justify the reasons for these cracks. data collected at the initial stage of construction and its serviceability period of 12 years is considered under this study. most of the walls have been in satisfactory condition, but few had to be repaired. csre wall tends to crack similar to other masonry technology due to faulty construction and environmental changes. major issues are the cracks due to shrinkage of csre material which appeared after one year period of construction. detailing the construction with the provision of shrinkage cracks is required to mitigate the vertical cracks on csre walls. keywords–cement stabilized rammed earth; shrinkage; steel slip-form; timber formwork; wall cracks i. introduction rammed earth is a traditional technology for building house walls used in many parts of the world. originally, these walls were made using freely available natural earth mixed with water and tamped manually in timber molds to make very thick dense walls. application of this technology is being developed now due to the eco-friendly qualities of earth and to reduce construction cost. cement stabilized rammed earth (csre) is one of the developed technologies for making load bearing walls of houses and it has been introduced to sri lankan housing sector in 2004. two different formwork methods were adopted for casting csre walls [1, 2] and technicians and masons were trained by conducting practical training programs. possible quality controlling measures were taken while constructing walls to meet standards. cracks are commonly found on walls mainly due to age, natural and environmental causes, and poor workmanship or faulty construction. cracks in csre walls are analyzed by using the information from the experience of constructing csre houses and from the data collection through field survey of ten houses at four different places. the findings of this study are useful for house builders who want to mitigate such situations and encourage them to adopt this technology as it has been globally recognized as a suitable, cost effective, and environmental friendly housing technology. ii. objectives the main objective of this study is to investigate and analyze the wall cracks encountered on cement stabilized rammed earth walls of houses. the specific objectives are to: • recognize wall cracks on buildings masonry walls. • examine the most common cracks on csre walls at their initial stage of construction or their serviceability stage. • determine the causes of these cracks with respect to the theory of cracks in masonry buildings. • propose good practices for mitigating such situations. iii. literature review a. cement stabilized rammed earth (csre) csre is a mixture of soil, portland cement and water compacting manually or mechanically in the formwork to cast a dense mass. structural properties and non-structural properties of rammed earth have been developed by adding cement as stabilizer where the quantity of stabilizer can be determined with respect to the expected compressive strength [3]. successful use of csre for walls can be seen in many countries [4]. the basic control factors for satisfactory achievement in cement stabilization are selection of good soil, adequate cement content, proper moisture content and adequate compaction [3, 5]. the composition of 5-20% gravel, 45-60% sand, 20-35% silt and clay has been recommended for better performance of wall construction [3]. in [7], csre load bearing walls were designed structurally by using british standard code of practice for the use of masonry [6] and csre walls were constructed in a two floor house in sri lanka using steel-slip form mold for the purpose of disseminating the technology as an affordable housing method. it was found that earth building technology has been continuously developed in many parts of the world [8, 9]. some earthen structures built centuries back are still performing satisfactorily [10]. in australia there are many rammed earth buildings over 100 years old still in use, therefore earth construction could be considered as a durable kind of construction [11]. the corresponding author: g.w.t.c. kandamby engineering, technology & applied science research vol. 9, no. 4, 2019, 4349-4354 4350 www.etasr.com kandamby: investigation and analysis of wall cracks in cement stabilized rammed earth technology shrinkage of stabilized soil should also be considered as an outcome of stabilization, given the potential for weakening of earth walls caused by shrinkage or tensile cracking [11]. b. wall cracks in masonry buildings cracks are the presence of faults or breakage of building materials mainly caused by uneven internal stress or stress concentration [12]. it is necessary to ensure the safety, durability and serviceability of the buildings. wall cracking is a typical drawback noticed in most of the low rise masonry buildings and the cracks are attributed to various effects ranging from unit properties, climatic boundaries, poor construction, and bad design. these reasons may lead to cracking and ultimately can result in failure [13]. cracks can be classified as either structural cracks or non-structural cracks depending on the way of internal stress failure of the building material. structural defects consist of complete or incomplete separation within a single element or between contiguous elements of construction or a line along which a material is broken into parts [14]. non-structural cracks develop due to the inducement of internal stresses in building materials and their depth is less, only a few mm, i.e. they exist on the surface only [14]. the potential for cracking in loadbearing masonry members is less than in nonloadbearing masonry members because compressive stresses from dead and live loads help offset the effects of any movement [15]. the walls in the external environment (temperature and humidity) under different influences and stresses demonstrate the ability of antistress and with the passage of time the pressure will be accumulated to a part of the wall, the stress concentration area. when the wall structure cannot bear the stress, there will be cracks and wall discontinuity [12]. shrinkage cracks in rammed earth walls can be repaired by pointing or filling with dampened soil of similar characteristics. the surface of the crack must be moistened to ensure adhesion and the fill mixture should have as little linear shrinkage as possible [11]. c. theory of wall cracks cracks on masonry walls are caused by different reasons. the following are selected for discussion as they are more relevant to the cracks identified on csre walls. • expansion joint: it occurs due to changes in temperature, moisture expansion, elastic deformation, settlement and creep. the differential strains can occur as a result of different expansion characteristics of two walls, or a wall and a column. external walls are subjected to fluctuations of temperature and deform differently than internal walls, causing cracks in the connecting walls [13]. • shrinkage cracks: temperature stress and shrinkage of masonry is one of the main causes of wall cracks. sometimes the cracks are caused by shrinkage of the plastering and they are surface cracks [14]. • foundation settlement: uneven soil foundation will cause the mixed compression of the soil, resulting in uneven settlement [12]. settlement cracks are usually larger at the top diminishing to a hairline crack at the bottom or vice versa, depending upon the relative direction of the settlement and its location with respect to wall length. [13]. • slab (roof) deflections: when a roof resting on a wall is loaded, the end rotation of the slab can develop cracks at the wall slab interface. cracking risk decreases as the force in the wall (and the restraining moment on the slab end) increases. theoretically, cracks will be formed if the induced tensile forces at the outer face of the masonry wall exceed the permissible tensile stress of the wall [13]. iv. methodology the study was conducted as follows: • records maintained for wall cracks encountered at the initial stage of construction and the records of remedial measures taken were used (three houses). • a field survey was conducted in order to investigate wall cracks using ten constructed houses at four different locations (one town and three villages) which are more than twelve years of age. • the observed cracks were analyzed according to the theory of cracks in masonry buildings to justify reasons for cracking. v. data collection a. details of constructed houses the total data collection consisted of 13 houses constructed at seven locations of the country. table i. details of constructed csre houses location houses construction year csre wall age initial stage of construction 1.pellawatta, battaramulla a 2004 one year 2. kekirawa b 2006 no age 3.panadura c 2014 one year serviceability stage 1.madampagama, hikkaduwa d, e, f 2005 13 years 2.akuressa g 2006 13 years 3.athurugiriya h 2006 12 years 4.puwakpitiya k-o 2007 12 years total houses 13 b. construction method this technology has been introduced in sri lanka in 2004. the author has been engaged in development and dissemination activities of this technology and some information from past experience has been presented through technical papers [1-3, 7]. trained masons were allowed to deploy as possible and technical details were given to all supervisors and the contractors through the practical training programs. • method 1: use of steel slip-form with cseb columns at wall junctions. this method was applied at the initial stage of csre wall technology in sri lanka for house construction [1]. • method 2: use of timber mold to build walls and wall junctions. vertical groves were provided at the junctions to engineering, technology & applied science research vol. 9, no. 4, 2019, 4349-4354 4351 www.etasr.com kandamby: investigation and analysis of wall cracks in cement stabilized rammed earth technology form adequate bonding with the wall. this method is applied for csre wall technology since 2010 [16]. construction of houses a, b, c and g were supervised and construction of d, e, f, h, k, l, m, n and o was inspected at several occasions by the author as a party of the dissemination process of csre technology in sri lanka. vi. analysis and discussion a. cracks detected at the initial stage of construction 1) house a method 1 was applied for this house and vertical cracks were detected after six months at wall junctions. (a) (b) fig. 1. seperation vertical cracks: (a) constructed house, (b) crack at wall junctions cracks were throughout the total width (145 mm) and walls were separated from the cseb wall junctions. there were separation cracks due to high soil shrinkage. 2) house b there were 8 walls and 2 horizontal cracks were identified at the stage of construction. all other walls were free of cracks. one crack had 1m length, passing the full wall width (145mm) at sill level of the window and the other was a 0.8m length at the middle of the wall about 2m height from the floor. (a) (b) fig. 2. poor workmanship: (a) at sill level of a window, (b) at the middle of the wall the materials used (soil, cement, water) and the method adopted was not the issue when compared with the performances of the other walls. observing the loose particles at those locations, it was realized that the mixture was not mixed and not compacted well. those walls were reconstructed after demolishing due to poor construction. 3) house c for this two-floor house, csre was used only for load bearing walls of ground floor structurally designed using [17] and the walls were constructed with good supervision. quality precautions were taken according to [2]. therefore, the walls were constructed with good quality control measures on csre technology. at the completion there was a 1.65m length of horizontal crack on the internal wall 600mm below the slab level. it was through the full width of the wall and shifted about 2mm out from its vertical alignment. slab was under hot sunrise before constructing the upper floor for about three months and the reason of such cracks may be the high temperature [13] or density banding between the lift of csre introducing a horizontal plane of weakness [18]. (a) (b) fig. 3. (a) horizontal crack in house c, (b) repaired cracks were cut to ‘v’ shape and filled with cement mortar 1:5 (1 part of cement and 5 parts of sand) after total house completion and the wall was afterwards in satisfactory condition. if the cause of cracking has been dealt completely and no further structural movement occurs, then a crack can confidently be filled [18]. in addition, there were three vertical cracks of 1mm width detected in house c, one year after construction. details of cracks are presented in table ii. table ii. details of vertical cracks of house c wall cracks no length (mm) depth (mm) internal wall 1 1980 50mm internal wall 2 2630 full wall width external wall 3 1400 full wall width external wall, inside the garage 4 max 1600 only on the plaster cracks no.1-3 were found at very critical places for construction as they were very close to the wall junctions and to the location of the electrical plug (300mm from the floor) where the electrical conduit of 12mm pvc pipes was inserted vertical through the total height up to the slab level, though full attempt was taken to compact the area of pvc conduit by using small timber sticks. the lengths of these walls are 3.96m, 3.28m and 3.30m respectively. the walls have shrunk and vertical cracks have appeared along their weak lines. cracks were cut to ‘v’ shape and were filled with cement 1:5 before painting. cracks are now at satisfactory condition. (a) (b) (c) fig. 4. vertical cracks csre contains clay which is prone to shrink while drying while the water in the mixture rapidly evaporates and leads to shrinkage cracks. shrinkage is a very slow process of losing moisture [18] hence the cracks were noticed nine months after engineering, technology & applied science research vol. 9, no. 4, 2019, 4349-4354 4352 www.etasr.com kandamby: investigation and analysis of wall cracks in cement stabilized rammed earth technology the construction completion. shrinkage cracks should be considered inevitable in soil-cement stabilization, and are generally 3–6mm wide at a spacing of 3–6m [11]. as clay is the component responsible for shrinkage, rammed earth deformations can be significantly minimized by reducing the clay content and compensating it with stabilizing binders such as cement. also, material shrinkage without cracking is possible by separating larger rammed earth parts with control joints [11]. if any structural movement occurs, then material separation may occur, and this separation (cracking in a homogeneous material) will take place at the weakest point. as butted vertical joint between two rammed earth blocks cannot carry any tensile stress, the joint between the blocks will open [12]. (a) (b) (c) fig. 5. vertical crack below window the cause of these cracks is the shrinkage of the csre material and the construction details showed that there were incorrectly staggered vertical joints so shrinkage took at the weak line vertically. the wall was repaired by cutting both sides to take 30mm width of strip and filled with 1:5 cement and sand mortar. it works well up to today. b. cracks at serviceable stage all these walls are load bearing walls of single floor houses which were originally constructed by introducing the affordable csre wall technology. after a 12 year period, it can be said that there were no serious structural cracks in any house showing good adoptability results of csre walling technology for housing. no diagonal cracks were found anywhere during this investigation. 1) houses e, f and g it is realized that the major issues regarding csre wall cracks are at the wall junctions where cseb were used to caste those walls with the support of slip-form. it is noted that wall cracks were identified in the investigation and the method 1 was adopted for constructing. they were finished without plaster in perfect level and line because of the use of steel mold ending with affordable cost as expected at the constructions beginning. the reasons for the vertical cracks are exactly similar to the case explained in house a due to the use of cseb columns at wall junctions. though they are not structural defects, occupants paid more attention about the existence of those houses. the linear expansion of csre and cseb are significantly different so the cracks often appear at the junction of the wall and the top or the floor plate position because of the increasing internal and external pressure difference. (a) (b) (c) fig. 6. vertical wall cracks at wall junctions 2) houses k, l, m, n and o all csre walls were built with cseb wall junctions. some very common vertical cracks were identified in these houses in which method 1 was adopted. (a) (b) (c) fig. 7. houses k, l, m, n and o: vertical and horizontal cracks there is only one horizontal crack (1.5mm depth) identified on the front wall in the living area at the level of lintel going through the full width of the wall. these five houses were constructed by cutting and leveling the high level ground. this particular wall of house o is very close to the embankment and the foundation of this wall may have been constructed on the filled ground. the reason of this horizontal crack is the settlement of the foundation [12]. the crack has not yet been repaired. 3) house h csre walls were applied in this house only to the ground floor with reinforced cement concrete columns in order to build the whole two floor house. by the way of applying this technology, csre acted as partitioning wall and all vertical wall junctions had fine hair cracks (less than 1.0mm) at the joints of columns and csre walls. the reason is the same as in the case of cseb columns. no other cracks were observed in this house. these cracks have not been repaired yet. (a) (b) (c) fig. 8. vertical crack at wall junctions, (a) construction stage, (b)-(c) vertical crack this is particularly the case when a different material is used at the corner (for example brick) and no tie exists between the rammed earth block and this material. this lack of tie engineering, technology & applied science research vol. 9, no. 4, 2019, 4349-4354 4353 www.etasr.com kandamby: investigation and analysis of wall cracks in cement stabilized rammed earth technology means that any structural or ground movement is not restrained by the perpendicular walls and allows opening of the joint between the two materials [18]. c. walls free of cracks since there are no structural cracks found on csre walls under this study, the reasons of cracks that appeared at several occasions are found to be due to problems during construction. the information collected regarding csre walls where no cracks appeared is discussed to appreciate the better practices. 1) method 1 some walls constructed by following this method have been finished by providing soil based molding work along the vertical joints at cseb wall junctions as shown in figure 9(b) giving better appearance. it was also found that some vertical joints were neatly made with the applied plaster which was prepared with soil and cement and had a good external finish. (a) (b) (c) fig. 9. (a) moulding work, (b) soil based plaster, (c) finishes at wall junctions 2) method 2 among the houses considered in this investigation, this method has been applied only to houses c and g. in house g there were no cracks at all and the maximum length of the 150mm thick wall was 4.35 m. (a) (b) (c) fig. 10. good construction practices: (a) house g, (b)-(c) house c there were no vertical cracks at the joints even in house c as the wall junctions were built simultaneously with the walls. tapered grooves were provided on timber molds at the vertical joints to enable walls to take shrinkage without cracking [2]. the maximum length of the 200mm thick walls was 2.51m and the thickness with soil based plaster was 250mm. vii. results • csre walls exhibit poor construction durability through horizontal cracks and remedial actions can be taken to rectify them. • reinforced cement concrete slabs supported by csre walls may have horizontal cracks below the slab level due to the expansion of slab exactly as in the case of brickwork. • vertical cracks have been identified in 11 out of 13 houses which is a major issue regarding csre walls. vertical shrinkage cracks are possible due to high soil shrinkage. • if steel slip-form is used for casting csre walls, cseb can be used as vertical support at wall junctions where vertical groves are to be made at these places allowing shrinkage with better finishing. • two horizontal cracks were analyzed because of rcc slab expansion and foundation movement, which are common in any masonry load bearing walls. • there is good evidence that csre performed well as load bearing walls without any cracks with timber mold by moving horizontally with adequate lap distance for the vertical joint. it is understood that the linear shrinkage of csre mixture governs the extent of shrinkage for each particular wall depending on the dimensions of the wall panel. further study is necessary in order to determine the provision of shrinkage of csre walls. viii. conclusions csre walls which were constructed fulfilling the structural requirements demonstrated good performance as load bearing walls of houses for a period of twelve years consisting of a cost-effective technology for housing. they have a tendency to react in the way of presenting cracks similar to other masonry technologies in the presence of faulty construction and environmental changes. they do not show serious cracks during these 12 years of service, and the main issues are determined as shrinkage cracks at the weak locations of the walls. since the construction method is the key factor to answer this shrinkage, construction detailing prior to wall casting is required. in the case of use of timber molding, vertical groves can be located appropriately on its horizontal layer staggering joints with adequate lap while casting walls. steel slip-form showed good performance on building walls without plaster, maintaining its line and level perfectly where provision was made for shrinkage aesthetically by means of soil based molding or with plaster applied along vertical joints. references [1] n. kamaladasa, c. jayasinghe, “development of an efficient construction technique for rammed earth”, annual transactions of iesl, vol. 2005, pp. 1-6, institution of engineers, sri lanka, 2005 [2] g. w. t. c. kandamby, work norm for cement stabilized rammed earth wall, annual transactions of iesl, vol. 2016, pp. 87-93, institution of engineers, sri lanka, 2016 [3] c. jayasinghe, n. kamaladasa, “compressive strength characteristics of cement stabilized rammed earth walls”, construction and building materials, vol. 21, no. 11, pp. 1971-1976, 2007 [4] b. v. v. reddy, p. p. kumar, “compressive strength and elastic properties of stabilized rammed earth and masonry”, mansory international, vol. 22, no. 2, pp. 39, 2009 [5] g. p. makusa, soil stabilization methods and materials, lulea university of technology, 2012 engineering, technology & applied science research vol. 9, no. 4, 2019, 4349-4354 4354 www.etasr.com kandamby: investigation and analysis of wall cracks in cement stabilized rammed earth technology [6] british standards institution, bs 5628-1: 2005: code of practice for use of masonry. structural use of unreinforced masonry, british standards institution, 2005 [7] g. w. t. c. kandamby, cement stabilized rammed earth for load bearing walls in two storey house, msc thesis, university of moratuwa, 2015 [8] m. hall, y. djerbib, “rammed earth sample production: context, recommendations and consistency”, construction and building materials, vol. 18, no. 4, pp. 281–286, 2004 [9] v. maniatidis, p. walker, a review of rammed earth construction, university of bath, 2003 [10] q. b. bui, j. c. morel, b. v. v. reddy, w. ghayad, “durability of rammed earth walls exposed for 20 years to natural weathering”, building and environment, vol. 44, no. 5, pp. 912-919, 2009 [11] j. norton, building with earth, a handbook, practical action, 1997 [12] h. luan, q. kang, t. liu, “cause analysis and control measures of cracks in filling wall of reinforced concrete structure”, chemical engineering transactions, vol. 59, pp. 529–534, 2017 [13] m. a. almherigh, “common causes of cracking in masonry walls diagnosis and remedy”, international journal of sciences: basic and applied research, vol. 14, no. 1, pp. 25-33, 2014 [14] w. o. ajagbe, o. s. ojedele, “structural investigation into the causes of cracks in building and solutions: a case study”, american journal of engineering research, vol. 7, no. 8, pp. 152–160, 2018 [15] brick industry association, technical notes on brick construction, brick industry association, 2009 [16] c. jayasinghe, g. w. t. c. kandamby, “load bearing rammed earth wall construction with pre-cast earth wall junctions”, masonry international, vol. 26, no. 1, pp. 1-6, 2013 [17] engineering design of earth buildings, nzs 4297 (1998): building code compliance documents b1 (vm1), b2 (as1), engineering design of earth buildings, 1998 [18] p. a. jaquin, analysis of historic rammed earth construction, phd thesis, durham university, 2008 [19] l. keefe, earth building: methods and materials, repair and conservation, taylor and francis, 2005 microsoft word etasr_v10_n5_pp6282-6289 engineering, technology & applied science research vol. 10, no. 5, 2020, 6282-6289 6282 www.etasr.com almabrouk et al.: geometry investigation and performance optimization of a single-mass piezoelectric … geometry investigation and performance optimization of a single-mass piezoelectric 6-dof imu hela almabrouk université de sfax, ecole nationale d’ingénieurs de sfax, sfax, tunisia faculté des sciences de monastir, université de monastir, monastir, tunisia geeps laboratory, université paris sud, gif sur yvette, france brahim mezghani université de sfax, ecole nationale d’ingénieurs de sfax ur-mets, sfax, tunisia guillaume agnus université paris sud, c2n umr 9001 cnrs palaiseau, france sinda kaziz université de sfax, ecole nationale d’ingénieurs de sfax, sfax, tunisia faculté des sciences de monastir, université de monastir, monastir, tunisia yves bernard geeps laboratory, université paris sud gif sur yvette, france fares tounsi université de sfax, ecole nationale d’ingénieurs de sfax, ur-mets, sfax, tunisia abstract-this paper explores the fundamental steps towards the development of a 6-axis piezoelectric inertial measurement unit (imu). the main specification of the reported device is its ability to concurrently detect 3-axis acceleration and angular velocity using a single mass-based design. this work represents a detailed numerical analysis based on a finite element model. experimental reported data are exploited to validate the fem model in terms of acceleration detection which is ensured through the direct piezoelectric effect. the angular rate is detected thanks to the coriolis effect by ensuring drive and sense modes. using a finite element analysis (fea), light was shed on the different basic parameters that influence the sensor performance in order to present an optimized design. a detailed geometrical investigation of factors such as anchor position, optimized locations for sensing electrodes, proof-mass dimensions, pzt thickness, and operating frequency is illustrated. the 6-dof sensor outputs are extracted in terms of the original and the optimized design. the amelioration rate of sensitivity is found to be up to 165% for linear acceleration, while for angular rate sensing, the lateral sensitivity is ameliorated by about 330% and is multiplied by around ten times in the normal axis. the optimized design exhibits a good acceleration sensitivity of 260mv/g in the lateral axis and 60.7mv/g in the z-axis. for angular rate sensing, the new design is more sensitive along the longitudinal axis than the lateral one. sensitivity values are found to be 2.65µv/rad/s for both x-and y-axis, and 1.24v/rad/s for the z-axis. keywords-acceleration; coriolis effect; angular rate detection; fem simulations; inertial measurement unit; piezoelectric detection i. introduction the development of multi-axis inertial sensors has been rising considerably. the scientific community has shed light on multi-motion sensing exemplified in inertial measurement units (imus). such systems are employed to measure linear and rotational motion data such as gravitational forces and angular rates. nowadays, imu systems are becoming important and are largely investigated [1-4] due to the fact that they are among the primary used systems in various fields, e.g. they are the main means of environment interaction for robotic applications and their system development [5, 6]. also, imu devices have shown great contribution in medical rehabilitation fields [7, 8], they have been broadly investigated in industrial quality control systems [9], navigation systems [10, 11], motion sensing and portable positioning systems [12, 13], and in smart sensors for internet of things (iot) applications [14, 15]. multiple-axis sensing systems have been developed relying on several physical effects, most known for motion capture are capacitive, thermal, piezoelectric and piezoresistive. nevertheless, piezoelectric materials have presented great performance in many inertial sensors. especially, the piezoelectric effect exhibits many advantages compared to other sensing mechanisms such as low power consumption, wide dynamic range frequency, and compatibility with reduced device dimensions [16, 17]. furthermore, their self-powering feature is the most attractive advantage of piezoelectric sensors. indeed, the piezoelectric effect is manifested by a transfer of mechanical energy into electrical and vice versa, i.e. the direct effect is triggered by a deformation that will generate a mechanical stress which in turn produces an electrical voltage. similarly, the converse effect is illustrated when an electric field input induces a mechanical deformation. for imus, the number of degrees of freedom (dof) reflects the number of axes that the system is sensitive to. therefore, a 6-dof motion sensing application is incorporating x-, y-, and z-axis measurement of all possible accelerations and 3-axis angular rate components. several 3corresponding author: hela almabrouk (hela.almabrouk@enis.rnu.tn) engineering, technology & applied science research vol. 10, no. 5, 2020, 6282-6289 6283 www.etasr.com almabrouk et al.: geometry investigation and performance optimization of a single-mass piezoelectric … dof or multi-axis sensors for accelerometers and for gyroscopes have been reported [18-22]. these devices can be co-integrated into a single system to form a 6-axis imu. however, their size and cost, composed by an assembly of two or more separate sensors, can be annoying for certain applications. in addition, each multi-axis accelerometer or gyro sensor requires generally separate drive and sense electronics, leading to an increase in cost and complexity of the designed inertial unit. therefore, 6-axis detection for linear and angular motion sensors were proposed using piezoresistive [23], and piezoelectric principle sensing [24-25] based on a single inertial mass. in exploiting the coriolis effect with piezoelectric sensors, a sole work has been carried out to cointegrate these two different inertial measurement types into one device through the same detecting elements [25]. in the current study, an in-depth analysis of a single-mass piezoelectric imu structure to be used as a 6-axis inertial sensor was carried out. the output of this sensor under development (sud) is proportional to each of the 3-axis angular rate components in addition to the 3-axis linear accelerations. the structure of this sud is inspired from the one presented in [25, 26]. using the reported experimental values, a newly developed fem model, using comsol multiphysics software, has been performed and validated. this 3d fem model was then used for the performance analysis of the sud behavior in both drive and sense modes. the novelty of this work is mainly manifested through the investigation of key parameters that influence the performances of the reported structure and their analysis. the main aim of this study is to evaluate a 6-dof piezoelectric detection system and enhance its sensing performance through the optimization of its key geometrical parameters. ii. imu design presentation the sud structure is able to detect 3-axis accelerations and 3-axis angular velocities using a single-mass design. the analyzed design, based on the scheme reported in [25], uses nine electrodes implemented on the top of a piezoelectric membrane for both drive and sense modes as presented in figure 1. sense electrodes, placed on the inner and outer rings, are used to detect induced stresses and are denoted sx1, sx2, sy1, sy2, and ring. drive electrodes, located on the middle ring, are used to actuate the imu design and are denoted as dx1, dx2, dy1, and dy2. a circular bottom conductive membrane, made of high precision elinvar (nickel-iron-chromium alloy), is used as a potential reference and a supporting substrate (anchor). a proof-mass is attached at the bottom center of the elinvar thick membrane and used as an oscillator. the linear acceleration detection is based on the use of the direct piezoelectric effect. hence, an incident acceleration motion on the seismic mass induces strain in the piezoelectric membrane and the generated voltage is collected by the corresponding sensing electrodes placed on the top piezoelectric membrane. for angular rate detection, the coriolis effect is exploited. this phenomenon is designated when a moving object is subjected to an angular motion in a rotating frame. practically, the act of the applied rotation on the oscillated proof-mass gives rise to a new fluctuation component that is produced by the coriolis effect. fig. 1. design presentation of the piezoelectric 6-dof imu. iii. fem model validation no dimensions’ details were given in [25] concerning the proof-mass. only the used material, stainless steel (or sus), and its weight, 0.65g were declared. thus, the length and radius of the seismic mass will be determined based on a comparison study between our fem simulations and the experimental values specified in [25]. fem simulations have been extended for an acceleration range of 1 to 10g. in response to 10g of x and z-axis linear accelerations, distributions of output voltages on the membrane are shown in figures 2(a)-(b). for normal acceleration input, the output voltage is collected from the sum of all four sense electrodes (figure 2(a)). for longitudinal accelerations, the voltage is collected from the potential difference between the two electrodes located in the direction of acceleration (figure 2(b)). the corresponding results of output voltages are plotted in figure 3. this good agreement between simulation and the reported experimental results is obtained for radius r=1mm and length l=26.52mm. (a) (b) fig. 2. distribution of the output voltages on top of the imu membrane using r=1mm and l=25.83mm in response to a 10g acceleration along the (a) x-axis and (b) z-axis. (a) (b) fig. 3. fem simulation values and experimental results from [25] of the imu using r=1mm and l=25.83mm in response to accelerations along (a) x-axis and (b) z-axis. engineering, technology & applied science research vol. 10, no. 5, 2020, 6282-6289 6284 www.etasr.com almabrouk et al.: geometry investigation and performance optimization of a single-mass piezoelectric … iv. geometry optimization in this section, an in-depth analysis of the structural system’s behavior in response to different design factors is introduced. fem simulations of the basic structure design are investigated in order to highlight the geometrical parameters that influence the system’s performance. the structure optimization is based on the specific location of the anchor position, sense and drive electrode locations and proof-mass dimensions, pzt thickness, and optimum operating frequency. thus, our contribution is to enrich the characterized sensor with an fea study in order to optimize the design. a. position of anchor and sense electrodes the anchor design and the electrode positions are important design parameters. three different positions are inspected to explore and then determine the most efficient anchor position in order to localize the induced optimum stress. as illustrated in figure 4(a), position 1 consists in fixing the middle bottom surface between the elinvar and the pzt cylinders. in position 2, which is the original anchor position, the bottom of the elinvar cylinder is fixed up to the limit of the pzt cylinder and position 3 consists in fixing the bottom of the elinvar cylinder beyond the limit of the pzt element. (a) (b) fig. 4. (a) illustration of the three possible imu structure anchoring cases, (b) 2d stress profile on the top piezoelectric membrane under a 10g z-axis acceleration for the 3 case position. for each of the three anchor positions given in figure 4(a), xand z-axis excitation accelerations are applied on the imu structure through fem simulations, and lateral stress on the pzt cylinder top surface is inspected. this provides preliminary valuable information that help choosing the optimal anchor setting between the three examined ones. in figure 4(b), the generated stress distribution is shown using position 3 when the imu is submitted to 10g acceleration along the z-axis. stress distribution along the pzt diameter when the imu is submitted to xand z-axis accelerations are plotted in figure 5(a) and figure 5(b) respectively. we note that the stress is opposite and symmetrically distributed along the piezoelectric membrane with respect to its center. for the xaxis force, the stress values produced with position 2 and position 3 are close. nevertheless, our choice is pointed to position 3 since it is the only position that provides optimum stress in ring location which is useful for z-axis detection. it is worth noting that the structure is less sensitive to vertical excitations, and especially at the external ring, which could be explained by the fact that the seismic effect of the mass is reduced during a vertical excitation due to the high normal stiffness of the imu structure. consequently, priority will be given to placing the ring in the zone of maximum stress. (a) (b) fig. 5. illustration of 1d stress profile relative to positions 1 to 3 of the anchor when the imu is under (a) x-axis and (b) z-axis acceleration. by analyzing figure 5, we can conclude that all sense electrodes (i.e. sx1, sx2, sy1, sy2 and ring) should be localized in such a way that their median lines coincide with the stress peak. this will ensure that they will cover the distributed stressed area as depicted in figure 4(b). the electrodes’ width has been set to 575µm with a spacing of 125µm. these dimensions allow placing all electrodes properly in the available area where the stress is maximum. b. proof-mass length vs. mechanical resonance frequency the seismic mass is considered as a key performance element since it is used as an oscillator for drive mode generation and motions are transmitted to the piezoelectric membrane only through the proof-mass causing its deflection. hence, proof-mass dimensions should be carefully optimized for best performance. the cylindrical proof-mass length l is related to its weight, m, radius r, and material density, ρ=7800kg/m 3 by: � � ����� (1) for maximum proof-mass oscillation, the frequency of the drive signal used for excitation should be set around the mass resonance frequency, which is closely related to the mass length. therefore, the effect of the proof-mass length on the natural frequency of the structure has been examined. on the other hand, it is essential to examine the proof-mass tip flexibility along the xand z-directions to find which direction is more sensitive. hence, the sud design is simulated under x and z-axis acceleration excitation motion (10g) as a function of the proof-mass length. in figure 6, natural frequency and displacement magnitude are plotted, in both x-and z-directions, of the seismic mass middle tip for different mass lengths. a point worth emphasizing is that displacement and frequency are inversely proportional, i.e. when the mass is longer, displacement increases, but natural frequency decreases. moreover, it should be noted that the structure is more sensitive along the x-axis than the z-axis since x-axis displacement is much more pronounced. this would certainly influence the sensor outputs versus lateral and longitudinal excitations. c. pzt thickness influence piezoelectric properties and device sensitivity can be dependent on several factors, one of them being the pzt s tr e s s p ro fi le ( k p a ) s tr e s s p ro fi le ( k p a ) engineering, technology & applied science research vol. 10, no. 5, 2020, 6282-6289 6285 www.etasr.com almabrouk et al.: geometry investigation and performance optimization of a single-mass piezoelectric … thickness [29, 30]. in this context, we exhibit the effect of the pzt film thicknesses, ranging from 200 to 400µm on the produced tensor stress under an applied static acceleration force to the sud design. the results are exhibited in figure 7. fig. 6. tilt displacement of the proof-mass middle tip and structure resonance frequency versus length of the proof-mass under 10g accelerations. fig. 7. stress profile in response to different pzt thickness under static acceleration input. it has been underlined that the stress tensor is directly dependent on the pzt film thickness. the optimal film thickness for maximum mass-sensitivity of the design is in the range of 200µm. however, two points worth noting must be considered: firstly, the optimum pzt thickness must be chosen not only in terms of highest stress values but also in terms of respect to the maximum stress allowed by the material in order to avoid structural damages during system operation. in fact, the maximum allowable stress is commonly evaluated at 50mpa for soft pzt ceramics [28]. secondly, we have to pay attention to the additional stress generation by the mass oscillation. thus, stress values are considered in response to linear and angular motion under drive mode and it has been found that with 200µm of pzt thickness, a safety factor of 12 and 3 is ensured for linear and angular motion sensing respectively. these values are listed in table i. therefore, with this optimal thickness, imu outputs can be significantly ameliorated with no mechanical damages. table i. stress tensor of the sud design (200µm pzt thickness) in response to maximum load values under drive mode load (max) stress tensor safety factor acceleration 10g 4mpa 12 angular rate 2000 rad/s 14mpa 3 d. frequency response the operating frequency is very important since it defines the drive mode frequency which is the basic part of the angular rate detecting system. this mode must be accurately set to ensure a proof-mass oscillation in the x/y plan for 3-axis angular rate sensing. the choice of the drive signal frequency is preliminarily extracted from an eigen frequency study of the sud structure showing its behavior under each mode (figure 8). this study shows that the first resonant frequency mode is manifested by two symmetrical modes (mode 1a and mode 1b) showing deformations along xand y-axis respectively which corresponds well to our desired case. furthermore, the dynamic system response of the sud is analyzed under the acceleration motion input in order to assure that the chosen frequency is suited for both linear and angular motion sensing. the dynamic response is based on (2) governing a second order system of the acceleration sensing model [27] (mass-spring damper system): � � � � � � ��� � �� (2) where m is the mass of the proof-mass, a is the acceleration experienced to the proof-mass, x is the corresponding displacement, c is the damping coefficient, and k is the spring constant. by taking the laplace transform of this equation, the dynamic response is depicted in (3): ���� � ������������ (3) fig. 8. modal analysis of the analyzed imu structure. fig. 9. bode plot of the dynamic response of the sud. 16 18 20 22 24 26 28 proof mass length (mm) 0 200 400 600 800 1000 1200 1400 d is p la c e m e n t (n m ) 2000 3000 4000 5000 6000 f re q u e n c y ( h z ) x-axis displacement z-axis displacement 1st natural frequency engineering, technology & applied science research vol. 10, no. 5, 2020, 6282-6289 6286 www.etasr.com almabrouk et al.: geometry investigation and performance optimization of a single-mass piezoelectric … the transfer function is numerically examined and the magnitude (in db) and phase (in degrees) of the system response are depicted in figure 9. through this illustration, the first eigen frequency mode is manifested and the bandwidth of the sud is found to be 110hz. accordingly, the excitation frequency to be chosen is in the vicinity of the oscillation mode 1. indeed, exciting in the vicinity of the first resonant frequency avoids the appearance of nodes during the oscillation, and it permits consequently full exploitation of the seismic effect of the proof-mass. v. six-dof detection evaluation taking in account all the optimized parameters, the 6-dof outputs of the new design have been investigated. fem simulations were performed on the oscillating design to estimate acceleration and angular velocity responses retrieved directly from the detection electrodes, i.e. before being processed by the conditioning electronic blocks. applied accelerations are converted into a mechanical force given by newton's second law. the movements of the seismic mass are firstly transformed into a corresponding displacement on the piezoelectric surface, and then into an output voltage produced on sense electrodes thanks to the direct piezoelectric effect. in the presence of a rotational motion, a coriolis force fc is generated and acts always perpendicularly to the directions of angular rate to be measured and the proof-mass oscillation. thus, the new displacement amplitude raised by the coriolis effect is proportional to the angular rate to be measured using the direct piezoelectric effect. the efficiency of the piezoelectric effect, used for both excitation and detection modes, contributes significantly to the determination of the imu performance. the coriolis force is given by: ������ � 2����� ! " ω��! (4) where v is the applied drive velocity component on the oscillator having a mass mosci and ω is the angular rate to be measured. the coriolis force expression depends directly on the drive velocity of the proof-mass which represents the derivative of its displacement. hence, in order to improve the generated coriolis force, proof-mass displacement should be maximized. a. drive mode setting drive mode must be configured in such a manner that an oscillation motion of the proof-mass in the x/yplane is ensured. this is obtained through the application of four different ac signals that are phase shifted by 90 o with the same magnitude to the four drive electrodes. under these specific applied drive signals, the three displacement components of the seismic mass are extracted through fea in response to a frequency sweep. figure 10 exhibits the displacement magnitude of the central point of the proof-mass as a function of the excitation frequency under 300mv drive signal amplitude. indeed, displacements along both xand y-axes are equal and optimum exactly around the first eigen frequency (1681.5khz). displacement along the z-axis exists with very low amplitude, so it will not be taken into consideration and we can confirm that the proof-mass undergoes a circular oscillation motion in the x/y-plane. as the excitation frequency is in the vicinity of the resonance frequency, it is expected that the structure's vibration will increase, and thus the bias drive voltage will decrease. the choice of the excitation voltage amplitude (drive mode amplitude) is also essential since it influences the mass tip oscillation magnitude which increases linearly with the applied drive voltage as shown in figure 11. fig. 10. proof-mass middle tip displacement in x-, yand z-axes vs frequency under drive mode. fig. 11. proof-mass middle tip displacement in response to varying drive voltage amplitude. indeed, the choice of the excitation amplitude must respect the fact that the delivered voltage on sense electrodes due to drive oscillation must be minimal in order be able to visualize acceleration and angular rate effects on sensing voltages. when respecting this assumption, it will be always possible to distinguish motion response, from the oscillation one which is permanently present. it is worth noting that during the oscillation (i.e. in drive mode), the recovered voltage from the ring electrode is insignificant since half of its surface is located in an expansion zone, while the other half is located in a compression zone. hence, the average stress at the level of the whole connected ring is very weak unlike the s-ring (where the four sense electrodes are located) which is divided into four zones. the velocity components of the proof-mass versus time can be extracted and examined as shown in figure 12. in fact, as a very much lower displacement of the proof-mass is obtained in the z-direction, velocity would also be too low compared to the in-plane components. engineering, technology & applied science research vol. 10, no. 5, 2020, 6282-6289 6287 www.etasr.com almabrouk et al.: geometry investigation and performance optimization of a single-mass piezoelectric … fig. 12. x-, yand z-axis velocity components of the proof-mass oscillation. b. linear acceleration sensing evaluation under a lateral acceleration along the xor y-axis, the seismic-mass will tilt in the opposite direction, and thereafter the distributed stress in sense electrodes located on the line application of the acceleration will be positive on one side and negative on the other. then, a continuous offset voltage, which is proportional to the acceleration undergone by the mass, will be superimposed to the drive voltage generated by the proofmass oscillation as depicted in figure 13(a). similarly, in the case of z-axis acceleration, the summation of the four sense electrodes together will register an offset voltage which will also be superimposed on the excitation voltage. we note that the offset value of each acceleration output signal under proofmass oscillation is equal to the value corresponding to the pure acceleration effect (figure 13(b)) which validates the simulation results. (a) (b) fig. 13. x-axis acceleration response with the application of (a) drive mode and (b) static mode. c. angular rate sensing evaluation when subjected to a rotation motion, the coriolis force triggers a tilt force and excites the vibration of the second mode, called sense mode. the oscillation amplitude of the generated force will be proportional to the applied angular rate: �$ � 2 ����� & ' ( )*˄, -'-(-). (5) 1) case 1 in the presence of angular velocity around the x-axis ωx, two components of coriolis force are created: one along the zaxis and another along the y-axis, given by (6) and (7): �( � 2����� )-' (6) �) � �2����� (-' (7) the numerical values of displacement and velocity components are extracted through fem simulations,. this allows us to get the magnitude of the produced coriolis force in zand y-directions as exhibited in figure 14(a). it is obvious that the z-axis component of the coriolis force dominates since the x-direction displacement amplitude is much higher than in the z-direction one. consequently, in response to the x-axis angular rotation, the planar oscillation trajectory of the proofmass will be affected by the coriolis force along the z-axis and the effect of this force could be measured from the ring electrode by substituting the shifted new voltage from the initial drive voltage as shown in figure 14(b). indeed, the ring voltage keeps its sinusoidal shape, with a higher amplitude which is proportional to the undergone angular rotation. in addition, attention must be paid to the fact that because of the presence of the y-axis component of the coriolis force, the seismic mass will undergo a little additional oscillation stretched in the y-direction which can slightly increase the voltage recovered from the sense electrodes in the y-direction. consequently, the seismic mass will then undergo an elliptical curve oscillation stretched in the y-direction instead of a perfect circular trajectory which will increase the amplitude voltage recovered from the electrodes sy1 and sy2, compared to the one obtained from sx1 and sx2. (a) (b) fig. 14. (a) illustration of coriolis force along the z-and y-axes in response to x-axis angular rate, (b) output voltage from the ring electrode when subjected to x-axis angular rate. 2) case 2 in response to the y-axis angular velocity input, ωy, two coriolis forces are induced. however, only the dominant one is considered, which is along the z-axis (same logic as in case 1). in fact, the velocity oscillator along the x-axis is combined with ωy to give rise to a dominant coriolis force along z-axis as: �) � 2� '-( (8) similar to ωx, the ring electrode will be used to detect the yaxis angular rates. however, since xand y-axis proof-mass velocities are π/2 phase shifted, then the output signal of ωx and ωy will also have a π/2 phase shift. hence, a phase detector is proposed to distinguish ωx from ωy. 3) case 3 two coriolis force components are generated with the same magnitude under the z-axis angular rate. this is because engineering, technology & applied science research vol. 10, no. 5, 2020, 6282-6289 6288 www.etasr.com almabrouk et al.: geometry investigation and performance optimization of a single-mass piezoelectric … the z-axis angular input is perpendicular to the x-y oscillation plane. hence, the produced coriolis force will enclose two compounds: �( � 2����� '-) (9) �' � �2����� (-) (10) as noticed, the produced forces in xand ydirections are equal but they are phase-shifted due to the phase shift of the initial drive signals in xand y-directions. using fem simulations, under the z-axis angular rate, we were able to evaluate the generated coriolis effect on sense signals. in fact, the diameter of the oscillation circle of the seismic mass will either increase or decrease. then, the amplitude of the sinusoidal component of all sense electrodes located in the inner ring will either increase or decrease, depending on the direction of the angular rotation. the simulation result of the output voltage is plotted in figure 15. the output voltage versus time is extracted with the use of the potential difference between electrodes sx1 and sx2 as well as sy1 and sy2. (a) (b) fig. 15. sense voltage in response to the z-axis angular rate input: (a) output voltage (sx1-sx2) vs. time and (b) output voltage (sy1-sy2) vs. time. vi. comparison and discussion the sensitivity of the studied design is calculated in the three axes for angular velocity and linear acceleration sensing. when the results of the optimized design are compared to the results of the original one, an amelioration rate of sensitivity is found to be up to 165% for linear acceleration, whereas for angular rate sensing, the lateral sensitivity is ameliorated by about 330% and is multiplied by a factor of around 10 in the normal axis. sensitivity values relative to the original and the optimized design are listed in table ii. table ii. performances of the original and the optimized design in terms of linear and angular sensitivities angular rate sensitivity acceleration sensitivity xand y-axis z-axis xand y-axis z-axis original design 0.62µv/rad/s 0.13v/rad/s 98mv/g 45mv/g optimized design 2.65µv/rad/s 1.24v/rad/s 260mv/g 60.7mv/g the new 6-axis imu presents very good sensitivity especially in terms of z-axis angular velocity and 3-dimentional acceleration detection. this good performance is related to the precise setting of the geometrical design parameters that directly influence the output of the sensor. in fact, taking advantage of the most suitable anchor position, the optimized locations for sensing electrodes, the perfect choice of the operating frequency, and the minute thickness of the detecting element allows designing a high-performance sensor. this method of geometry investigation represents a reliable and efficient way to improve the mechanical and electrical sensor outputs. vii. conclusion inertial measurement unit sensors are widely used in various applications due to the important information they can provide including acceleration and angular rate data of a movable object. however, because of the use of two separate blocks, one for the accelerometer and one for the gyroscope, there are several limitations bound the imu development, consisting mainly in size, cost, and energy consumption. therefore, imus are restricted to relative bulk application and thus, despite its importance, the conventional imu becomes unsuitable to consumer applications unless the size of the devices is reduced. in this paper, we have detailed the design performance of a 6-axes single-mass piezoelectric imu. the derived fem model was based on an original design proposed in [25]. a meticulous analysis of geometry investigation was performed including anchor position, optimized locations for sensing and driving electrodes, proof-mass dimensions, and resonance operating frequency. this geometrical analysis highlighted the design optimization and presented a considerable amelioration in terms of linear and angular sensitivity. references [1] a. s. kundu, o. mazumder, p. k. lenka, and s. bhaumik, “hand gesture recognition based omnidirectional wheelchair control using imu and emg sensors,” journal of intelligent & robotic systems, vol. 91, no. 3, pp. 529–541, sep. 2018, doi: 10.1007/s10846-017-0725-0. 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[30] s. bhuvana, s. h. prathiksha, v. t. sindhu, and h. vasudha, “design and analysis of piezoelectric cantilever based vibration sensor,” in international conference on system, computation, automation and networking, pondicherry, india, jul. 2018. ab and cav nu wa ph use usi (su equ str tra nu par vol por app oce eng con tra foo sum inc of and hor gra has con con kn me sub con engineerin www.etasr num m la univer ab bstract—in this d mass transfe vity filled w merically. the alls while the ysical model f e of the darcy ing a finite vol ur) method i uation. the r reamlines, isoth ansfer rate in usselt and she rameters. keywords-nat lumes; inclined double-diffu rous medium plications in eanography, c gineering app ntained in fib ansport in pac od processing, mmary of the cluding differe solutions, mo d mass grad rizontally alo adients impose s been given t nvection wh ncentration ar owledge, no edium where t bject of this w i consider s nvection in an ng, technology r.com merica mass t 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ctive heat and ve hea us med djezzar f energetic phy exact science mentouri cons ntine, algeria @umc.edu.dz ntal walls o f solute and th ttom and top thermally insu ons, high conce at the right wa otheses of in and the saturat mogeneous wit ion between oret and du n by combined concentration tion of both he boussinesq  s ls s  l model and geom ons, the dimen m, energy and s are given by ( s ( )) t s n x x s n x          3223 mass transfer at and dia ysics es stantine 1 z of the cavity hey are subject walls, respect ulated and the entration at th all of the cavi ncompressible ted porous me th constant th the thermal ufour effects) d buoyancy f variations. so h temperature approximation (1) metry nsionless equa species transpo (2)-(4): ) s x (2) r in … y are ted to tively ey are he left ity as and edium hermo and are forces o, the and ns: ations ort in engineering, technology & applied science research vol. 8, no. 4, 2018, 3223-3227 3224 www.etasr.com latreche & djezzar: numerical study of natural convective heat and mass transfer in … 2 2 . . 2 2 t t t t y x x y x y                          (3) 2 21 . . 2 2 s s s s y x x y le x y                          (4) where the dimensionless variables are: t ty ψx , , , t t s s s s lx y t h h a h l ls h l           (5) the dimensionless boundary conditions are: 0 : 1, 0 0 s x and y t and y         (6) 1: 0, 0 0 s x and y t and y         (7) 0 : 1, 0 0 t y and x s and x         (8) : 0, 0 0 t y and x a s and x         (9) the present problem is governed by 5 parameters: the buoyancy ratio n, the lewis number le, darcy-modified rayleigh number ra*, the inclination angle and the aspect ratio a. the average values of nusselt number evaluated on the bottom wall and sherwood number evaluated on the left side wall are given by: 11 , 0 00 0 a t s nu dx sh dy a y xy x          (10) iii. numerical solution the volume finite method [22] is employed to solve numerically the governing equations together with the boundary conditions. the computation domain is divided into rectangular control volumes with one grid located at the center of the control volume that forms a basic cell. the set of conservation equations are integrated over the control volumes, leading to a balance equation for the fluxes at the interface. the iterative process, employed to find the stream function, temperature and concentration fields, was repeated until the following convergence criterion was satisfied:  , , 6 , 10 new old i j i j i j new i j i j        (11) where φ stands for ψ, t and s. the subscripts i and j denote grid locations in the (x, y) plane. a further decrease of the convergence criteria, 10−6, does not cause any significant change in the final results. numerical tests, using various mesh sizes, were done for the same conditions in order to determine the best compromise between accuracy of the results and computer time. a mesh size of 121×61 was adopted. the accuracy of the code was checked, modifying the thermal and solutal boundary conditions, to reproduce the results reported in 20. good agreement can be seen from table i with a maximum deviation of about 3.4%. table i. validation of the numerical code le max nu sh present work [20] present work [20] present work [20] 0.1 11.625 11.706 4.484 4.633 1.209 1.221 1 9.505 9.609 4.130 4.276 4.840 5.086 10 9.104 9.171 3.983 4.078 15.870 17.02 =0, ra*=200, n=0.3 and various le, in terms of  max, nu and sh iv. results and discussion a. considered situations in present work, the results are displayed in the form of stream, iso-thermal and iso-concentration lines to investigate the effect of inclination angle (0°≤α≤90°), buoyancy ratio (−5≤n≤5) and lewis number (0.1≤le≤10) while darcymodified rayleigh number, aspect ratio and prandtl number are taken as 200, 2 and 0.71 respectively. the rate of heat and mass transfer at different conditions in the cavity is measured in terms of the average nusselt and sherwood numbers. b. flow structure, temperature and concentration fields, and heat and mass transfer visualization. to show the effects of the inclination angle α, isotherms, stream functions and iso-concentration lines are presented in figure 2 for le=10 and n=0.1. for no inclination angle (α=0°) four regions of important concentration gradients can be observed. two of these regions are located in the vicinity of the upper part of the right wall and the lower part of the left wall where the cells exchange important quantity of solute with these boundaries. the two other regions are located in the vicinity of the upper and the lower central parts of the enclosure, in the interface between the cells where the solute exchange is by diffusion. for 0°<α<15° the previous regions exchange just their positions (the upper becomes lower and vice versa). the vortex strength of the fluid in the porous medium is lower when α15° and it increases when the angle of inclination decreases. when α>15° the secondary circulations disappear and the vortex strength of the fluid in the porous medium increases with the increase of the angle of inclination. the temperature field obtained shows the presence of thermal boundary layers near the upper and lower walls and parallel to the two other walls stratification of the temperature in the core region. the two regions of important concentration gradients located in the vicinity of the upper and the lower central parts of the enclosure disappeared. fig ra* str and the bif eng in the lay inc engineerin www.etasr g. 2. isotherm *=200, pr=0.71, a figure 3 pres ream functions d for the oppo e strength of furcates into tw genders a decr favor of the ere is a tende yers, this beha creases. ng, technology r.com s, iso-concentrat a=2, le=10 and n sents the isoth s with differen osed flow (n= the flow circ wo weak analo rease of the si upper one. t ency to the de avior decrease y & applied sci (a) (b) (c) (d) tionand and stre n=0.1 with differe herms, iso-con nt angles of inc =−2). it is seen culation decre ogical circulati ize and intensi the temperatu evelopment of es when the a ience research latreche & eam function lin ent inclination an ncentration line clination α for n that as α incr eases and the ions. exceedin ity of the lowe ure field show f thermal bou angle of inclin h v djezzar: nume nes for ngles. es and r le=5 reases e flow ng 45° er cell ws that undary nation fig. ra* vol. 8, no. 4, 20 erical study of n 3. isotherms =200, pr=0.71, a 018, 3223-3227 natural convec ( ( ( ( ( , iso-concentrat a=2, le=5 and n= 7 ctive heat and (a) (b) (c) (d) (e) ion and stream =-2 with different 3225 mass transfer m function line inclination angle r in … es for s. (α= ver the gra 15 upp wh the wh enc exc c. nu ra nu nu fu wh sig sh wh tha sh fig a=2 nu α= sig n sh sam and n wh engineerin www.etasr the concent =0°), shows th rtical walls an e core region adients can be °. two of the per part of the here the cells ese boundarie hich links the closure (the in change is by d heat and ma to show th usselt and she a*=200, pr=0. mber. in gen usselt number urthermore, wh hen the angle gnificant chang herwood numb hen the angle at the maximum happens when g. 4. average 2, n=2 with diffe figure 5 sho usselt and she =45° for differe gnificant chang increases un herwood numb me behavior f d 1, where the increases. th hen n increas ng, technology r.com tration field, o he presence of nd vertical stra n. three regi e observed wh ese regions ar e left wall and exchange im s. the third r two previous nterface betwe diffusion. ass transfer p he effects of erwood numbe .71, a=2, n=2 neral, when th decreases and hen (α<30°) of inclination ge on the nu ber decreases a of inclination m nu happens n (α20°). nusselt and sh rent lewis numbe ows the effect erwood numb ent lewis num ge on the nuss ntil the value bers increase w for (le=1 and e nusselt and s he nusselt an ses only when y & applied sci obtained for n f solutal bound atification of t ions of impo hen the inclina re located in d the lower pa mportant quan region is loca regions at the en the two cel parameters f the inclinati ers are presen 2 and differen he lewis num d the sherwood the sherwood n increases, w usselt number. and the nussel increases. pre s when (α=90° erwood number er and inclination of buoyancy ber for ra*=2 mbers. for (le selt and sherw e n=1 where when n increa 5) until n re sherwood num nd sherwood n 1 1n   . ience research latreche & no inclination dary layers ne the concentrat ortant concent ation angle ex the vicinity o art of the righ ntity of solute ated in the dis central parts lls) where the ion angle, av nted in figure nt values of l mber increase d number incr d number incr while there is when (α>30 lt number incr evious results °) and the max for ra*=200, p n angle values . ratio n on av 200, pr=0.71, e=0.1), there is wood numbers e the nussel ases. we can s eaches the valu mbers increase numbers dec the maximu h v djezzar: nume angle ear the tion in tration xceeds of the ht wall e with stance of the solute verage 4 for lewis es the reases. reases not a 0°) the reases, show ximum pr=0.71, verage a=2, s not a when lt and ee the ues -3 when crease um of both (n= an hor gen equ this (0°≤ (−5 rati resp dec num the max resp n=5 fig. a=2 vol. 8, no. 4, 20 erical study of n h nu and sh h =5). numerical ste inclined por rizontal solut neralized mod uations. a num s paper for dif ≤α≤90°), lew 5≤n≤5), while o and prandtl pectively. res creases and the mber increases inclination a ximum nu a pectively, and 5. 5. average n 2, α=45° with diffe a as a th d so da d g gr h ca k th k pe l en le l n bu nu n p pr p di pr pr ra r ra* d s di 018, 3223-3227 natural convec happens when v. co eady of double rous media w tal gradients del has been mber of relevan fferent values o wis number (0. e darcy-mod l number have sults show th e sherwood nu s, although, th angle and the and sh happe d both of them nusselt and she ferent lewis numb nomen spect ratio, [=l/h hermal diffusivity olutal diffusivity, darcy number, [=k ravitational accele avity height, m hermal conductivi ermeability of po nclosure length, m ewis number, [=a uoyancy ratio, [= nusselt number ressure, kg.m-1s-2 imensionless pres randtl number, [= rayleigh number, darcy-modified ra imensional conce 7 ctive heat and n n reaches th onclusions e-diffusive na with vertical has been used to sol nt results have of inclination 1≤le≤5), and dified rayleig e been taken a hat the averag umber increas hey change th e buoyancy r en when (α= m reach max erwood number f ber and buoyancy nclature h] y, m2.s-1 m2.s-1 k/h2] eration, m.s-2 ity of porous layer orous layer, m2 m a/d] ssh-sl)/tth-tl ssure, [=ε2h2p/0a =/a] [=gβt(th-tl)h 3/ ayleigh number, [ ntration, kg.m-3 3226 mass transfer he maximum v atural convecti temperature investigated. lve the gove e been present angle of the c the buoyancy gh number, a as 200, 2 and ge nusselt nu ses when the l heir behavior ratio. furtherm =90°) and (α ximum value w for ra*=200, pr y ratio values. r, w.m-1.k-1 l)] a2] a] [=ra.da] r in … value ion in and the rning ted in cavity ratio aspect d 0.71 umber lewis with more, 20°) when r=0.71, engineering, technology & applied science research vol. 8, no. 4, 2018, 3223-3227 3227 www.etasr.com latreche & djezzar: numerical study of natural convective heat and mass transfer in … s dimensionless concentration sh average sherwood number t dimensional temperature, k t dimensionless temperature, [= (t-tl) /(th-tl)] x,y coordinates system, m x, y dimensionless coordinates system, [=x(y) /h]  inclination angle, ° s solutal expansion coefficient, k -1  thermal expansion coefficient, m 3.kg-1  dimensional stream function, m2.s-1  dimensionless stream function  density of fluid, kg.m-3 h higher l lower max maximum value references [1] r. w. schmitt, “double diffusion in oceanography”, annual review of fluid mechanics, vol. 26, pp. 255–285, 1994 [2] j. s. turner, “double diffusive phenomena”, annual review of fluid mechanics, vol. 6, pp. 37–56, 1974 [3] s. ostrach, “natural convection with combined driving forces”, physicochemical hydrodynamics, vol. 1, no.4, pp. 233–247, 1980 [4] d. nield, a. bejan, convection in porous media, spinger, 2006 [5] d. b. ingham, i. pop, transport phenomena in porous media, elsevier, oxford, 2005 [6] p. vadasz, emerging topics in heat and mass transfer in porous media, spinger, 2008 [7] r. viskanta, t. l. bergman, f. p. incropera, “double diffusive natural convection”, in: natural convection: fundamentals and applications, hemisphere, 1985 [8] h. j. s. fernando, “buoyancy transfer across a diffusive interface”, journal of fluid mechanics, vol. 209, pp. l–34, 1989 [9] t. makayssi, m. lamsaadi, m. naimi, m. hasnaoui, a. raji, a. bahlaoui, “natural double-diffusive convection in a shallow horizontal rectangular cavity uniformly heated and salted from the side and filled with non-newtonian power-law fluids: the cooperating case”, energy conversion and management, vol. 49, no. 8, pp. 2016–2025, 2008 [10] m .a. teamah, “numerical simulation of double diffusive natural convection in rectangular enclosure in the presences of magnetic field and heat source”, international journal of thermal sciences, vol. 47, no. 3, pp. 237–248, 2008 [11] h. s. harzallah, a. jbara, k. slimi, “double-diffusive natural convection in anisotropic porous medium bounded by finite thickness walls: validity of local thermal equilibrium assumption”, transport in porous media, vol. 103, no. 2, pp. 207–231, 2014 [12] z. alloui, p. vasseur, “convection of a binary fluid in a shallow porous cavity heated and salted from the sides”, computers & fluids, vol. 81, pp. 85–94, 2013 [13] r. nikbakhti, j. khodakhah, “numerical investigation of double diffusive buoyancy forces induced natural convection in a cavity partially heated and cooled from sidewalls”, engineering science and technology, an international journal, vol. 19, no. 1, pp. 322-337, 2016 [14] m. a. teamah, m. k. dawood, w. m. el-maghlany, “double diffusive natural convection in a square cavity with segmental heat sources”, scientific research, vol. 54, no.2, pp. 287-301, 2011 [15] v. trevisan, a. bejan, “mass and heat transfer by high rayleigh number convection in a porous medium heated from below”, international journal of heat and mass transfer, vol. 30, no. 11, pp. 2341–2356, 1987 [16] v. j. bansod, r. k. jadhav, “an integral treatment for combined heat and mass transfer by natural convection along a horizontal surface in a porous medium”, international journal of heat and mass transfer, vol 52, no. 11-12, pp. 2802–2806, 2009 [17] f. zhao, d. liu, g. tang, “natural convection in an enclosure with localized heating and salting from below”, international journal of heat and mass transfer, vol. 51, no. 11-12, pp. 2889–2904, 2008 [18] l. abdelkrim, d. mahfoud, “convective heat and solute transfer in newtonian fluid saturated inclined porous cavity”, international journal of physical research, vol. 2, pp. 78-84, 2014 [19] a. a. mohamad, r. bennacer, “natural convection in a confined saturated porous medium with horizontal temperature and vertical solutal gradients”, international journal of thermal sciences, vol. 40, no. 1, pp. 82–93, 2001 [20] m. bourich, a. amahmid, m. hasnaoui, “double diffusive convection in a porous enclosure submitted to cross gradients of temperature and concentration”, energy conversion and management, vol. 45, no. 1112, pp. 1655–1670, 2004 [21] s. roy, t. basak, “finite element analysis of natural convection flows in a square cavity with non-uniformly heated walls”, international journal of engineering science, vol. 43, no. 8-9, pp. 668–680, 2005 [22] s. patankar, numerical heat transfer and fluid flow, hemisphere, 1980 microsoft word 29-3178_s_etasr_v9_n6_pp5029-5032 engineering, technology & applied science research vol. 9, no. 6, 2019, 5029-5032 5029 www.etasr.com chand et al.: numerical simulations on mixing dynamics of spherical and non-spherical tablets in … numerical simulations on mixing dynamics of spherical and non-spherical tablets in a pan coater ram chand physics department, college of sciences, university of hail hail, saudi arabia ra.chand@uoh.edu.sa ramzi hadj lajimi chemistry department, college of sciences, university of hail hail, saudi arabia r.lajimi@uoh.edu.sa saeed uddin national center of excellence in analytical chemistry, faculty of science, university of sindh, pakistan chairman.bsek@hotmail.com sujo meghwar geography department, faculty of science, university of sindh jamshoro, pakistan sujo@usindh.edu.pk umer farooq physics department, college of sciences, university of hail hail, saudi arabia u.farooq@uoh.edu.sa najeh rekik physics department, college of sciences, university of hail hail, saudi arabia na.rekik@uoh.edu.sa abstract—discrete element simulations provide valuable insight into the mixing dynamics of granular materials in industry. in this paper, numerical work is conducted in order to find the influence of pan rotational velocity and particle shape on mixing behavior. four types of particles of different shapes were chosen: spherical, non-spherical type 1 (disk shape), non-spherical type 2 (capsule shape), and non-spherical type 3 (triangular shape). the pan mixer was filled with ~ 30 % volume of the same shape with the particles and was rotated at 15 rpm, 30 rpm, 45 rpm, and 60 rpm. the particles were colored as bottom-particles, middleparticles, and top-particles in order to visualize mixing efficiency. the homogeneity of the mixtures was determined by using contact dynamics of particles. the results show that fast-rotating pan (30-60 rpm) provides good mixing for all shapes of particles. however, non-spherical particles do not show as good mixing as spherical particles. keywordsgranular mixing; dem; rotaing pan; tablet coating i. introduction granular material is common in daily life [1-3], demonstrating a variety of complicated behaviors, some of which are not thoroughly perceived [3-7]. one of the issues in this material is mixing and de-mixing or segregation of granules [8-10]. mixing and de-mixing of granular material with various properties is a strikingly testing procedure, pertinent to numerous mechanical applications [7-11]. in industry, particle mixing is an important process. mixing and segregation phenomena describe an important issue into the process of mixing granular particles having various physical properties like size, density, shape, etc. distinctly from liquids and gases, solid granules are not a thermal agitated system. in order to get a definite level of mixing they need to be mechanically activated. traditionally, three mixing mechanisms are largely recognized: dispersion, convection, and shear mixing. shear mixing is especially relevant to the granular material. it is a combination of both dispersion and convection mechanisms [12-13]. these mechanisms are performed in a solid system known as mixer. there are two types of mixers: tumbling mixers and agitated mixers [13]. in tumbling mixers, a completely confined container is rotated about an axis resulting in tumbling over of the granules in the mixture area inside the container. in contrast, convective mixers are characterized by the action of impellers in order to incorporate more shear into the mixture and provide a good mixing product in the end. in this study, pan coater mixer was used, which is a type of convective mixer, to study the mixing of tablet coating. in pharmaceutical industries, tablet coating is important for masking the unpleasant taste of a medicine, enhancing the appearance of the product, modifying its dissolution rate, etc. [14-20]. many studies were conducted focusing on the mixing of grains with different sizes [12-13], but only a few studies considered shape and elongation, which are identified as important characteristics for inducing segregation [21-22]. the impact of different parameters on segregation is studied in [22]. the authors concluded that spherical grains have a higher flow-ability, leading to smaller repose angles and are more prone to segregation. instead, irregular-shape particles are preventing them from free flowing and percolation [13, 17]. the shape of granular particles has also a direct impact on the packing density of the granular media which is the main cause of segregation [12], but their work doesn’t demonstrate the influence of the rotational speed of pan on non-spherical particles of complex shapes. in this work, discrete element method (dem) simulations are performed to study the mixing of binary mixtures of tablets having the same volume but different shapes. the mixing dynamics of a layered tablet was characterized in a rotating pan, highlighting the impact of the spherical and non-spherical shape, of the pan angular speed, and of contact dynamics between particles. particle mixing is a significant but ineffectively comprehended part of coating of pharmaceutical tablets which is usually done in the rotating pan coaters [16]. corresponding author: najeh rekik engineering, technology & applied science research vol. 9, no. 6, 2019, 5029-5032 5030 www.etasr.com chand et al.: numerical simulations on mixing dynamics of spherical and non-spherical tablets in … ii. dem simulation and results a. model description dem [23-25] has been increasingly applied for the investigation of tablet motion in coating mixers. in this method, newtonian equations of motion are used to calculate particle motion and interactions. the force on each particle i is calculated by the sum of gravitational and inter-particle components according to: ∑�� � ��� � � � � (1) where �� and � are normal and tangential components of force respectfully. the torque � on each particle is the sum of the moment of the tangential forces � arising from inter-particle contacts: ∑�� � �� � (2) the normal forces � and the tangential forces � are calculated according to hertzian contact model and mindlinderesiewicz model respectively. both normal and tangential force models are described by damping components where the damping coefficient is related to the coefficient of restitution as given in [26]. accordingly, the normal force � is given by: � � � � �∗√�∗ � � � (3) where �∗ is the equivalent young’s modulus, �∗ and the equivalent radius which are defined by: � �∗ � ��υ� � �� � ��υ� � �� (4) � �∗ � � �� � � �� (5) where �� , �� , �� and �� , �� , �� are the young’s modulus, poisson ratio and radius of particles i and j in contact. these models are implemented in a commercially available dem code called edem academic 2.6.1 [27]. this code has already been validated for such types of particle flows and mixing in various conditions [28-29]. b. simulation settings the dem particles and the container are made of the materials defined in table i. the container is modeled as a pan mixer by an open source mesh generator 3d application. the mesh cylinder has a total length of 16.6cm along the axial direction with 20cm diameter. in order to mix the particles, some baffles are created inside this pan. the schematic setup with all the measurements of the pan are given in figure 1. after generating the geometry, this pan mesh is imported into edem code. we modeled 4 types of granular particles by edem code as shown in figure 2. first, we will initialize the spherical particles randomly by pouring from injector. the diameter of the particle is 3mm. we color them as red for bottom, green for middle and blue for top particles so that mixing can easily be deduced from their contact dynamics. in the same way, we will generate 3 other types of particles in the mixer. all other parameters of the particles are given in table i. after pouring the particles of the same shape into the pan, the tablets in the 25%-filled mixer were allowed to settle under the effect of gravity. after settling of all particles, the mixer pan is set to rotate with a rotational speed � in the unit of revolution per minute (rpm or rmp). we set the rotational speed at 15rpm, 30rpm, 45rpm, and 60rpm for 10000s. snapshots of the settled states and the mixed states are shown in figure 3 for non-spherical type 2. table i. simulation input parameters property symbol unit value coefficient of static friction (particle-wall) !" 0.2 coefficient of static friction (particle-particle) ! 0.3 coefficient of rolling friction # 0.1 coefficient of restitution (particle-particle) $! 0.3 coefficient of restitution (particle-wall) $!" 0.4 poisson ratio (particle) % 0.30 poisson ratio (wall) % 0.33 shear modulus (particle) �! mpa 1.0 shear modulus (wall) �& gpa 27.9 density of particle '! kg m�⁄ 2000 density of wall material '& kg m�⁄ 8050 fill level 25% angular velocity of the pan � rpm 15, 30, 45, 60 fig. 1. simulation setup: internal and external properties of mixing pan fig. 2. shapes of particles: (a) spherical, (b) disk-type (non-spherical type 1), (c) capsule (non-spherical type 2), (d) triagulate (non-spherical type 3) fig. 3. snapshot of mixing of non-spherical particles (before and after) engineering, technology & applied science research vol. 9, no. 6, 2019, 5029-5032 5031 www.etasr.com chand et al.: numerical simulations on mixing dynamics of spherical and non-spherical tablets in … c. mixing behavior deduced from contact number in order to measure the variance of the mixture, contact dynamics of particles was used. note that initially the number of contacts among bottom, middle, and top was zero. after the mixer was rotated, the number of contacts increases and reaches a steady value, which indicates that the particles are fully mixed. after deducing the number of contacts, we can plot it for the various types of particles. d. mixing profile from the rotating pan mixing profiles showing the contact dynamics of all types of particles are depicted in figure 4, for all rotation velocities. in all mixing profiles, the study was focused to bottom-top layers of particles only. in the beginning, both layers were not in contact with each other, so the mixing state was zero. once the mixing starts, the number of contact increases which can be clearly seen from the plots of figure 4. all simulations were run for 1000s duration, but the results show that steady state mixing was achieved after 30s of rotation. also, the results show that, slowly rotating pan takes a little bit longer time to achieve the same mixing state. fig. 4. mixing of spherical and non-spherical particles (bottom-top layers) fig. 5. mixing profiles of spherical and non-spherical particles after rotations are completed (bottom-top layers) the mixing profiles from 30s to 60s are shown in figure 5. we see that steady states of mixing are achieved. for nonspherical particles, the slowly rotating pan doesn't exhibit good mixing state. the spherical particles mix repeatedly at all rotational speeds as plotted in figure 6. fig. 6. time taken for the final mixing for all rotational speeds e. maximum mixing in order to study the influence of angular velocity of the pan on the mixing of particles over time, we further define the parameter maximum mixing ,&-. as follows: χ &-. � / /012 (6) where 3 is the contact number after the rotations are completed and 3&-. is the total number of contacts for a particular shape type particle. in figure 7 the data taken from edem for maximum mixing ,&-. of all profiles are shown. fig. 7. maximum mixing (,&-.) achieved the result shows that type 3 shape particles don’t show good mixing as compared to spherical particles, because nonspherical particles reveal more opposition to motion and mix. the reason is that non-spherical shape creates irregular voids engineering, technology & applied science research vol. 9, no. 6, 2019, 5029-5032 5032 www.etasr.com chand et al.: numerical simulations on mixing dynamics of spherical and non-spherical tablets in … between the particles that prevent them from further mixing. even though blades were used inside the pan to provide more shear to the particles, the voidage in non-spherical particles transfers a little shear to nearby particles [8, 11, 30-32]. consequently, lower granular temperature is achieved which reduces the mixing [8, 11, 31]. further work in this regard is needed to study the mixing mechanism of non-spherical granular particles mixed with fluids such as water. iii. conclusion in this work, dem simulations were performed to study the influence of pan rotational velocity and the shape of granules on mixing behavior. four types of particles having different shapes were poured. the pan mixer was filled with ~ 30 vol % of the same shape particles and was rotated at 15 rpm, 30 rpm, 45 rpm, and 60 rpm. the homogeneity of the mixtures was determined by using contact dynamics of particles. it has been found that fast rotating pan such as 30-60 rpm provides good mixing for all shapes of particles. the triangulate shape particles do not show good mixing while the spherical particle have the best mixing among all four types of particles studied in this work. acknowledgment this research was funded by the deanship of scientific research (dsr) of the university of hail, saudi arabia (project number: 0150298). references [1] r. d mindlin, “elastic spheres in contact under varying oblique forces”, journal of applied mechanics, vol. 20, pp. 327-344, 1953 [2] r. chand, saeeduddin, m. a. khaskheli, a. m. soomro, h. saleem, w. a. bhutto, a. h. nizamani, m. y. soomro, n. m. shaikh, s. v. muniandy, “fractional analysis of light scattering data from gravitydriven granular flows”, international journal 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statistical mechanics and its applications, vol. 391, no. 20, pp. 4590-96, 2012 [12] a. hassanpour, m. pasha, m. alizadeh, m. ghadiri, a. bayly, “the effect of particle shape on predicted segregation in binary powder mixtures”, powder technology, vol. 319, pp. 313-322, 2017 [13] c. piacenza, m. marconati, c. hare, a. c. santomaso, m. ramaioli, “mixing grains with different elongation in a rotating drums”, available at: https://arxiv.org/abs/1809.00153, 2018 [14] j. bridgwater, “mixing of particles and powders: where next?”, particuology, vol. 8, no. 6, pp. 563-567, 2010 [15] j. bridgwater, “mixing of powders and granular materials by mechanical means-a perspective”, particuology, vol. 10, no. 4, pp. 397-427, 2012 [16] e. sahni, r. yau, b. chaudhuri, “understanding granular mixing to enhance coating performance in a pan coater: experiments and simulations”, powder technology, vol. 205, no. 1-3, pp. 231-241, 2011 [17] a. dubey, r. hsia, k. saranteas, d. brone, t, misra, f. j. muzzio, “effect of speed, loading and spray pattern on coating variability in a pan coater”, chemical engineering science, vol. 66, no. 21, pp. 51075115, 2011 [18] g. r. chandratilleke, a. b. yu, j. bridgwater, “a dem study of the mixing of particles induced by a flat blade”, chemical engineering science, vol. 79, pp. 54-74, 2012 [19] l. obregon, a. realpe, c. rinaldi, c. velazquez, “mixing of granular materials, part i: effect of periodic shear”, powder technology, vol. 197, no. 1-2, pp. 9-16, 2010 [20] l. obregon, a. realpe, c. velazquez, “mixing of granular materials, part ii: effect of particle size under periodic shear”, powder technology, vol. 201, no. 3, pp. 193-200, 2010 [21] c. henrique, g. batrouni, d. bideau, “diffusion as a mixing mechanism in granular materials”, physical review e, vol. 63, article id 011304, 2000 [22] y. fan, k. m. hill, “theory for shear-induced segregation of dense granular mixtures”, new journal of physics, vol. 13, article id 095009, 2011 [23] p. a. cundall, o. d. l. strack, “a discrete numerical model for granular assemblies”, geotechnique, vol. 29, no. 1, pp. 47-65, 1979 [24] f. bertrand, l. a. leclaire, g. levecque, “dem-based models for the mixing of granular materials”, chemical engineering science, vol. 60, no. 8-9, pp. 2517-2531, 2005 [25] m. rajabi, h. s. rad, m. s. masoudian, “a numerical model for caprock analysis for subsurface gas storage applications”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2438-2446, 2018 [26] y. tsuji, t. tanaka, t. ishida, “lagrangian numerical simulation of plug flow of cohesionless particles in a horizontal pipe”, powder technology, vol. 71, no. 3, pp. 239-250, 1992 [27] www.edemsimulation.com [28] y. wang, f. tonon, “dynamic validation of a discrete element code in modeling rock fragmentation”, international journal of rock mechanics and mining sciences, vol. 48, no. 4, pp. 535-545, 2011 [29] c. p. alonso, j. a. delgadillo, “experimental validation of 2d dem code by digital image analysis in tumbling mills”, minerals engineering, vol. 25, no. 1, pp. 20-27, 2012 [30] m. alian, f. e. mozaffari, s. r. upreti, j. wu, “using discrete element method to analyze the mixing of the solid particles in a slant cone mixer”, chemical engineering reseach and design, vol. 93, pp. 318329, 2015 [31] d. nguyen, a. rasmuson, i. n. bjorn, k. thalberg, “cfd simulation of transient particle mixing in a high shear mixer”, powder technology, vol. 258, pp. 324-330, 2014 [32] j. f. camenen, y. descantes, “geometrical properties of rigid frictionless granular packings as a function of particle size and shape”, physical review e, vol. 96, article id 012904, 2017 microsoft word 9-2719_s1_etasr_v9_n3_pp4120-4124 engineering, technology & applied science research vol. 9, no. 3, 2019, 4120-4124 4120 www.etasr.com japitana et al.: a geoinformatics-based framework for surface water quality mapping and … a geoinformatics-based framework for surface water quality mapping and monitoring michelle v. japitana school of engineering, university of san carlos, cebu city and college of engineering and geosciences, caraga state university, butuan city, philippines mvjapitana@carsu.edu.ph marlowe edgar c. burce school of engineering, university of san carlos, cebu city, philippines mcburce@yahoo.com chul-soo ye image and vision system laboratory, department of aviation and it convergence, far east university, gamgok-myeon, korea csye@kdu.ac.kr abstract—the management of water systems must be sustainable, something that requires systematic and comprehensive monitoring. however, the attempts to obtain a comprehensive water quality monitoring (wqm) program in developing countries are challenged due to the lack of an integrated framework and limited resources. at present, the philippines has no systematized technical and operational monitoring approach, poor coordination and data collection system, and weak law enforcement. on the other hand, geoinformatics promises a more convenient and cost-effective wqm to complement the traditional method. the goal of this study is to demonstrate how to maximize the use of geonformatics in developing methods and models to address the lack of spatial trends, timely monitoring, and integrated monitoring framework that could lead to a sustainable wqm system. this study employs remote sensing and gis technique combined with ground-based water quality data as geoinformatics-based framework to derive water monitoring and assessment information. results of this study showed that satellite images can be utilized to derive empirical models to estimate wq parameters. the validation results showed that the estimated wq values using the rs-based models have no significant difference when compared with the actual wq values. also, the wq maps derived using geographic information system (gis) were proven useful in providing better representation and analysis of spatial and temporal information that can provide a comprehensive and cost-effective reference for wq monitoring and assessment. keywords-landsat; water quality monitoring framework; water quality modeling; water quality trends i. introduction water sustainability is of high importance, as water is one of the most vital resources. water and its quality are one of the vital elements in the sustainable development goals (sdgs) of the united nations (un) development program. water serves as a common link among other sdgs [1], but the world is not yet on track in achieving water-related sdg indicators. in fact, the attempts to obtain a comprehensive water quality monitoring (wqm) program in developing countries are challenged due to the lack of an integrated framework and limited resources. it is, therefore, reasonable to give full attention to how emerging technologies can aid in transforming current water management and water quality monitoring practices, especially in less-developed countries. geoinformatics emphasized in a formal approach to handle geoinformation and was described as an integrated approach to gis, photogrammetry, remote sensing, and cartography [2]. integration of remotely-sensed data, gps, and gis technologies provides a valuable tool for monitoring and assessing waterways [3]. there is a high feasibility of integrating geoinformatics technologies in the existing water quality monitoring framework. remote sensing technology has allowed measurements on a global scale over long periods and is now proving useful in monitoring coastal waters [4], estuaries [5], and lakes and reservoirs [6, 7]. biological oxygen demand (bod) is among the most common water quality parameters measured using remote sensing [8] while rs-based model development studies for water ph are very limited. the ph level is a measure of acid content in water, thus water containing a great deal of organic pollution will generally tend to be acidic [9], while bod is a measure of the amount of oxygen that bacteria will consume under aerobic conditions while decomposing organic matter [8]. the goal of this study is to develop a geoinformatics-integrated water quality monitoring framework that can provide comprehensive and cost-effective water quality (wq) assessments. this study aims to demonstrate the use of remote sensing and gis technologies for wq model development and validation, wq estimation and mapping, and in wq spatial and temporal trends analysis. ii. study area tubay river is one of the classified class “a” water bodies in agusan del norte, philippines. its headstream is the main outlet of lake mainit and the river traverses the municipalities of jabonga, santiago, and tubay. there are two major tributaries of the river, the aciga river is at its upstream portion and the kinahiluan river at the mid-downstream part. tubay river is situated in a 22,000-hectare catchment area with diverse land uses that include mining, irrigation and other agricultural uses, fishery, livestock production [10], and mining. the environmental management bureau (emb) pointed out that tubay river is a receptor of domestic solid and liquid wastes and other non-point sources of pollution [10]. corresponding author: michelle v. japitana engineering, technology & applied science research vol. 9, no. 3, 2019, 4120-4124 4121 www.etasr.com japitana et al.: a geoinformatics-based framework for surface water quality mapping and … iii. proposed framework figure 1 shows the schematic diagram outlining the proposed geoinformatics-integrated wqm framework. in the proposed framework, the use of remote sensing and gis techniques are combined with ground-based water quality data to derive wq monitoring and assessment information. the developed geoinformatics-integrated framework is further proposed to be employed to any satellite sensor and wq of interest. the different components of the proposed framework are described in this section. fig. 1. proposed geoinformatics-integrated wqm framework a. satellite data and water quality datasets quarterly wqm data of emb for the years 2014-2016 were available during the conduct of this study. the dates of measurements of these datasets that closely matched the time of acquisition of the satellite images were considered in the model development, model validation, and wq estimation and mapping. also, satellite images with different dates of acquisition were utilized for the model development and for validating the models. table i shows the list of landsat images downloaded from usgs earth explorer and employed in delineating river map and in estimating ph and bod. table i. input images for water body detection, model development and validation, and wq estimation. input image acquisition date purpose landsat 8 (bands 2,3, 5-7) march 29, 2017 waterbody detection landsat 8 (bands 1-7) april 19, 2015 wq model development landsat 8 (bands 1-7) july 26, 2016, august 27, 2016 wq model validation for ph and bod landsat 8 (bands 1-7) april 19, 2015, october 12, 2015, july 26, 2016, august 27, 2016 wq estimation/mapping b. image processing first, the landsat images were pre-processed to apply radiometric and atmospheric corrections. then, the surface reflectance bands were used to perform principal component analysis (pca), band ratio, and multi-band water indices which were computed using (1)-(3) respectively: �� � �� ��⁄ (1) ( ) ( )6363 ρρρρ +−=mndwi (2) ( ) 7sh 0.25 awei ρρρρρ ×−+×−×+= 6532 5.15.2 (3) where �� is ultra-blue (coastal/aerosol) band, � is the blue band, � is the green band, �� is the nir band, �� is the swir 1 band, and �� is the swir 2 band of landsat 8 oli image. c. waterbody detection the mndwi and awei water indices were classified using minimum distance algorithm to delineate tubay river (figure 2) from the landsat 8 image. the delineated river map is employed as a mask image during river wq maps generation. fig. 2. derived river map using the combination of mndwi and awei water index. d. water quality model development and validation the wq models for ph and bod were derived as described in [11]. the two remote sensing-based wq models were given as follows: � � 8.339 � �0.827 � ��� (4) ��� � 0.382 � �28.746 � pc4� (5) the models were then applied to the corresponding input bands and the estimated wq values for ph and bod at the specific locations of the emb monitoring stations were calculated. to evaluate the reliability of the models, t-tests were performed by comparing the estimated wq values with that of the actual values measured by the emb. e. wq estimation and mapping the validated wq models were applied to the whole input bands of using band math of envi 5.1 software to derive the wq images. then, the wq images were loaded in qgis 2.16 software to generate the wq maps. using qgis, non-water areas in the wq image were masked out using the river map as mask image. and finally, gradient colors and histogram engineering, technology & applied science research vol. 9, no. 3, 2019, 4120-4124 4122 www.etasr.com japitana et al.: a geoinformatics-based framework for surface water quality mapping and … stretching were applied for better representation of the spatial and temporal distribution of ph and bod in the study area. iv. experimental results the models were validated using two sets of landsat images, the validation results with the best performance are shown in tables ii and iii, which show the estimated versus the actual wq data and the result of the t-test for ph and bod, respectively. the differences between the estimated and actual ph values are very small having an average value of 0.11. at emb stations 3 and 5, the estimated ph value is very close to the actual ph value with difference values of 0.04 and 0.08, respectively. when t-test was performed to compare the two datasets for ph, the result showed that the t value is less than the critical t value resulting to a p-value higher than 0.05, hence there’s no significant difference between the two measurements. table iii shows that the average difference between the two bod measurements is 0.32. the lowest difference values between the predicted and the actual bods are at emb stations 1 and 7. the t-test results showed a p-value greater than 0.05, hence the null hypothesis that there is a significant difference between the two groups of measurements can be rejected. table ii. estimated and actual ph station ph difference t-test estimated actual t value p-value 1 8.12 7.94 0.18 t=2.08<t critical value=2.16 0.06 2 8.16 7.99 0.17 3 8.16 8.12 0.04 4 8.33 8.05 0.28 5 8.27 8.19 0.08 6 8.23 8.07 0.16 7 8.29 8.05 0.24 average difference value 0.11 table iii. estimated and actual bod station bod difference t-test estimated actual t value p-value 1 0.49 0.30 0.19 t=0.08<t critical value=2.45 0.94 2 0.62 1.00 0.38 3 0.63 0.30 0.33 4 0.61 1.00 0.39 5 0.43 0.10 0.33 6 0.62 1.00 0.38 7 0.62 0.40 0.22 average difference value 0.32 a total of four wq maps for each ph and bod were generated, portraying the spatial and temporal distribution of wq in tubay river. figures 3 and 4 show the 1-month and 6month intervals of ph maps while figures 5 and 6 are showing the bod maps for the same time intervals. figure 3 showed a slight increase of ph level in tubay river, except in some portions near the tributaries. the ph map for august showed a significant decrease in the downstream of aciga-tubay river junction and in the upstream of kinahiluan-tubay river junction in figure 4, the two ph maps with a 6-month interval show an overall increase in ph throughout the river except in the downstream of kinahiluan-tubay river junction where the red color in the october ph map depicts a significant ph level decrease. in analyzing the spatial and temporal distributions of bod (figure 5), the wq maps imply an overall increase of bod in tubay river, while the 6-month interval bod maps (figure 6) show an overall decrease of bod levels. fig. 3. wq maps showing the spatial and 1-month temporal distribution of ph in tubay river fig. 4. wq maps showing spatial and 6-month temporal distribution of ph in tubay river fig. 5. wq maps showing spatial and 6-month temporal distribution of bod in tubay river fig. 6. wq maps showing spatial and 6-month temporal distribution of bod in tubay river engineering, technology & applied science research vol. 9, no. 3, 2019, 4120-4124 4123 www.etasr.com japitana et al.: a geoinformatics-based framework for surface water quality mapping and … by visually contrasting the two bod maps, it can be observed that many locations throughout the river have noticeable changes in bod levels. these locations include the upstream of kinahiluan river, downstream of kinahiluantubay river junction, and downstream of aciga-tubay river junction. this kind of visual assessments drawn from figures 3-6 proves that wq maps derived using geoinformatics approaches can provide easy spatial and temporal distribution analysis. this possibility is lacking in the traditional pointspecific wq data. also, the derived wq maps can be a good reference to identify the part of the river that did not pass the minimum criteria and those parts of the river where prominent changes are consistently observed. these locations could then be recommended as new sampling areas for the next wq monitoring campaigns. to demonstrate this practical advantage in using rs-based wq maps, new random points (rps) were added in the existing emb sampling points using the qgis software as shown in figure 7. the identification of the locations of rps is based on the spatial patterns observed in figures 3-6. from this new set of points, the ph and bod levels at four time-scales were then extracted to generate wq profiles shown in figures 8-11. fig. 7. map showing the locations of the rps and emb sampling points. fig. 8. ph profiles for july and august 2016. in the 2016 profile graphs of figure 8, the ph level almost follows the same pattern except for emb6, rp3, rp5, and rp6. also, by comparing the two ph profiles, it can be observed that there were significant changes in ph levels in emb5, rp5, and rp6. in figure 9, the profile graphs for april and october 2015 show an overall increase of ph levels except for rp2 where ph significantly decreased to 7.9. it can be further observed that ph levels of tubay river did not vary considerably within a 6-month interval. the average ph of all rp and emb points in tubay river is is 8.09 and 8.23 during april and october of 2015 respectively. fig. 9. ph profiles for april and october 2015. fig. 10. bod profiles for july and august 2016. fig. 11. bod profiles for april and october 2015. on the other hand, bod profiles in figure 10 show there were remarkable changes in bod levels between july and august 2016. notable differences were observed in emb5, rp1, rp2, and rp6. slight changes were observed only in emb2, emb 3, and rp3 to rp5 while the bod levels are almost constant at emb4 and emb6. in comparing the 6month interval bod profiles (figure 11), it can be observed that there’s a significant increase in the bod level in rp1 in contrast to rp2 where a significant decrease in the bod was engineering, technology & applied science research vol. 9, no. 3, 2019, 4120-4124 4124 www.etasr.com japitana et al.: a geoinformatics-based framework for surface water quality mapping and … observed. overall, an increase in the bod level was observed in all observing points within the 6-month time difference. v. summary of findings this study described a geoinformatics-integrated wq monitoring framework to demonstrate the practical advantage of using rs datasets like landsat imageries in analyzing spatial and temporal distributions of wq parameters. in this study rsbased models for ph and bod were developed and validated. the wq data estimated by the validated models were statistically proven to have no significant difference between the actual measurements taken by emb. the derived wq maps showed a good representation of the spatial distribution of ph and bod where end-users can visually assess the spatial trends of the wq parameters throughout the river. the advantages of using rs datasets for wq modeling and monitoring were also proven useful in this study as it can provide various wq maps at different temporal scales. though this study only considered one-month and six-month time differences, it showed that water managers can take advantage of the 15-day return periods of the landsat missions to augment the existing wq monitoring data taken using the traditional methods. furthermore, the wq maps presented in this study showed that they can be an excellent reference to identify the parts of the river that did not pass the minimum criteria and areas where prominent changes are consistently observed. these locations could then be recommended as new sampling areas for the next wq monitoring campaigns. vi. conclusion and recommendations a simple workflow describing a geoinformatics-based wq monitoring framework was presented in this study to perform model development and validation, wq estimation and mapping, and wq spatial and temporal trends analysis. results of this study showed that a geoinformatics-based wqm, can provide convenient and comprehensive monitoring and assessment of wq distributions that the traditional pointspecific wq data don’t have. also, since landsat imageries can be downloaded for free, the proposed wqm framework is cost-effective and can complement the traditional methods. though this study presented promising results, it is also important to note that the developed wqm framework is not yet rigorously optimized to achieve a dynamic and comprehensive wqm system. it is rather a simple method outlined to systematically extract spectral information from satellite images to develop wq empirical models and transform spectral signatures into wq information. the framework employed in this study aimed to provide an operational method of converting wq information into visually-convenient reference guides to assess and monitor wq spatial and temporal trends. there still remains one crucial phase in the proposed wqm framework that has to be implemented and tested for further study, which is the wq data management and dissemination. the existing wqm scenario in this country is far from realizing the implementation of a centralized and online wq data management and dissemination. given the fast-paced advancement of technology, especially in ict and the internet of things, research and development studies must be initiated to keep up with these technologies. future development steps in line with achieving a dynamic, systematic, and comprehensive wqm system include the development of a comprehensive and interactive web platform for wq data display and dissemination and the development of an online platform that promotes online wq data sharing and archiving. acknowledgment this paper was supported by the engineering research and development for technology grant of the philippine’s department of science and technology. authors would like to thank j. e. b. cubillas and r. tacubao of emb-caraga for their assistance. references [1] a. bhaduri, j. bogardi, a. siddiqi, h. voigt, c. vorosmarty, c. pahlwostl, s. e. bunn, p. shrivastava, r. lawford, s. foster, h. kremer, f. g. renaud, a. bruns, v. r. osuna, “achieving sustainable development goals from a water perspective”, frontiers in environmental science, vol. 4, pp. 64, 2016 [2] m. ehlers, “geoinformatics and digital earth initiatives: a german perspective”, international journal of digital earth, vol. 1, no. 1, pp. 17-30, 2008 [3] j. c. j. ritchie, p. p. v zimba, j. h. j. everitt, “remote sensing techniques to assess water quality”, photogrammetric engineering and remote sensing, vol. 69, no. 6, pp. 695-704, 2003 [4] m. nazeer, j. e. nichol, “development and application of a remote sensing-based chlorophyll-a concentration prediction model for complex coastal waters of hong kong”, journal of hydrology, vol. 532, pp. 80-89, 2016 [5] m. hartnett, s. nash, “an integrated measurement and modeling methodology for estuarine water quality management”, water science and engineering, vol. 8, no. 1, pp. 9-19, 2015 [6] f. mushtaq, m. g. nee lala, a. c. pandey, “assessment of pollution level in a himalayan lake, kashmir, using geomatics approach”, international journal of environmental analytical chemistry, vol. 95, no. 11, pp. 1001-1013, 2015 [7] l. c. gonzalez-marquez, f. m. torres-bejarano, a. c. torregrozaespinosa, i. r. hansen-rodriguez, h. b. rodriguez-gallegos, “use of landsat 8 images for depth and water quality assessment of el guajaro reservoir, colombia”, journal of south american earth sciences, vol. 82, pp. 231-238, 2018 [8] m. gholizadeh, a. melesse, l. reddi, “a comprehensive review on water quality parameters estimation using remote sensing techniques”, sensors, vol. 16, no. 8, pp. 1298, 2016 [9] g. srivastava, p. kumar, “water quality index with missing parameters”, international journal of research in engineering and technology, vol. 2, no. 4, pp. 609-614, 2013 [10] environmental management bureau caraga region, tubay river water quality assessment, 2015 [11] m. v. japitana, m. e. c. burce, “a satellite-based remote sensing technique for surface water quality estimation”, engineering, technology & applied science research, vol. 9, no. 2, pp. 3965-3970, 2019 microsoft word 5-2698_s_etasr_v9_n3_pp4105-4107 engineering, technology & applied science research vol. 9, no. 3, 2019, 4105-4107 4105 www.etasr.com memon et al.: marble powder as fine aggregates in concrete marble powder as fine aggregates in concrete muhammad jaffar memon department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan jaffar.memon@muetkhp.edu.pk ashfaque ahmed jhatial department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan ashfaqueahmed@muetkhp.edu.pk zaryab ahmed rid department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan zaryabrid@gmail.com touqeer ali rind department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan touqeerali@muetkhp.edu.pk abdul razzaque sandhu department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs’, pakistan abdulrazzaque@muetkhp.edu.pk abstract—marble industry contributes significantly to the socioeconomic development of any country. due to the abundance of marble reserves, pakistan relies on marble industry, which in turn contributes to its gdp. marble powder (mp), produced from the marble industry is also increasing, which constantly remains a source of hazards to the environment. at the same time, natural sand deposits are decreasing, causing an acute need for a product that matches the properties of sand in concrete. this study has been conducted to demonstrate the possibility of using mp as a replacement of sand in the manufacturing of concrete. the mp was used in 5 different dosage percentages ranging from 0% to 100% by weight of sand with an increment of 25%. the effect of mp on the strength behavior of concrete was studied at three different curing ages (7, 14 and 28 days). it was observed from the results that mp could potentially replace sand up to a certain limit without compromising on strength. it was also noticed that 50% sand replacement with mp was optimum at which 13.52% and 35.54% increase in compressive and flexural strength was achieved compared to the control sample. based on the results of this experimental study, it is clear that mp can partially be used in place of sand in concrete. keywords-partial fine aggregates replacement; marble powder; solid waste materials; concrete; natural resources conservation i. introduction construction industry is vital for the development of a country’s economy and infrastructure [1, 2]. in the modern era, concrete has become the most widely used construction building material in the world [2], due to its availability, flexibility, serviceability and durability [3, 4]. concrete is an artificial material comprised of cement, aggregates (fine and coarse) and water. aggregates represent approximately 60%75% of the total concrete’s volume [5], therefore, they play a significant role in the fresh and hardened concrete properties [6]. in construction industry, aggregates obtained from natural resources are utilized in the manufacturing of concrete. throughout the years, the consumption of concrete throughout the world has reached overwhelming scales. it has been reported that 11.5 billion tons of concrete is consumed every year out of which 9 billion tons of aggregates [7]. the alarmingly high amount of consumption of aggregates has become an environmental concern, depleting natural resources at much faster rate than they are being regenerated. due to the natural resource depletion and its negative impact on the environment [8], research has focused on finding alternative materials to be used as aggregates. there are many solid waste materials that have the potential to be used as fine and coarse aggregate replacements. these materials are being generated through agro-industrial processes and are typically disposed-off into landfills causing additional health and environmental issues. this experimental work studies the effect of one such solid waste material, marble powder (mp), on the strength properties of concrete when utilized as fine aggregate replacement. marble is one of the most extensively used types of rock/stone nowadays. it is the end-product of the metamorphism process of sedimentary carbonate rocks, most commonly limestone or dolomite rock [9]. marble has retained its importance over time, due to its attractive decorative purposes [10] and its variety of appearances and colors. in ancient times, marble was mainly used in sculptures. nowadays, marble is most likely to be found in and on buildings. marble has the tendency to withstand elements, and survive for a long time while retaining its look. marbles are utilized in floors, stairs, walls, counters, sinks and foundations etc. despite its attractiveness, the powder produced from marble waste has significantly adverse impact on the environment and public health [11, 12]. mp is a by-product which is typically produced during the sawing and polishing of marble blocks [11]. it has been reported that approximately 25% of the processed marble is converted into powder form [11]. the production of marble has been increasing, thus the marble powder generation is on the rise as well. like other waste materials, the disposal of the marble powder has become a serious environmental problem [13, 14]. the marble industry corresponding author: ashfaque ahmed jhatial engineering, technology & applied science research vol. 9, no. 3, 2019, 4105-4107 4106 www.etasr.com memon et al.: marble powder as fine aggregates in concrete impacts significantly on the socio-economic development of developing countries, such as pakistan, by providing jobs to thousands of people, as well as contributing to the gdp of the country [15]. according to tdap [16], it is estimated that pakistan has marble reserves of approximately 300 billion tons, mainly in three provinces (khyber pakhtunkhwa, punjab and baluchistan). the finally generated waste material (mp) is usually dumped at open grounds. with industrial growth, waste has also tremendously grown which is a serious threat to the environment and people. so, to overcome this serious problem we can use several types of waste coming from the industry, e.g. by replacing or partially replacing the constituents of concrete (cement, sand or aggregates) thus conserving natural resources. marble industry is producing a huge amount of waste. as a fine aggregate which is very important component of concrete, natural river sand is mostly used. marble waste can be utilized in various ways and marble slurry can be used as fine aggregates in concrete replacing, at least partially, river sand. the utilization of marble dust powder (mdp) as cement replacement was studied in [12]. the cement was partially replaced with mdp up to 20% by weight with an increment of 5%. it was determined that 10% to 15% mdp achieved maximum higher strength compared to control sample, suggesting that mdp could be potentially be used as supplementary cementitious material, reducing the cement content in concrete. authors in [17] also conducted an experiment on mp as partial cement replacement. their findings agreed with [12], determining 10% to be the optimum replacement. the mp has been reported to be used as partial cement replacement in [18-20], with the optimum dosage ranging from 5% to 15%. though mp has been studied by various researchers as partial cement replacement material, the study on the utilization of mp as fine aggregate replacement is limited to certain dosage, maximum 50% [9, 19, 21, 22]. therefore, in this experimental work, the effect of mp as fine aggregates on the strength properties of concrete is studied. ii. research methodology a. materials in this study, the mix ratio of 1:2:4 was utilized with watercement ratio of 0.55. marble waste was obtained from the karachi marble factory situated in khairpur mirs’, pakistan. to achieve mp, the obtained marble waste was crushed into powder form. the fine aggregates were replaced using mp from 0% to 100% with an increment of 25% as shown in table i. the mp chemical composition is shown in table ii. b. experimental procedure to determine the effect of mp on the strength properties of concrete, when utilized as fine aggregate, cubes of 150mm dimension were cast and tested for compressive strength according to astm c39/c39m-18 [24]. also, beams of 100mm×100mm×500mm were cast and tested for flexural strength in accorance to astm c78/c78m-18 [25]. every batch contained 3 cubes and 3 beams. the concrete was taken out of the moulds after 24h and was taken for curing. after the curing process, the specimens were tested at the age of 7, 14 and 28 days to check the strength at different ages. table i. mix proportions mix proportion name sand (%) marble (%) mp0 100 0 mp25 75 25 mp50 50 50 mp75 25 75 mp100 0 100 table ii. mp vs natural aggregates composition [23] component marble waste (%) natural aggregates (%) loi 45.07 5.08 sio2 3.75 53.7 cao 33.12 4.83 mgo 17.91 2.01 fe2o3 0.13 10.66 al2o3 traces nil sulphate content nil nil iii. results and discussion a. compressive strength the results of average compressive strength tests of concrete incorporating mp as fine aggregate replacement are shown in table iii. mp25 and mp50 showed increase in comparison with control (mp0). however, as the percentage of mp increased to 75% and 100%, the samples showed a decline in compressive strength. the rise was observed to be 13.52% on mp50 while declination of 28.22% was noted at mp100 in comparison to control. the results are in line with the findings in [26-28]. powdered material contains the characteristic of a filler thus could increase the strength of concrete up to a certain level. it can be said that the desired result can be achieved in concrete with smaller amounts of mp, due to its filler role, because slight increments in the total amount of cement help achieving the targeted compressive strength levels. table iii. concrete average compressive strength mix compressive strength (mpa) 7 days 14 days 28 days mp0 23.53 28.43 31.80 mp25 25.69 30.81 34.20 mp50 27.08 32.54 36.10 mp75 22.45 26.66 29.96 mp100 18.37 22.29 24.80 b. flexural strength the average flexural strength of concrete incorporating different percentages of mp as fine aggregates is shown in table iv. the behavior of concrete flexural strength is similar to that of its compressive strength with the incorporation of mp. samples containing 25% and 50% of mp showed gain in flexural strength compared to the control sample, a maximum of 35.54% increase was noticed at 50% replacement. further increase in mp resulted in decline on all curing stages, suggesting that the optimum replacement is 50%. the decline in strength can be attributed to the granular surface of the mp which is exposed as the crack developed under the load [29]. the samples containing 75% mp (mp75) showed the least decline of 4.27% in strength, which could also be utilized taken into account the rapid rate of depletion of natural resources. engineering, technology & applied science research vol. 9, no. 3, 2019, 4105-4107 4107 www.etasr.com memon et al.: marble powder as fine aggregates in concrete table iv. concrete average flexural strength mix flexural strength (mpa) 7 days 14 days 28 days mp0 3.47 4.12 4.22 mp25 4.14 4.90 5.47 mp50 4.31 5.05 5.72 mp75 3.14 3.46 4.04 mp100 2.96 3.42 3.93 iv. conclusion the conclusions that can be drawn from the results of our experimental work are: • compressive strength of concrete tends to increase initially with increasing replacement percentage up to an optimum limit, but then it continuously decreases. • flexural tensile strength did also show similar trend. it continually increases up to an optimum limit, and from there it decreases. • the optimum limit for mp was observed to be 50% replacement of sand where it resulted in 13.52% and 35.54% increase in compressive and flexural strength of concrete respectively in comparison with the control sample. • the strength gain of concrete when sand was partially replaced with mp showed that it can be effectively utilized in the manufacturing of concrete and thus contribute to the reduction of natural resources utilization in concrete. references [1] a. a. jhatial, s. sohu, n. k. bhatti, m. t. lakhiar, r. oad, “effect of steel fibres on the compressive and 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[15] q. khan, s. maqsood, s. b. khattak, m. omair, a. hussain, “evaluation of activity hazards in marble industry of pakistan”, international journal of engineering & technology, vol. 15, no. 5, pp. 73-78, 2015 [16] m. a. korai, s. hussain, a. j. abro, a report on marble & granite, tdap, 2017 [17] r. chandrakar, a. singh, “cement replacement in concrete with marble dust powder”, international research journal of engineering and technology, vol. 4, no. 5, pp. 1409-1411, 2017 [18] a. ergun, “effects of the usage of diatomite and waste marble powder as partial replacement of cement on the mechanical properties of concrete”, construction and building materials, vol. 25, pp. 806-812, 2011 [19] a. a. aliabdo, a. e. m. abd elmoaty, e. m. auda, “re-use of waste marble dust in the production of cement and concrete”, construction and building materials, vol. 50, pp. 28–41, 2014 [20] c. vaidevi, “study on marble dust as partial replacement of cement in concrete”, indian journal of engineering, vol. 4, pp. 14-16, 2013 [21] r. baboo, n. h. khan, k. abhishek, r. s. tabin, s. k. duggal, “influence of marble powder/granules in concrete mix”, international journal of civil and structural engineering, vol. 1, no. 4, pp. 827-834, 2011 [22] h. binici, h. kaplan, s. yilmaz, “influence of marble and limestone dusts as additives on some mechanical properties of concrete”, scientific research and essays, vol. 2, no. 9, pp. 372-379, 2007 [23] s. d. kore, a. k. vyas, “impact of marble waste as coarse aggregate on properties of lean cement concrete”, case studies in construction materials, vol. 4, pp. 85-92, 2016 [24] astm c39/c39m-18, standard test method for compressive strength of cylindrical concrete specimens, astm international, 2018 [25] astm c78/c78m-18, standard test method for flexural strength of concrete (using simple beam with third-point loading), astm international, 2018 [26] m. vijayalakshmi, a. s. s. sekar, g. g. prabhu, “strength and durability properties of concrete made with granite industry waste”, construction and building materials, vol. 46, pp. 1-7, 2013 [27] a. m. rashad, “a preliminary study on the effect of fine aggregate replacement with metakaolin on strength and abrasion resistance of concrete”, construction and building materials, vol. 44, pp. 487-495, 2013 [28] k. e. alyamac, a. b. aydin, “concrete properties containing fine aggregate marble powder”, ksce journal of civil engineering, vol. 19, no. 7, pp. 2208-2216, 2015 [29] m. singh, k. choudhary, a. srivastava, k. s. sangwan, d. bhunia, “a study on environmental and economic impacts of using waste marble powder in concrete”, journal of building engineering, vol. 13, pp. 8795, 2017 microsoft word 35-3289_s_etasr_v10_n1_pp5288-5294 engineering, technology & applied science research vol. 10, no. 1, 2020, 5288-5294 5288 www.etasr.com kumar et al.: impact assessment of groundwater quality using wqi and geospatial tools: a case … impact assessment of groundwater quality using wqi and geospatial tools: a case study of islamkot, tharparkar, pakistan natesh kumar institute of environmental engineering and management, mehran university of engineering and technology jamshoro, pakistan ali asghar mahessar sindh barrages improvement project irrigation department government of sindh sindh, pakistan sheeraz ahmed memon institute of environmental engineering and management, mehran university of engineering and technology jamshoro, pakistan kamran ansari u.s.-pakistan centers for advanced studies in water mehran university of engineering and technology jamshoro, sindh pakistan abdul latif qureshi u.s.-pakistan centers for advanced studies in water mehran university of engineering and technology jamshoro, sindh pakistan abstract–groundwater is the only source of fresh water in the thar desert which is located in an arid region of pakistan with dense population and spreads over 19,638km 2 . low rainfall, low groundwater recharge, high evaporation and absence of perennial streams are the general reasons for water scarcity. being the single water source for drinking, domestic and industrial uses, and livestock activities, this source is highly overexploited. realizing the gravity of the situation, this paper presents a groundwater quality evaluation of islamkot, tharparkar, using water quality index (wqi) and geospatial tools. 40 samples were collected from dug wells. the tds of 28 samples was found higher than 3000mg/l and 12 samples ranged from 1500 to 3000mg/l. many (28) samples were not further analyzed due to their very high tds which made the water unfit for drinking. twelve samples with tds ranging from 1500 to 3000 mg/l were further analyzed. the analyzed results revealed the average values of ph, ec, tds, salinity, chloride, total alkalinity, fluoride, and arsenic. the results did not meet neqs and who guidelines. pearson correlation analysis was conducted among parameters. further, groundwater quality was assessed by wqi and indicated that water quality varied from very poor to unsuitable for drinking. the consumption of polluted groundwater has been the main cause of prevalent waterborne diseases and poses a very high risk for public health. keywords-statistics; physicochemical analysis; islamkot; wqi; gis models; public health i. introduction surface and ground water are the main resources of drinkable water, since the 97.5% of the total water on the globe is saline. the 68.9% of the drinkable water falls within glaciers and permanent snow at the poles, 29.9% is in groundwater, only 0.3% of the fresh water exists in rivers, and 0.9% is in soil moisture and swamp water from groundwater [1]. the surface and ground water are major water sources [2]. groundwater is a significant natural resource particularly in rural areas [3]. owing to the lack of surface water facilities, groundwater plays a pivotal part in overcoming drinking and agricultural needs in both arid and semi-arid areas [4]. groundwater table is naturally recharged through rainfall, streams, lakes, rivers and swamp wetlands [5]. the groundwater becomes free from impurities of organic wastes by the filtration which occurs naturally through sediments and soil [6]. the quality of groundwater is an essential defining factor for its potentiality for drinking, agricultural and industrial usages [7]. the presence of some chemical elements in drinking water at concentrations above the standard levels can lead to health problems. drinking water contains various elements essential for human health. however, high concentrations of these parameters (tds, alkalinity, as, f, cu, zn, fe, cd, ni, and hardness) might create severe health complications [8-9]. contamination of groundwater by organic and inorganic material of anthropogenic origin poses a severe problem. safe drinkable water plays a vital role in human health, while water unfit for drinking is known a major source of waterborne diseases [10]. about 1.8 million people in the world die from diarrhea related diseases annually, many of which have been interrelated to the consumption of contaminated water [11]. globally, over 80% of people live with unimproved drinking water and 70% without improved sanitation. the adverse health effects of drinking water pose a serious problem in several parts of the world [11]. severe problems have been reported even in pakistan, especially in rural areas [12-17]. it is estimated that 30% of all diseases and 40% of all deaths are related to poor water quality. water borne diseases are reported as a leading cause of death in infants and children in pakistan while about 20% of the citizens suffer from polluted water related symptoms [18]. corresponding author: ali asghar mahessar (amahessar@yahoo.com) engineering, technology & applied science research vol. 10, no. 1, 2020, 5288-5294 5289 www.etasr.com kumar et al.: impact assessment of groundwater quality using wqi and geospatial tools: a case … groundwater quality has received widespread attention since the demand of water of high quality is rising. until recently, groundwater quality assessment has been based on laboratory investigation, but the emergence of satellite technologies such as remote sensing (rs) and geographical information system (gis) has made it easy to integrate various databases for water quality assessment. rs has been used to land classification, land cover and land use changes [19]. gis can be used as a powerful tool for finding water resource solutions, assessing water quality and availability, assisting in the prediction of local and regional floods, and understanding the natural environment. the wqi model is widely used worldwide for groundwater quality assessment, evaluation, and management [20]. like many other countries, pakistan also faces the problem of safe and clean drinking water availability. in the rural areas, the primary source of drinking water is groundwater. poor water quality is a major health risk in pakistan [21]. fresh water resources in thar region are scarce. moreover, crops are totally dependent upon rainwater [22]. this study was conducted in order to evaluate groundwater quality by using wqi and gis. in order to use these models for groundwater sustainably, groundwater resource monitoring and mapping are essential. statistical analysis of groundwater quality data was performed using descriptive statistics and pearson correlation. ii. study area tharparkar district consists of seven talukas. the total area of the district is 19,638km 2 mostly covered with sand dunes. the population is 1,649,661 (2017 census). islamkot is a taluka of the tharparkar district which is at a distance of 35km from mithi city and around 450km from karachi. islamkot is geographically positioned between 24°42'4.9680''n and 70°10'41.9592''e with an altitude of 193 feet. the area selected for research is islamkot city area including the villages falling within its vicinity. the map of the study area is shown in figure1. fig. 1. map of tharparkar district, sindh, pakistan fig. 2. map of the study area a. climate of the study area the climate of the studied area is dry with annual precipitation of 200–300mm whereas the temperature fluctuates between 9 o c in winter to 48 o c in summer. in summer, it is extremely hot during the day, but nights are remarkably cooler. april, may and june are the hottest months during the year, while december, january and february are the coldest. the inhabitants mostly rely on rainfall for agriculture and livelihood [23]. agricultural practice depends upon the rainwater and is the major occupation of locals. the main sources of drinking water are dug wells and low-lying areas (tarais) which recharge during rainfall. b. geology of the study area tharparkar is the largest subtropical desert spread over 19,638km 2 and lies in pakistan's southern sindh province. tharparkar district is specially named according to the geographical conditions, ie. thar and parkar. “thar” means desert while parkar refers to a rocky and hilly terrain. iii. materials and methods a. samples collection forty samples were collected in one-liter clean polyethylene bottles. at the time of sampling, the bottles were thoroughly rinsed with distilled water and labelled properly before transporting to laboratory and preserved with nitric acid. gps coordinates were noted for sampling locations using handheld gps (62s). the samples were collected from the study area and were sent to the lab of institute of environment, mehran university of engineering and technology, jamshoro. the values of ph, tds and salinity were taken in situ at samples’ collection sites. the ph measurements were made with calibrated ph meter with glass electrode and reference internal electrode. electrical conductivity (ec), salinity and total dissolved solids (tds) were recorded with a calibrated salinity and conductivity meter (hach 8163). furthermore, physicochemical parameters have been measured in the laboratory using standard analysis procedures. the locations of samples’ collection, their latitudes and longitudes are listed in table i. engineering, technology & applied science research vol. 10, no. 1, 2020, 5288-5294 5290 www.etasr.com kumar et al.: impact assessment of groundwater quality using wqi and geospatial tools: a case … table i. samples’ collection numbers and locations locations of collected samples no. latitude longitude no. latitude longitude s1 24.701 70.217 s21 24.727 70.223 s2 24.736 70.156 s22 24.737 70.223 s3 24.703 70.183 s23 24.733 70.223 s4 24.701 70.179 s24 24.734 70.225 s5 24.701 70.177 s25 24.734 70.228 s6 24.705 70.179 s26 24.730 70.227 s7 24.700 70.190 s27 24.738 70.225 s8 24.689 70.221 s28 24.740 70.217 s9 24.706 70.206 s29 24.740 70.217 s10 24.702 70.202 s30 24.740 70.217 s11 24.690 70.228 s31 24.740 70.217 s12 24.691 70.220 s32 24.737 70.215 s13 24.687 70.233 s33 24.737 70.217 s14 24.682 70.228 s34 24.745 70.233 s15 24.683 70.226 s35 24.696 70.178 s16 24.684 70.227 s36 24.685 70.229 s17 24.751 70.150 s37 24.677 70.227 s18 24.754 70.150 s38 24.678 70.229 s19 24.758 70.146 s39 24.693 70.191 s20 24.729 70.223 s40 24.690 70.225 b. water quality index (wqi) model wqi is an indicator of measuring water quality and suitability for drinking and surmises many parameters of water samples’ results for understanding if the water is drinkable or not. the equation of wqi model is given: n i=1 qwi wi*qi= ∑ (1) where qi is the i th wq parameter, wi is the weight associated with the i th wq parameter, and n is the total number of wq parameters. table ii. water qulity index rating s. no. qwi value rating 1 0-25 excellent 2 25-50 good 3 50-75 poor 4 75-100 very poor 5 >100 unsuitable for drinking c. karl peason correlation matrix karl person linear correlation matrix [24] has been used to analyze the relationship among various physicochemical parameters (table iii). d. gegrophical information system model rs has proved to be a beneficial and valuable tool in providing data for gis in order to study various environmental aspects including groundwater. various gis techniques methods are used, such as cokriging, spilain, natural neighbors, kriging and inverse distance weight (idw) for the spatial distribution of water quality parameters in the globe. idw and krinng techniques have been used for generating geospatial analysis in this study, which comprises of three distinct phases: (1) data acquisition, (2) data processing, and (3) data analysis. iv. results and discussion a. geospatial analysis of collected samples 1) ph according to national environmental quality standards (neqs) and who guidelines, water used for drinking should have a ph between 6.5 and 8.5. the ph values found in the study area's groundwater samples ranged from 7.6 to 8.7 as shown in the geospatial distribution of ph in figure 3. all samples are within the range of who standard except of s9 and s10. the locations of these high samples’ values are in islamkot city. the ph is the primary parameter used to evaluate water quality and it has no immediate impact on health [25]. fig. 3. spatial distribution of ph using gis 2) tds the analyzed levels of tds ranged from 1900 to 2688mg/l with an average value of 2202mg/l. the tds values of all samples are higher than 1500mg/l. in general, high tds concentration is due to natural minerals in the rocks. the samples having tds more than 3000mg/l were either brackish or saline in taste. a similar tendency of tds concentration is reported in the groundwater of thatta, badin and thar, the southern areas of sindh province [17] and in tharparkar district [23]. the high level of tds impairs the study area's drinking water quality. figure 4 shows the spatial distribution of tds. 3) electrical conductivity (ec) it is the main parameter used to evaluate drinking water quality. the ec in the sampled groundwater ranged from 2970 to 4200us/cm with an average value of 3441us/cm. the samples’ conductivity is generally higher than the who standard. higher dissolved salt concentration gives water mineral taste and generates aesthetic issues for consumers. the spatial distribution of ec is been shown in figure 5. 4) total hardness (th) water hardness is due to cations and anions like calcium and magnesium, sulphate, carbonate, bicarbonate and chloride. engineering, technology & applied science research vol. 10, no. 1, 2020, 5288-5294 5291 www.etasr.com kumar et al.: impact assessment of groundwater quality using wqi and geospatial tools: a case … in the sampled groundwater, th ranged from 110 to 520mg/l. the acceptable limit for th is 500mg/l as per who guidelines. total water hardness levels higher than 500mg/l bring about scale formation in pipes, whereas total hardness concentrations lower than 100mg/l can reduce the ph of the water and render the water corrosive. the use of hard water may cause kidney or bladder diseases, stomach illnesses, and produce urinary concretions in the human body. the geospatial distribution of hardness is demonstrated in figure 6. fig. 4. spatial distribution of tds using gis fig. 5. spatial distribution of ec using gis 5) chloride (cl) who has defined 250mg/l as the acceptable chloride limit. natural water generally contains chloride, but its concentration depends on the region’s geology. chloride is completely soluble in water. in this study, chloride concentration in the sampled groundwater ranged from 319 to 968mg/l with an average value of 588mg/l. the values of all samples were found to be higher than the permissible limit. the highest concentration of chloride was recorded in sample s7 of islamkot city. indigestion and kidney disease patients should avoid drinking water with greater concentration of chloride [23-25]. figure 7 represents the geospatial distribution of chloride in the study area. fig. 6. spatial distribution of hardness using gis fig. 7. spatial distribution of chloride using gis 6) alkalinity (alk) the alkalinity value in the sampled groundwater ranged from 170 to 725mg/l and the average value was 403.3. the permissible limit of alkalinity according to who is 500mg/l. the alkalinity geospatial distribution is shown in figure 8. 7) fluoride (f) fluoride is an important micronutrient which reinforces skeleton tissues and teeth at concentrations below 1mg/l, whereas elevated concentrations, exceeding 1.5mg/l, result in dental and skeletal fluorosis, kidney and neuronal disorders. engineering, technology & applied science research vol. 10, no. 1, 2020, 5288-5294 5292 www.etasr.com kumar et al.: impact assessment of groundwater quality using wqi and geospatial tools: a case … according to who, the maximum allowable level of fluoride in drinking water is 1.5mg/l. the analyzed results show that fluoride average value is 1.36mg/l and ranging from 1.01 to 2.02mg/l as shown in figure 9. the highest amount of fluoride was found in sample s2 (village arbab memon). fig. 8. spatial distribution of alkalinity using gis fig. 9. spatial distribution of fluoride using gis 8) arsenic (as) the highest permissible amount of arsenic in drinking water is 0.01mg/l according to who. in the study area, it ranged from 0.0007 to 0.019mg/l with an average value of 0.0097mg/l (figure 10). high-arsenic groundwater shows an alarming condition for individuals who use this water for drinking. the arsenic contaminated groundwater causes diseases of gastroenteritis, skin pigmentation changes, skin, dental, skeletal fluorosis, liver, cardiovascular problems, and even cancer. fig. 10. spatial distribution of arsenic using gis b. pearson linear correlation model karl person linear correlation matrix [26] was used to analyze the relationship among the physicochemical parameters. the correlation computation matrix is shown in table iii. the correlation of ec with tds and salinity is strong with positive and weak correlation with alkalinity, hardness, chloride, arsenic and fluoride. the ph has weak negative relation with ec, tds, and hardness. c. wqi analysis the groundwater quality of the study area calculated by wqi indicates that the water lies in the unsuitable for drinking category while only one sample (s9) lies under the very poor category having satisfactory result with wqi below 100. in this study, the computed wqi values range from 98 to 153. the overall view of the wqi of the study area signifies its deteriorated water quality. table iii. pearson correlation matrix parameter ph ec tds salinity chloride hardness alkalinity arsenic fluoride ph 1 ec -0.041 1 tds -0.041 1.000 1 salinity -0.071 0.976 0.976 1 chloride 0.266 0.495 0.495 0.320 1 hardness -0.154 -0.108 -0.108 -0.153 0.277 1 alkalinity 0.126 0.062 0.063 0.154 -0.421 -0.44 1 arsenic 0.111 -0.193 -0.193 -0.288 0.276 0.03 -0.190 1 fluoride -0.133 0.254 0.254 0.396 -0.484 -0.65 0.672 -0.317 1 engineering, technology & applied science research vol. 10, no. 1, 2020, 5288-5294 5293 www.etasr.com kumar et al.: impact assessment of groundwater quality using wqi and geospatial tools: a case … d. health assessement figure 11 shows the frequent occurrence of various diseases. kidney problems, hepatitis, gastroenteritis, blood pressure and heart problems, cancer, bone pain and skin problems are common among the residents in the study area. the consumption of polluted groundwater is a high risk for locals. table iv. wqi ratings sample location wqi type sample location wqi type 70° 13' 01.4916" e 24° 42' 02.1384" n 115 us 70° 11' 23.1432" e 24° 42' 01.2420" n 153 us 70° 09' 22.1760" e 24° 44' 08.3040" n 142 us 70° 13' 16.0248" e 24° 41' 21.7500" n 139 us 70° 10' 58.0548" e 24° 42' 11.8368" n 123 us 70° 12' 23.0976" e 24° 42' 19.9476" n 98 vp 70° 10' 44.3964" e 24° 42' 03.8988" n 124 us 70° 12' 08.8632" e 24° 42' 08.0352" n 117 us 70° 10' 37.8156" e 24° 42' 04.0320" n 119 us 70° 13' 42.3156" e 24° 41' 22.6500" n 147 us 70° 10' 44.2596" e 24° 42' 16.3872" n 140 us 70° 13' 12.1800" e 24° 41' 27.6432" n 128 us us: unsuitable, vp: very poo fig. 11. reported health issues in the study area v. conclusions after physicochemical analysis of the collected 40 samples from dug wells, it was shown that the tds of 28 samples was found higher than 3000mg/l which indicates that water consumption poses a direct health threat on locals. hence, 28 samples were not further analyzed due to their very high tds values. twelve samples with tds ranging from 1500 to 3000mg/l were further analyzed. the 12 analyzed samples had average ph, ec, tds, salinity, chloride, alkalinity, fluoride and arsenic values of 8.158, 3441.66, 2202.4, 1.83, 588, 265.4, 403.3, 1.366, and 0.093 respectively. the resultantly parameters did not meet neqs and who guidelines. the geospatial distribution of all physicochemical parameters shows the real groundwater picture. pearson correlation analysis shows weak, moderate and strong correlation among physicochemical parameters. groundwater quality was assessed by wqi which indicates that the water quality of the 12 collected groundwater samples varies from very poor to unsuitable. the consumption of polluted groundwater is related to waterborne diseases and poses very high risk for public health. it is also concluded, from the health impact assessment survey, that the occurrence of various waterborne and waterrelated diseases is common among the residents of the study area. consequently, the use of degraded groundwater should instantaneously be stopped and new techniques should be adopted such as rainwater harvesting and storage/tarais, irrigation network expanse, manufacturing of reverse osmosis, de-arsenic and fluorination plants, and also freshwater supply schemes should be introduced in thar. water quality monitoring and health impact assessment must be conducted constantly. acknowledgment the authors are thankful to the institute of environmental engineering and management, mehran university of engineering and technology, jamshoro, sindh and sindh irrigation department for providing the 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[24] a. a. mahessar, a. l. qureshi, a. n. leghari, s. qureshi, s. f. shah, f. a. shaikh, “impact of hairdin, miro khan and shahdad kot drainage on hamal dhand, sindh”, engineering, technology & applied science research, vol. 8, no. 6, pp. 3652-3656, 2018 [25] a. a. mahessar, a. n. laghari, s. qureshi, i. a. siming, a. l. qureshi, f. a. shaikh, “environmental impact assessment of tidal link failure and sea intrusion on ramsar site no. 1069”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4136-4139, 2019 [26] s. sener, e. sener, a. davraz, “assessment of groundwater quality and health risk in drinking water basin using gis”, journal of water and health, vol. 15, no. 1, pp. 112-132, 2017 engineering, technology & applied science research vol. 9, no. 2, 2019, 3985-3989 3985 www.etasr.com sharma & joshi: knowledge-based method for word sense disambiguation by using hindi wordnet knowledge-based method for word sense disambiguation by using hindi wordnet pooja sharma department of computer science banasthali university tonk, india poojasharma_bu@outlook.com nisheeth joshi department of computer science banasthali university tonk, india jnisheeth@banasthali.in abstract—the purpose of word sense disambiguation (wsd) is to find the meaning of the word in any context with the help of a computer, to find the proper meaning of a lexeme in the available context in the problem area and the relationship between lexicons. this is done using natural language processing (nlp) techniques which involve queries from machine translation (mt), nlp specific documents or output text. mt automatically translates text from one natural language into another. several application areas for wsd involve information retrieval (ir), lexicography, mt, text processing, speech processing etc. using this knowledge-based technique, we are investigating hindi wsd in this article. it involves incorporating word knowledge from external knowledge resources to remove the equivocalness of words. in this experiment, we tried to develop a wsd tool by considering a knowledge-based approach with wordnet of hindi. the tool uses the knowledge-based lesk algorithm for wsd for hindi. our proposed system gives an accuracy of about 71.4%. keywords-word sense disambiguation; lesk; wordnet i. introduction ambiguity is one of the characteristics of a natural language. a word can have multiple meanings, varying with the context in which it is used. wsd has always been characterized as an ai-complete issue which is related to npcompleteness. wsd is a process to determine the exact sense of the word with respect to the context it is used in. examples: • उसने लाल कलम सॆ ललखा (usne lal kalam se likha). here, the ‘कलम' meaning is a red pen. sentence example: he wrote with a red pen. • गुलाब के फूल की कलम को माली नॆ काट दिया (gulab ke phool ki kalam ko mali ne kaat diya). here, the ‘कलम' meaning is graft cutting of rose. sentence example: the gardener has cut the stem of a rose flower. • नाई ने कलम को काटा (naayi ne kalm ko kaata). here, the ‘कलम' meaning is graft cutting of hairs. sentence example: the barber trims the temple. wsd mainly relies on knowledge. the wsd system can be interpreted to work as follows: it takes as input an arrangement of words or a sentence, then nlp techniques are applied which utilize at least one source of knowledge to identify the most appropriate senses of the words regarding the context. words possess different meanings that vary with the context in which they are used and our undertaking is to figure out which sense of word is intended in a particular context. this is one of the basic issues which are often experienced by any nlp framework. wsd is an area of exploration in nlp, which is gaining popularity nowadays. wsd makes use of a dictionary to achieve better identification of all word senses. knowledge resources can also vary depending on corpora of textual content, labeled or unlabeled with word senses or more arranged resources like machine-readable dictionaries, semantic systems etc. knowledge of the words is the key ingredient to distinguish the meaning whether we are referring to about humans or machines. wsd finds applications in many areas such as speech recognition (sr), information extraction (ie) and information retrieval (ir). wsd is a critical element for word knowledge. there are many different approaches to deal with wsd, for example, knowledge-based approach, selectional restriction, machine learning approach in order, which may further incorporate four types of approaches: supervised, unsupervised, semi-supervised, or hybrid. in this paper, we revolve around approaches like selectional restriction with hindi wordnet for wsd in case of hindi language. ii. related work author in [1] proposed a knowledge-based wsd algorithm which selects the word that most overlaps with words in context. many knowledge-based systems are based on this lesk algorithm. authors in [2] estimated semantic separation amongst lexemes and ideas. authors in [3] tried to figure the most helpful knowledge sources and whether their mix prompts enhanced outcomes. authors in [4] elaborated the ssi algorithm, which is a structural algorithm for wsd used for pattern matching. this algorithm can be refined to get high precision (possibly low recall), a benefit that will be more sensible for viable applications using wsd. as of now, the framework is tuned for disambiguating nouns by extending semantic graphs related to verbs. authors in [5] offered a new graph-based method, which uses knowledge in lkb (based on wordnet) to do unsupervised wsd. they showed that the algorithm can easily be used with good results in other corresponding author: pooja sharma engineering, technology & applied science research vol. 9, no. 2, 2019, 3985-3989 3986 www.etasr.com sharma & joshi: knowledge-based method for word sense disambiguation by using hindi wordnet languages, with the only requirement of having a wordnet. authors in [6] investigated the wsd frameworks to particular areas using knowledge-based techniques, based on the graph based wsd framework that uses the data in wordnet. three corpora were utilized i.e. one adjusted corpus (bnc), and two area particular corpora. the outcomes demonstrated that in every one of the three corpora, the knowledge-based wsd calculation enhances the past outcome and gets better results by using words related to the context than actual context words on the domain-based datasets. the outcomes are better for an area dependent corpus than for a general one, raising the chances for improving current wsd frameworks when connected to particular domains. authors in [7] tried to develop wordnet for punjabi by using extension approach from hindi wordnet under the indradhanush wordnet project. they explained the morphology, symbols, origin and syntactic features of punjabi language and lexical semantic relations used in punjabi wordnet. authors in [8] presented an algorithm for domain specific all-word wsd with an approximate accuracy of 69% (f1-score) with the domain corpus baseline standing at 65. authors in [9] dealt with graph-based algorithms for wsd. they reported results on standard data sets, and demonstrated that graph-based approach performs comparably to the state of the art. author in [10] utilized a knowledge-based way to deal with wsd with hindi language. dictionaries and thesauri were the outside lexical assets used. appropriate senses were assigned to a word in hindi by using statistical strategy. their work depicts the use of selectional restriction for hindi language which is again a knowledge-based approach. authors in [11] used the genetic algorithm including elitism to find the appropriate meanings of polysemous nouns in the given context. a lexical knowledge base for hindi was used. the obtained outcomes depict the optimized disambiguation of hindi words. based on the personalized page rank on the generated graph using wordnet, authors in [12] presented an unsupervised wsd approach. it is produced by contributing substance words to the wordnet graph and associating to that synset in which they are visible in the form of strings. then, the personalized page rank (ppr) algorithm was used to calculate the corresponding weight of the synset according to their relative structural significance, and as a result, for each content word, synset with the highest ppr weight is taken as the appropriate meaning. authors in [13] further enhanced lesk by using word embeddings to calculate the similarity between sense definitions and words in the context. authors in [14] presented a graph-based unsupervised wsd framework which amplifies complete combined probability of all the senses in the context by displaying the wsd problem as a markov random field developed utilizing the wordnet and a dependency parser and utilizing a maximum a posteriori (map) query for deduction. knowledge-based systems have been proposed for wsd for any low asset language [15]. as knowledge-based, bengali wordnet has been utilized as a part of this work. the conventional lesk algorithm has been utilized as the standard information-based approach. iii. proposed methodology wsd is a process for assigning the appropriate sense of an ambiguous word according to context. a fixed class in wsd is portrayed by knowledge-based methods. such strategies for wsd are generally connected to all words in a continuous text, in-spite of corpus-based methods, which are available for those words only for which annotated corpora are accessible. wsd makes use of dictionaries or thesauri to achieve better identification of word senses. knowledge resources can also vary depending on corpora of textual content, labeled or unlabeled with word senses or more arranged resources like machine-readable dictionaries, semantic systems etc. knowledge of the words is the critical ingredient to distinguish the meaning. wsd finds its applications in many areas such as information retrieval (ir), information extraction (ie), and speech recognition (sr). wsd has seen different approaches. most of the approaches are established on various statistical techniques. few approaches include corpora which has been tagged for senses and others employ unsupervised learning. in this paper, we utilize lesk approach [1], which involves appearing for overlap among the words in given definitions with words from the text surrounding the word to be disambiguated. the flowchart is shown in figure 1. fig. 1. flowchart of wsd utilizing lesk algorithm a. hindi wordnet wordnet is a giant database consisting of nouns, verbs, adjectives, and adverbs. these are clustered into equivalent word sets or synsets. these sets are related by methods of applied lexical and semantic relations. wordnet is finishing for hindi and it is being designed for marathi at iit bombay. it is an electronic, huge, lexical database and it is a perfect mixture of thesaurus and dictionary which is made and handled by the cognitive science lab of princeton university. the wordnet of hindi is similar to the wordnet of english. the words are assembled together as indicated by their comparability of engineering, technology & applied science research vol. 9, no. 2, 2019, 3985-3989 3987 www.etasr.com sharma & joshi: knowledge-based method for word sense disambiguation by using hindi wordnet implications. two or more words that may be different in a context can be synonymous in some other context. similar synsets are present within the hindi wordnet for every word, denoting a lexical thought. this is achieved to expel ambiguity in situations where a solitary word has numerous implications. the fundamental building squares of wordnet are the synsets. the hindi wordnet manages the content words or words with open class categories. thus, the hindi wordnet comprises of the accompanying category of words: noun, adjective, verb and adverb. all entries in the hindi wordnet consist of the following attributes: • synset: it is a collection of words with similar meanings i.e. synonyms. for example “पेन, कलम, लेखनी" (pen, kalam, lekhanee) describes an instrument for writing with ink. the words are arranged in the synset according to the popularity of usage. • gloss: it elaborates the concepts. it contains 2 parts: text definition which describes the concepts denoted by the synset (for example: “स्याही के सहयोग से कागज आदि पर ललखने का उपकरण” (syaahee ke sahayog se kaagaj aadi par likhane ka upakaran) explains the concept of a device for writing or drawing with ink), and example sentence which gives the importance of words in a sentence. generally, the words in a synset can be easily replaced in a sentence (for example: "यह पेन ककसी ने मझु ेउपहार में प्रिान की है|” (yah pen kisee ne mujhe upahaar mein pradaan kee hai) gives the utility of words in the synset describing an instrument for writing or drawing with ink). • semantic relations: it affirms the connection between the form and the meaning of a word. the hindi wordnet is influenced through the english wordnet, and it is utilising lexical data. they are primarily used to construct the lexicon, and the semantic relations are shown in table i. b. lesk algorithm: lesk algorithm [1] is a traditional knowledge-based wsd algorithm which disambiguates a word by choosing a sense whose definition overlaps the most with the words in its context. alongside there are considered different sources like synonyms, hypernyms, homonyms, meronyms, and example sentences. numerous ensuing knowledge-based systems are situated on the lesk algorithm. a knowledge-based approach utilizes outer lexical assets like thesauri and wordnet. suppose w i.e. ‘राज्य’ (rajyaa) is an ambiguous word and there is a group of a context word sets i.e. c in the window surrounding it. we search w in wordnet and then discover the senses of w. by using lesk algorithm, we search the most appropriate sense of w. the maximum overlapping sense will be the output of the algorithm. we can use simulated annealing to remove ambiguity if there is more than one word in the sentence. the steps of the lesk algorithm are: function lesk (word, sentence) returns best sense of word best-sense ← 0 max-overlap ← 0 context ← set of words in sentence for each sense in senses of word do content ← set of words in the gloss and examples of senses overlap ← computeoverlap (content, context) if overlap > max-overlap then max-overlap ← overlap best-sense ← sense end return (best-sense) figures 2-4 show the multiple senses of an ambiguous word as shown in hindi wordnet according to the various parts of speech. table i. relations in hindi wordnet relation meaning example hypernymy/ hyponymy is-a (kind-of) बेलपत्र (belapatr) is a kindof पत्ता (patta) entailment/ troponymy manner-of (for verbs) खराटा लेना, नाक बजाना → सोना (kharaata lena, naak bajaana → sona) meronymy/ holonymy has-a (part-whole) जड़ (jad) is the partof पेड़ (ped) antonymy holds between two words that express opposite meanings मोटा→पतला (mota→patala) causative the pattern of making causation खाना→ खखलाना (khaana→ khilaana) fig. 2. senses of the word ‘पास’ (paas) as an example let’s find the correct meaning of this sentence: ‘मोहन के पास एक अच्छी कलम है।’ (mohan ke paas ek achchi kalam hai). in the given sentence ‘पास’ (paas), ‘अच्छा’ (achcha) and ‘कलम’ (kalam) contain multiple senses. the 7 different senses in hindi wordnet for the word ‘पास’ (paas) are shown in figure 2. if we link that ‘पास’ (paas) word with ‘अच्छा’ (achcha) and ‘कलम’ (kalam) word then there will be several senses for the sentence ‘पास अच्छी कलम’ (paas achchi kalam). the 14 different senses in hindi wordnet for the word ‘अच्छा’ (achcha) are shown in figure 3 and the 11 different senses of word ‘कलम’ (kalam) are shown in figure 4. lesk algorithm helps us in fetching the actual meaning of the word according to its usage. this reduces the number of engineering, technology & applied science research vol. 9, no. 2, 2019, 3985-3989 3988 www.etasr.com sharma & joshi: knowledge-based method for word sense disambiguation by using hindi wordnet iterations required for wsd. according to lesk algorithm, the best sense of ‘पास’ (paas) is ‘अधिकार’ (adhikaar), the best sense of ‘अच्छा’ (achcha) is ‘स ुंदर’ (sundar), and the best sense of ‘कलम’ (kalam) is ‘पेन’ (pen). in such a process we are avoiding stop words such as का, के, की, है, हो, से, मे, ने (ka, ke, kee, hai, ho, se, me, ne) etc. fig. 3. senses for the word ‘अच्छा’ (achcha) fig. 4. senses for the word ‘कलम’ (kalam) iv. evaluation we developed a tool for wsd by using the wordnet for hindi. for this purpose, we considered a small corpus that contains 3000 ambiguous sentences. from this, we correctly identified 2143 sentences. the accuracy of the system was calculated by dividing the correctly identified senses with the total ambiguous sentences as shown in (1). the overall accuracy of our system is 71.43% and the error was 28.57%. as calculated by (2). the summary of the evaluation is shown in table ii and figure 5. 𝐴𝑐𝑐𝑢𝑟𝑎𝑐𝑦 = 𝐶𝑜𝑟𝑟𝑒𝑐𝑡𝑙𝑦 𝐼𝑑𝑒𝑛𝑡𝑖𝑓𝑖𝑒𝑑 𝑆𝑒𝑛𝑠𝑒𝑠 𝑇𝑜𝑡𝑎𝑙 𝐴𝑚𝑏𝑜𝑔𝑖𝑜𝑢𝑠 𝑆𝑒𝑛𝑠𝑒𝑠 (1) 𝐸𝑟𝑟𝑜𝑟 = 𝐼𝑛𝑐𝑜𝑟𝑟𝑒𝑐𝑡𝑙𝑦 𝐼𝑑𝑒𝑛𝑡𝑖𝑓𝑖𝑒𝑑 𝑆𝑒𝑛𝑠𝑒𝑠 𝑇𝑜𝑡𝑎𝑙 𝐴𝑚𝑏𝑖𝑔𝑢𝑜𝑢𝑠 𝑆𝑒𝑛𝑠𝑒𝑠 (2) table ii. evaluation summary total ambiguous senses 3000 correctly identified 2143 accuracy 71.43 error 28.57 fig. 5. accuracy in error measure v. conclusion in this paper, focus was given in hindi language. wsd has been a significant issue of nlp and ai, but the issue was to find the correct senses of words in respective contexts. we utilized a knowledge-based approach by implementing lesk algorithm for hindi. our system gave 71.4% accuracy for finding the correct sense of an ambiguous word. we plan to add more knowledge sources like part-of-speech (pos) tagger to improve accuracy. it would be interesting to see how selectional restrictions can improve the accuracy of the current system. references [1] m. lesk, “automatic sense disambiguation using machine readable dictionaries: how to tell a pine cone from an ice cream cone”, in: proceedings of the 5th annual international conference on systems documentation, pp. 24-26, amc, 1986 [2] j. j. jiang, d. w. conrath. “semantic similarity based on corpus statistics and lexical taxonomy”, arxiv preprint cmp-lg/9709008, 1997 [3] m. stevenson, y. wilks, “the interaction of knowledge sources in word sense disambiguation”, computational linguistics, vol. 27, no. 3, pp. 321-349, 2001 [4] r. navigli, p. velardi, “structural semantic interconnections: a knowledge-based approach to word sense disambiguation”, ieee transactions on pattern analysis and machine intelligence, vol. 27, no. 7, pp. 1075-1086, 2005 [5] e. agirre, a. soroa, “personalizing page rank for word sense disambiguation”, in: proceedings of the 12th conference of the european chapter of the association for computational linguistics, pp. 33-41, association for computational linguistics, 2009 [6] e. agirre, o. l. de lacalle, a. soroa, i. fakultatea, “knowledge-based wsd and specific domains: performing better than generic supervised wsd”, twenty-first international joint conference on artificial intelligence, pasadena, usa, july 11-17, 2009 [7] r. kaur, r. k. sharma, s. preet, p. bhatia, “punjabi wordnet relations and categorization of synsets”, 3rd national workshop on indowordnet under the aegis of the 8th international conference on natural language processing (icon 2010), kharagpur, india, december 8-11, 2010 [8] m. m. khapra, s. shah, p. kedia, p. bhattacharyya, “domain-specific word sense disambiguation combining corpus based and wordnet based parameters”, 5th international conference on global wordnet, january 31-february 4, mumbai, india, 2010 [9] r. navigli, m. lapata, “an experimental study of graph connectivity for unsupervised word sense disambiguation”, ieee transactions on pattern analysis and machine intelligence, vol. 32, no. 4, pp. 678-692, 2010 [10] p. bala, “knowledge based approach for word sense disambiguation using hindi wordnet”, international journal of engineering and science, vol. 2, no. 4, pp. 36-41, 2013 [11] s. kumari, p. singh, “optimized word sense disambiguation in hindi using genetic algorithm”, international journal of research in computrer & communication technology, vol. 2, no. 7, pp. 445-449, 2013 javascript:void(0) javascript:void(0) engineering, technology & applied science research vol. 9, no. 2, 2019, 3985-3989 3989 www.etasr.com sharma & joshi: knowledge-based method for word sense disambiguation by using hindi wordnet [12] e. agirre, o. l. de lacalle, a. soroa, “random walks for knowledgebased word sense disambiguation”, computational linguistics, vol. 40, no. 1, pp. 57-84, 2014 [13] p. basile, a. caputo, g. semeraro, “an enhanced lesk word sense disambiguation algorithm through a distributional semantic model”, 25th international conference on computational linguistics, dublin, ireland, august 23-29, 2014 [14] d. s. chaplot, p. bhattacharyya, a. paranjape, “unsupervised word sense disambiguation using markov random field and dependency parser”, in: proceedings of the twenty-ninth aaai conference on artificial intelligence, pp. 2217-2223, association for the advancement of artificial intelligence, 2015 [15] a. r. pal, d. saha, a. pal, “a knowledge based methodology for word sense disambiguation for low resource language”, advances in computational sciences and technology, vol. 10, no. 2, pp. 267-283, 2017 authors profile pooja sharma received her mca degree from the banasthali vidyapith, rajasthan, india in 2016 and is currently doing m.tech in computer science in banasthali vidyapith, rajasthan, india. her research activity is mainly focused at the development of wsd algorithms and their techniques for indian languages. she also has interest in other fields of nlp and ai. nisheeth joshi is an associate professor in the department of computer science, faculty of mathematics and computing, banasthali vidyapith, rajasthan, india. he has done his phd in the area of natural language processing. he is involved in teaching and research for over 10 years and also has a vast experience of handling large scale research projects sponsored by various funding agencies he has authored several papers in international journals and conferences regarding ai and nlp. n ab cou of sta opp hav nu un for con mi ent an coe an she sta nu exp dif int of alt pro req sou cur urb sus the suf rea far tur ide be [2] wh engineerin www.etasr numer a co national r bstract—this p unter-rotating a two stage ve age. the mode position to eac ve been perfo umerical analy steady simulat r the two stage nformal interf nimize numer tropy changes nsys fluent so efficient for e nother, more edding, impin ages at differ merical resu perimental dev fferent free stre keywords-cf concerns re terest of resea renewable en ernative to c oportion of quirements in urces. both v rrently employ ban areas. v stainable energ eir robustness ffer from self ach a self-sus rms make use rbines, the va eally suited fo often unpredi ] are limited t hen compared ng, technology r.com rical a ounter ion m cfd de research and d gas turbin bucharest ion.malael@ paper investig vertical axis w ertical h-type el has an inne ch other. both ormed in ord ysis is based tions using a d s to self-adjust faces are defin rical artifacts s. fully turbul oftware. one k each stage at qualitative, ou ngement and rent positions ults have be vice which wa eam speeds. fd; counter rota i. in egarding glob archers for inn ergy. wind en conventional p wind power january of vertical and h yed, with a he vawts repre gy landscape f s in terms of f-starting lack stained operat e of the large awt indepen or urban enviro ictable [1]. co to a tsr of o d against the d y & applied sci malael & d and ex r-rota malael epartment development i nes comoti t, romania @comoti.ro ates the conce wind turbine turbine with t er and an oute numerical an er to validate on the use dof type of an t their rotation ned between t such as art lent urans w key outcome w different tip utcome is the 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vertica centric sisting n each ting in al tests oncept. sional, allows g mesh ains to ons or out in entum values. vortex en the y, the scaled nnel at ine d the e field ewable a, the ational power es are ts for urban due to h they nce to wind wind s them ns can types ficient other han star hav from or con of a two cou on t con gen rota of t spe sec that and can con bein app win pos effe pap sup vol. 8, no. 4, 20 rimental efficie effici al axi national nd, darrieus rting, making h ve seen a signi m the classica rigid [7] and nfigurations. t an original var o stages are unter-rotating top of one ano nstructive adva nerator. howe ating and in p the machine, eed ratio and ondary stage i t would otherw d hence to ele n approach bet in profiling th nsidered the n ng well under plications. tab nd turbine. by sition of the tu ect. the cad per is presente pporting system 018, 3282-3286 ency evaluation iency e is win valeri cfd d research and gas turbi buchare valeriu.drag vawts hav high torque ap ificant number al savonius and flexible [8] the focus of th riation of the d assembled c configurations other, have bee antages in term ever, having parallel does li leaving the c power coeffi in series, a sig wise be inacc ectric power. t tz's limit [11]. ii. cfd he blades of t naca 0021 ai rstood by its u ble i presents y inverting the urbine blades d assembly of ed in figure 1 m can be obser fig. 1. 3d w 6 n of a counterevalu nd tur iu dragan department d developmen ines comoti est, romania gan@comoti.r ve difficultie pplications diff r of vawt v d darrieus typ combinations his paper is to darrieus [9] co coaxially and s, such as sta en proposed ea ms of their link the two hal ittle to further lassical relatio cient unaltere gnificant part cessible is con this way, the d simulation this new wind irfoil which ha use in other s s the geometr e leading edge we achieve th f the embodim , where the th rved. wind turbine mod 3282 -rotating vertic uation rbine nt institute for i ro es 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counter-rota value urbine outer 5 7 5 4 naca 0021 500 3 10÷16 sis, a computa subdomains: ner turbine, r omain for aro mal interfaces ch connect the ws the structur rface between the boundary n 1, and the g f the cr-vawt c hree structured nd 500k elem one around lving the navi art in the w authors in [12 that the flow history not ju considered in 3]. the insta ent on the torq roughout a fu analysis less ter rotating wi m (dof) metho for each win ional point of cteristics of t very import the turbine w from airfoil p used where th his is an inh have difficul making this reg of method, th ience research dragan: numer ating in-series v unit turbine 70 mm 450 mm mm m/s ational domai stator for the rotor for the und of the tu have been de e rotors to the s red mesh gen n the two stage layer, the y+ growth ratio o concept d meshes were ments, the me 1200k. the ier-stokes syst wind turbine 2] studied the b w pattern is h ust the current n constant tsr antaneous rota que, but the mo ull rotation, m accurate [14] ind turbine co od, which wor nd turbine ro f the turbine. i the turbine ca tant-particular works at high a polar diagram he lift-drag ra herently ineff lties attaining gime an inter e parameters h v rical and exper vawt ts m m m in has inner outer urbine efined stators erated es. to value of the e used. edium cfd tem of cfd bladehighly t flow r (tip ational oment making ]. the ncept, rks by tor in in this an be rly to angles m, only atio is ficient g selfresting of the ana allo turb opt pre t m the sst reco turb k-ε area bou insu pur of intr tran (ω) turb carb imp cur and thu 120 foll tech mil mo clos dev the vol. 8, no. 4, 20 rimental efficie alysis were th owing the sof bine at every t timal point. sented in tabl table ii. ge parameters mass momentum inert due to the tim unsteady re t, was used i ord of accur bines [17-18]. model and the a, which is co undary layer [ ured by the u rpose of activa interest. thes roducing a diff nsport equation 1 γ . k k k k k 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mental tests w figuration of t he results from d. figure 7 sho fig. 6. pm e mechanical the relation b y & applied sci malael & d odel is connec enerator with molds for inner tu ned for this wi hich spin in o ction of this by the turbine uit which acte s permanent m ures of the coil mg cross section pmg main parts internal effic were carried this testing be m pmg tests a ows this pmg mg testing bench power gener between the m ience research dragan: numer cted to a one h a purpose urbine ind turbine co opposite direc pmg. in ord e, the generato ed as a resist magnet generat ls, the shaft, ca n ciency of this out on the t ench in presen an electric effic map. h rated by the measured elec h v rical and exper of the built ncept, ctions. der to or was tor. in tor are asings pmg testing nted in ciency wind ctrical qua ord mea sch pre whe carr stat the win inte sys min con ball man vol. 8, no. 4, 20 rimental efficie antities, torqu der to determ asured with hematic diagr sented. f fig. 8. 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v=12m/ h v rical and exper ounter everal od. to fferent akes it gative ne. in e case s /s /s of max con hig whe valu the exp vol. 8, no. 4, 20 rimental efficie figures 14-15 outer and inn ximum value ntribution of th hest. the num ere the exper ues between 1 power coef perimental test fig. 13. vor fig. 14. mo fig. 15. mo fig. 16. 018, 3282-3286 ency evaluation 5 show the va ner turbine fo e is obtain he inner turbin merical data rimental mode 10m/s and 16m fficient for n ts is presented. rticity magnitude omentum coeffici omentum coeffici tip speed ratio v 6 n of a counterariation of the r different ve ed at v=12 ne in the conce was validated el was investi m/s. in the ch numerical sim . for theta 90 degr ient variation for t ient variation for t variation within str 3285 -rotating vertic e torque coeffi elocity values. 2m/s, where ept efficiency d in wind tu igated for vel hart from figu mulation and ees, for v=12m/s the outer turbine the inner turbine ream velocity cal … ficient . the the is the urbine locity ure 17 d for s tw adv tes ae va fou can thi rot com tes ma exp per opt the con sta con exp pro aer de fun [1] [2] [3] [4] [5] [6] engineerin www.etasr fig. 17. p a new conc o stage, in se vantage regar sted both in erodynamic m awt model und that the na nnot be easily is method, only tors, leaving mputed using sts of the conce anufactured perimental re rformance but timization the e inner and nsideration. a age solidity an ncept towards perimental m ovide less fric rodynamics of this work w evelopment in nds on wind tu p. a. costa r e.vieira da sil effects of blad turbine in urba t. wenlong, m savonius win renewable en r. gupta, a. bucket savoni bladed darrieu 1981, 2008 j. gavalda, j. m darrieus—sav no. 4, pp. 457a. ghosh, a. b of flow physic rotor”, journal k. sahim, d. radius rotor ng, technology r.com power coefficient v. c ept for vaw eries h-type d rding the pow cfd and w modeling of c was done us atural rotating y predicted thr y an inertial m the acceler the unsteady ept feasibility specifically esults from w t an aerodynam e blade airfoil outer turbine a better under nd specific sp its full potent model where a ction, allowing f the concept. acknow was carried ou nstitute for g urbine field. refe rocha, j. w.carn lva, d. albiero, c de pitch angle o an environments”, m. zhaoyong, b. nd rotor with d ergy, vol. 117, pp biswas, k. k. s ius rotor with a us rotor”, renew massons, f. diaz vonius wind mach -461, 1990 biswas, k. k. sh cs of a combine of the energy in santoso, d. pusp r in combined y & applied sci malael & d t variation within conclusion wt was propos darrieus turbin wer extractio wind tunnel w counter rotati ing dof me rate of the tw rough classica momentum is s ration to ae sst rans m were also con for this wind tunnel mic optimizatio l selection and e diameter w rstanding of th peed will lead tial. future wo a magnetic b g more focus t wledgment ut within nati gas turbines erences neiro de araujo, c. f. de andrade, on the performan , energy, vol. 148 zhanga, y. li, “ different convex p. 287-299, 2018 sharma, “compar combined threewable energy, vo z, “experimental hine”, solar & w harma, r. gupta, “ ed three bladed d stitute, vol. 88, n pitasari, “investig d darrieus-savo ience research dragan: numer stream velocity sed, consisting nes. the envis on capabilities with good re ing straight b ethods since i wo stages differ l calculations. specified for th erodynamic e model. experim nducted with a application. showed accep on is needed. i d the ratio be will be taken he relation be d to furtherin ork will focus o earing system to be placed o ional researc comoti res r. j. pontes lim f. o. m. carneir nce of small-scal 8, pp. 169-178, 20 “shape optimizati x and concave rative study of a -bucket savonius ol. 33, no. 9, pp study on a self-a wind technology, “computational a darrieus savoniu no. 4, pp. 425-437 gations on the ef onius wind tu h v rical and exper g of a sioned s was esults. bladed it was 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axis wind t ds”, applied mec sics of starting p ind and tidal of dy of the dual v wind engineerin 2018 n, “permanent m ro-wind turbine” conference, hera nd tunnel and num ewable energy, v cal … cle id turbine ce and ational on the rbine”, h blade 2009, urbatu, awts”, pellers 1146ions of 07 using urbine: cfd”, critical ewable e delft energy turbine chanics process ffshore vertical ng and magnet , 52nd aklion, merical vol. 35, microsoft word 36-3419_s_etasr_v10_n3_pp5803-5807 engineering, technology & applied science research vol. 10, no. 3, 2020, 5803-5807 5803 www.etasr.com rafiammal et al.: reconfigurable hardware design for automatic epilepsy seizure detection using … reconfigurable hardware design for automatic epilepsy seizure detection using eeg signals s. syed rafiammal department of electronics and communication engineering b.s. abdur rahman crescent institute of science and technology chennai, india rafiammal@crescent.education d. najumnissa jamal department of electronics and instrumentation engineering b.s. abdur rahman crescent institute of science and technology chennai, india najumnissa.d@crescent.education s. kaja mohideen department of electronics and communication engineering b.s. abdur rahman crescent institute of science and technology chennai, india kajamohideen@crescent.education abstract—reconfigurable circuit designs for automatic seizure detection devices are essential to prevent epilepsy affected people from severe injuries and other health-related problems. in this proposed design, an automatic seizure detection algorithm based on the linear binary support vector machine learning algorithm (lsvm) is developed and implemented in a field-programmable gate array (fpga). the experimental results showed that the mean detection accuracy is 86% and sensitivity is 97%. the resource utilization of the implemented design is less when compared to existing hardware implementations. the power consumption of the proposed design is 76mw at 100mhz. the experimental results assure that a physician can make use of this proposed design in detecting seizure events. keywords-seizure detection; fpga; high level synthesis; mahalanobis distance; automatic detection i. introduction abnormal brain nerve cell functioning prompts seizures. sudden abnormalities of electrical activity affecting certain regions of the brain are the root cause of seizures and the affected individuals may get injured during one. some may experience jerky movements. few may exhibit vague reactions. two or more consecutive seizures are considered as epilepsy. electroencephalogram (eeg), magnetic resonance imaging, functional magnetic resonance imaging, computed tomography may assist in seizure detection. most of the physicians rely on eeg reports to diagnose epilepsy. apart from that, the neurologists take the help of automatic epilepsy detection systems. there are several methods to analyze the eeg signal for seizure detection. most reviewed methods are time domain, frequency domain, and time-frequency domain. to analyze the eeg signals, we can make use of time domain features, such as amplitude, regularity, synchronicity, coefficient of variance, and higher order spectra. in frequency domain analysis, we extract fast fourier transform, power spectral density, average brand frequency, and dominant frequency features from the eeg signals. time domain and frequency domain methods may not provide the exact location of a particular event. time frequency domain methods were developed to overcome this problem. most widely used time frequency domain methods are spectrograph gabor atoms (sga), wigner wille distribution (wwd), and wavelet analysis (wa). most of the authors refer to the wavelet method which is computationally intensive during fine analysis with less directionality. to classify features extracted from the eeg signals as seizure or non-seizure, machine learning methods are used. support vector machine (svm), is one of the machine learning algorithms, which provides better results since it learns by solving constrained quadratic programming whose performance is dependent on large size training sample. hence, there is a need to develop an algorithm which is data intensive for smaller training sample sizes. from the physician’s point of view, there is an immediate need to classify the seizure and non-seizure events from eeg signals for quick diagnosis. so it has become necessary to design a device that can help this classification process. to achieve this purpose, researchers are working on different classification methods. neural networks, machine learning, and distance based classifications are some of them. distance based classification is the simplest among these methods. svm is widely used in designing automated systems for epilepsy detection. ii. literature review svm, k-nearest neighbor (knn), and random forest (rf) are generally used for classification problems. svm method is basically divided to linear and non-linear. both these methods are used in hardware design for automatic epilepsy detection. a non-linear guassian function based svm was implemented in soc [1-4]. a hybrid svm was implemented to detect seizure segments, where the kernel parameters were optimized using optimization techniques as genetic or particle swarm algorithm or radial basis function [5-8]. whale optimization algorithm (woa) with radial basis function kernel svms were developed for seizure detection with 100% detection accuracy in [9]. this methodology includes complex wavelet transforms and time domain feature extraction. universum svm is proposed in [10] having 99% accuracy, with, however, high computational time. binary svm was proposed in [11], but improvement is needed in this algorithm to reduce computational time. the constrains of designing a hardware for automatic epilepsy detection are that the corresponding author: s. syed rafiammal engineering, technology & applied science research vol. 10, no. 3, 2020, 5803-5807 5804 www.etasr.com rafiammal et al.: reconfigurable hardware design for automatic epilepsy seizure detection using … algorithm should utilize a smaller number of features and less hardware resources, power consumption, detection accuracy, and feasibility of training the classifier. in this paper, a hardware implementation with minimum hardware resources, low power design, and facility to train the classifier for patient specific detection system is proposed. iii. methodology the proposed method consists of the eeg signal acquisition module, the segmentation and feature extraction module, the svm training module, and the classification module. its block diagram is given in figure 1. fig. 1. block diagram of the proposed method a. data the proposed algorithm has used the database of the university of bonn [12, 13]. there are 5 sets of data available in this data base. the datasets available are of types z, o, n, f, and s. z and o segments are classified as normal, n and f segments consists of eeg segments which occur before seizure and the dataset s is composed of seizure events. each segment consists of 100 single channel data recordings of 23.6s duration. the data sampling frequency is 173.6hz and the bandwidth is 0.5hz to 85hz. figure 2 depicts the power spectrum of normal, inter-ictal and seizure signals. fig. 2. amplitude spectrum of the eeg signals b. feature extraction the segmentation of eeg data is necessary for feature extraction. the impact of variable segment length is discussed in [14]. for this proposed design, the eeg signals are divided into 20s duration segments using the non-overlapping windowing method. time domain features are then extracted from each segment for further processing. mobility, standard deviation, sign slope change, sum of square root, mean of square root features are calculated for each segment’s primary units.the sum of squared data point in a segment, and its mean value are taken as features. the remaining features are: • hjorth mobility: the mean frequency of the time series is represented by the mobility parameter: mobility= )'(var*)(var xiancexiance (1) where x is the feature vector, which is segmented using windowing method. variance is calculated by the squared deviation of data points from their mean values. • standard deviation: the amount of data spread is measured from standard deviation. it is defined by: standard deviation= ∑ = − − l i i l uxx 1 2 1 )( (2) where xxi is a data point, i goes from 1 to the total number of data points in a segment l, and u is the mean of data segment. • slope sign change in the direction of feature vectors. it is defined by (3): 1 1 1 if ( )*( ) 0 1 otherwise 0 l k k k k k xx xx xx xx s s + + = − − ≥ = = ∑ (3) c. principle component analysis the principal component analysis (pca) is a statistical method which is used to convert data vectors to linearly uncorrelated variables. pca gives increased accuracy in classification of data points. it also reduces the dimension of data. in the proposed method, pca is used for pre-processing the training and testing feature sets in order to get better classification results. d. moving average moving average is a data transforming technique used in technical analysis. it consists of successive means of a segment in a time series. the moving average for the first ‘n’ data points in a time series is given as (x1+x2+...+xn)/n where xi is a data point in the series. e. log transformation log transformation is a widely used method for data interpretation. this method is used to convert highly asymmetric distributions to less skewed. the logarithmic values of individual feature values are calculated for data transformation. f. binary linear svm classifier the classification of normal, pre-ictal and seizure signals were obtained using binary linear support vector machine (lsvm) learning method with linear kernel. the lsvm uses a hyper plane to separate data classes. support vectors are data engineering, technology & applied science research vol. 10, no. 3, 2020, 5803-5807 5805 www.etasr.com rafiammal et al.: reconfigurable hardware design for automatic epilepsy seizure detection using … points which are close in the hyper plane. the binary lsvm will classify the eeg signals either as non seizure or seizure signals. non seizure signals are classified as +1 and seizure signals as -1. the svm classifier with linear kernel was proposed in [15]. authors in [16] proposed a simple data adjustment algorithm on the binary lsvm classifier. optimization of weight vectors and bias were not necessary. data adjustment was used to calculate weight vectors and bias values. this proposed classification algorithm is based on [16] with a modification in the classification step. the classifier program can be implemented using any programming language which uses simple mathematical operations. due to its reduced complexity, this classification algorithm can be implemented in hardware. 1) algorithm: set : matrix x=[feature vector of test data set ]; matrix x=[feature vector of training data set]; matrix y=[class identity of corresponding training data vectors]; for i=1 to n, where n is the number of sample data points in the training data set for j=1 to n, (multiply: matrix x(i,:) by matrix x(j,:)' ) set: matrix a(i,j)=x(i,:)*x(j,:)'; end end for k=1 to n, for l=1 to n, do : multiply matrix a(k,l) by matrix y(l) set : matrix a(k,l)=a(k,l)*y(l); end end inverse: matrix c= inverse(a) for m=1 to n, multiply : matrix c(m) * matrix y(m) * matrix x(m,:) set : matrix z(m,:)=c(m)*y(m)*x(m,:); end set : matrix w=[sum of the first column of matrix z, sum of the second column of matrix z, sum of the third column of matrix z, sum of the fourth column of matrix z, sum of the fifth column of matrix z]; calculate : bias parameter ‘ b’ =y(1)-w*x(1,:)'; set the classification function g=w*x'+b classification result g if (sign{g}==1) then x=normal else x=seizure for training, 50% of eeg data were used and the remaining 50% were used for testing. the lsvm classifier was trained using feature sets of the training dataset. the training and testing datasets each consist of 1.64 hours of eeg recordings. separate segments were used for training and testing. the training and testing data are comprised of normal eeg segments, pre-ictal eeg segments, and seizure segments (see table i). table i. details of training and testing data data set normal inter-ictal seizure time training 39.3 min 39.3 min 19.66 min 1.64 h testing 39.3 min 39.3 min 19.66 min 1.64 h iv. results and discussion a. simulation results seizure detection accuracy is calculated in order to assess the performance of the proposed classification method. bonn epilepsy database [12] was utilized. the data were segmented into 20s segments using non-overlapping rectangular windowing method. in addition, time domain features were calculated for each segment to form the feature vector. the results are shown in figure 3. fig. 3. time domain features of eeg signals the data transformation methods of pca and data smoothing using simple moving average were applied to the feature vector before classification. the proposed classifier performance on discriminating normal and seizure eeg signals is given in table ii. table ii. classifier performance of normal and seizure signals transformation method accuracy sensitivity no transformation 72% 86% pca 80% 92% moving average 86% 97% log 86% 92% the proposed svm classification is tested with 3 types of data transformation methods. in pca method, the accuracy of the classifier is 80% and its sensitivity is 92%. in moving average method, the accuracy is 86% and the sensitivity is 97%. log transformation method shows an accuracy of 86% and a sensitivity of 92%. hence, log transformation method produces better results in classification of inter-ictal eeg signals and seizure signals. b. hardware implementation the proposed algorithm is implemented in a zynq board zc 706 fpga. high level synthesis (hls) software is very useful in asic design [17].the algorithm is written in c language and it is implemented using vivado hls. this design is divided into the training and testing phases. the training phase consists of the feature extraction module and lsvm parameter calculation (bias and weight of svm) module. the engineering, technology & applied science research vol. 10, no. 3, 2020, 5803-5807 5806 www.etasr.com rafiammal et al.: reconfigurable hardware design for automatic epilepsy seizure detection using … testing phase is composed of classification modules which contain feature extraction testing data and classification of eeg signals. both modules are implemented in the fpga. for the training of the lsvm, 1.64h of data were used with 204800 data samples. the feature vector extracted from eeg samples is given to the lsvm training module in order to calculate the weights and biases. during the testing phase, for each clock pulse, a 20s data segment is given as input to the testing module .the testing module result will be either +1 for the non seizure signal or -1 for the seizure signal. the fpga consists of resources as the look up table (lut) where the programming logic is implemented. the lut is constructed using a multiplexer and static ram. since static ram is volatile memory, the program logic will be loaded from the memory to sram while executing the algorithm. a flipflop (ff) is a single bit memory used to hold the status of program execution. flipflops are used to construct memory luts. since this proposed design is a patient specific detection system, the hardware design utilizes the block ram of the zynq board to store the training parameters. the weight and bias values will be stored in the ram. xilinx zynq board consists of a dsp processor to handle the signal processing feature extraction applications. the dsp processor consists of adder, subtractor, multipler, barrel shifter, fir filter, square root calculation block, and a multiply and accumulation unit. input and output pins were used to interface real time signals into the fpga board for online detection. the entire proposed design is written in c and vivado hls generated the ip blocks. the ip blocks were then called in the vivado simulator block design. the simulations and implementation are completed using the vivado simulator. the resource utilization of each module is given in table iii. due to the smaller number of features and simple classification, the proposed method will require a small number of the fpga’s resources. the power utilization comparison with existing methods is given in table iv. table iii. fpga resource utilization fpga resources feature extraction module svm training module classification module available resources in zynq706 fpga slice 2568 1898 2733 lut 8217 5145 8692 218600 flip flop 6425 3770 7026 437200 dsp 20 14 30 900 bram 24 779 8 545 srl 129 74 130 table iv. comparison of power utilization of seizure detection module design method platform power (mw) [18] cyclone ii 143.9 [18] cyclone iii 90.5 [1] asic 1.83 µj/class [4] cyclone ii 58 µv proposed zynq -7 zc706 76 fig. 4. ip block diagram v. conclusion an automatic seizure detection hardware system to classify non-seizure and seizure eeg signals will help the medical practitioners to diagnose epilepsy disorders. the eeg signal is segmented in 20s segments and features were calculated for each segment. the linear svm is used to classify the eeg signal as a seizure or non-seizure event. a high level synthesis based detection algorithm is developed and it is implemented in zynq 706 hardware. the performance of this system is tested by using the bonn eeg data base [12]. the results show that the proposed method achieves high detection selectivity of 97% with a minimum number of features. in addition, this design has better performance in comparison with the existing methods. due to less dynamic power, this design can be developed as application specific integrated circuit design for a standalone device, which may be used by physicians. references [1] m. a. b. altaf, j. yoo, “a 1.83 µj/classification, 8-channel, patientspecific epileptic seizure classification soc using a non-linear support vector machine”, ieee transactions on biomedical circuits and systems, vol. 10, no. 1, pp. 49–60, 2015 [2] y. wang, z. li, l. feng, h. bai, c. wang, “hardware design of multiclass svm classification for epilepsy and epileptic seizure detection”, iet circuits, devices & systems, vol. 12, no. 1, pp. 108– 115, 2018 [3] j. b. m. hugle, s. heller, m. watter, m. blum, f. manzouri, m. duempelmann, a. schulze-bonhage, p. woias, j. boedecker, “early seizure detection with an energy-efficient convolutional neural network on an implantable microcontroller”, international joint conference on neural networks, rio de janeiro, brazil, july 8-13, 2018 [4] l. feng, z. li, y. wang, “vlsi design of svm-based seizure detection system with on-chip learning capability”, ieee transactions on biomedical circuits and systems, vol. 12, no. 1, pp. 171–181, 2018 [5] j. yoo, l. yan, d. el-damak, m. bin altaf, a. shoeb, h. j. yoo, a. chandrakasan, “an 8-channel scalable eeg acquisition soc with fully integrated patient-specific seizure classification and recording processor”, 2012 ieee international solid-state circuits conference, san francisco, ca, usa, february 19-23, 2012 engineering, technology & applied science research vol. 10, no. 3, 2020, 5803-5807 5807 www.etasr.com rafiammal et al.: reconfigurable hardware design for automatic epilepsy seizure detection using … [6] a. subasi, j. kevric, m. a. canbaz, “epileptic seizure detection using hybrid machine learning methods”, neural computing and applications, vol. 31, pp. 317–325, 2017 [7] y. elhazek, a. ibrahim, m. amer, a. abubakr, h. mostafa, “hardware accelerated epileptic seizure detection system using support vector machine”, 8th international conference on modern circuits and systems technologies, 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http://epileptologiebonn.de/cms/front_content.php?idcat=193&lang=3 [13] r. g. andrzejak, k. lehnertz, f. mormann, c. rieke, p. david, c. e. elger, “indications of nonlinear deterministic and finite-dimensional structures in time series of brain electrical activity: dependence on recording region and brain state”, physical review e, vol. 64, no. 6, article id 061907, 2001 [14] k. d. tzimourta, l. g. astrakas, a. m. gianni, a. t. tzallas, n. giannakeas, i. paliokas, d. g. tsalikakis, m. g. tsipouras, “evaluation of window size in classification of epileptic short-term eeg signals using a brain computer interface software”, engineering, technology & applied science research, vol. 8, no. 4, pp. 3093–3097, 2018 [15] b. e. boser, i. m. guyon, v. n. vapnik, “a training algorithm for optimal margin classifiers”, fifth annual workshop on computational learning theory, pittsburgh, usa, july 27-29, 1992 [16] x. song, h. wang, l. wang, “fpga implementation of a support vector machine based classification system and its potential application in smart grid”, ieee 2014 11th international conference on information technology: new generations, las vegas, usa, april 7-9, 2014 [17] m. dossis, g. dimitriou, “are hls tools healthy ?”, engineering, technology & applied science research, vol. 5, no. 2, pp. 790–794, 2015 [18] s tamilarasi j, sundararajan, “fpga based seizure detection and control for brain computer interface”, cluster computing, vol. 22, no. 5, pp. 11841–11848, 2019 engineering, technology & applied science research vol. 7, no. 2, 2017, 1523-1527 1523 www.etasr.com touahmia: performance of geosynthetic-reinforced soils under static and cyclic loading performance of geosynthetic-reinforced soils under static and cyclic loading mabrouk touahmia college of engineering, department of civil engineering university of hail hail, saudi arabia m.touahmia@uoh.edu.sa abstract—this paper investigates and discusses the composite behavior of geosynthetic reinforced soil mass. it presents the results of a series of large-scale laboratory tests supported by analytical methods to examine the performance of geogrid reinforcement subjected to static and cyclic pullout loading. the testing equipment and procedures used for this investigation are outlined. the results show that geosynthetic reinforcement can mobilize great resistance to static pulling load under high confining pressures. the reinforcement exhibits gradual deformation under cyclic loading showing no sign of imminent pullout failure for all levels of applied loads. in general, the results demonstrate that geosynthetic can be used in situations where loads are non-static, although care will be required in ensuring that appropriate factors of safety are applied to control the resulting deformation. a simplified analytical model for calculating the pulling capacity of geosynthetic reinforcement is proposed. keywords-geosynthetics; reinforced soil; geogrid; static loading; cyclic loading i. introduction geosynthetic-reinforced soil technology has become a significant part of civil and environmental engineering practice all over the world due to its numerous advantages such as, costeffectiveness, easy construction and time saving. it has proven to offer sustainable alternative solutions to many soft and unstable ground problems where the use of conventional construction techniques would be restricted or significantly expensive. various types of geosynthetic products have found several aspects of earthwork applications such as in earth retaining structures, steep slopes, roadway embankments, railway tracks, load-bearing foundations, and subsurface drainage. the inclusion of geosynthetic reinforcement in soil mass improves the shear resistance of the soil due to the interlocking of the soil particles with the reinforcement apertures, thereby improving its structural capability. under applied external load the reinforcement mobilizes resistance along its length according to the laws of bond and bearing. the transfer of stress between soils and various soil reinforcement systems involves two basic mechanisms: frictional resistance and/or passive resistance. a great deal of research has been undertaken to understand the interaction mechanisms and the operational behavior of the geosynthetic-soil composite material [1-3]. however, design methodologies used for geosynthetic reinforced soil systems have remained variable and sometimes confusing. up to now, there are no uniform standards and specifications for reinforced soil systems, and in fact, there are different design criteria and procedures for each system. most reinforced soil structures have been designed using limit equilibrium methods, which are generally considered to be very conservative [4-6]. these designs consider the peak strengths of the materials without regard to the strain compatibility between the two dissimilar materials and treat all types of loads as pseudo static loading [7]. to date, engineers are faced with many uncertainties regarding the selection of appropriate types of reinforcement and the evaluation of design parameters for these systems. geosynthetic reinforced soil systems are frequently subjected not only to static loads but also to non-static loads such as repeated or cyclic loads. such loading conditions can result from traffic loads on reinforced embankments and bridge abutments, pavements supported by reinforced soil retaining walls, reinforced earth structures subjected to significant tidal variations or to extremes temperature daily. the effect of cyclic loading on the interaction behavior of soil-geosynthetic systems has not yet been sufficiently addressed in research. it is considered however that the development of any reliable design methodology for geosynthetic reinforced soil systems will require a thorough understanding of the interaction mechanism and failure characteristics of the soil-geosynthetic composite material under different types of loading conditions. the main objective of this paper is to examine the pullout behavior of geogrid reinforcements under static and slow cyclic loading conditions. a large amount of laboratory test data has been generated in order to investigate the effects of various parameters on the interactive behavior of the composite material. the mechanics of load mobilization and reinforcement deformation under loading and unloading modes has been analyzed. ii. experimental investigation the schematic diagram of the large-scale pullout apparatus used for the purpose of this experimental program is shown in engineering, technology & applied science research vol. 7, no. 2, 2017, 1523-1527 1524 www.etasr.com touahmia: performance of geosynthetic-reinforced soils under static and cyclic loading figure 1. it consisted basically of a rigid soil container of inside dimensions 4.0m´0.3m´0.3m, a horizontal pullout loading system with the capacity to apply either static or slow cyclic loads to the reinforcement and a normal pressure setup. fig. 1. pull-out test device. the static loading tests were carried out by adding dead weights to the load hanger situated at the rear end of the container and connected to the reinforcement. the cyclic loads were applied through lifting and releasing a moveable rider with weights on it by a reciprocating electrical motor. the repeated cycles of loading changed every 20 seconds between an upper and a lower load level to give a square-shaped pattern. the confining stress, which could be controlled from 0 to 300 kn/m2, was applied to the top of the soil sample via a pressure plate loaded through a water bag. a data acquisition system was used to record the collected test results. the soil used in this investigation was a uniformly graded dry sand of medium size. the properties of the sand are given in table i. table i. soil sample properties property value specific gravity coefficient of uniformity coefficient of curvature maximum dry density (mg/m3) minimum dry density (mg/m3) maximum void ratio minimum void ratio friction angle 2.67 1.86 0.84 1.78 1.42 0.87 0.49 30.4 the soil samples were prepared by raining method to a targeted relative density of 53%. to obtain a uniform density throughout the filling operation, the sand was poured into the pullout box from a constant height of 0.35 m and placed in 0.05 m thick equal layers. the reinforcements used in this investigation were formed by cutting tensar sr2 geogrid into a row of two ribs in width and 35 bars length (approximately 4 m). special axial movement gauges were provided at 5 locations along the reinforcement to measure the axial strains with applied load. the test specimen was located at the midheight of the soil sample and connected to the loading levels system with a special clamp. the applied cyclic load levels were expressed as a percentage of the index load (pi = 3.25 kn) of the geogrid, defined as the ultimate rupture load of an identical (4 bars x 2 ribs) geogrid element in air. iii. static load test result a series of static pullout tests were conducted to examine the load-deformation behavior of the geogrid reinforcement and assess its mode of failure under static loading. four levels of normal stress namely 25, 50, 75 and 100 kpa were applied to the sand surface. the embedded geogrid was subjected to a series of short-term incremental axial pullout loads of 0.196 kn/5min. the collected data from the pullout tests includes the variation of the geogrid deformation with the applied load at the frontal end and along the reinforcement length. all tests were performed till the total pullout displacement of the geogrid reaches a maximum of 40 mm, which represents 1% of the reinforcement length. figure 2 shows the pulloutdisplacement relationships of the geogrid reinforcement under different confining stresses (σn). fig. 2. load-displacement relationships of the geogrid. the general pattern of these relationships is characterized by a continuous increase in the geogrid movement with increase in applied loads showing no pullout failure from the beginning till the end of the test. no peak load could be observed with the system of loading used, and the relationship between load and deformation became linear at larger displacements. the surcharge pressure was found to have a great effect on the deformation of the geogrid. as shown, the reinforcement mobilized greater resistance to pulling loads when the surcharge pressure increased and that is clearly visible under the high loading increments. this resistance to pullout of the reinforcement is offered by two main components, the frictional resistance provided mainly by the longitudinal members of the geogrid, and the passive-bearing resistance provided by the transverse members of the geogrid. the recorded movements along the length of the geogrid reinforcement for different applied pullout loads are given in figure 3. as shown, the total deformation of the reinforcement consists only of an extension of the front part of the reinforcement and neither slip nor extension along the rear segment of the geogrid length was observed. this means that the applied load was mobilized over the front part of the strip only, the parts towards the distal end being unstrained. the magnitude of deformation along the geogrid is highly dependent on the applied confining pressure, with higher surcharge pressures resulting in very small or no load being transmitted to the rear part of reinforcement. this observation would indicate that unless a very low confining stress be used it would be impossible to pull out the geogrid reinforcement. consequently failure of the geogrid by rupture appears to be an easier mode. engineering, technology & applied science research vol. 7, no. 2, 2017, 1523-1527 1525 www.etasr.com touahmia: performance of geosynthetic-reinforced soils under static and cyclic loading fig. 3. axial deformation along the geogrid. iv. cyclic load test result a large amount of cyclic loading tests has been performed in order to obtain a better understanding of the effect of cyclic loading on the pullout behavior of geosynthetic soil reinforcements. a wide range of loading levels and amplitudes was chosen to examine the pullout behavior and the failure pattern of the geogrid under such loading condition. in some cases the tests were taken to 100000 load cycles while the confining pressure was kept constant at 100 kpa for comparison purpose. the cumulative movement of the reinforcement versus the number of loading cycles is presented in figure 4. fig. 4. displacement-log number of load cycles relationships. as shown, the general behavior of the reinforcement was characterized by a continual increase in displacements with ian ncrease in loading cycles from the starting till the end of the test. despite the large number of load repetitions none of the tested strips failed by pulling out. all the geogrid reinforcements were gradually pulling through the soil, as the number of load cycles increased, showing no sign of absolute failure. the gradual deterioration of the geogrid performance can be attributed primarily to the bearing resistance developed by the bars of the grid which acted as a series of anchors and, secondly, to the high extensibility characteristic of the geogrid material. it can be noted that the behavior of the geogrid reinforcement was highly dependent upon the magnitude of the cyclic load, with higher amplitude causing a rapid deterioration of the reinforcement performance. the life span of the geogrid was prolonged from 400 cycles to a nearly 10000 cycles by a reduction in the load amplitude from 50% pi to 35% pi and the reinforcement sustained more than 105 cycles when it was subjected to a loading amplitude of 25% pi. with further lowering of the loading amplitude to 10% pi, the geogrid remained stable for over 105 cycles showing a nearly linear relationship between the reinforcement frontal displacement and the log number of load cycles. for further examination of the geogrid failure mechanism, the rate of movement per cycle is plotted against the number of load cycles on log-log scale. as shown in figure 5, all the curves showed a similar trend which is characterized by a linear relationship of a decreasing rate of movement with increasing number of load cycles from the beginning till the end of the testing period. such behavior indicates no sign of imminent pullout failure despite the large number of load cycles and the large amount of displacement. fig. 5. rate of displacement-log number of load cycles relationships. the effect of the loading condition is further clarified in these diagrams, where different load levels gave different straight lines. an interesting feature is that the slopes of all plots are predominantly the same which indicate that the relationship is essentially independent of the stress level, and increases in stress serve only to shift the line vertically upwards. based on this series of constant lines the frontal deformation δνof the geogrid reinforcement at n number of load cycles can be expressed as: ( )1 log (1)i p s n n e d d é ù+ +ê úë û= where δi is the deformation after one cycle and sp is the slop of the deformation-number of cycles relationship. the total deformation at any section along the geogrid and its variation with load reversals is shown in figure 6. these movements were expected to comprise two components as the number of cycles increases, the slip movement of the reinforcement together with the extension of the geogrid material. however, as can be seen, the total deformation consists only of an extension of the front segments and neither slip nor extension along the distal end of the reinforcement was engineering, technology & applied science research vol. 7, no. 2, 2017, 1523-1527 1526 www.etasr.com touahmia: performance of geosynthetic-reinforced soils under static and cyclic loading observed even at the highest loading level 0.5 pi. this observation would indicate that no load was transmitted to the lattermost half of the reinforcement which remained unstressed during all the cyclic loading tests. fig. 6. change in axial strain with number of load cycles. it can be noted that the load was mobilized over the front part of the strip only, the parts towards the distal end being unstrained. this observation would indicate that unless a very low confining stress be used it would be impossible to pull out the geogrid. consequently, failure of this reinforcement by rupture appears to be an easier mode. v. analytical model due to geometrical and mechanical characteristics, geogrid can only carry tensile stresses through contact zone and anchorage members. under applied external load the reinforcement mobilizes progressively resistance along its length according to the laws of band and bearing. thus, the pullout resistance of the geogrid reinforcement would consist of two parts; (i) frictional resistance due to skin friction (fa) and (ii) passive-bearing resistance against traverse members (fb). the overall pullout capacity of the geogrid (tmzx) can be computed as: ba fft max  (2) the frictional resistance is offered mainly by the longitudinal members due to interfacial shearing between soil and the geogrid surface and can be expressed as:  dxxbf l ana    0 2   (3) where σn the applied normal pressure at the soil-reinforcement interface, τα(x) the soil adhesion at the interface and b and l are the reinforcement effective width and length. the passive-bearing resistance results from the interlocking of the soil at the geogrid apertures, which are normal to the pullout direction. the transverse members of a grid reinforcement can be considered analogous to a series of strip footings in succession which have been rotated through 90o to the horizontal and pulled through the soil. the maximum bearing stress can be calculated by invoking the theory of bearing capacity [8-9] which can be expressed in cohesionless soil as:                       2 45tan tan 2    enf nb (4) where n is the number of transverse members in the geogrid and  is the frictional angle for soil. the total pullout resistance can be then expressed in general form as:                          245tan2 tan 2 0 max     endxxbt n l an (5) the experimental results showed that as the reinforcement is loaded the resistance available at the soil-reinforcement interface is gradually mobilized along the reinforcement surface. this means that at an applied load t adhesion is mobilized over a part of the reinforcement length only, the remaining part remains unloaded. at some average adhesion the strength of the interface is mobilized and failure migrates along a distance x of the reinforcement length. increase of t by dt causes an additional displacement d of the reinforcement. this incremental displacement maybe expressed by: x e dfdf d ba   (6) where adf is the additional frictional load over the length x, dfb is the load taken by the bearing members, and e is a constant which depends on the reinforcement stiffness and properties. putting ba kdfdf  and rearranging (5) gives: a an a df keb f d          1 1 2   (7) integration of (6) yields the displacement of the geogrid reinforcement  as:          keb f an a 11 4 2     (8) the unloading of the reinforcement may be studied by incrementally adding a reverse or negative loads until the gross effect is that of zero external applied load. thus, the mechanics of unloading are similar to those described for the loading case, except the adhesion resistance is no longer τα but τα mobilized in the reversed direction. this will cause a reverse displacement  u of the reinforcement, which can be expressed by:          keb f an u u 1 1 4 2     (9) engineering, technology & applied science research vol. 7, no. 2, 2017, 1523-1527 1527 www.etasr.com touahmia: performance of geosynthetic-reinforced soils under static and cyclic loading hence, the residual displacement r under zero applied load can be computed as:                   a u a a n ur ff keb   22 1 1 4 1 (10) on reloading the displacement may not equal to the original displacement which resulted on first loading unless the interface adhesion remains constant. this indicates that the act of subjecting a reinforcing element to a package of cyclic loading modifies the stress state along the reinforcement which leads to a progressive pullout of the reinforcement. vi. conclusion this study investigated the composite behavior and performance of geosynthetic reinforced soil mass under static and cyclic loading. a series of pullout tests were conducted on geogrid embedded in a uniformly graded dry sand of medium density under different vertical confining pressures. the tests provide a better understanding of the interaction mechanism and failure mode of soil-geogrid composite systems that can be used for validation of analytical models. the findings demonstrate that geosynthetics have great potential to be used in situations where loads are non-static, although care will be required in ensuring that appropriate factors of safety are applied to control the resulting deformation. the study brings the following conclusions for geogrid reinforcement: • under static loading the geogrid mobilizes greater resistance to pulling load under higher confining pressure. • under cyclic loading the geogrid exhibits a gradual deformation showing no sign of imminent pullout failure for all levels of applied load. the accumulation of deformation increases with increase in the number of load repetitions and load amplitude. • the deformation of the geogrid consists of an extension of the front part of the reinforcement only and neither slip nor extension along the rear segment was observed. • based on the test results analysis, a simplified analytical model for calculating the pulling capacity and deformation of geogrid reinforcements under loading and unloading conditions is proposed. acknowledgment the research reported herein was funded by the deanship of scientific research at the university of hail, saudi arabia, under the contract (0150215). the author would like to extend his gratitude to the deanship of scientific research and to the college of engineering at the university of hail for providing all facilitations required for this research. references [1] m. b. hossain, m. z. hossain, t. sakai, “interaction properties of geosynthetic with different backfill soils”, international journal of geosciences, vol. 3, no. 5, pp. 1033-1039, 2012 [2] j. p. giroud, “quantification of geosynthetic behavior”, geosynthetics international, vol. 12, no. 1, pp. 2-27, 2015 [3] e. m. palmeira, “soil–geosynthetic interaction: modelling and analysis”, geotextiles and geomembranes,vol. 27, no. 5, pp. 368-390, 2009 [4] j. g. zornberg, d. leshchinsky, “comparison of international design criteria for geosynthetic-reinforced soil structures” in landmarks in earth reinforcement, ochiai et al. (eds), vol. 2, pp. 1095-1106, 2003 [5] k. h. yang, p. utomo, t. l. liu, “evaluation of force-equilibrium and deformation based design approaches for predicting reinforcement loads within geosynthetic reinforced soil structures”, journal of geoengineering, vol. 8, no. 2, pp. 41-54, 2013 [6] m. p. pinho-lopes, a. m. paula, m. l. lopes, “soil–geosynthetic interaction in pullout and inclined-plane shear for two geosynthetics exhumed after installation damage”, geosynthetics international, vol. 23, no. 5, pp. 331-347, 2016 [7] a. mcgown, “the behaviour of geosynthetic reinforced soil systems in various geotechnical applications”, 2nd european conference on geosynthetics, eurogeo 2000, bologna, italy, 1, pp. 3-26, 2000 [8] r. a. jewell, g. w. e. milligan, r. w. sarsby, d. dubois, “interaction between soil and geogrids”, in polymer grid reinforcement, thomson telford limited, london, uk, pp. 18-30, 1984 [9] m. j. i. alam, s. r. lo, m. r. karim, “pull-out behaviour of steel grid soil reinforcement embedded in silty sand”, computers and geotechnics, vol. 56, pp. 216-226, 2014 microsoft word 18-3666_s_etasr_v10_n4_pp5986-5991 engineering, technology & applied science research vol. 10, no. 4, 2020, 5986-5991 5986 www.etasr.com saeed: a machine learning based approach for segmenting retinal nerve images using artificial … a machine learning based approach for segmenting retinal nerve images using artificial neural networks alotaibi najm saeed prince saud al faisal institute for diplomatic studies saudi arabia alotaibinajim@gmail.com abstract-artificial intelligence (ai) based machine learning (ml) is gaining more attention from researchers. in ophthalmology, ml has been applied to fundus photographs, achieving robust classification performance in the detection of diseases such as diabetic retinopathy, retinopathy of prematurity, etc. the detection and extraction of blood vessels in the retina is an essential part of various diagnosing problems associated with eyes, such as diabetic retinopathy. this paper proposes a novel machine learning approach to segment the retinal blood vessels from eye fundus images using a combination of color features, texture features, and back propagation neural networks (bpnn). the proposed method comprises of two steps, namely the color texture feature extraction and training the bpnn to get the segmented retinal nerves. magenta color and correlationtexture features are given as input to the bpnn. the system was trained and tested in retinal fundus images taken from two distinct databases. the average sensitivity, specificity, and accuracy obtained for the segmentation of retinal blood vessels were 0.470%, 0.914%, and 0.903% respectively. results obtained reveal that the proposed methodology is excellent in automated segmentation retinal nerves. the proposed segmentation methodology was able to obtain comparable accuracy with other methods. keywords-machine learning; texture feature; retinal nerves; segmentation; neural networks; feature extraction i. introduction utilizing computer-assisted diagnosis of retinal fundus images is becoming an alternative to the manual inspection known as direct ophthalmoscopy. moreover, computer-assisted diagnosis of retinal fundus images is proven to be as reliable as direct ophthalmoscopy, and requires less time to process and analyze. various eye related pathologies that can result in blindness, such as macular degeneration and diabetic retinopathy, are routinely diagnosed by utilizing retinal fundus images [1]. one of the fundamental steps in diagnosing diabetic retinopathy is the extraction of retinal blood vessels from fundus images. although several segmentation methods [2, 3] have been proposed, this segmentation remains challenging due to variations in retinal vasculature network and image quality. currently, the main challenges in retinal vessel segmentation are the noise (often due to uneven illumination) and thin vessels. furthermore, the majority of the proposed segmentation methods focus on optimizing the preprocessing and vessel segmentation parameters separately for each dataset. hence, these approaches can often achieve high accuracy for the optimized dataset, whereas their application to other datasets has reduced accuracy. although vessel segmentation methods usually contain preprocessing steps aimed at enhancing the appearance of vessels, some approaches skip the preprocessing steps and start with the segmentation step. nowadays many segmentation methods rely on machine learning [4] concepts combined with traditional segmentation techniques for enhancing the segmentation accuracy, by providing data statistical analysis to support segmentation algorithms. these machine-learning concepts can be broadly categorized into unsupervised and supervised approaches, based on the use of labeled training data. in a supervised approach, each pixel in the image is labeled and assigned to a class by a human operator, i.e. vessel and non-vessel. a series of feature vectors is generated from the data being processed (pixel-wise features in image segmentation problems) and a classifier is trained by using the labels assigned to the data. unsupervised approaches use predefined feature vectors without any class labels, where similar samples are gathered in distinct classes. this clustering is based on some assumptions about the structure of the input data, i.e. two classes of input data where the feature vectors of each class are similar to each other (vessel and not vessel). based on the problem, this similarity metric can be complex or defined by a simple metric such as pixel intensities. this paper discusses briefly the retinal vessel segmentation methods to provide some insight into different methods and is by no means an exhaustive review of these methods. for a detailed discussion on different vessel segmentation methods please refer to [5]. authors in [6] proposed a supervised retina vessel segmentation where a k-nearest neighbor (k-nn) classifier was utilized for identifying vessel and non-vessel pixels by using a feature vector based on a multi-scale gaussian filter. authors in [7] proposed a similar approach that utilized a feature vector constructed by using a ridge detector. based on a feature vector constructed by using multi-scale gabor wavelet filters, authors in [8] proposed the use of a corresponding author: alotaibi najm saeed engineering, technology & applied science research vol. 10, no. 4, 2020, 5986-5991 5987 www.etasr.com saeed: a machine learning based approach for segmenting retinal nerve images using artificial … bayesian classifier for segmenting vessel and non-vessel pixels. in [9], a neural network (nn) based classifier was proposed, by utilizing calculated features that use momentinvariant features. retinal vessel segmentation by using a classifier based on boosted decision trees was proposed in [10]. meanwhile authors in [11] proposed a classifier by utilizing a support vector machine coupled with features derived that used a rotation-invariant linear operator. the main advantage of using an unsupervised segmentation approach instead of a supervised one is its independence from labeled training data. this can be considered as an important aspect in medical imaging and related applications that often contain large data. popular unsupervised retinal vessel segmentation methods can be categorized as vessel tracking, matched filtering, and morphology-based methods. starting from a set of initial points, defined either manually or automatically, vessel-tracking methods try to segment the vessels by tracking their centerline. this tracking can be performed by utilizing different vessel estimation profiles, such as gaussian [12], generic parametric [13], bayesian probabilistic [14] and multi-scale profiles [15]. one of the earliest examples of vessel tracking based segmentation methods was proposed in [16], based on the maximum a posteriori (map) technique. initial seeding positions corresponding to centerline and vessel edges were determined by using statistical analysis of intensity and vessel continuity properties. afterwards, gessel boundaries were estimated by using a gaussian curve fitting function applied to the vessel cross-section intensity profile. authors in [17] proposed a similar approach by combining map technique with a multiscale line detection algorithm, and their method was able to handle vessel tree branching and crossover points with good performance. based on the notion that vessel profile could be modeled by using a kernel (structuring element), filtering concepts try to model and segment the vessels by convolving the retinal image with a 2d rotating template. a rotating template is used to approximate the vessel profile in as many orientations as possible (known as the filter response), with the response being the highest in places where the vessels fit the kernel. techniques based on filtering utilize different kernels for modeling and enhancing retinal vessels, such as matched filters [18], gaussian filters [19], wavelet filters [20, 21], gabor filters [8] and cosfire filters [22, 23]. methods utilizing morphological operations can be used to enhance retinal images for use either with other segmentation methods, or for segmenting blood vessels from the background [24]. machine-learning algorithms are often utilized as supportive tools to automate and/or enhance most segmentation methods, by providing statistical analysis on a set of data generated by other segmentation methods. therefore, any existing unsupervised segmentation algorithm could be enhanced by employing and integrating machine-learning concepts. complex segmentation tasks and problems are usually solved by using a whole pipeline of several segmentation algorithms belonging to various image processing concepts. in this study an automated vessel extraction method in retinal fundus images is proposed, based on a hybrid technique comprising of genetic algorithm enhanced spatial fuzzy c-means algorithm with integrated level set method evaluated on real-world clinical data. furthermore, a combination of filters is utilized to enhance the segmentation, as each filter responded in a distinct way to different pixels in the image. considering the different image characteristics between datasets, the segmentation approach can be made more robust by combining filters. as the aim of this study was to propose an optimal segmentation method for use on various datasets, this method was not optimized for any specific dataset. ii. proposed methodology this section describes the overall proposed process in the segmentation of nerves or the blood vessels in retinal images. retinal images were used as testing datasets. figure 1 shows the overall architecture of the proposed methodology for segmenting the retinal nerves. fig. 1. overall architecture of the proposed methodology. a. dataset retinal images were taken from publicly accessible digital retinal images from drive [4], and stare [25] databases for the process of nerve segmentation. these datasets are used for developing and testing the performance of various retinal segmentation methods. datasets drawn manually are called as the ground truth. b. grey scale conversion and pre-processing pre-processing is the process of removing the noise and artifacts present in images. a contrast limited adaptive histogram equalization is performed in order to equalize the entire image. a mean filter is utilized to reduce the noise and the artifacts present in the input retinal images. afterward, the retinal images are converted to grey for further processing. since the grey scale converted image has various shapeless image boundaries, the pixels outside the image or the nerve boundaries were considered to remove the missing nerves present in the boundary. the original, equalized, grey scale and its pre-processed retinal images are depicted in figure 2. c. texture feature extraction texture provides some important features about the structural arrangement of various surfaces. texture features are used for classifying the possible nerve regions that have been identified with previous processing [26, 27]. gray level cooccurrence matrix (glcm) features were calculated for the regions present inside the retinal image. in general, glcm creates a grey-co matrix by calculating the frequency of a pixel with grey-level (greyscale intensity) value i occuring horizontally adjacent to a pixel with the value j. each element engineering, technology & applied science research vol. 10, no. 4, 2020, 5986-5991 5988 www.etasr.com saeed: a machine learning based approach for segmenting retinal nerve images using artificial … (i,j) in glcm specifies the number of times that the pixel with value i occurs horizontally adjacent to a pixel with value j. the correlation features obtained are shown in table i. in this method, color and texture features are considered as the input to train the bpnn. (a) (b) (c) (d) fig. 2. (a) original, (b) equalized, (c) grey scale, and (d) pre-processed retinal images. d. correlation correlation is a measure of how a particular pixel correlates to its neighboring the pixels. the correlation cr of an image can be calculated by the following equation. ∑ ���������������,�� � �,� (1) table i. correlation feature values for different retinal images 21.4424 24.5872 22.6780 13.6716 22.2245 24.4419 21.4232 21.9096 21.1245 22.7387 22.3906 21.0447 21.5332 24.3650 24.6506 24.4419 21.4232 21.9096 21.1245 23.2861 23.3021 23.9773 22.9697 25.1126 21.8625 e. color feature extraction rgb color format is a widely used format for processing digital images. its main drawback is that it is not perceptually uniform for all images. fig. 3. color formation process. the hue, saturation, value (hsv) representation of rgb color space is compatible with the human perception of color. in this method, in order to obtain the color features, histograms of a square window centering around each pixel on an equidistant grid in each plane of the image were calculated using both lab and hsv color spaces. a 5×5 window size, used for extracting the mean histograms, was obtained for two image spaces. the process of color formation is shown in figure 3. f. constructing feature vectors: color texture using neighborhood statistics gabor filters are often used for extracting texture features in order to segment images. but gabor filters have a major setback as they induce a lot of redundancy generating enormous amounts of feature channels. this method proposed a new color and texture feature extraction using the higher order image statistics, defining the texture regularity of the total image with in its neighborhood structures more effectively. an unsupervised learning process was used for recovering image statistics as in [9]. the whole image is considered as a random field x with a set of lattice points s, where {ss}∈s is the total set of pixels present in the entire image. for extracting this feature, an unsupervised adaptive filter is also used. this improves the probability of the pixel intensities by decreasing their joint entropy hy (x|y=y), of the conditional probability for each and every neighborhood pair of pixels, (x = x,y = y). this can be done by changing the entire value of each pixel x present in the center. in each iteration for the entire image region ζ m , the following equation is computed: ∂h�x|y � ���/∂�� (2) an image i m+1 is constructed using the finite forward differences method on the gradient descent, with intensities: ���� � �� �� � ���/��� (3) with λ being the time step. pixel updating process is stopped after few iterations when ||���� ���|| 2< δ, a small threshold. the process of magenta color formation is executed on the entire image for extracting the color texture features [9]. the color formation process is shown in figure 3. g. constructing feature vectors the mean weighted histogram process performed the feature vector construction. since color and texture in a colortextured image play complementary roles in image segmentation, this combination enhanced the final segmentation result more accurately. if there are c channels present in n feature histograms, the weighted mean histogram which is computed as channel wise, !� can be computed as: !� � ∑ "� # �$� ��� (4) where wi is the weight which is allocated to each histogram. the mean of histogram is calculated through channel wise weighted mean histograms, h= { !� }(j=1…c). when all color texture features are extracted, it has to inherent similarity, i.e. wi=1⁄n. the features which are obtained from the feature vector construction process using the color texture using neighborhood statistics process are given as input to the bpnn. the color texture feature was used in this method since these engineering, technology & applied science research vol. 10, no. 4, 2020, 5986-5991 5989 www.etasr.com saeed: a machine learning based approach for segmenting retinal nerve images using artificial … features represent the color texture of an image more accurately. iii. color texture based bpnn the color and texture feature based back propagation neural network (ctbpnn) was trained with pixel values as shown in figure 4. the nn has an input layer, a hidden type layer hin(j) and an output layer. the initial seed point is assumed as xi and the final seed point is assumed as x2. the pixel values as color texture features are given as input to the input layer. the framework of the ctbpnn is as follows. the hidden layer input hij(j)was defined as: �# # �%� � ∑ &�� #�� # ' (� #) �$� (5) where xi is the input feature, ωij is the weight between the neurons from the input and the hidden layer, and aj represents the threshold. the estimates of ctbpnn are: 2 1 1 ˆ argmin p p j j j j j y x β β λβ β = = = − +∑ ∑ (6) where, λ is a non-negative regularization parameter, x is the blood vessel width and blood vessel tortuosity of retinal images, y is the average accuracy and βs is the regression coefficient. the neuron number for the hidden layer is: � * + �1 (7) � * -�� ' +� '( (8) where n, h, and m are the total number of neurons belonging to the input, the hidden, and the output layer respectively, and α is a threshold between 0 and 20. in this work, n was assumed as 80, m was set to 3, and h ranges from 20 to 32. correlation features were separately calculated for each training and testing phase. the results obtained from various other segmentation methods were compared with the proposed. correlation features are separately calculated for each training and testing phases. the results obtained from other segmentation methods are compared with the proposed. fig. 4. proposed ctbpnn architecture. iv. results and discussion in this research, different retinal images taken two distinct databases were used. metrics such as sensitivity, specificity, and accuracy were considered for the accuracy estimation process. sensitivity represents the probability that the segmentation method will correctly identify vessel pixels. specificity is the probability the segmentation method will correctly identify non-vessel pixels. accuracy represents the overall performance of a segmentation method. they can be computed using the following equations: sensitivity � 6� 6��78 (9) specificity � 68 68�7� (10) accuracy � 6��68 6��78�68�7� (11) where true positive (tp) denotes vessel pixels correctly segmented as vessel pixels, and true negative (tn) denotes non-vessel pixels correctly segmented as non-vessel pixels. false positive (fp) denotes non-vessel pixels segmented as vessel pixels, while false negative (fn) denotes vessel pixels segmented as non-vessel pixels. segmented results along with original images, pre-processed, border detected, color formation, ground truth and segmented results of the retinal nerve images are shown in figure 5. the segmented images are very close to the ground truth images. in this approach, images specified by ophthalmologists and doctors are considered as ground truth for the calculation of segmentation accuracy. original equalized preprocessed color formation segmented result 1 2 3 4 5 fig. 5. segmented retinal vessels. table ii depicts the performance comparison of the proposed with the most recent segmentation methods for stare and drive datasets. methods are compared using sensitivity, specificity and accuracy. the proposed method obtained sensitivity, specificity and accuracy of 0.470%, 0.914%, and 0.903% respectively, for different retinal images indicating that it can achieve better segmentation results for engineering, technology & applied science research vol. 10, no. 4, 2020, 5986-5991 5990 www.etasr.com saeed: a machine learning based approach for segmenting retinal nerve images using artificial … segmenting retinal nerves. in general, lower sensitivity and specificity improves the performance of the segmentation algorithm [1]. since the sensitivity and specificity of the proposed method are lesser than the previous methods, the slighter lower accuracy is not affecting its actual accuracy. the accuracy is slightly lesser than the previous methods since the magenta color formation is done. moreover, the proposed method gives lesser sensitivity and specificity for both the datasets. the comparison between different retinal nerve segmentation methods is shown in table iii. the proposed method needed 24s in average to segment the retinal nerve, making it comparable to most known methods from the literature. table ii. comparison between different retinal vessel segmentation method using drive and stare datasets method drive dataset stare dataset sensi tivity speci ficity accu racy sensitiv ity speci ficity accu racy radial projection and semisupervised method [25] 0.741 0.975 0.943 0.726 0.975 0.949 gray-level and moment invariantsbased features [9] 0.706 0.980 0.945 0.694 0.981 0.952 combination of detecting the centerlines and morphological reconstruction [28] 0.734 0.976 0.945 0.699 0.973 0.944 trainable cosfire filters [22] 0.766 0.970 0.944 0.763 0.966 0.951 bit planes and centerline detection[10] 0.715 0.976 0.943 0.722 0.971 0.946 gray-voting and gaussian mixture model [29] 0.736 0.972 0.942 0.777 0.955 0.936 self-adaptive matched filter [30] 0.528 0.959 0.929 0.514 0.939 0.916 proposed 0.470 0.914 0.903 0.447 0.919 0.911 table iii. comparison between the runtime of different retinal vessel segmentation methods method time to process one image (s) platform morphological hessian based approach [31] 150 matlab wavelets and edge location refinement [20] 220 matlab trainable cosfire filters [22] 118 matlab gray-voting and gaussian mixture model [29] 106 matlab line tracking method [32] 93 matlab graph cut approach with retinex and local phase [33] 46 matlab and c++ self-adaptive matched filter [30] 30 matlab proposed 24 matlab v. conclusion and future work this paper proposed a novel method for segmenting nerves of retinal images using the combination of color and texture features with bpnn. various mages taken from two databases were used for the process of training and testing the nn. this approach improved the segmentation accuracy of nerves in retinal images, by segmenting the exact nerve region present in it. color and texture features were computed and the obtained seed points were given as input for training and testing the proposed method. comparing the proposed with various retinal nerves segmentation methods in the literature, the proposed performed well for processing the fundus image in its vessel segmentation with sensitivity, specificity and accuracy of 0.470%, 0.914%, and 0.903% respectively for the drive dataset and 0.447%, 0.919%, and 0.911% respectively for the stare dataset. this method could segment the nerve region better than other methods in less time. future enhancements can be the proposal of a novel method for detecting the glaucoma or other abnormalities present in retinal images. 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[33] y. zhao, y. liu, x. wu, s. p. harding, and y. zheng, “retinal vessel segmentation: an efficient graph cut approach with retinex and local phase,” plos one, vol. 10, no. 4, 2015, doi: 10.1371/journal.pone.0122332, art no. e0122332 microsoft word 06-3090_s_etasr_v9_n6_pp4893-4900 engineering, technology & applied science research vol. 9, no. 6, 2019, 4893-4900 4893 www.etasr.com akpeke et al.: contribution of facts devices to the transient stability improvement of a power … contribution of facts devices to the transient stability improvement of a power system integrated with a pmsg-based wind turbine nice enyonam akpeke department of electrical engineering pau institute for basic sciences technology and innovation, nairobi, kenya niceenyonam@gmail.com cristopher maina muriithi department of electrical engineering murang’a university of technology murang’a, kenya cmainamuriithi@gmail.com charles mwaniki school of engineering and technology machakos university machakos, kenya cmwaniki@mksu.ac.ke abstract—the increasing penetration of wind energy to the conventional power system due to the rapid growth of energy demand has led to the consideration of different wind turbine generator technologies. in fault conditions, the frequency of the power system decreases and eventually leads to speed differences between the grid and the interconnected wind generator. this can result to power system problems such as transient instability (ts). this paper focuses on enhancing the ts of a permanent magnet synchronous generator (pmsg)-based power system during 3ph fault conditions using facts devices. the power system considered is connected to a large wind farm which is based on pmsg. critical clearing time (cct) is used as an index to evaluate the transient state of the system. under the study of an ieee-14 bus system using psat as a simulation tool, the integrated cct with pmsg-based wind turbine is improved with three independent facts devices. one of the synchronous generators in the test system has been replaced at random with the pmsg-based wind turbine which is meant to generate an equivalent power. time domain simulations (tdss) were carried out considering four study cases. simulation results show that the (cct) of the system with the facts devices is longer than the cct without them, which is an indication of ts improvement. keywords-critical clearing time; facts; generator; transient statbility; wind i. introduction among renewable power sources, wind has been noted to be the fastest growing one due to its clear and numerous advantages [1]. transient stability (ts) which is the tendency of synchronous generators remaining in synchronism following a severe disturbance [1-4], is one of the major aspects of a power system that gets affected with the integration of large wind turbines. globally, squirrel cage induction generator (scig), doubly fed induction generator (dfig), and permanent magnet synchronous generator (pmsg) are common wind generator technologies considered in wind energy conversion. unlike dfig, the pmsg has a full-scale power converter [5]. it enables more reliable operation of wind turbines and reduces the required maintenance [6]. these features make pmsg more advantageous than dfig. currently, most wind energy conversion technologies employ turbines with pmsg [7, 8]. even though the pmsg has a better reactive power capability, it is still not adequate as the principal precaution during transient conditions [9-10]. there is therefore a need to augment the dynamic reactive power capability of facts devices in order to strengthen the transient state of the system to which it is connected. ts is considered one of power system’s dynamic behaviors having been analyzed and improved by various approaches. however, since ts study can only be considered in the presence of a severe fault [4], there is need to mention the clearing time of faults which will keep the system transiently stable. for a particular given system, the critical clearing time (cct) must be specified or stated to allow easy system operation during faults. in addition, ts study time is short and so faults need to be cleared as quickly as possible to prevent synchronism loss of the system generators, knowing the cct can allow fault clearing within the time limit thereby maintaining the stability of the system. an impact study for pmsg-based wind generation on the ts was carried out in [7]. the study considered a method of equal area criteria theory. an active current control strategy taking into account a perturbation estimation was proposed in [11] for enhancing the ts of a power system connected with a pmsg-based turbine. a simulation study was conducted in [12] by using a tssc to improve the efficiency of a wind turbine. authors in [8] compared the ts augmentation between doubly fed induction generators and permanent magnet synchronous generators. it was deduced that the ts of the system with dfig wind generator can be improved by including a permanent magnet synchronous generator in the same system. authors in [13] investigated the effects of series compensation on the ts improvement for a dfig wind turbine power system. in [14], a study of the assessment of wind energy based on scig penetration effect on ts was provided. different penetration levels were considered and cct was analyzed. the current paper focuses on the ts analysis with consideration of critical clearing time index. thus, conclusions on the improvement of the ts of the system are based on the ccts of all the cases considered. corresponding author: nice enyonam akpeke engineering, technology & applied science research vol. 9, no. 6, 2019, 4893-4900 4894 www.etasr.com akpeke et al.: contribution of facts devices to the transient stability improvement of a power … ii. implementation of the system in psat this paper employed the ieee-14 bus system for the simulation process. power system analysis toolbox (psat) was used in implementing the considered system. psat is a matlab package which uses simulink libraries for network designs. it is appropriate for analysis of small and medium size power systems [15]. psat also supports both dynamic and static power system analysis and control studies. aside time domain simulations, psat also includes optimal power flow, continuation power flow and small signal analysis. the data used in implementing the system in psat are taken from [16] with 20s simulation time. a. the ieee 14-bus system model the implementation of the proposed test system is executed using psat 2.1.10. synchronous generator models, wind turbine model, wind turbine generator model, constant loads, and facts devices are all inherent models adopted from matlab/simulink library. the test system consists of 5 generator buses and 8 load buses. out of the 5 generator buses, there is one slack (bus 1), one pv (bus 2) and 3 additional synchronous condensers (buses 3, 6, 8). table i shows a summary of the system characteristics. table i. modified ieee-14 bus, 5-machine test system equipment quantity buses 14 generators 5 transformers 4 transmission lines 16 loads 11 three different voltage levels were chosen for the whole system equipment with a power rating of 100mva. blue indicates a 13.8kv bus, green indicates an 18kv bus and red indicates a 69kv bus. bus 1 is defined to be the reference bus (where the wind turbine is integrated). the purpose of integrating the wind at the slack is to allow the wind turbine generate a greater percentage of the whole system capacity. b. modeling of the pmsg-based turbine the pmsg, also referred to as direct drive synchronous generator (ddsg), is a type of synchronous generator whose rotor windings are replaced with a permanent magnet and hence the name permanent magnet synchronous generator (pmsg). its excitation field is created by the permanent magnet in the rotor [10]. this arrangement has led to the elimination of excitation losses that will take place in the rotor during starting of the generator. fig. 1. block diagram of the variable speed connected grid wind energy system based on pmsg consequently, the pmsg has better performance and higher efficiency as compared to other wind turbine generators since the rotor losses contribute to about 20-30% of total generator losses [17]. even though the pmsg is a synchronous machine, its contribution to the grid inertia is little compared to that of the conventional synchronous generators. this is due to the power electronic based converters through which it is interfaced with the grid as shown in figure 1 [9]. the purpose of the power electronics based back-back converter equipment is to control the generator rotor angle and convert the electrical power available at the shaft of the generator into high quality power to be integrated to the power grid. the total power generated by the wind turbine is represented in (1) with � defined in (2) [18]: � � � � ��� ��� (1) � � ��� �� (2) where p is the active power generated by the turbine, � is the air density, � is the swept area of the turbine blades, � is the power coefficient, � is the tip speed ratio, v is the wind speed, and n is the generator rotor speed. since there is no gearbox in the pmsg, the aerodynamic torque (n/m) is equal to the mechanical torque [19] transferred to the generating unit as represented in (3): �� � � � (3) the modified ieee 14-bus system with the integration of the pmsg module is shown in figure 3. the generator is connected to the entire grid via a fully-scaled back to back voltage source power converter (ac/dc/ac). equations (4) and (5) are the state equations, (6) is the electrical equation, and (7) is the mechanical equation of the pmsg. ��� �� � � ����� �� !� " #$. &'( " ')*. !( " +�� (4) ��, �� � � �,��� �� !( � #$'� " ')�!� " ./0 " +(� (5) #$ � 1#2 (6) 3$ � 1.51 '� � ')�!�!( " !(./� (7) where d and q subscripts represent the physical quantities transformed to the d-q reference frame. � is the stator resistance (ω), '� and '( are d and q-axis inductances (h), '� is the leakage inductance, ./ is the permanent magnetic flux (weber), +� and +(are d and q-axis voltages, #$is the electromagnetic speed of the generator (rad/s) and p is the number of pole pairs. figures 2 and 4 illustrate respectively the d and qaxis equivalent circuits of the pmsg. fig. 2. d-axis equivalent circuit engineering, technology & applied science research vol. 9, no. 6, 2019, 4893-4900 4895 www.etasr.com akpeke et al.: contribution of facts devices to the transient stability improvement of a power … fig. 3. modified ieee-14 bus test system integrated with pmsg-based wind turbine at bus 1 fig. 4. q-axis equivalent circuit c. modeling of the facts devices three facts devices were employed one from each of the three generations of facts [20]. generally, facts devices have a unique feature of rapidly controlling the system by their reactive power management [18, 21]. this characteristic was exploited for the system’s ts improvement. just like the wind generator, the simulation models of the thyristor controlled series capacitor (tcsc), unified power flow controller (upfc) and the static synchronous compensator (statcom) were utilized. tcsc is an important facts device which is connected in series in the power system [3]. the total reactance of the tcsc (represented by 67898) is given in (8) with :$ and ; representing the electrical angular frequency and the firing angle of the thyristor. the tcsc basically improves the power system’s ts by adjusting the transmission line impedance: 67898 � � <=>8>� ?@a?bcdef ?b� h>i@ (8) the makeup of a upfc combines characteristics of static synchronous compensator together with static series compensator. it simultaneously acts as a shunt and phase shifting device [22]. statcom is a voltage source based converter and a shunt connected device. it controls the bus voltage at the place where it is connected [18, 23, 24]. voltage stability index tool was used to analyze the weakness of the buses in the ieee-14 bus test system for proper placement of the facts devices. the use of voltage stability index creates awareness of the closeness of a power system to voltage collapse or voltage instability [25-26]. using figure 5 as an example of the power system’s line model (e.g. from bus a to bus b), the fast voltage stability index (fvsi) of any line in the ieee-14 bus test system is calculated using (9): j+klmn � op?qr st ?u (9) fig. 5. power system line model engineering, technology & applied science research vol. 9, no. 6, 2019, 4893-4900 4896 www.etasr.com akpeke et al.: contribution of facts devices to the transient stability improvement of a power … in (9), z and x are the line impedance and reactance, +m and vn are the sending end voltage and receiving end reactive power respectively. the closest line to 1 is considered the weakest of all the lines in the system. from the fvsi calculation, line 3 which is found between bus 2 and 3 was identified as the weakest and hence appropriate for integration of facts devices. figure 6 illustrates a plot of the fvsi of all the 20 transmission lines in the system with line 3 indicating the highest value of fvsi aside line 9 (transformer). this means that, more reactive power will be injected through line 3 in each case in order to boost the voltage level and hence improve the ts of the whole system. the modified ieee-14 bus test system with the integrated pmsg-based wind turbine (at bus 1) and tcsc (between bus 2 and 3) is shown in figure 7. fig. 6. a bar chat of the fast voltage stability index of the various lines fig. 7. modified ieee-14 bus test system integrated with pmsg-based wine turbine and tcsc iii. simulation results and discussion simulations were carried out for four different cases during a three phase to ground fault created in bus 2, in order to compare the transient response of all the systems. the four different cases were: • power system integrated with pmsg-based wind turbine • power system integrated with wind turbine and tcsc • power system integrated with wind turbine and upfc • power system integrated with wind turbine and statcom the fault was created in bus 2 and was set to clear automatically by the system after some time. the fault clearing time varied until the system lost synchronism. the time immediately after the system lost its synchronism was noted and stated as the critical clearing time in each of the above systems. all the synchronous generators in the system were monitored and the critical clearing time in each case was noted with emphasis laid on the generator that was closer to the position of the three phase fault. engineering, technology & applied science research vol. 9, no. 6, 2019, 4893-4900 4897 www.etasr.com akpeke et al.: contribution of facts devices to the transient stability improvement of a power … a. case 1: power system integrated with pmsg-based wind turbine only figures 8-11 illustrate the time domain response of the speed and angle for the synchronous generator 1 (g1) when the fault clearing time is at 2.319s and 2.320s. fig. 8. rotor speed of g1 at 2.319s fault clearing time fig. 9. rotor speed of g1 at 2.320s fault clearing time fig. 10. rotor angle of g1 at 2.319s fault clearing time from the swings of both rotor angle and speed deviation, it is discovered that the g1 remains stable when the fault is cleared at or before 0.319s (figures 8, 10) following the occurrence of the fault. on the other hand, delaying the fault by 0.320s after its occurrence causes the system to lose synchronism (figures 9, 11). thus, the speed of the synchronous generator deviates and continues to increase without returning to its original value. in this system, the maximum clearing time for which the synchronous generator remains in synchronism is 2.319s. beyond this time, the system is unstable. therefore the cct of the system integrated with only pmsg-based wind turbine without any facts device is 0.319s after the fault. fig. 11. rotor angle of g1 at 2.320s fault clearing time b. case 2: system integrated with wind turbine and tcsc figures 12 and 14 describe the time domain simulation (tds) results of both rotor speed and angle for the g1 when the fault is cleared at 2.540s whereas figures 13 and 15 show rotor speed and angle with clearing time of 2.541s. the simulation results of this system show that g1 remains stable with fault clearing time at 2.540s. fig. 12. rotor speed of g1 at 2.540s fault clearing time fig. 13. rotor speed of g1 at 2.541s fault clearing time fig. 14. rotor angle of g1 at 2.540s fault clearing time engineering, technology & applied science research vol. 9, no. 6, 2019, 4893-4900 4898 www.etasr.com akpeke et al.: contribution of facts devices to the transient stability improvement of a power … however, delaying fault clearing time to 2.541s makes the system unstable. in other words, clearing the fault at 2.541s instead of 2.540 makes g1 lose synchronism with respect to other synchronous generators in the system. in this case, the cct of the system is 0.540s following the fault. fig. 15. rotor angle of g1 at 2.541s fault clearing time c. case 3: system integrated wind turbine and upfc figures 16 to 19 show the simulation results for both rotor angles and speed deviations when the fault is cleared at 2.435s and 2.436s. the results show that, clearing the fault before or at 2.435s makes g1 not to lose synchronism (figures 16, 18) but delaying the fault clearing time to 2.436s causes g1 to lose synchronism (figure 17, 19). this indicates that the cct of this system is 0.435s following the occurrence of the three phase fault. fig. 16. rotor speed of g1 at 2.435s fault clearing time fig. 17. rotor speed of g1 at 2.436s fault clearing time d. case 4: system integrated with wind turbine and statcom figures 20-23 illustrate the time domain response of the speed and angle of g1 when the fault clearing time is 2.416s and 2.417s. fig. 18. rotor angle of g1 at 2.435s fault clearing time fig. 19. rotor angle of g1 at 2.436s fault clearing time fig. 20. rotor speed of g1 at 2.416s fault clearing time fig. 21. rotor speed of g1 at 2.417s fault clearing time at fault clearing time of 2.416s, g1 regains synchronism just as shown in figures 23 and 25 for rotor speed and angle respectively. with fault clearing time delayed to 2.417s the g1 does not regain synchronism, making the system unstable as shown in figures 24 and 26 for speed deviation and rotor angle respectively. therefore, in this system, clearing the fault at 0.417s instead of 0.416s after the occurrence makes the system totally unstable. hence, the cct is 0.416s. engineering, technology & applied science research vol. 9, no. 6, 2019, 4893-4900 4899 www.etasr.com akpeke et al.: contribution of facts devices to the transient stability improvement of a power … fig. 22. rotor angle of g1 at 2.416s fault clearing time fig. 23. rotor angle of g1 at 2.417s fault clearing time iv. cct evaluation and improvement it was concluded from the simulation results that cct differs from one system to another for all facts devices. a summary of the cct for each case is provided in table ii. the three phase fault was created at bus 2 and at 2s. table ii. system cct summary cases fct (stable) fct (unstable) cct case1 (pmsg only) 2.320s 2.319s 0.319s case2 (pmsg and tcsc) 2.540s 2.541s 0.540s case3 (pmsg and upfc) 2.4435s 2.436s 0.435s case4 (pmsg and statcom) 2.416s 2.417s 0.416s it can be noted that the system with pmsg and tcsc has the longest cct. in order to visualize clearly the individual contributions of the facts devices to the ts improvement in terms of cct, the cct of the pmsg-based system is subtracted from the cct of the systems connected with each of the facts devices as shown in (10): ��� !w1xy�zwz[\�m � ���� � ����]9^ (10) where subscript a represents tcsc, upfc or statcom. subscript n represents the individual cases (cases 2, 3 and 4). this means that, the cct of the system with the wind turbine only (case 1) which is 0.319s was subtracted from 0.540s, 0.435ss and 0.416s for systems with tcsc, upfc and statcom respectively. the results are summarized in table iii in descending order of improvement. these results indicate that tcsc has the longest cct among the three facts devices. therefore, tcsc improves a system integrated with wind turbine better than upfc and statcom. it is also observed that statcom has the shortest cct, so is the weakest facts device regarding the ts improvement of the power system. this is in agreement with the findings in [15] for a larger power system. table iii. facts devices contribution the cct improvement facts devices cct cct(improvement) tcsc 0.540s 0.221s upfc 0.435s 0.116s statcom 0.416s 0.097s v. conclusion this paper aimed at studying the transient stability improvement of a power system connected to a large scale wind turbine using facts devices based on the critical clearing time index. three facts devices were considered and each of them was connected individually to investigate their respective contributions to the cct improvement. in each case, the cct was stated and the improvement time was identified. this study showed that all the three facts devices have different critical clearing times. thus, they improve the system ts to different extents. it was also discovered that the best facts device for ts improvement is tcsc while statcom is the weakest facts device for transient stability improvement. acknowledgment the authors of this paper wish to thank the pan african university institute for basic sciences, technology and innovation (pauisti) for the financial support towards the completion of this work. references [1] m. k. nigam, s. singh, c. francis, “effects on power system stability due to integration of distributed generation”, journal of science and engineering education, vol. 2, pp. 56–60, 2017 [2] n. w. miller, m. shao, s. pajic, r. d. aquila, western wind and solar integration study phase 3: frequency response and transient stability, national renewable energy laboratory, 2014 [3] a. d. patel, “a review on facts devices for the improvement of transient stability”, global journal of engineering science and resources, vol. 2, no. 12, pp. 85–89, 2015. 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procedia engineering, vol. 90, pp. 698–703, 2014 [9] m. n. i. sarkar, l. g. meegahapola, m. datta, “reactive power management in renewable rich power grids: a review of grid-codes, renewable generators, support devices, control strategies and optimization algorithms”, ieee access, vol. 6, pp. 41458–41489, 2018 engineering, technology & applied science research vol. 9, no. 6, 2019, 4893-4900 4900 www.etasr.com akpeke et al.: contribution of facts devices to the transient stability improvement of a power … [10] r. k. tiwari, k. k. sharma, “simulation and modeling of wind turbine using pmsg”, international journal of recent research and review, vol. 7, no. 2, pp. 46–50, 2014 [11] p. shen, l. guan, z. huang, l. wu, z. jiang, “active-current control of large-scale wind turbines for power system transient stability improvement”, energies, vol. 11, article id 1995, 2018 [12] d. kalpaktsoglou, s. pouros, k. kleidis, “improving the efficiency of a wind turbine using thyristor switched series 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electronics, seoul, south korea, july 5-8, 2009 [18] r. jadeja, s. patel, s. chauhan, “statcom: a preface to power quality in power systems performance”, engineering, technology & applied science research, vol. 6, no. 1, pp. 895–905, 2016 [19] m. a. husain, a. tariq, “modeling and study of a standalone pmsg wind generation system using matlab/simulink”, universal journal of electrical and electronic engineering, vol. 2, no. 7, pp. 270– 277, 2014 [20] b. t. r. rao, p. chanti, n. lavanya, s. c. sekhar, y. m. kumar, “power system stability enhancement using fact devices”, international journal of engineering research and applications, vol. 4, no. 4, pp. 339–344, 2014 [21] m. y. a. khan, u. khalil, h. khan, a. uddin, s. ahmed, “power flow control by unified power flow controller”, engineering, technology & applied science research, vol. 9, no. 2, pp. 3900–3904, 2019 [22] r. chavan, r. s. lodhi, “selection of facts devices for better reactive power compensation through capacitor”, international journal of engineering and techniques, vol. 2, no. 5, pp. 28–35, 2016 [23] a. s. yome, n. mithulananthan, k. y. lee, “static voltage stability margin enhancement using statcom, tcsc and sssc”, ieee/pes transmission & distribution conference & exposition: asia and pacific, dalian, china, august 18, 2005 [24] k. g. damor, d. m. patel, v. agrawal, h. g. patel, “comparison of different fact devices”, international journal of science technology & engineering, vol. 1, no. 1, pp. 12-17, 2014 [25] a. s. telang, p. p. bedekar, “application of voltage stability indices for proper placement of statcom under load increase scenario”, international journal of energy and power engineering, vol. 10, no. 7, pp. 998–1003, 2016 [26] i. a. samuel, a new voltage stability index for predicting voltage collapse in electrial power system networks, covenant university, 2017 microsoft word 28-3554_d_etasr_v10_n3_pp5742-5747 engineering, technology & applied science research vol. 10, no. 3, 2020, 5742-5747 5742 www.etasr.com danikas et al.: a short review of some of the factors affecting the breakdown strength of insulating oil… a short review of some of the factors affecting the breakdown strength of insulating oil for power transformers michael g. danikas democritus university of thrace, dpt department of electrical and computer engineering, power systems laboratory, xanthi, greece mdanikas@ee.duth.gr ramanujam sarathi indian institute of technology madras, department of electrical engineering, high voltage laboratory, chennai, india rsarathi@iitm.ac.in sayidul morsalin university of new south wales, school of electrical engineering and telecommunications, high voltage laboratory, sydney, australia sayidul.morsalin@unsw.edu.au abstract-the present short review investigates some of the factors affecting the breakdown strength of transformer oil. factors such as the conditioning effect, effect of oil flow, influence of impurities, type of applied voltage and electrode configuration and geometry are further discussed. it should be noted that this review does not discuss the effect of factors such as area, volume and capacitance. velocity, impurities, electrodes’ shape and the type of applied voltage are among the factors documented to have a significant effect on breakdown strength. keywords-transformer oil; breakdown strength; velocity; flow; electrodes; geometry; configuration i. introduction liquid dielectrics are used as insulating media in high voltage systems as they can easily fill any space and can also be circulated to dissipate heat. their main disadvantage is that they get contaminated over time/use. oil, of certain type, is one of the most frequently used liquids for electrical insulation, frequently referred to as transformer oil due to its wide use within transformers. previous research was concerned with attempts to understand the physics of breakdown in transformer oil [1, 2] as well as with efforts to elucidate the various factors affecting its breakdown strength [3]. the breakdown strength of transformer oil in a lab, depends on a variety of factors either due to the test conditions or to the oil itself. thus, the breakdown strength of the oil is something which cannot be defined simply by its arithmetic value. test conditions have to be fully and accurately described. since most practical insulating liquids depart from the ideal liquid state, it is convenient to call “weak links” all the departures from the ideal state. the breakdown mechanism is assumed to be initiated by a ‘weak link’, i.e. all sorts of irregularities existing either on the electrode surfaces or in the liquid itself. an increase to the number of “weak links’ results to an increase of the probability for breakdown at a given stress. an increase in the size of specimen implies therefore a reduction in breakdown strength. this is the so-called size effect [4]. transformer oil is used as insulating medium for many decades. early work in the field of breakdown of liquid dielectrics was done many decades ago [5]. a comprehensive review on breakdown of insulating liquids was also published [6]. it is generally agreed that electrical breakdown in liquids is statistical in nature and the breakdown strength depends on additives, pressure, field geometry, size of the whole system, electrode material and finish, impurities, voltage waveform, past history, time and magnitude of pre-stress. it is the purpose of the present short review to give some aspects of the research performed over the past years regarding some of the factors affecting the breakdown strength of transformer oil. ii. the conditioning effect the conditioning process is the process according to which a change in strength is obtained with successive breakdowns. quite early a gradual increase in the breakdown strength with increasing number of measurements was observed. a lack of conditioning effect in n-hexane was probably due to the fact that particles larger than 10 µm were removed by filtration [7]. other researchers showed that the conditioning process varied for different electrode metals and it also depended on the treatment of the electrode surface. it was pointed out that the conditioning phenomenon was due to the gradual degassing of the electrodes which accompanies the successive discharges [8]. also, that the conditioning effect was less marked for pure than for impure liquids, agreeing in that with [7]. other researchers also agreed with [7], attributing the conditioning effect to the removal of moisture and the destruction of fibers by successive breakdowns [9]. experiments with impulse voltages showed an upward trend, then a plateau value of the conditioned state and finally a downward trend in breakdown strength [10]. commenting on these findings, some years later it was remarked that the full conditioning effect may be masked by a reduction in strength associated with electrode damage [11]. the conditioning effect is not absent even with the transformer oil circulating between breakdowns. such experimental data tends to reject theories of fiber or moisture removal [12]. a downward trend of the breakdown strength of an oil sample rested in the middle of a series of conditioning breakdowns was also observed [10], whereas other researchers corresponding author: michael g. danikas engineering, technology & applied science research vol. 10, no. 3, 2020, 5742-5747 5743 www.etasr.com danikas et al.: a short review of some of the factors affecting the breakdown strength of insulating oil… observed an upward trend under similar conditions [13]. the observed downward trend was explained by some researchers, who suggested that the conditioning effect is mainly governed by a dielectric layer on the cathode which plays a part in the breakdown process by acting as a barrier to positive ions which were formed in the gap by electron bombardment of molecules. the positive ions, prevented from reaching the cathode itself, enhance the electric field at the cathode, increasing thus the field emission of electrons [14]. the above process was contested in [11], where it was pointed out that such process can only take place with clean and highly polished electrodes. in [1], another explanation was given for the downward condition, namely that this occurs when a relatively large energy is dissipated at breakdown leading to the melting of a greater quantity of electrode metal and the contamination of the liquid by electrode material and decomposed liquid products, especially if these are not given time to clear from the gap. such an explanation – regarding the downward trend is in agreement with the explanation given in [15, 16]. in accordance with the above is also the model put forward in [17], where the upward or downward trend in conditioning is explained by the creation of an insulating layer on the electrodes (for upward conditioning) and its subsequent destruction (for downward trend) because of chemical transformations. a slight conditioning effect is also observed with mineral oil using standard foster test cell electrodes [18]. the authors, however, did not give any particular reason as to why this should be so. given that their electrodes were polished and clean, one can reasonably assume that possible removal of moisture may be the reason for the slight conditioning effect. such an interpretation may be supported particularly in view of recent research, which claims that the breakdown strength remains high when moisture saturation is below 20% but it decreases significantly as relative moisture saturation increases [19]. conditioning of the electrodes is not observed if the oil is replaced after each breakdown. on the other hand, if the oil is not replaced and the volume is small, previous breakdowns may reduce the breakdown strength because of contamination by products of its decomposition and by the electrode metal [20]. another factor which has to be taken into account is the settling time between consecutive breakdowns. in this respect, past research as well as more recent work indicate that conditioning is influenced by the settling time, i.e. the longer the time interval between breakdowns, the higher the probability for higher breakdown values [21, 22]. this is due to the fact that shorter settling times do not allow either the bubbles from the previous breakdown to dissolve or the decomposition products to settle under the influence of gravity. iii. the velocity effect since in contaminated liquids breakdown events are dominated by a variety of phenomena associated with the contamination, it is only logical to suppose that by trying to destroy possible foreign particle bridges between the electrodes, the breakdown strength will increase [1]. if oil is pumped through a gap between the electrodes, or the electrodes are rotated, the breaking of fiber chains, movement of gas accumulations and possibly the disturbance of electrochemical processes at the electrodes, will affect the breakdown strength [1]. although in [3] no significant change in breakdown strength was observed when circulating oil instead of stationary oil was used, other researchers found that the breakdown strength and the mean gap velocity were related almost linearly for ac testing voltages [11]. however, the latter researcher was cautious as to the effect of oil velocity as there was no information on the variation of oil density, its viscosity and its surface tension over the period of the experiment [11]. later on, it was noted that the oil flow caused the distributions of breakdown values to be normal instead of extreme, as it was the case with static oil. an enhancement of the breakdown strength was observed when flowing oil was used. it was also noted that normalization takes place gradually with the increase of velocity. it was also remarked that the oil velocity cannot be raised indefinitely because cavitation will eventually cause a reduction of the breakdown strength [23]. the increase of breakdown strength with flowing oil was explained either by the continuous removal of decomposition products from the test gap or by the prevention of particle bridges to be formed in the gap [11]. the flowing oil may also impede the entry of impurities into the test gap [24]. the reported change in breakdown strength with flowing oil is achieved at oil velocities up to 3 cm/s [25]. earlier work indicated that with even lower oil velocities (up to 0.5 cm/s) higher breakdown strength can be achieved [23]. an indefinite increase of breakdown strength is not envisioned since the increase of the oil velocity causes the flow to be turbulent. turbulent flow will cause the creation of bubbles in the volume of the liquid as a result of the difference in pressure. the approach of [23] and [25] seems to be in agreement with the view that the breakdown strength of the oil increases up to a certain velocity but as soon as this limit is passed, it falls [26]. in fact the limit of 3 cm/s discussed in [25] agrees well with the data presented in [26], where a limit of about 5 cm/s was observed for ac and dc voltages. the oil flow and its beneficial effects is intimately linked with the presence and eventual removal of foreign particles and impurities in the oil. under both ac and dc voltages a bridge between the electrodes is highly likely to occur and thus breakdown probability is increased [27]. talking about foreign particles in oil, it has been indicated that metallic particles tend to lower the breakdown strength more than non-metallic particles [25, 28]. iv. the effect of impurities impurities play a critical role in the breakdown of transformer oil [3, 6]. impurities can be classified as particles of dust or fibers which are present in the liquid, sometimes escaping the filtration process as being very small, particles produced by previous discharges, such as carbon particles resulting from the decomposition of the liquid or minute metallic particles removed from the electrode surface by high energy sparks, water, additives deliberately introduced into the liquid to change its properties. it has been reported that with voltages applied for a long period, particles or fibers in the bulk of the liquid are attracted to the region of highest stress, forming a bridge and consequently causing a breakdown [9]. under both ac and dc voltages the addition of even small amounts of water to treated oil causes a significant reduction in the breakdown strength. the reduction is even more engineering, technology & applied science research vol. 10, no. 3, 2020, 5742-5747 5744 www.etasr.com danikas et al.: a short review of some of the factors affecting the breakdown strength of insulating oil… pronounced when the oil contains already suspended matter [29]. agreeing with [29], it was indicated that the effect of moisture depends entirely on the nature and the amount of other impurities present in the bulk of the liquid [30]. moreover, above a certain stress level, 300 kv/cm according to [31], particle activity may stop because of either an ejection of impurities from the gap or an adhesion to the electrode surfaces. the influence of impurities also depends on the molecular structure of the liquid [32], as foreign particles can be attracted into the gap and form a bridge distorting the electric field between the electrodes [7]. an improvement in breakdown strength can be achieved by increasing the number of filtering cycles of the oil. it has been shown that, by using small size bruce profile electrodes, the mean breakdown strength can be increased by about 8% after 5 filtration cycles and by about 10% after 8 filtration cycles [25]. such an improvement is probably due to the fact that the distribution of particle sizes moves to smaller sizes as the number of filtration cycles increases. if after a certain number of filtering cycles no change in breakdown strength is observed, this means that extremely small particles pass through the filter in the actual oil volume, limiting thus its breakdown strength. metallic particles have a more dramatic effect on breakdown strength than non-metallic particles [25]. the dominant role of impurity particles is due to the possibility of bridge formation and the establishment of convenient nucleation sites for bubble formation [6, 24, 33-36]. moreover, the propagation rate of pre-breakdown disturbances increases with the contamination of the oil with the consequent effect of the reduction of the formative time lag, which eventually leads to a decrease of the breakdown strength [37]. carbon particles affect the breakdown strength as was reported in [25], where with small size bruce profile electrodes and small gaps (1–4 mm) a decrease of breakdown strength was observed up to 12%. more recently, research has shown that the influence of carbon particles on breakdown strength depends also on the type of applied voltage, i.e. with plane-plane electrodes and ac voltages the breakdown strength was higher than with dc voltages. this means that under ac voltages, bridges of particles are more difficult to be formed. on the other hand, a composite ac/dc voltage gives breakdown strength results between the ac voltage and the dc voltage [38]. it has also been indicated [39] that with dc voltages, point-plane electrodes and pure oil, the breakdown strength was higher with the point electrode negative, whereas with contaminated oil -and especially at higher applied voltagesthere was an inversion in experimental results, i.e. the positive point gave the higher breakdown strength. such an inversion was explained as due to space charges, which may be particularly noticed in contaminated oil [39]. different kinds of particles (metallic, cellulose and mixed) were investigated with dc voltages and uniform electrode arrangement in [40] and it was observed that mixed (i.e. metallic with cellulose) particles lower indeed the breakdown strength of transformer oil. in fact, mixed particle bridges were the densest between the electrodes. metallic particles do not form stable bridges since they tend to go to the bottom of the test cell. it is evident that the formation of bridges depends on voltage duration and the type of particles involved. the influence of moisture in combination with foreign particles was noted quite early [29], where it was remarked that the influence of moisture is very harmful when the oil contains particles of various sizes although, as commented in [41], the size of particles plays a more dominant role rather than the high concentration of particles itself. such observations were confirmed in [42]. furthermore, in [42] it was pointed out that 5 purification cycles are enough for the oil to be cleaned, something which is in rough agreement with data from [25]. as a general comment, it can be pointed out that foreign particles do indeed lower the breakdown strength of transformer oil, particularly if they are combined with moisture. inclusions of moisture more than about 10 ppm at normal temperature may be enough to cause a lowering of breakdown strength. on the other hand, high breakdown strength does not necessarily mean that there is an absence of foreign particles. it may well mean that the quantity of foreign particles is not large enough to influence the breakdown strength [43, 44]. v. the voltage duration effect many phenomena observed in measuring the breakdown strength of insulating liquids are time dependent [11, 23]. although the duration of impulse voltages is very short compared to ac voltages, there were reports confirming that the breakdown strength is independent of the duration of the voltage application for both dc and ac voltages [29]. breakdown in oil occurs at the tail of the impulse voltage [29]. according to [45], impulse testing furnishes some information about the breakdown mechanism, namely that the breakdown time-lag can be divided into two intervals, the statistical time lag and the formative time lag, pointing out that the latter depends on the nature of the breakdown process and the test conditions. for pure organic liquids the breakdown strength is independent of the pulse duration above a certain time-lag [14, 46]. they explained that by assuming that the formative timelag is associated -at least partly– with the time required for some charge species to cross the gap between the electrodes. in [46], a streamer-like mechanism was suggested, composed by two parts, firstly the time required for a single electron avalanche to produce sufficient field distortion near the anode to favor the growth of the streamer, and secondly the time required for the streamer to cross the gap. it has also been suggested that the breakdown strength is determined by the liquid properties for long pulses and by the emission characteristics of the cathode for short pulses [47]. agreeing with [46], the authors of [47] suggested that breakdown is initiated by an extra-large localized burst of electrons from the cathode. these bursts are likely to occur at certain active sites where emission momentarily becomes easy, possibly because of irregularities or inclusions or surface deposits. in analyzing the breakdown process under both constant stress and ramp stress conditions, [48] concluded that statistical procedures allow the formative time lag to be separated from the total breakdown time. slow ramps cause the smallest breakdown values. furthermore, [48] indicated that even the slightest alterations in experimental conditions may cause considerable changes in breakdown strength. in yet another publication [49], the same authors showed that for unit step engineering, technology & applied science research vol. 10, no. 3, 2020, 5742-5747 5745 www.etasr.com danikas et al.: a short review of some of the factors affecting the breakdown strength of insulating oil… waveforms, the mean statistical time lag for breakdown in nhexane is inversely proportional to electrode area for uniform field geometry but independent of the gap spacing. they remarked, agreeing with [47], that there is strong evidence for the location of the initiating event on the electrode surface. voltage duration affects the particle movement in transformer oil and consequently its breakdown strength as was reported in [50]. dc voltage is more prone to create bridges of iron particles than ac voltage, the reason being that with ac voltage iron particles are under the influence of alternative electric forces, which render the lining up more difficult. with pulsating dc voltage the situation is between the two aforementioned cases. what is reported in [50] is in line with the findings of [38]. the results reported in [38] and [50] generally agree with those of [51], where it was shown that with dc or pulses longer than 50 ms foreign particles can form a bridge that may initiate a breakdown. in [51], it is cautiously suggested that for pulsed conditions at frequencies of up to 100 hz, one can afford to decrease the insulation thickness by 10% to 20% relative to those required at dc voltage. further evidence in validation of [38, 50, 51] was offered in [52], where a distinct difference between dc and ac voltages regarding the movement of foreign particles in transformer oil was described. according to [51], bridging of foreign particles under dc voltage is encouraged by dielectrophoretic (dep) forces and as the voltage increases the velocity of particles also increases with the rate of bridge formation intensified. the associated conduction current increases and the bridges become wider but not denser. the effect of impurities with short duration pulses (~1µs), however, is rather small [53]. generally speaking, it can be said that voltage duration has indeed an effect on the breakdown strength of transformer oil. it is certainly to be noted that fast pulses cause higher breakdown strength than longer pulses or even dc voltages. the effect of voltage duration also depends, on the other hand, also on the quality of the transformer oil tested [1, 54]. more contaminated oils are prone to be more sensitive to the type of the applied voltage. vi. the effect of geometrical configuration of the electrodes the geometrical configuration affects the degree of the uniformity of the electric field. electrodes with bruce (or rogowski) profiles show approximately uniform field distributions. uniform field configurations are useful since they give fundamental information on the breakdown parameters. non-uniform field configurations are also very useful since they supply information about the expected performance of practical devices as was pointed out in [55]. non-uniform field configuration affects the breakdown mechanism [56], with the authors claiming that –regarding paper/oil insulation– gas evolution is of primary importance with decomposition starting from the decomposition of water in the paper. in [29], the authors using non-uniform field configurations suggested that the initiation of the breakdown can be divided into two parts: one including the formation of gas bubbles in the liquid at the cathode, and the other, being an adequate multiplication by a gaseous ionization in the bulk of the liquid. they also suggested that the formation of bubbles depends on the magnitude of the electric field, on the external pressure and on the amount of gas available at or near the electrodes. polarity effect is affected by the gas content of the liquid as was pointed out in [57]. uniform field configurations are used on many occasions in order to see the relation between the applied voltage and the gap spacing. according to [58], the mean breakdown voltage (v) varies linearly with the logarithm of gap spacing (d) following the general formula below v=kd n , where, n takes values between 0 and 1. such a relation was also proposed in [59], where it was noted that the breakdown voltage increase is somehow less proportional to the gap length for uniform field electrodes (plane-plane arrangement). experimenting with different electrode shapes, some researchers reached the conclusion that foreign particle bridge is thick and strongly bonded for spherical electrodes under dc voltage, whereas a thinner bridge is formed with needle-plane electrodes under dc voltage. this can be explained by considering that the dep force is very strong in the first case but only strong near the needle electrode in the second case [60]. such observations are in agreement with those of [52]. somewhat similar results were obtained in [61], where it was remarked that gas bubbles have a minimum effect with a nonuniform field arrangement because the movement of the bubbles and the corona will prevent the bubbles’ discharge path. discharge characteristics have been investigated in [62] with different electrode arrangements varying from point-plane to semi-homogeneous sphere-plane configuration, where it was reported that they depend on applied voltage, time of application and moisture content. non-uniform electrodes help in defining the various modes of streamer propagation in oils. earlier research indicated that the breakdown mechanism is better studied with a point-plane arrangement and it was indicated that there are three modes, with modes 2 and 3 having velocities 3 km/s and 10 km/s respectively [63, 64]. such streamer modes, albeit with different velocities, were also recorded in [65], where experiments with plane-plane electrodes were performed with a combination of mineral oil and solid spacers. it is evident that electrode geometry affects greatly the breakdown process and strength of transformer oil. things become even more complicated because far too often there are bubbles and minute foreign particles in an oil gap [51, 61]. especially, non-uniform electrode arrangements may indicate the breakdown streamer mechanism in an oil gap [66, 67]. vii. some general remarks this short review points out some of the factors affecting the breakdown strength in transformer oil. certainly, not all of the factors were described and analyzed. a volume effect and/or an area effect may result if weak links are present in the liquid itself and/or on the electrode surfaces [68, 69]. earlier on, it was shown that with impulse voltages a simple volume effect may exist since the area and gap effects were approximately equal but for ac voltages the breakdown strength dependence on gap spacing was found to be much greater than on area [3]. experimental data also confirmed this [25]. such a stronger dependence on gap length may be traced back for explanation to [70], where it was reported that the charge of a particle in contact with an electrode is proportional engineering, technology & applied science research vol. 10, no. 3, 2020, 5742-5747 5746 www.etasr.com danikas et al.: a short review of some of the factors affecting the breakdown strength of insulating oil… to the gap voltage and not to the local applied field. no comment was offered in the context of the present review about the capacitance effect, namely the effect according to which by putting a capacitance of known value in parallel to the test cell of the electrodes the conditioning effect may be altered. there is an optimum value of capacitance which, by delivering the right amount of energy into the electrode gap, may improve this process by destroying the most prominent irregularities on the electrode surfaces [25, 71]. regarding some future work, it would be of great interest if the role of bubbles and/or foreign particles could be studied in relation to nanofluids since the latter show some promise for replacement of the more traditional liquids [72, 73]. the so-called velocity effect is also a promising field of work w.r.t. the nanofluids as well as to the proposed ester and vegetable oils [74, 75]. viii. conclusions in this short review, some factors affecting the breakdown strength of 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university, delhi, india prateek.jain2903@gmail.com palak girdhar department of computer science & engineering, bpit, guru gobind singh indraprastha university, delhi, india palakgirdhar@bpitindia.com pakhi bamdev department of computer science & engineering, bpit, guru gobind singh indraprastha university, delhi, india bpakhi97@gmail.com abstract—face detection and recognition are being studied extensively for their vast applications in security, biometrics, healthcare, and marketing. as a step towards presenting an almost accurate solution to the problem in hand, this paper proposes a face detection and face recognition pipeline face detection and recognition embednet (fdrenet). the proposed fdrenet involves face detection through histogram of oriented gradients and uses siamese technique and contrastive loss to train a deep learning architecture (embednet). the approach allows the embednet to learn how to distinguish facial features apart from recognizing them. this flexibility in learning due to contrastive loss accounts for better accuracy than using traditional deep learning losses. the dataset’s embeddings produced from the trained fdrenet result accuracy of 98.03%, 99.57% and 99.39% for face94, face95, and face96 datasets respectively through svm clustering. accuracy of 97.83%, 99.57%, and 99.39% was observed for face94, face95, and face96 datasets respectively through knn clustering. keywords-convolution neural network; contrastive loss; histogram of oriented gradients; knn clustering; siamese technique; svmcclustering i. introduction the recognition of a face in an image is a tedious task as it depends on many factors like camera resolution, posture, face size, image brightness, lightening conditions, etc. prior to face recognition, face detection is a necessity which is subjected to deep learning or classification for training and testing purposes. there are various techniques for face detection like skin color isolation [1, 2], haar cascading [3], histogram of oriented gradients [4, 5]. after having the faces detected, the next step is to recognize them in any given frame or a picture. various deep learning models [6-8] are provided to extract features of an image and indirectly teach the network how a particular face looks like. this approach was challenged first by facenet [9], which introduced a new type of loss called triplet loss that allowed deep learning models to find similarities and dissimilarities within different faces. facenet requires three inputs, an anchor (image in question), a positive (image of the same class as that of the anchor) and negative (image not from the same class as that of the anchor). later a technique based on likeness loss called siamese network was introduced which worked on two image inputs and a binary number defining if two images belong to the same class or not. facenet achieved state of art accuracy of 99.63% on lfw dataset while it achieved 95.12% of accuracy on youtube faces db dataset. face recognition based on convolution siamese networks [10] used the siamese network technique allowing the network to learn similarities and dissimilarities between faces. it achieved an accuracy of 98.63% on lfw dataset. face detection and recognition using viola-jones with pca-lda and square euclidean distance [11] worked on the face94 face95 and face96 datasets which will be also used in this paper. the approach discussed in this paper is face detection and recognition pipeline (fdrenet) which involves studying existing face detection methodologies, finding the best one for the task, and employ siamese training technique to train our proposed deep learning network. after training embeddings of the dataset are produced from the trained model and svm and knn clustering is applied to achieve the best results. ii. literature survey face detection is the most important step prior to face recognition. this section focuses on the comparative study of popular algorithms: skin color isolation [1, 2], haar cascading [3], and histogram of oriented gradients [4, 5] to detect faces in an image. for this task, the open source datasets face94, face95, and face96 are used. some random images from the datasets are shown in figure 1. in the end, a brief approach to present face recognition algorithms is discussed. fig. 1. sample images from face94, face95 and face96 datasets corresponding author: prateek jain engineering, technology & applied science research vol. 9, no. 2, 2019, 3933-3938 3934 www.etasr.com virmani et al.: fdrenet: face detection and recognition pipeline a. skin color isolation detection of skin color in an image is useful in many areas like face and gesture recognition. skin detection by segmentation is highly affected by various factors like illumination, artificial lighting vs sunlight, shadows, and camera resolution, therefore, skin pixel classification is not an easy task. the algorithm in [1, 2] involves selecting a range which will differentiate between skin and non-skin pixels. the range is decided such that most of the skin color values fall in that range so that different color skins can be segmented. hsv is an alternate color representation of the rgb color space. the algorithm to convert rgb color space to hsv color space is shown in figure 2. hsv is designed in a way similar to human color perception. therefore, hsv color space is a better approach to segment skin color than rgb color space. hsv is a cylindrical geometry which is defined by three components: • hue: hue represents color and it ranges between 0 and 360 • saturation: saturation is the amount of grey in the color ranging between 0 (primary color) and 1 (gray). as we go towards the vertical axis of the cylindrical representation, pure colors start to fade. • value or brightness: it describes the brightness/intensity of the color and works in conjunction with saturation. it ranges between 0(dark) and 1. • the steps of skin color isolation algorithm are shown in figure 3. the steps of skin color isolation algorithm are shown in figure 3. fig. 2. rgb to hsv conversion flowchart fig. 3. algorithm for face detection using skin color isolation as we move from the top to bottom vertically, the color starts to be less bright. pure colors are arranged at the outside edge of the cylindrical representation. after conducting a few experiments, the best values for this algorithm to work were in the range: 100-179 for hue, 0-15 for saturation and 65-255 for brightness. some results of the skin color isolation algorithm are shown in figure 4. fig. 4. results of face detection using skin color isolation b. haar cascading haar cascading is an object detection algorithm which can detect objects in images at high rates. it is a machine learning based approach which requires the data to train the model. training data consist of positive images (images which contain objects to be detected) and negative images (images which don’t contain those objects). after the classifier is trained, we can then use it to detect an object in other images. haar cascading algorithm works in three steps [3]: • integral image: the algorithm uses features of the image to classify data. features contain more information than individual image pixels. moreover, a feature based model works faster than a pixel-based model. for features extraction from a given image, haar features are used. haar features are values obtained by subtracting the sum of pixels within the first rectangle from the sum of pixels within another rectangle. possible sizes and locations of rectangles need to be considered, so, the number of features for an image is quite high. • constructing a classifier by selecting a small number of important features using adaboost: most of the features calculated in the above step do not provide any useful information and are superfluous. therefore, we need a method to dump those features which do not contain any relevant information. this is done using adaboost classifier which excludes a large number of available features and retains only the critical ones. the haar cascading algorithm is shown in figure 5. • the attention cascade: there are many regions in the image which do not contain the object we want to detect and a lot of computational power is wasted on these regions. for this reason, the last step is to use a cascade of classifiers. instead of applying all the selected features on the subregion/window, the features are grouped into different stages of the classifier and are applied one by one. if a window fails the first stage, it is discarded. if the stage passes, second stage is applied and so on. if a window passes all the stages that means the window consists of the object. figure 6 shows the results of haar cascading algorithm. engineering, technology & applied science research vol. 9, no. 2, 2019, 3933-3938 3935 www.etasr.com virmani et al.: fdrenet: face detection and recognition pipeline fig. 5. algorithm for face detection using haar cascading fig. 6. results of face detection using haar cascading c. histograms of oriented gradient (hog) hog is an object detection algorithm which works by converting pixels into gradients [4, 5]. gradients are arrows whose direction represents the change in pixel illumination from light to dark. to calculate the gradient of each pixel, the current pixel is compared to its neighboring pixels and the direction of change from light pixels to dark pixels is noted. the gradients are helpful in detecting target objects in conditions where there is a change in brightness. in face detection, a person’s face will have different pixel values in light and dark conditions. but the change from light pixels to dark pixels remains almost the same. therefore, gradients solve the problem of object detection even in dark conditions. it would be costly to calculate the gradient for each pixel. therefore, a window is dragged on the image. each window calculates the gradients and then the strongest gradient is chosen for that window. this process is continued for every window in the image. to detect an object in the image, the part of the test image which best matches up with the hog representation of the trained image, contains the target object. the described algorithm is shown in figure 7 and the results are shown in figure 8. fig. 7. algorithm for face cetection using hog fig. 8. results of face detection using hog d. comparative study of face detection methods after using each of the above-mentioned face detection methods we conclude that hog is the best algorithm for facial detection, especially when live video streaming is concerned. though the above depiction of results of each algorithm looks alike, if one looks closer, the exactness of facial area covered by the detected frame is easily observed. skin color detection has the flaw of taking the area that matches the skin tone. using hsv tuning to detect skin tone colors, this algorithm can detect the similar colored objects as humans. haar cascade and hog have comparable results. for its ability to get zoomed in face features at a detected face, we preferred the hog algorithm for the face detection task. e. face recognition methods the most popular technique used for face recognition is deep learning. it was google’s facenet deep learning model [9] that introduced the new technique of training deep learning models via triplet input and triplet loss. this technique allowed the network to learn the features that distinguish two images instead of just categorizing alike images together. this technique produced a variant of siamese network [10] that achieved the same task as that of triplet loss network by using just two input images and a binary value to define the relationship of the input images, whether they belong to the same class of not. the proposed approach is a siamese technique used to train a proposed convolution neural network to achieve state of the art accuracy. iii. fdrenet a. framework embednet is the proposed approach for an efficient detection through hog algorithm and a deep learning model aided by siamese technique to differentiate and recognize the faces. the self-modeled deep learning convolution neural network (embednet) is responsible for extracting features from the input images and is majorly responsible for producing embeddings for the recognition task. here, the motive is to teach the network to differentiate between facial identities of different individuals as it simultaneously learns to find similarities between one individual’s facial features, snapped at a different time with varying emotions. doing so, the model not only learns to identify the images belonging to the same class but also tends to assimilate the features that mark one class’s element relatively closer or farther from the other classes in terms of euclidean distance of their encodings. encodings may also be referred to as embeddings throughout this paper. to implement this idea, siamese network with contrastive loss is favored. fdrenet after the detection task through hog basically subsumes a pair of proposed identical engineering, technology & applied science research vol. 9, no. 2, 2019, 3933-3938 3936 www.etasr.com virmani et al.: fdrenet: face detection and recognition pipeline convolution neural networks which is given the name embednet. these twin networks which share the weights are trained by the siamese technique. for the recognition task, the first sub part is to build a siamese network architecture keeping the embednet as the core deep learning model being trained. siamese network takes in two input images which can be either a positive-positive pair or a positive-negative pair. each of these embednets receives one of the input images to produce an 128x1 encoding for both images. these encodings are then fed to the contrastive loss function, which governs the training of the network. figure 9 provides a brief summary of the whole approach undertaken for the proposed fdrenet. fig. 9. the framework of the proposed embednet b. loss function for fdrenet the objective of the siamese network is to learn how to differentiate between two input images rather than performing a simple classification task. thus, to train the network (see figure 10), we can’t use any loss function like cross entropy loss, which is primarily a classification loss function. the required loss function must have the ability to calculate the variance, which will account for learning the differences between the two images. the best fit for this use case scenario is contrastive loss. intuitively, it evaluates how different two given images are as learned by the network. the embeddings of the images obtained from the embednet are sent to euclidian distance function (1) which finds the distance between the two embeddings. 𝑑(𝑝, 𝑛) = √(𝑛 − 𝑝)2 + (𝑛 + 𝑝)2 (1) where p is the first image’s encoding, n is the second image’s encoding and d(p,n) is the calculated euclidean distance. fig. 10. siamese network architecture 𝐿𝑜𝑠𝑠 = (1 − 𝑦)(0.5)(𝑑(𝑛, 𝑝)) 2 − (𝑦)(0.5){0, max (0, 𝑚𝑎𝑟𝑔𝑖𝑛 − 𝑑(𝑛, 𝑝))}2 (2) equation (2) displays the contrastive loss function. here y is 1 if the two images belong to the different class, it is 0. the margin is a value that we decided to it keep as 2. it is a value greater than 0 that helps to determine when not to let contrastive loss contribute to the total loss. margin indicates that any value beyond this positive integer must not add up to the total loss. this optimizes network to consider image pairs that seem to be alike but are actually dissimilar. figure 11 summarizes the use of contrastive loss and assignment of value to y. fig. 11. inputs to contrastive loss function this loss helps to train the inner embedding model (embednet) in such a way that facial identities (images) belonging to the same individual will have closer embeddings and will be farther from the embeddings of other individual’s facial identities. c. fdrenet’s convolution neural network: embednet as discussed above, fdrenet subsumes two identical embednets having shared weights. embednet is a simple convolution neural network which is solely responsible for extracting features from the input images. the extracted features are the latent features of the input image as produced by the last output layer of the embednet by a feed forward operation. we used four convolution layers, each followed by an relu activation function, a max-pooling layer, a dropout, engineering, technology & applied science research vol. 9, no. 2, 2019, 3933-3938 3937 www.etasr.com virmani et al.: fdrenet: face detection and recognition pipeline and a batch normalization layer as a regularization technique. this is followed by 3 linear layers with a relu activation function and the final output layer of dimension 128x1 is considered as the final encoding of the input images. fig. 12. architecture of embednet iv. about the datasets the open source datasets provided by the university of essex (face94, face95, face96) are used for the research work. face94 has a total of 3060 images of 180x200 pixels of 153 individuals. face95 has 1440 images of 72 individuals of 180x200 pixels and face 96 has 3040 images of 152 individuals of 196x196 pixels. these 24-bit rgb, jpeg images were combined to form a single dataset of 7540 images. table i shows the composition of each dataset. table i. dataset description dataset name total images face 94 3060 face 95 1440 face 96 3016 v. dataset preparation for fdrenet we used the above mentioned three datasets to test and train our model. each dataset is divided into test and train sets of 20-80 images. siamese dataset builder is used to creating around 1 lakh (0.1 million) siamese pairs. before loading the pairs, each image is subjected to hog face detection technique and preprocessing to 64x64 grayscale. figure 13 displays a subset of train images from the dataset. siamese dataset builder creates an array of random true and false values with length equal to that of the dataset or simple the batch size. this array makes sure that we create a random dataset having both positive-positive and positive-negative image pairs. the rest of the steps for creating a suitable dataset for siamese network training are briefly explained in figure 14. vi. experiment to train the siamese network with embednet as core model, we performed hyper-parameter tuning and decided to use adam optimizer set to learning rate of 0.01. the siamese pairs are fed to the network which is trained for 100 epochs. graphs of iteration vs loss while training are presented in figures 15-17. as siamese network produces dissimilarity factor, we plotted a few test images with their dissimilarity factor printed on top. figure 18 shows the results in terms of dissimilarity factor produced via trained fdrenet. fig. 13. preprocessed dataset fig. 14. siamese dataset builder fig. 15. loss vs iteration graph while training face94 fig. 16. loss vs iteration graph while training face95 engineering, technology & applied science research vol. 9, no. 2, 2019, 3933-3938 3938 www.etasr.com virmani et al.: fdrenet: face detection and recognition pipeline fig. 17. loss vs iteration graph while training face96 fig. 18. plotting dissimilarity factor for sample test images vii. results ideally, after training embednet through fdrenet framework, it should be able to distinguish faces based on similarities and dissimilarities. we expect embednet to produce results that are close for one person and far for different persons. if so, the embeddings predicted by embednet for the training dataset can be clustered to find the accuracy of the classification. to determine the accuracy of this model we resort to clustering algorithms like k-nearest neighbor and support vector machine. for each case, the dataset is split into training set (80%) and test set (20%), and 25% of the training set is dedicated to validation. tables ii and iii display the results of svc and knn clustering algorithms. table ii. fdrenet accuracy by svm clustering data set training accuracy validation accuracy test accuracy face 94 99.68 99.36 98.03 face 95 100.00 100.00 99.57 face96 100.00 100.00 99.39 table iii. fdrenet by knn clustering data set training accuracy validation accuracy test accuracy face 94 99.89 98.88 97.83 face 95 100.00 100.00 99.57 face96 100.00 100.00 99.39 viii. conclusion using the proposed fdrenet, state of the art accuracy was achieved. accuracy from clustering techniques justifies that the contrastive loss used with the deep learning model of the proposed fdrenet is successful in learning dissimilarities and similarities between faces in the given dataset, as well as classifying the faces into their labels (names). acknowledgement we thank the university of essex for the provision of face recognition data, namely for face94, face95 and face96 datasets (https://cswww.essex.ac.uk/mv/allfaces/) which are used for the research work in this paper. references [1] m. a. rahman, i. k. e. purnama, m. h. purnomo, “simple method of human skin detection using hsv and ycbcr color spaces”, 2014 international conference on intelligent autonomous agents, networks and systems, bandung, indonesia, august 19-21, 2014 [2] j. das, h. roy, “human face detection in color images using hsv color histogram and wld”, 6th international conference on computational intelligence and communication networks, bhopal, india, november 14-16, 2014 [3] p. viola, m. jones, “rapid object detection using a boosted cascade of simple features”, 2001 ieee computer society conference on computer vision and pattern recognition, kauai, usa, december 8-14, 2001 [4] h. s. dadi, g. k. m. pillutla, “improved face recognition rate using hog features and svm classifier”, iosr journal of electronics and communication engineering, vol. 11, no. 4, pp. 34-44,2016 [5] o. deniz, g. bueno, j. salido, f. d. l. torre, “face recognition using histograms of oriented gradients”, pattern recognition letters, vol. 32, no. 12, pp. 1598-1603, 2011 [6] u. aiman, v. p. vishwakarma, “face recognition using modified deep learning neural network”, 8th international conference on computing, communication and networking technologies, delhi, india, july 3-5, 2017 [7] w. wang, j. yang, j. xiao, s. li, d. zhou, “face recognition based on deep learning”, in: lecture notes in computer science, vol. 8944, pp. 812-820, springer, 2014 [8] h. kulkarni, g. tofighi, “unconstrained facial recognition using supervised deep learning on video”, available at: https://www.researchgate.net/publication/325071878_deep_learning_fo r_facial_recognition, 2018 [9] f. schroff, d. kalenichenko, j. philbin, “facenet: a unified embedding for face recognition and clustering”, ieee conference on computer vision and pattern recognition, boston, usa, june 7-12, 2015 [10] h. wu, z. xu, j. zhang, w. yan, x. ma, “face recognition based on convolution siamese networks”, 10th international congress on image and signal processing, biomedical engineering and informatics, shanghai, china, october 14-16, 2017 [11] n. h. barnouti, w. e. matti, s. s. m. al-dabbagh, m. a. s. naser, “face detection and recognition using viola-jones with pca-lda and square euclidean distance”, international journal of advanced computer science and applications, vol. 7, no. 5, pp. 371-377, 2016 [12] p. viola, m. jones, “rapid object detection using a boosted cascade of simple features”, 2001 ieee computer society conference on computer vision and pattern recognition, kauai, hawaii, usa, december 8-14, 2001 [13] c. shu. x. ding, c. fang, “histogram of the oriented gradient for face recognition”, tsinghua science and technology, vol. 16, no. 2, pp. 216-224, 2011 [14] h. s. dadi, g. k. m. pillutla, “improved face recognition rate using hog features and svm classifier”, iosr journal of electronics and communication engineering, vol. 11, no. 4, pp. 34-44, 2016 microsoft word 26-3137_s_etasr_v9_n6_pp5011-5015 engineering, technology & applied science research vol. 9, no. 6, 2019, 5011-5015 5011 www.etasr.com chachar et al.: establishing ipr in gas-condensate reservoir: an alternative approach establishing ipr in gas-condensate reservoir: an alternative approach muhammad hanif chachar ppl chair, institute of petroleum & natural gas engineering mehran university of engineering and technology jamshoro, pakistan mhanifchachar@gmail.com sarfraz ahmed jokhio ppl chair, institute of petroleum & natural gas engineering mehran university of engineering and technology jamshoro, pakistan sjokhio1@hotmail.com abdul haque tunio institute of petroleum & natural gas engineering mehran university of engineering and technology jamshoro, pakistan haque.tunio@faculty.muet.edu.pk haris ahmed qureshi ppl chair, institute of petroleum & natural gas engineering mehran university of engineering and technology jamshoro, pakistan harisqureshi12.hq@gmail.com abstract—inflow performance relationship (ipr) accuracy in the condensate reservoir is a long-standing problem in the oil industry. this paper presents a new approach to project the gas phase ipr in condensate reservoirs. ipr is estimated by rawlins and schellhardt equation whereas the gas pseudo-pressure function is solved by two methods and their iprs are compared. additionally, an average of both ipr’s is estimated and compared. at the reservoir pressure, the difference between both flow rates is negligible i.e. at 6750 psi, the flow rate difference is 0.55 mmscf/d. as pressure declines the difference is increasing at one stage, it is observed approximately 15 mmscf/d. keywords-gas; condensate; condensate reservoir; pseudopressure; well productivity; relative permeability; permeability; ipr i. introduction the gas condensate reservoirs are difficult to predict due to its multiphase behavior. petroleum industry is struggling to obtain the accurate inflow performance relation (ipr) in condensate reservoirs for decades. there is not much research conducted in the case of calculating gas phase ipr in a condensate reservoir. it is possible to calculate ipr by using gas phase pseudo-pressure function without using the relative permeability data. pseudo-pressure equation is solved using effective permeability data which can be obtained by pressure buildup test [1]. in the solution gas drive reservoir, two phase flow causes the curvature in ipr due to the reduction in the relative permeability of the oil phase with the depletion [2]. two phase pseudo-steady state equation was solved [3] based on weller’s approximation of constant gas oil ratio (gor) and constant de-saturation [4]. in this study, the proposed approach is compared with the conventional method. to generate the ipr, the relative equation in [5] is preferred. in several case studies, it has been shown through production data and well test data that condensate blockage may reduce the production from two to four times. the major cause of production loss is condensate blockage near the wellbore [6]. to understand the condensate behavior, it is divided into three regions. region-1 (near wellbore), where both phases are presented and mobile, region-2 where both phases are present but only gas phase is mobile, and region-3 (above dew point pressure) where only the gas phase is present and mobile [7]. experimental work on the long core of sandstone formation outcome shows that the mobility is increased with capillary number near the wellbore region [8]. authors in [9] verified the existence of the three regions by using a compositional simulator. the estimation of total well productivity in condensate reservoir is complicated. condensate extent must be known to identify the blockage effect so that remedial action can be taken [10]. in [11], common problems associated with the condensate reservoirs were investigated and several proposed solutions were reviewed. this paper provides key improvements in the calculation of gas phase pseudo-pressure function using the integral effective permeability technique proposed in [12]. ii. model description and working equations a. gas pseudo-pressure function it completely depends on the pressure. to calculate real gas pseudopressure function linearly, kirchhoff integral transformation is used as follows [13]: ���� = 2� � �� �� (1) where p: pressure, �: viscosity, and z: compressibility factor. authors in [7] modified and introduced the pseudopressure equation in form of three regions [7]. the total gas pseudopressure equation is: ���� = � � ��� ��� �� + ��� ��� � � �� �� (2) where ���: relative permeability of oil, ��: viscosity of oil, ��: oil formation volume factor, rs: the solution gas-oil ratio, and corresponding author: muhammad hanif chachar engineering, technology & applied science research vol. 9, no. 6, 2019, 5011-5015 5012 www.etasr.com chachar et al.: establishing ipr in gas-condensate reservoir: an alternative approach g: gas. authors in [12] modified the pseudopressure equation to calculate it with the single-phase effective permeability of either gas or oil by using well test data. they proposed the following equation, using gas pvt properties: ���� = !� ��.����� �� #$�%&#�#'� #$&#' ��� �� � �� ( (3) where rp: producing gas-oil ratio and ro: oil vapors in gas. calculations of the classic and the proposed method are given in table vi and vii respectively. b. derivative of gas pseudo-pressure function time dependent derivative of the pseudopressure function is required in order to obtain the integral of effective permeability. to calculate the derivative, it is necessary to obtain a pseudopressure equation. at first, the pseudopressure equation was calculated by ignoring the permeability data. then, the derivative of pseudopressure equation is calculated. c. integral of effective permeability the effective permeability data were calculated from the semi log straight line (ssl) from shut-in versus time in figure 1. the start of ssl shows the mtr (middle time region) on pbu (pressure build-up) plot. the following equation is used to calculate the integral of effective permeability: � )�* + �� �� = � )�.�� + �� �� = 162.6 . /�,123' 4 5 % ∆7� �8 (5) where �* : gas effective permeability, 9 ,7*:�: flow rate of gas measured, h: bed thickness and ∆m(p)΄: change in pseudopressure derivative. now, extrapolate the integral of effective permeability versus pressure to zero using curve fit software. the equation from curve is used to calculate its integral on the desired pressure (figure 4). d. effective permeability once the integral of effective permeability is calculated, we take its derivative using a two-point numerical derivative as a function of pressure: �* = )��2�+;& )��2�+< � ;& <� (6) this effective permeability is used to calculate the final pseudopressure function as shown in table vii. e. gas flow rate for ipr to establish gas phase ipr, the equation from [5] is used. additionally, both gas pseudopressure equations are solved and their iprs are plotted and compared. figures 6 and 8 show the classic and the proposed ipr whereas figure 9 shows the comparison of both iprs with their average. 9 = = × ?)���� + @ a − )���� + cd a ef (7) where c: flow coefficient, n: deliverability exponent, ���� : gas pseudopressure function, �g : initial pressure and �cd : wellbore flowing pressure. iii. step-by-step procedure to generate ipr this method of calculating ipr is slightly different from the classic one. its steps are: 1. calculate gas properties (viscosity, density, compressibility) by conventional equations. 2. convert well test data into gas pseudopressure function, ignoring permeability terms. 3. calculate the derivative of the time log .h∆7� �hij�k� 5 of pseudopressure data. 4. plot well test data pressure versus time on semi-log and find the straight-line. 5. estimate the integral of effective permeability following the straight line from the previous step. 6. plot the estimated integral of effective permeability versus pressure extrapolated to zero limits. to get good curve fit the equation’s both limits should be extrapolated to zero. 7. calculate the integral of effective permeability values using the generated equation from the curve obtained in step 6. 8. calculate the effective permeability using a two-point numerical derivative as a function of pressure from the previous step. 9. calculate the pseudopressure function again this time including the effective permeability data. 10. finally, establish condensate well performance by using the equation from [5]. iv. concluding interpretation ipr is often used to predict the natural flow of the well so it should be properly selected. this study presents a new approach to estimate ipr in a gas condensate reservoir. furthermore, it concludes with the following observations: • a method is proposed to calculate pseudopressure equation for plotting ipr in gas condensate reservoir. it does not require relative permeability data, as effective permeability can be easily calculated from its integral. • effective permeability must be used before solving the pseudopressure integral. the comparison of ipr with the classic method shows that as pressure declines the flow rate difference in classic method and the proposed one increases. it can reduce the error by 1-15mmscf/d. v. recommendations ipr can obtain optimum flow of the well. it is highly recommended to use the proposed method to reduce errors in ipr calculations. the error percentage shows the reliability of this work. for additional research, three-phase reservoir should be considered, and optimum flow can be obtained by plotting tpr vs. ipr. a. abbreviations and acronyms ppf = pseudopressure function gor = gas oil ratio ssl = semi-log-straight-line r-1 = region-1 engineering, technology & applied science research vol. 9, no. 6, 2019, 5011-5015 5013 www.etasr.com chachar et al.: establishing ipr in gas-condensate reservoir: an alternative approach r-2 = region-2 r-3 = region-3 bg = gas formation volume factor µg = gas viscosity keg = gas effective-permeability krg = gas relative-permeability qg = gas flow-rate qo = oil flow-rate rp = producing gas-oil ratio rso = solution gas-oil ratio m(p) = pseudo-pressure function m(p)’= derivative of pseudo-pressure function ∆����= change in pseudo-pressure function b. figures and tables table i. reservoir and fluid data [14] symbol value unit symbol value unit pi 6750 pisa qg 75.4 mscf/d pd 6750 pisa qo 2.8 stb/d rp/gor 10417 scf/stb h 216.5 ft t 814 °r ф 0.062 gas sg 0.94 rw 0.54 ft mw 27.17 api 50 [assumed] ∆t 2.85 °f/100ft table ii. well test data [14] lmno (hrs) p (psi) lmno (hrs) p (psi) lmno (hrs) p (psi) 0 1083.1 6 2759.4 50 6487.3 0.167 1174.5 8 3246.5 58 6507.6 0.333 1226.7 12 4210 68 6526.5 0.5 1303.6 16 5162 82 6556.9 1 1490.6 22 6161 97 6574.3 2 1751.6 28 6336.5 112 6587.3 3 2046 34 6406.1 141 6601.8 4 2279.4 42 6452.5 pr 6750 table iii. gas pvt properties at well test pressure p psi q rs bbl/scf ts gm/cc μs cc vw scf/stb vx stb/scf 1083.1 0.9145 0.0034 0.0539 0.0080 297.945 1.4e-05 1174.5 0.9101 0.0031 0.0585 0.0082 327.131 1.55e-05 1226.7 0.9075 0.0030 0.0611 0.0083 343.959 1.63e-05 1303.6 0.9038 0.0028 0.0649 0.0085 368.948 1.75e-05 1490.6 0.8947 0.0024 0.0742 0.0090 430.644 2.04e-05 1751.6 0.8820 0.0020 0.0872 0.0097 518.739 2.41e-05 2046.0 0.8672 0.0017 0.1019 0.0105 620.549 2.82e-05 2279.4 0.8716 0.0015 0.1135 0.0113 702.899 3.14e-05 2759.4 0.8807 0.0013 0.1374 0.0130 876.247 3.81e-05 3246.5 0.8899 0.0011 0.1617 0.0151 1056.97 4.54e-05 4210 0.9157 0.0008 0.2097 0.0200 1426.45 6.22e-05 5162.0 0.9962 0.0007 0.2572 0.0273 1804.60 8.39e-05 6161.0 1.0806 0.0007 0.3069 0.0376 2213.14 0.000115 6336.5 1.0954 0.0007 0.3157 0.0397 2286.02 0.000121 6406.1 1.1013 0.0007 0.3192 0.0406 2315.01 0.000124 6452.5 1.1052 0.0007 0.3215 0.0413 2334.36 0.00012 6487.3 1.1082 0.0007 0.3232 0.0417 2348.89 0.00012 6507.6 1.1099 0.0007 0.3242 0.0420 2357.37 0.000128 6526.5 1.1115 0.0006 0.3252 0.0422 2365.27 0.000129 6556.9 1.1140 0.0006 0.3267 0.0427 2377.98 0.000130 6574.3 1.1155 0.0006 0.3275 0.0429 2385.26 0.000131 6587.3 1.1166 0.0006 0.3282 0.0431 2390.70 0.000131 6601.8 1.1178 0.0006 0.3289 0.0433 2396.77 0.000132 6750.0 1.1304 0.0006 0.3363 0.0454 2458.94 0.000138 table iv. ppf, its derivative and integral of effective permeability p psi ∆y(z) mmpsi 2 /cp ∆y(z)’ ∫ \]s 1083.1 19.87139 1174.5 23.33366 1226.7 25.40711 1303.6 28.58367 7.475785 1490.6 36.87831 11.75797 1751.6 49.68891 29.24621 2046 65.64563 38.57398 2279.4 79.14166 55.36694 2759.4 108.0837 75.90609 3246.5 138.2613 107.2502 4210 196.2917 139.7734 5162 246.5346 135.301 6161 287.666 93.06389 ssl 6336.5 293.6161 56.13135 0.001008854 6406.1 295.8697 15.22777 0.003718756 6452.5 297.3387 8.76812 0.006458438 6487.3 298.423 5.343989 0.010596647 6507.6 299.0485 4.866248 0.011636966 6526.5 299.6263 4.524248 0.012516635 6556.9 300.5464 3.375618 0.016775701 6574.3 301.0679 3.658003 0.015480678 6587.3 301.4551 2.58145 0.021936645 6601.8 301.8845 6750 306.1246 table v. pvt properties at assumed pressure p psi q rs bbl/scf ts gm/cc μs cc vw scf/stb vx stb/scf 100 0.98995 0.04061 0.0049 0.0062 19.08302 1.4e-05 300 0.97359 0.01331 0.0149 0.0065 67.76515 3.4e-06 600 0.94906 0.00648 0.0298 0.0070 150.7455 4.83e-06 900 0.92348 0.00421 0.0448 0.0076 240.6389 1.09e-05 1200 0.90888 0.00310 0.0597 0.0083 335.3379 1.59e-05 1500 0.89428 0.00244 0.0747 0.0090 433.7788 2.05e-05 1800 0.87969 0.00200 0.0896 0.0098 535.3081 2.48e-05 2100 0.86826 0.00169 0.1046 0.0107 639.48 2.89e-05 2400 0.87393 0.00149 0.1195 0.0117 745.9688 3.31e-05 2700 0.87962 0.00133 0.1345 0.0128 854.5257 3.73e-05 3000 0.88530 0.00121 0.1494 0.0140 964.9535 4.16e-05 3300 0.89099 0.00110 0.1644 0.0153 1077.092 4.62e-05 3600 0.89668 0.00102 0.1793 0.0168 1190.809 5.11e-05 3900 0.88955 0.00093 0.1943 0.0184 1305.991 5.63e-05 4200 0.91490 0.00089 0.2092 0.0202 1422.542 6.2e-05 4500 0.94025 0.00085 0.2242 0.0222 1540.379 6.82e-05 4800 0.96561 0.00082 0.2391 0.0244 1659.429 7.49e-05 5100 0.99096 0.00079 0.2541 0.0268 1779.628 8.23e-05 5400 1.01632 0.00077 0.2690 0.0295 1900.917 9.05e-05 5700 1.04167 0.00075 0.2840 0.0324 2023.246 9.94e-05 6000 1.06702 0.00073 0.2989 0.0357 2146.567 0.000109 6300 1.09238 0.00071 0.3139 0.0393 2270.839 0.00012 6750 1.13041 0.00068 0.3363 0.0454 2458.946 0.000138 the curve in figure 4 is obtained from the equation generated by the curve fit. the smooth curve is an indication of accuracy and it should be used to calculate the other required data. the curve in figure 6 shows the trend of effective permeability of gas against pressure. as the pressure is increased, the effective permeability of the gas is also increased. the graph trend in figure 9 shows that error is reduced by 1-15 mmscf/d. the difference between average ipr and classic ipr is 0.5-7.5 mscf/d. engineering, technology & applied science research vol. 9, no. 6, 2019, 5011-5015 5014 www.etasr.com chachar et al.: establishing ipr in gas-condensate reservoir: an alternative approach table vi. final ppf and flow rate classic method p psi y(z)s mmpsi 2 /cp ∫ \]s y(z)s (final) mmscf ^s mmscf/d 100 0.196978075 6.50266e-05 1.28088e-05 94.05954 300 1.742696934 8.13784e-05 0.00014181 94.04973 600 6.778583051 0.000100002 0.00067787 94.009 900 14.82858679 0.000117101 0.001736445 93.92854 1200 25.52693376 0.000134243 0.003426806 93.80002 1500 38.4846738 0.000152154 0.005855598 93.61529 1800 53.3722675 0.000171361 0.009145922 93.36488 2100 69.85112141 0.000192357 0.013436386 93.03811 2400 87.42029189 0.000215685 0.018855232 92.62498 2700 105.6132162 0.000241992 0.025557541 92.11336 3000 124.1582217 0.000272102 0.03378372 91.48445 3300 142.8181289 0.000307105 0.043860203 90.71261 3600 161.3865833 0.000348495 0.056242486 89.76188 3900 179.8151745 0.000398395 0.071637542 88.57631 4200 197.7524845 0.000459941 0.090954501 87.08307 4500 214.7604013 0.000537981 0.11553694 85.17347 4800 230.77076 0.00064044 0.147794924 82.65125 5100 245.7339194 0.000781243 0.191977821 79.16496 5400 259.6153259 0.000987312 0.256321205 74.01772 5700 272.3926848 0.001318394 0.359120865 65.6006 6000 284.0536412 0.001939033 0.550789526 49.10788 6300 294.5938878 0.003527854 0.811762171 27.12217 6750 308.3105787 0.003211887 0.990258889 0 table vii. ppf and flow rate proposed method p (psi) _]s y(z)s �mmpsi2/cp) ^s (mmscf/d) 100 0 3.9e+08 80.29606 300 8.17589e-08 1.41e+08 80.40645 600 6.2078e-08 4.88e+08 80.25238 900 5.69979e-08 9.64e+08 80.04083 1200 5.71385e-08 1.57e+09 79.76904 1500 5.97042e-08 2.33e+09 79.43118 1800 6.4023e-08 3.26e+09 79.01951 2100 6.99885e-08 4.36e+09 78.52535 2400 7.77579e-08 5.66e+09 77.94393 2700 8.76901e-08 7.17e+09 77.26862 3000 1.00368e-07 8.91e+09 76.48462 3300 1.16677e-07 1.09e+10 75.572 3600 1.37967e-07 1.33e+10 74.50349 3900 1.66333e-07 1.61e+10 73.23101 4200 2.05152e-07 1.94e+10 71.71536 4500 2.60132e-07 2.34e+10 69.90629 4800 3.41533e-07 2.82e+10 67.69041 5100 4.69341e-07 3.42e+10 64.87688 5400 6.86896e-07 4.22e+10 61.11419 5700 1.10361e-06 5.35e+10 55.66273 6000 2.0688e-06 7.17e+10 46.58986 6300 5.29607e-06 1.1e+11 25.98219 6750 7.0215e-07 1.45e+11 0 fig. 1. pseudopressure function and its derivative vs. time fig. 2. integral of gas effective permeability as a function of pressure fig. 3. integral of gas effective permeability as a function of pressure extrapolated to zero fig. 4. integral of effective permeability versus pressure at assumed pressure points fig. 5. ipr via classic method fig. 6. gas effective permeability vs. pressure engineering, technology & applied science research vol. 9, no. 6, 2019, 5011-5015 5015 www.etasr.com chachar et al.: establishing ipr in gas-condensate reservoir: an alternative approach table viii. proposed and classic method comparison p (psi) ^s (mmscf/d) ^s (mmscf/d) ^s (difference) (mmscf/d) ^s(avg) (mmscf/d) 100 94.05954 80.29606 13.76348 87.1778 300 94.04973 80.40645 13.64328 87.22809 600 94.009 80.25238 13.75662 87.13069 900 93.92854 80.04083 13.88771 86.98468 1200 93.80002 79.76904 14.03098 86.78453 1500 93.61529 79.43118 14.18411 86.52323 1800 93.36488 79.01951 14.34537 86.1922 2100 93.03811 78.52535 14.51276 85.78173 2400 92.62498 77.94393 14.68105 85.28445 2700 92.11336 77.26862 14.84475 84.69099 3000 91.48445 76.48462 14.99984 83.98453 3300 90.71261 75.572 15.14061 83.1423 3600 89.76188 74.50349 15.25839 82.13268 3900 88.57631 73.23101 15.3453 80.90366 4200 87.08307 71.71536 15.36771 79.39921 4500 85.17347 69.90629 15.26718 77.53988 4800 82.65125 67.69041 14.96084 75.17083 5100 79.16496 64.87688 14.28808 72.02092 5400 74.01772 61.11419 12.90353 67.56595 5700 65.6006 55.66273 9.937865 60.63167 6000 49.10788 46.58986 2.518028 47.84887 6300 27.12217 25.98219 1.139977 26.55218 6750 0 0 0 0 fig. 7. ipr via the proposed method fig. 8. iprs via classic and proposed method and their average fig. 9. variation in gas flow rate versus pressure acknowledgment the authors are grateful to pakistan petroleum ltd, and the institute of petroleum & natural gas engineering, mehran university of engineering & technology, jamshoro. references [1] s. a. jokhio, d. tiab, “establishing inflow performance relationship (ipr) for gas condensate wells”, spe gas technology symposium, calgary, usa, 30 april-2 may, 2002 [2] h. h. evinger, m. muskat, “calculation of theoretical productivity factors”, transactions of the aime, vol. 146, no. 1, pp. 126-139, 1942 [3] j. t. vogel, “inflow performance relationships for solution-gas drive wells”, journal of petroleum technology, vol. 20, no. 1, pp. 83-92, 1968 [4] w. t. weller, “reservoir performance during two phase flow”, journal of petroleum technology, vol. 18, no. 2, pp. 240-245, 1966 [5] e. l. rawlins, m. a. schellhardt, backpressure data on natural gas wells and their application to production practices, literary licensing, 1935 [6] d. afidick, n. j. kaczorowski, s. bette, “production performance of a retrograde gas reservoir: a case study of the arun field”, spe asia pacific oil and gas conference, melbourne, australia, november 7-10, 1994 [7] o. fevang, c. h. whitson, “modeling gas condensate deliverability”, spe reservoir engineering, vol. 11, no. 4, pp. 221-230, 1995 [8] r. mott, a. cable, m. spearing, “a new method of measuring relative permeabilities for calculating gas-condensate well deliverability”, 1999 spe annual technical conference and exhibition, houston, usa, october 3–6, 1999 [9] a. c. gringarten, a. al-lamki, s. daungkaew, r. mott, t. m. whittle, “well test analysis in gas-condensate reservoirs”, spe annual technical conference and exhibition, dallas, usa, october 1-4, 2000 [10] m. s. abdallah, m. a. al-zawad, m. l. fraim, “common misinterpretations of gas condensate reservoirs”, spe kingdom of saudi arabia annual technical symposium and exhibition, dammam, saudi arabia, april 24-27, 2017 [11] m. h. chachar, s. a. jokhio, a. h. tunio, “investigating gas phase productivity in gas condensate reservoir: a review”, engineering science & technology international research journal, vol. 2, no. 3, pp. 95-99, 2018 [12] s. a. jokhio, d. tiab, s. baladi, a. h. tunio, “estimating pseudopressure function without relative permeability [kr(sw)] for two and three phase gas condensate systems”, spe asia pacific oil and gas conference and exhibition, melbourne, australia, october 8-10, 2002 [13] r. al-hussainy, h. j. ramey, p. b. crawford, “the flow of real gases through porous media”, journal of petroleum technology, vol. 18, no. 5, pp. 624-636, 1966 [14] p. gherson, c. faruk, “gas-condensate well test analysis with and without relative permeability curves”, spe annual technical conference and exhibition, dallas, usa, october 1-4, 2000 [15] v. n. gopal, “gas z-factor equations developed for computer”, oil and gas journal, oil and gas journal, vol. 75, no. 8, pp. 8-13, 1977 [16] a. l. lee, m. h. gonzalez, b. e. eakin, “the viscosity of natural gases”, journal of petroleum technology, vol. 18, no. 8, pp. 997-1001, 1966 engineering, technology & applied science research vol. 8, no. 4, 2018, 3255-3259 3255 www.etasr.com donza et al.: a simple electronic circuit for an automatic train safety stop system a simple electronic circuit for an automatic train safety stop system andre donza department of electrical engineering federal university of para department of trains maintenance, brazilian company of urban trains (cbtu), recife, brazil andredonza@cbtu.gov.br riley jones laboratory of electronics brazilian company of urban trains (cbtu), recife, brazil rileyrupert@cbtu.gov.br rafael teixeira department of trains maintenance brazilian company of urban trains (cbtu), recife, brazil rafaelteixeira@cbtu.gov.br bruno da silva department of trains maintenance brazilian company of urban trains (cbtu), recife, brazil brunogsilva@cbtu.gov.br abstract—a particular safety system known as “dead man’s circuit” detects the presence of human command in the conduction of the trains operated by the brazilian company of urban trains (cbtu) in recife, brazil, thus consisting a security mechanism that makes automatic braking of any train composition circulating in the transportation system of the city feasible in incidents of loss or apparent loss of driving. originally, the electrical signal indicating human control in the conduction of the vehicles came from the descent of the traction lever in the driving cabins, which caused the switching of a pair of electrical contacts. given the importance of the system and the need to avoid repetitive strain injuries to drivers, the need to push the traction knob was eliminated by the use of an electronic device developed by an outsourced company and deployed in the trains of the older fleet. however, the high failure and downtime rates associated with the circuit acquired from the referred contracted company caused the need to develop a more robust and maintenance-friendly design for the dead man’s system. in fact, despite the good performance of the purchased system, the strength of the resin coating that accommodated the capacitive touch sensor assembly at the end of the traction lever prevented the corresponding electronic circuit from any access for research or corrective interventions. thus, the content of this paper essentially presents the specifications and the description of operation of the alternative electronic circuit designed for the dead man’s system, which is operating normally without electrical defects in 4 old trains for almost a year. keywords-urban trains; safety system; touch sensor; automatic braking i. introduction a large number of techniques based on different maintenance approaches have been proposed to solve various types of maintenance problems [1]. these techniques and approaches must be adequate to specific situations and must be adapted to the singular needs of a company [2]. obviously, in any approach, reliability assessments play a key role in determining whether or not a critical system or equipment should be replaced. the older fleet of the metropolitan trains operated by the brazilian company of urban trains (cbtu) in recife, brazil, is composed by vehicles from a brazilian company, namely cism. a particular system of these trains, known as dead man’s circuit detects the presence of human command in the conduction of the trains, thus consisting of a security mechanism that makes feasible in incidents of loss or apparent loss of driving, automatic braking of any train composition circulating in the transportation system of the city. the high failure and downtime rates associated to the dead man system developed by an outsourced company for the old fleet caused the need to deploy another design of this system. thus, the current paper essentially presents the specifications and the description of operation of the alternative electronic circuit designed for the dead man’s system, which is operating normally without electrical defects in 4 trains since august 2017. ii. history of the system originally, the electrical signal indicating human control in the conduction of the old railway vehicles of cism came from the descent of the traction lever in the driving cabins, which caused the switching of a pair of electrical contacts, being continuously necessary for the driver to be with a hand supported on the traction knob to get or keep any train moving. given the importance of the system and the need to avoid repetitive strain injuries to drivers, the need to push the traction lever to conduct the trains of the old fleet was eliminated by the use of a set consisting of two devices: a touch sensor, installed at the end of the traction handles, and an electronic main module, both shown in figure 1, developed and installed by an outsourced company admitted by cbtu. despite the ergonomic advantage, the implemented modification did not increase the reliability of the system and the maintenance quality. the strength of the resin coating that accommodated the touch sensor assembly at the end of the traction lever prevented the corresponding electronic circuit from any access for research or corrective interventions. due to the lack of technical documentation of the circuits implemented by the outsourced company and the impossibility of accessing the sensor assembly without damaging it, the initial solution adopted to reduce the time of unavailability of trains for commercial operation due to failures in the dead man system was the acquisition of adjustable sensitivity capacitive cyl tra the res sim of agg po ma rev lim ele fig sen fig on the tog out dea exp and mo in cap con wi cap sen [4] fai mo tra in of fai the ele engineerin www.etasr lindrical sens action levers on e cbtu's own sin encapsulat mplicity of the the capacitiv gravated by t ssible inversio ain control mo verse polariza mitations of sp ectrical or mec g. 1. main mo nsor in the right g. 2. first chan leaked silicone be therefore, g e old fleet, the gether with t tsourced comp ad man’s sys perienced in t d cost-effectiv odule, in order the trains of pacitive senso nsumers, indu de range of pacitive senso nsitivity to tem ]. as shown in ilures of the d odule, 6% from action lever an the capacitive the old elec ilures directly e capacitive s ectromechanic ng, technology r.com ors, which w n leaked silico n workshop, r ted assembly e new device, t ve sensor by the vibrations ons of the ele odule and the ations difficul pace that made chanical protec odule box in the l nge in the traction eads. given the parti capacitive sen the main con pany, did not s stem. the hig the old trains r ve touch senso r to adjust the the old fleet. ors are rapidly ustrial and aut f advantages. ors are suscep mperature, no n figure 3, in dead man’s sys m electrical ca nd the control m e sensor of the ctromechanica related to the ensors and 20 al system, a y & applied sci were installed one beads (fig replacing the . despite the the routing of y very tight of the trains ectrical conne sensor, cause lt to avoid d e it difficult to ction device. left and cover of n lever. capacitiv icular conditio nsor, despite it ntrol module seem to be the gh cost and th raised the nee or along with a operation of s . in general, h proliferating tomotive appl the major ptibility to elec on-linear respo the first half o stem came fro ables or conne module and 2 e traction leve al system. fr e traction leve 0% from the as presented ience research donz at the end o gure 2), produc previously ad e effectivenes the electrical c ducts, a con s in operation ections betwee ed short circuit due to the ex o install any s the old capacitiv ve sensors were in ons of the tra ts known relia developed b e best option f he relative fra ed of a new re a compatible c such security s however, prox across thousan ications [3], w disadvantag ctromagnetic onse and hyst of 2017, 14% om the main c ections betwee 9% were orig er or in the co rom these 29 er, 80% came contacts of th in figure 4. h v za et al.: a simp of the ced by dopted s and cables ndition n, and en the ts and xtreme simple ve touch nstalled ains of ability, by the for the agility eliable control system ximity nds of with a es of noise, teresis of the control en the inated ontacts 9% of e from he old . the rem from the man larg pro and syst fig. dead fig. leve plac sen sen sou the pin tran con the     vol. 8, no. 4, 20 ple electronic c maining 51% is m the extensiv electrical sign n’s system for ge set of e ogrammable li d electromech tem. 3. percentag d man’s system. 4. percentag er in the first half iii. ic 555 is th ced at the end nsors, as shown nsor to the ma urce of the radi output of the 8 of the “5 nsistor q1 to nnects to the g e main compon ic 555. diode 1n400 figure 5). 15mohms re total resistanc electrolytic ca 018, 3255-3259 circuit for an a s almost entire ve brake circu nal from the m r processing. t equipment fo inear controlle hanical relays ge of equipment fa ge of equipment of 2017 descriptio he main comp d of the tractio n in figures 5 ain module, po io system in th voltage regul 555”. the sec the output pin ground, provid nents of the to 04 (installed b esistor of 1/8w ce close to that apacitor of 22 9 automatic train ely caused by uit of the trai main control m thus, this per ormed by so ers, electric ca of the gene ailures during the failures directly on of the gen ponent of the on lever to rep 5 and 6. three owered by the he train. the f lator (l7812), cond connect n 3 of the ic ding negative ouch sensor are behind the boa w (or two resis t) 0uf/16v. 3256 n safety stop sy equipment fai ins, which rec module of the rcentage refers olid state re ables, bypass eral brake co first half of 2017 related to the tr neral assemb new touch s place the capac cables connec e 24v dc vo first one starts taking 12v d s the base o c. the last of reference to p e: ard, so not se stors in series system ilures ceives dead s to a elays, keys ontrol 7 in the raction bly ensor citive ct the oltage from dc to of the them pin 1. een in s with   are bo mo ma       com fol   engineerin www.etasr 100nf polyes 100kohms re f fig. 6. as pointed o e its stability, ard (figure 7) odule board, s ain component 2 relays of 12 ic 7812 (vol electrolytic c 7,5kohms re 1kohm resist transistor bc f ne555 time mparator, a v llowing pins [6 trigger: for this pin, the o threshold: c inverting inp ng, technology r.com ster capacitor. esistor. ig. 5. new tou electrical circu out in [5], the m cheap cost an ), measures 5 shown in figu ts of the contro 2v/7a. ltage regulator capacitor of 1u esistor of 1/8w tor of 1/8w. c546b. fig. 7. design er ic is an voltage divide 6, 7]: r voltages belo output is high. connected to put terminal. y & applied sci uch sensor with ic uit diagram of the main reasons nd easy availa 5mm x 29mm ure 8, is 100m ol module boa r). uf/50v. w. n of the sensing b 8 pin dip p er and a sr ow 1/3 of the the first com ience research donz c 555 touch sensor of using the ic ability. the se m, while the c mm x 100mm ard are: board package ic w flip-flop, wit e voltage sour mparator at the h v za et al.: a simp c 555 ensing control m. the with a th the rce on e non      the in rece filte osc fig. (hig syste the prev inte curr deli acti tou con vol. 8, no. 4, 20 ple electronic c reset: turns t of the trigger control: by im a pot between the output wa pin should be to prevent any discharge: us and monostab output: load ground: refe of the dc vol supply: the p fig. 8. the voltage voltage sourc turn, is pow eiving 12v d ered by the cillations, as sh 9. simplified ghlighted in yello em the use of th capacitor c2 vent voltage fl egrated circuit rents greater ivered by the ivation of the ch switch on t ntact and ensu 018, 3255-3259 circuit for an a the output of t input. mposing a vol n this pin and ave can be var e bypassed to y noise problem sed to discharg ble modes. s are tied to th erence point c ltage source. power supply c design of the iv. regulator l78 ce of the radio wered by the dc from the vo 100nf capa hown in figur d electrical sche ow) along with t he control pin 2 was placed fluctuations fro t. in the voltag than 1a, the radio system control modu the 555's trigg ure good perf 9 automatic train the ic 555 to z ltage on this pi d the ground, ried. when no ground with m. ge the timing c his pin. connected to th can vary from main control mod operating m 812 (u3) rece system in the gnd (1) an oltage regulato acitor c4 to res 9 and 10. ematic diagram the control modu of the ic 555 between term om affecting th ge input circu capacitor c3 m and the led ule. the drive ger terminal (p formance, me 3257 n safety stop sy zero, independ in or by conne the pulse wid ot used, the co a 0.01uf capa capacitor in as he ground term m 5v to 18v. dule board mode ives 24v dc e train. the ic nd vcc (8) or output, whi o avoid elec of the touch ule of the dead is unnecessar minals 1 and he sensitivity o it, the fuse f1 filters the vo d d2 indicate er's hand acts pin 3). to refin etal receivers system dently ecting dth of ontrol acitor stable minal from c 555, pins, ich is ctrical sensor man’s ry, so 5 to of the 1 cuts oltage es the s as a ne the have bee fig ma hig rec rel (te rec con ind to rap cap slig clo eno of ver con reg to col in tra op engineerin www.etasr en incorporate gure 11. fig. 10. as the 555 tr agnitude of th gh level when ceiver, which lays k1 and k erminal 2) is q ceiver, the lev ntact occurs, duced voltage low level. th pidly, only sub pacitor c1. t ghtly different osed metal str ough to activa the traction h ry small electr fig. the transisto ntacts of the re gion. consider 110, as repo llector saturati (1), the bas ansistor to oper sat cc min sat the resistor eration of the ng, technology r.com ed into the se electrical circuit rigger is activa he supply volt n one of the causes, as alre k2. the inpu quite high an vel is high ( a potential d in the human hen the switchi bjected to the the operation t from its beh ructure, a sim ate the 555’s o andle was ext ric current by t 11. metallic re or q1, respons elays k1 and k ring the minim orted in the c ion current of e current mu rate as a closed24150 160160110 1,45ma r2 of 7,5 e transistor in y & applied sci ensor circuit b t diagram of the c ated for voltag tage, its outpu hands of the eady seen, the ut impedance d, without tou (vcc) on that difference is body, turning ing of relays k rapid loading of the senso avior outside. mple touch on output. theref tended, to enab the operator's h eceptor for trigger sible for switch k2, must oper mum transistor corresponding approximately ust be at leas d switch, as dema a then ensure n the saturatio ience research donz board, as show control module ges below 1/3 ut state switch driver touche e energization of the 555 t uching the m t port. when established b g the input of k1 and k2 ha or unloading or inside a tr since the trai n the handle fore, the coppe ble the passag hands (figure r terminal hing the state rate in the satu r current gain datasheet, an y 160ma, as s st 1.45ma fo etailed in (2). (1) (2) es satisfactoril on region, sinc h v za et al.: a simp wn in of the hes to es the of the trigger metallic hand by the port 2 appens of the rain is in is a is not er ring ge of a 12). of the uration equal nd the shown or the ly the ce the bas as d fig. sens max poin the leve aga an o is p way indu bein wil the the vol. 8, no. 4, 20 ple electronic c se current prod described in (3 bb be 12. traction l sor installed. resistor r4 l ximum of 0.48 discharg... 7,5 | then, after al nt between r erefore, when er, making ter ain, the transis open switch an protected again y that if at th uction of high ng polarized i l absorb the en the mounting main module scheme outlin fig. 13. 018, 3255-3259 circuit for an a duced by the o 3). 12 ,, 1,5 lever with extend limits the disc 8s as shown in|| ∗|1 ∗ 220 ∗ most half a se resistors r2 n the driver p rminal 3 of th stor takes less nd to deactiva nst reverse vo he moment of h current in th in the same d nergy that cou v. g process is si e, shown in fi ned in table i. main module en 9 automatic train output of the 51ma 1,45 ded metal ring an charge time of n (4). ∗ ln ...10 *ln 0,712 cond, the volta and r4 drop pulls his hand he ic 555 rece than half a se ate relays k1 a oltage by the d f suppression he coils of the direction of th uld damage the installat imple and take igure 13, the c nclosure and elec 3258 n safety stop sy ic 555 is 1,5 5ma (3) nd with the new f capacitor c1 0,48 (4) age of the com ps to about 0 ds off the tra eive a high vo econd to opera and k2. the sy diode d4 in su of current the e relays, the d he induced vol e transistor q1 tion es about 1 hou connections fo tronic board system 1ma, w touch 1 to a mmon 0.7v. action oltage ate as ystem uch a ere is diode, ltage, . ur. in ollow engineering, technology & applied science research vol. 8, no. 4, 2018, 3255-3259 3259 www.etasr.com donza et al.: a simple electronic circuit for an automatic train safety stop system table i. electrical connections in the main module box terminal electrical connections cable function 7a 7.a 24vcc gd gd.a gd 2510.a 2510.a nc contact 2510.b 2511.a nc contact 2514.a 2514.a no contact 2503a 2503.a no contact 3 white signal 2 grey gd 1 black 12vcc a. scheme of connections in the main module board.. vi. conclusion the decision about replacing a critical system is sometimes controversial within the planning of the maintenance processes of a company. in fact, resolutions such as these consume time, resources, manpower, and should be carried out by objective considerations about the costs and benefits of the change. therefore, its effects should also be revised so that new actions can be taken after the disclosure of any unwelcome unrolling. so far, no incident has exposed any relevant vulnerability of the new dead man’s system, which is operating normally in four trains for almost a year. there are no electronic components damaged in these vehicles and no complaints from drivers regarding the new traction levers. although no unexpected event has happened, the operation of the new system continues to be monitored to evaluate the durability and the reliability of the system. in the path between the dead man’s system and the programmable logic controller of the brake control circuit, there is a device that can have its timing function incorporated through the ci 555 of the touch sensor. future developments of the project include this modification. references [1] r. ahmad, s. kamaruddin, “application and comparison of three maintenance techniques for replacement decision making – a case study in the pulp manufacturing industry”, international journal of process systems engineering, vol. 2, no. 2, pp. 135-153, 2012 [2] e. viles, d. puente, m. j. alvarez, f. alonso, “improving the corrective maintenance of an electronic system for trains”, journal of quality in maintenance engineering, vol. 13, no. 1, pp.75-87, 2007 [3] b. osoinach, proximity capacitive sensor technology for touch sensing applications, white paper, freescale semiconductor, 2008 [4] z. kappassov, j. a. corrales, v. perdereau, “tactile sensing in dexterous robot hands – review”, robotics and autonomous systems, vol. 74, part a, pp. 195-220, 2015 [5] v. gupta, a. deb, “speed control of brushed dc motor for low cost electric cars”, ieee international electric vehicle conference, greenville, usa, march 4-8, 2012 [6] k. kotcherlakota, v. chinta, “smart home automation based on 555 timer”, international journal of engineering research and application, vol. 6, no. 5, pp. 77-80, 2016 [7] h. goyal, “understanding of ic 555 timer and ic 555 timer tester”, international journal of inventive engineering and sciences, vol. 3, no. 2, pp. 4-6, 2015 microsoft word 41-2903_s_etasr_v9_n4_pp4534-4537 engineering, technology & applied science research vol. 9, no. 4, 2019, 4534-4537 4534 www.etasr.com saand et al.: experimental study on the use of rice husk ash as partial cement replacement in … experimental study on the use of rice husk ash as partial cement replacement in aerated concrete abdullah saand department of civil engineering, quaid-e-awam university of engineering, science &technology, nawabshah, sindh, pakistan abdullah@quest.edu.pk manthar ali keerio department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, sindh, pakistan mantharali99@quest.edu.pk tariq ali department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, sindh, pakistan tariqdehraj@gmail.com daddan khan bangwar department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, sindh, pakistan daddan@quest.edu.pk abstract—this paper adopts an experimental approach on the use of rice husk ash as a partial replacement of cement in the production of concrete and the consequent effects on density, compressive strength and split tensile strength of the formulated product. rice husk ash is used as replacement of cement in different dosages of 0%, 2.5%,5%, 7.5%, 10%, 12.5%, and 15%. results showed that 10% replacement of cement with rice husk ash is optimum. at 10% replacement of cement with rha, the density is increased by 5.02%, the compressive strength by 22.22% and the split tensile strength by 20.45% in comparison with control aerated concrete. keywords-aerated; non-autoclaved; rha; aluminium powder; autoclaved i. introduction nowadays, the tendency is towards the use of lightweight materials in building construction that not only help in the structural stability of the structure but also contribute in cost reduction. aerated concrete, also known as cellular concrete, is a type of lightweight concrete [1]. aerated concrete is produced by adding aluminum powder in the concrete matrix which generates hydrogen gas in the cement slurry. aerated concrete is further classified into two main types depending on the nature of curing: one is aac (autoclave aerated concrete) and the other is naac (non-autoclaved aerated concrete) [2-5]. the major advantage of aerated concrete is its light weight which helps in minimizing the self-weight of the structure including foundation and walls. aerated concrete is also very useful in heat and sound insulation. a wide density range (300±1800kg/m 3 ) of aerated concrete is available and it can be mould and cut into any desired shape. also it provides structural, partition and insulation flexibility in manufacturing products. cement is the most important component in concrete production. but cement production in huge amounts pollutes the environment as it entails huge emissions of co2 accounting for over 50% percent of all industrial co2 emissions. large numbers of natural resources are required for the production of cement which are not renewable. waste materials can be used in concrete by partially replacing cement, which not only protects the environment from pollution, but also reduces the cement demand [6]. in such pursuit the properties of aerated concrete incorporated with industrial and agriculture byproducts have been studied. these industrial and agriculture by-products can also improve concrete durability. pofa, blast furnace slag, pfa and rice husk ash, etc., have been used as cement replacement materials [7-10]. in pakistan, the most abundantly harvested crop is rice. world’s annual production of rice is about 5 million tons per year [11]. three major organic by-products from rice are rice bran, rice straw and rice husk [12]. rice husk is a waste material which is not useful for animal feeding due to its low protein content. rice husk contains a high concentration of silica, generally more than 80%-85% [13]. rice husk, in actual, is the outer layer of the rice grain, produced by the rice milling industries. rice husk consists of 30% lignin group, 20% silica and about 40% cellulose. on combustion, the cellulose-lignin matrix of rice husk burns off and leaves a porous silica skeleton only. hence, rice husk ash (rha) contains a large amount of silica [11-15]. rha is fine powder having a high surface area, produced when porous silica skeleton of rice is grinded [16]. the chemical composition of rha is attributed to calcinations process [17]. rha can be utilized as a mineral admixture for cement and concrete [18, 19] and its cementitious properties mostly depend upon its source [20-22]. ii. materials used in this study aerated concrete mixture was produced by using rha, ordinary portland cement, quartz sand, water, and aluminum powder. opc complies with the type i portland corresponding author: tariq ali engineering, technology & applied science research vol. 9, no. 4, 2019, 4534-4537 4535 www.etasr.com saand et al.: experimental study on the use of rice husk ash as partial cement replacement in … cement as in astm c150 (1992) and bs 12 (1991). the rice husk was collected from a rice mill and the rha was synthesized in the laboratory with the use of an electric furnace for an hour at 500 o c. it was grounded before being passed through a no. 325 sieve. approximately 76.75% of the content of rha is oxide (i.e. alumina, iron oxide and silica). the rha follows the specifications of astm c 618. over the entire casting, sand passing from 600µm was used. aluminum powder was used as an aerating agent. table i. opc and rha physical characteristics sample specific gravity opc 3.15 rha 2.12 iii. experimental work seven different mixes were prepared, including control mix (for details, see table ii). each mix consisted of 5 samples. at first, cement, sand and rha were mixed in dry state and then the aluminum powder was mixed properly in that dry mix. after that, water was added properly as per mix requirements, and then cubic moulds of 100mm×100mm×100mm size and cylindrical moulds of size 150mm×300mm were filled. the moulds were filled up to 80% and then they were placed for 24h in open atmosphere. pouring expansion started due to aluminum powder and approximately after 3h, the specimens became rigid, inflexible, hard enough and ready to trim the expanded portion above the top of the specimens. after demoulding, samples were placed in water for curing for the next 28 days. figures 1 and 2 show the aerated concrete cubical and the aerated concrete cylindrical specimens respectively, before trimming. before being subjected to compression and splitting tensile testing, the samples were weighed and their density was determined. table ii. mix proportions cement replacement level (%) mix proportion cement (kg) rha (kg) sand (kg) w/c ratio (%) aluminum content (% by wt. of binder) 0.0 1:1 10 0 10 0.60 0.5 2.5 1:1 9.75 0.25 0.61 0.5 5.0 1:1 9.5 0.5 0.62 0.5 7.5 1:1 9.25 0.75 0.63 0.5 10.0 1:1 9.0 1.0 0.64 0.5 12.5 1:1 8.75 1.25 0.65 0.5 15 1:1 8.5 1.5 0.66 0.5 iv. results and discussion this study aimed to investigate the properties of aerated concrete composite with rha in order to produce aerated concrete. the specific gravity of opc is 3.15, this value indicates that cement particles are heavier than rha whose specific gravity is 2.12 as mentioned in table i. the most important characteristic of aerated concrete is its lower density when it is compared with the density of conventional concrete it ranges from 300kg/m 3 to 1800 kg/m 3 . from table iii and figure 3, it is observed that using rha in aerated concrete production causes an increase in density. cement replacement with rha reduced the aeration process which ultimately increased the density of aerated concrete. maximum density, 1066kg/m 3 , was found at 10% rha replacent (i.e. 5.02% increase) as compared to the control mix of aerated concrete and then density started decreasing at 12.5% and 15% replacement ratios due to the difference between specific gravity values of cement and rha. fig. 1. aerated concrete cubical specimens before trimming fig. 2. aerated concrete cylindrical specimens before trimming table iii. density and compressive strength by partial replacement of cement with rha at 28 days curing aerated concrete mix density (kg/m 3 ) compressive strength (mpa) split tensile strength (mpa) 0% 1015 3.6 0.44 2.5% 1022 3.7 0.46 5% 1035 3.9 0.47 7.5% 1050 4.1 0.49 10% 1066 4.4 0.53 12.5% 1060 4.2 0.51 15% 1056 3.8 0.49 all the densities found in this research lie in the range of aerated concrete as shown in table iii. it was observed that with the increase in replacement ratio of cement with rha, the compressive strength and split tensile strength increased due to the pozzolanic properties of rha. compressive strength and split tensile strength increased as compared to control mix by the substitution of cement with the rha from 2.5% to 10% and on further substitution of cement, compressive and split tensile strength decreased. at 10% replacement of cement with rha, the maximum compressive strength and split tensile strength were found to be 4.4mpa (22.22% increase) and 0.53mpa (20.45% increase) respectively as compared to the control the of aerated concrete (figures 45). engineering, technology & applied science research vol. 9, no. 4, 2019, 4534-4537 4536 www.etasr.com saand et al.: experimental study on the use of rice husk ash as partial cement replacement in … fig. 3. density of rha aerated concrete fig. 4. compressive strength of rha aerated concrete fig. 5. split tensile strength of rha aerated concrete it is worth noting that with the increase in the rha percentage, more water was required (the water-binder ratio is shown in table ii). as the quantity of water increased and cement was replaced by rha in percentages above 10% in increasing order, the compressive and split tensile strength decreased. v. conclusions this paper mainly focused on the utilization of the waste agricultural material rha, as a potential replacement of cement in the production of aerated concrete. based on the research the following conclusions are made: • the density of modified mixes increased as compared to the control mix by the substitution of cement with rha from 2.5% to 10% and decreased on further substitution. at 10% replacement, the maximum density was found at 1066kg/m 3 (5.02% increase). • the compressive strength of modified mixes increased with the substitution of cement with rha from 2.5% to 10%. on further substitution, the compressive strength decreased. at 10% replacement, the maximum compressive strength was found at 4.4mpa (22.22% increase). • split tensile strength of modified mixes increased as compared to control mix by the substitution of cement with rha from 2.5% to 10% and on further substitution, it decreased. at 10% replacement of cement with rha, the maximum split tensile strength was found as 0.53 mpa (20.45% increase) as compared to the control mix. • on the basis of conducted parameters of aerated concrete, 10% replacement of cement with rha is optimum. at 10% replacement, a slight increase in density (5.02%) and more in compressive and split tensile strength (22.22% and 20.45% respectively) were observed as compared to control aerated concrete. acknowledgement the authors acknowledge the quaid-e-awam university for the provision of the necessary funds required for this research. references [1] a. m. neville, j. j. brooks, concrete technology, pearson education, 2010 [2] l. b. yen, study of water ingress into foamed concrete, msc thesis, national university of singapore, 2006 [3] z. li, advanced concrete technology, john wiley & sons, 2011 [4] a. j. hamad, “materials, production, properties and application of aerated lightweight concrete: review”, international journal of materials science and engineering, vol. 2, no. 2, pp. 152-157, 2014 [5] n. narayanan, k. ramamurthy, “structure and properties of aerated concrete: a review”, cement and concrete composites, vol. 22, no. 5, pp. 321-329, 2000 [6] t. mehmannavaz, s. r. sumadi, m. a. r. bhutta, m. samadi, s. m. sajjadi, “effect of waste materials in lightweight concrete”, australian journal of basic & applied sciences, vol. 7, no. 11, pp. 513-519, 2013 [7] n. a. memon, s. r. sumadi, m. ramli, “lightweight aerated concrete incorporating various percentages of slag and pfa”, journal of applied sciences, vol. 6, no. 7, pp. 1560-1565, 2006 [8] n. a. memon, s. r. sumadi, m. ramli, “ferrocement encased lightweight aerated concrete: a novel approach to produce sandwich composite”, materials letters, vol. 61, no. 19-20, pp. 4035-4038, 2007 [9] n. narayanan, k. ramamurthy, “microstructural investigations on aerated concrete”, cement and concrete research, vol. 30, no. 3, pp. 457-464, 2000 [10] p. k. mehta, “reducing the environmental impact of concrete”, concrete international, vol. 23, no. 10, pp. 61-66, 2001 [11] g. r. d. sensale, “strength development of concrete with rice husk ash”, cement and concrete composites, vol. 28, no. 2, pp. 158-160, 2006 [12] r. begum, a. habib, s. mostafa, “effects of rice husk ash on the nonautoclaved aerated concrete”, international journal of engineering innovations and research, vol. 3, no. 1, pp. 116-120, 2014 [13] r. siddique, waste materials and by-products in concrete, springer, 2008 engineering, technology & applied science research vol. 9, no. 4, 2019, 4534-4537 4537 www.etasr.com saand et al.: experimental study on the use of rice husk ash as partial cement replacement in … [14] v. sata, c. jaturapitukkul, k. kiattikomol, “influence of pozzolan from various by-product materials on mechanical properties of high-strength concrete”, construction and building materials, vol. 21, no. 7, pp. 1589-1598, 2007 [15] p. chindaprasirt, c. jaturapitukkul, u. rattanasak, “influence of fineness of rice husk ash and additives on the properties of lightweight aggregate”, fuel, vol. 88, no. 1, pp. 158-162, 2009 [16] s. aroni, “on energy conservation characteristics of autoclaved aerate concrete”, materials and structures, vol. 23, no. 1, pp. 68-77, 1990 [17] g. r. d. sensale, “effect of rice-husk ash on the durability of cementitious materials”, cement and concrete composites, vol. 32, no. 9, pp. 718-725, 2010 [18] p. k. mehta, rice-husk ash-a unique supplementary cementing material, advances in concrete technology, 1992 [19] 73-sbc rilem committee, “final report siliceous by-products for use inconcrete”, material and structures, vol. 21, no. 1, pp. 69-80, 1988 [20] v. m. malhotra, p. k. mehta, pozzolanic and cementitious materials, gordon and breach publishers, 1996 [21] j. james, m. s. rao, “reactivity of rice husk ash”, cement and concrete research, vol. 16, no. 3, pp. 296-302, 1986 [22] k. kunchariyakun, s. asavapisit, k. sombatsompop, “properties of autoclaved aerated concrete incorporating rice husk ash as a partial replacement for fine aggregate”, cement and concrete composites, vol. 55, pp. 11-16, 2015 microsoft word 04-3455_s_etasr_v10_n3_pp5603-5607 engineering, technology & applied science research vol. 10, no. 3, 2020, 5603-5607 5603 www.etasr.com bouazzi et al.: computational modeling of quasi-periodic rudin-shapiro multilayered band gap … computational modeling of quasi-periodic rudinshapiro multilayered band gap structure yassine bouazzi industrial engineering department university of hail hail, saudi arabia yassine.bouazzi@enit.utm.tn naim ben ali industrial engineering department university of hail hail, saudi arabia naimgi2@yahoo.fr haitham alsaif electrical engineering department university of hail hail, saudi arabia hal-saif@hotmail.com attia boudjemline industrial engineering department university of hail hail, saudi arabia a_boudjemline@hotmail.com youssef trabelsi physics department king khalid university aseer, saudi arabia youssef_trabelsi@yahoo.fr ahmed torchani industrial engineering department university of hail hail, saudi arabia tochahm@yahoo.fr abstract—the optical transmission spectra proprieties of the onedimensional quasi-periodic multilayered photonic structures according to the rudin-shapiro distribution are studied theoretically in this paper by using a theoretical model based on the transfer matrix approach for normal incidence geometry. the influence of the layer number has been studied, i.e. the iteration order of the generating sequence of the quasi-periodic structure on the structure spectral behavior and the width of the photonic band gap (pbg). it was found that the width of the pbg is proportional to the index contrast. keywords-photonic crystal; rudin-shapiro distribution; transfer-matrix method; transmittance; photonic band gap i. introduction photonic crystals are new, artificially created materials in which the refractive index is periodically modulated in a scale compared to the wavelength of operation [1-4]. in fact, the periodic modulation of the refractive index of such a structure causes the appearance of frequency ranges for which the light cannot propagate [5]. photonic crystals at the end of the last century became one of the most active research topics in various technological disciplines, e.g. communications, optoelectronics, and optics [6, 7]. the simplest form of a photonic crystal is the one-dimensional periodic structure, known as the bragg mirror. it consists of a stack of alternating layers with low and high refractive index and a thickness in the order of ��/4, where �� is the reference wavelength, i.e. the thicknesses satisfy the bragg condition. there is currently a need to design photonic materials with broader band gaps and multiband. the first manifestation of this goal was the realization of a new class of artificial crystals, called quasiperiodic photonic crystals [8]. these structures are formed by the stacking of two or more deposited materials according to a predefined recursive inflation rule, so that they can be considered as intermediate systems between an ordinary periodic crystal and random amorphous solids. these quasiperiodic structures have become the subject of intense research. they have led to many technological achievements in the fields of photonics, telecommunications, and microwaves [9]. this paper aims to study the optical properties of the photonic quasi-periodic unidimensional multilayer structures from their spectral response using theoretical modeling and numerical simulation based on the transfer matrix method (tmm). ii. modeling procedure and numerical simulation a. structure presentation the rudin-shapiro sequence, also known as the golayrudin-shapiro sequence, is an infinite automatic sequence [10, 11] introduced in 1950 [12]. rudin-shapiro's 1d multilayered distribution system was exploited for the first time to study light confinement in multilayer structures in 2008 [13]. the rudin-shapiro sequence can be defined by [14-15]: rs(�) = ����� ...ε� ...ε�����. (1) with: �� = (−1)�(�) (2) where u(i) represents the number “11” in the binary development of the integer i. the use the rudin-shapiro distribution in the photonics field remains very limited due to the construction peculiarity of this structure. it is represented by quaternary elementary layers (a, b, c and d) with substitution rules given by: � as={a, b, c, d} → ab, b → ac, c → db, d → dc (3) corresponding author: yassine bouazzi engineering, technology & applied science research vol. 10, no. 3, 2020, 5603-5607 5604 www.etasr.com bouazzi et al.: computational modeling of quasi-periodic rudin-shapiro multilayered band gap … the generation starts with the element labeled by the letter a. for example, a multilayer structure of iteration order 2 is given by: s2 acab, order 3 by s3 acabacdc… (figure 1). table i presents the generation of the structure of iteration order k=1,2,3. table i. the first generations of the 1d multilayer structure according to the rudin-shapiro distribution iteration order alphabetic sequence rs(0) a rs(1) ac rs(2) acab rs(3) acabacdc in this work, we chose a multilayer photonic system composed of four dielectric layers a, b, c and d, distributed according to the rudin-shapiro sequence, having refraction indices �" , �# , �$ and �% , and optical thicknesses ��/n" , ��/n# , ��/n$ and ��/n% respectively, where �� is the reference wavelength. furthermore, the optical and geometrical parameters of the structure obey the quarter wavelength condition or bragg condition as indicated by (4): �"'" �#'# �$'$ �%'% ()* (4) fig. 1. one-dimensional rudin-shapiro multilayer dielectric structure for the 3 rd iteration rs(3): acabacdc b. simulation method for the calculation of reflection and transmission, we used tmm, which is a technique well suited to the study of pbg materials. this technique can solve the standard problem of the photonic band structures to find transmission, reflection, and absorption spectra. this method consists in expressing the reflected field +,-�� from a multilayer structure as a function of incident fields +,-�. in a matrix form. the studied multilayer structure consists of a stack of m layers with different thicknesses '� and refractive indices ��, as shown in figure 2. the amplitudes of the electric fields of incident and transmitted wave are expressed by the following matrix for stratified films within m layers: /+�.+�� 0 = ∏ 234.�� /+4.� .+4.�� 0 (5) where 23 is the propagation matrix for the jth layer, given by: 23 = 5 �67 exp ��;<3�� =767 exp �;<3�� =767 exp ��;<3�� �67 exp ��;<3�� > (6) where <j-1 denotes the change in the phase of the wave between �a � 1 6b and a6b layers, and can be obtained by: c d� 0d3�� f( �g3��'3�� hijk3�� (7) l3 and m3are the fresnel transmission and reflection coefficients at the interface between �a � 1 6b and a6b layer. the fresnel coefficients are expressed using the complex refractive index �3 and the complex refractive angle k3: for the tm mode, the coefficients are: m3no �g7pq rst u7��g7 rstu7pq�g7pq rst u7.�g7 rstu7pq (8) l3no �g7pq rst u7pq�g7pq rstu7.�g7 rstu7pq (9) and for the te mode: m3nv �g7pq rst u7pq��g7 rst u7�g7pq rst u7pq��g7 rst u7 (10) l3nv �g7pq rst u7pq�g7pq rst u7pq.�g7 rst u7 (11) fig. 2. multilayer system with m components taking +4.�� = 0, there will be no reflections from the interface of the final structure. convenient formulas have been obtained for the total reflection and transmission coefficients, which correspond to the amplitude reflectance r and transmittance t respectively, as follows [16-19]: m = nwqnqq (12) l = �nqq (13) where x�� and x � are the matrix elements of the product matrix: ∏ 234.�� = /x�� x� x � x� 0 (14) starting from (12) and (13), the reflection r and the transmission t are given by [6]: y = |m| = [nwqnqq [ (15) x |l| [ �nqq[ (16) high index layer na low index layer nc zzzz θθθθ incident wave xxxx yyyy high index layer nb low index layer nd engineering, technology & applied science research vol. 10, no. 3, 2020, 5603-5607 5605 www.etasr.com bouazzi et al.: computational modeling of quasi-periodic rudin-shapiro multilayered band gap … iii. numerical results and discussion figure 2 shows the reflection spectra with normal incidence for the quasi-periodic multilayer system distributed according to the generalized rudin-shapiro model. we choose the following four materials as elementary layers of the stack: tio2 (na=2.3), hfo2 (nb=2), sio2 (nc=1.45) and tao5 (nd=2.2). (a) (b) (c) (d) fig. 3. the reflection spectra of rudin-shapiro distribution multilayer photonic structures for: (a) 4 th , (b) 5 th , (c) 6 th , and (d) 7 th iteration we notice from the spectra in figure 3 that the width of the photonic band gap of the studied system increases with the order of generation k. the width of the pbg (figure 4) observed near λ0=0.5µm increases when progressing from one iteration to another. fig. 4. variation of the pbg width as a function of the number of iterations (k) table ii. width and limitations of pbgs iteration k ∆∆∆∆λλλλpbg (µµµµm) 6 0.0898 7 0.0972 8 0.1002 9 0.1025 10 0.1039 11 0.1039 12 0.1039 figure 5 and table iii show the evolution of the maximum reflection rmax(%) as a function of the iteration k. we can consider that the first pbg appears for the 6 th iteration with pbg width ∆λpbg=0.1039µm. table iii. variation of rmax (%) according to k iteration k rmax (%) 2 0 3 29.7051 4 81.2423 5 96.2897 6 99.9874 7 99.9999 8 100 9 100 10 100 fig. 5. variation of rmax (%) as a function of the iteration value k we notice that starting from the 7 th iteration two transparent windows (figure 6) located in the central pbg and almost symmetrical to λ0=0.5µm with t=100% appear. these optical windows indicate a strong light confinement in the microcavities of low refractive indices formed by the quasiengineering, technology & applied science research vol. 10, no. 3, 2020, 5603-5607 5606 www.etasr.com bouazzi et al.: computational modeling of quasi-periodic rudin-shapiro multilayered band gap … periodic stack for the corresponding wavelengths. this last characteristic makes the system a good candidate for the design of an optical filter. fig. 6. number and position of optical windows according to the number of iterations k table iv. widths of pbgs, number of optical windows and their positions, according to the number of iterations k k ∆λpbg optical windows number positions 6 0.0898 7 0.0972 2 0.4636-0.5421 8 0.1002 2 0.4568-0.5515 9 0.1025 2 0.4548-0.5550 10 0.1039 2 0.4544-0.5564 11 0.1039 2 0.4542-0.5564 12 0.1039 2 0.4542-0.5564 the objective of the remaining part of this work is to check the correlation between the width of the pbg and the indices ratio nh/nl, with nh and nl representing the high and the low refractive indices respectively. we studied the reflection of the one-dimensional rudin-shapiro photonic structure as a function of the index contrast. the index contrast or the optical contrast is defined as the ratio between the high and low refractive indices of the layers constituting the structure. for a one-dimensional structure, the index contrast is given by [14]: \ = �]/�^ (17) figures 7(a) and (c) show the optical reflection of a multilayer structure based on the rudin-shapiro model for the 5 th and 6 th iterations respectively, as a function of the index contrast and wavelength. figures 7(b) and (d) illustrate the maps of the pbgs for the 5 th and 6 th iterations, respectively, where the blue zone represents the forbidden bands and the white zone the permissible ones. we observe that for the 5 th iteration, the first pbg appears with index contrast δ≈1.774 and the width and number of pbgs increase considerably with the index contrast. moreover, from table v, we notice that the difference between the middle of the pgb (λm) and the reference wavelength (λ0=0.5) increases with the increase in the index contrast. (a) (b) (c) (d) fig. 7. spectral aspect as a function of the contrast variation for the rudin-shapiro distribution. (a), (c) variation of reflection spectra as a function of contrast and wavelength for the 5 th and 6 th iterations respectively. (b), (d) pbgs maps as a function of contrast and wavelength for the 5 th and 6 th iterations respectively table v. variation of the pbgs width and positions according to the index contrast δδδδ=nh/nl 5th iteration 6th iteration λmax λmin λm ∆λbpg λmax λmin λm ∆λbpg 1,6 0,4625 0,5437 0,5031 0,0812 1,9 0,4581 0,5506 0,5044 0,0925 0,4452 0,5718 0,5085 0,1266 2,2 0,4420 0,5746 0,5083 0,1326 0,4344 0,5898 0,5121 0,1554 2,5 0,4332 0,5922 0,5127 0,1590 0,4280 0,5998 0,5139 0,1718 2,8 0,4260 0,6038 0,5149 0,1778 0,4044 0,6310 0,5177 0,2266 iv. conclusion based on the simulation of the photometric response of the rudin-shapiro multilayer structures as a function of the iteration k we found that the number of pgbs and their widths increase with k due to the increase of the number of layers from one iteration to another, which results in the generation of multiple internal reflections in the structure giving rise to more constructive interferences. the latter prevents certain wavelengths from propagating in the system in order to increase the width of the pbg. additionally, the influence of the index contrast on the photonic band gap was investigated. it was found that the width of the pbg is proportional to the engineering, technology & applied science research vol. 10, no. 3, 2020, 5603-5607 5607 www.etasr.com bouazzi et al.: computational modeling of quasi-periodic rudin-shapiro multilayered band gap … index contrast. moreover, the number of pgbs increases considerably and their position shifts according to the index ratio so that the medium becomes more and more inhibiting for the propagation of light. indeed, the increase of the index contrast generates more internal reflections on the interfaces of the high refractive indices’ layers. acknowledgment we would like to acknowledge the research deanship of university of hail for the funding under the project rg191250. references [1] k. yasumoto, electromagnetic theory and applications for photonic crystals, crc press, 2006 [2] m. johri, y. a. ahmed, t. bezboruah, “photonic band gap materials: technology, applications and challenges”, current science, vol. 92, no. 10, pp. 1361-1366, 2007 [3] p. k. bhattacharya, “photonic crystal devices”, journal of physics d: applied physics, vol. 40, no. 9, 2007 [4] s. hong-yi, l. zhi-yean, g. ben-yuan, “defect modes in multipleconstituent one-dimensional photonic crystals examined by an analytic bloch-mode approach”, chinese physics letters, vol. 22, no. 2, pp. 365-368, 2005 [5] a. h. aly, “electromagnetic propagation characteristics in one dimensional photonic crystal”, in wave propagation in materials for modern applications, intech, pp. 193-200, 2011 [6] w. a. goddard, handbook of nanoscience, engineering, and technology, crc press, 2003 [7] i. iliev, m. nedelchev, e. markov, “a novel 2d z-shaped electromagnetic bandgap structure”, engineering, technology & applied science research, vol. 5, no. 1, pp. 760-763, 2015 [8] d. schechtman, i. blech, d. gratias, j. w. cahn, “metallic phase with long-range orientational order and no translational symmetry”, physical review letters, vol. 53, no. 20, article id 1951, 1984 [9] a. bousselmi, a. gharsallah, t. p. vuong, “a novel high-gain quadband antenna with amc metasurface for satellite positioning systems”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4581-4585, 2019 [10] m. rattier, h. benisty, c. j. m. smith, a. bernaud, d. cassagne, c. jouanin, t. f. krauss, c. weisbuch, “performance of waveguide-based two-dimensional photonic-crystal mirrors studied with fabry-perot resonators”, ieee journal of quantum electronics, vol. 37, no. 2, pp. 237-243, 2001 [11] j. h. kim, l. chrostowski, “fabry-perot cavity design in algaas/gaas using a photonic crystal slab for a resonant cavity detector”, 19th annual meeting of the ieee lasers and electro-optics society, montreal, canada, october 29-november 2, 2006 [12] j. p. allouche, p. liardet, “generalized rudin–shapiro sequences”, acta arithmethmetica, vol. 60, no. 1, pp. 1-27, 1991 [13] v. agarwal, m. e. mora-ramos, b. alvarado-tenorio, “optical properties of multilayered period-doubling and rudin-shapiro porous silicon dielectric heterostructures”, photonics and nanostructures– fundamentals and applications, vol. 7, no. 2, pp. 63-68, 2008 [14] w. rudin, “some theorems on fourier coefficients”, proceedings of the american mathematical society, vol. 10, no. 6, pp. 855-859, 1959 [15] h. s. shapiro, extremal problems for polynomials and power series, msc thesis, massachussetts institute of technology, 1951 [16] z. y. li, “principles of the plane-wave transfer-matrix method for photonic crystals”, science and technology of advanced materials, vol. 6, no. 7, pp. 837–841, 2005 [17] y. zeng, y. fu, x. chen, w. lu, h. agren, “extended planewave-based transfer-matrix approach to simulating dispersive photonic crystals”, solid state communications, vol. 139, no. 7, pp. 328-333, 2006 [18] a. mouldi, m. kanzari, “design of microwave devices exploiting fibonacci and hybrid periodic/fibonacci one dimensional photonic crystals”, progress in electromagnetics research b, vol. 40, pp. 221– 240, 2012 [19] k. ben abdelaziz, j. zaghdoudi, m. kanzari, b. rezig, “a broad omnidirectional reflection band obtained from deformed fibonacci quasi-periodic one dimensional photonic crystals”, journal of optics a: pure and applied optics, vol. 7, pp. 544–549, 2005 microsoft word 26-3499_s_etasr_v10_n3_pp5728-5731.doc engineering, technology & applied science research vol. 10, no. 3, 2020, 5728-5731 5728 www.etasr.com chandio et al.: effect of fly ash on the compressive strength of green concrete effect of fly ash on the compressive strength of green concrete sheeraz ahmed chandio department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan sheerz.ahmed030@gmail.com bashir ahmed memon department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan bashir_m@hotmail.com mahboob oad department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan engrmahboob04@gmail.com faraz ahmed chandio department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan farazahmedchandio04@gmail.com muhammad usama memon department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan usama.memon9344@gmail.com abstract—this research paper aims at investigating the effects of fly ash as cement replacement in green concrete made with partial replacement of conventional coarse aggregates with coarse aggregates from demolishing waste. green concrete developed with waste materials is an active area of research as it helps in reducing the waste management issues and protecting the environment. six concrete mixes were prepared using 1:2:4 ratio and demolishing waste was used in equal proportion with conventional aggregates, whereas fly ash was used from 0%-10% with an increment of 2.5%. the water-cement ratio used was equal to 0.5. out of these mixes, one mix was prepared with all conventional aggregates and was used as the control, and one mix with 0% fly ash had only conventional and recycled aggregates. the slump test of all mixes was determined. a total of 18 cylinders of standard size were prepared and cured for 28 days. after curing the compressive strength of the specimens was evaluated under gradually increasing load until failure. it is observed that 5% replacement of cement with fly ash and 50% recycled aggregates gives better results. with this level of dosage of two waste materials, the reduction in compressive strength is about 11%. keywords-green concrete; recycled aggregates; demolishing waste; fly ash; compressive strength i. introduction the research of finding alternatives or partial replacements of concrete ingredients is active, aiming at minimizing the environmental impact of concrete making and increasing the strength of the final concrete. the management of demolishing waste poses a serious problem, and this is a reason why it has been tried as coarse aggregates in new concrete. however, due to the age of concrete and old mortar adhered affects, the properties of aggregate and produced green concrete (concrete made with recycled aggregates from demolishing waste), particularly strength, are reduced and ways of mitigating this problem constitute an active research area. recent developments on use of waste, its processing to develop coarse aggregates of required size, etc. have been presented in [1]. environmental effects of green concrete [2] and green concrete towards sustainable environment [3] have also been studied. the scatter in published results of using waste shows that more work is required in the area to develop confidence in its practical use. fly ash is a very fine powder which is a combustion byproduct. large volumes of this waste are generated every year posing a serious environmental problem. to reduce the waste to some extent, it may be used as pozzolanic (siliceous and aluminous) material, replacing cement in concrete. with the addition of water it reacts with calcium hydroxide and produces cementitious compounds. the use of fly ash in concrete as sustainable material has been reviewed in [4-7]. authors in [8] used fly ash to develop concrete without increasing co2 emissions. they also proposed stainless steel as reinforcement and a cladding system for better durability. the use of fly ash in conventional high strength concrete has been studied in [9]. from the test results the authors observed an increase in strength and a reduction in sorptivity at 28-day curing. authors in [10] used 20%, 40% and 60% replacement of cement by fly ash to develop m15, m20, and m25 concrete. after studying the basic and strength properties of concrete, the acquired curves can be utilized to determine the dosage of fly ash for a required strength of the concrete. authors in [11] studied the use of fly ash as engineered cementitious composite in high volumes to investigate micromechanics properties. they concluded that the use of the fly ash increases tensile strain capacity. however, the dosage of fly ash depends on compressive strength. in a research attempt to develop cement corresponding author: mahboob oad engineering, technology & applied science research vol. 10, no. 3, 2020, 5728-5731 5729 www.etasr.com chandio et al.: effect of fly ash on the compressive strength of green concrete free concrete, authors in [12] used fly ash with alkaline solutions to develop mix design standards. to justify their proposal, the authors developed specimens and studied the properties of concrete. the comparison of the results with conventional concrete’s shows good correlations between the two sets. authors in [13], based on laboratory investigations on the use of fly ash from 10% to 30% by volume of cement, argued that the use of fly ash has a negative impact on concrete’s compressive strength. moreover, the use of fly ash in a percentage up to 20% results in increase in tensile strength and density. authors in [14] on the other hand developed m20 grade concrete with 0%-20% fly ash with increment of 5%. test results of 7and 28-day cured samples showed improvement in terms of strength and durability. authors in [15] used rice husk ash (rha) in concrete and concluded that the compressive and tensile strength of the concrete specimens increased 11.8% and 7.31%, respectively when 10% rha was used and after 28 days of curing. authors in [16] used palm kernel shell ash (pksa) in concrete to assess the compressive strength and discussed that the use of pksa as a partial replacement for cement in concrete, at lower volume of replacement, enhances the reduction of cement usage in concrete, thereby reducing production cost. authors in [17] also studied the effect of fly ash. they used a dosage of fly ash from 0%-30% and quarry dust. from the obtained results, they concluded that the combined use of quarry dust and fly ash showed improvement in strength while reducing the environmental impact. from the above discussion it may be observed that the use of fly ash as cementitious material, particularly in concrete made with partial replacement of coarse aggregates from demolished concrete, is very little and the scattering of results indicates that more work is required in order to have clear understanding of the combined effects of the materials on the strength properties of concrete. therefore, this research work proposes the study of the effects of the addition of fly ash as replacement of cement on the compressive strength of recycled aggregate concrete (green concrete). ii. materials and testing ordinary portland cement (pak land) was used in the mixes. fine aggregates (hill sand) were obtained from the local market. the sand was sieved to remove lumps and larger particles before used in the concrete mixes. a demolished 2story reinforced concrete building in nawabshah was the source of demolishing waste. the large blocks were hammered to produce coarse aggregates of maximum size equal to 25 mm. after removing the unwanted material, the aggregates were washed and dried. conventional coarse aggregates of the same size, obtained from the local market, were also washed and dried. the fly ash used in the current work was class c fly ash obtained from the thar power plant. it was used in percentages of 0%, 2.5%, 5%, 7.5% and 10% by weight as replacement of cement. figure 1 shows photos of the materials. sieve analysis of both of the aggregates, conventional and recycled was done following the standard procedure to ensure well graded aggregates in the concrete mix (figure 2). coarse aggregates from demolishing waste and conventional coarse aggregates were used in 50%-50% ratio following the recommendations of [18]. all the ingredients were mixed in 1:2:4 proportions with 0.5 water-cement ratio. a total of six concrete mixes were prepared. in four concrete mixes, fly ash (fa) and recycled aggregates (ra) from demolishing waste were used. in one mix only demolishing waste as coarse aggregates was used, and one concrete mix was prepared with all-conventional ingredients (control). the batching of all the mixes was done by weight in a concrete mixer. the water used was obtained from the local water supply and had a ph value equal to 6.7. fig. 1. concrete ingredients: large blocks of old concrete, recycled coarse aggregates after sizing, fine aggregates, and fly ash fig. 2. aggragates sieve analysis a. workability to check the workability of concrete slump cone test was done for all concrete mixes. the test was performed following the standard procedure prescribed by the relevant testing standard. the obtained results are given in table i. table i. slump cone test results batch no description slump (mm) 1 conventional concrete 23.0 2 0% fa & 50% ra 15.0 3 2.5% fa & 50% ra 16.3 4 5% fa & 50% ra 16.0 5 7.5% fa & 50% ra 15.8 6 10% fa & 50% ra 14.9 b. preparing and curing of specimens from each concrete mix, three cylinders of standard size 6"×12" were prepared. mould preparation, pouring of concrete and compaction was done in accordance with astm 943–17. engineering, technology & applied science research vol. 10, no. 3, 2020, 5728-5731 5730 www.etasr.com chandio et al.: effect of fly ash on the compressive strength of green concrete after 24 hours, the specimens were demoulded and left to airdry. all the specimens were cured by fully immersing in potable water for 28 days. figures 3 and 4 show the specimens after drying and during curing respectively. fig. 3. concrete cylinders fig. 4. curing of specimens fig. 5. strength testing c. compressive strength after the completion of curing time, the specimens were air dried for 24 hours. then, the test for compressive strength was performed in a universal testing machine (utm). the utm was set to apply the load at a rate of 0.5kn/sec. the load was increased until failure (figure 5). the compressive strength computed from the failure load and correctional dimensions of the specimens was recorded and is listed in table ii. table ii. compressive strength results batch no description load compressive strength kn n/mm 2 psi kg/cm 2 1 conventional concrete 493.2 27.06 3923.37 275.99 515.1 28.26 4097.58 288.24 510.7 28.02 4062.58 285.78 2 0% fa & 50% ra 456.9 25.07 3634.61 255.68 366.7 20.12 2917.07 205.20 394.9 21.66 3141.40 220.98 3 2.5% fa & 50% ra 391.6 21.48 3115.15 219.13 395.6 21.70 3146.97 221.37 380.9 20.90 3030.03 213.15 4 5% fa & 50% ra 412.1 22.61 3278.22 230.61 494.6 27.13 3934.51 276.77 448.7 24.62 3569.38 251.09 5 7.5% fa & 50% ra 484.9 26.60 3857.34 271.34 406.9 22.32 3236.86 227.70 360.6 19.78 2868.55 201.79 6 10% fa & 50% ra 393.0 21.56 3126.29 219.92 397.5 21.81 3162.08 222.44 305.2 16.74 2427.84 170.79 iii. results and discussion the sieve analysis results shown in figure 2 show that both aggregates confirm the standard requirements of well graded aggregates. the trend of both curves is almost similar, with minor differences in range values over a sieve. the slump test results of the fa and ra mixes were less than that of the conventional concrete. the percentile reduction in slump of the tested proposed mixes is shown in figure 6. it may be observed that increasing dosage of fa increased the reduction in the slump value of the mix. minimum reduction in slump was observed for 2.5% and 5% replacement levels of cement with fa and was about 30%. this shows that the mix water requirements are more with fa. this should be considered while selecting the water/cement ratio for the mix otherwise more mechanical effort or admixture will be required to maintain the required workability. fig. 6. percentile reduction of slump engineering, technology & applied science research vol. 10, no. 3, 2020, 5728-5731 5731 www.etasr.com chandio et al.: effect of fly ash on the compressive strength of green concrete the compressive strength of all specimens presented above is averaged and compared with the average compressive strength of control mix in figure 7. the percentile reduction of average compressive strength with respect to control mix and the mix cast with 50% recycled aggregates is shown in table iii. it may be observed that the addition of 5% fa along with 50% ra gives maximum compressive strength among all proposed mixes. the reduction in the average strength in comparison to the control mix is equal to 10.77%. this reduction is comparable with the result presented in [13]. therefore, 5% of the fly ash is the optimum dosage of this material, and it can comfortably be used in new concrete along with 50% recycled aggregates from demolishing waste. however, the concrete may initially be used in low load areas as it has about 11% less strength than conventional concrete. fig. 7. average compressive strength table iii. average compressive strength reduction batch no description error (%) 1 conventional concrete 0.00 2 0% fa & 50% ra -19.78 0.00 3 2.5% fa & 50% ra -23.10 -4.14 4 5% fa & 50% ra -10.77 11.24 5 7.5% fa & 50% ra -17.55 2.78 6 10% fa & 50% ra -27.87 -10.08 iv. conclusion in this research paper, fly ash and recycled aggregates obtained from demolishing waste were used in concrete mixes and their effect on the compressive strength of concrete was studied. workability and compressive strength of the prepared mixed were measured and compared with all-conventional concrete’s. the results show that slump value reduces with increase in fly ash dosage, hence the concrete requires more mechanical effort in compaction or use of admixture to maintain its workability. compressive strength results showed that 5% dosage of fly ash is optimum as it gives minimum reduction (about 11%) in compressive strength among all studied mixes. this concrete can be used in new constructions, but it is proposed to be initially utilized in low load areas. references [1] b. a. memon, “recent development on use of demolished concrete as coarse aggregates”, international journal of emerging technology and innovative engineering, vol. 2, no. 1, pp. 1-16, 2016 [2] z. tafheem, s. khusru, s. nasrin, “environmental impact of green concrete in practice”, international conference on mechanical engineering and renewable energy, chittagong, banglades, december 22-24, 2011 [3] b. suhendro, “toward green concrete for better sustainable environment”, procedia engineering, vol. 95, pp. 305-320, 2014 [4] v. s. vairagade d. k. parbat, s. a. dhale, “fly ash as sustainable material for green concrete: a state-of-art”, international journal of research in engineering, science & technology, vol. 1, no. 2, pp. 1724, 2015 [5] n. m. altwair, s. kabir, “green concrete structures by replacing cement with pozzolanic materials to reduce greenhouse gas emissions for sustainable environment”, 6 th international engineering and construction conference, cairo, egypt, june 28-30, 2010 [6] s. c. k. bendapudi, p. saha, “contribution of fly ash to the properties of mortar and concrete”, international journal of earth sciences and engineering, vol. 4, no. 6, pp. 1017-1023, 2011 [7] n. m. altwair, s. kabir, “reducing environmental impacts through green concrete technology”, 3 rd technology and innovation for sustainable development international conference, khon kaen university, thailand, march 4-6, 2010 [8] c. edvardsen, k. tollose, “environmentally “green” concrete structures”, fib symposium: concrete and environment, berlin, germany, october 3-5, 2001 [9] p. nath, p. sarker, “effect of fly ash on the durability properties of high strength concrete”, procedia engineering, vol. 14, pp.1149-1156, 2011 [10] a. jatale, k. tiwari, s. khandelwal, “effects on compressive strength when cement is partially replaced by fly ash”, iosr journal of mechanical and civil engineering, vol. 5, no. 4, pp. 34-43, 2013 [11] s. wang, v. c. li, “engineered cementitious composites with highvolume fly ash”, aci materials journal, vol. 104, no. 3, pp. 233-241, 2007 [12] b. s. kumar, v. p. arunachalam, r. thenmozhi, t. s. vadive, “effect on strength characteristics of low calcium fly ash based geopolymer concrete: an initiative towards green concrete”, international journal of applied environmental sciences, vol. 11, no. 1, pp. 173-182, 2016 [13] c. m. helepciuc, m. barbuta, d. babor, “investigations on a green concrete obtaining through a partial cement replacement by fly ash”, advances in environmental sciences, vol. 9, no. 3, pp. 207-214, 2017 [14] s. a. k. reddy, k. c. reddy, “effect of fly ash on strength and durability parameters of concrete”, international journal of science and research, pp. 2319-7064, 2013 [15] n. bheel, a. w. abro, i. l. shar, a. a. dayo, s. shaikh, z. h. shaikh, “use of rice husk ash as cementitious material in concrete”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4209-4212, 2019 [16] d. f. a. olutoge, h. a. quadri, o. s. olafusi, “investigation of the strength properties of palm kernel shell ash concrete”, engineering, technology & applied science research, vol. 2, no. 6, pp. 315-319, 2012 [17] a. krishnamoorthi, g. m. kumar, “properties of green concrete mix by concurrent use of fly ash and quarry dust”, iosr journal of engineering, vol. 3, noi. 8, pp. 48-54, 2013 [18] m. oad, b. a. memon, “compressive strength of concrete cylinders using coarse aggregates from old concrete”, 1st national conference on civil engineering (modern trends and advancements), pakistan, april 28–29, 2014 microsoft word 15-3374_s1_etasr_v10_n2_pp5423-5427 engineering, technology & applied science research vol. 10, no. 2, 2020, 5423-5427 5423 www.etasr.com qamar et al.: edams: efficient data anonymization model selector for privacy-preserving data … edams: efficient data anonymization model selector for privacy-preserving data publishing tehreem qamar department of computer science and software engineering jinnah university for women karachi, pakistan tehreem.qamar@juw.edu.pk narmeen zakaria bawany department of computer science and software engineering jinnah university for women karachi, pakistan nsb@juw.edu.pk najeed ahmed khan department of computer science & information technology ned university of engineering & technology karachi, pakistan najeed@neduet.edu.pk abstract—the evolution of internet to the internet of things (iot) gives an exponential rise to the data collection process. this drastic increase in the collection of person’s private information represents a serious threat to his/her privacy. privacy preserving data publishing (ppdp) is an area that provides a way of sharing data in their anonymized version, i.e. keeping the identity of a person undisclosed. various anonymization models are available in the area of ppdp that guard privacy against numerous attacks. however, selecting the optimum model which balances utility and privacy is a challenging process. this study proposes an efficient data anonymization model selector (edams) for ppdp which generates an optimized anonymized dataset in terms of privacy and utility. edams inputs the dataset with required parameters and produces its anonymized version by incorporating ppdp techniques while balancing utility and privacy. edams is currently incorporating three ppdp techniques, namely k-anonymity, l-diversity, and t-closeness. it is tested against different variations of three datasets. the results are validated by testing each variation explicitly with the stated techniques. the results show the effectiveness of edams by selecting the optimum model with minimal effort. keywords-data anonymization; privacy-preserving data publishing; k-anonymity; l-diversity; t-closeness i. introduction the advent of iot, high processing speed hardware, and cloud storage with high bandwidth communication produces vast amounts of data which would be unthinkable a couple of decades ago. due to these advancements, around 2.5 quintillion bytes of data are created each day [1]. such huge production of information not only advances users’ quality of life, but also enhances various vital administrations. the data collection process is not governed by a single entity [2]. the applications used in order to perform daily routine activities efficiently are constantly saving, collecting, and tracking user data. moreover, companies are encouraged to release their micro-data in order to facilitate data analysis that eventually supports providing new business opportunities [3, 4]. however, the release of micro-data results in tracking the public and private lives of concerned individuals, thus putting their privacy at risk [3, 5, 6]. a typical data collecting and publishing scenario is depicted in figure 1. in the data collection phase, data holders gather data from individuals, i.e. record owners (e.g. ahmed, haris, laraib, sana). in the publishing phase the data are provided to data recipients who can be data miners or other third parties that can make use of that data for their own purposes. fig. 1. data collection and data publishing the published records may contain sensitive information [7-11]. to secure data owners’ privacy and to avoid data exploitation, eradicating identifiable attributes like name, address, telephone number, and social security numbers is a common practice prior to data release. however, this simplistic technique is not sufficient to guarantee the protection of record owners. data publishing in a way that they contain no sensitive information and the privacy of record owners remains intact is termed as ppdp [7]. typically, ppdp deals with publishing of data in an anonymized way, i.e. the data contain sensitive information but that information cannot be linked with its owner, while being still useful for the interested parties. various methods have been proposed [12-15] for transforming data into their anonymized version. these methods differ in their capabilities of preventing linking of data owners which can eventually harm their privacy. there is no standard method for selecting a particular anonymization technique. technique selection is highly dependent on the type of dataset and its sensitive attributes. the publisher has to anonymize data by using multiple techniques in order to select the most suitable. this is not only expensive in terms of time and resources but also requires sufficient knowledge in order to choose the appropriate method to convert the actual data into their corresponding author: tehreem qamar engineering, technology & applied science research vol. 10, no. 2, 2020, 5423-5427 5424 www.etasr.com qamar et al.: edams: efficient data anonymization model selector for privacy-preserving data … anonymized version. selection of an inappropriate method may cause data loss therefore it is necessary to select a method which could provide results at the optimum level of its utility with the least possible loss of data. keeping in view the aforementioned problems, this study aims to propose a model that can identify the most suitable technique for anonymizing a certain dataset with minimum information loss. the main contributions of the current study are: • the development of a model that helps the data holder who has no particular knowledge of data anonymization techniques to release data anonymously. • the selection of the most appropriate method according to the nature of the respective dataset. • the generation of an anonymized dataset with least information loss and maximized utility. ii. literature review various real world attacks indicate the significance of preserving individual privacy when distributing personal information. many times data released by companies for research purposes ended up with hurting individual privacy. the re-identification of individuals happens when they get linked with some other available external information is termed as linking attack [12]. some reported incidents regarding released data that got linked with external information are summarized in table i. table i. uncidents reported against linking attacks privacy breach dataset used results [16] health dataset from washington state 43% identification by linking the dataset with newspaper stories containing the word “hospitalized”. [17] prescription data of south korean residents 100% individuals in the dataset were reidentified. data were encrypted prior release. [12] medical records of state employees of massachusetts governor of massachusetts was identified when the dataset was linked with the publicly available voter enrollment list. [18] three month credit card records 90% identification by analyzing buying patterns [9] aol dataset one of the users was identified and interviewed by new york times within three days of data release [19] netflix dataset 99% of records were identified with 8 movie ratings authors in [16] collected a health dataset from washington state, which did not contain patient names. however, 43% of the individuals were successfully identified by linking the dataset with the newspaper stories containing the word “hospitalized”. authors in [17] conducted experiments on the encrypted prescription data of 23,163 south korean resident registration numbers (rrns). they claimed that they were able to re-identify 100% of the data and concluded that encrypted data are also vulnerable. author in [12] described the re-identification of the dataset released by group insurance commission (gic) that included medical records of the state employees of massachusetts and was intended to facilitate medical research. the dataset contained demographic data, for example, birth date, gender, and zip code. it was explained how easily william weld (the then governor of massachusetts) was identified by linking the massachusetts voter enrollment list with the information given by gic. authors in [18] studied a credit card report of 3 months consisting of 1.1 million individuals and uniquely identified 90% of them via analyzing only four spatiotemporal points. they reported that the buying patterns with a use of a credit card make an individual’s privacy vulnerable. a similar incident has been reported in 2006 when aol released 20 million search queries of its users and within three days of its release one of its users was identified and interviewed by new york times [9]. a few months later, netflix also faced re-identification of its users in the dataset it released for the development of an accurate movie recommendation algorithm. the data were attacked by authors in [19], and they showed that external information can be linked to identify or to link the data with the respective individual. ppdp is a way of releasing anonymized data while preserving individual privacy [6]. in ppdp, the data are generally represented as a table of explicit identifiers, quasi identifiers, sensitive attributes, and non-sensitive attributes, where explicit identifiers is a set of attributes that explicitly identifies the individual, and quasi identifiers are those that could potentially identify the individual. sensitive personspecific information such as salary, real time location and disability status are considered as sensitive attributes while the term non-sensitive attributes contains all attributes that do not fall into the previous three categories. numerous techniques and models have been proposed in ppdp for producing anonymized data such as k-anonymity [12], l-diversity [13], and t-closeness [20], which have become the foundation of many other models [22-26] and are therefore used in edams. iii. the edams model a. preliminaries let t be an original data table of the following form: t = {di1, di2,……, dij, qi1, qi2,……, qik, sa1, sa2,… san} where, dis are direct identifiers, the attributes which should be removed prior data publishing, qis are quasi identifiers, the non-sensitive attributes which when linked with external data can reveal the identity of a record owner, and sas are sensitive attributes, the private information related to a record owner. b. methodology the proposed data anonymization model initially makes use of k-anonymity, l-diversity and t-closeness as privacy models, and generalization and suppression as ppdp operations. the utility that guarantees the optimum information loss is information loss (iloss) metric [27], which measures the loss of information by calculating the uncertainty that occurred in generalizing a value which relies upon how many other values cannot be distinguished from it. the overall anonymization process is depicted in figure 2. engineering, technology & applied science research vol. 10, no. 2, 2020, 5423-5427 5425 www.etasr.com qamar et al.: edams: efficient data anonymization model selector for privacy-preserving data … fig. 2. edams’s data anonymization process the process comprises of 5 steps. in the first step, the original data are taken as input that clearly marks the dis, qis and sas. after realizing the attribute’s nature, the sensitivity of the overall dataset is calculated. as the sensitivity is computed, the generalization hierarchy of the qis is generated. and, on the basis of sensitivity of the dataset, the optimum privacy model is selected for its anonymized version. the sensitivity of the dataset is calculated by: sensitivity percentage � ������ �� �� ������ �� �� x 100 (1) if the sensitivity is 0 that means no sensitive attribute is present in the dataset and k-anonymity privacy model will be used. applying k-anonymity requires the value of k to be used optimally because it is responsible for the utility ratio of the dataset [28]. edams makes use of two ppdp operations, i.e. generalization and suppression. the generalization lattice is created for each qi. di and the attributes that cannot be generalized will get suppressed in the resulting anonymized table. when the above two steps are completed then the optimum model is chosen on the basis of sensitivity. the information loss is calculated via iloss metric [7] and the data holder will get the anonymized version of the data with least cost. figure 3 depicts the applied algorithm. fig. 3. data anonymization algorithm for edams iv. experiments edams is developed using java that run on a 2.4ghz intel core i5 processor with 6gb ram. three datasets with their customized versions were examined for the assessment of the model, namely uci adult dataset [29], employee’s salary dataset [30], and crime incident dataset [31] along with their different variations. each dataset has been evaluated twice. firstly with edams and secondly with each method separately applied to it in order to get the optimal result in a process termed as hit and trial. its results are shown in table ii. a. case 1: adult dataset the dataset in [29] contains 30,162 records. it consists of 9 attributes in total: sex, age, race, marital-status, education, native-country, work class, occupation, and salary-class. three variants of this dataset were considered of having no di. the first variation took all attributes as qis. the second variation considered occupation as an sa and the rest of them as qis, and the third variation included six of them as qis and two of them, i.e. marital-status and occupation, as sensitive. 1) selection via edams when dataset is taken as input to edams, its sensitivity is calculated, i.e. the ratio of sa over quasi attributes. considering the first variation, when there is no sa the sensitivity between sa and qi becomes 0% which means although the dataset has no direct sensitive information, it can serve as a tool for linking attacks. in this case, edams suggested k-anonymity for the respective dataset with maximum information loss of 60%. table ii represents the chosen models with maximum information loss when the same procedure was applied to all of its variants. table ii. result of adult dataset via edams di qi sa privacy model sensitivity ratio max. information loss 0 9 0 k-anonymity 0% 60.37% 0 8 1 l-diversity 11% 62.50% 0 7 2 l-diversity 22% 57.14% 2) selection via hit and trial model for the verification of the results obtained by edams each variant of the dataset is tested with each privacy model in order to find the best suitable model for the respective dataset. the threshold values are selected from the lowest possible values to the values where change in threshold values does not affect the result. considering the same variant, the data holder has to try each and every possible combination of different methods which demands a substantial amount of time. table iii depicts the results obtained from different combination of methods employed through hit and try model. table iii. hit and trial model results privacy model threshold value max. information loss k-anonymity 3 17.08% 5 57.31% 7 57.31% l-diversity 3 54% 5 61% 7 61% t-closeness 0.02 100% 0.2 91% 0.8 54% k-anonymity and l-diversity k=3, l=2 54% k=5, l=3 61% k=5, l=7 61% k-anonymity with t-closeness k=3, t=0.002 100% k=5, t-0.2 91% k=5, t=0.8 61% k-anonymity with l-diversity and tcloseness k=3, l=2, t=0.002 100% k=5, l=3, t=0.2 91% k=7, l=5 t=0.9 61% engineering, technology & applied science research vol. 10, no. 2, 2020, 5423-5427 5426 www.etasr.com qamar et al.: edams: efficient data anonymization model selector for privacy-preserving data … it can be seen that minimum information loss occurs when k-anonymity model is applied. but the identification of this least information loss method became possible after trying each model and their combinations with different threshold values. however, the same model is recommended by the edams without requiring any extra effort. b. case 2: employee’s salary dataset this dataset [30] contains 1,999 records and comprises on five attributes (name, gender, telephone number, zip code, salary). two variations were created, in which two attributes (name and telephone number) were considered as dis. the first variant considers the rest of the three attributes as qis while the second variation considers salary as sa and rest of the two, i.e. gender and zip code as qi. 1) selection via edams the process of selection of privacy model through edams will remain the same for every dataset. considering its second variation, there are two dis and one sa. the dis were removed out rightly from its anonymized version while ldiversity was selected as the privacy model. table iv shows its results. table iv. selection through edams di qi sa privacy model sensitivity ratio max. information loss 2 3 0 k-anonymity 0% 8.12% 2 2 1 l-diversity 20% 0.00% 2) selection via hit and trial model analyzing the same dataset yields the results shown in table v. the two models are providing the same results, however one of them has already been suggested by edams (l-diversity). table v. hit and trial model results privacy model threshold value max. information loss k-anonymity 3 8.11705% 5 8.11705% 7 8.11705% l-diversity 3 0.00007% 5 0.00007% 7 0.00007% t-closeness 0.02 100% 0.2 100% 0.8 0.0023% k-anonymity and l-diversity k=3, l=2 0.00007% k=5, l=3 0.00007% k=5, l=7 0.00007% k-anonymity with tcloseness k=3, t=0.002 100% k=5, t-0.2 100% k=5, t=0.8 0.0023% k-anonymity with l-diversity and t-closeness k=3, l=2, t=0.002 100% k=5, l=3, t=0.2 100% k=7, l=5 t=0.02 100% c. case 3: crime incident dataset this dataset [31] contains a total of eight attributes, namely last name, first name, block, gender, race, date of birth, case number, and crime_code with 1,058 records. four versions of this dataset were formed. last name, first name, and date of birth served as dis in the first two versions and the remaining five attributes were taken as qis in the first variant while crime_code was taken as sensitive attribute in the second version and the rest as qis. the third and fourth variant took only the first name and date of birth as dis and the rest of the structure remained the same. 1) selection via edams analyzing its second variant there is one sa along with four qi and three di. the sensitivity is calculated to 13% and ldiversity is suggested by edams. table vii summarizes the results of all variants. table vi. selection model in crime dataset from edams di qi sa privacy model sensitivity ratio max. information loss 3 5 0 k-anonymity 0% 60.54% 3 4 1 l-diversity 13% 55.68% 2 6 0 k-anonymity 0% 15.26% 2 5 1 l-diversity 13% 64.54% 2) selection via hit and trial model table vii shows the results in finding the appropriate method for the second variant of this dataset. it is evident from this example that edams chose the most appropriate model required for the respective dataset. table vii. selection from hit and trial model privacy model threshold value max. information loss l-diversity 3 55% 5 75% 7 75% t-closeness 0.002 100% 0.2 75% 0.9 50% k-anonymity and ldiversity k=3, l=2 100% k=5, l=3 100% k=5, l=7 100% k-anonymity and tcloseness k=3, t=0.002 100% k=5, t=0.2 100% k=5, t=0.8 100% k-anonymity with l-diversity and tcloseness k=3, l=2, t=0.002 100% k=5, l=3, t=0.2 100% k=7, l=5, t=0.9 100% v. discussion the cost of producing anonymized data via hit and trial model is high as there is no standard method for anonymizing data. data holder has to keep checking different models over different thresholds to achieve data anonymity with greater utility. moreover, absence of knowledge regarding privacy models makes it more difficult for the data holder to modify the data into their unidentified version. however, edams is capable of selecting the appropriate model for the respective dataset by applying some initial effort thereby minimizing the overall cost with good efficiency. engineering, technology & applied science research vol. 10, no. 2, 2020, 5423-5427 5427 www.etasr.com qamar et al.: edams: efficient data anonymization model selector for privacy-preserving data … vi. conclusion and future work available vast data can provide immense benefits when analyzed carefully. many companies are sharing their data for research or other purposes. however, the data are becoming highly personalized as everything becomes automated, thus the companies need to make the necessary arrangements to protect their clients’ privacy. ppdp is a promising approach that can be used to publish data while preserving individual privacy to a great extent. many techniques are available in this domain for the generation of anonymized data but choosing one is a challenging decision. this study presented the data anonymization model selection tool edams that is capable of generating anonymized data with minimal effort. edams requires the dataset and the nature of attributes to proceed with the selection of the optimal method among k-anonymity, ldiversity and t-closeness. the results were validated by applying the techniques separately one by one on the same datasets and the conclusion was that edams efficiently selects the most appropriate method. ppdp is still in its development stage as the researchers are coming up with more efficient algorithms. edams is currently providing limited anonymization algorithm selection, however it has the capability to work as a classifier when trained rigorously. as a result, it will be capable of anonymizing any type of data by selecting the most efficient algorithm. edams is dealing with linking attacks using generalization and suppression as ppdp techniques and k-anonymity, l-diversity, and t-closeness as anonymization algorithms. however in the future it is planned to accommodate more anonymization techniques to protect individual privacy against probabilistic 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no. 3, pp. 4203-4208, 2019 [29] uci, adult data set, available at: archive.ics.uci.edu/ml/datasets/adult [30] employee salary dataset, available at: www.kaggle.com/varungitboi/ employee-salary-dataset [31] open data philly, crime incidents, available at: www.opendataphilly. org/dataset/crime-incidents microsoft word 04-farhadi-ed.doc etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 151-154 151 www.etasr.com sojoudi et al: achieving steady and stableenergy from algaasgaas solar cells achieving steady and stable energy from algaasgaas solar cells m. sojoudi electrical engineering dpt, azerbaijan higher education & research complex, iran mosaddegh_sojoudi@yaho o.com r. madatov inistitute of radiation problems, national science academy of azerbaijan, baku, azerbaijan msrahim@mail.ru t. sojoudi young researchers club, parsabad moghan branch islamic azad university parsabad moghan, iran tsojoudi@iaupmogan.ac.ir p. farhadi young researchers club, parsabad moghan branch islamic azad university parsabad moghan, iran pfarhadi@iaupmogan.ac.ir abstract— the hetero junction operating as a solar cell is based on n-gaas-p-gaas-p-al0.75ga0.25as. this paper investigates the influence of radiation electron ray on layers of hetero-junction algaasgaas. long term operation in the radiation zone degrades solar cell power operating parameters and reduces overall cell’s life. the impact of radiation electron ray has been analyzed with various doses on layers of the algaasgaas hetero-junction. v-a characteristics and parameters such as the photocurrent density (jsc), voltage at open circuit (voc) and energy conversion efficiency ( (η), are evaluated for different doses of electron radiations. it is shown that current and voltage decrease when irradiation doses increase. further, jsc and η parameters decrease proportionally to the increase of the electron radiation doses whereas voc is only slightly decreased. keywords: solar cells; hetero-junction; electron rays; v-i characteristics; steady and stable snergy. i. introduction the sun is a staggering amount of free, environmentally friendly, quiet and reliable energy supply and the use of solar electricity to produce a substantial portion of the required electrical power has been proposed since 1970 [1]. earth’s ultimate recoverable resource of oil is estimated at 3 trillion barrels, which equals to 1.7×1022 joules of energy, which the sun delivers in only 1.5 days [2]. since 120,000 tw of solar radiation strike the surface of the earth, a 10% efficient solar conversion systems covering 0.16% of the land would produce 20 tw of power, nearly twice the annual global energy consumption [3]. high efficiency solar cells use multiple materials with band gaps that span the solar spectrum. multi-junction solar cells are composed of some single-junction solar cells stacked upon each other, so that each layer going from the top to the bottom has a smaller band gap than the previous, and absorbs and converts the photons that have energies greater than the band gap of that layer and less than the band gap of the higher layer [4]. triple-junction solar cells currently in production are made of gainp (1.9 ev), gaas (1.4 ev), and ge (0.7 ev); advanced multi-junction solar cell concepts anticipate use of algainp (2.2 ev), algaas (1.6 ev), gainp (1.7 ev), gainas (1.2 ev), gainnas (1.0-1.1 ev) [5]. though solar cells (sc) are prepared on the basis of a 3 b 5 compounds and their solid solutions are used in different technical fields, the problem of their radiation resistance still remains. degradation of operation parameters and decrease of cell’s life time is observed during long-term operation of the cell in the radiation zone due to the decrease of the inner quantum effect, the generation and recombination processes and the increase of surface recombination velocity in the junction area. on the other hand, it should be taken into account that the degradation of the structure parameters (β, r and j0) depends on the nature of structural defects, probability of complexes’ formation and interaction of defects. namely from this reason, in spite of using different methods to increase radiation resistance of raw material, the problem has not found its solution. for this purpose, the influence of accelerated electron rays on the photoelectric properties of the sc prepared on the basis of algaas-gaas is investigated [6-10]. ii. general explanations of cell properties the photocurrent generated by a solar cell under illumination at short circuit is dependent on the incident light. to relate the photocurrent density, jsc, to the incident spectrum we need the cell's quantum efficiency, (qe). qe(e) is the probability that an incident photon of energy e will deliver one electron to the external circuit. the photocurrent density is given by: de)e(q)e(bqj ssc ∫= (1) where bs(e) is the incident spectral photon flux density, the number of photons of energy in the range e to e + de which are incident on unit area in unit time, and q is the electronic charge. qe depends upon the absorption coefficient etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 151-154 152 www.etasr.com sojoudi et al: achieving steady and stableenergy from algaasgaas solar cells of the solar cell material, the efficiency of charge separation and the efficiency of charge collection in the device, but not on the incident spectrum. it is therefore a key quantity in order to describe solar cell performance under different conditions. qe and spectrum can be given as functions of either photon energy or wavelength λ. energy is a more convenient parameter for the physics of solar cells and it will be used in this paper. the relationship between e and λ is given by: λ = hc e (2) where h is planck's constant and c is the speed of light in vacuum. a convenient rule for converting between photon energies, in electron-volts, and wavelengths, in nm, is given by e/ev= 240/(λ/nm). iii. hetero-junction and electron radiation ray several techniques are employed to produce solar cells of a 3 b 5 complex, and their solid solution used in different fields of technology, and the problem to have a steady radiation still remains unsolved. it has been found that the power operating parameters of solar cells are degraded after a long-term operation in the radiation zone which in turn results in a reduced life time of the cell. because of the reduction of inner activity, production process and recombination as well as velocity of recombination will be increased in the junction. in lux-ampere characteristic voc and jsc will vary at different irradiation doses. voc and jsc will increase with the increase of electron radiation dose at the lux constant amount. in addition, the quality degradation of structural parameters (β, r, j0) which modifies the structure and depends on the nature of structure defects and the probability of complex layers and their impact should be considered. to research this issue, the influence of accelerated electron ray on properties of photoelectric for alga-gaas is investigated. the hetero-junction has been prepared on the base of n-gaas-p-gaas-p-al0.75ga0.25as. the n-gaas layer with a density of n=1-3×1017cm-3 is on the layer of zinc, with a thickness 15-20µm as a solid solution. the thickness of p-gaas layer is 1µm. during construction zinc metal powder is poured on its surface. zinc layer is placed to reduce thickness of player, with high concentration and low contact resistance. the case study surface is 2cm 2 . at the firm of measurement, the curve of electrical characteristics of solar radiation spectrum (am-1,5) is used to determine the v-i characteristics of solar cells under the uniform radiation. this solar cell is uniform under radiation with power of pg=91mw/cm 2 , jsc=20-25ma/cm 2 , voc=0.92-0.95 (v) and efficiency η=16-20%. this sample was under radiation with electric energy 4.5mev by electron ray of elit-6 equipment. the n-gaas-p-gaas-p-al0.75ga0.25as solar cell structure has been checked by different kinds of v-i characteristics by electron rays. iv. various doses of radiation solar cell’s v-i characteristics have been illustrated in figure 1 before and after irradiation. increasing the electron ray dose causes jsc to decrease, while voc is slightly changed. fig. 1. v-i characteristics of solar cell before and after irradiation: 1. 0, 2. 10 15 , 3. 10 16 (el/cm 2 ) the parameters calculated according to the curves of figure 1, independently to the radiation dose, are shown in figure 2. it is shown that the influence of electron rays on solar cells cause a significant alteration in jsc while voc is only slightly altered. jsc(p) and voc(p) are functions of electron ray radiation and because of the electron ray, the photo current variation is observed as shown in curves 1-3 of figure 4. fig. 2. dependence of jsc, voc, η on the different radiation from figure 3 it can be observed that the change of voc(p) depending on the radiation dose is about 20% in comparison to jsc(p). as in the irradiated samples at the results of an isochronous sealing (t=4000c, t=30min) jsc is not completely recovered which is justified by the fact that the radiation defects formed in p-al0.75ga0.25 layer is much more resistant. comparing theoretical and practical results reveals that defects caused by electron ray radiation exist on p-al0.75ga0.25 region with wide band gap. to explain this fact, the influence of electron radiation on the spectral characteristic of these elements has been investigated. etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 151-154 153 www.etasr.com sojoudi et al: achieving steady and stableenergy from algaasgaas solar cells fig. 3. lux-ampere characteristics at different irradiation doses: jsc: 1.0, 2. 1015, 3. 1016 (el/cm2), voc: 4. 0, 5. 1015, 6. 1016 (el/cm2) in figure 4, showing the photo current (if (λ)), the curves 1 to 3 as a function of light intensity are compared, and it is shown that changes of photo current (if (λ)) will occur for short-wave radiation region. fig. 4. spectral characteristics at different irradiation doses: 1. 0, 2. 1015 (el./cm2), 3. 1016 (el./cm2) the obtained results confirm the theoretical and experimental results obtained in the hetero-junctions radiated by electrons with 1mev energy [5]. comparison of theoretical and practical research shows that the hetero-junction has the most part of solar radiation on p-gaas-p-algaas layer. diffusion path (ln) is decreased due to the radiation and loss of recombination in p-layer, (after radiation ln decreases from 7.5 to 5 µm). τ= → µτ = µ = dln q kt ln q kt d (3) where ln and d are the diffusion path and coefficient respectively. v. results and discussion to provide maximum efficiency of solar cells, a 1016cm thickness should be chosen for pal0.75ga0.25as layer. the comparison of these facts and the obtained results proves once more that the electron radiation ray generates defects on the p al0.75ga0.25as layer. to determine the effect of the electron radiation ray on structural parameters, and the characteristics of solar cells, the v-i characteristic curve of solar cells in the presence of surface temperature have been studied before and after the radiation of electron radius in the temperature of 300 o c. as shown in figure 5, i(v) depends on the radiation ray for small doses (2×1014 elec/cm2) and will be as usual for v≥vd (vd is threshold voltage, curves 1 and 2). this means that, at first, the amount of electron ray irradiation may considered to be an error [6-7]. high dose radiations (10 16 -10 17 (el. /cm 2 )) causes changes to the v-i characteristic, especially appearing for voltage v<vd. to clarify the facts, log (i (v)) is to be determined based on its dependence to the maximum radiation flow. it is shown that, for small voltages in the biased voltage direction, change will follow an exponential rate whereas for voltages over 0.6 (v), change will follow a linear rate. fig. 5. v-i characteristics of solar cell before and after irradiation: 1. 1016 (el./cm2) , 2. 1015 (el./cm2) , 3. 0 the time trend of β and j0 shows that the mechanism of current transfer depends on generation recombination and processes progressing in volumetric charging region. during the radiation of electron ray, (1012-1016 (elec/cm2)), β and j0, have the amount of 1.5-2.6 and 10-8-10-7 (a/cm2), respectively. during the radiation of electron ray on hetero-junction, recombination centers will be produced in the divider layer [7]. in order to determine the photoactive concentration centers, the linear part of 1/c2~f(v0) dependence has been used and it has been revealed that before and after radiation, the concentration of the centers is equal to 4.5×1015cm-3 and 1.1×1015 (ф=1016 (el/cm 2 )), respectively. etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 151-154 154 www.etasr.com sojoudi et al: achieving steady and stableenergy from algaasgaas solar cells the thickness of potential barrier in the concentration level of impurity (vd, .a, .d) is calculated and foung 0.9v, 1.5×109cm-3 and 2×1017 cm-3. the relation .a-.d<.f shows that recombination concentration centers are generated on pgaas layer and an increase of concentration of recombination centers at hetero-boundary and in sacrificial region is observed. vi. summary and concluding remarks because of reduction of inner activity, production process, recombination and velocity of recombination will increase in the junction. to solve this problem the influence of accelerated electron ray on photo electric properties of alga-gaas was investigated. a case study surface of about 2 cm 2 was employed. electron ray of elit-6 equipment was used. it was found that jsc and η are decreasing due to the increase of electron ray dose whereas voc is only slightly decreased. changes of photo current [i (λ)] was investigated in the shortwave radiation region. diffusion path (ln) is decreased due to radiation and loss of recombination in p-layer. this process was performed in the temperature of 300 o c. during the radiation of electron ray on hetero-junction, recombination centers were produced in the divider layer. increase of concentration of recombination centers at hetero-boundary and in sacrificial region under the influence of radiation is observed. references [1] a. luque and s. hegedus, handbook of photovoltaic science and engineering, john wiley and sons, 2003. [2] g. w. crabtree, n. s. lewis, “solar energy conversion”, physics today, 2007, vol. 60, pp. 37-42, 2007. [3] r. m. nault, basic research needs for solar energy utilization, argonne national laboratory, 2005. [4] b. burnett, the basic physics and design of iii-v multijunction solar cells, u.s. department of energy national center for photovoltaics, 2002 [5] f. dimroth et al., “next generation gainp/gainas/ge multi-junction space solar cells”, proc. 17th photo-voltaic european conference, wipmunich and etz-florence, 2001 [6] v. m. andreev, v. r. larionov, v. d. rumyantsev, o. m. fedorova, sh. sh. shamukhamedov, “palgaas-pgaas-ngaas solar cells with efficiencies of 19 percent at am 0 and 24 percent at am 1.5”, pis'ma v zhurnal tekhnicheskoi fiziki, vol. 9, pp. 1251-1254, 1983 [7] r. sahai, d. d. edivall, j. s. harris, “high efficiency algaas/gaas concentrator solar cells”, appl. phys. lett, vol. 34, pp .147-149, 1979 [8] v. m. andreev, b. v egorov, v. m. lantratov, v. d. rumyantsev, sh. sh. shamukhamedov, “solar heterophotocells with increased p-n junction depth”, zhurnal tekhnicheskoi fiziki, vol. 53, pp. 1658-1660, 1983 [9] g. h. walker, e. j. conway, “short circuit current change in electron irradiated gaalas/gaas solar cells”, proc/intern, solar energy soc. cong.-n.y, pergamon press, pp. 575-579, 1978. [10] b. v. egorov, v. m. lantratov, s. i. troshkov, “analysis of dark characteristics of solar cells on the basis of heterojunction algaas/gaas”, in coll.of abst. 111 of ussr conf. on physical processes in semiconductor heterojunctions. odessa, vol. 1, pp.200202, 1982 authors profile mosaddegh sojoudi was born in 1958 in azerbaijan, iran. he received the b.sc. and m.sc. degrees from tabriz university. now, he is pursuing a ph.d from the institute of radiation problems of azerbaijan national academy of science, baku, azerbaijan. he is a faculty member at the electrical engineering department of azerbaijan higher education and research, tabriz, iran (ministry of power). his research is in the field of solar cell energy and distributed generation. rahim madatov was born in 1949 in shaki, azerbaijan. he received the b.sc. in physics from azerbaijan nation academy of science and the m.sc and ph.d degrees in solar cell from moscow state university, russia, 1992. dr. madatov is an academic member of radiation problems of azerbaijan national academy of science, baku, azerbaijan. tina sojoudi was born in 1988. she is pursuing the b.sc. degree in electrical engineering at i.a.u, tabriz , iran. her areas of interest are in renewable energies, distribution systems optimization and planning, and distributed generation. payam farhadi was born in 1985. he received the b.sc. and m.sc. degrees both in electrical engineering from i.a.u, in 2009-ardebil and in 2011-ahar, respectively. his research interests are distribution system planning and optimization, distributed generation and facts devices. mr. farhadi is an elite member of young researchers club (yrc) in iran, and a faculty member of i.a.u. at the department of electrical engineering -parsabad moghan branch, parsabad moghan, iran. microsoft word 18-2525_s1_etasr_v9_n3_pp4165-4168 engineering, technology & applied science research vol. 9, no. 3, 2019, 4165-4168 4165 www.etasr.com al-dwairi et al.: an efficient and highly secure technique to encrypt and decrypt color images an efficient and highly secure technique to encrypt and decrypt color images majed o. al-dwairi department of communication technology engineering, faculty of engineering technology, al-balqa' applied university, amman, jordan majeddw@bau.edu.jo amjad y. hendi department of communication technology engineering, faculty of engineering technology, al-balqa' applied university, amman, jordan amjad_svyaz@yahoo.com ziad a. alqadi computer & network engineering department, faculty of engineering technology, al-balqa' applied university, amman, jordan natalia_maw@yahoo.com abstract—digital color images are considered as the most widely used data. they are exchanged frequently on the internet and via email, so an efficient and highly secure method of color image encryption and decryption is needed. different methods of encryption-decryption are used, but most of them suffer from low efficiency or low-security level or both. in this paper, an efficient and highly secure method of encryption-decryption will be proposed, tested, and implemented. the efficiency parameters will be calculated and compared with other methods’ parameters to prove the efficiency of the proposed method. keywords-encryption-decryption times; throughput; speedup; mse; psnr i. introduction digital images are one of the most widely used data types, and they are exchanged widely through e-mail and web browsing. a digital image may be confidential or contain highly confidential information [1]. in this case, it is necessary to encrypt it in order to make it difficult to identify or the information stored in it. the person authorized to view the image can decrypt it and return it to the original form without any errors. the digital image has a large size, so encoding it may take a lot of time, which leads us to build an effective method that reduces the encryption time as much as possible. ii. encryption-decryption parameters regarding the effectiveness of the image encryption method, the following parameters must be taken into account: • encryption time: the time needed to process the encryption method in order to convert the original image to an encrypted image. • decryption time: the time needed to process the decryption method in order to convert the encrypted image to the original image. encryption and decryption times must be as reduced as possible. • throughput: the number of bits encrypted or decrypted per time unit. it is equal to the image size in bits divided by the encryption or decryption time. • speedup: the proposed technique enhancement, which is equal with the proposed technique throughput divided by the throughput of another method. • block: the number of bytes to be encrypted/decrypted at the same moment. • key size: the number of values (elements) for a secret key, which must be equal with the block size. • hacking time: the time needed by an unauthorized person to guess the original image. this time must be as large as possible. this time depends on the length of the key used for encryption-decryption. • mean square error (mse) and peak signal-to-noise ratio (psnr): mse is a measure of the quality of an estimator— it is always non-negative, and values closer to zero are better. but for measuring it between the original image and the encrypted one, the value must be very large. psnr is an engineering term for the ratio between the maximum possible power of a signal and the power of corrupting noise that affects the fidelity of its representation. for ideal encryption, the psnr between the original image and the encrypted image must be very low, and between the original image and the decrypted one must be infinite (zero errors). these parameters can be calculated using the following formulas: ��� = ∑ ∑ ∑ ��� , �, � − �� , �, � �� ������ (1) d=max{xi,j,k,yi,j,k}, $�%& = 10)*+ ,-� ���. / (2) where x and y are color image matrices, r: rows, c: columns, p: number of colors. iii. related work some authors take data encryption standard (des) [2], or advanced encryption standard (aes) [3, 4] as bases for encryption-decryption, but most of these works suffer from high encryption-decryption time, which makes these methods inefficient. author in [5] suggested a method of encryptiondecryption by reshaping the 3d color matrix to a 2d matrix, squaring the matrix, generating a secret key with size equal to corresponding author: majed o. al-dwairi engineering, technology & applied science research vol. 9, no. 3, 2019, 4165-4168 4166 www.etasr.com al-dwairi et al.: an efficient and highly secure technique to encrypt and decrypt color images the image size, and applying matrix multiplication to get the decrypted image. this method provides a good throughput, but it is very difficult to remember the key, and thus the method requires storing and transferring the key. in [6] an efficient image encryption scheme using double logistic maps was proposed, in which the image matrix was confused from row and column. confusion effect is carried out by the substitution stage and chen's system is employed to diffuse the gray value distribution. in [7], a method of encryption-decryption was proposed, this method was based on matrix reordering and it has a medium throughput. in [8], a chaotic algorithm was presented applying encryption-decryption by using power and tangent functions instead of linear function. the process of encryption is one-time-one-password system and is more secure (but not enough) than the des algorithm, also it has low efficient parameters with big encryption-decryption time and low throughput. in [9], an asymmetric image encryptiondecryption method was proposed, this method is based on matrix transformation, but it has high encryption-decryption time and thus low throughput. in [10] a method based on rubik's cube principle was proposed with a good security level, but low throughput. in [11] a method of encryption-decryption was presented, this method is based on using chaos-controlled poker shuffle operation, both variants of this method (a-i and a-ii) have a poor throughput. iv. proposed method the proposed technique of color image encryptiondecryption requires the following operations (figure 1): • dividing the original image matrix into equal size blocks (in our testing experiment the block size was equal to 8 bytes). • selecting several secret keys (in our testing experiment we selected 4 keys). • key size must equal block size. • key value must in the range from 0 to 255. fig. 1. proposed encryptor-decryptor the encryption phase can be implemented applying the following steps: • get the original color image matrix. • reshape the color image matrix from 3d to 1d. • divide the 1d matrix into equal blocks with size equal to 8 bytes. • define 4 private keys with 8 elements each. • each data matrix block must be submitted to exclusive-or operation with key1, key2, key3, and key4 consecutively. • the obtained blocks are the encrypted blocks. the decryption phase can be implemented applying the following steps: • get the encrypted color image matrix. • reshape the color image matrix from 3d to 1d. • divide the 1d matrix into equal blocks with size equal to 8 bytes. • use the defined 4 private keys with 8 elements each. • each data block be submitted to exclusive-or with key4, key3, key 2, and key1 consecutively. • the obtained blocks are the decrypted blocks which must be reshaped back to get the decrypted image. the proposed algorithm provides a high level of security, the number of combinations to guess the four keys is very high and equal to 2563 4 2563 4 2563 4 2563 = 2565� making the hacking process very difficult. figure 2 shows an example of the keys, while figures 3-5 show the original, encrypted and decrypted images obtained by applying the proposed method. from figures 4 and 5 we can see that the original and decrypted images are the same. fig. 2. keys example fig. 3. original image and histograms fig. 4. encrypted image and histograms original image 0 100 200 0 1 2 3 x 10 4 red histogram 0 100 200 0 1 2 3 x 10 4 green histogram 0 100 200 0 1 2 3 x 10 4 blue histogram encrypted image 0 100 200 0 1 2 x 10 4 red histogram 0 100 200 0 1 2 x 10 4 green histogram 0 100 200 0 1 2 x 10 4 blue histogram engineering, technology & applied science research vol. 9, no. 3, 2019, 4165-4168 4167 www.etasr.com al-dwairi et al.: an efficient and highly secure technique to encrypt and decrypt color images fig. 5. decrypted image and histograms v. results and discussion the proposed method can be used to encrypt-decrypt color images of any type or size. several images were treated by the proposed technique, and table i shows the results of the implementation. from table i we can conclude the following: • calculated encryption/decryption times are significantly small and grow linearly (as shown in figure 6) when the image size grows. • the proposed technique is accurate by keeping the decrypted image the same with the original image (zero mse and infinite psnr). • the proposed technique distorts the encrypted image by maximizing mse and minimizing psnr between the original image and the encrypted one. • the throughput of the proposed technique is always between 28 and 29 mbits per second, which is considered a high-performance index. table i. calculated parameters image number size (mbits) encryption time (s) decryption time (s) throughput (mbps) 1 2.0672 0.0710 0.0710 29.1151 2 1.1587 0.0410 0.0410 28.2613 3 0.3750 0.0130 0.0130 28.8462 4 8.5876 0.2940 0.2940 29.2097 5 4.1199 0.1410 0.1410 29.2190 6 25.9100 0.8930 0.8930 29.0145 7 18 0.628000 0.628000 28.6624 8 7.0862 0.2470 0.2470 28.6890 9 3.2959 0.1150 0.1150 28.6600 10 1.1547 0.0390 0.0390 29.6085 to prove the correctness of the proposed technique, mse and psnr were calculated (table ii). the proposed technique was compared with other existing techniques and the results of the comparison are shown in table iii. from these results we can see that the proposed technique enhanced efficiency by minimizing encryption-decryption times, and maximizing throughput which speeds up the proposed technique. note that increasing the block size will increase the technique efficiency by decreasing the encryption-decryption time and increasing the throughput. table ii. mse and psnr calculations image number comparing encrypted image with original comparing decrypted image with original mse psnr mse psnr 1 1.6997e+004 13.4173 0 infinite 2 7.8742e+003 21.1118 0 infinite 3 6.0695e+003 23.7150 0 infinite 4 7.7992e+003 21.2075 0 infinite 5 1.1871e+004 17.0068 0 infinite 6 1.4770e+004 14.8217 0 infinite 7 1.3579e+004 15.6623 0 infinite 8 1.3214e+004 15.9352 0 infinite 9 1.0662e+004 18.0805 0 infinite 10 1.2664e+004 16.3601 0 infinite table iii. comparison results method encryption time (s) decryption time (s) throughput (mbits) speedup of the proposed method order proposed 0.0513 0.0513 29.2398 1 1 [4] 0.06469 0.062727 23.1876 1.2610 2 [6] 0.23 0.23 6.5217 4.4835 4 [7] 0.5 0.5 3 9.7466 6 [8] 0.4 0.4 3.7500 7.7973 5 [9] 0.12 0.12 12.5000 2.3392 3 [10] v. a-i 0.56 0.56 2.6786 10.9161 7 [10] v. a-ii 1.01 1.01 1.4852 19.6874 8 image size=256×256×3×8=1572864bit=1.5000mbits fig. 6. relationship between image size and encryption time the proposed technique was implemented using the previous images with a block size equal to 16 pixels and with one 16 element key, the results of the implementation are shown in tables iv-v. table iv. parameters for block size =16, one key image number size (mbits) encryption time (s) decryption time (s) throughput (mbps) 1 2.0672 0.0290 0.0290 71.2817 2 1.1587 0.0170 0.0170 68.1597 3 0.3750 0.0050 0.0050 75.0000 4 8.5876 0.1250 0.1250 68.7012 5 4.1199 0.0560 0.0560 73.5692 6 25.9100 0.3670 0.3670 70.5993 7 18 0.2540 0.2540 70.8661 8 7.0862 0.1010 0.1010 70.1602 9 3.2959 0.0470 0.0470 70.1255 10 1.1547 0.0160 0.0160 72.1707 decrypted image 0 100 200 0 1 2 3 x 10 4 red histogram 0 100 200 0 1 2 3 x 10 4 green histogram 0 100 200 0 1 2 3 x 10 4 blue histogram engineering, technology & applied science research vol. 9, no. 3, 2019, 4165-4168 4168 www.etasr.com al-dwairi et al.: an efficient and highly secure technique to encrypt and decrypt color images here the technique efficiency was rapidly increased but with some negative effects by increasing the psnr between the original and the encrypted image, which means that the encrypted image moves toward the original image. however, this level of psnr is still acceptable. table vi shows the efficiency speedup of increased block size. table v. mse and psnr for block size =16 and one key image number comparing encrypted image with original comparing decrypted image with original mse psnr mse psnr 1 9.1362e+003 19.6253 0 infinite 2 7.4460e+003 21.6710 0 infinite 3 7.3327e+003 21.8243 0 infinite 4 7.5590e+003 21.5203 0 infinite 5 8.6746e+003 20.1437 0 infinite 6 8.5122e+003 20.3327 0 infinite 7 8.7733e+003 20.0305 0 infinite 8 8.1958e+003 20.7116 0 infinite 9 7.7113e+003 21.3209 0 infinite 10 7.3976e+003 21.7362 0 infinite table vi. speedup with increased block size image number throughput (mbps) speed up of (2) block size=8 number of keys=4 (1) block size=16 number of keys=1 (2) 1 29.1151 71.2817 2.4483 2 28.2613 68.1597 2.4118 3 28.8462 75.0000 2.6000 4 29.2097 68.7012 2.3520 5 29.2190 73.5692 2.5179 6 29.0145 70.5993 2.4332 7 28.6624 70.8661 2.4724 8 28.6890 70.1602 2.4455 9 28.6600 70.1255 2.4468 10 29.6085 72.1707 2.4375 vi. conclusions an efficient and highly secure technique for color image encryption-decryption was proposed. the proposed technique was implemented and tested, and the experimental results showed the following conclusions: • the proposed technique is very efficient by increasing the throughput and decreasing encryption-decryption times. • the proposed technique is 100% accurate by achieving zero mse and infinite psnr between the original image and the decrypted one. references [1] m. j. aqel, z. alqadi, a. a. abdullah, “rgb color image encryptiondecryption using image segmentation and matrix multiplication”, international journal of engineering and technology, vol. 7, no. 3.13, pp. 104-107, 2018 [2] j. thakur, n. kumar, “des, aes, and blowfish: symmetric key cryptography algorithms simulation based performance analysis”, international journal of emerging technology and advanced engineering, vol. 1, no. 2, pp. 6-12, 2011 [3] s. a. m. rizvi, s. z. hussain, n. wadhwa, “a comparative study of two symmetric encryption algorithms across different platforms”, international conference on security and management, world academy of science, las vegas, usa, july 18-21, 2011 [4] s. wang, y. zheng, z. gao, “a new image scrambling method through folding transform”, ieee international conference on computer application and system modeling, taiyuan, china, october 22-24, 2010 [5] j. n. abdel-jalil, “performance analysis of color image encryption\decryption techniques”, international journal of advanced computer technology, vol. 5, no. 4, pp. 13-17, 2016 [6] g. ye, “an efficient image encryption scheme based on logistic maps”, international journal of pure and applied mathematics, vol. 55, no. 1, pp. 37-47, 2009 [7] t. sivakumar, r. venkatesan, “a novel image encryption approach using matrix reordering”, wseas transactions on computers, vol. 12, no. 11, pp. 407-418, 2013 [8] h. gao, y. zhang, s. liang, d. li, “a new chaotic algorithm for image encryption”, chaos, solitons & fractals, vol. 29, no. 2, pp. 393399, 2006 [9] g. chen, y. mao, c. k. chui, “a symmetric image encryption scheme based on 3d chaotic cat maps”, chaos, solitons & fractals, vol. 21, no. 3, pp. 749–761, 2004 [10] k. loukhaoukha, j. y. chouinard, a. berdai, “a secure image encryption algorithm based on rubik's cube principle”, journal of electrical and computer engineering, vol. 2012, article id 173931, pp. pp. 1-13, 2012 [11] x. wang, j. zhang, “an image scrambling encryption using chaos controlled poker shuffle operation”, ieee international symposium on biometrics and security technologies, islamabad, pakistan, april 23-24, 2008 authors profile majed o. al-dwairi, phd in communication systems. he was born in 1968 in jordan. he received his diploma degree in 1994 and his phd degree from ukraine state academy in 1998 in the field of multichannel communication. an associate professor in the department of communication engineering technology, faculty of engineering technology, al-balqa’ applied university, amman, jordan. his research interests include optical communication networks, digital communications, signal and image processing, antenna design, and microstrip patch antennas. amjad y. hendi, phd in radio and tv systems. he received his diploma degree in 1994 and phd degree from the ukraine state academy in 1998 in the field of radio & tv systems. his research interests include digital communications, signal and image processing, antenna design, optimization techniques in antenna design, and antenna measurement techniques and microstrip patch antennas. ziad a. alqadi, phd in computer engineering. he was born in 1955 in jordan. he received his diploma degree in 1980 and phd degree from ukraine in 1986 in the field of computer engineering. currently he is a professor at the computer engineering department, faculty of engineering technology, al-balqa’ applied university, amman, jordan. microsoft word 01-3032_s_etasr_v9_n6_pp4863-4869 engineering, technology & applied science research vol. 9, no. 6, 2019, 4863-4869 4863 www.etasr.com nguyen et al.: performance comparison between pso and ga in improving dynamic voltage stability … performance comparison between pso and ga in improving dynamic voltage stability in anfis controllers for statcom huu vinh nguyen ho chi minh city power corporation ho chi minh city, vietnam nguyenhuuvinhdlhcm@gmail.com hung nguyen hutech institute of engineering ho chi minh city university of technology (hutech) ho chi minh city, vietnam n.hung@hutech.edu.vn minh tien cao faculty of telecommunications engineering telecommunications university nha trang city, vietnam caominhtienkvtd@gmail.com kim hung le faculty of electrical engineering the university of danang-university of science and technology, vietnam lekimhung@dut.udn.vn abstract—one of statcom’s advantages is its quick response to disturbances in the power systems. the controller of statcom is commonly a pid controller. however, the pid controller is usually only highly effective at one or some operation points. in order to improve operational efficiency of the controller of statcom, the proposed anfis-pso and anfis-ga controllers have been studied and applied to the studied power system. to demonstrate the performance of the proposed controllers, simulations of the voltage response in timedomain were performed in matlab to evaluate the effectiveness of the designed controllers for statcom. the simulation results showed that the proposed controllers can be used to improve the system stability as well as the voltage quality more effectively than the conventional pid controller. the anfis pso controller carried out the best response after the occurrence of a three-phase short circuit fault. keywords-statcom; adaptive neuro-fuzzy inference system (anfis); particle swarm optimization (pso); genetic algorithm (ga); proportional integral derivative (pid); voltage stability i. introduction voltage stability issues are always concerned by the power system operator. in enhancing voltage stability using reactive power compensator [1], the series capacitors can minimize reactive power loss, enhance voltage and gain the power transfer ability of the transmission line. the use of capacitors for compensating is very beneficial but it cannot improve transient stability after fault conditions or other complicated operation conditions as short-circuit in two-phase or threephase. for solving this case, flexible ac transmission system (facts) devices were proposed to be implemented to the power grid for improving the stability of the power system. static synchronous compensator (statcom) is one of the most suitable devices that can be used not only to maintain the voltage at the connected bus but also to improve the dynamic stability of the system [2-7]. statcom is applied to improve the operational and control performance of the power system such as power transfer capability, voltage regulation, reactive power management, stability limits, power factor improvement, etc [2]. in [3], a new control strategy using a full-power wind permanent-magnet generator (pmg) with a statcom is proposed to compensate reactive power for improving transient voltage stability during and after faults. authors in [4] examined the use of statcom in improving voltage stability and performance of a dfig-based wind farm interconnected to a weak distribution system due to the effects of transient disturbances such as three phase fault, step load change, voltage swelling and sagging in the system. in [5], the results showed that statcom can significantly improve the high voltage ride through capability of type-d wind turbine and prevents it from being disconnected from the grid during voltage swell in the grid side. authors in [6] presented a design procedure for statcom which constantly updates the parameters of the pi controller to enhance the voltage profile of the multi-machine system under dynamic disturbances. besides that, statcom can be combined with power system stabilizer (pss) in multi-machine power systems for improving the voltage profile and damping oscillations of synchronous generators under normal and abnormal network conditions [7]. commonly, pid controllers are used to control statcoms. the pid controllers have robust performance across a wide range of operating conditions and functional simplicity. however, the high nonlinearity of the power system means that a pid controller can provide robust performance at a particular operating range. recently, many controllers have been applied to improve the efficiency of the device, such as the hybrid proportional integral plus fuzzy logic (pi+fl) corresponding author: huu vinh nguyen engineering, technology & applied science research vol. 9, no. 6, 2019, 4863-4869 4864 www.etasr.com nguyen et al.: performance comparison between pso and ga in improving dynamic voltage stability … damping controller designed for statcom to improve the voltage stability of a multi-machine system when a three phase short circuit occurs [8]. in addition, a fuzzy logic controller is designed for statcom to enhance the transient stability of an interconnected power system during fault occurrence. the results indicate that the fuzzy logic based statcom controller gives improved performance compared with the pi based statcom controller [9]. however, the main disadvantage of fuzzy logic controllers is that they depend on the programmer's experience. combining algorithms to exploit the advantages of each is a good solution that is being widely researched. in [10], the author proposed an algorithm that combined fuzzy logic and artificial neural networks called adaptive-network-based fuzzy inference system (anfis). anfis is a good structure for designing a controller of svc to damp power system oscillations and enhance system stability [11]. the effectiveness of the proposed controller is demonstrated on an svc located at the middle of a transmission line connecting a generator to an infinite bus. the anfis control algorithm gained attention due to its robustness in nonlinear systems. an intelligent controller that combined anfis and fuzzy turning of pid was designed to control a statcom to enhance power quality in a power system in [12]. this paper presents the anfis-pso and anfis-ga controllers of statcom for transient stability improvement of the power system after large disturbances. the controllers combine the optimal searching method of pso and ga in anfis controller for optimal system operation. simulation results illustrate the effectiveness of the proposed controllers in enhancing system stability. ii. system configuration a. studied system configuration the studied system in this paper is the power network installed in ho chi minh city, vietnam, shown in figure 1 fig. 1. single line diagram of the thu duc power network. during the last year some faults occurred in the thu duc power network, which is relevant to the intel bus. intel is a semiconductor producing company and it is very sensitive to power faults. the requirements for the power network stability are extremely strict in the current circumstance. for these reasons, it was decided to study the issue of thu duc power network using matlab. as shown in figure 1, a statcom is installed at the intel bus for investigating its efficiency in gaining voltage value. the thu duc power transmission system has a 220kv power source instead of the transmission line transferring the power from other 220kv bus and five 250mva step-down transformers for reducing the voltage from 220kv to 110kv, which is a loop circuit from thu duc bus to cat lai bus. besides, a 15mva statcom is also installed at the intel bus for researching its effectiveness and the voltage stability of the studied system. there are six load buses, namely thu duc bac, intel, tang nhon phu, thu duc dong, sao mai, cong nghe cao. b. statcom modeling a statcom is designed for regulating the voltage at its terminals by compensating the amount of reactive power in or out of the power system. when the system voltage is low, the statcom injects the reactive power to the power system. when the voltage is high, it absorbs the reactive power. besides, a statcom can be designed to act as an active filter to absorb system harmonics [13]. for analyzing the statcom, a mathematical model is used, in which the output voltage is separated into two components represented in d and q axes as follows [14-15]: vdsta = vdcsta⋅kmsta⋅sin(θbus + αsta) (1) vqsta = vdcsta⋅kmsta⋅cos(θbus + αsta) (2) where vdsta and vqsta are the voltages of d and q axes at the output terminals of the statcom, kmsta is the modulation index of the statcom, αsta is the phase angle of the statcom, θbus is the voltage phase angle of the common ac bus, and vdcsta is the dc voltage of the dc capacitor cm. the relationship between dc voltage and current of the dc capacitor can be described as: (cm)p(vdcsta) = ωb[idcsta − (vdcsta/rm)] (3) where idcsta is the pu dc current flowing into the positive terminal of vdcsta, rm is the pu equivalent resistance considering the equivalent electrical losses of the statcom, and iqsta and idsta are the currents in q and d axes flowing into the terminals of the statcom respectively. the fundamental control block diagram of the statcom including damping controller is shown in figure 2. the dc voltage vdcsta is controlled by the phase angle αsta while the voltage vsta is varied by changing the modulation index kmsta. fig. 2. control scheme of statcom engineering, technology & applied science research vol. 9, no. 6, 2019, 4863-4869 4865 www.etasr.com nguyen et al.: performance comparison between pso and ga in improving dynamic voltage stability … iii. adaptive neuro-fuzzy inference system anfis discriminates itself from normal fuzzy logic systems by its adaptive parameters, i.e. both premise and consequent parameters are adjustable. a typical architecture of the used anfis is shown in figure 3, in which a circle indicates a fixed node, whereas a square indicates an adaptive node. for simplicity, we consider two inputs x, y and one output f. among the many fis models, the sugeno fuzzy model is the most widely applied one for its high interpretability and computational efficiency, and built-in optimal and adaptive techniques. for each model, a common rule set with two fuzzy if-then rules can be expressed as [16]: rule i: if x is ai and y is bi then fi = pix+ qiy + ri. where ai and bi are fuzzy sets in the antecedent and z=f(x,y) is a crisp function in the consequent. pi, qi, ri are the updating parameters of the rule. fig. 3. configuration of anfis each anfis consists of five layers [16]: • layer 1: in this layer, input fuzzification takes place. mathematically, this function can be expressed as: )( )1()1( ijjij io µ= (4) where � �� ��� is the layer 1 node’s output which corresponds to the j-th linguistic term of the i-th input variable � �� ��� , i is the number of input variable and j is the number of linguistic terms of each input. in this research, i=2 and j=5. ijb ij iji ijj a cx i − + = 1 1 )( )1(µ (5) where the triplet of parameters (aij, bij, cij) are referred to as premise parameters or non-linear parameters and they adjust the shape and the location of the membership function. those parameters are adjusted during the training mode of operation by the error back-propagation algorithm. • layer 2: the total number of rules in this layer is 25. each node output represents the activation level of a rule, with k representing rule number: ∏ == q i ijkk owo 1 )1()2( (6) • layer 3: the output of the k-th node is the firing strength of each rule divided by the total sum of the activation values of all the fuzzy rules. this results in the normalization of the activation value for each fuzzy rule. this operation is simply written as: ∑ = == y m m k kk o o wo 1 )2( )2( )3( (7) • layer 4: each node k in this layer is accompanied by a set of adjustable parameters �� , � , …, ��� ��� , �� , ��, and implements the linear function: )...( 0 )1( 1 )1( 22 )1( 11 )4( )4( kninputkkkk kkk dididido fwo ++++= = (8) • layer 5: the single node in this layer computes the overall output as the summation of all incoming signals, which is expressed as: ∑ ∑ ∑∑ = = == === y k k y k kky k kk y k kk w fw fwoo 1 1 11 )4()5( (9) a. particle swarm optimization (pso) algorithm pso is a meta-heuristic algorithm, inspired by the collective intelligence and behavior of birds and fish. this algorithm was at first based on simple mathematical relations, considering the movement patterns of birds for the optimization of complex problems [17]. the algorithm starts by randomly creating an initial population. in fact, each particle shows a possible response. each particle starts to move and search in the problem space in order to find the most appropriate point. in each step, this particle is fitted by its objective function and is placed toward the most appropriate direction to determine the most accurate and precise response. each particle continues its movement each time using its experience and its neighbors in the problem search space. other particles move towards the particle with the best position and correct their directions. therefore, the movement of particles in the problem search space depends on three factors including the present position of the particle, the best location that a particle has experienced, and the best location of all the particles. in each cycle, the aim is to identify a particle that finds the best momentary position and the other particles move towards it considering the superiority of the most appropriate particle in terms of location. this continues until all particles gather together at the best point [18]. these calculations are based on (10) and (11): ( 1) ( ) ( ) 1 1 ( ) 2 2 ( ) ( ) k k k i i i i k i i v wv c r pbest x c r gbest x + = + − + − (10) )()()1( k i k i k i vxv += + (11) in (10), i=1,...,n, where n is the population size, and k=1,2,3,... is the iteration number in the algorithm process. engineering, technology & applied science research vol. 9, no. 6, 2019, 4863-4869 4866 www.etasr.com nguyen et al.: performance comparison between pso and ga in improving dynamic voltage stability … � � � ��� is the new velocity vector for the i th particle, � � � � indicates the existing velocity vector for the i th particle, pbesti is the best position that the i th particle has experienced, and gbest is the best experienced position of all particles. in (11), � � � � is the present position of the i th particle and the new position of the i th particle, w is the weight inertia, which is used in the class of particles to ensure the convergence and is suggested to be in the range of 0.4-0.9, r1 and r2 are random numbers from 0 up to 1, c1 and c2 are two fixed and positive values that are introduced as the personal learning factor and the global learning factor respectively, and have a significant role in the algorithm’s convergence controlling process. it is worth mentioning that the condition c1+c2≤4 must always be met. the steps of pso are: (1) initialize the swarm of particles in random positions within the hyperspace. (2) evaluate the performance of each particle, using its current position. (3) compare the performance of each individual to its best performance. (4) change the velocity vector for each particle. (5) move each particle to a new position. (6) go to 2 and repeat until convergence. the parameters are initialized randomly in step (1), then they are being updated in each cycle. in the first iteration {ai} are updated, then in the second iteration {bi} are updated, then {ci} are updated and then after updating all parameters again {ai} are updated and the process is repeated. b. genetic algorithm (ga) ga is a random search technique that imitates natural evolution with darwinian survival of the fittest approach. it can handle any kind of objective function and constraints without many mathematical requirements. the population strategy enables ga to search near optimal solutions from various parts and directions simultaneously within a search space [19]. ga uses random choice and probabilistic decision to guide the research, where the population improves towards near-optimal point from generaton to generation. in ga, the problem’s variables are represented as genes in a chromosome, and the chromosomes are evaluated according to their fitness values. the chromonosomes with better fitness are found through the three basic operations of ga: selection, crossover and mutation. the genetic operators alter the composition of genes in order to create new chromosomes, called offspring, and with the selection operator, chromosomes with better fitness have higher probabilities of being selected in the next generation. genetic algorithm’s steps are: 1. generate the initial population. 2. generate the consequent parameters for every chromosome. 3. evaluation of each chromosome in the population using the objective function, and storing the best chromosomes. 4. employing the genetic operator to obtain new chromosomes (selection, crossover, and mutation). 5. generate the parameters for each of the new elements. 6. evaluation of each chromosome, and storing of the new best chromosomes. 7. if the stopping criterion is validated then the paramerters are stored, else return to step 4. 8. recover of the best particle. iv. simulation results the task of a learning algorithm is to tune all the modifiable parameters to make the anfis output match the training data. the overall output is a linear combination of the modifiable parameters. the training algorithms require a training set between inputs and outputs. in this paper, both training algorithms pso and ga were used to optimize membership function parameters of anfis in order to minimize the cost function which is rmse. 2 1 1 ( ) n i i i rmse x y n = = −∑ (12) the data sets that are required for training purposes are obtained using a pid controller with a sample time of 0.001s. characteristics of the initial parameters of anfis, pso and ga are shown in tables i, ii, and iii respectively. table i. characteristics of the anfis model anfis parameter value type sugeno number of clusters 5 inputs/outputs [2 1] number of input mfs [5 5] number of training data 1250 table ii. pso parameters pso parameter value population size 25 maximum number of iterations 1000 inertia weight (w) 1 personal learning coefficient (c1) 1 global learning coefficient (c2) 2 inertia weight damping ratio (wdamp) 0.99 table iii. ga parameters ga parameter value population size 25 maximum number of iterations 1000 crossover percentage (pc) 0.4 mutation percentage 0.7 mutation rate (µ) 0.15 selection pressure (β) 8 the proposed models have acceptable accuracy and rmsepso=0.20036 and rmsega=0.20037. simulation results of the proposed anfis-pso and anfis-ga controllers of statcom after training, were used to compare the damping characteristics on transient stability improvement of the studied system under a three-phase short-circuit fault at the specified buses of the power grid. it was assumed that the three-phase short circuit fault happened on the transmisstion line from the 110kv thu duc bac substation to 110kv intel substaton in 0.1s. simulation results are presented in figures 5 and 6. these figures plot the comparative transient responses of the studied system with the proposed statcom in the cases of pid controller (black dotted line), with anfis-pso controller (red line) and anfis-ga controller (blue line) subject to a threephase short-circuit fault in 0.1s from 0.3s to 0.4s. engineering, technology & applied science research vol. 9, no. 6, 2019, 4863-4869 4867 www.etasr.com nguyen et al.: performance comparison between pso and ga in improving dynamic voltage stability … fig. 4. pso and ga training results (a) (b) fig. 5. the voltage of intel bus after a three-phase fault. (a) voltage, (b) zoom in of voltage wave (a) (b) (c) (d) (e) (f) fig. 6. response at each bus of the system when a three-phase short circuit fault happened in the intel bus: (a) thu duc dong bus, (b) sao mai bus, (c) thu duc bac bus, (d) cong nghe cao bus, (e) tang nhon phu bus, and (f) cat lai bus. figure 5 shows the voltage wave of intel bus after a threephase fault, while figure 6 shows the voltage of the six buses. with these figures, it can be easily seen that by applying the hybrid pso-anfis and anffis-ga controllers for statcom, the output values of these parameters are more stable and more effective, the voltage of each node is improved on overshoot and setting time after a three-phase short circuit fault occured. engineering, technology & applied science research vol. 9, no. 6, 2019, 4863-4869 4868 www.etasr.com nguyen et al.: performance comparison between pso and ga in improving dynamic voltage stability … table iv. controller result comparison items bus pid anfis ga anfis pso setting time (s) intel 0.5373 0.4904 0.487 thu duc dong 0.5374 0.4876 0.4876 cong nghe cao 0.4979 0.4571 0.4465 tang nhon phu 0.5475 0.5067 0.4877 thu duc bac 0.4976 0.4468 0.4462 cat lai 0.4977 0.4569 0.428 maximum voltage (pu) intel 2.53 1.15 1.11 thu ducdong 2.18 1.12 1.09 cong nghe cao 1.36 1.06 1.04 tang nhon phu 2.35 1.13 1.10 thu duc bac 1.46 1.06 1.04 cat lai 1.36 1.06 1.04 percent of overshoot (pot) (%) intel 158% 17% 13% thu duc dong 123% 14% 11% cong nghe cao 38% 8% 6% tang nhon phu 139% 15% 12% thu duc bac 49% 8% 6% cat lai 38% 8% 6% by observing the voltage response at the intel bus shown in figure 5, it can be seen that the voltage dropped to zero during the fault. the voltage response at thu duc dong and and tang nhon phu also dropped to zero due to these buses neighboring with the intel bus. however, as shown in the response plotted in figure 6(b), 6(c), 6(e), and 6(f) the voltage magnitude of sao mai, thu duc bac, cong nghe cao, and cat lai bus only dropped to 0.4p.u. based on the operation of the statcom and its controllers, a large amount of reactive power was supplied in order to improve the voltage response of the buses. in order to compare the efficiency between controllers, percent of overshoot (pot) indice and setting time were used. these indexes are shown in table iv. in the case of using anfis pso controller, the pot of voltages at intel, thu duc dong, cong nghe cao substations were 13%, 11%, and 6%, respectively. when using the anfis ga controller, the pot of voltages at intel, thu duc dong, cong nghe cao substations were 17%, 14%, and 8%, respectively. meanwhile, the voltage overshoot in the case of pid controller was 158%, 123%, and 38%. regarding voltage setting times after fault isolation, which is the time of voltage recovery within the permissible range of 5%, the anfis-pso controller gave the smallest values. with the anfis-pso controller, the voltage setting time at intel, thu duc dong, cong nghe cao substations was 0.4871s, 0.4876s, and 0.4465s, respectively. in the case of pid controller, the voltage setting time was 0.5373s, 0.5374s, and 0.4979s, respectively. for a clearer exhibition of the effectiveness of the proposed controllers, figure 7 shows the simulation results of the studied system when a three-phase short circuit fault occurs at the 110kv cong nghe cao substation. all the simulation results demonstrate that the preoposed anfis-pso and anfis-ga controllers are more effective than the conventional pid controller, and anfispso controller exhibited the best response. v. conclusions this paper presented the results of a research on finding the parameters of membership functions of an adaptive system using particle swarm optimization and genetic algorithms. hybrid anfis-pso and anfis-ga controllers for statcom were designed and applied in the thu duc power network. statcom can support fast response to the system to balance reactive power in the grid, in order to help improving dynamic voltage stability. the simulation results showed that the proposed controllers improve system stability and voltage quality more effective than the conventional pid controller. the anfis pso controller carried out the best response after the occurrence of a three-phase short circuit fault. (a) (b) (c) fig. 7. responses at each bus of the system when a three-phase short circuit fault happened in the cong nghe cao bus: (a) intel bus, (b) thu duc dong bus, and (c) cong nghe cao bus. references [1] m. kowsalya, k. k. ray, d. kothari, “voltage stability margin enhancement through the optimal location of var compensator”, ieee 2008 international conference on sustainable energy technologies, singapore, november 24-27, 2008 engineering, technology & applied science research vol. 9, no. 6, 2019, 4863-4869 4869 www.etasr.com nguyen et al.: performance comparison between pso and ga in improving dynamic voltage stability … [2] r. jadeja, s. patel, s. chauhan, “statcom: a preface to power quality in power systems performance”, engineering, technology & applied science research, vol. 6, no. 1, pp. 895-905, 2016 [3] m. n. eskander, s. i. amer, “mitigation of voltage dips and swells in grid-connected wind energy conversion systems”, 2009 iccas-sice, fukuoka, japan, august 18-21, 2009 [4] b. pokharel, w. gao, “mitigation of disturbances in dfig-based wind farm connected to weak distribution system using statcom”, north american power symposium (naps), arlington, usa, september 2628, 2010 [5] y. m. alharbi, a. m. s. yunus; a. a. siada, “application of statcom to improve the high-voltage-ride-through capability of wind turbine generator”, 2011 ieee pes innovative smart grid technologies, perth, australia, november 13-16, 2011 [6] a. ganesh, r. dahiya, g. k. singh, “development of simple technique for statcom for voltage regulation and power quality improvement”, ieee international conference on power electronics, pedes, trivandrum, india, december 14-17, 2016 [7] g. shahgholian, e. mardani, a. fattollahi, “impact of pss and statcom devices to the dynamic performance of a multi-machine power system”, engineering, technology & applied science research, vol. 7, no. 6, pp. 21132117, 2017 [8] h. v. nguyen, h. nguyen, k. h. le, “hybrid damping controller for statcom to enhance power quality in multi-machine system”, international conference on system science and engineering, ho chi minh city, vietnam, july 21-23, 2017 [9] a. awasthi, s. k. gupta, m. k. panda, “design of a fuzzy logic controller based statcom for ieee9 bus system”, european journal of advances in engineering and technology, vol. 2, no. 4, pp. 62-67, 2015 [10] j. s. r. jang, “anfis: adaptive-network-based fuzzy inference system”, ieee transactions on systems, man, and cybernetics, vol. 23, no. 3, pp. 665–685, 1993 [11] a. albakkar, o.p. malik, “adaptive neuro-fuzzy facts controller for transient stability enhancement”, 16th national power system conference, december 15-17, osmania university, india, 2010 [12] h. v. nguyen, h. nguyen, k. h. le, “anfis and fuzzy tuning of pid controller for statcom to enhance power quality in multi-machine system under large disturbance”, aeta 2018: recent advances in electrical engineering and related sciences: theory and application, ostrava, czech republic, september 11-13, 2018 [13] a. ganesh, r. dahiya, g. k. singh, “development of simple technique for statcom for voltage regulation and power quality improvement”, ieee international conference on power electronics, drives and energy systems, trivandrum, india, deccember 14-17, 2016 [14] a. varshney, r. garg, “comparison of different topologies of fuzzy logic controller to control d-statcom”, 3rd international conference on computing for sustainable global development, new delhi, india, march 16-18, 2016 [15] d. shen, p. w. lehn, “modeling, analysis and control of a current source inverter based statcom”, ieee transactions on power delivery. vol. 17, no. l, pp. 248-253, 2002 [16] j. jang, c. sun, e. mizutani, neuro-fuzzy and soft computing, prentice hall, 1997 [17] j. kennedy, r. c. eberhart, “particle swarm optimization”, ieee international conference on neural networks, perth, australia, november 27-december 1, 1995 [18] p.s. you, “an efficient computational approach for railway booking problems”, european journal of operational research, vol. 185, no. 2, pp. 811-824, 2008 [19] f. solomonese, c. barbulescu, s. kilyeni, m. litcanu, “genetic algorithms. power systems applications”, 6th international conference on human system interactions, sopot, poland, june 6-8, 2013 authors profile huu vinh nguyen was born in vietnam. he received his bsc and msc degrees from the electrical and electronics engineering department of ho chi minh city university of technology, vietnam in 2001 and 2009 respectively. he is now working for ho chi minh city power corporation, vietnam. his research fields include power system operation, facts, renewable energy, and power quality. minh tien cao was born in vietnam. he received his bsc degree from telecommunications university, vietnam in 2008. he received his msc degree from posts and telecommunications institute of technology, vietnam in 2011. he is now working for the telecommunications university, nha trang city, vietnam. his research fields include operation and stability of power systems, facts, and renewable energy. hung nguyen was born in vietnam. he received his bsc and msc degrees from the electrical and electronics engineering department of ho chi minh city university of technology, vietnam in 2000 and 2004 respectively. he received his phd from the pukyong national university, korea, in 2010. he is currently a associate professor in the hutech institute of engineering, ho chi minh city university of technology (hutech), vietnam. his research interests include nonlinear control, facts, power system operation, and renewable energy. kim hung le was born in vietnam. he is currently a professor in the faculty of electrical engineering, university of science and technology, university of danang, vietnam. his research interests include facts, power system protection, and renewable energy. engineering, technology & applied science research vol. 8, no. 6, 2018, 3502-3504 3502 www.etasr.com papadakis et al.: surface discharges and flashover voltages in nanocomposite xlpe samples surface discharges and flashover voltages in nanocomposite xlpe samples c. papadakis democritus university of thrace department of electrical and computer engineering power systems laboratory xanthi, greece m. g. danikas democritus university of thrace department of electrical and computer engineering power systems laboratory xanthi, greece y. yin shanghai jiao tong university department of electrical engineering school of electronic, information and electrical engineering, shanghai, china c. charalambous democritus university of thrace department of electrical and computer engineering power systems laboratory xanthi, greece abstract—dc cable insulation is a field of intensive research activity. special attention is being given to polymer nanocomposites, as promising insulation for such cables. relatively little is known regarding surface discharges and flashover voltages for the aforementioned materials. in this paper, a comparison is made between samples of cross-linked polyethylene insulation with added mgo nanofillers and samples of pure polyethylene w.r.t. the behavior of surface discharges and flashover voltages in arrangements of water droplets of various conductivities on the said polymeric surfaces under the influence of uniform electric fields. experimental evidence indicates that the flashover voltages of xlpe with mgo nanofillers are higher that the ones obtained with pure pe. keywords-discharge; flashover; cable; xple; nanocomposite i. introduction power transmission through dc voltage becomes increasingly popular, especially in countries with extended areas, such as china or the usa. recently, efforts are being undertaken in the direction of polymer nanocomposite insulation for dc applications [1-3]. a possible candidate for such applications is the cross linked polyethylene (xlpe) with added mgo nanofillers 0.5 wt%. surface discharges and subsequent flashovers constitute, among others, a danger for such insulation [4]. in this paper, surface discharges and flashover voltages of the above mentioned polymer nanocomposite are compared with those of pure polyethylene (pe). water droplets of various conductivities are put on the polymeric surfaces and the discharge phenomena are studied under the influence of uniform electric fields. ii. experimental set-up in the context of this work, a transformer with a rated voltage of 20 kv was used. the electrodes used were of brass and they are shown in figure 1. the distance between the electrodes was set at 2.5 cm in all experiments. uniform electric fields were applied in all experiments. the water droplets were positioned on the polymeric surface with the aid of a 10 ml syringe and a special arrangement consisting of a metallic frame and three rules, one of which had two laser indicators. the positioning of the droplets w.r.t. the electrodes can be seen in figure 2. the insulation materials investigated were pure pe and xlpe with added mgo nanofillers (having 0.5 wt% nanofillers). the water droplets were of the following conductivities: 0,8 μs/cm, 100 μs/cm, 200 μs/cm, 500 μs/cm, 1000 μs/cm, 2000 μs/cm, 5000 μs/cm and 10000 μs/cm. each single droplet has a 0.05 ml volume. fig. 1. the brass electrodes used for the experiments engineering, technology & applied science research vol. 8, no. 6, 2018, 3502-3504 3503 www.etasr.com papadakis et al.: surface discharges and flashover voltages in nanocomposite xlpe samples fig. 2. the various water droplet arrangements used the experimental procedure was the following: once the water drops of specified volume and conductivity was placed on the insulating material in one of the aforementioned arrangements, the output voltage of the power supply was gradually increased until the flashover of the gap and the recording of the breakdown voltage. after cleaning the insulating surface with alcohol, we repeated the same procedure by increasing the voltage of the power supply until the last recorded value not to bring about the flashover of the gap was reduced by 1,2 kv. at this point we left the output voltage of the power supply steady for five minutes to provide the necessary time for the process of deformation of the drop to be developed, the occurrence of partial discharges and/or ultimately the flashover to occur. if there was no flashover, the voltage was increased at 0.4 kv steps until the occurrence of a flashover. this was the value of flashover voltage that was finally recorded. the parameters that were investigated were: 1) the water droplet arrangements, 2) water conductivity, 3) water droplet volume, 4) the insulating material used and 5) the positioning of the droplets w.r.t. the electrodes. iii. experimental results and discussion a water droplet on a polymeric surface is affected by the surface tension of the liquid, the surface tension of the solid, the interfacial tension between the droplet and the solid as well as by the applied electric field. the latter causes deformation/elongation of the droplet. such deformation will affect the distribution of the electric field, which in turn will again act upon the droplet. there is a so to speak a feedback mechanism, which will eventually cause local field intensifications and microdischarges. dry zones will ensue and finally the flashover will result [5]. in figure 3, the flashover voltages of pure pe, for water droplet arrangements, such as those of figure 2 (each water droplet of 0.05 ml volume), are shown with varying conductivity. it is evident that the twodroplet horizontal arrangement gives the lower results, whereas the other three droplet arrangements seem to give more or less similar flashover voltages for the various conductivities, with the one droplet arrangement giving the best results and with the three droplet arrangement giving somehow lower flashover voltages in higher conductivities. evidently the positioning of the droplets w.r.t. the electrodes plays a vital role in determining the flashover voltage. fig. 3. flashover voltages for various droplet arrangements on pe surfaces in figure 4, the flashover voltages for the xlpe with added mgo nanofillers are shown (each droplet having 0.05 ml volume). again we observe that the two droplet horizontal arrangement gives the worst flashover voltages whereas the other three droplet arrangements give somehow similar flashover voltages. in this case again, the three droplet arrangement gives lower flashover voltages at higher conductivities. fig. 4. flashover voltages for various droplet arrangements on xlpe surfaces with added mgo nanofillers if one compares figures 3 and 4, it seems that xlpe with added nanofillers gives higher flashover voltages compared to pure pe, for all droplet arrangements and for all conductivities tested. although the experiments performed in the context of the present work are not of long duration, one may see a difference between xlpe with nanofillers and pure pe. the reason as to why this should be so was given some years ago in [6-7], where it was proposed that with polymer nanocomposites, discharge activity tends to force the nanofilers (or agglomerations of them) to come onto the surface, hindering thus the propagation of surface discharges. recent saxs measurements of xlpe samples (with added nanofillers) as well as of pure pe samples showed that the engineering, technology & applied science research vol. 8, no. 6, 2018, 3502-3504 3504 www.etasr.com papadakis et al.: surface discharges and flashover voltages in nanocomposite xlpe samples surface of the former after discharging tends to be more compact [8]. this is in agreement with [6-7]. xlpe with mgo nanofillers after discharge shows increasing crystallinity, which again can be explained with increasing nanofillers agglomerates. the aforementioned interpretations seem to be in agreement with [9], where it was reported that there can be surface modifications of the nanocomposites and of the nature of the interface in the region around the nanofillers. these views are also shared in [10, 11]. it is true that the present research was carried out using ac voltages whereas it is intended that the tested materials will be used for dc transmission. nevertheless, after the dc transmission the voltage has to be changed to ac, and this fact underlines the importance of studying the above materials also under ac conditions. further steps towards a better clarification can be taken, such as more experiments with a larger variety of droplet arrangements, experiments with xlpe having various mgo nanofiller percentages and comparative contact angle studies between xlpe with mgo nanofillers and pure pe. especially about the latter, there were reports that the addition of nanofillers in xlpe increases the contact angle [12]. the interpretation related to the hardening of the nanocomposite surface needs to be further explored, especially in view of recent research indicating that nanofillers may accelerate the dissipation of surface space charge, i.e. rapid charge dissipation may be due to high shallow trap density created by nanofillers. shallow traps can capture electrons and fast electrons can be converted to slower electrons [13]. iv. conclusions in this paper, indications that the xlpe with added nanofillers of mgo performs better than pure pe regarding the flashover voltage, were presented. this may be due to the gradual erosion of the base polymer and the coming onto the surface of the nanocomposite of the nanofillers (or agglomerations of them) which eventually hinder the further propagation of surface discharges. more experiments will further elucidate the phenomena of surface discharge and flashover in nanocomposites. acknowledgments the samples of the present work have been prepared at shanghai jiao tong university by the group of prof. yi yin. references [1] c. w. reed, “an assessment of material selection for high voltage 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and babic: implementation of a flexible bayesian classifier for the assessment of patient’s… implementation of a flexible bayesian classifier for the assessment of patient’s activities within a real-time personalized mobile application vanja miskovic faculty of ιnformation τechnology slobomir p university, spu bijeljina, bosnia and herzegovina vanja.elcic@gmail.com djordje babic school of computing union university belgrade, serbia djbabic@raf.edu.rs abstract—this paper presents an implementation of a mobile application that provides a real-time personalized assessment of patient’s activities by using a flexible bayesian classifier. the personalized assessment is derived from data collected from the 3-axial accelerometer sensor and the counting steps sensor, both widespread among nowadays mobile devices. despite the fact that online mobile solutions with bayesian classifier have been rare and insufficiently precise, we have proven that the accuracy of the proposed system within a defined data model is comparable to the accuracy of decision trees and neural networks. keywords-activity recognition; real-time mobile application; flexible bayesian classifier. i. introduction major goals of an intelligent system for patient monitoring are detection of health deterioration and notifying medical staff if a patient's health condition is life-threatening. a basic prerequisite for making a correct assessment is a reliable, accurate, timely source of raw data which indicate patient's vital signs. further, the collected raw data is modeled with context-aware approach, in other words, the raw data is placed in an appropriate context. this is necessary because the collected data as raw facts cannot help in decision-making. it is necessary to analyze data features that can contribute to the making of the right decision. the development of the sensor network technologies (bluetooth [1] and zigbee [2]) focuses on health care ("healthcare" profiles) and development of standardized wearable medical sensing devices (continua health alliance [3]). the following parameters can be pointed out as the most important quality of context (qoc)-parameters [4]: precision, probability of correctness, trust-worthiness, resolution and up-to-datedness. in addition to the vital signs, a very important precondition for assessing the patient's health condition is also a correct assessment of physical activities which the patient performs at a given time. therefore, all intelligent systems designed for patient monitoring, as for an example the system in [5], firstly assess the patient physical activity and secondly provide an evaluation of the patient's health. the considerable physical activities of the patient are resting, sitting, standing and physically demanding activities, for example climbing up the stairs or running. in order to estimate the activity of the patient, appropriate sensing devices are required. a very common approach to estimate activity is a combination of 3-axial accelerometers and/or 3-axial gyroscope and/or 3-axial magnetic sensors. the patient should always carry/wear the aforementioned sensors because he/she should be monitored by the system continuously in everyday activities. various placements of the sensing devices on human body have been proposed. the most common placements of sensing devices are: mobile phone in a front pocket of trousers [6], accelerometer sensors on five different positions: elbow, wrist, knee, ankle and hip [7], mobile phone in left pocket, right pocket, belt, wrist and upper arm [8], mobile phone in hand or where patient typically holds it while doing specific activity in [9] etc. usually the research focus is on offline testing of designed systems, whereas very few researchers implement and test systems in a real time (online) [9, 10]. from the beginning, the basic concept has been that these systems are generally applicable to any patient, while the latest studies show examples of personalized systems [8]. the personalized system gives an estimate for the patient based on his/her collected data. in a personalized system, the data must be collected for every patient in order to train the system and later to make an assessment. this type of systems should be more accurate than the generalized systems which are based on a common large database with collected data, where the same data are used for assessment for any patient. this paper presents an implementation of the mobile application that provides real-time personalized assessment of physical activity. the presented personalized mobile application collects sensor data from a patient using his/her mobile phone in a free living environment, both for system training and decision making. a target group for the presented application is a group of chronic patients and process of collecting sensor data for certain activities may be limited. in addition, in real life, a certain activity is done less often than other, for example we climb up the stairs less often than we walk, and unfortunately sitting is the most common body engineering, technology & applied science research vol. 7, no. 1, 2017, 1405-1412 1406 www.etasr.com miskovic and babic: implementation of a flexible bayesian classifier for the assessment of patient’s… posture. therefore, the application allows that a different number of data instances are collected per activity. the patient's movement data is gathered using a 3-axial accelerometer sensor and sensor for counting steps, both available in nowadays mobile devices. the mobile phone is designated to be carried in pockets of trousers, skirts or track suits where it fits in the execution of certain activity. all above system's features are selected in accordance with the understandable desire of patients that the monitoring system has to be easy to carry and use [11]. in the proposed personalized mobile application, the flexible bayesian classifier (fbc) is a chosen algorithm for the assessment and it is implemented according to [12]. flexible and naïve bayesian classifiers (nbc) with minor changes are implemented in the weka environment, as well [13], but it is not applicable for android platforms. there are several sources, such as [10], stating that the naïve bayesian classifier shows a very low accuracy. in [10], its accuracy is 48% while the k-nearest neighbor (knn) algorithm has an average accuracy of 92%. both algorithms showed that mobile phones’ resources are sufficient for them. naïve bayesian classifier demanded more processing power (42% compared to knn's 29%). however, when it comes to memory the situation is opposite and the knn needed about 21.9 mb while the nbc demanded about 12.6 mb. in [9], a 1-nearest neighbor classifier has been implemented in a mobile phone, while a naïve bayesian classifier has been tested offline within weka environment. although it seems to be too simple and the current real-time implementations are rare and aren't promising, nbc with the careful selection of the training data showed [14, 15] that in some applications, even in medicine, its effectiveness can be compared with neural networks and decision trees. therefore, one of the objectives of this paper is to identify the relevant features of the collected data from accelerometer and sensor that counts steps. the following standard activities are selected for testing: sitting, standing, walking, running or jogging, climbing up the stairs and descending the stairs. we show here that, the real-time personalized mobile application using fbc implemented on a mobile phone with average performances provides activity assessment with satisfying accuracy. convenient periods for prediction as well as the minimum amount of samples in a training data model are determined experimentally. offline tests are carried out in weka environment and the fbc is compared to other algorithms, such as j48 and multilayer neural network. a real-time testing of the proposed mobile application is conducted in a free living environment, and the results are presented in this paper. ii. raw data collection and pre-processing an assessment of activities is made based on the time series obtained from the real-time signals. the data is collected by accelerometer sensor for all three axes: x, y and z. the android api offers four abstract frequencies for its accelerometer: fastest, game, normal, and ui. however, the various sensors implemented in mobile phones do not support all four frequencies, but they support only one or two frequencies. the fastest frequency supported by the most mobile phones at the market is 50 hz. this is quite acceptable for the recognition of physical activity of the patient [8]. the chosen time period for signal analyses is 8s with an overlap of 4s. this practically means that an assessment is actually provided every 4s. the signal features used for the assessment are calculated for all three x, y, z axes, and resulting acceleration r, which is calculated as: 222 zyxr    android os runs onsensorchanged() event every time there is a change in the sensor values. usually, this event does not occur more frequently than 50hz. therefore, it is convenient to use a special timer task that is executed on a separate thread. the application runs the thread every 20ms and stores currently detected accelerations on x, y, z axes along with data from sensor which counts steps for later use. in this manner, there are 50 samples for x, y and z axes collected in one second. within chosen period of 8s there are 400 samples per axis, and all together 1200 samples for all three axes. the obtained signal is preprocessed in order to calculate the energy of the signal. the role of preprocessing is to eliminate noise in the signal which occurs as a result of irregularities in the sensor operation. the noise can be generated also by quick movements of person, such as turning a mobile phone, or walking over obstacles, and so on. first, the signal is smoothed by signal interpolation increasing the number of samples per second to 100. after that, a simple moving average filter of length five is applied. the filter proved to be enough to smooth false peaks, but also to preserve specific forms of signals that allow us to distinguish activities. after preprocessing the signal contains 800 samples within the interval of 8s. algorithms for data classification extract appropriate features from the raw or smoothed signal, in the same way which human would use to classify activity by observing signals charts. all statistical features are calculated from the raw data. these calculations are acceptable to the capabilities of mobile phones, while calculation of energy of smoothed signal represents moderately demanding task. analyzing previous studies [6, 8, 9, 15, 16], we select the following signal features: 1. the signal energies for all three axes: x, y and z, as well as the resultant acceleration r are calculated by using fft. fft is performed over 512 samples twice for each interval with an overlap of 224 samples (2x512-224=800). before fft, hann window function is applied to the signal. the obtained fft coefficients are normalized with sum of window function coefficients. for the resulting complex fft coefficients x[i], energy is calculated as [15]:   w w i ix e   1 2   where w is a window length. engineering, technology & applied science research vol. 7, no. 1, 2017, 1405-1412 1407 www.etasr.com miskovic and babic: implementation of a flexible bayesian classifier for the assessment of patient’s… the signal energy of an acceleration data can discriminate low intensity activities such as lying from moderate intensity activities such as walking and high intensity activities such as jogging [16]. 2. arithmetic means for all three axes x, y, z and resultant r are calculated using raw data. 3. minimum and maximum values for all three axes x, y, z and resultant r are calculated using raw data. 4. standard deviations for all three axes x, y, z and resultant r are calculated using raw data:   , 1 1 2 _      n n i savg i s    where n is a number of samples. 5. skewness is a measure of the asymmetry of the probability distribution. a negative skewness means that distribution is skewed to the left, and in the other words aboveaverage values are more frequent. a positive skewness means that distribution is skewed to the right and below-average values are more frequent. 3 , 3 22 3 2 ( _ ) ( _ ) 1 13 , 2 m skew m n n s avg s s avg si ii i n n m m          6. kurtosis is a measure that indicates whether a probability distribution is flatter or more peaked than the normal distribution. kurtosis has a negative value for flattened and positive value for pointed probability distribution. n n i savgis m m kurt m      1 4 )_( ,3 22 4 4   7. in [15], it is stated that by using correlation between axes it is possible to differentiate walking and jogging from climbing the stairs up and down. therefore, the correlations of x and y, x and z, x and r, y and z, y and r, z and r are calculated. the correlation of x and y is calculated using a covariance as: ( , ) ( , ) , ( _ )( _ ) 1 1 ( , ) cov x y corr x y x y n x avg x y avg yi ii n cov x y           8. in addition to the data collected from the accelerometer, the mobile application collects data from the sensor for counting steps (sensor step counter).the patient can carry mobile phone in different pockets in clothing, thus the step counter can register more steps or some steps can be skipped. the counter is only reset when the device is rebooted and in the meantime continues to count the detected steps. therefore, an interesting feature for a single 8s time interval is a number of steps counted during interval. the number of steps is not reliable feature to distinguish the activities, for example the difference between walking and climbing the stairs. however, it is important feature to identify the resting compared to the significant physical efforts. the [6] gives the signal properties for x, y and z axes for several activities under controlled conditions. these activities are still standing and sitting, and walking/jogging while the phone with sensor is placed in the pants front pocket. in the case of still sitting a mobile phone with sensor is usually positioned horizontally, thus the earth’s gravitation causes that the accelerometer measures a value of about 9.8 m/s2 on the axis z. in this case, there are very small changes of acceleration on the axes x and y. aforementioned values are typical for any activity which is based on sitting without any significant movements, examples of such activities can be working at the computer, turning around, moving the legs, etc. in the same way, for the still standing with a phone in the pants front pocket, the acceleration on y-axis is close to the gravitational acceleration. this is due to the fact that for standing the mobile phone is in its vertical orientation and its axis y is orthogonal to the ground. leg movements and turning around can disturb these features. the test data collected during everyday activities, which are not strictly controlled; show that they are a reflection of patient’s habits and behavior. figure 1 illustrates the measured signals for all three axes in the case of sitting (above) and standing (below). the signals are shown after preprocessing with resolution of 100 samples per second. thick lines represent the signal after smoothing explained above, and thin lines which are visible in some areas represent raw interpolated signal. figure 2 shows signals collected for activities of walking (above) and running (below). a difference between smoothed and raw interpolated signal is more visible here. figure 2 shows signals when a mobile phone was located in the trousers pocket for walking and in the wider tracksuits front pocket for running. in repetitive activities (i.e. walking and running) regular peaks can be seen at y and z axes. in the case of different placement of the phone, a frequency of peaks does not have to follow the same rule [6]. for example in [6], the time between successive peaks on the y-axis is: ½ s for walking and ¼s for running. these peaks clearly indicate that it is the activity with periodic behavior and frequency of these peaks is the highest for running. if signal smoothing decreases significant peak values, minimum and maximum values of raw data will preserve higher peak values on the axis y. the signals for activities descending the stairs (above) and climbing the stairs up (below) are illustrated in figure 3 the descending the stairs signal has a noticeable feature of the series of small peaks on the axis y. the z-axis values show a engineering, technology & applied science research vol. 7, no. 1, 2017, 1405-1412 1408 www.etasr.com miskovic and babic: implementation of a flexible bayesian classifier for the assessment of patient’s… similar trend with negative acceleration, reflecting the regular movement down each stair [6]. the peaks on the axis x are small and semi-periodical. the acceleration on the axis x alternates between positive and negative values. the signal on axis x has a similar behaviour in both examples. when climbing up the stairs the patient is usually slower and the frequency of peaks on the y axis should be lower. in the case of climbing up the stairs z axis has higher positive peaks, and again as with the descending down the stairs it is negative where y is positive and vice versa. based on the presented signal in figure 3, one can conclude that it is very difficult to distinguish climbing up and descending down the stairs. sitting and standing are different from all other activities. moderate walking is differentiated easily from running, as exhaustive activity. for the system for patient monitoring, even these classes of activities: resting, moderate and exhaustive; provide sufficient information for the assessment of vital signs. fig. 1. examples of x, y and z signals for sitting (above) and standing (below). iii. flexible and naïve bayesian classifier naïve bayesian classifier (nbc) has a high accuracy if classification model learns from data set that can be represented as a conjunction of discrete and/or continuous attributes [12]. as a result, the classifier gives the most probable class from a limited set of classes c. the classifier learns from a set of samples. the sample is an n-tuple of attribute values (a1, a2, ..., an). testing is usually performed using a special set of samples or a training data set is divided into n folds. in such case, the classifier learns iteratively. in each iteration one fold is used for testing and n-1 folds are used for learning. a task of trained classifier is to determine the class of a new example. fig. 2. examples of x, y and z signals for walking with phone in a right trousers pocket (above) and running with mobile phone in a wider tracksuits front pocket (below). bayesian classifier is a conditional probability model and it can be abstractly described as .),...,3,2,1( anaaacp here, c is a set of possible classes and a1,…, an is an example of input test data. bayesian classifier computes the conditional probability of each class for a given tuple of attributes and then predicts the most probable class. using bayes' theorem, the conditional probability can be decomposed as: ),...,3,2,1( ),...,3,2,1(*)( ),...,3,2,1( anaaap canaaapcp anaaacp    the numerator of the previous equation can be rewritten as: ( )* ( 1, 2, 3,..., ) ( )* ( 1 )* ( 2, 3,..., , 1) ( )* ( 1 )* ( 2 )* ( 3,..., , 1, 2) ... ( )* ( 1 )* ( 2 )* ( 3 )*...* ( , 1, 2, 3,..., 1) p c p a a a an c p c p a c p a a an c a p c p a c p a c p a an c a a p c p a c p a c p a c p an c a a a an        engineering, technology & applied science research vol. 7, no. 1, 2017, 1405-1412 1409 www.etasr.com miskovic and babic: implementation of a flexible bayesian classifier for the assessment of patient’s… fig. 3. examples of signals for activity taking the stairs down (above) and taking the stairs up (below). the "naive" conditional independence assumes that each attribute ai is conditionally independent of any other attribute aj for j ≠ i, when the class is c. in other words: p(ai│c, aj) = p(ai│c) for i ≠ j. under independence assumption explained above new expression for the numerator is:    n i caipcpcanaaapcp 1 )(*)(),...,3,2,1(*)(   then the bayes' theorem of (7) is given as: ),...,3,2,1( 1 )(*)( ),...,3,2,1( anaaap n i caipcp anaaacp     the denominator is often omitted from the calculation of probability, because for each class c it has the same value. the sum of all probabilities of all possible classes should be equal to the probability of certain event. thus all calculated probabilities are normalized with sum of all probabilities. the probability of a certain class (prior) can be easily calculated from the learning data set as a ratio of number of samples in the class and total number of samples. furthermore, if a domain of an attribute is finite (discrete) set of values, then its probability can be expressed as the number of samples where the attribute has a certain discrete value a from a set of discrete values a and given class is c from c, p (a = a │c = c). however, in the most cases attributes have continuous values and the probability for the given class is modeled by some continuous probability distribution function over the range of its values for the given class. the probability of continuous attributes is often modeled using normal or gaussian distribution, and it is calculated as [12]: 22 2)( * 2 1 ),,( ),,,()( c ca e c cc ag where cc agccaap           for each continuous attribute and each class it is required to calculate mean and standard deviation. the standard deviation is a measure that is used to quantify the amount of variation or dispersion of data values. a low standard deviation means that elements of given set tend to be very close to the mean, and a high standard deviation indicates that elements of given set have a wider range of values. to clarify the estimation process, consider a small data set in which there are two classes (+ and ), a nominal attribute x1 which takes values a and b, and a continuous attribute x2 [12]. if there are five training examples: (+; a; 1); (+; b; 1.2); (+; a; 3.0); (-; b; 4.4); (-; b; 4.5), then the corresponding conditional probabilities are [12]: p(c = +) = 3/5 p(x1 = a /c = +) = 2/3 p(x1 = b/ c = +) = 1/3 p(x2 = x/c = +) = g(x; 1.73; 1.21) here, 1.73 is the average value of x2 where the class is +, while 1.21 is the standard deviation of x2 where the class is +. in [12] the advantage of using the kernel function over gaussian normal distribution is highlighted. a kernel is a nonnegative real-valued integrable function k satisfying the following two requirements [17]: uofvaluesallforukuk duuk )()( ;1)(       the kernel estimation with gaussian kernels (one can use other kernel functions as well) look much the same, except that the estimated probability is averaged over a large set of kernels [12]: 1 ( ) , 1 ( , 0,1) c c x jp x x c c k n h hj where k g x and h n               engineering, technology & applied science research vol. 7, no. 1, 2017, 1405-1412 1410 www.etasr.com miskovic and babic: implementation of a flexible bayesian classifier for the assessment of patient’s… kernel functions are calculated for each xj from x i where the class c is from c and μj = xj. also nc is a number of samples for the given class c. a parameter h is called width parameter and it shrinks to zero as the number of instances goes to infinity. thus, as flexible bayesian classifier (fbc) observes more training samples, its probability estimates become increasingly local [12]. fbc is far more demanding when it comes to storage and computational complexity compared to the nbc. however, fbc proved that for 200 samples its accuracy is as high as accuracy of the nbc. while for the distribution of data that does not meet the requirement of normality it is much more accurate than nbc. a weka [13] is an environment for testing algorithms of artificial intelligence and it is very often used in the scientific researches for offline testing. weka supports both types of bayesian classifier. a width parameter h of the kernel function is calculated as an average of the sum of differences of successive attribute values. attributes from the collected data set are sorted. differences of successive values are summed, if values are not identical. at the end this sum is divided with a number of different attribute values. this parameter is called precision in the weka environment and it is used to compute the kernel function and for rounding up attribute values. in order to avoid redundancy of the attribute values after rounding up only different values are allocated and stored with the number of repetitions of these values (weight). in this way, the amount of data for storing is significantly reduced when the attribute has values which change rarely. this leads also to the reduction of the number of evaluations of kernel function. for example, the step counter sensor has a value zero for activity of sitting. iv. offline testing of modeled data in the weka environment the data is prepared for testing in the weka testing environment in the following manner. eight features explained in section 2 are extracted from the raw class labelled data, and after that the data is normalized by scaling it between 0 and 1. the selected method of testing is a cross-validation with ten folds. it is a fact that there are certain sorts of activities which are done more frequently, for example sitting, standing and walking, compared to activities which occur rarely, for example use of the stairs and running. taking this fact into account, a training data set is defined with more samples for more common activities. the simulation results show that the flexible bayesian classifier with kernel estimator correctly classifies 92.68% of all the samples. true positive rates, which measure the proportion of positives that are correctly identified as such, are: 1 for sitting, 1 for standing, 0.859 for walking, 0.958 for running, 0.761 for climbing the stairs, 0.866 for descending downstairs. furthermore, the naïve bayesian classifier with gaussian estimator correctly classifies 88.18% of all the samples. here true positive rates are: 0.99 for sitting, 0.988 for standing, 0.786 for walking, 0.952 for running, 0.658 for climbing the stairs, 0.724 for descending downstairs. these differences in accuracy can be seen in confusion matrix in table i and table ii. we have tested the accuracy of the flexible bayesian classifier for data set without features 5 and 6 (skewness and kurtosis). in this case fbc correctly classifies 90.21% of samples, and true positive rates by class are as follows: 1 for sitting, 1 for standing, 0.837 for walking, 0.958 for running, 0.662 for climbing the stairs, 0.756 for descending the stairs. in comparison with previous fbc results, the use of these two features slightly increases the percentage of correctly classified samples for activities of walking and using stairs. the accuracy of fbc for data set without feature 7 (correlation) is 91.64%, and true positive rates by class are as follows: 1 for sitting, 1 for standing, 0.823 for walking, 0.955 for running, 0.757 for climbing the stairs, 0.848 for descending the stairs. in comparison to the first results of fbc, it can be seen that the feature 7 affects all activities except sitting and standing. the accuracy of fbc for data set without feature 8 (number of steps) is 92.03%, and the true positive rates by class are as follows: 1 for sitting, 1 for standing, 0.853 for walking, 0.955 for running, 0.734 for climbing the stairs, and 0.843 for descending the stairs. in comparison to the first results of fbc it can be seen that this features 8 and 7 in the same way affect the estimates. table i. flexible bayesian classifiers confusion matrix a b c d e f classified as 507 0 0 0 0 0 sitting =a 0 501 0 0 0 0 standing = b 0 0 437 1 11 60 walking = c 0 0 14 338 0 1 running = d 0 0 33 0 169 20 upstairs = e 0 0 4 0 25 188 downstairs = f table ii. naïve bayesian classifiers confusion matrix a b c d e f classified as 502 0 0 0 5 0 sitting =a 0 495 0 0 0 6 standing = b 0 0 400 3 20 86 walking = c 0 0 17 336 0 0 running = d 0 0 49 0 146 27 upstairs = e 0 0 30 0 30 157 downstairs = f table iii. j48 decision tree confusion matrix a b c d e f classified as 507 0 0 0 0 0 sitting =a 1 500 0 0 0 0 standing = b 0 0 459 2 25 23 walking = c 0 0 1 351 1 0 running = d 0 0 30 0 177 15 upstairs = e 0 0 19 0 24 174 downstairs = f table iv. multilayer perceptron confusion matrix a b c d e f classified as 507 0 0 0 0 0 sitting =a 0 501 0 0 0 0 standing = b 0 0 491 0 10 8 walking = c 0 0 2 349 1 1 running = d 0 0 14 0 199 9 upstairs = e 0 0 12 0 12 193 downstairs = f engineering, technology & applied science research vol. 7, no. 1, 2017, 1405-1412 1411 www.etasr.com miskovic and babic: implementation of a flexible bayesian classifier for the assessment of patient’s… j48 decision tree algorithm correctly classifies 93.9% of samples, and true positive rates by class are as follows: 1 for sitting, 0.998 for standing, 0.902 for walking, 0.994 for running, 0.734 for climbing the stairs, and 0.802 for descending the stairs. the multilayer perceptron correctly classifies 97% of the samples, and true positive rates by class are as follows: 1 for sitting, 1 for standing, 0.965 for walking, 0.989 for running, 0.896 for climbing the stairs, and 0.889 for descending the stairs. v. real time testing of the proposed mobile application as stated above, we have designed the mobile application for testing purposes. it allows users to check the activity that will be carried out, and then to initiate the assessment of the activity. the application is based on the described flexible bayesian classifier which evaluates the data collected in periods of 8s, with 4s overlap. therefore, the process of assessment must be done in less than 4s. the flexible bayesian classifier used for the activity assessment uses a personalized patient’s data model that is implemented within java desktop application. at the first stage, the data collected from accelerometer and step counter is preprocessed and all described features are obtained, such as average, minimum or maximum value of signal or energy, etc. after that, the data is normalized. further, all prior probabilities and the total number of samples per class are calculated, including precision for each attribute, values of the kernel functions followed with their weights. all assessed activities and activities checked by user, along with the system time required for the assessment are stored in a log file for later analysis. we used device with android os 5.0.2. for testing. the cpu armv7 rev 3 (v7i) has four cores with maximum frequency equal to 1190.4 mhz, and minimum frequency equal to 300.0 mhz. the number of samples collected for all activities is roughly equal to 2300. the log files show that with used mobile phone and its cpu, the process of assessing the data with preprocessing can be executed in less than 2s. the required memory resources are approximately 40 mb. table v. real-time testing using mobile phone a b c d e f classified as 641 0 0 0 0 0 sitting =a 3 415 0 0 0 1 standing = b 0 0 715 0 8 11 walking = c 0 0 4 200 4 5 running = d 0 0 45 2 82 18 upstairs = e 0 2 60 0 6 94 downstairs = f the real-time analyses explained above shows similar behavior as the weka classifier in simulation. the mobile application is tested for all activities and the results are presented in table v. the activities of sitting and standing are mostly correctly assessed. the activities of walking and running are also highly accurately assessed, their true positive rates are: 0.974 and 0.939, respectively. the activities related to the use of stairs are more often wrongly assessed and falsely interpreted as walking. the testing of the stairs activities in the real-time situations shows that they are less accurate compared to the weka environment. the results of testing show that true positive rates are only: 0.558 climbing the stairs and 0.580 descending the stairs. vi. conclusion real-time testing using the mobile applications shows that it is possible to use the flexible bayesian classifier to predict accurately the patient's activity if features are carefully selected. the offline test results show that for the selected data model, the accuracy of the flexible bayesian classifier can be compared to the accuracy of the j48 decision tree and the multilayer perceptron. based on obtained results, it can be concluded that the flexible bayesian classifier can very precisely distinguish resting, moderate activities and exhaustive activities such as running. the patient carries the phone with sensor at arbitrary position making the proposed system nonintrusive. the presented data model can be extended with new sensor devices, for example with gyroscope, which would increase the accuracy even further. in this way, the presented fbc implementation shows that it is one of the best choices in the field of mobile healthcare services. references [1] bluetooth medical devices wg, “hdp implementation guidance white paper”, 2009, goo.gl/oyzhws [2] zigbee alliance, “zigbee wireless sensor applications for health, wellness and fitness”, 2009, goo.gl/9vuvny [3] continua health alliance, “overview presentation: the next generation of healthcare: personal connected health & wellness”, 2010, http://www.continuaalliance.org [4] t. buchholz, a. kupper, m. schiffers, “quality of context: what it is and why we need it”, 10th workshop of the open view university association ovua’03, geneva, switzerland, july, 2003 [5] t. garcia-valverde, a. muñoz, f. arcas, a. bueno-crespo, a. caballero, “heart health risk assessment system: a nonintrusive proposal using ontologies and expert rules”, biomed research international, article id 959645, vol. 2014, [6] j. r. kwapisz, g. m. weiss, s. a. moore, “activity recognition using cell phone accelerometers”, acm new york, newsletter, vol. 12, no. 2, pp. 74-82, 2010 [7] l. bao, s. s. intille, “activity recognition from user-annotated acceleration data”, lecture notes in computer science, vol. 3001, pp. 1-17, 2004 [8] m. shoaib, s. bosch, o. durmaz incel, h. scholten, p. j. m. havinga, “fusion of smartphone motion sensors for physical activity recognition”, sensors, vol. 14, pp. 10146-10176, 2014 [9] s. das, b. perez , f. w. olin, a. perrig, “detecting user activities using the accelerometer on android smartphones”, journal of multimedia and information system vol. 2, no 2, pp. 233-240, 2015 [10] m. kose, o.d. incel, c. ersoy, “online human activity recognition on smart phones”, in proceedings of the workshop on mobile sensing: from smartphones and wearables to big data, beijing, china, pp. 11– 15, april 2012 [11] m. ziefle, c. rocker, “acceptance of pervasive healthcare systems: a comparison of different implementation concepts”, pervasive computing technologies for healthcare (pervasivehealth), ieee 4th international conference, munich, pp. 1-6, march 2010 [12] g. h. john, p. langley, “estimating continuous distributions in bayesian classifiers”, 11th conference on uncertainty in artificial intelligence, morgan kaufmann publishers inc. san francisco, ca, usa, pp. 338-345, 1995 engineering, technology & applied science research vol. 7, no. 1, 2017, 1405-1412 1412 www.etasr.com miskovic and babic: implementation of a flexible bayesian classifier for the assessment of patient’s… [13] weka, weka 3: data mining software in java, http://www.cs.waikato. ac.nz/ml/weka/ [14] t. mitchell, machine learning, mcgraw hill, new york, 1997 [15] i. cleland, b. kikhia, c. nugent, a. boytsov, j. hallberg, k. synnes , s. mcclean, d. finlay, “optimal placement of accelerometers for the detection of everyday activities”, sensors, vol. 13, pp. 9183-9200, 2013 [16] g. j. welk, j. a. differding, r. w. thompson, s. n. blair, j. dziura, p. hart, “the utility of the digi-walker step counter to assess daily physical activity patterns”, medicine & science in sports & exercise, vol. 32, pp. s481–s488, 2000 [17] wikipedia, “kernel (statistics)”, https://en.wikipedia.org/wiki/kernel_ (statistics) microsoft word 28-2962_s_etasr_v9_n5_pp4729-4734 engineering, technology & applied science research vol. 9, no. 5, 2019, 4729-4734 4729 www.etasr.com elfaki et al.: a literature review on collaborative caching techniques in manets … a literature review on collaborative caching techniques in manets: issues and methods used in serving queries mohamed ahmed elfaki department of computer science, college of computing & information technology, shaqra university, riyadh, saudi arabia malfaki@su.edu.sa ali a. alwan department of computer science, international islamic university malaysia, kuala lumpur, malaysia aliamer@iium.edu.my majdi abdellatief department of health of informatics, inaya medical college, riyadh, saudi arabia khwaja24@yahoo.com abubaker wahaballa department of computer science, arab east colleges, riyadh, saudi arabia wahaballah@arabeast.edu.sa abstract—collaborative cache management in mobile ad hoc networks (manets) environment is considered as an efficient technique to increase data accessibility and availability, by sharing and coordination among mobile nodes. due to nodes’ mobility, limited battery power and insufficient bandwidth, researchers addressed these challenges by developing many different collaborative caching schemes. the objective of this paper is to review various collaborative caching techniques in manets. collaborative caching techniques are classified by methods used in serving queries, such as: hop-by-hop discovering, broadcasting messages, flooding, and query service differentiation. this review reveals that techniques utilizing hopby-hop methods have better performance compared to others, especially techniques using additional strategies. keywords-mobile ad hoc network; cooperative caching; caching methods i. introduction mobile computing is a new paradigm emerged from the exponential development of wireless networking. advances in wireless communication engage focus in mobile ad-hoc networks (manets). this allows a portable device to access required information services and data via a shared infrastructure, without considering physical location and movement behavior. dynamic mobility, disconnections, limited bandwidth, variable capacity links, limited resources and energy are the main characteristics of manets [1-4]. therefore, accessing distant data in such a situation reduces system’s performance in terms of average delay, hit ratio, and bandwidth. the typical wireless mobile network architecture for manets, consists of a wired network, mobile nodes (mns), base stations (bss) and a database server (db) connected to the wired network. bss communicate with mobile nodes located within the coverage range, known as wireless cell [5, 6]. there are two types of wireless channels, defined uplink and downlink. uplink channel is utilized for sending requests from mns to the bs, while downlink is used by the bs to send information to the mns within the cell range. one of the functions of the bs is to ensure mns are able to communicate with other networks by sending their queries. the bs also manages handoff and mobility functions [7]. caching frequently accessed data in mobile devices is an effective method to enhance performance in a manet. hence, while requests are satisfied locally, data retrieval response time is reduced [8]. however, a reliable cache management in manets is difficult to be achieved due to dynamic movement, disconnection, limited bandwidth, and limited energy consumption [9-11]. therefore, accessing distant data in manets is costly in terms of delay, energy consumption, and bandwidth usage [12, 13]. collaborative caching is developed in order to share the cache content among a number of participating nodes. figure 1 shows the four fundamental schemes for sharing cache content among participating nodes. in indexcache each node caches its own query result and a distributed index is built on top of these local caches to facilitate sharing. in cachedata each node is assigned a particular part of the cache data space and the results of each query are not stored in the node who requested it, but instead at the node that is responsible for that part of data space [14]. furthermore, intermediate nodes cache data to serve future queries. a limitation of cachedata is that cached data items in intermediate nodes could take a lot of space. cachepath provides the hop count information between source and destination. by caching the data path for each data item, bandwidth and query delay can be reduced since data can be obtained in even less hops [15]. cachepath is used to redirect future queries along the cached path. in manets, the node caching the data items might leave the transmission range or it corresponding author: mohamed a. elfaki engineering, technology & applied science research vol. 9, no. 5, 2019, 4729-4734 4730 www.etasr.com elfaki et al.: a literature review on collaborative caching techniques in manets … might replace or remove cached data items due to cache size limitations. hybridcache is developed to further improve performance by considering the advantages of both schemes cachedata and cachepath, while avoiding their weaknesses. fig. 1. caching schemes collaborative caching is particularly attractive in environments where the network is constrained in terms of bandwidth and disconnections. collaborative caching also offers several benefits, since it enables efficient utilization of available resources by storing different data items and sharing them among neighbor nodes [16, 17]. furthermore, by introducing peer-to-peer device partnership, it can reduce query latency, provide a higher number of hits and increase the accessibility of requested data items [18]. collaborative caching improves the performance of mobile query service compared to simple caching in manets for two reasons. at first, in collaborative caching, requested data items can be retrieved from neighboring nodes instead of the remote database server, reducing the risk of dropped packets caused by network congestions and link failures. additionally, nodes can still receive requested data items from neighboring nodes while network partitioning occurs [19]. ii. related works the survey in [20] outlines different studies on cooperative caching in mobile p2p networks. this survey described cooperative caching based on cache placement, replacement, consistency and security. authors concluded that most studies on cooperative caching in mobile p2p focus on resource searching instead of data access. authors in [12] classified and compared existing cooperative caching strategies based on performance metrics, such as query latency and cache hit ratio. authors in [12] found that having a strong consistency in caching schemes, lead to efficient information retrieval architecture. a hypothetical analysis of various cooperative caching schemes is proposed in [10, 21], where authors presented the advantages and limitations of previous schemes in a manet, in finding a data item with less resources (e.g. network bandwidth, energy etc.) and improving the performance interim of data availability and latency time. this review not only extends and updates previous reviews [10, 12, 20, 21] but also proposes collaborative caching for future researches in manets and has the following differences: • different goal: our main purpose is to understand, classify, and analyze the existing methods used to serve queries in collaborative caching techniques in manets, in order to direct future research, while other reviews [10, 12, 20, 21] mainly aimed to provide an overview of quality cache management and performance metrics analysis. • comprehensive studies: this paper reviews 35 studies. authors in [10, 21] examined only 14 articles, while authors in [12] and [20] examined 7 and 30 respectively. comprehensive study has advantages, since it reduces the bias and allows for a general conclusion. iii. analysis and discussion this section classifies previous studies based on methods utilized to access and discover data items in collaborative caching in manets. these methods are: hop-by-hop discovering, broadcasting messages, flooding, and query service differentiation. a. hop-by-hop discovering hop-by hop discovering is one of the methods utilized by collaborative caching approaches. works presented in [14, 15, 22] contain collaborative caching approaches to enhance data access in ad hoc networks. these approaches have similar schemes like indexcache, cachedata, cachepath and hybridcache, while their cache discovery method is hop-byhop forwarding. in other words, each node along the way to the db is queried for the data. there are several routing algorithms that have been designed to route messages in manets. some of them are proposed to reduce bandwidth consumption and query delay, where the amount of hops between data center and the requesting node should be as few as possible. however, a drawback of these schemes is that caching information of a node cannot be shared if the node does not lie on the path between the requesting node and the db [9, 29, 23]. besides that, in case a failure on the path, the request packet might be lost, or delayed until the node reestablishes the connection. furthermore, they do not provide different services for different classifications of queries. another example of collaborative caching using clusters is proposed in [24], which is called the cluster cooperative (cc) caching. the main purpose of this approach is to reduce the cache discovery overhead and enhance collaborative caching performance. cc divides the manet on geographical networks (clusters) which are equal in size. in each cluster, cc dynamically elects a node as cache state node (csn) to maintain the cluster cache state (ccs) information of different nodes within its cluster domain. the ccs for a client is the list of cached items along with their ttl field. to improve system’s performance, all mobile clients within the same cluster form a collaborative cache system among them. in cc, if a query is missed locally, the client requests the data item from the cluster members by forwarding a request to the csn. if the required data item is missed within the cluster members’ cache, the query is forwarded to clients along the path towards the db. if the required data item is found along the path towards the db (remote cache hit), the request can be served, without further redirecting towards the db. however, if the query is missed locally, within the cluster’s members and remote cache, the query is forwarded to the db. one of this approach drawbacks is that caching information of a client cannot be shared if does not lie on the path between the requesting node and the db [9, 29]. furthermore, the query in cc is only served through node engineering, technology & applied science research vol. 9, no. 5, 2019, 4729-4734 4731 www.etasr.com elfaki et al.: a literature review on collaborative caching techniques in manets … by node forwarding along the path towards the db and not guided and coordinated to a particular data source. zone cooperative (zc) caching approach is proposed in [16] in order to minimize caching overhead by providing cache replacement policy. in zc, each data item is stored in a particular data source, which acts as server, where each mobile host (mh) caches frequently accessed data items. the advantage of the zc caching design is that it enables nodes to share their cached data items with neighboring nodes located in the same zone. thus, cached data items satisfy not only the node’s own needs but also the needs of other nodes that are passing through it towards the db. in zc, each mh first searches the data item in its local cache, its zone cache after miss occurred at local cache, before forwarding the request to the next node that lies on a path towards the db. in zc, mh caches the required data items based on server’s location. therefore, a data item is not cached if the server of the requested data item resides in the same zone of the requested mh. if there is not sufficient cache space for the data item, zc utilizes a least utility value (luv) based replacement policy to enhance the efficiency of caching. however, query latency might increase if intermediate nodes lying between the requested node and the db do not have the required data item [10]. furthermore, there is no query service differentiation in zc, where in real applications some queries should be served urgently. group caching (gc) is proposed in [11], which uses one-hop neighbors to maintain a localized caching status for performing the tasks of data item discovery and caching replacement, when a query is initiated by a mobile host. in gc, each mh maintains only one-hop neighbors in a group. each mh sends its caching status to its group members. each mh sends a “hello” message within transmission range to form a group of one-hop neighbors. a query is checked in the local cache once an mh receives it. if the local cache is missed, group table is checked to redirect the request to group members in order to serve the request, which is known as remote cache hit. if the remote cache is missed the request is forwarded to the next group along the path towards the db. once the intermediate group along the path receives the request, it checks the group table for the requested data; if the requested data item is found, it sends the request’s response directly to the mh requester. if a miss occurred at the intermediate groups, the query is forwarded to the db. however, gc consumes more energy to check the requested data item within the group members along the path towards the db. besides, no service differentiation is utilized in serving queries. thus, gc consumes energy in mh since each group members towards the db have to be checked [10]. another collaborative caching design is proposed in [19], based on cluster collaborative caching scheme for mobile ad hoc networks. this scheme improves caching performance in terms of data accessibility, query delay, and distance compared to caching schemes without collaborative caching policy. information searching is based on clustering architecture, combining different methods, ranging from local to global search. in this scheme, mhs search for the required data items within neighbor nodes after a local miss. initially, an mh checks whether the data server is its neighbor. if it is, the query is sent to the data server. in case the data server is not a neighbor of the mh, two cases are possible: a) mh is a cluster header, or b) mh is a cluster member. if mh is a cluster header, the id list is checked for the required data item. if the id is found, the query is forwarded to the corresponding cluster member. if the id is not found, the cluster header forwards the query to the data server. on the other hand, if mh is a cluster member, it unicasts the query to its cluster header. although the broadcasts based data search locates the nearest required data item, the energy and bandwidth cost of the flooding search is significantly high for a manet. this flooding search can be problematic for network communication [17, 23]. furthermore, queries are served without considering service differentiation. this causes query delay in fetching the requested data items. authors in [9] introduced a cooperation and adaptive database caching system for manets known as coacs. its main idea is that node caches submitted queries by indexing them to facilitate the process of locating the required data item in less delay. nodes in coacs can play one of two possible roles, which are cache node (cn) and query directory (qd). qd is responsible for caching previously queries submitted by the requesting nodes, while cn is responsible for caching data items that are responses to queries. if a node requires a data item not cached in the system, the requesting node (rn) is served by retrieving the data item from the database server. rn could be any node including a qd or a cn. once rn received the response, it will act as a cn by caching the data item. the nearest qd caches the query and makes an entry in its hash table to link the query to its corresponding data item. the query is checked at the nearest qd, and if is not indexed, the request is forwarded to another qd. to minimize the response time of the system, coacs forms several qds that are used as a distributed indexing system, whereby if one qd receives a query that is not indexed, it is forwarded to the nearest qd. this is continued until the query is satisfied by one of the qds or the database server. however, even though coacs decreases the query delay to some extent, it is inefficient as requests are served through multiple qds in order to locate the required data item. a query may be forwarded from one qd to another even though some of the qds did not index it . this causes delay and lowers the hit ratio in serving queries. besides, coacs serves queries without considering service differentiation, where in real applications some queries need to be served urgently. the approach proposed in [25] considers the progress of data discovery. in this approach, nodes within a zone form a cooperative cache, since a zone transmission range is formed based on a set of one-hop neighbors. each node has a local cache to store frequently accessed data, not only for its requests, but also for other nodes passing requests through it. once the data are updated at the server, nodes’ cached copies become invalid. if a data miss happens in the local cache, the node first checks the requested data items in its zone before forwarding the request to the next node lying on the path towards the server. however, latency may increase if the requested data item is not cached in intermediate neighbor's nodes. in [26] the group-based cooperative caching scheme (gcc) is described. this scheme is based on the concept of group caching, where each mobile host and its k-hop neighbors are allowed to form a group. each mobile host maintained a engineering, technology & applied science research vol. 9, no. 5, 2019, 4729-4734 4732 www.etasr.com elfaki et al.: a literature review on collaborative caching techniques in manets … directory of cached data items. each mn broadcasts a message to the group in order to obtain the directories of its k-hop group members. however, overhead might be generated by mobile host’s requests [27]. b. broadcasting messages the approach proposed in [28], introduced a new type of caching, known as distributed group based cooperative caching in a mobile broadcast environment, called tightly-coupled group (tcg). the main idea is to capture data affinity of individual peers and their mobility patterns in mobile broadcast environments where all tcgs are dynamic. it consists of two types of cooperative cache management protocols: cooperative cache replacement and cooperative cache management admission control. the latter is applied when mh experiences a local cache miss and sends a request to its peers. if some peers turn in the required data item to the mh and the local cache is not full, mh caches the data item, no matter whether it is returned by a peer in the same tcg or not. however, after a peer sends the required data item to the requesting mh, if they belong to the same tcg it must update the last access timestamp of the data item in order to raise its ttl in the global cache. in cooperative cache replacement, mh replaces the least valuable data item related to the mh itself and other members in the same tcg. this replacement satisfies three useful properties. first, the most valuable data item is always retained or kept in the local cache. second, data items in local cache not accessed for a long period will be replaced eventually. third, a data item in global cache which “spawns” replicas is first replaced in order to achieve an effective cache size. this approach focuses more on the availability of data items in a mobile broadcasting environment through scalable broadcast channels. however this approach relies on broadcasting messages to discover the required data items. the broadcasting message is received by all network’s nodes, including those who have not cached the required data items. in addition, queries in tcg are served without considering service differentiation. thus, serving queries based on broadcasting messages in tcg caused network congestion and delay [21]. besides, the tcg approach does not consider the mobile limited resources as it applied push and pull based data dissemination. authors in [23] proposed a collaborative caching technique to enhance data access in ad hoc networks. there are two protocols based on the notion of a zone. the first protocol is index push (ixp) protocol, where an mn broadcasts an index message to regional nodes in order to promote a caching event. basically, ixp is used to fetch the requested data item from a nearby neighboring node, if a node knows that its neighbor has cached it. the second protocol is called data pull/index push (dpip) protocol, where a requesting node may broadcast a special request message to nodes in its zone, asking them to serve its demand. this type of process works as pull-based with implicit index pushing property. dpip allows a wider scope of local resources caching cooperation without involving any additional communication overhead. however, the protocol works well in environments where the zone contains a small number of nodes. thus, this can be a drawback in ixp and dpip protocols, as when a new node joins a zone, its nodes are not aware about the join node updates [29]. therefore, less collaboration among nodes in the same zone consequently affects the cost in terms of delay when locating a data item. furthermore, it lacks a query directory at the global level to guide queries to data sources, especially when queries cannot be served locally. hence, lack of coordination and service differentiation in serving queries leads to inefficient bandwidth usage and server overload, since each node forwards queries directly to the db. authors in [30] proposed a scheme called cooperative caching (coca) for conventional mobile database systems. coca introduces a new logical layer between the mobile client cache and mss layer, which is known as peer cache layer. this layer is invoked into two situations: firstly, when a miss occurs in local cache and secondly, when the query needs to be served by neighboring nodes. the request in coca is served in the following stages: a) the required data item is checked in mh’s local cache. b) if a local miss occurs, mh broadcasts the request to its neighboring nodes. if any of its neighboring nodes has cached the required data item, it responds to the mh. c) if none of the neighboring nodes has the required data item, mh sends the request to the mss. when the mh is residing outside of the service range and encounters a global cache miss, it suffers from an access miss. furthermore, coca can reduce communication attempts with the server by allowing mhs to share their cache among them. however, coca has longer access latency, especially when mhs encounter a global cache miss, while the request is not served based on its classification, not coordinated and not guided to a particular data source as it broadcasts the request to all neighbor nodes furthermore, coca is inefficient in terms of bandwidth usage due to broadcasting, which lowers system’s throughput because of network flooding with request packets [21]. c. flooding authors in [31, 32] proposed a new type of caching to improve data availability and access efficiency, by collaborating local resources of mobile nodes and utilizing cooperation zones and hop-by-hop resolution. there are two basic fundamentals of cooperative caching that are tackled in [31, 32], which are cache resolution and cache management. for cache management, coop maximizes the capacity of cooperative caching by reducing caching duplications within a short distance cooperative neighborhood. on the other hand, cache resolution addresses how to serve a query with less delay, bandwidth, and energy. furthermore, coop resolution is a cocktail scheme that develops based on three basic schemes. in the first scheme, adaptive flooding is used to estimate a proper flooding range based on the cost to retrieve the required data items. this limited flooding is not only used for the purpose of discovering a cached node around the requesting node, but also as an announcement method to share and manage cached contents among the neighborhood. the second scheme, profile-based resolution, utilizes a historical profile of previously resolved queries to determine the nearest data item source to a requesting node. if the required data item is not fetched using those two schemes, the query is redirected to the original data item source. in the third scheme, roadside resolution resolves the query via hop-by-hop along the forwarding path towards the database server. to improve data availability and access efficiency, authors in [31, 32] utilized flooding to discover data items instead of coordinating the engineering, technology & applied science research vol. 9, no. 5, 2019, 4729-4734 4733 www.etasr.com elfaki et al.: a literature review on collaborative caching techniques in manets … query to particular data sources that cached it. serving queries using flooding and hop-by-hop resolution caused network traffic since all queries are served without considering service differentiation and are not guided to a particular data source. hence, using flooding can be problematic for network communication [23], and consequently leads to query latency, especially when the number of queries or the number of forwarding nodes to the remote data source is increased [29]. d. query service differentiation due to limited mobile resources, such as insufficient wireless bandwidth, disconnections and client’s mobility, collaborative cache management faces vast challenges. query latency is one of the issues that are tackled in collaborative caching management. a priority-based caching service in web caching and content distribution is proposed in [33], describing a service that differentiates the caching mechanism based on priority queues. it provides the ability to differentiate services in terms of hit rate and object lifetime, with minimal efficiency penalties compared to conventional caching techniques. therefore, service differentiation can be beneficially applied to proxy caches and content distribution network (cdn) server. however, most of the existing collaborative caching techniques in manets environments have been developed without considering service differentiation. serving requests by checking each node towards the database server without considering the urgent needs for required data items causes delay and increases the number of hops. authors in [34] review the current quality of service (qos) routing mechanisms and frameworks for multimedia traffic in manets. they review two qos categories: qos solutions that depend on routing protocols for selecting a new hop based on qos parameters and qos solutions based on some specific design frameworks along with integration of various modules that are applicable with any routing protocol. however, there is still a wide area of research before proposing a qos framework for manets, particularly for multimedia traffic, to overcome limitations such as resource reservation, connection admission control, etc. which will help in reducing the delay of query responses. the approach presented in [35] can be categorized under hop-byhop discovery with some enhancements that apply query service differentiation. this approach attempts to enhance the data access efficiency and cache discovery performance in hopby-hop, by adding some new features, such as node cached data item information indexing that facilitates in guiding the queries to a particular data source. hence, this approach attempts to increase the collaborative caching among neighbor nodes, since each node is provided a recent priority table (rpt) to index its neighbor nodes’ cached data item information. query classification either as priority or normal, which is specified by the requesting node, is utilized to determine to which data source the query should be forwarded. this enhances the hop-by-hop method by coordinating and serving queries with less forwarding hops. this helps serving queries in manets with minimum cache discovery overhead and delay. table i presents a summary of the existing collaborative caching works, proposed to improve the efficiency of data item access and cache discovery in manets. two points can be highlighted: at first, most approaches utilize hop by hop while others utilize flooding and broadcasting messages to access the data items. however, these flooding and broadcasting methods can be problematic for network communication and consequently cause query latency, if the neighbors of intermediate nodes do not have the requested data items to serve the request. moreover, most of the presented approaches, served queries without considering service differentiation. table i. summary of collaborative caching approaches methods reference bc fl hbh qsd [9] × × ✓ × [11] × × ✓ × [14] × × ✓ × [15] × × ✓ × [16] × × ✓ × [19] ✓ × ✓ × [22] × × ✓ × [23] ✓ × ✓ × [24] × × ✓ × [25] × × ✓ × [26] ✓ × ✓ × [28] ✓ × × × [30] ✓ × × × [31] × ✓ ✓ × [32] × ✓ ✓ × [33] × × × ✓ [35] × × ✓ ✓ bc: broadcast, fl: flooding, hbh: hop-by-hop, qsd: query service differentiation iv. conclusion this paper presented a review of various collaborative caching techniques in manets. the collaborative caching techniques increase the efficiency of data accessibility and availability in manets environments by sharing and coordination among mobile nodes. we discussed the advantages of methods utilized in each technique, in order to improve the performance of fetching a data item in manets by using less bandwidth, and power. moreover, we addressed the limitations faced by the mobile database environments in manets. the analysis reveals that techniques utilizing hopby-hop methods have better performance compared to those utilizing flooding or broadcasting methods this review will be helpful to future research in terms of improving data accessibility and data availability in manets. references [1] h. safa, h. artail, m. nahhas, “enhancing cache invalidation in mobile environments”, mobility ’08 international conference on mobile technology, applications, and systems, yilan, taiwan, september 1012, 2008 [2] t. lin, mobile ad-hoc network routing protocols: methodologies and applications, phd thesis, virginia polytechnic institute and state university, 2004 [3] d. d. perkins, h. d. hughes, c. b. owen, “factors affecting the performance of ad hoc networks”, 2002 ieee international conference on communications, new york, usa, april 28–may 2, 2002 [4] j. yoo, s. choi, c. kim, “control overhead reduction for neighbour knowledge acquisition in mobile ad hoc networks”, electronics letters, vol. 39, no. 9, pp. 740-741, 2003 engineering, technology & applied science research vol. 9, no. 5, 2019, 4729-4734 4734 www.etasr.com elfaki et al.: a literature review on collaborative caching techniques in manets … [5] a. madhukar, t. ozyer, r. alhajj, “dynamic cache invalidation scheme for wireless mobile environments”, wireless networks, vol. 15, no. 6, pp. 727-740, 2009 [6] z. wang, m. kumar, s. das, h. shen, “dynamic cache consistency schemes for wireless cellular networks”, ieee transactions on wireless communications, vol. 5, no 2, pp. 366-376, 2006 [7] l. ni, y. zhu, b. li, q. deng, “optimal mobility-aware handoff in mobile environments”, 2011 ieee 17 th international conference on parallel and distributed systems, tainan, taiwan, december 7-9, 2011 [8] g. anandharaj, r. anitha, “an improved architecture for 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“a replication based caching strategy for manets”, 2011 international conference on selected topics in mobile and wireless networking (icost), shanghai, china, october 10-12, 2011 [14] k. lillis, e. pitoura, “cooperative xpath caching”, 2008 acm sigmod international conference on management of data, vancouver, canada, june 9-12, 2008 [15] g. cao, l. yin, c. r. das, “cooperative cache-based data access in ad hoc networks”, computer, vol. 37, no. 2, pp. 32-39, 2004 [16] n. chand, r. c. joshi, m. misra, “cooperative caching in mobile ad hoc networks based on data utility”, mobile information systems, vol. 3, no. 1, pp. 19-37, 2007 [17] m. denko, “cooperative data caching and prefetching in wireless ad hoc networks”, international journal of business data communications and networking, vol. 3, no. 1, pp. 1-15, 2007 [18] x. shen, m. m. akon, a. singh, “low cost peer-to-peer collaborative caching for clusters”, 2007 4th ieee consumer communications and networking conference, las vegas, usa, january 11-13, 2007 [19] j. tian, m. k. denko, “exploiting clustering and cross-layer design approaches for data caching in manets”, third ieee international conference on wireless and mobile computing, networking and communications (wimob 2007), white plains, usa, october 8-10, 2007 [20] x. zhou, z. zou, r. song, y. wang, z. yu, “cooperative caching strategies for mobile peer-to-peer networks: a survey”, in: information science and applications (icisa) 2016 – lecture notes in electrical engineering, vol. 376 springer, 2016 [21] p. kumar, n. chauhan, “a review of cooperative cache management techniques in manets”, international journal of it & knowledge management, vol. 3, no. 1, 2010 [22] l. yin, g. cao, “supporting cooperative caching in ad hoc networks”, ieee infocom 2004, hong kong, china, march 7-11, 2004 [23] c. r. young, g. m. chiu, f. l. wu, “efficient cooperative caching schemes for data access in mobile ad hoc networks”, international conference on embedded and ubiquitous computing, nagasaki, japan, december 6-9, 2005 [24] n. chand, r. c. joshi, m. misra, “an efficient caching strategy in mobile ad hoc networks based on clusters”, 2006 ifip international conference on wireless and optical communications networks, bangalore, india, april 11-13, 2006 [25] s. umamaheswari, g. radhamani, “enhanced antsec framework with cluster based cooperative caching in mobile ad hoc networks”, journal of communications and networks, vol. 17, no. 1, pp. 40–46, 2015 [26] i. w. ting, y. k. chang, “improved group-based cooperative caching scheme for mobile ad hoc networks”, journal of parallel and distributed computing, vol. 73, no. 5, pp. 595–607, 2013 [27] a. larbi, l. bouallouche-medjkoune, d. aissani, “improving cache effectiveness based on cooperative cache management in manets”, wireless personal communications, vol. 98, no. 3, pp. 2497–2519, 2018 [28] c. y. chow, h. v. leong, a. t. s. chan, “distributed group-based cooperative caching in a mobile broadcast environment”, 6th international conference on mobile data management, ayia napa, cyprus, may 09-13, 2005 [29] p. kumar, n. chauhan, l. k. awasthi, n. chand, “proactive approach for cooperative caching in mobile adhoc networks”, international journal of computer science issues, vol. 7, no. 3, pp. 21-27, 2010 [30] c. y. chow, h. v. leong, a. chan, “peer-to-peer cooperative caching in mobile environments”, 24th international conference on distributed computing systems workshops, hachioji tokyo, japan, march 23-24, 2004 [31] y. du, s. k. s. gupta, “coop a cooperative caching service in manets”, joint international conference on autonomic and autonomous systems and international conference on networking and services (icas-icns ‘05), papeete–tahiti, french polynesia, october 23-28, 2005 [32] y. du, s. k. s. gupta, g. varsamopoulos, “improving on-demand data access efficiency in manets with cooperative caching”, ad hoc networks, vol. 7, no. 3, pp. 579-598, 2009 [33] m. feldman, j. chuang, “service differentiation in web caching and content distribution”, the iasted international conference on communications and computer networks, cambridge, usa, november 4-6, 2002 [34] s. soni, j. s. shah, “qos frameworks for multimedia traffic in mobile adhoc networks: a comparative review”, engineering, technology & applied science research, vol. 7, no. 3, pp. 1708-1712, 2017 [35] m. a. elfaki, h. ibrahim, a. mamat, m. othman, h. safa, “collaborative caching priority for processing requests in manets”, journal of network and computer applications, vol. 40, pp. 85-96, 2014 microsoft word 19-2837_s1_etasr_v9_n4_pp4419-4422 engineering, technology & applied science research vol. 9, no. 4, 2019, 4419-4422 4419 www.etasr.com kote & nangare: hydraulic model investigation on stepped spillway's plain and slotted roller bucket hydraulic model investigation on stepped spillway's plain and slotted roller bucket alka sunil kote department of civil engineering, dr. d. y. patil institute of technology, pune, india alkakote26@gmail.com prakash baburao nangare department of civil engineering, dr. d. y. patil institute of technology, pune, india pbnangare@aissmscoe.com abstract—in ogee spillway, the released flood water from crest to toe possesses a high amount of kinetic energy causing scour and erosion on the spillway structure. the dam projects normally have a stilling basin as an energy dissipater which has specific energy dissipation limitations. the stepped spillway is a better option to minimize kinetic energy along the chute and safely discharge water in the river domain. the khadakwasla dam is situated in pune, maharashtra (india), and has scouring and erosion issues on the chute of ogee spillway and on the stilling basin. the present study develops a physical hydraulic model for the dam spillway with steps, plain and slotted roller bucket as per is code 6934 (1998) and is code 7365 (2010). experiments were performed at heads of 4m (low head) and 6m (high head) on the developed physical models, namely on the plain and slotted roller bucket model for the ogee spillway and the plain and slotted roller bucket model for the stepped spillway. it was found that the plain roller bucket of ogee spillway dissipates 81.26% of energy at the low head, whereas the stepped spillway with slotted roller bucket dissipates the 83.86% of the energy at the high head. keywords-stepped spillway; slotted roller bucket; physical hydraulic model; energy dissipation i. introduction the toe portion of an ogee spillway plays an important role in dissipating specific energy and discharging floodwater safely on the downstream side. the released water acquires high kinetic energy at the toe of the spillway causing scouring and erosion of the channel bed. stepped spillway is a better option to minimize the intensity of kinetic energy on its chute profile [1]. it discharges flood water safely and achieves significant energy dissipation along the chute due to the roughness of the steps. it thus reduces the length of the stilling basin. many researchers performed experiments on stepped spillways and observed that energy loss mainly depends on the nondimensional parameter of the ratio of critical depth to step height (yc/h≤0.8) [2-6]. energy dissipation is effective when the actual head is less than 1.4 times the design head [7, 8]. stilling basin is generally preferred for guiding flow safely from the spillway to downstream river for energy dissipation [9]. the selection of stilling basin occurs on the basis of froude number and the hydraulic jump characteristics. however, it requires a longer span to stabilize the flow in the downstream channel [10]. if the tail water is sufficient in the stilling basin for the development of the hydraulic jump, the roller bucket is the suitable option for energy dissipation [11, 12]. the provision of roller bucket minimizes the length of stilling basin, scouring and erosion on a downstream bed of a river [13]. in khadakwasla dam spillway located in pune, india there are issues in stilling basin and on ogee spillway chute due to improper energy dissipation. plain and slotted roller bucket is a good option to overcome the scouring and erosion issues of the dam spillway [14]. the present study focuses on a hydraulic model investigation regarding the khadakwasla dam with plain roller bucket, slotted roller bucket and modifications on stilling basin for ogee profile stepped spillway. ii. materials and methods in this study, a new methodology is proposed to minimize the issues of scouring and erosion by improving the performance of energy dissipation and minimizing the length of stilling basin. khadakawasla dam is located on the mutha river basin with a cultivable area of 677.43km 2 and annual irrigation capacity of 621.46km 2 in pune district. it supplies pune city with 280.3mm 3 of water. the ogee spillway has a design discharge of 2700m 3 /s, crest height of 23.75m, design head of 4.29m and 14 spans of 10m width. a. design of an ogee spillway a physical hydraulic model was developed on the existing tilting hydraulic flume in the fm laboratory and designed with a model scale ratio of 1:33 [15]. the model investigation is done as per hydraulic similarities. froude's model law and the model dimensions are shown in table i. b. design of stepped spillway the stepped spillway model is designed for a single span of 10m width with a scale of 1:33. the design is based on the froude’s model law as in [15]. the assumed hydraulic conditions are: i) the actual head should be less than 1.4 times the design head [7, 8], ii) tailwater depth is maintained in proportion with the sequent depth and the froude number is more than 4.5 [11, 12]. the condition for effective energy dissipation is: if yc/h=2.5, the profile surface is effective for energy dissipation, for 2.5<yc/h<6, the effect is still appreciable and for yc/h>6, the energy dissipation starts reducing [16]. in the proposed ogee stepped spillway model (on prototype) the following parameters are estimated: yc=3.35m, h=1.33m, corresponding author: alka sunil kote engineering, technology & applied science research vol. 9, no. 4, 2019, 4419-4422 4420 www.etasr.com kote & nangare: hydraulic model investigation on stepped spillway's plain and slotted roller bucket yc/h=2.51. this satisfies the appropriate condition for effective energy dissipation. the effectiveness of stepped spillway is maximized for actual head lower than the design head [17]. also, more steps on the spillway chute mean better energy dissipation and decrease of the hydraulic jump length. the heights of step are decided on the basis of dam height (hdam) [18]: hlarge= � �� hdam , hsmall= � �� hdam. large steps are proposed in the design of stepped spillway with step height h=40mm, tread l=33mm, step angle=50 ᵒ and number of steps=12. table i. hydraulic model for ogee spillway dimensions hydraulic dimensions prototype model (scale 1:33) unit span width 10 0.30 m spillway height 23.75 0.76 m spillway length 15.73 0.47 m downstream slope 0.75:1 0.75:1 design discharge 2700 0.41 m 3 /s velocity 0.59 0.10 m/s design head 4.29 0.13 m c. design of roller buckets roller bucket is a relatively short structure compared to the hydraulic jump type of stilling basin used for energy dissipation. it requires tail water depth in the range of 1.1 to 1.4 times the sequent depth and froude number greater than 4.5 [11]. two types of roller buckets, namely plain and slotted roller bucket were considered. the roller bucket model is designed after the design of the grand coulee and angostura dam type bucket (usa). the hydraulic parameters of roller buckets are designed as per [20] and displayed in table ii. table ii. roller buckets and stilling basin dimensions energy dissipater type hydraulic parameters prototype (m) model (mm) plain roller bucket radius 5.93 180 slotted roller bucket width 0.3 9 spacing 0.3 9 bottom width 0.74 22 top width 0.30 9 height of lip from depression 2.96 88 stilling basin bucket length 11.00 330 sloping apron length 18.67 560 depression bucket depth 5.93 178 d. modifications in the stilling basin the performances of plain and slotted roller bucket were found satisfactory for discharge intensity less than 50m 3 /s/m [13]. before modification of the stilling basin there is a need to locate the hydraulic jump for the developed models to fix its length. hence, the stilling basin is modified with v notch and end sills (figure 1). a stilling basin depression bucket and an end sill (sloping apron) were provided for flow control using a movable v-notch [20]. the modifications suggested in the stilling basin are: i) provision of a depression bucket to dissipate the hydraulic jump, ii) provision of sloping apron of 3h: 1v slope, and iii) provision of a movable v-notch on the end sill. fig. 1. modified stilling basin with depression bucket e. experimental set up the hydraulic model of the ogee profile stepped spillway was developed with a foam sheet, an acrylic sheet of 6mm thickness and polyvinyl chloride sheet. the acrylic sheet was raised on both sides of the spillway chute by 300mm for diverting floodwater towards the downstream side. twenty piezometers were installed along the spillway chute to measure the static head using a multitube manometer. the piezometer taps with brass holes of 6mm diameter were set at 45mm intervals. the invert level of the roller bucket was kept above the river bed level in order to prevent the entry of silt-laden water. the developed set-up of the ogee stepped spillway model was attached to the tilting hydraulic flume of 6m length, 300mm width and 300mm depth. the experiments were performed on ogee and stepped spillway hydraulic models with plain and slotted roller buckets as shown in figure 2, with: i) plain roller bucket (oprb model), ii) ogee slotted roller bucket (osrb model), iii) stepped plain roller bucket (sprb model), and iv) stepped slotted roller bucket (ssrb model). the laboratory experiments were conducted on a tilting hydraulic flume for 4m and 6m head. the experiments were performed at discharge of 0.0053m 3 /s at low head (4m) and 0.00649m 3 /s, at high head (6m). continuous flow of 0.0053m 3 /s and 0.00649m 3 /s was maintained in the flume which was kept horizontal. the water was pumped by a 3hp motor and the total head on a model was measured by a pressure gauge attached at the inlet of the flume. in this model, provision was made to replace the plain roller bucket, slotted roller bucket, and steps. performance with respect to specific energy and energy dissipation of all models was checked for varying heads and flume discharges. the experimental results of all models were compared with the hydraulic parameters for low and high water head. fig. 2. hydraulic model of the ogee rofile stepped spillway engineering, technology & applied science research vol. 9, no. 4, 2019, 4419-4422 4421 www.etasr.com kote & nangare: hydraulic model investigation on stepped spillway's plain and slotted roller bucket iii. results and discussion the performance of oprb, osrb, sprb and ssrb models was evaluated for 4m and 6m head by comparing the specific energy and energy dissipation along the chute surface. the hydraulic jump was observed for plain and slotted roller bucket at 4m and 6m head as shown in figure 3. i) plain roller bucket (4m) ii) plain roller bucket (6m) iii) slotted roller bucket (4m) iv) slotted roller bucket (6m) fig. 3. hydraulic jump on roller buckets without stilling basin a. hydraulic jump location on the hydraulic model the hydraulic jump is located on a model with a combination of roller bucket and steps for ogee profile stepped spillway (table iii). figure 3 shows that the hydraulic jump is swept out from the hydraulic structure and falls on the stilling basin at a longer distance. according to the location of the hydraulic jump, the further part of the stilling basin type ii is modified as shown in figure 1. the performance of all models was evaluated for 4m and 6m head. the results regarding specific energy and energy dissipation are compared below. table iii. hydraulic jump locations head (m) description location of hydraulic jump model (m) prototype (m) 6 plain roller bucket 0.83 27.66 6 slotted roller bucket 0.85 28.33 5 plain roller bucket 0.80 26.66 5 slotted roller bucket 0.83 27.66 1) specific energy for ogee and stepped spillway models at low head (4m) the specific energy possesses by ogee and stepped spillway models along the chute of ogee profile are shown in figure 4. in the ogee spillway model, it is seen that 82% of the specific energy is reduced by the oprb model and 78% of the specific energy is reduced by the osrb model due to the steps along the chute. in stepped spillway model, 58% of the specific energy is reduced in both sprb and ssrb models. this shows that maximum reduction in specific energy is observed in ogee spillway models. this reduction in specific energy is observed in both models due to the formation of rollers and the separation of boundary layers below the toe end. in stepped spillway, it is observed due to the roughness of steps. therefore, it is found that sprb and ssrb model reduce the maximum specific energy at the toe end of the spillway at the low head of 4m. fig. 4. specific energy for ogee and stepped spillway model at low head 2) specific energy for ogee and stepped spillway models at high head (6m) for high head, it is observed that 79% of the specific energy is reduced in the oprb model and 82% in the osrb model. in stepped spillway, the reduction of the specific energy is 79% for the sprb model and 57% for the ssrb model. the maximum reduction in specific energy is observed in oprb, osrb and sprb models. this shows that slotted roller bucket of stepped spillway (ssrb) consistently reduces the kinetic energy from crest to toe end on the spillway chute surface. thus, this model is more suitable for energy dissipation. it creates larger turbulence effect on steps and hydraulic jump falls on each step, which helps reduce the intensity of kinetic energy for the high head of 6m. fig. 5. specific energy graphical representation for 6m head 3) energy dissipation for ogee and stepped spillway models at low head all model performances were tested for energy dissipation. it was observed that in stepped spillway, sprb and ssrb models dissipate energy consistently along the spillway chute for low head. the energy dissipation is increased consistently with the sprb model due to the combination of steps and roller bucket. slotted roller bucket of stepped spillway is achieving energy dissipation consistently on its chute due to the turbulence effect and air entrainment occurring on each step. regarding the ogee spillway models, the oprb model dissipated 81.26% of the specific energy up to the spillway toe end for the 4m head but it needs sufficient tail water in stilling basin for stabilizing the hydraulic jump. this shows that plain roller bucket of ogee spillway is a suitable dissipater for energy dissipation at the low head of 4m. engineering, technology & applied science research vol. 9, no. 4, 2019, 4419-4422 4422 www.etasr.com kote & nangare: hydraulic model investigation on stepped spillway's plain and slotted roller bucket fig. 6. energy dissipation for ogee and stepped spillway at low head 4) energy dissipation for ogee and stepped spillway models at high head the specific energy dissipation for ogee and stepped spillway models at a high head (6m) is shown in figure 7. considering stepped spillway models, it is observed that the ssrb model dissipates energy consistently on its chute surface because of the development of hydraulic jump on each step and its swept on the next step. the enhancement of energy dissipation is observed consistently up to the toe end on the model and observed due to the combination of steps and roller bucket. the energy dissipation by the ssrb model ranges from 65% to 80% on the spillway profile for the high head. however, in ogee spillway, oprb and osrb models dissipate 80% of the energy in the stilling basin at the downstream channel. in comparison with the other models, it was found that the ssrb model of stepped spillway dissipates maximum energy of 83.36% at the 6m head. fig. 7. energy dissipation for ogee and stepped spillway at high head iv. conlcusion stepped spillway models are found to be highly effective for energy dissipation due to their combination of steps and roller buckets. it was also observed that the oprb model of ogee spillway dissipated 80% of specific energy for the low head of 4m but needed a longer span of stilling basin. slotted roller bucket model (ssrb) of stepped spillway dissipated 83.86% of specific energy at the high head of 6m. in comparison with the other models, it was seen that the stepped spillway with slotted roller bucket dissipated maximum specific energy for a discharge of 0.00649m 3 /s at 6m.thus the slotted roller bucket (ssrb) of the stepped spillway model was found to be a suitable model to minimize scouring and erosion problems on the khadakwasla dam spillway. acknowledgement the experiments were performed in the fluid mechanics laboratory at all india shri shivaji memorial society college of engineering, pune. references [1] m. ashiq, a. sattar, “optimization of energy dissipation works for nai gaj dam project”, world environmental and water resource congress, rhode island, usa, may 16-20, 2010 [2] m. r. chamani, n. rajaratnam, “characteristics of skimming flow over stepped spillways”, journal of hydraulic engineering, vol. 125, no. 4, pp. 361-368, 1999 [3] g. c. christodoulou, “energy dissipation on stepped spillway”, journal of hydraulic engineering, vol. 119, no. 5, pp. 644-649, 1993 [4] h. chanson, “comparison of energy dissipation nappe and skimming flow regime on stepped chutes”, journal of hydraulic research, vol. 32, no. 2, pp. 213-218, 1994 [5] g. degoutte, “skimming flow in stepped spillway, discussion”, journal of hydraulic engineering-asce, vol. 118, no. 1, pp. 111-113, 1992 [6] n. rajaratnam, k. subramanya, “profile of the hydraulic jump”, journal of hydraulic division, vol. 94, no. 3, pp. 663-674, 1998 [7] j. g. chatila, b. r. jurdi, “stepped spillway as an energy dissipator”, canadian water resource journal, vol. 29, no. 3, pp. 147-158, 2004 [8] r. m. sorensen, “stepped spillway hydraulic model investigation”, journal of hydraulic engineering, vol. 111, no. 12, pp. 1461-1472, 1985 [9] a. liaghat, a. adib, h. r. gafouri, “evaluating the effects of dam construction on the morphological changes of downstream meandering rivers (case study: karkheh river)”, engineering, technology & applied science research ,vol. 7, no. 2, pp. 1515-1522, 2017 [10] y. k. tung, l. w. mays, “optimum design of stilling basins for overflow spillway”, journal of the hydraulic division, vol. 108, no. 10, pp. 1163-1178, 1982 [11] r. m. khatsuria, hydraulics of spillways and energy dissipators, crc press, 2004 [12] s. k. mazumder, p. l. patel, “model study of a ski-jump type energy dissipator”, national conference on hydraulics and water resourceshydro 2001, pp. 425-432, 2001 [13] v. v. bhosekar, m. r. bhajantri, b. s. sunderlal, s. patnaik, “limitations of spillway roller bucket”, water and energy international, vol. 69, no. 7, pp. 47-54, 2012 [14] p. b. nangare, a. s. kote, “experimental investigation of an ogee stepped spillway with plain and slotted roller bucket for energy dissipation”, international journal of civil engineering and technology, vol. 8, no. 8, pp. 1549-1555, 2017 [15] bureau of indian standards, is 6934 (1998): hydraulic design of high ogee overflow spillways-recommendations, bureau of indian standards, 1998 [16] c. chafi, a. hazzab, a. seddini, “study of flow and energy dissipation in stepped spillway”, jordan journal of civil engineering, vol. 4, no. 1, pp. 1-11, 2010 [17] l. peyras, p. royet, g. degoutte, “flow and energy dissipation over stepped gabion weirs”, journal of hydraulic engineering, vol. 118, no. 5, pp. 707-717, 1992 [18] a. h. k. al-shukur, s. k. h. aal-khalaf, i. m. a. al-sharifi, “study of optimum safe hydraulic design of stepped spillway by physical models”, international journal of scientific and engineering research, vol. 5, no. 1, pp. 1356-1365, 2014 [19] bureau of indian standards, is 7365 (2010): criteria for hydraulic design of bucket type energy dissipators, bureau of indian standards, 2010 [20] w. h. hager, l. damei, “sill-controlled energy dissipator”, journal of hydraulic research, vol. 30, no. 2, pp. 165-181, 1992 microsoft word 01-3593_setasr_v10_n4_pp5869-5874 engineering, technology & applied science research vol. 10, no. 4, 2020, 5869-5874 5869 www.etasr.com vardakis et al.: partial discharges in cavities and their connection with dipoles, space charges … partial discharges in cavities and their connection with dipoles, space charges, and some phenomena below inception voltage george e. vardakis department of electrical and computer engineering democritus university of thrace thrace, greece michael g. danikas department of electrical and computer engineering democritus university of thrace thrace, greece anastasios nterekas department of electrical and computer engineering democritus university of thrace thrace, greece abstract—this paper tries to relate pedersen’s model on partial discharges and work carried out by bruning and co-workers on the possibility of the existence of charging phenomena below inception voltage, which may eventually cause deterioration of polymeric insulation. moreover, with the aid of the electromagnetic theory, some aspects of the pedersen’s model are tried to be clarified, especially those which are correlated with space charges, electric dipoles, charge distribution, charge dynamics, and partial discharge activity. keywords-pedersen’s model; partial discharges; dipoles; inception voltage; space charges i. introduction pedersen’s model [1] was proposed as an alternative to the traditional capacitive model [2, 3] for the interpretation and/or prediction of partial discharges in enclosed cavities in solid dielectrics. this model is based on electromagnetic theory and gives the magnitude q induced on the measuring electrode by the partial discharge in a cavity, in terms of a variety of parameters, as is shown in (1): q = kωεrε0 (ei – el) ∇����� (1) where k is the geometrical cavity factor, ω the cavity volume, ei the inception electric field for streamer inception, el the limiting electric field for ionization, εr and ε0 are the relative permittivity of the surrounding dielectric material and the permittivity of the free space respectively, and λ0 is the function giving the ratio of the electric field at the position of the cavity (in the absence of the cavity) to the voltage between the electrodes. according to [1], the charge deposited on the cavity surface s can be considered as an electric dipole, the moment of which µ, is given as: µ = ∫ rσds (2) where r is a radius vector which locates the position of the surface element ds. the induced charge which will eventually arise from the dipole is given as: � = − � ∙ ∇���� (3) with λ being a dimensionless scalar function which depends on the position of ds only. function λ is given by laplace’s equation: ∇�����∇���� = 0 (4) where ε is the permittivity of the insulating material and with the following boundary conditions: • λ= 1 at the electrodes where q is distributed, • λ=0 at all other electrodes. moreover, authors in [4] utilized the principle of superposition with the calculation of d-field (maxwellian approach) and the calculation of p-field (quasi-molecular description). in addition to this, the induced charge, according to [4], can be expressed as the difference between the charge on an electrode following discharge activity and the charge on the same electrode prior to the activity. at the maxwellian approach (d-field) and the corresponding establishment of λfunction, all electrodes are supposed to hold at zero potential and the resulting electric field owned only to the space charges (and surface charges) in the interelectrode volume. also in [5], the pd event is separated into two distinct time intervals: • the 1st time interval is determined as the duration of the void discharge development 0<t<t1 • the 2nd time interval is the time following the cessation of discharge development t1<t<t2 where t denotes time, t1 denotes the duration of the void discharge development, and t2 is the time of occurrence of the next discharge. for t1<t<t2, the induced charge q is given by either (12) for d-field analysis or (13) for p-field analysis � = −∬���� (12) � = −∭�� ∙ ∇���− ∬ ����� (13) it is evident from the above that the notion of dipole and/or dipole moment plays a decisive role in pedersen’s model which tries to relate the partial discharge taking place in a cavity with the dipole moment of the charge distribution on the surface (or in the interior) of the cavity. corresponding author: michael g. danikas engineering, technology & applied science research vol. 10, no. 4, 2020, 5869-5874 5870 www.etasr.com vardakis et al.: partial discharges in cavities and their connection with dipoles, space charges … ii. pedersen’s model re-considered a criticism leveled against pedersen’s model was that it is confined to a certain type of partial discharges, namely that of streamer-type discharges and it cannot be applied to all types of discharges. it is a model rather for initial experimental conditions and not for an estimate of the long-term developed discharges [6]. moreover, as was noted in [6], λ does not seem to be a function without physical meaning but it is the relative potential and can be expressed in terms of a percentage. however, even though there is a disagreement as to whether the net charge within the cavity remains zero [1, 6], it is evident from [1] that pedersen’s model tries to relate dipole moment with charge dynamics inside the cavity and thus with even minute discharge currents. the resulted electric field at the void exerts forces causing charge generation, which consequently has as a result, electric dipoles appearance within the cavity. the partial discharge activity inside the void leads to charge distribution and redistribution inside the void, and thus, induced charge appears at the electrodes [1]. shortly, dipole moments within the cavity are supposed to induce charges and eventually cause the recorded partial discharge currents. consequently, it is reasonable to assume that, agreeing with [6], the net charge within the cavity is not zero. if the opposite is valid (i.e. net charge is zero), this cannot explain the findings of [7] as well as some ideas put forward by other people [8]. charge dynamics means that even elementary charge motion can cause somehow minute currents that may circulate inside the insulating material. such minute currents, related to charging phenomena below inception voltage, were noticed in [7], where it was remarked that chemical by-products below and above the inception voltage were quite similar. further work on polymers and nanocomposite polymers reinforced this viewpoint, namely that there were some below-inception charging phenomena [9-12]. to be sure, previous published work does not prove that such phenomena exist in all insulating materials but, at least, there are some indications that this may be the case. further evidence that that may be the case comes from other sources as well [13]. the topic of very small partial discharges (barely detectable from partial discharge detectors) was dealt with in numerous publications [14-19], where it was discussed whether such small events are of pulsive or of non-pulsive nature. in [10, 20], it was remarked that, having an enclosed cavity in polyethylene, a conducting path caused the magnitude of quite low current pulses (1-10ma) which is substantially different and quite lower than current pulses of about 1a measured with other more conventional arrangements [21]. it was mentioned in [6] that there are doubts whether the net charge in a cavity is zero or can supposed to be equal to zero. however the fact that inside the cavity we have a dipole (or a number of dipoles or a distribution of dipoles) does not necessarily mean that the total electric charge is zero. various approaches point out the possibility of having small currents (or small charge displacements) inside the dielectric causing phenomena that may not be detected, but which may still provoke damage. thus the discussion of the pulsive or non-pulsive nature of partial discharge phenomena at and/or above inception voltage is shifted to a more fundamental question whether charge movement inside the dielectric causes deterioration, even below the inception voltage. table i. short presentation of the d-field and p-field analysis [4] d-field (maxwellian analysis) p-field (quasi-molecular analysis) the induced charge depends in a unique way on the location and magnitude of the space charge. an infinitesimal dq located anywhere in the interelectrode region induces charges dq at all over electrodes: dqi=-λdqi (5) the polarization p in the dielectrics is an important property, especially in insulating materials containing polarizable regions. the polarization effect is included in the λ–function in the d-field analysis. the whole interelectrode region is considered as a vacuum supposing that the solid dielectric itself is a distribution of electric dipoles, with polarization (density) p. dµ = qdr (6) applying green’s reciprocal theorem (7), two states are discriminated. in the first state, all electrodes are held at ground potential and the only charge left on the electrode will be the induced charge associated with the space charge, deposited in the space subtended by these electrodes. in the second state, ρ=0, σ=0 everywhere, so all electrodes are at zero potential (8), (9). ∭� ∙ ���� = ∭�′ ∙ ��� (7) �� ∙ !� + ∭�!���� + ∬�!���� = 0 (8) �� = −∭����� − ∬����� (9) the polarization p in a point of a solid dielectric depends on : applied voltages (pa) and space charge formed by partial discharge (∆p). p=pa+∆p (10) the resulting induced charge on the i-th electrode is given by (11): �� = −∭#��� + $� · &��'�� − ∬����� (11) iii. remarks on cavities in relation to pedersen’s model: discussion and comments there is a large amount of experimental data on cavities enclosed in insulating materials. very often, however, the experimentalists do not go below 1mm or 0.1mm in radius [1, 22]. there is though some evidence that cavities may become dangerous even below such dimensions [23]. certainly this is a topic needing further investigation. further confirmation of the above is offered in [24], where computer calculations indicated that, in the case of electrical machine insulation, cavities as small as 0.01mm (or even smaller) in radius near a conductor, there may be electric fields as high as 25kv/mm. other evidence regarding the existence and effect of small cavities (in the range of up to 120µm) was recorded in [25], where work was carried out with photovoltaic modules and components. moreover, a lot of emphasis was given in the past decades on the role of partial discharge detection by electrical means. in [25] offers another perspective, since it stresses the importance of both optical and electrical measurements. in [26] stresses also the limitations of the electrical measurements of pd. according to [26], simultaneous imaging and pd measurements may reveal the successive stages of some treeing growth phenomena. studying a cavity, one should not forget that its surface may not necessarily be smooth. in other words, its surface may have protrusions, not necessarily metallic but engineering, technology & applied science research vol. 10, no. 4, 2020, 5869-5874 5871 www.etasr.com vardakis et al.: partial discharges in cavities and their connection with dipoles, space charges … consisted of dielectric material. recent research reveals that dielectric protrusions may be the sites of high field intensifications and thus contribute to the breakdown mechanism [27]. such data agree with preliminary efforts in [9, 10], where it was indicated that even small irregularities on the surface of the cavity can contribute to the rise of minute currents below inception. a further remark concerning the pdextinction voltage: this can be determined with limited accuracy because of the influence from temperature and humidity [28]. even without such parameters, pd-extinction voltage may somehow vary from measurement to measurement due to the highly statistical nature of pd phenomena. this may be a further indication as to the possibility of charging events below inception. the whole issue of damage below inception voltage (which we try to relate with charge packets) is not unrelated to the uncertainties of defining the level of inception [29]. moreover, material composition plays a crucial role in determining the inception voltage [30]. cavity position affects also the inception voltage [31]. yet on another question related to considerations developed in [7], namely that charging phenomena are possible below inception voltage (because of some minute irregularities on the cavity surface), there is some indirect confirmation in [32], where the morphology and surface topography of polyethylene may affect space charge packet characteristics. although the authors of [32] do not mention partial discharges and related phenomena, it is evident that surface treatment plays a role in determining charge packets. in agreement to the above, in [33] it is noted that the formation of packet-like charge is a result of a high conductivity region that is caused when traps are filled by electronic carriers (electrons or holes). in [34], various partial discharge models are presented. in all models, the role played by surface charge accumulation is evident. furthermore, gas conductivity inside a cavity is also important. such comments – on gas conductivity – were made earlier [7,9]. however, gas conductivity may appear even in the absence of partial discharges, conductivity which will not necessarily be “translated” (or transformed) into something detectable. such ideas conform to [35], where it was reported that in minute cavities partial discharges may have very long statistical time lag and the number of initial electrons may indeed be very small. in relatively low voltages, ionization processes of low energy may occur, which means that charges appearing in the cavity may result to clusters of space charges on the cavity walls. such a space charge results in an electric field which – in the case of ac fields is added to the applied electric field on the insulation [36]. although what was described is the normal process of a pd, no one can exclude the possibility of having such events even below the inception voltage. a careful reader can observe that the whole approach of space charge phenomena is related to the model proposed many years ago by some distinguished researchers [37], namely that the electrodes, under ac conditions, inject and extract charges. some electrons are emitted or injected into the dielectric during the negative half cycle for a short distance, limited by the declining stress away from the points. they will be drawn back into the point on the positive half cycle and re-injected in the following cycle. on each cycle some of the electrons will gain sufficient energy to cause some polymer decomposition and thus create space charges in the bulk of the polymer. the estimated distance within which injected electrons can interact with the material to produce electrical trees near the tip of a needle is thought to be less than 20µm. tree initiation time (t) is related to the electric field (e), the effective work function φ (i.e. the difference between the work function of a metal and the electron affinity of a dielectric) with the following equation ln(t) = bφ3/2 /e + ln (c/a) (14) where a, b, and c are constants. moreover, in [1], it is stated that λ function is given by: ∇�����∇���� = 0 (4) where ε is the permittivity of the dielectric. solving the above equation in the appropriate area of interest, λ can be evaluated. initially, none can ignore that the space where the above equation is solved, includes, conducting (electrode, ionized air void), non-conductive (dielectric) and of course interfaces between the aforementioned materials. the analysis in [1, 5], needs more clarification, because (4) is laplacian, while in all interfaces, in the interior of the solid dielectrics, at the electrodes and inside the air void, space charges are present, determining the electric potential distribution. shortly, in [1, 5], the authors prove with a maxwellian approach for λ function : fig. 1. after pd activity, the presence of space charge in the void is considered to be poissonian (left rectangle). in [5], after a maxwellian analysis, (4) with the conditions (17) which are laplacian, are finally utilized (right rectangle). so, in [5], it is stated clearly that the defining equation of λi is: �� � �∭����� � ∬����� (9) the first integral corresponds to the space charge in all space ω between the electrodes (consequently including air void) and the second integral calculates the surface charge between dielectrics (at the interfaces between them). the discrimination of electric field into basic laplace and poisson (general and basic) field also needs more clarification since, among others, uses in [5]: � � &������� (18) while the divergence of electric displacement d depends only on the free charge density [38]: �)*)+, � � � �" �. � �� &�� ∙ ��� (19) ∮���� ∙ ������� � 0� 1 �-2 �� (20) ∮���� ∙ ������� � 1 &��2 ⋅ ������ (21) comparing (20) and (21), results to: �� &�� ∙ ���� (22) engineering, technology & applied science research vol. 10, no. 4, 2020, 5869-5874 5872 www.etasr.com vardakis et al.: partial discharges in cavities and their connection with dipoles, space charges … in addition to this, in [5], the electric field is assumed to be laplacian, before the pd activity and after pd activity, the presence of space charges in the void dictates us to solve poisson’s equation. in a mixed system, constituting from at least 2 electrodes, one solid dielectric and one air void enclosed in the aforementioned solid insulator, the voltage application u at the electrodes, creates space charges. the existence of space charges does not depend on the occurrence of a pd activity or not. generally speaking, space charges are localized states of charge, deriving from various sources. a first source of space charges is the polarization that took place at the dielectric. every molecule of the solid dielectric in the interelectrode area, before the electric field application, may exist in two states. either the molecule has symmetrical distribution of the electric charge, with a coincidence of the negative and positive charge (zero dipole moment), or it is polarized due to the asymmetry in the negative charge distribution (non-zero dipole moment or permanent dipole moment). after the electric field application, the molecules of the first category gain an induced dipole moment due to the separation of the centers of positive and negative charge distributions. molecules of the second category rotate into the direction of the field. as it is known from fundamental electromagnetism, dielectric hysteresis loop appear in solid dielectrics, but in the present paper relaxation time for solid dielectrics is not taken into account, similarly with [1, 5]. moreover, the interelectrode system includes the air void. it is known that the electric field inside an air slit enclosed in a solid dielectric is k times bigger than the mean electric field. e0=ε·emean (23) where eo is the value of the electric field inside the air void, ε is the relative permittivity of the dielectric (dielectric constant) and emean is the mean value of the electric field inside the dielectric. the bigger value of e0 is due to the polarization charges in the interior of air void. of course, (23) is valid whether partial discharge sparks inside the air void or not. thus, a dielectric after a voltage application shows polarization and/or polar charges at various positions, which in turn is itself one of the major factors for the space charge existence, independently or not from the pd activity. �. � �&�� ∙ ��� (24) a second source, contributing to space charges, independently again from the pd occurrence or not, are the free charges. in our system (electrodes, solid dielectric, air void, interfaces), free charges exist at: • electrodes (before pd as charge q and after pd as q+qinduced) and • air void (before pd and after pd). at the region in front of the injecting electrode. this procedure is most common and usual from point electrode. the space charge injection distorts the electric field and reduces or enhances the local electric strength, in the region around the tip of the needle electrode. in case of homocharges, reduces the electric field e and in case of heterocharges enhances the local electric field. this category is free charges which have lost their kinetic energy to break bonds and they have converted to thermal ones. table ii. two situations for potential and charge before and after induced charge appearance on the electrode. 1 st state (before pd) 2 nd state (after pd) volume and surface density are equal to zero ρ=0, σ=0. all electrodes are held in ground potential. one electrode (the i-th electrode) has potential uci. almost all charges (linked with partial capacitances) are zero. all other electrodes are at zero potential. the only charges left on the electrode will be the induced charges associated with space charges. so, it is evident, that space charges (free charges and polarization charges), exist at the interelectrode area, after the voltage application and their existence is not dependent from the occurrence or not of the partial discharge activity in the interior of the enclosed air void. thus, the electric field, after voltage application is not laplacian but it is clearly poissonian. the electric field, of course, is poissonian before and after pd activity. it must be pointed out that in [4], a fundamental theorem of electromagnetism, green’s reciprocal theorem, [39, 40] is utilized according the following: according to [39], the green reciprocal theorem states that if separate charge densities ρ and ρ’ then give rise to electric potentials v and v’ respectively having as a result : ∭� ∙ ���� = ∭�′∙ ��� (25) in case, the charge resides solely to the surfaces of n fixed conductors: ∑ �� ∙ �� � =5�67 ∑ ��′ ∙�� 5 �67 (26) where charges qi on the conductors correspond to respective potential vi and charges qi’ correspond to vi’. applying green’s reciprocal theorem in a system containing electrodes, void, dielectric and interfaces before and after partial discharge activity (table i), the following equation is used in [39]: �� ∙ !� + ∭�!���� + ∬�!���� = 0 (27) where !� is the applied voltage and �!� is the scalar potential at dω and ds. a point of further investigation is the application of (26), which refers to charges residing solely to conductors (e.g. electrodes). at conductors, normally there are free charges ρf and not polarized charges. in (27), volume charge density ρ includes, among others, the polarized charges (bound charges per unit area) in the interior of the solid insulating material. these charges are not free charges. furthermore in (27), charges before pd activity (either in the form of volume density ρ or in the form of surface density σ are equal to zero ρ=0, σ=0). this is the reason which the second term in (27) (or the second term in (25), (26)), is equal to zero. this hypothesis neglects the various charges, mostly bound polarized charges which form and appear inside solid dielectric in the time period, after the voltage application and before the partial discharge activity. finally, in [1] it is stated that the dipole engineering, technology & applied science research vol. 10, no. 4, 2020, 5869-5874 5873 www.etasr.com vardakis et al.: partial discharges in cavities and their connection with dipoles, space charges … moment of a charge distribution left on the surface of an ellipsoid is given by the following equation : � � 89:;< [>������ � ?1 " +.!a#:bc:' d: e>,����] (28) where a, b, c are the semiaxes of the ellipsoid, e0 is the ambient field when the internal field is equal to the inception field ei and el is the limiting field when the discharge is quenched. equation (28), is one of the basic equations leading finally to (1). however, in [41], there is a clear discrimination for the potential calculation φ as can be seen in table iii. table iii. potential expressions φ for two kinds of ellipsoid (conducting and dielectric) inside a parallel electric field [41] conducting ellipsoid in parallel field dielectric ellipsoid in parallel field the potential at the ellipsoid is a constant φs �g � ��[1" hi jk 1 lm#ξnαi'op q � ] (29) the potential at any interior point of the ellipsoid: �c � � rbs∙t 7n uvw ixi #ykcyi'zk (30) and the field intensity in the interior of the dielectric ellipsoid is: [\ c = ]b^ 7n _`a ibi #:kc:i'<k (31) equation (31), belonging to the case of a dielectric ellipsoid inside a parallel electrical field, according to [41], is apparently a part of (28), or has close relation with the analysis about a dielectric sphere inside a parallel field. equation (28), in [1], which calculates the dipole moment inside an ellipsoid needs further clarification because it seems to correspond to the case of dielectric ellipsoid and how it affects the electric field inside and outside the ellipsoid. the ellipsoid after pd activity, is conducting, due to the electrons, positive and negative ions produced during the ionization activity. the ellipsoid, before the pd activity can considered to be insulating (dielectric e.g. air) but (28) and the final important equation (1), are utilized for induced charge calculation, which is a phenomenon which clearly happened after pd activity. it seems that (28), as referred to [1], is not compatible with the conducting behavior of the void after pd activity. recapitulating we may say that the present paper tries to clarify some aspects of pedersen’s model about the induced charge after pd activity. there is no proposal of a new model but a criticism is presented of a very important model from two different aspects. the first aspect is concerned with experimental data below the so-called inception voltage whereas the second aspect is related to the electromagnetic theory and mostly to the conducting behavior of dielectric materials. an effort was made – in the context of the present work – to enlighten some aspects of pedersen’s model. furthermore, the present paper – as is evident from the title tries to correlate pd activity with space charges and electric dipoles under the prism of electromagnetic theory. it is true that a criticism may be levelled in the fact that pedersen’s model is rather old. however, it remains one of the most prominent and used models regarding pd activity and the authors consider that it has significant explanatory power. it is also true that the authors use many references published long time ago. it is also true that more recent criticism of pedersen’s model has been published [42, 43], their comments, however, are beyond the scope of the present paper since they are concerned with the notion of capacitance. iv. conclusion the present paper tries to enlighten some aspects of the pedersen model relating partial discharge activity inside air voids and the induced charge at the electrodes after pd activity and charge redistribution. electromagnetic analysis is fundamental in pedersen’s model and in the present paper some points which need further investigation are demonstrated. the discrimination between conducting and insulating air void, the presence or not of space charges in the interelectrode area, the precise description of the charge kinetics after the voltage application and before partial discharge activity, the role of dipoles and dipole moments, the partial activity below inception voltage, the cavity dimension (especially those with dimensions less than 0.1mm), the pd extinction voltage are some points which are analyzed in the present paper and an effort of a correlation with pedersen’s model is being made. references [1] g. c. crichton, p. w. karlsson, and a. pedersen, “partial discharges in ellipsoidal and spheroidal voids,” ieee transactions on electrical insulation, vol. 24, no. 2, pp. 335–342, apr. 1989, doi: 10.1109/14.90292. 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[42] z. achillides, m. g. danikas, and e. kyriakides, “partial discharge modeling and induced charge concept: comments and criticism of pedersen’s model and associated measured transients,” ieee transactions on dielectrics and electrical insulation, vol. 24, no. 2, pp. 1118–1122, apr. 2017, doi: 10.1109/tdei.2017.006013. [43] z. achillides, e. kyriakides, and m. g. danikas, “partial discharge modeling: an advanced capacitive model of void,” ieee transactions on dielectrics and electrical insulation, vol. 26, no. 6, pp. 1805–1813, dec. 2019, doi: 10.1109/tdei.2019.008163. microsoft word 5-2976_s_etasr_v9_n5_pp4600-4604 engineering, technology & applied science research vol. 9, no. 5, 2019, 4600-4604 4600 www.etasr.com jatoi et al.: comparative study of the electrical characteristics of different photovoltaic modules in … comparative study of the electrical characteristics of different photovoltaic modules in outdoor environment abdul rehman jatoi energy and environment engineering department, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan arjatoi@quest.edu.pk saleem raza samo energy and environment engineering department, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan sfaizsamo@yahoo.com abdul qayoom jakhrani chemical engineering department, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan aqbaloch@quest.edu.pk abstract—the electrical characteristics of photovoltaic (pv) modules are affected by solar radiation and module temperature in outdoor environment. it was found that polycrystalline gained a yearly 0.50°c more average module temperature than monocrystalline. non-crystalline amorphous modules got a yearly 0.83°c more average temperature than thin film modules. the attainment and release of module temperature was related with material properties of pv module technologies. the amorphous module gave 5.7%, 2.7% and 15.0% more yearly average opencircuit voltage than polycrystalline, monocrystalline and thin film modules. besides that, the thin film modules gave 6.5% and 1.7%, 9.3% and 4.0%, and 11.3% and 8.8% more yearly average normalized short-circuit current and power output than polycrystalline, monocrystalline and thin film modules respectively. it was shown that the maximum annual average open-circuit voltage was given by amorphous modules and maximum short-circuit current and power output by thin film modules during the study period. keywords-climatic conditions; module temperature; iv characteristics i. introduction solar pv systems produce electricity by converting sunlight directly into electricity. pv modules are normally connected in series and in parallel to produce the desired voltage and current [1-3]. each pv module is rated under standard test conditions [4-5] and such conditions could not be maintained in outdoor environments [6-7]. the power output (i-v, current-voltage) of modules is influenced by the intensity of solar radiation and module temperature [8]. module temperature is one of the most important parameters responsible for deteriorating and reducing its power output [8, 9-10]. pv modules give their maximum performance in cold climates and sunny skies rather than cloudy and hot climates [11]. in general, the efficiency of a pv module decreases [12] by 0.2%/ºc-0.5%/ºc rise in ambient temperature beyond nominal cell operating temperature [13]. authors in [14] concluded that monocrystalline modules were found more efficient than polycrystalline and amorphous in january during high radiation conditions, and amorphous showed higher average performance ratio in low irradiance. authors in [15] reported that the efficiency of gaas/ge cells was 9.47% when they were exposed to the sun light at an air mass of 1.5 and at 26.85°c. authors in [16] presented the pv systems and net metering in greece. authors in [17] improved the efficiency of pv and thermal systems by reducing the solar cell temperature from 51°c to 33°c by increasing wind velocity from 0.5m/s to 3m/s. authors in [18] stated that the iv characteristics of pv modules depend on the intensity of solar radiation. authors in [19] analyzed the climatic data of two different cities namely nawabshah and quatta, pakistan. authors in [20] analyzed the electrical characteristics of polycrystalline, monocrystalline, amorphous, and thin film pv modules at 8:00, 12:00 and 16:00 hours from april to june 2016, and found that the polycrystalline module performed better than the others. this analysis was performed for a period of only three months, whereas the performance of modules requires to be examined for the entire year. therefore, this study was conducted to determine the impact of module temperature on the electrical characteristics of pv modules for an entire year. ii. materials and methods four commercially available pv module technologies were investigated in the climate of nawabshah, pakistan. the pv modules were fixed to south at an angle of 12° with respect to the horizon. the experimental setup is shown in figure 1 and the specifications of the examined pv technologies are given in table i. the basic climatic variables were measured with the help of a professional weather station hp-2000. the electrical characteristic and module operating temperatures (surface and backside) of each pv module were recorded through prova-210 and prova-830. a total of eight k-type thermocouples were used for the recording of modules’ temperature. to obtain sufficient outcomes, the data were recorded from november 2015 to october 2016. furthermore, data loggers were connected with a computer for storing and further analyzing the data [20, 21]. the average module temperature is considered as [20-22]: corresponding author: abdul rehman jatoi engineering, technology & applied science research vol. 9, no. 5, 2019, 4600-4604 4601 www.etasr.com jatoi et al.: comparative study of the electrical characteristics of different photovoltaic modules in …         + = 2 bs t s t m t (1) where, tm is module temperature, ts and tbs are surface and backside module temperature. equation (2) is used to normalize the measured electrical characteristics values (ecvs) of four modules for comparison and performance analysis [14, 20]: ( ) 100 ( ) ecvs measured output ecvs stc    = ×     (2) where, stc is the standard test conditions. fig. 1. experimental setup table i. electrical characteristics of pv modules [20, 21] module parameters unit module technologies (p-si) (m-si) (a-si) thin film model - sun 40p sun 40m tps 40 gs 50 voc v 43.00 21.50 29.00 62.00 isc a 1.29 2.55 2.30 1.42 vmax v 35.00 17.50 18.00 43.00 imax a 1.14 2.29 2.20 1.17 pmax w 40.00 40.00 40.00 50.00 area m 2 0.27 0.24 0.76 0.74 iii. results and discussion a. basic climatic variables figure 2 demonstrates the hourly average values of global solar radiation (gsr), ambient temperature (ta), wind speed (wv) and relative humidity (rh). the yearly average values of gsr, ta, wv and rh were found 518.69w/m 2 , 30.11ºc, 2.14m/s and 42.66%. it was noted that gsr and ta were rising from morning until noon, and then were decreasing gradually until the evening. the level of rh was more when ta was low, and vice versa. it is deduced that the rh is inversely proportional to the intensity of gsr and ta during the study period in outdoor conditions. b. operating module temperature the operating temperature of each pv module (tm) during the study period is illustrated in figure 3. the average pv module temperatures of polycrystalline, monocrystalline, amorphous and thin film modules were 43.96°c, 43.46°c, 44.38°c, and 43.55°c respectively. in comparison of crystalline modules, polycrystalline gained 0.50°c more yearly average temperature monocrystalline. by matching noncrystalline modules, the amorphous got 0.83°c more yearly average temperature than thin film modules. in general, it was observed that the polycrystalline module warms-up quickly in the morning, before noon, and attains more temperature between 07:00 and 11:00. amorphous module gains lightly more temperature from 07:00 to 14:00 than the other modules until the evening. thin film modules reached and released temperature more slowly than the other pv modules. the attainment and release of module temperature is directly related with the material properties of pv module technologies. fig. 2. yearly hourly average climatic condition fig. 3. hourly average module temperatures. c. electrical characteristics the electrical characteristics, namely open-circuit voltage (voc), short-circuit current (isc), and power output (p) of the four modules were recorded and analyzed. the results of current-voltage (i-v) and power-voltage (p-v) characteristics of polycrystalline are given in figures 4 and 5. maximum and minimum hourly average voc of polycrystalline were reported as 94.00% at 9:00 hours and 66.39% at 18:00 hours. the yearly average voc was 89.05%. similarly, maximum and minimum hourly average isc was found 82.44% at 12:00 and 4.86% at engineering, technology & applied science research vol. 9, no. 5, 2019, 4600-4604 4602 www.etasr.com jatoi et al.: comparative study of the electrical characteristics of different photovoltaic modules in … 18:00, and the yearly average isc was 47.40%. maximum and minimum hourly average power (p) was 74.87% at 12:00 and 4.27% at 18:00, whereas, the yearly average power output (p) was 43.97%. fig. 4. current-voltage of the polycrystalline module fig. 5. power-voltage of the polycrystalline module. the yearly hourly average recorded values of voc, isc and power output of monocrystalline are shown in figures 6 and 7. maximum and minimum hourly average voc of monocrystalline was 96.87% at 09:00 hours and 69.29% at 18:00 hours. the yearly average voc was 92.07%. similarly, the maximum and minimum hourly average isc was 76.71% at 12:00 and 4.20% at 18:00, and the yearly average isc was 44.57%. maximum and minimum hourly average power (p) was 69.64% at 12:00 and 3.84% at 18:00. the yearly average power output (p) was 41.61%. the average results of i-v and p-v characteristics of amorphous modules are given in figures 8 and 9. maximum and minimum hourly average voc of amorphous pvs were 100.27% at 09:00 and 68.17% at 18:00. the yearly average voc was 94.73%. maximum and minimum hourly average isc was 74.65% at 12:00 and 3.63% at 18:00, and the yearly average isc was 42.57%. maximum and minimum hourly average power (p) was 62.24% at 12:00 and 3.27% at 18:00. the yearly average p output of the amorphous module was 36.79%. the average values of voc, isc and p of the thin film module are presented in figures 10 and 11. its maximum and minimum hourly average voc were 85.55% at 09:00 and 54.26% at 18:00. its yearly average voc was 79.75%. maximum and minimum hourly average isc were 94.75% at 12:00 and 4.24% at 18:00, and the yearly average isc was 53.85%. maximum and minimum hourly average p was 78.89% at 12:00 and 3.62% at 18:00. the yearly average p output of the amorphous module was 45.62%. fig. 6. current-voltage of the monocrystalline module fig. 7. power-voltage of the monocrystalline module fig. 8. current-voltage of the amorphous module fig. 9. power-voltage of the amorphous module engineering, technology & applied science research vol. 9, no. 5, 2019, 4600-4604 4603 www.etasr.com jatoi et al.: comparative study of the electrical characteristics of different photovoltaic modules in … fig. 10. current-voltage of the thinfilm module fig. 11. power-voltage of the thin film module it was found that the amorphous pv module gave 5.68%, 2.66% and 14.98% more yearly average voc than polycrystalline, monocrystalline and thin film modules. besides that, the thin film pv module gave 6.45% and 1.65%, 9.28% and 4.01%, and 11.28% and 8.83% more yearly average normalized isc and power output values than polycrystalline, monocrystalline and thin film respectively. maximum yearly average voc was noted from amorphous module, and both isc and p from the thin film module. in general, at higher global solar radiations, each pv module generated more isc and gave more power output and vice versa. the voltage outputs were found inversely proportional to module and ambient temperature. it was found that voc was dropping and isc was slightly increasing when module temperature was rising from standard test conditions. iv. conclusion in this research, the electrical characteristics of four commercially available pv module technologies were analyzed in the real climatic conditions of nawabshah, pakistan. during the experimental work, the average global solar radiation was 519w/m 2 , the ambient temperature was 30.1°c, the wind speed was 2.1m/s, and the relative humidity was 42.7%. polycrystalline, monocrystalline, amorphous and thin film modules exhibited 44.0°c, 43.5°c, 44.4°c, and 43.6°c average module temperature respectively. regarding crystalline modules, polycrystalline gained 0.50°c more yearly average temperature than monocrystalline. regarding non-crystalline modules, the amorphous got 0.83°c more yearly average temperature than thin film. in general, thin film modules accumulated and released temperature slower than the other pv modules. the yearly average voc, isc and power output were 89.05%, 47.40% and 43.97% for polycrystalline, 92.07%, 44.57% and 41.61% for monocrystalline, 94.73%, 42.57% and 36.79% for amorphous, and 79.75%, 53.85% and 45.62% for thin film respectively. the amorphous module gave 5.7%, 2.7% and 15.0% more yearly average voc than polycrystalline, monocrystalline and thin film modules. besides that, the thin film module gave 6.5% and 1.7%, 9.3% and 4.0%, and 11.3% and 8.8% more yearly average normalized isc and power output values than polycrystalline, monocrystalline and thin film respectively. it was concluded that maximum yearly average voc was given by amorphous and maximum isc and power output by thin film modules during the study period. all pv modules generated more isc and gave more power output at higher level of solar radiation. the voltage outputs of the pv modules were found inversely proportional to both module and ambient temperature. references [1] s. a. kalogirou, solar energy engineering: processes and systems, 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gas leakage detector and warning generator bader farhan alshammari electrical engineering department university of hail hail, saudi arabia baderfm97@gmail.com muhammad tajammal chughtai electrical engineering department university of hail hail, saudi arabia mt.chughtai@uoh.edu.sa abstract−this paper presents an industrial monitoring system design using the internet of things (iot). the gas sensor (mq-5) captured information is posted into a data cloud. the sensor detects the leakage of gas under most atmospheric conditions. all the components are controlled by an arduino (uno-1) that acts as a central processor unit in the setup t. as soon as a gas leakage is detected by the sensor, the alarm is raised in the form of a buzzer. this alarm is supported by an lcd to display the location of leakage, alert the observer, and activate the exhaust fan in the particular section to extract leaked gas. the requirement of a gas detection system is not only to monitor continuously the surroundings but also to help prevent the gas leakage hence minimizing the chances of fire and damage. keywords-internet of things; gas leakage detection; arduino; wifi ; lpg ; natural gases , oil and gas industry i. introduction safety at workplace and industry is always a priority. in this regard, the less costly options for accident and mishap prevention in oil and gas industries are commonly adopted, yet these measures ought to be effective. security is the level of protection against danger and loss [1]. the help of technology is needed to provide early warning alerts in order to ensure that enough time is available to prevent potential dangers. in this study, gas leakage detection systems have been highlighted along with troubleshooting directives [2, 3]. even though building a system with a gas sensor is not as easy as it may seem [4, 5], a warning system has been developed based on esp (wifi) network. the system detects the presence of natural gases such as methane and lpg. whenever a gas leakage occurs, the sensors used in the circuit will detect it, the esp modem will be activated and a notification alert to the user will be transmitted by a customized dashboard. the system provides a real-time notification, allowing immediate implementation of health and safety measures and increasing the available time span to overcome the situation [6, 7]. the same system can be utilized in several other places such as kitchens, oil and gas pipelines, gas storage facilities, etc. [4]. there is always a risk of leakage whenever gas is used, threatening human lives and property [8, 9]. therefore, designing a low cost gas leakage detector can help in minimizing this risk over a span of several years. there have been several accidents caused by gas (lpg or methane) leakages in homes and industries (mainly oil and gas industries). these leakages have led to the loss of several lives and properties through fire outbreaks and explosions [8, 10]. ii. problem description in pipelines gas transfer, gas leakage is inevitable as there is a necessity of joints and other transmission components. the gas leakage up to a certain mass level can be ignored, however it is very important to raise an alarm if it surpasses certain threshold values. during the training in oil and gas industry the problem was mainly identified at the connections of gas valves. iot can be utilized for efficient and easy monitoring of gas leakages in a continuous basis and from any distance. iot is basically a network of interconnected devices that are embedded with sensors, programing, and network connectivity to collect and exchange data [11, 12]. iii. discussion the aim of this paper is to design a system that can detect the presence of natural gases and send alert signals to the users and nearest engineers of the leakage occurrence, and by showing a dashboard to the operator. the difference between the proposed system and the proposed one in [2] is that it shows a full screen dashboard in a 24 hour basis, connected to wi-fi allowing the faster information sending to the dashboard. in [2] the gsm is not efficient to be read all the time. it takes time and the reading is done by a mobile and not an industry application. our system allows the user to be able to take immediate actions against the gas leakage. in addition, it makes the gas leakage information available, accessible, and monitored from the dcs room. this system can be used in oil and gas industries and even in our kitchen. iv. methodology and techincal background a. system methodology in this phase, the research focuses more on the study case and the project development based on gas and sensor. the microcontroller will continuously receive the concentration and temperature data from two sensors in analog data packets. it will process the data and convert them to ppm and celsius degrees respectively. the converted data will be displayed in the lcd. whenever the reading of the sensors exceeds the set limit, it will automatically send a reading alert to the dashboard by using esp 8266 network to the numbers which are already set on the source code. the project methodology shows the step by step development of the project. the methodology includes corresponding author: bader farhan alshammari engineering, technology & applied science research vol. 10, no. 4, 2020, 6142-6146 6143 www.etasr.com alshammari & chughtai: iot gas leakage detector and warning generator the planning, the development of the design, and the management of the project. b. hardware and software development arduino uno board plays an important role in this project as it plays the role of the project’s central process unit (cpu). it needs to be programmed to execute the required function. the program should clarify the digital and analog pins (input and output pins), transmit, receiver pins, input voltage, and output voltage (5v dc). the arduino uno is a microcontroller board with extraordinary functions. it contains fourteen digital (input and output pins), six analog pins, with data transferring speed up to 16mhz, a universal usb terminal, power connection, and a reset switch. the project basic diagram is presented in figure 1 and the software flowchart is given in figure 2 [6]. fig. 1. main diagram of the project. fig. 2. system’s flowchart. the hardware components of the module are: 1. transformer (230 – 12 v ac) 2. voltage regulator (lm 7805) 3. rectifier & filter 4. microcontroller (atmega328) 5. push buttons & lcd 6. in4007 & led 7. resistors & capacitors v. module desgin as shown in the circuit in figure 3, the model will be designed in a printed circuit board (pcb). the project will be containing several devices such as the microcontroller, transistors, diodes, transformer, resistors and filter capacitance. the circuit will be fed from the sockets (230v) by using the stepdown transformer to 12v. the voltage will become dc by a bridge rectifier. the output of the bridge rectifier will be smoothed with the use of a parallel 1000µf capacitance filter. the pcb should be designed before by using special programs such as proteus. it helps to simulate the circuit and check the number of pins and available connections for each component. the following steps show the arrangement to our model: • proteus gave us many advantages to minimize the number of wires and easy connection for each component. also, proteus facilitated all connections so that the circuit was completed in operational form. figure 4 shows the design of the pcb (3d). in addition, the condition of the circuit is applicable by testing the lcd, wi-fi, valve, and the fan. • proteus was used to view the circuit from other angles. the back view of the circuit helped us to inspect various solder components. figures 5-6 show the layout of the back of the pcb. • once we are satisfied with the simulation of the circuit, we were ready to take up the soldering of the components. fig. 3. final schematic of the project. engineering, technology & applied science research vol. 10, no. 4, 2020, 6142-6146 6144 www.etasr.com alshammari & chughtai: iot gas leakage detector and warning generator fig. 4. final circuit in black screen showing all the connections. fig. 5. 3d top of view of the pcb. fig. 6. 3d back view of the pcb showing pins and layout. vi. simulation results the circuit was tested using proteus by running the design. the tested mq-5 sensor was adjusted from 0% to 100%. at 100% the output voltage was 5v as shown in the datasheet of the sensor. when the program is running, the power on led and the green led are working. the red led and the alarm are not [5, 10]. by applying (1) and (2) to calculate the gas leakage for different gases, such as methane and lpg we got different results as shown in table i which the sensor working properly. � � ��� ��� (1) � � � (2) practical results were obtained using the pcb implemented gas leakage detector. the circuit was powered on and lpg gas was released from a lighter. the gas concentration was read on the lcd and recorded in iotgecko instrument panel (dashboard). the gas sensor sensed the gas from the lighter in different concentrations caused by different lighter distances from the sensor. the high accurate sensor could read up to 10000ppm [9]. when the gas is released, the green led goes off, the red led blinks, and the alarm goes on when the sensor output voltage is more than or equal to 2.5v. below 2.5v, the alarm is off and the green led is lit while the red led is off. the sensor output voltage is monitored using a push button that shows if the alarm is on or off. as shown in figure 7 the simulation results and the practical results of testing the sensor in different levels of voltage match. the dashboard (instrument panel) and lcd show the same condition for different gas readings. fig. 7. comparison between simulation and practical results. table i. comparison simulation and practical results sensor output (v) proteus results (ppm) practical results (%) 0 0 0 0.5 0 0 1.0 0 0 1.5 0 0 2.0 201 2% 2.5 402 4% 3.0 1418 14% 3.5 2600 26% 4.0 4295 43% 4.50 7765 77% 5.00 9945 99% engineering, technology & applied science research vol. 10, no. 4, 2020, 6142-6146 6145 www.etasr.com alshammari & chughtai: iot gas leakage detector and warning generator fig. 8. the pcb while connecting to the wi-fi and the server. vii. operation after plugging the 12v power supply from the main outlet the circuit is biased and the pcb starts its operation. supply of power to all the components must be assured for smooth operation. one way is to check the blinking led for internal components. the main led is also working as shown figure 8 according to [11]. after a couple of seconds, the pcb will connect to the wi-fi and will display the status of the connection on the lcd. the pcb is connected to the iotgecko. then, a dialogue box appears on the computer to seek the minimum and maximum values for gas detection. this is the setup of the level of sensitivity for the detection of leaked gas. fig. 9. pipe minimum and maximum gas concentration values input when connecting to the server. if the gas leakage is does not belong in the range defined by the maximum and minimum values for the pipe, the alert will start, and the warning light would turn on and an appropriate message will show on the server. in addition to this the gas valve changes its status from open to close and the exhaust fan will turn on immediately. viii. testing results for testing the project in the laboratory, a cigarette lighter was used in two particular cases as discussed below. a. without gas leakage from the pipe we assumed the gas has a leakage concentration of 6% as maximum and a minimum of 2%. in this case the cigarette lighter was not used to satisfy the condition. figure 10 shows the display of normal condition. the green led shows the normal condition, the fan and the valve don’t take any actions. fig. 10. display of normal concentrations. b. with gas leakage from the pipe fig. 11. display of abnormal concentrations. in this case we assume that the gas concentration has a maximum value of 10% and a minimum value of 2%. in this engineering, technology & applied science research vol. 10, no. 4, 2020, 6142-6146 6146 www.etasr.com alshammari & chughtai: iot gas leakage detector and warning generator case the cigarette lighter was used to satisfy the condition of risk. figure 11 displays the abnormal conditions in the server and in the module. the red led represents the abnormal condition, the fan and the valve they will take actions immediately. ix. conclusion after the design implementation, the device accurately detected the simulated gas leakages and a message was generated through the wi-fi network. the message was transmitted to the server to arm the buzzer for the purpose of user alert. on the same time the exhaust fans were automatically activated to suck out the leaked gas from the enclosed space, to prevent potential ignition and fire hazards. this smart device offers several safety benefits that are vital for early gas leakage detection, and response towards preventing lpg leakage. with small modifications the system can also be used for household purposes to prevent house gas leakages. aknowledgment the research was carried out under the research grant #rg191250, provided by the university of hail, hail, kingdom of saudi arabia. nomenlature v voltage (volt) dc direct current (ampere) ac alternative current (ampere) ρ gas density, (kg/m 3 ). t temperature of gas, (kelvin). p pressure, (n/m 2 ). qs flow rate at standard conditions (m 3 /s.). ru gas constant, 8.3144126 (n-m/mole-k) mw molecular weight of gas, kg/mole. w mass flow rate of gas (kg/s). ppm parts per million references [1] v. yadav, a. shukla, s. bandra, v. kumar, u. ansari, and s. khanna, “a review on microcontroller based lpg gas leakage detector,” journal of vlsi design and signal processing (e-issn: 2581-8449), vol. 2, no. 1, 2, 3, sep. 2018, accessed: jul. 23, 2020. [online]. available: http://matjournals.in/index.php/jovdsp/article/view/936. [2] “microcontroller based lpg gas leakage detector using gsm module,” engineers garage, jul. 04, 2019. https://www.engineersgarage.com/contributions/microcontroller-basedlpg-gas-leakage-detector-using-gsm-module/ (accessed jul. 23, 2020). [3] l. j. klein et al., “distributed wireless sensing for fugitive methane leak detection,” in 2017 ieee international conference on big data (big data), dec. 2017, pp. 4583–4591, doi: 10.1109/bigdata.2017.8258502. [4] a. gupta, “economical and optimal gas leakage detection and alert system,” international journal of scientific and research publications, vol. 7, no. 11, pp. 260–263, nov. 2017. [5] a. john, b. purbia, a. sharma, and m. a.s, “lpg/cng gas leakage detection system with gsm module,” international journal of advanced research in computer and communication engineering (ijarcce), vol. 6, pp. 536–540, may 2017, doi: 10.17148/ijarcce.2017.65103. [6] t. arpitha, d. kiran, v. s. n. s. gupta, and p. duraiswamy, “fpgagsm based gas leakage detection system,” in 2016 ieee annual india conference (indicon), dec. 2016, pp. 1–4, doi: 10.1109/indicon.2016.7838952. [7] i. allafi and t. iqbal, “design and implementation of a low cost web server using esp32 for real-time photovoltaic system monitoring,” in 2017 ieee electrical power and energy conference (epec), oct. 2017, pp. 1–5, doi: 10.1109/epec.2017.8286184. [8] r. n. anderson, “‘petroleum analytics learning machine’ for optimizing the internet of things of today’s digital oil field-to-refinery petroleum system,” in 2017 ieee international conference on big data (big data), dec. 2017, pp. 4542–4545, doi: 10.1109/bigdata.2017.8258496. [9] a. abbasi and f. m. hashim, “evaluating pressure in deepwater gas pipeline for the prediction of natural gas hydrate formation,” engineering, technology & applied science research, vol. 9, no. 6, pp. 5033–5036, dec. 2019. [10] g. stewart, c. tandy, d. moodie, m. a. morante, and f. dong, “design of a fibre optic multi-point sensor for gas detection,” sensors and actuators b: chemical, vol. 51, no. 1, pp. 227–232, aug. 1998, doi: 10.1016/s0925-4005(98)00199-3. [11] s. zafar, g. miraj, r. baloch, d. murtaza, and k. arshad, “an iot based real-time environmental monitoring system using arduino and cloud service,” engineering, technology & applied science research, vol. 8, no. 4, pp. 3238–3242, aug. 2018. [12] g. yadav and h. m. s. devi, “arduino based security system – an application of iot,” international journal of engineering trends and technology (ijett), no. special, pp. 209–212, 2017. microsoft word etasr_v11_n4_pp7326-7331 engineering, technology & applied science research vol. 11, no. 4, 2021, 7326-7331 7326 www.etasr.com al-shammari et al.: an edge – iot framework and prototype based on blockchain for smart … an edge – iot framework and prototype based on blockchain for smart healthcare applications naif khalaf al-shammari department of mechanical engineering college of engineering university of ha’il ha’il, saudi arabia naif.alshammarif@uoh.edu.sa thouheed ahmed syed school of computing and information technology reva university bangalore, karnataka, india syedthouheed.ahmed@reva.edu.in muzamil basha syed school of computer science and engineering reva university bangaluru, karnataka, india muzamilbasha.s@reva.edu.in abstract-the internet of things (iot) and the integration of medical devices perform hand-to-hand solutions and comfort to their users. with the inclusion of iot under medical devices a hybrid (iomt) is formulated. this features integrated computation and processing of data via dedicated servers. the iomt is supported with an edge server to assure the mobility of data and information. the backdrop of iot is a networking framework and hence, the security of such devices under iot and iomt is at risk. in this article, a framework and prototype for secure healthcare application processing via blockchain are proposed. the proposed technique uses an optimized crow search algorithm for intrusion detection and tampering of data extraction in iot environment. the technique is processed under deep convolution neural networks for comparative analysis and coordination of data security elements. the technique has successfully extracted the instruction detection from un-peer source with a source validation of 100 iot nodes under initial intervals of 25 nodes based on block access time, block creation, and ipfs storage layer extraction. the proposed technique has a recorded performance efficiency of 92.3%, comparable to trivial intrusion detection techniques under deep neural networks (dnn) supported algorithms. keywords-blockchain; intrusion detection; deep neural networking; iomt; iot i. introduction modern day medical infrastructure is expanding with the help of innovative technologies and engineering, such as the internet on things (iot). iot supports multiple fronts with incorporation on various devices and networking configurations. the iot enables users to connect and coordinate applications and services via demand-driven configurations. with a series of newer expansions, the iot has emerged with a new dimension of device configurations under medical applications, termed as internet of medical things (iomt). the iomt assures the data are secure and have a defied priority of operation under third party service channels, since the channel of communication is bound to operate under the standard operation policies. the iomt faces due to security and application concerns on internet-based connectivity. intrusion detection and managing plays a vital role in handling and improving the overall performance of iomt’s operation. the iomt's operation can be enhanced with blockchain management. the blockchain technologies assure the dependency of information and priority of operations under medical devices and applications. the blockchain manages the instruction of medical devices via a series of stacks and arrays. these stacks contain the information of nodes and users, maintaining addresses and operation tasks to assure connectivity. iomt devices under a predefined iot ecosystem perform an arbiter role of information management with respect to communication protocols. these protocols restrict the user behavior model and hence cause unexpected intrusion detection. these intrusions can cause system failure and deadlocks in managing information. the flow of connectivity and error rate of such nodes needs to be recorded. the agenda of this research is to provide a reliable solution when encountering such intrusion attacks. the principle order of intrusion detection is based on raising intrusion flags or counters. thus the iomt devices can assign a priority in order to the operating standards. the iomt based intrusion detection technique assures the management of remote incoming devices under error management to provide a systematic behavior and principle operating models. the model of such intrusion detection has to be highlighted with the support of blockchain approaches. the current article also states the operating principles of iomt protocol enhancement with respect to the validating approaches of intrusion detection system’s automation. the current article presents a standard protocol on corresponding author: naif khalaf al-shammari engineering, technology & applied science research vol. 11, no. 4, 2021, 7326-7331 7327 www.etasr.com al-shammari et al.: an edge – iot framework and prototype based on blockchain for smart … maintaining and reflecting the iomt operating standards and its primary functionalities when encountering intrusion detection using a blockchain approach. ii. literature review the operating and compatibility standards of iomt are defined and processed from iot based environment (ecosystem support, remote accessing, monitoring, and mentoring of information via demand-driven application services). the agenda of implementing iot is to support economical communication and lay standard operating protocols on the existing ecosystem or infrastructure. authors in [1] discussed various challenges and implementation protocols of iomt with reference to the convergence of technological impairment and operating standards under the healthcare sector. devices and data are sensitive and hence the coordination under remote accessing is a major challenge. since the protocol of iot governance has to be improved, a dedicated channel of cross layer protocol (clp) is discussed in [2] in the view of providing a reliable service and connectivity under iomt devices. the protocol improves the communication and bandwidth sharing among the systems governed under iot. with these protocols in place, application-driven services such as in [3] were introduced to support the exclusive claim of services via iot infrastructure. blockchain based instruction enhancement is proposed in [4] to support the variation and filtering of information via an enabled key management based authentication protocol for iomt servers. this bakmp protocol is supposed to store the data and monitor the reliability coefficient in order to access iomt devices and the supporting user information. detailed security communication challenges are reported in [5]. authors in [6] present a multi-dimensional medical dataset theory for a telemedicine ecosystem. the model can be enhanced and simulated for iomt device communication. the reliable telmed protocol for communication under remote accessing model is discussed in [7]. security concerns of implementing iomt are reported in [8] under an approach of highlighting the information and communication barriers for implementation. the study is focused on various malwares or generally intrusion detection with reference to [9, 10]. the functionality of streamlining is a concern of various studies and reports [11, 12] on iomt-based implementations. the conclusion and observations from this survey lack intrusion detection approach in iomt devices via blockchain terminology. the blockchain aims to provide a reliable solution in iomt and the current article discusses the influence of a protocol design on the edge of iomt implementation. iii. methodology the proposed methodology intends to be a reliable source of application and management unit. the detailed description of the proposed ids framework (figure 1) in the edge network is as follows: an intrusion detection dataset is generated by injecting several kinds of attacks in the edge network where iomt data are processed. in order to handle missing, noisy, and inconsistent data, preprocessing is performed on the dataset. to reduce the dimension of the dataset without losing information, pca (principal component analysis) feature selection algorithm is applied. there are several hyper parameters in the deep neural network (dnn) like the number of layers, the number of epochs, optimization functions, etc. fig. 1. proposed system architecture diagram. engineering, technology & applied science research vol. 11, no. 4, 2021, 7326-7331 7328 www.etasr.com al-shammari et al.: an edge – iot framework and prototype based on blockchain for smart … choosing the optimal values for these parameters will help improving the performance of the dnn. in order to accomplish this, crow search algorithm is used for hyper parameter tuning. 70% of the dataset is used for training and the remaining 30% is used to validate the proposed system. dnn algorithms are used to train the generated ids dataset. to prove the effectiveness of the proposed system, the results from various ids scenarios are compared with several state of the art machine learning algorithms [13]. iomt sensors are smart enough to acquire and transmit sensitive data to the edge of the network, but as these sensors have poor memory and limited processing units, they are not really smart enough to recognize how data are reliably transmitted or whether an attacker has been spotted during real-time analysis. fig. 2. system modeling design on ids handling of the iomt. iv. mathematical proof the proposed model of iomt-based intrusion detection is presented in figure. 2. the block diagram shows an understanding of managing and troubleshooting of intrusion via the crow optimization algorithm. the process is discussed as follows: 1) initial pre-processing and setup hypothesis the initial configuration includes the setup and environment alignment of the iomt ecosystem and operating standards. typically, the iot environment is stream-lined with basic networking and supporting devices for operation such as assigned routers, switches, end-users devices, and the network bandwidth. the setup of the proposed system must assure the reliability of the medical devices with the operating standards of iot setup. consider the initial iot setup ecosystem devices as ( ) 1 2 3, , ... nd d d d d i i i i i= where n end-user devices are connected and assigned for operations. the process of incorporating medical devices (mt) is represented as im under the given iot ecosystem id, such that [ ]1| / ,...m d m d m mn dni i i i i i⊆ ∈ ∀ ⊂ . the operation framework of im is reliable for operation. the im for each vector set is represented as ( ) 1 2 3, , ... nm m m m m i i i i i= for each order of processing and bandwidth sharing. 2) user configuration validation the overall incoming devices im are correlated with the matrix of user evaluation (u) as { }1 2 3, , ......u u u u= . the user ui is associated with the iot cloud matrix towards pairing users to respective cloud of medical devices im such that, the function of correlation is [ ]1 2 3, , ... |i i i n m iu i i i i i i i i∈ = ⊆u . the coordination elements are processed under independent devices im as m ii i∈ under open-alignment principle. the user collection of queries are reflected as: ( ) ( ) ( )1 12 n n m ij i o j i i it nf q t δ δδ λ δ − = = + × −  =     ∑ ∑ (1) the functional queries are based on ( )miδ and ( )iiδ using user correlation as show in (2): ( ) ( ) 0 lim n k m n t k q i u t δ δ λ δ→∞ =  ×  = × ∆       ∑ (2) the user to service correlation functions are mapped with respect to query or service on user demand. the rational function values are assured to maintain a difference from ( )miδ to prevent repeating. the query filtering operation mode qf is processed with reference to user-bandwidth (λ) and internet strength (termed as frequency (f) on operation) as shown in (3)-(5): engineering, technology & applied science research vol. 11, no. 4, 2021, 7326-7331 7329 www.etasr.com al-shammari et al.: an edge – iot framework and prototype based on blockchain for smart … ( ) ( )1 1 lim 2 n n n if j n i o j i ut nf u t δδ λ δ − − →∞ = = +  −  =     ∑ ∑ (3) ( ) ( ) ( ) 0 0 2 n i mf j i u it nf u r t δ δδλ δ ∞ ∞ − − − = × ∆      ∫ ∫ (4) ( ) ( ) ( ) 2 0 2 n i mf j i u it nf u r t δ δδλ δ − ∞ − − −  = × ∆           ∫ (5) where (t-nf) under the order of operations minimizes the intrusion error or error of connection to frame dependency with respect to rational value ( )r∆ . the frequency pattern (f) is an assurance pattern of ( )tλ∆ for bandwidth minimization with each user. ( )1nu − is a user’s coordination or association with internet ( )mi devices. the relationship is represented in (6): ( ) ( ) ( ) 2 2 n i mf j i r t i o u it nf u r t t δ δδλ λ δ δ − ∞ − =  −  = × ∆ ×          ∑ u (6) 3) configuration of intrusion detection an intrusion of user’s in internet connection is aligned with reference to connection patterns and configurations of the user devices. the configuration ( )fc is processed with respect to devices ( )mi and users (u) such for each device we have ( )( ):f m md c i i u⇒ → ⊆ under the operation principles of networking. the configuration setup is demonstrated in (7): ( ) ( )1 | lim n mf j n i o j i i i iu c d t t δδ δ δ ∞ − →∞ = =   − →    = ≅          ∑∑ (7) ( ) ( )| lim f m n t n u c i d t t δ δ λ δ δ ∞ →∞  →    = −        ∑ (8) from (8), the intrusion function can be integrated as a part of the configuration setting at user prospective as in: | f d c d= ∆ u (9) the resultant (d) values are patterned and mapped with supporting devices' values with a controlled configuration of monitored parameters (p) as rate of connection, rate of operation, refreshing rate, and time to reply on a query under iomt. these parameters are { }1 2 3, , ... np p p p p= on each parameter ( )|i m fp i c⇒ ⊆ under the operation of networking standards. 4) intrusion evaluation and secure communications framework with the rate of configuration inclusion in the users connection as shown in (9), the inter-dependency matrix is evaluated to reframe and process a secure communication channel via iomt services as shown in (10): ( ) ( ) 0 0 lim lim cf n fm f n n ci i t t δδ δ δ→∞ →∞     =        u (10) thus, the order of alignment ( )fc in configuration is managed and streamlined to detect the lightest change with respect to intrusion detection and report to the administrator. the intrusion support and vector configuration is limited to the range of the networking protocol as shown in (11) and thus, is further expanded into neighboring paradigms of features: ( ) ( ) ( ) 0 0 1 0.57 2π n f r m x i u i t t t δ δ δ λ δ δ ∞  −   = × × ×  ∆     ∫ (11) ( ) ( ) ( )log 0 0 0.57 2π x f m rt x i i u t t δ δ λ δ ∞ ∞ ∆ ∞   − ×   = ×  ∆     ∫ (12) where λ∞ is the representation of feature ranges with respect to the device and expanded into the higher grounds of information systems. the bandwidth becomes λ λ∞⇒ on the range shift with ratio of ( ) log 0.57 x t∆     for a reference value correction with ( ) ( )|f mi iδ δ as the internet interpretation matrix value. this, expanding (10) is recomposed as: ( ) ( ) 0 0 lim lim fm f n n ci i t t δδ λ δ δ ∞∞ →∞ →∞ ∞     ∞ = ×       u (13) with respect to (13), the repeated parameters of interdepending devices values in cf and im are expanded to infinite range of network tracking, making the process a reliable approach in shortlisting features set of instruction detection in the iomt ecosystem. v. experimental setup and results the iomt development has varying node cluster density. the throughput and accuracy of the evaluation are reported in figure 3. the node throughput is gradually improved and a saturation is achieved with reference to improved iomt enabled iot nodes under the operating standards. the resultant throughput is provided on evaluation paradigms of improving iomt devices and their ratio of computation. the improvisation helps the process of reliable factor improvisation with reference to device density. the accuracy is mapped with reference to the accuracy and validation factor as shown in figure 4 and figure 5 respectively. the approach has achieved an accuracy of 92.3% on average. engineering, technology & applied science research vol. 11, no. 4, 2021, 7326-7331 7330 www.etasr.com al-shammari et al.: an edge – iot framework and prototype based on blockchain for smart … (a) (b) fig. 3. (a) throughput evaluation and (b) iomt based throughput computation. fig. 4. accuracy computation on iomt devices. vi. conclusion and future work the proposed technique was discussed on various highlights and concerns on designing and developing iomt environment and its respective intrusion detection. the article has also focused its discussion on various algorithmic approaches involved in streamlining iot and iomt devices in the cloud ecosystem. various categories of intrusion detection and attacks were identified, detected, calibrated, studied, and reported. the mathematical representation and orientation approach of intrusion was defined using user-centric techniques in identifying vulnerable nodes/users with a 3-layered approach. the reliability of iomt devices has increased by strengthening the application framework of healthcare iot. fig. 5. accuracy comparison. acknowledgment this research work was funded by the makkah digital gate initiative under grand no. 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[13] n. k. al-shammari, h. b. almansour, and m. b. syed, "development of an automatic contactless thermometer alert system based on gps and population density," engineering, technology & applied science research, vol. 11, no. 2, pp. 7006–7010, apr. 2021, https://doi.org/ 10.48084/etasr.4103. authors profile naif khalaf al-shammari academic qualifications: 1993 b.s., m.e., ksu, rating (4.25/5), 1999 m.s., m.e., ksu, rating (4.56), 2011 ph.d., b.e., birmingham university, uk. professional experience: 1994-2000 saudi electric company, 2001-2010 sultan b.a al saud foundation. to date: mechanical engineering department, university of hail. research interests: rehabilitation engineering, robotics & control mechanisms, design of biomechanical systems and bio/nano-robotics dual-arm & flexible manipulator dynamics, smart materials, and mechatronics structures. syed thouheed ahmed works at the reva university as an assistant professor in the school of computing and information technology. he has graduated the b.e computer science and engineering from visveswaraya technological university in 2013, m.tech in computer science and engineering, reva institute of technology and management (now reva university), bangalore in 2015. currently, he is a doctoral fellow at the school of computers, information and mathematical sciences, bsa crescent university, chennai. he has published more than 45 research articles and papers in the field of machine learning, big data analytics, telemedicine, image and video processing, cloud computing, and iot at reputed international and national journals and conferences. syed muzamil basha completed his phd at vit university, vellore, india in january, 2020. his current research interests include bigdata analytics, blockchain management, internet of things. he has more than 30 publications, which include 21 research papers, 7 international conferences, 6 book chapters, and 2 letters. he is one of the editors of 4 textbooks. he has conducted guest lectures in various engineering colleges in india. he received an award for his contribution in 2018 from vit. microsoft word 43-2781_s_etasr_v9_n3_pp4301-4305 engineering, technology & applied science research vol. 9, no. 3, 2019, 4301-4305 4301 www.etasr.com shahbaz et al.: a novel classification of supply chain risks: a review a novel classification of supply chain risks a review muhammad saeed shahbaz faculty of technology management and business, universiti tun hussein onn malaysia, batu pahat, johor, malaysia msaeed.shahbaz@gmail.com samiullah sohu department of civil engineering, quaid-e-awam university of engineering, science & technology, sindh, pakistan sohoosamiullah@gmail.com farhan zeb khaskhelly institute of business administration, university of sindh, jamshoro, pakistan farhan.zeb@usindh.edu.pk arjumand bano institute of information & communication technology, university of sindh, jamshoro, pakistan arjumand@usindh.edu.pk muhammad afzal soomro dpt. of mathematics and statistics, quaid -e-awam university of engineering, science & technology, sindh, pakistan m.a.soomro@quest.edu.pk abstract—every organization is a complex supply chain system. if any fragment of this supply chain is disturbed, it will directly affect the entire structure. numerous studies have been conducted to categorize the supply chain risk sources, but very few available cover all types of risks. this study did an extensive literature review and content analysis on the subject. a supply chain is the flow of information, material, and money starting from suppliers and ending to end-users. to cover all types of risks, risk sources must be based on three perspectives: (i) internal to the firm, (ii) external to the firm but internal to the supply chain, and (iii) external to the supply chain. risks can be categorized into seven types under these three perspectives. regarding internal risks, three types of risks come from the supply side, process side, and demand side, while these members of the supply chain are connected with the supply affected by logistic side risks, finance side risks, and collaboration side risks. the external environment also affects the supply chain so the seventh type of risks comes from environmental side risks. this study extends the literature of supply chain risk management by identifying new risk sources. this study will help the managers to understand what kind of risks can affect their supply chain. future study can be conducted to empirically verify these risks sources. keywords-supply chain risks; risk sources; classification of risks i. introduction supply chain (sc) is the flow of material, finance, and information [1]. currently, the sc is involved in every business part, either directly or indirectly. any disruption, either natural or not, disturbs not only the core organization but the whole network and ultimately the economy [2]. in a few decades, scs gained notable attention due to globalization [3]. in a global survey, it was noted that political uncertainties, natural disasters, and economic issues would be among top risks regarding scs. in the same survey, it is exposed that loss of income due to this risks has been increased from 28% to 42% in just two years [2]. there are many examples in the history that add the value of sc risk management (scrm) [4]. in the current study, a thorough literature review has been conducted and a content analysis approach was followed. it was found that there is no study available, to the best of our knowledge, that categorizes the risks while following the flow of information, material, and finance from the supplier to the end user. it can be concluded that risks come from the supply side, process side, demand side, logistic side risks, collaboration side risks, finance side risks, and environment side risks. numerous studies have been conducted to categorize risk sources [5, 6] but no study covers all types of risks. identification, categorization, and mitigation are essential for the success of any sc, which is only possible when risks are identified. scrm can be categorized according to risk sources [6]. effective risk management can only be made possible if risks are properly identified, whether they are dealing with quality or safety challenges, supply shortages, legal issues, security problems, regulatory and environmental compliance, natural disasters, or terrorism [7]. risk sources are “any variables which cannot be predicted with certainty and from which disruptions can emerge” [8] and this research discovered by consensus, that risk sources have become more essential as scs become more complex and modern. a systematic review of 90 articles on sc risk sources shows that 25% of the articles considered only supply side risk, very few studies applied external risks and the studies that covered all dimensions of risks were very limited [9]. suthor in [7] reviewed 138 articles and found that less than 25% of them applied the quantitative technique in sc risk management. this study analyzed articles from 2000 to 2018 and found that most of the studies considered either operational risks, disruption risks or risks as general. the studies that use multi-dimensions of risks and corresponding author: muhammad saeed shahbaz engineering, technology & applied science research vol. 9, no. 3, 2019, 4301-4305 4302 www.etasr.com shahbaz et al.: a novel classification of supply chain risks: a review evaluate the effects of overall sc risks on performance are very limited. ii. literature review supply chain risk sources [5] can be divided into two categories: internal risks/operational risks and external risks/disruption risks [10] internal risks are divided into operational activities i.e., information risks and capacity related problems, customer demand, and quality related issues. external risks can be divided into competition, economic issues, political instability, natural disasters, and terrorist attacks [11]. there are various perspectives for developing risk sources, i.e. they can be classified in three different clusters: (i) environmental risks (those external to the supply chain), (ii) network-related risks, and (iii) organizational risks (which cannot be predicted with certainty and affect the supply-chainoutcome variables) [12]. similarly, they can also be categorized into three groups: (i) internal to the firm, (ii) external to the firm but internal to the sc, and (iii) external to the sc. the developed five risk sources are supply issues, process issues, demand issues, environmental issues and control issues [13]. the above two perspectives and categories can be combined into four groups: (i) internal to the organization, (ii) external to the organization, (iii) internal to sc, and (iv) external to the sc [14]. most of the relevant studies are based on this perspective and develop the risk sources either for internal risks or external risks or general. thus, researchers divide sc risks into three perspectives: internal to organization also called organizational factors, external to organization but internal to network, also known as industry factors, and external risks also called environmental factors and the sc risks are categorized into four risk sources: supply risk, process risks, demand risks and environment risks [16, 17]. fig. 1. classification of supply chain risks it is understood that if any fragment of the sc is disturbed, it will directly disturb the entire structure. thus, to cover all the risk sources has become essential. sc not only deals with internal operations but essentially considers the external relationship with partners. meanwhile, in another perspective, some researches define sc according to three types of flow: physical flow, information flow, and financial flow [23, 24]. sc is the relationship among sc partners and these partners are linked through flow, according to the adopted definition. material flow creates logistic side risks [19] whereas finance flow causes financial side risks and information flow originates information side risks [26, 27] a. supply side risks supply risk is the chance of occurrence of an event in inbound supply that impacts the organizational capacity in satisfying the customers, either it is due to individual or market supply side. authors in [22] describe the importance of supply side risks as most of the research in sc disruption is on supply disruptions. in supply, risks start form supplier’s supply to manufactures (backward integration). supply risk is defined as “the potential occurrence of an incident associated with inbound supply from individual supplier failures or the supply market, in which its outcomes result in the inability of the purchasing firm to meet customer demand or cause threats to customer life and safety”. toyota had to shut down plants and halt its 50% assembling for 6 weeks just because one of its suppliers had a fire incident in its plant and discontinued supply [8]. supply risks may arise from the reliability of the supplier, moral hazards, environmental compliances, purchasing decisions, multiple sourcing and security problems or it can be, sudden price change, quality issues, supplier’s bankruptcy, conflicts in goals, inventory problem, delays, product complexity, and problems in technology access [23]. this study is limited to poor logistics performance of suppliers, supplier quality problems, sudden default of a supplier (e.g. due to bankruptcy), poor logistics performance, and capacity fluctuations or shortages on the supply market [5]. b. process side risks imperfect production is an important element that can impact significantly the performance of a company. firms can have a massive loss, not only financial, but also in their reputation [22]. “process side risks/infrastructure risks/operational risks are losses resulting from inadequate or failed internal processes, people and systems or from external events”. an internal process risk is defined as the probability of occurrence of an event related with the principal organization that may disturb the internal ability of that organization, either producing goods or services. disturbance may be quality or timing issues. process side risks may be inefficiency in the manufacturing process, high level of changing in the process, material shortage or outdated technology [24]. the focus of this study is downtime or loss of production capacity due to local disruptions (e.g. labor strike, fire, explosion, industrial accidents), perturbation or breakdown of internal it infrastructure (e.g. caused by computer viruses, software bugs), loss of production capacity due to technical reasons (e.g. machine deterioration), and perturbation or breakdown of external it infrastructure [5]. c. demand side risks demand side risks are derived from the downstream of the sc, or from customer side issues [8]. demand risk is defined as “the possibility of an event associated with outbound flows that may affect the likelihood of customers placing orders with the focal firm, and/or variance in the volume and assortment desired by the customer” [25]. demand risks may be delays, engineering, technology & applied science research vol. 9, no. 3, 2019, 4301-4305 4303 www.etasr.com shahbaz et al.: a novel classification of supply chain risks: a review laziness in new product development, wrong forecasting, variation in demand, inaccurate information, industrial factors further explored as input market uncertainties, product market uncertainties, and competitive uncertainties. organizational factors also have a group of uncertainties, i.e. operating, liability, research and development, credit, and behavioral uncertainties [26]. very limited literature is available on demand fluctuation in the sc [22]. the side risks are unanticipated, e.g. very volatile customer demand and insufficient or distorted information from customers about orders or demand quantity. d. logistics side risks logistics uncertainty is viewed as a factor that causes delays or interruptions originating from the firm’s or partners’ logistics systems or natural disasters throughout the logistic process [19]. logistics are considered as the flow of goods from the supply side to the demand side. little attention has been paid to the logistics side. although, it has been noted that logistic disruption can “quickly cripple the entire supply chain” [27]. normally, logistic side risks originate from cargo damage, supply side or warehouse problems, delays in delivery [28], improper packaging [29], labor disputes, natural disasters, terrorist activities and transportation infrastructure failures [30], wrong choice of mode of transportation [31], and transportation complexity [32]. e. collaboration side risks collaboration can produce more effectual and considerable results, but it also carries numerous issues/risks. collaboration risk is “the apprehensive with cooperative relationships or the probability that the partner does not comply with the spirit of cooperation” [33]. it may also be defined as “risks refer to uncertainty in coordination and information” [34]. thus, it would be a serious issue if one member of the sc does not obligate itself to the cooperation as anticipated by the other members [27]. information risks are associated with the systems and flows of information and include data capture and transfer, integrity, information processing, and market intelligence or system failure. this study covers the risks generated from the information flow among partners of the sc. partners share information, but issues regarding trust, lack of coordination, lack of competency and high dependencies may occur [23]. this study enhanced the scope of information side risks and considered it as collaboration side risks. new challenges such as collaboration risks would arise when partners are involved in the sc, such as the decision making becomes complex when more partners are involved with various interests, culture, and preferences [35]. it has been learned from a validated sample of 162 responses that the complexity of partnerships has the most significant effect on sc risks and the collaboration risks are considered as the top risks that can impact sc performance to its most extent. collaboration side risks have gained little attention in the literature [20]. mainly, there are two types of flows: information flow and relationship flow. some studies measured information flow risks only [31], while some cover both [9]. this study changes the name from information side risks to collaboration side risks to cover both types of risks. f. financial side risks financial side risks are defined as risks “that a member of the supply chain encounters, financial challenges that could impact its ability to produce and supply particular goods/services”. the financial crisis was highlighted by both public (16%) and private organizations (17%) as one of the most recurrent disruptive occasions. the financial side risks have to do with cash flows, the incurrence of expenses and the use of investments for the entire network, payable accounts, settlements, and receivable accounts [33]. a financial side risk can also be defined as “the risk that a potential event will have a financial impact”. [36]. it is empirically verified for garment manufacturing sc financial risks has 46.3% of probability of loss, making it one the highest risks [37]. g. environmental side risks environmental side risks have low probability but dire consequences [38]. natural disasters obstruct smooth operations [39]. it has been mentioned previously that nature can disrupt not only one company, but the entire sc system. in some countries, regulations are also setting big obstacles in starting a business or operate it effectively. administrative decisions sometimes come to execution suddenly and can affect performance. regulatory laws are defined as legal enforcement and execution and their frequency and degree of change are potentially sc risks [5]. any change in the political environment due to new laws or modifications in existing ones may cause disruption in the sc operations. it may increase cost or even sometimes halt production [40]. it has been proved that regulation disruptions reduce the shareholder’s wealth by 3.8% [40]. environment side risks are categorized into political instability, macroeconomic uncertainties, social uncertainties, natural uncertainties, political instability, diseases or epidemics natural disasters, and international terrorist attacks [5]. iii. research methodology a two fold methodology was adopted for this study: systematic literature review approach to perform a first selection of the most relevant articles to be included in the analysis, and citation network analysis (cna) in order to perform a second selection based on citations [41]. a literature review is a tool to analyze the diversity of information under inquiry and enables researchers to assess existing knowledge and further research [42]. systematic literature review uses the relevant literature about risk sources in the sc. at first, keywords such as “topology of risk sources”, “categorization of supply chain risks”, “risk sources in the supply chain” and “types of supply chain risks” were identified. the retrieved articles were evaluated through manual screening and selected articles were considered for review. meanwhile, citation analysis and content analysis were performed on the selected articles. iv. discussion most of the researchers categorize sc risks into three categories: organizational factors, industry factors, and environmental factors [16]. regarding organizational factors, most studies divide further the sc risks into three types that are broadly referred to as supply side, process side and demand engineering, technology & applied science research vol. 9, no. 3, 2019, 4301-4305 4304 www.etasr.com shahbaz et al.: a novel classification of supply chain risks: a review side [1]. industrial factors describe relationships among sc partners and these partners are linked through the flow, which in has three kinds: information flow, material flow, and financial flow. hence, material flow creates logistic side risks [19] whereas finance flow cause financial side risks and information flow causes information side risks [20]. most of the researchers use information risks to cover information flow risks but this study argues that the information side covers information related risks and misses the relational risk coordination. to cover all these issues, the current study uses collaboration side risk and this argument is supported by [16]. to cover external factors, this study considers environmental factors like natural disasters and global issues. this view is supported by [31] which divides the overall sc risks into six factors, but it does not cover the financial side of risk. author in [7] categorized the overall sc risks into six factors ommitting logistic side risks. to cover all supply chain risks, the organization must consider seven aspects: supply, process, demand, logistics, collaboration, financial, and environmental side risks. additionally, from the operational definitions of this study, the sc not only deals with 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“supply chain risk management: a new methodology for a systematic literature review”, supply chain management: an international journal, vol. 17, no. 4, pp. 403–418, 2012 [42] h. singh, r. k. garg, a. sachdeva, “supply chain collaboration: a state-of-the-art literature review”, uncertain supply chain management, vol. 6, no. 2, pp. 149–180, 2018 microsoft word etasr_v13_n4_pp11085-11090 engineering, technology & applied science research vol. 13, no. 4, 2023, 11085-11090 11085 www.etasr.com long et al.: damage identification of suspension footbridge structures using new hunting-based … damage identification of suspension footbridge structures using new hunting-based algorithms nguyen ngoc long university of transport and communications, vietnam nguyenngoclong@utc.edu.vn nguyen huu quyet dx laboratory, university of transportation and communications, vietnam quyetutck57@gmail.com nguyen xuan tung university of transport and communications, vietnam ngxuantung@utc.edu.vn (corresponding author) bui tien thanh university of transport and communications, vietnam btthanh@utc.edu.vn tran ngoc hoa university of transport and communications, vietnam ngochoa@utc.edu.vn received: 21 april 2023 | revised: 10 may 2023 | accepted: 11 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5983 abstract metaheuristic algorithms have been applied to tackle challenging optimization problems in various domains, such as health, education, manufacturing, and biology. in particular, the field of structural health monitoring (shm) has received significant interest, particularly in the area of damage identification in structures. popular optimization algorithms such as genetic algorithm (ga), particle swarm optimization (pso), cuckoo search (cs), teaching learning based optimization (tlbo), artificial hummingbird algorithm (aha), moth flame optimizer (mfo), among others, have been employed to address this problem. however, notwithstanding the wide recognition of the current algorithms, their constraints are commonly acknowledged. hence, this article advocates for the adoption of innovative hunting-inspired algorithms, namely the ant lion optimizer (alo), african vulture optimization algorithm (avoa), grey wolf optimizer (gwo), marine predator algorithm (mpa), and whale optimization algorithm (woa), which emulate the behaviors of wildlife species, to discern the areas and magnitudes of deterioration in a suspension footbridge. moreover, in order to reduce computational time, only natural frequencies are applied as objective functions. the obtained results indicate that all the utilized algorithms can accurately detect the damages in the considered structure. keywords-structural health monitoring; metaheuristic algorithms; hunting-based; damage identification; suspension footbridge i. introduction structural health monitoring (shm) is a crucial monitoring and evaluation system for current bridge structures. basically, this system includes various types of sensors for data regarding acceleration, stress, displacement, deformation, temperature, wind speed, rainfall, etc. these sensors are installed and attached to the structure during the construction to monitor and ensure the quality during construction and operation. moreover, during the inspection and maintenance of old works and the construction of new bridges, the shm system makes a engineering, technology & applied science research vol. 13, no. 4, 2023, 11085-11090 11086 www.etasr.com long et al.: damage identification of suspension footbridge structures using new hunting-based … particularly important contribution in the management, operation, and repair. optimization algorithms have been studied and applied effectively in many different fields such as medical, biological, manufacturing design and many other fields [1-8]. the metaheuristic algorithms based on nature are the most researched, developed, and widely applied. they are inspired by traits, habits, or behaviors of animals, plants, humans, or laws of physics and chemistry. in the problem of damage detection, there have been many successful studies in applying these algorithms. ga was the first and laid the foundation for the development of applying optimization algorithms to the problem of diagnosing damage [9]. with a main content that adheres to the laws of genetics, the results from ga have solved the problem of diagnosing damage in some studies with highly accurate and reliable results [10]. the pso algorithm was introduced in 1995 [11]. it is inspired by the behavior of animals that live in swarms, such as fish schools and bird flocks. numerous research endeavors have also investigated the utilization of pso in discerning the areas and magnitudes of deterioration in various structures [12, 13]. other algorithms have also been studied, proposed, and applied to the problem of fault diagnosis [14-25]. during the recent years, many new algorithms have been introduced and proven effective in solving benchmark objective functions. these include ant lion optimizer (alo), african vulture optimization algorithm (avoa), grey wolf optimizer (gwo), marine predator algorithm (mpa), and whale optimization algorithm (woa). the common point of the above algorithms is that they are inspired by the hunting behavior of animals. therefore, in this paper, the application of the above algorithms to the problem of damage detection in a suspension footbridge is proposed. to the best of our knowledge, these newly proposed algorithms are applied for the first time to a pedestrian suspension bridges. ii. methodology a. ant lion optimizer ant lions is an insect species in the neuropteran family myrmeleontidae, belonging to the order neuroptera. alo [26] replicates the feeding behaviors of antlions in the desert. the predatory processes of this species consist of 5 main and iterative steps: random movement, trap digging, waiting for prey, capturing prey, and digging new traps. ������������ = �� � ��� � � (1) where ������������ presents position of the ��� ant at the ��� iteration, ��� and ��� are the positions of a ant walk randomly by a roulette wheel and the elite position, respectively. ant larvae will dig a funnel-shaped burrow about 2 inches deep and 3 inches wide to trap prey. after digging the 'grave' of the prey, the ant lion will lie down at the bottom of the funnel and bury itself in the sand, revealing only its sharp and strong jaw. when prey (usually small ants, arthropods, or spiders) steps in and with the trap's initial stable slope, a landslide occurs causing the animal to fall to the anthill. if there is any attempt to get out, it will be in vain because the ant lion at the bottom of the hole will throw up sand, causing the sand pit to collapse and drag the prey down. b. african vulture optimization algorithm vulture is the common name for a group of carnivorous and carrion birds that live on every continent except antarctica and oceania. one of the characteristics of vultures is that the head is often bald, without feathers due to the habit of eating carrion by sticking its head into the carcass of the animal to eat, so the head is stained with blood and body fluids. vultures are divided into 2 groups. the old world vultures in africa, asia, and asia belong to the family accipitridae. this family includes eagles, hawks, eagles, and magpies. avoa [27] was inspired by the hunting habits of african vultures. normally, in the wild, vultures are divided into 2 groups and the first stage of the algorithm is to identify the best individual in each group. next is to evaluate the survival rate through the energy in the body to decide the next stage is exploitation or exploration. the avoa metric is: ���� = ���� − � + ! × #�$� − %�� × � + %�& (2) where ����, ���� are respectively the position of a vulture at � = � + 1 and � iteration, � presents the satisfaction ratio, $� and %� are the upper and lower boundary, ! is a random number in #0,1&, and � has a value approximately equal to 1. c. grey wolf optimizer the grey wolf is a carnivorous mammal native to eurasia and north america. the grey wolf is the largest member of the canidae family and the most famous wolf species. grey wolves are social animals, they usually live in packs of about 5-11 children with 1-2 leaders including 1-2 adult wolves, 3-6 juvenile wolves, and 1-3 cubs or sometimes 2 or 3 such families, with particularly large herds consisting of up to the maximum known of 42 wolves. the grey wolf algorithm was introduced in 2014. the social hierarchy of gwo was modeled into 4 types: the alpha (�), beta (*), delta (+), and omega (,). accordingly, the hunting process includes stages such as: locating prey, approaching, encountering, or facing, ambush, chase. -⃗�� + 1� = /00⃗ �100⃗ �200⃗ 3 (3) in (3), -⃗�� + 1� is the best value of �� + 1� iteration, �⃗, *⃗, and +⃗ are the position of a grey wolf at current iteration. d. marine predator algorithm mpa was first introduced in 2020 [28]. the fundamental concept behind mpa is the adoption of optimal foraging strategies observed in ocean predators, particularly through lévy and brownian movements, as well as the encounter rate policy in predator-prey biological interactions. mpa adheres to the principles that govern these strategies and policies in marine ecosystems. when considering the speed ratio of the hunter to prey, mpa basically consists of 3 stages: (1) the highspeed ratio or when the hunter moves slower than prey, (2) the speed ratio unit velocity or when both the predator and the prey are moving at roughly the same speed, and (3) at the lowvelocity ratio when the prey is moving slower than the predator. engineering, technology & applied science research vol. 13, no. 4, 2023, 11085-11090 11087 www.etasr.com long et al.: damage identification of suspension footbridge structures using new hunting-based … 56 = 7��� + 8 (4) basically, mpa starts with (4) and uses other equations on each stage. in the initial stage, the first best value 56 is calculated with the minimum value of variables 7���, and 8 is a random number from 0 to 1. e. whale optimization algorithm woa was introduced in 2019 [29]. the whale is considered to be the world's largest mammal, the largest adult species discovered is the blue whale in antarctica. they can weigh up to more than 180 tons and possess a length of up to 30 meters. because of their large mass, the daily food requirement is very large, so they have a very special hunting habit. this routine is known as the "bubble-net feeding method". basically, it consists of 3 main steps: enveloping prey (mostly feeding on a school of fish and cephalopods), bubblenet attacking method (exploitation), and finally searching for prey (exploration). �000⃗ �� + 1� = ��90000000⃗ − :⃗ × ;<0⃗ × ��90000000⃗ − �000⃗ ���; (5) where �000⃗ �� + 1� , �000⃗ ��� are the vector presenting the current position at �� + 1� and � iteration, respectively, ��90000000⃗ is a random vector solution at the � iteration, and :⃗ and <0⃗ are the factor vectors. iii. case study a. general information and finite element model na xa bridge (chau hoan commune, quy chau district, nghe an province) is a suspension bridge built to serve residents in mountainous and remote areas. the bridge was built in august 2008 and put into operation in may 2009 with a main length of 78 m, excluding the mooring lines at the 2 ends of the bridge, and 2 planes of suspended cables with compartments of different dimensions. the longitudinal beam is i150-shaped steel and the crossbeam is i200, combined with d20 steel wind bracing. the main cable has an outer diameter of 56 mm, the hangers are d20 steel bars. in addition, the bridge also has an anti-shake system with a d21.5 cable that is cross-connected at the two tower legs. the bridge tower is assembled from many different types of steel with a height of 8m and embedded in the ground for about 1m as shown in figure 1. this is the typical design of the residential suspension bridges in vietnam. vibration characteristics such as frequencies and mode shapes of the bridge are extracted by using the stabil toolbox [30] in matlab. the model is updated based on the actual measurement results. fig. 1. general view of the na xa footbridge. fig. 2. finite element model of the na xa bridge. the model includes 198 nodes representing the intersections of the elements, 300 beam elements, namely longitudinal beams and transverse beams, main cables, wind bracing, suspension bars, and bridge towers. the finite element model of na xa bridge is shown in figure 2. the boundary conditions of the structure are arranged according to the actual bridge structure. steel is the main material with elastic modulus = = 21×104 mpa, poisson ratio > =0.3 and density ? =7850 kg/m 3 . the first 6 mode shapes of the bridge are depicted in figure 3. mode 1 – f = 0.5294hz mode 2 – f = 0.5426hz mode 3 – f = 0.8034hz mode 4 – f = 0.9360hz mode 5 – f = 1.0712hz mode 6 – f = 1.1485hz fig. 3. the 6 first mode shapes. b. damage identification in this section, we assume two cases of damage as shown in figure 4:  case 1 (single damage): there is only one damaged element in the structure with a loss of elastic modulus of 23%.  case 2 (multiple damage): there are two or more damaged elements in the structure with loss of elastic modulus of 26% and 27%, respectively. fig. 4. two cases of the damage identification issue. in this study, the natural frequencies are used as the objective function because they are sensitive to damage: engineering, technology & applied science research vol. 13, no. 4, 2023, 11085-11090 11088 www.etasr.com long et al.: damage identification of suspension footbridge structures using new hunting-based … @a�bc��>bde�c���� = ∑ ghijklhmijk_opqpr�os t hmijk_opqpr�o t uvw �v! where � = 6 is the corresponding frequency, yz[\ is the initial simulation frequency, and ymz[\_9]^]_�9 is the damaged structure frequency. the parameters used in the algorithms include: the number of spaces is ���? =200, the number of iterations is �`�b =300, and boundary #%�: $�& =[0.00:0.99]. the computer configuration used in the calculation is 12th intel® core™ i7-12700f 32gb ram, nvidia geforce 3060 rtx. figure 5 illustrates the convergence of the 5 considered algorithms. the best convergence is basically achieved at the 35 th iteration and is stable until the end of the loop. fig. 5. convergence curve of case 1: single damage. the results of damage location and extent determination in the structure are depicted in figure 6. they show high accuracy for gwo, alo, mpa, and avoa. however, woa misidentifies the damage level with an error of approximately 8.962%. in terms of computation time, as shown in figure 7, the algorithms take around 2300-2900 s to find the optimal result, except for mpa that spend 4623 s for this process. in terms of the multi-damage case, as shown in figure 8, it can be seen that, mpa has the highest convergence, followed by alo, gwo, woa, and avoa. fig. 6. results of case 1: single damage. fig. 7. the computational time of case 1: single damage. fig. 8. convergence curve of case 2: multiple damage. fig. 9. results of case 2: multiple damage. fig. 10. the computational time of case 2: multiple damage. 0 50 100 150 200 250 300 iteration number 10 -4 10 -3 10 -2 v a lu e o f f it n e s s f u n c ti o n gwo woa alo mpa avoa engineering, technology & applied science research vol. 13, no. 4, 2023, 11085-11090 11089 www.etasr.com long et al.: damage identification of suspension footbridge structures using new hunting-based … mpa demonstrates the best convergence but requires approximately 5000 s for damage identification in the structure. gwo and avoa exhibit accurate results in terms of location and extent of damages. alo produces inaccurate results for damage identification in the case of two damaged elements. iv. conclusion this paper proposes the utilization of algorithms based on predatory animal behaviors for damage detection in a suspension bridge structure. from the obtained results, several conclusions can be drawn:  the considered algorithms, namely gwo, woa, alo, mpa, and avoa are capable of accurately detecting the location of faults. however, fine-tuning input parameters may be necessary to achieve the highest accuracy rate. hence, each algorithm may be suitable for specific cases with an appropriate level of confidence.  further research is recommended to explore the application of these algorithms to other types of structures. additionally, incorporating additional shape modes in the objective function could potentially enhance the accuracy of the results.  overall, the findings suggest the potential of using these hunting-based algorithms for damage diagnosis in suspension bridge structures, with gwo being the most promising algorithm among the ones tested. further investigations and 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[30] s. françois et al., "stabil: an educational matlab toolbox for static and dynamic structural analysis," computer applications in engineering education, vol. 29, no. 5, pp. 1372–1389, 2021, https://doi.org/10.1002/ cae.22391. microsoft word etasr_v13_n3_pp10957-10962 engineering, technology & applied science research vol. 13, no. 3, 2023, 10957-10962 10957 www.etasr.com doan van & nguyen: the design method of traction power supplies in integrated metro systems the design method of traction power supplies in integrated metro systems dong doan van science and technology application for sustainable development research group, ho chi minh city university of transport, vietnam dongdv@ut.edu.vn (corresponding author) thai nguyen ho chi minh city university of transport, ho chi minh city, vietnam thai.nguyen@ut.edu.vn received: 9 april 2023 | revised: 24 april 2023 | accepted: 2 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5931 abstract integrated subway systems have emerged as a new trend that provides the highest quality service at the lowest investment cost by combining the advantages of the two largest passenger transport capabilities during peak hours. under the integrated model, designing the traction power supply is much more complex than for other independent systems. this article presents the results of a study on the method of calculating the design load of the power supply for the transport operation of the system. matlab r2017b/railway systems is a reliable software for simulating and analyzing some necessary data, and the research results show the feasibility of the method when applied to the case of asynchronous load on the system. the results meet the power supply design standards according to ieee p1653.2, en 50328, and iec 60146-1 overload allowances for class vi, and voltage standards according to en 50163, uic 600, and iec 60850. keywords-subway train; integrated subway system; urban integrated railway; traction substation i. introduction the integrated subway model mrc is a combination of subway trains (mrt) and suburban trains (cr). this combination model allows the operation with a very large transport capacity during peak hours in order to meet the demand for travel between the suburbs and the city center, which each type alone cannot meet, and to return to the separate normal operating state of each type during off-peak hours with the lowest investment cost and the highest service quality. this method allows for increasing the transport capacity and service frequency of the subway line without the need to increase the number of purchased trains operating on the line. on the other hand, the suburban train, when running on the line, will operate like a subway train. the diagram of the integrated train operation is described in figure 1 of [1], in which a to e are the terminal stations of the subway line, b to e (or b to a but stops at any station) the terminal stations of the suburban railway, and b to a is the integrated peak-hour suburban railway station. over the past few years, many studies have emphasized the advantages of having a subway system that is integrated [2-6]. to guarantee that the system operates in a manner that is flexible, efficient, dependable, and energy-saving, it must have a robust power supply system that can support maximum transportation capacity during peak hours. despite this, the majority of research studies have concentrated on planning, predicting, and handling transportation capacity and energy conservation while assessing the advantages it provides to the overall development of smart cities in the current integrated subway context [7-11]. some recent studies have been conducted on the method of designing the power supply for electric subway trains [12-20] and the study of operating voltage in a pure system [19]. this article presents the results of the research on calculating the design of traction power supply for the integrated system. in the design of the power supply for traction, to ensure continuous, flexible, reliable, safe, and efficient system operation, the traction power station capacity must meet two evaluation criteria: power supply capacity and minimum contact voltage allowed in normal operating conditions and emergencies. the majority of the research on creating power systems for subway trains uses computer simulations that are comprehensive, effective, and affordable. in this particular study, the software chosen for simulating and calculating a power supply that meets the global standards is matlab r2017b/railway systems. engineering, technology & applied science research vol. 13, no. 3, 2023, 10957-10962 10958 www.etasr.com doan van & nguyen: the design method of traction power supplies in integrated metro systems ii. methodology a. calculating the power of the traction substation there are many methods used to calculate the design load of the electric traction power supply for a subway or suburban railway system [12-20]. however, these methods only allow separate calculations for each system. for integrated systems that combine two systems with different capacities on the same power supply system, this difference, which arises from the characteristics of the train, is an important issue in load calculation. since the transport capacity of subway and suburban trains is different, the current used is also different. correspondingly, the acceleration and operating speed are different, so the mechanical resistance (rr) and acceleration resistance (ra) are also different. as a result, the maximum instantaneous traction force performed on each cycle of each train trip between the two stations is different. from all these differences, an asynchronous load is created over the range of the power supply of a traction substation. therefore, calculating this complex asynchronous load needs to meet the demand for the highest power usage during peak hours. the components of train motion resistance (rr), acceleration resistance (ra), curve resistance (rc), gradient resistance (rg), and tunnel resistance (rt) can appear in one cycle of the train motion starting at station j within the power supply range of a traction substation i. rrx,y = a + bv + cv 2 (1) rgi,j = ± g/1000 (2) rti,j = ft∙v 2 w (3) �rci,j = 650r ̶ 55 , r < 300 rci,j = 500 r ̶ 30 , r ≥ 300 (4) ra.x,y.i,j = aξ g (5) the maximum resistance is: �∑ ri,j = rci,j+ rgi,j + rti,j rmax.i,j ≤ ∑ ri,j < ra+rr (6) let mx and my be the total weight of the subway train x and the suburban train y at full load with maximum carrying capacity. the maximum instantaneous traction force of train x and y in each direction, within the supply range of a traction power station i and traveling from station j in the direction of k and towards h, can be calculated: fti,j-kx,max = mx∙�ra,x+rr,x+ ∑ rmax,j-kx � (7) ∑ rmax,j-kx = rc,j-kx+ rg,j-kx+ rt,j-kx (8) fti,j-hx,max = mx∙�ra,x+rr,x+ ∑ rmax,j-hx � (9) ∑ rmax,j-hx = rc,j-hx+rg,j-hx+rt,j-hx (10) fti,j-ky,max = my∙�ra,y+rr,y+ ∑ rmax,j-ky � (11) ∑ rmax,j-ky = rc,j-ky+rg,j-ky+rt,j-ky (12) fti,j-hy,max = my∙�ra,y+rr,y+ ∑ rmax,j-hy � (13) ∑ rmax,j-hy = rc,j-hy+rg,j-hy+rt,j-hy (14) the maximum traction force under normal conditions is: ∑ fti,j, �na�max1i=1 = ∑ pl,maxna. pl∈i,j ∙fti,j,(na)max (15) where: ⎩⎪⎨ ⎪⎧ ∑ pl,maxna. pl∈i,j = 60cl,max ∙ dtpsivsc ∙2 1,25 ≤ cl,max < cl,mrt, cl,max = cp,max ct,max fti,j,(na)max ∈ kx, hx, ky, hy (16) when an error (er) occurs: ∑ fti,j, �er�,maxi+12i=1 = ∑ pl,maxer.pl∈i,j ∙ fti,j,�er�max (17) where: ⎩⎪⎨ ⎪⎧∑ pl,maxer. pl∈i,j = 60cl,max ∙ 2vsc ∙ �dtpsi+ dtps(i+1)2 � 1,25 ≤ cl,max < cl,mrt, cl,max = cp,max ct,max fti,j,(na)max ∈ kx, hx, ky, hy (18) the maximum instantaneous power demand within an hour is described by: pti,j�na�max = ∑ fti,j, �na�maxpl�na�,maxi=1 ∙ v3,6∙η mc ∙η mt (19) pti,j�er�max = ∑ fti,j, �er�maxpl�er�,maxi=1 ∙ v3,6∙ηmc∙ηmt (20) where η mc and η mt are the mechanical and engine efficiency respectively: �ηmc,min < ηmc ≤ ηmc,maxηmt,min < ηmt ≤ ηmt,max vsc < v ≤ vpeak (21) the auxiliary power consumption is: p�x,y�,i�na�aux = ∑ pl,maxna. pl∈i � n�x,y�∙pd,�x,y� + m�x,y�∙pc,�x,y� � (22) p�x,y�,i�er�aux = ∑ pl,maxer. pl∈i � n�x,y�∙pd,�x,y�+ m�x,y�∙pc,�x,y�� (23) the maximum instantaneous total power requirement within an hour is defined as: ptpsi�na�max = pti,j�na�max + p�x,y�,i�na�aux (23) ptpsi�er�max = pti,j�er�max + p�x,y�,i�er�aux (24) if the system has regenerative braking, the percentage of energy recovered ηᵣₑ is: ptpsi�re, na�max = ptpsi�na�max�1 ̶ ηre� (25) ptpsi�re, er�max = ptpsi�er�max �1 ̶ ηre� (26) with criterion: engineering, technology & applied science research vol. 13, no. 3, 2023, 10957-10962 10959 www.etasr.com doan van & nguyen: the design method of traction power supplies in integrated metro systems �ηre,na. min < ηre[x,y] ≤ ηre,na,.maxη re,er. min < η re[x,y] ≤ η re,er.max (27) the power selection for the traction substation is: ptpsi�er,na�max ≤ ptpsi�na�, min (28) ptpsi�re, er�max ≤ ptpsi�re�, min (29) ptpsi�re�,min < ptpsi ≤ ptpsi�na�, min (30) therefore, the selected power for the traction substation according to (28)-(30) must comply with ieee p1653.2, en 50328, and iec 60146-1 standards. b. operating voltage let udc-o, ufdc, and utx:xi,yi be the operating voltage of the unloaded rectifier, the supply voltage, and the contact voltage, respectively: ii�na�max = ∑ ix,y (i)∈ ∑ pl,maxna. pl∈i,jcl,max1 (31) ii�er�max = ∑ ix,y (i)∈ ∑ pl,maxer. pl∈i,jcl,max1 (32) ufdc,�na, er� = udc-o − ii�na, er�max∙ ∑ rtpsi, cf (33) ∑ ∆udc:j, j+xmax = ii�na,er�,lx∙rcls∙lx + ii�na,er�,x∙rcls∙xmax (34) utx�na, er�,min = ufdc,�na, er� ̶ ∑ ∆udc:j, j+xmax (35) the minimum contact voltage at the end of the power supply section of a traction substation operating in normal or fault conditions must satisfy the operating voltage requirements of the en 50163, uic 600, and iec 60850 standards, as specified in (35). iii. system design a. load parameters the route profile from substation 3 to substation 4 can be seen in table i. tpsi is the i th traction substation, stj is the j th passenger station, g‰ is the lope of the railway, c is the curve radius, rt is the coefficient of tunnel resistance for smooth plane double track, and sp is the end of power supply section. the load parameters are exhibited in table ii and the traction parameters in table iii [1]. table i. profile of the route from traction substation no. 3 to no. 4 along the line km tpsi stj g‰ c rt 10.0 sp 11 11.00 12 11.50 +35 650 12.00 13 12.40 3 13.20 14 13.70 +5 500 14.00 sp 14.40 15 15.40 16 -5 17.14 15.80 -20 17.14 16.00 4 17.14 16.40 17 17.14 17.40 18 17.14 table ii. train load parameters symbol specifications description c��;� 45.000; 54.000 person/hour/direction n�, n� 2; 2 control car m�, m� 6; 5 locomotive unit m�,�;� 40 tons; 42 tons control car m ,�;� 38 tons; 41 tons locomotive unit sd,x 3.2×22 m� floor area of a passenger car sc,x 3.2×23 m� passenger area sd,y 3.27×25 m� floor area of a passenger car sc,y 3.27×26 m� passenger area fs.d,x;y 0.45%; 0.42% occupancy rate fs.c,x;y 0.55%; 0.45% occupancy rate fd,x 38 seats cabin seat fc,x 44 seats passenger seat fd,y 32 seats cabin seat fc,y 42 seats passenger seat mp 55 kg weight/passenger table iii. train traction parameters symbol metric value cl.p1 [p/h/d] 45,000 cl.p2 [p/h/d] 54,000 ax,max/βx,max [m/s 2 ] 0.9/1.0 ay,max/βy,max [m/s 2 ] 0.85/1.0 rx, ry [kg/tấn] rx= 3.25 + 0.039∙v + 0.000659∙v2 ry= 2.45 + 0.044∙v + 0.000374∙v2 vsc, vmax [km/h] 45/60 train load ix [a]: 400∙(4m)+200∙(2m)+200∙(2mc) train load [a]: 400∙(4m)+200∙(1m)+200∙(2mc) support load iaux [a]: 25.3333∙(6m)+24∙(2mc) support load iauy [a]: 26.6667∙(5m)+24∙(2mc) b. design of the calculation process the process of calculating the design of a pullable electrical supply is described as an algorithmic flowchart in figure 1. iv. results and discussion a. the result of selecting the power capacity for the traction substation 1) case 1 the calculated power capacity for traction substation no. 3 in case 1 is presented in table iv. in summary, the maximum calculated power required for the traction of both normal operation and contingency situations meets the actual power consumption demand of the selected train load. therefore, it satisfies the design calculation requirements. the selected power capacity of the traction substation must also meet the overload conditions in both normal and contingency situations. the chosen power per unit converter is 3,2000mw, and the traction substation power is 6,4000mw, which is less than the actual power consumption demand of 6,5113mw, but greater than the demand in cases of regeneration when braking normally and in contingency situations, which are 3,9068mw and 5,8602mw, respectively. engineering, technology & applied science research vol. 13, no. 3, 2023, 10957-10962 10960 www.etasr.com doan van & nguyen: the design method of traction power supplies in integrated metro systems fig. 1. flowchart of the load calculation process. table iv. the calculated power capacity for traction substation no. 3 in case 1 component phase 1 ph 2 n 3.0000 2.5000 fmax [kn] 244.4978 244.4978 pmax.na [mw] 7.9319 9.5183 pmax.er [mw] 11.8989 14.2775 pre.na [mva] 4.7592 5.7110 pre.er [mva] 7.1387 8.5665 pload.na [mw] 6.5113 7.8136 pload.er [mw] 9.7670 11.7203 pldre.na [mw] 3.9068 4.6881 pldre.er [mw] 5.8602 7.0322 prec [mw/dv] 3.2000 3.2000 nprec [dv] 2+1 3+1 ptps [mw] 6.4000 9.600 pol.na(2h) [mw] 9.6000 14.4000 pol.er(2h) [mw] 14.4000 14.4000 the power supply capacity of the traction substation with the ability to withstand overload for two continuous hours according to the ieee p1653.2, en 50328, and iec 60146-1 standards, is 9,6000mw, which is greater than the actual consumption demand of 6,5113mw and the theoretical calculation of 7,9319mw for normal operation. the ability to withstand overload for contingency situations is 14,4000mw (all three converters working together), which is greater than the actual consumption demand of 9,7670mw and the theoretical calculation of 11,8979mw. in phase 2, under normal circumstances, the station operates with three power supply units providing 9,6000mw, which is greater than the maximum calculated power requirement of 9,5183mw, the regeneration requirement under contingency situations of 8,5665mw, and the actual power consumption demand of 7,0322mw. if there is no regeneration, the overload capacity is 14,4000mw, which is greater than the maximum calculated power requirement of 14,2775mw and the actual power consumption demand of 11,7203mw. therefore, the analysis of the results shows that the selected power capacity is suitable for the required load demand. 2) case 2 in the case of an incident, traction substation number 3 must also supply power to an additional segment from traction substation number 4. the calculated power capacity for traction substation number 3 in case 2 is shown in table v. table v. the calculated power capacity for traction substation no. 3 in case 2 component phase 1 phase 2 ncr 4.5000 3.0000 ninter 3.0000 2.5000 fmaxcr [kn] 205.6862 205.6862 fmaxinter [kn] 244.4978 244.4978 pmax.na [mw] 4.5590 6.8385 pmax.er [mw] 9.2539 12.6911 pre.na [mva] 3.1913 4.7869 pre.er [mva] 6.4777 8.8838 pload.na [mw] 3.9758 5.9637 pload.er [mw] 7.5965 10.4181 pldre.na [mw] 2.7831 4.1746 pldre.er [mw] 5.3176 7.2927 prec [mw/dv] 3.2000 3.2000 nprec [dv] 2+1 2+1 ptps [mw] 6.4000 9.600 pol.na(2h) [mw] 9.6000 14.4000 pol.er(2h) [mw] 14.4000 14.4000 in this case, the selected power capacity for the station must meet two different loads. the capacity of each rectifier unit is 3.2000mw, and the station is designed with a (2+1) configuration for each load phase. in phase 1, the station supplies a capacity of 6.4000mw, which is greater than the normal maximum load calculation (4.5590mw) and the contingency load in case of regeneration inhibition (5.3176mw), but smaller than the normal maximum load calculation without any contingency (9.2539mw). however, the station's ability to withstand 150% overload for two consecutive peak hours is 9.6000mw, which is higher than the actual consumption load (7.5965mw) and even the maximum calculated contingency load without regeneration inhibition (9.2539mw), meeting the standards' requirements. in phase 2, under normal operating conditions, the station provides the rated power of 6.4000mw, which is lower than the maximum calculated load (6.8385mw), but the ability to withstand overload is up to 9.6000mw in the event of engineering, technology & applied science research vol. 13, no. 3, 2023, 10957-10962 10961 www.etasr.com doan van & nguyen: the design method of traction power supplies in integrated metro systems regeneration inhibition (8.8838mw and 7.2927mw), but cannot handle contingencies without regeneration inhibition. therefore, in this case, the station must operate with three rectifier units simultaneously with a total capacity of 9.6000mw, with the ability to handle overload up to 14.4000mw, which is higher than the actual consumption capacity of 10.4181mw and the maximum calculated capacity of 12.6911mw. thus, the analysis results show that the selected power capacity is suitable for the load requirements. the calculated and selected power capacity for the traction substation in both cases 1 and 2 are based on the comprehensive calculation method for the integrated subway train load. this method effectively meets the load requirements and ensures good performance for 150% overload capability for two consecutive hours. therefore, there is no need to consider overload cases of 200%, 300%, and 450%, as per the criteria for evaluating the design of traction substation power capacity specified by ieee p1653.2, en 50328, and iec 60146-1. b. operating voltage checking the operating voltage is the final step in designing the power supply for this integrated subway electrical load. in phase 1, the unloaded rectified voltage is 1.656v for two parallel rectifiers in normal operation and three rectifiers in the event of a failure, as shown in figure 2. fig. 2. operating voltage in phase 1. on the left segment, the supplied voltage at the supply station is 1.325v and the contact voltage at the furthest end of the left segment is 1.183v. on the right segment, the contact voltage at the end of the segment is 1.252v in normal operation and 1.161v in case of a failure, and the contact voltage at the extended segment is 1.047v. therefore, in phase 1, the smallest contact voltage at the end of the extended segment in case of a failure is 1.047v, which is higher than the minimum allowable limit of 1.000v. in phase 2, in normal operation with three parallel rectifiers, the no-load voltage is 1.656v, as shown in figure 3. in normal operation, the supply voltage at the supply station for both sections is 1.391v, the minimum contact voltage on the left section is 1.221v, and the minimum contact voltage on the right section is 1.266v, which is greater than the minimum allowed voltage of 1.000v. in the event of a fault, the supply voltage is 1.259v on both left and right sections, the minimum contact voltage on the left section is 1.089v, and the minimum on the extended right section is 957.5v. thus, although the station using 3 rectifiers, it exceeds the allowable overload power of 150% (14.4mw) according to the standard, violating the voltage standard (957.5v < 1.000v). therefore, the station's capacity must be increased by using 4 parallelconnected rectifiers, at which time the supply voltage on both sections is 1.358v, the minimum contact voltage on the left section is 1.188v, and the minimum contact voltage on the extended right section is 1.057v, which is greater than the minimum allowable voltage of 1.000v according to en 50163, uic 600, and iec 60850 standards. thus, increasing the power supply capacity at the traction substation can meet the demand of the load consumption, reduce voltage drop, and increase the contact voltage to satisfy the selection condition 1 (no.op1), without considering the selection condition 2 (no.op2) in the design calculation process. fig. 3. operating voltage in phase 2. v. conclusion the current paper proposes a calculative method for the power design of a traction substation based on the maximum instantaneous traction force calculation under the integrated subway railway model. the method was designed and simulated on matlab r2017b/railway systems, and its reliability was demonstrated through various cases of loads for maximum power during peak hours. the method also ensures transparency and logic when calculating data in a sequence with filtering and cross-referencing for backup situations to avoid power waste. the calculated power is higher than the load demand from 14.67% to 21.81%, allowing the selection of a substation power that meets the standards for the 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science & technology, nawabshah, sindh pakistan basher_m@hotmail.com abstract—in this research work, experimental investigation on flexural strength of reinforced concrete beams exposed to fire for 6-hours at the temperature of 1000˚c is presented. the beams are made with 50% replacement of natural coarse aggregates with recyclable concrete aggregates. a total of 12 reinforced concrete beams using 1:1.5:3 mix (rich mix) and 0.54 water-cement ratio were cast. the beams were prepared in two groups. group 1 beams were prepared with 50% recyclable aggregates, whereas group 2 beams were cast with all-natural aggregates (control specimens). all beams were exposed to fire at the abovementioned temperature followed by testing in universal load testing machine under central point load. comparison of the results reveals that proposed beams show comparable resistance even after exposed to 6-hours fire at 1000°c. keywords-fire effect; flexural strength; recycled concrete aggregates i. introduction for many years the search of alternative ingredients of concrete and of ways and means for proper disposal of construction and demolishing waste remained active among researchers and construction industry. a way of tackling both of these issues is by making use of demolishing and construction waste in new concrete. to this end, several attempts [1-3] have been made successfully to utilize demolishing waste as partial or full replacement of fine and coarse aggregates. as coarse aggregates occupy the most volume of the concrete body, replacement of natural coarse aggregates with recyclable concrete aggregates may solve the problem of demolishing waste treatment to a large extent [4]. the theme has been studied to a certain degree but still a lot of work is required to understand the behavior of the material. fire is one of the hazards a structure might face during its service life. therefore, the response of recyclable aggregates when exposed to fire should be understood not only to design a fire-resistant structure but also to help in taking decisions about rehabilitation and retrofitting after fire. in this regard, author in [5] presented a literature review about the effect of high temperature on both normal and high-strength concrete subjected to elevated temperatures, whereas, authors in [6] presented a review on the mechanical properties of concrete made with partial and full replacement of natural coarse aggregates, particularly compressive strength after fire. they concluded that a great deal of work is required to improve the confidence about the behavior of concrete with recycled concrete as coarse aggregates. in [7], authors presented a literature review about the use of old concrete for the period 2005-2014. they organized their work in three parts, i.e. use of rac in steel composite sections, reinforced concrete and longterm performance including fire resistance of composite members. they reported that reinforced composite members have slightly lower or similar structural behavior with certain replacements of natural coarse aggregates with recycled coarse aggregates. therefore, steel composite members with recycled aggregates can be applied in structural applications. authors in [8] experimented on the mechanical properties of concrete with recycled concrete as coarse aggregates used 20%, 50% and 100% replacement of conventional coarse aggregates. concrete specimens were exposed to fire at 400˚c, 600˚c and 800˚c for 1 hour. comparison of results of compressive strength, tensile strength and modulus of elasticity with those of conventional concrete showed that there was no difference in thermal response and post fire mechanical properties. in another study for the probable use of waste rubber as partial replacement of coarse aggregates, authors in [9] studied the effect of fire on proposed concrete at temperature and duration same like in [8]. based on the comparison of the results of proposed concrete specimen with those of conventional concrete, authors concluded that although the properties of proposed concrete specimens were affected, particularly at high temperatures yet the use of the material is possible in new concrete. authors in [10] used plastic and glass as replacements of fine aggregates and old crushed concrete as replacement of natural coarse aggregates to study the basic properties of concrete. based on the findings of their research they concluded that the wastes mentioned above can successfully be used in new concrete without compromising of the basic properties of the concrete. author in [11] presented details regarding factors affecting the fire response of concrete structural members. it was reported that thermal and structural behavior of concrete particularly spalling of high-strength-concrete depends on various factors. although good information about thermal and corresponding author: a. h. buller engineering, technology & applied science research vol. 9, no. 1, 2019, 3814-3817 3815 www.etasr.com buller et al.: flexural strength of reinforced concrete rac beams exposed to 6-hour fire – part 2 … structural behavior for normal and high strength concrete is available, yet little information is available for new of fire damaged and rehabilitated reinforced concretes i.e. selfcompacting concrete. author concludes that considerations should be given to batch mixing, heating rate, loading level etc. to ensure proper performance of concrete with respect to its exposure to fire. authors in [12] conducted research to prepare guidelines to determine fire safety provisions of old structures of age 50 years and more. they proposed that combined structural and fire engineering provisions should be used to mitigate the risk of concrete spalling. towards controlling of spalling of high-performance-concrete exposed to high temperature authors in [13] conducted experimental evaluations of compressive, tensile, flexural strength and modulus of elasticity of high-performance air-entrained concrete, polypropylene fiber-reinforced concrete and reference concrete having constant w/c ratio. the samples were exposed to 300˚c, 450˚c and 600˚c and tested. based on the obtained results authors concluded that both polypropylene fiber concrete and air entered concrete perform well. authors in [14] studied flexural performance of slabs and beams. they used 5 two-span rc slabs and 7 two span rc beams in their study. beams and slabs were tested for fire duration in accordance with iso 834 then cfrp strengthening was applied to the rc members. the specimens were then loaded till failure. the results showed that flexural capacity of the members decreased with increased fire duration. they also observed that fire had more effect on flexural rigidity than bearing capacity of the members. the results revealed that the bearing capacity of the rehabilitated members exceeded that of reference concrete members but rehabilitation had little effect on the recovery of their flexural rigidity. in a study to evaluate the effects of elevated temperature on green concrete, authors in [15] tested concrete specimens cast with 0%, 15% and 30% replacement of natural aggregates with aggregates from old concrete exposed to fire for 2 hours at 100˚c-600˚c. they reported that optimum replacement of natural coarse aggregates to yield maximum strength is 15% at 450˚c. test specimens showed hairline cracks in concrete even when exposed to fire, therefore, they concluded that with the above mentioned optimum values the performance of green concrete is in good agreement with natural concrete. looking at the state-of-the-art, it is clear that a good deal of work is still required for the subject matter. this motivates the research presented in this paper. in this research, experimental evaluation of the effects of 6-hour fire on rich mix reinforced concrete beams made with recyclable concrete was carried out. natural coarse aggregates were replaced with demolished concrete aggregates in 50% proportion. to compare the results, an equal number of reinforced concrete beams with all-natural aggregates was cast. the beams were exposed to fire (1000˚c) for 6 hours. flexural strength of all beams under central point load was tested in a universal load testing machine. the comparison of the results shows good resistance of the proposed beams against 6-hour fire duration. therefore, demolished concrete can be used as coarse aggregates in new concrete. it is worth mentioning that this research work is a part of a continuity of a project on the subject matter. experimental investigations of normal mix concrete are in the process of publication. ii. materials and design large blocks of demolished concrete were collected from the waste of a commercial 60-year-old office building. these large blocks were manually hammered down to approximate size of 20mm, followed by sieve analysis of both recyclable aggregates and natural aggregates in standard fashion. the comparison of sieve analysis of both aggregates is shown in figure 1. six reinforced concrete beams of 900mm×150mm×150mm size were cast with 1:1.5:3 mix and 0.54 water-cement ratio. in these beams 50% natural coarse aggregates were replaced with recyclable concrete aggregates [2]. these beams are referred as rac beams. in addition, 6 rc beams with all-natural aggregates were also cast. these beams are referred as control specimen and are used to compare the results. two #4 bars in both tension and compression zones were used along with #3 bars as stirrups at 150mm center to center throughout the length to reinforce the beams. the proposed beams were designed in accordance with [16] which ensures the durability of the member during service life. after casting the beams in standard fashion, all beams were fully immersed in water for 28-day curing. after the elapse of curing time the beams were left in the laboratory for 24 hours to air dry. then, all beams were exposed to fire in a purpose made oven for 6 hours at 1000˚c. the beams were then left in the oven for 24 hours to avoid damage due to abrupt temperature change. finally, all the beams were tested in a universal load testing machine with central point load for flexural strength as per astm recommendations. load, deflection and cracking in beams were carefully monitored at regular intervals. loaddeflection of both rca beams and nca beams is plotted in figures 2 and 3. fig. 1. gradation of aggregates fig. 2. load vs deflection of rca beams engineering, technology & applied science research vol. 9, no. 1, 2019, 3814-3817 3816 www.etasr.com buller et al.: flexural strength of reinforced concrete rac beams exposed to 6-hour fire – part 2 … fig. 3. load vs deflection of nca beams iii. results and discussion figure 1 shows that both recyclable concrete aggregates and natural aggregates used in the concrete mix are well graded with approximately the same pattern. figures 2 and 3 show the load-deflection behavior of both beam groups. it may be observed that within the group of beams and in comparison to each other the trend of load and deflection increase is almost symmetrical with the exception that rca beams showed more deflection and ruptured at load less than nca beams. flexural strength is computed from the maximum load at which beams fail. table i gives the average values of load, deflection and flexural strength of both beam groups. figure 4 shows the comparison of flexural strength of all beams. table i. average values of all beams description nca-beams rca-beams difference (%) load (n) 67668 62091 8.24 deflection (mm) 5.74 6.03 5.1 flexural strength (mpa) 27.07 24.84 8.24 fig. 4. flexural strength of all beams from table i it is observed that the proposed reinforced concrete beams showed 8.24% reduction in flexural strength and 5.1% increase in deflection in comparison to control specimens. these values are less than 10% which shows good fire resistance of the proposed concrete beams. cracking in the beams during loading process was monitored carefully. selected beams of natural aggregates and recyclable aggregates are shown in figures 5 and 6 respectively. it is observed that almost all beams failed in shear with diagonal cracks initiating from loading location towards supports. this also validates the use of the proposed aggregates in rich mix concrete. fig. 5. cracking in a nca beam fig. 6. cracking in a rca beam iv. conclusion this paper presents the experimental evaluation of the effects of 6-hour fire on rich mix reinforced concrete beams made with 50% replacement of natural coarse aggregates with recyclable aggregates from old demolished concrete. a total of 12 rc beams were cast using rich mix and were cured for 28 days. out of these beams, half of the specimens were cast with all-natural aggregates to compare the results. all the beams were exposed to fire for a 6-hour duration at 1000˚c followed by central point load testing in a universal load testing machine. load, deflection, and cracking were monitored at regular intervals. result comparison shows that both deflection and flexural strength of proposed specimens exhibited less than 10% reduction (all beams failed in shear testing). this proves the effective use of proposed aggregates in rich mix concrete without compromising much on the flexural strength of concrete. v. suggestions this paper used a limited number of beams and two commonly used concrete mixes with water cement ratio of 0.54. however, it is suggested that more beams, with different water-cement ratios, could be used. it is also suggested that the experimental work on the issue may be augmented with theoretical analysis regarding different concrete parameters, checking of the experimental results and establishing a theoretical frame for concrete with demolished concrete as aggregates. references [1] a. a. bhatti, b. a. memon, “strength, deflection and cracking behavior of concrete slab using demolished concrete as coarse aggregates”, international journal of engineering sciences & research technology, vol. 3, no. 6, pp. 492-506, 2014 engineering, technology & applied science research vol. 9, no. 1, 2019, 3814-3817 3817 www.etasr.com buller et al.: flexural strength of reinforced concrete rac beams exposed to 6-hour fire – part 2 … [2] m. oad, b. a. memon, “compressive strength of concrete cylinders using coarse aggregates from old concrete”, 1st national conference on civil engineering (ncce 2013-14)-(modern trends and advancements), april 28-29, 2014 [3] a. h. buller, b. a. memon, “effect of fire on strength of concrete cubes with rca as coarse aggregates”, 1st national conference on civil engineering (ncce 2013-14)-(modern trends and advancements), april 28–29, 2014 [4] b. a. memon, “recent development on use of demolished concrete as coarse aggregates”, international journal of emerging technology and innovative engineering, vol. 2, no. 1, pp. 1–11, 2016 [5] d. j. naus, the effect of elevated temperature on concrete materials and structures – a literature review, us nuclear regulatory commission, office of nuclear regulatory research, washington, 2006 [6] d. cree, m. green, a. noumowe, “residual strength of concrete containing recycled materials after exposure to fire: a review”, construction and building materials, vol. 45, pp. 208-223, 2013 [7] w. g. li, j. z. xiao, c. j. shi, c. s. poon, “structural behavior of composite members with recycled aggregates concrete – an overview”, advances in structural engineering, vol. 18, no. 6, pp. 919938, 2015 [8] j. p. b. vieira, j. r. correia, j. de brito, “post-fire residual mechanical properties of concrete made with recycled concrete coarse aggregates”, cement concrete research, vol. 41, no. 5, pp. 533-541, 2011 [9] a. m. marques, j. r. correia, j. de brito, “post-fire residual mechanical properties of concrete made with recycled rubber aggregate”, fire safety journal, vol. 18, pp. 49-57, 2013 [10] m. batayneh, i. marie, i. asi, “use of selected waste materials in concrete mixes”, waste management, vol. 27, no. 12, pp. 1870-1876, 2007 [11] v. kodur, “properties of concrete at elevated temperatures”, isrn civil engineering, vol. 2014, articleid 468510, 2014 [12] g. wang, d. barber, p. johnson, m. c. hui, “fire safety provisions for aged concrete building structures”, procedia engineering, vol. 62, pp. 629-638, 2013 [13] t. drzymała, w. jackiewicz-rek, m. tomaszewski, a. kus, j. galaj, r. sukys, “effects of high temperature on properties of high performance concrete (hpc)”, procedia engineering, vol. 172, pp. 256-263, 2017 [14] j. t. yu, y. liu, z. d. lu, k. xiang, “flexural performance of fire damaged and rehabilitated two span reinforced concrete slabs and beams”, structural engineering and mechanics, vol. 42, no. 6, pp. 799813, 2012 [15] m. a. salau, o. j. oseafiana, t. o. oyegoke, “effects of elevated temperature on concrete with recycled coarse aggregates”, iop conference series: materials science and engineering, vol. 96, articleid 012078, 2015 [16] american concrete institute, aci 318-05, building code reqirement for strucrural concrete, aci, 2005 microsoft word 1-2678_etasr_v9_n3_pp4079-4084 engineering, technology & applied science research vol. 9, no. 3, 2019, 4079-4084 4079 www.etasr.com danikas and morsalin: a short review on polymer nanocomposites for enameled wires … a short review on polymer nanocomposites for enameled wires: possibilities and perspectives m. g. danikas democritus university of thrace, department of electrical and computer engineering, power systems laboratory, xanthi, greece mdanikas@ee.duth.gr s. morsalin university of new south wales, scholl of electrical engineering and telecommunications, high voltage laboratory, sydney, australia sayidul.morsalin@unsw.edu.au abstract—polymer nanocomposites constitute a new generation of insulating materials, capable of offering better electrical, thermal and mechanical properties. past research indicated that such materials may replace conventional polymers for a variety of industrial high voltage applications. in the present paper, polymer nanocomposites are investigated regarding the insulation of enameled wires. possible nanocomposite candidates are discussed. keywords-enameled wires; nanocomposites; nanoparticles; partial discharges; charges; voltage rise time; insulation deterioration i. introduction the present paper aims to provide a short review on polymer nanocomposites for enameled wires. it is the aim of this paper to shed some light on the polymer nanocomposites and their possible applications in enameled wiring. in the light of the advent of power electronics and the ever more frequent use and interaction with high voltage apparatus, it is highly interesting to investigate such possibilities of applications of the new materials. the advent of power electronics arrangements into electrical networks provide additional efficiency to power converters [1, 2] however it also seems to be the cause of some distortions in current as well as in voltage. such distortions may in turn cause a reduction in the reliability of the insulation systems and premature aging. in fact, the largest discharges, one of the most deleterious causes of insulation degradation, tend to occur closest to the front of the applied voltage pulse [1]. polymer nanocomposites have been the subject of intensive research for the past 25 years [3, 4]. a wealth of experimental results as well as a number of proposed models has been published regarding polymer nanocomposites. nanocomposites, mainly because of the dispersed nanoparticles in a base polymer, seem to present interesting properties and provide improved electrical, thermal and mechanical properties compared to their conventional counterparts. polymer nanocomposites are being tried on both ac and dc applications [5]. no effort was taken to investigate possible lifetime relationships in the context of this paper since this is beyond the scope of the present work. it goes without say that the present review does not cover the whole issue of power electronics arrangements in conjunction with the whole range of insulating materials and systems. it is just an attempt to approach the subject of enameled wires in relation with the recently developed polymer nanocomposites. ii. enameled wires enameled wires are used for applications requiring tight coils, such as inductors and electrical motors. their insulation consists of films from polymeric materials, such as polyurethane, polyurethane resin, polyamide, polyester, polyimide and also several combinations of them [6, 7]. enameled wires have thin insulation. such insulation must be flexible, extensible, and tough. it must withstand mechanical vibrations, have good dielectric strength, be stable and have a long lifetime. in [8], detailed information is given on the variety of insulating materials for enameled wires regarding their thermal classes and their possible applications. such insulation may suffer from electrical, mechanical and thermal stresses. research referring to the ageing of such insulation systems indicates that thermal stresses are an important ageing factor [9]. in [9], it was pointed out that there are two basic ageing mechanisms determined by the critical temperature θc. below the critical temperature, a thermal ageing occurs whereas above the critical temperature a sudden thermal breakdown may occur. earlier studies indicated that with polyester-type magnet wires (and in general with film-coated magnet wires and impregnating varnishes) extrapolation of data is allowed only after realistic and appropriate requirements have been met in regard to linearity and other factors such as maximum and minimum average life data [10]. relevant effects, such as those of increasing temperatures because of repeated electric motor starts, and their influence on the lifetime of wires, were analyzed in [11]. serious reservations were expressed earlier about the possibility of data extrapolation, especially in the case in which two factors are accelerated simultaneously [12]. aging factors – interacting with each other and combining – are difficult to quantitatively analyze and study [12-14]. heat shock resistance, flexibility and windability are among the factors which matter in order to choose the appropriate material for enameled wires. polyurethane based with polyamide outer coating, among others, was developed for this purpose. corresponding author: m. g. danikas engineering, technology & applied science research vol. 9, no. 3, 2019, 4079-4084 4080 www.etasr.com danikas and morsalin: a short review on polymer nanocomposites for enameled wires … moisture resistance is another important factor for choosing the right material. it is usually difficult to make a choice since chemical options in some cases favor thermal life and functionality whereas at the same time they render the enameled wire less flexible and less heat shock resistant [15]. also properties, such as embrittlement, are affected by the formulation of the base polyester resin and by the choice of monomer [16]. iii. polymer nanocomposites and related models polymer nanocomposites have been the subject of intensive research in recent years [3-5]. it is interesting to note that the problem with the interfaces that is envisaged with conventional insulating materials is not the same in the context of polymer nanocomposites [17]. in polymer nanocomposites, interfaces seem to play a different role. nanoparticles dispersed in a conventional polymer interact with the surrounding polymer matrix and the so-called interaction zone contributes to the improvement of the properties of the base polymer [18]. a considerable amount of publications has dealt with the question of interfaces in polymer nanocomposites. as was mentioned before, main interface models – referring to nanocomposites – are the lewis model, the wilkes model, the tanaka multi-core model, tsagaropoulos’ model, the potential barrier model, the interphase model, the polymer chain alignment model, the water shell model, the dual layer model, the physical model for the explanation of surface degradation mechanism, the physical model for tree growth, chen’s model and the percolation model [19, 20]. all these models have been analyzed in detail in [20]. in a further attempt to explain electronic transport in polymer nanocomposites, a novel concept considering the nanoparticles as quantum dots (qds) was proposed. in such a consideration, nanoparticles are thought to be qds of nm size and are taken as carrier traps [21]. simulation studies regarding partial discharges and electrical trees for both conventional polymers and polymer nanocomposites have been reported in [22]. simulations have to certain extent considerable success, especially regarding qualitative (but not quantitative) comparisons. generally speaking, polymer nanocomposites present higher breakdown strength and they are more resistant to electrical trees because the nanoparticles they contain seem to act as nano-barriers [23-27]. iv. enameled wires and polymer nanocomposites enameled wires are a critical component of several significant devices (radios, televisions, computers, large and small electrical motors, automobiles, refrigerators). both world war i and world war ii resulted in rapid growth and expansion in the enameled wire industry [28]. breakdown strength and partial discharges have been some of the major concerns of the insulation in such wires [6, 7, 29]. the need of a more efficient control of the energy conversion equipment and the wider use of the pulse width modulated waveforms put additional stresses on the insulation systems. the aforementioned factors together with the advent of polymer nanocomposites create new challenges for potential applications [30-32]. high reliability of the insulation of enameled wires is required having in mind the use of electronic variable speed drives. the presence of fast rising or falling voltages can lead to overvoltages and consequently to the starting of partial discharge activity [33]. the results of [33] seem to favor some materials, either with or without nanoparticles. however, it seems that layered silicate is an appropriate additive to epoxy monocomponent resin and to solventedalkydic resin, giving rather encouraging inception voltages. the importance of the environment in which insulating systems function, is adequately emphasized in [34], where it was pointed out that standards used for land-based insulation systems are not likely to provide good guidance for ship insulation system design. sinusoidal voltage waveforms cause different electrical stresses from pulse voltages, since the latter can be repetitive with a high level of voltage rise fronts (slew rates). slew rates can attain values of tens of kilovolts per microsecond and voltage pulse repetition frequency of up to several tens of kilohertz. electric motor insulation systems may be affected by such phenomena [35, 36]. internal partial discharges consist a real threat since they are intimately related to resin-rich insulating systems [37]. various mixtures were tried in order to improve the electrical performance of enameled wires. thus in [38], different proportions of nanoparticles (1 wt%, 3 wt% and 5 wt%) from different substances (zro2, al2o3, cnt and zno) were tested. it was indicated that the optimum performance was given by the enamel filled with 3 wt% al2o3 nanoparticles regarding the inception and extinction voltages, whereas the enamel with 1 wt% zro2 nanoparticles presented the highest breakdown strength. electrical properties are not the only ones to take care of, as is pointed out in [39]. aromatic polyamide – imide resins (pai)-silica hybrid films seem to have a better heat and abrasion resistance when compared with conventional pai insulation. there seems to be a correlation between silica content and young’s modulus without, however, affecting the flexibility of the film. such wires were also surge-resistant to partial discharges, rendering them suitable for hybrid and electric vehicles, as later research showed [40]. relevant work on silica/polyamide-imide composite films for enameled wires revealed that the way the silica nanoparticles are treated plays a dominant role in determining the behavior of the nanocomposite. spherical silica nanoparticles modified with the cationic surfactant cetyltrimethyl ammonium bromide (ctab) were successfully dispersed into the pai matrix and improved the thermal stability and decomposition temperature of the pure pai polymer [41]. the partial discharge behavior was also improved since the authors of [41] considered that charged particles are reflected and scattered around the silica nanoparticles, improving thus the partial discharge resistance. their interpretation as to why partial discharges seem to be less in nanocomposites than in conventional polymers conforms with the interpretations given in [19, 23]. the authors of [41] suggested that the optimum percentage of nanoparticles into the pai matrix is 3 wt%. however, in yet another study by the same authors, no agglomerations of silica nanoparticles were observed up to 10 wt% [42]. in another study, polyesterimide and polyester were investigated and compared with their nanocomposite counterparts having nanoparticles of 1 wt% of nanosilica, 1 wt% of zinc oxide and 3 wt% montmorillonite (mmt). the nanocomposites presented better resistance to partial discharges, better water absorption and better thermal endurance [43]. polyimide film engineering, technology & applied science research vol. 9, no. 3, 2019, 4079-4084 4081 www.etasr.com danikas and morsalin: a short review on polymer nanocomposites for enameled wires … nanocomposites showed higher breakdown voltage and lower probability of breakdown when they have nanoparticles of sio2 with 1 wt% rather than with 3 wt% inclusions (results analyzed with the weibull distribution) [44]. further studies on polyamide-imide (pai) in combination with nanoparticles of alumina and silica revealed that alumina loadings of about 5–7.5 wt% offered an improvement in breakdown strength, better endurance testing results and moderate improvement in thermal performance compared with the unfilled material. alumina seems to offer a more significant improvement than silica regarding breakdown strength and partial discharge behavior, because of the larger difference in permittivity between pai and alumina. such a difference causes a larger scattering of electrons and thus a reduction of mean free path. experiments with twisted wires indicated that, as corona erodes the polymer during endurance testing, nanoparticles build up on the surface of the polymer. the nanoparticles have a higher resistance to damage from the discharges, and in this way they help to improve the endurance [45]. nanocomposites consisted of enamel, epoxy and zirconia nanoparticles (in mixtures of 1 wt%, 3 wt% and 5 wt%) were investigated in [46], where it was shown that the mixture with 5 wt% presented the highest inception and extinction voltages together with the highest melting point. silica nanoparticles were used in order to produce enameled wires from polyamideimide. the novelty in this case was the use of a lowhygroscopicity solvent consisted of mdi (diphenylmethane-4, 4’-diisocyanate) and of tma (trimellitic anhydride), so that to obtain a nanocomposite which had a better voltage endurance and thermal endurance than the conventional polyamide-imide polymer [47]. the nanocomposite also excelled regarding other critical parameters, such as flexibility, resistance to abrasion and partial discharge inception voltage. however, the aforementioned paper presented the improvements of nanoparticle contents in terms of ‘arbitrary units’ instead of the more convenient percentages in wt%. a comparison between round wires and rectangular wires was presented in [48], where the authors studied their performance with various temperatures (250 o c–2300 o c). although the round wires proved to be slightly better in electrical performance than the rectangular ones (regarding dielectric strength and partial discharge inception voltage), the authors proposed a mixed insulation for rectangular wires, which consisted of enamel layer and pai insulation, with the latter having a reduced permittivity. partial discharge studies is one of the most reliable processes in order to see what sort of material may be used for enameled wires, as discussed in [49]. although no nanocomposites were used in the latter paper, a discrimination between various materials as well as between aged and non-aged materials can be done based on partial discharge measurements. partial discharge inception voltage measurements with enameled wires with nanoparticles (sio2, tio2, al2o3), however, did not discriminate between nanocomposite enameled wires and the conventional ones, although the former showed an improved total life and residual life [50]. in [50], a critical partial discharge was observed which was consistent with the breakdown point, something also noted many years ago with conventional polymers [51]. nanofilled polyamide-imide twisted pair specimens were investigated in [52], where it was shown that they performed better regarding dielectric strength due to pulsed voltages as well as regarding partial discharge activity compared with conventional polyamide-imide specimens (the nanofilled specimens had nanoparticles of sio2 in portion of 8 wt%). as mentioned above, partial discharge measurements, especially in their more complete form (i.e. giving information w.r.t. the phase angle of the discharges, their pulse shape and their sequence), render an overall picture of the difference between nanocomposites and the conventional polymers. it was shown that a combination of micro and nano particles in a polymer may enhance the dielectric strength w.r.t. the conventional polymer. an addition of 5 wt% nanoparticles in epoxy resin may influence the permittivity of the resulting nanocomposite, since the change in permittivity may be due to the permittivity of the added nanoparticles and also to the immobilizing of the molecular chains in the interaction zone. once again, partial discharge measurements and erosion studies proved to be indispensable in order to classify the various types of micro and nanocomposites [53]. polyesterimide resin filled with nanosilica, montmorillonite and aluminium oxide in portions of 1.5 wt% were investigated in [54]. thermoanalytical methods, breakdown measurements and partial discharge measurements showed that hydrophilic nanosilica as well as aluminium oxide presented the best results w.r.t. thermal stability, dielectric strength and partial discharge resistance. the authors, however, did not explain why nanoparticles from the aforementioned substances presented better results than hydrophobic nanosilica and montmorillonite nanoparticles. the validity of partial discharge measurements when investigating the effect of repetitive square voltage frequency on enameled wires was discussed in [55], where it was noted that a higher voltage frequency would decrease the partial discharge events with lower magnitudes. such events would not be induced in some weak insulation points because of the inadequate time to generate the initial electrons. different square voltage frequencies may result in different surface charge decay ratios and different initial electron emission probabilities. reference [55], however, did not mention any comparison between various insulating materials for enameled wires. similar observations, regarding the higher voltage frequency and the partial discharge activity, were noted in [56]. in the same work, polyimide insulation was filled with nanoparticles of tio2 (which help in achieving better thermal conductivity and improved electrical properties), nanoparticles of fumed silica (sio2)(which have extremely large surface area, good thermal properties and impart excellent electrical and mechanical characteristics to dielectric coatings) and nanoparticles of al2o3 (which have excellent electrical and thermal properties). such nanoparticles were added to the base polymer at about 1 wt%. the improvement of dielectric strength was attributed in [56] to the impinging of charged particles on the nanoparticles, preventing thus further collisions with the organic material. in this way, the creeping distance is extended, and the collision energy of the charged particles is lowered considerably by the reflection and scattering so that the erosion is suppressed. this explanation is in perfect agreement with that reported some years earlier [57]. concentrations larger than 1 wt% may result in diminishing the engineering, technology & applied science research vol. 9, no. 3, 2019, 4079-4084 4082 www.etasr.com danikas and morsalin: a short review on polymer nanocomposites for enameled wires … mechanical strength as well as the dielectric strength. polyimide with fumed silica nanoparticles showed low surface roughness and higher dielectric strength as compared with polyimide with the other aforementioned types of nanoparticles. an interesting piece of work was presented in [58], where the authors compared polyamide-imide filled with nanoparticles of silica with the base polymer. no information on the content of the nanoparticles was given, although the authors mentioned that the silica nanoparticles were spherical and had a diameter of 2 to 4 nm. the interesting aspect of this publication is that, although it also indicates the superiority of the nanofilled enamel compared to the base polymer regarding life endurance and discharge resistance, it points out to the fact that relative humidity (rh) plays a vital role affecting the partial discharge behavior, rendering at higher values of rh (at about 80% rh) somehow blurred the distinction between the nanocomposite and the base polymer. for inverter-operated motors, materials such as ester amide, and amide-imide enamels were introduced, all of them with inorganic nanoparticles to enhance their thermal rating [59], although no precise details were given. in [59], it was emphasized that abrasion resistance and thermal enhancement are critical factors for choosing the right nanocomposite for enameled wires. in [60], besides other topics, the authors mentioned that a polyamide-imide/silica nanocomposite system is suitable for enameled wires since the colloidal state of silica is maintained by covering the silica surface with a new lowhygroscopicity solvent, encouraging thus the dispersion of silica nanoparticles. the latter publication is in agreement with [47]. in [61], the authors tried to modify the surface of silica nanoparticles with two kinds of silanes, with polyesterimide (pei) as base polymer. they suggested a content of silica nanoparticles of up to 20 wt%, which seems to be far too large. the authors, although the silica-pei nanocomposite presented a much longer lifetime than the neat pei in partial discharge conditions, did not give any hints as to the long term stability of such a mixture. polyamide-imide resin was mixed with nanoparticles of cr2o3 at 14.3 wt%. conventional samples and samples filled with the aforementioned nanoparticles were investigated w.r.t. their partial discharge behavior. the filled enamel was characterized by lower inception and extinction voltages, which may be due to the enhancement of electric field at wire surfaces owing to the presence of the highly dispersive filler. the exposure to partial discharges was reduced for the filled enamel, but only for the shortest voltage rise time, whereas the effect was not noticed for the longer voltage rise times. this may be due to the decay of charges on the wire surface [62]. the careful reader, however, has to note that the nanoparticle content was far too high. in [63], particular attention was paid to the way a nanocomposite is manufactured. according to the authors of [63], a colloidal state in which particles are dispersed without aggregation by an electrical double layer is preferred and thus a colloid-solution-mixture method was proposed in which the nanocomposite shows a remarkable stability and no viscosity change, even after several months. lifetime characteristics of enamel with silica nanoparticles were investigated in [64], where it was shown that the mixture with 5 wt% content had the best v-n characteristics under repetitive surge voltage application, and in descending order the mixtures with 2.5 wt% and 1 wt%. moreover, the nanocomposites indicated a better resistance to deterioration than the conventional enamel. the observations and conclusions of [64] were not different from those published in [65]. v. discussion and perspectives from the above it is evident that enameled wire insulation when mixed with nanoparticles presents a reasonable alternative to conventional enameled insulation. the present paper tries to give a short insight of the complexities of the enameled nanocomposite insulation. the present review is by no means a thorough review of the entire subject of enameled insulation. as discussed above, there is a variety of possibilities regarding the different inorganic nanoparticles. however, no definite conclusions have been reached as yet. there is still an ongoing debate about what are the best nanoparticles, what is the best method of forming a nanocomposite, what is the optimum percentage of the nanoparticles to be included. there is also an ongoing debate about the stability of nanocomposites in general [5], and of enameled nanocomposite insulation in particular [63]. as in other high voltage applications, nanocomposites in the present case depend on the base material, the type of the added nanoparticles, the way of mixing the nanoparticles with the base material and the percentage of the nanoparticles [66]. the response of the enameled nanocomposites depends (among other factors) – as with conventional insulating materials – on the level of applied voltage, temperature, humidity and the type of applied voltage waveform. since the present review is concentrated on the enameled nanocomposites, the effect of the applied voltage waveform as well as of the other factors will be the subject of another review paper. a subject which is rather neglected also in enameled nanocomposite insulation is that of the possible charging effects below the so-called inception voltage. some work, carried out in other insulating materials, indicated that there are charging effects below the inception voltage [67-69]. since there is a continuing discussion about charge packets in polymeric materials [70], it would be of interest to see whether charging effects below inception have a relation to the charge packets. furthermore, the lifetime of twisted pairs having nanocomposite insulation due to various types of voltages and under different environmental conditions is of immense interest to both the industry and the academy [58, 71]. a closer investigation of enameled nanocomposites may also give a better understanding as to the workings of interfaces [72]. vi. conclusion some crucial aspects have been discussed in the context of this paper. the advent of power electronics arrangements as well as of new materials poses new challenges to the insulation of enameled wires. well known issues and techniques have to be investigated under the light of the new materials. the advent of new insulating materials, such as nanocomposites, offers new ways of solving insulation challenges. however, new engineering, technology & applied science research vol. 9, no. 3, 2019, 4079-4084 4083 www.etasr.com danikas and morsalin: a short review on polymer nanocomposites for enameled wires … materials are not free of defects and/or problems. questions to be answered 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ecosystem for sustainable inter-island transport in philippines a pilot study eleonor v. palconit engineering graduate program, school of engineering, university of san carlos (usc), talamban, cebu city, philippines evpalconit@addu.edu.ph michael lochinvar s. abundo engineering graduate program, school of engineering, university of san carlos (usc), talamban, cebu city, philippines programme integration manager, rolls-royce@ntu corporate lab, nanyang technological university, singapore michael.abundu@ntu.edu.sg abstract—an electric boat system as a pilot study for the electric ferry was designed and field-tested in samal island, philippines, to verify sustainability for inter-island transport. this pilot study uses 4.5m monohull with a displacement weight of 343kg. during the experiment, two cases were compared: in the first case the boat was powered solely with batteries and in the other case with the aid of photovoltaic (pv) modules. for the first case, 24v electric propulsion was driven by two 12v, 100ah batteries, which resulted to a navigational range of around 18, 16 and 15 trips with energy consumption of 111.64wh, 117.19wh and 123.92wh respectively. in the second case, the photovoltaic modules were attached on the boat to supplement the pv used while on sail. results in the second case showed that pv module supplemented energy was about to 13.4%, 26.8% and 38.7% using three different speeds like 3.18, 3.32 and 3.84knots and the navigational range extended to 4km, 1km, and 14.4km respectively. therefore, the electric boat with the aid of pv module answers the problem in the energy management system that deals with the sustainability of the system in the inter-island transport in philippines. keywords-batteries; electric propulsion; electric boat; photovoltaic module i. introduction energy security, sustainability, pollution, and climate change are some major challenges the world is experiencing today. the conversion of the present transport system is one of the difficult aspects of the renewable transition. studies show that a 100% renewable transport system will consume 18% less energy. in the transition, the road transport sector will have an expected reduction of 69% of energy but in the shipping sector the consumption would increase by 163% [1]. the 11% of the petroleum used globally is consumed by the maritime sector, so a 100% renewable energy source will be beneficial [3]. authors in [4] showed that using electric vehicles powered by batteries or by hydrogen and fuel cell resulted in 80% reduction of greenhouse emissions, decreased oil dependency and reduced air pollution. reinforcing and implementing electric transportation, especially in maritime sector, is not impossible in the face of low specific energy, state of the art, batteries compared to fossil fuels [3]. mobility electrification is becoming reality, and batteries can be a sustainable solution not only in household and commercial sectors but also in transportation. in the case of islands and isolated communities in europe, the implementation of electric boats was materialized because of the challenges in the price increase of energy and the demand of renewable energy-efficient sources, which steered a new trend towards ferry electrification. the first fully electric ferry using li-ion batteries can be found in europe and became the “ship of the year” in 2014. another one was built and operated in sweden, it uses nickel-metal-hydride (ni-mh) batteries and its operation is expected to reduce co2 and nox emissions by 130 and 1.5tons per year respectively [2]. another solar powered ferry boat for the rural area of bangladesh has been retrofitted with a 48v, 500w motor, and 1kw solar panel with 9600vah battery. the boat is capable of covering 60km distance in one full charge [5]. an eco-friendly electric propulsion boat was developed for public transport in lake trasimeno. the development aimed to have zero emissions, the boat is powered by li-ion batteries that can be charged at any harbor [6]. moving towards green energy sources in the maritime transportation sector is the solution to the high price of fossil fuels and can reduce water pollution. the use of electric propulsion powered by batteries and renewable energy are efficient and effective solutions to the problem [7]. this study aims to implement an electric ferry ecosystem for inter-island transport in philippines. specifically, it aims to verify the suitability of the electric motor. also to observe the performance of the outboard applied in the existing boat in a real situation, and finally to evaluate the sustainability of the system using the battery source alone and the system with the aid of pv module charging the battery while on voyage. engineering, technology & applied science research vol. 8, no. 6, 2018, 3570-3575 3571 www.etasr.com palconit & abundo: electric ferry ecosystem for sustainable inter-island transport in philippines ii. samal island a. geology, climate, and hydrology the island garden city of samal, is a group of islands in the heart of davao gulf and unattached to the mainland of mindanao philippines. it is 900m east of davao city, it stretches over 116km of continuous coastline and covers a total land area of 30,130 hectares. the island is endowed with extensive mountain range at the eastern coast. the city enjoys a mild pleasant climate with no dry or wet season and it is typhoon-free [11]. samal island is one of the 7,000 tropical islands in philippines with a large number of soft white coral sand beaches with rustling coconut palms and gently lapping turquoise water [11]. b. transportation to samal island there are 205 registered sea transportations in philippines that operate in the area [12]. routes allowing the communication of the two islands and davao can be seen in table i, which shows the perspective route with the distance and the speed of the ferry from davao to potential destinations for electric ferries [13]. to showcase the feasibility of electric mobility in the area, this study conducted an experiment using a fishing motorboat (banca) with a capacity of four persons. the motorboat was converted with an electric motor without altering the design as shown in figures 1 and 2. fig. 1. existing boat fig. 2. solar electric boat table i. potential destinations routes distance (m) speed (knots) davao – babak 2300 6 davao – paradise beach resort 900 4.5 davao – costa marina 900 4.5 davao – chemas 1000 4.5 davao – blue waters 1000 4.5 davao – pearl farm 15000 5 sta ana davao – talikud 18800 8 iii. experiments a. the study area the converted to electric boat was field tested in samal island, particularly in the rocky beach resort. the electric boat navigated 1.3km from rocky beach as shown in figure 3 to verify the sustainability and functionality of the system. during the field-testing, data like the energy used of the electric propeller with the different speed of the motor was gathered. the charge and discharge of the energy source were also monitored to test the sustainability during navigation. fig. 3. the navigational range of the electric boat b. the existing boat the boat used for this study is monohulled and made of marine plywood as shown in figure 1. the existing boat is driven by a diesel motor, it has a capacity of 4 persons and it is used for fishing. the boat dimensions are shown in table ii. table ii. boat dimensions dimension length (m) weight (kg) number length overall (loa) 4.5 load waterline (lwl) 3.5 empty weight 30 displacement weight -343 no. of persons 4 the boat dimensions are needed for determining the basic requirements in converting the diesel engine into electric propulsion. table iii shows the estimated electric propulsion needed for navigation and the requirements for inter-island transportation sustainability. green mobility is very important for reducing the dependency on fossil fuels and carbon gas emissions. figure 2 shows the converted pilot electric propulsion motorboat that that will traverse 1.3km in the island of samal. the outboard motor is 11182w and was installed without the design alterations. two 100ah batteries and four 100w solar panels were attached to supplement the energy used during navigation. c. power management system a power management system is used to manage the energy onboard and monitor the exact power through an innovative measuring procedure based on the complete discharge and charge of the battery [6]. the monohulled house contains a battery bank with a battery management system and the outboard motor as shown in figure 4. the battery is connected in series, so it can cater the 24v outboard motor. the energy of engineering, technology & applied science research vol. 8, no. 6, 2018, 3570-3575 3572 www.etasr.com palconit & abundo: electric ferry ecosystem for sustainable inter-island transport in philippines the photovoltaic module is connected to the 50a maximum power point tracking (mppt) controller to charge the batteries while on voyage. pms helps monitor the status of the battery in terms of charging and discharging rate while in use as well as it measures the current and the voltage of the system, so it can figure out the energy usage of different navigational speeds. table iii. boat, solar panel and battery specifications boat specification water line length 3.5 m boat displacement 343 kg speed 4.54 knots equivalent engine 1.500 hp equivalent engine 1118.2 w energy 367.32 wh battery bank capacity nominal voltage 24 v days of autonomy 1 day ampere-hour 77.67 ah no. of batteries 2 pcs solar panel average daily exposure 4.5 hr solar panel 100 w wattage per panel 450 wh no. of solar panels 3.11 pcs daily electricity usage 1397.7 w fig. 4. electric system and outboard motor diagram iv. electric system endurance a. pv pvs systems are commonly known as solar panels, a pv is an interconnected cell that provides electricity for commercial or residential applications and it is extended to the transportation sector. different cell types have different power efficiency. monocrystalline cells are made up of monocrystalline silicon and have a single continuous lattice structure with almost no impurities [14]. furthermore, the main advantage of the monocrystalline cell pvs is their high efficiency, which increased from around 15% [14] to 16%-22% [15]. polycrystalline panels have efficiency of about 13%-15% [16, 17]. polycrystalline has a low-concentration photovoltaic system [18]. moreover, the amorphous silicon solar cell has a 1.1ev-1.3ev bandgap, it has low energy efficiency [19], and gallium arsenide which is modeled as a thin film device with band gap of 1.45ev which shows energy efficiency of 44% [20]. polycrystalline panels were utilized in this study thought monocrystalline has higher efficiency value, because polycrystalline is much cheaper. four polycrystalline photovoltaic modules of 100w each are attached to the boat based on the system requirements. table iv presents the specifications of the solar panels used in this study. philippines have a large potential in solar energy. but there are days that the solar radiance is not available as shown in figure 5 [21]. about 5.11 days per month are no-sunny (no-sun) days, which means that in that case, a utility grid must be used to charge the battery. table iv. specifications of polycrystalline pv parameter specification maximum power 100w tolerance ±5% maximum operating voltage 17.5v maximum operating current 5.71a open circuit voltage 21.5v short circuit current 6.46a irradiance (stc) 1000w/m 2 weight 3.5kg dimensions (l×w) 1000mm×510mm fig. 5. solar radiation and no-sun days b. mppt maximum power point tracker (mppt) is a power electronic system that extracts maximum power from the pv system. mppt varies the electrical operating point of the pv modules and enables them to deliver maximum available power [22]. the pv panels are connected to a mppt charge controller to improve the charge efficiency of supplying the desired power required by the load [23]. a charge controller protects the battery from overcharging preventing battery power from flowing back into the solar module. the mppt charge controller used in this study is a 50a charge controller with 12/24v system automatic recognition. c. electric propulsion equation (1) shows the formula in sizing electric motor [24]. as a result of our relevant investigation, the system uses an outboard motor with an input voltage of 24v, 48a, with maximum power input of 1152w and weight thrust of 37.2kg as shown in figure 4. furthermore, it has a speed controller, five levels of forwarding speed and three level of reverse speed. the outboard motor is mounted at one end of the boat through the metal holder. energy requirements were taken into consideration. figure 6 illustrates propulsion power vs speed. the desired power to operate the system is equal to 1118.2w, with a maximum hull speed of 4.54 knots. hp= �������� � � ����� ���.��� �� ���� � � (1) 0 10 20 30 40 ja n f e b m a r a p r m a y ju n ju l a u g s e p t o c t n o v d e c a v e . n o . o f d a y s no-sun days availability of sun (days) engineering, technology & applied science research vol. 8, no. 6, 2018, 3570-3575 3573 www.etasr.com palconit & abundo: electric ferry ecosystem for sustainable inter-island transport in philippines d. battery two 12v solar deep cycle lead acid batteries were used in this study. the batteries were connected in series to supply the power requirements of the outboard motor. the system needs were 24v and 48a that resulted in 1152w power consumption. the two batteries had a capacity of 100ah and a total voltage of 24v, so the system could navigate continuously for up to 1.5 hours considering a 75% discharging rate. the battery plays a very important role for the sustainability of the operation. equations (2) and (3) size up the battery bank needed for the operation [25]: energy demand=load, kw×time, hr (2) battery capacity & ' �(�) *� � * +,����� � �.��.. x 2 (3) fig. 6. speed vs propulsion power e. results and discussion 1) case 1: electric boat powered solely by a battery in this study, the diesel boat was converted by an electric boat powered by two 12v batteries connected in series to supply 24v volts electric propulsion, with a displacement weight of 343kg and with a target navigational range of 1.3km. the experiment evaluates energy used, speed, total navigational range, and battery discharge. in terms of speed evaluation, both time and distance were taken into consideration. figure 7 shows the energy consumption over the speed of the electric boat. for speed 1 (3.18 knots), the energy consumed was 111.64wh, while speed 2 (3.32 knots), consumed 117.19wh of the energy and speed 3 (3.84 knots) consumed 123.92wh. fig. 7. energy consumption vs speed figure 8 shows the range covered and the equivalent energy needed to reach the desired distance of 1.3km. for speed equal to 3.18 knots, the boat covers 18 trips with a total range of 23.4km and with an equivalent total energy consumption of 1.83kwh. for 3.32 knots, it can cover 16 trips with a total range of 28.8km with an equivalent energy consumption of 1.77kwh and with speed of 3.84 knots it covers 15 trips with 1.85kwh total energy consumption. figure 9 illustrates the battery capacity discharged over the equivalent number of navigational range or boat trips considering a 1.3km distance. figure 9 shows that the system can navigate safely, and it is sustainable. fig. 8. energy vs range fig. 9. battery discharging rate vs number of trips 2) case 2: electric boat supplemented with solar panels in this case, the existing boat was converted into an electric boat powered by a battery with an energy capacity of 1862.4wh. considering a 75% depth of charge it is supplemented with four 100w solar panels. the solar module charges the battery with the mppt controller during the navigational trips. during the experiment of travelling 1.3km distance, 343kg displacement weight and time traveled were taken into consideration in measuring the supplemented power coming from the photovoltaic module. figure 10 displays the supplemented energy coming from the pv module while on sail. results show that 13.4%, 26.8%, and 38.7% decrease is the equivalent energy supplemented by the pv module into the battery while on sail with speed of 3.18, 3.32 and 3.84 knots respectively. the result shows that pv module helps the sustainability of the system for inter-island transportation. this study investigates the range of the electric boat under the engineering, technology & applied science research vol. 8, no. 6, 2018, 3570-3575 3574 www.etasr.com palconit & abundo: electric ferry ecosystem for sustainable inter-island transport in philippines presence of pv modules. figure 11 shows the results of consumed energy with the equivalent navigational range. figure 12 shows the comparison of the navigational range of the electric boat with a battery source of energy over a battery source with the aid of pv module. the result shows that with the aid of the pv module, the navigation range extended to 4km, 1km and 14.4km using speed of 3.18, 3.32 and 3.84 knots respectively. fig. 10. comparison of the energy consume supplied solely with battery and with the pv module fig. 11. energy vs. navigational range with the aid of the pv module fig. 12. comparison of the navigational range with the use of battery alone and with the aid of the pv module. v. conclusions in this study, two cases were compared for the use of the same boat with a displacement weight of 343kg. during the experiment a 24v outboard motor was used, driven by two 12v, 100ah batteries which were connected in series. the electric boat would traverse for about 1.3km distance. in the first case, with total energy capacity of the battery equal to 1.8624kwh considering 75% depth of charge, the electric boat could navigate around 18, 16 and 15 trips with an energy consumption of 111.64wh, 117.19wh and 123.92wh respectively using the three different test speeds. in the second case, with the aid of the pv modules, the navigational range extended to 4km, 1km, and 14.4km respectively. the pv module attached to the boat helped replenish the energy consumed by the electric boat for about 13.4%, 26.8% and 38.7% using the three different test speeds of 3.18, 3.32 and 3.84 knots respectively. the electric boat with the aid of pv module answers the problem in the energy management system that deals with the sustainability and safety for inter-island transport in philippines acknowledgement authors are grateful for the scholarship grant given by the department of science and technology (dost) engineering research and development for technology (erdt). ateneo de davao university. references [1] a. garcia-olivares, j. sole, o. osychenko, “transportation in a 100% renewable energy system”, energy conversion and management, vol. 158, pp. 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low energy storage”, superlattices and microstructures, vol. 75, pp. 39-46, 2014 [24] cat, marine analyst service handbook, caterpillar, 2001 [25] r. reabroy, y. tiaple, s. pongduang, t. nantawong, p. iamraksa, “the possibility of using electrical motor for boat propulsion system”, energy procedia, vol. 79, pp. 1008-1014, 2015 microsoft word 29-3420_s_etasr_v10_n2_pp5501-5504 engineering, technology & applied science research vol. 10, no. 2, 2020, 5501-5504 5501 www.etasr.com shaaban & tawfik: classification of volcanic rocks based on rough set theory classification of volcanic rocks based on rough set theory shaaban m. shaaban department of electrical engineering northern border university, arar, saudi arabia and department of basic science engineering menofia university, menofia, egypt shabaan27@gmail.com sameh z. tawfik department of petrographic studies research division nuclear materials authority cairo, egypt samehzakaria@outlook.com abstract—classification of volcanic rocks is a fundamental task in the geologic studies. volcanic rocks are igneous rocks that cooled rapidly above the surface of the earth's crust. they are classified according to their oxide chemical content. furthermore, volcanic rocks can also be classified numerically by statistical means. but these methods are mostly dependent on human expert decision making and have a high cost. in this paper, a novel approach in the classification of volcanic rocks is proposed. this method is based on the rough set mathematical theory. the continuous data of the information system are firstly discretized using the information loss method. secondly, the discretized decision table is reduced and the decision rule sets are extracted. the results are consistent with previous methods and show that the proposed method reduces time and calculation costs. keywords-decision rules; information loss-discretization; rough set; volcanic rocks i. introduction one established area in geology is the research of volcanic rocks. mineral composition in volcanic rocks is affected by the chemical magma structure and the physical-chemical conditions during crystallization. different approaches are used for volcanic rock classification based on genetic, textural or chemical composition [1]. the genetic method classifies rocks according to their form. this method is only an initial solution, it does not say anything about mineralogy, rock chemistry, and cannot discriminate between basalt and andesite. texture methodology depends on the shape, size, and structure of the grain of different rock minerals. this method has the same limitations as a genetic classification [2]. chemical classification requires a complete chemical analysis of the rock. volcanic rocks are categorized on the basis of their mineral or chemical composition. they are classified into basic rocks, acidic rocks, intermediate rocks, and various types of ultrabasic rocks [3]. on the basis of mineral composition, igneous rocks are classified into silicic, intermediates, mafic, and ultramafic rocks [4]. several methods to develop classification architectures have been suggested including artificial neural networks (anns) [5-7], decision trees [8], statistical techniques [9-10], and decision-making rules [11-12]. rough set (rs) theory is one of the most motivating areas of computational intelligent research, having become increasingly popular with geologic applications. one of the main advantages of rs is that additional information on data such as probability distribution or grade participation is not needed [13], and it doesn't need mean and covariance matrices calculation. it takes time for anns to achieve acceptable accuracy, and the decision tree takes more time for computations because it depends on entropy, while such training in rs is not required. in this paper, the collected features were firstly discretized through information loss technique. then, rs was implemented as a feature reduction approach and rules extraction method was utilized on the discretized decision table to execute classification. the suggested technique finishes with a minimum of chemical composition that has a direct effect on the classification of volcanic rocks. the results indicate that the introduced method reduces significantly feature dimensions and increases classification accuracy while the results are consistent with previous approaches. the obtained results show that the proposed method reduces time and calculation cost. ii. rough set theory to extract volcanic rocks information effectively, a large number of characteristic data must be objectively filtered out. when the best combination of characteristic parameters is achieved, it can be used to identify volcanic rocks precisely. after evaluating many non-linearity computational methods, no further data or previous knowledge were found to be needed for rs theory [14]. it can exclude individual or unimportant characteristics to effectively reduce decision systems with the same database classification ability [15]. the study of geological and volcanic rock information based on rs is a sort of new solution to the mainly geological high-dimensional complex np (nondeterministic polynomial) problems. a. information system we take the identification and extraction problems of mineral material, such as classification of the volcanic rocks, as a restricted method expressed as ( ), , , a fs u v= , where, u is the non-empty finite set of samples called universe, a is nonempty finite set of parameters, a a a v v ∈ = ∪ , av are the different values of attribute a, :f u a v× → is the information function between u and a, a c d= ∪ , c d = ∅∩ , where c corresponding author: shaaban m. shaaban engineering, technology & applied science research vol. 10, no. 2, 2020, 5501-5504 5502 www.etasr.com shaaban & tawfik: classification of volcanic rocks based on rough set theory and d are the condition attributes and decision attributes respectively. the information system is called decision table. b. indiscernible relation let b a⊆ define a binary relation ( )aind b on the universe u, , ( ) i j a x x ind b∈ . if any a b∈ , ( ) ( ) i j a x a x= , then i x and j x are indiscernible and the equivalence relation r b is given by: { }2( ) ( , ) ( ) ( )a i j i jind b x x u a b a x a x= ∈ ∀ ∈ = (1) c. attribute reduction one way to reduce dimensions is to keep only the attributes that preserve the relationship of indiscernibility, i.e. the accuracy of classification. the same set of equivalence classes are provided by the selected set of attributes which can be accessed with the entire attribute set. the other attributes are redundant and can be reduced without affecting the precision of classification. typically there are many subsets of such attributes known as reducts, mathematically, b a⊆ . the element a is redundant attribute in b if ( ) ( { })ind b ind b a= − . the core is the set of all attributes of decision table, which cannot be removed from knowledge in the reduction process where ( ) ( )core b red b= ∩ . iii. discretization of data the real value of attributes should be quantified data when using the rs theory in dealing with information systems. discretization means dividing the continuous attribute into numerous sections, replacing each with a discrete value. there are different methods for discretization of data such as frequency algorithm, clustering method, the naive scalar algorithm, etc. we will use the discretization method in this paper dependent on loss of information. the steps of the algorithm are: step 1: let s be the universe set and x a feature set, s is ordered by ascending order according to x values. the result after sorting is 1 2 3 , , ,..., n x x x x . step 2: construct the initial interval distribution 1 2 3 , , ,..., n i i i i according to the equation 2 3 2 3 3 41 2 1 2 1 1 [ , ),[ , ),[ , ),...,[ , ] 2 2 2 2 2 2 n n n x x x x x xx x x x x x x x− + + ++ + + . then merge into an interval some neighboring intervals with the same parameter value of classification. step 3: evaluate the loss of information for each m neighboring intervals according to: 1 2 3 1 ( , , ,..., ) ( ) m p i p p p p m p i i i e i i i i e i i + + + + + + = = ∑ (2) 11 ( ) ( ) ( , )log ( , ) m m p i i i ii e i e i p d i p d i+ == = = −∑∪ (3) 1 2 3 ._ ( ) ( , , ,..., ) p p p p m inf loss e i e i i i i + + + + = − (4) where p i i + , i are the number and the values of the x parameter for these samples in the interval p i i + , i respectively, ( ) p i e i + is the identification information entropy of the interval p i i + , and ( , ) i p d i is the average of the number of samples which is equivalent to the classification attribute value i d to the total number of interval samples i . step 4: select one neighboring merger interval that has the least information loss and thus get a new interval. step 5: go to step 3 when the information loss from the present step is less than k times the last stage. then obtain the discretized samples. iv. volcanic rock classification based on rs theory a. extraction and assessment of parameters the presented volcanic rocks are parts of the egyptian basement along the red sea coast and southern sinai. in this research, 710 samples of the volcanic rocks were collected. according to the average chemical composition of the samples, the average chemical composition component was selected. materials such as silicon dioxide (sio2) a1, titanium dioxide (tio2) a2, and water (h2o) a13 were selected as the condition attributes, while there are 6 decision classes, namely basalt, basaltic andesite, andesite, dacite, rhyodacites, and rhyolites. the used samples are given in table i. as volcanic rock parameters have continuous values, the original information should be transferred to quantized data. after that, the values of the condition factors were divided into several intervals in accordance to the information loss, for instance the parameter’s a1 break points are 51.865, 54.785, 61.725 and 71.92. the discretized attribute values are shown in table ii. table i is converted into table iii according to the algorithm for quantization based on information loss. the rock types as decision attributes are expressed as {1, 2, 3, 4, 5, and 6}, as shown in table ii. b. volcanic rock type classification-rules once the decision table is established, the parameters should be reduced by applying the proposed approach and the rules for correlating information between features and volcanic rock types should be obtained. based on the approach of roughsets, the most important variables can be filtered from the initial variables, with the goal being to obtain the optimal combination of parameters (parameter structural optimization). without losing the essential information that has a direct and indirect relation to study objects, this filtration can reduce the dimensions of space and simplify the system. based on the rs analysis, the core parameter is { }1a and the reduction attribute set is { }1 3 10 11, , ,a a a a . the extracted rules are shown in table iv. consider the third rule of table iv as an instance to illustrate the meaning of this approach. when attribute values are 51.865≤a1<54.785, 3.525≤a10 and a11<2.015, the rock type is classified as 2 (basaltic andesite). “—” in the table implies that the property value is indispensable. engineering, technology & applied science research vol. 10, no. 2, 2020, 5501-5504 5503 www.etasr.com shaaban & tawfik: classification of volcanic rocks based on rough set theory table i. dokhan rock type decision table no. condition attributes decision attribute a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12 a13 d sio2 tio2 al2o3 fe2o3 feo feo t mno mgo cao na2o k2o p2o5 h2o rock type 1 49.94 0.67 14.48 3.95 4.92 8.48 0.15 9.64 8.48 3.07 0.64 0.08 3.98 basalts 2 53.59 1.89 12.94 5.19 8.84 13.52 0.12 1.99 6.15 3.34 1.57 0.29 4.39 basalts 3 61.97 0.63 16.65 4.08 1.97 5.65 0.08 3.63 4.68 2.96 2.26 0.20 1.24 dacites 4 68.79 0.13 13.63 3.72 0.00 3.35 0.10 0.85 4.82 3.71 1.75 0.00 2.60 rhyodacites 710 74.33 0.27 12.32 2.25 0 2.25 0.05 0.28 1.03 3.5 3.51 0.04 0.77 rhyolites table ii. attributes discretization table attribute discretization code c o n d it io n a tt r ib u te s a1 sio2 0: a1<51.865 1: 51.865≤a1<54.785 2: 54.785≤a1<61.725 3: 61.725≤a1<71.92 4: 71.92≤a1 a2 tio2 0: a2<1.25 1: 1.25≤a2 a3 al2o3 0: a3<15.53 1: 15.53≤a3 a4 fe2o3 0: a4<10.55 1: 10.55≤a3 a5 feo 0: a5<7.46 1: 7.46≤a5 a6 feo t 0: a6<6.586 1: 6.586≤a6 a7 mno 0: a7<0.125 1: 0.125≤a7 a8 mgo 0: a8<5.753 1: 5.753≤a8 a9 cao 0: a9<7.55 1: 7.55≤a9 a10 na2o 0: a10<3.525 1: 3.525≤a10 a11 k2o 0: a11<2.015 1: 2.015≤a11 a12 p2o5 0: a12<0.756 1: 1.756≤a12 a13 h2o 0: a13<1.886 1: 1.886≤a13 decision d rock type 1: basalts 2: basaltic andesite 3: andesites 4: dacite 5: rhyodacite 6: rhyolites v. comparing rs and linear regression method the linear regression approach represents the linear relationship between independent and dependent parameters. this approach presents the interaction as an equation that combines the condition attributes with the decision parameter. the decision variable is given by y and the condition attributes by 1 2 3 , , ,..., n x x x x , where n gives the number of condition attributes [15]. the relationship among y and 1 2 3 , , ,..., n x x x x , is estimated by: 0 1 1 2 2 3 3 ... n n y a a x a x a x a x= + + + + (5) where, 0 1 2 , , ,..., n a a a a represent the regression coefficients. in this article, an attempt was made to define the best chemical combination of minerals for rock type classification, so the dependent parameter is the volcanic rock type classification and the independent parameters are volcanic rock characteristics. nevertheless, problems remain in the formulation of regression equations used to choose the best chemical combination, since it is technically challenging or even impractical to use all parameters and variables to construct the regression equation. therefore, the stepwise approach is used to find the best arrangement of attributes. in this methodology, various parameters are utilized to build up the best linear relationship with the most significant estimation of 2 r by different condition variables. in this strategy, at first the magnitude of the correlation coefficient is determined between every independent and dependent variable. this is done to find which condition parameter can provide the greatest degree of correlation with the dependent parameter. this situation continues until the best second variable is established for the independent attributes. this procedure proceeds until the expansion of another condition parameter to the model negligibly affects 2 r . therefore the provided parameters are considered to be the most important defined parameters for volcanic rock classification in a linear regression equation that is developed in these steps. table v shows the results of the regression equations. the results show that the rs model has the highest 2 r . therefore, in the rs method the accuracy and precision of the approximations are better. table iii. discretized decision table no. condition attributes decision attribute a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12 a13 d sio2 tio2 al2o3 fe2o3 feo feo t mno mgo cao na2o k2o p2o5 h2o rock type 1 0 0 0 0 0 1 1 1 1 0 0 0 1 1 2 1 1 0 0 1 1 0 0 0 1 0 0 1 1 3 3 0 1 0 0 1 0 0 0 1 1 0 0 4 4 3 0 0 0 0 0 0 0 0 0 0 1 5 715 4 0 0 0 0 0 0 0 0 1 1 0 0 6 engineering, technology & applied science research vol. 10, no. 2, 2020, 5501-5504 5504 www.etasr.com shaaban & tawfik: classification of volcanic rocks based on rough set theory table iv. dokhan rock type decision rules rule no. condition attribute value decision attribute value certainty coverage a1 a3 a10 a11 1 0 ------1 1 0.75 2 1 0 ----1 1 0.25 3 1 --1 0 2 1 0.5 ---------------- table v. stepwise regression equations step parameters equation r 2 1 sio2 rock_type= -9.38+0.208a1 92.1% 2 k2o rock_type= -9.561+0.207a1+0.074a10 94.4% 3 na2o rock_type= -9.642+0.208a1+0.081a10+0.022a11 95.6% 4 al2o3 rock_type= -9.645+0.208a1+0.082a10+0.021a11+0.003a2 96.7% rough set result rock_type= -9.741+0.213a1+0.0913a10+0.023a11+0.001a3 96.85% vi. conclusions this study suggested a methodology for classifying volcanic rocks based on rough set theory. according to rough set theory, the factors that influence the classification of volcanic rocks were examined through reduced attributes and the four principal variables which influence the classification of volcanic rocks were silicon dioxide (sio2), titanium aluminum oxide (al2o3), sodium oxide (na2o) and potassium oxide (k2o). the implementation of this approach to volcanic rocks has shown that the method is realistic, workable and gives guidelines for future projects. in addition, the obtained results demonstrate that the proposed method reduces time and calculation cost. references [1] m. meschede, “a method of discriminating between different types of midocean ridge basalts and continental tholeiites with the nb-zr-y diagram”, chemical geology, vol. 56, no. 3-4, pp. 207-218, 1986 [2] m. j. le bas, a. l. streckeisen, “the iugs systematics of igneous rocks”, journal of the geological society, vol. 148, no. 5, pp. 825-833, 1991 [3] b. r. frost, c. d. frost, “a geochemical classification for feldspathic igneous rocks”, journal of petrology, vol. 49, no. 11, pp. 1955-1969, 2008 [4] f. tiecher, m. e. b. gomes, d. c. c. dal molin, “alkali-aggregate reaction: a study of the influence of the petrographic characteristics of volcanic rocks”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2399-2404, 2018 [5] z. wei, h. hu, h. w. zhou, a. lau, “characterizing rock facies using machine learning algorithm based on a convolutional neural network and data padding strategy”, pure and applied geophysics, vol. 176, no. 8, pp. 3593-3605, 2019 [6] g. cheng, j. yang, q. huang, y. liu, “rock image classification recognition based on probabilistic neural networks”, science technology and engineering, vol. 13, pp. 9231-9235, 2013 [7] g. cheng, w. guo, p. fan, “study on rock image classification based on convolution neural network”, journal of xi'an shiyou university (natural science edition), vol. 32, no. 4, pp. 116-122, 2017 [8] y. pu, d. b. apel, b. lingga, “rockburst prediction in kimberlite using decision tree with incomplete data”, journal of sustainable mining, vol. 17, pp. 158-165, 2018 [9] y. pu, d. b. apel, b. lingga, “regression analysis and neural network fitting of rock mass classification systems”, journal of science and engineering, vol. 20, no. 59, pp. 354-368, 2018 [10] r. w. le maitre, “a new approach to the classification of igneous rocks using the basalt-andesite-dacite-rhyolite suite as an example”, contributions to mineralogy and petrology, vol. 56, pp. 191-203, 1976 [11] t. miranda, l. r. sousa, a. t. gomes, j. tinoco, c. ferreira, “geomechanical characterization of volcanic rocks using empirical systems and data mining techniques”, journal of rock mechanics and geotechnical engineering, vol. 10, no. 1, pp. 138-150, 2018 [12] c. a. ozturk, e. nasuf , “strength classification of rock material based on textural properties”, tunnelling and underground space technology, vol. 37, pp. 45-54, 2013 [13] z. pawlak, rough sets: theoretical aspects of reasoning about data, kluwer academic publishers, 1991 [14] s. m. shaaban, “application rough set theory and decision network as a new approach to simplify airline hubs network location”, international journal of intelligent engineering and systems, vol. 9, no. 2, pp. 1-7, 2016 [15] s. m. shaaban, h. a. nabwey, “rehabilitation and reconstruction of asphalts pavement decision making based on rough set theory”, computational science and its applications–iccsa 2012, lecture notes in computer science, vol. 7334, pp. 316-330, springer, 2012 [16] w. m. a. w. ahmad, r. a. a. rohim, n. h. ismail, “forecasting parameter estimates: a modeling approach using exponential and linear regression”, engineering, technology & applied science research, vol. 8, no. 4, pp. 3162-3167, 2018 engineering, technology & applied science research vol. 8, no. 4, 2018, 3238-3242 3238 www.etasr.com zafar et al.: an iot based real-time environmental monitoring system using arduino and cloud service an iot based real-time environmental monitoring system using arduino and cloud service saima zafar department of electrical engineering national university of computer and emerging sciences, fast-nu, lahore campus, lahore, pakistan saima.zafar@nu.edu.pk ghosia miraj department of electrical engineering national university of computer and emerging sciences, fast-nu, lahore campus, lahore, pakistan ghosia.miraj25@gmail.com rajaa baloch department of electrical engineering national university of computer and emerging sciences fast-nu, lahore campus, lahore, pakistan rajaabaloch@gmail.com danish murtaza department of electrical engineering national university of computer and emerging sciences, fast-nu, lahore campus, lahore, pakistan danishmurtaza21@gmail.com khadija arshad department of electrical engineering national university of computer and emerging sciences, fast-nu, lahore campus, lahore, pakistan khadija.arshad62@gmail.com abstract—internet of things (iot) is expected to play a major role in our lives through pervasive systems of sensor networks encompassing our environment. these systems are designed to monitor vital physical phenomena generating data which can be transmitted and saved at cloud from where this information can be accessed through applications and further actions can be taken. this paper presents the implementation and results of an environmental monitoring system which employs sensors for temperature and humidity of the surrounding area. this data can be used to trigger short term actions such as remotely controlling heating or cooling devices or long term statistics. the sensed data is uploaded to cloud storage and an android application accesses the cloud and presents the results to the end users. the system employs arduino uno board, dht11 sensor, esp8266 wi-fi module, which transmits data to open iot api service thingspeak where it is analyzed and stored. an android application is developed which accesses the cloud and displays results for end users via rest api web service. the experimental results show the usefulness of the system. keywords-internet of things; cloud; mobile application; sensor network; environmental monitoring i. introduction internet of things (iot) is expected to revolutionize our world by enabling us to monitor and control vital phenomena in our environment through the use of devices capable of sensing, processing and wirelessly transmitting data to remote storage like cloud which stores, analyzes and presents this data in useful form. from the cloud this information can be accessed through various front end user interfaces such as web or mobile applications, depending upon suitability and requirements. internet lies at the heart of this transformation playing its role in efficient, reliable and swift communication of data from devices to the cloud and from the cloud to the end users. in this new paradigm, the concept of the typical end system or host in the internet is modified and hosts comprise of devices or things hence the name internet of things. the “things” are capable of sensing and transmitting data such as temperature, pressure, humidity, noise, pollution, object detection, patient vitals etc. environmental monitoring is an important iot application which involves monitoring the surrounding environment and reporting this data for effective short term measures such as remotely controlling the heating or cooling devices and long term data analyses and measures. this paper presents the implementation details and results of an environmental monitoring system. the system comprises of a central arduino uno board which interfaces at the input with temperature and humidity monitoring sensor dht11 and at the output with esp8266 wi-fi module which transmits the sensed data through internet to a remote cloud storage open iot api thingspeak. through thingspeak, matlab analytics are carried out on data and trigger is generated. a mobile application is developed based on android operating system and data is retrieved from thingspeak for user display from anywhere in the world. the developed is a low cost system which gives insight into the design and implementation of a complete iot application involving all aspects from sensing and wireless transmission to cloud storage and data retrieval from cloud via a mobile application. it involves comprehensive study and deployment of arduino development board, its interfacing with input and output modules such as sensors and wi-fi module, the usage of thingspeak open source api and finally the development of a mobile application based on the android operating system. the results of the project show the real-time monitoring of temperature and humidity levels from any location in the world and its statistical analysis. this system engineering, technology & applied science research vol. 8, no. 4, 2018, 3238-3242 3239 www.etasr.com zafar et al.: an iot based real-time environmental monitoring system using arduino and cloud service can be extended to enable remote controlling of appliances based on sensed data. ii. related work lately, iot has emerged as an area which has gained immense interest of both venture capitalists and tech giants, resulting in a plethora of research activities and business initiatives. some of the applications which have garnered attention include smart grid, smart city, smart wearable devices and smart home. almost all of the various iot applications involve some kind of sensors and transducers normally attached to a microcontroller along with wired or wireless transmission to either a local database or a remote cloud which transforms raw data into useful information which can be effectively utilized. the research and development activities comprise techniques of fabrication of smart objects or devices, suitable wireless technologies, development boards, designing network protocols, applications and much more. in the context of our project, we explored recent work accomplished in the development of useful and interesting applications using low cost development boards such as raspberry pi and arduino. some of the popular applications developed using these boards include home automation, patient monitoring systems and weather and environmental monitoring systems. in [1], temperature, humidity, light intensity, gas leakage, sea level and rain intensity are measured and the data are sent wirelessly to thingspeak using arduino uno. this work focuses considerably on matlab visualization and analysis. authors in [2] monitored and controlled environmental conditions like temperature, relative humidity, light intensity and co2 level using sensors and lpc2148 microcontroller. the data was sent to thingspeak cloud. in comparison with lpc2148, arduino uno used in our system is simple, low cost and less complex for a simple application. authors in [3] present an iot based real-time weather monitoring system using raspberry pi which is complex compared to arduino due to python language and raspbian operating system. an arduino based weather monitoring system is developed and presented in [4]. authors imported data from multiple sensors to excel which is cumbersome when compared to thingspeak. authors in [5] designed and developed a wireless sensor network system for environmental monitoring using raspberry pi and arduino. they employed xbee module to implement the ieee 802.15.4 standard for data collection from multiple sensor nodes at a base station (raspberry pi). their system can be extended to suit large scale applications, however in the present form, the system lacks cloud connectivity. iii. hardware design the central unit is a microcontroller (arduino uno), and acts as the main processing unit for the entire system, it interfaces with the sensor chip at the input for receiving temperature and humidity readings and interfaces with the wi-fi module at the output to send the received data to the cloud over the internet. the microcontroller polls the sensor to retrieve data and sends it over the internet to thingspeak cloud for analysis. a. microcontroller the central hardware component of our system is the microcontroller which interfaces with other components of the system. since the system comprises of temperature and humidity monitoring for which a single sensor interface is required and no local storage of data therefore we selected arduino uno microcontroller which serves our purpose well due to its simplicity, robustness and low cost [6]. figure 1 shows a picture of arduino uno microcontroller used in our system [6]. this microcontroller board is based on the atmega328p. it has 14 digital input/output pins, 6 analog input pins, a usb connection, 16 mhz quartz crystal, a power jack, and a reset button. it can be powered with a battery. it is programmable with the arduino ide (integrated development environment) via a type b usb cable fig. 1. arduino uno microcontroller board b. sensors we selected temperature and humidity for environmental monitoring and prefered a single sensor with both sensing capabilities instead of separate sensors for each parameter. for this reason, we selected dht11 composite sensor chip which gives readings for both temperature and humidity at the same time, it has high reliability and excellent long-term stability. it has small dimensions, low cost, good quality, fast response, strong anti-interference ability, digital signal output, and precise calibration. it can be easily interfaced with arduino uno board with the help of dht library and connecting wires. figure 2 shows a picture of the dht composite sensor which we used in our system. it has temperature range from 0 to 50°c and humidity range from 20 to 90%rh. it has signal transmission range of 20m. to interface it with arduino uno, we connected the ground and vcc of the dht11 sensor with the ground and 5v of the arduino. then we connect the data pin of the dht11 to the pin 2 of the arduino. then we installed the dht library and run the code for getting it started. c. wifi module in order to upload sensor readings from dht11 to the open source cloud thingspeak, arduino uno interfaces at the output with wifi module esp8266 (figure 3). it is a low cost wifi microchip with full tcp/ip stack. it works on the 3.3v that is provided by arduino uno in our system. the module is configured through at commands and needs the engineering, technology & applied science research vol. 8, no. 4, 2018, 3238-3242 3240 www.etasr.com zafar et al.: an iot based real-time environmental monitoring system using arduino and cloud service required sequence to be used as a client. the module can work as both client and server. it gets an ip on being connected to wifi through which the module and then communicates over the internet. after testing our esp8266 module, we connected it with arduino uno and then programmed arduino uno to configure esp8266 wifi module as tcp client and send data to thingspeak server which is an open iot platform to visualize and analyze live data from sensors. fig. 2. dht11 composite sensor for temperature and humidity fig. 3. esp8266 wifi module d. hardware block diagram figure 4 shows the hardware block diagram for our system. the figure shows the flow of the system functionality where dht11 gives live readings of temperature and humidity simultaneously to the microcontroller which sends these reading through the wi-fi module over the internet to the thingspeak cloud. fig. 4. hardware block diagram for the environmental monitoring system iv. software implementation software plays an important role in the integration and working of our hardware design. there are two parts to our software development: initialization and configuration of hardware, and the development of android based mobile application for user interface. a. software for initialization and configuration of hardware arduino ide was used to program the microcontroller for data retrieval from sensor and data transmission to the cloud. after testing the hardware components individually, we integrated them. first of all, the wi-fi shield was initialized by sending at commands in the required pattern to make it work as a client. after the initialization, we configured the wi-fi module esp8266 as a tcp/ip client. finally we wrote software for reading the sensor data from dht11 which simultaneously provides both temperature and humidity readings in real-time. once sensor data is read by the microcontroller and uploaded to the cloud, we use the iot analytics service of thingspeak to aggregate, visualize and analyze live data streams. thingspeak provides instant visualizations of the real-time data uploaded by our system [7]. the wi-fi module sends data to the cloud through its assigned ip. once connected to thingspeak, an api key is assigned to observe the results over a channel. therefore we wrote the api key before writing the actual data, and then the data was stored and displayed in the appropriate channel. b. android application we designed the android application using the google app-inventor integrated development environment (ide) and java programming language [8]. the android application communicates with the microcontroller through thingspeak cloud. using the rest api request methods such as get, post, put, and delete, we can create a channel and update its feed, update an existing channel, clear a channel feed, and delete a channel. we sent a java script object notation (json) get request to thingspeak by using rest api web service and channel id and field number within its parameters. we received the response from thingspeak in json format and populated the tables in the android application by using json parser. the end users run the android application and it allows them to monitor the real-time temperature and humidity readings for the monitored area e.g. a room. the user authentication interface is shown in figure 5. our application is efficient, flexible with a user friendly graphic user interface (gui). the user authentication feature of the application verifies the authorized users through login and password. after authentication, the user views the results in tabular form from the cloud which are shown in the next section. fig. 5. user authentication interface for android application v. experimental results the complete design of our environmental monitoring system is shown in figure 4. the implemented design is shown in figure 6 which shows the integration of all engineering, technology & applied science research vol. 8, no. 4, 2018, 3238-3242 3241 www.etasr.com zafar et al.: an iot based real-time environmental monitoring system using arduino and cloud service hardware components in working conditions. dht11 and esp8266 are connected to arduino uno. dht11 and thingspeak are interfaced using the arduino ide. the android application connects with thingspeak and displays the sensed data. table i shows the details of the system hardware, cloud and display. fig. 6. hardware implementation of system design table i. system component details system component details sensor dht11 connectivity wi-fi esp8266 microcontroller arduino uno cloud thingspeak user interface android application this section presents the experimental results of our system. we show the sensor data available to the mobile user through the mobile application and the graphical record of temperature and humidity monitoring. a. application user interface after the authentication phase in which the user enters login and password, the user logs in to the application to view the monitored data. figure 7 shows the gui of the android application which shows the data logging that is a view of the temperature and humidity record. fig. 7. temperature and humidity monitoring through the android application b. graphical record of temperature monitoring figure 8 shows the record of temperature monitoring over a period of time. the graph is temperature vs. time where the temperature changes are updated after an interval of 15 seconds. in order to accurately test our system, we varied the temperature around the sensor artificially by a lighting system, thus a spike can be viewed in the graph after which the temperature readings settle to average environmental temperature. fig. 8. record of temperature monitoring figure 9 shows the record of humidity monitoring over a period of time. the graph is humidity vs. time where the changes in humidity are updated after an interval of 15 seconds. similar to temperature monitoring, we varied the temperature around sensor artificially by a lighting system, the downward spike in humidity can be viewed in the graph after which the humidity readings settle to average environmental humidity. fig. 9. record of humidity monitoring c. temperature vs humidity figure 10 shows a graph of humidity versus temperature. as expected, temperature and humidity are inversely related to each other. the graph shows that the humidity level decreases with the increase in temperature. fig. 10. humidity versus temperature engineering, technology & applied science research vol. 8, no. 4, 2018, 3238-3242 3242 www.etasr.com zafar et al.: an iot based real-time environmental monitoring system using arduino and cloud service vi. conclusion this paper presents an environmental monitoring system for real-time monitoring of temperature and humidity of surrounding environment. the sensed data is sent through wi-fi to the cloud where both real-time data and its graphical analyses can be viewed. an android application is developed for the end user who can monitor the environment of the area where the hardware is deployed using a smart phone. this system can be extended to implement a home automation system where the monitored values of temperature and humidity can be used to trigger some action and control the devices for heating or cooling via the mobile application. this system is a crucial step in understanding the iot applications development and implementation and serves as a building block for a number of useful innovations in this direction. references [1] s. pasha, “thingspeak based sensing and monitoring system”, international journal of new technology and research, vol. 2, no. 6, pp. 19-23, 2016 [2] k. s. s. ram, a. n. p. s. gupta, “iot based data logger system for weather monitoring using wireless sensor networks”, international journal of engineering trends and technology, vol. 32, no. 2, pp. 71-75, 2016 [3] s. d. shewale, s. n. gaikwad, “an iot based real-time weather monitoring system using raspberry pi”, international journal of advanced research in electrical, electronics and instrumentation engineering”, vol. 6, no. 6, pp. 4242-4249, 2017 [4] r. ayyappadas, a. k. kavitha, s. m. praveena, r. m. s. parvathi, “design and implementation of weather monitoring system using wireless communication”, vol. 5, no. 5, pp. 1-7, 2017 [5] s. ferdoush, x. li, “wireless sensor network system design using raspberry pi and arduino for environmental monitoring application”, procedia computer science, vol. 34, pp. 103-110, 2014 [6] arduino, arduino uno rev 3 overview, available at: https://store.arduino.cc/arduino-uno-rev3 [7] https://thingspeak.com [8] https://developer.android.com microsoft word 39-3560_s1_etasr_v10_n3_pp5819-5823 engineering, technology & applied science research vol. 10, no. 3, 2020, 5819-5823 5819 www.etasr.com ganthia et al.: shunt connected facts devices for lvrt capability enhancement in wecs shunt connected facts devices for lvrt capability enhancement in wecs bibhu prasad ganthia school of electrical engineering kalinga institute of industrial technology bhubaneswar, india jb.bibhu@gmail.com subrat kumar barik school of electrical engineering kalinga institute of industrial technology bhubaneswar, india skbarikfel@kiit.ac.in byamakesh nayak school of electrical engineering kalinga institute of industrial technology bhubaneswar, india bknayakfel@kiit.ac.in abstract—when a double fed induction generator (dfig) primarily based type-iii wind turbine (wt) is connected to the grid without a digital power interface, the terminal voltage or reactive electricity output can’t be managed accordingly. many techniques have been developed to overcome the issue of low voltage due to faults. this paper tries to define such active methods by presenting a complete analysis of lvrt strategies for dfig-based wind energy conversion systems (wecs) in terms of overall adaptive performance, operation complexity of controllers, and cost-effectiveness. this paper aims to highlight the methods of increasing the ability of lvrt relying on the configuration of the relationship into 3 major areas according to its grid integrations. shunt connections of facts devices are used in wecs to study their effectiveness and benefits. the system models are simulated in matlab/simulink and the results are discussed. keywords-lvrt; dfig; type iii wt; facts; wecs i. introduction wind turbines (wts) are focusing on power system stability using grid integration to enhance power quality during faults [1]. however, grid integration of large wts can cause serious side effects in poor or weak grids. the inclination towards more wt integration caused by the need to deal with the present degree of unbalancing and to reduce voltage over the wind generator system can prompt fault clearances of the wt. many power system techniques alter their correspondence prerequisites for wind farms by different specialized models, known as grid codes. one of the significant necessities with respect to grid voltage control is the capacity of low voltage ride through (lvrt) [1]. depending on this principle, the wt must be connected to the grid when the voltage is above a certain threshold. wts can be disconnected from the grid only when the normal voltage profile is dropped close to the lvrt requirements and power must be injected to protect the voltage of the energy devices [2]. ii. wind energy conversion systems previously, only fixed speed wt (type i) and variable speed wt (type ii) systems were implemented on wecs for the study of lvrt. this paper studies the type iii wt system with variable speed operation and facts devices for low voltage sag improvement. the wecs model contains three key differentiators, i.e. the aerodynamic core, the mechanical system, and the electrical system of a type iii wt as can be seen in [2]. the electrical component of wecs can similarly be divided into 3 main co-systems, namely the utility grid, the power electronics converters (pecs), and the type-iii wind turbine generators (wtgs) [3]. the captured aerodynamic power of the wind turbine is: pwt= ½ ρπr 2 v 3 (1) where ρ is the air density [kg/m 3 ], v defines the wind speed [m/s], r is the blade radius [m], and pwt is the power. the mechanical power that a turbine can extract depends on power coefficient cp, and can be given by [1]: pmec= cppwt= ½ cpρπr 2 v 3 (2) from (1) and (2) it is obvious that the energy generated increases with blade area, wind speed, air density, and power coefficient [4]. iii. double fed induction generator another concept is a wind turbine with dfig, where the rotor winding feeds in a back to back source voltage converter [3, 12]. due to the disparity in rotor and generator speed phases, a gearbox is critical to couple the rotor to the generator much as the previous case. the dfig stator winding to the network and the rotor winding is coupled to the rotor side converter (rsc) [5]. the opposite side of the consecutive voltage source converter is then coupled to the system’s grid side converter (gsc) that takes care of the rotor winding. a dc connection is linked to the rsc and gsc decoupling frames [8]. iv. lvrt methods lvrt is the capability of generators to stay connected to the grid during short periods of low voltage. facts devices, are generally power electronic based systems that provide control of one or more ac transmission system parameters to enhance controllability and increase power transfer capability [13]. lvrt methodologies associated with wind energy systems are classified into series, shunt, and hybrid. in this paper, shunt connections will be investigated. the studied corresponding author: bibhu prasad ganthia engineering, technology & applied science research vol. 10, no. 3, 2020, 5819-5823 5820 www.etasr.com ganthia et al.: shunt connected facts devices for lvrt capability enhancement in wecs shunt connected facts devices are: static var compensator (svc), static synchronous compensator (statcom) and superconducting dynamic synchronous condenser (sdsc) (figure 1). these shunt connected solutions are discussed and comparisons based on their implementation are made [1]. fig. 1. classified lvrt capability enhancement methods (shunt) a. static var compensator (svc) thyristor controlled svcs have been introduced for voltage stabilization of critical loads during faults, reactive power compensation on demand, and transient stability enhancement in electrical power transmission systems. the svc is a hybrid connected thyristor controlled reactor (tcr) coupled with a thyristor switched condenser or msc which is a compensator unit effectively connected to the wt's pcc bus to provide effective voltage control and lvrt induction generator [4]. b. static synchronous compensator (statcom) statcoms can act either as sources or sinks of reactive power. they are most used to enhance grids with poor power factor, but stabilizing voltage is one of their uses. statcom’s most significant feature is its modular type voltage source converter (vsc), which is fitted with insulated bipolar gate transistors (igbts) operated by pulse width modulation (pwm) [1]. c. superconducting dynamic synchronous condenser (sdsc) sdscs are generally used to enhance system stability and maintain system voltage under contingencies. the active part of an sdsc can be seen in [2]. the sdsc is connected with hts wires entailed in rotor windings [1, 10]. facts sdscs are capable of working for a prolonged period at very high current, enabling the system to surplus the reactive power up to 3 times the rated capacity during every transient low voltage instance. by providing voltage control and increasing the reliability of a power grid, sdscs as a facts tool helps a we system fulfill the grid-tie structure [9, 11]. v. steady state analysis the wt harvests power from the air and changes it into mechanical and consequently electrical energy [9]. in steady state, under high speed wind variations, the power provided by wt can surpass its rated parameters. the aerodynamics of the accelerated wt control are categorized in uninvolved slow down, active slow down, and pitch control mechanisms intended for low, medium, and enormous wts [5, 7]. vi. transient state analysis when a fault occurs at the wt, it lessens the power yield from the electromagnetic torque and induction generator [8]. the mechanical torque stays steady during the fault, which makes the rotor's speed fall below its well-being limit [6]. vii. matlab/simulink model the three shunt connection types were designed and simulated in simulink. figure 2 shows the svc action in reactive power control during faults. figure 3 is associated with the statcom action and figure 4 highlights the use of a sdsc device connected in series with the system. fig. 2. svc in a wind driven grid integrated system fig. 3. wind turbine system using statcom fig. 4. wind driven induction generator using sdsc viii. results and performance comparison the results of the designed and simulated systems in simulink are shown in figure 5 which highlights the control action of the shunt connected facts devices. the simulink results depict: i) grid voltage, ii) electromagnetic torque, iii) stator flux, iv) active and reactive power, v) stator current, vi) rotor current, and vii) dc link voltage. the comparisons are made on the basic action of all shunt connected devices under transients and fault clearance. engineering, technology & applied science research vol. 10, no. 3, 2020, 5819-5823 5821 www.etasr.com ganthia et al.: shunt connected facts devices for lvrt capability enhancement in wecs fig. 5. dfig type-iii wts: (a) svc, (b) statcom, (c) sdsc table i. shunt-lvrt capability enhancement methods summary method conclusion limitation summary svc can control reactive power stable system under fault control over voltage sag and swell depends on the control actions of voltage unstable under heavy faults needs more reactive power for normal operation during faults statcom can control reactive power responsive towards faults reduction in sequence voltage a protective system is highly needed only operating on reactive power faster response towards fault clearance and transient action sdsc high performance under high pu less switching losses low voltage operation causes more instability calibrations required high reactive power is needed for swell and sag operations ix. analogy of enhancement and functional approaches for wecs table i summarizes the effectiveness results of the facts devices. the control action of statcom is faster compared to the other devices, while the reactive power can efficiently be controlled by all of them. it is concluded that the statcom is better than the other devices in operation quality, it is more sensitive to faults, more stable, and with faster response. its basic construction is simple and can be implemented in simple grid integration as well as in high voltage transmission lines. with the application of svc, the fault can be compensated in 14.2ms, whereas while using statcom it is compensated in 13.10ms which is better response than that of type ii wts. the sdscs fault clearance time is higher than the svc’s [4, 10]. the grid voltage is reduced by 5% due to the transients which can be compensated by the facts devices: 330v by svc, 600v by statcom, and 450v by sdsc. in [10] about 7% of power improvement was reported. using type iii wts, better control action for transient analysis and voltage compensations can be used for the voltage sags. in future work, the hybrid connected facts devices can be used for better response study. figure 6 shows the proposed model utilizing dfig and figure 7 shows the control action of series connected facts devices with different wind speeds on stator active power and reactive power. both steady state and transient state analysis are done in order to identify the optimum control action and its exact settling time after fault clearance. using these facts devices it is found that the settling time for the faults due to wind variations can be reduced up to 10%-20%. it is clear that the type iii wt is weak for the heavy wind speed variation which causes voltage sags of 450v. the stator active power gets settled at 14s for svc, 7s for sdsc, and 5s for statcom. the steady state and transient state performances were found to be more effective in statcom at 4s. table ii highlights the control action over faults with various wind speeds and different settling times after fault clearance. it can be concluded that control action on type iii wt statcom system is faster up to 13.7ms at 12m/sec wind speed. the svc and the sdsc are little slower at 15.2ms and 14.4ms respectively. (a) (b) (c) engineering, technology & applied science research vol. 10, no. 3, 2020, 5819-5823 5822 www.etasr.com ganthia et al.: shunt connected facts devices for lvrt capability enhancement in wecs fig. 6. proposed facts device connected wecs model fig. 7. dfig transient analysis using svc, sdsc, and statcom table ii. lvtr capability settling times (msec) controller svc sdsc statcom wind speed 8m/s 14.1 13.5 12.2 wind speed 12m/s 15.2 14.4 13.7 remark slow medium fast x. conclusion this paper examined the activity of facts devices and the advancements for lvrt ability improvement of type iii wts dependent on dfig with wts, which is generally another idea in keeping up the voltage profile of the wind power generation. three control approaches of shunt connected arrangements examining the lvrt action due to the variations in wind speed engineering, technology & applied science research vol. 10, no. 3, 2020, 5819-5823 5823 www.etasr.com ganthia et al.: shunt connected facts devices for lvrt capability enhancement in wecs which causes voltage sag critically were examined. facts devices connected in parallel to the grid were used, which can compensate the voltage during faults or transients due to variations of wind speed. the examination of these lvrt strategies for smooth performance, faster controller action, less cost and augmented application reliability are summarized in tables i and ii. the comparison on simulated lvrt methods concluded that statcom shunt connected facts device is most effective and reliable in lvrt capability enhancement as the voltage compensation is up to 35% more of other shunt devices and with faster settling time. svc and sdsc exhibited slower performance. this operation on wind energy system enables the use of type iii wt applications for grid integration and maintains power system stability. it is concluded that auxiliary devices are useful for the lvrt study, hence in future the hybrid connected facts devices can be implemented using type iii and fully controlled type iv wts for lvrt enhancement. references [1] a. moghadasi, a. sarwat, j. m. guerrero, “a comprehensive review of low-voltage-ride-through methods for fixed-speed wind power generators”, renewable & sustainable energy reviews, vol. 55, pp. 823–839, 2016 [2] s. l. s. louarem, d. e. c. belkhiat, t. bouktir, s. belkhiat, “an efficient active and reactive power control of dfig for a wind power generator”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4775-4782, 2019 [3] m. sedighizadeh, a. rezazadeh, m. parayandeh, “comparison of svc and statcom impacts on wind farm stability connected to power system”, international journal of engineering and applied sciences, vol. 2, no. 2, pp. 13-22, 2010 [4] t. y. liu, p. j. tavner, y. feng, y. n. qiu, “review of recent offshore wind power developments in china”, wind energy, vol. 16, no. 5, pp. 786-803, 2013 [5] s. m. muyeen, r. takahashi, t. murata, j. a. tamura, “variable speed wind turbine control strategy to meet wind farm grid code requirements”, ieee transactions on power systems, vol. 25, no. 1, pp. 331-340, 2010 [6] a. e. leon, j. m. mauricio, a. gomez, j. a. solsona, “an improved control strategy for hybrid wind farms”, ieee transactions on sustainable energy, vol. 1, no. 3, pp. 131-141, 2010 [7] m. h. syed, h. h. zeineldin, m. s. el moursi, “hybrid micro-grid operation characterization based on stability and adherence to grid codes”, iet generation transmission & distribution, vol. 8, no. 3, pp. 563–572, 2014 [8] p. d. chung, “voltage enhancement on dfig based wind farm terminal during grid faults”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4783-4788, 2019 [9] b. p. ganthia, v. agarwal, k. rout, m. k. pardhe, “optimal control study in dfig based wind energy conversion system using pi & ga”, international conference on power and embedded drive control, chennai, india, march 16-18, 2017 [10] s. n. mohammad, n. k. das, s. a. roy, “review of the state of the art of generators and power electronics for wind energy conversion systems”, 3rd international conference on the developments in renewable energy technology, dhaka, bangladesh, may 29-31, 2014 [11] w. qiuwei, x. zhao, j. ostergaard, “grid integration issues for large scale wind power plants (wpps)”, ieee pes general meeting, providence, usa, july 25-29, 2010 [12] irena, renewable energy technologies: cost analysis series, vol. 1: power sector, no. 5, wind power, irena, 2012 [13] ieee, “proposed terms and definitions for flexible ac transmission system (facts)”, ieee transactions on power delivery, vol. 12, no. 4, pp. 1848–1853, 1997 engineering, technology & applied science research vol. 8, no. 3, 2018, 2991-2997 2991 www.etasr.com jamalian and foukerdi: a hybrid data mining method for customer churn prediction a hybrid data mining method for customer churn prediction elham jamalian faculty of technology and information department of information technology university of qom qom, iran rahim foukerdi faculty of management department of industrial management university of qom qom, iran abstract—the expenses for attracting new customers are much higher compared to the ones needed to maintain old customers due to the increasing competition and business saturation. so customer retention is one of the leading factors in companies’ marketing. customer retention requires a churn management, and an effective management requires an exact and effective model for churn prediction. a variety of techniques and methodologies have been used for churn prediction, such as logistic regression, neural networks, genetic algorithm, decision tree etc.. in this article, a hybrid method is presented that predicts customers churn more accurately, using data fusion and feature extraction techniques. after data preparation and feature selection, two algorithms, lolimot and c5.0, were trained with different size of features and performed on test data. then the outputs of the individual classifiers were combined with weighted voting. the results of applying this method on real data of a telecommunication company proved the effectiveness of the method. keywords-customer churn; data mining; hybrid method; lolimot; c5.0; weighted voting i. introduction the way companies communicate with their customers has become a key point for competition in marketing. concepts such as customer acquisition, maintenance and satisfaction are internalized in companies. according to studies, the expenses for attracting a new customer are 5-10 times more than maintaining an old one [1]. on the other hand, customer maintenance has its own expenses and it’s not possible to have these expenses for all customers, because not all customers worth maintaining. thus, churn management systems are looking for customers that want to leave the company. the key point which shows the importance of churn management systems is that, studies show that a 5% increase in customer retention will have a 25% to 95% benefit increase for companies [2]. a lot of studies have been carried out in churn management, and different methods for recognizing downfall reasons and churn prediction and prevention have been used. among these, data analysis methods have been used widely. customer churn is a situation in which customers decide to leave the company. the meaning of churn is different in different areas [3-5]. most definitions keep the related behaviors with a product and a defined threshold with business rules in mind. when customer’s transaction is less than the threshold, churn occurs [6]. authors in [7], defined customer churn, in banking field, as those customers who close their accounts. authors in [6] define churn as those who have less than 2500 euro (save, and all other kind of properties) in banks. technically according to (1) churn is the customer loss in a defined time period. monthly churn=(c0+a1-c1)/c0 (1) here c0 means the number of customers at the beginning of the period, c1 is the number of customers at the end of the period and a1 is the number of new customers in the period. generally, customer churn prediction is a binary classification that its outcome shows the probability of customer churn [10, 11]. however, the special nature of the churn prediction problem causes analysis algorithms to face some limitations. for example, in these problems, data are imbalanced. this means that lost customers are just a small part of the data. in addition, extended learning programs will face some kinds of noise. in any case, churn prediction needs to classify customers according to the probability of churn [12]. different approaches work on this problem and they have some defects themselves. for example, although algorithms based on decision trees are used for classification, it is possible that some leaves have the same class probability. in addition, this method is noise sensitive. neural networks are looking for suboptimal solutions and when the number of parameters of models increases an overfitting happen. although genetic algorithms present accurate prediction models, they can’t make the probability of occurrence clear. and finally methods like support vector machines usually don’t lead to the best results. in table i, a summary of the above mentioned methods and their characteristics is shown. in this study, using data fusion and feature extraction techniques, a hybrid method is presented for a more accurate prediction of customer churn. after data preparation and feature selection, two algorithms, lolimot and c5.0, are trained with different size of features and the outputs of individual classifiers are combined with weighted voting. engineering, technology & applied science research vol. 8, no. 3, 2018, 2991-2997 2992 www.etasr.com jamalian and foukerdi: a hybrid data mining method for customer churn prediction table i. churn prediction models review reference goal applied techniques data, customer numbers, features numbers metrics sampling feature selection [13] explanation and application of modeling systems for automatic prediction of mobile service providers neural network telecommunication, 500000 customers, 200 features, (1) lift under sampling forward feature selection with decision tree and genetic algorithm [14] making churn prediction model by c4.5 algorithm with limited numbers of features c4.5 decision tree telecommunication, 114000 customers, 12 features, (1) lift, false positive rate, decision error oversampli ng visible [15] using a new data mining method for churn prediction c4.5 decision tree, neural network, datamining by evolutionary learning telecommunication, 100000 customers, 251 features, (1) top 5 lift, under sampling visible [16] churn prediction as a part of customer life value model (clv) logistic regression, decision tree, neural network telecommunication, 16384 customers, 200 features, (2) error rate, lift r2 method [17] studying variables and modeling methods for customer churn prediction logistic regression, linear regression, random forest, regression forests financial services, 100000 customers, 30 features, (1) auc [18] the comparative and functional study of customer churn prediction logistic regression, decision tree, applying neural network on clustered parts telecommunication, 160000 customers, 40 features, (1) hit rate, top decline lift oversampli ng visible and eda [10] improving and developing churn prediction models and testing them on real customer retention campaigns logistic regression(with markof chain), random forests pay-tv, 143198 customers, 81 features, (1) accuracy, lift, auc [19] using of support vector machine for churn prediction for newspaper subscribers logistic regression, support vector machine (svm), random forests newspaper subscribers, 90000 customers, 82 features, (1) accuracy, lift, auc under sampling [20] improving accuracy of churn prediction by combining the cost sensitive random weighted forests and oversampling of random forests improved balanced random forests (ibrf) chinese bank, 20000 customers, 27 features, (1) accuracy, top decline lift increasing the best features selection increasingly [21] customers churn behavior analysis for predicting churn and developing retention strategies decision tree, neural network, c4.5, logit, pls, nave bays telecommunication, 100000 customers, 171 features, (2) hit rate feature selection with pls and by use of vip scores [22] presenting a framework for churn prediction in electronic commerce area neural network, decision tree, svm, extended svm chinese e-commerce website, 50000 customers, 27 features, (1) accuracy, hit rate, cover rate, lift [23] direct usage of behavior data in prediction model without converting them to static data by using hierarchical model hierarchical multi kernel svm (hmksvm) telecommunication and food shop database, 6338842 customers, 47-79 features, (2) (1) private data, (2) public data ii. proposed model due to the fact that combining individual algorithms usually leads to better and more accurate predictions, in this study a hybrid method for customer churn prediction is suggested. generally three factors should be kept in mind when combining algorithms: (1) training set creation, (2) selection of individual algorithms that must be combined and (3) method or rules that results are combined. the suggested model for churn prediction includes the following steps: a. data preparation information needed for data mining models includes demographic data like living location, age, gender, number of children, salary, other financial data and bills and data related to customer usage [14]. there is no need for customers’ personal information such as name, email address, mailbox, father’s name, etc. and they can be deleted from the database in this stage. also missing data can be omitted or replaced with special amounts like average or predicted amount resulted from predicting techniques etc. engineering, technology & applied science research vol. 8, no. 3, 2018, 2991-2997 2993 www.etasr.com jamalian and foukerdi: a hybrid data mining method for customer churn prediction b. features selection or extraction and ordering this step is important because it uses important features and omits extra and noisy features and those which have little information helping to data cleansing and dimension reduction [8]. in this study principal component analysis (pca) is used for this purpose. in this step, the goal is achieve to a set of features which are the most effective in prediction by the use of pca. fk is the k th ordered feature that: 1 2 nf f ... f (2) c. constructing subsets of data according to the extracted features and training model(s): regarding to the literature and strengthened c5.0 and lolimot high performance [26], these models are used as individuals and by using weighted voting their accuracy is improved. 1) c5.0 algorithm c5.0 decision tree is a classification tree. c5.0 algorithm is an improved form of id3 algorithm that constructs the decision tree based on information theory. training data are classified sets of samples in the form of s= s1, s2,…. each sample is a vector of features s1= x1, x2,… training data include the vector that shows the class that each set belongs to, c= c1, c2,… in each tree node the feature which makes the best classification is selected in order to put the sample set in related classes. this classification is done by computing entropy (information gain). in this case the feature that has the highest information gain will be selected as decision maker. 2) boosting algorithm boosting algorithm is an ensemble method that trains a set of classification models [27]. it is the case when each train set is created based on the accuracy of previous classification models. in this algorithm, new classification methods are constructed to predict the samples, in which classification accuracy was weak, more accurately. this process is done by adaptive resampling. this means that samples that were classified incorrectly will have more chance to be selected in the next step. each sample has a weight and at the end of the classification these weights will be up to date. finally, the result of different methods will be ensembled with voting. strengthening can increase the accuracy of c5.0 algorithm but it needs more time for training. 3) lolimot algorithm linear tree model or lolimot is based on the divide and conquer strategy. in this method the complicated problem is solved by dividing to several smaller problems [9]. lolimot algorithm for achieving a better outcome (outcome with smaller error) will divide the problem area to several local linear models (llms). and after finding the worst llm, continues the algorithm by dividing it to two llms. this algorithm is used as a fast learning tree algorithm, in many pattern recognition and prediction problems and it has some remarkable results. lolimot algorithm was first introduced in locally linear neuro fuzzy model [28]. dividing the incoming area to small linear subsets by using fuzzy activation functions is the basic strategy in these networks. in locally linear neuro fuzzy model, the neural network has one hidden layer. but computing operation in its neurons is much more complex than that of a regular neuron. in this network, there are (p+1)*m weights (m is the number of neurons and p is the number of inputs). in (3) and (4) the matrix of weights and inputs can be seen. each neuron has a llm and a validity function. validity function will indicate validity area in the llm. validity function is also known as activation function, because it controls the actions of locally linear models.    0 1 p[ , , ..., ]ω (3)  t1 2 p[u ,u ,...,u ]u (4) it is clear that the first output is achieved by (5). it is the output of llm of the thi neuron.        i i0 i1 i1 ip ipy u ... u (5) activation function can be computed by using (6) and (7).      ii m ii 1 ( )( ) ( ) uu u (6)                      22 p ip1 i1i 2 2i1 ip (u c )(u c )( ) exp ... exp2 2u (7) where i( )u is a gaussian function which has two parameters, center ijc and standard deviation ij .      m i ii 1y y ( )u (8)     (sub) (sub) sub1 2 m, , ...,x x x x (9)                          1 p(s 1 p ub)i 1              1 u (1) u (1) u (n     ) u (n)   x (10) in lolimot, two parameters, center and standard deviation, are considered to be fixed and the weights are calculated by the least squares function. with the assumption that having m neurons and n train vector, regression matrix and train vector output can be defined as (7), (8) and (9). the output vector for train data, is considered as:     i i i iy [y (1),y (2),...,y (n)] (11) engineering, technology & applied science research vol. 8, no. 3, 2018, 2991-2997 2994 www.etasr.com jamalian and foukerdi: a hybrid data mining method for customer churn prediction and, finally, the network output is calculated by (12).  y xω (12) now, by considering a target function (13) through changing the weights, we try to minimize the error.    n 2 j 1i e (j) min (13) that,   y(je(j) y) (j) lolimot algorithm starts the training process by starting from one neuron or a specified numbers of neurons and the following three stages are done repeatedly:  the worst neuron with highest error is recognized by (14).    n 2i ii 1i e (j) ( (j))u (14)  all cases in which this neuron can be divided in one of its dimensions are considered and the case that has the least error is selected.  the worst neuron is recomputed. after selecting suitable data mining algorithms, subsets of training data are constructed based on feature sets and the proposed models train and test on each of these train sets. models are evaluated and cleaned according to their accuracy. 4) combining outputs of classifiers in this phase, the outputs of the remained classifiers from the previous step will ensemble with one of the voting algorithms that will be explained below. the simplest method to combine classifiers is majority voting which gathers all outputs of individual classifiers c1, c2, …, cn and then the output with the largest number of votes is selected as the final decision.  i ict argmaxcount (v(c )) (15) where v(ci) is the vote of ith classifier. the other voting method is the weighted voting, that is improved but more complicated version of majority voting. in this strategy, each classifier is assigned a weight according to its classification performance. in this case, the weights can be obtained by the following formula [29].     ii 1w (1 ).( )n 2 (16) where wi is the weight of ith ordered classifier in which the classifiers are arranged based on their accuracy performance,  is a regulatory parameter 0<α<1 and  n i1 w 1∑ w ≈ 1. then, the voting output will become:     ik v(c )ct arg max (17) based on this method different weights are given to outputs according to their accuracy. if the total weights of the methods that estimate customer is churner are more than the whole weights of other methods, the customer will be predicted as churner, if not the customer is loyal. iii. evaluation criteria the lift criterion is a performance measure which is the result of the ratio between the obtained outcomes with and without the use of the prediction model. the higher the lift means the model is more accurate, and instinctively, the more profitable a targeted proactive churn management program will be [5]. calculating lift criteria for all of churn management data base is not logical and also not practical. it is also not economically possible for the organization to apply churn management for all customers, so it concentrates on those with more churn probability. for this, the two mentioned outcomes are usually kept apart, and are about 10-20% in marketing [26, 30]. as the top decile lift is the main criterion in the churn management area [5], this criterion has been used to evaluate the performance of applied algorithms. the top decile lift focuses on the customers predicted most likely to churn. the first 10% are the most critical customers (i.e. with high churn probability) and this percentage is an ideal portion for targeting the retention marketing campaign [9]. so for computing top decline lift, first customers are sorted from predicted most likely to predicted least likely to churn. then the number of customers that were correctly recognized in the first 10% will be calculated. and finally this percent will be divided with the total churn. if all customers (in the first 10%) were recognized correctly and the ratio between churners and other customers is 50-50, the amount of top decline lift is equal to 100/50. in addition to lift, proposed algorithm was compared with some other algorithms that were mentioned in literature by the use of two other criterions, accuracy and area under roc curve (auc). iv. dataset the dataset is provided by the teradata center at duke university. the database contains of datasets of mature subscribers (i.e. customers who were with the company for at least six months) from a major u.s. telecommunication company. there are three different datasets in this database: calibration data, current score data and future score data. a total of 172 variables are included in the datasets, one for churn indication, and 171 variables for prediction. the prediction variables include three types of variables: behavioral data such as minutes of use, revenue, handset equipment, company interaction data such as customer calls into the customer service center, and customer household demographics. the churn response is coded as a dummy variable with churn=1 if the customer churns, and churn=0 otherwise. there are 100,000 records in the calibration dataset, 51,306 records in the current score and 100,462 records in the future score dataset. the 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gorithm sed model limot c regression c5.0 al network an network model compari orithm d model (1) mot(2) egression (3) .0 (4) network (5) network (6) vi. co a are usually n n not that accu nted to increas ed hybrid met necessary pre res were sele he results wer method was e on company th available imot and c5 r of algorithm ds that lead to fuzzy regress ca [36]) to p features, featu ediction accur imal number o refer kim, m. kim, j. y adoption process” 74, 2008 hanssens, b. ha . sriram, “model ch, vol. 9, no. 2, rowe, l. zhang, logistic regressio ons, vol. 38, no. 1 ng customer chur of survival anal ional (sugi27) o s. gupta, w. k roving predictive f business, dartm 97 hod for custom son according t gure 5) top de 2 1 1 1 1 1 l accuracy com accura 92% 70% 60% 50% 45% 44% ison according auc 0.67 0.62 0.58 0.62 0.62 0.57 onclusion noisy and imba urate. so, in t se the accurac thod, after gath eprocessing p ected and w re combined to evaluated by u and its highe methods, w 5.0 were used ms can be com more accurate ion [32], an roduce a mor ure subsets an racy. improvin of these subset rences y. woo, “organi ”, journal of busin ardie, w. kahn, ling customer life pp. 139–155, 200 y. tian, y. sh on and decision 12, pp. 15273–15 rn in the telecom lysis modeling u online proceeding kamakura, j. lu, e accuracy of cu mouth college, 200 2996 mer churn pred to top decline l ecline lift 2.51 1.94 1.87 1.84 1.43 1.35 mparison acy % % % % % % g to auc (figure c 7 2 2 2 7 alanced, non-h this study a h cy of classifier hering suitable phases, the were given to o achieve the using data fro er effectivenes was proved. in this method mbined, and e prediction ca nfis [33-34], e efficient sch nd training su ng the method ts can also imp izational characte ness research, v v. kumar, n. l etime value”, jour 06 hi, “credit card tree”, expert sy 5285, 2011 mmunications indu using sas”, sas gs, pp. 114–27, 20 , c. mason, def ustomer churn m 04 diction lift 6) hybrid hybrid rs. by e data most o 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1, pp. 153-69, 2013 [35] a. azadeh, s. m. asadzadeh, r. jafari-marandi, s. nazari-shirkouhi, g. baharian khoshkhou, s. talebi, a. naghavi, “optimum estimation of missing values in randomized complete block design by genetic algorithm”, knowledge-based systems, vol. 37, pp. 37-47, 2013 [36] s. nazari-shirkouhi, h. eivazy, r. ghodsi, k. rezaie, e. atashpazgargari, “solving the integrated product mix-outsourcing problem using the imperialist competitive algorithm”, expert systems with applications, vol. 37, no. 12, pp. 7615-7626, 2010 microsoft word review-17-2448_s_bibliografiki engineering, technology & applied science research vol. 9, no. 1, 2019, 3863-3870 3863 www.etasr.com khalid et al.: on the current state of scholarly retrieval systems on the current state of scholarly retrieval systems shah khalid school of computer science and communication engineering, jiangsu university, china and national university of sciences and technology (nust), islamabad, pakistan shahkhalid@ujs.edu.cn shah khusro department of computer science, university of peshawar, peshawar, pakistan khusro@uop.edu.pk irfan ullah department of computer science, university of peshawar, peshawar, pakistan, cs.irfan@uop.edu.pk godfrey dawson-amoah school of computer science and communication engineering, jiangsu university, china gdamoah@stmail.ujs.edu.cn abstract—the enormous growth in the size of scholarly literature makes its retrieval challenging. to address this challenge, researchers and practitioners developed several solutions. these include indexing solutions e.g. researchgate, directory of open access journals (doaj), digital bibliography & library project (dblp) etc., research paper repositories e.g. arxiv.org, zenodo, etc., digital libraries, scholarly retrieval systems, e.g., google scholar, microsoft academic search, semantic scholar etc., digital libraries, and publisher websites. among these, the scholarly retrieval systems, the main focus of this article, employ efficient information retrieval techniques and other search tactics. however, they are still limited in meeting the user information needs to the fullest. this brief review paper is an attempt to identify the main reasons behind this failure by reporting the current state of scholarly retrieval systems. the findings of this study suggest that the existing scholarly retrieval systems should differentiate scholarly users from ordinary users and identify their needs. citation network analysis should be made an essential part of the retrieval system to improve the search precision and accuracy. the paper also identifies several research challenges and opportunities that may lead to better scholarly retrieval systems. keywords-information retrieval; scholarly search; scholarly users; citation networks i. introduction a scholarly retrieval system is a sophisticated software that performs crawling, indexing, searching, and ranking to make scholarly data (research publications and related information including authors, publishers, citations, etc.), available to searchers. several scholarly retrieval systems including google scholar, microsoft academic search, citeseerx and chinese baidu academic [1] are frequently used by modern-day online searchers. the retrieved scholarly documents include journal articles, conference proceedings, books, dissertations, technical reports, and patents. while some of these documents are freely accessible to all members of the public, access to others is limited only to subscribers. the academic web is growing, but there seems to be no definite agreement on its size. one estimation of the number of scholarly documents is 120 million, of which 25% is freely accessible [2]. google scholar has indexed nearly 160 million scholarly documents [3]. microsoft academic search has indexed nearly 209.79 million [4]. the number of scholarly documents increases at an annual rate of over 1 million [5]. such a huge collection of research publications is therefore challenging to process and find relevant papers effortlessly. researchers are working on finding out a way for supporting scholarly search and making it more accessible. their efforts resulted in several indexing solutions, publication repositories, digital libraries, research paper recommender systems, and scholarly retrieval systems. this paper aims to report on the current state of the scholarly retrieval system by identifying the commonalities and differences between web and scholarly users, surveying the search techniques of the available scholarly retrieval systems, and understanding the potential role citation networks analysis in retrieval relevant research publications. ii. the current state scholarly retrieval systems scholarly retrieval solutions take the user search query as input and check its relevance with publications using different ranking features [6-10]. as a complementary tool to the academic search, a research paper recommender system employs different filtering algorithms to find and recommend relevant papers based on users’ implicit and explicit feedback as well as the content of these documents. in some cases, search and recommendation are employed in a searchrecommendation hybrid manner, where keywords are first used to find an initial list of search results and then recommendations are applied to refine the search [11]. without loss of generality, both architectures are highly related, and most of the techniques used for scholarly retrieval systems apply to scholarly recommender systems. recommender systems are covered in several recent papers [11-13]. corresponding author: shah khusro engineering, technology & applied science research vol. 9, no. 1, 2019, 3863-3870 3864 www.etasr.com khalid et al.: on the current state of scholarly retrieval systems a. the structure of scholarly documents unlike general web, the unit of information to be retrieved by a scholarly search system is a research article that is retrieved based either on its content or some specific parts. a scholarly publication can be a journal article, conference paper, technical report, pre-print, thesis/dissertation, or a book. this paper considers research articles only, excluding theses/dissertations, technical reports, and books. a research paper has a well-defined structure and well-organized content to which writers are customarily constrained. usually, the author follows the author guidelines or instructions for authors specifying the length, format, in-text citations, references, artwork, tables, etc., before the submission or after the manuscript is accepted for publication. the manuscript text is mainly unstructured [5], but it is sometimes considered semistructured or even structured. generally, research articles consist of a header, main-content, a bibliography, algorithms, tables, figures, mathematical equations and so on [14]. the header contains a title, authors, their emails and affiliations, abstract, and publication year, venue (journal, conference, etc.), volume and issue number, number of pages, etc. figures and tables covey results and other structured information in a very symbolic and practical way. algorithms are the step-by-step approach and effective way to present how a computational problem works. the mathematical computation is usually written in the form of equations. bibliography (also known as references, incites, or notes) is a collection of cited publications listed at the end of the research article. they play a vital role in assessing the quality of the manuscript, helping the reader to learn more by accessing these links, and facilitates in creating citation networks. the extraction and usage of all essential components can enhance the ranking of scholarly retrieval systems [15-17]. by utilizing different tools such as ocr++ [18-20], apache tika [21], grobid for header extraction [22], pdffigures for table and figure extraction [23] and algorithm extraction [24], parscit for citations extraction [25], etc., documents can be parsed into different sections like title, abstract, body text, authors, venue, and references for optimizing retrieval. the metadata including title, author (name, email, affiliation), heading and section mapping, footnote, figures and table headings, url, citation, and references can be extracted and processed in a usable format like xml or json [18]. the extraction and storage of figures can also play a vital role in the retrieval of relevant papers [26]. however, for an efficient scholarly retrieval system, it is essential to consider the structure and associated metadata of the scholarly documents in search, ranking, and recommendation [27]. b. users of scholarly retrieval systems the scholarly users are different from the typical web searchers [28]. they have different search patterns: in general web search, the search activity is on a peak in the weekend and goes down during weekdays, but in scholarly search, the activity is on the peak during weekdays and (mostly) drops in weekends [29]. academic searchers use scholarly retrieval platforms. the web searchers widely use the general web search engines. table i summarizes the types of scholarly users and their requirements, based on [30]. table i. types of scholarly users user category goal tasks readers or authors updating bibliography on a topic • find scholarly and recent publications. • navigate through bibliography to find other relevant papers. reviewers freshness • check whether recent relevant papers are cited • check if relevant papers are missing. editors scope • check the relevance of the submitted paper and of the papers cited in it. • check if self-citations are present, count them and assess the paper. evaluators impact • check the number of citations of paper and author. • check why a paper is cited (is it relevant or just for self-citation?). • check citations evolution. event organizers participants • find relevant paper regarding event. • find authors of relevant papers. 1) readers/authors readers and authors usually search for and read scholarly documents to find novelties in literature either for learning or for developing new approaches to solve a problem. because of the massive size of the academic web, it is unrealistic for a researcher to read every article related to the research subject [31]. in order not to overwhelm researchers with information overload, it is essential to provide a result set that includes the most relevant documents related to a given query. 2) reviewers reviewers assess the quality of a submitted paper to ensure it meets the laid down standards. a critical aspect of a reviewer’s job is to evaluate the citations used. for any given topic, there usually exist a set of core scholarly documents that need to be referenced in any new work because they establish the theoretical foundations of the topic. it is essential to ensure that all relevant information is made available to a reviewer during the evaluation process, which may aid in reviewing the submitted manuscript more efficiently. 3) editors the core mandate of editors is to evaluate the scope of a submitted scholarly document to ensure that it fits the platform (journal, conference proceedings, etc.) it is intended for. they also evaluate the number and quality of self-references in situations where they are used. 4) evaluators evaluators belong to a category of users who usually carry out research aimed at determining the contributions of the author to the body of knowledge of a specific field of study. 5) event organizers event organizers are generally interested in getting to know the potential participants by using the citation network. the participants could include researchers working on insightful solutions in the given domain, students, authors of previously published relevant scholarly documents and any others who might have an interest in the event. engineering, technology & applied science research vol. 9, no. 1, 2019, 3863-3870 3865 www.etasr.com khalid et al.: on the current state of scholarly retrieval systems c. approaches to scholarly search and retrieval the following sections discuss the approaches with which the scholarly search systems use to mitigate the problem of information overload for academic searchers. 1) citation graph-based approaches the network of references forms the citation graph, in which the citing paper cites the cited ones. several approaches practice citation graph [32-37] e.g. sofia search [37] produces a citation graph by starting from the initial set of papers and following the links of citing and cited papers until the desired number of candidate papers is found. it mimics a human in identifying candidate publications from the citation graph. from the citation graph of the seed papers, the approach generates a list of relevant papers. however, in the growth rate of research papers, the use of sofia search is limited. at first, it needs seed papers and a lower bound. then, all the in-links and out-links are not equal and relevant [38-40]. another representative technique of citation graph is bibliographic coupling that considers only out-links of a paper [41]. the similarity between �� and �� is computed as ����∩ �� � ����∪ �� � [42, 43], where � � and � are the sets, having out-links of �� and ��, respectively. the similarity between the two papers is equal to 0 when both sets � � and � are empty. bibliographic coupling has been practiced and worked well for classification of scholarly documents [43], plagiarism detection [44, 45], and similar legal judgments [46]. however, it is limited in retrieving relevant papers due to two reasons: a) bibliographic coupling misses some important papers not present in the outcites, and b) it is unable to consider the in-cites of the papers. the citation context is used in [47] for retrieving relevant literature. however, extracting citation context is challenging due to the unavailability of full text and almost unable to reveal the main subject of the paper resourcefully [48, 49]. several popular academic search engines including google scholar, pubmed and citeseer use the links between academic articles, provided by citation networks for documents ranking. 2) content-based approaches content-based methods process textual content of the papers, which can be title, abstract, introduction, keywords and body of the articles. these methods weigh the article’s influence by the frequency and position of the terms in the article [50]. many techniques are based on the term weights to estimate the relevance of articles. the most widely used approach is the vector space model (vsm), which represents each article as a vector of term weights and the relevance is a measure in terms of some similarity measures such as cosine similarity between the query and document vectors. many retrieval systems and applications practice vsm (e.g. [51]) even though, the cosine similarity does not perform well in many situations [52, 53]. latent semantic analysis (lsa) improves the vector representation of a scholarly article by singular value decomposition (svd) method [54, 55]. however, for the efficient retrieval of scholarly articles, lsa does not perform well comparatively [53]. many scholarly retrieval systems prefer using bm25 which is among the best ranking techniques for scholarly retrieval [56]. however, to better meet the requirements of different scholarly users, researchers have also adopted hybrid approaches by combining contentand citation-based approaches, discussed below. 3) hybrid approaches the hybrid approaches [43, 57-59] combine the best of the citation graph-based and content-based techniques to compute the relevance of documents to the search query. the proximity of citations is supportive in locating related articles [60, 61]. two articles may be similar to each other if many articles in nearby locations cite them. however, all the papers are not publically available to locate the nearby locations and cannot guarantee the exact subject [48, 49]. the context passage around the citation indicates the main content of the cited paper [62], however, the cited paper can be focused on a different subject of context [62, 63]. context passages are used for several other purposes in literature, like inter-article similarity estimation [64], disambiguation of named entities [65], topicbased retrieval [9, 47], identification of biomedical articles [50], and newspaper citations in scholarly search [66]. however, extracting context passage is challenging due to the unavailability of full-text and therefore inability to conclude the subject of the paper efficiently [48, 49]. intuitively, many popular scholarly search engines like semantic scholar use hybrid approaches for ranking documents. much research has been done on the effectiveness of academic search engines. some authors use graph-based approaches for the effectiveness of the academic search [67-71] while bearing in mind that a citation graph is usually sparse and noisy[68]. the solution in [72] supports scholarly search using key-queries [73] and query covers [74] to enhance the effectiveness of the academic search. however, their approach takes a research article as input for key-phrase selection and weighting methods, which result in suboptimal ranking. due to the massive expansion in research paper repositories, the scholarly search is a very hot and challenging domain for both researchers and developers. although several approaches have been proposed in the literature to address the requirements of scholars, we are still away from an ideal academic search engine that meets the heterogonous needs of different categories of scholarly users with minimum effort. further research is required to address the requirements of academic searchers. d. ranking algorithms for scholarly search there is no universal ranking algorithm that scholarly retrieval systems use to rank documents in response to user queries. in most cases, scholarly retrieval models are quadruples {d, q, f, r (q, d)} [75]. d is the representation component that is usually searched in the collection set. q is the logical view of the user need. f is a framework and reasoning component for modeling document representation, query, and their relationship. r (q, d) is a reasoning component to rank the document as per the query terms. due to the advancements in ir, numerous technologies and techniques are used for enhancing scholarly retrieval systems. for instance, semantic scholar uses semantic technologies for accomplishing the task of locating relevant documents. acemap [76] academic search system analyzes big scholarly document datasets using the “map” approach. google scholar and dblp use text-based methods to navigate. these scholarly engineering, technology & applied science research vol. 9, no. 1, 2019, 3863-3870 3866 www.etasr.com khalid et al.: on the current state of scholarly retrieval systems retrieval systems use different ranking algorithms that place matching results in their order of relevance. some systems let the user choose the ranking factor (publication date, number of citations, author or journal name and reputation, and relevance of the document based on some predefined designed criteria). the factor selected by the user is given more weight in determining the relevance of documents. some other systems like google scholar do not allow users to intervene in the weighting factor of ranking. in most scholarly retrieval systems, the relevance of a document is measured by considering different document elements. for instance, how repeatedly the search term is found in the document and in which field (i.e., title, abstract, body, etc.). commonly, if the search term occurs more often in a document or a more important field of the document, it is considered more relevant. for example, the term in the title is weighted more heavily than its occurrence in the abstract and so on. the weight of each term in the document is assigned to the total ranking weight based on term position. some of the document fields that may be weighted differently by scholarly search systems are shown in table ii. due to the unavailability of data, the ranking algorithms and their attributes of all available scholarly retrieval systems was not considered. we slightly considered the ranking mechanism of google scholar, the most widely used scholarly search engine. it takes into account multiple factors such as relevance, citation count, author name, name of publisher etc. [77] when generating results to a user query. in assessing the relevance of a given document and query, google scholar gives higher weight to the title. the citation attribute also plays a vital role in the ranking, and therefore, the documents having relatively many citations are likely to be placed near the top of the result list. author and journal or conference name can also affect the ranking of documents, i.e. a query having an author or journal/conference name is likely to be positioned in the top of the search results list. for example, most of the top results of a search for “information retrieval” are likely to be articles about various ir topics from the information retrieval journal. google scholar also considers publication date and some other attributes in ranking [77]. intuitively, without loss of generality as the research paper repository is growing rapidly, it is essential to consider all the desired components of the scholarly domain in ranking algorithms that shatter the metaphor of scholarly retrieval systems. these citation networks are discussed in detail below. table ii. different fields of a scholarly document document text document metadata electronic files metadata title author names title abstract publication venue (journal, conference, etc.) author subheadings incites description body text outcites size figures social tags filename tables social annotations date author keywords author reputation no of terms iii. scholarly citation networks in the scholarly domain, a citation network is a significant and critical part of scholarly retrieval models. a citation is a link from one scholarly document to another. when a document uses a text excerpt, an idea, a concept, a figure, an algorithm, etc. from another scholarly document, it usually refers to that document [78-80]. citations are necessary because they help create links between publications and authors, give credit to authors, promote reusability and productivity, and provide a roadmap to discovery. professional associations encourage scholars to replicate findings, results, improve research standards and give desired credit to scholars by citing their work when deemed relevant and related. in most cases the impact of an author, institution, journal or even a country concerning a particular field of study is measured in terms of citations count. for instance, a document with a lot of incites is considered more influential. the academic policymakers use citation networks via google pagerank, and it’s variants to quantify scholarly texts [81, 82]. likewise, to credit authors, academic networks use the status of their citing authors to distinguish high-status authors in co-authorship networks [83, 84]. the citation networks also provide a technique to differentiate prestigious journals [85]. a journal is said to be prestigious if it has been cited by other prestigious journals and has numerous highly cited works. institutions and countries are assessed using the same criteria [86]. intuitively, citations are used in the retrieval models of many famous scholarly search engines such as google scholar in different ways like citation count, bibliographic coupling [41], and cocitation and citation context [47] in ranking results. citation networks form a complex graph. consider a paper network where nodes are the scholarly documents and the edges are the citations between the papers, i.e. g (p,c), where p is the set of nodes (papers), and c is the set of edges (citations, i.e., in-cites and out-cites). it is a substantial complex graph that can have several sub-graphs including but not limited to paper graphs, author graphs, collaboration graphs and semantic graphs. for a collaboration graph, an edge (x, y) exists if person x worked with person y. in the case of semantic graphs, an edge (x,y) exists if word x is associated with word y. the insightful utilization of all the subgraphs in the scholarly network and their associated metadata can play a significant role in the efficiency of scholarly retrieval systems. for example, authors in [87] extracted the metadata from scholarly documents with the aim to create a knowledge-base of each scholarly article for efficient document retrieval. citation networks can play a vital role in the systematic retrieval of scholarly literature. much research has been carried out about how useful information from scholarly citation networks can be extracted and utilized for better information retrieval. citnetexplorer [88] analyzes and visualizes citation networks to address citation-based scientific literature retrieval [89, 90]. the tool is helpful in finding full relevant papers about a specific topic for preparing a review article. author in [91] extends the co-citation network by incorporating satellite documents. co-citation is a relationship among two scholarly papers concurrently cited by a third scholarly document. when the co-citation linkage detects scholarly documents, it is conceivable to obtain more suitable search terms from the related document. such terms may not have been included in the original seed document. engineering, technology & applied science research vol. 9, no. 1, 2019, 3863-3870 3867 www.etasr.com khalid et al.: on the current state of scholarly retrieval systems despite their numerous benefits, the existing domain of citation networks considers all citations for a given document to be equally significant. this can lead to situations where inaccurate information is deemed to be relevant because several authors have cited it. for example, a paper titled “a vector space model for information retrieval” alleged to have been published in 1975 is considered the most commonly cited paper published by gerard salton even though it does not exist in reality [92]. the paper “read before you cite!” suggests that authors read just 20% of the work they cite [93]. other authors also concluded that 25% of the references are redundant, 40% are for aspiring only to minimum standards [94] and 62.7% address just definition, tools, etc. not attributed for a specific function [38-40]. all these show that to improve the quality of citation-based applications, citations should not be regarded as equally significant. to do this, several researchers have carried out research activities aimed at mitigating the challenges associated with citation networks [31], including: • scattering: there is no single authoritative place to keep a record of an entire academic citation network. due to the distributed nature of the academic web, different search platforms have different citation metrics and analytics. this can pose a significant challenge when using citation networks to credit a paper, author, journal, institution, country, etc. [95]. • uncertainty: the relationship between citations is not always available in repositories. for instance, in the acm digital library, 18.5% of publications have no citing details while 55.6% lack any cited information [96]. therefore different papers receive the same ranking score. handling the erroneous and missing citations metadata (incites and out-cites) of scholarly documents is a massive challenge for academic retrieval systems [97]. • restriction: as discussed earlier, the whole academic web is not freely available [2]. since the citations used in a document are part of that document, the unavailability of such a document can be a profound challenge to accurate academic information retrieval. • integrating scholarly metrics and analytics: a citation network is a handy assessment tool for distinguishing different scholarly mark units [90, 95]. it is beneficial when determining the impact of papers, authors, co-authors, conferences, journals, institutions, projects, countries, etc., in a particular field of study. however, due to the challenges associated with citations, it may not always produce optimal results. • accessibility: due to the growing rate of academic literature, it is challenging to locate relevant papers. more and more documents are published on a daily basis [97]. for instance, ploseone alone published 30,000 documents with an average 85 documents per day in 2014 [97]. these publications inadvertently result in the addition of billions of nodes to the already existing citation networks. web of science, for example, accumulates about 1 billion citations per year. this makes the accessibility of citation network more challenging [97]. • complex graph: citation network is a complex graph having some non-trivial features like instantaneous network evolution, complex nested topology, multiple nodes/edges and large-scale growing rate. these features make some of the algorithms needed to get optimal results inapplicable [98]. iv. conclusions and future research directions the academic search is a fascinating research area. several academic search engines exist today with google scholar being the dominant one. however, locating relevant documents is still challenging due to the high growth of the research papers repository. in this regard, much research is going on in the field of scholarly document ranking, retrieval, recommendation, and the proper exploitation of citation networks. we are still away from an efficient scholarly retrieval system. the reasons are many, including: • disambiguating authors: one can try google scholar while adding publications to his/her profile, where several articles are displayed being identified as possibly written by the user. for accurate disambiguation, email addresses, affiliations, city, country and field of expertise could be exploited together with the efficient classifier and machine learning algorithms. • the limited use of semantic web technologies, especially ontologies and linked open data, makes popular scholarly retrieval systems limited, where reasoning and machineunderstand-ability could bring fruitful results. • semantic web together with natural language processing could be employed in identifying and categorizing incitations to differentiate between relevant papers and ones that were used for self-citations or improving/increasing the number of references in the bibliography section. • user studies are required to understand the user interactions with scholarly retrieval systems to understand their information needs better so that more user-friendly solutions are produced. given the high growth rate of the academic web, it is necessary to develop tools that realize and emphasize users’ needs. • the use of citation networks in scholarly retrieval and assessing the impact of scholarly works has achieved many fruitful results. however, efforts are required to exploit them to their fullest in building the scholarly reputation of the authors, research publications, and journals so that users could be able to judge the quality of a publication better. in this regard, the challenges mentioned above need the attention of researchers and practitioners. • the performance of an academic search engine can be improved by in-depth insight into citation networks (i.e. paper network, author network, collaboration network and text network) and infer most influential citations. the relationship between citations, authors and publications can also be computed for each document to efficiently rank documents. engineering, technology & applied science research vol. 9, no. 1, 2019, 3863-3870 3868 www.etasr.com khalid et al.: on the current state of scholarly retrieval systems • the ranking algorithms of scholarly search engines are different, many factors of ranking documents are by nature ambiguous and confusing to formalize. most of them are proprietary making it difficult to understand how they work. therefore, detailed empirical studies are required, in order to understand their ranking techniques and devise solutions that are free, open-source, and which could be reproduced whenever required. this review paper is an attempt to bring the attention of researchers and practitioners towards the endless possibilities in which a more efficient scholarly retrieval system could be developed. it emphasizes on mitigating the information overload that currently researchers, especially newcomers, face while trying to access the most intended and relevant papers. for a more efficient solution, it is essential first to understand user information needs, develop approaches 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toughness, tenacity and maximum initial strength of rubber modified asphalt binders toughness, tenacity and maximum initial strength of rubber modified asphalt binders kazem jadidi howard r. hughes college of engineering, university of nevada, las vegas, usa kazem.jadidi@unlv.edu mehdi khalili howard r. hughes college of engineering, university of nevada, las vegas, usa mehdi.khalili@unlv.edu moses karakouzian howard r. hughes college of engineering, university of nevada, las vegas, usa moses.karakouzian@unlv.edu serji amirkhanian college of engineering, university of alabama, tuscaloosa, alabama, usa samirkhanian@eng.ua.edu abstract-the toughness and tenacity test method, which was developed in the 1980s, is popular for evaluating a polymermodified binder. several states like nevada require performing this test to evaluate non-modified binder samples, as well as other types of modified binders. in this regard, a toughness and tenacity test was performed on rubber-modified samples produced from virgin binder pg58-28, pg64-16 and ac-20. in order to take the rubber size, type and content into account, two rubber sizes, mesh #20 and #40, two rubber types, ambient and cryogenic, and three rubber contents, 10%, 15%, and 20% were produced and tested. the results then were compared with polymer-modified and terminally blended rubber-modified samples. the results show improvement in the amount of initial maximum strength, and a decline in the magnitude of elongation, toughness and tenacity for the rubber-modified binder, compared to other types of binders. keywords-rubber binder; ambient; cryogenic; toughness; tenacity i. introduction the toughness and tenacity is a test designed to discover the elastomeric properties of asphalt. asphalt’s ability to be stretched is measured and presented by these two parameters [1]. in addition, for the analysis of the results of this experiment, a third parameter called maximum initial strength is measured. toughness of the asphalt binder is the area underneath the curve of variation of force versus elongation, and represents the strength of the asphalt binder as well as the capability to be stretched. tenacity is the area underneath the curve of variation of force versus elongation after the initial strength has been overcome, and represents the capability of the asphalt binder to be stretched after the initial strength has been overcome [2, 4]. this method of testing, which is based on an experiment presented by benson in 1955 for rubberized asphalts, was developed for polymer modified asphalt in the 1980s [3]. toughness is equal to the total work that is required to separate the testing equipment ball from binder [5]. for bituminous material, high toughness will lead to more flexibility and consequently, better performance against repeated loadings. moreover, toughness is lower in cold temperatures in comparison to higher temperatures [6]. asphalt binders with higher strength and toughness demonstrate better resistance against surface abrasion [7]. toughness and tenacity reflects the adhesion properties of an asphalt binder [8]. it is possible to determine the tensile strength of an asphalt binder based on the results of a toughness and tenacity test [9]. sulphur improves the toughness and tenacity of polymer modified asphalt [10]. this test is among the quality assurance tests required for most state transportation departments [11]. asphalt binders with higher toughness and tenacity will demonstrate greater resistance against deformation in warm weather. moreover, aging will lead to a decline in toughness and tenacity properties of asphalt [12]. for a styrene– butadiene–styrene (sbs) modified binder, the highest toughness and tenacity happens with 6% sbs concentration [13], while it will decline with an sbs concentration over 7% [14]. increasing styrene copolymer content from 3 to 6 in a polymer modified binder improves toughness and tenacity of the original binder significantly [15]. other investigations demonstrate that styrene-butadiene rubber (sbr) modified asphalt also presents compatible toughness and tenacity values in comparison with other types of binders [16]. it has been discovered that an increase in rubber content leads to a decrease in toughness properties of rubberized asphalt concrete [17]. warm mix asphalt has lower toughness value compared to non-modified asphalt [18]. on the other hand, although crm additives diminish the modified asphalt stiffness at lower temperatures, they increase the toughness of rubber modified asphalt [19]. toughness has been investigated more in places with low temperature [20]. ii. methodolgy in order to produce rubber modified asphalt, virgin asphalt bitumen was obtained from local manufacturing companies and mixed with crumb rubber. virgin binders were used to produce rubber modified asphalt. three types of virgin binders used in manufacturing rubber modified asphalt were pg 64–16, pg 58–28, ac-20. in order to perform a better comparison, polymer modified asphalt as well as terminal blended rubberize asphalt also were provided. for this reason, polymer modified pg 64-28 nv and pg 76-22 nv, as well as terminally blend rubber modified asphalt pg64-22tr were prepared. from each sample, three specimens were tested, and at the end, the average values were used in the analysis. corresponding author: k. jadidi engineering, technology & applied science research vol. 9, no. 1, 2019, 3765-3769 3766 www.etasr.com jadidi et al.: toughness, tenacity and maximum initial strength of rubber modified asphalt binders a. sample preparation three crm contents, 10%, 15%, and 20%, were mixed with each virgin binder. in order to take into account the influence of rubber particle size and gradation in modified binders, two maximum sizes, mesh #20 and mesh #40, were selected for crm particles. both ambient and cryogenic crms were used. moreover, in order to modify asphalt binders, both cryogenic and ambient methods were used to produce crumb rubber. two main methods for grinding crumb rubber include the ambient and cryogenic methods. in the ambient method, the rubber particle distributions expand between 75µm and 5mm. rubber particles manufactured in this method have a rough texture which leads to higher surface area. this is because in the ambient method, rubber specimens are scraped in a tearing process. in contrast, in the cryogenic method, liquid nitrogen is used to freeze scrap tire, and then the frozen tire rubbers are crushed into particles between 025 inches and mesh #30 with a hammer [21]. figure 1 demonstrates the combination of original, rubber modified, and polymer modified asphalt samples, which were used in performing this research. fig. 1. asphalt source combination b. testing of the original and modified samples toughness and tenacity tests were performed on rubbermodified asphalt binders, as well as polymer-modified asphalt and terminally blended rubber modified binders. the results are presented in graphs and tables for better comparison. in order to compare the rubber-modified binders with other traditional specimens, both rubber size and content played a prominent role in evaluating the properties of rubber-modified binders. figure 2 illustrates a schematic of the toughness and tenacity test. iii. results and discussion because the results of the experiments are to be presented to the nevada department of transportation (dot), the toughness and tenacity tests were conducted in accordance with nev. 745i [22] and astm d5801. although both standards present recommendations for polymer modified asphalt and in general this type of testing is more popular for polymer modified binders, the same procedure was used in conducting this research to conform with nevada dot requirements. all tests were performed at 25◦c in accordance with the standard. fig. 2. schematic of toughness and tenacity test a. force anb elongation the virgin binder samples were modified with two rubber types and two rubber sizes, so the results will be presented in four sets of graphs. these sets of graphs include ambient (am) and cryogenic (cr) for rubber types, and #40 and #20 for rubber particle sizes. the results of the force and elongation for rubber modified binders made with virgin asphalt pg58-28 are presented in figure 3. in comparison with rubber modified binder pg 58-28, for modified binder ac-20, elongation forces do not follow a remarkable pattern for various rubber sizes and types, except for ambient #20. generally, there is a considerable increase in the amount force in which each sample failed. modified binder with 15% rubber ambient #20 presents the highest resistance force, which is about 150lbs. all binder samples were able to resist against more than 100lbs of stretching force. the results of the experiment for samples manufactured with binder pg64-16 is similar to ac-20, but with several differences. it can be seen from the graphs presented in figures 3-4 that 10% rubber leads to lower stretching forces while samples modified with 20% rubber demonstrate higher resistance to stretching before failure. on the other hand, adding more rubber improves the initial strength against stretching for modified binders. in terms of elongation, all samples presented lower magnitude. it is obvious from figures 3-4, that regardless of binder type and rubber particle size and type, the rate of stretching is less than 1.5 inches, which is not considerable. on the other hand, while rubber improves the initial strength of the binder, it decreases the elongation rate. however, polymer modified and terminally blended rubber modified binder samples demonstrated noticeably higher values of elongation, ranging between 4 and 18 inches. in contrast, the magnitude of force was slightly lower for these specimens in comparison to rubber modified binders. toughness, tenacity and maximum initial strength were calculated based on elongation vs. force graphs which were presented in figures 3-4. in order to make a better comparison, toughness, tenacity and maximum initial strength were calculated for a polymer modified binder and a terminally engineering, technology & applied science research vol. 9, no. 1, 2019, 3765-3769 3767 www.etasr.com jadidi et al.: toughness, tenacity and maximum initial strength of rubber modified asphalt binders blended rubber modified binder. the results are presented below. toughness (ts), tenacity (ty), maximum initial strength (mis), and elongation for non-modified pg58-28 and pg64-16, as well as polymer modified and terminally blended rubber modified samples are presented in table i. based on table i, non-modified binder samples present the lowest value for toughness, tenacity and maximum initial strength. for these samples, the amount of elongation is slightly higher than for rubber-modified binders, but still lower than polymer modified and terminally blended rubber modified specimens. in general, polymer modified and terminally blended rubber modified samples present the highest values, specifically in terms of toughness, tenacity, and elongation. (a) (b) (c) (d) fig. 3. force vs. elongation for binder ac 20 mixed with rubber: (a) ambient #20, (b) cryogenic #20, (c) ambient #40 and (d) cryogenic #40 (a) (b) (c) (d) fig. 4. force vs. elongation for binder pg64-16 mixed with rubber: (a) ambient #20, (b) cryogenic #20, (c) ambient #40 and (d) cryogenic #40 table i. test results sample ts (in–lb) ty (in–lb) mis (lb) elongation (in) pg58-28 15 3 26.3 2.5 pg64-16 46 6 77.3 3.5 pg64-28 nv 510 458 82.2 14 pg64-28 tr 365 316 77 18 pg76-22 nv 111 80 27.8 5 pg76-22 tr 126 88 35.8 4 b. toughness, tenacity and maximum initial strength the calculated toughness values for rubber modified samples, polymer modified samples, and terminally blended rubber modified samples are presented in figures 5-7. considering the fact that this test originally was developed for engineering, technology & applied science research vol. 9, no. 1, 2019, 3765-3769 3768 www.etasr.com jadidi et al.: toughness, tenacity and maximum initial strength of rubber modified asphalt binders polymer modified binder, in this experiment also, toughness and tenacity test was performed on polymer modified binder and the results were used as a base for comparison. in addition, the results are compared with the toughness and maximum initial strength of terminally blended specimens. fig. 5. toughness, rubber-modified binder pg (58-28) fig. 6. toughness, rubber-modified binder ac-20 fig. 7. toughness, rubber-modified binder pg (64-16) regarding figures 5-7, there is considerable difference in sample toughness between rubber modified binders and base specimens. binder pg64-28 presented higher toughness values compared to other binder sources, with polymer modified samples showing the highest values and terminally blended rubber modified of the same binder source in second place. polymer modified and terminally blended rubber modified binder pg76-22 lead to higher values in comparison to rubber modified samples, although the difference is not considerable compared to some rubber modified specimens like pg64-16 20% am #40 and pg64-16 20% am #20. among rubber modified specimens, the highest values, with toughness magnitude slightly over 90 in-lb, belong to pg64-16 modified with 20 percent ambient rubber. rubber modified pg64-16 and ac-20 presented higher values compared to pg58-28. moreover, no remarkable difference was observed between ambient and cryogenic rubber types or for various rubber gradations. in general, higher rubber content leads to greater toughness values which means rubber improves the toughness properties of modified binders. the tenacity values for rubber modified binders for all samples were considerably low. they were not comparable with base samples, so the graphs for tenacity results are not presented in this paper. in contrast, rubber modified specimens demonstrated higher maximum initial strength (mis) values. the results are illustrated in figures 8-10. fig. 8. mis of crm binder pg (58-28) and base samples fig. 9. mis of crm binder ac-20 and base samples fig. 10. mis of crm binder pg (64-16) and base samples rubber modified binders presented higher maximum initial strength values in comparison with polymer modified and terminally blended rubber modified binder specimens. similar to toughness, higher initial strength belongs to modified specimens manufactured with binder ac-20 and pg 64-16, while modified pg28-28 presented lower values. for most samples, a direct correlation between rubber content and initial strength was observed, which means that higher rubber content leads to enhancement in the initial strength of a modified binder. for each binder source, there was no indication that the rubber type and size had any influence. the lowest maximum initial strength values belong to polymer modified and terminally blended rubber modified pg76-22 specimens. engineering, technology & applied science research vol. 9, no. 1, 2019, 3765-3769 3769 www.etasr.com jadidi et al.: toughness, tenacity and maximum initial strength of rubber modified asphalt binders iv. summary and conclusions toughness and tenacity test method was used to evaluate rubber modified binder samples. the results were compared with polymer modified and terminally blended rubber modified binder specimens. consideration was taken to discover the influences of rubber size, type, and content. toughness, tenacity, and maximum initial strength of samples were calculated and compared. the results of this investigation are summarized as follows: • overall results indicated that the crm additives improve the maximum initial strength of virgin binders. • the amount of toughness, tenacity, and elongation declined remarkably for rubber modified specimens, in comparison with polymer modified and terminally blended samples. • for rubber modified binders, pg64-22 modified with 20% rubber ambient #20 presented the highest toughness value. • among rubber modified specimens, 20% ambient #20 rubber modified pg64-16 demonstrated the highest maximum initial strength. • increase of rubber particle content led to improvement of the toughness properties of modified samples, while rubber size and type did not show significant influence. references [1] astm d5801–17, standard test method for toughness and tenacity of asphalt materials, astm book of standards, astm, 2017 [2] o. e. brisco, asphalt rheology: relationship to mixture, astm special technical publication stp 941–eb. michigan, astm, 1987 [3] j. read, d. whiteoak, the shel bitumen handbook, thomas telford 2003 [4] j. s. chen, k. y. lin, “mechanism and behavior of bitumen strength reinforcement using fibers”, journal of materials science, vol. 40, no. 1, pp. 87-95, 2005 [5] j. s. chen, m. c. liao, h. h. tsai, “evaluation and optimization of the engineering properties of polymer-modified asphalt”, practical failure analysis, vol. 2, no. 3, pp. 75-83, 2002 [6] a. modarres, “investigating the toughness and fatigue behavior of conventional and sbs modified asphalt mixes”, construction and building materials, vol. 47, pp. 218-222, 2013 [7] j. s. clites, h. a. colvin, d. f. klemmensen, polymer for asphalt cement modification, u.s. patent no. 5,986,010, 1999 [8] p. liang, m. liang, w. fang, y. zhang, c. qian, s. ren, “improving thermo-rheological behavior and compatibility of sbr modified asphalt by addition of polyphosphoric acid (ppa)”, construction and building materials, vol. 139, pp. 183-192, 2017 [9] h. zhou, s. e. nodes, j. e. nichols, “evaluation of three polymer modified asphalt concretes”, transportation research record, vol. 1454, pp. 181-192, 1994 [10] f. zhang, j. yu, “the research for high-performance sbr compound modified asphalt”, construction and building materials, vol. 24, no. 3, pp. 410-418, 2010 [11] z. hossain, d. ghosh, m. zaman, k. hobson, “use of the multiple stress creep recovery (mscr) test method to characterize polymer-modified asphalt binders”, journal of testing and evaluation, vol. 44, no. 1, pp. 507-520, 2015 [12] z. jiang, c. hu, s. m. easa, x. zheng, y. zhang, “evaluation of physical, rheological, and structural properties of vulcanized eva/sbs modified bitumen”, journal of applied polymer science, vol. 134, no. 21, 2017 [13] j. s. chen, m. c. liao, c. h. lin, “determination of polymer content in modified bitumen”, materials and structures, vol. 36, no. 9, pp. 594598, 2003 [14] h. akiyoshi, s. ueno, a. kasahara, k. saito, “effect of the morphology of sbs modified asphalt on mechanical properties of binder and mixture”, journal of the eastern asia society for transportation studies, vol. 6, pp. 1153-1167, 2005 [15] l. h. lewandowski, d. f. klemmensen, sbr for asphalt cement modification, u.s. patent no. 6,136,899, 2000 [16] t. s. shuler, j. h. collins, j. p. kirkpatrick, “polymer-modified asphalt properties related to asphalt concrete performance”, in: asphalt rheology: relationship to mixture, astm, 1987 [17] f. xia, s. n. amirkhanian, “laboratory investigation of moisture damage-e in rubberised asphalt mixtures containing reclaimed asphalt pavement”, international journal of pavement engineering, vol. 10, no. 5, pp. 319-328, 2009 [18] f. xiao, w. zhao, t. gandhi, s. amirkhanian, “influence of antistripping additives on moisture susceptibility of warm mix asphalt mixtures”, journal of materials in civil engineering, vol. 22, no. 10, pp. 1047-1055, 2010 [19] h. wang, z. you, j. m. beale, p. hao, “laboratory evaluation on high temperature viscosity and low temperature stiffness of asphalt binder with high percent scrap tire rubber”, construction and building materials, vol. 26, no. 1, pp. 583-590, 2012 [20] k. w. kim, s. j. kweon, y. s. doh, t. s. park, “fracture toughness of polymer-modified asphalt concrete at low temperatures”, canadian journal of civil engineering, vol. 30, no. 2, pp. 406-413, 2003 [21] m. h. blumenthal, “producing ground scrap tire rubber: a comparison between ambient and cryogenic technologies”, in: proceedings of the 17th biennial waste processing conference, asme, 1996 [22] state of nevada, department of transportation, method of test for toughness and tenacity of polymer modified asphalt, test method nev. t745i, state of nevada, department of transportation, materials division 2011 microsoft word 16-3034_s1_etasr_v9_n5_pp4654-4658 engineering, technology & applied science research vol. 9, no. 5, 2019, 4654-4658 4654 www.etasr.com bhutto et al.: mohr-coulomb and hardening soil model comparison of the settlement of an … mohr-coulomb and hardening soil model comparison of the settlement of an embankment dam amjad hussain bhutto department of civil engineering, quaide-awam university of engineering science and technology, nawabshah, pakistan amjadbhutto62@gmail.com shahnawaz zardari department of civil engineering, quaide-awam university of engineering science and technology, nawabshah, pakistan shahnawazzardari@gmail.com ghulam shabir bhurgri department of civil engineering, quaide-awam university of engineering science and technology, nawabshah, pakistan ghulamshabirbhurgri14@gmail.com muhammad auchar zardari department of civil engineering, quaid-e-awam university of engineering science and technology, nawabshah, pakistan muhammad.auchar@quest.edu.pk riaz bhanbhro department of civil engineering, quaid-e-awam university of engineering science and technology, nawabshah, pakistan riaz@quest.edu.pk bashir ahmed memon department of civil engineering, quaid-e-awam university of engineering science and technology, nawabshah, pakistan bashir_m@hotmail.com muhammad munir babar u.s. pakistan centers for advanced studies in water, mehran university of engineering & technology, pakistan mmunirbabar.uspcasw@faculty.muet.edu.pk abstract—in this study, numerical analysis of an embankment dam was carried out to predict settlement behavior with the use of the mohr-coulomb model (mcm) and of the hardening soil model (hsm). the mcm was applied to all material zones of the dam and the hsm was used for four major material zones that occupied significant volume. the settlement response of the dam was similar for mcm and hsm for three material zones (clay core, sandy gravel and random fill), each having a modulus of elasticity (moe) in the range of 25000 to 50000kpa. however, it was found that after the end of the construction, the mcm showed about 57% and 50% more settlement as compared to hsm when moe of sandy siltstone varied from 70000 to 125000kpa respectively. the results regarding the dam settlement predicted with the hsm are in agreement with the findings in previous studies. keywords-settlement; embankment dam; hardening soil model; mohr coulomb model; modulus of elasticity i. introduction embankment dams are being constructed in order to meet the increasing demand of water and electricity. a number of embankment dams are currently being constructed and planned to be raised in the future to resolve water and electricity shortage issues in pakistan. in order to ensure the safety of embankment dams, in addition to stability [1-2], settlement plays an important role to be estimated with reliability [3-5]. nowadays, finite element programs are available which can be utilized for the estimation of settlement in the embankment dams. one such finite element program used in geotechnical engineering is the plaxis 2d which contains a library of different constitutive models that can be utilized for a wide variety of soils. starting from the linear elastic model, there are several advanced constitutive models implemented in plaxis 2d [6]. the use of a suitable constitutive model for particular soil and loading conditions depends on the availability of good type of advanced laboratory testing. normally the budget allocated for the geotechnical investigation of embankment dams is about 1 to 3% of the total cost depending upon the geology of the area [7]. augmenting the number of advanced tests means that more money would be needed for conducting these tests. as a result, there might be shortage of funds for the actual construction of the dams. for settlement computation of an embankment dam, the modulus of elasticity (moe) of the soil is a very decisive factor [8]. having a small amount of money reserved for geotechnical investigation, sometimes, the moe of foundations soils is not determined experimentally, but it is evaluated indirectly using correlations with experimentally determined material properties, since the stability and settlement response of an embankment dam are usually investigated simultaneously. mohr-coulomb model (mcm) is widely used for the stability computation of embankment dams [9-11]. the mcm is linear elastic and perfectly plastic model, which requires the following material properties: cohesion, friction angle, corresponding author: amjad hussain bhutto engineering, technology & applied science research vol. 9, no. 5, 2019, 4654-4658 4655 www.etasr.com bhutto et al.: mohr-coulomb and hardening soil model comparison of the settlement of an … dilatancy angle, unit weight, permeability and modulus of elasticity. however, the settlement of embankment dams predicted with mcm may not be realistic for different soil types. in such situations, there might be the need of using advanced constitutive models depending upon the types of involved soils. the use of advanced soil models for the settlement computation of an embankment dam may require advanced testing which may result to more cost. therefore, it is necessary to investigate the possible ways to evaluate material properties of an advanced constitutive model based on the mentioned above input parameters of mcm. in order to obtain a reliable estimate of the settlement of an embankment dam by utilizing material properties that are already determined during the geotechnical investigation phase, it might be necessary to find those material zones that may show variation in settlement computed with the mcm in comparison to the response predicted with an advanced constitutive model like the hardening soil model (hsm) [12]. in this paper, an attempt is made based on numerical analysis, to identify those material zones of an embankment dam, which have significant influence on settlement when computed with both mcm and hsm. ii. materials and methods figure 1 illustrates the cross section of nai gaj dam that is situated in dadu district, pakistan. the main materials used in the dam are: sandy gravel, random fill, clay core. the dam lies primarily on sandy siltstone. the height of the dam is 59m and its length is 1137m. it has been designed as a zoned embankment dam based on principles of geotechnical engineering. there is a series of curtain grouting and consolidation grouting provided under the clay core section of the dam to prevent seepage. the diameter of each of the curtain and consolidation grout is about 76mm. the length of the curtain grouting is 16m while the length of consolidation grouting is 45m. numerical analysis of the settlement of the dam was performed on the cross section (figure 1) using the finite element program plaxis 2d [6]. fig. 1. cross section of nai gaj dam the cross section of the dam shows that there are four zones which occupy the most of the dam’s volume. these zones are: clay core, sandy gravel, random fill, and sandy siltstone. now, it is important to investigate the effect of these zones on the overall settlement of the dam. for this purpose, mcm and hsm are used for numerical analysis. since the settlement of the dam depends on the magnitude of the moe of different soil types, therefore, the effect of variation of moe of the four major zones of the dam is investigated. for each of the three materials (clay core, sandy gravel and random fill), the moe varies from 25000 to 50000kpa separately. while for the fourth material zone (sandy siltstone), the moe varies from 70000 to 125000kpa. whenever the effect of a particular material zone on settlement is investigated, the properties of the other materials are utilized as presented in tables i and ii. table i. material properties of mcm for embankment and foundation of the nai gaj dam material type saturated unit weight (kn/m 3 ) cohesion (kn/m 2 ) friction angle (deg) moe (kn/m 2 ) permeability (m/day) clay 18.85 [13] 9.57 [13] 30 [13] 49795 [13] 0.00263 [13] sandy gravel 21.5 [14] 0 37 [15-17] 50000 [18] 86.4 [19] random fill 18.85 [13] 0 34 [13] 47880 [13] 0.263 [13] washed gravel 21.5 [14] 0 37 [15-17] 45000 [20] 864 [21] d/s slope protection 19.5 [22] 0 34 [15-17] 40000 [23-24] 8640 [21] riprap 19.5 [13] 0 34 [13] 40000 [23-24] 8640 [21] sand filter 18.85 [13] 0 36 [13] 40220 [13] 26.33 [13] drainage blanket 21.5 [14] 0 37 [15-17] 45000 [21] 864 [21] sandy siltstone 20.4 [13] 12 [13] 29 [13] 70000 to 125000 [25] 0.0063 [13] table ii. hsm parameters for the four main zones material type � �� ��� �mpa� � �� ��� �mpa� ��� ��� �mpa� clay core 50000 50000 150000 random fill 50000 50000 150000 sandy gravel 50000 50000 150000 sandy siltstone 125000 125000 375000 the moe of sandy siltstone was evaluated from its uniaxial compressive strength using the following correlation [25]: e/qu= 200 to 500 (1) where e is the moe (kpa) and qu is the uniaxial compressive strength (kpa). most of the results show that the value of the uniaxial compression strength of sandy siltstone is less than 2mpa. the minimum value is 0.35mpa [13]. the following values of moe of sandy siltstone are used in this study: e=200×0.35=70000kpa (minimum value) (2) e=350×0.35=125000kpa (maximum value) (3) consolidation analysis was performed to compute the settlement of the dam. in numerical modeling, the dam was constructed in a pace of three meters in thirty days. figure 2 shows the finite element model whose horizontal boundaries are given an extension of one hundred meters on either side to reduce the influence of boundaries on the computed results. refinement of the mesh (figure 3) was performed until the average size of the element was 2.148m, which showed no influence on the results. ground water level is marked fifteen meters below the surface and maximum flood water level is at 56.6m (figure 4). engineering, technology & applied science research vol. 9, no. 5, 2019, 4654-4658 4656 www.etasr.com bhutto et al.: mohr-coulomb and hardening soil model comparison of the settlement of an … fig. 2. finite element model of nai gaj dam fig. 3. finite element mesh of nai gaj dam fig. 4. maximum water level in the nai gaj dam iii. results and discussion a. comparison of dam settlement with the use of mcm and hsm all materials are modeled with the mcm (condition 1). each of the four materials (clay core, sandy gravel, random fill and sandy siltstone) is modeled separately with hsm, and the rest are modeled with mcm (condition 2). the calculations of settlement of the dam were performed for the end of construction (ec) and after the filling of reservoir (afr) conditions. the settlement response of the dam computed with mcm and hsm are compared for the ec and afr in figures 5-12. from the results (figures 5-10) it is concluded that there is less variation in settlement computed with the mcm and hsm for three of the major material zones (clay core, sandy gravel and random fill) at ec and afr conditions. for clay core, random fill and sandy gravel, the mcm overestimates the shear strength. therefore, the settlement predicted by the mcm was slightly lower than the one computed with the hsm. on the other hand, for sandy siltstone (foundation), the settlement predicted with the mcm is higher than the one predicted with hsm. fig. 5. comparison of dam settlement at ec computed with mcm (condition 1) and hsm applied to clay core only (condition 2) fig. 6. comparison of dam settlement at afr computed with mcm (condition 1) and hsm applied to clay core only (condition 2) fig. 7. comparison of dam settlement at ec computed with mcm (condition 1) and hsm applied to sandy gravel (condition 2) fig. 8. comparison of dam settlement at afr computed with mcm (condition 1) and hsm applied to sandy gravel (condition 2) engineering, technology & applied science research vol. 9, no. 5, 2019, 4654-4658 4657 www.etasr.com bhutto et al.: mohr-coulomb and hardening soil model comparison of the settlement of an … fig. 9. comparison of dam settlement at ec computed with mcm (condition 1) and hsm applied to random fill (condition 2) fig. 10. comparison of dam settlement at afr computed with mcm (condition 1) and hsm applied to random fill (condition 2) fig. 11. comparison of dam settlement at ec computed with mcm (condition 1) and hsm applied to sandy siltstone (condition 2) fig. 12. comparison of dam settlement at afr computed with mcm (condition 1) and hsm applied to sandy siltstone (condition 2) b. percentage increase of settlement predicted with mcm for the ec and afr compared with hsm figure 13 shows the comparison of dam settlement computed with the mcm and hsm for ec and afr conditions. the moe of sandy siltstone varies from 70000 to 125000kpa. it is observed that for ec, the mcm showed 56.65% and 49.40% more settlement than the hsm when the moe of sandy siltstone increased from 70000 kpa to 125000kpa respectively. it is observed that for afr, the mcm showed 58.85% and 50.30% more settlement than the hsm when the moe of sandy siltstone increased from 70000kpa to 125000kpa respectively. fig. 13. increase percentage of mcm as compared to hsm when the moe of sandy siltstone varied from 70000 to 125000kpa the settlement of the dam was calculated only at the crest of the dam. from the results, it is concluded that the sandy siltstone (foundation) has more influence on settlement as compared to the other zones of the dam. according to a study on 134 such embankments, it was found that most of the embankments settled as high as 1% of the dam height [25]. as mentioned above, the sandy siltstone (foundation) is sensitive to settlement when predictions were made with the mcm and hsm. the mcm showed a settlement of 2.5m (afr) when the moe of sandy siltstone is 70000kpa. this shows that the predicted settlement with the mcm is about 4.2% of the dam height. the mcm showed a settlement of 1.7m (afr) when the moe of sandy siltstone is 125000kpa. this shows that the predicted settlement with the mcm is about 2.9% of the dam height. the hsm showed a settlement of 1m (afr) when the moe of sandy siltstone is 70000kpa, with a predicted settlement with mcm of about 1.69%, and a settlement of 0.8m (afr) when the moe of sandy siltstone is 125000kpa, showing predicted settlement of about 1.35%. this implies that the 0.8m settlement of the dam is considered to be a reasonable estimate. iv. conclusions numerical analysis of an embankment dam was conducted to adopt a reasonable magnitude of moe of those zones of the dam, which have major influence on settlement. dam settlement was computed with morh-coulomb model (mcm) and hardening soil model (hsm), and the results were compared. the results suggest that out of the four major zones of the dam (clay core, sandy gravel, random fill and sandy siltstone), the sandy siltstone has the most influence on the engineering, technology & applied science research vol. 9, no. 5, 2019, 4654-4658 4658 www.etasr.com bhutto et al.: mohr-coulomb and hardening soil model comparison of the settlement of an … settlement of the dam for both mcm and hsm. the results suggest that the settlement predicted with the hsm is in match with the findings in similar studies. references [1] j. m. duncan, s. g. wright, t. l. brandon, soil strength and slope stability, john wiley & sons, 2014 [2] r. b. jansen, advanced dam engineering for design, construction, and rehabilitation, springer, 2012 [3] a. d. m. penman, instrumentation, monitoring and surveillance: embankment dams, routledge, 2017 [4] r. nayebzadeh, m. mohammadi, “the effect of impervious clay core shape on the stability of embankment dams”, geotechnical and geological engineering, vol. 29, no. 4, pp. 627-635, 2011 [5] q. chen, y. h. zou, m. tang, c. r. he, “modelling the construction of a high embankment dam”, ksce journal of civil engineering, vol. 18, no. 1, pp. 93-102, 2014 [6] r. b. j. brinkgreve, s. kumarswamy, w. m. swolfs, plaxis reference manual, plaxis, 2017 [7] p. novak, a. i. b. moffat, c. nalluri, r. narayanan, hydraulic structures, crc press, 2014 [8] p. pramthawee, p. jongpradist, w. kongkitkul, “evaluation of hardening soil model on numerical simulation of behaviors of high rockfill dams”, songklanakarin journal of science & technology, vol. 33, no. 3, pp. 325-334, 2011 [9] h. t. pham, h. z. oo, c. jing, “stability of slope and seepage analysis in earth dam using numerical finite element model”, study of civil engineering and architecture, vol. 2, no. 4, pp. 104-108, 2013 [10] e. conte, f. silvestri, a. troncone, “stability analysis of slopes in soils with strain-softening behaviour”, computers and geotechnics, vol. 37, no. 5, pp. 710-722, 2010 [11] m. a. zardari, h. mattsson, s. knutsson, l. ormann, “comparison of three-dimensional and two-dimensional axisymmetric finite element analyses of a corner section of a tailings dam”, scientia iranica, international journal of science and technology, vol. 24, no. 5, pp. 2320-2331, 2017 [12] t. schanz, “formulation and verification of the hardening-soil model”, in: beyond 2000 in computational geotechnics, pp. 281-290, crc press, 1999 [13] wapda, project planning report of nai gaj dam, water and power development authority pakistan, 2006 [14] a. j. schleiss, r. m. boes, dams and reservoirs under changing challenges, crc press, 2011 [15] m. carter, s. p. bentley, soil properties and their correlations, john wiley & sons, 2016 [16] f. cobb, structural engineer's pocket book, 2nd edition: british standards, elsevier, 2008 [17] r. f. craig, soil mechanics, springer, 2013 [18] r. a. rajapakse, geotechnical engineering calculations and rules of thumb, butterworth-heinemann, 2015 [19] g. e. barnes, soil mechanics: principles and practice, palgrave macmillan, 2010 [20] j. l. justo, j. saura, “three-dimensional analysis of infiernillo dam during construction and filling of the reservoir”, international journal for numerical and analytical methods in geomechanics, vol. 7, no. 2, pp. 225-243, 1983 [21] b. g. look, handbook of geotechnical investigation and design tables, crc press, 2014 [22] m. n. sara, site assessment and remediation handbook, crc press, 2003 [23] p. j. burgess, d. sarabia, j. small, h. g. poulos, j. sinha, “settlement behaviour of a major dam”, ancold 2006 conference: dams : the challenges of the 21st century, sydney, australia, november 19-22, 2006 [24] l. ormann, m. a. zardari, h. mattsson, a. bjelkevik, s. knutsson, “numerical analysis of strengthening by rock fill embankments on an upstream tailings dam”, canadian geotechnical journal, vol. 50, no. 4, pp. 391-399, 2013 [25] d. u. deere, r. p. miller, engineering classification and index properties for intact rock, illinois university at urbana, 1966 microsoft word 15-2234_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3380-3386 3380 www.etasr.com kahouli et al.: type-2 fuzzy logic controller based pss for large scale power systems stability type-2 fuzzy logic controller based pss for large scale power systems stability o. kahouli electrical engineering department, national engineering school of sfax, university of sfax, sfax, tunisia omarkahouli@yahoo.fr b. ashammari electrical engineering department, college of engineering, university of hail, hail, saudi arabia badr_ms@hotmail.com k. sebaa electrical and computer sciences engineering department, university of medea, medea, algeria sebaa.karim@univ-medea.dz m. jebali electrical engineering department, national engineering school of sfax, university of sfax, sfax, tunisia mariam.djebali@yahoo.fr h. hadj abdallah electrical engineering department, national engineering school of sfax, university of sfax, sfax, tunisia hsan.haj@enis.rnu.tn abstract—in this paper, the application of the fuzzy logic based power systems stabilizer (flpss) to damp power system oscillation is presented. various types of fuzzy logic controller are used to replace the conventional power system stabilizer (cpss). the classic fuzzy logic controller based pss (flcpss), the polar flc (pflcpss) and the interval type-2 fuzzy logic controller based pss (it2flcpss) are applied to the new england new york interconnected power system and the obtained results are compared. for coordination purposes, genetic algorithm (ga) is used to tune the flcpss’s gains. the non-linear simulation in the presence of noise confirms the robustness and the superiority of the it2flcpss. keywords-cpss; flcpss; pflcps; it2flpss; ga; prony analysis i. introduction nowadays, power systems are driven to work around their limits of stability in a fast and flexible way. hence, modern power systems may reach disagreeable conditions like poorly damped electromechanical oscillations. a possible change in the operating point could lead to weak interconnected lines. these lines will cause the generation of inter-area oscillations with poorly damped low frequency modes. improving the damping of these modes by the power systems stabilizers (psss) is an open research topic. psss are designed around some operating points, with the change in these operating points leading to un-damped oscillations, or even to instability. recently, fuzzy logic controllers (flcs) have attracted considerable attention as candidates for novel control strategies because of their advantages over conventional computational systems. unlike other classical control methods, flcs are model-free controllers, i.e. they do not require an exact mathematical model of the controlled system. moreover, rapidity and robustness are their most profound and interesting properties in comparison to the classical schemes. designing psss based on flc has become an active area and satisfactory results have been obtained [1-3]. these flcpsss use the concept of the t1fls (type-1 fuzzy logic system). the concept of the t2fls (type 2 fuzzy logic system) was initially proposed as an extension of the classical t1fls. t2fls is very useful in situations where it is difficult to determine an exact membership function (mf) for a fuzzy set. hence, it is very effective for dealing with uncertainties, such as those due to penetration of the distributed generation in power systems. however, t2flss are more difficult to use and understand than t1fls. despite these difficulties, t2fls has found applications in many fields [4–9]. the concept of the it2flcpss (interval type-2 fuzzy logic controller pss) has been introduced in power systems during the last decade. authors in [10] presented the use of the t2fs based adaptive synergetic pss to improve the stability of the power system. others proposed a pss based on t2fls to improve power system stability where differential evolution algorithm is applied to optimize the it2flcpss parameters and rule base [11, 12]. on the other hand, for improvement of the voltage stability, an it2flc is proposed and tuned based on the approximation of the system by the t1 ts fuzzy model [13]. its drawback is that the application of the it2flpss is only suitable for small scale power systems in which authors approximated the dynamics of the power system by the t1tsk (type 1 takagi, sugeno, and kang) fuzzy model which is then used to tune the it2 flc via the lmi approach. this method is tested on small systems (two machines) with the third-order single-axis dynamic model. for realistic large scale power systems with power electronic devices this method is time consuming and not easy to be applied as it requires: 1. two independent highly nonlinear functions by generator for building of the t1tsf approximation, which is difficult to obtain for large scale power systems with various power electronic devices, 2. four state feedback gains and two controller parameters tuning for each generator. also their work is related to the voltage control. in [14] an interval type-2 fuzzy controller-based thyristor controlled series capacitor (it2tcsc) has been used alongside cpss for improving power system stability on large scale power systems to damp out the speed and power oscillations engineering, technology & applied science research vol. 8, no. 5, 2018, 3380-3386 3381 www.etasr.com kahouli et al.: type-2 fuzzy logic controller based pss for large scale power systems stability following different critical faults. they use: i) the active power line as an input of the it2tcsc as opposed to the generator speed, for study of the power system oscillation. ii) the it2tcsc use of the sliding surface that leads to the charting problem. iii) implementation of two it2tcsc with the presence of cpss. based on the research described above, our goal is the damping of the power system’s oscillation. the proposed method requires only three gains per generator. then, attempts will be made to demonstrate that it can be applied to realistic power systems, and used for solving the coordination of it2flcpss for large scale power systems. hence, various types of pss controllers namely flcpss [2], pflcpss [1], cpss and our contribution of it2flcpss are presented in this paper. this is achieved by applying the previously mentioned flcpsss to a 68-bus, 16-machine power system, which is large and close to realistic power systems. several scenarios are considered to verify the robustness of the proposed method. the nonlinear simulation and eigenvalue analysis demonstrate the significant improvement of dynamic oscillations by the it2flcpss under each scenario. ii. type-2 fuzzy logic system design the structure of the t2fls is shown in figure 1. t2fls is similar to t1fls. the main difference between them is that t2fls requires a type-reduced process to convert the output of the fuzzy inference engine into a type-reduced set and at least one of the fuzzy sets is t2. the crisp output is obtained by the defuzzyfication of the type-reduced set. the t2fls can efficiently simplify the computational process of type-reduction and is very simple to use [5]. fig. 1. structure of a t2fls consider a type-2 tsk fuzzy logic system having n inputs, 1 1,..., ...n nx x x x x  = ∈ × ×  and one output y y∈ . in order to construct the fuzzy rules we assume that there are m rules in the type-2 fuzzy system, where the i th rule has the following form: 1 1 : is and...and is theni i i i i n n r if x f x f y c=� � (1) where 1 2, ,..., i i i n f f f� � � are antecedent linguistic terms modelled by the interval type-2 triangular fuzzy sets (figure 2), iy is the output of thi rule ir and the consequent parameter ic is an interval type-1 set. in figure 2, the footprint of uncertainty (fou) of each membership function (mf) can be represented as a bounded interval in terms of the upper mf ( )i j jf xµ � and the lower mf ( )i j jf xµ � , where: ( ) max(min( , ),0) ( ,a ,b ,c ) and ( ) 0.8 ( ) i j i i j j j j j j jf j j j j j j j j j jf f x a c x x b a c b tri x x x µ µ µ − − = − − ≡ = ⋅ � � � (2) , j a j b and j c are the parameters of triangular primary mf of the type-2 fuzzy set i j f� . fig. 2. interval type-2 triangular mfs for antecedents sets. the inference engine combines the fuzzy rules in order to map the crisp inputs to interval type-2 fuzzy output sets. based on the input and the antecedents of the rules, it calculates a firing interval for each rule and then applies these firing levels to the consequent fuzzy sets. the firing interval [ , ]i if f of the thi rule is an interval type-1 set, which is determined by its left-most and right-most points i f and i f such that : 1 2 1 2( ) ( ) ... ( )i i i n i nf f f f x x xµ µ µ= ∗ ∗ ∗ � � � (3) 1 2 1 2( ) ( ) ... ( )i i i n i nf f f f x x xµ µ µ= ∗ ∗ ∗ � � � (4) where ( )i j jf xµ � and ( )i j jf xµ � represent the membership values of the lower and the upper membership functions of the crisp input j x to the type-2 fuzzy set i j f� in the thi rule. when interval type-2 fuzzy sets are used for the antecedents, and interval type-1 fuzzy sets are used for the consequent sets of type-2 tsk rules, the final output can be expressed as [4, 5]: , l r y y y =   (5) the output y is an interval type-1 set, therefore, only its two endpoints l y and r y need to be computed which can be engineering, technology & applied science research vol. 8, no. 5, 2018, 3380-3386 3382 www.etasr.com kahouli et al.: type-2 fuzzy logic controller based pss for large scale power systems stability represented as an expansion of fuzzy basis functions (fbfs), as: 1 1 m mi i i l l l li i yu f u f = = = ⋅∑ ∑ (6) 1 1 m mi i i r r r ri i y f u f = = = ⋅∑ ∑ (7) where i l f and i r f denote the firing strength membership grades contributing to the left-most-point l y and the right-most-point r y respectively, i l u and i r u are the singleton lower and upper control actions of the consequences part. from the typereduction stage a type-reduced set exists for each output. the crisp output of the controller is equal to the mind point of the type-reduce set: 2 + = l r c y y y (8) using the iterative procedure given in [15]. the computation procedure is briefly provided below. initially, the right-most point r y is computed. without loss of generality, it is assumed that the parameters i u are arranged in ascending order, i.e., 1 2 3 ...... m u u u u≤ ≤ ≤ • step_1: compute r y in (7) by initially setting ( ) / 2i i i r f f f= + , for i=1, 2, ……., m and let ' r r y y= • step_2: find k ( 1 1k m≤ ≤ − ) such that 1k k r u y u +′≤ ≤ . • step 3: compute r y in (7) with i i r f f= for i k≤ and i i r f f= for i k> , then set r r y y′′ = . • step 4: if r r y y′′ ′≠ , then go to step 5. if r r y y′′ ′= then set r r y y ′′= and go to step 6. • step 5: set r r y y ′′′ = and return to step 2. • step 6: end. the procedure to compute l y is very similar, only two changes need to be made. in step 2, we need to find '1 1k m≤ ≤ − such that 1k k l u y u +′≤ ≤ , and in step 3, let i i l f f= for 'i k≤ and i i l f f= for 'i k> . iii. fuzzy logic based pss selection of the input variables of the flc based pss depends on the nature of the controlled plant and the desired outputs. generally, it is common to use the output error and their derivative (or their integral). since the goal of this work is the improvement of the system damping, the speed deviations and their derivative are used as shown in figure 3. fig. 3. fuzzy logic based pss. a. flcpss and it2flc the structure of these two controllers is similar, with small differences. the speed deviation i ω∆ and acceleration deviation i ω∆ � of ith generator are used as the inputs of the flcpss and the it2flcpss in this paper. the output control signal from the flcpss ( i flcpss u ) is injected to the summing point of the automatic voltage regulator (avr) where an eventual cpss should be connected. to convert the measured input variables of the flcpss into suitable linguistic variables, seven fuzzy subsets nb, nm, ns, zo, ps, pm, pb are chosen. the mfs for the input variables, as used in the present study, are shown in figure 4. in this study, both inputs of flcpss and it2flcpss have seven subsets. thus, a fuzzy table consisting of forty nine rules should be constructed. table i shows a rule table obtained by the trial error based on the result obtained from the cpss. table i. rules for flcpss and it2flcpss ∆ω nb nm ns zo ps pm pb �∆ω nb nl nl nl nm mn ns zo nm nl nl nm nm ns zo ps ns nl nm ns ns zo ps pm zo nm nm ns zo ps pm pm ps nm ns zo ps ps pm pl pm ns zo ps pm pm pl pl pb zo ps pm pm pl pl pl the triangular shape function is chosen to follow the work in [1, 2]. the gaussian shape function can also be used. however in our study, for better performance, triangular shape and 7 mfs are used. quicker response is observed with 3 mfs, but with poorer performance. the best compromise between performance and simulation time is realized by 7 mfs as is also suggested in [2]. in order to take a crisp control action, the fuzzy control action inferred from the fuzzy control algorithm must be defuzzyfied. to ensure that all the fired rules have some contribution in the control action, the method of the center of gravity is employed in this study. it2flcpss requires a reduction strategy. the reduction used in this paper is centroid method. the input gains i kω , i kω� and the output gain i flcpss ku , are used to properly scale the fuzzy input and output variables. engineering, technology & applied science research vol. 8, no. 5, 2018, 3380-3386 3383 www.etasr.com kahouli et al.: type-2 fuzzy logic controller based pss for large scale power systems stability (a) membership functions for flcpss (b) membership functions for it2flcpss fig. 4. membership functions. b. pflcpss pflcpss has been originally developed in [1]. the concept of this controller is based on the sign of ω∆ and ω∆ � . two membership functions are created (n(θ),ρ(θ)) to represent four situations. the stabilizing signal is calculated using the following steps: 1. determine the piecewise linear fuzzy mfs ν(θ) and ρ(θ) as described in [1] and reproduced in figure 5. these mfs use the angle θ obtained from the phase plane 1( tan ( / ))θ ω ω−= ∆ ∆� . 2. compute the stabilizing signal ( )u k using max ( ) ( ) ( ) ( ) ( ) ( ) n p u k gc k u n p θ θ θ θ − = ⋅ ⋅ + (9) where ( )gc k is the gain whose value is given by (10): ( ) 2 2 if 1 otherwise g rr k r d c ω ω  = ∆ +∆ <=   � (10) parameter dr should be adjusted to it optimal value. for optimal parameter setting, various performance indices can be used and minimized by traditional or meta-heuristic methods. in this paper, dr is equal to 0.98. the value of umax depends on the synchronous machine to be studied (it is equal to 0.02pu in this study). we call this stabilizer polar flpcss. fig. 5. membership functions for pflcpss c. cpss the pss or cpss is employed to add supplementary damping to the rotor oscillations of the synchronous machine by controlling its excitation. the electromechanical oscillations of the electrical generators must be effectively damped to maintain the system stability. the output signal of the pss is introduced as an additional signal to the avr (upss) to the excitation system block. the pss input signal can be the machine speed deviation. the pss can be modeled by the following non-linear system (figure 6): fig. 6. conventional power system stabilizer model block diagram. to obtain an adequate damping, pss should provide a moderate phase advance at frequencies of interest in order to compensate for the inherent lag between the field excitation and the electrical torque induced by the pss action. the model consists of a low-pass filter, a general gain, a washout highpass filter, a phase-compensation system, and an output limiter. the gain kpss determines the amount of damping produced by the stabilizer. the washout filter eliminates low frequencies that are present in the ω∆ signal and allows the pss to respond only to speed changes. the phase-compensation system is represented by a cascade of two first-order lead-lag transfer functions used to compensate the phase lag between the excitation voltage and the electrical torque of the synchronous machine. for comparison, a ω∆ conventional type pss (cpss) is designed under the same scenarios used in [16]. cpsss parameters can be obtained by the classical method of searching for the close fit to the ideal case from a number of phase compensator characteristics. pss parameters are computed by the root locus method [17]. however, in this paper pss parameters are taken from [16], in which ga was used to find the parameters that give the best damping ratio �. engineering, technology & applied science research vol. 8, no. 5, 2018, 3380-3386 3384 www.etasr.com kahouli et al.: type-2 fuzzy logic controller based pss for large scale power systems stability iv. multimachine power system model a 16-machine power system, as shown in figure 7, is used to test the proposed it2flcpss. this power system comprises of five coherent areas representing a reduced model of the new england and new york interconnected system. the solid lines indicate the major weak tie lines that cause the low frequency inter-area oscillations. each of the areas 1, 2 and 3 contains a single large generator, which is represented by its aggregated equivalent model. area 4 is modeled with an equivalent generator in addition to more normally sized generators. area 5 has the most detailed modeling that includes static exciters, thermal turbines and governors on all generators. the power system is modeled by a set of non-linear differential equations [18]: ( , )x f x u=� (11) where x is a vector state , , , , , q d d s x e eδ ω ψ ψ ′ ′′ ′ ′′=   and u is the vector of the pss, it2flcpss, pflcpss or flcpss output signals. details of network parameters are given in [17]. to assess the flcpsss four scenarios are tested (table ii). fig. 7. new england new york interconnected power system model table ii. scenarios considered scenario no description 1 line 28-29 out of service 2 line 1-2 out of service 3 lines 25-26 and 3-18 out of service 4 line 41-42 out of service a. tuning of the gains each fuzzy logic controller requires an adequate tuning of the input gains i k ω , i k ω� and the output gains flcpss i ku (figure 3). these gains are used to properly scale the fuzzy input and output variables of the flc based pss. generally, these gains can be obtained by a tedious trial-and-error process for small size systems. but for large scale systems the use of such a technique is impossible. as the aim of this work concerns large scale power systems, an optimization based ga method is proposed to compute these parameters. the objective of the off-line tuning algorithm is to change the controller gains to obtain the desired system response. the tuning algorithm tries to minimize the system overshoot index j: / 16 1 1 min ( , , ) ( ) i t ts i i flcpss ik i j k k ku kω ω ω = = = ∆∑ ∑� (12) where t is the simulation time (11 seconds). it is very time consuming to use the non-linear simulation. for this reason the linearized power system is used to speed-up this process. the main elements of the ga used to resolve this optimization problem are defined in [16]. ga is stopped when a maximum number of generations (100) is reached. obtained parameters by the ga are summarized in table iii. from figure 8 it is clear that this solution is stable as it is reached at 60 generations. table iii shows the input and the output gains. without control, the eigenvalue analysis confirms that the power system is unstable [16, 19]. four contingencies are applied to assess the performance of the four controllers (cpss, flcpss, pflcpss and it2flcpss). the parameters of cpss for generators 1 to 16 are obtained using the ga procedure [16]. fig. 8. convergence of the ga optimization table iii. gains constants mach. ι ω κ i k ω� flci ku mach. i k ω i k ω� flci ku #01 4.26 2.51 0.95 #09 2.86 8.36 0.98 #02 3.42 6.62 0.95 #10 1.38 4.82 0.81 #03 4.05 4.17 0.93 #11 1.46 3.02 0.87 #04 3.28 4.26 0.78 #12 3.12 3.04 0.89 #05 2.04 6.97 0.85 #13 4.45 1.35 0.83 #06 1.24 4.57 0.99 #14 2.79 0.39 0.66 #07 3.72 6.12 0.96 #15 2.15 1.81 0.41 #08 0.39 6.28 0.79 #16 3.34 2.82 0.31 the 1st (resp. 2nd, 3rd) contingency consists on the application of the three-phase to ground fault in line 1-2 (resp. line 28-29, line 41-42) at 0.1s, and cleared after 6 cycles. in the fourth contingency, the application of the three-phase to ground fault in line 3-18 at 0.1s is considered, which is then cleared after 6 cycles. for the system with cpss, linear analysis is carried out by the perturbation method for building the state space system, after which the modes correspond to the eigenvalues of the linearized system. however, in the presence of it2flcpss the modes are obtained by prony analysis as it is not possible to use the perturbation method, as in the case of g14 66 41 40 48 47 1 31 30 62 63 g10 g11 32 38 46 49 42 67 g15 52 68 g16 51 45 44 39 37 65 g13 64 36 34 33 9 50 35 g1 53 2 g8 60 25 26 28 29 g9 61 27 3 18 17 16 24 21 22 23 59 g7 g6 g4 g5 g2 g3 55 54 10 6 7 8 11 12 13 4 14 15 58 57 56 19 20 5 43 area 4 area 5 area 2 area 3 a re a 1 engineering, technology & applied science research vol. 8, no. 5, 2018, 3380-3386 3385 www.etasr.com kahouli et al.: type-2 fuzzy logic controller based pss for large scale power systems stability the presence of cpss. prony analysis is a method for extracting sinusoidal exponential signals from time series data, by solving a set of linear equations. assuming n complex data samples x[1],…, x[n] the investigated function can be fitted by m exponential functions: 1 1 (̂ ) 2 i i n tj i i f t ae φλ = =∑ (13) in order to perform the damping of the power system oscillations by psss, several sensors are necessary. however, sensor readings are often noisy. in order to simulate the impact of the measurement uncertainty on the performance of t1 flc based pss and t2 flc based pss, random noise with normal distribution is added to the measurement values of rotating speed and acceleration. to carry out a quantitative comparison between the controllers, three well known performance criteria are used [5]: the integral of square error, 16 2 1 ise ( ) nn t dtω = = ∆∑ ∫ , the integral of the absolute value of the error, 16 1 iae ( ) nn t dtω = = ∆∑ ∫ , and the integral of the time multiplied by the absolute value of the error, 16 1 itae ( ) nn t t dtω = = ⋅ ∆∑ ∫ . generally, these indexes of performance are used in the optimal tuning of the controller. in this work, these will be employed to assess the stability of the closed loop system. minimum value of ise means that the controller will eliminate large errors quickly, but will tolerate small errors persisting for a long period. a system with minimum iae tends to produce slower response than ise optimal systems, but usually with less oscillation. a system with small itae settles much more quickly than the other two errors. in table iv, the values for ise, iae and itae are summarized considering noise of 0.02pu and 0.05pu applied to the speeds and accelerations of all 16 machines and only in the case of the first contingency. table iv. performance criteria values under 1st contingency in presence of 0.02pu and 0.05pu noise noise of 0.02pu noise of 0.05pu avg. value std. dev. avg. value std. dev. cpss ise 2.46e-02 5.60e-03 3.49e-02 3.55e-02 iae 8.23e-01 7.99e-02 9.65e-01 3.09e-01 itae 5.26e+00 5.02e-01 5.91e+00 2.56e+00 pflcpss ise 1.75e-05 2.03e-07 2.05e-05 7.15e-07 iae 1.92e-02 1.63e-04 2.85e-02 5.77e-05 itae 5.27e-02 8.13e-04 1.12e-01 2.77e-03 flcpss ise 1.75e-05 2.95e-07 2.05e-05 6.17e-07 iae 1.99e-02 3.69e-04 2.86e-02 3.51e-04 itae 5.73e-02 9.39e-04 1.12e-01 2.98e-03 it2flcpss ise 1.74e-05 9.42e-08 1.98e-05 6.55e-08 iae 1.92e-02 1.63e-04 2.85e-02 3.51e-04 itae 4.92e-02 8.35e-04 1.11e-01 3.13e-03 in table v, the behavior of controllers with the influence of model uncertainty is presented. furthermore each value represents the average and the standard deviation of the three performance criteria which are calculated for 10 samples. a closer inspection of table v reveals that the criteria values for t1 flcpss and it2flcpss type-2 flc are similar. this is due to the mitigation effect of these uncertainties by the fls. in such a case, it is advisable to select a t1 flcpss since it is easier to implement. however, with the performance criteria values shown in table iv one can suggest that at the lower values of ise, iae, and itae, the best system response is obtained when using an it2flcpss. these results demonstrate the ability of the proposed controller to cope with an uncertain process and its potentiality to outperform its t1 counterpart. table v. performance criteria values for pss-various models (scenarios) scenarios # (modeling uncertainty) 1 2 3 4 ise cpss 0.0197 0.0298 0.0735 0.0040 pflcpss 0.0117 0.0196 0.0462 0.0007 flcpss 0.0116 0.0200 0.0461 0.0005 it2flcpss 0.0118 0.0198 0.0471 0.0011 iae cpss 4.6459 4.2780 6.2612 2.0789 pflcpss 1.9978 2.6958 3.7928 1.1379 flcpss 1.9626 2.6276 3.6820 0.9862 it2flcpss 2.1615 2.9320 4.2134 1.5209 itae cpss 6.7013 5.2684 8.0880 3.3461 pflcpss 2.0698 3.0261 4.2960 1.6868 flcpss 2.0020 2.8350 4.0587 1.3968 it2flcpss 2.5119 3.7904 5.3436 2.7344 v. conclusion the application of three fuzzy logic-based control algorithms as power system stabilizers is described in this paper. time domain simulation and modal analysis performed with various stabilizers, over a wide range of operating conditions with different disturbances, have demonstrated the effectiveness and robustness of this control algorithm. a comparison of the performance of the four algorithms (the three fuzzy logic-based and the conventional) shows that the three controllers generally provide better performance than a fixed parameter conventional stabilizer. although all four algorithms provide acceptable performance, it2flcpss is the most suitable when the presence of measurement uncertainties (noise) is more pronounced. also, due to its simplicity it can be easily implemented for the control of large scale power systems. references [1] t. hiyama, “development of fuzzy logic power system stabilizer and further studies”, 1999 ieee international conference on systems, man, and cybernetics, tokyo, japan, october 12-15, 1999 [2] m. sanaye-pasand, o. p. malik, “implementation and laboratory test results for a new fuzzy logic based pss”, 1996 canadian conference on electrical and computer engineering, calgary, canada, may, 26-29, 1996 [3] m. a. m. hassan, o. p. malik, “implementation and laboratory test results for a fuzzy logic based self-tuned power system stabilizer”, ieee transactions on energy conversion, vol. 8, no. 2, pp. 221-228, 1993 [4] q. liang, j. m. mendel, “an introduction to type-2 tsk fuzzy logic systems”, 1999 ieee international fuzzy systems, seoul, south korea, august, 22-25, 1999 [5] s. barkat, a. tlemcani, h. nouri, “noninteracting adaptive control of pmsm using interval type-2 fuzzy logic systems”, ieee transactions on fuzzy systems, vol. 19, no. 5, pp. 925-936, 2011 engineering, technology & applied science research vol. 8, no. 5, 2018, 3380-3386 3386 www.etasr.com kahouli et al.: type-2 fuzzy logic controller based pss for large scale power systems stability [6] x. lu, m. liu, j. liu, “design and optimization of interval type-2 fuzzy logic controller for delta parallel robot trajectory control”, international journal of fuzzy systems, vol. 17, no. 1, pp. 595-608, 2015 [7] t. kumbasar, h. hagras, “a self-tuning zslices-based general type-2 fuzzy picontroller”, ieee transactions on fuzzy systems, vol. 23, no. 1, pp. 991-1013, 2015 [8] a. padhi, hardware realization of interval type 2 fuzzy logic controller, phd thesis, national institute of technology, rourkela, india, 2015 [9] k. su, s. huang, c. yang, “development of robotic grasping gripper based on smart fuzzy controller”, international journal of fuzzy systems, vol. 19, no. 1, pp. 190-206, 2017 [10] e. nechadi, m. harmas, a. hamzaoui, n. essounbouli, “type-2 fuzzy based adaptive synergetic power system control”, electric power systems research, vol. 88, pp. 9-15, 2012 [11] z. sun, n. wang, d. srinivasan, y. bi, “optimal tunning of type-2 fuzzy logic power system stabilizer based on differential evolution algorithm”, international journal of electrical power and energy systems, vol. 62, pp. 19-28, 2014 [12] s. kamel, b. ziyad, h. m. naguib, a. mouloud, r. mohamed, “an indirect adaptive type-2 fuzzy sliding mode pss design to damp power system oscillations”, 7th international conference on modelling, identification and control, sousse, tunisia, december 18-20, 2015 [13] a. abbadi, l. nezli, d. boukhetala, “a nonlinear voltage controller based on interval type 2 fuzzy logic control system for multimachine power systems”, international journal of electrical power and energy systems, vol. 45, no. 1, pp. 456-467, 2013 [14] m. tripathy, s. mishra, “interval type-2-based thyristor controlled series capacitor to improve power system stability”, iet generation, transmission & distribution, vol. 5, no. 2, pp. 209-222, 2011 [15] n. karnik, j. mendel, q. liang, “type-2 fuzzy logic systems”, ieee transactions on fuzzy systems, vol. 7, no. 6, pp. 643-658, 1999 [16] k. sebaa, m. boudour, “optimal locations and tuning of robust power system stabilizer using genetic algorithms”, electric power systems research, vol. 79, no. 2, pp. 406-416, 2009 [17] g. rogers, power system oscillations, springer, 2000 [18] p. kundur, power system stability and control, epri, 1994 [19] k. sebaa, h. gueguen, m. boudour, “mixed integer non-linear programming via the cross-entropy approach for power system stabilisers location and tuning”, iet generation, transmission & distribution, vol. 4, no. 8, pp. 928-939, 2010 microsoft word 18-3139_s_etasr_v9_n6_pp4968-4973 engineering, technology & applied science research vol. 9, no. 6, 2019, 4968-4973 4968 www.etasr.com gururaj & gowri: performance optimization of an ecar by parametric analysis performance optimization of an ecar by parametric analysis banda gururaj department of eee, gprec r&d center andhra pradesh, india and jnt university anantapur ananthapuramu, andhra pradesh, india anilgururaj009@gprec.ac.in kolli sri gowri department of electrical and electronics engineering g. pulla reddy engineering college (autonomous) kurnool, andhra pradesh, india gowrivasu.3@gmail.com abstract—in this paper a method for performance optimization of an electric car (ecar) is proposed based on acceleration rate, maximum speed, and tractive force. since the total tractive force is exerted by propulsion motor alone, the driving performance of an ecar depends on the power of the propulsion motor and its control. the proposed pre-sizing methodology depicts the optimum power of the propulsion motor, and for the optimized motor the impact of road dynamics, acceleration rate, change in mass, and gear ratio on the ecar’s drive range are analyzed. the proposed electric propulsion system is modeled and the performance characteristics are analyzed using matlab to validate the behavior of an ecar propulsion. keywords-drive cycle; ecar; propulsion system; road dynamics; mass; gear ratio and range i. introduction in urban areas, there is a prodigious concern on intensifying air pollution caused by fossil fuels. hence, the use of zero emission vehicles emerged as a need. electric vehicles (evs) have been developed into battery electric vehicles (bevs), hybrid electric vehicles (hevs), plug-in hybrid electric vehicles (phevs), and fuel cell vehicles (fcvs), making a considerable impact in the automotive market. nowadays, evs accomplish the performance indices of traditional sport utility vehicles (suvs). the ev ecar is gaining more attention in the current automotive market being a zero emission vehicle offering higher energy efficiency, hushed operation and, frequent start-stop driving capability. the government of india and its state governments have initiated the “smart city”, faster adoption and manufacture of (hybrid and) electric vehicles (fame-i & fame-ii) schemes with thrust on providing “e-mobility” for citizens. authors in [1] discussed several aspects essential in creating an affluent ev market in india. authors in [2] specified some considerations to determine the local and global environment impact of the autonomy electric transport in contrast with gasoline vehicles. authors in [3] exemplified the real-world emissions and real driving behavior in real, cold, nordic climates. authors in [4] enlightened the transition of the automotive industry to electric mobility. authors in [5] presented fuel economy and emissions comparison for diesel, gasoline, gasoline hev, and bev under the environmental protection agency (epa) drive cycles. authors in [6] investigated the vision of introducing electric vehicles in real-life mobility, and their impression on the distribution grid. authors in [7] researched the challenges and issues when evs are charged from the grid. authors in [8] proposed a method to examine energy efficiency, emissions, noise, and operational availability of city buses. authors in [9] presented an online algorithm to regulate the energy consumption of bevs during driving based on vehicle physiognomies, driving pattern, route map, traffic, and climate. authors in [10] developed robust algorithms for range estimation of an ev and provided options for least energy use. authors in [11] discussed the confines and abilities of the bev and found scaling trends between the epa driving range for one charge cycle and regimenting the battery capacity by weight of the vehicle. authors in [12] formulated a multiobjective optimization problem to size the components of a split-transition vehicle based on engine maximum power rating, motor, battery, and final drive ratio. fig. 1. architecture of an ecar the architecture of an ecar is shown in figure 1. an ecar propulsion system comprises of various components such as a stack of lithium ion batteries, a charging unit, propulsion motor, advanced power electronic converters, controller, mechanical transmission system, and auxiliary components. an ecar is capable of smooth speed control, and provides high rates of acceleration/deceleration, high torque and low-speed hill climbing, low torque and high-speed cruising. even though there have been advancements in technology, compact, economic and high energy efficient batteries are still in developing stage and are expensive. batteries with integrated on-board and/or off-board charging facility, offering quick charge of less than 10 minutes and corresponding author: banda gururaj engineering, technology & applied science research vol. 9, no. 6, 2019, 4968-4973 4969 www.etasr.com gururaj & gowri: performance optimization of an ecar by parametric analysis normal charging of 30-60 minutes through the utility grid have been introduced. an integrated on-board charger is more compact, with higher efficiency. authors in [13] evaluated a variety of dc-dc converter topologies for application in bevs. authors in [14] introduced an advanced on-board vehicular battery charger used for bev application, which attains high power density by assimilating a bidirectional ac/dc converter and a dc/dc converter. authors in [15] described a procedure for estimating battery capacity, power, and cost. authors in [16] investigated the effect of mileage accrual and fast charging on driving range and battery energy of a light-duty bev. authors in [17] developed a method to choose electric traction motors for bevs. authors in [18] elaborated the developments in design and optimization of propulsion motors for general motor bevs. authors in [19] developed driving cycles based on empiric data from a large-scale field operational test for bevs. authors in [20] performed an analysis on real time indian road drive cycles (irdc) in terms of acceleration and deceleration rate, top speed, and average speed with road length. in this paper, a method for performance optimization of an ecar is proposed based on acceleration rate, maximum speed, and tractive force of the vehicle. motor performance characteristics are analyzed in matlab. ii. proposed methodology consider the position of the ecar shown in figure 2 with the applied forces on the vehicle, where m represents its mass in kg, v represents the linear velocity in m/sec, g represents the gravitational acceleration in n/kg, h represents the height of the vehicle from center to ground level, and α represents the gradient in degrees. thus, acceleration is computed for the given speed and power rating by using (1): acceleration = a = fac /m = dv /dt (1) the acceleration force fac, is the force required to accelerate the ecar during linear speed variations and is governed by newton’s second law as given in (2): fac = m × a = m dv /dt (2) fig. 2. ecar and applied forces the tractive effort needed to drive the ecar in the forward direction neglecting vehicle dynamics is given by (3): ft = fac = m × a (3) the friction of the ecar wheels at the road surface is the only force existing at first. the coefficient of rolling friction cr between the tire and the road varies with the type and the size of the tire. the expression for rolling resistance is: fr = cr × m × g for v=0, -cr × m × g for v≠ 0 (4) the aerodynamic drag is a function of speed and can be determined by the density of air d in kg/m3, air drag coefficient cd, vehicle frontal area af, and velocity v. thus, the aerodynamic drag force is: fad = 1/ 2 ×d × cd × af ×v 2 (5) the gradient force depends on m, α, and g. the expression for this force is: fg = m×g×sinα (6) fr, fad, and fg are summed up as road load frl: frl= fr+fad+fg (7) commonly, the tractive force ft to propel the ecar has to surmount the sum of the rolling resistance force fr, aerodynamic drag force fad, and hill climbing of gradient force fg. and consequently, the total tractive effort is the summation of acceleration force and road load and is given by (8): ft= fac + frl (8) the velocity of the vehicle is calculated by integrating acceleration and is given by (9): v = 1/m∫(ft-frl) dt (9) the time required to reach maximum speed and power rating of the motor are determined using (10), (11) and (12): tf = m ∫dv /fac = m ∫dv /(pmotor /v) (10) pmotor = m/tf ∫dv =m /2tf v 2 (11) or pmotor= ft × v (12) emotor = pmotor × t (13) at first, the tractive effort required to propel the ecar is found from (8). the product of tractive effort by the ecar velocity gives the amount of power required and is found from (12). assuming conversion efficiency factors, the energy required to propel is given in (13). to determine the optimum power size of the propulsion motor, a step by step procedure is presented in this paper and is as follows: • input speed and compute acceleration a using (1). • compute the value of acceleration force fac for the given m using (2). • compute the amount of road load frl using (7) by considering dynamics. • estimate total tractive force ft required by the propulsion using (8). • compute the value of maximum speed of an ecar by (9). • measure and compare the actual speed of an ecar with maximum speed. if the measured speed is equal to engineering, technology & applied science research vol. 9, no. 6, 2019, 4968-4973 4970 www.etasr.com gururaj & gowri: performance optimization of an ecar by parametric analysis maximum speed then determine the value of motor power rating using (11) and end the process, else repeat the first step. the output of the algorithm resolves the optimum power of the propulsion motor based on the maximum speed that an ecar can manage. iii. range determination to forecast the range of an ecar, the energy essential to propel it at every instant of the drive cycle is to be calculated, and the effect of this energy trench to be observed. the ecar range for varying mass m, gear ratio g, and air drag coefficient cd, for federal urban driving schedule (fuds), simplified fuds (sfuds), european urban driving schedule (eudc) (ece-47), and new european drive cycle (nedc) are given in table i. note that the range is maximum when m is 1200kg, gear ration is 10.8 and cd is 0.3, which are considered the optimum values. this procedure is further continued with 90% depth of discharge of the battery. the effects of change in m, g, and cd for sfuds cycle are depicted in figures 3-5 respectively. table i. drive cycles accomplished in a single charge drive cycle number of cycles varying mass varying g varying cd g=10.8, cd=0.3 m=1200, cd=0.3 m=1200, g=10.8 1540 1320 1200 30 10.8 6.8 0.8 0.3 0.01 fuds 59 62 64 68 64 59 64 64 64 sfuds 241 254 260 270 260 245 260 260 261 ece-47 112 139 156 208 156 101 153 156 159 nedc 100 120 134 166 134 95 132 134 135 fig. 3. effect of varying mass on drive range fig. 4. effect of varying gear ration on drive range in a similar way, the range for different drive cycles is determined and tabulated in table ii. the specifications of an ecar model considered for range determination are exhibited in table iii. from the data given in table iii, the acceleration time taken to drive the ecar at a speed of 15m/s from start with different acceleration rates a = 3.36m/s2, a = 3.0m/s2 and a = 2.26m/s2 is determined using (6) and gives 4.5s, 5.1s, and 6.8s respectively (figure 6). fig. 5. effect of varying cd on drive range table ii. drive range in a single charge drive cycle distance travelled (km) per charge varying mass, varying g, varying cd, g=10.8, cd=0.3 m=1200, cd=0.3 m=1200, g=10.8 1540 1320 1200 30 10.8 6.8 0.8 0.3 0.01 fuds 120 126 130 138 130 120 130 130 130 sfuds 128 135 138 143 138 130 138 138 139 ece-47 110 137 154 206 154 99 151 154 157 nedc 100 120 134 166 134 95 132 134 134 table iii. ecar specifications mass of the vehicle, m 1200 kg frontal area of the vehicle, af 0.2 sq.mt wheel radius, rw 0.2794 m coefficient of rolling resistance, cr 0.0015 air density, d 1.225 kg/m3 air drag coefficient, cd 0.3 gravitational constant, g 9.81 kg/m2 transmission gear ratio, g 10.8 slope or gradient angle, α 5o fig. 6. acceleration performance of an ecar as acceleration increases the time required to reach the desired speed decreases. higher acceleration demands more tractive force which increases the required power of the motor. for given mass and fixed acceleration of 3.36m/s2 the power required to propel the ecar to a maximum speed of 120km/h from zero speed is determined using (16). at zero road load condition the thick line curve shown in figure 7, depicts that a 90kw motor takes about 14s to propel the ecar and a 30kw motor takes about 35s. considering road load the dotted curve illustrates that a 30kw motor takes 60s and a 90kw motor requires 14s (figure 8). engineering, technology & applied science research vol. 9, no. 6, 2019, 4968-4973 4971 www.etasr.com gururaj & gowri: performance optimization of an ecar by parametric analysis fig. 7. propulsion motor power requirement vs acceleration time fig. 8. full power acceleration of a 90kw motor to reach 120km/hr speed with a tractive force of 1127nm the power of the motor needed is computed from (17) and is 88.9kw which is approximately 90kw. based on the derived conclusions, it is decided that the optimum power of the motor to drive an ecar is 90kw. the specifications of considered optimum propulsion motor of an ecar are given in table iv. table iv. specifications of a 90kw induction motor 3ф, ac induction motor motor power rating, pmotor 90kw nominal voltage, vn 380v, rms current rating, in 200a variable frequency, fs 0-400hz constant power 90kw @ 12000rpm constant torque 120nm @ 7200rpm motor inertia, jmotor 1.5kgm 2 pole pairs, p 2 nominal stator flux, ψs 0.98wb the matlab simulink model of the electric propulsion system of an ecar is shown in figure 9. the subsystem of the simulink model representing the applied vehicle dynamics is shown in figure 10 where constants a=72.84, b=0.0384, and c=0.32 represent the rolling friction coefficient, the gradient, and the aerodynamic drag coefficient respectively. the torquespeed curves for the optimized three phase induction motor as ecar propulsion motor are shown in figure 11. the torque versus time characteristics for the 90kw motor with varying gear ratio g are shown in figure 12. the power versus time characteristics for the 90kw motor with varying gear ratio g are shown in figure 13. the velocity curves for different gear ratios for the 90kw induction motor as a propulsion motor of an ecar are shown in figure 14. fig. 9. simulink model of the ecar fig. 10. the subsystem of the ecar model fig. 11. torque-speed characteristic for the 90kw induction motor fig. 12. torque characteristics with varying g the change in g predominantly affects the performance characteristics of the propulsion motor, a high g is required to operate the motor in constant power but limits the maximum speed of the vehicle. hence, an optimal value of 10.8 gear ratio is chosen for the drive train of an ecar, with propulsion motor engineering, technology & applied science research vol. 9, no. 6, 2019, 4968-4973 4972 www.etasr.com gururaj & gowri: performance optimization of an ecar by parametric analysis operating in filed weakening mode, this can be achieved with the help of field oriented control or direct torque control techniques [21-23]. fig. 13. power characteristics with varying g fig. 14. velocity of an ecar with varying g iv. conclusions a method for performance optimization of an ecar based on vehicle parameters is examined considering the impact of road dynamics, acceleration rate, change in mass and gear ratio of an ecar. the output of the proposed algorithm resolves the optimum power size of the propulsion motor based on the maximum speed and is derived as 90kw. from the acceleration characteristics, a 90kw motor may suffice the required tractive force to propel the ecar, attaining a speed of 120km/h in 14s with an acceleration of 2.38m/s2, which meets the customer’s needs. the ecar propulsion motor counting road dynamics is modeled with the help of mathematical relations. the performance characteristics of the 90kw induction motor for different gear ratios were obtained. it is seen that for higher gear ratios the maximum speed attained by the vehicle decreases, therefore a gear ratio of 10.8 is considered as optimum for the ecar. the proposed optimization technique is simple, efficient and can be applied on any configuration of the ecar. references [1] f. faisal, “an analysis of electric vehicle trends in developed nations: a sustainable solution for india”, journal of undergraduate research, vol. 9, no. 1-5, pp. 1-8, 2017 [2] i. lingvay, a. bors, d. lingvay, “considerations about the local and global environmental impact of autonomy electric transport”, electric vehicles international conference, bucharest, romania, october 5-6, 2017 [3] e. figenbaum, c. weber, “estimating real-world emissions of phevs in norway by combining laboratory measurement with user surveys”, world electric vehicle journal, vol. 9, no. 2, article id 31, 2018 [4] c. mazur, m. contestabile, j. g. offer, n. p. brandon, “understanding the automotive industry: german oem behaviour during the last 20 years and its implications”, world electric vehicle journal, vol 6, no. 4, pp. 1054-1067, 2013 [5] a. r. salisa, n. zhang, j. g. zhu, “a comparison on fuel economy and emissions for conventional hybrid electric vehicles and the uts plug-in hybrid electric vehicle”, ieee transactions on 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gauterin, “development of real-world driving cycles for battery electric vehicles”, world electric vehicle journal, vol. 8, no. 1, pp. 12-24, 2016 [20] v. parekh, v. shah, “measurement and analysis of indian road drive cycles for efficient and economic design of hev component”, world electric vehicle journal, vol. 7, no. 1, pp. 121-132, 2015 [21] h. aygun, m. aktas, “a novel dtc method with efficiency improvement of im for ev applications”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3456-3462, 2018 [22] p. r. tripathy, b. p. panigrahi, “study of direct torque controlled 3phase scim with two and three-level inverters using st-dtc and frengineering, technology & applied science research vol. 9, no. 6, 2019, 4968-4973 4973 www.etasr.com gururaj & gowri: performance optimization of an ecar by parametric analysis dtc scheme”, engineering, technology & applied science research, vol. 5, no. 1, pp. 748-752, 2015 [23] o. m. al-barbarawi, “improving performance of the braking process, and analysis torque-speed characteristics of the induction motor”, engineering, technology & applied science research, vol. 8, no. 6, pp. 3585-3591, 2018 authors profile banda gururaj was born in 1987. he received his btech degree from jawaharlal nehru technological university hyderabad, india in 2008 and his mtech degree in power electronics from sri krishna devaraya university, anantapur, india in 2011. at present he is pursuing his phd, at r& d center, gprec, kurnool, department of electrical and electronics engineering, jawaharlal nehru technological university anantapur, ananthapuramu, andhra pradesh, india. he has 10 years of teaching experience and has published 4 papers in reputed journals, 2 international conference papers, and 4 national conference papers. his areas of interest are electric and hybrid electric vehicle technology, power electronics and drives, control systems and artificial intelligence. k. sri gowri was born in 1974. she received her btech degree from sri venkateswara university college of engineering, tirupati, india, in 1996, her mtech degree in power electronics from jawaharlal nehru technological university, hyderabad, india, in 2005, and her phd degree from the jawaharlal nehru technological university, kakinada, india in 2011. she is presently working as a professor in the department of electrical and electronics engineering at g pulla reddy engineering college, kurnool, india. she has published 40 research papers in national and international conferences and journals. her current research interest include power electronic converters, pwm techniques, ac drives and control. microsoft word 33-3595_s_etasr_v10_n4_pp6076-6079 engineering, technology & applied science research vol. 10, no. 4, 2020, 6076-6079 6076 www.etasr.com patil & arakerimath: parametric optimization of biodiesel fuelled engine noise using taguchi method parametric optimization of biodiesel fuelled engine noise using the taguchi method satish a. patil mechanical engineering dr. d. y. patil institute of technology and pdea’s college of engineering pune, india sapcoeh@rediffmail.com r. r. arakerimath mechanical engineering g h raisoni college of engineering and management and savitribai phule pune university pune, india rachayya.arakerimath@raisoni.net abstract—biodiesel is a renewable, biodegradable, and efficient fuel that can be blended with petro-diesel in any proportion. the noise in the engine resulting from the combustion has a direct effect on the engine’s performance. many studies have examined the engines’ vibration and noise when using diesel and biodiesel blends. this study examines the optimization of diesel blends, load, and compression ratio in the aspect of reducing noise on a kirloskar single-cylinder diesel engine. noise was measured at the engine and its exhaust on a computerized setup and for different loads. the experimental results showed that a blend with 15% biodiesel, at 7kg load, and 18 compression ratio produced the lowest noise. moreover, the taguchi method was utilized, and experimental results were validated by an ann. keywords-transesterification; biodiesel; noise; optimization i. introduction any alternative to diesel fuel should be replicable, economical, and technically acceptable [1]. biodiesel is produced by the transesterification of renewable vegetable oils and animal fats with the use of alcohol. biodiesel is highly degradable and nontoxic. meanwhile, it has low emissions of carbon monoxide, particulate matter, and unburned hydrocarbons. due to these properties, biodiesel has attracted wide attention as a replacement to diesel fuel [1, 2]. biodiesel can be used without modifications in conventional compression ignition engines. noise and vibrations are major issues of diesel engines [3, 4]. engine body vibrations and noise are rich in information about the engine’s operating parameters and physical condition [4, 5]. excess noise and vibrations wear out components such as bearings, grouting, and couplings, increasing maintenance cost due to more component failures and unplanned operations. due to noise and vibrations’ importance, there is a need to study the effect of biodiesel and its blends on engine’s life and performance [6-8]. noise level depends on the load and the blending ratio of biodiesel [5]. as a result, it is necessary to extend an engine’s life by using optimal blends, after analyzing their impact in noise [5-9]. ii. experimental process a kirloskar tv1 vcr single cylinder, four stroke, constant speed, water-cooled diesel engine, having 3.5hp at 1500rpm, was used on a computerized test bed equipped with measuring instruments such as thermocouples, dynamometer, tachometer and flow meters. the engine’s specifications are shown in table i. table i. engine's specifications name kirloskar no. of cylinders 1 no. of strokes 4 type of cooling water cooled power developing capacity 3.5kw at 1500rpm compression ratio range 12-18 stroke 110mm bore 87.5mm cylinder volume 661 noise levels were measured by a noise meter for four different fuel blends on variable load conditions and compression ratios as per the taguchi array. the study focused on the input parameters of biodiesel blends for examining the diesel engine’s operating conditions. noise was measured at the engine and its exhaust. a noise meter was placed at 0.5m distance from the engine for measuring its noise, and another was placed outside the room near the exhaust pipe end to measure the noise at the exhaust [3-5]. the noise meter and its specifications are shown in figure 1 and table ii respectively. table ii. noise meter's specifications display 14mm (0.55ʺ) lcd with backlight parameter measurement lp, lmax, leq, ln frequency range 31.5hz~8khz measurement range lp: 30~130db (a) resolution 0.1 db accuracy ±1db fig. 1. noise meter. corresponding author: satish a. patil engineering, technology & applied science research vol. 10, no. 4, 2020, 6076-6079 6077 www.etasr.com patil & arakerimath: parametric optimization of biodiesel fuelled engine noise using taguchi method four fuel types were tested, namely: b0 consisting of 100% diesel, b15 consisting of 15% biodiesel and 85% diesel, b20 consisting of 20% biodiesel and 80% diesel, and b25 consisting of 25% biodiesel and 75% diesel [2, 3, 9]. biodiesel blend, load on the engine, and compression ratio were the parameters whose effects on the engine’s noise were studied. the parameters’ levels are listed in table iii. table iii. parametric conditions a: blend b: load c: compression ratio a1 = 0 b1 = 0 c1 = 16 a2 = 15 b2 = 4 c2 = 17 a3 = 20 b3 = 7 c3 = 17.5 a4 = 25 b4 = 10 c4 = 18 a. noise analysis the orthogonal array of the input parameters indicates the number of combinations for the experiments. this selection of orthogonal array is based on three parameters and four levels for each parameter [2,5]. the array was obtained by minitab using the following operating parameters: taguchi design design summary taguchi array l16(4^3) factors: 3 runs: 16 columns of l16 (4^5) array: 1 2 3 table iv. sample readings of taguchi array for parameter optimization blend load c.r. noise at the engine noise at the exhaust noise at the engine snr noise at the exhaust snr 0 0 16 92.75 108.9 -39.3463 -40.7406 0 4 17 93 109.25 -39.3697 -40.7684 15 4 16 93.75 112.15 -39.4394 -40.996 15 7 18 95 110.45 -39.5545 -40.8633 15 10 17.5 95.6 110.95 -39.6092 -40.9025 20 0 17.5 91.7 110.45 -39.2474 -40.8633 25 10 16 96.35 111.9 -39.677 -40.9766 the fourth row of table iv gives the optimum values of input parameters for noise among the various blends. signalto-noise ratio (snr) measures how the response varies relatively to the nominal or target value under different noise conditions. depending on the goal, different snrs may be chosen. in this experiment, lower snrs are better. optimal conditions were met with b15 blend, 7kg applied load, and 18 compression ratio, where the noise was 95db at the engine and 110.45db at the exhaust. b. taguchi analysis: noise versus blend, load, c.r. taguchi method analysis results for noise at the engine versus blend, load, and c.r are shown in table v, while the regression’s resulted equation is: 96.6 0.0507 0.371 0 . .2 . 55 blen nd lo oise at the engin ad r e c − + − = (1) table v. noise at the engine model summary s r-sq r-sq(adj) 0.2196 76.30% 40.76% taguchi model’s analysis results on noise at the exhaust versus blend, load, and c.r are shown in table vi, and the regression’s resulted equation is: 107.89 0.0518 . 0.1900 0.0 . 44 blnoise at t end load he exhau t s c r s = + + + (2) table vi. noise at the exhaust model summary s r-sq r-sq(adj) 0.0658 86.48% 66.21% c. validation of experimental results by artificial neural network (ann) the results of noise at the engine and the exhaust were validated by an ann. an ann script, shown in table vii, was used for obtaining the output from the input parameters. table vii. ann configuration script clc; close all; clear all; x = xlsread('input1'); y = xlsread('output2'); net = newff(minmax(x),[20,1],{'logsig','purelin','trainlm'}); net.trainparam.epochs = 1000; net.trainparam.goal = 1e-15; net.trainparam.lr = 0.01; net = train(net, x, y); y_net = net(x); plot(y);hold on; plot(y_net, 'r'); error = (y y_net); iii. results and validation a. noise at the engine the experimental results for noise at the engine, the values calculated by the ann, and the error between them are shown in table viii and a comparative graph of these values is shown in figure 2. apparently, there is a small difference, less than 1.2%, between the experimental and the ann calculated values. table viii. experimental and ann results blend load c.r. noise at the engine noise by ann error error % 0 7 17.5 97 96 -1 -1.0% 0 10 18 95.2 96 0.8 0.8% 15 7 18 95 96 1 1.0% 20 10 17 95.9 95.5 0 0.0% 25 7 17 94.8 95.6 0.8 0.8% 25 10 16 96.35 95.2 -1.15 -1.2% the regression plot obtained by the taguchi model for the experimental results was compared with the ann regression plot. the regressions’ r-square value was around 80%. the straight line in these plots shows that the data fit a normal probability distribution. there are very low residual values, as engineering, technology & applied science research vol. 10, no. 4, 2020, 6076-6079 6078 www.etasr.com patil & arakerimath: parametric optimization of biodiesel fuelled engine noise using taguchi method all residuals obtained are almost along the line in both plots. the similarity in these plots validates the results. fig. 2. comparison of experimental and ann noise values at the engine. (a) (b) fig. 3. residual plot for noise at the engine by (a) minitab, (b) ann. b. noise at the exhaust the experimental results of noise at the exhaust, the values calculated by the ann, and the error between them are given in table ix. moreover, a comparative graph of these values is shown in figure 4. apparently, there is a tiny difference between experimental and ann results, less than 0.3%, for noise at the exhaust. table ix. experimental and ann results blend load c.r. noise at the exhaust noise byann error error % 0 0 16 108.9 109.2 0.3 0.27% 0 4 17 109.25 109.1 -0.15 -0.14% 15 7 18 110.45 110.45 0 0.00% 15 10 17.5 110.95 110.95 0 0.00% 20 0 17.5 110.45 110.45 0 0.00% 25 10 16 111.9 111.9 0 0.00% after comparing the regression plots of experimental and ann results in figures 3 and 5, we can see that there are very few residual values, and all values obtained are almost along the line indicating a normal probability distribution. the regression’s r-square value was 86.48%. the similarity in these plots validates the results. fig. 4. comparison of experimental and ann noise at exhaust. (a) (b) fig. 5. residual plot for noise at the exhaust by (a) minitab, (b) ann. iv. conclusion this study examined the optimization of noise reduction at the engine and its exhaust with biodiesel blend, load, and compression ratio of the engine as input parameters. analysis was carried out utilizing the taguchi method, and optimization of the input parameters was performed by using snr [10, 11]. the experimental results obtained by minitab were validated by an ann. the main conclusions of this study are: • optimal input parameters were: a blend with 15% biodiesel, applied load of 7kg, and compression ratio 18, resulting to 95db noise at the engine and 110.45db at its exhaust. • r-square values obtained by regression analysis were around 80% and more, indicating that the obtained model fits to the actual data. • there are small to tiny differences between the experimental and the ann’s noise values. • all regression residuals of both minitab and ann were very low and almost along the line in both methods. the similarities in both plots validated the results. 3210-1-2-3 99 95 90 80 70 60 50 40 30 20 10 5 1 standardized residual p e rc e n t normal probability plot (response is sn ratios) 3210-1-2-3 99 95 90 80 70 60 50 40 30 20 10 5 1 standardized residual p e rc e n t normal probability plot (response is sn ratios) engineering, technology & applied science research vol. 10, no. 4, 2020, 6076-6079 6079 www.etasr.com patil & arakerimath: parametric optimization of biodiesel fuelled engine noise using taguchi method references [1] d. patil and r. arakerimath, “performance characteristics and analysis of jatropha oil in multi-cylinder turbocharge compression ignition engine,” international journal of engineering research and development, vol. 1, no. 10, pp. 50–55, jun. 2012. [2] s. a. patil and r. r. arakerimath, “optimization of biodiesel synthesis using heterogeneous catalyst (sio2) from karanja oil by taguchi method,” international journal of engineering and advanced technology, vol. 9, no. 2, pp. 5597–5600, dec. 2019. [3] a. a. khaskheli, h. j. arain, i. a. memon, u. a. rajput, and m. j. ahsan, “emission and noise characteristics of a diesel engine fuelled with diesel-chicken oil biodiesel blends,” engineering, technology & applied science research, vol. 10, no. 2, pp. 5387–5391, apr. 2020. [4] s. saridemir and u. agbulut, “combustion, performance, vibration and noise characteristics of cottonseed methyl ester–diesel blends fuelled engine,” biofuels, sep. 2019, doi: 10.1080/17597269.2019.1667658. [5] e. uludamar, e. tosun, and k. aydın, “experimental and regression analysis of noise and vibration of a compression ignition engine fuelled with various biodiesels,” fuel, vol. 177, pp. 326–333, aug. 2016, doi: 10.1016/j.fuel.2016.03.028. [6] h. yıldırım, a. n. özsezen, and a. çınar, “vibration and noise depending upon engine speed in adiesel engine fueled with biodiesel,” presented at the 6th european conference on renewable energy systems, istanbul, turkey, jun. 25-27, 2018. [7] b. heidary, s. r. hassan-beygi, b. ghobadian, and a. taghizadeh, “vibration analysis of a small diesel engine using diesel-biodiesel fuel blends,” agricultural engineering international: cigr journal, vol. 15, no. 3, pp. 117–126, jul. 2013. [8] j. a. grajales, h. f. quintero, c. a. romero, and e. henao, “engine diagnosis based on vibration analysis using different fuel blends | springerlink,” advances in condition monitoring of machinery in nonstationary operations, vol. 9, pp. 267–274, sep. 2017. [9] k. sivaramakrishnan and p. ravikumar, “performance optimization of karanja biodiesel engine using taguchi approach and multiple regresssions,” arpn journal of engineering and applied sciences, vol. 7, no. 4, pp. 506–516, apr. 2012. [10] s. jaikumar, s. k. bhatti, and v. srinivas, “emission and vibration characteristics of niger seed oil biodiesel fueled diesel engine,” journal of mechanical engineering and sciences, vol. 13, no. 4, pp. 5862–5874, dec. 2019, doi: 10.15282/jmes.13.4.2019.11.0467. [11] m. m. ettefagh, m. h. sadeghi, v. pirouzpanah, and h. arjmandi tash, “knock detection in spark ignition engines by vibration analysis of cylinder block: a parametric modeling approach,” mechanical systems and signal processing, vol. 22, no. 6, pp. 1495–1514, aug. 2008, doi: 10.1016/j.ymssp.2007.11.027. authors profile satish a. patil is a research scholar at the mechanical engineering, dr. d. y. patil institute of technology (dypit), pune (ms), india, and a assistant professor in the department of mechanical engineering, pdeas college of engineering, manjari (bk), pune, india. affiliated to savitribai phule pune university, pune. rachayya r. arakerimath is a professor and the head of the mechanical engineering department, savitribai phule pune university, pune g h raisoni college of engineering, pune, india. he has 24 years of teaching experience and has worked at various levels. he is an approved ph.d. guide under the universities of pune and nagpur. he has published more than 100 papers in conferences and journals. he is also a reviewer for international journals. microsoft word 18-1039-ed.doc engineering, technology & applied science research vol. 7, no. 2, 2017, 1546-1551 1546 www.etasr.com chew hernández et al.: supply chain cooperation by agreed reduction of behavior variability… supply chain cooperation by agreed reduction of behavior variability: a simulation-based study m.l. chew hernández ind. eng. dept. tecnológico de estudios superiores de coacalco coacalco, méxico mchew@ tesco.edu.mx l. viveros rosas ind. eng. dept. tecnológico de estudios superiores de coacalco coacalco, méxico lviverosr@ hotmail.com r. f. retes mantilla management dept. tecnológico de estudios superiores de coacalco coacalco, méxico retes1123@ hotmail.com g. j. espinosa martínez management dept. tecnológico de estudios superiores de coacalco coacalco, méxico gespinosam@ yahoo.com.mx v. velázquez romero management dept. tecnológico de estudios superiores de coacalco coacalco, méxico ing_ind_amb@ hotmail.com abstract—supply chain echelons normally base their operational decisions on average values of the parameters that depend on other members. however, in real-life operation the variability of said parameters decreases the link profits. thus, a cooperative arrangement may be devised in which a link agrees to reduce the variability of its behavior to enhance the performance of other links, receiving compensation in return. this work shows the application of simulation and decision trees to assess the feasibility of this cooperation scheme, from the perspective of the central link of a three member supply chain. first, the operational parameters of the link are optimized for mean values of the variables set by adjacent members. then, by simulating the system for different probability distributions of these variables, graphs of the expected link gain versus the variances of the distributions are plotted. the results are incorporated to decision trees to evaluate the collaboration feasibility. it was found that the increased variability of the behavior of one neighboring member decreases the benefit of lowering the variability of the behavior of the other. the manuscript closes with a discussion of the practical viability of this collaboration scheme. keywords-supply chain; uncertainty; collaboration; simulation i. introduction a supply chain is the set of companies (named “links”, “members” or “echelons”) that participate in delivering a product to an end user, including activities ranging from raw material extraction, production, transporting and retail operations [1]. when the companies belong to different owners or parent organizations, each one doesn´t normally have detailed information on the variables that depend on neighboring members (i.e. its supplier and customer). thus, each link designs its operational polices based on average values of variables like size and arrival time of customer orders and supplier delivery times [2]. however, the real-life variability of these variables causes the link profits to be lower than planned [3]. a collaboration arrangement can be devised to alleviate this: a link commits to decrease the variability of its behavior so to benefit a neighboring member, receiving a payment from the latter in exchange. for example, in a chain of supplier-retailer-customer, the retailer can offer reduced prices to the customer in exchange for his commitment to make his purchases with an even quantity and frequency. similarly, additional payments can be offered to the supplier if he commits to less variable delivery times, which can be provided by prioritizing inventory and transportation for this retailer. in this collaboration mode, customers and suppliers benefit the retailer by making their behavior less variable, without changing their average behavior. the size of the incentives that the retailer may offer for this partnership, however, depends on the benefits he reaps when the other links decrease their behavior variability. this work shows the usage of simulation [4] and decision trees to evaluate the feasibility of the collaboration between supply chain members through a compromise of reducing their behavior variability. simulation is used to assess the effect of the variability in the behavior of the upstream and downstream members on the performance of an intermediate link. the results are incorporated into a tree representing the decision of said link on whether to participate in an agreement of reduction of behavior variability. a simulation approach, such as presented here, allows a greater flexibility in the problem formulation than do the analytical expressions reported in the literature (for example in [3]). ii. literature review and justification there is a vast body of research literature on supply chain collaboration. empirical studies are shown in [5-7], dealing with the impact of inter-organizational systems on chain performance, and in [8], treating the effect of uncertainty and confidence. collaborative supply chain performance has been analyzed in [9, 10], with the latter concluding that, in many cases, the collaboration only benefits the retailer. planning and design models of the collaborative chain are shown in [11] for procurement planning, in [12] for cases in which the members have different manufacturing systems and in [13], where a link decision model incorporating cooperating members is shown. meanwhile, the model of [14, 15] incorporated the internet to engineering, technology & applied science research vol. 7, no. 2, 2017, 1546-1551 1547 www.etasr.com chew hernández et al.: supply chain cooperation by agreed reduction of behavior variability… joint decision-making and [16] applied fuzzy logic to chain design. models for chain cooperation under special situations have been developed. synergies between suppliers are considered in [17]. in [18], the cooperation of a distributor with several vendors, which may transfer inventory between them was treated. a cooperative health service supply chain is modelled in [19], while the cases of making joint investments in infrastructure and advertising are shown, respectively in [20] and [21]. other models treat the product-service case [22], include exchange rate uncertainty [23], advance notifications of returns in closed chains [24] and collaborative demand forecasting [25-27]. several authors deal with the division of the collaboration benefits. side payment calculation is approached through bargaining theory in [28-31]. the special case of supply chains with re-work is covered in [32], while [33] treats the effect of lying and misrepresentations on the contracts and [34] deals with gain sharing through wholesale pricing. a form of collaboration is the sharing of information. the effect on performance of different information sharing degrees is treated in [35]. in [36], authors showed how a global firm can improve its performance by sharing information with retailers. in [37], a model in which information on customer demand and adjustments of inventory position are shared through the chain is presented. in [38], authors discussed the convenience of sharing innovations with other links. game theoretical models for the convenience for the retailer to share demand information are shown in [39, 40], the latter finding that the retailer is inclined to increase the uncertainty of the other links and in [41] authors concluded that, only when there are product returns, it is beneficial for the producer to share demand information with the retailers. additionally, in [42] authors demonstrated that complete information sharing does not guarantee performance improvement. analytical results of the impact of information sharing on the supply chain bullwhip effect are presented in [43-45]. the issue is also addressed statistically in [46] and through process control theory in [47]. meanwhile, in [48] authors treated the case of chains with work returns and in [49] authors showed that, even with total information sharing, a residual bullwhip effect remains. finally, chain performance with information sharing is contrasted to that of a vendor-managed inventory policy in [50, 51]. the above mentioned reports do not address supply chain cooperation through a links’ agreement by which one member commits to decrease the variability of its behavior so to benefit another. while the benefits of this cooperation scheme may be lower than other cooperation forms treated in the literature, it has two qualities that render it appealing in practice. the first is that the member benefited by the variability reduction, does not need to disclose to the other the amount of this benefit. he just offers a payment for the variability reduction, which may or not be acceptable by the other. this makes it easy for the partners to find an agreement beneficial to both, without bargaining. the second advantage of this collaboration scheme is that, unlike other cooperation modes, it does not require the members to disclose information to each other. this is extremely important in practice, as many opportunities for cooperation between supply-chain members are hindered by the members’ fear that the revealed information can prompt the other member to become a direct competitor. for example, the retailer may reasonably believe that if he reveals to its wholesaler that some of the customer´s demand goes unsatisfied, the wholesaler may be tempted to launch a retail operation on its own. the collaboration scheme through payed reduction of behavior variability, with its minimal need for information revelation, allows an easy practical implementation, and thus may have a measurable impact on the operation of real supply chains. iii. case study description a case study supply chain of supplier, retailer and customer is shown in figure 1. the customers arrive to the retailer every tc time units and request the amount of product qc. if qc is greater than the retailer’s current inventory (it), the sale is lost. the retailer’s inventory policy is a point-of-reorder, continuous review scheme: when the value of it is less than a minimum inventory it,min, he ask the supplier for a load of product of size it,max, which takes te time units to arrive. for a given planning horizon, the retailer’s profit (g) can be calculated as g =pv  vt  pd  vd  ce  ne  ci  max (it) (1) where: pv = unitary product sale price to the customer. pd = unitary product purchase price from the supplier. ci = cost of retailer inventory, per unit. ce =shipment cost from the supplier, per trip. vt = total sale of the retailer. vd = total sale of the supplier. ne = number of deliveries from the supplier to the retailer. max (it) = maximum retailer inventory value during the planning horizon. fig. 1. supply chain case study equation (1) implies that the retailer pays the order delivery cost from the supplier. as mentioned in section i, the retailer optimizes its operation parameters (it,min and it,max) so to maximize his profit g, based on average values of variables tc, qc and te, that depend on other chain members. however, the real-life variability of these parameters causes the retailer profit to be lower than the optimized value. thus, the retailer can offer compensation to either supplier or customer (or both) for decreasing this variability. the maximum amount of this compensation depends on how much the variability reduction represents in increased retailer profits. in the following section, simulation is used to determine this maximum amount for a numerical case study. the results are then introduced in a decision tree to evaluate the feasibility of paying for supplier collaboration. the following sections assume the values of pv= $50/item, pd= $30/item, ce=$1000/trip and ci= $50/item and a simulation length of 1000 h. retailer customer supplier engineering, technology & applied science research vol. 7, no. 2, 2017, 1546-1551 1548 www.etasr.com chew hernández et al.: supply chain cooperation by agreed reduction of behavior variability… iv. methodology and results a. simulation results the results presented were produced using a simple simulation model of the retailer´s inventory, such as that shown in [52], coded in ms-visual basic. the retailer chooses the values of it,min and it,max to maximize his profits, assuming that the variables tc , qc and te remain constant at their average values of, respectively, e[tc], e[qc] and e[te]. the values of it,min and it,max so determined are named, respectively, it,min* and it,max*.the influence diagram of this decision is shown in figure 2. in these diagrams, doublebounded circles indicate variables with known value, rectangles stand for decisions and the hexagon represents the objective to be achieved [53]. figure 2 emphasizes that the retailer, when selecting it,min and it,max, considers only the average values of tc , qc and te. fig. 2. influence diagram for retailer´s determination of it,min and it,max setting the values tc=e[tc]=10h, qc=e[qc]=10 items and te=e[te]=70h and using simulation to evaluate different options of it,min and it,max, the optimal values of it, min*= 60 and it, max*= 200 items are found. these produce a profit, in a 1000 h operation length, of $12'000. to evaluate the retailer loss due to the variability of tc, qc, and te, different probability distributions are defined for these variables. the distributions retain the expected values previously set (e[tc]=e[qc]=10 and e [te]=70), but differ in variance. for tc and qc, the probability distributions of table i are defined, with table ii showing the corresponding distributions for te. in the tables, the notation var( ) refers to the variance of the variables for a probability distribution. the retailer’s profit, when adhering to it,min* and it,max* and with tc, qc and te following a probability distribution of tables i and ii, is calculated through simulation. table i. probability distributions for c δt and qc p(tc=xi) or p(qc=xi) xi (value of tc or qc) dist. i dist. ii dist. iii dist. iv dist. v 2 0 0 0 0.1 0.2 6 0 0.1 1/3 0.2 0.2 10 1 0.8 1/3 0.4 0.2 14 0 0.1 1/3 0.2 0.2 18 0 0 0 0.1 0.2 e [tc]=e[qc] 10 10 10 10 10 var(tc)= var(qc) 0 3.2 10.66 19.2 32 table ii. probability distributions for e δt p (te=xi) xi (value of te) dist. i dist. ii dist. iii dist. iv 50 0 0 0.05 0.2 60 0 0.1 0.3 0.2 70 1 0.8 0.3 0.2 80 0 0.1 0.3 0.2 90 0 0 0.05 0.2 e [te] 70 70 70 70 var(te) 0 20 100 200 figure 3 shows the expected value of the retailer’s profit (e[g]), derived from 10'000 simulation replications, for all combinations of the probability distributions of tables i and ii; e[g] is plotted against the variance of qc, with the variance of tc shown parametrically for the curves. in figures 3a-d, the variability of customer behavior is lower for the top curves (which are for probability distributions of low variance of time between arrivals) and for points closer to the left side of the figure (with low variance of the probability distribution of amount purchased). similarly, the progression from figure 3a to 3d shows e[g] values for increasing variability in the behavior of the supplier (increasing variance of the probability distribution of supplier delivery times). the following observations can be done by perusing figure 3: 1. in figures 3a-d, the bundle of curves is wider to the left (where there is less variability of qc) than to the right. this means that decreasing the variability of tc (i.e. shifting from the lowest curve to the highest), has a greater impact the less variable qc is. this is illustrated by comparing lengths a to a' in figure 3a. 2. in figures 3a-d, the vertical distance between the highest and lowest points of a curve, is greater for the top curve (for var(tc) = 0) than for the bottom one (var(tc) = 32). this is illustrated in figure 3a by comparing the dimensions b and b'. this indicates that the decrease in variability of qc has a bigger effect on e[g] the lower the variability of tc is. these points are synthesized by stating that, regarding tc and qc, the value of decreasing the variability of one is greater the lower the variability of the other is. the transit from figure 3a to 3d shows the effect of increasing the variability in supplier delivery time, te. from the curve bundle shape in these graphs, it can be noticed that, for an increased variability in te, the effect of changing the variability of tc and qc becomes smaller. this can be measured quantitatively by calculating, for figures 3a to 3d, the difference in e[g] between the point with the least variability in qc and tc (var(qc)=0 on the curve var(tc)=0) and that of the point with greatest variability in these variables (var(qc)=32 on the curve var(tc)=32). this difference is the impact of a reduced variability in the customer behavior. doing this calculation for the four graphs of figure 3, and plotting against the variance of te, produces figure 4. this plot shows that, as var(te) increases, the effect of reducing the variability of qc and tc decreases. e[te] supplier retailer’s profit it,min it,max g e[tc] e[qc] customer engineering, technology & applied science research vol. 7, no. 2, 2017, 1546-1551 1549 www.etasr.com chew hernández et al.: supply chain cooperation by agreed reduction of behavior variability… fig. 3. e[g] vs. variances of distributions in tables i and ii. fig. 4. increase in e[g] by reducing the variability of qc and tc vs. var (te) similarly, figure 5 shows the change in e[g] when the variability of te drops from var(te) = 200 to var(te)=0, for points with the same var(tc) and var(qc) values. for example, the value for var(tc)=var(qc)=0 is calculated by subtracting from the e[g] value of the point var(qc)=0 on curve var(tc)=0 in figure 3a, the value of e[g] of the analogous point of figure 3d. a trend similar to that of figure 4 can be seen in figure 5: the greater the value of var(tc) and var(qc), the smaller the worth of decreasing var(te). it can be concluded that the more variable the behavior of the customer is, the smaller the benefit to be reaped from a reduction in the variability of the supplier’s behavior. the same applies the other way around: as the supplier behavior grows variable, the benefit of decreasing the variability of the customer behavior shrinks. thus, the potential benefit of getting the compromise of one member to reduce its behavior variability depends drastically on the variability of the other member’s behavior. fig. 5. increase in e[g] by reducing the variability of te vs. var(qc) and var(tc) b. feasiblity of negotiating with the supplier the previous results are used to evaluate, from the retailer’s perspective, the feasibility of negotiating with the supplier a payed reduction in the variability of the delivery time te. the retailer´s decision of whether to pay the supplier for reducing the variability of te is shown as a tree in figure 6. in these trees, squares stand for decisions and circles represent (3a) var(qc) var(te)=0 e[g] a b b’ a’ var(te)=20 e[g] var(qc) (3b) e[g] var(qc) var(te)=100 (3c) e[g] var(te)=200 var(qc) (3d) var(tc)=0, var(tc)=3.2, var(tc)=10.6, var(tc)=19.2, var(tc)=32 x e[g](var(qc)=var(tc)=0) e[g](var(qc)=var(tc)=32) var(te) var(t )= var(q ) var(qc)=var(tc) e[g](var(te)=0) e[g](var(te)=200) engineering, technology & applied science research vol. 7, no. 2, 2017, 1546-1551 1550 www.etasr.com chew hernández et al.: supply chain cooperation by agreed reduction of behavior variability… uncertainties [53]. at the first decision square, "negotiate with supplier" the retailer can choose either 'yes' or 'no'. the alternative chosen influences the variability of te: [dist. te]or represents the original (i.e. not negotiated) probability distribution of te while [dist. te]ne stands for the probability distribution of te that the supplier agrees to maintain as a result of the deal with the retailer. it is understood that the variability of te implied by [dist. te]or is greater than that of [dist. te]ne. the retailer’s profit is written to the extreme right of the tree. it can be seen that this profit is affected by the probability distributions of qc and tc, whose variability depends on the customer. the deal between the retailer and supplier implies that the former pays the latter an amount cn ($), so the retailer’s profit for the top branch is g-cn. fig. 6. retailer’s decision tree on whether to negotiate a reduction in the variability of te the greatest value of cn that the retailer can pay for the supplier´s cooperation can be determined by substituting in the tree the relevant data from figure 3. for example, for a low variability in customer’s behavior (var(qc)=var(tc)=3.2), the highest value the retailer can pay for reducing the variability of te from var(te)=200 to var(te)=20 is $323. if, on the other hand, there is a high variability in the customer’s behavior (var(qc)=var(tc)=32) the maximum value of to pay for such variability reduction is only $109. v. conclusions normally the links of a supply chain design their operation based on average values of the parameters set by other chain members, and, as a result of the real variability of said parameters, their profits are diminished. the aim of this work is to explore the feasibility of a form of supply chain collaboration, consisting of the links reducing the variability of their behavior so to benefit another, in exchange for a monetary compensation. a key factor for the operability of this cooperation scheme is how much the profit of the members improves by such variability reduction. this work shows the use of simulation to determine this improvement, for a case study of supplier-retailer-customer. the retailer designs its operation using average values of the variables depending on other members and then, by simulating different probability distributions for these variables, the variability impact on the retailer’s profits is calculated. for the central link, the value of reducing the variability of the behavior of one neighboring member (upstream or downstream) is strongly related to the variability of the behavior of the other. reducing the variability of the behavior of either member is more valuable when the behavior of the other isn’t widely variable. if both members show a very variable behavior, a collaboration scheme with only one of them appears to be of little value. in this case, some reduction of the variability of both members’ behavior should be sought. while the feasibility conditions of this scheme seem somewhat restrictive, it should be noted that, given the practical advantages of this collaboration scheme (i.e. natural way of cutting win-win contracts, no information disclosure needed), a situation in which the retailer can get behavior variability 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sciences (nuces) karachi, pakistan asim ur rehman khan national university of computer and emerging sciences (nuces) karachi, pakistan haider mehdi national university of computer and emerging sciences (nuces) karachi, pakistan syed m. atif saleem national university of computer and emerging sciences (nuces) karachi, pakistan abstract—in this paper, performance of a device-to-device (d2d) communication system is analyzed over double-generalized gamma (dgg) fading channels. the dgg is a generic distribution for modeling double-scattering fading conditions. co-channel interference (cci) caused by various wireless devices in the system is also considered. the cci fading channel is assumed to be nakagami distributed. analytical expressions for important statistical metrics, i.e. probability density function (pdf) and cumulative distribution function (cdf) of signal-tointerference ratio (sir), are presented. based on these statistical parameters, expressions for the outage probability, channel capacity and symbol error rate (ser) of the d2d communication system are presented. the performance of d2d system is then discussed and analyzed with the help of numerical results with arbitrary channel fading, path-loss and interference conditions. keywords-channel capacity; device-to-device communication; double-generalized gamma; outage probability; signal-tointerference ratio; symbol error rate i. introduction the increased growth of smart phones and tablets having many multimedia applications and large file sharing are the motivations for the rapid development in cellular communication systems. these advancements in smart devices with the bandwidth consuming applications have led to increase in demand for higher data rates and this demand is projected to grow exponentially in the future. one of the promising solutions to this problem is device-to-device (d2d) communication system [1-3]. d2d communication system is one of the standards of the 5th generation (5g) cellular communication system. d2d communication is defined as the high data rate direct communication between two users’ equipment with high spectral efficiency, without passing through cellular infrastructures [4-6]. presence of large number of various types of wireless devices as well as d2d pairs sharing a cellular communication spectrum can cause unwanted and unintentional co-channel interference (cci) in the absence of proper coordination. therefore, cci should be considered while analyzing the performance of d2d communication systems [7-8]. outage probability, channel capacity and symbol-error rate (ser) are well-known parameters used for the performance analysis of the wireless communication systems. in [9], authors analyzed outage probability of d2d communication systems over rayleigh fading channels. the outage probability of d2d communication system under suzuki fading in presence of co-channel interference is studied in [10]. channel capacity of a d2d system, over a rician faded channel, is analyzed in [11]. authors in [12], studied d2d channel capacity over a correlated rayleigh fading channel in an interference limited environment. in [13], authors presented a study of ser of a multicarrier d2d video transmission over an independent rayleigh fading channel. in this paper, outage probability, channel capacity and ser of a d2d communication system are investigated. a d2d pair is assumed to be affected by various co-channel interferers in the system. the cci may arise from any wireless or d2d communication device in the system when proper coordination is lost or interrupted. the fading channel for the desired d2d system is considered to be double-generalized gamma (dgg). the dgg is a versatile and mathematically tractable fading distribution. the dgg variable is a product of two generalizedgamma variables [14]. the dgg includes various distributions like gamma-gamma, double-nakagami, double-weibull, weibull-gamma, and double-rayleigh. it can also model distributions like, generalized-gamma and nakagami/rayleigh -lognormal. in cellular communication systems, signals are often scattered and re-scattered around transmitter’s and receiver’s local surroundings. this double-scattering channel condition is observed when the transmitter and receiver devices are moving. the double-scattering conditions can be effectively modeled with the help of dgg distribution [15]. the propagation channel distribution for the cci is assumed to be nakagami. which is a well-known versatile distribution often used in the literature to model various channel fading conditions. the rest of this paper is organized as follows. section ii presents the d2d system model and the expressions for the outage probability, channel capacity and ser. the numerical results are discussed in section iii and section iv concludes the paper. ii. system model d2d communication network having n interferers is shown in figure 1. in this work, a co-channel interferer is assumed to be any wireless node or any d2d communication device. a d2d pair is considered here for the performance analysis. this d2 can env th th dg pai sys kee com are app rec ind dis int wh the ε2 mo the wh the fad im com engineerin www.etasr 2d pair is term n be many s vironment of he dgg distrib he channel for gg. the chann ir’s receiver i stem is consid ep the analy mpute mathem e adopted: proximately th ceiver. 2) c dependent and consi distance betw stance between i-t desire terference signal f comm the pdf of d     1 2 yf y      here δ1, δ2 and e severity of th are related to odified bessel e nakagami di 2 ( ) ( ) x f x    here μ is the fa e channel fad ding and γ(.) mportant factor mmunication ng, technology r.com med as desired small objects a d2d pair w bution can effe r the consider nel for the i-t is assumed to dered to be inte ytical work tr matical expres 1) co-chann he same distan co-channel in d identically di fig. 1. table i. idered or desired d i-th interfe ween the devices th interferer and t ed d2d pair comm from i-th interfere d2d pa munication signals dgg distributi       1 2 1 2 2 2 2 y          d β are the fad he fading cond o average pow l function of th istribution is [1 2 1 expx          ading paramete ding condition ) is gamma r that also affe system. a y & applied sci hussain et d or considere in the transm which can caus fectively mode red d2d pair th interferer t o be nakagam erference limit ractable and ssions, the foll nel interferers nce from the nterferers are stributed. system model nomenclat d2d pair device erer of the desired d2 the desired d2d p munication signal er to the receiver o air for other devices ion is [15]:  2 1 1 2k y         ding shape par ditions, ω=δ1δ wer of fading he second kin 18 2x ,         er which descr ns,  is the function [19 ects the perform simplified p ience research al.: analysis of ed d2d pair. mitter and re se double scatt el double scatt r is assumed to the desired mi distributed ted [16]. in or to obtain ea lowing assump s are locate desired d2d e assumed t ture 2d pair pair’s receiver l of the desired s 2 , > 0y y     rameters that δ2/ε1ε2 where ε g and  vk z nd [17]. the p 1 , 0, 0 2 x   ribes the sever average pow 9]. path-loss mance of a wi path-loss mod h v f device-to-dev there ceiver tering. tering. to be d d2d d. the rder to asy-tomptions ed at pair’s to be c d imply ε1 and is the df of 0 rity of wer of is an ireless del is con pair whe the path to 1 of t betw inte inte 100 be inte whe des var inte sys f whe sha ave tm sign whi cha vol. 8, no. 4, 20 vice communic nsidered here [ r is: 0 4 d d λ s p πc     ere pd is the considered d h-loss exponen 100m). simila the desired d2 0 = 4 ii p d         in (2), pi is th ween the rece erferer, b is erference sign 0m). generally equal. based o erference signa 2 2 1 , n i i g h      ere g and αi a sired d2d pai riable of the ierferers in the tem,  ,f r     0 sx f rxr      0 m f x r               4f rr     ere β a positiv ape parameter erage power ,nm where nal, paramete ich η is the annel. moreov    1 2 2 4 12             018, 3265-3269 cation over dou [20]. the pow 2 0 0 a c c         d2d signal p d2d pair devic nt (2≤α≤5) and arly, the power 2d pair is: 2 0 . b d d         he interferenc eiver of the co the path-lo nal and d0 is y, in this work on (1) and (2) al power ratio d i p c h= p d    are the indepen ir’s signal and -th interferer, r system. the s can be fo    ,if x dx [21]      1 2 12 4 1 2 exp( ( ) t t i m m t f x rx x x m               1 2 1 4, 4 , 4g            ve integer, δ1 rs of the des of the dgg e m is the sha er ω is given average pow er,       1 2 1 2 4 2 2 tm t m            9 uble-generalize wer at the desir power, c is the ces, λ is the w d c0 is the refe r of i-th interf e signal powe onsidered d2d oss exponent the reference k pd and pi ar ), the desired s (sir) of the d     2 0 2 0 , aa bb c d d      ndent dgg fad d independent respectively. n sir pdf expr ound by us ]        2 2 1 1 1 2 2 ) , sf rx k x dx               2 1 24 r          δ δ    and δ2 are the ired d2d, ω g fading ch ape parameter n as ω=φ/h w wer of the in   1 2 1 2 ,       3266 ed gamma cha red d2d recei (1) e distance bet wavelength, α i erence distance ferer at the rec (2) er, d is the dis d pair and the (2≤b≤5) of e distance (1 e not consider signal power t d2d system is (3) ding variable o t nakagami fa n is the numb ression of the sing the ide   4rx         (4) e dgg distrib ω is related to hannel. param of the interfer where m  nterference fa annels iver’s tween is the e (1m ceiver stance e i-th f the m to red to to the : of the fading ber of d2d entity, bution o the meter rence  in fading engineering, technology & applied science research vol. 8, no. 4, 2018, 3265-3269 3267 www.etasr.com hussain et al.: analysis of device-to-device communication over double-generalized gamma channels    1 2 1 2 1 1 4 4, , t tm m      δ           and 2 1 2 1 1 2 1 2 2 2 2 , , , 4 4 4 4       δ         with the help of (4), the cumulative distribution function (cdf) of sir of the d2d system is [22]      1 2 2 3 11 4,2 4 2 ,4 2 4 , ,4 r f r gr                   δ δ δ δ            (5) where:    1 2 1 2 3 1 4 4, ,              δ  ,    1 21 2 4 1 4, , 4     δ        . the probability of dropping of the sir of a system below a predefined threshold r is defined as the outage probability. by using 0 ( ) , r outp f r dr  the expression for the outage probability of the d2d system is [22]:    1 2 2 3 11 4, 2 4 2 , 4 2 4 , ,4 out r p r g                   δ δ δ δ           (6) now, the expression for channel capacity of the d2d communication system is obtained by using the formula 2 0 log (1 ) ( ) ,c r f r dr    as in [23]:   21 1 5 34 2 , 2 2 , 4 21 2 5 5 , , ,4ln(2) 2 c g                    δ ,δ δ δ δ δ           (7) where    1 2 1 2 5 1 4 4, ,      δ           . ser expression of the d2d communication system is now presented. m-ary phase-shift keying (m-psk) based modulation scheme is incorporated in this work. with the help of [22-24] the ser expression is   2 1 2 64,2 2 , 4 70 sin 4 sin m m ser g d m                                      δ δ           (8) where                  1 2 1 2 1 2 2 4 2 1 1 2 2 t t m m                            , 6 1 1 , ,1, ,t t m m  δ       and 2 2 1 1 7 1 1 , , , , , 2 2 2 2   δ       . expressions of the outage probability, capacity and ser are valid for arbitrary parameters of dgg and nakagami distribution, path-loss and co-channel interference. iii. numerical analysis and results in this section numerical results are presented and discussed. for analysis simplicity the reference distances c0 and d0 are assumed to be 1m. the sir threshold r is set at 10dbm. outage performance of d2d system with varying values of two of shape parameters i.e. δ1 and δ2 is shown in figure 2. transmit power pd, path-loss exponent a, and shape parameter β are fixed at 20dbm, 3 and 2, respectively. power pi, path-loss exponent b, the number of interferers n, the distance between the i-th interferer and the receiver of the desired d2d pair d, and the fading parameter m are assumed to be 10dbm, 3.5, 5, 50m and 2, respectively. it is observed that the fading conditions of the d2d system improve with the increase in the values of fading parameters, i.e. δ1 and δ2. a degradation in the outage performance of d2d system is also observed for the similar channel fading conditions of the desired d2d pair when the value of c is increased. as the desired d2d pair’s transmitter and receiver move away from each other, i.e. the value of c increases, outage performance of the d2d system degrades because of the power decreasing of the desired d2d signal caused by the path-loss effects. fig. 2. outage performance with varying values of two of shape parameters. the outage performance comparison of the d2d communication system for various values of dgg fading parameter, β and the path-loss exponent a is shown in figure 3. the values for the desired signal parameters pd, δ1, δ2 and c are fixed at 20dbm, 1.5, 2 and 25m, respectively. the values of interference parameters pi, b, n, d, m are assumed to be 10dbm, 4, 5, 60m and 1, respectively. it is observed that the outage performance of the d2d system is improved for the higher values of dgg shape parameter β of the desired signal. this happens because of the improved fading conditions with the increase in the values of the desired signal’s shape parameter. moreover, for the same values of fading shape parameter of the desired signal, outage performance deteriorates with increase in path-loss exponent a because of the worsened sir condition of the system when the value of a is increased. 30 35 40 45 c (meters) 10-6 10-5 10-4 10-3 10-2 10-1 p o u t δ1=0.7, δ2=1 δ1=1, δ2=1.5 δ1=1.5, δ2=2 engineering, technology & applied science research vol. 8, no. 4, 2018, 3265-3269 3268 www.etasr.com hussain et al.: analysis of device-to-device communication over double-generalized gamma channels fig. 3. outage performance with varying values of fading parameter β. outage performance of the d2d system for various values of path-loss exponent of the interference signal b is shown in figure 4. for the desired signal the values of pd, a, β, δ1 and δ2 are set to be 20dbm, 2.5, 2, 2 and 1, respectively. for the interference signals pi, m, n and d are assumed to be 10dbm, 2, 5 and 50m, respectively. it is noticed that the outage performance is better for the higher values of b because of the weakening of the interference signals at the desired d2d pair’s receiver when the value of the cci path-loss exponent b is increased. hence, an improved outage performance of the d2d system is observed. it is also observed that as the desired d2d pair’s devices move away from each other, the value of c increases and outage performance of the d2d system deteriorates because of the weakening of the desired d2d signal caused by the path-loss effects. fig. 4. outage performance with various values of path-loss exponent b figure 5 illustrates the outage performance with various values of the interference fading shape parameter m and distance d. the values of pd, pi, a, β, δ1, δ2, b, n and c are fixed at 20dbm, 10dbm, 2.5, 2, 1.5,3, 3 and 25m, respectively. it is observed that the system outage performance is almost insensitive to the interference fading conditions. moreover, for the same value of m it is observed that the outage performance of the system improves with increasing values of the distance d, because as the interferers move away from the desired d2d pair’s receiver the interference signal strength weakens due to path-loss effects. channel capacity performance of d2d communication system with varying values of n and the path-loss exponent a is shown in figure 6. the values of pd, pi, m, β, δ1, δ2, b, c and d are set to be 20dbm, 10dbm, 2, 1, 1, 2, 3, 30m and 60m, respectively. it is clear that the channel capacity performance of the system is better when the number of interferers n is decreased. it is also observed that as the path-loss exponent value of the desired signal is increased, the capacity performance of the system degrades due to the weakening of the desired signal strength due to path-loss effects. fig. 5. outage performance with various values of the shape parameter of cci fig. 6. channel capacity performance of d2d communication system for various n figure 7 shows the channel capacity performance of the d2d system for different values of distances d and c. the values of pd, pi, a, b, m, β, δ1, δ2 and n are assumed to be 20dbm, 10dbm, 3, 3.3, 2, 1, 1, 2 and 5, respectively. it is observed that the channel capacity is improved for higher values of the distance d because of the improvement of the sir conditions due to weakening of the interference signals at the desired d2d pair’s receiver. fig. 7. capacity performance of d2d communication system with varying distance d 2.8 3 3.2 3.4 3.6 3.8 4 a 10-10 10-8 10-6 10-4 10-2 p o u t β=1 β=2 20 25 30 35 40 45 c (meters) 10-7 10-6 10-5 10-4 10-3 10-2 p o u t b=2.8 b=3.5 b=4.2 30 35 40 45 50 d (meters) 10-6 10-5 10-4 p o u t m=0.5 m=1 m=3 m=5 2.5 3 3.5 4 a 0 1 2 3 4 5 6 c ( b it s/ s/ h z) n=5 n=10 n=15 25 30 35 40 45 c (meters) 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 c ( b it s/ s/ h z) d=30 d=45 d=60 engineering, technology & applied science research vol. 8, no. 4, 2018, 3265-3269 3269 www.etasr.com hussain et al.: analysis of device-to-device communication over double-generalized gamma channels ser performance of 8-psk scheme with various values of number of interference signals is shown in figure 8. the values of pd, pi, β, δ1, δ2, m, a, c and d are considered to be 20dbm, 10dbm, 1, 2, 3, 2, 3.7, 20m and 60m respectively. the ser performance improves when the number of interferers is reduced. moreover, for the same number of interferers, ser performance improves with an increase in the values of interferers’ path-loss exponent b. fig. 8. ser performance with various values of number of ccis iv. conclusion in this paper, the performance of a d2d communication system over a dgg faded channel is analyzed. the dgg distribution is a general distribution that includes all others that are used to model double-scattering which occur in wireless communication systems. effects of co-channel interference caused by various wireless devices in the system are included. expressions of the pdf and cdf of the sir of the d2d system are presented. based on the pdf of the sir, expressions of the performance metrics like outage probability, channel capacity and ser are presented. based on these expressions, numerical results are presented to discuss the performance of the d2d system under varying interference, path-loss and channel fading conditions. it is observed that the path-loss significantly affects the performance of the d2d communication system. moreover, co-channel interference, regardless of being affected by the channel fading and path-loss conditions, manages to affect the performance of the d2d system. references [1] m. waqas, m. ahmed, y. li, d. jin, s. chen, “social-aware secret key generation for secure device-to-device communication via trusted and non-trusted relays”, ieee transactions on wireless communications, vol. 17, no. 6, pp. 3918-3930, 2018 [2] j. z. moghaddam, m. usman, f. granelli, “a 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double-generalized gamma distribution and its application to v2v communications”, globecom 2017-ieee global communications conference, singapore, december 4-8, 2017 [16] s. parthasarathy, r. k. ganti, “impact of shadowing in d2d communication”, 2017 ieee wireless communications and networking conference, san francisco, usa, march 19-22, ieee, 2017 [17] wolfram research, besselk, modified bessel function of the secong kind, available at: http://functions.wolfram.com/bessel-typefunctions /besselk/02/ [last accessed july 2018] [18] a. mehbodniya, s. aissa, “outage and ber analysis for ultrawideband-based wpan in nakagami-m fading channels”, ieee transactions on vehicular technology, vol. 60, no. 7, pp. 3515-3520, 2011 [19] i. s. gradshteyn, i. m. ryzhik, table of integrals, series, and products, academic press, 2007 [20] a. goldsmith, wireless communications, cambridge university press, 2005 [21] i. trigui, a. laourine, s. affes, a. stephenne, “performance analysis of mobile radio systems over composite fading/shadowing channels with co-located interference”, ieee transactions on wireless communications, vol. 8, no. 7, pp. 3448-3453, 2009 [22] wolfram research, meijerg, meijer g-function, available at: http:// functions.wolfram.com/hypergeometricfunctions/meijerg/21/ [23] m. s. alouini, a. j. goldsmith, “capacity of rayleigh fading channels under different adaptive transmission and diversity-combining techniques”, ieee transactions on vehicular technology, vol. 48, no. 4, pp. 1165-1181, 1999 [24] b. barua, m. abolhasan, d. r. franklin, f. safaei, “sep of multihop relay networks in nakagami-m fading channels”, ieee 78th vehicular technology conference, las vegas, usa, september 2-5, 2013 2.8 3 3.2 3.4 3.6 3.8 4 b 10-8 10-7 10-6 10-5 10-4 10-3 10-2 s e r n=5 n=15 microsoft word abd-ed-f.doc etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 506-510 506 www.etasr.com boulenouar et al.: two-dimensional �umerical estimation of stress intensity factors and … two-dimensional numerical estimation of stress intensity factors and crack propagation in linear elastic analysis a. boulenouar mechanical engineering department, djilali liabes university of sidi-belabbes, algeria aek_boulenouar@yahoo.fr n. benseddiq mechanics laboratory of lille ecole polytech’lille university of lille1, noureddine.benseddiq@univ-lille1.fr m. mazari mechanical engineering department, djilali liabes university of sidi-belabbes, algeria mazari_m@yahoo.fr abstract—when the loading or the geometry of a structure is not symmetrical about the crack axis, rupture occurs in mixed mode loading and the crack does not propagate in a straight line. it is then necessary to use kinking criteria to determine the new direction of crack propagation. the aim of this work is to present a numerical modeling of crack propagation under mixed mode loading conditions. this work is based on the implementation of the displacement extrapolation method in a fe code and the strain energy density theory in a finite element code. at each crack increment length, the kinking angle is evaluated as a function of stress intensity factors. in this paper, we analyzed the mechanical behavior of inclined cracks by evaluating the stress intensity factors. then, we presented the examples of crack propagation in structures containing inclusions and cavities. keywords-stress intensity factor; crack propagation; mixed mode; inclusion i. introduction the use of crack propagation laws based on stress intensity factors (sifs) is the most successful engineering application of fracture mechanics. this characterizes the sifs as the most important parameters in fracture analysis. in elastic fracture analysis, sifs sufficiently define the stress field close to the crack tip and provide fundamental information on how the crack is going to propagate. basically, the estimation methods can be categorized into two groups, those based on field extrapolation near the crack tip and those which use the energy release when the crack propagates. the latter group includes jcontour integration, virtual crack extension and the strain energy release rate method. the main disadvantage of these methods is that the sif components, ki and kii in mixed mode application are either impossible or very difficult to be separated. nevertheless, the first group which is based on neartip field fitting procedures requires finer meshes to produce a good numerical representation of crack-tip fields. usually, the singular point elements are generated to facilitate the calculation [1]. one of the simplest and most frequently used methods is the displacement extrapolation method. it functions typically in obtaining displacement jumps along the crack faces and then applying the elasticity relations to compute a set of estimated sif values [2]. in order to predict the fracture direction and loading based on the concept of maximum potential energy release rate (mperr), a new general mixed-mode brittle facture criterion was applied by chang et al. [3]. the calculation and comparison of sifs for a cracked element free galerkin method (efgm) plate have been obtained by using several different numerical techniques in [4]. this paper aims to determine the sifs for the crack propagation problem under linear-elastic fracture analysis by means of the displacement extrapolation method implemented in the ansys finite element program. the method developed in this paper was applied to compute the stress intensity factors in elastic-plastic crack growth in plane stress problems. ii. stress intensity factor and crack propagation in linear elastic fracture mechanics the important parameters used are the stress intensity factors in various modes. several methods have been proposed to determine the stress intensity factors, such as the displacement extrapolation near the crack tip [5], the j-integral [6] and the energy domain integral [7]. in this paper, the displacement extrapolation method [8] is used to calculate the stress intensity factors as follows: ( )( ) ( ) ( ) , 2 4 2 113     − −− ++ = ec dbi vv vv lk e k π ν (1) ( )( ) ( ) ( ) , 2 4 2 113     − −− ++ = ec dbii uu uu lk e k π ν (2) where e is the modulus of elasticity, ν is the poisson’s ratio, l is the element length, u and v are the displacement components in the x and y directions, respectively and k is an elastic parameter defined by: etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 506-510 507 www.etasr.com boulenouar et al.: two-dimensional �umerical estimation of stress intensity factors and … 3 stress plane 1 . 3-4 strain plane k ν ν ν −  +  =     the near tip nodal displacements at nodes b, c, d and e, shown in figure 1 are of a great interest. the tangential and normal displacements to crack plane are denoted as u and v respectively. in order to simulate crack propagation under linear elastic condition, the crack path direction must be determined. there are several methods used to predict the direction of crack trajectory such as the maximum circumferential stress theory, the maximum energy release rate theory and the minimum strain energy density theory. the maximum circumferential stress theory asserts that, for isotropic materials under mixedmode loading, the crack will propagate in a direction normal to the maximum tangential tensile stress. in polar coordinates, the tangential stress is given by:       −= θ θθ π σθ sin 2 3 2 cos 2 cos 2 1 2 iii kk l (3) the direction normal to the maximum tangential stress can be obtained by solving 0=θσθ dd for θ. the nontrivial solution is given by: 0)1cos3(sin =−+ θθ iii kk (4) which can be solved as:         +      ±= 8 4 1 4 1 arctan2 2 ii i ii i k k k k θ (5) iii. numerical analysis and validation a. single edge cracked plate under plane stress condition the geometry of the single edge cracked plate under plane stress condition and its final mesh in the first step before crack propagation are shown in figure 2. the plate has an initial crack length of a=0.4 units, plate length of l=2 units, plate width of w=1 unit and thickness of t=1 unit. the modulus of elasticity e is 1, and poisson’s ratio ν is 0.3. the far-field tensile stress is σ=1 unit. fig. 1. quarter-point triangular elements around the crack tip figure 3 shows the final configuration corresponding to the last evaluated crack length obtained from the finite element software ansys in the present study, which are found to be almost the same as the results obtained from the franc2d/l program and the results given by alshoaibi et al. using the adaptive mesh strategy [9]. figure 4 shows the calculated values of stress intensity factors ki and kii during crack propagation steps for a cracked plate with an initial crack length of a=1 unit. the sif ki is increase nonlinearly as crack increment length increases and the values of factor kii are negligible i.e. the crack propagates towards the horizontal path under mode i loading condition. (a) (b) fig. 2. (a) problem statement and (b) the final mesh of the initial crack before crack propagates fig. 3. final configuration corresponding to the last evaluated crack length fig. 4. stress intensity factors ki and kii as functions of crack extension in a cracked plate etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 506-510 508 www.etasr.com boulenouar et al.: two-dimensional �umerical estimation of stress intensity factors and … b. single edge cracked plate with an off-center hole the following example concerns a cracked part with a hole of radius r=0.2 units. in this section, we show the effect of the existence of a hole on the path of crack propagation under mode i loading conditions. this plate is meshed by an 8 nodes quadratic element and by special element meshing at the crack tip (figure 5). the computation of the stress intensity factor is determined using the displacement extrapolation technique. at each increment of crack propagation the fork angle is evaluated using the maximum circumferential stress theory. the crack increment length ∆a is 8% of the initial crack length a. figure 6 shows the crack propagation trajectories for our geometric model. this figure shows that the crack is moving towards the hole since it creates a stress drop. once the crack tip has moved beyond the hole, the crack reorients horizontally in mode i loading. we obtain a similar crack path as in [10-14]. figure 7 illustrates the predicted values of the sifs for mode i loading during the crack propagation steps for our geometric model. fig. 5. problem statement and the final mesh for of the single edge cracked plate with an off-center hole fig. 6. crack trajectory in a cracked plate with a hole fig. 7. stress intensity factors ki and kii as functions of crack extension in a cracked plate with an off-center hole c. single edge cracked plate with an off-center inclusion in the present example, we replace the hole by an inclusion of a circular form and we study the influence of this inclusion on the crack path direction. a rectangular part is pre-cracked and submitted to a tensile test. this part contains an inclusion which may be more rigid or less rigid than the matrix. if ematrix is the young modulus associated with the matrix, and eincl the one associated with the inclusion, we define r as the ratio: r=ematrix/eincl. this example shows the ability of the discrete approach, implemented in the finite element software, to deal with multimaterial applications. figure 8 shows the geometrical of the cracked plate and the typical model mesh at the inclusion and at the crack. in figure 9, the crack propagation simulation is presented with a ratio r unit (ematrix/eincl=1), which means that we have an inclusion, but is made of the same material as the matrix. this figure shows five steps of crack propagation trajectories. as expected, the crack propagates horizontally, as in a homogeneous single-material. figure 10 shows five steps of crack propagation trajectories for the structure with a soft inclusion (r=10 and eincl=0.1), the inclusion is less rigid than the matrix; the crack is still attracted by the inclusion. the crack reorientation is however less pronounced than the one obtained with a hole. conversely, if the inclusion is more rigid than the matrix (r=0.1 and eincl=10), the crack is moving away from the inclusion (figure 11). good agreement is obtained for the crack path with the results presented in [15]. fig. 8. geometrical model and typical mesh model near the inclusion and the crack fig. 9. propagation of a crack in a part with an off-center inclusion (r=1) fig. 10. propagation of a crack in a part containing a soft inclusion (r=10) etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 506-510 509 www.etasr.com boulenouar et al.: two-dimensional �umerical estimation of stress intensity factors and … fig. 11. propagation of a crack in a part containing a hard inclusion r=0.1 the crack growth and its direction are determined by the calculated sifs. figure 12 shows the predicted values of the sifs for mixed mode during crack propagation steps. as shown, the increase in crack length causes an increase of ki. this factor has the same curves for the three cases (r=1, 0.1 and 10), i.e. it does not depend on the crack path direction. in the case of r=1, the values of kii are negligible i.e. the crack propagates towards the horizontal path under mode i loading condition. for a negative angle (hard inclusion case), kii takes negative values and for the soft inclusion case takes positive values. fig. 12. stress intensity factors ki and kii as functions of crack extension in cracked plate with : (a) r=1 (b) r=0.1 (c) r=10 figure 13 illustrates a comparison between the paths of propagation, for the various applications presented in this study. figure 14 shows the normal stress distribution for the final step chosen of the crack propagation, for four cases presented in this study. the maximum value of the normal stress is localized around the perturbated zone by the existence of a crack. fig. 13. crack trajectories comparison fig. 14. contour plots of the normal stress for cracked plate with (a) an offcenter hole (b) r=10 (c) r=1 (d) r=0.1 iv. conclusion the predicted values of stress intensity factors for the crack propagation problem under linear elastic fracture analysis using the finite element method (fem) and the displacement extrapolation technique was presented. in order to obtain a better approximation of the stress field near the crack tip, special quarter point finite elements as proposed by barsoum are used. the estimated sifs are used to further approximate the crack increment length and to predict the crack path etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 506-510 510 www.etasr.com boulenouar et al.: two-dimensional �umerical estimation of stress intensity factors and … direction. the prediction of the latter is based on the maximum circumferential stress theory. finally, the numerical finite element analysis for 2d with displacement extrapolation method and maximum circumferential stress theory, have been successfully employed to determine the effect of the inclusion on the crack path direction under linear-elastic analysis. references [1] t. denyse de araújo, t. n. bittencourt, d. roehl, l. f. martha, “numerical estimation of fracture parameters in elastic and elasticplastic analysis”, eccomas 2000, european congress on computational methods in applied sciences and engineering, barcelona, september, 2000. [2] a. b. de morais, “calculation of stress intensity factors by the force method”, engineering fracture mechanics, vol. 74, no. 5, pp. 739-750, 2007 [3] j. chang, j. xu, y. mutoh, “a general mixed-mode brittle fracture criterion for cracked materials”, engineering fracture mechanics, vol. 73, no. 9, pp. 1249-1263, 2006 [4] g. anlas, m. h. santare, j. lambros, “numerical calculation of stress intensity factors in functionally graded materials”, international journal of fracture, vol. 104, no. 2, pp. 131-143, 2000 [5] s. k. chan, i. s. tuba, w. k. wilson, “on the finite element method in linear fracture mechanics”, engineering fracture mechanic, vol. 2, no. 1, pp.1-17, 1970 [6] d. m. parks, “a stiffness derivative finite element technique for determination of crack tip stress intensity factors”, international journal of fracture, vol. 10, no. 4, pp. 487-502, 1974 [7] b. moran, c. f. shih, “a general treatment of crack tip contour integrals”, international journal of fracture, vol. 35, no. 4, pp. 295-310, 1987 [8] s. phongthanapanich, p. dechaumphai, “adaptive delaunay triangulation with object-oriented programming for crack propagation analysis”, finite element in analysis and design, vol. 40, no. 13-14, pp.1753-1771, 2004 [9] a. m. alshoaibi, a. k. ariffin, “finite element simulation of stress intensity factors in elastic-plastic crack growth”, journal of zhejiang university science a, vol. 7, no. 8, pp. 1336-1342, 2006 [10] p. o. bouchard, f. bay, y. chastel, i. tovena, , “crack propagation modelling using an advanced remeshing technique”, computer methods in applied mechanics and engineering, vol. 189, no. 3, pp. 723–742, 2000 [11] m. souiyah, a. alshoaibi, a. muchtar, a. k. ariffin, “finite element model for linear-elastic mixed mode loading using adaptive mesh strategy”, journal of zhejiang university science a, vol. 9, no. 1, pp. 32-37, 2008 [12] t. n. bittencourt, p. a. wawrzynek, a. r.ingraffea, j. l. sousa, “quasiautomatic simulation of crack propagation for 2d lefm problems”, engineering fracture mechanics, vol. 55, no. 2, pp. 321-334, 1996 [13] m. m. rashid, “the arbitrary local mesh replacement method: an alternative to remeshing for crack propagation analysis”, computer methods in applied mechanics and engineering, vol. 154, no. 1-2, pp. 133-150, 1998 [14] d. azócar, m. elgueta, m. c. rivara, “automatic lefm crack propagation method based on local lepp–delaunay mesh refinement”, advances in engineering software, vol. 41, no. 2, pp. 111–119, 2010 [15] p. o. bouchard, f. bay, y. chastel, “numerical modelling of crack propagation: automatic remeshing and comparison of different criteria”, computer methods in applied mechanics and engineering, vol. 192, no. 35-36, pp. 3887–3908, 2003 microsoft word 19-3667_dion2__etasr_v10_n4_5992-5997 engineering, technology & applied science research vol. 10, no. 4, 2020, 5992-5997 5992 www.etasr.com danikas et al.: space charges as pre-breakdown phenomena in solid dielectrics: a concise approach … space charges as pre-breakdown phenomena in solid dielectrics: a concise approach and some critical comments michael g. danikas democritus university of thrace department of electrical and computer engineering power systems laboratory xanthi, greece george e. vardakis democritus university of thrace department of electrical and computer engineering power systems laboratory xanthi, greece ramanujam sarathi indian institute of technology madras department of electrical engineering chennai, india abstract-this short review deals with some aspects of space charges in solid dielectrics, and, in particular, in polymeric materials. the relationship between space charges and prebreakdown events is discussed and the importance of space charges for the breakdown of solid dielectrics is emphasized. keywords-space charges; breakdown strength; polymers; interfaces; pre-breakdown phenomena i. introduction polymers have excellent electrical properties, which render them appropriate for applications in high voltage engineering with applications such as in underground cables, outdoor insulation, switchgrears, capacitors, electrical machines etc. a great deal of research has been performed regarding the breakdown of solid dielectrics and particularly polymers. breakdown by ionization, thermal breakdown, electromechanical breakdown, breakdown caused by partial discharges (pd), are some of the proposed mechanisms [13].efforts have been made in the past to relate space charges and breakdown [4]. it is the aim of the present paper to supply a short review on space charges and their relation to the prebreakdown phenomena. space charges are charges that are trapped inside a solid dielectric, loosing thus their energy without loosing their charge [5]. charges can be injected inside the solid dielectric from electrodes. such charges are called homocharges because they have the same polarity as the injecting electrodes. charges that come about from ionization and the migration of impurities under the influence of an electric field are called heterocharges because they have the opposite polarity from the neighboring electrode [6-8]. space charges depend on the physical and chemical structure of the polymer, possible additives, foreign chemical species, interface conditions, the nature of the applied voltage (ac, dc or impulse) and temperature [9]. space charges may be trapped in various chemical species, in interfaces between amorphous and crystalline regions, in the free volume between the molecular chains of polymers, in oxidation byproducts, in the interfaces between polymers and the electrodes and in asperities [10]. traps may be shallow or deep. in case of presence of low molecular weight chemicals, acting as space charge traps [8], the probability of space charges accumulation increases. trapping of space charges depends on the very structure of the polymer, i.e. on whether it amorphous, semi-crystalline or primarily crystalline. it has been observed that with amorphous polymers, space charge accumulation may be quite large [11]. as reported in [12], space charges become crucial in the case of dc cable insulation. with the application of dc voltage, the formation of space charges begins. space charge distribution reaches a steady state after a certain period of time. if such a space charge cannot move – in response to a sudden change of voltage – there is a danger of insulation breakdown. such situations may be caused by a reversal of polarity, by the malfunction of a converter or even by lightning overvoltages. the importance of ionic carriers for the dielectric behavior of an insulating system consisted of polypropylene and oil was noticed quite early [13]. at very low voltage levels, ionic carriers are accumulated near the interface without being trapped but as the voltage increases they are trapped near the interface causing a decrease in ionic concentration in the thin oil layer and consequently a decrease in dielectric loss. the importance of impurities (and consequently of space charges) was noted in [14, 15], where polyethylene insulation was investigated. in yet some other publications and considering needle-plane electrode arrangements, space charge distribution was taken into account in polymer breakdown [16-18]. more specifically in [16], the notion of field limiting space charge (flsc) is engineering, technology & applied science research vol. 10, no. 4, 2020, 5992-5997 5993 www.etasr.com danikas et al.: space charges as pre-breakdown phenomena in solid dielectrics: a concise approach … discussed and the radius of the space charge cloud for various geometries of the tip of the needle is calculated. publications [16-18] were significant in that they tried to relate injection of charges, treeing phenomena, insulation damage and breakdown. these publications proposed that, studying the injected charge w.r.t. time, two types of materials exist, i.e. materials of type i having a low value for the injection voltage (and leading to a great amount of injected charge) and materials of type ii having the onset of charge injection at higher voltages, causing thus the charge decrease with decreasing voltage. a point of criticism leveled against the aforementioned publications is that recombination effects were not taken into account, although such effects contribute to the increase of the rate of loss of carriers in an existing treeing structure [19, 20]. ii. the importance of space charges in the prebreakdown processes – earlier research quite early, experiments with polyethylene and needleplane electrode arrangement pointed out that the variation of breakdown strength with polarity and radius of curvature of the needle electrode indicated that the stress-enhanced conductivity and space charge accumulation reduce the stress near the sharp points to values much lower than those calculated geometrically [21]. according to other researchers, space charge exists ahead of the breakdown channel persisting for some time even after the removal of the voltage pulse. they reported that if another pulse not larger than the previous one and of the same polarity is applied, it does no damage to the insulation because the insulation ahead of the channel is shielded by the first space charge [22]. a physical model developed for electrical aging and breakdown of extruded polymeric (polyethylene, cross-linked polyethylene, ethylene propylene rubber) insulated power cables assumed the entering of space charge into gas channels, with the increase of the voltage stress above the pd threshold level. the space charge entering the channels decreases the insulation breakdown voltage in proportion to (e – ethac), with e being the applied voltage stress and ethac the threshold voltage stress. consequently, the depth to which the space charge penetrates into the channels of the insulation is also proportional to (e – ethac). in the case of ac voltages, the flow of charges forward and backward along the channels causes the scission of molecular chains of the insulation adjacent to the channels and in this way, the diameter of the channels increases. the largest amount of charge will flow in the stem of the tree-like pattern. as the diameter of the stem increases, it will transform into a crater. as the latter achieves a critical depth, the voltage stress at its end will become sufficiently high for the development of local pd, which subsequently will lead to an electrical tree causing the complete breakdown of the insulation. the crater depth will be proportional to the charge flowing forward and backward through the channel in the insulation adjacent to a void [23]. the weakness of this model is that it depends on the knowledge of distribution, shapes and sizes of microvoids, which in turn depend on a variety of complex factors [24].the gist, however, of the approach of [23] conforms with earlier observations, where it was noted that the observed tree length can be taken as a measure of the spatial distribution of the space charge [25]. publication [23] draws some ideas regarding the forward and backward flow of charges from an earlier paper [26]. according to [27], there is a possible link between the concentration of space charges in the crystalline-amorphous interfacial regions and the subsequent formation and propagation of tree channels. in [27], it was indicated that the electric field value for charge injection is emax=1.2x10 8 v/m, a value much higher than the one reported in [28] (3.3x10 6 v/m), but lower than that reported in [29] (10 9 v/m). the value mentioned in [27] for charge injection is not very different from the one reported in [30], where for a void-free insulation the maximum field to cause insulation deterioration was found to be 3x10 8 v/m. the above publications conform with the proposed mechanism of breakdown in [31], where it was remarked that space charges deform the electric field and the rate of collision ionizations increases near the cathode [32]. the importance of space charges and their role in prebreakdown processes was emphasized earlier on in [33], where –besides the proposed models for solid dielectric breakdownit was pointed out that cumulative ionization creates positive space charges, which distort the electric field weakening thus the dielectric. breakdown will occur when the electric field applied is so high that electrons travelling through the dielectric have a sufficient chance to traverse the maximum of the integral excitation function of the atoms. space charges are also implicitly mentioned in [34], where it was reported that in mixed or amorphous solid dielectrics, a large number of electrons trapped in energy levels due to lattice imperfections can transfer energy to the lattice vibrations. in [35], special attention was given to the space charges. it was considered that the presence of space charges modifies the local value of the electric field according to poisson’s law. collision ionization was assumed as the basic mechanism of space charge formation. the significance of space charges for breakdown was also stressed in [36], where discussing the breakdown of perspex cubes with sphere-sphere electrodes, emphasis was put on the electron emission into the dielectric from the cathode. as the field near the cathode reaches a critical value, electron multiplication by impact ionization may initiate a type of multiple avalanche breakdown mechanism. the importance of interfaces, and in particular of the crystalline-amorphous boundaries, was discussed in [37], where it was reported that injected electrons from the cathode are trapped at the crystalline-amorphous boundaries, forming thus homotype space charge suppressing avalanche formation in the crystalline part especially in the case of dc application. later publications [10, 27] agreed with the conclusions of [37] on the importance of the crystalline-amorphous boundaries. an implicit importance to the space charges –although in their model the sort of charge carriers is not specified– was also given in [38], where in the initial stage of field stressing charge carriers of low energies can extend pre-existing defects and increase their density, so that clusters of interacting defects will take place. such clusters will grow into macroscopic defects and subsequently the density of charge carriers and their ‘free paths” will increase until the macroscopic defects form a single channel of high probability of continuous conduction between the electrodes. engineering, technology & applied science research vol. 10, no. 4, 2020, 5992-5997 5994 www.etasr.com danikas et al.: space charges as pre-breakdown phenomena in solid dielectrics: a concise approach … iii. the importance of space charges in the prebreakdown processes – later research in [39], a variety of samples of cross-linked polyethylene samples (xlpe) was studied with dc as well as with ac electric stresses. no significant chargecan be observed in the sample subjected to 10 hz ac electric stress, while accumulation of negative charges was observed at frequencies of 1 and 50 hz. one possible explanation is the contribution of space charge on ac ageing is speculated to be mainly due to the fatigue mechanism associated with the electromechanicalenergy stored or released in trapping and detrapping as well as to the electromechanical forces exerted by the injected charge in each half cycle [40, 41]. with dc electric stress, the situation was more straightforward, in that the amount of homocharges increased with aging duration. the role of space charges as pre-breakdown events was discussed in [42], where it was noted that the injection depth of space charges is inversely proportional to the initial applied electric field. this may be somehow surprising but the authors of [42] explain it by considering space charge kinetics and the process of trapping/detrapping. the role of interfacial zones is also considered in [42]. trapping/detrapping of space charges as well as recombination process were studied in [43], where it was remarked that the latter is more energetic than the former mechanism. the findings of [43] justify the criticism of [19, 20] regarding [16-18]. it has to be noted that hints of the ideas of [43] were already present in an older doctoral thesis [44]. in [45], the authors tackled the space charge influence from another point of view, namely that of the influence of the thickness of the insulating sample. they found that, generally the accumulation of space charges increases with the increase of application time of the applied voltage, which results in a lower breakdown strength. consequently, the accumulation of space charges in a thicker sample is greater since the time required for the internal electric field to reach the breakdown threshold value becomes longer under the same ramp voltage. the accumulation of space charges in a thicker sample is more severe making the electrical breakdown of a thicker sample lower than that of a thinner sample. such observations were also noticed in [46]. the effect of sample thickness and of a slower ramp voltage in relation to space charges was noted as well in [47]. in [48], emphasis was given on the threshold voltage above which space charges appear, although as the authors remark there may be a second threshold voltage where the space charge behavior becomes even more complex, like the emergence of traveling space charge packets in the form of solitary waves. disappearance of hetero-charges with increasing thickness may be interpreted by enhance electronhole recombination in pure ldpe as well as with ldpe filled with sio2 nanoparticles. such a mechanism depends on the trap density [48, 49]. space charges play a role also in determining the breakdown strength of silicone-based elastomers, although it is not yet clear whether the observed breakdown failures were due to exclusively to charge delocation or a combination of both charge delocation and softness of the material due to excessive heating [50]. in fact, such an interplay between space charges and local heating was also noted in [51], where it was postulated that local current density due to space charges may cause heat flow conditions such that they may in turn lead to thermal instabilities. in [51], it was also noted that space charge currents may lead to filaments in the dielectric, which in turn will lead to treeing. this is in accordance with previously published seminal work [16-18, 52]. space charges contribute significantly to the initiation and propagation of trees in solid dielectrics. space charges, injected from asperities, may cause electroluminescence (el), which in turn may be related to a degraded region of the polymer. el occurs often prior to electrical treeing. el may determine the effect of space charge during charge injection under ac, dc and impulse voltages [53]. recombination processes may also be considered since they can eventually break the chemical bonds of a polymer [43, 54]. other researchers pointed out the intimate relationship between space charges, pd and treeing [55]. a factor also contributing to the treeing phenomenon is the surface resistivity of the inner void walls. the interplay between surface resistivity, space charges and treeing was discussed in [56], where it was reported that as the material deteriorates, the surface resistivity of the inner walls of a void is reduced and the electric field increases at the boundary between the void and the healthy material. such action, however, will further contribute to the extension of the damaged material. the latter thoughts bring us to another challenging problem, namely that of the relation between space charges and the ensuing pd activity inside the voids that may exist in a solid insulation. charges trapped in shallow traps at the boundary between solid dielectric and void may serve as initiatory electrons and may have been deposited from previous pd events but, as mentioned in [57], they can also be the result of charge transport from the electrodes to the void. however, earlier remarkable publications [58-60], did not shed light to the relation between space charges and pd, although efforts which were undertaken indicated that electrical trees may be caused from recombination effects and by an increase of trap density to the point where shallow traps can connect together in the form of a percolation cluster under the application of an electric field. impact excitation and impact ionization can ensue leading inevitably to filamentary damage and tree initiation [61, 62]. a study of space charges with both ac and dc voltages was reported in [63], where it was remarked that the comparatively lower ac breakdown strength (compared with dc breakdown strength) and the decreasing trend with increase in applied frequency are due to space charge induced electric field distortion in the vicinity of the electrodes. consequently, breakdown with ac voltages starts mainly in the vicinity of the dielectric/electrode interface. on the contrary, when a dc voltage is applied, breakdown initializes in the bulk of the solid dielectric. the results of [63] are somehow at variance with those of [64], where it was reported that with dc voltages, both electrodes may play a role. the authors of [64] stressed the importance of the thermal nature of breakdown on the condition of the presence of space charges. as a general comment, one may say that space charges have an influence on the applied electric field. the amount of engineering, technology & applied science research vol. 10, no. 4, 2020, 5992-5997 5995 www.etasr.com danikas et al.: space charges as pre-breakdown phenomena in solid dielectrics: a concise approach … charge formed in the sample of ldpe increases with the applied field and its duration. the maximum electric field shows time dependent and its position varies as well. the electric field enhancement can reach up to 60% at high applied fields [65]. this implies that space charge dynamics is a very complicated matter being dependent on the electrode material, the applied electric field and its duration. such data conforms with earlier experimental results on cable insulation [66]. in fact, [66] also showed the relation between space charge buildup, electrical treeing and breakdown. in [67] it was remarked that polarity reversal processes tend to show the effect of pre-existing fields on space charge reversal. space charges formed in the middle of cable insulation lead to currents which tend to move charges from the bulk of the insulation towards the electrodes, which in turn may be the source of damage [67]. iv. some additional remarks although it seems that space charges are related to electrical trees [66], and that electrical trees are a prebreakdown phenomenon [68-70], no effort is made under the context of the present work to refer to this relation. also, no detailed mention is being made of the various techniques used in order to measure space charges [6, 54, 71, 72] in the present paper. furthermore, space charge measurements have been proposed for industrial applications [73, 74] but such a subject needs a lengthy treatment which is beyond the scope of the present paper. the simulation of electrical trees in the presence of space charges (e.g. [5, 75-77]) is also not considered. all the aforementioned subjects can be treated in separate publications since the amount of theoretical and experimental data is too large. v. conclusions this short review indicates that space charges are an important phenomenon related to the breakdown of solid insulation. homocharges and heterocharges can significantly modify the electric field in a solid dielectric and thus shorten its lifetime. space charges is a very complex phenomenon depending on a variety of factors, such as, among others, the nature of the applied electric field, existing interfaces 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[77] y. shibuya, s. zoledziowski, and j. h. calderwood, “void formation and electrical breakdown in epoxy resin,” ieee transactions on power, apparatus and systems, vol. 96, no. 1, pp. 198–207, 1977. engineering, technology & applied science research vol. 8, no. 5, 2018, 3398-3404 3398 www.etasr.com al-sakkaf & almuhaini: power flow analysis of weakly meshed distribution network including dg power flow analysis of weakly meshed distribution network including dg abdulrahman al-sakkaf king fahd university of petroleum and minerals dhahran, saudi arabia mohammad almuhaini king fahd university of petroleum and minerals dhahran, saudi arabia abstract—power flow is one of the essential studies in power system operation and planning. all steady-state parameters for power distribution systems, such as bus voltage magnitudes, angles, power flows, and power losses, can be calculated by conducting power flow analysis. distribution system features differ from those of transmission system, rendering conventional load flow algorithms inapplicable. in this paper, three distribution power flow techniques are presented and tested to evaluate their performance when applied to a networked distribution system including distributed generation (dg). these are the distribution load flow (dlf) matrix, the enhanced newton raphson (enr), and the robust decoupled (rd) method. ieee 33-bus system is adopted for implementing the above methods. radial and weakly meshed configurations are applied to the tested system with dg inclusion to investigate their influence on the power flow study findings. keywords-power flow analysis; distribution systems; load flow algorithms; weakly meshed configuration; distributed generator i. introduction power flow analysis, also known as “load flow” analysis, is one of the most important power system techniques. this analysis can be performed to determine the steady state conditions of a power system for a set of specified power generations (dgs) and load demand conditions. power flow analysis is essential for power planning and operation, economic scheduling, and power exchange among utilities. furthermore, it is necessary for other analyses, such as fault analysis, stability, and power system reliability. power systems consist of three main parts: generation, transmission, and distribution system. since the distribution system is the final stage in the power system and is connected directly to the customers, its voltage profile must be investigated and evaluated to ensure high-quality service and identify any improvement needs. in order to improve the distribution network performance, dgs, management technologies, power electronic interfaces, and control systems are integrated into the system. this integrated system is called a “microgrid” or “active distribution network”. to study the voltage profile of an active distribution or microgrid system, power flow analysis must be performed. power flow calculation is usually carried out using the node voltage method. first, an admittance matrix for the system is formed, before deriving complex nonlinear power flow equations. finally, node voltages and other parameters are calculated by solving the power flow equations. the most common techniques used for load flow calculation are gaussseidel, newton-raphson, and fast decoupled iterative techniques [1, 2]. these methods were developed to solve the power flow for transmission systems. however, they may not work appropriately in distribution systems, as they exhibit the following special features [3]:  radial and sometimes weakly meshed structures  high resistance to reactance (r/x) ratios  multiphase and unbalanced orientation  extremely large number of branches and nodes for a distribution system, techniques based on nodes and branches have been developed and are widely used. one of the most common methods is the forward and backward sweep method [4]. this method can be used to solve power flow equations for weakly meshed distribution systems by converting the weakly meshed into a radial system and solving it directly by kirchhoff's voltage and current laws (kvl and kcl). in this case, the number of iterations is high due to the conversion process. a fast decoupled method using g-matrix (fdg) for application in distribution systems has been outlined in [5]. this method relies on the newton-raphson technique with rectangular coordinates and equivalent current injections. the fdg method is sensitive to the reactance (r/x) ratio. simple and efficient branch-to-node matrix-based power flow (bnpf) for radial distribution systems has been presented in [6]. a key feature of this method is that voltages for all nodes are calculated from the source voltage. a branch-to-node matrix is used to define the relationship between the branch current and node currents without the need for matrix inversion. a distribution power flow technique aiming to enhance the convergence rate by partially linearizing the power flow equations has been developed in [7]. this method is insensitive to the resistance to the r/x ratio and is suitable for large-scale distribution systems. on the other hand, forming, calculating, and inverting the jacobian matrix increases its complexity, making it more time-consuming. in this paper, three distribution power flow techniques will be presented and tested on an ieee 33-bus system. these are the distribution load flow (dlf) matrix, the enhanced newton engineering, technology & applied science research vol. 8, no. 5, 2018, 3398-3404 3399 www.etasr.com al-sakkaf & almuhaini: power flow analysis of weakly meshed distribution network including dg raphson (enr), and the robust decoupled (rd) method. radial and weakly meshed configuration will be implemented to evaluate the effect of the network structure on the power flow study. in addition, distributed generation (dg) will be included in order to study its impact on the distribution system voltage profile. ii. power flow techniques a. distribution load flow (dlf) method this method solves the distribution power flow directly by using two matrices: bus injection to branch current (bibc) and branch current to bus voltage (bcbv) matrix [8]. bibc and bcbv are formed based on the system configuration and are utilized for branch current and voltage drop calculations, respectively. multiplying those two matrices results in the distribution load flow (dlf) matrix, which is used in one step to compute bus voltages. the power distribution system shown in figure 1 is used as an example. at the beginning, we assume that all buses or node voltages are equal to that at the source node. specified data in the distribution system are load active power (p) and reactive power (q) for each bus. node currents can be computed in terms of specified p and q using (1): ∗ ∗ (1) fig. 1. sample distribution system by applying kcl to the distribution system, branch currents can be obtained in terms of node currents by applying the following equations: 1 2 3 4 5 2 3 4 3 4 4 5 = + + + = + = = branch node node node node branch node node branch node branch node i i i i ii i ii ii i (2) the relationship between branch currents and node currents in (2) can be expressed via the bibc matrix as follows: 1 1 1 10 1 1 000 00 10 01 (3) equation (3) can be expressed as: ∗ (4) bus voltages can be calculated in terms of drop voltages by applying the following equalities: ∗ ∗ (5) ∗ ∗ the relationship between branch currents and bus voltages in (5) can be expressed via the bcbv matrix as follows: 0 0 00 00 0 0 (6) by rewriting (6) in the general expression format, we obtain: ∗ (7) substituting (4) in (7) yields: ∗ ∗ (8) ∗ where dlf is the distribution load flow matrix: finally, bus voltages are computed as: (9) after solving the voltages for all buses by applying (9), we need to check for convergence. if the solution has converged, the process is terminated. otherwise, the algorithm is executed iteratively until the convergence criteria are met. figure 2 shows the algorithm of the dlf method. fig. 2. dlf algorithm. b. enhanced newton raphson (enr) method this method provides a solution for distribution load flow using the current-injection technique based on the newtonrapson method and rectangular coordinates [5]. the jacobian matrix in enr is called “g matrix.” unlike conventional newton raphson method, the matrix is formed only once and remains unchanged. for the first time, decoupling can be applied to the distribution power flow by assuming offengineering, technology & applied science research vol. 8, no. 5, 2018, 3398-3404 3400 www.etasr.com al-sakkaf & almuhaini: power flow analysis of weakly meshed distribution network including dg diagonal blocks of the g matrix to be zeros. for a distribution system with n buses, the specified node current can be calculated in terms of specified active power (p) and reactive power (q) as follows: ∗ ∗ (10) specified branch currents can be calculated as: ∗ (11) where c is a branch to bus matrix. bus voltage will be represented in rectangular coordinates as: (12) by substituting (10) and (12) in (11), equation (11) becomes: ∗ ∗ ∗ (13) branch current can also be calculated in terms of branch admittance in rectangular coordinates: (14) where i represents a particular bus in the system, where i=1, 2, 3,…, n, and j denotes the branches (j=1, 2, 3,..., n − 1). by separating the real and imaginary parts of (13) and (14), the newton-raphson solution for the load flow can be formulated as: ∆∆ ∆∆ (15) jacobians are calculated only once, as follows: , , , , , , current mismatches ∆ and ∆ are calculated using the expressions below: ∆ (16) ∆ correction values ∆ and ∆ can be obtained by factorizing (15): ∆∆ ∆∆ (17) finally, voltage magnitudes and angles are computed and updated by: ∆ (18) ∆ after computing and by applying (18), we need to check for convergence. if the solution has converged, the process is terminated. otherwise, the algorithm is executed iteratively until the convergence criteria are met. figure 3 shows the algorithm of the enr method. the g matrix can be decoupled by assuming that the off-diagonal blocks of g matrix have zero value. ∆∆ 00 ∆∆ (19) consequently, ∆ and ∆ can be calculated as: ∆ ∆ (20) ∆ ∆ a drawback of this assumption is that, in large systems, the solution may not converge. fig. 3. enr algorithm. c. robust decoupled (rd) method the main objective of the robust decoupled method is to decouple the newton-raphson equation into two sub-equations by a constant transformation matrix [9]. multiplying the jacobian matrix by the transformation matrix will result in zero off-diagonal blocks of the jacobian. equation (15) is multiplied by the transformation matrix in order to decouple the equation. ∆∆ ∆∆ (21) and are diagonal matrices of cosine and sine admittance angles, respectively. after decoupling, (21) will be represented as: t ∆e ∆i _ (22) t ∆f ∆i _ sub-jacobian matrix t, ∆ _ , and ∆ _ are calculated using the expressions below: , , (23) , , ∆ [∆ [∆ (24) ∆ [∆ [∆ engineering, technology & applied science research vol. 8, no. 5, 2018, 3398-3404 3401 www.etasr.com al-sakkaf & almuhaini: power flow analysis of weakly meshed distribution network including dg equation (23) is calculated only once as the jacobian. correction values ∆ and ∆ can be obtained by dividing (22) by : ∆ ∆ _ (25) ∆f t ∆i _ finally, voltage magnitudes and angles are computed by: ∆ (26) ∆ after computing and by applying (26), the voltage magnitudes and angles are updated until the convergence criteria are met, as shown in figure 4. fig. 4. rd algorithm. iii. impacts of weakly meshed connection & dg on power flow techniques a. weakly meshed distribution load flow a distribution system typically comprises of a large number of feeders and load points connected to these feeders, as well as open tie switches. tie switches are closed in contingency or when serving high-density loads. when some of the tie switches are closed, this creates loops in the distribution system, resulting in a weakly meshed rather than radial configuration. this new configuration leads to loss reduction, voltage profile improvement, as well as reliability and powerquality enhancement. a simple weakly meshed distribution system is shown in figure 5. fig. 5. a weakly meshed distribution system dlf method can be utilized in this case with few modifications. as shown in figure 5, a new branch ( ) is added to the system. the branch current flows through from node 4 to node 5. and will be calculated as [10]: = (27) = (28) dlf matrix will be modified as well. if a new branch is added from a bus to a bus , all elements in the column are subtracted from the corresponding elements in the column in the existing dlf matrix and the results represent the new column and row of the dlf matrix. the diagonal element of the row and column is found by summing all the impedances of the branches involved in forming the loop or “weak mesh.” after modifying the dlf matrix, kron's reduction must be applied to the new dlf matrix to ensure that it is of the same dimensions as before [1]: ∗ this technique is applicable to the dlf method only, as it requires dlf matrix modification. b. distribution load flow including dg distribution generation (dg) is a generation system that spreads through the distribution system for the purpose of improving service reliability. dg could be a photovoltaic system, a wind turbine, a fuel cell, a micro turbine, etc. these dg units have different operational modes [11]. they could supply a power with a predetermined amount of reactive power (fixed power factor). in this case, dg units are not controlling the voltage at the connection point. on the other hand, dg units could supply power by controlling and regulating the voltage at the connection points. fig. 6. a distribution system with distributed generator. if a dg unit generates a predetermined amount of reactive power, the dg is modelled as a pq bus and is treated as a load bus with negative p and q values. however, when a dg unit regulates and controls the voltage at the connection point, the dg is modelled as a pv bus. in the case of pv, active dg power is specified, reactive dg power is initially set to zero, and the voltage at the p-v node is set to the desired value. the dlf, enr, or rd method can be utilized here with some adjustments. branch currents will be calculated as: ∗ (29) engineering, technology & applied science research vol. 8, no. 5, 2018, 3398-3404 3402 www.etasr.com al-sakkaf & almuhaini: power flow analysis of weakly meshed distribution network including dg after computing the bus voltages, if | |≤error tolerance, the solution has converged. otherwise, will be generated by the pv node to maintain the voltage at the specified value. can be computed as: ∗ (30) where is the number of the dg bus, is the set voltage at the dg bus, and is the calculated voltage at the dg bus. the algorithm for solving distribution power flow with dg inclusion is the same as the previously described method based on those two equations. iv. tests and results tests and simulations for the presented methods were carried out. dlf, enr, and rd, were tested on a radial 33-bus distribution system. in addition, the dlf method was tested on a weakly meshed 33-bus distribution system. moreover, the dlf method was tested on a weakly meshed 33-bus distribution system including dg. line and load data for the system are based on [12]. the base data is 12.66kv and 10mw, and the convergence tolerance is 0.0001. a. radial distribution system the previously described distribution load flow methods, dlf, enr, and rd, were tested on a radial 33-bus [12] in order to assess their performance, accuracy, speed of calculation, robustness, and computational efficiency. figure 7 shows the ieee radial 33-bus system. solutions for dlf, enr, and rd for the radial 33-bus are shown in table i. fig. 7. 33-bus distribution system. table i. pf solution for radial 33-bus system bus no. dlf, enr, and rd bus no. dlf, enr, and rd 1 1 0 18 0.9131 -0.4950 2 0.9970 0.0145 19 0.9965 0.0037 3 0.9829 0.0960 20 0.9929 -0.0633 4 0.9755 0.1616 21 0.9922 -0.0827 5 0.9681 0.2283 22 0.9916 -0.1030 6 0.9497 0.1338 23 0.9794 0.0651 7 0.9462 -0.0965 24 0.9727 -0.0237 8 0.9413 -0.0604 25 0.9694 -0.0674 9 0.9351 -0.1335 26 0.9477 0.1733 10 0.9292 -0.1960 27 0.9452 0.2295 11 0.9284 -0.1888 28 0.9337 0.3124 12 0.9269 -0.1773 29 0.9255 0.3903 13 0.9208 -0.2686 30 0.9220 0.4956 14 0.9185 -0.3473 31 0.9178 0.4112 15 0.9171 -0.3849 32 0.9169 0.3881 16 0.9157 -0.4082 33 0.9166 0.3804 17 0.9137 -0.4855 results reported in table i indicate that all three methods provide the same solution, which is consistent with those reported in [13, 14]. for dlf, enr, and rd, the solution converged after the same number of iterations (4), thus, all three methods have good convergence. in terms of computational time, dlf outperforms enr and rd, as 46ms, 70ms, and 80ms were obtained, respectively. nonetheless, all three methods are accurate and efficient. however, dlf is simpler and faster than enr and rd. table ii shows the comparison among these three methods. table ii. comparison of the proposed methods rd enr dlf dpf methods accurate accurate accurate accuracy 4 4 4 number of iterations 80ms 70ms 46ms computational time inflexible inflexible flexible flexibility complex complex simple complexity insensitive insensitive insensitive sensitivity to r/x ratio b. weakly meshed distribution system dlf method with the adopted modification for a weakly meshed distribution system was tested on the 33-bus system having five loops [10], as shown in figure 8. the new mesh connections cause a reduction in the branch current values. this reduces drop voltage and power losses, while improving the voltage profile. the results obtained from the power flow solution are identical to the results reported in [10]. the voltage profile is improved due to closing the tie lines and all bus voltages, which are thus within ±5% of the base voltage, as shown in figure 12. the improvements range from -1.68% to +4.44%. although voltages at bus 19-22 and 24-25 decrease slightly, they remain within the acceptable voltage limits. figure 9 shows the percentage improvements in the voltage profile due to the mesh connections. red points on the graph indicate voltage deterioration. fig. 8. 33-bus distribution system with 5 closed tie lines fig. 9. voltage profile improvements due to mesh connections. c. weakly meshed distribution system with dg the dlf method with the additional equations required for including the dg unit in the distribution system was tested on the 33-bus weakly meshed distribution system. figure 10 shows that dg generating 1000kw was installed at bus 22. the engineering, technology & applied science research vol. 8, no. 5, 2018, 3398-3404 3403 www.etasr.com al-sakkaf & almuhaini: power flow analysis of weakly meshed distribution network including dg dg is modelled as a pv bus controlling the voltage at the connection point. the voltage at bus 22 is set at 1p.u. the voltage profile is improved because the weakly meshed and distributed generator is connected to the system, where dg generates 970kvar. this improvement extends from -0.1% to +5.80%, whereby only one bus voltage decreases by 0.1% (at bus 25), as shown in figure 11. fig. 10. a 33-bus weakly meshed distribution system with dg. fig. 11. voltage profile improvement due to 1000kw dg. an illustration of the voltage profile for the three aforementioned test systems is shown in figure 12. in the radial system, voltage violations occurred, and several buses had a voltage below 0.95p.u., as indicated by red dots. the weakly meshed connection improved the voltage profile and eliminated violations. moreover, all bus voltages were within the 1.05p.u.−0.95p.u. range. summarizing, installing dg at bus 22 in the weakly meshed system enhanced further the system voltage. fig. 12. voltage profiles of the radial, weakly meshed, and weakly meshed system with dg. 1) installing different sizes of dg a variety of dg sizes were tested to investigate the effects of dg size on the power flow study and voltage profile. three dgs (200kw, 800kw, and 1500kw respectively) were installed at bus 22, one at the time. error tolerance was reduced to 0.001 to ensure better convergence. figures 13 and 14 show maximum improvement and deterioration in the system voltage for each dg size. as previously noted, the deterioration occurred at bus 25 only. average voltage enhancements for the system with the dg of 200kw, 800kw, and 1500kw size are computed as 3.05%, 3.13%, and 3.20%, respectively. thus, the voltage profile is slightly enhanced with the increment in the dg size. fig. 13. maximum voltage improvement due to different dg sizes. fig. 14. maximum voltage deterioration due to different dg sizes. 2) installing a dg at different locations in addition to investigating the effects of different dg sizes, a 1000kw dg was installed at different locations in the system, and tests were performed to study the dg location influence on the system voltage. the dg was installed at bus 6, 18, 22, and 33, respectively, one at a time. power flow results for each case are shown in figure 15. the reactive powers required to obtain the power flow solution for the system with dg at bus 6, 18, 22, and 33 are 3485 kvar, 1047 kvar, 970 kvar, and 1540kvar, respectively. fig. 15. voltage profiles of the weakly meshed system with dg at different locations. 3) installing multiple dgs in this case, three dgs were installed at the same time in different locations to study the impact of multiple dgs on the system. two dgs were modeled as pv and were installed at bus 18 and 22, respectively, while the third dg was modeled as pq and was installed at bus 33. the two pv dgs produced 1000kw and were set at 1p.u. voltage, whereas the pq dg generated 500kw and 500kvar. measured improvements range from +0.18% to +9.53%, as shown in figure 16. in this case, all bus voltages are improved and none exhibits any engineering, technology & applied science research vol. 8, no. 5, 2018, 3398-3404 3404 www.etasr.com al-sakkaf & almuhaini: power flow analysis of weakly meshed distribution network including dg deteriorations. these voltage improvements arise as multiple dgs exhibit a greater effect than do individual dgs. fig. 16. voltage profile improvements due to multiple dgs. d. distribution system with peak load in this scenario, the system loads were increased by 20% to study the effect of peak loads on the system voltage profile. the ieee 33-bus distribution system was tested in radial configuration, with weakly meshed connections and multiple dgs. figure 17 shows the results of the three cases with peak loads. in the radial system, 21 buses have voltages below the limit, as indicated by the red dots on the graph. with the mesh connections, the voltage profile partially improved, as only 10 buses were below the limit. including multiple dgs improved the voltage profile substantially, eliminating all violations. these results show that increasing the load rate causes a greater number of voltage violations in the system. fig. 17. voltage profiles of the peak load radial, weakly meshed, and weakly meshed system with dgs. v. conclusions power flow analysis helps determine the steady state parameters of a power system. conventional power flow techniques for transmission systems are not applicable to the distribution systems due to their radial nature, extremely large number of components, multiphase operation, and high r/x ratios. in this paper, three power flow techniques (dlf, enr, and rd) suitable for distribution systems were presented. these methods were tested on the ieee 33-bus radial distribution system. the results showed that all three methods are accurate, have good convergence, are insensitive to r/x ratios, and are suitable for large systems. moreover, dlf was applied to a weakly meshed network including dg to assess its impact on the power flow study. different tests utilizing dgs were carried out, whereby the size, location, and the number of dgs varied. these three factors play an important role in the effectiveness of utilizing dgs, as they exert significant effects on the distribution system voltage profile. finally, radial, weakly meshed, and multiple dg tests were repeated with peak load to study the influence of the load rate on the load flow analysis. references [1] h. saadat, power system analysis, mcgraw hill, 2004 [2] r. guguloth, t. k. sunil kumar, “optimal power flow-based congestion management by classical and intelligent methods”, international journal of electrical power and energy systems, vol. 36, no. 3, pp. 104-111, 2016 [3] m. s. srinivas, “distribution load flows: a brief review”, 2000 ieee power engineering society winter meeting, singapore, singapore, january 23-27, 2000 [4] d shirmohammadi, h. w. hong, a. semlyen, g. x. luo, “a compensation-based power flow method for weakly meshed distribution networks”, ieee transactions on power systems, vol. 3, no. 2, pp. 753-762, 1988 [5] w. m. lin, j. h. teng, “three-phase distribution network fast decoupled power flow solutions”, international journal of electrical power and energy systems, vol. 22, no. 5, pp. 375-380, 2000 [6] p. aravindhababu, s. ganapathy, k. r. nayar, “a novel technique for the analysis of radial distribution systems”, international journal of electrical power and energy systems, vol. 23, no. 3, pp. 167-171, 2001 [7] r. ashokkumar, p. aravindhababu, “an improved power flow technique for distribution systems”, computer science, informatics and electrical engineering, vol. 3, no. 1, pp. 1-8, 2009 [8] a. alsaadi, g. gholami, “an effective approach for distribution sys-tem for power flow solution”, international journal of electrical and computer engineering, vol. 3, no. 1, pp. 1-5, 2009 [9] p. aravindhababu, r. ashokkumar, “a robust decoupled power flow for distribution systems”, energy conversion and management, vol. 52, no. 4, pp. 1930-1933, 2011 [10] k. prakash, m. sydulu, “topological and primitive impedance-based load flow method for radial and weakly meshed distribution systems”, iranian journal of electrical and computer engineering, vol. 10, no. 1, pp. 10-18, 2011 [11] h. shateri, m. ghorbani, n. eskandari, a. h. mohammad-khani, “load flow method for unbalanced distribution networks with dispersed generation units”, 47th international universities power engineering conference, london, uk, september 4-7, 2012 [12] m. e. baran, f. f. wu, “network reconfiguration in distribution systems for loss reduction and load balancing”, ieee transactions on power delivery, vol. 4, no. 2, pp. 1401-1407, 1989 [13] j. z. zhu, “optimal reconfiguration of electrical distribution net-work using refined genetic algorithm”, electric power systems research, vol. 62, pp. 37-42, 2002 [14] m. p. selvan, k. s. swarup, “distribution system load flow using object oriented methodology”, 2004 international conference on power system technology, 2004, singapore, singapore, november 21-24, 2004 microsoft word 33-3212_s1_etasr_v10_n1_pp5276-5280 engineering, technology & applied science research vol. 10, no. 1, 2020, 5276-5280 5276 www.etasr.com ying et al.: continuous progressive actuator robot for hand rehabilitation continuous progressive actuator robot for hand rehabilitation sii zhi ying centre for artificial intelligence and robotics universiti teknologi malaysia johor bahru, malaysia zhiying1125@gmail.com ahmad athif faudzi centre for artificial intelligence and robotics universiti teknologi malaysia johor bahru, malaysia athif@utm.my naif khalaf al-shammari mechanical engineering department university of hail hail, saudi arabia naif.alshammari@uoh.edu.sa yaser sabzehmeidani centre for artificial intelligence and robotics universiti teknologi malaysia johor bahru, malaysia yaser7002@gmail.com abstract—this paper presents the development of a soft rehabilitation robot to conduct continuous passive motion (cpm) for hand rehabilitation. the main contribution of this work is the implementation of a mckibben actuator as an artificial muscle due to its proven advantages: simple structure, light weight, and high power-to-weight ratio. the development worked successfully when tested on a healthy subject, where the flexion and extension of the finger were controlled with an antagonistic pair of actuators. however, there is a limitation of the mckibben actuator regarding its length-dependency. in this research, the concept of a pulley system was proposed to overcome this limitation. although there is a friction factor that reduces the contracting displacement by at least 15% of the original displacement, a pulley is still a potential solution as it can reduce the installation space of the actuator from 40 to 15cm while still producing sufficient force for the finger motion. throughout this research, it was found that the pattern of the flexor pulley system is affecting the system’s efficiency in terms of motion assistance. keywords-mckibben actuator; continuous passive motion; finger exoskeleton; hand rehabilitation i. introduction and background according to the national stroke association of malaysia (nasam), stroke is the third leading cause of mortality in malaysia, after heart disease and cancer [1]. an estimated 0.14% of the population (40,000) of malaysians succumbs to stroke each year. stroke is a type of brain injury, it can strike anyone, at any time and at any age [2]. stoke affects its sufferers in different ways, depending on the location and extension of the damage in the brain. most of the stroke patients suffer from hemiplegia, which is the loss of movement on one side of the body [1]. this leads to difficulties in many activities as most daily tasks can hardly be done without using both hands. hence, rehabilitation is a crucial step to help stroke patients to regain their capability in order to manage their daily activities. rehabilitation is usually conducted when the patient is still in acute care in order to prevent additional stroke and stiffness at the affected joint. the rehabilitation that is practiced in the early phase post-stroke patient is known as continuous passive motion (cpm). cpm provides regular movement to a particular joint for rehabilitation without patient’s muscles being used [3]. cpm is claimed to bring beneficial effects especially on gaining a range of motion. however, there are some disadvantages of conventional rehabilitation. conventional rehabilitation has to be either conducted with the help of a professional physiotherapist or monitored in hospital/nursing facilities [2]. as the number of stroke patients in malaysia increases year by year, there is a lack of physiotherapists in rehabilitation centers. in addition, current rehabilitation is subjective and not reliable as it is based on manual visual evaluation and there is no data collection [4]. there is no analytical data to evaluate the recovery progress of the stroke patients systematically. one alternative of conventional rehabilitation is rehabilitation robotics. it helps in reducing the dependency on manual labor and enables data collection. however, there are some drawbacks on current rehabilitation robotics. rehabilitation robots can be divided into two main types based on their actuators, which are electrical motors and soft actuators. electrical motors are heavy, bulky and difficult for the patients to wear by themselves. the rigid frame is putting the patients in an uncomfortable situation and it is quite dangerous when an accident occurs. for example, the hand-assist robot [5], is designed with 18 degrees of freedom (dof) consisting of four finger motion assist mechanisms, a thumb motion assist mechanisms and a wrist motion assist mechanism. it is driven by 22 servo motors that give limited flexibility and portability to the wearer. hexosys [6] is designed with a linkage mechanism for thumb and index finger to conduct continuous finger flexion and extension. however, the users have to wear the system that weighs 1kg on their hand. the system was corresponding author: naif khalaf al-shammari engineering, technology & applied science research vol. 10, no. 1, 2020, 5276-5280 5277 www.etasr.com ying et al.: continuous progressive actuator robot for hand rehabilitation improved and hexosys ii [7] was developed that weighs 600gr. assist on-finger has a lightweight frame that is adjustable to the users’ phalanges length but is still rigid and complex. the mri compatible finger rehabilitation robot [9] operates using an ultrasonic motor. this motor will have a rise in temperature when operating for a long period of time. therefore, it is designed so that the motor is located in a distance from the hand exoskeleton to ensure the safety of the user. 3d printed myoelectric robotic exoskeleton [10] was developed as a low-cost and lightweight finger exoskeleton. it is easy to fabricate but looks space consuming and fragile. meanwhile, the hand rehabilitation exoskeleton [11] that was designed to fit fingers of different thicknesses was constructed of gear and slider and would be worn on top of dorsal of the subject’s hand. another soft bending actuator for finger flexion was proposed by authors in [12], which developed a 3-d finite element analysis of fiber-reinforced actuator. conventional actuators mainly consist of electrical motors widely used in robotics the past decades, add excessive weight to robots. additionally, the rigid structure of the motor limits the application in some situations that require flexibility. hence, soft robotics technology emerged and became a popular research field. soft actuator refers to a device that transforms the power from the power source to mechanical power through the deformation of its materials in a particular structure [13]. soft actuator is being applied in various fields, mostly in biomimicry and medical applications. some soft actuators are bending pneumatic rubber actuator [14], p-elsa [15], ecoflex [16], mckibben soft actuator, etc. mckibben soft actuator was introduced in 1958 but was popularized at the beginning of the 1960s [17]. it is composed of a rubber inner tube and surrounded by a double-helix braided sleeve [17]. when it is pressurized, the inner tube will expand and the orientation of the braided sleeve will cause the actuator to contract, generating a pulling force [18]. this characteristic is very similar to muscles’ behavior, since the muscle will grow in width and shrink in length during contraction [19]. besides, it has high power-to-weight ratio compared to motors due to its simple structure and light weight [20]. it is also easy to be maintained and has a comparatively lower cost than other hard actuators. it does not produce heat except for friction, thus the risk of accidental fire is low. the elastic inner tube is also stretchable allowing it to be stretched when a greater opposing force acts on it. it promotes a safer interaction, so that it would not force human motion, something that could lead to severe injuries. therefore, this paper focuses on the implementation of the mckibben soft actuator as a pneumatic artificial muscle for the rehabilitation robot that conducts hand motion required for cpm. this information and capability could be distributed in the society and for e-health communication purposes [21]. ii. system design the system consists of two soft actuators that are connected in antagonistic pairs for each finger. it has a 24v operating voltage and 0.3mpa operating pressure. the pressure can be controlled and supplied to the system by using an analog regulator based on the programmed procedure for cpm. when the patients are given a task such as grabbing an object, the system will obtain the finger bending data from the flex sensors attached on top of each finger. the data collected will then be visualized as a data that can be used for recovery progress tracking. the finger exoskeleton is designed to mimic the flexor pulley system of human finger. dyneema rope is used as a tendon to pull the finger as it offers better strength to weight ratio. it is fixed on a few points on the gloves based on the location of ligaments in human fingers. the attachment of dyneema rope on gloves for the exoskeleton prototype is shown in figure 1. the pattern of the flexor pulley system used on the finger exoskeleton will affect its functionality. hence, several patterns were tested and compared to find the most suitable pattern. since the actuator works as an artificial muscle producing pulling force when it contracts, the end of the actuator needs to be fixed. the actuators that function for the extension of the fingers are fixed at the elbow by using elbow guard while the actuators that function for the flexion of the fingers are fixed at the shoulder by using shoulder support as shown in figure 1. both the elbow guard and shoulder support are easy to wear as they only need to be fastened using velcro fastener. fig. 1. prototype exoskeleton with attached dyneema fibre on gloves iii. results and analysis a. overall system the system is programmed with the repetitive exercise that is required for rehabilitation. the exercise focuses on the flexion and extension motion of the human finger and each finger is controlled by an antagonistic pair of mckibben actuators. one of the pair of actuators will contract to control the flexion motion while another actuator will control the extension motion as shown in figure 2. the cpm exercise includes either moving 5 fingers together or finger by finger movement. it can also be programmed to have a full flexion or partial flexion as shown in figure 3 as it is controlled by analog valves. these functions help the patients’ brain to relearn the lost skills of moving their hands. engineering, technology & applied science research vol. 10, no. 1, 2020, 5276-5280 5278 www.etasr.com ying et al.: continuous progressive actuator robot for hand rehabilitation (a) (b) fig. 2. programmed cpm exercise (a) (b) fig. 3. analog control of cpm: (a) full elexion (analogue:255), (b)partial flexion (analog:200) b. flexor pulley system when conducting cpm, the bending of the fingers was influenced by different types of flexor pulley system. (a) (b) (c) fig. 4. pattern of the flexor pulley system for flexion (a) (b) (c) fig. 5. results from the pattern of the flexor pulley system for flexion as the flexor pulley system of finger exoskeleton is different with the flexor pulley system embedded inside human fingers, they cannot be exactly the same. therefore, different pulley systems were tested to obtain the most suitable design. each pattern of flexor pulley system is shown in figures 4 and 5 for flexion and extension respectively. (a) (b) (c) fig. 6. pattern of the flexor pulley system for extension (a) (b) (c) fig. 7. results from the pattern of the flexor pulley system for extension c. space optimization for actuator installation the mckibben soft actuator has a contraction ratio of 20% when supplied with 0.3mpa pressure. this becomes its weakness as it makes the design length dependent and not space-effective. this issue is worsening when used in this application where its functionality will be affected by arm bending. therefore, a double groove pulley system is proposed to optimize the space consumption for the installation of the actuator. some experiments were conducted to examine how the pulley system affects the contraction of mckibben soft actuator. the double groove pulley is designed with different circumference on each groove as shown in figure 8. it works similar to the concept of gear. the mckibben actuator would connect to the groove with smaller circumference while the other groove would be connected to the load. the relation between the circumference of both grooves can be presented as pulley groove ratio as in (1). when mckibben muscle contracts and rotates the pulley by one rotation, the greater circumference on the other groove will amplify the contraction. �� � ��� ��� (1) � ��� (2) where �p=pulley groove ratio, �l=load groove diameter, �m= mckibben groove diameter, l=contraction length on load, and m= contraction length from mckibben. engineering, technology & applied science research vol. 10, no. 1, 2020, 5276-5280 5279 www.etasr.com ying et al.: continuous progressive actuator robot for hand rehabilitation fig. 8. double groove pulley some experiments were conducted to analyze the effects of double groove pulley towards the contraction ratio of mckibben muscles and the results are shown in figure 9. the operating voltage is 24v dc with the supplied air pressure of 0.4mpa. the results show that the contraction ratio can be improved with the aid of the double groove pulley. the greater the pulley groove ratio, the greater the improvement of the contraction ratio. the experimental contraction ratio is compared with the calculated contraction ratio in table i. for 1:1 pulley, the contraction ratio should be the same as without pulley, but the experimental contraction ratio is slightly higher. this is because the diameter of the load pulley groove will increase when the rope is rolled up into the pulley, hence further increase the pulley groove ratio. table i. calculated and experimental contraction ratio pulley groove ratio calculation experiment 1:1 0.1985 0.2424 1:2 0.3970 0.4242 1:3 0.5955 0.5924 1:4 0.7940 0.7606 1:5 0.9925 0.9091 fig. 9. effects of pulley groove ratio towards the mckibben contraction ratio of mckibben iv. conclusions in this work, a wearable robot was developed to carry out repetitive exercises with soft structure which is comfortable and safe for stroke patients. mckibben soft actuators were used as artificial muscles of the hand exoskeleton. the device contains two modes, one conducting cpm while the other mode keeps track of the patients’ recovery progress. the most suitable flexor pulley system for this finger exoskeleton was determined. a solution by making use of a pulley system to optimize space consumption was introduced. it was proved theoretically and experimentally that the mechanism decreases the installation space and increases the extension effectively. the experiment showed the force applied by mckibben soft actuator is sufficient for the flexion finger motion of both robotic and human hands. however, further considerations need to be concerned for improving the system. the fabric glove is not a good option for the fabrication of hand exoskeleton in terms of sterility and cannot be used for all hand sizes. for this reason, the suggested material is silicon rubber which can be washed or sterilized with alcohol. furthermore, the pulley system needs to be optimized for mechanical durability and less friction. acknowledgement the authors would like to thank the deanship of the scientific research of university of hail, saudi arabia for funding and supporting this research project (0161132). referencess [1] nasam, “what is stroke”, available at: https://www.nasam.org/what-isstroke/ [accessed: 29-nov-2019] [2] ahcpr, recovering after a stroke : a patient and family guide, ahcpr publication, no. 16, ahcpr, 1995 [3] m. karadesh, “flexor pulley system”, available at: www.orthobullets. com/hand/6004/flexor-pulley-system, [accessed: 29-nov-2019]. engineering, technology & applied science research vol. 10, no. 1, 2020, 5276-5280 5280 www.etasr.com ying et al.: continuous progressive actuator robot for hand rehabilitation [4] h. i. krebs, b. volpe, “rehabilitation robotics: performance-based progressive robot-assisted therapy”, autonomous robots, vol. 15, no. 1, pp. 7–20, 2003 [5] s. ueki, h. kawasaki, s. ito, y. nishimoto, m. abe, t. aoki, y. ishigure, t. ojika, t. mouri, “development 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mckibben pneumatic artificial muscles”, ieee transactions on robotics and automation, vol. 12, no. 1, pp. 90–102, 1996 [20] r. d. vocke, c. s. kothera, a. chaudhuri, b. k. s. woods, n. m. wereley, “design and testing of a high-specific work actuator using miniature pneumatic artificial muscles”, journal of intelligent material systems and strucures, vol. 23, no. 3, pp. 365–378, 2012 [21] f. e. idachaba, e. m. idachaba, “robust e-health communication architecture for rural communities in developing countries”, engineering, technology & applied science research, vol. 2, no. 3, pp. 237-240, 2012 authors profile sii zhi ying is currently an msc degree candidate in electrical engineering in universiti teknologi malaysia. she received her bsc in electronics (mechatronics) engineering from universiti teknologi malaysia in 2018. she is interested in rehabilitation engineering and robotics. naif k. al-shammari holds bsc and msc in mechanical engineering from king saud university (saudi arabia) and a phd in biomechanics from university of birmingham (uk). in 2005, he joined the birmingham automotive safety centre (basc). his current research interests focus on crash injuries from real world accidents including biomechanics of impacts, vehicle collision performance and epidemiology of traffic crashes. he has held the post of principal crash analyst and was working as a researcher in the co-operative crash injury study team (ccis) at the university of birmingham. he has published more than 25 papers and technical reports. his major fields of specialization are computer modeling, robotics and artificial intelligence. ahmad athif bin mohd faudzi is a lead researcher in robotics and automation. he received his bsc and msc degrees from universiti teknologi malaysia and his phd in system integration from okayama university, japan in 2004, 2006, and 2010 respectively. he is mainly engaged in the research fields of pneumatic actuators, soft actuators, robotics automation and their applications including rehabilitation engineering. he is currently the director of the centre for artificial intelligence and robotics, universiti teknologi malaysia. yaser sabzehmeidani received his bsc and msc degrees in mechanical engineering from the university of mazandaran in 2006 and 2008 respectively, and his phd degree in mechanical-mechatronics from universiti teknologi malaysia in 2013. after 5 years of experience in industry as an r&d manager, he joined cairo (center for artificial intelligence and robotics) as a senior researcher in robotics and biomedical. his research interests include cad/cam, robotics, mechatronics, and manufacturing. microsoft word 12-3750_onlinefirst_s_etasr_v10_n5_pp6214-6219 engineering, technology & applied science research vol. 10, no. 5, 2020, 6214-6219 6214 www.etasr.com buketov et al.: investigation of the influence of the synthesized iron-carbide mixture on the adhesive … investigation of the influence of the synthesized ironcarbide mixture on the adhesive and mechanical properties of epoxy composites for parts of transport machines andriy buketov department of transport technologies kherson state maritime academy kherson, ukraine buketov.andrey@gmail.com olha syzonenko department of pulse processing dispersed systems, institute of pulse processes and technologies of nas of ukraine, mykolaiv, ukraine sizonenko43@rambler.ru dmytro kruglyj department of innovative technologies and technical means of navigation kherson state maritime academy kherson, ukraine krughlyidmytro@gmail.com tetiana cherniavska department of transport technologies kherson state maritime academy kherson, ukraine tanya2181@ukr.net eduard appazov department of innovative technologies and technical means of navigation kherson state maritime academy kherson, ukraine eappazov1@gmail.com kostiantyn klevtsov department of transport technologies kherson state maritime academy kherson, ukraine klevtsovk@i.ua abstract−epoxy-diane oligomer ed-20, hardener polyethylene polyamine, and micro dispersed particles of iron-carbide mixture synthesized by high-voltage electric discharge have been used for the formation of composite materials (cms) and protective coatings for the transport industry. the dependence of the adhesive, physical, and mechanical properties and residual stresses of epoxy composites on the content of micro dispersed powders has been studied in this paper. it has been proved that for the formation of a composite material or protective coating with improved adhesion and cohesion properties, the optimal content of particles is 0.5 wt.% per 100 wt.% of epoxy oligomer ed-20. such materials are characterized by increased mechanical strength and the ability to resist static and shock loads, as their properties are significantly increased. the obtained results of the experimental studies of the physical and mechanical properties of composite materials correlate with the studied results of adhesive characteristics, which indicate their veracity. keywords-epoxy composite; modulus of elasticity; impact strength; flexural stresses i. introduction the development of various industries, including transport, involves the expansion of the scope of structural functional polymeric materials. the use of polymeric epoxy composite coatings is important for the corrosion protection of technological equipment, including parts of transport machines [1-5]. ensuring the compliance between the properties of materials used in mechanisms and structures in the complex conditions of their operation is one of the most significant problems of technological progress nowadays. the current level of production development involves primarily taking into account the economic factor due to the need to develop new effective functional materials. herewith, it is necessary to make allowance the latest approaches, which are based on the optimization of the components of materials of a specific functional purpose. at the same time, such optimization is carried out according to several criteria, such as adhesive strength, residual stresses, flexural stresses, and impact strength. today, the potential capabilities of known polymeric materials are far from being fully realized, due to the insufficient analysis of the physicochemical processes during their operation and destruction. in our opinion, only an approach that involves the analysis of properties in a complex will ensure the formation of new gradient composites with specified improved both adhesive and cohesive characteristics. authors in [6, 7] showed that the creation of new materials with high performance is impossible without understanding the mechanism of interaction at the interface of the phases “protective coating – metal base” and “polymer matrix – filler”, which is the basis for the formation of chemical and physical bonds that determine the durability of materials. to implement the above, dispersible filler particles are introduced into the polymer binder. the presence of the active groups on the surface of the additives, which during the polymerization of the matrix form a significant number of bonds per unit volume of polymer is important. in this regard, it is important to preactivate the filler. authors in [8, 9] showed that the use of corresponding author: a. buketov engineering, technology & applied science research vol. 10, no. 5, 2020, 6214-6219 6215 www.etasr.com buketov et al.: investigation of the influence of the synthesized iron-carbide mixture on the adhesive … synthesized (including high-voltage electric discharge) powders with particles of insignificant dispersion is perspective. given this, it is important to conduct a study to determine the optimal content of iron-carbide mixture synthesized by high-voltage electric discharge in the formation of protective polymer coatings to improve the adhesive and mechanical properties of transport vehicle parts. the aim of the work is to investigate the influence of the content of synthesized iron-carbide mixture on the adhesive and mechanical properties of epoxy composites for the transport industry. ii. materials and methods epoxy diane resin ed-20 (gost 10587-84) was selected for the formation of the polymer matrix. epoxy resin is a highly viscous transparent liquid that can be cross-linked at room or elevated temperature without external pressure. the ability to cure these resins without the release of by-products provides low shrinkage, high density, and low porosity of materials, which is important when working with composite products and protective coatings based on them in difficult conditions. polyethylene polyamine – pepa (tu 6-02-594-70) was selected for curing the epoxy compositions. hardener pepa is used for the cross-linking of epoxy resins at room and low temperatures in conditions of high humidity. the composites were crosslinked by introducing the hardener into the composition at a stoichiometric ratio of components at content (wt.%) – ed-20 : pepa – 100 : 10. synthesized iron-carbide mixture (sicm) was used as a microdisperse filler in the experiment. the filler was formed by high-voltage electric discharge (hved) synthesis. for the hved synthesis of the filler an experimental stand was used, described in detail in [8, 9]. a mixture of powders of fe (75%) and ti (25%) was used as the starting material. during the synthesis, the accumulated energy of a single discharge (w1) was 1kj, and the integrated specific energy of the processing (w) was 25mj/kg. variations can be performed in the process in the distribution of the electric field and plasma formations in the volume of the discharge chamber by using different types of electrode systems. in this work, a 15-point design of the electrode system is used [8]. the use of different electrode systems allowed controlling the distribution of the intensity of the main factors of hved [9]. thus, in the case of using a 1-point system, a larger share of the accumulated energy was transformed into shock waves, then the use of a 15-point system allowed increasing the intensity of thermal and current factors. the results of the research showed that as a result of hved treatment all the treated particles were crushed and their phase composition was changed with the synthesis of high-modulus compounds tic and fe3c (table i). the technology of forming epoxy composites is as follows. at the initial stage, the epoxy resin was heated to a temperature of t=353±2k, kept during for a time duration of τ=20±0.1min. at the next stage, the resin was hydrodynamically combined with the dispersed filler for 10±0.1min and then ultrasonic processing (usp) of the composition was performed for 1.5±0.1min. after cooling the mixture to room temperature (τ=60±5min), a hardener was introduced and the composition was blending for 5±0.1min. the prepared compositions were formed and were polymerized according to the following procedure: • casting of specimens • keeping for 12.0±0.1 hours at room temperature (293±2k) • heating to 393±2k (at a rate of υ=3k/min) • keeping at a given temperature during 2.0±0.05 hours • slowly cooling to 293±2k. at the final stage, the specimens were kept for 24 hours in the air at a temperature of 293±2k to internal stress relaxation, which allowed stabilizing the developed materials properties. the following properties of сm were investigated in this work: adhesive strength, residual stresses, flexural stresses, and modulus of elasticity at bending and impact strength. table i. results of the hved synthesis of the filler composition composition after treatment electrode system diameter after treatment d (µm) dmin dmax dav fe (75 %) + ti (25 %) fe (70 %) + tic (25 %) + fe3c (5 %) 15 ~1 147 17 the influence of the content of additives of different nature on the adhesion properties of composites to the metal base was investigated. the destructive tension (“fungal method”) was measured with a uniform separation of a pair of glued samples in accordance with astm d897-08(2016). the adhesive strength was investigated on an automated tensile testing machine um-5 at a loading speed of 10n/s. the diameter of the working part of the steel specimens was 25mm. residual stresses in coatings were determined by the cantilever method according to [10]. residual stresses σr were found by: 3 3 3 ( ) r he l δ σ δ δ δ ∗ ∗ = + (1) where н is the substrate deflection from the initial position (m), е is the elasticity modulus of the substrate (е=2.1×10 8 pa), l is the length of the substrate with the adhesive (m), δ is the substrate thickness (m), and δ*is the adhesive thickness (m). at the initial stage, a coating with thickness δ=0.1–0.2mm on a steel substrate was formed by the spray method. the parameters of the substrate were: total length l=100mm, working length l0=80mm, thickness δ=0.2mm. at the next step, during the polymerization process, the chemical bonds between the adhesive and the substrate are forming, which involves the occurrence of residual stresses in the coating. this leads to the deflection of the console up (in the form of a substrate with a coating), as the dominant in this case is the tensile stress. the value of this deflection (h) was determined after complete crosslinking of the material in the form of a protective coating (for a duration of 72 hours). flexural stresses at bending and the modulus of elasticity at bending were determined in accordance with astm d 790 – 03. the dimensions of the testing specimens were: length l=120±2mm, width b=15±0.5mm, height h=10±0.5mm [11]. the impact strength engineering, technology & applied science research vol. 10, no. 5, 2020, 6214-6219 6216 www.etasr.com buketov et al.: investigation of the influence of the synthesized iron-carbide mixture on the adhesive … was determined by the charpy method according to astm d6110 – 18. this method is based on a test in which a specimen placed on two supports is subjected to a pendulum impact, the line of impact being midway between the supports and directly opposite the notch (in the case of notched specimen). the dimensions of the testing specimens were: (63.5×12.7×12.7)±0.5mm. the distance between the supports was 40±0.5mm. the deviation of values of adhesive and physical and mechanical properties of cm was 4–6% from nominal during the study. iii. results and discussions it has been experimentally established that the adhesion strength at break of the epoxy matrix modified by usp is σа=24.8mpa (figure 1). the introduction of sicm particles (d=15–18µm) into the epoxy binder leads to a monotonic increase in the adhesive strength of the composite. it is shown (figure 1, curve 1) that the maximum in the “adhesive strength at break–filler amount” curve was observed at content of particles of q=0.5 wt.% by 100 wt.% of ed-20 (hereinafter wt.% are given per 100wt.% of epoxy resin ed-20). the adhesive strength of the material increases from σа=24.8mpa (epoxy matrix) to σа=44.7mpa at this introduction. further increase in the particle content leads to a deterioration of the adhesive properties of epoxy composites. it has been proved (figure 1) that the content increase of particles amount to q=2.0 wt.% promotes the cm formation. the adhesive strength of such cm decreases from σа=44.7mpa (for cm with filler content of q=0.5 wt.%) to σа=33.2mpa. based on the above experimental results, it was considered that the further increase of the sicm amount in the epoxy composite is not advisable, since the adhesive properties of the materials monotonically deteriorate. fig. 1. dependence of adhesive strength and residual stresses in cm on the content of sicm particles: 1 – adhesive strength at break (σa); 2 – residual stresses (σr). substrate material – steel. the obtained experimental results allow stating the efficiency of using the sicm for the formation of cm on the basis of epoxy binder. authors in [8, 9] showed that before the synthesis of filler particles at the initial stage they formed a mechanical mixture of powders at a predetermined content: fe(75%)+ti(25%). in the process of high-voltage electric discharge according to predetermined modes, a synthesized powder is formed, which contains components of the following composition: fe(70%)+tic(25%)+fe3c(5%). it was proved, that the improvement of adhesion characteristics of materials as a result of the loading of active dispersed particles into the epoxy oligomer is presented. it was assumed that the active centers of fe, tic and fe3c, which are contained both in the volume and on the surface of the dispersed phase during the polymerization process interact with the segments and pendent groups (oh-, ch-, c=o) of the epoxy oligomer. at the same time, the degree of crosslinking of the three-dimensional polymer net increases, which improves the adhesive properties of cm. in addition, authors in [8, 9] proved that, after the synthesis, on the surface of the particles areas, titanium and iron carbides are localized, which are mainly activators of physical and chemical interfacial bonds in the structure of materials. at the same time, it should be noted that the maximum number of chemical bonds per volume unit of the polymer was observed at a critical content of dispersed particles in the amount of q=0.5 wt.%. this explains the highest values of adhesive strength of composites with such a filler content among the entire range of investigated materials. it is known [12] that the occurrence of residual stresses in polymer composites is one of the determining criteria for the durability of protective coatings, including anti-corrosion coatings, especially in the transport industry. therefore, in the context of adhesion tests, it was considered necessary to investigate the value of residual stresses in the formed coatings depending on the content of the sicm. it is established (figure 1, curve 2) that the initial epoxy matrix is characterized by residual stresses σr=1.4mpa. the introduction of sicm particles at low content (q=0.2–0.5 wt.%) provides a decrease in residual stresses from 1.4mpa (for epoxy matrix) to 0.7mpa. further increase in the particle content (q=0.7–2.0 wt.%) leads to an increase in the value of residual stresses in the protective coatings to σr=0.8–1.0mpa. comparing the values of adhesive strength and residual stresses depending on the content of particles, we can state the following: the highest values of adhesive strength (σа=44.7mpa) among the whole range of test materials is a composite containing filler in the amount of q=0.5 wt.%. at the same time, such a material is characterized by the lowest residual stresses, which are σr=0.7mpa. this indicates that the developed composite and the protective coating based on it can be used quite effectively to improve the performance of parts that work not only under static but also dynamic loads. hence, the optimal content of the sicm for the formation of epoxy protective coating with maximum adhesion characteristics and low residual stresses was determined. it is proved that at the introduction of the powder in the amount of q=0.5 wt.% a material with the following properties is formed: adhesive strength at break σа=44.7mpa and residual stresses σr=0.7mpa. this provides an increase in the adhesion strength at break by 1.8 times and a decrease in residual stresses by 2.0 times compared with the ultrasonically modified epoxy matrix. it should be noted that from a scientific and practical point of view it is interesting to study not only the adhesive properties of materials and residual stresses depending on the engineering, technology & applied science research vol. 10, no. 5, 2020, 6214-6219 6217 www.etasr.com buketov et al.: investigation of the influence of the synthesized iron-carbide mixture on the adhesive … content of sicm particles, but also the dynamics of mechanical characteristics at different amounts of active filler. therefore, at the next stage, physical and mechanical properties of epoxy composites filled with sicm were studied. in particular, the modulus of elasticity and flexural stresses at bending and impact strength of the developed materials were analyzed. it has been experimentally established (figure 2, curve 1) that the modulus of elasticity of the epoxy matrix modified by ups is e=2.8gpa. the introduction of filler particles at low content (q=0.2–0.5 wt.%) does not change this characteristic of the cm, since the modulus of elasticity at bending is 2.6–2.8gpa (values within experimental errors). further increase in the content of particles from 0.7 wt.% to 2.0 wt.% leads to a deterioration of the elastic properties of the cm. in particular, it was shown (figure 2, curve 1) that at such loading the modulus of elasticity decreases from 2.8gpa (for epoxy matrix) to 2.2–2.4gpa. note that the modulus of elasticity characterizes not only the elastic characteristics of materials, but also their brittleness. from another point of view, high values of the modulus of elasticity indirectly indicate increased values of residual stresses in materials and a significant stress state in their structure. it can be a cause of premature failure of composites, especially under the action of shock loads. taking into account the modulus of elasticity, it can be argued that the effective materials are composites filled with sicm particles in amounts of q=0.2–0.5 wt.%. fig. 2. dependence of physical and mechanical properties of epoxy cm at the sicm content: 1 – elasticity modulus at bending (е); 2 – flexural stresses at bending (σfl) according to the studied results of the dynamics of the values of flexural stresses at bending from the filler amount, the following can be stated: it was established (figure 2, curve 2) that the value of the flexural stresses of the epoxy matrix modified by usp was σfl=48.0mpa. it was proved that the introduction of sicm particles at low content (q=0.2–0.5 wt.%) leads to a monotonic increase in the value of flexural stresses from 48.0mpa (for the original matrix) to 67.2–84.9mpa. the maximum in the “flexural stresses at bending–filler content” curve was observed at 0.5 wt.% sicm content. the magnitude of the flexural stresses for such a material was σfl=84.9mpa. further increase in the content of particles leads to a deterioration of the cohesive properties of composites. it has been shown (figure 2, curve 2) that the loading of particles at a content of q=0.7–2.0 wt.% into the cm leads to a decrease in the flexural stresses from σfl=84.9mpa (for materials with a content of sicm 0.5 wt.%) to σfl=55.0–71.1mpa. the magnitude of the flexural stresses at bending indirectly indicates the plastic properties of the materials. as shown above, the modulus of elasticity, which characterizes the materials brittleness, for composites at a 0.5 wt.%. particle content is almost no different from the similar characteristic for the epoxy matrix. at the same time, the values of flexural stresses at bending of such cm are almost 2 times higher than the similar values of the matrix. based on this, the effectiveness of the additives introduction at such content to improve the elastic-plastic properties of composites for different functional purposes can be argued. it should be noted that one of the problems of modern materials science is the creation of materials and protective coatings based on them, which can be operated under the influence of static and shock loads. therefore, it was considered necessary to investigate the impact strength of materials with different filler content. it was experimentally found (figure 3) that the impact strength of the epoxy matrix modified by ups was w=7.4kj/m 2 . extreme dependence in the “w–q” values was observed when the sicm particles were loaded into the binder. maximum values among the whole spectrum of the studied materials were observed for cm with a 0.5 wt.% content of particles. the formation of such cm provides an increase in impact strength from 7.4kj/m 2 to 13.0kj/m 2 . further increase in the particles content leads to a decrease in the impact strength of epoxy composites. in order to analyze the mechanism of destruction of materials under the influence of shock loads in detail, their fracture structure was additionally investigated by optical microscopy. it should be noted that the fracture surface of the specimens was analyzed with pre-selected content of dispersed particles in cm: q=0.2 wt.%, q=0.5wt.%, and q=1.0 wt.%. fig. 3. the dependence of the impact strength (w) on the sicm content (q) in cm: (a) matrix (control specimen), (b) 0.2 wt.%, (c) 0.5 wt.%, (d) 1.0 wt.%, (e) 1.5 wt.% it is shown (figure 4(a)) that the destruction of specimens filled with sicm particles at a content of 0.2 wt.%, occurs in an almost straight line. this is evidence that the material does not sufficiently resist external loads, and the crack propagation front is rectilinear. on the fracture surface of such samples, a grid of chipping lines is visible (figure 4(b)-(c)), depressions and craters are observed, which is evidence of a sufficiently engineering, technology & applied science research vol. 10, no. 5, 2020, 6214-6219 6218 www.etasr.com buketov et al.: investigation of the influence of the synthesized iron-carbide mixture on the adhesive … tense state in such systems. it can be argued about the low reliability in the operation of such materials. (a) ×2 (b) ×4 (c) ×4 d) ×2 (e) ×4 (f) ×4 (g) ×2 (h) ×4 (i) ×4 fig. 4. fractograms of cm fracture at different content of microdisperse filler sicm q per 100 wt.% of epoxy oligomer ed-20: (a)-(c) 0.2, (d)-(f) 0.5, (g)-(i) 1.0. on the contrary, for 0.5 wt.% content of particles the curvilinear nature of the fracture surface was observed (figure 4(d)). this allows to state about the increased cohesion characteristics of composites with filler at such content. the presence of particles in such cms increases the resistance to the propagation of cracks during impact, as a result of which the trajectory of destruction of the specimens is wavy. additional analysis of the images shown in figure 4(d)-(e) allows to state the existence of a stress state in such systems, but the nature of the fracture is viscous, with noticeable petalshaped inclusions. this suggests the existence of areas with improved cohesive strength, which increases the durability of such materials during operation in critical conditions under the influence of shock loads. analysis of the fracture surface of the specimens of the cm at 1.0 wt.% particle content allows assert about the rectilinear character of crack propagation during the destruction of materials (figure 4(g)). at the same time, it should be noted that the fracture surface of such specimens is characterized by a tightly packed structure (figure 4(h)-(i)), which indicates the improved cohesive properties of such materials. the use of such composites in the operation of equipment under the influence of shock loads can be argued. iv. conclusion the optimal content of microdispersed filler of iron-carbide mixture synthesized by high-voltage electric discharge (d=15–18µm) for the formation of epoxy protective coating with improved adhesive and cohesive properties and insignificant residual stresses to increase the service life of transport parts was established. it has been found that when introducing particles of iron-carbide mixture in the amount of 0.5 wt.% by 100 wt.% of ed-20 epoxy oligomer, a material was formed with adhesive strength at break σa=44.7mpa and residual stress σr=0.7mpa. this provides an increase, compared to the epoxy matrix modified by ultrasonic processing of the adhesion strength at break by 1.8 times and a decrease in residual stresses by 2.0 times. it is proven that the active centers of fe, tic and fe3c, which are contained both in the volume and on the surface of the dispersed phase during the polymerization process, interact with the segments and pendent groups (oh-, ch-, c=o) of the epoxy oligomer. this increases the degree of crosslinking of the three-dimensional polymer net, which improves the adhesive properties of the composites. this is due to the fact that on the surface of the particles after synthesis areas of titanium and iron carbides, which are mainly activators of the formation of physical and chemical interfacial bonds in the structure of materials are localized. it has been established that the introduction of powder mixture particles in the amount of q=0.5 wt.% by 100 wt.% of epoxy oligomer ed-20 provides the formation of a material with the following properties: modulus of elasticity at bending e=2.7gpa, flexural stress at bending σfl=84.9mpa, and impact strength w=13.0kj/m 2 . the formation of such a material provides a 1.8-times increase in the flexural stresses at bending and impact strength compared to the epoxy matrix modified by usp, while the modulus of elasticity was closely unchanged. for composites at a particle content in the amount of q=0.5 wt.% the curvilinear nature of the fracture surface was observed. this allows to state about the increased cohesion characteristics of materials at such filler content. the presence of particles in such a composite increases the resistance to the crack propagation during impact, as a result of which the trajectory of destruction of the specimen is wavy. this allows to assert the existence of areas with improved cohesive strength, which increases the durability of such materials during operation in critical conditions of impact loads. references [1] y. zhan, j. zhang, x. wan, z. long, s. he, and y. he, “epoxy composites coating with fe3o4 decorated graphene oxide: modified bio-inspired surface chemistry, synergistic effect and improved anticorrosion performance,” applied surface science, vol. 436, pp. 756–767, apr. 2018, doi: 10.1016/j.apsusc.2017.12.095. 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[12] a. v. buketov, p. d. stukhlyak, i. g. dobrotvor, n. m. mytnyk, and n. a. dolgov, “effect of the nature of fillers and ultraviolet irradiation on the mechanical properties of epoxy composite coatings,” strength of materials, vol. 41, no. 4, pp. 431–435, jul. 2009, doi: 10.1007/s11223009-9136-1. microsoft word etasr_v11_n1_pp6662-6667 engineering, technology & applied science research vol. 11, no. 1, 2021, 6662-6667 6662 www.etasr.com gebretsadik et al.: application of ultrasonic measurement for the evaluation of steel fiber reinforced … application of ultrasonic measurements for the evaluation of steel fiber reinforced concrete belayhun gebretsadik clark county building and fire prevention las vegas, usa belayhun.gebretsadik@clarkcountynv.gov visar farhangi department of civil and environmental engineering and construction, university of nevada, las vegas, usa farhangi@unlv.nevada.edu kazem jadidi department of civil and environmental engineering and construction, university of nevada, las vegas, usa kazem.jadidi@unlv.edu moses karakouzian department of civil and environmental engineering and construction, university of nevada, las vegas, usa mkar@unlv.nevada.edu abstract-this study investigates the feasibility of the application of ultrasonic measurement to characterize steel-fiber-reinforced concrete (sfrc). specifically, the effects of steel fiber content, age, moisture content, and fiber orientation on ultrasonic-pulsevelocity (upv) were investigated. in this regard, beam and cylindrical samples were fabricated with different steel fiber contents. the result indicated that for beam specimens the upv increases with the addition of fiber up to 2% and decreases for higher fiber percentages. additionally, the fiber orientation within the beam specimens influences the upv measurements. for cylindrical samples, the rate of upv decreased with the addition of steel fiber reinforcement. in addition, it was discovered that the curing period affects the magnitude of upv. keywords-ndt; ultrasound; concrete; steel fiber; curing; pulse velocity; orientation i. introduction concrete is used extensively in most construction projects because its constituent materials are locally available. it has high compressive strength, and it the lowest cost-to-strength ratio compared to other available materials [1-5]. some of the characteristics of plain concrete are its low tensile strength and its low tensile strain capacities. concrete is a brittle material [610]. therefore, improving the ductility of concrete is very important, especially due to the fact that concrete structures may experience extreme loadings during their lifetime [11-14]. to address such a deficiency, a continuous reinforcing bar has been applied to resist the tensile force imposed on the structure [15-18]. unlike continuous reinforcing bars, fibers are short, discontinuous, and randomly distributed throughout the concrete to produce a more ductile and crack control matrix. fibers used in concrete [18-21] can be made of steel, glass, and polymer. authors in [22-23] investigated the mechanical behavior of polymers by infusing machine learning algorithms and asserted the advantages of using polymers on concrete’s characteristics which is applicable to real-world problems [12, 18]. the random and closely spaced distribution of steel fibers enabled them to control the development of cracks better than continuous bars. it is important to recognize that, in general, fiber reinforcement is not a substitute for conventional reinforcement [24]. the addition of steel fibers in concrete can improve its toughness [14, 25-38], ductility, and post-crack resistance [29]. self-compacted concrete (scc) [30] is the concrete which is allowed to compact with its own weight without applying any vibrational effort. the reason for selecting scc is to avoid steel fiber and aggregate segregation and bleeding. the use of scc has been gradually increasing [31]. basically, steel fiber reinforced scc is produced by introducing superplasticizers to improve the workability of the mix while reducing the waterbinder ratio. other supplementary cementitious materials are fly ash (fa) and silica fume [32-35]. silica fume also plays an important role in the chemical reaction (hydration) process to improve strength [36]. ultrasonic pulse velocity (upv) is one of the most dominant nondestructive test (ndt) methods of concrete characterization [37]. the most common application of ultrasonic surveying to evaluate materials is the monitoring of the wave travel time, both in direct and indirect transmission [38]. the basic idea the pulse velocity established is that the velocity of the pulse of compressional waves through a medium depends on the elastic properties and density of the medium [39]. even though the application of ultrasonic pulse velocity for construction materials characterization was initiated three decades ago, its response through steel fiber reinforced scc has not been identified yet. the main objective of this study is to investigate the response of ultrasonic pulse velocity through steel fiber reinforced scc with respect to the volume fraction of steel fibers, curing periods (7, 28, and 90 days), steel fiber and aggregate orientations, and wet/dry conditions. ii. methodology the direct-contact through transmission upv test method was employed in this experiment. based on astm c597-09 "standard test method for pulse velocity through concrete," this method is based on wave generated by an electrocorresponding author: visar farhangi engineering, technology & applied science research vol. 11, no. 1, 2021, 6662-6667 6663 www.etasr.com gebretsadik et al.: application of ultrasonic measurement for the evaluation of steel fiber reinforced … mechanical transducer placed on the surface of the test specimen. this experiment follows the through-transmission method. unlike the pulse-echo method, which relies on the reflected waves, the through-transmission method uses a separate transducer as a receiver. this test method can be applied to assess the uniformity and relative quality of concrete [40] in order to indicate the presence of voids and cracks. it also can be used to estimate the progress of cracks [41] and other deterioration kinds in the long run, by doing repeated tests on the same spot. ultrasound measurements could be used for failure monitoring in reinforced concrete [42]. the test begins when an ultrasonic pulse is generated and transmitted for an electro-acoustic transducer, placed in contact with the surface of the concrete. after passing through the concrete, the vibrations are received and converted by the electro-acoustic transducer placed on the opposite face. the travel time (µs) and energy loss (db) are displayed on the digital screen. a coupling agent, such as gel, should be applied between the transducers face and specimen’s surface to ensure that there is no air pocket between them. it is also equally important to align the two transducers so that the measured distance and the actual path length for the wave have a perfect match. iii. experimental procedure and materials in this study, the main variables are steel fiber content, sample saturation, curing periods, fiber orientation, and porosity. the effects of fiber content, ranging from 0-4% (by volume), on ultrasonic pulse velocity were investigated. in addition, the variation of upv through the saturated and air dried samples was also assessed. the curing periods were 7, 28, and 90 days. the steel fiber orientation effects were also studied. astm a 820-90 type ii deformed cut sheet carbon steel fibers were used, having an equivalent diameter of 0.584mm and a length of 19.05mm. the specific gravity of carbon steel fiber was 7.85g/cm 3 , which is much higher than any of the constituent materials. the steel fibers had rectangular cross-sections with dimensions of 0.406×0.838×19.05mm. the tensile strength of the steel fibers ranged between 379 to 763mpa. these fibers were selected in order to get a strong bondage between the concrete matrix and steel fibers which in turn would improve the ductility of concrete. coarse and fine aggregates were obtained from a local quarry in las vegas, nevada area. since the intended objective of this concrete mix design was ultimately to be used for thin plates and shells (about 25.4mm thick), the size of the coarse aggregates was limited to nominal sizes of 9.53mm and a #4 sieve. the type of aggregate used was crushed limestone. to meet the required gradation, pure natural sand fine aggregates were added to the mix. astm c 150 type v ordinary portland cement (opc), 404kg/m 3 , was used to prepare the test specimens. type v opc has a high sulfate resistance and lower setting time than type i opc. table i presents the sieve analysis of the fine aggregates used in this study. the fineness modulus of the fine aggregates was 3.04. both the gradation and the fineness modulus meet the astm c33 standards. the oven-dry specific gravity and absorption percentages of the fine aggregates following the astm c 12807-a were 2.78 and 0.65 respectively. table i. fine aggregate sieve analysis sieve number passing percentage fine aggregates min(%) max(%) 4 100 95 100 8 90 80 100 16 55 50 85 30 30 25 60 50 15 5 30 100 6 0 10 class f fa, 171kg/m 3 was used in this experiment. for this type of fa, the blaine fineness and specific gravities are 5.23×103cm 2 /g and 2100kg/m 3 respectively. fa is an important admixture to improve the workability and reduce the demand of cement or fine fillers in steel fiber reinforced scc (sfr-scc). it has a great role in creating a sufficient amount of cement paste in sfr-scc and improves the mechanical properties by filling the micro-pores in it [43]. silica fume consists of small-sized particles approximately 100 to 150 times smaller than portland cement particles, and has a high surface area and high amount of silicon dioxide. silica fume with unit weight of 30.4kg/m 3 was used in this experiment. this silica fume was selected for its chemical and physical benefits. superplasticizers, also known as high range water reducers (hrwr), play an important role to improve concrete workability and strength in sfr-scc with fa and silica fume [44]. adva 140 hrwr was selected for this experiment as superplasticizer. a constant amount of 6.3kg/m 3 hrwr was added to the cylindrical samples of the variable fiber content. the hrwr content varies with steel fiber content for the beam samples. a. mix proportions the mix proportion was designed so as to improve the common drawback (i.e. brittleness) of concrete and other mechanical properties. it consists of coarse aggregates, fine aggregates (sand), cement, fa, silica fume, water, superplasticizer, and deformed steel fibers as shown in tables i and ii. except for the volume percentage (vf) of steel fibers and superplasticizers, all the other constituent materials were kept constant for the beam samples. the amounts of superplasticizers were selected to provide the best workable concrete matrix for the respective percentages of steel fibers by trials and errors. the cylindrical samples, on the other hand, have all the constituent materials constant except the percentage volume steel fibers. however, unlike the beam samples, the amount of superplasticizer was kept constant for the cylindrical samples at 6.3kg/m 3 which was best for 0% fiber concrete workability, and adapted for the rest just for the sake of minimizing the number of variables and to realize the sole effect of steel fiber volumes in sfrc. slump spread (astm c 1611), j-ring flow (astm c 1621), v-funnel and u-box (astm c09.47) tests were conducted on nonreinforced fresh concrete. the results showed an average slump spread diameter of 759mm, flow diameter of 768.4mm with regard to j-ring test, and 8s flow time based on v-funnel test and 1.52mm for u-box test respectively. b. specimen preparation a total of 18 beam and 5 cylindrical samples were prepared for this experiment. the main experimental program is based engineering, technology & applied science research vol. 11, no. 1, 2021, 6662-6667 6664 www.etasr.com gebretsadik et al.: application of ultrasonic measurement for the evaluation of steel fiber reinforced … on the beam samples since relatively representative samples were already available. however, since the beam samples were aged (more than a year), it was not possible to see the curing period effect. therefore, cylindrical samples were prepared to investigate the curing period effect on upv. various studies suggest different fiber contents ranging from 1.5% to 6% [45], in order to reinforce the concrete specimens. in this study, the 18 beam samples were categorized in 5 groups: four of them had 4 members with steel fibers volumes of 0%, 1%, 2%, and 3%, respectively, and the fifth had 2 members with 4% fiber volume. similarly, the cylindrical samples had 3 groups: 1 (0%), 2 (1%), and 3 (2%) of steel fibers percentage respectively. the dimensions of all beam and cylindrical samples were 10cm×10cm×35cm and 10cm ϕ×20cm respectively. except for the amount of superplasticizers at 1% and 2% fibers, all the constituent materials were the same for all the cylindrical and beam samples. dry mixing of coarse aggregates, fine aggregates, cement, fa, silica fume, and steel fibers were performed for about 1-2min with a mechanical mixer. then, about 80% of the water was added and mixed thoroughly for the specified time. finally, the remaining portion of water and hrwr were added at the end before discharging the mix. the concrete matrix was poured into the mold and allowed to set without any vibration effort (i.e. scc). the samples were prepared based on astm c 192. figure 1 presents the prepared beam and cylindrical samples. fig. 1. prepared beam and cylindrical samples. c. test procedure once the instrument was set up, the next critical step was testing. this was critical because most errors occur in this part of the experiment. before starting the experiment, the test specimen was placed on a level and stable surface. a digital caliper was used to measure the length of specimen along the direction of the wave. a gel was applied on both faces of the specimen where the transducers were to be placed so that the two faces of the transducers and test specimen had full contact. there should not be any uneven surface and/or air pockets between the transducers and specimen contact faces. also, the two transducers needed to be aligned so that the measured dimensions and assumed wave travel path were the same. the same amount of pressure was applied on the two transducers to avoid the instability of amplitude of the wave, as shown in figure 2. moreover, 28-day compressive and flexural strength tests were performed on cylindrical specimens. the results are presented in tables iv and v. fig. 2. upv testing. table ii. mix proportions for beam samples mix category (percent fiber, by volume) mix component 0% 1% 2% 3% 4% 3/8'' coarse aggregate 22.8 22.8 22.8 22.8 22.8 #4 (4.75mm) coarse agg. 22.4 22.4 22.4 22.4 22.4 fine aggregates (sand) 57.6 57.6 57.6 57.6 57.6 water 10.22 10.22 10.22 10.22 10.22 cement type v 25 25 25 25 25 silica fume 1.9 1.9 1.9 1.9 1.9 fa (class f) 10.7 10.7 10.7 10.7 10.7 water/cement 0.41 0.41 0.41 0.41 0.41 hrwr (superplasticizer) 0.392 0.372 0.416 0.432 0.472 steel fibers by volume 0 1 2 3 4 steel fibers by weight 0 1.25 2.5 3.75 5 table iii. mix proportions for cylindrical samples mix category (percent fiber, by volume) mix component 0% 1% 2% 3/8'' coarse aggregate 22.8 22.8 22.8 #4 (4.75mm) coarse agg. 22.4 22.4 22.4 fine aggregate (sand) 57.6 57.6 57.6 water 10.22 10.22 10.22 cement type v 25 25 25 silica fume 1.9 1.9 1.9 fa (class f) 10.7 10.7 10.7 water/cement 0.41 0.41 0.41 hrwr (superplasticizer) 0.392 0.392 0.392 steel fibers by volume 0 1 2 steel fibers by weight 0 1.25 2.5 table iv. compressive test results fiber content (%) 0 1 2 3 4 compressive strength (mpa) 67.98 75.31 80.72 85.80 73.18 table v. flexural strength results fiber content (%) 0 1 2 3 4 load capacity (n) 30154 32529 35475 38662 37036 iv. results and discussion the objective of this study was to investigate the responses of upv within steel fibers reinforced scc. interpreting the engineering, technology & applied science research vol. 11, no. 1, 2021, 6662-6667 6665 www.etasr.com gebretsadik et al.: application of ultrasonic measurement for the evaluation of steel fiber reinforced … results and drawing conclusions are more difficult and challenging tasks than in any conventional destructive test methods. understanding the behaviors of ultrasonic wave velocity and its response to various factors within and around the test specimens are very important. the results are presented in the following paragraphs. a. cylindrical specimen results for cylindrical specimens, the upv measurement results are shown in figure 3. generally, adding certain amounts of steel fibers increases the upv of the mix due to its high specific gravity. hence, it was expected that the 0% fiber sample would have lower upv rate in comparison to specimens with higher fiber percentages. however, for cylindrical samples the opposite was observed. we are not sure why this happened. therefore, the highest upv was observed for the samples with 0% fiber in comparison to samples with 1% and 2% fibers respectively. moreover, the curing period had significant influence on the value of the upv test result, specifically for unreinforced samples. the pulse velocity increased rapidly at an early period for the specimen with 0% steel fibers, while for fiber reinforced samples, the amount of upv for 7 days and 28 days cured samples is not remarkable, due to the fact that for unreinforced specimens the main portion of the hydration process and gap filling were carried out within the early period of 28 days. on the other hand, the concrete got its maximum strength and density, during this period. while the presence of 1% and 2% steel fiber, delayed/retarded the gap filling or consolidation time of concrete, hence, the upv increased gradually and over a longer period of time. this is a good indication of the upv can be used to estimate the setting time of concrete. for both reinforced and unreinforced samples, the highest upv was observed after 90 days of curing. fig. 3. effect of the volume of steel fibers (vf) % on upv for cylindrical samples. b. beam specimen results for beam specimens, upv measurement was performed along three perpendicular sides of the specimen as shown in figure 4. the results are shown in figure 5. the presence of short, deformed, and randomly distributed steel fibers affected the upv measurement both positively and negatively. for all beam sections, the addition of up to 2% steel fibers to a plain concrete increased the average pulse velocity. however, further addition of fibers did not improve either the upv or other concrete properties. the reason could be that since the test samples were self-consolidated samples, the addition of more fibers initiated the formation of voids thus reducing the workability of the matrix. this, in-turn, decreased the speed of wave propagation through the sample and resulted in a lower upv value. though a properly match hrwr superplasticizer was added to the mix to improve its workability, the problem could not be solved and was even pronounced for higher fiber volume (4%). on the other hand, the lowest upv was observed to 6% steel fiber specimens. therefore, for a steel-fiberreinforced, self-compacted concrete, 2% by volume of steel fiber may be the recommended optimum amount to be added to improve the properties of concrete structures with a corresponding superplasticizer. fig. 4. fiber orientations of a beam sample. fig. 5. effects of fiber and aggregate orientation on upv for beam specimens. a remarkable difference was observed for upv measurements taken from different planes of the beam specimens. although all samples were self-consolidated, there seems to be a tendency for the aggregates and fibers to orient along the horizontal length and width of the specimen. the approximate count per square inch concentrations of fiber orientation can be estimated as 11.6fibers/in 2 , 32fibers/in 2 , and 50fibers/in 2 on the top plane, side plane, and front plane, respectively which corresponds to the upv measurements. accordingly, fiber orientation needs to be considered in evaluating the effect of the fibers on the strength of the fiber reinforced concrete. the orientation of steel fibers aligned with the horizontal plane is recommended for achieving the maximum concrete tensile strength, which would be comparable to the strength provided by vibrated frc. for similar samples, the upv was higher along the direction where the more fibers were oriented. the differences between the engineering, technology & applied science research vol. 11, no. 1, 2021, 6662-6667 6666 www.etasr.com gebretsadik et al.: application of ultrasonic measurement for the evaluation of steel fiber reinforced … upv readings along the length and the depth were cumulative effects of both fibers and aggregate orientation, since they had different pivots at 0% fiber and the difference increased with the fibers’ volume. therefore, the fibers and aggregate orientation made a significant difference on the upv value, which is increasing the upv in the direction of fiber and aggregate orientation. the comparison in table v and figure 5 indicates an identical trend between beam load capacity and ultrasound test results although there are some differences. the beam load capacity increases with the increase in fiber content and then declines. the highest load capacity was observed for 3% fiber content while the ultrasound survey indicates the highest upv for specimens reinforced with 2% fiber. the authors did not observe any trend between compressive strength and upv results for the cylindrical specimens. v. conclusions an ultrasonic survey was carried out on cylindrical and beam samples reinforced with various content percentages of steel fibers. the upv was measured and analyzed. the results show as that: • the optimum steel fiber content for beam sections is indicated to be 2%. • with the addition of fiber reinforcement from 0% up to 2%, the amount of upv increases for beam samples and then it decreases as fiber percentage increases from 2% to 6%. • the fiber orientation needs to be considered in evaluating the effect of the fibers on the strength of the fiber reinforced concrete. • the magnitude of upv decreases for cylindrical samples with the addition of steel fibers. • the curing period has inevitable influence on wave speed. for cylindrical samples the highest upv is observed after 90 days of curing. acknowledgement the authors appreciate the contribution of professor saman ladkany and dr. abebe tadesse berhe regarding the samples' data. 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[45] x. shi, p. park, y. rew, k. huang, and c. sim, "constitutive behaviors of steel fiber reinforced concrete under uniaxial compression and tension," construction and building materials, vol. 233, feb. 2020, art. no. 117316, https://doi.org/10.1016/j.conbuildmat.2019.117316. microsoft word etasr_v11_n4_pp7358-7362 engineering, technology & applied science research vol. 11, no. 4, 2021, 7358-7362 7358 www.etasr.com xefteris: developing steam educational scenarios in pedagogical studies using robotics developing steam educational scenarios in pedagogical studies using robotics an undergraduate course for elementary school teachers stefanos xefteris elementary education department university of western macedonia florina, greece sxefteris@uowm.gr abstract-in recent years we have observed a clear trend for the transformation and evolution of teaching practices using information and communication technologies (ict) and in particular educational robotics. as modern society gives great importance to scientific and technological literacy and new technologies, the educational process must play a central role in the development of the respective skills. thus, the training of future teachers in corresponding fields is especially important. in this paper, we present the curriculum design of a course named "s.t.e.a.m teaching scenarios using educational robotics" implemented for undergraduate pre-service teachers at the elementary education department of the university of western macedonia in florina, greece. the objectives of the course include the development of critical and computational thinking, familiarity with robots, and the process of their integration in curricula focusing on interdisciplinary practices facilitated by embodied learning affordances. keywords-educational robotics; steam education i. introduction steam is an approach to learning that uses concepts from natural sciences, technology, engineering, arts, and mathematics like springboards for the development of skills of active inquiry, cooperation, communication, creativity, and critical thinking. the desired result is students who are involved in experiential learning, are able to develop problemsolving skills facilitating scenarios, work together and explore learning environments within the context a creative process [1]. the "a" in acronym steam, introduces the dimension of creation and ingenuity, under one prism and aesthetics but also moral. in this publication we present a curriculum targeted to pre-service elementary school teachers, exploiting the symbiotic relationship between natural sciences, technology, engineering, art and, mathematics integrated in various educational robotics based teaching scenarios. students learn how to combine and implement innovative scenarios within an interdisciplinary framework based on inquiry based learning, project-based learning, and developing computational thinking in parallel with design based thinking [2, 4]. the ultimate goal of deploying these steam based sequences is for elementary school students to be familiar with elements of engineering (simple and complex machines), to algorithmic thinking (programming), to building robots [5], design and implement experimental devices, and incorporate elements from the arts and humanities indirectly (design, aesthetics, creativity, imagination, innovation, ethical extensions, creative script writing, etc.) or directly (e.g. a robot that paints, a robot that dances, etc.). the course is based on collaborative work, within immersive embodied environments that encourage more than just basic science skills (critical thinking, computational thinking, logic and application of science methodology) but also skills directly related to the arts and humanities such as creativity, imagination ,and reflection on ethical implications [6-8]. the course, in addition to educational robotics, integrates multiple ict tools that support and enrich teaching scenarios, such as scratch games, makey-makey and augmented reality applications [9, 10], an embodied learning teaching framework [11, 12], and utilizing robots as tools for simulation [13]. ii. course goals and description the philosophy of the course employs two distinct approaches in the teaching of educational robotics in an elementary school classroom: the first approach uses the robot as a means to teach computational thinking, algorithms, and design in and of themselves, i.e. robotics here is the goal. the second, and more interesting, pedagogical approach utilizes the robot as a "digital agent", an actor inside a wider scenario that is used as a tool that facilitates learning of various learning goals (such as fractions, or materials science, or even chess). the course focuses on creative thinking and communication/collaboration alongside design thinking and pedagogical efficacy. the curriculum didactic sequences utilize the lego mindstorms ev3 set and scratch 3.0. the course material is divided into 2 phases. in the first phase the students, who have already attended an introductory course in educational robotics and have a strong grasp of ev3 programming, get acquainted with advanced ev3 programming techniques (variables/constants, data logging, variable operations, advanced precision handling with sensors). in this phase we introduce the concepts of design-based thinking and its connection to the arts and creativity alongside the improvement of computational thinking skills and higher corresponding author: stefanos xefteris engineering, technology & applied science research vol. 11, no. 4, 2021, 7358-7362 7359 www.etasr.com xefteris: developing steam educational scenarios in pedagogical studies using robotics mental skills. in the theoretical part, on one hand we focus on scaffolding techniques and on the description and evaluation of teaching models such as samr, and at the same time get acquainted with digital storytelling techniques. moreover, we give guidelines for the use of multiple ict tools used to enhance the base teaching scenarios with multimedia or interactive capabilities (such as web 2.0 comics tools, ebooks, google forms for questionnaire creation, etc.). the main purpose in this phase is to begin combining computational thinking and science skills with creativity and imagination, which are grand aspects of arts and humanities. pre-service elementary school teachers are introduced to the concept of scientific method and learn to develop teaching scenarios, using educational robotics and embodied affordances, divided in 3 stages that encapsulate the essence of the scientific method: explore, create and test, share results and reflect. each scenario begins with an active brainstorming session where the students are prompted to explore and inquire about the subject empathizing with all its aspects and give initial input regarding the creation phase, then begin constructing and testing the robot itself, employing an iterative process of trial and error in design where they actively see what is working or not and making the necessary adjustments. then the robot is put to work inside the scenario parameters, which induces another, final, evaluation phase. in the end, the participants share the results with the lab groups and reflect on similarities and differences. in this phase we learn that the robot can be transformed from a "simple" tool to teach programming and computational thinking to a ubiquitous interface that acts as a medium between the digital and physical world, facilitating embodied learning and transforming into a multitude of aspects: in an astronomy scenario as a simulator of the earth’s movements, in a music and cryptography scenario as a decoder of colors into notes, in a fractions scenario (and football) as the tool that verifies the students’ mental calculations. in this first phase that lasts 6 weeks, the students get acquainted with the overall methodology in guided short projects (1 lab session of 3 hours each). during this phase, students apart from the live sessions, are assigned two homework projects where they are called to create lesson plans and worksheets for a multidisciplinary application of a steam scenario in a "real classroom". the lesson plans and worksheets are based on the "explore-create-share" workflow. during the covid pandemic, where lab access was not possible and distance learning was employed, the students were also familiarized with online robotics teaching tools such as microsoft makecode. in the second phase which lasts 7 weeks, the students are familiarized with tools and applications that enable them to create bigger, more immersive and demanding teaching sequences. we introduce students to mixed reality applications and a framework that utilizes scratch and makeymakey to create augmented spaces on which our robots participate in "missions" visualised by scratch 3, as seen in figure 1. in this phase we focus on digital storytelling via scratch scenarios in order to produce gamified contexts on which our robots enact their missions. this phase is designed to facilitate creative thinking and storytelling skills to the preservice teachers, while at the same time enables them to conceptualize and create multidisciplinary teaching environments that make use of multiple technological affordances and create novel learning spaces that will motivate their future school students and keep their interest high. in this phase, pre-service teachers are given a multitude of choices among teaching subjects and focus on translating traditional teaching goals (for example crete’s mythology or fractions) into scenarios that make use of a "game-like" interactive canvas with robots as the story’s main hero as seen in figure 2. fig. 1. sketch depicting the "augmented space" concept. a vertically placed projector augments a canvas with a scratch game. black targets mark the positions of makey-makey interface contacts. fig. 2. a scenario combining robotics and english language teaching with ev3 and a drone, over an augmented space depicting a city. fig. 3. synergies between ict tools and mindstorms in the creation of a steam teaching intervention. engineering, technology & applied science research vol. 11, no. 4, 2021, 7358-7362 7360 www.etasr.com xefteris: developing steam educational scenarios in pedagogical studies using robotics at the end of the second phase the students are assigned their final assignments and produce a project-based scenario that incorporates all aspects of what they have learned during the semester. in these final projects we facilitate the creation of complex teaching interventions that make use of multiple ict affordances as seen in figure 3. iii. curriculum breakdown the proposed curriculum is broken down in the following 13 weekly 3-hour lab sessions. in the following description we present some basic project ideas that follow the proposed framework precepts. it should be noted that in every iteration of the curriculum, assignments can change and weekly projects can vary depending on the specific needs of the students attending the course: • week 1: introduction to steam and advanced ev3 programming. using the model riley rover we cover variable operations, data logging, advanced sensors and precision. • weeks 2 and 3: the "a" in steam design based thinking, introduction to digital storytelling. the s.a.m.r model. bloom and solo taxonomies. web 2.0 digital creation tools. • week 4: 1 st guided project – ev3 spirograph: a scenario that involves geometry, art, the concept of symmetry as well as engineering aspects and precision handling of the gyroscopic sensor. • week 5: 2 nd guided project – historical weaponry, the catapult: an interdisciplinary scenario involving mathematics and physics (projectile motion), history (sieges using trebuchets) and engineering (creation of improved catapults and trebuchets, as shown in figure 4. begin incorporating the robotics element in wider scenarios, i.e. which siege to emulate, what props to use, what would be an appropriate diorama for the application of the scenario. fig. 4. building a trebuchet for a medieval siege in the lab. • week 6: 3 rd guided project – astronomy: look for precious metals in alien planets using a specially designed robot (advanced sensors, color separation, data logging). second possible scenario: materials science, measuring the insulation properties of various types of liquid containers (depending on the availability of ev3 temperature sensors in the laboratory), graphing the rate of temperature gain after a cold liquid is placed in a specific container. • weeks 7-8: scratch and makey-makey. mixed reality applications with augmented spaces and robots – assignment of final projects for week 13. here we produce scratch scenarios specifically designed to function as "placeholders" for our applications further on the road. the main goal here is that students are able to create treasure hunt-like games where in each stage, the story goes forward if the correct button is pressed. in figure 5, we can see such a placeholder scratch scenario with the traced trajectories and the "base stations" to be incorporated in the final scenario. the story here is another treasure hunt where the hero travels through his kingdom to find his kidnapped father. fig. 5. a scratch environment where we have traced the possible routes the robot should take. each destination marks the end of a mission and involves a makey-makey interface base. • weeks 9-10: mixed reality with scratch and makey-makey – 1 st unguided project. the first steam unguided mixed reality project here combines the mythical robot talos that guarded crete and the creations of artist jackson pollock. students design and build a robot guardian that patrols around crete and is ready to shoot at invaders. in the second phase of the scenario the robot transforms to a jackson pollock imitator and instead of shooting projectiles, shoots (or drips) paint on a canvas, creating abstract expressionist art. makey-makey here is used as an interface between the augmented space and the scratch game with buttons implemented as bases where the robot can touch and interact with the scratch scenario or as a touch interface for answering prompts by the environment as seen in figure 6. engineering, technology & applied science research vol. 11, no. 4, 2021, 7358-7362 7361 www.etasr.com xefteris: developing steam educational scenarios in pedagogical studies using robotics fig. 6. a makey-makey built interface used for creating instructions for the robot. • week 11: 2nd unguided project: cryptography and music. here the scenario is focused on the history of cryptography and messages and students are prompted to create a scenario where we encrypt the 7 basic notes of an octave with the 7 basic colors that ev3 can recognize, and then move on an color-coded pathway that is an encrypted song of their choosing, with the ev3 playing (decrypting) the melody. alternately, a treasure hunt scenario looking for "musical colors" can be deployed. in this case the robot as an ardent music fan, hunts for notes hidden in colors in various areas and learns about important musicians on the way, as seen in figure 7. fig. 7. the "musical treasure hunt" where the robot touches bases around greece, gathers color coded notes and at the end reveals a musical piece, played by arranging the colors in a line. • week 12: 3d unguided project: robot football and fractions. here we work on an augmented space depicting a football field. the teaching goal is fractions and their properties and students must make use of the diameter of the basic ev3 wheel (18cm) and combine it with the dimensions of the field in order to program their robotic footballers to score a goal as seen in figure 8, making mental calculations of fractions and programming the robot to move precisely. fig. 8. the template for the fractions learning scenario using football. the measurements are chosen for ease of application, not to be confused with actual analogies. • week 13: create teaching spaces and robot models for the final assignments, to be presented in the semester finals. in figure 9 we can see the result of a particularly successful intervention for teaching the day/night cycle, using a robotic model of the earth on an augmented canvas floor. in figure 10 we see an example from greek mythology, where the scenario involves finding out about minoan art and navigating through a maze. fig. 9. the robot depicting the earth as it moves arount its trajectory. fig. 10. minotaur’s maze and theseus on his robotic steed, learning about minoan art. iv. discussion and future goals the act of integrating educational robotics and other ict affordances to teaching interventions is not always straightforward or successful. the danger of using technology engineering, technology & applied science research vol. 11, no. 4, 2021, 7358-7362 7362 www.etasr.com xefteris: developing steam educational scenarios in pedagogical studies using robotics ineffectively and end at distracting the students instead of achieving the learning goals is always present. when we integrate technology we must always be aware of our teaching goals and use it to achieve them point by point instead of just mixing and matching various ict tools in an effort to motivate or engage students. in their present highly technological routine, students can be truly difficult to engage, but on the other hand if the content itself, the teaching scenario is weak, then no matter how exciting or impressive technology we employ, we will fail. as more affordances are made available, the present course aims at improving its evaluation capabilities with the inclusion of affective measures such as the inclusion of cameras for adult (for students) or children emotion recognition using available algorithms [14, 15] or adding emotiv epoc sensors for eeg evaluation of the subject’s affective response during the proposed interventions each time [16]. moreover, the inclusion of a wider theme base, integrating issues such as inclusiveness, humanitarian aid, and design of scenarios targeted to disabled people and environmental design, inside the framework of inquiry based projects, is one of our main future goals. unfortunately, the ongoing pandemic has put a total stop to the activities of the specific course, with distance learning providing a less than ideal substitute, since the positive effects of embodied learning -the core precept of the courseare nullified when the students don't have access to the materials and tools of the robotics laboratory. on the other hand, the pandemic provided us with new challenges and urged us to transform the teaching process, evolve it to adapt to the current needs and find new alternatives to our regular teaching routine. acknowledgment the author would like to thank the department of elementary education of the university of western macedonia for its unwavering support of the laboratory. moreover the author would like to acknowledge the hard work and dedication so many of our students showed, in creating novel and interesting teaching interventions. references [1] j. nemiro, c. larriva, and m. jawaharlal, "developing creative behavior in elementary school students with robotics," the journal of creative behavior, vol. 51, no. 1, pp. 70–90, 2017, https://doi.org/ 10.1002/jocb.87. 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[15] a. samad, a. u. rehman, and s. a. ali, "performance evaluation of learning classifiers of children emotions using feature combinations in the presence of noise," engineering, technology & applied science research, vol. 9, no. 6, pp. 5088–5092, dec. 2019, https://doi.org/ 10.48084/etasr.3193. [16] a. stein, y. yotam, r. puzis, g. shani, and m. taieb-maimon, "eegtriggered dynamic difficulty adjustment for multiplayer games," entertainment computing, vol. 25, pp. 14–25, mar. 2018, https://doi.org/ 10.1016/j.entcom.2017.11.003. authors profile stefanos xefteris holds a b.s. from the mathematics department of aristotle university of thessaloniki and a ph.d. in behavioral biometrics with computer vision from the national technical university of athens, greece. for the past 5 years he has been working as an adjunct lecturer in the elementary education department of the university of western macedonia in greece, where he teaches educational robotics and steam based teaching scenarios. engineering, technology & applied science research vol. 7, no. 2, 2017, 1444-1449 1444 www.etasr.com naziry kordkandy et al.: hydrogen gas production in a stand-alone wind farm hydrogen gas production in a stand-alone wind farm mohammad naziry kordkandy national iranian gas transmission company-8th district of gas transmission operation (nigtcdist8), tabriz, iran m_naziri@nigc-dist8.ir ardeshir arash department of electrical engineering, ardabil branch, islamic azad university, ardabil iran ardeshir.arash@gmail.com mohsen nazary kordkandy faculty of electrical & computer engineering, university of mohaghegh ardabili, ardabil iran mohsennazari90@gmail.com abstract—this paper is analyzing the operation of a stand-alone wind farm with variable speed turbines, permanent magnet synchronous generators (pmsg) and a system for converting wind energy during wind speed variations. on this paper, the design and modeling of a wind system which uses pmsg’s to provide the required power of a hydrogen gas electrolyzer system, is discussed. this wind farm consists of three wind turbines, boost dc-dc converters, diode full bridge rectifiers, permanent magnet synchronous generators, mppt control and a hydrogen gas electrolyzer system. the mppt controller based on fuzzy logic is designed to adjust the duty ratio of the boost dcdc converters to absorb maximum power. the proposed fuzzy logic controller assimilates, with (psf) mppt algorithm which generally used to absorb maximum power from paralleled wind turbines and stores it in form of hydrogen gas. the system is modeled and its behavior is studied using the matlab software. keywords-wind turbine; fuzzy logic; hydrogen; pmsg; mppt. i. introduction wind energy conversion systems (wecss), the interest is focused on small units, used to provide electricity supply in remote areas that are beyond the reach of an electric power grid or cannot be economically connected to a grid [1-2]. however, in order to use wind power as an independent power supply, it is necessary to equalize the change in the amount of power generated, due to the intermittent nature of wind. one such possible method is to use the wind power to produce hydrogen, hydrogen has attracted attention as a future source and it is an effective means of energy storage [3]. in case of grid-connected wind farms, the frequency fluctuations in the connected power grid due to wind power variations are also to be considered, as well as grid proximity [4]. various topologies have been proposed for hydrogen production in which the hydrogen electrolyzer is connected to dc link frequency converter and a battery is generally used [5]. using a battery has the disadvantages of losses and low energy density batteries. thus, a hydrogen is used [6, 7]. in this paper we propose a wecs that has multiinput/multi-output dc/dc boost converters [8] with a hydrogen production system shared between converters. in this system we connect three variable speed wind turbines, three permanent magnet synchronous generators (pmsg), three boost converters and a hydrogen electrolyzer. the hydrogen production system is composed of multiple wind generators. thus, multiple generators supply the total power to the hydrogen generator, and thus a smoothing effect can be obtained. therefore, this system can be operated without a battery [4]. schemes with multiple wind generators connected in parallel through power converters have been proposed with the generators output voltage delivered through a power converter to the load [9]. in this approach however ,a multi input dc/dc converter is employed. the paralleling of switching converters based on power supply contributes many advantages when compared with a single high power centralized power supply [10]. the connection of multi-input/multi-output dc-dc converters in parallel, with the load shared between modules reduces the current stress on the switching devices and increases system reliability [11]. for the reason that conventional pi controller generally does not work well for nonlinear systems, high-order systems and complex systems that have no precise mathematical models, fuzzy logic is chosen to overcome these difficulties due to its flexibility and facility to apply in real time control. with this proposed method, wind generator gives maximum power without any knowledge about generator’s characteristic or ambient condition. control algorithm is independent, achieving fast dynamic responses for the complex nonlinear system [12, 13]. ii. the proposed wind conversion system in designing the wind conversion system for the current study, a few points below will be considered. first, as in variable wind conversion system speed varies due to fluctuations in wind speed, voltage, power and frequency of the output, thus, the most important aspect of designing a wind system are considered using an appropriate algorithm for obtaining the highest power possible from a wind turbine. in this study, we will use psf algorithm along with intelligent fuzzy controller. in order to have the optimum use of the area engineering, technology & applied science research vol. 7, no. 2, 2017, 1444-1449 1445 www.etasr.com naziry kordkandy et al.: hydrogen gas production in a stand-alone wind farm potential for the installation of wind systems, some wind turbines are used in a combined manner. the advantages of this method include increasing the reliability of turbines operation, obtaining a total capacity of turbines and applying them to the hydrogen storage system. in this study, we have considered the use of hydrogen electrolysis system for hydrogen production in the output of wind systems. it should also be noted that a combination of low-capacity hydrogen electrolysis systems is used instead of a high-capacity electrolysis system. regarding the fact that measuring the wind speed is difficult and costly, the maximum power point tracking (mppt) function is generally computed without measuring the wind flow velocity by using the generators speed. this is also one of the strengths of this study. the overall schematic of the proposed wind system is shown in figure 1. as shown, the proposed system consists of three identical sets of wind turbines, permanent magnet synchronous generators, ac-dc full-wave bridge rectifiers, dc boost converters and a control system. wind turbine1 pmsg 1 ac -dc dc-dc h2 electrolyzer psf &fuzzy control system 1 wind turbine2 pmsg 2 ac -dc dc-dc psf &fuzzy control system 1 wind turbine3 pmsg 3 ac -dc dc-dc psf &fuzzy control system 1 mppt1 mppt2 mppt3 duty ratio1 duty ratio2 duty ratio3 p_dc1 p_dc2 p dc3 fig. 1. wind turbines configuration the dc power (pdc) generated from each generator is compared with a maximum turbine power (mppt) in each of the control blocks and this error signal provides a suitable duty ratio for each of the dc-dc boost converters by the fuzzy control systems. finally, the boost converters totally impose suitable voltages and powers for hydrogen electrolysis system. a. wind turbine model the turbine power is determined by the power coefficient cp=ƒ(λ, β) where λ is the tip speed ratio and the pitch angle β is determined by the shape of the wind turbine blade. turbine parameters are given in table i. wind energy depends on four parameters: volume (the amount of air), velocity (air speed), density (air mass) and flux (air flow through the area). mechanical power obtained from the wind turbines is defined as follows: 31 2 m pp c a v (1) pm: mechanical power in the moving air (watt) ρ: air density (kg/m3) a: area swept of the rotor blades (m2) v: velocity of the air (m/sc) cp: the power coefficient in (1), cp is a function of pitch angle β and tip speed ratio λ. the pitch angle β is determined by the shape of the wind turbine blade. the tip speed ratio λ is a controllable parameter that is influenced by the wind turbine rotation speed. the tip speed is defined as: m m r       (2) ωm: rotor angular velocity rad / s r: turbine blade radius m v: the average wind velocity m / s several kind of equations are used to express turbines cp (β,λ). the following equation is based on the modeling of the wind turbine features and is used for the wind turbine in our study [13]:   72 3 5 6, ( ) e x p ( ) p i i cc c c c c         (3) 9 3 8 c1 1 c β 1i       (4) c1 to c9 are c1=0.73, c2=151, c3=0.58, c4=0.002, c5=2.14, c6=13.2, c7=18.4 c8=-0.02 and c9=-0.003. figure 2 shows the curve of the power factor in λ according to different values of β for the turbine. it can be observed that firstly the highest power factor is obtained for β = 0. second, the highest power factor occurs due to a certain amount of tip speed ratio. therefore, the controller should set λ at its optimal value to absorb maximum power in different wind velocities. to calculate the optimal value of λ and the maximum cp: 2 6 7 2 9 7 2 7 0 0, 0 pm dcdp c c c c c c opt d d c c             (5) fig. 2. cp curves as function of tip-speed-ratio with different pitch angles (the optimum tip speed ratio λopt is 7.2064) the amount of maxp c is obtained by replacing λopt in (3): maxp c = 0.4412 . 2 3 engineering, technology & applied science research vol. 7, no. 2, 2017, 1444-1449 1446 www.etasr.com naziry kordkandy et al.: hydrogen gas production in a stand-alone wind farm replacing λopt in (2) results in: opt 0.2v op op r       (6) using the turbine rotor angular velocity in a range of variable speed wind turbine operation and there will be no need to measure the wind velocity. given that measuring the wind velocity is difficult and costly, then the mppt function, without measuring wind velocity, can be generally expressed by the following equation: 2 30.5 [ ] axmm ppt p r p r c opt     (7) figure 3 shows the characteristic curve of the wind turbine with regard to the turbine power, rotor speed and wind speed. the black line (dashed line) shows the direction of mppt and the output power of the turbo generator follows this line. in this study, the given wind speed is always lower than the rated wind speed, thus β is zero. b. hydrogen electrolyzer characteristic technical specifications of the electrolyzer system used in the study are chosen from a technical report as a high-purity hydrogen and oxygen (hhig) production [14,15]. an electrolyzer cell is an equivalent of an electromotive force v0 and internal resistance r0 (figure 4). during nominal operation, the electrolyzer consumes 44.075 kw of nominal power. nominal flow rate of hydrogen is 7.5 nm 3 / h when the amount of current and voltage is 410 amps and 107.5 volts, respectively. the hydrogen electrolyzer system used in this study is a combination of modules described in [14] that are 34 rows and two parallel rows. fig. 3. wind turbine power characteristics fig. 4. equivalent circuit of an electrolyzer cell iii. the proposed control system in this study, psf algorithms along with a fuzzy controller are used. in figure 5, the general principles of this method are shown for a set of wind turbines. optimum wind energy extraction is achieved by running the wind turbine generator (wtg) in variable-speed variable-frequency mode. the rotor speed is allowed to vary in sympathy with the wind speed by maintaining the tip speed ratio to the value that maximizes aerodynamic efficiency. in order to achieve this ratio, the permanent-magnet synchronous generator (pmsg) load line should be matched very closely to the maximum power line of the wind turbine generator. in such a case, a good matching exists between the generator and the load for the best performance of the system, as well as the maximum utilization of the wind driven pmsg. however, the recent advancements in power electronics and control strategies have made it possible to regulate the voltage of the pmsg in many different ways. power signal feedback controller gets all the inputs from electrical signals in circuit. wind speed sensor is not necessary for the power signal feedback method. however, it requires an accurate knowledge of wecs to make an estimation. using turbine rotor angular velocity in a range of variable speed wind turbine operation and there will be no need to measure the wind velocity. opt 0.2v op op r       and we use ωop instead of wind speed for power calculation. flc controller wind turbin pmsg dc-dc pdc(k) p_ref pwm v_ph v_rec i_rec error fig. 5. the proposed system with a fuzzy logic controller and psf algorithm for a wind turbine in this control system, p_ref, which is the same as p_mppt is calculated based on (3), whose only variable is ω (i.e. the permanent magnet synchronous generator speed), for each of the turbo-compressors and is compared with the power generated via the turbo-compressors and the error signal is applied to the fuzzy controller. the output of the fuzzy controller is modulated using a saw-tooth wave and the duty ratio of each boost converter is produced. the proposed mppt algorithm is based on a fuzzy logic controller that directly adjusts the dc/dc converter duty cycle to the control generator speed. engineering, technology & applied science research vol. 7, no. 2, 2017, 1444-1449 1447 www.etasr.com naziry kordkandy et al.: hydrogen gas production in a stand-alone wind farm a. fuzzy controller design designing two inputs-one output fuzzy controller of a mamdani-type includes the following steps: fuzzification, creating rule-bases, inference, defuzzification. a general schematic of a fuzzy control system with feedback is shown in figure 6. fig. 6. a schematic diagram of a fuzzy system with feedback. designing fuzzy controllers is based on a sufficient knowledge of a system’s behaviors instead of on an exact mathematical model [13]. there are two inputs for the fuzzy controllers of the boost converters. the first input is the output error of the system and is shown in (8). e(k)= iref p ip (k) (8) the second input is the difference between consecutive errors and is shown in (9).     k )e ( 1d e k e k  (9) both inputs are fed with the fuzzy controller and the fuzzy controller output is duty ratio changes dd(k). therefore, the control scheme is shown in figure 7. in this control system, the fuzzy controller output dd(k) is added to the previous value of duty ratio and the desired output is finally obtained for the duty ratio. fig. 7. block diagram of the flc d(k)=d(k-1) +dd(k) (10) in the fuzzification phase, crisp quantities change to fuzzy. however, before this phase, the scale of the two input signals of error (e) and change error (de) is altered in an appropriate manner using scaling factors,. then, two scaled signals are fuzzificated to two fuzzy variables called linguistic variables. fuzzy levels are not fixed and depend on the resolution of the required inputs applications. bigger fuzzy levels are indicative of high-resolution input. the fuzzy controller uses triangular membership functions in the controller input. the triangular one was chosen due to its simplicity. for an actual data, the fuzzification system finds its fuzzy membership degree in each language variable. in this study, we used a five-level fuzzification system. each of these variables includes 5 language clauses which shall be called adverbs and respectively include pb (positive big), ps (positive small), zo (zero), ns (negative small) and nb (negative big). the graphical representation of the categories is as shown in figure 8. the controller output is the duty ratio of the boost chopper and its membership functions respectively are: nb (negative small), ns (negative small), zo (zero), ps (positive small) and pb (positive big). the next step is creating rule-bases. the design of these rules depends on the knowledge and experience of its users. with two inputs and 5 linguistic variables for each input, there will be 25 rules. the rule-base used in this study is in accordance with table i. in the inference process, the introduction parts of all rules are compared with the inputs to determine the rules appropriate to the current situation. then, the appropriate rules are chosen and applied. iv. simulation and results the entire control system of the proposed flc based mppt algorithm was simulated by matlab/simulink. the control system consists of 3 wind turbines model, 3 fuzzy logic controller, 3 pmsg model, 3 dc/dc converter and a hydrogen production system. wind turbines and pmsg’s model parameters are shown in table ii. fig. 8. member ship functions of e,de and duty ratio table i. fuzzy table error duty ratio nb ns zo ps pb nb nb nb nb ns zo ns nb nb ns zo ps zo nb ns zo ps pb ps ns zo ps pb pb pb zo ps pb pb pb de nb nb ns zo ps pb (a) (b) (c) engineering, technology & applied science research vol. 7, no. 2, 2017, 1444-1449 1448 www.etasr.com naziry kordkandy et al.: hydrogen gas production in a stand-alone wind farm the simulation result of the proposed method compared to the conventional psf method with pi controllers is shown in figure 9. to have a better comparison of system output for both traditional psf methods and using intelligent algorithms (fuzzy), the system output is represented herein for both types of controllers. both control systems are simulated under the same conditions for 0.5 seconds. it should be noted that in both systems, wind is applied to all turbines at nominal rate. because, under the same conditions, three outputs will be identical in both systems, only the output of the first turbo generators of both systems will be shown and compared. first, we show the dc power output of the wind system with traditional psf controller (with pi) and fuzzy controller will be presented after simulation with software figure 9. simulation results show that the output power amplitude is much better than using the pi controller. in the next step, variable and different wind velocities are applied to each turbine and the results of the proposed control system is illustrated figure10. fig. 9. output power of 1th genrator in 0.5 s (a) with the proposed controller (b) with a pi controller fig. 10. three diffirent wind speeds as it is obvious from the figures, the output power of each wind turbine is subject to wind changes (figure 11). figure 12 shows the output power of total turbines, which is applied to the electrolyzer system. as it can be observed, this amount is approximately equal to the sum of three turbines, which is indicative of the validity of the proposed control system. figure 13 shows the ac [line-line] voltage of each of the generators. as it was mentioned in the introduction section, variable wind velocities in these turbines produce a voltage with variable range and frequency. v. conclusion in this study, an isolated wind system was proposed to produce hydrogen in remote areas. it uses a combination of three sets of turbo-compressors with fuzzy controllers. the power of the total production can be applied to a set of hydrogen electrolyzers to produce hydrogen. the advantage of this system is the parallel use of multiple turbines which increases the reliability of the system. this process is implemented using a fuzzy control algorithm and for every change of wind speed it was shown that the control system could satisfactorily meet the set objectives. as the rapid changes of the wind speed are carefully followed and responded in an appropriate manner and the maximum power is injected to load. compared to systems with traditional psf controller, the proposed system has a better performance in terms of range of fluctuations. on the other hand, since the fuzzy system is independent of the system internal specifications, this can also be regarded as one of the advantages of the proposed system. fig. 11. output power for each generator fig. 12. total output delivered to the electrolyzer (a) (b) engineering, technology & applied science research vol. 7, no. 2, 2017, 1444-1449 1449 www.etasr.com naziry kordkandy et al.: hydrogen gas production in a stand-alone wind farm fig. 13. output voltage of three pmsg[l-l] table ii. parameters of the turbine-generator system pmsg (salient-pole) rated output 1 [mva] rated voltage 1025 [v] d axis reactance 7 [mh] q axis reactance 5.5 [mh] winding resistance 0.01 [ω] back emf waveform sinusoidal pole pairs 51 frequency 20 [hz] flux linkage established by magnets 9.76 [wb] wind turbine rated power pwn 2 [mw] rated rotational speed 23.33 [rpm] rated wind speed 12.205 [m/s] radius of wind turbine 36 [m] maximum power coefficient cp 0.441 acknowledgment the authors are grateful to the national iranian gas transmission company-8th district of gas transmission operation (nigtc-dist8) for the support. references [1] l. barote, c. marinescu, m. n. cirstea. “control structure for singlephase stand-alone wind-based energy sources”, ieee transactions on industrial electronics, vol. 60, no. 2, pp. 764-72, 2013 [2] h. zhao, q. wu, c. n. rasmussen, m. blanke, “l1 adaptive speed control of a small wind energy conversion system for maximum power point tracking” , ieee trans. energy convers., vol. 29, no. 3, pp. 576-584, 2014 [3] h. kaneuchi, t. yachi, t. tani, “effect of an edlc in a wind turbine system for hydrogen production” , 29th ieee international conference on telecommunications energy (intelec), rome, october, 2007 [4] k. koiwa, r. takahashi, j. tamura, “a study of hydrogen production in stand-alone wind farm”, 2012 international conference on renewable energy research and applications (icrera), november 11-14, 2012 [5] r. j. mantz, h. de battista, “hydrogen production from idle generation capacity of wind turbines”, international journal of hydrogen energy, vol. 33, no. 16, pp. 4291-300, 2008 [6] a. gargoom, a. m. osman haruni, m. e. haque, m. negnevitsky, “hybrid stand-alone power systems with hydrogen energy storage for isolated communities”, transmission and distribution conference and exposition, april 19-22, 2010 [7] s. m. muyeen, r. takahashi, j. tamura, “electrolyzer switching strategy for hydrogen generation from variable speed wind generator”, electric power systems research, vol. 81, no. 2, pp. 1171-1179, 2011 [8] i. gadoura, t. suntio, k. zenger, “improved dynamic performance of multiloop operation of paralleled dc/dc converters using fuzzylogic control”, 2002 nordic workshop on power and industrial electronics, stockholm, sweden, 2002 [9] e. pican, e. omerdic, d. toal, m. leahy, “analysis of parallel connected synchronous generators in a novel offshore wind farm model”, energy, vol. 36, no. 11, pp. 6387-6397, 2011 [10] a. k. yadav, v. mehra, a. ray, a. markana, m. lokhande, “paralleled dc boost converters with feedback control using pso optimization technique for photovoltaic module application”, international journal of computer applications, vol. 84, no. 16, pp. 20-25, 2013 [11] a. natsheh, “chaotic behaviour in parallel-connected dc-dc buckboost converters”, ninth international conference on ecological vehicles and renewable energies (ever), monte-carlo, march, 2014 [12] y. geng, g. hua, w. huangang, g. pengyi, “a novel control strategy of induction motors for optimization of both efficiency and torque response”, 30th annual conference of ieee ind. elect. society, november 2-6, 2004 [13] h. q. minh, n. frederic, n. essounbouli, h. abdelaziz, “a new mppt method for stand-alone wind energy conversion system”, 2012 2nd international symposium on environment friendly energies and applications (efea), june 25-27, 2012 [14] k. l. lo, l. khan, “fuzzy logic based svc for power system transient stability enhancement”, international conference on electric utility deregulation and restructuring and power technologies, drpt 2000, april 4-7, 2000 [15] s. muyeen, j. tamura, t. murata, stability augmentation of a gridconnected wind farm, berlin: springer, 2009 microsoft word etasr_v13_n3_pp11042-11050 engineering, technology & applied science research vol. 13, no. 3, 2023, 11042-11050 11042 www.etasr.com albaker: reliability-constrained optimal scheduling of interconnected microgrids reliability-constrained optimal scheduling of interconnected microgrids abdullah albaker department of electrical engineering, college of engineering, university of ha’il, saudi arabia af.albaker@uoh.edu.sa (corresponding author) received: 18 april 2023 | revised: 7 may 2023 | accepted: 10 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the author | doi: https://doi.org/10.48084/etasr.5970 abstract this paper proposes a mixed-integer linear programming (milp) optimization model for the scheduling problem of the interconnected microgrid system. the proposed model is capable of efficiently minimizing the microgrids' total operating costs and improving the entire system's reliability, as it is constrained based on enhancing the interconnected microgrids' reliability. the expected energy not supplied (eens) is considered in order to ensure minimizing the interconnected microgrids' power deficiency. furthermore, the proposed model has the capability to solve the optimization problem considering the islanded operation of the interconnected microgrids, i.e. when disturbances occur on the upstream grid. numerical simulations on a test system containing three interconnected microgrids are performed to evaluate the effectiveness of the model and the results demonstrate the merits and features of the reliability-constrained optimal scheduling model in minimizing the interconnected microgrids' total operating costs and enhancing the interconnected system reliability. keywords-distributed energy resources; expected energy not supplied (eens); interconnected microgrids; islanded operation; optimization; optimal scheduling i. introduction the reliability of power systems is one of the most important factors of human quality of life, as power outages for a few minutes may cause serious problems [1-4]. therefore, it is significant to constantly develop and improve the reliability of power systems in order to maintain their quality and sustainability [5-8]. enhancing and evaluating the power systems’ reliability has been extensively researched and analyzed. authors in [9] investigated the reliability analysis of the ieee40-bus system coupled with enormous pv and wind systems. by dividing the power system layout into various parts, the zone branch approach was used to evaluate the reliability parameters of the distribution systems. in [10], a cost-reliability bi-objective optimization model was developed for microgrids to acquire the optimal sizing and sitting of energy storage systems. the developed model included minimizing the microgrid’s total cost and loss of load expectation (lole) and the ε-constraint method and fuzzy satisfying technique were utilized to solve the proposed problem. the uncertainty related to the availability of capacity and the load level was taken into consideration in [11] using a generic and coherent approach. in addition, applications were illustrated and a new method for the determination of the probabilistic assessment of reliability indices and performance quality metrics was described. in [12], a comprehensive methodological framework was proposed, based on quantitative and latin hypercube sampling methods, to study the prospective impact of vehicle-to-grid with utility-connected battery swapping station for enhancing the supply dependability in future distribution networks. the study in [13] utilizes the fmincon optimization tool to inspect the impact of integrating renewable energy resources into microgrids in terms of measuring and evaluating the enhancement of the system’s reliability. the obtained results indicated the improvement of measuring the system’s reliability. authors in [14] proposed an optimization model based on enhancing the reliability to solve the optimal scheduling problem of the integrated microgrids and evaluated some of the reliability indices of the system including caidi, saidi, and saifi. microgrids as an intelligent technique are partially intended to support power systems’ reliability [15-18]. microgrids are typically designed to facilitate integrating distributed energy resources (ders) into power systems to support the local load demand and expand the predicted economic benefits [19-21]. ders may involve nondispatchable renewable units, battery energy storage systems (besss), and dispatchable distributed generators (dgs) [2224]. once the microgrids are developed, achieving optimal scheduling is a crucial factor in realizing the desired objectives. several research studies have been extensively conducted in this field [25-31]. in [25], an optimization resiliency-oriented scheduling model was proposed to enhance the resiliency of the microgrid by reducing local load curtailment. authors in [26], proposed an optimization model to solve the scheduling problem of several integrated microgrids using the lagrangian relaxation method to preserve the microgrids’ privacy. in [27], a discretized step transformation scheme based on chanceconstrained programming was proposed considering the spinning reserve uncertainty to solve the scheduling problem for isolated microgrids. authors in [28] proposed an optimal engineering, technology & applied science research vol. 13, no. 3, 2023, 11042-11050 11043 www.etasr.com albaker: reliability-constrained optimal scheduling of interconnected microgrids scheduling strategy to regulate the microgrid operation and support its resiliency based on developed constraints that enable the islanding operation. authors in [29] proposed a multi-objective optimization approach to determine the optimal scheduling of unbalanced microgrids considering energy saving, improvement of power quality, and cost minimization. in [30], an automated reinforcement learning-based optimization scheme was proposed considering multi-period forecasting associated with load and renewable generation to solve the optimal scheduling problem of isolated microgrids. authors in [31] proposed a scheduling model considering radiation changes of photovoltaic systems and uncertainties associated with grid bid changes and load demand forecasting to solve the optimization problem. in addition, they utilized a modified bat algorithm to solve the proposed problem considering a variety of uncertainties. nonetheless, the microgrids can be interconnected to each other to maximize the anticipated goals. the optimal interconnected operation of the microgrids can maximize the reliability and resiliency of local power systems, boost the economic advantages of individual microgrids, and foster the use of renewable energy resources. the current paper proposes a generic optimization model to solve the optimal scheduling problem of interconnected microgrids considering enhancing the interconnected system’s reliability. based on the developed operational constraints, the proposed model minimizes each microgrid’s expected energy not supplied (eens), hence, maximizing the reliability of each microgrid involved in the system. in addition, it minimizes the entire interconnected system’s total operation cost. furthermore, it is featured with the capability to solve the scheduling optimization problem during the islanded operation. the proposed optimization problem is developed based on a mixed integer linear programming (milp) and solved over a completed 24-hour scheduling horizon. ii. model outline the proposed reliability-constrained optimal scheduling model of interconnected microgrids aims to minimize each microgrid's "involved in the integrated system" total operation cost and minimize the microgrid's eens. in addition, it considers the optimal scheduling of the interconnected microgrids during both grid-connected and islanded operations, i.e. during outages and disturbances. the microgrids will exchange the power (export and import) with the utility grid during the grid-connected mode to maximize their economic benefits, while they exchange power locally, i.e. among the interconnected microgrids, during the islanded mode to boost and maximize their reliability and own economic benefits. to clarify this significant point, there will be no local power exchange among the interconnected microgrids during the grid-connected mode since it will be more economical for the seller microgrid to sell its excess generation to the utility rather than the other interconnected microgrids. on the other side, the microgrid that experiences a power deficiency would prefer to buy the power from the utility, as they have the option to buy their further needs of power at cheaper prices at the hourly market prices. accordingly, there is no power exchange among the interconnected microgrids during the grid-connected mode, while they will observably exchange power during the islanded operation for mutual benefits, i.e. to increase the seller microgrids’ economic benefits and minimize the buyer microgrids’ energy deficiency. the proposed interconnected microgrid system is demonstrated in figure 1. it is worth mentioning that the developed model would significantly improve the individual microgrid’s reliability in addition to the overall reliability of the interconnected system as it pointedly encourages the microgrids to exploit all available ders of the interconnected system as much as possible. in other words, the proposed model inspires the microgrids to exploit all installed ders to supply the other microgrids that experience power deficiencies for mutual benefit. fig. 1. interconnected microgrid system. iii. problem formulation the objective function of the proposed reliabilityconstrained optimal scheduling problem of the interconnected microgrid system aims to minimize each microgrid's total operating costs and to minimize the probability of power deficiency occurrences within the microgrids, as follows: (1) the developed objective function involves four main expressions. the first expression represents the generated power from the installed dispatchable ders, which is further multiplied by a commitment binary indicator to specify the commitment state. the second expression represents exchanging the power with the utility grid. nonetheless, this expression could mean either cost or revenue depending on the power flow direction. the third expression represents the power exchange between the interconnected microgrids. however, this expression will bring cost for buyer microgrids and revenue for seller microgrids. the last expression is added to add value to the percentage of the power deficiency within the microgrids. the minus sign is added as the percentage of the power deficiency will be displayed in the negative. nonetheless, it is multiplied by an auxiliary cost value, which is supposed to be higher than the other costs to prioritize the reliability of the interconnected system. it should be indicated engineering, technology & applied science research vol. 13, no. 3, 2023, 11042-11050 11044 www.etasr.com albaker: reliability-constrained optimal scheduling of interconnected microgrids that the proposed optimization model is developed to be compatible with both, islanded and grid-connected, modes using the islanded operating indicator s. (2) (3) (4) the total generated and imported power must be balanced with the total power demand, which is satisfied by (2). however, it is worth mentioning that the eens is included in the power balance equation to achieve a feasible solution during outages or disturbances, i.e. during the islanded operation. the power exchange between the microgrids and the utility grid must be within the maximum line capacity limits, which is satisfied by (3). nonetheless, the line capacity limits are multiplied by the islanding binary variable to regulate the microgrids’ operating modes among the islanded and gridconnected operation. on the other side, the power exchange among the interconnected microgrids is also subjected to line capacity limits, which is satisfied by (4). however, it should be mentioned that this operational constraint is also multiplied by the islanding binary variable to force the power exchange between the interconnected microgrids to zero during the gridconnected operation. (5) (6) (7) (8) (9) the installed dispatchable units are subject to respective operational constraints to regulate their operation. each dispatchable unit can generate power only between the maximum and minimum capacity limits, which are satisfied by (5). in addition, they are multiplied by a commitment binary variable i to state whether the dispatchable unit is committed or not during the specified optimal scheduling hour. moreover, each dispatchable unit is restricted by the ramping up and down rate limits, as in (6) and (7), respectively. furthermore, once the dispatchable unit is switched on or off, it is restricted by the minimum up and down time limits, of (8) and (9), respectively. (10) (11) (12) the adjustable loads are regulated by constraints (10)-(12). each adjustable load in the microgrids is restricted by the minimum and maximum rated power, as in (10). however, some of the adjustable loads that are switched on might be subject to a minimum required energy to accomplish the operating cycle, which is regulated by (11). on the other hand, some adjustable loads must operate continuously for a certain amount of time after being turned on, which is satisfied by (12). (13) (14) (15) (16) (17) (18) (19) the connected besss are subject to several operational constraints to acquire their optimal scheduling. maximum and minimum charging and discharging restrictions apply to besss, as in (13) and (14). in accordance with the charging and discharging operations over the defined scheduling horizon, and taking into account the bess efficiency, the stored energy in the bess is calculated by (15). the minimum and maximum capacity restrictions impose additional limits on the besss, as in (16). each bess is restricted by time limits once it starts charging or discharging, as in (17) and (18), respectively. furthermore, the binary variables u and v are added to the bess operational constraints (19) to regulate their operation mode to either charge or discharge during the specified optimal scheduling time. (20) (21) the microgrids’ power deficiency is a significant factor in indicating the interconnected microgrids’ reliability; thus, it is restricted by the developed constraints (20) and (21). the probability of eens is calculated by (20). the percentage of the microgrids’ power deficiency is regulated and measured by (21). iv. numerical simulations three independent microgrids were utilized to study and investigate the proposed reliability-constrained optimal scheduling model of the interconnected microgrids, which are named mg a, mg b, and mg c. the microgrids' local installed dispatchable generators are specified in table i. the microgrids’ bess characteristics are demonstrated in table ii. the efficiency of all bess is supposed to be 90% [26]. each of the microgrids is accompanied with its own renewable, i.e. nondispatchable, generators, and their forecasted power generation is shown in figures 2 and 3, for solar pvs and wind engineering, technology & applied science research vol. 13, no. 3, 2023, 11042-11050 11045 www.etasr.com albaker: reliability-constrained optimal scheduling of interconnected microgrids turbines power, respectively. table iii shows the characteristics of the adjustable loads that are installed in the microgrids. table i. characteristics of installed dispatchable generators dg mg a mg b mg c price ($/mwh) g 1 28.1 30.9 38.7 g 2 38.9 45.7 46.9 g 3 62.2 73.5 75.4 g 4 66.3 78.4 – – minimum up and down time (h) g 1 3 4 5 g 2 3 4 4 g 3 1 2 2 g 4 1 3 – – minimum and maximum capacity (mw) g 1 1 – 5 1 – 2 0.5 – 2 g 2 1 – 5 0.5 – 2 0.8 – 2.5 g 3 0.8 – 3 0.5 – 1 0.5 – 3.5 g 4 0.8 – 3 1 – 3 – – ramp up and down rate (mw/h) g 1 2.5 1 1.5 g 2 2.5 2 1.5 g 3 3 1 2.5 g 4 3 1.5 – table ii. microgrids’ bess characteristics microgrid bess characteristics charging and discharging minimum and maximum power (mw) charging and discharging minimum operating time (h) capacity (mwh) mg a bess 0.4 – 2 5 10 mg b bess 0.2 – 1 4 5 mg c bess 0.8 – 2 4 6 fig. 2. solar pvs power in mg a, mg b, and mg c. the microgrids’ hourly fixed load data are shown in figure 4. all the microgrids are electrically connected to the utility grid as an infinite bus. the market price of the power exchange between the utility grid and the microgrids is demonstrated in figure 5. figure 5 also shows the price of the local power exchange among the interconnected microgrids, which is set to be 10% higher than the market hourly prices arbitrary to create incentive to local power exchanges. in addition, a marginal value of the power deficiency, i.e. , of $10/kwh is assumed [32]. the lines between each microgrid and the utility grid and the lines among the interconnected microgrids are subject to line capacity limits, which are restricted to 10mw and 2mw, respectively. a 24-hour scheduling horizon is considered to solve the proposed problem. in addition, 25-islanded-scenarios are considered to solve the optimization problem, where one scenario indicates the grid-connected operation and the rest indicate islanded operation in each specific hour. the optimization problem is programmed and solved using cplex 11.0 in gams [33]. five case studies were carried out to demonstrate the features and effectiveness of the proposed model. the summary of the microgrids’ total operation costs is shown in table ix for all cases. fig. 3. wind turbines power in mg a, mg b, and mg c. fig. 4. hourly fixed load in mg a, mg b, and mg c. fig. 5. hourly forecasted market prices and local power exchange prices. a. case 0-base case: individual microgrid optimal scheduling in this case, each microgrid in the system is optimized individually, i.e. there is no interconnection among the microgrids, to ensure the lowest potential operational cost and maximum reliability. the total operational costs of mg a, mg b, and mg c, considering the islanded operation scenarios, are computed as $14,699.19, $9,387.56, and $10,001.18, respectively. table iii. adjustable load engineering, technology & applied science research vol. 13, no. 3, 2023, 11042-11050 11046 www.etasr.com albaker: reliability-constrained optimal scheduling of interconnected microgrids microgrid adjustable load characteristics load type required energy (mwh) minimum and maximum capacity (mw) start and end time (h) minimum up time (h) mg a shiftable 1 1.6 0 – 0.4 11 – 15 1 shiftable 2 1.6 0 – 0.4 15 – 19 1 shiftable 3 2.4 0.02 – 0.8 16 – 18 1 shiftable 4 2.4 0.02 – 0.8 14 – 22 1 cuirtailable 5 47 1.8 – 2 1 – 24 24 mg b shiftable 1 1.6 0 – 0.4 12 – 16 1 shiftable 2 2.4 0.02 – 0.8 15 – 23 1 cuirtailable 3 47 1.8 – 2 1 – 24 24 mg c shiftable 1 2 0 – 0.5 9 – 13 1 shiftable 2 2.4 0.2 – 0.8 11 – 17 1 cuirtailable 3 36 0.8 – 1.6 1 – 24 24 fig. 6. microgrids’ power deficiency in case 0. in this case, each of the microgrids in the system experiences some power deficiency during the optimal islanded operation, which is illustrated in figure 6. the percentage of the power deficiency in the microgrids is calculated as 1.61%, 2.33%, and 7.67% for mg a, mg b, and mg c, respectively (see table viii). the hourly optimal scheduling of the installed besss in the microgrids is demonstrated in figure 7. this case study demonstrates that although optimal solutions for microgrids are identified, the lack of complementary power supplies may result in failure to reach maximum reliability. b. case 1: optimal scheduling when the interconnection is only between mg a and mg b in this case, the impact of integrating mg a and mg b on the optimization outcomes is investigated. mg a's total operation cost is slightly reduced by 0.34% to $14,648.59, while the total operation cost of mg b is slightly increased by 0.43% as it is computed to $9,428.60. it should be mentioned that the optimization outcomes of mg c are not impacted in this case study as its optimal scheduling results remained exactly the same as in the base case. fig. 7. optimal scheduling of the bess in case 0. table iv. local power exchange between mg a and mg b in case 1 scenario no. 1 2 3 4 5 6 7 8 p c(a-b) (mw) –0.26 –0.47 –0.36 –0.28 0.56 0 0.57 0.69 scenario no. 9 10 11 12 13 14 15 16 p c(a-b) (mw) 0.70 0.78 0.54 0.46 0.46 0 –0.32 –0.47 scenario no. 17 18 19 20 21 22 23 24 p c(a-b) (mw) –0.45 –0.12 –0.80 0 0 0 0 0 fig. 8. power deficiency differences in case 1 for mg a and mg b. the hourly power deficiency is reduced by 81.98% and 56.65% for mg a and mg b, respectively, as shown in figure 8. in this case, mg a and mg b experience power deficiency of 0.29% and 1.01%, respectively. the percentage of power deficiency is summarized in table viii for all cases. obviously, enabling the integration among these two microgrids would result in permitting local power exchange among them. the results of the optimal hourly power exchange among the interconnected microgrids are shown in table iv. it should be noted that the minus sign signifies that the power is transferred from mg a to mg b, and vice versa. observably, allowing the integration among certain microgrids engineering, technology & applied science research vol. 13, no. 3, 2023, 11042-11050 11047 www.etasr.com albaker: reliability-constrained optimal scheduling of interconnected microgrids demonstrates slight improvements in terms of interconnected microgrids’ economic benefits and improves their reliability as it authorizes further paths to optimize the microgrid scheduling. c. case 2: optimal scheduling when the interconnection is only between mg a and mg c in this case study, the interconnection among the interconnected microgrids is only enabled between mg a and mg c. the microgrids’ total operation cost is computed as $14,201.05 and $10,569.53 for mg a and mg c, respectively, while the total operating cost of mg b remained unchanged as in case 0. even though the total operation cost of mg c is increased by 5.68%, the power deficiency of mg c is obviously reduced by 87.39%. the percentage of the power deficiency is computed as 0.22% and 0.97% for mg a and mg c, respectively, while it remained unchanged for mg b, as shown in table viii. table v. local power exchange between mg a and mg c in case 2 scenario no. 1 2 3 4 5 6 7 8 p c(a-c) (mw) –2 –2 –2 –1.52 0.56 0 0.57 0.69 scenario no. 9 10 11 12 13 14 15 16 p c(a-c) (mw) 0.70 0.60 0.54 0.42 0.68 0.29 0 0 scenario no. 17 18 19 20 21 22 23 24 p c(a-c) (mw) 0 0 –1.06 –0.25 –1.66 –2 –1.94 –1.89 fig. 9. power deficiency differences in case 2 for mg a and mg c. the hourly power exchange between mg a and mg c is illustrated in table v. the minus sign indicates that the power is transferred from mg a to mg c, and vice versa. the improvements in the microgrids’ power deficiency are graphically illustrated in figure 9, which also shows the hourly load curtailment in mg a and mg c. d. case 3: optimal scheduling when the interconnection is only between mg b and mg c in this case, the interconnection among mg b and mg c is activated, hence, the power can be locally exchanged among these interconnected microgrids. the optimization results of the hourly local power exchange are illustrated in table vi, where the minus sign indicates that the power is exported from mg b to mg c and vice versa. the total operating costs of these two interconnected microgrids are slightly changed, as it is indicated in table ix. mg b’s total operating cost is reduced by 0.61% (computed as $9,329.68), while mg c’s total operating cost is slightly increased by 1.19% (computed as $10,120.02). however, the power deficiency of these two microgrids is noticeably decreased, by 65.23% and 58.15% for mg b and mg c, respectively. the changes in the power deficiency are graphically demonstrated in figure 10. the reduction percentage of total power deficiency is calculated as 0.81% and 3.21% for mg b and mg c, respectively, as it is shown in table viii. on the other side, the optimization results of mg a have not been changed compared with the base case, as it is excluded in this case study from the interconnection. table vi. local power exchange between mg b and mg c in case 3 scenario no. 1 2 3 4 5 6 7 8 p c(b-c) (mw) –0.74 –0.73 –0.84 –0.92 –0.90 –1.19 –0.84 –0.28 scenario no. 9 10 11 12 13 14 15 16 p c(b-c) (mw) –1.19 0 0 0 0 0 0.66 0.38 scenario no. 17 18 19 20 21 22 23 24 p c(b-c) (mw) 0.18 0.51 0.82 –0.21 –1.58 –1.22 –0.59 –0.73 fig. 10. power deficiency differences in case 3 for mg b and mg c. e. case 4: optimal ιnterconnected microgrids scheduling in this case, all microgrids are electrically interconnected in the studied system. this case study inspects and explores the potential impacts of interconnecting the microgrids on their total operating costs and reliability. the optimal local power exchange scheduling among the interconnected microgrids, over the scheduling horizon, is demonstrated in table vii. the optimization results of the optimal scheduling of the bess are slightly changed in this case study, which is demonstrated in figure 11. these slight changes are caused by the local power exchange among the microgrids. the total operating costs of the interconnected microgrids are computed as $14,379.87, $9,328.19, and $10,308.36 for mg a, mg b, and mg c, engineering, technology & applied science research vol. 13, no. 3, 2023, 11042-11050 11048 www.etasr.com albaker: reliability-constrained optimal scheduling of interconnected microgrids respectively. even though the total operating costs are slightly increased in some of the microgrids (by 3.07% in mg c), the encountered power deficiency in all the microgrids is dramatically minimized to zero, which emphasizes a significant improvement in the interconnected system reliability. table vii. local power exchange between all the microgrids in case 4 scenario no. 1 2 3 4 5 6 7 8 p c(a-b) (mw) –1.18 –1.42 –0.38 0 0.56 0 0.57 0.37 p c(a-c) (mw) –2 –2 –2 –1.13 0 0 0 0.32 p c(b-c) (mw) –0.72 –0.95 –0.02 –0.72 –0.90 –1.19 –0.84 0 scenario no. 9 10 11 12 13 14 15 16 p c(a-b) (mw) 0.70 0 0 0.17 0.46 0 –0.22 –0.47 p c(a-c) (mw) 0 0.78 0.54 0.42 0.68 0.27 0 0 p c(b-c) (mw) –0.39 0 0 0 0 0.48 0.44 0.38 scenario no. 17 18 19 20 21 22 23 24 p c(a-b) (mw) –0.45 –0.01 –0.80 0 0 0 0 0 p c(a-c) (mw) 0 0 –0.26 –0.04 –0.10 –0.91 –1.85 –1.66 p c(b-c) (mw) 0.10 0.48 0 –0.21 –1.56 –1.20 –0.90 –0.23 table viii. percentage of microgrids’ power deficiency in all case studies case no. mg a mg b mg c case 0 1.61% 2.33% 7.67% case 1 0.29% 1.01% 7.67% case 2 0.22% 2.33% 0.97% case 3 1.61% 0.81% 3.21% case 4 0% 0% 0% table ix. summary of microgrids’ total operation cost case no. mg a mg b mg c case 0 $14,699.19 $9,387.56 $10,001.18 case 1 $14,648.59 $9,428.60 $10,001.18 case 2 $14,201.05 $9,387.56 $10,569.53 case 3 $14,699.19 $9,329.68 $10,120.02 case 4 $14,379.87 $9,328.19 $10,308.36 fig. 11. optimal scheduling of the bess in case 4. v. conclusion this paper highlighted the potential benefits and features of enabling the interconnection among adjacent microgrids and proposed a reliability-constrained optimal scheduling model for interconnected microgrids. the proposed model was capable of economically minimizing the interconnected microgrids’ total operating costs and was capable of efficiently maximizing the interconnected system's reliability. the key features of the proposed optimization model can be summarized as follows: (i) it ensures the minimization of the microgrids' total operating costs and supports the optimization of the battery energy storage systems scheduling, (ii) it is capable of efficiently maximizing the interconnected system reliability by minimizing the expected energy not supplied in the microgrids, (iii) it takes the potentiality of islanded operation scenarios into account (i.e. in the event of disturbances and outages), and (iv) it is developed based on mixed-integer linear programming to facilitate reaching fast and efficient optimal solutions. the proposed model exploited all the distributed energy resources installed in the microgrids, including the battery energy storage systems, to support the reliability and economic benefits of the microgrids by enabling local power exchange among the interconnected system. the proposed optimization scheme was investigated in several case studies, including the optimal individual scheduling of the microgrids as a base case, to explore and validate its performance and feasibility. the obtained optimization results indicated its superior performance in minimizing the microgrids’ total operating costs and the expected energy not supplied in the microgrids. nevertheless, the proposed optimization model is generic, and various test systems could be applied to investigate its feasibility and performance without loss of generality. nomenclature indices: ch superscript for bess charging operation mode. d index for loads. dch superscript for bess discharging operation mode. i index for ders. s index for scenarios. m,n index for microgrids. t index for time. sets: da set of adjustable loads. g set of dispatchable generators. m set of microgrids. k set of islanded scenarios. s set of besss. t set of time periods. parameters: dr ramping down rate. d aggregated load demand. dt minimum down time. dmax adjustable load maximum rated power. dmin adjustable load minimum rated power. e total required energy of adjustable load. f(.) generation cost of ders. mc minimum charging time of bess. md minimum discharging time of bess. mu minimum operation time of adjustable load. pr aggregated forecasted renewable generation. ur ramping up rate. ut minimum up time.  forecasted hourly market prices.  value of power deficiency.  local power exchange prices. , adjustable loads’ defined start and end times.  bess efficiency. variables: c total stored energy in bess. eens expected energy not supplied. i binary variable for commitment status of dispatchable units. p ders generated power. pc local power exchange. pd power deficiency. pm power exchange with the utility. tch bess’s number of successive 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[32] estimating the value of lost load. austin tx, usa: ercot, 2013. engineering, technology & applied science research vol. 13, no. 3, 2023, 11042-11050 11050 www.etasr.com albaker: reliability-constrained optimal scheduling of interconnected microgrids [33] "ibm cplex — ampl resources," ampl development. https://dev.ampl.com/solvers/cplex/index.html. authors profile abdullah albaker received his m.s. and ph.d. degrees in electrical engineering, specializing in electric power engineering, from the university of denver, denver, co, usa, in 2014 and 2018, respectively. he is currently an assistant professor of electrical engineering at the university of ha’il, ha’il, saudi arabia. his research interests include microgrid planning and operation, renewable energy and distributed generation, power system economics and reliability, smart electricity grids optimization, and machine learning. microsoft word etasr_v10_n6_pp6578-6583 engineering, technology & applied science research vol. 10, no. 6, 2020, 6578-6583 6578 www.etasr.com khan et al.: a literature review on software testing techniques for smartphone applications a literature review on software testing techniques for smartphone applications muhammad naeem ahmed khan independent researcher islamabad, pakistan mnak2010@gmail.com aamir mehmood mirza balochistan university of information technology, engineering and management sciences quetta, pakistan mamehmood@msn.com raja asif wagan balochistan university of information technology, engineering and management sciences quetta, pakistan raja.asif@buitms.edu.pk mahwish shahid university of management and technology lahore, pakistan mahwish.shahid@umt.edu.pk imran saleem university of management and technology lahore, pakistan imran.saleem@umt.edu.pk abstract-smartphone applications are getting popular and have become a necessity. there numerous smartphone applications ranging from entertaining to gaming and from utility to missioncritical. almost everything on the web is now in hands of smartphone users, which makes this domain very important and its quality should not be compromised. achieving the desired quality is not an easy task for the mobile platform as it has its limitations. to produce a quality app, developers and testers need to test and assess the app in numerous ways to ensure the best trait of the application. in this concern, some efficient and mature techniques are required to test smartphone applications. in this study, the techniques, approaches, and models to assess mobile apps covering major prospects and angels to test mobile apps are identified. our focus is on assessing the existing techniques and to evaluate them on standard validation parameters. keywords-android; model based testing; functional testing; app testing; functional refactoring i. introduction smartphone applications are getting popular and have become a necessity. from banking to healthcare or from gaming and utility to mission-critical, there is a huge pool of smartphone applications [1, 2]. achieving the desired quality is not an easy task for the mobile platform as it has its limitations such as processor, battery etc. to produce a quality app, developers and testers need to validate it in numerous ways to ensure the best trait of the application [3]. in this concern, some efficient and mature techniques are required to test mobile applications. mobile applications have their quirks and challenges regarding testing, such as the high number of different events that need to be tested [4]. security is also an important aspect of smartphone applications [5]. these challenges mostly rely on the mobile platform, but some challenges arise due to the interoperability of the mobile platform to other platforms like the web, third party systems, and the cloud. in this study, the techniques, approaches, and models to assess mobile apps covering major prospects and angels to test mobile apps are identified. our aim is to assess the existing techniques and to evaluate them on standard validation parameters. ii. research methodology this review was conducted according to the guidelines proposed by [6]. for this purpose, we have formulated a search string and executed this search string on ieee explore, acm and science direct to identify research studies published from 2007 to 2020. by reviewing the title and the abstract we have initially selected 98 research papers for full text reading. from this initial database of research studies, we selected 19 research papers to include in this study which were aimed at testing smartphone applications. the database of the selected research papers covers journal and conference papers about testing techniques for smartphone applications. most of the research studies are primarily focused on theoretical reports, case studies, field studies, and experience reports. iii. literature review a. security and malware testing a study presented apset for detecting the intent-based vulnerabilities of android applications. apset takes vulnerable patterns proposed by domain experts and system specifications [5]. the major contribution of this study is test case generation via the automatic generation of partial specifications from applications. apset also detects issues in the data on the basis on intent mechanism. apset was tested on over 70 android applications and it detected 62 vulnerabilities which could be exploited by hackers or attackers to crash the application. this tool is founded over the modelbased testing technique along with the support of the iosts model to generate patterns besides the reverse engineering of corresponding author: mahwish shahid engineering, technology & applied science research vol. 10, no. 6, 2020, 6578-6583 6579 www.etasr.com khan et al.: a literature review on software testing techniques for smartphone applications system class diagram and specification to generate test cases for the application under test. the limitation of the proposed tool is that it only works over intent-based loopholes and pitfalls. apset cannot be used for any other vulnerability. a novel hybrid technique was proposed to detect malware in android applications based on static and dynamic analysis [7]. the proposed technique requires efficient data processing (pattern generation and detection). system calls are used to generate patterns for malware and normal apps which are done through the support of android os manipulation. the advantage of this approach is that it does not spend much time as it takes in the static analysis, neither it consumes a lot of resources as does the dynamic analysis. some disadvantages include that it needs to constantly gather new malware and benign apps to keep detection accuracy because new types of malware continue to emerge. this approach is based on the difference between malware and benign apps in runtime system calls. more normal and malware patterns are always needed. second, due to limited computing and storage resources, it is not suitable to perform large-scale data processing in the mobile phone. to achieve real-time detection, this approach requires the mobile phone to have powerful computing capabilities and sufficient data storage. authors in [8] presented a test automation technique for mobile platforms based on observation, extraction, and abstraction of the running sut by using its gui widget. the abstraction used in this tool is used to create a scalable state machine model using eventbased test coverage criteria, which automatically creates test cases for the sut. the study demonstrates that the generated test cases were effective and useful in detecting serious issues and defects in the applications. using the mentioned approaches, the authors developed a fully automatic tool for the detection of bugs and errors in android applications. this study also compares two famous android application testing tools: monkey and dynodroid. they configured monkey and dynodroid to test the same four mobile applications which they tested with mobiguitar under the same parameters and inputs. an experiment demonstrated that monkey and dynodroid both did not find all of the exceptions which their proposed tool did. b. cloud-based testing a systematically review the state of the knowledge of the empirical studies is presented in [9]. the study focuses on mapping the testing techniques for mobile applications. additionally, the study emphasizes the need for testing metrics to be included and adhere to address mobile application testing lifecycle conformance. the major lags in the mentioned techniques for a smartphone application testing lie in the automation of testing. according to the authors, this is an emerging and future of mobile and other testing, but very few of them implemented this technique over complex applications. automated testing techniques perform well over small to medium and simple mobile applications, but very little work is done over the implementation and analysis of this technique over complex mobile applications which put a question mark over its credibility and reliability. c. test automation authors in [10] proposed a novel framework for comparing automatic testing techniques for smartphone applications. the salient characteristics of every technique were picked to develop the parameters. a comparison was done among online testing techniques and in result, a general framework was proposed based on the unified online testing algorithm. the authors found that the random technique is more effective than an active learning technique, but it is approximately 100 times more expensive due to the nature of the experimental setup. active learning was cheaper and more efficient than the random one in some cases, but in most of the cases the random testing technique was better in execution but more expensive in cost. authors in [11] presented an experimental study to analyze and evaluate the mbt approach in modeling, concretization, and execution of automated tests in mobile applications. along with the usage of mbt they adopted the event sequence graph (esg) to design their test model. for the implementation of the test cases, they used the robotium framework. this study evaluated the perks and shortcomings of using mbt as an approach to automate test execution for this particular platform. several perks and challenges were identified including: automatic generation of test cases, capacity to detect faults, improvement in test quality, test time and cost reduction, and evolution of test models. the challenges in the usage of mbt in the mobile application that are related to this domain are: difficulties in test modeling and particularities in the concretization of test cases in mobility context and in-depth knowledge of robotium. the design and implementation of the mobile taas system called mtaas is presented in [12]. mtaas is an infrastructure for mobile application testing on the cloud which provides large scale remote mobile application testing for the android platform. some issues regarding resource allocation and sharing were discussed as this study focuses on the cloud to implement the proposed system where resource allocation and management is a very important factor to be handled. this issue is resolved through a hybrid model that aims to improve the system performance while reducing cost. the system was tested on different real time scenarios and use cases. mtaas was compared to perfecto mobile, testdroid, yiceyun, testin, and utest under the same parameters and inputs. the results showed that mtaas performed satisfactorily. further, some limitations were discussed like the security and privacy of the user’s data, security threats to multiple virtual machines, and intrusion detection. another issue that was highlighted was the lack of standards in mobile test environments and test automation for mobile application testing with the addition to the lack of well-defined test models and coverage criteria for cloud-based application testing. authors in [13] presented a tool named sit to test self-adaptive applications. sit framework stands on abstract trace (at) and trace segments (ts). test case generation was achieved by sampling-based test generation. as per experimental results, the sit improved defect detection significantly. sit was evaluated and analyzed over three online available context-sensitive and self-adaptive applications: robot car, phone adaptor and secondo. the study implemented random testing (rt) and dynamic symbolic execution (dse) for comparison purposes. overall the sit improved detection rate by 22.4-42.2%. despite all these advantages and good results, the sit has some limitations. it currently relies on application specific support, engineering, technology & applied science research vol. 10, no. 6, 2020, 6578-6583 6580 www.etasr.com khan et al.: a literature review on software testing techniques for smartphone applications which means if an application is running in a particular environment, that environment should not be easily changed or manipulated during testing. the improvement room is also available in the proposed approach in a way that assertions that were used to define program failures were composed manually in the application. it might be possible to derive these assertions automatically from specifications. in [14], a gui based automated testing tool called spag-c is proposed which uses a record-replay technique to perform gui testing. spag-c used event-based and smart wait function to eliminate the uncertainty of the reply process and by using gui layout information to verify the results testing process produces. the experimentation showed that spag-c maintains the accuracy to 99.5% in addition to the reduction of the time required to record test cases by verifying the process automatically with the increased reusability of the test oracles without compromising the accuracy. the proposed tool was compared with histogram, surf, and template matching tools and their techniques and results proved that spag-c outperformed them. the novelty of the spag-c is that for some apps only a small portion of the screen is changed when the app responds to an event. for such apps the tester can select the region of interest in the screen of the device and then spag-c will verify it which saves time to fully verify the screens once again. as a limitation, there is the problem that applications with non-deterministic gui cannot be tested by spag-c. this is because the camera cannot extract the necessary elements from the screen for later comparison and matching as aut screen keeps changing in video playing applications or gaming apps. this approach works on the image capturing mechanism so the camera which is used to capture screenshots of all ui could be affected by external factors of the environment like light, exposure etc. a controlled environment is required to execute this procedure. authors in [15] presented an empirical study in which mbt was applied to mobile applications to examine the effectiveness of their approach over mobile systems and applications. the study uses efsm to model a mobile app and implemented a commandline tool "kelevra" along with appium, an automation tool. gestures, clicks and keyboard inputs are examples of methods that can then be applied to the retrieved ui element objects. the mbt approach was also previously tested over an app "gmsec", which is quite simple as compared to "quiz-up". the experimental setup exhibits that mbt pays well off over the effort it requires. experiments show that applying mbt found non-trivial bugs and defects in quiz-up which was already being tested, proving the effectiveness of this approach towards mobile systems or applications. a possible extension to this would be to minimize the manual steps even more. another option would be to implement a language to describe a sut and its possible outcomes. for mobile applications, we can describe the ui elements and patterns in a particular view or scene under the test. the constructed textual description could then be translated into a model representation such as the efsm. the key limitation observed is that the proposed technique is suitable for testing small-sized apps. authors in [16] presented an adaptation model for testing mobile applications which is comprised of two sub-parts, mobile analyzer and test mobile [16]. the study was inspired by a framework used by web app testing, reweb and testweb, a tool for analysis, testing and restructuring application. refactoring is a key step in this proposed technique as refactoring minimizes code size without affecting the functionality of an app. the major focus of this study was to minimize the test effort by minimizing the test cases of an app, which can be achieved through refactoring aut (application under test), so that the transitions and paths of applications can be minimized which ultimately results in less test cases and efforts to test an app without compromising the coverage. based on this model, test cases were generated. at this point, applications entered the second module, test mobile, and generated test cases were selected upon defined criteria. after test case selection, the expected outcome and run time output were compared after the execution, and the result decided whether the test passed or failed. reweb and testweb were initially used for web domain applications and they were designed for a particular domain so they performed well. the advantage of this technique is that it minimizes test case space without compromising coverage. further advancement in this technique can be made by automating the process of refactoring which eases its use and lessens human involvement and effort on refactoring. authors in [17] presented an mbt approach for test case generation for smartphone applications. state machines were used for modeling and test case generation. test cases were generated through spin, an automatic tool for test case generation through model usage. the proposed approach used xml based transformations to translate the test cases to some executable form to activate the applications under test. for experimentation, facebook and youtube applications were used. the proposed approach was tested with other model-based approaches and techniques which include apset, mobiguitar, and swifthand. this approach uses the view state machine model to model any application, which involves excessive mathematics and prior working knowledge of state machines, as these models become very complex in large size programs. the second issue is that there is a lot of involvement of third-party tools which are assisting in the basic three steps of this approach. authors in [18] proposed a grey box approach for automatically reverse engineering gui-models of mobile applications. their system, orbit, uses a finite state machine for model generation and the results of an empirical evaluation on several real apps were presented. at first, the authors used static analysis of the application’s source code to extract the set of user actions supported by each widget in the app gui. then, a dynamic crawler was used to reverse engineer a model of the app, by systematically exercising the extracted actions on the live app. orbit was evaluated on 3 parameters, test coverage, time consumption, and precision. it was compared with monkey, mobiguitar, and android gui ripper in experimental steps. a limitation in this approach is that it requires a lot of manual work, consisting in manually selecting attributes of the executable components to compose the visual observable states for the gui. authors in [19] proposed a technique to test mobile applications using reverse engineering and pattern recognition of mobile aut. the process was based on the automatic and dynamic exploration of the apps' gui. to support the dynamic engineering, technology & applied science research vol. 10, no. 6, 2020, 6578-6583 6581 www.etasr.com khan et al.: a literature review on software testing techniques for smartphone applications exploration, static analysis was also conducted to verify how they are executed. gui widgets were examined through their execution and calls. the achieved patterns decided the errors and bugs, if found. the major contribution of this work is a reverse engineering approach to identify occurrences of behavioral patterns in mobile applications and a dynamic, run time, and on the go testing approach based on the application of test patterns associated with behavioral patterns identified in the mobile application. the proposed approach was found to perform better than the mbt approach as most of the gui mbt approaches use reverse engineering for model gain. a drawback of this study is that the pattern behavior judgment is not easy and can be a tedious task if done manually. since this study reverse engineers the app under test and analyzes its patterns statically, this static task of pattern recognition and extraction is not easy as apps get more complex day by day. future work in this study could be the automation of pattern identification and recognition, which would reduce and minimize execution time and minimize human error. authors in [20] proposed test adapters to test guis through automated testing of industrial applications. test generations through test adapters can be applied at the unit, integration and system test level. authors in [21] proposed the a3e approach to use static, taint style, data flow analysis on the app to develop a high level control flow graph that captures legal transitions on the app's screen. the experiment on 25 popular apps achieved 59.39-64.11% activity coverage and 29.5336.46% method coverage. model-based software testing can be used to automatically produce test cases from a formal model describing the sut. in addition to conventional test automation, it may increase the quality of testing and reduce the resources needed. a case study was presented to illustrate the ability of a mbt to produce long-term test cases and run parallel tests on multiple smartphone devices in [22]. authors in [23] introduced a novel method designed to identify irregular network traffic activities in a multimedia app and how different user experiences will lead to unexpected traffic patterns. it makes the generation of a test suite composed of a huge number of test cases that can be executed and measured with adequate automation. instead of random interactions, this test suite represents realistic user behaviors, which may reveal unforeseen consequences to users. iv. critical evaluation a systematic literature review was performed in order to find, analyze, and classify papers which focused on testing mobile applications. the aim of the current study was to provide practitioners and researchers a clear view of the state of the art so that they can easily find existing solutions pertinent to their issues. the papers have been classified based on the focused area, testing techniques/models, tool(s) (used and proposed), platform/os, tested applications domain, and validation methods and parameters. a summary of the approaches and techniques is presented in table i. table i. critical ev aluation ref. focused area testing techniques / models tools platform / os tested applications domain validation parameters comparison with other techniques, tools, and models [4] test oracle automation using model driven approach -state machine -object management group -class diagram -sequence diagram xunit (used) android utility app -bug detection -test case execution time -model transformation time [5] security testing for android based smartphones -reverse engineering of app class diagram -iosts model apset android -general utility -location based -entertainment -dictionary -vulnerability path coverage (80%) -bug detection (88%) -test terdicts (23%) tools: notepad, google map, youtube and searchable dictionary [7] malware detection in android smartphones -static analysis -dynamic analysis none android -learning apps -utility tools -games -malware detection -accuracy up to 90% tools: androguard and droidmat [8] model based automatic test cases generation and execution for mobile platforms -model based testing -reverse engineering -fsm mobiguitar android -android application testing tools -exception handling -defect detection -code coverage (70%) tools: aardict, monkey and dynodroid techniques: model based testing, random testing [9] mapping mobile application testing techniques to selfdefined classification schemes. -model based -data driven -search based -reverse engineering -contextual fuzzing -gui based testing -automated testing -scripted ui testing -event based testing none -android -symbian -windows -silverlight -news reader -spreadsheet applications -advertising -mobile learning -sales force automation -android testing -usability testing -security testing -test automation -context awareness -general mobile tools: appdoctor, jpf android, mobiletest, testdroid, droidchecker, caiipa, mobiguitar, and appinsight techniques: model based, gui based, automated and event based testing [10] comparing and evaluating automatic testing techniques for android mobile apps. -event based testing -graph based search none android -mobile games -calculator -shopping list manager -recipe manager -task managing -note taking -battery viewer -avg. code coverage (0.035%) -avg. testing cost (7.86ms) tools: aarddict, simplydo, tictactoe, trolly, tomdroid, taskman, bitesandmanpages techniques: active learning and random testing. model: gui tree engineering, technology & applied science research vol. 10, no. 6, 2020, 6578-6583 6582 www.etasr.com khan et al.: a literature review on software testing techniques for smartphone applications [11] test automation for mobile applications -model based testing -event sequence graph robotium android contacts and address manager -avg. event sequence execution time (99.93s) -fault detection rate -cyclomatic complexity (1,22) tools: address book app [12] cloud based testing for smartphone applications -mobility testing -security testing -functional testing -gui testing -service oriented testing mtaas -android -cloud android application testing tools -performance testing -avg. response rime: 181ms -avg. request hit rate: 35.6/s -avg. error ratio: 2.793% -test case success rate (100%) tools: perfecto mobile, testdroid, yiceyun, testinandutest infrastructure approach: crowd sourcing, emulation based, and device based [13] testing of selfadaptive mobile applications sampling based interactive testing sit android context aware applications -number of bugs: 91.4% -bug detection rate: 19.8% -test time efficiency: 82.6% -branch coverage: 12.3-47.9% -test effectiveness: 95.2% tools: robot car, secondo, caiipa and phone adapter techniques: random testing and dse [14] assessing accuracy, efficiency and reusability of testing oracles for android devices. -gui testing -event batching -smart wait function -record-replay spag-c android android application testing tools -accuracy (99.5) -efficiency (50-75%) -reusability (approx. 5h) based on -false positive rate -false negative rate tools: spag and monkeyrunner techniques: histogram, surf and template matching [15] mobile application testing through modelbased testing efsm model used: appium proposed: kelevra android learning apps -fault detection rate tools: gmsec [16] an adaptive model for mobile application testing source code refactoring reweb&test web (used) android calculator -bug detection -test suite/code minimization tool: calculator [17] a model-based testing approach for generating test cases for android apps. state machine spin (used) android n/a -app coverage -testing time duration tools: mobiguitar& apset techniques: swifthand [18] a model-based method of automatically reverse engineering guimodels of mobile applications finite state machine orbit android -business -productivity -entertainment -literary -test coverage: 79% -testing time duration: 51% -precision tools: monkey, android guitar & android gui ripper technique: depth first search & forward crawling [19] an automated gui testing approach to find defects/bugs in mobile applications -gui dynamic analysis -static analysis dalvik vm (used) android -e health -mobile games -business -communication defect rate tool: monkey techniques: model based testing [20] applied code level testing to test rich gui based applications. -unit testing -gui testing -manual testing randoop (used) windows industrial projects (case studies) -defect detection rate (51%) -test case generation (153) -coverage (63%) tools: junit techniques: manual testing, junit automated testing (java fx) [21] systematic exploration of android apps for testing purpose. -black box testing -dfs -targeted exploration -dynamic analysis a3e (proposed) android -entertainment -e commerce -media -social -music -health -method coverage -activity coverage -exploration time techniques: manual testing [22] model based gui testing approach for testing smartphones apps -mbt -gui testing tema test engine (used) android -camera -messenger -bug detection -app state coverage [23] identification of abnormalities in user interaction with multimedia apps using model based approach. -mbt -state machine diagram mve (proposed) android music -no. of executed test cases -state coverage v. conclusion in this study, several techniques and approaches in addition to models and tools were reviewed for smartphone app testing. we found a pool of testing strategies to assess the quality of mobile apps of various natures. while analyzing and evaluating the reviewed approaches for mobile app testing, we found the model-based approach more convenient and promising to test mobile apps because of its appealing approach to model the overall design of a system [24]. the main advantage of using the model-based approach is that the testers are well satisfied with the recused efforts and the level of test cases it helps produce [25]. another advantage to adopt model-based testing is that it supports several automated tools for test case generation and execution. in this study, we have presented an abstract model for testing smartphone apps which support engineering, technology & applied science research vol. 10, no. 6, 2020, 6578-6583 6583 www.etasr.com khan et al.: a literature review on software testing techniques for smartphone applications semi-automated testing. a potential future work in this context could be to evolve a fully automated approach in the form of a testing tool which takes an app as an input and generates test cases according to the chosen model. the proposed tool may possess more than one model for modeling that app and would present the test results after executing the generated test cases in accordance with the selected model. the proposed approach would significantly lessen the human efforts required to test mobile apps and would also minimize the chances of human error. references [1] z. u. rehman and f. a. shaikh, "critical factors influencing the behavioral intention of consumers towards mobile banking in malaysia," engineering, technology & applied science research, vol. 10, no. 1, pp. 5265–5269, feb. 2020, https://doi.org/10.48084/ etasr.3320. 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[22] r. dev, a. jääskeläinen, and m. katara, "model-based gui testing. case smartphone camera and messaging development.," advances in computers, vol. 85, pp. 65–122, 2012, https://doi.org/10.1016/b978-012-396526-4.00002-3. [23] a. r. espada, m. del m. gallardo, a. salmerón, and p. merino, "performance analysis of spotify® for android with model-based testing," mobile information systems, vol. 2017, feb. 2017, art. no. 2012696, https://doi.org/10.1155/2017/2012696. [24] a. m. mirza and m. n. a. khan, "an automated functional testing framework for context-aware applications," ieee access, vol. 6, pp. 46568–46583, 2018, https://doi.org/10.1109/access.2018.2865213. [25] s. mohacsi, m. felderer, and a. beer, "estimating the cost and benefit of model-based testing: a decision support procedure for the application of model-based testing in industry," in 2015 41st euromicro conference on software engineering and advanced applications, funchal, portugal, aug. 2015, pp. 382–389, https://doi.org/10.1109/seaa.2015.18. microsoft word 25-3743_s_etasr_v10_n5_pp6290-6293 engineering, technology & applied science research vol. 10, no. 5, 2020, 6290-6293 6290 www.etasr.com alzamil: assessment of uplink massive mimo in scattering environment assessment of uplink massive mimo in scattering environment ahmed a. alzamil electrical engineering department college of engineering university of hail hail, saudi arabia aa.alzamil@uoh.edu.sa abstract-this paper investigates the performance of massive mimo systems under the effect of multipath propagation environment. linear minimum mean squared error (mmse) is considered to assess the performance of bpbk/ofdm based uplink massive mimo transmission. bit error rate (ber) and channel capacity in non line of site (nlos) multipath fading environment are presented. the results show a correlation between the number of antennas and the performance of the system. keywords-massive mimo; ber; bpsk; ofdm; mmse; multipath i. introduction mimo technology is one of the essential factors that lead the development of wireless communications over the last couple of decades [1]. besides being extremely bandwidth efficient, recent mimo based communication systems are capable of providing reliable transmission in the order of several giga bits per second [2]. advancements in this area have been achieved through various mimo detection techniques that offer improved performance and reduced complexity [3-5]. multiuser mimo (mu-mimo) is a class of the mimo technology in which a group of users are able to communicate wirelessly with one or more antennas and space division multiple access (sdma) is exploited to transmit different signals on the same band. due to its tremendous advantages, mu-mimo has been adopted in most of the wireless communication standards during the last decade [6]. it has been shown that there is a correlation between the number of users that can be served concurrently and the number of antennas in the base station (bs). as a result, more users can communicate using the same time and frequency resources when the bs is equipped with a large number of antennas [7]. recently, the concept of mu-mimo has been developed to massive mimo where antenna arrays can be used at the bs [8, 9]. this means that the number of antennas at the bs is very large compared to the number of antenna users within a cell. this new technology has been adopted in the 5g nr (new radio) which has been developed by the 3 rd generation partnership project (3gpp) for 5g mobile networks [10]. its characteristics eliminate the problem of small scale fading and the multiuser interference which makes linear detection techniques optimal. as a result, energy and spectral efficiencies are substantially increased [9]. moreover, massive mimo leads to huge capacity improvement that could reach up to a 50 fold increase [11, 12]. it has been shown that increasing the number of antennas in the bs enhances link reliability and improves data rate due to the increased number of possible paths for the signal [13]. it also enables the targeted use of the spectrum via the beamforming technology which results in robustness against interference and jamming [14, 15]. this paper investigates the performance of massive mimo systems under scattering multipath environment. an ofdmbased uplink transmission case where the bs is equipped with a number of antennas larger than the number of users is considered. ii. system model the main characteristic of massive mimo is that the bs is equipped with antenna arrays which allow serving a large number of users in the same frequency band. the high multiplexing gain ensures reliable communication with linear processing. the system model of the uplink mu-massive mimo considered in this paper is shown in figure.1. fig. 1. uplink massive mimo multipath propagation. n single antenna users are served with a bs equipped with k antennas in the single cell scenario. let ��,� indicate the uplink channel coefficient between the n-th user and the k-th bs antenna [4]. ��,� � ��,���� (1) corresponding author: ahmed a. alzamil engineering, technology & applied science research vol. 10, no. 5, 2020, 6290-6293 6291 www.etasr.com alzamil: assessment of uplink massive mimo in scattering environment where ��,� and �� denote small scale fading and large-scale fading coefficients respectively. while the large-scale fading coefficients depend on the user’s position, users are assumed to have independent small-scale fading. as a result, the channel matrix is given by : � ��,� … � ,�⋮ ⋱ ⋮��, … ��, � � �� �� (2) therefore: � ���� (3) where: � � ���,� … � ,�⋮ ⋱ ⋮��, … ��, � (4) � � ��� ⋱ ��� (5) therefore, � ∈ � �� represents the uplink received signal which is expressed as: � � √� ! " (6) where � represents the transmit power, ∈ ���� denotes the vector of the uplink transmitted signal from the users, ∈ ���� is the uplink channel matrix in (2) and " ∈ � �� is a gaussian distributed noise vector with zero mean and unit variance. therefore, the n-th user is transmitting the #� sample which represents the n-th element of � $#� … #�%&. in this paper, data symbols needed to form the ofdm blocks are randomly selected from the bpsk alphabet with a normalized energy. while the coefficients of the small scale fading for different users are assumed to be independent and identically distributed, the channel vectors of the users become asymptotically orthogonal when the number of antennas at the bs grows to a very large value [16] and: ' � ����' ��� ( )� (7) where is the transpose conjugate (hermitian) of the channel matrix. the experimental measurements in [17] prove the favorable propagation characteristics of massive mimo which supports the assumption made in (7). therefore, the uplink channel capacity of the massive mimo system is: * � log.det23 ! σ ' 5 � ∑ log.21 !8�9� �:��5 ;<=>'? (8) iii. signal detection data streams which represent the different signals sent by the various users in the massive mimo system must be separated, which can be done by a number of detection techniques. one of these is the maximum likelihood (ml) detector. the problem with this kind of detection is the complexity which grows exponentially as the number of antennas increases. hence, it is not practical for massive mimo [18]. mmse, which is a linear sub-optimal detector, is an alternative with low complexity and is used in this paper. when the number of bs antennas is much larger than the number of users, asymptotic capacity can be achieved using the linear mmse detector. the received uplink mimo signal can be demultiplexed at the bs as: @ � a'� (9) where r is an n×1 vector that contains the data sent by n users and u is the k×n linear detection matrix given in (10) which represents the linear mmse estimator: a � b ' ! cdecf 3g h� (10) where i.� and ij represent the variances of the signal and the noise respectively. iv. system simulation table i shows the parameters that were used to assess the performance of the uplink massive mimo system according to the system model and the signal detection described above. a large number of flat fading channels and bpsk/ofdm realizations are generated when monte-carlo simulation that includes error counting method was exploited. matlab simulation of the uplink bpsk/ofdm block transmission was conducted according the flowchart diagram shown in figure 2. fig. 2. massive mimo flowchart diagram. engineering, technology & applied science research vol. 10, no. 5, 2020, 6290-6293 6292 www.etasr.com alzamil: assessment of uplink massive mimo in scattering environment after setting the system parameters, the random binary data are transformed to parallel data streams. data frames that consist of bpsk symbols go through an ifft with size = 2048 where cyclic prefix size is 128 in order to produce the ofdm modulated signal. this signal goes through the channel which represents the massive mu-mimo n×k as shown in (6). within the massive mu-mimo n×k flat rayleigh fading channel, each path that links the transmitter to the receiver antenna is modeled as an fir filter where the complex coefficient is gaussian with zero mean and unit variance. the received signal is then ofdm demodulated, were the cyclic prefix is removed and fft is applied. mmse detectors separate the received signal into different data streams which are bpsk demodulated. unlike the zero forcing (zf) detector that only minimizes the interference without reducing noise, the linear mmse detector selects the u that minimizes the mean squared error k � l$‖a'� n ‖.% and hence achieves an optimal balance between noise reduction and interference cancelation. however, the computational complexity which results in time complexity, of the mmse linear detectors is o2kn ! kn2 ! n35 [11]. table i. uplink massive mimo simulation parameters parameter specification signal constellation bpsk number frames 1000 bits per frame 10000 ifft size 2048 channel rayleigh fading cyclic prefix 128 equalizer mmse simulation tool matlab v. numerical results and discussion the ber results for various number of users n and a fixed number of bs antennas k=50 are shown in figure 3. it is observed that ber reduces as the number of users increases. the improvement is obvious when the entire eb/no range is considered. this results in a gap in the ber of different numbers of users. fig. 3. ber vs. k=50 for different number of users n. figure 4 shows the ber performance of the same system. however, the number of users n is fixed at 10 while the number of antennas k varies. increasing the number of antennas k at the bs results in enhanced transmission. thus, the ber decreases because the multipath fading and multi-user interference effects are almost eliminated when the number of antennas at the bs is much larger than the number of users: k>>n [19]. one of the advantages of massive mimo is that it provides service to a large number of users at the same time and its performance can be affected by the number of users [17]. the impact of the number of users on the channel capacity is illustrated in figure 5. the simulation results show a positive correlation between the number of users and the capacity of the channel: the uplink channel capacity increases as the number of users increases. therefore, spectral efficiency is proportional to the number of users within the cell in massive mimo systems. fig. 4. ber vs. users n=10 for different number of bs antennas k. fig. 5. uplink capacity for different users n vs bs with k=50. to further study the effect of the number of users on the uplink channel capacity in massive mimo systems, bss with engineering, technology & applied science research vol. 10, no. 5, 2020, 6290-6293 6293 www.etasr.com alzamil: assessment of uplink massive mimo in scattering environment 50 and 100 antennas were considered. the optimal capacities of the system depend on the number of antennas in the bs and the number of the users in the cell as shown in figure 6. when the bs is equipped with k=50 antennas, the capacity gradually grows until 40 active users are reached. after that, it starts degrading as the number of users increases. if the bs is equipped with k=100 antennas, the maximum capacity is around 125bits/s/hz at 64 users. therefore, the bs with a large number of antennas outperforms the one with a smaller number of antennas. different estimation techniques have been used in [9] to investigate the influence of the number of active users on the channel capacity and their results show that channel capacity starts degrading after a certain point. fig. 6. uplink capacity vs. number of users. vi. conclusion massive mimo is a wireless communication technology with many issues and aspects that must be investigated the performance of a massive mimo was studied in this paper. the studied scenario consists of a single cell that contains multiple users served through a single bs where linear detection techniques that process the uplink ofdm transmission were used. the ber results confirm the positive impact of making the number of receive antennas at the bs much larger than the transmit antennas which represent the number of users. hence, increasing the number of antennas in the bs is recommended if the number of users is large. it was shown that massive mimo improves spectral efficiency. it has been shown that the channel capacity increases by increasing the number of users, the number of bs antennas or both. acknowledgment the author would like to thank the deanship of the scientific research at the university of hail in saudi arabia for supporting and funding this project (ba-2009). references [1] a. elsanousi and s. oztürk, “performance analysis of ofdm and ofdm-mimo systems under fading channels,” engineering, technology & applied science research, vol. 8, no. 4, pp. 3249–3254, aug. 2018. 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[19] l. fang, l. xu, and d. d. huang, “low complexity iterative mmsepic detection for medium-size massive mimo,” ieee wireless communications letters, vol. 5, no. 1, pp. 108–111, feb. 2016, doi: 10.1109/lwc.2015.2504366. microsoft word 4-2497_s engineering, technology & applied science research vol. 9, no. 2, 2019, 3892-3895 3892 www.etasr.com alsaidi et al.: content based image clustering technique using statistical features and genetic … content based image clustering technique using statistical features and genetic algorithm bushra kh. alsaidi college of administration and economics, university of baghdad, baghdad, iraq dr.bushraalsaidi14@gmail.com baydaa jaffer al-khafaji computer science department, college of education for pure science/ibn al-haitham, university of baghdad, baghdad, iraq bjkh68@yahoo.com suad abed al wahab ministry of education, baghdad, iraq suaad71computer@yahoo.com abstract—text based-image clustering (tbic) is an insufficient approach for clustering related web images. it is a challenging task to abstract the visual features of images with the support of textual information in a database. in content-based image clustering (cbic), image data are clustered on the foundation of specific features like texture, colors, boundaries, shapes. in this paper, an effective cbic) technique is presented, which uses texture and statistical features of the images. the statistical features or moments of colors (mean, skewness, standard deviation, kurtosis, and variance) are extracted from the images. these features are collected in a one dimension array, and then genetic algorithm (ga) is applied for image clustering. the extraction of features gave a high distinguishability and helped ga reach the solution more accurately and faster. keywords-content based image clustering; statistical feature; genetic algorithm i. introduction content-based image retrieval (cbir) has become a broad field of research with applications in several fields like scientific research, design, industry, medicine and internet [1]. image retrieval started by retrieving images based on texts associated with the images. there are several issues connected with retrieving images based on text such as manual keyword annotation, variations in perceptions, explanations and other issues. as a result, researchers applied cbir where images are retrieved based on auto-derived features [2]. texture and color together with other features like shape, edge and surface play important roles in cbic for their ability of providing significant characteristics for automatic computer based image recognition. texture has appeared in many cbics, while color has been exploited to improve the clustering performance [3]. content based means that the retrieving system will analyze real content instead of metadata like image description, keywords or tags. content refers to the color information and textures that can be detected from the images. many search engines used image retrieval systems entirely dependent on metadata, leading to many erroneous results while the manual placing/editing of image descriptions in big databases is costly and time consuming. for this reason, this paper provides an effective algorithm for cbic using color and texture properties to eliminate the above problems. however, cbir systems face the problem of feature extraction complexity or the high dimensions of feature vectors. these problems made image retrieval results poor in accuracy and response time [4]. the aim of this research is to provide an efficient cbic technique with a one dimensional vector for color and texture properties. images are clustered by using statistical features and texture features of the gray image density rather than a color image because gray density takes less memory space and holds significant image properties. so the proposed technique does not require complex computations for feature extraction. ii. image clustering clustering is the process of assembling data objects in a way that all objects in the same group are similar and differentiating from the objects in other groups. numerous cluster analysis algorithms have been introduced. partition is one of the methods of effective clustering, where the database is divided into groups in an iterative process. clustering can be used to reduce the number of comparisons and improve recovery time when images are searched in a database [5]. image clustering is considered to be a demanding field. one of the most common problems faced by the image clustering algorithms is that there are many types of image representation, and this representation has different distinguish abilities, so it has different effects on clustering methods [6]. the most significant task of any cbic algorithm is feature extraction. when feature space rather than pixels is used, the similarity between stored images can be measured by these features [7]. feature extraction from the visual content of an image plays a significant role in many image processing and pattern recognition applications [8]. one of the significant features is color which plays an important role in cbic because of its strength and independence of image’s orientation and size [3]. a. texture feature extraction texture analysis plays an important role in many applications based on color brightness or local spatial diversity of density. texture analysis is commonly used in image classification, segmentation and retrieval. furthermore, texture feature extraction is the main component of texture analysis. the approaches of texture feature extraction are fractal approaches, statistical methods, and wavelet transform. statistical methods are simple, easy to implement, adaptive, corresponding author: bushra kh. alsaidi engineering, technology & applied science research vol. 9, no. 2, 2019, 3892-3895 3893 www.etasr.com alsaidi et al.: content based image clustering technique using statistical features and genetic … and robust for texture analysis [9]. in this paper entropy filtering and range filtering are utilized and the local standard deviation of the input images is calculated. b. color feature vector extraction in cbic the most commonly used visual feature is color, which is simple to represent and robust. several studies have been proposed to study color perception and color spaces [10]. color moments are utilized to distinguish images and to measure their similarity. the base of color moments is that the color probability distribution in an image can be interpreted by color distribution. if the color in the images has a specific probability distribution, this distribution can be considered as a feature determining that image [7]. before extracting color features, the rgb image is converted into a grayscale image. the grayscale image consists of 8-bit pixels, with values ranging from 0 to 255, unlike the color image which sets a value of 8 bits per red, green and blue color. the benefit from using a grayscale image is that it takes less memory and simplifies the amount of information. after extracting the texture feature, the second step is to extract the value of the color moments (mean, skewness, standard deviation, kurtosis, and variance) from the images. these moments are calculated for each image and are stored in one dimension array. iii. genetic algorithm ga is an effective, powerful and integrated search and adaptation technology. its basic components are: • chromosomes are a problem representation strategy. the candidate solutions for the optimization problem are encoded in a population of chromosomes. • a fitness function is utilized to evaluate each chromosome. in every generation, the individuals are evaluated by the fitness function, and the achievement of reproduction varies with fitness. the important components of the suggested approach are the definition of the fitness function for the problem and its utilization in ga. • selection/reproduction: the selection process copies chromosomes into a new population, according to their fitness values. tournament selection method was used in the proposed algorithm because of its low complexity. the basic notion of the tournament technique is the random choice of a number of individuals from the current population and the copying of the best fitted individuals from them into an intermediate population. • elitism, crossover, and mutation, which are called genetic operators. the central aim of crossover is to randomly exchange information between parent chromosomes by exchanging parts of their genetic information. there are many crossover approaches. in this paper two-point crossover was used. in mutation, random alterations in the chromosome structure are done representing genetic diversity into the population. elitism replaces the worst individuals of the current population with the best individuals of the prior population. iv. the proposed content-based ga the input of the suggested algorithm is a set of images. the output consists of a set of clusters and a set of images in each cluster. there is a group of parameters that should be set by the user. these parameters are the number of chromosomes that represent population size (pop-size), maximum generations (max-gen), mutation rate (p-m) and crossover rate (p-x). the steps of the proposed algorithm are: algorithm: image clustering. input: images to be clustered. tune: set of parameters pop-size, max-gen, p-m and p-x. outputs: the set of images in each cluster. begin: read the feature vector. initiate the population. for i=1 to pop-size create individual. calculate fitness function for the initial population. current population = initial population. while generation number less than max-gen do do elitism. select the parents of the next generation by tournament algorithm. generate the offsprings by crossover. mutate offsprings. calculate fitness function for the new population (offsrings). do elitism. current population = new population. output: the current population, its fitness and the set of images covered by each individual in the population. v. population representation and initialization ga works on a number of candidate solutions, called population, and contains multiple coding for the parameter specified at the same time [11]. to resolve image clustering, the population was started using 50 chromosomes of equal length in two different ways: a. first method to iinitiate population this method to initiate the population was proposed to avoid the bias of the algorithm for some images. the steps of the method, applied to each individual in the population are: • generate a random image number. this number must be smaller than the total number of images in the data set. • select the mean for the image with the random number generated in the previous step as the mean value of the candidate cluster. • generate another random image number. • select the standard deviation of this image as the standard deviation value of the candidate cluster. • generate another random image number. • chose the skewness of this image as the skewness value of the candidate cluster. • generate another random image number. engineering, technology & applied science research vol. 9, no. 2, 2019, 3892-3895 3894 www.etasr.com alsaidi et al.: content based image clustering technique using statistical features and genetic … • chose the kurtosis of this image as the kurtosis value of the candidate cluster. • generate another random image number. • chose the variance of this image as the variance value of the candidate cluster. • repeat the above steps until the pop-size is reached. after these steps are finished the population has been initialized. table i shows a snapshot of the initial population. each row of the table represents a candidate cluster that will be evaluated by the fitness function. the candidate cluster has 5 statistical features of the image (mean, slandered deviation, skewness, kurtosis, and variance). images that achieve a minimum manhattan distance with the candidate cluster will be allocated to this cluster. the fitness function of this individual or candidate cluster will be the number of images that have a minimum manhattan distance from it. table i. snapshot of the initial population mean std. skewness kurtosis var. 6.5398 11.622 13.0082 135.079 2.9488 12.6480 19.6358 5.2894 385.5637 1.7636 5.2544 6.5685 14.2042 43.1454 2.7611 7.4712 7.0551 7.9771 49.7747 1.6558 7.3502 10.7057 11.9982 114.6126 2.7449 4.7325 6.1222 8.9581 37.4817 2.1233 4.5854 5.5170 9.0047 30.4373 2.1259 3.4846 3.9387 10.2564 15.5134 2.2339 7.7545 7.3939 7.8977 54.6694 1.9488 63.8923 5.398 20.3111 29.1445 3.2706 6.0577 6.6078 9.9426 43.6630 2.2871 13.6771 9.5359 5.3893 90.9343 1.2311 12.4672 11.6368 11.0113 135.4144 2.3422 8.9082 8.0444 4.8876 64.7128 1.2228 b. second method to initiate population this method to initiate the population is proposed in order to exploit some of the prior knowledge contained in the set of images through which the speed of converging can be increased. the steps of the method, applied to each individual in the population are: • chose a random image number. • chose the feature vector of the image with the number generated in the first step from the feature vectors resulted from the feature extraction process. • repeat the above steps until the pop-size is reached. after these steps are completed, the population has been initialized (see table ii for a snapshot). vi. experimental results and discussion the experimental part of the suggested method was conducted on a set of images form the internet, a total of 1000 images were obtained. the data collection includes images of nature divided into 8 groups: birds, trees, forests, birds in the sky, coast, birds above the sea, and trees on the coast. all database images were resized to 180x180 resolution in the preprocessing step. then, images were converted to grayscale. after these steps, the feature extraction phase began then the ga has been applied. figure 1 shows examples of clusters presented by the proposed algorithm. table ii. snapshot of the initial population var. kurtosis skewness std. mean 1.9745 113.009 8.2814 10.630 8.474 1.7096 83.4892 8.2324 9.137 10.037 4.5214 27.4369 32.386 5.238 2.8662 6.4893 43.7347 57.220 6.613 2.592 1.6579 151.972 6.4979 12.327 17.473 1.4637 109.755 5.8171 10.476 12.557 3.0411 77.6918 16.064 8.814 9.594 1.8909 78.5613 10.197 8.863 13.699 1.4843 84.9521 6.1317 9.216 12.279 2.7077 43.3473 11.271 6.5839 3.689 2.6535 45.4687 15.526 6.743 6.997 2.0876 112.6048 8.1856 10.611 9.883 2.8186 64.5583 14.871 8.034 6.388 2.0691 90.2652 7.7772 9.50 6.968 1.8907 23.6883 9.4987 4.8671 6.974 1.3296 198.0311 4.8165 14.072 13.943 fig. 1. examples of clusters presented by the proposed algorithm. the experiments first studied the parameter sensitivity. one important parameter is population size. the study of the relation between the number of clusters presented by the proposed method and the size of the population showed that increasing population size leads to an increase in the number of clusters and a reduction in the number of images assigned to each cluster. therefore, determining the best size of the engineering, technology & applied science research vol. 9, no. 2, 2019, 3892-3895 3895 www.etasr.com alsaidi et al.: content based image clustering technique using statistical features and genetic … population depends on the size of the image data set and the number of clusters detected in the data set. table iii shows the effect of population size on the number of clusters and the number of images in each cluster. table iii. effect of population size on the number of clusters and the number of images in each cluster. experiment no. 5 4 3 2 1 no. of clusters images in cluster images in cluster images in cluster images in cluster images in cluster 14 1 8 17 4 1 54 28 20 5 2 2 3 4 5 3 18 3 28 11 27 9 6 4 31 38 25 22 4 5 9 12 2 6 6 19 16 2 2 7 9 9 6 1 8 11 4 2 8 9 1 4 0 0 10 28 8 12 4 11 4 20 6 16 12 11 5 7 1 13 38 27 1 7 14 4 1 15 19 4 16 5 6 17 3 18 1 19 4 20 4 21 8 22 2 23 6 24 4 25 1 26 7 27 4 28 fig. 2. performance evaluation of the proposed algorithm for first and second initialization method the second idea, which was studied through the experiments, is the effect of the method of population initialization on the performance of the algorithm. the performance of the algorithm was measured using precision and recall. the results showed that the second method, which exploits prior knowledge, improved the performance of the algorithm and reduced image clustering time. figure 2 shows the comparison of the performance of the algorithm using the above mentioned two different methods of population initialization. feature extraction method and similarity measurement are two main steps in image clustering [2]. in this paper, we tried several methods for the fitness function and manhattan distance showed the best results. vii. conclusion in the subject of image retrieval and image clustering, image feature extraction is a great challenge for the researcher. this paper presented a ga-based image clustering method using texture and statistical features. experimental results showed high distinguishability of these features. the main advantage of the proposed algorithm is that it does not need the class label to be provided, the image set has not need to be labeled first. also, the proposed extraction method reduces the feature vector dimension and improves the efficiency of the clustering method. references [1] n. ghosh, s. agrawal, m. motwani, “a survey of feature extraction for content-based image retrieval system”, lecture notes in networks and systems, vol. 34, pp. 305-313, springer, 2018 [2] j. wang, l. wang, x. liu, y. ren, y. yuan, “color-based image retrieval using proximity space theory”, algorithms, vol. 11, no. 8, articleid 115, 2018 [3] m. pham, g. mercier, l. bombru, “color texture image retrieval based on local extrema features and riemannian distance”, journal of imaging, vol. 3, no. 4, articleid 43,2017 [4] k. kumar, zain-ul-abidin, j. p. li, r. a. shaikh, “content based image retrieval using gray scale weighted average method”, international journal of advanced computer science and applications, vol. 7, no. 1, pp. 1-6, 2016 [5] e. m. f. el houby, “medical images retrieval using clustering technique”, international journal on recent and innovation trends in computing and communication, vol. 3, no. 5, pp. 3134-3141, 2015 [6] t. peng, h. gao, “a cluster priority level decision method for image features”, international journal of database theory and application, vol. 9, no. 2, pp. 171-182, 2016 [7] a. malakar, j. mukherjee, “image clustering using color moments, histogram, edge and k-means clustering”, international journal of science and research, vol. 2, no. 1, pp. 532-537, 2013 [8] a. obulesu, v. v. kumar, l. sumalatha, “content based image retrieval using multi motif co-occurrence matrix”, international journal of image, graphics and signal processing, vol. 4, pp. 59-72, 2018 [9] x. zhang, j. cui, w. wang, c. lin,”a study for texture feature extraction of high-resolution satellite images based on a direction measure and gray level co-occurrence matrix fusion algorithm”, sensors, vol. 17, no. 7, articleid 1474, 2017 [10] s. soman, m. ghorpade, v. sonone, s. chavan, “content based image retrieval using advanced color and texture features”, international conference in computational intelligence, guangzhou, china, november 17-18, 2012 [11] b. k. alsaidi, “automatic approach for word sense disambiguation using genetic algorithms”, international journal of advanced computer science and applications, vol. 7, no. 1, pp. 41-44, 2016 microsoft word etasr_v11_n5_pp7551-7557 engineering, technology & applied science research vol. 11, no. 5, 2021, 7551-7557 7551 www.etasr.com khanh & cuong: parameter selection to ensure multi-criteria optimization of the taguchi method … parameter selection to ensure multi-criteria optimization of the taguchi method combined with the data envelopment analysis-based ranking method when milling scm440 steel nguyen lam khanh faculty of mechanical engineering university of transport and communications hanoi, vietnam khanh_mxd@utc.edu.vn nguyen van cuong faculty of mechanical engineering university of transport and communications hanoi, vietnam nguyencuong@utc.edu.vn abstract-scm440 steel is a commonly used material for making plastic injection molds and components such as gears, transmission shafts, rolling pins, etc. surface roughness has a direct influence on the workability and durability of the parts and/or components, while the material removal rate (mrr) is a parameter that is used to evaluate the productivity of the machining process. furnished products with small surface roughness and large mrr is the desired result by all milling processes. in this paper, the determination of the values of input parameters is studied in order to ensure that during the process of milling scm440 steel, it will have the smallest surface roughness and the largest mrr. there are five parameters that are required to be determined, namely the cutting insert material, the tool nose radius, the cutting speed, the feed rate, and the cutting depth. the taguchi method was applied to design the experimental matrix with a total of 27 experiments. result analysis determined the influence of the input parameters on surface roughness and mrr. the data envelopment analysisbased ranking (dear) method was applied to determine the optimal value of the input parameters, which were used to conduct the milling experiments to re-evaluate their suitability. keywords-milling; scm440 steel; surface roughness; mrr; optimization; taguchi; dear i. introduction milling is a very common machining method in the mechanical engineering industry. it is considered to be the cutting method with the highest productivity. with the development of the cutting tool manufacturing technology as well as the emergence of the modern cnc machines, this method is capable of ensuring very high accuracy. research of solutions that improve the accuracy of milling machines and milling cutters is continuously conducted [1]. therefore, in some cases, this method is used as the final machining method for surfaces requiring high precision [2]. to make the most use of the achievements in the mechanical engineering technology and the cutting tool manufacturing technology, many researchers carried out experimental studies to determine the optimal value of parameters related to the machining process. the purpose of these studies is to determine the value of the machining process’s parameters to ensure minimum surface roughness and maximum material removal rate (mrr). this problem is known as milling operations optimization. when studying the milling operations optimization, many authors used the taguchi method to design the experimental matrix. when comparing the taguchi-based matrix design method with some other matrix design methods, it was found that the taguchi method requires a smaller number of experiments. an advantage that only the taguchi method possesses is that it can design a matrix with the input parameters being a qualitative (not a quantitative) parameter [3, 4]. in [5], the taguchi method was applied to design the experimental matrix when milling the aa6082t6 material by a tungsten carbide cutting tool. signal-to-noise (s/n) ratio was analyzed to determine the optimal values of spindle speed, feed rate, and depth of cut to ensure the minimum value of surface roughness. the taguchi method was also used to design the experimental matrix when milling aa6082t6 with pvdcoated and cvd-coated cutting tools. the determination of cutting speed, feed rate, and tool material type to ensure tool wear was similarly performed for surface roughness in [6]. in [7], the authors applied the taguchi method to design the experimental matrix when milling d2 steel with the carbide inserts cutting tool. cutting parameters including spindle speed, feed rate, and depth of cut were selected as input parameters for each experiment. the s/n ratio analysis method was applied to determine the optimal value of the cutting parameters to ensure the minimum value of surface roughness. when milling aisi p20 steel with the carbide inserts cutting tool, the authors in [8] used the taguchi method to design an experimental matrix with spindle speed, feed rate, and depth of cut as input parameters [8]. they also used s/n ratio analysis to determine the optimal value of the input parameters to ensure the minimum value of surface roughness. to determine the optimal value of parameters including cutting speed, feed, radial depth, and axial depth to ensure the minimum value of surface roughness when milling 1.2738 steel with the wnhu 04t310 cutting tool corresponding author: nguyen van cuong engineering, technology & applied science research vol. 11, no. 5, 2021, 7551-7557 7552 www.etasr.com khanh & cuong: parameter selection to ensure multi-criteria optimization of the taguchi method … (manufactured by palbit), the authors in [9] also applied the taguchi method to design the experimental matrix. the s/n ratio analysis method was applied to determine the optimal value of the cutting parameters. authors in [10] also designed the experimental matrix according to the taguchi method when milling 7075t6 aluminum alloy with an altin pvd-coated cutting tool. the optimal values of cutting speed, feed rate, radial depth, and axial depth were also determined by the analysis of the s/n ratio. this study also aimed to ensure the minimum value of surface roughness. to determine the optimum value of cutting speed, feed rate, depth of cut, and coolant flow to ensure the minimum value of surface roughness when milling aisi 1040 ms steel with the carbide inserts cutting tool, the authors in [11] also designed the experimental matrix according to the taguchi method and the s/n ratio analysis method was also used to determine the optimal value of the input parameters. authors in [12] also designed the experimental matrix according to the taguchi method when milling 7075 t6 aluminum alloy with a high-speed steel (hss) cutting tool. they also applied the s/n ratio analysis method to determine two sets of optimal values of cutting speed, feed rate, and depth of cut, one set that ensures the smallest surface roughness and another set that ensures the largest mrr. the experimental matrix design based on the taguchi method has been successfully applied in a number of studies to ensure a certain criterion of the machining process. however, if only the taguchi method is applied for the experimental design and the s/n ratio analysis to determine the optimal value of the machining process parameters, only one criterion of the machining process can be guaranteed. in order to resolve this shortcoming of the taguchi method, many studies combined the taguchi method with other methods to optimize the multiobjectives of the milling process: in [13], the taguchi method has been combined with anova to determine the values of the spindle speed, the feed rate and the cutting depth to ensure the minimum surface roughness and the maximum mrr when milling aisi 1005 steel with the tin coated cutting tool. in [14], the taguchi method and the weighted principal component analysis (wpca) were combined to determine the milling type and the values of milling parameters to simultaneously ensure minimum surface roughness and maximum mrr when milling al 6061 aluminum alloy with a high speed steel cutting tool. the taguchi method and the gray relational analysis (gra) method were combined to determine the values of cutting speed, feed rate, and cutting depth to ensure simultaneously minimum surface roughness and maximum mrr when milling inconel 718 super alloy by an uncoated tungsten carbide cutting tool in [15]. a combination of the taguchi method, topsis method, and anova analysis was performed to determine the optimal values of cutting speed, feed rate, and depth of cut to ensure simultaneously the minimum value of surface roughness and maximum value of mrr when milling ti-6al-4v titanium alloy with tin coated cutting tools in [16]. through the above studies, it is shown that the cutting tool parameters are commonly selected as the input parameters of the milling experiment process. these parameters can be easily adjusted by the operators. however, to the best of our knowledge, there have been no studies that consider all the 5 parameters of the cutting tool material, i.e. the insert material, the tool nose radius, the cutting speed, the feed rate, and the depth of cut. scm440 steel is a type of steel used quite commonly to make plastic injection molds and components such as gears, transmission shafts, and rolling pins [17]. due to the high content of cr, mo and mn elements, this steel has a low thermal conductivity. when machining this steel, the tool wears out quickly, thus it is required to select the right cutting tool [18-20]. a number of studies on milling steels equivalent to this steel have been carried out [17-23]. however, to the best of our knowledge, there are no published studies on milling scm440 (or equivalent) steel that consider all 5 parameters. dear is a method used for multi-criteria decision making that was introduced in 2002 [24]. this method has been used for the multi-objective optimization of the aisi 1055 steel turning process [25], the ti-6al-4v alloy turning process [26], the sae420 steel grinding with a segmented grinding wheel [27], of the electrical discharge machining (edm) with the material type aa 6082 [26], etc. however, to the best of our knowledge, there have been no published studies on the application of this method in multi-criteria decision making for milling methods in general and for milling scm440 steel in particular. in this study, milling parameters such as the cutting tool material, the tool nose radius, the cutting speed, the feed rate, and the cutting depth will be determined to simultaneously ensure the optimization of two criteria, minimum surface roughness and maximum mrr when milling this type of steel. a combination of the taguchi method and the dear method was used to solve this problem. ii. the dear method the purpose of the experimental process of this study is to ensure that surface roughness (ra) has the smallest value and the mrr reaches the maximum value. thus, it is required to determine the values of the input parameters that ensure the set out objectives. the dear method will be applied in this study to carry out the above-stated work [24]. the dear method's steps are [24]: • determine the weight of each response for all experiments. this value is calculated as the ratio of the value of each response to the sum of all responses. • transfer the response data to the weight data by multiplying the observed data by their respective weight. • divide the inversed data by the sum of all inversed data. • the multi response performance index (mrpi) is calculated by (1): ���� = �� ∗ �� + � �� ∗ ��� (1) the weights of the responses are calculated as: �� = � ∑� (2) � �� = � ��� ∑ � ��� (3) engineering, technology & applied science research vol. 11, no. 5, 2021, 7551-7557 7553 www.etasr.com khanh & cuong: parameter selection to ensure multi-criteria optimization of the taguchi method … iii. experiments on milling scm400 steel a. experimental system a cnc milling machine with the haa5 serial was used to carry out the experiments (figure 1). the experimental sample is scm400 steel with length, width, and height of 80mm, 40mm, and 30mm respectively. the steel’s chemical composition conducted with a spectrometer was: 0.43% c, 0.28% si, 0.72% mn, 1.05% cr, 0.23% mo, 0.024% p, and 0.026% s. fig. 1. the milling machine. table i. parameters of the cutting inserts parameter cutting insert r39011t303m -pm1025 r39011t305mpm1025 r39011t305m -pm1025 tool nose radius (mm) 0.3 0.5 0.8 back edge length (mm) 0.8 0.9 1.2 weight (kg) 0.0022 0.0026 0.003 coating material tin; ticn; tialn cutting thickness (mm) 3.59 main cutting angle (degree) 90 maximum cutting depth (mm) 10 shape style of cutting piece l edge width (mm) 6.8 effective length of edge (mm) 10 three types of cutting pieces were used in the experiment namely the tin-, ticn-, and tialn-coated pieces. these cutting pieces have high thermal resistance, and have been proven to be very suitable for machining scm440 steel. each cutting piece was used with 3 tool nose radius values of 0.3mm, 0.5mm, and 0.8mm. on the tool shank with 12mm diameter, 2 symmetrical cutting pieces were installed. each cutting insert was used only once for the purpose of eliminating the influence of tool wear on the output parameters of the milling process. in other words, the number of cutting inserts used in the experiment is twice the number of experiments to be carried out. the milling process has been carried out according to the method of symmetric milling, which means that the milling width was equal to the diameter of the milling cutter. table i shows some basic parameters of the cutting inserts used. the surface roughness was measured with a mitutoyo japan sj301 surface roughness tester of 0.8mm standard length. the surface roughness of each experimental sample was determined by averaging at least three consecutive measurements. the mrr was calculated according to: ��� = �� ∙ �� ∙ �� (mm 3/min) (4) where �� is the feed rate (mm/min), �� is the cutting depth (mm), and �� is the cutting width (mm). in this case the cutting width is just equal to the diameter of the milling cutter. b. experimental design the taguchi method was applied to design the experimental process in this study. five parameters were selected as the input parameters of the experimental process,. each selected parameter has three levels of values (corresponding to three encoding degrees of 1, 2, and 3). the values of the experimental parameters, selected within their range as recommended by the cutting tool manufacturer [29], are shown in table ii. table ii. input parameters parameter symbol unit value at level 1 2 3 insert material im tin ticn tialn tool nose radius r mm 0.3 0.5 0.8 cutting speed vc m/min 80 120 160 feed rate vf mm/min 250 320 390 depth of cut ap mm 0.20 0.30 0.40 the taguchi method was used to design the experimental matrix. when comparing the matrix design method by the taguchi method with some other matrix design methods, it can be found that it requires a smaller number of experiments. for example, with 5 input parameters, in which each parameter has 3 levels of values, the taguchi method only needs 27 experiments while the box-behnken design needs at least 46 experiments and the central composite design (ccd) method needs a minimum of 43 experiments. an advantage that only the taguchi method obtains is that it allows designing the experimental matrix with input parameters that are not quantitative parameters. in this case the qualitative parameter is just the cutting insert material type. so, the experimental matrix was designed according to the taguchi method with a total of 27 experiments, as shown in table iii. iv. results and discussion the experiments in table iii are given in accordance with the results shown in table iv. figure 2 shows the influence of the input parameters on surface roughness. the comparison of the difference at the lowest and highest levels, i.e. between level 1 and level 3 of the parameter line graph (red broken line) shows that the tool nose radius is the parameter that has the greatest influence on surface roughness, followed by the influence of the cutting insert material and the feed rate. the difference of the line graph of cutting speed and cutting depth is very small, showing that these two parameters have negligible influence on surface roughness. engineering, technology & applied science research vol. 11, no. 5, 2021, 7551-7557 7554 www.etasr.com khanh & cuong: parameter selection to ensure multi-criteria optimization of the taguchi method … table iii. experimental matrix no. code value actual value im r vc vf ap im r (mm) vc (m/min) vf (mm/min) ap (mm) 1 1 1 1 1 1 tin 0.3 80 250 0.2 2 1 1 1 1 2 tin 0.3 80 250 0.4 3 1 1 1 1 3 tin 0.3 80 250 0.6 4 1 2 2 2 1 tin 0.5 120 320 0.2 5 1 2 2 2 2 tin 0.5 120 320 0.4 6 1 2 2 2 3 tin 0.5 120 320 0.6 7 1 3 3 3 1 tin 0.8 160 390 0.2 8 1 3 3 3 2 tin 0.8 160 390 0.4 9 1 3 3 3 3 tin 0.8 160 390 0.6 10 2 1 2 3 1 ticn 0.3 120 390 0.2 11 2 1 2 3 2 ticn 0.3 120 390 0.4 12 2 1 2 3 3 ticn 0.3 120 390 0.6 13 2 2 3 1 1 ticn 0.5 160 250 0.2 14 2 2 3 1 2 ticn 0.5 160 250 0.4 15 2 2 3 1 3 ticn 0.5 160 250 0.6 16 2 3 1 2 1 ticn 0.8 80 320 0.2 17 2 3 1 2 2 ticn 0.8 80 320 0.4 18 2 3 1 2 3 ticn 0.8 80 320 0.6 19 3 1 3 2 1 tialn 0.3 160 320 0.2 20 3 1 3 2 2 tialn 0.3 160 320 0.4 21 3 1 3 2 3 tialn 0.3 160 320 0.6 22 3 2 1 3 1 tialn 0.5 80 390 0.2 23 3 2 1 3 2 tialn 0.5 80 390 0.4 24 3 2 1 3 3 tialn 0.5 80 390 0.6 25 3 3 2 1 1 tialn 0.8 120 250 0.2 26 3 3 2 1 2 tialn 0.8 120 250 0.4 27 3 3 2 1 3 tialn 0.8 120 250 0.6 table iv. experimental results no im r (mm) vc (m/min) vf (mm/min) ap (mm) ra (µm) mrr (mm 3 /min) 1 tin 0.3 80 250 0.2 0.771 600 2 tin 0.3 80 250 0.4 1.457 1200 3 tin 0.3 80 250 0.6 1.697 1800 4 tin 0.5 120 320 0.2 1.538 768 5 tin 0.5 120 320 0.4 0.905 1536 6 tin 0.5 120 320 0.6 0.986 2304 7 tin 0.8 160 390 0.2 2.205 936 8 tin 0.8 160 390 0.4 1.582 1872 9 tin 0.8 160 390 0.6 0.863 2808 10 ticn 0.3 120 390 0.2 1.024 936 11 ticn 0.3 120 390 0.4 1.112 1872 12 ticn 0.3 120 390 0.6 0.801 2808 13 ticn 0.5 160 250 0.2 1.076 600 14 ticn 0.5 160 250 0.4 2.908 1200 15 ticn 0.5 160 250 0.6 1.014 1800 16 ticn 0.8 80 320 0.2 0.985 768 17 ticn 0.8 80 320 0.4 3.019 1536 18 ticn 0.8 80 320 0.6 1.549 2304 19 tialn 0.3 160 320 0.2 0.927 768 20 tialn 0.3 160 320 0.4 0.877 1536 21 tialn 0.3 160 320 0.6 0.892 2304 22 tialn 0.5 80 390 0.2 1.234 936 23 tialn 0.5 80 390 0.4 1.929 1872 24 tialn 0.5 80 390 0.6 0.824 2808 25 tialn 0.8 120 250 0.2 0.545 600 26 tialn 0.8 120 250 0.4 1.549 1200 27 tialn 0.8 120 250 0.6 1.601 1800 because the cutting insert material, the tool nose radius and the cutting speed do not exist in the mrr calculation formula (4), they have no influence on mrr. figure 3 shows the influence of the feed rate and the cutting depth on mrr. the difference between level 1 and level 3 of cutting depth line graph is greater than the one of the feed rate line graph. this engineering, technology & applied science research vol. 11, no. 5, 2021, 7551-7557 7555 www.etasr.com khanh & cuong: parameter selection to ensure multi-criteria optimization of the taguchi method … shows that the cutting depth has a greater influence on mrr than the feed rate. thus, we see that the influence of the input parameters on surface roughness and mrr is different, even adverse, e.g. the tool nose radius has a great influence on surface roughness without any influence on mrr, the feed rate and the cutting depth are two parameters needed for calculating the mrr, but they do not significantly affect surface roughness, etc. thus, it can be said that being based only on the two graphs of figures 2 and 3, limits the determination of the values of the input parameters to ensure minimum surface roughness and maximum mrr. table iv shows that surface roughness has the smallest value in experiment #25, while mrr has the maximum value in experiments #9, #12 and #24. thus, if we only observe table iv, it is not possible to determine the value of the input parameters to ensure both minimum surface roughness and maximum mrr. the dear method will be used to solve this problem in the next section. fig. 2. main effect plot for surface roughness. fig. 3. main effect plot for mrr. v. selection of the value of the input parameters from the experimental data in table iv, the weights of the responses and the mrpi value at each experiment are calculated according to (1) (3), as shown in table v. from the data in table v, the mrpi values of all input parameters at all degrees were calculated. this value is calculated as the sum of the mrpi value of each parameter at the respective degree, as shown in table vi. from the data in table vi, it can be seen that the cutting insert material (im) has the smallest value of mrpi corresponding to level 3, tool nose radius (r) has the smallest value of mrpi corresponding to level 1, cutting speed (��) corresponding to level 2, and feed rate (��) and cutting depth (��) corresponding to level 3. thus, the optimal value of the parameters of the cutting insert material, the tool nose radius, the cutting speed, the feed rate, and the cutting depth are tialn, 0.3mm, 120m/min, 390mm/min, and 0.6mm respectively [24]. the mrpi value with the maximum maxmin of 0.52972 is the cutting depth. thus, the cutting depth is the parameter that has the greatest influence, followed by the tool nose radius, the cutting insert material, the cutting speed, and the feed rate [24]. table v. experimental response weight and mrpi no. ��� ���� mrpi 1 0.02168 0.07506 45.05364 2 0.04096 0.03753 45.09661 3 0.04771 0.02502 45.11789 4 0.04324 0.05864 45.10343 5 0.02544 0.02932 45.05996 6 0.02772 0.01955 45.06426 7 0.06199 0.04812 45.17362 8 0.04448 0.02406 45.10729 9 0.02426 0.01604 45.05787 10 0.02879 0.04812 45.06641 11 0.03126 0.02406 45.07169 12 0.02252 0.01604 45.05497 13 0.03025 0.07506 45.06948 14 0.08175 0.03753 45.27467 15 0.02851 0.02502 45.06584 16 0.02769 0.05864 45.06421 17 0.08487 0.02932 45.29317 18 0.04355 0.01955 45.10439 19 0.02606 0.05864 45.06109 20 0.02466 0.02932 45.05855 21 0.02508 0.01955 45.05930 22 0.03469 0.04812 45.07974 23 0.05423 0.02406 45.14154 24 0.01473 0.01604 45.04465 25 0.01532 0.07506 45.04528 26 0.04355 0.03753 45.10439 27 0.04501 0.02502 45.10899 table vi. total mrpi parameter level max min 1 2 3 im 405.83457 406.06482 405.70353 0.36129 r 405.64016 405.90357 406.05920 0.41904 vc 405.99584 405.67938 405.92771 0.31646 vf 405.93679 405.86835 405.79778 0.13901 ap 405.71690 406.20787 405.67815 0.52972 vi. experiments with the optimal values of the parameters the optimal set of the 5 input parameters defined above was used to experiment on the milling process with 3 steel samples. the surface roughness of each experimental sample is shown in table vii. the mrr value at each experiment has also been calculated and is included in this table. the average value of surface roughness in these cases is 0.724µm. if compared with the surface roughness values in table iv, it can be seen that although 0.724µm is still larger than the value of surface roughness at experiment #25, this value is very small engineering, technology & applied science research vol. 11, no. 5, 2021, 7551-7557 7556 www.etasr.com khanh & cuong: parameter selection to ensure multi-criteria optimization of the taguchi method … when compared to the total of 27 experiments that were carried out. for mrr, when calculated according to (4), in the three test samples, the mrr is equal to 2808mm3/min, which is also larger than the data in table iv. from that, it can be seen that when machining with the optimal values of the input parameters, mrr reaches its maximum value and surface roughness is also significantly improved. this result ensures the reliability when using the optimal value of the input parameters and proves the success in using the dear method in this study. table vii. output parameters when experimenting with the optimal values of the input parameters no. optimization value ra (µµµµm) mrr (mm 3 /min) im r (mm) vc (m/min) vf (mm/min) ap (mm) 1 tialn 0.3 120 390 0.6 0.726 2808 2 0.721 2808 3 0.725 2808 mean 0.724 2808 vii. conclusion an experimental process of milling scm 440 steel was carried out in this study. three types of cutting inserts were used, coated with tin, ticn, and tialn. the tool nose radius, the cutting speed, the feed rate, and the cutting depth were also determined as input parameters of the experimental process. the dear method was applied to determine the optimal value of the input parameters. some of the conclusions drawn from this study are: • the tool nose radius is the parameter that has the greatest influence on surface roughness, followed by the influence of the cutting insert material and the feed rate. the cutting speed and the cutting depth have no significant influence on surface roughness. • only the feed rate and the cutting depth have an influence on mrr, and the influence of the cutting depth on mrr is greater than the one of the feed rate. • the parameter set that ensures simultaneously the two objectives is: tialn cutting insert material, 0.3mm tool nose radius, 120mm/min cutting speed, 390mm/min feed rate, and 0.6mm cutting depth. • dear method was not only successful in determining the optimal values of the input parameters in this study as well as in [25-28] but it is also quite promising to being successful in the future when applied to determine the value of input parameters to simultaneously ensure multi-criteria optimization of the machining process. acknowledgment this research is funded by university of transport and communications (utc) under the grant number t2021-ck003. references j. p. hung, k. d. wu, w. z. lin, and w. c. shih, "analyzing the [1] dynamic characteristics of milling tool using finite element method and receptance coupling method," engineering, technology & applied science research, vol. 9, no. 2, pp. 3918-3923, apr. 2019, https://doi.org/10.48084/etasr.2463. d. d. trung, "influence of cutting parameters on surface roughness [2] during milling aisi 1045 steel", tribology in industry, vol. 42, no. 4, pp. 658-665, dec. 2020, https://doi.org/10.24874/ti.969.09.20.11. m. s. phadke, quality engineering using robust design, printice hall, [3] 1989. s. k. karna, r. v. 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"sandvik coromant manufacturing tools & machining solutions," [29] sandvik coromant. https://www.sandvik.coromant.com/en-gb/pages/ default.aspx (accessed aug. 18, 2021). microsoft word 01-3231_s_etasr_v10_n1_pp5099-5103 engineering, technology & applied science research vol. 10, no. 1, 2020, 5099-5103 5099 www.etasr.com tran & nguyen: reliability assessment of steel plane frame's buckling strength considering … reliability assessment of steel plane frame's buckling strength considering semi-rigid connections ngoc long tran department of civil engineering vinh university, vinh, vietnam longtn@vinhuni.edu.vn trong ha nguyen department of civil engineering vinh university, vinh, vietnam trongha@vinhuni.edu.vn abstract—the buckling strength of a structure depends hugely on material properties, geometry dimensions, and boundary conditions that are potentially random. this paper presents an assessment of the safety of buckling strength of steel plane frame semi-rigid beam-column connections. the newton-raphson method is used to solve the nonlinear equation for the buckling limit of the column. the reliability of the structure is evaluated by the monte carlo simulation method. the effects of input parameters are also investigated. keywords-plane frames steel; semi-rigid connection; reliability; monte carlo simulation i. introduction the analysis of steel frame with semi-rigid connections is always an interesting research topic. straight-line common beam method was used to classify semi-rigid connection in [1]. authors in [2] considered the stiffness of the connection in the research on the moment distribution method. author in [3] investigated the influence of semi-rigid connections on the frame subjecting to shake. research and application of the stiffness matrix method to analyze the plane frame with semirigid connections, in which the stiffness matrix and nodal force vector of each element depend on the linear stiffness of the connection, was conducted in [4]. a novel method to analyze the spatial frame considering the material nonlinearity and large deflection effect was presented in [5]. linear and nonlinear semi-rigid connection models have been presented in [6]. there are many studies about buckling analysis of steel structures considering semi-rigid connection, like the in-plane buckling behavior of pitched-roof steel frames with semi-rigid connections and elastic buckling [7], second-order behavior of pitched-roof steel frames [8], and the buckling analysis of nonprismatic columns using slope-deflection method [9]. the buckling and post-buckling behavior of gabled frames was studied in [10]. stability analysis of semi-rigid composite frames has been studied in [11]. stiffness analysis on semirigid joints in gabled frames was studied in [12], and the elastic buckling of end-loaded, tapered, cantilevered beams with initial curvature in [13]. in this research, buckling analysis of steel gabled frames with tapered members and flexible connections was used. concerning the reliability assessment of the structure, authors in [14] assessed the reliability of steel frame under dynamic loads generated from the el centro earthquake in 1940 using the β probability index method. the same method was used in [15] to study the steel frame according to the plastic limit state. the reliability of the steel structure under corrosion was studied in [16]. the monte carlo simulation method to investigate steel frame with flexible beam-column joint was utilized in [6]. rotational stiffness and momentresisting of the connection were referred in [17]. this model of flexible joint is not correct [18]. instead a novel model based on empirical tests and eurocode-3 was proposed. this paper performs reliability assessment of the buckling strength for steel plane frame considering semi-rigid connections. an algorithm using monte carlo simulation is proposed to be used in analysis and assessment. in addition, the effects of input parameters, which are safety factor and coefficient of variation, on the reliability of structures have been examined. ii. theoretical framework a. stiffness of the beam-column joint the rotational stiffness of flexible beam-column joint of an i-section steel portal frame is determined by the experimental formula proposed in [18]: ini ϕ ϕ η = (1) where ϕ is the elastic rotational stiffness of the joint (knm/rad), η is the hardness adjustment coefficient depending on the connection type and presented in eurocode-3, ini ϕ is the initial stiffness (knm/rad) determined as [18]: 0.44 1.2 0.35 0.005 1 2ini c b p k h h t d kϕ = − (2) where c h (mm) is the height of the column section (heb), b h (mm) is the height of the beam section (ipe), p t (mm) is the thickness of the end plate, and d (mm) is the bolt diameter, corresponding author: trong ha nguyen engineering, technology & applied science research vol. 10, no. 1, 2020, 5099-5103 5100 www.etasr.com tran & nguyen: reliability assessment of steel plane frame's buckling strength considering … and k1=1.5 and k2=19211 are empirical coefficients from the experimental results in [18]. because of their empirical origin, these coefficients possess potential randomness. b. monte carlo simulation method monte carlo simulation method is based on the use of pseudo-random numbers and the law of large number to assess the reliability of any system. if the safe domain is defined by the condition ( ) 0,f >x where x is a random vector containing all the input random variables, the unsafe probability of the system is determined by: ( ) ( ) ( )xx 0 x 0f f fp i f x dx e i< < = =  ∫ (3) where ( )x 0fi < is the indicator function defined by: ( ) ( ) ( )x 0 1 if x 0 0 if x 0 f f i f < < =  ≥ (4) according to the theory of statistics, if we have n realizations of the random vector ,x by propagating the randomness, we obtain a sample of n realizations of the indicator function. the expected value of the indicator function can be approximatively determined by taking the mean of the samples: ( ) ( )x 0 x 0 1 1 n i f f f i p e i i n < < =  = =  ∑ � (5) a 95% confidence interval of the estimation is defined by [20]: 1 1 1 200 1 200 f f f f f f f p p p p p np np    − −    − ≤ ≤ +         � � � � � � (6) c. displacement method this method is commonly used when analyzing stability structures by analytical method. this method is determined in [19] and the stability equations are shown by: 11 1 1 ... det 0 ... j i ij r r r r     =      � � � (7) where ij r is the reaction from a generalized relocation of ties. iii. methodology a. reliability of buckling strength of the steel plane frame considering semi-rigid connections 1) safe condition although the buckling strength of the steel plane frame considering semi-rigid connections beam-column is determined by (13), in reality we often introduce a safety factor n and the safe condition of the steel plane frame considering semi-rigid connections beam-column will be written as: cr p p n ≤ (8) where p is the external load which can fluctuate randomly. 2) deterministic model and uncertainty model the deterministic model deals with the above buckling analysis problem, in which the input parameters are those of geometry ( )1 2 1 2, , , , , , , , , , , , , ,c fc fc wc b fb fb wb pl l h h h b t t h b t t t d material (e) load (p) and flexible joint (k1, k2). this model can be written as: ( ) cr p = ℑ x (9) with 1 2 1 2 1 2, , , , , , , , , , , , , , , , ,c fc fc wc b fb fb wb pl l h h h b t t h b t t t d e p k k =  x . in this paper, we consider the steel plane frame considering semirigid connections with the deterministic input parameters shown in table i. the uncertainty model is constructed based on the deterministic model by taking into account the randomness of some input paramters. in this paper, we distinct two vectors of input parameters: the first one of the parameters assumed to be deterministic 1 1 2 1 2, , , , , , , , , , , , ,c fc fc wc b fb fb wb pl l h h h b t t h b t t t d =  x and the second one of the parameters assumed to be ramdom [ ]2 1 2( ) ( ), ( ), ( ), ( )p k k eω ω ω ω ω=x with ω representing the randomness of the parameters. this model can be written as: ( )1 2( ) , ( )crp ω ω= ℑ x x (10) table i. deterministic input parameters variable value variable value h1 (cm) 400 l1 (cm) 400 h2 (cm) 800 l2 (cm) 600 hc (mm) 400 hb (mm) 400 bfc (mm) 200 bfb (mm) 200 tfc (mm) 15 tfb (mm) 15 twc (mm) 10 twb (mm) 10 tp (mm) 20 d (mm) 22 table ii. random input variables and their representative parameters random variable ( )p kn law of probability norm representative parameters p µ p cv 1.5088×10 4 0.1 random variable 2 (kn/cm )e law of probability norm representative parameters e µ ecv 2×10 4 0.1 k1 k2 uniform uniform reference interval reference interval 1.5 [0.95 1.05]÷ 19211 [0.95 1.05]÷ engineering, technology & applied science research vol. 10, no. 1, 2020, 5099-5103 5101 www.etasr.com tran & nguyen: reliability assessment of steel plane frame's buckling strength considering … b. column reliability assessment by monte carlo simulation by introducing the uncertainty model in the monte carlo simulation method, we obtain the scheme of the reliability assessment of the steel plane frame considering semi-rigid connections shown in figure 1. fig. 1. scheme of the reliability assessment of the steel frame considering semi-rigid connection using monte carlo simulation method iv. numerical results a. validation of the steel frame buckling strength considering semi-rigid connections in order to validate the matlab code, the steel frame considering semi-rigid connection shown in figure 2 was considered with the input parameters shown in table iii. the validation of the program was performed in articulation joints (stiffness of the joint is zero) and rigid joints (stiffness of the joint is infinitely high). the result of the computer program and its comparison with the result of [19] is shown in table iv. table iii. input parameters geometry and section details beam l (cm) hwb (cm) bfb (cm) tfb (cm) twb (cm) 600 40.0 20.0 2.0 1.0 column h (cm) hwc (cm) bfc (cm) tfc (cm) twc (cm) 600 40.0 20.0 2.0 1.0 fig. 2. plane frame semi-rigid connections for validation table iv. validation by comparison with [19] articulation joints rigid joints matlab code [2] error (%) matlab code [2] error (%) pcr (kn) 545.47 545.16 0.31 759.86 761.00 1.14 we can observe that the error is very small in the case of button joint (<0.31%) and slightly increases in the other case (<1.14%). this result can be explained by the fact that in our program the rigid joint is modeled by setting a very high value to the stiffness of the joints. this result confirms the reliability of our program. b. convergence of the monte carlo simulation consider the steel plane frame semi-rigid beam-column connections shown in figure 3 with the deterministic input parameters and the random input parameters presented in table i and table ii respectively. the compression load p (kn) and young’ modulus are assumed to be normal variables with mean , p e µ µ and coefficients of variation , , p e cv cv whereas the empirical coefficients k1, k2 are assumed to be uniform variables in the interval [0.95, 1.05] of the reference value [18]. figure 4 shows the convergence of the safe probability of the frame in the monte carlo simulation to the value of 0.9312 or 93.12% after about 1051 samples in 30 minutes. the used convergence criterion of 2.5% justifies the confidence of the estimated reliability. this result also shows that although the safety factor was taken as 1.1 in the analysis, because of the randomness of some input parameters the reliability of the structure is only 93.12%. thus the assessment of the reliability of the structure is necessary. fig. 3. semi-rigid connection plane frame analysis fig. 4. convergence of the safe probability in the monte carlo simulation c. coefficient of variation and safety factor effects we know that the variation of input random variables and the safety factor influence directly but inversely the safe probability of the structure. thus in order to clear the effect of l h p i i c d d d d d 1 2 2 2 1 1 2 p 4p 4p p l l l l l h h i i 2i i i i i 2i 2i c c c engineering, technology & applied science research vol. 10, no. 1, 2020, 5099-5103 5102 www.etasr.com tran & nguyen: reliability assessment of steel plane frame's buckling strength considering … these parameters, one reconsiders the above column with different coefficients of variation of the compression load cv=0.05; 0.1; 0.15; 0.2; 0.25 and different safety factors n=1.1; 1.15; 1.2; 1.25; 1.3. the randomness of the empirical coefficients k1, k2 is assumed to be unchanged in the interval [0.95, 1.05] of the reference value. the results of the safe probability are listed in table v and presented in figure 5. table v. effects of the coefficient of variation and of the safety factor on the safe probability of the frames n cv 0.05 0.10 0.15 0.20 0.25 1.10 0.0276 0.1514 0.2566 0.2833 0.3500 1.15 0.0000 0.0676 0.1302 0.2222 0.2553 1.20 0.0000 0.0225 0.1166 0.1313 0.2166 1.25 0.0000 0.0067 0.0572 0.0964 0.1722 1.30 0.0000 0.0000 0.0278 0.0609 0.1031 (a) (b) fig. 5. (a) effect of the coefficient of variation and (b) effect of the safety factor on the safe probability of the column we can easily observe the inverse effect of the coefficient of variation and of the safety factor in figure 5. the safe probability of the column decreases when the coefficient of variation increases, whereas it increases when the safety factors increase. this result seems to be obvious, but it has a very important significance. it shows that if there are many input random parameters or furthermore, with high randomness in the structural design or in the optimization problem, the use of local coefficients such as the overload coefficient seems to be not sufficient. the structure can be in a dangerous state. in this case, it is necessary to determine a global safety factor, as is done in this study, to assure the absolute safety of the structure. for example, in this test, if the coefficient of variation is 0.05, the global safety factor needs to be only 1.15 to obtain a safe probability of 100%. if the coefficient of variation is 0.1, the global safety factor needs to be 1.3. v. conclusions this paper studies the reliability assessment of a steel plane frame with semi-rigid beam-column joint connections. the authors have successfully established the deterministic model using the newton-raphson method to solve the transcendental equation of the column’s equilibrium. this model was then combined with the monte carlo simulation method to construct the column’s reliability assessment program. parametric tests were also performed to study the input parameter effects on the reliability of the structure. the obtained results show the significance of this research. acknowledgment this research was funded by vinh university. reference [1] c. batho, h. c. rowan, “investigations on beam and stanchion connections”, in: second report of the steel structures research committee, pp. 61-137, department of scientific and inductrial research, his majesty’s stationery 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journal, vol. 30, no. 3, pp. 90-107, 1993 [18] a. kozlowski, r. kowalczyk,m. gizejowsk, “estimation of the initial stiffness and moment resistance of steel and composite joints”, ctbuh 8th world congress, dubai, march 3-5, 2008 [19] v. q anh, advance analysis and design frame semi-rigid connections, publishing of contruction, 2013 (in vietnamese) [20] m. lemaire, fiabilite des structures: couplage mescano-fiabiliste, european journal of computational mechanics, vol. 15, no. 7-8, pp. 989-992, 2005 microsoft word 04-3713_setasr_v10_n5_pp6176-6182 engineering, technology & applied science research vol. 10, no. 5, 2020, 6176-6182 6176 www.etasr.com touahmia et al.: a foresight study about the skills and competencies needed for quality professionals … a foresight study about the skills and competencies needed for quality professionals in 2030 an empirical study of saudi arabia mabrouk touahmia college of engineering university of hail hail, saudi arabia m.touahmia@uoh.edu.sa mohamed aichouni college of engineering university of hail hail, saudi arabia m.aichouni@uoh.edu.sa abdulaziz alghamdi college of engineering university of hail hail, saudi arabia a.alghamdi@uoh.edu.sa lioua kolsi college of engineering university of hail hail, saudi arabia l.kolsi@uoh.edu.sa hasan alzamil college of engineering university of hail hail, saudi arabia h.alzamil@uoh.edu.sa abstract−this paper presents the results of a foresight study examining the future knowledge, skills, and competencies required by quality professionals to meet the goals and objectives of the saudi vision 2030. the study aims to develop a methodology allowing the forecasting of skills and competency demands in the future. data collection was conducted through the design of a web-based questionnaire that was distributed online to academic and quality management specialists in saudi arabia. the questionnaire consisted of four sections and forty items aiming to identify the necessary competencies that quality professionals should develop to deal with the changing business environments. the validity and reliability of the questionnaire were confirmed by cronbach’s alpha and the data were analyzed using descriptive tests (mean and standard deviation). one-way anova method was also used to test the significant differences in participants’ attitudes. the results of the study clearly emphasize on the emerging need for new effective skills to face this new era of the rapid pace of technological changes. the outcomes of this study may be used by policy-makers, local authorities, employers, academics, and researchers to set up future-oriented education and training policies to bridge the gap between skills demand and supply which arises out of labor market changes. keywords-foresight; knowledge; skills; competencies; quality professionals; saudi vision 2030 i. introduction the kingdom of saudi arabia is undertaking an enormous development through the implementation of its ambitious 2030 vision. launched in 2016, the vision intends to build a thriving, diversified and sustainable economic model away from the dependence on oil and making the private sector the key generator of growth and jobs [1]. the vision envisages a more productive and prosperous society in which people are at the heart of economic growth and social development. to achieve these goals, a series of programs and national strategic plans were developed by the saudi government for the industrial sector in order to turn the vision objectives into practice and move on with the achievement of its goals. within this significant socio-economic transition combined with fast technological breakthroughs and the advent of the 4th industrial revolution, best known as industry 4.0, it is of great importance to foresee the skills, competencies, and new job tasks that the saudi labor market must develop to successfully address this new era of rapid change and innovation. however, what the future of work market may hold and how will this be affected by the accelerating technological changes has sparked widespread debate among politicians, businessmen, scholars and academics [2-3]. the industry 4.0 is characterized by the development of smart factories able to govern themselves by means of cyber-physical systems, internet of things (iot), internet of systems (ios), artificial intelligence, cloud technology, and big data [4]. as a result, public and private sectors need to up-skill their workforces to prepare them for the tasks and competencies required by this new industry revolution. it is widely agreed that knowledge and skills are the key factors for employability and economic growth of countries [5-6]. during recent years, the topic of foresight has attracted many government agencies, organizations, and academic researchers in order to design strategies, scenario planning models, and visions [7]. the increasing importance of foresight as a strategic policy development at national and organizational levels can be assessed by the extensive published papers and technical reports that can be found in the literature [8-9]. with the availability of a bench of foresight methods and techniques that have been successfully implemented in different contexts, it is possible to anticipate the required skills and competencies corresponding author: mabrouk touahmia engineering, technology & applied science research vol. 10, no. 5, 2020, 6176-6182 6177 www.etasr.com touahmia et al.: a foresight study about the skills and competencies needed for quality professionals … that the job market needs. by using foresight techniques, decision-makers, organizations, and companies can develop the ability of formulating a broader framework of the necessary qualifications, skills and competencies needed for the job market over the next years. authors in [10] conducted a foresight study on the necessary competencies that leadership should develop to deal with the rising uncertainties of the changing business environments. similarly, authors in [11] investigated the variation in skill demands across the united states labor market during the period 2010-2015. they reported similar techniques to anticipate skills and future job requirements based on big data analysis of job postings in professional networks. their results showed a large correlation between firm wages and employee levels of cognitive and social skills. despite the growing body of research in the area of the future of work, there are only limited studies conducted on the skill requirements across the saudi labor market. organizations in saudi arabia, either public or private, are working within a national momentum driven by the saudi vision 2030. it is in this context that the saudi ministry of education is supporting researches for the anticipation of future skill needs in order to enable strategic responses and bridge the gap between demand and supply of skills. this paper presents the results of a foresight study on future knowledge, skills, and competencies needed by saudi quality professionals to meet the requirements of the new labor market. the study aims to develop a methodology allowing the forecasting of future competency needs based on the analysis of the saudi vision 2030 goals. the significance of the study lies in the fact that the obtained results would support saudi decision-makers to identify key strategies and investments in human capital development through education and training programs. it is expected that the outcomes of this study will be of considerable value for the saudi government, companies, and academics in their efforts to bridge the gap between the skill demand and supply, which arises out of labor market change. ii. methodology the methodology used in this study was based on an online survey questionnaire that was designed with the primary objective to identify future competencies needed by saudi quality professionals to align with the saudi vision 2030. google forms was used to create and manage the questionnaire. the design of the survey has undergone different stages and pre-tests which have resulted in eliminating, reclassifying, and rephrasing its elements. the resulting questionnaire is organized into 4 sections and comprises of 40 items (appendix a): • section i: respondents’ characteristics: aimed to identify respondents’ characteristics such as position, education level, age, gender, professional experience, organization size, work sector, existence of a quality manager at the organization, certification status of the organization, and the development of a strategic plan in line with the vision 2030. • section ii: future knowledge needs: aimed to recognize respondents’ attitudes towards future knowledge needs and specializations required for saudi quality professionals. • section iii: future skill needs: aimed to anticipate the future skills required for saudi quality professionals. • section iv: future competencies needs: assesses respondents’ attitudes toward future competencies needs of saudi quality professionals. the questionnaire was sent out to 200 academics, researchers, and quality practitioners working in different organizations across the kingdom of saudi arabia. survey respondents were asked to assess each statement according to a five-point likert rating scale which enables eventual comparative deductions since the same scale is used in similar studies. after answering the questionnaire by the respondents, the data was automatically recorded in a google docs spreadsheet. the data were analyzed using descriptive tests (mean and standard deviation). the internal consistency of the questionnaire same group elements was measured by cronbach’s alpha and its content validity was examined based on expert's reviews from academic institutions. iii. data analysis and results out of the 200 questionnaires sent, 120 replies were received, making a 60% response rate. the authors believe that such a high response rate is mainly attributed to the efficiency of online web surveys. the respondents were of different ages, qualifications, and have different jobs. a. survey validity in survey studies, internal consistency is a common concern before data analysis is performed. internal consistency is a measure of how well the different items measure the same concept in the survey. internal consistency is measured by calculating cronbach’s alpha statistical factor. it measures the internal consistency among a group of items combined to form a single scale, and reflects the homogeneity of the scale. a value of cronbach’s alpha greater than 0.7 indicates homogeneity and consistency of the survey element. table i shows the cronbach’s alpha coefficients of the survey elements of this study. as can be seen, the values of the cronbach’s alpha range from 0.860 to 0.943, indicating the reliability of the scales in achieving valid results for the objectives of the study. table i. cronbach's alpha domain no. of items cronbach's alpha knowledge 10 0.920 skills 10 0.860 competence 20 0.943 scale 40 0.947 the survey’s internal consistency was further evaluated through pearson correlation coefficients between the terms of each dimension and the dimension to which they belong. the results are shown in table ii and indicate clearly that there is a highly statistically significance at the 0.05 level of significance between the items and the elements of the survey (knowledge, skills, competencies). the high values of the coefficients presented in tables i and ii, indicate the validity and the reliability of the survey to measure what is designed for, i.e. the future skills and competencies of the quality professional in the saudi context. engineering, technology & applied science research vol. 10, no. 5, 2020, 6176-6182 6178 www.etasr.com touahmia et al.: a foresight study about the skills and competencies needed for quality professionals … table ii. pearson correlation coefficients knowledge skills competence item pearson corr. coef. item pearson corr. coef. item pearson corr. coef. item pearson corr. coef. 1 0.741** 1 0.717** 1 0.732** 11 0.734** 2 0.641** 2 0.658** 2 0.654** 12 0.854** 3 0.915** 3 0.576** 3 0.679** 13 0.783** 4 0.634** 4 0.842** 4 0.822** 14 0.501* 5 0.820** 5 0.799** 5 0.704** 15 0.487* 6 0.910** 6 0.512** 6 0.860** 16 0.583** 7 0.826** 7 0.707** 7 0.496* 17 0.783** 8 0.626** 8 0.654** 8 0.582** 18 0.570** 9 0.903** 9 0.694** 9 0.677** 19 0.805** 10 0.820** 10 0.578** 10 0.897** 20 0.887** ** significant at 1%level * significant at 5% level b. respondent profiles the respondent profiles are summarized in appendix b. the participants are of both sexes, of different ages, from different social stata, with different scientific qualifications, different jobs, experiences, have different monthly incomes, and are of different nationalities. a careful examination shows that 51.7% of the respondents are from middle and executive leadership categories, and the majority of them (70.8%) work in organizations that possess single certificates for global management such as iso 9001, 14001, 26001, or accreditation certificates specific to the organization's field of activity. c. data analysis and interpretation the data obtained were analyzed using the statistical package for social science (spss) 25.0 program. a descriptive statistical analysis using mean, frequency, percentage, and standard deviation was used to describe the demographic variables and to answer the research question: “which knowledge, skills and competencies should the country develop towards 2030?” the participants answered the survey using a 5-point likert-type scale ranging from 1 for strongly disagree, to 5 for strongly agree. the range between the maximum and minimum mean values was classified into five levels reflecting the respondents’ attitudes towards the questionnaire components (table iii). the mean scores and standard deviation values for the questionnaire components are presented in table iv. as shown, all components scored mean values between 4.29 and 4.15, giving an overall mean score of 4.21. this result indicates a very strong attitude of the participants towards the needs for new knowledge, skills and competencies. analysis of variance (anova) was used to determine if there are significant differences between the means of the groups. an important question was raised in this study: “do the attitudes of participants vary based on the participant’s background, such as years of experience, nature of their jobs, or the nature of the organization's work?”. a null hypothesis (h0) was set for the study as follows: “there are statistically significant differences in the way participants view the future of quality professionals in align with the vision 2030.” these differences are based on the participants’ background, such as their positions, years of experience and nature of work. the level of statistical significance of the data is expressed in terms of the p-value as shown in table v. the p-value approach is usually used as a substitute to rejection points to provide the smallest level of significance at which the null hypothesis would be rejected. a p-value above 0.05 is not considered statistically significant and indicates strong evidence for the null hypothesis. as can be seen in table vi, the data analysis gave p-values between 0.159 and 0.781 (>0.05) for all groups, which indicates no statistically significant differences in how participants view the future of quality professionals and the null hypothesis should be accepted. table iii. mean ranges and participant attitudes mean range respondent attitudes 1.00 to 1.80 very weak 1.81 to 2.60 weak 2.61 to 3.40 moderate 3.41 to 4.20 strong above 4.20 very strong table iv. overall means and std deviations questionnaire components mean std. deviation respondent’s attitude knowledge 4.29 0.506 very strong skills 4.21 0.518 very strong competencies 4.15 0.546 strong total 4.21 0.468 very strong table v. anova for participents attitudes with respect to the nature of jobs job type knowledge skills competencies total mean p -v al u e = 0 .7 81 mean p -v al u e = 0 .4 91 mean p -v al u e = 0 .1 59 mean p -v al u e = 0 .3 30 senior leadership category 4.23 4.14 4.10 4.14 middle leadership category 4.38 4.35 4.34 4.35 executive leadership category 4.33 4.17 3.96 4.10 academic 4.21 4.05 4.10 4.11 administrative employee 4.28 4.17 4.22 4.22 other 4.19 4.23 4.13 4.17 the respondents were asked to rank, from the most to the least important, the future domains of knowledge, skills, and competencies with reference to the saudi vision 2030 requirements. the outcomes of the survey are presented in figures 1-3 and table vi. as can be seen, all items scored high values of mean ranging from 4.64 to 3.78. moreover, more than 80% of the surveyed domains attained mean values above the target level (4), indicating very strong attitude of the respondents towards the need for new/evolving knowledge and skills. the results showed that particular knowledge domains such as good knowledge of tqm tools, organizational context and customer needs are greatly required by quality professionals. the study outcomes also emphasize the importance of the interpersonal competencies that quality professionals should develop to address this new era of technology and job market changes. this is consistent with previous studies that have shown an increasing demand for social skills in the new labor market all over the world [12]. engineering, technology & applied science research vol. 10, no. 5, 2020, 6176-6182 6179 www.etasr.com touahmia et al.: a foresight study about the skills and competencies needed for quality professionals … there are good reasons to think that these demands will continue to increase as technological and managerial approaches in economy are keeping to progress incessantly. table vi incorporates the most required domains of knowledge, skills and competencies according to the outcomes of this study and the recommendations of other researchers [713]. these findings may serve as a reference for saudi decision-makers to design future-oriented education and training policies for quality professionals to ensure sustainable employment, economic growth, and social development. 3 3.3 3.6 3.9 4.2 4.5 risk management management for industry 4.0 quality engineering quality management systems accreditation processes cost aspects statistical analysis costumer needs organizational context tqm tools mean values k n o w lo dg e n ee d s fig. 1. respondents’ assessment of future knowledge needs. 3 3.3 3.6 3.9 4.2 4.5 it skills team management skills constructive feedback system thinking organizational skills effective planning effective communication problem solving data analysis quality auditing mean values s k il ls n ee d s fig. 2. respondents’ assessment of future skills needs. iv. conclusions this study sought to develop a methodology that would allow the forecasting of future knowledge, skills and competencies required by quality professionals to align with the saudi vision 2030 goals. the analysis and interpretation of the collected data were made with various statistical tools. the results of the study clearly emphasize on the emerging need for new effective skills to face this new era of rapid pace of technological change. the data showed that particular knowledge domains such tqm tools, organizational context, and customer needs are greatly essential for quality professionals in the future. the results also emphasize the importance of the interpersonal competencies that quality professionals should develop to address the emerging requirements of the job market. the findings of this study complement the current research on skills needs, by infusing a foresight methodology capable of analyzing the labor market evolution in an attempt to anticipate future skills in most organizational contexts. the outcomes of this study may be used by policy-makers, local authorities, employers, and researchers to build up a vision for skill development, and therefore could set up future-oriented education and training policies to bridge the gap between skill demand and supply which arises from the labor market changes. 3 3.3 3.6 3.9 4.2 4.5 conflict management entrepreneurial thinking emotional intelligence research intelligence social intelligence adaptive thinking creativity & innovation achieving goals organizational experience objective driven educating and training critical & analytical thinking change management decision making problem solving & resolution conscientiousness promote acceptance efficient communication business strategy leadership behavior mean values c o m p et en ci es n ee d s fig. 3. respondents’ assessment of future competencies needs. table vi. ranking of required domains of knowledge, skills and competencies knowledge needs rank skills needs rank tqm tools 1 quality auditing 1 organizational context 2 data analysis 2 statistical analysis 3 problem solving 3 costumer needs 4 effective communication 4 cost aspects 5 effective planning 5 accreditation processes 6 organizational skills 6 quality management systems 7 system thinking 7 quality engineering 8 constructive feedback 8 management for industry 4.0 9 team management skills 9 risk management 10 it skills 10 competencies needs rank competencies needs rank leadership behavior 1 objective driven 11 business strategy 2 organizational experience 12 efficient communication 3 achieving goals 12 promote acceptance 4 creativity & innovation 14 conscientiousness 5 adaptive thinking 15 problem solving 6 social intelligence 16 decision making 7 research intelligence 17 change management 8 emotional intelligence 18 critical thinking 9 entrepreneurial thinking 19 educating and training 10 conflict management 20 acknowledgment the authors acknowledge the deputy for research and innovation, ministry of education in saudi arabia for funding the present research work through the project number ss-116 under the social sciences initiative. engineering, technology & applied science research vol. 10, no. 5, 2020, 6176-6182 6180 www.etasr.com touahmia et al.: a foresight study about the skills and competencies needed for quality professionals … appendix a: survey questionnaire please complete the following sections by ticking (√) where appropriate: section i: characteristics of survey participants no. profile of respondents √ nature of job senior leadership category (general manager / ceo) or owner of a company 1 middle leadership category (director of quality / hr / projects manager...) executive leadership category / supervisor / section head academic / researcher administrative employee other 2 educational qualification ph.d. msc bsc 3 age (years) 21 to 30 31 to 40 41 to 50 more than 50 4 gender male female 5 work experience (years) less than 1 1 to 5 6 to 10 11 to 20 more than 20 6 organization size (employees) less than 50 51 to 100 101 to 500 501 to 1000 more than 1000 7 work sector government sector private sector 8 does the organization have a quality management department? yes no 9 does the organization possess single certificates for global management or accreditation certificates? yes no i don’t know 10 does the organization have a strategic plan in line with the saudi vision 2030? yes no i don’t know section ii: future knowledge needs with reference to the saudi vision 2030, how would you assess the following knowledge needs for quality professionals in the future? (1=strongly disagree, 2=disagree, 3=unsure, 4=agree and 5=strongly agree) no. item 1 2 3 4 5 1 the quality professional must have a good knowledge of quality management systems 2 the quality professional must have a good knowledge of the cost aspect. 3 the quality professional must have a good knowledge of statistical analysis. 4 the quality professional must have a good knowledge of how to use tqm tools. 5 the quality professional must have a good knowledge of quality engineering. 6 the quality professional must have a good knowledge of risk management. 7 the quality professional must have a good knowledge of the requirements of the 4th industrial revolution. 8 the quality professional must have a deep understanding of customer needs. 9 the quality professional seeks to understand the context of the organization. 10 the quality professional must ensure that professional certificates are accredited by international bodies. section iii: future skills needs with reference to the saudi vision 2030, how would you assess the following skills needs for quality professionals in the future? (1=strongly disagree, 2=disagree, 3=unsure, 4=agree and 5=strongly agree) no. item 1 2 3 4 5 1 quality professional must have team management skills 2 quality professional must have effective planning skills 3 the quality professional is skilled in organizing effectively 4 the quality professional must have a system thinking methodology 5 quality professional is competent to provide constructive feedback 6 quality professional must have data analysis skills 7 the quality professional has skills in auditing quality management systems 8 quality professional must have problem solving skills 9 quality professional must have it skills 10 quality professional must have effective communication skills section iv: future competencies needs with reference to the saudi vision 2030, how would you assess the following competencies needs for quality professionals in the future? (1=strongly disagree, 2=disagree, 3=unsure, 4=agree and 5=strongly agree) no. item 1 2 3 4 5 1 the quality professional must have the ability to strategically understand of the organization's policy for linking quality goals to the organization's strategy 2 the quality professional has the skill to manage change 3 the quality professional has teamwork skills engineering, technology & applied science research vol. 10, no. 5, 2020, 6176-6182 6181 www.etasr.com touahmia et al.: a foresight study about the skills and competencies needed for quality professionals … 4 the quality professional shows appropriate driving behavior 5 the quality professional has the competence for methodologies to solve problems in operations 6 the quality professional must be fully aware and pay attention to detail 7 the quality professional must have sufficient experience in the organization's field of work 8 the quality professional must focus on achieving goals. 9 the quality professional must be able to make decisions 10 the quality professional must have analytical and critical thinking 11 the quality professional must be qualified to teach and train his coworkers 12 the quality professional must have effective communication skills 13 the quality professional must work to gain quality acceptance for all members of the organization 14 emotional intelligence is an essential feature of a quality professional. 15 social intelligence is a required feature of a quality professional. 16 creativity and innovation skills are essential for the quality professional 17 personnel management and conflict management are key features of a quality professional 18 entrepreneurial thinking is an important skill for the quality professional 19 research intelligence is an essential feature of the quality professional 20 thinking with the methodology of adapting to the emerging data (adaptive thinking) is a required feature for the quality professional in the era of technical acceleration and digital transformation. appendix b: characteristics of the respondents no. profile of respondents no. p% nature of job senior leadership category (general manager / ceo) or owner of a company 21 17.5 middle leadership category (director of quality / hr / projects manager...) 36 30.0 1 executive leadership category / supervisor / section head 26 21.7 academic / researcher 13 10.8 administrative employee 9 7.5 other 15 12.5 2 educational qualification ph.d. 17 14.2 msc 47 39.2 bsc 56 46.7 3 age (years) 21 to 30 31 25.8 31 to 40 30 25.0 41 to 50 42 35.0 more than 50 17 14.2 4 gender male 112 93.3 female 8 6.7 5 work experience (years) less than 1 4 3.3 1 to 5 31 25.8 6 to 10 14 11.7 11 to 20 34 28.3 more than 20 37 30.8 6 organization size (employees) less than 50 14 11.7 51 to 100 9 7.5 101 to 500 29 24.2 501 to 1000 12 10.0 more than 1000 56 46.7 7 work sector government sector 69 57.5 private sector 51 42.5 8 does the organization have a quality management department? yes 109 90.8 no 11 9.2 9 does the organization possess single certificates for global management or accreditation certificates? yes 85 70.8 no 25 20.8 i don’t know 10 8.3 10 does the organization have a strategic plan in line with the saudi vision 2030? yes 85 70.8 no 14 11.7 i don’t know 21 17.5 references [1] “saudi vision 2030.” https://vision2030.gov.sa/en/node (accessed aug. 06, 2020). [2] t. b. and a. elsheikhi, “the future of work: a literature review,” working paper, apr. 2018. accessed: aug. 06, 2020. [online]. available: http://www.ilo.org/global/research/publications/workingpapers/wcms_625866/lang--en/index.htm. [3] m. yazdanifar, “effect of social capital on innovation: a mediating role of employee motivation,” engineering, technology & applied science research, vol. 8, no. 4, pp. 3098-3102, 2018. [4] m. manda and s. ben dhaou, “responding to the challenges and opportunities in the 4th industrial revolution in developing countries,” presented at the 12th international conference on theory and practice of electronic governance (icegov2019), may 2019, accessed: aug. 06, 2020. [online]. available: https://collections.unu.edu/view/unu:7324. [5] s. k. bishwas and . s., “life: an integrated view of meta organizational process for vitality,” journal of management development, vol. 35, no. 6, pp. 747–764, jan. 2016, doi: 10.1108/jmd-07-2015-0103. 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[13] h. p. ingason, e. r. jónsdóttir, and s. liu, “the house of competence of the quality manager,” cogent business & management, vol. 4, no. 1, jul. 2017, art. no. 1345050. microsoft word 47-2841_s_etasr_v9_n4_pp4566-4573 engineering, technology & applied science research vol. 9, no. 4, 2019, 4566-4573 4566 www.etasr.com el abid amrani et al.: a novel deep learning approach for semantic interoperability between … a novel deep learning approach for semantic interoperability between heteregeneous multi-agent systems noureddine el abid amrani ssdia laboratory, enset mohammedia, hassan ii university, casablanca, morocco and iga, casablanca, morocco noureddine.elabid@iga.ac.ma mohamed youssfi ssdia laboratory, enset mohammedia hassan ii university, casablanca, morocco med@youssfi.net oum el kheir abra ssdia laboratory, enset mohammedia, hassan ii university casablanca, morocco abra.oek@gmail.com omar bouattane ssdia laboratory, enset mohammedia hassan ii university, casablanca, morocco omar.bouattane@gmail.com abstract—this article focuses on the issue of semantic interoperability in heterogeneous distributed multi-agent systems. existing middleware technologies offer programming models that strongly combine agents’ learning models and communication models, which can lead to performance weaknesses when the number of agents is very important. moreover, existing methods in the field of semantic interoperability solve the problem of understanding messages exchanged between distributed agents with heterogeneous ontologies, using several techniques to combine these ontologies. the first category of these methods relies on the fusion principle, others use alignment, and finally, there are those founded on semantic web technique. all these methods are limited to abstract concepts and do not deal with concrete concepts such as those represented by images. we propose in this paper a new approach that addresses the problem of semantic interoperability between heterogeneous distributed agents based on two principles: at first, the communication aspect of the agent from the learning aspect is separated. then, we propose extending semantic interoperability to concrete concepts by combining two techniques: semantic web technology, which allows terms representing abstract concepts to be interpreted and deep learning technology, which is introduced as a new method to ensure semantic interoperability in the case of concrete concepts such as images. a detailed description of the proposed approach is provided, showing that it is very useful in solving the disadvantages of existing multi-agent platforms. keywords-multi-agent system; middleware; semantic interoperability; ontology; web semantic; deep learning i. introduction multi-agent systems (mass) are an interesting solution for the modeling of a complex and massively distributed system. the distributed elements of such a system need to communicate and interact with each other despite their technological heterogeneity. interoperability between distributed information systems has been the subject of several studies. it is first concerned with technological interoperability (transport of messages from one system to another and necessary communication protocols for exchanging messages). two solutions can be used to satisfy this need: (a) web services [1], agents can publish their abilities as invocable web services by other agents and this independently of the conceptual (architecture, interaction model, etc.) and technical characteristics of these agents (platform, programming language, etc.). (b) middleware technology. indeed, the only mode of communication between heterogeneous multi-agent systems lies in sending messages asynchronously. so a message oriented middleware (mom) can be used as a broker to transport messages between two heterogeneous platforms. based on the comparative in [2], we have opted for middleware using the amqp protocol such as rabbitmq and excluded other solutions such as jms which is monolingual and therefore does not ensure any interoperability, and activemq which may be an open source solution, but authors in [2, 3] confirmed the presence of unidentifiable problems at the queue level. interoperability between heterogeneous mass also concerns semantic interoperability, which means interpretation of exchanged messages between different agents at the meaning level. this problem has been raised by many organizations such as the foundation for intelligent physical agents (fipa) [4]. fipa provides standards and requirements needed to ensure interoperability between multilevel mass: fipa-acl [5] at the communication level, daml + oil [6] corresponding author: noureddine el abid amrani engineering, technology & applied science research vol. 9, no. 4, 2019, 4566-4573 4567 www.etasr.com el abid amrani et al.: a novel deep learning approach for semantic interoperability between … at the semantic level, aaa (abstract agent architecture) at the architectural level, etc. fipa has also encouraged the development of different platforms within the specifications it has proposed such as jade [7] and zeus [7]. these middleware offer programming models that strongly couple agent learning models and their communication models. in the majority of cases, when the number of agents is very important, the communication models used have drawbacks in term of performance. furthermore, various studies have proposed ontologies as a mean to solve the semantic interoperability problem between heterogeneous agents. most of these approaches have presented methods for interpreting the conceptualizations of a given ontology based on mapping, merging [8-10] or aligning ontologies [11-13]. nevertheless, the limitations of these approaches lie in the fact that they rely on interpretation or translation techniques such as wordnet, allowing to search for synonyms that represent a concept or an ontological relationship. the case of concepts represented by concrete objects such as images, to the best of our knowledge, has not yet been processed. it would be interesting to be able to deal with concrete objects because of the spectacular evolutions of information technologies: internet of things (iot), mobile applications and social networks. in this context, a comprehensive approach is proposed, which addresses the problem of interoperability between heterogeneous agents by using semantic web technology to interpret terms representing abstract concepts and deep learning technology to recognize and interpret concrete concepts such as images. the recognition and interpretation of image-type objects would be useful in the automated management of fields like road traffic, for the interpretation of road signs by driverless vehicles, medical imaging diagnostics for anomaly detection, etc. ii. related work semantic interoperability between mass solves the problem of understanding messages exchanged between agents with heterogeneous ontologies. in order to improve semantic interoperability in heterogeneous distributed systems, many techniques for combining these ontologies have been introduced and can be classified into three main categories: first, we find those based on the principle of fusion, others use alignment, and finally those based on the semantic web. in this section, we present a brief overview of these techniques: a. ontology fusion this technique is typically used when source ontologies cover similar or related domains. the principle is to merge source ontologies to produce a new coherent ontology that represents the union of these ontologies. in [8], each agent has his own ontology created by its owners. when agents meet other agents with ontologies in the same domain, they exchange their ontologies and decide to merge them. this merge is performed as follows: identical concepts, syntactic or semantic concepts already known to the current agent are identified. the syntactical comparison is performed using a syntactic similarity measure using the levenshtein distance modification method. the semantic comparison is performed using the wordnet dictionary. once all similar concepts are identified, various relationships between these concepts and already known concepts are created (by merging with their corresponding classes). then, for all the unknown concepts of the agent at the moment, they are incorporated into the knowledge base and learn new relationships between them and already understood concepts. finally, to link the classes added to the ontology with the classes that already exist, wordnet is still used to identify the types of relationships that should be used such as the relationships of hypernymia (super-class), hyponymy (sub-class), holonymy (is-part-of), meronymy (hasfor), etc. authors in [9] presented a method of fusion of heterogeneous ontologies to build a more complex ontology, based on the wordnet tool. the principle of this method is to merge heterogeneous domain ontologies according to a methodology that includes four main steps: wordnet mapping, selection of concepts, similarity calculation and rebuilding hierarchy. using the values obtained in the previous steps, the two domain ontologies are merged in a newly rebuilt hierarchy. b. ontology alignment the ontology alignment takes two input ontologies and outputs the result of the alignment between the incoming ontology entities. this technique is typically utilized when source ontologies cover complementary application domains. it is about establishing semantic links between these ontologies so that the one uses the knowledge of the other. there are several ontology alignment algorithms. one of the most used techniques is the approach in [10] where the authors propose an algorithm working on distributed agent’s knowledge bases to establish ontology correspondences. this algorithm is applied at the reception level of each message exchanged between two agents. the receiving agent will bring into play the different mechanisms to understand the message it receives and updates his ontology by adding the new knowledge. it begins by checking, in his ontology, the existence of the terms necessary for the interpretation of a message. in case of failure, the receiving agent transmits all unknown terms to the issuing agent for clarification. the latter searches for synonyms in its own ontology and sends clarifications on the terms found. if unknown terms persist, the receiving agent may request an external text service such as wordnet to obtain other synonyms and other words to correctly interpret the message. finally, the receiving agent can introduce new terms into his ontology in order to update it. authors in [13] present a dynamic multi-strategy ontology alignment framework, named rimom. the key insight in this framework is that similarity characteristics between ontologies may vary widely. they propose a systematic approach to quantitatively estimate similarity characteristics for each alignment task and propose a strategy selection method to automatically combine matching strategies based on two estimated factors while they take into account the textual and structural characteristics of ontologies. c. ontology semantic web techniques ontology semantic web methods use the semantic web rdf and owl languages to implement source ontologies and propose techniques to align or merge. thereby, in [11] the authors use the owl semantic web language to implement two source ontologies and propose an algorithm that receives two input (.owl) files and applies a 4-step strategy: lexical engineering, technology & applied science research vol. 9, no. 4, 2019, 4566-4573 4568 www.etasr.com el abid amrani et al.: a novel deep learning approach for semantic interoperability between … alignment, semantic alignment, verification of similarity, and heuristic functions. to eliminate unnecessary comparisons, the authors propose browsing the first file from top to bottom and the second from bottom to top. first, the output file is initialized by the first ontology o1. then, a lexical analysis between two classes c2 of o2 and c1 of o1 is launched. in case of failure of the lexical analysis, the semantic analysis is executed instead. when c2 of o2 is compared to all c1 classes of o1, a heuristic function is called to write the output file. to solve the data translation problem, authors in [14] propose the “processing ontology alignments with sparql” approach, where the sparql query language is used for extracting data from ontology, and through its construct statement, for generating new data. to deal with the limitations of this language, the authors propose to combine two recent extensions of sparql in order to be able to transform data according to complex alignments: sparql++ provides aggregates, value generating built-ins and (possibly recursive) processing of mappings expressed in sparql and psparql providing queries on path expressions (made from regular expression patterns) which are sufficient for expressing those of the expressive language. d. conclusion in this section, we presented a brief review of the literature of some existing methods for interpreting ontology conceptualizations such as fusion, alignment, and semantic web. other approaches rely on interpretation or translation techniques to search for synonyms that represent a concept or an ontology relationship. the main goal of these approaches is the semantic interpretation of concepts, while most of them are based on a concept-to-concept negotiation technique. the scope of these methods is restricted to term type concepts. this bibliographic study shows that the existing techniques of interpreting concepts of a given ontology do not deal with those represented by concrete objects such as images. with the continual progress of the iot, mobile applications and social networks, we believe that the use of image-like concepts, such as in the medical field and road safety, is booming. in this context, we consider that the proposed approach for semantic interoperability would be useful for heterogeneous distributed applications exchanging image-type information. the proposed approach therefore addresses the problem of interoperability between heterogeneous agents by using semantic web methods to interpret terms representing abstract concepts and deep learning methods to interpret objects representing concrete concepts. iii. main concepts and tools of our approach in the following, we give some definitions of the main concepts and tools utilized in the design of our approach, and then we focus on the description of the two technologies we adopted to ensure semantic interoperability: semantic web and deep learning. a. main concepts 1) agent an agent can be a physical or virtual entity that can act, perceive its environment (in a partial way) and communicate with others, is autonomous and has skills to achieve its goals [15]. 2) multi-agent systems an mas is defined as: a multi-agent system is a network of problem-solving entities (agents) that work together to find answers to problems that exceed the individual capabilities or knowledge of each entity (agent). a mas agent must be able to interpret messages sent by other agents, based on his knowledge, which is considered as a certain knowledge and knowledge of these agents. in this way, this technique allows the agent to acquire the skills necessary to interpret new knowledge and understand messages sent by other agents [16]. 3) agent communication language in an mas, agents are heterogeneous because each agent must meet very specific needs of an application. therefore, the agent implementation is dependent on its field of application. to ensure reliable cooperation between heterogeneous agents, they have to communicate their needs to each other through a agent communication language (acl). such a language must follow a well-defined syntax so that agents can interpret the messages in the same way. two most commonly used languages in mass are kqml (knowledge query and manipulation language) [17] and fipa-acl. fipa-acl provides a set of messages with associated semantics, i.e. conditions that the sender must respect and expected effects on the recipient. fig. 1. an example of a fipa-acl code 4) ontology ontology is a formal specification of a shared conceptualization [18]. in mas, ontology is a description of the concepts and relationships that can exist for an agent or a community of agents. in our approach, ontology represents a specific vocabulary to describe a conceptualization at the sending level. this vocabulary will be used to interpret a message at the recipient's level. 5) rabbitmq broker rabbitmq [2] is an open source message broker based on the advanced message queuing protocol (amqp). a message broker is an architectural model for the validation, transformation and routing of messages. it gives applications a common platform to send and receive messages and a safe place to store messages until they are received. amqp is a message protocol that manages traffic between producers and consumers. producers provide the messages and consumers engineering, technology & applied science research vol. 9, no. 4, 2019, 4566-4573 4569 www.etasr.com el abid amrani et al.: a novel deep learning approach for semantic interoperability between … retrieve them and process them. rabbitmq is responsible for ensuring that messages reach the right consumers. to do this, rabbitmq uses two key components: exchanges and queues. the main function of amqp is the routing of messages using its different exchange modes as required, independently of the tcp/ip, http, and smtp transport protocols. b. semantic web authors in [19], define semantic web as follows: “the semantic web will bring structure to the meaning full content of the web pages, creating an environment where software agents roaming from page to page can readily carry out sophisticated tasks for users”. the www was developed for humans. documents on the web are machine readable but not machine understandable. the main aim of semantic web is to enrich documents with semantic information about the content and to develop powerful mechanisms capable of interpreting this information. these goals are achieved through implementation of models, standards as well as annotation of resources at layers [20]. the semantic web uses tools to describe document content, such as the resource description framework (rdf), which is an entity relationship model used to represent resource information on the world wide web. the basic principle is that everything on the web can be unique, identified with uris (uniform resource identifiers) and then described in terms of triples representing resources, their properties and values. for semantic web purposes, rdf properties can be organized into classes and subclasses, with attributes and values. languages such as rdfs, daml+oil, or recently owl, allow a complete description of the complex ontological relationships between rdf properties, in an rdf/xml format. c. deep learning the problem of learning visual information is generally categorized in image classification, location and detection of objects, semantic segmentation and instance segmentation, etc. (machine learning before deep learning). deep learning [21] is a learning technique that allows a machine or a program to give a semantic and exact interpretation at the meaning level of an image, a video or understand the spoken language. it can be supervised as the learning techniques used in the ai domain, but the structure is different, it is a complex system composed of thousands of units, the neurons, which perform each of the elementary calculations. the specificity is that the results of a layer of neurons will serve as input to the calculation of the next layer. as it can be unsupervised, the technique used relies on data that is not labeled. the interpretation of visual information has been approached in several ways [22] but the goal remains the same: examine images for the purpose of identifying objects and judging their meaning. iv. the proposed approach this work presents a contribution to the development of a new asynchronous communication middleware model adapted to massively distributed architectures based on micro-agents. the proposed middleware should provide an api, with different multi language implementations, which allows exchanging messages between micro-agents implemented with different languages while respecting mas standards recommended by fipa. in this context, our goal is to ensure interoperability between agents deployed in heterogeneous multi-agent platforms based on existing protocols such as amqp. to ensure technological interoperability, we chose to use a message oriented middleware (mom) that relies on the amqp protocol, such as rabbitmq broker. with amqp protocol, rabbitmq ensure the transport of end-to-end messages independently of platforms, languages and communication protocols such as http, smntp, etc. below, focus is given on the communication aspect of an agent and its learning aspect to achieve our main goal, which is semantic interoperability. the model we propose is built on the principle of separating communication aspect and learning aspect of an agent (an extract of class diagram in figure 2). this allows agents to adapt to expected changes and to integrate future learning solutions. with this middleware, it is possible to create and deploy heterogeneous agents evolving in distributed containers. to communicate with the other agents of the platform, each agent can use polymorphic communication models adapted to its context. to achieve this, we use the pattern “strategy” to define a communication adapter family. each adapter, relating to a given communication protocol, is encapsulated. these adapters are dynamically interchangeable and offer an open model for expansion. the developer using this middleware can thus create his own adapter according to the communication model that he wishes to implement. currently, we think it is appropriate to create implementations of messaging adapters for exchanging acl messages and messaging protocols like amqp, stomp and mqtt using the rabbitmq broker. using the same principle adopted for the communication aspect, we use a polymorphic and scalable learning model based on the “strategy” pattern. an agent can use at any time any learning model among the “abstractlearningstrategy” implementations such as deep learning, semantic web, etc. depending on its context. we therefore, ensure an open extension middleware by offering scalability for the community of developers using it. to achieve this objective, we must implement an ontology adapted to this context. ontology is a vocabulary in a given field presented as a set of related concepts which can be either concrete or abstract. a concrete concept is represented by a concrete object such as a term, an image, etc. an abstract concept can only be represented by a general term such as “vehicle”. hence, ontology can be considered as a graph of nodes and arcs (relations). a node can be seen as a set of words that designate the same concept, such as a car that is represented by the set {car, automobile ...}. to interpret a message sent by an agent, we need a system with a tool to implement such ontology and another tool to query the implemented file to answer a question about an incomprehensible word. to do this, we investigate two technologies: engineering, technology & applied science research vol. 9, no. 4, 2019, 4566-4573 4570 www.etasr.com el abid amrani et al.: a novel deep learning approach for semantic interoperability between … fig. 2. an extract of class diagram of our approach • semantic web which is a technology that has appropriate languages to meet our needs. rdf, rdfs and owl languages are used to implement the agent ontologies and the sparql language is used to query the implemented files. • deep learning is a technique based on a trained neural network to recognize an object (image) that represents a concrete concept. the outputs obtained are produced in the form of terms. among the obtained results, it is possible to find terms that the agent cannot understand. in this case, the semantic web will be used for the correct interpretation of these terms. so, our strategy (figure 3) is: the semantic web technology languages can be used to solve the problem of semantic interoperability in case of abstract concepts. in fact, rdf, rdfs or owl languages can be used to implement source ontologies at sending level and sparql queries can query these ontologies to determine the list of synonyms for the purpose of interpreting these concepts. and in the case of a concrete concept represented by an image for example, a trained neural network is implemented to recognize this concept. a. architecture of the proposed approach our proposed approach scheme of interoperability is depicted in figure 4 according to two levels: • mediation level is the intermediate layer between multiagent systems achieving technological interoperability that addresses technical problems of link between these systems, interface definition and data format. it also provides protocols and standards that allow messages to be transported and exchanged reliably. in our approach, we opted for rabbitmq broker, which allows exchanging messages based on amqp protocol and hence provides interoperability between different systems. the message can be deposed in exchange and from that point, the message can borrow a path and is then placed at the end of queue of receive agent before processing and consumption. • semantic level layer ensures semantic interoperability between agents. the main objective of this layer is to guarantee that exchanges between agents keep their meaning using semantic web and deep learning. fig. 3. simplified diagram of our approach engineering, technology & applied science research vol. 9, no. 4, 2019, 4566-4573 4571 www.etasr.com el abid amrani et al.: a novel deep learning approach for semantic interoperability between … fig. 4. architecture of the proposed approach b. illustrative examples 1) abstract concept case rdf, rdfs or owl files that implement the ontology of a sending agent designate an abstract concept by a set of synonyms that indicate its semantics and vocabulary to facilitate understanding meaning of that concept. sparql language queries are used to question these files to elucidate messages not understood by the receiving agent. sparql queries produce a list of synonyms provided by the sending agent on this concept. if the list includes one or more words that are incomprehensible by the receiving agent, the use of a translation tool such as wordnet is proposed. to illustrate our approach, let us consider the field of automatic detection and recognition of road signs by driver software agents of autonomous vehicles. for this purpose, we need to build a traffic codes ontology: a) traffic code road signs are classified into three categories, shown in figure 5. road signs get generally the form of a square, a triangle or a circle. detection of these shapes in an image provides an interpretation of traffic signs. each category groups a number of subcategories (figures 6-8). fig. 5. categories of road sign forms b) proposed ontology in this context, we propose the ontology shown in figure 9. c) implementation of the proposed ontology to implement our ontology, we select a free and open source tool “protege” which is an ontology and knowledge editor. in the following, we present an owl code snippet of our application context (figure 10). fig. 6. prohibition/obligation signs fig. 7. danger signs fig. 8. indication signs fig. 9. proposed ontology fig. 10. an owl code extract from our ontology d) ontology query using sparql the “apache jena fuseki” tool is used to interrogate our ontology. apache jena fuseki is a sparql query editor for ontology querying. let’s take the example of a driver who requests all the information concerning the a14 road sign. the question is translated into a sparql query (figure 11). the answer is given in a table form (table i), which displays all the information about the road sign: type, border color, background color, image and description. from the obtained information, the driver can interpret the traffic sign and therefore comply with the traffic code. engineering, technology & applied science research vol. 9, no. 4, 2019, 4566-4573 4572 www.etasr.com el abid amrani et al.: a novel deep learning approach for semantic interoperability between … fig. 11. an example of a sparql request table i. response of a sparql request in figure 11 predicate object trafficsign:hasimage “exclamation mark” http://.../#type trafficsign:permanentdanger trafficsign:hasbgcolor “white” trafficsign:hasdescription “other danger” if this response is sufficient to interpret the message, the agent driver (ad) replies by taking into account several parameters (such as the time of day), which also influence the driver's behavior, updates his ontology, and queries source ontology for next concept. otherwise, other translation techniques can be used to interpret the concept, such as wordnet. 2) concrete concept case to make the agent driver able to interpret the road signs, a trained neural network is implemented. to achieve this goal (figure 12), it is necessary to compile a set of learning images to perform deep learning. this set collects thousands of images of different road signs converted into data and transferred to the neural network. artificial neurons then assign a weight to the different elements. the last layer of neurons will then gather different information to deduce the sign of the circulation. fig. 12. neural network training the neural network will then compare this response to the correct answers given by the experts. if the answers match, the network keeps this success in memory and will use it later to recognize the signs. in case of failure, the network takes note of its error and adjusts the weights placed on the different neurons to correct it. the process is repeated many times until the network becomes able to recognize a road sign in various forms and circumstances. in the given example, the trained neural network returns the term “danger” as an answer. if the receiving agent understands this response, he updates his ontology by adding the new concept. in the opposite case, the receiving agent moves to the method used in the first “abstract concept” case to search the synonyms for “danger”. v. conclusion and future work in a mas, communication between agents is achieved by sending structured messages based on acls describing agent’s messages in “performative” (message content) form. nevertheless, in an open environment, the acls suffer from some drawbacks in message interpretation when received by an agent, due to their ontology. this latter describes vocabulary of a given domain, useful for interpreting messages sent by agents. while many techniques for combining heterogeneous ontologies have been introduced for the purpose of improving semantic interoperability in heterogeneous distributed systems, they still are restricted to abstract concepts and don’t deal with concrete concepts. to address this issue, this paper introduced a new semantic level interoperability architecture based on two principles: the first principle is the separation (decoupling) of the agent’s communication model and learning pattern. the second principle is to extend semantic interoperability to concrete concepts by combining two techniques: semantic web and deep learning. the key idea of the proposed architecture is that the semantic web is utilized to interpret abstract concepts and deep learning is performed as a new method to ensure semantic interoperability in case of concrete concepts like images. the purpose of the proposed method is twofold: agent’s learning model is performed independently of its communication model and the ability is given to an agent to interpret a concrete concept. the proposed approach is very suitable to ensure semantic interoperability between heterogeneous distributed applications exchanging image-type information, as in the medical domain or in road traffic. for our future work, we intend to implement and validate our approach in the field of road traffic. references [1] a. shajjar, n. khalid, h. f. ahmad, h. sugun, “service 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saidi et al: transient stability analysis of photovoltaic system with experimental shading effects transient stability analysis of photovoltaic system with experimental shading effects abdelaziz salah saidi king khalid university, college of engineering, abha, saudi arabia and electric systems laboratory, national engineering school of tunis, tunisia marwa ben slimene sime laboratory, ecole nationale supérieure d' ingénieurs (ensit), university of tunis, tunisia mohamed arbi khlifi hail university, community college, hail, saudi arabia and sime laboratory, ecole nationale supérieure d' ingénieurs (ensit), university of tunis, tunisia abstract—this paper presents the transient stability analysis of a photovoltaic (pv) system with account shading effects. voltage and transient stability effect of pv system are assessed functions of an experimental study. the current advances in shading effect and temperature control of pv panels are studied. the study is performed on modeling and simulation of pv system with account shading effect. a shading effect system is introduced to reflect the transient response characteristics of pv generation model. an experimental setup is designed, constructed and assembled. the setup is provided with the necessary measuring instruments to carry out the required tests. a perspective on the other shading techniques for pv panels will be discussed in this paper. keywords-stability analysis; static/transient voltage stability; grid connected photovoltaic systems; shading effect i. introduction due to the growing demand on electricity, the limited stock and the rising prices of conventional sources (such as coal and petroleum), pv energy becomes a promising alternative as it is universal, freely available, environment friendly and has less operational and maintenance cost. power generation using solar power increased dramatically because it is considered pollution free when compared to fossil fuel power generation. it has low maintenance cost, it is noise free and has no moving parts. solar power uses solar panels to convert sun irradiation into electric energy using the pv effect. the output voltage of a solar panel is varying depending on sun irradiation and temperature [1]. large scale solar power generation presents technical challenges on power system dynamics and operation due to its behavior: low inertia, power output variability. in response to an increase of pv capacity, the capacity of conventional synchronous generator needs to be reduced relatively. this leads to lower system inertia and higher generator reactance, and hence the power system transient stability may be negatively affected. such concerns are more and more apparent for planning, security assessment, operation and protection setting of a power system. authors in [2] presented the impact of grid-connected pv generator on dynamic voltage stability of the ieee-13 bus power system by considering solar intermittency, pv penetration level, and contingencies such as line outage and load increase. author in [3] analyzed the effect of large scale pv on the ieee-14 bus system on two criteria: constant load and maximum load, investigating the optimal location of solar pv generator and the maximum safe instantaneous penetration with considering some system stability and security constraints. as for transient stability, it occurs in response to large disturbance, such as three-phase fault. the occurrence of such a fault results in either sudden disconnection of the pv system or shut down of the pv inverters. disconnecting a large number of pv causes a negative effect on power system transient stability. authors in [4] studied the transient response characteristics of pv model connected to ieee 9 bus system. authors in [5] analyzed the effect of diversity in power sources, fault location, load characteristics, and low-voltage ride-through on transient stability of ieee 9 bus system with connected high penetration pv system. authors in [6] investigated the transient response of solar pv generation of the mv tunisian power system. the response of the solar farms to short-circuits shows the capacity of the pv farms in withstanding voltage dips and their participation in voltage support. therefore, these simulations demonstrate that these types of solar photovoltaic generation are recommended to better meet the requirements of some network operators. it has been shown that overall efficiency of pv cells drops steeply with temperature increase, with a rate of decrease ranging from 0.25% to 0.5% per celsius degree, depending on the cell material used, it has been observed that high temperatures decrease greatly the working life of the whole pv system. cooling techniques produce more power, and reduce the cost of generally expensive pv equipment. it has been shown that a sizable portion of power can be gained, up to a total of 5% [7]. authors in [8] investigated the improvement of voltage stability in ieee 9 bus system as an impact of connecting a pv system to the system including the impact of temperature variation based on the location which was modeled in matlab. in this work, we focus on pv systems operating under high temperature environment such as hot desert conditions. the purpose is twofold: at first, study and engineering, technology & applied science research vol. 8, no. 6, 2018, 3592-3597 3593 www.etasr.com saidi et al: transient stability analysis of photovoltaic system with experimental shading effects modeling of the pv system is detailed. then, voltage stability, transient stability and general performance are assessed of an experimental study. the study is performed on the ieee 9-bus system model. the simulation platform is established in digsilent/powerfactory consisting of pv arrays, power inverters, transformers, transmission lines and grid as shown in figure 1 [9]. fig. 1. block diagram of a pv system ii. modelling of a solar pv system operation a. dc/dc boost converter and circuit of solar cell figure 2 shows the dc chopper type boost converter consisting of diode d, inductor l, capacitor c, igbt switch s, input voltage source and load resistance r. vin is the input voltage and the vo is the output voltage. the circuit used in this paper is presented in figure 3. the pv module used in this system is a 24 multi-crystalline solar cell in series able to provide 32.2w of maximum power. the circuit is completed by a parallel resistor rsh and a series resistor rs. figure 4 illustrates the instantaneous evolution of voltage and current. simulations were performed in the same conditions of irradiation and time. fig. 2. configuration of dc/dc boost converter fig. 3. circuit of pv cell the pv model is based on an equivalent circuit with a single diode shown in figure 3. the diode based model with a controlled current source can be used to predict the behavior of the pv system under various levels of irradiation, temperature and load conditions. the parallel resistance rsh represents the leakage currents at the cell edges. the series resistance rs represents the voltage drop during the transfer of charge carriers from the semiconductor junction to the external contacts. with the variation of cell temperature and irradiation, there will be considerable change in voltage and current which result in the increase or decrease of pv cell power output [1011]. fig. 4. v-i characteristics b. stability models load flow model: the load flow analyzes the controlled variables as a result of load flow calculation. in digsilent/powerfactory there are preferred control conditions supported by the built in pwm converter. the chosen control mode for this study is the vdc-q. typical control modes are: • vac-phi: specifies magnitude and phase of the ac-terminal. typical control modes for motor-side converters in variable speed drive applications. • pwm-phi: load-flow setup without control. the pulsewidth modulation factor is directly set in magnitude and phase. • vdc-q: specifies dc-voltage and reactive power output/flow. typical applications: statcom, shunt converter of upfc, grid-side converter of doubly-fed induction machines, vsc-hvdc applications. • vac-p: specifies ac-voltage magnitude and active power. this is equivalent to a “pv” characteristic of conventional synchronous machines. typical applications: grid-side converter of converter driven synchronous machines, vschvdc. • p-q: specifies p and q at the ac-side. this control mode is equivalent to a “pq”characteristic of synchronous machines. typical applications: same as “vac-p”. • vdc-vac: specifies dcand ac-voltage. typical applications similar ‘vdc-q’ to the control mode: statcom, grid-side converter of doubly-fed induction machines, vsc-hvdc applications. the western electricity coordinating council (wecc) renewable energy modeling task force recommends the use of the single-machine equivalent representation shown in figure 5 to model central-station pv plants in wecc based cases [11]. this representation is also considered adequate for positive-sequence transient stability simulations at the bulk system level. if present, the interconnection transmission line, station transformer and plant-level reactive compensation should be represented explicitly, according to established industry practice. in this model, the equivalent generator engineering, technology & applied science research vol. 8, no. 6, 2018, 3592-3597 3594 www.etasr.com saidi et al: transient stability analysis of photovoltaic system with experimental shading effects represents the total generating capacity of all the inverters, the equivalent pad-mounted transformer represents the aggregate effect of all step-up transformers, and the equivalent collector system branch represents the aggregate effect of the pv plant collector system. with the proper model parameters, this model should approximate pv plant load flow characteristics at the interconnection point, collector system real and reactive losses and voltage profile at the terminals of the “average” inverter in the pv plant. the recommended load flow representation for high penetration pv scenarios is shown in figure 6 [12]. fig. 5. single-machine equivalent load flow representation fig. 6. recommended load flow model for high pv penetration iii. results and discussion a. experimental study of shading effects on pv system shade covered one complete cell area of the panel. in order to show the effect of the partial shadow many scenarios have been studied using the pv panel. a photograph of the pv with a water cooling system is shown in figure 7. fig. 7. photograph of the pv panel in a closed-loop water system, the incoming potable water is routed to water storage through valve, the cold water in the tank is pumped to the pv with water cooling system and the hot water produced in it flows to the water storage. the setup is provided with the necessary measuring instruments to carry out the required tests. a solar power meter of type amprobe (model solar-100) was used to measure the instantaneous value of the total incident solar radiation intensity (s, w/m 2 ). voltage, current and resistance were measured with a digital multimeter and rheostat connected with a data logger. the experimental investigation took place during the clear days of june. figure 8 shows the variation of array voltage with incident solar intensity (s). figure 9 presents the variation of array current with time. figure 10 shows the experimental results of both characteristics voltage and current. from this curve, this situation may also result in the development of hotspots in the panel. such situations must be avoided as they may not only cause drop in power output and efficiency but also damage the cells permanently. the experimental and the computational study are in good agreement. the computational study will be more close to the experimental value if the setup is modeled inside an enclosure with actual pv. fig. 8. array voltage curve fig. 9. array current curve fig. 10. array current and voltage (i-v) characteristic b. transient stability analysis of the pv system we used the ieee 9-bus standard system model which has 3 synchronous generators, 3 large equivalent loads with a total engineering, technology & applied science research vol. 8, no. 6, 2018, 3592-3597 3595 www.etasr.com saidi et al: transient stability analysis of photovoltaic system with experimental shading effects of 315mw and 115mvar connected in a meshed transmission network through 6 transmissions lines, and 3 two-winding power transformers (figure 11). the base mva is 100 and system frequency is fs=60hz. the base kv levels are 13.8kv, 16.5kv, 18kv, and 230kv. the line complex powers are around hundreds of mva each. for system data see [13]. the model was chosen mainly to investigate the voltage stability. the modified ieee 9-bus test system schematic is shown in figure 11. the synchronous generator in bus 3 is replaced by an aggregated model of pv generator. the reactive power of the pv generators is not plotted for all simulations because the pv generator is operating at unity power factor and therefore the reactive power consumed or produced by the pv generator is equal to zero. the characteristic parameters of pv array are listed in table i. fig. 11. modified ieee 9-bus system with pv system connected at bus 3 table i. pv array parameters [9] parameter symbol value rated apparent power sn 0.5mva rated power of the panel ppk 500kw rated voltage at mpp umpp 80v rated current at mpp impp 6a open circuit voltage uoc 90v short-circuit current isc a for dynamic simulations, a dynamic model of the power system is necessary and load flow data are not sufficient. in order to obtain a dynamic model of the test system from figure 1, the dynamic models of generators, governors and automatic voltage regulators are included in the overall system model. the system is modeled in digsilent/powerfactory. block diagrams of these models including parameter values for the ieee 9 bus test system are shown in [13]. the system is simulated with varying temperature inputs and disturbances and analyzed under various operating conditions. the focus is to investigate the impact of various variables on the fault response. during simulation, it is studied how different controllers perform under various circumstances and how far they contribute in the minimization of voltage deviation in the system. 1) load flow results in load flow studies, pv generators are commonly assimilated to solar pv integrated pv type generator bus due to their active power generation and voltage control capability. when their reactive generation limits are reached, they are considered load buses. we have represented the pv according to this hypothesis. to create a realistic steady state operating point, this system was modeled in steady state and the load flow results are given in figure 12. (a) (b) (c) fig. 12. load-flow results: (a) voltage magnitude, (b) generation (red: active power in mw, green: reactive power in mw), (c) general load (red: active power in mw, green: reactive power in mw) the results show that the bus voltages for every node are within the acceptable range, i.e. between 0.93p.u. and 1.07p.u. and no overvoltage is detected as illustrated in figure 12(a). the active and reactive powers injected to the different nodes are shown in figure 12(b). the active and reactive powers injected to the loads are represented by the histogram in figure 12(c). note that all the reactive power consumption is supplied by the source 1 'swing bus'. 2) dynamic simulation figures 13(b) and 13(c) show the power output of the pv generator under specific environmental conditions and time (during 10:00–16:00). in addition, these figures indicate that for peak temperature (58⁰c) at 13:45, the power is 0.375p.u. the current values change following the power changing values while the voltage values decrease gradually as shown in figures 13(d) and 13(e). the default operating mode of the inverter is with fixed unity power factor. however, the generator reactive power will be qmax=qmin=0 as shown in figure 13(c). 3) fault analysis fault occurs when temperature drops to zero in conditions such as extreme and sudden changes in whether as shown in figure 14. in time between 13:00 and 14:00, and in case of using cooling system on pv system, the active power raises to the peak value of 0.47p.u. (figure 14(b)) and drops to the minimum value of 0.385p.u. the voltage across the pv array drops to a minimum value of 620v at the time of zero temperature (figure 14(c)), while the current supplied by it rises to the maximum value of 680a following the change of the active power delivers by pv array as shown in figures 14(d) and 14(b). thus, more active power is delivered by the pv system when the temperature is decreased by using a cooling system or as impact of specific weather conditions. engineering, technology & applied science research vol. 8, no. 6, 2018, 3592-3597 3596 www.etasr.com saidi et al: transient stability analysis of photovoltaic system with experimental shading effects (a) (b) (c) (d) (e) fig. 13. system response in base case: (a) ramp temperature, (b) and (c) power output of the pv generator, (d) pv voltage and (e) pv current (a) (b) (c) (d) fig. 14. pv generator response to fault: (a) ramp temperature, (b) power output of the pv generator, (c) pv voltage and (d) pv current 4) transient stability simulation in this section, the dynamic interaction between the pv generator with power transmission system during and immediately after grid faults is illustrated and explained. the transient stability studies are conducted by applying a sudden three-phase short-circuit near the pv generator at the highvoltage terminals of the generator transformer at t=13.30 with a fault clearance time of 150ms by permanent isolation (tripping the relays). during the fault, it is assumed that the pv operates at its rated capacity with unity power factor. the short circuit path has an impedance zfault=0p.u. figures 15(a) and 15(b) present the pv active and reactive power during the pre-fault, fault and post fault phases which improve the voltage profile as shown in figure 15(c). before the fault is applied, the active power output of the pv is 0.45mw while the reactive power output is kept constant at 0.0mvar, while the initial terminal voltage of the pv is 1.03p.u. it is observed that when the short circuit occurs in the middle of line 5 (between bus 8 and bus 9), voltage responses indicate significant transient voltage drop profile in pv bus. the voltage in pv bus suddenly drops to a value of 0.08p.u. and recovers once the short circuit is cleared. in the period of the utility voltage recovery, reactive power injected from the pv generation fluctuates and reaches the setting value of the protection. thus, the reactive power injection curve improves voltage profile and the ride-through capability as shown in figure 15(c). as the active power is reduced, the power control can be implemented to fulfill grid code requirements when the transients have decayed. after fault clearance, the pv system can continue with nominal operation. thus, the pv panel connected to the grid increasing the ride-through capacity. this result is important because it indicates that the pv generator has a significant impact on the lvrt and the stability of the associated power system. (a) (b) (c) fig. 15. system response of the to fault event: (a) pv active power, (b) pv reactive power, (c) voltage iv. conclusion in this paper, the dc/dc converter, the circuit of solar cell of the pv module and their i-v characteristic are presented at various temperatures and irradiances. further, some aspects of stability issues of pv systems operating under high temperature environment were investigated. an experimental study of shading effects on the pv system has been presented. voltage stability, transient stability and general performance were assessed as functions of an experimental temperature profile. the study on the effects of temperature variation on the transient stability of the system was performed on the ieee 9bus system model. the simulation platform was established in digsilent/ power factory consisting of pv arrays, power inverters, transformers, transmission line and grid. the experimental results are in good agreement with the computational results. references [1] m. a. khlifi, “study and control of photovoltaic water pumping system”, journal of electrical engineering and technology, vol. 11, no. 1, pp. 117-1240, 2016 [2] z. a. kamaruzzaman, a. mohamed, “dynamic voltage stability of a distribution system with high penetration of grid-connected photovoltaic type solar generators”, journal of electrical systems, vol. 12, no. 2, pp. 239-248, 2016 [3] c. v. chandran, “ga based optimal control for maximizing pv penetration at transmission”, student journal of energy research, vol. 1, no. 1, articleno 3, 2016 engineering, technology & applied science research vol. 8, no. 6, 2018, 3592-3597 3597 www.etasr.com saidi et al: transient stability analysis of photovoltaic system with experimental shading effects [4] l. qu, d. zhao, t. shi, n. chen, j. ding, “photovoltaic generation model for power system transient stability analysis”, international journal of computer and electrical engineering, vol. 5, no. 3, pp. 297300, 2013 [5] m. yagami, s. ishikawa, y. ichinohe, k. misawa, j. tamura, “transient stability assessment of synchronous generator in power system with high penetration photovoltaics (part 2)”, ieee 2013 international conference on electrical machines and systems, busan, south korea, october 26-29, 2015 [6] s. abdelaziz, b. k. khadija, e. mohamed, “impact of large scale photovoltaic generation on voltage stability in distribution networks”, european journal of electrical engineering, vol. 18, no. 1-2, pp. 117138, 2016 [7] h. hussein, a. aloui, b. alshammari, “anfis-based pi controller for maximum power point tracking in pv systems”, international journal of advanced and applied sciences, vol. 5, no. 2, pp. 90-96, 2018 [8] s. a. g. stella, t. k. m. babu, k. gnanambal,“capacity and location effects of photo voltaic power generators on power systems stability”, advances in natural and applied sciences, vol. 9, no. 17, pp. 336-342, 2016 [9] h. jerbi, “design and performance analysis of a pv solar powered water pumping system”, international journal of advanced and applied sciences, vol. 4, no. 5, pp. 127-132 , 2017 [10] b. m. al shammari, m. a. khlifi, “analysis of dc\dc converter of photovoltaic system with mppt algorithms comparison”, 19th international conference on solar energy and energy storage, copenhagen, denmark, october 2-3, 2017 [11] s. soni, g. g. karady, m. morjari, v. chadliev, “comparison of full and reduced scale solar pv plant models in multi-machine power systems. conference”, 2014 ieee pes t&d conference and exposition, chicago, il, usa, july 24, 2014 [12] m. h. selamat, a. h. ahmad, “application of dye sensitized solar cell (dssc) from dammar carbon ‐ fe2o3 (iron (iii) oxide) composite counter electrode”, international journal of advanced and applied sciences, vol. 3, no. 7, pp. 35-40, 2016 [13] a. salah, a. k. mohamed, d. azzedine, “voltage and frequency regulation for an autonomous induction generators in small wind power plant”, international journal of advanced and applied sciences, vol. 6, no. 1, pp. 1-7, 2019 microsoft word etasr_v13_n4_pp11091-11095 engineering, technology & applied science research vol. 13, no. 4, 2023, 11091-11095 11091 www.etasr.com boubaker: a predictive vaccination strategy based on a swarm intelligence technique for the case of … a predictive vaccination strategy based on a swarm intelligence technique for the case of saudi arabia: a control engineering approach sahbi boubaker department of computer and network engineering, college of computer science and engineering, university of jeddah, saudi arabia sboubaker@uj.edu.sa (corresponding author) received: 22 april 2023 | revised: 13 may 2023 | accepted: 15 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5987 abstract the covid-19 pandemic caused high damage to health, social, and economic systems globally. saudi arabia has conducted a relatively successful experience in mitigating the virus. saudi authorities have started a vaccination campaign by the end of 2020 with more than 60 million doses being administered to citizens and residents by february 2, 2022. the objective of this study is to propose an optimal vaccination strategy in short and medium terms in order to help the local health authorities to first assess the vaccination campaign and to propose a predictive vaccination plan for eradicating the disease. for this purpose, a control engineering approach was used where the disease dynamics was identified and an optimal control law using the daily number of vaccines as input and the daily number of new infections as output was proposed and evaluated. the vaccination process was modeled as a discrete-time transfer function. the parameters of the transfer function were identified based on the particle swarm optimization (pso) algorithm while considering the routh-hurwitz stability criterion for analyzing the system stability. the final step of this study was dedicated to synthesize three controller variants (p, pi, and pid) for the case study of saudi arabia. the obtained results for the modeling and the controllers’ design were found to be promising. the results were found to be generic and can therefore be used to control other diseases or any other occurrence of covid-19 or similar viruses. keywords-covid-19; optimal control; model identification; vaccination strategy; disease mitigation i. introduction despite the control measures including social distancing, compulsory mask wearing, and schools’ closure (switching to online education), covid-19 disease continues to spread worldwide with several severe economic and public health consequences. around the end of 2020, many vaccines have been approved and adopted. saudi arabia has faced the first wave of the disease successfully and continues implementing several measures to eradicate it. however, the disease is showing a fluctuating behavior and multiple waves have appeared. vaccination is considered among the most important actions to be taken to control the disease spread and progressively return to the normal lifestyle. however, a tradeoff (compromise) between pharmaceutical intervention such as vaccine and "non-pharmaceutical interventions" (npis) like partial or complete lock-downs as well as social distancing practices, were highly required to ensure some kind of balance. despite the relative resistance to the vaccine at the beginning of the vaccination campaign (december 17, 2020), the number of administered doses in saudi arabia has increased reaching more than 60 million as of february 28, 2022. several researchers and healthcare specialists have worked on covid-19 mitigation from analysis, prediction, forecasting, and control perspectives. however, few works have handled the disease dynamics and control from a pure engineering control perspective. authors in [1] evaluated the impact of mass vaccination in ontario, canada using an agent-based transmission model. they reported that pfizer-biontech and moderna vaccines have contributed to reduce hospitalization by 27% and deaths by 31%. they concluded also that vaccination can substantially eradicate the virus. authors in [2] studied the modeling of covid-19 dynamics in a heterogenous population based on a compartmental model. the estimated structure of the disease has been then used to assess the effect of mass vaccination on the future progression of the epidemic. vaccination has been found to contribute to stopping the disease in a heterogenous population composed of two subpopulations with high and low disease transmission (ht and lt). authors in [3] proposed optimal vaccination schedules (how and when). several scenarios exploring the efficacy of vaccines in reducing the number of deaths were proposed. the main contribution of the paper was the design of optimal vaccine policies and its application to the case study of mexico. the proposed schedules may help the decision-makers to mitigate the disease. the authors in [4] have proposed a engineering, technology & applied science research vol. 13, no. 4, 2023, 11091-11095 11092 www.etasr.com boubaker: a predictive vaccination strategy based on a swarm intelligence technique for the case of … decision-making supporting system (dmss) for predicting the covid-19 effects under several control measures including vaccination. different data from several countries and regions were used. the results showed reduced number of deaths if 25% of the population is vaccinated. authors in [5] considered the quantification of the uncertainty of a mathematical model for covid-19 epidemic. a compartmental model including the vaccination as control variable was considered. social distancing measures are found to introduce uncertainty in the model which should be quantified correctly. this approach has been found to help in mitigating the disease under different strategies including two doses. the authors proposed a schedule for mass vaccination. since covid-19 dynamics are known to be complex, authors in [6] developed dynamic models for the disease based on data from the uk. they reported that vaccination alone is insufficient in eradicating the disease and that nonpharmaceutical interventions (npis) are needed. based on the modified sir model, authors in [7] tackled the problem of optimally reaching the end of covid-19 pandemic under an effective vaccination plan in india, brazil, and usa. the case of gamma variant of covid-19 in brazil was studied in [8] where an optimal vaccination strategy was designed and different scenarios were considered. moreover, authors in [9] analyzed the effect of different vaccination profiles in italy. additional insights about the effect of vaccination strategies for different variants, under various scenarios and in different countries/locations can be found in [10-14]. other aspects of covid-19 pandemic related research include early detection of the virus based on image processing [15], machine and deep learning (ml/dl) techniques for detection, forecasting, analysis and control of the disease [16], and contactless thermometer for temperature measurement [17], to cite a few. to the best of our knowledge, only a handful of studies have studied the vaccination process of covid-19 from a control engineering perspective. for that purpose, the main objective of the present study is to provide an optimal mass vaccination strategy to be applied in saudi arabia under different scenarios. this study will first model the disease dynamics and identify its parameters and then design a control strategy in terms of vaccination schedules optimal controllers. ii. methodology in this section, the steps of implementing an optimal vaccination strategy for the case study of saudi arabia will be presented in detail. first, the overall architecture of the work will be outlined. second, a transfer function model using the daily number of administered vaccines as input and the number of daily new infections as output will be established and calibrated. third, different optimal controllers (three variants of the proportional-integral-differential (pid) controller) will be synthesized under different scenarios using real records. figure 1 depicts the architecture of the followed steps. in this study, the vaccine administration and its effect on the daily new infections are viewed as a dynamic system modeled using the transfer function: ���� � �������� (1) ���� � � �� �⋯� �� ��� � ������ � �� �⋯���� ��� ������ (2) based on the previous equations, the effect of the daily number of administered vaccines and the number of daily new infections is expressed as: ���� � ∑ �� ��� � �������� � ∑ � ��� � !� �" �� (3) where ���� is the number of daily new infections and ���� is the number of vaccines administered daily to control the evolution of ���� , both considered at the tth day. � is an operator such that z -1 indicates the one-day delay. fig. 1. architecture of the optimal vaccination strategy. fig. 2. optimal vaccination strategy closed loop representation. in the first step, the system will be considered as an open loop to identify its parameters (coefficients in (3)). for this purpose, the pso technique is used (see the flowchart in figure 3). the transfer function parameters are assigned to the position vector components (j) of the i th particle, pos(i,j). as per the pso paradigm, velocity, vel(i,j), personal best position, pers(i,j), and the global best position, glob(i,j) are also associated. after a random initialization inside the search-space of each component and for each dimension, the swarm (group) of particles is flown progressively toward the sub-optimal solution of the optimization problem. in the current study, the objective of the optimization problem is to minimize the quadratic between the actual daily number of infections and the same number provided by (3). minimize ∑ �� #$ � �%&$ '(� � (4) engineering, technology & applied science research vol. 13, no. 4, 2023, 11091-11095 11093 www.etasr.com boubaker: a predictive vaccination strategy based on a swarm intelligence technique for the case of … where n is the number of observations (daily administered vaccines and daily new infections). the movement equations are described as follows:               1 1 1 1 1 , , , , , , t t t t t t t vel i j w vel i j c r pos i j pers i j c r pos i j glob i j       (5)    1 1, , , )(t t tpos i j pos i j vel i j   where t is the iteration number, w is an inertia weight decreasing from 0.9 to 0.4, c1 and c2 are two constant parameters and r1 and r2 are two random numbers inside the interval [0 1]. for more details about the pso technique, the interested reader can refer to [18] and the references therein. fig. 3. pso flowchart for modeling covid-19 dynamics. as per routh–hurwitz stability criterion for discrete-time linear systems, the search-space limits for all coefficients are chosen to be the interval [-1 1]. routh–hurwitz stability criterion has been extensively used in stability analysis. the main feature of this criterion is that it allows deciding about the stability of linear and nonlinear systems only through analyzing the model coefficients without any need to calculate the eigenvalues [19]. due to its practicability, the routh-hurwitz criterion has been used in many applications such as gridconnected filters and connectors [20] and tuberculosis disease transmission stability [21]. iii. results and discussion the dataset used to conduct this study was collected from [22]. it included records of covid-19 around the world (infections, recoveries, deaths, vaccines, hospitalizations, etc.). 358 observations of new daily infections and administered vaccines in saudi arabia covering the period between 2021-3-8 and 2022-2-28 were used. n=300 observations were used for the identification of the model open-loop parameters of (3) using the algorithm described above. the remaining 58 observations were used to validate the calibrated model. three metrics were used to measure the quality of the model and to justify the extent it can reproduce real observations. these metrics are described as follows [18]: mean absolute percentage error ()*+,): )*+, � ���( ∑ |./01�$�2.341�$�| ./01555555 ($�� (7) coefficient of determination (r 2 ): 6' � 1 � 8 ∑ �./01�$�2.341�$��981: 8 ∑ �./01�$�2./01555555�981: (8) root mean square error (rmse): 6);, � < �( ∑ �� #$ ��� � �%&$ ����'($�� (9) where � #$ and �%&$ are the estimated and the actual number of new infections recorded at the t th day and �5 is the average value. fig. 4. actual and estimated new daily infections during the testing phase. the model coefficients and performance metrics (obtained for the testing phase) are shown in table i. as depicted in figures 4-5, the actual and estimated curves are almost the same. in addition, the performance metrics are high since the coefficient of determination is almost close to 1 (1 corresponds to the ideal fit) and the mape is low (3.1675%). an rmse of 132 can be considered as interesting when compared to the total number of infections. the open-loop transfer function identification convergence process is depicted in figure 6. it can be observed that the optimal criterion started from high values at the beginning of the pso-based optimization process n e w i n fe c ti o n s engineering, technology & applied science research vol. 13, no. 4, 2023, 11091-11095 11094 www.etasr.com boubaker: a predictive vaccination strategy based on a swarm intelligence technique for the case of … and converges to small values (around zero) starting from iteration 30 (the number of iterations was chosen as 100 and that was considered as the stopping criterion of the optimization process). the model coefficients are all inside the unit circle (between -1 and 1) as per the routh-hurwitz criterion of stability. table i. model optimal parameters and performance metrics for the testing phase parameter mape r 2 rmse a0 a1 a2 b1 b2 b3 value 3.1675% 0.9933 132 5.3523e-05 1.0446e-04 -1.7041e-04 -0.995 0.327 -0.334 fig. 5. scattered plot of actual and estimated (by the model) new daily infections during the testing phase. fig. 6. convergence of the model identification process. table ii. optimal controllers for the vaccination process in saudi arabia controller type controller parameters p pc(z) = kp = -235 pi 1 ( ) ts kppic ki z z    with kp = -1.57e+03, ki = -4.54, ts = 1 pid ( 1 1 ) ts z ts kp ki kd z ts pidc z       with kp = 8.76, ki = 0.00016, kd = 1.2e+05, ts = 1 using matlab's proportional-integral-derivative (pid) tune command, proportional (p), proportional-integral (pi), and pid controllers were synthesized. the transfer functions of the regulators as well as the corresponding closed-loop transfer functions are provided in table ii. the main objective of the designed pid controller is to force the output (daily new infections) to follow a predefined profile imposed by the decision makers. this imposed profile may have as a purpose to flatten the disease spread curve within a fixed period. in addition, disturbance factors such as unpredictable events or pilgrims coming from different countries for performing hajj and umrah (as saudi arabia is hosting the two holey mosques in makkah and madinah) are considered as disturbances which are rejected by the pid (or derivative) controller. iv. conclusion in this paper, an optimal vaccination strategy for covid19 was designed based on the discrete-time linear system theory and the swarm intelligence approach, namely the particle swarm optimization (pso). the vaccination process modeled as a transfer function having the daily number of administered vaccines as input and the daily number of new infections as output, was optimally tuned taking into consideration stability issues based on routh-hurwitz necessary and sufficient stability condition (the poles of the transfer function should be inside the unit circle). three different controllers (p, pi, and pid) were designed. the designed controllers should generate optimal vaccination profiles (control signals) that should drive the number of new daily infections to track any profile of new infections that may be targeted by the decision-makers. the obtained results are generic in their broad sense and they can be easily extended to other diseases. as perspectives, we can expect to collect datasets from other diseases and test the feasibility of the approach presented in this paper. in terms of decision-making, the proposed approach constitutes a strong tool that can help the decision makers to mitigate the virus and limit its spread using pharmaceutical interventions such as vaccines in addition to non-pharmaceutical interventions. acknowledgment this work was funded by the university of jeddah, jeddah, saudi arabia, under grant no. (uj-21-dr-36). the authors thank the university of jeddah for the technical and financial support. references [1] t. n. vilches, k. zhang, r. van exan, j. m. langley, and s. m. moghadas, "projecting the impact of a two-dose covid-19 vaccination campaign in ontario, canada," vaccine, vol. 39, no. 17, pp. 2360–2365, apr. 2021, https://doi.org/10.1016/j.vaccine.2021.03.058. [2] v. volpert, m. banerjee, and s. sharma, "epidemic progression and vaccination in a heterogeneous population. application to the covid-19 epidemic," ecological complexity, vol. 47, sep. 2021, art. no. 100940, https://doi.org/10.1016/j.ecocom.2021.100940. 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[11] g. b. libotte, f. s. lobato, g. m. platt, and a. j. silva neto, "determination of an optimal control strategy for vaccine administration in covid-19 pandemic treatment," computer methods and programs in biomedicine, vol. 196, nov. 2020, art. no. 105664, https://doi.org/ 10.1016/j.cmpb.2020.105664. [12] m. angeli, g. neofotistos, m. mattheakis, and e. kaxiras, "modeling the effect of the vaccination campaign on the covid-19 pandemic," chaos, solitons & fractals, vol. 154, jan. 2022, art. no. 111621, https://doi.org/10.1016/j.chaos.2021.111621. [13] a. thongtha and c. modnak, "optimal covid-19 epidemic strategy with vaccination control and infection prevention measures in thailand," infectious disease modelling, vol. 7, no. 4, pp. 835–855, dec. 2022, https://doi.org/10.1016/j.idm.2022.11.002. 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[22] "owid/covid-19-data," github. https://github.com/owid/covid-19-data. microsoft word 9-2242_s6 engineering, technology & applied science research vol. 8, no. 5, 2018, 3350-3354 3350 www.etasr.com jayaswal & palwalia: performance analysis of non-isolated dc-dc buck converter using resonant … performance analysis of non-isolated dc-dc buck converter using resonant approach kuldeep jayaswal department of electrical engineering rajasthan technical university kota, india kuldeep12555@gmail.com dheeraj kumar palwalia department of electrical engineering rajasthan technical university kota, india dheerajpalwalia@gmail.com abstract—dc-dc converters preserve or control the output dc voltage. due to parasitic constituents such as leakage capacitance of both diode and inductor, and transformer leakage inductance, dc-dc converters mostly operate on rigid switching conditions which result in high switching losses. these parasitic constituents affect the dc-dc converter’s operational reliability, instigate electromagnetic interference issues and limit the converter’s operation at higher frequency operations. in this paper, resonant or soft-switch approach has been employed to improve the operating performance and design-oriented principle investigations have been carried out for overcoming the issues of parasitic constituents in 24-12v dc-dc step-down (buck) converter. this paper divulges the analysis and matlab simulation results for 24-12v buck converter based on resonant or soft-switching approach. keywords—operational reliability; dc-dc converter; resonant converter; matlab simulation; step-down converter i. introduction dc-dc conversion technologies are an important subject of research in the power engineering and drives area. these devices are electronic platforms used to customize dc electric voltage efficiently [1]. these converters are mostly used for changing the different voltage level [2-5]. mainstream pwm converters do not work on soft-switch approach, they mostly operate on hard switching conditions. semiconductor devices suffer from switching losses and electro-magnetic interference problems during switching-on and off which results in poor converter performance [5-6]. there are various factors which are accountable of switching loss like capacitance of both diode and switch [7-11]. this paper shows the softswitch/resonant approach based on null voltage switching operation for reduction of all uncertainties related to customary dc-dc buck converter. ii. non-isolated dc-dc converter topologies and resonant/soft-switch approach a. the concept behind the requirment of resonant approach dc-dc semiconductor devices like bjt, mosfet or igbt work as a switch at required frequency (f) [12]. the elementary circuit topologies of non-isolated dc-dc converters are shown in figure 1 [13-19]. the voltage and current waveforms of the switch may have different shapes. as the voltage and current across the switch are not zero during switching times, there will be switching losses. due to this, the switching frequency is bounded in pulse-width modulating converters. if the frequency is increased, then high electromagnetic interference problems will occur [2]. high stress will be on device during switching times due to high spikes in switch voltage and current. that’s why such a switching results to low switching losses. fig. 1. non-isolated dc-dc converter topologies without resonant/softswitch approach in this paper, the buck non-isolated topology has been used as a principal platform to revamp performance and operational reliability of the converter. for this purpose, zero voltage switch operational approach has been used via appropriate placement of resonant switches. mosfets and igbts are mostly used as a switch in electronic conversions where at a particular time period they have to operate either in fully on or off condition. being a current controlled device, mosfets are much faster in switching operation in comparison to bjt [8]. thus, these devices are most eligible to work at higher switching frequencies. engineering, technology & applied science research vol. 8, no. 5, 2018, 3350-3354 3351 www.etasr.com jayaswal & palwalia: performance analysis of non-isolated dc-dc buck converter using resonant … b. switch configuration concept for zvs approach switching losses are related to the switching frequency fs, and these losses limit the maximum switching frequency. the energy reserved in output capacitance co of switch just before the transistor turns on is given as ��� = ����� � 2⁄ (1) where ����=transistor voltage during off-instant. when the switch turns on, the energy imposed on the switch, causes transistor switching loss � �(���) = ����� �� 2⁄ (2) in this approach, a special switch configuration has been used which is made up with combinations of two different resonant elements with an anti-parallel diode. figure 2 shows the switch configuration for resonant or smooth switching [1419]. here a capacitor is coupled in counterpart with sw and resonant inductor in series. in this paper, resonant or zero voltage, switch operational approach has been used for the analysis of 24-12v dc-dc step-down converter. according to this when the switch is on, the voltage at the switch becomes zero, and that’s why the energy reserved in the output capacitance of switch is null during turn this time. hence, the switching on losses becomes zero, which provides smooth efficient operation at high frequencies and results in the reduction in the amplitude of the converters. during this period, the above mentioned switch configuration plays a crucial role. in this, the resonant capacitor will resonate to null voltage before sw is turned-on. on the other hand, when the switch is turned-off, a little time is required to charge the resonant capacitor and hence the voltage over the sw is not increased abruptly. so, there is a very small overlapping between the sw current and voltage. so, the zero voltage switch operation is achieved. the main idea behind this approach is the fact that these soft-switch converter topologies absorb different parasitic components, like transformer’s leakage inductance, output capacitance of both transistor and diode. figure 3, exhibits the proposed topology for non-isolated buck (step-down) converter based on resonant technique. initially the switch remains in off situation during this instant current across switch is null but the voltage is not. fig. 2. zvs approach based on resonant switch configuration fig. 3. topology for non-isolated buck converter based on zero voltage switch/resonant approach during the switch-on, the voltage is forced to be zero and the current is a little-bit delayed so that it will start to lift after the zero voltage as shown in figure 4(b). in zero current switch approach, a switch is off during zero current. the voltage through it might be zero but the current across the device is not. voltage is granted to lift after current becomes zero as illustrated in figure 4(c). fig. 4. (a) firm-switching converter incident, (b) zero or null voltage switching case, (c) zero or null current switching case iii. analysis of dc-dc buck converter with and without soft switch approach figure 5 shows the conventional buck or step-down converter without resonant or soft switch approach, which is a cheap electronic device used to obtain reduced voltage. fig. 5. dc-dc buck converter topology without resonant or soft switch approach the switch operation is regulated by a modulator and turned-on and off at duty ratio “d” and at required switching frequency � = 1/�. closed loop control has been used for stable operation: �� = ��� ⇒ ��� ∕ (��� + ����) = ���� (3) the operational strategy consists of two stages. at t=0, the switch is in on state and the diode is in off state because vd =−vi. further current across the inductor increases continuously due to voltage difference vl=vi–vo. at this time the current through the inductor and switch are both equal and energy is delivered to energy storage elements. in the second stage, at t=dt, the switch is in off state by gate driver, but during this time the inductor still has the previously stored current which turns the diode on. during this instant, the voltage over the inductor is given as (–vo) and the voltage over the switch is given as (vi). that’s why il decreases continuously with a slope of (–vo)/l. input voltage is unplugged from the circuit and doesn’t transfer any energy to the storage elements. the average output voltage in the buck converter is given by (4), which does not depend on load [6]. �� ��⁄ = � ⇒ �� = ��� (4) the buck converter circuit based on the proposed approach is shown in figure 8. time time time (a) (b) (c) power loss voltage curve voltage curve current curve current zvs switching current zcs switching conventional conventional on off voltage engineering, technology & applied science research vol. 8, no. 5, 2018, 3350-3354 3352 www.etasr.com jayaswal & palwalia: performance analysis of non-isolated dc-dc buck converter using resonant … fig. 6. circuit state & waveform for time interval 0 <t≤dt fig. 7. circuit state for time interval dt<t≤t fig. 8. buck topology based on resonant approach the current through the inductor l remains somewhat constant so energy storage element is modelled as current sink, �. table ii, shows the analysis and operational process under four time segments, zero to t1, t1 to t2, t2 to t3 and finally t3 to t.. for simulating dc-dc converter with and without resonant approach, complete mathematical analysis has been done for the design of a 24v-12v converter through different parametric equations. the converter based on the proposed approach has been analyzed through parametric equations for 24v input and 12v output for 100khz and 1mhz. by considering the different level of currents, loss calculations have been made for both types of converter and final remarks have been obtained which are depicted in figure15 that shows the reliable or efficient performance of the converter. table i. parameteric equations parameters used expressions transfer function for dc voltage !" $� ≡ ��/�� = 1 − ' 0.90 �� + �, characteristics impedance (z0) -./ /⁄ or (0)1�=(1/./ /) max. current across switch from 0 to dt 2 = (∆45)/2 + 4� quality factor (q) 65/./0� resonant frequency ‘f0’ 0.909*�,/(1-d) or � /�� device stress for ‘s’ and ‘d’ ( � 278) = 2 � & :;<= = 1 $278 = 2 1 & �$278 = ��/ �� = 1/� calculation of inductor’s value .> 65./?0�. calculation of capacitor’s value > ?/650�. max. voltage across switch � 2 (1 + !@ab ?⁄ ) iv. simulation results a. without resonant/soft-switch approach fig. 9. current across inductor fig. 10. output current of buck converter (current versus time) fig. 11. output voltage (12v) of buck converter (voltage versus time) engineering, technology & applied science research vol. 8, no. 5, 2018, 3350-3354 3353 www.etasr.com jayaswal & palwalia: performance analysis of non-isolated dc-dc buck converter using resonant … table ii. operational process for non-isolated dc-dc buck converter using resonant or soft-switch approach time interval circuit models/states response/behavior waveforms 0<t≤t1 (inductor charging time ) • diode and switch both are on. • the voltage over the switch, voltage over diode and current over the capacitor are zero. • only voltage across resonant inductor is equal to input supply i.e. vlr=vi t1<t≤t2 • switch is on and diode becomes off. • at this instant diode is reverse biased because @$ = −�� • in this duration switch and resonant inductor’s current become equal to output current. t2<t≤t3 • diode and switch are both off. • switch current and diode current will be zero. • further voltage across resonant inductor will also be zero. t3<t≤t • diode is on state and switch is off • switch and diode current will be zero. • further current across resonant inductor will be equal to the output current and voltage across resonant capacitor and switch voltage will be equal to supply voltage. b. with resonant/soft-switch approach fig. 12. output current of buck converter via resonant/soft-switch approach fig. 13. output voltage (12v) of buck converter via resonant/soft-switch fig. 14. outputs of proposed buck converter using resonant/soft-switch approach engineering, technology & applied science research vol. 8, no. 5, 2018, 3350-3354 3354 www.etasr.com jayaswal & palwalia: performance analysis of non-isolated dc-dc buck converter using resonant … fig. 15. plot between efficiency and output current iv. conclusions in this paper, analysis has been done for transformer-less dc-dc buck converter topology with and without resonant approach. pulse width modulating dc-dc converters operate on rigid switching conditions where voltages and currents show their rapid change from high to low value and vice-versa. because of this, semiconductor devices cause switching loss problems during on and off states which affect the overall system performance. basically these losses are caused by the capacitance of both diode and transistor. in this research paper, 24-12v transformer-less dc-dc buck converter has been analyzed. simulation results acquired for the proposed topology justified the soft-switch or resonant approach. this paper shows that if a capacitor is connected in counterpart with switch and a resonant inductor is connected in series with the switch, it absorbs the parasitic elements which provide smooth operation of conversion even on higher switching frequencies. due to this topology, voltage is zero through the switch during switch-on. that’s why, the accumulated energy in output capacitance co is reduced to zero. hence, the switching on losses becomes zero, which improves the operational reliability of the dc-dc converter. it has been shown that resonant or zero voltage switch approach makes the buck converter more efficient in comparison to the conventional buck converter. it is also evident that as the current increases, efficiency decreases. so the resonant or soft switch approach plays a crucial role in improving the buck converter efficiency over custom switching buck converter which ultimately improves the performance of the converter. references [1] b. w. williams, “basic dc-to-dc converters”, ieee transactions on power electronics, vol. 23, no. 1, pp. 387-401, 2008 [2] h. a. huynh, y. han, s. park, j. hwang, e. song, s. kim, “design and analysis of the dc – dc converter with a frequency hopping technique for emi reduction”, ieee transactions on components, packaging and manufacturing technology, vol. 8, no. 4, pp. 546-553, 2018 [3] l. huber, l. gang, m. m. jovanovic, “design-oriented analysis and performance evaluation of buck pfc front end”, ieee transactions on power electronics, vol. 25, no. 1, pp. 85-94, 2010 [4] v. vorperian, “synthesis of medium voltage dc-to-dc converters from low voltage, high-frequency pwm switching converters”, ieee transactions on power electroics. vol. 22, no. 5, pp. 1619-1635, 2007 [5] m. f. schlecht, l. f. casey, “comparison of the square-wave and quasi-resonant topologies”, ieee transactions on power electronics, vol. 3, no. 1, pp.83-92, 1988 [6] k. jayaswal, d. k. palwalia, g. jain, p. kumar, “design-oriented analysis of non-isolated dc-dc buck converter”, ciencia e tecnica vitivinicola journal, vol. 30, no. 2, pp. 177-213, 2015 [7] g. chen, y. deng, x. he, y. wang, j. zhang, “zero-voltage-switching buck converter with low-voltage stress using coupled inductor”, iet power electronics, vol. 9, no. 4, pp. 719-727, 2015 [8] n. mohan, t. m. undeland, w. p. robbins, power electronics: converters, applications, and design, john wiley and sons, 2002 [9] t. w. ching, k. u. chan, “review of soft-switching techniques for high-frequency switched-mode power converters”, ieee vehicle power and propulsion conference, harbin, china, september 3-5, 2008 [10] k. shenai, m. trivedi, p. g. neudeck, “characterization of hardand soft-switching performance of high-voltage si and 4h-sic pin diodes”, ieee transactions on electron devices, vol. 49, no. 9, pp. 1648-1656, 2002 [11] f. mihalic, d. kos, “conductive emi reduction in dc-dc converters by using the randomized pwm”, ieee isie, dubrovnik, croatia, june 23-25, 2005 [12] c. y. chiang, c. l. chen, “zero-voltage-switching control for a pwm buck converter under dcm / ccm boundary”, ieee transactions on power electronics, vol. 24, no. 9, pp. 2120-2126, 2009 [13] t. f. wu, s. a. liang, “a systematic approach to developing singlestage soft switching pwm converters”, ieee transactions on power electronics vol. 16, no. 5, pp. 581-593, 2001 [14] b. lin, h. chiang, c. chen, c. huang, “implementation of the soft switching dc/dc converter”, 2nd ieee conference on industrial electronics and applications, harbin, china, may 23-25, 2007 [15] w. lee, d. han, c. morris, b. sarlioglu, “minimizing switching losses in high switching frequency gan-based synchronous buck converter with zero-voltage resonant-transition switching”, 9th international conference on power electronics-ecce asia, seoul, s. korea, june 15, 2015 [16] n. z. yahaya, k. m. begam, m. awan, “experimental analysis of a new zero-voltage switching synchronous rectifier buck converter”, iet power electronics, vol. 4, no. 7, pp. 793-798, 2010 [17] g. yanik, e. isen, “quasi resonant full wave zero current switching buck converter design , simulation and application”, balkan journal of electrical & computer engineering, vol. 1, no. 2, pp. 71-77, 2013 [18] m. salem, a. jusoh, n. r. n. idris, i. alhamrouni, “performance study of series resonant converter using zero voltage switching”, ieee conference on energy conversion (cencon), 2014, johor bahru, malaysia, october 13-14, 2014 [19] k. p. sijin raj, p. george john, “buck converter using soft switching pwm converter with current sharing in switches”, international journal of engineering and innovative technology, vol. 2, no. 10, pp. 47-50, 2013 [20] k. h. liu, f. c. y. lee, “zero-voltage switching technique in dc-dc converters”, ieee transactions on power electronics, vol. 5, no. 3, pp. 293-304, 1990 88 90 92 94 96 98 100 1 2 3 4 5 6 7 8 9 10 11 ŋ % output current efficency conventional buck converter efficency proposed buck converter efficency engineering, technology & applied science research vol. 8, no. 4, 2018, 3199-3202 3199 www.etasr.com bhatti et al.: implementation of building information modeling (bim) in pakistan construction industry implementation of building information modeling (bim) in pakistan construction industry imtiaz ali bhatti faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia engrimtiaz290@gmail.com abd halid abdullah faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia abdhalid@uthm.edu.my sasitharan nagapan faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia sasitharan@uthm.edu.my nabi bux bhatti u.s.-pakistan centers for advanced studies in water mehran university of engineering & technology, sindh, pakistan nabibuxbhatti76@gmail.com samiullah sohu faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia sohoosamiullah@gmail.com ashfaque ahmed jhatial faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia aajhatial@hotmail.com abstract—this paper examines the implementation of building information modeling (bim) in construction industry. various initiatives and approaches are used in different countries to promote the bim implementation in their construction industries. the real implementation and use of bim remains a major concern of the construction industry. this study investigates the implantation of bim globally, in developed countries and the percentage of implementation of bim in constriction industry of sindh, pakistan. this research demonstrates 131 responses from bim users regarding bim implementation whose collaboration aspects produce the highest positive impact. the adopted methodology is an online questionnaire survey and literature review which was conducted to find out the implementation of bim in construction industries of developed countries. this research reveals that bim implementation is increasing continuously over the past few years. a number of developed countries are emerging successful bim implementation strategies, united states, united kingdom, germany, france are generally leading the way. however, according to our study findings, only 11% of industries have implemented bim in sindh, pakistan. keywords-building information modeling; implementation; construction industry; developed & developing countries i. introduction building information modeling (bim) is a new innovative technology. the use of bim technology is not limited only to the design of 3d models, but it can be used for detailed design and analysis, to create project documentation, to prepare estimates and to monitor the progress for ongoing project until completion [1]. except that, bim can be used for operation, maintenance and demolition of existing projects. bim technology is used as a three-dimensional 3d model-based process which provides architecture, engineering and construction (aec) professionals with more efficient planning, design, construction and management of buildings and infrastructure projects [2]. bim can be viewed as a virtual process that encompasses all aspects, disciplines, and systems of a facility within a single virtual model, allowing all design team members (owners, architects, engineers, contractors, subcontractors, and suppliers) to collaborate more accurately and efficiently than using traditional processes [3, 4]. bim also facilitates us to enhance decision making and implementation throughout the life cycle of a project [5-6]. previously most of design decisions were taken by experts who were designing the project according to client specifications and requirements because the client himself or other technical people could not take decisions on their behalf. but in modern days, bim technology has brought all stakeholders to one platform where they can contribute from the initial design process to the end of the project. the implementation of bim is a problem for developed and developing countries, whereas in developed countries their government, technical organizations and institutions are performing great role to implement bim technology and it has been found that they have succeeded to a certain level. the implementation of bim is a chronic concern for developing countries like, malaysia, sri lanka, india, pakistan etc. this research is limited for sindh, pakistan. the primary objective of this study is to identify the percentage of bim implementation in pakistan construction industry. bim as an official term was used in 1992 and later on in a 2000 software called “revit software”. after that the same software was sold to autodesk and they brought many new changes in 2004. currently that software is known as autodesk revit. bim has brought revolutionary change in the field of building design to some high level of extent [2]. according to [7] bim provides a platform to work with collaboration. in engineering, technology & applied science research vol. 8, no. 4, 2018, 3199-3202 3200 www.etasr.com bhatti et al.: implementation of building information modeling (bim) in pakistan construction industry bim, a single project can be subdivided into different phases because in a single project there is involvement of different experts of various fields depending upon the nature and type of project. they accumulate their work together into a single project. therefore, different experts in various fields using bim software don’t have worry about the design process because integration and coordination will be dome by the system automatically. a wide research is ongoing to realize the issues for bim implementation in construction industry [8-10] and to communicate the advantages of real bim implementation to construction industry [11-12]. authors in [13] have been tracking the evolution and implementation of bim in global construction industry. they report that bim implementation was 26% in 2007 and over doubled in less than a decade, reaching 57% in 2016. bim is widely used in united states, united kingdom and western europe. familiarity of bim spread out among developed and developing countries and, after 2007, the ratio of bim users increases. increasing ratio of bim usage is considerably higher in developed countries rather than in developing countries. in north america a survey was carried out regarding bim implementation in construction industry. in 2008 it was recorded that only 28% of construction companies were using bim, but when construction industry got familiar with the advantages of bim, the escalation reached to 72% in 2012. authors in [13] predicted that this will continue to escalate, with bim market from 1.8 billion usd in 2012 to reach 6.5 billion usd by 2020. sudden increase in number of bim projects is anticipated over the next 18 months transforming well beyond the achievement to date. authors in [13] carried out a survey and collected responses of 727 contractors from developed and developing countries regarding bim implementation in the top ten of the largest national construction markets in the world. united states, united kingdom, germany, malaysia, france, australia, canada, india, singapore, sri lanka and middle east had been reviewed as described below. a. united states a significant number of construction companies in us believe that bim has a potential to reduce the cost of the projects. this is the reason why 72% of companies are using it. b. united kingdom according to [15] bim implementation in uk had reached 54%, whereas in 2015 it was 48%. since april 2016, the government has issued a strategy for construction companies, which aims to achieve 20% savings in procurement cost. c. germany bim implementation in germany has reached up to 90% [14]. most of the construction companies and clients are aware about bim technology so there is a demand for it. d. malaysia only 20% of the architectural firms are implementing bim while 10% of surveying firms are using it [11, 16, 17]. e. france in 2014 the government of france decided to develop 500,000 houses in 2017 by using bim for that project [18]. they digitized the building industry by investing 20 million euros. today 65% of construction companies are using bim aiming to achieve sustainability and reduced costs [18]. f. australia a research was carried out through a series of interviews with 25 construction companies from two major cities in the state of queensland. they found that 51% of companies use bim [19]. g. canada canada has founded various organizations to adopt and implement bim, like canada bim council, institute for bim in canada and building smart canada. this is the reason why the ratio of implementing bim has reached 67% and still keeps on increasing. h. india bim adoption in india is very low compared to other countries. according to research, it is found that only 22% construction companies are using bim. in india bim is also known as virtual design and construction (vcd) [20]. i. singapore bim has transformed the construction industry. singapore bim implementation rate is rising rapidly [21]. j. middle east according to [22] bim is implemented by 10% of construction companies on their projects. ii. benefits of using bim based on the survey responses and interviews conducted in previous studies, it is found that bim has potential and must be deployed in construction industry. most respondents have significantly reduced cost and time with the use of bim [24], some professionals using bim reported that it helps improve coordination among different stakeholders, such as architects, contractors, suppliers and other project team members. publications, researches and policies have been developed to implement bim. the governments of us, uk, germany, canada and other developed countries have made the implementation of bim compulsory in their industries [24]. in uk and canada there’s a high level of bim awareness because uk government has invested on their professionals to be trained in bim technology, whereas a number of institutions launched by canadian government are specialized to aware professionals about bim, while european countries like finland, denmark, norway and sweden are known as bim leaders [25]. iii. methodology based on the collected information, an online questionnaire was developed and distributed for collecting data regarding the practical implementation of bim in construction industry of sindh, pakistan from targeted participants. the link to the questionnaire survey was sent to contracting companies, consultant and architectural firms and engineers. the firms’ email addresses were obtained from their websites, whereas the engineers were contacted through social networks. the engineering, technology & applied science research vol. 8, no. 4, 2018, 3199-3202 3201 www.etasr.com bhatti et al.: implementation of building information modeling (bim) in pakistan construction industry questionnaire was consisting of personal information and just only 11 questions regarded the bim evaluation. the combined sample size of the study is summarized in table i. table i. construction contributor types of contributors questionnaires distributed contracting companies 50 consultant & architecture 50 engineers (1-5 years’ experience) 100 iv. survey questionaire the questionnaire consisted of two sections, section a inquiring the demographics of the respondents while section b was related to bim in construction industry of pakistan. the survey questionnaire is depicted in the appendix. v. results and discussion a. survey analysis the questionnaire survey respondents were contracting companies, consultant and architectural firms and engineers. the response rate from contracting companies was 58%, from consultant and architectural firms 62% and from engineers 71%. all the companies were of medium size having 1-100 employees and all engineers had 3-5 years of experience. the survey analysis is shown in table ii. table ii. survey results survey analysis respondents sample size respond rate respond percentage contracting companies 50 29 58% consultant & architectural firms 50 31 62% engineers 100 71 71% b. response analysis 1) contracting companies questionnaires were distributed among 50 contracting companies and only 29 of them responded. when their responses were further analyzed, 4 companies were using revit architecture software which is a bim application to generate only 3d geometrical models, 11 companies had known bim but were not implementing it and 14 companies were unaware about bim. this shows that only 8% of contracting companies were using a bim application which is a very limited and initial stage of bim, and only to generate 3d geometrical models. 2) consultant and architectural companies questionnaires were distributed among 50 companies and only 31 companies responded. only 7 companies were using a bim application to generate 3d geometrical models for architectural and mep services, their percentage being 14% which only shows that these firms are also using bim to a very limited level. 24 companies were familiar to bim but they were using other applications to generate 3d models. 3) engineers questionnaires were distributed among 100 engineers and 71 of them responded. only 11 engineers were familiar with bim and their knowledge of bim applications was focused only in 3d geometric model generation. the rest of the engineers were not familiar with bim. vi. conclusion bim has altered the way of designing, constructing and operating buildings. bim utilization led to augmented profitability, reduced cost, reduced project duration and enhanced customer-client relationships. implementation of bim has progressed rapidly. in a global scale, in 2007 it was 26% and in 2016 it reached 57%. bim implementation is an enduring problem in developing countries. in pakistan only 11% of related industry has implemented bim and only to generate 3d models which is a very limited part of bim. appendix the survey questionnaire which was distributed among the respondents, section-wise follows. section a: demographics 1. name and address of company / organization 2. type of your organization consultant contractor client other (please specify) 3. type of building project undertaken by your company residential building non-residential building others (please specify) 4. the size of projects you have involved in terms of contract amount: 0-50 million pkr 51-100 million pkr 101-500 million pkr above 500 million pkr 5. level of your academic qualification diploma bachelors masters ph.d 6. years of working experience in construction industry 0-5 years 6-10 years 11-15 years 16-20 years 21-25 years more than 25 years 7. current position in the organization engineer construction manager planner project manager quantity surveyor resident engineer contracts manager general manager section b: implementation of bim in construction industry of pakistan 1. are you aware of bim and its benefits? yes no 2. is your company aware of bim and its uses? yes no 3. does your company use any bim software? yes no 4. which bim software is used in your company/organization if any? revit (arch, struct, mep) archicad vectorworks architect microstation 5. 5. do you believe that industry is not yet clear enough of what bim actually is? yes no engineering, technology & applied science research vol. 8, no. 4, 2018, 3199-3202 3202 www.etasr.com bhatti et al.: implementation of building information modeling (bim) in pakistan construction industry references [1] s. frolov, a. hovorun, m. ostapenko, “prospects for the innovative development of information technology in ukraine during economic crisis”, innovative marketing, vol. 13, no. 1, pp. 55–60, 2017 [2] a. t. haron, a. j. marshall-ponting, g. f. aouad, “building information modelling in integrated practice”, 2nd construction industry research achievement international conference, kuala lumpur, malaysia, november 3-5, 2009 [3] a. bataw, on the integration of building information modelling in undergraduate civil engineering programmes in the united kingdom, phd thesis, university of manchester, 2015 [4] i. petri, s. kubicki, y. rezgui, a. guerriero, h. li, “optimizing energy efficiency in operating built environment assets through building information modeling: a case study”, energies, vol. 10, no. 8, pp. 1167-1183, 2017 [5] m. bilal, l. o. oyedele, j. qadir, k. munir, o. o. akinade, s. o. ajayi, h. a. alaka, h. a. owolabi, “analysis of critical features and evaluation of bim software: towards a plug-in for construction waste minimization using big data”, international journal of sustainable building technology and urban development, vol. 6, no. 4, pp. 211–228, 2015 [6] m. gerges, o. ahiakwo, m. jaeger, a. asaad, “building information modeling and its application in the state of kuwait”, international journal of civil, environmental, structural, construction and architectural engineering, vol. 10, no. 1, pp. 81–86, 2016 [7] s. b. mohd, building information modelling (bim) implementation model for construction project design stage, msc thesis, universiti tun hussein onn malaysia, 2015 [8] hm government, building information modelling. industrial strategy: governement and idustry in partnership, crown, 2012 [9] p. smith, “bim implementation global strategies”, procedia engineering, vol. 85, pp. 482–492, 2014 [10] h. son, s. lee, c. kim, “what drives the adoption of building information modeling in design organizations? an empirical investigation of the antecedents affecting architects’ behavioral intentions”, automation in construction, vol. 49, part a, pp. 92–99, 2015 [11] m. harris, e. ismail, a. h. hussain, “business value of bim in malaysia’s aec industry: preliminary findings”, malaysian construction research journal, vol. 16, no. 1, pp. 31–41, 2015 [12] s. scheer, r. mendes jr., t. f. campestrini, m. c. garrido, “on-site bim model use to integrate 4d/5d activities and construction works: a case study on a brazilian low income housing enterprise”, 2014 international conference on computing in civil and building engineering, orlando, usa, pp. 455–462, june 23-25, 2014 [13] mcgraw hill construction, the business value of bim for construction in major global markets, mcgraw hill, 2014 [14] w. natephra, a. motamedi, t. fukuda, n. yabuki, “integrating building information modeling and virtual reality development engines for building indoor lighting design”, visualization in engineering, vol. 5, 2017 [15] nbs, national bim report, available at: https://www.thenbs.com /knowledge/national-bim-report-2016, 2016 [16] n. f. azmi, c. s. chai, l. w. chin, “building information modeling (bim) in architecture, engineering and construction (aec) industry: a case study in malaysia”, in: proceedings of the 21st international symposium on advancement of construction management and real estate, pp. 401-412, springer, 2018 [17] s. a. abdullah, n. sulaiman, a. a. latiffi, d. baldry, “building information modeling (bim) from the perspective of facilities management (fm) in malaysia”, international real estate research symposium, april 29-30, 2014 [18] r. davies, f. crespin-mazet, a. linne, c. pardo, m. i. havenvid, c. harty, c. ivory, r. salle, “bim in europe: innovation networks in the construction sectors of sweden, france and the uk”, 31st annual arcom conference, lincoln, uk, pp. 1135-1144, september 7-9, 2015 [19] k. panuwatwanich, m. l. wong, j. h. doh, r. a. stewart, t. j. mccarthy, “integrating building information modelling (bim) into engineering education: an exploratory study of industry perceptions using social network data”, australasian association for engineering education conference , pp. 1–9, 2013 [20] a. sawhney, state of bim adoption and outlook in india, rics school of built environment, 2014 [21] τ. kaneta, s. furusaka, a. tamura, n. deng, “overview of bim implementation in singapore and japan”, journal of civil engineering and architecture, vol. 10, pp. 1305-1312, 2016 [22] beale & company, bim implantation in the uae on the rise, beale & company, 2017 [23] h. m. hamada, a. haron, z. zakiria, a. m. humada, “benefits and barriers of bim adoption in the iraqi construction firms”, international journal of innovative research in advanced engineering, vol. 3, no. 8, pp. 76-84, 2016 [24] b. wang, end user oriented bim enabled multi-functional virtual environment supporting building emergency planning and evacuation, phd thesis, cardiff university, 2014 [25] d. bryde, m. broquetas, j. m. volm, “the project benefits of building information modelling (bim)”, international journal of project management, vol. 31, no. 7, pp. 971–980, 2013 microsoft word 18-2449_s engineering, technology & applied science research vol. 9, no. 1, 2019, 3762-3764 3762 www.etasr.com soomro et al.: causes of time overrun in construction of building projects in pakistan causes of time overrun in construction of building projects in pakistan faheem ahmed soomro department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs, pakistan faheemahmed_soomro@yahoo.com muhammed jaffar memon department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs, pakistan ja2far@gmail.com abdul fattah chandio department of electronics engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan fattahchandio@yahoo.com samiullah sohu department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan sohoosamiullah@gmail.com rizwanullah soomro faculty of civil engineering, universiti teknologi malaysia rizwantn16@gmail.com abstract—time overrun in construction projects is a very serious issue in developed and developing countries. the main object of this research is to find the main causes of time overrun in the construction of building project and its possible mitigation measures. quantitative approach was adopted in this research to achieve object and riw (relative importance weight) approach was used for collecting data. financial issues faced by the contractor, contractor’s inexperience, weather impacts, late delivery of material, mistakes in design, shortage of skilled labor, incompetent subcontractor and mistakes in time estimation were identified as main causes of time overrun in construction projects and possible mitigation measures were also proposed from experts. this research will help in giving awareness to stakeholders to narrow down the factors of time overrun in construction projects in pakistan. keywords-time overrun; causes; building projects; mitigation measures; pakistan i. introduction time overrun is one of the most serious issues in construction industry globally [1]. “construction time overrun is the change between a project’s actual contract period at the time of tender and its final contract period on which construction project finished” [2]. time overrun can result in many negative impacts on the construction project like budget overrun, low productivity, contract expiration, work acceleration resulting in bad quality, and disputes among construction stakeholders [3]. it is observed that many construction projects face the issue of time overrun worldwide both in developing and developed countries like usa or uk [4, 5]. authors in [6] stated that more than 40% of projects in construction industry experiences time overrun. construction industry is not famous in terms of project completion within time. ignorance of time overrun analysis resulted in many construction projects failing to complete on the given time frame [7]. according to [8] only 47% of projects were completed within approved time frame, around 38% of construction projects were behind time frame and 15% of construction projects were completed ahead of time in indonesia. like other countries, time overrun is one of the most severe problems in the construction industry of pakistan [9, 10]. author in [11] reported that the majority of the pakistan construction projects were 11% to 30% below their approved time fame. only a few studies have been carried out to find factors of time overrun in the construction of building projects in pakistan. ii. previous studies many researchers conducted studies on the causes of time overrun in different kinds of construction projects to find factors and causes of time overrun. authors in [12] conducted survey on 130 randomly selected engineers. identified causes of time overrun were delayed payments, material shortage, changes in selected material prices, poor site management, and problems in bank credit. authors in [13] identified 83 common factors of time overrun and arranged these factors in 8 groups. by using relative importance index five causes of time overrun were identified which were poor supervision at site and site management, delay in making decisions, owner interference in the project, ground conditions, and necessary changes from the owner. authors in [14] identified 16 causes of time overrun, the top 5 being: financial problems faced by the contractor, poor contract management, site supervision, lack of planning, and delay in material supply. authors in [15] carried out a survey through questionnaire distribution to selected experts of construction industry in nigeria. identified causes of time overrun were inexperienced sub-contractors, shortage of labor, poor site management, shortage of selected materials and mistakes during works. authors in [16] conducted survey about the causes of time overrun in infrastructure projects of qatar. the results of the survey revealed that major causes of time overrun were design changes, inadequate planning and corresponding author: s. sohu engineering, technology & applied science research vol. 9, no. 1, 2019, 3762-3764 3763 www.etasr.com soomro et al.: causes of time overrun in construction of building projects in pakistan scheduling, changes in scope of project, inadequate estimation project time duration, and shortage of skilled labour. authors in [17] identified the major causes of time overrun through quantitative approach in construction projects of vietnam. the main causes of time overrun were poor monitoring, poor project management and financial problems faced by owner. iii. research methodology this study was divided in two phases. in the first phase the objective was to find the main causes of time overrun and in the second phase was to find the mitigation measures of these identified causes. in the first phase, a literature review was carried out providing a total of 51 probable causes of time overrun. a questionnaire was developed, in which the aforementioned causes were imposed and respondents were asked to rank them. in the second phase, another questionnaire was distributed in which mitigation measures from literature review and unstructured interviews were incorporated. iv. data collection and analysis for the first phase, the developed questionnaire was distributed among 131 professional respondents (either consultants, clients or contractors) involved in handling the construction of building projects, 87 were received back and 84 were usable for data analysis (table i). table ii indicates the respondents’ qualification and table iii indicates their experience. table i. survey details parameter value total distributed questionnaires 131 received back questionnaires 87 invalid questionnaires 3 valid questionnaires 84 percentage of valid questionnaires 96 table ii. qualification of respondents degree name frequency percentage bachelor 68 80.9 master 14 16.7 phd 2 2.40 total 84 100 table iii. experience of respondents experience frequency percentage 0-5 years 8 9.52 6-10 years 24 28.58 11-15 years 21 25.00 16-20 years 18 21.43 20 and above 13 15.47 total 100 100 for the first phase respondents were given questionnaires and were asked to rank each cause on a likert scale. riw approach was successfully used in previous studies giving accurate and good results [18]. the weight formula in riw was calculated as shown in (1): i i i a x riw x = ∑ ∑ (1) where ai shows a constant which represents the weight given to i, and xi is a variable denoting the frequency of the answer for i. the values are established from x1 having the least importance and a1 being 1, to x5 for most significant and a5 equal to 5. the results are shown in table iv. table iv. causes of time overrun rank identified causes riw value 1 financial issues faced by contractor 0.834 2 inexperienced contractor 0.831 3 weather impact 0.812 4 delay in supply of materials 0.783 5 mistakes in design 0.769 6 shortage of skilled labour 0.761 7 incompetent subcontractor 0.688 8 errors in time estimation 0.511 a. financial issues faced by contractor financial issues faced by the contractor were found as the most major cause of time overrun. contractors play important role from execution to completion of a project. construction activities are suspended and stopped by the contractors due to financial issues [19]. continuous funding to contractors can help to complete project on approved time. b. inexperienced contractor inexperienced and incompetent contractor can cause time overrun. selection of contractor on favoritism causes time overrun in construction projects [20]. c. weather impact most buildings constructed in tropical regions face chances of heavy rains, floods and earthquakes which affect construction activities causing delays on building projects. weather impact causes time overrun from approved time in construction projects [21]. d. delay in supply of materials at site construction site of building is often located at remote and sometimes in tropical areas, so it is difficult to have a continuous supply of materials on time. delay in material supply creates gaps in construction activities at site which causes time overrun in construction projects [22]. e. mistakes in design before project tendering, easy and accurate design should be prepared. mistakes in design delay the project construction activities which can lead the project to time overrun [23]. f. shortage of skilled labor shortage of skilled labor is one of the main causes of time overrun in the construction industry. pakistan is a developing country and many workers are not skilled enough. another cause of shortage of skilled labour is that many construction projects are running simultaneously [24]. g. incomplete subcontractor contractor appoints subcontractors for the completion of different activities of the project but appointment of incompetent subcontractor, can cause construction activities to run very slow compared to the given schedule. incompetent, engineering, technology & applied science research vol. 9, no. 1, 2019, 3762-3764 3764 www.etasr.com soomro et al.: causes of time overrun in construction of building projects in pakistan with no experience contractors and subcontractors do many mistakes during construction [25]. h. errors in time estimation errors in making estimation of time duration because of lack of experienced engineers or planners leads to improper estimation of completion period of project. estimation of project length is based on resources and their output [26]. v. mitigation measures the second phase of this study was to identify mitigation measures of the identified causes. a questionnaire was developed having mitigation measures identified from literature review and interviews from experts. the respondents were asked to highlight their relative importance on a likert scale. the collected data were analyzed by using rii (relative importance index) and the results are shown in table v. table v. mitigation measures of critical factors mitigation measure value adequate funds should be allocated for each project. 3.0 highly experienced contractors should be appointed. 2.97 proper arrangements should be done in flood and rainy seasons 2.94 suitable resources should be used for supply of materials. 2.91 well reputed consultants should be hired. 2.90 skilled labor should be with facilities. 2.89 favorite subcontractor should not be appointed. 2.88 proper filed investigation should be made. 2.86 vi. conclusion the purpose of this study was to find the major causes of time overrun in the construction projects in pakistan and possible mitigation measures. after statistical analysis, the major causes of time overrun were: financial issues faced by the contractor, inexperienced contractor, weather impact, delay in supply of materials at site, mistakes in design, shortage of skilled labour, incompetent subcontractor, and errors in time estimation. possible mitigation measures to control these causes were recognized and are depicted in table v. the outcomes of this study will help stakeholders to control causes of time overrun. references [1] r. f. aziz, a. a. abdel-hakam, “exploring delay causes of road construction projects in egypt”, alexandria engineering journal, vol. 2, no. 5, pp. 16-23, 2016 [2] m. y. honrao, d. b. desai, “study of delay in execution of infrastructure projects–highway construction”, international journal of scientific and research publications, vol. 5, no. 6, pp. 1-8, 2015 [3] g. kikwasi, “causes and effects of delays and disruptions in construction projects in tanzania”, australasian journal of construction economics and building-conference series, vol. 1, no. 2, pp. 52-59, 2013 [4] m. tafazzoli, dynamic risk 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alaghbari, m. r. a. kadir, a. salim, ernawati, “the significant factors causing delay of building construction projects in malaysia”. engineering, construction and architectural management, vol. 14, no. 2, pp. 192-206, 2007 [21] a. h. al-momani, “construction delay: a quantitative analysis”, international journal of project management, vol. 18, no. 1, pp. 51-59, 2000 [22] a. s. faridi, s. m. el-sayegh,“significant factors causing delay in the uae construction industry”, construction management and economics, vol. 24, no. 11, pp. 1167-1176, 2006 [23] r. f. aziz, “ranking of delay factors in construction projects after egyptian revolution”, alexandria engineering journal, vol. 52, no. 3, pp. 387-406, 2013 [24] m. sambasivan, y. w. soon, “causes and effects of delays in malaysian construction industry”, international journal of project management, vol. 25, no. 5, pp. 517-526, 2007 [25] a. senouci, a. ismail, n. eldin, “time delay and cost overrun in qatari public construction projects”, procedia engineering, vol. 164, pp. 368-375, 2016 [26] g. sweis, r. sweis, a. a. hammad, a. shboul, “delays in construction projects: the case of jordan”, international journal of project management, vol. 26, no. 6, pp. 665-674, 2008 microsoft word etasr_v11_n1_pp6703-6707 engineering, technology & applied science research vol. 11, no. 1, 2021, 6703-6707 6703 www.etasr.com buller et al.: experimental characterization of bacterial concrete against mechanical and durability … experimental characterization of bacterial concrete against mechanical and durability performance abdul salam buller department of civil engineering quaid-e-awam university of engineering science & technology larkana campus, pakistan buller.salam@quest.edu.pk abdul mannan buller department of civil engineering quaid-e-awam university of engineering science & technology nawabshah, sindh, pakistan abmannan54@gmail.com tariq ali department of civil engineering the islamia university of bahawalpur punjab, pakistan tariqdehraj@gmail.com zaheer ahmed tunio department of civil engineering quaid-e-awam university of engineering science & technology nawabshah, pakistan zaheerahmedtunio@gmail.com muhammad akbar malik department of civil engineering the islamia university of bahawalpur punjab, pakistan m.akbarmalik@iub.edu.pk samreen shabbir department of civil engineering nfc institute of engineering and technology multan, pakistan samreen.shabbir@yahoo.com abstract—this study experimentally investigates the mechanical and durability performance of bacteria concrete in terms of density, compressive strength, split tensile strength, and water absorption capacity. the concrete specimens were produced with a ratio of 1:2:4, w/c ratio of 0.45, and having a bacteria dosage level ranging from 1 to 6% by weight of water. to investigate the usefulness of the bacteria dosage level, cubic and cylindrical specimens were cast and tested after 28 days of water curing in a universal testing machine with a constant loading rate. the density of each specimen was also recorded soon after casting and after the curing period ended. moreover, the water absorption test was similarly conducted on cube specimens at various time intervals to record the penetration depth. the test results of normal concrete (without bacteria) were compared with the ones of the specimens containing bacteria. the optimum level of bacteria was found to be 3.5%, which showed the highest values in terms of compressive strength, split tensile strength, and density. bacteria tend to generate more crystalline materials inside the concrete mass due to reactions with the surrounding moisture which produces a compact surface, thus strength properties were improved and water penetration was blocked which suggests better durability of the concrete. keywords-bacteria; curing; compressive strength; tensile strength; density; water absorption i. introduction concrete is commonly used in almost every kind of construction, but, apart from its many advantages, it has some limitations. due to its week tensile ability, it is less resistant to early-age cracking and has low durability. various researches have been conducted to control such kind of deficiencies in concrete and make it more sustainable [1-7]. the research in the field of solid innovation has shown extraordinary advancements in concrete with regard to the amount of time of development, the quality of cement, the toughness of cement, and the mixture with natural materials such as fly debris, impact heater slag, silica smolder, metakaolin, etc. microbial mineral precipitation has been proposed due to the metabolic reaction of microbes in concrete enhancing the general conduct of cement. frequently bacterial reactions trigger an adjustment in the arrangement science that prompts over immersion and mineral precipitation [6], while the behavior of concrete produced from bacteria was enhanced because of inorganic sleet generated from metabolic activities of auspicious microbes in concrete. these kinds of reactions may occur on the inner or the outer side of the microbial cell or even some distance away within the concrete. bacterial actions also merely cause a variation in solution chemistry that leads to over-saturation and precipitation of minerals. bacterial concrete came into existence because of the use of bio mineralogy perceptions in concrete [8, 9]. various studies have been conducted to investigate the performance of concrete with embodied bacteria. the bacterial degradation of urea locally increases the ph and promotes the microbial deposition of calcium carbonate in a calcium-rich environment. through this process, the bacterial cell is coated with a layer of calcium carbonate [10]. microbial calcium carbonate precipitation in a cement mortar/concrete is a complex mechanism. based on continuous research, several innovations have been made to improve the strength and durability performance of cement mortar/concrete [11]. the abundant significance of microbially induced calcium carbonate precipitation (miccp), also known as carbonatogenesis, has attracted attention from both basic and applied points of view in civil engineering [12]. the caco3 precipitation is a function of ionic strength and ph in the medium. the increase of compressive strength of mortar is due corresponding author: abdul salam buller engineering, technology & applied science research vol. 11, no. 1, 2021, 6703-6707 6704 www.etasr.com buller et al.: experimental characterization of bacterial concrete against mechanical and durability … to the complex interaction between the bacterium and cement matrix [13]. the present study includes the usage of bacteria and their effect on the early age mechanical behavior of concrete under different exposure conditions. the core purpose of the carriedout work was to correlate the physical properties of healed/unhealed to that of normal concrete. compressive strength, tensile strength, density, and water absorption were tested during this study. ii. objectives the specific objective of the present study is to investigate the mechanical and durability performance of concrete by adding bacteria as partial water replacement. various dosage levels varying from 0% to 6% were used and the performance was determined at 28 days of water curing. iii. materials and methods a. materials the materials which were used in this study are described below. • cement: ordinary portland cement (opc) of type-i complying with the astm c150-05 (2005) and bs 12 (1991) was used. it was purchased from the local market of nawabshah under the trade name ‘lucky cement’ manufactured by the lucky cement industries. • fine aggregates: 4.75mm sieve was used to obtain fine aggregates from locally available sand. the sand was washed and dried up to ssd (saturated surface dry) before mixing. • coarse aggregates of size 10-15 were used. the sieved aggregates were washed to separate any sticky material and were left to dry up to ssd. • water: normally, drinking water is considered to be suitable for the manufacture of cement concrete/mortars/ grouts, and it was also used in this study. b. size and shape of samples specimens of standard size, as specified for each parameter of the study were cast and tested. the standard size and shape for compressive strength tests were 100mm×100mm×100mm cubes and for tensile strength tests and density measurement, 100mm×200mm cylinders, were cast. c. casting and curing all the materials were weighed before mixing (by hand). initially, sand and binder (opc and silica fume-sf) were mixed thoroughly for 3-5min to ensure the uniform dispersion of sf in the mix. then, water was added slowly into the mix and mixing continued for about 3min. specific specimens of standard size were cast (figure 1). after 24h, the specimens were demoulded and cured accordingly. for the testing, the specimens were taken out from the specific curing regime one day before testing and were cleaned properly with a dry cloth to remove foreign particles. the specimens were checked for any kind of deformation such as broken edges and cracks. the tests were conducted in the structure’s laboratory of the civil engineering department, quest, nawabshah. only wet curing for 28 days was adopted for all the specimens. for this purpose, the specimens were kept in water immediately after their demoulding. (a) (b) (c) fig. 1. casting of concrete: (a) concrete mixing, (b) cubes for compressive strength tests, (c) cylinders for tensile strength and density tests. d. testing 1) density measurement the density of all the cylindrical specimens was recorded after one day of casting and after the demoulding stage. the density was calculated by dividing the specimens' weight by their volume. 2) compressive strength measurement the compressive strength test is a key test for the mechanical/physical performance evaluation of concrete specimens. in this study, all the specimens with and without bacteria were tested for compressive strength, after 28 days of water curing, with a universal testing machine (utm) as shown in figure 2 with a constant loading rate using (1), in which fcu is the compressive strength, p is the maximum load taken by the specimen during testing and a is the area of the specimen. � �� � � � (1) fig. 2. a cubic specimen before and after compression testing. engineering, technology & applied science research vol. 11, no. 1, 2021, 6703-6707 6705 www.etasr.com buller et al.: experimental characterization of bacterial concrete against mechanical and durability … 3) tensile strength measurement tensile strength test was conducted on the cylindrical specimens, as shown in figure 3, with and without bacteria, with constant loading rate, after 28 days of water curing using (2): �� � � �� (2) fig. 3. a cylindrical specimen before and after tensile testing. 4) water absorption measurement the water absorption test is generally carried out to determine the degree of penetration of water inside the concrete cubes by measuring the weight of samples due to suction of water w.r.t the time duration only on the top surface of samples as presented in figure 4. the smaller the amount of water that penetrates the concrete the better the results. this water penetration does not correspond with any reaction but just shows the water tightness of samples. fig. 4. apparatus used for water penetration depth measurements. iv. results and discussions a. density density is an important factor to be considered when regarding strength and permeability. density increase due to the use of different bacteria dosage levels is depicted in figure 5 and table i based on the obtained test results. it should be noted that the density of concrete with the addition of bacteria rises up to the dosage of 3.5% of total water by weight. it may be noted that the concrete with 3.5% of bacteria dosage at w/c ratio 0f 0.45 exhibited a density high of 1783kg/m 3 which is 5.1% higher than that of the concrete without bacteria. the density enhancement at that optimum dosage level of bacteria is due to the fact that the concrete pores were filled by bacteria, thereby more compacted surfaces can be achieved. fig. 5. average density values vs. dosage level of bacteria after 28 days. table i. average density of concrete with bacteria batch bacteria (%) average density (kg/m 3 ) difference in values compared to b-1 (%ag) increase decrease b-1 0 1697 …. …. b-2 1.0 1736 2.2 …. b-3 2.5 1755 3.4 …. b-4 3.5 1783 5.1 …. b-5 4.5 1740 2.5 …. b-6 6.0 1715 2.1 …. 0.45w/c ratio b. compressive strength the results of the compressive strength tests of concrete with a 0.45w/c ratio are shown in table ii and figure 6. it can be observed that the compressive strength of concrete with the addition of bacteria rises up to the dosage of 3.5% of total water by weight, in which it reaches its maximum value. it should be noted that the concrete with 3.5% of bacteria dosage exhibited compressive strength of 31.7mpa which is 25% higher than that of the concrete without bacteria. fig. 6. average compressive strength vs. bacteria dosage. engineering, technology & applied science research vol. 11, no. 1, 2021, 6703-6707 6706 www.etasr.com buller et al.: experimental characterization of bacterial concrete against mechanical and durability … table ii. average compressive strength of concrete with bacteria batch bacteria (%) average compressive strength (mpa) difference in values compared to b-1 (%ag) increase decrease b-1 0 25.2 …. …. b-2 1.0 27.2 8 …. b-3 2.5 29.3 16 …. b-4 3.5 31.6 25 …. b-5 4.5 28.4 13 …. b-6 6.0 27.8 10 …. 0.45w/c ratio this increase is caused by the higher concentration level and increased calcite precipitation which generates more c-s-h gel, resulting in more strength at the same curing level. the addition of bacteria demands a lesser w/c ratio for the mixing and hydration process because the calcite precipitation is more responsible for higher compressive strength values, which has been observed and during this study. c. tensile strength the results of the split tensile strength tests are presented in table iii and figure 7. we can see that at 28 days of curing, the optimum replacement percentage of water with bacteria is 3.5% with a value of split tensile strength of 2.4n/mm 2 (19% more than that of normal concrete). the maximum tensile strength is 13.1% of the respective compressive strength, while the minimum value obtained is 12.4%. the average value is 12.7%. normally, the tensile strength of concrete lies between 5% and 15% of compressive strength. the same trend is observed during the current study. fig. 7. average split tensile strength vs. bacteria dosage. table iii. average split tensile strength batch bacteria (%) average tensile strength (mpa) difference in values compared to b-1 (%ag) increase decrease b-1 0 2.01 …. …. b-2 1.0 2.18 8 …. b-3 2.5 2.3 14 …. b-4 3.5 2.4 19 …. b-5 4.5 2.24 11 …. b-6 6.0 2.16 7 …. d. water absorption the water penetration depth results for different time durations for various specimens due to the use of different bacteria dosage levels are presented in figure 8. due to the use of bacteria, the penetration depth decreases as the dosage of bacteria increases and the same optimum level of bacteria dosage (3.5%) was found to be obtained in minimizing the water penetration in concrete cubes. the results showed that due to the better reaction of carbonates available in bacteria, a strong gel covering is produced on the concrete cubes, which prevents water from penetrating the pores of specimens. thus, not only the durability is improved but also the water-resisting power of concrete cubes is enhanced by the strong gel formation. fig. 8. water absorption in terms of penetration depth vs time (72h). e. test result comparison this study focuses on the use of bacteria in concrete to investigate its mechanical and durability performance, a combination that has not been widely researched. the present study depicted compressive strength 4% higher than that of [6, 14] at the same curing age and 6% higher than in [15] which used nanomaterials in order to investigate the difference of the molecular level of bacteria/nanomaterial on material's performance [16]. v. conclusions from the experimental results, it is concluded that bacteria can enhance the physical properties of cement concrete i.e. compressive strength, tensile strength, and density. the maximum compressive strength value of 31.6mpa was achieved at the optimum level of bacteria by weight of water (3.5%), which is 25% higher than the concrete without bacteria. this enhancement in strength is caused by the better calcite precipitation and generation of c-s-h gel inside the concrete mass. maximum split tensile strength of 2.7mpa was achieved at the optimum level of bacteria, which is 19% higher than that of concrete without bacteria. strength increase was achieved mainly due to the increased concentration of bacteria, which triggers the hydration process and improves strength, mainly tensile strength. a maximum density value of 1783kg/m 3 was achieved at the optimum level of bacteria (3.5%), which is 5% higher than engineering, technology & applied science research vol. 11, no. 1, 2021, 6703-6707 6707 www.etasr.com buller et al.: experimental characterization of bacterial concrete against mechanical and durability … that of concrete without bacteria. this density enhancement at the optimum dosage level of bacteria is due to the filling by bacteria of the existent pores of concrete, thereby more compacted surface was achieved. water penetration depth was also minimum (3.90mm) at the same optimum dosage level of bacteria. from the above findings, it can be concluded that the optimum bacterial level according to the test results is 3.5%. this optimum level of bacteria dosage showed better performance by generating better c-s-h gel as well as sufficient calcite precipitation which not only enhanced strength but also helped in improving concrete durability. references [1] a. amiri, m. azima, and z. b. bundur, "crack remediation in mortar via biomineralization: effects of chemical admixtures on biogenic calcium carbonate," construction and building materials, vol. 190, pp. 317–325, nov. 2018, https://doi.org/10.1016/j.conbuildmat.2018.09.083. [2] n. chahal, r. siddique, and a. rajor, "influence of bacteria on the compressive strength, water absorption and rapid chloride permeability of concrete incorporating silica fume," construction and building materials, vol. 37, pp. 645–651, dec. 2012, https://doi.org/10.1016/ j.conbuildmat.2012.07.029. [3] s.-g. choi, k. wang, z. wen, and j. chu, "mortar crack repair using microbial induced calcite precipitation method," cement and concrete composites, vol. 83, pp. 209–221, oct. 2017, https://doi.org/10.1016/ j.cemconcomp.2017.07.013. [4] w. de muynck, d. debrouwer, n. de belie, and w. verstraete, "bacterial carbonate precipitation improves the durability of cementitious materials," cement and concrete research, vol. 38, no. 7, pp. 1005–1014, jul. 2008, https://doi.org/10.1016/j.cemconres.2008.03. 005. [5] n. kunal, r. siddique, a. rajor, and m. singh, "influence of bacterialtreated cement kiln dust on strength and permeability of concrete," journal of materials in civil engineering, vol. 28, no. 10, p. 04016088, oct. 2016, https://doi.org/10.1061/(asce)mt.1943-5533.0001593. [6] c. v. s. r. p. lakshmi t. v. s. vara, "effect of crushed sand and bacillus subtilis on the cantabro loss of bacterial concrete," ijtech international journal of technology, vol. 10, no. 4, pp. 753–764, jul. 2019, https://doi.org/10.14716/ijtech.v10i4.2299. [7] r. mors and h. m. jonkers, "bacteria-based self-healing concrete: evaluation of full scale demonstrator projects," rilem technical letters, vol. 4, pp. 138–144, 2019, https://doi.org/10.21809/ rilemtechlett.2019.93. [8] n. d. belie and j. wang, "bacteria-based repair and self-healing of concrete," journal of sustainable cement-based materials, vol. 5, no. 1–2, pp. 35–56, mar. 2016, https://doi.org/10.1080/21650373. 2015.1077754. [9] a. khalifeh, b. roozbehani, a. m. moradi, s. i. moqadam, and m. mirdrikvand, "isolation of crude oil from polluted waters using biosurfactants pseudomonas bacteria: assessment of bacteria concentration effects," engineering, technology & applied science research, vol. 3, no. 2, pp. 396–401, apr. 2013, https://doi.org/ 10.48084/etasr.265. [10] j. dick et al., "bio-deposition of a calcium carbonate layer on degraded limestone by bacillus species," biodegradation, vol. 17, no. 4, pp. 357– 367, aug. 2006, https://doi.org/10.1007/s10532-005-9006-x. [11] p. k. mehta, "advancements in concrete technology," concrete international, vol. 21, no. 6, pp. 69–76, jun. 1999. [12] c. rodriguez-navarro, m. rodriguez-gallego, k. b. chekroun, and m. t. gonzalez-muñoz, "conservation of ornamental stone by myxococcus xanthus-induced carbonate biomineralization," applied and environmental microbiology, vol. 69, no. 4, pp. 2182–2193, apr. 2003, https://doi.org/10.1128/aem.69.4.2182-2193.2003. [13] s. stocks-fischer, j. k. galinat, and s. s. bang, "microbiological precipitation of caco3," soil biology and biochemistry, vol. 31, no. 11, pp. 1563–1571, oct. 1999, https://doi.org/10.1016/s0038-0717(99) 00082-6. [14] j. rex, j. s. babu, and s. p. s. reddy, "strength and durability aspects of bacterial concrete," international journal of innovative technology and exploring engineering, vol. 8, no. 2s2, pp. 9–13, dec. 2018. [15] v. nagarajan, t. k. prabhu, m. g. shankar, and p. jagadesh, "a study on the strength of the bacterial concrete embedded with bacillus megaterium," international research journal of engineering and technology, vol. 4, no. 12, pp. 1784–1788, dec. 2017. [16] z. y. ilerisoy and y. takva, "nanotechnological developments in structural design: load-bearing materials," engineering, technology & applied science research, vol. 7, no. 5, pp. 1900–1903, oct. 2017, https://doi.org/10.48084/etasr.1414. microsoft word 37-3566_s_etasr_v10_n3_pp5808-5813 engineering, technology & applied science research vol. 10, no. 3, 2020, 5808-5813 5808 www.etasr.com govindarajan et al.: performance analysis of four smart energy monitoring systems performance analysis of smart energy monitoring systems in real-time r. govindarajan department of electrical engineering scsvmv university kanchipuram, india govind@kanchiuniv.ac.in s. meikandasivam school of electrical engineering vellore institute of technology vellore, india meikandasivam.s@vit.ac.in d. vijayakumar school of electrical engineering vellore institute of technology vellore, india vijayakumar.d@vit.ac.in abstract—the use of smart energy monitoring systems in buildings offers significant potential for energy saving. the introduction of a new kind of energy monitoring system is essential in the consumer-side in order to meet the demands of energy conservation. in this paper, four energy monitoring systems based on advanced wireless technology are proposed. the design and implementation of the smart real-time energy monitoring systems is analyzed with respect to their performance. the proposed systems utilize advanced wireless technologies like the zigbee module, internet of things (iot), android mobile apps, and cloud computing for interfacing the information between the meters and the consumer end. a digital power meter is installed in the main panel, interfaced with a communication gateway and parameters such as voltage, current, power, power factor, and the harmonics of household appliances are measured in real-time. these systems provide power consumption details to the consumer and allow interacting with them by giving instant data such as live power tracking, identification of abnormal patterns of energy usage, energy bill estimation, and energy usage information. keywords-zigbee; internet of things; gsm communication; cloud computing; smart grid i. introduction smart grid (sg) gives the energy industry the opportunity to move into a new era of more reliable and efficient systems. the smart energy monitoring system (sems) is one of the most important devices used in a smart grid. it is an advanced energy metering unit that obtains the information from consumers and provides information to the utility company and system operators. several sensors and control devices that are supported by dedicated communication infrastructure are utilized in the sems. in addition, sems uses a smart meter developed using system’s communication technologies [1]. the sems is expected to work in the following way: it collects data from nodes, establishes two-way communication, analyzes data, and supports controlling based on the analysis. initially, the data are collected from the appliances and are recorded at regular time intervals. the collected data are stored in the memory and data prioritization is done. the command signals are received from the utility center from which the smart meter plans for load scheduling and controlling based on consumer behavior. automatic electricity billing system can also be implemented in sems, because the system supports bidirectional information flow and is deployed at the end user premises to collect the data of electrical usage from all the appliances. the data from the individual smart meters are collected by local data aggregators and then the information is passed to the utility center. similarly, the utility center also can send some commands or signals to the smart meters at end user premises whenever required. the sems should communicate the data to the utility center in a highly reliable and secured way. the system collects the data from local smart meters and sends them to the utility companies using different wired and wireless technologies involving han, nan and wan. the data communication in han is carried out by using power line communication (plc), radio frequency (rf), zigbee, wifi. the data communication in nan involves copper or optical fiber, wi-fi, general packet radio service (gprs) and wimax. the data communication using wan includes optical fibers, cellular networks, and satellite connections [2]. with the advancement in the field of computer and wireless communication technology, a wide range of possibilities is available for the design and implementation of sems in future smart homes [3]. computer and wireless communication technology is used to integrate a number of sensor devices, actuators, and computing devices which in turn have great potential to contribute to energy efficiency in everyday usage. energy efficiency is becoming increasingly important in industry and in the residential sector [4]. however, due to the complexity and diversity of computing devices, integrating energy monitoring resources is still in its infancy [5]. adding advanced devices into the energy metering environment is a very challenging task. after deciding which particular device to integrate, the smart metering developer must determine how to configure it and interface with it [6]. the smart energy monitoring environment makes use of a wireless communication platform to integrate various devices. these devices should communicate with each other independently to provide information to the consumers [7]. manufacturers of wireless interfacing devices use many different communication modules. therefore, the integration of household appliances and consumer electronics is not straightforward at any layer of the sensor network platform. additionally, apart from the technical difficulties of the integration, due to the complexity of the systems, users are often unable to fully understand their corresponding author: r. govindarajan engineering, technology & applied science research vol. 10, no. 3, 2020, 5808-5813 5809 www.etasr.com govindarajan et al.: performance analysis of four smart energy monitoring systems systems [8]. to fully take advantage of smart energy monitoring technologies, any energy monitoring system should transparently communicate with all the household energy meters and make available all important information to the users with respect to saving energy and user convenience [9]. keeping these in mind, semss using wireless communication module and an intelligent gateway circuit are proposed. the proposed systems continually record and update the electricity consumption data in order to provide real-time information. users can easily monitor and control their power consumption of household appliances in order to save energy. to enable the feasibility of the proposed systems, zigbee transceivers and a gsm communication gateway are implemented. in order to find the most suitable energy monitoring system for consumers, the following systems are designed and implemented using various wireless technologies and the experimental results are discussed. • sems using the zigbee module. • sems using iot. • sems using android apps. • sems using cloud computing. ii. impementation a. design and implementation in a zigbee module the zigbee module (ieee 802.15.4) is a promising wireless communication protocol for low rate communication and home automation. conventional wired and wireless communication interfaces like ethernet, ieee 1394, wi-fi, plc, and bluetooth can be used for the home network. wireless network interfaces are preferred to wired communication, because they are easy to deploy and install. additionally, zigbee has a higher maximum number of cell nodes than other protocols. for example, bluetooth has only 8 nodes as maximum number of cell nodes, while zigbee can have more than 65000 nodes [10]. the proposed zigbee-based energy monitoring system includes an energy surveillance monitor (esm) that has a zigbee transceiver and multiple energy surveillance devices (esds). the esm is used for displaying the collected data to the user and the esdss perform functions like energy consumption measurement, adaptive setting of standby power-off level and zigbee communication. the main function and performance requirements of the system are [11]: • adaptive standby power level setting. • standby power-off control. • power consumption measurement. • zigbee communication. zigbee is one of the most economical and reliable modules which also consumes less power for monitoring processes. it covers a wireless range of 10-100 meters. an energy meter can be interfaced with the zigbee transmitter module and a laptop or computer is used for data acquisition [12]. in this system, an embedded c programming is developed for the interfacing process and a power metering ic is used to collect the data from the energy meters. the collected data will be communicated to the zigbee module using the arduino controller. finally, the measured electrical parameters will be received by the zigbee transceiver. this way, the data are presented in the form of an energy report, are viewable to the consumers, and can be accessed from a pc or a laptop. the hardware implemented for an energy monitoring system using the zigbee module is shown in figure 1. in this system, the digital meter is interfaced with the zigbee transmitter board and a pc is interfaced with the zigbee receiver board. there is no other wired connection between the energy meter and the pc. the system is implemented for wireless energy monitoring. this wireless setup can cover a maximum distance of 100m and the configuration is as per ieee standard [12, 13]. the system collects energy data from the digital energy meter using an arduino controller through a power amplifier. the collected data will be indicated in the arduino board by the flickering led. the signal status is also updated by it [3]. the the power amplifier ic will act as a data splitter. it is used to provide the data to the controller without any jungle values of the energy meter. the measured energy parameters will be sent to the pc and displayed as a text report as shown in figure 2. fig. 1. hardware implementation of the zigbee-based energy monitoring system fig. 2. energy meter values display format on computer screen for this system interfacing, the coding was developed with the arduino processor by embedded c [14]. the system engineering, technology & applied science research vol. 10, no. 3, 2020, 5808-5813 5810 www.etasr.com govindarajan et al.: performance analysis of four smart energy monitoring systems provides the information to users with a delay time of 15s and the data communication speed between the energy meter and the pc is 250kbps. b. design and implementation using iot an iot (ieee 1451-99) based sems allows the devices to remotely sense using the existing internet infrastructure and also develop the interfacing process between the transmitter end (energy meter) and the receiver end. in addition, it reduces human participation in process handling. this system is implemented with customized embedded programming between iot and the digital meter through the arduino controller [14, 15]. in the proposed system, the consumer can maintain energy consumption by knowing the energy usage from time to time. this method not only provides two way communication between the utility and the consumer but also it provides other functions, e.g. when the consumer fails to pay the electricity bill, the energy supply will be cut down from the utility side and once the bill is paid the energy supply can be reconnected automatically without human intervention. iot is a major part of the communication between the energy meter and the web server. the sensor collects data from load and the energy meter, which data are then sent to the arduino through uart communication. the controller then performs the operation logically and automatically using mqtt protocol. these data are then stored on the cloud and they can be monitored any time. the stored data are displayed on the web, where the user and the utility company can monitor them and perform suitable actions. the data are updated with the real time status of the connected device and are sent to the controller to take the appropriate action. the designed system will provide data transferring speed from the monitoring unit to server of 2mbps with a time delay of 2s. the monthly bill will be sent to the consumer in the form of an energy report with ip address accessing mode. figure 3 demonstrates the operation of a developed iot based energy monitoring system. the system consists of a user-interface dashboard and it was developed in html, which is used to view data as an energy monitoring report [16]. the system is designed to find the minimum period of data transmission delay time with high communication speed. the normal digital energy meter was connected with an interfacing unit [17]. the interfacing unit consists of the arduino, a splitter circuit, a data amplifier circuit, and the iot module. the interfacing unit collects the energy parameters from the energy meter and sends them to the local server through iot. in this system, the splitter circuit will split the data into voltage, current, and power and send them to the power amplifier circuit. the amplifier circuit and the arduino processor will store the values and make a live report as shown in figure 4. the measured energy parameters were collected with an interfacing unit and then were sent to the local server through a wi-fi router. before that, the energy report is prepared as an html file in the background and all the fields are developed on consumer basic requirements. based on the programming, the data will appear in content menu or field [18]. each consumer can view its energy consumption report by accessing its already given ip address [20]. hence, this proposed system achieves fast communication with very small data transmission delay time. fig. 3. hardware implementation of the energy monitoring system using iot fig. 4. energy report in html format c. design and implementation using android mobile app in this system, the control is using android mobile app (ieee 1914.1) (a free and an open source framework for multiple platform mobile application development) developed as a part of user interfaced (ui) mosync application program implemented on an android mobile phone. the user must have a mobile phone with internet or wi-fi access in most platforms except ios. the application must be transferred and installed in the mobile phone. when the user launches the application, it displays the initial screen shown in figure 6. this screen has an option to exit the application or to connect to the embedded system which is interfaced with nodemcu module. the user gets messages for the entire application activities comfortably. once the application is installed in the mobile phone, it will automatically connect to the nodemcu module using the static url provided by the application itself. if the connection is successful then the client application gives an appropriate message and instructions to operate the system using the mobile device. depending upon the type of the available input with the user’s mobile device, the user can monitor power utilization. in our designed system, android mobile app was utilized to develop a wireless energy monitoring system. it can sense the energy meter value and communicate with the consumer by showing energy information instantly [4]. it works with the android operating system and the module developed with engineering, technology & applied science research vol. 10, no. 3, 2020, 5808-5813 5811 www.etasr.com govindarajan et al.: performance analysis of four smart energy monitoring systems nodemcu, which is interfaced with our existing digital energy meter. the daily usage of power consumption will be measured as usual by a digital energy meter and the measured data will be received by the nodemcu. then the data will be sent to the existing mobile app, called blynk which acts as a server. the blynk app is one of the interfacing apps which can be installed on all android smart phones and it works with iot based platforms. once the data are received, they will be displayed as a prompt view on the mobile screen. the system obtains the energy parameters from the existing energy meter instantly, making them easily accessible with a mobile phone which is a user friendly device [1, 25]. in other modules, more interfacing devices are utilized to develop an energy monitoring system, whereas in this system the number of interfacing devices is minimal, thereby reducing the data transferring speed considerably. the system consists of an energy meter, nodemcu, and a smart phone. nodemcu is a low-cost open source iot platform. it runs on the esp8266 wi-fi soc and the hardware in which it is based on is the esp-12 module. fig. 5. hardware implementation of the android mobile app-based energy monitoring system fig. 6. energy meter value displayed in mobile screen blynk is a customizable app, hence, based on the monitoring system requirements, the blynk app page can be designed by the user. once the app is installed in the mobile phone, the energy meter values will be stored in the mobile app by getting nodemcu log in id in the app. the developed module is shown in figure 5. at an interval of 1s, the parameters will be updated automatically. the output format of the energy monitoring system is shown in figure 6. d. design and implementation using cloud computing cloud computing is a most excellent and advanced method for smart energy monitoring due to its scalable and flexible characteristics and its capacity to handle large volumes of data. its reliability, mobility, high speed, among other characteristics make it more adaptable than other methods. the design of a sems facilitates large-scale real-time computing capabilities in order to cope up with the communication, transport and storage of huge transferable data. but once the expected entities are in place, cloud computing will unload the smart system by offering automatic updates, remote data storage while demanding reduced maintenance of the it systems, thus saving money, manpower, and energy. this system includes a two way digital energy meter and a gsm communication gateway (ieee 802.21). the system is implemented in real time in order to achieve daily power utilization without delay. the consumer can check his energy usage as an instant report [21]. the system is designed with a smal number of interfacing devices to reduce development cost and data transferring time [22]. here, the meter is directly connected with the gsm communication gateway and the measured parameters will be stored in our personal cloud. the gsm communication gateway is especially developed to collect the data from the meter and send them to the server hence it will act as the main processor. in order to get customized screens in the cloud server, programming is developed in super java. based on the consumer requirements the measured energy parameters will be formed as a report which can be chosen for different time periods (daily, monthly or live). this prototype achieved cloud transmission level of 14tbps without any delay [23]. the satec power meter is used to collect the data from the main panel to the consumer end. gsm based communication gateway circuit [24] was used. this system has been developed keeping in mind the aspects of reducing delay time for data transfer, increasing wireless coverage distance limit, and getting more values form the meter. in zigbee based monitoring systems, the power metering ic and arduino controllers were used and the system provided 15s delay time in transferring data. in the iot-based monitoring system, a splitter circuit, a data amplifier and the arduino controller were used to collect the data and send them through the wifi router. by ip address accessing mode we can view the data in an html file while the data are updated every 2s. in order to achieve fast communication with reliable data and more values from the meter, the wireless coverage limit is increased. in order to obtain the data storage unit, the cloud based smart energy monitoring is developed. hence instead of power metering ic and splitter circuit we used the gsm communication gateway circuit directly interfaced with the smart meter as shown in figure 7. the communication gateway will send the data to the server and the data will be saved as per our customized program in the cloud. the data can be accessed from anywhere and we can get a customized report without any difficulties. the transmission speed is 14tbps without any delay time as the coding is developed for a fully online system. the system gives a customizable master report as shown in figure 8. the coding has been developed in super java for the communication unit and the measured values can be viewed as a report in a customized html file. engineering, technology & applied science research vol. 10, no. 3, 2020, 5808-5813 5812 www.etasr.com govindarajan et al.: performance analysis of four smart energy monitoring systems (a) (b) fig. 7. hardware installation of the energy monitoring system using the gsm gateway fig. 8. real time energy monitoring live report from the cloud iii. performance analysis the implemented semss with their real time measurements employing different communication modules are compared in figures 9-10. the sems using gsm communication gateway and developed with cloud computing shown exhibits improved performance in lt consumers for daily utilization. this system provides detailed information to the lt consumers about their power consumption which includes live chart, day chart, and month wise chart. the overall comparison is shown in table i. fig. 9. comparison chart of data transferring delay time in energy monitoring systems fig. 10. comparison chart of the number of values obtained by the energy monitoring systems table i. performance of the implemented sems system speed delay (s) no of values network coverage limit zigbee based 250kbps 15 4 100m iot based 2mbps 2 6 92m android based 424kbps 1 10 cloud based 14tbps real time 16 iv. conclusion different types of energy monitoring systems were developed and the performance of all aspects of the systems was analyzed and investigated by comparing the concept and technology used. the comparison of real time output results based on the communication module proves that the cloud computing-based smart energy monitoring system using gsm communication gateway produces improved performance in a number of parameters, namely high speed data communication, online data transfer, customized report making and in providing instant updated information. the cloud computing system practically responds in real time. with these systems, the consumers can know about their power utilities easily, making their power consumption schedule with this knowledge and calculate their electricity usage cost. power consumption can be reduced by developing this kind of innovative model in real time. references [1] j. zheng, d. w. gao, l. lin, “smart meters in smart grid: an overview”, ieee green technologies conference, denver, usa, april 4-5, 2013 [2] k. vikram, s. kumar, “role of smart meters in smart grid”, electrical india, vol. 57, no. 6, pp. 38-46 2017 [3] k. baraka, m. ghobril, s. malek, r. kanj, a. kayssi, “low cost arduino/android-based energy-efficient home automation system with smart task scheduling”, 5 th international conference on computational intelligence, communication systems, and networks, madrid, spain, june 5-7, 2013 [4] m. m. albu, m. sanduleac, c. stanescu, “syncretic use of smart meters for power quality monitoring in emerging networks”, ieee transactions on smart grid, vol. 8, no. 1, pp. 485-492, 2017 [5] 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international journal of engineering research & technology, vol. 3, no. 2, pp. 13491353, 2014 [23] r. govindarajan, s. meikandasivam, d. vijayakumar, “cloud computing based smart energy monitoring system”, international journal of scientific and technology research, vol. 8, no. 10, pp. 886-890, 2019 [24] p. naveen, w. k. ing, m. k. danquah, a. s. sidhu, a. abu-siada, “a cloud associated smart grid admin dashboard”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2499-2507, 2018 [25] i. androulidakis, g. kandus, “mobile phone brand categorization vs. users’ security practices”, engineering, technology & applied science research, vol. 1, no. 2, pp. 30-35, 2011 authors profile r. govindarajan was born in tamilnadu, india, on 1982. he received his be degree in electrical and electronic engineering from sri chandrasekharendra saraswathi viswa mahavidyalaya, kanchipuram, tamilnadu, india, mtech. degree in applied electronics from bharath university, chennai, tamil nadu, india and he is currently pursuing his phd in electrical engineering in scsvmv university, tamilnadu, india. he has published four research papers in scopus indexed journals and two in other reputed journals. his areas of interest include smart gird, smart energy management, wireless communication, and cloud computing. s. meikandasivam received his bsc degree in electrical and electronics engineering from anna university, chennai, tamilnadu, india in 2002, the msc degree in power systems in 2005, and a phd degree from the maulana azad national institute of technology, bhopal, india in 2010. he has been an associate professor and head of the school of electrical engineering, vellore institute of technology, tamilnadu, india. d. vijayakumar received his be degree in electrical and electronic engineering from madras university, chennai, india, in 2002, me degree in power systems from scsvmv university, tamil nadu, india in 2005, and his phd degree in electrical engineering from maulana azad national institute of technology, bhopal, india in 2010. he has been a professor with the school of electrical engineering, vellore institute of technology, tamilnadu, india. engineering, technology & applied science research vol. 8, no. 4, 2018, 3172-3176 3172 www.etasr.com qasem & massadeh: solving cell placement problem using harmony search algorithms solving cell placement problem using harmony search algorithms rose m. al qasem department of computer engineering faculty of engineering technology al balqa applied university amman, jordan rose.alqasem@fet.edu.jo samah m. massadeh department of computer engineering faculty of engineering technology al balqa applied university amman, jordan samah.massadeh@fet.edu.jo abstract—cell placement is a phase in the chip design process, in which cells are assigned to physical locations. a placement algorithm is a way that satisfies the objectives and minimizes the total area while keeping enough space for routing. cell placement is an np-complete problem of very large size. in order to solve this problem, diversified heuristic algorithms are used. in this work, a new algorithm is proposed based on the harmony search algorithm. the harmony search algorithm mimics music improvisation process to find the optimal solution. cell placement problem has many constraints, so in this work, the harmony search algorithm is modified to adapt to these constraints. experiment results show that this algorithm is efficient for solving cell placement and is characterized by good performance, solution quality and likelihood of optimality. keywords-optimization; harmony search ; cell placement i. introduction chip design is a process of consecutive phases, and one of the important phases in creating a vlsi circuit is physical design. the physical design process has four consecutive steps, namely partitioning, cell placement, routing and compaction. in the cell placement stage, the description of the physical layout of the cells is produced by assigning geometric coordinates to the cells. the smaller feature size is the objective of this placement. the small size has many advantages like higher performance and lower power consumption. the objective of the placement algorithm is to find a layout that optimally or nearly optimally minimizes a cost function. the cost function realizes that the major part is the area, but quite often involves the aspect ratio, to make the chip as close to square as possible. cell placement is one of the np-complete problems which are generally combinatorial in nature and have a noisy solution space. several heuristic optimization techniques have been produced to solve the placement problem by using a set of diversified algorithms like genetic algorithms [1] and simulated annealing [2]. a comprehensive summary of those techniques is introduced in [3]. harmony search (hs) is a phenomenon-mimicking metaheuristic algorithm which has been proposed in [4]. hs is a novel approach inspired from the musical process of searching a perfect state of harmony as in music improvisation where the pitch of each musical instrument is improved to accomplish this better state of harmony. the pitch determines the quality of music, just as the fitness function value determines the quality of solutions. furthermore, the musician improvisations are analogous to local and global search schemes in optimization strategies. hs has been used to solve various types of optimization problems, such as traveling salesperson problem [4], function optimization [5], mechanical structure design [6], tour routing [7], water network design [8], pipe network optimization [9], vehicle routing [10] and optimization of data classification systems [11]. it is showing significant improvements over other heuristics. it can be produced for both continuous and discrete variables. a special discrete variation of the hs is produced on the basis of introducing the stochastic derivatives for the discrete variables involved [12]. for the class of binary optimization problems, the hs algorithm is equivalent to a certain evolutionary algorithm as shown in [13]. a lot of modified hs algorithms have been studied in order to enhance the performance of the original version [14, 15]. in this work, we present a solution to the cell placement problem using the hs methodology, and in future work we will compare its performance with well-known evolutionary algorithms. the results show that the proposed algorithm can improve the quality of the solution. the rest of the paper is organized as follows: section ii describes briefly the cell placement problem. section iii gives a formal description of the hs theory, and section iv demonstrates the proposed hs algorithm for cell placement, followed by presentation and discussion of the experimental results in section v. finally, section vi wraps up our work. ii. cell placement problem: representation and fitness in this work, each solution is a sequence represented by the normalized polish notation (rpn) [16]. the sequence includes module names and two relational operators: for n blocks, a string with n blocks (cells) and n-1 operators of the + or * type, corresponding to a vertical or horizontal cut respectively. as an example, the expression (12+34*+5+67+*) is an encoding for the arrangement representing a possible solution as illustrated in figure 1. exi [16 fitn far cal wh pla enc ass rel val of rat sum im com the bet the sta pit the po var the or hs heu or hs par con wh wh fun by 1) ma sol engineerin www.etasr commonly, isting ones by 6, 17]. the q ness value. th r the solution i lculated by the f= (1 here, t is th acement, l an closing all the sociated with t lative significa lue of the fact α are used to tio is not optim iii. hs algorith mmarize hs, mprovisation d mposed, the m e music pitche tter state of ha e optimal solu age, the musici tch from the m e memory or ssible pitches riable picks a e memory, tak take a random s algorithm fo uristic and the consideration s algorithm co rameters: har nsideration rat a. the gs the hs alg here a single hich optimizes nction. the de the following step 1 initialize the atrix contains lutions to th ng, technology r.com fig. 1. s the new solu y using certain quality of the he proposed m is from the op e following eq1 ) he total area nd w are the l e cells and the the solution. t ance of the as tor α is within favor square mized. . harmony m has been , it is requir done for the h musicians try v es stored in t armony is anal utions to the p ian can select memory, perfor perform a ran s. similarly, value from th ke a value adja m value from t ormalized thes e three corresp n, pitch (soluti ontrols the thre rmony mem te (hmcr), an sa behavior gorithm tries t objective is s (minimizes o etails of the h g steps. harmony sear s a certain n he problem u y & applied sci slicing structure. utions are rep n methods whi new solution measure of the ptimal one. th quation: of all cells length and wid e product wl the factor α us spect ratio to n the range of arrangements y search algo proposed in red to idealiz harmony. wh various possib the memory. t logous to the p problem. in m one of three o rm a pitch adja ndom pitch fro in hs algori hree options: t acent to any v the domain of e three option ponding proce ion) adjustmen ee options by m mory (hm), nd pitch adjust to solve optim considered, b or maximizes) harmony algor rch memory (h number of ra under conside ience research qasem & m produced from ich are presen n is evaluated fitness reflect he fitness meas (1) regardless o dth of the rect represents th sed to determin the actual are [0–1]; small v . if α=1 then a orithm n [4]. in ord ze the proce hen the harmo ble combinatio this search fo procedure of fi music improvi options: perform acent to any ot om the range ithm each de take any value value in the me f all possible v ns for making ess are memor nt and random means of three harmony me tment rate (pa mization prob by finding a v ) a certain obj rithm are illus hm), the initia andomly gen eration. for a h v massadeh: solv m the nted in d by a ts how sure is of the tangle e area ne the ea, the values aspect der to ess of ony is ons of for the inding isation m any ther in of all ecision e from emory values. a new ry use mness. e main emory ar). blems, vector ective strated al hm erated an ndim mem whe dim 2) pro com       whe loca  whe the use 3) eva the rep is d 4) max effe of t app vol. 8, no. 4, 20 ving cell placem mension proble mory size) is r hm= ,, , ere, (x ,x ,… mension of the step 2 improvise a n oduced based mponent of new generate a ran compare the hmcr is d component fr if r1<hmcr hm, it is cho vector the obtained par, where candidate solu generate a ne if r2<par, tx = x ± ere bw is ba al search if the conditio solution is genx = l ere l, u is the e generation o e of all the hm step 3 update hm: aluated. if its worst memb laced by the n deleted. step 4 repeat step ximum iteratio the paramete ects in the opti the challengin propriate valu 018, 3172-3176 ment problem u em, a hm w represented by, ,…,, ,…,... ,…,…,x ) is a c problem. new solution on harmony m w solution xj i ndom number e random num defined as th rom the hm m r, the xj of th osen from the d solution xj the par de ution selected ew random num then adjust therand(0,1).bw andwidth facto on r1<hmcr nerated randomu l .rand lower and upp f new solution m vectors. after the n objective func ber in the hm new solution. o 2 to step 3 u ons) is satisfie ers of hmcr imization perf ng topics for th ues for these 6 using harmony with the size o y the following candidate solu from the hm memory consi is obtained as r r1 within the mber r1 wit he probabilit members. he new solutio jth dimension is further mu etermines the from the hm mber r2 withi e obtained soluw or, which is u r fails, the xj v mly as followsd(0,1) per bound for ns in the hs st ew solution ction value is m, the worst otherwise, the until a termina ed. r and par us formance of th he hs algorith e parameters. 3173 y search algor of hms (harm g matrix: (2) ution and n i m. each soluti idering rules. follows: e range [0-1] th a hmcr. ty of selectin on comes from n of a random utated accordin e probability to be mutated in the range [0 ution as follow (3) used to contro variable of the s: (4) the given prob trategies make is generated, better than th t member wi e generated sol ation criterion sually have cr he hs strategy hm is choosin authors in rithms mony s the ion is each the ng a m the m hm ng to of a d. 0-1] ws: ol the e new blem. es full it is hat of ill be lution (e.g. ritical . one ng the [18] engineering, technology & applied science research vol. 8, no. 4, 2018, 3172-3176 3174 www.etasr.com qasem & massadeh: solving cell placement problem using harmony search algorithms produced an adaptive method for adjusting par and bw parameters in the improved hs (ihs) algorithm. in this method, in order to improve the performance of the hs, the values of par and bw increase and decrease dynamically and respectively with the growth of hs iterations. the updates of par and bw are often case dependent and are therefore difficult to determine. iv. hs algorithm based cell placement problem as mentioned above, cell placement can be represented as a two-dimensional bin packing problem, where its main goal is to order the cells in a way that minimizes the area and produces near square shape while providing enough space for routing. in this work, we propose a new algorithm for cell placement problem based on hs algorithm, in which each pitch will be an agent looking for an optimal solution in the search space. it is difficult to solve the cell placement problem by the traditional hs algorithm, because this problem needs meet simultaneously several constraints. for this reason, the update of pitch (solution) depends on some rules, so as to solve the cell placement problem by using harmony search algorithm, there are some modifications that must be done as will be shown in the following procedure. the hs algorithm based cell placement problem is outlined as follows: 1. harmony memory initialization 1.1 randomly generate initial population harmony memory of vectors (solutions) (x1,x2,…,xhms ) as many as the hms where xi =x , i=1…hms and j=1…n, n is the dimension of the problem. 1. 2 store the vectors in hm matrix as shown in (2). 2. construction and evaluation of new solution candidate. 2. 1 generate a new vector xnew: for each component (decision variable) x of the new vector xnew do { generate random number r1 within the range [0-1] if (r1<hmcr) then { let the decision variable in x new be the jth dimension of a randomly selected hm member( ). this selection must meet the constraints of the cell placement problem, otherwise another hm member should be selected. generate random number r2 within the range [0-1] if (r2<par) then apply pitch adjustment distance bw to mutate as follows: if selected hm member is cell then x = ± bw (5) otherwise x = (6) } else let in x new be a random value. where ∈ {1, 2… m}, m is the number of cells. } 2.2 evaluate the fitness of xnew by objective fitness function f as in (1). 3. update harmony memory if the fitness of new solution xnew is better than the fitness of the worst hm member then replace the worst hm member with new solution xnew. else disregard xnew. 4. if stopping criteria not met then go to step 2 else stop. the effects of parameters are analyzed. the best performance of hs algorithm for solving placement problem is detected, when the values of the parameters are set as follows: hms is the size of the hm. it generally varies from 50 to 100 and the used value is 60. hmcr is the rate of choosing a value from the hm. it generally varies from 0.7 to 0.99 and the used value is 0.8. par is the rate of choosing a neighboring value. it generally varies from 0.1 to 0.5 and the used value is 0.22. bw is the amount of maximum change in solution adjustment and the used value is 1. it is possible to vary the parameters values as the search progresses. v. results the quality measures used in this study include the following: average fitness value for a set of runs, number of iterations employed (elapsed time), and number of successes in a set of runs (success rate). in this work, the performance of the hs algorithm for solving the cell placement problem was evaluated by using two methods. in the first method, instances from mcnc benchmark are chosen to assess the quality of the solutions. in the second method, the algorithm is performed on three cases of cell placement problem generated randomly and have known optimal solutions to measure the possibility of reaching the optimal solution. in the first test, three cases from mcnc benchmarks, xerox with 10 cells, ami33 with 33 cells, and ami49 with 49 cells, were chosen and tested. table i shows a summary of the obtained results. the measure used in this test is the quality of solution in terms of wasted area. the number of replicates which carried out for each problem is 10 runs, each with different random starts. the algorithm is brought to stop when 6000 iterations have passed since the last improvement was happened or the number of iterations reaches 20,000, 40,000 and 60,000 for xerox, ami33 and ami49 respectively. the results for the three instances of mcnc benchmark are summarized in table i. the percentage of wasted area for the best, worst and mean case is noted in the last three columns of the table. the obtained results present that the proposed algorithm achieves good area utilization in the best and mean wasted area. figure 2 illustrates the search improvement of the algorithm through time, waste area versus iterations number for ami49 and ami33. the figure clearly indicates that through the res 10 in wit the wit in wit th ini sol 25 me lik res col har ran mo alg the ta engineerin www.etasr e passage of ti sults. t # of c xerox 10 ami33 33 ami49 49 fig. 2. searc in order to p , 20 and 30 ce the first case th total area o e second case th total area o the third case th total area o he number of itial populatio lution is achie ,000 and 40,00 etric used to ev kelihood of op sult for the suc lumn of table rmony search ndom trials. t ost runs. in gorithm is 70% e last case. fig. 3. able ii. art # of cells 10 20 30 ng, technology r.com ime the propo table i. b cells # of iter 0 20,0 3 40,0 9 60,0 ch progress. wast perform the se ells were gene e, an instance f 25 square un , an instance of 100 square e, an instance of 225 square trials for each on. the algo ved or the num 00 for case1, c valuate the pro ptimality or s ccess rate for e ii, in the fir based cell pla the algorithm the second c %, whereas the artificial proble tificial problem # of iteration 10,000 25,000 40,000 y & applied sci osed algorithm benchmark resu w rations best 000 3.3 000 5.4 000 7.5 te area vs iteration cond test, thre erated. as illu is produced b nits into 10 var is produced b units into 20 v is produced b units into 30 v h case is 10 t orithm is halt mber of iterati case2 and case oposed algorith success rate. t each case. as rst case, the s acement is 90% obtained the case, the suc e success rate ems for known op m of known opti ns success r ience research qasem & m m can achieve ults wasted area (%) worst m 6.2 4 8.8 6 9.5 8 ns (ami49, ami3 ee optimal cas ustrated in fig by cutting a s rious size bloc by cutting a s various size b by cutting a s various size b times with dif ted if the op ions reaches 10 e3 respectively hm in this test table ii show s shown in the success rate fo % over 10 dif optimal solut ccess rate fo dropped to 5 ptimal solution imal solution rate(out of 10) 9 7 5 h v massadeh: solv better ) mean 4.8 6.5 8.5 33). ses for gure 3, square cks. in square blocks. square blocks. fferent ptimal 0,000, y. the t is the ws the e third for the fferent ion in r this 0% in pro bett size plac pro solu exp algo find real ave that cell com algo [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] vol. 8, no. 4, 20 ving cell placem it is clear th oblems, but on ter performan e. in this work a cement probl oposed algorith ution quality periments sho orithm appea ding the optim lizes promisin erage of waste t the hs algor l placement pr mparison betw orithms. t. w. manikas and standard c and systems, v g. nan, m. li standard cell p notes in compu k. shahookar, p computer surv z. w. geem, optimization al pp. 60–68, 2001 k. s. lee, z. w engineering op computer meth no. 36–38, pp. k. s. lee, z. w the harmony se 9-10, pp. 781–7 z. w. geem, c orienteering pro science, vol. 36 z. w. geem, “o harmony search 277, 2010 z. w. geem, optimization: ap of modelling an ] z. w. geem, k vehicle routin 12, pp. 1552–15 ] x. wang, x. z. and harmony systems”, intern 1-2, pp. 80–88, ] z. w. geem, “n design variables 1, pp. 223–230, ] m. padberg, “ problems”, in: o 2012 ] m. g. h. omra mathematics an 018, 3172-3176 ment problem u hat this algor n the other si nce for the pr vi. co a new algorithm em which is hm has achie y and the l ow that the ars in terms mal solution, ng area utiliza ed area for a se rithm is one ef roblem. hence ween this alg refer , m. h. mickle, “ cell placement”, vol. 2, pp 115-118 i, d. lin, j. ko placement”, adv uter science, vol p. mazumder, “v ey, vol. 23, no. 2 j. h. kim, g lgorithm: harmon 1 w. geem, “a new ptimization: har hods in applied 3902–3933, 2005 w. geem, “a new earch algorithm”, 798, 2004 c. l. tseng, y. oblem: best tourin 612, pp. 741–750 optimal cost desi h”, engineering j. h. kim, g pplication to pipe nd simulation, vo k. s. lee, y. par ng”, american jo 557, 2005 . gao, s. j. ovask search method i national journal o 2009 novel derivative o s”, applied math , 2008 “harmony search operations resea an, m. mahdavi, nd computation, v 6 using harmony rithm is robu de it needs en roblems with onclusion m was present based on h eved good res likelihood of performance of increasing and the qual ation in terms et of trials. th fficient algorit e, in future wo gorithm and o rences “a genetic algor 45th midwest s 8, 2002 ou, “adaptive sim vances in natural . 3612, pp. 943-9 vlsi cell placem 2, pp. 143–220, 1 g. v. loganatha ny search,” simu w meta-heuristic al rmony search t mechanics and 5 structural optimi computers and s park, “harmony ng in china”, lec 0, springer, 2005 ign of water distr optimization, vo g. v. loganath e network design ol. 22, no. 2, pp. rk, “application ournal of applied ka, “fusion of clo in optimisation of bio-inspired co of harmony searc hematics and com h algorithms fo arch proceedings, “global-best har vol. 198, no. 2, p 3175 y search algor ust for small nhancement t medium and ted to solve th hs algorithm. sults regarding f optimality. of the prop g success rate lity of solutio s of minimum his study evide thm for solvin ork we will m other optimiz rithm for mixed symposium on c mulated anneali l computation, l 47, springer, 200 ment techniques”, 991 an, “a new he ulation, vol. 76, n lgorithm for cont theory and pra engineering, vol zation method ba structures, vol. 8 search for gener cture notes in com ribution networks ol. 38, no. 3, pp han, “harmony n”, international j 125–133, 2002 of harmony sea d sciences, vol. onal selection alg of fuzzy classifi omputation, vol. ch algorithm for d mputation, vol. 19 or binary optimi pp. 343–348, sp rmony search”, a pp. 643–656, 2008 rithms size to get large he cell the g the the posed e for on. it m and ences ng the make a zation macro circuits ng for lecture 05 , acm euristic no. 2, tinuous actice”, l. 194, ased on 82, no. ralized mputer s using p. 259search journal arch to 2, no. orithm fication 1, no. discrete 99, no. ization ringer, applied 8 engineering, technology & applied science research vol. 8, no. 4, 2018, 3172-3176 3176 www.etasr.com qasem & massadeh: solving cell placement problem using harmony search algorithms [15] q. k. pan, p. n. suganthan, j. j. liang, m. f. tasgetiren, “a local-best harmony search algorithm with dynamic subpopulations”, engineering optimization, vol. 42, no. 2, pp. 101–117, 2010 [16] d. f. wong, c. l. liu, “a new algorithm for floorplan design”, 23rd acm/ieee design automation conference, las vegas, nevada, usa, pp. 101–107, february 6, 1986 [17] j. p. cohoon, s. u. hedge, w. n. martin, d. s. richards, “distributed genetic algorithms for the floorplan design problem”, ieee transactions on computer-aided design, vol. 10, no. 4, pp. 483–492, 1991 [18] m. mahdavi, m. fesanghary, e. damangir, “an improved harmony search algorithm for solving optimization problems”, applied mathematics and computation, vol. 188, no. 2, pp. 1567–1579, 2007 microsoft word 36-3264_s_etasr_v10_n1_pp5295-5300 engineering, technology & applied science research vol. 10, no. 1, 2020, 5295-5300 5295 www.etasr.com faruque et al.: cmos compatible plasmonic refractive index sensor based on heavily doped silicon … cmos compatible plasmonic refractive index sensor based on heavily doped silicon waveguide md. omar faruque department of electrical and electronic engineering islamic university of technology gazipur, bangladesh omarfaruque@iut-dhaka.edu rabiul al mahmud department of electrical and electronic engineering islamic university of technology gazipur, bangladesh rabiul.eee@iut-dhaka.edu rakibul hasan sagor department of electrical and electronic engineering islamic university of technology gazipur, bangladesh sagor@iut-dhaka.edu abstract—in this study, a plasmonic refractive index (ri) sensor using heavily n-doped silicon waveguide is designed and numerically simulated using finite element method (fem). the reported sensor is based on gratings inside a heavily doped silicon waveguide structure instead of a conventional metal-insulatormetal structure. this feature enables the device to overcome the limitations of conventional plasmonic devices like optical losses, polarization management, etc. besides, it makes the device compatible with complementary metal oxide semiconductor (cmos) technology and thus provides an easier way of practical fabrication and incorporation in integrated circuits. the presented sensor has a highest sensitivity of 1208.9nm/riu and a resolution as small as 0.005 which is comparable with conventional plasmonic sensors reported to date. the main advantage of this plasmonic sensor is that it has a very simple structure and uses silicon instead of metal which provides an easier way of fabrication. keywords-cmos technology; heavily doped silicon; metalinsulator-metal; ri sensor i. introduction when light interacts with a metal, the free electron cloud inside the metal oscillates and creates an electromagnetic wave at the surface which tends to propagate along with the metal surface [1]. this electromagnetic wave is known as surface plasmon polaritons (spps) and is the basis of most of the advanced plasmonic applications. spps can confine electromagnetic field to a metal-dielectric interface, allowing for nanofocusing with tremendous field enhancement [2, 3]. the diffraction limit is one of the key factors for the minimization of optical devices [4, 5]. in order to overcome this diffraction limit in nanophotonic devices and photonic integrated circuits (pics), spps are utilized. thus, plasmonic devices are making their way towards realizing low cost, high sensitivity, and small size, leading to many biological, environmental, and chemical applications [6-9]. recent plasmonic applications include a number of different plasmonic devices like plasmonic filters [10-12], plasmonic splitters [1315], mach-zehnder interferometers [16, 17], plasmonic bragg reflectors [18-20], plasmonic sensors [10, 11, 13-18], etc. most of the plasmonic devices reported to date are based on a metalinsulator-metal (mim) waveguide structure. among the plasmonic devices, plasmonic sensor is one of the most important parts of the photonic integrated circuits as most of the integrated circuits require sensing a number of parameters in order to operate smoothly. as a result, plasmonic sensors have drawn a lot of attention in recent days. different types of proposed plasmonic sensors include biosensors [21-23], temperature sensors [24, 25], refractive index sensors [24, 26, 27], etc. material technology is playing a vital role in the recent development of plasmonics and plasmonic devices. when light is incident on a material, spps are created depending mostly on the plasmonic properties of that material. also, the spp propagation is greatly affected by the plasmonic properties. plasmonic materials also act as the building block while realizing the plasmonic devices practically. thus, in order to have a realizable plasmonic device with good performance, a suitable plasmonic material is the most important thing to look for. since plasmonic materials are mainly used for their ability to interact with light, their plasmonic properties can be described by two parameters, dielectric permittivity ε, and magnetic permeability µ [28]. but, at optical frequencies, the permeability becomes close to unity. thus, their behavior can be fully described by the dielectric permittivity only. gold and silver are the most common plasmonic materials used as the metal in the mim structure. both of these metals have a negative real part of the complex permittivity which is one of the most important requirements for spp production and propagation. but they are always associated with losses because of loss mechanisms like interband transition, intraband transitions, and scattering losses [29, 30]. the higher amount of these three above mentioned losses makes the imaginary part of the complex permittivity larger. also the large value of the real part of the permittivity causes a lot of problems in plasmonic devices which require a balanced polarization response [31]. both the real part and the imaginary part of the permittivity depend on the carrier concentration of the material which is comparatively very high in natural metals like gold and silver (≈10 23 cm -3 ). some of the above-mentioned problems could be solved if the carrier concentration could be reduced in natural metals. but the carrier concentration in a natural metal is not usually changeable keeping its other properties intact. another important challenge is the fabrication of the devices using corresponding author: md. omar faruque engineering, technology & applied science research vol. 10, no. 1, 2020, 5295-5300 5296 www.etasr.com faruque et al.: cmos compatible plasmonic refractive index sensor based on heavily doped silicon … metals. the optical properties of thin metal films are quite different compared to bulk metal [32, 33]. metal films are very difficult to fabricate keeping their optical properties constant with conventional fabrication techniques. thus, the plasmonic devices made up of metals like gold and silver are not compatible in most of the integrated circuits. in this paper, an investigation is made to find a suitable alternative of metal which can support spp propagation and will help overcome the problems with conventional metals at the same time. since the optical behavior of metals is described by the dielectric permittivity, which has got a negative real part and a positive imaginary part for metals. similar dielectric permittivity can be achieved for silicon semiconductor when doped over a certain carrier concentration. the doping concentration in silicon can be controlled during the doping process which will make its dielectric permittivity tunable. thus, most of the problems with metals can be overcome. besides, silicon photonics is cmos compatible which will provide an easier way of fabrication. the plasmonic refractive index sensor reported here is of a very simple structure. a straight waveguide is formed with air inside doped n-silicon layer which has a number of gratings in it. the n-doped silicon will support spp propagation when the electromagnetic wave will be incident at one terminal. the material under sensing will be placed inside the hollow space with silicon at both sides. the proposed sensor can have a sensitivity of 1200nm/riu which is comparable with the sensitivity of other reported plasmonic refractive index sensors. it can detect refractive index change as small as 0.005. the sensor has a much simpler structure compared to the other plasmonic sensors which make it convenient for being incorporated in an integrated circuit. ii. theoretical modeling and device design the relative permittivity of a material is a complex quantity with a real part and an imaginary part. the permittivity of optical materials is also a frequency-dependent quantity. the complex relative permittivity of highly doped silicon can be described by lorentz-drude model [34] as follows: ( ) ( ) 2 2 1 (1 ) p i ω ε ω ε ω ωτ∞ = − + (1) if the real and imaginary parts are separated, (1) becomes: ( ) ( ) 2 2 2 2 2 2 21 1 p p i ω τ ω τ ε ω ε ω τ ω ω τ ∞   = − +  + +  (2) where ωp is the plasma frequency, ε∞ is the infinite frequency relative permittivity or the background permittivity, τ is the electron/hole relaxation time, ω=2πc/λ is the angular frequency, c is the speed of light in vacuum and i is the imaginary unit. in the case of the highly doped degenerate intrinsic semiconductor, 2 2 0p eff ne mω ε= and eff m eτ µ= where n is the free carrier concentration, µ is the electron/hole’s drift mobility and meff is the averaged electron/hole effective mass [35]. usually, the angular frequency p ω ω� and 1ωτ � [36]. thus (2) can be rewritten as: ( ) 2 3 2 0 0 i σ σ ε ω ε ω ε τ ω τ ε∞   = − +    (3) where, enσ µ≈ is the conductivity of the doped silicon, e is the charge of an electron, and ε0 is the free space permittivity. the infinite frequency relative permittivity or the background permittivity is the high-frequency limiting value that is approximately 11.7 for silicon and is independent of the doping concentration [37, 38]. here, µ=80 [39] and meff=0.26×m0, where m0 is the mass of the electron [40]. in order to support spp propagation like metal, the real part of the complex permittivity must be negative. the real part and imaginary part of the complex permittivity value for different carrier concentrations and at different wavelengths can be calculated from (2). at 1550nm wavelength, the carrier concentration required for achieving a negative real permittivity of -1 is 16×10 20 cm -3 . the relationship of the real part and the imaginary part of the complex permittivity with carrier concentration at different wavelengths is shown in figure 1 and the relationship with wavelength at different carrier concentration is shown in figure 2. (a) (b) fig. 1. relative permittivity: (a) real part (b) imaginary part versus carrier concentration at different wavelengths the basic structure of the sensor is very simple. it consists of a hollow straight waveguide with grating inside a layer of ndoped silicon. the hollow space in the straight waveguide will be used to hold the material under sensing. the number of engineering, technology & applied science research vol. 10, no. 1, 2020, 5295-5300 5297 www.etasr.com faruque et al.: cmos compatible plasmonic refractive index sensor based on heavily doped silicon … gratings may vary depending on the application. here, the best result is obtained for two gratings in the waveguide. the basic model of the sensor is shown in figure 3. for practical designing, a silicon substrate must be used under the main sensor structure. the width of the straight waveguide and the grating w is chosen to be 20nm, the length of the grating h=450nm and the gap between two gratings, d=250nm. (a) (b) fig. 2. relative permittivity: (a) real part (b) imaginary part versus wavelength at different carrier concentrations though, for practical designing, the height of the device is also an important parameter, the sensor proposed here has been simulated in 2d like most other proposed work in order to enforce an efficient simulation [41]. practically, any height greater than 50nm will provide a result which will be very close to the simulation result [21]. the 2d designing parameters of the sensor are varied during the simulation process and the best parameters are chosen after observing the transmission characteristics. iii. results and discussion to simulate the designed sensor, commercial simulation software comsol multiphysics is employed [42]. for the simulation purpose, it utilizes fem with scattering boundary condition. the device is simulated for a single grating, two gratings, and three gratings sequentially. the transmission characteristics are shown in figure 4. it is observed that the transmission peak with a single grating is not sharp enough. as a result, the shifting of the wave shape with the change of refractive index will not be detectable very easily. thus, it is not considered as a suitable structure to be used as a refractive index sensor. as the next step, the number of grating is increased to two. as the wave shape with two gratings indicates, the resonance peak is sharper than the peak with a single grating and thus, can be considered as a suitable structure for the refractive index sensor. with three gratings, two resonance peaks are obtained. but, the transmittances of both peaks are lower than the peak with two gratings. nevertheless, it can also be utilized for the sensor structure. the number of gratings is not increased further since more gratings will cause the transmittance to be much lower. (a) (b) (c) fig. 3. the basic structure of the sensor with (a) single grating, (b) two gratings, (c) three gratings the width of the straight waveguide and the gratings w is then varied and the transmission characteristics are observed. as w increases, the transmittance increases and the resonance peak suffers a left shift. since we tried to design a sensor that operates between 1300nm and 1400nm, we have chosen w=20nm. for the sensors which will be operated in any other ranges like greater than 1400nm, 1100nm to 1200nm, smaller than 1100nm, the values of w=15nm, 25nm and 30nm respectively may be chosen. for the values of w less than 20nm, the transmittance is too low which may degrade the performance of the device. the distance between the two gratings d is then varied from 200nm to 350nm and the transmission characteristics are analyzed. the transmission characteristics are shown in figure 6. engineering, technology & applied science research vol. 10, no. 1, 2020, 5295-5300 5298 www.etasr.com faruque et al.: cmos compatible plasmonic refractive index sensor based on heavily doped silicon … fig. 4. transmission characteristics with different number of gratings with w=20nm, h=400nm, and d=250nm fig. 5. transmission characteristics of the sensor with h=400nm, d=250nm for different values of w fig. 6. transmission characteristics of the sensor with w=20nm, h=400nm for different values of d with the increase in distance between the gratings, the transmittance of the resonance peak gradually reduces and the resonance peak suffers a right shift. the structure with a smaller gap between the gratings has provided a better transmittance of the resonance peak. the resonance peak of the smallest gap, d=200nm, is obtained in the range smaller than 1200nm. thus the value of d is chosen to be 250nm in order to have a reasonably high transmittance (>0.3) of the resonance peak and also to keep the operating point between 1300nm and 1400nm. the length of the grating h is varied and the effects are evaluated. the smallest value of h is chosen to be 300nm, as the transmittance becomes very low with h smaller than 300nm. h is then varied up to 450nm. the transmission characteristics with different values of h are shown in figure 7. we can see that the transmittance of the resonance peak is highest for the largest value of h. the resonance peak is also within the operating range of 1300nm to 1400nm. thus, h=450nm is chosen for further simulations. with the parameters of the sensor structure chosen to be w=20nm, d=250nm and h=450nm, the refractive index of the material under sensing n is gradually increased from 1 with a step of 0.005 and the transmission characteristics are observed as shown in figure 8. the resonance peaks are observed to be shifted with the change of the value of n. the sensitivity can be calculated from the resonance shift by using (4): s n λ∆ = ∆ (4) where, s is the sensitivity, ∆λ is the resonant wavelength shift and ∆n is the change of refractive index. fig. 7. transmission characteristics of the sensor with w=20nm, d=250nm for different values of h fig. 8. transmission characteristics of the sensor with w=20nm, d=250nm, h=450 nm for different values of n 1000 1200 1400 1600 1800 wavelength (nm) 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 t ra n s m it ta n c e w = 10 nm w = 15 nm w = 20 nm w = 25 nm w = 30 nm 1000 1200 1400 1600 1800 wavelength (nm) 0 0.1 0.2 0.3 0.4 0.5 t ra n s m it ta n c e h = 300 nm h = 350 nm h = 400 nm h = 450 nm 1250 1300 1350 1400 1450 1500 wavelength (nm) 0 0.1 0.2 0.3 0.4 0.5 t ra n s m it ta n c e n = 1 n = 1.005 n = 1.01 n = 1.015 n = 1.02 n = 1.025 n = 1.03 engineering, technology & applied science research vol. 10, no. 1, 2020, 5295-5300 5299 www.etasr.com faruque et al.: cmos compatible plasmonic refractive index sensor based on heavily doped silicon … the resonance peak shift with the change of refractive index of the sensing material and the sensitivities for different values of n are shown in table i. we can see that a maximum sensitivity of 1208.9nm/riu is obtained for the designed sensor. it can detect a change in the refractive index as small as 0.005. the plot of the resonance peak against the refractive index is shown in figure 9 which shows that the resonance wavelength shift with the change of refractive index is almost linear. thus, it can be expected to have a linear resonance shift for refractive indices beyond 1.03 and can be used to sense those. the number of gratings nanofocusing to three and the transmission characteristics are analyzed for refractive indices 1 and 1.01. the transmission spectrum is shown in figure 10. table i. resonan ce sh ift and sensitivity for vario us values of n n resonance peak (nm) resonance shift (nm) sensitivity (nm/riu) 1 1337.7 ------------ 1.005 1343.1 5.4128 1082.6 1.01 1348.9 5.7879 1157.6 1.015 1354.4 5.4754 1095.1 1.02 1360.3 5.9145 1182.9 1.025 1365.8 5.5395 1107.9 1.03 1371.9 6.0444 1208.9 fig. 9. resonant wavelength shifts with the change of refractive index fig. 10. transmission characteristics of the sensor with three gratings with w=20nm, d=250nm, h=450nm and n=1 and 1.01 the resonant peaks are obtained at 1050.3nm and 1058.5nm for n=1 and n=1.01 respectively. the sensitivity obtained here is 825.64nm/riu. since the sensitivity of the device reduces for this structure, the sensor with three or more gratings is not taken into consideration. iv. conclusions a plasmonic sensor with heavily doped n-silicon was designed. the sensor has a very simple structure having only a straight waveguide with gratings. thus, it can be easily manufactured and incorporated in photonic integrated circuits. the device is made up of silicon only, which makes it similar to silicon-on-insulator (soi) structures. thus, it is compatible with cmos technology and can provide an easier way of fabrication. the maximum sensitivity of the device is 1208.9nm/riu and it can sense refractive index change as small as 0.005 which 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technology islamabad, pakistan arehman780@yahoo.com muhammad naeem ahmed khan department of computer science shaheed zulfikar ali bhutto institute of science and technology islamabad, pakistan mnak2010@gmail.com abstract—a customer relationship management system is used to manage company relationships with current and possible customers. following a thorough review of contemporary literature, different data mining techniques employed in different types of business, corporate sectors and organizations are analyzed. a model that would be helpful to identify customers’ behavior in the banking sector is then proposed. three classifiers, k-nn, decision tree and artificial neural networks are used to predict customer behavior and are assessed in order to determine which classifier performs better for predicting customer behavior in the banking sector. keywords-customer; relationship; management; profitability; behavior; data mining; prediction i. introduction understanding customer nature and characteristics is very important for successful business growth. if we know the customer needs or customer buying patterns then we can design a market strategy to improve business and services. company correspondence with customers is an element which affects customer loyalty. authors in [1] proposed an efficient crmdata mining model for customer behavior prediction which manages associations between organizations and customers. the model improves decision making process for retaining customers. the study compares two classification methods, naïve bayes and neural networks, and results show that neural networks performance is better. authors in [2] evaluated classifiers performance in the banking sector. data mining techniques are used in different domains for instance banking, crm, medical, business strategy, weather forecasting and bioinformatics. a classification technique is used for prediction and based on accuracy of correctly classified instances, the study proposed a framework to evaluate performance of different classifiers such as logistic regression, naïve bayes and nearest neighbors. authors in [3] designed an expert system for promotional marketing campaigns using fuzzy logic. fuzzy logic is based on fuzzy sets. in fuzzy sets boundaries are not precisely defined. a fuzzy model is proposed for the selection of customers who should be targeted for deposit subscription schemes. the study selects customers based on age, annual income and loan attributes. direct bank marketing dataset obtained from uci repository is used for fuzzy logic model evaluation. authors in [4] analyzed bank direct marketing using data mining techniques. the study investigates analyzed different classifiers such as multilayer perceptron neural network, nominal or logistic regression, bayesian networks and decision tree model and applied on direct bank marketing dataset obtained from uci repository. the classifiers performance was measured by sensitivity, specificity and accuracy. after experiments it is concluded that decision tree classifier had the higher accuracy. author in [5] presents a case study of data mining modeling techniques for direct marketing. crisp-dm is a standard data mining project lifecycle and consists of six stages. the study focuses only on data preparation, modeling and evaluation stages of crisp-dm and identifies gaps like the role of variable selection and data saturation, selection of model hyper-parameters and controlling the problem of over-fitting and under-fitting. authors in [6] extracted actionable knowledge for direct marketing using decision tree and naïve bayes classifiers. the study used decision tree and naïve bayes classifiers to predict whether a client will subscribe a term deposit. authors in [7] applied semi-supervised learning technique to improve crm processes and its efficiency. it is generally believed that retaining existing customers is more profitable than attracting new ones. customer data is rapidly growing, therefore, companies face problems in analyzing customer for retention. the study investigates the proposed algorithm on bank and insurance datasets. authors in [8] develop a classification model to support cross selling in a mobile telecom market using fusion data mining techniques. telecom sector is using state-of-the-art value added services (vas) which generates more average revenue per user (arpu). vas is a digital service and adds extra features in the mobile phone network, for example, online games, image download, ringtones download, email, voucher and electronic transactions etc. authors in [9] utilized a customer clustering technique to investigate customer behavior. the clustering is generally performed in services, revenue, usage and user categories attributes. then inter-cluster analysis is performed on the generated clusters and evaluated the scattering of customers among the dissimilar group of attributes. engineering, technology & applied science research vol. 8, no. 3, 2018, 2949-2953 2950 www.etasr.com rahman and khan: a classification based model to assess customer behavior in banking sector authors in [10] developed an online information system and used it to store large amount of transaction data of customers that is available on the internet. these systems automatically capture customer transaction records from web browsing histories. authors developed a new algorithm intended for produce rfm sequential patterns based on rfm notions. authors in [11] focused on the profitability element in the banking sector. web data and commercially accessible data are studied for predictive performance. different data mining techniques are applied for predictive performance like decision trees, logistic regression and bagged decision trees. authors in [12] analyzed ski resort’s impact on sales and propose promotional and advertising strategies using decision tree. ski resort uses different communication methods like public relations, advertising and sales promotion to communicate with their key market segments. the technologies and services incorporate micro blogging services, resort websites and online coupon services. ski resorts segment customers into two major categories i.e. millennial or generation y (less than or equal to 35) and non-millennial (greater than 35) and use promoting and advertising for them. authors in [13] analyzed data mining based framework to identify shopping patterns. understanding the key reasons why buyers enter their preferred stores plays an important role in achieving competitive advantage and retaining their market shares. today, business analytics are helpful to explore a huge amount of data in order to gain customers insights and improve customer relationships. authors propose a data mining based framework which could be used to discover patterns in customers’ visits to a supermarket and identify their shopping missions. authors in [14] analyzed customer loyalty in crm using clustering and classification techniques. the study used a k-means algorithm for clustering purpose. this study extends the traditional rfm model by adding a weight (w) parameter thus renaming it as wrfm. the study classifies customer product loyalty for b2b concept joining wrfm with k-means and applied k-optimum for better cluster selection. authors in [15] calculated clv for customer segmentation and applied it in a health and beauty company. generally, companies are concentrating on customer profitability and loyalty to improve their market share. marketing analysis method based on rfm is used for customer segmentation. secondly, a count item parameter is added in the rfm model. authors in [16] proposed two methods: cluster analysis for data mining and apriori algorithm for association rules mining. tourism plays a major role in regional and national economic development. many companies in the world are designing product for tourism industry and this is a growing source of domestic and foreign earnings. their proposed model is implemented in phoenix tours international company in taiwan. rules, knowledge and knowledge patterns are extracted from the dataset and they proposed solutions and suggestions for a tourism company for new product development and crm. authors in [17] analyzed lifestyle segmentation of customers using data mining technique. authors in [18] developed a crm approach using association rules and sequential patterns for a small size online shopping mall. authors in [19] evaluated a data mining based crm technique for enhancing profitability in terms of rfm and drew a critical review of significance of the proposed techniques. in corporate sector, particularly banking sector, the retention of customer is an important factor. we propose a classification based model to assess the customer behavior in banking sector with respect to rfm. three classification models like decision tree, anns and k-nn are studied and evaluated. in any case, certain concepts are to be further defined and elaborated: a. customer life time value (clv) or customer loyalty customer happiness and attraction are the core objectives of any company. therefore, customer loyalty or customer lifetime value (clv) is calculated in terms of recency, frequency and monetary variables (rfm). b. rfm analysis customer relationship management (crm) system is used to manage company relations with the existing and prospect customers. rfm stands for recency, frequency and monetary. this technique is commonly used in database marketing and direct marketing to identify customer behavior or purchasing behavior. we represent customer behavior in three variables. • recency: how recently did the customer purchase? this is the interval between the time of most recent and current customer purchase. • frequency: how frequently do they purchase? this is the number of transactions in a specific period. • monetary (value): how much do they spend? this is the amount of money that customer spent during a specific period. c. decision tress decision tree is a data mining and classification technique. this technique is mostly used for prediction and classification. a tree consists of paths, branches and nodes. a collection of branches is called path and represents the attribute value. class value is represented by leaves. each path in decision tree represents a rule which is used for classification or prediction. decision tree divides data into subsets or nodes. root node is the top node. root node represents the complete dataset. tree pruning is preformed when tree is completely built. pruning is started from the leaf node. d. weka tool it is a machine learning toolkit extensively used for education, projects and research. it is an open source tool and developed by waikato university, new zealand. all the major machine learning algorithms are implemented in weka. data mining tasks like classification, clustering, association rules, data preparation or data preprocessing etc. can be performed using this tool. e. ann (artificial neural network) ann is a data mining classification technique and it is used as a classifier. this structure consists of layered approach. collection of neurons is called a layer. we can define multiple engineering, technology & applied science research vol. 8, no. 3, 2018, 2949-2953 2951 www.etasr.com rahman and khan: a classification based model to assess customer behavior in banking sector or hidden layers in the ann structure. computation is performed in the hidden layer. f. k-nearest neighbors (k-nn) k-nn is a very simple data mining technique and is used for classification purposes. here the symbol "k" is a static value and mostly it takes an odd value like 3, 5 and 7. euclidean distance formula is used for measuring distances between the two entities and serves as a similarity index. ii. proposed classification model in the proposed model, three classifiers are employed. the purpose of using three classifiers is to determine which of them performs better for banking sector related datasets. the scheme of the proposed model is shown in figure 1. fig. 1. proposed classification model. a. dataset our model starts with acquiring the dataset which has been made available in the form of a csv (comma separated values) file and is later on stored in an sql table. the dataset is related to the direct marketing campaigns of a portuguese banking institution between may 2008 and november 2010. the dataset details are: name: bank-full.csv, number of instances: 45,211, number of attributes per instance: 16 (plus one attribute indicating class label). b. feature extraction we used the bank marketing dataset available at uci machine learning repository which consists of 45,211 instances and 17 attributes. there are 16 input variables and one output variable. the dataset attributes are: age, job, marital status, education, default (for credit information), balance, loan (housing), loan (personal), contact, day, month, duration, campaign, p-days, previous, p-outcome and class label. we analyzed data and selected 8 input attributes that provide sufficient information for classification. for preprocessing and classifier evaluation, we created mapping code based on heuristics and details are provided in table i. table i. selected attributes for classification attribute mapping code job pca, knn & dt ann blue-collar 1 0100 management 2 0101 technician 3 0110 admin. 4 0111 services 5 1000 retired 6 1001 self-employed 7 1010 entrepreneur 8 1011 unemployed 9 1100 housemaid 10 1101 student 11 1110 unknown 12 1111 attribute mapping code marital status pca, knn & dt ann married 1 01 single 2 10 divorced 3 11 attribute mapping code education pca, knn & dt ann secondary 1 00 tertiary 2 01 primary 3 10 unknown 4 11 attributes values mapping code pca, knn, dt & ann credit yes/no 1/0 housing loan yes/no 1/0 personal loan yes/no 1/0 term deposit yes/no 1/0 c. pca (based on dataset conversion) the selected attributes are then passed to pca (principal component analysis) for dimensionality reduction as we have a total of 16 attributes which are surely high in dimensions to classify accurately. we employed pca, a feature available in the weka tool, to obtain the pertinent set of attributes which are most suitable for classification purposes. we achieved better accuracy (99.61%) than the contemporary studies as shown in table ii. also, we found from the experimental results that k-nn outperformed the other two classifiers dt and ann used in our study on the basis of the accuracy measure. a comparison of true positive rates and false positive rates is provided in table iii. d. feature selection the set of attributes returned by the pca in the form of eigenvalue constitute our “feature vector” to be used for training the classifier. engineering, technology & applied science research vol. 8, no. 3, 2018, 2949-2953 2952 www.etasr.com rahman and khan: a classification based model to assess customer behavior in banking sector table ii. results comparison ref classifier total sensitivity specificity accuracy [2] ann 4521 40.88 94.85 88.63 [7] ann 31589 65.67 93.28 90.92 [18] k-nn 18084 93.87 37.87 87.33 [7] dt 31589 76.75 94.92 93.23 [18] dt 4521 64.68 97.78 93.96 o ur m od el k-nn 31648 100.00 93.24 99.61 k-nn (k=3) 31648 99.60 13.68 94.74 k-nn (k=5) 31648 99.90 2.79 94.40 k-nn (k=7) 31648 99.99 0.56 94.36 dt 31648 0.00 100.00 94.34 ann 31648 0.00 100.00 94.34 sensitivity, specificity and accuracy are % percentages table iii. true positive and false positive rates ref classifier true positive rate false positive rate roc area [2] ann 0.410 0.052 0.847 o ur m od el k-nn 0.996 0.064 1 k-nn (k=3) 0.947 0.815 0.952 k-nn (k=5) 0.944 0.917 0.915 k-nn (k=7) 0.944 0.938 0.885 dt 0.943 0.943 0.5 ann 0.943 0.943 0.567 fig. 2. true positive and false positive rates. e. preprocessing the feature vector obtained in the previous step is then preprocessed to check if any noise (missing value, duplication values, and typos) are checked in the dataset. in addition, another important activity performed in the preprocessing is the encoding of the dataset in order to make it suitable for feeding the classifier for training. f. classifier training (learning) we used three data mining classifiers: dt, k-nn and ann. we applied the weka tool for preprocessing and data classification. firstly, we applied unsupervised preprocessing filter pca in weka on the dataset for attributes selection. for k-nn classifier, (lazy. ibk) algorithm is used to trained our model using different values of k such as k=1, k=3, k=5 and k=7. for the ann classifier, we applied the multilayer perceptron algorithm. for the dt classifier, we trained the model by using the j48 algorithm. the dataset is divided between 70:30 ratios as training data and test data. the weka tool is used for training and testing (learning) model. learning model accuracy is checked through mse (mean squared error). if desired data accuracy is met then the trained model will be saved, otherwise the preprocessing step will be performed again. test data is passed to the learned model to evaluate model accuracy. classifiers’ accuracy is measured through false positive and false negative values and is helpful in the model prediction. iii. experimentation we used three classifiers k-nn, dt and ann. we applied all classifiers on a bank marketing dataset that has been obtained from uci website and weka tool was used for model accuracy and prediction. results are compared based on correctly and incorrectly classified instances. sensitivity, specificity and accuracy have been calculated for model evaluation. • sensitivity or true positive rate (tpr) is calculated on the basis of the following formula: tpr = tp/p = tp/tp+fn (1) • specificity (spc) or true negative rate (tnr) is calculated on the basis of the following formula: spc = tn/n = tn/fp+tn (2) • accuracy (acc) is calculated on the basis of the following formula: acc = tp + tn/p+n (3) • precision or positive predictive value (ppv) is calculated on the basis of the following formula: ppv = tp/tp+fp (4) a. k-nn we performed multiple experiments using different values of “k” like 1,3,5,7 and their results are shown in table iv. b. decision tree (dt) we run decision tree on the training dataset and predicted the test dataset result. the comparison of results shows that knn performs better than dt. c. ann we performed ann experiments on the same dataset (training dataset and test dataset) and found that knn performs better than ann. table iv. k-nn results value of k tp rate fp rate precision roc area 1 0.996 0.064 0.996 1.000 3 0.947 0.815 0.935 0.952 5 0.944 0.917 0.927 0.915 7 0.944 0.938 0.931 0.885 table v. dt results tp rate fp rate precision roc area 0.943 0.943 0.890 0.5 engineering, technology & applied science research vol. 8, no. 3, 2018, 2949-2953 2953 www.etasr.com rahman and khan: a classification based model to assess customer behavior in banking sector table vi. ann results tp rate fp rate precision roc area 0.943 0.943 0.890 0.567 iv. conclusion and future work a model used to identify customer behavior in the banking sector using k-nn, dt and ann is proposed in this paper. multiple experiments are performed on bank marketing datasets in order to evaluate the model. model specificity, sensitivity and accuracy are recorded. it is concluded that ann outperforms dt and k-nn. references [1] t. f. bahari, m. s. elayidom, “an efficient crm-data mining framework for the prediction of customer behaviour”, procedia computer science, vol. 46, pp. 725-731, 2015 [2] a. shrivastava, b. kumari, “implementation of classifiers and their performance evaluation”, international journal of engineering research online, vol. 3, no. 2, pp. 71-78, 2015 [3] n. khan, f. khan, “fuzzy based decision making for promotional marketing campaigns”, international journal of fuzzy logic systems, vol. 3, no. 1, pp. 64-77, 2013 [4] h. a. elsalamony, “bank direct 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patterns”, expert systems with applications, vol. 39, no. 9, pp. 7736-7742, 2012 [19] a. rahman, m. n. a. khan,”an assessment of data mining based crm techniques for enhancing profitability”, international journal of education and management engineering, vol. 7, no. 2, pp.30-40, 2017 microsoft word 3-2278_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3508-3511 3508 www.etasr.com ahmed et al.: common factors of cost escalation in construction industry of pakistan common factors of cost escalation in construction industry of pakistan salman ahmed department of civil engineering, quaid-e-awam university of engineering, sciences & technology, nawabshah, pakistan engr.salamahmed@gmail.com aftab hameed memon department of civil engineering, quaid-e-awam university of engineering, sciences & technology, nawabshah, pakistan aftabm78@gmail.com noor ahmed memon department of civil engineering, quaid-e-awam university of engineering, sciences & technology, nawabshah, pakistan nahmedmemon@gmail.com abdul nasir laghari department of chemical engineering, quaid-e-awam university of engineering, sciences & technology, nawabshah, pakistan laghari@hotmail.com muhammad akram akhund department of civil engineering, mehran university of engineering and technology, jamshoro, pakistan akhund42@gmail.com hafiz usama imad department of civil engineering, mehran university of engineering and technology, jamshoro, pakistan usamaimad@yahoo.com abstract—cost escalation is a ubiquitous problem, especially in government organizations. though bigger projects encompass escalation cost, in smaller projects, it is generally ignored. several internal and external factors are responsible for the undesirably increased cost of a project. among them some are tangible, and some are intangible. the scope of this study is to highlight most common remittable and non-remittable factors responsible for cost escalations. thirty most common factors responsible were listed. a survey was done in order to have the stakeholder’s opinion on identifying the most common factors. out of 102 generally identified escalating factors, 30 factors were shortlisted based on literature and initial study. participants responded on a 1 to 5 likert’s scale. out of 200 distributed questionnaires, 52 reliable set of questionnaires were selected for data analysis. clients, consultants, and constructors were selected from different projects like roads, structure, public amenities etc. minimum threshold to participate in the survey was that a respondent must had at least a diploma or bachelor’s degree in the field of civil engineering. results highlighted that financial problems, slow payments, and inflation are the top-ranked identified factors responsible for cost escalation in the construction industry of pakistan. the weighted average of all factors ranges between 0.355 and 0.688, having 0.668, 0.629 and 0.625 for the top three factors. keywords-cost escalation; stakeholders; construction industry; pakistan i. introduction cost escalation is referred as the change in the price of a given commodity or services for a given period of time in a given economy. in pakistan, cost escalation is a ubiquitous problem, especially in government organizations. cost escalation is the adjustment or settlement of unit price of contract component which includes labor, construction materials and equipment to contract the value during bid and is almost inevitable in large construction projects [1]. cost escalation often offsets the industry’s contribution to the economy. escalation and contingency expenses include unnecessary costs caused by the underestimation of the actual cost that exceeds the budget amount [2]. cost escalation problem has various causes, therefore it is necessary to study the common factors responsible for cost escalation in construction industry of pakistan. results of a research regarding zambian road construction projects indicate that bad weather and flooding were major main reasons for cost increase. another major reason was the payment delays from client to the contractors. researchers suggest that there is no simple solution to control the cost increase and schedule delay. however, it can be controlled through good project management [3]. cost escalation reasons occurring in projects of nigeria's construction industry are unstable material prices and changes [4]. in pakistani industry the main reason for rising costs is customer behavior [5]. another survey of pakistani construction works among key stakeholders indicated escalation of material prices and discontinuity of funds. researchers suggested that there is immense need of proper planning at the earlier stage of estimation. proper provision for contingencies should be kept to cover the escalation of material prices [6]. the office of government accountability indicated that 77% of road projects in the united states failed in achieving completion within estimated cost. on the other hand, authors in [7] concluded that 9 out of every 10 construction projects experienced cost escalation. in jordan, road projects were reported as overran due to terrain and weather conditions [8]. analysis of cost issues in construction projects of india showed that changes in engineering, technology & applied science research vol. 8, no. 6, 2018, 3508-3511 3509 www.etasr.com ahmed et al.: common factors of cost escalation in construction industry of pakistan designs by the clients, fluctuations in material prices, delay in payments, changes in material types and specifications during construction, and reworks caused by errors during construction are considered seriously [9]. during the construction phase of vietnam highway projects, land acquisition, capital and contract constraint, infrastructure construction investment management system, survey and design scheme, construction unit fiscal and management ability as threats for project cost were indicated in [10]. poor planning, labor and material shortfall are considered as key reasons that affect project cost in india [11] while poor site management, lack of coordination, contractor’s lack of experience and fraudulent practices were reported as major issues in nigerian construction projects [12]. road construction projects of palestine showed fluctuation in prices, incomplete drawings, short time to prepare cost estimation, contract size and lack of experience as key factors affecting project cost [13]. similarly, a survey investigation on road works of saudi arabia revealed administrative problems, delay payments, delay in decision making and poor communications between parties as most affecting factors [14]. authors in [15] highlighted as major reason of cost escalation the inadequate project preparation. after a comprehensive review of the above mentioned studies, 30 top common factors were identified and considered for further investigation with respect to local construction industry. the factors are listed in table i. table i. top cost escalation factors factors references 1 fluctuation in material prices [4, 8-10, 13, 17-18] 2 weather conditions [2-4, 8, 14] 3 frequent design changes [8-10, 12, 14] 4 cash flow and financial difficulties faced by contractors [4, 10, 11, 17] 5 slow payments of completed works [9-11, 14] 6 lack of coordination on site [2, 4, 12, 14, 17] 7 poor site and project management [2, 12, 14, 17] 8 inflation [2, 3, 7, 9, 14] 9 poor contract management [2, 7, 10, 11] 10 labour productivity [8, 10, 17] 11 local government pressures [2, 3, 8, 10] 12 poor technical performance [2, 8, 10, 11] 13 incorrect planning and scheduling [12, 16, 18] 14 shortage of materials [9, 15, 17] 15 low speed of decision making [4, 8, 11, 14] 16 government policies and political instability [4, 8,12,14] 17 increasing of loan interest rates [10, 12, 14, 16] 18 project location [2, 10, 19] 19 insufficient/incomplete drawings [4, 13, 19] 20 ground conditions [8, 12, 19] 21 inaccurate estimate [2, 4, 17, 19] 22 unrealistic schedule [4, 12, 19] 23 number of change/extra work orders [2, 6, 9, 17, 19] 24 timeliness of subcontractors and suppliers [2, 7, 9] 25 delay in land acquisition [2, 6, 10, 18] 26 inadequate contractor experience [3, 5, 12, 13] 27 strikes [3, 7, 11, 18] 28 absence of construction cost data [4, 8, 12] 29 unavailability of competent staff [6, 17, 18] 30 reworks due to the errors [2, 8, 9, 11] ii. aim of study the main aim of this research is to find the common factors of cost escalation in construction projects of pakistan. the main objectives set under this scope were to explore cost escalation factors in construction projects throughout the world and to identify the common factors influencing cost escalation in construction projects of pakistan. iii. research methodology this study is based on a questionnaire survey, in which identified factors are presented to respondents from different contractor organizations working in pakistan’s construction industry. the respondents are requested to rate each specific factor on a five point likert scale. to keep the reliability of the collected data, only respondents having minimum diploma or bachelor’s degree in the field of civil engineering are selected. statistical analysis of the collected data is done by statistical software package (spss) version 20 and microsoft excel. the questionnaire was designed according to the 30 factors of table i from the total 102 cost escalation factors identified from the mentioned literature review and with the help of a pilot study. the questionnaire is divided into two parts, the first one focuses the respondent’s demography, while the second one identified the probability of occurrence (poc) of factors causing cost escalation expressed in likert scale from 1 to 5, with 1 meaning not occurrence and 5 meaning that the considered factor is very often occurring. iv. data collection and analysis in this quantitative and qualitative research the designed questionnaire was distributed among 200 construction practitioners involved in construction industry. fifty two fully filled and valid questionnaires were received. reliability test was conducted using cronbach’s alpha, and its value was found to be 0.88, which indicates well reliable data [20]. all successfully validated and reliable questionnaires from construction practitioners were analyzed by using weighted average (wa). figure 1 illustrates the ratio of respondents involved in construction industry. the threshold value to rank the factor as common factor is 0.35 [3]. figure 2, presents the ratio of data collection on the nature of project. client 36% consultant 10% constructor 54% fig. 1. ratio of respondents from different organizations the respondents were asked to rank the probability of occurrence level of each cost escalation factor in construction engineering, technology & applied science research vol. 8, no. 6, 2018, 3508-3511 3510 www.etasr.com ahmed et al.: common factors of cost escalation in construction industry of pakistan industry projects of pakistan. the responses were analyzed with spss v 20 for determining frequency level. weighted average (wa) was calculated with microsoft excel. the results regarding the probability of occurrence for all 30 factors are presented in table ii. fig. 2. nature of construction projects table ii. overall factor occurrence level and ranking factor frequency wa r a n k 1 2 3 4 5 t o ta l cash flow and financial difficulties 1 7 23 12 7 50 0.668 1 slow payments 5 9 15 14 6 49 0.629 2 inflation 1 17 15 5 10 48 0.625 3 fluctuation in material prices 1 16 15 14 5 51 0.624 4 number of change/extra work orders 5 22 12 8 5 52 0.546 5 frequent design changes 3 26 15 3 5 52 0.527 6 shortage of materials 3 29 7 9 1 49 0.502 7 incorrect planning and scheduling 8 23 11 7 3 52 0.500 8 poor contract management 7 25 10 9 1 52 0.492 9 government policies and political instability 7 27 10 4 4 52 0.488 10 lack of decision making timely 13 14 15 8 1 51 0.482 11 weather conditions 5 25 14 4 1 49 0.482 11 poor site and project management 7 28 9 3 4 51 0.478 12 delay in land acquisition 8 25 9 6 2 50 0.476 13 timeliness of sub-contractors and suppliers 13 17 15 3 3 51 0.467 14 influence of local government 10 24 9 2 4 49 0.461 15 insufficient/incomplete drawings 13 20 10 5 2 50 0.452 16 inaccurate estimate 9 27 10 4 1 51 0.447 17 unrealistic schedule 17 17 8 6 3 51 0.447 17 lack of coordination on site 8 32 8 1 3 52 0.442 18 rework due to errors 16 16 16 4 0 52 0.431 19 inadequate contractor experience 20 15 10 5 2 52 0.423 20 unavailability of competent staff 17 19 13 1 2 52 0.415 21 strikes 23 14 8 3 4 52 0.412 22 ground conditions 14 24 8 4 0 50 0.408 23 labour productivity 20 17 9 5 1 52 0.408 23 poor technical skills 19 18 7 5 1 50 0.404 24 absence of contract cost data 18 23 4 2 2 49 0.384 25 project location 19 21 8 1 1 50 0.376 26 increasing of loan interest rates 19 23 6 1 0 49 0.355 27 1=not occurring, 2=slightly, 3=moderately, 4=often, 5=very often from table ii we can define the top factors of cost escalation in construction projects in pakistan. results indicate that cash flow and financial difficulties is the most commonly occurring factor in the construction projects of pakistan. the factor slow payments is ranked second, inflation is third, fluctuation in material prices is ranked fourth, and the number of change/extra work orders is placed fifth. these results are in accordance with [16]. finance ability is the key driving force for each project, so normally cash flow and financial difficulties are identified as the top cost escalation factor. it is necessary to have a smooth transition and money flow among clients, consultants and constructors which are the prime stakeholders of any construction project. slow payment flow is an important cause of cost escalation in the construction projects of any country. cost inflation of material, labor and equipment is one of the most uncertain and uncontrolled factors, causing delay and cost escalation in the project. it is highlighted as third most common factor of cost escalation by this study. this factor of cost escalation is common in developing countries. v. conclusion pakistan construction industry is vulnerable to several threats. two of the most important are cost escalation and time overrun. through a review of previous research works, carried out globally, in cost escalation area of study, a total of 30 factors were considered. these factors were used in a survey form to collect the perception of the respondents regarding factors of cost escalation in construction projects of pakistan. data analysis revealed that cash flow and financial difficulties, slow payments, inflation, fluctuation in material prices, and number of change/extra work orders were reported as the most common occurring cost escalation factors in a construction project. vi. recommendations for overcoming the issues mentioned above, all stakeholders have to play their role for removing barriers, specially clients, consultants and contractors, who are mostly directly or indirectly involved in causing escalations. following are some recommendations that should be thought upon in mitigating and minimizing cost escalations and time overrun. • clients should ensure adequate funds, land possession, feasibility study, proper designing, accurate estimation, uninterrupted allocation of requisite budget and timely decisions before or during execution. • clients play the most important role in reducing the impact of financial problems. • non-availability of construction materials issue can be avoided by a pre-planned purchase strategy. • the project needs to be completed on time and if delay is caused by slow work progress by the contractor, financial damages may be imposed. references [1] y. s. w. broto, t. j. w. adi, e. suryani, j. w. soetjipto, “project cost escalation prediction models based on system dynamic approach”, third international conference on civil engineering research, surabaya, indonesia, august 1-2, 2017 [2] m. muya, c. kaliba, b. sichombo, w. shakantu, “cost escalation, schedule overruns and quality shortfalls on construction projects: the engineering, technology & applied science research vol. 8, no. 6, 2018, 3508-3511 3511 www.etasr.com ahmed et al.: common factors of cost escalation in construction industry of pakistan case of zambia”, international journal of construction management, vol. 13, no. 1, pp. 53-68, 2013 [3] c. kaliba, m. muya, k. mumba, “cost escalation and schedule delays in road construction projects in zambia”, international journal of project management, vol. 27, no. 5, pp. 522-531, 2009 [4] n. z. muhammad, a. keyvanfar, m. z. a. majid, a. shafaghat, a. m. magana, s. balubaid, “assessment of cost escalation factors for building and civil engineering projects in nigerian construction industry: a multiple regression approach”, jurnal teknologi, vol. 74, no. 4, pp. 85-91, 2015 [5] m. abas, s. b. khattak, r. akhtar, i. ahmad, m. ullah, i. u. haq, “identification of factors affecting cost performance of construction projects”, technical journal, university of engineering and technology (uet) taxila pakistan, vol. 21, no. 1, pp. 72-78, 2016 [6] n. ejaz, i. ali, m. f. tahir, “assesment of delays and cost overruns during construction projects in pakistan”, available at: http://dl.lib.mrt.ac.lk/handle/123/9431, 2013 [7] b. flyvbjerg, m. k. s. holm, s. l. buhl, “what causes cost overrun in transport infrastructure projects?”, transport reviews, vol. 24, no. 1, pp. 3-18, 2004 [8] n. al-hazim, z. a. salem, “delay and cost overrun in road construction projects in jordan”, international journal of engineering and technology, vol. 4, no. 2, pp. 288-293, 2015 [9] p. jadhav, d. desai, a. gupta, “analysis of construction cost overrun causes by contractor’s view”, imperial journal of interdisciplinary research, vol. 2, no. 8, pp. 908-910, 2016 [10] h. a. vu, j. wang, l. min, s. h. mai, “research on cost overrun risk of construction phase of vietnam highway international contracting project”, scientific research publishing, vol. 8, pp. 86-98, 2016 [11] d. bhatia, e. m. r. apte, “schedule overrun and cost overrun in the construction of private residential construction project: case study of pune india”, international journal of technical research and applications, vol. 4, no. 2, pp. 174-177, 2016 [12] a. haruna, s. u. kunya, m. mohammad, “factors affecting the contractor’s cost overrun of building project in kano state, nigeria”, journal of multidisciplinary engineering science and technology, vol. 3, no. 1, pp. 3648-3652, 2016 [13] i. mahamid, a. bruland, “cost overrun causes in road construction projects: consultants perspective”, 2nd international conference on construction and project management, singapore, september 16-18, 2011 [14] a. alhomidan, “factors affecting cost overrun in road construction projects in saudi arabia”, international journal of civil and environmental engineering, vol. 13, no. 3, pp. 1-4, 2013 [15] a. ebrahim, a. y. akal, “modeling schedule overrun and cost escalation percentages of highway using fuzzy approach”, engineering, construction and architectural management, vol. 24, no. 5, pp. 809-827, 2017 [16] m. a. akhund, t. h. ali, n. a. memon, s. h. khahro, “causal attributes of cost overrun in construction projects of pakistan”, international journal of civil engineering and technology, vol. 8, no. 6, pp. 477-483, 2017 [17] d. s. tejale, s. d. khandekar, j. r. patil, “analysis of construction project cost overrun by statistical method”, international journal of advanced research in computer science and management studies, vol. 3, no. 5, pp. 349-355, 2015 [18] s. durdyev, s. ismail, n. a. bakar, “factors causing cost overruns in construction of residential projects: case study of turkey”, international journal of science and management, vol. 1, no. 1, pp. 3-12, 2012 [19] k. knight, a. r. fayek, “a preliminary study of the factors affecting the cost escalation of construction projects”, canadian journal of civil engineering, vol. 27, no. 1, pp. 73-83, 2000 [20] m. a. akhund, a. r. khoso, a. a. pathan, h. u. imad, f. siddiqui, “risk attributes, influencing the time and cost overrun in joint venture construction projects of pakistan”, engineering, technology & applied science research, vol. 8, no. 4, pp. 3260-3264, 2018 microsoft word etasr_v11_n1_pp6620-6625 engineering, technology & applied science research vol. 11, no. 1, 2021, 6620-6625 6620 www.etasr.com pathan et al.: virtual impedance-based decentralized power sharing control of an islanded ac microgrid virtual impedance-based decentralized power sharing control of an islanded ac microgrid erum pathan department of electrical power engineering universiti tun hussein onn malaysia johor, malaysia erumasad79@gmail.com mubashir hayat khan department of electrical power engineering university tun hussein onn malaysia johor, malaysia mubashir.uthm@gmail.com haider arshad department of electrical power engineering university tun hussein onn malaysia johor, malaysia haiderarshadkhan@gmail.com muhammad kashif aslam electrical engineering department comsats university islamabad, pakistan kashif_aslam11@yahoo.com dawar jahangir electrical engineering department nuces university islamabad, pakistan jahangir@gmail.com muhammad asad substation automation engineer ng csd-c, saudi electricity company riyadh, saudi arabia csd_sec@yahoo.com muhammad imran rabani department of electrical contracting & maintenance xervon, saudi arabia imran.shafaat@xervon-me.com abstract-the future of power systems depends on the microgrid (mg) which includes distribution generators utilizing renewable energy resources (rers) and storage facilities. decentralized control techniques are more reliable and stable in comparison with centralized controlled techniques. in this paper, a decentralized control strategy is presented for an islanded ac mg system. the control strategy includes improved droop control and virtual impedance. control strategy with pi controllers to control the voltage and current is implemented to two voltage source inverter (vsi) distribution generation units connected in parallel through a point of common coupling (pcc). circulating current and power-sharing deviations caused by the mismatched line impedance were taken into account. the proposed control scheme was tested in matlab/simulink. power-sharing accuracy and circulating current suppression were obtained by implementing the proposed virtual impedancebased decentralized control strategy. keywords-pi controller; decentralized control; droop control; virtual impedance i. introduction globally, power systems are often overburdened due to the excessive electricity usage. the inclusion of renewable energy resources (rers) in modern power systems is one of the most popular solutions to cope up with the electricity demand. more and more rers are being added to the power systems which may cause many critical issues regarding control and management [1, 2]. microgrids (mgs) may face different challenges with different operating modes. in the islanded mode, power sharing according to the capacity of the inverterbased dg units connected in parallel, and combined with loads to form a complete system, is not accurate, whereas in the connected mode, the case is not same [3]. voltage source inverters (vsis) are solely responsible for voltage and frequency control in islanded mgs. different kinds of issues may occur in isolated mg, for example voltage and frequency errors, line impedance mismatch and the consuquent production of circulating current [4, 5]. when many dg units are operating in parallel in the same system, the overall impact of circulating currents could be very high and could damage the entire system. unlike the traditional power systems, in which the circulating currents do not affect the system due to the large synchronous generators, in mgs even the presence of the smaller line impedance is considered to be a serious issue that needs to be handled carefully [6]. in the literature, virtual impedance is implemented, most of the times, in order to get corresponding author: erum pathan engineering, technology & applied science research vol. 11, no. 1, 2021, 6620-6625 6621 www.etasr.com pathan et al.: virtual impedance-based decentralized power sharing control of an islanded ac microgrid rid of circulating currents. droop control which has the ability to operate without a communication link has been implemented with virtual impedance [7, 8] to achieve power sharing accuracy. virtual impedance-based techniques need to have line impedance exact values which are very difficult to calculate at every instant. in [11, 12], the dependency of line impedance was eliminated by utilizing a method which can control droop gains. unfortunately, the droop coefficient regulation technique has some serious concerns related to voltage and system stability. a frequency controller with nonlinear matrix inequality was presented to ensure the stability of the system in [9] and the improved droop-based control with autonomous operation for ac-dc mg control was proposed in [10]. modification in droop with complex line impedance has been implemented in [13] for power sharing accuracy but the system stability and reliability was not considered. an adaptive virtual impedance multi-agent consensus control scheme was presented in [14]. the scheme significantly improves power sharing accuracy but with slow system response. however, control techniques related to power sharing control and circulating current suppression have different issues. this paper presents an improved droop-based simple control technique for power sharing and circulating current suppression in ac islanded mgs. the proposed control technique is implemented to two vsi units and their virtual impedance is also considered. proportional integral (pi) controllers control the voltage and current for accurate power sharing between the two vsis connected in parallel at the point of common coupling (pcc). moreover, the circulating currents between the vsis are suppressed in the proposed control scheme. ii. system description this paper presents a virtual impedance-based, voltage source inverter, vsi-based islanded mg power sharing control scheme which is implemented on two dg inverters as shown in figure 1. the system is composed of lcl output filters and distribution lines. it worth mentioning, that the system is designed considering ideal dc voltage sources where storage and losses are not considered. the system has resistive inductive load which is shared by two dg inverters. figure 1 shows the islanded mg with two identical dg inverters connected to the lcl filter, virtual impedance, and distribution lines. both the dg inverters are connected to the pcc and a load is connected directly to the pcc. iii. reactive power analysis and droop control in inverter-based systems, more and more dg units are connected in parallel to increase the capacity of the mg. a single phase of parallel connection of the mg is given in figure 2. input voltage and currents for dg1 and dg2 with their respective power angle δ and impedance angle θ are: vo1<δ1, vo2<δ2, i1<θ1, and i2<θ2 respectively. the active and reactive powers (p and q) for the i th inverter are expressed in (1), (2). pcc load line1 line2 dg1 dg2 fig. 1. islanded mg. 0pccv ∠ 1 1o v δ∠ 1 1 i θ∠ o z o i 2 2 i θ∠ 2 2o v δ∠ 1 1 1 z r x= + 2 2 2 z r x= + fig. 2. two parallel inverters' connection with pcc. ipcc vlixipcc voivir lixir oiv ip δδ sin)cos([22 +− + = (1) [ sin ( cos ) 2 2 voi q r v x v vi i i oi ilipcc pcc r x i li δ δ= − + − + (2) when xv+xl is much greater than r and the angle δ is very small, the above equations can be simplified as: cosv voi ipcc pi x i δ = (3) ( )v v voi oi pcc qi x i − = (4) where x≃xv+xl. p and q are providing the conventional droop basics which are expressed as: * m pi i iω ω= − (5) *v v n qooi i i = − (6) where ω*, v*, and n, m are the nominal frequency, and voltage and droop coefficients respectively. droop control is good for active power sharing accuracy while reactive power sharing is not easily achieved because of the effect of line impedance mismatch. iv. proposed virtual impedance-based control a. inner voltage and current loop for the sake of voltage regulation, a proportional resonant controller is employed. figure 3 shows the voltage and current control loops with the filter. the transfer function for the pi controller is: engineering, technology & applied science research vol. 11, no. 1, 2021, 6620-6625 6622 www.etasr.com pathan et al.: virtual impedance-based decentralized power sharing control of an islanded ac microgrid 2 2 2 2 k sciv g kv pv s sc f ω ω ω = + + + (7) g k pii = (8) where kpv and kpi are related to the controller (pi) gains. the closed loop transfer function with no virtual impedance is given as: * ( ) ( ) ref v g s v z s ic o o= − (9) where g(s) and zo are voltage gain and output impedance respectively. (1 ) ( ) 2 ( ( 1) ) 1 g g sc rv i f d g s s l c s r c g c r g r c g gv vi if f f f f d d f + = + + + + + + (10) ( )((1 ) ( ) 2 ( ( 1) ) 1 sl r g sc r if f f d z so s l c s r c g c r g r c g gv vi if f f f f d d f + + + = + + + + + + (11) ic g pwm g dq v ∗ odq v ldq i ∗ cli g _ +_+ odq i odq v cli g _ + dq v ∗ _+ _ + 1/(ri+lis) zv v*ref gv iref current controller (1+/(rdcfs+1) fig. 3. voltage and current control and impedance loops. a. virtual impedance loop for frequency and voltage magnitude regulation, conventional droop control is commonly recommended, which may be in the form of p-ω or q-v in mg control for medium voltage networks. in medium voltage mgs, the behavior of the lines is predominately inductive. considering the low voltage mgs, the predominant inductive behavior does not exist, so the conventional droop control is not very effective while the mismatch in line impedance makes the control system more complicated. complex virtual impedance is proposed to mitigate line impedance mismatch and power sharing accuracy can be attained. voltage reference is adjusted by utilizing the virtual impedance. * * * ( ) ( ) re v v i z s v i r r slo v o v vf vd = − = − + + (12) from (12), *zo can be written as: * ( ) ( ) ( )( )z s z s g s r r slo o v vvd = + + + (13) the overall block control diagram with the virtual impedance is shown in figure 4. the droop control and the virtual impedance are utilized to overcome mismatch in line impedance and mitigate the circulating current. fig. 4. virtual impedance-based control. the impact of the virtual impedance as per the parameters given in table i can be seen in the diagrams given in figures 56. the output voltage of each unit connected in parallel successfully tracks its respective reference with negligible phase delay. with the proper voltage tracking and voltage controller design considering the complex virtual impedance given in the above equations, proper power sharing can be achieved. table i. system parameters dc voltage 700v line voltage 311v inverter side resistance 100mω grid side inductor 1.5mh inverter side inductor 1.5mh capacitor 25µf line impedance 1 0.125+j0.396ω line impedance 2 0.085+j0.293ω virtual impedance 1 0.049+j0.191ω virtual impedance 2 0.06-j0.083ω virtual impedance 3 0.029+j0.081ω virtual impedance 4 0.029+j0.081ω voltage controller gains kp=1.796 ki=1.21 *10 3 current controller gains kp=0.237 ki=1.62 *10 3 dg1 and dg2 ac mg load power rating pl1 500w, 50var pl2 500w, 50var pl3 3˟ (500w, 50var) v. simulation results the proposed control scheme was tested under in matlab/simulink. the control strategy and the sub model are shown in figure 5(a)-(b). the matlab/simulink model is designed for three phase ideal voltage sources with power and control section. lc filter 1 and lc filter 2 are connected to the vsi 1 and vsi 2 respectively with common loads at the pcc. the utilization of virtual impedance ultimately enhances the power sharing accuracy in the two dg inverter model and suppresses the circulating current. engineering, technology & applied science research vol. 11, no. 1, 2021, 6620-6625 6623 www.etasr.com pathan et al.: virtual impedance-based decentralized power sharing control of an islanded ac microgrid in the proposed control, the predominating inductive output impedance is considered. the simulation results are taken at different time intervals to illustrate the effectiveness of the proposed control technique. three different time intervals were taken into consideration: • from 0 to 1s, the system results are taken without using any virtual impedance loop, only the droop control is considered. • from 1 to 2s, the virtual impedance zv1 is applied. the addition of the virtual impedance compensates the output line impedance. • from 2 to 3s, the virtual impedances zv2, zv3, and zv4 are applied to the system. at the same time interval, an additional load equal to three times the previously connected load is applied to the system to prove the validity of the proposed control system for two parallel connected inverters. the virtual impedances are added in the dg inverters in such a way that zv1 and zv4 are added in dg inverter 1 in order to compensate the output impedance mismatch and zv2 and zv3 are added to dg inverter 2. it can be seen in figure 6 that the proposed control scheme is working properly and tracks the reference currents while enabling the two dg inverter systems to share power accurately. thus, the system voltage quality is maintained. voltage and current waveforms are given in figure 6(a)-(b). the voltage remains the same and accurate even when the virtual impedance loops are added after 1s. moreover, the voltage stays the same when the load is increased (table i). nevertheless, the current waveform is accurate at all the different conditions applied to the mg system. the current waveform is stable even after the addition of the load. (a) (b) fig. 5. simulation (a) model of the parallel inverter and the proposed controller, (b) submodel of the vsc of the proposed controller. in figure 6(c), the mg total active power accuracy is shown. during 0-1s, the sharing is not accurate because there is no virtual impedance. there are some fluctuations and the same is observed just after the 1-2s interval. droop control having p-f, can easily attain active power sharing accuracy. after 2s, the power is increased along with the additional load, but is still accurate as per the load. in figure 6(d) the mg power sharing accuracy starts after 1s because during 0-1s there is no virtual loop. after 1s, the virtual loop is added and sharing is accurate. after 2s, when the triple load is added, mg reactive power and sharing of reactive power are shown in figures 6(e)-(f). before the addition of the virtual impedances the power sharing during 0-1s was not accurate. when virtual impedance was added (after t=2s), the power sharing of both the dg inverters is accurate despite their different output impedances. during the 2-3s time interval, the reactive power sharing remains accurate even after the addition of the triple load. figures 6(g)-(h) show the accuracy of the voltage and frequency stability when there is convention setting. after the virtual impedances were added, the voltage drop was lower than the voltage drop after 2s because of the additional load. the circulating current is shown in figure 6(i). it can be seen clearly that during 0-1s there are significant fluctuations and the circulating current is higher. during the 1-2s time interval and after the addition of the virtual impedances, the circulating current is approximately 0. from t=2s, when the additional load was added, it can be seen that the circulating current is suppressed effectively. engineering, technology & applied science research vol. 11, no. 1, 2021, 6620-6625 6624 www.etasr.com pathan et al.: virtual impedance-based decentralized power sharing control of an islanded ac microgrid (a) (b) (c) (d) (e) (f) (g) (h) (i) fig. 6. virtual impedance-based control technique results: (a) current wave form at load, (b) voltage wave, (c) mg active power, (d) active power sharing, (e) mg reactive power, (f) reactive power sharing, (g) frequency at pcc, (h) voltage at pcc, and (i) circulating current. vi. conclusion in this paper, the virtual impedance loop was used to solve the power sharing issues of an mg without compromising the voltage quality of the system. active and reactive power sharing accuracy can be attained very easily. voltage drops due to the mismatch of output impedances were also minimized in this control scheme. the proposed control scheme is applied to the mg with two parallel connected inverters having different output impedances. the mismatch was covered by introducing the virtual impedance control loop. the system was tested with different load conditions and showed satisfactory results. one of the critical issues of islanded mgs with mismatch in line impedance is the production of circulating currents, something that is also addressed in this paper. the virtual impedance loop is helpful to mitigate the circulating current issues, even after the addition of extra load, the circulating current was effectively suppressed to almost zero. references [1] t. adefarati and r. c. bansal, "reliability, economic and environmental analysis of a microgrid system in the presence of renewable energy resources," applied energy, vol. 236, pp. 1089–1114, feb. 2019, https://doi.org/10.1016/j.apenergy.2018.12.050. 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[14] a. s. alsafran and m. w. daniels, "consensus control for reactive power sharing using an adaptive virtual impedance approach," energies, vol. 13, no. 8, jan. 2020, art. no. 2026, https://doi.org/ 10.3390/en13082026. microsoft word etasr_v13_n3_pp10922-10930 engineering, technology & applied science research vol. 13, no. 3, 2023, 10922-10930 10922 www.etasr.com munshi: randomly-based stepwise multi-level distributed medical image steganography randomly-based stepwise multi-level distributed medical image steganography asmaa munshi college of computer science and engineering, university of jeddah, saudi arabia ammunshi@uj.edu.sa (corresponding author) received: 9 april 2023 | revised: 28 april 2023 | accepted: 29 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5935 abstract steganography deals with concealing sensitive information that can either be communicated across a network or stored in a secured location. the concealment of information is accomplished through the carrier, making data access by an unauthorized person more difficult. there are many stenographic techniques that have been used. unfortunately, the hybrid-multi-level approach was ignored. for this reason, the current research utilized image steganography on a hybrid-multi level involving encryption, data compression, and two-stage high data concealment. the proposed technique can be used to conceal information in medical images without any distortion, allowing flexible and secure transfer capability. after using the trible des algorithm to encrypt the secret text at the beginning of the process, the next step involves embedding the secret encrypted cipher message into the host image while keeping the image intact. the findings indicate that the value of psnr and ncc are satisfactory when compared to the sensitivity of the human eye. as a direct impact, the confidential message is hidden from the adversary. it can be seen that the psnr value is quite high. therefore, this indicates that the image after the stenographic process is relatively similar to the original image. keywords—steganography; multiple-embedding; encryption; multi-level analysis i. introduction image steganography involves the collection of images and the embedding of secret data inside them [1]. security and confidentiality of data transmissions are two of the most important factors for which image steganography is so important [2]. as new technologies emerge and people become increasingly reliant on data communications and the information they hold, the need for greater levels of security and privacy has never been greater [3]. despite the claims of many protocols and applications, attackers are always one step ahead of the security measures. every day, new threats emerge that increase the danger of data and communications being compromised [4]. due to this, the current study feels that it is vital to continue researching the security concerns related with data transmission. image steganography is a part of the field of information security and the art of information concealment. despite other approaches of information security that also play crucial roles, steganography is mostly dominated towards the used of images [5]. cryptosystems have traditionally been thought of as the most effective methods for concealing information. however, they do not hide information entirely. they rather convert information into a format that is unreadable [6]. unfortunately, the use of encryption methods can be broken due to the widespread availability of powerful devices and tools that can break complex algorithms [7], because their concealed format can be seen. as a consequence of this ever-increasing threat landscape, there is a requirement for a method of data protection that is both secure and effective. it is essential to have algorithms based on steganography that not only provide security but also keep data confidential. as part of this research, a steganography tool is provided in order to boost the level of security in data transfer. in recent years, a vast number of various steganographic tools have been proposed to safeguard the transfer of data [8-11]. in most cases, steganographic methods that are suited to the multimedia realm end up gaining a great deal of popularity [8]. from a different point of view, the implementation of invertible image steganography has also demonstrated a significant applicability [9]. jpeg format steganography with content similarity has also demonstrated significant applicability [10]. also, the hybrid algorithm approach to low-level spacebounded image steganography, which aims to enhance payload capacity, has gained a lot of interest [11]. however, the least significant bit (lsb) methodology is a method that is continually being adjusted and improved [12-14]. maintaining consistency with the earlier research is essential to the process of ensuring that the adopted steganographic method is both robust and extremely reliable. the aim of this study is to propose a method of enhancing stenographic security by applying a multi-layer security strategic approach, which involves applying various eventdriven security routines. this tool will boost the security of the secret text message under many different protection levels. the research takes into account the use of the lsb, of an image. steganography is another form of covert communication that engineering, technology & applied science research vol. 13, no. 3, 2023, 10922-10930 10923 www.etasr.com munshi: randomly-based stepwise multi-level distributed medical image steganography can be strengthened by the application of cryptographic methods [15]. many prior studies have examined spatial picture steganography techniques. the lsb method has gained a lot of traction recently. for inserting data into a cover image, the lsb replacement is an ideal, easy execution [13]. depending on the spatial approach, an improved strategy for hiding information in areas of an image with abundant noise was proposed in [16]. the key aspect of this article is the ability to hide information 8 times more effectively than standard lsb, which is achieved through the use of deep neural networks. it is important however, that the image used as a cover for the secret message fit certain parameters, which are established by the results of the network test. it is therefore impossible to use this technique on any image. in addition, the use of networks increases the method's complexity and implementation costs. using the imagenet database, the neural network in [16] was trained and tested on random images and achieved high accuracy. an improved method of concealing information within an image was proposed in [17] and it relies on a spatial approach. using a genuine image, the authors also applied quicker methods for region-based convolutional neural networks by mapping features or elements in order to discover the most appropriate and safest areas to hide the image. the highly undetectable stego algorithm was used as well, which provided greater secrecy and a higher bit count than lsb. authors in [18] came up with an idea for compressing sensitive data, encoding them, and then using the aes algorithm to establish an encryption procedure for them. finally, they were buried within the arabic text in particular characters and places, so that the main text is not affected by their presence. aside from that, the use of protocols that are hidden within the text, audio, graphics, or headers was proposed. authors in [19] hid personal information before it is communicated by utilizing an lsb method. authors in [20] investigated when it would be appropriate to use deep learning in order to make steganography suitable for protecting inference privacy. other studies that were conducted in the past have shed light on a significant number of issues connected to steganography. it is imperative that the number of participants utilizing counting-based secret sharing must be increased as much as possible through the utilization of involved matrices and functional steganography [21]. this is of the utmost importance due to the fact that secure communication can be achieved based on the swift response associated with robust concealment [22]. furthermore, authors in [23] proposed a gan-based spatial picture steganography equipped with a cross-feedback mechanism. enhancing grayscale steganography in order to prevent the disclosure of personally identifiable information [24] is a practice that is quite common. as a consequence, authors in [25] developed a method of chaotic video steganography as a means of concealing a wide variety of covert communications in a variety of contexts. in addition, authors in [26] investigated the robustness of a secure and undetectable image steganography in discrete wavelet transform by employing the logical function of xor and the genetic algorithm. using an image disentanglement autoencoder for steganography without embedding results brings an increased level of security [27]. authors in [28] proposed a dynamic four-step data security model for cloud computing data that was based on steganography and cryptography to protect data from unauthorized access. a method for protected image steganography that makes use of the ballot transform and the genetic algorithm was suggested in [29]. it was recently discovered that dna nano sensing systems are now capable of tunable detection of metal ions and molecular crypto-steganography [30]. ii. research methodology the methodology of this study consists of experimental simulation for embedding, followed by the application of attacks, and ends with a performance evaluation of the proposed technique. the study asserts that people are able to innately seek out and recognize the areas of a medical image that have the most intriguing attributes. the integrity of this area must never be compromised, and it must be preserved in the initial state. however, this does not necessarily mean that the quality of the visual presentation should be upheld while the confidential data are being concealed inside the image. additionally, the mechanism used in the embedding process should permit the operation to be carried out in a batch format. to put it another way, there is the need of a technique that lowers the needed computational complexity while still allowing for the inclusion of multiple photographs at once. a. the steganography process the following primary phases are carried out during the embedding process:  encrypt the message using the triple des algorithm.  select the first cover image to upload.  implement the lsb technique with the first image (embed text in image): this method embeds the text in the image by substituting the lsb of the first cover image with the bits of the message to be hidden.  upload the second cover image.  implement the lsb technique with the second image (embed image in image): this function is implemented by replacing the lsb of the second cover image with the bits of the first cover image that contains the secret text. following the successful execution of the embedding, an extraction process was carried out, consisting of the following steps:  upload the stego image: this function uploads the stego image.  extract the first image: this function decodes and then extracts the first image from the second image.  decrypt the message: this function decrypts the message using the key and was originally stored in the image. b. the embedding technique this study sought to have a batch embedding, while maintaining the computational complexity as low as possible. d. the steps of the procedure are outlined in figure 1. engineering, technology & applied science research vol. 13, no. 3, 2023, 10922-10930 10924 www.etasr.com munshi: randomly-based stepwise multi-level distributed medical image steganography fig. 1. multilevel random embedding algorithm pseudocode. the host image (h), the secret message (s), and the embedding process are the three things that the steganography algorithm takes in as input (o). the stego picture is the produced output. during the embedding process, the secret message is multiplied by the embedding operation that is connected to the encryption and is necessary in order to produce a ciphertext. after this, the randomization process will take place, during which a two-level matrix that will be searching for hidden areas within the lsb will be established using either random bit manipulation or random bit generation. the host picture is going to be looking for the embedding of the confidential information. after determining the appropriate site for the lsb, the embedding process can then begin. the ability to conceal the secret text was put to the test, and the procedures were tested regarding their ability to either decipher the hidden message or corrupt it in some way. the capacity to extract safely secret information from an image and a high level of concealment of that information can only be ensured by selecting a suitable embedding factor. iii. experimental sequence analysis in this paper, the secret message is embedded into the host image to obtain the stego image, thereafter the stego image is evaluated and the performance of the technique is measured. finally, the secret message is extracted from the stego image. the experiment was carried out on a personal computer that featured an intel(r) 1.60 ghz processor, with 4 gb ram and simulation software written in c#, python, and visual studio. during the experimentation process, both subjective vision and objective quantitative analysis were used to evaluate the invisibility and robustness of the algorithm. the experiment uses a cover image with dimensions of 1024×1024 pixels and data in the form of text as the steganography medium for the hidden message. in the first step of this project, the psnr and ncc were utilized. a. performance of the embedding technique after making the stego-image, the subsequent step is to conduct an assessment of the performance of the technique used in order to determine whether or not the stego image was distorted. the peak signal-to-noise ratio (psnr) is a popular metric used to evaluate this performance [31]. stego-images have the capability of retaining both their visual quality and content integrity, only when they can resist any attack that falls under the umbrella of difference distortion techniques. the degree to which the steganographic image is concealed within the information that is intended to remain secret is an essential factor to consider during the evaluation of the effectiveness of the steganography algorithm. the condition of the stego image can be evaluated based on the psnr and the structural similarity values of the original image by normalized cross correlation (ncc). as a result, the psnr is measured by: ���� = 10 ∗ log� ����� � ��� � (1) mse stands for the mean square error between the host image and the stego embedded image, while the maximum pixel value in the host image is denoted by rmax. mse is measured by: ��� = ∑ (�(�, !"�#(�, !!�$∗% �∗ (2) the ncc, which provides a comparison of the original and the stego image on the basis of similarity values is measured by: �&& = ∑ '(�, !∗'((�, !$∗% )∑ '(�, !�∗'($∗% (�, !� (3) b. embedding process embedding is particularly done in order to ensure the security of the secret message. however, it should be made in such a way that the human visual system cannot see the trace of the secret message in the stego image. the steganographic technique has been deployed as a part of this research, and a graphical user interface (gui) has been developed to facilitate the execution of the steganography (see figure 2). the proposed method necessitates that the phases of steganography begin with the process of encryption, during which the confidential text message will be encrypted utilizing the data encryption standard (des) algorithm. there were 3 different experimental analyses conducted with 6 different host images. in the first experiment, the first host image is denoted by (a), and the second host image is denoted by (b). in the second experiment, the first image is denoted by (c), and the second by (d). in the third experiment, the first host image is denoted by (e), and the second by (f). after the encryption, the hidden ciphertext message will be embedded on the first host image using a random pick of its lsb. this will result in the production of the very first stego image. therefore, a linear lsb will be utilized in order to incorporate the current stego picture into the second host image. the deployed gui provides the option of giving a text entry as the secret message which then will be made available to the system, accompanied with a push button that activates the encryption feature. upon the completion of the encryption, a selection option for the host image is made available. the user has to select from a list of sample steganography standard host images. engineering, technology & applied science research vol. 13, no. 3, 2023, 10922-10930 10925 www.etasr.com munshi: randomly-based stepwise multi-level distributed medical image steganography fig. 2. the gui of the deployed steganography process. at this time, the program may commence dual processing, since there will be a choice regarding the uploading of a second host image. one single hidden message can be inserted into each of these host images at the same time. this is the main contribution of the current research to the existing body of knowledge. the first host image, after the embedding of the secret ciphertext in it, can be embedded in a second host image. the next step is the presentation of an option weather to embed the secret message in both host images, or in the first only. after the user's selection, the final stego image will be created and downloaded. iv. results and discussion when the psnr ratio is greater than 37db, the secret information embedded in the cover image is invisible to the human visual system, and when the structural similarity is greater than 0.93, the steganography image is not much different from the cover image [32]. according to this, once the embedding process is complete, the psnr will reveal whether the inserted secret message distorted the original content or not in order to validate the efficacy of the applied method. this will allow the effectiveness of the method to be evaluated. in addition, taking into account the values that are being used as a benchmark, the analysis for this study was carried out using 3 distinct methods. a text-cipher was embedded on each host image separately (text-image) in the first instance, which was the embedding using the random check for the lsb within the host image. this was then followed by embedding the corresponding stego-image to the second host image (imageimage). the psnr and ncc values for the experiment (textimage) are significantly better than the benchmarking values, meaning that there is no difference between the steganographic image and the original cover image, and that the extracted secret image contains all of secret information in its entirety. it should be noted that the psnr of the image (a) is 57.065 db and the ncc value is 0.96511, which is the highest among the psnr values. however, the image (f) has the highest value of ncc (see table i). the next step is the embedding process, which involves using the sequence of the lsb within the host image. this process involves embedding a secret image on each host image (image-image). the total values of the psnr and ncc are significantly higher than the bench-marking values. this indicates that, from the point of view of human vision, there is no difference between the steganographic image and the original cover image, and that the extracted secret image contains all the secret information in its entirety. it is important to note the fact that the psnr of the image (b) is 56.132 db, which is the highest, and its ncc value is 0.98853. however, the image (c) has the highest value of ncc. in this instance, it is clear that the method was executed in an excellently appropriate manner. in the second scenario, the embedding was conducted using the random check for the lsb within the host image. the textcipher was first embedded on the first host image separately (text-image), and then the stego-image that was formed was embedded in the second host image using the operation that was described in figure 1. on the second stego picture, the calculations for determining the psnr and ncc values for this procedure were carried out (text-image-image). after that, a stego picture was used to embed a new host image, and the stego image associated with that host image was likewise included in another stego image (image-image-image). in this instance, all of the psnr and ncc values are either above the benchmark or significantly above it. this indicates that, from the point of view of human vision, there is no difference between the steganographic image and the original cover image, and that the extracted secret image contains all the hidden information in its entirety. it is important to point out engineering, technology & applied science research vol. 13, no. 3, 2023, 10922-10930 10926 www.etasr.com munshi: randomly-based stepwise multi-level distributed medical image steganography that in the experiment, the image with the highest psnr is the (d) image, however, the image with the highest value of ncc is the (e). the psnr of the image with the secret image message is 55.837 db, and its ncc value is 0.98168 (table ii). table i. psnr and nc values for the first experiment text-image image-image image psnr(db) ncc psnr(db) ncc (a) 57.065 0.96511 47.95 0.98566 (b) 55.247 0.96798 56.132 0.98853 (c) 52.407 0.97046 53.292 0.99101 (d) 48.245 0.99251 47.691 0.96447 (e) 56.427 0.99538 50.047 0.96823 (f) 53.587 0.99786 53.178 0.9713 table ii. psnr and nc values for the second experiment text-image-image image-image-image image psnr(db) ncc psnr(db) ncc (a) 50.342 0.97508 48.576 0.98502 (b) 53.473 0.97815 50.932 0.98878 (c) 47.655 0.97881 54.063 0.99185 (d) 55.837 0.98168 47.36 0.97196 (e) 52.997 0.98416 55.542 0.97483 (f) 48.281 0.97817 52.702 0.97731 the third example demonstrates good values between the steganographic image and the original host image. the highest psnr value of 55.542 db is observed in image (e), while its ncc value is 0.97483. when it comes to this instance, it is clear that the strategy used was excellent. the difference between the third scenario and the first two is that the embedding of text and images was done simultaneously for both the first and second host images (text-image-text-image and image-image-image-image), whereas in the first two scenarios, the embedding of text and images was done sequentially. in a similar vein, every single value of the psnr and ncc throughout this operation was superior to the standard setting (see table iii). this indicates that, from the point of human eyesight, there is no discernible difference between the stego image and the original host image. table iii. psnr and nc values for the third experiment text-image-text-image image-image-image-image image psnr(db) ncc psnr(db) ncc (a) 48.576 0.98502 47.95 0.98566 (b) 50.932 0.98878 56.132 0.98853 (c) 54.063 0.99185 53.292 0.99101 (d) 48.871 0.99187 47.36 0.97196 (e) 51.227 0.99563 55.542 0.97483 (f) 54.358 0.9987 52.702 0.97731 the performance is about stable, even while repeatedly performing the experiment while taking into consideration different embedding series. in the scenario where a text message was concealed within an image cover file and then the stego-image was concealed within a different cover image, both experiments produced appropriate results. in this scenario, both psnr (figure 3) and ncc (figure 4) are greater than the threshold. it should be noted that the psnr of the cover image that was utilized in text-image or image-image embedding or mixing of the cover image and the stego-image reached the very high value of almost 58 db in every case. this is a crucial point that needs to be emphasized. the obtained ncc value was nearly 0.99, making it the highest of the 3 possibilities (figure 4). the application of these findings is driven by the wish to acquire knowledge regarding which of the sample images, from (a) to (f), possesses the highest performance value in terms of embedding capacity. even though the experiment considers mainly the embedding process, which involves using the searching sequence within the host image, embedding in general requires that a secret message on each host should be within a trade-off of capacity, robustness, and imperceptibility, due to the fact that the capabilities of the host determine the degree to which the message can be embedded effectively. the obtained total values of the psnr and ncc are significantly higher than the benchmark values, suggesting that there is no difference between the steganographic image and the original cover image, and that the extracted secret image contains the secret information in its entirety, which indicates that the research has achieved an unbreakable level of success. although the first experimental scenario was successful in achieving imperceptibility, the subsequent experiment focused on embedding a text-cipher within the host image. following that, the stego-image will be concealed under another image. on the other hand, an image can be inserted inside another image, and the stego image itself can be embedded inside another image. this circumstance is connected to striking a balance in a specific system between capacity, resilience, and imperceptibility. as a direct result, the experiment to embed images on the host image was carried out, and after that, the produced stego-image was inserted in the second host image making use of the same approach. the findings indicate that there is no difference between the steganographic image and the original cover image. in addition, the findings of the trials suggest that the human eye is unable to differentiate between the steganographic image and the original cover image. during the test, the image with a psnr value of 58 db was found to have the highest contrast (figure 5) and the highest value of ncc was 0.98 (see figure 6) regardless of the specifics of the situation that it is viewed in. given the data that were gathered during the study, in particular those that were associated with this circumstance, it would appear that the investigation has reached a stage where it is no longer appropriate to proceed, given the findings. the most crucial thing to do when comparing the results of the experiment is to search for ways in which they differ from one another. in a typical run of this experiment, all the previous hosts and hidden messages were likewise put to use. the implementation of multiple layers was used in this stage of the process. the performance analysis showed that every possible outcome had satisfactory results (see figures 7 and 8), due to the fact that the technology that is being utilized has resulted in many alternatives in achieving similar levels of imperceptibility. in a similar vein, this research has demonstrated that it is possible to covertly embed a message in any and all available mediums at the same time. all the performed procedures were improvements over the regular routine. there is no discernible difference between the stego image and the original host image, in any tested case. engineering, technology & applied science research vol. 13, no. 3, 2023, 10922-10930 10927 www.etasr.com munshi: randomly-based stepwise multi-level distributed medical image steganography (a) (b) fig. 3. the psnr values for the first scenario. (a) (b) fig. 4. the ncc values for the first scenario. (a) (b) fig. 5. the psnr values for the second scenario. (a) (b) fig. 6. the ncc values for the second scenario. engineering, technology & applied science research vol. 13, no. 3, 2023, 10922-10930 10928 www.etasr.com munshi: randomly-based stepwise multi-level distributed medical image steganography (a) (b) fig. 7. the psnr values for the third scenario. (a) (b) fig. 8. the ncc values for the third scenario. the findings of this study were compared to the findings of other studies in terms of the carried out procedures. according to table iv, the psnr obtained in this study was significantly better than those of the considered past studies. table iv. result comparison study psnr(db) [9] 44.19 [11] 46.4381 [33] 44.6229 [34] 44.6229 this study 60 v. conclusion steganography refers to the act of concealing confidential data in a manner that enables their transmission over a network or storage in a secure location. the concealment of information through the carrier is a common practice, as it enhances the security of the data by rendering it less accessible to unauthorized parties. several methods have been proposed, disregarding the implementation of hybrid-multi-level approaches. the present study employed a hybrid-multi-level approach for achieving high data concealment, in conjunction with image steganography. the experimental models demonstrated that the proposed approach has the ability to conceal data within images. the aforementioned feature enables the provision of transfer options that are both secure and flexible. the process of embedding an encrypted cipher message into a host image was deemed necessary, utilizing the least significant bit (lsb) approach in a sequential manner subsequent to the initial encryption of the message with the triple data encryption standard (des) algorithm. this measure guaranteed the preservation of the cover image's authenticity. peak signal-to-noise ratio (psnr) can be utilized to determine the extent to which the inclusion of a covert message alters the primary data. by employing this approach, one can assess the effectiveness of the strategy. three distinct analytical methodologies were employed to examine the data in this investigation. the findings indicate that the psnr and ncc metrics demonstrate satisfactory results when compared to the sensitivity of the human eye. the psnr value surpassed the benchmark values in every experiment. the results indicate that the image produced following the stenographic process bears a resemblance to the initial image and the contained information is undetectable by the human eye. references [1] s. kaur, s. singh, m. kaur, and h.-n. lee, "a systematic review of computational image steganography approaches," archives of computational methods in engineering, vol. 29, no. 7, pp. 4775–4797, nov. 2022, https://doi.org/10.1007/s11831-022-09749-0. 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[36] m. tarhda, r. e. gouri, and l. hlou, "implementation of an optimized steganography technique over tcp/ip and tests against well-known security equipment," engineering, technology & applied science research, vol. 8, no. 6, pp. 3515–3520, dec. 2018, https://doi.org/10.48084/etasr.2334. engineering, technology & applied science research vol. 13, no. 3, 2023, 10922-10930 10930 www.etasr.com munshi: randomly-based stepwise multi-level distributed medical image steganography [37] t. akhtar, n. g. haider, and s. m. khan, "a comparative study of the application of glowworm swarm optimization algorithm with other nature-inspired algorithms in the network load balancing problem," engineering, technology & applied science research, vol. 12, no. 4, pp. 8777–8784, aug. 2022, https://doi.org/10.48084/etasr.4999. authors profile asmaa munshi received the b.sc. degree in computer science from king abdulaziz university, saudi arabia, in 2004, and the master’s degree (hons.) in internet security and forensic and the ph.d. degree in information security from curtin university, australia, in 2009 and 2014, respectively. she is currently an associate professor with the cybersecurity department, college of computer science and engineering, university of jeddah, saudi arabia. she also holds the position of the vice dean (female section) of the college of computer science and engineering, university of jeddah, is a supervisor of the cybersecurity department (female section) of the college of computer science and engineering, and is the vice dean of the faculty of computing and information technology (female section), khulais branch, university of jeddah. her research interests include computer forensics, information security, and the internet of things. microsoft word 11-3751_s_etasr_v10_n5_pp6209-6213 engineering, technology & applied science research vol. 10, no. 5, 2020, 6209-6213 6209 www.etasr.com ghaly: indirect evaluation of program educational objectives and student outcomes for engineering … indirect evaluation of program educational objectives and student outcomes for engineering programs: a case study sidi m. ahmed ghaly electrical engineering department college of engineering al imam mohammad ibn saud islamic university riyadh, saudi arabia smghaly@imamu.edu.sa abstract—outcome and objective assessment is a method for determining whether students and graduates have learned, have retained, and can apply what they have been taught. assessment plans have to include a statement of educational objectives, measurements of attainment of the objectives, and use of the assessment results for continuous improvement. in this paper, the experience of the electrical engineering program at al imam mohammad ibn saud islamic university is used as an example of how an indirect assessment method is established and implemented. many surveys have been used and contributed to the numerical analysis for the indirect assessment of the program outcomes and achievements. the indirect assessment results indicate that the target levels are achieved for all the seven program outcomes and the three objectives that have been considered. keywords-engineering; education assessment; learning outcomes; educational objectives; accreditation; assessment loop; abet i. introduction the last few years have witnessed a growing recognition of the need for assessment and evaluation of the learning outcome [1-2]. these are directed not only at large-scale, standardized tests but also at classroom assessment practices. at least two factors have contributed to the demands for assessment and evaluation: the changing nature of educational objectives and the relationship between assessment, teaching, and learning. assessment is defined as one or more processes that identify, collect, and prepare the data necessary for evaluation. evaluation is defined as one or more processes for interpreting the data acquired through the assessment processes to determine how well the program objectives are attained. the electrical engineering (ee) department at al imam mohammad ibn saud islamic university (imsiu) has been implementing different assessment and evaluation approaches [3-5] for learning outcomes and program educational objectives (peos), the concept of which is adopted to meet the international and national accreditation requirements. this paper describes an indirect method used to assess and evaluate the achievement of program outcomes and objectives. student outcomes (sos) or program outcomes describe what students are expected to know and be able to do by the time of graduation while peos describe what graduates are expected to know and be able to do after graduation. the ee program is very keen on developing and implementing high quality education. for this reason, it requests periodic input from its constituents [6]. to improve the curriculum and the overall improvement of instructional delivery, review and evaluation of the program outcomes and objectives are conducted in each academic cycle. this principal feedback loop affects curriculum organization and content. also, faculty members provide a collection of feedback forms that are specific to a course or relating to the entire program. the ee department receives feedback through these forms to encourage an unencumbered exchange of ideas and responses to the material presented in class and to the overall curriculum design. this is particularly helpful for students to be able to receive and benefit from current and most up to date content and knowledge. the ee program periodically consults the industry, to ensure that the department’s efforts align well with its needs [7]. the ee program educational objectives serve its constituencies. the program constituencies are any entity or organizations that benefit from the outcomes of the program. the current ee educational objectives require periodic revisions to reflect the needs of the program constituencies in greater depth. the ee department keeps in contact with current and prospective employers of its graduates. such constituents are strongly encouraged to join the industrial affiliates program which provides valuable feedback to the department faculty members for student preparation. when necessary, appropriate actions take place through the advising unit and/or the quality committee. exit survey is very important in program outcomes evaluation. alumni and employer surveys also provide important feedback regarding employment opportunities for students, and the opportunity to assess and evaluate the program educational objectives. although many studies have been published on the direct assessment methods of different engineering programs [8-10], the indirect assessment approach does not receive much attention. in this study, the measurement of sos and peos achievements provides considerable information on the effectiveness of an ee program seeking to meet the accreditation criterion [11]. corresponding author: sidi m. ahmed ghaly engineering, technology & applied science research vol. 10, no. 5, 2020, 6209-6213 6210 www.etasr.com ghaly: indirect evaluation of program educational objectives and student outcomes for engineering … ii. background a. program outecomes or student outcomes the ee program has adopted the new sos for the engineering program as prescribed in accreditation board for engineering and technology (abet) criterion 3 [12]. the abilities that students must demonstrate at the time of graduation are attained through various courses taken by all students during the program, which are: 1. identify, formulate, and solve complex engineering problems by applying principles of engineering, science, and mathematics. 2. apply engineering design to produce solutions that meet specified needs with consideration of public health, safety, and welfare, as well as global, cultural, social, environmental, and economic factors. 3. communicate effectively with a range of audiences. 4. recognize ethical and professional responsibilities in engineering situations and make informed judgments, which must consider the impact of engineering solutions in global, economic, environmental, and societal contexts. 5. function effectively on a team whose members together provide leadership, create a collaborative and inclusive environment, establish goals, plan tasks, and meet objectives 6. develop and conduct appropriate experimentation, analyze and interpret data, and use engineering judgment to draw conclusions. 7. acquire and apply new knowledge as needed, using appropriate learning strategies. b. program educational objectives graduates of the ee program should attain at least one of the following educational objectives after graduation: • peo1: serve competently the needs of industry and academia by demonstrating high-quality knowledge, research, and skills in the area of ee. • peo2: pursue professional development through professional study and self-learning with full gratitude of the importance of professional and ethical responsibility. • peo3: contribute to the welfare of society through the responsible practice of engineering, leadership, and teamwork. c. consistency of the peos with the mission of the institution the following statements summarize the university, college, and department missions: • mission1: high-quality education (university/college/ department). • mission 2: conduct innovative research/leadership in scientific research/ (university/college/department) • mission 3: local and global community service/offer professional services (university/college/department). • mission 4: equip students with the skills to be life-long contributors to their profession (department). table i shows the mapping between the institution’s missions and the peos indicating the consistency of the peos with the mission of the institution. table i. peos mapping to the missions of the institution mission 1 mission 2 mission 3 mission 4 peo 1 x x x peo 2 x x peo 3 x x d. relationship of sos to peos sos support the peos. the first objective (peo1) is supported by most of the sos (1, 2, 5, and 6). the second objective (peo2) is supported by 4, 5, and 7 sos. the third objective (peo3) is supported by sos 4, 5, and 7. table ii summarizes the mapping between the sos and the peos. table ii. sos to peos mapping peos sos 1 2 3 1 x 2 x 3 x 4 x x 5 x x x 6 x 7 x x iii. indirect assesment indirect assessment and evaluation at the ee program were conducted the academic years 2017-18 and 2018-19 (two cycles). the frequency of data collection and review process for the indirect assessment approach of sos and peos are summarized in table iii. table iii. data collection frequency and review process assessment tool frequency of assessment expected level of attainment exit survey every year 70% industrial advisory survey every year 70% alumni survey every three years 70% employer survey every three years 70% faculty survey every year 70% student survey every year 70% the ee program has approved a benchmark level of outcome and objective achievement (two thresholds) for the indirect assessment. these thresholds are an average score of 20% (unsatisfactory) and 70% (satisfactory). for an outcome or objective to be considered achieved, the indirect assessment should reach an average score of at least 70% [13]. this should be considered as evidence illustrating that the level of the student outcome and program objective achievement is satisfactory. engineering, technology & applied science research vol. 10, no. 5, 2020, 6209-6213 6211 www.etasr.com ghaly: indirect evaluation of program educational objectives and student outcomes for engineering … iv. results of the evaluation process in this section, the results and evaluation process are presented. at first the process in cycle 2 is discussed and then a comparison is performed between the results from cycles 1 and 2. to evaluate the results obtained from the surveys, the performance targets were defined to assess the level of attainment. table iii summarizes the tools for the indirect assessment and evaluation of program outcomes and objectives. the surveys listed in table iii, are being used in the assessment process at various stages. these surveys provide feedback on the weaknesses and strengths of the sos and the peos. the exit survey contributes to the measurement of the indirect assessment of student outcomes 1-7 and provides the program with useful information to aid the development of an action plan for continuous improvement. a. so assesment through the exit survey at the end of each semester, the ee program carries out a survey of its graduating students. the exit survey contributes to the measurement of the indirect assessment of student outcomes 1-7 and provides useful information that aids the development of an action plan for the continuous improvement of the program. in this survey, it is useful to ask students to rate the program learning outcomes or sos in order to indicate the extent of their achievement. the total number of respondents for both cycles is 40 students. the survey questions are related to the specific outcomes 1-7 using the same key performance indicators (kpis) that are used in direct assessment [14-16] as seen as example for the outcome 1 in table iv. the data collected from the students' evaluation are stored and analyzed electronically and the results are considered for further evaluation and taking appropriate actions. table iv. typical indirect assessment from so 1 so 1 level kpi attribute question 5 4 3 2 1 1.1 your ability to apply mathematical and scientific principles to formulate models and systems relevant to electrical engineering. 1.2 your ability to solve electrical engineering problems by using the concepts of integral and differential calculus and/or linear algebra. 1.3 your ability to execute calculations correctly 1.4 your ability to translate academic theory into engineering applications. 1.5 your ability to apply analytical, graphical or numerical methods to solve complex problems 1.6 your ability to solve practical engineering problems logically using correct theoretical concepts. 1.7 your ability to formulate alternative solutions to a complex engineering problem. 1.8 your ability to identify the governing concept of a complex engineering problem. the results obtained for the outcome 1 are summarized in figure 1. this figure is shown as an example of the average obtained for each kpi of the outcome 1 from the survey questions on a scale of 5 is very satisfied down to 1 for very dissatisfied and then changed to percentage and shown graphically. figure 2 represents the exit survey results of cycle 2 (fall 2018 and spring 2019) based on all program outcome assessment data (1 through 7). fig. 1. kpis assessment results–outcome 1. fig. 2. indirect assessment results for all program outcomes. the achievement is considered satisfactory if the weighted average is greater than or equal to 70%. as seen, all program outcomes meet the program expectations. b. comparison of assessment results the comparison of the direct assessments' results of the program outcomes (sos 1-7) for both cycles (2017-18 and 2018-19) is depicted numerically in table v and graphically in figure 3, where the satisfactory results for cycles 1 and 2 are shown in blue and red respectively. table v. comparison of the assessments’ results student outcomes (sos) achievements 1 2 3 4 5 6 7 cycle 1 2017-18 84 80 84 75 89 76 87 cycle 2 2018-19 78 84 85 81 85 84 82 it can be observed that the program outcome attainment for both cycles is well above the satisfaction target. however, some attainments in cycle 1 have degraded to some extent as compared to cycle 2. this issue was investigated in the early part of the 2019-2020 fall and the faculty’s opinion was sought to suggest measures for improvement. engineering, technology & applied science research vol. 10, no. 5, 2020, 6209-6213 6212 www.etasr.com ghaly: indirect evaluation of program educational objectives and student outcomes for engineering … fig. 3. comparison of the two cycles of indirect assessment results. c. so and objective assessment from the alumni survey during both cycles, the ee department conducted a survey of alumni to assess their knowledge, skills, and perceptions of relevant aspects of their college experiences in order to evaluate the program objectives. the alumni were asked many questions, including sos and program objective achievement. the presented data are based on a random sample of 13 alumni. again the achievement is considered satisfactory if the weighted average is greater than or equal to 70%. the results are shown in table vi and it can be observed that program outcomes and objectives indicate satisfaction. if a weighted average was less than 70% for an so, it would be discussed in the ee quality committee to analyze the reason(s) behind it. the matter might also be escalated to the department council for remedial measures to be taken. table vi. typical indirect assesment alumni form my education at imsiu has given me the ability to: 5 4 3 2 1 averag e % # attribute question 1 apply disciplinary reasoning, critical thinking, and hands-on skills to analyze, design, and solve engineering problems. 3 5 4 1 0 61 2 consider professional, ethical, and social responsibility of engineering technology practices. 5 5 3 0 0 77 3 communicate effectively. 0 10 2 1 0 77 4 perform effectively, think independently, and work collaboratively in a team environment. 5 6 2 0 0 84 5 participate in professional development, including continuous self-improvement and lifelong learning. 5 6 2 0 0 84 6 peo1 6 5 1 1 1 84 7 peo2 2 8 2 1 0 77 8 peo3 4 6 3 0 0 77 d. so and objective assessment from the employer survey the employer survey is also assessed at intervals of 3 years. a set of randomly selected employers are requested to fill a questionnaire available online. the employer was asked many questions, including so and program objective achievement. the presented data are based on a sample of 6 employers. the same satisfaction criterion of 70% is applied. the results are shown in table vii and it can be observed that all program outcomes indicate satisfaction. table vii. typical indirect assesment employer form the following section of the questionnaire is intended to seek your feedback on “demonstrated abilities of our graduates” while they are employed at your company: 5 4 3 2 1 average % # attribute question 1 apply knowledge of mathematics, science, and engineering. 3 2 1 0 0 83 2 design and conduct experiments. 5 1 0 0 0 100 3 solve engineering problem, analyze and interpret data. 4 2 0 0 0 100 4 design a system, component, or process to meet desired needs. 1 3 2 0 0 66 5 understand professional and ethical responsibilities. 0 5 1 0 0 83 6 communicate effectively. 3 3 0 0 0 100 7 understand the impact of engineering solutions in a global and societal context. 2 4 0 0 0 100 8 recognize the need to engage in lifelong learning. 1 3 2 0 0 66 9 use techniques, skills, and modern engineering tools necessary for engineering practice. 1 3 2 0 0 66 10 serve competently the needs of industry and academia by demonstrating high-quality knowledge, research, and skills in the area of electrical engineering 3 3 0 0 0 100 11 pursue professional development through professional study and self-learning with full gratitude of the importance of professional and ethical responsibility 2 3 1 0 0 83 12 contribute to the welfare of society through the responsible practice of engineering, leadership, and teamwork 3 2 0 1 0 83 e. so assessment through the industrial advisory board (iab) and the senior students table viii shows the response of the iab to the question “to what extent you are satisfied with the formulation of the ee peos?” table viii. iab survey for peos to what extent you are satisfied with the formulation of the ee peos? peo1 peo2 peo3 very satisfied 4 1 3 2 satisfied 3 4 3 2 neutral 2 1 0 1 dissatisfied 1 0 0 1 very dissatisfied 0 0 0 0 result 93% 100% 68% also, a total of 23 students (seniors) responded to the contacted survey. these 23 students are all in level 7 and 8 classes. the students were presented with the formulation of peos along with a brief explanation for each peo. the results and of the survey are shown in table ix. engineering, technology & applied science research vol. 10, no. 5, 2020, 6209-6213 6213 www.etasr.com ghaly: indirect evaluation of program educational objectives and student outcomes for engineering … table ix. senior student survey results senior student survey results ee peo peo1 peo2 peo3 very satisfied 4 7 (30%) 8 (35)% 12 (50%) satisfied 3 8 (40%) 6 (25%) 8 (35%) neutral 2 7 (30%) 7 (30%) 2 (10%) dissatisfied 1 0% 1 (5%) 1 (5%) very dissatisfied 0 0% 1(5%) 0% more than 65% of the surveyed ee senior students are either satisfied or very satisfied with the ee’s peos v. conclusion in this work, various surveys were used and contributed to the indirect assessment of the program outcomes and objectives attainment. the results of the exit survey for the last two cycles show that students’ perspective on their attainment of the program outcomes is satisfactory, since all the student outcomes are above the minimum required level of attainment. a meeting with the students is arranged every semester to clarify the objectives and the content of the indirect assessment. additional surveys, such as the employer survey and the alumni survey are assessed every three years to get feedback from the employers and the alumni in the market about the program objectives and at which level they met their carrier requirements. references [1] m. alsuwaiket, a. h. blasi, and r. a. al-msie’deen, “formulating module assessment for improved academic performance predictability in higher education,” engineering, technology & applied science research, vol. 9, no. 3, pp. 4287–4291, jun. 2019. [2] p. shayan and e. iscioglu, “an assessment of students’ satisfaction level from learning management systems: case study of payamnoor and farhangian universities,” engineering, technology & applied science research, vol. 7, no. 4, pp. 1874–1878, aug. 2017. [3] s. m. ahmed ghaly, “optimization of quality assessment and evaluation approach for engineering program accreditation,” in 2019 ieee global engineering education conference (educon), apr. 2019, pp. 1267–1274, doi: 10.1109/educon.2019.8725162. [4] h. al-nashash et al., “improving electrical engineering education at the american university of sharjah through continuous assessment,” european journal of engineering education, vol. 34, no. 1, pp. 15–28, mar. 2009, doi: 10.1080/03043790802710169. [5] y. bai and r. pigott, “assessing outcomes using program assessment portfolio approach,” journal of professional issues in engineering education and practice, vol. 130, no. 4, pp. 246–254, oct. 2004, doi: 10.1061/(asce)1052-3928(2004)130:4(246). [6] c. crosthwaite, i. cameron, p. lant, and j. litster, “balancing curriculum processes and content in a project centred curriculum: in pursuit of graduate attributes,” education for chemical engineers, vol. 1, no. 1, pp. 39–48, jan. 2006, doi: 10.1205/ece.05002. [7] m. besterfield-sacre et al., “defining the outcomes: a framework for ec-2000,” ieee transactions on education, vol. 43, no. 2, pp. 100– 110, may 2000, doi: 10.1109/13.848060. [8] j. b. biggs and c. tang, teaching for quality learning at university: what the student does, 4th ed. uk: mcgraw-hill education, 2011. [9] i. warren, “teaching patterns and software design.,” presented at the seventh australasian computing education conference (ace 2005), newcastle, australia, feb. 2005. [10] l. alzubaidi, “program outcomes assessment using key performance indicators,” in proceedings of 62 nd iserd international conference, boston, usa, jan. 2017. [11] y. kalaani and r. haddad, “continuous improvement in the assessment process of engineering programs,” proceedings of the 2014 american society for engineering education southeast section conference, mar. 2014, [online]. available: https://digitalcommons.georgiasouthern.edu/ electrical-eng-facpubs/43. [12] r. petrova, a. tibrewal, and t. sobh, “an electronic web-based assessment system,” journal of stem education, vol. 7, no. 3, dec. 2006. [13] l. alzubaidi, i. jabur, and r. alzubaidi, “course assessment tool using the combination approach,” in proceedings of the world congress on engineering and computer science 2015, oct. 2015, vol. 1. [14] b. ramasamy, “attainment of course outcomes in outcome based education: a case study,” journal of engineering education transformations, vol. 30, no. 2, pp. 82–85, oct. 2016, doi: 10.16920/ jeet/2016/v30i2/105449. [15] y. abosalem, “assessment techniques and students’ higher-order thinking skills,” international journal of secondary education, vol. 4, no. 1, pp. 1–11, mar. 2016, doi: 10.11648/j.ijsedu.20160401.11. [16] j. mcgourty, c. sebastian, and w. swart, “performance measurement and continuous improvement of undergraduate engineering education systems,” in fie 1997, 1997, vol. 3, pp. 1294–1301, doi: 10.1109/ fie.1997.632658. microsoft word 06-3745l_s_etasr_v10_n5_pp6187-6190 engineering, technology & applied science research vol. 10, no. 5, 2020, 6187-6190 6187 www.etasr.com alshammari: comparison of a chaotic cryptosystem with other cryptography systems comparison of a chaotic cryptosystem with other cryptography systems ahmed s. alshammari department of electrical engineering college of engineering, university of hail hail, saudi arabia ahm.alshammari@uoh.edu.sa abstract—the keyspace of a cryptography system must be long enough in order to protect it from brute force attacks. the onetime pad (otp) encryption is unconditionally secure because of its truly random keystream that is used only once. this paper proposes a new chaotic symmetric cryptosystem approach, comparable to otp. the proposed system utilizes two lorenz generators, a main and an auxiliary, where the aim of the second one is to make one of the main lorenz generator’s parameters to vary continually with time in a chaotic manner. this technique was built on digitizing two lorenz chaotic models to increase the security level. the scrambling scheme was developed and the lorenz stream cipher binary stream successfully passed the nist randomness test. the cryptosystem showed a high degree of security, as it had a keyspace of 2 576 , and it was compared with existing symmetric key cryptography systems, such as des, 3des, aes, blowfish, and otp. keywords-chaotic; aes; one-time pad; keyspace; lorenz system; nist; des i. introduction cryptography and cryptanalysis are two primary techniques for facilitating secure communications. cryptography is used in building secure systems to prevent transmitted data (plaintext, the key, or both) from being intercepted by unauthorized people. such a system is called a cryptosystem, and cryptanalysis is the process to evaluate it. furthermore, cryptanalysis is used to recover the data transmitted by detecting weaknesses in a cryptosystem. cryptanalysis is an important step for evaluating the components of a new cryptosystem, such as its security and reliability [1-3]. two types of cryptosystems exist: symmetric and asymmetric. a symmetric key cryptosystem uses the same private key in both the transmitter and the receiver to quickly encrypt and decrypt a plaintext, which is suitable for applications requiring high data rates, such as video encryption. furthermore, symmetric key cryptography is divided into two types: block cipher and stream cipher. the block cipher always encrypts and decrypts the plaintext in the same way by using a fixed binary key. the block cipher is widely used in applications, such as triple data encryption standard (3des), advanced encryption standard (aes), and rivest cipher (rc5) [4-5]. on the other hand, a stream cipher is generated using a random binary stream as a secret key to encrypt plaintext to output known as a keystream. the stream cipher key length is based on cryptosystem’s features, and it could range from 32 to 256 bits. the most popular stream cipher cryptosystems are encryption algorithm (a5/2), rc4, and software-optimised encryption algorithm (seal). a cryptosystem is asymmetric when it uses two different keys for encryption and decryption, where the first key is publicly distributed and the second key is private. such cryptosystems are primarily used for small amounts of data, such as authentication, secret key agreement, and digital signature, because they are slower. the public key length could range from 1024 to 4096 bits. a widely used public key algorithm is the rivest-shamir-adleman (rsa) [6]. evaluating security and performance of a communication system is not an easy task. however, many guidelines exist for enhancing a system’s robustness and security. these guidelines introduce many cryptographic requirements for building up and analyzing a new chaos-based cryptosystem. the major cryptographic requirements and analysis for a chaos-based cryptography system are discussed in this paper. furthermore, the system should pass the tests for confusion and diffusion, randomness of bit stream sequence, encryption speed and sensitivity of mismatched key [7-24]. according to [22], the conditions for characterizing an algorithm as safe are: • the time required for breaking an algorithm is longer than the time the encrypted information must be kept secret. • the cost required to break the algorithm is greater than the value of the encrypted information. • the amount of data encrypted using one key is less than the amount of data required to break the algorithm. unconditionally secure and computationally secure are two terms used to describe an algorithm. in an unconditionally secured algorithm the cryptanalyst does not have complete information to retrieve the plaintext, no matter how much of the cipher text is present. a computationally secure algorithm is hard to break with the available or even future resources [24]. according to [25] the breaking of an algorithm is categorized as: • total break: the cryptanalyst finds the key. • global deduction: the cryptanalyst determines a different algorithm that decrypts the cipher text without the key. corresponding author: ahmed s. alshammari engineering, technology & applied science research vol. 10, no. 5, 2020, 6187-6190 6188 www.etasr.com alshammari: comparison of a chaotic cryptosystem with other cryptography systems • local deduction: the cryptanalyst extracts a plaintext from the received cipher text. • information deduction: the cryptanalyst finds some information from the key or the plaintext. ii. the proposed cryptosystem figure 1 displays a block diagram of the proposed cryptosystem. one of the main lorenz generator’s parameter varies with time based on the auxiliary lorenz output signal. the plaintext is encrypted by the key stream generated from the main lorenz generator using the multiplication block. the cipher text is generated and transmitted to the receiver. the receiver system has identical main and auxiliary lorenz generators with the transmitter. the decryption process is started by multiplying the keystream with the cipher text to retrieve the plaintext. the first step is to synchronize the clocks of the transmitter and the receiver. in order to decrypt the cipher text, the receiver and the transmitter must have identical chaotic generators. this means that any intruder must have complete knowledge of the chaotic system’s parameters and initial conditions in order to be able to decipher the message. fig. 1. block diagram of the cryptosystem. the encryption technique utilizes the output of the main lorenz generator to encrypt the data stream, while both the main and the auxiliary lorenz generators are based on (1). the lorenz system is described by the following state equations, written in differential equation form, where a, b, and c are system parameters, and ��, ��, and �� are state variables. �� � ��� � � (1) �� � � � � � �� �� � �� � �� the a parameter of the main system is continuously varied by the auxiliary generator. furthermore, the parameters and initial conditions of the cryptosystem are changing in every usage to satisfy the third condition of otp. the constant block was used to manipulate the 32 bit length. thus, the last 12 bits, starting from the least significant bit, of the x-state keystream were extracted. the variable selector block is used to extract a subject of rows from each matrix. the same operation is used for the y-state keystream. however, the 20 bits are extracted from the y-state of 32 bits, starting from the least significant bit. after that, 12 bits and 20 bits are concatenated using the matrix concatenation block to produce 32 bits. then, the 32 bits are serialized using the buffered block. the auxiliary lorenz generator was pre-configured with a different set of initial conditions and system parameters. this system continuously varies the a parameter of the main lorenz generator. intensive care was taken to ensure that the main generator always remains in the chaotic region, and the output of the auxiliary lorenz generator (a[n]) remains within the range (7≤x[n]≤11). therefore, the signal response of the main lorenz generator changes continually in a chaotic manner, based on the parameter supplied by the auxiliary. figure 2 shows the results from simulink of the lorenz state variables, x, y, and z. fig. 2. lorenz state variables: (a) x-state variable, (b) y-state variable, and (c) z-state variable. iii. randomness test of the keystream the keystream must satisfy the randomness test to avoid any weaknesses in system’s security. in this experiment, 100 binary sequences each sized 1,000,000 bits were generated by the lorenz generator. the cryptosystem was evaluated using a nist randomness test, and the chaotic keystream of the proposed generator passed all nist 800-22 statistical randomness tests .the results are shown in table i. table i. nist randomness test statistical test status p-value frequency pass 0.242425 block frequency pass 0.8221413 cusum-forward pass 0.252325 cusum-reverse pass 0.232325 runs pass 0.645146 long runs of ones pass 0.344309 rank pass 0.463485 fft test pass 0.2342325 non-overlapping pass 0.841218 overlapping pass 0.211425 approximate entropy pass 0.811318 serial pass 0.622146 linear complexity pass 0.460485 since the lorenz system generates an analog signal, an analog-to-digital converter (adc) is necessary for digital applications. figure 3 shows the simulation results of the adc. engineering, technology & applied science research vol. 10, no. 5, 2020, 6187-6190 6189 www.etasr.com alshammari: comparison of a chaotic cryptosystem with other cryptography systems (a) (b) (c) (d) (e) (f) fig. 3. analog chaotic signal converted to digital signal. (a) analog signal of the x-state variable, (b) analog signal of the y-state variable, (c) analog signal of the z-state variable, (d) digital signal of the x-state variable, (e) digital signal of the y-state variable, and (f) digital signal of the z-state variable. fig. 4. the keystream of the chaotic cryptosystem. iv. keyspace of the proposed cryptosystem the transmitter has two lorenz generators, and each of them has three constants, three initial conditions, and three frequency multipliers. thus, the total number of the parameters is 18. the word length is 32-bits.the key space of the system is 2(18*32)=2576. as suggested in [2], the keyspace of a secure cryptosystem should be greater than 2100. thus, the cryptosystem’s keyspace is enough to resist any brute force attack. table ii shows the properties’ comparison of the proposed chaotic and five other cryptosystems. table ii. cryptography systems’ properties v. conclusion this paper presented a new cryptosystem based on lorenz chaotic generators. the system used a stream cipher and the encryption key varied continuously. furthermore, one lorenz generator parameter was controlled by an auxiliary chaotic generator for increasing security. this technique was built on digitizing two lorenz chaotic models, increasing security. the scrambling scheme was developed and lorenz stream cipher binary stream successfully passed the nist randomness test. data encryption used a symmetric cipher with a 576-bit key, and system’s keyspace was 2576. the proposed cryptosystem was compared with some existing symmetric cryptography systems such as des, 3des, aes, blowfish and otp in terms of key length and keyspace. security analysis showed that the system has a high degree of security compared to the other communication systems. the proposed approach is comparable to otp. references 1. a. s. alshammari, “synchronization of two chaotic stream ciphers in secure cdma communication systems,” engineering, technology & applied science research, vol. 10, no. 4, 2020, pp. 5947-5952, aug. 2020. 2. i. ahmad, a. saaban, a. ibrahin, and m. shahzad, “a research on the synchronization of two novel chaotic systems based on a nonlinear active control algorithm,” engineering, technology & applied science research, vol. 5, no. 1, pp. 739–747, feb. 2015. 3. a. elsharkawi, r. m. el-sagheer, h. akah, and h. taha, “a novel image stream cipher based on dynamic substitution,” engineering, technology & applied science research, vol. 6, no. 5, pp. 1195–1199, oct. 2016. 4. a. a. khare, p. b. shukla, and s. c. silakari, “secure and fast chaos based encryption system using digital logic circuit,” international journal of computer network and information security, vol. 6, no. 6, pp. 25–33, may 2014. 5. r. clayton and m. bond, “experience using a low-cost fpga design to crack des keys,” in cryptographic hardware and embedded factors proposed des 3des blowfish aes otp key length 576 bits 56 bits 168 bits varies between 32 bits to 448 bits 128,192 or 256 bits same as length of the plaintext (lp) cipher type symmetric stream cipher symmetric block cipher symmetric block cipher symmetric block cipher symmetric block cipher symmetric stream cipher block size 32 bits 64 bits 64 bits 64 bits 128,192 ,or 256 key space 2 576 256 2168 232~2448 2128, 2192 or 2256 2lp security considered secure not secure against brute force attack not secure considered secure considered secure considered secure engineering, technology & applied science research vol. 10, no. 5, 2020, 6187-6190 6190 www.etasr.com alshammari: comparison of a chaotic cryptosystem with other cryptography systems systems ches 2002, berlin, heidelberg, 2003, pp. 579–592, doi: 10.1007/3-540-36400-5_42. 6. t. kean and a. duncan, “des key breaking, encryption and decryption on the xc6216,” in proceedings. ieee symposium on fpgas for custom computing machines (cat. no.98tb100251), apr. 1998, pp. 310–311, doi: 10.1109/fpga.1998.707930. 7. g. heidari-bateni and c. d. mcgillem, “chaotic sequences for spread spectrum: an alternative to pn-sequences,” in 1992 ieee international conference on selected topics in wireless communications, jun. 1992, pp. 437–440, doi: 10.1109/icwc.1992.200803. 8. x. wang, x. wang, j. zhao, and z. zhang, “chaotic encryption algorithm based on alternant of stream cipher and block cipher,” nonlinear dynamics, vol. 63, no. 4, pp. 587–597, mar. 2011, doi: 10.1007/s11071-010-9821-4. 9. w. wong, l. lee, and k. wong, “a modified chaotic cryptographic method,” computer physics communications, vol. 138, no. 3, pp. 234– 236, aug. 2001, doi: 10.1016/s0010-4655(01)00220-x. 10. m. s. baptista, “cryptography with chaos,” physics letters a, vol. 240, no. 1, pp. 50–54, mar. 1998, doi: 10.1016/s0375-9601(98)00086-3. 11. m. a. aseeri, m. i. sobhy, and p. lee, “lorenz chaotic model using filed programmable gate array (fpga),” in the 2002 45th midwest symposium on circuits and systems, 2002. mwscas-2002, aug. 2002, vol. 1, p. i–527, doi: 10.1109/mwscas.2002.1187274. 12. g. r. goslin, “guide to using field programmable gate arrays (fpgas) for application-specific digital signal processing performance,” in highspeed computing, digital signal processing, and filtering using reconfigurable logic, oct. 1996, vol. 2914, pp. 321–331, doi: 10.1117/12.255830. 13. k. m. cuomo, a. v. oppenheim, and s. h. strogatz, “synchronization of lorenz-based chaotic circuits with applications to communications,” ieee transactions on circuits and systems ii: analog and digital signal processing, vol. 40, no. 10, pp. 626–633, oct. 1993, doi: 10.1109/82.246163. 14. l. cong and w. xiaofu, “design and realization of an fpga-based generator for chaotic frequency hopping sequences,” ieee transactions on circuits and systems i: fundamental theory and applications, vol. 48, no. 5, pp. 521–532, may 2001, doi: 10.1109/81.922455. 15. m. s. azzaz, c. tanougast, s. sadoudi, and a. dandache, “real-time fpga implementation of lorenz’s chaotic generator for ciphering telecommunications,” in 2009 joint ieee north-east workshop on circuits and systems and taisa conference, jun. 2009, pp. 1–4, doi: 10.1109/newcas.2009.5290495. 16. d. majumdar, r. moritz, h. leung, and j. m. brent, “an enhanced data rate chaos-based multilevel transceiver design exploiting ergodicity,” in milcom 2010 military communications conference, oct. 2010, pp. 1256–1261, doi: 10.1109/milcom.2010.5680115. 17. p. giard, g. kaddoum, f. gagnon, and c. thibeault, “fpga implementation and evaluation of discrete-time chaotic generators circuits,” in iecon 2012 38th annual conference on ieee industrial electronics society, oct. 2012, pp. 3221–3224, doi: 10.1109/iecon.2012.6389382. 18. l. merah, a. ali-pacha, n. h. said, and m. mamat, “design and fpga implementation of lorenz chaotic system for information security issues,” applied mathematical sciences, vol. 7, pp. 237–246, 2013, doi: 10.12988/ams.2013.13022. 19. s. liu, j. sun, z. xu, and z. cai, “an improved chaos-based stream cipher algorithm and its vlsi implementation,” in 2008 fourth international conference on networked computing and advanced information management, sep. 2008, vol. 2, pp. 191–197, doi: 10.1109/ncm.2008.11. 20. s. sadoudi, c. tanougast, and m. s. azzaz, “a new robust additive hyperchaos masking algorithm for secure digital communications,” in 2013 international conference on control, decision and information technologies (codit), may 2013, pp. 501–504, doi: 10.1109/codit.2013.6689595. 21. y. wu, y. zhou, and l. bao, “discrete wheel-switching chaotic system and applications,” ieee transactions on circuits and systems i: regular papers, vol. 61, no. 12, pp. 3469–3477, dec. 2014, doi: 10.1109/tcsi.2014.2336512. 22. g. alvarez and s. li, “some basic cryptographic requirements for chaos-based cryptosystems,” international journal of bifurcation and chaos, vol. 16, no. 8, pp. 2129–2151, 2006. 23. g. álvarez, f. montoya, m. romera, and g. pastor, “cryptanalyzing a discrete-time chaos synchronization secure communication system,” chaos, solitons & fractals, vol. 21, no. 3, pp. 689–694, jul. 2004, doi: 10.1016/j.chaos.2003.12.013. 24. a. shehata, “secure computer communications and databases using chaotic encryption systems,” ph.d. dissertation, university of kent, 2000. 25. l. r. knudsen, “block ciphers-analysis, design and applications”, ph. d. dissertation, department of computer science, aarhus university, 1994. microsoft word 20-3668_s_etasr_v10_n5_pp6253-6258 engineering, technology & applied science research vol. 10, no. 5, 2020, 6253-6258 6253 www.etasr.com nagao: effect of foundation width on subgrade reaction modulus effect of foundation width on subgrade reaction modulus takashi nagao research center for urban safety and security kobe university kobe city, japan nagao@people.kobe-u.ac.jp abstract—structures are subjected to vertical and horizontal loads. vertical subgrade reaction acts on the foundation bottom surface, and in the case of an embedded structure, horizontal subgrade reaction acts on the embedded part. the subgrade reaction is obtained by multiplying the displacement of the foundation by the subgrade reaction modulus (srm). in practice, srm is calculated using an equation that incorporates the negative power relationship of the foundation width (fw). if the structure is evaluated to be poorly seismic resistant, it is necessary to widen fw. however, when the fw is widened, the design value of srm decreases. in this case, it is not possible to expect an increase in the subgrade reaction proportional to the increase of fw. therefore, when the inertia force is very high, the fw has to be very wide. however, underestimating srm can lead to structural overdesign. in this study, the relationship between srm and fw, for a structure in which vertical and horizontal load act simultaneously, was analyzed. compared with the design practice assumptions, the horizontal srm was found to be highly dependent on fw while the vertical srm was shown to be less dependent on fw. keywords-subgrade reaction modulus; soil stiffness; foundation width i. introduction during an earthquake, structures undergo vertical loads, such as dead weight, and horizontal loads, such as the inertia force. in response to these loads, the vertical subgrade reaction acts on the bottom surface of the structure foundation. for structures with embedded foundations, the horizontal subgrade reaction acts as a resistance force on the embedded foundation. the subgrade reaction is obtained by multiplying the subgrade reaction modulus (srm) by the displacement of the foundation. parameters that affect srm include ground stiffness and foundation width (fw). it has been pointed out that srm increases with increasing ground stiffness and decreases with increasing fw [1-6]. for this reason, srm calculation equations comprising ground stiffness and fw have been incorporated into various design specifications [7]. although various equations have been proposed for the evaluation of srm, the degree of dependence of srm on fw varies in different studies. when an external force such as the seismic load is evaluated to be large, or when a large lateral spreading pressure is expected to act during an earthquake [8], fw needs to be widened to enhance seismic resistance. however, since the srm calculation equation with negative power relationship of fw is used in design practice, widening fw lowers srm. as a result, an increase in the subgrade reaction proportional to the increase in fw cannot be expected. therefore, if the seismic load is very large, fw should be very wide. conversely, an experimental study on the seismic resistance of piers with various fws has shown that the piers with wider fws are extremely seismic resistant due to the increase in vertical subgrade reaction [9]. the results have shown that the calculation equation of the design practice could underestimate srm for wide fw conditions. therefore, applying the srm calculation equation of current design specifications can lead to structural overdesign under very high seismic loads. in this study, the relationship between srm and fw was analyzed for structures under simultaneous vertical and horizontal loads. ii. conventional evaluation method of srm numerous studies have been performed to evaluate srm. the following are typical srm calculation equations: 108.0 4 2 1 95.0             − = ei bee b k s s s s ν (1) 2 3.0 2 3.0       + = b b kk s (2) 12 4 2 1 65.0 ei bee b k s s s s       − = ν (3) 4 3 3.03.0 1 −       = b ek ss α (4) where ks is the srm, k0.3 is the srm obtained by a plate loading test with a width of 0.3m, b is the fw, es and νs are young’s modulus and poisson’s ratio of the ground respectively, and ei is the flexural rigidity of the foundation. equations (1)–(3) have been proposed in [1–3] respectively. equation (4) is an equation of the japanese specifications for highway bridges (jshb) [7]. the jshb equation is based on the results of field horizontal loading experiments [4] in which the dependence of horizontal srm on the width of a loading corresponding author: takashi nagao engineering, technology & applied science research vol. 10, no. 5, 2020, 6253-6258 6254 www.etasr.com nagao: effect of foundation width on subgrade reaction modulus plate was discovered. in (4), coefficient α is specified as 2 (for example) when es is evaluated by n-values from the standard penetration tests to obtain the srm values during an earthquake. all these equations show that srm decreases with increasing fw. figure 1 shows how the srm varies over the fw range of 4–10m. the values of (1) to (4) are shown in red, blue, green, and black lines respectively. the srm results from (2) (blue line) are slightly affected by fw, whereas the other results are significantly influenced by fw. the srm results of (4) show the largest decrease with increasing fw. fig. 1. comparison of srm results. the characteristics of ground stress propagation are briefly explained to understand the reason why the srm calculation equation has been proposed in accordance with fw. when a distributed load is applied on the ground from the structure, the stress propagates in the ground. the propagated stresses caused by loads at different locations on the ground surface are superimposed in the ground. the values of stresses superimposed in the ground increase with increasing fw. therefore, even if the stresses on the ground surface are the same, the amount of ground deformation increases with increasing fw. since srm is a value obtained by dividing a ground surface stress by the amount of displacement, it becomes smaller when the fw is wider. therefore, the existing equations are dependent on fw, and srm decreases with increasing fw. however, the degree of the dependency of srm on fw may be different for horizontal and vertical srms. since the ground normally has a constant stiffness (young’s modulus) in the horizontal direction, the above idea may be valid. however, in the vertical direction, young’s modulus generally increases with increasing depth. if the young’s modulus is large, the deformation becomes small even if the same stress is applied. therefore, even under the same stress increments, the amount of ground deformation decreases with increasing depth. since the amount of deformation at the ground surface is calculated as the sum of the amounts of deformation in the ground, the degree of decrease in vertical srm with respect to the increments of ground stress may be insignificant. moreover, for structures with embedment, the foundation is usually embedded in soil layers with very high young’s modulus. for this reason, vertical srm is less dependent on fw than horizontal srm. iii. evaluation of vertical srm boussinesq’s equation is known for evaluating the stress in the ground when a concentrated load acts on a semi-infinite elastic three-dimensional ground surface. the equation for calculating the stress in the ground under distributed load acting on two-dimensional elastic ground is obtained by integrating boussinesq’s equation [10]. as shown in figure 2, the vertical ground stress (σz) at point p under a uniformly distributed load is obtained by: { })cos()sin( 212121 θθθθθθ π σ +−+++= q z (5) fig. 2. uniformly distributed load. when a structure undergoes vertical and horizontal loads simultaneously, (i) a horizontally distributed load and (ii) a vertically trapezoidal (or triangular) distributed load act simultaneously on the ground surface. when the horizontal load is relatively small compared to the vertical load, the vertically distributed load on the ground surface shows a trapezoidal distribution, and when the horizontal load is large, it shows a triangular distribution. since a trapezoidal distributed load can be expressed as a combination of a uniformly distributed load and a triangular distributed load, the equation for calculating the ground stress under a triangular distributed load can be explained. as shown in figure 3, when a triangular distributed load with intensity q at the origin is applied, the vertical stress at point p is calculated as [11]: 2 1 1 2 1 1 1 2 sin( ) cos( ) ( ) sin( ) cos( ) sin( ) z q θ θ σ θ θ θ θ π θ θ   = + +  +  (6) furthermore, as shown in figure 4, when a horizontally distributed load is applied, the vertical stress at point p is calculated as follows [11]: )sin()sin( 1221 θθθθ π σ −+= q z (7) regarding the ground condition, it was considered to be composed of two layers with a thickness of 10m. the saturated unit weight of soil in each layer was 20kn/m 3 , poisson’s ratio (ν) was 0.33, and the water table was on the ground surface. two ground conditions were assumed: soft ground condition (case 1) and hard ground condition (case 2). n65 was set for each layer to evaluate young’s modulus of the ground under 4 6 8 10 0.5 0.6 0.7 0.8 0.9 1 foundation width(m) s r m q θ 2θ 1 p o x z engineering, technology & applied science research vol. 10, no. 5, 2020, 6253-6258 6255 www.etasr.com nagao: effect of foundation width on subgrade reaction modulus each condition. here, n65 represents the n-value when the effective overburden pressure (σv’) is 65kpa. in case 1, n65 was 10 in the middle of the upper layer and 20 in the middle of the lower layer. in case 2, n65 was 30 in the middle of the upper layer and 45 in the middle of the lower layer. the relationship between n65 and n-value under σv’ is [12]: ( ) ( ) 0.165'0041.0 65'019.0 65 +− −− = v v n n σ σ (8) fig. 3. triangular distributed load. fig. 4. horizontally distributed load. to calculate young’s modulus of the ground, the shear modulus g (kpa) was obtained from the n-value using (9) [13]. young’s modulus e was calculated with (10): 88.0 14400ng = (9) ( )ge ν+= 12 (10) young’s modulus of the soil was treated as the average effective confining stress dependent as follows: a mg ma m ee       = ' ' σ σ (11) where e is the young’s modulus, ea is the reference young’s modulus, ' m σ is the average effective confining stress, ' ma σ is the reference average effective confining stress, and mg is the exponent that represents the average effective confining stress dependency of the modulus (= 0.5 in this study, based on [14]). it is assumed that there is a bedrock with a very large young’s modulus below the lower layer in which the deformation can be ignored. as shown in figure 5, a case with a structure with 20kn/m 3 unit weight and 8m height installed on the ground surface was considered. fw was set to 4, 6, 8, and 10m. the structure was assumed to receive a seismic load with a seismic coefficient of 0.3 at a height of 4m from the ground surface, which was the gravity center of the structure. the seismic coefficient is the ratio of seismic load to dead weight. the vertical load distribution on the ground surface became a trapezoidal distribution under the current study condition. a rotational resistance moment was generated due to the distributed load to resist the moment load caused by the seismic load. the intensity of the vertically distributed load on the ground surface was calculated from the moment balance equation. for comparison, the calculation was also performed under the condition that there was no horizontal load and only a uniformly distributed vertical load was applied on the ground surface. fig. 5. study condition. figures 6 and 7 illustrate the depth distributions of σz for fws of 4m and 10m respectively. the red, blue, and green lines are the results at x = b/8, b/4, and b/2 in figures 2–4, respectively, where b is the fw. when only uniformly distributed vertical loads were applied, the stresses on the ground surface were the same regardless of the position in the horizontal direction. the ground stresses were smaller near the foundation edge and larger near the foundation center due to the superposition of ground stresses. the ground stresses decreased rapidly with increasing depth and became almost the same regardless of the horizontal position below −10m for fw equal to 4m and below −20m for fw equal to 10m. the narrower the fw, the smaller the difference in ground stress due to the difference in horizontal positions, because the narrower the fw, the smaller the effect of stress superposition. when a vertically trapezoidal distributed load was applied, the stress on the ground surface changed significantly depending on the distance from the foundation edge, but the stress decreased sharply as the depth increased. the stresses did not differ depending on the horizontal position at −5m depth for fw 4m and at −10m for fw 10m. q θ 2θ 1 p o x z q θ 2θ 1 p o x z 10m 10m upper layer lower layer 8m bedrock engineering, technology & applied science research vol. 10, no. 5, 2020, 6253-6258 6256 www.etasr.com nagao: effect of foundation width on subgrade reaction modulus fig. 6. vertical stress depth distribution (4m width). fig. 7. vertical stress depth distribution (10m width). the stresses due to the horizontally distributed loads on the ground surface became very small ranging from zero on the ground surface to maximum at depths of −2 to −3m. the stress was zero at the foundation center regardless of the depth, with positive and negative reversal around the foundation center. figures 8 and 9 compare the depth distributions of stresses at positions from the foundation edge of b/4 and b/2 respectively, under the condition that vertically trapezoidal and horizontally distributed loads were applied simultaneously. the red, blue, green, and black lines are the results for b = 4, 6, 8, and 10m, respectively. when the fw was narrow, the stress at the b/4 position became large on the ground surface. however, the stress sharply decreased with increasing depth, and when the fw became narrower, the ground stress below −2m became smaller. at the foundation center, the stresses on the ground surface were the same, and with increasing depth, the stresses decreased sharply. the stresses were always smaller for narrower fws. fig. 8. vertical stress depth distribution (at b/4). fig. 9. vertical stress depth distribution (at b/2). figure 10 exemplifies the foundation settlement distribution under uniformly distributed loads for fw equal to 4m in case 1. since the theoretical equations were adopted in this study, the boundary conditions at the foundation edge were not sufficiently considered. although only uniform vertical loads were applied to the ground surface, the foundation settlement distribution was not uniform. therefore, the srm was calculated by excluding the results at the foundation edge. figures 11 and 12 demonstrate the changes in srm with changing fw. the red line shows the results in the case of only uniformly distributed loadings, and the blue line represents the results of simultaneous vertically trapezoidal and horizontally distributed loadings. these results were not significantly different. the results obtained from the jshb equation (shown by the green line) show changes in srm with changing fw under the condition where the srm results from the jshb equation and the theoretical srm were the same when vertically trapezoidal and horizontally distributed loads were applied simultaneously to a fw of 4m. as can be seen in the engineering, technology & applied science research vol. 10, no. 5, 2020, 6253-6258 6257 www.etasr.com nagao: effect of foundation width on subgrade reaction modulus figures, the impact of fw was present, and srm decreased with increasing fw, but the degree of srm decrease with increasing fw was very small for every ground condition. the jshb equation overestimated the effect of fw, and when the fw was extended, srm was significantly underestimated. this was because the amount of settlement was small at greater depths due to the ground stiffness. furthermore, the ground stress increased with increasing fw, but the amount of settlement did not increase significantly when the fw increased. as mentioned above, the jshb equation is based on the horizontal loading test results and is not suitable for evaluating the vertical srm. fig. 10. settlement distribution (fw 4m). fig. 11. vertical srms (case 1). fig. 12. vertical srms (case 2). iv. evaluation of horizontal srm the ground conditions are similar to the previous section, and the effects of fw on the horizontal srm with embedded structures are discussed in the current section. figure 13 shows the study conditions. it was assumed that the structures with a width of 2m and different dimensions in depth were embedded to the lower end of the upper soil layer. unit weight, seismic coefficient, and location of seismic loads in the structure are the same as in the previous chapter. the srm evaluation position is in the middle of the upper layer. equation (5) can be applied to the calculation of the horizontal ground stress caused by seismic load, since a uniformly distributed horizontal load is assumed in the depth direction. when a structure with high flexural rigidity rotates around the bottom due to the action of seismic load, it is linearly displaced from the bottom of the structure toward the ground surface, resulting in linear ground deformation and ground stress. the ground stress at the srm evaluation position was calculated under this assumption. fig. 13. study condition. figure 14 illustrates the changes of horizontal ground stress distribution due to the changes in fw, plotted against the horizontal distance from the srm evaluation position. the horizontal ground stress distributions were similar to the stress distribution pattern shown in figure 9. however, since young’s modulus is constant in the horizontal direction, a large difference occurred in the amount of deformation due to differences in ground stress at points away from the foundation. as a result, when the fw were different, the srm values were significantly different. fig. 14. horizontal ground stress distribution. 0 2 4 6 3 10 3− × 4 10 3− × 5 10 3− × 6 10 3− × 7 10 3− × 8 10 3− × foundation width(m) se tt le m e n t( m ) 4 6 8 10 1 10 4 × 1.5 10 4 × 2 10 4 × 2.5 10 4 × foundation width(m) s r m (k p a /m ) 4 6 8 10 3 10 4 × 4 10 4 × 5 10 4 × 6 10 4 × 7 10 4 × foundation width(m) s r m (k p a /m ) 10m 10m upper layer lower layer 8m bedrock 2m srm evaluation position 0 5 10 15 20 0 15 10 5 0 horizontal stress(kpa) d is ta n c e (m ) engineering, technology & applied science research vol. 10, no. 5, 2020, 6253-6258 6258 www.etasr.com nagao: effect of foundation width on subgrade reaction modulus figures 15 and 16 demonstrate the changes in srm with changes in fw (red line) with an obvious dependence on fw. the green lines in the figures represent the srm results obtained from the jshb equation. they show changes in srm in response to the changes in fw when the srm results obtained from the jshb and the theoretical equations were the same at the fw of 4m. the jshb equation overestimates the fw dependence but to a lesser extent compared to the vertical srm results. therefore, the jshb equation has some applicability in evaluating horizontal srm. fig. 15. horizontal srms (case 1). fig. 16. horizontal srms (case 2). v. conclusions this study discussed the applicability of the srm design equations by comparing the analytical results with the ones produced by the jshb equation at various fws. for horizontal srm, the effect of fw was relatively high, and the jshb equation was found to be applicable to some extent. however, in the case of vertical srm, since young’s modulus of the ground depends on depth, the effect of fw was found to be weak, and for wide fw, the jshb equation underestimated srm significantly. the relationship between stress and deformation of the soil is linear and the srm is the ratio of stress to deformation, therefore the effect of fw on srm found in this study applies regardless of the ground and loading conditions. when the seismic load is expected to be large, the fw needs to be widened. however, underestimating vertical srm may result in structural overdesign. therefore, a successful design practice requires proper evaluation of vertical srm. acknowledgment this research was supported by jsps kakenhi, grant number jp18k04324. references [1] m. a. biot, “bending of an infinite beam on an elastic foundation,” journal of applied mathematics and mechanics, no. 203, pp. a1-a7, mar. 1937. [2] k. terzaghi, “evalution of conefficients of subgrade reaction,” géotechnique, vol. 5, no. 4, pp. 297–326, dec. 1955, doi: 10.1680/geot.1955.5.4.297. [3] a. b. vesic, “beams on elastic subgrade and the winkler’s hypothesis,” in proceedings of 5th international conference of soil mechanics, 1963, pp. 845–850. [4] t. yoshinaka, “subgrade reaction coefficient and its correction based on the loading width,” pwri report 299, 1967. [5] r. ziaie-moayed and m. janbaz, “effective parameters on modulus of subgrade reaction in clayey soils,” journal of applied sciences, vol. 9, pp. 4006–4012, doi: 10.3923/jas.2009.4006.4012. [6] j. lee and s. jeong, “experimental study of estimating the subgrade reaction modulus on jointed rock foundations,” rock mechanics and rock engineering, vol. 49, no. 6, pp. 2055–2064, jun. 2016, doi: 10.1007/s00603-015-0905-9. [7] specifications for highway bridges, part iv, substructures. japan road association, 2016. [8] t. nagao and d. shibata, “experimental study of the lateral spreading pressure acting on a pile foundation during earthquakes,” engineering, technology & applied science research, vol. 9, no. 6, pp. 5021–5028, dec. 2019. [9] t. nagao, “an experimental study on the way bottom widening of pier foundations affects seismic resistance,” engineering, technology & applied science research, vol. 10, no. 3, pp. 5713–5718, jun. 2020. [10] j. h. michell, “on the direct determination of stress in an elastic solid, with application to the theory of plates,” proceedings of the london mathematical society, vol. s1-31, no. 1, pp. 100–124, 1899, doi: 10.1112/plms/s1-31.1.100. [11] t. kimura, “analytical investigation on mechanical behaviors of twolayer systems,” proceedings of the japan society of civil engineers, vol. 1969, no. 162, pp. 31–48, feb. 1969. [12] technical standards and commentaries for port and harbour facilities in japan. overseas coastal area development institute of japan, 2009. [13] t. imai and k. tonouchi, “correlation of n–value with s−wave velocity and shear modulus,” in proceedings of the 2nd espt, rotterdam, netherlands, 1982, pp. 67–72. [14] i. suetomi and n. yoshida, “nonlinear behavior of surface deposit during the 1995 hyogoken-nambu earthquake,” soils and foundations, vol. 38, supplement, pp. 11–22, sep. 1998, doi: 10.3208/sandf.38.special_11. 4 6 8 10 6 10 4 × 8 10 4 × 1 10 5 × 1.2 10 5 × 1.4 10 5 × foundation width(m) s r m (k p a /m ) 4 6 8 10 1.5 10 5 × 2 10 5 × 2.5 10 5 × 3 10 5 × 3.5 10 5 × 4 10 5 × foundation width(m) s r m (k p a /m ) microsoft word 03-3213_s_etasr_v10_n1_pp5108-5112 engineering, technology & applied science research vol. 10, no. 1, 2020, 5108-5112 5108 www.etasr.com apsara et al.: a review on secure group key management schemes for data gathering in wireless … a review on secure group key management schemes for data gathering in wireless sensor networks m. b. apsara information science and engineering department j.s.s academy of technical education bangaluru, india iseapsaramba@gmail.com p. dayananda information science and engineering department j.s.s academy of technical education bangaluru, india dayanandap@gmail.com c. n. sowmyarani computer science and engineering department rv college of engineering bangaluru, india sowmyaranicn@rvce.edu.in abstract—wireless sensor networks (wsns) is a fast-emerging technology which has become an integral part of the research. wsns have various applications covering military, environment monitoring, health care, surveillance, national security, etc. due to the inherent nature of wireless communication, such types of networks are more vulnerable to security attacks, and the authentication and confidentiality of wireless networks are much more critical. wsns needs include efficient clustering methods, data aggregation methods, data compression methods, data encryption and authentication methods, and data gathering methods. wsns are more vulnerable to attacks due to their ad hoc nature, so the design of a good key management scheme to provide security is necessary. in this paper, different methods of clustering, data aggregation, data compression, data encryption and authentication, and data gathering are analyzed. a survey is conducted on the key management schemes of wsns. keywords-wireless sensor networks (wsns); data compression; data aggregation; data gathering; clustering; key management i. introduction wireless sensor networks are a simple and economic approach in deploying monitoring and control devices. such networks can be deployed easily and economically in any type of application environment where sensor nodes sense their surroundings. wsns are typically self-healing and selforganizing in nature. they organize themselves to maintain communication between the nodes of the network. the network sensors sense environmental parameters such as temperature, humidity, pressure, acoustic vibrations, mechanical stress, and more. due to the finite battery power and low computing capacity of the sensors, their main need is to design protocols which perform computing with less energy. a wsn consists of a number of nodes which are battery driven devices. basically, they perform the following tasks: they sense the physical quantity from the surroundings where they are deployed, they process the acquired data, and they transfer the data through wireless communication to data collection points which are called base stations, destinations or sink nodes. self-organizing means that the network allows newcoming nodes to automatically join the network. some of the basic topologies they use are star, mesh, and point to point. in wsn security, data confidentiality is the most important requirement. to achieve this, malicious nodes should not have access to the network. due to the nodes’ limited energy and resources, many secure cluster-based protocols have been developed for routing. to achieve the security requirements, an efficient scheme for group key management is needed. energy is one important concern in wsns. here, wireless transfer plays a vital role in energy consumption, so data gathering techniques (tree based, cluster based, or chain based). are a significant part of the wireless communication. aggregation methodology also reduces energy consumption in data transferring. a wsn usually consists of a sink node and many small sensor components. aggregation methodologies reduce the traffic in the network. the main points in network security are data confidentiality and data integrity. by using the existing encryption, end to end confidentiality can be achieved. in data gathering process, a malicious node may communicate with the valid nodes which may compromise the entire network. so, it is necessary to develop an efficient key management scheme. key management is mainly classified into static and dynamic. in the static key management schemes all the keys are pre-distributed in the sensor nodes and then each node chooses a set of keys from a key pool. in dynamic key management schemes some keys or key seeds are redistributed, and the session keys are established on demand. figure 1 shows an overview of the secure group key management scheme for data gathering in wsn. initially, the network is set up and by using an efficient clustering algorithm a cluster head is selected for each cluster. then, the data sensed by the sensors are aggregated by existing data aggregation methods. to reduce the size of the data to be transferred, data compression is used. data encryption is done for security purposes. finally, by using efficient data gathering methods, the data are gathered at the base station. to perform the above operation, a secure group key management is necessary. corresponding author: p. dayananda engineering, technology & applied science research vol. 10, no. 1, 2020, 5108-5112 5109 www.etasr.com apsara et al.: a review on secure group key management schemes for data gathering in wireless … fig. 1. overview of the secure group key management for data gathering in wsns ii. literature survey the main objective of the current survey is to highlight the limitations and advantages of the various existing security methods. there are different techniques for encryption, data compression, key management, clustering, and aggregation, which are presented and compared. a. clustering clustering in wsns is a process of grouping sensor nodes. all the nodes are linked to the cluster head for maintaining communication. the cluster head is chosen randomly. after the cluster head selection, all the nodes communicate locally through the cluster head. the clustering algorithm should provide solutions on minimizing energy consumption, reducing communication, and organizing the messages among the cluster head and member nodes. authors in [1] provide solution to the isolated nodes which are not in the range of the cluster head. to solve this, the o-leach (orphan low energy adaptive clustering hierarchy) routing algorithm was proposed which takes care of the orphan nodes. the o-leach maintains full coverage for the applications which requires transferring data to the entire area. o-leach performs better than the leach algorithm in terms of energy, connectivity rate, coverage and scalability [1]. the energy balanced clustering algorithm based on leach for wsns is an improved version of the leach protocol to enhance the energy of the network. different versions of leach are collated to perform better than the existing protocols. the sleep leach outperforms all the existing leach versions in terms of residual energy, throughput, and packet delivery ratio [2]. energy efficient clustering is very important in prolonging the lifespan of a wsn. hence, authors in [3] provided a clustering algorithm which minimizes the intra cluster distance to optimize the usage of network energy. the clustering with pso presented a better clustering via the uniform allocation of ch throughout the network [3]. authors in [4] presented the flc-pso algorithm for wsns which outperforms leach, conventional flc, and flc-ga in terms of the number of dead nodes, remaining energy level, number of cluster heads and surviving nodes. a review of the surveyed literature is summarized in table i with the advantages and improvements of clustering protocols. most of the key features of the methods are mentioned in the table. table i. clustering algorithms comparison algorithm year advantages improvements o-leach [1] 2016 connectivity rate &coverage improves energy consumption sleep leach [2] 2016 outperforms the existing leach versions improves energy consumption cluster formation with pso [3] 2017 better network stability improves energy efficiency and network life span flc-pso [4] 2018 efficient energy method only the remaining energy and the number of dead nodes are the considered factors b. compression and aggregation compression is the process of reducing the transmitted data. it reduces the needed memory space and increases transmission ratio. data aggregation is the process which forms the set of data from data sets from different physical quantities. the universal lzw data compression is a lossless data compression algorithm. in this method, a dictionary is created while encoding data. choosing a large dictionary reduces overflow but spoils compression. the algorithm in [5] performs best on images and text files. by using this method, a compression ratio of 60-70% is achieved. authors in [6] mainly concentrated on reducing the amount of communication needed for data transmission by sensors. they proposed a routing algorithm called funneling which reduces network energy consumption. the method used for compression was coding by ordering. combining both funneling and coding by ordering, the energy consumption is reduced by half, while the collisions in the wireless medium were also reduced. good compression ratio can be achieved by coding by ordering, which is a lossy technique so there is a chance of losing data at the end. authors in [7] described the data distributed wavelet transform (dwt) compression method which is based on the lifting scheme. in wsns the energy consumption is the main issue which effects the life time of the network. the dwt method performs better than the other distributed wavelet algorithms in terms of calculation complexity and time. a novel data transmission mechanism named data selecting mechanism (dsm) was also proposed and simulated. it was concluded that this method reduces the network’s redundant data and increases its lifetime by reducing energy consumption. authors in [8] proposed a data aggregation technique using the rsa key management approach for the wsns. the data sampled by the sensor nodes contain redundant data, so data aggregation becomes very engineering, technology & applied science research vol. 10, no. 1, 2020, 5108-5112 5110 www.etasr.com apsara et al.: a review on secure group key management schemes for data gathering in wireless … important to eliminate data redundancy. this reduces transmissions and saves energy. ant colony algorithm was used to aggregate the data. dynamic routing protocols were employed with the data aggregation to transfer the data. to make the aggregation more efficient, the authors used the rsa for implementing key based data transmission. this proposed method sends data via a secure path and performs time to time key value change in the network. authors in [9] proposed a deterministic code allocation technique for data compression. this method obtained better compression performance with less computation complexity. a review of the studied literature is summarized in table ii with the advantages and improvements of compression and aggregation techniques. table ii. comparison of the compression and aggregation methods algorithm year advantages improvements funneling and coding by ordering [5] 2003 high compression ratio more cr can be achieved wsm with dsm [6] 2013 less energy consumption compression ratio is improved lzw [7] 2014 more compression ratio for monochrome images and text files 60-70% of compression ratio is achieved ant colony and rsa [8] 2014 send data packets through secure routing dynamically key value changes deterministic code allocation algorithm [9] 2019 better compression performance with less computational complexity this algorithm can be embedded in the real wsn hardware c. key management and data gathering authors in [10] proposed group key management using symmetric key and threshold cryptography (egkmst) for cluster based wsns. key management plays a very important role in group communication and protection from attacks in sensor networks. since limited resources are providing security in the wsns, it has become a must for them. the proposed method uses the hierarchical cluster structure and adopts the pair-wise key and group key management based on threshold cryptography, which efficiently generates key and distribute it among the clusters, while periodically updates the key. so egkmst, offers continuous security from attacks during data transmission. by this method low overhead, low cost, and more energy saving can be achieved, compared to existing methods. authors in [11] described an efficient key management scheme for wsns. due to their inherent nature, the wsns are more vulnerable to attacks than the traditional networks. so, providing authentication and confidentiality is more critical in such networks. the authors proposed a novel key management method called makm (modular arithmetic based key management), based on congruence property. each sensor node stores the key seed, this key seed is used to generate the shared key with its cluster head and the group key is shared with the other members in the same cluster. makm demands less storage space. it outperforms the key pool-based methods in terms of delay and energy for large scale wsns. the wsns led to the development of various new data gathering protocols. authors in [12] proposed the seladg (secure energy efficient location aware data gathering approach for wireless sensor networks) for gathering data securely. they used the ecdhke algorithm for key generation and key exchange between the sensor nodes to protect the data from malicious nodes and provide security. this scheme outperforms the existing eeha and smart methods. authors in [13] proposed a data gathering technique in wsns through an intelligent compressive sensing scheme for efficient data gathering. recently emerge compressive sensing (cs) theory provides a whole new era for data gathering in wireless sensor networks. due to the disadvantages of existing compressive sensing methods, they proposed an adaptive data gathering scheme by using compressive sensing. they introduced a concept named autoregressive (ar) model into the reconstruction of the sensed data. the reconstructed data were then evaluated by utilizing the successive reconstructions, the relation between measurements and error. testing on real data and experimental results confirm the efficiency of this scheme. a review of the studied methods is summarized in table iii with the advantages and improvements of each studied key management and data gathering method. table iii. comparison of key management and gathering methods algorithm year advantage improvement makm and ecdsa [11] 2011 reduces energy consumption reduces delay intelligent compressive sensing [13] 2012 more efficient than conventional cs improved reconstruction quality egkmst [10] 2014 low cost, low memory overhead, energy saving 100% connectivity is achieved seladg and ecdhke [12] 2015 achieves better performance than the existing eeha and smart improve the network life time d. encryption and authentication a wsn consists of low cost and small sized sensor nodes with no predetermined location as they are randomly spread in the application terrain. for such networks authentication and key agreement are important. in [14], the authors proposed an enhanced authentication and key agreement protocol, the elliptic curve-based authentication and key agreement protocol, which satisfies all security issues. there are many security mechanisms used in wsns, the authors in [15] described rsa and biometric based authentication for wsns which are very effective methods in securing information and message security by cryptographic mechanism and give the best authentication results in wsn. authors in [16] proposed a secure aggregation using an efficient key management technique for wsns. data aggregation is an effective method in wsns because it reduces engineering, technology & applied science research vol. 10, no. 1, 2020, 5108-5112 5111 www.etasr.com apsara et al.: a review on secure group key management schemes for data gathering in wireless … the number of packets to be sent to the base station. this technique uses the clustering mechanism reducing network traffic and contention in the wireless channel. so, aggregation increases network lifetime by reducing energy usage. authors in [16] propose the key exchange management protocol which helps two users to exchange key securely while these keys can be used to encrypt the messages efficiently. sande–tukey algorithm is proposed to provide the key. this technique is developed to aggregate the total computation outputs and to identify the number of failures in the environment. table iv. comparison of data encryption and authentication methods algorithm year advantage improvement elliptic curves [14] 2013 low computation cost satisfies all necessary security requirements sande-tukey [16] 2014 security to selective discrete method in wsn lifetime of the system is improved. consumes less time and eliminates traffic with less energy. rsa [15] 2016 cost efficient the life time of sensor nodes is increased ec based key management scheme [17] 2016 better computational complexity and resist to side channel attacks satisfies high security requirements cl-ekm [18] 2016 secure communication in dynamic wsn effective against attacks cl-akm [19] 2016 economical key revocation. ensures backward and forward key secrecy. effective against several attacks authors in [17] presented the hardware implementation of an efficient key management scheme for wsns in the applications which require high security. the basic functions of authentication and random number generation are performed by using elliptic curves-based algorithms instead of using aes or sha. this method was implemented on a kintex7 fpga board. by this method better computational complexity and resistance to side channel attacks can be achieved. even though a lot of research is done on key management, it remains an important issue in wsns. in [18], the authors proposed the certificate less effective key management method. it supports the economical key revocation when the node joins or exits from the network and it ensures backward and forward key secrecy. by using cl-ekm, secure communication is established. it was confirmed by simulations that the proposed protocol performs well in terms of memory, energy and communication. authors in [19] presented the active key management in dynamic wireless sensor networks. they used the certificate less technique in key management. it supports the economical key revocation when a node joins or exits the network and it ensures backward and forward key secrecy. this proposed scheme is effective in several attacks. simulation is done to assess its delay, threshold, and energy. a review of the studied methods is exhibited in table iv. iii. conclusion in this paper, a study on different clustering, data compression, aggregation, authentication, encryption, data gathering, and key management approaches has been done. various approaches for the above mentioned tasks have been explained with their objectives and limitations. this paper is a short description and analysis of the proposed and implemented methods and techniques for key management and data gathering. various techniques for data compression, aggregation, clustering, encryption and authentication, data gathering, and key management have been presented. these techniques provide complete security for wsns and transfer the data efficiently. it was observed that in spite of the research conducted in this regard, there is still space for future work. references [1] w. jerbi, a. guermazi, h. trabelsi, “a novel clustering algorithm for coverage a large scale in wireless sensor networks”, international journal on computational science & applications, vol. 6, no. 2, pp. 116, 2016 [2] d. charaan, r. ramesh, e. uma, “energy balanced clustering algorithm on leach protocol for wsn”, international journal of innovation and scientific research, vol. 23, no. 2, pp. 293-302, 2016 [3] s. p. singh, s. c. sharma, “a novel energy efficient clustering algorithm for wireless sensor networks”, engineering, technology & applied science research, vol. 7, no. 4, pp. 1775-1780, 2017 [4] c. cao, x. zhu, “energy management using optimal fuzzy logic control in wireless sensor network”, international journal of online and biomedical engineering, vol. 14, no. 9, pp. 35-52, 2018 [5] h. n. dheemanth, “lzw data compression”, american journal of engineering research, vol. 3, no. 2, pp. 22-26, 2014 [6] d. petrovic, r. c. shah, k. ramchandran, j. rabaey, “data funneling: routing with aggregation and compression for wireless sensor networks”, ieee international workshop on sensor network protocols and applications, anchorage, usa, may 11, 2003 [7] d. ye, c. shen, “data compression algorithm for wireless sensor networks”, available at: https://pdfs.semanticscholar.org/ 33dd/f5fe6f7fe396622e25dd3471637fd89d1f40.pdf, 2013 [8] g. malathy, c. krishnan, “data aggregation using rsa key management technique in wireless sensor networks”, international journal of innovative research in science, engineering and technology, vol. 3, no. 1, pp. 274-277, 2014 [9] h. anwer basha, s. arivalagan, p. sudhakar, r. p. narmadha, “a new deterministic code allocation technique for data compression in wireless sensor networks”, international journal of recent technology and engineering, vol. 7, no. 5c, pp. 80-86, 2019 [10] a. diop, y. qi, q. wang, “efficient group key management using symmetric key and threshold cryptography for cluster based wireless sensor networks”, i. j. computer network and information security, vol. 8, pp. 9-18, 2014 [11] d. du, h. xiong, h. wang, “an efficient key management scheme for wireless sensor networks”, international journal of distributed sensor networks, vol. 2012, article id 406254, 2011 [12] m. r. juliana, s. srinivasan “seladg: secure energy efficient location aware data gathering approach for wireless sensor networks”, international journal on smart sensing and intelligent systems, vol. 8, no. 3, pp. 1748-1767, 2015 [13] j. wang, s. tang, b. yin, x. y. li, “data gathering in wireless sensor networks through intelligent compressive sensing”, 2012 ieee infocom, orlando, usa, march 25-30, 2012 engineering, technology & applied 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intelligent computing research, vol. 7, no. 1, pp. 663-671, 2016 [18] d. dhayalan, s. nandhini, “certificate less effective key management in dynamic wireless sensor network”, imperial journal of interdisciplinary research, vol. 2, no. 4, 2016 [19] a. g. priyanga, c. narmadha, “a certificate less active key management in dynamic wireless sensor networks”, international journal of advanced research in computer and communication engineering, vol. 5, no. 1, pp. 119-123, 2016 microsoft word etasr_v11_n1_pp6734-6739 engineering, technology & applied science research vol. 11, no. 1, 2021, 6734-6739 6734 www.etasr.com bakar et al.: decentralized virtual impedance-based circulating current suppression control for … decentralized virtual impedance-based circulating current suppression control for islanded microgrids afarulrazi abu bakar department of electrical power engineering faculty of electrical and electronic engineering university tun hussein onn malaysia johor, malaysia afarul@uthm.edu.my erum pathan electronic engineering department quaid-e-awam university of engineering science and technology nawabshah, pakistan erumasad79@gmail.com mubashir hayat khan department of electrical power engineering faculty of electrical and electronic engineering university tun hussein onn malaysia johor, malaysia mubashir.uthm@gmail.com muhammad ahsan sadiq department of electrical engineering faculty of engineering & technology university of poonch rawalakot poonch, pakistan engr.ahsan@upr.edu.pk muhammad imran rabani department of electrical contracting & maintenance xervon saudia arabia mimranbzu@gmail.com sai babu goli commissioning division-coa saudi electricity company saudia arabia saibabu27@hotmail.com farheen pathan department of telecommunication engineering mehran university of engineering and technology jamshoro, pakistan engrfarheen83@gmail.com muammad asad shaikh protection and sas commission national grid sa saudi arabia csd_sec@yahoo.com abstract-parallel connected inverters in islanded mode, are getting momentous attention due to their ability to increase the power distribution and reliability of a power system. when there are different ratings of distributed generation (dg) units, they will operate in parallel connection due to different output voltages, impedance mismatch, or different phase that can cause current to flow between dg units. the magnitude of this circulating current sometimes can be very large and damage the dg inverters and also cause power losses that affect powersharing accuracy, power quality, and the efficiency of the microgrid (mg) system. droop control, improved droop control, and virtual impedance control techniques and modifications in the virtual impedance control technique are widely used to suppress the circulating current. however, the addition of the virtual impedance to each inverter to compensate the output impedance is resistive or inductive in nature. the resistive nature of the output impedance always causes a certain voltage drop, whereas the inductive nature of the output impedance causes phase delay for the output voltage. both problems are addressed by the proposed control mechanism in this paper. negative resistance, along with virtual impedance, is utilized in the proposed control strategy. the output impedance is to be maintained as inductive in nature to achieve good load sharing in droop control mgs. the simulation results validate the proposed control scheme. keywords-circulating current; droop control; virtual impedance; distributed generations; decentralized control i. introduction in a microgrid (mg) system the i-th power electronic interface is integrated utilizing different distributed generations (dgs) in both islanded and grid-connected mode. besides the many advantages of the mg system, it can also operate at a plug and play function and as bidirectional energy management system [1-3] for continuous power supply. however, there are some control issues in mgs, the islanded mode of operation in particular may have power quality and stability issues. in islanded mode, the suppression of circulating current is much needed, because it may cause instability in the system. overheating of the system components can lead the corresponding author: afarulrazi abu bakar engineering, technology & applied science research vol. 11, no. 1, 2021, 6734-6739 6735 www.etasr.com bakar et al.: decentralized virtual impedance-based circulating current suppression control for … entire system to failure because large circulating currents flow through the inverters. the circulating current is also a significant cause of reduction of mgs' transmission efficiency. moreover, the decentralized control mechanism of the dg inverters connected in parallel faces more circulating current issues than the centralized control mechanism [4-7]. line impedance mismatch in parallel connected inverters is the main cause of the generation of circulating currents between the inverters and can affect power-sharing among different dgs. voltage output inequalities between dgs connected in parallel is another cause of generation of circulating currents. several techniques have been implemented to reduce circulating currents. a multicarrier pwm method was implemented on parallel two-level converters to suppress the circulating currents in [8]. the generation mechanism of circulating currents was studied in [9-11] and a mathematical model was established for circulating current generation. in the islanded (stand-alone) mode of operation, droop control is widely used due to its favorable characteristics such as simplicity, good active power, and the reactive power sharing capability in multiple distribution generation systems [12]. conventional droop control is basically designed for inductive transmission lines with primary control level [13] that do not need a communication link [14]. meanwhile, for low voltage grids with resistive impedance characteristics, the conventional droop control is not able to provide active and reactive power-sharing [15-18]. in the presence of local loads and large line impedance, mgs face voltage deviation issues and that causes an increase in the circulating currents and power sharing issues. to fix the voltage deviation problem, the conventional droop is required to be modified [19-20]. therefore, the mitigation of the frequency issue is done by angle droop control, while voltage regulation and powersharing accuracy [20] use q-u dot droop control. in order to create a suppression of the circulating current a multi-loop control mechanism for parallel-connected inverter control is needed to improve system reliability and adaptability with effective utilization of droop capability with voltage and current control mechanism [21]. non-dominated sorting sine cosine algorithm (nssca) and improved particle swarm optimization control techniques were used in [22, 23] for mg control in order to enhance power quality. in the context of circulating current suppression, an impedance mismatch has been addressed through adaptive virtual impedance where the values change at every instant, inequalities are removed, and the circulating current is minimized, hence, the accuracy on power-sharing is improved [24-26]. in the presence of local loads during an abrupt change in loads, a conventional virtual impedance control strategy does not give appropriate results. faster response to load variation can be attained by virtual complex impedance [27] to improve power-sharing accuracy. one of the methods is by having a coupling inductor to overcome the circulating current issue in the voltage source converters. saturation of the coupled inductor may occur when the low frequency circulating current is high because the coupled inductor is sensitive to low order harmonic contents that occur due to the inequalities of the converters. the mismatch in line impedance leads the system to inaccurate power-sharing in parallel connected inverters with the same power rating. an improved droop with voltage drops compensator with no load was suggested in [24], while a proportional resonant controller was used to ensure system stability by reducing the low frequency circulating current. a control technique for the suppression of cross circulating current based on virtual impedance control was presented in [28]. this paper presents the decentralized virtual impedancebased control technique for parallel-connected islanded mgs to suppress the circulating current. voltage and current tracking are conducted with load changing conditions. the proposed controller responded accordingly and mitigated voltage, frequency, and power sharing accuracy errors and the circulating current was suppressed effectively. the proposed control scheme was tested to a multi dg mg system with different loads. the conventional droop control was modified and implemented with virtual impedance. moreover, the stability of the mg system was within the permissible limits. ii. droop based control methods for circuilating current suppression in figure 1, an inverter with given voltage impedance parameters: open-circuit voltage v<ϕ, output impedance of the inverter z<θ, apparent power (s), and output current of the inverter (i), is shown. fig. 1. inverter equivalent circuit. the active and reactive powers p and q in simplified form are taken as: 2 cos( ) cos o ovv v p z z θ φ θ= − − (1) 2 sin( ) sin o ovv v q z z θ φ θ= − − (2) neglecting output impedance resistance, the above equations are further simplified with a same voltage phase difference, such as θ = 90o, z=x, sinϕ=ϕ and cosϕ=1. ovv p x φ= (3) ( )ov v v q x − = (4) from (3) and (4) it is concluded that p and q are dependent on phase difference ϕ and voltage magnitude difference (v-vo) respectively. subsequently, the control equations with frequency voltage droop can be given as: mpω ω∗= − (5) v v nq∗= − (6) engineering, technology & applied science research vol. 11, no. 1, 2021, 6734-6739 6736 www.etasr.com bakar et al.: decentralized virtual impedance-based circulating current suppression control for … where ω*, v*, n, and m are frequency, voltage, and drop coefficients respectively. iii. virtual impedance analysis droop control technique has two major flaws: a) it neglects the resistive component, which is not practically applicable and b) for double-loop control, the control parameters are affected, so the load sharing accuracy is not guaranteed. the different aspects of output impedance are given below. a. inverter output impedance practically, when different dg inverters are connected in parallel, the possibility to have the same parameters for each dg inverter is significantly less. the difference in the output impedance of every unit of the dg inverter causes circulating current, which needs to be suppressed. droop control provides wireless control with virtual impedance, as shown in figure 2. droop characteristics and virtual impedance control technique with the transfer function of output impedance are given as: 2 1 2 2 1 2 2 ( ) ( ) ( 1) pi pwm o pi pwm pi pwm pv pi pwm pv ls r k k k s z lcs k k k c rc s k k k k s k k k k + + = + + + + + (7) where k1 and k2 are the current and voltage co-efficients and kpi, kpv, and kpwm are the proportion parameters and equivalent parameters respectively. from (7), it is clear that the output impedance is influenced by the controller parameters. the virtual impedance shown in figure 3 aims to manipulate the output impedance features. fig. 2. virtual impedance loop control. fig. 3. virtual impedance implementation. b. resistive virtual impedance in figure 4, (7) is plotted for different values of rvir with the condition zvir = rvir. the virtual impedance influences the output impedance and both are changing accordingly. c. inductive virtual impedance equation (7) is plotted in figure 5 with the different values of lvir for zvir = lvir, when the values of output impedance are purely inductive. it is clearly shown that the output impedance is influenced by the virtual impedance and both are changing accordingly. fig. 4. bode plot zo with rvirtual. fig. 5. phase, frequency, and magnitude plot. d. proposed negative resistance control in parallel-connected inverter-based mgs, the mismatch in line impedance is covered by virtual impedance. the above analysis indicates that the changing virtual impedance changes the output impedance. this means that the virtual impedance characteristics are manipulated in such a way that the output impedance of the parallel-connected dg units in the mgs changed according to the demand of the load for accurate load sharing. figures 4 and 5 illustrated that there is a massive drop in voltage amplitude and a phase delay while utilizing the resistive or inductive virtual impedance. the output impedance is changed by adding the inductive virtual impedance. the overview of the control scheme is shown in figure 6. to analyze the output impedance, bode plots are shown in figure 7 where the parameters for the controller are given in table i. it is clearly shown that the addition of the virtual impedance increases the phase when it is compared with figure 5. the change in phase is approximately from 86.96º to 89.99º, which is quite significant. it is noticed that the output impedance is purely inductive in nature after the addition of the virtual impedance. from the above analysis, it can be concluded that the improvement in active and reactive power decoupling improves the load sharing in parallel connected inverters, and the circulating current is also suppressed. fig. 6. proposed virtual impedance control. engineering, technology & applied science research vol. 11, no. 1, 2021, 6734-6739 6737 www.etasr.com bakar et al.: decentralized virtual impedance-based circulating current suppression control for … fig. 7. bode plot of the proposed control technique. iv. simulation results the proposed control strategy was built in matlab/simulink for two parallel-connected inverters with the system parameters given in table i. the comparison between the conventional strategies and the proposed control strategy is conducted considering fixed load and sudden change in load conditions. figure 8 shows the matlab/simulink model and the sub model of the proposed control system. (a) (b) fig. 8. simulation (a) two vsc-based inverters system, (b) sub-model of the proposed controller. table i. system parameters parameters inverter1 inverter 2 voltage amplitude at no load=v* (v) 700 700 dc bus voltage =vdc (v) 400 400 active power=p (kw) 450 450 reactive power=q (kvar) 350 350 output frequency at no load =f (hz) 50 50 line impedance = z (ω) 0.3 + j0.0002 0.167 + j0.00052 integral parameter of voltage controller = kpi 2400 2200 inverter switching frequency = f (khz) 20 20 droop coefficient frequencies=m,n 6.5*10-5, 2.2*10-3 6.5*10-5, 2.2*10-3 output filter capacitor = c (µf) 30 30 output filter inductor resistance =r (ω) 0.11 0.17 a. comparison in fixed load conditions the fixed load conditions are categorized in three cases: • case 1 at t=0.5s, conventional droop control is applied to the system, as shown in figure 9. circulating current, output power ratio and output power magnitude difference are shown separately for each inverter. • case 2 after t=1s, improved droop control is applied to the system up to t=1.5s. circulating current, output power ratio, and output power magnitude difference are shown separately for each inverter (figure 9). • case 3 from t=1.5s up to t=2s, the proposed virtual impedance control scheme is applied to the system. it is clearly shown in figure 9 that the circulating current is not reduced initially when even there is a same voltage for each inverter. the circulating current is suppressed only when a voltage drop is recompensed by equalizing impedance mismatch in the engineering, technology & applied science research vol. 11, no. 1, 2021, 6734-6739 6738 www.etasr.com bakar et al.: decentralized virtual impedance-based circulating current suppression control for … connected feeders. the output magnitude difference of the inverters is separately presented here. when t=0.5s, both dg inverters have the same voltage to the load connected to the system in convention droop control. the circulating current is larger and power distribution deviations are clearly observed due to the mismatch in line impedance. from t=1s, by implementing the improved droop control the errors due to line impedance mismatch are reduced and the circulating current is suppressed effectively to some extent. it is clearly shown that from t=1.5s to 2s, by implementing the virtual impedance control scheme, the mismatch of line impedance is covered efficiently, and the circulating current is suppressed. moreover, power-sharing accuracy increased by implementing the proposed control scheme. b. comparison in suddden load change implementing the proposed virtual impedance control scheme to an mg based on dg inverters connected in parallel, the circulating current is suppressed efficiently and the power sharing accuracy improves in the case of sudden load change. during the sudden load change, the conditions are the following: p=450kw and q=350kvar. it is clearly shown that when t=0.5s the system is instable. when the power is reduced to 50% from 450kw to 225kw and from 350kvar to 175kvar for p and q respectively, at time t=1.0s, each load is analyzed as in condition 2. in condition 3, the power is raised by 20 % as of condition 1 at time t= 1.5s. in figure 10, it is shown that the deviation in frequency is in the allowable range and the circulating current for each inverter is less than 5% of the rated current. fig. 9. comparison of control techniques with different schemes for inverters 1 and 2: (a) circulating current, (b) magnitude difference, (c) output power ratio. fig. 10. simulation results with load change for inverters 1 and 2: (a) frequency of the system, (b) output power ratio, (c) lvi , (d) circulating current, (e) output power, and (f) rvi. v. conclusion a circulating current suppressed scheme that utilizes the virtual impedance along with improved droop control and negative resistance is presented in this paper. the proposed control strategy offers decentralized control, which is the most 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[28] b. wei, j. m. guerrero, and x. guo, "cross-circulating current suppression method for parallel three-phase two-level inverters," in 5th international conference on consumer electronics, berlin, germany, sep. 2015, pp. 423–427, https://doi.org/10.1109/icce-berlin.2015. 7391297. microsoft word etasr_v10_n6_pp6515-6520 engineering, technology & applied science research vol. 10, no. 6, 2020, 6515-6520 6515 www.etasr.com rija et al.: microcontroller based automatic power factor correction for single-phase lagging … microcontroller based automatic power factor correction for single-phase lagging and leading loads bahaulddin makaiber rija electrical and electronics engineering department gaziantep university şehitkamil-gaziantep, turkey bahaaaldeenmakhaiber@gmail.com mohammed khalil hussain department of energy engineering university of baghdad baghdad, iraq mohammedkhalil@uobaghdad.edu.iq ahmet mete vural electrical and electronics engineering department gaziantep university şehitkamil-gaziantep, turkey mvural@gantep.edu.tr abstract-the power factor (pf) correction is a major power quality function in electrical distribution systems. this paper proposes a low cost automatic power factor correction (apfc) system to increase the pf of both lagging and leading singlephase loads. the arduino mega 2560 microcontroller was used to calculate the pf and activate the relays that connect the capacitor/inductor banks to the load in parallel. thus, the required capacitive or inductive reactive power was produced by the apfc system by automatically connecting the capacitor/inductor banks to the load in parallel. the apfc system can also measure and display many electrical parameters of the load such as the rms voltage, the rms current, pf, and the real, reactive, and apparent power on an lcd display. two zero crossing detector circuits are used to find the phase angle difference between voltage and current waveforms of the load. the measurement ability of the apfc system was tested for resistive, inductive, and capacitive loads with two different sizes. the measurements results were compared with the measurements of a commercial digital power meter and a measurement error less than 8.0% was observed. the pf correction ability of the apfc system was verified for inductive and capacitive loads with two different sizes. the experiments show that the pf increased to close to unity for both lagging and leading loads. keywords-power factor correction; reactive power compensation; arduino mega 2560 microcontroller i. introduction power factor (pf) is a critical performance indicator of the power quality in ac power systems [1, 2]. the pf of an electrical load is defined as the ratio between the real and apparent power of the load [1-3]. the pf can have any value between 0 and 1. ideally, the pf is equal to unity or 1, which means that a given load matches that of a pure resistance having voltage and current waveforms which are in phase [4]. this means that the real and apparent power of the load are equal to each other. in this situation, the load neither consumes nor delivers reactive power. on the other hand, if the pf is not unity, then the pf type can be either "lagging" or "leading". lagging pf means that the current waveform lags the voltage waveform by some angle. instead, if the current waveform leads the voltage waveform, then the pf is said to be leading. for lagging pf loads, such as induction motors, power transformers, and lighting ballasts, the minimization of reactive power is very essential [3, 5]. the reactive power is the energy stored in inductive elements which continuously oscillates between the load and the source. this continuous oscillation causes an increase in the amount of current drawn by the load [2, 6]. if the reactive power is not minimized, a relatively higher amount of current will be drawn by the load, which makes imperative to use a relatively high cross-section of the conductors that increase the cost and losses of the distribution system [7]. reactive power minimization is called "pf correction" or "reactive power compensation". it is a process that makes the pf of a load close to 1. with the pf correction, the load current is minimized without changing the real power consumed by the load [1, 8]. so, the load continues to make the same work by the drawn electrical energy with a relatively smaller amount of current when compared with the uncompensated case. moreover, minimum and maximum allowable limits of reactive power drawn from the system are defined in regulations and the electric distribution companies give penalties to the industrial consumers for any violation of these limits. as a summary, the advantages of pf correction are reduced system losses, increased load carrying capability of the conductors and the transformers, and improved voltage profile and system corresponding author: bahaulddin makaiber rija engineering, technology & applied science research vol. 10, no. 6, 2020, 6515-6520 6516 www.etasr.com rija et al.: microcontroller based automatic power factor correction for single-phase lagging … stability [9-13]. although there are some expensive solutions to handle the reactive power compensation function, the capacitors are still used globally due to their simplicity and low cost. when compared, the capacitors are much cheaper and easier to implement than static var compensators, static synchronous compensators, and active power filters [1-3]. on the other hand, many studies proposed the use of a microcontroller to improve the pf of only lagging loads by adding parallel connected capacitor banks to the load [1-9]. arduino uno has been used to improve only the lagging load by using capacitor connection in parallel with only the inductive load [1, 6, 7] and to improve the pf of different loads by using filter and capacitor bank [8]. pic18f452 type microcontroller for the correction of the pf in constant level of load was proposed in [2]. the contribution of this paper is the use of an arduino microcontroller for apfc to improve the pf of different types of loads with different sizes. not only the capacitor banks are used to improve the pf of lagging loads, but also the inductor banks are used to improve the pf of leading type loads with different sizes. two different sizes for resistive, inductive, and capacitive loads are used to show the reliability of the apfc. in this paper, the pf improvement of both lagging and leading loads is proposed. an arduino mega 2560 microcontroller is programmed to decide the number of the capacitors or inductor banks that are automatically connected to a single-phase load by relays to approach load pf close to unity (0.98 lagging). three different loads are considered in this work: resistive, inductive, and capacitive loads with two different sizes. the purpose of using resistive load is to verify the operation of the zcd circuits. the designed apfc system can also measure and display many electrical parameters on an lcd display, such as rms voltage, rms current, pf and its type, and real, reactive, and apparent power of the single-phase load. all the measurements were verified with reed r5000 digital power meter. the comparison results show that the measurement errors are relatively small with an error of less than 8.0%. on the other hand, it is experimentally verified that the designed apfc system can improve the pf by 39% for small inductive load, 52% for high inductive load, 12% for low capacitive load, and 29% for high capacitive load. ii. system design this section explains the block diagram of the proposed apfc system. figure 1 shows the complete diagram of the designed hardware to calculate the necessary amount of capacitor or inductor banks to improve the pf of a single-phase load. at first, the voltage and current of the load connected to single-phase voltage source are sensed by an asl 150212 voltage transformer (pt) and a zmct 103c current transformer (ct), respectively. then the voltage and current waveforms are sent to the zcd circuits, which are used to change the sinusoidal voltage and current waveforms to square waveforms. then, the two square waves, synchronized to voltage and current waveforms, are summed by a summer circuit made by an xor logic gate. the output of the xor gate is connected to one i/o pin of the arduino mega 2560 microcontroller to send the phase angle difference. the pf is calculated and its type is defined with a program written in c. based on these calculations, the arduino mega 2560 microcontroller decides the value and number of capacitors or inductor banks to be connected in parallel with the load. the design also includes a 2004a lcd display to show the measurements. fig. 1. the block diagram of the apfc system. iii. mathematical model one of the inputs of the arduino mega 2560 microcontroller is related with the phase angle difference (�) between the voltage (�) and the current (�) of the load. these values are read in the microcontroller by using the function pulsein (pin, value, timeout) [1, 2]. the pf is then calculated by: �� = �� � (1) based on voltage and current measurements and the pf calculation, real (�), reactive (q), and apparent power (�) of the load are calculated by: � = � ∗ � (2) � = � ∗ �� (3) q = √�� − �� (4) the pf could be unity, lagging, or leading based on the load type. if the load is resistive, then the pf becomes unity and no action is needed from the microcontroller. only the electrical parameters are calculated and shown on the lcd display. if the load is inductive, the pf becomes lagging. in this case, the microcontroller calculates the size of the capacitor banks to be connected in parallel with the load. this is achieved by controlling the relays between the load and the capacitors. if the load is capacitive, the pf becomes leading. in that case, the microcontroller calculates the size of the inductor banks to be connected in parallel with the load. again, this task is achieved by controlling the relays between the load and the inductors. the following steps are used to calculate the required capacitance or inductance for the apfc system: • calculation of the pf angle (∅�) of the load: ∅� = cos ��(pf) (5) • calculation of the the reactive power (��) of the load: �� = � ∗ sin ∅� (6) • calculation of the desired phase angle (∅�) if the desired pf is 0.98 lagging: ∅� = cos ��(0.98) (7) engineering, technology & applied science research vol. 10, no. 6, 2020, 6515-6520 6517 www.etasr.com rija et al.: microcontroller based automatic power factor correction for single-phase lagging … • calculation of the amount of reactive power (��) for the desired pf: q$ = � ∗ tan∅� (8) • calculation of the amount of reactive power (�') needed to improve the pf: �' = �� − q$ (9) • calculation of the capacitance (c) or inductance (l) required to be connected in parallel with the load: ( = )* �+∗,∗-. (10) / = -. �+∗,∗)* (11) iv. flowchart of the algorithm the flowchart of the algorithm used in the apfc system is shown in figure 2. after starting the system, at first, the voltage and the current of the load are measured. these are stepped down by a pt and ct. zcd circuits are used to convert the sine waveform to square waveform. this circuit is used to measure the phase angle between the voltage and the current of the load. the xor circuit represents the time difference between the voltage and the current. in this sense, the arduino mega 2560 microcontroller has three inputs: voltage, current, and the time delay between the voltage and current. the arduino mega 2560 microcontroller is programed in the following steps: • step1: read voltage, current, and time delay • step2: calculate the pf based on the angle between the voltage and current of the load • step3: specify load pf type • step4: calculate the required capacitance or inductance to improve the pf to 0.98 lagging • step5: switch on the relay(s) to connect the capacitor(s) or inductor(s) to the load. fig. 2. the flowchart of the algorithm. fig. 3. complete experimental circuit of the apfc system. engineering, technology & applied science research vol. 10, no. 6, 2020, 6515-6520 6518 www.etasr.com rija et al.: microcontroller based automatic power factor correction for single-phase lagging … v. experimental circuit and results this section explains the hardware circuit of the proposed apfc system and its components. the experimental results are presented and evaluated for different sizes and types of load. a. experimental circuit the complete experimental circuit of the apfc system is shown in figure 3. in this circuit, a pt and a ct are used to step down and measure the voltage and the current of the load. the voltage and current waveforms obtained from pt and ct1 are sent to the zcd circuits which contain lm324 operational amplifiers to change the waveform of the voltage and current from sinusoidal to square. the outputs of the zcd circuits are fed to the xor3040 gate. the output of the xor 3040 gate is a series of pulses. the amplitude and the width of these pulses depend upon the output of the two signals from the zcd circuits. the ct2 is used as a sensor that measures the load current and sends this information to the microcontroller. all these outputs are connected to the inputs of the arduino mega 2560 microcontroller. the microcontroller measures and evaluates the difference in the pulse width of the two square waves to calculate the pf. there are four different values of inductors in the inductance bank and five different values of capacitors in the capacitor bank. the connections of these components are handled by the microcontroller by the relays. according to the type and value of the pf, the microcontroller decides how many capacitors or inductors would be connected in parallel with the load in order to approach the pf to 0.98 lagging. finally, the rms voltage, rms current, real, reactive, and apparent power of the load, and the information about the connected capacitors or inductors are shown in the lcd display. figure 4 shows the experimental setup of the proposed apfc system. fig. 4. experimental setup of the apfc system. b. experimental results three different load types and two different load sizes were used to test the performance of the proposed apfc system. to show the accuracy of the measurements taken by the microcontroller, (12) is used to calculate the percentage of error between the measurements of the apfc system and the digital power meter measurement: % error = 45678 97�78 :;<=7�>4,' :;<=7 45678 97�78 :;<=7 (12) 1) resistive load in this case, a small and a big resistive load were used. the purpose of this case study was to verify the measurement performance of the proposed apfc system. the small resistive load is a 100w incandescent light bulb. a big resistive load is the combination of these two light bulbs with a total power of 200w. table i shows the measurements taken by the arduino microcontroller and the commercial digital power meter. the measured data of the resistive load are the rms voltage, the rms current, the pf, and the active, reactive, and apparent power. the percentage of error for each measured data is also represented in table i by comparing the measurements taken from the microcontroller with the digital power meter. the error for the voltage measurements for both loads remains less than 1.0%. the error of current and power measurements for both cases is between 2% and 7%. it can be concluded that the proposed apfc system measures many electrical parameters of the resistive load with an error of maximum 7.2%. table i. measurements for small and big resistive loads load type: small resistive load proposed apfc system value digital power meter value % error voltage 228.66v voltage 230.4v 0.75 current 0.42a current 0.43a 2.32 pf 1.00 pf 1.00 0 active power 95.33w active power 99w 3.70 reactive power 3.58var reactive power 3.77var 5.03 apparent power 95.40va apparent power 99.072va 3.70 load type: big resistive load proposed apfc system value digital power meter value % error voltage 227.83v voltage 230v 0.94 current 0.81a current 0.87a 6.89 pf 1.00 pf 1.00 0 active power 185.52w active power 200w 7.24 reactive power 6.47var reactive power 6.32var 2.37 apparent power 185.63va apparent power 200.1va 7.23 2) inductive load in this case, two different inductive loads were used. the small load is a single-phase ac motor with ratings of 220v, 50hz, 43w. the big load is a single-phase ac motor with ratings of 220v, 50hz, 110w. in this experimental case, both measurements and the compensation performance of the proposed apfc system were verified for lagging pf loads. table ii shows the measurements taken by the microcontroller and the digital power meter before and after compensation for the small load. the error for the voltage measurements before and after compensation was less than 1.0%. the obtained error for current measurements before and after compensation has a maximum of 7.69%. on the other hand, the errors for the power measurements before and after compensation stay between 1% and 8%. when the compensation function is activated, the apfc system connects one 2.5uf capacitor to the load in parallel to improve the pf from 0.6 to 0.99 lagging. it is engineering, technology & applied science research vol. 10, no. 6, 2020, 6515-6520 6519 www.etasr.com rija et al.: microcontroller based automatic power factor correction for single-phase lagging … deduced that the proposed apfc works well in increasing the pf of the 43w rated single-phase ac motor. table iii shows the measurements taken by the microcontroller and the digital power meter before and after compensation for the big load. the voltage errors stay again less than 1.0% before and after compensation. the errors for the current measurements before and after compensation remain around 3-4%. on the other hand, the errors for the power measurements before and after compensation are between 2% and 7%. when the compensation function is activated, the apfc system connects three capacitors with capacitances of 0.5uf, 1.5uf, and 5uf to improve the pf from 0.45 to 0.97 lagging. in this case study, it is verified that the measurements taken from the apfc system have a maximum error rate of 7.93% and the pfs of the inductive loads with different sizes are effectively increased to be close to unity. table ii. measurements for small inductive load load type: small inductive load (before compensation) proposed apfc system value digital power meter value % error voltage 228.27v voltage 229.9v 0.70 current 0.21a current 0.21a 0 pf 0.60 pf 0.61 1.63 active power 29.62w active power 29w 2.13 reactive power 39.26var reactive power 38.58var 1.76 apparent power 49.18va apparent power 48.27va 1.88 load type: small inductive load (after compensation) proposed apfc system value digital power meter value % error voltage 228.9v voltage 230v 0.47 current 0.14a current 0.13a 7.69 pf 0.99 pf 0.97 2.06 active power 31.30w active power 29w 7.93 reactive power 7.16var reactive power 7.28var 1.64 apparent power 32.11va apparent power 29.9va 7.39 table iii. measurements for big inductive load load type: big inductive load (before compensation) proposed apfc system value digital power meter value % error voltage 230.8v voltage 231.5v 0.30 current 0.62a current 0.65a 4.61 pf 0.45 pf 0.47 4.25 active power 64.69w active power 70w 7.58 reactive power 129.49var reactive power 133.19var 2.77 apparent power 144.75va apparent power 150.47va 3.80 load type: big inductive load (after compensation) proposed apfc system value digital power meter value % error voltage 228.45v voltage 229.9v 0.63 current 0.31a current 0.32a 3.21 pf 0.97 pf 0.97 0 active power 69.28w active power 71w 2.42 reactive power 17.26var reactive power 18.37var 6.04 apparent power 71.39va apparent power 73.34va 2.65 3) capacitive load in this case, two different capacitive loads were used. the small load consists of a 470ω resistor connected in series with a 10uf capacitor. the big load consists of a 235ω resistor connected in series with a 12uf capacitor. in this experimental case, the measurements and the compensation performance of the proposed apfc system are verified for leading the pf loads. table iv shows the measurements taken by the microcontroller and the digital power meter before and after compensation for the small load. the maximum error for the voltage measurements before and after compensation is 1.17%. the maximum error for the current measurements before/after compensation is 2.70%. on the other hand, the errors for the power measurements before and after compensation stay between 0.75% and 7.35%. when the compensation function is activated, the apfc system connects one 2.91h inductor to the load in parallel to improve the pf from 0.85 leading to 0.97 leading. it is deduced that the proposed apfc works well in increasing the pf of the small capacitive load. table v shows the measurements taken by the microcontroller and the commercial digital power meter before/after compensation for the big load. table iv. measurements for small capacitive load load type: small capacitive load (before compensation) proposed apfc system value digital power meter value % error voltage 227.61v voltage 228.8v 0.52 current 0.39a current 0.39a 0 pf 0.85 pf 0.85 0 active power 75.12w active power 77w 2.44 reactive power 46.91var reactive power 45.09var 4.03 apparent power 88.56va apparent power 89.232va 0.75 load type: small capacitive load (after compensation) proposed apfc system value digital power meter value % error voltage 227v voltage 229.7v 1.17 current 0.36a current 0.37a 2.70 pf 0.97 pf 1.00 3.0 active power 78.98w active power 84w 5.97 reactive power 13.87var reactive power 12.92var 7.35 apparent power 80.19va apparent power 84.989va 5.64 table v. measurements for big capacitive load load type: big capacitive load (before compensation) proposed apfc system value digital power meter value % error voltage 228.51v voltage 229.9v 0.60 current 0.61a current 0.63a 3.17 pf 0.68 pf 0.68 0 active power 95.22w active power 99w 3.81 reactive power 102.02var reactive power 105.71var 3.49 apparent power 139.55va apparent power 144.83va 3.64 load type: big capacitive load (after compensation) proposed apfc system value digital power meter value % error voltage 228.4v voltage 230.9v 1.08 current 0.49a current 0.51a 3.92 pf 0.97 pf 0.99 2.02 active power 108.87w active power 116w 6.14 reactive power 21.84var reactive power 20.27var 7.74 apparent power 111.04va apparent power 117.759va 5.70 the maximum voltage measurement error before/after compensation is 1.08%. the errors for the current measurements before and after compensation remain around 3.17% and 3.92%. the error of the power measurements before and after compensation is between 3.49% and 7.74%. when the compensation function is activated, the apfc system connects one 1.01h inductance to the load to improve the pf from 0.68 leading to 0.97 leading. in this case study, it is verified that the measurements taken from the apfc system engineering, technology & applied science research vol. 10, no. 6, 2020, 6515-6520 6520 www.etasr.com rija et al.: microcontroller based automatic power factor correction for single-phase lagging … have a maximum error rate of 7.74% and the pfs of the capacitive loads with different sizes are effectively increased to be close to unity. vi. conclusion in this study, a single-phase automatic power factor correction system based on the arduino 2560 microcontroller has been proposed and experimentally implemented. this system is capable of correcting the power factor of lagging and leading loads. moreover, the system can also measure many electrical parameters of single-phase loads such as the rms voltage, the rms current, the pf and its type, active, the 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[12] w. qin, p. wang, x. han, and x. du, "reactive power aspects in reliability assessment of power systems," ieee transactions on power systems, vol. 26, no. 1, pp. 85–92, feb. 2011, https://doi.org/ 10.1109/tpwrs.2010.2050788. [13] p. n. ekemezie, "design of a power factor correction ac-dc converter," in africon 2007, windhoek, south africa, sep. 2007, pp. 1–8, https://doi.org/10.1109/afrcon.2007.4401519. engineering, technology & applied science research vol. 7, no. 6, 2017, 2139-2146 2139 www.etasr.com veladi and najafi: effect of standard no. 2800 rules for moment resisting frames on the elastic … effect of standard no. 2800 rules for moment resisting frames on the elastic and inelastic behavior of dual steel systems hedayat veladi department of structural engineering faculty of civil engineering university of tabriz tabriz, iran hamideh najafi department of structural engineering faculty of civil engineering university of tabriz tabriz, iran abstract—according to most valid design codes including the iranian seismic design code (standard no. 2800), moment resisting frames in dual systems must have the ability of resisting the 25% of the total lateral load of the dual system independently. this study is conducted to investigate the implementation of this rule for dual steel structures with two types of steel braced frame. also, its effect on the strength of the structure and the distribution of lateral load between the frames and the bracing system is evaluated. in order to investigate the effect of that rule, structural models with 5, 10 and 15 floors are modeled. nonlinear static analysis is employed and results are discussed. following the standard no. 2008 seems to increase the structure’s lateral resistance and decrease the number of elements entered into the inelastic behavior stage. in general, the structure has a more desirable inelastic behavior. keywords-dual system; moment resisting frame; bracing system; lateral resistance; non-linear analysis i. introduction a dual system is defined as a structure which resists horizontal loads by a combination of shear wall and rigid frames or, in the case of steel structures, by braced frames and rigid frames. previously, in the traditional design of dual structures, it was assumed that the bracing systems resisted all lateral loads and the frames were designed considering only the gravity loads. when a dual structure is loaded laterally, the horizontal interaction is due to the different free deflection forms of the walls and frames. so, the individual distribution of lateral loading on the bracing system and the frame may be very different from the distribution of lateral loading. the affectivity of a dual structure depends on the amount of horizontal interaction, which is influenced by the relative stiffness of the bracing system and the height of the structure [1]. recent studies show that the characteristics of the moment resisting frame in the dual system are of the most important factors affecting interaction [2]. in dual systems, the braced frame (bf) is named the primary system and the moment resisting frame (mrf) is named the secondary or backup system. actually, the mrf intends to provide a secondary supply of strength and energy dissipation for the dual system and also acts as a secondary line of defense against damage caused by severe earthquakes. experimental studies have shown that mrfs are assumed as the first system after failing the bfs [3-4]. researchers have proposed a variety of different methods for analyzing dual structures. each of these methods is based on different assumptions and models. authors in [5] presented a numerical and iterative method to analyze a dual structure. this method of converging approximations provides a solution that can be carried to any degree of refinement by increasing the number of cycles until the desired result is attained. the proposed numerical solution requires no simplifying assumptions of the structural behavior of configurations that are not checked during some steps of the analysis. in this method, analysis has been performed in two steps. in the first step, the deflected shape and amount of lateral load distributed to bf and mrf have been determined at each floor. the second step of analysis has been performed by subjecting isolated bend to the deflection pattern derived from the iteration solution for the entire structure. authors in [6] obtained the differential equations of a dual system with uniform stiffness along the height. they derived closed-form solutions to the lateral deformations, bending moment and shear forces for cases subjected to uniform or triangular static lateral load distributions. authors in [7] presented an approximate method for the sway estimation of dual buildings. the results were similar to those from stiffness matrix analysis for a building uniform in height. authors in [8] presented another concept to increase the lateral stiffness of dual tall building structures by stiffening the floor of the frame system either at the top or at an intermediately optimized level. the shear rigidity of the frame system is increased in floor level by infilling one or more bays of the frames in floor with concrete or masonry panel or adding bracing to the floor or increasing the size of the columns and girders surrounding it. this concept is simple, easy to apply and it can reduce the top deflection and increase the lateral stiffness of a dual structure by a large magnitude. authors in [9] presented a method to derive the governing equations of the dual structure with outriggers formulated through the continuum approach. in this method, the whole structure has been idealized as a shearengineering, technology & applied science research vol. 7, no. 6, 2017, 2139-2146 2140 www.etasr.com veladi and najafi: effect of standard no. 2800 rules for moment resisting frames on the elastic … flexural cantilever with rotational springs. the effects of shear deformation and flexural deformation of the dual system and outriggers trusses have been regarded and incorporated in the formulation of the governing equations. this method is relatively simple and efficient and provides reasonably accurate results in the early design stage of tall building structures. authors in [10] presented a simple analytical method based on a continuum model. this method evaluated the sway of dual building subjected to various types of lateral loads. limited floor drifts can be controlled by this method. a stability index equation without sway terms was determined by using the developed analytical expressions. additionally, dual structure interaction can be modeled simply and the moment at the base level can be computed. authors in [11] studied the significance of 25% design requirement for the secondary moment frames in dual systems with consideration of current structural practice. results of this study displayed that a secondary moment frame designed to resist less than 25% of seismic demand may be adequate for consideration as a dual system regardless of the 25% rule. authors in [12] investigated the performance of dual structures. their analysis indicated that adding special moment resisting frame (smrf) to the buckling restrained braced frame (brbf) system changes the natural period slightly and provides the optimum stiffness proportion for dual systems. also, based on the findings of this research, it was proposed to perform nonlinear analysis for predicting deficiencies related to inherent differences of behavior of the two systems, since this deficiencies cannot be predicted and recognized in linear static analysis. authors in [13] evaluated the stiffness limit value required for the secondary system for brbf and smrf dual systems. this study indicated that the suitable stiffness combination ratio is obtained when the brbf and smrf subsystems are 65% and 35% of the total stiffness respectively. also, implementation of the suitable relative stiffness leads to a uniform plasticity profile in the height of structures. since shear distribution between bf and mrf in a dual structure is important, valid codes including asce 7 [14] and iranian seismic design code (standard no. 2800) [15] have specified special criteria for dual structures. according to standard no. 2800, mrf must be able to resist at least 25% of the required lateral load independently. this study is conducted to investigate the effect of the considering lateral load bearing of mrf in the dual system. in other words, the structures with mrf resistance of 25% of lateral load independently are compared with structures without implementation of this rule. additionally, the results are compared in elastic and inelastic behavior stages. ii. modeling hypothesis and analysis the models used in this paper are of dual structures (steel moment resisting frame and steel bracing system) with 5, 10 and 15 floors. each frame has three panels of which the middle panel is braced with two types of x and inverted v bracing systems. the length of each panel in frames is 5 m and the height of stories is 3.2 m. scale modeling of the 5 floor structure with x and inverted v bracing system are shown in figure 1. supports are fixed and bf and mrf existing in the dual system are medium ductility moment resisting frame and bracing system. plan of structures in both main orthogonal directions is assumed symmetric, therefore models are considered 2d. according to asce7 [14], dead and live gravity load at stories and roof are considered as 500 kg/m2 and 200 kg/m2, respectively. partition load is assumed to be 100 kg/m2 which is added to the dead load of stories. the steel used is mild steel with yield strength of fy = 2400 kg/m 2, ultimate strength of fu = 3700 kg/m 2, young's module of e = 2 x 10 6 kg/m2 and poisson's ratio of 0.3. the seismic load was calculated by equivalent static seismic load method according to the iranian seismic design code (standard no. 2800). models are assumed in regions with high seismicity level with design base acceleration (a) equal to 0.35 and moderate importance with an importance factor of 1.0. it was assumed that structures are located on type 2 soil. in order to control the lateral load bearing of mrf in dual structures, in calculating of seismic load, the building behavior factor (r) was considered to be 7.0 which is the building behavior factor of intermediate ductility, steel moment resisting frame and steel concentric braced frame. frames are analyzed and designed by the allowable stress design (asd) method according to aiscasd 89 [16]. cross section of beams, columns and braces are selected ipe, ipb and box profiles, respectively. iii. lateral load bearing of mrf according to rule 1-9-4 of the standard no. 2800, the following criteria are specified for dual structure: a) an essentially complete space frame that provides support for gravity loads. b) resistance of the lateral load is provided by shear walls or braced frames and moment resisting frames. floor shear for each group at each floor is evaluated according to their lateral stiffness. c) moment resisting frame shall be capable of carrying at least 25% of the design base shear, independently. note: when a system fails to conform to criterion (c), the system shall be classified as a building frame system. according to the above-mentioned requirements, in order to evaluate the lateral load bearing of mrf, structures were analyzed and designed in two cases. in the first case, gravity and seismic loads were applied on mrf and bf at the same time. in other words, rule 1-9-4 was not applied (model (a)). in the second case, rule 1-9-4 was not applied (model (b)). dual structures were modeled and analyzed in two steps. at first, elastic design and analysis were performed using etabs2000 software and then, nonlinear static analysis was performed using the sap2000 software. in order to control lateral load bearing of mrf, it was needed to increase and strengthen the cross section of some beams and columns; therefore assigned cross sections were bigger in the second model. iv. member sections of models tables i-vi present member sections of structures with xbracing system for both models, (a) and (b). in case (b) some beams and columns have sections bigger than the model (a) because of the bearing of 25% of seismic loads independently by mrf. engineering, technology & applied science research vol. 7, no. 6, 2017, 2139-2146 2141 www.etasr.com veladi and najafi: effect of standard no. 2800 rules for moment resisting frames on the elastic … table i. (a): members cross section 5 floor structure x brace brace side beam middle beam side column middle column story box90x90x10 ipe300 ipe300 ipb160 ipb240 1 box90x90x10 ipe300 ipe300 ipb160 ipb200 2 box90x90x7.1 ipe300 ipe300 ipb160 ipb16 3 box80x80x8 ipe300 ipe300 ipb140 ipb140 4 box70x70x5.9 ipe300 ipe300 ipb140 ipb120 5 table ii. (a): members cross section 10 floor structure x brace brace side beam middle beam side column middle column story box100x100x14.2 ipe330 ipe300 ipb220 ipb550 1 box100x100x12.5 ipe330 ipe300 ipb220 ipb400 2 box100x100x10 ipe330 ipe300 ipb200 ipb360 3 box100x100x10 ipe300 ipe300 ipb200 ipb280 4 box100x100x7.1 ipe300 ipe270 ipb200 ipb260 5 box100x100x7.1 ipe300 ipe270 ipb200 ipb220 6 box90x90x8 ipe300 ipe270 ipb180 ipb180 7 box90x90x5.9 ipe300 ipe270 ipb180 ipb160 8 box80x80x5.4 ipe300 ipe270 ipb140 ipb140 9 box70x70x4.5 ipe300 ipe270 ipb140 ipb120 10 table iii. (a): members cross section 15 floor structure x brace brace side beam middle beam side column middle column story box100x100x14.2 ipe360 ipe300 ipb320 ipb1000 1 box100x100x14.2 ipe360 ipe300 ipb320 ipb900 2 box100x100x14.2 ipe360 ipe300 ipb280 ipb800 3 box100x100x12.5 ipe360 ipe300 ipb260 ipb600 4 box100x100x12.5 ipe360 ipe300 ipb260 ipb450 5 box100x100x10 ipe330 ipe300 ipb240 ipb400 6 box100x100x10 ipe330 ipe300 ipb240 ipb340 7 box100x100x8 ipe330 ipe300 ipb240 ipb300 8 box90x90x10 ipe330 ipe300 ipb240 ipb280 9 box90x90x8 ipe300 ipe300 ipb220 ipb240 10 box90x90x7.1 ipe300 ipe300 ipb220 ipb220 11 box90x90x5.9 ipe300 ipe300 ipb200 ipb200 12 box80x80x7.1 ipe300 ipe300 ipb180 ipb180 13 box80x80x4.5 ipe300 ipe300 ipb160 ipb160 14 box60x60x5 ipe300 ipe300 ipb140 ipb120 15 table iv. (b): members cross section 5 floor structure x brace brace side beam middle beam side column middle column story box90x90x10 ipe330 ipe300 ipb200 ipb240 1 box90x90x10 ipe300 ipe300 ipb160 ipb200 2 box90x90x7.1 ipe300 ipe300 ipb160 ipb180 3 box80x80x8 ipe300 ipe300 ipb160 ipb160 4 box70x70x5.9 ipe300 ipe300 ipb140 ipb120 5 table v. (b): members cross section 10 floor structure x brace brace side beam middle beam side column middle column story box100x100x14.2 ipe330 ipe300 ipb240 ipb550 1 box100x100x12.5 ipe330 ipe300 ipb220 ipb400 2 box100x100x10 ipe330 ipe300 ipb220 ipb360 3 box100x100x10 ipe330 ipe300 ipb200 ipb280 4 box100x100x7.1 ipe330 ipe300 ipb200 ipb260 5 box100x100x7.1 ipe330 ipe300 ipb200 ipb220 6 box90x90x8 ipe330 ipe300 ipb200 ipb180 7 box90x90x5.9 ipe330 ipe300 ipb180 ipb160 8 box80x80x5.4 ipe330 ipe300 ipb140 ipb140 9 box70x70x4.5 ipe300 ipe300 ipb140 ipb120 10 table vi. (b): members cross section 15 floor structure x brace brace side beam middle beam side column middle column story box100x100x14.2 ipe360 ipe330 ipb320 ipb1000 1 box100x100x14.2 ipe360 ipe330 ipb320 ipb900 2 box100x100x14.2 ipe360 ipe330 ipb280 ipb800 3 box100x100x12.5 ipe360 ipe330 ipb260 ipb650 4 box100x100x12.5 ipe360 ipe330 ipb260 ipb500 5 box100x100x10 ipe360 ipe330 ipb260 ipb400 6 box100x100x10 ipe360 ipe330 ipb240 ipb340 7 box100x100x8 ipe360 ipe300 ipb240 ipb300 8 box90x90x10 ipe330 ipe300 ipb240 ipb280 9 box90x90x8 ipe300 ipe300 ipb220 ipb240 10 box90x90x7.1 ipe300 ipe300 ipb220 ipb220 11 box90x90x5.9 ipe300 ipe300 ipb200 ipb200 12 box80x80x7.1 ipe300 ipe300 ipb180 ipb180 13 box80x80x4.5 ipe300 ipe300 ipb160 ipb160 14 box60x60x5 ipe300 ipe300 ipb140 ipb120 15 v. non-linear modeling of structures fema-356 [17] was used to perform the nonlinear static analysis. the designing procedure in fema is based on performance levels. building performance is a combination of the performance of both structural and nonstructural components; therefore, performance levels are defined according to structural and non-structural damages. the structural performance level of building shall be selected from three discrete structural performance levels. the discrete structural performance levels are immediate occupancy (io), life safety (ls) and collapse prevention (cp). io structural performance level means the post-earthquake damage state in which only very limited structural damage has occurred. the basic vertical and lateral force resisting system retain nearly all of their pre-earthquake strength and stiffness. ls structural performance level means the post-earthquake damage state in which significant damage to the structure has occurred. some structural elements are severely damaged but this has not resulted in large falling debris hazards. cp structural performance level means the post-earthquake damage state in which the building is on the verge of partial or total collapse. substantial damage to the structure has occurred, potentially including significant degradation in the stiffness and strength of the lateral force resisting system and large permanent lateral deformation of the structure [17]. criteria of performance level shall be selected in accordance with primary and secondary elements. it should be mentioned that in the considered structures, only beams, columns and braces were modeled; therefore the conducted non-linear static analysis was considered as simplified analysis and acceptance criteria were selected in accordance with primary elements. a target displacement is a characteristic displacement in the structure that serves as an estimate of the global displacement experienced by the structure. in this paper target displacement, δt, at each floor level calculated according to (1) which has been provided by fema-356: 2 0 1 2 3 24 e t a t c c c c s g   (1) where: engineering, technology & applied science research vol. 7, no. 6, 2017, 2139-2146 2142 www.etasr.com veladi and najafi: effect of standard no. 2800 rules for moment resisting frames on the elastic …  c0=modification factor to relate spectral displacement of an equivalent sdof system to the roof displacement of the building mdof system.  c1=modification factor to relate expected maximum inelastic displacement to displacement for the linear elastic response.  c2=modification factor to represent the effect of pinched hysteretic shape, stiffness degradation and strength deterioration on maximum displacement response.  c3=modification factor to represent increased displacement due to dynamic p-∆ effects.  sa=response spectrum acceleration, at the effective fundamental period and damping ratio of the building.  g=acceleration of gravity  te=effective fundamental period of the building in the direction under consideration, sec. the multi-linear curve was used in order to simplify the behavior of members. multi-linear curves used in sap2000 software and fema-356 are shown in figures 2 and 3. in other words, behavior diagram of “plastic force-displacement” and “plastic moment-rotation” has been defined for each degree of freedom of force or moment. it should be mentioned that the slope of strain hardening (slope from b to c) was considered 3%, according to fema. in non-linear behavior modeling of structure, which have been provided by femas-356 "deformation controlled components" expected yield and ultimate strength of steel were calculated according to (2) and (3): 1.1ye yf f (2) 1.1 ue uf f (3) where:  fye=expected yield strength  fyu=expected ultimate strength  fy=yield strength  fu=ultimate strength since the connection of beams and columns is fixed and also because of that the gravity load is not much, plastic hinges have been assigned at the two ends of these members. so, plastic hinges approximately have been extended by the length equal to the depth of the member’s cross section. therefore, plastic hinges have been considered at relative distances of 0.05 and 0.95 of element lengths. vi. results of linear static analysis a. shear distribution between mrf and bf figures 4 and 5 show the share of x and inverted v bracing system from floor shear for both models (a) and (b) in each floor. it is observed that the share of floor shear in a bracing system generally has decreased at the model (b). it is due to strengthening mrf in model (b), that the bracing system has not changed. it is noted that, due to the increase of weight in model (b), base shear in this case is increased. at the structure with the x-bracing system, the share of mrf from the base shear, in models (a) and (b) at 5-floors structure are 9% and 11.2%, at a 10-floors structure 21.7% and 22.2% and at a 15floors structure are 35.8% and 36.8% respectively. also, these values at the structure with the inverted v bracing system in the case of 5-floors structure are 4.5% and 5.1%, at 10-floors structure are 15.4% and 16% and at 15-floors structure are 32.3% and 32.7%, respectively. it is observed that by increasing the number of stories, the share of mrf from base and story shear has increased. fig. 1. scale modeling of 5 story structure with x and inverted v bracing system. fig. 2. fema multi-linear curve. fig. 3. sap2000 software multi-linear curve. b. effect of bracing system type in figure 6, the share of x and inverted v bracing system from the floor shear has been shown for the model (b). a structure with the x-bracing system is called x and with the inverted v bracing system is called in v. it was observed that in all cases an increase in the floor number leads to increase in the share of mrf from the share force, especially in higher stories. in general, the share of mrf from floor and base shear in the structure with the x bracing system is larger than in the structure with the inverted v bracing system. additionally, in both structures, much of the base shear is resisted by the bracing system. engineering, technology & applied science research vol. 7, no. 6, 2017, 2139-2146 2143 www.etasr.com veladi and najafi: effect of standard no. 2800 rules for moment resisting frames on the elastic … fig. 4. share of x bracing system from floor shear in linear static analysis (shear force of the bracing system to floor shear (%)). fig. 5. share of inverted v bracing system from floor shear in linear static analysis (shear force of the bracing system to story shear (%)). fig. 6. share of x and inverted v bracing system from floor shear in linear static analysis (model (b)) (shear force of the bracing system to story shear (%)). vii. results of non-linear static analysis a. pushover curves of structures according to fema-356 guideline in the non-linear static analysis, the seismic load was applied with two triangular and uniform lateral load patterns on structures. in all of the models, triangular lateral load pattern (appropriate with the lateral load in the linear static analysis) was the critical pattern and so it was used. the pushover curve of 5, 10 and 15 floor structures with x and inverted v bracing systems have been shown in figures 7-12. generally, the capacity of structure in the model (b) has been increased in comparison with model (a). b. maximum base shear maximum base shear of 5, 10, and 15 floor structures with two types of bracing system have been presented in tables vii and viii. as it is observed in the tables, generally amounts of base shear have increased in the model (b) due to the strengthening of beams and columns. fig. 7. pushover curve of 5 floor structure (x brace). fig. 8. pushover curve of 10 floor structure (x brace). engineering, technology & applied science research vol. 7, no. 6, 2017, 2139-2146 2144 www.etasr.com veladi and najafi: effect of standard no. 2800 rules for moment resisting frames on the elastic … fig. 9. pushover curve of 15 floor structure (x brace). fig. 10. pushover curve of 5 floor structure (v brace). fig. 11. pushover curve of 10 floor model (v brace). fig. 12. pushover curve of 15 floor model (v brace). table vii. maximum base shear of structures with x bracing system floor maximum base shear (ton) relative difference b to a a b 5 88.95 78.54 -11.7 10 97.38 109.63 12.6 15 131.88 136.04 3.2 table viii. maximum base shear of structures with inverted v bracing system floor maximum base shear (ton) relative difference b to a a b 5 61.51 62.24 1.2 10 91.43 95.13 4 15 103.19 105.98 2.7 c. formation process and distribution of plastic hinges the formation process and the distribution of plastic hinges have an important effect in seismic design. therefore, formation and distribution of plastic hinges were evaluated for 5, 10, and 15-floor structures for both models (a) and (b). it was observed that model (b) has fewer elements entering an inelastic behavior stage compared to model (a) and less plastic hinges formed. also, these plastic hinges have formed in later time step. in addition, by the strengthening of the mrf in model (b), less plastic hinges have formed in beams and columns and plastic hinges mostly were formed in braces. d. structural performance level of models the number of plastic hinges at different performance levels has been summarized in tables ix and x for both types of bracing systems. at both b to io and io to ls performance levels, it is observed that the number of plastic hinges for model (b) is generally lower, so it can be said that model (b) has a more desirable nonlinear behavior. it is worth noting that the reduction of hinges is larger for inverted v bracing systems compared to x bracing systems. at the ls to cp performance level, there have not been any plastic hinges in the structures with inverted v bracing and the structures remained at the ls performance level; whereas the number of plastic hinges has decreased and increased respectively in the 10 and 15 floor buildings of model (b) with the x bracing system. generally, it can be concluded that model (b) has better performance level in all cases. the coordination of the performance point of structures obtained from fema365 and sap2000 has been presented in tables xi and xii. table ix. number of plastic hinges at different performance level (x bracing system) performance level 5 floor structure 10 floor structure 15 floor structure a b a b a b a to b 58 60 108 119 178 174 b to io 9 6 22 17 32 29 io to ls 1 2 14 5 27 24 ls to cp 0 0 3 2 2 7 cp to c 2 2 4 2 0 4 c to d 0 0 0 0 0 0 d to e 10 10 9 15 1 2 table x. number of plastic hinges at different performance levels ( inverted v bracing system) performance level 5 floor structure 10 floor structure 15 floor structure a b a b a b a to b 70 76 146 149 208 232 b to io 8 2 4 6 27 2 io to ls 1 1 6 4 4 5 ls to cp 0 0 0 0 0 0 cp to c 0 0 0 0 0 0 c to d 0 0 0 0 0 0 d to e 1 1 2 1 1 1 engineering, technology & applied science research vol. 7, no. 6, 2017, 2139-2146 2145 www.etasr.com veladi and najafi: effect of standard no. 2800 rules for moment resisting frames on the elastic … e. share of bracing system from shear force in nonlinear static analysis shares of the bracing system from the floor shear of the structure with both types of bracing system in models (a) and (b) are shown in figures 13 and 14. diagrams are presented at the maximum base shear step. it is observed that in model (b) with both types of bracing system, the share of the bracing system has decreased in the 5 and 10-floor structures but in the 15-floor structure it has fairly increased in some floors. at the base level, the share of mrf in models (a) and (b) in the 5floor structure with the x-bracing system are 13.4% and 23.4%, in the 10-floor structure are 19.4% and 19.8% and in the 15-floor structure are 36% and 50%, respectively. also, these values at the structure with the inverted v bracing system in case of the 10-floor structure are 7.2% and 6.3%, at 10-floor structure are 18.5% and 19.5% and at 15-floor structure are 39.7% and 40%, respectively. comparison of non-linear and linear static analysis showed some differences between the base shear resisted by mrf in the structure with two types of bracing systems in elastic and inelastic stages. table xi. the coordination of the performance point of structures at pushover curve (x bracing system) floors model point of (v,d) 5 a (70,10) b (65.4,7) 10 a (93,15) b (105,15) 15 a (117.6,25) b (118.2,25) table xii. the coordination of the performance point of structures at pushover curve (inverted v bracing system) floors model point of (v,d) 5 a (43,6) b (55.5,7) 10 a (68,14) b (75.12) 15 a (83,23) b (97,23) fig. 13. share of x bracing system from floor shear in nonlinear static analysis (shear force of the bracing system to floor shear (%)). fig. 14. share of inverted v bracing system from floor shear in nonlinear static analysis (shear force of the bracing system to floor shear (%)). viii. conclusion this study is conducted to investigate the implementation of rule 1-9-4 of the iranian seismic design code (standard no. 2800) over dual steel structures by two types of steel braced frame. the effect of this rule was evaluated for resistance of the structure and distribution of lateral load between mrf and bracing system. for this purpose, 5, 10, and 15-floor frames with two types of x and inverted v bracing system were modeled and analyzed. the structures were modeled and analyzed in two cases ((a) and (b)) by not following and following the standard no. 2800. results of non-linear static analysis showed that the structure capacity in model (b) generally has increased and the model (b) has better a performance level and thus a more desirable nonlinear behavior. the distribution of lateral force between the mrf and the bracing system was different in linear and non-linear static analysis. furthermore, the distribution of lateral force is changed between mrf and bracing system in model (b). the investigation of plastic hinges formed showed that following the standard no. 2008 leads to fewer elements entering the inelastic stage. in other words, less plastic hinges are formed in beams and columns and the formation of hinges is observed mostly in the bracing system. engineering, technology & applied science research vol. 7, no. 6, 2017, 2139-2146 2146 www.etasr.com veladi and najafi: effect of standard no. 2800 rules for moment resisting frames on the elastic … references [1] b. stafford smith, a. coull, tall building structures: analysis and design, wiley, 1991 [2] a. s. whittaker, c. m. uang, v. v. bertero, an experimental study of the behavior of dual steel systems, university of california, berkeley, 1990 [3] a. k. jain, r. g. redwood, f. lu, “seismic response of concentrically braced dual steel frames”, canadian journal of civil engineering, vol. 20, no. 1, pp. 672-687, 1993 [4] f. a. charney, v. v. bertero, an evaluation of the design and analytical seismic response of a seven-storey reinforced concrete frame-wall structure, university 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applications”, the structural design of tall and special buildings, vol. 22, no. 15, pp. 1156–1172, 2013 [11] l. j. aukeman, p. laursen, “evaluation of the asce7-05 standard for dual systems: response historey analysis of a tall buckling-restrained braced frame dual systems”, structure congress, pp. 2707-2717, 2011 [12] a. mehdipanah, s. r. mirghaderi, s. a. razavi, “evaluation of seismic behavior of buckling restrained braced frames as dual system in combination with special moment restring frames”, 15th world conferences on earthquake engineering, 2012 [13] a. mehdipanah, s. r. mirghaderi, s. a. razavi, “seismic performance of stiffness-based designed buckling-restrained braced frame and special moment-resisting frame dual systems”, structure and infastructure engineering, vol. 12, no. 8, pp. 918-935, 2016 [14] american society of civil elilgineers, asce7-05, minimum design loads for building and other structures, asce, 2005 [15] permanent committee of revising the code of practice for seismic resistant design of buildings, iranian code of practice for seismic resistant design of building (standard no. 2800), 3rd edition, building & housing research center, 2007 [16] american institute of steel construction, specification for structural steel buildings: allowable stress design and plastic design, aisc, 1989 [17] federal emergency management agency, prestandard and commentary for the seismic rehabilitation of buildings, asce, 2000 microsoft word 35-2529_s1 engineering, technology & applied science research vol. 9, no. 1, 2019, 3852-3858 3852 www.etasr.com shahbaz et al.: identification, assessment and mitigation of environment side risks for malaysian … identification, assessment and mitigation of environment side risks for malaysian manufacturing muhammad saeed shahbaz faculty of technology management and business, universiti tun hussein onn malaysia, batu pahat, johor, malaysia msaeed.shahbaz@gmail.com abdul ghafoor kazi department of management science, shaheed zulfiqar ali bhutto institute of science and technology, hyderabad, sindh, pakistan agkazi78@gmail.com bestoon othman erbil polytechnic university, iraq, and faculty of technology management and business, universiti tun hussein onn malaysia, malaysia bestoon2011@yahoo.com mudaser javaid faculty of technology management and business, universiti tun hussein onn malaysia, batu pahat, johor, malaysia mudaserjavaid@gmail.com khawar hussain faculty of technology management and business, universiti tun hussein onn malaysia, batu pahat, johor, malaysia khawarpm786@gmail.com raja zuraidah r. m. rasi faculty of technology management and business, universiti tun hussein onn malaysia, batu pahat, johor, malaysia rzuraidah@uthm.edu.my abstract—malaysia has faced many supply chain issues that not only have affected enterprises but also the overall economy. natural disasters that badly affect the performance of malaysian enterprises strongly demand a comprehensive investigation of supply chain risks. effective mitigation strategy can only be operationalized when risks are appropriately identified and assessed. supply chain collaboration has been verified to have a positive impact on the performance but only a limited number of studies investigate it as a risk mitigation tool. the current study presents a guiding framework for identification, assessment, and migration of environment side risks for malaysian manufacturing. a questionnaire has been developed and distributed by systemic probability sampling. data have been collected from the federation of manufacturing malaysia through an online survey. the data were purified from missing values and outliers and were analyzed through structural equational modeling through smart pls. a total of nine environment side risks were identified. in risk assessment, it has been found that an environment side risk has negative effects on supply chain performance. while these risks can be mitigated through supply chain collaboration, they cannot be mitigated completely. this study will help managers to understand how environment side risks are affecting enterprise performance and how they can avoid these risks. this study covers only environment side risks while future research can be on operational risks and various other approaches that can be proposed for mitigation. keywords-environment risks; supply chain; supply chain performance i. introduction any disruption, either natural or unnatural, has become the highest risk for business [1-3]. about 67% of managers agree that risk management is more important than before and 89% of companies accept that after financial crises their main concern is natural disasters [2]. in [1], it has been revealed that political uncertainties, natural disasters, and economic issues are among top risks. the last few decades the supply chain (sc) has gained notable attention due to globalization [4]. there are many examples that prove the value of sc risk management (scrm), like a fire in new mexico electronic chip manufacturing plant stopped the supplying to ericsson and, as a result, the company bared a loss of $2.34 billion [5]. among the operation management fields, production inventory and sc management are considered the most studied research areas [6]. malaysia has faced many sc issues that not only affect the enterprises, but also the overall economy, e.g. the 2008 airport closure in thailand [1], maritime piracy in the straits of malacca [7], delays in physical distribution in electronic and electric industry [8], rapid technological changes [9], increased outsourcing, product variation and suppliers’ defaults [10], oil prices, china economic slowdown and foreign capital outflow [11], natural hazards causing disasters like the loss of malaysia airlines 370, the devastation of malaysia airline over ukraine, and floods [12] and the operation blocking by greenpeace of the malaysian palm oil company ioi, world’s largest palm oil producer and trader, because of forest demolition and child labor [13]. from the sc viewpoint, these disruptions not only affect organizational performance but also disturb the other sc elements. it can be concluded that natural disasters demand a comprehensive investigation of sc risks. effective mitigation strategy can only be operationalized when risk is appropriately identified and assessed. meanwhile, sc collaboration has been verified to have positive impact on performance, but only a corresponding author: m. s. shahbaz engineering, technology & applied science research vol. 9, no. 1, 2019, 3852-3858 3853 www.etasr.com shahbaz et al.: identification, assessment and mitigation of environment side risks for malaysian … limited number of studies investigate it as a risk mitigation tool. the current study proposes a guiding framework for identification, assessment, and mitigation of environment side risks for malaysian manufacturing. ii. literature review a. supply chain risk management (scrm) scrm is vast in its objectives and has become more complex [14]. there is no clear definition of scrm [15-17]. this study adopts the definition of scrm as “the identification and management of risks for the supply chain, through a coordinated approach amongst supply chain members, to reduce supply chain vulnerability as a whole” [18] for several reasons. first, this definition covers all processes of scrm, second, this study aims to reduce vulnerability as a whole that means it focuses on the whole sc and all its members, not an organization only. third, this definition proposed coordination among members as a mitigation strategy that is the current study’s suggestion. last, this definition conceptualizes the sc risks as does the current study. b. risks identification effective risk management can only be made possible if risks are properly identified, whether it is dealing with quality or safety challenges, supply shortages, legal issues, security problems, regulatory and environmental compliance, natural disasters, or terrorism. risk sources are “any variables which cannot be predicted with certainty and from which disruptions can emerge” [19]. risk sources have become more essential as sc becomes more complex and modern. scrm can be categorized according to its risk sources [20]. authors in [9] revealed that the main function of scrm is to identify the potential risk sources. authors in [21] studied 90 articles on sc risk sources and concluded that 25% of articles used only supply side risks and very few applied disruption risks. this study follows the criteria of [22] and generates a pool of items, then by pretesting, pilot testing, and exploratory factor analysis purifies the items. c. environment side risks environment side risks have low probability but high consequences [23]. natural disasters create hurdles in operations [24]. it has been mentioned above that nature can disrupt not only one enterprise but also the whole sc system. fires in forests and peat have become a global threat. smokes from these fires killed about 110000 humans in southeast asia and caused huge global warming through carbon emissions [25]. in some countries, regulations are a big hurdle in starting a business or operate it effectively. administrative decisions sometimes can affect the performance badly [26] as do regulatory laws [27]. according to [28], any change in the political environment due to new laws or modifications in the old ones causes disruption in sc operations and may increase cost or even sometimes halt production. it has been proved that regulation disruptions reduce shareholder’s wealth by 3.8% [28]. environment side risks categories are political instability, macroeconomic uncertainties, social uncertainties, natural uncertainties like diseases or epidemics, natural disasters, and terror attacks [27]. d. assessment it has been proved that environment side risks affect performance [29-31]. relevant studies have been done in other regions, but now there is severe need to apply scrm in malaysia. the importance of environment side risks can be realized from the example of the malaysian palm oil company ioi incident mentioned above [13]. it has been found that environment side risks have variation in effects, some studies found significant effects while some did not. based on the literature review the below hypothesis has been developed to assess the environment side risks: h1: environment side risks have negative effects on supply chain performance for malaysian manufacturing. e. supply chain performance (scp) deciding for an appropriate combination of performance indicators for measuring scp is always challenging [32]. performance measures should have some characteristics like sustainability, relevance, effectiveness, coherence, efficiency, and robustness [33]. risk sources in sc, and risk mitigation approaches have been adapted from different studies, in which multiple ways were used to measure performance. the current study adopts the indicators of performance measure from [34], which are product quality, order fill capacity, delivery dependability, delivery speed and customer satisfaction as mentioned in table i. in [34], risk sources and collaboration that affect performance are discussed. the numerous problems of current performance measures and their solutions in detail are discussed. so, [34] is the closest, most updated and comprehensive relevant study, to the best of our knowledge, so that is why this study adopts indicators from there. table i. descriptive information business incorporation no. of respondents (%) private limited 219 64 public limited 66 20 partnership 38 11 sole proprietorship 19 1 employee experience (years) 1-5 161 48 6-10 90 26 11-15 56 16 16-20 24 1 21 and more 11 1 departmental position purchase 34 11 logistic/supply chain 40 12 production and operation 64 19 sales and distribution 71 21 finance/hr/it 70 21 general managers (director, ceo etc.) 58 14 f. mitigation after a clear understanding of risk, the enterprise needs to take appropriate measures to mitigate it. scrm practices cover a set of approaches and strategies that effectively and efficiently integrate stakeholders to improve sc and overall business performance [35]. there are numerous approaches to deal with risks, deciding which one to adopt depends upon the situation [36]. according to [37], global sc risk mitigation engineering, technology & applied science research vol. 9, no. 1, 2019, 3852-3858 3854 www.etasr.com shahbaz et al.: identification, assessment and mitigation of environment side risks for malaysian … strategies are sc collaboration, excess of inventory and other sources, visibility system, redesign of network and product. authors in [38] summarize scrm approaches as take the risk (keep excess resources), share the risk (share it with partners), transfer the risk (agreements with suppliers to send all risk to them), reduce the risk (take measures to minimize the intensity of risks), eliminate the risk and monitor the risk (keep eyes on suppliers or any entity that can affect negatively). in [39], 6 sc mitigation strategies are presented: postponement, speculation, hedging, control, security and avoidance. the rapid growth in global sc requires interconnectedness among members. as a result, a high level of interdependency and complexity were developed in the sc [4, 31, 40]. empirical studies proved that sc collaboration increases performance [41, 42]. authors in [34] revealed that sc collaboration reduces risks. as an example the auto part supplier takata corp. is referred. in march 2006, one of its airbag production facilities was destroyed, but its customers did not face a disruption because takata’s competitors worked together in order to support its customers [43]. consequently, there are many studies available on sc mitigation approaches. this study is limited to the collaboration with suppliers and customers. currently, more organizations are depending on their fellows in a sc network, so the competition is not among organizations but among networks [7]. g. supply chain collaboration authors in [44] reported that currently organizations firmly need to employ collaboration with external partners to meet global challenges. authors in [45] describe the need for an explanation of the relationship among partners sc in sc collaboration. authors in [21] state an example of how japanese automobiles defeated u.s. industry. it is revealed that the only reason behind this success is the high dependability of external collaborative partners. according to a global survey, managers report that the most predominant and daunting risks to their supply chains are those controllable risks associated with the performance of their sc partners [46]. there is a strong bond between an organization’s information and joint planning with their stakeholders and organizational performance in risk mitigation [47]. collaboration with trading partners should be the main focus for better performance [48]. collaboration has improved approximately 23.7% of enterprises’ performance variability [49] and it explained 8.5% of organizations’ performance variability in malaysia [50]. conclusively, collaboration through information processing has become crucial in highly uncertain environments [51]. it has been revealed that 53% articles in sc consist of theoretical studies while the remaining are empirical or mixed. the majority of empirical studies consist of two major sectors: automobile and electronic. it can be concluded that there is a further need to elaborate on other sectors [52]. based on the literature review the following hypothesis has been developed h2: sc collaboration positively moderates the relationship between environment side risks (er) and scp. h. research framework figure 1 shows the proposed research framework based on the developed hypotheses. this framework consists of one independent variable (environment side risks) that has a negative effect on the dependent variable (scp) and one moderator (sc collaboration). it has been proposed that sc collaboration positively moderates the negative relationship between er and scp for malaysian manufacturing companies. fig. 1. research framework iii. research methodology this is an empirical investigation of the hypotheses. a questionnaire has been distributed by probabilistic systematic sampling to the registered manufacturing organizations in federation of manufacturing malaysia-2017. the total number of listed manufacturing enterprises is 2250 and by applying krejcie & morgan sampling technique the sample size should be 331 for 2400 population [53]. a questionnaire to 480 organizations was sent and after 2 reminders within one month, a total of 358 responses were received. the respondents were given 7 options (7-point likert scale) from strongly disagree to strongly agree for each question. meanwhile, scc measurements have been adopted from [21] (table iii). table ii. scp measurements [21] variable items supply chain performance quality (overall product or service quality) customer satisfaction order fill capacity (provision of desired quantities on a consistent basis) delivery speed (time between order and customer delivery) delivery dependability (anticipated delivery dates and quantities on a consistent basis) iv. results and discussion data have been analyzed through spss. at first, special codes have been assigned to all items and data have been put in an spss file. the second step was a manual screening of data, responses with high mission values and the same responses were deleted. furthermore, data have been cleaned from missing values and outliers. then, descriptive analysis has been performed with two demographics: industry related and employee related. the validity and reliability of the questionnaire have been assessed and lastly, the structural model has been evaluated by multiple regressions. a. descriptive information the studied population consists of business incorporations belonging to fmm 2017 and its descriptive information are shown in table i. most of the respondents (64%) are from private limited organizations. most of the respondents have less than 5 years of experience. the highest numbers of respondents are from sales, distribution, finance, hr, it, and production and operation. although the lowest number is from purchase, still it is enough for representation. engineering, technology & applied science research vol. 9, no. 1, 2019, 3852-3858 3855 www.etasr.com shahbaz et al.: identification, assessment and mitigation of environment side risks for malaysian … b. measurement model reliability and validity are crucial for the quality of any research [54]. this study calculated composite reliability, convergent validity, and discriminant validity to verify the measurement model. smart pls 3 has been used for reliability and validity. figure 2 shows the pls algorithm results for a direct relationship while figure 3 illustrates the pls bootstrapping for the direct model. moderation hierarchy analysis has been applied to assess mitigation. figure 4 explains the pls algorithm for the moderation model and figure 5 shows the pls bootstrapping for the moderation model. fig. 2. pls algorithm fig. 3. pls bootstrapping for the direct model fig. 4. pls algorithm for the moderation model fig. 5. pls bootstrapping for the moderation model the range of composite reliability is between 0 and 1, the higher the values, the higher the reliability. its threshold value is considered good at 0.70. composite reliability below 0.60 indicates a deficiency of internal consistency and above 0.90 is not required as it means that all the items are measuring the same phenomenon [55]. an ave value of 0.50 or higher indicates that the construct explains more than half of the variance of its indicators. while an ave of less than 0.50 indicates that more error remains in the items than the variance explained by the construct [55]. high factor loadings indicate convergence for a latent construct. average of all factor loadings should be statistically significant, a good rule is that standardized loading estimations should be at least 0.5 or higher and 0.7 or higher is considered ideal [56]. most of the researches prefer fornell-larcker criterion as a conservative approach [57]. it compares the square root of the ave values with the latent variable correlations. specifically, the square root of each construct's ave should be greater than its highest correlation with any other construct. table iii. factor loading item code items factor loading er1 policy uncertainty (changes in the political environment due to the introduction of new laws) 0.691 er5 non-availability of skilled manpower 0.827 er6 natural disasters (e.g. earthquake, tsunami) 0.866 er8 administrative barriers for the setup or operation of scs (e.g. authorizations) 0.513 er9 technological changes 0.910 scc 1 we and our key sc partners inform each other in advance of changing needs 0.723 scc 2 we include our key sc partners in our planning and goalsetting activities 0.683 scc 3 we and our key sc partners jointly work out solutions for main changes 0.704 scc 4 we facilitate our key sc partners’ ability to seek technical, operational, and financial assistance from us 0.666 scc 5 we allocate benefits fairly to our key sc partners 0.762 scc 6 we are willing to make adjustments with our sc partners 0.775 scc 7 we regularly solve problems jointly with our sc partners 0.675 table iv. validity and reliability constructs environmental side risks sc collaboration number of items 5 5 cronbach’s α 0.854 0.830 composite reliability 0.880 0.871 average variance extracted 0.602 0.577 table v. discriminant validity er scp er 0.776 scp 0.149 0.759 c. structural model this study applied smart pls to the examined coefficient of determination r 2 , standardized path (beta coefficient) and tstatistics. a standardized path value shows the strength of the relationship. if the value is negative this shows negative relationship between the variables and vice versa. statistical engineering, technology & applied science research vol. 9, no. 1, 2019, 3852-3858 3856 www.etasr.com shahbaz et al.: identification, assessment and mitigation of environment side risks for malaysian … level of t-value shows the significant level of a relationship. this study chose 10% level of significance as this is predictive study so chances of error are high. r 2 examines the effect of the independent variables on the dependent variables. meanwhile, both independent and moderator variables are continuous so interaction terms were calculated from standardized values to avoid collinearity problem. the aim of this study is to evaluate the effects of er on scp. this effect is calculated by the coefficient of determination r 2 . r 2 is a measure of the proportion of an endogenous construct’s variance that is explained by its predictor constructs. figure 2 applies pls and it was found that r 2 =0.22. it means all er caused a decrease in performance by -0.167 or -16.7%. the low value of r 2 is not surprising as it is consistent with previous studies. it is known that scp is dependent on numerous factors besides sc risks [27, 28]. in figure 3 the value of t-statistic is 1.824 which is greater than 1.645. it means er has a significant negative relationship on performance. thus h1 is accepted. there is a need to know that either scc has the significant positive effect of scc or not before analyzing scc as a moderator. figure 4 shows that the value of r 2 is 0.293 which means that all variables contribute 29.3%. previous with one independent variable the value of r 2 was 22%. thus, there is decrease that means scc has effect on scp. furthermore, in figure 5 the t-value is 1.196 that is less than 1.645 so h2 is rejected. it can be concluded that er has a negative and significant effect of scp while scc is positively moderating the relationship but this relationship is not significant. v. discussion the current study proposed that environment side risks negatively affect scp for malaysian manufacturing and this hypothesis is accepted. these findings are in line with the findings in [58-60]. however, according to authors in [22] environment side risks rank last when compared to others, but this study is limited to indian heavy industry only, and it includes limited risk factors under environment side risks. this study anticipated that sc collaboration moderates the relationship between environment side risks and scp. figure 4 shows that path coefficient for environment side risks is 0.069 while it can be found in figure 5 that the t-value is 1.196, whereas path coefficient for a direct relationship between environment side risks and scp in model 1 is -0.167. this means that sc collaboration reduces the negativity between the sc risk sources and scp. these findings are in line with the findings in [61, 62]. meanwhile, some other studies argue that collaboration/integration mitigate the environment side risks [63-66]. on the other hand, authors in [67] empirically verified that higher environmental uncertainties reduce the resource sharing among organizations, but, in that study, resource sharing meant sharing information and assets for the humanitarian organization in southeast asia. it is explained that only humanitarian organizations do not need coordination because they work in extreme levels of uncertainty anyway (disasters, donors’ generosity, beneficiaries’ demand etc.), so it is very difficult for them to supply and coordinate effectively. furthermore, regional infrastructure in numerous disaster areas may not be available, and the extent of post-disaster infrastructure disruption may not be predictable. vi. conclusion it can be concluded that malaysian manufacturing is risky in terms of environment side risks. this study identified 9 types of risks and after systemic 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improvement indicators of walkability to the bus stops in penang island nur sabahiah abdul sukor school of civil engineering engineering campus universiti sains malaysia nibong tebal, pulau pinang, malaysia cesabahiah@usm.my siti fadhlina muhammad fisal school of civil engineering engineering campus universiti sains malaysia nibong tebal, pulau pinang, malaysia fadhlinafisal@student.usm.my abstract−this study investigates the determinants of walkability by evaluating assessment indicators by constructing a path model based on on-site data collected in penang. based on the path analysis, safety (β2=0.691, t=9.301, p<0.01) and connectivity (β1=0.559, t=8.048, p<0.01) have a positive correlation to walkability. meanwhile, walkability shows a negative correlation with the number of private vehicles. the findings of this study allow the authorities to focus on enhancing the safety of walking facilities that give access to bus stops which will probably increase the likeliness of using the public bus services. the findings from this study also reveal the underlying factors that can boost the public to adopt walking as an active mode of transport and thus reduce the dependency on private vehicles. keywords-walkability; structural equation modelling (sem); factor analysis; sustainable transport; public transport i. introduction walkability has many social and environmental benefits. walking not only decreases the risk of obesity [1-6], but also prevents the incidence of other chronic diseases [7]. nowadays, there is a decline in the walking behavior of people due to the increasing reliance on the use of private automobiles. regardless of the negative health consequences that may arise, people still tend to rely on private vehicles instead of practicing active modes of transport. apart from its negative health consequences, decreased practicing of active modes of transport has adverse consequences to the environment, such as air and noise pollution, while the number of fatal car accidents rises. statistics from the world health organization (who) reported that malaysia was ranked as one of the top three countries in the world with the deadliest roads after thailand and south africa [8]. a total of 7,152 deaths related to road accidents were recorded in malaysia in the year 2016, mainly involving motorcyclists. one of the major factors of these accidents is of course the high reliance on vehicles for transportation. in conjunction with government’s goal to achieve a 40:60 modal split, representing 40% dependency on public transport and 60% on private vehicles by 2030, the current high reliance on private vehicles should be alleviated immediately. in this study, the indicators related to walking facilities at bus stops were investigated for their association with the number of private vehicles. this study can be a future reference for transport engineers and planners to improve the accessibility for walking infrastructure and thus reduce the dependency on private vehicles. ii. related work the most influential factor on encouraging walkability is the accessibility to a good walking environment. authors in [9] reported a few determinants of walking behavior such as land use mix, street connectivity, distance to transit stops, and destination accessibility. the walking behavior can also be associated with highly urbanized areas [10], destination types [11], and aesthetics factors on choosing a route for walking [12]. another study reported that connectivity is an important attribute to ensure high-quality public transit [13]. physical connectivity criteria such as continuously connected sidewalks and place-based barriers do affect the last-mile trip. also, the origin and destination of the walking trip is one of the built-in environmental factors that affect the willingness to walk [14]. walkability is also affected by factors such as walking distance, walking time, and the purpose of the trip [15]. in addition to the above factors, gender, age, marital status, shorter travel time and distance, income, education, and vehicle ownership were also claimed as contributing factors to walkability [10, 12, 16, 17]. safety is another feature that has been prioritized by pedestrians. most motorcycle-taxi users are reluctant to walk because of safety concerns and most of them are afraid of accidents [18, 19]. a high rate of accidents involving pedestrians also discourages their willingness to walk which increases their dependency on vehicles. in addition, comfort is also associated with walkability: most people would like to walk if the walkway is comfortable [20]. this should be supported by good environmental design, proper space for walking, and good walking surfaces [21]. it is believed that comfortable walkways should be safe, with no obstacles, and smooth for strollers and wheelchair users [22]. the current study focuses on identifying the criteria that improve walkability, especially regarding the accessibility of public bus stations in penang island of malaysia. the most corresponding author: nur sabahiah abdul sukor engineering, technology & applied science research vol. 10, no. 6, 2020, 6450-6455 6451 www.etasr.com sukor & fisal: safety, connectivity, and comfortability as indicators to improve walkability to the bus … significant criteria will be selected through path modeling analysis. iii. research methodology a. data collection the study was conducted along the proposed bayan lepas light rail transit (bllrt) in penang island. the aim of the study is to investigate the readiness of walking facilities to give access to the bus stops as one of the integrated links to the rail stations. even though the proposed bllrt alignment is still in the construction stage, this study can still be used as a baseline for further walkability studies. the proposed alignment for the rail network can be seen in [25]. in this study, the alignment was divided into 19 zones based on the location of the proposed train stations. one zone was considered to have 800m radius by considering the maximum distance of willingness to walk to a train station [18, 23, 24]. in total, 123 bus stops located in all zones were identified and grouped as shown in table i. the data collection involved two types of data: traffic count of private vehicles and a checklist’s inspection results of the 123 bus stops. the private vehicle data were used as input (dependent variable) in the sem path analysis. meanwhile the scores in the checklists were applied as independent variables. the traffic count in this study was done in the morning and evening peak hours by considering only cars and motorcycles as private vehicles. table i. zones and bus stops involved in this study zone id bus stop id no of bus stops 1 komtar zone (k) k1-k24 24 2 macallum zone (m) m1-m9 9 3 bandar sri pinang zone (b) b1-b8 8 4 skycab zone (s) s1-s6 6 5 east jelutong zone (e) e1-e4 4 6 the light zone (tl) tl1-t7 7 7 gelugor zone (g) g1-g3 3 8 usm zone (usm) usm1-usm3 3 9 batu uban zone (bu) bu1-bu9 9 10 pesta zone (p) p1-p9 9 11 sg nibong zone (sn) sn1-sn7 7 12 bukit jambul zone (bj) bj1-bj8 8 13 spice zone (ss) ss1-ss8 8 14 jalan tengah zone (jt) jt1-jt9 9 15 fiz north zone (fn) fn1-fn2 2 16 fiz south zone (fs) fs1 1 17 sg tiram zone (st) st1-st2 2 18 penang airport zone (pa) pa1-pa7 7 19 permatang damar laut zone (pdl) pdl1-pdl2 2 fig. 1. location of 123 bus stops at 19 zones. engineering, technology & applied science research vol. 10, no. 6, 2020, 6450-6455 6452 www.etasr.com sukor & fisal: safety, connectivity, and comfortability as indicators to improve walkability to the bus … auditing tasks were done at the selected bus stops with the use of a checklist. the criteria for the walkability indicators in the checklist were taken from international guidelines, national guidelines, and previous studies shown in table ii. the indicators were audited based on the scores: 0 = the indicator does not exist, 1 = the indicator is available but not following the guidelines, and 2 = the indicator is available and follows the guidelines. the results were inserted into the statistical package of social science (spss) for factor analysis. the checklist went through a pilot study and amendments were made to suit the specification of local context at 123 bus stops in penang island. figure 2 shows briefly the way the design of the checklist was developed. a total of 18 indicators were identified. fig. 2. brief framework on the audit procedure and design. table ii. walkability vriteria indicator id walkability criteria source w1 connecting pedestrian walkways either paved or unpaved to the nearest main attraction within 400m of a bus stop [26-30] w2 the walkway should not be obstructed [30, 31] w3 provision of bollards/shrubs/fences/ditches at the end of the walkway to segregate it from the car lanes [32] w4 provision of bollards at road intersections (if there are intersections) w5 provision of a median refuge island with a minimum of 1m width at crossings for roads that exceed 2 lanes w6 provision of a crosswalk at road intersections [28] w7 well maintained walkways (smooth pavement, not overgrown shrubs, and not fallen trees) [33] w8 signs in good condition (clearly seen/not broken) [34, 35] w9 crosswalk/markings are clearly seen [29, 32] w10 pedestrian signals must be in good condition w11 smooth incline at the end of walkways or towards road intersections which can be used by wheelchair users and strollers [26, 28] w12 seats at bus stops [30, 31] w13 rubbish bins at bus stops w14 sidewalk width must not be less than 1.5m w15 availability of street trees/awnings/arcades w16 provision of signs for the pedestrian walkway w17 provision of signs that warn motorists about the presence of pedestrian walkways w18 provision of a divider of minimum 1m width (low shrubs/plants/fence/any safety barriers) between the road and the walkway. [28, 34] b. data analysis this study aims to investigate the walkability indicators by developing a structural equation path model. spss was used for data computation and analysis. data analysis was conducted in three stages which were: exploratory factor analysis (efa), confirmatory factor analysis (cfa), and the development of pls path-modelling. 1) exploratory factor analysis the efa was conducted in order to investigate the relationship between the above mentioned indicators and walkability. efa identifies the individual constructs and explores the consistency of the proposed latent factors with the actual data. the principal component analysis (pca) method was used to examine the factor loading among the measurement items for each factor. the value for factor loading of the measurement items should be more than the threshold of 0.5. in this study, the evaluated indicators in the latent variables were extracted based on the output values of kaiser-meyerolkin (kmo) measures. the components possessing higher factor loading of kaiser criterion, i.e. more than 0.55 were accepted. 2) confirmatory factor analysis the cfa or reliability test was conducted based on internal consistency that consists of composite reliability (cr) and cronbach’s alpha value and convergent validity that composed of average variance extracted (ave). the acceptable value for cronbach’s alpha is 0.7. however, it is suggested to accept lower values (0.6) in the research model [35]. the indicators should adhere the threshold of cr which is not more than 0.6 and ave above 0.5 to be carried forward for path analysis. factor loadings for indicator also should be above 0.6. 3) sem path analysis the path model was constructed with a structural equation model (sem) by using smartpls 3.0 software. sem-pls was chosen because it can be applied for theoretical confirmation or theory development. figure 3 shows the conceptual path model for walkability which consists of three latent variables (connectivity, comfort, safety) connecting to the dependent variable, i.e. the number of private vehicles. a total of 18 walkability indicators were constructed as underlying indicators for independent variables (iv). meanwhile, the number of private vehicles collected from the traffic count was considered as the dependent variable (dv). this study aims to investigate the hypotheses below: h1: connectivity is positively associated with walkability to the bus stop h2: safety is positively associated with walkability to the bus stop h3: comfort is positively associated with walkability to the bus stop. positive association in this context means that the more the provision of evaluated indicators provided at the bus stop, the more the walkability element is promoted at the bus stop which has a tendency to attract people to walk and makes more likely the use of public buses. engineering, technology & applied science research vol. 10, no. 6, 2020, 6450-6455 6453 www.etasr.com sukor & fisal: safety, connectivity, and comfortability as indicators to improve walkability to the bus … fig. 3. conceptual path model for walkability. iv: independent variable, dv: dependent variable. iv. results and discussion a. efa results before a model is constructed, factor analysis is implied to summarize the data by assessing the structure of variables for further analysis [36]. theoretically, factor analysis was used to solve the problem by combining variables that are collinear [37]. a pca was conducted on the 18 walkability indicators with oblique rotation (varimax). meanwhile, the kmo measure verified the sampling adequacy for the analysis: kmo = 0.733 [38]. based on table iii, all kmo values for the items were bigger than 0.7, which is well above the limit of 0.50. bartlett’s test (χ 2 (153) = 728.586, p < 0.01) indicated that the correlation matrix is significantly different from an identity matrix, in which correlations between items are all zero and which is not random. out of 18 indicators, 8 indicators were removed and indicators with factor loadings higher than 0.5 were considered highly correlated with the factors extracted and were retained. table iii. kmo and bartlett’s test results kmo measure of sampling adequacy 0.733 bartlett's test of sphericity approx. χ 2 728.586 df 153 sig. 0.000 b. cfa results table iv shows the reliability and validity results of the constructed model. after cfa assessment, the indicators that surpassed the threshold value of factor loadings (0.7) were only 6, 3 belonging to connectivity (w2, w7, w14) and 3 to safety (w6, w9, w10). notably, the variable comfort (w) was removed due to the low value of cronbach’s alpha which depicts that this variable is not reliable for further analysis. connectivity and safety were found to fulfill all requirements by possessing a value of cronbach’s alpha higher than 0.6 [39, 40]. meanwhile, values higher than 0.6 are suggested for indicator loadings [41, 42] and for composite reliability [43]. for average variance extracted (ave), 0.5 is the suggested threshold value [43] and values above this limit are considered acceptable. the results for connectivity and safety in table iv confirm the convergent validity and good internal consistency of the measurement model. table iv. assessment results of the model indicator cronbach's alpha loadings cr ave connectivity w2 0.766 0.844 0.864 0.680 w7 0.859 w14 0.768 safety w6 0.819 0.864 0.893 0.736 w9 0.902 w10 0.803 c. path analysis as shown in figure 3, the latent variables safety and connectivity were related to the latent variable walkability, whereas walkability is related to the number of private vehicles. meanwhile, connectivity and safety were connected to their respective indicators. bootstrapping was performed on the model to test the significance of the relationships between adjacent constructs [44]. based on figure 4, the t-statistic for all independent variables satisfied the threshold value (t ≥ 1.96, p < 0.05) [45]. all the t-statistics are larger than 1.96 which shows that the variables are highly significant. based on the result run by the pls-algorithm, safety shows a path coefficient value of β2 = 0.691 (t = 9.301, p < 0.01) and connectivity β1 = 0.559 (t = 8.048, p < 0.01). the path analysis shows positive results depicting the direct effect on walkability. safety shows strong correlation due to the higher value, compared to connectivity, of the coefficient β towards walkability. hence, safety had a huge influence on walkability which is in accordance with the results in [46, 47]. path analysis also shows a significant negative correlation of walkability towards the number of private vehicles (β = −0.114, (t = 1.208, p < 0.05). this means that decreased provision of infrastructure for walkability element at a bus stop will be less likely to reduce the number of private vehicles passed in front of the bus stop. inadequacy of high quality of public transportation is also argued to give impact on high dependency of private vehicles [48]. the indicators that can improve walkability at the bus stop are presented in table v. fig. 4. the constructed path model for walkability. table v. indicators with description indicator description w2 the walkway should not be obstructed w7 well maintained walkways (smooth pavement, not overgrown shrubs, and not fallen trees) w14 sidewalk width must not be less than 1.5m w6 provision of a crosswalk at road intersections w9 crosswalk/markings are clearly seen w10 pedestrian signals must be in good condition engineering, technology & applied science research vol. 10, no. 6, 2020, 6450-6455 6454 www.etasr.com sukor & fisal: safety, connectivity, and comfortability as indicators to improve walkability to the bus … v. conclusion in this study, walkability is proven to be negatively significant towards the number of private vehicles. it means that the provision of better walking facilities will reduce the number of private vehicles being used. it is also indicating that the infrastructure at the bus stop should be enhanced. the findings show that safety has the strongest correlation towards walkability depicting that walking facilities should be safe in terms of provision of crosswalk, road markings, and pedestrian signals. this is concurrent with the findings of previous studies which showed that upgrading the walking infrastructure will increase the likeliness to walk [14, 50-51]. however, most of the previous studies were based on the preferences of users [22, 52], whereas this study focuses more on auditing the walking facilities according to the guidelines. as a conclusion, all the indicators that significantly affecting the likeliness to walk can be suggested to be included in the improvised version of traffic assessment guidelines, especially in malaysia. this could simultaneously improve the quality to access the bus stops which may reduce the reliance on private vehicles. for countries that practice traffic impact 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technology karachi, pakistan umer@neduet.edu.pk usama ahmed department of computer science and it ned university of engineering & technology karachi, pakistan ahmed.pg13900@cloud.neduet.edu.pk wajahat raza department of computer science and it ned university of engineering & technology karachi, pakistan raza.pg13722@cloud.neduet.edu.pk abstract-static ip addresses make the network vulnerable to different attacks and once the machines are compromised, any sensitive information within the network can be spoofed. moving target defense (mtd) provides an efficient mechanism for proactive security by constantly changing different system attributes. software defined networks (sdns) provide greater flexibility in designing security solutions due to their centralized management and programming capabilities. in this paper, a mechanism for the protection of endpoint security is developed using ip address host shuffling. in the proposed approach, the real ip address of the host is masked and a virtual ip address is assigned. the virtual ips are mined from the pool of unassigned ip addresses. the address pool is created using a pseudo-random number generator to guarantee high randomness. this approach helps in invalidating the intelligence gathered by the adversaries through the changes in the network configuration that will disturb attack execution, eventually leading to attack failure. transparency is attained via preserving the actual ip intact and mapping a virtual ip to it. the proposed solution is implemented using the ryu controller and mininet. the efficient results obtained from the experiments substantiate the effectiveness of the mtd approach for enhancing endpoint security. keywords-ip shuffling; endpoint security; moving target defense; software defined networking; virtual ip i. introduction static networks are an easy target for attackers, even from a remote network. the attackers send probes using various scanning tools to random hosts in the network to identify the victims and attack them. however, dynamic allocation can be carried out using protocols like dhcp or nat. even though nat and dhcp provide dynamic ip address assignment schemes for hosts, they cannot provide adequate security and can also be tracked. the moving target defense (mtd) technique has been adopted to different domains including network security, cyber-physical systems security, software defined network (sdn) security, etc. [1, 2]. however, to the best of our knowledge, mtd for endpoint security has not been covered in depth so far. endpoint security is gaining importance, especially with the advent of technologies like the internet of things (iot) [3]. in this paper, we exploited the ryu sdn controller [4] to design an mtd framework that can be used to provide dynamic ip assignments to end hosts periodically. moreover, the solution ensures that all the communication inside the network is based upon virtual ip addresses assigned to different hosts. this provides a way to counter different threats generated against the endpoints. the solutions are scalable and programable due to the sdn architecture [5]. this approach of hiding the actual ips of the endpoint/hosts substantially corresponding author: muhammad faraz hyder engineering, technology & applied science research vol. 11, no. 4, 2021, 7483-7488 7484 www.etasr.com hyder et al.: towards enhancing the endpoint security using moving target defense (shuffle-based … enhances their security as the attackers are unable to get their correct information. the purpose of mtd is to increase confusion and uncertainty for the attacker who is attempting to breach a system by exploiting vulnerabilities [6]. mtd changes the system/network configurations thus the information gathered by the attacker becomes invalid as the target attack surface is changing continuously. mtd techniques are categorized in terms of redundancy, shuffling, and diversity [7]. shufflingbased mtd changes the system's configuration such as ip shuffling or service reconfiguration. mtd is mostly combined with sdn by using sdn controllers as a central controlling point for network topology shuffling-based mtd, or random host mutation using openflow and port hopping. diversitybased mtd gives the ability to implement various executions of same services of functionalities. this provides diversity in programming language to avoid code injection attacks and software stack diversity to enhance service provisions and network resilience. redundancy-based mtd enhances the reliability of the system by generating many images of network components. the authors in [8, 9] used mtd for network security, especially in sdn networks. mtd has also been adopted for cloud security [10, 11]. the authors in [12] exploited mtd for the security of cyber-physical systems. there is a recent trend of the adaptation of mtd for wireless ad hoc networks as well [13, 14]. the main contributions of this paper are: • the development of shuffle-based mtd mechanism in a distributed sdn environment. • the mtd mechanism for the enhancement of endpoint security in the sdn environment. ii. the proposed scheme this section will cover the way we have implemented and deployed the sdn based shuffling mtd. we have set up a mtd mechanism using ryu as a python controller for the sdn which consists of 3 switches interconnected with 8 user hosts. communication between host one and host two is being shown in figure 1. the local networking of the system is: 1. in the first step, the packet will be coming into switch one with the real source address and a virtual destination address. 2. a packet will then go to the ryu controller. 3. the ryu controller will check for the attachments of the hosts in the ip pool if the switch one is directly connected to the destination address of the host. 4. the ryu controller will receive a negative response in a message. 5. the packet will go out of the ryu controller and will ask for a virtual ip address since it was detected with a real ip address. 6. the packet now will come to switch two with the virtual source address and virtual destination address. 7. the packet will then go to the ryu controller. fig. 1. traffic flow sequence. 8. the ryu controller will now check for the attachments of the hosts in the ip pool if the switch two is associated directly to the destination address of the host. 9. the ryu controller will receive a negative response in a message. 10. a packet going out of the switch will now message to forward it to next available hopping. 11. the packet will come to switch three with the virtual source address and virtual destination address. 12. the packet will then go to the ryu controller. 13. the ryu controller will check for the attachments of the hosts in the ip pool if switch three is directly connected to the destination address of the host. 14. the ryu controller will receive a positive response in a message. 15. the packet going out of switch will now change to the real destination address. 16. the packet goes out to the destination host, i.e. host two. 17. host two will now respond with the real source address and the virtual destination address. 18. the packet will go to the ryu controller. 19. the ryu controller will now check for the attachments of the hosts in the ip pool if switch three is attached directly to the destination address of the host. 20. the ryu controller will receive a negative response in a message. engineering, technology & applied science research vol. 11, no. 4, 2021, 7483-7488 7485 www.etasr.com hyder et al.: towards enhancing the endpoint security using moving target defense (shuffle-based … 21. the packet going out of switch will now receive message to change into virtual source address. 22. the packet will come to switch two with the virtual source address and virtual destination address. 23. the packet will then go to the ryu controller. 24. the ryu controller will now check for the attachments of the hosts in the ip pool if switch two is directly connected to the destination address of the host. 25. the ryu controller will receive a negative response in a message. 26. a packet going out of the switch will now message to forward it to next available hopping. 27. the packet will come to switch one with the virtual source address and the virtual destination address. 28. the packet will then go to the ryu controller. 29. the ryu controller will now check for the attachments of the hosts in ip pool if switch one is attached directly to the destination address of the host. 30. the ryu controller will receive a positive response in a message. 31. a packet going out of switch will now message to change into the real destination address. 32. the packet mentioned in the first step has now reached host one, i.e. its destination. in figure 1, we have shown the working flow of the ip shuffling from real to virtual ip address. this workflow shows the architecture of the way our sdn environment containing mtd is implementing random host mutation using a timeout event. the timeout event is triggered every 30 seconds and then shuffles the ip address for every host. figure 2 represents the real-virtual ip address life cycle. virtual addresses are being shuffled in a random manner and are updated in every host. this system in general transforms real addresses to virtual addresses and vice versa. the real address is allocated the same way as before and nothing is changed on it, but all the communication is being done through virtual addresses inside the sdn network. at every timeout event triggering, the old flows are also deleted to be seemingly synchronized with packets and flow mappings. iii. experimental setup a. sdn controller we have used ryu as our sdn controller which is a python-based controller and it will be responsible for controlling real and virtual ips between switches and hosts using the random host mutation technique. it will also be controlling the communication between each host via virtual ips and mac addresses. it is a controller through which we execute and control both network configuration and real-time control of the network. figure 3 indicates the experimental topology. fig. 2. virtual-real ip address life cycle. fig. 3. experimental topology. b. network simulation we have used mininet [15] as our network simulation tool to deploy our network topology containing 3 switches and 8 hosts containing class a ip addresses. it is a network simulator that can generate virtual switches, hosts and attach these to the sdn controllers, in our case with the ryu controller. we emulated this via python-based programming scripts where modifications are required at a certain level to grip the project with the required topology that we created. c. network monitoring we have used sflow [16] as our network monitoring tool which is used to monitor our network devices which include switches and hosts. it will also be used for monitoring any kind of traffic and attacks on the network. we will also use sflow engineering, technology & applied science research vol. 11, no. 4, 2021, 7483-7488 7486 www.etasr.com hyder et al.: towards enhancing the endpoint security using moving target defense (shuffle-based … for generating attack graphs. it is a monitoring tool through which we see the graphical interface of a topology and different shuffling of ips and hosts in our environment. also, we can identify the main and virtual ips from its interface. shuffling of ip addresses and mac addresses and blocked source ips can be identified. iv. results and discussion first, the sflow-rt is started as shown in figure 4. afterwards, the ryu controller starts along with our proposed algorithm and gui topology as depicted in figure 5. the network is created as presented in figure 6. now, the hosts try to ping each other through their real ip. since our algorithm is activated, the packets drop on the real ip addresses as indicated in figure 7. the controller is blocking this communication as presented in figure 8. after finding the virtual ip address of the remote machine, host 2 is able to ping the host 8 successfully as indicated in figure 9. the controller’s log confirms this connectivity as depicted in figure 10. fig. 4. initiation of the sflow network monitoring tool. fig. 5. initiation of ryu controller with gui topology and our mtd algorithm. fig. 6. custom topology network creation. fig. 7. host 1 to host 2 icmp communication through their real ip addresses. in order to evaluate the effectiveness of our proposed scheme, we launch an attack on the end-hosts on their real and virtual ip address using hping [17]. fig. 8. the controller is blocking the communication after identifying a real ip address. fig. 9. now we have first ping host 2 to host 8 through its virtual ip and mac addresses. fig. 10. the controller is allowing the communication after identifying a virtual ip address. figure 11 represents the hping based udp flood from host 1 to host 3. since it is based upon the real ip address, no traffic will be generated if the attacker is able to somehow find the virtual ip address of the host. then the attack will be generated against the virtual ip as shown in figure 12. however, since our algorithm is periodically generating random ips after 30 seconds, the attack can be generated for a maximum duration of 30 seconds. figure 13 indicates the flooding traffic passing through different switches. fig. 11. hping flood from real host ip to another real host. fig. 12. hping flood from real host ip to the virtual ip of the host. fig. 13. attack traffic generation across each switch. engineering, technology & applied science research vol. 11, no. 4, 2021, 7483-7488 7487 www.etasr.com hyder et al.: towards enhancing the endpoint security using moving target defense (shuffle-based … figure 14 shows that the attack traffic on virtual ip is reduced after 30 seconds as the virtual ip is changed. this approach ensures that ddos attacks cannot proceed beyond the limit of the ip shuffling period. the solution is adaptable to change in the frequency of ip shuffling. it means that ddos period can further be reduced with higher frequency of movement. fig. 14. the attack is generated on said hosts but due to the mtd algorithm, the connection will be terminated in 30 seconds. table i shows the comparison of the proposed approach with the existing solutions. the proposed scheme implemented endpoint protection using sdn and mtd approaches. moreover, the proposed solution does not require any specific agent to be installed on the endpoint. this is a substantial attribute of our proposed solution and makes the proposed scheme flexible enough. the authors in [18] used the commercial tool "fireeye" for the enhancement of endpoint security. their solution is based on anti-virus based approach. the authors in [19] proposed a mechanism for endpoint security along with estimation of its effectiveness. the author in [20] proposed a mechanism for endpoint security improvement. table i. comparison of the proposed implementation with existing solutions. sdn enabled mtd enabled separate user-agent on the endpoint proposed � � not required [18] x x required [19] x x required [20] x x required v. conclusion and future work in this work, we have implemented mtd by randomly metamorphosing ip addresses of endpoints using sdn. the fundamental aim of mtd is to thwart the discovery of machines by the probes generated by numerous worms and scanning tools. the actual ip addresses are hidden from both internal and external scanners to avoid attacks. the ryu controller was used to mutate the ip addresses. a host’s real ip address is assigned with a virtual ip address at a high mutation rate from an unused resource pool of ip addresses by using a pseudo random number generator. a brief description of the implementation of dns response interception by the controller follows: when a host requests for the ip address of 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[20] s. j. yoo, "study on improving endpoint security technology," convergence security journal, vol. 18, pp. 19–25, 2018. microsoft word 07-3646_s_etasr_v10_n4_pp5914-5920 engineering, technology & applied science research vol. 10, no. 4, 2020, 5914-5920 5914 www.etasr.com yilmaz et al.: analysis of the risks arising from fire installations in workplaces analysis of the risks arising from fire installations in workplaces using the ranking method fatih yilmaz department of labour economics and industrial relations bandirma onyedi eylul university balikesir, turkey fatihyilmaz@bandirma.edu.tr beytullah oz department of chemical engineering corum hitit university corum, turkey beytullahoz@hitit.edu.tr selcuk alp department of industrial engineering yildiz technical university istanbul, turkey alp@yildiz.edu.tr ahmetcan alkoc department of industrial engineering yildiz technical university istanbul, turkey acanalkoc@gmail.com abstract—the aim of this study is to analyze the risks arising from fire installations in workplaces. it also aims to propose a risk analysis method in the form of a “fire safety risk ranking system” for enterprises with a closed work area of more than 1000m 2 in accordance with regulations in turkey. the relative weights of fire safety factors were determined by fuzzy ahp. the ranking points of the enterprises were calculated by using the weights obtained with fahp. from the 45 enterprises where the risk assessment was applied, only 3 enterprises scored 100 full points according to the fire risk ranking method, and 30 enterprises had a score below 80 points. out of these, 6 scored below 60 points, which is considered a low score. the distribution of enterprises within sectors was not equal. according to the results, only 6.6% of the enterprises are in compliance with legislation and standards, about 67% are inadequate in terms of fire safety and continue to operate under serious fire risks. keywords-arising risks; ranking method; fuzzy ahp; fire installatiıons i. introduction the number of factory fires in turkey in 2017 showed 7.8% and 25.9% increase compared to 2016 and 2014. according to the instanbul metropolitan municipality [1] statistics in 2017, a total of 166 fire department interventions in factories were reported [1]. along with the developing technology and legal obligations, the importance of fire risk assessment and establishment and supervision of fire safety systems has been increased in order to create a safer working environment for the employees and the people living near the factory. in accordance with the occupational health and safety act in turkey, employers are obliged to assess risks for the identification and elimination of hazards that may or may not exist in workplaces. keeping the risk assessment as up-to-date as possible it is also important in terms of ensuring the continuous improvement at the workplace [2]. periodic inspections of fire installations are mandatory at least once a year in turkey. there are similar applications in many countries. the regulation on the protection of buildings from fire also aims at minimizing the fires that can occur during the stages of design, construction, operation, maintenance and use of all types of structures and facilities. its aim is to ensure that the loss of life or property is minimized and eliminated, and regulations published to determine the basis for the organization, training and inspection procedures and principles of the measures to be taken before and during the fire. sensitive equipment used in enterprises, high-rise and multi-purpose buildings and valuables kept in warehouses bring about various risks. safety measures have changed as new risks arise. one of the most important of these risks is fire due to its destructive consequences, so new safety measures are being developed to eliminate fire risks. the number of new devices and systems that detect, warn, and provide suitable solutions is increasing. by considering the potential damage that fire can cause in enterprises, fire protection, extinguishing and security systems are getting more important every day [3]. in order to determine the most appropriate safety measures against fire in the premises or in public places such as shopping malls, hospitals, and schools, the risk of fire must be determined realistically and appropriate methods should be developed. fire risks are also addressed by various risk assessment techniques [4]. fire risk analysis aims to determine the criteria that define risk, its importance level, and ways to set prevention and protection measures in order to reduce these risks [5]. when each designed structure is examined from a risk analysis point of view, it is assumed that the possibility of fire cannot be eliminated. for this reason, it is not possible to ensure perfect fire safety. however, it is important to examine fire protection and fire safety issues in a holistic and systematic way to reduce risks. first, it is necessary to identify the criteria and the importance ratings of these criteria in line with a plan, then form and formulate a strategy that will satisfy these criteria and lead to the identified targets [6]. fire is a disaster corresponding author: selcuk alp engineering, technology & applied science research vol. 10, no. 4, 2020, 5914-5920 5915 www.etasr.com yilmaz et al.: analysis of the risks arising from fire installations in workplaces that may cause death, injury, and major financial loss. fire risks vary widely and some of these risks are due to fire installations. fire risk analyses based on standards in the form of a detailed but traditional checklist may produce unrealistic results for older fire installations. for this reason, new and more holistic approaches need to be implemented. this article proposes a risk analysis method considering the fire safety risk ranking system for enterprises in turkey. for this purpose, a survey was carried out in 45 enterprises with a closed area of more than 1000m 2 , in accordance with the regulation on the protection of buildings from fire, which entered into force in 2007. the fire safety criteria used in calculating the risk score are based on national and international legislations and standards. these criteria are building properties, fire safety systems, and management systems. first, the weights for these criteria were determined by the fuzzy analytical hierarchy process (fahp) method. for this intent, a questionnaire was applied to fire experts. calculated weights were recalculated by ranking method, and fire risk score and ranking charts were prepared for the enterprises. ii. literature review authors in [7] proposed the nonlinear fahp in the coal mine safety assessment, compared it to ahp, and found it to be more appropriate, precise, and complete in the evaluation process. authors in [8] examined the social benefits of occupational health and safety management systems of mines in china and sweden based on fahp with a comparative study. authors in [9] determined and evaluated the risk of modular structure using fahp and simulations. in [10], an fahp approach was proposed to determine the level of faulty behavior risk in work systems. their proposed method was applied to a manufacturing company. authors in [11] established an fahp assessment model for gas station safety status. in [12], a risk assessment methodology for conducting systematic risk assessment using fuzzy reasoning approach and fahp was presented. the purpose of the authors in [13] was to compare how canadian experts and public rank different food hazards, with a view to better understand their underlying rationales for making decisions on food safety. authors in [14] studied the accident risk ranking of the major facility hazards. consequently, a risk ranking model and methods for determining scenario probability and fatality number were developed. in [15], a new reliability interval method for manipulating the weightings of attributes and a synthetic model on the basis of grey system theory was presented. in [16], a fire safety ranking system, excluding the fire safety management at the moment, was proposed for assessing the fire safety provisions for existing karaoke establishments in hong kong. authors in [17] evaluated the fire risks of public buildings by using simultaneously the ahp and fault tree analysis (fta) methods. fta reflects how important key events are for the most important event. ahp also reflects the importance of the alternative level attribute to the general goal. based on the consistency of these two methods, an improved ahp was introduced. using this improved method, fire safety of public buildings (olympic venues in china) was analyzed. authors in [18] developed an approach to integrate ship fire safety assessment and decision making using the ahp method. they suggested that this approach could be used to reduce the likelihood of a fire during the operating phase of a cruise ship and the severity of its possible consequences. ahp method has been used to sort fire incidents and an integrated system has been proposed to minimize fires using the obtained results. in [19], a new approach was presented for the rapid assessment and relative ordering of the hazards of chemicals, installations and facilities. this approach is based on the use of a multicriteria decision-making technique based on fuzzy logic for hazard assessment of substances and facilities. based on the proposed method, the substance fire hazard index (sfhi) and consequences index (ci) have been developed to evaluate the results of the potential of an accident at the facility. in this study, in contrast with the studies given above, ranking method, which is frequently used in occupational safety, and fahp, which is a multi-criteria decision making method in fuzzy environment, were used simultaneously. in this way, more consistent results were obtained. moreover, by using the obtained results (weighted fire safety criteria), the applicability of the method was shown. iii. methods the safety of work systems is affected by many factors. therefore, measuring work system safety requires a holistic approach [7]. in this study, the work safety issue is studied through the fahp approach, which allows multi-criteria and simultaneous evaluation, and the ranking method. a. multi-criteria decision-making the decision-making problem can be defined in the most general sense as the choice of the most appropriate option according to at least one objective or criterion from a set of choices. decision-making is a very difficult task when many parameters determine the goal to be reached in a problem and where each of the alternatives to be evaluated for selection has its own advantages. the aim of using mcdm methods is to keep the decision-making mechanism under control and to get the decision result as easy and quick as possible [20]. various scientific methods have been put forward in order to find solutions to decision-making problems with more than one criteria. these solution methods are called mcdm methods [21]. mcdm is a selection process that a decision maker applies using a minimum of two criteria in a set of countable finite or uncountable number of choices [22]. b. fuzzy analytical hierarchy process the ahp is one multi-criteria decision-making method developed by thomas l. saaty in the 1970s. the ahp, which is based on human-natured binary comparisons, assesses how important, preferential, or dominant these binary comparisons, options and criteria are to each other [23]. this method of determining the best option is often used to solve complex decision problems due to both quantitative and qualitative factors considered and its ease of use [24]. despite the fact that it finds application in many decision problems, it has not been accepted without criticism. for starters, the uncertainties regarding the decisions, criteria and alternatives in the evaluations made with ahp are not taken into consideration engineering, technology & applied science research vol. 10, no. 4, 2020, 5914-5920 5916 www.etasr.com yilmaz et al.: analysis of the risks arising from fire installations in workplaces and this affects the decision to be made to a great extent [25]. if a worse alternative than the existing alternatives is added in a decision problem solved by the ahp method, the order of the alternatives is likely to change. this shows that decisionmaking problems solved by the ahp method may not always give accurate results. fahp method produces more precise results compared to the ahp method [26, 27]. while decision makers in ahp use exact values when making their assessments, evaluations that are more accurate can be made using fuzzy numbers or linguistic variables in fahp. various fahp methods have been suggested [20, 27]. as an example of these methods, van laarhoven and pedryey's direct expansion of saaty’s ahp method with triangular fuzzy numbers method, buckley's method of developing the saaty’s ahp method with aij fuzzy comparison rates, the extended fahp method proposed by cheng, the fahp method based on entropy weight, the limited fahp method and enumeration methods of fuzzy numbers revealed by enea and piazza can be given [21]. in the fuzzy set theory, the ratio provided by the decision makers is a fuzzy number, which is defined as a membership function. the membership function defines the value of the elements in the decision interval of the priority set. it would be more appropriate for the experts to give verbal assessments instead of a definite number of opinions on one subject. these verbal evaluations are the triangular fuzzy numbers (tfn) [27], shown as (1|m, m|u) or (1, m, u). for a fuzzy event, the parameters l, m, u show the smallest possible value, the most expected value and the largest possible value respectively [28]. the extended fahp method proposed in [29] is used in this study. the steps for this method are outlined below. step 1: the fuzzy synthetic dimension value according to the object i is calculated as in (1): �� = ∑ ������ ⊗ �∑ ∑ ������ � �� (1) the sum of the m dimension analysis matrix ∑ ������ in (1) is calculated by (2): ∑ m����� = �∑ l��� ∑ m��� ∑ u��� � (2) again, fuzzy addition is performed on the ���� values to compute the �∑ ∑ ������ � �� expression in (1). at the end of this step, the inverse vector is calculated by: �∑ ∑ ������ � �� = � ∑ ���� ! , ∑ ��#�� ! , ∑ $��� ! % (3) step 2: the �&((&,)&,*&) ≥ � (( ,) ,* )) probability value, with m1, m2, being tfns, is calculated in (4): -(�& ≥ � ) = sup0 ≥ 12min567!(1),678(0)9: (4) the expression -(�& ≥ � ) in (4) is calculated as: -(�& ≥ � ) = ℎ<=(� ∩ �&) = 6�&(?) (5) -(�& ≥ � ) = @ 10($!��8)(�8��8)�(�!�$!) ;)& ≥ ) ; ( ≥ *& ;d=ℎefghie (6) step 3: the likelihood of the probability level of a convex fuzzy number is greater than k convex numbers mi (i=1,.2,….,k) is calculated as: -(� ≥ � ,�&,…,�k) = )hl-(� ≥ ��) (7) it is assumed that dn(o ) = min (-(�� ≥ �k)) for h = 1,2,…,q and q ≠ i and so the weight vector (sn) is calculated by: sn = (?n(o ),?n(o&),…,?n(o ))t (8) the form o� in the formula consists of n elements(h =1,2,…,l). step 4: the weight vector given in (7) is the normalized weight vector s = (?(o ),?(o&),…,?(o ))t after the normalization process. the calculated weight vector w is no longer a fuzzy number [16]. c. ranking method this method is known as the fire safety ranking system, the fire risk ranking system or the fire safety assessment system in scientific studies [20-33]. it is a process where the ranking of fire safety criteria is made by using multi criteria decisionmaking [23, 33-36]. the purpose of a fire safety ranking system is to assess the performance of various fire safety criteria of existing buildings and to measure the level of fire risk. the fire risk levels obtained are the basis for prioritizing the actions to be taken to improve fire safety performance [31]. in many countries, fire safety risk ranking methods have been developed and implemented to help assess the fire safety level of buildings. for example, a fire safety assessment system was developed based on fire risk ranking in the united states [37]. this system offers a multi-featured approach to determining equivalencies to the nfpa l0l life safety standard for specific workplaces [38]. authors in [39] have proposed a fire safety ranking system for entertainment venues in hong kong. another application of the ranking method, similar to our study, was used to determine the fire safety performance of student accommodation enterprises in saudi arabia [30]. fire risk ranking systems offer many advantages, such as ease of use, cost effectiveness, and a quick and simple estimation of the relative risk of fire. to the best of our knowledge, there is no other study using the ranking method for the analysis of risks from fire installations. ranking method has been used in other similar areas, such as maintenance management, improvement of building security systems, and prioritization of materials [30, 40]. however, there are disadvantages in using fire safety ranking systems. to begin with, it is not a uniform system. for this reason, it is stated that different methods should be developed for different usage type structures [41]. the basic assumption of the ranking method is the existence of the relative importance levels of fire risk factor criteria against each other. different enterprises have different fire risk criteria. however, these criteria can increase or engineering, technology & applied science research vol. 10, no. 4, 2020, 5914-5920 5917 www.etasr.com yilmaz et al.: analysis of the risks arising from fire installations in workplaces decrease the total fire risk level. moreover, uniform risk analyzes made with the 0-1 or present/not present checklist do not contain sufficient numerical data, which makes evaluation of fire risks difficult and reduces accuracy. the purpose of this method is to calculate the importance of each risk criterion with the fahp, which is an mcdm method according to the opinions of fire experts. the calculated risk scores are then reflected to the application of the risk analysis in the enterprises and the total fire risk score is calculated for the enterprises. with this method, fire risks are calculated quantitatively and the sensitivity level of risk assessment increases. in this way, quantitative data are produced in the planning of preventive activities, with the determination of the measures and priorities to be taken care of in the business, which can support the occupational health and safety experts. this study, prepared by the fire risk ranking method, was carried out in three stages. in the first stage, each risk factor for the fire installations of enterprises was determined in accordance with the current legislations and standards. subsequently, the criteria and sub-criteria specified in tables ii and iii were determined by a questionnaire applied to fire experts. the results obtained were calculated by the fahp method and the weighted risk scores of each fire safety criterion and its sub-criteria were determined. in the second phase, the weighted risk scores calculated with fahp were multiplied by the risk scores obtained from the risk analysis application conducted by the control list method in the enterprises within the scope of application, and the total risk score for each enterprise was determined. in the last stage, figures obtained from the total risk scores and the fire risk ranking score chart of the enterprises were drawn. iv. data collection and results a. data collection in order to develop a fire risk ranking system within the scope of the research, a survey was prepared in accordance with the fahp method to calculate the weight of fire safety criteria and sub-criteria determined according to the literature review and current standards. the study has simplified the fire safety criteria and qualifications in paired comparison tables, as shown in table i. table i. double-sided comparison scale 9 7 5 3 1 3 5 7 9 x absolutely important very important important somewhat important equally important somewhat important important very important absolutely important y table ii. total relative importance of fire safety factors fire safety factor relative weight calculation fire safety criteria building properties 0.4217 structural status of the building fire safety systems 0.4762 pump system fire cabinets and cylinders emergency exits, fire detection, and smoke control systems fire extinguishing systems management systems 0.1021 firefighting and fire precautions responses were collected through personal interviews with fire experts with 20 years or more of experience. the questionnaire was applied to five specialists. the participants were asked to set the fire risk criteria given on each line in the questionnaire according to the other risk criteria specified at the end of the line. for example, if two criteria are equally important, it is desirable to mark the “1 equally important” box, if the criterion in the right column is very important, the “7 very important” box on the right side and the “3 slightly important” on the left. the fahp method was used to calculate the criterial weights by a matrix based on the scores in the questionnaire. the calculated values are given in tables ii and iii. the questionnaire was presented as comparative titles for the detailed calculation of the risk factors and the weighted scores of the criteria and sub-criteria were identified as “building properties”, “fire safety systems” and “management systems”. table ii summarizes the six fire safety criteria. for calculating the total relative weight of each fire safety factor, measures were compared by experts and the results were given. then, weights of the fire safety criteria were summed up to form the total weight of the fire safety factors. in table iii, the experts compared the sub-criteria representing “building structural condition criteria” and firefighting and fire precautions sub-criteria representing “management systems criteria”. the sub-criteria of the pump system, fire cabinets and tubes, emergency exits, fire extinguishing system, fire detection and smoke control systems, which represent the “fire safety systems criteria”, were compared and evaluated by experts in separate tiles. in addition, risk ranking is presented as a percentage of the relative fire safety criteria weighted in table iii. b. application of fire risk analysis with the ranking method the application was made in 45 enterprises in istanbul with total indoor usage area more than 1000m 2 , in which it is obligatory to have a water extinguishing system according to the relevant legislation. the fire safety criteria and the subcriteria set out in table iii are in accordance with the standards set by the health and safety conditions regulation for the use of work equipment which entered into force in 2013 and the regulation on fire protection of buildings which entered in force in 2007. the inspections at the enterprises were carried out in cooperation with the occupational safety experts in order to ensure that measures were made in accordance with the criteria presented in table iii, as accurately as possible. the evaluated as appropriate installations were given a value of 1 whereas inappropriate were given a value of 0. engineering, technology & applied science research vol. 10, no. 4, 2020, 5914-5920 5918 www.etasr.com yilmaz et al.: analysis of the risks arising from fire installations in workplaces table iii. relative importance values calculated from fire safety sub-criteria fire safety factors no fire safety criteria weights local global pump system a1 pump station 0.00630750 0.0319 a2 spare diesel engine propulsion pump or electric pump (with generator support) 0.00516780 a3 fire pumps sequential regular work 0.00480240 a4 all components of the pumps work or not 0.00936410 a5 pump station 0.00630750 fire cabinets and cylinders b1 fire tubes 0.00609000 0.0290 b2 fire cabinet 0.00609000 b3 fire hose 0.00609000 b4 fire valve 0.00609000 b5 fire cabinet and tube warning signs, maintenance records and instructions 0.00464000 emergency exits, fire detection, and smoke control systems c1 escape staircases on the buildings, fire resistant doors 0.04720480 0.2896 c2 suitable dimensions of escape routes 0.05838336 c3 smoke flame detectors and audible warning systems 0.06840352 c4 alarm systems and energy sources 0.06840352 c5 exit signs and emergency lighting 0.04720480 firefighting and fire precautions d1 emergency action plan 0.02390161 0.1021 d2 fire drill training 0.02288061 d3 fire crew instructions 0.01412043 d4 fire panel 0.01412043 d5 periodic inspection report of fire system 0.02707692 structural status of the building e1 building fire installation project 0.08324358 0.4217 e2 differences in installation metrics and application in the building installation project 0.11963629 e3 materials used in the structural state of the building 0.09420778 e4 300ma fire alarm on the main panel in the electrical installation 0.05047749 e5 electrical interior installation and ground measurements 0.07413486 fire extinguishing systems f1 mains, fire water, hydrant lines, and tank connections 0.02340520 0.1286 f2 flow rates and pressures of fire pumps 0.02694170 f3 raw water storage and sufficiency 0.02655590 f4 sprinkler system project suitability 0.02494840 f5 fire resistance test 0.02674880 step-by-step analysis follows: u��vu�� = i� ∗x� (9) �� = ∑u��vu�� (10) u�vu�� = �� ∗o� (11) u� = u�vu�� (12) where fs is the final score, fscfs is the fire safety criteria final score, si is the fire safety criterion score, ai the fire safety criteria weight, fsscfs the fire safety sub-criteria final score, si the fire safety subscale score, and ai the fire safety sub-criteria. • each fire safety criterion in table iii has been converted into scores based on the data of table iv. • the weighted risk score for each criterion was calculated by multiplying these scores by the weighted scores calculated by the fahp method presented in table iii. • to obtain the final score for each risk factor (building characteristics, fire safety systems and management systems), the outcome scores of all sub-criteria derived in stage 2 under each criterion were summed and multiplied by the weighted scores calculated for the criteria in table ii. • the sum of the final scores of the criteria is the final total score of the enterprise. • fire safety rankings of the enterprises were made as a result of comparison of the general scores. c. results the total working area of all the installations examined in the study is > 1000m 2 and all of them have a sprinkler system. table iv provides general information of the enterprises. table iv. general information information feature frequency hazard class less dangerous 11 dangerous 28 very dangerous 6 sector accommodation operations 3 administrative building 2 hospital 5 machine production 25 textile 5 warehouse 5 the risk scores of the installations were obtained by multiplying the control scores with sub-criteria weights. the highest and lowest 8 total risk scores according to the fire safety risk factors are given in table v. table vi shows the mean and weighted mean values of fire safety risk factors for the enterprises. in order to determine the normalized weighted mean values, the mean values calculated for the enterprises and the weighted values which were previously found with the fuzzy analytical hierarchy process were considered. engineering, technology & applied science research vol. 10, no. 4, 2020, 5914-5920 5919 www.etasr.com yilmaz et al.: analysis of the risks arising from fire installations in workplaces table v. total risk scores enterprise fire risk final scores of enterprises (%) building properties fire safety systems management systems total score e17 42,17 47.62 10.21 100 e41 42.17 47.62 10.21 100 e5 42.17 47.62 10.21 100 e28 42.17 47.62 7.5 97.29 e19 42.17 47.16 7.5 96.83 e39 42.17 45.94 7.5 95.61 e23 42.17 45.28 7.5 94.95 e18 42.17 47.62 3.7 93.49 … … … … … … … … … … e21 9.42 31.8 7.5 61.18 e1 21.88 31.65 7.5 61.03 e45 21.88 30.2 7.5 59.58 e22 21.88 29.58 7.5 59.06 e33 21.88 25.99 7.5 55.37 e43 21.88 31.51 0 53.39 e24 21.88 23.95 7.5 53.33 e4 21.88 22.34 2.39 47.61 average 27.87 39.55 6.96 74.68 table vi. fire safety risk factors mean weighted normalized weighted mean building properties 27.8651 42.17 37.5243 fire safety systems 39.5493 47.67 60.2049 management systems 6.9649 10.21 2.2709 total score 74.6807 100.00 100.00 descriptive statistics of the study according to the sectors in which the enterprises operate are given in table vii. although the frequencies are very different, this table can give overview information. table vii. descriptive sector statistics n mean minimum maximum std. dev. machine production 25 77.4104 53.33 100.00 14.40924 textile 5 64.7620 47.61 72.07 10.44201 hospital 5 70.7600 55.37 90.48 13.50202 warehouse 5 76.0620 63.10 95.61 13.22125 accommodation 3 75.9533 53.39 100.00 23.34038 administrative building 2 69.7950 59.58 80.01 14.44619 total 45 74.6807 47.61 100.00 14.27252 among the 45 studied enterprises, only 3 scored 100 full points according to the fire risk ranking method, whereas 30 with a score below 80 were found. of these, 6 had a very low score, below 60 points. according to the results, only 6.6% of the enterprises are in compliance with legislations and standards, about 67% are inadequate in terms of fire safety, partly or mostly, and continue to operate under a serious fire risk. some of the facilities had structural alterations to buildings added after inspections. there are cases of inadequate training of firefighting squads and delays and lack of discipline while performing fire drills. it has been observed that emergency action plans are outdated in some enterprises. fire escape routes are not clear from obstacles and are often used as temporary storage areas. v. conclusions the fire safety level of many industrial buildings is not in line with current legislations and standards. insufficient care and control comes at the forefront of this situation. many workplaces do not have daily, weekly, monthly, and yearly maintenance and inspection, are non-functioning or have defective or disabled installations. enterprises operating under these conditions are at serious fire risk. in addition, it is costly and takes a long time to make the majority of old buildings compliant with legislation and standards. as the enterprises avoid this cost and time loss, the installations are not secured. there are dangerous production processes in manufacturing enterprises that increase the fire risk compared to other businesses. fire risks in these enterprises may arise from building designs, raw materials and equipment used, and from flawed or uncontrolled fire installations. during the periodic inspections of the fire systems, the risk analysis made in the form of a checklist is insufficient because it does not contain quantitative data. existing conventional standards and methods cause limited and inadequate assessments of fire safety performance of the enterprises, often consisting of old buildings with poor infrastructure. for this reason, a holistic approach that allows quantitative assessments such as ranking systems can be preferred in fire risk analysis. another advantage of the ranking systems is their cost effectiveness and ease of use. the ranking method has been proposed and applied in structures such as high-rise office buildings and student dormitories. however, it is also suggested that the fire safety levels of different building types should be examined in more detail and be supported by different methods. the importance of fire risk assessment and inspection of fire safety systems has been increased with the developing technology and legal obligations. in order to create a safer working environment for the employees and the people living in the immediate vicinity of the factory, the risk of fire must be determined realistically and appropriate methods should be developed. in this paper, a case study has been done on this subject. in this study, fahp and ranking methods were utilized. there are only a few similar studies on occupational health in the literature. references [1] m. d. a. | www.mavigen.com, “istanbul fire department,” istanbul fire department. http://itfaiye.ibb.gov.tr/en/ (accessed jun. 18, 2020). 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[41] a. g. copping, “application of a systematic fire safety evaluation procedure in the protection of historic property,” fire protection engineering, vol. 14, pp. 12–17, 2002. microsoft word renal-xefteris-etasr3.doc etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 251-258 251 www.etasr.com xefteris et al: a method for improving renogram production and detection of renal pelvis… a method for improving renogram production and detection of renal pelvis using mathematical morphology on scintigraphic images stefanos xefteris electrical and computer engineering department national technical university of athens athens, greece xefteris@mail.ntua.gr konstantinos tserpes electrical and computer engineering department national technical university of athens athens, greece tserpes@mail.ntua.gr theodora varvarigou electrical and computer engineering department national technical university of athens athens,greece dora@telecom.ntua.gr abstract— dynamic renal scintigraphy is a well-established imaging technique in nuclear medicine, used to detail both the organ's anatomy and function. however, the quality of the produced scintigrams provides an often unreliable diagnostic tool because of a rather bad signal-to-noise ratio and the fact that in certain occasions the regions of interest are too concentrated making it difficult for physician evaluation. the goal of this paper is to achieve a more accurate production of the renal activity graph, by avoiding the inclusion of image artifacts in the detection process. this is achieved by treating pixels as points in a two-dimensional euclidean space, and exploiting set-theoretic properties and morphological operators. the evaluation of the method in a number of real patient’s scintigrams obtained in a depth of 5 years, showed that, in the majority of the cases, it is feasible to produce a more accurate renogram, for both kidneys and the renal pelvis region, that was helpful for the interpretation of the findings keywords: renal scintigraphy; mathematical morphology; imaging; pattern analysis; detection i. introduction renal scintigraphy is a sensitive mean for detection, evaluation and quantification of numerous renal conditions. scintigraphy is a diagnostic test in which a two-dimensional picture of a body radiation source is obtained through the use of radioisotopes. radioisotopes are taken internally, and the emitted radiation is captured by gamma cameras equipped with a parallel-hole collimator to form two-dimensional images, called scintigrams, that detail both the organ's anatomy and function. periodic capturing and post-processing of these images produces a sequence of kidney instances throughout time, along with a renogram a graphic record that depicts the brightness variation throughout time in the image. these may help in the quantification of certain parameters of the renal function, such as the effective renal plasma flow (erpf), the excretory index, the glomerular filtration rate (gfr), and the differential renal function. through the assessment of the abovementioned metrics, the physician can detect anatomic or functional abnormalities of the kidneys or the urinary tract by interpreting images and/or digital data of diagnostic quality. such abnormalities include, but are not limited to, the detection, evaluation and quantification of possible urinary tract obstruction, the detection and evaluation of renovascular disease, the detection of pyelonephritis and parenchymal scarring, the detection and evaluation of functional and anatomic abnormalities of transplanted kidneys, the qualitative measurement of renal function and the detection of congenital and acquired anatomic renal abnormalities [1] there are various quantitative renal function protocols followed by physicians in order to detect different renal abnormalities such as those mentioned above. a protocol suitable for routine clinical use includes the injection to the patient of some kind of renal tracer such as 99mtc-mag3 and the monitoring of its flow in the kidneys using a gamma camera in order to evaluate three distinct phases: perfusion, concentration and excretion [2]. these are depicted in the resulted images and in the renogram which help the physician to conduct visually two types of diagnoses: • quantitative analysis, in which the physician identifies the existence of one or both kidneys, kidney deformities, and abnormalities in the renal parenchyma and finally • renogram analysis, in which the physician examines the renal behavior throughout time, i.e. if the absorption and excretion of the radiopharmaceutical is normal. the accurate diagnosis from the physician is subject to the physician’s experience and ability to identify patterns. the physician interprets the potential findings visually, examining dynamic images, and through the washout curve shape (concave vs. convex) of the renogram. further, the diagnosis is usually obscured by low image quality due to naturally inserted noise [3]. it should be noted that a crucial region of interest etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 251-258 252 www.etasr.com xefteris et al: a method for improving renogram production and detection of renal pelvis… (roi) in the scintigraphic images (scintigram) is restricted to a small area of the kidney, called renal pelvis, which acts as the main output funnel of the kidney. by examining the renal pelvis area, the physician can evaluate the flow of the radioisotope of the kidney. in this paper we advocate that the above mentioned practice can become more accurate if we deploy an image processing technique that will process the renal images and isolate the roi (renal pelvis), filter the picture from unwanted artifacts inserted by noise and finally estimate the flow of the renal tracer through the production of the renogram (renal activity graph) and of the activity graph of the renal pelvis. this is achieved by a series of algorithms applied on the scintigram with the purpose to measure the absorption and excretion of the radioisotope. we argue that the application of the overall algorithm is efficient in terms of performance and quality and we compare our results with those produced by applying a regular scintigraphy protocol without post-processing. the paper is structured as such: section 2 presents the related work. section 3 analyzes the proposed algorithm. section 4 presents details about the system implementation and the evaluation dataset. finally, section 5 details the conclusions reached through this endeavor. ii. related work dynamic renal scintigraphy is a well-established imaging technique in nuclear medicine [4]. the intervention of the computer in the identification of important artifacts is usually reaching to the point of the depiction of the brightness of the images throughout time in the production of the renogram. the resulting graph can provide information to the physician about the flow of the radioisotope in the kidneys. however, several approaches have been proposed in the literature for postprocessing of the results in order to assist the physician to better interpret the results. specifically, several studies ([4] [8] have shown that the automatic definition of renal rois that helps in minimizing user interaction in the evaluation of dynamic renal scintigraphy is generally required in the practice of nuclear medicine. authors in [9] state that it is a common practice to apply post-processing tools to improve the quality of the images for viewing, such as altering the display window levels and the use of filters such as smoothing or metz. rois can be used to mask out areas of high uptake not related to the back such as the kidneys and bladder as well as areas of physiological high uptake within the back and pelvis such as tuber coxae, to allow better visualization of other areas within the image. rois can also be drawn around anatomical structures to give uptake ratios. moreover, authors in [10] applied fuzzy methods in order to extract time–activity curves corresponding to renal parenchyma, renal pelvis, vascular and spatially homogeneous background. their method is applied to factor images of the renal parenchyma and identifies fuzzy regions of interest in contrast to those obtained manually in order to produce a more accurate graph for physician evaluation. similarly to what the current paper proposes, the authors of [10] achieve the exclusion of artifacts that do not add value to the creation of the time-activity curve. however, their method is applied on a different examination protocol and they aim into isolating the activity rois rather than the rois that present the clinical interest as the current paper suggests, based on well-established practices. in [11], the singular value decomposition method is presented as a potential tool for analysis and semiquantification of scintigrams. the results conclude that it is possible to “objectify” the interpretation of clinically relevant information contained in the images. they reduce the signal-tonoise ratio by forming the image with those singular vectors that have the greatest impact in the decomposition they use. other approaches are focusing on filtering out noise from the nuclear images. the most representative is [12] where the authors used signal processing methods to obtain a representation of the image in a domain where salient information could be separated from noise. the information that is contained in the noisy scintigrams is then transformed into a small number of coefficients. in turn, the coefficients are analyzed so as to derive their statistical significance. this way, the authors managed to decompose the image to its signal and noise components and to restore it once the noise components were eliminated. iii. production of activity graphs for complete renal activity and renal pelvis activity the isolation of the kidney roi is the result of a workflow that includes a sequence of small procedures and the execution of a number of algorithms. this process is depicted in figure 1. fig. 1. sequence of applied algorithms etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 251-258 253 www.etasr.com xefteris et al: a method for improving renogram production and detection of renal pelvis… in the following subsections we analyze the steps of the algorithm in detail. a. detection of kidney and renal pelvis in this section the main algorithm for the isolation of the area in the image that depicts the kidney and the renal pelvis is described. in brief, the developed algorithm analyzes the scintigraphic image in order to identify the roi and produces the renogram and radiograph of the isolated renal pelvis. these radiographs are then used for the measurements. 1) isolating the kidney region the boundary tracing algorithm is taking advantage of the brighter regions of the original radiograph in order to detect the contours that delineate the boundaries of the kidney. the algorithm is performed on a binary image where nonzero valued pixels belong to an object and zero value pixels constitute the background. regions with high brightness that are out of the roi, and appearing in scintigraphic images in the extreme upper and lower parts of the image (namely the heart and the bladder) were isolated by cropping the extremities of the image. after cropping the out-of-interest regions, a stretching function is applied on the image, in order to enhance the overall brightness of the image. stretching is a procedure where we multiply the brightness of all the pixels in the image by a factor α, where 1, with max_b=the maximum brightness value in the image. so, after stretching, for every pixel in the image we have: #ew brightness value= ⋅a old brightness value this resulted in a first approach of the isolating the roi as seen in figure 2. fig. 2. results after cropping extremes and stretching image brightness the next step in the preparation of the image for the application of the boundary tracing algorithm is the adaptive equalization of the image, in order to enhance contrast. with this procedure, we aim in further improvement of the clarity in the image, and better brightness separation between the rois and the rest of the image. the result of adaptive equalization improves the contrast in regions of the image, so that the resulting histogram follows as much as possible, the normal distribution. neighboring regions are combined with bilinear interpolation to remove artificial boundaries created by the equalization. we can see the results of adaptive equalization in figure 3. fig. 3. (left) image before adaptive equalization, (right) image after adaptive equalization in order to better facilitate the application of the boundary tracing algorithm, we have to split the image in two halves, each containing one kidney. in a sample of more than eight hundred (800) renal scintigrams taken in a clinic, the result was that the image can be split in the exact center without affecting the rois. so, from the initial matrix of 128x128 pixels, we produce two 128x64 pixels matrices, each containing one kidney. the next step in the workflow is to estimate the imagespecific statistical properties, in order to further adjust the image contrast, and then re-calculate them after the image adjustment. the statistical measures used are: the mean value, the median and the maximum of brightness for each of the two matrices containing the kidneys. by applying image adjustment we further improve the image contrast by transforming the brightness values so that 1% of the image data is saturated in high and low brightness. after these preparatory procedures our image is now ready for the detection of the rois. our purpose here is to make the kidney contours in the two matrices as “clear” as possible, and remove isolated bright pixels in the images, in order to feed the data to the boundary tracing algorithm. by exploiting the statistical properties of the images, i.e. the mean, the median and the maximum brightness values, we compute a threshold (specific and different for different scintigraphic images), under which a pixel in the image is considered to be outside the roi. this method was applied to a database of a private doctor’s clinic, on about 850 different scintigrams and procured expected results in more than 90% of the sample. another method that was tried on these samples was the a priori definition of a brightness threshold, only depending on maximum brightness value and ranging from 120 to 130, was found to be inadequate, producing good results in less than 60% of the sample. the issue that rises, after the aforementioned procedures, is that of –not only possible, but almost always presentisolated etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 251-258 254 www.etasr.com xefteris et al: a method for improving renogram production and detection of renal pelvis… pixels that were bright enough to be included in the image. another issue that has to be tackled is also that of pixels inside the rois that were not included because of their low brightness (which is crucial for the final diagnosis, since low brightness pixels inside the rois are indicative of a pathology).thus, in order to erase small or larger brightness regions, outside our main rois and re-include regions that were removed but are inside the rois, we apply binary mathematical morphology operators on the images. in binary morphology the image is considered to be a subset of an euclidean space d r or the integer grid d ℤ for a dimension d. the morphology operators used are the clearing operator, the majority detection operator and the erosion operator. the clearing operator [13] removes isolated pixels that may still exist in the image, as shown in figure 4. fig. 4. example of an isolated pixel the “majority detection” [13] operator is responsible for refilling “holes” inside the kidney regions, which were created by false-positive extractions due to low brightness. the majority detection operator checks if a pixel has value 1 and at least 5 neighbouring pixels have non-zero values. if not, the pixel’s value is then set to zero, as shown in figure 5. fig. 5. pixels before and after mazority detection finally, we perform the erosion morphological operator [13], with the unitary structural element, in order to cover regions at the edges of the kidneys, that may have been omitted from the roi. erosion of a binary image a in the euclidean space e with a structural element b is defined by: where bz is the translation of b by the vector z, i.e ezbbzbbz ∈∀∈+= }|{ with the erosion procedure we conclude all preparatory steps concerning our rois and we are now ready to isolate them from the background and apply the boundary tracing algorithm. thus, we set the brightness value of all pixels outside the kidneys to zero. the result can be seen in figure 6. the next step in our process is the application of the boundary tracing algorithm. since we have “filled” all the probable gaps inside the roi’s, there is no chance that “holes” will appear in the kidney regions and thus we will later take into account every pixel belonging to them, using its brightness value to produce the renal activity graph. the boundary tracing algorithm [14] returns the coordinates of the edges of and area, beginning from a pixel on its boundary, as shown in figure 7. fig. 6. kidney roi’s isolated and zeroing of other regions fig. 7. boundary tracing. (a) connectivity 4, (b) connectivity 8, (c) tracing sequence in an area with connectivity 4, (d),(e) tracing sequence in an area with connectivity 8 (f) boundary tracing in area with connectivity 8 (dotted lines indicate pixels tested during the application of the algorithm). now that the boundaries of the roi’s have been traced, and we have their coordinates, we proceed with the creation of two masks, one for each kidney. the masks will be used as a etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 251-258 255 www.etasr.com xefteris et al: a method for improving renogram production and detection of renal pelvis… blueprint for the kidneys in all 26 images of the scitintigraphy test, applied to each one of them, in order to calculate the sum of the brightness value of all pixels in them, and thus produce the renal activity graph. so, we create the two masks, in the form of logical arrays of size 128x64. in these masks, points inside the kidney regions have a value of 1, and points outside of these regions have a value of 0. next, the algorithm counts how many images are included in the exam folder (usual number is 26 – one image taken per minute in the course of the exam, but, depending on the needs of the doctor and the patient, this number could vary), and then it splits each image in the two parts already explained. the algorithm then superimposes the masks on the actual images of the exam, one by one, and records for each image –separately for right and left kidney-in a new array the sum of brightness values of pixels inside the areas marked with 1 in the masks. now, we have two 1xn arrays (n being the number of individual images in the exam). let l(1,n) and r(1,n) be the two arrays, indicating the left and right kidney respectively. now l(1,i) is the sum of the brightness values of the i-th image of the left kidney. the remaining step is to plot these two brightness arrays in a graph that shows brightness vs. time for each kidney. in figure 8 we can see an example result of the application of the algorithm. fig. 8. activity graph – (a) initial image (b) detected kidney regions (c) activity graph 2) renal pelvis detection in this section we will analyze the code for the detection of the rois belonging to the kidney’s renal pelvis. the renal pelvis is a funnel-shaped part that connects the ureter to the kidney. its function is to funnel urine flowing from the kidney to the ureter. fig. 9. frontal renal section, with the pelvis depicted in the middle the algorithm for the isolation of the renal pelvis is quite similar to the algorithm described for the isolation of the whole kidneys, in the previous section. the problem of detecting the renal pelvis is quite complex and it is a very difficult part of the organ to detect due to its uneven shape, as depicted in figure 9. since the images produced by renal scintigraphy are “grainy” and of low definition, the renal pelvis detection is an arduous task, performed only by the doctor at the time of the exam. although it is very hard to discern in such small images, we have two basic “guidelines” stemming from the actual practice of isolating it visually, which we will try to exploit, in order to detect it automatically: the most prominent one is its position, at the inner edge of the kidney, and the secondary one is a very mild fluctuation of brightness at the inner edge of the pelvis, in the areas where the calyxes border with the papillae. this approach combines mathematical morphology and a “game of life”-type of approach, centered around the expected time of its maximum brightness during the exam. after examining the physician’s archives of true patients’ renal scintigrams and following the physicians’ guidelines, the result was that the renal pelvis was more discernible to the human eye, between the 12th and 15th minute of the examination. at this point of the scintigram, the radionucleoid is mainly concentrated on the renal pelvis, since it has began flowing from the kidney to the ureter, as depicted in figure 10. fig. 10. showing the brightness of the renal pelvis (outlined in black) in the 12th minute of the exam in this figure – converted to rgb color for better discernibilitywe can see the bright red spot that marks the renal pelvis in the left kidney of the patient, and the somewhat darker blue region in the right kidney (reversed image). apparently, the specific patient’s right kidney is dysfunctional, while the left may be over-active. this algorithm follows the same steps with the previous one, concerning the steps up to the boundary tracing of the kidneys. a) creating a wide bounding box around the roi our task after that, is to create a wide roi around the renal pelvises, and shrink it incrementally until we have obtained a more-or-less satisfactory boundary for the pelvis itself. thus our first concern is to build a bounding box around the wider area of the pelvis, based on the data of the boundary tracing algorithm and the spatial properties of the pelvis (inner part of the kidney). etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 251-258 256 www.etasr.com xefteris et al: a method for improving renogram production and detection of renal pelvis… the first rough outline of the pelvis region is now calculated, as depicted in figure 11. fig. 11. rough outlines of the renal pelvis roi’s as acquired after boundary tracing b) detect pelvis exploiting statistical measures since we have roughly defined our initial roi’s for the renal pelvis, we can now begin tightening our knot around the area, exploiting brightness and its statistical measures. our aim here is to produce two new images (one for each kidney) each of which will have its maximum brightness value inside the renal pelvis, and which will be used to “build” an as-close-aswe-can approximate outline of it. more specifically we exploit the mean, median and maximum value of the brightness inside the bounding box, “evicting” from it pixels with brightness less than a certain threshold, specific for each exam, but greater than the 75% of the maximum brightness value. in this case too, it has been experimentally observed that a good rule of thumb is to initially exclude pixels with brightness less than 120-130, but this posed inaccuracies in exams with low overall brightness, so the use of the mean and maximum value was necessary to adapt the algorithm to each individual exam. c) applying mathematical morphology to roi’s this is the most crucial part in the procedure of renal pelvis detection. as we previously discussed, the shape of the renal pelvis is quite irregular and could not be described by the usual elementary structural elements, used in mathematical morphology. nevertheless, beginning from a small core of pixels with adequate brightness and at the right position, we can create a shape which will be an adequate –although not perfectapproximation of the renal pelvis. before performing our structural transformations, we have to clear the area of any possible isolated pixels outside the bounding box we have created, so one more time we perform mathematical cleaning operations in both images. after our image is cleared from isolated pixels, we now calculate the dimensions of the bounding box, and following, we create the structural elements of “line” and “rectangle”: • the “line” structural element is defined by its length and its angle to the horizontal axis. if our bounding box is larger than 10 pixels in length, then the length of the “line” structural element is defined as : ] 2 )( [ xboundingbolength l = , where [ ] denotes the integral part. • if the bounding box is smaller than 10 pixels in length, then the “line” structural element has length equal to it. • the angle of the structural element was experimentally calculated, to be 55o for the right kidney and 125o for the left kidney, so the structural element approximates the angle of the kidneys in the scintigram (relevant to the horizontal axis). • the “rectangle” structural element has always dimensions of 2x1 pixels. it is adequately small to create an initial centre of reference for the mask to be extracted later. • having created the structural elements in the brightest spot of our bounding box, we recursively perform the procedure of mathematical erosion already described, in order to acquire an area approximating the area of the renal pelvis. fig. 12. approximation of the renal pelvis area, using mathematical morphology (structural elements and erosion) d) completing the procedure after having procured an approximation of the renal pelvis roi, we follow the steps for mask creation described in previously, with the addition of a step of conversion of the image to rgb colour for a better visual clarity of the final image. in figure 13 the results of the application of the algorithm in two separate patient files are shown. etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 251-258 257 www.etasr.com xefteris et al: a method for improving renogram production and detection of renal pelvis… fig. 13. : results of renal pelvis detection algorithm – (a) initial image, (b) image with renal pelvis areas in blue, (c) renal pelvis activity graph the algorithm produced adequate results in more than 80% of the tested samples of the physician’s patients’ archives. although the algorithm is not perfect and there are imperfections in the final results of the produced activity graphs, this first implementation shows promising results and will be further exploited to produce a first computer aided diagnosis tool, to help physicians in their initial evaluation of the patients’ health. iv. test and evaluation the algorithm was implemented exclusively in matlab 7.3. our sample consisted of more than eight hundred (800) scintigrams, taken in a private clinic in a span of 5 years. the scintigrams were taken from adult patients of various ages and both sexes, both healthy and suffering from various conditions. the scintigrams were produced with ge’s 3000 γ camera attached to a starcam computer, each exam consisting of 26 images, one per minute. the patients were injected with weight adjusted doses of 99mtc-mag3 before the exam and lasix during it, to evaluate excretion rate. the inputs of the algorithm consisted solely of the kidney images produced by the starcam and no other evaluative input was used. the images were in png format. we evaluated the results of our algorithm in comparison to the results from the starcam computer. the main advantage of our algorithm was the removal of irrelevant to the kidneys areas outside of them. in most cases, the starcam computer did successfully trace the boundaries of the kidneys, but included in this trace bright areas outside the kidneys, owed to artifacts and image noise. with the present algorithm we had a success rate of more than 90% in successfully detecting the correct areas of the kidneys and more than 95% success at removing artifacts, thus resulting in a better production of the renal activity graph and aiding the doctor in a better diagnosis. in figure 14 we can see a comparison between the detection of the kidneys by the starcam, on the left, and our algorithm, on the right. on the left there are inclusions of areas outside the kidneys, but on the right, after processing of the image, the algorithm outputs clear outlines of the kidneys and no other irrelevant area is included. this results in a more accurate production of the renal activity graph. nevertheless, the differences in the end result of the produced renal activity graph are either way not huge. since, even in the case of other areas inclusion, their total area and brightness sum are not adequate enough to influence the original activity graph in a way that would produce extreme misleading results in the doctor’s evaluation. doctors were also always taking into account in their diagnosis this fact and thus eliminated intuitively the small error factor imposed by such imperfections in the original algorithm. fig. 14. left – kidney areas as detected by starcam, right – kidney areas detected by our algorithm the bigger innovation of this algorithm though, lies in the detection and production of the activity graph for the renal pelvis area. the renal pelvis is a very difficult area to detect and trace, but our algorithm showed good results in more than 70% of the sampled images. being an area that lies on the inner-edge of the kidney, but also with an “inconsistent” shape, and due to the numerous conditions that can be affecting it, it is deemed extremely hard to automatically detect it with extreme accuracy. thus, the initial idea of the doctors’ requirements was to produce an algorithm that would let them manually pick the area and then produce the activity graph. but since the initial algorithm performed extremely well with the whole kidneys, the idea of auto-detecting the renal pelvis with a promising success ratio was not deemed to be impossible. the production of the activity graph for the renal pelvis was judged by the evaluating physicians to be of big help in their diagnostic procedure, although of course, since the accuracy of the algorithm results varies, it was used with prudence, depending on the judgement of the doctor. v. conclusions the application of the algorithm in numerous cases produced satisfactory results. the main algorithm showed great promise in accurate detection of the kidneys and production of etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 251-258 258 www.etasr.com xefteris et al: a method for improving renogram production and detection of renal pelvis… the renal activity graph. the renal pelvis detection algorithm provided us with satisfactory first results in many cases, but showed weaknesses in some cases, by either over-covering the area of the pelvis or detecting smaller parts of it. these weaknesses were owed to brightness fluctuations in the area, exceeding the limits posed by the algorithm, which leads us to the conclusion that the algorithm needs improvement in its adaptive part, to cope for extreme conditions. thus, both algorithms can be improved, aiming at two distinct goals. the first one being to further improve the renal pelvis detection function in order to have more accurate trace of it and thus facilitate the production of better activity graphs for it. the second goal is to evaluate modified applications of the algorithm in different kinds of medical imaging data, sourcing not only from radio-nuclear-generated imagery but from other sources as well. it is very important to note that the purpose of the abovementioned study is not to provide a diagnosis replacing the physician but rather to provide more accurate results so as to assist him in the interpretation of findings. references [1] acr guidelines and standards committees, nuclear medicine & pediatric radiology, acr resolution 12, practice guideline for the performance of adult and pediatric renal scintigraphy, 2008 [2] f. jamar, r. barone, "renal imaging" in diagnostic nuclear medicine, c. schiepers, ed. springer, ch. 5, pp. 89-112, 2006. [3] m. marcuzzo, p. r. masiero, j. scharcanski, "quantitative parameters for the assessment of renal scintigraphic images", 29th annual international conference of the ieee in engineering in medicine and biology society, lyon, pp. 3438-3441, 2007 [4] k. e. britton, n. j. g. brown, c. c. nimmon, "clinical renography: 25 years on", european journal of nuclear medicine and molecular imaging, vol. 23, no. 11, pp. 1541-1546, 1996. [5] d. j. li, k. a. miles, r. w. barber, e. p. wraight, "computer-derived regions of interest for the determination of renal parenchymal transit time", nuclear medicine communications, vol. 14, no. 3, pp. 176–180, 1993 [6] h. bergman, e. dworak, b. konig, m. samal, “improved automatic separation of renal parenchyma and pelvis in dynamic renal scintigraphy using fuzzy regions of interest”, european journal of nuclear medicine and molecular imaging, vol. 26, no. 8, pp. 837-843, 1999 [7] y. tomaru, t. inoue, n. oriuchi, k. takahashi, k. endo, "semiautomated renal region of interest selection method using the doublethreshold technique: inter-operator variability in quantitating 99mtcmag3 renal uptake", european journal of nuclear medicine, vol. 25, no. 1, pp. 55-59, 1998. [8] a. houston, d. white, w. sampson, m. macleod, j. pilkington, "an assessment of two methods for generating automatic regions of interest", nuclear medicine communications, vol. 19, no. 10, pp. 1005–1016, 1998 [9] a. nelson, "nuclear scintigraphy," in equine back pathology: diagnosis and treatment, f. henson, ed. wiley-blackwell, ch. 9, pp. 94-104, 2009 [10] h. bergmann, e. dworak, b. könig, a. mostbeck, m. šámal, "improved automatic separation of renal parenchyma and pelvis in dynamic renal scintigraphy using fuzzy regions of interest", european journal of nuclear medicine, vol. 26, no. 8, pp. 837-843, 1999 [11] s. savolainen, k. liewendahl, "analysis of scintigrams by singular value decomposition (svd) technique", annals of nuclear medicine, vol. 8, no. 2, pp. 101-108, 1994. [12] g. jammal, a. bijaoui, "dequant: a flexible multiresolution restoration framework", signal processing, vol. 84, no. 7, pp. 1049-1069, 2004 [13] i. pitas, digital image processing algorithms and applications, 1st ed. new york, ny: john wiley & sons, 2000 [14] o. demirkaya, m. asyali, p. sahoo, image processing with matlab: applications in medicine and biology, 1st ed. crc press, 2008 microsoft word 9-2450_s engineering, technology & applied science research vol. 9, no. 2, 2019, 3915-3917 3915 www.etasr.com akhtar et al.: low-cost synthesis and characterization of silver nanoparticles for diverse sensing … low-cost synthesis and characterization of silver nanoparticles for diverse sensing application sarah akhtar federal urdu university of arts, science and technology, karachi, pakistan sarah@fuuast.edu.pk zahid farid department of electrical engineering, university of science and technology, bannu, pakistan zahidfarid@ustb.edu.pk hasham ahmed federal urdu university of arts, science and technology, karachi, pakistan hasamsiddiqui@gmail.com shayan ali khan department of electrical engineering, university of engineering and technology, taxila, pakistan shayan.alikhan@yahoo.com zeeshan najam khan center for advanced electronics and photovoltaic engineering, islamabad, pakistan shaani75@hotmail.com abstract—silver (ag) nanoparticles (nps) are synthesized and characterized by a low-cost chemical reduction method. silver nanoparticles (ag nps) have pre-occupied the consideration of the scientific community due to their wide range of functions, utility and industrial applications, particularly in the fields of sensing technologies and medicine (particularly their efficiency against microbes, the ability of healing the wound and antiinflammatory properties). ag nps are synthesized by a low-cost fabrication method. x-ray diffraction (xrd), scanning electron microscopy (sem), energy dispersive x-ray diffraction (edx) and photometry techniques are used in this work to identify their nature and potentiality for diverse applications in sensing technologies. keywords-scanning electron microscopy (sem); energy dispersive x-ray diffraction (edx); sodium dodecyl sulphate (sds) i. introduction the study of nano-sized particles has gained a lot of attention in research and technology due to their growing applications in electronic industry and health sciences. improvements in fundamental understanding of nps may yield better methods of their manufacturing [1]. metal nano-sized particles have been the subjects of research and exploration due to their distinctive electronic, optical, mechanical, magnetic and chemical properties. due to their size and large specific surface area [2], metallic nps can be used in many application areas such as catalysis, electronics, and photonics [3]. ii. literature review diverse research techniques have been found for the synthesis of the metallic nps, including reverse miscellaneous processes, salt diminution, ultrasonic irradiation, microwave dielectric heating reduction, radiolysis, thermal synthesis, electrochemical synthesis, etc [4]. nano sized particles of ag have displayed fascinating characteristics [4]. presently, such nps have regained importance in research due to the rise of bacterial resistance against antibiotics. the idea of using ag nps as an anti-bacterial agent is comparatively new [5]. because of their high reactivity due to their large surface to volume ratio, nps have taken over in exhibiting a critical behavior in inhibiting bacterial growth in a liquid and solid medium. ag may be used to eliminate organisms on textile fabrics/yarn or they can be used for water purification [6]. opposing to germicide effects of ionic ag, the greater antimicrobial effect may be enhanced with the smaller size of particles [7]. ag nps have been optimized via various techniques such as microwave irradiation, thermal decomposition, an electrochemical method, laser ablation and chemical synthesis [7]. the easiest and the most cost effective is the bulk-solution synthetic technique for metal nano-sized particles is the chemical reduction of metal salts/crystals. the manufacturing of nanoscale metal silver particles, of distinct morphologies and sizes by chemical reduction of ag salts has been reported [8]. this artificial technique follows the reduction of an ionic salt in a suitable medium in the presence of surfactant using various reducing agents. produced ag nps exhibit intense colors due to the plasmon resonance absorption [9]. the metal exterior is the same as plasma, which has free electrons in the conduction band and also has positively charged nuclei. iii. experimental details a. preparation of ag nps two stabilizing agents, sodium dodecyl sulphate (sds) and citric acid were used for the synthesis of ag nps, agno3 solution (1.0mg per 50ml) and 6% (w/w) sds were used as a metal salt predecessor and a stabilizing agent, respectively. hydrazine hydrate (n2h4-h2o) solution with a concentration of 2.0mm and citric acid solution (1.0mg per 50ml) were used as reducing agents. the transparent colorless solution was sufficiently heated and transformed to the characteristic pale yellow when hydrazine hydrate (n2h4-h2o) was used as the corresponding author: z. farid engineering, technology & applied science research vol. 9, no. 2, 2019, 3915-3917 3916 www.etasr.com akhtar et al.: low-cost synthesis and characterization of silver nanoparticles for diverse sensing … stabilizing agent. the occurrence of color indicated the formation of ag nps. the ag nps were then purified by centrifugation (21000rpm at 10 0 c). to remove excess silver ions, the silver colloids were washed with ethanol and dried powder of the ag nps was obtained for further analysis and characterization. fig. 1. a) sds and b) agno3 for the synthesis of ag nps b. x-ray diffraction (xrd) technique powder xrd data were collected on a siemens d5000 powder diffraction meter using cu radiation. data were collected for angle 2θ ranging from 10˚ to 90˚, using a step size of 0.05 degree/sec as placed in table i. first, we grounded the sample to powdered form and place it in the center of the sample holder having dimensions of 5cm×5cm. the sample was analyzed at random intervals. phase and mineral identification of the sample were evaluated and analyzed by diffraction searching software comprising of over 136,895 patterns. this software contains an automated search-match option that compares the pattern of the sample by the international center for diffraction data (icdd) database. table i. xrd and lattice size of ag nps chord mid. 2θ 2θ (rad) fwhm 2θ fwhm (rad) d (nm) hkl 0 a 1.00 0.66 0.28 30.00 35.77 111 4.07 44.38 0.77 0.38 0.00 29.29 220 5.77 64.56 1.12 0.37 0.00 48.87 311 4.78 77.54 1.35 0.42 0.00 86.18 511 6.39 particle diameter=50nm and concentration=1mmol/50ml c. sample analysis xrd analysis (figure 2) of the sample suggests the presence of rutile ag in major phase according to icdd no. 00-004-0783(1). the average crystallite size from the sharp peak is 50nm, which is estimated by using the scherrer’s formula. d. microscopic study sem was undertaken by using the apparatus sem, jsm6380 which provides information in relation to the size and morphology of the nps. there was a fixed conductive carbon tape to an aluminum tip and the fine particles were placed on top of it. the spot sizes were 1, 5 and 10um with a working distance of 2mm and acceleration voltage set at 25.00kv. fig. 2. x-ray diffraction (xrd) of ag nps with diameter 50nm. fig. 3. sem images of ag nps with diameter 50nm table ii. edx of ag nps by using zaf method element kev mass% error% at% c 0.277 11.72 0.53 18.69 o 0.525 40.40 0.39 48.34 na 1.041 8.08 0.23 6.72 mg 1.253 1.90 0.21 1.49 al 1.486 1.10 0.19 0.78 si 1.739 31.36 0.18 21.37 ca 3.690 5.44 0.27 2.60 total 100.00 100.00 standard less quantitative analysis fitting coefficient: 0.3351 particle diameter=50nm and concentration=1mmol/50ml e. photometry (ultraviolet visible spectroscopy (uv-vis)) we confirmed the presence of ag nps by measuring the wavelength of the sample in the spectrum uv-vis of the perkinelmer spectrophotometer lambda 265 at a resolution of 2nm (200nm to 800nm). plasmonic metal nps have greater probability for biological and chemical sensor applications, because of their insightful spectral response to the local surroundings of the nps facade and easy to monitor the light signal because of their sturdy scattering or absorption [10]. in the current study, we discovered the surface sensitivity dependence on plasmon resonance (frequency and bandwidth) reaction to changes in their neighboring environment alongside the role of optical scattering on the shape and size of nps and the kind of metal, which is, ag. the conjectural concern with the surface plasmon resonance situation exposed the spectral sensitivity. we can state that relative shift in resonance wavelength with regard to the refractive index change of neighboring materials, has two controlling factors:  first is the bulk plasma wavelength, a property reliant on the metal nature, and second on the feature ratio of the element which is a engineering, technology & applied science research vol. 9, no. 2, 2019, 3915-3917 3917 www.etasr.com akhtar et al.: low-cost synthesis and characterization of silver nanoparticles for diverse sensing … geometrical factor [11]. it is shown that the sensitivity is directly proportional to both these parameters. in order to precisely discover the dependence of the spectral sensitivity on the discrete dipole, an estimate method was used for the calculation of optical spectrum of ag [12]. though, if we utilize smaller nps they may stimulate an extreme expansion of the resonance spectrum [12]. this bounds the sensing resolution. the insensitivity of the plasmon reaction for the metal composition is attributable to the reality that the bulk plasma frequency of the metal, which indicates the spectral dispersion of the factual dielectric function of metals and the surface plasmon resonance state, has the same value for the pure metal [13]. the measured absorbance data can be correlated to the sample's concentration. samples were synthesized by dispersion of the calculated quantity of sample (very diluted) and then 3ml of the solution was kept in a cuvette and submitted to the measurement. fig. 4. curve of ag nps a diameter of 50nm and mass concentration 1mmol/50ml fig. 5. absorption spectra of silver nanoparticles with diameters ranging from 10nm to50 nm at mass concentrations of 1mmol iv. conclusion ag nps were successfully synthesized using the simple and cost-effective chemical reduction method. xrd showed the formation of high purity ag nps. sem and edx viewgraphs confirmed the presence of nps. from the photometry analysis we discovered the surface plasmons and the resonance condition. it was apparent that the spectral sensitivity or relative shift in resonance wavelength with respect to the reflective index by varying neighboring materials has two controlling factors: the bulk plasma wavelength, a property reliant on the metal nature, and the aspect ratio of element which is a geometrical parameter. the optical band gap of ag nps from the absorption spectrum by the tauc’s relation is calculated by [14]: ��� � ���� � �� (1) acknowledgment authors are grateful to the pakistan council of science and industrial research (pcsir), ministry of science and technology, pakistan for their help in np synthesis for this research. we are also thankful to the dean of sciences for providing the research fund. references [1] a. l. nogueira, r. a. f. machado, a. z. de souza, f. martinello, c. v. franco, g. b. dutra, “synthesis and characterization of silver nanoparticles produced with a bi-functional stabilizing agent”, industrial & engineering chemistry research, vol. 53, no. 9, pp. 34263434, 2014 [2] w. zhang, x. qiao, j. chen, “synthesis and characterization of silver nanoparticles in aot micro-emulsion system”, chemical physics, vol. 330, pp. 495-500, 2006 [3] m. rehan, h. m. mashaly, s. mowafi, a. a. el-kheir, h. e. emam, “multi-functional textile design using in-situ ag nps incorporation into natural fabric matrix”, dyes and pigments, vol. 118, pp. 9-17, 2015 [4] p. f. gutierrez, l. olive, a. banuelos, e. orrantia, n. nino, e. m. sanchez, f. ruiz, h. bach, y. av-gay, “synthesis, characterization, and evaluation of the antimicrobial and cytotoxic effect of silver and titanium nanoparticles”, nanomedicine: nanotechnology, biology and medicine, vol. 6, no. 5, pp. 681-688, 2010 [5] p. devaraj, p. kumari, c. aarti, a. renganathan, “synthesis and characterization of silver nanoparticles using cannonball leaves and their cytotoxic activity against mcf-7 cell line”, journal of nanotechnology, vol. 2013, articleid 598328, 2013 [6] n. singh, p. khanna, “in situ synthesis of silver nano-particles in polymethyl methacrylate”, materials chemistry and physics, vol. 104, no. 2, pp. 367-372, 2007 [7] s. parveen, r. misra, s. k. sahoo, “nanoparticles: a boon to drug delivery, therapeutics, diagnostics and imaging. nanomedicine: nanotechnology”, biology and medicine, vol .8, no. 2, pp. 147-166, 2012 [8] s. sarkar, a. d. jana, s. k. samanta, g. mostafa, “facile synthesis of silver nano particles with the highly efficient anti-microbial property”, polyhedron, vol. 26, no. 15, pp. 4419-4426, 2007 [9] n. ghobadi, “band gap determination using absorption spectrum fitting procedure”, in: international nano letters, vol. 3.no. 2, springer, 2013 [10] r. geethalakshmi, d. v. l. sarada, “characterization and antimicrobial activity of gold and silver nanoparticles synthesized using saponin isolated from trianthema decandra l”, industrial crops and products, vol. 6, no. 2, pp.107-115, 2013 [11] s. baset, h. akbari, h. zeynali, m. shafie, “size measurement of metal and semiconductor nanoparticles via uv-vis absorption spectra”, digest journal of nanomaterials and biostructures, vol. 6, no. 2, pp. 709-716, 2011 [12] n. sahu, d. soni, b. chandrashekhar, b. k. sarangi, d. satpute, r. a. pandey, “synthesis and characterization of silver nanoparticles using cynodondactylon leaves and assessment of their antibacterial activity”, bioprocess and biosystems engineering, vol. 36, no. 7, pp. 999-1004, 2013 [13] g. a. valencia, l. c. d. o. vercik, r. ferrari, a. vercik, “synthesis and characterization of silver nanoparticles using water-soluble starch and its antibacterial activity on staphylococcus aureus”, starch, vol. 65, no. 11-12, pp. 931-937, 2013 [14] u. t. khatoon, k. v. rao, j. v. rao, y. aparna, “synthesis and characterization of silver nanoparticles by chemical reduction method”, international conference on nanoscience, engineering and technology, chennai, india, november 29-30, 2011 microsoft word 16-3236_s_etasr_v10_n1_pp5186-5190 engineering, technology & applied science research vol. 10, no. 1, 2020, 5186-5190 5186 www.etasr.com bourouba & ladaci: a novel non-integer indirect adaptive control for non-integer order systems … a novel non-integer indirect adaptive control for non-integer order systems with non-prior knowledge bachir bourouba department of electrical engineering ferhat abbas setif-1 university setif, algeria bourouba_b@yahoo.fr samir ladaci department of electronics, electrical engineering and automation, national polytechnic school of constantine constantine, algeria samir_ladaci@yahoo.fr abstract—in this study, a new non-integer indirect adaptive control method with reference model is suggested for the class of non-integer order systems. the objective of model reference control is to include the output of the given reference fractional model in tracking the output of a controlled plant by using the concept of on-line goal adaptation. the stability of the closed-loop system is analyzed via the lyapunov method. finally, matlab simulation results are presented to illustrate the effectiveness of the proposed method of indirect fractional model reference adaptive control. keywords-non integer order system; fractional adaptive control; mrac; control system; lyapunov stability i. introduction model reference adaptive control (mrac) is one of the main approaches of adaptive control. the fundamental goal of adaptive control is to treat with system uncertainty and/or time varying system parameters. the essential idea in adaptive control is to design a controller which adapts itself to plant uncertainty or time variance in the plant dynamics. adaptive control is one of the most important topics in the literature on control when the model of the system is uncertain [1-7]. fundamental research efforts have been focused on mrac designs for linear plants with parametric uncertainty. generally in model reference adaptive control, the goal is to have a system that follows a certain system as a reference model. in reality, an adaptive controller is designed to achieve this goal, despite the uncertainties that may occur in the parameters of the system [8]. fractional-order calculus is an area of mathematics that deals with integrals and derivatives of non-integer orders. in other words, it is a generalization of the traditional calculus that leads to similar concepts and tools, but with a much wider applicability. in the last three decades, fractional calculus has been rediscovered by engineers and scientists. it is applied in an increasing number of fields, including control theory among them. as an example, the modeling of viscoelastic materials has been done in many old and recent works using fractional order derivatives [10-11]. the success of non-integer order controllers is unquestionable due to the emergence of effective methods in differentiation and integration of non-integer order equations [12-13]. in recent years, an increasing number of studies related with the application of the fractional calculus (fc) theory are observed in many areas of science and engineering [14]. in this paper, a new control structure named non-integer indirect adaptive control for a class of non-integer order system with non-prior knowledge is proposed to investigate the control for a class of fractional system. this novel method of control is based in mrac configuration. based on already reported results, in this paper, we propose a novel method to control a class of linear fractional-order systems based in mrac configuration. this novel methodology of non-integer indirect adaptive control with reference model is proposed to guarantee stability and the tracking of the reference model. two simulation examples are given to illustrate the performance obtained by the proposed indirect adaptive fractional control scheme. ii. fractional-order definition and preliminaries fractional-order calculus or non-integer-order calculus is the generalization of the classical integer order calculus. there are several definitions for fractional order derivative and integral. fractional calculus is considered as an extension of integer-order calculus to non-integer order calculus. the theory of derivatives and integrals of non-integer order was firstly mentioned by leibnitz. after that, other definitions were generated by liouville, grunwald, letnikov and riemann. the integro-differential operator is given by a t d α where: ( ) re( ) 0 1 re( ) 0 re( ) 0 a t t a d dt d d α α α α α α τ α−   >   = =   <  ∫ (1) where a denotes lower limits and t are the upper limits respectively of the operator, and a∈r is the order of integration or differentiation[9, 15, 16]. corresponding author: bachir bourouba engineering, technology & applied science research vol. 10, no. 1, 2020, 5186-5190 5187 www.etasr.com bourouba & ladaci: a novel non-integer indirect adaptive control for non-integer order systems … the riemann–liouville derivative definition of the order α is described as: 1 1 ( ) ( ) ( ) ( ) tn a t n n a d g d g t d ndt t α α τ τ α τ − +   =   γ − −  ∫ (2) where 1 ,n n nα− < < ∈� and 1 0 ( ) x x e αα ∞ − −γ = ∫ is the gamma function, and f(t) is a continuous time function. the following definition is given in [13, 14]: ( ) 1 1 ( ) ( ) ( ) ( ) t n a t n a g d g t d n t α α τ τ α τ − + = γ − −∫ (3) the grunwald–letnikov’s derivative definition can be written as [15, 16]: 0 0 1 ( ) lim ( 1) ( ) t a h k h j d g t g t jh jh α α α −      → =   = − −    ∑ (4) ( ) ! ! !j j j α α α   =  −  where h denotes the time increment, t a h −      is a flooring operator and the binomial coefficients. as the grunwald–letnikov’s fractional operator is more consistent than others, then the grunwald–letnikov’s fractional-order differential equations operator will be employed in this paper for computer numerical simulations due to its wide applications in engineering and well-understood physical interpretation. if the initial conditions are taken as zero, the laplace transform of differintegral operator ( )a td g t α is obtained as: { } { }( )( ) ( )a t d g t l d g t l s l g t dt α α α α   = =    (5) in general, any fractional-order single input single output (siso) system can be described by a fractional differential equation of the form [9, 11]: 1 0 1 0 1 0 1 0 ( ) ( ) .... ( ) ( ) ( ) ... ( ) n n m m n t n t t m t m t t a d y t a d y t a d y t b d u t b d u t b d u t α α α β β β − − − − + + + = + + + (6) where 0 1 2 0 1 2 , .... ... n m α α α α β β β β < < < <  < < < < indicates the fractional-orders and 0 1 2 , , ,...., n a a a a 0 1 , ,..., m b b b denote the system parameters. if 0 1 0 1 , .... ... n m andα α α α β β β= = = = = = = , the system (8) is called a commensurate order system, otherwise system (6) indicates an incommensurate order system. iii. model reference adaptive fractional control adaptive control is a well-researched topic in control theory spanning several decades in research. the model reference adaptive control system is an important scheme in adaptive control. it may be treated as an adaptive system in which the desired performance is expressed in terms of a reference model. the configuration of the model reference adaptive control block is given in figure 1. in the configuration mrac the desired behavior is specified by a reference model, and the parameters of the controller are adjusted based on the error, which is the difference between the outputs of the closedloop system and the outputs of the reference model. the mechanism for adjusting the parameters of the controller in a model reference adaptive control can be obtained by applying the stability theory of lyapunov. the mrac structure is divided in four main parts: the plant, the controller, the reference model and the adjustment mechanism. fig. 1. block diagram scheme of adaptive control with reference model to introduce the model reference fractional adaptive control problem, we consider a class of commensurate fractional order systems formulated as: ( ) . ( ) . ( ) q t d y t a y t b u t= + (7) where ( )x t ∈� and ( )u t ∈� are the system state and the control variable respectively, a and b are unknown constant parameters but sgn(b) is known. the fractional reference model was chosen to generate the desired trajectory ( ) m y t which the plant output ( )y t has to flow. the reference model is given by: ( ) . ( ) . ( ) q t m m m m d y t a y t b r t= + (8) subject to 0 (0) m m y y= , the reference model is stable, i.e., am<0 and r(t) is the reference input. the parameters m m a and b are known constants, ( ) and ( ) m y t r t are measured at each time t. the design objective is to make the tracking error ( ) ( ) ( ) m e t y t y t= − converge to 0. let us first design a model reference control (mrc), that is, the control design assuming all the parameters are known, to ensure that the output ( )y t follows ( ) m y t . we express the closed-loop system in terms of the time derivative of the tracking error ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) q q q m m m m e t y t y t a a b a e t b u t y t r t b b = − −  = + − −    (9) engineering, technology & applied science research vol. 10, no. 1, 2020, 5186-5190 5188 www.etasr.com bourouba & ladaci: a novel non-integer indirect adaptive control for non-integer order systems … the basic state-feedback state tracking problem of this section is to design a state feedback law u(t) to control the plant given by (7). firstly, we define an ideal controller that perfectly cancels out the uncertainty and enables ( )x t as: * * 1 2 ( ) . ( ) . ( )u t y t r tψ ψ= + (10) where * 1 m a a b ψ − = and * 2 m b b ψ = (11) the superscript (∗) denotes ideal constant values which are unknown. the tracking error equation is established as: ( ) ( ) ( ) 0 q m e t a e t− = (12) the tracking error converges to zero exponentially and the system is asymptotically stable. when the plant parameters a, b are unknown, (10) cannot be implemented. to solve the control problem, we develop a new fractional indirect adaptive control design, which first adaptively updates the estimates of the plant parameters a and b and then calculates the controller parameters 1 ( )tψ and 2 ( )tψ in (10) from the plant parameter estimates. the real control input is: 1 2 ( ) ( ). ( ) ( ). ( )u t t y t t r tψ ψ= + (13) where: 1 ˆ( ) ( ) ˆ( ) m a a t t b t ψ − = (14) 2 ( ) ˆ( ) m b t b t ψ = (15) ˆ( )a t and ˆ( )b t are the estimates of a and b respectively, at time t, and search for an adaptive law to generate ˆ( )a t and ˆ( )b t online. let ˆ( )a a t a= −� and ˆ( )b b t b= −� be the estimation errors. now, the plant model (7) is expressed as: ( ) ˆ( ) . ( ) ( ( ) ). ( ) q t d y t a y t b t b u t= + − � (16) substituting (15), (16) and (17) into (18) we get: ( ) ˆ( )ˆ( ) . ( ) ( ( ) ). ( ) ( ) ˆ ˆ( ) ( ) ˆ( )ˆ. ( ) ( ). ( ) ( ) ˆ ˆ( ) ( ) ˆ( ) . ( ) ( ) ˆ ˆ( ) ( ) ˆ( ) ( ) ( ) ( ) . ˆ( q m m t m m m m m m m a a t b d y t a y t b t b y t r t b t b t a a t b a y t b t y t r t b t b t a a t b b y t r t b t b t a a t a a y t b r t b b t  − = + − +      − + +      =    − − +      − = − + − � � �� ( ) ( ) ˆ) ( ) m b y t r t b t   +    (17) based in the tracking error ( ) ( ) ( ) m e t y t y t= − , from (17) and (7) we have: ( ) ˆ( ) ( ) ( ) ( ) ( ) ( ) ˆ ˆ( ) ( ) q m m m a a t b e t a e t ay t b y t r t b t b t  − = − − +    �� (18) lemma 1: assume ( )f t ∈� is a continuous and derivable function. then, for any time instant t≥t0 the following inequality holds [12, 17, 18]: 0 0 21 ( ) ( ) ( ) 2 c c t t t t d f t f t d f t α α≤ (19) stability proof. in order to analyze the closed-loop stability and to find the adaptive laws we consider the following measure for the error e(t), ( )a t� , and ( )b t� . 2 2 2 1 2 1 1 1 ( , , ) 2 2 2 v e a b e a b ϕ ϕ = + +� �� � (20) the positive real design parameters 1 0ϕ > and 2 0ϕ > are often referred to as adaptive gains, as they can affect the speed of parameter adaptation. taking fractional derivative of (22) with respect to time and using lemma 1, we have: ( ) ( ) ( ) ( ) 1 2 1 1q q q q v ee a a b b ϕ ϕ ≤ + + � �� � (21) ( ) 2 1 ( ) 2 ˆ ( ) ˆ ˆ m q m m a a e a ey a a bb b y t r e b b α ϕ ϕ    − + +      ≤   −  − +       � � � � (22) ( ) ( ) ( ) 1 2 ˆ ( ) ˆ ˆ 1 1 m m m q q q a a b e a e ay b y t r b b v a a b b ϕ ϕ   −   − − +       ≤   + +     �� � �� � (23) note that ˆ( )a a t= ��� and ˆ( )b b t= ��� . based on the updated estimates of ˆ( )a t and ˆ( )b t , we can calculate the parameters: ( ) 1 ( ) 2 ˆ ( ) . ( ). ( ) ˆ( )ˆ ( ) ( ) ( ) ( ) ˆ ˆ( ) ( ) q q m m a t e t y t a a t b b t y t r t e t b t b t ϕ ϕ  = −   − = − +    (24) from (22) and (24) we have: ( ) 2q m v a e≤ (25) this implies that ( , , )v e a b�� as a function of t does not increase, that ( )e t , ( )a t� , and ( )b t� are bounded and so is u(t) in (18). then, from (25), 2 0 ( )e t dt ∞ < ∞∫ , and ( ) ( ) q e t in (17), is 2 ( )e t l∈ . finally, by using the lemma of barbalat’s given in [5, 15-17] we conclude that the system is lyapunov stable and engineering, technology & applied science research vol. 10, no. 1, 2020, 5186-5190 5189 www.etasr.com bourouba & ladaci: a novel non-integer indirect adaptive control for non-integer order systems … the tracking error [ ]lim ( ) ( ) 0m t y t y t →∞ − = converges asymptotically to zero. iv. numerical simulations in this section, some numerical simulation studies are carried out to show the effectiveness of the proposed control scheme to the non-integer order system. firstly, let us consider an unstable non integer order system defined by: ( ) ( ) 2. ( ) q t d y t y t u t= + (26) to build the adaptive controller we choose a model reference given by : ( ) ( ) ( ) q t m m d y t y t r t= − + (27) where 0.98q = . the values of the parameters of adaptive gain were chosen as: φ1=20 and φ2=80. the control law necessitates the reference model, which has two design parameters am and bm. both of them can be chosen without restraint, nevertheless it is worth to set am=1 and bm=1 to get a 0.78 gain of reference dynamics. the initial conditions of the system and reference model are y(0)=0 and ym(0)=0. the reference input signal r(t) is given by: ( ) cos(2 )r t tπ= (28) if the parameters of the system and reference model are known, the control law can be calculated as: * * 1 2 ( ) . ( ) . ( )u t y t r tψ ψ= + (29) from (10) we obtain: * 1 2m a a b ψ − = = − (30) and: * 2 1 m b b ψ = = (31) the simulation results for this case are shown in figures 23, where we show the time responses of the plant state y(t) and the output of the reference model ym(t) and the control u(t). in the case where the system parameters are known, we can calculate the parameters of the controller directly, and from simulation the output of the system y(t) converges quickly to the output of the reference model ym(t). when the parameters of the system are unknown, a and b are estimated by ˆ( )a t and ˆ( )b t respectively. to determine the controller parameter gains 1 ( )tψ , 2 ( )tψ , (14) and (15) are used. the on-line estimate is generated by the adaptive law (24). the control law, based on the certainty equivalence principle, is given by (13). fig. 2. comparison of the state plant signal with reference signal fig. 3. control u(t) the initial conditions of the system and reference model are ( ) 0 and ( ) 0 m y t y t= = . we chose the same parameter values of the adaptive controller of the first case for this simulation, φ1=20 and φ2=80. the simulation results are shown in figures 4-8. the results show the time responses of the plant state and the state of the reference model, the follow up error, and the control. figures 6 and 7 show that the estimated parameters a(t) and b(t) converge to the true values of the system. figures 2-8 indicate that the proposed method is quite efficient. the follow up error converges to zero and the control is bounded. the results are shown in figure 4. it can be seen that e(t)→0 and y(t)→ym(t) as t→∞. the convergence rate can be increased by increasing the adaptation rates φi, i=1, 2, but a large value of φi can lead to an increase in the sensitivity of the control system to noise and unmodeled dynamics that can lead to instability. fig. 4. state plant signal with reference signal fig. 5. estimate of a(t) engineering, technology & applied science research vol. 10, no. 1, 2020, 5186-5190 5190 www.etasr.com bourouba & ladaci: a novel non-integer indirect adaptive control for non-integer order systems … fig. 6. control u(t) fig. 7. estimate of b(t) fig. 8. tracking error results by the proposed approach iv. conclusion a systematic design procedure for the design of a noninteger indirect adaptive controller for a class of non-integer systems has been presented in this paper and a new fractional indirect adaptive control scheme was presented based on a lyapunov function. the proposed control strategy uses a mrac configuration. it was shown that by using the proposed novel non integer adaptive controller it is possible to design a controller for the non-integer system. the effectiveness of the proposed scheme was confirmed by numerical simulations. these simulations were carried out in matlab running in windows 7. the step size was set to 0.001s, and the other settings were kept at default values. simulation results verified the correctness of the developed theoretical approach. references [1] f. a. zaid, p. ioannou, k. gousman, r. rooney, “accommodation of failures in the f-16 aircraft using adaptive control”, ieee control systems magazine, vol. 11, no. 1, pp. 73–78, 1991 [2] b. mirkin, p. o. gutman, “model reference adaptive control of state delayed system with actuator failures”, international journal of control, vol. 78, no. 3, pp. 186–195, 2005 [3] k. j. astrom, b. wittenmark, “on self-tuning regulators”, automatica, vol. 9, no. 2, pp. 185-199, 1973 [4] p. caines, s. lafortune, “adaptive control with recursive identification for stochastic linear systems”, ieee transactions on automatic control, vol. 29, no. 4, pp. 312-321, 1984 [5] g. tao, adaptive control design and analysis, john wiley & sons, 2003 [6] p. a. ioannou, j. sun, robust adaptive control, prentice-hall, 1996 [7] i. d. landau, r. lozano, m. saad, a. karimi, adaptive control, springer, 1998 [8] m. abedini, m. a. nojoumian, h. salarieh, a. meghdari, “model reference adaptive control in fractional order systems using discrete-time approximation methods”, communications in nonlinear science and numerical simulation, vol. 25, no. 1-3, pp. 27-40, 2015 [9] b. bourouba, s. ladaci, “comparative performance analysis of ga, pso, ca and abc algorithms for ractional pi λ d µ controller tuning”, 8th ieee international conference on modelling, identification and control, algiers, algeria, november 15–17, 2016 [10] b. bourouba, s. ladaci, a. chaabi, “moth-flame optimization algorithm based fractional order pi λ d µ controller with mrac tuning configuration”, international journal of systems, control and communications, vol. 9, no. 2, pp. 148-171, 2018 [11] s. ladaci, a. charef, “on fractional adaptive control”, nonlinear dynamics, vol. 43, no. 4, pp. 365-378, 2006 [12] i. podlubny, fractional differential equations, academic press, 1999 [13] i. podlubny, “fractional-order systems and pi λ d µ controllers”, ieee transactions on automatic control, vol. 44, no. 1, pp. 208–214, 1999 [14] r. hilfer, applications of fractional calculus in physic, world scientific, 2000 [15] b. bourouba, s. ladaci, a. chaabi, “reduced-order model approximation of fractional-order systems using differential evolution algorithm”, journal of control, automation and electrical systems, vol. 29, pp. 32–43, 2018 [16] p. l. butzer, u. westphal, an introduction to fractional calculus, world scientific, 2000 [17] m. p. aghababa, “stabilization of a class of fractional-order chaotic systemsusing a non-smooth control methodology”, nonlinear dynamics, vol. 89, no. 3, pp. 1357–1370, 2017 [18] k. khettab, s. ladaci, y. bensafia, “fuzzy adaptive control of a fractional order chaotic system with unknown control gain sign using a fractional order nussbaum gain”, ieee/caa journal of automatica sinica, vol. 6, no. 3, pp. 816–823, 2019 engineering, technology & applied science research vol. 8, no. 6, 2018, 3565-3569 3565 www.etasr.com masmoum & alama: required separation to mitigate pounding of adjacent building blocks required separation to mitigate pounding of adjacent building blocks mohammed s. masmoum civil engineering department king abdulaziz university jeddah, saudi arabia ms.masmoum@gmail.com mohammed-sohaib alama civil engineering department king abdulaziz university jeddah, saudi arabia sohaib.alama@hotmail.com abstract—this research discusses the feasibility of using the required minimum separation distance based on sbc 301-2007. moment resistance frames were designed with expansion joints requiring 400mm separation distance. nonlinear response history analysis was conducted with four ground motions selected and scaled to match the risk-targeted response spectrum of neom city based on asce 7-16 provisions. an equivalent spring constant value based on floor lateral stiffness was selected as a gap link stiffness. finally, an evaluation for the pounding response of adjacent blocks is presented along with the conclusions. keywords-pounding; expansion joint; minimum seperation i. introduction saudi arabian cities witness major development due to the high demand for residential housing and high-rise buildings. high-rise buildings require sophisticated designs since these flexible structures might include expansion joints that separate them from adjacent rigid structures. this scenario can be idealized by a high-rise tower surrounded by a podium or adjacent parking structure. the difference in mass and stiffness might make them move out-of-phase during strong ground motion events. this movement makes adjacent building blocks prone to pounding hazard. saudi building code [1] requires a minimum separation distance to reduce or eliminate pounding hazard. the minimum separation distance is calculated based on the square root sum of squares (srss) of maximum inelastic drifts of adjacent building blocks. this article discusses the feasibility of using the required minimum separation distance by saudi building code to guard against pounding hazards. ii. literature review over 40% of buildings were reported to be severely damaged or collapsed during the 1985 mexico city earthquake. about 15% of these buildings collapsed due to pounding [2]. a survey following the 1989 loma prieta earthquake showed that more than 200 buildings were damaged due to pounding in a distance around 90km from the epicenter which indicates that pounding could be catastrophic for cities near or far from active faults. the survey concluded that a rational method is required to be enforced to mitigate the pounding hazard [3]. many methods have been proposed to account for minimum required separation: 1) absolute sum of displacement (abs), 2) square root sum of squares (srss), and 3) spectral difference method using double difference combination (ddc) rule [4-8]. sbc 301-2007 did adopt the concept of srss because of its simplicity, high accuracy and small differences in the minimum required separation distance comparing to dcc [9-10]. a comparison between these methods had been conducted with conclusion that srss can be practical and provide the required separation distance [11-12]. this article is discussing the feasibility of using the minimum separation distance required by sbc 301-2007. iii. methodology neom city was selected as the study site. the building blocks are designed to satisfy code requirements for gravity and seismic loads. also, those building blocks have different fundamental periods in order to increase the pounding likelihood. a 12-story building will be designed adjacent to 6story building block. variable separation distance values between the building blocks are assumed. a set of ground motions is selected and scaled based on asce 7-16 [13] §16.2.2&3 criteria. nonlinear response history analysis was performed by sap2000 [14]. modeled building blocks are linked by gap link in order to measure the pounding force due to variable separation distances. finally, a discussion for the results and research findings will be presented. a. building design sbc 301-2007 seismic uniform-risk probabilistic hazard maps indicate that neom has a moderate risk of earthquake hazards comparing to other cities in saudi arabia. values for short period (ss=0.5sec) and 1 sec-period (s1=0.13sec) accelerations have been selected. sbc 301-2007 §9.4.3 requires modifying these factors based on soil type. due to absence of such information, soil class d had been assumed for conservatism. the modified accelerations (sms=0.70sec) and (sm1=0.285sec) will produce a response spectrum defined as risk-targeted maximum considered earthquake (mcer) response spectrum. sbc 301-2007 §9.4.4 requires to divide sms and sm1 by 1.5 to produce design response spectrum accelerations (sds=0.446sec) and (sd1=0.19sec). also, it is assumed that the study location will include commercial engineering, technology & applied science research vol. 8, no. 6, 2018, 3565-3569 3566 www.etasr.com masmoum & alama: required separation to mitigate pounding of adjacent building blocks buildings that have an occupancy important factor of type ii (ie=1). the suitable lateral force-resisting system for the study location based on the seismic design category (sdc=c) and (ie=1) was intermediate reinforced concrete moment resisting frame. structural system, response modification factor (r=4), over-strength factor (ω0=3), and deflection amplification factor (cd=4.5) have been selected based on sbc 301-2007 table 10.2 with reliability factor (ρ=1) based on sbc301-2007 §10.3.3 requirements. cast-in-place reinforced concrete frame with hollow-core slab system has been selected to resist all gravity loads. 12-story and 6-story building blocks with length of 18m and 3.6m story elevation were assumed. figure 1 shows a plan for a high-rise tower and adjacent parking structure. the hatched area represents the effective slab width supported by the beam. the self-weight of the slab is equal to 53.6kn/m. the super-imposed dead load had been estimated to be 20.92kn/m. live load had been assumed to be 19.2kn/m. fig. 1. plan view for adjacent building blocks. sbc 301-2007 §2.3.1 introduces basic load combinations. based on sbc 301-2007 §2.3, for strength design approach, all structural elements must be designed using factored loads that are generated from different load combinations. the critical combination will govern the design of the member. the following combinations are required by the saudi building code: 1.4d (1) 1.2 1.6d l+ (2) 1.2 1.0 0.5d e l+ + (3) 1.2933 1.0 0.5 e d q l+ + (4) 0.9 1.0d e+ (5) 0.8066 1.0 e d q+ (6) note that substitution for horizontal and vertical values for e in (3) and (5) had resulted in values of (4) and (6), where qe is defined as the horizontal lateral load due earthquake. values of 35mpa and 45mpa concrete compressive strength were assumed for beams and columns respectively. the modulus of elasticity had been assumed as 4700√𝑓′𝑐 based on sbc 3042007 §8.5.1. the concrete will have a density of 2430kg/m3 and thermal expansion coefficient of 9.9×10-6. takada hysteresis model was selected for concrete material. stressstrain curve was defined based on unconfined mander model with ultimate unconfined strain capacity of 0.005, strain at unconfined 𝑓′𝑐 0.002, and -0.1 for final compression slope. grade 420mpa reinforcing steel rebars confirm astm a-615 [15] specification. the modulus of elasticity had been estimated as 200,000mpa. the steel rebars will have a density of 7850kg/m3 and thermal expansion coefficient of 11.7×10-6. kinematic hysteresis model was selected for the steel rebars material. simple stress-strain curve’s defined based on ultimate strain capacity was 0.09, and the strain at onset of strain hardening was 0.01, and -0.1 for final compression slope. sbc 301-2007 §10.9 permits the use of equivalent lateral force to estimate the base shear with sdc c. the following equation estimates the base shear. s v c w= (7) where v is the estimated base shear (v12story=455.73kn, v6story=437.52kn), w is the seismic effective weight depending on member self-weight and 100% of the dead load (w12story=19691.82kn, w6story=10169.61kn), and cs is the seismic coefficient (cs12story=0.0232, cs6story=0.0433). sbc 301-2007 §10.9.3 requires that the fundamental period value from the computational model (t12story=2.885sec, t6story=1.082sec) should not exceed the product of approximate period and the upper limit variable. the upper limit approximate period values had been used to calculate base shear (ta(upper)12story=2.127sec, ta(upper)6story=1.140sec). sbc 3042007 [16] §10.11.1 requires to reduce the moment of inertia during the elastic analysis to account for cracking of concrete. this approach is enforced if the bending moment at service level passes the cracking moment. the threshold values are 0.35ig for beams and 0.70ig for columns. different reinforced concrete cross sections were defined in the computational model shown in figure 2. rigid zone had been defined for all column and beam joints with a value of 0.5. all cross sections satisfied the design requirements of sbc 304-2007 due to prescribed loading conditions. sbc 301-2007 §10.9.7.1 permits to use the fundamental period from the computational model in drift check calculations. the inelastic drift will be used to check inter-story drift limit. inter-story drift should not exceed the product of 0.02 by story height as explained in sbc 301-2007 §10.12.1. sbc 301-2007 §10.12.2 requires a minimum separation distance between adjacent building blocks based on square root square sum of the maximum of maximum inelastic drift of the two adjacent building blocks at the same story level. the inelastic drift of the 6th floor from the 12-story and 6th roof from 6-story building block was used to determine the required separation distance (δx12story=198.9mm, δx6story=104.35mm). it is concluded that a separation of 224.61mm will be enough to reduce or eliminate the pounding hazard based on code provision. b. selection and scaling of ground motion records asce 7-16 §16.2.2 requires the use of at least 11 ground motion records collected from the study site. fewer ground motion records can be used when the study site ground motion intensity is considered low because of the expected low sensitivity of nonlinear model response [17]. in this study, four ground motion records were selected with respect to study site engineering, technology & applied science research vol. 8, no. 6, 2018, 3565-3569 3567 www.etasr.com masmoum & alama: required separation to mitigate pounding of adjacent building blocks design spectrum curve as shown in table i. there were no available records for the study site. fig. 2. elevation view with cross sections detail. asce 7-16 §16.2.2 permits to use records from another site with similar parameters in the absence of site ground motion records. those parameters are joyner-boore distance (rjb), fault control mechanism, and moment magnitude. rjb distance is defined as the shortest distance from the study site to the surface projection of the fault. rjb distance is measured from the projected area of aqaba fault and is estimated between 15 to 45km. slip-strike faulting style is assumed for the aqaba fault [18]. the intensity of the historical earthquakes in the study site is ranged from 4 to 6mw. the record of maximum horizontal acceleration spectrum will be scaled to match risktarget response spectrum (2% probability of exceedance) and the average of records spectrum should not be less than 10% from the risk-target response spectrum curve within a range from 1.5 times structural fundamental period until 0.2 times the fundamental period as shown in figure 3. fig. 3. scaled ground motions. c. nonlinear response parameter analysis asce 7-16 11§16.3.2 requires using a 100% of the dead load as the initial condition for nonlinear response history analysis. ramp function with duration of 30sec had been assumed for the initial condition load case. the proceeding nonlinear response history cases had been solved by implicit direct integration with newmark-beta method with values of γ=0.5 and β=0.25. the time step had been discretized with a value of 0.005sec, since all the ground motion records are discretized with similar value or more. the accuracy of the results has been verified by rerun of the analysis with half step size. it is found that both runs were stable, converged, and had similar pounding force [17]. asce 7-16 §16.3.5 requires a damping ratio that does not exceed 0.25 for building equivalent viscous damping. the value of 0.25 for damping had been selected for all the response history analysis load cases. based on that, specified stiffness and mass proportional damping coefficients had been selected with 1st and 3rd period values from the flexible building blocks [19]. geometric nonlinearity was not considered. for load case of nonlinear parameters, maximum and minimum time step was kept on default value. the maximum iteration for constant-stiffness and newtonraphson were taken as 10 and 40 per step respectively. the convergence tolerance had been selected with a value of 0.0001. table i. ground motion record details record serial number* rsn0020 rsn0169 rsn0175 rsn0729 scale factor 0.93 0.87 1.50 1.09 earthquake name northern calif-03 imperial valley-06 imperial valley-06 superstition hills-02 station ferndale city hall delta el centro array #12 imperial valley wildlife liquefaction array year 1954 1979 1979 1987 rjb distance (km) 26.72 22.03 17.94 23.85 control mechanism strike slip strike slip strike slip strike slip moment magnitude 6.50 6.19 6.53 6.54 *records were collected through university of california, berkeley peer ground motion database (nga-west2). d. gap link stiffness gap link is a numerical tool assigned to connect two joints located around the expansion joint which can be used to measure the pounding force intensity between the adjacent building blocks by defining a specific opening. if the total value of the displacement and opening exceed zero the link will not measure any pounding force since the building blocks are away from each other as shown in (8): ( ) ( ) ( ) ( ) 0 0 0 gap if d open f k d open if d open +  =  + +  (8) engineering, technology & applied science research vol. 8, no. 6, 2018, 3565-3569 3568 www.etasr.com masmoum & alama: required separation to mitigate pounding of adjacent building blocks if the total value of the displacement and opening are less than zero, the link will measure the pounding force using linear elastic relationship as shown in (8). it is observed that there is a positive correlation between gap link stiffness and pounding force. the intent from using the link is to measure pounding force without any superfluous stiffness. the right stiffness value should assist finding a converged solution with reasonable pounding force. the nonlinearity of the pounding response analysis and its sensitivity to ground motion scaling intricate the process of finding the appropriate stiffness value. there are many proposals that relate axial stiffness of the connecting element to link stiffness. these relations are usually multiplied by the order of magnitude to reach a converged solution [7-12]. authors suggest the use of in-series equivalent spring from lateral stiffness of the connected floors as shown in (9): ( )12 6 12 6 story story gap story story k k k k k = + (9) the floor lateral stiffness values in (10) and (11), can be quantified by restraining all the translation degree of freedom in the model for all the floors except the 6th floor of each building blocks. a dummy force equal to 100kn was assigned as a lateral force on the 6th floor of each building block. building blocks have been analyzed separately to get the floor displacements (d6th-floor=0.0004m, d6th-roof=0.0008m). note that that all columns have been modified with 0.7ig (k12story=250,000 kn/m, k6story=125,000kn/m). 12 6 story th floor f k d − = (10) 6 6 story th roof f k d − = (11) from the previous relations, it is concluded that the equivalent spring stiffness is equal to 83,333kn/m. this value was used for response time history analysis. iv. results and discussion pounding forces were measured and summed from all assigned links. various values of separation distance have been used to see the feasibility of the code required provision as shown in figure 4. it was found that the sbc 301-2007 recommendation for approximately 400mm did successfully mitigate the pounding force for all the scaled records. record rsn0175 required half of the code separation to eliminate pounding force. it was noticed that record rsn0169 was recorded from the same event but it required a full separation distance to mitigate to pounding force. a potential reason for rsn0175 result is the low frequency content comparing to rsn0169 and difference in recording station location. furthermore, it was observed that separation distance smaller than 50mm results in high pounding intensity. this gives an indication that adjacent building blocks do not support each other in the case of small separation distances since the force intensity amplified. a potential reason behind this amplification is the difference in fundamental periods between the adjacent building blocks. fig. 4. maximum pounding force as function of seperation distance. it was also observed that the pounding force of record rsn0020 was not reduced by increasing the separation distance from 50mm to 100mm. a similar characteristic can be noticed for record rsn0729 from 100mm and 200mm. this shows the importance of providing a full sbc 301-2007 code separation distance to mitigate pounding force. it also contradicts the finding of the record rsn0175 which require half of the recommended distance. all records exhibit a unique pounding response due to increase in the separation distance. the pounding force of rsn0175 reduces rapidly with the separation distance, unlike rsn0020 and rsn0169 records which had a moderate reduction. noticeably, rsn0729 pounding reduction was affected slowly by the increase of the separation distance. it can be seen that this record had been taken from a site with liquefied soil. this result shows that pounding response could not easily be mitigated in soil site class f [20] based on soil classification of sbc 301-2007 §14.1.1 or asce 7-16 §20.3.1. v. conclusion on the basis of the results obtained during the course of this work and the assumptions made, the following conclusions were found: • the code that required separation provision did successfully mitigate the pounding hazard based on study assumptions. • it is important to adopt the exact separation distance since nonlinear response history analysis revealed that pounding force exists in separation distance less than the required value. • nonlinear response history analysis can be used routinely to evaluate the pounding hazard for new designed structures. • equivalent spring stiffness based on floor lateral displacement can be assumed as gap link stiffness to give a converged solution. if the integration still does not converge, the stiffness value might need a further multiplicand to reach a converged solution. • it is important to conduct a nonlinear response history analysis for sites that are characterized with liquefied soil. engineering, technology & applied science research vol. 8, no. 6, 2018, 3565-3569 3569 www.etasr.com masmoum & alama: required separation to mitigate pounding of adjacent building blocks since pounding response could not be mitigated easily by applying the code separation provision. • it is encouraged to seek more reliable methods to mitigate pounding hazard other that separation. for example, it was required to have 400mm to fully mitigate the pounding hazard based on the study assumption. a lot of technical effort and financial resources are required to cover this separation distance. references [1] sbc committee 301, structural loading and forces. saudi building code national committee, 2007 [2] e. rosenblueth, r. meli, “the 19875 earthquake: causes and effects in mexico city”, concrete international, vol. 8, pp. 23-34, 1986 [3] k. kasai, b. f. maison, “building the 1989 pounding damage during loma prieta earthquake”, engineering structures, vol. 19, no. 3, pp. 195-207, 1997 [4] v. jeng, k. kasai, b. f. maison, “a spectral difference method to estimate building separations to avoid pounding”, earthquake spectra, vol. 8, no. 2, pp. 201-223, 1992 [5] j. penzien, “evaluation of building separation distance required to prevent pounding during strong earthquakes”, earthquake engineering & structural dynamics, vol. 26, no. 8, pp. 849-858, 1997 [6] j. h. lin, “separation distance to avoid sesmic pounding of adjacent buildings”, earthquake engineering and structural dynamics, vol. 26, no. 3, pp. 395-403, 1997 [7] r. e. valles, a. m. reinhorn, evaluation, prevention and mitigation of pounding effects in building structures, national center for earthquake engineering research, state university of new york at buffalo, 1997 [8] h. p. hong, s. s. wang, p. hong, “critical building separation distance in reducing pounding risk under earthquake excitation”, structural safety, vol. 25, no. 3, pp. 287-303, 2003 [9] d. lopez-garcia, t. t. soong, “evaluation of current criteria in predicting the separation necessary to prevent seismic pounding between nonlinear hysteretic structural systems”, engineering structures, vol. 31, no. 5, pp. 1217-1229, 2009 [10] r. jankowski, s. mahmoud, earthquake-induced structural pounding, springer international publishing, 2015 [11] m. j. favvata, “minimum required separation gap for adjacent rc frames with potential inter-story seismic pounding”, engineering structures, vol. 152, pp. 643-659, 2017 [12] m. isteita, k. porter, “safe distance between adjacent buildings to avoid pounding in earthquakes”, 16th world conference on earthquake engineering, santiago, chile, january 9-13, 2017 [13] asce/sei standard 7-10, minimum design loads for buildings and other structures, american society of civil engineers, reston, va, usa 2010 [14] computers and structures inc, csi analysis reference manual, computers and structures inc., berkeley, california, usa, 2016 [15] astm a615/a615m-18e1, standard specification for deformed and plain carbon-steel bars for concrete reinforcement, astm international, 2018 [16] sbc committee 304, structural concrete structures, saudi building code national committee, 2007 [17] applied technology council, guidelines for nonlinear structural analysis and design of buildings. part i general, national institute of standards and technology, u.s. department of commerce, 2017 [18] h. s. saffarini, “ground motion characteristics of the november 1995 aqaba earthquake”, engineering structures, vol. 22, pp. 343351, 2000 [19] d. r. pant, a. c. wijeyewickrema, “structural performance of a base-isolated reinforced concrete building subjected to seismic pounding”, earthquake engineering & structural dynamics, vol. 41, no. 12, pp. 1709-1716, 2012 [20] s. naserkhaki, m. el-rich, f. n. a. a. aziz, h. pourmohammad, “separation gap, a critical factor in earthquake induced pounding between adjacent buildings”, asian journal of civil engineering, vol. 14, no. 6, pp. 881-898, 2013 a ab pr of pr (sr the rel pe eq mo cal vo sho av sta dio en sim for of mi un ran ho att vo eo of bo 11 de liq co stu eq fug pre engineeri www.etas a nu and pe h school of national u bil bstract—mixtu operties have flash calculat oblem. in this rk) and peng ermodynamic lated compoun rformed. by uations of sta onitored. th lculations is lume and mol ows consider ailable in the l keywords-pe ate; mathemati oxide; hydrogen thermodyna ngineering app mulations [1]. r an appropria f phase behav ixtures contain nable to predic nge of tempe owever, the tribution of t olume pressure oss are mostly f vapor-liquid oth polar and ]. however, nsity, constan quid equilibriu mpared to sr udy of vapor quilibrium [16 gacity, and o ediction by ing, technology sr.com umeric eng-r hydro bilal h f chemical an university of s islamabad lal.h_che3@sc ure phase e a significant r tion generates research, a co g-robinson (pr properties of nds in a critic applying m ates, the beha e numerical applied to st le fraction. th rable converg literature. eng-robinson; ical modeling; n i. in amic propertie plications for the equation ate, valid and ior at vapor-l ning light gas ct liquid dens erature, acentr prediction c temperature d e parameter in y used in chem equilibrium a nonpolar com the pr eos nt critical co um for hydrog rk [12-15]. t r liquid, liqu 6]. for the liq on subcritica srk is relia gy & applied sc hussain an cal co robins carbon hussain nd material en sciences and t d, pakistan cme.nust.edu. quilibrium a role in industry s an appropri omparison of s r) equations o f a mixture o cal region at mathematical avior of binar analysis o tudy the pres he approach u gence with e soave redlich flash calculati ntroduction es play a vit r chemical p n of states (eo robust solutio liquid equilibr ses or heavy l sity more accu ric factor and can be made dependence f n the eos [7-9 mical industri and thermodyn mpounds conta s prediction ompressibility gen and nitro the equations uid-liquid and quid compoun l and superc able, but wh cience research d ahsan: a nu ompari son eq ns’ th ngineering technology .pk and thermod y. numerical a iate solution soave redlich of state predict of hydrocarbo phase equilibr modeling of ry gases mixt f isothermal ssure behavio used in this re experimental h-kwong; equa ion; methane; n tal role in ch process desig os) is mostly a on for the pre rium for all k iquids [2-6]. e urately under d on critical e precisely b factor and ef 9]. the srk a ies for the pre namic propert aining mixtur of saturated y factor and ogen is more are involved d vapor-liquid nds the predic critical the fu hen the temp h umerical comp ison o quation hermo ynamic analysis for the kwong ting the on and rium is f both tures is flash or with esearch results ation of carbon hemical gn and applied ediction kind of eos is r a vast points. by the ffective and pr ediction ties for res [10, liquid vaporprecise d in the d-liquid ction of fugacity perature be gi th is ac pa eo m bo ca un ga ca iso eq in nu ex nu co inp liq co ge alg iso co vol. 8, no. 1, parison of soav of soav ns of s odynam school o national u ecomes high in ve accurate p he critical com kept constan centric factor arameter and oss. however mean field para oth equations arbon dioxide nder study in as solubility an arbon dioxide othermal flas quilibrium for n figure 1. the purpos umerical app xperimental d umerical appr ompressibility nput and mole quid and vapo ondition of ra enerate more gorithm. the othermal cond ompared, and 2018, 2422-242 ve redlich kwo ve red state f mic pr muhamm f chemical an university of s islamabad ahsan@scm n case of pola redictions [17 mpressibility fa nt for all mix is involved in the effective r, the relation ameter and the s [23]. hydr e/propane and this research nd phase equi containing m sh, the calcu separation of fig. 1. isot se of this stu proach used data obtained roach for bot factor, pressu e fraction of e or phases is ob atio between precise k-v e relationship ditions for bo d pressure mo 26 ng and peng-r dlich k for pr ropert mad ahsan nd material en sciences and t d, pakistan me.nust.edu.pk ar and heavy c 7, 18]. in pr actor and the p xture compoun n the estimatio e volume for nship of an ace e effective vo rogen/propane d methane/n-d h. because in ilibrium of hy mixtures have ulation is do f liquid and va thermal flash pro udy is to com for srk a d from the th cubic equ ure and tempe every mixture btained as resu liquid and va value than i of pressure oth srk and ole fraction r 2422 robinson equa kwon edictin ties ngineering technology compounds, it and srk calc pitzer acentric nds [6, 19-22 on of the mea both srk a entric factor w olume is differ e, methane/ndecane mixtu chemical ind drogen, metha e vital role [2 one at vapo apor phases as ocess mpare the inn and pr eos literature. i uations of sta erature as algo e component ult under the apor fugacity in the start and volume pr eoss m relationship o ations … ng ng t cannot culation c factor 2]. this an field and pr with the rent for -butane, ures are dustries, ane and 24]. at r-liquid s shown novative s with in this ates the orithm’s in both applied y which of the e under model is of both engineering, technology & applied science research vol. 8, no. 1, 2018, 2422-2426 2423 www.etasr.com hussain and ahsan: a numerical comparison of soave redlich kwong and peng-robinson equations … models is compared with experimental data for all given mixtures. the comparison shows that in a mixture containing organic compounds the pr model is more precise in both phases. however, when the mixture contains both organic and inorganic compounds, the srk model is more precise in the liquid phase compared to pr model. ii. mathematical modeling the isothermal flash calculation is carried out for the phase equilibrium by iterating pressure to get the liquid and vapor fraction of the mixture. for satisfying the applied condition, iterating pressure applies the loop whereas the temperature and pressure are independent variables for this system. for kvalues, where i i i y k x  (1) in literature, empirical correlations are available for k values. in this case, the empirical correlation used is wilson equation for k-value which is further used for the calculation of phase fraction. if the k-value approaches equilibrium, the convergence occurs for the solution. 1 exp[5.37(1 )(1 )]i ri i ri t k p    (2) for the calculation of liquid and vapor mole fraction, the richford rice procedure is followed. on (5) for liquid mole fraction, the newton-raphson method is used, and the method uses the condition given in (7). (1 ) i i i z x l l k    (3) i i iy k x (4) 0 (1 ) ( ) (1 ) cn i i i i k z f l l l k      (5) ( ) old old new old l f l l l df dl         (6) 51 10 new old l l       (7) i i i i z y l x y    (8) equation of state parameters is calculated from given equations: 1 1 ( ) ( )c c n n m i j iji j aa x x aa      (9) ( ) (1 ) ( ) ( )ij ij i jaa k aa aa  (10) 1 cn m i ii b xb    (11) for the suitable vle behavior of the given mixture, we can solve the srk and pr eos to get molar volumes of both phases [25]. because of the difference in phase’s composition, the two solutions are essential for roots of both cubic eos. the iterative approach is applied to (12) for cubic roots of srk eos and to (13) for cubic roots of pr eos. ( ) ( ) m m m m m m aart p v b v v b     (12) 2 ( ) ( 2 ) m m m m m m m aart p v b v v b b      (13) compressibility factor is calculated by using (14): ml l pv z rt  (14) the fugacity and pressure relation give a dimensionless number which is the fugacity coefficient. the liquid phase fugacity for all components is calculated from (15) and for vapor phase a change is made in (15) by replacing xi with yi and l subscript with v. = 1 2 exp n 2 ( ) ln ( ) ln ln c ml i ml ml ml ml n j ijj ml ml ml ml i ml ml ml ml ml ml ml ml l i v b p v b v b x aa v rtb v b b aa v b b rtb v v b z x                                        (15) to satisfy the equilibrium, (16) is used to converge the solution at certain liquid and vapor composition [26]. if the equilibrium is not satisfied, (21) is used for new k-value and again iterate the process until the satisfaction of equilibrium. − 1 < 10 (16) ∅ = (17) ∅ = (18) ∅∅ = (19) ∅∅ = (20) k = k (21) the overview of the iterative method is explained in the flow chart shown in figure 2. the operating parameters for eos modeling are given in table i. engineering, technology & applied science research vol. 8, no. 1, 2018, 2422-2426 2424 www.etasr.com hussain and ahsan: a numerical comparison of soave redlich kwong and peng-robinson equations … table i. operating parameters parameters hydrogen propane methane n-butane hydrogen propane methane n-butane tc (k) 33.2 370 190.82 425.32 pc (atm) 12.8 41.8 45.8 37.42 ω 0.205 0.153 0.012 0.199 t (k) 310.93 310.93 p (atm) 13 433 3.536 136 carbon dioxide propane methane n-decane carbon dioxide propane methane n-decane tc (k) 304.2 370 190.82 617.8 pc (atm) 73 41.8 45.8 21.1 ω 0.268 0.153 0.012 0.49 t (k) 277.56 477.594 p (atm) 5.4 37.9 3.536 136 fig. 2. flow chart of the flash calculation iii. results and discussion numerical analysis approach is applied for both srk and pr eos on four sets of binary mixtures: hydrogen/propane, methane/n-butane, carbon dioxide/propane and methane/ndecane with a tolerance level of 10-7. under isothermal conditions for hydrogen, methane, and carbon dioxide the behavior of pressure with volume is observed. figures 3-5 show the decrease in pressure by the increasing volume for srk and pr eos when the temperature is less than the critical compared to when the temperature is close to critical. after some interval, the point from where there is no remarkable change in pressure is reached. in the case of mixture of hydrogen/propane, wide deviation has been reported. this is caused by the presence of hydrogen in the system. in order to overcome this deviation the binary interaction parameter is used. in vapor phase, the phase behavior shows no difference between srk and pr eos model results with experimental data [27] but in the liquid phase, the phase behavior results of srk model show less deviation compared to the results of pr model. fig. 3. isotherms for hydrogen fig. 4. isotherms for methane fig. 5. isotherms of carbon dioxide engineering, technology & applied science research vol. 8, no. 1, 2018, 2422-2426 2425 www.etasr.com hussain and ahsan: a numerical comparison of soave redlich kwong and peng-robinson equations … fig. 6. mole fraction of hydrogen at various pressures fig. 7. mole fraction of methane at various pressures fig. 8. mole fraction of carbon dioxide at various pressures fig. 9. mole fraction of methane at various pressures however, the graphical trend of srk and pr model follow the same trend of experimental outcomes as shown in figure 6. the presence of carbon dioxide in the mixture will generate a deviation in the prediction of phase behavior. figure 8 shows that in the liquid phase the deviation of pr eos from experimental results is less than that of srk model, however in vapor phase the deviation of srk is less compared to pr model but the trend of phase behavior for both srk and pr eos model follows the experimental phase behavior. in a binary mixture of methane/n-butane and methane/n-decane the phase behavior predicated by pr eos model is more precise with experimental results compared to srk model in liquid phase but in the vapor phase, both srk and pr eos are both accurate as shown in figures 7, 9. this shows that in critical conditions the prediction of phase behavior can be done in a precise way for hydrocarbon mixtures. however, there is a wide difference in volatilities of methane and n-decane, but the mixing rules of the eos have applied accurately. iv. conclusions in this study, numerical analysis is applied on srk and pr eos for pressure relation with mole fraction and volume for binary mixtures of hydrogen/propane, methane/n-butane, carbon dioxide/propane and methane/n-decane. the mole fraction relation with pressure for all binary mixtures is acquired at vapor-liquid equilibrium by making an iteration of pressure in the certain domain under critical conditions. the prediction of phase behavior by srk and pr eos models show that both models give an accurate prediction for the system of methane/n-butane and methane/n-decane with experimental results under critical conditions. however, in hydrogen/propane mixture the phase behavior in liquid phase predicted by srk model show less deviation with experimental data compared to pr model. this is due to the presence of lighter gases such as hydrogen in the mixture and low mixture pressure. vle is affected by the presence of carbon dioxide in carbon dioxide/propane mixture due to which deviation is reported up to a finite range of pressure. the pr model shows less deviation with experimental data in the liquid phase, but srk model shows less deviation in the vapor phase. the trend of deviation for both srk and pr with experimental data decreases with increase in pressure and at high pressures it engineering, technology & applied science research vol. 8, no. 1, 2018, 2422-2426 2426 www.etasr.com hussain and ahsan: a numerical comparison of soave redlich kwong and peng-robinson equations … become almost insignificant. the isotherm from srk and pr showed that the pressure initially decreases, after it starts increasing and finally reaches constant behavior. in a mixture containing only organic compounds the approach used for pr eos is more precise with experimental data of pressure and mole fraction at both phases. however, when the mixture contains inorganic and organic compounds the approach used for srk eos results in more precise pressure and mole fraction relationship with experimental data in the liquid phase. nomenclature pr eos = peng-robinson equation of state fl = fugacity of a component in a mixture (pa) ki = k-values of nth component (dimensionless) k = binary interaction parameter (dimensionless) l = liquid mole fraction (dimensionless) pc = critical pressure (atm) p = pressure (pa) r = ideal gas constant t = time (seconds) tc = critical temperature (kelvin) t = temperature (kelvin) v = vapor 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soave, s. gamba, l. a. pellegrini, “srk equation of state: predicting binary interaction parameters of hydrocarbons and related compounds”, fluid phase equilibria, vol. 299, no. 2, pp. 285-293, 2010 [26] t. sugahara, s. murayama, s. hashimoto, k. ohgaki, “phase equilibria for h 2+ co 2+ h 2 o system containing gas hydrates”, fluid phase equilibria, vol. 233,no. 2, pp. 190-193, 2005 [27] g. soave, “equilibrium constants from a modified redlich-kwong equation of state”, chemical engineering science, vol. 27, no. 6, pp. 1197-1203, 1972 microsoft word 23-2411_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3609-3613 3609 www.etasr.com solangi et al: investigation of quantity, quality and energy content of indigenous sugarcane trash … investigation of quantity, quality and energy content of indigenous sugarcane trash in naoshehro feroze district, sindh sajjad hussain solangi department of mechanical engineering, quaid-e-awam university college of engineering, science and technology, larkano, pakistan sajjad05me14@yahoo.com abdul qayoom jakhrani department of chemical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan aqunimas@hotmail.com kishan chand mukwana department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan kcmukwana@quest.edu.pk abdul rehman jatoi department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan arjatoi@quest.edu.pk muhammad ramzan luhur department of mechanical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan ramzanluhur@yahoo.com abstract—quantity, characteristics, and energy content in sugarcane trash of six different indigenous sugarcane varieties were computed for their possible utilization. results revealed that the total sugarcane trash weight percentage was 24.0% of the total sugarcane crop. among all examined varieties, variety 240 produced the highest and the variety hs12 the lowest percentage of sugarcane trash with 28% and 18.6% respectively. moisture and ash content were found less in brown leaves and more in the tops of sugarcane trash parts. the fixed carbon values in brown leaves, green leaves, and tops of the variety thatta10 were the highest found, with 18.4%, 15.5%, and 17.3% respectively. carbon element’s percentage in brown leaves of variety hs12 was the highest with 50.0% and in thatta10 was the lowest with 43.4%. highest heating value was found in thatta10 with 16.0mj/kg, which is close to the literature reported values. keywords-energy content; higher heating value; proximate analysis; ultimate analysis; sugarcane trash i. introduction the major sources of biomass are crop residues, animal manure and municipal solid waste. some major crop residues are wheat straw, rice husk, rice straw, sugarcane trash, bagasse and cotton sticks [1]. sugarcane is a suitable agricultural energy crop [2]. sugarcane crop can be divided into different parts: stem, fresh leaves, and dry leaves. sugarcane trash is the field residue remaining after harvesting green leaves (fresh leaves), dry leaves (brown leaves) and tops. the brown sugarcane trash almost remains un-utilized and is burnt openly in the fields and the remaining trash (green leaves and tops) is collected to feed farm animals [2]. sugarcane produces mainly two types of biomasses, namely sugarcane trash and bagasse. sugarcane trash or cane trash is an excellent biomass resource, as it is being used as a raw material for energy production. the worldwide bioenergy potential of sugarcane trash is around 9475gwh/year [3]. it is estimated that around 26,280,000 hectares of land are under cultivation in pakistan [3]. sugarcane is one of the major crops in pakistan, being cultivated on 1,029,000 hectares in 2010-2011, which is about 4% of the total cropped area in the country. it is estimated that about 5,752,800 metric tonnes of sugarcane trash are being generated from a total sugarcane production of 63,920,000 metric tonnes [4, 5]. the production of sugarcane trash depends on the plant variety, crop age, type of soil and weather conditions of the area. there are different varieties of the sugarcane in pakistan. these differ from each other in color, production magnitude and size. the major sugarcane varieties cultivated in sindh province are thatta10, 240, 246, 234, hs12 and sibea. the yield of the sugarcane crop can be estimated by measuring the production of the sugarcane (tonnes) per unit of cultivated area (acre). the sugarcane trash quantity can be evaluated by measuring the sugarcane trash produced per unit tonne of the sugarcane crop. it is reported that the average sugarcane trash (green leaves, brown leaves and tops) per yield (tonne) of sugarcane crop is around 13% [6] and 15% [3]. the energy content of the sugarcane trash can be determined either through direct measurement of the heating value of the crop residue through bomb calorimeter or indirectly by proximate and ultimate analysis. in proximate analysis, moisture content, volatile matter, ash content and fixed carbon are determined. in ultimate analysis, the quantitative analysis of various elements present in the matter such as carbon, hydrogen, sulfur, oxygen, and nitrogen is determined. the proximate and ultimate analysis of the sugarcane trash showed that the volatile matter engineering, technology & applied science research vol. 8, no. 6, 2018, 3609-3613 3610 www.etasr.com solangi et al: investigation of quantity, quality and energy content of indigenous sugarcane trash … was 74% to 80%, ash 6% to 10%, and fixed carbon 12% to 17%. the moisture content in sugarcane trash was about 19.3% [7, 8]. the tops of sugarcane contained 1.5% to 5% more fixed carbon than the leaves. the heating values of sugarcane trash ranged from 17.7 to 18.9mj/kg [7], and 17 to 21mj/kg [9]. nitrogen (n), sulfur (s), and chlorine (cl) in the trash were less than 1%. authors in [10] and [11] determined the proximate and ultimate analysis of sugarcane trash as shown in tables i and ii respectively. sugarcane leaves were found as sustainable biomass feedstock for the production of biofuels. authors in [12] reported that the sugarcane tops, leaves and bagasse can generate 9twh electricity in thailand, which could decrease greenhouse gas emissions by 4.8mt of co2 equivalents per year. author in [13] reported that about one-third of the energy is available in the tops and leaves of sugarcane crop. at present, sugarcane residues in pakistan are being burnt outdoors, which not only damages the natural environment but it is also a waste of energy. sugarcane growers do not have the knowledge of its energy content, and environmental benefits. besides, there is no proved scientific method for proper quantification and quality analysis of sugarcane trash. the purpose of this study was to determine and quantify the composition and energy content of sugarcane trash in district naushahro feroze of sindh province, pakistan. table i. proximate and ultimate analysis results [10] proximate analysis ultimate analysis properties values properties values fixed carbon [wt.%] 21.26 carbon (c) 51.21 volatile matter [wt.%] 70.86 hydrogen (h) 5.16 moisture content [wt.%] 4.55 nitrogen (n) 1.93 ash [wt.%] 3.33 oxygen (o) 40.33 heating value [mj/kg] 18.3 sulfur (s) 1.37 table ii. proximate and ultimate analysis results [11] proximate analysis (% weight) parameters dry leaves green leaves tops bagasse moisture content 13.5 67.7 82.3 50.2 ash 3.9 3.7 4.3 2.2 fixed carbon 11.6 15.7 16.4 18 volatile matter 84.5 80.6 79.3 79.9 ultimate analysis (%) carbon (c) 46.2 45.7 43.9 44.6 hydrogen (h) 6.2 6.2 6.1 5.8 nitrogen (n) 0.5 1.0 0.8 0.6 oxygen (o) 43.0 42.8 44.0 44.5 sulfur (s) 0.1 0.1 0.1 0.1 chlorine (cl) 0.1 0.4 0.7 0.02 ii. materials and methods a. study area the study was carried out in the geographical area of naushahro feroze district, sindh, pakistan. the district is located at the center of sindh province covering an area of 2,945km 2 . in this district, about 25 to 30 thousand acres are being used for cultivation of sugarcane, and a huge quantity of sugarcane trash is produced and wasted. the average sugarcane yield per acre is about 20 tonnes with the sugarcane trash of around 4.8 tonnes. two fields in the district, namely, dhearan and moro were selected for collection, quantification, and characterization of sugarcane trash samples. six varieties of sugarcane crop, namely 240, sibea, 234, hs12, thatt10 and 246 were investigated. b. quantification of sugarcane trash the quantification of the sugarcane trash was done by estimating the total cultivated area of the sugarcane crop and by the knowing of the average sugarcane trash (brown leaves, green leaves and tops) quantity produced per tonne and sugarcane crop. the total sugarcane cultivated area in the district was estimated by survey, interviews of farmers, landlords and administrators of different sugar mills, and through satellite pictures. the production of sugarcane trash per tonne of sugarcane crop was determined by taking 40kg of sugarcane crop of each variety from the selected fields. the sugarcane trash produced per 40kg of the crop was weighted. green leaves (gl), brown leaves (bl) and tops of each variety were collected and weighted separately. c. characteristic and energy content of sugarcane trash the characteristic and energy content of sugarcane trash was determined by taking three samples of each variety. proximate and ultimate sample analyses were carried out for the determination of their physical and chemical characteristics, and indirect computation of energy content. the energy content or heating value of the samples was also directly determined using bomb calorimeter. in proximate analysis, moisture, volatile matter, ash, and fixed carbon content were determined. the moisture content (mc) of the samples was computed by the percentage of loss in weight. the equipment used was a drying oven, china crucible of 32cc volume, electronic micro balance and desiccators following the astm-e871. the mc of the samples was determined by (1) [16]: 100[%] ×         − − = ci fii ww ww mc (1) where wi is the initial sample weight, wfi is the final sample weight and wc is the crucible weight. the volatile matter (vm) was found by percentage in weight loss by astm-e872. the equipment used was chromium-nickel crucible with lid and an electrically operated electric furnace. the vm content of the samples was determined by (2) [16]: 100100[%] ×         − − ×= ci fii ww ww vm (2) similarly, the ash content (ac) of the samples was calculated by the mass percentage of the remains after process of dry oxidation at 575 ºc for a time period of 3 hours by adopting astm-e1755. the equipment used was a crucible, electric muffle furnace, drying oven and desiccator. the ac of the samples was determined by (3): 100[%] ×        − − = contod contash mm mm ash (3) where mash is the final mass of the ash, mcont is the tare of the container, and mod is the initial mass of 105ºc dried sample and container. the fixed carbon (fc) was calculated from the engineering, technology & applied science research vol. 8, no. 6, 2018, 3609-3613 3611 www.etasr.com solangi et al: investigation of quantity, quality and energy content of indigenous sugarcane trash … resultant of the summation of the percentage of mc, vm and ac subtracted from 100 as in (4): [%][%][%]100[%] ashvmmcfc −−−= (4) the ultimate (elemental) analysis of the samples was carried out by adopting the procedures given by the association of official analytical chemists (aoac), (aoac2005), and international organization for standardization (iso-17025). in this analysis carbon, hydrogen, nitrogen, sulfur and oxygen concentrations of the samples were determined. the total carbon content of sugarcane trash samples was estimated by dividing the organic matter with the factor 1.82 [17]. the amount of the hydrogen was measured using thermo scientific flash method (thermo scientific flash ea series usa). total nitrogen content was measured using kjeldahl apparatus buchi k-314, with 0.1m naoh as standardized titrant and 0.50% methyl red solution was employed as an indicator. the sulfur content was computed as per astm-2007 by precipitating sulfur in the form of baso4 using 40% bacl2 solution. oxygen content of the samples was calculated with the use of the difference method by using (5): 100o[%] c[%] h[%] s[%] n[%] ash[%]= − − − − − (5) energy content, i.e. the higher heating value (hhv) of sugarcane trash samples was determined using adiabatic bomb calorimeter by adopting astm-e-711. the calibration of the calorimeter was done by the burning of benzoic acid. after that, the burned sample was weighted. finally, the hhv was determined by the difference of the temperature before and after combustion taking place. moreover, the quantification of sugarcane samples and their characteristics were compared with the results of other studies. the comparison was done in order to know the quantity and quality of sugarcane with respect to other areas of the world, whether the results obtained provide similar trends or variations from other researchers. iii. results and discussion the results include quantification, proximate and ultimate analysis, and energy content of different sugarcane trash varieties. a. quantification of the sugarcane trash the total average sugarcane trash was found about 24% of the sugarcane crop. average gl, bl, and tops produced per 40kg of sugarcane crop were 8%, 11% and 5% respectively. it is observed that the variety 240 gave 11.19kg/40kg (28.0%), which is the largest quantity and the variety hs12 gave 7.42kg/40kg (18.6%), which is the least quantity among all examined sugarcane crop varieties (figure 1). it is shown that the variety 240 showed maximum bl value with 5.16kg/40kg, and sibea bl had the minimum value with 4.08kg/40kg. similarly, the maximum gl quantity was produced from the variety 234 and was 4.0kg/40kg and the minimum was from hs12 with a value of 2.0kg/40kg. likewise, the top produced from the variety 240 was 3.0kg/40kg which was the greater, and hs12 produced 1.2kg/40kg, which was the lowest among all examined varieties. the average values of bl, gl and tops produced from all varieties were 4.5kg, 3.3kg and 2.2kg respectively. b. characterization of the sugarcane trash the characterization of the sugarcane trash consists of proximate and ultimate analysis. 1) proximate analysis the results of proximate analysis of the sugarcane trash samples are presented in figure 2, with moisture content (mc), volatile matter (vm), ash and fixed carbon (fc) measured for each part of each variety. mc in the brown leaves of all examined varieties was less, and tops was more among the different parts of sugarcane trash. the average moisture content in bl, gl and tops was 5.0%, 6.6% and 37.0% respectively. the least mc was found in bl of sibea with 2.3%, the gl of 246 with 4.7%, and the tops of 234 with 23.6% therefore, these parts of sugarcane trash were found more practicable. as far as the vm was concerned, it was found more in the bl and less in the tops. fig. 1. weight of sugarcane trash per 40kg of sugarcane crop. fig. 2. average proximate analysis results of sugarcane trash. the average vm of all the varieties in bl, gl and tops is 75.1%, 74.4% and 41.5% respectively. in general, the vm in the tops was less and in the bl more among the other parts in all varieties. the average ash content (ac) was found more in the tops, and less in the bl as compared to different parts of sugarcane trash. the average ac in bl, gl and tops was 3.8%, 4.3% and 4.9% respectively. the average fc was found greater in the bl, and less in the gl as compared to different parts of sugarcane trash. the average fc in bl, gl and tops engineering, technology & applied science research vol. 8, no. 6, 2018, 3609-3613 3612 www.etasr.com solangi et al: investigation of quantity, quality and energy content of indigenous sugarcane trash … was 16.7%, 14.5% and 15.9% respectively among all varieties. fc content was found greater in thatta 10. the fc content in bl, gl and tops of thatta 10 were 18.4%, 15.5% and 17.3% respectively. the fc content was found less in the gl and more in bl than the other parts of sugarcane trash. 2) ultimate analysis the results of ultimate analysis are given in figures 3 to 5. three samples of each part of sugarcane trash of all varieties were examined. it was found that the percentage of carbon is greater than other elemental percentages in the samples with oxygen being the second major element. the carbon percentage of all varieties and samples lied between 40% and 50%. the percentage of hydrogen ranged from 3.5% to 6%, nitrogen ranged from 0.25% to 1%, oxygen ranged from 34.5% to 42.5% and sulfur ranged from 0.13% to 0.21%. the average values of carbon in bl, gl, and tops were found 46.6%, 44.3% and 41.8% respectively. the respective hydrogen percentage was 5.0%, 4.8% and 4.4%. likewise, the nitrogen percentage was 0.4%, 0.8% and 0.62% respectively. the oxygen percentage was 39.7%, 37.5% and 39.0% and the sulfur percentage was 0.2%, 0.2% and 0.2%. fig. 3. ultimate analysis results of different varieties of sugarcane trash fig. 4. ultimate analysis results of different components of sugarcane trash 3) higher heating value energy content i.e. the hhv of the sugarcane trash was determined with the help of a bomb calorimeter. eighteen samples of all parts of sugarcane trash, namely bl, gl and tops of all six varieties were examined as shown in figure 6. the recorded results showed that the energy content of the sampled bl lied between 14.0 and 17.7mj/kg. the heating value of the sampled gl lied between 10.0 and 13.7mj/kg. the heating value in tops was found between 11.0 and 15.0mj/kg. fig. 5. nitrogen and sulphur content of different components of sugarcane trash fig. 6. energy content of different varieties of sugarcane trash it is observed that bl had the highest average hhv and gl the lowest among the other parts of sugarcane trash. the average heating values were: 16.0mj/kg for bl, 12.5mj/kg for gl and 14 mj/kg for tops. iv. obtained results-reported values comparison the results obtained during quantification, proximate and ultimate analysis and hhv were compared with the work of other researchers in the same field. the total sugarcane trash quantity in weight percentage reported in [18] was 25.0% and 23.0% in [13] and the obtained value was 24.0%. the bl percentages reported in [11] and [13] were 14.0% and 12.3% respectively, whereas, the measured value was slightly less with 11.0%. regarding the results of proximate analysis, it was found that the mc in bl, gl and tops of sugarcane trash determined in [11] were 13.5%, 67.7% and 82.3% and the obtained values were 5.0%, 6.6% and 37.0%. the vm content vm in bl, gl, and tops of sugarcane trash determined in [11] were 84.5%, 67.7% and 79.3% and the obtained values were 75.1%, 74.4% and 41.5% respectively. the ac in bl, gl and engineering, technology & applied science research vol. 8, no. 6, 2018, 3609-3613 3613 www.etasr.com solangi et al: investigation of quantity, quality and energy content of indigenous sugarcane trash … tops of sugarcane trash determined in [11] were 3.9%, 3.7% and 4.3%, and the obtained values were 3.8%, 4.3 and 4.9%. the fc content in bl, gl and tops determined in [11] were 11.6%, 15.7 and 16.4% and the obtained values were 16.7%, 14.5% and 15.9%. regarding the ultimate analysis parameters, the carbon percentage reported in [11] and [10] was 45.3% and 51.2% respectively and the measured values were 44.2%. the hydrogen content given in [11] was 6.2% and in [10] 5.2% and the measured value was 4.7%. the nitrogen given in [11] was 0.8% and in [10] 1.9%, and the measured one was 0.6%. the oxygen level reported in [11] was 43.3% and in [10] 40.3%, while the measured value was 38.7%. the sulphur percentage reported in [11] was 0.1%, in [10] 1.4% and the measured value was 0.2%. the energy content (i.e. hhv) of sugarcane trash reported in [11] was 17.1mj/kg and in [10] 18.3mj/kg, while the measured value was 16.0mj/kg. it is found that all results are comparable with the reported values of other researchers. v. conclusions the total sugarcane trash weight percentage reported by two different researchers was 25.0%, 23.0%, and the measured value was 24.0%. the variety 240 produced the highest, and the variety hs12 the lowest percentage of sugarcane trash with 28% and 18.6% respectively among all examined varieties. moisture and ac in bl was less and the tops gave more among sugarcane trash components and examined varieties. the fc values in bl, gl and tops of thatta10 were found the greatest with 18.4%, 15.5% and 17.3% respectively. on the basis of ultimate analysis, the most carbon percentage was found in the bl of hs12 and the least in thatta10. the hhv in the bl of sugarcane trash samples reported in [11], [10] and [19] were 17.1mj/kg, 18.3mj/kg and 17.4mj/kg respectively and the measured value was 16.0mj/kg. the obtained value of energy content in the examined samples and the reported values were found comparable with ±6% diversity. it is suggested that the quantification of different components of sugarcane trash may be carried out separately using different varieties and areas with higher, moderate and lower yield fields. water and soil analysis may be carried out in order to see the reason behind sugarcane crop yield variation. in addition, sugarcane trash samples may be tested for making charcoal briquettes and for cogeneration systems with biomass gasification gas turbine integrated with sugar mills. references [1] n. aziz, “biomass energy potential in pakistan”, available at: 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cellatoglu, m. ilkan, “solar torrefaction of solid olive mill residue”, bio resources, vol. 11, no. 4, pp. 10087-10098, 2016 [17] g. selvaraju, n. k. a. bakar, “production of a new industrially viable green-activated carbon from artocarpus integer fruit processing waste and evaluation of its chemical, morphological and adsorption properties”, journal of cleaner production, vol. 141, pp. 989-999, 2017 [18] b. nachiappan, z. fu, m. t. holtzapple, “ammonium carboxylate production from sugarcane trash using long-term air-lime pretreatment followed by mixed-culture fermentation”, bioresource technology, vol. 102, no. 5, pp. 4210-4217, 2011 [19] j. parikh, s. a. channiwala, g. k. ghosal, “a correlation for calculating hhv from proximate analysis of solid fuels”, fuel, vol. 84, no. 5, pp. 487-494, 2005 microsoft word etasr_v10_n6_pp6533-6541 engineering, technology & applied science research vol. 10, no. 6, 2020, 6533-6541 6533 www.etasr.com bahig et al.: speeding up the multiplication algorithm for large integers speeding up the multiplication algorithm for large integers hazem m. bahig computer science and information dept. college of computer science and engineering, university of ha’il ha’il, saudi arabia h.bahig@uoh.edu.sa amer alghadhban electrical engineering dept. college of engineering university of ha’il ha’il, saudi arabia a.alghadban@uoh.edu.sa mohammed a. mahdi computer science and information dept. college of computer science and engineering, university of ha’il ha’il, saudi arabia m.mahdi@uoh.edu.sa khaled a. alutaibi computer engineering dept. college of computer science and engineering university of ha’il ha’il, saudi arabia alutaibi@uoh.edu.sa hatem m. bahig mathematics department faculty of science ain shams university cairo, egypt h.m.bahig@gmail.com abstract-multiplication is one of the basic operations that influence the performance of many computer applications such as cryptography. the main challenge of the multiplication operation is the cost of the operation as compared to other basic operations such as addition and subtraction, especially when the size of the numbers is large. in this work, we investigate the use of the window strategy for multiplying a sequence of large integers to design an efficient sequential algorithm in order to reduce the number of bit-multiplication operations involved in multiplying a sequence of large integers. in our implementation, several parameters are considered and measured for their effect on the proposed algorithm and the best-known sequential algorithm in the literature. these parameters are the size of the sequence of integers, the size of the integers, the size of the window, and the distribution of the data. the experimental results prove the effectiveness of the proposed algorithm are compared to the ones of the best-known sequential algorithm, and the proposed algorithm is able to achieve a reduction in computing time greater than 50% in most cases. keywords-multiplication; big data; cryptography; algorithm performance; computer arithmetic i. introduction computer arithmetic plays an essential role in every layer of computing and it is an important consideration when developing computer solutions for many problems such as cryptography, image processing, and numerical computations. in computer arithmetic, we use different operations such as addition, subtraction, multiplication, and division to achieve the goal of computation. among these, the operation that has particular significance for many applications is the multiplication operation [1]. the multiplication operation is important, mainly for three reasons. first, the time cost of performing the multiplication operation is greater than that of other operations such as addition and subtraction. for example, given two integer numbers of �-bits each, the addition and multiplication of the two integer numbers require ���� and ����� bit operations, respectively, using the naïve method [1]. this means that there is a significant difference between the costs of the two operations. second, many primitive and essential arithmetic operations, such as division, squaring, inverse multiplication, and modulo operations, are based on the multiplication operation. therefore, the running time of the multiplication operation affects these operations. third, several complex applications in computer science, such as cryptography and digital signal processing, are based on a huge number of multiplication operations [2-6]. for example, in rsa and el-gamal public-key cryptosystem, the multiplication operation is necessary. so, a more efficient multiplication method would lead to the speeding up of the computation process in complex applications. for the above reasons, different strategies have been suggested to reduce the total number of operations required for multiplication. two main research directions have been followed to improve the efficiency of the multiplication operation on a data set that consists of � integer numbers each of size �. the first direction has been to reduce the cost of multiplying two numbers, � and �, of size � each and thereby decrease the total cost of the multiplication operations for a data set. the second direction has been to reduce the cost of multiplying the data set by proposing an efficient strategy to multiply the � numbers. regarding the first research direction, many methods have been proposed to reduce the time complexity of multiplying two integers in both sequential [723] and parallel computation [24-29]. in the case of sequential computation, several techniques have been proposed such as the naïve multiplication algorithm [1], karatsuba’s algorithm corresponding authors: hazem m. bahig engineering, technology & applied science research vol. 10, no. 6, 2020, 6533-6541 6534 www.etasr.com bahig et al.: speeding up the multiplication algorithm for large integers [1,15], the toom–cook multiplication algorithm [20], and a fast fourier transform-based algorithm [18]. the time complexity of the naïve multiplication method is ����� , whereas karatsuba’s algorithm uses a divide and conquer strategy to multiply the two integers in ��� �, where = log� 3 ≈ 1.585. the toom–cook multiplication method is a generalization of karatsuba’s algorithm using r-way multiplication and has a cost of � ������� ���� �⁄ !". in contrast, schonhage and strassen utilize the fast fourier transform to reduce the time complexity of multiplication. they propose two algorithms, where the best one runs on ��� log� loglog�� and uses an arithmetical modulo operation. another two algorithms are proposed to reduce the running time of the schonhage-strassen algorithm to achieve ��� log� 2�����∗ ��!, where log∗ � = �%�%�&�'%: )*+�,�� ≤ 2. and )*+�/�� = �. the first algorithm is based on arithmetic over complex numbers [12], while the other is based on modular arithmetic [10]. on the other hand, many different attempts have been made to parallelize the multiplication problem using different parallel models [24-29]. most of these attempts have been based on the shared memory model, where the processors in this model communicate through shared memory. also, some research studies have focused on implementing some parallel algorithms on real machines, such as fpgas, gpus, and multicore [2527]. in the case of the second research direction, a few algorithms have been proposed to reduce the time complexity of the multiplication of � integers in both sequential and parallel computation. in the case of sequential computation, the best-known algorithm is the naïve method, which scans the sequence of integer numbers and multiplies one number in each iteration. in the case of parallel computation, a few strategies [30] have been proposed that use a shared memory model and are implemented on specific real machines such as the multicore system [31]. in this paper, we are interested in contributing to the second research direction that focuses on using sequential computation because, despite the progress that has been made toward developing an effective strategy, there is still room for improvement. here, we present an efficient improvement sequential algorithm to multiply a large number of integers, each of large size. a comparison of the proposed algorithm and the best-known sequential algorithm indicates that, from a practical perspective, the proposed algorithm performs better. our improved algorithm speeds up the best-known sequential algorithm when � and � are large. ii. the optimal algorithm in this section, first we describe the optimal sequential algorithm that is used to multiply � numbers, 0 = ��/�� … �23��. then we give an example to illustrate the number of multiplication operations required to multiply � numbers. a. the optimal multiplication algorithm the optimal multiplication algorithm, denoted as om, multiplies � numbers by sequentially scanning the input array of � − 1 iterations. in each iteration %, the algorithm multiplies the number �, with 5, where % ≥ 1 and 5 is initially equal to �/ and finally 5 = ∏ �823�8 9 / . in the light of the above, the algorithm requires ��� :2;<� time. the term �is is derived from � − 1 iterations, where ���� = ��� − 1�, while the term :2;< is the total number of operations required to multiply two numbers. the value of :2;< depends on the size of the two numbers. if we have two numbers of size n each: �, = ��,��3��,�,��3��, …,�,�,�,/! and �8 = ��8��3��, �8��3��, …,�8�,�8/!, then multiplying �, and �8 requires ����� multiplication operations using the naïve method, while the best-known time complexity for :2;< is ��� log � 2����� ∗ ��! [10, 12]. to differentiate between the multiplication operation for the two integers �, and �8, and the multiplication operation for the two digits/bits �,< and �, , we name the second type of operation as the digit-multiplication or bit-multiplication operation. so, the multiplication of �, and �8 requires ����� digit-multiplication or bit-multiplication operations. the main problem when multiplying � numbers, each of size � bits, is the size of the result of the multiplication, which increases with the increase in the value of �. for example, when � = 4, initially 5 = �/ and in the first iteration, the algorithm computes 5 = �/ × ��, of size 2� using �� bit-multiplication operations in the worst case. the second iteration of the algorithm involves multiplying 5 = �/ × �� of size 2� with �� of size � to produce 5 = �/ × �� × �� of size 3� using 2�� bitmultiplication operations. in the last iteration, the algorithm computes 5 = �/ × �� × �� × �@ of size 4� using 3�� bitmultiplication operations. hence, the overall number of bitmultiplication operations to compute 5 = �/ × �� × �� × �@ is �� + 2�� + 3�� = 6�� in the worst case. furthermore, in general, the multiplication of � integer numbers, of size � bits each, requires �� + 2�� + 3�� + ⋯ + �� − 1��� bitmultiplication operations, which is equal to � � �� − 1�/2 in the worst case. b. illustrative example an illustrative example is given to explain the total number of digit-multiplication operations required to multiply m numbers using the sequential om algorithm. the notation :∗ represents the total number of digit-multiplication operations. for simplicity, let us assume that we have an array of � = 20 integer numbers and that the value of each element in the array is 5, i.e.: 0 = �5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5� the execution of the optimal sequential algorithm on 0 is described below. initially, 5 = �/ = 5 and :∗ = 0 , and the algorithm executes 19 iterations to compute 5 = 5�/. these iterations are represented in figures 1–4. each figure consists of many subfigures, where each subfigure represents an iteration in the execution of the om algorithm. three pieces of information are associated with each iteration. the first is the number of digit-multiplications for multiplying the two numbers and is denoted by ∗ � �, where is the number of digit-multiplication engineering, technology & applied science research vol. 10, no. 6, 2020, 6533-6541 6535 www.etasr.com bahig et al.: speeding up the multiplication algorithm for large integers operations. for example, in figure 1(c), the algorithm multiplies 5 with the digits 5, 2, and 1, so the number of digitmultiplication operations is 3, and is denoted by ∗ �3�. the second piece of information is the total number of digitmultiplication operations from the start to the current iteration and is denoted by :∗. for example, in figure 1(c), the total number of digit-multiplication operations is equal to the number of digit-multiplication operations for the current iteration, % � 3, plus the total number of digit-multiplication operations for the previous iterations. therefore, :∗ � :∗ a∗ �3� � 3 a 3 � 6 . the third and last piece of information in each subfigure consists of the iteration number, %, and the value of 5 that is equal to ∏ �8 , 8 9 / . figures 1-4 display the complete execution of the om algorithm on 0 for iterations 1–5, 6–10, 11–14, and 15–19, respectively. fig. 1. number of operations of the iterations 1-5 for the om algorithm. fig. 2. number of operations of the iterations 6-10 for the om algorithm. fig. 3. number of operations of the iterations 11-14 for the om algorithm. fig. 4. number of operations of the iterations 15-18 for the om algorithm. iii. the modified algorithm in this section, at first the idea and the steps of the suggested strategy for speeding up the execution time of the multiplication of � numbers, each of size �, where � is a large value are introduced. then two examples are given to illustrate the proposed approach by applying it to the array discussed in section ii. a. the algorithm the proposed algorithm is based on dividing the array into blocks, each of size f, where f g � . then the algorithm computes the multiplication of the elements in each block independently. the result of the multiplication for each block, say :h�i, is accumulated to produce the final result of the multiplication, 5. so, after computing the multiplication of each block the value of 5 is updated by calculating 5 = 5 × :h�i, see algorithm bm0. initially, the algorithm computes the total number of blocks, �j , by calculating k� f⁄ l . then the algorithm computes the multiplication of f elements in an auxiliary engineering, technology & applied science research vol. 10, no. 6, 2020, 6533-6541 6536 www.etasr.com bahig et al.: speeding up the multiplication algorithm for large integers variable :h�i , where the initial value of :h�i is the first element in the block. after that, the algorithm updates the value of the final result by multiplying it with the value of :h�i. after it has finished multiplying all the elements in all the blocks, the algorithm updates the final result by multiplying it with the remaining elements, � − k� f⁄ l × f . the time complexity of the proposed algorithm is equal to �k� f⁄ l× f + �� − k� f⁄ l × f�! × :2;<m , which is ��� :2;<�. the proposed algorithm executes � multiplication operations, while the om algorithm executes � − 1 multiplication operations. algorithm bm0 input: an array of � numbers, 0 = ��/,��,…,�23�� and f. output: 5 = ∏ �,.23�,9/ begin 1. �j = k� f⁄ l 2. 5 = 1 3. for % � 0 to �j 4 1 do 4. n = % × f 5. :h�i = �8 6. while (n g �% + 1�f) do 7. n � n a 1 8. :h�i = :h�i × �8 9. end while 10. 5 = 5 × :h�i 11. end for 12. if � o �j × f then 13. for n = �j × f to � − 1 do 14. 5 � 5 ? �8 15. end for 16. end if end. in order to reduce the number of multiplications in the proposed algorithm, bm0, from � to � − 1, we apply the following modifications. first, we compute the multiplication of the first block using the final result 5. hence, the total number of multiplications is f 4 1, whereas the first block of the initially proposed algorithm required f multiplications: f 4 1 to compute :h�i and one to update 5 . second, the remaining elements of the array are divided into blocks, k�� 4 f� f⁄ l, and then the same steps are performed as in the initial version of the proposed algorithm. the modification of the proposed algorithm is denoted as bm. now, we compute the number of multiplications, to compute 5 for the bm algorithm. thus, the first block requires f 4 1 multiplication operations, see lines 1–3. each block, in the other blocks, requires f 4 1 multiplication operations, see lines 7–12, and the updating of the value of 5, for each block, requires only one multiplication. so, each iteration in the do-while loop requires f multiplication operations. therefore, the total number of multiplications for the do-while loop is k�/f 4 1l ? f where the term �/f-1 represents the number of windows in the do-while loop. additionally, the total number of the remaining elements is � 4 k�/fl ? f. hence, the total number of multiplications for the bm algorithm is � 4 1. hence, the running time and memory consumption of the bm algorithm are ���� and ��1�, respectively. algorithm bm input: an array of � numbers, 0 = ��/,��,…,�23�� and f. output: 5 = ∏ �,.23�,9/ begin 1. 5 = �/ 2. for n = 1 to f 4 1 do 3. 5 = 5 × �8 4. end for 5. �j = k�� − f� f⁄ l 6. for % = 1 to �j 4 1 do 7. n = % × f 8. :h�i = �8 9. while (n g �% + 1�f) do 10. n = n + 1 11. :h�i = :h�i × �8 12. end while 13. 5 = 5 × :h�i 14. end for 15. if � o ��j + 1� ? f then 16. for n = �j × f to � − 1 do 17. 5 � 5 ? �8 18. end for 19. end if end. b. illustrative example in this section, we illustrate how the proposed bm algorithm reduces the total number of digit-multiplication operations by applying it on the same array as in section ii.b and using two values of f: 5 and 10. we also show how different block size values affect the total number of digitmultiplication operations. fig. 5. execution of the bm algorithm when b=5. engineering, technology & applied science research vol. 10, no. 6, 2020, 6533-6541 6537 www.etasr.com bahig et al.: speeding up the multiplication algorithm for large integers fig. 6. execution of bm algorithm when b=10. first, let us assume that the size of the block is f = 5. initially, the algorithm assigns 1 to 5 and executes lines 2–3. in the first iteration, the algorithm computes the multiplication of the first five numbers as 5 = 3125. the total number of digit-multiplication operations to compute 5 is nine, :∗ � 9, similar to figure 1(a)–(d). this step is shown in figure 5(a), where the information in the figure refers to the block number instead of the iteration number. the algorithm computes the multiplication of the second block in :h�i � 3125 using nine digit-multiplication operations. then, the algorithm updates the value of 5 by multiplying it with :h�i, using 16 digit-multiplication operations. therefore, the total number of digit-multiplication operations until the end of this step is :∗ � 9 a 16 a 9 � 34 , see figure 5(b). figures 5(c)–(d) represent the result of executing the third and fourth blocks, respectively. the total number of digit-multiplication operations for the final result of 5 is :∗ � 124. in the second example illustrated in figure 6, when f � 10 , the bm algorithm computes the first block in 5 � 5�/ using 36 digit-multiplication operations, which is similar to figures 1(a)–(e) and 2(a)–(d). the second block is calculated by performing two steps. the first step involves computing the auxiliary variable :h�i � 5�/ using 36 digitmultiplication operations. the second step involves multiplying 5 with :h�i using 49 digit-multiplication operations to produce 5 � 5�/. so, the total number of digitmultiplication operations is :∗ = 36 a 49 a 36 � 121. hence the bm algorithm requires fewer digit-multiplication operations when f � 10. in other words, the bm algorithm performs better when f � 10 than when f � 5 and f � 1 . also, the bm algorithm performs better when b = 5 than when f = 1. iv. experimental study in this section, we study the bm algorithm experimentally to find the answers to the following research questions: 1. does the value of f have an effect on the running time of the bm algorithm experimentally, and if so, is this effect significant? 2. do certain parameters (the size of the sequence of integers, the size of the integers, the size of the window, and the distribution of the data) have an effect on the performance of the bm algorithm? 3. does the bm algorithm have a faster running time as compared to the om algorithm? the above questions are addressed in the following subsections. subsection a contains a brief description of the platform (hardware and software) and the methodology used to test and measure the running time of both the bm and om algorithms. subsection b contains the answers to the first and second questions. subsection c answers the third question. a. methodology the experimental studies were conducted on a machine consisting of a 2.4 ghz processor with 32 gb of memory and a windows operating system. both algorithms, om and bm, are implemented using c++ language and the gmp (gnu multiple precision arithmetic) package. the gmp package is used to achieve two objectives. first, when we multiply many integer numbers of size 16 bits or more, the result is a number that is greater in size than 64 bits, and numbers of such size cannot be manipulated by the integer range in c++ language. second, some of the applications that use the om algorithm, such as cryptography, require a data of sizes greater than 64 bits. the experimental studies are based on the following four parameters: • the first parameter is the size of the integer number, �, and is measured in bits. in the experiment, we used � = 32, 64, 128, 256, and 512. • the second parameter is the size of the array, �. in the experiment, we use � = 1/4 , 1/2 , 1 , 2 , 4 , 8 , 16 , and 32 , where � 1024. • the third parameter is the size of the block, f, used in the computation. in the experiment, we use different values of block size: 25,50,…,500, except when � 512, the last value of f is 250. • the fourth parameter is the data range, q, that is used to generate the elements of the array. in the experiment, we use two types of data range. the first data range is q� = r2�3�,2� 4 1s, which means that all data in the array of size � bits exactly, i.e., 2�3� �, g 2 �. the second data range is q� � r0,2 � 4 1s, which means that all data in the array of size less than or equal � bits, i.e., 0 �, g 2 �. the running time for each of the algorithms (bm and om) is measured by taking the average time for 50 instances for fixed parameter values. the running time of the algorithms is measured in seconds. b. behavior of the bm algorithm in this subsection, we study the effect of changing the value of f on the running time of the bm algorithm using different values of �,� and q. to verify this goal, we first generate a data set by determining the values of �, � and q. then we generate a data for one instance, t � ��, �,q�. for example, we set � � 4 , � � 512, and q � q�. after that, we execute the bm algorithm on different values of f as described in section iv.a and the running time for bm algorithm is measured for each value of f. next, we repeat the previous steps using different values of data t � ��,�,q�. following that, the same procedure is applied on bm algorithm using q� and different values of �, and �. figure 7 shows the running time behavior of the bm algorithm using different values of �,�,q, and f. the results of our experiments lead to four observations for fixed values of � and �. engineering, technology & applied science research vol. 10, no. 6, 2020, 6533-6541 6538 www.etasr.com bahig et al.: speeding up the multiplication algorithm for large integers (a1) � = 32, � � 32 , 16 (a2) � � 32, � � 8 , 4 (a3) � � 32, � � 2 , 1 (a4) � � 32, � � 1/2 , 1/4 (b1) � � 64, � � 32 , 16 (b2) � � 64, � � 8 , 4 (b3) � � 64, � � 2 , 1 (b3) � � 64, � � 1/2 , 1/4 (c1) � � 128, � � 32 , 16 (c2) � � 128, � � 8 , 4 (c3) � � 128, � � 2 , 1 (c4) � � 128 , � � 1/2 , 1/4 (d1) � � 256, � � 32 , 16 (d2) � � 256, � � 8 , 4 (d3) � � 256 , � � 2 , 1 (d4) � � 256, � � 1/2 , 1/4 (e1) � � 512 � � 32 , 16 (e2) � � 512, � � 8 , 4 (e3) � � 512, � � 2 , 1 (e4) � � 512 , � � 1/2 , 1/4 fig. 7. running time behavior of bm algorithm using different values of d, where the x-axis represents the different values of b. engineering, technology & applied science research vol. 10, no. 6, 2020, 6533-6541 6539 www.etasr.com bahig et al.: speeding up the multiplication algorithm for large integers first, the running time of the bm algorithm decreases with different values of f . for example, when � = 32 and � = 32768, the running time of the bm algorithm when f = 25,50,75,100,125,150,175,200,225 , and 250 is 2.93, 2.3, 2.08,1.77,1.66,1.60,1.42,1.36,1.29 , and 1.27 , respectively. second, it is not always the case that increasing the value of b leads to a decrease in the running time of the bm algorithm. for example, when � = 256, � = 1/2 and f = 25, 50, 75, 100, 125, 150, 175, 200, 225, and 250, the running time of the bm algorithm is 0.021, 0.018, 0.017, 0.017, 0.017, 0.018, 0.020, 0.020, 0.022, and 0.024, respectively. usually, this case occurs when � and � are small or when f is close in value to �. this means that not all values of f lead to an improvement in the running time of the bm algorithm, especially when � and � are small. third, it is clear that between two successive values of f, the improvement is small. however, when the difference between the two values of f is large, with a certain limitation, the improvement is significant. for example, when � = 16 , � = 128, and f = 75 and 100, the running time of the bm algorithm is 3.99 and 3.68, respectively, while the running time for the bm algorithm when f = 75 and 250 is 3.99 and 2.35, respectively. fourth, the running time of the bm algorithm on q� is a little faster than on q� . the reason for this is that all the numbers in q� have n bits exactly, while the numbers in q� have a maximum length �. c. comparison of om and bm algorithms in this subsection, the running times of the om algorithm and bm algorithm are compared based on two values. the first value is the minimum running time obtained from the experimental results for the bm algorithm using different values of f, this value is denoted as bmmin. the second value is the average running time calculated from all running times of the bm algorithm using different values of f , denoted as bmavg. therefore, two running time values for the bm algorithm are considered: bmmin and bmavg. table i lists the running times of both algorithms, om and bm, when the data range for the elements of the array taken from q�. several observations arise from the analysis of the data results in table i. table i. running time (in seconds) of om and bm algorithms in the case of q� table ii. percentage of improvement by the bm algorithm as compared to the om algorithm in the case of q� . v w bits 32 64 128 256 512 bmmin bmavg bmmin bmavg bmmin bmavg bmmin bmavg bmmin bmavg x/yz 0.00% 0.00% 22.22% 11.11% 50.00% 36.67% 54.21% 35.51% 59.72% 38.78% x/[z 0.00% 0.00% 33.33% 33.33% 54.55% 36.36% 59.95% 43.46% 69.00% 47.35% xz 33.33% 0.00% 57.14% 50.00% 61.36% 54.55% 69.63% 60.86% 74.80% 65.49% [z 50.00% 14.29% 65.45% 60.00% 69.94% 64.74% 75.52% 71.05% 80.50% 75.97% yz 56.52% 23.08% 72.15% 64.38% 76.30% 70.66% 80.62% 76.60% 84.18% 81.39% \z 61.11% 27.08% 77.01% 66.90% 80.49% 73.62% 84.32% 78.85% 87.51% 84.19% x]z 64.86% 29.73% 79.43% 68.37% 83.12% 74.92% 86.63% 80.66% 90.38% 85.93% ^[z 66.10% 30.91% 80.55% 68.86% 84.41% 75.46% 88.52% 82.28% 91.99% 86.89% first, the running time of the bm algorithm is faster than that of the om algorithm for all data sets, except for two cases: t � �256,32,q�� and t = �512,32,q�� where the running time of the two algorithms are equal. second, two factors have an effect on the difference in the running times of the two algorithms. the first factor is the size of array, �, while the second factor is the size of the integer number, n. for small values of � and � , the difference in w algorithm v x/yz x/[z xz [z yz \z x]z ^[z 32 om 0.0003 0.001 0.003 0.012 0.046 0.18 0.74 2.92 bmmin 0.0003 0.001 0.002 0.006 0.02 0.70 0.26 0.99 bmavg 0.0003 0.001 0.002 0.007 0.026 0.096 0.370 1.433 64 om 0.0009 0.003 0.014 0.055 0.219 0.87 3.50 13.37 bmmin 0.0007 0.002 0.006 0.019 0.061 0.200 0.720 2.600 bmavg 0.0008 0.002 0.007 0.022 0.078 0.288 1.107 4.163 128 om 0.003 0.011 0.044 0.173 0.709 2.87 11.49 45.62 bmmin 0.0015 0.005 0.017 0.052 0.168 0.56 1.94 7.11 bmavg 0.0019 0.007 0.02 0.061 0.208 0.757 2.882 11.197 256 om 0.0107 0.042 0.171 0.694 2.761 10.8 49.59 191.13 bmmin 0.0049 0.017 0.052 0.17 0.535 1.694 6.628 21.943 bmavg 0.0069 0.024 0.067 0.201 0.646 2.285 9.59 33.864 512 om 0.0435 0.171 0.666 2.579 10.302 42.084 172.42 750.41 bmmin 0.0175 0.053 0.168 0.503 1.63 5.256 16.581 60.094 bmavg 0.0266 0.09 0.23 0.62 1.917 6.652 24.262 98.396 engineering, technology & applied science research vol. 10, no. 6, 2020, 6533-6541 6540 www.etasr.com bahig et al.: speeding up the multiplication algorithm for large integers running time between the two algorithms is small. for example, when � � 64 and � = 512 the running times of om, bmmin and bmavg are 0.003 , 0.002 , and 0.002 , respectively. on the other hand, when � = 128 and � = 16 , the running times of om, bmmin and bmavg are 11.49, 1.94, and 2.88 seconds, respectively. third, based on the second observation, the percentage of improvement achieved by the bm algorithm, in terms of bmmin and bmavg, as compared to om algorithm increases with an increase in the values of � and �. this means that the improvement occurs in two cases: when � is fixed and � is varied and when � is fixed and � is varied. for example, if � = 128, the percentage of improvement achieved by the bm algorithm when � = 1/4 , 1/2 , 1 , 2 , 4 8 , 16 and 32 is 50%, 54.55%, 61.36%, 69.94%, 76.30%, 80.49%, 83.12%, 84.41% respectively in the case of bmmin, while the percentage of improvement in the case of bmavg is 36.67%, 36.36%, 54.55%, 64.74%, 70.66%, 73.62%, 74.92%, and 75.46%, respectively. also, if � = 1 , the percentage of improvement achieved by the bm algorithm when � = 32, 64, 128 , and 256 is 33.33%, 57.14%, 61.36%, and 69.59%, respectively in the case of bmmin, while the percentage of improvement in the case of bmavg is 0.0%, 50%, 54.55%, and 60.82% respectively. the full details of the percentage improvement achieved by the bm algorithm as compared to the om algorithm are shown in table ii. fourth, referring to table ii, it is clear that the percentage of improvement achieved by the bm algorithm in the case of bmmin is better than in the case of bmavg, for fixed � and �, because the running time for bm algorithm in case of bmmin is less than the running time for bm algorithm in case of bmavg. note that, with increasing � and �, the running times for bm in case of q� is near to the case of q�, so we neglect the comparison between bm and om algorithms in case of q�. v. conclusion in this paper, we studied the multiplication operation because it has a higher time cost as compared to other basic arithmetic operations and therefore has a significant influence on the performance of many applications such as cryptography and digital signal processing. to reduce the cost of this operation, we developed an efficient algorithm for sequential computation tasks that require the multiplication of a sequence of big integers. the algorithm is based on using the window strategy to reduce the cost of multiplying the sequence of big integers. the algorithm has the same time complexity as the best-known sequential algorithm but performs fewer digitmultiplication operations. in our experimental studies to test the performance of the proposed bm algorithm, we considered four parameters of different values: sequence size (� � 1/4 , 1/2 , 1 , 2 , 4 , 8 , 16 , and 32 ), integer size (� = 32, 64, 128, 256, and 512), block size (f = 25, 50, …, 500), and data range (fixed and varied sizes). the results showed the effectiveness of the proposed algorithm as compared to the best-known sequential algorithm, where the percentage of improvement achieved by the proposed algorithm was 90% when � and � were large. there are different future directions related to this study. firstly, the study of the behavior of the bm algorithm when � ≥ 1 . secondly, the study of the effect of increased value of f on the bm algorithm. third, the question of the existence of a relation between the values of f and �. fourth, how to use the gpu to speedup the running time for the bm algorithm. fifth, 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[31] h. m. bahig, h. m. bahig, and k. a. fathy, "fast and scalable algorithm for product large data on multicore system," concurrency and computation: practice and experience, apr. 2019, art. no. e5259, https://doi.org/10.1002/cpe.5259. microsoft word 32-2843_s_etasr_v9_n4_pp4490-4494 engineering, technology & applied science research vol. 9, no. 4, 2019, 4490-4494 4490 www.etasr.com nguyen: analysis of rectangular plates on resting winkler and two-parameter elastic foundation … analysis of rectangular plates on resting winkler and two-parameter elastic foundation models by finite difference method trong ha nguyen department of civil engineering, vinh university, vinh city, vietnam trongha@vinhuni.edu.vn abstract—analysis of rectangular plates on a rising elastic foundation is common when designing the foundation of civil, traffic, and irrigation works. the current research presents the results of the analysis of rectangular plates on rising winkler elastic and two-parameter foundation using the finite difference method. the computational programming was done on matlab. the results of the research verify the accuracy of the fem and are in agreement with findings in the literature. in addition, this research also compares the calculation results of two foundation models and investigates the change of plate height ratio to plate size. keywords-finite difference method; kirchhoff’s plate; winkler foundations; two-parameter elastic foundation i. introduction a plate on a rising elastic foundation is a common type of structure when designing the foundation of civil works. analysis of this problem is related to the solution of the differential equations that describe it. finding a simple calculation method that still yields accurate results is the topic of this research. the combination of kirchhoff's classic plate theory with finite difference method (fdm) has been the topic of many studies. authors in [1] proposed the application of fdm to study of the phenomenon in the theory of thin plates. authors in [2] analyzed rectangular thin plates by using fdm. in [3] fdm was proposed to analyze a rectangular steel plate. the plate was considered to be subjected to an arbitrary transverse uniformly distributed loading and was considered to be clamped on two opposite edges and free at the other two edges. authors in [4] presented an investigation of the validity of fdm on simulations of a thin sectorial steel plate under the effect of uniform and concentrated loads with different types of boundary conditions. authors in [5] analyzed the rectangular kirchhoff plate on winkler foundation using finite fourier sine transform. the plate was assumed homogeneous, isotropic, and simply supported at the four edges. analysis of plate on a rising elastic foundation is an also interesting topic. authors in [6] proposed simple computer analysis of circular rafts under varying axisymmetric loading and elastic foundation conditions and authors in [7] analyzed the circular tank foundations with fdm. in [8], authors used finite element approach to study elastic soil-structure interaction. finite and infinite dynamic plate-soil interaction, flexible and rigid plates on homogeneous, layered or winkler soil were studied in [9]. finite/infinite element analysis of a thick plate on a layered foundation was proposed in [10]. one can conclude that the research on the analysis of rectangular plates on resting winkler and twoparameter elastic foundation models by using fdm is still limited. therefore, this study aims at analyzing rectangular plates on resting winkler and two-parameter elastic foundation models by fdm. the matlab program combines the kirchhoff’s classic plate theory, winkler foundation model, two-parameter foundation model, and fdm. in addition, this research also compares the calculation results of the two foundation models and investigates the change of plate height ratio to plate size. ii. theoretical framework a. finite diffrence method fdm is a popular numerical method due to its straightforward approach and minimum requirements regarding computer resources. it is based on a mathematical discretization of the equations of boundary problems. the contents of the method are to replace the derivative by a finite estimation. this method is sufficiently accurate for thin plate analysis [11, 12]. b. elastic foundation models the elastic foundation is modeled by a one-, twoor manydimensional elastic spring. several mathematical descriptions of the elastic foundation are proposed in [12, 13]. in this research, the winkler model and the two-parameter elastic foundation will be presented and used. 1) winkler foundation model winkler foundation model was proposed in [14]. it is based on the assumption that the foundation’s reaction q(x, y) at any point (x, y) on the plate is directly proportional to the displacement w(x, y) at the point, and the proportionality constant k, called winkler modulus, is a constant for the entire corresponding author: trong ha nguyen engineering, technology & applied science research vol. 9, no. 4, 2019, 4490-4494 4491 www.etasr.com nguyen: analysis of rectangular plates on resting winkler and two-parameter elastic foundation … foundation (or the foundation modulus) as shown in (1): ( ) ( ), ,q x y kw x y= (1) 2) two-parameter elastic foundation model two-parameter elastic foundation model was proposed in [5, 15]. the foundation reaction is shown in the following expression: ( ) ( ) ( )2, , ,q x y kw x y t w x y= − ∇ (2) where k and t are the foundation model parameters. equation (2) can be rewritten for rectangular or circular foundations: ( ) ( ) ( )2 2 , , , d w x y q x y kw x y t dx = − (3) equation (2) can be rewritten for the hetenyi foundation as [5]: ( ) ( ) ( )4, , ,q x y kw x y d w x y= − ∇ (4) where ( ) 3 2 12 1 p p p e h d µ = − is the flexural rigidity of the elastic plate and k is winkler modulus. k and d are the model parameters. ep and µp are the young’s modulus and poisson’s ratio of the plate material, and hp is the plate thickness. equation (2) can be rewritten for the pasternak foundation as [15]: ( ) ( ) ( )2, , ,q x y kw x y g w x y= − ∇ (5) where,g is the shear modulus of the shear layer. k and d are the pasternak foundation model parameters. equation (2) can be rewritten in two-parameter pasternak foundation form as: ( ) ( ) ( )2, , ,sq x y kw x y k w x y= − ∇ (6) where k is the first elastic foundation parameter (winkler modulus) and ks is the second elastic foundation parameter. c. classical thin plate theory (kirchhoff) analysis of a thin plate subjected to loads acting normal to its surface requires solution of differential equations of threedimensional elasticity. authors in [17] proposed the exact bending analysis for thin plates. however, this method is somewhat complex and time-consuming. to overcome the above disadvantages in technical applications, kirchhoff’s classical theory of thin plates yields sufficiently accurate results without the need of carrying out full three-dimensional stress analysis. the governing differential equation for deflection of thin plates by kirchhoff’s theory is [18]: ( ) ( )4 , , z p x y w x y d ∇ = (7) where w denotes the deflection in z direction due to the load z p on surface x-y. d is the flexural rigidity of the elastic plate expressed as: ( ) 3 2 12 1 eh d µ = − . in this expression: e is the modulus of elasticity of the plate material, h is the thickness of plates, µ is poisson’s ratio for the plate material. equation (7) is solvable by using fdm. iii. methodology a. rectangular kirchhoff plate on winkler foundation model consider a rectangular plate a×b resting on a winkler foundation model as shown in figure 1. the governing equation is: ( ) ( ) ( )4 , , , z p x yk w x y w x y d d ∇ + = (8) for 0 , 0x a y b≤ ≤ ≤ ≤ , where k is the winkler modulus, ( ),w x y is the deflection of the plate middle surface, ( ),q x y is the external distributed load applied to the plate, and a b are the length and width of the plates. fig. 1. rectangular plate resting on a winkler foundation b. rectangular kirchhoff plate on two-parameter foundation model consider a rectangular plate a×b resting on a twoparameter foundation (pasternak foundation) as shown in figure 2. fig. 2. rectangular plate resting on two-parameter (pasternak foundation) the governing equation can be expressed by: ( ) ( ) ( ) ( )4 2 , , , , z s p x y w x y k w x y kw x y d ∇ + ∇ + = (9) for 0 , 0x a y b≤ ≤ ≤ ≤ , where k is the winkler xo y b a xo y b a t t t t engineering, technology & applied science research vol. 9, no. 4, 2019, 4490-4494 4492 www.etasr.com nguyen: analysis of rectangular plates on resting winkler and two-parameter elastic foundation … modulus, ( ),w x y is the deflection of the plate middle surface, ( ),zp x y is the external distributed load applied to the plate, and and a bare the length and width of the plate. c. flowchart the steps taken on the analysis of a rectangular kirchhoff plate on an elastic foundation are: • assume displacement and make finite difference grid. • replace the corresponding partial differential equations (8)(9) of the problem at the same transform with the finite difference equation or difference equation. • establish algebraic equations with the displacements as variables • solve the system of equations to determine the displacement. • determine stress and deformation from displacement by differential method. figure 3 shows the respective flowchart. fig. 3. flowchart of the analysis of rectangular kirchhoff’ plates on an elastic foundation iv. numerical results a. validation of sample plates on matlab the flowchart of the program is shown in figure 3. in order to validate this program, square plates of a/b=1 and plate thickness h=1/100(cm) were considered. differential mesh division in two cases ∆x=∆y=a/4(cm) and ∆x=∆y=a/8(cm) was considered. uniformly distributed load was p=−100kn/m 2 and young’ modulus was e=2.1×10 5 mpa, while poisson’s ratio of the plate material was µ=0.3. non-dimensional deflections and stresses, defined in [18] are: ( ) 3 4 0,0 eh w w a p   =     , 2 2 , , 2 2 2 xx xx a b h h a p σ σ    =       and 2 2 , , 2 2 2 yy yy a b h h a p σ σ    =       . the generation of nodes in the two studied cases is shown in figures 4 and 5. fig. 4. experimental plate with unknown nodes displacement (case 4x4) fig. 5. experimental plate with unknown nodes displacement (case 8x8) the obtained results are compared in table i. the small errors in table 1 confirm the reliability of our program. table i. non-dimensional deflections and stresses of validation sample models non-dimensional deflections non-dimensional stresses w xxσ yyσ case study (4x4) 0.0440 0.2813 0.2813 case study (8x8) 0.0443 0.2839 0.2839 [18] 0.0444 0.2873 0.2873 fem (sap2000) 0.0443 0.2839 0.2839 the difference between the results does not exceed0.5% , while the case studies (8x8), [9] and fem give equivalent results. this means that the research using fdm gives reliable and simple calculations. b. fdm analysis of rectangular plates on elastic foundation models the obtained results of non-dimensional deflections and stresses of the analysis of rectangular plates on rising winkler and two-parameter elastic foundation models are shown in tables ii-iii and figures 6-7. we can see that the deflection of the plate changes when the elastic modulus increases. the rate of change of the non-dimensional deflection of the winkler foundation model is about 5% of the two parameter xo y 0w 000 0 0 000 0 0 0 0 0 0 0 0 1w1w 3w3w 2w 3w3w 2w 3w3w 2w3w3w 2w1w 3w 3w 1w 3w 3w a b x y o 0w 1w 2w 3 w 4 w 1w 2w 3 w 1w 2w 3 w 4 w 1w 2w 3 w 5w 6w 7 w 8 w 5w 6w 7 w 6w 7 w 8 w 5w 6w 7 w 5w9w 10w 11 w 12 w 9w 10w 11 w 9w 10w 11 w 12 w 9w 10w 11 w 13w 14w 15 w 13w 14w 15 w 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1w 1w5w 5w9w 9w13w1w 2w 3 w 4 w 1w 2w 3 w 1 w 1 w 5 w 5 w 9 w 9 w 13 w1w 2w 3 w 4 w 1w 2w 3 w b a engineering, technology & applied science research vol. 9, no. 4, 2019, 4490-4494 4493 www.etasr.com nguyen: analysis of rectangular plates on resting winkler and two-parameter elastic foundation … foundation model. on the other hand, the variable dimension of the non-dimension variation of the two models is equivalent. the non-dimension stress of the two foundation models has also the same change. table ii. non-dimensional deflections and stresses on rising winkler foundation model by fdm k non dimensional deflections non dimensional stresses w xx σ yyσ 0 0.0443 0.2839 0.2839 1000 0.0431 0.2755 0.2755 2000 0.0419 0.2675 0.2675 3000 0.0408 0.2600 0.2600 4000 0.0398 0.2528 0.2528 5000 0.0388 0.2460 0.2460 table iii. non-dimensional deflections and stresses on rising two-parameter foundation model by fdm k sk non dimensional deflections non dimensional stresses w xxσ yyσ 1000 0 0.0431 0.2755 0.2755 1000 1000 0.0409 0.2617 0.2617 2000 2000 0.0398 0.2541 0.2541 3000 3000 0.0387 0.2470 0.2470 4000 4000 0.0378 0.2402 0.2402 5000 5000 0.0368 0.2337 0.2337 fig. 6. non-dimensional deflections on rising winkler foundation fig. 7. non-dimensional deflections on rising two-parameter foundation c. effect of a/b to non-dimensional deflections and stresses the obtained results for rectangular plates on rising winkler foundation with a/b=[1.0 1.5 2.0 2.5 3.0], plate thickness h=a/100(cm), differential mesh division ∆x=a/8(cm) and ∆y=b/8(cm), uniformly distributed load p=-100kn/m 2 , young’s modulus e=2.1×10 5 mpa, poisson’s ratio µ=0.3 and winkler modulus k=ks=1000, are shown in table iv. table iv. non-dimensional deflections and stresses a/b non-dimensional deflections non-dimensional stresses w xxσ yyσ 1.0 0.0422 0.2696 0.2696 1.5 0.0162 0.1313 0.1869 2.0 0.0068 0.0663 0.1144 2.5 0.0032 0.0351 0.0670 3.0 0.0016 0.0194 0.0387 (a) (b) fig. 8. effect of the a/b of variability on (a) non-dimensional deflections, and (b) non-dimensional stresses in table iv and figure 8, we can see that the effect of a/b to the non-dimensional deflections and stresses is significant. the variability of non-dimensional deflections is [0.0422 ÷ 0.0016], of non-dimensional stresses xx σ is [0.2696÷0.0194] and has a larger fluctuation range yy σ of [0.2696 ÷ 0.0194]. these obtained results confirm that the research is consistent with previous researches’ results on the problem of plates on rising elastic foundation. n o n d im e n s io n a l d e fl e c ti o n s s ig m a n o n d im e n s io n a l engineering, technology & applied science research vol. 9, no. 4, 2019, 4490-4494 4494 www.etasr.com nguyen: analysis of rectangular plates on resting winkler and two-parameter elastic foundation … d. effect of the a/h to non-dimensional deflections and stresses consider rectangular plates on rising winkler foundation with input parameter a/b=1 and plate thickness a/h=[50 100 150 200 250], differential mesh division ∆x=∆y=∆=a/8cm, uniformly distributed load, p=-100kn/m 2 , young’ modulus e=2.1×10 5 mpa, poisson’s ratio of the plate material µ=0.3 and winkler modulus k=ks=1000. the obtained results are shown in table v and figure 9. table v. non-dimensional deflections and stresses a/h non dimensional deflections non dimensional stresses w xxσ yyσ 50 0.0441 0.2828 0.2828 100 0.0431 0.2755 0.2755 150 0.0404 0.2573 0.2573 200 0.0361 0.2274 0.2274 250 0.0307 0.1899 0.1899 (a) (b) fig. 9. effect of the a/h variability on (a) non-dimensional deflections, and (b) non-dimensional stresses in table v and figure 9 we can see that the effect of a/h to non-dimensional deflections and stresses is influential but not great. the variability of non-dimensional deflections is [0.0441 ÷ 0.0307] and of non-dimensional stresses and xx yy σ σ is [0.2755÷0.1899]. v. conclusion this paper studied the analysis of rectangular plates on resting winkler and two-parameter elastic foundation models by using the finite difference method. authors 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51-59, 1996 [10] l. sadecka, “finite/infinite element analysis of thick plate on a layered foundation”, computers and structures, vol. 76, no. 5, pp. 603-610, 2000 [11] s. p. timosenko, j. n. dudier, theory of elasticity, mcgraw hill education, 1962 [12] j. c. ezeh, o. m. ibearugbulem, c. i. onyechere, “pure bending analysis of thin rectangular flat plates using ordinary finite difference method”, international journal of emerging technology and advanced engineering, vol. 3, no. 3, pp. 20-23, 2013 [13] j. s. horvath, soil-structure interaction research project, manhattan college, 2011 [14] e. winkler, die lehre von elastizitat und festigkeit, dominicius, 1867 [15] p. l. pasternak, “on a new method of analysis of an elastic foundation by means of two foundation constants”, gosudarstvennoe izdatelstvo literaturi po stroitelstvu i arkhitekture, moscow, 1954 [16] m. hetenyi, beams on elastic foundation, the university of michigan press, 1946 [17] s. timoshenko, s. woinowsky-krieger, theory of plates and shells, mcgraw-hill, 1959 [18] j. n. reddy, theory and analysis of elastic plates and shells, crc press, 2006 n o n d im e n s io n a l d e fl e c ti o n s s ig m a n o n d im e n s io n a l engineering, technology & applied science research vol. 8, no. 3, 2018, 2875-2878 2875 www.etasr.com detho et al.: evaluation of road traffic accidents (rtas) on hyderabad karachi m-9 motorway section evaluation of road traffic accidents (rtas) on hyderabad karachi m-9 motorway section amir detho energy & environment department quaid-e-awam university of engineering, science & technology nawabshah, pakistan aamir_detho@yahoo.com saleem raza samo energy & environment department quaid-e-awam university of engineering, science & technology nawabshah, pakistan sfaizsamo@yahoo.com kishan chand mukwana energy & environment department quaid-e-awam university of engineering, science & technology nawabshah, pakistan mukwana_99@yahoo.com kamran ahmed samo electrical engineering department quaid-e-awam university college of engineering, science & technology larkana, pakistan kamransamo2@gmail.com asif ali siyal energy & environment department quaid-e-awam university of engineering, science & technology nawabshah, pakistan asifsiyal2007@quest.edu.pk abstract—pakistan is a developing country and its development depends upon its transports facilities. this paper describes the findings of a survey for the evaluation of road traffic accidents (rtas) that focused on the hyderabad-karachi m-9 motorway section. the objectives of the survey are the collection the data of traffic accidents including the human and property losses and the evaluation of rtas causes. during a two year period (i.e. 2015 and 2016) it was revealed that 145 rtas occurred on the motorway. in those rtas, 109 persons died and 293 got injured and 251 vehicles were damaged. high risk percentages were recorded for both pedestrian and vehicle users. keywords-road traffic accidents; rtas; evaluation; causes of rtas i. introduction in pakistan, highways were initially used as feeders to railways that were the main transport utility for long distances and goods. nowadays however, the use of highways has increased and their length has expanded from 249,972 km (in 2000-01) to 263,356 km (in 2015‐16). a similar increase is recorded on the number of vehicles, from 4,701,600 (in 200001) to 17,317,600 (in 2015-16) [1]. the maintenance and construction of roads in pakistan falls under the state government and national highway department. for this research, an extensive literature survey was carried out to determine and learn the past findings in the area of rtas. authors in [2] state that road studies and road safety learning are very necessary, especially for those who are often directly involved in rta injuries, for example students. they introduced the road safety concept for pre schooling students through animal world stories. it is concluded that it is needed to improve the driving skills, to adopt strict rules and regulations, to adapt more comprehensive rules and to use more traffic controlling devices. during the issuance of driving license to public transport drivers, first aid training must be undertaken. author in [3] states that the rtas are the 8th main cause of deaths in the world. according to who (2004), rtas will become the 3rd main cause of death by the year 2020, if not controlled properly. furthermore, the available data is not trustworthy due to under reporting. anyhow, rtas are one of leading causes of death and injury worldwide. author in [4] states that huge losses due to road accident were reported in tanzania. in 1994, the (high) cost of accident losses was estimated and it was established that it kept increasing. road safety issues are now been under consideration by the tanzania government. the speed limit of the buses has been controlled. however, the rtas still keep increasing. therefore, a research was conducted by swedish international development cooperation agency (sida)/sarec with the collaboration of the department of statistics at the university of dar es salaam. in this research, a survey was conducted to investigate the possible reasons of rtas. in the survey, people (including drivers of buses, motor cyclist and pedestrians) were asked their opinion regarding the reasons on rtas. it was identified that the mistakes done by the drivers were the main reason of the accidents. it was concluded that drivers should be welltrained before they are allowed to drive on the road. authors in [5] remind that accidents cause not only economic losses but also intangible consequences such as pain, grief etc. the increasing number of cars and other vehicles is one of the major causes of rtas during the last two decades. for reducing the impacts of rtas, many safety programs have been organized. they concluded that for reducing the number of accidents, the safety programs of developed countries should be implemented in their country. author in [6] states that a little amount of research has been conducted on the road engineering, technology & applied science research vol. 8, no. 3, 2018, 2875-2878 2876 www.etasr.com detho et al.: evaluation of road traffic accidents (rtas) on hyderabad karachi m-9 motorway section accidents in india which is the second-largest populated country in the world. to make the policies workable and effective, the safety plan must be based on the local research and evidence. these plans must be designed to suit the local environment and circumstances. authors in [7] state that the complexity of the flow pattern of the vehicles on the highways is the major reason of the accidents. the rate of the road accidents has increased from 2001 to 2011. it is estimated that 12 persons per 100 accidents were killed in 2011, whereas 7 were killed in 2001. because of damaged roads in rural areas, the road accidents are more likely to happen. author in [8] states that road accidents are considered as human tragedy because of deaths, injuries and loss of income. extensive research has been conducted to investigate the causes of the road accidents. however, the road safety programs are still not as per standard as reveled by the data. in 2010, ten road accidents in every minute have been reported and one death due to road accidents occurred in every 4 minutes. it is difficult for the government to solve this problem alone. authors in [9] dealt with districts with repeating accidents, ernakulam and alappuzha. with the use of weighted severity index (wsi) method, ten spots in ernakulam and six spots in alappuzha was selected for data collection and analysis. on the basis of data collection, kalamassery and mulamthuruthy in ernakulam and kalavoor in alappuzha, were the most repeated accident locations and valuable and effective measures were taken and improved the transport system in the district. author in [10] collected rtas data in kerala state of india from 2010 to 2016. he concluded that 12 persons were killed per 100 accidents in 2016. nowadays, in modern societies, road traffic safeties have become a major concerning issue. in pakistan, the population increases along with road traffic control problems something that is very common in all country’s big cities. day by day the road traffic, the rtas increase, the roads become more dangerous day by day. the fatalities and injuries due rtas have a great impact on socioeconomic development and societal well being. according to world health organization [11], each year an estimated 1.2 millions of people lose their lives and around 50 millions got injured worldwide due to rtas. rtas are caused by technical faults, dangerous driving, bad weather, bad road design and signage. however, in terms of automobile technology safety has been achieved progress. in view of the aforementioned issues, the key objectives of this study work are: 1. to survey the project area in terms of rtas, loss of lives and vehicles. 2. to evaluate the causes of the occurrence of rtas. ii. research methodology in order to achieve the mentioned objectives, a survey on hyderabad-karachi highway was conducted for two years (2015 and 2016). the data source was the national highway & motorway police (nh&mp). the two year rtas data include the total number of accidents (i.e, fatal and non-fatal), the number of people who died and got injured anb the number of damaged vehicles. iii. results and discussion a. fatal and non-fatal accident during 2015 and 2016 the total number of reported accidents from the data of rtas during 2015 and 2016 are categorized as fatal and nonfatal. the road accidents in which death occurs are called fatal accidents and non-fatal accidents are those in which no of life happens. after analyzing the data, it was found that 85 accidents were reported from january to december, 2015. among these, 41 were classified as fatal and the rest as nonfatal. with 60 accidents in the year 2016, 31 and 29 were reported as fatal and non-fatal, respectively. the fatal and nonfatal number of accidents during the years 2015 and 2016 are summarized in table i. table i. rtas during 2015 and 2016 year total accidents fatal non-fatal 2015 85 41 44 2016 60 31 29 b. analysis of rtas occured during 2015 and 2016 as mentioned above the total numbers of rtas reported are 85 and 60 in years 2015 and 2016, respectively. the data collected were further sub-divided depending on the number of deaths, the number of injured and the number of damaged vehicles. 1) number of deaths figure 1 shows the number of deaths reported in fatal rtas during 2015 and 2016. the horizontal axis shows the months while vertical axis represents the number of deaths. it can be seen from the figure that 56 and 53 deaths occurred in 2015 and 2016, respectively. in 2015, the maximum number of deaths accrued in february. but in april, june and november only one loss of life was reported. in the following year, the maximum (i.e. 16) number of deaths occurred in april. however, no death occurred in last two months of the year. comparing the years 2015 and 2016, the total number of deaths are more or less same. 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 jan feb mar apr may jun jul aug sept oct nov dec n u m b er o f d ea th s 2016 2015 fig. 1. number of deaths in rtas reported in 2015 and 2016 engineering, technology & applied science research vol. 8, no. 3, 2018, 2875-2878 2877 www.etasr.com detho et al.: evaluation of road traffic accidents (rtas) on hyderabad karachi m-9 motorway section 2) number of injuries figure 2 illustrates the number of injured persons reported in non-fatal rtas during year 2015 and 2016. it can be observed from the figure that 170 and 123 number of injuries occurred in 2015 and 2016, respectively. in 2015, the maximum number of injured persons was reported in october. the minimum number of injured persons (i.e. 2) was reported in april. among 123 reported injured persons in 2016, the highest number (i.e. 28) of injuries was documented in january. two injuries (which is the least number for 2016) were reported in june and november. among the 24 months 2015 and 2016, the rtas’ data revealed that the maximum number of injuries occurred in october of 2015. 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 jan feb mar apr may jun jul aug sept oct nov dec n u m b er o f in ju re d 2016 2015 fig. 2. number of injured persons in rtas reportd in 2015 and 2016 3) number of damaged vehicles besides the loss of human lives, it is necessary to look at the economic loss caused by accidents. for this reason the number of damaged vehicles was documented in the collected rtas data. figure 3 shows the number of damaged vehicles during each month of the years 2015 and 2016. it can be seen that the numbers of damaged vehicles were documented as 141 and 110 in 2015 and 2016 respectively. in 2015, the maximum number of damaged vehicles (i.e. 18) was reported in july. the minimum was in february with five damaged vehicles reported. in the following year (i.e. 2016), the maximum (i.e. 27) and minimum (i.e. 1) number of damaged vehicles were reported in april july respectively. it is evident that the loss of human lives and economic loss the maximum in april of 2016. 4) causes of rtas on highway the causes of accidents were also documented. five different causes were identified at the accidents sites. these are (1) careless driving, (2) bursting of tyres of vehicles, (3) brake failure of vehicle, (4) bad road conditions and (5) pedestrian crossing. data revealed that careless driving is the major cause of the rtas on the motorway. due to this reason, 29 and 19 people died in 2015 and 2016 respectively and total 293 people got injured in both the reported years. as for the economic loss 93 vehicles were damaged in 2015 and 110 vehicles were damaged are 2016. besides human error while driving, the vehicle condition was another one of the reasons of rtas. tire bursting and brake failure belong in this category. because of brake failure and tire bursting 48 deaths occurred in the reported period while 110 people got injured and 66 vehicles got damaged. the condition of the road/highway has been recognized as another reason for rtas. data have shown that 16 people died in accidents due to bad road conditions. furthermore, 40 people got injured and 34 vehicles were damaged in the accidents which occurred due to bad road conditions. the numbers of loss of human lives and vehicles damaged in rtas due to different reasons are summarized in table ii. 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 jan feb mar apr may jun jul aug sept oct nov dec n u m b er o f v eh ic le d a m a g ed 2016 2015 fig. 3. number of reported damaged vehicles in rtas in 2015 and 2016 table ii. human lives/economical loss and their causes y ea r h u m a n l iv es / e co n o m ic a l l o ss t o ta l causes c a re le ss d ri v in g t ir e b u rs t b ra k e fa il u re b a d r o a d c o n d it io n p ed es tr ia n c ro ss in g 2015 deaths 56 27 16 9 3 1 injuries 170 90 36 28 16 0 vehicles damaged 141 93 19 20 4 5 2016 deaths 53 19 7 14 13 0 injuries 123 50 24 22 24 3 vehicles damaged 110 52 12 15 30 1 iv. summary and conclusions based on accident data collected from january, 2015 to december, 2016 on m9 motorway, the following conclusions are drawn: 1. the findings indicate that human error (careless driving & pedestrian crossing), mechanical fault (tire burst and brake failure) and bad road condition were the major causes for the motorway rtas. engineering, technology & applied science research vol. 8, no. 3, 2018, 2875-2878 2878 www.etasr.com detho et al.: evaluation of road traffic accidents (rtas) on hyderabad karachi m-9 motorway section 2. in 2015, the number of accidents (in percentage) due to careless driving, tire burst, brake failure, pedestrian crossing and bad road condition are 59, 20, 15, 1 and 5, respectively. 3. in 2016, the number of accidents (in percentage) due to careless driving, tire burst, brake failure, pedestrian crossing and bad road condition are 53, 15, 16, 3 and 13, respectively. 4. based on collected accident data, 109 human lives were lost and 293 persons were reported as injured. in addition, 251vehicles were damaged. acknowledgment the authors are grateful to the quaid-e-awam university of engineering, science and technology, nawabshah for providing the research facilities. references [1] government of pakistan, ministry of finance, pakistan economic survey 2015-16, available at: http://www.finance.gov.pk/survey_ 1516.html [2] n. jha, d. k. srinivasa, g. roy, s. jagdish, “epidemiological study of road traffic accident cases: a study from south india”, indian journal of community medicine, vol. 29, no. 1, pp. 20-24, 2004 [3] g. al-haji, road safety development index: theory, philosophy and practice, phd thesis, linkoping university of technology, 2007 [4] r. r. akkarro, “peoples opinion on the causes of road accidents in selected places of tanzania”, european journal of social sciences, vol. 9, no. 4, pp.615-626, 2009 [5] b. b. pillai, k. joseph, “causes and consequences of road accidents in kerala”, international journal of research in it & management, vol. 1, pp. 83-95, 2011 [6] m. m. ruikar, “national statistics on road traffic accidents in india”, journal of orthopedics, traumatology and rehabilitation, vol. 6, no. 1, 2013 [7] b. v. sreekumar, v. sreedevi, “impact of road accidents in kerala during 2001 to 2011-a case study”, singaporean journal of scientific research, vol. 6, no. 1, pp. 51-57, 2014 [8] p. deshpande, “road safety and accident prevention in india”, international journal of advanced engineering technology, vol. 5, no. 2, pp. 64-68, 2014 [9] l. isen, a. shibu, m. s. saran, “identification and analysis of black spots using geographic information system”, international journal of innovative research in science, engineering & technology, vol. 2, no. 1, pp.131-139, 2013 [10] a. chand, “a case study of raod accidents in kerala during 2010 to 2016”, international journal of innovative research in science, engineering & technology, vol. 6, no. 4, pp. 199-203, 2017 [11] world health organization(who), word report on road traffic injury preventation: summary, world health organization, 2004 microsoft word etasr_v13_n4_pp11177-11181 engineering, technology & applied science research vol. 13, no. 4, 2023, 11177-11181 11177 www.etasr.com magashi et al.: indicative factors for saccos failure in tanzania indicative factors for saccos failure in tanzania cosmas magashi department of information technology, system development, and management (itsdm), nelson mandela african institution of science and technology (nm-aist), tanzania magashi80@yahoo.com (corresponding author) anael sam department of information technology, system development, and management (itsdm), nelson mandela african institution of science and technology (nm-aist), tanzania anael.sam@nm-aist.ac.tz john agbinya school of information technology and engineering, melbourne institute of technology (mit), australia jagbinya@mit.edu.au jimmy mbelwa department of computer science and engineering, university of dar es salaam (udsm), tanzania jimmymbelwa@gmail.com received: 23 april 2023 | accepted: 1 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5989 abstract saccos are viewed as a feasible opportunity toward financial inclusion in an economy where most of the citizens are poor, as they are very essential for the socio-economic development of members, the community, and the world at large. however, saccos sometimes do not realize the expected socioeconomic potential, especially when they fail. this study aimed to comprehensively assess financial and non-financial factors, at institutional and personal levels, that contribute to the failure of saccos in tanzania. the data were collected using a questionnaire on 5,000 members of saccos, obtained using stratified random sampling. data collected were analyzed using descriptive statistics and binary logistic regression. the findings showed that both financial and non-financial factors, at personal and institutional levels, had a statistically significant and positive relationship with the failure of saccos. therefore, the performance of saccos and other microfinance financial institutions (mfis) should be addressed from a comprehensive view of both financial and non-financial factors, at personal or institutional levels. in other words, the failure of mfis should be addressed from a holistic point of view. keywords-saccos failure; financial factors; non-financial factors i. introduction the business ecosystems are continually evolving in the current era of science and technology [1], and savings and credit cooperative organisations (saccos) form one of these ecosystems. saccos are defined as voluntary associations where members are encouraged to make regular savings and subsequently obtain credit for use in different activities [2]. saccos are viewed as a feasible opportunity for financial inclusion in an economy where the majority of citizens are poor [3-5] and are considered very essential for the socio-economic development of members, the community, and the world at large [6-8]. saccos have attracted the interest of several studies for their contributions to the socio-economic development of their members and the community at large. saccos have been an engine for mobilizing human, financial, and capital resources for national development [6]. saccos help their members accumulate capital and loans for social needs, such as building houses, buying clothes, paying school fees, organizing weddings, and other social activities [5]. they enable easy access to financial services, encourage savings, create employment opportunities, and directly support community development efforts, such as helping the community access social services, stimulating growth, etc. [7]. saccos make finance more accessible to underprivileged members, limit the incidence of financial exclusion, stimulate a thrift culture, aware ordinary people how engineering, technology & applied science research vol. 13, no. 4, 2023, 11177-11181 11178 www.etasr.com magashi et al.: indicative factors for saccos failure in tanzania to create assets, and generally improve the economic performance of developing countries [9-10]. regardless of such socioeconomic development and contributions, some unexpected issues of saccos' failures are noted. some saccos fail from time to time due to not being operationally and financially stable [2, 5, 11]. some studies revealed financial and non-financial factors for the failure of saccos [12-15], but they were not comprehensive, as they addressed limited factors and focused mainly on financial factors. in addition, these studies used only descriptive statistics to analyze these few factors that contribute to sacco failure, instead of advanced statistical methods, such as logistic regression, which could show more logical relationships. furthermore, several studies concentrated on the failure of mfis and not specifically on saccos. the failure was addressed indirectly as poor loan repayment or loan default and not directly as a failure. the failure of saccos is more than poor loan repayment or loan default. therefore, this study aimed to identify comprehensive statistical relationships between financial and non-financial factors that contribute to the failure of saccos in tanzania. various studies investigated the failure of saccos after their formation. for example, out of 103 saccos in tanzania, 61% and 51% failed operationally financially, respectively [2]. the number of saccos in tanzania decreased from 4,177 at the end of december 2018 to 3,714 at the end of december 2019 [7]. several saccos failed to provide adequate socioeconomic benefits to members as expected. the failure of saccos is reflected directly or indirectly in terms of loan repayment or loan default. as loans are the key products of saccos, failure of loan repayment causes them to fail [19]. poor loan repayment or loan default is the decline and failure of some microfinance institutions, including saccos [10]. the failure of saccos is caused by both internal and external factors, such as financial constraints, weak leadership, unreliable loan interest rates, and poor record-keeping systems [5]. in [11], it was shown that poor monitoring of loan use, poor intrapreneurship and environmental business opportunities, unfavorable loan repayment conditions, and poor strategies for choosing borrower groups were important factors for the failure of saccos. in [12], six factors out of ten were found to influence the failure of saccos, namely: poor educational level, lending methods, the proximity of borrower's residence to the institutions, family size, income from loanfinanced activities, and training. in [13], clients' age, interest rates charged, and loss of collateral were noted as the principal factors leading to the failure of saccos. in [14], it was shown that factors such as training, education level, and annual income could cause the failure of saccos. the institutional theory stresses the evaluation of mfis, such as saccos, indicating that many saccos do not experience a proper circle of money market, mass distribution of credit, and uplifting microfinance systems as best practices for improving efficiency due to poor management systems, finance and accountability, marketing, and service delivery. additionally, working capital management theories (wcmt) indicate that the failure of saccos depends on existing or anticipated internal and external constraints, which vary from operational, managerial, or resource constraints. the information asymmetry theory (iat) portrays that the lack of proper information may be one of the non-financial factors that cause the failure of saccos in tanzania. lenders fail to adequately differentiate the information between one borrower and another [16-18]. misaligned information between lenders and borrowers may lead to losses when the money issued is delivered to the wrong borrowers. furthermore, prospective sacco borrowers may lack or have limited information, making them not borrow as expected [13]. this study attempted to distinguish the factors mentioned above into predictor and outcome variables. these factors were categorized into financial and non-financial factors and further divided into personal (saccos clients) and institutional (saccos) factors. the personal non-financial factors were clients' age, education level, family size, proximity of borrowers' residence to the institution, gender, type of business, and entrepreneurship/business environment. the institutional non-financial factors were the supervisory environment, record keeping, infrastructure, supportive regulations, human resources, choosing borrowers, training, and lending method. personal financial factors were loan repayment, collateral loss, annual income, loan utilization, high transaction cost, client credit experience, knowledge of financial management, and loan management strategies. financial institutional factors were loan interest, loan amount, loan category, lending methodology, criteria used in granting micro credits, unfavorable loan repayment conditions, income from loanfinanced activities, and interest rates charged. ii. methodology this study used a quantitative approach, following the nature of the specific objective which is characterized by a causal-effect relationship, attempting to explain the relationship between variables. this approach uses statistical data as a tool to save time and resources by focusing on numbers and figures in data collection and analysis [20]. this study applied the explanatory cross-sectional survey research design, due to various reasons following the nature of its objective. each sacco was treated as a unit of analysis covering a large geographical area of tanzania, to provide fast, well-organized, and precise means of analyzing failure information. the study was dominated by "what" questions, which prompt the explanatory cross-sectional survey research design [21-22]. the study was carried out in tanzania, based on five regions, namely dar es salaam, arusha, mbeya, mwanza, and dodoma, which have high concentrations of saccos and can represent the country as a whole. these regions have both successful and failed saccos, and also have saccos with the alert of the possibility of being closed by tcdc. the population of this study included members, staff, and management of saccos, and tcdc management. the members were considered because they were the owners of the saccos; hence, they were very well informed of their performance. the saccos staff and management and the tcdc management are the key informants on any performance, success or failure, regarding saccos. first, the sample was chosen from the dar es salaam, arusha, mbeya, mwanza, and dodoma regions and the sample engineering, technology & applied science research vol. 13, no. 4, 2023, 11177-11181 11179 www.etasr.com magashi et al.: indicative factors for saccos failure in tanzania population of saccos members was obtained. the population of saccos members obtained from the given regions was 5,000, i.e. 1011 in dar es salaam, 1000 in arusha, 1030 in mbeya, 999 in mwanza, and 960 in dodoma. the formula in [23] was used to calculate the sample size for this study as indicated below: � = �$��� �$ � �� �$��� (1) where n is the sample size for a finite population, n is the size of the population that is the number of saccos members (5000), p is the population reliability (or frequency estimated for a sample of size n) taken as 0.5 for all developing countries population, p+q=1, e is the margin of error considered 3%, and z $ is the normal reduced variable at 0.05 level of significance, which was chosen as 1.96. according to the above formula, the sample size for this study was: � = �.���$× �.�×�.��×���� �.���$× ���� �� �.���$×�.�×�.� (2) � ≈ 880 the primary data of this study were collected mainly using a questionnaire and 880 questionnaires were distributed to the members of saccos. however, only 500 questionnaires were received and found to be complete and useful for data analysis. the response rate was 57% and could not affect the assumption (sample size) of the binary logistic regression model for data analysis. the questionnaire was able to produce information from the respondents at a low cost with a large and geographically spread population. the questionnaire provided the respondents with a suitable time to give well-thought responses and allowed not easily approachable respondents to be reached. it was a structured questionnaire, prepared in advance with fixed, concrete, and predetermined questions. the questions had the same wording and order for all respondents, with the same stated responses, and had closed answers. the respondents completed the questionnaire on their own. furthermore, the secondary data of this study were collected using a documentary review of published and non-published reports on the performance of saccos in tanzania and other developing countries, such as kenya, ethiopia, nigeria, and others. secondary data provided the basis for collecting primary data and finally making comparisons. to ensure the quality of the findings, the questionnaire was first pre-tested and piloted in a small intended sample to examine its reliability and variability. the comments given during the pre-testing and pilot study were scrutinized and incorporated accordingly. cronbach's alpha coefficient was used to investigate whether the study scales were free from random error, of which a minimum level of 0.7 was used [24]. the use of multiple data collection methods, i.e. questionnaire and documentary reviews, also ensured validity and reliability. the use of various respondents, i.e., saccos members, staff, management, and tcdc management, likely ensured triangulation, validity, and reliability of the findings. this study adapted scales from previous empirical studies to ensure empirical evidence and confidence of definitions, measurements, and operationalization of variables and scales as a way to ensure validity and reliability. the collected data were analyzed using binary logistic regression. the model was used to test and predict a dichotomous dependent variable from several categorical or continuous independent variables. specifically, the dependent variable is sacco's sustainability, where 0 indicates "fail" and 1 indicates "successful". the model allowed for the establishment of the predictive ability of sets of independent variables. data analysis was performed using r statistics version 4.0.5. iii. findings table i briefly describes the personal information of the respondents, to ensure that homoscedasticity, independence of residuals/relations, normality, sample size, outliers, and multicollinearity were met before running the model. table i. participants' information personal information scale frequency % gender male 300 60 female 200 40 total 500 100 age 21-24 years 95 19 25-29 years 150 30 21-24 years 95 19 25-29 years 150 30 30-34 years 185 37 35-39 years 50 10 40 years and above 20 4 total 350 100 family status single 295 59 married 150 30 divorced 30 6 widow 25 5 total 500 100 region arusha 100 20 dar es salaam 102 20 mbeya 103 21 mwanza 99 20 dodoma 96 19 total 500 100 educational level formal education 95 19 primary education 150 30 secondary education 185 37 undergraduate education 50 10 postgraduate education 20 4 total 500 100 this study had one main question: "what are the factors that predict the failure of saccos in tanzania?", or alternatively: "how well does a set of factors predict and explain the failure of saccos in tanzania?". the question was answered using a binary logistic regression model. although the model produced a lot of information, this section just highlights the results that are straightforward in explaining the influence of financial and non-financial factors on saccos failure in tanzania. regarding the overall model fit, the omnibus test of model coefficients was used to indicate in general how well the model performed, frequently referred to as the goodness of fit. the results showed that this value was 0.000 (p<.0005). the overall model fit was also tested using chi-square, showing a value of 87.02 with 4 degrees of freedom (df). additionally, the results of the hosmer-lemeshow test engineering, technology & applied science research vol. 13, no. 4, 2023, 11177-11181 11180 www.etasr.com magashi et al.: indicative factors for saccos failure in tanzania portray the reliability of the model fit. the chi-square value for the hosmer-lemeshow test was 17.019 with a significance level of 0.309, and as this value is larger than 0.05 it indicates support for the model. it should be noted that the hosmerlemeshow goodness of fit is indicated by a significance value greater than 0.05, while the omnibus test of model coefficients is indicated by a significance value less than 0.05 [25-26]. the usefulness of the model was also established. this information provides the variation capacity in the outcome variable explained by the used model, i.e. the usefulness of the model. table ii shows these results, along with the cox and snell r squared and the nagelkerke r squared values. however, the pseudo-r square statistics were used rather than the true r square values as provided in the multiple linear regression results. the results indicated two values of 0.371 and 0.463, meaning that between 37% and 47.3% of the variability is explained by this set of variables. table ii. the overall model fit omnibus tests of model coefficients chi-square df sig. step 1 87.02 4 0.000 block 87.02 4 0.000 model 87.02 4 0.000 hosmer and lemeshow test step chi-square df sig. 1 17.019 8 0.309 model summary step 2-log likelihood cox and snell r 2 nagelkerke r 2 1 352.376 a 0.371 0.463 the contribution of financial and non-financial factors to the failure of saccos was similarly established. table iii shows the predictive ability of each predictor variable using the wald test. the results indicated that all predictor variables were statistically significant. all factors influenced the failure of saccos: poor loan repayment or excessive loan defaults. checking the contribution capacity of each factor, it is noted that clients' and institutional financial factors had major contributions to the failure of saccos compared to nonfinancial factors. the direction of all predictor variables was positive, showing that all financial and non-financial factors positively impact the failure of saccos. table iii. influence of financial and nonfinancial factors on saccos' failure b s. e wald df sig. step 1a clients' f.n. fs 1.987 .325 37.311 1 0.023 inst. f.n fs 3.634 .336 37.311 1 0.012 clients' f. fs. 5.012 .365 39.671 1 0.000 inst. f fs. 4.339 .315 38.331 1 0.000 constant 2.954 2.434 2.825 1 0.006 a. variable (s) entered on step 1: personal f.n. fs, inst. f.n fs, personal f. fs., inst. f fs. table iv displays the predictive ability of each variable on saccos' failure, showing that all predictor variables had a statistically significant and positive relationship (p ≤ 0.05) with the failure of saccos. generally, both financial and nonfinancial factors at personal or institutional levels lead to the failure of saccos. these results are consistent with previous studies [10-13] that did not exhaust such a large set of predictor factors. these studies noted the inconsistency of some factors, but this study did not. these factors apply not only to sacco's failure but also to other sectors. for example, time, price, costs, designs, labor issues, scarce preparation, and resource shortage have been found to cause failure in construction projects [26]. these factors are similar to the ones highlighted in sacco failure, except for the language used. smes are similarly affected by financial resources, technical upgrading, marketing, training and development of human resources, lack of strategic planning, and lack of advanced industrial digital technologies [1]. total productive maintenance (tpm) in different companies is affected by strategic, managerial, departmental, financial, and social constraints, and workers' insufficient training and lack of commitment [28]. table iv. influence of factors on saccos failure b s. e wal d df sig. credit experience 1.907 0.341 4.356 1 0.000 loan amount 1.523 0.333 7.311 1 0.000 annual income 1.978 0.329 6.673 1 0.000 loan mgt/utzn. 0.769 0.386 7.733 1 0.032 loan interest 3.328 0.288 8.125 1 0.000 age 0.328 0.088 0.738 1 0.024 gender 0.717 0.191 6.531 1 0.043 family size 1.591 0.298 7.037 1 0.012 residence distance 1.175 0.397 6.319 1 0.002 business type 1.175 0.395 7.017 1 0.004 business env/ment 1.444 0.360 6.913 1 0.001 record keeping 1.733 0.638 8.072 1 0.000 infrastructure 1.733 0.392 4.754 1 0.030 regulations 1.034 0.371 7.031 1 0.065 hrs 1.461 0.325 7.171 1 0.001 loan category 1.361 0.325 6.732 1 0.000 collateral 1.284 0.219 5.621 1 0.000 training 1.339 0.219 7.079 1 0.024 lending method 0.915 0.162 5.127 1 0.007 constant 5.123 4.931 7.923 1 0.002 examining the classification of cases in table v shows that the overall percentage of correctly classified cases was approximately 77%, meaning that there was a higher percentage of respondents regarding a particular financial and non-financial factor leading to the failure of saccos. table vi highlights the results of a set of predictor variables to improve the accuracy of the predictions, i.e., testing the set model of predictor variables, showing that these factors contributed to the saccos' failure by 82%. table v. classification table a,b observed predicted prob failure recode 01 % correct no yes step 0 prob failure recode no 0 117 100.0 01 yes 0 383 0.0 overall percentage 76.6 table vi. classification tablea observed predicted prob failure recode 01 % correct no yes step 1 prob failure recode no 89 294 17.8 01 yes 32 85 82.2 overall percentage 100.0 engineering, technology & applied science research vol. 13, no. 4, 2023, 11177-11181 11181 www.etasr.com magashi et al.: indicative factors for saccos failure in tanzania iv. conclusion and recommendations the failure of saccos is caused by several financial and non-financial factors at personal or institutional levels. this study showed that the performance of saccos and other mfis should be addressed from a comprehensive view of both financial and non-financial factors, whether at personal or institutional levels. these results conclude on the statistical and significant relationship between financial and non-financial factors on saccos' failure in tanzania and established their prediction/explanatory capacity in 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[28] m. a. munir, m. a. zaheer, m. haider, m. z. rafique, m. a. rasool, and m. s. amjad, "problems and barriers affecting total productive maintenance implementation," engineering, technology & applied science research, vol. 9, no. 5, pp. 4818–4823, oct. 2019, https://doi.org/10.48084/etasr.3082. microsoft word etasr_v11_n1_pp6766-6774 engineering, technology & applied science research vol. 11, no. 1, 2021, 6766-6774 6766 www.etasr.com almaleki: the precision of the overall data-model fit for different design features in confirmatory … the precision of the overall data-model fit for different design features in confirmatory factor analysis deyab almaleki department of evaluation, measurement, and research umm al-qura university meccah, saudi arabia damaleki@uqu.edu.sa abstract-factor analysis (fa) is the study of variance within a group. within-subject variance (wsv) is affected by multiple features in a study context such as the experimental design (ed) or the sampling design (sd). the aim of this study is to provide an empirical evaluation of the influence of different aspects of ed and sd on wsv in the context of fa in terms of model precision. the study results showed that the precisions of the overall model fit indices tli and cfi, as functions of vtf, stv, h 2 , and their interaction, varied, as did the precisions of the overall model fit indices gfi, agfi, and rmsea as functions of vtf, stv, and their interactions. overall, when the vtf is 4:1 or 7:1, the required stv is 16:1 or above 32:1 or above to show precision in factor solution. keywords-model-precision; factor-analysis; model-fit; modeldesign i. introduction factor analysis (fa) is a useful and flexible analytic family of methods that plays a critically important role in many empirical applications. fa is the study of variance within a group, as opposed to statistical analysis, which focuses on partitioning variance among groups [1]. fa is extensively applied in education and behavioral science research. a recent two-year analysis (from 2003 to 2005) of the use of fa methods as indexed by the psycinfo database revealed that more than 1,700 studies used some form of fa [2]. however, fa is a generic term for a family of statistical techniques, including exploratory fa (efa) and confirmatory fa (cfa). the fundamental purpose of efa is to identify unknown latent constructs in a relatively large set of measured indicator variables that can summarize (or reproduce) the observed covariance or correlation pattern among a set of indicator variables. efa is often used when the researcher may not have specific expectations of the number of constructs or factors underlying the dimensional structure of the observed correlational pattern, or even in cases when the researcher has emergent ideas about the underlying dimensional structure of the observed correlational pattern among a larger set of indicator variables [1-3]. when conducting an efa study or analysis, the researcher faces a multitude of methodological and technical decisions. for example, there are two different efa statistical models to choose from: (a) the full component model, or (b) the common factor model [4-6]. the implications of choosing either one need to be well understood. cfa is a form of factor analysis that tests hypotheses regarding how well the measured indicator variables represent the number of constructs [7, 8]. cfa is a confirmatory method that can be used to examine, evaluate, and/or test the number of hypothesized factors underlying the variance/covariance in a set of measured indicator variables. cfa allows testing hypothetical and plausible alternative latent variable structures for the observed indicator variance/covariance [9, 10]. more recently, cfa has also been used in exploratory analysis too. both efa and cfa attempt to understand the variance of the observed indicator variables through studying the withinsubject variance (wsv). it is well understood that wsv is affected by many features of the study conduct, such as the study experimental design (ed) and the sampling design (sd). thus, anything that influences or changes variance may affect the conclusions related to fa. previous studies have isolated one or two elements within ed and sd [8, 11, 12]. however, to the best of our knowledge, no study provided a comprehensive examination of multiple wsv factors, yet this is precisely what a researcher must do when planning a wsv study. to understand the impact of ed and sd or other influences on wsv, a systematic structure for evaluating wsv changes is necessary. one possibility to evaluate wsv systematically is to use factorial invariance (fiv) [13-17]. the fiv methods offer a structure that allows disentangling measurement elements from structural elements in the factor model. via fiv and the evaluation of data-model fit, the impact of ed and sd on wsv can be compared among groups by examination of model precision [1, 12, 13, 18, 19]. previous researches investigated the precision of factor solutions by the examination of chisquare value (χ�) and overall model fit (omf) indices such as goodness-of-fit index (gfi), adjusted gfi (agfi), tuckerlewis index (tli), comparative fit index (cfi), and root mean square error of approximation (rmsea) [3, 9, 20-22]. the overall model fit indices examine the global measures of data-model fit. corresponding author: deyab almaleki engineering, technology & applied science research vol. 11, no. 1, 2021, 6766-6774 6767 www.etasr.com almaleki: the precision of the overall data-model fit for different design features in confirmatory … there are three key features of design that are of paramount importance and generally overshadow all the technical decisions a researcher faces. these three features are: (a) the selection and the number of indicator variables, (b) the nature and size of the sample, and (c) the communality magnitude. understanding the impact of variable-to-factor (vtf) ratio, sample size or subject-to-variable (stv) ratio, and communalities (h 2 ) magnitude in fa analysis is relevant because these features affect the model precision and operationalized (measured) latent variable (factor) variance, which determines the model invariance of fa findings. the benefit of fa is based on its ability to produce well-built, reliable, and understandable estimates of factor loadings [23]. therefore, understanding how vtf, stv, and h 2 interact in fa and how they possibly influence or change the model precision and operationalized (measured) latent variable (factor) variance is the basic problem investigated in this study. the model precision in this research is operationalized along psychometric and not statistical lines. statistically, precision is inversely related to the standard error of the sampling distribution and related to the minimizing of the standard error of a statistic. psychometrically, precision can mean this, but additionally, in a reliability context, it can also refer to the accuracy of the estimator to be near (or the same) as the theoretical latent variable (e.g. the true score) [9, 13]. thus, as the standard error of measurement decreases the precision/accuracy of the observed scores converges to the true score. however, no comprehensive study has been found in the existing literature to have systematically examined the incremental or combined impacts of two features of ed and sd and the optimum way to estimate the model. therefore, evaluating the impact of ed and sd effects on wsv in fa findings is the basis of the proposed monte carlo simulation study [24, 25]. ii. ed: variable-to-factor ratio previous research indicates that cfa yields more precise results when each common factor is represented by multiple indicator variables in the analysis [5, 21, 26]. while this concern is related to model identification [1, 14, 18, 27, 28], this is not the focus given here. specifically, given an identified model, the way the sample and number of indicator variables inform the understanding of the latent factor is an important question which has not received great attention in the cfa literature [2, 12, 17, 28-30]. authors in [18] concluded that the vtf ratio was important for factor stability with more indicator variables per factor yielding more stable result. however, the researchers who investigated vtf ratio have not reached a mutual decision on an optimal vtf. authors in [18, 31] concluded that a vtf of 3:1 is sufficient for factorial precision, whereas authors in [11] found that 24.6% of the studies published in journal of personality and social psychology (jpsp) and 34.4% of the studies published in journal of applied psychology (jap) have vtf ratio of 4:1 or less. however, other researchers who have investigated the effects of indicator variable sampling did not attempt to systematically manipulate conditions that could potentially affect the pattern stability of cfa findings. the issue of variable sampling has been used extensively in conceptual development, but the existing literature has received almost no empirical evaluation that generally has sampled indicator variables at random from the universe of variables. the assumption of random sampling is useful to minimize sampling issues and for developing generalizability rather than a prescription for applied research procedures. iii. underlying factor structure one of the broad domains in social science is the big five personality traits, which is used to describe human personality and includes extraversion, agreeableness, openness, conscientiousness, and neuroticism. most commonly used in academic psychology, this model incorporates five different factors into a conceptual model for describing personality traits [3, 8, 32]. it has been selected as the structural model for this study because of its wide use in social sciences. the model structure of the big five personality traits theory has received favorable attention from researchers in the psychological discipline. the author in [3] concluded that the measurement structure of the big five personality traits is an orthogonal solution and the variation on each one of the big five personality trait dimensions is commonly proposed to be independent of variation on each of the others. iv. sd: subject-to-variable ratio authors in [4, 12, 13, 15, 18-19, 22, 26, 33-36] found a mixed range in fa sample sizes described by either the absolute size of the sample or the stv ratio. authors in [37] reviewed 60 studies utilizing fa and found the average minimum sample size was 42, and the minimum stv ratio was 3.25:1, with most of the studies using a stv ratio less than 5:1. similarly, authors in [11] reviewed fa studies published in jpsp and jap (from 1991 to 1995) and found that 18.9% of the published articles utilizing fa in jpsp and 13.8% in jap had an average minimum sample size of 100 or less. authors in [2] examined publications utilizing fa from the psychinfo database between 2003 and 2005. they found that 15.4% of the studies reported stv from 10 to 20:1 and only 3% of the studies used a stv of 20-100:1. high absolute sample size or stv ratio is important to predict precise outcomes, increase the generalizability of the findings, and maximize the accuracy of population estimates [2, 4, 7, 22, 29]. there are many common practice rules of sample size in the literature, most of them not empirically based [18]. moreover, a limited number of studies have empirically investigated the effect of stv on model precision [38]. selecting the adequate sample size is an important decision in study design. the researcher must determine how large the sample should be and what is the most appropriate sampling frame. there are tremendous guidelines for estimating an adequate sample size for fa [2, 4, 11, 35, 39]. v. sd: communalities (ℎ�) magnitude the communality of a variable can be interpreted as the proportion of variation estimated by the common factors. communalities range from 0 to 1, where 0 means that the factors do not explain any of the variances and 1 means that all the variances are explained by the factors. a large value of communality suggests a strong effect by an underlying engineering, technology & applied science research vol. 11, no. 1, 2021, 6766-6774 6768 www.etasr.com almaleki: the precision of the overall data-model fit for different design features in confirmatory … construct [7, 20, 40]. communality is the sum of the squared factor loadings for observed variables variances accounted for by all the factors [17, 19]. communality measures the percentage of variance in the observed variables explained by all the factors. the larger the communality for each variable, the more successful the factor analysis solution is, and the smaller the communality, the more questionable the solution [4, 31, 39, 41]. communality ranges between 0 and 1. if the communality exceeds 1.0, there is something wrong with the data, which may reflect model specification or sd problems. low values of communalities across the set of observed variables indicate the variables are marginally related to each other and the factors provide little explanation of the variance in the observed variables [2, 20, 26, 39]. vi. methods the current study was designed to investigate the empirical evaluation of the influence of different aspects of ed and sd on wsv in terms of model precision and operationalized (measured) latent variable (factor) variance relative to a known factor structure via monte carlo simulations. the study manipulated: (a) the vtf ratio (4:1, 7:1, and 10:1) randomly sampled from a population of 100 indicator variables, (b) the stv ratio from 2:1 to 32:1 in multiples of 2 (2:1, 4:1, 8:1, 16:1, and 32:1), and (c) the communality magnitude (high, moderate, low, and mixed). these factors were varied in a known factor structure with: (a) continuous variables (measurement scale), (b) normal distribution, (c) 5-factor solutions (common factor), and (d) orthogonal solution (factor structure). the precision of factor solution was evaluated by the examination of cfa for an orthogonal 5-factor (common factor) model. chi-squared value and overall model fit indices criteria were used to evaluate the models for all conditions. chi-squared value and four model fit indices were treated as dependent variables (dvs) in threeway analysis of variance (anova) using the level of h 2 , vtf ratio, and stv ratio as independent variables. figure 1 illustrates the study design. fig. 1. design of interaction conditions. vii. results the monte carlo simulation populated 60 three-way cells between subjects’ factorial design matrix: h 2 (high, moderate, low, and mixed) by vtf ratio (4:1, 7:1, and 10:1) and stv ratio (2:1, 4:1, 8:1, 16:1, and 32) with 1000 replicate samples (see figure 1). chi-squared values and overall model fit indices (gfi, rmsea, tli, and cfi) were treated as dvs in parallel three-way anova. to control for multiplicity among dvs a type i error rate was adjusted by a bonferroni correlation: 0.05/7=0.007. a. chi-squared test (��) the descriptive statistics for the chi-squared values among all design cells are presented in table i. table i. descriptive statistics for �� averaged over 1000 replications vtf stv h 2 high moderate low mixed m sd 4:1 2:1 220.0 23.8 219.86 24.60 219.37 23.41 220.42 23.53 4:1 190.8 20.9 190.00 20.53 189.98 20.92 189.54 20.48 8:1 179.3 19.2 179.20 19.64 180.09 19.59 178.70 19.13 16:1 174.2 19.2 174.41 18.70 174.69 19.18 174.07 18.33 32:1 171.7 18.6 171.53 19.68 172.81 18.08 171.63 17.72 7:1 2:1 709.5 43.6 709.71 42.05 705.16 43.12 709.22 42.58 4:1 620.0 38.2 621.19 36.03 618.77 37.49 622.59 37.60 8:1 588.4 34.5 589.28 36.56 587.06 34.58 589.76 36.09 16:1 573.3 34.5 574.42 34.97 573.77 34.94 574.10 34.05 32:1 566.2 33.9 566.33 33.26 568.73 33.68 568.56 33.57 10:1 2:1 1471.88 61.4 1469.46 59.60 1473.04 60.34 1472.52 60.92 4:1 1298.02 55.8 1297.31 52.89 1296.04 53.45 1296.67 52.45 8:1 1231.67 49.5 1230.17 49.97 1228.86 51.12 1228.82 50.92 16:1 1203.03 48.4 1203.64 50.24 1201.30 50.37 1201.90 48.66 32:1 1186.37 47.6 1187.40 49.00 1188.81 50.89 1187.65 49.20 the overall anova findings for the �� revealed the statistically significant model, f(59,59940)=137546, p<0.0001. as can be seen in table ii, there were statistically significant results for the main effects of vtf and stv, and a statistically significant interaction between vtf*stv. surprisingly, no statistically significant main effect or interaction involving communality was found. table ii. three-way anova for �� by conditions conditions df f p-value h 2 3 0.49 0.6876 vtf 2 3967031 <0.0001 h 2 *vtf 6 1.39 0.2143 stv 4 32825.9 <0.0001 h 2 *stv 12 0.94 0.5024 vtf*stv 8 6224.92 <0.0001 h 2 *vtf*stv 24 0.70 0.8589 h 2 engineering, technology & applied science research vol. 11, no. 1, 2021, 6766-6774 6769 www.etasr.com almaleki: the precision of the overall data-model fit for different design features in confirmatory … post hoc analysis of the vtf*stv interaction focused on splitting out the levels of stv and examined five one-way anovas for the levels of vtf. visual examination of the mean �� values suggests a small, but significant decrease in mean �� values as stv increases among all levels of vtf that decreased in magnitude as vtf increased (see figure 2). table iii presents the simple anova effect on vtf for each stv level. pairwise comparisons among the levels of vtf at each level of stv, e.g. vtf 4:1 vs. 7:1 @ stv=2:1, were statistically significant with all p-values <0.0001, and the directional pattern in means confirmed the decreasing trends seen in figure 2. fig. 2. �� mean values of interaction between stv and vtf ratios. table iii. one-way anova simple effect of stv by levels of vtf stv df ss ms f p-value 2:1 2 3184 1592 104503 <0.0001 4:1 2 2490 1245 817419 <0.0001 8:1 2 2243 1121 736161 <0.0001 16:1 2 2149 1074 705261 <0.0001 32:1 2 2096 1048 688051 <0.0001 b. goodness-of-fit index the averaged gfi statistics over 1000 replications for the 60 cells in the three-way design are presented in table iv. the standard threshold of acceptable fit percentage is 0.90. the overall anova findings for gfi revealed an overall statistically significant model, f(59,59940)=138368, p<0.0001. as can be seen in table v, there were statistically significant main effects of vtf and stv, and a statistically significant interaction between vtf*stv. once again, the communality factor was not significant. post hoc analysis of vtf*stv interaction focused on splitting out the levels of stv and examined five one-way anovas for the levels of vtf. visual examination of the mean gfi values suggests a significant increase in mean gfi values as stv increases mixed with decreasing mean gfi as vtf ratios increased (see figure 3). table iv. descriptive statistics for gif averaged over 1000 replications vtf stv h 2 high moderate low mixed m p 4:1 2:1 0.69 0.00 0.69 0.00 0.69 0.00 0.69 0.00 4:1 10.82 0.00 0.82 0.00 0.82 0.00 0.82 0.00 8:1 0.90 65.60 0.90 65.70 0.90 61.60 0.90 68.00 16:1 0.94 100.00 0.94 100.00 0.94 100.00 0.94 100.00 32:1 0.97 100.00 0.97 100.00 0.97 100.00 0.97 100.00 7:1 2:1 0.68 0.00 0.68 0.00 0.68 0.00 0.68 0.00 4:1 0.81 0.00 0.81 0.00 0.81 0.00 0.81 0.00 8:1 0.90 28.80 0. 90 30.90 0. 90 31.70 0.90 28.60 16:1 0.94 100.00 0.94 100.00 0.94 100.00 0.94 100.00 32:1 0.97 100.00 0.97 100.00 0.97 100.00 0.97 100.00 10:1 2:1 0.67 0.00 0.67 0.00 0.67 0.00 0.67 0.00 4:1 0.80 0.00 0.80 0.00 0.80 0.00 0.80 0.00 8:1 0.90 7.60 0. 90 7.80 0. 90 9.10 0.90 8.80 16:1 0.94 100.00 0.94 100.00 0.94 100.00 0.94 100.00 32:1 0.97 100.00 0.97 100.00 0.97 100.00 0.97 100.00 table v. three-way anova for gfi by conditions conditions df f p-value h 2 3 1.27 0.2820 vtf 2 6671.43 <0.0001 h 2 *vtf 6 1.52 0.1683 stv 4 2036352 <0.0001 h 2 * stv 12 1.41 0.1534 vtf *stv 8 610.99 <0.0001 h 2 * vtf *stv 24 0.85 0.6733 fig. 3. goodness-of-fit index of interaction between stv and vtf ratios. table vi presents the simple anova effect on the vtf for each stv level. pairwise comparisons among the levels of engineering, technology & applied science research vol. 11, no. 1, 2021, 6766-6774 6770 www.etasr.com almaleki: the precision of the overall data-model fit for different design features in confirmatory … vtf at each level of stv, e.g. vtf 4:1 vs. 7:1 @ stv=2:1, were statistically significant with all p-values <0.0001, and the directional pattern in means confirmed the patterns seen in figure 3. table vi. one-way anova simple effect of stv by levels of vtf stv df ss ms f p-value 2:1 2 0.7851 0.3925 4941.23 <0.0001 4:1 2 0.4301 0.2150 2707.26 <0.0001 8:1 2 0.1641 0.0820 1032.93 <0.0001 16:1 2 0.0537 0.0268 338.14 <0.0001 32:1 2 0.0152 0.0076 95.83 <0.0001 c. root mean square error of approximation rmsea statistics were averaged over 1000 replications for the 60 cells in the three-way design and are presented in table vii. the standard threshold of acceptable fit is 0.05. the overall anova findings for rmsea revealed an overall statistically significant model, f(59,59940)=4901.85, p<0.0001. as can be seen in table viii, there were statistically significant main effects vtf and stv, and a statistically significant interaction between vtf*stv. once again, the communality factor was not significant. table vii. descriptive statistics for rmsea averaged over 1000 replications vtf stv h 2 high moderate low mixed m p 4:1 2:1 0.08 7.50 0.08 8.80 0.08 7.10 0.08 6.70 4:1 0.03 73.80 0.03 75.50 0.03 75.70 0.03 76.00 8:1 0.01 99.90 0.01 99.70 0.01 99.60 0.01 99.90 16:1 0.00 100.00 0.00 100.00 0.00 100.00 0.00 100.00 32:1 0.00 100.00 0.00 100.00 0.00 100.00 0.00 100.00 7:1 2:1 0.06 11.50 0.06 8.80 0.06 13.20 0.06 10.60 4:1 0.02 100.00 0.02 100.00 0.02 100.00 0.02 100.00 8:1 0.01 100.00 0.01 100.00 0.01 100.00 0.01 100.00 16:1 0.00 100.00 0.00 100.00 0.00 100.00 0.00 100.00 32:1 0.00 100.00 0.00 100.00 0.00 100.00 0.00 100.00 10:1 2:1 0.05 47.20 0.05 45.20 0.05 47.20 0.05 46.70 4:1 0.02 100.00 0.02 100.00 0.02 100.00 0.02 100.00 8:1 0.00 100.00 0.00 100.00 0.00 100.00 0.00 100.00 16:1 0.00 100.00 0.00 100.00 0.00 100.00 0.00 100.00 32:1 0.00 100.00 0.00 100.00 0.00 100.00 0.00 100.00 post hoc analysis of vtf*stv interaction focused on splitting out the levels of stv and examined five one-way anovas for the levels of vtf. the visual examination of the mean rmsea values suggests a significant decrease in mean rmsea values as stv increases and an increasing mean rmsea as vtf ratios decreased (see figure 4). table viii. three-way anova for rmsea by conditions conditions df f p-value h 2 3 0.41 0.7467 vtf 2 6698.38 <0.0001 h 2 *vtf 6 1.45 0.1919 stv 4 66127.9 <0.0001 h 2 * stv 12 0.75 0.7077 vtf *stv 8 1408.03 <0.0001 h 2 * vtf *stv 24 0.72 0.8337 fig. 4. rmsea of interaction between stv and vtf ratios. table ix presents the simple anova effect on the vtf for each stv level. pairwise comparisons among the levels of vtf at each level of stv, e.g. vtf 4:1 vs. 7:1 @ stv=2:1, were statistically significant with all p-values <0.0001, and the directional pattern in means confirmed the patterns seen in figure 4. table ix. one-way anova simple rffect of stv by levels of vtf stv df ss ms f p-value 2:1 2 2.3236 1.1618 10188.3 <0.0001 4:1 2 0.3222 0.1611 1413.01 <0.0001 8:1 2 0.1021 0.0510 447.68 <0.0001 16:1 2 0.0436 0.0218 191.23 <0.0001 32:1 2 0.0206 0.0103 90.34 <0.0001 d. non-normed-fit index non-normed-fit index (or tucker-lewis index-tli) statistics were averaged over 1000 replications for the 60 cells in the three-way design and are presented in table x. additionally, the percentage of tli statistics meeting the standard threshold of acceptable fit, e.g. 0.96, was tabulated. the overall anova findings for tli revealed an overall statistically significant model, f(59,59940)=4556.25, engineering, technology & applied science research vol. 11, no. 1, 2021, 6766-6774 6771 www.etasr.com almaleki: the precision of the overall data-model fit for different design features in confirmatory … p<0.0001. as can be seen in table xi, there were statistically significant main effects and interactions, including a statistically significant triple interaction between h 2 *vtf*stv. the visual examination of the mean tli values reveals a differential increase in mean tli within levels of stv as a function of h 2 magnitude. in the h 2 =high condition, the mean tli values show minimal gains even between 2:1 and 4:1 stv levels. within the mixed and moderate h 2 conditions, the mean tli values show asymptotic gains after stv>4:1. however, in the low h 2 condition, the mean tli values were markedly lower in the 2:1 and 4:1 stv levels, only showing asymptotic values when stv>8:1 (see figure 5). table x. descriptive statistics for tli averaged over 1000 replications vtf stv h 2 high moderate low mixed m p 4:1 2:1 0.92 15.90 0.81 4.60 0.53 1.90 0.82 3.90 4:1 0.98 93.10 0.95 48.50 0.86 22.90 0.96 50.90 8:1 0.99 100.00 0.98 91.30 0.96 48.20 0.99 94.40 16:1 0.99 100.00 0.99 99.90 0.99 77.20 0.99 100.00 32:1 0.99 100.00 0.99 100.00 0.99 95.90 0.99 100.00 7:1 2:1 0.93 10.50 0.86 0.20 0.60 0.00 0.90 1.60 4:1 0.98 99.90 0.97 71.80 0.88 14.70 0.97 94.50 8:1 0.99 100.00 0.99 100.00 0.97 63.20 0.99 100.00 16:1 0.99 100.00 0.99 100.00 0.99 95.60 0.99 100.00 32:1 0.99 100.00 0.99 100.00 0.99 100.00 0.99 100.00 10:1 2:1 0.94 7.30 0.88 0.00 0.68 0.00 0.91 0.20 4:1 0.98 100.00 0.97 87.60 0.91 10.80 0.98 99.90 8:1 0.99 100.00 0.99 100.00 0.98 86.50 0.99 100.00 16:1 0.99 100.00 0.99 100.00 0.99 100.00 0.99 100.00 32:1 0.99 100.00 0.99 100.00 0.99 100.00 0.99 100.00 table xi. three-way anova for tli by conditions conditions df f p-value h 2 3 13451.2 <0.0001 vtf 2 1437.33 <0.0001 h 2 *vtf 6 211.73 <0.0001 stv 4 36383.3 <0.0001 h 2 * stv 12 5964.08 <0.0001 vtf *stv 8 659.74 <0.0001 h 2 * vtf *stv 24 80.84 <0.0001 post hoc analysis of the 3-way interaction of h 2 *vtf*stv first focused on the simple effect interaction of h 2 *vtf after blocking on stv, specifically the test of 2-way interaction h 2 *vtf at each level of stv. the results revealed statistically significant 2-way interactions at all stv levels: stv=(2:1), f(6,11988)=160.34, p<0.0001; stv=(4:1), f(6,11988)=40.07, p<0.0001; stv=(8:1), f(6,11988)=18.51, p<0.0001; stv=(16:1), f(6,11988)=3.48, p=0.0019; and stv=(32:1), f(6,11988)=0.43, p=0.0115. further analysis of the four by three 2-way interactions focused on the simple-simple effects of stv blocking on the stv*h 2 interaction. specifically, the analysis examined differences in mean tli values among vtf levels for each stv*h 2 interaction. table xii presents these findings. fig. 5. non-normal-fit index mean values for the interaction between stv and vtf ratios at different levels of communalities. table xii. simple-simple effect of stv*vtf*h 2 sliced by stv*h 2 h 2 stv df f p-value vtf 4:1vs7:1 4:1vs10:1 7:1vs10:1 low 2 2 344 <0.001 <0.0001 <0.0001 <0.0001 4 2 69.7 <0.001 <0.0001 <0.0001 <0.0001 8 2 28.9 <0.001 <0.0001 <0.0001 0.0023 16 2 5.1 0.005 0.3846 0.0041 0.1474 32 2 3.4 0.031 0.6692 0.0266 0.1945 moderate 2 2 446 <0.001 <0.0001 <0.0001 <0.0001 4 2 85.3 <0.001 <0.0001 <0.0001 0.0563 8 2 19.7 <0.001 <0.0001 <0.0001 0.2112 16 2 3.7 0.023 0.1040 0.0251 0.8368 32 2 0.1 0.932 --- high 2 2 156 <0.001 <0.0001 <0.0001 0.2111 4 2 35.2 <0.001 <0.0001 <0.0001 0.0470 8 2 6.3 0.001 0.1169 0.0011 0.2606 16 2 0.6 0.522 --- 32 2 0.2 0.797 --- mixed 2 2 1304 <0.001 <0.0001 <0.0001 0.0008 4 2 204 <0.001 <0.0001 <0.0001 0.0322 8 2 43.2 <0.001 <0.0001 <0.0001 0.1836 16 2 9.26 <0.001 0.0025 0.0002 0.7672 32 2 1.02 0.3604 --- e. comparative-fit index (cfi) cfi values were averaged over 1000 replications for the 60 cells in the three-way design and are presented in table xiii. additionally, the percentage of cfi values meeting the standard threshold of acceptable fit, e.g. 0.95 was tabulated. the overall anova findings for cfi revealed an overall statistically significant model, f(59,59940)=6535.47, p<0.0001. as can be seen in table xiv, there were statistically engineering, technology & applied science research vol. 11, no. 1, 2021, 6766-6774 6772 www.etasr.com almaleki: the precision of the overall data-model fit for different design features in confirmatory … significant main effects and interactions, including the statistically significant triple interaction h 2 *vtf*stv. table xiii. descriptive statistics for cfi averaged over 1000 replications vtf stv h 2 high moderate low mixed m p 4:1 2:1 0.93 28.90 0.83 6.10 0.57 2.30 0.84 5.60 4:1 0.98 99.20 0.95 61.90 0.85 25.70 0.96 67.00 8:1 0.99 100.00 0.98 97.90 0.95 55.40 0.98 98.90 16:1 0.99 100.00 0.99 100.00 0.98 85.80 0.99 100.00 32:1 0.99 100.00 0.99 100.00 0.99 99.60 0.99 100.00 7:1 2:1 0.94 30.90 0.87 0.70 0.62 0.00 0.91 6.60 4:1 0.98 100.00 0.97 91.20 0.89 18.50 0.98 99.40 8:1 0.99 100.00 0.99 100.00 0.96 67.40 0.99 100.00 16:1 0.99 100.00 0.99 100.00 0.98 99.20 0.99 100.00 32:1 0.99 100.00 0.99 100.00 0.99 100.00 0.99 100.00 10:1 2:1 0.94 41.00 0.88 0.00 0.69 0.00 0.92 3.00 4:1 0.98 100.00 0.97 98.70 0.91 18.90 0.98 100.00 8:1 0.99 100.00 0.99 100.00 0.97 96.20 0.99 100.00 16:1 0.99 100.00 0.99 100.00 0.99 100.00 0.99 100.00 32:1 0.99 100.00 0.99 100.00 0.99 100.00 0.99 100.00 table xiv. three-way anova for cfi by conditions conditions df f p-value h 2 3 21591.5 <0.0001 vtf 2 2208.58 <0.0001 h 2 *vtf 6 359.17 <0.0001 stv 4 51446.3 <0.0001 h 2 * stv 12 8444.73 <0.0001 vtf *stv 8 626.81 <0.0001 h 2 * vtf *stv 24 87.90 <0.0001 visual examination of the mean cfi values reveals a differential increase in mean cfi within the levels of stv as a function of h 2 magnitude. in the h 2 = high condition, the mean cfi values evidence minimal gains even between 2:1 and 4:1 stv levels. within the mixed and moderate h 2 conditions, the mean cfi values show asymptotic gains after stv>4:1. however, in the low h 2 condition, the mean cfi values were markedly lower in the 2:1 and 4:1 stv levels, only showing asymptotic values when stv>8:1 (see figure 6). post hoc analysis of the 3-way interaction h 2 *vtf*stv first focused on the simple effect interaction h 2 *vtf after blocking on stv, specifically the test of 2-way interaction h 2 *vtf at each level of stv. the results revealed statistically significant 2-way interactions at all stv levels: stv=(2:1), f(6,11988)=168.36, p<0.0001; stv=(4:1), f(6,11988)=93.29, p<0.0001; stv=(8:1), f(6,11988)=109.95, p<0.0001; stv=(16:1), f(6,11988)=96.87, p<0.0001; and stv=(32:1), f(6,11988)=92.47, p<0.0001. further analysis of the four by three 2-way interactions focused on the simple-simple effects of stv blocking on the stv*h 2 interaction. specifically, the analysis examined the differences in mean tli values among vtf levels for each stv*h 2 interaction. table xv presents these findings. fig. 6. comparative-fit index mean values for the interaction between stv and vtf ratios at different levels of communalities. table xv. simple-simple effect of stv*vtf*h 2 sliced by stv*h 2 h 2 stv df f p-value vtf 4:1vs7:1 4:1vs10:1 7:1vs10:1 low 2 2 354 <0.001 <0.0001 <0.0001 <0.0001 4 2 163 <0.001 <0.0001 <0.0001 <0.0001 8 2 179 <0.001 <0.0001 <0.0001 <0.0001 16 2 156 <0.001 <0.0001 <0.0001 <0.0001 32 2 150 <0.001 <0.0001 <0.0001 <0.0001 moderate 2 2 355 <0.001 <0.0001 <0.0001 <0.0001 4 2 142 <0.001 <0.0001 <0.0001 0.0345 8 2 131 <0.001 <0.0001 <0.0001 0.0012 16 2 134 <0.001 <0.0001 <0.0001 0.0105 32 2 138 <0.001 <0.0001 <0.0001 0.0127 high 2 2 95.3 <0.001 <0.0001 <0.0001 <0.0001 4 2 50.4 <0.001 <0.0001 <0.0001 0.0327 8 2 59.6 <0.001 <0.0001 <0.0001 0.0015 16 2 81.8 <0.001 <0.0001 <0.0001 0.0004 32 2 87.1 <0.001 <0.0001 <0.0001 <0.0001 mixed 2 2 1151 <0.001 <0.0001 <0.0001 <0.0001 4 2 334 <0.001 <0.0001 <0.0001 0.0120 8 2 251 <0.001 <0.0001 <0.0001 0.0024 16 2 216 <0.001 <0.0001 <0.0001 0.0164 32 2 206 <0.001 <0.0001 <0.0001 0.0037 viii. discussion the study findings refuted some of the guidelines found in the literature, e.g. authors in [18] reported that sample size was not an important factor in determining model stability, and authors in [4] reported that the subject-to-variable ratio should be no lower than 5. the results of the current study revealed that sample size did have a strong effect on both stability and precision of the simulated models. for instance, when the vtf ratio was 4:1, the mean values related to data-model fit indices engineering, technology & applied science research vol. 11, no. 1, 2021, 6766-6774 6773 www.etasr.com almaleki: the precision of the overall data-model fit for different design features in confirmatory … were adequate at stv ratio >= 4:1. however, looking at the frequency of rejections based on conventional thresholds over the 1000 replications depicted a different conclusion. the percentage of stable (invariant) models ranged from 77% at 4:1 stv to 91% at 32:1 stv clearly indicating that larger stv ratios are related to higher stability levels with a model. these findings validated the authors in [42], who reported that the percentage of invariance tests varied depending on the sample size of the group. the findings of the current study do agree with those in [43], where in some models a stv of 30:1 was needed to produce a stable model and minimize the amount of misfit. the study findings also contradicted some previous research on the effect of vtf ratio on the precision and stability of factor solutions. authors in [18] concluded that the vtf ratio was important for factor stability with more indicator variables per factor yielding more stable result. in the current study, there was a trend in the findings over all rq1 analyses that suggests that data-model fit diminished as vtf increased. most probably this is a result of the increasing complexity of the measurement models, i.e. the number of paths. for example, in the 10:1 vtf condition there are 100 estimated paths, whereas in the 4:1 condition there are 40 estimated paths. the accumulation of many small deviations from the population correlation matrix impacted negatively the global fit statistics more in the high vtf conditions than in the low vtf conditions. the overall model fit indices tli and cfi all varied as functions of vtf, stv, h 2 , and their interaction. chi-square value and overall model fit indices gfi, and rmsea only varied as functions of vtf, stv, and their interactions. ix. conclusion this study provided empirical evaluation of the influence of ed and sd on wsv in terms of model precision relative to a known factor structure via monte carlo simulations. the results revealed that the means of �� and rmsea values significantly decrease as stv increases and increase as vtf ratio decreased. however, the examination suggests significant increase in mean gfi values as stv increased, and decreasing mean gfi values as vtf ratio increased. overall, when the vtf is 4:1 an stv ratio of 16:1 or above is required to show precision in factor solution and stability of the model as indicated by four fit indices. when the vtf ratio is 7:1 or 10:1, an stv ratio of 32:1 or above is required to show precision in factor solution and the stability of the model. if a researcher is interested in minimizing misfits or meeting more than four overall model fit indices criteria, stv and vtf ratios more than 32:1 and 10:1 respectively would be necessary in order to gain a precise and stable model. references [1] l. crocker and j. algina, introduction to classical and modern test theory. bristol , uk: eric, 1986. 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[43] s. v. paunonen and d. n. jackson, "what is beyond the big five? plenty!," journal of personality, vol. 68, no. 5, pp. 821–835, 2000, https://doi.org/10.1111/1467-6494.00117. microsoft word 17-2251_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3392-3397 3392 www.etasr.com hussain et al.: maximum power tracking system based on power electronic topology for wind… maximum power tracking system based on power electronic topology for wind energy conversion system applications musavir hussain department of electrical engineering, mehran university of engineering & technology, jamshoro, pakistan mazhar h. baloch department of electrical engineering, mehran university of engineering & technology, jamshoro, pakistan farhana umer department of electrical power engineering, islamia university of bahawalpur, bahawalpur, pakistan abdul h. memon department of electrical engineering, mehran university of engineering & technology, jamshoro, pakistan noman k. pathan department of electrical engineering, mehran university of engineering & technology, jamshoro, pakistan abstract—wind energy has emerged as a dominant alternative power generation source. conventional energy resources are depleting and their increasing cost cannot be ignored. wind energy has taken an important role in replacing fossil fuels and nuclear energy. however, optimal exploitation of wind energy systems has remained a thought-provoking problem due to the nonlinear behavior of the wind speed. distribution generation system and isolated micro-grid (mg) are mainly used in a wind energy system in order to utilize maximum potential of wind through the maximum power tracking algorithm based on dcdc boost power electronic converter. in this paper, authors propose a technique which is effectively workable, highly reliable, of low cost and induces less mechanical stress on the wind generator system (wgs). experimental results of the proposed system verify that the effectiveness near optimal wgs output power increased approximately up to 50%. thus, better exploitation of the available wind power is obtained under low wind speeds. keywords—boost converter; maximum power tracker system (mpts); variable speed; wind-generator system (wgs) i. introduction there is a continuous rise in power demand. additional cost is required to control and minimize resultant environmental pollution due to conventional energy production methods. this has stimulated the exploit of non-conventional energy resources. wind energy is the most prevailing and dominant source of energy among all non-conventional energy resources. being pollution free, endless and very cheap source for power generation, it is rapidly gaining popularity [1]. in pakistan and malaysia research has been conducted in renewable energy systems, consisting of feasibility studies in renewable energy utilization [2-5]. figure 1 depicts the global cumulative installed capacity of wind energy and figure 2 depicts the annual installed capacity of wind energy from 2001 to 2017. the trend clearly depicts that it will increase in the future. region wise wind power installed capacity is depicted in figure 3 with asia on the top [6-8]. optimal exploitation of wind energy systems has remained a challenging problem over the last decades. generally, power generated from wind turbine systems is not at optimal level due to the nonlinear behavior of the wind speed. the output power of wind energy system depends upon wind speed and wind speed varies throughout the day, hence it is a challenging task for the power engineer to track maximum power output from the wind turbine for all wind speed conditions. hence, it is conducive to propose a based on experiment algorithm that can track maximum power under variable speed. many researchers develop their model and simulate their proposed algorithm before real implementation. modeling and simulation also provide effective ways of analyzing different parameter associated with the wind energy conversion system. but to understand the nonlinear behavior of wind turbine, real time study is the best choice. fig. 1. commulative globally installed wind energy in mw fig. 2. annual globally installed wind energy in mw. engineering, technology & applied science research vol. 8, no. 5, 2018, 3392-3397 3393 www.etasr.com hussain et al.: maximum power tracking system based on power electronic topology for wind… fig. 3. region-wise installed capacity of wind energy in mw. mppt (maximum power point tracker), also known as power point tracker (ppt), is a technique commonly utilized for wind energy systems to optimize the output power under variable speed. however, wind turbines are controlled, in order to operate in a particular array. a wind turbine operates in four different zones [9, 10]. zone-i is a zero power area where wind speed is too low to generate electrical power. zone-ii, lies between cut-in and rated speed. in this zone, the generator runs under-rated power. in zone-iii, the output power is controlled by the turbine. this happens when wind motion is sufficient for the wind turbine to reach its rated output power. zone-iv is during stronger winds, where the wind power is so much that it could be unfavorable to the wind turbine, consequently the turbine will shut down [10]. ii. maximum power tracking techniques a. power signal feedback power signal feedback (psf) technique is based on speedsensor less power signal feedback algorithm and has many advantages compared to others used for mppt. in this mppt technique, it is necessary to know the basic training of optimal curve in order to search optimal power. many studies discussed that psf is better than otc, because the optimal power curve needs to be obtained through simulations/off line experiments on individual wind turbines and the reference power signal is produced through a recorded power curve or mechanical power formula [11-13]. the basic block diagram of psf is depicted in figure 4. psf method uses a reference power which is maximum power at that particular wind speed. this presents an issue, as the prior knowledge of the wind turbine characteristics and wind speed measurements is required [13]. b. tip speed ratio technique tip speed ratio (tsr) mppt technique is a simple technique because wind motion is directly and uninterruptedly estimated and can be calculated analytically and experimentally [13-15]. the finest tsr for a specified wind turbine is fixed independently from wind speed. however, wind speed is measured for achieving optimal rotor speed via optimum tip speed level as shown in figure 5. the estimation technique is based on support vector regression, where inputs to the wind speed approximate are power and rotational speed of the wind turbine [14-15]. fig. 4. basic block diagram of psf. fig. 5. basic block diagram of tsr. tsr control offers good performance with fast response and high efficiency. however, continuous precise wind speed measurements are not possible in reality. an accurate anemometer is expensive and adds extra cost to the system [13]. c. optimal torque control technique its block diagram is visualized in figure 6. the basic principle of this technique is to regulate the electrical generator torque at optimal power reference torque of the desired wind speed of the wind turbine system. fig. 6. basic block diagram of optimal torque control technique. turbine power can be expected as a function of tip speed ratio and turbine speed [15-18]. therefore, optimal torque equation can be written as follows in order to obtain the wind speed. we know that: 5 3 _ _ _ _3 1 1 ; , 2 t opt t p opt t opt t opt tc p r c t pπρ ω ωλ = = (1) 5 2 2 _ _3 1 ; 2 t opt p opt t opt t c t r c kπρ ω ω λ = = (2) 5 2 _3 1 , 2 opt t p opt c k r cπρ ω λ = (3) where (2) is the analytical expression of the optimal torque curve, and can be used as a mechanical torque control. authors ÷ wind turbine controller wecs model +/generator torque generator speed generator speed ×{ }optk 2 { } gen ω pmax engineering, technology & applied science research vol. 8, no. 5, 2018, 3392-3397 3394 www.etasr.com hussain et al.: maximum power tracking system based on power electronic topology for wind… in [19] reported that there is no big difference between power signal mppt & otc mppt controller regarding performances and complexities. in reality, the optimal torque control technique is efficient, rapid in operation and easy to construct. otc does not directly estimate the wind speed, that’s why its efficiency is lower compared to that of tsr [17]. d. summary the above mentioned techniques have some limitations, e.g. they require expensive devices like anemometers, which add extra cost to the system and they also require advanced knowledge of wind turbine characteristics. our major aim is to seek an optimum tracker for a variable speed wind energy conversion system application which does not require advanced knowledge of the wind turbine characteristics or expensive devices for wind speed measurement. this paper compiles and investigates optimal tracking control algorithms, particularly squirrel cage induction machine (scim) based on its configuration model. iii. wind generator model characteristics the power produced at the impact area on the turbine is expressed as [21, 27, 30, 31]: ( ) 2 3,0.5 pwp c r vωπ λ βρ= (4) where 3 1.25kg/mρ = is the wind density, r is the length of the turbine blade, vω is the wind speed, 0.3 0.59pc = − is the coefficient of power, β is the pitch angle (in degrees) assuming zero degrees for zone-ii, λ is the tip speed ratio and can be described as: v r ω ω λ = (5) whereω is the wind generator rotor speed (in rad/sec). the turbine power relations with the wind power are defined as: ( ),t t t p wp t c pω λ β= == (6) ( ) 1 1 1 0.73 151 13.635e 0.003p t t c v v r r ω ωω ω −   = − −    (7) from (4) to (7), the turbine power of the wind generator captured by the wind turbine system is described by the wind speed and wind turbine speed can be defined as [22-31]: 1 55.155 0.09exp 0.003 t t t v v p a r r ω ωρ ω ω −   = − −    (8) from (8), the wind turbine power versus wind turbine speed is shown in figure 7. it is observed that turbine power varies with respect to turbine speed at different wind speeds. from figure 7, we see that maximum power moves on a 3 rd order curve, which illustrates the maximum power produced by the wind turbine at each wind speed. iv. controller design for wind generator system a grid connected wind power system circuit diagram before booster is shown in figure 8. the back electromagnetic force of the wind-generator system consists of a 3-phase sinusoidal voltage which is inverted to dc-voltage in v（ ）through a rectifier. in this study, our main intension on maximum power tracking control is performed by regulating the duty cycle of the dc-dc boost converted to the dc side. dc-dc equivalent circuit diagram for the generator control is shown in figure 10. the dc-dc boost converter adjusts in v（ ） through current/voltage control, and the dc-link voltage dc v（ ）is controlled through an inverter on grid side converter (gsc). fig. 7. power versus turbine speed at different wind speeds. fig. 8. circuit diagram without booster. fig. 9. circuit diagram with booster. v. proposed mppt technique the proposed technique uses duty cycle as control variable to vary the generator speed with respect to turbine in the same proportion. this technique is basically based on the topology of power electronics which vary the duty cycle according to the measurement of output power taken successively and compare it with previous obtained result. the major problem of tracking the output power with the help of power electronic converter using duty cycle as a control variable, is effectively resolving the abrupt climb technique [32]. the technique is quite simple, independent and flexible, and does not need prior knowledge of wind turbine characteristics and expensive devices for speed measurement. 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 x 10 5 ω t (rad/s) p t (w ) vw = 7 vw = 9 vw = 11 vw = 13 max power locus duty cycle 0 to 44.1% p t (w ) ωt (rad/s) engineering, technology & applied science research vol. 8, no. 5, 2018, 3392-3397 3395 www.etasr.com hussain et al.: maximum power tracking system based on power electronic topology for wind… vi. experimental set up and discussion for real time study of wecs, a wind tunnel is required, which is usually built to generate artificial controlled wind speed to run a wind energy conversion system. however, it is costly and space demanding. a software simulator is simple but it has many restrictions on real time analysis. a good solution is to emulate the wind turbine characteristic using a motor generator (mg)-set, in which the motor is run and controlled to reproduce the wind turbine profile under variable wind speeds. through comprehensive study, a mg-set is employed as a model of the wind energy conversion system based on completely experimental setup. the machine used for power generation is scim. permanent magnet dc machine is used as wind turbine emulator to analyze the non-linear behavior of wind turbine. in this application, a motor is operated at variable speed to analyze the output power of squirrel cage induction generator without and with dc-dc booster. our main goal is to analyze the importance of maximum power point tracking in variable speed conditions. figure 10 shows the experimental setup assembled on basis of dc-dc boost converter as discussed above. fig. 10. experimental set up desk for maximum power tracking system. initially, wind enrgy system was operated without dc-dc booster connected to the rectified output of the squirrel cage induction generator to analyze the output parameters like voltage, current, power under variable speed conditions. a resistive load was used as dummy load to take successive power measurements to analyze the generator output. to analyze the importance of power point tracking, the rectified output of the wind generator system was fed to the dc-dc booster consisting of one mosfet and the calculated capacitor values from primary to secondary are 235µf, 900v and 470µf, 450v respectively. the output inductor rated value is 1.8mh, 2.5a, having switching frequency around 240khz (table i). the effectiveness of the system response of the proposed mpts control strategy based on dc-dc boost converter by varying duty cycle was confirmed. vii. experimental results and discussion through the experimental setup, results were obtained by varying the prime mover speed at different time durations in order to analyze the output of the wind-turbine system considering the squirrel cage induction generator. prime mover is a pmdc permanent magnet direct current motor which acts as wind turbine emulator. squirrel cage induction generator is coupled with wind turbine emulator and runs at variable speed. table i. equipment list and discription name of equipment discription with model no prime mover (dc permanent magnet machine) 180vdc, 2.7a, 0.4kw, 2500rpm. type: em-3330-1a, s/n: 201 3 phase squirrel motor (scig) 3-phase, 220v,1.4a, 50/60hz, 0.3kw, 1420/1670rpm. type:em-3330-3c s/n: 201 tachometer tachometer 20713a rectifier (for 3phase) pe-5310-5a measuring instrument company yalong: yl195 load (resistor) 1-1000ω 500w capacitor (excitation cap) 15uf ±5%, 350-400vac power supply power electronics universal supply mod: aep-1/ev booster capacitor : 470uf 450v*3 inductor: 1.8mh 5a diode: p600j function generator gw instek gfg-8219a digital oscilloscope gwinstek gds-1062a, 60mhz parameters related to wind energy conversion system like speed, current, voltage and power were observed without any tracking technique applied to the wind generator system output and with the proposed technique applied to it. squirrel cage induction generator operated at various speed conditions and its output power was analyzed either at different time durations or at regular intervals. speed response is shown in figure 11, which shows that generator output power varies with generator speed. it can be seen that at first the generator operated at 1110rpm and the power output was almost less than 10w. when speed varied from 1110rpm to 1130rpm, observed power at output was almost 20w. from 1130rpm to 1140rpm the observed power was between 40w and 50w. with further increase in speed, the output power increased and vice versa. fig. 11. power response with varying rpm. in this research study, our major intention was to extract the maximum power under varying speed of the prime mover. this application basically uses duty cycle as control variable to vary the generator speed with respect to wind turbine. in the proposed system, duty cycle varies with the help of pulse width modulation on the pulse applied to the gate of the mosfet used in dc-dc booster. speed and duty cycle vary and the generator output is observed so that power can be maximized by changing the point of energy conversion. in this application, the duty cycle of mosfet used in the dc-dc booster varied from 20% to 44.1%. the cumulative response of duty cycle at different timings can be shown in figure 12. one of the main objectives of this research was to analyze the importance of the maximum power tracking technique 1 1.5 2 2.5 3 3.5 4 4.5 5 1110 1120 1130 1140 1150 1160 1170 time (sec) s p e e d ( rp m ) 10 20 30 40 50 60rpm engineering, technology & applied science research vol. 8, no. 5, 2018, 3392-3397 3396 www.etasr.com hussain et al.: maximum power tracking system based on power electronic topology for wind… applied at the rectified output of the squirrel cage induction generator. the rectified output was analyzed by successive power measurements. figure 13 shows the response of power without booster at different time durations. the maximum output from the generator is 42.67w at 1170rpm without booster connect at the output. the squirrel cage induction generator is coupled with wind turbine emulator, runs at variable speed, and parameters related to wind energy conversion system like speed, current, voltage were observed without and with booster. it was found that current and voltage increased/boosted individually. in the power response without booster we found that maximum output power of the generator was 42.67w at almost 1170rpm. when we applied this rectified output to booster, it was also changed in the same proportion. at 1170rpm duty cycle changed by 44.1% and the output power with booster was 69.08w. power response at different time durations with booster can be seen in figure 14. maximum output power with booster was 69.08w which is greater in comparison to the one without booster. fig. 12. power response with varying duty cycle. fig. 13. power response without booster. fig. 14. power response with booster. viii. conclusions in this paper, a prototype experimental model was developed for a maximum power tracking system with a stepup dc-dc power converter. the advantages of the proposed mtps technique are: no prior knowledge is required for maximum power characteristics and wind speed. the wind turbine system operates at varying speed, so wgs takes minimum stress on a varying factor as the shaft/gear system. the proposed mtps is dependent neither on wind speed and rotor speed rating of the wind generator system nor on the capacity of the dc-dc boost converter. the experimental results of the proposed model represent the output power generated by the wind generator system. they verify that wgs maximum power at the grid side is around 20% to 50% larger by varying duty cycle than when with directly connected with the rectifier. the proposed system utilizes more effectively the existing wind energy, in particular in the minimum wind speed region. acknowledgment authors wish to acknowledge the support regarding the research of the start-up research grant hec pakistan, under grant no. 1652. appendix acronyms wgs wind generator system wecs wind energy conversion system scig squirrel cage induction generator dc direct current mppt maximum power point tracking mpts maximum power tracking system mosfet metal oxide semiconductor field effect transistor tsr tip speed ratio olt optimal load torque psf power signal feedback references [1] r. saidur, m. r. islam, n. a. rahim, k. h. solangi, “a review on global wind energy policy”, renewable and sustainable energy reviews, vol. 14, no. 7, pp. 1744-1762, 2010 [2] m. h. baloch, g. s. kaloi, j. wang. “feasible wind power potential from costal line of sindh pakistan”, research journal of applied sciences, engineering and technology, vol. 10, no.4, pp. 393-400, 2015 [3] s. f. khahro, k. tabbasum, a. m. soomro, x. liao, m. b. alvi, l. dong, m. f. manzoor, “techno-economical evaluation of wind energy potential and analysis of power generation from wind at gharo, sindh pakistan”, renewable and sustainable energy reviews, 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turbines”, electric power systems research, vol. 80, no. 3, pp. 328-338, 2010 [31] g. s. kaloi, j. wang, m. h. baloch, “dynamic modeling and control of dfig for wind energy conversion system using feedback linearization”, journal of electrical engineering and technology, vol. 11, no. 5, pp. 1137-1146, 2016 [32] e. koutroulis, k. kalaitzakis, “design of a maximum power tracking system for wind-energy-conversion applications”, ieee transactions on industrial electronics, vol. 53, no. 2, pp. 486-494, 2006 microsoft word etasr_v11_n2_pp6869-6872 engineering, technology & applied science research vol. 11, no. 2, 2021, 6869-6872 6869 www.etasr.com memon et al.: storage optimization using adaptive thresholding based motion detection storage optimization using adaptive thresholding motion detection muhammad atif memon computer science department sukkur iba-iet khairpur, pakistan muhammadatif.cs@iba-suk.edu.pk sajid khan computer science department sukkur iba university sukkur, pakistan sajidkhan@iba-suk.edu.pk zahid hussain khund computer science department sukkur iba university sukkur, pakistan zahid@iba-suk.edu.pk faheem akhtar computer science department sukkur iba university sukkur, pakistan fahim.akhtar@iba-suk.edu.pk asif rajput computer science department sukkur iba university sukkur, pakistan asifali@iba-suk.edu.pk abstract-data storage is always an issue, especially for video data from cctv cameras that require huge amounts of storage. moreover, monitoring past events is a laborious task. this paper proposes a motion detection method that requires fewer calculations and reduces the required data storage up to 70%, as it stores only the informative frames, enabling the security personnel to retrieve the required information more quickly. the proposed method utilized a histogram-based adaptive threshold for motion detection, and therefore it can work in variable luminance conditions. the proposed method can be applied to streamed frames of any cctv camera to efficiently store and retrieve informative frames. keywords-storage optimization; adaptive threshold; motion detection; video mining i. introduction image and video processing involves the transmission and storage of large data volumes in the form of frames and images. several researchers [1-3] worked on reducing bandwidth requirements, whereas others [4] worked on optimizing storage utilization. in today’s modern world, a huge amount of data is being generated [5], therefore, extracting the required information from large data volumes is a difficult task, while the storage of large data volumes is an issue [6]. multimedia mining is a subfield of data-mining that addresses the issues of extracting information such as audio, text, links, images, or digital writing from multimedia files. many researchers [7-12] worked on video mining, motion detection in cctv cameras, and crime rate reduction. the importance of cctv cameras and their placement was discussed in [7], concluding that although placing cameras in both random and expert-suggested sites reduced crime rates, the latter had more impact on crime rate reduction. many methods have been proposed for motion detection for security purposes. in [8], matlab was used for detecting motion after getting video images, converting to grayscale, using erosion to remove noise, and finally comparing two consecutive images by using absolute difference. a threshold value between 0.5 and 2 was suggested initially, but further experiments indicated that the ideal threshold value was between 1.3 to 1.5 in most cases. as the use of an image's morphology slows down the processing of every frame, this method cannot be used in real-time video processing. in [9], an external motion sensor and a wireless camera were controlled by an android device. the observer was notified by an email with photos when the motion sensor detected any activity. the suggested system incorporated both an alarm based alert system and a password-based camera power control system. this method's drawbacks were the need for an external sensor for motion detection and the numerous emails in case of continuous motion. a genetic algorithm was utilized for motion detection in [12] to reduce surveillance data storage. the use of genetic algorithms for motion detection resulted in increased complexity and slow frame processing. in [11], motion detection was achieved by calculating the difference between a reference and the current frame. if their difference exceeded a threshold, the frame was marked and transmitted to the observer. two methods were proposed in [4] for motion-based storage optimization. the first method used a sensor to detect and store the frames containing significant motion. this method had two problems: the use of an external sensor and its range. if the sensor is less sensitive, several sensors are required to cover the whole region of interest. however, if the sensor is more sensitive, it could consider motions out of the region of interest. the second method optimized storage by using neighboring frame differences and a fixed threshold. fixed threshold-based motion detection will not work well on variable luminance conditions [14-15]. this paper proposes a novel method for optimizing motion detection and video storage without using external sensors. the proposed method uses a single color channel for detecting corresponding author: faheem akhtar engineering, technology & applied science research vol. 11, no. 2, 2021, 6869-6872 6870 www.etasr.com memon et al.: storage optimization using adaptive thresholding based motion detection motion instead of the rgb. moreover, an adaptive threshold, calculated every 10,000 frames using a frame's histogram, was utilized to detect motion based on significant changes in neighboring frames the proposed method was faster than the previously proposed methods as it used one color channel and the frame's histogram. furthermore, the proposed method is dynamic in nature due to its adaptive threshold. ii. methodology figure 1 shows a summary of the proposed method, while figure 2 shows the proposed algorithm's flowchart. the adaptive threshold was recalculated every 10,000 frames, and it was applied to the red layer difference of each frame. fig. 1. summary of the proposed method. fig. 2. flowchart of the proposed algorithm. a. using red channel for processing an rgb frame can be converted to grayscale when the color of the scene is unnecessary. the simpler rgb to grayscale conversion requires two additions and one assignment per pixel, whereas advanced conversion requires several arithmetic operations [7]. as the proposed method was based on the simple differences of neighboring frames, converting each rgb frame to grayscale would not simplify the algorithm significantly. for example, the conversion of an input frame sized 100×100×3 using exhaustive loops would require 20,000 additions, 30,000 multiplications, and 10,000 assignments per frame. moreover, the difference calculation requires 10,000 subtractions and 10,000 assignments per frame. so, conversion and difference calculation require in total 30,000 additions/subtractions and 20,000 assignments. on the other hand, using an rgb frame without converting it to grayscale requires 30,000 subtractions and 30,000 assignments. hence, converting to grayscale would save 10,000 assignments in total for exhaustive differences' calculation. the proposed method used only the red channel instead of the three rgb or grayscale conversion, as color information was unnecessary. using the red channel required only 10,000 subtractions and respective assignments for a 100×100×3 sized frame, even if using exhaustive loop-based subtraction instead of vectorization. moreover, the green channel may be used instead of the red. on the other hand, using the blue channel may not provide good results, as human skin and natural luminance contain fewer blue channel contributions. b. adaptive threshold calculation this study aimed to propose a real-time luminanceinvariant optimization for motion detection. the luminance of a scene captured by a cctv camera changes throughout the day due to different atmospheric conditions and daylight changes. if a cctv camera captures video at 30 frames per second, it takes slightly less than six minutes to capture a ten thousand frame video, while this duration is reduced to three minutes when using 60 frames per second. the first frame after every ten thousand is used for calculating the next threshold. the histogram of this frame is used to calculate the next threshold by using: ���� � �� � �� � (1) where and � are the frame's amount of rows and columns, respectively. �� is the value of � that can be calculated as the index value that minimizes the difference, given by: �� � ��� �∑ ���� � ���� ����� ,��,� ,…..,���" #$� (2) this corresponds to the frequency of the intensity level in the image's histogram, and it is a count of the 80% of the image's pixels obtained by using: �� � � 0.8 (3) ' in (2) refers to the index of the peak of the histogram. () is a parameter that controls the sensitivity of motion detection. a smaller value of () will result in more motion detection and vice versa. the possible range of () is: 0 * () + 0.17. based on the experience of extensive simulations, the recommended value of () was 0.11. it should be noted that all calculations were made for a non-normalized 8-bit image having intensities between 0-255. engineering, technology & applied science research vol. 11, no. 2, 2021, 6869-6872 6871 www.etasr.com memon et al.: storage optimization using adaptive thresholding based motion detection c. application of threshold a frame is marked to have motion if: ∑./0112314 5 ���� (4) where /011231 is given by: /011231 � 67.04� 67.0 �14∨ (5) where 67.04 and 67.0 � 14 are the red channel layers for the current and the previous frame respectively. each frame having motion is stored in the database, where the others are neglected. figure 3 shows a test case during the daytime displaying an original frame, a grayscaled frame, and the red channel's histogram. figure 4 shows a test case during the nighttime, displaying an original frame, a grayscaled frame, and the red channel's histogram. (a) (b) (c) fig. 3. daytime case test: (a) original colored image, (b) grayscaled image, and (c) pixel intensity count of the red channel. (a) (b) (c) fig. 4. nightime case test: (a) original colored image, (b) grayscaled image, and (c) pixel intensity count of the red channel. iii. results and discussion the proposed method was applied on datasets obtained from sukkur iba iet (institute of emerging technologies), khairpur cctv cameras, youtube, and the venom movie. results were obtained for both the threshold calculation and storage optimization processes. figure 3 shows a test case during daytime, used for calculating the threshold. as it can be noted, the histogram was well distributed. any object moving during the daytime would result in a significant change of intensities and it could be detected using a higher threshold. on the other hand, figure 4 shows a test case during nighttime. as it can be noted, the histogram is not well-distributed. any object moving during the nighttime would produce less change of intensities and hence it would require a smaller threshold for motion detection. moreover, the size of the frame plays a significant role, as a high-resolution frame would require a engineering, technology & applied science research vol. 11, no. 2, 2021, 6869-6872 6872 www.etasr.com memon et al.: storage optimization using adaptive thresholding based motion detection higher threshold when compared to a lower-resolution frame of the same scene. as both 3(a) and 4(a) figures had 1920×1080 resolution, the total frame's pixels were 2,073,600. the thresholds calculated for the day and nighttime frames were 182,476 and 68,428, respectively. the values of were 62 and 30 for day time and night time frames respectively. when these frames were downscaled to 960×540, the values of thresholds were 45,619 and 17,107 for day and nighttime, respectively. table i shows the results of applying the proposed method to the venom movie and a cctv camera footage. venom movie's total duration was 92 minutes, and after applying the proposed method it was reduced to 52 minutes. the total frames of the venom movie were 11,040, while 6,112 frames were preserved. the frame reduction of this movie was 44.63%. table i. performance comparison of the proposed scheme with the original video size video sample of venom movie video sample of cctv recording actual size 807 mb 14.4 gb size after applying the proposed method 220 mb 251 mb regarding the application of the proposed method to a cctv camera stored footage, significant optimization was observed. a video having 268.741 minutes duration was reduced to 32.25 minutes since the cctv footage had rare motion. the total frames of the input video were 32,249, while after ignoring the redundant frames only 3,714 were preserved. in terms of percentage, the total frame storage was reduced up to 88.4%. the proposed method worked faster than conventional methods by saving many computations due to the use of a single color channel for motion detection. moreover, the proposed method expedited the calculation process by utilizing frame histograms. furthermore, the proposed method is dynamic in nature, due to its adaptive threshold and it achieved a significant reduction in storage needs. iv. conclusion this paper presented a video optimization method that reduced storage needs by ignoring frames without significant information. a significant informative frame is decided based on the proposed motion detection method. the conventional motion detection methods use fixed thresholds that make them sensitive in variable illumination. for efficient processing, the new threshold was calculated using a histogram every 10,000 frames, considering the illumination of the current scene. the absolute difference was calculated between consecutive frames, and its sum was compared with the threshold to decide whether the frame should be stored in memory or not. furthermore, the red channel of each frame was used, instead of grayscale or rgb in conventional methods. the proposed method provided efficient video optimization, and it can be applied to any streaming cctv camera irrespective of the radiance of any scene's light source or the illumination of the cctv camera. references [1] s. khan and d. lee, "efficient deinterlacing method using simple edge slope tracing," optical engineering, vol. 54, no. 10, oct. 2015, art. no. 103108, https://doi.org/10.1117/1.oe.54.10.103108. [2] s. khan, d. lee, m. a. khan, a. r. gilal, and g. mujtaba, "efficient edge-based image interpolation method using neighboring slope information," ieee access, vol. 7, pp. 133539–133548, 2019, https://doi.org/10.1109/access.2019.2942004. [3] s. khan et al., "image interpolation via gradient correlation-based edge direction estimation," scientific programming, vol. 2020, apr. 2020, art. no. 5763837, https://doi.org/10.1155/2020/5763837. [4] s. arora, k. bhatia, and v. amit, "storage optimization of video surveillance from cctv camera," in 2016 2nd international conference on next generation computing technologies (ngct), oct. 2016, pp. 710–713, https://doi.org/10.1109/ngct.2016.7877503. [5] m. hazas, j. morley, o. bates, and a. friday, "are there limits to growth in data traffic? on time use, data generation and speed," in proceedings of the second workshop on computing within limits, irvine, ca, usa, jun. 2016, pp. 1–5, https://doi.org/10.1145/2926676.2926690. [6] m. h. padgavankar, "big data storage and challenges," international journal of computer science and information technologies, vol. 5, no. 2, pp. 2218–2223, apr. 2014. [7] j. m. caplan, l. w. kennedy, and g. petrossian, "police-monitored cctv cameras in newark, nj: a quasi-experimental test of crime deterrence," journal of experimental criminology, vol. 7, no. 3, pp. 255–274, sep. 2011, https://doi.org/10.1007/s11292-011-9125-9. [8] f. n. tawfeeq, "real time motion detection in surveillance camera using matlab," international journal of advanced research incomputer science and software engineering, vol. 3, no. 9, pp. 622– 626, sep. 2013. [9] m. rushambwa, t. chamunorwa, and k. nyachionjeka, "real time wireless surveillance system with motion detection and device control over internet," international journal of scientific and research publications, vol. 6, no. 3, mar. 2016, art. no. 470. [10] s. huang, "an advanced motion detection algorithm with video quality analysis for video surveillance systems," ieee transactions on circuits and systems for video technology, vol. 21, no. 1, pp. 1–14, jan. 2011, https://doi.org/10.1109/tcsvt.2010.2087812. [11] a. upasana, b. manisha, g. mohini, and k. pradnya, "real time security system using human motion detection," international journal of computer science and mobile computing, vol. 4, no. 11, pp. 245– 250, 2015. [12] j. c. m. butil, m. l. f. magsisi, j. h. pua, p. k. se, and r. sagum, "the application of genetic algorithm in motion detection for data storage optimization," international journal of computer and communication engineering, vol. 3, no. 3, pp. 199–202, may 2014. [13] c. saravanan, "color image to grayscale image conversion," in 2010 second international conference on computer engineering and applications, mar. 2010, vol. 2, pp. 196–199, https://doi.org/10.1109/iccea.2010.192. [14] m. v. sarode and p. r. deshmukh, "image sequence denoising with motion estimation in color image sequences," engineering, technology & applied science research, vol. 1, no. 6, pp. 139–143, dec. 2011, https://doi.org/10.48084/etasr.54. [15] a. b. altamimi and h. ullah, "panic detection in crowded scenes," engineering, technology & applied science research, vol. 10, no. 2, pp. 5412–5418, apr. 2020, https://doi.org/10.48084/etasr.3347. microsoft word etasr_v11_n2_pp7060-7067 engineering, technology & applied science research vol. 11, no. 2, 2021, 7060-7067 7060 www.etasr.com behih & attoui: backstepping terminal sliding mode mppt controller for photovoltaic systems backstepping terminal sliding mode mppt controller for photovoltaic systems khalissa behih department of electrical engineering lsi laboratory ferhat abbas sétif 1 university sétif, algeria khalissabehih@univ-setif.dz hadjira attoui department of electrical engineering quere laboratory ferhat abbas sétif 1 university sétif, algeria attoui_hadjira@univ-setif.dz abstract-in this paper, a new maximum power point tracking (mppt) control for a photovoltaic (pv) system is developed based on both backstepping and terminal sliding mode approaches. this system is composed of a solar array, a dc/dc boost converter, an mppt controller, and an output load. the backstepping terminal sliding mode controller (btsmc) is used via a dc-dc boost converter to achieve maximum power output. the stability of the closed-loop system is guaranteed using the lyapunov method. this novel approach provides good transient response, low tracking error, and very fast reaction against solar radiation and pv cell temperature variations. furthermore, chattering, which constitutes the main disadvantage of the classic sliding mode technique is eliminated. to show the effectiveness and robustness of the proposed control, different simulations under different atmospheric conditions are conducted in matlab/simulink. keywords-backstepping; terminal sliding mode control; lyapunov stability; maximum power point tracking; photovoltaic system i. introduction renewable energy sources are nowadays an important part of power generation. photovoltaic (pv) generation is one of the most promising renewable sources since it exhibits many merits such as availability, cleanness, little maintenance, and no noise pollution. however, all pv systems have two problems: very low electric-power generation efficiency, especially under low-irradiation states and the interdependence of the amount of the electric power generated by solar arrays and the weather conditions. load mismatch can occur under these weather varying conditions and maximum power may not be extracted and delivered to the load. this issue constitutes the so-called maximum power point tracking (mppt) problem [1-4]. many methods have been developed to determine the maximum power point (mpp) under varying conditions [5-7]. some of them are based on the well-known principle of perturb and observe (p&o) [8], others are based on sliding mode control [9-12], on artificial neural networks, or on fuzzy logic algorithms [1, 2, 7]. in [12-14], maximum power voltage (mpv) based approaches are developed using a two-loop mppt control scheme. the first loop is to determine the mpv reference of the pv array and the second loop is to regulate the pv array voltage to the reference voltage. the procedure repeats the mpv reference searching and the pv voltage tracking until maximum power is reached. to track mpp more efficiently a hybrid method consisting of two loops is proposed in [15]. in the first loop, the mpp is estimated using an incremental conductance method, and in the second loop a terminal sliding mode controller is developed to drive the system to the searched reference mpp. authors in [16] proposed the use of backstepping sliding mode control for the second loop. the backstepping sliding mode control law is based on the asymptotic stability analysis whilst the system trajectories evolve to a specified attractor reaching the equilibrium in an infinite time. many authors have proposed an alternative way to get a finite time convergence based on terminal attractor techniques [15-18], providing high-precision performance besides disturbance attenuation. moreover, chattering in bsmc remains the problem that has to be overcome. in order to avoid chattering, the major disadvantage in the sliding mode methodology, various methods have been proposed. one of them consists in replacing the sign function by a continuous approximation in the vicinity of the sliding surface. saturation function or sigmoid function was used in fuzzy logic to build the transition band [9, 21, 22]. the authors of [22] proposed to vary the sliding gain using a fuzzy system which adjusts the distance between the system and the sliding surface. thus, its value decreases as the system state approaches the sliding surface. however, the ultimate accuracy and robustness of the sliding mode are partially lost. in this paper, a backstepping terminal sliding mode controller (btsmc) is developed for mppt. by using a dc/dc boost converter in the power control circuit, the btsmc is proposed to drive the system to the mpv reference in the second loop. using this approach, finite time convergence of the error is guaranteed and the chattering effect is eliminated without losing robustness. ii. pv system modeling a dc-dc boost converter constituting the heart of the mppt is inserted between the pv module and its load to achieve optimum power transfer, as can be seen in figure1. corresponding author: khalissa behih engineering, technology & applied science research vol. 11, no. 2, 2021, 7060-7067 7061 www.etasr.com behih & attoui: backstepping terminal sliding mode mppt controller for photovoltaic systems fig. 1. structure of the pv system. the converter is used to regulate the pv module output voltage vpv in order to extract as much power as possible from the pv module. referring to [15], the dynamics of the boost converter are given by: ( ) ( ) ( ) ( ) ( ) ( ) 2 2 2 1 2 2 1 11 1 1 1 1 1 1 1 pv pv l cl pv l c dc c c c l c c c dv i i dt c r ddi v i rdt l l r d v dr v l r r l dv d i v rdt c r r c r    = −   − = −   +      − −   + − −   +   − = − +   +     (1) where the three states variables pvv , li and 2cv are respectively the output voltage of the pv module, the inductor current and the voltage of the capacitor 2c (i.e. the voltage across the load). dv is the forward voltage of the power diode, d is the duty ratio of the pwm control input signal, and r is the resistive load. by taking ( ) ( ) ( ) ( ) 2 t pv l cx t v t i t v t =   , the set of equations in (1) can be written in the following form [15]: ( ) ( ) ( ) ( ) ( )2 1 1 1 2 2 1pv pv l l c dv i i dt c di f x g x d dt dv f x g x d dt  = −   = +   = +  (2) where: ( ) 21 1 1 1 1 c c d pv l c c c r r v f x v i v rl l r r l l r   = − + − −  +   +    ( ) ( ) 22 2 2 1 1 1 l c c c f x i v r c r r c r = − +  +    ( ) 21 1 1 1 c c d l c c c r r v g x i v r l r r l l r   = − − +  +   +    ( )2 2 1 1 1 l c g x i rl c r = −   +    iii. design of the backstepping terminal sliding mode mppt controller the overall control structure is illustrated in figure 2. here, ipv and vpv are measured from the pv array and transmitted to the mpp searching algorithm, which generates the reference maximum power voltage vref. then, the reference voltage is given to the mpv based btsm controller for maximum power tracking. a. mpp searching algorithm to seek the mpp voltage vref, we use an incremental conductance method [1, 15]. the power slope pv pvdp dv can be expressed as: pv pv pv pv pv pv dp di i v dv dv = + (3) when the power slope 0, pv pv dp dv = i.e pv pv pv pv di i dv v = − , the pv system operates at maximum power generation. therefore, the update law for vref is given by the following rules [1, 15]: ( ) ( ) 1 , 1 ,  = − + ∆ > −    = − − ∆ < −  pv pv ref ref pv pv pv pv ref ref pv pv di i v v k v for dv v di i v v k v for dv v (4) b. backstepping terminal sliding model controller the backstepping terminal sliding mode controller is designed to extract maximum power from a pv panel. the objective of the controller is to let the panel pv voltage vpv track the reference maximum power voltage vref by acting on the duty cycle d(t) of the boost converter switch. the recursive nature of the proposed control design is similar to the standard backstepping methodology. however, the proposed control design uses backstepping to design controllers with a terminal sliding surface at the last step [22-23]. the design proceeds as follows: for the first step we consider a zero-order sliding surface: 1 1 refe x v= − (5) considering an auxiliary tracking error variable: engineering, technology & applied science research vol. 11, no. 2, 2021, 7060-7067 7062 www.etasr.com behih & attoui: backstepping terminal sliding mode mppt controller for photovoltaic systems 2 1 1e e α= +& (6) let the first lyapunov function candidate is: 2 1 1 1 2 v e= (7) the time derivation of (7) is given by: ( ) 1 1 1 1 2 1 2 1 1 1 2 v e e e e e e e α λ = = − = − + & & (8) the stabilization of 1e can be obtained by introducing a new virtual control 1α , such that: 1 1 1 1, 0eα λ λ= > (9) where � � is a positive feedback gain, such that 1α can be chosen in order to eliminate the nonlinearity and getting ( )1 0<&v x . equation (8) shows that, if the designed control law makes 2e converge, then ( )1 0v x <& which guarantees global stability. in order to make 2e converge in finite time and improve the convergence rate and the steady-state tracking accuracy of the system, the higher-order non-singular terminal sliding mode surface is designed for 2e as follows: 2 2 , 1 2, 0 p q s e e p qγ γ= + < < >& (10) where γ>0 is a positive constant that contributes to force the error 2e to converge to zero while p and q are positive impair constants such that 1 2< <p q . this last inequality must be enforced to avoid the inherent singularity in such types of control. the surface selected in (10) is called nonsingular terminal sliding mode (ntsm). it is used to realize a secondorder smc, enabling to have 0s s s= = =& && , often called higherorder sliding mode. if the system converges on rt , s converges to zero, which means ( ) 0s t = , rt t≥ then from (10), it can be shown that 2e and 2e& will converge to zero in finite time, given by: ( ) ( )2γ − = + − p q p q p s r r p t t e t p q (11) the system will remain on the second-order sliding mode ( )2 2 0 ,= =&e e according to (11), and by selecting the parameters p, q, and γ one can adjust the convergence speed of 2e . fig. 2. simulink pv system model. c. stability and robustness analysis the stability and robustness issues of the controller are addressed here by using lyapunov stability theory as follows: the augmented lyapunov function is given by: 2 2 1 2 v s= (12) the time derivative of ( )2v s is then: 2v s s=& & (13) engineering, technology & applied science research vol. 11, no. 2, 2021, 7060-7067 7063 www.etasr.com behih & attoui: backstepping terminal sliding mode mppt controller for photovoltaic systems 1 2 2 2 2 1 2 2 2 2 1 p q p p q q p v s e e e q p q s e e e q p γ γ γ   −        − −           = +         = +      & & & && & && & (14) with: 2 1 1 1 α α = + = − + && && && && & pv ref e e v v (15) 1 2 2 2 2 1 2 2 2 2 1 γ γ γ   −        − −           = +         = +      & & & && & && & p q p p q q p v s e e e q p q s e e e q p (16) to satisfy the lyapunov stability condition, the input signal control is designed as in (17): ( ) ( ) ( ) ( ) ( )1 2 1 1 1 , 0d t d t d t g x g x = + ≠   (17) where ( ) ( )1 1 1 1 1α= − + − +& && &pv refd t f x i c v c (18) and ( ) ( ) 2 2 1 2 0 1 η γ   −         = +         ∫ & pt qq d t c e sign s dt p (19) equation (14) can therefore be developed to give: 1 2 2 .γ η   −   =−& & p qp v e s q (20) if 0s ≠ , as p and q are odd and 1 2< <p q , then 1 2 0 p q e − ≥& , which means 2 0v ≤ & . if 0s ≠ , we will consider the two following conditions: • if 0nz ≠ , then 1 2 2 . 0 p qp v e s q γ η   −   =− <& & and • if 0nz =& , 0nz ≠ then 2 0v = & cannot be kept continuously. thus, according to lyapunov stability theory, the system can reach the manifold in finite time, for 2e converges to zero in finite time. iv. simulation results the simulink pv system model shown in figure 2 was selected to assess the performance and the effectiveness of the proposed btsmc controller. fixed-step type and ode4 (runge kutta) solver were the simulink solver selection parameters. the specification parameters for pv power generation are given in table i. the parameters of the boost converter used are: l=12mh, rl=0.15ω, rc=39.6ω, c2=1000µf, r=25ω, and vd=0.82v. the controller parameters used are: γ=50, η=0.01, p=7, q=5. in this section, we present the simulation results when applying the backstepping terminal sliding mode control law. table i. electrical specifications of the kc200gh-2p pv module parameter value maximum power mppp 200w short circuit current scri 8.21a open circuit voltage ocv 32.9v voltage at maximum power point mppv 26.3v current at maximum power point mppi 7.61a p-n junction characteristic factor a 1.8 a. simulation results with standard operating conditions the simulation results with standard operating conditions (s=1000w/m 2 , t=25 o c) are shown in figures 3–6. from the obtained results, it is clearly noted that vpv reaches quickly the desired set point vref. fig. 3. evolution of vpv and vref. fig. 4. evolution of ipv. engineering, technology & applied science research vol. 11, no. 2, 2021, 7060-7067 7064 www.etasr.com behih & attoui: backstepping terminal sliding mode mppt controller for photovoltaic systems fig. 5. evolution of ppv. fig. 6. evolution of duty cycle d(t). the ppv achieves maximum power in a settling time of 0.008s. moreover, it can be deduced that the proposed approach presents good transient response, low tracking error, and a very fast system reaction against set point change. figures 5-6 present a comparative study between the proposed controller and the bsmc. when comparing these results, it is obvious that the proposed method provides faster responses while eliminating the phenomenon of chattering. fig. 7. solar irradiation variation. b. simulation results under solar irradiation rariation it is known that meteorological parameters, especially the temperature, do not remain constant all day long, but change significantly. it is then worth investigating the influence of the daily average temperature variation on the performance of the optimized system. in order to evaluate the effect of changing irradiation conditions, an irradiation ramp change was used as shown in figure 7. the temperature is considered constant with a value of 25°c during the simulation tests. the performances including vpv, ipv, ppv , and duty cycle are given in figures 8-11. fig. 8. evolution of vpv and vref. fig. 9. evolution of ipv. fig. 10. evolution of ppv. fig. 11. evolution of duty cycle d(t). engineering, technology & applied science research vol. 11, no. 2, 2021, 7060-7067 7065 www.etasr.com behih & attoui: backstepping terminal sliding mode mppt controller for photovoltaic systems as shown in figures 8-11, when the irradiance level changes, the mppt controller can quickly track the mpp. it can be seen from the results that the proposed mppt controller follows the direction of the mpp perfectly. c. simulation results under temperature variations simulations were carried out to evaluate the effect of changing temperature (figure 12). the solar irradiation is considered constant with a value of 1000w/m 2 . the performances including vpv, ipv, ppv, and duty cycle are given in figures 13-16. fig. 12. temperature variation. fig. 13. evolution of vpv and vref. fig. 14. evolution of ipv. it can be seen in figures 13-16 that when the temperature changes, the mppt controller can quickly track the mpp. the proposed mppt controller provides a good performance in all simulation tests. figure 17 shows that the trace of the operating point stays close to the mpps during the simulation. fig. 15. evolution of ppv. fig. 16. evolution of duty cycle d(t). fig. 17. pv pvv p− characteristics under solar irradiation variation. d. simulation results under load variation considering load change from 25ω to 80ω under the same irradiance and temperature, the corresponding results are shown in figures 18-20. it can be easily concluded that the proposed controller achieves strong robustness and has satisfactory response under these types of disturbance. in all the simulation results, the proposed btsmc provides a good performance. the proposed mppt controller follows the direction of the mpp perfectly and in finite time. furthermore, the elimination of the chattering problem permits the smoothness of the control law. v. conclusion in this study, a backstepping sliding mode control scheme for mppt of a pv system has been developed, which integrates the backstepping methodology and the terminal sliding mode engineering, technology & applied science research vol. 11, no. 2, 2021, 7060-7067 7066 www.etasr.com behih & attoui: backstepping terminal sliding mode mppt controller for photovoltaic systems control strategy. the combined strategies proved to have the advantages of both the terminal sliding mode and the backstepping approach. the parameters of the proposed controller are adjusted using adaptation laws, based on the lyapunov synthesis in order to ensure, in the presence of external disturbances, the stability of the closed-loop system and the tracking performance is achieved in finite time. the objective of the study was accomplished. low tracking error, very fast system reaction against solar radiation change, and good transition response without overshoot was obtained. moreover, it has been shown that the chattering phenomenon appearing in the classical backstepping sliding mode control was 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[23] b. k. oubbati, m. boutoubat, a. rabhi, and m. belkheiri, "experiential integral backstepping sliding mode controller to achieve the maximum power point of a pv system," control engineering practice, vol. 102, sep. 2020, art. no. 104570, https://doi.org/10.1016/j.conengprac. 2020.104570. microsoft word etasr_v11_n1_pp6775-6780 engineering, technology & applied science research vol. 11, no. 1, 2021, 6775-6780 6775 www.etasr.com nguyen et al.: cutting parameter optimization in finishing milling of ti-6al-4v titanium alloy under … cutting parameter optimization in finishing milling of ti-6al-4v titanium alloy under mql condition using topsis and anova analysis van canh nguyen department of manufacturing technology faculty of mechanical engineering hanoi university of industry hanoi, vietnam nguyenvancanh@haui.edu.vn thuy duong nguyen department of machine tool and tribology school of mechanical engineering hanoi university of science and technology hanoi, vietnam duong.nguyenthuy@hust.edu.vn dung hoang tien department of manufacturing technology faculty of mechanical engineering hanoi university of industry hanoi, vietnam tiendung@haui.edu abstract-titanium and its alloys give immense specific strength, imparting properties such as corrosion and fracture resistance, making them the right candidate for medical and aerospace applications. there is a wide range of engineering applications that use titanium alloys in a variety of forms. the cost of these alloys is slightly higher in comparison to other variants due to the problematic extraction of the molten process. to reduce costs, titanium alloy products could be made by casting, isothermal forging, radial swaging, or powder metallurgy, although these techniques require some kind of finishing machining process. titanium and its alloys are difficult to machine due to skinny chips leading to a small cutting tool-workpiece contact area. the thermal conductivity of titanium alloys is too low and the stress produced is too large due to the small contact area, which results in very high cutting temperatures. this paper deals with the experimental study of the influence of the minimum quantity lubricant (mql) environment in the milling of ti-6al-4v alloy considering the optimization of surface roughness and production rate. taguchi-based topsis and anova were used to analyze the results. the experimental results show that mql with vegetable oil is successfully applied in the milling of ti-6al-4v. the research confirms the suitability of topsis in solving the multiple criteria decision making (mcdm) issue, by choosing the best alternative at vc=120m/min, fz=0.065mm/tooth, and ap=0.2mm, where the surface roughness and material removal rate are 0.41µm and 44.1492cm 3 /min respectively. besides, anova can be used to predict the best parameters set in the milling process based on the regression model. the parameters predicted by anova analysis do not coincide with any implemented parameters. keywords-surface milling; surface roughness; taguchi-based topsis; titalium alloy; ti-6al-4v; mcdm; mql i. introduction according to the thermophysical properties at elevated temperatures, titanium alloy ti-6al-4v is considered as the best material to manufacture parts in medical or euro space industry [1, 2]. however, machining ti-6al-4v is complicated because the temperature is usually very high in the contact area between the workpiece and the cutting tool [3–9]. to reduce cutting heat, metalworking fluids (mwfs) have been selected as the most common solution [10]. due to the harmful effects of wmf to the operator’s health and environment, reducing mwf consumption is always considered. in this aspect, dry machining and minimum quantity lubricant (mql) are two of the most effective alternatives. for the past 20 years, many publications have confirmed the effectiveness of using mql metalworking in general and ti-6al-4v machining in particular. authors in [11] researched the role of mql condition in tool wear and surface quality in turning process with an uncoated cutting tool. the research showed the encouraging results where the mql environment leads to the significant reducing of tool wear and surface roughness mainly through the declining of the temperature in cutting area and the change of the interaction between chip-tool and tool-workpiece during machining. authors in [12] studied the grinding of ti6al-4v titanium alloy and the effects of different lubrication conditions on the surface quality. the research showed that vegetable oil can be applied in the milling of titanium alloys under mql conditions. hence, the mql technique was applied in this study work to replace conventional lubricants in the milling process. corresponding author: thuy duong nguyen engineering, technology & applied science research vol. 11, no. 1, 2021, 6775-6780 6776 www.etasr.com nguyen et al.: cutting parameter optimization in finishing milling of ti-6al-4v titanium alloy under … authors in [13] carried out a study research to apply a multiple criteria decision making (mcdm) approach for enhancing university accreditation process. the results showed that mcdm is suitable to solve multi response optimization problems. taguchi-based techniques, namely topsis, moora, vikor, copras, etc. have been often used to solve mcdm problems with high accuracy. authors in [13, 14] used the topsis method to solve the mcdm problem. these researches show that topsis could be applied to find the best alternative easily and quickly. the problem here is that the topsis or other taguchi-based technique can help finding the best solutions from the conducted experiments only. this means that this method cannot help predicting or finding the exact optimum parameters set. to come over this disadvantage, new methods can be applied, for example genetic algorihm or combinations of some of the conventional methods. authors in [7] used statistical and soft computing techniques to determine the optimum surface roughness in the milling of ti-6al-4v. their results show that the rsm model could be applied in predicting the optimum surface roughness value in the milling of titanium alloys. however, the predictive result given by artificial neural networks (anns) is more accurate than by the response surface method (rsm). authors in [15] applied an experimental model to optimize and predict the effect of the cutting tool on surface roughness and geometrical characteristics in the drilling of h13 steel. the evolutionary multiple attribute optimization algorithm was employed to find the optimum parameters set. nsga-іі (nondominated sorting genetic algorithm) method was developed, and the regression functions were considered to find the optimum of surface roughness. the successful optimization results are consistent with the experimental findings, and ultimately the optimal set of cutting parameters can be chosen by machining operators according to the application. the study also showed that increased cutting speed and liquid coolant intensity decline surface quality. by contrast, the rising of cutting depth, tool diameter, and feed rate led to better surface quality. many other studies showed that mql and vegetable oil are suitable for machining titanium alloy surfaces. the machining of titanium alloys is a major research topic. the challenge is mainly the cost, due to the very high price of the material and the cutting tools leading usually to a reduced number of experiments. in this case, using the taguchi design method of an experiment is addressed as one of the best solutions [16]. the technique for order preference by similarity to ideal solution (topsis) effectively identifies the best alternative quickly. authors in [17] succeeded in applying an mcdm model to find the optimum shot-peening parameters set. authors in [18] were successful in multi-objective optimization on surface quality optimization and mrr in the face milling of aisi 304 steel. the results show that a significant influence of all milling parameters on the mrr and both the feed-rate and the depth of cut have a significant effect on the cutting force. in the current work, information entropy is performed to derive the objective weights of the evaluation criteria. an entropy-based topsis is employed to rank the alternatives in order of preference and then choose the best solution that conforms to the decision maker’s idea [19, 21] ii. research methodology a. optimization issues surface roughness and production rate are two standard and essential criteria that must be considered in machining. improving surface quality leads to reduced material removal rate (mrr). so, finding the best solution to balance surface roughness and production rate is a critical issue. in this study, two primary responses, including the arithmetical mean roughness (ra) and specific material removal rate (mrr), are optimized simultaneously using the entropy-based topsis model. the average roughness value is calculated as: �� = ���������� ��� ���� � (1) where rai is the arithmetic roughness at the i-th position. the production rate is the amount of material removed per time unit and is determined by: mrr = �.��.�� ���� (2) where mrr is the production rate in cm 3 /min, ap is the depth of cut in mm, w is the width of cut in mm, and vf is feed speed in m/min. for the milling process, the cutting parameters, including cutting speed (vc), depth of cut (ap), and feed rate (vf) can be considered as inputs. the values of cutting parameters are chosen by the suggestions of the cutting tool’s manufacturer and the recommendations of any mold manufacturers. the variance factor data are shown in table i. in this study, the mql is fixed at 150ml/h flow rate and 2mpa air pressure. the experiment is performed in 5-axis cnc machine dmg dmu50 (germany), and the surface roughness results were measured with the mitutoyo surftest js-310 (japan). table i. the value set of cutting parameters no. parameter symbol unit level -1 0 1 1 cutting speed vc m/min 120 210 300 2 feed fz mm/tooth 0.02 0.06 0.10 3 depth of cut ap mm 0.1 0.5 0.9 the optimizing issue is described below. the study's approach uses the mcmd method for selecting the best solution for minimizing surface arithmetic roughness (ra) and maximizing the production rate (mrr). table ii. experimental data run vc fz ap ra mrr 1 60 0.03 0.2 0.281 5.42 2 60 0.065 0.4 0.336667 1.08 3 60 0.1 0.6 0.737333 16.25 4 90 0.03 0.4 0.328 21.67 5 90 0.065 0.6 0.321333 10.83 6 90 0.1 0.2 0.506667 2.17 7 120 0.03 0.6 0.358667 32.5 8 120 0.065 0.2 0.411667 43.33 9 120 0.1 0.4 0.635667 16.25 engineering, technology & applied science research vol. 11, no. 1, 2021, 6775-6780 6777 www.etasr.com nguyen et al.: cutting parameter optimization in finishing milling of ti-6al-4v titanium alloy under … b. multi-response optimization framework the topsis method was presented in [22, 23], and its steps are: step 1: given a set of alternatives, � = ���|� = 1,2, . .��, and a set of criteria, � ! "|# � 1,2, . .$% , where & � !'�"|� � 1,2, . .�,# � 1,2,…$% denotes the set of performance ratings and ) � !)"|# � 1,2,. .$% is the set of weights. the information table i=(a, c, x, w) can be represented as shown in table iii. table iii. the information table of topsis alternative c1 c2 … cm a1 x11 x12 … x1m a2 x21 x22 … … … … … an xn1 xn2 … xnm w w1 w2 … wm step 2: calculating the normalized rating by [20, 21, 2428]: *�" � +,-.∑ 0+,-� 12,3� , � � 1,2 …$;# � 1,2…� (3) step 3: calculating the weighted normalized rating by: 5�"0'1 � )"*�"0'1, � � 1,2…�;# � 1,2…$ (4) step 4: calculating a positive ideal point (pis) and a negative ideal point (nis) by: pis � �� � �5��0'1,59�0'1,…,5:�0'1� � !<max� 5�" 0'1|# ∈ a�b,<min� 5�"0'1| # ∈ a9b| � � 1,2…�% (5) nis � �f � �5�f0'1,59f0'1,…,5:f0'1� � !<min� 5�" 0'1| # ∈ a�b,<max� 5�"0'1| # ∈ a9b | � � 1,2…�% (6) where j1 and j2 are the benefit and non-benefit criteria respectively. step 5: calculating the separation from the pis and the nis among alternatives using the euclidean distance, which is given as: g�∗ � .∑ i5�"0'1 j 5"�0'1k9:"l� , � � 1,2,…� (7) g�f � .∑ i5�"0'1 j 5"f0'1k9:"l� , � � 1,2,…� (8) step 6: determining the similarities to the pis by the formula: �∗ � m, n <m,∗�m,nb , � � 1,2,…� (9) where �∗ ∈ o0,1q ∀� � 1,2,…�. step 7: arranging pis0 �∗1 and choosing the best and the worst alternatives according to their ranking. in this study, the weight set in (4) would be replaced by a new set, which is determined by entropy, given as in the following step. step 8: calculating the entropy by: s" � j �tu0:1 ∑ i*�". ln<*�"bk:�l� , � � 1,2,…$;# � 1,2,…� (10) then the objective weight for each criterion can be determined as: )" � w �fx-∑ 0�fx-1y-3� z , # � 1,2,…� (11) iii. experimental procedure in this work, the titanium alloy ti-6al-4v is selected, and the five-axis milling center dmg dmu50 is used for the machining experiment. the experimental workpiece and machine are shown in figures 1 and 2. the surface roughness value was measured 3 times at 3 different positions for each experiment by a mitutoyo surftest js-310. the average value is shown in table iv. fig. 1. experimental set-up. fig. 2. workpiece specimen. iv. results and discussion a. optimization using entropy-based topsis step 1: the given selected responses are arranged in the information table of topsis according to table iv. table iv. topsis experimental information alternative ra mrr a1 0.281 5.42 a2 0.336667 1.08 a3 0.737333 16.25 a4 0.328 21.67 a5 0.321333 10.83 a6 0.506667 2.17 a7 0.358667 32.5 a8 0.411667 43.33 a9 0.635667 16.25 step 2: the given responses are transformed to nondimensional form by (3). the result is presented in table v. step 3: the weigh set is calculated using entropy by (10) and (11). the summarized results are shown in table vi. engineering, technology & applied science research vol. 11, no. 1, 2021, 6775-6780 6778 www.etasr.com nguyen et al.: cutting parameter optimization in finishing milling of ti-6al-4v titanium alloy under … table v. the non-dimensional form alternative conversion vector r1 r2 a1 0.204 0.085 a2 0.244 0.017 a3 0.534 0.254 a4 0.238 0.339 a5 0.233 0.169 a6 0.367 0.034 a7 0.260 0.509 a8 0.298 0.678 a9 0.460 0.254 table vi. entropy weight set e1 e2 2.6831 5.1092 w1 w2 0.2906 0.7094 step 4: the weighted normalized rating is calculated by (7), using an entropy weight set. the result is shown in table vii. step 5: the best and the worst solutions are determined using (5) and (6). the result is shown in table viii. step 6: pis and nis are calculated among the alternatives by (7) and (8). step 7: pis ( "∗1 can be derived according to (9). step 8: pis ( "∗1 is arranged and the best and the worst alternatives are selected (table ix). table vii. entropy weighted normalized rating alternative v1 v2 a1 0.0591 0.0602 a2 0.0709 0.0120 a3 0.1552 0.1804 a4 0.0690 0.2406 a5 0.0676 0.1202 a6 0.1066 0.0241 a7 0.0755 0.3608 a8 0.0867 0.4810 a9 0.1338 0.1804 table viii. best and worst solutions ra mrr a + 0.059148495 0.011989059 a 0.155203335 0.481005487 table ix. the ranking of the alternatives alternative v1 v2 s + s c * ranking a1 0.0591 0.0602 0.4317 0.0482 0.1004 7 a2 0.0709 0.0120 0.4765 0.0117 0.0240 9 a3 0.1552 0.1804 0.3006 0.1939 0.3921 4 a4 0.0690 0.2406 0.2554 0.2288 0.4725 3 a5 0.0676 0.1202 0.3713 0.1086 0.2263 6 a6 0.1066 0.0241 0.4595 0.0490 0.0964 8 a7 0.0755 0.3608 0.1442 0.3492 0.7077 2 a8 0.0867 0.4810 0.0686 0.4698 0.8727 1 a9 0.1338 0.1804 0.3014 0.1842 0.3794 5 according to table ix, the a8 is the best alternative, with ra and mrr values of 0.41166µm and 43.33 respectively. the worst is a2 with ra value at 0.336667 µm. the production rate accounted for was 1.08 cm 3 /min. the value of surface quality in a8 alternative is worse than in a2, but its mrr is about 40 times higher. v. anova analysis in table x we can see the snr versus vc, fz, ap (smaller is better). table x and figure 3 illustrate that in the milling of the titanium alloy ti-6al-4v under mql conditions, the feed rate value impacts significantly on surface roughness, followed by the effect of cutting speed vc. on the other hand, the influence of depth of cut ap on the surface quality is fuzzy. table x. response table for signal to noise ratios level vc fz ap 1 7.710 9.872 8.214 2 8.483 9.009 7.691 3 6.850 4.163 7.138 delta 1.633 5.709 1.076 rank 2 1 3 fig. 3. main effects signal to noise ratios. table xi. solution ranking by anova analysis solution vc fz ap mrr fit ra fit composite desirability 1 120 0.03 0.6 44.1492 0.369511 0.897796 2 120 0.03 0.2 33.2325 0.334549 0.819577 3 120 0.065 0.6 36.6512 0.411079 0.775842 4 120 0.03 0.4 30.7508 0.351432 0.770634 5 120 0.065 0.2 26.7734 0.370215 0.699454 6 120 0.065 0.4 24.5508 0.389908 0.650340 7 90 0.03 0.6 18.8877 0.312368 0.626507 8 90 0.065 0.6 14.1041 0.344462 0.515162 9 60 0.03 0.6 13.4869 0.329394 0.512360 table xii. error of calculated and anova results calculated values predicted values error mrr 43.330 44.1492 1.856% ra 0.4116667 0.369511 10.24% multi-response optimization is performed by the anova tool in minitab, and the result is presented in figure 4. the engineering, technology & applied science research vol. 11, no. 1, 2021, 6775-6780 6779 www.etasr.com nguyen et al.: cutting parameter optimization in finishing milling of ti-6al-4v titanium alloy under … anova analysis gives similar results. its best solution is at 0.32µm of surface roughness and 34.3078cm 3 /min mrr, while the predicted results are 0.41 and 43.33 respectively (table xiii). fig. 4. multiple response optimization analysis results. table xiii. anova and topsis multi optimization results comparison best solution set determined by topsis anova vc (m/m) 120 120 fz (mm/tooth) 0.065 0.03 ap (mm) 0.2 0.6 ra (µm) 0.41 0.32 mrr (cm 3 /min) 43.33 34.30 vi. discussion the results in table ix confirm that topsis is the right tool for multiple responses in milling ti-6al-4v. multiresponse optimization analysis with topsis and anova tools in minitab showed relatively similar best choice results. topsis shows the a8 alternative at vc=120m/min, fz=0.065mm/tooth and ap=0.2 as the best parameters set, where ra=0.412µm and production rate accounts for 43.330cm 3 /min. meanwhile, for anova analysis, the most optimal choice is ra=0.36µm, mrr=44.1492cm 3 /min. the analytical results in table x show that the difference between these two methods is 1.856% in mrr and 10.24% in roughness. noticeable, topsis helps selecting the best one out of 9 experimental options only, which means that the set of parameters of cutting mode is one of the implemented parameter sets, whereas the anova allows the prediction of the best cutting parameters based on the experimental data. in this case, the optimal set of parameters is predicted to be (vc=120 m/min, fz=0.03 mm/tooth, and ap=0.6mm). this predicted parameter set does not coincide with any implemented parameters. this study shows that combining topsis and anova analysis could be applied to approve the multiple optimization of the cutting process. vii. conclusion the current work aimed at optimizing the cutting parameters in the milling of ti-6al-4v under mql condictions. topsis method and anova analyis were performed and the following findings of this research should be considered: • mql with vegetable oil is successfully applied in the face milling of ti-6al-4v. • the impact of feed rate on surface roughness is significant. increasing feed rate or cutting speed lead to rising production rate (mrr) but reduce the quality of surface roughness. • the best solution chosen by topis is (vc=120m/min, fz=0.065mm/tooth, and ap=0.2mm), where the surface roughness and the material removal rate are 0.41µm and 44.1492 cm 3 /min respectively. • the best solution predicted by minitab is (vc=120m/min, fz=0.03mm/tooth, and ap=0.6mm), where the surface roughness is 0.32µm and the material removal rate is 34.4cm 3 /min. • the topsis model can be applied to find the best parameters set in the milling of ti-6al-4v. this model can be used in different machining processes or materials. • anova analysis by software can be used to predict and find the best alternative of the milling process based on the regression model. the parameter set predicted by anova analysis does not coincide with any implemented parameters. acknowlegement the authors appreciate the assistance from the hanoi university of industry for the support in the research process. references [1] m. a. elfghi and m. gunay, "mechanical properties of powder metallugry (ti-6al-4v) with hot isostatic pressing," engineering, technology & applied science research, vol. 10, no. 3, pp. 5637–5642, jun. 2020, https://doi.org/10.48084/etasr.3522. 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[24] b. singaravel, d. p. shankar, and l. prasanna, "application of mcdm method for the selection of optimum process parameters in turning process," materials today: proceedings, vol. 5, no. 5, part 2, pp. 13464–13471, jan. 2018, https://doi.org/10.1016/j.matpr.2018.02.341. [25] r. v. rao, decision making in the manufacturing environment: using graph theory and fuzzy multiple attribute decision making methods. london, uk: springer, 2007. [26] g.-h. tzeng and j.-j. huang, fuzzy multiple objective decision making, 1st edition. florida, united states: crc press, 2013. [27] j. xu and x. zhou, fuzzy-like multiple objective decision making, 2011th edition. berlin, germany: springer, 2011. [28] g.-h. tzeng and j.-j. huang, multiple attribute decision making: methods and applications. florida, usa: crc press, 2011. author profiles van canh nguyen is a lecturer at the department of manufacturing technology, faculty of mechanical engineering, hanoi university of industry. he is a phd candidate, and his research work focuses on the multiple optimization of metal cutting process under minimum quantity lubricant. thuy duong nguyen is a phd in the department of machine tool and tribology, school of mechanical engineering, hanoi university of science and technology. her research focuses on the effects of friction and tribology on machine parts. dung hoang tien is an associate professor at the department of manufacturing technology, faculty of mechanical engineering, hanoi university of industry. his research work focuses on multi-optimization, addaptive machining, and micro-machining. microsoft word 19-3756_s_etasr_v10_n5_pp6249-6252 engineering, technology & applied science research vol. 10, no. 5, 2020, 6249-6252 6249 www.etasr.com phan: influence of tack speed on the rheological properties of mortar in fresh state influence of tack speed on the rheological properties of mortar in fresh state van tien phan faculty of construction vinh university vinh city, vietnam vantienkxd@vinhuni.edu.vn abstract-in the present work, squeeze flow techniques were used to investigate the influence of tack speed to the rheological properties of mortar in fresh sate, including yield stress and extensional viscosity. the tested samples were prepared under similar conditions of room temperature and atmospheric pressure. compositions of mortars were tested at two different squeezing rates (20 and 200mm/s) 15min after mixing. the results indicate that mortar’s yield stress increases with increasing pulling speed. this increase is evident at low tensile speeds. at high tack speeds, this increase is not obvious, especially in the case of high squeeze speed of 200mm/s. it can be concluded that the optimal speed for removing the mortar and the upper surface is lower than 20mm/s. the extensional viscosity of fresh mortars significantly decreases as the tack speed increases. also, the elongation viscosity decreases as the gap increases. the increase of the gap during the tack experiment stimulates different units causing the observed decrease of the mortars' elongation viscosity. keywords-squeeze flow technique; tack speed; fresh mortar i. introduction the fresh state of a cement-based material corresponds to only a minor part of its lifetime, nevertheless, the behavior of the material within this frame has major consequences on its hardened properties. the currently applied methods for testing these materials during the fresh state are simple but limited. flow table (astm-c1437, en-1015-3) and dropping ball (bs4551) methods investigate fresh mortar by using single point measurements [1]. these methods are unable to dissociate the contribution of the yield stress or the viscosity on the resulting measurements [1, 2]. in order to overcome the limitations of the traditional methods, rotational rheometers have been used, in which the mortar’s rheological behavior and parameters such as yield stress and viscosity were determined in either shear stress or shear rate-controlled procedures [3, 4]. this technique is an important tool for controlling and developing cementitious materials formulations, including mortar, especially for the simulation of mixing and pumping. during the application, the mortar is spread over a substrate and then squeezed between bricks (masonry and tile adhesive mortar) or projected and spread over a surface for internal and external rendering purposes. the mortar fraction of a concrete mix is also squeezed locally between coarse aggregates during the flow of the fresh concrete [5]. therefore, the rotational rheometry is not suitable in these cases. the behavior of the material after squeezing under different tack speeds provides important information of its rheological performance. the main objective of the current research was to investigate the influence of tack speed on the rheological properties of fresh mortar, including yield stress and extensional viscosity. ii. squeeze flow experiment the squeeze test is widely used to determine the flow properties of highly viscous pastes (food, cosmetic, polymers, composites, ceramic pastes and others) [6-10], as it overcomes some of the common problems of conventional rheometry such as slip, disruption of plastic materials, and the difficulty to load very thick and fiber-containing fluids in rotational devices [5]. fig. 1. a squeezing experiment of mortar in process. squeezing technique characterizes cementitious materials by compressing a cylindrical specimen between two parallel surfaces by controlled force or displacement rate. this method has been used for characterizing the rheological behavior of cement pastes [11], herschel bulkley fluids [12], bingham plastic [13], etc. the typical load versus displacement profile of a constant velocity squeeze flow experiment was determined in [11] and it is used to determine the rheological parameters of corresponding author: van tien phan engineering, technology & applied science research vol. 10, no. 5, 2020, 6249-6252 6250 www.etasr.com phan: influence of tack speed on the rheological properties of mortar in fresh state testing materials, including yield stress and viscosity. direct measurements of yield stress are uniquely performed by stresscontrolled rheometry [3, 4]. squeeze flow tests carried out with constant displacement velocity do not allow such direct measurements [5] since the material flow occurs regardless of the existence of the material yield stress, unless the force required to overcome this value exceeds the load limit of the testing device. in the current study, the testing material was firstly compressed/squeezed between two parallel surfaces until a predefined thickness, followed by a relaxation period of 1.5min, and the surfaces were finally separated with a predefined tack velocity (figure 1). a typical curve of squeezetack experiment is presented in figure 2 of [14], in which three periods can be observed, compression, relaxation and traction. it is possible to conduct indirect yield stress determination by the extrapolation of the flow curves in the squeeze stage of the experiment. the yield stress is calculated by dividing the maximum force recorded by the area at that time: �� = �� max � (1) in which as is the average area of the testing sample at the moment that the recorded load is max: as= �� = ��� �� (2) where h is the predefine thickness of the test mortar, r is the radius of the sample and ℎ� is the mortar’s thickness at the moment of the maximum tack force. during the third stage of the squeeze flow experiments conducted with a constant upward velocity of the upper plate, the sample height increased linearly, as: h=h0 + vt (3) where h is the momentary height of the sample, h0 is the initial sample height at the beginning of the tack step, v is the tack speed of the upper plate and t is the time elapsed after the beginning of the tack period [6]. the biaxial extensional strain rate or elongational strain rate is equal to one-half the vertical hencky strain rate [6]: ��� = ��� � = � (��) (3) the extensional viscosity (ηb) is defined as the ratio between the biaxial extensional stress (σb), which is calculated by (1), and the extensional strain rate: ƞ�= �� ��� = 2�[ �!(�") � �� ] (4) where l is the load and r is the radius of the sample [6]. iii. experimental set-up the material used in this investigation is referenced in [5, 15]. the detailed composition of the tested material is presented in table i. in order to minimize the effect of sand grading on the rheological properties of concrete, strict grading, normalized cen 196-1 sand, was used. this is european standard sand (iso 679), which is very clean, with particles of the same size and round shape. it is dried, screened and prepared in a factory, ensuring quality and consistency, packed in bags containing 1350 ± 5g. waloceltm mkx 70000 pp01 hydroxyethyl methyl cellulose has been added in the composition of mortar with fixed percentage of dry mixture (0.5%). it is characterized by well-balanced properties, including open time, adhesion, and shear strength, adds good workability and enhances water retention. the selected particle size distribution provides quick, lump-free dissolution. it is compatible with all conventional mineral and organic binders. for evaluating the influence of the squeezing rate to the yield stress of the mortar, the testing samples were squeezed at 20 and 200mm/s speed. after the relaxation time, the testing samples were pulled out at different speeds. by analyzing the recorded flow curves during the experiments, the variation of the yield stress of the testing material can be calculated. the height of the sample should be at least 10 times greater than the maximum particle size in order to avoid wall effects [5]. hence, the predefined thickness of the testing material is taken as 3.5mm. table i. material’s composition constituents white cement normalized sand mkx 70000 pp01 water % wt. of dry mixture 30 70 0.5 25 iv. results and discussion a typical flow curve obtained in the squeeze tack experiment is presented in figure 2. the maximum calculated stress is considered as the yield value of the material. from the flow curves, the value fmax is recorded and given in table ii. the yield stress of the materials is calculated (1) and is presented in table iii. fig. 2. a typical curve obtained in the tack period of squeeze flow test. table ii. recorded maximum load) traction velocity vt=2mm/s vt=20mm/s vt=200mm/s squeeze velocity vs=20mm/s 8.5604 14.603 25.513 squeeze velocity vs=200mm/s 8.0569 14.771 18.128 -5 0 5 10 15 20 25 30 1 10 100 1000 2mm_s20_t2 3,5mm_s20_t2 5mm_s20_t2 7mm_s20_t2 10mm_s20_t2 l o a d ( n ) time (sec) engineering, technology & applied science research vol. 10, no. 5, 2020, 6249-6252 6251 www.etasr.com phan: influence of tack speed on the rheological properties of mortar in fresh state table iii. yield stress of testing materials squeeze – tack velocity s20 t2 s20 t20 s20 t200 s200 t2 s200 t20 s200 t200 yield value 0.0045 0.0068 0.01156 0.00367 0.0067 0.0079 the variation of mortars’ yield stress in tension versus the tack velocity is plotted in figure 3 for two values of squeeze speed, 20mm/s and 200mm/s. it can be seen that at a constant squeeze velocity, the mortar’s yield stress increases with the increase of pulling speed. this increase is evident at low tensile speeds (2mm/s and 20mm/s). at high tack speed of 20mm/s, this increase is not obvious, especially in the case of high squeeze speed of 200mm/s. the result indicates that the optima speed for removing the mortar and the upper surface (masonry bricks, tiles adhesive, etc.) is lower than 20mm/s. fig. 3. yield stress in tension of mortars versus tack velocity at different squeeze speeds. fig. 4. extensional viscosity of mortars versus tack speed. the behavior of mortars’ extensional viscosity versus the tack speed is represented in figure 4. the interpretation of viscosity results obtained by squeeze flow must consider that, although the squeeze velocity remains constant (20 and 200mm/s), the extensional viscosity of fresh mortars significantly decrease as the tack speed increases. similar observations were recorded at different experiments with squeeze speeds of 20mm/s and 200mm/s. elongation viscosity values decreased as a result of gap increasing for all the tested samples. furthermore, unlike in rotational rheometry, where the gap is constant and the decrease of viscosity with the strain rate in fact represents shrinkage, the increase of the gap during the tack experiment stimulates different units (grains getting far apart to each other) causing the observed decrease of the mortars' elongation viscosity. this finding is similar to the findings in [4]. v. conclusions the squeeze flow is a simple and versatile method for the rheological characterization of mortars in a wide range of consistencies, providing important information of the rheological behavior of materials in practical applications. from the obtained flow curves from the squeeze tack experiments, the rheological parameters, including yield stress in tension and mortar’s extensional viscosity, have been investigated. the results indicate that mortar’s yield stress increases with increasing pulling speed. this increase is evident at low tensile speed values. at high tack speed, this increase is not obvious, especially in the high squeeze speed of 200mm/s. it can be concluded that the optima speed for removing the mortar and the upper surface (masonry bricks, tiles adhesive, etc) is lower than 20mm/s. the extensional viscosity of fresh mortars significantly decreases as the tack speed increases. elongation viscosity values decreased as a result of increasing gap. the increase of the gap during tack experiment stimulates different units (grains getting far apart to each other) causing the observed decrease of the mortars' elongation viscosity. references [1] p. f. g. banfill, “use of the viscocorder to study the rheology of fresh mortar,” magazine of concrete research, vol. 42, no. 153, pp. 213–221, dec. 1990, doi: 10.1680/macr.1990.42.153.213. [2] r. g. pileggi, “novel tools for the study and development of refractory castables,” ph.d. dissertation, federal university of são carlos, são carlos, brazil, 2001. [3] v. t. phan, “influence of re-dispersible powder on the properties of mortars,” journal of materials and engineering structures, vol. 1, no. 1, pp. 2–10, jan. 2014. [4] v. t. phan and d. d. nguyen, “influence of squeezing rate on yield stress and viscosity of fresh mortar,” engineering, technology & applied science research, vol. 10, no. 4, pp. 5921–5924, aug. 2020. [5] j. f. steffe, rheological methods in food process engineering. freeman press, 1996. [6] g. h. meeten, “yield stress of structured fluids measured by squeeze flow,” rheologica acta, vol. 39, no. 4, pp. 399–408, aug. 2000, doi: 10.1007/s003970000071. [7] n. özkan, c. oysu, b. j. briscoe, and i. aydin, “rheological analysis of ceramic pastes,” journal of the european ceramic society, vol. 19, no. 16, pp. 2883–2891, dec. 1999, doi: 10.1016/s0955-2219(99)00054-0. [8] j. engmann, c. servais, and a. s. burbidge, “squeeze flow theory and applications to rheometry: a review,” journal of non-newtonian fluid mechanics, vol. 132, no. 1, pp. 1–27, dec. 2005, doi: 10.1016/ j.jnnfm.2005.08.007. [9] o. campanella and m. peleg, “squeezing flow viscosimetry of peanut butter,” journal of food science, vol. 52, no. 1, pp. 180–184, aug. 2006. [10] b. h. min, l. erwin, and h. m. jennings, “rheological behaviour of fresh cement paste as measured by squeeze flow,” journal of materials science, vol. 29, no. 5, pp. 1374–1381, mar. 1994, doi: 10.1007/ bf00975091. engineering, technology & applied science research vol. 10, no. 5, 2020, 6249-6252 6252 www.etasr.com phan: influence of tack speed on the rheological properties of mortar in fresh state [11] b. belahcene, a. mansri, and a. benmoussat, “investigation on the rheological behavior of multigrade oil under the effect of organic and inorganic impurities,” engineering, technology & applied science research, vol. 4, no. 6, pp. 711–713, dec. 2014. [12] d. n. smyrnaios and j. a. tsamopoulos, “squeeze flow of bingham plastics,” journal of non-newtonian fluid mechanics, vol. 100, no. 1, pp. 165–189, sep. 2001, doi: 10.1016/s0377-0257(01)00141-0. [13] f. a. cardoso, a. k. agopyan, c. carbone, r. g. pileggi, and v. m. john, “squeeze flow as a tool for developing optimized gypsum plasters,” construction and building materials, vol. 23, no. 3, pp. 1349– 1353, mar. 2009, doi: 10.1016/j.conbuildmat.2008.07.017. [14] v. t. phan, “evaluation of some rheological properties of xanthan gum”, engineering, technology & applied science research, vol. 10, no. 5, pp. 6172-6175, oct. 2020. [15] s. lee, m. chung, h. m. park, k.-i. song, and i. chang, “xanthan gum biopolymer as soil-stabilization binder for road construction using local soil in sri lanka,” journal of materials in civil engineering, vol. 31, no. 11, nov. 2019, art. no. 06019012, doi: 10.1061/ (asce)mt.1943-5533.0002909 microsoft word etasr_v11_n4_pp7489-7494 engineering, technology & applied science research vol. 11, no. 4, 2021, 7489-7494 7489 www.etasr.com el kolli & el kolli: preparation and characterization of gelatin-based films cross-linked by two … preparation and characterization of gelatin-based films cross-linked by two essential oils at different concentrations and plasticized with glycerol hayet el kolli multiphase polymeric materials laboratory university of ferhat abbas setif 1 setif, algeria meriem el kolli laboratory for the valorization of biological natural resources university of ferhat abbas setif 1 setif, algeria abstract-gelatin cross-linking has recently been discovered to be a very appealing production method. the current research looks at various commercial gelatin (type b) films to improve their physical qualities. bunium alpinum and bunium incrassatum essential oils (eos) in two quantities (5% and 25%) were added to the films, which showed substantial biological activity (antibacterial, antioxidant, antihemolytic, and antiinflammatory). according to electronic scanning microscopy results, the basic gelatin matrix had changed and there were multiple dense spots on the cross-linked films. the particles appear to be more bonded in an isotropic form. infrared spectroscopy cannot provide substantial accuracy on the new characteristics and chemical interactions formed due to the complex system of gelatin and eos. according to the uv transmission test results, adding eos to gelatin films improves the barrier properties against uv rays and prevents uv light transmission. finally, the swelling water test revealed that included eos in the film composition reduce the film's swelling. keywords-gelatin; bunium alpinum; bunium incrassatum; crosslinking; barrier property against uv; food packaging i. introduction polymeric materials are required in a variety of routine applications, from food packaging to cosmetics and other specialized sectors, e.g. the biopharmaceutical and pharmaceutical sectors [1]. for more than 20 years researchers try to improve conventional polymers by adding particles into the polymer matrix, thus changing its properties [2]. the agriculture and food sectors are increasingly concerned about the preservation of commonly consumed items against deterioration caused by environmental (heat, sunlight) or biological (bacterial and fungal) factors [3]. bio-packaging is currently being researched as a healthy and environmentally friendly option [4]. traditional polymers used in the product packaging are being replaced with healthier, less toxic and biodegradable alternatives in the agri-food, pharmaceutical, and cosmetic industries through technological procedures. as a result, biopolymers like gelatin are gaining popularity in this sector. film-making gelatin is a form of gelatin. it becomes more stable and manageable when mixed with other substances [5]. in innovative packaging applications, biopolymers are coupled with natural products such as medical plant extracts (essential oils and plant powders) and pure or semi-purified natural components (polyphenols, flavonoids, pigments, etc.) [6]. this link bestows all of the qualities and benefits associated with natural items on the designed bundle. the use of essential oils in packaging systems, imparts the flavors of the essential oils used and the antibacterial and antifungal properties that characterize them [3, 7]. phenolic compounds protect packaged commodities from degradation caused by external conditions and bacteria by acting as antioxidants [8]. this study aims to develop a novel type of gelatin packaging that is cross-linked with glycerol. this polymer contains antibacterial, antifungal, and antioxidant essential oils (eos) from bunium incrassatum and bunium alpinum [9]. ii. matherials and methods a. chemicals hydro-distillation in a clevenger-style device was used to extract the volatile eos, and each separated oil was kept at 4°c in a refrigerator. the eos were analyzed using gas chromatography-mass spectrometry (gc-ms). the contents of the eos were determined by comparing the mass spectral pattern and retention indices (ris) of the eos to those of pure compounds available in the literature as well as a laboratorybuilt database of authentic chemicals [10]. fluka and biochemika synthetized gelatin powder from porcine skin (with a medium gel strength 180 blooms) was utilized. b. preparation of biofilms the methodology defined in [11] is employed in this work with minor modifications. to make the film-forming solution, 3.5g gelatin powder (180 bloom porcine skin gelatin) was mixed with 100ml distilled water for 30min, then 2ml glycerol (plasticizer) were added. this mixture was heated at 70°c for 30min and was constantly stirred. at the same time, a 3:1 (v/v) mixture of eos and tween-20 (emulsifier) was prepared. the corresponding author: meriem el kolli (elkollim@yahoo.fr) engineering, technology & applied science research vol. 11, no. 4, 2021, 7489-7494 7490 www.etasr.com el kolli & el kolli: preparation and characterization of gelatin-based films cross-linked by two … combination was added to the initial solution in percentages of 5% and 25%. a vortex mixer (3500rpm) was used to homogenize the generated solution for 3min. the dissolved air in the films was then extracted with a vacuum pump. finally, 13ml of liquid were placed in plastic petri dishes and were allowed to air dry for 4 days at room temperature. the films were then carefully peeled and assessed. control films were made using the same procedure as the test films but without the eos. c. characterization • thickness in compliance with the french standard nf q 03-016, the film thickness (e) was measured with a foot electronic slidetype mitutoyo digimatic 500-123u. three discs were cut from each formulation (each measuring 4.5cm). each disc was measured for thickness in 5 different spots at random [12]. • areal density the film's mass determines the areal density in g/m 2 based on a unit area. the french standard nf q 03-019 was used to determine it. each formulation was sliced into 3 discs (each measuring 4.5cm) and was weighed precisely. the film density (d) was calculated using the equation d=ad/e from the thickness and basis weight [13]. • scanning electronic microscopy (sem) sem was used to evaluate sample films' morphology or surface topography (a jeol jsm 6360lv scanning electron microscope was utilized). to make them conductive a 25 to 30nm thickness layer was placed to the surface and the samples were first metalized with gold in a cressington sputter coater metallizer. electron acceleration voltages ranging from 3 to 10kv were used to obtain the photos [12]. • fourier transform-infrared (ft-ir) infrared spectroscopy was used to determine the physical states of organic and inorganic molecules based on their vibrational properties. chemical bonds do vibrate in specific modes as a result of infrared light (deformation, stretching). as a result, comparing the sample's incidence and transmission is sufficient to disclose the sample's fundamental chemical functions [14]. the ftir-8400s device was used (fourier transform infra-red spectrophotometer, shimadzu). the data were read using ir-solution software. • transparency and light transmission the film's light transmission in ultraviolet and visible light was measured using a uv-visible spectrophotometer (unicam uv 300 type 200-800nm). vision32 software v1.10 was used to read the data. the film's transparency value (tv) is calculated by [14]: �� = ��� (� )/ (1) where � : 600nm transmission fraction, : the thickness of the film (mm). a high �� value is indicative of low film transparency. • swelling test the film samples (40mm/30mm) were dried for 24h at 104°c in an air-circulating oven until they were consistent in weight. the initial weight (�� ) was measured. the film samples were immersed in a 100ml erlenmeyer flask with 50ml distilled water for 24h at room temperature. after removing from the flask and rubbing it between filter papers to remove any residual surface water, each sample was weighed and the ultimate weight (��) was calculated. equation (2) [15] was used to compute the weight gain or swelling percentage (s %): � (%) = ( −�� / ��) 100 (2) at least three measurements were taken in each test. iii. results and discussion this is a new line of research which aims to synthesize biodegradable matrices, based on gelatin or another biopolymer, with new formulations by adding safe to use and low cost natural metabolites such as eos, known for their broad antimicrobial spectrum with the aim of using them in packaging, as patches for the release of drugs, or in the case of the encapsulation of active ingredients. table i shows the thickness, areal density, and density of the several gelatin films supplemented with varying concentrations of eos, as well as the control film. • training films the chains of gelatin unfold during the solubilization of gelatin in water, generating the polymer network. the viscosity of the film-forming fluids increases substantially as the gelatin molecules flocculate and transform into a gel at temperatures above the gelling temperature (60°c). reduced hydration layers around polymer chains increase hydrophobic interactions, resulting in increased hydrophobic interactions [16]. gelatin's methyl groups interact with the molecules around them, forming intermolecular connections. the hydrogen-type intermolecular bonds are formed by isolating the hydration solvent (water) from the polymer chains. glycerol is a low-molecular-weight (92g/mol) hydrophilic molecule that can readily be placed between gelatin segments. hydrogen bonds arise between the hydroxyl groups of the glycerol and gelatin during the gelling or evaporation of the solvent. • look and flexibility control films and films with eos and have a smooth, continuous appearance with no surface imperfections. it is worth noting that the flexibility of the films is proportional to the amount of eo used [16, 12]. the film that contained the most bunium incrassatum eo (25%) was the most flexible and yellow-tinted (since this eo is darker than the other). based on this finding, the films developed a stable emulsion system. there is no emulsion breakdown or change during the dehydration process, and no bubbles or cracks appear. • thickness the eo-enhanced films were all thicker in consistency than engineering, technology & applied science research vol. 11, no. 4, 2021, 7489-7494 7491 www.etasr.com el kolli & el kolli: preparation and characterization of gelatin-based films cross-linked by two … the control film (0.22mm). droplets of eos can be incorporated into the film network, obstructing the link between gelatin chains, lowering network compactness, and obstructing orderly alignment. the formation of gelatin chains might increase density. this can be controlled by surface tension and/or changes in the size of the oil droplets. furthermore, eos are available in various formulations, each of which interacts with the gelatin chain in the film matrix in a distinct way [10]. as a result, the gelatin molecules' arrangement in the film matrix can shift, resulting in changes in film thickness [17]. as a consequence, adding glycerol to the control film enhanced dramatically the surface density. combining glycerol and eos increases the film thickness, but has a significant impact on the density. this is because glycerol has a density of only 1257kg m -3 . table i. thickness, areal density, and volume mass of the films sample thickness (mm) areal density (g m -2 ) volume mass (kg m -3 ) control 0.22 ± 0.004 72.705 3304.802 film with 25% of bunium incrassatum 0.36 ± 0.005 70.651 1962.547 film with 25% of bunium alpinum 0.32 ± 0.008 64.846 2026.441 film with 5% of bunium incrassatum 0.34 ± 0.005 69.268 2037.306 film with 5% of bunium alpinum 0.24 ± 0.008 63.861 2660.878 • sem and determination of the morphology according to sem, the control film has a smooth, continuous, compact, and completely transparent surface (figure 1). for films having varying concentrations of eos, several dense zones develop on the same sample, where the particles appear more bound with anisotropic structure, without pores, and without micro-fractures (figure 1). the most densely built-up areas are those with the highest percentage of eos, meaning that eos' droplets modify the transverse distribution of protein-protein inside the film matrix (improving roughness), most likely within the film network. because of the eo droplets, water molecules will not travel through the film network [18]. terpene compounds make up many eo compositions [29, 20]. these molecules can combine with different proteins or amino acids in gelatin to form "protein cross-links," which change the gelatin's underlying matrix and give rise to various morphologies [21]. • ft-ir the ftir spectra of gelatin and gelatin / eo films are shown in figures 2 and 3. the purpose of this classification was to determine how various functional groups interacted with each another. because each film has a large number of functional groups, the ftir spectra generated from each film include a large number of overlapping absorption bands, offering more information than all of the chemical components analyzed independently. the distinction was made using proteins and polypeptides, which are the essential components that determine function in food systems. the infrared spectra of nearby peptide groups are affected by vibrational coupling. film without eo film enriched with 5% of bunium incrassatum film enriched with 25% of bunium incrassatuum film enriched with 5% of bunium alpinuum film enriched with 25% of bunium alpinuum fig. 1. sem micrographs of the gelatin and gelatin/eo films. fig. 2. ft-ir spectra of gelatin films with bunium alpinum and bunium incrassatum eos at various concentrations (4000-500cm -1 ) the vibratory features of ft-ir can be used to show the presence of species adsorbed and/or grafted to the surface of the film. ft-ir does not provide considerable precision on the features and newly developed connections due to the various activities of gelatin and eo, and glycerol in all films [12]. the same prominent peaks with various amplitudes appeared in all ft-ir spectra (figure 2). engineering, technology & applied science research vol. 11, no. 4, 2021, 7489-7494 7492 www.etasr.com el kolli & el kolli: preparation and characterization of gelatin-based films cross-linked by two … fig. 3. ft-ir spectra of control and modified films with eos (1500500cm -1 ) the notable peaks in both films with and without eos were nearly identical: both film samples contained a band with a wavenumber of 1165.32cm -1 . it refers to an amine having a short c-n chain that can be used as a primary, secondary, or tertiary amine [12]. several bands in the 1940–1847cm -1 range are also found in gelatin and eos and are linked to nh2 bending vibrations and c=o, c=c, and c=n stretching vibrations. at 3826 cm -1 , an amide-a band and an amide-b band with nh-stretching combined with hydrogen-bonding and ch stretching were identified. • transparency and light transmission the spectrum in figure 4 depicts the transmittance of uv rays and visible light in the wavelength range of 200-800nm of gelatin films enhanced with various eos. there was no uv transmission in any of the films at 200nm, including control. they had all started transmitting light at wavelengths less than 300nm. the use of eos in gelatin films has been suggested as a means to improve uv barrier properties. these coatings effectively reduce uv light transmission. it can generally bind excellent uv barrier qualities and absorb uv radiation because of the rich amino acid content that produces the amino acids' gelatin and interactions with the eo's diverse components [22, 16]. the control film transmission ranged from 52, 61 to 86, and 51% for visible light (300-800nm). the lowest values were seen in the films enriched with eos (independent of eo type but proportionate to their concentration) (table ii). fig. 4. transmittance of films at 200-800nm wavelengths. these data suggest that adding eos to the films lowered light transmission considerably. the eo droplets in the matrix may be able to block uv and visible light from going through. in the visible range, the film containing 25% eo of b. incrassatum had the lowest light transmission (from 10.65 to 78.64%), followed by the film containing the same proportion of eo of bunium alpinum. the film with 5% of the eo of bunium incrassatum comes third, whereas the film with 5% of bunium alpinum comes fourth. the presence of eos in the films might cause light scattering in variable degrees. for light transmission through the films, the arrangement or alignment of the polymer chains in the film network is crucial. when considering the maximum transparency, the lowest transmittance value is employed [23]. authors in [24] demonstrated their hypothesis by using lemon eo to lower the opacity of chitosan films. they discovered that the size and placement of eo droplets in the film network can influence the occurrence of this event. the findings in [25] are consistent with this discovery. table ii. transparency values of the films glycerol (%) eo light transmission (%) at different wavelengths transparency value 20% 200 300 350 400 500 600 700 800 control 0 52.617 71.836 78.456 82.189 83.635 85.26 86.513 3.579 bunium incrassatum 25% 0 10.651 36.241 52.243 65.958 71.917 76.027 78.645 3.300 bunium incrassatum 5% 0 33.435 59.623 70.344 78.329 81.302 83.582 85.003 3.378 bunium alpinum 25% 0 29.315 55.122 69.077 78.231 81.163 83.052 84.304 3.404 bunium alpinum 5% 0 43.050 65.850 74.586 80.858 82.887 84.718 85.911 3.538 • swelling test when eos were introduced, the swelling of gelatin films was considerably reduced (table iii). gelatin is a hydrophilic substance, which means it soaks up water molecules. porous gelatin films have a higher swelling capacity due to their network architecture, allowing more water to pass. because eos are hydrophobic, it is possible that adding them to gelatin films reduces their swelling potential. hydrophobic contact between gelatin's hydrophobic domains and eos improves the interfacial interaction between matrix (gelatin) and filler (eos) [26]. this causes the eos to saturate the gelatin network, preventing water molecules from migrating into the gelatin and reducing swelling [27]. these findings show that gelatin sheets containing eos could be promising liquid-absorbing packaging materials. table iii. swelling values sample swelling (%) control 542 ± 7 film with 5% of bunium alpinum 530± 3 film with 5% of bunium incrassatum 547±3 film with 25% of bunium alpinum 527±12 film with 25% of bunium incrassatum 512±4 engineering, technology & applied science research vol. 11, no. 4, 2021, 7489-7494 7493 www.etasr.com el kolli & el kolli: preparation and characterization of gelatin-based films cross-linked by two … iv. conclusion plastic packaging has many drawbacks, one of which being its negative influence on the environment. biodegradable films and coatings made from natural bio-based polymers can be promoted as a viable plastic substitute. in the current study, the eos of bunium alpinum and bunium incrassatum were shown to be very compatible with gelatin, resulting in flexible and easy-to-handle films in the studied concentration range. including eos in the gelatin films resulted in a significant reduction in edema, depending on the dose. according to the sem results, the eos were well dispersed 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[27] s. chaoui, d. smail, a. hellati, and d. benachour, "effect of starch nanocrystals on the properties of low density polyethylene/ thermoplastic starch blends," engineering, technology & applied science research, vol. 10, no. 4, pp. 5875–5881, aug. 2020, https://doi.org/10.48084/etasr.3608. engineering, technology & applied science research vol. 8, no. 5, 2018, 3310-3315 3310 www.etasr.com tsipouras: uterine emg signals spectral analysis for pre-term birth prediction uterine emg signals spectral analysis for pre-term birth prediction markos g. tsipouras department of informatics and telecommunications engineering, university of western macedonia kozani, gr47100, greece mtsipouras@uowm.gr abstract—a methodology for prediction of pre-term births is presented in this paper. the methodology is based on the analysis of ehg signals and data mining techniques. initially, spectral and non-linear characteristics of the ehg are extracted, forming a pattern that is used to train a classifier to discriminate between term and pre-term cases. the method has been tested using a benchmark ehg database, and the obtained results indicate its effectiveness in accurate pre-term/term labour prediction. keywords-preterm delivery; electrohysterogram; ehg signal processing; uterine electromyogram; prediction i. introduction according to the world health organization (who) 15 million babies are delivered before the 37th week of gestation every year, being more than 1 in 10 cases [1]. premature birth is the leading cause of death in children under 5 years, while premature babies develop lifetime disabilities, including learning disabilities and visual and hearing problems [2]. in addition, premature births create an enormous economic impact on the health care systems, estimated at 3 billion £ in england and wales [3], and continues to be significantly higher for preterm born children in the first 5 [4] and 10 [5] years of life. thus, developing techniques for premature birth prediction is an important task that have gained attention in the past decades, since accurate prediction of premature labour can lead to their significant limitation. premature birth prediction has been mainly based on calculating risk factors, largely associated with the medical condition of the mother, including diabetes, hypertension, smoking, abnormalities of the uterus and others [6]. an alternative approach that have gained significant interest is the analysis of the electrohysterogram (ehg), which is the electromyogram (emg) of the uterus, thus recording the muscular activity of the uterine during gestation. being noninvasive (recorded on the abdominal surface) and simple to obtain, ehg have proven to be a significant monitoring tool during pregnancy and labour [7]. moving a step forward, several studies have successfully used ehg signal to forecast pre-term labour [8-14]. these approaches mainly focus on the ehg signal processing, by extracting several time, frequency and/or non-linear characteristics from it, and then applying statistical analysis [8, 12] or classification techniques [9-11, 13-14] for pre-term/term cases discrimination. in this study, a methodology for ehg signal analysis for predicting premature births is presented. the methodology is based on the analysis of the ehg signal, focusing on its spectral and non-linear characteristics, while the prediction is made using intelligent techniques. a benchmark ehg database has been used for the development and validation of the methodology, and the obtained results indicate its effectiveness in accurate pre-term labour prediction. ii. related work a. database the term-pre-term electrohysterogram database (tpehg db) [8] is a collection of ehg records (uterine emg records), obtained at the university medical centre ljubljana from 1997 to 2005. the records were obtained around the 22nd week of gestation or around the 32nd week of gestation, during regular check-ups. the database contains 300 records from equal number of pregnancies, with 262 records obtained from pregnancies with on-term delivery (pregnancy duration > 37 weeks) and 38 records obtained from pregnancies which ended prematurely (pregnancy duration ≤ 37 weeks). also, 162 records obtained before the 26th week of gestation (being 143 term and 19 pre-term) while 138 obtained during or after the 26th week of gestation (with 119 term and 19 pre-term). for each recording, 4 electrodes were used: e1, placed 3.5 cm to the left and 3.5 cm above the navel; e2, placed 3.5 cm to the right and 3.5 cm above the navel; e3 placed 3.5 cm to the right and 3.5 cm below the navel; e4, placed 3.5 cm to the left and 3.5 cm below the navel. the differences in the electrical potentials of the electrodes were recorded, producing 3 channels: s1=e2–e1; s2=e2–e3; s3=e4–e3. the sampling frequency was 20hz, with each record having duration of 30 minutes with a 16-bit resolution over a ±2.5 millivolts range. an example of ehg recording (all channels) is illustrated in figure 1. b. realted works presented in the literature authors in [8] presented a comparison of various linear and non-linear features extracted from ehg to separate term and pre-term records. their analysis included filtering of the signals in several different frequency bands, being 0.08–4 hz, 0.3–4 hz and 0.3–3 hz, and extraction of several features, such as engineering, technology & applied science research vol. 8, no. 5, 2018, 3310-3315 3311 www.etasr.com tsipouras: uterine emg signals spectral analysis for pre-term birth prediction root mean square, median frequency of the signal power spectrum, autocorrelation zero-crossing, maximal lyapunov exponent, correlation dimension and sample entropy. student’s t-test was used to evaluate the features for their ability to separate term and pre-term groups. fig. 1. ehg recording: s1, s2 and s3 chanels. authors in [9] focused on the analysis of the channel 3 of the ehg signals, filtered in the 0.34–1hz band. root mean squares, peak and median frequency, and sample entropy features were extracted from the signals and several different classification algorithms were employed, being linear discriminant (lda), quadratic discriminant (qda), uncorrelated normal density, polynomial, logistic, k nearest neighbours (knn), decision tree (dt), parzen and support vector machines (svm). the dataset was oversampled, using the synthetic minority over-sampling technique (smote) to generate 262 pre-term records, using the 38 already available records. monte carlo cross-validation (mccv) (80% holdout, 100 iterations) and the n-fold cross validation (with n=5) techniques were applied. authors in [10] employed neural networks (nns) for the same problem. in this case the signals were filtered in the 0.34 to 1hz band, and root mean square, median frequency, peak frequency and sample entropy features were extracted. the dataset was oversampled using the same technique as in [9] (smote) to generate 262 pre-term signals from the 38 already available. classification was performed using six different nn classifiers (backpropagation feedforward nn, levenberg–marquardt feed-forward nn, automatic nn, radial basis function nn, random nn, perceptron linear classifier). mccv (80% holdout, 30 iterations) and 5-fold cross-validation techniques were employed to validate the obtained results. following the same methodology of [9, 10], authors in [11] analysed channel s3 of the ehg signals, filtered in the 0.34–1hz band, using the same features. again, several classifiers are tested, including selforganized network inspired by the immune algorithm (sonia) and fuzzy sonia. the pre-term class is oversampled using min and max to produce 262 pre-term records. cross-validation was performed using 60% of the data for training, 25% for validation and 15% for testing (30 iterations). authors in [12] presented a methodology for classification of ehg records using median frequencies of power spectra and sample entropy. in their study, filtering of the signal using several different frequency sub-bands was tested (0.08–4 hz; 0.3–4 hz; 0.3–3 hz; 0.34–1 hz). the median frequency (frequency value for which the sums of the power above and below it, are equal) of the mean power spectrum, estimated by the adaptive autoregressive (aar) method with recursive least squares (rls) algorithm. also, sample entropy of each signal was calculated. furthermore, clinical information available for the ehg records (age, parity, abortions, weight, hypertension, diabetes, placental position, bleeding in the first and second trimester, funnelling, smoking) was employed. the tested classifiers included knn, lda, qda, svm and dt while smote was employed to generate synthetic data so as to balance the two classes. authors in [13] extracted several time and spectral features from the signal (integrated emg, mean absolute value, simple square integral value, wavelet length, log detector, root mean square value, variance, difference absolute standard deviation value, maximum fractal length, average amplitude change, peak frequency, median frequency). then, feature analysis was performed based on statistical significance, several linear discriminant analysis techniques and gram-schmidt analysis, resulting to the four most discriminating features, which were used as input to a classifier. several artificial nn classifiers were tested, including back-propagation feed-forward nn, levenberg– marquardt feed-forward nn, perceptron linear classifier, radial basis function nn, random nn, voted perceptron and discriminative restricted boltzmann machine. as in [9], the dataset was oversampled smote, to generate 262 pre-term records (using the existing 38 records). cross-validation was applied using the mccv technique (80% holdout, 30 iterations) and the 5-fold technique. authors in [14] presented a methodology for prediction of pre-term delivery based on empirical mode decomposition (emd) combined with wavelet packet decomposition (wpd) of the ehg signals. the signals were filtered with cutoff frequencies of 0.3–3 hz, and emd was performed up to 11 levels to obtain the intrinsic mode functions, which were further analysed with 6-level wpd. from the coefficients obtained after the analysis, eight features are extracted (fractal dimension, fuzzy entropy, interquartile range, mean absolute deviation, mean energy, mean teager-kaiser energy, sample entropy, standard deviation) and particle swarm optimization (pso) method for feature selection was applied. adaptive synthetic sampling approach (adasyn) was applied to increase the number of pre-term signals from 38 to 244. several different classifiers were tested, such as linear discriminant analysis, quadratic discriminant, analysis, decision tree, knn, radial basis, and svm, while 5-fold and 10-fold cross-validation techniques were employed. iii. methodology in this study, the ehg signals are analysed with respect to their spectral characteristics. initially a set of filters are used to filter all channels of each recording to specific frequency subbands, and then the fractional energy of each frequency subband is calculated. also, non-linear characteristics are extracted engineering, technology & applied science research vol. 8, no. 5, 2018, 3310-3315 3312 www.etasr.com tsipouras: uterine emg signals spectral analysis for pre-term birth prediction from the signals. the extracted features are used to train a random forest classifier, to discriminate term and pre-term recordings according to their spectral behaviour. the flowchart of the proposed methodology is presented in figure 2. fig. 2. flowchart of the proposed methodology. a. ehg records the ehg records used in this study are obtained from the tpehg db. all available records (300) are included in the study, and from each record, all three channels (s1, s2 and s3) are analysed. the unfiltered signals are used. b. signal processing initially each channel is filtered with a high pass filter with cut-off frequency of 0.3 hz and subsequently with a low pass filter with cut-off frequency of 4hz. then, to access the spectral characteristics of each ehg record, a set of filters are used to filter each channel to a specific frequency sub-band. several researchers have reported that the uterine electrical activity occurs in the 0hz 5hz frequency band [8], with the majority laying at the <1hz spectrum [9]. furthermore, main respiration rates are <0.33 hz. based on the above, the frequency sub-bands used for this study are: 0.33hz – 0.65hz, 0.65hz – 1hz, 1hz – 2hz, 2hz – 3hz and 3hz – 4hz, selected so as: (i) to exclude respiration rates, (ii) to additionally examine the energy distribution over the 0.33hz – 1hz frequency band, and (iii) to include information from frequency bands > 1hz. the 0.33hz – 1hz band has been the sole focus of several studies [9-11, 13-14], however an attempt to look into this band with greater detail (i.e. by examining sub-bands) has never been attempted in the literature before. c. features extraction 1) fractional energy after filtering all channels in the specific frequency subbands, the energy of each of the filtered signals for all channels, is calculated. based on the energy values, the fractional energy of each frequency sub-bad is calculated: _ ∑ 1 where is the channel (with 1, 2, 3 , is the frequency sub-band (with 0.3 – 0.65 , 0.65 – 1 , 1 – 2 , 2 – 3 , 3 – 4 , is the energy of the channel after filtered in the frequency sub-band and _ is the fractional energy of the channel after filtered in the sub-band. 2) spectral entropy spectral entropy (spen) is defined as the shannon entropy of the power spectrum density. thus, it is calculated for each channel of the ehg signal as follows: ∑ _ ∙ _ 2 is the spectral entropy of the channel and is the number of frequency sub-bands ( 5). 3) approximate entropy approximate entropy (apen) can detect changes in the underlying signal behaviour, which are not directly related to peaks or amplitude variations [15]. is calculated for each sub-band of each channel : ∑ 1 ∑ 3 ∑ 1 4 where is the ehg signal, ∙ is the heaviside step function, ‖∙‖ is the euclidian norm and and are parameters defined as 0.15 and 2 chosen based on the results of previous studies [15] for good statistical validity of apen. 4) features vector for each channel, five fractional energies, spectral entropy and five apen values are calculated. furthermore, a binary feature representing the week of recording is used ( ), being 0 for records obtained before the 26th week of gestation and 1 for records obtained during or after the 26th week of gestation. thus, the feature vector for each record includes 12 features for a single channel, and 34 features for all channels. d. classification the database contains 300 records, with 262 term and 38 pre-term records. since this unbalance between the number of data in the two classes has a major impact in classification algorithms, all researchers employing classification have used data balancing techniques (smote, adasyn, min&max), mainly by creating artificial data from the existing to boost the number of data in the minority class. to address this issue in this study (i) the number of pre-term data is increased by repeating all pre-term data twice, and thus the final number of data used in the classification is 262 term and 76 pre-term, and (ii) an appropriate classifier is selected. classification is performed using the random forest (rf) classifier [16], which is an ensemble learning technique based on the construction of multiple dts using sub-sets of the initial dataset. rf is constructed with 100 dts. the selection of this classifier is based on the basic characteristic of the dataset, i.e. being unbalanced, since rf have been reported to appropriate for handling unbalanced datasets, against many other wellengineering, technology & applied science research vol. 8, no. 5, 2018, 3310-3315 3313 www.etasr.com tsipouras: uterine emg signals spectral analysis for pre-term birth prediction known classifiers (such as neural networks) [17]. furthermore, rf performs two feature selection steps, an initial random selection in the feature bagging step and a subsequent selection of the feature with the highest normalized information gain for each tree node, thus it can cope with the large number of extracted features (34 when all channels are used) without the need of an additional feature selection technique. the 10-fold stratified cross-validation technique has been employed in the classification process of this study. thus, the dataset has been divided into 10 equally sized subsets, and then nine of them are used to train the classifier, and the final for test. special care has been made so as not to have data from the same subject into both training and test phases. thus, both records of preterm data (since each pre-term record is repeated twice), are included in the same fold. iv. results in order to assess the spectral characteristics of each channel of the ehg signals, the features from each channel are initially used individually to predict the term/pre-term pregnancy outcome. the obtained results are in term of sensitivity, positive predictive value (ppv) and classification accuracy, and they are presented in table i. individual channel s3 obtained the best results, however the employment of features from all 3 channel has beneficial effect on the classification results. table i. results channel class sensitivity (%) ppv (%) classification accuracy (%) s1 term 95.00% 98.80% 95.24% pre-term 96.05% 84.88% s2 term 95.04% 99.20% 95.56% pre-term 97.37% 85.06% s3 term 95.80% 99.21% 96.15% pre-term 97.37% 87.06% all term 98.09% 99.23% 97.93% pre-term 97.37% 93.67% v. discussion in the proposed methodology for ehg analysis and term/pre-term classification, a comparison among the results obtained from the features extracted from each channel separately and their combination, is presented. the obtained results indicate that analysing features extracted from all channels (s1, s2 and s3) has a positive impact; although results for term class ppv are almost unaffected and the same applies for the pre-term class sensitivity, the sensitivity of the term class increased by more than 2%, while the ppv result for the pre-term class increased by more than 6%. the same applies for the classification accuracy results, where the value for features from all 3 channels is 97.93%, with the best obtained result for an individual channel being 96.15% (obtained for channel s3). most of the works presented in the literature are based on the analysis of only the s3 channel [911, 13], since it has been reported to be the most informative [8]. this has been confirmed with the findings of this study, since channel s3 produced the best results among individual channel analysis. however, the employment of features from all three channels in the analysis lead to significantly more accurate prediction of pre-term births; this has not been reported in the literature before. furthermore, the 0.33hz – 1hz frequency sub-band has been the focus of several studies [9-11, 13-14], without however attempting to examine the energy distribution within this band. also, frequency bands > 1 hz have been excluded from these studies, although there has been evidence that they contain important information [12]. in this work the frequency sub-bands have been selected so as to lift both of these limitations by: (i) examine in greater detail the most informative sub-band (0.33hz–1hz), and (ii) include several frequency sub-bands > 1hz in order to access information in higher frequencies. a comparative study of similar methods presented in the literature is presented in table ii. all methods have been developed and tested using the same database, being the tpehg db, however having different classification datasets, since different data balancing techniques have been employed. most researches employed classification techniques [9-11, 13-14] while also statistical analysis of the extracted features has also been presented. the proposed methodology compares well with other approaches presented in the literature, obtaining 97.4% sensitivity, 98.1% specificity, 93.7% ppv, 99.2% negative predictive value (npv) and 97.9% classification accuracy. these results are the best reported so far, improving the best previously reported sensitivity [14] by 2.3% and the respective classification accuracy by 1.6%. the differences are higher with other previously reported results (up to 8.4% for sensitivity, 19.1% for specificity, 3.7% for ppv, 9.2% for npv and 10.9% for classification accuracy). however, it should be noted that although the tpehg db was employed in all cases, the classification datasets significantly differ since large number of synthetic data are generated in several cases [9-14], while the size of the classification dataset also varies. the issue of balance in the dataset has been reported by all researchers employing classification techniques [9-11, 13-14], with data balancing techniques being employed in all cases. smote has been employed in several works [910, 12-13] to generate additional pre-term data; 262 pre-term cases are generated from the 38 already available. min&max was employed in [12] to produce 262 pre-term records, while in [14] adasyn was applied to increase the number of preterm signals from 38 to 244. in both cases, the number of generated data is many times larger than the number of existing data (for the pre-term class), thus significantly disturbing the term/pre-term ratio in the initial dataset, which is 12.67% preterm and 87.33% term, closely related to the actual reported percentage [1]. furthermore, the obtained results regarding the pre-term class are mainly (or solely) based in synthetic data. in this study, no synthetic data are generated or employed in the classification. instead, to address the unbalanced dataset issue, all pre-term data are included twice in the dataset (resulting to 76 pre-term records). thus, there are no artificial generated data and the obtained results concern only real cases. also, the term/pre-term ratio has been kept to values close to the actual recorded ratio (22.48% pre-term and 77.51% term records in the classification dataset). furthermore, the folds selection has been made so as this repetition not to disturb the validation procedure by having the same record into both engineering, technology & applied science research vol. 8, no. 5, 2018, 3310-3315 3314 www.etasr.com tsipouras: uterine emg signals spectral analysis for pre-term birth prediction training and test phases; each pair of repeated pre-term data is included in a single fold. table ii. comparative study of methods presented in the literature, using the tpehg db reference channel/ frequency analysis/features analysis/ classification data balancing results validation results [8] all / 0.08-4hz, 0.3-4hz, 0.3-3 hz linear and non-linear/ root mean square, median frequency of the signal power spectrum, autocorrelation zerocrossing, maximal lyapunov exponent, correlation dimension and sample entropy. student’s t-test [9] ch. 3 / 0.34-1hz root mean square, median frequency, peak frequency, sample entropy 9 classifiers/ lda, qda, uncorrelated normal density, polynomial, logistic, knn, dt, parzen, svm smote (generated 262 pre-term records) mccv (80% holdout, 100 iterations) 5-fold cv sensitivity: 96.7% specificity: 90.0% [10] ch. 3 / 0.34-1hz root mean square, median frequency, peak frequency, sample entropy 6 nn classifiers/ backpropagation feedforward nn, levenbergmarquardt feed-forward nn, automatic nn, radial basis function nn, random nn, perceptron linear classifier smote (generated 262 pre-term records) mccv (80% holdout, 30 iterations) 5-fold cv sensitivity: 96.1% specificity: 91.9% [11] ch. 3 / 0.34-1hz root mean square, median frequency, peak frequency, sample entropy 7 classifiers/ sonia network. mlp, fuzzy-sonia, knn, dynamic self organising multilayer network, decision tree, svm min & max (produce 262 preterm records) training: 60%, validation: 25%, testing: 15% (30 iterations) sensitivity: 89% specificity: 91% ppv: 90% npv: 90% accuracy: 90% [12] all / 0.34-1hz 0.3-4hz aar/ median frequency, sample entropy, clinical information (age, parity, abortions, weight, hypertension, diabetes, placental position, bleeding in the first and second trimester, funnelling, smoking) 5 classifiers/ knn, lda, qda, svm and dt smote sensitivity: 96% specificity: 79% accuracy: 87% [13] ch. 3 / 0.34-1hz integrated emg, mean absolute value, simple square integral value, wavelet length, log detector, root mean square value, variance, difference absolute standard deviation value, maximum fractal length, average amplitude change, peak frequency, median frequency 7 nn classifiers/ back-propagation feedforward nn, levenberg– marquardt feed-forward nn, perceptron linear classifier, radial basis function nn, random nn, voted perceptron, discriminative restricted boltzmann machine smote (generated 262 pre-term records) mccv (80% holdout, 30 iterations) 5-fold cv sensitivity: 91%, specificity: 84% [14] ch. 3 / 0.3-1hz emd (11 levels) & wpd (6 levels) / fractal dimension, fuzzy entropy, interquartile range, mean absolute deviation, mean energy, mean teager-kaiser energy, sample entropy, standard deviation 6 classifiers/ linear discriminant analysis, quadratic discriminant analysis, decision tree, knn, radial basis functions, svm adasyn (increase pre-term signals from 38 to 244) 5-fold and 10fold cv sensitivity: 95.1% specificity: 97.3% accuracy: 96.3% this study all / 0.33-5hz fractional energies, spen, apen random forests resampling (increase pre-term signals from 38 to 76) 10-fold cv sensitivity: 97.4% specificity: 98.1% ppv: 93.7% npv: 99.2% accuracy: 97.9% most of the studies presented in the literature experimented with several classification algorithms to identify the most appropriate. in this study rf classifier has been selected, since it has been reported to be able to deal with unbalanced datasets [17]. to validate this selection, several well-known classifiers are additionally tested, including knn, neural networks, svm, nns and deep nns. all alternative classification algorithms presented significantly lower results, with the neural approaches (both classical and deep) constantly classifying samples biased to the larger (term) class. vi. conclusions a methodology for premature birth prediction, based on ehg analysis, is presented in this work. the methodology has been evaluated using a publicly available database, and the obtained results indicate its ability for accurate pre-term labour prediction. the results clearly demonstrate that using engineering, technology & applied science research vol. 8, no. 5, 2018, 3310-3315 3315 www.etasr.com tsipouras: uterine emg signals spectral analysis for pre-term birth prediction information from all 3 recorded channels (instead of only one, which is common practice in the literature) and assessing frequency sub-bands >1hz (usually not included in the analysis in the literature) leads to improved classification accuracy. furthermore, the combination of spectral and non-linear characteristics carries sufficient information for this task. during the validation procedure, only real data were used (no synthetic recordings were included), while the term/pre-term data ratio was kept close to the one reported from who, thus the obtained results are more robust. the methodology achieved higher sensitivity and classification accuracy than the best presented in the literature so far. future work will mainly focus on the application of the methodology on different data, so as to validate its findings into larger and multicentre datasets. references [1] march of dimes, pmnch, save the children, who. born too soon: the global action report on preterm birth. eds 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2017 [15] s. m. pincus, a. l. goldberger, “physiological time-series analysis: what does regularity quantify?”, american journal of physiology, vol 266, pp. h1643-h1656, 1994 [16] l. breiman, “random forests”, machine learning, vol. 45, no. 1, pp. 5–32, 2001 [17] i. brown, c. mues, “an experimental comparison of classification algorithms for imbalanced credit scoring data sets”, expert systems with applications, vol. 39, pp. 3446–3453, 2012 author profile markos g. tsipouras was born in athens, greece, in 1977. he received the diploma degree in computer science from the university of ioannina, greece, in 1999, and m.sc. and ph.d degrees in computer science, in 2002 and 2008 respectively, from the same department. he has participated in several european and national r&d projects as a researcher/developer and he has published 100 papers in peer-reviewed scientific journals and conference proceedings. also, he has published 7 book chapters, and he has co-authored one book. his research interests include digital signal and image processing, medical informatics, artificial intelligence, fuzzy logic, data mining, decision support systems and expert systems. microsoft word 5-bendouba.doc engineering, technology & applied science research vol. 4, no. 1, 2014, 587-590 587 www.etasr.com bendouba et al.: fatigue life prediction of composite under two block loading fatigue life prediction of composite under two block loading abstract— the damage evolution mechanism is one of the important focuses of fatigue behaviour investigation of composite materials and also the foundation to predict fatigue life of composite structures for engineering applications. this paper is dedicated to damage investigation of composite materials under two block loading cycle fatigue conditions. the loading sequence effect and the influence of the cycle ratio of the first stage on the cumulative fatigue life are studied. two loading sequences, i.e., high-to-low and low-to-high cases are considered. the proposed damage indicator is connected cycle by cycle to the s-n curve and the experimental results are in agreement with model expectations. previous experimental research is employed for validation. keywordsfatigue; damage acumulation; composite i. introduction composite materials were first used in aircraft engine rotor blades in the 1960s [1] and their use became more and more important in the construction of several framework in various domain. fatigue behavior of these materials was a subject of thorough and extensive studies, due to the large utilization of these materials in different applications. fatigue life assessment has been described with more than 70 cumulative damage hypotheses [2], the best known is the miner rule [3]. several researchers have investigated the fatigue phenomenon in composite materials [4-9] howe and owen [10] studied the accumulation of damage during cyclic loading with the objective of obtaining useful working relationships of the miner-rule that might be used in design. with the aid of optical microscopy they studied the development of debonding sites and resin cracks in choppedstrand-mat/polyester composites and they suggested that, although debonding did not itself cause reductions in strength, it served to initiate resin cracks which did weaken the material. mandell, et al [11] demonstrated that the data from various fiberglass composite materials in the data base may be characterized by a power law curve fit when they are normalized to the ultimate tensile or compressive strength of the composite. wohler curve for different loading ratios (r), require a correction using the goodman diagram there are many studies of the behavior of composite materials under cyclic loading, and reviews are given in [1214]. approaches in the fatigue problems of composites can be divided into two classes: the wöhler curve method and the damage accumulation theory. the wöhler curve method [15– 19] has been widely employed in engineering to deal with the fatigue issue of composites. however, only under the conditions of low stress and simple stress state, is the method suitable. the damage accumulation theory, which can be applied under complex loading conditions, is a hotspot in the research of the fatigue of composites. several approaches have been proposed, such as the residual strength model presented in [20-24]. ii. some damage models for composite materials the mechanism of damage in composites is one of the important topics in the study of the fatigue behavior of composite materials and also the basis for predicting the fatigue life of composite structures for engineering applications [25]. the fatigue damage of composites is more complex than those of metals. failure of composite materials under cyclic loading can occur following four scenarios:  cracking of the matrix  interfacial debonding  delamination  breaking fibers a. the dzenis model the dzenis model [26] treats the process of fatigue damage in composite materials as a process related to the load. that is to say, the accumulation of damage in the load cycles is time dependent. for this study the effects of variable amplitude, frequency and shape of the cycle on the fatigue behavior of composite materials are considered. the dzenis model is given by the following formula: iji sjjji dtksd )(2, 2 ,    mostefa bendouba mascara university algeria bendoubamos@yahoo.fr abdelkrim aid mascara university algeria aid_abdelkrim@yahoo.com mohamed benguediab djillali liabes university of sidi bel abbes, algeria benguediab_m@yahoo.fr engineering, technology & applied science research vol. 4, no. 1, 2014, 587-590 588 www.etasr.com bendouba et al.: fatigue life prediction of composite under two block loading where ,i js is the laminate compliances, , jk is the correlation functions, ( )j t is the applied stresses and ij sd is the dispersion. b. the kang-kim model kang and kim [27] presented the fatigue behaviour of laminated carbon/epoxy with an impact-induced damage under two blocks tensile loading. to describe this behaviour, the concept of reduction in the strength of the material is introduced. the model is given by the equation: ,1 ,20 re e 1 re 2 0 2 0 2 ,1 0 2 ,2 . . imp imp rr r imp r imp r n n d n n                                where 0  is the ultimate tensile strength, 1  , 2  are the applied stresses, re  is the residual tensile strength, ,1imp n is the number of cycles at 1  , , 2imp r n is the number of cycles at 2  , ,1imp r n is the residual life in the first loading and , 2imp r n is the residual life in the second loading. c. the rognin et al model the authors [28] used experimental data and numerical methods to characterized the composite material. the effects of fatigue are often evaluated by conducting experiments with two blocks loading ( high-low/low-high ). the purpose of the study was to predict, using probability methods, the fatigue resistance of the coupon and show the relationship between fractions accumulation of damage during the experiment. the authors propose a formula for the accumulation of damage as follows: 1 1 m i m r i i m n n d n n            where dr is the fatigue damage variable, ni and ni are respectively the actual applied number of cycles and the number of cycles to failure d. the jen-yang model jen and yang [29] studied experimentally the cumulative damage of carbon nanotubes in composite material under two blocks loading. the content of the chemically modified carbon multiwall nanotubes used for the sample is 0.5% by weight. the effect of loading and the influence of the cycle rate of the first block on the cumulative damage were studied. the authors make their proposal as following: n f s i f s s d s s      where , i s , n s and f s are the magnitudes of stiffness corresponding to the initial cycle, the nth cycle, and the final stable cycle, respectively. e. the proposed model under cyclic stress, structural loading will occur in the field of micro cracks in composite materials and these loads lead to fatigue damage. with an increase in the number of charging cycles, the amount of the loading increases and the damage to the material will accumulate in phase that leads to a change in the microscopic and macroscopic mechanical properties of materials. based on experimental studies [4, 11, 18, 26, 29] we can conclude that the damage evolution of composite material is not linear. during the initial period of loading cracks appear in the matrix and the matrix cracks when it reaches saturation, fiber breakage occurs, and the damage is growing rapidly in this material as we can as shown in figure 1. fig. 1. the evolution of fatigue damage in a unidirectional composite material. according to the mechanisms of fatigue damage of composite materials, findings and observations from previous models, a new comprehensive model of fatigue damage is presented to describe the rule and stiffness degradation of composite materials for two blocks loading, as follows: 1 2 2 1 1 1 1                               ff n n n n u    where 1 n is the cycle number corresponding to 1  , 2 n is the cycle number corresponding to 2  , 1f n is the number of cycles to failure corresponding to 1  , 2f n is the number of cycles to failure corresponding to 2  and u  is the ultimate tensile strength. engineering, technology & applied science research vol. 4, no. 1, 2014, 587-590 589 www.etasr.com bendouba et al.: fatigue life prediction of composite under two block loading iii. application and validation of the proposed model the proposed model is verified using experimental results from the literature. these results are consisted of two-block loading sequences with transitions from low to high (l–h) and high to low (h–l) load levels. plumtree et al [30] conducted tests for fatigue in cyclic tests on [±45]2s angle ply carbon– epoxy specimens using stress ratios with an r (minimum/ maximum stress) of 0.1 and -1.0. after a given number of cycles under known loading conditions, the cyclic stresses were changed and the test continued to failure under the new conditions. the loading conditions, the test results reported in [30], the theoretical predictions of the proposed model and miner’s rule are given in table i for increasing and decreasing block types of loading respectively. table i. experimental results and the predictions of the proposed model. 1  (mpa 2  (mpa) 1 n 1f n 1f n 2 n (exp) 2n (predicted) 2 n (miner) 105 64 675 1406 196807 108244 158733 102340 96 58 511 4258 410417 578688 408543 361167 101 61 511 2222 285291 407966 276482 219674 106 64 511 1246 199721 131816 171820 117836 110 66 511 763 155130 141168 87982 51193 64 110 85960 199907 764 1153 744 435 64 108 85960 199907 972 846 947 554 64 109 85960 199907 866 745 844 494 according to the experimental data [30], the results show that the difference between the predicted residual fatigue life and the experimental data are acceptable because of the big scatter of fatigue life and most points are within 1.5 times range as shown in the figure 2, on the other side predicted life calculated by the miner’s rule are 2.5 greater than the experimental results in two cases. the predicted residual fatigue life by the proposed algorithm is in good agreement with the experiment, considering the bigger scatter of composites. fig. 2. experimental and predicted residual fatigue lives of laminates table ii compares the experimental results reported in [31] and the predictions of model proposed in this paper. as shown in figure 3, the majority of the results calculated by the proposed prediction model is conservative, as they are in the neighborhood of the experimental results. table ii. experimental results and the predictions of the proposed model. 1  (mpa 2  (mpa) 1 n 1f n 1f n 2 n (exp) 2n (predicted) 2 n (miner) 315 340 87200 115150 8800 520 343 2136 315 340 87000 115150 8800 150 345 2151 315 340 86300 115150 8800 1408 355 2205 315 340 57700 115150 8800 1750 827 4390 315 340 57550 115150 8800 2280 830 4402 315 340 40300 115150 8800 2027 1226 5720 315 340 28700 115150 8800 3320 1584 6607 315 340 26500 115150 8800 2640 1666 6775 315 340 25300 115150 8800 2464 1713 6867 315 340 17650 115150 8800 6170 2068 7451 315 340 17000 115150 8800 38140 2104 7501 315 340 13000 115150 8800 14300 2356 7807 315 340 12500 115150 8800 24030 2392 7845 340 315 8500 8800 115150 15250 235 3926 340 315 7480 8800 115150 17060 1096 17273 fig. 3. experimental and predicted residual fatigue lives of laminates in this investigation, the relative error of prediction represents the relative difference between the experimental and calculated lines using the proposed model and the miner’s rule. the rep is defined by : exprimental calculated exprimental n n rep(%) 100 n x   (6) the corresponding predictions of the proposed model and those calculate by miner’s rule are gathered and presented in figure 4. it is clear in this figure that the predictions are very good. all the relative errors in the proposed model are less than 10% except for one load condition, which leads to an error of engineering, technology & applied science research vol. 4, no. 1, 2014, 587-590 590 www.etasr.com bendouba et al.: fatigue life prediction of composite under two block loading 28.42% (decreasing blocks). it should also be noticed that the rep in the absolute value calculated by the proposed model are lower than the rep calculated by miner’s rule. fig. 4. relative errors of prediction for calculate lives using the proposed model and miner’s rule iv. concusion the paper presents a non-linear damage accumulation model to predict the remaining fatigue life of the second stage. the use of this model is simple, it has no parameters to be determined, and requires only the knowledge of the s-n curve. a comparison between our proposition and the miner’s rule was made and some deviation is evident. the two-level loading examples show that the model can predict residual fatigue life of composite materials quite well. the theoretical analyses are well in conformance and are in good agreement with the experimental data for all materials tested in this investigation for the residual life as well as for the cumulative damage. from this viewpoint, we hope that our model may eventually find broad use. the proposed model may be extended to complex random loading. v. reference [1] d. h. middleton, composite materials in aircraft structures, longman scientific & technical, harlow, 1990 new york, j. wiley, 1990 [2] a. fatemi, l. yang, “cumulative fatigue damage and life prediction theories: a survey of the state of the art for homogeneous materials”, international journal of fatigue, vol. 20, no 1, pp. 9–34, 1998 [3] m. a. miner, “cumulative damage in fatigue”, journal of applied mechanics, vol. 12, pp.159-164, 1945 [4] a. varschavsky, “the matrix fatigue behaviour of fibre composites subjected to repeated tensile loads”, journal of materials science, vol. 7, no. 22, pp. 159-167, 1972 [5] k. reifsnider, “fatigue behavior of composite materials”, international journal of fracture, vol. 16, no. 6, pp. 563-583, 1980 [6] z. hashin, c. laird, “cumulative damage under two level cycling: some theoretical predictions and test data”, fatigue & fracture of engineering materials & structures, vol. 2, no. 4, pp. 345-350, 1979 [7] m. aslam, s. jeelani, “prediction of cumulative fatigue damage”, journal of materials science, vol. 20, no. 9, pp. 3239–3244, 1985. [8] a. poursartip, p.w.r. beaumont, “the fatigue damage mechanics of a carbon fibre composite laminate: ii-life prediction”, composites science and technology, vol. 25, no 4, pp. 283-299, 1986 [9] t. adam, g. fernando, r. f. dickson, h. reiter, b. harris, “fatigue life prediction for hybrid composites’, international journal of fatigue, vol. 11, no 4, pp. 233-237, 1989 [10] m. j. owen, r. j. howe, “the accumulation of damage in a glassreinforced plastic under tensile and fatigue loading”, journal of physics d: applied physics, vol. 5, no. 9, 1972 [11] j. f. mandell, h. j. sutherland, r. j. creed, a. j. belinky, g. wei, “high cycle tensile and compressive fatigue of glass fiber-dominated composites”, astm, sixth symposium on composites: fatigue and fracture, denver, colorado, 1995 [12] k. l. reifsnider, “life prediction analysis: directions and divagations”, 6th international conference on composite materials (iccm-vi), london, england, 1987 [13] p. p. oldyrev, v. p. tamuzh, "multicycle fatigue of composite materials", zhurnal vsesoyuznogo khimicheskogo obshchestva imeni d.i. mendeleeva, 24, no. 5, 545552, 1989 (in russian). 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yao, “a fatigue damage model of composite materials”, international journal of fatigue, vol. 32, no. 1, pp. 134-138, 2010 microsoft word etasr_v13_n3_pp10814-10819 engineering, technology & applied science research vol. 13, no. 3, 2023, 10814-10819 10814 www.etasr.com shamsan: spectrum sharing of haps and fixed link in millimeter waves spectrum sharing of haps and fixed link in millimeter waves zaid ahmed shamsan department of electrical engineering, college of engineering, imam mohammad ibn saud islamic university, saudi arabia shamsan@ieee.org (corresponding author) received: 9 april 2023 | revised: 20 april 2023 | accepted: 22 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5937 abstract a high altitude platform system (haps) is an emerging technology that can potentially bring connectivity to areas that are not partially or totally covered by cellular networks. however, allocating certain frequency bands for the haps alongside wireless fixed service (fs) imposes some restrictions on operating the haps systems to ensure no interference occurs between the two systems (haps and fs). this paper presents an analytical study of the spectrum sharing between the haps and the fs in millimeter waves, namely in 38and 47-ghz bands. some potential and significant interference scenarios have been applied in order to investigate the spectrum-sharing situations in urban and suburban areas. the carrier to interference plus noise ratio (cinr) has been adopted as the main criterion to assess the performance of the haps. it is found that the haps and fs systems can simultaneously share the 38and 47-ghz bands with some restrictions to haps altitude, allowable cinr, and location of the haps user. these restrictions differ depending on the area coverage type. keywords-interference; cinr; haps; urban; suburban; signal power; fs i. introduction recently, the high altitude platform system (haps) has attracted much attention, as an emerging technology, due to its integration with 5g services, internet of things (iot) support, temporary coverage for events and tourist hotspots, emergency communications, terrestrial site backhaul, and disaster recovery infrastructure without any ground-based network [1, 2]. unlike satellites, hapss are aircrafts that fly or float in the stratosphere, typically at altitudes of around 17-22km. haps systems could be high-altitude free-floating balloons, dirigibles, or powered fixed-wing aircrafts that employ either solar power or an onboard energy source. all haps systems can be manned or unmanned aeronautical platforms however in the stratosphere they are unmanned. a haps runs in a harsh medium in which solar radiation is high and temperatures may reach very low levels, while the system is prepared to be airborne for long time periods [3]. there are two categories of hapss authorized to operate depending on the type of service they provide, i.e. fixed or mobile services. in the case of systems that are intentionally designed to add coverage to fixed locations on the ground, the platform must have its own power in order to remain "on station" at a specific location [4]. international telecommunication union (itu) radio regulations determined new frequency bands (according to wireless radio conferences (wrc)) to be used for the operation of the two categories of haps. the spectrum frequency bands that have been allocated to fixed haps services include 38ghz (approved in wrc-97) and 47ghz (approved in wrc-19) which are globally allocated to haps, [5, 6]. in addition, these two bands are also allocated to wireless fixed-link service (fs). such a situation of spectrum sharing creates a potential for intersystem interference between the haps and fs which can lead to the deterioration of the performance of both systems [7, 8]. thus, this study investigates the spectrum sharing feasibility between the haps and the fs using the carrier to interference plus noise ratio (cinr) as a standard criterion to ensure that both systems can safely share the allocated spectrum. in general, the role of spectrum sharing studies is to investigate the ability of various wireless systems co-existing in a geographical area to share a certain frequency band with no harmful interference. interference power created from a wireless system to another can be categorized as either cochannel interference or adjacent channel interference [8]. essentially, adjacent channel interference can be mitigated using a suitable filter, however, co-channel interference is the most dangerous one, and is the topic of this paper. it can be mitigated by increasing the distance between the interferer and the interfered systems. this procedure is done because it leads to increase the interference power attenuation and then reduce its impact on the other system. in this regard, several studies addressed spectrum sharing between haps and other wireless systems in different frequency bands [9-13]. in [9, 10], the authors investigate the spectrum sharing between haps and fixed satellite service stations at 5850–7075mhz. they determined the interference coupling loss between the systems [9] and statistically modeled the haps gateway link and fixed satellite service interoperability at 5850–7075mhz [10]. in [11], the downlink performance of wimax from haps and engineering, technology & applied science research vol. 13, no. 3, 2023, 10814-10819 10815 www.etasr.com shamsan: spectrum sharing of haps and fixed link in millimeter waves terrestrial base stations at 3.5ghz was simulated. the coexistence of haps and terrestrial systems using gigabit links to serve dedicated users was considered in [12] at 28ghz. in [13], spectrum sharing of haps and fixed satellite service (fss) in the frequency range of 5850–7075mhz was investigated. the contribution of this paper is the exploration of the spectrum sharing status between the haps and the fs in millimeter waves by assuming intersystem interference scenarios between the two systems within urban and suburban areas and with various haps altitudes and different terrestrial distances to connect the fs link. these interference scenarios have not been studied in the literature at millimeter waves [14, 15], namely 38 and 47ghz. consequently, some recommendations that ease spectrum sharing are proposed. ii. spectrum sharing scenarios spectrum sharing studies assume intersystem interference scenarios between systems that use the same frequency band and operate in the same geographical area. the general intersystem interference situation considered in this paper is illustrated in figure 1. the haps service is proposed to share the same frequency band (38 or 47ghz) with the fs system. the haps coverage area in figure 1 is assumed to be either urban or suburban. the haps platforms are manufactured to suit the stratospheric conditions [16] and are situated at an altitude of 17-22km. the reason behind this high altitude selection is that the wind speed at this height is quite low and suitable for the operation of haps [17]. the haps user receives a desired signal from the haps station while at the same time it receives undesired signal (interference) from the fs link. the haps user can move along the terrestrial path between the fs transmitter (tx) and fs receiver (rx), which is 100km, to examine the interference impact on the haps user. in addition, the haps station altitude changes between 17 and 22km to investigate the effect of different height on the spectrum sharing situations in each case. fig. 1. the general hapsfs interference scenario. the signal propagation from the haps station to its ground users was implemented in this paper by the line-of-sight (los) model for all selected locations in the coverage area of haps which has a radius of 50km. on the other hand, the terrestrial propagation environment of the fs link is characterized by two propagation models which are the free space path loss model and the clutter loss propagation model. the latter is explained below. to make sure that both systems can operate concurrently with no interference, cinr was adopted to assess the performance of the haps user. iii. interference calculation method in spectrum sharing, the distance/physical path separation plays a significant role in determining the possibility of sharing the same frequency band (co-channel spectrum sharing). the separation distance defines the optimum distance that can provide the required protection criteria level. therefore, it plays a major factor in determining the amount of interference to the victim receiver (user), where the increase in distance between the fs transmitter and the user leads to attenuation of the interfering power and vice versa. a. downlink received power the downlink received power, �� , or the desired signal (dbw) that arrives to the haps user from the haps system in the sky can be expressed as the carrier c [18]: �� = � = �����, �� + ��, �� − ��� (1) where �����, �� is the effective isotropic radiated power (dbw) of the haps station in the sky (the transmitter), ��, �� is the haps user antenna gain (dbi) in the ground (the receiver), and ��� is the path loss in the free space (db). to estimate the service area of the haps transmitter, we calculate the �����, �� as follows: �����, �� = ��, �� + ��, �� (2) where ��, �� is the haps transmitter power (dbw), and ��, �� is the haps transmitter antenna gain (dbi). the loss due to the free space propagation between the haps transmitter and the user can be expressed as: ������� = 32.45 + 20 log"# $ + 20 log"# % (3) where $ is the operating frequency (mhz), and % is the distance (km) between the sky haps station and the land station of the haps antenna (the haps user). b. interference power the interference due to the fs link into the haps system (the land user) is expressed as: � = �����,& + ��,& − ��� − �' (4) where �����,& is the effective isotropic radiated power (dbw) of the fs transmitter (tx), ��,& is the haps user antenna gain (dbi), ��� is the path loss due to free space propagation (db), and �' is an additional loss due to protection from local clutter (db). the additional loss is given by [19]: �' = 10.25 )*+, -1 − tanh 26 ' '4 5 − 0.62565 (5) where �7 is the distance from the nominal clutter point to the received antenna (km), ℎ is the received antenna height (m), and ℎ9 is the nominal clutter height (m). these values are tabulated in table i for both urban and suburban areas. engineering, technology & applied science research vol. 13, no. 3, 2023, 10814-10819 10816 www.etasr.com shamsan: spectrum sharing of haps and fixed link in millimeter waves table i. nominal clutter heights and distances clutter (groundcover) category nominal height :; (m) nominal distance <= (km) suburban 9 0.025 urban 20 0.02 c. spectrum sharing feasibility criterion in order to examine whether the two systems under consideration can share the same frequency band, the cinr (db) is taken into account. it is expressed as: ��>� = � − �� + >� (6) where � is the received power (dbw), � is the interference power (dbw), and > is the noise received power (dbw). it is worth mentioning that the summation of i+n is done linearly first and then it is converted into decibel. the noise of the receiver, n, (dbw), can be expressed as [18]: > = ? + @ − �a, �� − bc (7) where ? is the boltzmann's constant, t is the system noise temperature (dbk), �a, �� is the haps receiver bandwidth (dbhz), and bc is the receiver noise figure, in db. iv. system specifications the main parameters for the haps and fs systems are shown in tables ii and iii for both the frequency bands considered [18, 20-22]. in table ii, the parameters are mentioned for urban area coverage (uac) and suburban area coverage (sac) [23] which are categorized by clutter height as shown in table i [15, 20]. table iii [21, 22] shows the fs system parameters. table ii. downlink path from haps to the user parameters value uac sac uac & sac frequency (ghz) 47.0 47.0 38-39.5 channel bandwidth (mhz) 11.0 11.0 11 tx power (dbw) 1.3 1.3 antenna gain (dbi) 27.0 27.0 37 hybrid/waveguide loss (db) 0.5 0.5 eirp (dbw) 27.8 27.8 22 atmospheric loss (db) 2.3 5.2 received antenna gain (dbi) 23 38 49.8 receiver antenna hight (m) 1 1 1 polarization loss (db) 0.5 0.5 table iii. fixed service parameters (to haps user) parameters value frequency (ghz) 47.0 38 maximum antenna gain (dbi) 46 47 maximum transmitter power (dbw) -11 -15 maximum eirp (db(w/mhz)) 28 32 receiver bandwidth (mhz) 2 3.5 receiver noise figure (db) 11 7.5 interference criteria (db(w/mhz)) -143 -143 haps user height (m) 4 4 v. results and discussion the findings from this study depend on several factors such as haps altitude, frequency band, type of area coverage, fs antenna height, etc. for instance, haps stations with different altitudes will provide different path losses affecting the spectrum sharing feasibility. similarly, each area, either uac or sac, has different clutter characteristics that can introduce a certain loss to the interfering signal as shown in table i [18]. moreover, the height of the fs antenna may be varied to examine the impact of interferer power on the haps user (the receiver). in this section, the physical separation distances between the haps transmitter and the haps receiver are considered. various situations of the haps carrier signal and cinr at the haps user were simulated over different haps altitude levels, from 17 to 22km for all selected locations in the coverage area of haps which has a radius of 50km. a. spectrum sharing in urban areas an urban area refers to a town, city, or suburb. these areas are highly developed and have a high density of infrastructure, including houses, commercial buildings, roads, bridges, and railways. the received power in urban area scenarios for 38 and 47ghz frequency bands was simulated. in figure 2, the received powers for 38ghz at the haps user are calculated for various haps transmitter altitudes. the values of the received power depend on the height of the haps transmitter and the location of its user. for instance, when the haps user is at the center of haps coverage (0km) and the haps station altitude is 17km, the power received is maximum and is -76.9dbw, while the received power is minimum (-79dbw) at the height of 22km. on the other hand, when the haps user is at the edge of the haps coverage area (50km), the maximum received power is -86.7dbw (at 17km) and the minimum received power is -87dbw (at 22km). these results and their curve shape agree with the results of figure 4 in [24]. figure 3 shows the cinr levels at the haps user for the 38ghz-urban area scenario, where the carrier represents the power received (that transmits voice, video, data, or a combination of the three) from the haps in the sky to the user on the ground (downlink). for a cinr of 19db for the haps user, the minimum distance from the fs to the haps user which is required to prevent interference is 50.4, 52.6, 55.6, 58.6, 61.6, and 64.7km for haps transmitter heights of 17, 18, 19, 20, 21, and 22km, respectively. fig. 2. the received power at the haps user for urban area using 38ghz. engineering, technology & applied science research vol. 13, no. 3, 2023, 10814-10819 10817 www.etasr.com shamsan: spectrum sharing of haps and fixed link in millimeter waves fig. 3. the cinr at the haps user for urban area using 38ghz. figure 4 displays the received powers in the urban area for an operating frequency of 47ghz. the received power directly under the sky haps station ranges between -102.4 and -104.8dbw, while it is -112.3 to -102.7dbw at the coverage edge of the haps system. when using the frequency of 47ghz, the power received is lower than that in the case of 38ghz because the higher frequency of 47ghz severs higher attenuation, leading to increased power loss of the 47ghz system. moreover, it can be noticed in figure 5 that the haps system only can work using 47ghz, if it is elevated up to a height of 17km above the earth surface because the cinr at the haps user is approximately 19db, whereas, if the haps is raised to altitudes more than 17km, the received power at the haps user from the haps transmitter will be weak and the fixed service will cause interference enough to disturb the haps user receiving mode where the cinr is always less than 19db. as mentioned above, the haps user can work only for a minimum cinr of 19db (the haps interference protection criteria), but this is not the case (as shown in figure 5) for altitude levels greater than 17km where the two systems cannot run concurrently because the required interference protection criteria is not realized. fig. 4. the received power at the haps user for urban area using 47ghz. fig. 5. the cinr at the haps user for urban area using 47ghz. b. spectrum sharing in suburban areas suburban areas are mixed-use or residential areas. these areas are often a large and active community of employed people. in some metropolitan areas, they are residential subdivisions within commuting distance of the city. in figure 6, the received power levels are similar to that in figure 2 related to the urban area due to the fact that the carrier received in the suburban area is affected by the same factors considered in the urban area. this means that the received power from haps station is the same even if the terrain is different because the connection between the haps transmitter and receiver is only under los condition for both cases. thus, when the haps user is at the center of the haps coverage (0km: the haps user is directly under the haps sky station), the maximum power received is -76.9dbw for an altitude of 17km and the minimum is -79dbw for 22km. when the haps user is at the edge of the coverage area (50km), the maximum received power is -86.7dbw for a height of 17km and the minimum is about -87dbw for a height of 22km. in figure 7, the values of the cinr in the suburban area are smaller than the values shown in figure 3 for frequency sharing in urban areas when using 38ghz. this difference in the cinr is a result of the effect of the clutter loss that is high in urban areas. urban areas include high-rise buildings and many obstacles which all play a significant part in blocking the interference signals, which in turn leads to an increase in the values of cinr at the haps user. for a cinr of 19db for the haps user in figure 7, the minimum distance from the fs to the haps user which is required to prevent interference is 63.6, 66.7, 70.7, 74.8, 78.8, and 81.9km for haps transmitter height of 17, 18, 19, 20, 21, and 22km, respectively. spectrum sharing was also investigated when the two systems use 47ghz. this scenario is shown in figures 8 and 9. in figure 8, the received power at the haps user is calculated. it is found that the received power in the suburban areas is higher than that in the urban areas due to the difference in the values of the atmospheric loss. the receiver antenna in the suburban area has a higher gain than that in the urban areas. in addition, the cinr in the suburban areas (see figure 9) is also higher than that in the urban areas for haps altitudes of 17, 18, engineering, technology & applied science research vol. 13, no. 3, 2023, 10814-10819 10818 www.etasr.com shamsan: spectrum sharing of haps and fixed link in millimeter waves and 19km. however, the two systems cannot operate concurrently for haps altitudes of 20, 21, and 22km due to the weak signal arrived at the haps user which in turn makes the cinr smaller than 19db. these results are tabulated in table iv which shows the required distance between the fs and haps user for a cinr of 19db for different haps altitudes in urban and suburban areas. it is worth mentioning that more flexible cinr values can reduce the required distance to achieve spectrum sharing between the systems. fig. 6. the received power at the haps user for suburban area using 38ghz. fig. 7. the cinr at the haps user for suburban area using 38ghz. table iv. required distance between the fs and haps user for cinr= 19db haps altitude (km) required distance (km) urban areas suburban areas 38 ghz 47 ghz 38 ghz 47 ghz 17 50.38 ≈ 100 63.64 90.91 18 52.61 > 100 66.67 95.96 19 55.56 > 100 70.71 ≈ 100 20 58.60 > 100 74.75 > 100 21 61.62 > 100 78.79 > 100 22 64.65 > 100 81.82 > 100 fig. 8. the received power at the haps user for suburban area using 47ghz. fig. 9. the cinr at the haps user for suburban area using 47ghz. vi. conclusion spectrum sharing can be a solution to spectrum scarcity, enabling various wireless systems access the same frequency bands. this paper presents a spectrum sharing study between the haps and fs in the frequency bands of 38 and 47ghz. various spectrum sharing scenarios were investigated in both urban and suburban areas. cinr was used to assess the feasibility of spectrum sharing between the haps and fs systems. the findings showed that the cinr values are better for the lowest haps altitude of 17km and the lower spectrum frequency band of 38ghz. spectrum sharing is more feasible in urban than in suburban areas because urban areas are crowded with buildings and obstacles which act as blocking objects against interference. the findings of this paper can help service providers and communication regulators to provide more efficient uses of the frequency spectrum. acknowledgment the author extends his appreciation to the deanship of scientific research, imam mohammad ibn saud islamic university (imsiu), saudi arabia, for funding this research work through grant no. 221414014. engineering, technology & applied science research vol. 13, no. 3, 2023, 10814-10819 10819 www.etasr.com shamsan: spectrum sharing of haps and fixed link in millimeter waves references [1] z. wei et al., "spectrum sharing between high altitude platform network and terrestrial network: modeling and performance 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[24] s. c. arum, d. grace, and p. d. mitchell, "a review of wireless communication using high-altitude platforms for extended coverage and capacity," computer communications, vol. 157, pp. 232–256, may 2020, https://doi.org/10.1016/j.comcom.2020.04.020. microsoft word 38-3746_s1_etasr_v10_n5_pp6374-6379 engineering, technology & applied science research vol. 10, no. 5, 2020, 6374-6379 6374 www.etasr.com gotekar et al.: a single phase grid connected pv system working in different modes a single phase grid connected pv system working in different modes pritee s. gotekar electrical engineering department priyadarshini college of engineering nagpur, india p_somkuwar@yahoo.com s. p. muley electrical engineering department, priyadarshini college of engineering, nagpur, india muleyshubhada68@gmail.com d. p. kothari gaikwad patil group of institutions nagpur, india dpkvits@gmail.com abstract-the current grid standards for the single-phase residential pv system expect it to operate at maximum power point tracking (mppt) mode under normal operating conditions and to maintain the voltage profile whenever a grid fault occurs. the proposed system supplies power to the load under stable conditions and the pv system works in mppt mode. when the fault occurs at the point of common coupling (pcc) and the voltage is reduced, the proposed controller maintains the voltage profile by injecting the current fed by the current controller at the pcc. the controller shifts from mppt to the faulty mode and maintains voltage as per grid requirements. during islanding conditions, the pv system successfully caters to the requirements of the load by shifting the control from mppt to islanding mode. when the pv system is in operation the power quality is enhanced. keywords-maximum power point tracking (mppt); photovoltaic (pv) systems; perturb and observe (p and o); point of common coupling(pcc) i. introduction due to the incessant reduction of the photovoltaic (pv) module price and to the increase of the pursuit for eco-friendly energy systems, there is a spurt in the demand for solar pvs. the future pv systems would have to fulfill the requirements for the generation closer to the consumption points [1, 2]. the pv modeling technique and implementation of fuzzy based mppt systems to track maximum power efficiently is explained in [3-4]. the precise control of the duty cycle with respect to various atmospheric conditions is obtained in [5]. a peak current controller strategy is used to generate the gate pulses of semiconductor switches which control both active and reactive powers [6-8]. pv systems in the future should perform a number of functions like reactive power control, maximum power point tracking (mppt), islanding detection, power quality improvement and fault ride-through (frt) capability [9-11]. phase, amplitude, and frequency of the grid voltage are key information for the operation of inverter systems connected to the grid. in grid-connected inverters, the correct and accurate detection of the phase angle, amplitude and frequency of the grid voltage are essential in ensuring the correct generation of reference signals and to meet future standards, which can be estimated using a phase-locked loop (pll) [12-13]. power electronic devices draw large amounts of reactive power and inject harmonics in the network [14]. a multilevel single phase inverter using pi controller is used to improve power quality in [15]. voltage sag occurrence is a common issue which may cause unnecessary tripping in the case of a single phase system that is working in grid connected or islanded mode [16-17]. to address the reactive power control issue caused by the use of loads which affects the current being drawn from the source, a pv system is used in [18]. in islanding mode, the amplitudes and waveforms of load voltages are maintained sinusoidal by the voltage controller. the transfer of modes (islanded to grid connected and vice-versa) is implemented using the synchronization controller as per the accessibility of the grid [19-21]. the objective of the proposed research is to design a single phase grid connected pv system. the key contributions of this paper are: • the design of a pv system depending upon the load requirements using perturb and observe (p and o) for mppt. • a dc-dc boost controller is proposed to maintain the output voltage constant. • the implementation of a pv system controller capable to supply active and reactive power during normal operating conditions. • the proposed controller injects reactive current when fault occurs at the point of common coupling (pcc) during voltage sag conditions. • the pv system needs to operate in islanded mode. ii. system configuration figure 1 shows the block diagram of the system under consideration. the pv system is configured as dual stage with pv system connected to the pcc through dc-dc boost controller and inverter with the grid. this system operates in two modes, grid connected and islanded mode. the block diagram includes the pv array, the boost converter, an inverter, and the power control system [10]. corresponding author: pritee s. gotekar engineering, technology & applied science research vol. 10, no. 5, 2020, 6374-6379 6375 www.etasr.com gotekar et al.: a single phase grid connected pv system working in different modes fig. 1. block diagram of the system. iii. reactive power control under normal conditions, the pv system is operating in mppt mode in order to supply as much energy as possible to the grid. as per the grid requirements, when fault occurs at pcc, the pv inverter should inject reactive current to bolster up the grid voltage. the control system consists of the mppt, an orthogonal signal generator (osg) unit, controllers to generate current reference generation, and a pwm generation block. as the inverter output voltage is nonsinusoidal, a lowpass filter is connected between the inverter and the grid. igα and igβ represent the grid currents in the ‘αβ’ frame and vgα and vgβ represents grid voltage in the same frame. equations (1) and (2) represent active power (p) and reactive power (q) [11]. the current references are generated using pi controllers p = �� � v� ∗ i� + i� ∗ v� � (1) q = �� � v� ∗ i� − i� ∗ v� � (2) a. pv system a pv system consists of pv modules connected in series and in parallel depending upon dc system voltage and power. the peak value of product of voltage and current represents the maximum power point (mpp) pmax. to extract maximum power from the given irradiance conditions the solar module should always be operated within that region. the implemented technique to extract that point is p and o. a 2kw pv system is considered. the system parameters are indicated in table i. table i. system parameters sr no device components 1 dc link capacitor c=2500µf, reference voltage=350v. 2 boost converter l=2.9mh, c=70µf, switching frequency =5khz 3 lc filter l=0.1mh, c=100µf 4 linear load non linear load 1kw and 500 var 1kw and 500 var 5 source 230v (rms), 50hz b. boost converter it is used to step up the input voltage and mpp. the main equations used for analysis are (3)-(5) [2] and the nomenclature is given in table ii. m = ���� = �(���) (3) l = ���∗���∆! (4) c �# = $%&(�∗(ɷ ∗�%& ∗∆�%&) (5) where m is the modulation index, vin is the input voltage, l is the boost inductance and c is the capacitance of the boost converter. c. synchronisation to assist the computation of active power (p) and reactive power (q) and for proper grid synchronization, the osg is used. p and q are calculated by using the osg system whereas t/4 delay pll is considered in this research. the osg for single phase system is indicated in figure 2 and the simulink model is shown in figure 3. fig. 2. orthogonal signal generation for a single phase system. the reactive power injection depends upon: i( � + i) � = i* � ≤ imax (6) the minimum reactive current (iq) to be injected to the grid is given by (7). active power is restored to maintain the frequency limits, based on the peak value of (8). iq = 01 2 13 deadband , 0.9 ≤ �� �= ≤ 1 2x ���� x i*, 0.5 ≤ ���= ≤ 0.9 i* , 0.1 ≤ ���= ≤ 0.5 (7) ip = 01 2 13 im , 0.9 ≤ �� �= ≤ 1 @i* − (2 x ���= x i*)�, 0.5 ≤ ���= ≤ 0.9 0, 0.1 ≤ ���= ≤ 0.5 (8) the quality of power to be injected to the grid depends on the current controller. the exquisite design of filters and selection of harmonics compensators is prerequisite of power quality. the gain of the proportional resonant (pr) and harmonic compensator (hc) control in the bc reference frame is shown in (9) and (10): � g$e(s)� = k$ + hijjkl (ɷm )k (9) � gn#(s)� = hiojjkl (pɷm )k (10) engineering, technology & applied science research vol. 10, no. 5, 2020, 6374-6379 6376 www.etasr.com gotekar et al.: a single phase grid connected pv system working in different modes fig. 3. osg transformation and gpr+hc controller. gp(s) gq(s) ig 1 1 ls vg ig p* p q q* vgα vgβ lcfs 2 +1 vg 2 α + vg 2 β gpr(s) +ghc(s) 1+1.5s fig. 4. control diagram of single phase grid connected pv system based on pq theory. fig. 5. simulink model of the pv system connected to load and grid. table ii. nomenclature symbol description symbol description proportional gain v� voltage of the grid l inductance of the dc-dc boost converter ton time during which the semiconductor switch of the boost converter is on ppv power output of the pv system during faulty conditions v grid instantaneous voltage imax maximum power point current from pv iq reactive current requirements of the grid ip active current requirements of the grid pmpp maximum power output of the pv system i� current of the grid in nominal inverter current vn nominal grid voltage k�p harmonic compensator gain c�# dc link capacitance d duty cycle of the dc-dc boost converter ∆i allowed current ripple (10%) p* reference active power pdc average power of dc link q* reference reactive power vdc average voltage of dc link ɷ frequency of grid (r/s) ∆vdc amplitude of voltage ripple c capacitance of the filter g$�s� pi controller for active power g)�s� pi controller for reactive power engineering, technology & applied science research vol. 10, no. 5, 2020, 6374-6379 6377 www.etasr.com gotekar et al.: a single phase grid connected pv system working in different modes gpr(s) is the transfer function of pr controller while ghc(s) is the transfer function of the harmonic compensator. the combination of pr and hc is involved to obtain a better control during dynamic conditions when operating mode switches from mppt to low voltage ride through. the current controller is shown in figure 4 and the simulink model is shown in figure 5. iv. simulation results system parameters are given in table ii. figure 6 shows the p-v curves for the given system. it is observed that mpp changes with change in irradiance. it is shown that the grid is supplying power to the load until t=1s. at this instant, a fault occurs and the pv system completely starts supplying power to the load. various conditions were considered for the simulations in simulink. fig. 6. pv curves for varying irradiance a. load supplied by source the simulation was run for 1.5s. figure 7 shows the dc link voltage across a capacitor which is maintained constant at 350v. initially up to 1s only the grid was acting as a source, supplying power to the linear load as shown in figure 8. power supplied to the linear and nonlinear load is shown in figure 9. fig. 7. dc link voltage fig. 8. active and reactive power of linear load. fig. 9. active and reactive power of linear and nonlinear load. b. load supplied by the source and the pv system a combination of linear and nonlinear load is supplied up to 1s to the source. due to the occurrence of fault at pcc at t=1s, when the source fails to fulfill the requirements of the load, the pv system starts supplying power after t=1s. the simulation is run for 1.5s as shown in figure 10. fig. 10. load supplied by the source and the pv system. start read v vn,in,vpv, ipv if 1.1≥vg ≥ 0.9 vn p* = pmpp q* = 0 p* = ppv q* = 1 * v * iq 2 p* = pmpp q* = 0 if 0.9 ≥ vg≥ 0.5 vn if 0 <vg˂ 0.5 vn if vg = 0 p* = 0 q* = 1 * v * iq 2 stop yes yes yes yes no no no no lvrt mppt islanding ,vg fig. 11. flowchart for reference power generation. c. islanding a single phase double stage pv system is subjected to fault at t=1s. when the fault occurs at pcc and the grid is disconnected, fulfilling the load demand by pv will be a engineering, technology & applied science research vol. 10, no. 5, 2020, 6374-6379 6378 www.etasr.com gotekar et al.: a single phase grid connected pv system working in different modes priority. the power requirement of the load is supplied by the pv system in islanded mode. the generated pv power is sufficient to supply the load. the prime concern is to disconnect the grid and use the photovoltaic system power as it is available. during islanding, the mppt mode is switched to fault operating mode as shown in the flowchart of figure 11. the source voltage during the fault is shown in figure 12 and active and reactive power supplied to the linear and nonlinear load are given in figure 13 respectively. fig. 12. source voltage when fault occurs to t=1s. fig. 13. active and reactive power supplied during islanding. d. voltage sag due to the occurrence of fault, a voltage sag appears at t=0.3s and continues until t=0.7s. during this period, the system is shifted to fault mode and although the source voltage sags as shown in figure 14, the current controller injects reactive current for compensation as per grid requirements. fig. 14. source voltage during sag from t=0.3s to t=0.7s. fig. 15. current supplied by the current controller. when the sag occurs the load voltage remains unaltered due to the compensating current supplied by the inverter given by figure 15. it is clear that during voltage sag conditions, the load voltage and hence the supply to the load is maintained by the pv system. figure 16 shows the active and reactive powers during this period. fig. 16. active and reactive power during the voltage sag. e. fft analysis figure 17 shows the load current. the fft analysis shows that thd is 17.74% (figure 18) when the source is supplying the load, i.e before t=1s, but when the pv system supplies the load after the occurrence of fault at t=1s, the thd is reduced to 4.07% as shown in figure 19. fig. 17. load current fig. 18. thd when the source is supplying the load. fig. 19. thd when the pv system is operating. engineering, technology & applied science research vol. 10, no. 5, 2020, 6374-6379 6379 www.etasr.com gotekar et al.: a single phase grid connected pv system working in different modes v. conclusion from the simulation results presented above, the following conclusions can be drawn: • a single phase connected grid was designed under stable conditions. depending upon variations in irradiations, mppt operates to deliver power to the grid. • the designed pv system is able to supply power in the occurrence of grid failure. • the inverter supports the utility by injecting reactive current in order to avoid grid collapse. • a pv system can be used as an independent source of power during supply outing conditions and to feed the load through the existing inverter by effectively maintaining the dc link voltage constant. • the proposed controller handles loading conditions such as linear and nonlinear loads successfully. references [1] d. barater, e. lorenzani, c. concari, g. franceschini, and g. buticchi, “recent advances in single-phase transformerless photovoltaic inverters,” iet renewable power generation, vol. 10, no. 2, pp. 260– 273, 2016, doi: 10.1049/iet-rpg.2015.0101. [2] r. teodorescu, m. liserre, and p. rodriguez, grid converters for photovoltaic and wind power systems. hoboken, nj: wiley-ieee press, 2007. [3] h. mahamudul, m. saad, and m. ibrahim henk, “photovoltaic system modeling with fuzzy logic based maximum power point tracking algorithm,” international journal of photoenergy, vol. 2013, sep. 2013, art. no. 762946, doi: 10.1155/2013/762946. [4] a. sangwongwanich and f. blaabjerg, “mitigation of interharmonics in pv systems with maximum power point tracking modification,” ieee transactions on power electronics, vol. 34, no. 9, pp. 8279–8282, sep. 2019, doi: 10.1109/tpel.2019.2902880. [5] p. s. gotekar, s. p. muley, and d. p. kothari, “fuzzy inference based control of single phase grid connected photovoltaic system,” in 2019 innovations in power and advanced computing technologies (i-pact), llore, india, mar. 2019, vol. 1, doi: 10.1109/i-pact44901. 2019.8960041. [6] n. vosoughi, s. h. hosseini, and m. sabahi, “single-phase commongrounded transformer-less grid-tied inverter for pv application,” iet power electronics, vol. 13, no. 1, pp. 157–167, 2020, doi: 10.1049/ietpel.2019.0364. [7] s. s. ghosh, k. s. nathan, y. p. siwakoti, and t. long, “dual polarity dc–dc converter integrated grid-tied single-phase transformer less inverter for solar application,” the journal of engineering, vol. 2019, no. 17, pp. 3962–3966, 2019, doi: 10.1049/joe.2018.8041. [8] a. datta, r. sarker, and i. hazarika, “an efficient technique using modified p–q theory for controlling power flow in a single-stage single-phase grid-connected pv system,” ieee transactions on industrial informatics, vol. 15, no. 8, pp. 4635–4645, aug. 2019, doi: 10.1109/tii.2018.2890197. [9] a. anurag, y. yang, and f. blaabjerg, “thermal performance and reliability analysis of single-phase pv inverters with reactive power injection outside feed-in operating hours,” ieee journal of emerging and selected topics in power electronics, vol. 3, no. 4, pp. 870–880, dec. 2015, doi: 10.1109/jestpe.2015.2428432. [10] y. yang, h. wang, and f. blaabjerg, “reactive power injection strategies for single-phase photovoltaic systems considering grid requirements,” ieee transactions on industry applications, vol. 50, no. 6, pp. 4065–4076, nov. 2014, doi: 10.1109/tia.2014.2346692. [11] y. yang, f. blaabjerg, and z. zou, “benchmarking of grid fault modes in single-phase grid-connected photovoltaic systems,” ieee transactions on industry applications, vol. 49, no. 5, pp. 2167–2176, sep. 2013, doi: 10.1109/tia.2013.2260512. [12] n. ikken, a. bouknadel, a. haddou, n.-e. tariba, h. el omari, and h. el omari, “pll synchronization method based on second-order generalized integrator for single phase grid connected inverters systems during grid abnormalities,” in 2019 international conference on wireless technologies, embedded and intelligent systems (wits), fez, morocco, apr. 2019, pp. 1–5, doi: 10.1109/wits.2019.8723856. [13] h. z. butt, m. awon, and h. a. khalid, “performance analysis of a continuous and discretized second order generalized integrator based phase lock loop for single phase grid connected pv systems,” in 2018 international conference on power generation systems and renewable energy technologies (pgsret), sep. 2018, pp. 1–6, doi: 10.1109/pgsret.2018.8686038. [14] a. k. panda and n. patnaik, “combined operation of a new power angle control unit vector template based unified power quality conditioner and fuel cell stack supply with effective utilization of shunt and series inverter,” electric power components and systems, vol. 44, no. 18, pp. 2048–2058, nov. 2016, doi: 10.1080/ 15325008.2016.1210264. [15] a. nouaiti, a. mesbahi, a. saad, m. khafallah, and m. reddak, “realization of a single-phase multilevel inverter for grid-connected photovoltaic system,” engineering, technology & applied science research, vol. 8, no. 5, pp. 3344–3349, oct. 2018. [16] s. krithiga and n. g. ammasai gounden, “power electronic configuration for the operation of pv system in combined gridconnected and stand-alone modes,” iet power electronics, vol. 7, no. 3, pp. 640–647, mar. 2014, doi: 10.1049/iet-pel.2013.0107. [17] p. sarathi subudhi and s. krithiga, “pv and grid interfaced plug-in ev battery charger operating in p-vg, p-v and v-g modes,” international journal of recent technology and engineering, vol. 8, no. 2, pp. 3431– 3443, jul. 2019, doi: 10.35940/ijrte.b2680.078219. [18] v. r. reddy and s. e. s., “a feedback-based passive islanding detection technique for one-cycle-controlled single-phase inverter used in photovoltaic systems,” ieee transactions on industrial electronics, vol. 67, no. 8, pp. 6541–6549, aug. 2020, doi: 10.1109/ tie.2019.2938464. [19] s. a. raza and j. jiang, “a benchmark distribution system for investigation of residential microgrids with multiple local generation and storage devices,” ieee open access journal of power and energy, vol. 7, pp. 41–50, 2020, doi: 10.1109/oajpe.2019.2952812. [20] l. h. lam, t. d. h. phuc, and n. h. hieu, “simulation models for three-phase grid connected pv inverters enabling current limitation under unbalanced faults,” engineering, technology & applied science research, vol. 10, no. 2, pp. 5396–5401, apr. 2020. [21] m. jamil, m. rizwan, and d. p. kothari, grid integration of solar photovoltaic systems, 1st edition. boca raton, fl: crc press, 2017. [22] d. p. kothari, k. c. singal, and r. ranjan, renewable energy sources and emerging technologies, 2nd ed. new delhi, india: phi learning pvt. ltd., 2011. authors profile p. s. gotekar completed her m.tech from vnit, nagpur in 2001 and is a research scholar in the priyadarshini college of engineering, nagpur. her interest areas include power electronics, solar energy system and its applications. s. p. muley completed her ph.d from vnit, nagpur in 2013. her research areas include drives, control and renewable energy systems. she has 20 papers in international journals to her credit. she has over 25 years of experience in industry and research. d. p. kothari is a fellow ieee, fellow institution of engineers, india and life member of the iste. he has authored over 60 books and presented 842 papers in international conferences and journals. microsoft word etasr_v10_n6_pp6427-6431 engineering, technology & applied science research vol. 10, no. 6, 2020, 6427-6431 6427 www.etasr.com dif et al.: trajectory tracking control design of a mass-damping-spring system with uncertainty … trajectory tracking control design of a massdamping-spring system with uncertainty using the bond graph approach ismail dif electrical engineering department laadi laboratory university of djelfa djelfa, algeria difismail@yahoo.fr khier benmahammed ferhat abbas university setif 1 lsi laboratory setif, algeria khierben@ieee.org abdallah kouzou electrical engineering department laadi laboratory university of djelfa djelfa, algeria kouzouabdellah@yahoo.fr ahmed hafaifa electrical engineering department laadi laboratory university of djelfa djelfa, algeria hafaifa@hotmail.com abstract-this paper deals with the simulation, and design of a trajectory-tracking control law for a physical system under parameter uncertainty modeled by a bond graph. this control strategy is based on the inversion of the system through their causal input/output (i/o) path using the principle of bicausality to track the desired trajectory. the proposed control strategy is validated with the use of a simple mechanical mass-springdamper system. the results show that the bond graph is a very helpful methodology for the design of control laws in the presence of uncertainties. this proposed control can be applied in several applications and can be improved to ensure robust control. keywords-bond graph; trajectory-tracking; bicausality; inverse system; uncertainty; 20-sim simulation i. introduction bond graph modeling is a rapidly developing powerful tool for modeling multidisciplinary physical systems with graphic and algebraic characteristics that help analyzing system properties and synthesizing control laws or algorithms for system monitoring. the work presented in this paper is based on the application of the control law introduced in [1] on a system modeled by a bond graph which was improved by the study of parametric uncertainties introduced in [2, 3] and the work in [3] regarding incremental bond graphs for the derivation of the state model for the study of robustness of bond graph models. these uncertainties are included by adding some bond graph elements which describe their effect in the system, as described in section iv. this work consists of the design of a trajectory-tracking control law using uncertain bond graph models, in the same way as they are used in the development of diagnostic algorithms for industrial systems [57]. therefore, this work can represent a foundation stone for the design of robust control laws using bond graphs to ensure the control of complex systems. ii. bond graph modeling the bond graph methodology for modeling physical systems was first introduced in 1961 [10] and was formalized in [11, 12]. it is based on the principle of conservation of energy between interconnected physical systems. it formalizes the transfer of power in different parts of the physical system, which is represented by a graphical link of half-arrow (figure 1), which is modeled by the product of two conjugate variables that form the power, the effort, and the flux. all phenomena in a physical system can be modeled by their characters: a power producer or active elements as effort source “se” or flow source “sf”, power consumers or passive elements such as resistances with “r”, energy storages with “i” or “c”, power transformation with direct transformation, (“tf”) or mixed transformation (“gy” or gyrator), conservative power (“0” junction for common effort or “1” junction for common flow). fig. 1. power transfer between systems a and b. the bond graph modeling of such physical systems always goes through the following steps: • the word bond graph, which is the abstract modeling of the system, dividing it into sub-systems interconnected by corresponding author: ismail dif engineering, technology & applied science research vol. 10, no. 6, 2020, 6427-6431 6428 www.etasr.com dif et al.: trajectory tracking control design of a mass-damping-spring system with uncertainty … graphic links. • the causal bond graph model is the representation of physical phenomena by bond graph elements, with connecting elements in the directions of power transfer. • the causality application is the mathematics of bond graph modeling. it is the representation of cause and effect between interconnected systems. it is represented with a perpendicular stroke to bond representing the direction that the effort is known (see figure 2). it is covered through selected assignment rules [13]. fig. 2. causality in bond graph. as all modeling methods, the bond graph model allows its models to switch to other modeling forms such as block diagram, state space, or transfer function [13-14]. to better illustrate this methodology, the mechanical system and its bond graph model are presented in figure 3. fig. 3. bond graph model of the mass-spring-damper system. by following the bond graph modeling steps in figure 3, the junction 1 shows the speed movement of the system, due to the force u applied to the mass m which is modeled by the inertia i, as system input or se element. the output is represented by a flow detector df, which is a speed sensor. the shock absorber and spring are modeled by r and c elements respectively. the concept of bicausality in a bond graph was introduced in 1995 [8]. it is used for the design of the inverse model of a system modeled by a bond graph. it is also used to estimate the parameters of such a model and/or to estimate its state evolution. in the causality concept, the causal stroke indicates the direction where the effort is known, while in the bicausality, the causal stroke is divided into two strokes, top and bottom, perpendicular to the two sides of the bond. the top line indicates the orientation of effort and flow, while the lower line indicates the source of the effort and flow. figure 4 shows the difference between causality and bicausality. (a) (b) fig. 4. bond graph (a) causality vs. (b) bicausality. iii. trajectory-tracking control by bond graph the synthesis of a control law is generally based on a model describing the behavior of the system under study. physical systems vary from linear [15] to non-linear [16] and may or may not vary in time with several control techniques to regulate or track trajectory, leading to several control laws which may be linear such as the lqr control [17], lqr control based on bond graph model [18], pid and intelligent pid control [19], and nonlinear control in several techniques based on graphical model (bond graph) [20-21], mathematical model (ctc, vsc, backstepping, h∞, mpc, etc.) [22-24], or intelligent and meta-heuristic model optimization [19, 25-26], etc. [27-28]. in this paper, the tracking trajectory law is based in the technique initiated in [1] by the application of an algorithm of 5 steps which allows finding the control law for each junction block along with the causal i/o path. the algorithm steps are grouped in table i. table i. trajectory-tracking law control design steps steps step name operations step 1 causal inversion inversion of i/o minimal causal dynamic path in the bond graph model using the bicausality step 2 inverse equation derivation on the bond graph model of the minimum dynamic equation i/o (mde), which presents the error step 3 output substitution output substitution in mde : y(t)=y*(t)-e(t) step 4 error dynamics constraining the error dynamic: ( ) * ( )e t k e t= −� step 5 error substitution error substitution by: e(t)=y*(t)-y(t) y(t): system output, y*(t) : desired output or trajectory by applying the above procedure on the bond graph model of figure 3, the steps can be described as follows: step 1: bond graph inversion, which is to build the inverse i/o model along the causal i/o path, as shown in figure 5. fig. 5. inverse bond graph model. step 2: derivation of the (mde) following the inversion equation. the virtual input is obtained as: 1 . . dv u b v m vdt dt c = + + ∫ (1) step 3: output substitution. the error of the output is defined as: * ve v v= − (2) this leads to: engineering, technology & applied science research vol. 10, no. 6, 2020, 6427-6431 6429 www.etasr.com dif et al.: trajectory tracking control design of a mass-damping-spring system with uncertainty … ( ) ( ) ( )* * *1.v v vu b v e m v e v e dt c = − + − + −∫� � (3) step 4: error dynamics. the dynamics of the error is defined as a 1st order equation (integrator): 0,0 >=+ vvvv kwitheke� (4) where (3) becomes: ( ) ( ) ( )∫ −+++−= dtevcekvmevbu vvvv *** 1. � (5) step 5: error substitution. using (2) into (5) yields (6): ( ) *** ...1 vkmvmvdt c vmkbu vv +++−= ∫ � (6) equation (6) is the relationship of the control input, so that the output v follows the reference v*, with a well appropriate choice of constant kv for a better solution. the application of this technique was done with the utilization of 20-sim [9] version 2.3 which allows the simulation of systems modeled by bond graphs. using the available toolboxes, the bond graph model of the presented system is implemented (figure 4) and with the control law developed by (6), the graph in figure 6 is obtained for speed with square trajectory and a choice of kv=200. the graph in figure 6 shows that the system tracks well the desired path with the proposed control technique. in the next section, the uncertainty modeling parameters in a bond graph model are introduced and the control law for the uncertain model is recalculated. fig. 6. tracking-trajectory control simulation. iv. uncertainty in bond graph the bond graph tool by its graphical character and its analytical and structural performances are also used to represent modeling uncertainties as action elements on the system bond graph model. the introduction of uncertainty addition [2, 3] was followed by [4]. this technique can be applied to the design of robust diagnosis algorithms of bond graph models [5-7]. in the literature, two types of consideration can be found on the study of uncertainties: structured and unstructured uncertainties [29]. the current work is focused in the second type, which includes modeling uncertainties of physical phenomena, such as additive and multiplicative uncertainty at the input or the output. in bond graph modeling, both types of uncertainty (additive and multiplicative) are studied in [3], whereas in this work, the effect of input multiplicative uncertainty in the synthesis of control law is proposed. this is done using the standard interconnection model shown in figure 7. fig. 7. standard interconnection model. the standard interconnection model can be represented by the following system of equations:      ++= ++= ++= udwdxcy udwdxcz ubwbaxx 22212 12111 21� (7) where x is the state vector, u the input vector, w the auxiliary input vector, z the auxiliary output vector, y the output vector, m(s) is the nominal system, and ∆ the diagonal uncertainty matrix, where w=∆.z with ( )idiag δ=∆ and iδ is the i th parameter of the system. in the bond graph model, only passive components (r, c, and i) are assumed and are subject to uncertainty with transformation elements (tf and gy). an example of the design of the standard interconnection model for the i element in integral causality, is presented as follows: the constitutive law of the i element in integral causality is: ∫= dte i f . 1 (8) by introducing the term of the multiplicative error, it is found that: ( )∫+= dte i f i n .1 1 δ with ii i n ∆+ ∆ −=δ (9) the bond graph model of the uncertain element i and in the last relation (9) gives the representation of figure 8. by the addition of uncertainty on the i element of our model in figure 3, the model in figure 9 is obtained. (a) (b) fig. 8. bond graph model of the element i: (a) nominal (b) with uncertainty. engineering, technology & applied science research vol. 10, no. 6, 2020, 6427-6431 6430 www.etasr.com dif et al.: trajectory tracking control design of a mass-damping-spring system with uncertainty … fig. 9. bond graph model with uncertainty. v. design of the control law by applying the control law design procedure stated above on the bond graph model with the uncertainty of the system presented in figure 3, the following steps can be deduced. step 1: bond graph model inversion. applying the inversion procedure of the causal path input/output on our model, using the principle of bicausality, the following scheme is obtained: fig. 10. inverse i/o causal path. step 2: derivation of the dynamic equation. using the structural equations of junctions leads to: • junction 1: vm : 76 ee = with mn vme �.7 = • junction 0 : 564 fff −= with: 4 6 7 5 . m m m f v f f v f v δ =  = =  = − (10) hence: ( ) mm vv .1 δ+= (11) • junction 1 :v 4321 eeee ++= with: 1 2 3 4 6 7 1 . . . .n m e u e v dt k v dt c e bv e e e m v =   = =   =  = = = ∫ ∫ � (12) hence: ∫++= dtvkvmvbu mn ... � (13) replaces the speed v using (10) and (12) takes the following form: ( ) ( )∫++++= dtvkvmvbu mmmnmm .1.1 δδ � (14) step 3: output substitution. the output error is defined as: m mv m m m m v e v v v v e ∗ ∗= − ⇒ = − (15) this leads to the relation: ( )( ) ( ) ( ) ( ) 1 1 . m m m m m v n m v m m v u b v e m v e k v e dt δ δ ∗ ∗ ∗ = + − + − + + −∫ � � (16) step 4: error dynamics. the dynamics of the error is defined as a 1st-order equation (integrator): 0=+ mmm vvv eke� with 0 mv k 〉 then mmm vvv eke −=� (17) equation (16) becomes: ( )( ) ( ) ( ) ( ) 1 1 . m m m m m m v n m v v m m v u b v e m v k e k v e dt δ δ ∗ ∗ ∗ = + − + + + + −∫ � (18) step 5: error substitution. returning to (15) yields to (18): ( ) ( ) ( ) 1 1 . m m mm n v m n m v v m m u b m k v m v k e k v dt δ δ ∗ = + − + +  + + ∫ � (19) which is the control law. the output vm follows the desired trajectory v*m. to validate the proposed control for this system, the control relation (19) is implemented on the 20-sim simulator, with a choice of nominalized values of parameters, and a value of kvm which allows reaching the control objective (tracking the trajectory of the desired speed), with a square-shaped signal, which for example simulates the motion of a rail traction chain. after choosing the uncertainty of the i element, which simulates additional load in a random form, the result shown in figure 11 is found. the uncertainty of the presented case is chosen as random fluctuations bounded by the value (±0.5) around the normalized nominal value. figure 11 shows the desired trajectory (curve b) followed by the output of our system (curve a), which confirms the efficiency of the designed control to the uncertainties of the system parameters. the error between the desired and the tracked velocity is around 10% from the nominal value, which is accepted in a control law. the contribution of this work is in the use of graphical and algebraic properties of the bond graph tool for the design of the control law, when the model is in presence of uncertainties, without the need for mathematical equation derivation, such as used in [18, 20-21]. engineering, technology & applied science research vol. 10, no. 6, 2020, 6427-6431 6431 www.etasr.com dif et al.: trajectory tracking control design of a mass-damping-spring system with uncertainty … fig. 11. simulation result of designed control with 20-sim simulator. for the implementation of this control law, a platform is needed that integrates bond graph models, such as the 20-sim software in later versions than the one used in this paper, which allow interaction with practical systems. we are working on the integration of bond graph models in embedded systems to use them in the design of control and diagnostic systems. vi. conclusion the main aim of this paper was to design a robust trackingtrajectory control system which considers the uncertainties of system parameters, based on bond graph modeling. it has been proved that the bond graph is a powerful tool for modeling a dynamic system to ensure the analysis of interconnected physical systems. it is also very efficient for the design of control laws. the simulation results show the effectiveness and the robustness of the proposed and designed controller against parametric changes of the presented application. on the other side, the proposed control algorithm can be improved to be a promising solution for several industrial control applications. references [1] s. junco, a. donaire, and g. garnero, “speed control of series dc motor: a bond graph based backstepping design,” in ieee international conference on systems, man and cybernetics, yasmine hammamet, tunisia, oct. 2002, vol. 3, https://doi.org/10.1109/ icsmc.2002.1176035. [2] c. s. kam and g. dauphin-tanguy, “bond graph tools for standard interconnection structure determination,” in proceedings of the 2001 international conference on bond graph modeling and simulation (icbgm’01), phoenix, az, usa, jan. 2001. [3] c. sié kam and g. dauphin-tanguy, “bond graph models of structured parameter uncertainties,” journal of the franklin institute, vol. 342, no. 4, pp. 379–399, jul. 2005, https://doi.org/10.1016/ j.jfranklin.2005.01.005. [4] w. borutzky and g. dauphin-tanguy, “incremental bond graph approach to the derivation of state equations for robustness study,” simulation modelling practice and theory, vol. 12, no. 1, pp. 41–60, apr. 2004, https://doi.org/10.1016/j.simpat.2003.11.002. [5] m. a. djeziri, b. ould bouamama, and r. merzouki, “modelling and robust fdi of steam generator using uncertain bond graph model,” journal of process control, vol. 19, no. 1, pp. 149–162, jan. 2009, https://doi.org/10.1016/j.jprocont.2007.12.009. 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[13] p. borne, g. dauphin-tanguy, j. p. richard, f. rotella, and f. zambettakis, automatique : modélisation et identification des processus, tome 2. paris, france: editions technip, 2000. [14] g. dauphin-tanguy, les bond graphs. paris, france: hermès, 2000. [15] p. j. antsaklis and a. n. michel, a linear systems primer. boston, ma, usa: birkhäuser, 2007. [16] h. khalil, nonlinear systems, 3rd edition. upper saddle river, nj, usa: pearson, 2001. [17] s. a. ajwad, j. iqbal, r. u. islam, a. alsheikhy, a. almeshal, and a. mehmood, “optimal and robust control of multi dof robotic manipulator: design and hardware realization,” cybernetics and systems, vol. 49, no. 1, pp. 77–93, jan. 2018, https://doi.org/ 10.1080/01969722.2017.1412905. 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[24] j. iqbal, “modern control laws for an articulated robotic arm: modeling and simulation,” engineering, technology & applied science research, vol. 9, no. 2, pp. 4057–4061, apr. 2019, https://doi.org/10.48084/etasr.2598. [25] m. fouzia, n. khenfer, and n. e. boukezzoula, “robust adaptive tracking control of manipulator arms with fuzzy neural networks,” engineering, technology & applied science research, vol. 10, no. 4, pp. 6131–6141, aug. 2020, https://doi.org/10.48084/etasr.3648. [26] n. dif, e. boudissa, m. bounekhla, and i. dif, “firefly algorithm improvement with application to induction machine parameters identification,” revue roumaine des sciences techniques serie electrotechnique et energetique, vol. 65, no. 1, pp. 35–40, 2020. [27] w. e. dixon, a. behal, d. m. dawson, and s. p. nagarkatti, nonlinear control of engineering systems: a lyapunov-based approach. basel, switzerland: birkhäuser, 2003. 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[29] d. alazard, p. apkarian, c. cumer, g. ferreres, and m. gauvrit, robustesse et commande optimale. toulouse, france: cepadues, 1999. microsoft word 04-3238_s_etasr_v10_n1_pp5113-5116 engineering, technology & applied science research vol. 10, no. 1, 2020, 5113-5116 5113 www.etasr.com kara et al.: ca and ce effect on the corrosion resistance of hot-rolled az31 mg alloys ca and ce effect on the corrosion resistance of hotrolled az31 mg alloys ismail hakki kara metallurgical and materials engineering department karabuk university, karabuk, turkey ihakkikara@karabuk.edu.tr hayrettin ahlatci metallurgical and materials engineering department karabuk university, karabuk, turkey hahlatci@karabuk.edu.tr taher ali issa yousef metallurgical and materials engineering department karabuk university, karabuk, turkey taher_yousef@yahoo.com yunus turen metallurgical and materials engineering department karabuk university, karabuk, turkey yturen@karabuk.edu.tr abstract—in this study, az31 mg alloys with added ca and ce were produced by low pressure die casting and were rolled at 400°c. the corrosion properties of the materials were determined by immersion test for 72 hours at a 3.5% nacl solution. the microstructure of the samples was investigated by light optical microscopy (lom) and scanning electron microscopy (sem) before the corrosion test. twins, dynamic recrystallization (drx), and the alloying elements have an important role in imparting the final corrosion resistance of the investigated materials. keywords-mg alloys; ca; ce; hot rolling; corrosion i. introduction because of their low density and high specific strength, magnesium alloys have received great interest as structural materials for applications in the automotive and aerospace industries [1]. however, low corrosion resistance is still the main deficiency of mg alloys which could be solved by alloying, coating, or heat treatment processes [2, 3]. to get finer grains, rolling is especially utilized to form the billet from high thickness to thin sheets. the twins are the main deformation mechanism of rolling which deteriorates the corrosion resistance of wrought mg alloys because of the fact that stresses resulted from twin boundaries impart site to cathodic corrosion [3, 4]. moreover, the secondary phases of mg17al12 are the second cathodic corrosion contributor for mg alloys finer formed and non-homogenous distributed inside the matrix and on grain boundaries [2]. alloying with ca is suggested to improve the oxidation resistance of mg alloys due to its more affinity to oxidation than mg which acts as a barrier during the corrosion of mg [5]. rare earth elements (rems) are another option to change secondary phases. the ce is more electronegative than mg to compound with al which results in more stable corrosion phase while non-homogeneously distribution of mg17al12 could be replaced by ce-al including secondary phases mostly showing regular shapes on grain boundaries [6, 7]. in this study, to improve the commercially widespread mg alloy of az31, ca and ce elements were added to the composition and hot rolling was utilized to get finer grains and homogeneous secondary phases on the microstructure. the corrosion resistance of the produced materials was tested at 3.5% nacl solution at room temperature. to understand the ce contribution on the corrosion resistance of az31 lom, and sem characterization methods were used. ii. experimental part az31 mg alloys containing 1% ca (wt.%) were produced by low pressure die casting. in argon gas protected environment, pure mg alloys were allowed to melt at 750°c for 1 hour and then ca-mg and ce-mg master alloys were added to the ladle and alloyed. in sf6-co2 protective atmosphere, the alloy was transferred to a stainless steel 36×36×200mm mold, heated at 350°c by applying 2atm pressure. the billets with dimensions of 36×12×80mm were cut from the alloys and were left to cool in the molds. the billets were used in the homogenization process before rolling. the surfaces of the billets which were homogenized for 24 hours at 400°c were sanded with 800 sanding sheets and made ready for rolling after pre-rolling at 400°c for 30 minutes. the samples were reduced at 400°c rolling temperature from 12mm wall thickness to 2mm wall thickness in 5 passes and were allowed to cool in the air after the last pass. in this study, the rolling parameters were 30% cross-sectional reduction per pass and the rolling speed was 1.5m/min and 10m/min. the rollers of the rolling machine used are made of stainless steel with a diameter of 110mm. no lubricant was used in the rolling process. the 2mm sheet materials were exposed to corrosion in 3.5% nacl environment for 72 hours. after corrosion, the materials were cleaned in chromic acid solution by an ultrasonic cleaning device and then the surface materials were dried with alcohol and their weight was measured on a sensitive balance machine. after the corrosion test, microstructure images of the samples were taken by optical microscope (nikon eclipse ma200 + clemex software) and sem (carl zeiss ultra plus gemini fesem). corresponding author: hayrettin ahlatci engineering, technology & applied science research vol. 10, no. 1, 2020, 5113-5116 5114 www.etasr.com kara et al.: ca and ce effect on the corrosion resistance of hot-rolled az31 mg alloys table i. alloy chemical composition (%wt.) alloys al zn mn ca ce mg az31-1ca 2.69 0.92 0.14 0.80 bal. az31-1ca-0.5ce 2.99 0.90 0.24 0.96 0.43 bal. iii. results and discussion a. microstructure results figure 1 shows the lom images of the studied alloys. it can be seen that the grains of all samples were mainly formed after the rolling process. however, the average grain size varies, depending on rolling speed. lower rolling speed gives larger grains and more black points are distributed mainly inside the grains when the rolling speed is 4.7m/min (figure 1(a)). on the other hand, the twins activated during rolling occur more often in the microstructure at higher rolling speeds of az31-1ca alloy (see figure 1(b)). regarding the ce addition to az31-1ca alloy, larger grains were formed. the ce added alloy deformed at 10m/min shows larger grains and contains more twins. (a) (b) (c) (d) fig. 1. lom images of az31-1ca alloys deformed with (a) 1.5m/min and (b) 10m/min and az31-1ca-0.5ce alloys deformed with (c) 1.5m/min and (d) 10m/min rolling speeds the investigated samples show that higher rolling speeds activate more twin formations for both alloy groups (figures 1(d) and 3(b)). the formation and distribution of the secondary phases were examined by the sem images of the alloys presented in figure 2. (a) (b) (c) (d) fig. 2. sem images and edx results of az31-1ca alloys deformed with: (a) 1.5m/min and (b) 10m/min, and az31-1ca-0.5ce alloys deformed with: (c) 1.5m/min and (d) 10m/min rolling speeds engineering, technology & applied science research vol. 10, no. 1, 2020, 5113-5116 5115 www.etasr.com kara et al.: ca and ce effect on the corrosion resistance of hot-rolled az31 mg alloys the secondary phases of 1ca deformed at 1.5m/min rolling speed are finer and homogeneously distributed inside the grains and grain boundaries in surface and cross-section. however, the size of the secondary phases was larger when the rolling speed was 10m/min and the distribution of the larger secondary phases was especially placed on grain boundaries (figure 2). the ce added materials contain more homogeneously distributed equiaxed grains, although the secondary phases of the samples rolled at 1.5m/min were formed at a larger size and placed on grain boundaries. the edx examination shows that the secondary phases of ca-added deformed alloy at 1.5m/min rolling speed were formed as small spherical shapes which are dominantly al-ca rich. however, the rising of rolling speed to 10m/min dissolved the generally smaller sized secondary phases in the matrix where the al-mn rich secondary phases that occurred mostly on grain boundaries have a larger size and complex or rectangular shapes. however, a small number of the finer and spherical shaped secondary phases were detected on twins’ boundaries. when we examine the ce added az311ca alloys, the ce mostly has been solved in the matrix of 1ca0.5ce alloy deformed at 1.5m/min rolling speed due to the chemical composition of secondary phases. however, the same alloy contains spherical shaped secondary phases that contain ce, when the rolling speed is 10m/min, more than when rolled at 1.5m/min. the average grain size results show that finer grains of 7.8µm were obtained for 1ca alloy deformed at 10m/min rolling speed. higher rolling speed imparts finer grains to 1ca added alloys, although the finer grains were obtained in 1ca-0.5ce added alloys after 10m/min rolling speed. as for the twins, both alloys showed an increase in twins fraction along with the rising of rolling speed. moreover, the highest twins’ density is introduced on 1ca-0.5ce added alloy deformed at 10m/min rolling speed (figure 3). b. immersion corrosion results the immersion test results of the investigated alloys are exhibited in figure 4. at the first test period the inclinations of corrosion rate belonging to alloys are similar for 9 hours. rising of metal loss after 9 hours was observed, and the higher amount was detected on 1ca alloy deformed at 1.5m/min rolling speed. the increased inclination of corrosion rate endured up to 12 hours. afterwards the inclination did not show any higher rising. most alloys illustrated a similar trend between 12 and 48 hours. however, the inclination line of corrosion rate decreased until the end of the test for all samples. during the immersion tests, the highest corrosion resistance was obtained with 1ca-0.5ce alloy deformed at 1.5 m/min. as mentioned above, ce mostly diffuses into the matrix where the solutes of ce have a significant influence on the corrosion behavior of the material due to the galvanic effect occurring softly between the matrix and the grain boundaries [5, 8]. on the other hand, the poorest resistance to corrosion was detected in 1ca alloy deformed at 1.5 m/min which has fine and continuously distributed al-ca rich secondary phases highly accelerate corrosion. ce compounds with al, thus eliminates the stable mg17al12 secondary phases from the structure which are replaced by alre3 types [9]. (a) (b) fig. 3. a) average grain size, b) twins fractions of investigated alloys fig. 4. immersion corrosion test results of the investigated alloys iv. conclusion in this study, ce and rolling speed effects on the corrosion resistance of az31-1ca alloys were proved by microstructure analysis, where the solid solution of ce element in a matrix held an important role as a dominant stability determiner in 3.5% nacl solution. moreover, the rolling speed changed the size and shape of the secondary phases distributed on grain boundaries when the rolling speed was 1.5m/min, controlling the corrosion resistance positively. acknowledgment this work was financially supported by the scientific research projects coordination unit of karabuk university, project number: kbü-bap-16/2-dr-081. engineering, technology & applied science research vol. 10, no. 1, 2020, 5113-5116 5116 www.etasr.com kara et al.: ca and ce effect on the corrosion resistance of hot-rolled az31 mg alloys references [1] a. imandoust, c. d. barrett, t. al-samman, k. a. inal, h. el kadiri, “a review on the effect of rare-earth elements on texture evolution during processing of magnesium alloys”, journal of materials science, vol. 52, no. 1, pp. 1-29, 2017 [2] i. h. kara, h. ahlatci, y. turen , y sun, “microstructure and corrosion properties of lanthanum added az31 mg alloys”, arabian journal of geosciences, vol. 11, no. 18, pp. 535, 2018 [3] g. l. song, corrosion of magnesium alloys, woodhead publishing, 2011 [4] j. h. lee, j. u. lee, s. h. kim, s. w. song, c. s. lee, s. h. park, “dynamic recrystallization behavior and microstructural evolution of mg alloy az31 through high-speed rolling”, journal of materials science & technology, vol. 34, no. 10, pp. 1747-1755, 2018 [5] j. yang, j. peng, e. a. nyberg, f. s pan, “effect of ca addition on the corrosion behavior of mg–al–mn alloy”, applied surface science, vol. 369, pp. 92-100, 2016 [6] p. liu, h. jiang, z. cai, q. kang, y. zhang, “the effect of y, ce and gd on texture, recrystallization and mechanical property of mg–zn alloys”, journal of magnesium and alloys, vol. 4, no. 3, pp. 188-196, 2016 [7] s. m. rajaa, h. a. abdulhadi, k. s. jabur, g. r. mohammed, “aging time effects on the mechanical properties of al 6061-t6 alloy”, engineering, technology & applied science research, vol. 8, no. 4, pp. 3113-3115, 2018 [8] l. wang, b. zhang, t. shinohara, “corrosion behavior of az91 magnesium alloy in dilute nacl solutions”, materials & design, vol. 31, no. 2, pp. 857-863, 2010 [9] j. liu, e. h. han, y. song, d. shan, “effect of twins on the corrosion behavior of mg–5y–7gd–1nd–0.5 zr mg alloy”, journal of alloys and compounds, vol. 757, pp. 356-363, 2018 authors profile ismail hakki kara is a research assistant at karabuk university, turkey. he obtained his bsc degree from the department of metallurgical and material engineering, itu, istanbul, turkey, in 2012. currently, he is a msc student at karabuk university. his research interests include welding technology, p91 and p92 steels, microstructure characterization, sem, microscopy as well as magnesium alloys. taher ali issa yousef, was born 1972 in triboli, obtained his bsc degree from libya. presently, he is a phd. student in the department of metallurgical and materials engineering, faculty of engineering, karabuk university, turkey. hayrettin ahlatci, was born 1969 in karabuk. he obtained his bsc degree from the department of metallurgical and material engineering, istanbul technical university (itu), turkey, in 1994. he started his academic career as a research assistant at karaelmas university in zonguldak, turkey. he completed his msc and phd degrees at the institute of science at itu. presently, he is an associate professor in the department of metallurgical and materials engineering, faculty of engineering, karabuk university, turkey. yunus turen, was born in 1965 in karabuk. he obtained his bsc degree from the department of metallurgical and material engineering, gazi university, turkey, in 1999. presently, he is an associate professor in the department of metallurgical and materials engineering, faculty of engineering, karabuk university, turkey. microsoft word etasr_v13_n4_pp11298-11317 engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11298 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand the mineralogical and chemical composition of the strongly magnetic egyptian black sand altered ilmenite mohamed ismail moustafa nuclear materials authority, egypt ismail2251962@yahoo.com received: 9 may 2023 | revised: 30 may 2023 | accepted: 6 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6025 abstract the egyptian black sand contains several types of altered ilmenite grains which have various magnetic susceptibility values, ranging from the strongly paramagnetic, such as ilmenite, to the non-magnetic, such as rutile grains. the altered ilmenite grains of relatively higher mass magnetic susceptibility, separated at 0.1, 0.2, 0.25, and 0.35 a using the frantz isodynamic magnetic separator, were investigated. both brown and black altered grains were investigated using the binocular microscope and the cameca sx-100 microprobe. most analyzed spots of grains are composed mainly of pseudorutile (psr) and leached pseudorutile (lpsr), with the contents of tio2 and fe2o3 ranging between 56.76 and 78.09% and 37.98 and 12.16%, respectively. the ti/(ti+fe) ratio ranges between 0.59 and 0.85. the chemical formula range of the investigated psr-lpsr is fe2.07-0.54ti3o9-4.68(oh)0-4.32. the lowest cationic iron content of the lpsr phase is 0.5 with a corresponding molecular formula of fe0.5ti3o4.5(oh)4.5. in the detected leached ilmenite spots, the cationic fe 2+ ranges between 0 and 2.46, while the cationic fe 3+ ranges between 0.17 and 1.94. the ti/(ti+fe) ratio ranges between 0.51 and 0.6, and the fe/ti ratio ranges between 0.91 and 0.67. considering the chemical formula of ilmenite is fe3ti3o9, the leached ilmenite formulas have the composition fe2.72-2.02ti3o9 with the minimum value of total iron being equal to 2.02. some of the contained inclusions may be responsible for the acquired magnetic characteristics of some of the detected altered grains. the powdered x-ray diffraction patterns of the investigated different magnetic grains were detected before and after heating at 1100 o c for one hour. the hexagonal psr/lpsr structure is more unstable at 1100 o c than the tetragonal rutile structure. according to the calculations of the molecular formulas for the detected alteration phases, the lowest iron content of the altered lpsr is much lower than that previously reported. also, during the alteration process, the alteration mechanism is changed in the region of 68-70 wt % of contained tio2. then, in the late alteration stages, the lpsr structure does not suddenly collapse but gradually produces other associated mineral phases. keywords-egypt; black sand; magnetic; nonmagnetic; leucoxene; leached ilmenite; leached pseudorutile i. introduction the discovery of a new mineral, arizonite, of a chemical composition closely corresponding to fe2o3.3tio2 was reported in [1]. arizonite is regarded as merely weathered ilmenite [2]. according to [3], most of the studied ilmenite concentrates from several beach sand deposits contain ore grains ranging from fresh ilmenite to a highly altered product approaching pure tio2 in composition. the nature and chemical composition of leucoxene are known to be variable [4]. leucoxene is commonly considered to be microcrystalline rutile [3, 5-7]. occasionally some leucoxene have also yielded x-ray patterns corresponding to either sphene [4], brookite [4, 5, 7], anatase [5], or mixtures of rutile with anatase or brookite [7]. there is an abundance of co-occurrence of pseudobrookite and altered ilmenite in quilon sands, india [8]. however, the authors in [9] do not agree with karkhanavala's explanation unless the primary pseudobrookite was early present in the source area. when the ilmenite structure is broken down by alteration and the material is turned amorphous, a marked decrease in mass magnetic susceptibility, an increase in tio2 and h2o contents and a high fe 3+ /fe 2+ ratio occur. the term hydroilmenite is given for the obtained amorphous phase [10]. in fact, authors in [11] prefer the term altered or weathered ilmenite since the chemical and mineralogical composition varies with the degree of alteration, and the amount of water present is very small. the name pseudorutile is proposed for the product of oxidation and progressive partial removal of iron due to the alteration of ilmenite giving an intermediate iron titanate of a definite structure [12]. the identification of the intermediate altered compound pseudorutile was difficult in earlier studies due to its occurrence in fine grain size (30 o a), its poor crystallinity, and its coincidence for most of its diffraction lines with those of other phases [13]. thus, it is safe to say that the distinct isotropic phase, previously called arizonite [1], engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11299 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand amorphous iron titanate [6], and pro-arizonite [14], is pseudorutile. many grains of ilmenite may remain unchanged for long burial times, perhaps at shallow depth, but below the oxidation zone [15]. authors in [15] believe that the major part of the alteration of the sand ilmenite takes place neither in the crystalline rocks nor on the beach, but while they were buried in sediments during their journey. authors in [16, 17] agree that ilmenite may be altered under reducing conditions. on the other hand, authors in [18] explained that the rate of alteration of ilmenite to secondary tio2 might control the formation of a polymorph. also, the occurrence of impurities affects the formation of polymorphic forms. according to [19], the change from ilmenite to psr involves a phase change in the oxide structure. aluminum and silicon are also enriched due to the iron depletion during the first stage of alteration, but their concentrations remain quite low, i.e. al2o3 ≤ 0.4 wt % and sio2 ≤ 0.1 wt % [20]. for ti/ (ti+fe) > 0.7, corresponding to the second stage of alteration proposed by [21], the aluminum and silicon levels increase rapidly with increasing ti/(ti+fe) ratios, to maximum values near 1.5 wt % al2o3 and 0.5 wt % sio2. this increase is due to the co-precipitation or adsorption of these elements from the surrounding soil solutions onto the freshly-formed alteration products. the occurrence of gibbsite and clay minerals within the pores of the weathered grains was reported in [22]. the authors explained the increase of al and si contents with the increase of ti/(ti+fe) ratio as a consequence of the increase of the abundance of pores available for the crystallization of clay minerals, as ilmenite and pseudorutile alter isovolumetrically to porous rutile. according to [23], the model of [21] has several weaknesses, the two model's reactions require different environments to proceed, the first an oxidizing one and the second a reducing one with its reliance on reducing conditions in near surface conditions. authors in [24] explained that the detrital ilmenite grains of heavy mineral sands in brazil are extremely altered sometimes in psr and anatase (grain boundaries), and also leucoxene. in some leucoxenated grains of the egyptian black sand, residual particles of ilmenite are enclosed in many of the altered ilmenite grains and a few grains still preserved the crystal form of the parent ilmenite [25]. the mineralogy of the egyptian black sand ilmenite is well defined in [26, 27]. in [28], most of the given individual examples of psr and lpsr are considered ideal cases with respect to their given values of tio2 and feo, the reverse relation between these two oxides, and the values of the total oxide sum. the given examples of the three analyzed psr spots were: the tio2 wt % contents were 62.16, 64.62, and 66.04, respectively, the feo wt % contents were 28.28, 25.62, and 24.21, respectively, and the total oxide sum values were 93.71, 92.98, and 92.67, respectively. also, the given examples of the lpsr spot chemical analysis were: the tio2 wt % contents were 70.67, 72.02, and 74.57, respectively, the feo wt % contents were 15.79, 13.95, and 10.32, respectively, and the total oxide sum values were 89.96, 88.18, and 89.08, respectively. it is obvious from the above, that most literature dealt with bulk ilmenite concentrates from friable sediments (e.g. beach sand deposits). a few studies dealt with the altered ilmenite from sedimentary and igneous rocks. most depended in their investigation on the microscopic investigation, microprobe chemical analysis, and the xrd identification. also, almost all past studies dealt with the occurrence of al2o3 and sio2 contents in the altered ilmenite phases considering both as impurities. in the present study, some of the strongly magnetic altered ilmenite grains are investigated to explain their mineralogical and chemical composition characters. the purpose of the current work is to detect the different lpsr phases, the lowest iron content in these phases, and the most stable molecular formulas of the detected lpsr phases. also, the real role of sio2 and al2o3 contents in ilmenite alteration will be checked. several excel sheets were constructed to solve the chemical formulas of the various ilmenite alteration products. ii. materials and methods a large bulk sample was collected from the surficial naturally highly concentrated black sand from the beach area at the mediterranean coast, 7 km to the east of rosetta estuary, egypt. the sample represents the raw sand in a 4 km stretch with a variable width of a few up to 20 meters. the sand was manually scraped from the mantle to a depth ranging between 10 and 30 cm. using the difference in physical character between the various minerals, the collected surficial naturally highly concentrated beach raw sand was processed using the following equipment: 1. the reading cross–belt magnetic separator for primary magnetic separation. 2. full size wilfley shaking tables for wet-gravity concentration of the obtained bulk nonmagnetic fraction. 3. the carpco (hp 167) high-tension roll-type electrostatic separator for treating the obtained tabled concentrate of the last obtained nonmagnetic fraction. 4. the carpco (mih 13-231-100) industrial high intensity induced roll dry magnetic separator for the magnetic separation of the obtained rutile conductor fraction. 5. the frantz isodynamic magnetic separator. the last obtained three successive magnetic fractions were mixed as a bulk magnetic fraction, composed of hematite, ilmenohematite, different varieties of magnetic primary rutile [29], and various grades of altered ilmenite grains, in addition to minor cr-bearing and other magnetic minerals [30]. a relatively smaller representative sample was obtained from the bulk magnetic fraction and was subjected to magnetic differentiation using the separator where the used adjustments of operating conditions were: longitudinal slope of 20 o , side slope of 5 o , feeding rate of 30 g/hour, and successive current values of 0.1, 0.2, 0.25. 0.35, 0.5, and 1 a, where six magnetic fractions and one nonmagnetic fraction were obtained. in the present paper, only the first four magnetic fractions, separated at 0.1, 0.2, 0.25 and 0.35 a are investigated. 6. the microprobe analysis. the investigation of the different altered ilmenite grains was carried out by a cameca sx100 electron micro probe analyzer (empa). the engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11300 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand microprobe instrument is equipped with three wavelength dispersive spectrometers (wdss) and an energy dispersive spectrometer (eds). the whole surface of the polished sections was examined by back scattered electron (bse) images, so that grains with 10 m size, or even smaller, could be detected. the conditions were: 15 kv accelerating voltage, 15 na electron current, 180 s counting time for each analyzed spot in the investigated grains, and a focused electron beam diameter of 1 to 4 m. the following standards were used: diopside for mg and ca, albite for na, corundum for al, orthoclase for si and k, rutile for ti, rhodonite for mn, fe2o3 for fe, cr2o3 for cr, v for v, and sphalerite for zn. the lines used for the analysis were k for each of the analyzed elements. for each detected altered ilmenite variety, a definite number of grains was picked individually and polished for the investigation using the microprobe. 7. the x-ray diffraction (xrd) instrument. philips x-ray generator (pw 3710/31) with automatic sample changer (pw 1775, 21 positions) using a scintillation counter, cutarget tube and ni filter at 40 kv and 30 ma were used. this instrument is connected with a computer system using the x-40 diffraction program and astm cards for mineral identification. iii. calculations the calculations of trivalent iron, h2o, and the chemical formulas for the intermediate products of ilmenite alteration were carried out after the calculation of the following two values [28]:  the molecular proportion for each analyzed oxide was obtained by dividing its analyzed wt % by its molecular weight. for all altered phases, the analyzed iron is given as feo wt %.  the mole % for each cation on the basis of ti=3, considering that the ilmenite formula is [3 (fetio3)]. an example is the calculation of the mole % of si, which is equal to 3×[sio2 (mole proportion)/tio2 (mole proportion)]. the authors in [28] do not give any explanation about the various used steps in their calculations. they gave three individual examples of the calculation results for each of leached ilmenite, pseudorutile, and leached pseudorutile phases. in these 9 examples, they considered the mole % for each cation as the same as the mole % value of its corresponding oxide irrespective of the number of cations in the oxides molecular formula. in fact, the chemical analyses of various ilmenite ores do not contain only feo, mgo, mno, cao, tio2, sio2, and zno but may contain relatively higher contents of v2o3, cr2o3, nb2o3, ta2o3, fe2o3, and/or al2o3 and maybe others. so, it is better to take the number of cations in the corresponding oxide into consideration in the calculation of the cation mole %. also, in the calculation of ferric iron (fe 3+ ) in the cases of pseudorutile and leached pseudorutile chemical formulas, the authors in [28] considered that the mole % of fe 3+ is equal to that of the divalent iron fe 2+ in the analyzed feo% multiplied by 1.1113. however, this factor is related to the difference of the oxygen content between the oxides feo and fe2o3. in fact, the cationic ferrous iron content of the analyzed iron as feo must be the same as that of the corresponding fe2o3 when feo is recalculated as fe2o3. in one of the given three examples of psr, the mole% of feo and hence of fe 2+ is calculated as 1.223 and the recalculated mole% of fe 3+ is 1.36, which is 1.223×1.1113. this method of calculation was followed for all the given six examples, three for psr and three for lpsr, see tables 2-3 in [28]. however, a relatively more precise method for the calculation of fe 3+ content from the analyzed feo wt % in ilmenite was given in [31]. the authors considered the value excessing 1 for the calculated mole% of fe 2+ from the analyzed feo, as corresponding to the present fe 3+ as feo1.5. then by multiplying the excess, e.g. 0.12 as given from their example, in 1.1113 and by dividing the obtained value by 2, the mole % of fe2o3 (0.067) is obtained. the various constructed excell spreadsheets in the present study are: a. the constructed molecular formula of leached ilmenite in the construction of the molecular formula of leached ilmenite (fe 2+ 3ti3o9), the iron content of the analyzed spots of leached ilmenite is given as feo wt % and the number of cations in the analyzed cation oxide molecular formula is taken into consideration. the adopted procedure includes the following steps:  the calculation of the molecular proportion for each analyzed oxide of each spot of an individual ilmenite grain.  the calculation of ti-factor which equals to 3 divided by the calculated molecular proportion of the analyzed tio2 wt % of each individual analyzed spot.  the calculation of the number of cations of each analyzed oxide after the normalization to 3 ti (mole % cations). hence, the calculated molecular proportion of the oxide will be multiplied in the ti-factor and also, in the number of cations present in its corresponding analyzed oxide formula.  the calculation for the sum of all cation numbers except those of ti and fe. this sum is called "other cations".  the calculation of the sum of all cation charge values (w1), except those of ti and fe, by summation of each cation mole % × cation charge.  considering that y= fe 3+ , x = fe 2+ , k is the content of the mole % of total iron (iron cations normalized to 3 ti), then the sum of the quotients of the total anionic charges. o9 = -18 and total cation charges, (3y + 2x + w1 + 3ti 4+ ), must be equal to zero: x + y = k , then, x = k – y (1) then: 3 y + 2x + w1 + 3ti 4+ 18 = 0 then: 3y + 2 (k-y) + w1 + 12 – 18 = 0 engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11301 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand and y = 6 – (w1 + 2 k) (2) because the number of cations in the calculated mole % of each cation will be taken into consideration, the value of the calculated cationic charges for the analyzed minor oxides containing cations that have oxidation states more than that of fe 2+ , such as al 3+ , cr 3+ , v 3+ , nb 5+ , and ta 5+ , will considerably affect the calculated values of x and y. however, their summation (x+y) is always equal to k.  the calculation of the new feo wt % equals to: the original analyzed feo wt % * x/(x+y) (3)  the calculation of the contained fe2o3 wt % equals to: the original analyzed feo wt % * y/(x+y) (4)  the determination of the molecular formula will be: fe 2+ ferrous, fe 3+ ferric, other cations, ti3, o9. b. the constructed molecular formula of pseudorutile and leached pseudorutile 1) the first method of calculating the number of oxygen anions and the number of hydroxyl groups in the molecular formula of psr or lpsr the iron content of the analyzed spots of psr and lpsr is given as fe2o3 wt % and not as feo. in fact, it is detected that in the majority of the studied altered ilmenite grains, most of the iron content is present as ferric iron (fe 3+ ). considering that the psr formula is fe2ti3 (ox, ohy), where x + y =9, the adopted procedure includes the following steps:  the analyzed iron is given as fe2o3.  the calculation of the molecular proportion for each analyzed oxide.  the calculation of ti-factor by dividing 3 by the calculated molecular proportion of the analyzed tio2 wt %.  the calculation of the number of cations for each analyzed oxide by the normalization to 3 ti (cation norm or cation mole %). hence, the calculated molecular proportion of each oxide will be multiplied by the ti-factor and also by the number of cations in its corresponding oxide formula.  the calculation of cation norm sum except for ti.  the calculation of cation charge values sum (w1), except that of ti. the cation charge value is calculated by multiplying each cation norm in cation charge inside its corresponding oxide.  now, in the psr formula of fe2ti3(ox + ohy), the calculation of the number of oxygen and hydroxyl anions is calculated as follows: because the number of positive charges must equal those of the negative charges, the sum of all cation charges except ti + 12 (charges of 3ti 4+ ) is equal to: 2x + y (5) where: x+y= 9. then, x = 9 – y (6) substituting the value of x of (6) in (5), we get: ∑all cation charges except ti + 12 = 2(9 y) + y = 18 – y then, ∑ all cation charge except ti + 12 = 18 y then, ∑ all cation charge except ti = 18-12 – y then, y= 6-∑ all cation charges except ti (7)  the calculation of oh wt % inside the psr formula (fe2ti3oxohy), is: oh wt % =17×y×100/{(17×y)+(16×x)+(3×47.9)+w2} (8) where the molecular weights of oh, o, and ti are 17, 16, and 47.9, respectively, and w2 is the sum for each cation norm to 3ti, except of ti, multiplied by its atomic weight.  the calculation of h2o wt % is: 2 oh = h2o + o 34.015 g = 18.015 g then, 100% oh gives 52.96 wt % h2o. then, the h2o wt % corresponding to the definite value of oh wt % is calculated as: h2o wt % = {oh wt % × 52.96}/100 (9) substituting the value of oh wt % of (8) into (9), we get: h2o wt % = y×900.85/(y×17) + (x×16) + 143.7 + w2 (10) applying this constructed psr and lpsr procedure for some of the spots under investigation, the calculated structural h2o wt %, sometimes gets too high. the new calculated total oxide sums (n total or nt), which include also the calculated structural water in the analyzed psr or lpsr spot, are much more than 100 wt %. the reason for such cases can be explained as follows:  if some of the analyzed tio2 wt % of a definite analyzed spot of psr is not included within the psr formula, it may be included in another associated individual mineral phase mixed with psr. in this case, the calculated value of tication proportion [tio2 wt % / molecular wt of tio2], will be relatively higher than that supposed to be actually present. then, the calculated value of ti-factor [3/the calculated ti-cation proportion], will be relatively lower. then, most of the calculated cation values, corresponding to the various analyzed cation oxides will be relatively lower when normalized by 3ti. hence, the calculated oh and the corresponding structural water wt % will be relatively higher. on the other hand, the presence of a definite portion of individual fe2o3 with the analyzed amount of psr spot do not have the same effect as that of tio2, and does not affect the calculated values of the other cations inside the psr formula structure.  the presence of considerable contents of some elements, such as mn 2+ , that have charge of relatively lower value than fe 3+ , which decrease the sum value of (7). hence, the engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11302 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand calculated values of y and oh and the corresponding structural water wt % will be relatively higher.  the presence of cations relatively lighter than iron and of charges ≥ 3 in considerable contents in the analyzed psr spot will affect the calculated value of y, see (7). the reason is that their calculated cation proportions and their corresponding charges will be relatively higher and hence also the sum value of (7) will be. then, the calculated values of y and oh and the corresponding structural water wt % will be relatively lower. 2) the second method for calculating the number of oxygen anions (x) and the number of hydroxyl groups (y) in the molecular formula of psr or lpsr in the lpsr stage, fe 3+ starts to leave the psr structure and hence oxygen must be also substituted or hydrogenated and replaced by oh anions. then, the removal of each ferric iron cation will be associated with the substitution of three oxygen anions (3o 2) by three hydroxyl anions (3oh ) to achieve the electrical neutralization and also to prevent the collapse of the psr structure. then: fe2ti3o9 → feti3o6(oh)3 (11) then, in the structural molecular formula of lpsr: number of lost fe 3+ cations = 1/3 × number of lost o 2 = 1/3 × number of added or formed oh hence, in the calculated lpsr formula, the difference of the present fe 3+ in the molecular formula from 2 must be multiplied by 3 to obtain the number of added or formed oh inside the lpsr molecular formula of the analyzed spot. 3) the third method for calculating the number of oxygen anions (x) and the number of hydroxyl groups (y) in the molecular formula of psr or lpsr for a definite spot chemical analysis of psr or lpsr, when all the present analyzed cations are normalized to 3ti, the calculated sum of oxygen anions is corresponding to the actual present cation positive charges in the psr molecular formula. then, by multiplying the calculated number of oxygen anions by 2, the value of negative charges required to neutralize these positive charges is acquired. if the number of the calculated oxygen anions (o 2) is lower than 9, the number of oh anions present in the lpsr formula is obtained by multiplying the deficient value by 2. but because in the molecular formula of psr or lpsr, the number of o 2 anions plus the number of oh anions must be equal to 9, the correct number of o 2 anions in the lpsr formula equals to 9 minus the predicted number of oh . for example, for a definite spot chemical analysis and if the number of the normalized calculated oxygen anions is equal to 7.5, then the predicted number of present oh anions is 9-7.5 = 1.5 × 2 = 3. but o 2+oh 1 = 9. so, the correct occurred o 2 anions are 9 – 3 = 6. 4) the calculation of lost iron from the formula structure of psr and lpsr there are two methods of calculating the lost iron from the psr and lpsr formula structure.  lost iron = the number of the calculated oh anions of psr or lpsr /3.  lost iron = 2sum of all calculated cations in psr and lpsr with the exception of ti. when comparing the results of the different psr and lpsr analyzed spots using these two different methods for the calculation of lost iron (fe 3+ ), the following remarks can be concluded:  in some analyzed spots, the calculated lost fe 3+ by the first method is relatively lower than that calculated by the second method. some of the lost cations may be not be associated by the entrance of oh anions into the psr or lpsr formula structure or they are associated by the entrance of less oh , i.e. two not three. for example, if one cation of mg 2+ or mn 2+ , mixed with iron in the original ilmenite, is lost during alteration, then only two oxygen anions are replaced or changed with two oh anions inside the psr formula structure. in this case, the number of lost iron equals to the half, not third, of the number of oh anions. hence, the calculated lost iron by the first method in this case is increased. therefore, it was detected in the chemical analysis of some lpsr spots, that the difference of the calculated lost iron using these methods is more noticeable as the content of the analyzed mgo and/or mno is relatively higher. in fact, many of the investigated lpsr spot chemical analysis containing tio2 ranging between 70 and 80 wt % have the calculated lost iron by the second method relatively greater than that calculated by the first one by values ranging between 0.07 and 0.2. the reason is that in this composition range of tio2, most of mg 2+ , mn 2+ are mostly lost from the structure.  on the other hand, in other analyzed spots, the calculated lost fe 3+ by the first method is relatively higher than that calculated by the second method. an amount of some analyzed oxides, hence their corresponding calculated cations, are not contained in the psr formula structure. they are mixed as impurities or as another mixed individual phase inside psr. therefore, the calculated value of the total cations of the second method is increased and hence the lost iron is decreased.  however, in a definite psr spot chemical analysis, all sio2, al2o3, cao, na2o, and k2o are considered as impurities and must be neglected. then, the other analyzed oxides must be multiplied by the factor: 100/100-( sio2+al2o3+cao+na2o+k2o) (12) to correct their values. in this case, the calculated iron by the first method is still more than that calculated by the second method with values ranging between 0.09 and 0.11. then, some of the other analyzed oxides, such as mgo, mno, zno, or cr2o3 may be present as individual impurity phases not related to the content of iron contained in the psr. engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11303 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand c. others stereoscopic binoculars and reflected-light polarizing microscopes were used. the heavy liquid separation technique was carried out for some investigated samples using clerici’s solution (sp. gr.= 4.05). jones riffle splitters of various sizes were also used. iv. results the majority of the studied grains were obtained in the magnetic fractions of 0.1 and 0.2 a. they were composed mainly of fine hematite and ilmeno-hematite grains, some of magnetic primary rutile in addition to minor of altered ilmenite grains of elongated and spherical, rounded grains of highly pitted surfaces. they are mostly of black (figure 1(1)) and dark brown (figure 1(2)) colors. the obtained magnetic fraction at 0.25 a is composed mainly of altered ilmenite varieties the same as those detected in the fractions at 0.1 and 0.2 a. they are black (figure 1(1)) and dark brown (figure 1(2)) grains with highly pitted surfaces. the black grains represent the 75 wt %, while the other variety the 25 wt % of the altered ilmenite grains in the fraction. the obtained magnetic fraction at 0.35 a is composed mainly of the same two altered ilmenite grains, black and dark brown. the brown grains (figure 1(3)) are more abundant, coarser, and more rounded than the black ones. the relatively lighter brown, creamy, and yellowish brown colored grains (figure 1(4)) are increased in the fraction. a considerable number of the black colored grains are stained to partially coated with relatively lighter opaque (dark brown, yellowish and reddish brown) colored soft material while the others are coated or stained with silica. the obtained magnetic fraction at 0.5 a is composed mainly of the black and brown altered ilmenite grains. the black grains are more abundant, angular, finer, and with highly pitted surfaces than the various brown grains. the grains of light brown, reddish and yellowish brown colors (figure 1(5)) are highly increased in this fraction. the same characteristic stained and coated black grains are detected also within the black colored grains of the fraction. the obtained magnetic fraction at 1 a is composed of light brown, brownish yellow, and creamy colored grains (figure 1(6)), in addition to minor black grains. most grains are spherical, sub-rounded to wellrounded. the relatively coarser grains have highly pitted surfaces while the relatively finer ones have smooth surfaces. some grains of the magnetic fraction at 1 a are separated as light fraction of clerici's solution (sp. gr. = 4 g/cm 3 ). the grains have several colored tints of pale brown, yellow, and creamy with highly pitted surfaces (figure 1(7)). they contain a considerable number of the forementioned stained and coated grains. several yellowish grains seem to be completely to partially coated with siliceous material. some of these last grains were immersed in a solution of hf acid for 48 hours and then investigated under the binocular microscope. it was noticed that the coated materials for at least 50% of the grains are partially removed showing a core of highly pitted reddish, dark brown, and black rutile of vitreous luster (figure 1(8)). the obtained nonmagnetic fraction at 1 a is very close to the relatively heavier magnetic grains at 1 a, but they have relatively lighter colors. a chosen number of altered ilmenite grains from each obtained magnetic fraction, giving a total of 84 grains including 586 determined spots, were investigated using the cameca sx-100 empa. also, a definite number of altered ilmenite grains from some of the obtained individual magnetic fractions were chosen and subjected to investigation using the xrd instrument. fig. 1. the different leucoxenated altered ilmenite varieties: (1) the black and dark brownish black colored altered ilmenite varieties separated as magnetic at 0.1, 0.2, or 0.25 a. (2) the dark brown colored altered ilmenite varieties separated as magnetic at 0.1, 0.2 or 0.25 a. (3) the dark brown and brown colored altered ilmenite varieties separated as magnetic at 0.35 a. (4) the relatively lighter brown, creamy, and yellowish brown colored grains separated as magnetic at 0.35 a. (5) the grains of light brown, reddish and yellowish brown of highly pitted surfaces separated as magnetic at 0.50 a. (6) the light brown, brownish yellow, creamy and white grains separated as magnetic or as non-magnetic at 1 a. most of the grains are spherical, subrounded to well rounded grains of highly pitted surfaces. (7) the pale brown, yellow, creamy, and white colored grains with highly pitted surfaces, separated as magnetic at 1 a. the grains are separated as a light fraction of clerici's solution (sp. gr. = 4 g/cm 3 ). (8) the yellowish grains have completely to partially coatings of siliceous material after immersed in a solution of hf acid for 48 hours. the coated materials are partially removed showing a core of highly pitted reddish, dark brown and black rutile of vitreous luster. all images are acquired with a binocular microscope, x50. engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11304 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand v. discussion a. the separated magnetic fractions at 0.1 and 0.2 a 1) the investigated brown colored grains six brown grains were investigated. the investigated grains, the analyzed spots, their chemical analysis, and their corresponding molecular formulas are shown in figure 2 and table i. the spots of the grain (figure 2(1), table i), are pseudorutile (psr) and leached pseudorutile (lpsr). the tio2 content ranges between 65.34 and 70.4 wt %, the fe2o3 content between 30 and 19.59 wt %, and the ti/(ti+fe) ratio between 0.64 and 0.75. spots 1, 8, and 9 are individual inclusions. the inclusion size is relatively finer (spot 9), as the degree of the alteration gets relatively higher. hence, spot 9 contains the highest tio2 content (70.4 wt %) and the lowest fe2o3 content (19.59 wt %). fig. 2. the bse images of the brown altered ilmenite grains, (1) to (6), separated as magnetic at 0.1 and 0.2 a. in grain (2), the spots from 1 to 7 are a definite silicate mineral. most of the constituent oxides of sio2, al2o3, fe2o3, mgo, and k2o are lost and an enrichment of the minor immobile tio2 is obtained. in the spots from 8 to 15, most of the two major oxides, sio2 and al2o3, of the altered silicate mineral are highly lowered and an individual tio2 bearing phase is formed, most probably a triple rutile phase (figure 2(2)). both spots 8 and 9 are located at the edges of the grain and are relatively enriched with the leached fe2o3 from the contained altered silicate mineral of the grain. it is obvious that spots 8, 9 seem falsly as lpsr (table i). some spots of altered silicate minerals can be falsely considered as psr or lpsr according to their chemical compositions. therefore, bse images of the analyzed spots and chemical composition analyses are at least required for the correct interpretation of such spots. it is obvious that the dependence on the powdered xrd analysis may be not enough to give correct decisions during the investigation of some analyzed grains related to psr and/or lpsr. the single crystal xrd may be a more efficient technique in such situations. also, the investigation of the grains (1) and (2) reflects that some of the associated contained inclusions may be responsible for the acquired magnetic characteristics of some detected altered ilmenite grains. grains (3)-(6) (figure 2, table i), are psr and lpsr. in these grains, the tio2 content ranges between 62.23 and 78.09 wt %, the fe2o3 content ranges between 33.21 and 14.47 wt %, and the ti/(ti+fe) ratio ranges between 0.65 and 0.81. in grain (3), the content of tio2 increases as the contents of sio2, al2o3, cao, and structural water increase. on the other hand, the content of mno follows the content of fe2o3. a comparison is made between the original total oxides sum (ot) and the new total oxides sum (nt). ot, in addition to the calculated h2o wt % corresponding to structural water in the calculated chemical formula, reflects that the calculated structural water content for most of grain (3) spots is incorrect. in other words, not all the analyzed tio2 wt % of the spot are contained in the chemical formula of the lpsr phase. there are other phases of tio2 and are mixed with the lpsr phase. it is obvious that in the region of 68-70 tio2 wt % for the analyzed lpsr spots, the mechanism of ilmenite alteration may have changed. in grain (4), except of the spots 3, 4, and 8, the other spots consist of psr and lpsr. spots 3 and 4 are located inside relatively larger cracks where the activity of molecular water seems to be high and hence the rate of alteration is relatively higher. when comparing the ot and nt, the existence of molecular water will be also assumed as the decrease of 100 wt % of the nt value (table i). the values of the analyzed oxides must be recalculated and corrected by multiplying by (100/nt). in this case, all the obtained nt values are around 100 wt %. the same case is present with spot 8 which is located inside several cracks on the edge of grain (4). hence, both tio2 and fe2o3 contents in spots 3, 4, and 8 are relatively greater than those recorded (table i). in these spots, which have obvious lower fe2o3 content, the mno content has relatively lower values. it is obvious that fe2o3 and mno contents are interdependent. grains (5) and (6) are psr and lpsr. when comparing ot and nt, it is detected that the calculated structural water contents are incorrect, especially with spots that have relatively higher tio2 content. hence, not all the analyzed tio2 values are contained within the psr phase, some individual tio2-phases may exist in association with psr. this individual phase may be inherited from the originally altered ilmenite. such explanation is obvious in grain (6) which seems as it was originally titanhematite-ferriilmenite exsolved intergrowth. grain (5) may be ilmenite with some individual tio2-phase content present in solid solution with ilmenite. engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11305 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand table i. microprobe chemical analyses and the corresponding molecular formulae of the analyzed spots of the brown altered ilmenite grains (1)-(6) of figure 2, separated as magnetic at 0.1 and 0.2 a grain spot sio2 mgo mno cao zno fe2o3 al2o3 cr2o3 na2o k2o tio2 ot oh% h2o% nt fe2 ti3 ox ohy lost fe ti/ (ti+fe) fig. 2(1) 2b 1 1.82 0.70 0.62 0.19 0.00 29.22 0.73 0.05 0.02 0.04 63.73 97.13 4.63 2.45 99.58 1.66 3 7.98 1.02 0.34 0.64 8 0.84 0.29 0.67 0.20 0.00 22.48 0.46 0.11 0.04 0.02 69.81 94.92 12.91 6.84 101.76 1.13 3 6.34 2.66 0.87 0.73 9 0.90 0.30 0.59 0.26 0.00 19.59 0.55 0.11 0.06 0.03 70.40 92.78 14.97 7.93 100.71 1.00 3 5.98 3.02 1.00 0.75 fig. 2(2) 8 8.69 0.25 0.13 0.32 0.00 9.76 7.31 0.11 0.06 0.10 70.13 96.85 5.86 3.11 99.96 1.47 3 7.82 1.18 0.53 9 7.97 0.47 0.10 0.37 0.00 4.76 5.56 0.07 0.07 0.26 71.56 91.18 12.30 6.51 97.69 1.10 3 6.64 2.36 0.90 10 10.71 0.26 0.00 0.21 0.00 3.12 6.69 0.06 0.04 0.10 76.95 98.14 11.04 5.84 103.99 1.13 3 6.89 2.11 0.87 11 7.84 0.10 0.01 0.21 0.00 1.44 5.71 0.04 0.06 0.06 80.36 95.83 17.43 9.23 105.06 0.81 3 5.77 3.23 1.19 12 7.78 0.24 0.09 0.35 0.00 3.88 5.17 0.09 0.05 0.08 80.87 98.58 16.14 8.55 107.13 0.88 3 5.97 3.03 1.12 13 5.13 0.07 0.04 0.11 0.00 2.20 3.51 0.04 0.06 0.03 88.72 99.90 23.52 12.45 112.35 0.51 3 4.74 4.26 1.49 14 3.87 0.07 0.00 0.23 0.00 1.67 2.63 0.05 0.05 0.05 89.74 98.37 26.13 13.84 112.21 0.39 3 4.31 4.69 1.61 15 0.66 0.01 0.04 0.02 0.00 1.08 0.41 0.04 0.00 0.01 97.94 100.20 32.79 17.37 117.57 0.08 3 3.28 5.72 1.92 fig. 2(3) 2d-2e 2 0.33 0.14 0.39 0.16 0.00 27.00 0.23 0.10 0.05 0.00 66.79 95.20 10.02 5.31 100.51 1.30 3 6.87 2.13 0.70 0.70 3 0.35 0.18 0.56 0.21 0.00 26.95 0.27 0.13 0.02 0.01 68.10 96.77 10.23 5.42 102.18 1.29 3 6.83 2.17 0.71 0.70 5 0.43 0.22 0.35 0.24 0.00 23.78 0.41 0.13 0.06 0.01 70.25 95.89 12.82 6.79 102.68 1.13 3 6.35 2.65 0.87 0.73 13 0.90 0.25 0.11 0.43 0.00 15.97 0.72 0.21 0.11 0.06 76.37 95.13 18.76 9.94 105.07 0.79 3 5.34 3.66 1.21 0.79 15 0.90 0.19 0.05 0.47 0.00 14.63 0.74 0.22 0.09 0.04 78.09 95.42 20.08 10.64 106.06 0.72 3 5.13 3.87 1.28 0.81 fig. 2(4) 3 0.35 0.12 1.00 0.16 0.00 25.55 0.38 0.37 0.00 0.01 63.49 91.44 9.35 4.95 96.39 1.35 3 7.00 2.00 0.65 0.69 4 0.43 0.12 0.82 0.19 0.00 24.16 0.49 0.42 0.03 0.01 63.94 90.59 10.34 5.47 96.07 1.29 3 6.82 2.18 0.71 0.70 8 0.65 0.16 0.84 0.23 0.00 18.82 0.59 0.42 0.04 0.03 65.68 87.45 14.38 7.62 95.07 1.04 3 6.08 2.92 0.96 0.74 fig. 2(5) 2 2.02 0.76 0.41 0.17 0.00 25.60 1.01 0.14 0.05 0.09 66.60 96.84 7.55 4.00 100.83 1.46 3 7.39 1.61 0.54 0.67 5 0.72 0.70 0.53 0.14 0.00 26.82 0.56 0.18 0.04 0.02 67.97 97.67 9.11 4.83 102.50 1.38 3 7.06 1.94 0.62 0.69 fig. 2(6) 1 0.40 0.25 1.23 0.19 0.00 23.85 0.72 0.14 0.05 0.04 67.05 93.92 11.10 5.88 99.80 1.25 3 6.67 2.33 0.75 0.71 5 0.30 0.21 1.19 0.17 0.00 24.22 0.42 0.15 0.05 0.01 68.19 94.89 11.68 6.19 101.08 1.21 3 6.56 2.44 0.79 0.71 7 0.28 0.19 1.16 0.21 0.00 22.03 0.64 0.16 0.07 0.02 70.56 95.32 13.64 7.22 102.55 1.10 3 6.20 2.80 0.90 0.73 the psr-lpsr of these investigated six grains have a chemical formula of fe1.66-0.72ti3o7.98-5.13(oh)1.02-3.87 (table i). 2) the investigated black grains fourteen black grains are investigated. except spot 1 of grain (7) (a definite silicate mineral), spot 1 of grain (16), spots 3, 4 of grain (18), spots 4, 5, 6 of grain (20) (leached ilmenite), and spot 5 of grain (17) (rutile and hematite), the rest spots of the grains (7)-(17) are composed of psr of various chemical formulas (figure 3). the content of tio2 ranges between 57.5 and 73.71 wt %, the content of fe2o3 between 37.98 and 19.34 wt %, and the ti/(ti+fe) ratio between 0.60 and 0.74 (table ii). in spots 3-5 of grain (7), the comparison between ot and nt reflects that either the calculated structural water (oh ), is incorrect or not all the analyzed tio2 content is included in the psr formula structure. hence, some individual tio2-phases are mixed with the psr in the various analyzed spots of the grain. grains (8)-(10) are psr. in these grains, the content of tio2 and fe2o3 and most of the other analyzed oxides seem to be homogeneous. grain (11) seems that was originally titanhematite-ferriilmenite exsolved intergrowth where most of the titanhematite component was leached out while the ferriilmenite was altered to psr (spots 1-5). spot 6 seems to be a mixture between tio2 and fe2o3 phases and is not a psr phase. in this spot, ot equals to 98.8 wt %. if the remaining percentage (1.2 wt %) is totally structural water, it will be much lower and not accepted in a psr formula with such content of tio2 (68.8 wt %) and fe2o3 (23.1 wt %). the analyzed value of mno is another reason that spot 6 is not a psr phase where most of the analyzed altered ilmenite (spots 1-5) contain a definite amount of mixed pyrophanite component (up to 2.56 wt % mno). in spot 6, there is a high decrease of the altered ilmenite component, and hence, the followed pyrophanite is reflected in its mno content (1.2 mno wt %). fig. 3. bse images of the black altered ilmenite grains (7)-(20), separated as magnetic at 0.1 and 0.2 a. grains (12), (13) are somewhat homogeneous psr. grains (14)-(17) are psr (figure 3, table ii). grain (15) seems to be originally exsolved intergrowth of titanhematite-ferriilmenite. when comparing the ot and nt of the grain, either the calculated structural water is incorrect or not all the analyzed tio2 content is included in the psr chemical formula. also, the recorded al2o3 contents in grain (15) seem to be associated with the components of the original exsolved intergrowth. it may be most probably mixed with the titanhematite one. in engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11306 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand fact, grain (15), spreads light on some problems during the calculations of the various altered ilmenite phases. in much of the literature, the recorded sio2 and al2o3 contents are considered as impurities and must be subtracted from the total oxide sum followed by the recalculation and correction of the other analyzed oxides. however, the most abundant analyzed oxide of the spot, tio2, will be highly affected by the recalculation and correction. it increases with a relatively much more percentage than the other analyzed oxides, especially fe2o3, the second major oxide of spot analysis. if sio2 and/or al2o3 are not impurities, and are originally associated with only tio2 or with only fe2o3 then, some misleading results will be obtained by considering these two oxides as impurities. table ii. microprobe chemical analyses and the corresponding molecular formulae of the analyzed spots of the black altered ilmenite grains (7)-(20) of figure 3, separated as magnetic at 0.1 and 0.2 a grain spot sio2 mgo mno cao zno fe2o3 al2o3 cr2o3 na2o k2o tio2 ot oh% h2o% nt fe2 ti3 ox ohy lost fe ti/ (ti+fe) fig. 3(7) 1 25.38 7.09 0.24 0.24 0.00 24.09 0.23 0.10 0.02 0.61 36.56 94.55 -46.53 -24.64 69.91 6.07 3 22.61 -13.61 -4.07 3 0.92 0.60 0.20 0.34 0.00 20.09 1.45 0.31 0.05 0.05 73.16 97.18 14.05 7.44 104.62 1.07 3 6.16 2.84 0.93 0.74 5 0.90 0.56 0.26 0.34 0.00 20.49 1.49 0.32 0.03 0.04 72.98 97.40 13.73 7.27 104.68 1.08 3 6.21 2.79 0.92 0.73 fig. 3(8) 1 0.15 1.77 0.55 0.04 0.00 33.46 0.09 0.02 0.01 0.01 61.22 97.32 2.66 1.41 98.73 1.87 3 8.40 0.60 0.13 0.62 6 0.15 1.75 0.55 0.03 0.00 31.68 0.09 0.02 0.03 0.00 62.25 96.55 4.27 2.26 98.81 1.75 3 8.04 0.96 0.25 0.63 fig. 3(9) 1 0.15 2.42 0.54 0.10 0.00 34.14 0.10 0.03 0.04 0.02 59.69 97.23 0.95 0.50 97.73 2.02 3 8.78 0.22 -0.02 0.60 3 0.16 2.20 0.51 0.07 0.00 33.65 0.07 0.02 0.01 0.03 60.57 97.29 1.90 1.01 98.29 1.94 3 8.57 0.43 0.06 0.61 fig. 3(10) 1 0.22 0.21 0.60 0.20 0.00 29.10 0.98 0.08 0.00 0.01 60.90 92.30 5.74 3.04 95.34 1.60 3 7.73 1.27 0.40 0.65 4 0.39 0.12 0.43 0.18 0.00 29.73 0.25 0.11 0.07 0.01 65.86 97.14 7.72 4.09 101.23 1.45 3 7.33 1.67 0.55 0.67 fig. 3(11) 1 0.24 0.10 2.38 0.16 0.00 31.70 0.35 0.09 0.05 0.02 57.50 92.57 2.35 1.24 93.82 1.87 3 8.46 0.54 0.13 0.62 2 0.22 0.07 1.92 0.09 0.00 35.95 0.32 0.10 0.03 0.00 60.19 98.89 0.98 0.52 99.41 1.96 3 8.77 0.23 0.04 0.60 6 2.86 0.24 1.20 0.11 0.00 23.09 2.22 0.13 0.04 0.07 68.79 98.75 7.86 4.16 102.91 1.43 3 7.34 1.66 0.57 0.68 fig. 3(12) 3 0.24 1.54 0.37 0.07 0.00 32.20 0.31 0.39 0.01 0.01 64.21 99.34 4.33 2.30 101.63 1.73 3 8.03 0.97 0.27 0.63 fig. 3(13) 3 0.31 0.13 1.53 0.17 0.00 30.65 0.27 0.14 0.02 0.01 62.51 95.73 5.44 2.88 98.61 1.63 3 7.79 1.21 0.37 0.65 fig. 3(14) 3 0.29 0.13 1.45 0.14 0.00 29.09 0.33 0.10 0.03 0.02 67.84 99.43 8.32 4.41 103.83 1.43 3 7.20 1.80 0.57 0.68 fig. 3(15) 3 0.40 0.10 0.41 0.17 0.00 28.09 1.14 0.29 0.03 0.02 67.45 98.11 8.35 4.42 102.53 1.41 3 7.21 1.79 0.59 0.68 4 0.38 0.10 0.63 0.18 0.00 26.11 1.23 0.27 0.04 0.02 68.89 97.85 9.95 5.27 103.12 1.31 3 6.90 2.10 0.69 0.70 fig. 3(16) 1 0.09 0.14 2.28 0.06 0.00 38.21 0.00 0.05 0.03 0.00 59.19 100.04 -0.60 -0.32 99.72 2.10 3 9.14 -0.14 -0.10 4 0.46 0.07 0.32 0.19 0.00 31.10 0.17 0.11 0.02 0.01 65.07 97.51 6.66 3.52 101.04 1.52 3 7.54 1.46 0.48 0.66 fig. 3(17) 4 0.15 0.38 0.97 0.07 0.00 34.49 0.03 0.09 0.06 0.01 61.25 97.49 2.96 1.57 99.06 1.81 3 8.33 0.67 0.19 0.62 5 3.24 0.21 0.07 0.86 0.00 6.21 0.73 0.16 0.18 0.03 78.31 90.00 23.38 12.38 102.38 0.54 3 4.68 4.32 1.46 0.85 fig. 3(18) 1 47.83 5.59 0.02 0.30 0.00 13.20 13.92 0.06 0.11 3.23 4.38 88.62 -176.16 -93.30 -4.67 79.49 3 269.27 -260.27 -77.49 2 0.00 0.07 1.90 0.02 0.00 52.94 0.00 0.00 0.02 0.01 47.51 102.46 -15.39 -8.15 94.31 3.49 3 13.33 -4.33 -1.49 3 0.31 0.13 1.67 0.07 0.00 37.33 0.15 0.02 0.05 0.03 57.45 97.21 -0.93 -0.49 96.72 2.11 3 9.22 -0.22 -0.11 4 0.15 0.08 1.80 0.03 0.00 38.73 0.05 0.02 0.00 0.02 57.88 98.75 -1.30 -0.69 98.06 2.14 3 9.31 -0.31 -0.14 5 0.92 0.34 0.96 0.19 0.00 28.85 0.78 0.11 0.02 0.04 58.12 90.33 3.83 2.03 92.35 1.73 3 8.14 0.86 0.27 0.63 6 0.10 0.10 1.14 0.05 0.00 37.76 0.05 0.02 0.00 0.03 59.01 98.26 0.15 0.08 98.34 2.01 3 8.96 0.04 -0.01 0.60 7 0.12 0.08 1.35 0.04 0.00 36.42 0.05 0.04 0.04 0.01 59.34 97.49 1.04 0.55 98.04 1.95 3 8.76 0.24 0.05 0.61 8 0.32 0.15 1.04 0.11 0.00 31.87 0.12 0.03 0.02 0.03 62.83 96.51 5.22 2.76 99.27 1.63 3 7.84 1.16 0.37 0.65 9 0.42 0.11 2.07 0.17 0.00 25.70 0.19 0.02 0.06 0.04 67.88 96.65 10.33 5.47 102.12 1.31 3 6.81 2.19 0.69 0.70 10 0.43 0.16 1.56 0.16 0.00 24.29 0.19 0.03 0.08 0.02 69.86 96.78 12.09 6.40 103.18 1.19 3 6.48 2.52 0.81 0.72 11 1.12 0.37 0.31 0.24 0.00 12.16 0.98 0.15 0.08 0.04 72.83 88.27 20.43 10.82 99.09 0.70 3 5.09 3.91 1.30 0.81 12 1.69 0.51 0.21 0.32 0.00 12.36 0.91 0.12 0.07 0.09 73.96 90.24 19.73 10.45 100.69 0.74 3 5.21 3.79 1.26 0.80 fig. 3(19) 1 0.18 0.09 1.77 0.16 0.02 28.27 0.15 0.10 0.00 0.00 55.61 86.34 4.71 2.50 88.83 1.69 3 7.94 1.06 0.31 0.64 4 0.22 0.18 1.44 0.12 0.14 30.29 0.21 0.05 0.00 0.00 64.10 96.75 6.46 3.42 100.17 1.56 3 7.58 1.42 0.44 0.66 fig. 3(20) 1 0.00 0.15 2.31 0.00 0.16 48.58 0.00 0.00 0.00 0.00 49.90 101.11 -11.64 -6.17 94.95 3.11 3 12.13 -3.13 -1.11 2 0.00 0.18 2.12 0.02 0.20 49.25 0.00 0.00 0.00 0.00 50.32 102.09 -11.75 -6.22 95.86 3.11 3 12.16 -3.16 -1.11 6 0.00 0.19 1.79 0.02 0.07 43.96 0.00 0.00 0.00 0.00 52.76 98.79 -7.00 -3.71 95.08 2.64 3 10.78 -1.78 -0.64 8 0.06 0.16 0.98 0.03 0.02 33.33 0.05 0.03 0.00 0.00 57.27 91.92 2.49 1.32 93.24 1.83 3 8.43 0.57 0.17 0.62 12 0.02 0.22 0.56 0.05 0.04 33.28 0.06 0.00 0.00 0.00 58.40 92.61 3.22 1.70 94.32 1.78 3 8.27 0.73 0.22 0.63 13 0.12 0.24 0.48 0.07 0.03 30.70 0.09 0.02 0.00 0.00 60.82 92.57 5.81 3.08 95.65 1.59 3 7.71 1.29 0.41 0.65 grain (16) seems that was originally titanhematiteferriilmenite exsolved intergrowth. some of the remaining individual components of minor tio2 and/or minor fe2o3 may be still mixed with the formed psr after the ilmenite alteration. in grain (17), because spot 5 is in a crack, the rate of alteration is relatively higher than those of the other spots due to the increased water activity bearing for sio2, al2o3, and maybe cao. hence, the leaching of the contained fe2o3 from the psr is highly increased and another lpsr phase is attained which may be followed by the collapse into two individual phases for tio2 and fe2o3. in grain (18), spot 1 is a definite silicate mineral. spot 2 is most probably ferriilmenite. spots 3 and 4 are leached ilmenite. when comparing ot and nt, spot 5 contains a relatively higher content of molecular water (table ii). from the ot value, both structural and molecular water types reach 9.7 wt %, while from the nt value the structural water is 2.03 wt %. the content of molecular water almost equals to 7.66 wt %. if the values of tio2 and fe2o3 are engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11307 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand corrected by multiplying by (100/92.35), then they become 62.95 and 31.25 wt %, respectively. then, spot 5 will have a composition like that of spot 8 (table ii). also, in grain (18), it is obvious that the content of molecular water increases as the contents of the associated sio2 and al2o3 increase (table ii). spots 6-8 are psr with ti/ti+fe ratio ranges between 0.6 and 0.65. according to the nt values, the spots 9 and 10 are psr mixed with minor tio2 and/or fe2o3 individual phases. the ti/ti+fe ratio ranges between 0.7 and 0.72. spots 11 and 12 are lpsr of different chemical formulas. their ti/ti+fe ratio ranges between 0.8 and 0.81. the mno content in these two spots is highly lowered due to the decrease of the corresponding fe2o3 content which insures the direct relation between fe2o3 and mno. also, the investigation of spots 11 and 12 insures that as the content of structural water contained in the lpsr phase increases, the associated sio2 and/or al2o3 contents also increase. grain (19) is originally exsolved intergrowth of titanhematite-ferriilmenite. most of the hematite component is leached out and the associated ilmenite component is altered to psr. spot 1 is psr associated with a considerable amount of molecular water reaching a value of 11.17 wt % (table ii). in grain (20), the spots 1-3 are ilmenite. spots 4-6 are leached ilmenite and spots 7-13 are psr. it is noticed that spots 7-13 contain a considerable amount of molecular water which reflects the role of water in the initial alteration stages of ilmenite alteration. the psr-lpsr of these investigated grains have the chemical formula range of fe2.02-0.54ti3o8.78-4.68(oh)0.22-4.32 (table ii). only 3 spots have fe content ranging between 2.01 and 2.02 due to the appreciable contents of mg 2+ and/or mn 2+ which have relatively lower oxidation states than fe 3+ . b. the separated magnetic fraction at 0.25 a twenty one opaque brown grains and 18 black grains were investigated. 1) the investigated brown grains most of the analyzed spots of the grains (figure 4, table iii) are composed of psr and lpsr whereas the spots 1-5 in grain (1) and the spots 2 and 5 in grain (2) are leached ilmenite (table iii). in psr and lpsr analyzed spots, the tio2 content ranges between 57.63 and 69.79 wt %, the fe2o3 content between 20.97 and 37.27 wt %, and the ti/ti+fe ratio between 0.6 and 0.75. in the grain (3) of figure 4, spots 1 and 2 contain a considerable amount of molecular water (table iii). the molecular water may have reached 16.6 wt % in spot 1 which is located at the edge of the grain while it reaches 10.3 wt % in spot 2 which is located beside several pores of a preexisting leached titanhematite. also, in spot 1 of grains (4) and (5), the contained molecular water is relatively higher and attains 8.8 and 16.38 wt %, respectively (table iii). in fact, most of the spots having an appreciable content of molecular water (spots 1 and 2 in (3), spot 1 in (4), and spot 1 in (5)), also contain relatively higher contents of sio2 and al2o3. this may indicate the ability of these two oxides of bearing molecular water or oh anions. fig. 4. bse images of the brown altered ilmenite grains (1)-(21), separated as magnetic at 0.25 a. grains (6)-(9) in figure 4, are composed of psr. also, most of the analyzed spots of these four grains contain definite amounts of molecular water. the comparison of the values of ot and nt (table iii) reflects the occurrence of some molecular water. both grains (10) and (11) are psr of various chemical formulas. in these two grains, the content of structural and/or molecular water is increased, as the analyzed zones are relatively darker. grains (12) and (13) are psr. spot 1 of grain (13) is in a location of a preexisting leached titanhematite, hence there is a definite content of molecular water (table iii). however, these grains show that the presence of preexisting leached phases bearing for tio2 affects the calculation of the nt of the detected psr chemical formulas, since it exceeds 100 wt %. in the rest 8 investigated grains, (14)-(21) (figure 4 and table iii), except spot 5 (mixture of silica and psr), and spots 13 and 14 (silica) of grain (18), all the other investigated grains are psr and lpsr with tio2 content ranging between 64.77 and 76.35 wt %, fe2o3 content ranging between 12.24 and 28.96 wt %, and ti/ti+fe ratio ranging between 0.67 and 0.79. in spots 3 and 4 of grain (14), the content of fe2o3 becomes relatively lower, as the contents of sio2, al2o3, cr2o3, and cao become relatively higher while the contents of mgo and mno become relatively lower. the increment of sio2 and al2o3 contents seems to be correlated with the enrichment of tio2 content which correlates directly with the contained structural water of the formed lpsr phase. however, the nt of the spots 3 and 4 is much more than 100 wt %. then, either the calculated structural water is incorrect or not all the analyzed tio2 content is included within the lpsr phase formula. such tio2 content may be preexisting as a solid solution with the original ilmenite or is individually separated outside the lpsr phase structure at a definite alteration stage. the same situation is also recorded in the spots of grains (17)-(21), especially when the content of tio2 exceeds the value 68 or 69 wt %. grains (15) and (16) are lpsr. except spots 13 and 14 of grain (18), the other analyzed spots are composed of lpsr. also, spots engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11308 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand 7-12 have the same remarks explained with spots 3-4 of grain (14). the psr-lpsr of these investigated grains have the chemical formula range of fe2.03-0.81ti3o9-5.4(oh)0-3.6 (table iii). only 2 spot analyses have fe content ranging between 2.01 and 2.03 due to the appreciable contents of mn and/or mg which have oxidation state of 2 + . 2) the investigated black grains except spots 1-4 of grain (34), spots 1-8, and 10 of grain (35), and spots 1, 2 of grain (37) which are leached ilmenite, all the other spots of grains (22)-(39) (figure 5, table iv), are composed of psr. the tio2 content ranges between 58.05 and 63.34 wt %, the fe2o3 content between 37.7 and 26.96 wt %, and the ti/ti+fe ratio between 0.60 and 0.67. in spot 7 of grain (27), it is difficult to accept that the ot is 96.86 wt % and that nt equals to 111.97 wt % (table iv). the value of the analyzed fe2o3 equals to 2.44 wt %. in fact, the lpsr of this spot is broken into individual phases of tio2 and fe2o3 where most of the contained fe2o3 is leached out. both sio2 and al2o3 contents in this spot are relatively much higher than those of the other spots. however, there is a considerable amount of molecular water in the spot, which reaches 3.14 wt % (100 wt % 96.86 wt %). both sio2 and al2o3 may be related to the associated molecular water. table iii. microprobe chemical analyses and the corresponding molecular formulae of the analyzed spots of the brown altered ilmenite grains (1)-(21) of figure 4, separated as magnetic at 0.25 a grain spot sio2 mgo mno cao zno fe2o3 al2o3 cr2o3 na2o k2o tio2 ot oh% h2o% nt fe2 ti3 ox ohy lost fe ti/ (ti+fe) fig. 4(1) 1 0.18 0.60 0.53 0.06 0.10 39.94 0.10 0.06 0.00 0.01 57.78 99.36 -2.13 -1.13 98.23 2.20 3 9.51 -0.51 -0.20 6 0.11 0.70 0.71 0.09 0.03 35.41 0.09 0.04 0.00 0.02 60.09 97.29 1.75 0.93 98.21 1.90 3 8.60 0.40 0.10 0.61 fig. 4(2) 2 0.09 0.45 1.02 0.10 0.14 37.61 0.06 0.07 0.00 0.00 58.06 97.60 -0.52 -0.27 97.32 2.08 3 9.12 -0.12 -0.08 5 0.06 0.63 0.91 0.06 0.00 37.46 0.03 0.03 0.03 0.01 58.57 97.77 -0.12 -0.07 97.71 2.05 3 9.03 -0.03 -0.05 fig. 4(3) 1 2.85 0.14 0.25 0.17 0.00 28.70 2.16 0.05 0.05 0.21 48.82 83.39 -4.18 -2.22 81.18 2.29 3 9.99 -0.99 -0.29 2 0.73 0.20 0.16 0.10 0.00 31.56 0.16 0.00 0.01 0.03 56.71 89.66 2.94 1.56 91.22 1.78 3 8.33 0.67 0.22 0.63 3 0.00 0.15 0.47 0.02 0.05 36.63 0.00 0.00 0.00 0.00 57.63 94.94 0.79 0.42 95.36 1.95 3 8.82 0.18 0.05 0.61 fig. 4(4) 1 0.60 0.77 0.61 0.12 0.00 29.88 0.76 0.09 0.01 0.04 56.82 89.72 2.81 1.49 91.21 1.82 3 8.37 0.63 0.18 0.62 6 0.18 1.78 0.43 0.14 0.00 28.98 0.33 0.08 0.00 0.00 62.00 93.93 5.68 3.01 96.94 1.65 3 7.75 1.25 0.35 0.65 fig. 4(5) 1 2.21 0.27 1.11 0.13 0.06 28.15 0.68 0.04 0.00 0.05 50.93 83.62 -0.47 -0.25 83.37 2.02 3 9.11 -0.11 -0.02 6 0.02 0.02 0.64 0.09 0.09 22.91 1.16 0.03 0.00 0.02 62.10 87.06 11.01 5.83 92.90 1.25 3 6.69 2.31 0.75 0.71 fig. 4(6) 1 0.32 0.19 2.01 0.15 0.03 31.97 0.26 0.21 0.01 0.02 59.98 95.14 3.23 1.71 96.84 1.80 3 8.27 0.73 0.20 0.63 7 0.60 0.19 1.74 0.20 0.00 26.20 0.40 0.19 0.04 0.01 65.02 94.60 8.67 4.59 99.19 1.41 3 7.14 1.86 0.59 0.68 fig. 4(7) 1 0.18 1.17 0.37 0.12 0.00 31.09 0.18 0.15 0.00 0.01 59.85 93.11 4.09 2.17 95.28 1.74 3 8.08 0.92 0.26 0.63 4 0.21 1.06 0.34 0.15 0.10 30.25 0.22 0.14 0.00 0.00 61.41 93.88 5.26 2.79 96.66 1.65 3 7.83 1.17 0.35 0.64 fig. 4(8) 1 0.12 0.09 1.21 0.07 0.13 33.00 0.06 0.06 0.05 0.02 60.21 95.03 3.63 1.92 96.95 1.76 3 8.18 0.82 0.24 0.63 7 0.27 0.10 0.82 0.13 0.11 29.07 0.31 0.04 0.02 0.03 62.89 93.78 7.13 3.77 97.55 1.50 3 7.44 1.56 0.50 0.67 fig. 4(9) 1 0.36 0.12 0.99 0.23 0.05 25.54 0.54 0.00 0.00 0.03 62.86 90.72 9.18 4.86 95.58 1.37 3 7.04 1.96 0.63 0.69 6 0.39 0.11 1.13 0.24 0.16 23.72 0.31 0.02 0.05 0.02 66.81 92.95 11.75 6.22 99.18 1.21 3 6.54 2.46 0.79 0.71 fig. 4(10) 1 0.23 0.06 0.95 0.10 0.00 33.01 0.32 0.09 0.01 0.03 62.67 97.46 4.39 2.32 99.78 1.69 3 8.01 0.99 0.31 0.64 5 0.53 0.13 0.38 0.23 0.00 24.17 0.87 0.23 0.09 0.01 68.13 94.77 11.36 6.01 100.79 1.22 3 6.63 2.37 0.78 0.71 fig. 4(11) 1 0.37 0.07 0.35 0.17 0.00 22.92 0.39 0.16 0.02 0.00 64.95 89.39 12.29 6.51 95.90 1.16 3 6.45 2.55 0.84 0.72 5 0.36 0.06 0.33 0.14 0.00 20.97 0.42 0.16 0.04 0.00 67.71 90.18 14.51 7.69 97.86 1.02 3 6.05 2.95 0.98 0.75 fig. 4(12) 1 0.70 0.15 1.19 0.16 0.00 31.43 0.51 0.11 0.01 0.01 62.83 97.08 4.53 2.40 99.48 1.68 3 7.99 1.01 0.32 0.64 6 0.49 0.21 0.96 0.24 0.00 23.90 0.44 0.21 0.04 0.02 69.37 95.87 12.03 6.37 102.24 1.19 3 6.50 2.50 0.81 0.72 fig. 4(13) 1 0.67 0.17 0.45 0.25 0.00 23.00 1.39 0.15 0.11 0.15 60.20 86.54 8.87 4.70 91.24 1.39 3 7.11 1.89 0.61 0.68 7 0.42 0.24 0.43 0.20 0.00 24.69 0.59 0.19 0.02 0.02 69.79 96.59 11.83 6.26 102.86 1.19 3 6.54 2.46 0.81 0.72 fig. 4(14) 3 0.77 0.44 0.21 0.33 0.00 19.67 0.38 0.18 0.01 0.04 74.38 96.40 16.16 8.56 104.96 0.93 3 5.77 3.23 1.07 0.76 4 0.87 0.30 0.23 0.42 0.00 17.03 0.43 0.23 0.04 0.04 77.09 96.68 18.40 9.74 106.42 0.81 3 5.40 3.60 1.19 0.79 fig. 4(15) 3 2.37 0.96 0.33 0.22 0.00 21.83 1.01 0.21 0.05 0.17 68.60 95.75 10.11 5.36 101.10 1.30 3 6.90 2.10 0.70 0.70 fig. 4(16) 2 1.75 1.08 0.38 0.13 0.00 21.77 0.75 0.18 0.04 0.14 68.35 94.57 11.04 5.85 100.42 1.25 3 6.71 2.29 0.75 0.71 fig. 4(17) 1 0.34 0.15 0.55 0.15 0.00 26.54 0.32 0.09 0.00 0.03 68.08 96.24 10.57 5.60 101.84 1.27 3 6.77 2.23 0.73 0.70 3 0.46 0.15 0.38 0.21 0.00 22.81 0.40 0.13 0.06 0.02 71.15 95.78 13.77 7.30 103.07 1.07 3 6.18 2.82 0.93 0.74 fig. 4(18) 1 0.43 0.12 0.13 0.28 0.00 26.64 0.19 0.05 0.07 0.02 66.78 94.70 10.31 5.46 100.16 1.28 3 6.82 2.18 0.72 0.70 4 0.41 0.10 0.17 0.26 0.00 25.71 0.22 0.07 0.07 0.02 67.57 94.59 11.18 5.92 100.51 1.23 3 6.65 2.35 0.77 0.71 5 6.60 0.14 0.17 0.29 0.00 21.47 0.31 0.08 0.07 0.02 68.39 97.54 7.05 3.73 101.28 1.40 3 7.53 1.47 0.60 0.68 7 0.61 0.16 0.23 0.29 0.00 23.39 0.36 0.10 0.07 0.04 69.39 94.64 12.81 6.79 101.42 1.13 3 6.36 2.64 0.87 0.73 8 0.50 0.14 0.11 0.35 0.00 21.01 0.30 0.10 0.02 0.02 71.65 94.21 15.35 8.13 102.34 0.97 3 5.90 3.10 1.03 0.75 10 0.59 0.15 0.14 0.33 0.00 20.20 0.35 0.15 0.05 0.04 72.56 94.56 15.91 8.42 102.99 0.94 3 5.81 3.19 1.06 0.76 12 0.59 0.17 0.15 0.33 0.00 21.16 0.42 0.14 0.04 0.04 72.76 95.79 15.19 8.04 103.83 0.98 3 5.93 3.07 1.02 0.75 13 97.88 0.00 0.00 0.02 0.00 0.35 0.00 0.01 0.00 0.03 0.73 99.02 -273.98 -145.10 -46.08 539.47 3 2158.49 -2149.49 -537.47 14 97.38 0.02 0.00 0.04 0.00 0.35 0.17 0.00 0.01 0.04 0.80 98.80 -273.04 -144.60 -45.80 490.84 3 1962.36 -1953.36 -488.84 fig. 4(19) 1 0.42 0.16 0.54 0.29 0.08 21.94 0.52 0.10 0.01 0.03 69.00 93.09 13.62 7.21 100.31 1.08 3 6.21 2.79 0.92 0.73 5 0.62 0.19 0.35 0.40 0.02 18.11 0.69 0.08 0.03 0.01 72.49 92.99 16.88 8.94 101.93 0.89 3 5.65 3.35 1.11 0.77 fig. 4(20) 1 0.38 0.51 1.22 0.24 0.00 23.73 0.50 0.11 0.05 0.02 69.40 96.16 11.87 6.29 102.45 1.21 3 6.53 2.47 0.79 0.71 5 0.40 0.53 1.12 0.23 0.03 21.82 0.52 0.09 0.04 0.02 71.53 96.33 13.77 7.30 103.63 1.09 3 6.18 2.82 0.91 0.73 fig. 4(21) 1 1.07 0.30 0.23 0.38 0.00 19.64 1.09 0.23 0.04 0.04 74.22 97.22 15.11 8.00 105.23 0.99 3 5.97 3.03 1.01 0.75 5 1.14 0.22 0.18 0.43 0.04 16.94 1.29 0.33 0.02 0.02 76.35 96.96 17.17 9.09 106.06 0.87 3 5.62 3.38 1.13 0.77 engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11309 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand table iv. microprobe chemical analyses and the corresponding molecular formulae of the analyzed spots of the black altered ilmenite grains (22)-(39) of figure 5, separated as magnetic at 0.25 a grain spot sio2 mgo mno cao zno fe2o3 al2o3 cr2o3 na2o k2o tio2 ot oh % h2o % nt fe2 ti3 ox ohy lost fe ti/ (ti+fe) fig. 5(22) 1 0.20 0.02 1.27 0.10 0.00 32.46 0.18 0.10 0.01 0.00 59.68 94.01 3.66 1.94 95.95 1.75 3 8.17 0.83 0.25 0.63 fig. 5(23) 1 0.23 0.12 0.60 0.12 0.00 32.72 0.12 0.04 0.00 0.01 60.98 94.95 4.30 2.28 97.23 1.69 3 8.03 0.97 0.31 0.64 5 0.21 0.10 0.57 0.10 0.02 31.87 0.10 0.07 0.04 0.01 61.95 95.05 5.29 2.80 97.85 1.62 3 7.82 1.18 0.38 0.65 fig. 5(24) 4 0.55 0.16 1.17 0.16 0.46 26.96 0.32 0.11 0.06 0.01 63.34 93.30 7.92 4.19 97.49 1.46 3 7.28 1.72 0.54 0.67 fig. 5(25) 1 0.12 0.08 0.93 0.07 0.03 37.48 0.09 0.10 0.00 0.00 59.19 98.08 0.41 0.22 98.29 1.99 3 8.90 0.10 0.01 0.60 fig. 5(26) 3 0.18 0.10 0.88 0.12 0.08 32.16 0.16 0.01 0.01 0.01 63.14 96.83 5.38 2.85 99.67 1.62 3 7.80 1.20 0.38 0.65 fig. 5(27) 6 0.10 0.05 5.55 0.04 0.00 31.32 0.00 0.03 0.01 0.00 60.92 98.03 3.07 1.62 99.65 1.87 3 8.29 0.71 0.13 0.62 7 1.60 0.14 0.10 0.71 0.00 2.44 1.62 0.17 0.07 0.04 89.98 96.86 28.53 15.11 111.97 0.30 3 3.90 5.10 1.70 fig. 5(28) 2 0.70 0.19 2.52 0.07 0.03 34.36 0.32 0.17 0.02 0.03 59.99 98.40 0.92 0.49 98.89 1.97 3 8.79 0.21 0.03 0.60 5 0.20 0.08 2.94 0.07 0.09 32.99 0.08 0.10 0.03 0.02 61.62 98.23 3.21 1.70 99.93 1.81 3 8.27 0.73 0.19 0.62 fig. 5(29) 1 0.10 0.28 0.62 0.13 0.01 35.40 0.16 0.05 0.00 0.01 60.61 97.36 2.31 1.22 98.58 1.85 3 8.47 0.53 0.15 0.62 5 0.08 0.25 0.80 0.11 0.03 33.42 0.13 0.03 0.01 0.00 62.73 97.58 4.45 2.36 99.94 1.69 3 8.00 1.00 0.31 0.64 fig. 5(30) 1 0.79 0.09 1.40 0.18 0.00 35.23 0.27 0.06 0.00 0.02 59.76 97.80 0.88 0.47 98.27 1.95 3 8.80 0.20 0.05 0.61 5 0.71 0.10 1.18 0.21 0.00 32.77 0.30 0.08 0.02 0.02 63.26 98.65 4.00 2.12 100.77 1.72 3 8.10 0.90 0.28 0.64 fig. 5(31) 1 0.12 0.13 1.35 0.09 0.10 36.30 0.11 0.06 0.04 0.01 60.30 98.60 1.33 0.70 99.30 1.93 3 8.69 0.31 0.07 0.61 5 0.08 0.11 1.69 0.06 0.05 33.21 0.04 0.00 0.04 0.01 62.03 97.34 4.09 2.17 99.51 1.73 3 8.08 0.92 0.27 0.63 fig. 5(32) 4 0.22 0.32 1.31 0.08 0.00 32.24 0.16 0.14 0.02 0.01 63.14 97.63 4.82 2.55 100.18 1.67 3 7.92 1.08 0.33 0.64 fig. 5(33) 3 0.11 0.63 0.57 0.07 0.01 36.63 0.09 0.04 0.00 0.02 57.33 95.50 -0.09 -0.05 95.45 2.04 3 9.02 -0.02 -0.04 0.60 4 0.28 0.68 0.68 0.06 0.00 35.63 0.19 0.03 0.00 0.01 57.46 95.02 0.25 0.13 95.15 2.01 3 8.94 0.06 -0.01 0.60 fig. 5(34) 1 0.13 0.32 0.92 0.06 0.00 38.09 0.10 0.10 0.03 0.01 57.59 97.35 -0.93 -0.49 96.86 2.10 3 9.22 -0.22 -0.10 5 0.11 0.29 1.04 0.07 0.00 36.47 0.09 0.11 0.04 0.02 58.79 97.02 0.66 0.35 97.37 1.98 3 8.85 0.15 0.02 0.60 fig. 5(35) 1 0.30 0.26 1.91 0.13 0.00 39.29 0.79 0.08 0.00 0.01 51.39 94.17 -6.17 -3.27 90.90 2.56 3 10.54 -1.54 -0.56 9 0.16 0.03 0.46 0.06 0.00 35.49 0.43 0.08 0.02 0.00 57.22 93.96 0.77 0.41 94.36 1.95 3 8.82 0.18 0.05 0.61 10 0.08 0.92 0.94 0.04 0.00 38.17 0.16 0.07 0.00 0.00 57.38 97.75 -1.54 -0.82 96.93 2.17 3 9.37 -0.37 -0.17 fig. 5(36) 1 15.91 1.82 1.02 0.36 0.00 24.64 8.14 0.05 0.16 1.21 39.03 92.34 -36.22 -19.18 73.15 5.10 3 19.13 -10.13 -3.10 3 0.14 0.05 1.92 0.06 0.00 37.27 0.07 0.06 0.04 0.04 59.11 98.74 0.07 0.04 98.78 2.04 3 8.98 0.02 -0.04 0.60 fig. 5(37) 1 0.00 0.34 4.02 0.00 0.00 47.28 0.00 0.02 0.00 0.01 54.04 105.71 -9.36 -4.96 100.75 2.92 3 11.46 -2.46 -0.92 2 0.00 0.33 2.84 0.06 0.00 42.13 0.00 0.04 0.00 0.00 56.88 102.30 -4.41 -2.34 99.96 2.43 3 10.09 -1.09 -0.43 6 0.13 0.38 2.21 0.07 0.00 32.77 0.13 0.11 0.03 0.02 61.30 97.15 3.40 1.80 98.95 1.80 3 8.23 0.77 0.20 0.63 fig. 5(38) 1 0.15 0.42 1.20 0.10 0.00 32.39 0.14 0.07 0.02 0.01 63.14 97.66 4.80 2.54 100.20 1.68 3 7.93 1.07 0.32 0.64 5 0.36 0.45 1.12 0.19 0.00 24.90 0.27 0.10 0.05 0.01 67.16 94.62 10.83 5.73 100.35 1.27 3 6.72 2.28 0.73 0.70 fig. 5(39) 1 0.57 0.11 0.87 0.20 0.00 26.40 1.07 0.17 0.04 0.03 68.47 97.93 9.49 5.03 102.95 1.34 3 6.99 2.01 0.66 0.69 5 0.74 0.25 0.85 0.29 0.00 20.77 1.39 0.29 0.07 0.08 72.09 96.82 13.54 7.17 103.99 1.10 3 6.24 2.76 0.90 0.73 fig. 5. bse images of the black altered ilmenite grains (22)-(39), separated as magnetic at 0.25 a. in figure 5, grains (28)-(32) consist of well-defined psr phases. spots 1-3 in grain (33) are leached ilmenite where the tio2 content ranges between 56.95 and 57.33 wt % and the fe2o3 content ranges between 37.82 and 36.63 wt %. spot 4 is psr with some molecular water. the analyzed tio2 (57.46 wt %) and fe2o3 (35.63 wt %) are relatively higher than those recorded. the correction of these values by multiplying by [100/(1004.85)], gives 60.45 wt % for tio2 and 37.48 wt % for fe2o3. spots 1-4 in grain (34) are leached ilmenite while spot 5 is psr with ti/ti+fe ratio of 0.6. in grain (35), spots 110, except spot 9, are leached ilmenite. they have tio2 content ranging between 51.39 and 57.38 wt % and fe2o3 content ranging between 39.3 and 38.17 wt %. spot 9 is psr, with a ti/ti+fe ratio of 0.61. according to the ot values, most of these spots contain molecular water between 8.66 and 2.25 wt %. in grain (36) (figure 5, table iv), spot 1 is a composite between an inclusion of sio2 and leached ilmenite or psr. spots 2 and 4 are leached ilmenite. it is obvious that some little amount of fe ++ is still present in the structure. spot 3 is psr with a ti/ti+fe ratio equal to 0.6. spots 1 and 2 of grain (37) are not ilmenite, but leached ilmenite. most iron content seems to be fe ++ . some individual tio2 phases, most probably rutile, are present with the ilmenite as a solid solution. spots 3-6 are psr. they have tio2 content ranging between 59.7 and 61.3 wt %, fe2o3 content ranging between 32.77 and 36.66 wt %, and ti/ti+fe ratio ranging between 0.6 and 0.63. spots 1-5 of grain (38) are psr. the tio2 content ranges between 63.14 and 67.16 engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11310 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand wt %, the fe2o3 content between 24.9 and 32.39 wt %, and the ti/ti+fe ratio between 0.64 and 0.70. some of the tio2 content was mixed with the original ilmenite. the amount of tio2 which is not included in the psr formula and/or the content of included structural water in psr may affect the darkness of the color of the analyzed spots. spots 1-5 in grain (39) are psr. the tio2 content ranges between 68.47 and 72.09 wt %, the fe2o3 content between 20.77 and 26.40 wt %, and the ti/ti+fe ratio between 0.69 and 0.73. this grain was originally exsolved intergrowth of titanhematite-ferriilmenite, where most of the hematite content was leached. some individual tio2 and/or fe2o3 phases are still mixed with the formed psr. hence, the calculated nt is much more than 100 wt %. the psr-lpsr of these investigated grains have the chemical formula range of fe2.07-1.1ti3o8.83-6.24(oh)0.17-2.76 (table iv). only 2 spot analyses have fe content ranging between 2.01 and 2.03 due to the appreciable contents of mn and/or mg which have oxidation state of 2 + . c. the separated magnetic fraction at 0.35 a 1) the investigated dark brown grains the investigated dark brown grains are the grains (1)-(12) (figure 6, table v). except of spots 1 of (2), 2 of (11) and 1 and 2 of (12), most of the other analyzed spots are psr. in these grains, the tio2 content ranges between 58.69 and 73.92 wt %, the fe2o3 content ranges between 14.42 and 33.38 wt %, and the ti/ti+fe ratio ranges between 0.62 and 0.80. all the analyzed spots of grain (1) are psr. the spots in grain (2) are psr and lpsr, except spot 1 which consists of remnants of leached ilmenite. in grain (3), the original grain seems to be ferriilmenite-titanhematite exsolved intergrowth where most of the contained hematite was leached out during the alteration to psr. when comparing spots 1 and 7 regarding their mno% and fe2o3% content, it is obvious that the content of mno is directly correlated with the content of fe2o3. grain (4) includes different phases of lpsr. in spots 4 and 5, both sio2 and al2o3 contents are relatively higher due to the decreasing content of fe2o3 while the mno content is relatively lower. at a definite decreasing limit of fe2o3 content inside the lpsr phase, the mno content starts to diminish while the opposite occurs in relation to sio2 and al2o3. also, the reason of the darkness of the bse of spots 4 and 5 is most probably the increasing content of the included structural water. spot 1 in grain (5) is psr. the remaining spots are composed of various phases of lpsr. spots 4, 5, and 7 reflect that the increased sio2 and al2o3 content may be correlated with the decreased fe2o3 content. in grain (6), the psr of spots 1-3 is different than that of spots 4 and 5. in spots 4 and 5, either the calculated amount of structural water is incorrect or not all the recorded tio2 content is contained within the lpsr phase, and some of the analyzed tio2 is present as individual phases which were originally mixed with the original ilmenite or were separated individually outside the lpsr phase during the late alteration stages. the grains (7)-(9) are psr. the lpsr of spots 4-5 in grain (9) is different than that of spots 1-3. in grain (10), the nt of the analyzed spots is much more than 100%. so, either the calculated structural water is incorrect or there are mixed phases rather than the psr phase alone. spots 1-5 have tio2 contents ranging between 70.09 and 78.04%, fe2o3 content between 12.64 and 22.68%, and ti/ti+fe ratio between 0.73 and 0.82. in spots 6 and 7, the contained lpsr phase is most probably broken out into definite individual phases of tio2 and fe2o3. the enrichment of sio2 content seems to be correlated directly with the enriched individual tio2 phase. also, in these two last spots, the content of mno is diminished due to the decreased fe2o3 content (table v). fig. 6. bse images of the brown altered ilmenite grains (1)-(12), separated as magnetic at 0.35 a. spot 1 of grain (11) was originally titanhematite altered to goethite. spot 2 is leached ilmenite. spots 3-6 are various phases of psr and lpsr. the darkness of some analyzed spots in the bse image is due to the presence of structural and/or molecular water. spot 7 is mixed individual phases of tio2 and fe2o3 after psr. when comparing spots 1 and 7 regarding their contents of mno% and fe2o3%, it is obvious that they are directly correlated. spots1 and 2 of grain (12) are leached ilmenite while spot 3 is psr. spots 4 and 5 are lpsr of different phase than that of spot 3. in spots 4 and 5, either the calculated structural water is incorrect or not all the recorded tio2 content is included in the lpsr phase. there is an enrichment of an individual tio2 phase. the psr-lpsr of the investigated brown altered ilmenite grains have the chemical formula range of fe1.65-0.66ti3o7.88-4.96 (oh)1.12-4.04 (table v). in spots 6, 7 of grain (10), spot 7 of grain (11), and spots 4 and 5 of grain (12), the content of cationic iron in the calculated psr-lpsr chemical formula ranges between 0.28 and 0.44. the investigation of the bse images, especially of grains (10) and (11) ensures the change of mineral phases into an individual tio2 mineral phase, most probably rutile. then, these cationic fe values are discarded as minimum values for the existence of psr-lpsr phases. engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11311 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand table v. microprobe chemical analyses and the corresponding molecular formulae of the analyzed spots of the brown altered ilmenite grains (1)-(22) of figure 6, separated as magnetic at 0.35 a grain spot sio2 mgo mno cao zno fe2o3 al2o3 cr2o3 na2o k2o tio2 ot oh% h2o% nt fe2 ti3 ox ohy lost fe ti/ (ti+fe) fig. 6(1) 1 0.38 0.09 0.49 0.25 0.07 26.00 0.40 0.12 0.03 0.02 63.89 91.74 9.49 5.03 96.77 1.34 3 6.98 2.02 0.66 0.69 6 0.24 0.09 0.48 0.16 0.06 24.79 0.42 0.09 0.02 0.01 65.89 92.24 11.24 5.95 98.19 1.23 3 6.64 2.36 0.77 0.71 fig. 6(2) 1 1.54 0.19 1.96 0.08 0.11 37.46 0.69 0.08 0.00 0.05 54.91 97.07 -4.48 -2.38 94.69 2.38 3 10.09 -1.09 -0.38 7 0.21 0.09 0.30 0.16 0.00 23.54 0.25 0.11 0.03 0.01 69.47 94.18 13.44 7.12 101.30 1.09 3 6.23 2.77 0.91 0.73 fig. 6(3) 1 0.50 0.19 1.58 0.24 0.00 26.93 0.59 0.06 0.03 0.00 62.17 92.29 7.28 3.85 96.14 1.50 3 7.42 1.58 0.50 0.67 7 0.61 0.19 0.98 0.17 0.02 23.95 1.48 0.11 0.03 0.03 65.92 93.47 9.89 5.24 98.71 1.32 3 6.91 2.09 0.68 0.69 fig. 6(4) 4 0.45 0.12 0.90 0.26 0.03 23.01 0.35 0.11 0.02 0.00 67.33 92.56 12.44 6.59 99.15 1.16 3 6.42 2.58 0.84 0.72 5 1.29 0.17 0.50 0.29 0.03 18.73 0.81 0.06 0.01 0.01 69.42 91.31 14.83 7.86 99.16 1.00 3 6.01 2.99 1.00 0.75 fig. 6(5) 1 0.39 0.20 1.75 0.09 0.04 33.38 0.11 0.04 0.01 0.00 58.69 94.70 2.09 1.11 95.81 1.87 3 8.52 0.48 0.13 0.62 5 1.58 0.31 0.89 0.31 0.09 22.70 0.61 0.15 0.00 0.04 64.38 91.05 9.87 5.23 96.28 1.31 3 6.92 2.08 0.69 0.70 7 1.20 0.31 0.47 0.34 0.02 18.24 0.53 0.13 0.00 0.04 67.72 89.00 14.98 7.93 96.94 1.00 3 5.98 3.02 1.00 0.75 fig. 6(6) 1 0.33 0.12 0.62 0.21 0.11 26.91 0.25 0.10 0.00 0.03 65.42 94.10 9.47 5.02 99.12 1.34 3 6.98 2.02 0.66 0.69 2 0.45 0.13 0.46 0.28 0.20 23.90 0.33 0.16 0.02 0.02 67.89 93.84 12.06 6.39 100.22 1.18 3 6.49 2.51 0.82 0.72 5 0.33 0.10 0.50 0.33 0.22 20.45 0.31 0.11 0.01 0.01 71.65 94.02 15.66 8.29 102.32 0.96 3 5.84 3.16 1.04 0.76 fig. 6(7) 5 0.65 0.22 0.83 0.25 0.07 24.80 0.65 0.13 0.04 0.05 67.28 94.96 10.47 5.54 100.51 1.28 3 6.79 2.21 0.72 0.70 fig. 6(8) 6 0.19 0.10 1.53 0.32 0.09 26.33 0.27 0.07 0.00 0.01 65.79 94.69 9.64 5.10 99.79 1.35 3 6.94 2.06 0.65 0.69 fig. 6(9) 1 0.58 0.19 0.63 0.30 0.05 20.32 0.79 0.31 0.02 0.02 69.50 92.71 14.23 7.54 100.24 1.05 3 6.11 2.89 0.95 0.74 3 0.59 0.16 0.66 0.29 0.03 20.17 0.77 0.34 0.00 0.02 70.12 93.16 14.51 7.68 100.84 1.03 3 6.06 2.94 0.97 0.74 5 0.75 0.17 0.36 0.40 0.07 14.42 1.05 0.46 0.00 0.00 73.92 91.59 19.10 10.12 101.70 0.77 3 5.29 3.71 1.23 0.80 fig. 6(10) 1 0.47 0.15 0.44 0.24 0.15 22.68 0.58 0.51 0.01 0.01 70.09 95.33 13.03 6.90 102.23 1.12 3 6.32 2.68 0.88 0.73 5 0.80 0.15 0.20 0.37 0.07 12.64 0.71 1.02 0.04 0.02 78.04 94.04 21.11 11.18 105.22 0.66 3 4.96 4.04 1.34 0.82 6 1.61 0.23 0.07 0.61 0.08 4.34 0.75 0.92 0.03 0.04 80.75 89.44 26.64 14.11 103.55 0.38 3 4.16 4.84 1.62 0.89 7 1.45 0.13 0.08 0.60 0.00 4.03 0.78 0.97 0.03 0.04 84.35 92.45 27.46 14.55 107.00 0.34 3 4.03 4.97 1.66 0.90 fig. 6(11) 1 0.17 0.05 0.41 0.14 0.09 86.88 0.24 0.04 0.03 0.01 1.82 89.88 -91.87 -48.65 41.23 145.63 3 438.52 -429.52 -143.63 2 0.18 0.10 3.14 0.05 0.07 37.70 0.00 0.06 0.00 0.01 55.99 97.29 -2.22 -1.17 96.12 2.24 3 9.54 -0.54 -0.24 3 0.31 0.02 2.36 0.11 0.09 30.89 0.08 0.04 0.01 0.02 63.21 97.12 5.46 2.89 100.02 1.64 3 7.78 1.22 0.36 0.65 6 0.30 0.13 0.24 0.11 0.02 16.94 0.09 0.09 0.02 0.01 76.69 94.63 19.88 10.53 105.16 0.72 3 5.13 3.87 1.28 0.81 7 3.40 0.86 0.02 0.10 0.00 3.70 1.03 0.06 0.03 0.05 87.53 96.79 25.96 13.75 110.54 0.41 3 4.31 4.69 1.59 0.88 fig. 6(12) 1 0.38 0.19 1.31 0.25 0.07 39.74 0.48 0.18 0.00 0.01 53.87 96.49 -4.74 -2.51 93.98 2.42 3 10.17 -1.17 -0.42 4 2.88 0.02 0.26 0.23 0.03 7.58 0.07 0.11 0.00 0.01 84.42 95.62 24.86 13.17 108.78 0.44 3 4.43 4.57 1.56 0.87 5 0.45 0.03 0.18 0.13 0.00 6.72 0.07 0.13 0.00 0.01 86.84 94.58 28.54 15.12 109.69 0.28 3 3.84 5.16 1.72 0.92 2) the investigated black grains the investigated grains from (13) to (25) (figure 7, table vi), are composed of leached ilmenite, psr, and lpsr. spots from 1 to 4 of grain (24) and spot 4 of grain (25) are leached ilmenite. the spots of psr and lpsr have tio2 content ranging between 56.76 and 70.20 wt %, fe2o3 content ranging between 22.02 and 36.13 wt %, and ti/ti+fe ratio ranging between 0.6 and 0.74. both grains (13) and (14) are composed of psr. in grain (15), spots 1 to 3 are psr of definite chemical composition while spots 4, 5 are another psr phase. the regions of these two last spots are relatively darker due to the increasing content of included structural water. the spots of grain (16) are psr. the grains (17), (18), and (19) are psr. in grain (20), the spots from 1 to 7 are psr. spot 5 is inside a relatively large fissure where the rate of alteration is relatively higher. hence, due to the relatively higher leaching rate of fe +++ from the psr, the structure is broken and most fe2o3 content is hydrolyzed (or hydroxylated) by the water captured by silica and/or alumina or by water containing both. that is the reason for the enrichment of sio2 and al2o3 in spot 5. spots 8 and 9 of grain (20) are lpsr of different formulas than those of spots 6 and 7. spots 8 and 9 spots have more structural water, hence they have relatively darker bse image regions. this grain seems that was originally ferriilmenite associated with several titanhematite exsolved bodies which were leached out causing several empty pits. the analyzed spots of grain (21) are psr. spot 1 of grain (22) is a definite altered silicate mineral. the remaining analyzed spots of grains (22), (23) are mainly psr. grains (21), (22), (23) were originally titanhematite-ferriilmenite exsolved intergrowths. most titanhematite components have been leached out lefting partially empty small pits and voids or longitudinal cracks in grain (21). these empty spaces are favorable locations for saturation with molecular water. that is the reason for the relative values of ot and nt. grain (23) contains the lowest psr chemical composition (spot 1). the original ilmenite of this grain was mixed with the pyrophanite component, hence the content of mno ranges between 2.33 and 6.85 wt %. the investigation of grains (22) and (23) may indicate that the presence of the original titanhematite component accelerates the rate of alteration for the associated ferriilmenite component. in grain (24), spots 1-4 are leached ilmenite while spots 5-8 are psr. in spots 5-8, the tio2 content ranges between 57.59 and 58.2 wt %, the fe2o3 content ranges between 35.62 and 37.22 wt % and the ti/ti+fe ratio range between 0.60 and 0.61. also, the total oxide sum indicates that most of the analyzed spots contain molecular water. grain (25) is composed of leached ilmenite (spot 4), and psr (spots 3, 5, and 6). spots 5 and 6 have a ti/ti+fe ratio ranging between 0.68 and 0.70. spots 1 and 2 are definite silicate mineral composites with individual tio2 phase. comparing the bse images of spots 1 engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11312 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand and 2 indicates that the increased sio2 content causes the relative dark color of the spot area. the psr-lpsr of these investigated magnetic black altered grains have the chemical formula range of fe2.02-1.06ti3o9-6.15(oh)0-2.85 (table vi). only one spot analysis gave fe content of 2.02 due to the appreciable content of mn. fig. 7. bse images of the black altered ilmenite grains (13)-(25), separated as magnetic at 0.35 a. the psr-lpsr chemical formulas of all the investigated altered ilmenite grains of figures 2-7 and tables i-vi are: fe2.07-0.54ti3o9-4.68(oh)0-4.32. the ti/(ti+fe) ratio for these formulas ranges between 0.59 and 0.85. the given values of the ti/(ti+fe) ratios for psr in the literature are different: 0.50.7 [32], 7-0.7 [31], 0.6-0.7 [33], 0.6 [34], and 0.6-0.79 or 0.80 [35]. the given lower limit of [32] for psr is not precise, it is overlapped with the phases of ilmenite and leached ilmenite. d. the detected leached ilmenite analyzed spots forty two spots were analyzed and detected to be leached ilmenite within all the studied altered ilmenite grains. the analysis of these spots did not give the psr/lpsr chemical formulas. in these 42 spots, taking into consideration that the ilmenite chemical formula is fe3ti3o9, the contents of tio2, feo, and fe2o3 range between 51.39-59.19, 39.84-0.02, and 337.02, respectively. the cationic fe 2+ ranges between 0 and 2.46, while the cationic fe 3+ ranges between 0.17 and 1.94. the ti/(ti+fe) ratio ranges between 0.51 and 0.6, almost the same as that reported in [33]. the fe/ti ratio ranges between 0.91 and 0.67 (table vii), which is different than that given by [36] which is 1.02 and decreases to about 0.84 for pseudoilmenite and to 0.64 for pseudorutile. although the new calculated nt ranges between 90.24 and 101.27 wt %, most of its values are much less than 100 wt %. this reflects the role of molecular water in the process of ilmenite alteration into leached ilmenite. note that in table vii, the other cations are composed mainly of mg and mn whereas the oxide percentages of other cations (sio2, al2o3, cr2o3, na2o3 and k2o) are minor. according to [31], leached ilmenite stable up to the composition of fe2.35-2.3ti3o9 with tio2 wt % ranges between 56 and 58 wt %. in the present study (table vii), where the leached ilmenite formulas have the composition fe2.72-2.02ti3o9 with the minimum value of iron equal to 2.02 (grain (24) of figure 7, spot 3). there are two methods for calculating the lost fe 2+ cations of ilmenite fe3ti3o9 and leached ilmenite: in the first method (m1), the sum of total fe 2+ and fe 3+ iron in addition to all other cations except ti (mainly mg and mn) must be subtracted from 3. the number of iron cations in the given ilmenite formula structure (fe3ti3o9) is: lost iron = 3 – [total iron + all other cations except ti] (13) the second one (m2), is an established rule by the present author: it has been explained [37, 38] that the fetio3 structure is derived from ꭤ-fe2o3 by replacing every layer of fe atoms in the (0001) planes by a layer of ti atoms, thus producing alternating layers of fe and ti atoms between slightly distorted, hexagonally close-packed o layers. by the losing of one fe 2+ cation, two fe 2+ cations are oxidized into two fe 3+ cations to meet the deficiency of the two lost positive charges from the ilmenite-leached ilmenite structure. the number of the lost fe 2+ cations corresponds to half the number of the formed fe 3+ inside the leached ilmenite structure. it also corresponds to the deficiency of the calculated oxygen anion number normalized to 3 ti in the leached ilmenite structure. this number must be equal to 9 when there is no losing of fe 2+ iron outside the given ilmenite formula structure (fe3ti3o9): number of lost fe 2+ cations = half the number of formed fe 3+ cations = deficiency of the calculated normalized oxygen to 3 ti. (14) in fact, there is a difference of the calculated lost iron by using the two most postulated methods. the value of lost iron calculated with the first method is relatively higher than that calculated with the second, due to one or more of the following:  some of the existing fe 3+ cations are related to an individual fe2o3 component present in association with ilmenite, not to the ilmenite mineral structure, in the analyzed spot.  some individual tio2 components are present with ilmenite. then, in calculating the normalized cations on the basis of 3 ti, all the calculated cation values are affected. the percentage of the individual tio2 component is mixed and contained within the total analyzed tio2 of the spot, hence the calculated ti-factor (3/the calculated ti cations), will be relatively lower, causing the lowering of the calculated fe cations when normalized to 3 ti. a relatively higher value of the calculated lost iron is obtained.  if some of the ferrous iron is substituted with other definite cations, the lost fe 2+ iron may be not offseted with the oxidation of two fe 2+ into two fe 3+ cations. for example, if fe 2+ is replaced with al 3+ or si 4+ then: engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11313 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand 2 al 3+ = 3 fe 2+ , or si 4+ = 2 fe 2+ (15) in the first equation, one fe 2+ is lost without a corresponding formation of fe 3+ . in this case, the number of lost iron equals to half the number of the present al 3+ in the analyzed spot. in the second equation, one fe 2+ is lost without a corresponding formation of fe 3+ . in this case, the number of lost iron equals to the number of the present si 4+ in the analyzed spot. then, an electrical neutralization in the leached ilmenite crystal structure can occur due to the substitution of fe 2+ cations with other cations of relatively higher oxidation number (3 + or 4 + ) without the formation of the corresponding fe 3+ cations. this explanation may be the reason for the following correct relation in the analyzed leached ilmenite spots of the present study (table vii): calculated lost iron by the first method–the calculated lost iron by the second method = si 4+ + 0.5 al 3+ (16) however, the majority of the analyzed leached ilmenite spots contain negligible amounts of si and al and maybe cao, na2o, and k2o. if these oxides are treated as impurities, the most major analyzed oxide (tio2) in the spot will be affected by the correction of the analyzed oxide values. hence, the calculated ti-factor (3/the calculated ti cations), will be relatively lower, leading to the lowering of the calculated fe cations normalized to 3 ti. hence, the calculated lost iron value using the first method of calculation, will be relatively bigger. finally, it was remarked that the microprobe chemical analyses of some detected ilmenite spots have tio2 content similar to those classified as leached ilmenite (tio2 ranges between 56 and 59 wt %). this analysis does not response to the adopted chemical formula of leached ilmenite. the sum of all the analyzed oxides in each of these spots is very close to, or slightly lower than, 100 wt %. in these spots, the occurrence of solid solutions or exsolved intergrowth of tio2 with ilmenite are postulated. it maybe also, exsolved intergrowths of titanhematite where a selective leaching of the fe2o3 component occurs, resulting in an enrichment of the tio2bearing component in the analyzed spots. table vi. microprobe chemical analyses and the corresponding molecular formulae of the analyzed spots of the black altered ilmenite grains (13)-(25) of figure 7, separated as magnetic at 0.35 a grain spot sio2 mgo mno cao zno fe2o3 al2o3 cr2o3 na2o k2o tio2 ot oh % h2o % nt fe2 ti3 ox ohy lost fe ti/ (ti+fe) fig. 7(13) 1 0.92 0.67 0.75 0.13 0.02 30.59 0.38 0.06 0.06 0.01 60.76 94.36 3.96 2.10 96.45 1.73 3 8.12 0.88 0.27 0.63 5 0.23 0.41 0.67 0.13 0.00 31.05 0.16 0.03 0.00 0.02 62.44 95.14 5.67 3.00 98.14 1.61 3 7.74 1.26 0.39 0.65 fig. 7(14) 1 0.98 0.22 2.34 0.10 0.08 28.12 0.61 0.04 0.04 0.03 62.03 94.59 5.40 2.86 97.45 1.64 3 7.80 1.20 0.36 0.65 5 0.68 0.26 1.72 0.25 0.13 23.76 0.52 0.08 0.04 0.03 67.36 94.84 10.80 5.72 100.56 1.28 3 6.73 2.27 0.72 0.70 fig. 7(15) 3 0.28 0.13 0.74 0.19 0.00 28.78 0.41 0.06 0.00 0.04 64.99 95.60 7.95 4.21 99.81 1.44 3 7.28 1.72 0.56 0.68 4 0.36 0.17 0.62 0.26 0.03 25.39 0.48 0.07 0.04 0.00 67.75 95.17 10.94 5.80 100.96 1.25 3 6.70 2.30 0.75 0.71 5 0.46 0.16 0.51 0.28 0.00 22.02 0.46 0.13 0.05 0.00 70.20 94.27 13.93 7.38 101.65 1.06 3 6.15 2.85 0.94 0.74 fig. 7(16) 3 0.14 0.37 1.53 0.09 0.11 32.53 0.10 0.06 0.04 0.01 59.50 94.47 3.21 1.70 96.17 1.80 3 8.27 0.73 0.20 0.62 fig. 7(17) 1 0.13 0.07 0.62 0.09 0.06 31.10 0.14 0.02 0.01 0.01 61.43 93.66 5.75 3.04 96.71 1.59 3 7.73 1.27 0.41 0.65 5 0.55 0.10 0.59 0.22 0.00 24.36 0.37 0.13 0.03 0.03 65.87 92.26 11.08 5.87 98.13 1.24 3 6.68 2.32 0.76 0.71 fig. 7(18) 1 0.20 0.15 2.00 0.12 0.09 29.05 0.08 0.03 0.00 0.01 62.36 94.06 6.65 3.52 97.58 1.55 3 7.54 1.46 0.45 0.66 6 0.30 0.12 1.36 0.15 0.03 26.13 0.18 0.09 0.02 0.00 65.73 94.12 9.91 5.25 99.37 1.32 3 6.89 2.11 0.68 0.69 fig. 7(19) 1 0.29 0.77 0.90 0.10 0.00 31.79 0.10 0.02 0.02 0.02 59.90 93.90 3.76 1.99 95.89 1.76 3 8.15 0.85 0.24 0.63 2 0.07 0.88 2.03 0.05 0.07 32.12 0.00 0.00 0.04 0.01 60.39 95.65 3.40 1.80 97.45 1.81 3 8.23 0.77 0.19 0.62 6 0.22 0.61 0.64 0.12 0.04 31.00 0.11 0.03 0.03 0.01 62.94 95.74 5.76 3.05 98.79 1.61 3 7.73 1.27 0.39 0.65 fig. 7(20) 1 0.15 0.05 2.18 0.10 0.01 33.84 0.02 0.02 0.00 0.02 57.03 93.42 1.38 0.73 94.15 1.94 3 8.68 0.32 0.06 0.61 5 1.34 0.28 1.66 0.21 0.01 27.52 0.50 0.04 0.02 0.04 59.27 90.89 4.74 2.51 93.40 1.67 3 7.95 1.05 0.33 0.64 6 0.06 0.08 2.76 0.11 0.06 31.89 0.02 0.00 0.00 0.00 59.57 94.55 3.55 1.88 96.43 1.79 3 8.19 0.81 0.21 0.63 7 0.19 0.07 2.97 0.12 0.07 29.96 0.02 0.05 0.03 0.00 60.28 93.75 4.84 2.57 96.32 1.70 3 7.91 1.09 0.30 0.64 8 0.46 0.15 1.49 0.28 0.16 24.63 0.18 0.03 0.02 0.01 65.24 92.64 10.44 5.53 98.16 1.29 3 6.79 2.21 0.71 0.70 9 0.46 0.17 1.52 0.24 0.11 24.66 0.20 0.00 0.02 0.02 65.57 92.96 10.53 5.58 98.54 1.29 3 6.77 2.23 0.71 0.70 fig. 7(21) 1 0.12 0.17 1.59 0.08 0.04 33.46 0.11 0.07 0.01 0.02 58.99 94.65 2.57 1.36 96.01 1.84 3 8.41 0.59 0.16 0.62 4 0.24 0.22 1.44 0.13 0.09 30.97 0.54 0.05 0.04 0.01 59.47 93.18 3.87 2.05 95.23 1.75 3 8.13 0.87 0.25 0.63 fig. 7(22) 1 23.49 1.87 1.15 0.65 0.08 14.84 17.36 0.04 0.05 0.26 25.80 85.58 -73.18 -38.75 46.83 9.29 3 33.67 -24.67 -7.29 2 2.05 0.36 2.82 0.11 0.03 23.26 0.84 0.01 0.01 0.05 53.15 82.68 3.38 1.79 84.47 1.78 3 8.24 0.76 0.22 0.63 3 0.22 0.11 2.97 0.08 0.18 32.52 0.05 0.10 0.03 0.02 57.85 94.13 1.92 1.02 95.15 1.92 3 8.56 0.44 0.08 0.61 fig. 7(23) 1 0.15 0.37 2.33 0.07 0.09 33.78 0.15 0.04 0.00 0.01 56.76 93.75 0.77 0.41 94.15 2.00 3 8.82 0.18 0.00 0.60 5 0.08 0.29 2.66 0.04 0.05 31.70 0.01 0.04 0.02 0.00 59.72 94.60 3.61 1.91 96.51 1.79 3 8.18 0.82 0.21 0.63 fig. 7(24) 1 1.49 0.23 0.82 0.07 0.00 36.68 0.74 0.04 0.02 0.03 55.43 95.56 -3.13 -1.66 93.90 2.24 3 9.75 -0.75 -0.24 4 0.07 0.15 0.83 0.06 0.00 37.53 0.05 0.07 0.03 0.00 57.32 96.11 -0.33 -0.18 95.93 2.05 3 9.08 -0.08 -0.05 5 0.11 0.14 0.94 0.06 0.16 35.62 0.06 0.06 0.00 0.01 57.59 94.76 0.90 0.48 95.24 1.96 3 8.79 0.21 0.04 0.61 8 0.09 0.13 0.82 0.07 0.00 36.16 0.09 0.10 0.00 0.01 58.20 95.68 0.90 0.48 96.15 1.95 3 8.79 0.21 0.05 0.61 fig. 7(25) 1 18.15 0.44 0.07 0.21 0.06 4.59 19.01 0.02 0.07 0.04 43.43 86.09 -33.70 -17.85 68.24 4.15 3 16.99 -7.99 -2.15 2 6.77 0.17 0.40 0.18 0.04 15.14 14.11 0.04 0.00 0.01 48.21 85.05 -14.42 -7.64 77.41 2.95 3 12.33 -3.33 -0.95 3 0.16 0.22 0.75 0.10 0.00 36.13 0.10 0.04 0.01 0.02 57.03 94.56 0.29 0.15 94.71 2.00 3 8.93 0.07 0.00 0.60 4 0.07 0.89 0.65 0.06 0.10 36.16 0.05 0.03 0.02 0.01 57.06 95.09 -0.11 -0.06 95.03 2.06 3 9.03 -0.03 -0.06 5 0.28 0.30 0.11 0.16 0.02 28.33 0.18 0.03 0.00 0.01 62.80 92.21 8.00 4.24 96.45 1.43 3 7.27 1.73 0.57 0.68 6 0.45 0.25 0.03 0.19 0.07 26.03 0.25 0.03 0.05 0.03 65.18 92.54 10.16 5.38 97.92 1.29 3 6.85 2.15 0.71 0.70 engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11314 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand table vii. microprobe chemical analyses and the corresponding molecular formulae of the detected analyzed spots of leached ilmenite from the different magnetic altered ilmenite grain varieties g r a in s p o t s io 2 m g o m n o c a o z n o f e o a l 2 o 3 c r 2 o 3 n a 2 o k 2 o t io 2 o t n t f e o % f e 2 o 3 % f e f e r r o u s f e f e r r ic o th e r c a ti o n s t o ta l f e t i o l o st f e ( m 1 ) l o st f e ( m 2 ) s i a l s i+ 0 .5 a l t i/ (t i+ f e ) f e /t i fig. 3(16) 1 0.09 0.14 2.28 0.06 0.00 34.38 0.00 0.05 0.03 0.00 59.19 96.21 99.74 2.54 35.37 0.14 1.79 0.16 2.10 3 9 0.90 0.90 0.01 0.00 0.01 0.59 0.70 fig. 3(18) 3 0.31 0.13 1.67 0.07 0.00 33.59 0.15 0.02 0.05 0.03 57.45 93.47 96.78 3.80 33.10 0.22 1.73 0.16 2.11 3 9 0.89 0.86 0.02 0.01 0.03 0.59 0.70 4 0.15 0.08 1.80 0.03 0.00 34.85 0.05 0.02 0.00 0.02 57.88 94.87 98.14 5.40 32.72 0.31 1.70 0.13 2.14 3 9 0.86 0.85 0.01 0.00 0.01 0.58 0.71 fig. 3(20) 4 0.01 0.14 2.17 0.02 0.00 39.98 0.00 0.02 0.00 0.00 52.13 94.48 95.45 31.20 9.75 2.00 0.56 0.16 2.72 3 9 0.28 0.28 0.00 0.00 0.00 0.52 0.91 5 0.00 0.17 1.63 0.02 0.11 40.31 0.00 0.00 0.00 0.00 52.29 94.54 95.57 31.01 10.33 1.98 0.59 0.13 2.70 3 9 0.30 0.30 0.00 0.00 0.00 0.53 0.90 6 0.00 0.19 1.79 0.02 0.07 39.56 0.00 0.00 0.00 0.00 52.76 94.39 95.65 28.20 12.62 1.78 0.72 0.14 2.64 3 9 0.36 0.36 0.00 0.00 0.00 0.53 0.88 fig. 4(1) 1 0.18 0.60 0.53 0.06 0.10 35.94 0.10 0.06 0.00 0.01 57.78 95.36 98.36 8.86 30.09 0.51 1.56 0.13 2.20 3 9 0.80 0.78 0.01 0.01 0.02 0.58 0.73 2 0.08 0.66 0.66 0.06 0.14 34.56 0.08 0.07 0.00 0.01 58.50 94.82 98.27 3.47 34.54 0.20 1.77 0.13 2.10 3 9 0.90 0.89 0.01 0.01 0.01 0.59 0.70 3 0.07 0.66 0.55 0.06 0.05 34.64 0.05 0.11 0.01 0.00 58.52 94.72 98.21 3.25 34.88 0.19 1.79 0.12 2.10 3 9 0.90 0.89 0.00 0.00 0.01 0.59 0.70 4 0.08 0.66 0.70 0.06 0.01 34.10 0.09 0.06 0.03 0.01 58.66 94.45 98.05 1.68 36.02 0.10 1.84 0.13 2.07 3 9 0.93 0.92 0.01 0.01 0.01 0.59 0.69 5 0.22 0.75 0.66 0.08 0.00 33.38 0.13 0.10 0.00 0.01 59.03 94.37 98.07 0.07 37.01 0.00 1.88 0.15 2.04 3 9 0.96 0.94 0.01 0.01 0.02 0.60 0.68 fig. 4(2) 2 0.09 0.45 1.02 0.10 0.14 33.84 0.06 0.07 0.00 0.00 58.06 93.83 97.35 2.13 35.23 0.12 1.82 0.13 2.08 3 9 0.92 0.91 0.01 0.00 0.01 0.59 0.69 5 0.06 0.63 0.91 0.06 0.00 33.71 0.03 0.03 0.03 0.01 58.57 94.02 97.71 0.51 36.88 0.03 1.89 0.13 2.05 3 9 0.95 0.95 0.00 0.00 0.00 0.59 0.68 fig. 5(33) 1 0.08 0.62 0.61 0.04 0.10 37.82 0.06 0.00 0.00 0.01 56.95 96.28 98.77 15.37 24.94 0.90 1.31 0.12 2.34 3 9 0.66 0.66 0.01 0.01 0.01 0.56 0.78 2 0.40 0.66 0.73 0.07 0.14 35.44 0.30 0.02 0.00 0.00 57.21 94.98 97.70 10.89 27.28 0.63 1.43 0.18 2.24 3 9 0.76 0.72 0.03 0.03 0.04 0.57 0.75 3 0.11 0.63 0.57 0.07 0.01 36.63 0.09 0.04 0.00 0.02 57.33 95.50 98.30 11.39 28.04 0.66 1.47 0.12 2.25 3 9 0.75 0.73 0.01 0.01 0.01 0.57 0.75 fig. 5(34) 1 0.13 0.32 0.92 0.06 0.00 34.28 0.10 0.10 0.03 0.01 57.59 93.54 96.92 3.81 33.85 0.22 1.76 0.12 2.10 3 9 0.90 0.88 0.01 0.01 0.01 0.59 0.70 2 0.06 0.30 0.77 0.05 0.00 34.94 0.04 0.10 0.01 0.00 57.60 93.87 97.23 4.72 33.58 0.27 1.75 0.09 2.12 3 9 0.88 0.87 0.00 0.00 0.01 0.59 0.71 3 0.12 0.16 1.09 0.04 0.00 33.99 0.08 0.09 0.07 0.00 57.73 93.36 96.88 2.31 35.19 0.13 1.83 0.11 2.08 3 9 0.92 0.91 0.01 0.01 0.01 0.59 0.69 4 0.13 0.33 1.20 0.05 0.00 33.57 0.08 0.10 0.04 0.00 58.03 93.51 97.09 1.32 35.83 0.08 1.85 0.13 2.06 3 9 0.94 0.93 0.01 0.01 0.01 0.59 0.69 fig. 5(35) 1 0.30 0.26 1.91 0.13 0.00 35.36 0.79 0.08 0.00 0.01 51.39 90.23 91.51 23.79 12.85 1.54 0.75 0.27 2.56 3 9 0.44 0.38 0.02 0.07 0.06 0.54 0.85 2 0.42 0.10 0.56 0.14 0.00 35.37 0.81 0.09 0.04 0.01 51.72 89.26 90.88 20.71 16.29 1.34 0.95 0.18 2.46 3 9 0.54 0.47 0.03 0.07 0.07 0.55 0.82 3 0.33 0.13 0.77 0.10 0.00 32.62 0.71 0.09 0.05 0.02 52.90 87.71 90.24 9.90 25.23 0.62 1.43 0.17 2.23 3 9 0.77 0.72 0.02 0.06 0.06 0.57 0.74 4 0.23 0.17 3.07 0.06 0.00 32.49 0.54 0.10 0.04 0.02 54.72 91.43 93.96 9.76 25.26 0.59 1.39 0.29 2.27 3 9 0.73 0.69 0.02 0.05 0.04 0.57 0.76 5 0.15 0.57 1.71 0.07 0.00 34.21 0.36 0.08 0.01 0.02 55.63 92.81 95.42 10.75 26.06 0.64 1.41 0.22 2.27 3 9 0.73 0.70 0.01 0.03 0.03 0.57 0.76 6 0.16 0.73 1.25 0.06 0.00 34.31 0.26 0.08 0.02 0.01 56.03 92.90 95.65 9.52 27.54 0.57 1.48 0.20 2.24 3 9 0.76 0.74 0.01 0.02 0.02 0.57 0.75 7 0.09 1.28 0.67 0.06 0.00 34.08 0.22 0.07 0.02 0.00 56.37 92.86 95.70 8.52 28.39 0.50 1.51 0.21 2.23 3 9 0.77 0.76 0.01 0.02 0.02 0.57 0.74 8 0.12 0.26 2.08 0.05 0.00 33.04 0.26 0.05 0.00 0.01 56.88 92.73 95.97 3.85 32.43 0.23 1.71 0.19 2.12 3 9 0.88 0.86 0.01 0.02 0.02 0.59 0.71 10 0.08 0.92 0.94 0.04 0.00 34.35 0.16 0.07 0.00 0.00 57.38 93.93 97.04 6.33 31.13 0.37 1.63 0.18 2.17 3 9 0.83 0.81 0.01 0.01 0.01 0.58 0.72 fig. 5(36) 2 0.09 0.02 1.66 0.02 0.00 34.53 0.01 0.06 0.02 0.00 58.75 95.14 98.75 2.02 36.12 0.11 1.85 0.11 2.07 3 9 0.93 0.92 0.01 0.00 0.01 0.59 0.69 4 0.10 0.07 2.10 0.07 0.00 33.81 0.01 0.06 0.04 0.03 59.11 95.40 99.08 0.62 36.87 0.03 1.87 0.15 2.06 3 9 0.94 0.94 0.01 0.00 0.01 0.59 0.69 fig. 5(37) 1 0.00 0.34 4.02 0.00 0.00 42.54 0.00 0.02 0.00 0.01 54.04 100.97 101.27 39.84 3.00 2.46 0.17 0.29 2.92 3 9 0.08 0.08 0.00 0.00 0.00 0.51 0.97 2 0.00 0.33 2.84 0.06 0.00 37.91 0.00 0.04 0.00 0.00 56.88 98.08 100.21 18.66 21.40 1.09 1.13 0.21 2.43 3 9 0.57 0.56 0.00 0.00 0.00 0.55 0.81 fig. 6(2) 1 1.54 0.19 1.96 0.08 0.11 33.71 0.69 0.08 0.00 0.05 54.91 93.32 95.06 17.98 17.47 1.09 0.96 0.33 2.38 3 9 0.62 0.48 0.11 0.06 0.14 0.56 0.79 fig. 6(11) 2 0.18 0.10 3.14 0.05 0.07 33.92 0.00 0.06 0.00 0.01 55.99 93.51 96.28 9.02 27.67 0.54 1.48 0.22 2.24 3 9 0.76 0.74 0.01 0.00 0.01 0.57 0.75 fig. 6(12) 1 0.38 0.19 1.31 0.25 0.07 35.76 0.48 0.18 0.00 0.01 53.87 92.51 94.39 18.87 18.77 1.17 1.05 0.21 2.42 3 9 0.58 0.52 0.03 0.04 0.05 0.55 0.81 2 0.21 0.24 1.18 0.18 0.00 32.86 0.43 0.21 0.02 0.02 57.69 93.01 96.45 1.92 34.37 0.11 1.79 0.17 2.07 3 9 0.93 0.89 0.01 0.03 0.03 0.59 0.69 fig. 7(24) 1 1.49 0.23 0.82 0.07 0.00 33.01 0.74 0.04 0.02 0.03 55.43 91.88 94.17 12.45 22.85 0.75 1.24 0.26 2.24 3 9 0.76 0.62 0.11 0.06 0.14 0.57 0.75 2 0.06 0.14 0.83 0.07 0.13 34.03 0.05 0.05 0.00 0.00 56.96 92.31 95.77 2.82 34.67 0.17 1.83 0.09 2.08 3 9 0.92 0.91 0.00 0.00 0.01 0.59 0.69 3 0.08 0.13 0.75 0.05 0.13 33.34 0.05 0.03 0.02 0.01 57.27 91.84 95.54 0.02 37.02 0.00 1.94 0.08 2.02 3 9 0.98 0.97 0.01 0.00 0.01 0.60 0.67 4 0.07 0.15 0.83 0.06 0.00 33.77 0.05 0.07 0.03 0.00 57.32 92.35 95.95 1.35 36.02 0.08 1.89 0.09 2.05 3 9 0.95 0.94 0.00 0.00 0.01 0.59 0.68 fig. 7(25) 4 0.07 0.89 0.65 0.06 0.10 32.53 0.05 0.03 0.02 0.01 57.06 91.47 95.03 0.44 35.65 0.03 1.88 0.15 2.06 3 9 0.94 0.94 0.01 0.00 0.01 0.59 0.69 e. the detected xrd patterns the identification for most economic minerals of the egyptian black sand and other sand deposits using the xrd technique has been explained in [30, 39]. a small representative sample was taken from the magnetic fraction at 0.25 a. a total of 200 grains were picked from the fraction using a needle under the binocular microscope, consisting of 100 grains of brown and 100 grains of black altered ilmenite. these grains were split into two equal samples, each sample composed of 50 grains of each variety. the first sample was treated using the xrd instrument while the second was heated at 1100 o c for one hour and then treated with the xrd instrument. the first sample gave the patterns corresponding to pseudorutile, rutile and only one line of hematite (figure 8(1)). the second sample gave a composition of rutile, pseudobrookite and only one line of hematite (figure 8(2)). in these altered phases, it is obvious that the hematite is minor. also, the hexagonal psr structure is unstable in comparison with tetragonal rutile, where a considerable tio2 content escaped from the broken psr structure and diffused inside the rutile structure. the remaining tio2 and most of the fe2o3 contents of the broken psr are modified into the orthorhombic pseudobrookite structure. another small representative sample was taken from the magnetic fraction at 0.35 a. two hundred grains were picked from each of the two detected varieties. the grains of each color variety were split into two equal samples, each of 100 grains. one sample was subjected to xrd and the other was heated at 1100 o c for one hour and then treated with the xrd instrument. the sample of the non-heated brown colored variety gave the composition of only pseudorutile (figure engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11315 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand 8(3)), while the sample after heating gave the composition of pseudobrookite, rutile, quartz and, only one line for hematite (figure 8(4)). it is obvious that minor contents of amorphous hydrated silica were contained with psr. after heating, the water molecules were lost and the sio2 was recrystallized into minor quartz. also, a considerable amount of tio2 content was separated from the relatively unstable psr structure and formed the relatively more stable rutile structure. the remaining tio2 and fe2o3 of the unstable psr were modified into pseudobrookite. some fe2o3, either from the psr structure or contained as an amorphous phase was recrystallized as minor hematite. the sample of the non-heated black colored variety gave the composition of psr and hematite (figure 8(5)), while the sample after heating gave the composition of pseudobrookite, rutile and, only one line for hematite (figure 8(6)). the same interpretation of the brown variety is correct except that the content of the associated amorphous fe2o3 is relatively more here. fig. 8. xrds of the different altered ilmenite grains: the magnetic altered ilmenite of 0.25 a (1) before and (2) after heating. the magnetic brown altered ilmenite of 0.35 a (3) before and (4) after heating. the magnetic black altered ilmenite of 0.35 a (5) before and (6) after heating. the detected mineral patterns are in accordance to the astm card numbers 4-0551 for rutile, 19-182 for pseudorutile, 9-182 for pseudobrookite, 13-534 for hematite, and 4-0477 for anatase. it is worth mentioning that in the last two magnetic fractions, at 0.25 and 0.35 a, after heating, most of the stained and/or coated materials changed into translucent-transparent yellow and red rutile. vi. conclusions in the detected leached ilmenite spots, the cationic fe 2+ ranges between 0 and 2.46, while the cationic fe 3+ ranges between 0.17 and 1.94. the ti/(ti+fe) ratio ranges between 0.51 and 0.6, and the fe/ti ratio ranges between 0.91 and 0.67. the leached ilmenite formulas have the composition range of fe2.72-2.02ti3o9 with a minimum value of iron equal to 2.02. in leached ilmenite, the number of lost fe 2+ cations is equal to half the number of formed fe 3+ cations which is equal to the deficiency of the calculated normalized oxygen to 3 ti. in the analyzed spots of psr-lpsr, the contents of tio2 and fe2o3 range between 56.76-78.09 wt % and 37.98-12.16 wt %, respectively. the ti/(ti+fe) ratio ranges between 0.60-0.82. the psr-lpsr chemical formula is: fe2.07-0.54ti3o9-4.68(oh)0-4.32. the cationic fe content ranges between 0.28 and 0.44 values are discarded as minimum for the existence of psr-lpsr phases. it is concluded that the lower cationic iron content of still present lpsr phases is 0.5 with a corresponding molecular formula of fe0.5 ti3o4.5(oh)4.5. the concluded molecular formula of the present study is different than others proposed in the literature. the lower chemical composition formula limit of psr is fe2ti3o9 [21], fe1.5ti3o7.5(oh)1.5 [33], while authors in [31] reported that the average composition of lpsr has the formula feti3o6(oh)3, and the lower stability limit lies around 0.6 mol% fe or slightly higher, as related to 3 mole% ti. it is noticed that the process of leucoxenation is selective and relatively faster in the exsolved component (like the titanhematite component), or the replacement component (like the sphene component) within the altered ilmenite grain. the remaining fresh ilmenite component within the same grain has a relatively slow rate of alteration and seems to be altered later. the comparison between the original ot and nt for the various spot chemical analyses of the detected grains reflects that the calculated structural water content values of some of the analyzed spots are incorrect, whereas not all the analyzed tio2 wt % is contained within the calculated psr/lpsr formulas. there are other individual phases of tio2 mixed with the lpsr phase. it was concluded that in the region of 68-70 tio2 wt %, the mechanism of ilmenite alteration is maybe changed. some spots of altered silicate minerals can be falsely considered as psr and lpsr according to their chemical compositions. also, it is obvious that the dependence on the powdered xrd analysis may be not enough to give correct results during the investigation of some analyzed spots related to psr and lpsr. the single crystal xrd may be a more efficient technique in such situations. some of the associated contained inclusions may be responsible for the acquired magnetic characteristics of some detected grains. in many published studies, both the recorded sio2 and al2o3 contents are considered as impurities and must be subtracted from the total oxide sum followed by the recalculation and correction of the other analyzed oxides. however, the most abundant analyzed oxide, tio2, of the spot will be highly affected by the recalculation and correction. it increases with a relatively bigger percentage than the other analyzed oxides, especially fe2o3, the second most abundant oxide of the spot analysis. if sio2 and/or al2o3 are originally engineering, technology & applied science research vol. 13, no. 4, 2023, 11298-11317 11316 www.etasr.com moustafa: the alteration processes of the altered ilmenite of the strongly magnetic egyptian black sand associated with only tio2 or with only fe2o3 then, some misleading results will be obtained. the content of structural water contained in the lpsr phase increases, as the associated sio2 and/or al2o3 contents increase. in fact, most of the spots having an appreciable content of molecular water contain relatively higher contents of sio2 and al2o3. this may indicate the ability of these two oxides of bearing molecular water, or oh anions, or both. sio2 and al2o3 may be associated with the molecular water itself. it is noticed that the content of mno is directly correlated with the content of fe2o3. the xrd power patterns of the detected different magnetic altered ilmenite grains ensure the presence of several mineral phases in the altered grains. they give the composition of either only pseudorutile or psr associated with hematite and maybe also rutile. after heating, all the obtained patterns contain pseudobrookite in addition to rutile and hematite and maybe quartz. in these heated altered varieties, it is obvious that the hematite is minor. also, the hexagonal psr structure is unstable in comparison with the tetragonal rutile, a considerable tio2 content escaped from the broken psr structure and was diffused inside the rutile structure. the remaining tio2 and most of the fe2o3 contents of the broken psr were modified into the orthorhombic pseudobrookite structure. also, a minor content of amorphous hydrated silica contained with psr was detected after heating. the water molecules were lost and the sio2 was recrystallized into minor quartz. acknowledgement the author wishes to express his deepest greatitude to dr. h.j. massonne, dr. thomas theye and the microprobe unit of the 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[39] m. i. moustafa, m. a. tashkandi, and a. m. el-sherif, "detecting mineral resources and suggesting a physical concentration flowsheet for economic minerals at the northern border region of saudi arabia," engineering, technology & applied science research, vol. 12, no. 3, pp. 8617–8627, jun. 2022, https://doi.org/10.48084/etasr.4894. engineering, technology & applied science research vol. 8, no. 5, 2018, 3373-3379 3373 www.etasr.com zaky et al.: pfc control for led lamp driver using sensorless predictive current controller pfc control for led lamp driver using sensorless predictive current controller mohamed s. zaky department of electrical engineering northern border university arar, saudi arabia mszaky78@yahoo.com haitham z. azazi faculty of electrical engineering menoufia university shebin el-kom, egypt haitham_azazi@yahoo.com ezzeddine touti department of electrical engineering tunis university montfleury, tunisia touti.these09@gmail.com abstract—light-emitting diodes (leds) have recently become of utmost significance to replace conventional lighting sources. power factor correction (pfc) control of led lamps requires three sensors which cause more cost, increase time delay, and increase noise, thus reducing drive reliability. alternative methods to estimate the inductor current instead of its measurement are mandatory. this paper proposes a sensorless predictive current controller to enhance power factor (pf) of led lamp driver and reduce driver cost. the inductor current is estimated instead of employing current sensor relying on measured input and output voltages. zero-crossing detector is utilized to accomplish robust performance during distorted supply voltage. the controller and power circuit are isolated. the control algorithm employs a two-loop control to achieve a high pf with sinusoidal input current. rapid speed performance is accomplished. the influences of pfc on input current value, pf and harmonic orders are presented. a prototype led lamp driver with the suggested pfc structure is tested practically by a digital signal processor (dsp) ds1104 platform to validate its effectiveness. experimental tests under various working conditions are provided to prove the usefulness of the suggested pfc control. keywords-led lamp; power factor correction; sensorless control; predictive control; dc/dc converter i. introduction twenty percent of worldwide consumed power is spent on lighting. to decrease the price of the consumed lighting power, light-emitting diode (led) lamps were deployed. they have various advantages over conventional light sources, like long lifetime, high resistance to mechanical vibrations, high reliability, higher optical efficiency, uncomplicated interface circuit, smaller size, and they are mercury-free [1-3]. ac/dc converters are wanted to energize led lamps [4]. traditional ac/dc rectifier circuit using filter capacitor was used in [5]. filter capacitor minimizes considerably the ripples of the output voltage [6]. however, it causes ripples in the supply current. moreover, it draws discontinuous current from utility [6]. this creates some difficulties such as decrease of available power and increase of losses [7]. power factor correction (pfc) circuits are commonly utilized to give sinusoidal input current [8]. pfc circuit must achieve the needs of international harmonic standards. ac/dc led drivers for lighting with power larger than 25w must fulfil current harmonic borders, iec61000-3-2 class c [9]. single-stage pfcs were considered the best converters regarding lighting purposes. in [10], pfc and regulator structures were combined together. these guarantee ease circuit control, minimized size, a close to unity power factor (pf), and increased efficiency [11]. numerous methods to enhance pf and current distortions for led lamps were employed in [12-14]. the majority of these approaches were depending on traditional analog control principles. they fundamentally carry out analog control principles in a digital form [15]. in traditional digital execution, division and multiplication processes can be realized via software. as all computations are performed in each switching period, so, implementation of traditional approaches needs rapid digital controllers. while various discrete pfc techniques were offered in [16, 17], many issues of digital applications like high computation burden, augmented price, and restricted switching frequency in comparison to analog control needed to be remedied. to attain large switching frequency with the required specifications, a predictive digital pfc scheme was employed in [16]. it achieves minimized cost, small computation burden, and improved behaviour compared with the traditional pfc approaches. pfc control of leds, requires three kinds of sensors for detecting input current, inductor current and output voltage. current sensors are commonly utilized in order to capture inductor current. but, using sensors with interface circuits costs more, increases time delay, and increases noise. this reduces the drive reliability. the input current sensing is considered a significant issue. a resistive sensor is generally utilized in practice. nevertheless, it introduces extra cost, power loss, and heating. so, sensorless current control pfc schemes were employed. in [16, 18], the current was predicted for improving the power section behavior. pfc algorithms using digital current reconstruction suffer from difficult mathematical computation [19]. also, the supply current may be distorted and there is a phase difference in the input voltage. in [20], pfc-based on kalman filters for current sensorless controller was presented. however, it has large computation modeling and the input current has some distortion. in [21, 22], control approach using current law was introduced, in which, the instantaneous input current and proportional gain was applied engineering, technology & applied science research vol. 8, no. 5, 2018, 3373-3379 3374 www.etasr.com zaky et al.: pfc control for led lamp driver using sensorless predictive current controller to manage a constant dc link voltage. but, this approach neglects current compensation. for these issues, alternative methods to estimate the inductor current instead of its measurement are mandatory. thus, sensorless current techniques are considered a suitable solution in terms of cost and reliability. moreover, stable performance during transition state besides protecting instruments against over current is considered a big challenge. this paper suggests a sensorless predictive current controller to improve the pf of led lamp driver and reduce cost. inductor current is estimated. the power circuit and the controller using the proposed scheme are isolated. the control structure is relied on a two-loop control to attain a high pf with sinusoidal input current. rapid speed performance is also accomplished. the impact of pfc on the input current is presented. theoretical analysis, simulation modeling, and experimental verifications of led lamp driver with the proposed pfc control are presented. ii. led lamp driver a. system structure the structure of the led lamp driver with its proposed sensorless predictive current controller is demonstrated in figure 1. the system is consists of a led lamp string fed from a dc-dc boost converter. the boost converter is fed from single-phase full bridge rectifier and step-down transformer. the proposed sensorless pfc control consists of two control circuits. a proportional-integral (pi) controller in the external circuit is employed for the voltage control to adjust the led lamp output voltage (vo). reference and actual voltages are compared and the difference is fulfilled with the pi voltage controller. the resultant output is considered the scaling factor of the rectified voltage vin. the reference current ilref can be obtained by multiplying this scaling factor with vin and dividing by the square of the root mean square (rms) of vin. the second control circuit can be considered the current controller. this circuit is structured with the inductor current ^ l i and a predictive current controller. the current estimation module is using rectified voltage and output voltage to estimate the inductor current. is vs + c + l d s gate driver dsp control platform il + vin tran led string vo voltage controller + predictive current controller vref ilref (m+1) current estimator il(m) adcadc vin (m) vo (m) d (m) d (t) fig. 1. led driver topology and proposed control b. modeling of leds to appropriately design the proposed pfc converter, modeling of the load of the led is needed. a comparison between i-v characteristics of led load and resistive load is displayed in figure 2. the resistance of each load can be obtained by the inverse of each curve slope. the dynamic resistance of the led load is much lesser than the corresponding resistive load. as obvious, the led characteristics cause instability problems. fig. 2. comparisons of i-v characteristics of led and resistive loads. the i-v relationship of led shown in figure 2 is given by: = bv i ae (1) where, a and b are separate gains. the correlation in (1) shows the minimum dynamic resistance of led at operating condition. this is a simple model that considers only the device equivalent resistance during normal working point. but, this assumption causes undesirable errors. these errors result from the large variation of the equivalent and dynamic resistances at the working point. the actual dynamic resistance is much smaller than the equivalent resistance. thus, the most common approximation model is the one containing a threshold voltage connected in series with a dynamic resistance, as seen in figure 3 [23]. fig. 3. approximate equivalent circuits of led string. therefore, the i-v model of the led load can be as: d di d i v r i v  = + (2) where vd is the forward voltage drop on one led, rdi the dynamic resistance, id the led forward current, and vγi the threshold voltage. the relationship of the output voltage for a complete string in series is described by the product of (2) with the number of leds connected in series: ( ) o di d i di d i v n r i v r i v   = + = + (3) where, vo is the led string output voltage and n the number of leds connected in series. led model can be attained via capturing the voltage vo and forward current id in the laboratory to get the dynamic resistance and load threshold voltage. the rated power demand for most led street lights ranges from 60w to 150w. the engineering, technology & applied science research vol. 8, no. 5, 2018, 3373-3379 3375 www.etasr.com zaky et al.: pfc control for led lamp driver using sensorless predictive current controller led lamp selected in this paper consists of three branches in parallel. each branch consists of 19 leds. each led current is 350ma. this provides a total of 60 leds consuming 60w at string output voltage 60v. the led threshold voltage and dynamic resistance are 2.8v and 1.03ω. iii. design of predictive current controller the predictive current controller for led lamp driver working in continuous conduction mode (ccm) as demonstrated in figure 1 is presented in this section. some assumptions for analysis simplification are: • the switch s and diode d can be considered ideal. • the input voltage vin(t) is a full-wave rectified, i.e., vin(t)=vm|sin(ωe t)|, where vm is the peak value of ac supply voltage and ωe=2πf is the angular frequency. • the capacitor c is large enough to ignore the frequency voltage ripple. • the switching frequency should be greater than the supply frequency. thus, input and output voltages of the boost converter are assumed as constant through one switching period t. the suggested led driver has two modes of operation during a switching cycle. figure 4 illustrates these two operation modes. (a) mode 1 (b) mode 2 fig. 4. two equivalent circuits of the boost led driver working in ccm 1) mode 1: ( ) r s m t m d m t  + referred to figure 1, when the switch s is on. accordingly, the inductor voltage is vin(t). therefore, il(t) is obtained from: ( ) ( ) l in di t v t l dt = (4) where l is the coil inductance. 2) mode 2: ( ) 1 r s m d m t t m+   + the switch s is off. therefore, il(t) decreases linearly as: ( ) ( ) ( ) l in o di t v t v t l dt − = (5) the equations of mode 1 and mode 2 can be arranged as (6) and (7) because the switching frequency is much higher than the supply frequency. ( ( ) ) ( ) ( ) ( ) l r s l in r s i m d m t i m v m l d m t + − = (6) ( 1) ( ( ) ) ( ) ( ) 1 ( ) l l r s in o r s i m i m d m t v m v m l d m t + − + − = − (7) where, m and (m+1) are the starting moments of mth and (m+1)th switching periods, and dr(m) is the duty ratio in the mth switching period. il(m) and il(m+1) are the values of il(t) at the starting of mth and (m+1)th switching periods. figure 5 shows il(t) at one switching period. mode 1 mode 2 t ( ) l i t ( ) l i m ( )+ l r s i m d t ( 1)+ l i m ( 1 )+ + l r s i m d t ( 2)+ l i m s t st m 1+m 2+m ( ) r s d m t ( )+ r s m d t ( 1 )+ + r sm d t ( 1)+ r s d m t fig. 5. inductor current waveform in one switching period under predictive current control. equation (6) is used to derive il(t) at the moment of switching off, m+dr(m)ts, by: ( ) ( ( ) ) ( ) ( )r s l r s l in d m t i m d m t i m v m l + = + (8) il(t) during the starting moment at (m+1) using (7) is given in (9): ( ) [(1 ( )) ] ( 1) ( ( ) )) ( ) ( ) r s l l r s in o d m t i m i m d m t v m v m l − + = + + − (9) using (8) and (9), il(t) at the (m+1) th instant using il(t) at the mth moment, is obtained by: ( ) ( )[1 ( ) ] ( 1) ( ) in o r s l l v m v m d m t i m i m l − − + = + (10) transforming (10) to a digital structure gives: ( ) ( )[1 ( ) ] ( 1) ( ) in o r s l l v k v k d k t i k i k l − − + = + (11) it is observed that the inductor current in the next switching period il(k+1) is calculated by the inductor current il(k), the output and input voltages and the present duty ratio. the duty ratio is obtained from (11) as: ( 1) ( ) ( ) ( ) ( ) ( ) ( ) l l o in r s o o s l i k i k v k v k d k t v k v k t  + − − = +    (12) equation (12) indicates that the desired duty ratio dr(k) for the present switching cycle is derived depending on the boost engineering, technology & applied science research vol. 8, no. 5, 2018, 3373-3379 3376 www.etasr.com zaky et al.: pfc control for led lamp driver using sensorless predictive current controller inductance, l i , in v , and o v . for properly pfc design for the led driver, the current controller forces il(k+1) to track iref (k+1). also, the voltage controller forces vo(k) to track vref . alternatively, actual il(k) is replaced with the estimated value ˆ ( ) l i k . hence, the duty ratio is written by using (13): ( 1) ( ) ( ) ( ) ref l ref in r s ref ref s i k i k v v kl d k t v v t   + − −  = +      (13) the reference current is calculated by integrating the difference between vo(m) and vref. then, this integration output is multiplied by a generated absolute sine wave of unity amplitude. this sine wave can be completely synchronized with vin using the zero-crossing detection concept. the zerocrossing detector can be employed in the suggested scheme to attain high performance during distorted supply voltage. the inductor reference current iref (m+1) is obtained from figure 6 as: ( )( 1) ( ) ( ) ( ) sin( ( 1))ref p i si m k e t k t e t dt t m+ = + + (14) where e(t) is the voltage error, kp is the proportional gain, and ki is the integral gain. a/dvo(t) + vref e(t) pi a/dvin(t) zero-crossing detector sine wave look up table sin(wst(m+1)) iref(m+1) fig. 6. inductor reference current estimator. iv. current estimate method the proposed method of pfc control is employed without employing the current sensor to attain a close to unity pf of a led lamp driver fed from a single-phase rectifier. the inductor current is estimated instead of the current sensor relied on the measured input and output voltages. the inductor current can be estimated from the two states of boost converter as follow: • the rebuilt ˆ ( ) l i k in on-state is introduced by: ( ) ˆ in l v t i dt l =  (15) • the rebuilt ˆ ( ) l i k in off-state is expressed by: ( ) ( ) ˆ in i l v t v t i dt l − =  (16) the above two integration processes are bilaterally incorporated to estimate the inductor current ˆ ( ) l i t . figure 7 displays the block diagram of the inductor current estimator for pfc of led driver to attain pf close to unity. the inductor current is computed using the actual output and input voltages. estimated and reference currents are considered the inputs of the predictive current controller. then, the output is used as a feedback to control the command signal’s one and off state. furthermore, it is used as an input to the pulse with modulator (pwm) for controlling the boost converter switch states. switch on off on and off pulses l a/dvo(t) a/dvin(t) a / b + a / b  il(m) + pwm pulsesa b a b dsp iref (m+1) predictive controller fig. 7. inductor current estimator v. results and discussion a. laboratory system setup to examine the performance of the led system, a laboratory implementation of the led system is carried out using the proposed controller approach. figure 8 shows a photo of the real-time experimental system using dsp-ds1104 control platform. the experimental system consists of 60w led streetlight, dc-dc boost converter, single-phase auto transformer, gate drive and interface circuits, voltage sensors, and a ds11104 control board. fig. 8. photo of the real-time experimental system of the led system using dsp-ds1104 control platform. the experiment is implemented with a grid phase voltage of 220v, and the led lamp is fed from the boost converter, which is consisting of coil, fast recovery diode (desi 60), single power switch (igbts) and a gate interface board. the igbt used in the experimental system is mitsubishi igbt module (cm50dy-24h) 50a/1200v. the led lamp consists of three branches in parallel. each branch has 19 leds. single led current is 350ma. the input voltage and output voltage are measured using voltage sensors (lv25-p) and sent to the dspace-ds1104 control board via the a/d converter port. the dsp platform uses a dspace-ds1104. matlab/simulink software is employed for model built. the dspace board has facilitated to capture the experimental engineering, technology & applied science research vol. 8, no. 5, 2018, 3373-3379 3377 www.etasr.com zaky et al.: pfc control for led lamp driver using sensorless predictive current controller waveforms and exports them numerically per sample. table i provides the main converter specifications used for the experimental system. table i. system parameters parameters values vs (rms) 220v f 50hz vo (avg) 60v io ( avg) 1a pled 60w l 2mh c 1000µf tr 220:24v rms b. results figure 9 shows the steady state simulation and experimental tests of supply voltage and current waveforms for led lamp driver. this figure implies that the supply current is and the supply voltage vs are sinusoidal and in phase. figure 10 displays the harmonics spectrum of is (up to 20 th) in simulation and experimental tests. as noted, thd of the supply current using the suggested led driver is 3% and the pf is 0.9996. this meets iec-61000-3-2 class c limit with large margins. 0.5 0.52 0.54 0.56 -400 -200 0 200 400 time (sec) is [2 amp./div] vs [200 v/div] (a) simulation 0.5 0.52 0.54 0.56 -400 -200 0 200 400 time (sec) is [2 amp./div] vs [200 v/div] (b) experiment fig. 9. steady-state tests showing the supply voltage and current. fig. 10. harmonics spectrum of supply current. steady-state results showing the actual current and estimated coil current are displayed in figure 11. as obvious, the estimated coil current is precise enough, permitting the inductor current immediately tracks the reference current variation and achieve the required response. figure 12 displays the led voltage and current at steady-state. 0.5 0.52 0.54 0.56 0 1 2 3 4 5 time (sec) il [amp] ˆ l i [amp] (a) simulation 0.5 0.52 0.54 0.56 0 1 2 3 4 5 time (sec) il [amp] ˆ l i [amp] (b) experiment fig. 11. steady-state results showing the actual current and estimated coil current. 0.5 0.52 0.54 0.56 0 20 40 60 time (sec) vo [10v/div] io [0.5 amp./div] (a) simulation 0.5 0.52 0.54 0.56 0 10 20 30 40 50 60 time (sec) vo [10v/div] io [0.5 amp./div] (b) experiment fig. 12. steady-state results led voltage and current. voltage and current of the led driver are dc nearly without ripples. figures 13-15 demonstrate the waveforms of supply voltage and current under various voltage levels. these 3 5 7 9 11 13 15 17 19 0 10 20 30 harmonic order t h d i s ( % ) experimental simulation iec61000-3-2 class c engineering, technology & applied science research vol. 8, no. 5, 2018, 3373-3379 3378 www.etasr.com zaky et al.: pfc control for led lamp driver using sensorless predictive current controller figures prove that the supply current is and the supply voltage vs are sinusoidal and in phase. 0.5 0.52 0.54 0.56 -200 -150 -100 -50 0 50 100 150 200 time (sec) is [1 amp./div] vs [100 v/div] (a) simulation 0.5 0.52 0.54 0.56 -200 -150 -100 -50 0 50 100 150 200 time (sec) is [1 amp./div] vs [100 v/div] (b) experiment fig. 13. supply voltage and current at 100v rms. 0.5 0.52 0.54 0.56 -300 -200 -100 0 100 200 300 time (sec) is [1 amp./div] vs [100 v/div] (a) simulation 0.5 0.52 0.54 0.56 -300 -200 -100 0 100 200 300 time (sec) is [1 amp./div] vs [100 v/div] (b) experiment fig. 14. supply voltage and current at 150v rms. the robustness of the proposed control technique is checked at step changes in the reference voltage as displayed in figure 16. it is evident that the proposed converter achieves a fast recovery time to its reference voltage. figure 17 demonstrates transient response of supply voltage variations. the transient response of output voltage and current during supply voltage changes is displayed in figure 18. as noted, the output voltage can be attainted at its reference value under the changes in supply voltage and the system has a good dynamic response against sudden variations of the source voltage. 0.5 0.52 0.54 0.56 -400 -300 -200 -100 0 100 200 300 400 time (sec) is [0.5 amp./div] vs [100 v/div] (a) simulation 0.5 0.51 0.52 0.53 0.54 0.55 0.56 -400 -300 -200 -100 0 100 200 300 400 time (sec) is [0.5 amp./div] vs [100 v/div] (b) experiment fig. 15. supply voltage and current at 250v rms 0.5 1 1.5 2 0 10 20 30 40 50 60 70 time (sec) vo [10v/div] io [0.5 amp./div] vref [10v/div] (a) simulation 0.5 1 1.5 2 0 10 20 30 40 50 60 70 time (sec) vo [10v/div] io [0.5 amp./div] vref [10v/div] (b) experiment fig. 16. transient response due to reference voltage changes (a) simulation (b) experiment fig. 17. transient response showing supply voltage changes. 1 1.5 2 -400 -200 0 200 400 time (sec) 1 1.5 2 -400 -200 0 200 400 time (sec)time (sec) time (sec) engineering, technology & applied science research vol. 8, no. 5, 2018, 3373-3379 3379 www.etasr.com zaky et al.: pfc control for led lamp driver using sensorless predictive current controller 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 0 10 20 30 40 50 60 time (sec) vo [10v/div] io [0.5 amp./div] (a) simulation 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 0 10 20 30 40 50 60 time (sec) vo [10v/div] io [0.5 amp./div] (b) experimental fig. 18. transient response showing output voltage and current due to supply voltage changes. vi. conclusion a sensorless predictive current controller for led lamp driver was proposed. the sensorless current scheme was designed to estimate the inductor current relied on the sampled value of input and output voltages. this scheme achieves reliability and simplicity on estimating inductor current. this remedies the issues of a current sensor. the predictive current controller generates the duty cycles in advance relied on the reference and estimated inductor currents and input and output voltages. the proposed pfc control technique has low computation burden and it has been executed using a minimum cost digital signal processor to accomplish high switching frequency. results demonstrated the advantages of the suggested driver with a high pf and sinusoidal supply current waveform with low harmonics, complying with iec 61000-3-2 class c. the proposed scheme can attain good dynamic performance for reference and supply voltage changes. acknowledgement authors acknowledge the approval and support of this research study by the grant no. eng-2017-1-8-f-7217 from the deanship of scientific research at northern border university, arar, ksa. references [1] e. f. schubert, light-emitting diodes, e. fred schubert, 2006 [2] a. zukauskas, m. s. shur, r. gaska, introduction to solid-state lighting, wiley, pp. 79-82, 2002 [3] c. c. wang, k. h. wu, y. c. liu, c. y. yang, m. m. alam, y. k. lo, h. j. chiu, “study and implementation of an improved power factor alternating-current-light emitting diode driver”, iet power electronics, vol. 8, no. 7, pp. 1156-1163, 2015 [4] c. moo, y. chen, w. yang, “an efficient driver for dimmable led lighting”, ieee transactions on power electronics, vol. 27, no. 11, pp. 4613-4618, 2012 [5] j. c. lam, p. k. jain, “isolated ac/dc offline high power factor single-switch led drivers without electrolytic capacitors”, ieee journal of emerging and selected topics in power electronics ,vol. 3, no. 3, pp. 679-690, 2015 [6] s. w. lee, h. l. do, “a single-switch ac-dc led 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power electronics, vol. 29, no. 1, pp. 347-355, 2016 [18] s. bibian, h. jin, “high performance predictive deadbeat controller for dc power supplies”, ieee transactions on power electronics, vol. 17, no. 3, pp. 420-427, 2002 [19] a. p. finazzi, l. c. de freitas, j. b. vieira, e. a. a. coelho, v. j. farias, l. g. freitas, “current-sensorless pfc boost converter with preprogrammed control strategy”, ieee international symposium on industrial electronics, gdansk, poland, june 27-30, 2011 [20] k. i. hwu, h. w. chen, y. t. yau, “fully-digitalized implementation of pfc rectifier in ccm without adc”, 26th annual ieee applied power electronics conference and exposition, fort worth, usa, march 6-11, 2011 [21] f. j. azcondo, a. de castro, v. m. lopez, o. garcia, “power factor correction without current sensor based on digital current rebuilding”, ieee transactions on power electronics, vol. 25, no. 6, pp. 1527-1536, 2010 [22] j. w. kimball, p. t. krein, “a current-sensorless digital controller 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college of science university of hail hail, saudi arabia naglaaf2002@yahoo.com abstract—the influence of adding glycerol and petroleum jelly during the tinning process of steel shell base of babbitt-steel bimetal is studied in this paper. the morphology of interface layer is changed from a discontinuous layer in case of using flux+tin to a continuous one by adding glycerol or petroleum jelly to the flux+tin mixture. also, the nterface layer thickness and the unbonded interface layer area increase by adding glycerol or petroleum jelly to flux+tin mixture due to their physical properties. keywords-babbitt; steel; flux; glycerol; petroleum jelly i. introduction depending on the specific application requirements (corrosion resistance, wear resistance, electrical conduction, etc.), the working face layer of a bimetal should be characterized by high performance properties [1-3]. tin-based babbitt alloys are usually used as working surface layers, especially in sliding bearings. tin-based babbitt alloys are mainly composed of sn–sb–cu containing about 0.5–8% cu and less than 8% sb. the microstructures of tin-based babbitt alloys are characterized by a solid solution matrix in which needles of cu6sn5 copper-rich constituent and fine, rounded particles of precipitated sbsn are distributed. the proportion of the copper rich constituent increases with copper content containing about 0.5–8% cu and higher percentage of sb and sb which exhibit primary cuboids of sbsn, beside copper-rich constituent in the matrix [4-6]. although, babbitt-steel bimetal alloys are widely used materials for sliding bearings, the production of high performance babbitt-steel bimetals still needs more effort due to the poor wettability of the steel with babbitt alloy. fluxing and tinning processes are usually used to improve the adhesion of the babbitt layer on steel substrate [7, 8]. usually, after grinding the surface of the steel substrate shell, it is briefly immersed in multi-chlorides aqueous flux solution (24kg zinc chloride, 6 kg sodium chloride, 3kg ammonium chloride, 1l hci, and enough water to make 100l) for 60 seconds followed by coating of the steel surface with either pure tin (sn) or a sn-lead alloy (called tinning process) to promote adhesion between the bearing and the babbitt metal [7, 8]. the current study is investigating the interface microstructure of babbitt-steel by using a mixture of powder tin, flux and glycerol and a mixture of powder tin, flux and petroleum jelly additives. the mixing of the powder tin with flux as one direct tinning process is successfully used for fabricating babbitt-steel bimetal composite that is promising for flat and horizontal bearing applications [9]. glycerol and petroleum jelly are added to the tin-flux mixture to facilitate tin-flux application for curvature surface steel shells. ii. experimental work carbon steel base specimens with a chemical composition that is shown in table i of dimension 400x400x9mm3 are grinded with sand papers of 240 and 320-grit for two minutes each. the homemade flux is prepared using the chemicals listed in table ii mixed with the tin powder. the tin to flux ratio is 1:5 (1g of tin, and 5g of flux). the necessity of using flux in bimetal production is the fact that the oxides which always form up on all the brightened metal surfaces prevent the proper joining of the pieces. the flux by removing the oxides allows the tin to stick directly to the metal. table i. steel chemical composition (wt %) c mn cr ni cu fe 0.15 0.33 0.03 0.05 0.02 bal. table ii. flux chemical composition wt %, ml. zncl2 nacl2 nh4cl hcl h2o 24g 6g 3g 1ml 1ml in the current research work, fluxing and tinning processes are merged in one step by mixing the flux with the tin powder. this research work aims to study the effect of the homemade tinning mixture of flux with glycerol and petroleum jelly additives on tinning quality and bonding characteristics of the engineering, technology & applied science research vol. 8, no. 3, 2018, 3028-3031 3029 www.etasr.com fathy: interface microstructure investigation of babbitt-carbon steel composite using flux with … steel babbitt bimetal. influence of the different tinning mixtures on the microstructure mechanical properties and bonding characteristics of the carbon steel babbitt bimetal is studied for three groups of samples  the first group of steel babbitt bimetal was produced using flux+ tin(5:1 ratio).  the second group was produced using homemade flux+tin+glycerol (ratio 4:1:1)  the third group was produced using homemade flux+tin+petroleum jelly (vaseline) in a ratio of 4:1:1. glycerol and petroleum jelly are used to study their effects on the evaporation process, the homogeneity of the tinning mixture, and how it holds the flux in its place. if the flux is easy to distribute and able to hold in its place, this will make it good for curved surfaces. in the tinning process 1g of the tinning mixture is distributed on the steel base shell. then the base is placed on a preheated hot plate of 360oc for 5min. after heating time the steel shell is removed from the hot plate and the tinned surface is cleaned using towel and tap water. then the samples are cooled to room temperature. babbitt metal with the chemical composition shown in figure 3 is melted in an electrical furnace at 4000c. after holding for about 30min the crucible of molten metal is removed from the furnace and is poured onto metallic mold containing a preheated (at 3600c for 7min.) tinned steel shell. the volume of liquid babbitt to solid steel ratio is kept to be 1:1. table iii. chemical composition of the babbit tin base alloy element sb cu sn wt.% 6.5-7.5 2.5 bal. in order to reveal the microstructure of the bimetal interface region between the babbitt and the carbon steel base, metallographic examination is conducted by optical microscopy. optical examination is conducted after grinding, polishing, and etching with 4% nital to define any discontinuities, crack, lack of bonding, voids, holes etc. the measurements were taken for as cast samples of the three groups of the carbon steel babbitt bimetal. iii. results and discussion it is reported in [7] that the microstructure of babbitt has a significant influence on the operating life of lined bearings. for sn based babbitt, the percentage of sb and cu alloyed with sn controls the microstructure constituents. in the current study (see figure 1(a)) and previous ones [4-6] it is reported that tinbased babbitt alloys that contain about 2.5% cu and about 6.57.5% sb usually have a microstructure of a solid solution matrix, distributed needles of cu6sn5 copper-rich constituent and rounded particles sbsn precipitate. the strength and hardness of babbitt with a fine-grained microstructure is 20% higher than that of a babbitt with a coarser-grained microstructure. it is reported in [10] also that the shear stress and ultimate strength of the bond between the babbitt alloy and the metal shell are higher for the fine-grained babbitt compared with the coarse one. (a) babbitt microstructure (b) steel base microstructure fig. 1. microstructures of babbitt steel base region. figure 1 shows the microstructures of the babbitt alloy and the steel base regions. the microstructure of steel region shows mainly ferrite matrix and some pearlite due to lower carbon percentage. for all the conditions of bimetal casting in the current research, microstructures of babbitt working surface and steel solid base show the same constituents. figure 2 shows the interface microstructure of as-cast babbitt-steel bimetal for three different groups after applying fluxing and tinning processing conditions. group 1 shows the interface microstructure of the sample prepared using flux and tin. group 2 shows the interface microstructure of the sample prepared using flux, tin and glycerol. group 3 shows the interface microstructure of the sample prepared using flux, tin and petroleum jelly. it is clear that addition of glycerol and petroleum jelly to the mixture of flux and tin has a significant effect on the morphology of the interface zone of babbittsteel bimetal castings. using flux+tin produces a discontinuous interface layer, while by using additions of glycerol or petroleum jelly produces a continuous interface layer. figure 3 shows the effect of flux type on interface layer thickness for samples prepared using flux+tin, flux+tin+glycerol and flux+tin+petroleum jelly. it is clear that by using flux+tin (group 1) a minimum interface layer thickness of 150m is achieved. the addition of glycerol or petroleum jelly to flux+tin increases the interface layer thickness that reaches about 240m for the glycerol addition case. it is reported in [11-12] that the bonding energy of the bimetal interface when using sn as an intermediate layer is relatively 10% larger compared to that of the bimetal interface without a sn layer. so, babbitt and steel bimetal interfacial bonding performances with an intermediate layer of sn are better than those of an interface without sn layer. in the current engineering, technology & applied science research vol. 8, no. 3, 2018, 3028-3031 3030 www.etasr.com fathy: interface microstructure investigation of babbitt-carbon steel composite using flux with … research, by the addition of glycerol or petroleum jelly, a continuous interface sn layer is achieved instead of the discontinuous sn layer in the case of flux+tin only. this means that the addition of glycerol or petroleum jelly is stronger and more stable during pouring the molten babbitt on the tinned steel base. our current gravity casting technique is still the standard method of applying babbitt to bearing steel shells. this process involves the use of a preheated tinned steel shell. many process parameters should be considered in order to fabricate a high performance and long life babbitt-steel bimetal bearing. one parameter of most importance is the tinning process. the optimization of the tinning process is essential for achieving a good strength bond between babbitt and steel shell. although, the addition of glycerol and petroleum jelly to the flux and tin mixture stabilized the sn layer, the unbonded area increases (see figure 4), although further research on the optimum percentage should follow. (a) flux+tin (b) flux+tin+glycerol (c) flux+tin+petroleum jelly fig. 2. interface microstructure of three samples made by using different combinations of flux, tin, glycerol and petroleum jelly. fig. 3. the effect of flux type on the tin layer thickness for samples prepared using flux+tin, flux+tin+glycerol and flux+tin+petroleum elly. (a) (b) fig. 4. microstructure of babbitt bimetal for samples prepared using a) flux+tin+petroleum jelly b) flux+tin+glycerol the typical interface microstructures of as-cast samples with addition of glycerol and petroleum jelly are shown in figure 4. the addition of glycerol or petroleum jelly to flux+tin mixture increases the unbonded interface area (figure 5). the largest unbonded area is observed by addition of glycerol to the flux+tin mixture. the interface has partial joint, which is characterized by the presence of the so-called “bimetallic connecting bridges” or unbounded areas. it is believed that the unbounded areas are a result of the gases produced by the combustion of glycerol or petroleum jelly residuals in the tinning layer during the preheating process and pouring of the babbitt. it is well known that petroleum jelly and glycerol are not physically similar. petroleum jelly is mainly a non-polar hydrophobic hydrocarbon and insoluble in water otherwise glycerol is mainly an alcohol that is strongly hydrophilic. this means that petroleum jelly is water-repelling material and on the other side glycerol is water-attracting material. the physical properties of glycerol explain that why large unbonded 0 50 100 150 200 250 flux + tin + petroleum jelly flux + tin + glycerol flux + tin in te rf ac e la ye r th ic kn es s,  m engineering, technology & applied science research vol. 8, no. 3, 2018, 3028-3031 3031 www.etasr.com fathy: interface microstructure investigation of babbitt-carbon steel composite using flux with … areas are observed by adding it to the flux+tin mixture. petroleum jelly is flammable only when heated to liquid. its product fumes are light. generally, glycerol is considered to be a crucial part of the production of antifreeze and waxes. also it is used to generate resins, paints and waxes, for creating cleaning and purifying agents for soldering. residual glycerol and/or petroleum jelly in the preformed tinned surface layer have great influence on the morphology and the formation of unbonded areas in the interface between babbitt and steel. this effect is significant in adding glycerol due to its attractive nature for water besides producing fumes after pouring molten babbitt metal. fig. 5. the effect of flux type on unbonded interface area iv. conclusions the effect of adding glycerol and petroleum jelly to flux+tin mixture on interface morphologies of babbitt-steel bimetal composites was investigated. based on the obtained results, the main conclusions can be summarized as:  the morphology of the interface layer is changed from discontinuous in case of using flux+tin to continuous by adding glycerol or petroleum jelly to the mixture.  the thickness of the interface layer increases by addition of glycerol or petroleum jelly to the mixture.  unbonded interface layer area increases by the addition of glycerol or petroleum jelly to flux+tin mixture due to their physical properties.  more future investigations using a small percentage addition of glycerol or petroleum jelly to flux+tin mixture, long tinning heating time and higher babbitt pouring temperature are needed to improve the quality of interface bond between babbitt and steel alloys. acknowledgment the author would like to thank dr. mohamed ramadan of casting technology lab., manufacturing technology dept., cmrdi, egypt for the useful discussion and technical support. references [1] t. wróbel, “characterization of bimetallic castings with an austenitic working surface layer and an unalloyed cast steel base”, journal of materials engineering and performance, vol. 23, no. 5, pp. 1711–1717, 2014 [2] m. ramadan, k. m. hafez, k. s. abdel halim, n. fathy, t. chiba, h. sato, y. watanabe, “influence of heat treatment on interface structure of stainlesssteel/gray iron bimetallic layered castings”, applied mechanics and materials, vol. 873, pp. 3-8, 2017 [3] m. ramadan, “interface characterization of bimetallic casting with a 304 stainless steel surface layer and a gray cast iron base”, advanced materials research, vol. 1120-1121, pp. 993-998, 2015 [4] r. r. dean, c. j. eavans, “plain bearing materials: the role of tin”, tribology international,vol. 9, no. 3, pp. 101–108, 1976 [5] g. c. pratt, “materials for plain bearings”, international metallurgical reviews,vol. 18, no. 2, pp. 62–88, 1973 [6] m. moazami goudarzi, s. a. jenabali jahromi, a. nazarboland, “investigation of characteristics of tin-based white metals as a bearing material”, materials and design, vol. 30, no. 6, pp. 2283–2288, 2009 [7] p. diouf, a. jones, “investigation of bond strength in centrifugal lining of babbitt on cast iron” metallurgical and materials transactions a, vol. 41, no. 3, pp. 603-609, 2010 [8] p. k. liaw, m. n. gungor, w.a. logsdon, y. ijiri, b. j. taszarek, s. frohlich, “effect of phase morphologies on the mechanical properties of babbitt-bronze composite interfaces”, metallurgical transactions a, vol. 21, no. 2, pp. 529-538, 1990 [9] n. fathy, m. ramadan, “influence of vol. ratio of liquid to solid and low pouring temperature on interface structure of cast babbitt-steel bimetal composite”, aip conference proceedings 1966, pp. 020028-1 020028-6, aip publishing, 2018 [10] a. g. gromyko, “influence of casting method of plain bearings on the structure of babbitt”, metal science and heat treatment, vol. 32, no. 9, pp. 708-711, 1990 [11] j. wang, q. xia, y. ma, f. meng, y. liang, z. li, “interfacial bonding energy on the interface between zchsnsb/sn alloy layer and steel bodyat microscale”, materials, vol. 10, no. 10, p. 1128, 2017 [12] j. koutsky, j. vesela, “evaluation of white metal adhesion (conventional casting and thermal wire arc spraying) by ultrasonic non-destructive method”, journal of materials processing technology , vol. 157–158, pp. 724–728, 2004 microsoft word 13-3265_s_etasr_v10_n1_pp5168-5174 engineering, technology & applied science research vol. 10, no. 1, 2020, 5168-5174 5168 www.etasr.com guldibi & demir: aging effect on microstructure and machinability of corrax steel aging effect on microstructure and machinability of corrax steel ahmet serdar guldibi faculty of technology karabuk university karabuk, turkey aserdarguldibi@karabuk.edu.tr halil demir faculty of technology karabuk university karabuk, turkey hdemir@karabuk.edu.tr abstract—in this paper, the influence of the aging process on the microstructure and machinability of corrax steel was investigated for four samples: a solution heat-treated (a0) and three samples aged at 400ºc (a4), 525ºc (a5.25) and 600ºc (a6) for four hours. the effect of aging temperature on hardness was examined. machining tests were carried out using a cnc lathe with a multi-layer coated pvd (altin) cutting tool, at various cutting speeds (50, 100, 150, 200, 250, 300, 350m/min) with constant feed rate (0.1mm/rev) and 1mm constant cutting depth. the microstructure was investigated using an optical microscope and eds attached sem. the effect of aging on reverted austenite formation was also evaluated. in order to understand the changes in surface topology, cutting forces and vibrations were measured. with increasing aging temperature, the lath martensite was transformed to plate martensite because of the formation of precipitates and reverted austenite. aging at different temperatures increased hardness up to 58%, cutting forces up to 117% and surface roughness up to 450%. the results describe the effect of the aging treatment on cutting forces, surface topology, tool wear and vibrations. keywords-dry turning; corrax; cutting force, surface roughness; vibration i. introduction investigation of martensitic steels started in usa during the 60’s. martensitic steels have low carbon and have high strength and corrosion resistance [1]. these properties are reached by convenient composition and properly applied aging treatments. corrax is a maraging steel appropriate for many applications such as plastics processing, extrusion dies, plastic extruder’s screws, guideways, landing gears, dental, and medical equipment [2-4]. the main goal of manufacturing companies is advanced productivity, improving surface finish and dimensional precision while reducing cost [5]. however, these goals are difficult to achieve especially during machining, as hardened maraging steels are as hard to machine materials [6]. cutting forces, specific cutting energy, shear angle, shear stress, friction coefficient and shear stress rates for aisi 420 steel at various cutting conditions and with various cutting tools have been investigated. according to test results, feed rate effects cutting forces, while cutting speed is the major effect of energy consumption. in [7], cutting forces and cutting energy reached maximum value at 60m/min and were reduced at higher cutting speeds. the machining of ph 15-5 maraging steel, aged at 482ºc to receive peak hardness value, was investigated in [8]. the machining tests were carried out using tialn coated tungsten carbide inserts with various nose radiuses (0.4, 0.8 and 1.2mm) at different cutting speeds and feed rates. increasing feed rate increased cutting forces: 0.8mm nose radius caused higher cutting forces than 0.4mm and 1.2mm. high cutting speed, low feed rate and middle tool nose (0.8mm) generated minimum surface roughness value (0.447µm). the heat formation during hard turning of chromium hardfacing materials was studied in [9]. results showed that increasing cutting speed or feed rate increased cutting temperature. the temperature increase rates depended on the microstructure of the material. machining finer structures cause higher temperature increment rate. the predicted temperature for fine structured materials is 650700ºc, while for coarser structured materials is 600ºc. the temperature and cutting forces during machining of sae 4140 steel was investigated in [10]. results showed that increasing cutting speed increases the temperature on the rake face, enlarging the tool-chip contact area. the effects of hot turning on cutting forces, tool wear and surface topology, were examined in [11]. experiments were carried out at room temperature, 300ºc and 600ºc. the outcomes showed that the increase of temperature decreased cutting forces, reduced tool wear, and improved surface topology. machining monel 400 at room temperature caused bue formation, which enhanced tool’s life compared to inconel 625 and inconel 718. bue formation increased tool’s life but also increased the surface roughness in the machining of monel 400. hot turning enhanced tool’s life, but this enhancement was poor for inconel 625 and monel 400 compared to inconel 718. the effects of different types of cutting fluid on cutting temperature, chip thickness, surface roughness, cutting forces and shear angle were investigated in [12]. experiments were carried out under dry, conventional cutting fluid and cryogenic carbon dioxide at three different cutting speeds and four feed rates at 1mm cutting depth. results showed that breakability was improved under cryogenic machining chips when compared to wet and dry machining. co2 penetrated better the cutting zone improving lubrication. improved lubrication reduced the cutting temperature and cut chip thickness. increasing cutting speed corresponding author: ahmet serdar guldibi engineering, technology & applied science research vol. 10, no. 1, 2020, 5168-5174 5169 www.etasr.com guldibi & demir: aging effect on microstructure and machinability of corrax steel decreased cutting forces because of the heat generated on the cutting zone. under cryogenic cutting conditions, increasing cutting speed caused higher decrease in cutting forces, because of the improved lubrication. increased cutting speed reduced surface roughness, cutting forces and vibration during machining. increased feed rates also increased the surface roughness. there are several researches about the aging treatment, strength, hardness, fracture toughness, strength in high temperature, reverted austenite formation, and hydrogen embrittlement of maraging steels [13-16]. however, there is a lack of extensive study on the machining of corrax steel. this study investigated the machinability of solution heat treated and aged at three different conditions corrax steel, under different cutting speeds, in order to understand the effect of aging on its microstructure, hardness, and machinability. ii. experimental procedure a. workpiece materials corrax steel was obtained from uddeholm turkey corporation. the samples were solution heat treated at 850ºc for 0.5h and subsequently air-cooled. table i shows the chemical composition of steel, analyzed by the gnr atlantis optical emission spectrometry. table i. chemical composition of corrax steel element c si mn p s % 0.048 0.203 0.253 0.012 0.026 element cr mo ni al % 12.24 1.388 9.064 1.582 b. heat treatment and microstructure the supplied corrax steel had 350mm length and 35mm diameter. four samples were obtained for the aging treatment. the samples were solution heat treated at 850ºc for 0.5h and then cooled at room temperature before the aging treatment. after the solution heat treatment all samples, except one (a0), were aged at three different temperatures (400, 525, 600ºc) for four hours and cooled in room temperature. at the end of the aging treatment, four sets of samples were obtained: (i) solution heat treated (a0), (ii) aged at 400ºc (a4), (iii) aged at 525ºc (a5.25) and (iv) aged at 600ºc (a6). conventional metallographic methods such as grinding, polishing and etching were used for microstructural investigation. kalling’s reagent was used for etching at various etching times, depending on material’s hardness. etching time depended on the hardness of each sample. the microstructure of the samples was examined using a nikon epiphot 200 optical microscope and an eds equipt carl zeiss ultra plus gemini fesem scanning electron microscopy (sem). xrd investigations were carried out using a rigaku ultima iv. xrd, sem and eds examinations were carried out in iron and steel institute (margem) at karabuk university. microhardness testing was conducted using a shimadzu vickers microhardness testing machine, with an hv1 (9,807n) load and 15s holding time. at minimum five hardness measurements were made on each sample and their average was accepted as hardness value. c. machine and cutting tool machining tests were accomplished using a fanuc control unit equipped with a johnford tc-35 lathe having 10kw power. the turning tests were carried out using pvd multilayer-coated cementite carbide inserts with a cnmg120408rp geometry. the cutting inserts were designed by kennametal. the inserts were mechanically fixed on a tool holder with a dclnr2525 geometry. the inserts were designated by kc5010 kennametal which is equivalent to p1020. d. cutting parameters machining tests were performed under dry cutting conditions without any cooling liquid. cutting parameters were determined into the recommended, by the manufacturer, limits in order to observe the performance of the cutting inserts. the cutting parameters are exposed in table ii. table ii. cutting parameters workpiece samples vc (m/min) f (mm/rev) ap (mm) a0 a4 a5.25 a6 50 0.1 1 100 150 200 250 300 350 cutting forces were measured using kistler 9257b piezoelectric 3-axes dynamometer. the mutitoyo surftest 211 surface roughness tester was used for measuring the surface roughness. three different measurements were made on each surface and their average was accepted as the surface roughness value. vibration measurements were performed using idynamic application [17] with an mtk sensor having 0.00390625 m/s2 resolution. iii. results and discussion a. workpiece materials optical micrographs of a0, a4, a5.25 and a6 are shown in figure 1, while similar microstructure investigations for ph 138 mo were carried out in [18, 19]. as it can be observed, the microstructure of the sample a0 has large and irregular massive martensite blocks. increasing aging temperature transforms the martensite structure from lath to plate. while massive martensite structures are seen in figure 1(a)-1(c), figure 1(d) shows the plate martensite structure. figure 1(c) shows the microstructure of the a5.25 sample with molybdenum carbides in the aged martensite structure [20]. the martensitic structure is smaller, compared to a0 and a4 samples. the microstructure of the a6 sample, seen in figure 1(d), has the highest amount of reverted austenite, indicated by white areas [21]. the transformation of massive to plate martensite with the increase of aging temperature can be explained by the formation of reverted austenite on the martensite borders [15, 22]. the growth of reverted austenite into martensite reduced massive martensite to plate martensite. in addition, the al content allows nial precipitations through aging which caused resistance to coarsening, even at high temperatures [23]. engineering, technology & applied science research vol. 10, no. 1, 2020, 5168-5174 5170 www.etasr.com guldibi & demir: aging effect on microstructure and machinability of corrax steel (a) (b) (c) (d) fig. 1. microstructure of: a) solution heat treated (a0), b) aged at 400℃ (a4), c) aged at 525℃ (a5.25). d) aged at 600℃ (a6) maraging steels are designed to form a martensitic structure and austenite transforms completely into martensite during cooling [29-32]. the xrd patterns of the samples, presented in figure 2, indicate that the dominant microstructure consisted of martensite phase. the significant intensity peaks of bcc(110) with small intensity of bcc(200) and bcc(211) show the martensite phase formation. the aging treatment causes a reverted austenite formation in the microstructure. increasing the aging temperature also increases the amount of reverted austenite in the microstructure, as seen in figure 2. fig. 2. xrd patterns of samples figure 3 shows the eds analysis with the spectrum points 1-6 white marked on the microstructure of the a5.25 sample. the selected points contain different percentages of c, cr, ni, mn, fe and al elements. the existence of these elements demonstrates a small amount of nial, crc, moc, fe3c and nimn precipitates, which affect the strength of steels [13, 2426]. the precipitations in the martensite structure hinders the dislocation motion that enhances the strength of steel [27, 28]. aging at temperatures over 525ºc causes a significant amount of reverted austenite [14]. reverted austenite nucleates at the martensite lath boundary and low amounts of reverted austenite are not visible under a light microscope [33]. this austenite formation is the result of an uncompleted transformation of austenite into martensite. the aging process causes an inverse transformation from martensite to austenite [34, 35], while similar results were reported for corrax [36, 37]. the solution heat treated sample (a0) has less than 2% retained austenite [38]. increasing aging temperature and time, increased the reverted austenite formation [39, 40]. retained austenite, which is free of precipitates, decreased toughness and strength as reported in [41]. the reason for this decrease in toughness and strength can be explained by the brittle character of the matrix, in which the overaged particles serve as crack nucleation sites [42-44]. fig. 3. sem image of a5.25 sample aged at 525ºc table iii. eds of indicated particles in a5.25 spectrum c al cr mn fe ni mo 1 17.22 1.35 20.20 2.11 51.72 6.26 1.14 2 6.95 1.11 23.16 2.82 54.00 10.64 1.32 3 2.07 1.88 19.11 6.01 60.49 9.14 1.30 4 2.74 1.54 19.17 3.81 62.13 9.50 1.12 5 3.89 1.55 18.67 1.02 62.50 11.19 1.19 6 2.50 1.48 18.83 4.41 62.43 9.89 0.46 mean value 5.89 1.49 19.86 3.36 58.88 9.44 1.09 sigma 5.82 0.25 1.71 1.77 4.77 1.73 0.32 sigma mean 2.38 0.10 0.70 0.72 1.95 0.71 0.13 b. micro hardness micro hardness tests were carried out at room temperature and the results are shown in figure 4. hardness was affected by aging temperature. the lowest hardness was measured for the a0 sample. increasing aging temperature up to 525ºc increased hardness and its highest value was obtained at aging temperature of 525ºc. the increase on hardness can be explained by the diffusion assisted mechanism that hinders the dislocation movements. the principle of the particle strengthening is hindered by the dislocation movement of nanometer-sized particles precipitation [45, 46]. higher aging temperatures decrease hardness, because of the growth of precipitations and reverted austenite formation in the microstructure [16, 47-49]. c. cutting forces turning experiments were carried out at seven different cutting speeds (50, 100, 150, 200, 250, 300, 350m/min), at a constant feed rate of 0.1mm/rev and 1mm cutting depth. engineering, technology & applied science research vol. 10, no. 1, 2020, 5168-5174 5171 www.etasr.com guldibi & demir: aging effect on microstructure and machinability of corrax steel cutting forces are shown in figure 5. aged samples cause higher cutting forces than the solution heat treated sample a0, e.g. the cutting forces increased by 85% for a4, 103% for a5.25 and 96% for a6 samples respectively, compared to those of the a0 sample. the highest cutting force was measured during the machining of the a5.25 sample, which is attributed to its highest material hardness. the lowest cutting force was measured in a0, which had the lowest hardness (332hv). the results showed that the aging treatment has a great influence on cutting forces because of the precipitation formation in the microstructure. precipitations hinder the movement of dislocations, reducing the cutting forces increment. however, overaging causes a decrease of cutting forces and hardness because of the overgrowth of precipitations. these reasons explain the decrease of cutting forces during the machining of the a6 sample. fig. 4. hardness of the samples fig. 5. cutting forces versus cutting speed the effect of cutting speed on the cutting forces was also investigated for each sample. the lowest cutting forces were measured at 200m/min, for all samples with the exception of a6. the lowest cutting forces for a6 sample were obtained at 350m/min. machining a0 sample at different cutting speeds caused irregular cutting forces, which can be attributed to vibrations as seen in figure 6 [50]. the cutting forces of aged samples, except from a5.25 decrease for cutting speeds up to 200m/min. this can be explained by the temperature increments on the cutting zone [51]. while machining materials harder than 45hrc (hard turning) the temperature on the cutting zone reaches an austenization temperature softening the material while machining [52-56]. machining of a5.25 caused high cutting forces at cutting speeds higher than 200m/min because of serious tool wear. tool wear changes the shape of the rake angle and the tool-chip interface. a small decrease at 350m/min can be noted in figure 5. this can be explained by the extreme tool wear, as seen in figure 7, which changes the cutting depth. the cutting forces depend on the material’s hardness: increasing hardness increases cutting forces. the a6 sample has the lowest cutting forces, compared to the other samples. this can be explained by its lowest hardness value and the retained austenite formation in its microstructure. retained austenite decreases strength and hardness. in general, increasing cutting speed decreases cutting forces. this can be explained by the decreased on tool-chip interface and the increased heat on cutting zone that soften shear strength [57]. fig. 6. root mean squaer values at different cutting forces tool wear changes tool’s geometry, affecting the cutting process. this is the reason why cutting forces and vibrations are high at excessive cutting speeds, as seen in figures 5 and 6. a small increment of vibrations, as seen in figure 6 at 150m/min cutting speed for a0, can be explained by the continuous chip formation. the increment of vibrations at 150m/min caused the increase of cutting forces. the lowest vibrations were measured in the a6 sample, which can be explained by the reverted austenite in the microstructure that reduced hardness and toughness. as a result, it can be noted that vibrations have great effect on cutting forces. (a) (b) (c) (d) fig. 7. sem images of worn cutting tools for a5.25 samples after machining at: a) 200m/min, b) 250m/min, c) 300m/min, and d) 350m/min d. surface roughness figure 8 shows the workpiece surface roughness values for a0 (332hv), a4 (426hv), a5.25 (525hv) and a6 (404hv) engineering, technology & applied science research vol. 10, no. 1, 2020, 5168-5174 5172 www.etasr.com guldibi & demir: aging effect on microstructure and machinability of corrax steel samples. the measured surface roughness value for each sample is the average of three measurements. cutting speed has great influence on the produced surface roughness. increasing cutting speed decreases surface roughness. however, increasing cutting speed for the hardest sample, a5.25, caused serious tool wear, which disrupted the surface topology. machining of the a0 and a6 samples showed the lowest surface roughness. this is explained by the lowest hardness value of a0 and the reverted austenite formation in the microstructure of a6, which decreased toughness and hardness. low hardness and toughness ease the cutting process, enhancing surface roughness. fig. 8. surface roughness versus cutting speed machining a0 at a 50m/min cutting speed showed an increase of surface roughness comparing to the a6 sample. this is explained by the continuous chip formation, as seen in figure 9, which damaged the machined surface. (a) (b) (c) (d) fig. 9. chip formation at 50m/min for: a) a0, b) a4, c) a5.25, and d) a6 the lowest surface roughness was obtained at 350m/min, as 0.51µm for both a0 and a6 samples. however, surface roughness values for the a4 sample were not usual. the peak surface roughness value for a4 sample was obtained at a 100m/min cutting speed, which is explained by the vibration peak, as it can be noted in figure 6 [58]. machining a5.25 (525hv) at 50m/min caused a tool overhang and the highest vibration, as it can be noted in figure 6, being the reason of the high surface roughness [59]. extreme high surface roughness values for a5.25 were obtained at 250, 300 and 350m/min cutting speeds because of serious tool wear, which also caused vibrations, as it can be noted in figure 6. as a conclusion, the vibration has great effect on surface topology. there are many reasons for cutting forces and surface roughness correlation. one of the main is the effect of the vibrations while machining. the rise of vibrations depends on cutting speed, tool wear, and the samples’ microstructure. the increase of vibrations caused an increase of cutting forces. serious tool wear also increased vibration formation. the lowest vibrations were obtained during the machining of the a6 sample, something that can be explained by the reverted austenite formation that reduced hardness and toughness. iv. conclusion this study investigated the influence of precipitation and reverted austenite formation on cutting forces and surface roughness of corrax steel. machining tests were carried out for a0 (332hv), a4 (426hv), a5.25 (525hv) and a6 (404hv) samples. the results showed that: • the aging treatment has a major effect on the formation of precipitation that causes an increase on hardness. the highest hardness was measured for the sample aged at 525ºc for four hours. hardness increase is a result of precipitation formation in the microstructure. aging temperatures higher than 525ºc decreased hardness due to overaging which caused reverted austenite formation and the growth of precipitations in the microstructure. • aging treatment improves the mechanical properties and makes the cutting process more difficult. machining of the hardest sample (a5.25) caused serious tool wear at high cutting speeds such as 250, 300 and 350 m/min. cutting forces were increased by sample’s aging temperature up to 525ºc. aging at 600ºc caused a cutting forces decrease because of the reverted austenite formation and the growth of precipitations. • cutting speed, vibration and tool wear affected seriously surface roughness. the lowest surface roughness values were measured for a0 and a6 samples. vibration and tool wear have a serious effect on the surface roughness values, as well as cutting forces. reverted austenite formation also reduced vibrations and improved surface roughness. acknowledgment this research was supported by the scientific research projects department of karabuk university (bap) with 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inverter fed induction motor zouhir boumous laboratory of electrical engineering and renewable energies mohamed cherif messaidia university souk ahras, algeria zsid3@yahoo.fr samira boumous laboratory of electrical engineering and renewable energies mohamed cherif messaidia university souk ahras, algeria boumous@yahoo.fr abstract-this article provides an improved fault-tolerant control scheme for inverter-powered induction motors. the proposed strategy addresses the cancellation of power switch failures (igbts) regardless of their location in a reconfigurable induction motor control. the proposed fault-tolerant topology requires only minimal hardware modifications of the conventional sixswitch three-phase drive, mitigating igbt failures through reconfiguration based on the substitution of an entire inverter arm. the detection mechanism is based on the tridimensional method from which a database will be used for the learning of the neural network. in this method, the current from the stator is used as input to the system, so access to the induction motor is not necessary. keywords-inverter; induction motor; artificial neural networks; diagnosis; fault tolerant control i. introduction it is estimated that around 38% of faults in variable speed drives in the industry are caused by power supply device failures [1]. most of the inverters use isolated igbts as power devices. this percentage would be higher if the control circuit failures were taken into account. they consist of faults such as intermittent inverter misfiring due to faults in the control circuit elements or electromagnetic interference which results in gate drive opening faults, and therefore leads to an open igbt circuit. although igbts are rugged, they experience failures due to the excessive electrical and thermal stresses that are felt in harsh environments. igbt failures can be broadly classified as open circuit faults, short circuit faults, and intermittent gate trip faults [2]. variable speed drives, and the inverter in particular, are occupying more and more space. this rapidly increases the concern for fault tolerance due to availability problems [1, 3]. when inverter faults appear, the conventional topology of the ev powertrain cannot perform its function of traction of the vehicle, therefore the need to develop fault tolerant systems emerges. the two most common types of power converter faults that have been widely investigated are the transistor gate driver open fault or the igbt open circuit switch and the short circuit switch. these two faults can lead to catastrophic drive failures or significantly degraded performance [4]. it is therefore crucial to be able to detect and diagnose these two faults in order to take the appropriate corrective measures to mitigate their effects [5-8]. a priori knowledge of faults is assumed in this paper and the emphasis will be on corrective actions in the event of a fault. once the fault is detected and located, corrective action must be taken to mitigate the effects of the fault [9-11]. many inverter architectures based on some hardware redundancy have been suggested to add reconfigurability to the system [12, 13]. several studies have invested in this subject. authors in [14] have proposed a detection mechanism based on a new wavelet transformation technique. authors in [15] proposed a non-intrusive faultdiagnosis method for open-circuit faults in inverter semiconductor power switches, whereas authors in [16] proposed another model: when an open-circuit fault occurs regardless of the position of the rectifier leg, an indication will be generated in the absence of any additional sensors to accurately identify the defective leg. authors in [17] described a method based on vector space decomposition and double three-phase space vector modulation. diagnostic and tolerant control methods have been developed comprehensively for three types of faults, open-switch faults, open-phase faults and short-switch faults in a three-level type t inverter supplied by a double three-phase pmsm drives. the strategy proposed in [18] belongs to the bridge-arm level, with a redundant bridge arm in parallel. when the bridge arm is an open or short circuit during operation, the redundant bridge arm will replace it and keep the system working as normal. authors in [19] proposed a fault-tolerant scheme based on changing the inverter topology from six to four switches to ensure proper operation. in the event of a fault, a connection to the midpoint of the circuit based on an external switch and a disconnection of the phase terminal of the motor of the defective inverter arm is obtained. the proposed diagnosis method is based on the neural network analysis of the mean values of the stator currents of the mas in a tridimensional space, by calculating all the angles that separate them, and subsequently the fault tolerant command reconfigures the system and its operation returns to normal. ii. circuit topology of traction inverter the circuit topology of the two-level three-phase inverter is shown in figure 1. t1, t2...t6 are igbts and d1, d2…d6 are anti-parallel diodes. an induction motor is located at the load side. corresponding author: zouhir boumous engineering, technology & applied science research vol. 10, no. 6, 2020, 6504-6509 6505 www.etasr.com boumous & boumous: new approach in the fault tolerant control of three-phase inverters fed … fig. 1. circuit yopology of a two-level three-phase inverter. iii. igbt open-circuit fault analysis in order to show the robustness of the proposed approach, the open circuit faults in the igbts given in figure 2 are considered. the previously proposed approaches treat cases (a) and (b) but remain unable to deal with the case (c) because they are based on the substitution of the whole arm. in case (c) of figure 2, the switches are placed in two different arms [20], thus, they are obliged to double the emergency arms. the proposed approach consists in replacing the faulty switch by an adequate reconfiguration according to the position of the switch shown in figure 2. so, a second redundant switch is always available and ready to emerge to remedy other faults in other locations. (a) (b) (c) fig. 2. open circuit fault positions: (a) one igbt, (b) two igbts in the same arm, (c) two igbts in two different arms. a. double-switch faults in the same bridge arm (t1-t4) the two switches are located on the first arm of the inverter so the current isa is seriously affected in relation with the other two currents isb and isc. when open-circuit faults occur in the double switches in the same bridge arm, taking open-circuit faults in t1 and t4 as an example, they cannot be turned on normally. neither positive nor negative half-cycle currents can complete the continuation, therefore phase a is equivalent to an open circuit. the other two-phase switches are working normally. the current of phase a is zero and the current of the other two phases is distorted. the current waveform is shown in figure 3. fig. 3. current waveforms of two switch faults in the same bridge arm. after opening the switches t1 at t = 0.2s we can clearly see in figure 3 that the positive half-wave of isa becomes zero and a slight modification appears on the isb and isc currents. at t = 0.4s, t4 joins t1 and becomes open and the current isa becomes zero. opening an arm is similar to opening a phase. the amplitudes of the other two currents are 15 to 20a. b. double-switch faults in different bridge arms (t1-t5) when double switches in different bridge arms are in opencircuit fault status, the situation can be further classified into two cases. the first is the one where two igbts at the same half-bridge position in the two bridge arms (such as t1 and t5) are in open circuit fault status. the second is where two igbts at different half-bridge positions in the two bridge arms are in open-circuit fault status. faults in t1 and t5 are taken here as an example of double switches in different bridge arms in open-circuit fault status. the current waveform is shown in figure 4. fig. 4. current waveforms of two switch faults in different bridge arms at two different times. engineering, technology & applied science research vol. 10, no. 6, 2020, 6504-6509 6506 www.etasr.com boumous & boumous: new approach in the fault tolerant control of three-phase inverters fed … fig. 5. current waveforms of two switch faults in different bridge arms at the same time. by introducing the open-circuit fault, the waveforms of the three-phase currents are distorted and become asymmetric, so the output electromagnetic torque of the traction motor is reduced and oscillates severely, which is harmful for the system’s security and stability. the increase in the amplitudes of the currents leads to the motor heating up, especially when the load torque becomes greater, so the winding risks being damaged. immediate intervention, i.e. replacing the faulty switch in a very short time becomes essential for the continuity of service, otherwise the risk of an abrupt shutdown is very high. the developed intervention strategy is summarized in figure 6. fig. 6. flowchart of the control and fault detection strategy. iv. tridimensional method for fault diagnosis from the synthesis of the results obtained previously, it is concluded that the three-phase current will be distorted in the event of an open circuit fault, which can be considered as a fault signature, whether the fault phase current is zero or not. in order to accurately acquire fault features and determine the fault location, we extract characteristics from the tridimensional analysis of the three-stator current. the feature extraction is the most important step in the proposed defect detection and classification process. better features will lead to better performance and to a more reliable system. in this research, the feature extraction technique transforms the threephase output into instantaneous waveforms constructed from the average values of stator currents. under normal conditions, these instantaneous values create a circle-like shape with some fluctuations in a tridimensional presentation space, as shown in figure 7. each system failure causes disturbances in the threephase current which changes its shape in a unique way. fig. 7. the shape of the ismean stator currents in a healthy state. the defect reaches the two sizes: • the radius of the tridimensional circle: r 2 =i 2 a(mean)+ i 2 b(mean)+ i 2 c(mean) (1) this property can be restricted to the analysis of the mean values of the currents: ia(mean)=∑ia/n (2) • the angles of the mean values: the average values of the three stator currents are placed on the axes of an orthogonal three-dimensional coordinate system. angles 1-6 are based on these average values, the presence of a fault affects the average value of the currents which directly influences these angles as shown in figure 8. fig. 8. representation of the 6 characteristic angles. the next characteristic to extract is the angle of each mean with respect to its axis. the angle at the mean value gives us the exact location of this point in the tridimensional space of figure 8. these angles are explicitly calculated as : angle (1) : ��� ( �) � �� � ( ������ ������ � (3) angle (2) : ��� �� � � �� � � ������ ������ � (4) engineering, technology & applied science research vol. 10, no. 6, 2020, 6504-6509 6507 www.etasr.com boumous & boumous: new approach in the fault tolerant control of three-phase inverters fed … angle (3) : ��� (� ) � �� � ( ������ ������ � (5) angle (4) : ��� � �� � �� � � ������ ������ � (6) angle (5) : ��� ���� � �� � � ������ ������ � (7) angle �6� ∶ ��� ���� � �� � � ������ ������ � (8) v. neural network learning procedure this technique has very interesting characteristics such as learning and self-organization. neural networks can be thought of as black boxes [21-22]. the calculation of the mean values of the currents and the angles which separate them in the tridimensional space leads to the results presented in tabulated form in figure 9. fig. 9. extract characteristics table. the table in figure 9 is used to train the neural network which contains: • an input layer of 9 elements which are the three average values of the currents and the 6 characteristic angles. • a hidden layer of 24 neurons. • a 6 element output layer that indicates the damaged switch (figure 10). the output layer presents faulty switches by thresholds, (1 indicates that the switch is damaged, 0 for healthy switches). fig. 10. the proposed artificial neural network architecture. vi. control strategy after the detection of a fault by the monitoring system, the ftc command intervenes to replace the faulty switch with a backup one, along with its appropriate command, to restore the correct functioning of the system. the simulation blocks for the monitoring of the system are shown in figures 11-12. from the stator currents, angles and average values are calculated (figure 12). these parameters train the artificial neural network which has the role of detecting the faulty switch and locating its location in a precise way, i.e. the neural network must provide three signals (figure 13). two signals control two multi-port switches which control the signals of the six switches (figure 14(a)), one for the upper part of the inverter half bridge and the other for the lower part. in the faulty case these signals give the number of the switch in question, whereas in the healthy case these signals are equal to 0. fig. 11. global simulation model. fig. 12. the configuration system by ftc. fig. 13. switches control selection and inverter reconfiguration strategy. figure 14(a) shows the output signals of the neural network when t3 is in open circuit. we see that the signal corresponds to the upper part is equal to 3. this indicates that the third switch of the upper part of the half bridge of the inverter is faulty and the signal from the lower part is equal to 0, i.e. that all the switches on the lower part of the inverter half-bridge are healthy. the third signal (figure 14(b)) controls a reconfiguration card based on breaker circuits which has the role of isolating the faulty switch and putting an emergency switch in its exact place. engineering, technology & applied science research vol. 10, no. 6, 2020, 6504-6509 6508 www.etasr.com boumous & boumous: new approach in the fault tolerant control of three-phase inverters fed … (a) (b) fig. 14. detecting single switch in the upper half bridge inverter t3 by the ann: (a) detection and localization of a single switch fault by the ann, (b) signals obtained by ann for t3 open circuit. vii. reconfiguration system test and simulation results for this type of fault, the appearance of a single fault and of two faults at the same time (multiple) are examined. 1) single switch fault the opening of the switch t1 at the instant t = 0. 3s is shown in figure 15. fig. 15. ftc for a single switch open circuit. 2) failure of two switches of the same arm the switch t1 breaks down at the instant t = 0.3s and the switch t4 at the instant t = 0.55 s as shown in figure 16. 3) faults of two switches in two different arms we examine the opening of the second arm t1 at t = 0.3s and t5 at t = 0.55s as shown in figure 17. fig. 16. ftc for an open circuit of two switches in the same inverter arm. fig. 17. ftc for an open circuit of two switches in different inverter arms. the fault appears at t = 0.3s: the switch t1 remains open due to a fault (figure 17). this clearly results in the disappearance of the positive half-wave of the current isa. ensured by t1, the system employ detects, locates, and replaces it by a redundant switch by reconfiguring the inverter connections in order to isolate the faulty igbt and connect the reserve one in its place to ensure the continuity of service. the procedure lasts for a very short time of around 0.01s. its robustness and its ability to deal with multiple faults are proved in situations such as the one described in figure 16, where two switches of the same arm t1 and t4 break down. the intervention of the system is very fast and the current becomes sinusoidal with two alternates, symmetrical and equal. the same observations remain valid for the third studied case, although the two switches are not on the same arm t1 in the first arm while t5 is located on the second arm. figure 17 shows that the two currents isa and isb are clearly affected, the first by the absence of a positive half-wave and the second by the absence of the negative half-wave. the intervention of the monitoring system to be used again proves a very satisfactory efficiency by eliminating the faults in a very short time of the order of 0.01s. at this stage, we can deduce that the strategy employed in the present work is very reliable, fast and acts in all possible engineering, technology & applied science research vol. 10, no. 6, 2020, 6504-6509 6509 www.etasr.com boumous & boumous: new approach in the fault tolerant control of three-phase inverters fed … fault scenarios. but the strong point that distinguishes this approach from other works is its simplicity. a simple mathematical calculation is enough to accomplish the task. in addition, the reconfiguration card does not require much to compose which facilitates the practical realization of this strategy with a reasonable price. most other works are based on complicated techniques such as the fast fourier transform [23], the wavelet transform [24], clarke vectors [25], etc. viii. conclusion in an effort to ensure the continuity of service in induction motor drives, this article has summarized all the possible open circuit fault conditions in a three-arm inverter with two back-up switches. the fault detection method used is based on a neural network which learned from a database extracted from the tridimensional analysis of the stator currents. finally, a fault tolerance strategy has been put in place which takes care of the reconfiguration of the inverter deemed necessary by the neural network by replacing the faulty switch with one of the two emergency available switches. 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[11] s. chafei, f. zidani, r. nait-said, and m. s boucherit, “fault detection and diagnosis on a pwm inverter by different techniques,” journal of electrical systems, vol. 4, no. 2, pp. 1–12, jun. 2008. [12] b. d. e. cherif, a. bendiabdellah, m. bendjebbar, and l. souad, “a comparative study on some fault diagnosis techniques in three-phase inverter fed induction motors,” fault detection and diagnosis, nov. 2018, https://doi.org/10.5772/intechopen.79960. [13] y. b. s. s. gupta and s. s. rao, “a modified inverter topology for faulttolerant direct torque control induction motor drive,” international journal of electronics, apr. 2020, https://doi.org/10.1080/ 00207217.2020.1756445. [14] m. s. khanniche and m. r. mamat-ibrahim, “fault detection and diagnosis of 3-phase inverter system,” in rev. energ. ren. : power engineering, 2001, pp. 69–75. 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[21] k. s. belkhir, “intelligent maximum power tracking control for a wind energy system based on magnetic gear generator,” engineering, technology & applied science research, vol. 9, no. 4, pp. 4329–4333, aug. 2019, https://doi.org/10.48084/etasr.2851. [22] j. chakravorty, s. shah, and h. n. nagraja, “ann and anfis for short term load forecasting,” engineering, technology & applied science research, vol. 8, no. 2, pp. 2818–2820, apr. 2018, https://doi.org/10.48084/etasr.1968. [23] b. cai, y. zhao, h. liu, and m. xie, “a data-driven fault diagnosis methodology in three-phase inverters for pmsm drive systems,” ieee transactions on power electronics, vol. 32, no. 7, pp. 5590–5600, jul. 2017, https://doi.org/10.1109/tpel.2016.2608842. [24] s. qiang and y. li, “motor inverter fault diagnosis using wavelets neural networks,” in 2013 ieee international conference on systems, man, and cybernetics, manchester, uk, oct. 2013, pp. 3168–3173, https://doi.org/10.1109/smc.2013.540. [25] a. rohan and s. h. kim, “fault detection and diagnosis system for a three-phase inverter using a dwt-based artificial neural network,” international journal of fuzzy logic and intelligent systems, vol. 16, no. 4, pp. 238–245, dec. 2016, https://doi.org/10.5391/ijfis.2016. 16.4.238. microsoft word 42-2850_s_etasr_v9_n3_pp4298-4300 engineering, technology & applied science research vol. 9, no. 3, 2019, 4298-4300 4298 www.etasr.com shah et al.: evaluation of the mechanical behavior of local brick masonry in pakistan evaluation of the mechanical behavior of local brick masonry in pakistan tajik mustafa shah department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs', sindh, pakistan tajikmustafashah@live.com aneel kumar department of civil engineering, mehran university of engineering and technology, jamshoro, sindh, pakistan aneel.kumar@faculty.muet.edu.pk syed naveed raza shah department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs', sindh pakistan naveedshah@muetkhp.edu.pk ashfaque ahmed jhatial department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs', pakistan ashfaqueahmed@muetkhp.edu.pk mudasar hussain janwery department of civil engineering, mehran university of engineering and technology, shaheed zulfiqar ali bhutto campus, khairpur mirs', pakistan mudasar.hussain999@gmail.com abstract—masonry is the oldest form of construction in the world [1]. research shows that it is the most widely used construction material in pakistan and it has remained as such for more than the past hundred years. the majority of buildings in pakistan are load-bearing burnt-brick masonry structures. unfortunately, the brick masonry structures in pakistan are not designed with respect to any regulatory code, because none exist. consequently, these structures are not constructed according to a safe design and thus become hazardous and often face considerable damage and sometimes prove to be fatal. this study aims to study the behavior of local brick masonry under normal, shear and thermally challenging conditions and to model its behavior by relating the crushing strength (f’m) to the height-to-thickness ratio and temperature. keywordsbrick masonry; elevated temperature; stress-strain diagram i. introduction brick masonry as a structural material is being used widely in the developing nations, while in the developed nations its use is complementary. a research has been conducted in order to obtain a view of the problems pertaining to this material. failure of brick masonry structures or their roofs is a commodity. in pakistan, all the research conducted to date is not based on the engineering and structural properties of this material, only the qualitative analysis of materials has been conducted. there is thus a need of experimental evaluation of the properties of brick masonry as a material. one of the first studies on the generalized characteristics of the brick masonry in canada was carried out in [2]. this study evaluated the properties and the approximate behavior of brick masonry under different conditions. author in [3] tried to evaluate the material properties of brick masonry. one of the first studies on the brick masonry of pakistan was carried out in [4]. the author travelled across pakistan and concluded that the majority of buildings in pakistan were load-bearing structures. this study led to the generation of the 173 rd report on world housing for pakistan [5]. following this, the very first engineering study on the local brick masonry in sindh, pakistan was conducted in [6]. authors in [7-11] tried to model the behavior of brick masonry on various finite element packages. this led to the orientation of a whole new era on the engineering study of brick masonry. recently, author in [12] studied a new way of brick masonry construction in azad kashmir. the behavior of local brick masonry in pakistan is unknown because the material and its engineering properties are not known completely, furthermore, there are no codes in pakistan governing the design and construction of brick masonry [5]. the most relevant code in terms of material, the is 1905-87 [13] is limited to the uniaxial behavior of brick masonry. the materials and brick unit dimensions used in pakistan are of different proportions as compared to the neighbouring states [6], so the properties will be utterly distinct. this study aims to append the available engineering data for brick masonry in pakistan so that an easy design method can be made and to lay a foundation for the numerical simulation of brick masonry for easier virtual experimentation and for the creation of regulatory codes. the objective of this work is to study the behavior of local brick masonry under normal, shear and thermally challenging conditions, to model its behavior by relating the crushing strength (f’m) to the height-to-thickness ratio (h/t) of brick masonry and temperature and to obtain the engineering properties of local brick masonry to make a base for numerical simulations. corresponding author: tajik mustafa shah engineering, technology & applied science research vol. 9, no. 3, 2019, 4298-4300 4299 www.etasr.com shah et al.: evaluation of the mechanical behavior of local brick masonry in pakistan ii. materials and methodology a. materials the bricks were collected from a local supplier, in khairpur mirs’. the bricks were carefully examined to be of the same dimensions and consistency. the brick properties are shown in table i. the mortar was made from sieved sui sand and ordinary portland cement manufactured by the lucky cement ltd. the masonry units were built using a mason’s trowel and finishing trowel by a local mason. table i. mechanical properties of bricks [6] property value modulus of elasticity 20.23kn/mm 2 poisson’s ratio 0.21 specific weight 13.165kn/m 3 specific gravity 2.549 b. experimental procedure compressive testing of bricks was done according to [14]. the mortar was tested as per [15]. the brick masonry under direct axial compression was tested according to [14, 16], according to [17] under shear compression, and at elevated temperature using the unstressed residual strength method employed in [18]. three specimens were tested for each case, i.e. for one single brick, two-brick prisms, three-brick prisms, four-brick prisms and five-brick prisms. three specimens of five-brick prisms were tested for each temperature of 50°c, 100°c, 150°c, 200°c and at 250°c. three three-brick specimens were used for evaluation of shear behavior of brick masonry. iii. results and discussion the specimens were tested in a universal testing machine (utm) under direct compression. the average stress-strain behavior of brick masonry obtained is shown in figure 1. table ii shows the variation of strength with increase in height to thickness ratio of brick masonry. figure 2 shows the increase in slenderness of brick masonry with respect to the number of bricks in prism. table iii shows the variation of strength with respect to increase in temperature. figure 3 shows the variation of strength with respect to increasing temperature. the average shear behavior of brick masonry is shown in figure 4. table iv shows the data obtained from the shear testing of samples. fig. 1. stress-strain behavior of local brick masonry table ii. data obtained from experimentation at ambient temperatures n o . o f b r ic k s in p r is m h e ig h t (m m ) t h ic k n e s s (m m ) h e ig h t to th ic k n e s s r a ti o s tr e n g th (m p a ) c o r r e c ti o n f a c to r c o r r e c te d st r e n g th a s p e r i s 1 9 0 5 8 7 ( m p a ) 1 90 97.5 0.923 13 0.46 5.98 2 160 97.5 1.641 5 0.673 3.365 3 235 97.5 2.41 4.1 0.786 3.226 4 330 97.5 3.384 3.8 0.9 3.42 5 380 97.5 3.897 3.6 0.942 3.391 fig. 2. variation of strength with respect to change in h/t ratio. table iii. data obtained from experimentation at elevated temperatures n o . o f b r ic k s i n p r is m h e ig h t (m m ) t h ic k n e s s (m m ) h e ig h t to th ic k n e s s r a ti o t e m p e r a tu r e s tr e n g th ( m p a ) c o r r e c ti o n f a c to r c o r r e c te d st r e n g th a s p e r i s 1 9 0 5 -8 7 ( m p a ) 5 380 97.5 3.897 50°c 5.435 0.942 5.11977 5 380 97.5 3.897 100°c 5.4 0.942 5.0868 5 380 97.5 3.897 150°c 5.107 0.942 4.81079 5 380 97.5 3.897 200°c 4.512 0.942 4.2503 5 380 97.5 3.897 250°c 4.794 0.942 4.51595 fig. 3. variation of strength of brick masonry with increasing temperature fig. 4. the shear behaviour of brick masonry engineering, technology & applied science research vol. 9, no. 3, 2019, 4298-4300 4300 www.etasr.com shah et al.: evaluation of the mechanical behavior of local brick masonry in pakistan table iv. data obtained from shear test no. of bricks in prism overall height (mm) overall thickness (mm) shear strength (mpa) 3 257 178 0.523 iv. conclusions • the average compressive strength of a single local brick is around 13mpa. • the average compressive strength of local brick masonry is around 3.764mpa. • the stress-strain behavior of brick masonry follows a concave down curve. • the strength of brick masonry decreases slightly with increasing slenderness. • there is no significant effect of elevated temperature on the strength or behaviour of brick masonry, but the strength decreases slightly with increasing temperature. • the average shear strength of local brick masonry is around 0.523mpa. references [1] a. khan, c. lemmen, “bricks and urbanism in the indus valley, rise and decline”, available at: https://arxiv.org/pdf/1303.1426.pdf, 2013 [2] t. kaaki, behaviour and strength of masonry prisms loaded in compression, dalhousie university, 2013 [3] d. tensing, c. c. freeda, s. r. mercy, “experimental study on axial compressive strength and elastic modulus of the clay and fly ash brick masonry”, journal of civil engineering and construction technology, vol. 4, no. 4, pp. 134-141, 2013 [4] s. h. lodi, “brick masonry in pakistan”, international conference on sustainable development in civil engineering, jamshoro, pakistan, november 21-25, 2017. [5] s. h. lodi, a. j. sangi, a. abdullah, housing report: brick masonry construction in pakistan, world housing encyclopedia, 2013 [6] s. khoso, f. h. wagan, j. s. khan, n. u. k. bhatti, a. a. ansari, “qualitative analysis of baked clay bricks available in larkana region, pakistan”, architecture–civil engineering–environment, vol. 7, no. 2, pp. 41-50, 2014 [7] m. a. rahemia, a. a. tasnimib, a. sarvghad-moghadam, “micromodeling of masonry infilled rc moment resisting frames to investigate arrangement of compressive diagonal struts”, ije transaxtions c: aspects, vol. 27, no. 6, pp. 865-880, 2014 [8] s. ravi, s. viswanathan, t. nagarajan, v. srinivas, p. narayanan, “experimental and numerical investigations on material behaviour of brick masonry”, 2nd international conference on research in science, engineering and technology, dubai, uae, march 21-22, 2014 [9] s. r. sarhat, e. g. sherwood, “the prediction of compressive strength of ungrouted hollow concrete block masonry”, construction and building materials, vol. 58, pp. 111-121, 2014 [10] s. viswanathan, s. ravi, t. nagarajan, v. srinivas, p. narayanan, “numerical simulation of compression and shear behaviour of unreinforced brick masonry”, international conference on biological, civil and environmental engineering, dubai, uae, march 17-18, 2014 [11] h. s. vindhyashree, a. rahamath, w. p. kumar, m. t. kumar, “numerical simulation of masonry prism test using ansys and abaqus”, international journal of engineering research and technology, vol. 4, no. 7, pp. 1019-1027, 2015 [12] r. langenbach, “recovering the lost moment: how timber-laced masonry may hold the secret to stopping pancake collapse of concrete moment frames”, first south asia conference on earthquake engineering, karachi, pakistan, february 21-22, 2019 [13] bureu of indian standards, is 1905 (1987): code of practice for structural use of unreinforced masonry, bureu of indian standards, 2010 [14] bureu of indian standards, is 3495-1 (1992): methods of tests of burnt clay buildind bricks, bureu of idian standards, 1992 [15] bureu of indian standards, is 4031-6 (1988): methods of physical tests for hydraulic cement, 2006 [16] british standards institution, bs en 1052-1:1999, methods of test for masonry. determination of compressive strength, bsi, 1999 [17] british standards institution, en_1052-3: 2002, methods of test for masonry. determination of initial shear strength, 2002 [18] l. t. phan, n. j. carino, “code provisions for high strength concrete strength-temperature relationship at elevated temperatures”, materials and structures, vol. 36, no. 2, pp. 91-98, 2003 microsoft word etasr_v11_n4_pp7464-7468 engineering, technology & applied science research vol. 11, no. 4, 2021, 7464-7468 7464 www.etasr.com zisopol et al.: theoretical and experimental investigations on 20 inches threaded casing connections … theoretical and experimental investigations on 20 inches threaded casing connections failure under field conditions dragos gabriel zisopol mechanical engineering department petroleum-gas university of ploiesti ploiesti, romania zisopol@zisopol.ro marius badicioiu mechanical engineering department petroleum-gas university of ploiesti ploiesti, romania mbadicioiu@upg-ploiesti.ro mihaela madalina caltaru mechanical engineering department petroleum-gas university of ploiesti ploiesti, romania miki@upg-ploiesti.ro mihail minescu mechanical engineering department petroleum-gas university of ploiesti ploiesti, romania mminescu@upg-ploiesti.ro abstract-this paper brings forward the results of theoretical and experimental investigations performed to determine the causes that led to the failure of 20 inches threaded casing connections during the tubing of the lupşa sat no. 1 oil well, romania. the failure occurred due to the breakout of the threaded casing connections assembled in the factory. in order to establish the main causes of failure, theoretical investigations were taken into consideration to highlight the influence of the thread element errors on the correct make-up casing pin–coupling (box) conditions and to the axial tensile strength of the threaded casing connection. in addition, experimental investigations were performed on the failure casing connections, consisted of measuring the dimensional characteristics of the thread elements to determine the performance and monitor the technical condition of the tubular material used in the petroleum industry. keywords-threaded casing connections; failure; investigation; expertise i. introduction well casing is necessary after the drilling of the borehole in order to consolidate the well, to protect the borehole from falling, to protect the fresh water aquifers by preventing the drilling fluids used or oil to seep into the underground water reservoirs, and to facilitate the execution of work operations (drilling or exploitation). for this purpose, surface casing is used, consisting of casings assembled together by threaded casing connections (figure 1). the casings used for well casing are steel pipes with both ends threaded (casing pin). the casing manufacturer, according to references standards, assembles in the factory the coupling (box) at one casing threaded end (threaded casing connections-factory assembled), and during the well casing, the other threaded end of the casing is assembled in the operation field (threaded casing connections– borehole assembled), by makeup to the coupling (box) of another casing (figure 2). deviations of shape and dimensions of the threaded casing connection can conduct to failure, often manifested by losing the sealing capacity and, more seriously, by jump-out or even by fracture of the thread connection [1]. therefore, the international standards in the petroleum field predict the dimensions of the threaded casing connections used for well casing to fit within in a very restrictive tolerance field. any deviation from the prescribed limit leads to pulling out the use of the respective connection. in order to prevent any incident due to non-compliance with the shape and dimensions, the international test standards of the casing connections impose a rigorous inspection of the threaded casing connection prior to their use. the statistical dates reveal the fact that 86% of the surface casing failure occurs due to the threaded casing connections [2]. the present paper brings forward theoretical and experimental investigations performed to determine the causes that led to an accident during the construction of the lupşa sat no. 1 oil well, romania. the accident occurred during the well casing, at a depth of 262.88m, and consisted of the failure of casing connections (figure 1) by breakout of the threaded factory assembled casing connections. the breakout occurred during the stationary period at a hook load value of 42 tons. this load value shows that the weight of surface casing in the drilling fluid, under the failure area, was inferior to the tensile strength of the threaded casing connection, properly made-up by the manufacturer, which does not justify its breakout. there is no information available regarding the failure of the surface casing in the operation field, occurring due to the breakout of the threaded factory assembled casing connection. in order to establish the main causes that led to the breakout of corresponding author: marius badicioiu engineering, technology & applied science research vol. 11, no. 4, 2021, 7464-7468 7465 www.etasr.com zisopol et al.: theoretical and experimental investigations on 20 inches threaded casing connections … the threaded casing connections, a theoretical study according to standardized information to reveal the influence of the threaded elements errors on the makeup conditions of casing connection was performed along with an experimental study necessary to establish precisely and rigorously the failure causes. the failure analysis performed in this work can be proved useful for specialists in the petroleum field, to prevent the occurrence of such event by taking into consideration the influence of the thread elements errors to the correct make-up threaded casing connection. the current investigation brings forward and justifies the importance of correct makeup threaded casing connection in the factory to avoid possible failures in the operation field. fig. 1. schematically representation of the surface casing. fig. 2. threaded casing connections. ii. theoretical investigations to the thread element error influences the main target of the theoretical study was to investigate, according to reference standards and specialized literature, the influences of the thread element errors to the correct make-up casing pin–coupling (box) conditions and to the axial tensile strength of the threaded connection of the casing connection. the tensile strength of the threaded casing connection represents the lowest value of the following: the fracture load in the section next to the last perfect thread, the force corresponding to the shearing of the thread, and the jump-out force in the thread. because the fracture load (corresponding to the mechanical characteristics) is much higher than the value at which the breakout of the thread connection occurred, and the shearing of the thread does not occur practically at the round api thread, the only failure form considered possible is the jump-out of the thread connection. the specialized literature shows that approximately 91% of the failure casing connection occurs due to jump-out of the thread connection [3, 4]. the role of the make-up torque is to develop a radial contact pressure between the threads (pre-tensioning) by performing a diametral tightening due to the relative axial displacement between the coupling (box) and the casing pin. radial pre-tensioning is achieved by mechanically applying approximately 4 rotations in addition to manual make-up and it is intended both to ensure the sealing of the thread connection and to avoid relative radial displacement of the casing pin and box threads that allow the jump-out of the thread under the action of radial component of the tensile force. the thread parameters contained in the formula for determining the jumpout force of the thread are also decisive for the makeup torque value [2], and it was found that the experimentally determined makeup torque (in ft.lb.) to achieve a quality threaded casing connections represents 1% from the jump-out force value of the thread (in lb.) [2]. in the specialized literature, this predication is the base for establishing the recommended values for the make-up torque [2], and also highlights the close correlation between the make-up torque and the jump-out force of the thread connection. make-up torque lower than the recommended value can lead to jump-out thread because the radial pressure between the threads is not achieved to provide the standardized value of the axial tensile force [5]. the causes of the reduction for the jump-out strength of the thread are indicated as improper make-up of the casing connection by the manufacturer and the ovality of the casing (deviation from the cylindricity) [6]. in order to make a correlation between the causes of failure and the results of laboratory investigations on threaded connections, the influence of errors (deviations) on the average diameter in the measurement plan for manual makeup was studied along with the influence of ovality to the correct makeup casing pin – coupling (box) conditions. a. effect of the thread pitch diameter deviations in the year that this investigation took place, the pitch diameter in the plane of hand-tight engagement, e1 (figure 3), was not provided with limit deviations in the specific standards. under the conditions in which the pitch diameter of the box connection corresponds to the standardized value, and the pitch diameter of the pin connection is ∆� mm smaller than the standardized value, the box connection will move axially with the value ∆� beside the position that theoretically corresponds to the manually make-up connection: ∆� � ∆� � (1) in which � is the thread taper. at 2mm reduction of the pin thread diameter, the axial displacement of the box connection, given by (1) has the value: ∆� � � � 32 mm (2) engineering, technology & applied science research vol. 11, no. 4, 2021, 7464-7468 7466 www.etasr.com zisopol et al.: theoretical and experimental investigations on 20 inches threaded casing connections … representing an about 10 thread lead. in fact, due to the ovality of the pin thread, the maximum diameter of the pin can be taken into account which is only 0.3mm lower than the standardized value. this leads to an axial displacement of the box connection of: ∆� � �,� � 4.8 mm (3) therefore, 2 of the 4 recommended revolutions are consumed at casing connection make-up. this hypothesis is not realistic because, during the make-up connection, the pin connection is elastically deformed to the direction of the maximum diameter. on the basis of these considerations, in order to avoid the improperly make-up connection, the manufacturers have established their own precision requirements for the pitch diameter in the plane of hand-tight engagement, e1, and for ovality, [7-10], such as those specified by the gagemaker company [11], for the ovality tolerances of the pin and box connection: 0.060in (1.524mm). the study of the literature has led to the observation that the tolerances practiced globally for ovality by different companies and norms are very close or identical. b. effect of the ovality on the improper make-up casing connection the standards do not contain prescriptions regarding the tolerance of the thread's ovality or casing. indirectly, the ovality of the casing is controlled by the tolerance to the outer and inner diameters. the usual tolerance values of +1% (for the outside diameter) and of -0.5% (for the inside diameter) correspond to an ovality of 1.5%. the threads made by cutting present much lower deviations of ovality. the gauges are used to control the pitch diameter in the measuring plane. determining the standoff can lead to the acceptance of an oval casing connection, but it can have a value for the pitch diameter below the specified one [10]. the ovality is reduced by elastic deformation during the make-up casing connection, but leads to additional non-uniform stresses on the circumference of the threaded connection, which overlaps with the stresses induced by the make-up torque. at an oval casing connection, the theoretical contact of the threads for pin and box connection onto the entire circumference is achieved only by contact realized on two opposing generating lines, which correspond to the maximum diameter of the pin cone. this situation is confirmed by the galling marks on the threads next to these generating lines. in this situation, the contact of the threads only at one side of the circumference gives incorrect indications about the make-up torque and leads to a sensible reduction of the jump-out force in the thread. in api specification 5ct/iso 11960: 2001, it is noted that the assembly of the box connection to the casing, realized by the casing manufacturer, although sealed at the time of make-up connection, does not always maintain its sealing after transport, handling, or usage. iii. experimental investigation to the threaded casing connections the casing connection involved in this accident, manufactured according with the api specification 5ct/iso 11960 and api specification 5b, is a threaded connection for casing having an outer diameter of 20in, material grade type j55, and wall thickness of 11.13mm, fitted with a round thread type api 8-round (figure 3) [7]. the box of the casing connection has an outer diameter of 21in and a length of 230mm. fig. 3. round threads casing connection. as a result of the visual examinations it was found that there were no traces of thread deterioration to highlight the fact that the casing has been jump-out from the box, but there were only slightly traces of damage by bumping or galling. investigation was performed in order to explain the causes of breakout of the casing connections (factory assembled). all the submitted documents for casing connections involved in the event were studied regarding the technical manufacturing conditions and the accident's occurrence conditions. also, experimental research and analysis were performed in the laboratories of the petroleum-gas university of ploiesti for determining the mechanical characteristics of the material, its chemical composition and all the elements of the pin and box casing connection were measured. in order to establish the casing material, tests were performed on specimens taken from the failed casing connection and the obtained results confirmed the fact that the material used for manufacturing correspond to grade j55, according to api specification 5ct [12]. the dimensional characteristics of the thread elements were determined on the two elements of the casing connection (figure 4), made available by the beneficiary. thread element measurement was performed according to [7] using the gagemaker verification tools and procedures (figure 5), and instruments for thread profile verification starrett hf600 and allen # 3285 (figure 6). thus, the dimensions of the thread elements for casing connection (pin and box), provided with tolerances in the api 5b spec standard (thread profile, thread height, thread lead, thread taper, pitch diameter and ovality, total thread length between the end of pipe to vanish point, andeffective thread length), were measured. engineering, technology & applied science research vol. 11, no. 4, 2021, 7464-7468 7467 www.etasr.com zisopol et al.: theoretical and experimental investigations on 20 inches threaded casing connections … fig. 4. analyzed casing connection. fig. 5. instruments utilized for measuring the geometrical elements of the thread: a) thread profile gauge type gagemaker tp-rtc-8r, b) internal and external thread height gauge type gagemaker th-3000r, c) thread lead gauge type gagemaker lg-5002, d) external taper gauge type gagemaker et-7000, e) internal thread taper gauge type gagemaker it-6001, f), g) pitch diameter and ovality gauge type gagemaker mrp-2001. fig. 6. equipment utilized for examination of the thread profile: a) portable optical comparator type allen #3285, b) profile projector type starrett hf600. during the inspection, it was found that: • the profile of the two threads (pin and box), examined in the areas where there was no evidence of degradation, does not present any shape deviations. the thread root, the thread crest, and the thread flank angle correspond to api 8 – round standardized thread values. • the pin and box threads have the appropriate heights, within the tolerance specified in api specification 5b. • the values obtained for thread lead errors per inch, thread taper, total thread length l4, and effective thread length l2, determined for both casing connection elements (pin and box), fall within the limits specified in api specification 5b. • verification of the pitch diameter revealed that the differences between the standardized value and the average values of the pitch diameter, determinated in the case of the box thread, are very small and fall within the range of -0.31 ÷ 0.33mm (-0.012 ÷ 0.013in), and in the case of the pin thread, they have negative values, ranging in the range -2.31 ÷ -0.31mm (-0.091 ÷ -0.012in), with a maximum value of -2.7178mm. • the thread ovality values determined after the box measurements were found to be within the limits recommended by the api 8 short round thread, but the ovality values obtained for the pin thread exceeds the recommended limits (2.464mm from the recommended maximum 1.524mm). figure 7 shows photographs taken during the thread geometry measurements. taking into consideration all the theoretical analyses and experimental investigations performed on the casing connection, we proceeded to interpret the causes of the failure of the surface casing by breakout the threaded connections (factory assembled). fig. 7. images during the performed thread geometry measurements. so, the analysis concerning the specialized literature and the prescriptions of standards api bul. 5c2 [13] and api bul. 5c3 [14], highlights the recommended values for make-up torque and jump-out strength (tensile strength) of the thread connection type api 8 short round thread (8 thread/inch) shown in table i, corresponding to casing having outer diameter of 20in, material grade type j55, and wall thickness of 11.13mm. by comparing the tensile strength of the threaded connection (3484kn) with the hook load value at which the engineering, technology & applied science research vol. 11, no. 4, 2021, 7464-7468 7468 www.etasr.com zisopol et al.: theoretical and experimental investigations on 20 inches threaded casing connections … damage occurred (420kn), it was found that, even though a casing connection, like the examined one, is correctly made-up, the jump-out strength is approximately 8 times greater than the load at which the threaded connection breakout occurred. as has been shown from the measurements made on the geometric elements of the threaded connection, all thread dimensions are within the standard tolerance field, except for the pitch diameter of the pin thread and ovality. taking into consideration the above mentioned facts, it can be concluded that the mechanized make-up box and pin connection, respecting the indication as the frontal face to be corresponding to the base of the casing triangle stamp in the plane of vanish point, does not lead to the development of the radial contact pressure between the threads taken into consideration when establishing the conditions for achieving the correct make-up connecting. table i. recommended values make-up torque minimum 7960nm 5870ft.lb. optimum 10620nm 7830ft.lb. maximum 13270nm 9790ft.lb. tensile strength 3483kn 783000lb. as a conclusion, the probable cause of the breakout casing connection (factory assembled) is represented by make-up connection with a make-up torque value insufficient to assure the standard jump-out strength, due to the deviations to pitch diameter and ovality. although the breakout casing connection (factory assembled) did not lead to a serious failure, the event highlights the need to pay extra attention to the threading operations and especially to the control of threaded connection and make-up conditions. also it is recommended to perform a risk management evaluation [15]. iv. conclusions in order to explain the causes of failure during the well casing of the surface casing due to the breakout threaded casing connections (factory assembled) during the field operation, theoretical and experimental investigations were performed. it was established that all thread element errors are important factors for the assurance of optimum makeup torque of the casing connections. in the case of the investigated casing connection, the deviation from the ovality led to the nonachievement of the optimal makeup torque, which allowed the breakout of the threaded connections (factory assembled) in the borehole. references [1] n. konkong, "an investigation on the ultimate strength of coldformed steel bolted connections," engineering, technology & applied science research, vol. 7, no. 4, pp. 1826–1832, aug. 2017, https://doi.org/10.48084/etasr.1243. [2] v. ulmanu, material tubular petrolier. bucharest, romania: editura tehnică, 1992. [3] t. h. hill, "what you should know about octg inspections," world oil, vol. 199, no. 5, pp. 64–68, oct. 1984. [4] t. h. hill, "tracking octg inspection results saves time and money," world oil, vol. 201, no. 5, pp. 70–72, oct. 1985. [5] k. k. biegler, "conclusions based on laboratory tests of tubing and casing connections," presented at the spe annual technical conference and exhibition, sep. 1984, https://doi.org/10.2118/13067ms. [6] iadc drilling manual. technical toolboxes inc., 2000. [7] api spec 5b : threading, gauging, and inspection of casing, tubing, and line pipe threads. api, 2010. [8] "seal-lock ht ancillary specification." hunting. [9] m. l. payne, r. e. leturno, and c. a. harder, "improving operational procedures can reduce fatigue failure in 8-rd casing," oil and gas journal; (united states), vol. 92, no. 48, nov. 1994. [10] quality procedures. energy technology manufacturing & threading, llc. [11] tdwin taper thread disk for tapered threads. hou, usa: gagemaker, 2011. [12] technical committee iso/tc 67/sc 5, iso 11960:2001: petroleum and natural gas industries — steel pipes for use as casing or tubing for wells. 2001. [13] bulletin on performance properties of casing, tubing, and drill pipe. api, 1989. [14] bulletin on formulas and calculations for casing, tubing, drill pipe and line pipe properties. api, 1989. [15] a. chenarani and e. a. druzhinin, "a quantitative measure for evaluating project uncertainty under variation and risk effects," engineering, technology & applied science research, vol. 7, no. 5, pp. 2083–2088, oct. 2017, https://doi.org/10.48084/etasr.1530. microsoft word 28-3217_s_etasr_v9_n6_pp5021-5028 engineering, technology & applied science research vol. 9, no. 6, 2019, 5021-5028 5021 www.etasr.com nagao & shibata: experimental study of the lateral spreading pressure acting on a pile foundation … experimental study of the lateral spreading pressure acting on a pile foundation during earthquakes takashi nagao research center for urban security and safety kobe university kobe city, japan nagao@people.kobe-u.ac.jp daisuke shibata engineering department japan port consultants, ltd. tokyo, japan daisuke_shibata@jportc.co.jp abstract—in the seismic design of pile foundations, the safety of the pile is assessed by considering the inertial force during an earthquake and subgrade reaction as external forces against the pile. the amount of deformation of the pile must be limited to a small value to maintain the safety of the pile. in the event of a large earthquake, quay walls and seawalls are subjected to lateral spreading because of the influence of biased seaward earth pressure. the amount of lateral spreading is considerably larger than what can be expected in a typical pile seismic design and may reach several meters. in this study, loading experiments that reproduced lateral spreading were conducted to evaluate the lateral spreading pressure acting on a pile when considerably large lateral spreading occurred. the experiment results showed that lateral spreading pressure depended on the ratio of pile spacing to pile diameter while the peak value of lateral spreading pressure was larger than the one assumed in practical design. keywords-pile foundation; lateral spreading pressure; subgrade reaction i. introduction in the seismic design of pile foundations, the safety of piles against the inertial forces generated by earthquakes is examined by considering the bending rigidity of a pile and a horizontal subgrade reaction. the horizontal subgrade reaction is obtained by multiplying the horizontal displacement of the pile by the subgrade reaction coefficient corresponding to the ground modulus. the subgrade reaction has an upper limit value, and shear strength of the ground or passive earth pressure is used as the upper limit value in design practice [1, 2]. as the yielding of the pile is not considered in the design, the deformation of the pile is expected to remain small. quay walls and seawalls are subjected to large lateral spreading toward the sea because of biased seaward earth pressure and deterioration of ground rigidity due to earthquakes [3-7]. for example, the 1995 south hyogo prefecture earthquake (kobe earthquake) caused severe damage to port and harbor structures, and gravity-type quay walls were displaced toward the sea by up to 4m. damage to a pile-supported wharf was also confirmed at takahama pier at the port of kobe, and the head and underground parts of the piles suffered buckling. the buckling in the underground parts of the piles was caused by the lateral displacement of the revetment behind the pier on the sea side, the pushing of the rubble layer under the wharf, and the lateral spreading pressure applied to the pile [3]. the lateral spreading pressure that acts on an underground pile during a large earthquake is not taken into account in design practice. nonlinear finite element analysis (fea), which models structures and the ground, is sometimes used as a method for evaluating the seismic response of pile foundations during a large earthquake. nonlinear fea has the advantage that the nonlinear behavior of the ground and structural members can be expressed, and therefore, the dynamic interaction between the pile and the ground can be considered. presently, 2d analysis is often used for fea from the viewpoint of computational load. in 2d fea, piles discretely arranged must be modeled as a continuous wall having equivalent rigidity per unit depth. when foundation piles are affected by lateral spreading, the ground on the front of the piles exerts lateral spreading pressure on the piles while the ground between the piles slips between them. such a 3d effect cannot be accurately reproduced by a 2d analysis in which the piles are modeled as a continuous wall. attempts have been made to include a soil spring element as a method of expressing 3d effects in a 2d analysis [8, 9]. in such a model, the soil spring element is interposed between the pile and the ground to transmit the load mutually. 2d nonlinear fea examples using soil spring elements for pile-supported wharves have been studied [10-12]. however, some point out that 3d effects cannot be sufficiently reproduced by such a 2d analysis [12]. the deviation between a physical 3d model and the assumptions made in design calculations is expected to be a serious problem in the case of lateral spreading, which can reach several meters in the event of a massive earthquake. many experimental studies have been conducted on the dynamic interaction between the pile and the ground where the subgrade reaction was measured by shaking table and horizontal loading tests at the pile heads [13, 14]. however, the displacement of piles during an earthquake is very small because of their high rigidity compared with the amount of lateral spreading. to the best of our knowledge, no studies exist in which the lateral spreading pressure was examined during large-scale lateral spreading. in this study, a horizontal loading experiment of the ground against a pile was performed to evaluate the characteristics of lateral spreading pressure acting on the pile foundation in case of large lateral spreading. corresponding author: takashi nagao engineering, technology & applied science research vol. 9, no. 6, 2019, 5021-5028 5022 www.etasr.com nagao & shibata: experimental study of the lateral spreading pressure acting on a pile foundation … ii. method a. outline of the experiment the experiment was carried out using a soil tank shown in figures 1-2. a steel model pile with a length of 200mm was bolted onto the soil tank slab with a width of 1000mm and a depth of 500mm (figure 3). using two loading plates and fixed rods, a soil tank frame with internal dimensions of 500mm width, 500mm depth, and 500mm height was constructed in the soil tank. horizontal displacement was applied to the model ground in the soil tank frame by horizontally loading the loading plate with a mega torque motor, and the situation in which the ground slipped through the spaces between the piles during lateral spreading was reproduced. fig. 1. photo of the soil tank fig. 2. experimental soil tank steel pipe piles and concrete piles with diameters of the order of 1m cannot withstand large lateral spreading pressure. therefore, in this experiment, a reinforced concrete caisson was assumed as a foundation pile. considering the dimensions of the caisson foundation in the field and the size of the experimental soil tank, the length scaling factor (prototype/model) was set to 100, and the model specifications were determined by applying the similitude for shaking table tests on a soil-structure-fluid model in a 1 g gravitational field [15, 16]. five experimental cases were examined with varying pile diameters and spacing (table i). according to the similitude, the pile diameter and the pile spacing are 100 times larger in the actual scale. fig. 3. pile model installation status the horizontal loading speed applied to the model ground was set to 20cm/s on the actual scale with reference to past seismic response analyses. the loading speed in the experiment was 1/31.6 of the actual scale from the similitude. the maximum moving distance was 10cm, which corresponds to 10m on the actual scale. the ground was prepared by air pluviation so that the relative density (dr) was approximately 75%, using tohoku silica sand no. 6 in the dry state. the relative density during the actual experiments was dr=74.0%– 77.8%. the sand depth was 100mm. table i. test cases diameter (mm) spacing (mm) case 1 55 200 case 2 55 240 case 3 60 220 case 4 65 200 case 5 65 240 b. measured items the items measured in these experiments were i) lateral spreading pressure and wall earth pressure, ii) horizontal displacement, iii) load on the loading side wall, and iv) ground surface vertical displacement after loading. time-history data were recorded by a data logger for i) through iii). the lateral spreading pressure was measured using earth pressure gauges attached to the model piles using a fitting jig. these were installed at a height of 25mm and 75mm from the bottom slab on the loading side and at a height of 75mm from the bottom slab on the unloading side. gauges for measuring the wall earth pressure were installed at heights of 25mm and 75mm from the bottom slab on the loading side and at 75mm from the bottom slab on the unloading side (figure 2). five traverse lines with the same elevation positions from the loading side wall to the unloading side wall were constructed using sewing threads to measure the vertical displacement of the ground surface after loading. the vertical displacement was obtained by measuring the vertical distance from the traverse line to the model ground surface using a measuring scale with an accuracy of 1mm. in engineering, technology & applied science research vol. 9, no. 6, 2019, 5021-5028 5023 www.etasr.com nagao & shibata: experimental study of the lateral spreading pressure acting on a pile foundation … addition, colored sand was laid on the ground surface at equal intervals perpendicular to the traverse line to monitor the ground slip between the piles. the deformation of the colored sand was monitored by a video camera installed above the test equipment. iii. results and discussion a. lateral spreading pressure the earth pressure gauge readings fluctuated drastically due to the frictional resistance acting on the soil tank frame and the sand during loading and the consecutive cycles of locking and slipping of the sand particles. therefore, the measured data were fast fourier transformed, and after performing low-pass filtering at 1hz, the inverse fast fourier transform was taken to obtain smooth time-history data. figure 4 shows an example of the result of this smoothing process using data from the upper part of the pile for case 4. the gray line denotes the measured data, and the red solid line is the data after the filtering process. the same processing was performed on all measured data. fig. 4. example of filtering (case 4) figure 5 shows the lateral spreading pressure on the loading side. the blue line represents the lateral spreading pressure at the lower part of the pile, the red line denotes the lateral spreading pressure at the upper part of the pile, the dotted line shows the lateral spreading pressure on each of the two piles, and the solid line is the average value. the circles indicate the values at which the lateral spreading pressure peaks first. all the lateral spreading pressures shown in this study indicate increments from the pre-load. the lateral spreading pressures at the upper sensors decreased after they peaked at a displacement of around 10mm–15mm and became almost constant for displacements larger than 50mm. the lateral spreading pressure at the lower part also showed a peak in the vicinity of 10mm–15mm and thereafter remained almost constant without significantly decreasing, before gradually increasing in the displacement range over 40mm to the end of loading. when the lateral spreading pressure first peaks, the ground displacement is 1–2m when converted to the local scale, and it is almost the same as the lateral spreading displacement experienced by the quay wall and the revetment when large earthquake ground motions are applied. therefore, this value will be referred to as the “peak lateral spreading pressure” in the following discussion. the earth pressures on the unloading side of the pile and the unloading side of the wall were almost zero during loading, because the high rigidity of the pile results in a small bending deformation of the pile in comparison to the ground deformation, so the subgrade reaction does not act on the back surface of the pile. fig. 5. lateral spreading pressure 0 2 4 6 8 10 12 14 16 18 5− 0 5 10 15 time(s) p re ss u re (k p a ) 0 20 40 60 80 100 0 10 20 30 40 50 case 1 displacement(mm) p re ss u re (k p a ) 0 20 40 60 80 100 0 10 20 30 40 50 case 2 displacement(mm) p re ss u re (k p a ) 0 20 40 60 80 100 0 10 20 30 40 50 case 3 displacement(mm) p re ss u re (k p a ) 0 20 40 60 80 100 0 10 20 30 40 50 case 4 displacement(mm) p re ss u re (k p a ) 0 20 40 60 80 100 0 10 20 30 40 50 case 5 displacement(mm) p re ss u re (k p a ) engineering, technology & applied science research vol. 9, no. 6, 2019, 5021-5028 5024 www.etasr.com nagao & shibata: experimental study of the lateral spreading pressure acting on a pile foundation … figure 6 shows the relationship between the peak value of the lateral spreading pressure and the pile diameter, and figure 7 illustrates the relationship between the peak lateral spreading pressure and the pile spacing. the red triangles indicate the values at the upper part of the pile, and the blue circles denote the values at the lower part of the pile. the pile spacing is defined as the distance between the outer surfaces of the piles, not the distance between the centers of the piles, because this expresses the space available for the ground to pass between the piles. although the peak lateral spreading pressure appears to be positively correlated with the pile diameter and negatively correlated with the pile spacing, the relationship is not clear. the larger the diameter of the pile, the greater the degree to which the pile becomes a barrier to the lateral spreading of the ground, and the wider the interval between the piles, the greater the lateral spreading of the ground. therefore, the ratio of the pile spacing to the pile diameter (sdr) is proposed to express the magnitude of the peak lateral spreading pressure. figure 8 illustrates the relationship between sdr and the peak lateral spreading pressure. the fact that the peak lateral spreading pressure depends on sdr is clear. fig. 6. relationship between peak lateral spreading pressure and pile diameter fig. 7. relationship between peak lateral spreading pressure and pile spacing as described above, the wall earth pressure on the unloading side was almost zero during loading, but it increased with loading on the loading side. the relationship between the wall earth pressure on the loading side and the lateral spreading pressure is shown in figure 9, taking case 4 as an example. red lines indicate the pressure in the upper part, blue lines denote the pressure in the lower part, solid lines express the values of the pile, and dotted lines indicate the value of the wall. the wall earth pressure peaks before the lateral spreading pressure of the pile, and the peak wall earth pressure is lower than the peak lateral spreading pressure. in addition, the wall earth pressure decreases after reaching a peak, as does the lateral spreading pressure on the upper part of the pile, and subsequently shows an almost constant value. fig. 8. relationship between peak lateral spreading pressure and sdr fig. 9. relationship between wall earth pressure and lateral spreading pressure (case 4) figure 10 shows the relationship between the peak wall earth pressure and the peak lateral spreading pressure in the range of displacement up to 20mm in all cases. fig. 10. relationship between peak wall earth pressure and peak lateral spreading pressure 50 55 60 65 70 0 5 10 15 20 diameter(mm) la te ra l p re ss u re (k p a ) 180 200 220 240 260 0 5 10 15 20 spacing(mm) la te ra l p re ss u re (k p a ) 3 3.5 4 4.5 0 5 10 15 20 spacing/diameter la te ra l p re ss u re (k p a ) 0 20 40 60 80 100 0 10 20 30 40 50 displacement(mm) p re ss u re (k p a ) 0 5 10 15 20 0 5 10 15 20 wall pressure(kpa) la te ra l p re ss u re (k p a ) engineering, technology & applied science research vol. 9, no. 6, 2019, 5021-5028 5025 www.etasr.com nagao & shibata: experimental study of the lateral spreading pressure acting on a pile foundation … the dotted line is a 1:1 auxiliary line. the larger the peak lateral spreading pressure, the larger the peak wall earth pressure. the results indicate that the influence of the lateral spreading pressure acting on the piles extends to the loading side wall. the rapid increase in wall earth pressure immediately after loading indicates that the ground between the pile and the loading wall is compressed. the reason the wall earth pressure decreased after the peak was that the soil around the piles moved along the pile surface while the soil between the piles slipped through the pile space. b. horizontal displacement figure 11 shows a planar image after loading, taking case 2 as an example. figure 12 shows the displacement of the soil on the ground surface by measuring the displacement of the colored sand along traverse lines 1–5. blue dotted lines indicate the positions before loading and red solid lines denote the positions after loading. in traverse lines 2 and 4, where the piles are located, the pile resisted the displacement of the soil and it was compressed, so the intervals between the colored sand lines at the front surface of the pile were narrower after the loading than before the loading. conversely, in traverse lines 1 and 5, where no pile was present, the soil was minimally displaced and there was almost no difference in the interval between the colored sand at the front surface of the pile before and after the experiment. this trend was the same for all cases. in traverse line 3, between the piles, the amount of movement of the inter-pile soil differed depending on the pile spacing and diameter. fig. 11. post-load plane (case 2) fig. 12. horizontal displacement of ground surface after loading (case 2) focusing on the fifth colored sand line from the loading side wall at traverse line 3, between the piles, the displacement of the colored sand after loading was used to define the amount of soil displacement between piles. figure 13 shows the relationship between the amount of soil displacement between the piles and sdr. although the amount of soil displacement between the piles tends to increase as sdr increases, the correlation between the two is not strong. fig. 13. relationship between soil displacement between the piles and sdr c. vertical displacement figure 14 shows case 2 as an example of the vertical displacement of the ground surface after loading. the horizontal axis is the distance from the unloading side wall. the gray hatching indicates the location of the piles. in traverse lines 2 and 4, where the piles are located, the ground surface after loading has risen on the loading side and subsided on the unloading side. as confirmed from the image captured by the video camera, no remarkable rise in the ground surface occurred in the range of horizontal displacement of 10mm to 15mm, and vertical displacement occurred when the horizontal displacement was about 20mm or more. in comparison, in traverse lines 1, 3, and 5, away from the piles, the ground surface on the loading side rose after loading as in traverse lines 2 and 4, in line with the piles, but almost no vertical displacement occurred on the unloading side. this trend was the same for all cases. fig. 14. vertical displacement of ground surface after loading (case 2) figure 15 shows the relationship between the amount of ground rise and sdr. the red triangles denote the average values on the loading side, and the blue circles indicate the values of traverse line 3, between the two piles. there is no correlation between the amount of ground rise and sdr. 2 2.5 3 3.5 6 8 10 12 14 spacing / diameter d is p la c e m e n t( m m ) engineering, technology & applied science research vol. 9, no. 6, 2019, 5021-5028 5026 www.etasr.com nagao & shibata: experimental study of the lateral spreading pressure acting on a pile foundation … fig. 15. relationship between the ground rise and sdr iv. discussion on lateral spreading pressure as a range for the assumed normal lateral spreading amount, the lateral spreading pressure for ground displacement up to an experimental value of about 40mm will be discussed. as already mentioned, lateral spreading pressure peaks at the same level of ground displacement in both the upper and lower parts of the pile, but the lateral spreading pressure at the upper part decreases after the peak, whereas the lateral spreading pressure at the lower part becomes almost constant after the peak. this results in the ground in front of the pile on the loading side rising, which indicates that it has been compressed. this is the reason the lateral spreading pressure increases in both the upper and lower parts, but in the upper part, the compressed and raised soil gradually moves from the front surface of the pile to the side surface and eventually slides out behind the pile. for this reason, the effect of ground compression is alleviated, and the lateral spreading pressure does not increase after the peak. since the effect of relaxation of the ground compression due to slip-through is especially large in the upper part, the lateral spreading pressure decreases after peaking. in the lower part, since the relaxation effect of the ground compression is small, the value is almost constant after the peak. in seismic design of a structure having a pile foundation, the soundness of the pile is checked by applying the subgrade reaction due to the deformation of the pile as a force in a direction perpendicular to the axis. the subgrade reaction is calculated by multiplying the subgrade reaction coefficient by the displacement of the pile, and the upper limit of the subgrade reaction is either the shear strength of the ground or the passive earth pressure. this paper compares the values measured by experiment with those calculated using the conventional design method. evaluation of the subgrade reaction coefficient is based on the technical standards for port and harbor structures in japan [16] as: kh = 1.5n (1) where kh is the coefficient of horizontal subgrade reaction (n/cm 3 ), n is the average n-value of the ground down to a depth of about 1/β, and β is the characteristic value of the pile, which is calculated as: β = (khd/4ei) 1/4 (2) where d is the diameter of the pile (cm), and ei is the flexural rigidity of the pile (ncm 2 ). fig. 16. comparison of lateral spreading pressure experimental values and design values 2 2.5 3 3.5 0 10 20 30 spacing/diameter g ro u n d r is e (m m ) 0 5 10 15 20 0 5 10 15 20 case 1 displacement(mm) p re ss u re (k p a ) 0 5 10 15 20 0 5 10 15 20 case 2 displacement(mm) p re ss u re (k p a ) 0 5 10 15 20 0 5 10 15 20 case 3 displacement(mm) p re ss u re (k p a ) 0 5 10 15 20 0 5 10 15 20 case 4 displacement(mm) p re ss u re (k p a ) 0 5 10 15 20 0 5 10 15 20 case 5 displacement(mm) p re ss u re (k p a ) engineering, technology & applied science research vol. 9, no. 6, 2019, 5021-5028 5027 www.etasr.com nagao & shibata: experimental study of the lateral spreading pressure acting on a pile foundation … in the calculation of soil parameters, n-values were obtained from dr in accordance with [17] as: dr = 21{n/(σv’ + 0.7)}0.5 (3) where dr is the relative density (%), n is the n-value of the soil, and σv’ is the effective vertical stress of the soil (kgf/cm 2 ). the upper limit of the subgrade reaction force was calculated as the passive earth pressure. the shear resistance angle required for the calculation of the passive earth pressure coefficient was obtained from the relative density by referring to [17] as: ϕ = 0.0003dr 2 + 0.0426dr + 36.682 (4) where ϕ is the shear resistance angle (deg), and dr is the relative density (%). a comparison of the experimental and design values of the lateral spreading pressure is shown in figure 16. the red solid line represents the experimental value at the upper part of the pile, the blue solid line denotes the experimental value at the lower part of the pile, the broken black line represents the design value at the upper part of the pile, and the broken green line denotes the design value at the lower part of the pile. the design value shows reasonably good correspondence with the experimental value in the range up to the upper limit value, but the design subgrade reaction upper limit value is small in comparison with the peak lateral spreading pressure, especially in the upper part of the pile. figure 17 shows a comparison between the design subgrade reaction upper limit value and the lateral spreading pressure peak value for all cases. the red triangles represent the values at the upper part of the pile, and the blue circles are the values at the lower part of the pile. the conventional design method underestimates the upper limit of the lateral spreading pressure, and when large-scale lateral spreading occurs, the conventional design method falls on the dangerous side. the passive earth pressure is a calculation model for a continuous wall, and a uniform stress state is assumed in the depth direction. however, in reality the ground around the pile is in a highly inhomogeneous state, and strong stress concentration occurs around the pile. therefore, current design methods underestimate the peak lateral spreading pressure. fig. 17. comparison of lateral spreading pressure peak values and design values v. conclusion in this paper, experiments examining the horizontal loading of the ground against pile foundations were carried out to understand the relationship between the ground displacement by lateral spreading and the lateral spreading pressure acting on the pile foundation. the main conclusions drawn from the study are: • the lateral spreading pressure increases with increasing horizontal displacement after loading and peaks at a horizontal displacement of about 10–15mm (1.0–1.5m on the field scale). after the occurrence of the peak, the lateral spreading pressure gradually decreases at a position close to the ground surface but becomes almost constant at a deep position. after the lateral spreading pressure peaks, the surface of the ground on the loading side of the pile rises. the lateral spreading pressure increases with the increase of the horizontal displacement immediately after loading because the ground in front of the pile is compressed, and the compressed and raised soil gradually moves from the front to the side of the pile at a position close to the ground surface after a peak in pressure. for this reason, the effect of ground compression is alleviated, and the lateral spreading pressure does not increase after the peak. this relaxation effect due to ground slip-through is especially large at a position close to the ground surface, and, therefore, the lateral spreading pressure decreases after a peak is reached. since this relaxation effect is small at a deep position, the pressure remains substantially constant after the peak is exhibited. • the peak value of the lateral spreading pressure depends on the pile spacing to diameter ratio (sdr), and the smaller the sdr, the larger the peak lateral spreading pressure. this is because the smaller the sdr, the greater the degree to which the pile becomes a barrier to ground deformation. • as a result of comparing the relationship between the horizontal displacement of the ground and the lateral spreading pressure with the relationship assumed by the conventional design method, the design method agrees with the experimental results until the lateral spreading pressure peaks. however, with respect to the peak value of the lateral spreading pressure, the design method underestimates the experimental value. the degree of this underestimation is particularly exhibited at a position close to the ground surface, and it is necessary to appropriately evaluate the peak value of the lateral spreading pressure in case a large lateral spreading occurs in the event of an earthquake. acknowledgment this work was supported by jsps kakenhi, grant number jp18k04324. the authors thank dr. masahiko oishi of oriental shiroishi co., ltd., for his valuable opinions on the implementation of this study. references [1] american association of state highway and transportation officials, aashto lrfd bridge design specifications, seventh edition, with 2015 interim revisions, aashto, 2014 0 5 10 15 20 0 5 10 15 20 design value(kpa) e x p e ri m e n t( k p a ) engineering, technology & applied science research vol. 9, no. 6, 2019, 5021-5028 5028 www.etasr.com nagao & shibata: experimental study of the lateral spreading pressure acting on a pile foundation … [2] japan road association, specifications for highway bridges, part 4, substructures, ver. 2012, maruzen co., ltd., 2016 [3] international navigation association (pianc), seismic design guidelines for port structures, a.a. balkema publishers, 2001 [4] g. mondal, d. c. rai, “performance of harbour structures in andaman islands during 2004 sumatra earthquake”, engineering structurs, vol. 30, no. 1, pp. 174–182, 2008 [5] r. a. green, s. m. olson, r. brady, b. r. cox, g. j. rix, e. rathje, j. bachhuber, j. french, s. lasley, n. martin, “geotechnical aspects of failures at port-au-prince seaport during the 12 january 2010 haiti earthquake”, earthquake spectra, vol. 27, no. s1, pp. s43–s65, 2011 [6] s. werner, n. mccullough, w. bruin, a. augustine, g. rix, b. crowder, j. tomblin, “seismic performance of port de port-au-prince during the haiti earthquake and post-earthquake restoration of cargo throughput”, earthquake spectra, vol. 27, no. s1, pp. s387–s410, 2011 [7] t. sugano, a. nozu, e. kohama, k. shimosako, y. kikuchi, “damage to coastal structures”, soils and foundations, vol. 54, no. 4, pp. 883– 901, 2014 [8] o. ozutsumi, y. tamari, y. oka, k. ichii, s. iai, y. umeki, “modeling of soil-pile interaction subjected to soil liquefaction in plane strain analysis”, 38th annual conference of japan geotechnical society, akita, japan, july 2-4, 2003 (in japanese) [9] s. miwa, o. ozutsumi, y. tamari, y. oka, s. iai, s. tagawa, “twodimensional analysis of horizontal cross section for soil-pile interaction in liquefied ground”, 38th annual conference of japan geotechnical society, akita, japan, july 2-4, 2003 (in japanese) [10] s. iai, “seismic analysis and performance of retaining structures”, geotechnical earthquake engineering and soil dynamics iii, seattle, united states, august 3-6, 1998 [11] a. takahashi, j. takemura, “liquefaction-induced large displacement of pile-supported wharf”, soil dynamics and earthquake engineering, vol. 25, pp. 811–825, 2005 [12] g. li, r. motamed, “finite element modeling of soil-pile response subjected to liquefaction induced lateral spreading in a large-scale shake table experiment”, soil dynamics and earthquake engineering, vol. 92, pp. 573–584, 2017 [13] w. chang, j. chen, h. ho, y. chiu, “in situ dynamic model test for pile-supported wharf in liquefied sand”, geotechnical testing journal, vol. 33, no. 3, pp. 212-224, 2010 [14] l. su, l. tang, x. ling, c. liu, x. zhang, “pile response to liquefaction-induced lateral spreading: a shake-table investigation”, soil dynamics and earthquake engineering, vol. 82, pp. 196–204, 2016 [15] p. yin, w. he, zj. yang, “a simplified nonlinear method for a laterally loaded pile in sloping ground”, advances in civil engineering, vol. 2018, article id 5438618, 2018 [16] s. iai, “similitude for shaking table test on soil-structure-fluid model in 1g gravitational field”, soil and foundations, vol. 29, no. 1, pp. 105-118, 1989 [17] ports and harbours bureau, ministry of land, infrastructure, transport and tourism, national institute for land and infrastructure management, port and airport research institute, technical standards and commentaries for port and harbour facilities in japan, the overseas coastal area developement institute of japan, 2009 [18] t. morita, s. iai, h. liu, k. ichii, y. sato, simplified method to determine parameter of flip, technical note of the port and harbor research institute, no.869, 1997 (in japanese) engineering, technology & applied science research vol. 7, no. 6, 2017, 2319-2323 2319 www.etasr.com ayed et al.: an automated surveillance system based on multi-processor and gpu architecture an automated surveillance system based on multiprocessor and gpu architecture mossaad ben ayed alghat college of science and humanities al majmaah university, ksa and university of sfax, tunisia mm.ayed@mu.edu.sa sabeur elkosantini college of engineering king saud university kingdom of saudi arabia selkosantini@ksu.edu.sa mohamed abid sfax national school of engineers university of sfax tunisia mohamed.abid@enis.rnu.tn abstract–video surveillance systems are a powerful tool applied in various systems. traditional systems based on human vision are to be avoided due to human errors. an automated surveillance system based on suspicious behavior presents a great challenge to developers. such detection is a rather complex procedure and also a rather time-consuming one. an abnormal behavior could be identified by: actions, faces, route, etc. the definition of the characteristics of an abnormal behavior still present a big problem. this paper proposes a specific architecture for a surveillance system. the aim is to accelerate the system and obtain a reliable and accelerated suspicious behavior recognition. finally, the experiment section illustrates the results with comparison of some of the most recent approaches. keywords—surveillance system; suspicious behaviors; multiprocessor; gpu i. introduction surveillance systems are increasingly monitored by computers. the main goal of a surveillance system is identifying suspicious or undesirable behaviors such as theft and loitering with intent [1]. by definition, suspicious behavior is an anomalous behavior which is likely to threaten human life, health, property and freedom. developers propose three essential steps, to recognize suspicious behavior: object detection, tracking, and behavior exploration. the first challenge is to define models to recognize a suspicious behavior. an anomalous behavior is not a fixed action but it is a complex behavior combining a series of actions and simple behaviors. thus, it is difficult to be recognized accurately. the object’s actual detection presents a previous step which must be considered in order to recognize the potentially suspicious people. a comparison among the main background subtraction methods is used to detect objects. then the tracking step is essential to define trajectory or behavior kind/type. several algorithms are used in literature but the results are not always satisfactory [2]. this paper is focused on a specific case: detect the attempt of theft or scam in the case of atm security surveillance. this detection is performed by the exploration of tracking and squatting action. the second challenge is the design of a real-time surveillance system. it is known that video/image processing requires a specific architecture to obtain real-time results. in this paper, we present different techniques used to accelerate the execution speed and we propose an attempt based on decoc classifier to ensure the real-time execution. existing surveillance systems suffer from several issues: 1. most traditional methods in surveillance are based on manual/visual detection [4]. 2. most of today’s surveillance is not used to prevent an incident but only used to identify what has already happened [5]. 3. most of surveillance system suffers from no real-time detection of suspicious behavior. this problem is due of the complexity of the algorithms [5]. 4. surveillance system violates the privacy of citizens. for example, in usa, many groups are against the use of surveillance system in public areas [6]. in light of this brief introduction on suspicious behavior based on surveillance system, this paper purports to contribute the following tentative proposals: 1. it proposes an embedded intelligent camera for real-time execution. the intelligent camera ensures the privacy of citizens because all the treatment will be done in camera. 2. it applies the proposed design with respect to the atm system. ii. related work a. suspicious behavior recognition algorithms video surveillance systems pass by three phases in literature. the first phase uses analog cctvs and the automation is little exploited (1960-1980). the second phase was based on computer vision using digital cctvs (19802000). from 2000, the third phase is based on semi-automated video-surveillance systems [7]. as mentioned in the previous section, each suspicious behavior recognition is composed essentially by three steps: object detection, tracking, and behavior exploration. engineering, technology & applied science research vol. 7, no. 6, 2017, 2319-2323 2320 www.etasr.com ayed et al.: an automated surveillance system based on multi-processor and gpu architecture 1) object detection there are many algorithms related to object detection, but they still suffer from complexity due to different specific situation. one of the most used methods for object detection is the subtraction of the background [8, 9]. other works based in the last method are improved by formulated technique [10]. multi-layer background subtraction represents another method based on color and texture [11]. second works are based on segmentation algorithms [12]. as conclusion, the object detection is commonly done by using the background subtraction method [13]. 2) tracking tracking methods is widely described in previous works. but these works suffer from low accuracy. tracking object system is used in many fields as: crowded environment [14], traffic situation [15] and maritime surveillance [16]. in the field of surveillance, the essential goal of the tracking object is to analyze or to extract the human behavior: trajectory, gesture, event [13, 17-18]. 3) behavior recognition all suspicious behavior recognition methods can be classified into two categories: single-layered and hierarchical approaches [3]. the first is suitable for gesture recognition and the second is adopted for complex activities (figure 1). singlelayered approaches can be classified into two types depending on how they model human activities: space–time approaches [19-22] and sequential approaches [23-25]. space–time approaches consider the input video as a set of frames at a particular point of time. these approaches recognize behavior by extracting trajectories or local interest points. whereas sequential approaches interpret an input video as a sequence of observations and recognize it by exemplar based methodologies or model-based methodologies. hierarchical approaches are classified based on the recognition methodologies they use: statistical approaches [26], syntactic approaches [27], and description-based approaches [28, 29]. but all the previous works cannot be applied in real-time due to the enormous amount of computation required [30]. fig. 1. different behavior recognition approaches. b. real-time detection based on hardware acceleration one of the most important goals of security surveillance is to collect and disseminate real-time information and provide situational awareness to operators and security analysts [5]. there are many research works that propose an advanced architecture in the field of video-surveillance. in [41] a codesign strategy is adopted with fpga to ensure automated video surveillance in the case of the object detection. other works are focused in embedded cameras for tracking systems [42, 43]. in [41, 44, 45], advanced designs are proposed to accelerate the detection of human motion. surveillance systems are facing different challenges like the low accuracy of tracking due to the low quality videos, and the real-time detection. the present paper proposes an accelerated architecture for suspicious behavior. this attempt uses arena tool as a higher level of description for modeling and simulation. based on obtained results, an automated and accelerated architecture is proposed to ensure real-time recognition. iii. proposed surveillance system: modeling and simulation embedded system is used in industries, surveillance, smart cities, intelligent systems, etc. there are several environments for modeling and simulation depending on level description and system’s field. arena environment provides the description of an event-discrete system at conceptual level. based on suspicious behavior’s recognition steps, arena’s model is composed by three processes: object detection, tracking, and behavior exploration. two models could be adopted for design, (figures 2, 3): (1) mono-processor, (2) multi-processor. a. model 1: mono-processor architecture entity: name: frames arrivals arrival time: const (0.1) (s) process: name: object detection resources: processor delay type: tria (0.02,0.04,0.05) (s) process: name: tracking resources: processor delay type: tria (0.05, 0.08, 0.1) (s) process: name: behavior exploration resources: processor delay type: tria (0.4, 0.5, 0.9) (s) engineering, technology & applied science research vol. 7, no. 6, 2017, 2319-2323 2321 www.etasr.com ayed et al.: an automated surveillance system based on multi-processor and gpu architecture b. model 2: multi-processor architecture entity: name: frames arrivals arrival time: const (0.1) (s) process: name: object detection resources: processor1 delay type: tria (0.02,0.04,0.05) (s) process: name: tracking resources: processor2 delay type: tria (0.05, 0.08, 0.1) (s) process: name: behavior exploration resources: processor3 delay type: tria (0.4, 0.5, 0.9) (s) the simulation is run for 1 hour. the simulation results of model 1 are shown in figure 3a. they show that an architecture based on single processor is insufficient for surveillance system. the system should have big buffers between components to ensure the safety of data and that the bandwidth is quickest than the time treatment. the real-time execution capability is not proved for this model. the simulation results of model 2, are shown in figure 3b, and are better than those of model 1. the multi-processor architecture proposed for surveillance system improves speed and requires a big buffer between processor2 and processor3. the design still suffers from no real-time execution. based on the simulation results, a specific architecture is described in the next section iv. experiment results this section presents the implementation of the surveillance system using a hybrid architecture based on multi-processor and gpu. this solution is well justified by simulation results presented in the previous section. the aim of this section is to describe a hardware accelerator based on the gabor filter. the proposed architecture is composed by microblaze soft-core processors interfaced with shared memory using the axi4 bus [46]. all processor elements, on-chip memories, and the axi4 bus are clocked at 100 mhz. off-chip memory is clocked at 200 mhz and the axi-lite bus is clocked at 50 mhz. frames arrival object detection tracking exploration behavior decision 0 0 0 0 0 fig. 2. surveillance system model. a) mono-processor architecture b) multi-processor architecture fig. 3. simulation results. the surveillance system’s architecture is divided into:  hardware components: behavior exploration.  software applications: object detection and tracking. the frame is received by a professional camera with frame size of 640x840 pixels. the proposed design is composed by sram memory, control unit, 2 processor elements (cores) and hardware accelerators based on behavior exploration, see figure 4. the proposed architecture belongs to simd/mpsoc field [47]. the control unit represents an essential component in design. the last aims to handle all processes:  arbitrating the access of processors unit to/from memory  handling and commanding all the processor units at first, the frame is captured with the camera and saved into global memory. the algorithm of surveillance system is divided into software modules (object detection and tracking) and hardware components (behavior exploration). in table i, the proposed design is compared with others and it shows the best execution time for a surveillance system. our proposition’s speed-up factor is about 20 times the ones in [40], and [37], about 2 times the one in [30], 10 times the one in [39] and 4 times the one in [38]. engineering, technology & applied science research vol. 7, no. 6, 2017, 2319-2323 2322 www.etasr.com ayed et al.: an automated surveillance system based on multi-processor and gpu architecture fig. 4. multi-processor and gpu architecture for surveillance system. from the experiment’s results mentioned in table i, the proposed algorithm has the best result in terms of reliability and speed. this proves that the proposed architecture based on combination between multi-processor and gpu ensures the real-time execution. table i. a comparison between different suspicious behavior detection methods based on execution time method execution time (s) [37] 0.2> [38] 0.041 [39] 0.1 [40] 0.2> [30] 0.02 proposed method 0.01 v. conclusion this paper resumes the different automated surveillance systems in the literature. the goal is to obtain a reliable detection of suspicious behavior with respect to the real-time constraint for an atm system. this successful attempt proposes a hybrid architecture based on multi-processor and gpu to accelerate the treatment time of a frame. this architecture ensures the no loss of data between processes. as a main contribution, a whole hardware design based on multiprocessor architecture is described. the proposed design combines with 2-cores and gpu. compared with other works cited, our design achieves the best execution time. acknowledgment the authors would like to thank deanship of scientific research at majmaah university for funding this work. references [1] e. r. davies, computer and machine vision, academic press, 2012 [2] r. arroyo, j. j. yebes, l. m. bergasa, i. g. daza, j. almazan, “expert video-surveillance system for real-time detection of suspicious behaviors in shopping malls”, expert systems with applications, vol. 42, no. 21, pp 7991-8005, 2015 [3] j. k. aggarwal, m. s. ryoo, “human activity analysis: a review”, acm computing surveys, vol. 43, no. 16, 2011 [4] r. shimonski, “digital reconnaissance and surveillance”, chapter 1 in cyber reconnaissance, surveillance and defense, elsevier, 2015 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engineering, aswan, egypt mohamed m. hamada department of electrical engineering, minia university, faculty of engineering, minia, egypt abstract—this paper introduces the load flow on the egypt electricity network system. the effect of capacitor compensation has been studied from three points. first, the problem of the series capacitor compensation was considered. the second type of compensation considered is shunt compensation. finally, a mixed of shunt and series capacitors compensation was implemented. the analysis results were discussed based on the maximum reduction in the generated mvar. the load variation is accounted for by considering three different load levels classified as light, medium and peak load with pre-specified durations. when solving the capacitor placement problem, the number, size, location and control settings of the capacitors at different load levels were determined. the load flow program is solved by the power world simulator (pws) software. the results of series capacitor, shunt capacitor, and mixed compensation were studied. the investigation has been done for single capacitor and multi-capacitor compensation. both 500kv and 220kv overhead lines have been considered. keywords—voltage; frequency; reactive power; load flow; egyptian i. introduction egypt is the largest non-member of the organization of the petroleum exporting countries oil producer in africa and the second-largest dry natural gas producer on the continent. egypt is the largest oil and natural gas consumer in africa, accounting for more than 20% of continent’s total oil consumption and more than 40% of total dry natural gas consumption in 2013 [12]. automatic generation control (agc) is an important problem in power system operation and control. whenever a small load perturbation occurs, it causes changes in tie-line power flow and frequency deviation. many investigations in the area of agc of interconnected power systems have been carried out in the past [3-5] and a number of control strategies have been proposed to improve the performance of agc. consequently, the non-linear nature of the load frequency control (lfc) problem makes it difficult to ensure stability for all operating points when an integral controller is used [6-7]. the application of adaptive control theory to the lfc problem eliminates some of the problems associated with classical and modern control [8-10]. voltage instability has been observed in several forms, which was reached to complete blackouts of power systems in several countries [11]. power system institutes such as ieee, cigre, iee and epri have turned great attention to the subject [12]. an ieee subcommittee was formed in 1986 for its study [13-15]. in future, the subject will have a direct access to other interests such as power system security, reliability, planning, control methods and power system harmonics suppression. electronic static var compensators, flexible ac transmission systems and hvdc systems will be widely used to counteract the effect of such devices and to improve the voltage stability situation of large systems [16-18]. power quality is a recent subject that appeared with the complication of power systems [19-22]. reactive power compensation is an important issue in electric power systems, involving aspects of service like operation, economy and quality. consumer loads (residential, industrial etc.) impose active and reactive power demand, depending on their characteristics. active power is converted into useful energy, like light or heat. reactive power must be compensated to guarantee an efficient delivery of active power to loads, thus releasing system capacity, reducing system losses, and improving system power factor and bus voltage profile. due to this, optimization of the capacitor placement problem (cpp) is important for studying the effect of capacitor compensation of a certain system. the problem of reactive power control for the egypt electricity network (een) has been addressed in this paper. ii. een description and data een operates a large and extensive transmission system consisting of six major subareas. these areas are upper egypt, corresponding author: youssef a. mobarak engineering, technology & applied science research vol. 9, no. 1, 2019, 3699-3704 3700 www.etasr.com mobarak et al.: reactive power compensation on egypt electricity network for optimal energy saving cairo, medium delta, canal, west delta and alexandria (alex.). the peak load is about 21051mw and is increasing at an average rate of 6-7mw per year. the system consists of large steam units (9698mw) and many different sizes of gas turbines in about 10 major and several smaller power plants such as 937 hydraulic, 106.4mw w-level and 49.61mw wind turbine. een is shown in figure 1 for single line diagram. the load flow solution has been carried out using pws. the program solves the load flow problem using the newtonraphson method. the results of the peak, medium and light load levels solutions are presented and explained. the results were compared with actual load flow in the company file and were found identical. fig. 1. single line diagram of the studied een system. in general, the total peak load for een was 19,677mw. the total power consumption in cairo was the largest compared to the other cities at 6255mw which represented about 32% of the total area load. upper egypt network is considered the second largest load sink representing around 21% of total area load. upper egypt, alexandria, middle delta, west delta and canal peak time power consumption is 4133mw, 2421mw, 3034mw, 2476mw, 1358mw respectively. table i gives the active, reactive and complex power consumption of each area. table i. load consumption at peak time power area active (mw) reactive (mvar) complex (mva) upper egypt 4133 2528 4845 cairo 6255 3848 7344 alexandria 2421 1456 2825 m. delta 3034 1872 3565 w. delta 2476 1472 2881 canal 1358 832 1593 total 19,677 12,008 23,053 iii. results and discussion the load flow solution considered 500/220kv network at light, medium, and peak time. this represents a single line diagram of een in which all bus voltages, loads and flow lines are presented. the load flow solution of the 500/220kv een, shows that there are 31 transmission lines carrying power between the 500/220kv substations. the total generated active power from the stations, at peak time, was about 21051mw. on the other hand, the reactive power generation at peak time was about 17239mvar. a. conventional load flow figure 2 shows the voltage profile of all buses of the egyptian 32-bus system as obtained from the load flow. it can be seen that all bus voltages are within the acceptable level (±7%) except buses 24 to 32, which have about 0.9pu. the participating factor for this mode has been calculated and the result is shown in figure 3. the result shows that, buses 11 (naj-hammadi), 19 (qena) and 20 (sohag) have the highest participation factors for the critical mode. the largest participation factor value (0.2294) at bus 20 indicates the highest contribution of this bus to the voltage collapse. fig. 2. voltage profiles of all buses of the eenps. fig. 3. participating factor of all buses b. load flow dependent on voltage and frequenccy let us consider a nominal voltage conventional load flow as shown in figure 4, when load is voltage dependent (the factors kpv and kqv are 2 and 2 respectively), and load flow when load is voltage and frequency dependent. slack bus power is specified. the factors kpf and kqf are 2 and -2 respectively, and pg1=16pu. the solution for system frequency is such that loadgeneration-loss balance is achieved at that frequency. with the specifications given above, the total generation is greater than the load and losses at the nominal frequency. therefore, frequency will be higher than the nominal frequency (50.8494hz). if kpf is changed to 3.0, the frequency will be higher than the nominal frequency (52.275hz). engineering, technology & applied science research vol. 9, no. 1, 2019, 3699-3704 3701 www.etasr.com mobarak et al.: reactive power compensation on egypt electricity network for optimal energy saving fig. 4. voltage profiles of all buses of the eenps at different load models. c. effect of series compensation on een in this section, the effect of series capacitor compensation on 500/220kv overhead lines is studied. single, double and triple compensations were considered separately. beyond triple capacitor compensation, the difference of benefits is not significant and hence we don't recommend the implementation of more than three series capacitors at a time. it has been found that the best location to install the single capacitor compensation will be in the transmission line connecting the 500kv substations number 14 and 16. as shown in figure 5 we can get a reduction in total generated reactive power of 3671.9mvar which is about 21.3 of the total generation during peak time. on the other hand, the generated active power will be increased by 112mw in this case. regarding the double series capacitor compensation for 500kv network, the best locations in 500 kv network will be in the lines connecting substations (14-16), and (15-17) which should compensate at 65% of line impedance. by implementing the above two series capacitors the total reduction in the total generated complex power will be around 4172mvar, which is about 24.2% of the total generation, at peak time. on the other hand, the generated active power will be increased by 151mw in this case. regarding the results of the triple series capacitor compensation for een, it was found that the best locations at peak time should be in the lines overhead line connecting substations (14-16), (15-17), and (18-24) which should compensate at 66% of line impedance. fig. 5. the effect of single capacitor series compensation applied on een. fig. 6. the effect of double capacitor series compensation applied on een. installing these capacitors will reduce the total generated mvar in een by around 25.5%. the reduced reactive generated power is 4396mvar at peak time. however, the generated active power will be increased by about 151mw.the impact of triple compensation on medium and light load are shown in figure 7. when series compensation was applied in the 500/220kv overhead lines, it was found that the best reduction in the generated mvar was obtained after using triple compensation. the reduction was about 25.5% of total system generated mvar at peak time. but generally, there was no big difference in the reduced mvar when using single, double or triple series compensation. the reduction generated mvar while using single, double or triple series compensation at system peak load was 3671.9, 4172, and 4396 respectively as shown in figure 8. fig. 7. the effect of triple capacitor series compensation applied on een. fig. 8. reduced generated mvar of een series compensation. engineering, technology & applied science research vol. 9, no. 1, 2019, 3699-3704 3702 www.etasr.com mobarak et al.: reactive power compensation on egypt electricity network for optimal energy saving d. effect of shunt compensation on een shunt capacitor compensation has been seen based on the hypothesis that een can reduce up to 9050mvar. the reduction represents around 52.5% of total system generation. this is achievable only when the shunt capacitive units are installed at the right buses. analysis has been conducted for single, double and triple capacitor compensation. it was seen that shunt compensation in more than three locations does not worth the effort. in case of single-bus compensation, only around 5378mvar can be saved in the generation at peak time. this reduction is about 31.2% of the system generation. the reactive power compensation should be installed at substation number 14. the rating at the capacitor bank should be 636mvar (figure 9). the compensation factor is 94% of bus load at this value. the value of the capacitive bank at peak medium and light loads is also given. on the other hand, the system generation can be declined by about 8688mvar, which is almost 50.4% of system generation, by applying double-bus compensation. the shunt elements should be installed at buses 17 and 28 with 138 and 541mvar respectively. the values of shunt compensation are presented for peak, medium and light periods in figure 10. for 3-bus shunt compensation, the best reduction in the generated mvar was almost 9050mvar which is better than the 2-bus compensation case by around 326mvar. this reduction is about 52.5% of total generated mvar. to achieve this reduction, three shunt elements should be installed at buses 28, 30 and 16 with rated values of 541, 437 and 153mvar respectively (figure 11). all peak, medium and light load compensation values are shown in figure 11. fig. 9. the effect of single capacitor shunt compensation applied on een. fig. 10. the effect of double capacitor shunt compensation applied on een. fig. 11. the effect of triple capacitor shunt compensation applied on een. result comparison of shunt capacitor compensation has been done for each network based on the value of reduced mvar of generation. for een, the maximum achievable reduction in the generated mvar was 9050mvar, which is 52.5% of total system generation, at triple capacitor compensation at peak time. figure 12 compares single, double and triple compensation on ee network. fig. 12. reduced mvar generated of een shunt compensation. e. effect of mixed compensation on een this section presents the results of mixed shunt and series capacitor compensation on 500/220kv network. applying mixed capacitor compensation on een system results in a reduction of 7997mvar of total system generation during peak time. this is representing about 46.39% of total system generated mvar. mixed compensation increases the total generated mw by almost 6mw during peak time. this testing was performed for single and double mixed capacitor compensation. in the case of single mixed compensation, maximum reduction in the generated mvar obtained during peak load is 7130mvar which is about 41.36% of total generated mvar. the single shunt compensation should be added on bus number 14 with a size of 298mvar. on the other hand, single series compensation should be added into the 380kv transmission connecting substations (16-14). the compensation rate of the line should be 65 of line impedance. figure 13 shows the results of single mixed compensation on een system. in this figure, the best locations are sorted based on maximum reduction of the generated mvar. compensation values of all three load levels (peak, medium and light) are also presented. engineering, technology & applied science research vol. 9, no. 1, 2019, 3699-3704 3703 www.etasr.com mobarak et al.: reactive power compensation on egypt electricity network for optimal energy saving fig. 13. the effect of single mixed compensation applied on een. in the case of double mixed compensation, total reduction of 7997mvar of total generation was achieved. this is about 46.4% of the system generation. the two shunt elements to be added are on buses 14 and 17 with values of 602 and 67mvar respectively. on the other hand, two 500kv lines, connecting substations (14-16) and (17-15), should be compensated by series capacitive elements at 70% and 65% of the investigation results of double-mixed compensation case on een (figure 14). the best locations are based on maximum reduced generated mvar, and compensation values of all three load levels (peak, medium and light) are presented. the results of the mixed shunt and series capacitor compensation were compared for each network and bench marked. the comparison has been done for each network based on the value of reduced generation mvar. another results comparison is to compare the increased mw in the generation. fig. 14. the effect of double mixed compensation applied on een. fig. 15. reduced generated mvar of een mixed compensation. for the 500kv network, the maximum achievable reduction in the generated mvar was at double capacitor compensation at 930.6mvar, which is 46.4% of total system generation, at peak time. figure 15 compares single and double compensation on the 500kv network. prior to capacitor installation, a load flow study was run to obtain the present een system condition presented in table ii which shows the generated active power, generated reactive power, generated complex power, system kw losses, the cost of energy losses during peak, medium and light load levels and the cost of system energy losses. table ii. system conditions before capacitor placement load condition light medium peak total generated active power p (mw) 19567 18335 21051 total generated reactive power q (mvar) 18284 15057 17239 total generated complex power s (mva) 26780 23725 27209 real power losses (mw) 7088 2441 1373 cost of energy losses ($) 931,363 641,495 180,412 total cost of energy losses ($/year) 2,043,138 iv. conclusion the installation of series, shunt or mixed capacitors reduced energy losses in the system. the maximum obtained reduction in generated mvars was 25.5%, 52.5% and 46.6% for the 500/220kv network. shunt compensation at substations with large loads results in a better reduction of the generated mva than at substations with low loads. the reduced mva of shunt compensation is more than the one of mixed or series compensation. references [1] a. alshehri, a. hussain, y. a. mobarak, “energy-conversion measures in the industries of saudi arabia and development of methodology for certification of energy personnel in the kingdom”, energy policy, vol. 64, no. 1, pp. 203-208, 2014 [2] y. a. mobarak, “voltage collapse prediction for egyptian interconnected electrical grid eieg”, international journal on electrical engineering and informatics, vol. 7, no. 1, pp. 79-88, 2015 [3] m. al-amin sarker, a. k. m. kamrul hasan, “load frequency control in power system”, seu journal of science and engineering, vol. 10, no. 2, pp. 24-30, 2016 [4] k. s. s. ramakrishna, p. sharma, t. s. bhatti, “automatic generation control of interconnected power system with diverse sources of power generation”, international journal of engineering, science and technology, vol. 2, no. 10, pp. 51-65, 2010 [5] r. s. shekhawat, s. garg, “automatic generation control–an enhanced review”, international journal of engineering trends and technology, vol. 5, no. 2, pp. 75-84, 2017 [6] a. delassi, s. arif, l. mokrani, “load frequency control problem in interconnected power systems using robust fractional pid controller”, ain shams engineering journal, vol. 9, no. 1, pp. 77-88, 2018 [7] r. umrao1, s. kumar, m. mohan, d.k.chaturvedi, “load frequency control methodologies for power system”, 2nd international conference on power, control and embedded systems, allahabad, india, december 17-19, 2012 [8] y. l. abdel-magid, m. a. abido, “agc tuning of interconnected reheat thermal systems with particle swarm optimization”, 10th ieee international conference on electronics, circuits and systems, sharjah, united arab emirates, december 14-17, 2003 [9] d. rerkpreedapong, a. hasanovic, a. feliachi, “robust load frequency control using genetic algorithms and linear matrix inequalities”, ieee transactions on power systems, vol. 18, no. 2, pp. 855-861, 2003 engineering, technology & applied science research vol. 9, no. 1, 2019, 3699-3704 3704 www.etasr.com mobarak et al.: reactive power compensation on egypt electricity network for optimal energy saving [10] c. s.chang, f. u. weihui, “area load frequency control using fuzzy gain scheduling of pi controllers”, electric power systems research, vol. 42, pp. 145-152, 1997 [11] p. nagendra, t. datta, s. halder, s. paul, “power system voltage stability assessment using network equivalents a review”, journal of applied sciences, vol. 10, pp. 2147-2153, 2010 [12] a. dhamanda, a. k. bhardwaj, “automatic generation control of thermal generating unit by using conventional and intelligent controller”, international journal of electrical engineering & technology, vol. 5, no. 10, pp. 56-64, 2014 [13] g. a. chown, r. c. hartman, “design and experiences with a flc for automatic generation control agc”, ieee transactions on power systems, vol. 13, no. 3, pp. 965-970, 1998 [14] y. a. mobarak, a. m. elnoby, “improvement of dynamic performance of interconnected power systems with static synchronous series compensator”, international journal of electrical and electronics engineering, vol. 7, no. 2, pp. 21-30, 2015 [15] y. a. mobarak, s. a. deraz, m. el-shahat dessouki, r. almazmomi, “optimal control techniques in applicable values of turbine speed governor regulation”, ssrg international journal of electrical and electronics engineering, vol. 2, no. 8, pp. 24-35, 2015 [16] a. m. elnoby, g. el-saady, y. mobarak, m. a. a. wahab, m. m. hamada, m. a. abdel-moamen, “robust technique lfc of two-area power system with dynamic performance of combined smes and sssc control”, international journal of advances in engineering & technology, vol. 8, no. 2, pp. 46-58, 2015 [17] y. l. karnavas, d. p. papadopoulos, “agc for autonomous power system using combined intelligent techniques”, electrical power systems research, vol. 62. no. 3, pp. 225-239, 2002 [18] k. sabahil, m. a. nekouil, m. teshnehlab, m. aliyari, m. mansouri, “load frequency control in interconnected power system using dynamic modified neural networks”, 2007 mediterranean conference on control & automation, athens, greece, june 27-29, 2007 [19] g. shabib, y. a. mobarak, m. h. el-ahmar, “combined svc and sssc controllers for power system transient stability improvement”, 13th international middle east power systems conference, assiut, egypt, december 21-23, 2009 [20] y. a. mobarak, m. m. hussein, “voltage instability of initiation fault duration as influenced by nodes short circuit levels nscl”, international journal of electrical and computer engineering, vol. 6, no. 3, pp. 130513018, 2016 [21] y. a. mobarak, “fault duration for voltage instability and voltage collapse initiation as influenced by generator voltage magnitudes gvm”, journal of engineering sciences, vol. 40, no. 3, pp. 846-866, 2012 [22] y. a. mobarak, “effects of the droop speed governor and automatic generation control agc on generator load sharing of power system”, international journal of applied power engineering, vol. 4, no. 3, pp. 21-30, 2015 authors profile youssef a. mobarak was born in egypt. he received his b.sc. and m.sc. degrees in electrical engineering from south valley university, aswan, egypt, in 1997 and 2001 respectively and his ph.d. from cairo university, egypt, in 2005. he joined the electrical engineering department, faculty of energy engineering, aswan university as a demonstrator, assistant lecturer, and assistant professor during the periods of 1998–2001, 2001–2005, and 2005–2013 respectively. in 2014 he obtained the associate professor rank. he joined artificial complex systems, hiroshima university, japan as a researcher in 2007–2008. also, he joined king abdulaziz university, rabigh, faculty of engineering 2010 to present. his research interests are power system planning, operation, and optimization techniques applied to power systems, nanotechnology materials via addition of nano-scale particles and additives for usage in industrial field. a. m. hemeida was born in el-menia, egypt, on october, 21, 1968. he obtained his b.sc., and m.sc. in electrical power engineering from faculty of engineering, minia university, minia, egypt in 1992 and 1996 respectively. in 1992, he joined the higher institute of energy, aswan as teaching assistant. from 1998 to 1999 he was a full time ph.d. student in the electrical and computer engineering department, university of new electrical engineering department, faculty of engineering, assiut university, assiut egypt. from oct. 2000 till august 2005 he was assistant professor at the electrical engineering department, higher institute of energy, south valley university, egypt. in nov. 2005 he obtained associate professor rank. from sept. 2006 until april, 2010 he was the chairman of computer science department, arrass faculty of science and arts, qassim university, saudi arabia. his research interests include power systems operation and control, artificial intelligence application in power systems, facts applications, voltage stability, and advanced control techniques in power systems a. el-bahnasawy was born in egypt. he received his b.sc. and m.sc. degrees in electrical engineering from south valley university, aswan, egypt, in 2004 and 2010 respectively. he joined the electrical engineering department, high institute of energy, south valley university as a demonstrator and assistant lecturer, during 2005–2010. he is a phd student in minia university from 2013. mohamed m. hamada was born in 1951. he received his b.sc. and m.sc. from assiut university, egypt in 1974 and 1982, respectively and ph.d. from manchester university institute of science and technology (umist), uk, all in electrical engineering. from 1975 to 1983 he worked as a teaching assistant at minia university, egypt. from 1983 to 1989 he was with umist working with ipsa group and studying for ph.d. since 1989, he has been a staff member at the department of electrical engineering, minia university. his main fields of interest are harmonics in power systems, hvdc, high voltage phenomena, voltage stability. microsoft word 24-2465_s1 engineering, technology & applied science research vol. 9, no. 1, 2019, 3790-3795 3790 www.etasr.com pathan et al.: small signal modeling of inverter-based grid-connected microgrid to determine … small signal modeling of inverter-based gridconnected microgrid to determine the zero-pole drift control with dynamic power sharing controller erum pathan department of electrical power engineering, faculty of electrical and electronic engineering, universiti tun hussein onn malaysia, johor, malaysia erumasad79@gmail.com shamsul aizam zulkifli department of electrical power engineering, faculty of electrical and electronic engineering, universiti tun huseein onn malaysia, johor, malaysia aizam@uthm.edu.my usman bashir tayab school of engineering and built environment, griffith university, nathan campus, brisbane, queensland, australia usmanbashir.tayab@griffithuni.edu.au ronald jackson department of electrical power engineering, faculty of electrical and electronic engineering, universiti tun hussein onn malaysia, batu pahat, johor, malaysia ronaldjacknen.91@outlook.com abstract—this paper presents a small signal state space modeling of three-phase inverter-based microgrid (mg) system with consideration of improved droop control. the complete system matrices for one distribution source-grid connects to the local load have been elaborated by applying high, medium and lowfrequency clusters to the system without considering the switching action on the inverter during power-sharing. moreover, the final matrices will be used to determine the location of the eigenvalues for the control parameters gains due to dynamic effect of the mg, by observing the root locus graph on cluster identification. sensitivity analysis of all types of frequency cluster showed that power-sharing control parameters such as load current, source current, and inverter voltage are influencing system stability and must be considered when designing the proportional-integral (pi) control when different load scenarios have been applied from the zero-pole drifting. those eigenvalues of the system model are indicating the frequency and damping oscillatory components when there is sudden changed at the inverter-grid connection. the matrices’ eigenvalues are being plotted using matlab/simulink to identify system stability region and find the pi controller parameters. keywords-power sharing control; microgrid; power-sharing control; small-signal stability i. introduction renewable energy sources are attracting more and more attention [1-2] due to the limited resevers of non-renewable resources. power electronic converters are commonly used to interface distributed sources and grid to a microgrid (mg) which can operate either on islanded or grid-connected mode [3-5]. the small signal state space modelling of mg is the best way to observe its performance. authors in [6-8] proposed a small signal modeling of mg and did not consider filter dynamics or damping filter resistance. similarly, authors in [910] presented a natural, reference frame based, mathematical model to evaluate inverter based microgrid stability against communication time delay. moreover, the effect of unintentional islanding stability and dc link small modeling have been developed in [11] while in [12] a small signal model of the n-th interconnected synchronous machine was investigated by applying the advanced control techniques which can be described the state space representation of the system. authors in [6-12] focused on small signal modeling of mg with droop controller and did not consider power sharing response. computational algorithms used for calculating the active and reactive power [13-15] are needed to observe the response. in this paper, we present a small signal modeling of three phase inverter based mg using improved droop control with consideration of power-sharing response. the main contribution of this paper is the performance investigation of the proposed small signal modeling of improved droop control with consideration of low-frequency cluster stability, sensitivity of the dynamic power sharing controller gain, and effect of the line impedance parameters in different scenarios. furthermore, by implementing this technique, the exact location and drift flow movements can be estimated in order to maintain system stability. as a model, the mg is divided into power and control blocks reconstructed into a single state space mode while transmission line, voltage source inverter, and filter are included in the power block transformation. the control block is based on dual loop controllers, i.e. inner current control and outer voltage control. in addition, it is compared with the conventional droop control to show the effectiveness of the proposed small signal model of improved droop control. corresponding author: e. pathan engineering, technology & applied science research vol. 9, no. 1, 2019, 3790-3795 3791 www.etasr.com pathan et al.: small signal modeling of inverter-based grid-connected microgrid to determine … the proposed model is verified through matlab simulation. based on the simulation results, it can be concluded that transient response and poor damping have been eliminated by the use of the proposed small signal model. ii. islanded and grid-connected system overview distributed renewable sources are interfaced to a mg by power converters, filters, transmission lines, loads, utilities, and points of common coupling, either in islanded or in gridconnected mode (figure 1). concurrently, the mg could also be operated in single or multilevel parallel inverters. this paper investigates only grid-connected mode using power-sharing technique which is based on improved droop control. threephase voltage and current measurement signals are used to transform the time signal to a constant time signal. calculated active and reactive powers are filtered by low pass filters and are sent to power-sharing controllers based on the dq components. hence, the power-sharing controller will generate amplitude, angle and frequency references. in the islanded mode all the calculation of three-phase to direct park transforms are driven by using the reference angle from the power sharing controller. fig. 1. control and power system block diagram in grid-connected mode, a phase lock loop (pll) is used to generate the reference angle for response to the grid phase. therefore, in a direct park transformation based pll, the frequency is measured by forcing the q axis component of a voltage to zero. cascaded controllers for controlling the inner current and outer voltage control of the system are needed to record the dynamic behavior of the load changes. the voltage reference for the voltage controller is obtained from the frequency and amplitude signals by the power controller. the overall system dynamics including power, voltage, current controller, inverter, and line impedance are given in state space based small signal modeling section when it is in gridconnected mode. if the system is used in islanded mode, load parameter dynamics can also be considered. iii. state space-based small signal model the mg model needs to be linearized around the operating point by the use of small signal techniques in order to study the dynamics of power and control system. in this section, the mathematical model of the system is discussed in detail. a. dynamics of synchronous voltage, current control, and lcl filter the dynamic model equations start when the inverter controller is modeled based on dual loops performance. the pi controller is used to get zero steady-state error. in (1), φdq is the error between the measured and set point voltage. this error is sent to the voltage controller for tracking the reference signal and generating input reference signal for current controller [16]. the algebraic dynamic of voltage control is given as: ( ) ( ) i c v k v v ko oq pv ivld f od od d i c v k v v ko pv oq oq qivlq f od ω ϕ ω ϕ ∗ ∗ = − + − + ∗ ∗ = + + − + (1) where ��� ∗ and ��� ∗ are the inputs for current controller, �� and � are the pi regulator gains. the current controller ensures that the inverter output voltage follows the reference signal which is coming from the output of the voltage inverter. it produces the difference between measured and reference filter inductor current and produces measured voltages. in addition, it eliminates the cross-coupling terms by using the dq format to determine the signal reference for the generation of pulse width modulation (pwm) for the inverter switching. as for the inner loop control, the voltages are given in (2): ( ) ( ) v l i k i i ko pci icid lq ld ld d v l i k i i ko pc qiq icif ld lq lq ω γ ω γ ∗ ∗ = − + − + ∗ ∗ = + + − + (2) where ��� ∗ and ��� ∗ are the measured signal, ��� and � � are the pi regulator gains. b. power-sharing and proposed power-sharing controller instantaneous active and reactive inverter power are calculated by using the direct and quadratic axis-based inverter output current � �� and voltage � �� of the system [17]. in order to cancel high-frequency components and ripples, the instantaneous power is passed through a low pass filter to obtain the average power of the system which is given in (3), where �� is the cut off frequency: 1.5( ) 1.5( ) cp v i v ioq oqinv od ods c cq v i v ioq oqinv od ods c ω ω ω ω = × + + = × − + (3) in the islanded mode the inverter does not use any reference as external signal but only the current controller. hence, the inverter output frequency and voltage can be adjusted by applying droop theory mechanism for power sharing. the characteristics equations of droop controller are given in (4) as for grid-connected mode. ( ) ( ), 0 m p po inv ref v v n q q vo oqinvod ref ω ω= − − ∗ ∗= − − ∆ = (4) by considering ���� and ���� are equal to zero in islanded mode, so is the droop. hence, the phase angle of the inverter is engineering, technology & applied science research vol. 9, no. 1, 2019, 3790-3795 3792 www.etasr.com pathan et al.: small signal modeling of inverter-based grid-connected microgrid to determine … set by taking the integral of frequency • -mp inv δ = . the proportional frequency droop coefficient m and the proportional voltage droop coefficient n are calculated by: , v voo odm n p q inv inv ω ω ∗−− = = (5) the complete dynamic linear small signal state space model of the inverter in grid-connected mode can be obtained by combining all equations of power controller, voltage controller, current controller, lcl filter, line, and bus: 2 2 1 2 0 0 0 0 0 0 0 0 0 0 0 0 14 14 1 14 inv odq p p v vc lcl i bus a b b b x c b c dinv e f g h b b δ δ                                                             ∆   ∆   •   •   •    ∆   ∆   • ∆ = × × (6) where _ 1 1 1 1 2 2 1 1 1 3 1 1 1 1 1 2 2 , , , ( ) p p com pw v pv v v pv c v c lcl c v pv lcl pw lcl c v lcl c lcl lcl c v c a a b c b b c c b d c d b d b e b d d c b c f b d c g b c h a b d d d = + = = = + = + = = = + + in order to improve the system transient response and reduce the system oscillation, the differential of power in conventional power-sharing control should be added. the proposed power sharing control system is: ( ) ( ) dp invm p p mo inv ref d dt dq invv v n q q no invod ref d dt ω ω= − − − = − − − (7) consequently, the complete inverter model can be modified as per the dynamic power sharing controller and the proposed bus model is given in (8): 1 11 1 11 1 11 12 1 11 12 13 14 1 14 14 2 14 0 0 0 0 0 0 0 0 0 0 0 0 1 inv invdyn odq pa a b b x c c c d d d d d ie δ δ                                                                                       ×        × ∆ ∆ • • •∆ = • ∆ ∆ (8) where: 1 11 1 1 11 2 1 1 1 1 11 1 1 12 1 2 1 2 2 1 1 1 1 3 , , , , dynamic dynamic dynamic dynamic dynamic dynamic p pcom pw p dynamic v v v pvpv dynamic v v c v pccpv dynamic c v pv c v c dynamic dynam lcl c v pv lcl pw a a b c a b b b c b b b d c b d c c b c e b c b d d b d b d b d d c b c = + = = = + = = = = + + = + 11 1 1 12 1 14 2 13 1 1 2 2 1 1 1 3 , , ( ) ic lcl c v lcl c lcl dynamic dynamic lcl lcl c v c lcl c v pv lcl pw d b d c d b c d b d a b d d d b d d d b d = = = = + + + + iv. state space based proposed system model the previous section is based on the complete system model of mg as illustrated in figure 1, which is based on 14 state variables. however, the reduced system model is only based on 5 state variables that are mostly effects on powersharing accuracy and stability. a. reduced model of power-sharing controller the reduced matrixes model can be taken into account using low frequency-based system parameters consisting of line impedance, power-sharing controller and filter only. compared to medium and high frequency-based system model, the filter and cascaded controller parameters would not be affected by the stability when the sharing is happening to the inverter. _ 1 1g odq odq o oqd odq pcc dq g g g r i i i v v l l l ω • − = ± − + (9) the reduced system model based on the low-frequency system parameters and line impedance is given in (10): 0 0 0 0 1.5 1.5 1 2 0 1.5 1.5 3 4 cos( ) 0 5 mp a a v vc c c oqod p inv a a v vc oq c od q inv n qa li lined i lineq δ ω ω ω ω ω δ                                                                                                      −• ∆ − − − • ∆ − • ∆ = • ∆ • ∆ sin( ) 0 6 p inv q inv r ig linedlg g i lineq n rq ga l lg g δ ω δ ω                                                                                                                   ∆ ∆ ∆ ∆− ∆ − −                            (10) where: 1 1.5 ( ( sin( ) cos( )) ( cos( ) sin( )) c lined od oq lineq oq od a i v v i v vω δ δ δ δ= − − − − 2 1.5 ( cos( ) sin( )) c q lined lineq a n i iω δ δ= − − 3 1.5 ( ( sin( ) cos( )) ( cos( ) sin( )) c lineq od oq lined od qd a i v v i v vω δ δ δ δ= − − − − 4 1.5 ( cos( ) sin( )) c c q lineq lined a n i iω ω δ δ= − + − + 6 5 ( cos( ) sin( )) ( sin( ) cos( )) , od oq od oq g g v v v v a a l l δ δ δ δ− − − = − = − b. proposed power sharing controller a reduced system model of dynamic power sharing controller is based on only 5 out of 14 states of the system because the reduced model is only based on the line impedance effect and dynamic power sharing controller parameters. the reduced state space matrix is given below: engineering, technology & applied science research vol. 9, no. 1, 2019, 3790-3795 3793 www.etasr.com pathan et al.: small signal modeling of inverter-based grid-connected microgrid to determine … 1 2 3 4 5 6 8 9 10 11 13 14 15 16 18 1 5 21 23 5 5 0 0 0 c inv inv g inv inv o g lined lined lineqg o lineq g a a a a a a a a a p a a a a p r qq a a l i i ir a a i l δ ω δ ω ω • • • • ו ×    ∆    − ∆     ∆    ∆     ∆=  ∆  −     ∆   ∆  ∆    −  ∆    (11) where: 1 3 2 4 5 9 10 6 1.5 ( ( sin( ) cos( )) ( cos( ) sin( )) , 1.5 , 1.5 , 1.5 , 1.5 1.5 ( ( sin( ) cos( )) ( cos( ) sin( ) ω δ δ δ δ ω ω ω ω ω ω δ δ δ δ = = − − − − − = − + = − = − = = = − − + − c d lined od oq lineq oq od d c d c oq d c od c od c oq c lined od oq lineq oq od a a m i v v i v v a m m a m v a m v a v a v a i v v i v v 8 14 11 13 15 ) 1.5 ( ( )cos( )) ( )sin( ))), 1.5 1.5 ( ( sin( ) cos( )) ( cos( ) sin( )) 1.5 ( ( )cos( )) ( )sin( ))) ω ω δ ω δ ω ω δ δ δ δ ω ω ω δ ω δ = − + + − + = − = − − − − − = − + − + − − + c lined c d lineq c d c oq c lined od oq lineq oq od c c lined c d lineq c d a i n n i n n a v a i v v i v v a i n n i n n a 16 18 21 23 28 ( sin( ) cos( )) ( )cos( )) 1.5 , , ( cos( ) sin( )) ( )sin( )) , δ δ ω δ ω δ δ ω δ − − − + = = − = − − − + = − = = − od oq c d c od g g od oq c d g g v v n n v a a l l v v n n a a a l l v. results and discussion the small signal modeling of the mg system given in figure 1 has been tested and evaluated using the eigenvalues technique applied to matlab/simulink. the eigenvalues are found from (6) and (8) with a specific pi gain value technique that observes transient behavior, damping and stability of the system. the control system plant will be stable if the poles of the characteristic equations lie on the left half plan. when the dynamic controller has been applied, an imaginary complex conjugate of the characteristic equation is exhibited on the oscillatory behavior of the dynamic system and a more transient oscillation can be observed. on the other hand, if the imaginary eigenvalues are going away from the left half plan a faster transient and reduced rise time are disclosed. a. stability test of complete and reduced system model parameters effect. the individual small signal model by its differential equations of lcl filter, line impedance, cascaded current, voltage, and power-sharing controller, is embedded in order to study the dynamic behavior of the power-sharing mechanism of the mg. this approach is also used to analyze the stability of the system. table i shows the parameters of the initial condition of the system. the wide band of dynamic modes of the power-sharing mechanism of the mg system can be seen in figure 2. the frequency scale separation between different modes of different control loops can be observed in figure 3. it should be noted that timescale separation is crucial for designing a typical reduced power system. the filters and current controllers are mainly designed with high-frequency modes. the switching frequency is mainly chosen as per the inverter’s rating and of switching losses. the inner current controller bandwidth should be higher than the resonance frequency of the passive filter and 4 to 10 times less than the switching frequency of the inverter. moreover, the lcl filters resonance frequency should be half times less than the switching frequency and 10 times greater than the nominal frequency. cluster 3 from figure 2 illustrates the dynamic behavior of the inner controller of the power-sharing mechanism of the mg. table i. initial condition system parameters parameters values parameters values � 0.1ω δ2 2 � 1.8e-3h m 1e-5 �� 0.23ω n 1e-5 �� 0.1h md 2e-6 �� 25e-6f nd 2e-6 ������ 311v ��� 5.3 ������ 2.2kw � � 0 �� �� 726w � 100 � 31.415rad/s �� 0.04 �� 62.831rad/s δ 0 fig. 2. eigenvalues of dynamic power sharing and power sharing based complete signal model (x=proposed, o=conventional model) fig. 3. effect of proportional droop coefficients m and n on dynamic power sharing controller and power-sharing controller (x=proposed, o=conventional model) cluster 2 from figure 2 illustrates the dynamic effect of voltage controller which is designed on medium bandwidth and based on medium frequency modes. the voltage controller bandwidth should be 5 to 10 times less than the inner current controller in order to keep monitoring the tracking resolution and the stability of the inner control loop. outer control loop dynamics are illustrated by cluster 1 in figure 2 which is based on power-sharing controller and low pass filters. this control loop is mainly designed with very low bandwidth, since the average outer power-sharing controller in grid-connected mode needs gradual change in the reference voltage. average power is extracted from the synchronous reference frame based on the instantaneous power components and low pass filters with low cut-off frequencies. consequently, this controller bandwidth should be lower than voltage controller bandwidth. engineering, technology & applied science research vol. 9, no. 1, 2019, 3790-3795 3794 www.etasr.com pathan et al.: small signal modeling of inverter-based grid-connected microgrid to determine … b. the effect of power-sharing co-efficient and dynamic power-sharing coefficient the eigenvalues of the power-sharing controller are illustrated in figure 3, which presents how the power-sharing coefficient controller effects on system stability. figure 4 shows the dynamic power sharing controller with the effect of the power-sharing coefficient. in figure 3, when the active power gain is varied from 1e-5 to 5e-4, the dynamic power sharing controller real poles are moving towards the left side whereas the real poles of power-sharing controller are moving towards the right side. similarly, the dynamic power sharing controller-based system is said to be stable but the powersharing controller-based system leads towards instability and system response becomes more oscillatory. when the active dynamic power sharing gain is increased, the dominant poles of the imaginary axis are varying and the system becomes faster. the effect of active dynamic power sharing gain is illustrated in figure 4. fig. 4. effect of dynamic active power droop gain md on dynamic power sharing controller and power-sharing controller (x=proposed, o=conventional model). c. effect of line impedance parameters the line impedance parameters also affect the system stability of the dynamic power sharing controller as well as the power sharing controller-based system. the effect of the line impedance variation is illustrated in figures 5-6. fig. 5. effect of line impedance lg is varying and rg is fixed (x=proposed, o=conventional model) fig. 6. effect of line impedance (x=proposed,o=conventional model) when the inductance of line impedance is increased, the system never becomes unstable, but the large values of the inductive part could not be the real line impedance values. hence, the xg/rg is directly affected on system dynamics, so the leading of inductance of the line impedance reduces the steady state error while the system transient response for increasing value of the resistive part of line impedance is damped. d. validation by matlab/simulink sim power tool power-sharing controller and dynamic power sharing controller effect were validated by matlab/simulink. the set point of active power was considered 726w. poor damping, slow transient response, and maximum by using the conventional power-sharing controller overshoot can be seen in figure 7. poor damping and transient have been improved by using the dynamic power sharing control without compromising the steady-state performance. fig. 7. transient active power of conventional and proposed model. vi. conclusion a small signal modeling of high-frequency cluster, medium frequency cluster and low-frequency cluster based mg for dynamic power control is presented in this paper. all the submodel parts have been combined on common reference frame in order to get the complete model of the mg. analyzation of sensitivity and stability of system parameters is based on the eigenvalues technique of the developed small signal state space model and the reduced small signal state space model in different scenarios. it is concluded that power-sharing and dynamic power sharing based low-frequency mode are highly sensitive in a network of mgs. cascaded inverter controller, loads and network dynamic sensitivity is based on the highfrequency cluster. low-frequency cluster stability and sensitivity of the active power sharing and of the proposed dynamic power sharing controller gain, and the effect of the line impedance parameters have been investigated in different scenarios. it can be concluded that transient response and poor damping have been improved by the proposed dynamic power sharing controller. acknowledgement authors gratefully acknowledge the support of universiti tun hussein onn malaysia (uthm), advanced control on power converters (acpc) group, fkee, and research university grant program (u998), uthm for undertaking this research activity. engineering, technology & applied science research vol. 9, no. 1, 2019, 3790-3795 3795 www.etasr.com pathan et al.: small signal modeling of inverter-based grid-connected microgrid to determine … references [1] f. blaabjerg, r. teodorescu, m. liserre, a. v timbus, “overview of control and grid synchronization for distributed power generation systems”, ieee transactions on industrial electronics, vol. 53, no. 5, pp. 1398-1409, 2006 [2] a. vidal, f. d. freijedo, a. g. yepes, p. fernandez-comesana, j. malvar, o. lopez, j. doval-gandoy, “assessment and optimization of the transient response of proportional-resonant current controllers for distributed power generation systems”, ieee transactions on industrial electronics, vol. 60, no. 4, pp. 1367-1383, 2013 [3] ieee standards 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multiple parallel dg inverters based on a virtual synchronous generator scheme”, energies, vol. 11, no. 1, pp. 1-22, 2018 [17] k. hashmi, m. m. khan, s. habib, h. tang, “an improved control scheme for power sharing between distributed power converters in islanded ac microgrids”, international conference on frontiers of information technology, islamabad, pakistan, december 8-20, 2017 microsoft word etasr_v11_n2_pp7001-7005 engineering, technology & applied science research vol. 11, no. 2, 2021, 7001-7005 7001 www.etasr.com ahmed et al.: analysis of text feature extractors using deep learning on fake news analysis of text feature extractors using deep learning on fake news bilal ahmed department of electrical engineering sukkur iba university sukkur, pakistan bilal_ahmed@iba-suk.edu.pk gulsher ali department of electrical engineering sukkur iba university sukkur, pakistan gulsher@iba-suk.edu.pk arif hussain department of electrical engineering sukkur iba university sukkur, pakistan arif.hussain@iba-suk.edu.pk abdul baseer buriro department of electrical engineering sukkur iba university sukkur, pakistan abdul.baseer@iba-suk.edu.pk junaid ahmed department of electrical engineering sukkur iba university sukkur, pakistan j.bhatti@iba-suk.edu.pk abstract-social media and easy internet access have allowed the instant sharing of news, ideas, and information on a global scale. however, rapid spread and instant access to information/news can also enable rumors or fake news to spread very easily and rapidly. in order to monitor and minimize the spread of fake news in the digital community, fake news detection using natural language processing (nlp) has attracted significant attention. in nlp, different text feature extractors and word embeddings are used to process the text data. the aim of this paper is to analyze the performance of a fake news detection model based on neural networks using 3 feature extractors: td-idf vectorizer, glove embeddings, and bert embeddings. for the evaluation, multiple metrics, namely accuracy, precision, f1, recall, auc roc, and auc pr were computed for each feature extractor. all the transformation techniques were fed to the deep learning model. it was found that bert embeddings for text transformation delivered the best performance. td-idf has been performed far better than glove and competed the bert as well at some stages. keywords-fake news; natural language processing; feature extractors; deep learning i. introduction due to the easy and excessive use of the internet and the incremented use of social media, the probability of fake news circulation is increased. this has impacted the trust on news from the media nowadays specially since the 2016 us elections. authors in [1] conducted a survey in which they found that global trust on the news from the media of different countries ranged from 23% to 62%. the big challenge for the researchers is to encounter this problem and provide a feasible solution. the main aspects of this problem are the fact that the same sources may provide both fake and real news, the language used can be deceiving, and biasness of the dataset and machine learning models may occur. also, due to advancement of artificial intelligence applications in natural language generation has brought considerable negative impact when used in generating fake news. in [2], news sources were under consideration instead of single articles. the idea is based on the frequency of the news sources providing fake news. the more the frequency of fake news from a source, the more the chances are that that source will provide more fake news in the future. the motive of the authors was to build an algorithm that can identify the fake news in its source before it spread. in their paper they targeted multiple sources such as urls, twitter accounts, wikipedia pages and articles, and found articles to be more real than the other kind of sources. automatic text generation using artificial intelligence is also a popular way to spread fake news at a fast pace [3]. fake news is one of the most difficult and sensitive topics in the field of nlp. when dealing with fake news one must keep tricky things in mind like the source of the news, the language of the news, and its pattern. different types of text transformation techniques, machine learning algorithms and state-of-the-art methods have been introduced and applied to address this problem. td-idf is one of the simplest text transformation techniques which transforms each word to a corresponding author: bilal ahmed engineering, technology & applied science research vol. 11, no. 2, 2021, 7001-7005 7002 www.etasr.com ahmed et al.: analysis of text feature extractors using deep learning on fake news float number as its weight according to the frequency of words in documents. this simple technique is very useful when working on a simple task. but when encountering a tricky topic like fake news detection, td-idf can be less effective. to encounter the complexity of text-based data in machine learning, text transformation techniques, also called as embeddings, are developed which deal with the phenomenon of the relation of words with respect to their meanings. however, td-idf was used before the contextual embeddings came out and became common. authors in [4] used td-idf vectorizer to extract features from news articles. authors in [5] proposed a tool for fake news detection in which they used bag of words, bigram frequency, and td-idf vectorizer to extract features from news articles which were tested with probabilistic classification and linear classification. authors in [6] analyzed different machine learning models including naïve bayes, support vector machine (svm), logistic regression and recurrent neural networks (rnn) on a fake news dataset from twitter. they concluded that the naïve bayes and svm are the classifiers with the best performance. ensemble or combination of machine learning models is a technique used by researchers to deal with complex machine learning tasks. authors in [7] analyzed different ensembles of different machine learning models and finally came with the an ensemble of decision tree, logistic regression, bagging classifier used with hardvoting ensemble technique which gave accuracy of 88%. for other nlp tasks, ensemble techniques give nice results. authors in [8] used the ensemble technique to improve the translation quality from english to hindi and used 6 different machine translation engines. for nlp problems, neural networks provide a great range of algorithms to process and learn on sequence-based or textual data. dense, rnn, lstm, 1d-convolutional (conv1d) and gru layers are being used in processing of textual or sequence-based data. authors in [9] used convolutional neural networks to build a model that can classify the arabic text. authors in [10] used convolutional layers and bidirectional rnns on large movie review and sentiment treebank datasets. embeddings do not consist a feasible solution for every textbased problem, as there are two kinds of texts, static and context-based and so there should be two kinds of embeddings. thus, the contextual embedding has been developed which works well on the text data having context with respect to every word. this paper discusses and analyzes different word transformation algorithms on fake news datasets using deep learning for each word transformation technique. it covers some well-known word transformation techniques such as bert [11], glove [12] and td-idf [13]. the main objective of this paper is to analyze whether contextual embeddings outperform the static word transformation techniques or not. ii. the datasets two balanced datasets openly available on kaggle were used. both datasets contain both true and false news about western politics and international issues. the first dataset [14] contains 6335 articles about different topics mostly on politics and has 3164 fake and 3171 true articles and the second [15] contains 20,800 articles of the same nature with 10,387 fake articles and 10,413 valid articles (figure 1). in both datasets, article text was only analyzed and the other columns were dropped to avoid probability of false pattern learning and to reduce computational cost while training the model. for both datasets, train/test ratio was 80/20 and from the train data, 10% was kept for validation to monitor the model behavior during training. fig. 1. pictorial presentation of the used datasets iii. methodology and feature extractors the objective of this study is to analyze the performance of 3 feature extractors, bert embedddings, glove embeddings and td-idf vectorizer using anns on two fake news datasets. the ann model contains two dense hidden layers and an output layer with 8, 16 and 1 neuron(s) respectively. the feature extractors were chosen because they cover all broader classes of text feature extractors. the old fashioned td-idf vectorizer computes the word count (frequency) of a word, glove is a static embedding context-independent method which works on the principle of computing the similarity between words according to their semantics, and bert is a contextual embedding model which does not just compute the similarity between words but takes care of the context in which a specific word is used, since the word's meaning may be varied according to the context. anns were used as classifiers due to their ability to handle efficiently large datasets in comparison with other machine learning models. other ann types (lstm, rnn, etc.) were not used, since, in this paper, the analysis of feature extractor has not been conducted on the basis of different ann models. also, a simple ann requires less computational time. the bert model was itself quite heavy. for extracting features of our dataset from glove and td-idf, a personal i7 laptop with 8gb ram was used. feature extraction and model training took hardly 2-3 minutes for tdidf and 4-5 minutes for glove. however, for bert the required computational power surpassed the available resources, as feature extraction requires very high computational power. for bert, the cloud-based kaggle platform was utilized, which offers free gpu and tpu usage for higher computational tasks. for this task 15 gb gpu and 16 gb ram were used to extract the features and pass to the ann classification model which took about 28 minutes in total for each dataset. this study was carried out using python language and its available tools. the datasets were loaded from kaggle, then engineering, technology & applied science research vol. 11, no. 2, 2021, 7001-7005 7003 www.etasr.com ahmed et al.: analysis of text feature extractors using deep learning on fake news they were split into train and test groups with 80/20 ratio. the feature extractors were applied on each dataset and the output was fed to the ann model. we used sklearn library to implement the td-idf vectorizer and keras for the implementation of the ann model having tensorflow at the backend. we used built-in functions in sklearn for the evaluation of the models trained on each feature extractor for both datasets. accuracy, precision, recall, f1, auc roc and auc pr score were computed for both datasets using all three feature extractors to compare their performances. the flowchart of the process from dataset loading to the final evaluation is given in figure 2. fig. 2. flowchart of ann model analysis for 3 feature extractors. a. td-idf vectorizer td-idf vectorizer is one of the simplest techniques to transform text into numerical values which can be fed to a machine learning model for processing. it statistically computes and finds the relevancy of a word from a document in other documents. it is computed by multiplication of two metrics: how often a word appears in a document and how rare it appears in other documents. td-idf vectorizer has nothing to do with the similarity between words because it is not an embedding. it is very commonly used as feature extractor for various nlp tasks [16, 17]. b. glove embeddings glove embedding is an unsupervised model for word representation in the form of vectors. these embeddings are achieved by mapping words to a meaningful space in which the distance between words is related to their semantic meaning. cosine similarity and euclidean distance are used in glove embeddings to compute the distance between words. glove comes with the advantage that it does not just depend on local context (surrounding) information of words but on the global co-occurrence of words in a given corpus by creating a cooccurrence matrix of words in a given corpus unlike word2vec which relies on local contextual (surrounding) word information. glove embeddings has been used in many text problems [18, 19]. embedding comes in some versions with respect to the size of tokens used. we have used a pre-trained glove model with 6 billion tokens, each of 300-dimensional vector size. c. bert embeddings contextual embeddings [20, 21] differ from static embeddings like word2vec [22] and glove. these embeddings do not just compute the similarity between words which similarity in their semantics, but also they compare the context as well in which the words are used. they are more efficient on contextual problems like sentiment analysis, sentence classification, text summarization, etc.. an interesting thing about bert is that it does not just compute words or token embeddings, but also sentence embeddings to differentiate the sentences and positional embedding of the word in a given sequence. these combined embeddings can clearly help context each word in a given corpus. another interesting thing in the development of the bert model is the use of the concept of masked language modeling. this means that they hid 15% of words and used their positional embeddings to address or infer them to make the learning more effective. as a result, the bert model outperformed all state-of-the-art existing language models even before its convergence. authors in [23] used a bert model with bayesian network to classify text data of people’s livelihood governance. the bert model comes in various versions with respect to the number of layers, heads, hidden units, cased, uncased and for languages other than english. we used the bert base uncased model with 12 layers with 768 hidden units, 12 attention heads which has 110 million learning parameters. iv. classification model and experiments features from the split data into train and test sets were fed to a simple classifier 2-layer feed forward ann model which evaluated each feature extractor (td-idf, glove and bert). the same ann model was used for all 3 feature extractors’ outputs to balance and rationalize the experimental results. a. the artificial neural network a simple ann was selected to classify the news in two classes (fake and real) after getting the features from all 3 feature extractors. the ann contains two hidden dense layers having 8 and 16 neurons respectively with a final output layer with a single neuron as this is a binary classification problem. relu activation function was used in hidden layers and sigmoid in the output layer with adam optimizer to update the leaning weights while training. b. experimental results in this section, the results obtained from the 3 feature extractors are analyzed and compared. accuracy is commonly used as an evaluation metric to analyze performance [24]. figures 3, 4 illustrate the obtained results including accuracy, precision, and auc roc for both datasets. outperforming the td-idf and glove, bert achieved 96% accuracy on the first dataset and 99% accuracy on the second dataset. td-idf achieved 93% on the first dataset and 96% on the second. engineering, technology & applied science research vol. 11, no. 2, 2021, 7001-7005 7004 www.etasr.com ahmed et al.: analysis of text feature extractors using deep learning on fake news in the first dataset, bert outperformed glove and td-idf by 12% and 3% in accuracy. the precisions of bert and tdidf do not differ much but achieved better by 13% than glove. the auc roc scores of td-idf and bert are similar and better than glove. in the second dataset, glove performed better. this time bert outperformed td-idf by 3% as was in first dataset and glove by 7% in accuracy. in precision, bert outperformed glove and td-idf by 7% and 3% respectively, and on the auc roc score, both bert and td-idf achieved 3% higher than glove. the reason because glove performed a bit better in the second dataset (but not better than bert and td-idf), is that the second dataset is 3 times the size of the first dataset as we implemented an ann which requires large datasets to perform better. all feature extractors’ performances are better on the second dataset. the detailed comparisons of all discussed evaluation metrics are given in tables ii and ii. in both datasets, bert performed better than the other feature extractors. td-idf also performed well, but glove embeddings did not because the problem at hand is a contextual one and glove computes static embeddings. surprisingly, td-idf performed far better than glove and reached bert's performance at some stage in the first dataset. there are 3 explanations for this. the first reason for this surprise performance of td-idf is that the word length of the document for glove and bert was fixed. td-idf uses all words in given documents and normally we do not fix the size of td-idf word length in its implementation, but for embeddings a size must be defined. the second reason is that glove and bert might have over fit the data as their vocabulary size is too large. the third reason may be that signal from embeddings is noisy as they have complex architecture in their implementation which can cause the model to learn false information from the given data during training. fig. 3. analysis of feature extractors' performance on the first dataset. fig. 4. analysis of feature extractors' performance on the second dataset. table i. performance evaluation of feature extractors on dataset 1 feature extractor accuracy precision recall f1 score auc roc score auc pr score bert 96.37 94.71 98.27 96.46 99.08 98.71 td-idf 93.68 94.85 92.47 93.65 98.70 98.77 glove 84.21 81.80 87.31 84.47 84.26 87.67 table ii. performance evaluation of feature extractors on dataset 2 feature extractor accuracy precision recall f1 score auc roc score auc pr score bert 99.23 99.14 99.33 99.24 99.97 99.98 td-idf 96.61 96.71 96.57 96.64 99.46 99.48 glove 92.95 92.99 92.94 92.97 92.95 94.73 v. conclusion the easy access of social media to everyone has obvious advantages but also it has some disadvantages, such as the rapid quick spread of fake news. it is a very tedious job to check every news item manually, so, in order to overcome this problem, researchers are developing algorithms to detect fake news automatically. fake news identification is a contextual problem in which the meaning of the same words may be different depending on the context. various feature extractors have been built to efficiently solve this problem. in this paper, we analyzed two publicly available fake news datasets using three different feature extractors: td-idf vectorizer, glove static embeddings, and bert contextual embeddings on the fake news datasets and the outputs were fed to an ann model for classification. it was found experimentally that the bert model outperformed the td-idf and glove in both datasets. td-idf outperformed glove for both datasets and competed well with bert. references [1] t. lima-quintanilha, m. torres-da-silva, and t. lapa, "fake news and its impact on trust in the news. using the portuguese case to establish lines of differentiation," communication & society, vol. 32, no. 3, pp. 17–32, apr. 2019, https://doi.org/10.15581/003.32.3.17-32. engineering, technology & applied science research vol. 11, no. 2, 2021, 7001-7005 7005 www.etasr.com ahmed 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[20] t. wolf et al., "transformers: state-of-the-art natural language processing," in proceedings of the 2020 conference on empirical methods in natural language processing: system demonstrations, online, oct. 2020, pp. 38–45, https://doi.org/10.18653/v1/2020.emnlpdemos.6. [21] m. zaheer et al., "big bird: transformers for longer sequences," arxiv:2007.14062 [cs, stat], jan. 2021, accessed: mar. 19, 2021. [online]. available: http://arxiv.org/abs/2007.14062. [22] t. mikolov, k. chen, g. corrado, and j. dean, "efficient estimation of word representations in vector space," arxiv:1301.3781 [cs], sep. 2013, accessed: mar. 19, 2021. [online]. available: http://arxiv.org/ abs/1301.3781. [23] s. liu, h. tao, and s. feng, "text classification research based on bert model and bayesian network," in 2019 chinese automation congress (cac), hangzhou, china, nov. 2019, pp. 5842–5846, https://doi.org/10.1109/cac48633.2019.8996183. [24] a. hussain, g. ali, f. akhtar, z. h. khand, and a. ali, "design and analysis of news category predictor," engineering, technology & applied science research, vol. 10, no. 5, pp. 6380–6385, oct. 2020, https://doi.org/10.48084/etasr.3825. microsoft word etasr_v11_n3_pp7233-7239 engineering, technology & applied science research vol. 11, no. 3, 2021, 7233-7239 7233 www.etasr.com palconit et al.: resource assessment of tidal stream power in pakiputan strait, davao gulf, philippines resource assessment of tidal stream power in pakiputan strait, davao gulf, philippines eleonor v. palconit school of engineering ateneo de davao university and mindanao renewable energy r&d center davao city, philippines evpalconit@addu.edu.ph josef rene villanueva school of engineering ateneo de davao university and mindanao renewable energy r&d center davao city, philippines jrlvillanueva@addu.edu.ph nelson enano jr. school of engineering ateneo de davao university and mindanao renewable energy r&d center davao city, philippines nhenanojr@addu.edu.ph mario buhali jr. mindanao renewable energy r&d center davao city, philippines mariobuhalijr@gmail.com arby christy mascariñas mindanao renewable energy r&d center davao city, philippines acpmascarinas@addu.edu.ph gabriel earl galope mindanao renewable energy r&d center davao city, philippines gedgalope@addu.edu.ph johna marie tabanguil school of engineering ateneo de davao university and mindanao renewable energy r&d center davao city, philippines johmrtabanguil@addu.edu.ph abstract-during the last years, there are ongoing efforts on the development of tidal energy conversion systems in the philippines. this study conducts tidal energy resource assessment in the pakiputan strait following a methodology outlined as stage 2a tidal resource assessment published by the european marine energy centre (emec). the study assessed the preliminary results of the tidal velocities at pakiputan strait with a mean spring peak velocity (vmsp) of 1.7m/s at 3m from the water surface from 15 days of continuous data collection using a seabed-mounted acoustic doppler current profiler. this corresponded to an estimated annual energy production (aep) of 1350kwh/y for 1m 2 of capture area of the generic device. sensitivity analysis showed that the spatial distribution of hydrodynamic model results does not vary significantly with variations in certain input parameters. it further showed that a 10% decrease in the nominal value of vmsp on-site led to a 15% decrease in the nominal value of aep, while a 10% increase in the nominal value of vmsp led to a 30% increase in the nominal value of aep, assuming that the considered vmsp still corresponded to the velocity distribution from observations. a static survey and the use of computational fluid dynamics modeling are recommended to further enhance the analysis of the study. keywords-tidal energy; ocean renewable energy; resource assessment; davao gulf i. introduction the global interest in renewable energy has increased over the past decade, mainly due to the global mandate to mitigate anthropogenic climate change. one of the renewable energy technologies that are exploited nowadays is ocean energy. the ocean provides a vast source of potential energy that can be captured through tidal, wave, salinity gradient, and ocean thermal energy conversion systems [1]. energy from tidal currents is one of the most promising renewable energies due to the several advantages compared to other renewable energy sources [2]. among its advantages are the high predictability of tidal currents [3], the higher density of seawater (over 800 times that of air) that assures larger potential energy as compared to wind [2], lesser environmental impact compared to tidal barrage facilities [4], and d) the absence of extreme flow velocities that might damage the equipment or complicate its maintenance [4]. the last point mentioned depends on the strong flow profile brought by the local bathymetry near the tec deployment site [5]. with highly predictable tidal current benefits in tidal stream energy conversion, it has a high potential to contribute to the decarbonization of the energy supply and, at the same time, provide energy security [1]. in exploring a potential site for ocean energy extraction, the first consideration is the energy resource assessment [6]. one corresponding author: eleonor v. palconit engineering, technology & applied science research vol. 11, no. 3, 2021, 7233-7239 7234 www.etasr.com palconit et al.: resource assessment of tidal stream power in pakiputan strait, davao gulf, philippines method of identifying potential sites is by analyzing tidal range distributions and resources. this method was particularly followed by the authors in [7] in order to select tidal range sites in east malaysia suitable for power generation. another method is by producing a hydrodynamic model and analyzing its outputs. in the northern part of the gulf of california in mexico, a detailed qualification of the theoretical tidal range energy, performed using level from a depth-averaged barotropic hydrodynamic model and 0-d operation modeling approach was applied to determine the power that can be extracted at four key sites [3]. in [1], delft3d modeling suite was used in assessing the strait of larantuka, indonesia, wherein the flow conditions of the tidal stream were considered for the energy conversion. the bathymetric data have been obtained with the use of a single-beam echo sounder (sbes) and srtm15 plus to have a more accurate determination of the potential energy to be harnessed, and the resource assessment showed that the strait of larantuka in indonesia has a potential for the production of ocean renewable energy with current velocities up to 3-4m/s and average kinetic power densities around 10kw/m 2 [1]. the same modeling suite was also used in [8] along with mike system, to observe the morphological behavior of the nhat le estuary which is located in the northcentral coast of vietnam. numerous numerical modeling methods have been used in many researches in order to understand the hydrodynamic characteristic of the tidal stream energy sites and the current turbine technology. an example of this is the investigation of the tidal induced lagrangian circulation in the north-western coastal waters of brittany, france, including islands, shoals, and straits with strong potential for tidal turbine farm implementation [9]. with the increase of interest in different renewable energy sources, the philippines is now exploring ocean renewable technologies as alternative energy sources that can be implemented in potential areas. the current study aims to assess the tidal stream power in pakiputan strait, davao gulf, philippines and to locate a potential site for the implementation of the tidal energy converter system. the structure of the assessment follows the steps described by the emec, which start from the regional assessment and site selection through the estimation of current speed and spatial distribution using hydrodynamic modeling. the preliminary results of this study show that tidal current velocities above 0.5m/s exist in the identified area. these currents could drive a generic energy harvesting device and occur frequently enough to ensure significant availability of power. ii. background information of the study site a. the philippine oceans and coasts the philippines, is an archipelago with 7,641 islands, with a total coastline stretching at 36,289km [10]. it is bounded by the philippines sea to the east, the celebes or sulawesi sea to the south, the sulu sea to the southwest, the west philippine sea to the west, and the south china sea to the north [11]. it has three major island groups, namely luzon, visayas, and mindanao. the sibuyan sea separates luzon and the visayas. the islands in the visayas are surrounded by the visayan and camotes seas. the bohol sea extends down to the north of mindanao, with several straits connecting the internal and marginal seas to the ocean [10]. the total land area amounts to 298,170km 2 , with a sea area of 1,830km 2 , 6% of which are considered marine protected areas [12]. the population has reached 109,763,425 in 2020, with around 62% living in the coastal areas [12]. it was ranked 83 rd among 221 countries with exclusive economic zones (eez) with an overall ocean health index score of 71 [13]. the national ocean economy contributed us$ 11.9 billion in 2015, amounting to 7% of the gross domestic product (gdp) [12]. some of the key contributors to this belong to coastal and marine tourism (25%), fisheries and aquaculture (20%), manufacturing (19%), and port and shipping (12%) sectors [12]. the country’s coastal and marine habitats include coral reefs (25,060km 2 ), natural mangroves (2,472.68km 2 ), mudflats, and tidal swamps (2,000km 2 ), seagrass (978km 2 ), and planted mangroves (765.14km 2 ) [12]. the blue economy initiatives that the country focuses on are sustainable fisheries and aquaculture, sustainable tourism, sustainable ports, marine renewable energy, marine biotechnology, pollution reduction, and habitat restoration and management [12]. the davao gulf is a 308,000-hectare body of water found in the southeastern part of mindanao [14]. it is one of the richest zones for fish production in the country and is considered as one of the priority conservation areas of the sulusulawesi marine ecoregion. there are currently 19 marine protected areas in the 5 cities and 5 municipalities surrounding the gulf [15]. it is home to a diverse species of cetaceans with at least 15 identified species identified in 2018 [16]. according to the permanent service for mean sea level (psmsl), there is a tide gauge station located at 7.08333°n, 125.633333°e, in the davao gulf. it was considered a revised local reference (rlr) station in 2010. there are two neighboring rlrs in the davao gulf, one in mati, davao oriental and the other in makar, general santos city [17]. aside from being home to diverse marine life, marine traffic is a commonality in the davao gulf. there were usually around 5 to 11 arrivals per day and about the same number of departures from july 22, 2020, to august 19. the majority of the vessels arriving in the port are cargo vessels with several tankers. other ports in the davao gulf include the davao therma south port (6.9621405°n, 125.48615°e), and the davao anchorage port (7.0515755°n, 125.65395°e) [18]. b. oceanographic conditions in the philippine straits dynamics experiment (philex), global ocean models were used to investigate the internal circulation in the philippine archipelago, both spatially and temporally. however, realistic modeling was difficult for a global model due to the numerous straits and small interior seas [19]. in general, the bathymetry of the philippine waters between islands is highly complicated, consisting of narrow shelves, steep slopes, and deep basins connected by shallow sills. ocean circulation is highly influenced by the bathymetry, the seasonally reversing northeast monsoon, locally known as amihan, and southwest monsoon, locally known as habagat, and the tidal and nontidal circulation between the south china sea and the western pacific [20]. in addition to the reversing engineering, technology & applied science research vol. 11, no. 3, 2021, 7233-7239 7235 www.etasr.com palconit et al.: resource assessment of tidal stream power in pakiputan strait, davao gulf, philippines winds, the monsoon brings a change in the rainfall pattern, which affects the surface layer thermohaline seasonal stratification [21]. the amihan brings less rainfall while the habagat more. comparing actual rainfall for a specific year to the average annual cycle, however, reveals precipitation anomalies, which may affect the surface layer thermohaline stratification [21]. this can be further complicated due to the interannual el niño or la niña phenomena [21]. numerous factors make the analysis of the circulation within the philippines challenging. however, with further studies, a better understanding of these dynamics can be achieved. c. ocean energy potential the philippines’ department of energy (doe) estimates the theoretical ocean energy potential of the country to about 170gw, which was based on an assessment done by the mindanao state university – iligan institute of technology (msu-iit) [22]. since then, several studies have been conducted in line with ocean energy resource assessment in the country. one such study reviews the ocean energy status in southeast asia [23]. it focuses not only on the potential resource but also the enabling and hindering factors, particularly in government initiatives that affect its development. in the study, a map of the potential sites for tidal in-stream energy, wave energy, and ocean thermal energy conversion (otec) in the philippines was presented. for tidalinstream energy, four sites were identified, namely the luzon strait, san bernardino strait, surigao strait, and basilan strait. in its national renewable energy program (nrep), which started implementing in 2011, the philippines’ doe has targeted to increase the country’s renewable energy capacity to an estimated 15,304mw by 2030. this included an ocean energy share of 70.5mw, with a target of achieving the country’s first ocean energy facility, a 10mw pilot ocean thermal energy conversion plant in cabangan, zambales, in 2018 [24, 25]. however, in 2019, the doe moved to update its target after falling short of its original goals. instead, it has focused on increasing the share of renewables in the total generation, instead of capacity, with a targeted 20,000mw installed capacity by 2040 [25, 26]. there are 8 awarded ocean projects by the doe as of june 30, 2020, as presented in table i. all the projects, however, are still in the pre-development stage, with 3 projects that have to determine their target capacity. the total capacity of the projects amounts to 26.00mw [27]. it is worth noting that 7 of these awarded projects involve tidal in-stream energy technology. this is a testament to its commercial readiness and maturity in terms of research and development. iii. methodology and apllication a. methodology the process flow diagram of the methodology for the prefeasibility assessment is shown in figure 1. the inputs for the hydrodynamic model, such as bathymetry and grid resolution, are mainly based on the area of interest. a desktop was conducted to identify the potential sites in davao gulf. the area of interest was narrowed down into pakiputan strait with a two-day transect survey. table i. awarded ocean energy projects by the doe as of june 30, 2020 region location technology developer type of contract total capacity (mw) iii cabangan, zambales otec bell pirie power corp. predevelop ment 5.00 v san bernardino strait, matnog, sorsogon tise h&wb corp. predevelop ment 5.00 viii northwest capul, northern samar tise oceantera energy corp. predevelop ment tbd san bernardino strait, between bicol peninsula and samar leyte corridor, area 2op tise h&wb corp. predevelop ment 5.00 capul pass, dalupiri island, san antonio, northern samar, tisecproject site (area 6) tise poseidon renewable energy corp. predevelop ment tbd san bernardino strait and northern samar, tisecproject site (area 4&5) tise poseidon renewable energy corp. predevelop ment tbd san bernardino strait, between bicol peninsula and samar leyte corridor, area 3op tise h&wb corp. predevelop ment 5.00 xiii gaboc channel, surigao del norte tise adnama power resources corp. predevelop ment 6.00 engineering, technology & applied science research vol. 11, no. 3, 2021, 7233-7239 7236 www.etasr.com palconit et al.: resource assessment of tidal stream power in pakiputan strait, davao gulf, philippines the surface and depth-averaged velocities, along with their gps coordinates, obtained from the transect survey were postprocessed to identify potential locations for a tidal turbine. bathymetry data were collected. continuous on-site data collection of tidal currents was also carried out to collect empirical data as inputs for a harmonic analysis. the bathymetry data and the results of the harmonic analysis were used as inputs to the hydrodynamic modeling. finally, a forecast estimate of the mean electrical power and annual energy production was determined from the collected tidal current data. fig. 1. methodology flow diagram. b. site selection this research closely follows the methodology of site definition and selection described in assessment of tidal energy resource, a document prepared in consultation with the european marine energy centre ltd (emec) and with other interested parties in the uk marine energy community [6]. the site selection methodology used in the study was the stage 2a, which is the first stage of the pre-feasibility of the tidal resource assessment [6]. the determined region was davao gulf. the channel considered was pakiputan strait in the northern part of the gulf, with the aim of selecting a localized area for the tidal energy converter implementation. c. estimation of current speeds the modeling suite used in the hydrodynamic modeling was delft3d [28]. other inputs, such as the grid, land boundary file, and enclosure, were also generated from the modules included in delft3d. rectangular structured grids were used to coincide with the given grid resolution for each stage of the resource assessment. for stages 1 and 2a, the grid resolutions should be less than 5km and 500m, respectively [6]. as shown in figures 2, 3, the model has a grid resolution of 1km for the regional assessment (stage 1) and a grid resolution of 100m for the pre-feasibility assessment (stage 2a). in stage 2a, the area of interest was narrowed down into a channel. the bathymetry data were acquired from the french research institute for exploitation of the sea (ifremer) [29-31] and the general bathymetric chart of the oceans (gebco) [32]. the raw bathymetric data were processed with delft 3d as shown in figures 4-5. the bathymetric data from the 2020 gridded bathymetry of gebco have soundings with spacing of approximately 450m. however, the soundings for ifremer bathymetric data were not specified in the obtained raw data. as for the harmonic analysis, 15 tidal constituents (o1, k1, p1, n2, nu2, m2, l2, s2, k2, mk3, m4, s4, m6, s6, and m8) were extracted from the empirical tidal velocity data that were continuously collected on site for 15 days. the amplitudes and phases of these tidal constituents were used in the tidal forcing needed by the model. aside from the open boundary, physical parameters and flow conditions were also added. parameters such as salinity, temperature, and other meteorological inputs were not yet considered in the simulation of the model. observation points were added in the model to check the modeled tidal currents in specific areas. fig. 2. davao gulf 1km grid resolution. fig. 3. pakiputan strait 100m grid resolution. fig. 4. bathymetric data for davao gulf. fig. 5. bathymetry for pakiputan strait. desktop study data collection harmonic analysis hydrodynamic modelling engineering, technology & applied science research vol. 11, no. 3, 2021, 7233-7239 7237 www.etasr.com palconit et al.: resource assessment of tidal stream power in pakiputan strait, davao gulf, philippines several simulations were made, as a part of the sensitivity analysis, with varied inputs. it was found out that nonastronomical attribute files have a significant influence on the output of the model. three simulations showed more realistic results. from these three simulations, it was determined, using their respective east vs. north graphs (see figure 6), that the current in pakiputan strait is reversing. this was also evident in the results of the harmonic analysis for the eccentricity of all the harmonic constituents that are almost equal to 1. fig. 6. east vs. north components (m/s). the potential sites from the spatial variation of the depthaveraged velocities, as shown in figure 7, were similar to those that can be identified from the desktop study. however, though the spatial variation gave similar sites to those from the desktop study, the current velocities from the model did not show a positive linear relationship with the actual current velocities obtained from the 15-day data collection. hence, to improve the model performance and outputs, the grid, location of the open boundary, tidal forcing, and other parameters of the model must be reviewed. in the new model, the number of layers will be increased to generate predicted surface velocities and not just depth-averaged velocities. the new hydrodynamic model will then be validated using in-situ measurements. fig. 7. spatial variation for depth-averaged velocities. d. energy yield an estimate of the mean electrical power and annual energy production from tidal in-stream energy was obtained simulating a generic device, as described in [6]. a generic device was used for the study since no device had yet been tested. the available power ������ for every vertical bin i across the depth of the water is given by: ������ � 0.5�� � � (1) where � is the density of seawater, assumed constant for simplicity at 1025kg/m 3 , � is the capture area of the device, assumed to be 1m 2 (bin size), and � � is the tidal stream velocity at the bin. combining this with the rotor efficiency ��, the electrical power per bin �� �� is given by: �� �� � ������ ∙ �� (2) for a generic device, �� was considered to rise from 38% at cut-in speed to reach 45% at the rated velocity. the rated velocity was taken as 71% of the mean spring peak velocity ���� at the hub height. the vmsp is defined in [6] as the peak velocity that has been reached for 10min during the whole month from the results of a static field survey, model, or harmonic analysis. from the results of a static field survey conducted during february 2020 to collect empirical data for harmonic analysis, the vmsp was estimated to be at 1.7m/s at a hub height of 3m below the water surface (i.e. vmsp = �). the data set was comprised of velocity data collected at 1min intervals for each 1m vertical bin across the depth continuously over a 15-day period on the same site. this vmsp of 1.7m/s was significantly higher compared to that which had been determined from an earlier transect survey using a boatmounted acoustic doppler current profiler (adcp) on the same site conducted in august 2019, generating a value of 1.5m/s. hence, the rated velocity for the generic device was determined as 0.71×1.7 ≈ 1.2m/s. the cut-in speed (the minimum velocity required for device operation) was assumed constant at 0.5m/s. this assumption greatly simplified the analysis without imposing significant limitations on the accuracy, since the available energy from tidal currents at speeds below 0.5m/s is usually less than 5% of the total available energy. a velocity distribution �� �� is also defined to be derived from the tidal harmonic analysis [6]. the data set from the 15-day data collection was instead used to develop �� �� . as part of the preliminary results, this distribution was assumed to represent an annual distribution. the chart in figure 8 displays the energy yield from a generic device, showing ������, �� ��, and �� ��. fig. 8. velocity distribution and estimated power from the site. engineering, technology & applied science research vol. 11, no. 3, 2021, 7233-7239 7238 www.etasr.com palconit et al.: resource assessment of tidal stream power in pakiputan strait, davao gulf, philippines the mean annual electrical power ����� was obtained by combining the velocity distribution �� �� with the average absorbed power for each velocity bin �� �� by using (3): ����� � ∑ �� �� ∙ �� �� �� ��� (3) the number of vertical bins � considered was only one (i.e. the 1m vertical bin at 3m below the water surface). after taking the summation, ����� was determined to be at 0.154kw for 1m 2 of the capture area. e. sensitivity analysis performing sensitivity analysis on the hydrodynamic model showed that varying the input parameters to the model resulted in a visually similar spatial distribution of the currents in pakiputan strait. figure 9 illustrates several results from these variations. certain inputs to the model, particularly the tidal constituents and the bathymetry data, were kept constant during the sensitivity analysis. fig. 9. the hydrodynamic model spatial results did not vary significantly with varying input parameters. due to the inherent dependence of the nominal value of energy and power to the cube of the nominal value of tidal velocities, as shown in (1), it was reasonable to expect significant variations of power corresponding to any changes in observed velocity values. fig. 10. aep varied significantly with varying vmsp. sensitivity analysis (figure 10) showed that a 10% decrease in the nominal value of the vmsp on site will lead to a 15% decrease in the nominal value of the aep. this observation was also true for every 10% decrease up to 30%. on the other hand, a 10% increase in the nominal value of the vmsp on site led to a 30% increase in the nominal value of aep. checking for sensitivity beyond a 20% increase in the nominal value of the vmsp was not realistic because the velocity distribution shows no instances of such velocities occurring. this analysis assumed that the considered vmsp still corresponded to the velocity distribution derived from observations. iv. conclusion based on preliminary results, pakiputan strait is a candidate site for the deployment of a tidal energy conversion system. from the results of a static field survey conducted during february 2020 and the collected empirical data for harmonic analysis, the vmsp was to be at 1.7m/s at a hub height of 3m below the water surface (i.e. vmsp = �). the data set was comprised of velocity data collected at 1min intervals for each 1m vertical bin across the depth continuously over a 15-day period on the same site. the velocities from modeled and empirical data show that tidal power from a generic device will be potentially available for the 60% of the time. the results of the study are not yet conclusive and could be improved by the collection of more data and conducting a field survey as a validation step. much motivation could be derived from the preliminary results, as it responds to technological questions by showing tidal velocities that can run a generic device. similarly, it beckons the need to design devices suitable to harness the resource given in this site. additional sections of the channel could be used as generation sites once the identification of constraints is completed at the end of the resource assessment and during its further stages. acknowledgment the ocean renewable energy (ore) project of mrec is made possible by the generous funding of the philippine department of science and technology philippine council for industry, energy, and emerging technology (dostpcieerd) and also of the university research council of the ateneo de davao university. much of this research has been the output of the first year of the project. the authors would like to thank dr. michael abundo and weslie capute of the ocean pixel ltd for the technical assistance during the conduct of the tidal current survey in the pakiputan strait, davao gulf, and its project staff, namely janice ivy jumao, vince peter cortez, and hazel dioso. references [1] k. orhan and r. mayerle, "assessment of the tidal stream power potential and impacts of tidal current turbines in the strait of larantuka, indonesia," energy procedia, vol. 125, pp. 230–239, sep. 2017, https://doi.org/10.1016/j.egypro.2017.08.199. 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[32] "gebco_2020 grid," gebco. https://www.gebco.net/data_and_ products/gridded_bathymetry_data/gebco_2020.html (accessed may 13, 2021). engineering, technology & applied science research vol. 8, no. 2, 2018, 2785-2789 2785 www.etasr.com bhatti et al.: ground water quality assessment of daur taluka, shaheed benazir abad ground water quality assessment of daur taluka, shaheed benazir abad nadeem-ul-karim bhatti department of civi engineering quaid-e-awam university of engineering, science & technology larkana, pakistan knadeem_b@quest.edu.pk salem raza samo department of energy & environment quaid-e-awam university of engineering, science & technology nawabshah, pakistan sfaizsamo@yahoo.com abdullah saand department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan abdullah@quest.edu.pk manthar ali keerio department of civil engineering quaid-e-awam university of engineering, science & technology larkana, pakistan mantharali99@quest.edu.pk ahsan ali bhuriro department of civil engineering quaid-e-awam university of engineering, science & technology larkana, pakistan ahsanone@gmail.com abstract—the aim of this study was to assess the ground water quality of daur taluka of district shaheed benazir abad for drinking purposes. forty groundwater samples were collected from different locations and brought to pakistan council of research in water resources (pcrwr) for analyzing various groundwater physical, chemical and biological parameters. the results of this study revealed that color, ph, magnesium, alkalinity and nitrate of all samples were found within the permissible limits of world health organization (who). analytical results revealed that the percentage of samples that were beyond who standards was 15% regarding taste, 42.5% regarding tds, 20% regarding chlorine, 12.5% regarding sulfate 12.5 regarding sodium and 32.5% regarding hardness. microbiological contamination was found positive in the 25% of samples. the findings of this study revealed that the most (82.5%) of the samples of the study area belong to the category of hard to very hard water and their nature were alkaline. keywords-water quality parameters; arsenic; taluka daur; shaheed benazir abad; who standards i. introduction water is one of the most important ecosystem and climate components. water quantity and quality determine the biodiversity of an ecosystem. water quantity and quality is not distributed evenly in the world [1, 2]. safe drinking water is not only a fundamental requirement of all living organisms but also an indispensable human right [3, 4]. insufficient availability of fresh water coerces people to use ground water for meeting their needs. about 70% of pakistan households use ground water for domestic purposes [5 ,6]. water also becomes a vital source of increasing demand for agriculture and industry [7]. the quality of ground water in sindh region is worsening due to overuse of fresh water layer. sindh is an arid region, so ground water is recharged only during flooding time along the water channel sides [8, 9]. about 78% of sindh province has saline ground water whose salinity varies and at maximum is 9ds/m [7, 10]. the groundwater is polluted due to various natural and anthropogenic factors. the disposal of untreated effluents from industries and household sewage, seepage of fertilizers and land degradation are the main sources of groundwater pollution [11-14]. the quality of ground water of sindh urban and suburban areas is very poor and chemically and bacteriologically not fit for drinking purposes [15]. the consumption of contaminated water causes various diseases [16]. about 98% of the households of shaheed benazir abad are using ground water [17]. the aim of this study is to assess the ground water quality of four sites of taluka daur of shaheed benazir abad for drinking purposes. ii. methodology forty groundwater samples were collected from different locations of four union councils of taluka daur (daur, bandhi, jam sahib and bucheri) of district shaheed benazir abad. ten water samples have been taken from each union council. sterilized plastic bottles were used for collecting the samples which were washed with distilled water twice prior to sampling. the samples were collected by using standard methods suggested in [18, 19]. the collected water samples were brought to pakistan council of research in water resources (pcrwr) regional laboratory for analyzing regarding the following selected physical and chemical groundwater parameters (methods of analysis and concerned instruments employed for each water quality parameter are summarized in table i). engineering, technology & applied science research vol. 8, no. 2, 2018, 2785-2789 2786 www.etasr.com bhatti et al.: ground water quality assessment of daur taluka, shaheed benazir abad a. physical water parameters under study these parameters of water are turbidity, electrical conductivity, ph, taste and color. b. chemical water parameters under study these parameters were bicarbonate (hco3), chlorine (cl), sulfate (so4), hardness, calcium (ca), magnesium (mg), sodium (na), potassium (k), alkalinity (caco3), total dissolved solids (tds) and nitrate (no3). c. biological water aspects under study presence-absence test kit was used to evaluate the water samples for microbiological contamination. american public health association's guidelines were followed for examining the water samples and calibrating the equipment and instruments [20]. table i. water quality parameters and methods of analysis s. no. water quality parameter method of analysis 1 tds 2540c, standard method (1992) 2 conductivity (µs/cm) e.c. meter, syber scan con 11 singapore 3 ph jenco handheld ph meter, model 6230n 4 color (tcu) sensory test 5 taste sensory test 6 bicarbonate (mg/l) 2320, standard method (1992) 7 chloride(mg/l) titration standard method (1992) 8 sulfate spectrophotometer optizen 2120uv plus korea 9 hardness (mg/l) edta titration standard method (1992) 10 calcium (mg/l) 3500-ca-d, standard method (1992) 11 magnesium (mg/l) 234-c, standard method (1992) 12 sodium (mg/l) flame photometer italy 13 potassium flame photometer 14 alkalinity 2320, standard method (1992) 15 turbidity turbidity meter lovibond pc check kit germany 16 nitrate colorimeter, hachdr2800, usa 17 b.c presence /absence test kit statistical methods were used to find the minimum, maximum, mean and range of all water quality parameters. the results were compared and evaluated with the help of who guidelines for physical and chemical water characteristics. iii. results and discussion a. color pure water is usually considered as colorless but it actually possesses a slightly blue hue. the sources of color in ground water are natural and anthropogenic. the particular geological formation or some metallic species of the region or seepage of effluent impact the groundwater color. who set the 15 tcu limit for the color of drinking water. all samples were aesthetically good and clear. b. taste and odor the taste and odor of 34 samples are non-objectionable. only 6 samples possessed objectionable taste. c. tds tds level is a good indicator of taste. less than 300mg/l is excellent, in the range between 300 and 600mg/l is good, from 600 to 900mg/l is fair, between 900 and 1200mg/l is poor and greater than 1200mg/l is not acceptable [19]. the upper limit of tds of drinking water should be 1000mg/l according to who standards. figure 1 shows the results of tds for all samples. results indicate that the tds of 23 (57.5%) samples is within the permissible limits. the range of tds of the entire samples was 100-3290mg/l and the average value was 1273mg/l. further analysis showed that 3 samples were excellent, 7 were good, 5 were fair and 7 were poor in taste while the remaining samples were not acceptable. fig. 1. comparison of results of tds of the entire samples d. electrical conductivity (ec) no guide line value has been given by who and usepa for ec. the range of ec of all 40 samples was found as 3895140μs/cm and the average value was 2103.7μs/cm. e. ph ph is a very important water quality parameter which describes its acidic or alkaline nature. drinking water ph should range from 6.5 to 8.5 according to who standards. results show that the ph of all samples is within permissible limits. the range of ph of all samples was 6.7-7.6 and the average value was 7.2. the ph values of 8 samples were below 7 and the values of the remaining samples were greater than 7. this shows that the nature of most of the ground water in the study area is alkaline. f. bicarbonate bicarbonate is the main anion in ground water. it derives from co2 released as a consequence of organic decay in the soil. no guide line value of bicarbonate (hco3) has been given by who. the range of hco3 of all tested 40 samples was 60680mg/l and the average value was 295.25mg/l. engineering, technology & applied science research vol. 8, no. 2, 2018, 2785-2789 2787 www.etasr.com bhatti et al.: ground water quality assessment of daur taluka, shaheed benazir abad g. chlorine (cl) there are the various cl sources in groundwater. these sources are leaching from mineral rock or soil, seepage of domestic and industrial effluent, sea water intrusion etc. [21]. ground water shows higher cl concentration compared to surface water. cl is essential for metabolic activity and other physiological processes of human body but excess concentration of cl is also detrimental [5]. the highest desirable limit of chloride in drinking water is accredited as 250mg/l by who. results of cl concentration for all study area samples are shown in figure 2 fig. 2. comparison of results of cl of all samples figure 2 indicates that the cl concentration of 32 samples is within the limit given by who while 20% of the samples are exceeding it. water containing cl in concentration greater than 250mg/l has salty taste. the range of cl of all the samples was 25-437mg/l and the average value was 172.47mg/l. h. sulfate (so4) laxative effect is associated with water ingestion containing elevated sulfate level [22]. the highest desirable limit of sulfate is acknowledged as 250mg/l in drinking water by who. figure 3 shows the results of sulfate (so4) concentration in the study area samples. fig. 3. comparison of results of so4 of all 40 samples results exhibit that the sulfate (so4) concentration of 35 samples is within the maximum permissible limit specified by who. the sulfate concentration of 12.5% of the samples is above the permissible limit while the sulfate concentration of 10 samples was lower than the desirable limit of 50mg/l. the range so4 of the samples was 20-302mg/l and the average value was 115mg/l. i. magnesium(mg) mg is one of the important minerals of water and is very essential for human health. the content of mg in water is used to determine the quality of water for various purposes [5]. who has specified 150mg/l of mg for drinking water. mg concentrations of all samples are within the maximum permissible limit. the magnesium content varied from 10 to 121mg/l and the average value was 50.65mg/l. j. calcium (ca) calcium is one of the most significant minerals of water which is indispensable for bones, teeth and cell physiology. excess calcium consumption is very detrimental for human health [5]. who has not set any guide line value of ca for drinking water. the range of ca of all samples was 16-160mg/l and the average value was 71.5mg/l. k. hardness water hardness is a very important parameter determining its potential use. various minerals are dissolved in water impacting its hardness. water hardness is often calculated as calcium carbonate concentration. it should be 500mg/l in drinking water according to who. drinking water has been classified on the basis of hardness as follows: soft :between 0 and 75mg/l, moderately hard: between 75 and 150mg/l, hard: between 150 and 300mg/l and very hard: greater than 300mg/l [21]. the results of degree of hardness are shown in figure 4. fig. 4. comparison of results of hardness of all 40 samples results indicate that the hardness of 27 samples is within the permissible limit, while 32.5% of the samples have hardness above the permissible who limit. the range of hardness of all 40 tested samples was 11-900mg/l and the engineering, technology & applied science research vol. 8, no. 2, 2018, 2785-2789 2788 www.etasr.com bhatti et al.: ground water quality assessment of daur taluka, shaheed benazir abad average value was 384.27mg/l. only one groundwater sample was soft according to the above criteria. while 6 samples were moderately hard, 14 samples belonged to hard and the remaining 19 samples comprised very hard water. the analytical result shows that 82.5% of ground water samples of the study area fall in the category of hard to very hard water. elevated level of water hardness creates heart and kidney problems [23]. l. sodium (na) sodium is one of the most common water metallic elements. proper quantity of na is very essential for the human body. elevated na level imparts its flavor to water and can be harmful for human health [24]. its concentration should be 200mg/l in drinking water according to who. the results of na concentration are shown in figure 5. fig. 5. comparison of results of na of all samples results indicate that the sodium concentration of 35 samples was found within the permissible limit given by who the remaining 12.5% of the samples possessed higher na concentration. the range of na concentration of all samples was 14-301mg/l and the average value was 115.32 mg/l. m. potassium (k) potassium is an alkali element. it is very essential for all living organisms, it is particularly found in cell tissues and helps in hydration [25]. who has not specified a permissible value of k. however european commission set 12mg/l in water for drinking purpose. the results of k of all samples are shown in figure 6. results indicate that k concentrations of 39 samples are within the permissible limit given by ec and only 1 sample is beyond it. the range of k of all samples was 113mg/l and the average value was as 4.61mg/l. n. alkalinity alkalinity is the presence of different components in water which make it alkaline. alkalinity elevated level may create various health problems. no guide line value of alkalinity has been given by who. the range of alkalinity of the samples was 1.2-13.6m.mol/1 and the average value was calculated as 5.96m.mol/1. fig. 6. comparison of results of potassium of all samples o. nitrate (no3) nitrate is an inorganic and water soluble compound derived from nitrogen and essential for plant life. the natural source of nitrate in groundwater is the atmosphere through the nitrogen cycle. anthropogenic sources are leaching from industrial effluent, agricultural chemicals and sewage [26]. the consumption of groundwater having elevated level of nitrate may cause diabetes, thyroid disease, gastric cancer and methemoglobinemia [27]. who set the maximum permissible limit of nitrate as 10mg/l in drinking water. the results show that nitrate levels of all samples are within this limit. the range of nitrate of the samples was 0.25-2.7mg/l and the average value was 1.27mg/l. p. microbiological contamination the microbial contamination of groundwater is a severe cause of health concern. dysentery, diarrhea, cholera, typhoid and polio are diseases which can be transmitted through contaminated water. the main sources of microbial contamination of water are human or animal feces and agricultural activity [27, 28]. presence-absence test kit was used to evaluate the ground water samples for microbiological contamination. the results indicate that 75% of samples were free from microbiological contamination while 25% of samples showed positive results. iv. conclusions results of this study revealed that 82.5% of groundwater samples of the study area belong to the category of hard to very hard water and the most (82.5%) of the samples are alkaline in nature. color, ph, magnesium, alkalinity and nitrate of all the samples are found within the permissible limits of who. the analytical results revealed that the percentage of samples beyond permissible limits, regarding the tested parameters were taste (15%), tds (42.5%), cl (20%), sulfate (12.5%), na (12.5%) and hardness (32.5%). the microbiological contamination of 25% of the samples was found positive. engineering, technology & applied science research vol. 8, no. 2, 2018, 2785-2789 2789 www.etasr.com bhatti et al.: ground water quality assessment of daur taluka, shaheed benazir abad groundwater with parameters beyond permissible limits should not be used for drinking purpose. references [1] h. annapoorna, m. r. janardhana, “assessment of groundwater quality for drinking purpose in rural areas surrounding a defunct copper mine”, aquatic procedia, vol. 4, pp. 685-692, 2015 [2] k. m anwar, v. aggarwal, “analysis of groundwater quality of aligarh city, (india): using water quality index”, current world environment, vol. 9, no. 3, pp. 851-857, 2014 [3] r. b. jackson, s. r. carpenter, c.n. dahm, d. m. mcknight, r. j. naiman, s. l. postel, s. w. running, “water in a changing world”, ecological applications, vol. 11, no. 4, pp. 1027-1045, 2001 [4] n. bhatti, s. r. samo, m. a. keerio, a. q. jakhrani, n. z. shar, “assessment of ground water quality of taluka kazi ahmed district shaheed benzirabad”, engineering science and technology international research journal, vol. 1, no. 2, pp. 64-74, 2017 [5] m. mohsin, s. safdar, f. asghar, f jamal, “assessment of drinking water quality and its impact on residents health in bahawalpur city”, international journal of humanities and social science, vol. 3, no. 15, pp. 114-28, 2013 [6] a. azizullah, m. n. k. khattak, p. richter, d. p. hader, “water pollution in pakistan and its impact on public health—a review”, environment international, vol. 37, no. 2, pp. 479-497, 2011 [7] a. s. qureshi, p. g. mccornick, a. sarwar, b. r. sharma, “challenges and prospects of sustainable groundwater management in the indus basin, pakistan”, water resources management, vol. 24, no. 8, pp. 1551-1569, 2010 [8] m. y. khuhawar, s. a. majidano, “an investigation of quality of groundwater of taluka nawabshah”, pakistan journal of chemistry, vol. 1, no. 1, pp. 65-71, 2011 [9] a. s. qureshi, p. g. mccornick, m. qadir, z. aslam, “managing salinity and waterlogging in the indus basin of pakistan”, agricultural water management, vol. 95, no. 1, pp. 1-10, 2008 [10] a. s. qureshi, m. a. gill, a. sarwar, “sustainable groundwater management in pakistan: challenges and opportunities”, irrigation and drainage, vol. 59, no. 2, pp. 107-116, 2010 [11] m. a. malik, m. azam, a. saboor, water quality status of upper kpk and northern areas of pakistan, pakistan council of research in water resources (pcrwr), water resources research centre, 2010 [12] r. ullah, r. n. malik, a. qadir, “assessment of groundwater contamination in an industrial city, sialkot, pakistan”, african journal of environmental science and technology, vol. 3, no. 12, pp. 429-446, 2009 [13] a. q. jakhrani, s. r. samo, i. nizamani, “impact of wastewater effluents on physico-chemical properties of groundwater”, sindh university research journal-surj (science series), vol. 41, no. 1, pp. 75-82, 2009 [14] w. m. daudpota, n. u. n. memon, t. f. miano, “determination of ground water quality for agriculture and drinking purpose in sindh, pakistan. (a case study)”, science international, vol. 28, no. 1, pp. 701704, 2016 [15] m. a. a. beg, status of safe drinking water in sindh, sindh ombudsman’s secretariat, shahrah-e-kamal ataturk, 2002 [16] m. memon, m. s. soomro, m. s. akhtar, k. s. memon, “drinking water quality assessment in southern sindh (pakistan)”, environmental monitoring and assessment, vol. 177, no. 1, pp. 39-50, 2011 [17] pakistan bureau of statistics, pakistan social and living standards measurements survey (2014-15), statistics division islamabad pakistan, 2016 [18] j. bartram, r. ballance, water quality monitoring: a practical guide to the design and implementation of freshwater quality studies and monitoring programmes, crc press, 1996 [19] world health organization, guidelines for drinking water quality, surveillance and control of community supplies, vol. 3, who, 1997 [20] a. d. eaton, l. s. cleceri, e. w. rice, a. e.greenberg, (eds), standard methods for the examination of water and wastewater, american public health association, 2005 [21] s. s. prasanth, n. s. magesh, k. v. jitheshlal, n.chandrasekar, k. gangadhar, “evaluation of groundwater quality and its suitability for drinking and agricultural use in the coastal stretch of alappuzha district, kerala, india”, applied water science, vol. 2, no. 3, pp. 165-175, 2012 [22] united states enviromental protection agency, drinking water advisory: consumer acceptability advice and health effects analysis on sulfate, 2003 [23] s. m. sadat-noori, k. ebrahimi, a. m. liaghat, “groundwater quality assessment using the water quality index and gis in saveh nobaran aquifer, iran”, environmental earth sciences, vol. 71, no. 9, pp. 38273843, 2014 [24] a. j. kandhro, a. m. rind, a. a. mastoi, k. f. almani, s. meghwar, m. a. laghari, m. s. rajpout, “physico-chemical assessment of surface and ground water for drinking purpose in nawabshah city, sindh, pakistan”, american journal of environmental protection,vol. 4, no. 1, pp. 62-69, 2015 [25] w. orzepkowski, k. pulikowski, “magnesium, calcium, potassium and sodium content in groundwater and surface water in arable lands in the commune gmina of katy wroclawskie”, journal of elementology, vol. 13, no. 4, pp. 605-614, 2008 [26] h. t. basavarajappa, m. c. manjunatha, “groundwater quality analysis in precambrian rocks of chitradurga district, karnataka, india using geo-informatics technique”, aquatic procedia, vol. 4, pp. 1354-1365, 2015 [27] j. p. s. cabral, “water microbiology. bacterial pathogens and water”, international journal of environmental research and public health, vol. 7, no. 10, pp. 3657–3703, 2010 [28] p. k. pandey, p. h. kass, m. l. soupir, s. biswas, v. p. singh, “contamination of water resources by pathogenic bacteria”, amb express, vol. 4, no. 1, p. 51, 2014 microsoft word 31-2413_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3646-3651 3646 www.etasr.com chung: retaining of frequency in micro-grid with wind turbine and diesel generator retaining of frequency in micro-grid with wind turbine and diesel generator phan dinh chung faculty of electrical engineering, the university of danang-university of science and technology, danang, vietnam pdchung@dut.udn.vn abstract—this paper aims to compare the performance of frequency regulation with two control modes of controller including power control scheme and rotor speed control scheme. the frequency control in this research is based on the frequency droop control method but fuzzy logic is used to define the frequency droop coefficient. to compare the performance of these control modes, a simulation of a micro-grid with the existence of a group of doubly fed induction generator wind turbine system and a diesel generator is fulfilled in matlab/simulink. simulation results indicated that the frequency in the micro-grid with two control schemes always remains in the operation range. with the power control scheme, the frequency in the micro-grid is smoother than that with the rotor speed control. additionally, dfig wind turbine with the power control scheme has a better performance in terms of electrical energy when compared to the rotor speed control scheme, and hence the cost of fuel used by diesel is less costly. keywords-wind generation; frequency control; doubly-fed induction generator (dfig); wind-diesel hybrid power system; micro-grid i. introduction clean and renewable energy sources such as wind energy, solar energy, geothermal energy, etc. are abundant. these sources have been utilized to replace fossil energy sources which have negative impacts on the environment. recently, the electricity production from these sources has been prospective, especially from the wind source. according to [1] around 540gw of wind turbine capacity has been installed. depending on the wind farm capacity, a wind farm can be integrated to a power system through transmission grid or distribution grid [2, 3]. it cannot be denied that electricity generation from wind energy has a positive effect to the environment. however, the integration of wind farms to a power grid brings issues concerning power quality [2] due to the natural fluctuation of wind speed, especially in weak grids [4]. many researches aimed to mitigate the wind farm’s impacts on the connected grid. a simple solution is to install an energy storage system such as battery, super capacitor, super inductor, fly-wheel, pump-reservoir system, etc., to stabilize the power output of the wind turbine-generator system [5, 6]. these schemes have good performance, however, the storage system in general is still quite expensive and has low life expectancy so it may face problems in real life applications. for a weak power grid without a battery energy storage system, some methods to support the frequency adjustment were proposed in [2, 7-10]. generally, reference power is defined by two components. the first component is a deloaded power calculated from wind speed signal and a deloaded power coefficient. the second component is power contribution by frequency sensitive supplementary control. for the second component, many schemes were used. in [9], a fuzzy-based control is employed to determine it directly. in [2, 7, 8], the droop control method with a constant droop coefficient is used. in [9], authors used a combination of droop control and inertia control but the droop coefficient is defined by a fuzzy-based control and in [10], authors used wind speed as an input signal of the fuzzy logic control. in terms of control objective applying to wind turbine, there are two familiar control objectives: power control and rotor speed control [11]. in [11], authors indicated that with the rotor speed control, the wind turbine has a better performance than that with the power control. regarding wind turbine supporting frequency adjustment, wind turbine with the power control was studied in [12, 13] while the wind turbine with the rotor control was studied in [14]. however, the performance of these two control schemes in the frequency control has not yet been compared. in this paper, the performances of frequency regulation method with two control modes of controller, power control and rotor speed control, are compared. the frequency control scheme in this research is developed from the frequency droop control method but a fuzzy logic rule is used to define the frequency droop coefficient. the wind turbine with power control will be compared to the one with rotor control by simulating a micro-grid with the existence of a group of doubly fed induction generators wind turbine system and a diesel generator. the current research consists of two contributions. the first contribution is the method to define the reference power/rotor speed. to determine the reference power/rotor speed, a wind speed sensor is not required. the second one is a comparison of the two control modes of the wind turbine when it participates in the frequency adjustment. the saturation of the magnetic core in equipment, the delay of measurement signal, and the measurement noise are neglected. engineering, technology & applied science research vol. 8, no. 6, 2018, 3646-3651 3647 www.etasr.com chung: retaining of frequency in micro-grid with wind turbine and diesel generator ii. micro-grid micro-grid in this research is supposed to have the form of figure 1. this micro-grid is normally connected to the power system via a circuit breaker (cb). when the micro-grid is isolated from the power system, the micro-grid must retain its operation thanks to two electrical sources, including a diesel generator (or a small hydro power plant) and a doubly fed induction generator (dfig) wind turbine group, to supply three loads. we suppose that load 3 is an important and constant load while load 1 and load 2 are variable loads. fig. 1. the configuration of micro-grid. a. wind turbine a dfig wind turbine consists of a blade system, a shaftgearbox, and a dfig [15], as shown in figure 2(a). the main duty of the blade system is to convert the wind's kinetic energy to mechanical energy on the turbine's shaft and then this mechanical energy is converted to electrical energy by the generator. the turbine's shaft and the generator one are coupled through a gearbox system. at wind speed v�(m/s) and wind turbine’s rotational velocity ω�(rad/s), the mechanical power on the turbine's shaft is computed as [16]: ���� �� �������,� ����� (1) where, is the air density (kg/m3), � the length of the blade (m), �� is the wind speed (m/s), and ����,� is the power coefficient of wind turbine, which depends on both tip-speed ratio � and pitch angle � of the wind turbine. according to [16], the tip-speed ratio is defined by: ��� ���� ����� . (2) for wind turbine, c �λ,β has a unique maximum value ��#$% at � �'�� as � 0. hence, if the wind turbine operates at �'��, �� will be maximum. ��#$%�� �� �����#$%��� � � ��) *+,-. /0+12 3�'��� �� (3) where, we used (2) as �'�� ��0+1�� ����� . (4) the locus of maximum points or maximum power point tracking curve (mppt curve) can be defined by: �#����3� 4'��3�� , (5) 4'�� ≜ �� ��) *+,-. /0+12 . (6) the characteristic of the wind turbine, in the pu unit system, is shown in figure 2(b). (a) (b) fig. 2. wind turbine system: (a) configuration of dfig wind turbine, and (b) wind turbine characteristic. for the wind turbine to operate on the mppt curve, the rotational speed of the wind turbine must be calculated as in (4) or the mechanical power must be remained as in (3). in the case of wind sensorless control, we cannot determine the maximum power from (3) or the optimal rotor speed from (4) and hence, we must use the mppt curve and the feedback power output (or the feedback rotor speed) to determine the optimal rotor speed (or the maximum power). b. doubly fed induction generator in this research, the wind turbine employs a dfig to operate in variable speed as in figure 2(a). dfig is an induction generator, where the rotor windings are supplied through a partial back-to-back converter including a rotor side converter (rsc), a grid side converter (gsc) and a dc link [2, 17, 18]. thanks to the back-to-back converter, the dfig wind turbine can provide good control ability [19] to meet the operator’s requirements. in this micro-grid, thanks to this ability, the dfig wind turbine can support the diesel generator to retain the frequency in the normal operation range. the statespace equation of a dfig in 67 frame, where 6 axis is aligned with the stator flux vector, is described as [20]: 8 8� 9:�� ;:�� 9:�� < =:>:�� < ?:�� (7) where, ;:�� @ �ab c� @ 3d�� e, =: � b c� , (8) f:�� �gh,hg i�� j 0 1l @ ω�e9:�� , e j 0 @1 1 0 l, (9) m n: @ h, o hg , �� 1 @ pq�� pr�� , (10) where: 9: st:8 t:uvw is the current in the rotor side, >: sx:8 x:uvw is the voltage in the rotor side, nd, n:, n# are the inductance of the stator winding, rotor winding and mutual, �: is the resistance of the rotor winding, and ωy, ω� are the rotational speeds of the stator flux and rotor. for the dfig wind turbine without power losses, we have: engineering, technology & applied science research vol. 8, no. 6, 2018, 3646-3651 3648 www.etasr.com chung: retaining of frequency in micro-grid with wind turbine and diesel generator ���� �1 @ i �d pq�� pr�� �d�� , (11) �d�� @ �gh,hg t:u�� (12) where, �d is the power output in the stator side. hence, as the wind turbine generates maximum power, the optimal power output in the stator side is defined as: �d#$%�� pr�� pq�� ��#$%�� . (13) iii. scheme of frequency stability in micro-grid the micro-grid has two operation modes: the grid connected mode and the isolated mode. in the grid connected mode, the frequency in the micro-grid is retained by the power system. when the micro-grid is isolated from the power system, any active power imbalance between the consumption and generation leads to variations in the frequency and then, it can lead generators to shut down. hence, the frequency retaining in the normal operation range is necessary. in this research, the micro-grid’s rated frequency is 50hz and the normal operation range is between 49.8hz and 50.2hz. this means that the proposed frequency adjustment method is to keep the frequency in the micro-grid in that range when the micro-grid operates in the isolated mode. this paper proposes two frequency control schemes for the dfig wind turbine in a micro-grid operating in isolated mode. the first one is based on the power control of rsc and the second one is based on the rotor speed control of rsc. these schemes are named power control scheme and rotor speed control scheme, respectively. it is worth noting that these proposed schemes could apply in a quite small micro-grid without an energy storage system. in the case of a large network, the coordination of sources including distributed generators, storage systems, damping loads etc., and the scheme of shielding load should be considered. a. power control scheme to retain the frequency of the micro-grid in the operation range, the reference power output of the wind turbine is calculated by the available power of the wind turbine and the error of the frequency, ∆[. according to [7], to support the frequency control, the auxiliary signal comes from two components including the derivative of the actual frequency 6[/6� and the frequency error ∆[. however, by using the derivative of the actual frequency, measurement noises will be multiplied and this can impact on the results. the frequency adjustment with the power control scheme is shown in figure 3. it is worth noting that this wind turbine operates in the two afore mentioned modes: connected to the power system and isolated mode. when the micro-grid operates in the power system connected mode, the wind turbine does not need to adjust the frequency so the reference power is designated by �d#$%. when the micro-grid is disconnected from the power system, the wind turbine must support the diesel generator to adjust the micro-grid's frequency so the reference power output in the stator side of dfig is described as in (14): ] �d,:^_�� 4�`�� �d#$%�� < 4�`∆[�� 4�`�d#$%�� �:^_,#ab c �d,:^_�� c �d#$%�� (14) where, 4�` is a deloading constant and it is always 4�` d 1,4�` is a droop coefficient, 4�` is a design constant, ∆[ is the error of frequency, ∆[�� [:^_ @ [�� which [:^_ is the reference frequency and [ is the actual frequency, and �d#$% is the maximum power output in the stator side. (a) (b) fig. 3. frequency adjustment with the power control scheme: (a) flowchart, and (b) outer loop. to calculate �d#$%, we use (13). ideally, we calculate ��#$% from (3), however, in this research, we must use the feedback rotor speed and the mppt curve from figure 2(b). in this research, the droop coefficient is determined by a fuzzy logic rule (flr) of two input signals including ∆[ and the frequency deviation 6[/6�. the membership functions of the fuzzy logic rule are shown in figure 4 and table i, where ∆[�, ∆[�, ∆[�,6[�,6[�,ef,e�, e�,e� are design constants. the fuzzy rule is indicated in table ii. to obtain the above reference power, from (12), we must adjust the t:u component in the rotor side. here, pi control is employed to make the error between actual power �d and �d,:^_ become zero. the reference current t:u,:^_ is described by: t:u,:^_ 4��g�d,:^_ @ �dh < 4a� ig�d,:^_ @ �dh6j (15) where 4�� and 4a� are designed constants of the pi control. with this reference current, rsc must be controlled in a way that the actual current ilm reaches the reference value ilm,lno. table i. terms of figure 3 symbol linguistic symbol linguistic nv very negative de decrease n negative in increase z zero s small p positive h high vp very positive engineering, technology & applied science research vol. 8, no. 6, 2018, 3646-3651 3649 www.etasr.com chung: retaining of frequency in micro-grid with wind turbine and diesel generator (a) (b) (c) fig. 4. the membership function of fuzzy logic: (a) input ∆[, (b) input 6[/6�, and (c) output 4�`. table ii. fuzzy rules of 4�` ∆p qp/qr vn n z p vp de h h s z s z s s z s h in s z s h h b. rotor speed control scheme by adjusting rotor speed, we can adjust the power output of the wind turbine, and hence, the wind turbine can control the frequency in the micro-grid by adjusting the rotor speed. from (10), we have: 3��� g1 @ i�� h3y�� (16) clearly, when the micro-grid's frequency deviates amount of ∆[, the rotational speed of the wind turbine varies: ∆3��� g1 @ i�� h∆3d�� ���� _�� ∆[�� (17) to adjust the power output of the wind turbine, we can adjust the rotor speed. hence, to adjust the frequency, we need to compensate this deviation. in this paper, the frequency adjustment using the rotor speed control scheme is indicated in figure 5. the reference rotor speed when the wind turbine participates in the frequency adjustment in the micro-grid's isolation mode is described as: ]3�,:^_�� 4���� 3�'���� < 4��∆[�� 3�'�� c 3�,:^_�� c 3�#$% (18) where 4�� s 1 is a design constant, and 4�� is defined by the fuzzy logic rule, which is similar to figure 4 and table ii. because the wind turbine is operated in the right side of the mppt curve, the rotor speed is always over optimum speed. to avoid rotor speed increases to a too high values, the reference rotor speed 3�,:^_ should be limited between 3�'�� and 3�#$%. like the case of the power control scheme, the wind turbine will generate all available power as the micro-grid is connected to the power system. it means 3�,:^_ is equal to 3�'��. when the micro-grid is isolated from the power system, the reference rotor speed is designated as in (18). to make the rotor speed 3� approach its reference value, 3�,:^_, the rotor current in the q axis must reach to its reference value which is determined by the error in the rotor speed and a pi control as: t:u,:^_ 4��g3�,:^_ @ 3�h < 4a� ig3�,:^_ @ 3�h6j (19) where, 4�� and 4a� are designed constants of the pi control. (a) (b) fig. 5. frequency adjustment with the rotor speed control scheme: (a) flowchart and (b) outer loop. from this reference current, rsc must be controlled such that tau t:u,:^_ @ t:u approaches to zero. as can be seen from the two proposed schemes, a wind speed anemometer is not required. this is the difference from the method introduced in [10]. iv. rsc for current control above we defined the reference current t:u,:^_. to support the frequency adjustment in the micro-grid, the actual current t:u must be satisfied t:u,:^_. here, we desire that: ua�� �9:,:^_�� @ 9:�� → 0 (20) where 9:,:^_ s9:8,:^_ 9:u,:^_vw, 9:8,:^_ is designated by the voltage or reactive power control purpose. from the state space equation of dfig (7), we have: >:�� w:�� < ∆w:�� (21) engineering, technology & applied science research vol. 8, no. 6, 2018, 3646-3651 3650 www.etasr.com chung: retaining of frequency in micro-grid with wind turbine and diesel generator where: ∆w: s∆w:8 ∆w:uvw =:x�?: (22) w: sw:8 w:uvwis a new control variable. here, we employ pi controls to make the error ua 9:,:^_ @ 9:, so we have: w:�� y 4�� 0 0 4�z{ua�� < y 4a� 0 0 4az{iua�j 6j (23) where 4��, 4�z , 4a�, 4az are designed constants. by using (21), the rotor current can track their reference values. it means the active power/rotor speed is controlled and the wind turbine can support the frequency in the micro-grid. v. simulation results to evaluate and compare two frequency control schemes, we used matlab/simulink to simulate a micro-grid which is normally connected to a power system. this micro-grid consists of a dfig wind turbine group of 4.5mw, a diesel or a small hydro-power plant of 3.25mva, and loads as shown in figure 1. in these loads, load 3 is a static load of 2.7mva and the total power of the other loads is shown in figure 6. fig. 6. the power load in total of load 1 and load 2. we suppose that the micro-grid is isolated from the grid at 4s. it means before 4s, the micro-grid works in the grid connected mode and afterwards it operates in the isolated mode. the supposed wind speed is given in figure 7. simulation results are indicated in figures 8-11. the parameters used for the fuzzy membership functions in flr are defined in table iii. fig. 7. wind speed applied to the wind turbine. as can be seen from figure 8, before the 4s, the micro-grid is operating in the grid connected mode so the frequency in the micro-grid is almost constant. at the 4s, the micro-grid is disconnected from the power system and during a short transient interval (4s-7s), the frequency is over the operation range. however, after this transient period, the frequency in the micro-grid with both schemes is retained and then it remains in the normal operation range, between 49.8hz and 50.2hz. note that at 9s and 29s, the reduction of load makes the frequency increase rapidly but it still remains in the normal operation range. comparing to the power control mode, the frequency in the micro-grid has more variation and the frequency error, ∆[ [:^_ @ [, is higher. table iii. threshold values of membership function symbol |}~ |}� ∆[� 0.0005 0.0005 ∆[� 0.001 0.001 ∆[� 0.005 0.005 6[� 0.005 0.005 6[� 0.015 0.015 ef 20 5 e� 25 10 e� 60 80 e� 125 150 fig. 8. frequency in the micro-grid. (a) (b) fig. 9. the active power output from (a) the diesel and (b) the wind turbine group. in terms of the active power output (figure 9) we can see that with the rotor speed control scheme, the active power output generated from the wind farm has a significant fluctuation and hence, the power output of the diesel generator must vary. comparing to the rotor speed control scheme, with the power control scheme the active power output of the wind farm is smoother and hence, the active power output of the diesel generator is also smoother. concerning electrical energy, with the power control scheme the diesel generator only supplies around 8.5kwh during the simulation period while with the rotor speed control scheme it is around 10.9kwh as shown in figure 10(a). the main reason for this is that with the power control the electrical energy extracted by the wind farm is higher than that with the rotor speed control, 27.2kwh and engineering, technology & applied science research vol. 8, no. 6, 2018, 3646-3651 3651 www.etasr.com chung: retaining of frequency in micro-grid with wind turbine and diesel generator 24.8kwh, respectively (figure 10(b)). figure 11 indicates that with the rotor speed control, the wind farm shared around 65% of the electricity demand in the micro-grid and the diesel generator supplies the rest. on the contrary, with power control the wind turbine shares around 70% of the demand. it means that with the power control scheme, we can save fuel cost comparing to the rotor speed control scheme. (a) (b) fig. 10. the electrical energy from (a) the diesel and (b) the wind turbine group. (a) (b) fig. 11. the electrical energy sharing from (a) diesel and (b) wind turbine group. vi. conclusions this paper compared two schemes of frequency regulation applying to the dfig wind turbine in the micro-grid. the first scheme is based on power control and the second one is developed by the rotor speed control. simulation results indicate that with both schemes, the frequency in the microgrid remains in the operation range after the micro-grid is disconnected from the power system. however, the frequency in the micro-grid with power control is better than with rotor speed control. additionally, with power control, the energy of the wind is utilized better than that with the rotor speed control. references [1] global wind energy council, global wind report 2017, gwec, 2017 [2] r. g. almeida, j. a. p. lopes, “primary frequency control participation provided by doubly fed induction wind generators”, 15th power systems computation conference, liege, belgium, august 22-26, 2005 [3] k. suzuki, a. umemura, r. takahashi, j. tamura, n. hino, “frequency control of small power system with wind generators installed by using dfig based diesel generator”, 20th international conference on electrical machines and systems, sydney, australia, august 11-14, 2017 [4] y. zhou, d. d. nguyen, p. c. kjaer, s. saylors, “connecting wind power plant with weak grid – challenges and solutions”, ieee power & energy society general meeting, vancouver, canada, july 21-25, 2013 [5] a. m. howlader, n. urasaki, a. yona, t. senjyu, a. y. saber, “a review of output power smoothing methods for wind energy conversion systems”, renewable and sustainable energy reviews, vol. 26, pp. 135146, 2013 [6] d. g. francisco, s. andreas, g. b. oriol, v. r. roberto, “a review of energy storage technologies for wind power applications”, renewable and sustainable energy reviews, vol. 16, pp. 2154-2171, 2012 [7] y. xue, n. tai, “review of contribution to frequency control through variable speed wind turbine”, renewable energy, vol. 36, no. 6, pp. 1671-1677, 2011 [8] r. g. almeida, j. a. p. lopes, “participation of doubly fed induction wind generators in system frequency regulation”, ieee transactions on power systems, vol. 22, no. 3, pp. 944-950, 2007 [9] m. el mokadem, v. courtecuisse, c. saudemont, b. robyns, j. deuse, “fuzzy logic supervisor-based primary frequency control experiments of a variable-speed wind generator”, ieee transactions on power systems, vol. 24, no. 1, pp. 407-417, 2009 [10] c. pradhan, c. narayan bhende, “enhancement in primary frequency regulation of wind generator using fuzzy-based control”, electric power components and systems, vol. 44, no. 15, pp. 1669-1682, 2016 [11] l. fernandez, c. garcia, f. jurado, “comparative study on the performance of control systems for doubly fed induction generator (dfig) wind turbines operating with power regulation”, energy, vol. 33, no. 9, pp. 1438-1452, 2008 [12] m. garmroodi, g. verbic, d. j. hill, “frequency support from wind turbine generators with a time variable droop characteristic”, ieee transactions on sustainable energy, vol. 99, no. 2, pp. 676-684, 2017 [13] m. k. kim, “optimal control and operation strategy for wind turbines contributing to grid primary frequency regulation”, applied sciences, vol. 7, no. 9, pp. 927-923, 2017 [14] a. r. ardal, t. undeland, k. sharifabadi, “voltage and frequency control in offshore wind turbines connected to isolated oil platform power systems”, energy procedia, vol. 24, pp. 229-236, 2012 [15] o. rahat, i. riazy, “enhancing transient stability in limited variable speed induction generator (optislip) based wind turbine (case study: binalood wind farm)”, engineering, technology & applied science research, vol. 6, no. 6, pp. 1280-1287, 2016 [16] b. wu, y. lang, n. zargari, s. kouro, power conversion and control of wind energy system, john wiley & sons, 2011 [17] r. pena, j. c. clare, g. m. asher, “a doubly fed induction generator using back-to-back pwm converters supplying an isolated load from a variable speed wind turbine”, iee proceedings-electric power application, vol. 143, no. 5, pp. 380-387, 1996 [18] a. b. lajimi, s. a. gholamian, m. shahabi, “modeling and control of a dfig-based wind turbine during a grid voltage drop”, engineering, technology & applied science research, vol. 1, no. 5, pp. 121-125, 2011 [19] o. p. bharti, r. k. saket, s. k. nagar, “controller design of dfig based wind turbine by using evolutionary soft computational techniques”, engineering, technology & applied science research, vol. 7, no. 3, pp. 1732-1736, 2017 [20] d. c. phan, s. yamamoto, “maximum energy output of a dfig wind turbine using an improved mppt-curve method”, energies, vol. 8, pp. 11718-11736, 2015 microsoft word 13-3757l_s_etasr_v10_n5_pp6220-6223 engineering, technology & applied science research vol. 10, no. 5, 2020, 6220-6223 6220 www.etasr.com bhutto et al.: settlement response of a multi-story building settlement response of a multi-story building amjad hussain bhutto department of civil engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan amjadbhutto62@gmail.com ghulam shabir bhurgri department of civil engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan ghulamshabirbhurgri14@gmail.com shahnawaz zardari department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan shahnawazzardari@gmail.com muhammad auchar zardari department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan muhammad.auchar@quest.edu.pk bashir ahmed memon department of civil engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan bashir_m@hotmail.com muhammad munir babar institute of water resources engineering and management mehran university of engineering & technology jamshoro, sindh, pakistan mmunirbabar.uspcasw@faculty.muet.edu.pk abstract-the settlement calculation of a multi-story building is a challenging task due to the variation of soil properties and the use of an appropriate constitutive model for the reliable representation of soils’ stress-strain behaviors. in this study, the settlement response of a multi-story building was calculated with the simple mohr-coulomb model (mcm) and the hardening soil model (hsm). the effect of soil modulus of elasticity using both models was investigated on the overall settlement response of the building. results indicated that mcm overestimated immediate settlement in a range of 50 to 65% compared to hsm. the settlement response of the building calculated with both models was within the allowable range. the results of this study can be helpful for geotechnical engineers working on reliable predictions of the settlement of multi-story buildings. keywords-immediate settlement; finite element method; consolidation process; raft foundation; mohr-coulomb model; hardening soil model i. introduction the reliable prediction of a multi-story building’s settlement is a great challenge for geotechnical engineers [1-3]. several factors affect the settlement of a building, such as the type of soil, the degree of compactness, soil stratigraphy, and the location of water table [4-5]. modulus of elasticity is a main parameter that controls the settlement, as higher values result in lower settlement [6]. in modern geotechnical engineering, soils are considered as elastoplastic materials. this indicates that a part of the settlement is elastic and the remaining is plastic. with the advancement of low-cost computing in geotechnical applications, software programs are used for the calculation of settlement in various geotechnical structures. such programs utilize various constitutive models for calculating stress strain response of soils. thus, it is very important to choose the appropriate constitutive model that could realistically simulate the stress strain response of soils. several constitutive models for stress strain of soils are available in commercial software, e.g., plaxis2d/3d, geostudio, z-soil etc. however, choosing a constitutive model to run a settlement analysis is not easy task, as a thorough understanding of its main features and parameters is required. in general, the use of advanced constitutive models requires several input parameters. due to the lack of availability of laboratory tests, advanced constitutive models are not used for routine calculations. although the mohr-coulomb model (mcm) has several limitations, it is used in various applications due to its simple and easily obtained parameters. on the other hand, the hardening soil model (hsm) is a suitable constitutive model for predicting the settlement response of geotechnical structures. in [7], it was found that the settlement of the shallow foundation calculated with mcm was greater than the cam clay model. this showed that mcm overestimates the settlement of buildings. there are very few case studies on the settlement of geotechnical structures where the results from mcm are compared with hsm [8-9]. therefore, there is a necessity for more studies, in which the suitability of both mcm and hsm should be evaluated for a multi-story building’s settlement calculation. this paper presents the corresponding author: amjad hussain bhutto engineering, technology & applied science research vol. 10, no. 5, 2020, 6220-6223 6221 www.etasr.com bhutto et al.: settlement response of a multi-story building numerical analysis for calculating the settlement of a building using both mcm and hsm. moreover, the foundation soil profile and the material properties are presented. finally, the settlement is evaluated with both mcm and hsm, and the results are compared. ii. materials and methods a. finite element model numerical analysis of the multi-story building settlement was performed using finite element program plaxis 2d [10] for a 10-story residential building with a floor area of 25m×20m. the building’s geometry is shown in figure 1 and its finite element model is presented in figure 2. the model was extended 100m horizontally on both sides to consider the influence of deformations due to building loads. the bottom of the finite element model was fixed in both horizontal and vertical directions. the vertical boundaries of the model were fixed in horizontal direction and free in vertical. fifteen node triangular elements were adopted. the mesh was sufficiently refined in order to minimize the influence of coarseness on the results. the left and right vertical boundaries and the bottom of the finite element model were closed to prevent the dissipation of excess pore pressures. coupled deformation and consolidation analysis was performed in order to study the settlement behavior and the development and dissipation of excess pore pressures under the building’s loads [11]. fig. 1. foundation of soil profile along with load. fig. 2. finite element mesh of the building. b. loading condition the load of the building was calculated by considering live and dead loads. reinforced cement concrete (rcc) and steel are the major construction materials for raft foundation. the total load for each floor was calculated at 7kn/m 2 . c. soil properties three boreholes were conducted to determine the geotechnical properties of the soil. soil’s average moisture content was about 60%. the soil was classified as silty sand according to the unified classification system [12]. stress strain behavior of the soil was simulated with both mcm and hsm. the input parameters of hsm are presented in table i. the values of cohesion, unit weight, permeability, modulus of elasticity, and poisson’s ratio of the soil were obtained from laboratory tests. the remaining parameters were taken from [13-14]. mcm has five input parameters: cohesion, friction angle, dilatancy angle, poisson’s ratio, and modulus of elasticity. these parameters are shown in table i. soil’s modulus of elasticity (moe) varied from 1000 to 40000kpa to observe how the settlement of the building was reduced with increasing density of the foundation soil. water table was located 1m below the surface. in this study, 1m thick reinforced cement concrete raft was placed as building’s foundation. the material properties of the raft were adopted from literature [13] and are presented in table ii. table i. input parameters of hardening soil model parameter value saturated unit weight 17.5kn ��⁄ unsaturated unit weight 13kn ��⁄ permeability in horizontal direction 0.75 � 10 � � ���⁄ permeability in vertical direction 0.75 � 10 � � ���⁄ tangent stiffness modulus (����� 10000kn � �⁄ secant stiffness (� �� ��� � 10000kn � �⁄ reference modulus for unloading and reloading (��� ��� � 30000kn ��⁄ power (m) 0.5 poisson’s ratio 0.3 cohesion 10kn ��⁄ angle of internal friction 30 ͦ dilatancy angle 0 ͦ table ii. material properties of concrete parameter value unsaturated unit weight 24 kn ��⁄ modulus of elasticity 20�106kn ��⁄ thickness of raft 1m poisson’s ratio 0.15 iii. results and discussion the construction of the proposed ten-story building was assumed to be carried out in stages. the sequence of construction of the building is listed in table iii. the calculations were performed for various construction activities. table iii. calculation details for staged construction of 10-story building phases duration (days) type of analysis raft foundation 30 consolidation ground floor 365 consolidation first floor 270 consolidation second floor 270 consolidation third floor 240 consolidation fourth floor 240 consolidation fifth floor 240 consolidation sixth floor 240 consolidation seventh floor 240 consolidation eighth floor 240 consolidation ninth floor 240 consolidation tenth floor 240 consolidation vertical settlement of the multi-story building was calculated using both mcm and hsm. settlement was calculated for each floor starting from floor 1 to 10. the effect engineering, technology & applied science research vol. 10, no. 5, 2020, 6220-6223 6222 www.etasr.com bhutto et al.: settlement response of a multi-story building of soil’s moe was examined. settlement response of the multistory building computed with mcm and hsm is presented in tables iv and v respectively. as it can be observed, the maximum settlement of the building up to the 10th floor calculated with mcm was 52mm and 14mm when the values of soil’s moe were adopted as 10000kpa and 40000kpa respectively. table iv. mcm calculations of settlement soil modulus of elasticity (kpa) 10000 15000 20000 25000 30000 35000 40000 floor settlement of building (mm) 1 48 30 24 20 16 14 12 2 48 32 24 20 16 14 13 3 48 32 24 20 17 15 13 4 48 34 26 20 17 15 13 5 48 34 26 22 18 15 14 6 52 34 26 22 18 16 14 7 52 34 26 22 18 16 14 8 52 36 28 22 18 16 14 9 52 36 28 22 18 16 14 10 52 36 28 22 18 16 14 table v. hsm calculations of settlement modulus of elasticity of soil (kpa) 10000 15000 20000 25000 30000 35000 40000 floor settlement of building (mm) 1 st 17 12 9 8.5 7.2 6.4 5.6 2 17 12 9.5 9 7.6 6.8 6 3 18 13 10 9 7.6 6.8 6 4 19 13 10 9.5 8 7.2 6.4 5 19 13 11 9.5 8 7.2 6.4 6 20 14 11 9.5 8 7.2 6.4 7 20 14 11 10 8 7.2 6.4 8 20 14 11 10 8.5 7.2 6.4 9 22 14 11 10 8.5 7.2 6.4 10 22 14 11 10 8.5 7.2 6.4 fig. 3. comparison of settlement calculated with mcm and hsm. the settlement response of the building using mcm and hsm were compared. table v shows that there was comparatively less settlement predicted with hsm than with mcm. the maximum settlement of the building up to the 10th floor was 22mm and 6.4mm when the moe of the soil was 10000kpa and 40000kpa respectively. the comparison of building’s settlement calculated with mcm and hsm is presented in figure 3. as it can be observed for various loading conditions, the settlement predicted with mcm was about 50 to 65% higher than the one predicted by hsm. according to [15], the allowable settlement for a raft foundation is about 100mm. hence, the settlements of the building up to the 10th floor computed with mcm and hsm are within the allowable range. it has to be emphasized that the settlement response of the building is investigated after the end of the construction. this settlement does not involve long term settlement response. for this purpose, detailed numerical analysis is required to find the long term response of the building under sustained loading conditions. iv. conclusion this paper compared the calculated immediate settlement of a multi-story building using two soil constitutive models, i.e. mcm and hsm. mcm overestimated the settlement of the building in a range of 50 to 65% compared to hsm. overall, the magnitude of the settlement calculated with both models is within the permissible limits. future studies are needed to investigate the settlement response of such buildings under sustained long-term loads. the compared results of the settlement 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[online]. available: https://www.plaxis.com/support/manuals/plaxis-2d-manuals/ [15] a. w. skempton and d. h. macdonald, “the allowable settlements of buildings.,” proceedings of the institution of civil engineers, vol. 5, no. 6, pp. 727–768, nov. 1956, doi: 10.1680/ipeds.1956.12202. microsoft word etasr_v13_n4_pp11253-11257 engineering, technology & applied science research vol. 13, no. 4, 2023, 11253-11257 11253 www.etasr.com nguyen-van & bui-tien: investigation of the eigenvector of stochastic finite element methods of … investigation of the eigenvector of stochastic finite element methods of functionally graded beams with random elastic modulus thuan nguyen-van nha trang university, vietnam thuannv@ntu.edu.vn thanh bui-tien university of transport and communications, vietnam btthanh@utc.edu.vn (corresponding author) received: 26 april 2023 | revised: 5 june 2023 | accepted: 6 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5991 abstract this paper presents a stochastic finite element method to calculate the variation of eigenvalues and eigenvectors of functionally graded beams. the modulus of functionally graded material is assumed to have spatial uncertainty as a one-dimensional random field. the formulation of the stochastic finite element method for the functionally graded beam due to the randomness of the elastic modulus of the beam is given using the first-order perturbation approach. this approach was validated with monte carlo simulation in previous studies using spectral representation to generate the random field. the statistics of the beam responses were investigated using the first-order perturbation method for different fluctuations of the elastic modulus. a comparison of the results of the stochastic finite element method with the firstorder perturbation approach and the monte carlo simulation showed a minimal difference. keywords-perturbation method; eigenvector; fgm beam; fem i. introduction functionally graded materials (fgms) have attracted much attention the recent years [1-8]. the idea of fgm was introduced in 1984 when the space aircraft project was underway in japan [9]. compared to generally isotropic homogeneous materials, the fgm beams under consideration can acquire a high degree of uncertainty in their material constants. fgms are considered one of the most promising candidates for advanced composites in various industries, including aerospace, automotive, electronics, and, most recently, biomedical and aviation [10-11]. structures constructed of fgm have attracted attention in recent years. in [12], the free vibration property of a functionally graded beam was used with axial or transverse material gradation by thickness according to the power law, using the finite element method (fem). in [13], an innovative method was presented to create an fgm beam finite element by deriving approximation functions from the exact general solution to the static section of the governing equations. in [14], the geometric nonlinearity of von karman was considered in an euler-bernoulli beam to study the nonlinear vibration of beams constructed of functionally graded materials. many researchers have studied problems in mechanics with random parameters [15-18]. with stochastic problems of continuous systems, analytical methods are almost always challenging to find solutions, often using numerical methods such as stochastic finite element analysis [19-22] and stochastic isogeometric analysis [4, 23]. in [24], the variation of vehicle vibration frequency was studied with random stiffness and mass parameters of the vehicle. in [25], stochastic dynamic problems of a functionally graded material with random material properties were studied. in [26], a stochastic finite element with uncertain poisson's ratio was presented for bending plates. stochastic fem using the weighted integration approach for the static problem of nonuniform columns was presented in [27]. in [28], the karhunen-loève expansion was used to develop a stochastic spectral isogeometric analysis for the linear elasticity problem. in [29], the first-order reliability method and monte carlo simulation (mcs) were used to calculate the reliability of laminated composite shells. however, very few studies used the perturbation technique to determine eigenvector problems. this study attempted to extend [30-31], using the results obtained on the eigenvalues as a basis to develop the eigenvector problems of fgm beams as the form of the perturbation-based stochastic fem. ii. finite element formulation at first, the finite element formulation for the functionally graded beam was formulated with the case of deterministic system parameters. figure 1 illustrates the functionally graded beam with length l in the mid-surface coordinate system. engineering, technology & applied science research vol. 13, no. 4, 2023, 11253-11257 11254 www.etasr.com nguyen-van & bui-tien: investigation of the eigenvector of stochastic finite element methods of … fig. 1. coordinates and geometry of the functionally graded beam. following the feature of the fgm, young's modulus and mass density were assumed to vary continuously along the thickness direction (z-axis) according to the exponential function. it was also assumed that the elastic modulus and mass density was symmetric to the mid-surface, as given in the following expression: ���� = ��� �| |; ��� = �� �| | (1) where e0 and ρ0 are the elasticity modulus and mass density in the mid-plane (z=0), respectively, and β defines the variation trend along the z-axis. a 2-node finite element beam was adopted, having hermite functions as shape functions. the respective nodes have two degrees of freedom: translation w and rotation θ. accordingly, the vertical displacement along the z-direction w can be interpolated as follows: ���� = ��� �� �� ��� � ��������� (2) where ni are the interpolation functions: �� = 1 − ����� + �� � �� = � − ���� + � �� (3) �� = ����� − �� � �� = − ��� + � �� the strain energy of the beam element can be written as: !" = # �� $���%�,���'� (� (4) furthermore, the kinetic energy of the beam element can be written as follows: )" = # �� # $��� ���(�(�ℎ/�+ℎ/� �, �'�     = # �� .����, �(�'� (5) where, .��� = $��� # ���(�ℎ/�+ℎ/� and % = # ������ℎ/�+ℎ/� (�. hamilton's principle was used to find the eigenequation for the fgm beam structures within the fem framework. before that, it is necessary to have the strain and kinetic energy in terms of the nodal displacement vector. the final equation of motion can be derived by applying the hamilton's principle: / # �∑ !"1"2� − ∑ )"1"2� �3�34 (5 = 0 (6) where n denotes the number of finite elements used in the fgm beam model. taking the variation concerning harmonic motion, the following equation emerges for the eigenvalues and vectors: �7 − 89�: = 0 (7) the frequency equation that provides the solution for frequencies is obtained as: |7 − 89| = 0 (8) in these equations, k and m denote the assembled global stiffness and mass of the fgm beam, respectively, and λi denotes the square of the circular frequency ωi. iii. probabilistic analysis the perturbation method is the most commonly used technique for studying uncertain systems. this method uses a taylor series to construct an analytical solution for the variance of the desired response quantities by extending each random variable in an uncertain system around its associated mean value, such as the eigenvalues and eigenvectors of a structure, due to the smallest variations in the random variables. the stiffness and mass matrices of the beam and plate and their responses are represented in terms of a taylor series formulation concerning the parameters centered at the mean values. the taylor series is often only extended to the firstorder perturbation method. the elastic modulus is described as a one-dimensional gaussian homogeneous random field with zero mean r(x), given by: ���, �� = ���1 + ;����� �| | (9) the random field of elastic modulus in the element is approximated by averaging random variables within it: � ≈ �� =1 + >4?>�?...?>ab> c (10) let d = ⟨df ⟩, h = 1, id be a vector of the random variable, where nr is the number of coefficients of the random variable vector r. since two kinds of random parameters have to be considered, elastic modulus and mass density, the vector r is represented as d = ⟨j, 5⟩, where s and t are the random variable vectors for elastic modulus and mass density, respectively. for the mid-point rule, = kj�, j�, . . . , jb>l m, 5 = k5�, 5�, . . . , 5b>l m, and idn , id3 = i� is the number of finite elements in the domain. that is, each random variable is associated with the corresponding finite element. in the case of the local average scheme, j = kj�, j�, . . . , jb>l m, idn = i� × ip, where ip is the number of integration points within each finite element. similarly, 5 = k5�, 5�, . . . , 5b>l m , id3 = i� × ip . here it is assumed that the mean of the respective random variable is zero: ��j� = ��5� = 0. engineering, technology & applied science research vol. 13, no. 4, 2023, 11253-11257 11255 www.etasr.com nguyen-van & bui-tien: investigation of the eigenvector of stochastic finite element methods of … the taylor series of system matrices and vectors is: 7�d� = 7� + 7,q rjq + 7̸,q r5q + �� t7,qu rjq rju + 7̸,qu r5q r5u + 27̸,qu rjq r5u w (11) 9�d� = 9� + 9̸,q rjq + 9,q r5q + �� t9̸,qu rjq rju + 9,qu r5q r5u + 29̸,qu rjq r5u w (12) x�d� = x� + x,q rjq + x,q r5q + �� tx,qu rjq rju + x,qu r5q r5u + 2x,qu rjq r5u w (13) 8�d� = 8� + 8,q rjq + 8,q r5q + �� t8,qu rjq rju + 8,qu r5q r5u + 28,qu rjq r5u w (14) here, d = ⟨j, 5⟩ y� = y|>2�, y,q = z[z>\]>2�, y,qu = z[z>\z>^_>2� , `, a = 1,2, . . . , id (15) rjq = jq − j̄q = jq , r5q = 5q − 5̄q = 5q (16) it is apparent that stiffness is only a function of random elastic modulus and the mass matrix is of random mass density. the summation is implied with the repeated indices. by substituting the expanded expressions for the system matrices into the eigenanalysis expression, the equation in the same order can be obtained as follows: the 0-th order equation: �7� − 8�f 9��x�f = 0 (17) the 1-st order equation: �7� − 8�f 9��x�f = −�7,q − 8�f 9,q − 8,qf 9��x�f (18) considering only the linear terms, the linear variance of the eigenvalue and eigenvector is: 8,qf = xfc t7,q�n� − 8f 9,q�3�wxf (19) ded����x� = ���x − xf� ��x − xf� �c � = �gtx,q�n� jq + x,q�3�5q wtx,u�n�cju + x,u�3�c5u wh = x,q�n�x,u�n�c �gjq ju h + x,q�3�5q x,u�3�c5q �g5q 5u h +2x,q�n�jq x,u�3�c�gjq 5u h (20) where: x,q�n� = −ij+��7,q�n� − 8�9̸,q�n� − 8,qn 9��x� x,q�3� = −ij+��7̸,q�3� − 8�9,q�3� − 8,q�3�9��x� (21) ded��� �x� =−ij+� k7,q�n� − 8,q�n�9�l x�x�c k7,u�n� − 8,u�n� 9�lc ij+c ;nntmqu w +ij+� k8j9q�3� + 8q�3�9�l x�x�c k8j9,u�3� + 8u�3�9�lc ij+c ;nn tmqu w −ij+��7,q�n� − 8q�n� 9��x�x�c �8j9,u�3� + 8,u�3�9��ij+c ;nn tmqu w −ij+��8j9,u�3� + 8,u�3�9��x� x�c �7,q�n� − 8q�n�9��c ij+c ;nntmqu w (22) where ;nn �mqu � is the autocorrelation, ;n3 �mqu � is the crosscorrelation, nop is the coefficient correlation, and d is the correlation distance. ;nn �mqu � = qo� ��p k− r��s�l (23) the coefficient of variation (cov) of the response eigenvector shows the degree of dispersion of the distribution of the eigenvectors and is given as follows: cov = wx|yx| (24) where σx is the standard deviation of the random eigenvectors and μx is the mean of the random eigenvectors. iv. numerical examples the constituent geometric dimensions of the fgm beams were h = 1 m and l = 20 m. young's modulus ratio is ��/��, where �� and �� denote young's modulus at the middle and the top surface of the fgm beam, respectively. the mid-surface of the beam is 100% aluminum, with mean values of material parameters similar to [31]: �� = 70 gpa, � = 2,780 kg/m3, and ν=0.33. using the first-order perturbation expansions of the proposed stochastic fem analysis, the response variability of the eigenvector of the first mode was calculated and is shown in figures 2, 3, and 4. the results of the mcs using 10,000 samples generated by representative spectral [32] are given also. as seen in figures 2-4, the perturbation method results agree very well with the mcs [30] results in all cases of mean, standard deviation (sd), and cov of eigenvector. fig. 2. mean of eigenvector. figure 5 shows the effect of the correlation distance d of the stochastic field on the variability of the cov of the eigenvector, where the results of the proposed formulation are compared with those of the mcs for the same cases of the stochastic fem. the results designated by a dotted line denote the corresponding results of the mcs for correlation distances of 1, 10, 15, and 20. as seen in figure 5, the results of the perturbation method agree very well with the results of the mcs in all cases. it is observed that the increasing rate of the correlation distances is accelerated with a decrease in the cov of the stochastic field. engineering, technology & applied science research vol. 13, no. 4, 2023, 11253-11257 11256 www.etasr.com nguyen-van & bui-tien: investigation of the eigenvector of stochastic finite element methods of … fig. 3. sd of eigenvector. fig. 4. cov of eigenvector. fig. 5. cov of eigenvector as x coordinate of beam for different correlation distance d. fig. 6. effect of elastic modulus ratio on the cov of the eigenvector. figure 6 shows the effect of young's modulus ratio on the cov of the eigenvector. the cov of the eigenvectors is observed to be unaffected by the modulus ratio of the young parameter. the elastic modulus ratio affects only the specified stiffness of the beam and does not affect the random field properties, which are assumed to be unidirectionally varying along the axis beams. v. conclusions this paper extended the stochastic fem using the firstorder perturbation approach to develop the eigenvector of a beam. in the stochastic fem approach, the local average scheme was used to discretize random processes rather than the midpoint rule. the comparison of the mean, standard deviation, and coefficient of variation of the eigenvector in an fgm beam predicted by stochastic fem with those by mcs in previous studies considering random young's modulus produced the following conclusions for the systems:  the fgm model was analyzed to demonstrate the adequacy of the proposed formulation. the first-order perturbation results showed good agreement with the mcs results for mean, standard deviation, and coefficient of variation of the eigenvector.  the increasing rate of the correlation distances was accelerated with a decrease in the coefficient of variation in both fem and monte carlo simulation.  for both analysis methods, the results showed that the response variability of the eigenvector was not affected by either the elastic modulus ratio on the top or middle surfaces of the fgm beams. references [1] l. 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pakistan rafikullah deraman department of civil engineering technology, university tun hussein onn malaysia, johor, malaysia muhammad fikri hasmori department of civil engineering technology, university tun hussein onn malaysia, johor, malaysia nor haslinda abas department of civil engineering technology, university tun hussein onn malaysia, johor, malaysia abstract—construction waste generation has been perceived as a crucial issue that has critical consequences on the project effectiveness and ecological effect of the construction industry. the key objective of the current research is to identify the root causes of material construction waste generation in malaysia. a well-structured questionnaire was designed based on the 52 identified root causes of material waste generation. the developed questionnaire was distributed to 35 highly experienced in malaysian construction industry experts. the collected data was analyzed by the use of mean score analysis. the top identified root causes are poor supervision during the construction stage, lack of efficient site management, last minute changes, cutting uneconomical sizes of materials, and constant design changes during the construction period. the initial findings will aid construction practitioners to focus on these root causes in order to reduce the material construction waste generation at construction sites. keywords-preliminary survey; material waste; root causes; environment; malaysia i. introduction construction industry is considered a key part in any nation’s socio-economy growth. nowadays, construction industry is developing rapidly [1-2] but is generally considered environmental unfriendly [3]. this industry enhances considerably environmental problems such as exploration of the natural resources, irretrievable conversion of the environment, and increase of contaminants in the atmosphere [4]. construction waste is produced throughout site clearance, material utilization, overabundance acquirement of materials and human errors at construction site. 10-30% of the waste starts from construction works [5, 6]. therefore, initial identification of the root causes is essential in order to reduce material waste generation rate. ii. construction waste material waste can be generated throughout construction works. it may occur in preliminary design stage, during construction and with poor human behavior [7-9]. construction waste is considered as any material that is damaged, unnecessary and extra purchased, or noncompliant to specifications [2, 10]. according to [11, 12], annual construction waste generation has been increasing in malaysia. construction waste is being created through the entire construction time frame, from the earliest starting point of the outline arranged until the last stage. there are numerous root causes that prompt construction waste generation. it is essential to distinguish those causes in order to control waste generation. according to [1], there are several root causes of construction waste generation such as design, workers, management, procurement, site condition, handling and external factors. it is stated that poor site management is one of the major root causes in producing waste. absence of awareness or knowledge in construction waste, procurement of materials differing to specification, unsuitable storage causing damage and rework are among the key causes identified in contributing to waste generation rate [13]. it has been discovered that waste produced in malaysian construction projects are mainly initiated by employee and management problems [14]. these root causes should be controlled to reduce the quantity of generated waste. there are other aspects that are considered as sources of construction waste such as incomplete information, engineering, technology & applied science research vol. 8, no. 6, 2018, 3580-3584 3581 www.etasr.com kaliannan et al.: preliminary survey on the crucial root causes of material waste generation … weak material management, unskilled labor, and damage during transportation [15]. the root causes were categorized under common characteristics like material management on site, material handling, transportation and storage and site management and practices in [16]. iii. research methodology this study adopts quantitative technique in order to comprehend the viewpoint of construction experts towards the root causes of construction waste generation in malaysian construction industry. the exploration of this research is divided into 2 phases. the first phase includes extensive literature review after which 52 root causes contributing to material construction waste generation were identified. in the second phase, a questionnaire was developed. the questionnaire comprises of two parts, demography of the respondents and root causes of waste generation rate in malaysian construction industry. each respondent was asked to verify the crucial root causes for the environment of malaysian construction industry. iv. data collection and analysis the questionnaire was designed based on a five-point likert [17] scale ranging from 1 for disagree to 5 for strongly agree. the developed questionnaire was distributed to 35 experts in malaysian construction industry. the received questionnaires were analysed and reliability test was conducted. the cronbach’s alpha value was 0.970 which indicates a high level of consistency. according to [18, 19], if cronbach’s alpha value is higher than 0.7, the inner consistency of data is highly acceptable. figure 1 indicates the number of respondents and their corresponding working experience. the majority (12 out of 35, 34.3%) of the respondents have 16-20 years of experience in the construction industry. the total percentage of respondents with more than 10 years of experience in the industry is about 88.5%. this shows that the majority of the respondents are eminently experienced and vastly knowledgeable regarding malaysian construction industry. fig. 1. respondents’ working experience figure 2 exhibits the respondents’ organization/enterprise. most of the respondents are contractors with 62.9% (22 out of 35). the opinions of contractors are considered important as they are the ones who are stated at the site and have better understanding about the root causes of construction waste generation. clients’ and consultants’ inputs are crucial as well because they are also having good involvement in construction industry field. fig. 2. respondents’ enterprise type v. results and discussion the mean value of each root cause of material waste generation is presented in table i. result analysis showed that the root causes with the higher mean value for generation of waste in malaysian construction industry are “supervision during construction stage is poor”, “efficient site management is lacking”, “last minute changes due to client requirements”, “cutting uneconomical sizes of materials”, “constant design changes during construction period”, “unsuitable tools used during construction”, and “unsatisfactory attitude of workers”, the ranking of the root causes of construction waste generation is shown in table ii. there are 46 root causes which scored more than 4.00, however for this paper only the top root causes are elaborated. a. supervision during construction stage is poor supervision and coordination is clearly expected to guarantee great task conveyance. satisfactory supervision prompts quality employment yet accompanies extra cost for the successful supervision [19-21]. good project supervision is imperative as it might give important pointers to different elements that may cause problems [22, 23, 27]. therefore, poor supervision at site leads to more material waste generation. b. lack of efficient site management site management should have a work task flow according to the project’s needs [24-26]. teamwork should be incorporated for an efficient site management plan [27, 28]. this includes managing scope, issues, risks, communication and the work plan. if the site management is not systematic the work will be faulty and will cause reworks. if basic management is lacking, the construction waste generated will not be coordinated efficiently, thus a huge sum of waste such as concrete, metal, sand, timber will be generated. this root cause is one of the main contributors to construction waste generation. c. last minute changes due to client requirements changes in design occuring while construction has begun is one of the root causes of generating waste [23, 29, 30]. clients should be clear with their vision of the project from the beginning. d. cutting uneconomical sizes of materials cutting materials into different sizes and uneconomical shapes generates waste [23]. when timber or metal are being cut without considering the next usage, the excess becomes 11,4% 17,1% 34,3% 17,1% 20,0% 6 -10 years 11 15 years 16 20 years 21 25 years > 26 years 11,4% 25,7% 62,9% client consultant contractor engineering, technology & applied science research vol. 8, no. 6, 2018, 3580-3584 3582 www.etasr.com kaliannan et al.: preliminary survey on the crucial root causes of material waste generation … waste. this factor is one of the highest regarding the volume of waste in waste production [31, 32]. table i. root causes of construction waste generation and their mean values code root causes of material waste generation mean code root causes of material waste generation mean rc22 supervision during construction stage is poor 4.611 rc27 abandonments of materials on site without proper waste control 4.278 rc21 lack of efficient site management 4.528 rc44 supplier errors due to carelessness 4.278 rc1 last minute changes due to client requirements 4.472 rc31 ordering errors by the workers 4.250 rc35 cutting uneconomical sizes of materials 4.472 rc36 inadequate storage place at project site 4.250 rc4 constant design changes during construction period 4.444 rc43 miscalculation in quantity surveys 4.250 rc12 unsuitable tools used during construction stage 4.444 rc25 language problems among foreign and native workers 4.222 rc15 unsatisfactory attitude of workers 4.444 rc26 lack of environmental awareness by the site team 4.222 rc2 slow information flow among all parties involved in the project causing redundant work 4.417 rc42 error in shipping of materials 4.222 rc11 improper material handling by the workers 4.417 rc8 incomplete information provided in the drawing 4.194 rc24 rework due to miscommunication among engineers and workers 4.417 rc18 inappropriate use of materials 4.194 rc46 lack of possibility of ordering small quantities of materials 4.417 rc48 effect of weather conditions 4.194 rc3 lack of coordination among parties involved in the project 4.389 rc16 insufficient worker training by the employer 4.167 rc23 improper construction methods applied by the workers 4.389 rc28 inventory of materials not according to site conditions 4.139 rc34 usage of wrong materials 4.389 rc49 occurrence of accidents at site 4.139 rc38 poor quality of supplied materials 4.389 rc6 improper design quality produced by consultant 4.111 rc47 inefficient methods of unloading supplied materials 4.389 rc17 management and technical team are less experienced 4.083 rc10 inappropriate material storage at site 4.361 rc32 frequent variation orders due to carelessness 4.056 rc20 planning of technical team at site is weak 4.361 rc33 inadequate security and pilferage at site 4.056 rc7 design produced by consultant is complex 4.333 rc39 materials supplied in loose form 4.055 rc13 faults of workers during construction process 4.333 rc5 design errors due to inexperienced designer 4.002 rc14 workers at construction site are less skilful 4.333 rc50 vandalisms 3.833 rc45 inaccurate material delivery procedures 4.333 rc51 damages caused by third parties 3.806 rc19 poor workmanship 4.306 rc29 inadequate lights provided at night 3.750 rc30 unforeseen geological conditions 4.306 rc9 designing without considering wastage 3.667 rc37 damage of materials during transportation 4.306 rc40 packaging waste generated 3.556 rc41 items ordered are not in compliance with specifications 4.306 rc52 unpredictable local conditions 3.278 table ii. construction waste root causes ranking root causes mean rank supervision during construction stage is poor 4.611 1 lack of efficient site management 4.528 2 last minute changes due to client requirements 4.472 3 cutting uneconomical sizes of materials 4.472 3 constant design changes during construction period 4.444 4 unsuitable tools used during construction stage 4.444 4 unsatisfactory attitude of workers 4.444 4 slow information flow among all parties involved in the project causing redundant work 4.417 5 improper material handling by the workers 4.417 5 rework due to miscommunication among engineers and workers 4.417 5 lack of possibility of ordering small quantities of materials 4.417 5 e. constant design changes during construction period sudden drawing changes can lead to higher waste generation [25, 26, 33]. this is an issue among contractors, designers and clients during design work stage [23, 30, 31, 34]. when the design is not confirmed during the initial stage, frequent changes may occur in construction period generating material wastages. this could be avoided if all the parties involved could have frequent productive meetings during the design stage to confirm the design prior to the construction. f. unsuitable tools used during construction stage tools used during construction may not be appropriate or suitable [25, 27, 35] leading to augmented generation of construction waste. g. unsatisfactory attitude of workers in a construction site, poor behavior can distress everyone and cause conflicts among workers [36, 37]. laziness of workers can cause reworks in the project [26, 27]. hence bad attitude may have crucial effects on work, causing workers to become dispirited and unhappy which would cause mistakes to occur more often and output would likely be poor [38]. h. slow information flow among all parties involved in the project causing redundant work communication and effective information flow are a pivotal part in construction procedures [36, 39]. having an efficient information flow among all parties can give a focused favorable advantage to a construction project [19, 29]. bad information flow will cause redundant work. i. improper material handling by the workers all materials received at site should be unpacked and arranged properly to avoid any damage [23, 31-33]. if the materials are not handled with care, damage can occur generating construction waste [36, 38]. j. rework due to miscommunication among engineers and workers failure to communicate can ultimately lead to serious accidents at site, project rework, and employee problems [31]. when there is miscommunication among the team, rework will engineering, technology & applied science research vol. 8, no. 6, 2018, 3580-3584 3583 www.etasr.com kaliannan et al.: preliminary survey on the crucial root causes of material waste generation … occur often and more material waste will be produced. effective communication is critical for collaborative work [23, 32]. clear communication not only reduces rework, it can also significantly increase the efficiency of the construction process [1, 34]. k. lack of possibility of ordering small quantities of materials lack of possibility of ordering small quantities of materials is one of the common causes of construction waste generation [30]. usually, only bulk orders can be ordered from a supplier [7, 10, 33]. there would be a minimum ordering amount to be fulfilled even though the amount required is less than the minimum order. therefore, material waste such as cement, timber, etc. will occur if there is excess of unused material. vi. preliminary survey outcome while conducting the preliminary survey, the construction practitioners suggested six major root causes which contribute to waste generation of malaysia construction industry. they are “human mindset of ignorance”, “political involvement”, “errors during installation”, “less usage of prefabricated materials”, “breakdown of equipment during concreting work” and “lack of bim usage for design”. regarding the first, human nature is to be of no concern on the waste and environment and the actions that must be taken. for “political involvement”, we should note that there has been a change in recent government, thus, many construction projects have faced design changes, kept on hold or stopped [40], “errors during installation” occur during improper installation of scaffolding which may cause damage to the materials used [4], “less usage of prefabricated materials” shows that material wastage compared to conventional construction can be reduced, “breakdown of equipment during concreting work” may occur during malfunction of concrete pump where the leftover concrete in the pump will turn into waste. lastly, “lack of bim (building information modeling) usage” for design purpose shows that bim can help minimize double handling of work from the design stages. vii. conclusions this research found that construction waste generation is a major issue in the malaysian construction industry, thus it is crucial to identify the root causes which contribute to construction waste generation in order to minimize the generated waste. after analysis, 46 root causes with mean value more than 4.00 were considered as crucial root causes. the acquired root causes will aid the construction practitioners to curb the construction waste generation from the initial stages of construction. the outcome of this research will not only be valuable in minimizing material waste generation but it will also support cultivating environmental awareness in construction industry of malaysia. acknowledgment we would like to thank the ministry of education, malaysia for funding this study under the fundamental research 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gammal, “material waste in the egyptian construction industry”, 9th annual conference of the international group for lean construction, national university of singapore, singapore, 2001 [38] m. s. pakhare, a. b. more, n. v. bhalerao, “to identify the root causes for wastages of construction materials”, international journal of advance research and innovative ideas in education, vol. 3, no. 4, pp. 2137-2139, 2017 [39] s. senaratne, d. wijesiri, “lean construction as a strategic option: testing its suitability and acceptability in sri langka”, lean construction journal, vol. 2008, pp. 34-48, 2008 [40] the star online, “govt scraps mrt 3 project”, available at https://www.thestar.com.my/news/nation/2018/05/31/govt-scraps-mrt-3project-pm-we-must-reduce-our-borrowings, 2018 engineering, technology & applied science research vol. 9, no. 2, 2019, 3924-3932 3924 www.etasr.com el-dash et al.: duration prediction models for construction projects in middle east duration prediction models for construction projects in middle east karim m. m. el-dash civil engineering department, faculty of engineering, benha university, shoubra, egypt k_eldash@hotmail.com osman m. o. ramadan faculty of engineering, cairo university, higher technological institute, 10th of ramadan city, egypt omoramadan@yahoo.ca waleed mahfouz m. a. youssef structural engineering department, faculty of engineering, cairo university, giza, egypt cvlmaster@yahoo.com abstract—construction industry is one of the most influential motivators of a national economy. the success of construction projects is indispensable to sustain a robust economy. completion time is important for construction projects, nevertheless project multifaceted objectives, sophisticated nature, inherent uncertainties, and risks are success impediments and can cause time overrun. stochastic models and simulation scheduling techniques are developed to predict the risk and uncertainty effects on construction projects’ duration. the objective of this research is to develop models that predict the activity durations based on actual data from similar projects. the study introduces comprehensive statistical regression models using historical data of about 84,000 activities in egypt, kuwait, and saudi arabia. the activities encompass engineering, procurement and construction (epc) activities for most disciplines of construction projects. the regression models can be utilized to predict more reliably the activities’ duration. keywords-construction projects; duration prediction; regression models; middle east i. introduction a. construction industry construction is a fundamental activity and one of the most predominant motivating forces for any national economy. it plays a prime role in economic development, and it is influencing and influenced by the gross domestic product (gdp) of any country [1, 2]. construction projects are dissimilar in size, type, location, site conditions, inputs and outputs, something that makes each project unique and consequently the standardization of construction processes becomes extensively difficult and risky. b. construction projects performance intrinsic risks and increasing complexity of modern construction projects cause delays and cost overruns to become common facts in the construction industry. from the projects completed worldwide between 1974 and 1988, 90% were delivered late with a cost overrun varying between 50% and 80% [3]. moreover, delays ranged from one up to 252 months in some cases [4]. c. construction delays delays may lead to disruption of work, loss of productivity, late project completion, increased additional time-related costs, non-completion, termination of contract, etc. [5]. therefore, studying construction delays and potential risks becomes an exigent prerequisite in order to control the estimated time for a project’s duration. overall project’s duration enables contractors to prepare their strategy and methodology. authors in [6-9] studied diverse types of projects, e.g. large buildings and public utilities in kingdom of saudi arabia (ksa) [6-9], grouping the causes of delays in 6 groups: contractor performance, owner and consultant administration, early planning and design, government regulation and policies, site and environmental conditions and supervision and field inspection. the study in [7] allocated the delay responsibility first to contractors, which were responsible for about the 44% of delays. in kuwait, authors in [10, 11] identified the key causes of delays in private residential projects. author in [12] incorporated 42 risk factors affecting time overrun in uae founding that the most significant factors are inflation and sudden changes in prices. author in [13] studied the performance of construction projects in jordan and found that amongst 130 projects 106 were delayed (81.5%). he indicated the major three causes of delay as: poor design (24.6%), change in orders (15.4%), and weather (12.3%). d. estimation models for project duration the project's realistic duration is important because it always serves as a crucial benchmark for assessing performance efficiency of a project’s time and cost [8]. the project’s estimated duration is often based on an owner’s feasibility study irrelevant to the construction plan, the activities’ sequential strategy, or the available resources. consequently, the project’s estimated duration is often not reliable and therefore represents a significant threat during construction. therefore, the estimation of realistic project duration can be considered the prime parameter towards reducing the probability of delay. also, it consequently decreases the expected disputes between owners and contractors. the prediction of a project’s overall duration constitutes a continual concern for construction researchers and project managers. the techniques used for estimating project’s overall fair duration have been outlined in many researches and the considered input parameters include the degree of complexity, the scope of work, the area of the project, the corresponding author: w. m. m. a. youssef mailto:k_eldash@hotmail.com mailto:moramadan@yahoo.ca engineering, technology & applied science research vol. 9, no. 2, 2019, 3924-3932 3925 www.etasr.com el-dash et al.: duration prediction models for construction projects in middle east number of levels, the function of building, the client type, the procurement route, the market constraints or opportunities, and the starting date of the project [14-22]. a model was developed to predict project duration based on project time-budget relationship in 1974 through investigation of 370 building projects in australia [16]. another model using historical data to develop different quantitative regression models to estimate the project’s duration and price was developed in [13]. the sample consists of 130 public projects in jordan between 1990 and 1997. authors in [18] developed a third model through surveying the performance of 2554 distinct building projects in the uk between 1998 and 2004. they produced a linear regression model for project duration according to building function classification. authors in [23] developed another model, as they investigated real data for a sample of 140 construction projects in jordan between 1994 and 2002. authors in [24] developed a model by focusing the study on 113 public projects in jordan between 1994 and 2002. they derived multiple regression models that predict the project cost and duration depending on scope, area, estimated budget, and estimated duration of the project. e. estimation of activity duration another parameter in reducing the probability of construction delay is estimating activity duration properly. the duration estimate depends on numerous factors including, construction execution methodology, resource availability, work quantity, nature, work complexity, labor and equipment productivity, quality of field management, weather, site conditions, etc. [25]. it is believed that the more reliable are the activity calculated durations, the more accurate the project completion time will be. authors in [26, 27] pointed that it is not essential for duration estimates to be consistently exact. all durations are only required to be reasonable, and subsequently, variations in activity durations will compensate each other, resulting in reasonably accurate project duration estimation. this estimation can be classified as deterministic and stochastic depending on project’s nature, potential risks, productivity rates, available resources, site conditions, site location, project environment, levels of complexity, levels of quality, expert judgment, and degrees of uncertainty [28-31]. nonmaterialized parameters such as uncertainty levels and potential risks were incorporated as a contingency percentage [31]. stochastic estimations or simulation techniques were utilized to appraise and quantify the impact of uncertainty and potential risks on activity’s duration in [30-34]. the prime objective of the current study is to provide a reliable technique for estimating activity durations for construction projects. this technique considers the actual behavior of similar activities and their potential risks affecting the performance of large construction projects. a variety of distinct regression models were generated to delineate the relationship between the estimated deterministic durations and their actual durations. the generated models provide a practical and easy tool for estimating the activity duration stochastically. this derivation expands previously reported studies and evaluates model predictions against the actual results from completed or currently running projects. ii. methodology and scope in order to predict more reliably activity durations, historic data from real projects were collected and analyzed. estimated and actual durations, and budget values were compiled from existent construction projects in three countries: egypt, kuwait and ksa between 1998 and 2013. a set of descriptive statistical analyses and regression models were established in order to appraise the relationship between the estimated durations and budget against actual durations. thirteen distinct projects were investigated covering a diverse sample of large construction projects for both public and private sectors including hospitals, high buildings, malls, hotels, stadiums, banks, administrative buildings, houses, infrastructure, and highway projects. the study encompassed a large number of activities, approximately 84,000, inclusive of engineering, procurement and construction (epc). engineering activities represent all preparation activities such as shop drawings and materials submittals including samples, manufacturer data, mockups, and testing certificate activities. procurement activities represent all activities needed to guaranty the delivery of the materials including contracts, letter of credits, manufacturing, shipping and delivery. construction activities represent all tasks on site that require manpower and equipment to be carried out in order to produce a structure or a part of the structure. the analysis of activities categorized regression models based on the type of activities (epc), the country, and csi master format 1995 classification. during the study, various computer software packages such as microsoft access 2010, primavera project planner 3.1, primavera enterprise 6.7, table curve 2d 5.01, sigma plot 12.0 and spss 20.0 were utilized in order to collect, sort, analyze and derive statistical properties and regression models for actual and estimated durations. a. data description according to type of work the generated regression models were classified according to the type of activities as: (1) engineering-procurement activities (epas) and (2) construction activities (cas). descriptive statistical analysis of 66,500 cas and 17,500 epas grouped by the estimated duration value is summarized in table i. the results of the actual activity duration comparison with the estimated ones over 90 days aligned with the ones in [13] thus proving that they are close to each other. as illustrated in table i, the smaller the estimated duration, the higher the duration slippage is. the ratio z defines the relationship between the mean of actual durations and the estimated duration. z-values are high for small estimated durations and small for high estimated durations. this unexpected ratio might be explained in [26, 27] as there is no time margin to compensate improperly estimated small durations. in the case of higher values of estimated durations, there is sufficient time to recover the delays internally on every activity level. table i demonstrates that for estimated durations lesser than 4 days, the z-values for epas are greater than those for cas. henceforth z-values for epas become smaller than cas for all values of estimated durations. engineering, technology & applied science research vol. 9, no. 2, 2019, 3924-3932 3926 www.etasr.com el-dash et al.: duration prediction models for construction projects in middle east table i. statistics of actual duration values for construction activities and engineering-procurement activities construction activities engineering-procurement activities ed activity number mean ad median mode std deviation (days) cv z activity number mean ad median mode std deviation (days) cv z 1 1059 44 20 1 59.1 1.3 44.1 1927 86 55 7 105.6 1.2 85.6 2 4413 82 28 1 110.3 1.3 41.1 39 88 70 1 99.7 1.1 44.2 3 3987 62 8 2 107.2 1.7 20.7 56 35 6 6 92.9 2.6 11.7 4 3638 73 17 3 108.2 1.5 18.1 19 94 27 3 152.5 1.6 23.6 5 4086 83 17 5 158.0 1.9 16.6 75 75 39 4 85.9 1.1 15.0 6 4591 98 41 6 122.2 1.2 16.3 128 22 6 6 43.0 2.0 3.7 7 3340 93 31 7 140.0 1.5 13.3 285 36 10 6 65.1 1.8 5.2 8 4033 70 24 8 100.6 1.4 8.7 96 44 30 30 45.5 1.0 5.4 9 1120 80 25 9 114.2 1.4 8.9 4 66 15 4 109.2 1.7 7.3 10 7858 71 22 10 109.0 1.5 7.1 374 42 19 12 57.7 1.4 4.2 11 590 111 61 8 124.6 1.1 10.1 7 120 42 12 118.0 1.0 10.9 12 5757 118 58 7 138.4 1.2 9.9 1277 58 20 12 79.3 1.4 4.8 13 2602 36 18 10 75.7 2.1 2.8 43 46 43 7 43.7 0.9 3.6 14 3809 109 60 14 125.5 1.1 7.8 5516 65 25 13 90.9 1.4 4.6 15 2934 135 79 14 159.5 1.2 9.0 599 54 23 16 67.2 1.3 3.6 20 829 141 105 19 137.2 1.0 7.0 159 91 48 22 100.4 1.1 4.5 25 615 111 61 4 138.7 1.2 4.4 258 77 29 28 116.9 1.5 3.1 30 604 161 116 34 160.8 1.0 5.4 917 92 45 29 95.2 1.0 3.1 40 165 127 90 46 128.8 1.0 3.2 108 84 49 11 90.9 1.1 2.1 50 1778 76 53 4 90.0 1.2 1.5 54 145 105 9 148.5 1.0 2.9 60 144 130 97 61 108.6 0.8 2.2 547 126 98 47 113.6 0.9 2.1 90 119 152 115 19 123.9 0.8 1.7 347 149 120 36 116.6 0.8 1.7 120 10 380 355 50 318.4 0.8 3.2 324 188 170 47 123.9 0.7 1.6 150 4 274 151 5 351.7 1.3 1.8 144 218 197 196 141.7 0.6 1.5 180 87 208 186 33 153.5 0.7 1.2 ed=estimated duration (days), ad= actual duration (days), cv=std/ad, z=mean ad/ed the deduced coefficient of variation (cv) for actual duration values from table i shows that the cv for cas ranges from 0.72 to 2.1, whereas the cv for engineering-procurement ranges between 0.65 and 2.65. furthermore, the values of cv for epas are not always higher than the ones for cas for similar values of estimated duration. planners and project managers can utilize the data included in table i and the probability density functions published in [35, 36] to forecast a project’s overall duration. overall project duration could be more than the one normally expected due to the difference of calculated activities duration with the use of conventional estimation techniques over the deduced values. however, the deduced values allow the opportunity for early planning through innovative methodologies and alternative plans to avert any probable delays. b. regression models for construction activities regression models for cas were generated for the 3 countries under study to provide a regional model of middle east. the investigation encompassed 66,500 distinct cas to develop a regression model describing the relationship between activities’ estimated duration and their pertinent average actual durations as described by (1)-(2): 𝑦 = 𝑎 + 𝑏 𝑙𝑛(𝑥) (1) 𝑦 = 𝑎 + 𝑏𝑥 (2) where y is the average value of actual duration, x is the estimated duration value and 𝑎 , b are constants. figure 1 illustrates the exponential growth in the average actual duration against estimated duration until the estimated duration reaches approximately 30 days, afterwards the increasing rate remains, however, with a moderate slope. another analysis of the construction activities was conducted for each individual country in order to estimate the impact of potential risks and the particular uncertainty level specific to each country. the regression models extracted for construction activities in kuwait, egypt and ksa are shown in figure 1. fig. 1. regression model for actual durations versus estimated durations for construction activities in the three countries kuwait and egypt are represented by (1) while the case of ksa is mathematically represented by (2). these regression models can be utilized to predict the average anticipated duration for any activity based on its relevant estimated duration calculated based on activity’s scope and productivity rate. figures 2(a)-(c) show the relationships between the average actual duration and the estimated duration for construction activities in egypt, kuwait and ksa, respectively. as demonstrated in figure 2(a) the trend of average actual duration increases rapidly until the estimated duration of engineering, technology & applied science research vol. 9, no. 2, 2019, 3924-3932 3927 www.etasr.com el-dash et al.: duration prediction models for construction projects in middle east approximately 10 days. afterwards, the slope slowly decreases until estimated duration of 20 days. finally, the curve almost becomes horizontal. meanwhile, the average actual durations in kuwait are rapidly increasing until estimated durations reach 20 days, and then the slope becomes moderate as illustrated in figure 2(b). it is worth noting that the relation between the average actual and estimated durations in ksa is linear with consistent growth from the beginning till the end as shown in figure 2(c). in general, the values of average actual durations pertinent to estimated durations less than 30 days are higher in all cases. the highest values for this range were recorded in kuwait due to the fluctuated levels of productivity rates, the strict application of quality control program, the lack of workforce in the local market, and the lack of planning and control by the subcontractors [10]. (a) (b) (c) fig. 2. actual durations regression model for cas versus estimated durations in: a) egypt, b) kuwait; and c) ksa c. regression models for engineering-procurement activities the regression model for engineering-procurement activities was developed by analyzing 17,500 activities in the 3 countries. the best fit is a linear model as illustrated in figure 3 and formulated by (2). d. regression models for critical activities the study of the actual performance of critical activities included approximately 12,900 critical activities constituting nearly the 15.4% in a sample of about 84,500 activities. construction critical activities represent about 14% of total cas. the ratio of the critical epas is around 20% of the total epas. comprehensive statistical study on critical activities proved that critical activities for all phases as well as for cas are best described by (1), whereas, critical epas are best represented by (2). as evidently revealed in figure 4, the ratio (z-value) in cas is higher than those for epas until the estimated duration of 40 days. z-values are higher for epas than for cas for estimated durations above 100 days due to delays in material delivery and poor coordination between main contractors and international suppliers [10, 36-38]. the values of r2 coefficient and equations’ constants related to regression models of critical activities are exhibited in table ii. fig. 3. regression model for epas actual durations versus estimated durations in the three countries (a) (b) (c) fig. 4. regression models for actual durations in the 3 countries grouped by phase of work: a) all phases, b) cas, and c) epas e. regression models for kuwait grouped by csi divisions a thorough analysis was performed on the construction activities in kuwait with results categorized according to csi engineering, technology & applied science research vol. 9, no. 2, 2019, 3924-3932 3928 www.etasr.com el-dash et al.: duration prediction models for construction projects in middle east format. the analysis reveals that divisions: site works (02), masonry works (04), finishing works (09) and mechanical works (15) are best represented by (1). division concrete works (03) is represented by (3), division doors and windows works (8) by (2), and division electrical works (16) by (4). 𝑦 = 𝑎 + 𝑏√x (3) 𝑦 = 𝑎 + 𝑏/√𝑥 (4) 𝑦 = 𝑎 + 𝑏/𝑥 (5) (a) (b) (c) (d) (e) (f) (g) fig. 5. regression models for actual cas duration in kuwait analyzed by csi divisions: a) division 02, b) division 03, c) division 04, d) division 08, (e) division 09, f) division 15, and g) division 16 the graphical analysis of cas in kuwait categorized according to csi divisions is illustrated in figure 5. it is worth noting that all regression models for cas, particularly in kuwait, follow nonlinear models except (08). in general, the majority of construction regression models in kuwait start with exponential augmentation until an estimated duration of approximately 15 days. thereafter, most trends continue with a considerable growth for all divisions except for (09) that follows a slight growth to become nearly stationary as in (5). in brief, the generated regression models for cas demonstrate that (1) could be considered the best to represent the relationship between estimated durations and their respective actual durations. f. regression models for construction activities in an individual project grouped by csi divisions analysis was conducted on the construction activities of a distinctive large project in kuwait. the project’s budget was 55 million kuwaiti dinar and had scheduled nearly 6,400 cas. the diagrammatic illustration of the regression models is shown in figure 6 and the equations’ constants are summarized in table ii. it is interesting to recognize that the exceedingly dominant equation that could be considered the best to describe numerous regression models of construction activities in an individual project is (3). on the other hand, a focus at figures 5 and 6 reveals some striking dissimilarities in regression models for divisions (02), (03) and (15) in the selected project and between those of all studied projects in kuwait as illustrated in table ii. moreover, the regression model for division (03) is best represented by (6) for the case of construction activities an individual project: 𝑦 = 𝑎 + 𝑏 . 𝑥 2 (6) the provided information in table ii summarizes the cases of analysis, equations, equations’ constants, and r2 coefficients for all regression models used. as an overall observation, the engineering, technology & applied science research vol. 9, no. 2, 2019, 3924-3932 3929 www.etasr.com el-dash et al.: duration prediction models for construction projects in middle east values of r2 have evidenced considerable dissimilarities between engineering–procurement and construction regression models. (a) (b) (c) (d) fig. 6. regression models for actual ca duration in a single project in kuwait analyzed by csi divisions: a) all divisions, b) division 02, c) division 03, and d) division 15 g. influence of total float on the ratio of actual duration to estimated duration this study demonstrated that there is no direct relationship between the total float and the actual duration of activities as shown from the oscillation of results in figure 7. nevertheless, it could be presumed that preparing a schedule with a higher total float would lead to a higher time overrun. correspondingly, it could be concluded that the duration ratio (z-value) between the actual and estimated duration for various activities with total float range between 0 and 30 days does not follow a steady behavior. whilst, the ratio seems more stable for activities with total float ranges between 30 and 200 days. another leading note is that the ratio is small for critical activities that have a zero-total float owing to the much more concern or concentration that was directed from the client or the contractor towards the critical or the semi-critical activities. consequently, it is recommended to urge the project's stakeholders to focus commensurately towards all activities in order to avert delays. table ii. regression models, model constants, and r2 for all cases country equation constants r2 a b construction activities grouped by country all y=a+bln(x) 43.152146 25.791774 0.72 egypt y=a+bln(x) -31.315662 57.501272 0.64 kuwait y=a+bln(x) 39.278186 28.153913 0.72 ksa y=a+bx 25.808561 2.660858 0.76 engineering-procurement activities in all countries all y=a+b x 52.247198 0.935995 0.94 critical activities grouped by phase of work all y=a+bln(x) -6.546497 28.374720 0.85 construction y=a+bln(x) -8.330252 29.038051 0.81 engineering procurement y=a+bx 2.923219 1.662299 0.93 construction activities in kuwait grouped by csi divisions division 02 y=a+bln(x) -25.436390 44.141265 0.84 division 03 y=a+b√𝑥 -10.956444 17.486019 0.95 division 04 y=a+bln(x) -71.293389 76.259028 0.86 division 08 y=a+bx 42.765386 2.332210 0.86 division 09 y=a+b/x 75.103390 -91.72622 0.73 division 15 y=a+bln(x) 72.249936 27.216517 0.76 division 16 y=a+b/√𝑥 232.291363 -35.85608 0.84 construction activities in one project grouped by csi divisions all y=a+b√𝑥 14.575190 20.443443 0.86 division 02 y=a+b√𝑥 -36.682006 30.708906 0.98 division 03 y=a+bx2 57.499591 0.031131 0.92 division 15 y=a+b√𝑥 4.876508 19.171406 0.94 fig. 7. relationship between total float and increment in z-value h. relationship between activity budget and actual duration analysis was conducted to estimate activities’ duration by evaluating the relationship between the estimated budget and the actual duration. the study was conducted on nearly 35,000 construction activities in kuwait with a total budget of approximately 240 million kuwaiti dinar (1kd=3.5usd). the studied activities represent various projects and include most disciplines of work. it is found that the average budgeted rate per estimated duration is approximately 492.1kd/day, whereas engineering, technology & applied science research vol. 9, no. 2, 2019, 3924-3932 3930 www.etasr.com el-dash et al.: duration prediction models for construction projects in middle east the average budgeted rate per actual duration is around 83.7kd/day as summarized in table iii. in addition, it is found that the highest budget rate per actual duration is assigned to metal works, division (05), then to concrete works (03). the lowest allocated budget per day is for mechanical works (15) and electrical works (16). table iii. budget per ed and ad in kuwait for csi divisions csi division division budget % budget/ ed budget/ ad (kd/day) (kd/day) 02 site works 10.94 946.3 153.5 03 concrete works 40.91 694.5 203.5 04 masonry works 2.59 462.1 95.5 05 metal works 7.44 1,057.5 234.7 06 wood and plastic works 0.12 476.9 74.9 07 thermal and moisture protection 2.89 293.8 73.7 08 doors and windows works 3.08 383.3 70.3 09 finishes works 6.6 185.1 40.9 14 conveying system works 0.81 447.2 51.6 15 mechanical works 11.3 284.7 33.9 16 electrical works 11.65 504.7 45.3 all divisions 492.1 83.7 ed=estimated duration (days), ad= actual duration (days) the regressing models that describe the relationship between the average actual duration and their assigned budget for all construction activities are best represented by (3). moreover, the developed regression model is valid for construction activities with allocated budgeted values greater than 2,500kd. the regression model starts with a rapid increase and thereafter the slope continues with a little lower growth as illustrated in figure 8. fig. 8. relationship between activity average budget (1000kd) and ad i. relationship between activity budget and ad for each csi division an extra analysis was conducted to determine the relationship between the budget assigned to construction activities and their relevant actual durations. the objective of this study is to derive estimated durations for activities of construction projects with higher degrees of reliability by utilizing the activity’s budgeted value. it is found that the cases of all divisions together and division (15) follow the same regression model that is represented by (3) whereas, divisions (03), (09), and (16) follow regression models represented by (1) and division (02) follows (2). as shown in figure 9, the trends for divisions classified as civil works such as divisions (02), (03) and (04) start with quite moderate increasing rates. meanwhile, the curves for divisions (15) and (16) that represent electro-mechanical works start with a dramatic increase. this increase can be attributed to the distribution of items’ budget over their relevant construction activities. whereas, the electromechanical first fix activities always have smaller budgets than second or third fix activities. (a) (b) (c) (d) (e) fig. 9. regression models for predicting the relationship between ca budget and ad in kuwait: a) division 02, b) division 03, c) division 09, d) division 15, e) division 16 engineering, technology & applied science research vol. 9, no. 2, 2019, 3924-3932 3931 www.etasr.com el-dash et al.: duration prediction models for construction projects in middle east table iv. regression models, model constants, and r2 for construction activity budget per ads for each csi division division equation constants r2. a b all divisions y=a+b.√𝑥 -106.850042 63.9112922 0.90 division (02) y=a+b.x 63.92006073 2.14839692 0.52 division (03) y=a+b ln(x) -100.7569902 70.9025097 0.87 division (09) y=a+bln(x) -5.451089338 54.7762879 0.88 division (15) y=a+b√𝑥 -35.28792636 70.0599205 0.85 division (16) y=a+bln(x) 40.44178744 34.9312426 0.57 furthermore, the first fix activities often have interdependencies with various disciplines that always cause time slippage and duration overrun. meanwhile, the third fix activities are always installed in a short time and during one session. therefore, contractors should plan and make the necessary coordination for electromechanical first fix activities at earlier stages. in stark contrast, however, the same equipment from different vendors or brands may increase the assigned budget, but will not have a tangible impact on installation time. iii. summary and conclusions comprehensive statistical regression models were developed using real data from 13 large construction projects in egypt, kuwait and ksa including approximately 84,000 epc activities representing most disciplines of work. the regression models delineate the relationship between activities estimated and actual durations to predict actual durations based on their pertinent estimated duration through conventional estimation techniques. in addition, regression models were established utilizing 35,000 construction activities to predict the activities’ duration based on their budgets. it was found that: • the shorter the estimated duration is, the higher the duration slippage will be. therefore, contractors are recommended to prepare work breakdown structure with activities with no less duration than 15 days. most regression models for construction activities in kuwait start with rapid increasing slope until an estimated duration of about 15 days. • a project’s overall duration based on our proposed regression models may be greater than that conventionally calculated. nevertheless, the proposed values allow the opportunity for early planning through implementing innovative methodologies and substitutional plans. • average actual duration values relevant to estimated durations less than 30 days are very high, and the highest values for this range were recorded in kuwait. • the z-value ratio for construction activities with duration less than 40 days is higher than engineering–procurement activities. the ratio becomes higher for engineering– procurement activities with duration greater than 100 days. • there is no proof for a direct relationship between total float and the actual duration slippage of activities. the zvalue ratio is small for critical activities which have zerototal float. • the overall budget rates of all activities per estimated duration and per actual duration are about 492.1 and 83.7 kd/day respectively. • the highest budget rate per actual duration is assigned to division (05), metal works, and then to division (03), concrete works. the lowest budget rates per actual duration are divisions (15) and (16), mechanical and electrical works. • the regression models for electro-mechanical works start with an exponential increase because the first fix activities always have smaller budgets than the second or third fix activities. meanwhile, the first fix activities often have time slippage and duration overrun. therefore, contractors should plan and coordinate more accurately for electromechanical first fix activities at 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influence of starch content on the thermal and viscoelastic properties of syndiotactic … influence of starch content on the thermal and viscoelastic properties of syndiotactic polypropylene/starch composites naveed ahmad department of chemical and material engineering college of engineering northern border university arar, saudi arabia naveed.ahmad@nbu.edu.sa farooq ahmad department of chemical and material engineering college of engineering northern border university arar, saudi arabia farooq.ahmad@nbu.edu.sa ibrahim alenezi department of chemical and material engineering college of engineering northern border university arar, saudi arabia i.alenezi@nbu.edu.sa abstract—in this study, syndiotactic polypropylene/starch (spp/starch) composites were prepared using a solution mixing technique. the thermal characterization was performed using differential scanning calorimetry (dsc), and the melting point was measured for all polymer composites. the thermal degradation temperature was measured using thermal gravimetric analysis. the viscoelastic measurements were performed using the atomic rheometric expansion system (ares). both melting point and thermal degradation temperatures were found to decrease with increasing starch content. moreover, the elastic modulus was found to decrease when the starch content increased. keywords-aeration; melting point; spp/starch composites; thermal degradation temperature; elastic modulus; frequency sweep test i. introduction polymer composites are synthesized by embedding natural or synthetic materials into a polymer to increase its desired properties [1, 2]. several studies have been conducted on enhancing the properties of polymer products [3-23]. polymer composites with different combinations of filler and polymer are studied in order to obtain the desired and targeted properties of polymer products [3]. however, the final desired microstructure and macrostructure properties of polymers and composites depend on the nature, amount, geometry, and interfacial interactions of the components [4]. rheology is used as a tool to study a polymer's or a polymer composite's microstructure, as the rheological response is highly sensitive to the molecular structure of polymers and their composites [59]. while several studies have been conducted on the synthesis and the rheology of polymer and polymer/clay composites [1018], only a few have targeted the viscoelasticity of polymer/clay composites. the rheological properties of polyethylene oxide/montmorillonite clay gels and multilayered films were studied in [14], using an atomic rheometric expansion system (are-2 rheometer), and noticing a slight increase in both the loss modulus (g') and the storage modulus (g'') when increasing the clay content. the thermal properties were examined using differential scanning calorimetry (dsc) and thermal gravimetric analysis (tga), while the results were related to the microstructural properties of the composites and the films. the effect of clay content on the rheology of polypropylene/clay nanocomposites was investigated in [15], examining both linear and non-linear rheology, finding that loss modulus (g'), storage modulus (g''), and dynamic viscosities increased monotonically with organophilic montmorillonite nanocomposites. the viscoelastic properties of syndiotactic polypropylene (spp) were investigated in [16], examining the effect of the degree of syndiotacticity on the rheological parameters, including plateau modulus and entanglement molecular weight. this study indicated that increasing the degree of syndiotacticity enhanced the plateau modulus causing a decrease in the molecular weight between entanglements. in [17], the influence of clay contents on plateau modulus and entanglement molecular weight was studied on polypropylene/clay composites, concluding that an increase in the clay content increased the plateau modulus and consequently decreased the entanglement molecular weight. the rheological properties of a drilling fluid polymer treating agent named driscal-d using a fann 50sl rheometer were investigated in [24]. the effects of adding polymer, electrolyte, clay type, and antioxidant on the rheological properties of a corresponding author: naveed ahmad engineering, technology & applied science research vol. 11, no. 3, 2021, 7228-7232 7229 www.etasr.com ahmad et al.: influence of starch content on the thermal and viscoelastic properties of syndiotactic … driscal-d solution were examined, finding that solution's viscosity tends to increase when increasing polymer addition and decreased in the presence of an electrolyte. furthermore, adding clay in a driscal-d solution enhanced its rheological properties, which could improve cuttings transportation. the current study examines the viscoelasticity of syndiotactic polypropylene/starch composites (spp/starch), with starch content ranging from 0 to 8%, using an atomic rheometric expansion system (ares) to investigate the effect of starch content on the melt rheological response of composites. ii. methodology a. polymer composite synthesis 1) materials syndiotactic polypropylene (spp) having a 60% degree of syndiotacticity, supplied by zhongwei industrial co. ltd., was used as a matrix. starch, originating from potato, was used as the filler. xylene, provided by shanxi zhongwei industrial co. ltd., was used as a solvent in mixing. the samples' details are listed in table i. table i. samples' details number of samples name of samples percentage of starch content degree of syndiotacticity (%rrr) 1 spp/s-8 8% 2 spp-6 6% 3 spp/s-4 4% 4 spp/s-2 2% 5 spp 0 60 2) preparation of composite samples solution mixing was applied to create a set of syndiotactic polypropylene/starch composite samples with four different starch content proportions. the starch was accurately weighed and mixed with the polypropylene matrix using xylene as a solvent in a 1000ml beaker. the mixing temperature was kept at 120°c using a heating mantle until all syndiotactic polypropylene granules dissolved in a clear solution. the solvent containing syndiotactic polypropylene was initially shaken vigorously by hand and then stirred by a high-speed electrical stirrer keeping the heating conditions. the starch, dissolved in xylene, was added slowly to the syndiotactic polypropylene and xylene mixture. vigorous and continuous stirring helped the uniformity of starch mixing and the intercalation of spp to starch layers. the beaker operated for a few hours to evaporate the xylene. then, the size of the prepared polymer-starch composite was mechanically reduced. after the completion of xylene evaporation, the composite samples were created by compression molding at 170°c temperature and 7psi pressure for one and a half hour [10]. b. polymer composite analysis 1) differential scanning calorimetry (dsc) the melting temperature (tm) of all samples was measured using differential scanning calorimetry (dsc). the samples, weighing 4mg, were heated up to 350°c at a constant heating rate of 40°c/min. during the heating cycle, the melting point peak was obtained. afterward, the sample was kept under this annealing process for 7 minutes to eliminate crystallinity and remove thermal history. the analysis was performed using the instrument software ta-60 to find the melting temperature (tm) of all samples. 2) rheometry the spp/starch composites were pressed using hot press to prepare a uniform film for each composite. an atomic rheometric expansion system (ares) (ta instruments), having a geometry of 8mm diameter parallel plate, was used to perform the viscoelastic tests under nitrogen atmosphere to reduce sample degradation. all experiments were carried out at a different gap depending on the sample's thickness. at first, strain sweep and stability tests were carried out. after choosing the suitable strain value (0-10%), dynamic frequency sweep tests were performed at temperatures ranging from 100°c to 200°c to obtain both elastic and viscous moduli at different frequencies and the master curves using the time-temperature superposition principle. no tests were performed below 100°c due to the faster crystallization kinetic. iii. results and discussion frequency sweep tests were performed on all samples. the frequency sweep tests for samples having 2% and 6% starch contents are shown in figures 1 and 2 respectively. it can be noted that the elastic modulus increased along with the frequency range (0 to 100rad/s), while the viscous modulus tended to decrease. figure 1 shows a cross-over frequency at almost 1rad/s indicating that relaxation time was a little greater than 1s. figure 2 shows that viscous was greater than elastic modulus at lower frequencies, while the elastic modulus was higher than viscous at higher frequencies. the cross-over frequency of the 6% sample was found to be greater than the one in the 2% sample, indicating that relaxation time for the 6% sample was less than for the 2%. this result also indicates that increasing starch content decreased the elastic and increased the viscous response. in other words, a strength decrease occurs when the starch content increases. fig. 1. frequency sweep test for spp/s-2 at 200°c. engineering, technology & applied science research vol. 11, no. 3, 2021, 7228-7232 7230 www.etasr.com ahmad et al.: influence of starch content on the thermal and viscoelastic properties of syndiotactic … fig. 2. frequency sweep test for spp/s-6 at 200°c. a. effect of starch on melting point the effect of starch on the melting point temperature of spp/starch composites is shown in figure 3. as it can be noted, increasing starch content decreased the melting point temperature of spp/starch composites. the melting point of the composite was actually the melting point of starch. starch's thermal stability is low compared to the syndiotactic polypropylene polymer. therefore, increasing starch decreases the melting point temperature of spp/starch composites. fig. 3. relationship between starch and melting point (tm). b. effect of starch on thermal degradation temperature the thermal degradation temperature of all composites was measured using thermal gravimetric analysis (tga). the tga analysis for the spp sample containing 4% starch is shown in figure 4. this figure depicts two drops in mass: the first drop indicates the removal of water from the composite sample, i.e. the dryness of the sample, while the second drop indicates the degradation of the sample. thermal degradation temperature decreased when increasing starch content, as shown in figure 5. fig. 4. fdsc and tga analysis of spp/s-4. fig. 5. relationship of thermal degradation temperature and starch content. c. effect of starch on elastic modulus the elastic modulus was calculated using frequency sweep tests for all samples. the maximum value for each sample was noted. the elastic modulus indicates the mechanical response of a sample, and it was examined as a function of starch content. increasing starch content decreased the elastic modulus, as shown in figure 6. therefore, increasing starch content decreased the strength of the composites. this result comes in agreement with the findings of [17], which investigated the effects of clay content on the thermal and rheological properties of spp/clay composites. clay content and starch affected the rheological and thermal properties of spp/clay composites oppositely. clay content increased the melting point temperature and the plateau modulus of spp/clay composites. on the other hand, starch decreased both the thermal properties and the elastic modulus. an increase in clay content increased the mechanical response of the spp/clay composites, while an increase in starch content decreased the mechanical and increased the viscous response of syndiotactic polypropylene/starch composites. starch (%age) 0 2% 4% 6% 8% t h e rm a l d e g rd a ti o n ( c ) 280 300 320 340 360 380 400 420 440 starch (% age) vs t d (c) engineering, technology & applied science research vol. 11, no. 3, 2021, 7228-7232 7231 www.etasr.com ahmad et al.: influence of starch content on the thermal and viscoelastic properties of syndiotactic … fig. 6. relationship between starch contents and elastic modulus. iv. conclusion the viscoelastic and thermal analysis of spp/starch on melting point, thermal degradation temperature, and elastic modulus depend on starch content. this stydy's findings showed that viscoelasticity is a powerful tool to investigate the microstructure and the chain parameters of polymer/starch composites. thermal and viscoelastic properties were found sensitive to starch content proportions. starch alters both the melting point and the thermal degradation temperatures, as increasing starch content decreased both of them. the same trend was found for the elastic modulus, as it decreased when the starch content increased. in conclusion, increasing starch content results in a decrease of the mechanical 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[24] w. zheng, x. wu, and y. huang, "impact of polymer addition, electrolyte, clay and antioxidant on rheological properties of polymer fluid at high temperature and high pressure," journal of petroleum exploration and production technology, vol. 10, no. 2, pp. 663–671, feb. 2020, https://doi.org/10.1007/s13202-019-0732-8. microsoft word 2-428-ed.doc engineering, technology & applied science research vol. 4, no. 3, 2014, 631-635 631 www.etasr.com hakim et al.: seismic assessment of rc building using pushover analysis seismic assessment of an rc building using pushover analysis riza ainul hakim civil engineering department, king abdul-aziz university, jeddah, saudi arabia ainul7@yahoo.com mohammed sohaib alama civil engineering department, king abdul-aziz university, jeddah, saudi arabia sohaib.alama@hotmail.com samir a. ashour civil engineering department, king abdul-aziz university, jeddah, saudi arabia sashour@kau.edu.sa abstract— current research works and observations indicated that parts of the kingdom of saudi arabia have low to moderate seismic regions. major parts of buildings were designed only for gravity load and were poorly detailed to accommodate lateral loads. this study aims to investigate building performance on resisting expected seismic loadings. two 3d frames were investigated using pushover analysis according to atc-40. one was designed according to a design practice that considers only the gravity load and the other frame was designed according to the saudi building code (sbc-301). results showed that the building designed considering only the gravity load was found inadequate. on the other hand, the building designed according to sbc-301 satisfies the immediate occupancy (io) acceptance criteria according to atc-40. keywords-pushover; seismic analysis; capacity spectrum; sbc301; atc-40 i. introduction the kingdom of saudi arabia lies within a low to moderate seismic region. according to the u.s. global survey (usgs) data, earthquakes have been detected recently in tabuk (2009) and gizan (2013). in the past decades, the inclusion of dynamic loads in the design of buildings in saudi arabia was limited to important huge structures. recently, the saudi building code (sbc-301) has been released for trial application. this code provides minimum load requirements for the design of buildings and other structures. most of existing buildings do not meet the current design standards due to design shortage or construction shortcomings. there are various reasons such as the lack of a national code, the noncompliance with applicable code requirements, the updating of codes, the design practices and changes in the use of buildings. therefore, existing buildings should be evaluated regarding their capacity for resisting expected seismic effects before rehabilitation works [1]. it is believed that the conventional elastic design analysis method cannot capture many important aspects that affect the seismic performance of the building. the ability of a building to undergo inelastic deformations determines the structural behavior of building during seismic ground motions. for that reason, the evaluation of a building should be based on the inelastic deformation applied demanded by an earthquake, besides the stresses induced by the equivalent static forces as specified in seismic regulations and codes [2, 3]. nonlinear dynamic analysis is a principally convenient approach. however, it is very complex and not practical for every design. such analysis faces certain difficulties, such as the complexity of the three dimensional modeling structure, uncertainty of the structural properties, and the randomness of the ground motion data required for analysis. from the practical point of view, this method is not suitable for every design use, and for the time being it is mostly appropriate for research and design of important structure [4-6]. to estimate seismic demands for a building, the structural engineering profession is now using the non-linear static procedure, known as pushover analysis. it is a commonly used technique, which provides acceptable results. the term static implies that static analysis is applied to represent a dynamic phenomenon [7, 8]. pushover analysis is a series of incremental static analysis carried out to develop a capacity curve for the building. this procedure needs the execution of a nonlinear static analysis of the structure that allows the monitoring of the progressive yielding of the structure component [3]. the building is subjected to a lateral load. the load magnitude increases until the building reaches the targeted displacement. this target displacement is determined to represent the top displacement when the building is subjected to design level ground excitation. pushover analysis produces a pushover curve or capacity curve that presents the relationship between the base shear (v) and roof displacement (∆). the pushover curve depends on the strength and deformation capacities of the structure and describes how the structure behaves beyond the elastic limit [3, 6, 8]. structural response to ground motion during earthquake cannot be accurately predicted because of the complexity of the structural properties and ground motion parameters. in pushover analysis, a set of lateral displacement is used directly as design condition. the displacement is an estimate of the engineering, technology & applied science research vol. 4, no. 3, 2014, 631-635 632 www.etasr.com hakim et al.: seismic assessment of rc building using pushover analysis maximum expected response of the structure during ground motion [2, 3]. a. capacity spectrum the building performance level can be determined by target displacement using the capacity spectrum method (atc 40). the capacity spectrum method allows for a graphical comparison between the structure capacity and the seismic demand. the pushover curve represents the lateral resisting capacity and the response spectrum curve represents the seismic demand. the capacity spectrum method, which is described in figure 1, is started by producing a force-displacement curve that consider the inelastic condition. the result is then plotted to adrs (acceleration displacement response spectrum). the demand is also converted into adrs format so that the capacity curve and the demand curve are in the same format [9, 12]. fig. 1. capacity spectrum method. the general process for converting the capacity curve to capacity spectrum is to first calculate the modal participation factor (mpf1) and the modal mass coefficient (α), using the following equations: i i1 1 2 i 1 m φ mpf = (1) m φi   2 i i1 2 i 1 1 1 [ m φ ] = (2) [ ] [ m φ ] n n i i i i a w g      (2) where: iw g =mass assigned to level i 1φi =amplitude of mode 1 at level i n=level n then sa and sd are calculated for every point on the capacity curve using the following equations: a bs v 1= (3) g w a  1 roof d 1 roof δ s = (4) mpf φ where: v=base shear w=building load weight δroof=roof displacement to convert a demand spectrum from sa and t format to adrs format, it is required to calculate the value of sd for each point of the curve using the following equation: 2 a d 2 s s = (5) 4  the performance point is obtained by superimposing demand spectrum on capacity curve into spectral coordinate or adrs format. the capacity spectrum method has been built in sap2000 program. according to atc 40, the performance levels of buildings are as shown in table i. table i. performance level of building level description operational very light damage, no permanent drift, structure retains original strength and stiffness, all systems are normal immediate occupancy light damage, no permanent drift, structure retains original strength and stiffness, elevator can be restarted, fire protection operable life safety moderate damage, some permanent drift, some residual strength and stiffness left in all stories, damage to partition, building may be beyond economical repair collapse prevention severe damage, large displacement, little residual stiffness and strength but loading bearing column and wall function, building is near collapse b. nonlinear plastic hinge pushover analysis requires the development of the forcedeformation curve for the critical section of beams and column by using the guideline in [10]. such a curve is presented in figure 2. fig. 2. typical load-deformation relation and target performance level point a corresponds to the unloaded condition. load deformation relation shall be described by the linear response from a to an effective yield b. then the stiffness reduces from point b to c. point c has a resistance equal to the nominal strength then a sudden decrease in lateral load resistance to point d, the response at reduced resistance to e, final loss of resistance. the slope of the bc line is usually taken between 0 and 10% of the initial slope. the cd line corresponds to an engineering, technology & applied science research vol. 4, no. 3, 2014, 631-635 633 www.etasr.com hakim et al.: seismic assessment of rc building using pushover analysis initial failure of the member. the de line represents the residual strength of the member. these points are specified according to fema to determine hinge rotation behavior of rc members. the points between b and c represent acceptance criteria for the hinge, which is immediate occupancy (io), ls (life safety), and cp (collapse prevention). ii. descriptive of the building test the prototype building is a 6-story reinforced concrete structure, with a height story of 4.0 m. the overall plan is 18x18 square meters. figure 3 shows the typical structural layout. all beams are 600/400. the columns are 500/500 mm rectangular. the type of soil is soft rock or site class c according to the saudi building code 301. fig. 3. structure layout the structural system was designed using two methods, the first is a design practice that considers only the gravity load whereas the intermediate resisting frame (imrf) according to sbc 301 was considered for the second. a summary of the model’s assumption is presented in table ii. in this study, pushover analysis is carried out using the sap2000 program. a three-dimensional model of structure has been created as shown in figure 4. beams and columns are modeled as nonlinear frame elements at the start and the end of element. the fema 356 rule, which is built in sap 2000 with the io, ls, and cp limit states for hinge rotation have been used for the acceptance criteria. the pushover analysis is executed separately for the two designs. the pushover analysis is achieved using a displacement control strategy, where the building is subjected to the lateral load pattern until the roof displacement reaches a target value. the minimum number of state used is 10 and the maximum is 100. pushover analysis is performed in haql, which is the most severe seismic zone according to sbc-301 [11] and the type of soil is soft rock or site class c. a summary of seismic site parameters are presented in table iii. table ii. assumptions of the model material concrete 27.5 mpa steel a615gr60 loading self-weight automatically by software dead load 2.7 kn/m2 live load 2.5 kn/m2 wind load not considered modelling element linear element for beam and column shell element for slab p-delta effect not considered diaphragm shell element for slab support fixed fig. 4. 3d model (sap2000) table iii. site parameters ss s1 fa fv sms sm1 sds sd1 0.865 0.281 1.054 1.519 0.912 0.427 0.608 0.285 where: ss: the maximum spectral response acceleration at short periods s1: the maximum spectral response acceleration at a period of 1 sec fa: acceleration-based site coefficient fv: velocity-based site coefficient sms : the maximum spectral response acceleration at short periods adjusted for site class sm1: the maximum spectral response acceleration at a period of 1 sec adjusted for site class sds: the design spectral response acceleration at short periods sd1: the design spectral response acceleration at a period of 1 sec sbc-301 provides the required minimum standards for the equivalent lateral force procedure of seismic analysis of a structure as presented in table iv. the design response spectrum is developed as indicated in figure 5. engineering, technology & applied science research vol. 4, no. 3, 2014, 631-635 634 www.etasr.com hakim et al.: seismic assessment of rc building using pushover analysis table iv. seismic design parameter r i h ta (s) cs w (kn) v (kn) 4 1 12 0.412 0.152 9227.0 1402.1 fig. 5. design response spectrum iii. analysis results pushover curves for the building for both designs are presented in figure 6. these curves represent the global behavior of the frame with stiffness and ductility. under incrementally increasing lateral load, the structural element may be yield sequentially. at every step, the structure experience loss in stiffness. therefore, the slope of the pushover curve is gradually decreasing. the comparison of the pushover curve shows that the stiffness of frame is larger in imrf (sbc301) compared to the gravity load design. this means that sbc design has a greater capability to resist lateral load (seismic load) than the gravity load design. fig. 6. pushover curve the performance point has been obtained by superimposing the demand spectrum on the capacity curve into spectral coordinates as shown in figures 7 and 8. at every deformation step of the pushover analysis determine plastic rotation hinge location in the elements and hinges reach the fema limit state, which are io, ls, and cp using colors for identification (figures 9 and 10). the steps at which the three limit states of plastic hinges are reached and the corresponding values on the pushover curve are obtained from figure 7 and 8. for gravity load design, the structural frame is not satisfactory because the lower columns yields exceed c (collapse) condition. on the other hand, although most of elements in imrf design are in yield condition, the damage of the structure is still limited since yielding occurs at event b (yielding) to io (immediate occupancy). fig. 7. capacity spectrum for gravity load design fig. 8. capacity spectrum for imrf according to sbc fig. 9. plastic hinge formation for gravity load design engineering, technology & applied science research vol. 4, no. 3, 2014, 631-635 635 www.etasr.com hakim et al.: seismic assessment of rc building using pushover analysis fig. 10. plastic hinge formation for imrf design according to sbc iv. conclusion the test building is investigated using pushover analysis. these are conclusion obtained from this analysis:  pushover analysis can identify weak elements by predicting the failure mechanism and account for the redistribution of forces during progressive yielding. it may help engineers take action for rehabilitation work.  pushover analysis is an approximation method based on static loading. it may not accurately represent dynamic phenomena.  the results show that design considering only gravity load is found inadequate. therefore, a structural engineer should consider earthquakes in designing building.  on the other hand, the building that was designed according to sbc-301 is satisfactory. the performance point location is at io (immediate occupancy) level. it means the design satisfies pushover analysis according to atc -40. references [1] m. s. attar, “evaluation of the seismic performance of a typical school building”, m. s. thesis, king abdul aziz university, saudi arabia, 2003 [2] m. n. abd-alla, “application of recent techniques of pushover for evaluating seismic performance of multistory building”, m. s. thesis, cairo university, egypt, 2007 [3] p. i. giannopoulos, “seismic assessment of rc building according to fema 356 and eurocode 8”, 16th conference on concrete, tee, etek, 21-23/10/2009 [4] a. whittaker, g. hart, c. rojahn, “seismic response modification factors”, 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[12] a. k. chopra, r. k. goel, “capacity-demand-diagram methods based on inelastic design spectrum”, earthquake spectra, vol. 15, no. 4, pp. 637-656, 1999 microsoft word etasr_v11_n2_pp6845-6848 engineering, technology & applied science research vol. 11, no. 2, 2021, 6845-6848 6845 www.etasr.com yafooz et al.: arabic sentiment analysis on chewing khat leaves using machine learning and … arabic sentiment analysis on chewing khat leaves using machine learning and ensemble methods wael m.s. yafooz computer science department taibah university madinah munawarah, saudi arabia wyafooz@taibahu.edu.sa essa abdullah hezzam information systems department taibah university madinah munawarah, saudi arabia essa_alkadasi@yahoo.com waseem alromema information systems department taibah university madinah munawarah, saudi arabia wromema@taibahu.edu.sa abstract-sentiment analysis plays an important role in obtaining speakers' opinions or feelings towards events, products, topics, or services, helping businesses to improve their products. moreover, governments and organizations investigate and solve current social issues by analyzing perspectives and feelings. this study evaluated the habit of chewing khat (qat) leaves among the yemeni society. chewing khat plant leaves, is a common habit in yemen and east africa. this paper proposes a model to detect information about the khat chewing habit, how people explore it, and the preference for khat leaves among arabic people. a dataset consisting of user comments on 18 youtube videos was prepared through several natural language processing techniques. several experiments were conducted using six machine learning classifiers and four ensemble methods. support vector machine and linear regression had almost 80% accuracy, whereas xgboot was the most accurate ensemble method reaching 77%. keywords-sentiment analysis; machine learning; classification; ensemble methods i. introduction nowadays, the study of user opinions has attracted substantial attention in social perspectives, focusing on services, products, and habits through many data mining applications, recommender systems, and business intelligence applications. the analysis and interpretation of user opinions are altogether known as sentiment analysis, which is an area of natural language processing, also kwon as the voice of the customer in business intelligence [1, 2]. business owners need to be aware of feedback to improve future performance. such a time-consuming and difficult task is used in the analysis of huge unstructured data gathered through social media or internet comments. several studies have been conducted, classifying sentiments as positive, negative, or neutral [3, 4, 6]. more complex sentiment analysis [7-10], often referred to as fine-grained, classify datasets into five classes, namely very positive, positive, neutral, negative, and very negative. moreover, aspect-based sentiment analysis [11-14] classifies datasets by extracting entities from text. users' comments are often an outcome of their opinions, and they can be considered as the main factor in evaluating services or products. some studies focused on education [15, 16], while other researches focused on detecting health misinformation on social media users [18, 19]. khat is a type of plant that pleases and stimulates, and chewing khat leaves is a commonly seen habit in yemen and east africa [21-23]. although it is customary in these countries, several experiments showed its direct impact on human organs. this paper presents a model to study consumers' opinions regarding the habit of chewing khat leaves in yemeni and east african society. at first, the dataset was collected by extracting user comments from 18 youtube videos. the annotation process classified the data into positive and negative fractions. several nlp processes were executed to prepare the data for machine learning classifiers (mlcs) and ensemble methods (ems). ii. related works several studies utilized sentiment analysis in different ways. multilingual student comments, obtained through student feedback, were used to evaluate online courses' effectiveness and teachers' performance in [3, 15-17]. in [3], the dataset was collected using approximately 4000 student comments through surveys conducted on 25 university courses to evaluate the performance of a professor who had been teaching for 10 years, while the sentiment analysis was directed including positive, negative, and eight more emotions. similarly, authors in [15] proposed a system to evaluate a lecturer's performance by collecting data through student surveys via a rating system in a form of numerical data. the mlc naïve bays was employed to predicate the positive and negative students’ sentiments toward the lectures. a recurrent neural network of long and short term memory in deep learning was utilized in [16]. the dataset was collected from 3000 positive, negative, and neutral student comments on 30 courses. the performance improved when using the softmax activation function, reaching 89%, 99%, and 90% during training, testing, and validation, respectively. deep learning was applied on a course evaluation dataset with 3000 student comments using three predefined classes in [17], while the results showed that relu and softmax performed better. sentiment analysis is used to identify the main factors affecting the success of businesses, particularly start-ups. in [1], user comments were extracted from twitter using topic modeling and applying supervised vector machine learning to divide comments into three main classes. the textual analysis was applied based on the entities trained in the previous phase corresponding author: wael m.s. yafooz engineering, technology & applied science research vol. 11, no. 2, 2021, 6845-6848 6846 www.etasr.com yafooz et al.: arabic sentiment analysis on chewing khat leaves using machine learning and … using nvivo software. in [4], an analysis of a massive amount of user comments (approximately 1.6 million) from the yelp challenge dataset was conducted. the dataset was divided to 20% for testing and 80% for training, using four machine learning classifiers. the best accuracy rate reached 92.6% and 92.3% under stochastic gradient descent and linear support vector classification respectively. similarly, the same dataset was utilized in [2] to analyze restaurant reviews through a hybrid classifier ensemble method using naïve bayes, support vector machines, and genetic algorithms. some health sector studies have also been conducted [18, 19]. authors in [18] focused on tweets on breast cancer, collecting user comments from approximately 845 cancer patient accounts with 48,000 posts. the logistic regression classifier and a convolutional neural network was utilized in the process, and the model's performance accuracy was 97.6%. besides, it was found that positive experiences had more shares, providing more awareness to the general public. descriptive statistics of text mining and topic modeling were utilized in [19]. unstructured data from 3 million news articles on reuters assisted in identifying the 10 major health issues published in news articles from 2007 to 2017. on the contrary, the analysis of user reviews on mobile health applications was prioritized in [8], collecting data from 104 mobile health applications with approximately 88,125 user reviews. the data were categorized based on each comment's functionality (such as usability, content, customer support, and ethics), the polarity concept was divided into three classes, and five machine classifiers were applied. the best accuracy was recorded at 89.42% through stochastic gradient descent. iii. methods this section describes the main model phases, as shown in figure 1. there are four phases: data acquisition, preprocessing, machine learning classifiers, and model evaluation. fig. 1. model architecture. a. phase 1: data acquisition the dataset was collected using python 3.8 programming language and youtube api (googleapiclient package), for information extracting from 18 videos related to chewing khat. the criteria for selecting videos were: published date between 2015-2020, more than 50k views, more than 10k likes, and focus on arabic speakers. moreover, some keywords were used to locate the videos, such as khat, khat is dangerous, and disadvantages of khat. the main attributes for the extracted video information were: commenter_id, commenter_name, comment, video_id, number of views, number of likes, and date. table i shows the dataset description and the minimum and maximum length of user comments. table i. dataset description items description max length min length average negative 1436 427 1 17 positive 1296 total 2732 the initial step of data preprocessing was carried out, removing english or duplicate comments. the next step, data annotation, was a manual process conducted with the assistance of three annotators that were ph.d. holders, arabic native speakers, and computer science specialists. data annotation classified the comments into negative and positive. some unrelated, unclear, or ambiguous comments were removed. if two annotators classified comments as either positive or negative then comments were considered respectively, otherwise, the comments were removed. b. phase 2: pre-processing the natural language pre-processing steps were: data cleaning, tokenization, normalization of arabic words, lemmatization, deletion of special characters, and removal of repeating characters. then, the annotation was performed by three annotators into positive and negative. these preprocessing steps increased accuracy by removing "tshkeel", "tatweel", and "hamzah" using python 3.6 and a package called “tashaphyne”. c. phase 3: machine learning classifiers two types of mlcs were used: classic mlcs and ensemble methods (ems). the mlcs were linear regression (lr), naïve bayes (nb), support vector machine (svm), knearest neighbor (knn), stochastic gradient descent (sgd), and decision tree (dt). the ems were random forest (rf), adaboost (ada), gradient booting (bg), and xgboost (xg). d. phase 4: model evaluation the model's performance was verified using precision (1), recall (2), f-score (3), accuracy (4), and 5-fold crossvalidation on the dataset. precision �� ����� ��� ������� ��������� ��� �� ����� ��������� (1) recall �� ����� ��� ������� ��������� ��� ������� ��������� (2) f score 2 x $ ������� % ����� $ ������� & ����� (3) accuracy *��+� �, �� ��� ���������� .���� ���+� �, ���������� (4) iv. results and discussion this section presents the experiments and the results. two experiments were conducted on the dataset: classic mlcs and ems. in both experiments, the dataset was divided into 70% for training and 30% for testing, while 5-fold cross-validation was applied. a. classic machine learning classifiers as mentioned above, six classic mlcs were used. the ngram with unigram, bigram, and trigram was used with all six classifiers to examine their performance. table ii shows the results using unigram in the six classifiers. it can be observed engineering, technology & applied science research vol. 11, no. 2, 2021, 6845-6848 6847 www.etasr.com yafooz et al.: arabic sentiment analysis on chewing khat leaves using machine learning and … that the svm classifier had the highest performance accuracy (80.12%), while the lowest accuracy was noted on knn (65%). table ii. classifiers' performance using unigram mlcs class precision recall f-score accuracy lr negative 84% 78% 81% 79.39% positive 75% 81% 78% nb negative 63% 78% 70% 71.95% positive 81% 68% 74% svm negative 84% 79% 81% 80.12% positive 76% 82% 79% knn negative 94% 60% 73% 65.00% positive 34% 84% 49% sgd negative 81% 77% 79% 77.80% positive 74% 79% 76% dt negative 74% 71% 73% 71.34% positive 68% 72% 70% table iii shows the mlcs performance using bigram. svm had the highest accuracy (79.76%), whereas the lowest performance was noted on knn (65.24%). table iii. classifiers' performance using bigram mlcs class precision recall f-score accuracy lr negative 83% 78% 80% 78.90% positive 75% 80% 77% nb negative 63% 78% 70% 72.07% positive 82% 68% 74% svm negative 83% 79% 81% 79.76% positive 76% 81% 78% knn negative 91% 61% 73% 65.24% positive 37% 81% 51% sgd negative 79% 78% 79% 77.80% positive 76% 78% 77% dt negative 77% 69% 73% 70.49% positive 64% 72% 68% table iv shows the mlcs performance using trigram. the highest accuracy was 79.51% using svm, whereas the lowest was noted again for knn (65.12%). figure 2 depicts the overall mlcs results for unigram, bigram, and trigram. although svm had the highest accuracy, it was followed closely by both lr and sgd at almost 80%. nb's and dt's accuracies were near 70%, whereas knn was less accurate. table iv. classifiers performance using trigram mlcs class precision recall f-score accuracy lr negative 83% 78% 80% 78.90% positive 75% 80% 77% nb negative 63% 78% 69% 71.59% positive 81% 67% 73% svm negative 83% 78% 81% 79.51% positive 76% 81% 78% knn negative 91% 61% 73% 65.12% positive 37% 80% 51% sgd negative 76% 78% 77% 76.71% positive 77% 75% 76% dt negative 78% 67% 72% 69.15% positive 59% 72% 65% fig. 2. accuracy comparison for 6 mlcs on three n-grams. b. ensemble methods the four mentioned above common methods were used. table iv shows the accuracy of these ems. the highest accuracy was recorded for xg, while the lowest was noted for gb. figure 3 demonstrates the accuracy of the dt classifier using unigram, bigram, and trigram compared to rf. as it can be noted, rf outperformed dt. table v. ensemble classifiers' performance ems class precision recall f-score accuracy rf negative 83% 73% 78% 75% positive 68% 79% 73% ada negative 80% 75% 77% 75% positive 71% 77% 74% gb negative 81% 73% 77% 74% positive 68% 77% 72% xg negative 82% 76% 79% 77% positive 72% 79% 75% fig. 3. accuracy comparison between decision tree and random forest. v. conclusion this paper presented a study on users' opinions on chewing khat in yemen and east africa, using a dataset collected from youtube comments. several natural language processing steps were carried on the dataset to get the best performance using classifiers. classic mlcs and ems were applied. the best performance in terms of accuracy was recorded when using svm, followed by linear regression. the best accuracy using ems was recorded for xg. references [1] j. r. saura, p. palos-sanchez, and a. grilo, “detecting indicators for startup business success: sentiment analysis using text data mining,” engineering, technology & applied science research vol. 11, no. 2, 2021, 6845-6848 6848 www.etasr.com yafooz et al.: arabic sentiment analysis on chewing khat leaves using machine learning and … sustainability, vol. 11, no. 3, jan. 2019, art. no. 917, https://doi.org/ 10.3390/su11030917. 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[24] b. kalakonda, s. a. al-maweri, h.-m. al-shamiri, a. ijaz, s. gamal, and e. dhaifullah, “is khat (catha edulis) chewing a risk factor for periodontal diseases? a systematic review,” journal of clinical and experimental dentistry, vol. 9, no. 10, pp. e1264–e1270, oct. 2017, https://doi.org/10.4317/jced.54163. microsoft word etasr_v11_n1_pp6603-6608 engineering, technology & applied science research vol. 11, no. 1, 2021, 6603-6608 6603 www.etasr.com serbouti et al.: an innovative multicriteria decision-making tool for building performance optimization an innovative multicriteria decision-making tool for building performance optimization abdelhadi serbouti hassan first university of settat fst, laboratory of radiation matter & instrumentation settat, morocco abdelhadiserbouti@gmail.com el mostafa oualim hassan first university of settat isss, laboratory health sciences and technologies settat, morocco oualim@uhp.ac.ma mourad rattal hassan first university of settat fst, laboratory of radiation matter & instrumentation settat, morocco mourad.rattal@gmail.com azeddine mouhsen hassan first university of settat fst, laboratory of radiation matter & instrumentation settat, morocco az.mouhsen@gmail.com abstract-buildings are accountable for nearly 40% of global greenhouse gas emissions. their overall efficiency is thus a major pillar to optimize energy consumption and to mitigate engendered global warming. the current work takes part in this global dynamic. indeed, we developed a standalone decision-aid tool based on sensitivity analysis, multiobjective optimization, and artificial neural networks to design a new generation of energy-efficient buildings. the tool aims to allow benefiting from sobol’ sensitivity analysis samplings to instantaneously generate sensitivity indexes and perform multicriteria optimizations. this efficient process allows both understanding buildings’ complex behavior (by ranking the impact of the inputs parameters on the outputs and highlighting their interactions) and optimizing their overall performance. the main advantages of this method are the time gaining and the provision of relevant outputs to analyze the buildings’ design. the tool was successfully used to solve constrained 13-input parameters with 5-criteria on trnsys simulation program, considering the impact of global warming. keywords-energy efficiency; sensitivity analysis; multiobjective optimization; polynomial regression; global warming i. introduction climate change continues to have an impact on the planet and therefore requires global mobilization and commitment to encounter sustainable solutions, reducing its criticality for future generations. in those instances, the building sector is in the first category targeted to bring solutions to reduce energy consumption, while maintaining a high level of comfort to occupants. as a matter of fact, the production of building materials and their operation account for the 36% of the world’s final energy consumption and nearly 40% of carbon dioxide emissions in 2017 [1]. energy saving and the rationalization of resource use are paramount in all stages of any building’s life cycle. the implementation of efficient solutions starts from the early technical design phase of any project. this decisive step requires the development of models to control the energy consumption behavior of the building and of its components. the choice of a building configuration depends on several factors, including energy performance, occupant comfort, economic or environmental constraints. the implementation of energy-efficient buildings is thus subject to several criteria. to help designers and decision makers in taking better and faster decisions, the use of decision support tools is essential. among these tools, sensitivity analysis, metamodeling, and multiobjective optimization are very efficient in optimal building design. in state of the art energy efficiency, sensitivity analysis and multiobjective optimization are usually used independently. authors in [3] performed sensitivity analysis on the heating and cooling energy flexibility of residential buildings. their goal was to analyze the effects of the building envelope, users’ behavior, and weather conditions on the flexibility indicators for three reference apartments. authors in [4] performed sensitivity analysis of workspace conflicts according to changing geometric conditions. authors in [5] proposed a multi-objective particle swarm algorithm to optimize the energy performance of buildings. authors in [6] investigated a sustainable approach in the design of the administrative building where the design aims to deliver an energy-sufficient yet aesthetically pleasing building. the state of the art lacks studies combining the two methods. thus, the novelty of the current work is to propose a methodology that combines their strengths by incorporating them in a new standalone tool. the tool allows a relevant and efficient decision aid to buildings designers, and is easily interfaced to major dynamic simulation tools such as trnsys and energyplus [7]. ii. materials and methods many standalone graphical user interfaces (guis) perform multiobjective optimization on trnsys. authors in [8] did a corresponding author: abdelhadi serbouti (abdelhadiserbouti@gmail.com) engineering, technology & applied science research vol. 11, no. 1, 2021, 6603-6608 6604 www.etasr.com serbouti et al.: an innovative multicriteria decision-making tool for building performance optimization comparative study of these tools by answering "yes" or "no" to four questions (freeware, multiobjective optimization, parallel simulations, discrete and continuous input parameters). previous studies [9, 10] used genopt and mobo tools to optimize the energy performance of a building in the city of settat. these tools lack flexibility and do not offer a wide spectrum of decision-making to their users. to remedy these limitations, we developed our sensitivity analysis and multiobjective tool (samot) on python. the libraries salib [11], platypus [12] and scikit-learn [13] were adapted and used. the source code will be available for python skilled users along with a gui for less trained users. we summarize the decision-making methods, incorporated in samot tool, in the following diagram. we used the genetic algorithm nsga-ii for the multiobjective optimization. fig. 1. overall methodology. sensitivity analysis is an important step in the modeling process. it makes possible to rank the influence of the input parameters of a model on its outputs. thus, it highlights the inputs with a large impact on the studied output, and in the same time the parameters with a negligible effect. the sobol method is a relevant global sensitivity analysis method as it generates several sensitivity indices (by decomposing the variance of the output of the model). the first-order index allows assessing the impact of the variation of each parameter on the output, without studying its interaction with the other parameters. the total order index considers all the effects involving each parameter (first, second, and all other higher order effects due to parameter interactions). therefore, in order to take advantage from the computational time for generating these sensitivity indices (calculation of each combination on trnsys), we propose to combine it to a metamodeling method using artificial neural networks (anns). in fact, we consider the sampling of sobol as a design of experiments (doe), allowing us to train and build metamodels of the "black-box" functions' outputs of trnsys using polynomial regression methods. the sampling of sobol trains the machine learning polynomial model of the output objective functions. consequently, using sobol sensitivity analysis, allows generating the sensitivity indices and instantaneously performing polynomial modeling of all the studied functions. this "instantaneous" prediction of the objective functions values is relevant to run efficient and quick multiobjective optimization. iii. case study samot and trnsys were used to optimize the overall performance of a building in the city of settat in morocco, considering the effects of climate change, using the sequence shown in figure 2. fig. 2. workflow sequence. a. weather data the studied location is the city of settat-nouaceur: 33.4°n / -7.6°e /206m. settat has a warm climate with a dry summer. year-round temperatures range from 2 (in january) to 40°c (in july), with an annual average of 17.9°c. solar horizontal irradiation can reach up to 1030w/m². b. climate change scenarios meteonorm software allows the study of global warming according to different scenarios, defined by the ipcc (intergovernmental panel on climate change) [14]. we use these models to anticipate what would happen in the future under several conditions. under the un paris agreement, the countries are committed to limit global warming below 2 °c [15]. in our study, we will consider the b1 scenario (optimistic scenario, with 2°c warming by 2100). figure 3 shows the evolution of the degree-days (dds) in settat, following this scenario. fig. 3. heating (in red) and cooling (in blue) dds. y = -2,7342x + 6307,8 y = 2,6437x 4926,2 400 600 800 2000 2020 2040 2060 2080 2100 2120 d d years engineering, technology & applied science research vol. 11, no. 1, 2021, 6603-6608 6605 www.etasr.com serbouti et al.: an innovative multicriteria decision-making tool for building performance optimization heating dds decrease by 4.5% every decade, while cooling dds increase at an average rate of 5.5%. both dd types equalize around 2085. consequently, the current dominance of heating dds will start reversing 2080 at the latest. the increasing dominance of the cooling dds will jeopardize the current building design which is based on heating requirements. furthermore, based on the b1 scenario, the current mean temperature in settat (17.9°c) will increase to 18.8°c by 2050 and to 19.6°c by 2100. it is essential to take global warming into account to build comfortable buildings throughout their whole lifecycle. c. building model the model building designated for the study is a southfaced symmetrical 5m×5m×3m square house. each facade has a 3m² window. aderee [16] carried out the moroccan thermal regulation based on the properties of the walls seen in table i (excluding the additional layers of insulation for the roof and the low floor, and with an air slide for the external walls instead of insulation). the floor is in contact with the ground. authors in [17] modeled the vertical distribution of the soil temperature and in [18] demonstrated that the latter depends on the time and the depth of the soil below the surface. trnsys type 77 implements these equations. the initial building model (without insulation) requires high heating and cooling needs (185kwh/m²/year). in the following, we will present the input parameters and the objective functions of our model to improve its overall performance. for our study, we recommend the parameters exhibited in table ii. table i. wall properties materials width external walls brick 10cm insulation layer (glass wool) variable brick 10cm roof filler slab 16cm insulation layer (rock wool) variable floor insulation layer (rock wool) variable reinforced concrete slab 20cm table ii. input parameters parameter symb ol unit low bond high bond in su la ti o n external wall insulation x1 m 0.001 0.1 roof insulation x2 m 0.001 0.1 floor insulation x3 m 0.001 0.1 p a in ts & a ir ti g h tn e s s external walls painting color x4 0.1 0.9 roof painting color x5 0.1 0.9 air leakage x6 0.3 1.15 s h a d in g d e v ic e s south facing window x7 0 1 east x8 0 1 west x9 0 1 w in d o w t y p e south x10 0: single, 1:double, 2:triple glazing north x11 3:low-emissivity double glazing east x12 4:low-emissivity double glazing argon west x13 5: solar-controlled triple glazing all the input parameters are continuous except for the window types (discrete). the use of shading devices (in %) is applicable from mid-may to mid-october. air infiltration varies between 0.3 (good airtightness) and 1.15vol/h (poor airtightness). we define the absorption coefficients according to the colors of the paints (e.g. 0.57 for dark red, 0.94 for black). to study the overall performance of our building (energetic, economic, and environmental), the selected functions are: �� � �� ���� = � ��� ������ �������� , ��ℎ/�²/����� �� = � ��� ������ �2050 ,��ℎ/�²/���� �$�� = � ��� ������ �2100 ,��ℎ/�²/�����&�� = '(()�) ��� * ��, + � ,,�� -)�ℎ�� �+'�.�� = '(()�) ��� /��� ������,��ℎ (1) where x is the input parameters vector. total energy is the sum of the heating and cooling requirements, with set temperatures equal to 20°c (heating) and 26° (cooling). trnsys provides the values of this output. we will study the latter using the current weather data (�� function), by 2050 (� ), and by 2100 (�$) using the ipcc b1 scenario of climate change. additional cost corresponds to the sum of the costs associated with the various additional implemented components. this indicator allows assessing the needed extra capital. �& function calculates the additional cost induced by the variation of the input parameters (thermal insulation and glazing types). '(()�) ��� grey energy: to produce efficient buildings with a rational use of energy, it is essential to identify the environmental impacts of the different design solutions. during the construction or renovation of a building and during its entire life cycle, several environmental consequences must be predicted and optimized for several decades after its design. non-renewable grey energy is required to initially produce a building and maintain it throughout its lifecycle. kbob [19], a swiss database contains life cycle assessment data for building materials, technical building installations, energy supply, transport and disposal processes, etc. as part of this work, we will use it to evaluate the grey energy of the various solutions studied for our model building. iv. sensitivity analysis a. process the proposed prossess is shown in figure 4. fig. 4. sensitivity analysis indices calculation sequence. b. recommended number of simulations one of the main difficulties in carrying out sensitivity analysis is choosing the adequate number of model simulations (number of combinations of sobol’s sampling matrix), prior to the calculation of sensitivity indices. authors in [20] carried engineering, technology & applied science research vol. 11, no. 1, 2021, 6603-6608 6606 www.etasr.com serbouti et al.: an innovative multicriteria decision-making tool for building performance optimization out a classification of sensitivity analysis methods according to the number of model evaluations. they reported that sobol's method requires at least 1000. to determine the recommended value of n, we assess the error coefficient (st_conf) on the calculation of the total-order indices of sobol, for n from 10 to 100 (pitch of 10) and from 100 to 2000 (pitch of 100). we compare the error coefficients for the �� function. figure 5 shows the results. fig. 5. st_conf (x-axis) calculation. we notice that the st_conf indices stabilize around n = 1000, and stat getting acceptable values from n = 500. consequently, we recommend choosing a value of n > 500, which corresponds in our case study to 15×500 = 7500 simulations. c. sensitivity analysis indices we calculate sobol’s [21] total-order sensitivity indices for the black-box functions ��, � and �$. when the total-order is positive, increasing the input parameter value increases the output function, and vice-versa. fig. 6. total order sensitivity indexes for the functions f1, f2 and f3. for the model building, it is deduced from the analysis that: • the most influential parameter for the three functions is the roof insulation (x2). • the use of shading devices (x7 to x9) has a greater impact than the variation in the glazing type (x10 to x13). furthermore, the use of shading devices acquires more importance over time, given the unceasing increase of cooling degrees days as detailed before. • insulating the floor increases the energy needs in 2100, as it does not allow benefiting from the coolness of the ground during the summer to lower indoor temperatures. • dark color use for the roof and the exterior walls increases the energy requirements as time passes. the use of light colors is therefore recommended. v. multiobjective optimization in this section the optimization problem in (2) is studied: 0+)�)�)1� : ���� ,� �� ,�$�� ,�&�� ,�.�� 3�(�� , �����)��� ∶ ���� ,� �� ,�$�� 5 40 ���/�²/���� (2) we can perform polynomial regression using any polynomial order (although above a 5-order model the calculation time explodes). nevertheless, authors in [22] advice against the use of high-order polynomial regressions and recommend the use of linear and quadratic models. in the following, we will compare the accuracy of four polynomial models (see table iii) based on mean absolute error (mae) and r 2 : +'� � 7 ∑ |�: ; �<:| 7 :=� (3) � ; >��?� � � @ ∑ �a<bcad ef bgh ∑ �abcad ef bgh (4) where n is the number of input combinations, �: is the value of the output function to model (calculated using trnsys), �<: is the predicted value of the output function and �d � 7 ∑ �: 7 :=� (5) is the mean value of the function. we randomly generate 100 new combinations of input parameters to assess the accuracy of the metamodels. table iii. mae and r² of the four models function first order second order, interactions only complete second order third order, interactions only present: f1 r² = 0.81 mae = 8.6 r² = 0.8 mae = 8.4 r² = 0.87 mae = 8.7 r² = 0.74 mae = 10.1 2050: f2 r² = 0.84 mae = 11.6 r² = 0.84 mae = 11.7 r² = 0.91 mae = 10.1 r² = 0.79 mae = 11.3 2100: f3 r² = 0.88 mae = 5.3 r² = 0.91 mae = 4.6 r² = 0.94 mae = 3.7 r² = 0.88 mae = 5.6 for our case study, we notice that the best regression model for the three functions (total energy at 2020, by 2050, and by 2100) is the complete 2-order polynomial model. r² coefficients are generally above 0.9. we notice also that the quality of the regression deteriorates for the third-order model, the built model gets in fact too "specialized" in the input sampling (learning model), and the prediction of the results of new random samplings is then less accurate (overfitting issue). therefore, we recommend the use of the complete 2nd-order model, which is a good compromise between precision and engineering, technology & applied science research vol. 11, no. 1, 2021, 6603-6608 6607 www.etasr.com serbouti et al.: an innovative multicriteria decision-making tool for building performance optimization computation time. the 2d projections of the pareto front of the optimization problem are shown in figure 7. the pareto front is widely used in multiobjective optimization as it allows choosing the best results through the notion of dominance [23]. fig. 7. multiobjective optimization's non-dominant results-2d projections. the following conclusions can be drawn from the optimization: • the need to insulate the roof and the exterior walls to keep a high-performance building by 2100. • the floor requires a moderate insulation. in fact, the excess of insulation implies increasing the energy requirements by 2100 as deduced before from the sobol indices. • the external wall paint must be clear (e.g. white to orange) by 2100. the roof paint must be clear for all time frames (present, 2050, and 2100). • the infiltration rates must be very low (excellent airtightness). • the necessity of using shading devices for the three facades. • the north and east facade glazing must be efficient on the current horizon and the west one should perform well by 2050. • for the cheapest optimal variant, the insulation of the floor is not proposed, the paints are white and all facades have triple glazing. • for the most environment-friendly variant, the highest quality of glazing is in the northern facade. the other facades have single or double-glazing. in table iv, we display a comparison of the best-predicted solutions (1) for the 3 functions and their trnsys simulationbased results (2). the predicted values are very close to the simulation-based ones. table iv. optimal solutions and result comparison ij ∶ present ik ∶ 2050 il ∶ 2100 im in (1) (2) (1) (2) (1) (2) 9.9 13.3 13.5 11.3 13.8 15.5 23 380 6343 9.7 14.2 12.4 11.7 14.0 16.0 22 952 6099 10.3 16.7 16.6 10.7 12.3 13.1 24 837 6511 (1) : regression, (2) trnsys based vi. discussion we demonstrated through the case study that our methodology gives very efficient and satisfying results. the use of polynomial regression allows to model the "black-box" objective functions of trnsys with good accuracy, and to obtain optimization results within only a few minutes. thanks to this method, we can significantly reduce the calculation time compared to running direct optimizations on trnsys. furthermore, our methodology helps understanding the building model, through ranking the input parameters impact and their interactions, highlighted by the sensitivity analysis indices. sensitivity analysis and mono / multiobjective optimization are used independently, although these two methodologies are complimentary. our work will contribute to further combining these methods together, in order to provide the field decision-making stakeholders with relevant indicators at the early stages of the design of the buildings. vii. conclusion this work takes part in the current process of improving energy efficiency performance in the building sector. its main purpose is to develop efficient methodologies to study and to optimize the overall performance of buildings. in accordance with this objective, we developed the sensitivity analysis and multiobjective optimization tool (samot) to combine the strengths of sensitivity analysis and multiobjective engineering, technology & applied science research vol. 11, no. 1, 2021, 6603-6608 6608 www.etasr.com serbouti et al.: an innovative multicriteria decision-making tool for building performance optimization optimization, and to provide an efficient decision-aiding tool to building designers and researchers. sensitivity analysis allows understanding the impact of varying the value of input parameters (envelope, systems, etc.). sensitivity indices rank the impact of the latter on the outputs. we recommend a minimal sobol matrix sampling size of 500×(n+2), with n being the number of input parameters. in our case, the variation of the roof insulation influences largely the present and the forecasted 2050 and 2100 energy requirements. to optimize the overall performance of our inefficient building model (185kwh/m²/year of heating and cooling needs), a constrained (thermal regulation thresholds) 5-criteria problem is studied on trnsys and samot. we recommended the use of a 2 nd -order polynomial regression to avoid overfitting / under fitting issues. in our case, the correlation coefficients were generally higher than 90% for a random 100 new combinations set. the results are satisfactory and quasi simultaneous. this new method allows calculating sobol sensitivity analysis and then performing quick parallel optimization. our case study underlines the necessity of taking into account climate change in building design. we demonstrated also the worthiness of the proposed samot tool for building performance optimization. references [1] 2018 global status report towards a zero-emission, efficient and resilient buildings and construction sector. international energy agency, 2018. 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[23] f. ascione et al., "a real industrial building: modeling, calibration and pareto optimization of energy retrofit," journal of building engineering, vol. 29, may 2020, art. no. 101186, https://doi.org/10.1016/j.jobe.2020. 101186. microsoft word 2-ma-ed.doc etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 540-543 540 www.etasr.com ma et al.: current-mode cmos active inductor with applications to low-voltage oscillators current-mode cmos active inductor with applications to low-voltage oscillators minglin ma key laboratory of intelligent computing & information processing of ministry of education, xiangtan university, china minglin_ma@xtu.edu.cn zhijun li key laboratory of intelligent computing & information processing of ministry of education, xiangtan university, china lizhijun_320@163.com zili yao key laboratory of intelligent computing & information processing of ministry of education, xiangtan university, china yaozili@xtu.edu.cn abstract— this paper investigates a current mode active inductor. in the proposed active inductor, three current mirrors have been connected to each other to realize the negative feedback. this active conductor has a two layer transistor structure. a 4.257 ghz, 1.2-v power supply non-inductive lc negative resistor oscillator, base on two of the proposed active inductors, is demonstrated. keywords-active inductor; current mirror; low-voltage i. introduction wireless and mobile communications are two of the fastest growing microelectronics applications and have an enormous impact on everyday life. driven by the insatiable demand for lower cost, lower power and higher data rates in wireless and mobile communications systems, a growing demand for cmos wireless system-on-a-chip(soc) solutions is recorded. this trend has motivated the evolution and research on low voltage, low power, low cost rfic designs [1, 2]. the oscillator is an important building block in rf transceivers. inductive characteristics are critically needed in lc tank oscillators to realize frequency selection. traditionally, passive inductors are off-chip discrete components. the need for off-chip communications with these passive components severely reduces the reliability, and increases the cost. cmos active inductors have been widely used in the design of ring and lc tank oscillators because of their small chip area and wide tenability [3-6]. all these circuits [3-6] suffer from a tradeoff between low voltage and low cost. here, we propose a lc oscillator based on the current mode active inductor. current mode approach has several advantages, such as extended bandwidth, simple circuit structure, higher dynamic range, suitability of operation in reduced power supply environment, low power consumption, low voltage operation [7-12]. in the next section, the current mode active inductor is introduced and analyzed. in section iii, an lc oscillator based on the active inductor is described. section iv is the conclusion. ii. the proposed active inductor the active inductor proposed is depicted in figure 1. it is based on three current mirrors (m1,2, m3,4, m5,6). io is the bias current. consider the equivalent network shown in figure 2 where a current mirror can be equivalent to a trans-impedance (ti) and a trans-conductance (gm). go1 and go2 denote the total conductances at nodes 1 and 2 respectively. note that go1 is due to the finite output impedance of the gm1 and the finite input impedance of ti2. c1,2 are the parasitic capacitors. the following equations apply: 1 1 1 2 1 2 2 2 1 2 3 3 ( ) ( 1) (1) ( ) ( 2) m m i m in sc go v v g node sc go v v g t g i node          fig. 1. proposed current mode active inductor etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 540-543 541 www.etasr.com ma et al.: current-mode cmos active inductor with applications to low-voltage oscillators fig. 2. equivalent network of the current mode active inductor the admittance looking into port 2 of the equivalent network is obtained from 2 2 1 12 1 2 3 3 1 2 3 3 1 (2)in m m i m m m i m i y sc go c gov s g g t g g g t g      equation (2) can be represented by the rlc networks shown in figure 3 with parameters given by: 1 1 2 2 1 2 3 3 1 2 3 3 1 , , , (3) p p s m m i m m m i m go c r c c r l go g g t g g g t g     fig. 3. the admittance looking into port 2 the proposed circuit contains only three current mirrors that all are of a two layer transistor structure. the minimum voltage required for proper circuit operation is vgs+vdsat where vdsat is the minimum vds voltage required to keep a mos transistor in saturation. the compactness of the circuit results in low voltage supply and low power consumption. the active inductor has been simulated in cadence (5.10.41_usr6.12) using parameters for chartered 0.18 μm rf cmos process with vdd=1.2 v. all transistors have the same channel length of 0.18 μm. the width of the transistors and the value of io were chosen as w1=10 ， w2=30 ， w3=40 ， w4=120 ， w5=30 ， w6=42.85 ， io=3 ma. the simulated im(z) and re(z) is shown in figure 4. qlmax=7.8 is achieved at 4.257 ghz. fig. 4. simulated im(z) and re(z) etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 540-543 542 www.etasr.com ma et al.: current-mode cmos active inductor with applications to low-voltage oscillators iii. an lc-tank oscillators using the proposed active inductors the proposed low-voltage current mode active inductor is applied to lc oscillator shown in figure 5. this lc oscillator consists of two active inductors. the capacitor of the lc tank is the parasitic capacitors of transistors. the negative resistor, which is used to cancel the input resistance of the active inductors, is realized by the cross coupling between m7 and m27. fig. 5. current mode lc oscillator based on the active inductor figure 6 shows the output voltage of the lc oscillator shown in figure 5. its frequency is set to about 4.257 ghz. spectre from cadence design systems is used for the phase noise simulation. it is approximately -105 dbc/hz (1 mhz frequency offset). figure 7 shows the simulated phase noise. table i lists the comparison of the performance of previous active inductors oscillators to the one proposed in this paper. fig. 6. the output voltage of the proposed oscillator table i. comparison of active inductor oscillators performance ref. tech. (μm) vdd phase noise pdc (mw) f (ghz) [3] 0.18 1.8v -101~-118 6-28 3 [4] 0.18 1.8v 110 30 1.6 [5] 0.18 1.8v -122.9 ---1.6 [6] 0.18 1.8v -109.4 30.5 1.5 this work 0.18 1.2v -105 t 20 4.257 fig. 7. the simulated phase noise at the oscillation frequency of 4.257ghz iv. conclusion this paper proposes a current mode active inductor build with three current mirrors. a 4.257 ghz, 1.2-v power supply, lc negative resistor oscillator, based on the proposed active inductor, is also demonstrated. considering that the phase noise of the oscillator is approximately -105dbc/hz at 1 mhz frequency offset, it is hinted that it can be used in a current domain circuit or a voltage domain circuit with low-voltage supply and small size. acknowledgment this work was financially supported by a subproject of the nature science foundation of china (no. 11kh|kh01069), the nature science foundation of china(no. 61176032), and a project supported by the scientific research fund of hunan provincial education department (no. 12c0417) etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 540-543 543 www.etasr.com ma et al.: current-mode cmos active inductor with applications to low-voltage oscillators references [1] m. saito, m. ono, r. fujimoto, h. tanimoto, n. ito, t. yoshitomi, t. ohguro, h. s. momose, h. iwai, “0.15-μm rf cmos technology compatible with logic cmos for low-voltage operation”, ieee transactions on electron devices, vol. 45, no. 3, pp. 737 –742, 1998 [2] d. wang, j. ou, x. wang; “rf design challenges at 90nm rfcmos technology under low voltage applications”, icsict ì06. 8th international conference on solid-state and integrated circuit technology, pp. 1522 –1525, shanghai, 2006 [3] l. lu, h. hsieh, y. liao, “a wide tuning-range cmos vco with a differential tunable active inductor”, ieee transactions on microwave theory and techniques, vol. 54, no. 9, pp. 3462–3468, 2006 [4] a. tang, f. yuan, e. law, “a new cmos active transformer qpsk modulator with optimal bandwidth control”, ieee transactions on circuits and systems ii: express briefs, vol. 55, no. 1, pp. 11–15, 2008 [5] a. tang, f. yuan, e. law, “class ab cmos active transformers voltage-controlled oscillators”, issse '07, international symposium on signals, systems and electronics, pp. 501–504, montreal, 2007 [6] a. tang, f. yuan, e. law, “low-noise cmos active transformer voltage-controlled oscillators”, mwscas 50th midwest symposium on circuits and systems, pp. 1441–1444, montreal, 2007 [7] t. h. lee, “the design of cmos radio-frequency integrated circuits”, cambridge university press, 2003 microsoft word 31plusreview_29-2288_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3475-3478 3475 www.etasr.com chopra et al.: a review on machine translation in indian languages a review on machine translation in indian languages deepti chopra department of computer science banasthali university newai, india deeptichopra11@yahoo.co.in nisheeth joshi department of computer science banasthali university newai, india jnisheeth@banasthali.in iti mathur department of computer science banasthali university newai, india mathur.iti@rediffmail.com abstract—machine translation (mt) is considered an important task that can be used to attain information from documents written in different languages. in the current paper, we discuss different approaches of mt, the problems faced in mt in indian languages, the limitations of some of the current existing mt systems, and present a review of the work that has been done until now in mt in indian language perspective. keywords-machine translation; rule based approach; example based approach; natural language processing; bilingual evaluation understudy i. introduction machine translation may be defined as the task of conversion of text from one language, called source language, to another language, called target language. there are two kinds of mt, metaphrase and paraphrase. in metaphrase, an exact word to word translation takes place but the translated text may or may not have the similar semantics as the source text. in paraphrase, translation is not performed at word level but at sentence level. here, the semantics of source text are conserved while translating into translated text. mt is one application of natural language processing. mt involves five major goals: 1. morphological analysis is the process of generation of all possible roots from word level information. 2. part-of-speech tagging is the process of assigning part-ofspeech tags to every word in a given sentence. 3. chunking is the process of identification of phrases such as noun phrase (np), adjective phrase (jjp), verb phrase (vp) etc. in a given sentence. 4. parsing is the process of generation of a parse tree with the help of the information obtained from part-of-speech tagging and chunking. 5. word sense disambiguation is the process of identification of meaning of a word in a particular sentence when a given word has multiple meanings. ii. problems faced in mt in indian languages problems faced in mt in indian languages include: 1. indian languages are free word order languages. 2. they are morphologically and inflectionally rich languages. 3. named entity recognition (ner) can be used to improve mt. but, ner in indian languages is not an easy task since these languages do not provide capitalization information that helps in performing ner. 4. many common nouns exist as proper nouns. so, these languages involve a large amount of semantic ambiguity. 5. there is scarcity of resources pertaining to indian languages on web. today, there are many available machine translators pertaining indian languages but still these machine translators do not produce translations with very high accuracy. consider the following source text: “jammu and kashmir, india’s one of the most picturesque state lies on the peaks of himalayan ranges with varying topography and culture. jammu was the stronghold of hindu dogra kings and abounds with popular temples and secluded forest retreats. kashmir’s capital city, srinagar offers delightful holidays on the lakes with their shikaras and houseboats”. this source text in english is translated into hindi using different machine translators. the translations are shown in figure 1. it is undeniable that the translated texts obtained from existing machine translators are not of good quality. some of the words in the translated text appear in english, and some of the words are transliterated instead of translated. so, there is a need to develop machine translator that can produce good translations. iii. approaches of mt various approaches of mt are depicted in figure 2. these include the following: • direct machine translation • rule based machine translation • corpus based machine translation, including statistical machine translation and example based machine translation. the description, advantages and disadvantages of the engineering, technology & applied science research vol. 8, no. 5, 2018, 3475-3478 3476 www.etasr.com chopra et al.: a review on machine translation in indian languages different approaches are shown in table i. hybrid approach involves a combination of the above listed approaches. mt quality is expected to improve if hybrid approach is used to perform mt in indian languages. fig. 1. output of existing machine translators fig. 2. classification of approaches of mt iv. literature review the work done in mt pertaining indian languages is shown in table ii. v. evaluation for evaluation of mt system, automatic evaluation metrics or human evaluation metrics may be used. a. automatic evaluation metrics 1) precision, recall and f-measure: precision (p)=match/system output recall (r)=match/human output f-measure (r)=2×p×r/(p+r) here, precision is calculated by considering the number of matches between the two outputs divided by the total number of system outputs. recall is calculated by considering the number of matches between the two outputs divided by the total number of human outputs and f-measure would be the combination of the two. apart from these automatic evaluation metrics, bleu, meteor etc. can also be used for evaluation of mt output. table i. mt approaches approach description advantages/disadvantages direct mt no parallel corpus is used. it makes use of bilingual dictionary, target language and source language corpus. -produces good accuracy. -less tedious and less time consuming rule based mt rules are constructed. involves analysis of source and target text at syntactic, semantic and morphological level. -good quality translation. -complex rules are needed to be constructed. -it involves tedious tasks and is time consuming. corpus based mt rules are constructed by analysis of parallel corpus. accuracy can be improved by adding more examples to corpus. statistical mt statistical models are used to perform mt. mt quality can be improved by adding more examples to parallel corpora. example based mt it makes use of translation memories. it performs translation by analogy. mt quality can be improved by adding more examples to parallel corpora. 2) bilingual evaluation understudy (bleu) its value lies between 0 and 1. it indicates how close a machine translated text is to the expected translated text. average of bleu scores of all sentences is taken to get the whole corpus overall score. 3) nist apart from calculating n-gram precision, it also assigns weights to n-gram. a low weight is assigned if n-gram matches exactly with the expected translation otherwise high weight is assigned. 4) word error rate (wer) estimates the number of tokens that differ between machine translated text and expected translated text. 5) meteor estimates weighted harmonic mean of unigram precision and recall. it also involves matching of synonyms and lemmatized forms. 6) lepor involves a collection of different evaluation factors such as precision, recall, sentence length penalty, and word order penalty based on n-gram. engineering, technology & applied science research vol. 8, no. 5, 2018, 3475-3478 3477 www.etasr.com chopra et al.: a review on machine translation in indian languages table ii. description of mts of different language pairs reference about detailed description [1] english to hindi mt hybrid approach. ebmt and smt is used to perform mt. parallel corpus (54k english-hindi sentences) is used. training: 53k sentences. testing: 100 random sentences. bleu score:0.432. [3] english to assamese phrase based mt+transliteration. parallel corpus: 14,371 sentences of english and assamese. testing: 500 sentences. wordnet of assamese is used to improve mt output [9] hindi to punjabi mt overall accuracy: 95.12%. input taken from daily news, articles, official language quotes, blogs and literature. 95.4% sentences are found to be intelligible. accuracy obtained: 87.6% [10] bilingual hindi english text to pure hindi and pure english english and hindi morphological analyzers are used. plural forms are identified. unknown words are considered to be proper nouns. complex sentences are converted to simplified sentences and source text is translated to pure hindi and pure english. in 90% cases this approach has obtained satisfactory results. [13] english to hindi mt using smt approach training: 120153 words, testing: 8557 words. bleu score (using baseline approach) is 12.10. bleu score (by combining syntactic, morphological and baseline approach) is 15.88 [14] english to hindi mt ebmt+rbmt+post editing approach. can produce 90% correct results for sentences upto length of 20 words. [15] english-hindi bilingual text to hindi morphological analyzer is used to detect unknown words and unknown plural words of hindi and english. correct results: 90%. [19] transliteration of english to hindi using smt accuracy: 46.3%. alignment of english and hindi letters is done using giza++, srilm toolkit was used for training. mean f-measure obtained: 0.876. [20] english to tamil mt rule based text simplification approach is used for enhancing englishhindi mt. testing: 200 sentences. accurate results in 115 sentences. accuracy of mt system increased by 28% by introduction of text simplification approach. [21] hindi to english mt mt output is improved by simplification of source text. testing: 100 sentences. bleu score: 0.805 [22] tamil to english mt statistical machine translation system, performs tamil to english mt. a bilingual corpus comprising of tamil and english sentences is formed consisting of 1300 tamil-english sentence pairs. tamil side consisted of 24,000 tokens. [23] english to bangla mt (smt) phrase based mt is performed for english to bangla mt. transliteration approach is used to deal with the words not present in vocabulary. accuracy of transliteration module: 0.18. preposition handling is also performed. overall bleu score: 11.7. bleu score obtained for short sentences is 23.3 and 0.63 ter [24] hindi to english mt testing: 100 sentences taken from hindi treebank. source text simplification is used to improve mt. bleu score: 4.45. b. human evaluation metrics for human evaluation, authors in [10] used some linguistic features that include: • translation of gender and number of noun(s) • translation of voice in the sentence. • translation of tense in the sentence • identification of the proper noun(s) • use of adjectives and adverbs corresponding to nouns and verbs • selection of proper words/synonyms (lexical choice). • sequence of phrases and clauses in the translation. • use of punctuation marks in the translation. • fluency of translated text and translator’s proficiency. • maintaining semantics of source sentence in the translation. • evaluating the translation of source sentence (with respect to syntax and intended meaning). in order to access the translation quality, a five-point scale is used, which is shown in table iii. similarly, adequacy and fluency score may be calculated using five-point scales as represented in tables iv and v. table iii. fivepoint scale to access translation quality score meaning 4 ideal 3 perfect 2 acceptable 1 partially acceptable 0 not acceptable table iv. five point scale to access adequacy score meaning 5 complete information 4 most information 3 much information 2 little information 1 none table v. five point scale to access fluency score meaning 5 ideal 4 good 3 non native 2 disfluent 1 incomprehensible vi. conclusion in this paper we discussed about mt, problems faced in mt in indian language context, problems with existing machine translators, approaches of mt and the work that has been done till now in mt regarding indian languages. as we have seen, the quality of existing mt systems is not good, so there is a need to develop machine translators that can provide engineering, technology & applied science research vol. 8, no. 5, 2018, 3475-3478 3478 www.etasr.com chopra et al.: a review on machine translation in indian languages good translation with high accuracy. we have discussed about automatic evaluation metrics and human evaluation metrics that can be used to access the translation quality. references [1] v. ambati, u. rohini, “a hybrid approach to example based machine translation for indian languages”, 5th international conference on natural language, hyderabad, india, january, 2007 [2] b. babych, a. hartley, “improving machine translation quality with automatic named entity recognition”, 7th international eamt workshop on mt and other language technology tools, improving mt through other language technology tools: resources and tools for building mt, budapest, hungary, april 13, 2003 [3] a. k. barman, j. sarmah, s. k. sarma, “assamese wordnet based quality enhancement of bilingual machine translation system”, 7th global wordnet conference, tartu, estonia, january 25-29, 2014 [4] j. g. carbonell, s. klein, d. miller, m. steinbaum, t. grassiany, j. frey, “context-based machine translation”, 7th conference of the association for machine translation in the americas, cambridge, usa, august, 2006 [5] g. v. garje, g. k. kharate, “survey of machine translation systems in india”, international journal on natural language computing, vol. 2, no. 4, pp. 47-65, 2013 [6] a. hassan, h. fahmy, h. hassan, “improving named entity translation by exploiting comparable and parallel corpora”, amml07, 2007 [7] j. hutchins, “towards a definition of example-based machine translation”, mt summit x, workshop on example-based machine translation, phuket, thailand, september 16, 2005 [8] l. jiang, m. zhou, l. f. chien, c. niu, “named entity translation with web mining and transliteration”, ijcai-07, hyderabad, india, pp. 1629-1634, january 6-12, 2007 [9] n. joshi, h. darbari, i. mathur, “human and automatic evaluation of english to hindi machine translation systems”, in: advances in computer science, engineering & applications, pp. 423-432, springer berlin heidelberg, 2012 [10] n. joshi, i. mathur, h. darbari, a. kumar, “heval: yet another human evaluation metric”, international journal on natural language computing, vol. 2, no. 5, pp. 21-36, 2013 [11] n. joshi, implications of linguistic feature based evaluation in improving machine translation quality: a case of english to hindi machine translation, phd thesis, banasthali university, india, 2014 [12] s. nirenburg, c. domashnev, d. j. grannes, “two approaches to matching in example-based machine translation”, 5th international conference on theoretical and methodological issues in machine translation, kyoto, japan, 1993 [13] a. ramanathan, p. bhattacharyya, j. hegde, r. m. shah, m. sasikumar, “simple syntactic and morphological processing can help englishhindi statistical machine translation”, proceedings of the third international joint conference on natural language processing, vol. i, pp. 513-520, 2008 [14] r. m. k. sinha, a. jain, “anglahindi: an english to hindi machineaided translation system”, mt summit ix, new orleans, usa, september 23-27, 2003 [15] r. m. k. sinha, a. thakur, “machine translation of bi-lingual hindienglish (hinglish) text”, mt summit x, workshop on example-based machine translation, phuket, thailand, september 16, 2005 [16] v. goyal, g. s. lehal, “evaluation of hindi to punjabi machine translation system”, international journal of computer science issues, vol. 4, no. 1, pp. 36-39, 2009 [17] v. goyal, g. s. lehal, “web based hindi to punjabi machine translation system”, journal of emerging technologies in web intelligence, vol. 2, no. 2, pp. 148-151, 2010 [18] g. s. josan, g. s. lehal, “a punjabi to hindi machine translation system”, 22nd international conference on computational linguistics: demonstration papers, manchester, uk, august 18-22, 2008 [19] t. rama, k. gali, “modeling machine transliteration as a phrase based statistical machine translation problem”, 2009 named entities workshop: shared task on transliteration, suntec, singapore, august 7, 2009 [20] c. poornima, v. dhanalakshmi, m. a. kumar, k. p. soman, “rule based sentence simplification for english to tamil machine translation system”, international journal of computer applications, vol. 25, no.8, pp. 38-42, 2011 [21] a. soni, s. jain, d. m. sharma, “exploring verb frames for sentence simplification in hindi”, international joint conference on natural language processing, nagoya, japan, october 14-18, 2013 [22] u. germann, “building a statistical machine translation system from scratch: how much bang for the buck can we expect?”, workshop on data-driven machine translation, toulouse, france, july 7, 2001 [23] m. z. islam, j. tiedemann, a. eisele, “english to bangla phrase-based machine translation”, 14th annual conference of the european association for machine translation, st raphael, france, may, 2010 [24] k. mishra, a. soni, r. sharma, d. m. sharma, “exploring the effects of sentence simplification on hindi to english machine translation system”, workshop on automatic text simplification: methods and applications in the multilingual society, dublin, ireland, august 24, 2014 engineering, technology & applied science research vol. 8, no. 5, 2018, 3421-3426 3421 www.etasr.com chermat et al.: techno-economic feasibility study of investigation of renewable energy system for … techno-economic feasibility study of investigation of renewable energy system for rural electrification in south algeria lower cost for better environment faycal chermat automatic laboratory of setif, electrical engineering department, ferhat abbas university, setif, algeria chermat33@yahoo.fr mabrouk khemliche automatic laboratory of setif, electrical engineering department, ferhat abbas university, setif, algeria mabroukkhemliche@yahoo.fr abdessalam badoud automatic laboratory of setif, electrical engineering department, ferhat abbas university, setif, algeria badoudabde@yahoo.fr samia latreche automatic laboratory of setif, electrical engineering department, ferhat abbas university, setif, algeria ksamia2002@yahoo.fr abstract—this work aims to consider the combination of different technologies regarding energy production and management with four possible configurations. we present an energy management algorithm to detect the best design and the best configuration from the combination of different sources. this combination allows us to produce the necessary electrical energy for supplying habitation without interruption. a comparative study is conducted among the different combinations on the basis of the cost of energy, diesel consumption, diesel price, capital cost, replacement cost, operation, and maintenance cost and greenhouse gas emission. sensitivity analysis is also performed. keywords-renewable energy; energy management; technoeconomic; feasibility study; optimization i. introduction it is preferable to use renewable energy for cost reduction in rural areas where population growth is not proportional to the extension of the electricity grid [1]. this has paved the way for research on the use of autonomous renewable energies and on hybrid systems [2] by combining several types of power generation to reduce fuel consumption and therefore minimize operating cost [3]. however, prior to any implementation of a renewable energy system, a technical and economic feasibility study is necessary to justify the investment and allocated budget. several studies have discussed the sizing and economic analysis of hybrid systems. an optimal sizing procedure of the wind/pv/diesel hybrid system was introduced in [4]. this procedure has been designed for small applications in turkey. a techno-economic feasibility study of a house in urumqi in china fuelled with 100% renewable energy was developed in [5]. the effect of the introduction of a wind farm for the improvement of the dynamic economic dispatching of the western algerian network was studied in [6]. authors in [7] and [8] established models for the components of a hybrid wind-powered solar-pumped storage power system. authors in [9] presented an analysis of pv/wind hybrid systems for the power supply of a house, farm or enterprise, which demonstrated that these two sources could be independent or connected to the electrical grid with complex interactions. this complete hybridisation study has been considered expensive and laborious for many industrial technology departments. authors in [10] designed a 100% costeffective system with low cost of energy (coe) by studying an fm transmitter station powered by a pv/diesel hybrid system for rural communities. homer software was used in [11] to study the techno-economic feasibility of a pv/diesel/battery hybrid system for the power supply of the bin habbas town in saudi arabia. by analysing the solar radiation of rafha, the storage in batteries increased with the penetration of renewable energies, and the hours of the diesel generator (dg) operation were reduced. ii. methodology a. location and load demand specification this work is the first study about the center of sahara, namely the town of in salah, which is located in an altitude of 268m between the coordinates of 2°28′e longitude and 27°12′n latitude. the study is conducted on a habitation that requires 57kwh/day. figure 1 presents the average daily consumption. fig. 1. daily energy consumption. engineering, technology & applied science research vol. 8, no. 5, 2018, 3421-3426 3422 www.etasr.com chermat et al.: techno-economic feasibility study of investigation of renewable energy system for … b. meteorological data requirements are obtained through nasa’s site of meteorological surfaces and solar energy. figures 2 and 3 show the global horizontal radiation and wind speed at in salah, respectively. the average annual solar irradiance is 5.83kwh/m 2 /day, and the average wind speed is 5.1m/s. fig. 2. global horizonta radiation for in salah. fig. 3. wind speed for in salah. c. evaluation criteria our study covers net percent cost (npc) of the system, including investment or initial capital cost (icc), replacement cost (rc), and operating and maintenance cost (omc), fuel cost (fc), and the coe. npc is given by (1): 𝑁𝑃𝐶 = 𝐶𝑡𝑜𝑡𝐶𝑅𝐹 (𝑖,𝑇𝑝) (1) where 𝐶𝑡𝑜𝑡 is the total annualized cost of the system ($/year), 𝑖 is the annual real interest rate (%), 𝑇𝑝 is the project lifetime, and 𝐶𝑅𝐹 is the capital recovery factor, which is calculated in the following equation [12]: 𝐶𝑅𝐹 = 𝑖(1+𝑖)𝑛(1+𝑖)𝑛−1 (2) where 𝑖 is the real interest rate and n is the number of years. 𝐶𝑂𝐸 is calculated from the following equation: 𝐶𝑂𝐸 = 𝐶𝑡𝑜𝑡𝐸𝑡𝑜𝑡 (3) where 𝐸𝑡𝑜𝑡 represents the total consumption of electricity during the year (kwh/year). the fraction of pv energy and wind energy can be calculated as [13]: 𝑓𝑝𝑣 = 𝐸𝑝𝑣𝐸𝑝𝑣+𝐸𝑊𝐺 (4) 𝑓𝑊𝐺 = 𝐸𝑊𝐺𝐸𝑝𝑣+𝐸𝑊𝐺 (5) d. energy monitoring energy management is defined according to iso50001 as a “set of interrelated or interacting elements to establish an energy policy and energy objectives and process and procedures to achieve those objectives” [14]. an energy management algorithm is elaborated to explain the operation of the chosen hybrid system which satisfies the demand while taking into account the economic criteria described above. its flow chart is shown in figure 4 and its steps are: if 𝑃𝑤 > 𝑃𝑙𝑜𝑎𝑑 then the load is alimented directly from the wind generator. else we calculate 𝑃𝑝𝑣 if 𝑃𝑝𝑣 > 𝑃𝑙𝑜𝑎𝑑 then we alimented by the gpv. else we calculate 𝑃𝑤 + 𝑃𝑝𝑣 if 𝑃𝑤 + 𝑃𝑝𝑣 > 𝑃𝑙𝑜𝑎𝑑 then we powered directly from renewable resources. else we check 𝑆𝑂𝐶 if 𝑆𝑂𝐶 > 40% then we aliment the load by extracting the lack from batteries. else return to dg and fill the gap from renewable resources and in the same time charge the batteries. if 𝑆𝑂𝐶 > 95% then the dg is extinguished and the load is supplied by filling the mast from the batteries. fig. 4. flow chart of energy management. iii. system components figure 5 shows our proposed hybrid system. the load demand is coupled to the ac bus, whereas the wind generator, gpv and batteries are connected to the dc bus. a conventional backup dg is typically used to supplement the renewable engineering, technology & applied science research vol. 8, no. 5, 2018, 3421-3426 3423 www.etasr.com chermat et al.: techno-economic feasibility study of investigation of renewable energy system for … system for maximum loads and during periods of poor resource generation. fig. 5. hybrid system design. a. pv system the electrical power produced by the photovoltaic network is calculated using (6): 𝑃𝑝 = 𝑓𝑝𝑣 × 𝑌𝑝𝑣 (𝐼𝑡𝐼𝑠) (6) where𝑓𝑝𝑣,𝑌𝑝𝑣, 𝐼𝑡 and 𝐼𝑠 are respectively the reduction factor, the total installed capacity, the solar radiation and the incident radiation at the standard test conditions. b. wind system the mean power produced by an aerodynamic generator is given by [15]: 𝑃𝑤 = ∫ 𝑃(𝑣)𝑓(𝑣) 𝑑(𝑣)𝑉𝑜𝑢𝑡𝑉𝑖𝑛 (7) where 𝑉𝑖𝑛 is the wind speed at which electricity production starts, 𝑉𝑜𝑢𝑡 the wind speed at which electricity production stops, 𝑃(𝑣) is the aero-generator’s power curve (given by the manufacturer) and 𝑓(𝑣) is the weibull probability density function. c. power converter the energy flows between ac and dc components are maintained thanks to the use of an energy converter which converts the dc into ac for the supply of several devices and plays the role of a “controller” for the direct current conversion of the pv generator into direct current. d. battery the capacity of the storage unit expressed in ampere-hours is defined as follows: 𝐶𝐵 = 𝑁𝑗𝑎×𝐵𝑗𝑝𝑃𝐷×𝑅𝑡 (8) where 𝑁𝑗𝑎 is the number of days of the storage unit autonomy, 𝐵𝑗𝑝 is the daily requirement of the consumer expressed in (ah) and it is deduced from the energy requirement in (wh) and the chosen voltage of the batteries, 𝑃𝐷 is the maximum discharge depth of the storage unit and 𝑅𝑡 is the temperature correction factor [16]. the state of batteries charge can be calculated according to (9): 𝑆𝑂𝐶 (𝑡 + ∆𝑡) = 𝑆𝑂𝐶(𝑡) + ɳ𝑏𝑎𝑡 (𝑃𝐵 (𝑡) 𝑉𝑏𝑢𝑠⁄ )∆𝑡 (9) where ɳ𝑏𝑎𝑡 is equal to the round-trip efficiency in the charging process and is equal to 100% in the discharging process [17], 𝑉𝑏𝑢𝑠 is the dc bus voltage and δt is the hourly time step, set equal to 1 h. e. diesel generator currently, the price of diesel in algeria is 0.21$/l, having seen a 65% increase in a period of 4 years. the diesel generator operates according to constraint (10) [18]: 𝑃1𝑚𝑖𝑛 ≤ 𝑃1 ≤ 𝑃1𝑚𝑎𝑥 (10) iv. results and discussion the different configurations of the optimized systems are compared with different criteria, such as total npc (tnpc), coe, and energy production. obtained results for each configuration are presented in table i. the table is organized to encompass all the criteria necessary for the comparison in choosing the best configuration that meets our specifications. table i. configurations comparative study configuration case 1 case 2 case 3 case 4 gd 14 10 10 10 converter 0 15 15 15 battery 0 36 32 32 pv 0 13.8 0 6.9 wind 0 0 3 2 production kwh/year electricity 74043 28389 29900 29686 excess electricity 53140 2513 3960 4381 capacity shortage 0.1 0 0 0 unmet load 5.1 0.0000309 0.0000606 0.0000708 cost ($) total net present cost $ 229361 78593 76762 73880 leveled cost of energy $/kwh 0.858 0.294 0.287 0.276 o&m cost $/yr 89576 18105 25021 19951 generator & fuel hours of operation 8759 361 1019 290 fuel consumption l/yr 44330 1523 4365 1212 emissions kg/yr carbon dioxide (co2) 116735 4012 11495 3190 carbon monoxide 288 9.9 28.4 7.88 unburned hydocarbon 31.9 1.1 3.14 0.872 particulate matter sulphur 21.7 0.747 2.14 0.594 sulphur dioxide 234 8.06 23.1 6.41 dioxide nitrogen oxide 2571 88.4 253 70.3 a. optimization results the wind/pv/dg hybrid system (case 4) comprises a design of 6.9kw provided by the gpv, 6kw of wind turbine represented by two 500w generator types, a storage system that contains 8 strings mounted in parallel, each string containing 4 batteries connected in series, a 15kw power converter, and a 10kw dg. case 4 is the most economical system with a low tnpc of $73880, which accounts for 67.8% reduction of the dg system’s tnpc (case 1), 6% reduction of the pv/dg system (case 2) and 3.75% reduction of the wind/dg system (case 3). optimum coe produced by our system is $0.276. our system is the cheapest configuration, and has an energy production of 29686kwh/year, in which 43% is delivered by the gpv and 50% is provided by the supplied wind generator. the remaining energy production will be engineering, technology & applied science research vol. 8, no. 5, 2018, 3421-3426 3424 www.etasr.com chermat et al.: techno-economic feasibility study of investigation of renewable energy system for … guaranteed by the dg, which generates 2159kwh/year instead of 74043kwh/year, in case the system is used alone, whereas for ac primary load, the generation is near 21000kw/year. homer calculates the unmet load and its fraction by determining the ratio between the unmet loads and the annual electrical demand. for all our cases, the system can serve an electrical load that meets the demand. therefore, the unmet load is negligible and tends to be zero. figure 6 shows the monthly distribution of electricity produced in kw by all cases and confirms that energy production is dependent on meteorological data. notably, dg does not produce a considerable amount of energy during the months that strong winds and solar potential allow the production of a large amount of energy from renewable sources. the production is the opposite for the other months. for example, december is the least sunny month with low wind speed, thereby providing low power output from the gpv and wind generator. case 1: only dg case 2: pv/dg case 3: wind/dg case 4: wind/pv/dg fig. 6. monthly average electric production of 4 cases. black: dg, yellow: pv, green: wind. at this level, the efficiency of our system is illustrated in figure 7. if energy is lacking and the batteries are discharged, then gd intervenes, otherwise, it turns off, once the batteries are charged. fig. 7. efficiency of the best hybrid system. the selected hybrid system has a capacity shortage equal to zero and an excess electricity of 4381kwh/year that will be stored in the batteries. figure 8 shows the cash flow summary on the basis of the costs for the best configuration. the icc of our hybrid system is $43664. it is the highest and accounts for more than 59.1% of the tnpc due to the prices of each subsystem. the remainder is distributed as follows: 14.1% is the rc, 27% is the omc and the remaining 4.4% is the price of diesel consumption with electricity saving of almost 4.6%. fig. 8. cash flow summary based on cost. table ii shows the percentage of each cost on the basis of the npc of all configurations. the use of fossil resources is initially inexpensive, although it requires money during operation. the integration of one or more sources of renewable energy production requires an expensive icc but with a considerable reduction in operating budget and fc. table ii. distribution of costs relative to tnpc costs icc rc om c fuel salvage tnpc ($) ($) ($) ($) ($) ($) ($) case1 4500 16497 89576 119004 -215 229361 2% 7.2% 39% 51.9% 0.1% case2 49414 11412 18105 4090 -4428 78593 62.8% 14.5% 23% 5.2% 5.5% case 3 32464 9860 25021 11718 -2302 76762 42.3% 12.8% 32.6% 15.2% 2.9% case4 43664 10439 19951 3252 -3427 73880 59.1% 14.1% 27% 4.4 % 4.6% engineering, technology & applied science research vol. 8, no. 5, 2018, 3421-3426 3425 www.etasr.com chermat et al.: techno-economic feasibility study of investigation of renewable energy system for … the tnpc decreases from one scenario to another whilst adding renewable energy resources. in our hybrid system, we invested nine times the icc of a conventional installation with a major optimisation of more than 97% of diesel consumption by reducing it to 1212l/year whilst limiting the hours of operation of the dg to only 290. this investment is successful because the addition of $39164 for the icc of the hybrid system benefits us from the savings of more than $115752 regarding the diesel consumption throughout the project lifetime. b. emissions the use of renewable energy sources not only has an economical but also an environmental impact. it is beneficial for the protection of the environment, the climate, the planet, and our health. one of the most important factors for climate change due to greenhouse gas emissions is carbon dioxide (co2). co2 is reduced to 3190kg/year instead of 116735kg/year when using the dg only, which accounts for 97.3% reduction with a fraction of renewable energy of 93%. we can avoid injecting 2838625kg of co2 in a period of 25 years, which is the lifetime of our hybrid system, thereby decreasing all other air pollutants with the same percentage of 97.3%. c. sensitivity analysis this analysis provides information regarding if a particular system will be optimal to certain criteria whilst relying on economic study and eliminating impossible systems. in our case, wind speed (4–7m/s), solar irradiation (4–7kwh/m2/d), height of windmill gauge (15m and 20m) and diesel price ($0.21–$0.40) are our sensitivity variables. we aim to identify the effects of these changes on co2 emissions. figure 9 shows the optimal system by fixing the solar irradiation at 5.83kwh/m 2 /day and the wind speed at 5.1m/s. fig. 9. optimal system for fixed solar radiation and wind speed. notably, the proposed system is economically feasible for any height of the gauge, as long as the diesel price is less than $0.3. at $3.5, the wind/pv/battery system is most feasible, economically and environmentally with zero pollution. by fixing the diesel price at $0.21 and the height of windmill gauge at 15m, we obtain the results shown in figure 10. notably, the pv/dg/battery system is the least expensive under conditions where wind speed is less than 4.4m/s and solar irradiation is between 5.1kwh/m 2 /day and 6kwh/m 2 /day. the pv/battery system is the optimal solution for low wind speed and solar irradiation of more than 6kwh/m 2 /day with zero emissions. the wind/pv/dg hybrid system is economically feasible for proportional increases in meteorological data. however, the wind/dg/battery system will be feasible only by increasing the wind speed to more than 5m/s and decreasing the solar irradiation by less than 6kwh/m 2 /day. fig. 10. optimal system for fixed diesel price and hub height. figure 11 shows the surface plot for co2 emissions. co2 emission rises when dg intervenes. the emission decreases with the increase in meteorological data. the increase in wind speed decreases co2 emissions. however, emission does not occur when the solar irradiation reaches 6.4kwh/m 2 /day even with extremely low wind speed. hence, in our system, the solar energy contributes more effectively than the wind energy from the environmental perspective. fig. 11. surface plot for co2 emissions. v. concusions in this work, we investigated several configurations of energy resources. the use of a single source is not economically or environmentally feasible. hence, the use of two renewable energy sources, wind and pv coupled with a dg, is the optimum configuration. a new energy management algorithm was demonstrated, and shows how homer minimizes the dg operation, improves the energy efficiency of our system and increases the renewable fraction. we concluded with a feasibility study that has four defined sensitivity variables. we obtained the following satisfactory results:  the increase in the price of diesel increases tnpc and coe, and the increase of the height of the wind generator increases the penetration of wind energy. engineering, technology & applied science research vol. 8, no. 5, 2018, 3421-3426 3426 www.etasr.com chermat et al.: techno-economic feasibility study of investigation of renewable energy system for …  the wind/pv/diesel hybrid system is economically feasible for proportional increases in meteorological data.  the wind/dg/battery system requires high wind speed, whereas the pv/diesel system is the optimum solution for low wind speed.  increasing wind speed reduces co2 emissions. however, emissions do not occur when the solar irradiation reaches a certain level even with an extremely low wind speed. thus, in our system, the solar energy contributes more efficiently than wind energy from an environmental perspective.  using renewable energy sources with dg, battery storage supply, and sharing the load by adapting the current system seems to be the most applicable solution for today’s conditions. appendix technical & economical parameters of hybrid system  pv system rated power: 230w capital cost: 580$ replacement cost: 230$ omc: 100$  wind system rated power: 3 kw dc life cycle: 15 years starting wind speed: 3.5m/s capital cost: 6200$ replacement cost: 2100$ omc: 280$/yr  bidirectional converter capital cost: 4250$ replacement cost: 4250$ omc: 215$/yr efficiency: 90% rectifier efficiency: 85% rectifier capacity: 100%  battery nominal voltage (v): 6v maximum capacity: 9645 kwh capital cost: 200$ lifetime: 1168ah maximum charge current: 41 a  diesel generator diesel price: 0.21$ references [1] j. byrne, b. shen, b. wallace, “the economics of sustainable energy for rural development: a study of renewable energy in china”, energy policy, vol. 26, no. 1, pp. 45-54, 1998 [2] j. dekker, m. nthontho, s. chowdhury, s. p. chowdhury, “economic analysis of pv/diesel hybrid power systems in different climatic zones of south africa”, international journal of electrical power and energy systems, vol. 40, no. 1, pp. 104-112, 2012 [3] r. sebastian, “modelling and simulation of a high penetration wind diesel system with battery energy storage”, international journal of electrical power & energy systems, vol. 33, no. 3, pp. 767-774, 2011 [4] o. ekren, b. y. ekren, b. ozerdem, “break-even analysis and size optimization of a pv/wind hybrid energy conversion system with battery storage–a case study”, applied energy, vol. 86, no. 7, pp. 1043-1054, 2009 [5] c. li, x. ge, y. zheng, c. xu, y. ren, c. song, c. yang, “technoeconomic feasibility study of autonomous hybrid wind/pv/battery power system for a household in urumqi, china”, energy, vol. 55, pp. 263272, 2013 [6] a. belmadani, l. benasla, m. rahli, “amelioration d’un dispatching economique dynamique par l’introduction d’une ferme eolienne. application au reseau electrique ouest algerien”, revue roumaine des sciences techniques-serie electrotechnique et energetique, vol. 57, no. 3, pp. 269-280, 2012 (in french) [7] r. yan, l. yanpin, “simulation and optimization of hybrid wind-solarpumped-storage power system”, ieee international conference on electric information and control engineering, wuhan, china, april 1517, 2011 [8] y. ren, y. zheng, y. p. li, j. j. huang, d. zhang, “modelling and optimization of hybrid wind/pv pumped-storage power system”, applied mechanics and materials, vol. 48-49, pp. 693-696, 2011 [9] j. b. v. subrahmanyam, p. alluvada, bandana, k. bhanupriya, c. shashidhar, “renewable energy systems : developement and perspectives of a hybrid solar-wind system”, engineering, technology & applied science research, vol. 2, no. 1, 2012, pp. 177-181, 2012 [10] m. moghavvemi, m. s. ismail, b. murali, s. s. yang, a. attaran, s. moghavvemi, “development and optimization of a pv/diesel hybrid supply system for remote controlled commercial large scale fm transmitters”, energy conversion and management vol. 75, pp. 542551, 2013 [11] m. shaahid, i. el amin, “techno-economic evaluation of off-grid hybrid photovoltaic–diesel–battery power systems for rural electrification in saudi arabia—a way forward for sustainable development”, renewable and sustainable energy reviews, vol. 13, no. 3, pp. 625-633, 2009 [12] g. j. dalton, d. a. lockington, t. e. baldock, “feasibility analysis of renewable energy supply options for a grid-connected large hotel”, renewable energy, vol. 34, no. 4, pp. 955-964, 2009 [13] a. n. celik, “optimisation and techno-economic analysis of autonomous photovoltaic–wind hybrid energy systems in comparison to single photovoltaic and wind systems”, energy conversion and management, vol. 43, no. 18, pp. 2453-2468, 2002 [14] t. c. seng, energy management and economics, the instute of engineers & singapore and national environment agency, 2016 [15] r. hammouche, atlas vent de l’algerie, office national de la meteorologie, 1990 (in french) [16] s. diaf, m. belhamel, m. haddadi, a. louche, “technical and economic assessment of hybrid photovoltaic/wind system with battery storage in corsica island”, energy policy, vol. 36, no. 2, pp.743-754, 2008 [17] r. belfkira, l. zhang, g. barakat, “optimal sizing study of hybrid wind/pv/diesel power generation unit”, solar energy , vol. 85, no. 1, pp. 100-110, 2011 [18] j. b. fulzele, s. dutt, “optimium planning of hybrid renewable energy system using homer”, international journal of electrical and computer engineering, vol. 2, no. 1, pp. 68-74, 2012 https://www.scientific.net/author-papers/yan-ren-2 https://www.scientific.net/author-papers/yuan-zheng https://www.scientific.net/author-papers/yan-pin-li https://www.scientific.net/author-papers/jian-jun-huang https://www.scientific.net/author-papers/dun-zhang-3 http://www.sciencedirect.com/science/journal/13640321 http://www.sciencedirect.com/science/journal/13640321 http://www.sciencedirect.com/science/journal/13640321/13/3 i. introduction ii. methodology a. location and load demand specification b. meteorological data c. evaluation criteria d. energy monitoring iii. system components a. pv system b. wind system c. power converter d. battery e. diesel generator iv. results and discussion a. optimization results b. emissions c. sensitivity analysis v. concusions appendix references microsoft word 12-3242_s_etasr_v10_n1_pp5164-5167 engineering, technology & applied science research vol. 10, no. 1, 2020, 5164-5167 5164 www.etasr.com genc & kaya: vibration damping optimization using simulated annealing algorithm for vehicle … vibration damping optimization using simulated annealing algorithm for vehicle powertrain system mehmet onur genc research and development center valeo automotive systems bursa, turkey mehmet-onur.genc@valeo.com necmettin kaya mechanical engineering department bursa uludag university bursa, turkey necmi@uludag.edu.tr abstract—the clutch system in a vehicle’s powertrain system controls torque transmission and has vibration damping properties. a vehicle’s clutch system is subjected to high dynamic loads and vibrations, under operational conditions, that need further system analysis. the torque generated from the vehicle’s engine creates vibrations at different levels of frequencies. for this purpose, vibration damping systems have to be designed to make the vehicle work more efficiently. in this study, the 1-d modeling of powertrain system, including metallic clutch damper springs, was subjected to vibration optimization with the simulated annealing (sa) algorithm. this novel methodology accelerates the powertrain system vibration optimization and provides assumptions eliminating cost and time in real vehicle testing. keywords-clutch damper; simulated annealing; 1-d modeling; damper torque; powertrain system; driving comfort; vibration i. introduction clutch damper springs, used in vehicle powertrain systems, are of great importance as they damp engine vibrations during torque transmission (figure 1). prominent studies have been carried out on the optimization of the vibration on vehicles. torsional mode analysis was carried out in [1] investigating the modeling of powertrain systems, including automated transmission. the hydraulic hybrid powertrain system was analyzed in [2] using 1-d modeling. analysis using 1-d simulation at stiffness levels of the clutch disc damper were studied in [3]. the natural frequency of vehicle components were studied in [4], assuming on optimal weight values. in [5], an analysis on the vibration frequency level of a 3-cylinder engine proposed improvements to the clutch design. the study of a passenger car’s powertrain system modeling determined the clutch damper disc stiffness behavior on driving conditions in [6]. the frequencies of the gearbox vibrations on different gearbox types were analyzed in [7], while in [8] the engine vibrations were analyzed by fft method. harmonic investigations were performed on an engine’s behavior in [9], in order to reduce the noise in the power transmission system. the design of transmission gears and the optimization of clutch-damping factors, by applying harmonic analysis, were studied in [10]. the frequency ranges on heavy vehicles were examined by modal analysis in [11]. optimization algorithms are of high importance in vehicle engineering system design. the integrated genetic algorithm (ga) was used in [12] in order to provide optimized frequency levels on an electric engine powertrain. simulated annealing (sa) algorithm was used in [13] for the optimization of a machine tool movement during production cycles. the constrained and unconstrained shape optimization of cold-formed steel columns was examined in [14]. in [15], a logarithmic cooling schedule of the sa algorithm was studied in order to improve global searchability. the optimization of pneumatic clutch activator’s system behavior, by using the sa algorithm, was studied in [16]. the penalty added sa algorithm for constrained flow problems was examined in [17], while various penalty functions and their integration into the sa algorithm were studied in [18]. fig. 1. clutch system dampening effect this study examines the powertrain system of a gasoline engine vehicle, having 110nm torque, integrating the simulated annealing (sa) algorithm into powertrain system vibration optimization simultaneously with 1-d modeling, providing assumptions and precautions prior to production phases. ii. clutch damper system clutch damper systems are designed to damp excessive vibration transmission from engine to gearbox. the clutch damper disc can be observed in detail in figure 2. metallic damper springs, located in the clutch disc, enable damping under driving conditions. damper spring’s stiffness value is the sum of the stiffness of each spring (kequivalent). the importance corresponding author: m. o. genc engineering, technology & applied science research vol. 10, no. 1, 2020, 5164-5167 5165 www.etasr.com genc & kaya: vibration damping optimization using simulated annealing algorithm for vehicle … of the stiffness behavior can be observed on the model analysis of the powertrain system [6]. damper torque is applied on the clutch disc to get damper torque capacity which has high importance on the powertrain system optimization. damper torque’s graph indicates an hysteresis, due to the internal friction which has effect on the dampening ability (figure 3). figure 4 shows the loading and unloading phases of the clutch damper disc in operational condition. in this study, the clutch disc assembly can be compressed up to 6.5° radial travel. fig. 2. clutch disc modeling fig. 3. clutch disc damper torque torque (nm) vs. angle (°) fig. 4. clutch damper disc operation behavior iii. modeling of the powertrain system the powertrain system model belongs to a specific type of passenger vehicle. simcenter amesim was utilized to analyze the model (figure 5). the metallic spring was selected from the library of amesim. the stiffness value 16nm/°, according to the results of experimental disc measurements, was provided as input to the model interface (figure 6). figure 7 contains the sample output graph for the analyzed 1-d modeling. the vibration was taken from the gearbox model part. the selected values on this graph were used for the vibration optimization using the sa algorithm integrated in amesim. the gearbox in the powertrain system is important in displaying the dampening effects of the clutch system. in case the target dampening is not obtained from the clutch system, mechanical damages may occur in the powertrain system. fig. 5. 1-d modeling of vehicle powertrain system fig. 6. damper torque of clutch damper disc used in the analysis fig. 7. vibration analysis results on gearbox iv. sa algorithm integrated with 1-d modelling sa algorithm is designed to perform a global search, preventing the convergence to locally optimal solutions, by allowing movement to the worst solutions through the boltzmann factor, simulating the annealing process of metals. engineering, technology & applied science research vol. 10, no. 1, 2020, 5164-5167 5166 www.etasr.com genc & kaya: vibration damping optimization using simulated annealing algorithm for vehicle … its name comes from the simulating the behavior of metals in the annealing process, in which the metal is heated and kept at stabilized temperature while slowly cooling the optimization process starts by generating a random initial solution, while sa allows movement resulting in solutions that are worse (uphill moves) than the current solution in order to escape from local minima. each iteration of a new current solution leads to the decrease of the current temperature in the ratio of k which is called cooling rate (1): ���� � � ∗ �� ��� (1) uphill moves eliminate each local minimum, while the boltzmann probability factor enables the algorithm to take worst results in the range of the boltzmann probability equation, while the global minimum is searched and finally found. � ������� ���� � � 1/ ��� ��� !"#############$%&���'####$%( )* (2) the optimization is performed by a system programmed in python integrating the sa algorithm and amesim analysis. figure 8 shows the process of each main iteration. figure 9 describes the algorithm of the python script. at first, the function code of the amesim 1-d modeling is defined. then, sa algorithm is called, with a penalty function defining the stiffness constraint which is defined by taking into consideration the geometrical limits of the clutch damper disc. the stiffness value was defined as: 15.5≤x≤16.5. fig. 8. python script integrating amesim and sa algorithm 1 define amesim function run code 2 initialize → x0, t0, k, n, m, 3 call amesim function and calculate finitial with x0 ← f objective initial function 4 for i = 1: max iteration 5 construct a neighbor solution randomly (x0 ←→ xnew) 6 call amesim function and calculate fnew with xnew from amesim 7 if fnew < fn 8 xn ←xnew 9 if fnew < fbest 10 xnew ←xbest 11 calculate penalty parameters for given constraint (xc ) 12 else if penalty > random (0,1) 13 xn ← xnew 14 calculate penalty parameters for given constraint (xc ) 15 end 16 t = t * k 17 output: fbest, xbest fig. 9. amesim integrated sa algorithm figure 10 presents the sa algorithm’s flowcart in detail. spring stiffness value defines the initial search parameter and sa algorithm parameters such as temperature t, cooling ratio k and iteration parameters are entered into the algorithm. at the end of the algorithm the best value of fbest, xbest is obtained. fig. 10. sa algorithm vibration minimization through sa and amesim v. simulation results table i shows the obtained minimum vibration results on the gearbox. x represents the clutch damper stiffness level and optimum vibration values for each run are exhibited. table i. optimization results run 1 run 2 run 3 run 4 run 5 x (nm/°) 15.749 15.854 15.801 15.715 15.732 objective function (rad/s 2 ) 86 92 89 84 85 the result values of each run were very close. figure 11 shows the graph of the objective function and temperature for an example run. it seems that sa algorithm successfully eliminates local minima and converged to the global minimum point at each run. moreover, figure 11 also shows the vibration decrease. the optimum damper stiffness was 15.715nm/°. sa algorithm inputs have many effective parameters to change search capability. table ii shows a brief vibration result comparison obtained from the 1-d modeling. the base clutch disc design, having 16nm/°damper stiffness value, resulted in 105rad/s 2 on the gearbox utilizing the amesim program. conversely, the optimum stiffness value 15.715nm/° resulted in 84rad/s 2 on the gearbox showing a decrease of about 21%. the result analysis values are directly linked to the key parameters of the sa algorithm. therefore, in case the key parameters of the algorithm change, the obtained values are expected to change. this case needs detailed analysis in sa algorithm parameter variations. engineering, technology & applied science research vol. 10, no. 1, 2020, 5164-5167 5167 www.etasr.com genc & kaya: vibration damping optimization using simulated annealing algorithm for vehicle … fig. 11. sa algorithm: objective function vs temperature graph table ii. comparison results of base vs optimum design base design optimum design x (nm/°) 16 15.715 objective function (rad/s 2 ) 105 84 vi. conclusions this study analyzed and evaluated the vibration damping optimization of a vehicle’s powertrain system, designed for a middle segment vehicle having an 110nm torque gasoline engine. excessive vibrations are making the driving experience uncomfortable, while unwanted oscillations result in mechanical damages. new generation optimization algorithms approach optimum values, providing optimum key parameters for the system. for this purpose, a new methodology was presented in order to find optimum design parameters that reduce the vibration level. the sa algorithm was developed and used with 1-d modeling for torsional vibration optimization. vibrations in the gearbox were decreased by 21%, using the optimum clutch damper spring stiffness value. this method saves cost and time on the optimization of the vibration dampening in a powertrain system. acknowledgment this study was conducted with the collaboration of valeo automotive systems and bursa uludag university. references [1] s. j. hwang, j. s. chen, l. liu, c. c. ling, “modelling and simulation of a powertrain-vehicle system with automatic transmission”, international journal of vehicle design, vol. 23, no. 1, pp. 145-160, 2006 [2] a. macor, a. benato, a. rossetti, z. bettio, “study and simulation of a hydraulic hybrid powertrain”, energy procedia, vol. 126, pp. 11311138, 2017 [3] m. o. genc, n. kaya, “modelling and experimental investigation of clutch damper spring stiffness on truck driving comfort”, international journal of advances on automotive and technology, vol. 1, no. 2, pp. 121-136, 2018 [4] r. smith, “changing the effective mass to control resonance problems”, sound and vibration, vol. 35, no. 5, pp. 14-17, 2001 [5] h. acar, c. gul, m. avci, “clutch disc torsional characteristics optimization to reduce idle and gear rattle on passenger car”, international automotive congress, belgrade, serbia, april 14-15, 2015 [6] m. o. genc, b. budak, n. kaya, “modelling and vibration analysis of powertrain systems”, international journal of automotive science and technology, vol. 2, no. 1, pp. 17-25, 2018 [7] m. sofian, d. hazry, k. saifullah, m. tasyrif, k. salleh, i. ishak, “a study of vibration analysis for gearbox casing using finite element analysis”, international conference on applications and design in mechanical engineering, batu ferringhi, penang, malaysia, october 1113, 2009 [8] a. brandt, t. lago, k. ahlin, j. tuma, “main principles and limitations of current order tracking methods”, sound and vibrations, vol. 39, no. 3, pp. 19-22, 2005 [9] c. s. keeney, s. shih, “prediction and control of heavy duty powertrain torsional vibration”, sae transactions, vol. 101, pp. 805-814, 1992 [10] s. jadhav, “powertrain nvh analysis including clutch and gear dynamics”, sae technical paper 2014-01-1680, sae, 2014 [11] a. mazzei, b. alzahabi, l. k. natarajan, “analysis of the drivetrain bending response for a heavy truck driveline”, sae technical paper series, 2012 [12] k. soleimani, j. mazloum, “designing a ga-based robust controller for load frequency control (lfc)”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2633-2639, 2018 [13] a. a. afifi, w. a. khan, d. r. hayhurst, “adaptation of the simulated annealing optimization algorithm to achieve improved near-optimum objective function values and computation times for multiple component manufacture”, international journal of advanced manufacturing technology, vol. 60, no. 5-8, pp. 437-451, 2012 [14] j. leng, z. li, j. k. guest, b. w. schafer, “shape optimization of coldformed steel columns with fabrication and geometric end-use constraints”, thin-walled structures, vol. 85, pp. 271-290, 2014 [15] w. shao, g. guo, “multiple-try simulated annealing algorithm for global optimization”, mathematical problems in engineering, vol. 2018, article id 9248318, 2018 [16] m. g. skarpatis, f. n. koumboulis, a. s. ntellis, “robust control of pneumatic clutch actuators using simulated annealing techniques”, 21st mediterranean conference on control and automation, chania, greece, june 25-28, 2013 [17] x. q. yang, a. i. mees, k. campbell, “simulated annealing and penalty methods for binary multicommodity flow problems”, progress in optimization, vol. 39, pp. 93-105, 2000 [18] c. park, j. h. moon, “a penalized principal component analysis using simulated annealing”, communications for statistical applications and methods, vol. 10, no. 3, pp. 1025-1036, 2003 engineering, technology & applied science research vol. 8, no. 1, 2018, 2412-2416 2412 www.etasr.com murawwat et al.:. weed detection using svms weed detection using svms sadia murawwat armish qureshi saleha ahmad yousaira shahid electrical engineering department lahore college for women university lahore, pakistan electrical engineering department lahore college for women university lahore, pakistan electrical engineering department lahore college for women university lahore, pakistan electrical engineering department lahore college for women university lahore, pakistan abstract—the major concern in pakistani agriculture is the reduction of growing weed. this research aims to provide a weed detection tool for future agri-robots. the weed detection tool incorporates the use of machine-learning procedure explicitly implementing support vector machines (svms) and blob analysis for the effective classification of crop and weed. weed revealing is based on characteristic features i.e. red green blue (rgb) components which differentiate soil and plant. morphological features—centroidand length aid to distinguish shape of crop and weed leaves. following feature extraction, the positive and negative margins are separated by a hyper-plane. the separating hyper-plane acts as the decision surface. sample input consists of multiple digital field images of carrot crops. training samples of seventy two images are taken. accuracy of the outcomes discloses that svm and blob analysis attain above 50-95% accuracy. keywords—image segmentation; colour segmentation; binarization; morphological features; support vector machines i. introduction one of the major concerns of an economy is accelerating agricultural development. weeds are unwanted plants that can survive and reproduce in agricultural fields. they hinder agricultural development by disturbing production and quality through competing with crops for water, light, soil nutrients, and space. as a result, weed control strategies are critical to sustain crop productivity. agriculture is a vital sector of the economy of pakistan and recently accounted for a 5.28% growth according to government estimates [1]. the sector directly supports three-quarters of the country's population, employs half the labor force, and contributes a large share of foreign exchange earnings. up to 60% of yield is dependent on soil fertility, and weeds that rob nutrients from crops limit yield potential [2]. therefore, removal of weed from cultivated fields during early stages of crop growth is essential for a healthy and good harvest. for weed detection we need field photographs with good precision. taking photographs can be done by attaching a camera in the front of the tractor/machine or manually. then, by applying image processing techniques to that image by using matlab we can detect the weed in the field. in this algorithm, our main aim is detection and removal of the weed using image processing. hand weeding is the technique of detecting weeds by naked eye and plucking it by hand or some tool one by one. hand hoeing is the technique carried out with specific measured mechanical machines that are moved over the fields within plant rows because weeds mostly emerge in between the crop plants [3]. two other means include using chemical sprays applied consistently across the entire field area before planting seeds and after the rise of plants and biological methods that employ natural pests which attack only weeds. there are many parts of the field that have insignificant volume of weeds, but herbicides are also applied in those parts. applying herbicides by human laborers using back-pack sprayer is very time consuming and costly, but still remains a common practice in many developing countries. by applying same types of herbicides in a field repeatedly, for the removal of the weeds population, there is a probability of appearance of weeds that are tolerant to those types of herbicides. according to the international survey of herbicide resistant weeds [4], 346 herbicide resistant biotypes that belonged to 194 species (114 dicots and 80 monocots) are spread over 340,000 fields worldwide [5]. the objective of our paper is to present a new model for classifying crops and weeds in digital images by using support vector machines (svms) with blob analysis to evaluate its performance in an automated weed control system. blob analysis is a fundamental technique of machine vision based on the analysis of consistent image regions [6]. the most promising techniques to identify weed species in arable crops are based on image processing [7]. the aim of this algorithm is to detect crops and weeds based on their features: rgb, centroid, and length. after leaf image acquisition (stored image), image processing techniques are employed for weed detection. processed image will be handed over to robots. in order to separate soil from plants, image segmentation is used. binarization method is based on thresholding and is implemented to differentiate soil and plant. the idea that weed and crop seems greener than loam is used to apply the segmentation. let ‘g’ represent the green pigment of an rgb image. a grey-scale image is obtained by seeing the ‘g’ value only. a threshold ‘t’ value for ‘g’ is calculated. g > t (1) equation (1) shows the pixels that are plant pixels and vice versa. the binary version is found, where the pixels with a engineering, technology & applied science research vol. 8, no. 1, 2018, 2412-2416 2413 www.etasr.com murawwat et al.:. weed detection using svms value ‘0’ represent soil and pixels with a value ‘1’ represent plant [5]. svms has been chosen as the classifier because of their impressive generalization performance, the absence of local minima, and the sparse representation of its solution [8]. our simulation works in two stages: (1) performing a training process and (2) performing a decision making process, where a decision is made between crop and weed. ii. methodology this research work describes the methodology for weed detection process in carrot crops. it follows ten steps. the task flow is shown in figure 1. the tasks and process represents the steps of the algorithm. our algorithm includes the following steps. fig. 1. task flow  step 1: load input sample images. some input images are shown in figure 2.  step 2: svm sample is trained using different feature extraction parameters. the samples are being trained from two sets of data, i.e. required and unrequired data set. in our study, required data set is crop and unrequired data set is weed that is to be detected.  step 3: a sample array is formed. data from different sample images are assembled together as a single set by using multidimensional arrays. the information extracted form step 2 is stored here.  step 4: now try catch loop is implemented. this function is used in case if any image is not accessed, try catch loop will fetch another image from the stored data (sample images). it will iterate the loop eight times.  step 5: image resizing is done to completely process the whole image without losing data. 50% reduction in size is done for successful weed detection.  step 6: after resizing the image, color segmentation is done. in the image segmentation process different regions in the image are divided to examine the information.  step 7: binarization is the next step following image segmentation. the rgb image will be converted to black and white image. threshold used here is ten percent.  step 8: blob analysis procedure is used after binarization. blob analysis is a major technique of machine vision. this is a mean for applications that discriminate the object from background.  step 9: in last step decision is made. if the weed is present in the image it will be pointed out, if no weed is present then the algorithm will point out nothing and will take another image using try catch loop.  step 10: it is the termination step that ends the loop and algorithm. after that all the output samples are displayed. iii. results and discusion for better analysis and understanding, the subsequent samples are divided in to three different scenarios: maximum crop sample, maximum weed sample and marginal weed and crop sample a. scenario 1: maximum crop sample this is a situation in which crop is in abundance with respect to the weed or weed is absent in the sample. due to the presence of crop only, the specified algorithm will detect weed intelligently and after comparison of crop and weed it will not show any pointer as weed is absent. b. scenario 2: maximum weed sample any sample that will have more/maximum weed and minimum/no weed will be categorized in this scenario. usually the resultant image of scenario two is more clear and easy to analyze because it shows clear pointed weed. an example of scenario 2 can be shown in figure 4. engineering, technology & applied science research vol. 8, no. 1, 2018, 2412-2416 2414 www.etasr.com murawwat et al.:. weed detection using svms fig. 2. 8 input sample images fig. 3. scenario 1: maximum crop sample fig. 4. image showing maximum weed sample engineering, technology & applied science research vol. 8, no. 1, 2018, 2412-2416 2415 www.etasr.com murawwat et al.:. weed detection using svms c. scenario 3: marginal weed and crop sample practically, when we observe any field area we find overlapped weed and crop leaves. this intermingling makes the scenario more complex for weed detection. as leaf to leaf comparison is attained for sorting out weed and crop, so that is the most complicated scenario and the accuracy may fluctuate here. due to the problem’s complexity, we have divided scenario 3 into three distinct cases that will help the analysis: a) case 1: overlapping overlapping includes the situation when the leaves of carrot crop are too close to the weed, hence the shape of each leaf will not be prominent. as for leaf to leaf comparison that creates further difficulties to compare the leaf shapes and features, overlapping changes the actual shapes of leaves and that results in less accuracy and complex detection. these cases usually show the minimum accuracy. such a case is shown in figure 5. fig. 5. image showing maximum overlapping b) case 2: non-overlapping the position in which the leaves of weed and crop are close but their leaves are apart and their shapes are not distorted, we can say that only a minor/no overlapping is there that is fitted in case 2. due to non-overlapping maximum output is achieved. svm can clearly differentiate both species. accuracy in this case is 100%. such a case is shown in figure 6. c) case 3: poised overlapping if crop and weed are neither separated gently nor as much close to overlap they will be categorized in the moderate overlapping. the output of that image will be more precise. in this case, besides slight overlapping, maximum output is gained. accuracy rate is 90%. almost the entire weed is detected. such a case is shown in figure 7. fig. 6. image with no overlapping fig. 7. image having moderate overlapping engineering, technology & applied science research vol. 8, no. 1, 2018, 2412-2416 2416 www.etasr.com murawwat et al.:. weed detection using svms iv. conclusion weed is detected using svms and a feature extraction technique. the concept of svms is concentrated on decision planes that describe decision boundaries. the data is divided into two sets including seventy-two samples for training and eight samples for testing. algorithm’s accuracy varies according to image types and cases. accuracy varies from 50% to 95%. images that have distant weed and crop are observed with maximum accuracy while the images that include overlapping leaves have minimum accuracy. the basic three techniques including binary image conversion, svm, and blob analysis evidenced as a paramount combination of techniques that holds the comparison between weed and crop more wisely. the three techniques seem adaptive and can be applied to diverse images, as two entirely different images are used for testing with varying size, weeds, lighting conditions and backgrounds. references [1] samaa.tv, the pakistan economic survey 2016-17, available at: https://www.samaa.tv/economy/2017/05/the-pakistan-economic-survey2016-17-at-a-glance/ [2] mosaic company, who we are, available at: http://www.cropnutrition. com/who-we-are [3] s. j. leghari, u. a. leghari, g. m laghari, m. buriro, f. a. soomro, “an overview on various weed control practises affecting crop yield”, journal of chemical, biological and physical sciences, vol.6, no. 1, pp. 59-69, 2015 [4] international survey of herbicide resistant weeds, available at: http://www.weedscience.org/default.aspx [5] f. ahmed, h. a. al-mamun, a. s. m. hossain bari, e. hossain, p. kwan, “classification of crops and weeds from digital images: a support vector machine approach”, crop protection, vol. 40, pp. 98-104, 2012 [6] s. mallick, blob detection using opencv (python, c++), available at: https://www.learnopencv.com/blob-detection-using-opencv-python [7] m. weis, m. sokefeld, “precision crop protection-the challenge and use of heterogeneity”, in: detection and identification of weeds, first ed. springerverlag, pp. 119–134, 2010 [8] t. rumpf, c. romer, m. weis, m. sokefeld, r. gerhards, l. plumer, “sequential support vector machine classification for small-grain weed species discrimination with special regard to cirsium arvense and galium aparine”, computers and electronics in agriculture, vol. 80, pp. 89-96, 2011 engineering, technology & applied science research vol. 8, no. 3, 2018, 3032-3037 3032 www.etasr.com chigvinadze et al.: on the nature of superconducting precursors in bi-pb-sr-ca-cu-o compositions … on the nature of superconducting precursors in bi-pb-srca-cu-o compositions fabricated by hot shock wave consolidation technology j. chigvinadze andronikashvili institute of physics condensed matter physics department ivane javakhishvili tbilisi state university tbilisi, georgia chigvinadze@yahoo.com s. ashimov andronikashvili institute of physics condensed matter physics department ivane javakhishvili tbilisi state university tbilisi, georgia sabir.ashimov@tsu.ge g. mamniashvili andronikashvili institute of physics condensed matter physics department ivane javakhishvili tbilisi state university tbilisi, georgia mgrigor@rocketmail.com g. donadze andronikashvili institute of physics condensed matter physics department ivane javakhishvili tbilisi state university, tbilisi, georgia donadze_g@yahoo.com a. peikrishvili materials science department f. tavadze institute of metallurgy and materials science tbilisi, georgia akaki.peikrishvili@yahoo.com b. godibadze blasting technologies department g. tsulukidze mining institute tbilisi, georgia bgodibadze@gmail.com abstract—in this paper, the possibility of critical temperature increasing of superconducting precursor tс and the current bearing capacity in samples of bi-pb-sr-ca-cu-o superconducting system fabricated using hot shock wave consolidation (hswc) technology and investigated by the vibrating torsional magnetometry method, was studied. the advantage of hswc technology over the traditional technologies of superconducting composites synthesis is that the high-density materials are made from the bi-pb-sr-ca-cu-o superconducting system. after the action of explosive wave the superconductivity is retained. after the explosion a pronounced texture is formed indicating the creation of efficient pinning centers and thus, the increase of current-carrying ability of the obtained material. the critical temperature of potential superconducting precursor tc of transition to superconducting state increased from tc=107k for starting sample to tc=138k, using the hswc technology for synthesis of samples in range of pressures from p=5gpa up to p=12gpa. keywords-htsc; shock-wave consolidation; vibrating torsional magnetometry; ctitical temperature of superconducting transition; high-temperature superconducting phases; pinning i. introduction after the epoch-making discovery of high-temperature superconductors (htsc) great efforts were devoted worldwide to the further increase of the critical temperature of superconducting transition тс with aim to reach room temperatures. such a discovery would cause the creation of a new technological progress using htscs with тс higher than the ones currently used for cooling liquid helium, nitrogen and hydrogen (ybacuo and mgb2, as example) thereby opening great possibilities for their applications in electronics and energetics. from this point of view, particular interest attracts the bi-pb-sr-ca-cu-o system, because it is characterized by high тс=107к and the record high second critical magnetic field нс2~150t. in [1], the universal behavior of the superconducting (sc) precursor signifying the proliferation of sc clasters as a result of the inherent intrinsic inhomogeneity of cuprates, was revealed. understanding of its nature could be very important in fabrication of new htsc materials with tс close to the room temperatures. the nature of the superconducting (sc) precursor in the cuprates has been the subject of intense interest. different experimental researches have led to very different conclusions on the temperature range of superconducting fluctuations. the main challenges have been to separate the sc response from the complex normal state behavior. for this aim, in [1] a torque magnetometry method was used, a unique thermodynamic probe with extremely high sensitivity to sc diamagnetism in four distinct cuprate compounds. in torque magnetometry, the magnetization m is deduced from the mechanical torque τ=мхнsinα, where α is the angle between m and h, experienced by a crystal in an external magnetic field h. the torque is measured as a function of temperature t, magnetic field strength h, and orientation of the sample with respect to the field direction. this approach completely removes normalstate contributions and thus allows one to trace the diamagnetic signal above tc with great precision. results show that sc diamagnetism vanishes in an unusual universal exponential manner showing distinct possibility that this unusual behavior signifies the proliferation of sc clusters as a result of the engineering, technology & applied science research vol. 8, no. 3, 2018, 3032-3037 3033 www.etasr.com chigvinadze et al.: on the nature of superconducting precursors in bi-pb-sr-ca-cu-o compositions … intrinsic inhomogeneity known to be an inherent property of the cuprates. these results are significant for a number of reasons. first, they constitute an unequivocal thermodynamic determination of sc emergence in the cuprates, as we observe sc emergence directly via diamagnetism, a fundamental and prominent characteristic of superconductivity, and because such experimental approach does not resort to any background normal phase effects. as discussed in [1], one could understand the unusual sc emergence noting that the cuprates are lamellar, perovskite-derived materials that are intrinsically inhomogeneous at the nanoscale scale. evidence for inhomogeneity is observed on multiple energy scales in scanning tunneling microscopy (stm) and nuclear magnetic resonance measurements [1]. consequently, some of the spatially inhomogeneous sc gaps “survive” in the form of sc clusters at temperatures well above tc. as the temperature decreases, these clusters proliferate and grow in size, and eventually percolate near tc. the emergence of superconductivity may therefore be thought of as a percolation process, with a temperature scale controlled by the distribution of the sc gap rather than by tc. in [2], special technology was applied to synthesize htsc samples with increased local inhomogeneities. using recently developed solar fast alloys quenching technology (sfaq-т) [3], based on glass-crystal and x-ray amorphous precursors, authors synthesized samples by quenching at liquid nitrogen temperatures of melt which was produced by heating of precursors with solar radiation and obtained decompositionresistant textured superconducting systems bi1.7pb0.3sr2ca(n1)cuno10-y (n=2-30) with critical temperature of the superconducting transitions up to 200к [2]. to determine the critical temperature of the superconducting transition tc of these samples it was used an original vibrating torsional magnetometry method to study the torsion oscillations of samples in an applied magnetic field realized using an automated multipurpose device [4], having the sensitivity comparable with that of a squid magnetometer, designed at e. andronikashvili institute of physics (tbilisi, georgia). the investigation was carried out at low-frequency axially-torsion oscillations (0.1÷1hz) in a permanent magnetic field with strength h=150mt and showed a significant effect of the background of the experiment, the value of h, initial orientation of the sample and the direction of variation in the temperature of the sample (cooling or warming) on the obtained results. the torsion instrumentation used is especially sensitive to reorientation of magnetic moments of the materials under study in external magnetic fields. as all studied htscs possess their own magnetic moments, the experiments of this kind are quite informative when studying structural transitions, especially when such transitions are accompanied by reorientation of magnetic moments including the normal state at т>тc. using this method, a wide attenuation peak (δt~100к) with a maximum at т≈200к was detected in cuprate superconductors (htsc) bi1.7pb0.3sr2ca(n-1)cunoy (n=2-30), this peak was particularly pronounced in field cooling (fc) experiments, i.e. after abrupt cooling of the sample in the external magnetic field at the temperature т<тc with subsequent slow warming up to room temperature with invariance of the applied field. the attenuation peak height depended on the preliminary orientation (before cooling) of the samples θ in the measured permanent magnetic field н. on the one hand, it is well known that, after the fc procedure and subsequent slow warming up, at the temperatures close to the critical temperature тc, the attenuation peak associated with “melting” of the abrikosov frozen vortex structure and its disappearance at т>тc is detected in monophase samples. at the same time, in most multiphase bismuth htsc samples, synthesized using solar energy and superfast quenching of the melt, the attenuation peak with the maximum at т≈200 к was observed. depending on the synthesis conditions, the attenuation peak could be two-humped and could be located in the temperature range much wider than тc of the major superconducting phase. it was assumed that this is due to the existence of frozen magnetic fluxes (after fc) in superconducting “dropping” regions, which gradually (with increasing temperature) transfer into the normal state and release pinned vortex threads. this fact could be a cause of observed dissipative processes, so as also the evidence of the existence of superconductivity at т≥240к. in [2], the intrinsic inhomogeneity of htsc was increased using the sun melting of samples followed by their superfast quenching at liquid nitrogen temperatures. in current work for the modification of microstructure, introduction of efficient pinning centers and enhancement of intrinsic inhomogeneity of htsc samples we use the original hswc technology [5]. in powder mixtures, shock waves lead to an extremely rapid mass transfer and induce high velocity collisions among suspended solid particles. such interparticle collisions result in the extreme heating at the point of impact, which can lead to the effective localized melting and significant increase in rates of numerous solid state reactions. as a consequence, the morphology of the initial materials is significantly modified: individual grains are grinded, smoothed and welded together, ultimately resulting in more compact material. such a morphology change could lead to the better inter-grain coupling and annealing of intra-grain defects. it opens also ways for formation of new htsc phases at grain boundaries. the application of shock wave pressure proved to be an effective method to generate such superconducting interfaces [6]. the hswc technology was recently successfully applied for the fast production of superconducting mgb2 samples avoiding long-time solid state reaction procedures [7]. we present further the experimental results of study of the htsc samples of bi-pb-sr-ca-cu-o system fabricated by the hswc technology showing the possibility to increase significantly their critical temperature тc. ii. experimental results and discussion the novelty of the proposed hswc technology is in the consolidation of bulk samples of high density from superconducting powders of mixtures with the dimensions of the order of ~2-5mm, l~50-70mm. the process of consolidation performed into two stages [5]: 1. explosive pressing of powder precursor mixtures is made at room temperature with 5-20gpa loading for increasing the engineering, technology & applied science research vol. 8, no. 3, 2018, 3032-3037 3034 www.etasr.com chigvinadze et al.: on the nature of superconducting precursors in bi-pb-sr-ca-cu-o compositions … initial density and for activation of the surface of mixture particles. 2. the obtained cylindrical sample is pressed by explosive wave of 5-10gpa, but now at 700-800oc. the study of superconducting characteristics shows that after the action of the explosive wave, the material retains superconductivity and the explosive pressing of powder precursor mixtures at room temperature with 5gpa, 7gpa and 12gpa loading does not change significantly the superconducting state. after explosion, the pronounced texture is formed, which with the increase of pressure and the temperature up to 700-800oc, could result in the increasing of tc and the current-carrying abilities of synthesized superconducting bi-pb-sr-ca-cu-o material. we present further the results on the critical temperature increase of superconducting transition in bi-pb-sr-ca-cu-o htsc system samples fabricated using hswc technology. the temperature dependence of magnetic susceptibility χ for starting sample bipb-ca-cu-o (2223) is presented in figure 1 and the critical temperature of superconducting transition is defined which appeared to be t=107k. fig. 1. dependence of magnetic susceptibility χ on temperature for bi-pbsr-ca-cu-o sample. we measure the critical temperatures of superconducting transitions with three methods: two of them are the standard methods of tc measurement, the measurement of magnetic susceptibility χ=f(t) and electric resistance and the third one is the original supersensitive torsional mechanical method. at application of the supersensitive mechanical torsional magnetometry method we study the dependence of oscillation period of superconductive cylinder suspended by a thin elastic thread performing torsional oscillations in the transverse magnetic field t=f(t). the mechanical method of measurement of the critical temperature tc of transition in the superconducting state is a part of methods for study of pinning, dissipation processes and investigations dynamics of abrikosov vortex lattice in superconductors, is developed by us in the andronikashvili institute of physics, [8-11]. these methods proved to be much more sensitive when compared with the traditional ones for investigation of superconductors such as resistivity and magnetic susceptibility measurements. the measurement of critical temperature using supersensitive mechanical method is based on the change of oscillation period of a superconductive cylindrical sample suspended by a thin elastic thread and performing axial-torsional oscillations in transverse magnetic field h>hc1. at transition in the superconducting state superconductor quantized vortices of magnetic flux – abrikosov vortices are created [12]. abrikosov vortices are fixed on the crystal lattice defects, they cause the change of superconducting cylinder oscillation frequency. torn off ones give a change in the dissipation of oscillations. therefore the investigation of temperature dependence of frequency (period) and dissipation of oscillations give one opportunity to define the critical temperature of transition in the superconducting state, study dissipation processes taking place in vortex matter and reveal new htsc phases with higher critical temperatures tc if they are present in the investigated htsc samples. due to the high sensitivity of the method (of the order of ≈10-17w) it is possible to record superconducting phases at concentrations much lower than the one of the main phase of the investigated sample. we measured the pinning force which makes it possible to judge regarding the current bearing capacity of htsc. in figure 2 the results of tc measurements are presented which were obtained by the use of the above mentioned three methods for bi-pb-sr-ca-cu-o (2223) samples. as it is seen, all three methods give tc=107k. the method scheme and setup for measurements using the mechanical methods of the tc, pinning force, dissipation processes and abrikosov vortex lattice (magnetic flux quanta) dynamics is presented in figure 3. the temperature dependence of the oscillation period of the suspension system with a superconducting sample suspended by a thin elastic thread and performing axial-torsional oscillations in a magnetic field directed perpendicular to the axis of superconducting cylinder for the htsc system bi/pb (2223) sample synthesized by hswc technology at p≈5gpa is presented in figure 4. we see that the critical temperature of superconducting transition after the shock wave effect increases compared with the starting sample, from tc=107k to tc=115k. the surface photo of this sample presented in figure 5 shows the absence of surface contamination. fig. 2. the temperature dependence of electric resistance r (a), magnetic susceptibility  (b) and oscillation period t (c) of superconducting sample bi1.7pb0.3sr2ca2cu3o10- (2223) suspended on a thin elastic thread and making axial-torsional oscillation in transverse magnetic field. engineering, technology & applied science research vol. 8, no. 3, 2018, 3032-3037 3035 www.etasr.com chigvinadze et al.: on the nature of superconducting precursors in bi-pb-sr-ca-cu-o compositions … fig. 3. on the left, the diagram of the device is presented: (1) sample under study, (2) rod, (3) suspension filament, (4) rotating head, (1) motor, (6) reducer, (7) system of pulleys, (8) capron filament, (9) weigh beam, (10) bell jar, (11) weight, (12) manipulator, (13) electric heater, (14) thermocouples cu-cufe, (15) electromagnet, (16) illuminator, (17) and (18) circular scales, (19) illuminator, (20) linear scale disk, (21) disk and (22) bearing (demountable) part of the vibrating system. on the right, the schematic diagram and the geometry of the experiment: 1 sample, 2 upper elastic filament, 3 lower filament, 4 leading head, 5 glass rod. φ is an angle between m and h. fig. 4. dependence of period t on temperature t of superconducting sample suspended by a thin elastic thread and making axial-torsional oscillations in transverse magnetic field, at p~5gpa. in figure 6 similar results are presented for p≈7gpa. in this case the critical temperature increases further and turns to be of the order of t=130 k. figure 7 shows a rather good sample consolidation. in figure 8 similar results are presented for pressures of the order of p≈12gpa. in this case tc increases 8 additional degrees at тс=138к. the use of hsw consolidation for creation of new superconducting materials allows one to synthesize such high-temperature superconducting systems in which the critical parameters of superconductors can be increased significantly. pictures presented in figures 5, 7 and 9 show good consolidation. fig. 5. polishing of samples (p=5gpa) shows that there is no contamination and there is a reasonable consolidation, i.e. good densification results. fig. 6. dependence of period t on temperature t of superconducting sample suspended on a thin elastic thread and making axial-torsional oscillation in transverse magnetic field, at p~7gpa. fig. 7. sample is compacted at pressure p=7gpa. the figure is taken at x350 magnification. engineering, technology & applied science research vol. 8, no. 3, 2018, 3032-3037 3036 www.etasr.com chigvinadze et al.: on the nature of superconducting precursors in bi-pb-sr-ca-cu-o compositions … fig. 8. dependence of t-period on temperature t of superconducting sample suspended on a thin elastic thread and making axial-torsional oscillation in transverse magnetic field, at p~12gpa. fig. 9. sample is compacted at pressure p=12gpa. the figure is taken at x200 magnification. fig. 10. dependence of period t on temperature t of superconducting sample suspended on a thin elastic thread and making axial-torsional oscillation in transverse magnetic field, at p~5gpa, p~7gpa and p~12gpa. the effect of hswc on critical transition temperature in superconductive state tc of the high temperature superconductive system bi-pb-sr-ca-cu-o at room temperature and at p≈5gpa, p≈7gpa and 12gpa is presented in figures 4, 6 and 8. they show that pressure of p≈5gpa increases the critical temperature of transition into superconductive state t from tc=107k up to tc=115k, hswc with p≈7gpa makes tc=130k and hswc with p=12gpa makes tc=138k(differentiation of 31 degrees). iii. conclusion the possibility of increasing of tc and the current bearing capacity in htsc samples of bi-pb-sr-ca-cu-o systems fabricated using hswc technology and vibrating torsional magnetometry method was studied. the advantages of hot hswc technology over traditional technologies of the synthesis of superconducting composites are:  the materials of high-density are made from bi-pb-sr-cacu-o superconducting system.  after the action of explosive wave the superconductivity is retained.  after the explosion, a pronounced texture is formed indicating the creation of efficient pinning centers and thus, the increase of current-carrying ability of the obtained material.  the critical temperature of potential superconducting precursor tc of transition to superconducting state increased from tc=107k (starting sample) to tc=138k, using the hswc technology for synthesis in a range of pressures from p=5gpa up to p=12gpa with 31 k increase of tc on the 12gpa case. acknowledgment this work has been supported by the shota rustaveli national science foundation & stcu grant n 6317. references [1] g. c. yu, d.-d. xia, d. pelc, r.-h. he, n.-h. kaneko, t. sasagawa, y. li, x. zhao, n. barišić, a. shekhter, m. greven, “universal superconducting precursor in the cuprates”, arxiv:1710.10957, 2017 [2] j. g. chigvinadze, j. v. acrivos, s. m. ashimov, d. d. gulamova, g. j. donadze, “superconductivity at т≈200 k in bismuth cuprates synthesized using solar energy”, arxiv:1710.10430v1, 2017 [3] d. d. gulamova, d. g. chigvinadze, j. v. acrivos, d. e. uskenbaev, “obtaining and studying the properties of high-temperature superconductors of homologous series of bi1.7pb0.3sr2can-1cunoy (n=49), under influence of solar energy”, applied solar energy, vol. 48, pp. 135-139, 2012 [4] s. m. ashimov, dzh. g. chigvinadze, “a torsion balance for studying anisotropic magnetic properties of superconducting materials”, instruments and experimental techniques, vol. 45, no. 3, pp. 431-435, 2002 [5] t. gegechkori, g. mamniashvili, a. peikrishvili, v. peikrishvili, b. godibadze, “using fast hot shock wave consolidation technology to produce superconducting mgb2”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2374-2478, 2018 [6] n. s. sidorov, a. v. palnichenko, d. v. shakhrai, v. v. avdonin, o. m. vyaselev, s. s. khasanov, “superconductivity of mg/mgo interface engineering, technology & applied science research vol. 8, no. 3, 2018, 3032-3037 3037 www.etasr.com chigvinadze et al.: on the nature of superconducting precursors in bi-pb-sr-ca-cu-o compositions … formed by shock-wave pressure”, physica c: superconductivity, vol. 488, pp. 18-24, 2013 [7] g. mamniashvili, d. daraselia, d. japaridze, a. peikrishvili, b. godibadze, “liquid-phase shock-assisted consolidation of superconducting mgb2 composites”, journal of superconductivity and novel magnetism, vol. 28, no. 7, pp. 1925-1929, 2015 [8] e. l. andronikashvili, j. g. chigvinadze, r. m. kerr, j. lowell, k. mendelson, j. s. tsakadze, “flux pinning in thermodynamically reversible type ii superconductors”, cryogenics, vol. 9, no. 2, pp. 119121, 1969 [9] j. g. chigvinadze, “investigation of dissipative processes in singlecrystal type ii superconductors”, soviet physics, journal of experimental and theoretical physics, vol. 36, no. 6, pp. 1132-1135, 1973 [10] j. g. chigvinadze, “effect of surface and volume defects on the dissipative processes in type-ii superconductors”, soviet physics, journal of experimental and theoretical physics, vol. 65, no. 5, pp. 950-962, 1974 [11] j. g. chigvinadze, j. v. acrivos, s. m. ashimov, a. a. iashvili, t. v. machaidze, g. i. mamniashvili, th. wolf, “investigation of stimulated dynamics of vortex matter in high-temperature superconductors”, physics letters a, vol. 349, no. 1-4, pp. 264-270, 2006 [12] a. a. abrikosov, “on the magnetic properties of superconductors of the second group”, soviet physics, journal of experimental and theoretical physics, vol. 5, pp. 1174-1957, 1957 engineering, technology & applied science research vol. 8, no. 4, 2018, 3194-3198 3194 www.etasr.com daghouri et al.: enhanced model for evaluating information system success: determining … enhanced model for evaluating information system success: determining critical criteria ansar daghouri enset of mohammedia university hassan ii of casablanca casablanca, morocco dagh.ansar@gmail.com khalifa mansouri enset of mohammedia university hassan ii of casablanca casablanca, morocco khmansouri@hotmail.com mohammed qbadou enset of mohammedia university hassan ii of casablanca casablanca, morocco qbmedn7@gmail.com abstract—the purpose of this study is to enhance the delone and mclean information system success by adding a servqual instrument to evaluate the service quality dimension. an integrated model for evaluating the information system has been proposed. one of the most popular multi criteria decision making techniques, namely ahp was used to determine the weights of each criterion and sub-criterion of the model in order to identify the most influential criterion on information system’s evaluation. system quality dimension has a strong influence on information system success (0.39) followed by information quality (0.22). the proposed model could be used to enhance information system performance evaluation. keywords-delone & mclean information system success model;servqual; multicriteria decision making; ahp method; criteria i. introduction many definitions are given to define the information system (is). in [1], author considers is as an organized set of resources: hardware, software, personnel, data, procedures etc. to acquire, process, store information (in the form of data, texts, images, sounds, etc.) within and between organizations. there are many frameworks and models to evaluate is success. the most common issue is the choice of right and appropriate factors and assessing them. in the current work, we seek to propose a new model to evaluate information system success based on the model presented in [2] and the servqual instrument presented in [3]. an integrated model was generated and its criteria and sub-criteria were chosen from previous studies. analytical hierarch process (ahp) method [4] was applied to select the most influent criteria and sub-criteria on information system success. a sample of one hundred participants expressed their opinions about the importance of each proposed criterion via an online tool. the results show that participants believe that the system quality dimension has the highest impact on is success (56.70% strongly agreed and 27.40% agreed). ii. information systems’ evaluation models this work is based on two main research models: information system success model [2] which is a reference in the field of is evaluation and servqual model [3] widely developed and used in the last years. in this section, we will present an overview of the most used models: a. information system success model authors in [5] conducted a large review of is success literature to present a new model that consists of six variables and the interdependencies between them. they proposed a multidimensional model that recognizes the success as a process assessed by: system quality, information quality, system usage, use satisfaction, individual impact and organizational impact. in [2] they made three main changes based on the critics of those who have tested the initial model: the addition of a technical variable “service quality” mentioned in [6], the decomposition of the variable “system use” into two variables “intention to use” and “use” referring to the theory of reasoned action [7], the technology acceptance model [8] and the grouping of individual and organizational impacts under a “net benefits” variable. b. the servqual model authors in [9] developed a model designed to measure service quality by capturing respondents’ expectations and perceptions along with the dimensions of service quality. the servqual model was made of ten dimensions of service quality when created but later on, these dimensions were reduced to five because some dimensions were overlapping (table. i) table i. summary of servqual items [3, 10] dimensions definition reliability the ability to perform the promised service dependably and accurately assurance the knowledge and courtesy of employees and their ability to convey trust and confidence tangibles the appearance of physical facilities, equipment, personnel and communication materials empathy the provision of caring, individualized attention to customers responsiveness the willingness to help customers and to provide prompt service iii. mcdm methods multiple criteria decision making (mcdm) or multiplecriteria decision analysis (mcda) [11] is a sub-discipline of op cri ma eva fin bas [13 the mo ma ah stu and det suc a. dec hie cri the pai pre ele the kn attr den to engineerin www.etasr eration researc iteria in decis athematical an aluation of a nite number of se of all mcd 3] for a proble e decision tab∗ is the score many differe ost popular o acbeth, m hp method w udied compani d sub-criterio termine the m ccess. the ahp me ahp is a m composes a c erarchies. the iteria that affe e main criteria irwise comp eference scale ement at each e ahp involve step 1: con own as the ah step 2: co ribute i with a notes the com attribute j. in t step 3: cons = /∑ i=1, 2, 3,..., n step 4: cons =∑ / w= … step 5: calcu ng, technology r.com ch that explici sion making. nd computation finite number f performance dm methods em with m cr le will be dra e of alternative table ii. … … ent types of m of them are maut, mavt was used to d ies. subsequen n of the prop most influent ethod multiple criter complex mc e essential com ect the overall a and finally th parison matri e [16] to obta level, as show es the followin nstruct the st hp decision onstruct the p attribute j yiel mparative impo this matrix, a = ⋮ struct normaliz n and j=1,2,3, struct the weig /n,i=1,2,3,..., n ulate eigenvec y & applied sci d itly evaluates it is concern nal tools to sup r of decision a criteria and su is a decision riteria (c) and awn as showe e n related to c decision tabl … … … … … … … … mcdm metho ahp, anp t [11, 14]. in determine the ntly, the weigh posed model element on i ria decision m dm problem mponents are l goal, sub-cri he alternatives x was deve ain the degree wn in table ii ng steps [17-19 tructural hiera pairwise com ld a square m ortance of attr =1 when i=j a⋯⋱ ⋮⋯ zed decision m …,n hted normaliz n ctor and row m ience research aghouri et al.: multiple confl ned with desi upport the subj alternatives un ub-criteria [12 table. accord n alternative d in table ii criteria m. le … … ods are referre p, electre, n this research is performan hts of each cri were calculat information s making [4, 1 m into a syste the main goa iteria that infl s to the proble eloped using e of importan ii. the procedu 9]: archy, this st mparison matr matrix ∗ whe ribute i with re and =1/ matrix (1) ed decision m (2) (3) matrix h v enhanced mod licting igning ective nder a ]. the ding to es (a), while ed, the , gp, h, the nce of iterion ted to system 15]. it em of al, the luence em. a g 1-9 nce of dure of tep is rix of ere espect matrix rati whe gen sc 2 6 a. ser mo wer sys ben serv tang b. mea stud vol. 8, no. 4, 20 del for evalua e= rootva row matrix=∑ step 6: calcuλ =rowma step 7: calc io ci= (λ -n) cr= ci/ri ere n and ri nerated consist tabl cale def 1 equal i 3 moderat of one o 5 essenti imp 7 ver imp 9 extreme 2, 4, 6, 8 interme between jud proposed suc in accordanc rvqual [9] del for assess re proposed fo tem quality, s nefits. the mo vice quality u gibles, empath measurement we have ch asure each d dies as follows 018, 3194-3198 ting informatio lue/∑ root∑ ∗ ulate the maxim atrix/e culate the con ) / (n-1) i denote the tency index re le iii. pairw finition importance te importance over another ial or strong portance ry strong portance e importance ediate values two adjacent dgments iv. work ccess model ce with del ] models, thi sing is succes for measuring service quality odel uses the using five dim hy and respons fig. 1. propo t of variables hosen five s dimension (cr s: 8 on system succ tvalue mum eigenvalu nsistency inde order of mat spectively. wise comparison exp two elements co pr experience and favor one experience and favor one an element is str dominance is dem the evidence fa over another is possible ord comprise is ne jud methodolog lone & mcl is work propo s. consequent is success: in y, use, user s servqual mensions: reli siveness. (figu osed success mod specific items riteria) adapte 3195 cess: determini (4) (5) ue, λ (6) ex and consist (7) (8) trix and rand n scale planation ntribute equally to roperty d judgment slight over the other d judgment strong e over another rongly favored an monstrated in prac favoring one eleme s one of the highe der of affirmation eeded between tw dgments gy lean [2, 5] oses an integ tly, six dimen nformation qu atisfaction an model to me iability, assur ure 1) del s (sub-criteria ed from prev ing … tency domly o the tly gly nd its ctice ent est wo and grated nsions uality, nd net easure rance, a) to vious engineering, technology & applied science research vol. 8, no. 4, 2018, 3194-3198 3196 www.etasr.com daghouri et al.: enhanced model for evaluating information system success: determining … 1) system quality the success criterion system quality constitutes the desirable characteristics of an is. the measures (sub-criteria) of this criterion focus on studied system’s performance. the selected system quality elements are: access [20], ease of learning [21], flexibility [22], reliability [23] and response time [22, 23]. 2) information quality the success criterion information quality is an important factor relative to the characteristics of the information system’s output. the selected information quality sub-criteria are: accuracy [24], completeness [22, 24], understandability [20], security [25], and usefulness [26]. 3) service quality the success criterion system quality represents the quality of the support that the is offer to the users. the selected service quality elements are: reliability, assurance, tangibility, empathy and responsiveness [3]. 4) intention to use/use the success criterion intention to use/use represents the manner of using an is. the selected elements are: daily use [27], frequency of use [27], nature of use [2], number of site visits [2] and number of transactions [2]. 5) user satisfaction the success criterion user satisfaction constitutes the user’s level of satisfaction when using an is. the selected user satisfaction elements are: adequacy [27], effectiveness [27], efficiency [27], enjoyment [20] and overall satisfaction [27]. 6) nets benefits this success criterion constitutes the extent to which is is contributing to the success of different stakeholders, it subsumes the former separate individual and organizational impacts. the selected net benefits elements are: productivity [8], usefulness [8], competitive advantage [27], cost reduction [27] and overall success [27]. c. population and sample a structured questionnaire was used for data collection, based on the proposed success model criteria and sub-criteria. a sample of 150 participants belonging to different sectors was chosen randomly based on their use of is. questionnaire development and returns were done by an online google tool. the participants were asked to indicate their agreement with the influence of each criteria of is success model. a five point likert type scale was used with anchors from “strongly agree” to “strongly disagree”. a total of 100 questionnaires were returned for a response rate of 67%. table iv shows the demographic characteristics of the received sample according to gender, age and experience. v. implementation and results a. the purpose of this study the main purpose of this study is to present an is success model guided by the updated delone & mclean [2, 5] and servqual [9] models. the proposed model composes six interrelated constructs of is success measures: the quality dimension (system, information and service) which affects intention to use/use and user satisfaction. the net benefits dimension is a result of use and user satisfaction and could affect them. for our case, the quality service is measured by the servqual instrument. this study also aims to determine the critical and most dimension affecting is success criteria. ahp, one of the most used mcdm techniques, was used to calculate the weights of each criterion and sub-criterion in order to determine the criterion most affecting is success. the pairwise comparison matrix was developed according to the questionnaire responses. the criteria of our hierarchical model are the different dimensions of the model and the sub-criteria are the measures of each dimension chosen from previous studies (table v). table iv. sample distribution properties percentage gender female 29 male 71 age (years) less than 30 21.4 30-39 25 40-50 46.4 more than 50 7.2 experience (years) less than 5 16.1 5-15 19.4 more than 15 64.5 table v. hierarchical criteria presentation main criteria sub criteria system quality (c1) access (c11), ease of learning (c12), flexibility (c13), reliability (c14) and response time (c15) information quality (c2) accuracy (c21), completeness (c22), understandability (c23), security (c24) and usefulness (c25) service quality (c3) reliability (c31), assurance (c32), tangibility (c33), empathy (c34) and responsiveness (c35) use (c4) dailey use (c41), frequency of use (c42), nature of use (c43), number of site visits (c44) and number of transactions (c45) user satisfaction (c5) adequacy (c51), effectiveness (c52), efficiency (c53), enjoyment (c54) and overall satisfaction (c55) net benefits (c6) productivity (c61), usefulness (c62), competitive advantage (c63), cost reduction (c64) and overall success (c65) table vi. aggregated pairwise comparison matrix c1 c2 c3 c4 c5 c6 c1 1 3 5 7 3 5 c2 0.33 1 3 5 3 5 c3 0.2 0.33 1 3 5 7 c4 0.14 0.2 0.33 1 3 5 c5 0.33 0.33 0.2 0.33 1 5 c6 0.2 0.2 0.14 0.2 0.2 1 b. implementation after developing the proposed model, our objective is to select the most influential criterion on is success. the hierarchical model contains 6 criteria and 30 sub-criteria as sho cri col com the cal 0.2 pri com sub use con res val c. cri sys the inf ind on qu (0. sho engineerin www.etasr own in table iteria are est llection are co mparison matr e weights are lculated using tabl c c1 0. c2 0. c3 0. c4 0. c5 0. c6 0. then the priow =2.364/6=w =1.012/6=w =0.500/6= the normaliz 22, 0.17, 0.1, iority of 0. mputational w b-criteria pres ed (4), (5), an nsistency rati spectively (for lue of cr (0.0 t sub-crit survey resul ahp method iterion of the stem quality d e higher value formation syst dicate that sys information s ality (0.22), .10), user satis ows the weigh ng, technology r.com vii. the weig timated using ollected by an rix of criteria e given. a n (1). le vii. norm c1 c2 45 0.59 0 15 0.20 0 09 0.06 0 06 0.04 0 15 0.06 0 09 0.04 0 ority weights a = 0.39w =1.33 = 0.17w =0.57 = 0.08w =0.20 zed weight ve 0.08, 0.03), .39 is c “ way is anticipa sented in tab nd (6): λ =6 io (cr) are r ri=1.24): c 012) is less tha table viii. su teria weight 0.42 0.26 0.15 0.11 0.06 0.34 0.25 0.19 0.15 0.06 0.37 0.25 0.15 0.13 0.11 lts d was used to proposed mo dimension has e, it means tha tem success i stem quality h system succes service qualit sfaction (0.08) hts of each d y & applied sci d ghts of the ma g ahp meth online questio (table vi) an normalized m malized decision c3 c4 0.52 0.42 0.31 0.30 0.10 0.18 0.03 0.06 0.02 0.02 0.01 0.01 are calculated 36/6=0.22 74/6=0.1 06/6=0.03 ector of main c the most val “system qua ated to determ ble viii. to c 6.08. consiste calculated th ci=0.016 and an 0.10, it is ac ub-criteria wei sub-criteria o determine th odel. the res s a weight equ at the most infl is it system q has a strong s ss (0.39) follow ty (0.17), int ) and net bene dimension. the ience research aghouri et al.: ain criteria and hod and the onnaire. a pa nd the calculat matrix c has n matrix c5 c6 0.20 0.18 0.20 0.18 0.33 0.25 0.20 0.18 0.07 0.18 0.01 0.04 using (2): criteria is w= luable criteria ality”. the mine the weig calculate λ ency index (ci hrough (7) an cr= 0.012. a ccepted. ights a weight 0.42 0.23 0.15 0.12 0.07 0.45 0.24 0.15 0.11 0.04 0.46 0.21 0.19 0.09 0.04 he weights of sults show tha ual to 0.39 wh fluential criteri quality. the r ignificant infl wed by inform tention to use efits (0.03). fig e results show h v enhanced mod d subdata irwise tion of been =(0.39, a with same ghts of , we i) and nd (8) as the f each at the hich is ion on results luence mation e /use gure 3 w also that spe thes dist dev sho from d inf in sa ne mc eva sys thu lear sys com info dim thei vol. 8, no. 4, 20 del for evalua t service qual ecially the de se results, as w tributed and th veloped accor ows the degree m the participa dimension s tr o n g ly system quality 56 formation quality 55 service quality 5 ntention to use/use 48 user atisfaction 40 et benefits 3 this study pr clean is succ aluate service tem quality ha us, system dev rning, flexibi stem develo mpleteness, un ormation. fin mensions can b ir information 018, 3194-3198 ting informatio lity exhibited gree of servi we already me he aggregated rding to the q e of influence ants’ point of v table ix. s tr o n g ly a gr ee a g re e 6.7% 27.4% 5.8% 23.4% 0% 21.4% 8.2% 19.8% 0.6% 31.7% 5% 34.2% fig. 2. elem vi. co roposed an is cess model a quality. the as a strong sig velopers shoul ility, reliabilit opers shoul nderstandabili nally, the pro be used as a t systems. fig. 3. w 8 on system succ a stronger eff ice reliability entioned that a pairwise comp questionnaire e of each crite view. survey result a v er a ge 9% 11.5% 5 13.70% 8 13.80% 10 14.4% 1 12.80% ments' importance onclusion model based and the serv e analysis resu gnificant influe ld focus more ty and system d fully e ity, security oposed succe tool in organi eights of criteria 3197 cess: determini fect on is suc (0.37). to o a questionnaire mparison matrix results. tabl erion on is su ts d is a g re e s tr o n g ly d is a gr ee 5% 2% 5.3% 4% 8.6% 6.3% 0.40% 7.8% 0.3% 3% 10% 8% e on the delone vqual mod ults indicated ence on is suc e on access, ea m response exploit accu and usefulnes ss model an zations to eva ing … ccess, obtain e was x was le ix uccess r a n k 1 2 3 4 5 6 e and del to d that ccess. ase of 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of lip reading using concatenated three … improving the recognition performance of lip reading using the concatenated three sequence keyframe image technique lap poomhiran faculty of information technology and digital innovation king mongkut’s university of technology north bangkok bangkok, thailand lap.p@email.kmutnb.ac.th phayung meesad faculty of information technology and digital innovation king mongkut’s university of technology north bangkok bangkok, thailand pym@kmutnb.ac.th sumitra nuanmeesri faculty of science and technology suan sunandha rajabhat university bangkok, thailand sumitra.nu@ssru.ac.th abstract-this paper proposes a lip reading method based on convolutional neural networks applied to concatenated three sequence keyframe image (c3-ski), consisting of (a) the startlip image (sli), (b) the middle-lip image (mli), and (c) the end-lip image (eli) which is the end of the pronunciation of that syllable. the lip area’s image dimensions were reduced to 32×32 pixels per image frame and three keyframes concatenate together were used to represent one syllable with a dimension of 96×32 pixels for visual speech recognition. every three concatenated keyframes representing any syllable are selected based on the relative maximum and relative minimum related to the open lip’s width and height. the evaluation results of the model’s effectiveness, showed accuracy, validation accuracy, loss, and validation loss values at 95.06%, 86.03%, 4.61%, and 9.04% respectively, for the thdigits dataset. the c3-ski technique was also applied to the avdigits dataset, showing 85.62% accuracy. in conclusion, the c3-ski technique could be applied to perform lip reading recognition. keywords-concatenated frame images; convolutional neural network; keyframe reduction; keyframe sequence; lip reading i. introduction deep learning applications, especially convolutional neural network (cnn) applications, have recently achieved impressive success in diverse object detection and recognition tasks [1], however, cnns face some challenges, in particular in video recognition. a video may be incomplete and sound may be lacking during certain parts. if the audio at the crucial moment is missing, it may result in the video’s contents being misunderstood [2]. these videos will be more useful if they were edited and the missing words or messages could be found. most of the proposed solutions rely on the lip reading technique to help transcription by reading and observing the moving lips, including tongue and face to get the right words. moreover, the process of transcribing or translating the speech obtained by lip reading is a skill that requires learning and practice until becoming proficient at recognizing the lip movement or lip pattern related to the pronunciation of each syllable. in general, there are two popular multimodals or methods of supervised learning for lip reading: visual speech recognition (vsr) and audio-visual speech recognition (avsr). vsr uses a method to teach the machine with visualonly information from a video without using speech or audio for training [3]. on the other hand, avsr trains the machine by applied images combined with audio data from a video to achieve greater accuracy [4]. authors in [5] found that the use of visual-only (vo) data has better classification accuracy than that of audio visual (av) and audio only (ao) data. there are currently two groups of research studies on lip reading recognition, the first group uses images in vo [2, 3, 514] while the other group uses both audio and video together [4, 15-25]. both these groups have a model for extracting the features with a technique used in combination. nevertheless, the latter group differs in that they have to combine audio feature data with visual features when it comes to machine learning. av speech recognition is used commercially on various software or systems, but the recognition quality is reduced by environmental noise. this situation is not the same as using data from a quiet image, making lip reading a pivotal role in automatic speech recognition (asr) in harsh audio environments [6]. neural networks are commonly used to help extract features and recognize lip reading patterns in machine learning, such as in cnns [6, 11, 24], long short-term memory (lstm) [3, 10, 21], or a combination of cnn with lstm [2, corresponding author: lap poomhiran engineering, technology & applied science research vol. 11, no. 2, 2021, 6986-6992 6987 www.etasr.com poomhiran et al.: improving the performance recognition of lip reading using concatenated three … 12, 13]. as mentioned above, in machine learning for lip reading recognition, visual training is required. the images of the face or lips are an essential factor as the primary input. this makes the number of images arranged for use as a large input. in order to sort the images of the video frame, the lip movement is determined by the number of frames, for example, 40 frames per word [7], or the number of frames in seconds such as 0.2 seconds [8, 16] or 1 second, or maybe determined using every frame in the video wherein one video will have only one word and a short duration. the methods mentioned above also use multiple frames in machine learning processing, which consumes more resources and processing time. there are also real world problems, e.g. where a speaker speaks at a slowly speaking speed, resulting in a longer video file length while the words are spread out. therefore, limitations on the number of frames or the duration may differ from the words or messages conveyed. however, if there is a representation of the images or keyframes, it will reduce the number of images and cost used in machine learning. most lip reading studies are applied to english datasets of digits, alphabets, words, phrases, and sentences. the avdigits [26] is a popular dataset for testing and improving the performance of a model. there is a total of 540 videos with a resolution of 1920×1080 pixels (px). it consists of six speakers who speak numbers from 0 to 9 in english and each repeats the numbers 9 times. greek [12], myanmar [14], spanish [27], and czech [28] have been also studied, but there are no thai language datasets created for lip reading. it is difficult for the thai language to be in some words with similar lip patterns but with different meanings. since the vowels are pronounced similarly, the patterns of lip movements are similar. there is a pattern of intonation in thai language resulting from a combination of tones, resulting in intonation in five tonal sounds. therefore, this research aims to create a dataset in the thai language and reduce the image dimensions and the number of frames by finding keyframes to replace syllables or words for thai lip reading recognition using cnns. ii. research methodology the research methodology for the improving performance recognition of lip reading using c3-ski consists of 1) dataset preparation, 2) face detection and lip localization, 3) c3-ski creation, 4) model development, and 5) model effectiveness evaluation. a. dataset preparation the thai digit dataset is called thdigits. it was created as a thai video file containing numbers from 0 to 9, which are repeated three times with three different speaking speeds (slow, regular, and fast) by using 100 mixed-gender speakers. a total of 3,000 video files with length between 1 and 4 seconds were constructed. these videos have four different resolutions: 1920×1080, 1280×720, 960×540, and 720×404 px and were recorded with smartphones, regardless of model and brand. the thai numbering is shown in table i. b. face detection and lip localization before processing face detection and lip locating, each video prepared in the thai digit dataset was separated into individual frames, ordered from the first to the last frame. after that, the face was detected in each frame using the viola-jones [29, 30] technique based on the haar-like feature. the hypothesis t represents any distinguishing characteristic, h is the distinguishing characteristic, and β represents the percentage of error classification. the characteristic c(x) is given as (1) [29]: ( ) 1 1 1 1, ( ) 2 0, t t t t tt t h x c x otherwise α α = =  ≥ =   ∑ ∑ (1) where 1 log t t α β = . the difference of pixel sums or features on an image is compared using the haar-like feature with the black and white filter that assigned i and p values to represent n by n images as in (2) [30]: ( , ) ( , ) 1 1 1 1 ( , )1 ( , )1 p i j white p i j black i n j n i n j n i i j i i j= = ≤ ≤ ≤ ≤ ≤ ≤ ≤ ≤ −∑ ∑ ∑ ∑ (2) after face detection comes the lip positioning based on 68 facial landmarks [31]. lip localization determines the lip area or region of interest (roi) to leave only the desired feature area by cropping in each frame to the lip area only, illustrated in figure 1. table i. thai number pronunciation in thdigits dataset numbers thai pronunciation meaning 0 ṣ̄ūny̒ zero 1 h̄nụ̀ng one 2 s̄xng two 3 s̄ām three 4 s̄ī̀ four 5 ĥ̄ā five 6 h̄k six 7 cĕd seven 8 pæd eight 9 kêā nine fig. 1. face detection and lip localization on each image frame. c. the concatenated three sequence keyframe image recent research favorably replaces any word or syllable by concatenating frames as a single image before training. for example, some research uses frames together as a single image engineering, technology & applied science research vol. 11, no. 2, 2021, 6986-6992 6988 www.etasr.com poomhiran et al.: improving the performance recognition of lip reading using concatenated three … in 5 rows with 5 frames per row, in a total of 25 frames per image [6]. as mentioned above, if the speaker speaks slowly or extensively, the number of frames will be increased, but only one word or syllable will be conveyed. in this study, only the keyframes with pronounced lip movement were selected, relying on measuring the outer lip dimensional from the mouth’s height (h) and width (w) for each frame x as shown in figure 2. fig. 2. lip width (w) and lip height (h) for the current and the next frame. lip dimensions were calculated by (3) on each frame. with the help of the increasing function, decreasing function, relative maximum, and relative minimum of a graph related to lip dimensions, all keyframes were extracted and selected. the relative maximum and relative minimum are lying on the slope at the x interval. if the c is some x in a graph, where c is the relative maximum or relative minimum, then the slope at c would be zero, represented in (4). ( ) x x f x w h= + (3) ( ) 0f c′ = (4) f´(c) is the function that has a relative maximum or minimum at c, f(x)≤ f(c) for the relative maximum, and f(x)≥ f(c) for the relative minimum. fig. 3. image frame sequence from a sample video of the dataset. each video is possible to produce several relative maxima and relative minima as keyframes. in this experiment, there are three keyframes assigned as a single syllable. the first keyframe will represent the frame where the mouth starts to pronounce a syllable. this is the sli. the second keyframe (mli) is the frame where the mouth is at the maximum opening limit or movement of the syllable. the last keyframe (eli) is at the end of the pronunciation of that syllable. for example, the word ‘one’ in english is pronounced as ‘nueng’ (h̄nụ̀ng) in thai language. fifty one frames were split from a video in the dataset and the area of the lip was cropped as shown in figure 3. the frame sequence numbers 9, 18, and 32 are representing the three keyframes based on relative maximum and relative minimum, and are shown in figure 4. fig. 4. the three keyframes representing a single syllable. fig. 5. the image dimensions for training in the current study. after the three keyframes were selected, each keyframe image was scaled down to 32×32 pixels and merged into a single rgb color image with a dimension of 96×32 pixels, as shown in figure 5, while other studies use image dimensions of 80×60 or 224×224 pixels ([7] and [6] respectively). thus, each input color image frame as the dataset for building the model has a pixel density ratio of 3,072 pixels, which is less than the one used in other studies [6, 7]. d. model development the model was designed based on the cnns with a total of 13 layers. it consists of 1 normalization layer, 6 convolutional (conv) layers with or rectified linear unit (relu) activation function for each convolutional layer, 3 max-pooling layers, and 3 fully-connected (fc) layers, which include a flatten layer and two dense layers. there are a total of 846,890 parameters for training. the model architecture is shown in figure 6. engineering, technology & applied science research vol. 11, no. 2, 2021, 6986-6992 6989 www.etasr.com poomhiran et al.: improving the performance recognition of lip reading using concatenated three … fig. 6. model architecture for lip reading applied to c3-ski. all images of the thai digit dataset were used in the training and validation of the designed model. the training and validation images were the 80% and 20% of the dataset respectively. a total of 200 epochs of training was set with a minibatch gradient descent size of 32. the model was built using an intel core i7-7700hq pc at 2.80ghz, 16gb of memory, 512gb of samsung solid state drive, and a 3gb nvidia geforce gtx 1060. this system was running through python version 3.8.3 on windows 10 x64 architecture. e. model’s effectiveness evaluation the developed model has validated by the accuracy rate and loss value. the accuracy was calculated by (5), and the loss value or loss function, also known as cross-entropy which is the favorite function for classification is defined in (6) [32-38]: c accuracy n = (5) where c refers to the total number of samples recognized correctly, n refers to the total number of all samples. ( ), , 1 1 log n m i j i j i j cross entropy y p = = − = −∑∑ (6) where n refers to the total number of all samples, m refers to the total number of classes, yi,j refers to the true value when the sample i belongs to the class j, pi,j refers to the probability predicted by the sample model of i to belong to the class j. the model will stop training automatically using the ‘earlystopping’ feature supported by keras library with the callback function. the patience value was 5, and monitoring to the validation loss value. the model stopped training when there was no improvement in the validation loss for 5 consecutive epochs. the minimum validation loss was reached at 37 epochs of training. iii. results according to the experiments on the developed model, the accuracy and loss value were determined while building the model. after the 37 epochs of training, the model gave 95.06% accuracy and 4.61% loss value. the model stopped training after 47 epochs. considering the model’s validation, the model gave validation accuracy value of 86.03% and validation loss of 9.04%. the accuracy and loss for both training and validation are shown in figures 7-9. fig. 7. the accuracy value of training and validation (left) and the loss value of training and validation (right). fig. 8. the training accuracy and loss (left), and the validation accuracy and loss (right). fig. 9. the accuracy and loss of training and validation of the model. moreover, this experiment compares the accuracy of the technique for input image reduction with other studies using the avdigits dataset. it was found that the lip reading models built by mdbn [39], mdae [40], rtmrbm [26], am-lstm engineering, technology & applied science research vol. 11, no. 2, 2021, 6986-6992 6990 www.etasr.com poomhiran et al.: improving the performance recognition of lip reading using concatenated three … [41], and alm-gru [20] gave accuracy of 55.00%, 66.74%, 71.77%, 85.23%, and 85.53%, respectively while this work gave 85.62%. the model performances are shown in table ii and figure 10. table ii. the model’s effectiveness evaluation dataset method modality accuracy (%) avdigits mdbn [39] visual-only 55.00 avdigits mdae [40] audiovisual 66.74 avdigits rtmrbm [26] audiovisual 71.77 avdigits am-lstm [41] audiovisual 85.23 avdigits alm-gru [20] visual-only 85.53 avdigits c3-ski visual-only 85.62 thdigits c3-ski visual-only 86.03 fig. 10. comparison with the state-of-the-art methods. iv. conclusion and discussion this paper proposes the application of the c3-ski to a cnn for lip reading. the c3-ski consisting of sli, mli, and eli was tested in lip reading recognition on thdigits and avdigits datasets. its primary input is images applied to machine learning according to deep learning techniques. reducing the number of images can be used by finding the image keyframes based on the relative maximum and relative minimum values. in this paper, 32×32 pixels of 3 sequence keyframes were assigned to represent any syllable of a digit between zero and nine, and these keyframes were concatenated to produce a new 96×32 px image as an input to the neural network. these new input images make the resulting image dimensions and density of pixels less than most state-of-the-art methods. thus, there were 3,000 keyframe input images with 10 classes that were divided to 80% for training and 20% for validation. the developed cnn model included 1 normalization layer, 6 convolutional layers, 3 max-pooling layers, and 3 fully-connected layers. training took a total of 47 epochs and was finalized when the validation loss value reached its minimum and the model did not improve any further. as a result, the model had accuracy, validation accuracy, loss, and validation loss values of 95.06%, 86.03%, 4.61%, and 9.04% respectively. the model’s accuracy was 85.62% when it was applied to the avdigits dataset. therefore, the reduced number of keyframes with relative maximum and relative minimum can be applied in conjunction with cnn for lip reading. the results of this study conform to the conclusions of [6, 7] in which the cnn method with reduced concatenated frame images was applied to lip reading with a high level of effectiveness. these concatenated frame images have smaller dimension than the traditional images which are usually used to image classification in cnns (224×224 px). in future work, the researchers plan to create a dataset for thai sentences and test the c3-ski technique. new keyframes could be scaled down and compared to the number of keyframes used to represent each syllable for continuous speech or sentences, such as 5, 7, or 9 keyframe images sequentially. this technique will develop a function or equation to find the lip shift’s common point from one syllable to the following syllable. besides, word prediction methods from the corpus would be used for prediction combined with image processing to increase lip reading accuracy on deep learning in real-time processing. acknowledgment 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[41] c. tian, and w. ji, "auxiliary multimodal lstm for audio-visual speech recognition and lipreading," 2017, arxiv preprint arxiv:1701.04224v2. engineering, technology & applied science research vol. 11, no. 2, 2021, 6986-6992 6992 www.etasr.com poomhiran et al.: improving the performance recognition of lip reading using concatenated three … authors profile lap poomhiran is currently a ph.d. student in the department of information technology, faculty of information technology and digital innovation, king mongkut’s university of technology north bangkok (kmutnb), thailand. his research interests include web and mobile programming, augmented reality (ar) and virtual reality (vr) development, image processing, data mining, machine learning, deep learning, and the internet of things (iot). phayung meesad is an associate professor at the king mongkut’s university of technology north bangkok (kmutnb), thailand. his research interests include computational intelligence, artificial intelligence, machine learning, deep learning, data analytics, big data analysis, data science, data mining, digital signal processing, image processing, business intelligence, time series analysis, and natural language processing. sumitra nuanmeesri is an assistant professor in the department of information technology, faculty of science and technology at suan sunandha rajabhat university, thailand. her research interests include speech recognition, data mining, deep learning, image processing, mobile application, supply chain management systems, internet of things, robotics, augmented reality, and virtual reality. microsoft word 3-2467_kainoyrio_s_ca engineering, technology & applied science research vol. 9, no. 1, 2019, 3692-3695 3692 www.etasr.com ahmad et al.: estimate outcome value of doubling cell growth using fuzzy regression method estimate outcome value of doubling cell growth using fuzzy regression method w. m. a. w. ahmad universiti sains malaysia kubang kerian, malaysia wmamir@usm.my r. a. a. rohim universiti sains malaysia kubang kerian, malaysia adawiyah5350@yahoo.com n. h. ismail universiti sains malaysia kubang kerian, malaysia noorhuda@usm.my abstract—in this paper, the fundamental concepts used in different disciplines are described and these concepts are written into one common theme: assessing crossness agreement of observation. focus was given on continuous measurements and methodological approaches for expressing these methods mathematically, both for cases with and without reference. the build method was tested and applied to biological sciences data. the objective of the study was to determine the agreement between the two methods on microorganism data sets in order to determine if they can be used interchangeably and to estimate the fuzzy and bootstrap parameters of the models. the value of interclass correlation (icc) by using a linear equation is 0.79661 (substantial agreement) and the value of icc using fuzzy regression equation is 0.82692 (almost perfect agreement). keywords-agreement; fuzzy regression; bootstrap; icc i. introduction in social, behavior, physical, biological and medical sciences reliability and accurate measurements serve as the basis for evaluation. as new concepts, theories and technologies continue to develop, new scales, methods, tests, assays, devices and evaluation instruments become available. in simple, intuitive terms, reliability and accurate measurement may simply mean that the new measurement is the same as the truth or agrees with the truth. however, requiring the new measurement to agree to the truth is often impractical, either because (1) we are willing to accept a measurement up to some tolerable (or acceptable) error or (2) the truth is simply not available to us (either because it is not measurable or because it is only measurable with some degree or error). to deal with issues related to both (1) and (2), a number of concepts, methods and theories have been developed [1]. in this paper, the fundamental concepts used in different disciplines are described and compared and written in one common theme: assessing closeness ‘agreement’ of observations. we focus on methodological approaches for expressing these concepts and methods mathematically, and discuss the data structures for which they are to be used, both for cases with and without a reference (or truth) [2]. these approaches were developed for one or more types of the following data structures: predicted data of bacteria growth and original data of bacteria growth when they are available. a. fuzzy linear regression in fuzzy linear regression analysis two factors, the degree of fitness and the fuzziness of data sets are considered [3]. a fuzzy linear regression model is commonly presented as: ( ) xr axaaxfy ~~~~~ 1101 =+== (1) where 1 1 t x [ ,x ]= is a crisp vector of independent variables and y� is the estimated fuzzy output. 0 1 a a ,a =   � � � is a vector of fuzzy parameters of the fuzzy linear regression model. j a ~ is presented in the form of symmetric triangular fuzzy numbers denoted by ( ) 012j j ja ,c , j , , ,...n,α= =� where its membership function is shown as: ( ) 1 j j j a j j j j j j j a a a ,a c a a c c µ  −  = − − ≤ ≤ +     (2) where j a is the central value of the fuzzy number and j c is the spread. therefore the fuzzy linear regression model can be rewritten as: ( ) ( ) 11100 ,,~ xccy αα += (3) however, the interaction between variables and higher order terms is not included in the fuzzy linear regression defined in (1). in fact, interaction between variables and higher order terms often exist in physical systems. a simple procedure is commonly used to solve the linear programming problem [4]. linear regression is used to study the linear relationship between a dependent variable y and one or more independent variables x. the dependent variable y must be continuous, while the independent variables may be continuous, binary, or categorical. the initial judgement of a possible relationship between two continuous variables should always be made on the basis of a scatter plot [5]. b. bacteria growth (streptococcus sobrinus) bacteria colonize epithelial surfaces in certain parts of the body and there is a constantly on-going competition for space and resources between bacterial species. bacteria are ubiquitous and the vast majority is harmless or beneficial to the corresponding author: w. m. a. w. ahmad engineering, technology & applied science research vol. 9, no. 1, 2019, 3692-3695 3693 www.etasr.com ahmad et al.: estimate outcome value of doubling cell growth using fuzzy regression method host. our understanding with regard to the effect of microbes on human health has gradually developed from pathogens inducing infections to a mutually beneficial interaction with indigenous microorganisms that contribute to normal human physiology and homeostasis [6]. mutans streptococci are linked with the growth of dental caries in human. these bacteria are the most common pathogens isolated from human dental plaque, and their prevalence has been reported in epidemiological studies [7]. several methods have been employed for detecting and identifying mutans streptococci, including culturing, direct enzyme tests, enzyme-linked immunosorbent assays, and dna probes [8]. the mutans group of oral streptococci consist of seven species [9]. among the group, streptococci mutans and streptococci sobrinus are most frequently isolated from human dental plaque and closely associated with human dental caries [7, 10]. ii. materials and methods the data were composed of two variables, which are the days of culture (x) and bacterial growth (y). the rate of exponential growth of a bacterial culture is lny. the data was available from recent studies for nurturing selected microorganisms (streptococcus sobrinus). the data were recorded in sas to evaluate microorganism growth before analyzing by using the new proposed statistical methodologies. these approaches were developed for one or more types of the following data structures: predicted data of bacteria growth and original data of bacteria growth where covariates are available for assessing the impact of various factors on agreement measures. predicting value was done by the use of the linear equation y=82.9121e 0.00512 x. table i. sample of bacteria days of culture (x) original data *(y) predicted data * (y) exponential growth rate (lny) 1 82 83 4.41 2 84 84 4.43 3 86 84 4.45 5 86 85 4.45 9 87 86 4.47 11 87 88 4.47 13 87 89 4.47 * st. sobrinus a. the algorithm of exponential calculation the algorithm is the way of inserting data in sas programming and the way of calculating the quality of predicted data and original data using interclass correlation (icc). the name of the dataset is given as test-data. the data consist of two variables, read1 and read2, and pid. data test; /* read1 is predicted data */ /* read2 is original data */ input read1 read2 pid; cards; 83 82 1 84 84 2 84 86 3 85 86 4 86 87 5 88 87 6 89 87 7 ; run; datatest_data; set test; array s(2) read:; do judge=1 to 2; y=s(judge); output; end; run; ods output covparms=covp; procmixed data=test_data; class judge pid; model y=; random intercept /subject=pid; run; dataicc; set covp end=last; retain bvar; if subject~="" then bvar=estimate; if last then icc=bvar/(bvar+estimate); run; procprint data=icc; run; quit; data collection main algorithm : algorithm of an exponential with combining fuzzy method end process \*using secondary data*\ interpret the output performing exponential growth or decay to estimate the parameter adding bootstrapping to the main algorithm \*methodology building for bootstrap and this methodology will be add to the main algorithm*\ \* main methodology *\ \*performing an analysis*\ \*obtained an output*\ \*finish*\ predicting output from estimate equation linear equation and fuzzy regression equation calculating the predicted data and original data using icc fig. 1. algorith flowchart b. assessing closeness agreement of observations using linear equation the icc test is usually used in the assessment of agreement between different measurement methods. icc takes a value engineering, technology & applied science research vol. 9, no. 1, 2019, 3692-3695 3694 www.etasr.com ahmad et al.: estimate outcome value of doubling cell growth using fuzzy regression method from 0 to 1 (table ii). table iii shows the result of icc according to the predicted data and original data. the value of icc is 0.79661 and this is a substantial agreement for the use of linear equation model. table ii. icc classification icc description <0.00 poor agreement 0.01-0.20 slight agreement 0.21-0.40 fair agreement 0.41-0.60 moderate agreement 0.61-0.80 substantial agreement 0.81-1.00 almost perfect agreement table iii. icc reading covariate estimate icc 1 intercept 3.3571 2 residual 0.8571 0.79661 c. calculation of fuzzy regression for exponential growth the algorithm calculates the fuzzy regression for exponential growth. the complete set of calculations can be visualized by the following linear programming: ods rtf file='abc.rtf' style=journal; procnlp; min y; decvar a0c a0w a1c a1w; bounds a0w>=0, a1w>=0; lincon a0c+5*a1c-a0w-5*a1w<=4.45; lincon a0c+2*a1c-a0w-2*a1w<=4.43; lincon a0c+9*a1c-a0w-9*a1w<=4.47; lincon a0c+2*a1c-a0w-2*a1w<=4.43; lincon a0c+5*a1c-a0w-5*a1w<=4.45; lincon a0c+2*a1c-a0w-2*a1w<=4.43; lincon a0c+1*a1c-a0w-1*a1w<=4.41; lincon a0c+2*a1c-a0w-2*a1w<=4.43; lincon a0c+11*a1c-a0w-11*a1w<=4.47; lincon a0c+2*a1c-a0w-2*a1w<=4.43; lincon a0c+1*a1c-a0w-1*a1w<=4.41; lincon a0c+11*a1c-a0w-11*a1w<=4.47; lincon a0c+2*a1c-a0w-2*a1w<=4.43; lincon a0c+29*a1c-a0w-29*a1w<=4.55; lincon a0c+33*a1c-a0w-33*a1w<=4.6; lincon a0c+23*a1c-a0w-23*a1w<=4.54; lincon a0c+11*a1c-a0w-11*a1w<=4.47; lincon a0c+9*a1c-a0w-9*a1w<=4.47; lincon a0c+9*a1c-a0w-9*a1w<=4.47; lincon a0c+13*a1c-a0w-13*a1w<=4.47; lincon a0c+5*a1c-a0w-5*a1w<=4.45; lincon a0c+9*a1c-a0w-9*a1w<=4.47; lincon a0c+5*a1c-a0w-5*a1w<=4.45; lincon a0c+11*a1c-a0w-11*a1w<=4.47; lincon a0c+2*a1c-a0w-2*a1w<=4.43; lincon a0c+23*a1c-a0w-23*a1w<=4.54; lincon a0c+5*a1c+a0w+5*a1w>=4.45; lincon a0c+2*a1c+a0w+2*a1w>=4.43; lincon a0c+9*a1c+a0w+9*a1w>=4.47; lincon a0c+2*a1c+a0w+2*a1w>=4.43; lincon a0c+5*a1c+a0w+5*a1w>=4.45; lincon a0c+2*a1c+a0w+2*a1w>=4.43; lincon a0c+1*a1c+a0w+1*a1w>=4.41; lincon a0c+2*a1c+a0w+2*a1w>=4.43; lincon a0c+11*a1c+a0w+11*a1w>=4.47; lincon a0c+2*a1c+a0w+2*a1w>=4.43; lincon a0c+1*a1c+a0w+1*a1w>=4.41; lincon a0c+11*a1c+a0w+11*a1w>=4.47; lincon a0c+2*a1c+a0w+2*a1w>=4.43; lincon a0c+29*a1c+a0w+29*a1w>=4.55; lincon a0c+33*a1c+a0w+33*a1w>=4.6; lincon a0c+23*a1c+a0w+23*a1w>=4.54; lincon a0c+11*a1c+a0w+11*a1w>=4.47; lincon a0c+9*a1c+a0w+9*a1w>=4.47; lincon a0c+9*a1c+a0w+9*a1w>=4.47; lincon a0c+13*a1c+a0w+13*a1w>=4.47; lincon a0c+5*a1c+a0w+5*a1w>=4.45; lincon a0c+9*a1c+a0w+9*a1w>=4.47; lincon a0c+5*a1c+a0w+5*a1w>=4.45; lincon a0c+11*a1c+a0w+11*a1w>=4.47; lincon a0c+2*a1c+a0w+2*a1w>=4.43; lincon a0c+23*a1c+a0w+23*a1w>=4.54; y=a0w*26+237*a1w; run; ods rtf close; d. parameter estimation for fuzzy regression exponential cell growth table iv shows the optimization results for the parameter estimates. table iv. optimization results no parameter estimate gradient objective function 1 a0c 4.414107 0 2 a0w 0.009107 26.000000 3 a1c 0.005179 0 4 a1w 0.000179 237.000000 value of objective function=0.2791071429 from the results shown in table iv, the fitted model for fuzzy regression is: y=4.414107+0.005179 1 x (1) e. assessing closeness agreement of observations using fuzzy regression equation in table v we can see the predicted values using fuzzy regression equation from (1): table v. original vs predicted data original data* predicted data* 82 83 84 83 86 84 86 85 87 86 87 87 87 88 * st. sobrinus (y) to calculate regression based on fuzzy regression for exponential growth using icc, the full syntax is: engineering, technology & applied science research vol. 9, no. 1, 2019, 3692-3695 3695 www.etasr.com ahmad et al.: estimate outcome value of doubling cell growth using fuzzy regression method data test; /* read1 is predicted data */ /* read2 is original data */ input read1 read2 pid; cards; run; table vi. icc reading covariate estimate icc 1 intercept 3.0714 2 residual 0.6429 0.82692 the value of icc is 0.82692 and this is almost perfect agreement of predicted and original data. iii. summary and discussion the main objective of this research was to determine the agreement between two methods on microorganism data sets in order to determine if they may be used interchangeably and to estimate the linear and fuzzy regression parameters of the models using interclass correlation. using linear equation, the value of icc is 0.79661 which this is substantial agreement for assessing the quality of predicted data, while the value of icc using fuzzy regression equation is 0.82692 (almost perfect agreement). icc test is usually used in the assessment of agreement between different measurement methods. acknowledgment authors would like to express their gratitude to universiti sains malaysia for providing the research funding (grant no. 1001/ppsg/8012278, school of dental sciences, universiti sains malaysia) references [1] f. galton, “regression toward mediocrity in hereditary stature”, the journal of the anthropological institute of great britain and ireland, vol. 15, pp. 246-263, 1886 [2] j. m. bland, d. g. altman, “comparing methods of measuring: why plotting difference against standard method is misleading”, the lancet, vol. 346, pp. 1085-1087, 1995 [3] h. tanaka, j. watada, “possibilistic linear systems and their application to the linear regression model”, fuzzy sets system, vol. 27, pp. 275-289, 1988 [4] j. kacprzyk, m. fedrizzi, fuzzy regression analysis, omnitech press, warsaw, 1992 [5] a. schneider, g. homme, m. bletner, “linear regression analysis”, deutches arteblatt international”, vol. 107, no. 44, pp. 776-820, 2010 [6] s. rautava, r. luoto, s. salminen, e. isolauri, “microbiol contact during pregnancy, intestinal colonization and human disease”, nature reviews gastroenterology & hepatology, vol. 9, no. 10, pp. 565-76, 2012 [7] w. j. loeshe, “role of streptococcus mutans in human dental decay”, mirobiology reviews, vol. 50, no. 4, pp. 538-80, 1986 [8] t. igarashi, a. yamamoto, n. goto, “pcr for detection and identification of streptocccus sobrinus”, journal of medical microbiology, vol. 49, no. 12, pp. 1069-1074, 2000 [9] r. a. whiley, d. beighton, “current classification of the oral streptococci”, oral microbiology and immunology, vol. 13, no. 4, pp. 195-216, 1998 [10] s. hamada, h. d. slade, “biology, immunology and cariogenicity of streptococcus mutans”, microbiology reviews, vo. 44, no. 2, pp. 331384, 1980 microsoft word 3-2851_s_etasr_v9_n4_pp4329-4333 engineering, technology & applied science research vol. 9, no. 4, 2019, 4329-4333 4329 www.etasr.com belkhir: intelligent maximum power tracking control for a wind energy system based on magnetic … intelligent maximum power tracking control for a wind energy system based on magnetic gear generator kamel salim belkhir department of electrical engineering, faculty of technology, university ferhat abbas setif 1, setif, algeria ksbelkhir@univ-setif.dz abstract—this paper studies maximum wind power extraction from magnetic gear generator using an artificial neural network for the wind energy system. high speed can be reached with this representation either without mechanical gear or under low wind conditions often found inland. in order to track maximum power, the artificial neural network controller adjusts the outer rotor speed, and thus, inner rotor speed. the proposed system is supported by simulation results. keywords-artificial neural network; magnetic gear generator; wind power i. introduction given the rapid development of wind turbine technology, in the future focus will be given on huge offshore single wind turbines, due to their higher wind speed and more space characteristics [1]. bigger turbines reach higher heights above the ground, where stronger winds blow. this allows them to extract more energy, and to work more efficiently. using higher-capacity wind turbines reduces the number of turbines needed for a wind farm and results in dramatic reduction of the cost of wind energy [2]. wind turbines have grown from an average of 700kw to over 5mw during the last decade. due to reliable and efficient offshore wind energy, several offshore wind projects have been adopted. the offshore applications require lager turbine units, the size of wind turbine is about 7mw at the present time and the larger turbines of the near future would be about 20mw [3]. this virtual 20mw design is still not apt for manufacturing and is uneconomic. its weight would be about 880 tones standing on top of a tower, which means that the plan is not feasible. the support structures could not carry such a big generator, the lubrication system and the huge mechanical gearbox elevated up to 153 meters in height [4, 5]. by removing the mechanical gearbox and the lubrication system, we can reduce the nacelle size and weight. to achieve this goal, we used magnetic gear power-split. the high-torque magnetic gear was invented and demonstrated in 2001 [6]. it uses permanent magnets to transmit torque between an input and output shaft without mechanical contact. the topology and high performance of magnetic gear have been presented in [6] and it has been shown that by using rare-earth magnets, a high torque density can be achieved along with a reduced acoustic noise and vibration, reduced maintenance and improved reliability, precise peak torque transmission capability, and physical isolation between input and output shafts [7, 8]. the mechanical gearbox is used extensively to increase the rotational speed of wind power generators. it is usually more costly and weights more when a high-speed electrical machine is used along with a gearbox to transform speed and torque. the mechanical gearbox requires lubrication and cooling, while noise, vibration and reliability can be significant issues. the aim of this paper is mppt control of a 2.5mw magnetic gear generator, an artificial neural network controller is designed for the mppt control of this system. the controller adjusts the outer rotor speed, and thus, the inner rotor speed. the effectiveness of the proposed procedure is verified by simulation results. ii. operating system the proposed magnetic gear is showed in figure 1. there are two permanent magnetic rotors and between them there is a ferromagnetic pole-pieces rotor. one of the two permanent magnet rotors is held stationary. the numbers ns=166, pl=168 and ph=5, present the pole-pieces low-speed ferromagnetic rotor (input rotor), pole-pairs stationary permanent magnet, and pole-poles high-speed permanent magnetic rotor (output rotor) respectively. a wind turbine extracts kinetic energy from the swept area of the blades. the mechanical energy is transferred to the shaft of the input rotor, which is transmitted magnetically from the input rotor to the output rotor. the permanent magnet of the output rotor interacts with the stator windings to produce electromagnetic torque. thus, the power captured by the wind turbine is transmitted to the grid by the stator winding. the gear ratio of the proposed machine is: sr h ng p= (1) we can see that the speed which needs to be applied to the corresponding author: kamel salim belkhir engineering, technology & applied science research vol. 9, no. 4, 2019, 4329-4333 4330 www.etasr.com belkhir: intelligent maximum power tracking control for a wind energy system based on magnetic … output rotor is independent of the torques of the rotors, and is a function of the applied input speed and gear ratio. the equation of the motions of the magnetic gear is given by [1]: h h s sp nω ω= (2) where ωh and ωs are the speed of the output and input rotors respectively. the link between the torques is [1]: 1h srt tg= − (3) it is clear that the torque which needs to be applied to the output rotor is independent of the speeds of the rotors, and is a function of the applied input torque and gear ratio. fig. 1. radial cross section of magnetic gear generator. the equations of the rotors motion are given by [1]: � �� � � ����� � �������� � ���� � !"! # � $%#%& �% ���(��� � �� � ���� )(�* � !+$%#% � !)#), �� � -. $%+/ � 0 � / 0 �, (4) where θh and θs are the angular position of the output rotor and the input rotor respectively, φ is flux linkage, i is the current, s indicate the stator winding, tturbine is the wind turbine torque, te is the electromagnetic torque which results from the interaction between the permanent magnets on output rotor and the stator winding, tmax is the maximum torque which can be produced by the magnetic gear and jh and js are the inertias of the output rotor and the input rotor respectively. iii. control strategy of the proposed magnetic gear generator figure 2 displays the suggested control topology of the wind power generation system consisting of a magnetic gear generator connected to the grid through a back-to-back converter [9]. it includes two converters connected by a capacitor. the converter connected to the magnetic gear generator is used as a rectifier, while the converter connected to the grid is used as an inverter [15]. to determine the optimal generator speed that ensures maximum energy, a controller should be included that can track the maximum peak regardless of wind speed. many maximum power point tracking studies have been proposed [10-14]. since the wind energy system is a nonlinear form, an artificial neural network can be used to solve this problem. fig. 2. magnetic gear generation topology. a. magnetic gear generator side control the magnetic gear generator side converter is controlled the input rotor to the reference speed ωs * using maximum power tracking algorithm to extract maximum power from the wind turbine. a wind turbine extracts kinetic energy from the swept area of the blades, the power transferred to the wind turbine rotor is [17]: 1� � 2. 3)"4, 6&789 (5) where pt is the wind turbine power, cp the power coefficient, ρ the air density, a the swept area of rotor, v the wind speed, β the blade pitch angle, and α the angle of attack. the tip speed ratio is defined as the ratio between the blade tip speed and the wind speed v [17]: : � ; <= (6) where ω is the turbine rotor speed and r the radius of the wind turbine blade. the stator winding of the magnetic gear generator is modeled in the rotor reference frame dq-axes by: >9 � � �?�@�� � a � � ;%/ 09 0 � �?�b�� � a 0 c ;%/ � (7) where v is the stator voltage and r resistance. the flux linkages are: d/ � � e � � /fg/ 0 � e 0 (8) where φpm is the flux of the permanent magnets and l the inductance. the electromagnetic torque is: �� � -. $%+/ � 0 � / 0 �, (9) engineering, technology & applied science research vol. 9, no. 4, 2019, 4329-4333 4331 www.etasr.com belkhir: intelligent maximum power tracking control for a wind energy system based on magnetic … from (9), due to the cross-related flux terms, it is not easy to control the electromagnetic torque. so, the reference frame dq is chosen in such a way that: isd = 0 and isq = is (10) now, the electromagnetic torque can be simplified into: �� � -. $h/fg 0 (11) thus, the electromagnetic torque can be controlled through isq. the isd and isq errors can be tuned by a pi controller. the controller is based on two loops, the inner loop is a current controller and the outer loop is a torque controller. from (2), (4), (7), (8) and (11) the general structure of control strategy for magnetic gear generator inverter can be represented by figure 4. fig. 3. general structure of magnetic gear generator-side control b. artificial neural network based mppt control the mppt controller adopts a back-propagation artificial neural network and its structure is multilayer feed-forward network. the study uses the learning method to estimate speed of magnetic gear generator, the scheme of the proposed training is shown in figure 4. the rpm samples are used as targets to train a 3-layer network, with 1 linear neuron in the input layer, 7 tan-sigmoid neurons in the first hidden layer, and 1 linear neuron in the output layer. the input network parameter wind speed is in (m/s) and the output network parameter is a speed of magnetic gear (rpm). the training operation is made in a few cycles using 06 input-output patterns. fig. 4. training scheme using ann controller c. grid side control the grid side inverter controls the active and reactive power flowing between the inverter and the grid [14]. the active and reactive powers produced by the magnetic gear generator are: i1 � -. +j� � c j0 0,k � -. +j0 � � j� 0, (12) where e is the voltage at the output inverter and i the line current. to overcome the problem of cross-related voltage terms in (12), the dq reference frame, is chosen in such a way that: v'q = 0 and v'd =│v'│ (13) so the active and the reactive power will be proportional to id and iq respectively: i1 � -. j� � k � � -. j� 0 (14) now, the active power can be controlled via id and the reactive power can be controlled via iq. the iq is usually set to zero in order to achieved unit power factor [15]. the voltage equations of grid side inverter can be defined by: >j� � al � c el ��@�� � ;el 0 c m′�j0 � al 0 c el ��b�� � ;el � (15) where e is the voltage at the output inverter, rt and lt are the overall resistance and inductance of the grid-side converter and ω is the electrical angular velocity. from (14) and (15), the general structure of control strategy for grid-side inverter can be represented by figure 5. the inverter is based on two loops, the inner loop is a current controller, and the outer loop is a dclink and reactive power controllers. fig. 5. general structure of grid side control iv. simulation results to evaluate the high performance mppt controller, simulations were conducted with variable wind speed. table i shows the parameters of the magnetic gear generator. the wind speed variation is shown in figure 6. the magnetic gear side engineering, technology & applied science research vol. 9, no. 4, 2019, 4329-4333 4332 www.etasr.com belkhir: intelligent maximum power tracking control for a wind energy system based on magnetic … converter is controlled by the artificial neural network controller to maintain the output rotor to the rated speed to collect maximum power. as shown in figures 7 and 9, there is a good agreement between the reference values of the estimated high speed rotor and of output rotor speed. as revealed in figures 6 and 11, when the wind speed increases, the input mechanical power also increases and thus the electrical power produced by the generator increases. table i. system parameters magnetic gear generator rated power 2.5mw rated voltage 900v winding resistor 0.001ω inductance ld 0.0007h inductance lq 0.0007h number of pole-pairs inner rotor 166 number of pole-pairs outer rotor 5 transmission line resistance 0.01273ω/km inductance 0.0009337h/km distance 7km fig. 6. wind speed variation vs time fig. 7. the output of the artificial neural network controller figures 8 and 9 show the output and input rotors’ variation. for example, we can see that, from 18rpm of the inner rotor and without mechanical gear, the output rotor reached 600rpm. that means that even under low wind conditions often found inland, and without mechanical gear, high speed can be reached using magnetic gear generator. the performance of the proposed artificial neural network controller is compared with a fixed rated speed in figures 11 and 12. the artificial neural network controller provides superior performance, as it derives maximum possible power from the wind at different wind speeds. fig. 8. speed of the input rotor fig. 9. speed of the output rotor fig. 10. dc-link voltage fig. 11. power injected to the grid 0 1 2 3 4 5 6 5 6 7 8 9 10 11 12 13 time ( s ) t h e w in d s p e e d v a ri a ti o n ( m /s ) 0 1 2 3 4 5 6 350 400 450 500 550 600 650 time ( s ) t h e o u tp u t a n n c o n tr o ll e r e st im e te d h ig h s p e e d r o to r ( rp m ) 0 1 2 3 4 5 6 0 5 10 15 20 25 30 time ( s ) in p u t r o to r s p e e d ( r p m ) 0 1 2 3 4 5 6 0 100 200 300 400 500 600 700 800 900 1000 time ( s ) o u tp u t r o to r s p e e d ( r p m ) 0 1 2 3 4 5 6 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 time ( s ) t h e d c -l in k v o lt a g e ( p u ) 0 1 2 3 4 5 6 0 0.5 1 1.5 2 2.5 3 x 10 6 time ( s ) p o w e r in je c te d t o t h e g ri d ( w a tt ) with mppt controller with fixed speed engineering, technology & applied science research vol. 9, no. 4, 2019, 4329-4333 4333 www.etasr.com belkhir: intelligent maximum power tracking control for a wind energy system based on magnetic … fig. 12. mechanical turbine power to realize the feasibility of the grid side controller, figure 10 presents the dc link voltage variation. the controller gives good agreement between the actual and reference values of the dc link voltage thus the actual dc voltage is almost constant over the whole period. v. conclusion in this paper, an artificial neural network based mppt controller method applied to a 2.5 magnetic gear generator was proposed. it was shown that with low wind conditions, high speed variation can be achieved using the proposed magnetic gear generator. the proposed controller has fast dynamic characteristics, regardless of the changes in wind speed. simulation was performed on a 2.5mw magnetic gear generator and the results confirm the benefits of the proposed topology. references [1] v. markovitz, “sizing up wind energy: bigger means greener study says”, national geographic news, available at: https://news. 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inverter”, energy conversion and management, vol. 52, pp. 2688-2694, 2011 [17] z. qi, e. lin, “integrated power control for small wind power system”, journal of power sources, vol. 217, pp. 322-328, 2012 0 1 2 3 4 5 6 0 0.5 1 1.5 2 2.5 3 x 10 6 time ( s ) m e c h a n ic a l p o w e r ( w a tt ) microsoft word 14-3747_s1_etasr_v10_n5_pp6224-6230 engineering, technology & applied science research vol. 10, no. 5, 2020, 6224-6230 6224 www.etasr.com pinjari & bindu: compact solid-state marx generator for repetitive applications compact solid-state marx generator for repetitive applications neelam s. pinjari electrical engineering department fr. conceicao rodrigues institute of technology navi mumbai, india neelam.pinjari@gmail.com s. bindu electrical engineering department fr. conceicao rodrigues institute of technology navi mumbai, india bindubalu1970@gmail.com abstract-the marx generator plays a vital role in a pulsed power system. in this paper, a modified compact bipolar output pulse solid-state marx generator topology is developed. a three-stage prototype is designed and tested, in which pulse width, polarity, and peak voltage of the output pulse are made variable. it is possible to generate either positive or negative pulses with less rise time. various components which affect the repetitive frequency of the developed marx generator are evaluated. analysis reveals that the total time period to is a function of capacitor charging time. this is been validated experimentally by operating the marx generator for different pulse repetition frequencies. the type of charging method solely controls the charging time of the capacitor and hence the repetition frequency. keywords-capacitor; monopolar topology; pulse repetitive frequency; bipolar topology; charging time; high voltage time; hbridge circuit i. introduction pulse power technology is the discipline in which, the energy is accumulated over a period in a medium and is released into the load to generate a high voltage pulse instantaneously. it has many applications in fusion research, high power pulsed lasers, air pollution control, food processing, etc. [1-2]. in conventional marx generators, the repetitiveness of the marx generator is limited by switches and the charging method used. recovery characteristics of the gas medium used in a spark gap switch put limitations in the repetitive rate of conventional marx generators. the capacitor charging rate from a given power supply depends upon the charging method used. with the development of solid-state semiconductor technology, solid-state switches with high voltage blocking capacity were used to construct the solid-state marx generator [3-4]. the gate control in solid-state switches facilitates the flexibility in output pulse amplitude, pulse width, and repetition rates. several solid-state marx topologies, either monopolar or bipolar, with multiple switches for charging and discharging are available in the literature [8-12]. authors in [3] proposed a compact monopolar pulsed power generator using solid-state devices widely used in plasma source ion implantation (psii). however, in this topology, high return current flows through the dc source during the erection mode [3]. authors in [5] have developed a generalized solid-state marx modulator topology wherein, multiple charging paths were used to reduce the stresses on the switches. the five-switch topology proposed in [6] has more stresses on switches, as the same switches are repeatedly being used for discharging operations. the major limitations of the topologies used for developing bipolar output pulse are the number of switches per stage. this limitation was eliminated in [7]. the authors proposed a high voltage solid-state bipolar rectangular pulse modulator having an h-bridge circuit across the load. each stage comprises of switch, inductor, diode, and capacitor. stage inductors help boosting the output voltage. however, the rise time of the output pulse increases due to the inductor. in the recent years, there has been a remarkable innovation in high voltage application in the field of food technology [13-14]. in this paper, the topology proposed in [3] is converted to bipolar by including an h-bridge circuit across the load. per stage inductance is eliminated. the output pulse rise time of the circuit is much lower as compared to the output pulse generated by the topology proposed in [7]. marx grounding is provided through a high resistance to reduce the source current while in erection. this type of grounding protects the source from high return current pulses and improves the output pulse wave shape. a theoretical method is developed for the determination of the repetitive frequency of a solidstate bipolar output pulse marx generator and it is validated from the modified topology. the influence of various elements on repetitive frequency is analysed and the key parameters are identified. ii. the topology of the modified marx generator the working of the marx generator in bipolar mode is illustrated in figure 1. the basic principle of the marx generator topologies is that, all the capacitors for ‘n’ stages are charged to the input dc voltage magnitude in parallel through a charging element which can be a resistance, a combination of resistance and inductor or through an input switch and discharged in series into the load through the switches synchronously [3-5]. the solid-state marx (ssm) generator developed in [3] is modified to develop the bipolar output pulse topology. the circuit shown in figure 1(a) is the modified bipolar topology where in a section composed of four switches in the h-configuration is included at the load sides [7]. figure 1(b) shows the elements of an individual cell. it comprises of two diodes �� and �� �, an igbt switch and a stage capacitor corresponding author: neelam s. pinjari engineering, technology & applied science research vol. 10, no. 5, 2020, 6224-6230 6225 www.etasr.com pinjari & bindu: compact solid-state marx generator for repetitive applications ��. all capacitors are charged to the source voltage through the charging element and stage diodes. for first section it is �� and �� �. the bipolar pulses are obtained by switching alternately the pair of h-section switches. once the capacitors are charged, switches 1 and 2� of h configuration are triggered along with marx switches to generate positive output pulses. a dead band is followed after this operation, which allows the capacitor to charge again. negative pulses are obtained by switching 2 and 1�of h configuration along with the marx switches. every positive and negative pulse is followed by a dead band, to prepare the capacitor for the next discharging. it is also possible to generate either positive or negative pulses. the time taken for the capacitor to charge depends upon the charging method adopted, hence it is directly related to the repetitive frequency. (a) (b) fig. 1. (a) modified marx generator topology for n cell configuration, (b) individual cell components comprising of capacitor, diodes and igbt for the 1 st cell. an interesting fact about this h-bridge topology is that each diagonal pair of switches is made on along with the marx switches, reducing the switching losses, loading of the switches and hence, avoiding shoot-through faults in the switches of the same limb. iii. repetitive frequency evaluation for a solidstate marx generator the total time �� required to obtain the repetitive pulses across the load is the summation of charging time of marx capacitors ( �), high voltage time ( ��), and switch recovery time ( ��) as shown in (1). equation (2) depicts the repetitive frequency (��) which is the reciprocal of total time period. �� = � + �� + �� (1) �� = � �� (2) a. charging time (tch) marx charging time ( �) mainly depends on the charging method used. the rating of the charging element is decided based on the limitation of the charging currents. the equivalent marx with a resistive (r) charging method circuit is shown in figure 2 [15]. the capacitors in all the stages are charged through intermittent diodes in the modulator. it is assumed that all stage capacitances take the same time to charge to the supply voltage. the time required for marx capacitors to charge to the input voltage is given by (3). fig. 2. equivalent circuit of solid-state marx while charging [1, 2]. � = � ∗ln[1− �� �� ] (3) where ! is the charging resistance (ω), "# is the marx inductance (nh), c is the marx stage capacitance (µf), τ is the charging time constant (! �), � the charging time (µs), % is the voltage across the marx per stage capacitance c (v), and %&' is the input voltage (v). b. high voltage time (thv) high voltage time ( �� ) is calculated from (4). it is composed of two-time parameters, erection time ( (� ) and discharging time ( )& ). �� = (� + )& (4) the switch erection time ( (� �) for an igbt is composed of two parts, propagation delay time (turn-on delay time *�') and the sum of input transition rise time along with collector current rise time ( �) respectively: +,.ℎ 012. -34 �-52 ( (� �) = *�' + � (5) the trigger signal initiated from the controller is further sent through buffer and driver circuits to trigger the igbt switches. thus, the individual propagation delay time for the above components must be considered in the calculations of (�. buffer erection time is the summation of propagation delay (on) time 7) and input transition (rise) time 8 as shown in (6): 9:��21 012. -34 �-52 = 7) + 8 (6) driver erection time is illustrated in (7) which is the summation of propagation delay time to high output level ;<= and rise time �). �1->21 012. -34 �-52 = ;<= + �) (7) the total (� time is evaluated by: (� = +,.ℎ 012. -34 �-52 (?@9�)+ 9:��21 012. -34 �-52 +�1->21 012. -34 �-52 (8) the discharging time ( )& ) is considered from the instant of switching into the load until the load voltage decreases to a engineering, technology & applied science research vol. 10, no. 5, 2020, 6224-6230 6226 www.etasr.com pinjari & bindu: compact solid-state marx generator for repetitive applications minimum magnitude compared to peak output voltage %�. the marx discharging circuit is shown in figure 3. fig. 3. equivalent circuit of solid-state marx while discharging. the time required for the marx capacitors to discharge into the load, )& , is given by (9). t)& = − � b ln [ ��cd(efg eh)if ��c ] (9) a = efg eh <f (10) where % # is the voltage across the marx equivalent capacitance �# (v), "l is the marx inductance (nh), -l is the loop current (a), !l is the equivalent series resistance of capacitor (ω), !< is the load resistance (ω), and a is a constant depending on circuit parameters. c. switch recovery time (tswr) every output pulse is followed by a dead band where the capacitor is preparing or charging for the next cycle. during this time the marx switches are off. hence, it is essential to consider the recovery time of buffer and driver ics in the calculation of ��. normally, solid-state switches (sss) have nanosecond turn-on, turn-off, and switch recovery time ( ��). igbt recovery time ( mno�) is the summation of the turn-off delay time ( *�pp) and the fall time ( p): ?@9� !2.3>21q �-52 ( mno�) = *�pp + p (11) buffer recovery time is the summation of the propagation delay (off) time r 7)ps and the input transition fall time r 8ps: 9:��21 !2.3>21q �-52 = 7)p + 8p (12) the recovery time required for the driver ic given in (13) is the summation of the propagation delay time to low output level ( ;=<) and the fall time r p)s: �1->21 !2.3>21q �-52 = ;=< + p) (13) total switch recovery time ( ��) is given in (14): �� = ?@9� !2.3>21q �-52 +9:��21 !2.3>21q �-52 + �1->21 !2.3>21q �-52 (14) the minimum dead band required is the time taken by the capacitor to charge for the next section, which is �. this dead band time is equal to the �uu period as shown in figure 4. fig. 4. switching sequence for marx generator. iv. design and hardware implementation of the marx generator with bipolar output the three stage modified bipolar topology was designed, implemented, and tested. the circuit is designed for 1000v input voltage, 110hz switching frequency, 10% voltage droop and 14µs pulse width. igbt switches of 1700v, 32a ixgh32n170a were used for the marx generator and hbridge configuration. diodes with ratings of 1200v, 30a, rhr30120 were considered. per stage, the capacitor rating is 1µf, 1000v [4]. hcpl3120 drivers and sn74nc573n buffer ics were used for triggering the igbts. the trigger signals were initiated by the lpc214x series arm7 controller. the load is a resistive one with 1000ω resistance. the resistive charging method was used for testing. the selected resistance value was 100ω. dc auxiliary power supply of 5v and 15v was developed for the arm7 controller, buffer, and driver ics. a regulated dc power supply source of aplab with ratings of 100v, 2a and tektronix tbs1072b dso 70mhz,1gs/s was used for testing. a. experimental setup and testing of the modified marx generator topology when the circuit in figure 1(a) is in erection, the current can flow through two alternate paths. one is through the load and the other through the ground point at (cc) and the negative terminal of the source (source ground) as shown in figure 5(a). eventually an indirect short circuit of the dc source is caused through the alternate grounding path. this short circuit (caused by two different potentials) produces large stresses on the dc source. the reverse current through the dc source leads to its tripping. also, the output voltage waveform was not perfect. tripping occurs when the cc voltage equals to the dc voltage. hence, the input voltage for testing is restricted to lower potentials. the ringing effect is also observed in the output voltage waveform. to eliminate this problem, it is decided to control the magnitude of the reverse current flowing through the dc source. the circuit is modified by providing a ground resistance !nev (1000ω, 25w) as shown in figure 5(b). the additional ground resistance !nev changes the discharging time constant of the capacitor, as !nev and load resistance are now connected in parallel. !nev also helps improving the wave shape for the output voltage pulses [15-16]. engineering, technology & applied science research vol. 10, no. 5, 2020, 6224-6230 6227 www.etasr.com pinjari & bindu: compact solid-state marx generator for repetitive applications the assembled experimental setup of the modified topology is shown in figure 6. this is tested for an input voltage of 50v. (a) (b) fig. 5. circuit connections showing the short circuit of the dc source through cc terminals. fig. 6. experimental setup of the prototype bipolar topology. figure 7(a) represents the repetitive bipolar output pulses, with 110hz repetitive frequency. figures 7(b) and (c) represent the positive and negative voltage pulses with a slight droop, of amplitude 140v and 138v, respectively. the rise time of positive and negative pulse is in the range of ns. the 10 stage, 10kv, marx generator is modeled in simulink and tested to find the feasibility of its performance in high voltage. figure 7(d) illustrates the bipolar output pulses with amplitude of 9.9kv. (a) (b) (c) (d) fig. 7. (a) repetitive bipolar output pulses (50v/division, 1x probe), (b) positive pulse with 140v peak, along with igbt trigger signal pulse (upper blue trace), (c) negative pulse with voltage magnitude of 138v (50v/division, 1x probe), and (d) 9.9kv output pulse of 10 stage modified topology with 1000v input voltage from matlab simulation. engineering, technology & applied science research vol. 10, no. 5, 2020, 6224-6230 6228 www.etasr.com pinjari & bindu: compact solid-state marx generator for repetitive applications this topology provides a flexible control to change pulse width, polarity, and output pulse magnitude. the pulse width can be made variable by changing the code of the arm7 controller. switching each diagonal pair of igbts independently gives the monopolar output pulses of either polarity. trigger pulses to the driver input pin can be detached to prevent the inclusion of a cell, through which the output voltage across the load can be varied. b. repetitive frequency of a marx generator the total time period for any given marx modulator is calculated by (1). the charging time � required for capacitors to charge is calculated as 351µs from (3). the input voltage (%&'), charging resistance (! ) and stage capacitance (c) values considered are 50v, 100ω and 1µf respectively. marx inductance ("l) is obtained from the short circuit test on the marx generator and its value is 7.8nh. the discharging time )& for the marx circuit is 0.33ns as per (13). the circuit parameters considered are: % #=142v is the voltage across the marx equivalent capacitance, "l =7.8nh, loop current -l =0.14a, equivalent series resistance of capacitor r2=0.1ω, and load resistance rl=1000ω. the other time components are obtained from the respective data sheets. table i shows the detailed evaluation of time parameters essential for the calculation of �� . as )& xx (� , the �� is equal to (� . hence, �y is equal to (� as given by (15). hence, we can state that the minimum pulse width required for a given marx topology is its (� time. �y = (� (15) during the capacitor charging all the switches are off and the recovery of devices happened at this interval. from the data it can be seen that tz[\ xx t]^, hence the �uu is equal to the charging time of capacitances 6 �): �uu � � (16) therefore, the total time period can be represented by: �� � � � (� (17) table i shows that (� xx � , hence �� can be modified as mentioned in (18). �� depends on the type of charging method adopted and the value of stage capacitance [17]. �� � � (18) the repetitive frequency depends on charging time and can be improved by minimizing it. this can be attained by selecting a proper input charging method. the highest repetitive frequency for the designed monopolar marx generator is 2.85khz. figure 8 shows the detailed switching sequences of the given bipolar topology. the dead band selected is 351µs. the total time of operation calculated for the generation of bipolar pulses across the load of the modified topology is given by (19): �� � 26 � � (� $ (19) bipolar marx topology operates with half the frequency of the monopolar topology. hence, the maximum repetitive frequency obtained for the bipolar topology is 1.42khz. table i. time parameters concerned with the computation of to various time parameters concerned with the computation of `a calculated time datasheet specifications and remarks charging time � 351µs from (3) high voltage time /> � (� � )& from (4) switch erection time (� � *�'(46ns) 103ns from (5) at 25ºc � (57ns) buffer erection time 7) (44nsec) 59ns from (6) 8 (15nsec) driver erection time bcd (0.5µs) 600ns from (7) at -40ºc to 100ºc � (0.1µs) e\ 762ns from (8) discharging time )& 0.033ns from (9) )& xx (� �� � (� 762ns igbt, buffer and driver recovery time z[\ 969ns from (14) tz[\ xx t]^ igbt recovery time *�pp (260ns) 310ns from (11) p(50ns) buffer recovery time fgh (44ns) 59ns from (12) 8p (15ns) driver recovery time bdc (0.5µs) 600ns from (13) p) (0.1µs fig. 8. switching sequence for the bipolar topology. c. performance of the modified marx generator topology for variable pulse repetitive frequency (vprf) the modified marx generator circuit has been tested in order to find the highest repetitive frequency possible. the total time period �� was calculated from (18) and was 351µs. testing was carried out for an input voltage of 80v, prf of 1.42khz. figures 9(a)-(b) show the pulses obtained across the load. the output pulse is 440v pk-pk, with prf 1.42khz. the positive pulse has a magnitude of 246v. the above output voltage magnitude confirms that the stage capacitances charge is to its maximum, with � =351µs. for analysis purposes it was decided to reduce the time period � to half of the previous value, i.e. to 176µs. figure 9(c) shows the multiple output pulses generated at prf 2.79khz. from figure 9(d) we see that the repetitive output voltage waveforms developed across the load have a magnitude of 160v. this reveals that the charging of stage capacitances is reduced to nearly 66.66% at engineering, technology & applied science research vol. 10, no. 5, 2020, 6224-6230 6229 www.etasr.com pinjari & bindu: compact solid-state marx generator for repetitive applications prf of 2.79khz, keeping the input supply voltage constant. thus, we can conclude that the charging time � decides the prf for a marx modulator. this time, � depends upon the type of charging method adopted. the graph in figure 9(e) represents the variations of the output voltage against vprfs. analysis indicates that as the � is reduced the stage capacitors do not charge to their optimum magnitudes. (a) (b) (c) (d) (e) fig. 9. (a) repetitive bipolar pulses with magnitude of 220v with prf 1.42khz, (b) positive pulse of h-bridge circuit with voltage magnitude of 246v with prf 1.42khz (50v/division, 1x probe), (c) repetitive bipolar pulses with magnitude of 160v with prf 2.79khz (50v/division, 1x probe), (d) bipolar pulses with magnitude of 344v pk-pk with prf 2.79khz (50v/division, 1x probe), and (e) graph of the repetitive frequency vs the output voltage obtained across the load for various vprfs. v. conclusion a modified bipolar output pulse marx generator with rise and fall time in the nanosecond range was built and tested for low voltage. the design is flexible to generate output pulse with variable pulse width, polarity, and peak voltage. it is also able to generate either positive or negative pulses. the absence of stage inductance improves the output pulse rise time. therefore, we succeeded in building a simple marx generator with optimum number of switching devices which can generate flexible output pulse with lowest rise time. equations showing the repetitive frequency for the marx generator were developed. it is found that the limiting factor for repetitive operation in solid-state marx generator is only the capacitor charging time, since all the other time parameters are negligible compared to it. hence, the type of charging method adopted decides the repetitive frequency for ssm generators. feasibility of modified ssm generator in high voltage was checked with matlab simulink. for higher voltage applications, additional higher rating switches are required in bipolar topologies. thus, a single switch in h-bridge will not be capable to withstand the high voltages. references [1] m. dimitropoulou, d. pylarinos, k. siderakis, e. thalassinakis and m. danikas, “comparative investigation of pollution accumulation and natural cleaning for different hv insulators”, engineering, technology & applied science research, vol. 5, no. 2, pp. 764-774, april 2015. 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[16] w. ding, h. ren, q. zhang, and l. yang, “repetitive frequency marx generator based on magnetic switches and its application in dielectric barrier discharge,” ieee transactions on plasma science, vol. 40, no. 10, pp. 2373–2378, oct. 2012, doi: 10.1109/tps.2011.2174807. [17] n. s. pinjari, s. bindu, and r. d. singh, “analysis and comparative study of various charging methods implemented for solid-state marx generator,” in advances in energy research, vol. 2, singapore, 2020, pp. 773–785, doi: 10.1007/978-981-15-2662-6_70. authors profile neelam s. pinjari received the b.e. degree in electrical engineering from the pvg’s college of engineering and technology, pune university, pune, india, in 1999, and m.e. in power system from pune university in 2003. she is presently working as an assistant professor at lokmanya tilak college of engineering, navi mumbai. she is currently pursuing the ph.d. degree at fr. c. rodrigues institute of technology, department of electrical engineering, vashi, navi-mumbai. s. bindu has received her ph. d. degree from veermata jijabai technological institute (vjti), mumbai maharashtra in 2014. she received her b. tech. from m g univ. kerala and m.e in power systems from vjti. she is currently working as a professor and the head of the department of electrical engineering at fr. c. rodrigues institute of technology, vashi, navimumbai. her research interests include power systems, high voltage engineering and hvdc. she has many research publications in international journals, conferences and had taken up various research projects funded by the brns and the university of mumbai. microsoft word etasr_v11_n2_pp6857-6863 engineering, technology & applied science research vol. 11, no. 2, 2021, 6857-6863 6857 www.etasr.com djeldjeli & mahdjoub: cp-sdn: a new approach for the control operation of 5g mobile networks to … cp-sdn: a new approach for the control operation of 5g mobile networks to improve qos youcef djeldjeli department of technology nour bachir university center el-bayadh, algeria and laboratory of electromagnetism, photonics and optronics djillali liabes university of sidi bel-abbés sidi bel abbès, algeria youcef.djeldjeli@univ-sba.dz mahdjoub zoubir laboratory of electromagnetism, photonics and optronics djillali liabes university of sidi bel-abbés sidi bel abbès, algeria zoubir.mahdjoub@univ-sba.dz abstract-today, the software defined network (sdn) technology gives more efficiency and flexibility to the 5g mobile networks that are expected to support an enormous amount of data relating to various constrained services. the 5g network should implement newer approaches and technologies that allow supporting the scalability and mobility of the network. the sdn approach consists of decoupling between the control operation and the networking operation, where the control operation is held by the sdn controller that is responsible for defining the management and the control rules. data forwarding is performed by switches that apply rules defined by their controllers. in the current study, we have proposed and defined a new approach named cp-sdn: cooperative protocol-sdn, as an extension to the existing software defined networks, especially when the network experiences saturation due to the huge amount of exchanged data. this congestion may affect the constrained flow and leads to an undesired delay that affects the network quality of service (qos). cp-sdn consists of a cooperation technique between neighboring controllers that aims to relieve the congested centers and redirect the extra flow through neighbors. cp-sdn processing keeps controller databases updated and assures the optimized path for the extra flow when network congestion occurs. the performed simulations on calculating the e-mbb and m-iot delay performances for various probability densities show that cp-sdn brings more reliability and efficiency in reducing the transmission delay and overcome the existing sdn scheme. this makes it a prime candidate for the evolved high scalable 5g networks. keywords-5g; sdn; cp-sdn; qos; iot; m-iot; embb; mft i. introduction a huge increase of exchanged data is conducted globally by the deployment of 5g networks. these networks are expected to support several media services that need very high speeds, even internet of things (iot) networks that contain a dense amount of connected devices with different requirements and constraints. 5g networks are deployed to satisfy the need of multiple vertical industries over a shared infrastructure with the use of concepts inclusive of community slicing [1]. regarding the transport stream held by 5g, video-primarily based totally clients represent a big portion of the data stream carried, with approximately 79% of cell information [2]. the significant increase of the connected smart devices with greedy smart applications like video streaming, requires a higher spectral efficiency and represents a big challenge of 5g [3]. authors in [4] illustrate that 5g is expected to reach 4.7 times more data amount than the regular 4g, with more than 12.3 billion users, which exceeds the world population, in the next decade. the new 5g network systems need to deliver capacity a thousand times more than the current cellular 4g systems, synchronizing with the expansion of the application development with personal communications, knowing that mobile devices will reach an immense number timing with the 5g commercial initiation. owing to the mobile data explosion, current mobile networks suffer from scalability and performance degradation problems[4]. the main goal of the sdn technology resides in separating of the software network management and the hardware based management network (packet forwarding). sdn in its new version leads to an opened standard with optimization in resources with the virtualization development concept. even lte disruption level is less critical than sdn deployment. 5g could reap sdn technology features and benefit from combining other compaction technologies such as mm-wave, das (distributed antenna system) to achieve a 1000-fold capacity, 100-fold rate and 100-fold more active connections than lte existing networks [5]. sdn, as the up-and-coming technology, dissociates the forwarding logic from the management logic in the existing network. sdn abstracts all management functions into the centralized controller, whereas sanctioning programmability for the network [6, 7]. sdn/nfv is an emerging technology that intends to deploy flexible, more efficient, and cost-effective networks with a high security level [8]. moreover, sdn philosophy splits the network in two main planes, a management plane and user plane [9]. the management plane is considered as the brain of the network with a centralized controller that runs a software package and that is responsible for controlling the user plane. the latter consists of low-price network devices, such as common switches. the controller runs the open flow (of) protocol in order to configure routing tables and monitor packet statistics corresponding author: youcef djeldjeli engineering, technology & applied science research vol. 11, no. 2, 2021, 6857-6863 6858 www.etasr.com djeldjeli & mahdjoub: cp-sdn: a new approach for the control operation of 5g mobile networks to … of the user plane. in the other side, nfv offers operators the virtualization of the network operations and functionalities by implementing standard servers instead of high-expensive and non-standard appliances [10]. therefore, the sdn design pattern should keep the network infrastructure transparent for the applications level [11]. various resource allocation and management solutions have been proposed to contribute with 5g and 6g networks. virtual network embedding (vne) is such a strategy that meets with the knowledge of the management plane for 5g/6g. the radio atmosphere map (rem) is mainly considered as one of the pioneers of psychological feature systems. however, most of these schemes are close to gpp and gtp, and their quality management planes meet with some particular conditions. the future need of 5g networks needs a development of new patterns that satisfy, not only the decoupling between the management plane and the user plane, but should support hotspots with high-capacity and coverage functionalities [12]. in addition, the virtualization technology aims to emulate the hardware platforms running in software packages. these packages are installed in industrial servers named as cots (commercial off-the-shelf) servers, which are accessible via virtual machines (vms), instead of hardware dedicated appliances. these vms can be mounted over different platforms, which makes virtualization more flexible and the technology versatile [13]. more research articles and case studies have been proposed to depict the sdn features and what they can bring to the 5g mobile industry. authors in [10] proposed a solution for the adjustability support in sdn-based mobile networks. authors in [14] developed a protocol that evaluates the handover execution time. moreover, they focused on the open flow protocol to achieve s5/s8 constraint while keeping the main standard rules of sdn. sdn is presently known as a trending technology in the networking domain. in such networks, the controller runs as a network monitor and defines the forwarding rules of the data flows. switches perform the forwarding and dropping of packets according to the rules defined by the controller. thus, the controller should be able to implement a centralized control strategy for every exchanging data flow by using the header packet reporting technique [15]. the main advantage of the proposed approach in the current paper resides in the slicing feature that splits the processing functionality into more than a dedicated core for each service. this increases the delivering flexibility and ensures the qos requirements, instead of having ad-hoc u/c plane functionalities for each business case. moreover, this feature will assure high scalability and will lead to augmented efficiency in terms of signaling and latency, by avoiding the unnecessary processing. ii. models and methods a. sdn for 5g networks 5g mobile networks are expected to fulfill the users' and applications' increasing requirements in terms of bandwidth and qos [16]. the network function virtualization (nfv) is taking a part in the new it world and evolves the networking strategy. both sdn and nfv can operate together and lead to the deployment of sophisticated future networks [17]. despite the growth of several mobile networks in 2020, various challenges should be taken into account: high scalability with iot implementation, energy constraints for the devices and mobile stations, delay and bandwidth optimization, optimization of resource allocation, reduction of deployment costs, etc. [18]. although several types of mobile networks will dominate the 2020’s, there are also many challenges, such as the extenuating power consumption in devices and base stations, better resource allocation, higher data rates, ensuring lower round trip times, decreasing all costs, developing and boosting the mobility management policies, elasticity, agility, and scalability [18]. sdn is an innovative technology within the networking domain that consists on defining the network functionalities in software packages. it enhances the efficiency of the network configuration and its resources allocation. by the separation between the control plane and the data plane, sdn guarantees the transparency between the network infrastructure and the running applications. thus, each controller manages various network devices as switches and expects more flexible and intelligent control of the exchanged data [19]. unlike the trivial pattern networking which experiences a difficulty in the resource allocation and its arrangement, sdn is a favorable candidate for such unmanaged networks by decoupling the management and the user pane [20]. to do so, sdn implements openflow as a communication protocol that is standardized by onf (open networking foundation) [21]. in sdn, the topology discovery is considered as the masterpiece of the sdn controllers and it enables controlling various applications like data routing, network virtualization, live migration, resource optimization, etc. the network topology is not only intended to determine routing tables for forwarding data, but also to manage the network resources [8, 22]. within the sdn network, the data plane is responsible for forwarding data between the connected devices and the controllers. switches running the of protocol form the information plane, while the controllers are distributed and connected together in order to form the control plane [23]. this new organization may have a positive impact in terms of flexibility and programmability [24]. thus, sdn is a way to introduce the virtualization within the classical ip networks [25], offering a new vision and gathering new features in terms of knowledge and deployment. furthermore, mobile networks can in turn benefit from sdn advantages, leading to enhanced network control and management [26]. at the front haul part of the network, the present sdn technology does not define a clear vision due to the particular characteristics of this part in power consumption and cost of the elements that spread on a defined geographical area [27]. figure 1 illustrates the common sdn architecture. it can be seen that the network is divided into two main planes. the connected devices that constitute the data plane are responsible for forwarding the network traffic. to do so, the open flow enabled-switches should follow switching rules and strategies received form the sdn controller that forms the control plane. engineering, technology & applied science research vol. 11, no. 2, 2021, 6857-6863 6859 www.etasr.com djeldjeli & mahdjoub: cp-sdn: a new approach for the control operation of 5g mobile networks to … fig. 1. sdn architecture. b. switching in sdn sdn enables more flexibility in the routing operation than a traditional mobile network. unlike the existing cellular networks where the traffic passes through the middle boxes using the same routing path, the sdn strategy offers a flexible routing, where only the necessary traffic is conducted via the middle boxes reducing their complexity. moreover, this strategy allows a dynamic network topology with a flexible routing path that fulfills the change of the network behavior and the user needs [28]. to do so, data packets are forwarded by switches according to an existing matching rule. otherwise, the concerned switch sends a packet-in message to the controller which determines a forwarding rule for the present packet. then, the controller sends a flow-mod message to the switches concerned by the new route in order to update their routing tables. various studies focused on the pipeline mft process. in [29], authors proposed a framework that divides a large flow table into a number of smaller ones. an sdn switch implementing such method can be seen in [28]. it forwards all the data coming from mobile terminals and m-iot devices implementing the respective rules, enabling connectivity between the edge devices, and empowering the transport traffic between the core network and other edge clouds [30]. other studies [12, 30] focused on implementing learning techniques to improve the control performance while selecting the optimized links into the satellite communication system. c. cp-sdn this section describes the proposed framework, as a new scheme for enhancing the control flexibility of the existing sdn networks. cp-sdn is considered as en extension to the existing sdn technology. cp-sdn aims to optimize the delay and enhance the flexibility in the control operation when the network experiences saturation. this may happen when the network is very dense and supports a huge amount of traffic data, as it is expected in 5g technology. the network may contain millions of fixed and mobiles devices, or even iot systems. the idea consists on using two sdn controllers instead of one, as shown in figure 3. in the normal case, both controllers are responsible for defining and broadcasting the switching rules to the switches that belong to them. when the network experiences saturation, the saturated controller forwards the superfluous data packets to its cp-sdn neighboring controller in order to assure load balancing in terms of control. the second controller will be responsible of defining rules to assure the forwarding of the remaining data belonging to the first controller. this aims to relieve the saturated controller, to avoid packet loss and to optimize the data forwarding process. cp-sdn is a proactive protocol that allows controllers to periodically exchange their switching rules for updating the control operation. d. cp-sdn control in sdn, the controller is considered as the core of the system, by gathering the traffic requirements and the status of the network devices. based on this information, it defines the control rules to the data plane in order to provide an optimized and efficient network for forwarding data services [30]. in case of saturation due to the amount of exchanged data, the controller may take more time to perform the control operation and thus, the transmission delay may increase. this represents one of the main problems experienced by an sdn network. thereby, real-time services will be affected and the network qos will be degraded. cp-sdn as a proposed scheme, takes part when the network experiences a saturation issue. as depicted in figure 2, the cp-sdn consists on liaising between two or more controllers in order to unload the saturated point. the cp-sdn protocol operates between the two sdn centers by allowing the controllers to exchange control information and update their rules. thus, both centers will have the whole information of the connected data planes. fig. 2. cp-sdn architecture. e. cp-sdn control switching the sdn controller is updated to track each tcp connection state established between the switches belonging to its data plane [31]. the switching in cp-sdn is performed in two separate levels. the first level is between the sdn switches, while the second level is between the sdn controllers. cp-sdn implements an algorithm based on two tables (i,j). the first table contains the mft pipeline processing data for the first level (between switches), and the second table contains the respective data for the second level. as illustrated in figure 3, the sdn controllers are updated by the same control databases allowing each controller to take decisions about the traffic rules of data packets exchanged in their belonging data planes. furthermore, in case of an overload of a engineering, technology & applied science research vol. 11, no. 2, 2021, 6857-6863 6860 www.etasr.com djeldjeli & mahdjoub: cp-sdn: a new approach for the control operation of 5g mobile networks to … part of the network, the controllers should relieve each other and decide about the optimized path to route data packets from source to destination. the diagram illustrated in figure 4, shows the cp-sdn functioning. thus, in case of a constrained traffic such as a real-time service, the data will not be queued due to saturation, but processed by the relieved controller. by this way, network optimization is guaranteed and a certain network qos level for the constrained traffic is assured. fig. 3. cp-sdn switching. fig. 4. cp-sdn operational diagram. iii. results and discussion let us consider a sub-urban cell covering area a=2km 2 and having on average a β1=1000 embb (enhanced mobile broadband) users, with only a percentage pa=0.5, 0.6, and 0.7 active at a time, and an average of a β2= 1000 active m-iot (massive iot) devices, in each respective service slice. the slicing should be deployed across all network domains, i.e. a network slice instance consists of network slice subnet instances from different domains [32]. the data rates are kept at 50mbps for embbs and 100kbps for m-iot, following the standards [31]. we take µ=1024pkt/ms with a length l=2kbytes. these values are taken from one node from our network. figure 5 shows the embb packet control time in a single cell by varying number of embb slices (n) for the three probabilities pa=0.5, 0.6 and 0.7. fig. 5. embb delay performance for different numbers of slices. the embb delay performance for different numbers of slices shows the control time of the embb packets based on the number of slices (n). it can be seen that for n from 1 to 4, almost the same time is needed, which is <1µs. starting from n=4, the case p=0.7 shows a different behavior that indicates a start of saturation, where it shows a continuous increase, to reach 27µs for n=10. this needed control time may lead to network latency. the same behavior is shown in the case of p=0.6 and 0.5, where an increase is noticed from n=6 and n=5, to reach 24 and 20µs respectively for n=10. fig. 6. m-iot delay performance for different numbers of slices. figure 6 illustrates the m-iot packet control time in a single cell by varying number of m-iot slices (n) for three probabilities pa=0.5, 0.6 and 0.7. the m-iot delay performance shows the control time of the m-iot packets based on n. it can be seen that for n from 1 to 4, almost the same time is required, which is <1µs. beyond n=4, the case pa=0.7 shows a different behavior exhibiting the start of saturation, where it shows an increase to 27µs for n=10. this produced control time may affect the network latency. in the same diagram, in the case of pa=0.6 and 0.5, a growth is noticed from n=6 and n=5, to respectively reach 24 and 20µs for n=10. engineering, technology & applied science research vol. 11, no. 2, 2021, 6857-6863 6861 www.etasr.com djeldjeli & mahdjoub: cp-sdn: a new approach for the control operation of 5g mobile networks to … fig. 7. embb delay performance for different values of n using the sdn and the cp-sdn at pa=0.5. figure 7 depicts a comparison of the embb delay performance for different values of n using sdn and cp-sdn with the probability of 0.5. the simulation results show that both sdn and cp-sdn have the same performances for n≤6, where the time spent in the control is equal to 1µs. the cpsdn shows a slight increase compared to the sdn, for values of n from 6 to 10, where the induced delay in the case of sdn is 5 times greater than in cp-sdn. this enhancement is the result of the use of a second controller, to share the control operation. the difference in the behavior, noticed from n=6 (the beginning of the saturation), is due to the collaboration with a second station. the use of a second station is not always enough, where the cp-sdn shows a saturation from n=8, which requires a third collaborative station. figure 8 illustrates the comparison between the embb delay performance variation for different values of n when using sdn and cp-sdn. fig. 8. embb delay performance for different values of n using the sdn and the cp-sdn at p=0.6. the simulation results indicate that both sdn and cpsdn, express the same behavior for n≤5, where the time exhausted in the control operation is equal to 1µs. the cp-sdn shows an obvious improvement compared to the sdn, for values from 5 to 10, where the produced delay in the case of sdn is 6 times more than the cp-sdn. this efficiency in the case of cp-sdn is the result of using a second station, to divide control. the difference in the behavior noticed from n=5 that indicates the beginning of a saturation state, is due to the alliance with the second station. the use of a second station is not usually sufficient, where the cp-sdn shows a saturation from n=8, that requires a third corporate station. in figure 9, the same results are gained as in figure 7 and 8 with the change of saturation initiation, which occurs when n=4. the second saturation state remains n=8, the same as for pa=0.5 and pa=0.6. as depicted by the various simulations performed during our work, the cp-sdn acts better than sdn, especially when saturation occurs. this happens when the network is dense and supports a huge amount of data exchanged between various segments and supporting multiple services. cp-sdn implementation leads to an optimization in terms of the delay for processing packets and therefore, an enhancement in the qos of the 5g network. table i summarizes the cp-sdn performance compared to the basic sdn. fig. 9. embb delay performance for various values of n using the sdn and the cp-sdn at pa=0.7. table i. cp-sdn and sdn performance comparison packet control time (µs) network probability density 0.5 0.6 0.7 embb m-iot embb m-iot embb m-iot sdn, current work results 20 19 24 22.5 27 26 sdn [31] 15 10.5 18 13.8 23.5 16.4 proposed cp-sdn 3.5 3.4 3.6 3.5 4 3.9 in the case of cp-sdn, the control time doesn’t exceed 4µs for both e-mbb and m-iot slices, for various probabilities of network density. however, for the sdn case the control time is more significant and it increases when the network becomes dense and experiences congestion. this illustrates the outcome of the cp-sdn for dense networks and its efficiency for realtime traffic, compared to the basic sdn. this quality improvement is directly related to the new mechanism implementation of cp-sdn which relieves controllers by their neighbors. the main drawback of the cp-sdn that may be observed is the increase in the energy needed for the transmission. in the case of cooperation between two or more engineering, technology & applied science research vol. 11, no. 2, 2021, 6857-6863 6862 www.etasr.com djeldjeli & mahdjoub: cp-sdn: a new approach for the control operation of 5g mobile networks to … controllers, we can perceive more energy consumption in the cooperative station. more energy consumed means more cost charging of power consumption. iv. conclusion sdn technology involved in 5g networks has a leading role by giving more flexibility and efficiency in terms of network management and data traffic, knowing that 5g networks are very scalable and connect billions of stationed and mobile devices with different requirements and characteristics. the traffic flow passing through the 5g network has different throughput and priority needs that should be in charge by the networks elements. this is achieved by splitting the network into two planes, the control and the data plane. the proposed extension scheme named cp-sdn, gives more efficiency and optimization to the existing sdn network, by relieving centers that experience saturation due to the huge supported data traffic. the simulation results show that cpsdn offers a greater outcome for the 5g networks in terms of processing delay optimization and thus can assure a high qos level, especially for the constrained services. the obtained results make cp-sdn a strong candidate for future dense and mobile 5g networks. acknowledgement the authors express our sincere thanks to the general directorate of scientific research and technological development (dgrsdt) for their support in the development of this work. references [1] j. baranda et 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[32] a. esmaeily, k. kralevska, and d. gligoroski, "a cloud-based sdn/nfv testbed for end-to-end network slicing in 4g/5g," in 6th ieee conference on network softwarization, ghent, belgium, jul. 2020, pp. 29–35, https://doi.org/10.1109/netsoft48620.2020.9165419. microsoft word etasr_v13_n4_pp11393-11399 engineering, technology & applied science research vol. 13, no. 4, 2023, 11393-11399 11393 www.etasr.com ghaly et al.: a 12-electrode ect sensor with radial screen for fluid diagnosis a 12-electrode ect sensor with radial screen for fluid diagnosis sidi m. a. ghaly electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia | ecole normale supérieure, mauritania smghaly@imamu.edu.sa mohammed shalaby electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia myshalaby@imamu.edu.sa mohammad obaidullah khan electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia okkhan@imamu.edu.sa khaled a. al-snaie electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia kalsnaie@imamu.edu.sa asad ali mohammed electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia asad207@imamu.edu.sa faisal baloshi electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia fambaluchi@sm.imamu.edu.sa abdalmajid imad electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia aimlathkani@sm.imamu.edu.sa majdi oraiqat electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia mtoraiqat@imamu.edu.sa received: 9 may 2023 | revised: 24 may 2023 and 27 may 2023 | accepted: 29 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6030 abstract in this paper, the use of radial screens in an electrical capacitance tomography (ect) sensor is investigated with the aim of resulting in higher-resolution images. the effect of the screens on the quality of the reconstructed images was simulated. 12-electrode ect sensors with and without screens were designed and tested. the capacitance between different electrode pairs was measured for two permittivity distributions. the obtained capacitance data were used to reconstruct images using the projected landweber iteration algorithm based on linear and semi-linear ect models. the sensitivity of the measurements and the accuracy of the obtained images for the ect sensors with and without screens were analyzed. the main conclusion is that a little improvement in the quality of images can be achieved with the use of 12-electrode ect sensors with radial screen. engineering, technology & applied science research vol. 13, no. 4, 2023, 11393-11399 11394 www.etasr.com ghaly et al.: a 12-electrode ect sensor with radial screen for fluid diagnosis keywords-ect sensor; radial screen; permitivity; fluid dynamics; imaging sensitivity measurement i. introduction there are many two-phase flow systems in the fields of electrical power generation industry, petroleum industry, chemical industry, and metallurgy industry. in the present time, the two-phase flow pattern recognition is mainly employed as a measuring tool for the flow pattern change criterion or the flow chart to diagnose the flow mode with flow parameters. however, due to the complex nature of the flow mechanism, the use of conventional detection techniques cannot match the large variety of the flow conditions. electrical capacitance tomography (ect) is a tomography technique developed for the industrial multiphase flow measurement systems. different materials have different dielectric constants, which are used as a basic principle to calculate the spatial distribution of the dielectric constant inside a flow channel and to figure out the distribution of the working medium in the sensing zone by measuring the capacitance values between the electrodes fixed on the insulating surface of the channel [1-3]. besides, ect is a non-invasive technique, exhibiting features such as faster response, economical, being non-radioactive, so it is becoming an indispensable analysis tool in multiphase flow industry. with the increased popularity of ect, one of the areas that need improvement is the relatively low spatial resolution and this is more pronounced on the pixels further away from the electrodes. this issue is closely related to the soft-field nature of the electric field. when an image is reconstructed, most algorithms use a matrix called sensitivity map in the inverse process, or in both the forward and inverse steps for an iterative algorithm, such as the well-known landweber method [4-5]. recently, a preiteration scheme was developed that iteratively updates the sensitivity maps instead of the image, and then uses the final sensitivity map in real time ect measurement [6]. this method offers fast image reconstruction speed while maintaining the same image quality as the landweber algorithm does. in practice, the sensitivity maps are produced as the product of the inner electrode fields that are usually calculated by solving the poisson equations for electric fields. the soft-field nature can therefore be inherited during the construction of the sensitivity map. further, as the strength of the electrical field reduces, for the locations away from the electrodes, the sensitivity decreases correspondingly. to address such a weakness, different models have been proposed, such as the expanded sensitivity map [7], in which the sensitivity map elements can be produced based on a set of blocks of different sizes. the stability and quality of an image can be improved with the help of typical designed extended sensitivity maps. also, there are other recommendations on the proper distribution of the image elements in the measurement domain, such as those proposed in [8], where a hierarchical mesh algorithm was demonstrated for ect image reconstruction by locating progressively the boundaries by refining the mesh. at each step of the hierarchy the image was obtained using the gauss–newton (gn) algorithm or the hierarchical mesh regularized constrained gauss–newton (hm-rcgn) algorithm. these algorithms have two advantages: the speed of image reconstruction is significantly accelerated and the spatial resolution of the reconstructed images is enhanced. fig. 1. cross sectional view of a typical 12-electode ect system. fig. 2. a typical ect system with 12 electrodes. for ect sensors, the capacitance values are typically small, which requires mounting an earthed screen around the electrodes to eliminate problems related to parasitic capacitance variations that can affect the measurement. also, the mechanical stability is an important factor in the ect system. the electrodes are connected to the capacitance measurement system by coaxial connection cables. thus, in this paper, a 12-electrode ect sensor with radial screen for diagnosis of fluids was designed and tested. it was shown that it gives better performance in terms of image quality than the one without a radial screen. ii. electrical modeling of 12-electrode sensor with earthed screen let us consider an ect sensor with 12 external electrodes with radial screen as shown in figure 1. these electrodes can be developed with a flexible printed circuit board to a greater precision in its shape and size. in this case, as demonstrated in figure 1, a 12-electrode sensor needs 66 independent measurements of electrode pairs as:1-2, 1-3, ..., 1-12; 2-3, 2-4, ..., 2-12; ..., up to 11-12. the ect systems directly utilize the "raw" capacitance values captured from the sensor to reconstruct images using recursive or iterative algorithms. one of the commonly used algorithms is the linear back-projection (lbp) algorithm for its simplicity and high data rate for image engineering, technology & applied science research vol. 13, no. 4, 2023, 11393-11399 11395 www.etasr.com ghaly et al.: a 12-electrode ect sensor with radial screen for fluid diagnosis reconstruction. an lbp image is reconstructed by superposing the sensor sensitivity distribution maps for all electrode pairs by the corresponding measured changes in the normalized capacitance by properly weighting them. when the electrode 1 is biased with a potential, the charge q1j is generated on the electrodes j = 2, . . . n, that can be measured, similarly, q12, q13, . . . , q1,n, are repeated. thereafter, electrode 2 is excited and the rest of the electrodes are grounded with potential 0 and the induced charges q23, q24, . . . , q2,n are measured and tabulated. the measurement procedure is repeated until electrode n − 1 is energized or excited. using the measured values of the charge, the inter-electrode capacitances cij= cji (with earthed screen) can be calculated using the definition of the capacitance [9-11]: ��� = ���/δ �� (1) where qij is the induced charge on the electrode j when the electrode i is energized or excited with a known value of voltage. vij is the voltage between electrodes i and j (δvij = vi – vj). it is a known factor that the capacitance is dependent on the geometry of the electrode and the earthed screen. this can be determined once the size, screen diameter, and location of the electrodes and the permittivity distribution ε(x, y) is known. a change in the permittivity distribution effects the capacitance measurements and the values of capacitance change accordingly. the excitation switching of the electrodes in a sequence produce a rotating electric field inside the typical ect sensor. it should be noted that the excitation potential is also time varying with a frequency around 1 mhz. for this surrounding situation and the dimension of the ect sensor and its screen along with the wavelength involved, the electrostatic field theory yields the potential distribution φ(x, y) inside the ect sensor [12-13]. on solving the poisson’s equation, we get: �� , �� �� , �� = 0 (2) for the boundary conditions applied on the ect sensor headed by the measurement system, the potential distribution φ(x, y) can be computed. the electric field vector e(x, y) and the potential function φ(x, y) are related to each other by: �� , �� = − �� , �� (3) the charge on each of the electrodes, and the interelectrode capacitances, can be calculated using the definition of the capacitance and gauss’s law based on the surface integral given by: q�� = �∆��� � ��� � (4) d is the electric displacement defined by: ! = "� , ���� , �� (5) the material inside the ect sensor has a linear isotropic response [19]. sj is a surface enclosing electrode j, and ds is an infinitesimal area on it. to solve the poisson’s equation and to calculate the capacitances using gauss’s law, a forward model is considered which shows well behaved and response. the verifications of this forward model against measurements exhibits that the predicted capacitances are very accurate. at the same time the permittivity sensitivity as observed in [14], the prediction error may be enlarged for adjacent electrodes, when a high permittivity material is surrounded in their vicinity. more information on the use of finite element modelling (fem) of ect systems can be seen in [15-16]. fig. 3. electrical modeling. consider a model of measured capacitance cm for one pair of electrodes with the effect of the earthed screen. this can be assumed as the combination of an internal capacitance cx, two pipe wall capacitances cw1, cw2, an external capacitance cex, and two stray capacitances cs1, cs2 as demonstrated in figure 3 the equivalent capacitance cm can be calculated mathematically as: w x w x c c m ex c c c c    (6) the values of cex, cw, and cx can be obtained by filling a material of known relative permittivity r1 into the specimen pipe sensor. this procedure is repeated with another material of known relative permittivity r2 and the air. after this, by finding cex and cw, the internal capacitance with any fluid existing inside the region of interest in the pvc pipe can be obtained from the raw measured capacitance. iii. simulation of the 12-electrode ect sensor with earthed screens the simulation was conducted for a cross-sectional circular view point which can be a cylindrical container made up of insulating material. ect is difficult to perform on metallic container as the metals leak the electrical charge all over the surface and allow making wrong assumptions. on an insulating frame, the electrodes are fixed, an earthed screen is mounted around them, and a voltage is applied to it when the current passes through the non-metallic cylinder from inside and through the fluid or gas. this makes a small charge to hold in the fluid or gas and creates a capacitance. when one of the electrodes is excited, the other 11 electrodes will act as grounded, and the 12-ect will be like 11 capacitors along the surface of the cylinder. but since the permittivity and the voltage between the plates are very low and the distance between the electrodes is comparatively big, a very low capacitance could be measured. if the permittivity of the fluid or gas is known and its potential breakdown, an increase in voltage below the breakdown voltage can lead to a better performance of the ect technique. engineering, technology & applied science research vol. 13, no. 4, 2023, 11393-11399 11396 www.etasr.com ghaly et al.: a 12-electrode ect sensor with radial screen for fluid diagnosis the 12-electrode ect simulation was carried out in matlab. the simulation shows that with the existence of the earthed screen, the area of the circumference of the crosssectional area increases. as the number of electrodes is fixed, there will be a little improvement in the coverage of the region under investigation by means of the area for the number of capacitors used, improving the diagnosis of the flow medium in the pipes in the system [15]. the electric potential between the energized electrode 1 and grounded electrodes 2-12 are shown in figure 4. electrode 1 is energized at a low voltage of 0.02 v and the electrode 2 is grounded with some stray charge on it, as the metal electrodes cannot be charged after applying electric field. fig. 4. sensitivity pattern when electric potential is applied between electrodes 1 and 2 at low intensity. (a) (b) fig. 5. sensitivity pattern when the electric potential is applied between electrodes 1 and 11 at (a) normal and (b) low intensity. similarly, electrode 1 is energized at a low voltage of 0.02 v and the electrode 11 which has some stray charge on it, is grounded. the electrode potential for 1 and 11 is illustrated in figure 5. this can be demonstrated for all combinations of 1 to 12 electrodes in the ect sensor. in the simulation, the first electrode is energized and other electrodes are kept at ground, this process is repeated for all electrodes to be energized one after the other in a cyclic manner, keeping the other electrodes grounded. with increase in the number of electrodes, the circumference of the pipe is more covered and a continuity of measurement is achieved near the inner surface area of the pipe. (a) (b) fig. 6. sensitivity pattern map of the electric potential between electrodes (a) 1 and 2 and (b) 1 and 11. fig. 7. summation of the sensitivity pattern due to electrode 1 for all 12 electrodes. engineering, technology & applied science research vol. 13, no. 4, 2023, 11393-11399 11397 www.etasr.com ghaly et al.: a 12-electrode ect sensor with radial screen for fluid diagnosis it is evident from the simulations that mounting an earthed screen covers a comparatively large area. it is also seen that the voltage drops very fast as it moves from one end of the diameter to the other, and the increased distance between the electrodes drops the voltage, but for the electrodes which are placed in adjustment to each other there is a good capacitance response. thus, with an earthed screen, there will be a better accuracy towards the inner side of the pipe near the surface of the pipe compared to the center of the pipe where getting exact accuracy is difficult due to the low voltage measurement and thus the low capacitance measurement. the expected accuracy is more likely to increase with small cross-sectional area pipes compared to that of large cross-sectional area pipes in the system. iv. implementation for sensitivity measurement the ac-ect system comprises of hardware and software, software drivers, and ectgui. the hardware consists of a front-end unit with an internal power supply, and an ni daq board/card interfaced with each other. these are operated by a host laptop or desk top, as illustrated in figures 2 and 8. two ni daq units are employed: ni pci-6024e daq board working with a desktop pc and ni pcmcia 6062e daq card working with a laptop pc. both ni daq units are connected via a 68-way ribbon cable with the same female connectors in the end connecting to the 19" euro case, while a different female connector is used in the other end connecting to either the desktop pc or the laptop pc [17]. fig. 8. typical 12-electrode ect sensor setup and ect system. the experimental results using the 12-electrode ect sensor with and without screen are presented in this section. by quantifying the sensitivity, the accuracy of the sensor depends not only on the physical dimensions of the electrodes, but also on the specifications of the earthed screen. if the tube wall is manufactured using dielectric material, the electrodes can be installed inside or outside it, whereas, if the wall is made up of conductive material, the electrodes can be mounted externally. in the present case, the proposed design is employing dielectric materials, hence the electrodes are put outside the pipe and the earthed screen is mounted around them, thereby availing the simplicity of the design. the choice of the number of electrodes and the outer screen depend on the value of the capacitance, the complexity of the circuit, and the data acquisition rate. in case of using more electrodes, the quality of the image would be better at the cost of increased difficulty in measuring capacitances. commonly, the number of electrodes used is limited to 8 or 12 (in this article 12 electrodes are considered). a guard electrode is needed to improve the sensitivity measurement and to prevent the electric field from reaching the ground and the end of the measuring electrode. also, they must be employed if the length of the measuring electrodes is less than twice the sensor diameter approximately. further, it is essential to add a discharge resistor, in order to avoid the static charge and the damage of a measuring sensor, the resistor should be connected between each electrode and the driven guard and the ground [14]. the typical value of the resistance used is 1 mω. a photo shot of the typically developed prototype using 12 electrodes with earthed screen formed from a copper sheet which is bounded around the radial spacers is shown in figure 8. the images were obtained using the 12-electrode ect sensor having relatively long external measurement electrodes (length and width are 15 cm and 1.1 cm). the gap between the electrodes is 0.20 cm. the external circumference and the outer radius of the pipe are 15.6 cm and 2.48 cm. the inner pipe cross section area is 17.84 cm 2 and the total volume of the ect section (electrode region) is 17.84 cm 2 × 15.6 cm. a. sensitivity of the obtained image at first, in order to calibrate the typically designed sensor, two dielectric materials were taken, where the empty state is assumed to be lentils (density of lentils =46 kg/m 3 ), and the full state is considered as air. then, different amounts of lentils are introduced into the pipe where the air is surrounding the lentils. a set of measurements are obtained for each case. it can be observed that the smallest volume to be detected has a crosssectional area of 1.2 cm 2 (volume = 18 cm 3 ), and mass = 0.83 g). table i. ect images based on different amounts of lentil filling images based on large amount of lentil images based on small amount of lentil 12-electrode sensor with radial screen 12-electrode sensor without radial screen a figure of merit is proposed to describe the sensitivity [18] of the 12-electrode ect sensor with and without a radial screen. a parameter is defined showing the minimum detectable value according to: pos = &1 − ∆�( )*+ ),-,./ 0 × 100 (7) where pos is the percentage of sensitivity, ∆�( is the difference between the dielectric constants of the full and empty state, 23 is the minimum detectable volume of the object, and 45467 is the total volume of the ect sensor. in the engineering, technology & applied science research vol. 13, no. 4, 2023, 11393-11399 11398 www.etasr.com ghaly et al.: a 12-electrode ect sensor with radial screen for fluid diagnosis present case, lentil is the dielectric: ∆�( = 6. from the dimensions indicated above, and to calculate the sensitivity, referring to (7), pos equals to 59.6% with a radial screen and to 50.1% without radial screen. table i illustrates the obtained images based on different amounts of lentil searching for the minimum detectable volume of the objects � 23 �. b. image accuracy in the beginning, the calibration of the sensor was performed to measure its accuracy and authenticity. it is achieved by taking two different dielectric materials with the empty state as air, and the full state as lubricating oil (density = 823 kg/m 3 ). the amount of lubricating oil introduced in the sensor pipe is such that when the pipe is kept horizontally, it is half filled with the lubricating oil. figure 9 shows that the separation line between the lubricating oil and the air is deviating from a sharp line. the gradual change from blue color (air) to red color (lubricating oil) is an indication of the accuracy of the sensor with and without earthed screen and their difference. to quantify the accuracy of the ect sensor, the parameter poa (percentage of accuracy) is proposed as [18]: poa = ;1 − <=>? @a=bc>?dd=efg? h=fe?@?ij × 100 (8) in the present case and from figure 9, the poa is equal to 87%. figure 9 illustrates the use of 12-electrode ect sensors with and without an earthed screen in which line separation between the two different dielectric materials (lubricating oil and air) when the pipe is placed horizontally is demonstrated. fig. 9. the line separation between the two different dielectric materials with and without screen. v. discussion in this work, two new parameters, pos and poa, were defined with the aim to charactarize the quality of an ect image using an 12-electrode ect sensor with and without an earthed screen. from the conducted experiments, it is concluded that the use of outer earthed screen gives more accuracy and more sensitivity to the measurements. these conclusions were met while keeping the same gap between the electrodes and for the same cross-sectional area. the percentage of accuracy (poa) with radial screen is found be equal to 87%, whereas, without radial screen it lies below 84%. the percentage of sensitivity (pos) with a radial screen yields to be 59.6% and 50.1% without a radial screen. vi. conclusion in this paper, simulations and practical measurements of an ect sensor with 12 external electrodes with and without an outer screen were presented. from the simulations, it is evident that a mounted earthed screen covered a comparatively large area. it was also seen that the voltage drops very fast when moving from the one end of the diameter to the other. the experimental measurements were carried out on two different materials filling the space inside the pipe with different proportions in order to know the sensitivity of the measurements and the accuracy of the probe. the obtained images using the 12-electrode ect sensor with and without an earthed screen, with a line separation between the two different dielectric materials gave a little improvement in the quality of the images produced by developed sensor with a radial screen. acknowledgement this project was funded by the national plan 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[19] p. kshirsgar, "a robust noise reduction strategy in magnetic resonance images," annals of the romanian society for cell biology, vol. 25, no. 6, pp. 3938–3952, may 2021. microsoft word etasr_v13_n4_pp11078-11084 engineering, technology & applied science research vol. 13, no. 4, 2023, 11078-11084 11078 www.etasr.com gutipadi et al.: comparison of pulse width modulation techniques for diode-clamped and cascaded … comparison of pulse width modulation techniques for diode-clamped and cascaded multilevel inverters kishor gudipati e.e.e department, g.pulla reddy engineering college, india gudipatikishor@gmail.com (corresponding author) harsha vardhan reddy maramreddy e.e.e department, g.pulla reddy engineering college, india maramreddyharsha@gmail.com sri gowri kolli e.e.e department, g.pulla reddy engineering college, india gowrivasu.3@gmail.com vuyyuru anantha lakshmi e.e.e department, g.pulla reddy engineering college, india v.al@rediffmail.com girireddy sreenivasa reddy e.e.e department, g.pulla reddy engineering college, india nivasa7hills@gmail.com received: 11 april 2023 | revised: 29 april 2023 | accepted: 5 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5939 abstract multilevel inverter technology has become the most significant method of energy conversion from dc to ac for uninterrupted power supply. the quality of the power supply depends on the appearance of harmonics, which is considered a problem that needs to be overcome. this paper demonstrates the use of a new modulation technique to reduce the harmonics in both diode-clamped and cascaded multilevel inverters, examining its total harmonic distortion (thd) compared to other pwm methods. simulations were carried out in matlab/simulink for five-level diode-clamped and cascaded multilevel inverters. the simulation results of both multilevel inverters using the sinusoidal pwm, modified reference pwm, modified carrier pwm, and modified reference and modified carrier pwm methods showed that the latter had the best thd performance for both inverter types, especially for the cascaded multilevel inverter. keywords-harmonics; multi level inverter (mli); pulse width modulation (pwm) i. introduction the rapidly expanding field of multilevel power conversion technology in power electronics offers great potential for development. a new breed of multilevel inverters has emerged as a possible alternative to handle high voltage levels. the appropriate multilevel inverter for each application is not always obvious, as it depends on several agile methodologies. multilevel inverters (mlis) bring the output waveform closer to a sinusoidal waveform, minimizing total harmonic distortion (thd). core inverter designs include flying capacitor cascaded and diode-clamped circuits to get beyond the solid-state switching device rating restrictions and facilitate the adoption of multilevel inverter topologies in higher-voltage systems. a design feature of multiple voltage source inverters enables them to achieve high voltages with low harmonics without relying on transformers. the primary function of a multilayer inverter is to combine many layers of dc voltages to produce the desired ac voltage. table i shows that to accomplish the same number of voltage levels, inverters need an equal number of main switches and main diodes. as cascaded inverters do not require clamping diodes, they have the smallest component count [1-12]. engineering, technology & applied science research vol. 13, no. 4, 2023, 11078-11084 11079 www.etasr.com gutipadi et al.: comparison of pulse width modulation techniques for diode-clamped and cascaded … table i. switches for different multilevel inverters types of switches diode clamped mli capacitor clamped mli cascaded mli clamping diodes (n-1)*(n-2) 0 0 balancing capacitors 0 (n-1)*(n-2)/2 0 main diodes 2(n-1) 2(n-1) 2(n-1) dc bus capacitors (n-1) (n-1) (n-1)/2 main switching devices 2(n-1) 2(n-1) 2(n-1) ii. different multilevel techniques a. diode clamped inverter (dcmli) in a dcmli, the diode acts as the clamping device to reach stages in the o/p voltage, which makes it a unique mli when compared with other topologies. in an m-level diode-clamped inverter, the voltage over each capacitor is vdc/m-1. the phases are connected to a number of capacitors via the diode-clamped inverter, which produces multiple voltage levels, whether or not each action-switching device prevents vdc/m-1 [13-23]. b. cascaded multilevel inverter (cdmli) the flexibility of this arrangement facilitates maintenance and provides a straightforward method of system redundancy. cdmli is a combination of h-bridges that are connected in series. an n-level h-bridge mli has two (n-1)/2 switches, which are series-connected phases. a single phase makes up each cell. therefore, the requirement is four active switches in each cell, which can generate three voltage levels: 0, vdc/2, and –vdc/2. attaching all cells in a cascade will result in voltage stages, with the cell voltages added together making up the phase voltage van=v1+v2+v3+… +vn [24-31]. iii. different modulation techniques there are several different types of modulation techniques to generate pulses to trigger the switches of an inverter. a. sinusoidal pulse width modulation (spwm) in spwm, a high switching frequency carrier wave signal, i.e., a triangular wave signal, is compared with the reference sinusoidal signal. fig. 1. sinusoidal reference comparison with normal triangular waves. spwm modulates one sinusoidal signal with many triangular carrier signals [32-46]. the carriers' peak-to-peak amplitudes (ac) and frequencies (fc) are identical. the zero references of the carrier set are situated in the middle. a switch is triggered if the modulating signal is greater than the triangle carrier assigned to it [47]. b. modified reference pulse width modulation (mrpwm) in the general sinusoidal pwm approaches, for example at 2-level inverters, every phase voltage is set parallel to that of the triangular carrier signal, to generate the voltages [48]. to get the maximum of the common-mode voltage, voffset1 is connected to the phase voltages [49-50], therefore: �������� = (�� ������) � (1) while a reference phase voltage is measured throughout a sample, three recommended phase voltages are measured within a sampling time. vmax is the voltage at the maximum point and vmin is the voltage at the minimum point. when the commons mode voltage, voffset1, is included, the effective inverter switching vectors are minimal in a sample period. fig. 2. modified reference comparison with normal triangular waves. c. modified carrier pulse width modulation (mcpwm) figure 3 shows the carrier vertical offset for mli using the modified carrier technique. fig. 3. sinusoidal reference comparison with modified carrier waves. the source sine wave is positioned in the center of the four triangular carriers, which can be observed to be overlapped. each triangular wave is compared with the reference signal and, hence, the triggering pulses are generated. d. modified reference and modified carrier pulse width modulation (mrcpwm) figure 4 shows the carrier vertical offset mli using the modified reference and modified carrier technique. the four carriers may be observed to be overlapping, and a modified sine wave (or third harmonic wave) is positioned in the middle engineering, technology & applied science research vol. 13, no. 4, 2023, 11078-11084 11080 www.etasr.com gutipadi et al.: comparison of pulse width modulation techniques for diode-clamped and cascaded … of the four. each triangular wave is compared with the reference signal and, hence, the triggering pulses are generated. fig. 4. modified reference comparison with modified carrier waves. iv. simulation results for diode-clamped mli a. sinusoidal pwm (spwm) figures 5 and 6 show the line voltages and the fft analysis obtained from a diode-clamped five-level inverter using the spwm technique to trigger its switches. the obtained thd percentage was 18.09%. fig. 5. line voltages of diode-clamped mli with spwm. fig. 6. fft analysis of diode-clamped mli with spwm. b. modified reference pwm (mrpwm) figures 7 and 8 show the line voltages and the fft analysis obtained from a diode-clamped five-level inverter using the mrpwm technique to trigger its switches. the obtained thd was 13.20%, which was lower than the obtained for the same inverter with spwm. fig. 7. line voltages of diode-clamped mli with mrwm. fig. 8. fft analysis diode-clamped mli with mrwm. c. modified carrier pwm (mcpwm) figures 9 and 10 show the line voltages and the fft analysis obtained from the diode-clamped five-level inverter using the mcpwm technique to trigger its switches. the obtained thd was 11.10%, which was lower than those obtained for the same mli type with spwm and mrpwm. fig. 9. line voltages of diode-clamped mli with mcpwm. d. modified reference and modified carrier pwm (mrmcpwm) figures 11 and 12 show the line voltages and the fft analysis obtained from the diode-clamped five-level inverter using the μrmcpwm technique to trigger its switches. the obtained thd was 10.22%, which was lower than those obtained for the same type of mli with the other techniques. v. simulation results for cascaded mli a. sinusoidal pwm (spwm) figures 13 and 14 show the line voltages and the fft analysis obtained for the cascaded five-level inverter using the engineering, technology & applied science research vol. 13, no. 4, 2023, 11078-11084 11081 www.etasr.com gutipadi et al.: comparison of pulse width modulation techniques for diode-clamped and cascaded … spwm technique to trigger its switches. the percentage of thd obtained was 17.47%. as this pwm technique for the diode-clamped mli obtained 18.09% thd, this technique worked better for cascaded mli. fig. 10. fft analysis of diode-clamped mli with mcpwm. fig. 11. line voltages of diode-clamped mli with mrmcpwm. fig. 12. fft analysis of diode-clamped mli with mrmcpwm. fig. 13. line voltages of cascaded mli for spwm. fig. 14. fft analysis of cascaded mli for spwm. b. modified reference pwm (mrpwm) figures 15 and 16 show the line voltages and the fft analysis obtained for the cascaded five-level inverter using the mrpwm technique to trigger its switches. the thd obtained was 13.08%, showing that this technique also worked better for cascaded mli. fig. 15. line voltages of cascaded mli with mrpwm. fig. 16. fft analysis of cascaded mli with mrpwm. c. modified carrier pwm (mcpwm) figures 17 and 18 show the line voltages and the fft analysis obtained for the cascaded five-level inverter using the mcpwm technique to trigger its switches. the thd obtained was 11.05%. d. modified reference and modified carrier pwm (mrmcpwm) figures 19 and 20 show the line voltages and the fft analysis obtained for the cascaded five-level inverter using the engineering, technology & applied science research vol. 13, no. 4, 2023, 11078-11084 11082 www.etasr.com gutipadi et al.: comparison of pulse width modulation techniques for diode-clamped and cascaded … mrmcpwm technique to trigger its switches. the thd obtained was 10.14%, which is smaller compared to the result when using the same pwm technique for the diode-clamped mli. therefore, this technique works better for cascaded mli. fig. 17. line voltages of cascaded mli with mcpwm. fig. 18. fft analysis of cascaded mli with mcpwm. fig. 19. line voltages of cascaded mli with mrmcpwm. fig. 20. fft analysis of cascaded mli with mrmcpwm. vi. results and discussion table ii demonstrates the performance of the diodeclamped multilevel inverter in terms of thd using the spwm, mrpwm, mcpwm, and mrcpwm techniques. this table clearly shows that of all the mentioned pwm techniques, the mrcppwm technique worked better, as its thd percentage was lower. the lower the thd percentage, the higher the quality of power delivered by the inverter. table ii. dcmli thd results dcmli (diode clamped multilevel inverter) switching frequency(hz) sinusoidal pwm (% thd) mrpwm (%thd) mcpwm (%thd) mrcpwm (%thd) 1khz 23.54 18.40 16.2 14.13 5khz 20.01 15.14 13.0 11.12 10khz 18.09 13.20 11.1 10.22 table iii demonstrates the performance of cascaded mli in terms of thd using spwm, mrpwm, mcpwm, and mrcpwm. this table clearly shows that of all the mentioned pwm techniques, the mrmcpwm worked the best, as its thd percentage was lower for the cascaded mli. the cascaded mli is a widely used inverter where a small decrease in its thd makes the inverter suitable for wide applications. the power quality obtained by lowering the thd percentage in cascaded mli can fill the gap in many power quality issues. table iii. cdmli(cascaded multilevel inverter) cdmli (cascaded multilevel inverter) switching frequency(hz) sinusoidal pwm (% thd) mrpwm (% thd) mcpwm (% thd) mrcpwm (% thd) 1khz 23.00 18.30 16.0 13.92 5khz 19.89 14.52 12.7 11.01 10khz 17.47 13.08 11.0 10.14 table iv demonstrates the thd of both the cascaded multilevel and the diode-clamped inverters using mrmcpwm. the results show that the mrmcpwm is the best pwm technique compared to conventional pwm techniques. moreover, the higher the switching frequency, the lower the harmonics were observed for both inverter topologies. the lower harmonics in the power supply improved power quality, which affects the torque produced in motor drives. furthermore, the efficiency and life span of any motor drive is directly proportional to the quality of the power supplied to it. table iv. modified reference and modified carrier pwm (mrcpwm) switching frequency(hz) diode clamped mli (thd in %) cascaded mli (thd in %) 1khz 13.92 13.45 5khz 11.12 11.01 10khz 10.22 10.14 it should be noted that for both inverters with different pwm techniques, a resistive load of 10ω was taken, the modulation index was 0.8, and the dc link voltage was 400v. engineering, technology & applied science research vol. 13, no. 4, 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[50] r. teodorescu et al., "multilevel converters: multilevel converters," in epe’99 : european conference on power electronics and applications, lausanne, switzerland, sep. 1999. microsoft word 41-3648_s_etasr_v10_n4_pp6131-6141 engineering, technology & applied science research vol. 10, no. 4, 2020, 6131-6141 6131 www.etasr.com fouzia et al.: robust adaptive tracking control of manipulator arms with fuzzy neural networks robust adaptive tracking control of manipulator arms with fuzzy neural networks madour fouzia department of electronics university of ferhat abbas setif, algeria madour_fouzia@yahoo.fr nabil khenfer department of electronics university of ferhat abbas setif, algeria khenfer_n@yahoo.fr naceur-eddine boukezzoula department of electronics university of ferhat abbas setif, algeria nasrbou@yahoo.fr abstract—the learning space for executing general motions of a flexible joint manipulator is quite large and the dynamics are, in general, nonlinear, time-varying, and complex. the objective of this paper is to design a nonlinear system based on the fuzzy neural network control using supervised training, into executing reference trajectories by a flexible joint manipulator. the structure identifications of controller networks are performed by using the adaptive neural fuzzy inference system (anfis), with new parameters and weight coefficients automatically adapted and adjusted, in order to decrease position tracking errors. in order to adapt and reduce the number of undefined parameters in the network, a new technique is used. reported research works use the euler method for the resolution of the arm's dynamic function, in this paper, a more exact method was used, represented by the fourth-order runge-kutta (rk4) method. a comparative study has been carried out between these two methods in order to prove the effectiveness of the later. finally, in order to test the robustness of the proposed approach, it was also investigated considering parameter variations. the tracking speed of the model on the system control accuracy was also analyzed. the simulation results show that the proposed approach has a good tracking effect. keywords-adaptive neuro fuzzy interface system (anfis); fuzzy neural network (fnn) control; manipulator robot; supervised training; trajectory tracking; robustness i. introduction robotic manipulators have reshaped industrial processes. pressing requirements of improved and enhanced productivity in industrial applications have necessitated the deployment of robots to automate tasks [1]. some of the most common tasks for which robots are designed to are: transportation and material handling [2, 3], assembly and manufacturing [4], and point and arc welding [5, 6]. robotic manipulators can be categorized as rigid or flexible. rigid manipulators increase tensile strength with more precision due to the materials used such as steel or aluminum frames but have high cost and weight [7]. the advancements in material technology have enabled us to acquire low cost and weight flexible joint robotic manipulators, but quite often an oscillation is produced throughout the manipulator arm, posing a great challenge in terms of manipulator’s control [8]. linear control techniques (e.g. proportional-integral-derivative (pid)) are valid when a robot moves slowly and can be modeled by linear differential equations with constant coefficients [9]. the linear control fails when there is a need to tackle complex system dynamics [8], nonlinearities and parameter changes in the control laws, which require robust or adaptive control laws to handle the trajectories [9]. many nonlinear control strategies have been developed to deal with the nonlinearities present in the system, such as robust control [10], optimal control [11], adaptive control [12], nonlinear control [13, 14], and intelligent control [15]. in [9], authors present a systematic review of control strategies for multi-degree of freedom (dof) robotic manipulators, using one of the most commonly used modeling formulas, euler lagrange. a review of modeling of serial articulated robotic arms was recently presented in [7]. kinematics is usually derived using denavit-hartenberg (d-h) parameters. the problem of robust control law design for accurate trajectory tracking of a flexible joint manipulator is addressed in [14], by considering joint flexibility and actuator dynamics. the system’s model has been derived using the euler-lagrange approach. authors in [16] proposed an iterative control law to regulate the set-point of a flexible robotic system that is driven electrically and is subjected to model uncertainty. most of the reported techniques suffer from limitations related to the level of complexity resulting from iterative differentiations of nonlinear virtual functions and thus leading to complex and computationally expensive algorithms. the arm positioning is commonly performed by a fuzzy controller. regarding the fuzzy logic control, it incorporates in a control system the way human beings think. through fuzzy technology, the human operator experience, which controls processes and industrial plants, is captured in order to be included in computerized controllers with the same or better performance than humans. the fuzzy control does not need mathematical modeling of the process, but the modeling of actions from the knowledge of a specialist, using linguistic terms, i.e. verbal descriptions. moreover, fuzzy controllers also handle linear and nonlinear systems and are able to control complex multivariable systems [17]. but the fuzzy controller is unable to learn, in contrast to the neural networks. with favorable generalization ability and relatively simple structure, a neural network is not involved with complicated mathematical calculations and is characterized as the approximation to any nonlinear function with arbitrary precision [18]. therefore, it can be combined in many aspects corresponding author: madour fouzia engineering, technology & applied science research vol. 10, no. 4, 2020, 6131-6141 6132 www.etasr.com fouzia et al.: robust adaptive tracking control of manipulator arms with fuzzy neural networks of nonlinear research. from another point, the neural networks need minimum information to perform learning [19]. for that reason, we have used the hybridization of these two approaches in order to exploit their advantages. this hybridization allowed us to improve the performance of the network controller and achieve satisfactory results through online learning [20, 21]. the dynamics of a robot manipulator are, in general, nonlinear time-varying and complex [22]. therefore, most controllers are not able of effectively controlling movements of a flexible joint manipulator under different distance, velocity, and load requirements [23], and the use of a complicated nonlinear dynamic model makes real-time implementation difficult [24]. moreover, it is by no means an easy task to identify the model parameters accurately. in this work, two network controllers based on fuzzy neural network control using supervised training are proposed, where each network will control one joint of the arm manipulator with two dof. parameters and structure identifications of network are necessary in any modeling which aims to achieve a generalized model. anfis employs well-known parameter-identification techniques [25], where the determination of the optimal number of fuzzy rules will be determined by the identification scheme of the structure [26]. for most of fuzzy controllers, the rule composition is very difficult, it needs experts’ knowledge or perspective insight of system behavior [27]. we propose a solution based on supervised training, where each synaptic weight between the third and the fourth hidden layer of each controller network represents a fuzzy rule [20]. there are several learning algorithms. they can be classified into two main categories: supervised and unsupervised. in unsupervised learning, the system learns about the pattern from the data itself without a priori knowledge. on the other hand, supervised learning is guided learning, i.e. when the network is formed it compares the input and the desired result which is represented in our case by the reference joint. however, in this case, new parameters and weight coefficients are automatically adapted and adjusted, through online error learning, in order to decrease the position tracking error. meanwhile, the control system is analyzed. one of the major difficulties of this learning type is the local minimum error [28]. in order to overcome this problem, changes in the parameters of the learning law such as the learning step can be carried out. in the process, the resolution of the arm's dynamic function was performed by two comparative methods, rk4 and euler method. finally, control laws were subjected to various test inputs in a simulation to characterize the tracking performance, and some results are illustrated to show the validity of the proposed approach. ii. proposed approach in this approach, the fuzzy system is used to represent the abstract controller program, and the neural network is used to manage the parameters specifying the fuzzy rules, using learning and knowledge of sampled movements [18, 29]. the fuzzy system encodes knowledge by qualitative rules rather than a precise quantitative description [30]. however, the use of fuzzy qualitative rules is more effective and tends to cover a wider learning space. the fuzzy neural network (fnn) controller shown in figure 1 modulates the motion command via sensory feedback and uses the resultant signal to move the robot manipulator. first we have a reference movement block. this movement is defined by the angle and the angular speed assigned to each articulation of each rod of the manipulator arm. these sampled data are then processed in parallel by two fnn controllers to produce two outputs, torque �� and torque ��, applied to the manipulator arm which is simulated by its dynamic function. finally, a sensory feedback is carried out in order to calculate the error in position and angular speed. proper learning process is also imperative for determining the weights in the networks. parameters specifying the fuzzy rules for governing sampled movements are stored and manipulated by the n6eural network to process a wide range of movements. fig. 1. diagram block of robot learning control. the success of the proposed scheme depends on designing the fnn to generate proper motion commands for various motions. as indicated in the block diagram in figure 1, we use the feedback error of position (�) and error of velocity (��) between the reference and actual joints, denoted as: � � �� ∑ ��� ��� � �� (1) �� � �� ∑ ��� ���� � � �� (2) the performance of the trained model is evaluated while decreasing the error between the reference trajectory and the trajectory tracked by the robot manipulator where n represents the number of training examples. iii. controller design a fuzzy neural system is a fuzzy system presented in the network architecture. parameter identification of the fuzzy system is performed by an automatic learning technique of an adaptive neural network [21, 31]. anfis is one of the wellknown neural fuzzy approaches and it has shown good results in the modeling of complex non-linear problems [20, 21]. it must be noted that the application of anfis is not limited only to systems difficult for modeling, but we can also use this method to design controllers easier. different learning techniques have been developed for the tuning of the inputs and consequent parameters in the anfis [32, 33]. in this study, the fnn system employed the learning, because it is the most engineering, technology & applied science research vol. 10, no. 4, 2020, 6131-6141 6133 www.etasr.com fouzia et al.: robust adaptive tracking control of manipulator arms with fuzzy neural networks appropriate method for the anfis architecture. an initial takagi-sugeno (t-s) fuzzy inference system [34] is developed by defining the input and output membership functions. the determination of the optimum number of rules is very important in fuzzy modeling, it can be determined by a structure identification scheme [26], and the parameters of the initial fuzzy inference system are tuned in anfis architecture. finally, the performance of the trained model is evaluated while decreasing the error between the reference trajectory and the trajectory tracked by the robot manipulator. as mentioned above, two network controllers are proposed in this study, where each fnn system is implemented as shown in figure 2. the parameters of fuzzy reasoning are expressed by the connection weights or node functions of the neural network [35]. in figure 2, the inputs of the fnn are the reference position and the velocity trajectories of a sampled motion, and the output is the motion command. the reason of choosing this structure is that the numbers of fuzzy rules and membership functions for input and output are pre-specified in this type of fnn. thus, for various motions there are the same numbers of fuzzy parameters with the same attributes. consequently, these fuzzy parameters are appropriate to be generalized by the neural network in order to deal with a motion. fig. 2. the structure of the fnn. the structure adopted of each fnn, consists of five layers of nodes, which are of the same type within the same layer. each of the five layers performs one stage of the fuzzy inference process, as described below: a. layer 1 this layer is the input layer, and inputs are transmitted to the next layer directly without any calculation. in figure 2, we can see two input nodes ��� and ���� of motions of a single dof. b. layer 2 each input node in this layer is an adaptive node which produces the membership grade of linguistic label. it is a fuzzy layer. each node � in this layer has a node function ���. ��� � � �� � �� � ��� �� ����� �� � ∶ � → #0, 1' (3) where � is the degree of the gaussian membership function, � is the input to the node j, ( is the center of membership functions, and ) the width of membership functions. in this paper, it is chosen that ���, ���� and the torque � have the same kind of membership function, where � is composed by seven fuzzy subsets, nb, nm, ns, ze, ps, pm, pb: n represents negative, p positive, s small, m medium , b large and ze zero. ��� and ���� are composed by five fuzzy subsets, as shown in figure 3, which implies 5×5 = 25 nodes in the rule layer. fig. 3. degree of membership functions. c. layer 3 this layer is intended for the implementation of the fuzzy rules. each node in this layer corresponds to a rule, which is defined as a fuzzy conditional statement of the form rule [36, 37]: if x is a and y is b then z is c where x and y are fuzzy sets representing the inputs ��� and ���� . z represents the output τ, and a, b, and c represent linguistic variables. in this layer, the membership functions are multiplied and the output is: o+, � μ x�. μ y� (4) where � �� and � 0� denote the degree of membership functions. a control rule for each network is described as follows: if 12345 is nb and 1� 2345 is nb then 65 is nb. d. layer 4 in t-s model approach, the output model is a combination of the input variables according to fuzzy rules. the use of this model allows us to obtain an output according to the input variables [17, 34]. the fuzzy rules are structured as follows: 78 ∶ 94 : �� ;� <= >�8 ? & … & # � � ;� <= > �8 ' bc3d 08 ;� � �e8 f ��8 �� ;� f � g8 � g ;� i = 0, 1, … , nr, (5) engineering, technology & applied science research vol. 10, no. 4, 2020, 6131-6141 6134 www.etasr.com fouzia et al.: robust adaptive tracking control of manipulator arms with fuzzy neural networks where 78 is the i-th inference rule, �� the j-th input variable, >� the fuzzy set defined on the universe of discourse of the variable ��, used in i-th inference rule, 08 is the output of the ith input/output (i/o) local model, hi is the number of fuzzy rules, and p � # a�a� … alm b�b� … blo c�c� … clq' are parameters of i-th i/o local model. so the output of this layer is: o+r = τ+ = o+,. f+ = o+,. ( p+.qvwx + q+.q� vwx + r+) (6) where z� represents the t-s function, �� , �, and i� are the consequent parameters [38]. according to several studies, the synaptic weights between the hidden layers have no physical significance. in this work, through the network architecture we can take the synaptic weights between the second and the third hidden layer in the form of the consequent parameters of the t-s function. table i. rule bases for fnn-1 1�234[ 1234[ nb nm ze pm pb nb ze ps nb nb nb nm ps ns ze ps nm ze pm nb pb pm pb pm pm ze nm nb ps pb ns ns pb pb ze table ii. rule bases for fnn-2 1�2345 12345 nb nm ze pm pb nb nb ze pb ns ns nm ns ps pm nb ze ze pm pm ps pb ze pm nm nb ps ns nm pb pb pm pm ze ps e. layer 5 for given values of the input variables ��(;), the final output of the fuzzy plant model 0\ is inferred by taking the weighted average of the local model outputs 08 [39]. 0\(; + 1) = ∑ ]^ ._^`a^bc d�(e)f.g^(e)∑ _^`a^bc d�(e)f (7) �8d�(;)f = ∏ ��8 ���� � ��(;)� (8) μidx(k)f denotes the membership functions of the fuzzy set >�8, and k8 denotes the gravity centers of the output fuzzy sets associated with each rule. it means that a local model in the consequent part of each fuzzy rule describes each operation of the arm manipulator depending on the input values. in this layer only one node is needed for a single motion command τ. ��l = 6 = ∑ ] ̂mnon∑ mnpn = ∑ ]^ mnp�nn∑ mnpn because the number of rules in layer 3 is pre-specified by the number of nodes, and weights for the input and output layer are fixed, the parameters to learn in the fnn are the modifiable weights present on the input links to the rule layer and the output membership layer and the consequent parameters of the t-s function. iv. supervised training method the purpose of learning in an fnn controller is to adapt these synaptic weights, in order to generate a control vector τ corresponding to a sampled movement. during learning, an error rate related to the resultant motion is back-propagated to adjust the parameters from layer to layer sequentially [40, 41]. the error rate can be obtained by differentiating the error between the reference motion and the actual motion relative to the motion command. the training adopted for this error is the supervised training; this method is widely applied in minimization problems, optimal control, parameter identification, neural network training, etc. [42]. the adaptation law of the weights is: q8�e (r + 1) = q8�e (r) − μ . s�(t)st^nu(v) +w.�q8�e (r)− q8�e (r − 1)� 0 ≤ w < 1 (10) where q8�e (r) is the weight between the neuron j in layer ; and the neuron < in layer (k-1), r is the index of iteration, w is the momentum, and � the learning step. the output of the neuron j in layer ; is given by: 0�e(r) = z�z�e(r)� (11) z�e(r) = ∑ q8�e e8�� .08e��(r) (12) the connection weights are adjusted so that the feedback error �({) is minimized: �(q) = ��∑ ( ��� |� − 0�)� (13) where z is the neuron activation function, z�e(r) the input of neuron j, h; the number of corresponding neurons, n the number of training examples, |� the reference output, and 0� is the actual output. we use the feedback error to derive the error rate }�(q) }q8�e (r)⁄ . s�(t)st^nu (v) = s�(t)sgnu(v) . sgn u(v) st^nu (v) (14) ����(�)�t���(�) = ����n u(v)� �t���(�) = z�z�e(r)� . ��� �(�) �t���(�) (15) and ����(�)�����(�) = s∑ t^n u`u^bc . gû�c(v)st^nu (v) = 08e��(r) (16) so: sgnu(v)st^nu (v) = z�z�e(r)� . 08e��(r) (17) substituting the results obtained in (17) into (14) the derivative of the error rate is obtained as: engineering, technology & applied science research vol. 10, no. 4, 2020, 6131-6141 6135 www.etasr.com fouzia et al.: robust adaptive tracking control of manipulator arms with fuzzy neural networks s�(t)st^nu(v) = s�(t)sgnu(v) . z �z�e r�� . 08e�� r� (18) now by simply choosing: z�e r� � � s� t�sgnu v� . z �z�e r�� (19) the second term at the right side of (18) satisfies: s� t� st^nu v� � �z�e r� . 08e�� r� (20) finally, we get: q8�e r f 1� � q8�e r� f μ z�e r� . 08e�� r� fw �q8�e r� � q8�e r � 1�� (21) this final function represents the adaptation law of the weights used in the fnn controller. v. simulation to demonstrate the effectiveness of the proposed approach, a two-joint robot manipulator was used [43]. the dynamic equations for this planar manipulator of 2dof as shown in figure 4 are described by the joint positions, velocities, and accelerations as functions of time [44]: ��� = ���. �� f ���. �� � �. ��� f 2. ��. ��� f ���� � ���. �� f ���. �� f �. ��� f �� (22) where q and � are the actual position and velocity vectors and �� and �� are the torques. fig. 4. the flexible robot manipulator of 2dof. in this simulation, the parameters for robot manipulator are given as: ��� = ��. ���� f �� f ��. ��� f ���� f 2. ��. ���. ��= �� f �� ��� � ��. ���� f f�� ��� � ��. ��. ���. ��= � f ��. ���� f �� ��� � ��� (23) � � ��. ��. ���. =<h � �� � ��. ���. �. ��= � f ��. �. ���� . f��. ��= �� �� � ��. ���. �. cos � f �� where � , � are the positions of links, �� , �� are the masses, �� , �� the lengths, �� , �� express lengthwise centroid inertia values, and ��� , ��� are the half lengths. the resolution of the mathematical model with computed torques of the flexible robot manipulator of 2 dof requires transforming them in the form of the following differential functions. for the first joint: ��� �� ��c�v = � �� �v = , ��p�v = ¡c�¢cc.�p£¢.d�p £�.� .�pf�¤c¢c  (24) for the second joint: �� � �� ��c�v � � �� �v � , ��p�v � ¡ �¢ c.�p£¢.�  �¤ ¢   (25) these functions are derived by using two methods, euler, and runge-kutta method [45, 46]. in many cases, differential equation systems can take the form of an ordinary first-order differential equation of the type: ¥�g�v � z r, 0 r��0 0� � 0e 0 x r (26) where 0 r� is the function we are looking for and 0e its initial value. we note h as a step based on the discretization of the variable t, and 0 the approximate value of 0(r ) for the different instant r = h¦. by integrating the differential equation between r and r £� we have the relation: 0 r £� � � 0 r � � § zdr, 0 r�f|rv`¨© v` (27) the idea is to approach this integral with more precision than the euler method. a. euler method coming back to euler's method, the integral in (26) can be approached by the rectangle method on the left (explicit euler), or by the rectangle method on the right (implicit euler). the error produced corresponds to the area of quasi-triangular shape and of dimension h.ph where p is the slope of f at the instant r . so the error is about: �ª ≃ ��¬¦�. improvements to the runge-kutta method of order 2 consist in improving the integral by calculating the area of a trapezoid instead of that of a rectangle. the error is therefore related to the curvature of the function and not to its slope. in order to reduce the error of the later we used the runge-kutta method of order 4. b. runge-kutta method the runge-kutta method of order 4 is an additional step in the refinement of the calculation of the integral (26). instead of using the trapezoid method, we use the simpson method [47]. this consists of replacing the integrated function with a parabola passing through the extreme points and the midpoint. we have: engineering, technology & applied science research vol. 10, no. 4, 2020, 6131-6141 6136 www.etasr.com fouzia et al.: robust adaptive tracking control of manipulator arms with fuzzy neural networks § z(�)|� ≃ ­�®¯­® °z ±� f 4z �®£­� � f z ³�´ (28) applied to the integral (26), this gives: § zdr,0(r)f|r ≃ µ̄v`¨c v` °zdr ,0(r )f + 4z�r £�/� ,0dr £�/� f� +zdr £� ,0(r £� )f? hence the relationship: 0 £� = 0 + µ̄ :z(r ,0 )+ 4zdr £�/� ,0 £�/� f +z(r £� ,0 £� )' (29) here, a difficulty appears because the equation presents two unknowns: 0 £�/� and 0 £� . to make the diagram explicit, we must estimate 4zdr £�/� ,0 £�/� f and z(r £� ,0 £� ) from 0 , r and h. let's start with the term 4zdr £�/� ,0 £�/� f which we break down into two identical terms: 2zdr £�/� ,0 £�/� f + 2zdr £�/� ,0 £�/� f in the first, we replace 0 £�/� by its value deduced from the explicit euler method: 0 £�/�® = 0 + ¦/2.z(r ,0 ). in the second term, we replace 0 £�/� by its value deduced from the implicit euler method: 0 £�/�­ = 0 + ¦/2.zdr £�/� ,0 £�/� f that we will approach 0 + ¦/2.zdr £�/� ,0 £�/�® f. since the implicit and explicit euler methods produce quasi-opposite errors, there is a hope to minimize the error on the calculation of 4zdr £�/� ,0 £�/� f. to summarize, we will write: 4zdr £�/� ,0 £�/� f ≃ 2;� + 2;, {<r¦ ��� �� ;� = z(r ,0 ) ;� = z�r + 12¦,0 + 12¦;� � ;, = z�r + 12¦,0 + 12¦;� � as for the term z(r £� ,0 £� ), we approach it by estimating 0 £� by the midpoint method, i.e. by applying the rectangle method in the middle: 0 £� ≃ 0 f ℎzdr £�/� ,0 £�/� f ≃ 0 f ℎzdr £�/� ,0 £�/�­ f finally we obtain the explicit diagram of runge-kutta of order 4: 0 £� = 0 + ¦ °�̄;� + �,;, + �,;, + �̄;r ´ (30) {<r¦ �� � ��;� = z(r ,0 ) ;� = z�r + ��¦,0 + ��¦;� �;, = z�r + �� ¦,0 + ��¦;� �;r = z(r + ¦,0 + ¦;, ) compared to the rk2 method, this numerical diagram requires the double calculations at each step and therefore longer calculation time, without mentioning the rounding errors which accumulate faster. however, this defect is compensated by a gain in precision. finally, the algorithm developed for this method is: algorithm rk4 1. initialization of step h, of duration t. 2. initialization of the initial conditions 3. definition of the function z(r,0) 4. while r ≤ · do (a) calculate from ;� = z(r,0). (b) calculate from ;� = z�r + �� ¦,0 + ��¦;� �. (c) calculate from ;, = z�r + ��¦,0 + ��¦;� �. (d) calculate from ;r = z(r + ¦,0 + ¦;, ). (e) 0 = 0 + µ̄ #;� + 2;, + 2;, + ;r ';r = r + ¦. (f) save data. finally a comparative study will be carried out between euler's method and runge-kutta method in order to prove the effectiveness of the later. in each fnn controller, we have 2 nodes in layer 1, 10 nodes in layer 2, 25 nodes in layers 3 and 4, and 1 node in layer 5. consequently, a total of 125 parameters must be adapted for each joint during training. because between the second and the third layer we have 5.10=50 synaptic weights, and between the third and the fourth layer we have 25 synaptic weights to adapt, finally each neuron in layer 4 needs three parameters �8, 8 and i8 where �8r = �8 = �8,(�8 + 8 � + i8) . the parameter i8 represents an amplifier of the torque �8 , to simplify the calculation we take i8 = 0 . then total 50+25+50=125 parameters have to be set for each network. moreover, it is by no means an easy task to identify the model parameters accurately [48], but as we mentioned earlier, to adapt and reduce the number of undefined parameters in the network, a new technique is used. generally, for the adaptation of t-s function coefficients we use the genetic algorithm which is an optimization algorithm [32, 49]. in optimization, which is a field of mathematics, the goal is to come up with the member of a set that is the best according to some criterion [50].this method includes several steps and it takes a lot of time and calculations. in order to overcome this problem a new technique is used, with a simple idea: according to several studies, synaptic weights in the fnn controller have no physical significance, while in our work, the coefficients �8 and 8 represent the weights between the second and third hidden layer. this technique allows us to reduce the number from 125 to 75 parameters. the trajectory references tracked by joint-1 and joint-2 are expressed as follows [51]: ¹ ����(r) = �� . sin(2.¼.r) ����(r) = −½� + �� . sin(2.¼.r) r ≤ 3 (31) the simulation results are represented in figures 5-11. in general, several hundred learning tests have been used to learn how to govern a sampled movement. engineering, technology & applied science research vol. 10, no. 4, 2020, 6131-6141 6137 www.etasr.com fouzia et al.: robust adaptive tracking control of manipulator arms with fuzzy neural networks table iii. simulated system parameters variable value ¿� 0.32m ¿� 0.24m ¿�� 0.16m ¿�� 0.12m �� 1.8kg �� 1.2kg ��, �� 0.02kg.m2 � 9.8n/kg fig. 5. tracking position of joint-1 for the initial conditions [ �, ��, ��, �]t=[0.3,0,0,0]: fig. 6. tracking error of joint angle 1. fig. 7. tracking angular velocity of joint-1. fig. 8. tracking position of joint-2 for the initial conditions [ �, ��, ��, �]t=[-1,0,0,0]. fig. 9. tracking error of joint angle 2. fig. 10. tracking angular velocity of joint-2. fig. 11. fnns outputs. 0 0.5 1 1.5 2 2.5 3 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 time (sec) a n g le ( r a d ) q1rk qref1 q1eu 0 0.5 1 1.5 2 2.5 3 -0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 time (sec) e rr o r (r a d ) e rk e eu 0 0.5 1 1.5 2 2.5 3 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 time (sec) v e lo c it y ( ra d /s ) q'1rk q'ref1 q'1eu 0 0.5 1 1.5 2 2.5 3 -2.2 -2 -1.8 -1.6 -1.4 -1.2 -1 -0.8 time (sec) a n g le ( ra d ) q2rk qref2 q2eu 0 0.5 1 1.5 2 2.5 3 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 time (sec) e rr o r (r a d ) e rk e eu 0 0.5 1 1.5 2 2.5 3 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 time (sec) v e lo c it y ( ra d /s ) q'2rk q'ref2 q'2eu engineering, technology & applied science research vol. 10, no. 4, 2020, 6131-6141 6138 www.etasr.com fouzia et al.: robust adaptive tracking control of manipulator arms with fuzzy neural networks in order to solve the dynamic function, a comparative study was carried out between the two methods, the euler method and the rk4 method. the simulation time is r ∈ [0s,2.9s] and the sampling time is 0.01s. according to the simulation results, we can approve the efficiency of the rk4 method as can be seen from figures 5, 7, 8, and 10 where the outputs of the first and second joint can track the reference movements and angular velocity respectively. the output is the position of the manipulator’s end effector which can freely move. due to this flexibility at the joint, oscillations are produced near the ends [8]. vi. test of robustness robust control is an approach to controller design that aims to achieve robust performance and/or stability in the presence of uncertainties in the system [50]. in order to test the robustness of the proposed approach, changes of the weight and the lengths for each joint of the arm manipulator are carried out. also changes in the initial values were affected. table iv. simulated system parameters variable value ¿� 0.40m ¿� 0.30m ¿�� 0.20m ¿�� 0.15m �� 2.0kg �� 1.5kg ��, �� 0.028kg.m2 � 9.8n/kg fig. 12. tracking position of joint-1 for the initial conditions [q1,q2,q3, �]t=[-1.2,0,0,0]. fig. 13. tracking error of joint angle 1. we have chosen another motion execution described as follows [52]: � ���,(r) = −½� + �r . ° 2 .¼. v, − sin�2.¼. v,�´ ���r(r) = �r . ° 2 .¼. v, − sin �2.¼. v,�´ r ≤ 3 (32) fig. 14. tracking angular velocity of joint-1. table v. values of tracking error of joint angle 1 time (s) error with rk4 method (32á) (rad) error with euler method (3âã) (rad) 0.1 -0.3678 -0.3678 0.2 0 0 0.3 0 -0.0001 0.4 -0.0001 -0.0002 0.5 -0.0001 -0.0002 0.6 -0.0001 -0.0003 0.7 0 -0.0005 0.8 0 -0.0012 0.9 -0.0001 -0.0017 1 -0.0002 -0.002 1.1 -0.0003 -0.0019 1.2 -0.0002 -0.0014 1.3 -0.0001 -0.0007 1.4 0 -0.0001 1.5 0 0 1.6 -0.0001 -0.0001 1.7 -0.0005 -0.0009 1.8 -0.0016 -0.0025 1.9 -0.0031 -0.0047 2 -0.0047 -0.0072 2.1 -0.0058 -0.0099 2.2 -0.0052 -0.0119 2.3 -0.0067 -0.0147 2.4 -0.0104 -0.0162 2.5 -0.0116 -0.0163 2.6 -0.0113 -0.0159 2.7 -0.0098 -0.0169 2.8 -0.0136 -0.055 2.9 -0.0012 -0.0009 3 0 -0.0001 the difference between the reference and current trajectory is an input vector to the controller that generates joint rate commands. the simulation results of the proposed approach show the responses of joint positions, and position tracking errors, tracking angular velocities, and the outputs of the fnns, for joint 1 and 2, with different initial conditions. it can be seen from figures 12, 14, and 17 that the outputs of the first and 0 0.5 1 1.5 2 2.5 3 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 time (sec) a n g le ( r a d ) q1rk qref3 q1eu 0 0.5 1 1.5 2 2.5 3 -0.4 -0.35 -0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 time (sec) e rr o r (r a d ) e rk e eu 0 0.5 1 1.5 2 2.5 3 -0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 time (sec) v e lo c it y ( ra d /s ) q'1rk q'ref3 q'1eu engineering, technology & applied science research vol. 10, no. 4, 2020, 6131-6141 6139 www.etasr.com fouzia et al.: robust adaptive tracking control of manipulator arms with fuzzy neural networks second joint can track the reference movements. from figures 6, 9, 13, and 16 can be obtained that with the adaptation of the fuzzy neural network synaptic weights, the system error is gradually reduced. according to the results shown in table v, the average tracking error with the rk4 method is 3.10.10 -3 rad and with euler’s method it is -6.33.10 -3 rad. when the dynamic equations are derived by using the rk4 method, the system control effect is better, and tracking error of joint is smaller. fig. 15. tracking position of joint-2 for the initial conditions [q1,q2,q3, �]t=[0.3,0,0,0]. fig. 16. tracking error of joint angle 2. fig. 17. tracking angular velocity of joint-2. note that the proposed scheme bends the motion tracks near the ends, as shown in figures 7, 10, 14, and 17. this error in speed produces an error in position. this phenomenon occurs because the scheme did not fully accomplish a salient braking in the end of the motion tracking and could be diminished via further learning in motion governing. analogously, the human also demonstrates a similar behavior in performing fast movements: an overshoot in the end of the movement [53, 54]. as can be seen, the motions generated using the proposed approach capture the behaviors of the reference motions well and the simulation results verify the efficiency of the proposed solution. fig. 18. fnns outputs. vii. conclusion this paper presents a solution for the problem of learning and controlling a 2dof industrial manipulator. one of the major problems in applying learning controllers to govern general motions is that the dynamics of robot manipulators are, in general, nonlinear, time-varying, and complex, which makes implementation in real time difficult. to tackle this, we have developed a fuzzy neural network controller by taking advantage of the merits of the t-s fuzzy system and a neural network using supervised training. network parameters and structure identifications were performed by using the anfis system. this design allows new parameters of the controller to be adapted in order to decrease the position tracking errors. in order to solve the dynamic function, a comparative study was carried out between two methods, the euler method and the rk4 method, and 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[54] m. b. ayed, l. zouari, and m. abid, “software in the loop simulation for robot manipulators,” engineering, technology & applied science research, vol. 7, no. 5, pp. 2017–2021, oct. 2017. microsoft word etasr_v11_n2_pp6930-6934 engineering, technology & applied science research vol. 11, no. 2, 2021, 6930-6934 6930 www.etasr.com alshammari et al.: evaluation framework of the deficits and reliability quality measures of … evaluation framework of the deficit and reliability quality measures of the transmission system awad saud alshammari department of electrical engineering college of engineering university of ha'il sa.awwad.0923@outlook.sa tawfik guesmi department of electrical engineering college of engineering university of ha'il t.guesmi@uoh.edu.sa badr m. alshammari department of electrical engineering college of engineering university of ha'il bms.alshammari@uoh.edu.sa rabeh abbassi department of electrical engineering college of engineering university of ha'il r.abbassi@uoh.edu.sa abstract-power system planning faces various issues related to reliability and quality evaluation. the power system network planning is by nature a complex, huge-scale, and mixed-objective optimization problem, especially when concerning its non-linear behavior and the requirements of future unknown loads. in this regard, the electric power utilities attempt to maintain a balance between the generation energy, the transmission capacity, and the needed demand. the main purpose of the current paper is to utilize modern modeling techniques and computational procedures, including the advanced deficit transmission system evaluation method and sparse-matrix network analysis algorithms, in order to evaluate, with sufficient accuracy, the deficit and reliability levels in practical real-life large-scale power systems. the new evaluation methodology is based on three quantities representing the relationship between the generation push in the grid, the maximum limitation of the transmission capacity, and the needed load. the main contribution of the paper is assessing the deficit transmission system index with novel formulas. keywords-reliability evaluation; deficit index; transmission system; quality measures i. introduction the main objective of electric power utilities is to maintain a continuous and sufficient power supply to customers at a reasonable cost [1]. cost-effectiveness, security, adequacy, and reliability analyses of a power system have changed over the years to become a vital branch in today’s highly competitive business environment of power utility planning and operations. reliability and quality are considered two vital measures of power system planning and operational procedures. the engineers and utility technicians seek to design and synthesis a large-scale power system, they consider reliability as one of the key design factors [2-4]. power system development and planning, which include an essential part of reliability and quality assessment, form a complex, large-scale, and multiobjective optimization problem [5, 6], which is related to nonlinear characteristics, future demand uncertainty requirements, and system component availability. the issues of reliability and quality evaluation have seen a growing interest in power system reliability and quality assessment by power utilities and engineers. several authors were involved in the research aiming at conducting reliability and quality assessment in an efficient and accurate manner and with as much realization of the practical circumstances of the power utility as possible. in this regard, the reliability of an electric supply system is defined as the probability of providing the customers with continuous and satisfactory service. generation system reliability indices have been used as a standard for measuring system reliability in [7]. a model was proposed based on a convolutional algorithm that predicts how these indices vary as system annual peak increases. the proposed model was used to calculate and test the same indices of the benghazi north power plant (bnpp) before and after installing additional capacity. a power system by nature is complex, therefore there are multiple random events at different stages of power systems such as uncertainty in customer demand, intermittent outages of power generators and its related units, intermittent electricity production and its impact on the adequacy assessment [8]. therefore, probabilistic methods have given detailed and more realistic information about random events and their negative impact on power system supply and demand. in this direction, an analytical model of the inverse power system reliability evaluation problem was proposed and formulated to find the unknown component reliability parameter (ucrp) [9]. in addition, an application to power system planning was tested to examine the way the component reliability parameters can be modified quantitatively in order to achieve the desired system reliability improvement. the main purpose of this paper is to utilize modern modeling techniques and computational procedures, and focus on the deficit transmission system evaluation method and corresponding author: badr m alshammari engineering, technology & applied science research vol. 11, no. 2, 2021, 6930-6934 6931 www.etasr.com alshammari et al.: evaluation framework of the deficits and reliability quality measures of … sparse-matrix network analysis algorithms, in order to evaluate, with sufficient accuracy, the deficit and reliability levels in practical real-life large-scale power systems. the new evaluation methodology is based on three quantitative parameters of the power network, which are representing the relationship between generation push in the grid, the maximum limitation of the transmission capacity, and the needed load. the main contribution of the current paper is the assessment of the deficit transmission system index with novel formulas. ii. problem formulation a. power system network model the novel framework applied in this paper is based on the original work of [10], in which 3 dimensions were introduced to represent the relationship between certain system generation capacity and the demand. these dimensions relate to the following demand fulfilment issues: • the need of capacity for demand fulfillment. • the existence of capacity (availability for demand fulfillment). • the ability of capacity to reach the demand. the first dimension defines whether or not the capacity is needed, the second one defines whether or not the capacity exists, and the last one defines whether or not the capacity can reach (delivered to) the demand. the 8 possible combinations associated with the 0/1 (yes/no) values of the 3 dimensions, are illustrated in table i. the generation and transmission quality indices are defined in terms of the previously defined 1/0 states indicating the (needed, exists, can-reach) true/false values associated with each quality index. we shall use the symbol qgijk to indicate the generation quality index state. also, in the following expressions, we shall use min{x, y,..., z} to indicate the minimum of x, y, .., z. the notation <x> will be used to denote max {0, x}, i.e. is the maximum of x and zero (= x if x > 0, or 0 otherwise). table i summarizes the considered quality indices, namely the utilized generation capacity (q111), bottled generation capacity (q110), shortfall generation capacity (q101), deficit generation capacity (q100), surplus generation capacity (q011), redundant generation capacity (q010), spared generation capacity (q001) and saved generation capacity (q000). table i. illustration of quality assesement indices not needed (l = 0) needed (l >0) cannot reach can reach cannot reach can reach redundant qg010 surplus qg011 bottled qg110 utilized qg111 exist (c > 0) saved qg000 spared qg001 deficient qg100 short-fall qg101 not exist (c = 0) the evaluation of the above quality indices requires the knowledge of the following data types for the demand and various system facilities: • the value of the demand required to be supplied. • the value of the generation capacity and the maximum site capacity (the limit of potential increase in existing generation capacity). • the value of transmission capacity. b. linear program formulation in the computational scheme of [10], the integrated system quality assessment is performed via solving a master linear programming problem in which a feasible power flow is established which minimizes the total system load not served (lns) subject to capacity limits and flow equations. the master linear program, which utilizes the network bus incidence matrix a, is formulated as: objective function = ( minimize � � ∑ ���� � � � � ) with respect to pl, pg and pt subject to (1) the optimization software package cplex has been used to solve the master linear program. the overall process of the evaluation of power systems reliability and quality measures is summarized in a flowchart shown in figure 1. fig. 1. flow chart of the proposed methodology. c. application of performance quality assessment consider the 3-bus sample power system in figure 2, where a load of 130pu is supplied by two generators that have an available capacity of 170pu. the power system has three transmission lines having an available capacity of 60, 50, and 10pu respectively. for this simple system, the reliability and quality indices can be evaluated as shown in table ii. this paper concerns the indexes related with the deficit of the transmission system.      − =⋅ g l t p p pa 0p,pp lll ≤−≤ 0p,pp ggg ≤−≤ tttt pp,pp ≤−≤ engineering, technology & applied science research vol. 11, no. 2, 2021, 6930-6934 6932 www.etasr.com alshammari et al.: evaluation framework of the deficits and reliability quality measures of … fig. 2. the 3-bus sample power system. table ii. reliability and quality indices for the sample system index q111 q110 q101 q100 q011 q010 q001 q000 value 110 0 0 20 0 0 0 35 d. large-scale implementation on [10], the formulation of 5 reliability and quality performance indices is considered, namely the load notserved (lns), utilized generation capacity (qg111), bottled generation capacity (qg110), surplus generation capacity (qg011), and redundant generation capacity (qg010) are presented while the current research work is concerned with the deficit transmission capacity (qt100) and new formulas are established as follows: if: ∑ �� � � � > ∑ � �� � and [∑ � �� � ∑ � �� � ] ≤ [∑ �� � � � ∑ �� � � � ] and [ ∑ � �� � ∑ � �� � = 0 ] and [∑ � �� � ∑ � �� � ] > [∑ �� �� � � ∑ �� �� � � ] qt100 = [∑ � �� � ∑ � �� � ] [∑ �� �� � � ∑ �� �� � � ] (2) if: ∑ �� � � � > ∑ � �� � and [∑ � �� � ∑ � �� � ] ≤ [∑ �� � � � ∑ �� � � � ] and [ ∑ � �� � ∑ � �� � ≠ 0 ] and ∑ � �� � ≤ ∑ �� �� � � and ∑ �� � � � ≤ ∑ � �� � qt100 = ∑ �� � � � ∑ �� �� � � (3) if: ∑ �� � � � > ∑ � �� � and [∑ � �� � ∑ � �� � ] ≤ [∑ �� � � � ∑ �� � � � ] and [ ∑ � �� � ∑ � �� � ≠ 0 ] and ∑ � �� � ≤ ∑ �� �� � � and ∑ �� � � � > ∑ � �� � qt100 = ∑ � �� � ∑ �� �� � � (4) if: ∑ �� � � � > ∑ � �� � and [∑ � �� � ∑ � �� � ] ≤ [∑ �� � � � ∑ �� � � � ] and [ ∑ � �� � ∑ � �� � ≠ 0 ] and ∑ � �� � > ∑ �� �� � � and [∑ � �� � ∑ � �� � ] ≤ [∑ �� �� � � ∑ �� �� � � ] qt100 = ∑ � �� � ∑ � �� � (5) if: ∑ �� � � � > ∑ � �� � and [∑ � �� � ∑ � �� � ] ≤ [∑ �� � � � ∑ �� � � � ] and [ ∑ � �� � ∑ � �� � ≠ 0 ] and ∑ � �� � > ∑ �� �� � � and [∑ � �� � ∑ � �� � ] > [∑ �� �� � � ∑ �� �� � � ] qt100 =∑ �� �� � � ∑ �� �� � � (6) if: ∑ �� � � � > ∑ � �� � and [∑ � �� � ∑ � �� � ] > [∑ �� � � � ∑ �� � � � ] and ∑ �� � � � ∑ �� � � � ] > [∑ �� �� � � ∑ �� �� � � ] [ ∑ � �� � ∑ � �� � = 0 ] qt100 = [∑ �� � � � ∑ �� � � � ] [∑ �� �� � � ∑ �� �� � � ] (7) if: ∑ �� � � � > ∑ � �� � and [∑ � �� � ∑ � �� � ] > [∑ �� � � � ∑ �� � � � ] and ∑ �� � � � ∑ �� � � � ] > [∑ �� �� � � ∑ �� �� � � ] [ ∑ � �� � ∑ � �� � = 0 ] and ∑ �� �� � � ≤ ∑ � �� � and [∑ � �� � ∑ � �� � ] ≤ [∑ �� � � � ∑ �� � � � ] qt100 = ∑ � �� � ∑ � �� � (8) if: ∑ �� � � � > ∑ � �� � and [∑ � �� � ∑ � �� � ] > [∑ �� � � � ∑ �� � � � ] and ∑ �� � � � ∑ �� � � � ] > [∑ �� �� � � ∑ �� �� � � ] [ ∑ � �� � ∑ � �� � = 0 ] and ∑ �� �� � � ≤ ∑ � �� � and [∑ � �� � ∑ � �� � ] > [∑ �� � � � ∑ �� � � � ] qt100 = ∑ �� � � � ∑ � �� � (9) if: ∑ �� � � � > ∑ � �� � and [∑ � �� � ∑ � �� � ] > [∑ �� � � � ∑ �� � � � ] and ∑ �� � � � ∑ �� � � � ] > [∑ �� �� � � ∑ �� �� � � ] [ ∑ � �� � ∑ � �� � = 0 ] and ∑ �� �� � � > ∑ � �� � and ∑ �� �� � � ≤ ∑ �� � � � qt100 = ∑ �� � � � ∑ �� � � � (10) where �� � is the required value of the load, �� is the actual value of the load, � � is the sit capacity of generation, � � is the available capacity of generation, � the actual capacity of generation, ��� the capacity of the transmission lines, and �� the actual flow in the transmission lines. iii. application on a real-life network the main purpose of the presented applications is to illustrate the implementation of the developed methodology on real-life systems and to demonstrate the applicability of the theoretical and computational developments of this work to practical power systems. the wadi aldawasir network represents an isolated zone of the sec (saudi electrical company) system. figure 3 shows the single-line diagram of the wadi aldawasir network. the system under investigation contains 1 generator, 9 branches (transmission lines and power transformers), and 7 loads. the results (figure 4) show that the deficit transmission capacity (qt100) stays at zero value for all required load levels up to 198mw, where it starts to increase continuously to reach 80mw at a required load level of 270mw. since the available generation at wadi aldawasir is 263mw, this situation indicates that the unsupplied load (between 180-263mw of load levels) is essentially due to transmission limitations rather than generation availability. qg111 has a similar pattern with the qt100, where it increases to reach 73mw at a required load level of 270mw. on the other hand, the qg111 starts at 90mw and increases continuously to reach 180mw, when the required load level reaches 180mw, after which the qg111 increases at a slower rate and saturates at about 190mw when the required load engineering, technology & applied science research vol. 11, no. 2, 2021, 6930-6934 6933 www.etasr.com alshammari et al.: evaluation framework of the deficits and reliability quality measures of … level is 270mw. at this point, no more available generation capacity can be utilized. figure 5 shows a 3-dimensional graph depicting the variation of the qt100 with the required load and the available generation capacity levels of the wadi aldawasir network. it is noted from figure 4 that the qt100 stays at zero value for all available generation capacity levels between 50% and 150% of nominal as long as the required load level is below 100% of nominal. this situation, however, changes after a region between 50% and 150% of nominal for the available generation capacity levels and between 100% and 150% of nominal for the required load levels, where more required load levels would increase the amount of the qt100. this situation indicates that the unsupplied load is now caused by the generation unavailability and transmission limitations. fig. 3. single-line diagram of the wadi aldawasir network. fig. 4. variation of generation capacity indices qt100, qg111, and qg110 with the variation of required load levels of the wadi aldawasir network. fig. 5. 3-d graph of the variation of qt100 with the required load levels and the available generation capacity levels of the wadi aldawasir network. iv. conclusion in this paper, the evaluation of a new reliability and quality measures methodology is based on 3 quantities of the power network, which are representing the relationship between the generation push in the grid, the maximum limitation of the transmission capacity, and the needed load. at the same time, the maximum future expanded generation capacity that could be available at the same generation site, was discussed. the main purpose of the paper the utilization of modern modeling techniques and computational procedures, including the advanced deficit transmission system evaluation method and sparse-matrix network analysis algorithms, in order to evaluate with sufficient accuracy the deficit and reliability levels in practical real-life large-scale power systems. the main contribution of the paper is the assessment of the deficit transmission system index with novel formulas. the research work also includes a practical application to several operating scenarios in the saudi electricity system. most of the deficits on the power system are caused by generation unavailability and transmission limitations (contingency state). acknowledgment the authors would like to thank the deanship of the scientific research of the university of ha'il, saudi arabia for funding and supporting this research project (♯ rg-191245). references [1] s. de la torre, a. j. conejo, and j. contreras, "transmission expansion planning in electricity markets," ieee transactions on power systems, vol. 23, no. 1, pp. 238–248, feb. 2008, https://doi.org/10.1109/ tpwrs.2007.913717. engineering, technology & applied science research vol. 11, no. 2, 2021, 6930-6934 6934 www.etasr.com alshammari et al.: evaluation framework of the deficits and reliability quality measures of … [2] m. a. el-kady, m. s. el-sobki, and n. k. sinha, "reliability evaluation for optimally operated, large, electric power systems," ieee transactions on reliability, vol. 35, no. 1, pp. 41–47, apr. 1986, https://doi.org/10.1109/tr.1986.4335340. 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[10] b. m. alshammari, m. a. el‐kady, and y. a. al‐turki, "power system performance quality indices," european transactions on electrical power, vol. 21, no. 5, pp. 1704–1710, 2011, https://doi.org/10.1002/ etep.515. microsoft word 24-2415_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3614-3618 3614 www.etasr.com naeem & hussain: development of a matlab code for plane wave lens and its validation by audtodyn-2d development of a matlab code for plane wave lens and its validation by autodyn-2d khalid naeem school of chemical and materials engineering national university of sciences and technology islamabad, pakistan khalid.phd@scme.nust.edu.pk arshad hussain school of chemical and materials engineering national university of sciences and technology islamabad, pakistan principal@scme.nust.edu.pk abstract—plane wave generator is normally composed of two explosives having dissimilar detonation velocity. it is used for directing the spherically outgoing shock wave front to a planar form. plane wave generators are utilized to find material behavior under dynamic loading. this paper presents the shock arrival time for two plane wave generators by developed matlab code and its comparison with ansys autodyn. the diameter of both plane wave generators is kept the same. one plane wave generator is composed of octogen and barium nitrate and the other is composed of octogen and tri nitro toluene. obtained results were surprisingly in agreement. maximum and minimum obtained flatness for the plane wave were ±0.56 and ±0.08ms respectively within the whole diameter of the plane wave generator. the developed code can be utilized to find the profile of a plane wave generator, minimizing the time and cost many times. keywords-plane wave lens; hmx; tnt; matlab; shock front; explosive lens i. introduction in order to investigate materials at higher pressures, it is necessary to accelerate materials under consideration to higher velocities. the techniques or instruments required to achieve higher velocities are: gas gun, electromagnetic rail gun, van de graaf accelerator, plasma accelerators, electric gun or electric discharge technique, and plane wave generator. gas gun is a device which uses light gas to propel the specimen. before operation of the gun, a light gas is compressed, the compressed gas is then fed at once to the launching tube where the sample is accelerated. gas gun consists of a single or double stage. a pressure up to 100gpa can be achieved by a two stage gas gun [1]. electromagnetic rail gun can accelerate few grams to 77.5km/s [2]. van de graaf accelerators are used to accelerate atomic particles up to 100km/s [3]. a velocity up to 18km/s can be achieved with plasma accelerators and electrical discharge [4]. use of explosives is another means of attaining high impact velocity. it is utilized for material acceleration in two different ways. in the first method the explosive detonation front is directly used for accelerating the sample material and in the second method the detonation wave front is used to compress a light gas which is further utilized to launch the projectile [5]. plane wave generator (pwg) is also used to study hypervelocity impact. it is an explosive lens made up of two explosives [6]. pwg maneuvers the spherically outgoing detonation wave front to planar form. the planar detonation wave front can be achieved either by combining two explosives having dissimilar velocity of detonation (vod) or a single explosive having some inert barrier inside [6]. pwg is manufactured by machining. in this process both dissimilar explosives are first machined and then assembled in a costly process. it can be produced by pressing to shape with dies [7]. pwg designed from nitromethane and lead has been reported in [8]. due to its toxic nature, lead is difficult to handle. therefore a low equivalent liquid explosive lens without lead was presented in [9]. an explosive lens composed of two explosives gives better results than a single explosive having some inert material [10]. pwg is utilized to accelerate objects to hyper velocities in order to study their various parameters and to find the equation of state for gases [11]. it is also utilized for overdriving high explosives to get maximum jet velocity in case of shaped charges [12]. massive hypervelocity pellet can be obtained by firing the shaped charge. the liner is fabricated from the material to be tested. once fired the tip of shaped charge jet moving at a speed of 7.57 to 10.95mm/µs is isolated from the rest of the jet and slug [13]. pwgs are also used for shock hardening of materials. the specimen is shock hardened when a flyer plate accelerated by pwg hit the specimen encased within heavy metal casing [14]. ii. materials and methods a. mathematical model for pwg the assumptions made for the development of the mathematical model are: • the detonation is mature and a steady state vod is achieved at the start of detonation without any run distance. • the velocity of the detonation is uniform throughout the explosive regardless of its diameter. • low vod explosive is detonated without any misbehavior. the parameters shown in figure 1 are required for designing a pwg (height of pwg=h, diameter of pwg=d, vod of explosive-1=v1 and vod of explosive-2=v2). engineering, technology & applied science research vol. 8, no. 6, 2018, 3614-3618 3615 www.etasr.com naeem & hussain: development of a matlab code for plane wave lens and its validation by audtodyn-2d fig. 1. cross sectional view of a pwg pwg is designed in a way to get a plane detonation wave front at pp∗ given in figure 1. with the help of figure 1 this condition is written mathematically: t��� � � � (1) oc � √h� � r� (2) t��� � t� � t� (3) where: t� � �� � and t� � �� � (4) therefore (1), (3) and (4) can be written in the form of (5): � � � �� � � �� � (5) a small step size in the y direction is taken for granted (let ∆y=0.25) and the corresponding value for � coordinate is calculated using (4). the values of h1 and h2 are given by (6): h1=���� � ∆�� and h2= ���� � ��� (6) finally the boundary conditions are applied and the code is run in a loop. by decreasing the step size ∆y, the number of points increases. for the octogen (hmx) and barium nitrate (baratol) pwg height, diameter, velocities of detonation for hmx and baratol were taken as 50.0, 45.0, 8.73 and 4.90 respectively. matlab was selected for code writing as it contains built in functions for plotting. the flowchart given in figure 2 was followed during the writing of the code. b. methodology following the flow chart given in figure 2, code was written to obtain the profile of pwg at four decreasing step sizes of 0.5, 0.25, 0.125 and 0.0625mm. by reducing the step size in matlab by 50, 75 and 87.5 percent i.e. from 0.5 to 0.25, 0.125 and 0.0625 the percent increase in the number of steps was 97.4, 294.9 and 689.7 for the hmx-baratol pwg and 99, 298 and 696 for hmx tnt pwg respectively. fig. 2. flow chart of the code fig. 3. pwg profile of hmx and baratol at decreasing step size fig. 4. pwg profile of hmx and tnt at decreasing step size c. simulations the obtained profiles from matlab were plotted in cadkey. two arcs were fit to the entire points for simplicity, each arc engineering, technology & applied science research vol. 8, no. 6, 2018, 3614-3618 3616 www.etasr.com naeem & hussain: development of a matlab code for plane wave lens and its validation by audtodyn-2d was drawn by selecting three points on the profile so as a whole only six points were taken from the whole profile points. this practice was performed in order to model easily the pwg profile in ansys autodyn. simulations were run in two dimensional axial symmetry in order to save time and computer resources [15]. mesh density greatly affects the simulation results: increasing the mesh density increases the time required for simulation including accuracy and vice versa [16]. the employed mesh in all simulations had a cell size of 0.33mmx0.33mm per cell for the entire domain. the boundary condition for the problem was set to flow out, which mimics the condition that materials once moved out of the boundary do not participate in any sort of action. jones-wilkens-lee (jwl) equation-of-state was used to model hmx, tnt and baratol. general form of the jwl equation for the solid unreacted and gases reacted phase is given by (7) [17]: � !"1 � $%�&'( )%�& � * "1 � $%�&'( )%�& � $+& (7) where ,and . in the equation represent detonation pressure, relative volume and internal energy per unit volume of the explosive respectively, whereas !,*,/,0� and 0� are all constants. the jwl parameters for all the three explosives are given in table i. table i. jwl equation of state for hmx, baratol and tnt hmx [18] baratol [19] tnt [18] density (kg/mm 3 ) 1740 2600 1630 v (m/s) 8730 4900 6930 p (gpa) 31.1 11.0 21.0 a (gpa) 748 1265 373.7 b (gpa) 12.1 1.55 374.7 r1 4.5 5.8 4.15 r2 1.1 2.0 0.9 ω 0.3 0.6 0.35 ε (j/mm 3 )) 10.2 11 6.0 to study the effects of boat tailing and casing the following four cases were studied. 1) without boat tailing • without casing • with 2mm aluminum casing 2) with boat tailing • without casing • with 2mm aluminum casing d. simulation results shock front arrival times, obtained from autodyn for the hmxbaratol pwg without and with boat tailing and for each of the two cases, without and with two millimeter thick aluminum casing, at a distance of 50mm from the detonation points, are listed in table ii. shock front arrival times obtained from autodyn for the (hmx, tnt) pwg without and with boat tailing, without and with two millimeter thick aluminum casing at a distance of 67mm from the detonation points are given in table iii. matlab code was run to find the arrival time of shock front at 60mm from the point of detonation. additional 7mm of hmx were added to the hmx part in order to ensure the proper detonation of the second low explosive which may deflagrate in some cases if the shock wave does not have enough energy [20]. in some cases the shock wave slowly dies out or attenuates and changes to a sound wave. exploded views of hmx-baratol and hmx-tnt pwgs are given in figure 7. table ii. shock front arrival time for (hmx-baratol) pwg position without boat tailing with boat tailing without casing with casing without casing with casing x y time (µs) time (µs) 50 0 7.579 7.569 7.576 7.535 50 5 7.585 7.569 7.537 7.572 50 10 7.615 7.569 7.563 7.572 50 15 7.636 7.679 7.676 7.647 50 20 7.734 7.735 7.753 7.787 50 25 7.885 7.919 7.877 7.874 50 30 7.992 8.012 8.049 8.002 50 35 8.084 8.123 8.083 8.095 50 40 8.029 8.067 8.026 8.077 50 45 7.936 7.661 7.934 7.667 average time 7.808 ±0.505 7.790 ±0.554 7.807 ±0.546 7.783 ±0.560 table iii. shock front arrival time for (hmx-tnt) pwg position time (µs) without boat tailing time(µs) with boat tailing x y no casing 2 mm casing no casing 2 mm casing 67 0 9.270 9.253 9.275 9.278 67 5 9.234 9.237 9.235 9.234 67 10 9.173 9.221 9.222 9.222 67 15 9.206 9.205 9.208 9.209 67 20 9.173 9.205 9.205 9.209 67 25 9.199 9.202 9.202 9.203 67 30 9.199 9.202 9.202 9.209 67 35 9.196 9.197 9.195 9.198 67 40 9.141 9.119 9.191 9.110 67 45 9.199 9.202 9.198 9.198 average time 9.199± 0.129 9.204± 0.134 9.213± 0.084 9.207± 0.168 iii. results and discussion only six points were taken from the entire explosive profile for the modeling of the pwg profile in ansys autodyn. instead of these huge simplifications, flat detonation wave fronts were obtained for both pwgs. figures 3 and 4 show that decreasing step size increased the number of points for the profile. in other words, accuracy increased at the cost of computational time. these figures also depict that by selecting two explosives having a large difference in vod, a pwg with smaller height can be designed. current flatness given in tables ii and iii was achieved by drawing two arcs in autodyn to model and simulate the pwg profile. flatness can be further improved by fitting multiple arcs to the points generated by matlab. table iv depicts that boat-tailing of the pwg reduced the mass of pwg by 41.39% and 26.68% respectively for hmx-baratol and hmx-tnt pwg. this huge mass reduction decreases the cost of pwg without any sacrifice in its simultaneity. the reduction in explosive reduces the blast effect and the volume of the gases evolved during detonation which degrades the environment. replacing the baratol with tnt increased the engineering, technology & applied science research vol. 8, no. 6, 2018, 3614-3618 3617 www.etasr.com naeem & hussain: development of a matlab code for plane wave lens and its validation by audtodyn-2d pwg length. but the simultaneity of the later is better than the previous as can be seen in figures 5 and 6. in areas where smaller size is required, it is better to use two explosives which have large difference in their detonation velocity like hmx and baratol. fig. 5. effect of boat tailing and casing on simultaneity of hmx-baratol pwg fig. 6. effect of boat tailing and casing on simultaneity of hmx-tnt pwg fig. 7. exploded view of hmx-baratol and hmx-tnt pwg inclusion of casing does affect the timings as can be seen in figures 5 and 6 but this effect is very small and can be considered negligible. in order to make a pwg of 90mm diameter, it is better to model a pwg of 100mm diameter and then reduce the diameter to 90mm by turning. this will reduce the edge effects. these effects decrease the pwg performance by the late arrival of the shock front near the outer periphery. it happens because there is not enough high explosive in the periphery to properly detonate the second less sensitive explosive having lesser vod. this crude matlab code which only relies on the detonation velocity of explosives gives a good approximation for the profile of pwg. table iv. effect of boat tailing on the mass of pwg pwg variation hmx (gm) baratol/tnt (gm) total mass (gm) % decrease hmx, baratol without boat tailing 522.79 147.21 baratol 670 41.39 with boat tailing 245.46 147.21 baratol 392.67 hmx, tnt without boat tailing 535.97 204.77 tnt 740.74 26.68 with boat tailing 338.30 204.77 tnt 543.07 iv. conclusion matlab code was successfully written to obtain the pwg profile for any two explosives having dissimilar vod and the results were compared with the simulation runs on ansys autodyn. results were quite in agreement, even with the inclusion of aluminum casing and boat tailing. boat tailing reduced the mass of explosive by 41.39% and 26.68% without the cost of losing simultaneity. boat tailing reduced the amount of exhaust gases to the atmosphere by reducing the amount of explosives in the pwg. to check the effect of step size in matlab, four successive decreasing step sizes were employed. this increased the computational time and the number of data points or accuracy. with the developed matlab code any two explosives with dissimilar vod can be selected to design a pwg. it is better to have two explosives which have a wide gap in their vod. replacing baratol with tnt not only increased the length of pwg as shown in figure 7 but also improved its simultaneity as given in tables ii and iii. the developed code reduces the cost of pwg by decreasing the number of tests required to finalize the pwg. references [1] a. mitchell, w. nellis, “diagnostic system of the lawrence livermore national laboratory two‐stage light‐gas gun”, review of scientific instruments, vol. 52, no. 3, pp. 347-359, 1981 [2] l. c. chhabildas, m. d. knudson, “techniques to launch projectile plates to very high velocities”, in: high-pressure shock compression of solids viii, springer, pp. 143-199, 2005 [3] l. c. chhabildas, hypervelocity launch capabilities to over 10km/s, sandia national labs., albuquerque, nm, usa, 1991 [4] j. e. osher, h. h. chau, g. r. gathers, r. s. lee, r. c. weingart, “application of a 100-kv electric gun for hypervelocity impact studies”, international journal of impact engineering, vol. 5, no. 1-4, pp. 501507, 1987 [5] a. b. wenzel, “a review of explosive accelerators for hypervelocity impact”, international journal of impact engineering, vol. 5, no. 1-4, pp. 681-692, 1987 [6] w. xiong, x. zang, z. guan, y. he, l. qiao, l. guo, “study of simple plane wave generator with an air-metal barrier”, defence technology, vol. 10, no. 2, pp. 190-197, 2014 engineering, technology & applied science research vol. 8, no. 6, 2018, 3614-3618 3618 www.etasr.com naeem & hussain: development of a matlab code for plane wave lens and its validation by audtodyn-2d [7] b. olinger, solid explosive plane-wave lenses pressed-to-shape with dies, los alamos national laboratory, los alamos, nm, usa, 2007 [8] k. jin, x. m. zhou, x. h. liu, f. xi, “design of plane-wave lens utilizing nitromethane and lead [j]”, energetic materials, vol. 2, 2005 [9] s. n. li, x. zhou, s. yuan, p. song, w. wang, s. h. yei, “manufacture of low equivalent liquid explosive lens without lead [j]”, chinese journal of energetic materials, vol. 3, 2006 [10] j. crutchmer, slow pbx and plane-wave lens development, mason and hanger-silas mason, amarillo, usa, 1973 [11] r. h. christian, f. l. yarger, “equation of state of gases by shock wave measurements. i. experimental method and the hugoniot of argon”, the journal of chemical physics, vol. 23, no. 11, pp. 2042-2044, 1955 [12] h. kato, k. murata, s. itoh, y. kato, “application of overdriven detonation in high density explosive to shaped charge”, 23rd international symposium on ballistics, tarragona, spain, april 16-20, 2007 [13] a. merendino, j. m. regan, s. kronman, a method of obtaining a massive hypervelocity pellet from a shaped charge jet, ballistic research laboratories, usa, 1963 [14] m. a. meyers, u. r. andrade, a. h. chokshi, “the effect of grain size on the high-strain, high-strain-rate behavior of copper”, metallurgical and materials transactions a, vol. 26, no. 11, pp. 2881-2893, 1995 [15] k. naeem, a. hussain, “numerical and experimental study of wave shaper effects on detonation wave front”, defence technology, vol. 14, no. 1, pp. 45-50, 2017 [16] j. petit, v. jeanclaude, c. fressengeas, “breakup of copper shapedcharge jets: experiment, numerical simulations, and analytical modeling”, journal of applied physics, vol. 98, no. 12, pp. 123521-1– 123521-10, 2005 [17] m. ahmed, a. q. malik, s. a. rofi, z. x. huang, “penetration evaluation of explosively formed projectiles through air and water using insensitive munition: simulative and experimental studies”, engineering, technology & applied science research, vol. 6, no. 1, pp. 913-916, 2016 [18] e. lee, m. finger, w. collins, jwl equation of state coefficients for high explosives, lawrence livermore national lab., 1973 [19] c. m. tarver, j. w. kury, r. d. breithaupt, “detonation waves in triaminotrinitrobenzene”, journal of applied physics, vol. 82, no. 8, pp. 3771-3782, 1997 [20] b. narin, y. ozyoruk, a. ulas, “two dimensional numerical prediction of deflagration-to-detonation transition in porous energetic materials”, journal of hazardous materials, vol. 273, pp. 44-52, 2014 microsoft word etasr_v10_n6_pp6393-6398 engineering, technology & applied science research vol. 10, no. 6, 2020, 6393-6398 6393 www.etasr.com nguyen: nonlinear inelastic earthquake analysis of 2d steel frames nonlinear inelastic earthquake analysis of 2d steel frames phu-cuong nguyen department of structural engineering ho chi minh city open university ho chi minh city, vietnam cuong.pn@ou.edu.vn abstract—in this work, a new method for nonlinear time-history earthquake analysis of 2d steel frames by a fiber plastic hinge method is presented. the beam-column element based on the displacement-based finite element method is established and formulated in detail using a fiber plastic hinge approach and stability functions. geometric nonlinearities are taken into accounting by stability functions and the geometric stiffness matrix. a nonlinear dynamic algorithm is established based on the combination of the newmark integration method and the newton-raphson iterative algorithm for solving dynamic equations. the proposed program predicts the nonlinear inelastic responses of 2d steel frames subjected to earthquakes as efficiently and accurately as commercial software. this study also shows that the initial residual stresses of steel should be considered in nonlinear inelastic time-history earthquake analysis of 2d steel frames while sap2000 does not consider the effects of residual stresses. keywords-earthquake; inelasticity; geometric nonlinearity; stability functions; nonlinear algorithm; steel frames i. introduction nowadays, steel frames are widely used in civil engineering and pre-engineering buildings. there are two analysis methods for designing steel structures: first-order elastic analysis and direct analysis. in the first-order elastic analysis, structures are assumed to be still elastic, and the effects of nonlinearities are neglected, while in the direct analysis, all important nonlinear phenomena, such as the plasticity of materials, geometric nonlinearity, residual stresses, the flexibility of connections, etc., are considered. there are two common direct analysis methods: plastic hinge method [1-9] and distributed plasticity method [10-19]. distributed plasticity method is complicated, computationally expensive, but more accurate. plastic hinge method is simple, effective, and with acceptable accuracy. there are several studies on steel frames subjected to dynamic loadings using finite element method. in 1991, authors in [20] carried out 44 shaking table tests on steel frames with flexible, semi-rigid, and rigid connections. in 1994, authors in [21] studied the seismic behavior of two-story steel frames with semi-rigid connections. they concluded that the semi-rigid steel frame is suitable for earthquake-resistant design. authors in [22] studied the dynamic behavior of steel frames with beam flanges shaved around the weld connection. they discovered that the dissipation capacity of the new design connection is much better than traditional connections. in 2008, authors in [23] analyzed the nonlinear elastic dynamic behavior of steel portal frames with semi-rigid connections. authors in [24] developed a dynamic time-history analysis for steel frames using one element per member. authors in [25] studied the nonlinear dynamic collapse analysis of semi-rigid steel frames using the finite particle method. nguyen and kim developed a plastic hinge method using stability functions for nonlinear dynamic analysis of steel frames [6, 7, 13], including the effects of semi-rigid connections and also developed distributed plasticity methods using stability functions for nonlinear dynamic analysis of semi-rigid steel frames employed by the hilber-hughes-taylor method for solving dynamic equations [14, 15, 17]. recently, authors in [26-28] tried to investigate the behavior of steel frames with the effects of connections. to the best of our knowledge, there is no study on the fiber plastic hinge method using stability functions for nonlinear dynamic analysis of steel frames. in this paper, a fiber plastic hinge method for nonlinear inelastic time-history earthquake analysis of 2d steel frames was developped. stability functions are used for optimizing the number of finite elements for structural analysis and simultaneously considering the second-order effects. the plastic hinges are divided into several fibers for capturing accurately gradual plasticity of hinges and so that the impact of residual stresses are directly considering as initial stresses. the newmark integration method and the newton-raphson iterative algorithm are combined for solving dynamic equilibrium equations of structures. the proposed program can be developed for direct analysis and design of steel frames. ii. nonlinear 2d beam-column a. p δ− effect stability functions studied in [29] were utilized for predicting the p δ− effect. the second-order effect can be captured precisely by stability functions. with one element for the member, it is efficient to economize sources and analysis time. residual stresses are assigned as the initial stress pattern of eccs [30]. the force-displacement relationship using the incremental form of a 2d beam-column element can be written as: corresponding author: phu-cuong nguyen engineering, technology & applied science research vol. 10, no. 6, 2020, 6393-6398 6394 www.etasr.com nguyen: nonlinear inelastic earthquake analysis of 2d steel frames 1 2 2 1 / 0 0 0 0 i i j j p a i ei m s s l m s s δ θ θ ∆ ∆ ∆ = ∆ ∆ ∆                         (1) where p∆ , im∆ , and jm∆ are the axial force and moments, δ∆ , iθ∆ , and jθ∆ are the axial movement and rotations, a is the sectional area, i is the moment of inertia around the z axis, l is the elemental length, e is young’s modulus of steel, and 1s and 2s are stability functions [29]. b. fiber plastic hinge in figure 1 of [9] the fiber plastic hinge method is illustrated. in this method, two ends i and j of the element have monitored the behavior of stress and strain of fibers. if the fiber is yielding, the tangent elastic modulus of the fiber is assigned to be equal to zero. the force-displacement relation of a 2d element considering both the p δ− effect and plasticity can be formulated as: / 0 0 2 2 0 ( (1 ))1 2 1 2 20 ( (1 ))2 1 1 a i p se it m s si i j i j i l s m j j s s si j j i s δ η η η η θ θ η η η η         ∆   ∆       ∆ = − − ∆         ∆ ∆       − −     (2) where iη is a scalar parameter accounting for the gradual yielding of the fiber hinge at the i end, jη is a scalar parameter accounting for the gradual yielding of the fiber hinge at the j end. they are estimated as: ( )2 1 n tii i i i i i t e a y i e i η = + = ∑ (3) ( )2 1 n tji i i i i j t e a y i e i η = + = ∑ (4) where n is the sum of fibers on the sections at i and j, tiie and tjie are the tangent moduli of the th i fiber at i and j, ia is the area of the th i fiber, ii is the moment of inertia of the th i fiber, iy is the center coordinate of the th i fiber, and te is the tangent modulus of an element. c. shear deformation for calculating the effects of shear deformation, the incremental equilibrium equation is modified for 2d beamcolumn element as: / 0 0 0 0 t i ii ij i j ij jj j p e a l m d d m d d δ θ θ ∆ ∆ ∆ = ∆ ∆ ∆                         (5) where: 2 2 ii jj ij ii s ii ii jj ij s k k k k a gl d k k k a gl − + = + + + (6) 2 2 ii jj ij ij s ij ii jj ij s k k k k a gl d k k k a gl − + + = + + + (7) 2 2 ii jj ij jj s jj ii jj ij s k k k k a gl d k k k a gl − + = + + + (8) d. p −∆ effect figure 1 presents a 2d element with six degrees of freedom. the elemental tangent stiffness matrix considering the p −∆ effect is calculated as: [ ] [ ] [ ] 3 5 3 3 3 5 5 5 t e gt k t k t k × × × ×  = +     (9) where the transformation matrix [ ] 3 5 t × of the element is formulated as: [ ] 3 5 1 0 0 0 0 0 1 0 1/ 1/ 0 0 1 1/ 1/ t l l l l × −   = −   −  (10) and gk   is the geometric stiffness matrix written as: 2 2 5 5 2 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 i j i j g i j i j m m m m l l k m m p p l ll m m p p l ll × + + − = + − + − −                           (11) fig. 1. fiber plastic hinge method. iii. nonlinear solution the nonlinear solution algorithm invented in [31] is developed to find a solution to the structural system. the balanced iteration at each time step is adjusted by the newtonraphson iterative method. the dynamic equilibrium equation of steel frames is written as: [ ]{ } [ ]{ } [ ]{ } { }tm d c d k d f∆ + ∆ + ∆ = ∆�� � (12) engineering, technology & applied science research vol. 10, no. 6, 2020, 6393-6398 6395 www.etasr.com nguyen: nonlinear inelastic earthquake analysis of 2d steel frames where d ∆  �� is the vector of incremental acceleration, d ∆  � is the vector of incremental velocity, [ ]d∆ is the vector of incremental displacement, [ ]m is the structural mass matrix, [ ]c is the structural damping matrix, [ ]tk is the structural tangent stiffness matrix, and { }f∆ is the applied dynamic loading. the structural damping matrix [ ]c is calculated as the rayleigh damping matrix [32]: [ ] [ ]m k ic m kα β= +    (13) where mα is the mass-proportional damping factor, kβ is the stiffness-proportional damping factor, and ik   is the structural initial stiffness matrix. if both first vibration modes of the structure are assumed to have the same damping ratio ξ, then: 1 2 1 2 1 2 2 2 ; m k ω ω α ξ β ξ ω ω ω ω = = + + (14) where ω1 is the natural frequency of the first vibration mode and ω2 is the natural frequency of the second vibration mode. iv. verification and discussion in 1985, vogel [33] proposed a portal steel frame subjected to static loadings for verifying the accuracy of the nonlinear inelastic analysis of finite element programs. in this paper, the vogel steel frame subjected to earthquakes is studied as shown in figure 2. young’s modulus is e=205,000mpa, poisson’s ratio is v=0.30, and the yield stress of steel is σy=235pa. the columns are out-of-straightness of ψ=1/400 for considering initial imperfection. the lumped masses of 50kn.s 2 /m are put at the top of the columns. the frame was subjected to loma prieta and northridge earthquakes (the data were taken from [34] and can be seen in figure 3 and table i). the fiber plastic hinges are divided into 429 fibers, 6×33=198 fibers for each flange, and 33×1=33 fibers for the web. the obtained results by the proposed program are compared with those of commercial software sap2000 version 22 using the plastic hinge modeling of interaction p-m2-m3. fig. 2. vogel steel frame subjected to earthquakes. table i. time steps and ground acceleration peak of earthquakes earthquake time step (s) pga (g) loma prieta (1989) 0.005 -0.529 northridge (1994) 0.010 -0.640 (a) (b) fig. 3. time-history of earthquakes: (a) loma prieta, (b) northridge. (a) (b) fig. 4. nonlinear elastic time-displacement responses of column top: (a) loma prieta, (b) northridge 4.0 m m m 5 .0 m hea340 h e b 3 0 0 earthquake e = 205,000 mpa v = 0.30 yσ = 235 mpa m = 50 kn.s²/m ψ= 1/400 ψ= 1/400 h e b 3 0 0 ∆ -0.6 -0.4 -0.2 0.0 0.2 0.4 0 5 10 15 20 25 30 35 40 a c c e le ra ti o n ( g ) time (s) -0.7 -0.5 -0.3 -0.1 0.1 0.3 0.5 0 5 10 15 20 25 a c c e le ra ti o n ( g ) time (s) -95 -80 -65 -50 -35 -20 -5 10 25 40 55 70 85 100 115 0 5 10 15 20 25 30 35 40 l a te ra l d is p la c e m e n t (m m ) time (s) present sap2000 -110 -95 -80 -65 -50 -35 -20 -5 10 25 40 55 70 85 100 115 0 5 10 15 20 25 l a te ra l d is p la c e m e n t (m m ) time (s) present sap2000 engineering, technology & applied science research vol. 10, no. 6, 2020, 6393-6398 6396 www.etasr.com nguyen: nonlinear inelastic earthquake analysis of 2d steel frames figures 4 and 5 show the time-lateral displacement response at the right-column top of the frame subjected to loma prieta and northridge earthquakes performed by nonlinear elastic and inelastic dynamic analyses. it can be seen that the obtained results by the proposed program are in good agreement with those of sap2000. (a) (b) fig. 5. nonlinear inelastic time-displacement responses of column top: (a) loma prieta, (b) northridge. figures 6 and 7 show the time-rotational displacement response at the right-column top of the frame subjected to loma prieta and northridge earthquakes performed by nonlinear elastic and inelastic dynamic analyses. the obtained results by the proposed program are again in good agreement with those of sap2000. however, under the loma prieta earthquake in the nonlinear inelastic analysis, the timerotational displacement responses of the proposed program and sap2000 are different because the proposed program uses the proposed fiber plastic hinge method while sap2000 uses the plastic hinge method. we can see that the proposed method is accurate and effective in predicting the nonlinear behavior of 2d steel frames subjected to earthquakes. commercial software sap2000 does not consider the effects of residual stresses on the behavior and strength of steel frames. figures 8 and 9 show the nonlinear inelastic timedisplacement response of the column top of the frame considering the effects of residual stresses (present rs, red line) and without considering the effects of residual stresses (present, blue line). it can be seen that the lateral displacement responses of the frame are almost the same (figure 8), while the rotational displacement responses of the structure are clearly different if we consider the effects of residual stresses, as shown in figure 9. residual stresses may significantly impact the nonlinear inelastic behavior and strength of steel frames so they should be considered in engineering design. (a) (b) fig. 6. nonlinear elastic time-rotational displacement responses of column top: (a) loma prieta, (b) northridge. (a) (b) fig. 7. nonlinear inelastic time-rotational displacement responses of column top: (a) loma prieta, (b) northridge. -90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90 0 5 10 15 20 25 30 35 40 l a te ra l d is p la c e m e n t (m m ) time (s) present sap2000 -85 -70 -55 -40 -25 -10 5 20 35 50 65 80 95 0 5 10 15 20 25 l a te ra l d is p la c e m e n t (m m ) time (s) present sap2000 -0.012 -0.009 -0.006 -0.003 0.000 0.003 0.006 0.009 0.012 0 5 10 15 20 25 30 35 40 r o ta ti o n a l d is p la c e m e n t (r a d ) time (s) present sap2000 -0.012 -0.009 -0.006 -0.003 0.000 0.003 0.006 0.009 0.012 0 5 10 15 20 25 r o ta ti o n a l d is p la c e m e n t (r a d ) time (s) present sap2000 -0.009 -0.006 -0.003 0.000 0.003 0.006 0.009 0 5 10 15 20 25 30 35 40 r o ta ti o n a l d is p la c e m e n t (r a d ) time (s) present sap2000 -0.009 -0.006 -0.003 0.000 0.003 0.006 0.009 0 5 10 15 20 25 r o ta ti o n a l d is p la c e m e n t (r a d ) time (s) present sap2000 engineering, technology & applied science research vol. 10, no. 6, 2020, 6393-6398 6397 www.etasr.com nguyen: nonlinear inelastic earthquake analysis of 2d steel frames (a) (b) fig. 8. the effects of residual stresses on nonlinear inelastic timedisplacement responses of column top: (a) loma prieta, (b) northridge. (a) (b) fig. 9. the effects of residual stresses on nonlinear inelastic timerotational displacement responses of column top: (a) loma prieta, (b) northridge. v. conclusion a second-order inelastic analysis program based on the finite element method for 2d steel frames was developed successfully. the effects of p-δ, p-∆, material inelasticity, residual stresses, and imperfections were accounted for the nonlinear analysis by the generalized displacement method. the proposed method is simple, accurate, and efficient in predicting the strength and behavior of steel frames. the proposed method can directly consider the effects of residual stresses of steel as sap2000 cannot. the proposed method can be integrated into commercial software for daily engineering design using advanced analysis. acknowledgment the authors gratefully acknowledge the financial support granted by the scientific research fund of the ministry of education and training (moet), vietnam. 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[34] “peer ground motion database peer center.” https://ngawest2. berkeley.edu/ (accessed oct. 15, 2020). microsoft word 08-3266_s_etasr_v10_n1_pp5142-5147 engineering, technology & applied science research vol. 10, no. 1, 2020, 5142-5146 5142 www.etasr.com hyder & ismail: inmtd: intent-based moving target defense framework using software defined … inmtd: intent-based moving target defense framework using software defined networks muhammad faraz hyder department of software engineering ned university of engineering & technology karachi, pakistan farazh@neduet.edu.pk muhammad ali ismail computer & information systems engineering ned university of engineering & technology karachi, pakistan maismail@neduet.edu.pk abstract—intent-based networking (ibn) is an emerging networking paradigm while moving target defense (mtd) is an active security technique. in this paper, the intent-based moving target defense (inmtd) framework using software defined networks is proposed. inmtd is the first effort in exploiting ibn for the design of an efficient moving target defense (mtd) framework. inmtd uses the concept of shadow servers in order to counter the first stage of cyber-attacks, i.e. reconnaissance attacks targeted against servers running in sdn networks. inmtd comprises of an mtd application running on an sdn controller. the mtd application has reconnaissance detection, mtd movement, and mtd monitoring modules. the mtd application is integrated with the intent-based northbound api of sdn controller. inmtd not only provides protection against probing attacks, but it also provides high availability due to shadow servers. the proposed framework was implemented using mininet and onos sdn controller. the proposed framework was assessed in terms of defender cost, attacker’s effort, and introduced complexity in the system. the results substantiate the efficient protection against reconnaissance attacks at lower computational cost. keywords-cyber kill chain; intent-based networking; moving target defense; software defined networks; sdn security i. introduction nowadays, cyber security is of critical importance. moving target defense (mtd) is becoming one of the popular techniques, for providing active cybersecurity [1]. mtd makes the systems dynamic by constantly changing the attack surface, making it hard to predict and attack. mtd equalizes the cyber security field for defender and attacker by eliminating the advantages of the attackers. mtd has changed the concept of cyber defense since its first announcement in 2009 [2]. mtd constantly changes the attack surface to reduce the advantage of time of attackers. mtd changes the attributes periodically, for example, ports, ips, so that the attacker cannot gain knowledge of the attribute through which attack can be launched. the change can be of two types: movement or transformation. mtd can be divided into numerous categories which can be chosen according to the required difficulty level for attackers [3]. intent based networking (ibn) is an emerging networking paradigm [4]. in ibn, users define their applications’ network requirements through policy. these policy instructions are referred as intents. ibn can also be used to fulfil the dynamic security requirements. open networking foundation (onf) has taken the initial steps towards its regularization of intent based networking. onf provides recommendations for creating intent based north bound interfaces (nbi) [5]. software defined networking (sdn) has recently gained substantial popularity as a networking paradigm. it primarily segregates the control and data planes [6]. its architecture comprises of three fundamental layers namely application, control, and data planes. due to its dynamic nature and centralized control, numerous security applications can be implemented through it. sdn based mtd is an active area of research, while ibn is gaining popularity in the research community. however, to the best of our knowledge, no previous work has used ibn for an mtd solution. in this paper, open network operating system (onos) sdn controller based intent framework [7] was used. various extensively used sdn controllers have similar types of intent based nbis. the onos intent based framework receives intent instructions and converts them into a compilation form and then installs the intent [7]. these installations perform the required operations on the network. the intent can be withdrawn as per desire if it is no more required by an application. in this paper, an mtd solution is proposed using ibn and sdn. the notion is to exploit ibn for creating mtd based upon sdn. the proposed inmtd framework protects against the reconnaissance attack which is the first stage of any cyber-attack [8]. inmtd detects the reconnaissance traffic directed against the web server and redirects it towards the shadow servers using the intent based framework of onos controller. the proposed solution has low computational cost, high availability, and efficient redirections among its advantages. for the implementation of inmtd, mininet emulator and onos controller [9] were used. ii. related work an sdn based programming framework termed as open software defined framework (osdf) was proposed in [10]. network administrators mention their network requirements for each application using application manager interface (api). numerous network operations including setting up standard quality of network services, network configuration, and corresponding author: muhammad faraz hyder engineering, technology & applied science research vol. 10, no. 1, 2020, 5142-5146 5143 www.etasr.com hyder & ismail: inmtd: intent-based moving target defense framework using software defined … monitoring can be managed through osdf services. it also contains conflicting policy resolver. in a multilayer data center environment, ibn is implemented through virtualization abstraction networking [11]. for end-to-end service management, intent based reference architecture is proposed in [12]. the architecture is verified on openflow and iot based sdn testbeds and testing has been done in various domains. in [13], another intent based architecture is presented which facilitates automatic intent implementation in secure multilayer networks. the approach was also certified through testing on commercial testbeds. in [14], a reactive configuration using extended intent-based network modeling (nemo) language has been proposed. the reactive scheme will alter the network configuration automatically according to the shift in external environment. the change is representing the administrator’s intent. the routing paths are shifting through bandwidth utilization in said scenario. an approach for business networks is proposed in [15] that implements ibn. mtd architecture,developed in [16] using openflow, alters the ip addresses randomly. this technique is named openflow random host mutation (ofrhm). the process of ip address alteration is hidden from users. the system is developed to use mtd against scanning. a collaborative mutation strategy named network moving target defense technique based on collaborative mutation (tcm) is proposed in [17]. the combination of end-point mutation and routing mutation is set up which increases mutation space and reduces irregularity. fingerprinting based mutation collision avoidance mechanism is also used to circumvent mutation collision. according to authors, tcm is more competent as compared to ofrhm and other similar techniques. a protective mtd mechanism for cloud networks is developed in [18]. the protection was done through the scheme of port hopping. a scoring strategy was used to check which cloud services are at risk. the score was measured by pagerank algorithm. mtd decisions were based on the vulnerability information obtained from the score. the impact of this mtd solution is more noticeable in large cloud networks than small scale cloud networks. an sdn-based mtd system named chaos was proposed in [19]. the system mystifies only the unexpected traffic without disturbing usual traffic. this is done by obfuscating each with a diverse level of security. sdn based mtd was proposed in [20] for throttling finger printing attacks which are targeting towards collecting operating system information. the proposed model was termed as fph (fingerprinting hopping). fph utilizes a game theoretic approach for constructing the optimal strategy for mtd. frvm is a sdn based mtd framework [21]. the model derived its name based upon the multiplexing of virtual ip addresses. frvm multiplexed virtual ips based upon random fashion. in [22], a model was proposed for creating virtual topologies using sdn for protecting the reconnaissance attacks. the proposed framework utilizes the statistical information for potentially malicious nodes responsible for generating the probing traffic. in [23], the authors discussed the distributed denial of services (ddos) attacks on sdn networks. their work also highlighted the anomaly detection techniques for sdn. the authors emphasized that the central plane of sdn is a lucrative target of attackers. the challenges with respect to the adaptation of cloud computing environment by telecom operators were addressed in [24]. the work is targeted towards specific country requirements. however, it can be extended for different countries. iii. methodology in this section, inmtd methodology is discussed in detail. a. threat model the attackers can be directly or indirectly connected to the sdn network. they can run different networking probing attacks against the different servers connected at the data plane. for this paper, the attacker’s targets are the running web servers. as the first step of a cyber-kill chain, the attacker will attempt a reconnaissance attack. each unique ip address is considered as an attacker. each attacker can run up to 10 concurrent reconnaissance probes at a time. this will ensure a realistic probing frequency. b. proposed model the proposed framework comprises of an mtd application running in the control plane. this mtd application utilizes the intent-based framework of onos controller [9] in order to create mtd effect. figure 1 represents the overall architecture of inmtd and its core components. the core component of mtd application is the reconnaissance detection module (rdm). it will detect any reconnaissance traffic directed towards web servers. this module is fundamentally implemented using snort [25] which is an open source ids. the snort [25] code was modified in order to detect the reconnaissance traffic targeted towards the web server and then redirect the traffic towards the shadow web servers. the other important module of mtd application is the decision/movement strategy. as its name suggest its role is deciding the movement technique and frequency of the proposed mtd. fig. 1. inmtd architecture engineering, technology & applied science research vol. 10, no. 1, 2020, 5142-5146 5144 www.etasr.com hyder & ismail: inmtd: intent-based moving target defense framework using software defined … fig. 2. inmtd workflow the mtd monitoring module is responsible for the monitoring of the overall mtd system. the mtd application runs on the top of the onos northbound intent api [9]. this interface comprises of three parts: intent engine, compilation module, and the intent installation part. mtd application forwards the decision to the intent engine which performs the intent compilation through the intent compilation module. the compiled intents are finally installed in the required switch using the intent installation module. the installed intents will create flows in the switches. the fundamental advantage of inmtd is its effectiveness against probing traffic. the detection of probing traffic is difficult and there are false positive and false negative chances. our approach redirects the traffic to the shadow web servers. the shadow web servers are replicas of the original web servers. therefore, even if the rdm detects a legitimate user as an attacker, it still provides the web content to the user. algorithm 1 represents the probing traffic detection and redirection through intent modification. this algorithm detects the reconnaissance traffic through matching the source and destination ip and port addresses and reconnaissance frequency. algorithm 1: reconnaissance traffic detection & traffic redirection through intent modification 1: [initialization of sdn based network having different servers enabled intent based applications] 2: initialization of rdm 3: function packetarrival (srcip, srcport, dstip, dstport) 4: if (dstip = = webserverip and port=webserver_port and srcip==maliciousip 5: ##possibility of reconnaissance attack on web servers 6: rdm → intent_app(install_intent) 7: intent_app → modify the dest_ip using “setipdst” 8: selectedshadowwebserver == roundrobinselection (list of k shadow webservers) 9: selectedshadowwebserver_setipsrc == ip_address_web_server 10: shadow_webserver → attacker 11: endif 12: else 13: normal_sdn_forwarding () 14: end function once probing traffic is detected, it will be redirected towards the shadow web server while modifying the destination address of the server as one of the shadow servers. these shadow servers will be selected by the round robin fashion. the selected shadow server then responds to the probing traffic of the attacker. while responding to the probing traffic, the ip address of the shadow web server will be modified using the intent parameter of “setipsrc” to match the ip address of the original web server. the attacker will actually conceive that it is connected to the original web server, while actually it is connected to the shadow server. this way a moving target defense effect will be created. the overall flow of inmtd is presented in figure 2. mtd and intent based applications are running in the control plane. the rdm of inmtd is constantly monitoring the data plane for any reconnaissance traffic directed towards the web servers. there are two types of users, benign and attackers. benign users’ traffic will follow the normal sdn forwarding mechanism. the traffic from the attackers will be detected and directed towards the shadow web servers by the mtd application using intent based application. an example of intents that are installed for directing the traffic against web server to the shadow server and prepare a response to look like generated from the original web server is this: add-host-intent --ipsrc [ip address of attacker] --ipdst [ip address of web server] --tcpdst 80 --setipdst [ip address of one the shadow server] add-host-intent --setipsrc [ip address web server] --setipdst[ip address of attacker c. experimental setup for the deployment of experimental setup, a dell server with intel xeon cpu e5-2620 2.1ghz with 32 cores and 32gb ram was used. mininet [26] and onos controller [9] were used for the creation of the sdn topology. snort [25] was deployed as an ids (intrusion detection system) mode. nmap [27] was used for generating reconnaissance traffic. for the experimental analysis, the onos reactive forwarding application [9] was disabled. the reason is that only intent based forwarding was required. next, intents were inserted based upon the probing traffic. figure 3 represents the simulation setup for our proposed inmtd framework. engineering, technology & applied science research vol. 10, no. 1, 2020, 5142-5146 5145 www.etasr.com hyder & ismail: inmtd: intent-based moving target defense framework using software defined … fig. 3. simulation setup of inmtd iv. results and discussion for data plane security analysis, the case of one web server was considered. for one web server, there are k running shadow web servers. for the experimental analysis, we consider k=3. different numbers of scans were performed in order to evaluate the performance of inmtd. the number of scans ranges from 100 to 3200. each attacker can generate up to 10 scans. each distinct ip address belongs to an attacker. this number of scans is realistic because increasing the number of scans beyond this limit will cause the ids or the firewall system to permanently block the attacker’s ip address. table i presents the overall results of experiments. table i. results after inmtd n o . o f s c a n s n o . o f a tt a c k e r s s u c c e ss fu l r e d ir e c ti o n s s u c c e ss fu l r e d ir e c ti o n s ( % ) n o . o f fa il e d r e d ir e c ti o n s n o . o f in te n ts n o . o f fl o w s n o . o f b lo c k e d i p a d d r e s s e s 100 10 78 78.00 22 10 40 10 200 20 159 79.50 41 20 80 20 400 40 321 80.25 79 40 160 40 800 80 659 82.38 141 80 320 80 1600 160 1359 84.94 241 160 640 160 3200 320 2767 86.47 433 320 1280 320 a. attacker cost the fundamental goal of mtd is to increase the attacker’s effort. attacker’s cost primarily comprises of the number of scans performed while accurately detecting the platforms of the web server and port addresses, etc. table ii presents the attacker success for different numbers of scans for the cases of native sdn and inmtd enabled sdn. as evident from figure 4, attacker’s success substantially decreased after incorporating inmtd. attacker’s scanning attack success is around 97% to 98% against native sdn using nmap tool [27]. for the current analysis, there are 100 to 3200 scans performed against a native sdn environment without any protection available. the success rate of attacker ranges from 97% to 98%. however, attacker’s success reduced substantially when adopting the proposed inmtd. for 100 scans, the attacker success rate was 22.6% and it further reduced to 21% for 200 scans. in a similar fashion, the attacker success reduced as the number of scans increased, becoming 14% for 3200 scans. this is a substantial decrease in attacker scanning success rate. fig. 4. attacker success with and without inmtd table ii. attacker’s scanning success against native and inmtd based sdn total scans attacker success against native sdn attacker success against inmtd based sdn 100 97 22 200 195 41 400 391 79 800 788 141 1600 1569 241 3200 3150 433 b. defender cost defender’s cost primarily comprises of the intent installation, ids detection, and shadow web servers. generally ids is a part of any enterprise network. moreover, generally a web application runs on multiple web servers. therefore, the main cost is related to the intent compilation and installation. for this purpose we have calculated the number of flows injected for attacker’s probing traffic with and without intents as presented in table iii. as mentioned above, each attacker can run 10 concurrent probs. therefore, for each new ip address there will be a flow injected in the switches. it is clear from table iii that there is a slight increase in the number of flows, approximately 20% on average due to the addition of intents. figure 5 presents the graph of the number of flows inserted in the switch for probing traffic with and without intents. as evident form the table, for 100 scans, the number of flows before the intents’ addition was 20. afterwards, the number of flows increased to 22. similarly, for 200 scans, there are 40 flows without intents. the number of flows extended up to 46 after adding the intents. for 3200 scans, there are 640 flows without intents, which increased to 788 after the intents were added. therefore, the average intents increased the number of flows in the sdn switches approximately by 20%. engineering, technology & applied science research vol. 10, no. 1, 2020, 5142-5146 5146 www.etasr.com hyder & ismail: inmtd: intent-based moving target defense framework using software defined … hence, inmtd framework slightly increased the defender cost in terms of number of flows. table iv and figure 6 present the performance of inmtd for different numbers of scans. it is evident that inmtd successfully defended against probing attacks with accuracy from 78% to 86.5% for from 100 to 3200 scans. for 100 scans, the defender is capable of redirecting the probing traffic with accuracy of 78%. for 200 scans, the accuracy of inmtd increased to 79.5%. as the number of scans increased to 3200, the inmtd success reaches 86.47%. table iii. number of flows with and without intents total scans flows (after intents) flows 100 22 20 200 46 40 400 94 80 800 192 160 1600 390 320 3200 788 640 fig. 5. number of flows with and without intents fig. 6. inmtd success (%) for different scan numbers table iv. defender’s success total scans successful redirections (%) defender success 100 78.00% 78 200 79.50% 159 400 80.25% 321 800 82.38% 659 1600 84.94% 1359 3200 86.47% 2767 c. comparative analysis of inmtd with other sdn based mtd one of the novel contributions of the current work is the utilization of ibn for the design of sdn based mtd solution. to the best of our knowledge, no previous work has used ibn for the design of sdn based mtd solutions. another critical advantage of inmtd is the distributed control plane for higher availability. figure 7 represents the comparative analysis of the proposed inmtd with three other well-known sdn based mtd solutions, namely of-rhm [16], tcm [17], and frvm [21]. for the purpose of comparative analysis, the proposed inmtd model and the other models were analyzed on the basis of successful redirection for the reconnaissance traffic and computation cost. the computational cost is determined in terms of number of flows injected in the sdn devices after the adaptation of the protection mechanism. the number of scans ranges from 100 to 3200. for theses scans, computational cost and successful redirections were calculated for the proposed inmtd, and the existing solutions. as indicated in figure 7, inmtd achieves successful defense rate up to 86.5% with a computational cost of around 23%, while of-rhm [16] achieved a success rate of 74.4% with 28.7% increase in computational cost. tcm [17] provided a success rate of 79.5% with 27.4% increase in computational cost. frvm [21] had 83.2% success rate with 24.5% increase of the cost. inmtd has the highest success rate in comparison to the other three models. moreover, inmtd computational cost is lower than of-rhm [16] and tcm [17]. its computational cost is almost similar to that of frvm [21]. fig. 7. comparative analysis of inmtd with other sdn based mtd v. conclusion and future work in this paper, intent based mtd using sdn has been proposed. this is the first attempt in utilizing ibn for creating the mtd framework. the proposed inmtd model provides an efficient mtd effect at lower computational cost. inmtd successfully defended up to 86% of scanning attacks while redirecting them to shadow servers. the successful defense rate of the proposed inmtd is higher than the existing state-of-theart sdn-based mtds. the main computational cost is a slight increase in the number of flows while introducing the intents. this work confirms that intents are an effective mechanism for creating sdn based mtd. regarding future work, there is a need to further investigate ibn for designing mtd with especial emphasis on enhancing quality of service (qos). the engineering, technology & applied science research vol. 10, no. 1, 2020, 5142-5146 5147 www.etasr.com hyder & ismail: inmtd: intent-based moving target defense framework using software defined … current work is protecting the data plane of sdn. in the future we plan to extend the same protocol to protect the control plane. acknowledgment the authors are deeply thankful to the ncbc (national center of big data and cloud computing), ned university. references [1] a. aydeger, n. saputro, k. akkaya, “a moving target defense and network forensics framework for isp networks using sdn and nfv”, future generation computer systems, vol. 94, no. 1, pp. 496-509, 2019 [2] f. chong, r. b. lee, c. vishik, a. acquisti, w. horne, c. palmer, a. k. ghosh, d. 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s. kim, s. yoon, h. lim, j. h. cho, t. j. moore, “frvm: flexible random virtual ip multiplexing in software-defined networks”, 17th ieee international conference on trust, security and privacy in computing and communications/ 12th ieee international conference on big data science and engineering, new york, usa, august 1-3, 2018 [22] s. achleitner, t. f. l. porta, p. mcdaniel, s. sugrim, s. v. krishnamurthy, r. chadha, “deceiving network reconnaissance using sdn-based virtual topologies”, ieee transactions on network and service management, vol. 14, no. 4, pp. 1098-1112, 2017 [23] m. h. h. khairi, s. h. s. ariffin, n. m. a. latiff, a. s. abdullah, m. k. hassan, “a review of anomaly detection techniques and distributed denial of service (ddos) on software defined network (sdn)”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2724-2730, 2018 [24] m. ramzan, m. s. farooq, a. zamir, w. akhtar, m. ilyas, h. u. khan, “an analysis of issues for adoption of cloud computing in telecom industries”, engineering, technology & applied science research, vol. 8, no. 4, pp. 3157-3161, 2018 [25] m. roesch, “snort: lightweight intrusion detection for networks”, 13th systems administration conference, seattle, usa, november 7–12, 1999 [26] b. lantz, b. heller, n. mckeown, “a network in a laptop: rapid prototyping for software-defined networks”, 9th acm sigcomm workshop on hot topics in networks, monterey, usa, october 20-21, 2010 [27] g. f. lyon, nmap network scanning: the official nmap project guide to network discovery and security scanning, insecure, 2009 microsoft word 37-3219_s_etasr_v9_n6_pp5074-5079 engineering, technology & applied science research vol. 9, no. 6, 2019, 5074-5079 5074 www.etasr.com mahessart et al.: impact of right bank outfall drain-i (rbod-i) / main nara valley drain (mnvd) … impact of right bank outfall drain-i (rbod-i) / main nara valley drain (mnvd) on manchar lake, sindh, pakistan ali asghar mahessar sindh barrages improvement project irrigation department government of sindh sindh, pakistan kamran ansari u.s.-pakistan center for advanced studies in water, mehran university of engineering and technology jamshoro, pakistan ghulam murtaza arain pakistan council for research of water resources, ministry of science and technology, karachi, sindh, pakistan islamabad, pakistan shafi muhammad kori department of civil engineering mehran university of engineering and technology, jamshoro, pakistan sumera qureshi dr. m. a. kazi institute of chemistry university of sindh jamshoro, pakistan abdul latif qureshi u.s.-pakistan center for advanced studies in water, mehran university of engineering and technology, pakistan abstract-the lakes of sindh are in poor environmental condition due to the massive disposal of effluents. this paper presents the impact of water quality in manchar lake due to climate change and anthropogenic intervention. the lake is one of the biggest natural lakes in sindh, pakistan. the lake has three major sources of water supply: indus river, hill torrents from the khirthar mountain range and the right bank outfall drain (rbod-i)/main nara valley drain (mnvd). the water supply of the lake from the first two sources has been reduced due to morphological and climate changes. hence, there is only one, and polluted, water supply to the lake, the rbod-i/mnvd. at the same time, the use of poisonous materials for fishing has further contaminated the lake’s water. the rbod system is connected with rbod-iii, rbod-i/mnvd, indus link and rbod-ii on the right side of indus river for safe disposal of wastewater into the arabian sea, which is still not functioning. hence, more than 4500 cusecs of wastewater from the catchment area of rbod have directly been discharged into the lake causing severe impact on flora, fauna and the livelihood of locals. in order to analyze the lake water quality impact, the water quality index (wqi) model was used. the results indicate that the water quality of four samples was very poor, while the fifth sample was unsuitable for drinking. the results of statistical analysis of parameters such as tds, ec, so4, cl, na, and hardness are higher to their permissible limits. consequently, lake water possesses a high potential risk to local consumers and aquatic ecology. keywords-manchar lake; degradation; rbod system; indus river; hill torrent; ecology; drinking freshwater supply; fishermen; locals i. introduction lakes are natural water bodies that serve as sources of recharging groundwater reservoirs while improving its quality, but unfortunately have significantly been degraded due to growing population and economic development. these lakes are natural water providers, flood storages, natural habitats and breeding homes for indigenous and migratory birds including endangered species. there are 225 sites of wetlands covering an area of about 9.7% of pakistan [1]. they are broadly categorized as mountainous lakes, tropical freshwater and salt lakes, indus river, coastal wetlands and manmade reservoirs [2], but only 46 of them are listed as protected areas including 19 ramsar sites which have international importance [3]. the covered area of lakes in sindh is 78,000 hectares. some important lakes in sindh include manachar, hamal, keenjhar, haleji, hadero, drigh, pugri, langh, shakoor, sonhari, sadhari, phusna, charwo, khanjo, ghauspur/sindh dhoro, nara canal area, narri, mehro, sanhro, pateji, khipro, tando bagho, mehboob shah, shah bunder/jaferi, chotiari reservoir/lake and hub reservoir. sindh holds the privilege of hosting wildlife protected ramsar sites as they serve as sanctuaries for waterfowl migratory and local birds such as keenjhar lake (ramsar site no. 99), haleji lake, (ramsar site no. 101), drigh lake (ramsar site no. 100), jubho lagoon (ramsar site no.1067), and narri lagoon and guddu to sukkur stretch of indus river (ramsar sites). these lakes are almost under threat due to fresh water scarcity, less drainage, less rainfall, polluted water, increased sedimentation and eutrophication [4]. the lakes possess ecological value, especially for endangered species [5], and are natural reservoirs for rainwater harvesting, storing floodwater, recharge groundwater and water supplying sources [6]. entering river flows into the lakes regulating the level of sedimentation and nutrients which affect water quality and quantity [7]. the decline of freshwater quantity and quality alters the ecological ecosystem of the lakes [8]. a major cause of water quality degradation is also the disposal of effluents from agricultural, industrial, and municipal leachates into the lake [9, 10]. manchar lake, which is the biggest lake of sindh, was developed along with himalaya, karakorum and khirthar corresponding author: ali asghar mahessar (amahessar@yahoo.com) engineering, technology & applied science research vol. 9, no. 6, 2019, 5074-5079 5075 www.etasr.com mahessart et al.: impact of right bank outfall drain-i (rbod-i) / main nara valley drain (mnvd) … during the movement of eurasian tectonic plates. it has been getting millions of tons of sediments with torrential rainwater from hill torrents of bolan and khirthar and indus river [11]. now, it has turned into a shallow lake with an average depth of 0.5 to 3.75m. the lake had initially two natural sources of water supply, hill torrents from khirther range and inundation canals from indus river. a third source of main nara valley drain (mnvd) was also added in 1932. the release of water after the construction of mnvd into the lake started to degrade water quality. some studies regarding the water quality of manchar lake have been conducted [12] to assess its physicochemical properties and heavy metal concentrations which were found to be beyond the permissible limits [13]. moreover, high concentration accumulated sediment was oberved and analyzed. the sources of heavy metals entering the lake are soil erosions, rock weathering and anthropogenic activities on its watershed [14]. persistent organic pollutants (pops) tend to persist in the environment for long periods, are distributed worldwide, accumulate in the lipids of humans and animals and also bind to sediment [15]. significant amounts of ddt and coliform were found in the mnvd and the water body of manchar lake which is now unfit for human consumption [16]. this lake supports the livelihood of half a million locals through fishing and farming. thousands of the local mohana (fishermen) have built their boat villages in the lake [17]. decades of draining untreated domestic, industrial, and agricultural wastewater have polluted the lake [18], which once was a home for siberian birds from central asia [19]. the annual fish catch has also reduced from 2300 tons to 400 tons, while fish species have diminished from 200 to 14 since 1930. hence, the siberian birds no longer stop during their annual migration due to insufficient fish availability [20]. the fresh water of manchar lake was used for domestic and agricultural purposes by the local communities because the groundwater is unfit for drinking and domestic use [21]. however, the completion of rbod project, in which the effluents will bypass the lake and will ultimately get discharged into the sea, will generate series of positive impacts such as improving socio-economic and environmental conditions and reclaiming degraded lands and improving the quality of the lake [22, 23]. hence, the significance of the lake will be revived. the main aim of the present study is to have a thorough physicochemical analysis of the manchar lake water to ascertain the impact of rbod/mnvd on its quality. ii. study area the manchar lake is located at 26°27’21’’ latitude and 67°38’31’’ longitude. it is the biggest natural shallow lake of sindh, pakistan, situated at a distance of about 18km from sehwan sharif city in jamshoro district. it is a vast natural depression flanked by the khirthar hills in the west, laki hills in the south and river indus in the east. it is a shallow saucer shaped basin and the area of the lake varies depending on the influx of water. on northern and eastern side, an earthen embankment was constructed, the manchar containing bank of 36km length. historically, the lake was filled by the hill torrents and flood spills of the indus river. mnvd (figure1) is also one of its main, and more recent, sources. the area of the lake reduces during the winter season but it extends and its depth increases during monsoon season. it is a regular practice to feed the manchar lake during monsoon season from river indus through danister wah, aral head regulator and aral tail regulator, and by torrential water coming from the khirthar mountain range. besides this, it is depleted by draining out water into river indus through the aral tail regulator before the arrival of the monsoon season to maintain its safety level rl 100ft. the climate of the study area is arid. there is a seasonal variation of weather conditions such as temperature, pressure, humidity, evaporation, evapotranspiration, and precipitation. the maximum, average and minimum temperature is 48 o c, 40 o c and 35 o c in summer season while it is 26 o c, 22 o c and 16 o c in winter season, respectively. the maximum humidity has been observed in july and august and the minimum in october and may. the high and low observed pressure is 1018 and 995mb in january and july respectively and the evaporation varies from 10 to 15%. fig. 1. layout plan of rbod-i, iii and ii iii. materials and methods a walkthrough survey was carried out regarding the water quantity and quality of manchar lake assessment. there are three major feeding sources to the lake: 1) hill torrents from khirthar range, 2) mnvd, and 3) indus river through aral wah and danister wah (two natural canals). the draining of the lake is done through the aral tail wah into indus river. the lake is shallow, its depth varies from 0.5-3.5m and its bed level is about 5m lower than indus river bed. hence, the covering area varies seasonally from 140 to 200km 2 . there is limited eutrophication, and aquatic vegetation in the inner side of the lake, bad odor and greenish water color were observed due to low fresh water flow. sediment deposition is common practice which has reduced the storage capacity of the lake. the existing estimated annual inflows to manchar lake are shown in table i from various sources with total volume 0.899maf. the evaporation of manchar lake is calculated as 0.189maf, hence the store capacity of the lake would be 0.329maf. engineering, technology & applied science research vol. 9, no. 6, 2019, 5074-5079 5076 www.etasr.com mahessart et al.: impact of right bank outfall drain-i (rbod-i) / main nara valley drain (mnvd) … table i. estimation of inflows to man ch ar lake water supply source volume (maf) hill torrents 0.133 nai gaj 0.188 indus river 0.053 mnvd 0.525 total 0.899 evaporation loss 0.189 net inflows 0.710 (a) (b) fig. 2. water level gauge installed at manchar lake, (b) covered water body of manchar lake. screenshot from google earth, © 2019 google, image © 2019 maxar technologies, image © 2019 cnes/airubus water samples were collected from mnvd, the water body of the lake, and the aral tail wah for physicochemical and heavy metal analysis. the ph and tds values of collected samples were measured in situ. moreover, the collected water samples were preserved with nitric acid in an ice box for maintaining low temperature and were sent to hi-tech laboratory, sindh university, pakistan for analysis. samples have been collected from the following locations: • sample 1 (s-1): rbod-i/ mnvd rd-250, at latitude 25°30’38’’ and longitude 67°37’29’’ • sample-2 (s-2): western hill side, at latitude 26°26’23’’ and longitude 67°35’29’’ • sample 3 (s-3): lakhi hill side, at latitude 26°26’14’’ and longitude 67°45’50’’ • sample 4 (s-4): center of lake, at latitude 26°25’39’’ and longitude 67°37’19’’ • sample 5 (s-5): aral tail wah, at latitude 26°24’10’’ and longitude 67°51’49’’ it was observed that the fertility of the agricultural land has been degraded due to the presence of saline water and seepage. the water quality is such that it is unfit for drinking and not usable for agriculture practice, but the locals are using it anyway, because they have no other option. iv. results and discussion a. indus river aral head regulator the design discharge of aral head regulator is 10,000 cusecs taken from indus, when the downstream of sukkur barrage discharge exceeds 250,000 cusecs. the design discharge of aral tail regulator is 25,000 cusecs which is the main source of draining of the lake into indus when indus is at normal flow and the designed discharge of danister canal is 500 cusecs which is located at rd 62 of manchar containing bank. figure 3(b) shows the capacity of the lake in million cubic feet (mcft) and area in square miles. (a) (b) fig. 3. (a) water level gauge installed at the lake, (b) lake storage capacity against areea b. physicochemical analysis figure 4(a) shows the ph and total dissolved solids (tds) values of the collected samples. the ph is a measure of water acidity and values from 6.5 to 8.5 are suitable for aquatic life. the ph values of all samples varied between 7.5 and 8 and were within the permissible limits according to the national environmental quality standards (neqs). the tds of the collected samples were above the permissible (1000ppm) limit of neqs. the tds value of s-1 was found higher than the other samples because mnvd receives highly salt concentration water through rbod-iii. the tds of the other samples varies due to dilution. therefore, the water from mnvd and from the lake is unfit for drinking, agricultural practice, or fishing. the neqs permissible limits of biochemical oxygen demand (bod) and of chemical oxygen demand (cod) are 80mg/l and 150mg/l respectively. figure 4(b) shows that the bod and cod values of the samples are within these permissible limits. the conclusion is that there is no danger for the aquatic life regarding oxygen demand. ca and mg salts inhibit the formation of soapsuds. figure 5(a) shows the hardness values of the samples witch are all found higher than the permissible limit (500ppm). the sample values of calcium are within the permissible limit (200ppm). figure 5(b) shows the values of mg and na which are higher than their respected permissible limits (150ppm and 200ppm). engineering, technology & applied science research vol. 9, no. 6, 2019, 5074-5079 5077 www.etasr.com mahessart et al.: impact of right bank outfall drain-i (rbod-i) / main nara valley drain (mnvd) … (a) (b) fig. 4. (a) ph and tds values, (b) bod and cod values (a) (b) fig. 5. (a) hardness and calcium values, (b) mg and na the permissible limits of so4 and cl are 250ppm and 250ppm. the values of all collected samples (figure 6(a)) are higher than these limits. the higher so4 concentration of all samples is caused by the releasing of agricultural, industrial, and municipal wastewater through robd-i/mnvd into the lake. figure 6(b) shows the total coliform of the samples which is higher than the permissible limit which is 0mg/l. we can conclude that the importance of the lake is reduced due to the degradation of water quality, which is now unfit for human consumption, local flora and fauna or any other use. (a) (b) fig. 6. (a) sulphate and chloride values of samples, (b) total coliform values c. water quality index water quality index (wqi) indicates the overall water quality based on the parameters of water quality samples. wqi is computed by: 1 n n qwi wi qi − = ×∑ (1) where qi is the sub-index for the ith wq parameter, wi is the weight associated with the ith wq parameter, and n is the total number of wq parameters. wqi is an indicator to assess water quality suitability of surface/groundwater for domestic and drinking purposes and surmises many parameters of water samples [24]. the wqi standards are shown in table ii. figure 7 shows the wqi values of the five analyzed samples. the values of s-1 to s-4 were found in range of 75-100 of wqi which indicates very poor water quality, while s-5 was found to be even worse and unsuitable for drinking. this study exhibits that contamination with tds, ec, so4, cl, na and hardness in the lake water poses high potential risk to the locals, especially those who use it as drinking water. table ii. surface water ratin g based on wqi qwi value water quality rating 0-25 excellent 25-50 good 50-75 poor 75-100 very poor >100 unsuitable for drinking purposes engineering, technology & applied science research vol. 9, no. 6, 2019, 5074-5079 5078 www.etasr.com mahessart et al.: impact of right bank outfall drain-i (rbod-i) / main nara valley drain (mnvd) … fig. 7. wqi of manchar lake water (drinking water) d. impairment of aquatic and terrestrial lake ecosystem the major issues related to the degradation of the lake are the reduced supply of freshwater due to rainfall runoff reduction from the khirthar range, the high discharge of contaminated water from the mnvd and the lack of freshwater supply from indus river. there are various other sources of pollution such as chemical sediments from hill torrents, pollutants from cities, industries, and agricultural lands through mnvd/rbod-i via rbod-iii, sedimentation from indus river through aral head wah and poisonous chemicals used by fishermen. the climate change causes dry spells, less water is carried by indus river, the water requirement for agriculture is inevitably higher, and industries and urbanized population lead to polluted inflows having negative impact on the ecology of the lake. 1) poor lake water quality the water quality of the water body is very poor. the analysed values of collected samples’ parameters calcium, hardness, chlorine, manganese and sulphate of mnvd and lake water are much higher than their permissible limits. despite this, the locals are using contaminated lake water because the groundwater around the lake is highly saline. 2) degraded groundwater quality the lake is covered with mountain ranges from the western and eastern sides, but the southern side consists of alluvial soil. the groundwater quality has been degraded due to seepage of saline water from the lake and the groundwater table has been raised due to the twin problem of waterlogging and salinity. hence, the groundwater is unfit for drinking, agriculture, or any other purpose. 3) social value of manchar lake manchar is exclusively known for its “floating villages” where more than 1000 fishermen reside with their families. the population in surroundings and within the lake numbers in many thousands. the locals’ main occupations are farming, fishing, and tendering cattle. the living standards have been reduced because almost all the locals’ survival sources have diminished. 4) impact on health the consumption of degraded water by the locals who live in boat villages and around the lake caused the emergence of endemic waterborne diseases including gastroenteritis, malaria, asthma, hepatitis a, b and c, diarrhea, tuberculosis, respiratory diseases, typhoid fever, etc. 5) impact on fishing fish species including chitla (guddan), gibleon catla catla (thaili), labeo rohita (rohu or dumbra), labeo calbasu (balck rohu), wallago catfish (jarko), white carp (morakho), rita rita (khagga) and aorichthyas (seenghari) used to be abundant. now, all fish are extinct but a small exotic fish variety is available which can survive in saline and polluted water. hence, the fish catch is reduced and the average catch by an individual which used to be 30-40kg/day in 1970, now it is about 4-5kg/day. 6) impact on fertile land the fertile lands in the adjacent area of the lake do not get water from the irrigation system because this area is at the tail of the command area of dadu canal which intakes from sukkur barrage. therefore, there is a common practice of application of water from mnvd and the lake for growing crops and vegetation. this continuous practice of contaminated water use has severely affected soil fertility. the once fertile soil has been converted to saline and sodic which has reduced crop yield. it is feared that further use of this practice may convert fertile lands to unproductive lands for any crop. 7) impact on livestock livestock was the main source of milk, mutton, meat, and income. therefore, each household has buffaloes, cows, sheep, and goats. the household cattle use to get their food from the land and pastures nearby the lake, but the pastures have been diminished due to land degradation and waterlogging. 8) impact of the construction of the rbod system the natural drainage system took water from indus at downstream of guddu barrage which was the source of water supply to manchar lake via hamal during monsoon season. this natural drainage had been blocked due to road construction and agricultural land conversion. the rbod system covers rbod-iii, rbod-i/mnvd and rbod-ii. the rbod-iii receives wastewater from some parts of baluchistan and sindh and is connected with rbod-i at the zero point of mirokhan and shahdadkot drains. rbod-i/mnvd has been connected with robd-ii via indus link at manchar crossregulator (figure 1). hence, the rbod-ii is parallel to indus river from sewan to jamshoro which outfalls into gharo creek of arabian sea. therefore, there are constructive, negative or complex impacts of rbod on the manchar. at present time, about 4500 cusecs of wastewater from industries, municipalities, and agriculture are directly disposed to the lake through the rbod-i/mnvd because the rbod-ii is under construction. with the diversion of rbod-i/mnvd from lake to rbod-ii, the major pollutant source will be stopped but it may diminish the volume of lake water. the major sources of water supply (indus river, hill torrents from khirthar) have already been reduced. after the diversion of rbod-i/mnvd water, the lake may convert into a small pond which will be the end of its aquatic and terrestrial ecosystem. the overall impact of the system consists of safe wastewater disposal, rainfall runoff, waterlogging and salinity reduction, change in land use and capability, the reclamation of engineering, technology & applied science research vol. 9, no. 6, 2019, 5074-5079 5079 www.etasr.com mahessart et al.: impact of right bank outfall drain-i (rbod-i) / main nara valley drain (mnvd) … saline and sodic soils, and the improvement of groundwater quality. v. conclusions the results of wqi indicate that the water quality of the collected samples is very poor and unsuitable for drinking. statistical analysis of parameters such as tds, ec, so4, cl, na and hardness shows that they are higher than their permissible limits. consequently, lake water possesses high potential risk to local consumers and especially aquatic life. the estimated lake water supply quantity is 0.899 maf from major sources such as indus river, hill torrents, and mnvd but these supply sources are gradually diminishing, which threatens the lake’s very existence. therefore, the restoration of these sources of water supply should be a priority. the construction of river weir/barrage at sewan may raise water level to divert into the lake, the downstream inflow from the under construction of nai gaj dam must be ensured. sindh local government plans to restore the lake with additional supply of freshwater from the rice and dadu canals. these canals may supply fresh water into lake and address the problem of pollution. the rbod ii project was to be completed earlier but the task could not be accomplished timely due to insufficient funds. the rbod-ii project must be accomplished on a priority basis for diverting contaminated water from lake towards the arabian sea. besides this, there is a need to address the contamination of the lake by poisonous chemicals which have degraded the local ecology. moreover, a management and restoration of manchar lake plan should be developed through an integrated water resources management under sindh irrigation department with other stakeholders such as the sindh environmental protection agency, the agriculture, forests and wildlife, and livestock and fishery departments and the local government. these agencies must work together on the lake management program, to form a legal framework for lakes, to address drainage issues, to improve water quantity and quality, to restore ecology, to enhance ecotourism, and to conduct research studies to integrate scientific and engineering solutions for the system’s sustainability. references [1] m. z. khan, d. abbas, s. a. ghalib, r. yasmeen, s. siddiqui, m. nazia, a. v. latif, “effects of environmental pollution on aquatic vertebrates and inventories of haleji and keenjhar lakes: ramsar sites”, canadian journal of pure and applied scieces, vol. 6, no. 1, pp. 1759-1783, 2012 [2] a. k. asad, a. sana, “wetlands of pakistan: distribution, degradation and management”, pakistan geographical review, vol. 69, no. 10, pp. 28-45, 2014 [3] a. l. rao, protection and management of pakistan wetlands midterm review, ministry of environment, pakistan, 2009 [4] a. a. mahessar, a. l. qureshi, k. c. mukwana, a. q. jakhrani, “study of environmental impacts and threats to the ramsar haleji lake, sindh, pakistan”, international journal of applied environmental sciences, vol. 10, no. 5, pp. 1577-1590, 2015 [5] w. j. mitsch, j. g. gosselink, “the value of wetlands: importance of scale and landscape setting”, ecological economics, vol. 35, no. 1, pp. 25-33, 2000 [6] b. fisher, k. turner, m. zylstra, r. brouwer, r. de groot, s. farber, p. ferraro, r. green, d. hadley, j. harflow, p. jefferiss, c. kirkby, s. mowatt, r. naidoo, j. paavola, b. strassburg, d. yu, a. balmford, “ecosystem services and economic theory: integration for policyrelevant research”, ecological applications, vol. 18, no. 8, pp. 20502067, 2008 [7] p. g. whitehead, r. l. wilby, r. w. battarbee, m. kernan, a. j. wade, “a review of the potential impacts of climate change on surface water quality”, hydrological sciences journal, vol. 54, no. 1, pp. 101-123, 2009 [8] p. s. lake, “ecological effects of perturbation by drought in flowing waters”, freshwater biology, vol. 48, no. 7, pp. 1161-1172, 2003 [9] a. q. jakhrani, s. r. samo, i. nizamani, “impact of wastewater effluents on physico-chemical properties of groundwater”, sindh university research journal (science series), vol. 41, no. 1, pp. 75-82, 2009 [10] a. q. jakhrani, impact of oxidation ponds on groundwater quality at hyderabad, me thesis, mehran university of engineering and technology, jamshoro, 2002 [11] s. h. wadho, geological conditions of river indus and floods in sindh, sindhica academy, 2019 [12] m. b. arain, t. g. kazi, m. k. jamali, h. i. afridi, j. a. baig, n. jalbani, a. q. shah, “evaluation of physic-chemical parameters of manchar lake water and their comparison with other global published values”, pakistan journal of analytical & environmental chemistry, vol. 9, no. 2, pp. 1010-109, 2008 [13] w. m. achakzai, s. saddozaai, w. a. baloch, samiullah, m. a. panezai, z. masood, a. n. somroo, “comparison of water chemistry of manchar lake with who drinking water quality standards”, americaneurasian journal of agricultural and environmental sciences, vol. 15, no. 7, pp. 1224-1230, 2015 [14] t. m. jahangir, m. y. khuhawar, s. m. leghari, m. t. mahar, k. p. mahar, “water quality and sediment assessment of manachar lake, sindh pakistan: after effects of the super floods of 2010”, arabian journal of geosciences, vol. 8, pp. 3259-3283, 2015 [15] y. h. kang, g. y. sheng, j. m. fu, b. x. mai, g. zhang, z. lin, y. s. min, “polychlorinated river delta and macau”, marine pollution bulletin, vol. 40, no. 9, pp. 794-797, 2000 [16] z. a. soomro, m. ashrif, u. imran, j. wu, environmental assessment of manchar lake, pakistan council of research in water resource, 2017 [17] indus for all programme, wwf – pakistan, ecological assessment of fauna, at manchar lake, district dadu, sindh, 2001-2011 [18] n. anial, “mohannas of manchar lake sindh: an indigenous culture tradation pushed to the edge”, thaap journal, vol. 2015, pp. 97-118, 2015 [19] a. sheeba, s. bano, j. h. kazmi, “moniotring spatial distribution of the selected bird’s species in wetlands of sindg: a framework of remote sensing and gis”, international journal of biology and biotechnology, vol. 10, no. 1, pp. 7-20, 20013 [20] s. m. zehra, time series models of the electrical conductivity at the manchar lake in pakistan, msc thesis, the university of texas at austin, 2010 [21] t. m. jahangir, chemical assessment of surface and groundwater resources of sindh province, phd thesis, university of sindh, 2004 [22] a. a. mahessar, k. c. mukwana, a. l. qureshi, m. e. ul h. leghari, a. l. manganhar, “assessment of water quality of lbod system and environmental concerns”, quaid-e-awam university research journal of engineering, science & technology, vol. 15, no. 1, pp. 32-39, 2016 [23] a. a. mahessar, a. l. qureshi, a. n. leghari, s. qureshi, s. f. shah, f. a. shaikh, “impact of hairdin, miro khan and shahdad kot drainage on hamal dhand, sindh”, engineering, technology & applied science research, vol. 8, no. 6, pp. 3652-3656, 2018 [24] n. b. bhatti, a. a. siyal, a. l. qureshi, “groundwater quality assessment using water quality index: a case study of nagarparkar, sindh, pakistan”, sindh university research journal (science series), vol. 50, pp. 227-234, 2018 microsoft word 33-2389_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3652-3656 3652 www.etasr.com mahessar et al: impact of hairdin, miro khan and shahdad kot drainage on hamal dhand, sindh impact of hairdin, miro khan and shahdad kot drainage on hamal dhand, sindh a. a. mahessar sindh barrages improvement project irrigation department, government of sindh sindh, pakistan amahessar@yahoo.com a. l. qureshi u.s.-pakistan centers for advanced studies in water, mehran university of engineering and technology, jamshoro, pakistan alqureshi.uspcasw@faulty.muet.edu.pk a. n. laghari department of energy and environment, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan mashaalnasirlaghari@gmail.com s. qureshi dr. m. a. kazi institute of chemistry, university of sindh, jamshoro, pakistan s.dr582@gmail.com s. f. shah department of environmental engineering, mehran university of engineering and technology, jamshoro, pakistan syedafarwashah1@gmail.com f. a. shaikh department of chemical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan faheemakhtar86@yahoo.com abstract—safe drinking water is a basic need. surface water bodies are the primary source of safe water. drain water, industries, urban/rural effluents, and waste materials are often disposed into surface water bodies without any treatment. all major water bodies of sindh province are thus more or less polluted. these water bodies are interconnected with the indus river like the artery system for blood circulation in bodies of living things. the main source of contamination of hamal lake is the disposal of the effluents of hairdin drain, miro khan drain, and shahdad kot drain. this lake’s main source of fresh water is rained from khirthar mountains. hamal lake is connected through the main nara valley drain (mnvd) to manchar lake that eventually outfalls into indus river. hence, drain water pollutes not only hamal and manchar lakes but also indus river due to their interconnection. presently, right bank outfall drains (rbod i-iii) have been constructed for safe disposal of drain effluents thus avoiding the polluting of freshwater bodies. keywords-hamal lake; agricultural and industrial effluents; drainage system; rbod i. introduction wetlands areas contain unique land cover classes. they are some of the most diverse ecosystems in the world [1]. such areas, where moisture is produced due to saturation, comprise of distinctive land cover classes. many factors exert an influence on wetland stability or degradation. land use and land cover change influence wetlands in most regions [2-5]. the environment impact of drainage has reached a critical crossroads and requir extensive research. in the past, drainage systems have been designed for continuous operation, and very little consideration was given to the environmental impact of the drainage water on surface water quality. continuous operation of drainage systems in arid areas results in over drainage of irrigated fields with the resultant loss of water and an excessive load of salt being transported to surface water along with any dissolved agricultural chemicals [6-7]. the problem with salt accumulation in the wetlands/reservoirs highlights the environmental concerns associated with drainage from arid irrigated lands [8]. not only salinity, but also toxic elements found in the drainage water are issues of concern. there are major concerns regarding pollution and the discharge of phosphorus and pesticides in drainage water. in response to the environmental impacts of drainage water, research is being conducted on managing drainage water discharges to reduce the total load of pollution in the drainage water and the salinity in drainage water. human activities are polluting freshwater bodies. globally, about 1.5 billion people have no safe drinking water access and about 5 million deaths per year are attributed to waterborne diseases [9]. the untreated effluents of factories from lbod catchment area contain high amounts of dangerous ph, ec, tds, tss, bod5, cod, making them unfit and must not be discharged into irrigation and drainage systems [10]. the main sources of fresh water can be affected by the discharge of untreated wastewater and dumping of effluents which have an adverse impact on freshwater bodies [11]. safe drinking water is a basic and global human need [12]. the major cause of contamination was found to be the susceptibility of drinking water sources to intrusions from the nearest contamination sources [13]. many changes in physico-chemical parameters of water and biota were brought about by human activities which have significant impact on ecological conditions and fauna and flora. lakes are one of the most productive ecosystems engineering, technology & applied science research vol. 8, no. 6, 2018, 3652-3656 3653 www.etasr.com mahessar et al: impact of hairdin, miro khan and shahdad kot drainage on hamal dhand, sindh and the qualitative and quantitative study of species present in lakes is essential, especially for the development and improvement of natural resources [14]. it is shown by the physic chemical parameter tests that the algal flora of main nara valley drain (mnvd) made its way in to the manchar lake, district dadu, sindh. metals identified are mostly toxic such as al, cu, mn, pb, zn, co and fe. these metals are different from other toxic materials due to nondegradable nature in the environment. the physico-chemical properties like alkalinity, temp, do, conductivity, tds, turbidity, ph and hardness of kinjhar lake were investigated in [15-16]. hamal lake is located in the west of warrah town, in the shahdad kot district at 27°23′n, and 67°55′e. the covered area of the lake is about 25km in length and 10km in width. hamal lake comprised initially of three water bodies, namely sarroh, badram, and kachhari. on the western side of the lake, there is a hilly region of kachho called khirthar hills (jabal), which starts from karachi south and ends at balochistan north. on the eastern side, flood protective (fp) bund was constructed during the british period for the protection of fertile lands and populated areas from hill torrent waters. this fp bund was constructed parallel to hamal lake along the hills. during the flood season the excess of water drains through hamal regulator into mnvd and finally falls into manchar lake. hamal is a shallow lake with a maximum water depth of 5-11 feet which was initially free from contamination and pollution (figure 1). but due to water mismanagement, the lake got polluted, and the poor quality of lake water is threatening its ecosystem. fig. 1. hamal lake and rbod ii. materials and methods water samples of hamal lake were collected from 7 locations. two locations were selected at shadadkot, and miro khan drains outfall into hamal lake (figure 2). these samples were collected in polyethylene bottles and sent to the water analyzing laboratory of pakistan council of research in water resources (pcrwr). all samples were collected from the following locations. • sample 1: outfall of miro khan drain at zero point. • sample 2: outfall of shahdad kot drain at zero point. • sample 3: mixing points of drains in hamal drain. • sample 4: sarroh lake, outfall water of hairdin drain. • sample 5: badram lake, near the fishermen’s village. • sample 6: upstream of regulator mnvd. • sample 7: downstream of the regulator of mnvd. fig. 2. diagram view of the hamal lake iii. results and discussion figure 3 shows the ph values of the samples of the lake along with the lower and upper neqs (national environmental quality standards) limits. the ph values of samples 1-3 are below the lower limit. low ph values may harm the fauna of the lake. figure 4 exhibits the samples’ electrical conductivity (ec). this figure shows that the water is highly saline (see also figure 6), which is not suitable for drinking or for the local fish. fig. 3. ph values of samples collected from the lake total dissolved salts (tds), chlorides, hardness and sulfates are shown in figure 5. chloride values are much higher than those allowable under neqs. the hardness of all samples is higher than the neqs limits. sulphate values were 1071.4, 2073.8, 1457.2 and 2607mg/l in locations 1, 2, 4 and 5 respectively as shown in figure 5. the results of copper (cu) samples indicate that the value of cu is within the permittable limits except for the sample of location 3 (figure 7). results show that the values of the different parameters of the effluents are much higher than those allowablefrom neqs. people along shahdad kot drain and miro khan drain use drain effluents due to freshwater engineering, technology & applied science research vol. 8, no. 6, 2018, 3652-3656 3654 www.etasr.com mahessar et al: impact of hairdin, miro khan and shahdad kot drainage on hamal dhand, sindh unavailability. the consumption of this polluted water causes negative impacts. fig. 4. ec of samples fig. 5. values of tds, chloride, hardness and sulphate fig. 6. salinity of samples fig. 7. cu of samples a. adverse impact on the ecosystem of the lake 1) poor drinking water quality in the lake vicinity there are many villages situated in its banks and islands. groundwater was highly saline on both eastern and western banks of the lake. therefore, the locals have no option of drinking water besides the contaminated surface drain water. during the drought season, the locals were in dire need of drinking water. hand pumps have been installed at a depth of 15 to 20 feet at some locations. the villagers bring freshwater from hand pumps from 15 to 20km distance and when they can’t, they use drainage water. 2) adverse impact on health adverse environmental conditions have risen in the area. endemic water-borne diseases have been spread out in the hamal lake area, diseases including hepatitis-a, b and c, diarrhea, tuberculosis, gastroenteritis, malaria, asthma, respiratory diseases, and typhoid fever. 3) negative impact on soil local people cultivate wheat and oilseeds through pumping contaminated water from the lake located in the adjacent area while the people of kachho cultivate crops on rainfall water. cultivation on saline/contaminated water is severely affecting soil conditions, and it is feared that this practice would ultimately make soil unproductive for any crop. 4) degradation of fertile land the adjacent area and covered lands of the lake were fertile. these lands used to produce high yields of crops like wheat and oilseed. in the flood of 1976, the area of the lake was filled with water, and at the same time, the drainage effluents of various districts of sindh province and balochistan were diverted into the lake. the drainage water was highly saline, which contaminated the lake water. the effluent water maintained its level about 8 to 10 feet above fertile lands in the left (eastern) bank of the lake. therefore, seepage water has raised the water-table depth. this caused waterlogging and salinity which led to the deterioration of fertile lands. the problem spread out in an area of about 78km in width, and 25-30km in length. thus, thousands of acres of first-class lands fell victims to waterlogging and salinity. 5) impact on fishing there were many fishermen villages located in the vicinity and islands of the lake. the homes of fishermen were built of reeds, bushes, and wood. moreover, many fishermen migrated from district badin and indus river and the coastal areas of sindh. in 80’s the fish was caught in hundreds of tonnes, which is now reduced to only 5 or 7 tonnes per day. the leading cause of this reduction was the contaminated water released in the lake. many local species (paplate, goj, khagho, kurriro, theili, shakur, morakhi, seengari, jarco, ghandan, popri, mundhi, buhan, gulfam and dhangni ) of fish have become extinct. all lakes of sindh province had been given on contract (under thekedari system) to contractors including the hamal lake. engineering, technology & applied science research vol. 8, no. 6, 2018, 3652-3656 3655 www.etasr.com mahessar et al: impact of hairdin, miro khan and shahdad kot drainage on hamal dhand, sindh 6) adverse impact on birds when fresh water was available, millions of migratory and local birds used to visit in different seasons in these lands. 7) adverse impact on the forest the forest was filled with various types of trees and vegetation. the forests are mostly relics of an indus type dense canopy together with dominant grasses such as the wild sugar canes. 8) negative impact on wildlife and on livestock especially this forest had been playing a pivotal pasture role for livestock and wildlife. the locals used to prosper due to the selling of timber wood and honey. mountainous people migrated from the hilly areas for searching pasture for their sheep, goat, cow, and camel herds. now, local and mountainous people are anxious and worried about pasture and other resources. the locals told the visiting team that the forest was home to different kinds of animals, which used to be very wild and dangerous. b. positive impact of construction of rbod i, ii and iii system rbod projects are located on the right bank of river indus. construction of rbod is an essential, prerequisite for the development of surface drainage of the right bank area, since there is no natural outfall. completion of the rbod project will provide drainage facilities to the existing and proposed drainage projects in sindh, but will also provide a much desired relief to hamal lake from the drainage units of balochistan and sindh. rbod is being executed in three projects namely: • rbod-iii, from hairdin pump station (balochistan) to miro khan zero point. • rbod-i, from mkzp up to sehwan • rbod-ii, from sehwan to the arabian sea fig. 8. rbod-i and ii rbod iii has been constructed in balochistan which is connected at mirokhan drain zero point with rbod i and rbod i connects at cross regulator of manchar lake with rbod ii which ultimately outfalls into the arabian sea through the gharo creek. the catchment area of these drains covers some parts of balochistan and the entire area of the right side of indus river. presently, there are positive and negative impacts from the construction of the rbod system. the overall impacts of the construction of rbod are: reduction of groundwater level, changes of hydrological conditions, land drainage resulting in changes in land use and capability. the reclamation of wetlands or highly affected saline lands results in change of these lands to croplands. fig. 9. rbod-iii the direct impacts of the rbod drainage system generate a series of impacts: climatic, social, economic and environmental impacts, which affect soil crops and agriculture practices. the indirect impacts, can be biological, and/or hydrological, physical, or chemical. these impacts can be positive, negative or complex. positive impacts of the discharge are the removal of salts and other harmful substances from the soil, and the availability of drainage water for various purposes. negative impacts of the discharge include the excessive leaching of valuable nutrients from the soil. iv. conclusions the effluents of kot magsi and usta muhammad areas are being disposed into hamal lake from two different routes. they are found to be highly saline and polluted. they must be treated and brought to safer limits. the salinity control and reclamation projects (scarp) tube wells installed in the catchments of miro khan and shahdad kot drains have to operate appropriately. severe environmental and ecological issues have risen due to the unabated disposal of effluents into hamal lake. this has resulted in the loss of monumental and historical places. therefore, efforts for the conservation of the environment should be carried out. in this connection, environmental awareness among the locals may be created through various methods. water quality of engineering, technology & applied science research vol. 8, no. 6, 2018, 3652-3656 3656 www.etasr.com mahessar et al: impact of hairdin, miro khan and shahdad kot drainage on hamal dhand, sindh the lake and the drainage system should be appropriately monitored. the wetland management plan for the hamal lake should be prepared and implemented. hamal lake was historically a favorite nesting place for wildlife but is losing fast its wildlife flora and fauna. it may be declared a ramsar site for its proper attention and treatment. people in the area are deprived of basic facilities like pure water. besides that, the economic conditions are too weak. therefore, efforts should be carried out by the concerned agencies in order to provide the necessary facilities. natural resources are being explored in the hamal lake area. unfortunately very little has been done for the betterment of inhabitants lives. in this regard, it must be ensured that necessary funds are being spent on the welfare of the local people. apart from some cursory baseline studies made during the early stages, no systematic evaluation has been made on water quality, fish species and the seasonal distribution of migratory and resident birds in this coastal environment. this study, therefore, recommends the implementation of a program of physical, chemical and biological monitoring of the area. the construction of rbod on the right side of the indus river develops positive impacts for the reclamation of hamal lake. salinized and waterlogged lands will be reclaimed due to the construction of the rbod system. references [1] w. j. mitsch, j. g. gosselink, wetlands, van nostrand reinhold, new york, 1993 [2] millennium ecosystem assessment, ecosystems and human wellbeing: wetlands and water, pp. 3-15, world resources institute: washington, dc, usa, 200 [3] w. steffen, a. sanderson, p. d. tyson, j. jager, p. a. matson, b. moore iii, f. oldfield, k. richardson, h. j. schellnhuber, b. l. turner ii, r. j. wasson, global change and the earth system: a planet under pressure, pp. 14-18, springer-verlag press, berlin, germany, 2004 [4] j. j. feddema, k. w. oleson, g. b. bonan, l. o. mearns, l. e. buja, g. a. meehl, w. m. washington, “the importance of land-cover change in simulating future climates”, science, vol. 310, no. 5754, pp. 1674-1678, 2005 [5] e. lambin, x. baulies, n. bockstael, g. fischer, t. krug, r. leemans, e. moran, r. rindfuss, y. sato, d. skole, b. l. turner ii, c. vogel, land use and land cover change: implementation strategy, igbp report no.48, international geosphere-biosphere programme: stockholm, sweden, ihdp report no. 1, international human dimensions programme on global environmental change, bonn, germany, 1999 [6] e. j. doering, l. c. benz, g. a. reichman, “shallow-water-table concept for drainage design in semiarid and subhumid regions. advances in drainage”, fourth national drainage symposium, vol. 13, no. 4, pp. 34-41, 1982 [7] j. e. ayars, e. w. christen, j. w. hornbuckle, “controlled drainage for improved water management in arid regions irrigated agriculture”, agricultural water management, vol. 86, pp. 128-139, 2006 [8] anonymous, a management plan for agricultural subsurface drainage and related problems on the westside san joaquin valley: final report of the san joaquin valley drainage program, california department of water resources, sacramento, california, 2015 [9] m. a. mahar, w. a. baloch, s. i. h. jafri, “diversity and seasonal occurrence of planktonic rotifers in manchhar lake, sindh, pakistan”, pakistan journal of fisheries, vol. 1, no. 1, pp. 25-32, 2000 [10] a. l. korai, g. a. sahto, k. h. lashari, s. n. arbani, “biodiversity in relation to physicochemical properties of keenjhar lake, thatta district, sindh, pakistan”, turkish journal of fisheries and aquatic science, vol. 8, pp. 259-268, 2008 [11] k. a. onsdorff, “what the weitzenhoff court got wrong?”, journal of water environment law and practice, vol. 4, no. 1, pp. 14-18, 1996 [12] a. l. qureshi, a. a. mahessar, m. e. u. h. leghari, b. k. lashari, f. m. mari, “impact of releasing wastewater of sugar industries into drainage system of lbod, sindh, pakistan”, international environmental science and development, vol. 6 no. 5, pp. 381-386, 2015 [13] m. a. sohag, a. a. mahessar, i. a. bohio, “pollution of indus water and the drainage system of sindh”, the first international conference on environmentally sustainable development, abbottabad, pakistan, june 26-28, 2005 [14] r. ahmad, “studies on the chemistry control of some selected drinking and industrial waters”, pakistan journal of scientific and industrial research, vol. 48, no. 3, pp. 174-179, 2005 [15] t. m. jahangir, m. y. khuawar, s. m. leghari, w. a. baloach, a. a. leghari, a. leghari, “some studies on water quality and biological life at kinjhar and haleji lakes of district thatta, sindh, pakistan”, pakistan journal of biological sciences, vol. 3, no. 11, pp. 19651972, 2000 [16] international bank for reconstruction and development international development association, management report and recommendation in response to the inspection panel investigation report of the pakistan national drainage program project, 2006 microsoft word etasr_v11_n3_pp7191-7194 engineering, technology & applied science research vol. 11, no. 3, 2021, 7191-7194 7191 www.etasr.com vu et al.: study of the compressive strength of concrete with partial replacement of recycled coarse … study of the compressive strength of concrete with partial replacement of recycled coarse aggregates xuan hung vu department of construction vinh university vinh city, viet nam hungvukxd@vinhuni.edu.vn trong cuong vo department of construction vinh university vinh city, viet nam cuongvqc@gmail.com van tien phan department of construction vinh university vinh city, viet nam vantienkxd@vinhuni.edu.vn abstract-this paper presents a study on the compressive strength of concrete using recycled aggregates. the concrete was designed to have a 25mpa compressive strength and an 8cm slump. the rates of replacing natural aggregates with recycled coarse were 0%, 10%, and 20%. the test samples were compressed to determine their compressive strength value after 7, 14, and 28 days of curing. the results showed that the concrete slump did not change effectively at a 10% replacement rate. when using 20% recycled aggregates, the concrete was too hard and the homogeneity of the concrete mixture could not be guaranteed. the compressive strength slightly decreased using 10% of recycled aggregates and decreased significantly using 20%. therefore, 20% of recycled aggregate replacement is not suitable. the results showed that using recycled aggregates at a rate of 10% is optimal. keywords-compressive strength; recycled concrete; demolishing work i. introduction in recent years, developed countries deal with the recycling and treatment of construction solid waste. construction's solid waste treatment, solid waste minimization, pressure to change, and the approach to resolving these issues in the uk were studied in [1]. china faces a similar problem as the amount of solid construction waste was more than 1.5 billion tons per year in 2018, and it was predicted to reach 2.5 billion per year in 2020 [2]. the solid waste treatment in current construction sites, the life cycle of sustainable development, and the evaluation of the environmental impact of the construction materials consumed in china during 2000-2015 were studied in [3]. many studies have been conducted on recycled aggregates, such as their use in green concrete [4, 5], coarse aggregates for concrete [6], and fine concrete [7, 8]. while the reuse of construction solid waste as aggregates for concrete has been widely used and achieved remarkable efficiency, many studies have been conducted recently on the mechanical properties of concrete with recycled aggregates. the influence of the recycled aggregates on the compressive strength of concrete was studied in [9], concluding that they did not have a significant influence on compressive, flexural, and tensile strength. the use of recycled aggregates from demolished works after crushing and grading, helps to save natural aggregate sources and protect the environment, was studied in [10]. the compressive strength of concrete made from recycled coarse aggregates was studied in [11], with consideration of the source of the recycled aggregates and the strength of the target concrete. the toughness and soundness test results on the recycled coarse aggregates showed a higher percentage loss than the natural, but it remained within the acceptable limits. the compressive and splitting tensile strengths of concrete with recycled coarse aggregate depend on the mix proportions. in general, the strength of the recycled concrete can be 10-25% lower than the conventional made with natural coarse aggregates. this paper presents a study on the compressive strength of concrete having a partial replacement of natural with recycled coarse aggregates. ii. composition of recycled concrete the concrete obtained after a project's demolition was crushed and the resulting coarse aggregates were washed, dried, and pre-screened to remove any dust particles. these raw aggregates were screened to classify the particles and then mixed again to be graded as standard for concrete according to [12]. to avoid strongly absorbing recycled aggregates affecting the setting of the concrete, the coarse aggregates were soaked in water and then dried under normal conditions. in this study, a natural concrete aggregate was selected as a reference. the coarse aggregate was replaced partially by solid waste from the crushed demolition site. after casting according to the standard, the samples were stored under normal conditions and tested for compressive strength after 7, 14, and 28 days. fig. 1. recycled coarse aggregates corresponding author: van tien phan engineering, technology & applied science research vol. 11, no. 3, 2021, 7191-7194 7192 www.etasr.com vu et al.: study of the compressive strength of concrete with partial replacement of recycled coarse … a. sand the mechanical properties of the sand used in the experiment were: • density: 2.65g/cm 3 • modulus of magnitude: 2.50 • volumetric mass: 1660kg/m 3 b. cement a commercial portland cement pcb40 was used, having the following mechanical properties: • actual strength: 40mpa • density: 3.1g/cm 3 c. coarse aggregates natural coarse aggregates were mixed with recycled materials. in this study, 20mm aggregates, the most common size of aggregates used in construction, was used having the following mechanical properties: • density: 2.61g/cm 3 • volumetric mass: 1430kg/m 3 d. concrete the designed recycled concrete had the grade of b20, and the design slump was 8cm. the compressive strength of the concrete was tested according to the vietnamese standard 3118:1993. cylindrical samples with size d150×h300 were cast and cured in water before being compressed to determine their compressive strength. the loading speed was set to 0.5kn/s. the replacement rates of coarse aggregates were 0%, 10%, and 20% of the standard reference sample, respectively. the mix components for 1m 3 of concrete are presented in table i. table i. mix components for 1m 3 of con crete mix components for 1m 3 of concrete aggregates by mass cement (kg) sand (kg) aggregate (kg) water (kg) 292.5 648.3 1216.3 195.0 aggregates by volume cement (kg) sand (m 3 ) aggregate (m 3 ) water (l) 292.5 0.391 0.851 195.0 table ii. experimental details of concrete samples no. notation of samples description quantity 1 cp0 reference sample: mix according to table i 3 samples for 7 days, 3 samples for 14 days, and 3 samples for 28 days. 2 cp10 recycled aggregate replacement rate: 10% 3 cp20 recycled aggregate replacement rate: 20% iii. results and discussion the results of measuring the slump of the concrete with recycled coarse materials are shown in table iii and figure 2. table iii. the slump of the recycled concrete no. replacement rate slump (mm) 1 0% 73 2 10% 70 3 20% 12 fig. 2. the slump of recycled concrete at various recycled coarse aggregates replacement rates. from figure 2, it can be noted that the slump of concrete did not change significantly at 10% replacement rate. when using 20% recycled coarse aggregates, the drop was markedly obvious as it dropped from 73mm at 0% to 70mm at 10%, and finally to 12mm at 20%. thus, when using 20% recycled aggregates, the concrete was too hard and its homogeneity could not be guaranteed. fig. 3. samples after the compressive experiments. table iv shows the destructive force (kn) results obtained from the compression test. compressive strength (mpa) was calculated from the destructive force p (kn) for each sample having a 15cm diameter, using: � � � � �� � � � � 7.5� � 176.71 �� (1) compressive strength was calculated, using (1), as: � � � � �/� (2) where p is the destructive load of the sample, s is the compressive area, and α is the coefficient of converting the experimental results when compressing the samples with engineering, technology & applied science research vol. 11, no. 3, 2021, 7191-7194 7193 www.etasr.com vu et al.: study of the compressive strength of concrete with partial replacement of recycled coarse … different sizes from the standard samples (150×150×150mm). for a cylinder sample having 150mm diameter and 300mm height, α was calculated to 1.2. table v shows the compressive strengths of the experimental samples after 7, 14, and 28 days. table iv. destructiv e force results no. replacement rate of recycled aggregates (%) sample destructive force (kn) 7 days 14 days 28 days 1 0 185.55 231.94 309.25 2 0 196.30 199.47 316.61 3 0 200.32 239.73 328.39 4 10 195.36 224.52 291.58 5 10 186.26 228.32 300.41 6 10 176.80 240.82 304.83 7 20 130.95 178.79 251.82 8 20 135.02 173.24 254.76 9 20 126.93 161.77 248.87 table v. compressiv e stren gth results no. replacement rate of recycled aggregates (%) compressive strength (mpa) 7 days 14 days 28 days 1 0 12.6 15.75 21 2 0 13.33 13.545 21.5 3 0 13.603 16.279 22.3 4 10 13.266 15.246 19.8 5 10 12.648 15.504 20.4 6 10 12.006 16.353 20.7 7 20 8.892 12.141 17.1 8 20 9.169 11.764 17.3 9 20 8.619 10.985 16.9 as it can be noted, the experimental concrete samples did not reach the design strength. the reference sample reached only 86.4% of the design strength. this rate was 81.2% when using 10% and 68.4% when using 20% recycled aggregates. thus, using 10% recycled aggregates did not affect significantly the compressive strength of the concrete. when using 20% recycled aggregates, the compressive strength dropped significantly. for a clearer observation, the compressive strength results of concrete at various recycle aggregate replacement rates are shown in figure 4 and table vi. table vi. compressive strength mean values for each experiment no. replacement rate of recycled aggregates (%) compressive strength (mpa) mean value achieved compared with design (25 mpa) 1 0% 21 21.6 86.4 % 21.5 22.3 2 10% 19.8 20.3 81.2 % 20.4 20.7 3 20% 17.1 17.1 68.4% 17.3 16.9 the decrease of compressive strength when using recycled aggregates was predicted, as noticed in previous studies [11, 13, 14]. the higher compressive strength of the concrete having a lower recycled aggregate replacement rate may be attributed to the greater bonding force and strength when using the same type of aggregate. figure 5 shows the strength development of recycled concrete, which indicates that concrete strength reached 51-67% after 7 days and about 6375% after 14 days of curing. details are shown in table vii. fig. 4. compressive strength of concrete at various recycled coarse aggregate replacement rates. fig. 5. the development of concrete's compressive strength. table vii. comparison of the compressiv e stren gth of concrete with the strength after 28 d ay s of curin g (r28) no. compressive strength (mpa) 7 days ratio compared to r28 14 days ratio compared to r28 28 days 1 12.6 60% 15.75 75% 21 2 13.33 62% 13.545 63% 21.5 3 13.603 61% 16.279 73% 22.3 4 13.266 67% 15.246 77% 19.8 5 12.648 62% 15.504 76% 20.4 6 12.006 58% 16.353 79% 20.7 7 8.892 52% 12.141 71% 17.1 8 9.169 53% 11.764 68% 17.3 9 8.619 51% 10.985 65% 16.9 as it can be noted, the strength development of the concrete using recycled aggregates at a low rate (≤ 20%) is similar to ordinary concrete. however, a few notes can be pinpointed: • normal concrete grows up to 65% of its maximum design strength at the age of 7 days. the experimental samples did not reach this level. this growth rate was slowed down when using 20% recycled aggregates, with a ratio of 5153% to r28. engineering, technology & applied science research vol. 11, no. 3, 2021, 7191-7194 7194 www.etasr.com vu et al.: study of the compressive strength of concrete with partial replacement of recycled coarse … • at 14 days of curing, the experimental concrete achieved about 70-75% of the maximum design strength. however, most of the concrete samples using 20% recycled aggregate had slightly lower strength than normal. iv. conclusion this paper presents the results of a study on the compressive strength of concrete using recycled aggregate from demolition works. the concrete was designed to have 25mpa compressive strength and 8cm slump. the rates of replacing natural aggregates with recycled coarse were 0%, 10%, and 20%. the test samples were compressed to determine their compressive strength values at 7, 14, and 28 days of curing. the results showed that the concrete slump did not change significantly at samples having 10% recycled aggregates. when using 20% recycled coarse aggregates, the drop was markedly obvious. thus, using 20% recycled aggregate resulted in too hard concrete, while the homogeneity of the concrete mixture could not be guaranteed. the compressive strength decreased slightly when using 10% recycled aggregates and significantly when using 20%. therefore, it can be concluded that the 20% replacement rate is not appropriate. the results showed that using recycled aggregates at a rate of 10% is an optimal solution. references [1] m. osmani, "construction waste minimization in the uk: current pressures for change and approaches," procedia social and behavioral sciences, vol. 40, pp. 37–40, jan. 2012, https://doi.org/10.1016/j.sbspro.2012.03.158. [2] "people’s republic of china: construction and demolition waste management and recycling," aecom asia company limited, shatin, hk, ta-8906 prc, apr. 2018. [3] j. lei, b. huang, and y. huang, "chapter 6 life cycle thinking for sustainable development in the building industry," in life cycle sustainability assessment for decision-making, j. ren and s. toniolo, eds. elsevier, 2020, pp. 125–138. [4] v. radonjanin, m. malešev, s. marinković, and a. e. s. al malty, "green recycled aggregate concrete," construction and building materials, vol. 47, pp. 1503–1511, oct. 2013, https://doi.org/10.1016/ j.conbuildmat.2013.06.076. [5] n. jain, m. garg, and a. k. minocha, "green concrete from sustainable recycled coarse aggregates: mechanical and durability properties," journal of waste management, vol. 2015, feb. 2015, art. no. e281043, https://doi.org/10.1155/2015/281043. [6] l. butler, j. s. west, and s. l. tighe, "effect of recycled concrete coarse aggregate from multiple sources on the hardened properties of concrete with equivalent compressive strength," construction and building materials, vol. 47, pp. 1292–1301, oct. 2013, https://doi.org/10.1016/j.conbuildmat.2013.05.074. [7] r. sri ravindrarajah and c. t. tam, "recycling concrete as fine aggregate in concrete," international journal of cement composites and lightweight concrete, vol. 9, no. 4, pp. 235–241, nov. 1987, https://doi.org/10.1016/0262-5075(87)90007-8. [8] l. evangelista and j. de brito, "concrete with fine recycled aggregates: a review," european journal of environmental and civil engineering, vol. 18, no. 2, pp. 129–172, feb. 2014, https://doi.org/10.1080/ 19648189.2013.851038. [9] j. ahmad bhat, "effect of strength of parent concrete on the mechanical properties of recycled aggregate concrete," materials today: proceedings, vol. 42, pp. 1462–1469, jan. 2021, https://doi.org/10.1016/ j.matpr.2021.01.310. [10] j. junak and a. sicakova, "concrete containing recycled concrete aggregate with modified surface," procedia engineering, vol. 180, pp. 1284–1291, jan. 2017, https://doi.org/10.1016/j.proeng.2017.04.290. [11] s. w. tabsh and a. s. abdelfatah, "influence of recycled concrete aggregates on strength properties of concrete," construction and building materials, vol. 23, no. 2, pp. 1163–1167, feb. 2009, https://doi.org/10.1016/j.conbuildmat.2008.06.007. [12] "about the coarse recycled aggregates for concrete," vietnam, 11969:2018, 2018. [13] v. t. phan, t. h. nguyen, "the influence of fly ash on the compressive strength of recycled concrete utilizing coarse aggregate from demolition works," engineering, technology and applied science research, vol 11, no. 3, pp. 7107-7110, jun. 2021. [14] a. a. mohammed ali, r. s. zidan, and t. w. ahmed, "evaluation of high-strength concrete made with recycled aggregate under effect of well water," case studies in construction materials, vol. 12, jun. 2020, art. no. e00338, https://doi.org/10.1016/j.cscm.2020.e00338. microsoft word 10-3243_s_etasr_v10_n1_pp5153-5156 engineering, technology & applied science research vol. 10, no. 1, 2020, 5153-5156 5153 www.etasr.com abro et al.: understanding the effect of aluminum addition on the forming of second phase particles … understanding the effect of aluminum addition on the forming of second phase particles on grain growth of micro-alloyed steel shahid hussain abro department of materials engineering ned university of engineering & technology karachi, pakistan engrabro@neduet.edu.pk alidad chandio department of metallurgical engineering ned university of engineering & technology karachi, pakistan alidad@neduet.edu.pk hazim abdulaziz moriah department of mechanical engineering technology yanbu industrial college saudi arabia moriah@rcyci.edu.sa abdulaal z. al-khazaal department of chemical and materials engineering northern border university arar, saudi arabia abdulaal.alkhazaal@nbu.edu.sa abstract—the formation of second phase particles in the steel matrix during melting and casting plays an important role in controlling the grain size of steel. an attempt is made in the present work to find the role of nitrogen on forming nitride particles either with aluminum or titanium. two steel samples with the same titanium and aluminum weight percent in their chemical composition were collected after the hot rolling process. solution heat treatment at 1350°c for 60min holding time was used to dissolve the particles and then the steel samples were reheated at 800°c for 60min, water quenched and their microstructure was revealed by usual grinding and polishing process using 2% nital. a transmission electron microscope connected with eds was used to reveal the morphology of the second phase particles. the samples for tem analysis were prepared by the replica extraction method in 5% nital solution. the samples were then caught in 3mm copper grid for tem analysis. tem micrographs revealed the second phase particles in the matrix of steel. eds peaks were studied and titanium peaks were found in both samples and surprisingly there was not any peak found for aluminum. keywords-aluminum; steel; grain; morphology; micrographs i. introduction researchers working on grain refinement add deliberately aluminum in combination with nitrogen to form second phase particles, commonly known as aluminum nitride (aln) particles, which can be formed during melting and casting [15]. these are strong impurity elements which get together around the grain boundaries and provide dragging force that stops the mobility of the grain boundary when the steel is reheated or during heat treatment. consequently, they retard the grain growth and the grains remain finer [5-11]. this is a common and widely used technique adopted for increasing the strength of steel. it was found that it is the most cheap and easy method of grain refinement, but during the last twenty years there was not paid attention to the fact that the nucleation sites for forming these nitride particles are more valuable regarding their effect on limiting the grain boundary movement [11-14]. ii. experimental procedure grain size control is always a priority in obtaining small grains which simultaneously increase hardness and toughness. second phase particles are therefore a useful source for controlling the grain growth and grain growth is a decisive factor in increasing steel’s strength. when aluminum and titanium are combined with nitrogen, they can form aluminum nitrides and titanium nitrides respectively because nitrogen has good affinity with both elements. whenever titanium and aluminum are the alloying elements at the same time, it is quite difficult to find if nitrogen will be combined with only aluminum, only titanium or with both elements to form nitride particles, which, due to their higher melting point and stability, remain in the solid state when the steel is cooled from its melting point. this investigation took place in order to study and understand this effect. in this regard, two steels were obtained by hot rolling as shown in table i and figure 1. table i. steel specimens composition steel a b c 0.202 0.2 mn 1.04 1.04 al 0.042 0.042 ti 0.025 0.025 nb 0.047 b 0.0018 0.0019 n 0.0058 0.0061 si 0.25 0.251 cr 0.144 1.21 corresponding author: shahid hussain abro engineering, technology & applied science research vol. 10, no. 1, 2020, 5153-5156 5154 www.etasr.com abro et al.: understanding the effect of aluminum addition on the forming of second phase particles … fig. 1. coooling curve after hot rolling, both samples, a and b, were solution heat treated at 1350°c for 60min holding time to dissolve the particles in the solution at high temperature. after holding, the samples were rapidly cooled in tap water as shown in figure 2. fig. 2. heat treatment cycle (a) (b) fig. 3. optical micrographs (a) 800°c, (b) 1350°c to investigate the effective influence of particles, both samples were re-heated at the moderate temperature of 800°c for one hour and were then quenched. after the heat treatment process, the conventional grinding and polishing steps followed by etching in 2% nital and thus the samples revealed their microstructure (figure 3). immediately afterwards the samples were prepared for transmission electron microscopy (tem) by using the carbon extraction replica method as shown in figure 4. etching is an important method in this technique. usually it is performed in 3% to 5% nital solution because the precipitates exist in the steel matrix and therefore it is necessary to etch the steel matrix with etchant (5% nital) to drag the particles outside. the particles were then kept in the copper grid and were used for tem analysis. tem, connected with the edx, is a powerful instrument in revealing the second phase particles. fig. 4. extraction of carbon replica by using etching cell fig. 5. tem micrographs for sample a fig. 6. tem micrographs for sample b engineering, technology & applied science research vol. 10, no. 1, 2020, 5153-5156 5155 www.etasr.com abro et al.: understanding the effect of aluminum addition on the forming of second phase particles … fig. 7. eds peaks of sample a fig. 8. eds peaks of sample b iii. discussion to understand and discover the effect of aluminum addition on the forming of second phase particles on grain growth of micro-alloyed steel, a thorough investigation has been taken in this work. optical microscopy and tem analysis have been utilized by keeping in view the eds peaks. the relative atomic mass of titanium is 48 and of nitrogen is 14. the weight percent of titanium in steel sample a and steel sample b is 0.025. the weight percent of nitrogen required for forming tin is (0.025×14)/48=0.0073. it is therefore observed that although aluminum always shows affinity with nitrogen to form nitrides, in this case aluminum was combined with titanium to form titanium nitrides. the reason behind this is that the amount of nitrogen required to form the aluminum nitrides is not sufficient and a large portion of nitrogen has been consumed by the titanium. iv. conclusion on the basis of stoichiometric calculation, it is concluded that all the nitrogen atoms present in steel a and steel b were consumed by titanium to form tin. therefore, the eds spectrum from tem extraction replica experiments show only the peaks for titanium in sample a and b. aln probably did not form at all and the eds spectrum of particles in steel a and steel b confirms that result. references [1] s. h. abro, m. s. hanif, f. h. kandhro, “on the effect of austenite formation kinetics on microstructural features of cold heading quality (chq) steel”, nust journal of engineering sciences, vol. 13, no. 1, 2020 (to be published) [2] s. ishteyaque, s. jabeen, s. h. abro, “hazard and operability study of gas exploration field located in pakistan”, sindh university research journal (science series), vol. 51, no. 2, pp. 189-194, 2019. [3] n. n. cherenda, v. v. uglov, a. k. kuleshov, v. m. astashynski, a. m. kuzmitski, “surface nitriding and alloying of steels with ti and nb atoms by compression plasma flows treatment”, vacuum, vol. 129, pp. 170-177, 2016 [4] s. h. abro, a. d. chandio, a. s. alaboodi, i. a. channa, “role of automotive industry in global warming”, pakistan journal of scientific and industrial research series a: physical sciences, vol. 62a, no. 3, pp. 197-201, 2019 [5] s. h. abro, “effect of heating rate on microstructural developments in cold heading quality steel used for automotive applications”, international journal of science and technology, vol. 6, no. 5, pp. 818821, 2017 [6] k. a. abro, a. a. memon, s. h. abro, “enhancement of heat transfer rate of solar energy via rotating jeffrey nanofluids using caputo– fabrizio fractional operator: an application to solar energy”, energy reports, vol. 5, pp. 41-49, 2019 [7] s. h. abro, a. a. shah, a. d. chandio, “effect of al, ni, mo, ti, nb and temperature on grain size number in low carbon high alloyed steel”. sindh university research journal (science series), vol. 51 no. 1, pp. 59-64, 2019 [8] s. h. abro, s. a. a. shah, a. s. alaboodi, t. shoaib, “ageing analysis of power cable used in nuclear power plant”, mehran university research journal of engineering & technology vol. 39, no. 1, pp. 2413-7219, 2020 engineering, technology & applied science research vol. 10, no. 1, 2020, 5153-5156 5156 www.etasr.com abro et al.: understanding the effect of aluminum addition on the forming of second phase particles … [9] s. h. abro, a. chandio, a. r. jamali, s. a. shah, “influence of austenite phase transformation on existing microstructure of low c-mn steel”, engineering, technology & applied science research, vol. 8, no. 6, pp. 3525-3529, 2018 [10] a. d. chandio, m. b. ansari, s. hussain, m. a. siddiqui, “silicon carbide effect as reinforcement on aluminium metal matrix composite”, journal of the chemical society of pakistan, vol. 41, no. 4, pp. 650654, 2019 [11] s. h. abro, a. chandio, a. moria, a. azmat, s. asrar, “findings of grain coarsening temperature and grain growth of light weight steel used in automotive industry”, pakistan journal of engineering and applied sciences, vol. 25 no. 2, pp. 14-17, 2019 [12] s. h. abro, “a role of mn atoms on tensile properties of light weight chq steel”, journal of engineering and applied sciences, vol. 38, no. 1, (2019). [13] m. mehdi, m. akhtar, s. abro, z. qamar, m. m. nauman, s. aziz, z. u. khan, m. sufiyan, m. bin waseem, a. azraf “electrochemical synthesis of agnp and mechanical performance of agnp-eg coatings on soft elastomer”, journal of elastomers & plastics, available at: https://journals.sagepub.com/doi/10.1177/0095244319879973, 2019 [14] a. d. chandio, s. h. abro, “effect of temperature and time on nickel aluminide coating deposition”, mehran university research journal of engineering & technology vol. 37, no. 4, pp. 491-496, 2018 microsoft word 27-3180_s_etasr_v9_n6_pp5016-5020 engineering, technology & applied science research vol. 9, no. 6, 2019, 5016-5020 5016 www.etasr.com bhutto et al: parametric analysis of an embankment dam’s stability parametric analysis of an embankment dam’s stability amjad hussain bhutto department of civil engineering quaid-e-awam university of engineering science and technology nawabshah, pakistan amjadbhutto62@gmail.com shahnawaz zardari department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan shahnawazzardari@gmail.com ghulam shabir bhurgri department of civil engineering quaid-e-awam university of engineering science and technology nawabshah, pakistan ghulamshabirbhurgri14@gmail.com muhammad auchar zardari department of civil engineering quaid-e-awam university of engineering, science & technology, nawabshah, pakistan muhammad.auchar@quest.edu.pk riaz bhanbhro department of civil engineering quaid-e-awam university of engineering science and technology, nawabshah, pakistan riaz@quest.edu.pk muhammad munir babar institute of water resources engineering and management mehran university of engineering and technology jamshoro, sindh, pakistan mmunirbabar.uspcasw@faculty.muet.edu.pk bashir ahmed memon department of civil engineering quaid-e-awam university of engineering science and technology, nawabshah, pakistan bashir_m@hotmail.com abstract—this paper presents a stability parametric analysis of a 59m high embankment dam. the analysis was performed in order to evaluate the minimum values of strength parameters that satisfy the stability requirements of the dam. the parametric analysis was conducted for three main zones of the dam: upstream shell, core, and downstream shell, which consisted of sandy gravel, clay, and random fill respectively. the friction angles of these materials were gradually decreased in order to represent different soil conditions. it was observed that stability requirements for the end of construction and after the filling of the reservoir could be satisfied if friction angle values of the sandy gravel and the random fill are 34º and 32º, instead of 37º and 34º. however, the value of the core’s cohesion could be utilized as 30º without any reduction so that the dam could be safe after the filling of the reservoir. the results of this study could be beneficial to practicing engineers for the design of safe and economical embankment dams. keywords-embankment dam; slope stability; pore pressure; end of construction; filling of reservoir i. introduction embankment dams are large structures that require huge volumes of fill materials. many different sources of fill materials are identified within the boundaries of the embankment dam for economical purposes. in general, different soils from different sources may exhibit varied strength and stiffness properties. it is therefore important to investigate the effect of soil’s strength and stiffness properties on the stability of an embankment dam during the design stage, before the actual construction. therefore, parametric analysis is required in order to evaluate minimum strength and stiffness properties range of soils, which could be utilized for the safe and economical design of embankment dams [1-2]. pakistan is an agricultural country and its economy mainly depends on the availability of water and hydropower electricity. for this purpose, many dams have been or proposed to be constructed in the near future. in order to ensure the safety of both the existing and the proposed dams in pakistan, it is necessary to investigate the strength properties of local soils and their effects on the stability of the dams during their service life. there are very few case studies published on the stability issues of dams in pakistan [3-13]. to the best of our knowledge no parametric analysis on the effects of strength properties on the stability of embankment dams with respect to local site conditions in pakistan has been published. therefore, there is a need for more case studies that could address issues related to the safe and economical design of embankment dams, based on parametric analysis of local soils. this is because every dam is considered as a unique structure based on its design, materials used, and foundation geology. it is estimated that about half of embankment dams’ failures have occurred due to the buildup of excess pore pressure, seepage, internal erosion and excessive deformations [10]. these instability problems may occur at routine or unusual conditions (e.g. heavy rainfall, intense earthquake) during the corresponding author: amjad hussain bhutto engineering, technology & applied science research vol. 9, no. 6, 2019, 5016-5020 5017 www.etasr.com bhutto et al: parametric analysis of an embankment dam’s stability service life of an embankment dam [11]. the failure of a dam may cause loss of lives and financial resources. most slope failures in embankment dams have occurred either during or after the end of construction. the increase of pore water pressure depends on the water content of the fill and on the rate of construction [12]. due to the low permeability of soils, excess pore pressure might develop gradually during raising and filling of the reservoir. this increase in excess pore pressure may lead to slope instability or dam failure [13]. this paper presents the parametric analysis of the effect of soils’ strength properties on the stability of an embankment dam, the nai gaj dam. three main zones, involving large quantities of fill materials, are focused: upstream shell, core, and downstream shell. the nai gaj dam is located 65km northwest of dadu, in sindh province of pakistan. almost 50% of its construction is already completed. it is estimated that the dam will irrigate about 40,000 acres of land, meeting the water needs of the growers. the catchment area of the dam is 7019km 2 and 85% of this area lies in baluchistan, while 15% lies in sindh province. ii. materials and methods the cross section of nai gaj dam is shown in figure 1. the material zones in the dam are: sandy gravel, random fill, central impervious clay core, sand filter, coarse filter and drainage blanket. the foundation of the dam mainly consists of sandy siltstone. this embankment dam is 59m high. the dam is 1137m long, having a maximum design water level of 56.6m. the core has an upstream side slope of 1h:3v, and a downstream slope of 1h:4v. the upstream and downstream shoulders have slopes 1v:2.5h. drainage features, including a chimney drain and horizontal drainage blanket below the downstream shell, have been incorporated in the design to relieve the pore water pressure within the dam body and to dispose the seepage water in a safe manner in order to prevent erosion and boiling. numerical analysis was carried out on a typical section of the dam. stability and excess pore pressure analyses were carried out on a two dimensional plane strain condition, using the finite element program plaxis 2d [14], for two conditions: the gradual raising at the end of construction and after the reservoir filling. fig. 1. cross section of the nai gaj dam mohr-coulomb model [15] was used on all layers of the dam for computing the pore pressures and the safety factors at the end of the construction and during the reservoir filling. the material properties of the mohr-coulomb model, used for the computation of dam’s settlement during the end of construction and the reservoir filling, are presented in table i. coupled deformation and consolidation analyses were carried out in order to estimate the development and dissipation of excess pore pressure as a function of time. in addition, safety analysis was conducted to compute the safety factors of the dam. the raising of the embankment of the dam was decided based on the construction work that is being carried out on the site. the dam was mainly raised at a rate of three meters in 30 days. table i. materials of nai gaj dam and its foundation material type saturated unit weight (kn/m 3 ) cohesion (kn/m 2 ) friction angle (deg) modulus of elasticity (kn/m 2 ) permeability (m/day) clay 18.85 [19] 9.57 [19] 30 [19] 50000 [19] 0.000263 [19] sandy gravel 21.5 [20] 0 37 [17-19] 50000 [24] 86.4 [25] random fill 18.85 [19] 0 34 [19] 50000 [19] 0.0263 [19] washed gravel 21.5 [20] 0 37 [21-23] 45000 [26] 864 [23] d/s slope protection 19.5 [32] 0 34 [21-23] 40000 [29-30] 8640 [23] riprap 19.5 [19] 0 34 [19] 40000 [29-30] 8640 [23] sand filter 18.85 [19] 0 36 [19] 40220 [19] 26.33 [19] drainage blanket 21.5 [20] 0 37 [21-23] 45000 [31] 864 [27] sandy siltstone 20.4 [19] 12 [19] 29 [19] 125000 [31] 0.00063 [19] the finite element model of the dam was extended laterally, by 100m on each side, in order to minimize the effect of its boundaries, as shown in figure 2. the finite element mesh consisted of 6619 triangular elements with 53463 nodes. the average element size was 3.2m. the mesh was sufficiently refined to the extent that with further refinement of the mesh the results were almost the same (figure 3). water level in the finite element model is 15m below the surface (figure 2). the highest flood level of 56.6m in the finite element model is shown in figure 4. fig. 2. finite element model of the nai gaj dam fig. 3. finite element mesh of the nai gaj dam engineering, technology & applied science research vol. 9, no. 6, 2019, 5016-5020 5018 www.etasr.com bhutto et al: parametric analysis of an embankment dam’s stability fig. 4. maximum water level in the nai gaj dam iii. results and discussion a. excess pore pressure the magnitude of excess pore pressure increased when the embankment rose up to a level of 45m (figure 5-6). when the embankment rose from 45m to 59m, the excess pore pressure mainly decreased. the reason is that as the dam was raised higher, the width of layers gradually decreased. this indicates that the weight of the top layers of the dam was lower as compared to the bottom layers (figure 7). this implies that the rate of dissipation of the excess pore pressure was higher compared to the lower rate of loading of the upper layers. therefore the excess pore pressure decreased with respect to time. fig. 5. development of excess pore pressures at 15m raising of the dam fig. 6. development of excess pore pressures at 45m raising of the dam b. factor of safety dam’s factor of safety was computed to be 1.6 and 1.48 for the end of construction and after the reservoir filling conditions respectively. due to soils’ saturation, the factor of safety after the reservoir filling decreased compared to the end of construction. according to available guidelines [28], the safety factors for the end of construction and the reservoir filling at normal operating level are 1.3 and 1.5 respectively. this implies that the stability of the dam is considered satisfactory for both conditions. moreover the results of the study for the dam’s potential failure zones, for both conditions, are exhibited in figures 8 and 9. the potential failure zone for the end of the construction was at the upstream side of the dam, while the failure zone after the reservoir filling developed on the downstream side. the modes of failure are consistent with the literature. fig. 7. development of excess pore pressures at 59m raising of the dam fig. 8. potential failure zone of the dam at the end of construction fig. 9. potential failure zone of the dam after reservoir filling c. effect of sandy gravel’s friction angle on safety factor the upstream shell of the dam consists of sandy gravel and the effect of its friction angle on the dam safety factor was examined (figure 10). as expected, dam’s safety factor increased with increasing values of the sandy gravel’s friction angle. for both conditions, the stability of the dam is satisfactory if the minimum value of sandy gravel’s friction angle is 34º this implies that the friction angle value of the sandy gravel could be taken as 34º instead of 37º. engineering, technology & applied science research vol. 9, no. 6, 2019, 5016-5020 5019 www.etasr.com bhutto et al: parametric analysis of an embankment dam’s stability fig. 10. effect of sandy gravel’s friction angle on dam’s safety factor d. effect of random fill’s friction angle on safety factor the downstream shell of the dam consists of random fill material and its friction angle effect on dam’s safety factor was analyzed (figure 11). as expected, dam’s safety factor increased with increasing values of random fill’s friction angle. for post reservoir-filling conditions, increasing this friction angle to over 32º has no influence on the safety factor. this implies that random fill’s friction angle could be taken as 32º instead of 34º. fig. 11. effect of friction angle of random fill on safety factor of the dam fig. 12. effect of friction angle of clay core on safety factor of the dam e. effect of clay core’s friction angle on safety factor the center of the dam consists of clay core material and its friction angle effect on the stability of the dam was investigated (figure 12). as expected, dam’s safety factor increased with increasing values of clay core’s friction angle for both conditions. in partially dry state, the core was stronger and dam’s safety factor was more than sufficient, even for friction angles at 20º. however, clay is more sensitive to saturation, so the cohesion of the core decreases when moisture content increases. therefore, in order to increase the stability of the dam, it is necessary to fully compact the core and utilize the maximum value of cohesion, which is 9kpa. iv. conclusion in this study, the slope stability behavior of an embankment dam was analyzed, by investigating the effects of various materials, in different zones. the friction angles of the three main zones, sandy gravel, clay core, and random fill, of the embankment dam were gradually decreased. it was found that the stability of the dam was satisfactory for both the end of construction and after the reservoir filling conditions, if the minimum friction angle values of the sandy gravel and the random fill are decreased respectively from 37º to 34º and from 34º to 32º. for the dam to be stable after the filling of the reservoir, it is necessary to utilize the same value (30 0 ) of clay core. those results could be valuable for practicing engineers working on safe and economical design of embankment dams. acknowledgment the authors would like to thank water and power development authority (wapda) pakistan for their permission and the dam’s data provision. references [1] j. t. christian, c. c. ladd, g. b. baecher, “reliability applied to slope stability analysis”, journal of geotechnical engineering, vol. 120, no. 12, pp. 2180-2207, 1994 [2] a. s. al-homoud, n. tanash, “modeling uncertainty in stability analysis for design of embankment dams on difficult foundations”, engineering geology, vol. 71, no. 3-4, pp. 323-342, 2004 [3] f. s. khan, a. a. malik, “probability and sensitivity analysis of the slope stability of naulong dam”, pakistan journal of engineering and applied sciences, vol. 13, pp. 54-64. 2016 [4] k. farooq, h. mujtaba, a. nazir, a. h. khan, “effectiveness of upstream blanket and grouting in control of seepage at khanpur dam project”, pakistan journal of science, vol. 65, no. 2, pp. 228-233, 2013 [5] m. s. khan, t. a. gilani, m. a gul, “post impounding problems and management measures in carbonate geology at khanpur dam project, pakistan”, science international (lahore), vol. 23, no. 2, pp. 129-134, 2011 [6] i. a. jamali, u. mortberg, b. olofsson, m. shafique, “a spatial multicriteria analysis approach for locating suitable sites for construction of subsurface dams in northern pakistan”, water resources management, vol. 28, no. 14, pp. 5157-5174, 2014 [7] y. s khalil, m. arif, h. a. bangash, m. sajid, n. muhammad, “petrographic and structural controls on geotechnical feasibility of dam sites: implications from investigation at sher dara area (swabi), northwestern pakistan”, arabian journal of geosciences, vol. 8, no. 7, pp. 5067-5079, 2015 [8] m. hieatt, s. r. abbas shah, r. a. khan, m. ali, n. asghar, s. sheikh, i. a. humayun, p. j. mason, j. d. molyneux, g. r. khan, i. a. humayun, “some geotechnical aspects of raising the mangla dam, pakistan”, proceedings of the institution of civil engineers geotechnical engineering, vol. 165, no. 3, pp. 127-141, 2012 [9] y. honjo, p. h. giao, p. a. naushahi, “seepage analysis of tarbela dam (pakistan) using finite element method”, international journal of rock engineering, technology & applied science research vol. 9, no. 6, 2019, 5016-5020 5020 www.etasr.com bhutto et al: parametric analysis of an embankment dam’s stability mechanics and mining sciences and geomechanics abstracts, vol. 32, no. 3, article id 131a, 1995 [10] i. arshad, m. m. babar, “finite element analysis of seepage through an earthen dam by using geo-slope (seep/w) software”, international journal of research, vol. 1, no. 8, pp. 619-634, 2014 [11] i. arshad, m. m. babar, “comparison of seep/w simulations with field observations for seepage analysis through an earthen dam (case study: hub dam – pakistan)”, international journal of research, vol. 1, no. 7, pp. 57-70, 2014 [12] a. h. bhutto, s. zardari, m. a. zardari, g. s. bhurgri, b. a. memon, r. bhanbhro, m. m. babar, “mohr-coulomb and hardening soil model comparison of the settlement of an embankment dam” , engineering, technology & applied science research, vol. 9, no. 5, pp. 4654-4658, 2019 [13] a. h. bhutto, s. zardari, g. s. bhurgri, m. a. zardari, r. bhanbhro, b. a. memon, “post construction and long term settlement of an embankment dam computed with two constitutive models”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4750-4754, 2019 [14] m. foster, r. fell, m. spannagle, “the statistics of embankment dam failures and accidents”, canadian geotechnical journal, vol. 37, no. 5, pp. 1000-1024, 2000 [15] e. panulinova, s. harabinova, “methods for analyzing the stability of an earthen dam slope”, advanced materials research, vol. 969, pp. 245248, 2014 [16] s. ozcoban, m. m. berilgen, h. kilic, t. b. edil, i. k. ozaydin, “staged construction and settlement of a dam founded on soft clay”, journal of geotechnical and geoenvironmental engineering, vol. 133, no. 8, pp. 1003-1016, 2007 [17] d. t. bergado, c. teerawattanasuk, “2d and 3d numerical simulations of reinforced embankments on soft ground”, geotextiles and geomembranes, vol. 26, no. 1, pp. 39-55, 2008 [18] r. b. j. brinkgreve, plaxis reference manual, plaxis, 2017 [19] wapda, project planning report of nai gaj dam, water and power development authority pakistan, 2006 [20] a. j. schleiss, r. m. boes, dams and reservoirs under changing challenges, crc press, 2011 [21] m. carter, s. p. bentley, soil properties and their correlations, john wiley & sons, 2016 [22] f. cobb, structural engineer's pocket book, british standards edition, elsevier, 2008 [23] r. f. craig, soil mechanics, springer, 2013 [24] r. a. rajapakse, geotechnical engineering calculations and rules of thumb, butterworth-heinemann, 2015 [25] g. e. barnes, soil mechanics: principles and practice, palgrave macmillan, 2010 [26] j. l. justo, j. saura, “three dimensional analysis of infiernillo dam during construction and filling of the reservoir”, international journal for numerical and analytical methods in geomechanics, vol. 7, no. 2, pp. 225-243, 1983 [27] b. g. look, handbook of geotechnical investigation and design tables, crc press, 2014 [28] m. n. sara, site assessment and remediation handbook, crc press, 2003 [29] p. j. burgess, d. sarabia, j. small, h. g. poulos, j. sinha, “settlement behaviour of a major dam”, ancold bulletin, vol. 137, pp. 91-100, 2007 [30] l. ormann, m. a. zardari, h. mattsson, a. bjelkevik, s. knutsson, “numerical analysis of strengthening by rockfill embankments on an upstream tailings dam”, canadian geotechnical journal, vol. 50, no. 4, pp. 391-399, 2013 [31] d. u. deere, r. p. miller, engineering classification and index properties for intact rock, university of illinois at urbana, 1966 [32] r. fell, p. macgregor, d. stapledon, g. bell, m. foster, geotechnical engineering of dams, crc press, 2014 engineering, technology & applied science research vol. 8, no. 2, 2018, 2764-2769 2764 www.etasr.com rajhi et al.: an anisotropic elastic-plastic model for the optimization of a press machine’s auxiliary … an anisotropic elastic-plastic model for the optimization of a press machine’s auxiliary worktable plate thickness w. rajhi college of engineering university of hail hail, kingdom of saudi arabia b. ayadi college of engineering university of hail hail, kingdom of saudi arabia a. alghamdi college of engineering university of hail hail, kingdom of saudi arabia n. messaoudene college of engineering university of hail hail, kingdom of saudi arabia abstract—in this work an anisotropic elastic–plastic finite element model strongly coupled with ductile damage is applied to determine the suitable thickness of added auxiliary worktable plate to a 100 ton maximum capacity press machine. the major focus of this study is to minimize the amount of stress transmitted to the optional worktable plate and the press machine body while allowing them to withstand plastic deformation and damage during compression testing until final sample fracture. the worktable plates and the press machine body are made of trip800 grade steel. aisi 316l stainless steel is chosen as test material for the cylindrical billets. the proposed model is based on a non-associative plasticity theory and the “hill 1948” quadratic (equivalent) stress norm is considered to describe the large plastic anisotropic flow accounting for mixed isotropic and kinematic hardening with isotropic damage effect. for each material the model uses an experimental data base obtained from a set of tensile tests conducted until the final fracture in three directions, the rolling direction (rd) or 0, the transverse direction (td) or 90, and the 45 direction. after several numerical simulations of compression testing using abaqus/explicit fe® software, thanks to the user’s developed vumat subroutine, varying cylindrical billet diameters and material, worktable plates number and thicknesses and spatial plate configurations the solution of 100mm thick worktable plate is selected since in that case the cylinder specimen is totally damaged and the stress state inside the worktable plates and the press machine body remains admissible. keywords-compression testing; hardening; plastic anisotropy; ductile damage; iidentification; numerical simulation i. introduction the proposed elastic–plastic model coupled with isotropic ductile damage has been used in several researches to find solutions to a set of problems related especially to the occurrence of the ductile damage, which arises in metal working processes, in order to either delay the damage occurrence during the metal forming processes [1-5] or to stimulate cavitation growth and totally ductile failure in the case of metal cutting processes [5-8]. the extension to the anisotropic damage case of the proposed model in order to simulate the directional effect of the ductile damage in metal forming process has been deeply discussed in [5, 9, 10]. in this work, an isotropic version of the model presented in [9] is used to solve a mechanical engineering problem which consists to determine the suitable thickness of auxiliary worktable plates of a 100ton maximum capacity press machine, their number and their spatial positions in relation to each other, in order to carry out compression testing until final sample fracture while ensuring the protection of the worktable plates and the body of the press machine against plastic deformation and damage (section ii). section iii discusses the deduction of the elastic– plastic constitutive equations fully coupled with isotropic damage from the anisotropic damage model case. numerical aspects are well described in the case of the isotropic damage model in [1, 5, 11] and extended to the anisotropic damage case in [5, 9, 12]. section iv is devoted to the identification of the model parameters for the trip800 and the aisi 316l grade steels using experimental results from the tensile tests conducted until the final fracture of specimens loaded in three directions i.e., the rolling direction (rd) or 0, the transverse direction (td) or 90, and the 45 direction. thus, the methodology proposed to determine the suitable optional worktable plate thickness is presented and discussed. ii. problem formulation press master (see figure 1) is a testing press machine which is used in our mechanical laboratory for static three point bending flexural test of steels, aluminum alloys and rock materials under different control parameters. because the press machine is not equipped with auxiliary worktable, the operating cannot include compression testing. an auxiliary worktable is required to carry out compression testing of different cross sectional area parts. during compression testing the cylindrical specimens are placed between the piston rod and the worktable which is positioned upon the work platform beam. the auxiliary worktable may include one or more metallic plates. these plates and the work platform beam both are made of steel grade that may be assumed to behave elastoplastically with mixed isotropic and kinematic hardening. the trip800 steel which constitutes the material of the press engineering, technology & applied science research vol. 8, no. 2, 2018, 2764-2769 2765 www.etasr.com rajhi et al.: an anisotropic elastic-plastic model for the optimization of a press machine’s auxiliary … machine body is selected in this work for the auxiliary worktable plate’s material because trip steels offer an outstanding combination of strength and ductility being thus suitable for structural and reinforcement parts of complex shape. fig. 1. illustration of the critical press machine parts. the typical true stress–strain curves for the trip800, resulting from uniaxial tensile tests conducted along the rolling direction (rd) or 0, the transverse direction (td) or 90, and the 45 direction are given in figure 2. the trip800 flat tensile specimen is shown in figure 3 with all dimensions in millimeters. in figure 2, one can see that the trip800 steel exhibits slight plastic anisotropy with an overall ultimate stress around 1040.0mpa reached for an overall total strain value of about 24.5%, while the maximum total strain at the final fracture is observed for the rolling direction around 27.0 % i.e., about 26.0% of plastic strain at fracture. furthermore, the stress–strain curves obtained for the 45 and (td) directions have roughly the same elastic–plastic trend before reaching their necking points. the level for which the stress-strain responses bifurcate for each direction is shown in figure 2 where the 45 stress-strain curve reaches the ultimate stress before that of the (td) direction. hence, for many metallic orthotropic sheets, the ductile damage is highly anisotropic even if the anisotropy of the plastic flow is small. thus, it is worth noting that three tensile tests are performed for each loading direction in order to identify the tensile specimens containing the lower defects density so as to use the corresponding stress–strain curves i.e., revealing the greatest ductility during the model parameters identification. present work’s purpose is to allow the press machine, within its limit capacity, able to ensure compression testing until final fracture of metallic cylindrical specimens using optional worktable plates made of trip800 steel while optimizing the plates’ thickness, their number and their configurations according to various spatial arrangements. the problem may be modeled as illustrated in figure 4. the worktable plates shape is assumed to be square (400mm*400mm) of variable thickness. to achieve the above target, this study aims to predict through a set of numerical simulations of compression testing the limiting diameter of the cylindrical specimens, for a given material, allowing the continuity of the compression process until final fracture while remaining within the press machine capacity range. in addition, the number of the auxiliary plates, their thickness and spatial positions in relation to each other can be optimized so that the maximum values of the equivalent plastic strain and damage reached during the compression process inside the body of the press machine and the worktable plates remain negligible and the stress should have the lower criticality even if it is elastic. fig. 2. trip800 uniaxial tensile tests conducted along the rolling direction (rd) or 0, the transverse direction (td) or 90, and the 45 direction. fig. 3. trip800 flat tensile test specimen dimensions. fig. 4. schematic representation of the critical press machine parts. iii. constitutive equations during compression loading test, the cylindrical sample materials as well as the trip800 steel assigned to both the work platform beam and the worktable plates are assumed to behave elastoplastically with mixed isotropic and kinematic hardening according to an anisotropic elastic–plastic model fully coupled to the ductile damage. in this work, only the piston rod will be considered as a rigid part. the proposed model is based on a non–associative plasticity theory and the “hill 1948” quadratic (equivalent) stress norm is considered to describe the large plastic anisotropic flow accounting for mixed isotropic and kinematic hardening with isotropic damage effect. however, in the context of cdm, when the anisotropic effect of the ductile damage is taken into account (see [10]), a fourthrank damage–effect tensor is used [14-16] to define the effective state variables needed to describe the stress–strain engineering, technology & applied science research vol. 8, no. 2, 2018, 2764-2769 2766 www.etasr.com rajhi et al.: an anisotropic elastic-plastic model for the optimization of a press machine’s auxiliary … behavior accounting for the full effects of the anisotropic ductile damage. in this case, the damage variable may be modeled using a symmetric forth or second rank tensor in order to represent the ductile damage of orthotropic metallic materials. following the concept of effective stress with the hypothesis of total energy equivalence, the matrix representations of the effective stress and the kinematic stress tensors are given by: -1 : m   (1) -1 : x m x (2) where m is the fourth rank damage effect tensor. in the cdm literature, several forms of damage effect tensor m are formulated [14]. the effective isotropic hardening stress is given by: 1r r    (3) and m defines an euclidean norm of the second order damage tensor  . according to the damage effect tensor forms presented in [14], it is clear that when the ductile damage is assumed to be isotropic the damage effect tensor m can be written under the following form:             1 1 1 , , , 1 1 1 , , iso f f f m diag f f f                  (4) where  is the isotropic damage variable and  f  is a degreasing function of ω called the damage effect function. to make the link between the constitutive equations of the anisotropic damage model and those of the isotropic damage case, the following damage effect function is chosen to describe the stress–strain behavior accounting for the full effects of the isotropic ductile damage:   1-f    (5) the constitutive equations for the isotropic damage case may be deduced readily from those of the anisotropic case by substituting the damage effect tensor m by the isotropic damage effect tensor given by: 1 1 iso m   (6) where 1 is the fourth order unit tensor. thus, in the isotropic damage case, the euclidean norm  of the second order damage tensor transforms to the scalar damage variable ω. in this work the plastic anisotropy is taken into account via the fourth rank symmetric and positive definite operator h which defines the anisotropy of plastic flow. it is expressed in terms of hill’s anisotropic parameters f, g, h, l, m and n: . 0 0 0 2 0 0 g h sym h h f g f f g h l     0 0 2 0 0 0 0 0 2 m n                    (7) using the non-associative framework, the anisotropic plastic flow is modeled using a yield function fp :  , , ; -p yhf x r x r      (8) the parameter σy is the initial size of the plastic yield surface. the norm h x  defines the “hill 1948” quadratic equivalent stress in the effective stress space. the fully coupled anisotropic plasticity–isotropic damage model constitutive equations accounting for the kinematic and isotropic hardening are given by: (1) ee    (9) (1)x c   (10) (1 )r q r  (11) where e, c and q are the elasticity, kinematic and isotropic hardening modules. the application of the generalized normality rule leads to the evolution relations for plastic flow with hardening and anisotropic damage effect: p n      (12)  1 1 r br        (13) p a         (14) where n represents the outward unit normal to the plastic yield surface in the damaged state. the material constants a and b are the non-linearity parameters for kinematic and isotropic hardening respectively.   is the plastic (lagrange) multiplier. the effect of the damage is crucially governed by (6) and (15):   • • 01sy y s           (15) where y is the total energy release rate density tensor. in conclusion, noting that both the anisotropic and isotropic damage models have the same number of material parameters which are the elastic proprieties e and υ to describe the isotropic elastic behavior, eleven plastic parameters σy, f, g, h, l, m, n, c, q, a and b for the plastic anisotropy and four engineering, technology & applied science research vol. 8, no. 2, 2018, 2764-2769 2767 www.etasr.com rajhi et al.: an anisotropic elastic-plastic model for the optimization of a press machine’s auxiliary … damage parameters s, s, β and y0 to control the damage evolution. finally, the related numerical aspects are deeply described in [1, 5, 11]. iv. results this section is devoted to the numerical simulation of compression testing of cylinder specimens made of different materials according to the schematic representation illustrated in figures 3-4. the identification of the elastic–plastic and damage parameters of the isotropic damage model presented above are required to perform the numerical simulation of compression testing. two grade steel materials are considered for each compression testing simulation. the trip800 steel for the press machine parts (the work platform beam and the worktable plates) and the aisi 316l stainless steel assigned beforehand to the cylindrical specimen. the identification procedure is based on two main steps. the first step consists on the determination of the elastic–plastic parameters through a set of uncoupled (without damage effect) tensile test calculations under abaqus/explicit® using the user subroutine vumat while respecting the specimen geometry (see figure 4). the tensile specimen given in figure 3 is meshed using hexahedral tri–linear elements (c3d8r) with a meshing refinement (minimum mesh size of 1.0mm3) located on the central region or gage length of the specimen. the numerical tensile test was carried out with a constant velocity of 3.0mm/s. anisotropic parameters g and h and the set of hardening parameters are varied in order to get the best fit between the numerical force– displacement curve and the one obtained experimentally along the rolling direction while respecting two following conditions: 1) g+h=1 and 2) the retained plasticity parameters should provide a numerical response comparable with experience, up to a plastic strain range between 15% and 20%, from which the two responses bifurcate due to the emphasized effect of ductile void growth on experimental response. the trip800 (td) 90 and 45 force–displacement experimental responses are explored later to determine the remaining parameters f and n respectively taking into account that 90 /y f h   and 45 2 / 2y f g n    . in the second identification step, fully coupled calculations are performed taking into account the damage effect in order to recover the optimum damage parameters which provide the best fit between the end of numerical and experimental force– displacement curves. in conclusion, the same vumat is used with a flag parameter (ncd) allowing to perform an uncoupled analysis when ncd=0 and a fully coupled analysis when ncd=1. τhe superposed experimental, numerical uncoupled and fully coupled force–displacement curves for the three loading directions rd, 45 and td for the trip800 steel are not presented here (see [9] for more details concerning the aisi 316l material parameters identification) and we limit ourselves only to report in τable 1 the best values of the trip800 and aisi 316l steels parameters resulting from the identification procedure described above. the parts shown in figure 5, excluding the piston rod, are meshed using hexahedral tri– linear elements (c3d8r) with an overall meshing size of about 2.0mm3 for the 50mm length cylinder specimen, 7mm3 for the 100mm thick worktable plate and 20mm3 for the encastred work platform beam. τhe piston rod is considered as a rigid part meshed using bilinear rigid quadrilateral elements (r3d4) with meshing size of about 5.0mm3. if a modification of the meshing size defined during the fully coupled analysis of the identification procedure is intended, before performing the compression testing simulations with the new meshing size, the damage parameters values given in table i particularly the parameter s should be adjusted by supplementary set of identification calculations for each material as the proposed model is written in local approach where the damage parameters depend strongly on the meshing size [18]. the numerical compression testing was carried out with a constant piston velocity of 100.0mm/s. the friction coefficient defined between the different parts is about 0.3. in order to reduce the cpu time in the followed dynamic explicit algorithm, a mass scaling value of 10-6 is defined through all the compression testing simulations. according to figure 6, 36mm is the limiting diameter value of the aisi 316l cylinder specimens which the press machine can totally damage without exceeding its maximum loading capacity range. otherwise, beyond this limiting diameter, the loading amount provided by the press machine is unable to ensure the total failure as revealed by the numerical simulation of the compression testing of the aisi 316l cylinder specimens given by figure 6, where the damage doesn’t exceed 5% and 10% for 44 and 40mm cylinder diameters respectively when the loading reaches the maximum capacity force of the press machine. table i. trip800 and aisi 316l model parameters model parameters grade steel trip800 aisi 316l [9] elasticity e 195000mpa 200000mpa υ 0.3 0.3 anisotropic plasticity σy 406mpa 225mpa f 0.45 0.8 g 0.47 0.76 h 0.53 0.24 l 1.5 1.5 m 1.5 1.5 n 1.45 1.55 c 49000mpa 15000mpa q 4000mpa 2000mpa a 380 300 b 4.2 0.6 damage s 102mpa 140mpa s 1 1 β 1.5 1.5 y0 0 0 the first set of compression testing simulations checks the suitable aisi 316l cylinder specimen diameter which the press machine can deform until total failure occurs without exceeding the capacity specified by the manufacturer. in figure 5 initial geometries, mesh and boundary conditions of the compression testing simulation are schematized. the worktable is assumed to be made from one plate 100mm thick. the distribution of the von mises stress, the damage and the equivalent plastic strain inside the 36mm diameter cylinder at the end of the compression testing process is shown in figure 7. the mechanical field distribution within the worktable plate engineering, technology & applied science research vol. 8, no. 2, 2018, 2764-2769 2768 www.etasr.com rajhi et al.: an anisotropic elastic-plastic model for the optimization of a press machine’s auxiliary … and the body of the press machine analysis will be discussed later. furthermore, the compression testing simulation was successfully accomplished as the maximum values of the damage and the equivalent plastic strain were located at the center of the aisi 316l cylinder correctly at the intersection of the two well-known shear bands. this result is marked by the fast drop of the force–displacement curve (not presented here) at the end of the compression testing. according to figure 7(a), the maximum vom stress obtained at the end of the compression process within the cylinder σend (σend=860mpa) is considerably greater than the ultimate stress of the aisi 316l [9] as significant dissimilarity between the tensile and the compression behaviors at large deformations is often expected in ductile materials. fig. 5. geometry, boundary conditions, and meshing of the parts. fig. 6. numerical force–damage curves of the aisi 316 l compression testing obtained for different diameters a second set of compression testing simulations was carried out altering trip800 worktable plate’s number, plate thickness and configuration according to various spatial arrangements of plates from one calculation to another until obtaining the optimal configuration which ensures the protection of the worktable plates and the body of the press machine against plastic deformation and damage. furthermore, the solutions exhibiting low criticality were collected. it is worth noting that the appropriate configuration means the numerical solution allowing the compression testing until total failure of the aisi 316l cylindrical specimen without exceeding the press machine capacity and giving the lowest elastic stress value inside both the trip800 worktable plates and the press machine body. after several numerical simulations of compression testing, the solution of 100mm maximum thickness is selected for a well-defined number of worktable plates. accordingly, eleven configurations based on how worktable plates with different number and thicknesses are arranged spatially, were analyzed. in proposed configurations, the plates are positioned from the piston rod to the work platform beam across the plates thickness direction according to the rank reported in table ii. (a) (b) (c) fig. 7. (a) distribution of the von mises stress, (b) the damage and (c) the equivalent plastic strain, at the end of the compression testing of 36mm diameter cylindrical aisi 316l billet. table ii. configurations and related maximum vom stress states obtained during compression testing of the aisi 316l samples configuration vom stress maxi in plates σp (mpa) vom stress maxi in machine body σb (mpa) a 1 plate of 50mm 462 200 b 1 plate of 75mm 429 110 c 3 plates of 25mm 556 319 d 2 plates of 37.5mm 463 208 e 2 plates of 50mm 430 129 f 1 plate of 100mm 421 81 g 2 plates of 2550mm 481 181 h 2 plates of 5025mm 439 166 i 3 plates of 255025mm 478 156 j 3 plates of 502525mm 445 152 k 2 plates of 7525mm 432 99 maximum vom stress values reported in table ii are reached immediately before the total rupture of the first meshing element generally located at the specimen center. configurations reported in table ii are judged to be of low criticality as the maximum vom stress within the body of the press machine is less than the yield stress of the trip800 steel. the above configurations are chosen among harshest stress state configurations causing a significant problem within the worktable plates and the press machine body. in fact, as illustrated in figure 8(a), the use of two 20mm thick plates engineering, technology & applied science research vol. 8, no. 2, 2018, 2764-2769 2769 www.etasr.com rajhi et al.: an anisotropic elastic-plastic model for the optimization of a press machine’s auxiliary … leads to the excessive bending distortion of the trip800 worktable plates before the total fracture of the aisi 316l specimen occurs. likewise, as illustrated in figure 8(b), high stress i.e., 98% of the trip800 yield stress, is detected within the press machine body with a slight bending distortion of the inferior plates owing to the use of five 20mm thick plates. the results reported in table ii prove the trip800 steel's validity while giving the worktable plates excellent combination of strength and ductility under extreme loading conditions since almost the maximum vom stress values inside the plates σp for various configurations are not very far from the yield stress value of the trip800 steel. the slight decrease of the billet diameter carries the greater part of the configurations below the elastic barrier. nevertheless, the maximum vom stress values within the press machine body σb remain below the elastic limit for all configurations. according to the configurations sets (b, c, d) and (f, k, i or j), the higher the number of plates, the higher the maximum vom stress within the plates and the press machine body. the couple of values defined by the gaps between σend and the maximum vom stress within both the worktable plates and the press machine body (σend-σp, σend-σb) is used as criterion for the selection of the suitable configuration. accordingly, the f and k configuration provides the maximum pair gap values of about (440, 780mpa) and (428, 761mpa) for the plates and the press machine body respectively and may be chosen as the appropriate configurations. (a) (b) fig. 8. (a) excessive bending distortion of two 20mm thick plates, (b) high stress in the machine press body due to the use of five 20mm thick plates v. conclusion in this work, a mechanical engineering problem related to the optimization of the press machine optional worktable thickness was solved using an anisotropic elastic–plastic finite element model strongly coupled with ductile damage. the numerical simulation of compression testing of different materials varying worktable plates’ thickness, their number and their spatial positions in relation to each other is crucial in order to find the best solution allowing the worktable plates and the press machine body to withstand against plastic deformation and damage. the use of 100mm worktable plate reduces greatly the amount of stress transmitted to the press machine parts. eventually, the above solution will be considered practically to perform compression testing of cylindrical samples made of any material. references [1] k. saanouni, j. f. mariage, a. cherouat, p. lestriez, “numerical prediction of discontinuous central bursting in axisymmetric forward extrusion by continuum damage mechanics”, computers & structures, vol. 82, no. 27, pp. 2309-2332, 2004 [2] m. khelifa, h. badreddine, a. daoud, m. a. gahbich, k. saanouni, a. cherouat, a. dogui, “effect of anisotropic plastic flow on the ductile damage evolution in hydrobulging test of thin sheet metal”, international journal of forming processes,vol. 8, no. 2, pp. 271-289, 2005 [3] h. badreddine, c. labergere, k. saanouni, w. rajhi, a. rassineux, d. kircher, “fe elastoplastic damage model with 2d adaptive remeshing procedure for fracture prediction in metal forming simulation”, international journal of material forming, vol. 1, pp. 109-112, 2008 [4] c. labergère, k. saanouni, p. lestriez, “numerical design of extrusion process using finite thermo-elastoviscoplasticity with damage. prediction of chevron shaped cracks”, key engineering materials, vol. 424, pp. 265-272, 2010 [5] k. saanouni, damage mechanics in metal forming: advanced modeling and numerical simulation,wiley, 2012 [6] m. issa, k. saanouni, c. labergere, “prediction of serrated chip formation in orthogonal metal cutting by advanced adaptive 2d numerical methodology”, international journal of machining and machinability of materials, vol. 9, no. 3, pp. 295–315, 2011 [7] k. saanouni, n. belamri, p. autesserre, “3d numerical simulation of anisotropic thin sheet metal slitting process using fully coupled constitutive equations including ductile damage”, international journal of material forming, vol. 2, no. 1, pp. 535-538, 2009 [8] c. labergère, a. a. rassineux, k. saanouni, “2d adaptive mesh methodology for the simulation of metal forming processes with damage”, international journal of material forming, vol. 4, no. 3, pp. 317-328, 2011 [9] w. rajhi, k. saanouni, h. sidhom, “anisotropic ductile damage fully coupled with anisotropic plastic flow: modeling, experimental validation, and application to metal forming simulation”, international journal of damage mechanics, vol. 23, no. 8, pp. 1211-1256, 2014 [10] k. saanouni, j. l. chaboche, “computational damage mechanics: application to metal forming simulation”, comprehensive structural integrity.vol. 3, pp. 321–376, 2003 [11] h. badreddine, k. saanouni, a. dogui, “on non-associative anisotropic finite plasticity fully coupled with isotropic ductile damage for metal forming”, international journal of plasticity, vol. 26, no. 11, pp. 15411575, 2010 [12] h. badreddine, k. saanouni, t. d. nguyen, “damage anisotropy and its effect on the plastic anisotropy evolution under finite strains”, international journal of solids and structures, vol. 63, pp. 11-31, 2015 [13] k. saanouni, a. cherouat, y. hammi, “numerical aspects of finite elastoplasticity with isotropic ductile damage for metal forming”, revue européenne des elements finis, vol. 10, no. 2-4, pp. 327-351, 2001 [14] c. l. chow, t. j. lu, “a normative representation of stress and strain for continuum damage mechanics”, theoretical and applied fracture mechanics, vol. 12, pp.161–187, 1989 [15] c. l. chow, j. wang, “an anisotropic theory of continuum damage mechanics for ductile fracture”, engineering fracture mechanics, vol. 27, pp. 547558, 1987 [16] c. l. chow, j. wang, “ductile fracture characterization with an anisotropic continuum damage theory”, engineering fracture mechanics vol. 30, pp. 547–563, 1988 [17] j. lemaitre, r. desmorat, m. sauzaya, “anisotropic damage law of evolution”, european journal of mechanics, vol. 19, pp. 187–208, 2000 [18] k. saanouni, m. hamed, “micromorphic approach of finite gradientelastoplasticity fully coupled with ductile damage: formulation and computational approaches”, international journal of solids and structures, vol. 50, pp. 2289–2309, 2013 microsoft word etasr_v11_n4_pp7424-7429 engineering, technology & applied science research vol. 11, no. 4, 2021, 7424-7429 7424 www.etasr.com haj hamad et al: a takagi-sugeno fuzzy model for greenhouse climate a takagi-sugeno fuzzy model for greenhouse climate imen haj hamad laboratory of automatic research national engineering school of carthage university of carthage carthage, tunisia imen.hadjhamad@enicar.u-carthage.tn amine chouchaine laboratory of application for energy efficiency and renewable energies, faculty of sciences of tunis university of tunis el manar tunis, tunisia amin.chouchain@laposte.net hajer bouzaouache laboratory of application for energy efficiency and renewable energies (laper) national engineering school of tunis university of tunis el manar tunis, tunisia hajer.bouzaouache@ept.rnu.tn abstract-this paper investigates the identification and modeling of a greenhouse's climate using real climate data from a greenhouse installed in the laper laboratory in tunisia. the objective of this paper is to propose a solution to the problem of nonlinear time-variant inputs and outputs of greenhouse internal climate. combining fuzzy logic technique with least mean squares (lms), a robust greenhouse climate model for internal temperature prediction is proposed. the simulation results demonstrate the effectiveness of the identification approach and the power of the implemented takagi-sugeno fuzzy model-based algorithm. keywords-ts fuzzy modeling; climate greenhouse; fuzzy clustering; identification i. introduction greenhouse cultivation is a way to protect plants from bad meteorological conditions and to take advantage of the internal climate to guarantee the high quality and the low cost of production. optimal management of the greenhouse climate is the most appropriate way to meet the needs of industrial agricultural production. this management is essentially based on the efficient use of solar energy, air heating, ventilation, and cooling. for these reasons, greenhouse modeling is very difficult in terms of the non-linearity that describes the function between the outputs (internal humidity, internal temperature) and the inputs (external temperature, external humidity, solar radiation, wind speed, etc.) [1]. in order to develop a control technique, a good model of the greenhouse is needed for simulation and for real time control. various methods have been proposed in the past for modeling a greenhouse. in the literature, there are two main categories of mathematical modeling techniques for real processes [2]: physical modeling and system identification. the first is based on the physical laws involved in the process and the second on the analysis of the input-output data of the model. in [3-6], the dynamic temperature model is based on the energy balance. the physical model of a greenhouse by researching thermal radiation and ventilation was developed in [7]. the modeling of the system was described from the process of mass-energy exchange in [8]. authors in [9] studied the heat exchange by internal convection, plant transpiration, and natural ventilation to establish a greenhouse model. authors in [10] analyzed the auto-regressive models with external data based on the gdgcm model. in [11], the modeling of the internal temperature of the greenhouse was based on a hybrid system. identification based on takagi-sugeno (ts) fuzzy model was used in [12]. in [13], clustering was utilized to acquire the main modeling greenhouse parameters. in [14], hierarchical strategy was used to minimize the number of fuzzy rules in the modeling of the system. fuzzy modeling based on neural network learning techniques was developed in [15, 16]. to obtain the consequence of the rules, we can see the use of least squares for the modeling in [17, 18]. in [19], calculus of variations and nonlinear optimization-based algorithm for optimal control of hybrid systems with controlled switching were utilized. in this paper, principal focus is given on the modeling phase. the paper is dedicated to the modeling of a class of nonlinear dynamic processes by merging local linear models. these local linear models are the fuzzy models of ts type [20]. the output of these fuzzy systems is obtained by simple interpolation of locally approved linear models. this approach allows a linguistic interpretation of the fuzzy rules. on the other hand, classical methods of linear control can be applied to local fuzzy models [21, 22]. the information system from fuzzy models can be used by a great variety of command methodologies. thus, the performance of control depends heavily on the accuracy of the model used. therefore, a large part of the design effort must be dedicated to modeling. so, our corresponding author: imen haj hamad engineering, technology & applied science research vol. 11, no. 4, 2021, 7424-7429 7425 www.etasr.com haj hamad et al: a takagi-sugeno fuzzy model for greenhouse climate objective is to have the simulation results of a fuzzy inference system (fis) that seeks to generate a linguistic model optimized by back-propagation and the least mean squares algorithm for predicting the climate of the greenhouse. ii. experimental set-up a. description of the experimental greenhouse the actual greenhouse is located at the laboratory of application for energy efficiency and renewable energies (laper). the external structure of the greenhouse is oriented east-west and has the form of a chapel, as illustrated in figure 1. the geometric characteristics of the greenhouse are: length = 150cm, width = 100cm, height = 115cm. fig. 1. the experimental greenhouse. b. description of the measuring equipment the database is obtained using the following equipment: • the air temperature is measured by an lm35 sensor, with an accuracy of 0.4°c in the temperature range between -24°c and 48°c. • the relative humidity is measured by a sy-230 sensor. these sensors have an accuracy of about 3% in the measurement range between 0 and 95%. • a pyranometer type lpyra03 was used to measure the global solar radiation level on a horizontal surface. its accuracy is about 5%, its measuring range from 0 to 2000w/m 2 and its typical sensitivity about 10µv(w/m 2 ). iii. takagi-seguno fuzzy model a. basic structure fuzzy logic can provide an interesting alternative to mathematical modeling for many physical processes that are too complicated to be described by precise and simple mathematical equations or formulas. there are several classes of fuzzy systems, the most commonly used are the mamdani fuzzy systems [12] and the ts fuzzy systems. the particularity of these systems is that the consequence of each rule does not correspond to a fuzzy set but to a local model of the system to be estimated. the ts model is composed of if-then rules with fuzzy antecedents and mathematical functions in the consequent part [23]. the antecedents of fuzzy sets divide the input space into a number of fuzzy regions, while the consequent functions are used to describe the behavior of the system in these regions [24]. for an i th rule, a ts fuzzy system has the following form: ( ) ( ) ( ) ( )i i iif x k is m , then x k +1 = a x k + b u k (1) where x(k) represents the state vector and mi represents the vector of the fuzzy set of the i th rule. the output of the ts model corresponds to every rule. therefore, it is necessary to attribute a weight to describe the similarity ratio of each rule to the actual behavior of the process: ( )( ) ( )( ) p i ij j j=1 w x k = m x k∏ (2) where ( )( )ij jm x k is the membership degree of the jth state variable of the i th rule. in addition, ( )( )iw x k is the product of all the membership degrees of the i th rule, which shows the weight of this rule in the whole model. therefore, the output can be defined by the weighted average of all rules: ( ) ( )( ) ( ) ( )( ) ( )( ) n i i i i=1 i n i i=1 w x k a x k +b u k x k +1 = w x k ∑ ∑ (3) thus, in the whole ts fuzzy system, the weighting of the element x(k ) is described in the form : ( )( ) ( )( ) ( )( ) i i n i i=1 w x k x k = w x k φ ∑ (4) so, the output of the ts model is: ( ) ( ) ( )( ) n i i i=1 x k +1 = x k +1 x kφ∑ (5) b. fuzzy clustering fuzzy clustering consists on identifying natural groupings of data from a large data set to produce an accurate representation of a system's behavior. it is useful to divide a fuzzy data set into a certain number of groups by mapping membership probabilities to each object [25]. the membership of each data item to each group is illustrated by the membership matrix with size c×l for grouping the data set }{ 1 2 lx = x ,x ,...x : 11 1 1 1 1 l l c c cl u u u u u uu = u u u β α αβ α β                 l l m o m n m l l m n m o m l l (6) engineering, technology & applied science research vol. 11, no. 4, 2021, 7424-7429 7426 www.etasr.com haj hamad et al: a takagi-sugeno fuzzy model for greenhouse climate where uαβ corresponds to the membership degree of the β th (β=1,2,…l) element to the α th clustering. in the present matrix, there are several limitations: • [ ]αβu 0,1∈ • c αβ α=1 u = 1∑ • 0 l αβ =1 u l β ∑p p the objective function during the clustering is defined as: ( ) ( ) ( ) l c m 2 αβ αβ β=1 α=1 j u,v = u d∑∑ (7) where ( )1 cv = v ,...,v represents a vector whose elements represent the center of each clustering, m is the weight factor with a usual value of 2. the euclidean distance between the β th element and the center of the α th fuzzy clustering is defined by: ( ) 2 2 d x vαβ β α= − . thus, the objective function aims are to calculate the sum of the weighted values. to obtain the minimum of the objective function, it is necessary to search for the partial derivatives and make them equal to zero. finally, the limit conditions are: ( ) ( ) l m αβ β β=1 α l m αβ β=1 u x v = u ∑ ∑ (8) 2 m-1 β α αβ 2 -c m-1 β α α=1 x v u = x v∑ (9) where vα calculates the center of α th clustering while uαβ renews the membership degree of each element. in the clustering process, the iteration will be completed when the convergence condition is satisfied [26] or the iteration time is reached. c. parameter estimation generally, it is recommended to start with a linear model and determine the structure of the system based on the available tools to use the best model possible as a starting point for the nonlinear modeling. this is possible with the ts models' ability to use the local linear models obtained by fuzzy identification and interpolate them with each other to optimize the nonlinear structure of the system and obtain optimal results. the most common way to identify the parameters is the least mean squares (lms) method. however, different rules play a different role in the ts fuzzy model. for this reason, the ordinary lms method should be applied [12]. firstly, the consequence must be rewritten in the following form: ( ) 1 1 p p 1 1 q qx k +1 = a x + + a x +b u + +b ul l (10) where x(k +1) is the output of this rule and x and u are the system inputs. thus, the data can be described as follows: ( ) ( ) ( ) ( ) ( ) ( ) ; y 2 x 2 x 1 y = = x = y k +1 x k +1 x k                              m m m (11) the parameters of an ordinary lms identification are determined by the following equation: -1 t t i i i θ = x q x x qy   (12) where θi represents the consequent parameter vector and qi represents the weight matrix that contains the weight of all the data: ( )( ) ( )( ) i i x 1 0 0 q = 0 0 0 0 x n φ φ            o (13) iv. greenhouse fuzzy modeling and simulation results the main objective of fuzzy identification is to improve the accuracy acquired by a nonlinear physical model. for this simulation, a database was recorded on october 5, 2020 at the laper laboratory to do the greenhouse fuzzy modeling. the sampling rate was fixed to 15s. from the obtained data we have fixed 2 membership functions for the inside temperature, the outside temperature, the humidity, and the solar radiation. the data of each input will be classified and indexed using the cmean fuzzy algorithm and then they will be approximated by trapezoidal membership functions. the results obtained for each input are represented by figures 2-5, designating the membership functions of the discrete fuzzy model as well as the groupings established by the c-mean fuzzy algorithm. for each input, we select a small number of clusters to minimize the number of rules in the ts fuzzy system. fig. 2. membership of internal temperature (°c) (solid line) and data clusters (points). the prediction of the internal climate is given by the diagram illustrating the fuzzy rule architecture of the fis in the engineering, technology & applied science research vol. 11, no. 4, 2021, 7424-7429 7427 www.etasr.com haj hamad et al: a takagi-sugeno fuzzy model for greenhouse climate matlab environment, when the trapezoidal membership function is adopted. the architecture consists of 32 fuzzy rules. in the preliminary experiments, the proposed architecture proved to be sufficiently capable of extracting the climate model of the greenhouse from the control actuators and meteorological data. figure 6 presents the flow chart of the internal climate prediction by fis. fig. 3. membership of external temperature (°c) (solid line) and data clusters (points). fig. 4. membership of internal humidity (%) (solid line) and data clusters (points). fig. 5. membership of radiation (w/m 2 ) (solid line) and data clusters (points). fig. 6. diagram of the internal climate prediction of the fis system. the consequent output of a rule i of the ts fuzzy model to be identified has the form: ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) i 1i 2i i 3i e 4i i 5i e 6i s 7i i 8i ch t k +1 = a +a t k +a t k +a rh k +a rh k +a r k +a v k +a q k (14) where ti is the internal temperature, te is the external temperature, rhi is the internal humidity, rhe is the external humidity, rs is the solar radiation, vi is the internal air speed, and qch is the heat delivered by the thermal system. subsequently, the practical results show that the fuzzy identification system generated with the lms method is more accurate than the dynamic modeling (figure 9) because a good convergence to the real data of the figure 7 may be observed. moreover, in figure 8, we notice that the error is of the order of 1% proving the efficiency of the proposed system, since the classical dynamic modeling reaches an error value of 2%-4% (figure 10). in order to evaluate the result quantitatively, the vaf function [27] was adopted, to compare the difference degree between two signals. this function is given as follows: ( ) ( ) 1 2 1 var y y vaf = 1,0 ×100% var y         (15) where y1 represents the real data, y2 represents the simulation result, and var is the variance. the result is more accurate if the vaf value is closer to 100% and less accurate if it is closer to 0%. after the calculation, the temperature variation value for the physical model is vaf=89.38% and the temperature engineering, technology & applied science research vol. 11, no. 4, 2021, 7424-7429 7428 www.etasr.com haj hamad et al: a takagi-sugeno fuzzy model for greenhouse climate variation value for the fuzzy model is vaf=97.47%. we can see that the performance of the proposed modeling method is successful for any kind of greenhouse. furthermore, when we compare the results of this study with the ones from [5] that used the dynamical modeling method [5], we notice that our fuzzy system is more accurate. a good agreement has been obtained between the calculated and the measured data, which indicates the efficiency of our proposed model in comparison with other methods. fig. 7. inside temperature of the greenhouse and the output of the fuzzy model. fig. 8. difference between the temperature inside the greenhouse and the output of the fuzzy model. fig. 9. inside temperature of the greenhouse and the output of the dynamic model. fig. 10. difference between the temperature inside the greenhouse and the output of the dynamic model. v. conclusion this paper proposes a greenhouse model method based on a ts fuzzy model using the fuzzy c-means algorithm for clustering and the lms method for adjusting the model. this method has the following advantages: it allows modifying the hierarchical structures by adding or removing a sub-model or rules at any time without the need to repeat the whole identification process and to use all the collected data. these sub-models have similar correspondences in the physical modeling, which represent the contributions of the process mechanisms involved in the global process. the comparison of the results obtained by the fuzzy model and the experimental results confirmed the efficiency and the accuracy of the proposed model in predicting the internal greenhouse climate. in following work, we intend to integrate the developed model in an adaptive control system in order to obtain increased production and quality of horticultural products and to reduce energy consumption. acknowledgment the authors would like to thank the laboratory of automatic research, national 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[27] j. c. gomez, a. jutan, and e. baeyens, "wiener model identification and predictive control of a ph neutralisation process," iee proceedings control theory and applications, vol. 151, no. 3, pp. 329–338, may 2004, https://doi.org/10.1049/ip-cta:20040438. engineering, technology & applied science research vol. 9, no. 2, 2019, 3881-3886 3881 www.etasr.com belhaj salah & fourati: systems modeling using deep elman neural network systems modeling using deep elman neural network latifa belhaj salah control and energy management laboratory (cem-lab) university of gabes, tunisia latifa.belhadjsalah@enis.tn fathi fourati control and energy management laboratory (cem-lab) university of sfax, tunisia fethi.fourati@ipeis.rnu.tn abstract—in this paper, the modeling of complex systems using deep elman neural network architecture is improved. the emphasis is to retrieve better deep elman structure that emulates perfectly such dynamic systems. to achieve this goal, sigmoid activation functions in the hidden and output layer nodes are chosen and data files on considered systems for modeling and validation steps are given. simulation results prove the ability and the efficiency of a deep elman neural network with two hidden layers in this task. keywords-elman neural network; recurrent neural network; deep learning; complex systems; modeling i. introduction recently, deep neural networks (including recurrent networks) have been successfully applied in several areas [1]: modeling and control of complex systems, fault detection, text understanding [2, 3], speech recognition [4, 5] and computer vision [6, 7]. the advantage of deep learning is reflected on the modeling of high-level abstractions from the data by its architecture which is consisted of several non-linear learning layers. each layer replies to several levels of nonlinear abstraction. [8]. in [9], authors used recurrent neural networks with long-term memory units (lstms) to find a solution to the vanishing gradient problem observed in simple recurrent neural networks (rnns) [9-10]. authors in [11] used the pre-training and fine-tuning steps to ensure the effective training of deep learning. deep learning has a significant success in big data since it can recover valuable information from complex processes [12]. in [13], authors have described a combination between deep learning and reinforcement learning for the prediction and control of intelligent laser welding. the effectiveness of using deep elman rnn for modeling complex systems was demonstrated in [14]. in order to improve the performance of deep learning with multiplayer perceptron (mlp), a new technique was used that requires a combination of adaptive learning rate and laplacian score concept to vary the weights. in [15], authors proposed a new method for automatic modulation classification (amc) based on unsupervised feed-forward deep learning. the performance of this approach was compared to conventional amc techniques. in [16], authors used the application of end-to-end deep learning to solve the classification problem of speech emotion recognition. they showed the limitations and benefits of these architectures in speech recognition. in [17], authors used deep elman rnn (ernn) for acoustic modeling. they compared the performance of this technique with other rnn architectures like lstm, gru, and simplified lstm [18-20]. in [21], authors developed two novel deep rnn models with lstm units to predict building electricity consumption. in [22], authors proposed a new learning algorithm based on simplified convolutional neural network to achieve visual tracking with adaptive filtering of particles. in [23], authors used convolutional deep learning neural networks to detect and diagnose plant diseases from leaves images of healthy and diseased plants. in [24], authors exploited deep learning to solve the problem of large data analysis which is found in several areas. in [25], authors proposed the use of a new method based on deep belief networks and multiple models (dbns-mms) to detect faults of complex systems. the novelty in this paper is the use of a deep neural network that improves modeling systems tasks. in fact, comparing to results given in [26], an elman neural network with two hidden layers gives more accuracy when modeling complex systems. ii. elman neural network the elman network is a type of recurrent network [27]. it has been applied in many areas such as dynamic system identification [28] and financial prediction [29]. in [27], a simple recurrent neural network was proposed: the input and output units are in contact with the external environment, in contrast to the context and hidden units. this network is characterized by context units that are used to save the previous hidden unit activations. hidden unit activations at time k are returned to the context units and stored for the next training step. the elman network is named partially recurrent network because the feed forward connections are modifiable and the recurrent connections are fixed. to train this kind of neural network, the back propagation algorithm can then be used and the hidden units activation functions can be linear or non-linear [17, 27, 30]. figure 1 represents an elman neural network architecture. the l-th input unit to the network is represented by 𝑉𝐸𝑙(𝑘) and the m-th network output unit by 𝑛𝑒𝑡𝑜𝑚(𝑘). the total input to the i-th first hidden layer unit is denoted as 𝑛𝑒𝑡𝑖 1(k). the output of the i-th first hidden layer unit is denoted as 𝑛𝑒𝑡𝑖 11(k). the output of the j-th context layer unit is 𝑉𝑗 𝑐(𝑘). the total input to the ii-th second hidden layer unit is denoted corresponding author: latifa belhaj salah engineering, technology & applied science research vol. 9, no. 2, 2019, 3881-3886 3882 www.etasr.com salah & fourati: systems modeling using deep elman neural network as 𝑛𝑒𝑡𝑖𝑖 2(𝑘). the output of the ii-th second hidden layer unit is denoted as 𝑛𝑒𝑡𝑖𝑖 22(𝑘). the output of the jj-th second context layer unit is 𝑉𝑗𝑗 𝑐1(𝑘). the total input to the i..i-th (n-1-th) hidden layer unit is denoted as 𝑛𝑒𝑡𝑖..𝑖 𝑛−1(𝑘).the output of the i..i-th (n1-th) hidden layer unit is denoted as 𝑛𝑒𝑡𝑖..𝑖 (𝑛−1)(𝑛−1) (𝑘). the output of the j..j-th (n-1-th) context layer unit is 𝑉𝑗..𝑗 𝑐𝑛−1(𝑘). the total input to the i..ii-th (n-th) hidden layer unit is denoted as 𝑛𝑒𝑡𝑖..𝑖𝑖 𝑛 (𝑘). the output of the i..ii-th (n-th) hidden layer unit is denoted as 𝑛𝑒𝑡𝑖..𝑖𝑖 𝑛𝑛(𝑘). the output of the j..jj-th (n-th) context layer unit is 𝑉𝑗..𝑗𝑗 𝑐𝑛 (𝑘). the total input to the m-th output layer unit is denoted as 𝑛𝑒𝑡𝑚 𝑠 (𝑘) . 𝑤𝑗,𝑖 𝑐 (. ) , 𝑤𝑙,𝑖 𝑉𝐸(. ) , 𝑤𝑖..𝑖𝑖,𝑚 𝑛𝑒𝑡𝑜 (. ) , 𝑤𝑖,𝑖𝑖 𝑛𝑒𝑡2(. ) , 𝑤𝑗𝑗,𝑖𝑖 𝑐1 (. ), 𝑤𝑖..𝑖,𝑖..𝑖𝑖 𝑛𝑒𝑡𝑛 (. ) , 𝑤𝑗..𝑗𝑗,𝑖..𝑖𝑖 𝑐𝑛 (. ) are the weights of the links, respectively between the first context layer and the first hidden layer, the input layer and the first hidden layer, the i..ii-th (n-th) hidden layer and the output layer, the first hidden layer and the second hidden layer, the second context layer and the second hidden layer, the (n-1)-th hidden layer and the n-th hidden layer and the n-th context layer and the n-th hidden layer. fig. 1. elman neural network architecture. iii. elman neural network learning step the training of the elman neural network to emulate direct dynamics of a system amounts to minimize the squared error criterion defined as: 2 1 1 ( ( ) ( )) 2 = = − sn k m m m e vs k neto k (1) where vs(k) is the desired output vector. in the training step the back propagation algorithm is used to adjust the elman neural network connection weights, in order to emulate the dynamics of a system. in the case of many hidden layers, the elman neural network is governed by the following equations: 1 , , 1 1 ( ) ( 1) ( ) ( 1) ( ) = = = − + −  c ven n c c ve i j i j l i l j l net k w k v k w k ve k (2) 11 1 ( ) ( )= i i net k f net (3) 11 ( ) ( 1)= − c j j v k net k (4) 1 2 1 12 11 , , 1 1 ( ) ( 1) ( ) ( 1) ( ) = = = − + −  ch nn c cnet ii i ii i jj ii jj i jj net k w k net k w k v k (5) 22 2 ( ) ( ( ))= ii ii net k f net k (6) 1 22( ) ( 1)= − c jj jj v k net k (7) 1 ( 1)( 1) .. .. , .. .. .. 1 .. , .. .. .. 1 ( ) ( 1) ( ) ( 1) ( ) − − − = = = − + −   hn n cn n n n n net n n i ii i i i ii i i i i n c c j jj i ii j jj j jj net k w k net k w k v k (8) .. .. ( ) ( ( ))= nn n i ii i ii net k f net k (9) .. .. ( ) ( 1)= −n c nn j jj j jj v k net k (10) .. , .. .. 1 ( ) ( 1) ( ) = = − hn n s neto nn m i ii m i ii i ii net k w k net k (11) ( ) ( )= s m m neto k f net (12) where , , c h ve n n n , 1 1 , h c n n , 1nh n − , , n nh c n n represent the number of units respectively in the first context layer, the first hidden layer, the input layer, the second hidden layer, the second context layer , the (n-1)th hidden layer, the n-th hidden layer and the n-th context layer. the squared error at the network output is defined as in (1). for .. , ( 1)− neto i ii m w k the error gradient is: .. .. , ( ( ) ( )) ( ) ( 1)  = − −  − s m nnk m m i iineto net i ii m e vs k neto k f net k w k (13) for , ( 1)− ve l i w k , , ( 1)− c j i w k , 2 , ( 1)− net i ii w k , 1 , ( 1)− c jj ii w k , .. , .. ( 1)− n net i i i ii w k and .. , .. ( 1)−n c j jj i ii w k . 2 1 2 1 .. .. .. , , .. , .. , ( ( ) ( )) ( 1) ( 1) ( 1) ... ( 1) ( )−  = − − −  −    − − s m n n n i ii i i ii i netok m m i ii mve net l i net net i i i ii i ii lnet net net net e vs k neto k f w k w k f w k f f w k f ve k (14) 2 1 2 1 .. .. .. , , .. , .. , ( ( ) ( )) ( 1) ( 1) ( 1) ... ( 1) ( )−  = − − −  −    − − s m n n n i ii i i ii i netok m m i ii mc net j i net net c i i i ii i ii jnet net net net e vs k neto k f w k w k f w k f f w k f v k (15) 1 2 .. .. .. ,2 , 11 .. , .. ( ( ) ( )) ( 1) ( 1) ( 1) ... ( )−  = − − −  −   − s m n n n i ii i i ii netok m m i ii mnet net i ii net i i i ii inet net net e vs k neto k f w k w k f w k f f net k (16) 1 1 1 2 .. .. .. , , .. , .. ( ( ) ( )) ( 1) ( 1) ( 1) ... ( )−  = − − −  −   − s m n n n i ii i i ii netok m m i ii mc net jj ii cnet i i i ii jjnet net net e vs k neto k f w k w k f w k f f v k (17) .. .. , .. , .. ( 1)( 1) .. ( ( ) ( )) ( 1) ( 1) − −  = − − −  −  sn m n i ii netok m m i ii mnetnet i i i ii n n i inet e vs k neto k f w k w k f net (18) engineering, technology & applied science research vol. 9, no. 2, 2019, 3881-3886 3883 www.etasr.com salah & fourati: systems modeling using deep elman neural network .. .. , .. , .. ( 1)( 1) .. ( ( ) ( )) ( 1) ( 1) − −  = − − −  −  sn m n i ii netok m m i ii mnetnet i i i ii n n i inet e vs k neto k f w k w k f net (19) in (13)  s mnet f denotes the derivative of f representing s m net . the general weight modification in the gradient descent method is:    = −  k e w w (20) where: • the weight adjustment between the output and the n-th hidden layer are: .. , .. ( ) ( ( ) ( )) ( )s m neto nn i ii m m m i iinet w k vs k neto k f net k  = − (21) • the weights adjustment between the first hidden layer and the input layer are: .. 2 1 2 1 .. , .. , .. , .. , ( ) ( ( ) ( )) ( 1) ( 1) ... ( 1) ( )  −   = − −   − − s n m i ii n n i i ii i ve neto l i m m i ii mnet net net net i i i ii i ii lnet net net w k vs k neto k f w k f w k f f w k f ve k (22) • the weights adjustment between the first hidden and the context layers are: .. 2 1 2 1 .. , .. , .. , .. , ( ) ( ( ) ( )) ( 1) ( 1) ... ( 1) ( )  −   = − −   − − s n m i ii n n i i ii i c neto j i m m i ii mnet net net net c i i i ii i ii jnet net net w k vs k neto k f w k f w k f f w k f v k (23) • the weights adjustment between the first hidden layer and the second hidden layer are: 2 1 2 .. .. , .. , 11 .. , .. ( ) ( ( ) ( )) ( 1) ( 1) ... ( )  −  = − −   − s m n n n i ii i i ii net neto i ii m m i ii mnet net i i i ii inet net net w k vs k neto k f w k f w k f f net k (24) • the weights adjustment between the second hidden and the context layers are: 1 1 1 2 .. .. , .. , .. , .. ( 1) ( ( ) ( )) ( 1) ( 1) ... ( )  −  − = − −   − s m n n n i ii i i ii c neto jj ii m m i ii mnet cnet i i i ii jjnet net net w k vs k neto k f w k f w k f f v k (25) • the weights adjustment between the n-th hidden and context layers are: .. .. , .. .. , .. ( ) ( ( ) ( )) ( 1)  = −  − n n s n m i ii c j jj i ii m m cneto i ii m j jjnet net w k vs k neto k f w k f v (26) • the weights adjustment between the n-th hidden layer and the (n-1-th) hidden layer are: .. .. , .. ( 1)( 1) .. , .. ( ) ( ( ) ( )) ( 1)  − −  = − − n s m n i ii net i i i ii m m net neto n n i ii m i inet w k vs k neto k f w k f net (27) iv. considered systems complex systems are generally multi-variable, described by non-linearity, characterized by uncertainties and subject to disturbances [31]. the goal of modeling a complex system consists of constructing a concise and efficient neural elman structure to emulate the dynamics of a system [32, 33]. at first we consider a single input and a single output (siso) system with a non-linear function f (.), as in figure 2. fig. 2. a siso sytem here, sin( ) ( )= =y u f u (28) the complex system to be modeled is a greenhouse with multi-inputs, multi-outputs (mimo), disturbances and uncertainty. it is composed of sensors to measure internal and external climate. the greenhouse outputs are defined by the internal climate (“internal temperature and internal hygrometry”). it is equipped with actuators to control the internal climate, consisted with a sliding shutter with an opening between 0° and 35°, a heater which operating in on/off mode with a power of 5kw, a sprayer and a curtain with a length varying between 0 and 3m. the considered greenhouse is a classical one, it is characterized by physical quantities that constitute its functioning [34, 35]: • measurable but not controllable input: te (external temperature (in ºc), he (external hygrometry in %), rg (global radiant in w/m2), vv (wind speed in km/h). • measurable and controllable input: ch (heating input varying between 0 and 1), ov (sliding shutter in degrees), br (sprayer varying between 0 and 1), om (curtain in m). • outputs: ti (internal temperature in ºc), hi (internal hygrometry in %). fig. 3. greenhouse functional bloc diagram. v. simulation results three neural network structures are considered for both systems: the first is with one hidden and context layers, the second one is constituted of two hidden and context layers and the third one has three hidden and context layers. table i presents the deep elman neural network caracteristics modeling the non-linear process. engineering, technology & applied science research vol. 9, no. 2, 2019, 3881-3886 3884 www.etasr.com salah & fourati: systems modeling using deep elman neural network table i. deep elman neural network -non-linear process. parameters one hidden and context layers two hidden and context layers three hidden and context layers 𝒏𝟏 1 1 1 𝒏𝒔 1 1 1 𝒏𝒄𝟏 4 4 4 𝒏𝒉𝟏 4 4 4 𝒏𝒄𝟐 4 4 𝒏𝒉𝟐 4 4 𝒏𝒄𝟑 4 𝒏𝒉𝟑 4 iterations 3000 3000 10000 learning coefficient 0.2 0.2 0.4 figures 4-6 represent the evolution of the criterion (1) for the first non-linear process. table ii presents deep elman neural network characteristics modeling the greenhouse. figures 7-9 present the evolution of the criterion ek in the case of the second process (greenhouse). from the figures and for the two considered systems we conclude that the error ek is lower in the case of two hidden and context layers network. thus, the convergence of the error is faster in the case of the neural structure with a single hidden and context layer than the other neural structures. fig. 4. evolution of ek in the case of one hidden layer network. fig. 5. evolution of ek in the case of two hidden layers network. fig. 6. evolution of ek in the case of three hidden layers network. table ii. deep elman neural networkw-greenhouse parameters one hidden and context layers two hidden and context layers three hidden and context layers 𝒏𝟏 8 8 8 𝒏𝒔 2 2 2 𝒏𝒄𝟏 4 4 4 𝒏𝒉𝟏 4 4 4 𝒏𝒄𝟐 4 4 𝒏𝒉𝟐 4 4 𝒏𝒄𝟑 4 𝒏𝒉𝟑 4 iterations 10000 10000 20000 learning coefficient 0.1 0.2 0.4 fig. 7. evolution of ek in the case of one hidden layer network. fig. 8. evolution of ek in the case of two hidden layers network. fig. 9. evolution of ek in the case of three hidden layers network. in order to compare and validate the three neural models the criterion (29) is considered: ( ) 1 1 ( ) ( ) = = = − snnb m t i i k i e abs y k y k (29) where, nb is the operating interval, k is the sample time, ns is the number of outputs, ( ) i y k is the i-th output of the system at time k and ( )m i y k is the i-th output of the neural model at time k. in the case of the first system, nb=1000. figures 10-12 represent the evolution of the process output (continuous line) and the neural model output (dashed lines). engineering, technology & applied science research vol. 9, no. 2, 2019, 3881-3886 3885 www.etasr.com salah & fourati: systems modeling using deep elman neural network fig. 10. evolution of the process and the one hidden layer neural model outputs. et=59.496. fig. 11. evolution of the process and the two hidden layer neural model outputs. et=57.8332. fig. 12. evolution of the process and the three hidden layer neural model outputs. et=58.9947. in the case of the second system (greenhouse), we have a data file of the whole parameters’ values acting on the greenhouse during one day. the sampling time is one minute, so in one day (24 hours), we obtain a data file with 1440 lines. we divided the data file in two parts, each part constituted of 720 lines. the first part was used for learning (training) and the second was used for the validation. in our case: vel(k)=[ov(k),ch(k),br(k),om(k),te(k),he(k),rg(k),vv(k)] t ,netom(k)=[ti(k) hi(k)]. here nb=720. figures 13 and 14 represent the evolution of the real internal climate (temperature and hygrometry) with continuous lines and the one hidden layer neural model outputs with dashed lines and using the validation data file part. here et=88.7962. fig. 13. evolution of the internal temperature. fig. 14. evolution of the internal hygrometry. figures 15 and 16 represent the evolution of the real internal climate (temperature and hygrometry) with continuous lines and the two hidden layers neural model outputs with dashed lines and using the validation data file part (et=82.4499). figures 17 and 18 represent the evolution of the real internal climate with continuous lines and the three hidden layers neural model outputs with dashed lines and using the validation data file part (et=90.5219). fig. 15. evolution of the internal temperature. fig. 16. evolution of the internal hygrometry. fig. 17. evolution of the internal temperature. fig. 18. evolution of the internal hygrometry. engineering, technology & applied science research vol. 9, no. 2, 2019, 3881-3886 3886 www.etasr.com salah & fourati: systems modeling using deep elman neural network from the previous figures and results, we conclude that the total error is lower in the case of two hidden and context layers than the one of the other neural networks. this elman neural structure gives better performance results for the modeling and validation steps. vi. conclusion in this paper, we trained a deep elman neural network to improve the modeling of complex systems. after observing the simulation results, we concluded that the direct model reproduces the dynamic behavior of two processes with acceptable performance. we 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speech recognition system on … a robust feature extraction method for real-time speech recognition system on a raspberry pi 3 board aymen mnassri department of physics, faculty of sciences of tunis, tunis-el manar university, tunisia mnassri.aymen46@gmail.com mohamed bennasr department of physics, faculty of sciences of tunis, tunis-el manar university, tunisia bennasr.mouhamed@gmail.com cherif adnane department of physics, faculty of sciences of tunis, tunis-el manar university, tunisia adnene.cher@fst.rnu.tn abstract—the development of a real-time automatic speech recognition system (asr) better adapted to environmental variabilities, such as noisy surroundings, speaker variations and accents has become a high priority. robustness is required, and it can be performed at the feature extraction stage which avoids the need for other pre-processing steps. in this paper, a new robust feature extraction method for real-time asr system is presented. a combination of mel-frequency cepstral coefficients (mfcc) and discrete wavelet transform (dwt) is proposed. this hybrid system can conserve more extracted speech features which tend to be invariant to noise. the main idea is to extract mfcc features by denoising the obtained coefficients in the wavelet domain by using a median filter (mf). the proposed system has been implemented on raspberry pi 3 which is a suitable platform for real-time requirements. the experiments showed a high recognition rate (100%) in clean environment and satisfying results (ranging from 80% to 100%) in noisy environments at different signal to noise ratios (snrs). keywords-automatic speech recognition; discrete wavelet transform; mel frequency cestrum coefficients; median filter; support vector machines; raspberry pi i. introduction speech recognition technology has been widely spread and has been applied in many research areas such as mobile robots [1-33], consumer electronics [4], car audio systems [5], security system manipulators [6], and manipulators in industrial assembly lines [7]. however, robust performance poses a problem for any real-time application due to various conditions such as noisy background, different accents, and speaker variations. thus, high performance asr systems are required. the accuracy of such systems obtained in laboratory environments is not sufficient. moreover, it is practically lower in real conditions. recently, several embedded asr systems have been presented. some of them have been implemented on digital signal processors (dsps) [8-10], while others have been deployed on field programmable gate arrays (fpgas) [11-13] without satisfactory enough accuracy rates. state-of-the-art on asr provides good performance if the used and trained conditions are reasonably controlled and similar, and their performance is degraded in the case of mismatching conditions. in many recent works, the speech feature extraction methods have been discussed, such as the linear prediction coefficients (lpcs), the relative spectral-perceptual linear prediction (rasta-plp) [14], and the linear-predictive cepstral coefficients (lpccs) which have been used because of their efficiency and simplicity in speech and speaker recognition [15]. another technique that has been widely discussed in the speech recognition research area, is called the mel-frequency cepstral coefficients (mfcc) [16]. in spite of its good performance in clean background condition, the mfcc’s feature extraction for speech recognition is weak in noisy environments. in previous researches, a number of feature extraction methods have been proposed in order to enhance asr performance under noisy conditions. the most cited ones are the power-normalized cepstral coefficients (pncc) [17], the cepstral mean subtraction (cms) [18], and the cepstral mean normalization (cmn) [19] which is considered as one of the most popular feature extraction techniques for dealing with convolutional noises. furthermore, many works have highlighted the wavelet-based feature extraction method [2023] which has led to reach better performance improvements in comparison to traditional cepstral features. in this paper, a new robust feature extraction method for a real-time speech recognition system is presented and implemented on a raspberry pi 3 board. at first, the dwt transforms the received speech signal to the wavelet domain. then, an iterative median filter is carried out over all output wavelet transformation coefficients to remove noisy samples. in the next state, the obtained coefficients are assembled into one vector and across the mfcc procedure to produce the final result. the proposed method provides excellent recognition rate under clean and noisy states. this can conserve more speech signal features which will be robust against noise effects this can conserve more speech signal features which will be robust against noisy effects. this method has a stronger ability in separating signal from noise compared to the threshold denoising method which preserves the details. the applied noise elimination method can improve the denoising effect which is one of the main speech recognition system objectives. finally, a feature vector is carried out via the obtained mfcc corresponding author: aymen mnassri engineering, technology & applied science research vol. 9, no. 2, 2019, 4066-4070 4067 www.etasr.com mnassri et al.: robust feature extraction method for real-time speech recognition system on … coefficients concatenation. the performed vector will be used as an input parameter for the svm multi-class. the proposed method has outstanding performance in clean and noisy environments. ii. proposed algorithm methodology figure 1 shows the procedure of the proposed speech recognition system. the main idea is to give more significant coefficients for the performance of the system in a clean and noisy environment. at first, the input speech from a microphone is sampled at 16khz. voice activity detector (vad) is applied as silence detector to only keep signal parts where the speech is heard. the vad output presents a binary activity founded on the comparison between the input speech signal and the threshold value. thus, the vad value is true (vad=1) when the measured input is superior than the threshold. in this case, the signal is considered as a soundtrack. however, when the vad value is false (vad=0), the signal frame is considered as a silent frame. fig. 1. block diagram of the proposed speech recognition system after receiving the speech signal, the next step consists of decomposing the speech signal using dwt. the dwt result is a multilevel decomposition, in which the signal is separated into an ‘approximation’ and a ‘detail’ coefficient at each level. this is fabricated from a similar process to low and high pass filtering, respectively. in this step, a median filter is performed to detail the approximation coefficients separately and to ensure a robust noisy speech removing process. the applied filter expression is indicated by (1): ( ,..., ,...., ) − + =� t t d t t d x med x x x (1) where med(..,..,..) defines the median operator used to select elements within the sliding window and to take out the dth largest one. median filtering (mf) is a rank-order filtering method which proves its ability to eliminate data speckle noise without harming the embedded sharp contrasts. the main concept of mf is the use of a (2d+1) point sliding window to range through a signal, changing every signal point with a sliding window median value which is centered at that point. the mfcc function has then been used to extract the characteristics from the dwt output vector after the median filter application. finally, the obtained cepstral coefficients are concatenated to construct one input for the svm-classifier. this method is applied also to our proper training speech database containing arabic speech words which are recorded by multiple speakers (women and men) for voice command. for the samples’ classification, the “one against one” and “one against all” approaches were used. a. feature extraction the main objective of all feature extraction techniques is to select relevant and robust characteristic coefficients from the spoken utterance to improve the performance of the speech recognition system. in the present work, a new and robust hybrid feature extraction based on the mfcc and the dwt techniques was employed. the used experimental parameters of these techniques are presented below. 1) discrete wavelet transform dwt technique is a very popular tool used for the analysis of non-stationary signals. it can be thought of as an equivalent of filtering the speech signal with a bank of band pass filters, whose impulse responses are all approximately given by scaled versions of a mother wavelet [24]. in this work, the dwt will be used as a feature extraction tool because of its simplicity and reduced computation time. to compute the wavelet features, the decomposition is performed by one level, owing to the fact that the coefficients in this level include the essential frequency constituent of the speech signal. various mother wavelets are used and validated for the decomposition such as harr, symlets and daubechies. the latter presents the most suitable mother wavelet for our application, in particular to the first order db1. after applying the daubechies wavelets and extracting the features from each input speech command, the obtained coefficients were concatenated and used as the input vector for the next process. 2) mel frequency cepstral coefficients the analysis of the mfcc coefficients is the most popular and powerful in terms of demonstration that aims to present the data by coefficient vectors. fig. 2. calculation of the mfcc coefficients engineering, technology & applied science research vol. 9, no. 2, 2019, 4066-4070 4068 www.etasr.com mnassri et al.: robust feature extraction method for real-time speech recognition system on … the cepstral coefficients (mfcc) are frequently used in the asr domain due to their low complexity of the estimation algorithm and their high performance. in addition, the mfcc representation can describe the structure of the human auditory system better than the traditional linear predictive features [25]. the calculation process can be implemented as shown in figure 2. table i illustrates the experimental parameters used for extracting the mfcc coefficients. table i. experimental parameters used for extracting the mfcc coefficients parameters value coefficient of preemphasis filter 0, 9 ccepstrum number 12 coefficients analysis window length 20ms analysis window hamming recovery (%) 50 % b. classification regarding classification, our choice is the svm method, which is a very interesting progress in terms of implementation and extension to multi-class problems. the svm method is applied with success to applications such as facial recognition and handwriting recognition. furthermore, the svm is a kernel technique, which means that the hyperplane is found in a feature space using a non-linear transformation that aims to transform the input space in a feature space which has a much bigger dimension. machine learning methods (svms) are basically based on binary classifiers, whereas the acoustic classifier step in the asr can be fixed as a multiclass problem. in order to extend the binary algorithm to multiclass decision, we used two approaches which are: the “one-against-one” (oao) [26] and the “one-against-all” (oaa) [27]. the oaa approach compares each class with the other classes in order to categorize k classes and to construct k binary svm classifiers. in contrast, the oao approach consists in employing a classifier for each pair of classes. for the k-classes problem, the “oao” method discriminates the samples of one class from the samples of another class, so that k(k−1)/2 svms are constructed. in this work, the classification accuracy is evaluated with two approaches of multi-class svm’s by using the gaussian kernel. the parameters of this kernel (c, σ) are fixed according to the optimization obtained by the genetic algorithm described in [28]. iii. real time implementation this part is dedicated to the hardware and software description used for the real-time implementation. to prove the reliability of the proposed speech recognition method, a realtime simulation is required. for that, the adopted algorithm has been tested on a flexible embedded raspberry pi 3 board which seems to be convenient with the particularity of our application. the raspberry pi system is a broadcom bcm2837 system-onchip (soc) multimedia processor, which has 64-bit quad-core armv8 cortex a53 with 1gb of ram, 16gb (expandable to 128gb) sd card slot, 1.2ghz processor (soc). table ii represents the raspberry pi software specifications for the proposed framework. to test the implemented raspberry pi algorithm, the experiment data acquired in real-time environment are given to calculate response time. for that, a prototype robot similar to a wheelchair has been designed and tested using the raspberry pi board (figure 1). for the control of the moving robot, arabic voice commands have been set up to regarding direction and robot speed. two male and two female speakers were requested to issue voice commands under silent environment (table iii). table ii. raspberry pi software specifications name configuration operating system noobs (rasbian) programming language python 2.7 libraries numpy, scipy, pylab, matplotlib, rpi.gpio audio libraries pyaudio, pydub, wave performance monitoring utilities bcmstat, time, htop table iii. voice commands arabic commands robot action go forward تقدم go forward with speed امام speed أسرع go left يسار go right يمين turn استدر stop توقف go back with speed تراجع go back خلف keep going واصل fig. 3. hardware architecture of wheelchair prototype the wheelchair prototype (figure 1) contains two motors (1) used for the left and the right wheels. these motors are controlled separately by an h-bridge motor based on the l298n component (2). the cpu board can dictate the rotation speeds of the motors individually using pulse-width modulation (pwm). the h-bridge motor and the raspberry pi board (3) are directly powered by the power bank battery (4). the raspberry pi 3 requires a 5v dc power source with typical engineering, technology & applied science research vol. 9, no. 2, 2019, 4066-4070 4069 www.etasr.com mnassri et al.: robust feature extraction method for real-time speech recognition system on … bare-board active current consumption of 400ma and the hbridge motor requires approximately +6v of minimum power supply for operation. the voice acquisition command is done using a microphone (6) with an external usb sound-card (5). iv. tests and results to prove the performance of our proposed speech recognition algorithm based on mf-dwt/mfcc, we compared it through the use of several types of features such as mfcc, dwt/mfcc and mf-mfcc based on the two multiclass approaches, oaa and oao the recognition experiments were performed using noisy testing data with different various noisy conditions: white gaussian and babble noise, with a noise ratio (snr) ranging from -10db to 10db. a comparatives study between feature extraction (mfcc, mfmcc, dwt-mfcc and mfdwt-mfcc) methods in babble and white noise states under different snrs is summarized in tables iv and v. this comparison is obtained according to the classification rate based on the oao and oaa approaches. it can be observed that the performance of mfcc, mfmcc and dwt-mfcc methods degrades considerably in the presence of noise for snrs less than 0db. on the contrary, our proposed method based on mfdwt-mfcc gives good results even for snrs lower than 0db. it can increase the classification rate up to 23% in comparison with dwt-mfcc and more than 50% compared to mfmfcc for white noise with a snr of -5db. the proposed feature extraction gives the best results for the two multi-class svm based methods (oao, oaa). these results justify the importance of the use of the denoising module with median filter in wavelet domain which provides a significant improvement in recognition accuracy, especially in lower snrs. we can conclude that the proposed feature extraction based on mfdwt-mfcc performs better than the other ones all test conditions, with noisy and clean testing data. therefore, we can obtain a perfect and encouraged reconnaissance rate with the mfdwt-mfcc for a real-time voice command system. table iv. classification accuracy in babble noise for feature extraction methods using oaa and oao approches classification rate (%) oaa oao snr (db) features -10 -5 0 5 10 -10 -5 0 5 10 mfcc 10.9 30.90 59.09 68.13 76.36 27.27 34.54 54.54 74.54 87.27 dwt-mfcc 61.81 78.18 85.45 90 93.63 60 83.63 94.54 97.27 100 mfmfcc 10.9 37.27 68.13 70.90 85.45 33.63 41.81 60 75.45 87.27 mfdwt-mfcc 65.45 80.09 97.27 100 100 80.09 88.18 97.27 99.09 100 table v. classification accuracy in white noise for feature extraction method using oaa and oao approches classification rate (%) oaa oao snr (db) features -10 -5 0 5 10 -10 -5 0 5 10 mfcc 10.09 27.27 43.63 90.90 90.90 10,09 30 54 83.63 90.90 dwt-mfcc 69 70.90 85.45 98.18 100 69 92.72 97.27 100 100 mfmfcc 27.27 43.63 69.09 92.72 94.54 27.27 41.81 69.09 92.72 94.54 mfdwt-mfcc 80 94.54 98.18 100 100 80 96.36 100 100 100 in table vi, the results of our tests regarding cpu usage, memory performance, and execution time required to run the proposed real-time speech recognition system, are summarized. to validate performances, our choice was htop which is an interactive process for linux and a very reliable monitoring tool for performance metrics. the results show the average usage of our raspberry pi cpu which is 10.8% when tested with the proposed algorithm. when using mfcc, dwtmfcc and mfmfcc, the cpu usage is at 9.1%, 9.5% and 10.3% respectively. also, the recorded maximum execution time does not exceed 15ms when compared with the other algorithms. according to these low differences in resource consumption and execution time, we conclude that they will have no effect on our algorithm quality in real-time usage. table vi. resourse consumption and execution time comparison algorithm memory consumption (byte) memory usage (%) cpu usage (%) running time (ms) mfcc 8325 9,1 5,9 645 dwt/mfcc 8376 9,1 5,9 650 mf-mfcc 8450 10,3 6,2 652 mfdwt/mfcc 8499 10,8 6,2 660 v. conclusion in this paper, a new robust feature extraction system for real-time speech recognition has been presented. this technique is based on a hybridization between dwt and mfcc. the proposed system proves its reliability by having 100% recognition rate when tested in clean environment. the recognition rate ranges from 80% to 100% in noisy environments from -10 db to 10db. regarding the real-time problem the performances of the proposed methodology were evaluated by implementing a voice command application 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helali et al.: real time speech recognition based on pwp thresholding and mfcc using svm real time speech recognition based on pwp thresholding and mfcc using svm wafa helali faculty of sciences of tunis university tunis el-manar tunis, tunisia zied hajaiej faculty of sciences of tunis university tunis el-manar, tunis, tunisia adnen cherif faculty of sciences of tunis university tunis el-manar tunis, tunisia abstract−the real-time performance of automatic speech recognition (asr) is a big challenge and needs high computing capability and exhaustive memory consumption. getting a robust performance against inevitable various difficult situations such as speaker variations, accents, and noise is a tedious task. it’s crucial to expand new and efficient approaches for speech signal extraction features and pre-processing. in order to fix the high dependency issue related to processing succeeding steps in ars and enhance the extracted features’ quality, noise robustness can be solved within the ars extraction block feature, removing implicitly the need for further additional specific compensation parameters or data collection. this paper proposes a new robust acoustic extraction approach development based on a hybrid technique consisting of perceptual wavelet packet (pwp) and mel frequency cepstral coefficients (mfccs). the proposed system was implemented on a rasberry pi board and its performance was checked in a clean environment, reaching 99% average accuracy. the recognition rate was improved (from 80% to 99%) for the majority of signal-to-noise ratios (snrs) under real noisy conditions for positive snrs and considerably improved results especially for negative snrs. keywords-automatic speech recognition; perceptual wavelet packet transform; mel frequency cestrum coefficients; svm; raspberry pi 3 i. introduction speech recognition technology is a widespread dynamic research area. automatic speech recognition (asr) has been vastly used in many human–machine interaction applications, such as electronics [1], mobile robots [2-4], car audio systems [5], manipulators in industrial assembly lines [6], and security systems [7]. nonetheless, robust performance constitutes obviously a real concern for any real-time application due to various difficult conditions such as noisy background, accents, and speaker variations. as a result, the need for accuracy, high performance and fast embedded asr are growing continuously. many projects have been invested in asr techniques in order to achieve proficient embedded systems that are able to imitate human behavior at all levels. the asr accuracy obtained in laboratory environments is quite high, but once the recognition system is placed in a real background, the recognition rate gets roughly low. several embedded voice recognition systems have been reported and some of them are implemented in field programmable gate arrays (fpgas) [810] or in digital signal processors (dsps) [11, 12], all of them with a modest accuracy rate. asr state-of-the-art systems are linking the performance to reasonable and controlled training conditions. considering the noise impact, the system accuracy may become unacceptably low in some sensitive environments. several researchers have shown their interests on speech feature extraction methods such as linear prediction coefficients (lpc) [13], perceptual linear predictive (plp) [14] and linear predictive cepstral coefficients (lpcc) which are used due to their effectiveness and simplicity in speech/speaker recognition [15-16]. mel frequency cepstral coefficients (mfccs) constitute feature parameters that present widely popular acoustic features mostly used in speech recognition [17]. in spite of its good performance achieved in clean background, the mfccs feature extraction for speech recognition has been used to enhance speech recognition system performance in noisy environments. the most cited methods are the cepstral mean subtraction (cms) [18], the power-normalized cepstral coefficients (pnccs) [19], and the cepstral mean normalization (cmn) [20] which is a popular feature compensation method dealing with convolutional noise. in this same context, the majority of the published works demonstrated that the wavelet-based feature extraction [21-24] has better performance improvement than traditional cepstral features in noisy environments. the already presented wavelet-based techniques rely on the multiresolution pwp properties and combine the extracted mfcc features from various frequency sub bands to a unique feature vector. in this paper, a new method for real-time speech recognition is proposed under both clean and noisy corresponding author: wafa helali (wafa.helali@yahoo.fr) engineering, technology & applied science research vol. 10, no. 5, 2020, 6204-6208 6205 www.etasr.com helali et al.: real time speech recognition based on pwp thresholding and mfcc using svm environments, and it is presented and implemented on a raspberry pi3 board. the proposed method is based on mfcc extraction from speech signal after applying wavelet thresholding. the main idea relies on obtaining coefficient exploitation which represents the wavelet transform decomposition after eliminating the small coefficients associated with the noise usually located in high frequencies. then, the mfccs method is applied to the signal. finally, a feature vector is acquired by the obtained mfcc concatenation that constitutes one input parameters of the svm used for classification. our main contribution resides in ensuring a good recognition rate, close to 100%, for positive snrs. in real noisy areas, particularly within the range of [0, -10db], challenging results have been reached using the proposed real time approach. obviously, real time implementation with raspberry pi gives excellent recognition performance in clean and noisy states. ii. feature extraction feature extraction is the process of retaining useful information within a speech signal when rejecting the redundant and unwanted information. it represents merely the speech signal parameterization. this process includes: • segmentation of the speech signal into windows. • speech signal frequency decomposition into critical bands by transforming it into pwp. • parameter extraction. • coefficient calculation. the feature extraction is mostly used, thanks to its better performance for asr and low computational complexity under standard environment. mfcc and its hybrid feature extraction technique with pwp will be employed. a brief outline of the proposed method is described in figure 1. inverse cosine transform idft speech signal • pre-emphasis • elimination of cc • hamming windows dft pwp coefficient s pwtfcc log (.) threshold coefficients 2 fig. 1. pwtfcc algorithm. a. mel frequency cepstral coefficients meaning mfccs are frequency field features based on the human ear scale. the scale [25] is approximately linear until 1khz and logarithmic at higher frequencies. these frequency domain features [26] offer more accuracy than time domain ones. in this technique, the same information can be incorporated in less coefficients, making it more compact. the calculation proceeds as described in our previous work [27]. afterwards, fft is computed for each speech frame so that signal frequency components could be extracted in time-domain. then, the logarithmic mel scaled filter bank is applied to the fft frame. the log filter bank energies are calculated using the dct. only the first thirteen dct coefficients are kept and the rest are discarded. these dct coefficients decorrelate the features as well they arrange them in decreasing information order. b. perceptual wavelet packet the wavelets offer a technique that represents the timefrequency domain. it has usually been used for signal decomposition into high and low frequency components. its coefficients depict frequency content similarity measured between a chosen wavelet function and a given signal. these coefficients are calculated as a convolution of the signal and the scaled wavelet function, which can be explained as an expanded band-pass filter due to its band-pass spectrum [2728]. subsequently, the resulted wavelet transforms are exploited as a filter bank named perceptual wavelet packet (pwp). the pwp results to a non-redundant restoration, which gives better spectral and spatial localization of signal configuration. compared with other multi-scale representations such as gaussian and laplacian pyramid the pwp represents the privilege of multilevel decomposition, where the signal is decomposed in ‘approximation’ and ‘detail’ coefficients at each level [29], through an equivalent process to high-pass and low pass filtering components. as mentioned above, the wavelet transform was introduced for time and frequency analysis of transient signals and it was extended to multiresolution wavelet transform theory via a finite impulse response (fir) filter approximation. the discrete wavelets used in multi-resolution analysis constitute an orthonormal basis. the pwp decomposition steps are explicated taking into account details and approximation coefficients. iii. real time implementation slant the proposed speech recognition system’s block diagram is illustrated in figure 2. the various system steps are explained in this section. the microphone input speech is sampled at 16khz. first of all, we mention that a voice activity detector (vad) is used as a noise estimator. the vad’s output presents the binary signal resulting of the comparison between the speech input signal and the threshold value. thus, vad value is either true (vad=1) when the measured input is greater than the threshold and the signal is considered as a voiced frame, or the vad value is false (vad=0) and the signal frame is considered as a noisy frame. the second approach step consists on speech signal decomposition with the pwp. the pwp outcome is a multilevel decomposition, in which the signal is divided into ‘approximation’ and ‘detail’ coefficients at every stage. this process is similar to low-pass and high pass filtering. the simplest way to remove noise is by using the wavelet coefficients, which are the result of the wavelet transform decomposition. the small coefficients associated with the noise through the threshold step are eliminated. indeed, the threshold purpose offers the ideal components from the noisy signal giving the noise level estimation. there are various threshold methods. between the most commonly used are the hard and soft threshold. they are used and adopted in this work and modeled by: engineering, technology & applied science research vol. 10, no. 5, 2020, 6204-6208 6206 www.etasr.com helali et al.: real time speech recognition based on pwp thresholding and mfcc using svm ( )( )y sign x x λ= − (1) where x, y and � present respectively the input signal, the threshold signal, and the threshold value. the mfccs are applied to the signal after the threshold and concatenation steps. the signal is filtered and windowed by the hamming window for fft transformation. next, the signal passes through a mel-filter to obtain the twelve cepstral coefficients. finally, the resulted cepstral coefficients are concatenated to construct the svm classifier input. similarly, this technique is applied also to our proper training speech database containing spoken words which are recorded by a mono-speaker. vad approximation coefficients cd pwp thresholding concatenation mfcc svm classifier decision future extraction trainin model training set « .wav » approximation coefficients ca thresholding speech fig. 2. the pwp decomposition steps of a 1d signal for three levels. in order to increase the performance of our proposed speech recognition algorithm, a denoising module was added to the proposed system to enhance its robustness. this denoising module relies on adaptive median filtering (amf) [30] which is able to eliminate the data speckle noise without harming the embedded sharp contrasts. it’s noticeable that the noise impact can be significantly reduced by applying the amf to the temporal modulation spectrum, which is the fourier transform for either real or imaginary acoustic spectrograms along the time axis. thus, the resulting speech features can be more noise-robust and give better speech recognition performance. figure 3 represents the modified speech recognition system in which the amf is introduced as a speech denoising module. learning phase learning (words, phonomenon) acoustic vector extraction calculation of models (words, phonomenon) learning base speech acquisition acoustic vector extraction decoding recognition recognized word fig. 3. the modified speech recognition system. iv. test performing and obtained results in order to build the speech recognition system, voice commands and speech models have to be optimized based on a solid training database. in this experiment, the training database contained eleven commands recorded five times by a monospeaker for a voice command under a silent environment. each recorded data consisted of up to 4s of utterance. the speech recognition application needs more than just the simulation and the proposed algorithm was tested on a particularly suitable flexible platform. the complete setup has been implemented and tested on a raspberry pi 3 board. a. used raspberry pi card synopsis and system pattern the raspberry pi 3 is simply a performed sized card processor [31], containing a micro-controller and a cpu. the raspberry pi processor core system is a broadcom bcm2837 system-on-chip (soc) multimedia processor, which has 64-bit quad-core armv8 cortex a53 with 1gb of ram. besides, it’s equipped with 16gb expandable to 128gb. an sd card slot ,1.2ghz soc processor, video core iv gpu, 4 usb ports, 1 hdmi port, 40 gpio pins which could be configured as digital output or input and a jack audio output. the raspberry pi is controlled by an amended version of linux (raspbian) optimized for the arm architecture. as raspbian is built based on debian, it implicitly has all the compatibilities and features required for the program. python 2.7 or 3.5 is already installed in the raspbian operating system and therefore a new installation is not compulsory. python 2.7 was selected because it owns more store community support accessible contrary to python 3.5. the project requires some external python packages that need to be separately installed. we have also installed some other measurement packages in order to evaluate the program performance. all specifications are mentioned in table i. table i. raspberry pi’s software specification for the proposed framework [30] name configuration os noobs (rasbian) programming language python 2.7 libraries numpy, scipy, pylab, matplotlib, rpi.gpio audio libraries pyaudio, pydub, wave performance monitoring utilities bcmstat, time, htop b. real-time performance in order to validate the proposed speech recognition, based on mf-pwp/mfcc, algorithm’s performance, a comparison was made of the improvements in speech recognition accuracy that can be obtained through the use of several types of features such as mfcc, pwp/mfcc and mf-mfcc. the recognition experiments were performed using noisy testing data with various noisy conditions: white gaussian and babble noise, with a noise ratio (snr) from -10db to +10db. figure 4 compares the results for speech in white (figure4(a)) and babble noise (figure 4(b)) under different snrs for several methods. specifically, the recognition accuracy percent was compared for pwp/mfcc and mf-pwp/mfcc methods as described above, along with baseline mfcc and mf-mfcc. it engineering, technology & applied science research vol. 10, no. 5, 2020, 6204-6208 6207 www.etasr.com helali et al.: real time speech recognition based on pwp thresholding and mfcc using svm can be seen that the pwp/mfcc processing provides better accuracy than mfcc features for all the tested noises, although improvements are small in high snrs. the lack of improvement observed for clean speech and high snrs is a common observation for many approaches to robust speech recognition. it is also noted that the denoising module provides a trivial improvement in recognition accuracy expressly in lower snrs. (a) (b) fig. 4. comparison of recognition accuracy in: (a) white noise and (b) babble noise for several feature extraction methods. finally, it can be observed that the proposed features based on mf-pwp/mfcc perform better than other features under all test conditions. with clean and noisy data testing, we can obtain a great and expectant recognition rate with the mf pwp/mfcc for real-time speech recognition system. aiming to validate the proposed speech recognition algorithm performance with several feature extractions we have measured the memory use, the cpu use, and the execution time. table ii presents the cpu and memory use. this verification is obtained using htop, a popular linux text mode utility, which is ideal for monitoring system processes and performance metrics. table ii. comparison of resource consumption and execution time for different feature extraction methods algorithm memory consumption (bytes) cpu usage (%) memory usage (%) extraction time (ms) mfcc 8460 9.2 5.8 670 pwp/mfcc 8486 9.2 5.8 675 mf-mfcc 8500 10.6 6.4 678 mf-pwp/mfcc 8580 10.9 6.4 680 table ii shows that the average cpu usage is 10.9% in mf pwp/mfcc. on the other hand, in mfcc, pwp/mfcc and mf-mfcc, it is around 9.2%, 10.6% and 10.9% respectively. in addition, the maximum time execution difference of the proposed algorithm to the other algorithms doesn’t exceed 15ms. it was noticed that this low difference in time execution and resources consumption did not affect the proposed algorithm’s robustness. c. recognition rate comparison the negative recognition rate part was given much attention and it represents the main contribution of this study. the comparison with the work in [30]is shown in table iii: table iii. recognition rate result comparison in babble noise snr (db) mfcc mfcc [30] pwpmfcc pwpmfcc [30] mfmfcc mfmfcc [30] mfpwpmfcc mfpwpmfcc [30] -10 19 10.9 64 61.81 38 10.09 80 65.45 -5 38 30.9 84 78.18 40 37.27 91 80.09 0 59 59.09 98 85.45 60 68.15 99 97.27 5 87 68.15 100 90 77 70.9 100 100 10 90 76.36 100 93.65 84 85.45 100 100 generally, the published works do not take into account the range [0,-10db]. recognized words in this noisy area are very hard to extract. although, the recognition rate within the range [0, 10db] reaches nearly 100% which is also the current case. v. conclusion a new real-time speech recognition algorithm has been proposed in this paper. the proposed algorithm exploits the pwp combined with mfcc in order to match speech features in addition to the svm classification block. the proposed method proves its effectiveness to pick up an ideal recognition rate of about 100% in clean environment. the recognition rate ranges from 98.18% to 100%, even in noisy environments from 0db to10db with the use of adaptive median filter as a denoising module. in the real noisy part, principally inside the range [0, -10db], good results have been reached with the proposed real time method. for real-time experimentation a raspberry pi has been used as the hardware platform. the proposed system’s performance was sufficient for a wide range of speech-controlled applications. as future work, resource consumption and its impact of speech embedded applications in addition to accuracy and timing will be investigated. references [1] d. karaboga and e. kaya, “adaptive network based fuzzy inference system (anfis) training approaches: a comprehensive survey,” artificial intelligence review, vol. 52, no. 4, pp. 2263–2293, dec. 2019, doi: 10.1007/s10462-017-9610-2. 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[31] s. n. truong, “a low-cost artificial neural network model for raspberry pi,” engineering, technology & applied science research, vol. 10, no. 2, pp. 5466–5469, apr. 2020. microsoft word 39-3825_s_etasr_v10_n5_pp6380-6385 engineering, technology & applied science research vol. 10, no. 5, 2020, 6380-6385 6380 www.etasr.com hussain et al.: design and analysis of news category predictor design and analysis of news category predictor arif hussain department of electrical engineering sukkur iba university sukkur, pakistan arif.hussain@iba-suk.edu.pk gulsher ali department of electrical engineering sukkur iba university sukkur, pakistan gulsher@iba-suk.edu.pk faheem akhtar department of computer science sukkur iba university sukkur, pakistan fahim.akhtar@iba-suk.edu.pk zahid hussain khand department of computer science sukkur iba university sukkur, pakistan zahid@iba-suk.edu.pk asif ali department of computer science sukkur iba university sukkur, pakistan asifali@iba-suk.edu.pk abstract−recent technological advancements have changed significantly the way news is produced, consumed, and disseminated. frequent and on-spot news reporting has been enabled, which smartphones can access anywhere and anytime. news categorization or classification can significantly help in its proper and timely dissemination. this study evaluates and compares news category predictors' performance based on four supervised machine learning models. we choose a standard dataset of british broadcasting corporation (bbc) news consisting of five categories: business, sports, technology, politics, and entertainment. four multi-class news category predictors have been developed and trained on the same dataset: naïve bayes, random forest, k-nearest neighbors (knn), and support vector machine (svm). each category predictor's performance was evaluated by analyzing the confusion matrix and quantifying the test dataset's precision, recall, and overall accuracy. in the end, the performance of all category predictors was studied and compared. the results show that all category predictors have achieved satisfactory accuracy grades. however, the svm model performed better than the four supervised learning models, categorizing news articles with 98.3% accuracy. in contrast, the lowest accuracy was obtained by the knn model. however, the knn model's performance can be enhanced by investigating the optimal number of neighbors (k) value. keywords-category predictor; naïve bayes; random forest; knn; svm; accuracy i. introduction technology has a significant impact on society and has significantly changed the way people access information. news is a well-known and standard service. recent technological advancements have considerably changed the way news is produced, consumed, and disseminated. it has enabled more frequent and on-spot news reporting that smartphones can access anywhere and anytime. therefore, people now expect to receive news of their interest in real-time. the news sources are already flooded with colossal information. therefore, it is essential to automatically classify the news in specific categories based on the information content to allow timely and efficient information dissemination. automatic document classification (atc) can be used to efficiently manage textbased information (i.e. news) [1-3]. it allows timely and efficient information retrieval in the search phase. atc can assign a relevant category to a news from a predefined set of reference categories based on the text feature extraction by correctly understanding the meaning and context of words. the time required to categorize the news correctly is directly proportional to the quantity of the text. in the newspaper’s archive, the comprehensive range of articles varies from business to technology, so it is inconceivable that humans could manage this abundant content of information in a reasonable time frame. manual document classification is cumbersome and resource-exhaustive. the news category predictor aims to recognize and categorize different articles based on content/information type. the automatic news classification plays a vital role in processing a massive amount of articles. it can classify and label the news articles by analyzing the content (i.e. extracting feature values) to quickly access where they are focused in, allowing efficient and speedy news dissemination. additionally, news websites can also increase their visibility by developing a recommendation system that suggests/ recommends relevant news to attract more attention. several corresponding author: faheem akhtar engineering, technology & applied science research vol. 10, no. 5, 2020, 6380-6385 6381 www.etasr.com hussain et al.: design and analysis of news category predictor studies have been carried out to study modeling and performance evaluation of news category predictors using machine learning (ml) algorithms over different datasets (which differ in languages and range of categories) [4-10]. in these studies, well-known machine algorithms, such as naïve bayes (nb), svm, random forest (rf), etc. are used to model news category predictors. the findings/results show that the category predictor's performance can vary with the machine algorithm deployed and the dataset used to train the model. in contrast, ml is envisioned to solve problems in various related domains [11, 12]. for a given ml algorithm, prediction performance can vary significantly depending upon the dataset. to quote a few, the nb algorithm's precision in categorizing news articles is reported to be 0.92 in [3] and 0.88 in [5]. in these cases, different datasets were used to train the same ml model, and the prediction performance is different. in the past few years, much research is carried out using different ml algorithms in natural language processing (i.e. text/news classification [13-17]). however, the current review paper is focused on evaluating and comparing category predictors' performance based on well-known ml algorithms. a standard bbc dataset was chosen having news of five categories: business, sports, technology, politics, and entertainment. this is a balanced dataset and quite different from traditional datasets that usually contain biases. the main contribution of this research is that and it is the first time a multi-class news category predictor was developed by training four well-known machine learning algorithms (i.e. nb, rf, knn, and svm) on the same dataset. each category predictor's performance was evaluated by analyzing the confusion matrix and quantifying the test dataset's precision, recall, and overall accuracy. finally, the performance of all category predictors was studied and compared. ii. methodology and dataset the ultimate aim of this study is to classify the news into specific categories and analyze the performance of the category predictor. initially, data are collected and preprocessed, then the content of text document (dj) is converted into useful features (w1j... wkj) by feature extraction algorithms such as unigrams. the extracted features are transformed into numeric data that act as inputs for machine learning algorithms or classifiers (nb and rf). finally, the ml models are trained on these transformed features, and the performance is evaluated on the test dataset. the research methodology/work flowchart is given in figure . a. dataset in this study, a bbc-originated news data set was used, which is obtained from kaggle. it consists of 1490 documents from the bbc news website corresponding to stories in five typical areas: business, sports, technology, politics, and entertainment. the dataset is almost balanced: it contains an approximately equal portion of each class (figure 2). however, most samples (23.2%) belong to the sports category, whereas the tech category has the least. the distribution of classes plays an important role in classification, and balanced datasets result in better learning models. in this study, the dataset is broken into 1,192 (80%) records for training and 298 (20%) testing. fig. 1. workflow. fig. 2. class distribution in the dataset. b. text cleaning/preprocessing text preprocessing or cleaning is a preliminary and crucial step of news classification, which reduces the required space and makes the classification more efficient [18]. most of the times, the dataset is unstructured in combinations of useful and useless data. unnecessary information such as stop words, punctuations, special characters, irrelevant sentences, quotations, and dates do not add any predictive power to the classifier/model. they only consume space and can distort the ml model. therefore, before extracting any feature from the raw dataset, a cleaning process should be performed to minimize the distortions introduced to the model. in this paper, several steps have been followed to preprocess the news text. 1) transforming text engineering, technology & applied science research vol. 10, no. 5, 2020, 6380-6385 6382 www.etasr.com hussain et al.: design and analysis of news category predictor transforming text in the same letter size (i.e. lower case) to eliminate homologous words that are different only in their case. for instance, the words “fruit” and “fruit” are the very same in a real sense and should not be considered separately for prediction. 2) removing punctuations and special characters characters such as ?, !, ; and . are disposed of, this process simplifies computations in the next steps. any special character and unnecessary whitespaces are also removed because they don't contribute to prediction power. 3) filtering stop words this technique is mainly used to remove unnecessary words or words with no specific meaning, such as “the”, “an”, “a”, “what”, etc. so that classifier cannot co-relate stop words and important class features. furthermore, the most frequent or rarely used words do not contribute to the predictive power model. therefore, they must be removed from the training set. in this study, we have downloaded a list of english stop words from the nltk library and then removed them from the dataset. iii. feature enigineering/text representation the ml decision models (classifiers or regression algorithms) can only process and learn from numerical feature vectors. therefore, the text features must be converted to a numeric representation [19, 20]. feature engineering is a process to transform data (in this case, text) into numeric features that can act as inputs for ml algorithms. it involves two steps: feature extraction to extract the unique features/patterns and feature representation to represent each feature numerically. bag of words (bow) and n-grams are commonly used techniques to create text features [21, 22]. bow is the simplest feature extraction technique. it simply breaks apart the words in a document into individual word count statistics such as each word count/occurrence is used as a feature, but without considering the order. in contrast, n-grams is simply a sequence of n tokens (words) in the text. it not only finds the frequency of a word in the document but also considers the order and relationship between words. the ngrams can be unigram (n=1), bigram (n=2), or trigram (n=3) depending upon the number of tokens taken into consideration. these extracted features values can be represented by different techniques such as binary representation (br), term frequency (tf), term frequency inverse document frequency (tf-idf), and normalized tf-idf [23, 24]. in this study, the tf-idf feature representation technique is used. tf-idf technique disposes of the most common words and extracts only the most important feature words from the text [25]. the tf-idf algorithm works on the principle that if a word (wk) is more frequent in one document (j) and appears less frequently in a specific corpus, then it has a stronger ability to distinguish the category of texts, and it should be given more weight. the tf-idf can be estimated by: ��� = ���� × �� ��� (1) where ��� is the weight of the word k in the document j, n represent the total number of documents, ���� is the frequency of the word k in the document j and ���� represents the number of documents containing the word (k). iv. class representation/encoding news category prediction is multi-class classification. for instance, the dataset used in this study corresponds to five classes: business, sports, technology, politics, and entertainment. each class is labeled to make it more understandable and often labeled in words. for ml models, label encoding is used to transform labels into numeric values. it can be done by a label encoder, which converts class labels into values between 0 and n-1, where n is the number of unique class labels. the actual and encoded labels of the dataset used in this study are given in table i. table i. class representation encoding labels encoded business 0 entertainment 1 politics 2 sports 3 tech 4 v. machine learning algorithms/classifiers a classifier is a ml model that maps input data to a proper category. in this study, nb, rf, knn, and svm algorithms are used to train a model that can classify news articles into categories. a. naïve bayes nb is a probabilistic classification algorithm based on bayes’ theorem. it is simple, yet quite useful in a model, especially in text classification. the probability of any specific event is estimated by calculating its frequency in the past [26]. the fundamental nb assumption is that each feature is independent and unrelated to any other class feature. the bayes theorem is: � �� | � ) = � �� | � )∗� � � ) � � � ) (2) � �� | � ) is the probability of occurrence of c given that event f has already occurred. the event f is termed as evidence, p(c) is the prior probability of the class, � �� | �) is termed as the likelihood and � �� | � ) is the posterior probability. in text classification, features can be numerous such as � � �1, �2 , �3 , �4 … … . . �! ) so by substituting f and expanding using the chain rule we get: � �� | �" , �# !, … . . �! ) = � ��$ | � )∗ � ��% | � )∗ ….� ��& | � )∗ � � � ) � � �$ )∗ � � �% )∗… � � �& ) (3) thus, we can find the category by finding the class with maximum probability. b. random forest random forest (rf) is a machine learning algorithm based on a set of trees classifiers [27]. the rf is an ensemble method used for classification that constructs several decision trees at training time and makes a final decision on majority voting. it uses bootstrap sampling in which data samples are sampled engineering, technology & applied science research vol. 10, no. 5, 2020, 6380-6385 6383 www.etasr.com hussain et al.: design and analysis of news category predictor independently and with the same distribution for all trees in the forest [26]. c. k-nearest neighbors knn is an intuitive supervised learning algorithm and an easy method to implement. it is used to classify objects based on their nearest examples in training sets space. the procedure to identify an object is classified by the majority vote of its neighbors like an object is assigned to a common class among its closest neighbors. the new vector classification is found by classes of its k-nearest neighbors where k is a positive integer. this algorithm is implemented using euclidean distance metrics to detect the nearest neighbor [29-31]. the main challenge in knn is to determine the optimal value of k. a higher value of k will increase the rise of over-learning so, it is necessary to take a valid value of k that reduces over-learning. the euclidean distance metric d(x, y) between two points is computed as: � �', () = ∑ *�'+ #) − �(+ #) +-" (4) where n is the number of features like ' = { '" , '# , '/ , … … , ' } and ( = { (" , (# , (/ , … … , ( } . the number of kneighbors used to test a new vector varies from 1 to 10. d. support vector machine the svm is a kernel-based ml algorithm that can categorize input data input into specific classes or categories. svm constructs a classifier that makes the decision boundary for every class and defines the hyper-plane to linearly or nonlinearly separate them. the accuracy of categorization can be increased by increasing the hyper-plane margin that also enlarges the distance among classes. hence, the farthest hyperplane provides more immunity against noise. svm is a kernelbased classifier that defines the process of mapping the training data set to develop its similarities to a linearly independent data set. the main reason to use mapping is to enhance the depth of the data set done by kernel function like some commonly used kernel are linear, rbf, and quadratic, etc. [32,33]. vi. perfomance evaluation metrics to precisely gauge the performance of the category predictor, there are different performance evaluation techniques and metrics such as confusion matrix, accuracy, precision, recall or sensitivity, and f1-score. in this study, the confusion matrix is evaluated first, and accuracy, precision, and recall are analyzed to get a true insight of the prediction performance. the confusion matrix is a table that is often used to quantify the performance of a category predictor or classification model on a set of test data for which the true/actual values are unknown. the confusion matrix summarizes the prediction performance by quantifying the correct and incorrect predictions (misclassification) broken down into each class. it gives a detailed insight into ways in which category predictor is confused while classifying the input data. therefore, a confusion matrix is a good option for evaluating the performance of the multi-class category predictor. vii. results and discussion the performance results of multi-class category predictors based on different supervised learning models are evaluated and compared in this section. this study's learning models are nb, rf, knn, and svm. the evaluation was done by observing each category predictor's prediction results by analyzing the confusion matrix and quantifying precision, recall, and overall accuracy. this analysis was made on a test dataset consisting of 298 news samples. the confusion matrices of each category predictor are given in figure 3. figure 3 shows the confusion matrix of nb (a), rf (b), knn (c), and svm (d). in general, every category predictor has achieved good accuracy. svm based category predictor achieved the highest accuracy for the given dataset. the svm based category predictor predicts the news category with an accuracy of 98.3%, and this can be verified from figure 3(d), as it shows only five wrong predictions out of 298 samples. the nb model's performance was observed to be as good as svm’s with an accuracy of 97.3%. in the nb model, the most misclassified category was technology with four incorrect predictions, while the most accurately classified category was sports having no wrong predictions. the detailed category/class wise analysis of precision and recall for svm and nb is given in table ii and table iii, respectively. table ii. performance evalution of category predictor using svm category precision recall business 0.98 0.98 entertainment 0.97 0.98 politics 0.98 0.98 sports 1.00 1.00 tech 0.98 0.96 table iii. performance evalution of category predictor using naïve bayes category precision recall business 0.97 0.98 entertainment 0.97 0.97 politics 0.96 0.98 sports 1.00 1.00 tech 0.96 0.92 if we analyze the category predictor model based on rf algorithm, the prediction performance is satisfactory. however, there more incorrect predictions as compared to svm and nb. the most misclassified category was business with seven inaccurate predictions, while the most accurately classified category was sports. rf model achieved an accuracy of 94.9%, with 283 correct predictions out of 298 test samples. the detailed category/class wise analysis of precision and recall for the nb model is given in table iv. knn based category predictor achieved the lowest accuracy. it achieved an accuracy of 94.2% with 17 wrong predictions, as shown in figure 3(c). the detailed category/class wise analysis of precision and recall for the knn model is given in table v. although knn has achieved the lowest accuracy grades as compared to svm, nb, and rf, its performance is still consideredsatisfactory. engineering, technology & applied science research vol. 10, no. 5, 2020, 6380-6385 6384 www.etasr.com hussain et al.: design and analysis of news category predictor (a) (b) (c) (d) fig. 3. confusion matrices of multi-class category predictors: (a) nb, (b) rf, (c) knn, (d) svm. table iv. performance evalution of category predictor using random forest category precision recall business 0.93 0.89 entertainment 0.94 0.97 politics 0.92 0.91 sports 0.94 0.98 tech 0.92 0.91 table v. performance evalution of category predictor using knn category precision recall business 0.92 0.89 entertainment 0.95 0.92 politics 0.91 0.94 sports 0.96 0.98 tech 0.91 0.94 viii. conclusion and future work this paper presents a comparative analysis of the multiclass category predictor's prediction performance. news category predictors were developed by deploying/training wellknown machine learning algorithms (naïve bayes, random forest, k-nearest neighbor, and support vector machine) on a bbc news dataset having five categories (business, sports, technology, politics, and entertainment). later, using performance evaluation metrics, we analyzed the confusion matrix and quantified the test dataset's precision, recall, and overall accuracy. as a result, the svm model was proven to be the best among the four supervised learning models in correctly categorizing news articles with 98.3% accuracy. the lowest accuracy was obtained by the knn model with k=5. however, the knn model's performance can be enhanced by investigating the value of the optimal number of neighbors k. as future work, deep learning schemes will be introduced to further improve the classifier 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[33] j.-y. jiang, r.-j. liou, and s.-j. lee, “a fuzzy self-constructing feature clustering algorithm for text classification,” ieee transactions on knowledge and data engineering, vol. 23, no. 3, pp. 335–349, mar. 2011, doi: 10.1109/tkde.2010.122. microsoft word etasr_v11_n2_pp7041-7046 engineering, technology & applied science research vol. 11, no. 2, 2021, 7041-7046 7041 www.etasr.com eloget et al.: the effect of sisal juice extract admixture on compressive and flexural strength of … the effect of sisal juice extract admixture on compressive and flexural strength of cement concrete michael o. eloget smartec, jomo kenyatta university of agriculture and technology nairobi, kenya miklate2@gmail.com silvester o. abuodha department of civil engineering university of nairobi nairobi, kenya sochieng@yahoo.com mathew m. o. winja department of civil engineering jomo kenyatta university of agriculture and technology nairobi, kenya mathewwinja@yahoo.com abstract-the characteristics of concrete are influenced by the ratio of water to cementitious materials (w/c) used in the mixture. an increase in paste quality will yield higher compressive and flexural strength, lower permeability, increased resistance to weathering, improve the bond between concrete and reinforcement, reduced volume change from drying and wetting, and reduced shrinkage cracking tendencies. admixtures are used to improve the properties of concrete or mortar. the current study investigates the effect of sisal juice extract (sje) as an admixture on concrete durability. sje contains unrefined minerals which can be used as organic retarders to increase the rate of strength development at an early age. a total of 84 concrete cubes were produced in 7 sets of 12 samples each. one set was the control mix which had zero sje content. the remaining sets had varying dosages of sj namely 5%, 10%, 15%, 20%, 25%, and 30%. twelve beam specimens were also cast and subjected to the three-point flexural test. to establish the effect on strength of concrete, compressive strength was tested at 7, 14, 28, and 56 days while flexural strength was tested at 28 days. the highest compressive strength was achieved at 5% dosage beyond which a decrease in strength occurred for all the higher dosages. keywords-sisal juice extract; compressive strength; flexural strength i. introduction concrete is one of the most commonly used construction materials [1]. the production of concrete is achieved by mixing predetermined proportions of cement and aggregates with water to form a plastic material which transforms to a hard strong and load bearing material when dried [2]. the hardening of concrete is attained through hydration which is an exothermic reaction between cement and water. the addition of water to concrete during mixing enables hydration to take place while the excess quantity forms a slurry with the cement which coats the aggregates in the mix, lubricating them and allowing easy movement during compaction [3]. the first stage of hydration that leads to stiffening is caused by the reaction between water and a chemical constituent of cement called tricalcium silicate (c3s) [4]. the time taken for concrete to harden after the addition of water to the cement–aggregate mix is referred to as setting time. the last stage occurs over a longer period, called final setting time, and is caused by the reaction of water with calcium silicate (c2s). it is during this stage that hardening occurs, as a result of the exothermic nature of hydration. the higher the rate of hydration is, the higher the rate of both heat generation and strength development [5-7]. the expansion and contraction of the hardened concrete are associated with the generated heat which causes stresses that lead to microscopic cracks within the concrete structure. this phenomenon causes problems when constructing large concrete structural members such as piers, dams and bridges and generally when concreting structures in hot climates [8, 9]. in order to slow both the rate of hydration and the generation of heat and strength development, admixture materials called retarders may be used as they have the effect of delaying the initial setting time of concrete thereby providing enough time for concrete operations [10, 11]. retarding admixtures reduce the rate of hydration by blocking cement from reacting with water [12-15]. this happens because the retarding admixtures are mainly based on materials having lignosulfonic acids and their salts, hydroxyl-carboxylic acids and their salts, sugars including their derivatives, inorganic salts such as borates phosphates, and zinc and lead salts. [7, 16-19]. admixtures come in various forms and are usually imported and expensive to acquire, hence cheaper admixture materials need to be established from locally available sources [20, 21]. the ability corresponding author: michael o. eloget engineering, technology & applied science research vol. 11, no. 2, 2021, 7041-7046 7042 www.etasr.com eloget et al.: the effect of sisal juice extract admixture on compressive and flexural strength of … of retarders to reduce the rate of heat generation and strength development when concreting large structural members also helps to prevent the occurrence of capillary cracks that compromise the durability of concrete structures [22]. in [23], the effects of sugar on the setting time of cement and the compressive strength of concrete were investigated. in all curing periods the compressive strength was found minimum for concrete with 0.3% sugar and maximum for concrete with 0.08% sugar. only in 0.3% sugar, the compressive strength was found less than the strength found for concrete with 0% sugar. the compressive strengths of all the other sugar percentages were found increased in comparison with plain concrete's. the authors concluded that the concrete compressive strength was maximum for 0.08% sugar in all curing periods among the sugar percentages used. authors in [24] evaluated the effect of sugar on the compressive strength of concrete. ordinary portland cement-opc (acc cement) of 43 grades was used for the cube casting. the cubes having sugar dosages of 0%, 0.06%, 0.08% by weight of cement were cast and the compressive strength of cubes for 7, 21, and 28 days were tested. it was observed that the setting time and workability of concrete increased with the increase in sugar dosage and that there was an increase in the compressive strength of about 16.02% at 28 days compared to ordinary concrete [24]. authors in [25] studied the effect of sugar on strength and durability of hvfac concrete with similar results. it was observed that the addition of sugar increased the workability and compressive strength of concrete. waste materials can be used to produce new products or can be used as admixtures so that natural resources are used more efficiently and the environment is protected from waste deposits [26]. kenya, like many other countries, grows sisal in large quantities for extraction of fiber but the remains after extraction are not fully utilized. the objective of this paper is to study the potential of utilizing sje that is generated from sisal waste as an economical admixture. statistical assessment on compressive strength, flexural strength, and setting time has been conducted in order to investigate the effectiveness of sje as an admixture. in addition, the utilization of the sisal waste will address the environmental pollution by making good use of sisal fiber waste material ii. materials and methods a. materials 1) cement opc class 53 conforming to kebs srn 103 was used in the production of the concrete for all mixes. 2) fine and coarse aggregates natural river sand obtained from local suppliers was used as fine aggregates. coarse aggregates originated from crushed stone type of nominal size of 10/20 mm. their properties can be seen in table i. 3) sisal juice the sj used for the experiment was obtained from sisal leaves harvested from a local single plantation to ensure the use of a single species. the juice was extracted by squeezing the leaves in a cleaned improvised machine that allowed collection in a container. table i. properties o f fine and coarse aggregates properties river sand coarse aggregates fineness modulus 2.70 4.82 silt content 0.5 specific gravity 2.48 2.50 water absorption (%) 2.1 3.10 4) water water conforming to the requirements for concreting and curing as per is: 456-20009 was used. b. test methods the preparation of specimens was done by measuring the required proportions of fine and coarse aggregates and cement and thereafter mixing was done in dry state before the addition of water and sj. water was mixed with different dosages of sj before addition to the concrete mix. a homogenous mix was achieved through thorough mixing of the concrete ingredients. two concrete mixes were produced. mix "a" was produced without any addition of sje while mix "b" had different dosages of sje. batched concrete mixes were prepared by replacement of 5%, 10%, 15%, 20%, 25% and 30% water with sje in six sets as shown in table ii. table ii. details of mix proportions class 25 concrete mix a (opc) mix b (opc + sj) mix set 1 2 3 4 5 6 7 dosage (%) 0 5 10 15 20 25 30 table iii. concrete specimen details no. of cubes (specimen size: (150×150×150mm) no. of beams (specimen size: (150×150×530mm) mix a 12 2 mix b 72 10 1) sisal juice ph test the ph value of the fresh sj was tested in the laboratory using the universal ph scale. sje was subjected to chemical analysis using xrf technology (x-ray florescence spectra analysis). 2) compressive strength test concrete specimens were compacted into a detachable mould with dimensions of 150×150×150mm. the specimens were demoulded after 24 hours and were immersed in water to cure. a total of 84 cubes were cast, and they were cured for 7, 14, 28, and 56 days. compressive strength tests were conducted after the respective curing days. a compression machine was used in the laboratory, in accordance with bs en 12390. 3) flexural strength test the test was carried out to determine the strength of concrete according to bs en: 12390-5: 2009. the specimens engineering, technology & applied science research vol. 11, no. 2, 2021, 7041-7046 7043 www.etasr.com eloget et al.: the effect of sisal juice extract admixture on compressive and flexural strength of … for various sj dosages were prepared and cast in moulds measuring 150×150×530mm and were cured for 28 days. a total of 12 beams were tested using the three point flexural test method. the beam specimens were placed between two supports in the universal testing machine and load was applied at the center until failure occurred. 4) setting time of cement mortar the setting time of cement mortar made with replacement of water with sj by 0%, 5%, 10%, 15%, 20%, 25% and 30% were obtained in accordance with bs en 196-3:1995. iii. results and discussion a. chemical analysis of sisal juice extract the fresh sje was subjected to a litmus test giving a ph of 5, which is acidic. the decrease in compressive strength of concrete cubes with increase in the quantity of sje was caused by the fact that the components of concrete break down during contact with acid [18]. from the results in table iv, it can be noted that the content of calcium oxide (cao) is the most predominant element at 35% followed closely by potassium oxide (k2o). these two ingredients are also found in gypsum which is a mineral used for retarding the setting of cement during manufacture. other elements found in both gypsum and sje include magnesium oxide (mgo) and sulphur (s) [27, 28]. table iv. chemical compo sition of sisal juice element percentage by weight (%) calcium oxide (cao) 35.88 potassium oxide (k2o) 32.40 magnesium oxide (mgo) 13.74 aluminum oxide (al2o3) 4.19 silicon dioxide (sio2) 4.08 iron (fe) 3.55 sulphur (s) 2.95 phosphorous pentoxide (p2o5) 1.48 chlorine (cl) 1.00 zinc (zn) 0.62 manganese (mn 0.38 titanium (ti) 0.23 strontium(sr) 0.11 b. effects of sje on compressive strength table v. effect of sisal juice on compressive strength mean strength (n/mm) percentage 0% 5% 10% 15% 20% 25% 30% days 7 17.02 20.18 16.74 15.63 11.86 12.43 9.76 14 22.10 24.87 20.85 19.55 17.29 14.97 11.92 28 25.00 26.08 21.97 22.79 20.27 18.07 17.96 56 28.90 30.47 25.03 23.38 21.21 19.53 18.69 the test results in table v indicate an increase in strength between control and cement with 5% of sj but beyond 5%, the strength decreased steadily. the steady decrease in compressive strength can be attributed to the fact that sje is acidic and an increase of sje breaks down the components of concrete during contact as shown in [18]. the results in figure 1 point out a strength gain trend with 5% dosage attracting the highest compressive strength while 30% sje gained the least strength at all ages. in figure 2, the compressive strength difference between the control mix and 5% sj dosage is 4.32%. the results show that there is a low rate of decrease in strength between 10% and 15% of sj dosage but beyond 15% to 25% sj, the rate increases. this result is in line with the results demonstrated in [23]. fig. 1. strength of concrete at different ages. fig. 2. effects of sj dosage on concrete's strength. c. flexural strength test the test was conducted in accordance with bs en 12390:2009 by using the three point load system. beams, with a size of 150×150×550mm were used (figure 3). fig. 3. three point load system. the results for flexural strength of sje concrete are plotted against various percentages of sje dosage. in figure 4, it can be seen that when sje dosage is increased, a significant increase in flexural strength is obtained. the predominant increase in flexural strength is found at 20% sje dosage. the percentage of increase in flexural strength is 18% compared to control concrete. there was a slight decrease in flexural strength at 25% and 30% dosage. engineering, technology & applied science research vol. 11, no. 2, 2021, 7041-7046 7044 www.etasr.com eloget et al.: the effect of sisal juice extract admixture on compressive and flexural strength of … table vi. flex ural strength test results fig. 4. flexural strength of concrete at different sj dosages. the outcomes demonstrated that beam flexural performance increased rapidly by the addition of sj, up to 20% and then it decreased slightly which is in line with results presented in [29]. furthermore, diagonal cracks were observed on all the beams, including the control. ultimate collapse occurred by concrete crushing within the compression zone for all the beams. fig. 5. ultimate collapse of a concrete beam. d. comparison between flexural and compressive strength table vi shows the relationship between the flexural and the compressive strength of concrete with sje. table vii. flex ural and compressive stren gth comparison at 28 days sisal dosage (%) flexural strength (n/mm 2 ) compressive strength (n/mm 2 ) 0 4.3 25.00 5 4.4 26.08 10 4.6 21.97 15 4.9 22.79 20 5.1 20.27 25 4.9 18.07 30 4.5 17.96 fig. 6. comparison between flexural and compressive strength at different sisal dosages. flexural strength must be between 10 to 20% of compressive strength depending on the type, size and volume of coarse aggregates used, see table viii. table viii. acceptable ran ge of flex ural strength sisal dosage (%) flexural strength (n/mm 2 ) compressive strength (n/mm 2 ) acceptable range of flexural strength remarks on the range of flexural strength 0 4.3 25.00 2.2 to 4.4 acceptable 5 4.4 26.08 2.6 to 5.2 acceptable 10 4.6 21.97 2.3 to 4.4 unacceptable 15 4.9 22.79 2.3 to 4.6 unacceptable 20 5.1 20.27 2.0 to 4.1 unacceptable 25 4.9 18.07 1.8 to 3.6 unacceptable 30 4.5 17.96 1.8 to 3.6 unacceptable high flexural strength is essential for stress-bearing restorations, when high pressure/stress is exerted on the material or restoration. from table viii, an increase of about 4.32% in compressive strength is witnessed and a significant improvement in flexural toughness is observed in the case of replacing water by 5% sje. the flexural strength of 4.4n/mm 2 falls within the required range of 10% to 20% of compressive strength. the appropriate sj dosage for the production of sje concrete was found to be 5%. the water replacement by sje enhanced the flexural strength compared to control mix. e. effects of sje on setting time figure 7 shows that both the initial setting time and the final setting time increased at an average of 14% and 23% respectively with increase in sj dosage. according to table ix, the initial setting time of the cement paste increased with increase in sj dosage when compared to the reference value. the final setting time also increased exponentially with increase in replacement of water by sje. this can be attributed to the adsorption of the retarding sj on the surface of cement sj dosage s/no load (n) flexural strength (n/mm 2 ) avg. 0% specimen 1 32.21 4.29 4.3 specimen 2 32.40 4.32 5% specimen 1 33.00 4.40 4.4 specimen 2 33.00 4.40 10% specimen 1 33.75 4.50 4.6 specimen 2 34.88 4.65 15% specimen 1 36.00 4.80 4.9 specimen 2 36.75 4.90 20% specimen 1 39.98 5.33 5.1 specimen 2 36.98 4.93 25% specimen 1 37.95 5.06 4.9 specimen 2 36.00 4.80 30% specimen 1 31.50 4.20 4.5 specimen 2 36.00 4.80 engineering, technology & applied science research vol. 11, no. 2, 2021, 7041-7046 7045 www.etasr.com eloget et al.: the effect of sisal juice extract admixture on compressive and flexural strength of … particles, forming a protective skin which slows down the process of hydration hence the reason why there is a steady rise of setting time. the layer of retarding admixture around the cement particles acts as a diffusion barrier. due to this diffusion barrier, it becomes difficult for the water molecules to reach the surface of the un-hydrated cement grains and hence the hydration slows down, and the dormant period (period of relatively inactivity) is lengthened and thus the paste remains plastic for a longer time. table ix. initial and final setting times of cement mortar with varying dosages of sisal juice extract sje dosage (%) initial setting time (min) percentage increase (%) final setting time (tin) percentage increase (%) 0 179 334 5 214 20 467 40 10 234 31 521 56 15 237 32 620 86 20 242 35 893 167 25 265 48 1767 429 30 372 107 1840 451 fig. 7. effects of sje on initial and final setting time. iv. conclusions the following conclusions can be drawn from the experimental study: • sje is acidic in nature and contain elements like calcium oxide (cao) and potassium oxide (k2o) which are predominant in 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[29] m. t. lakhiar, s. sohu, i. a. bhatti, n. bhatti, s. a. abbasi, and m. tarique, "flexural performance of concrete reinforced by plastic fibers," engineering, technology & applied science research, vol. 8, no. 3, pp. 3041–3043, jun. 2018, https://doi.org/10.48084/etasr.2084. microsoft word 5-dokic-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 6, 2013, 552-561 552 www.etasr.com dokic: a review on energy efficient cmos digital logic a review on energy efficient cmos digital logic branko l. dokić university of banja luka faculty of electrical engineering patre 5, 78000 banja luka bosnia and herzegovina bdokic@etfbl.net abstract— autonomy of power supply used in portable devices directly depends on energy efficiency of digital logic. this means that digital systems, beside high processing power and very complex functionality, must also have very low power consumption. power consumption depends on many factors: system architecture, technology, basic cells topology-speed, and accuracy of assigned tasks. in this paper, a review and comparison of cmos topologies techniques and operating modes is given, as cmos technology is expected to be the optimum choice in the near future. it is shown that there is a full analogy in the behavior of digital circuits in sub-threshold and strong inversion. therefore, synthesis of digital circuits is the same for both strong and weak operating modes. analysis of the influence of the technology, mos transistor threshold voltage (vt) and power supply voltage (vdd) on digital circuit power consumption and speed for both operating modes is given. it is shown that optimal power consumption (minimum power consumption for given speed) depends on optimal choice of threshold, and power supply voltage. multi vdd /vt techniques are analyzed as well. a review and analysis of alternative logical circuit's topologies – pass logic (pl), complementary pass logic (cpl), push-pull pass logic (ppl) and adiabatic logic – is also given. as shown, adiabatic logic is the optimum choice regarding energy efficiency. keywords: topology; technology; power consumption; logic delay; cmos; strong and weak inversion; static and dynamic characteristics; pass logic; adiabatic logic; pl; cpl; ppl; ecrl i. introduction designers of digital circuits are confronted with two often conflicting demands: how to achieve higher operating speeds and lower energy consumption. usually, the same circuit family could not satisfy both demands at the same time, i.e. high-speed circuits have high level of consumption and vice versa. that’s how series of integrated circuits called low-power circuits or high-speed circuits were created. optimally designed digital system includes a variety of different series of the same integrated circuits' family. today, as the whole digital system is manufactured as a single integrated circuit, the designing problem is reduced to the choice of a design that can ensure maximum energy efficiency. that implies the design with minimum power consumption inside the specified frequency range or maximum operating speed for a given energy consumption level. the usage of low-power sources of power supply, which collect their primary energy from the environment, has increased lately. thus, the art of design of low power circuits is brought down to the selection of optimal (intelligent) solutions that will reduce the speed of information processing as much as possible, without violating certain system characteristics. such an optimal project implies the decomposition of the system architecture, good choice of the circuit topology that will provide the optimal synthesis of different functions in the defined architecture, and good choice of the circuit design technology. this requires the designer to be familiar with components, circuits and systems. consumption of each system is determined using the following five guidelines of each project: given task, technology, circuit topology, operating speed and accuracy. since these five guidelines can be placed on the fingers of one hand, they are known as “low-power hand” [1]. therefore, optimization of energy consumption is a multidimensional problem that requires taking into consideration the level of consumption at each stage of the vlsi integrated circuit design. the biggest savings of electrical energy consumption (10 to 20 times), with least waste of time (at the level of a minute) is done in the early stages of designing, in which the project is presented as a set of abstract communication tasks [2]. the application of optimization techniques and consumption provides an estimation at each project stage, leading to optimal consumption project [3]. at lower levels of the design (transistor, deployment and connectivity), possible energy savings are significantly lower (10 to 20%), and time estimation can last for days, because the project is presented with all detail. thus, it is necessary to process a very large amount of data [3]. cmos digital circuits’ technology based on silicon will most likely be dominant for the next twenty years or more [4, 5, 6], with standard low power consumption, technology for reducing the transistor size to a scale of about ten nanometers and operating speed in the ghz domain. during the last ten years, more attention from researchers as well as manufacturer of integrated circuits is paid to digital cmos circuits operating in the sub-threshold (weak inversion) regime. supply voltage in this regime is lower than the threshold voltage vt of mos transistors (vdd<vt) and is about a few hundred millivolts. thanks to that fact, the dynamic consumption level is significantly reduced in regard to cmos circuits operating in the strong inversion regime. since the operating area in the sub-threshold regime is overlapped with the area of a disconnected transistors in strong inversion regime, current ratio in on and off the state has been significantly reduced. consequently, cmos circuit logic delay etasr engineering, technology & applied science research vol. 3, �o. 6, 2013, 552-561 553 www.etasr.com dokic: a review on energy efficient cmos digital logic in the sub-threshold regime is several orders of magnitude higher. designers of cmos digital devices, especially portable ones, have a challenging requirement: how to ensure high processing power and very complex functionality along with low power consumption. certainly part of the solution is a proper choice of cmos technology as well as weak and strong inversion regime operating areas. although mos transistor static characteristics in weak inversion and strong inversion regimes are functionally very different, it will be shown that there is an absolute analogy in the behavior and functional dependency of cmos circuit parameters in those regimes. thanks to that, design techniques of more complex cmos circuits are the same in sub-threshold and strong inversion regime. this fact considerably facilitates designer's work of cmos circuit in a sub-threshold regime and enables faster development. optimal consumption generally does not mean minimal consumption. minimal consumption and minimal logic delay are mutually opposite requirements. taking into account only the minimization of consumption, a project with unacceptable logic delay could be delivered. the consumption as well as the logic delay of cmos circuit depends on mos transistor threshold voltage vt and supply voltage vdd . because of that, one part of this paper is devoted to consumption optimization techniques in systems with multiple levels of vt and vdd . specific part of this paper refers to the big toe of “lowpower hand”– topologies. review of topologies of cmos logic series that ensure low-power within the specified range of operating frequencies is given, which implies their use in both strong and weak inversion regimes. the analysis is based on simplified current-voltage models of mos transistors and pspice software using parameters of 180 nm technology. ii. cmos operating in the weak inversion regime in essence, there are three areas of mos transistor static characteristics [7]. figure 1 shows the logarithmic dependence of nmos transistor drain current as a function of gate-source voltage (vgs), at a constant drain-source voltage (vds) and source-substrate voltage (vsb). in the literature, the smallest attention is paid to the medium (moderate) area which is mostly considered as a part of strong inversion threshold area [8, 9]. in digital circuits, it is assumed that vgs>vt, where vt is a mos transistor’s threshold voltage, transistor is operating in strong inversion regime, and for vgs<vt in the sub-threshold (weak inversion) regime. therefore, from today’s application point of view, it can be said that vt is a gate-source voltage on a border between the weak and the strong inversion regime. it is a well-known fact that the id (vds, vgs) characteristic in the strong inversion regime has two areas: non-saturated and saturated. in the non-saturated area, it holds that id ~vgs and id~vds 2 , while in saturated area id ~ vgs 2 and id ≠ f(vds), that is id ≈const as a function of vds. mos transistor characteristics in the weak inversion regime are defined as follows: ( ) ( ) ϕ ϕ ϕ ϕ ϕ − − −   − < =   > / 0 0 1 , 3 , non-saturated area , 3 , saturated area, 1 gs t t ds t gs t t v v n v ds t dsub v v n ds t i e e v i i e v where ( )µ ϕ= − 20 0 1ox t w i c n l (2) is a drain current on a border between weak and strong inversion. fig. 1. log id characteristic as a function of vgs at a constant vds and vsb the meaning of the parameters in (1) and (2) are the following: µ0 is a mobility of major charge carriers (electrons and holes in nmos to pmos transistor), cox = εox / tox is gate capacitance (εox is a dielectric constant, tox is a thickness of the gate oxide), w and l are the width and length of the channel, respectively, φt=kt/q is a thermal potential (φt=26 mv at t=300k), where n=1+cd /cox≈1.5 is a gradient factor. for vds>3φt, drain current is almost independent of the voltage vds (figure 2), so that the area analogous to strong inversion regime, can be treated as saturated area. in this area it holds ~ gs v d i e . for vds<3φt, at vgs=const., ds v d ei ~ , transistor is in the non-saturated area. thanks to the analogy in the field of mos transistor characteristics, there is an appropriate analogy of operation and cmos logic circuit characteristics [8]. thus, for example, voltage and current static characteristics in the weak inversion regime (figure 3) have the same shape as in the strong inversion regime. even inverter threshold voltage vtsub is etasr engineering, technology & applied science research vol. 3, �o. 6, 2013, 552-561 554 www.etasr.com dokic: a review on energy efficient cmos digital logic obtained in the same way – equating of nmos and pmos drain currents in the saturated area of characteristics. fig. 2. id(vgs, vds) in weak inversion regime it results with inverter threshold voltage vtsub in the subthreshold regime [8]: ϕ    = −     ln , 2 2 ddsub t on tsub op v n i v i (3) and maximal current from the voltage source: ϕ − = /2 , ddsub t t v v nop ddmsub on on i i i e i (4) where ϕ < < = =3 t ddsub t tn tp v v v v (5) is a supply voltage, vtn and vtp threshold voltages, and ion and iop currents on the border between weak and strong inversion of nmos and pmos transistors, respectively. for a symmetric inverter (ion=iop), threshold voltage is, just like in strong inversion regime, vtsub=vddsub/2. minimal supply voltage, according to [7] is vddmin=3φt=78 mv. for vddsub>3φt , the id(vgs, vds) characteristic has both saturated and non-saturated areas, which is necessary for satisfying the quality of digital circuit transfer characteristic vo(vi). however, logic circuits can operate even at vdd<3φt. thus, for example, some authors [9] state constraints vdd>57 mv, while others [10] claim that vdd>48 mv. as in strong inversion regime, threshold voltage vtsub and maximal current iddmsub in the sub-threshold regime both depend on nmos and pmos transistor geometry (figure 3), except that iddmsub~(wn/wp) -1/2 and vtsub ~ln(wn /wp), where wn and wp are the channel widths of nmos and pmos transistors, respectively. vin1 50mv 100mv 150mv 200mv 250mv id(mn) 0a 50pa 100pa 150pa sel>> v(2) 0v 100mv 200mv 300mv fig. 3. (a) pspice voltage and (b) current transfer characteristic of cmos inverter in the sub-threshold regime, for channel width ratios wp /wn={1, 8/3, 5, 9} at equal channel length (ln=lp) and vddsub = 300 mv considering the behavior analogy and cmos inverter characteristics in the weak and strong inversion regime, there is an analogy even at synthesis of more complex circuits. in both regimes, more complex digital circuits consist of dual nmos and pmos transistor networks (figure 4). duality implies that a serial connection of nmos transistors is corresponding to a parallel connection of pmos transistors and vice versa. fig. 4. topology of the circuit with logical function +ab c consisted of dual networks: +ab c (nmos) and +( )a b c (pmos) in both regimes, logic circuit transfer characteristic depends on the number of inputs and number of active inputs [8]. figure 5a shows the transfer characteristics of nor3 logic circuit with all inputs activated, and when the activated input is the one applied to the gate of a pmos transistor whose source is connected on a power-supply line vdd . 1 5 9 8/3 9 8/3 5 1 a) b) vtsub iddmsub etasr engineering, technology & applied science research vol. 3, �o. 6, 2013, 552-561 555 www.etasr.com dokic: a review on energy efficient cmos digital logic 0.05 0.1 0.15 0.2 0.25 0 0.05 0.1 0.15 0.2 0.25 0.3 vin [v] v o u t [v ] 0.05 0.1 0.15 0.2 0.25 0 0.05 0.1 0.15 0.2 0.25 0.3 vin [v] v o u t [v ] fig. 5. pspice transfer characteristics of (a) nor3 and (b) nand2 circuits in the weak inversion regime, with all inputs activated, and when the activated input is the one applied on the gate of a serial transistor whose source connected on power supply line. in nand circuits, the highest threshold voltage is obtained when all inputs are active, and the lowest when the active input is only the one applied to the gate of nmos transistors, whose source is connected to the ground (figure 5b). optimal transistor geometry of m-input nand and nor circuits is the same in both regimes and is defined as follows [12]: µ µ µ µ = = / / / 1 . / pn n p p n pn n p p n w l m w l w l w l m (6) iii. cmos circuit power consumption electric power consumption consists of two components: static and dynamic d ds dd p p p= + . (7) static consumption is a result of existing mos transistor currents in static states and is defined as: , ds s dd p i v= (8) where is represents the static current in total. there are four main sources of static current in cmos circuits: • tunneling current through the gate (ig), • sub-threshold drain current (idsub), • inverse polarized p-n junction current (idss), • hot charge carrier injection gate current (ih). the first three components have dominant influence on cmos circuit static consumption level. scaling of the dimensions of mos transistors decreases oxide thickness below the gate (tox). therefore, the electric field through gate oxide increases, which leads to the tunneling effect of charge carriers from gate to substrate or from substrate to gate. the gate current has four components: gate-channel (igc), gate-drain (igd), gate-source (igs) and gate-base (igb) (fig. 6). the total gate current is: . g gd gb gs gc i i i i i= + + + (9) vdd igd igb igc igs +vdd vo=0 +vdd vo=vdd isgibg icg idg fig. 6. gate leakage currents of (a) nmos and (b) pmos transistor gate currents depend on supply voltage vdd and on the employed technology (table i) [11]. thus, for example, when increasing the supply voltage level from vdd=0.2 v to vdd=1.2 v, the gate current increases from ig ≈1.2 na to ig≈1.7 µa. the increase ratio is approximately 1.4·10 3 times. when reducing the transistor dimensions, gate current increases as well. for nmos transistor, according to table i, that increase for 45 nm in regard to 65 nm cmos technology, depending on vdd, is approximately 7 (at vdd=1.2 v) to 14 (at vdd=0.2 v) times. table i. nmos transistor gate current as a function of supply voltage for two different technologies ig vdd [v] 45 nm tech. 65 nm tech. 0.2 1.1996 na 85.506 pa 0.4 14.258 na 1.2376 pa 0.6 66.954 na 6.5488 na 0.8 225.97 na 25.244 na 1.0 647.38 na 82.378 na 1.2 1.6811 µa 243.21 na the nmos transistor leakage current is greater than in pmos, because the probability of holes tunneling is greater than the probability of electrons tunneling through the gate oxide. that increase, depending on supply voltage is 40 times [11]. the sub-threshold leakage current is a cutoff transistor (vgs=0) drain to source current (figure 7) and it is given as: nim: nilim: a) b) v i v i v i “1” v i etasr engineering, technology & applied science research vol. 3, �o. 6, 2013, 552-561 556 www.etasr.com dokic: a review on energy efficient cmos digital logic dd t t v v n ddsub o i i e η ϕ − = (10) where η is the dibl (drain–induced barrier lowering) factor [9]. this current values depend on the supply voltage, the dimensions of elements (technology) and the temperature. in table ii, comparative values of gate current and sub-threshold drain current as a function of supply voltage vdd and temperature are given, for 45 nm technology. it is evident that the dependency of ig on vdd and in function of temperature dependency of idsub is more expressed. on the other hand, at temperature of 25°c it holds vdd ≤ 0.6 v, ig<idsub, while for vdd >0.6 v, ig >idsub. thus, for example, for vdd =1.2 v holds that ig≈13idsub. vdd +vdd 0 +vdd vdd idnsub idpsub fig. 7. sub-threshold currents of (a) nmos and (b) pmos transistors in cmos inverter table ii. gate and sub-threshold drain current of nmos transistor as a function of vdd and temperature gate current ig [na] sub-threshold current idsub [µa] vdd [v] 25°c 110°c 25°c 110°c 0.2 1.1996 1.2689 40.999 0.88086 0.4 14.258 15.776 56.437 1.1586 0.6 66.954 75.437 72.47 1.4401 0.8 225.97 256.33 89.397 1.7334 1.0 647.38 736.31 107.42 2.0428 1.2 1681.1 1914.3 127.12 2.3785 inverse saturation current idss of the p-n junction of a turned off transistor depends on the p-n junction surface and temperature. for 0.25 µm technology, it is between 10 and 100 pa/µm 2 at a 25°c temperature per area unit. in nanometer technologies, this current is less than ig and idsub, and can be ignored. dynamic consumption consists of two components: switching consumption and transition (short-circuits) consumption. switching consumption is the result of charging and discharging of a load capacitor and in both regimes is defined as: = = 2 , d ddsub l dd p p c v f (11) where cl is the effective output parasite capacitance, and f is the switching state frequency of the cmos logic circuit. transition consumption occurs due to conduction of both transistors or transistor networks (nmos or pmos) during switching states (transition area) (figure 3). in strong inversion regime, transition consumption is defined with [12] and is: ( )( )= − +1 2 , 3 dp ddm dd t r f p i v v t t f (12) where ( ) µ µ µ − =    +     2 2 2 2 / 1 / dd tox n ddm n n n n n p p p v vc w i l w l w l (13) is the maximal voltage supply current in transition area, and tr and tf are the rise time and fall time input signals. in sub-threshold regime, dissipation power of transition is defined with [8] : ( )ϕ= +2 ,dpsub t ddmsub r fp n i t t f (14) where iddmsub is defined with (4), and f is an input signal frequency. usually, dynamic dissipation power is calculated (estimated) in regard to clock frequency. namely, most number of logic circuits does not change their state during every cycle of clock signal. therefore, expressions for dynamic consumption have to be multiplied with activity factor α≤1, regarding to clock frequency, so that: ( )( ) ( ) α α α α ϕ = + − + = + + 2 2 , 3 2 . ddm dd c l dd c dd t r f ddsub c l ddsub c t ddmsub r f i p f c v f v v t t p f c v f n i t t (15) product αfc, where fc is the clock frequency, is the activity of the circuit indicating the number of state changes. mostly, activity factor is α<0.5. it is determined empirically that static cmos digital circuits have α ≈ 0.1 [13]. iv. low power design techniques optimal project implies a compromise between operating speed and low power, which all design levels take into account [2]. in this section, we will speak about the optimal project considering the choice of transistor threshold voltage vt and system power supply voltage vdd. in the previous paragraph, it was shown that both static and dynamic consumptions are decreased with the reduce of vdd. dynamic switching consumption in both regimes is proportional to vdd 2 . transition consumption in the strong inversion regime is pdp~(vdd vt) 3 , and in sub-threshold regime /2 ~ dd t v v dpsub p e − . static currents, depends on supply voltage as well (tables i and ii), so that ps ~vdd n , where n is usually in the range of 1<n<4. etasr engineering, technology & applied science research vol. 3, �o. 6, 2013, 552-561 557 www.etasr.com dokic: a review on energy efficient cmos digital logic logic delay also depends on vdd and vt. namely, in the strong inversion regime, capacitor charging/discharging current is id~(vdd vt) 2 in the saturated area, and id ~ (vdd vt)vo in the non-saturated area (figure 8). in the sub-threshold regime that current is ( ) ~ t dddd t v vv v dsub i e e − −− = (figure 8). thus, reduction of vdd increases the logic delay in both regimes. in order to maintain the logic delay at lower vdd , threshold voltage vt should be reduced. over a long period of time, cmos digital circuit's performance increasing scenario was conducted in the process of reduction of element's dimensions, by lowering vdd and vt. however, reduction of vt below 200 mv leads to exponential increase of sub-threshold current as shown in (4). this may cause the static consumption to be higher than the dynamic. consequently, it can be said that the reduction of threshold voltage is limited to approximately vtmin=200 mv. fig. 8. discharge currents of capacitor cl in the strong and weak inversion regime v. multi vdd /vt optimization techniques a compromise between low power and sufficient speed can be achieved using transistors with different threshold voltages. this technique is known as the multi-threshold technique or mtcmos [14, 15]. critical signal path is designed using logic with lower threshold voltages. transistors with higher vt are used where delay is not critical. the second approach with the mtcmos technique is based on the so-called gated voltage supply (figure 9). in static states, relatively in time of logic inactivity (standby mode), voltage supply is turned off using transistors with high threshold voltage. thus, the small subthreshold current is secured, along with low static dissipation. logic block transistors are designed with low vt so that the needed speed is preserved. using control “wake up” signal sl (sleep), over a pmos transistor with high vt, the connection between true vdd and virtual power supply vddv is controlled. while mp is turned off, capacitor cb maintains the virtual power supply of the logic block. reduction of the leakage currents of inactive components can be achieved using nmos transistors between the logic block and the ground, or with pmos and nmos transistors at the same time [15]. the state of the pmos transistors is then controlled with the sl signal, and of the nmos with the sl signal. the ratio between the consumption and the speed of data processing is optimized using several power supplies in the same design. logic circuits over critical delay paths are supplied with higher vddh, and circuits whose delay is not critical with lower voltage vddl (figure 10). the number of voltage levels can be greater, but it turns out that the largest effect is achieved using two power supplies [16]. it should be noted that the transition from logic with vddl to logic with vddh power supply is achieved using logic voltage level converters. this as well limits the number of power supply levels. fig. 9. mtcmos block diagram with gated voltage supply fig. 10. two registers connected with different delay paths often in the same digital system, techniques with several power supplies and several threshold voltages have been used – multi vdd /vt techniques [16, 17]. optimal operating point (vddopt, vtopt) is determined on vdd -vt plane with constant power consumption lines (equi-power) and speed lines (equi-speed) (fig. 11). these lines depend on technological process and project architecture. the choice of the optimal (vddopt,vtopt) pair depends on technological process constraints. let say that those constraints are: vdd=3.3v±10% and vt=0.55 v±0.1. the area of allowed values for these limitations is shown in figure 11, with a larger rectangle. for all values of vdd and vt inside this rectangle, system fulfills all given specifications. in a corner, system will have the highest delay, and in b corner the highest energy consumption. constant speed and constant consumption lines are normalized at points a and b by normalization factors ks and kp, respectively. based on that, we determine the influence etasr engineering, technology & applied science research vol. 3, �o. 6, 2013, 552-561 558 www.etasr.com dokic: a review on energy efficient cmos digital logic of position changes and the rectangle size in vdd-vt plane, onto consumption and system speed. for example, smaller rectangle on figure 11 is defined with constraints vdd=2.1 v±5% and vt=0.18 v±0.05, and consumption is 60% (kp=0.4) lower for the same operating speed (ks=1). fig. 11. vdd-vt plain with constant power consumption and delay lines from all possible vdd-vt combinations that meet given time constraints, only one combination (vddopt, vtopt) guarantees minimal consumption. shuster et. al. [18] proposed an equation, based on the transistor alpha model, for the calculation of total system consumption with the optimal (vddopt, vtopt) pair. nevertheless, it should be stated that the continual change of vddopt and vtopt is unpractical. designers are mostly allowed to choose between several discrete (vddopt, vtopt) values. by applying the multi vdd technique, dynamic consumption can be reduced from 10%, up to 50%, whereas by applying the multi vt technique, static consumption can be reduced for 50%, even up to 80% [3]. in [16], the optimal ratio between vdd and vt is given (table iii). table iii. optimal ratio of vdd and vt considering consumption vddi, i=1,2,3,4, vt=const (vdd1,vdd2): 2 1 1 0.5 0.5dd t dd dd v v v v = + (vdd1,vdd2, vdd3): 2 3 1 2 1 0.6 0.4dd dd t dd dd dd v v v v v v = = + (vdd1,vdd2, vdd3, vdd4): 2 3 4 1 2 3 1 0.7 0.3dd dd dd t dd dd dd dd v v v v v v v v = = = + vti, i=1,2,3,4, vdd=const (vt1,vt2): vt2=0.1vdd+vt1 (vt1,vt2, vt3): vt2=0.06vdd+vt1 vt3=0.07vdd+vt2 (vt1,vt2, vt3, vt4): vt2=0.04vdd+vt1 vt3=0.05vdd+vt2 vt4=0.06vdd+vt3 vi. cmos low power topologies standard cmos combinational logic demands a cmos transistor pair per every input. however, various alternative topologies with the lower number of transistors have been developed. besides, the increase of scale of function integration in vlsi integrated circuit, has led to a reduce of consumption or increase of speed at the same consumption level. among the first alternative cmos digital logics is the transmission-gate logic. unlike standard logic where the basic cell is the inverter, in transmission-gate logic, the basic cell is the transmission gate. while in standard logic circuits, output signals are separated from the inputs, here the input signal is transferred to the output via the transfer gate. figure 12 shows a 2/1 multiplexer (2/1 mux) in transmission-gate logic. since the complementary signals are needed for transmission gate control, inverters are integral part of the network as well. the 2/1 mux in figure 12 consists of only three cmos transistor pairs, while standard logic needs seven pairs. fig. 12. mux 2/1 in transmission-gate logic transmission gate logic can be additionally simplified by applying signals b and b to the inverter power line as in the example of xor and xnor circuit synthesis shown in figure 13. the inverters with the (mn, mp) transistor pair are powered by b and b signals. in the synthesis of logical functions in transmission-gate logic, it must be taken into account that between the output and at least one input, a contour of small resistance exists. otherwise, output would be in the state of high impedance with the undefined logic level. fig. 13. (a) xor and (b) xnor circuits as a transmission gate, instead of a cmos pair, only nmos transistors can be used (fig. 14). the number of transistors is halved and the static consumption and the parasite v t (v ) etasr engineering, technology & applied science research vol. 3, �o. 6, 2013, 552-561 559 www.etasr.com dokic: a review on energy efficient cmos digital logic capacitance are reduced as well, which significantly increases the scale of function integration in a vlsi circuit. d0 d1 d2 d3 a a b b vdd z z dd fig. 14. mux 4/1 in pass-transistor nmos logic with true and complementary output the problem with the nmos pass-transistor logic is that the maximal voltage variation on one nmos transistor is vdd-vtn and lower, for threshold voltage vtn comparing to the cmos transmission gate. that limits the number of serial transistors. therefore, nmos transistors with very low (ntl-aon threshold logic) or zero threshold voltage (ztt-zero threshold logic) have been used. the problem of mentioned logics lies in the low noise immunity. reduction of logic amplitude in nmos transmission-gate logic is especially a problem when nmos network ends with an inverter. that problem can be solved using a pmos transistor mp as shown in figure 16. when z = 0, mp is on and maintains the value of nmos network output voltage at vdd. low threshold transistors are used in the so-called cpl (complementary pass-transistor logic). this logic consists of two nmos transistor networks with common control and complementary transfer signals (figure 15). ppl (push-pull pass-transistor logic) [19] also have two transistor networks: one nmos and the other pmos (figure 16). the control signals are common, and inputs are complementary. output logic levels have been restored to vdd and 0 by transistors mp and mn, respectively. table iv shows full adder comparative characteristics using different logics, implemented in 0.8 µm technology at vdd=3.3 v. although pmos transistors are slower than nmos, logic delay of ppl is approximately like cpl, but the consumption is significantly lower. table iv. full adder comparative characteristics parameter cmos cpl ppl logic delay [ns] 1.57 0.84 0.83 cons. [mw/100hz] 1.90 1.33 0.42 p·td (normalized) 1 0.38 0.12 a b b b ab ab a b a a b ab ab b a+b a+b a+b a+b a b a b a b a b a a b a a a b a b a) b) c) a b a b a b b a b b b fig. 15. and/nand (a), or/nor (b) i xor/xnor (c) logic circuits in cpl fig. 16. ppl block sheme vii. adiabatic logic the term “adiabatic” describes thermodynamic processes in which the amount of heat remains constant (there is no exchange of energy with the environment). adiabatic logic in the ideal sense, designate digital circuits without loss (dissipation) of electrical energy. in practice, it denotes the logic with minimal consumption of electrical energy during the switching of states. adiabatic switching state shifting is a charge/discharge mechanism which returns accumulated etasr engineering, technology & applied science research vol. 3, �o. 6, 2013, 552-561 560 www.etasr.com dokic: a review on energy efficient cmos digital logic energy to the source inside the load capacitor using the dynamic power supply. dynamic power supply or clocked power has a very important role in adiabatic logic, because beside power supply, it provides energy recovery. nowadays, there are many techniques of adiabatic logic [20-25]. energy recovery process will be explained on the example of ecrl (efficient charge recovery logic) inverter (figure 17). power supply pc is with trapezoidal pulses. pc mp1 mp2 mn1 mn2 c l c l q q a a 0 vdd accumulation (chargingc l ) energy recovery (discharging c l ) fig. 17. ecrl inverter scheme in the initial state holds a=1, and the mn1 is conducting (q=0). while pc rises from 0 to vdd, over conductive transistor mp2 the output q follows the variation of pc. when pc reaches the vdd value, then it holds q =1, and q =0 and those conditions are valid logic states at inputs of next stage. during the fall of pc from vdd to zero, the right capacitor cl discharges over the conductive mp2 and pc, and therefore recovers accumulated energy to the pc supply. more complex ecrl circuits have two complementary nmos transistor networks with complementary excitations (figure 18), instead of mn1 and mn2 transistors. complementary networks are obtained by complementing input signals and switching of logic operators as a function of fn nmos network. for example, fn 2/1 multiplexer function is ( ) n f sa sb= + and the function of complementary network is ( )( ) n f s a s a= + + (figure 18b). other adiabatic topologies should be mentioned as well: pal (pass-transistor adiabatic logic) [21], cpal (complementary pal), pfal (positive feedback adiabatic logic) [20] etc. reduced energy consumption comparing to standard cmos logic is around 50 to 90%. s b s b { fn } network b a s s { fn } network b) fig. 18. (a) block scheme of complex ecrl circuit (b) with n f and nf mux2/1 network viii. conclusion to enable the design of energy-efficient digital systems, designers must take into account the electrical energy consumption through all design phases, from functional description to transistor level. the biggest energy saving (10 to 20 times) with the least time needed for consumption analysis is acquired on the system design level. in the sub-threshold regime, consumption is several orders of magnitude lower, but operating speed is lowered by nearly the same amount in comparison to the strong inversion regime. rescaling of transistor dimensions increases gate current ig which is very dependent on power supply. multi vt /vdd design techniques provide the reduction of consumption to a scale of about ten percent at the same operating speed. digital systems with two power supplies and/or two threshold voltages are optimal as well. using two threshold voltages, static consumption can be reduced up to 80%. alternative topologies provide larger scale of function integration per single vlsi circuit, lower consumption level and higher-speed rate. the transfer logic has the widest application in vlsi digital circuit design whereas adiabatic logic ensures the greatest energy saving (up to 90%). references [1] r. sarpeshkar, “universal principles for ultra low power and energy efficient design”, ieee transactions on circuits and systems ii: express briefs, vol. 59, no.4, pp. 193-198, 2012 [2] j. rabaey, low power design essentials, springer-verlag, new york, 2009 etasr engineering, technology & applied science research vol. 3, �o. 6, 2013, 552-561 561 www.etasr.com dokic: a review on energy efficient cmos digital logic [3] b. jovanovic, analytic model for dynamic consumption evaluation of arithmetic circuits implemented on fpga, phd thesis, elektronski fakultet niš, 2013 [4] s. r. nassif, “waiting for the post-cmos godot”, int. acm great lakes symposium on vlsi, lausanne, switzerland, 2011 [5] k. itoh, “a historical review of low-power, low-voltage digital mos circuits development”, ieee solid-state circuits magazine, vol. 5, no. 1, pp 27-39, 2013 [6] t. makimoto, “the age of the digital nomad: impact of cmos innovation”, ieee solid-state circuits magazine, vol. 5, no. 1,pp 4047, 2013 [7] y. tsividis, c. mcandrew, operating and modeling o the mos transistor, oxford university press, 2011 [8] b. dokic, a. pajkanovic, “subthreshold operated cmos analytic model”, indel 2012, ix symposium on industrial electronics, banja luka, bosnia and herzegovina, 2012 [9] a. wang, b. h. calhoun, a. p. chandrakasan, sub-threshold design for ultra low-power systems, springer, 2006 [10] l. nazhandali, b. zhai, j. olson, a. reeves, m. minuth, r. helfand, s. pant, t. austin, d. blaauw, “energy optimization of subthresholdvoltage sensor network processes”, isca’05, proc. of the 32nd int. symp. on computer architecture, madison, wisconsin usa, 2005 [11] a. mishra, r. a. mishra, “leakage current minimization in dynamic circuits using sleep switch”, sces 2012, students conference on engineering and systems, pp. 1-6, allahabad, uttar pradesh, india, 2012 [12] b. l. dokic, “integrated circuits–digital and analog”, glas srpski, 1999 [13] p. m. petkovic, “design of cmos integrated circuits with mixed signals”, elektronski fakultet niš, 2009 [14] m. amis, s. areibi, m. elmasry, “design and optimisation of multithreshold cmos (mtcmos) circuits”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 22, no 10, pp. 1324 – 1342, 2003 [15] s. shigematsu, s. mutoh, y. matsuya, y. tanabe, j. yamada, “a 1-v high-speed mtcmos circuit scheme for power-down application circuits”, ieee journal of solid-state circuits, vol. 32 no. 6, pp. 861– 869, 1997 [16] m. hamada, y. ootaguro, t. kuroda, “utilizing surplus supplies timing for power reduction”, ieee conference on custom integrated circuits, pp. 89-92, san diego, usa, 2001 [17] c. piguet, c. schuster, j. nagel “static and dynamic power reduction by architecture selection”, integrated circuit and system design. power and timing modeling, optimization and simulation. lecture notes in computer science, vol. 4148, pp. 659-668, 2006 [18] c. schuster, j. l. nagel, c. piguet, p. a. farine, “architectural and technology influence on the optimal total power consumption”, proceedings of design, automation and test in europe (date '06), pp 13-19, munich, 2006 [19] w. h. paik, h. j. ki, s. w. kim “low power logic design using pushpull pass-transistor logics”, international journal of electronics, vol. 84, no. 5, pp. 467-478, 1998 [20] r. k. yadav, a. k. rana, s. chauhan, d. ranka, k. yadav, “adiabatic technique for energy efficient logic circuits design”, international conference on emerging trends in electrical and computer technology (icetect 2011), pp 776-780, tamil nadu, 2011 [21] v. g. oklobdzija, d. maksimovic, l. fengcheng, “pass-transistor adiabatic logic using single power-clock supply”, ieee transactions on circuits and systems ii: analog and digital signal processing, vol. 44, no. 10, pp. 842-846, 1997. [22] a. k. maurya, g. kumar, “energy efficient adiabatic logic for low power vlsi applications”, international conference on communication systems and network technologies (csnt 2011), pp. 460-463, katra, jammu, 2011 [23] j. hu, q. chen, “modelling and near-threshold computing of powergating adiabatic logic circuits”, przegląd elektrotechniczny (electrical review), vol. 88, no. 76, pp. 277-280, 2012 [24] d. markovic, c. c. wang, l. p. alarcon, l. tsung-te, j. m. rabaey, “ultralow-power design in wear-threshold region”, proceedings of the ieee , vol. 98, no. 2, pp. 237-252, 2010 [25] a. pajkanovic, t. j. kazmierski, b. l. dokic: adiabatic digital circuits based on sub-threshold operation of pass-transistor and slowly ramping signals, proceedings of small systems simulation symposium, pp 48-53, niš, 2012 microsoft word etasr_v11_n2_pp7006-7010 engineering, technology & applied science research vol. 11, no. 2, 2021, 7006-7010 7006 www.etasr.com al-shammari et al.: development of an automatic contactless thermometer alert system based on … development of an automatic contactless thermometer alert system based on gps and population density naif k. al-shammari department of mechanical engineering college of engineering university of ha’il hail, saudi arabia naif.alshammarif@uoh.edu.sa husam b. almansour department of health management college of public health and health informatics university of ha’il hail, saudi arabia h.almansour@uoh.edu.sa muzamil basha syed school of computing and information technology reva university bangaluru, karnataka, india muzamilbasha.s@reva.edu.in abstract-in today's out-breaking covid-19 circumstance, treatments are preferred to be contactless. social distancing has become a mandate in order to prevent disease spreading. in such a scenario, checking the body temperature is preferable to be made contactless because it helps the doctors and social workers to stay away from the symptomatic patients. infrared (ir) contactless thermometers are employed in measuring the temperature while preventing direct contact with the body. improved functionalities in the contactless thermometer can provide accurate precision in measurements and calculations. technological advancement in pharmacy has cohesively improved over time. coupling machine learning (cml) will revolutionize the process of testing. the demand for automated temperature test equipment is likely to grow at a significant pace, with the continuous advancements in technology and the adoption of ate (automated test equipment). the global positioning system (gps) easy tracking and navigation can be used for easy tracking. population density can be used to calculate the amount of population in a particular area. the proposed automatic contact-less thermometer system has the potential to replace the traditional temperature measuring techniques and safeguard from human-to-human transmission diseases. keywords-covid-19; ir technology; ate; gps; population density i. introduction the global positioning system (gps) is used to determine locations using a satellite navigation process. it is well suited for different kinds of tracking applications [1] and is used for safety and security purposes. the main components of the gps system are the space segment, control segment, and user segment. these segments collaborate with each other and process the signals received from the satellites and use them for further information processing like tracking, security in banking applications, automatic toll services, location identification, and navigation [2]. in our example, the idea is to develop an automatic contactless thermometer system based on gps location (latitude-longitude) and population density. population density is used to calculate the amount of population in a particular area. it is calculated as [3]: pn pd ln = (1) where pd is the population density, pn is the total population, and ln the total land area covered by the population. the calculation of population density varies depending on environmental (climate, resources) and human (economic and societal) factors [4]. globally, millions of covid-19 and temperature tests are conducted every day. testing temperature for every person is very crucial: most enterprises, governments, and organizations are following very strict protocols in order to minimize the impact. educational organizations are struggling to reopen schools, colleges, and research centers, mainly due to the lack of testing centers. testing is time-consuming, and is conducted with low accuracy. the automatic contactless thermometer provides a solution. the contactless process is efficient and provides easy scalability among large groups. automatic temperature test-centers will be the future regarding this matter. public places, and the transportation sector need such technology during these hours. in figure 1, the details of the product development stages are presented. the first and second stages of the project are already completed, with stage three being our future plan. the increased adoption of smartphones brings a great opportunity to corresponding author: naif khalaf al-shammari engineering, technology & applied science research vol. 11, no. 2, 2021, 7006-7010 7007 www.etasr.com al-shammari et al.: development of an automatic contactless thermometer alert system based on … locate people affected with covid-19. smartphones enable the governments to track and locate affected people and virtually fencing people is now possible. technological advancement in pharmacy has improved with times. coupling machine learning (cml) will revolutionize the way we test. the demand for automated temperature test equipment is likely to grow at a significant pace along with the continuous advancement in technology and the adoption of ate (automated test equipment). the increased adoption of smartphones brings great opportunity to locate covid-19 affected people. focusing on minimizing error in detection is a very important task. using an automated contact-less thermometer and geolocation feature from a smartphone will help monitoring on a large scale. however, technology nowadays has become more sophisticated. for example, the number of available infrared (ir) detectors has highly increased, and thanks to their selective filtering capabilities, these detectors can promise more efficiency and speed. fig. 1. design and development steps of the complete product. minimizing error in detecting is a very important task. public transportation is highly dynamic, testing the public in a fast phase and with high accuracy is essential. non-contact temperature measurement is the preferred technique for monitoring [5]. during the covid-19 pandemic, the bolometer ir sensor is commonly used, since it provides an ir based solution to measure the temperature and it is efficient with ~4% error rate. gps provides satellite tracking that is very useful in many ways. the main objective of this research work is to develop and deploy an automatic alert system based on the ir thermometer. the two main parameters that are taken into consideration to fully automate the body temperature measurements are the population density and its accurate location identification. the hardware circuit diagram of the traditional non-contact ir thermometer is presented in figure 2. in the proposed work, focus is given on developing the contact-less thermometer to work in a situation where there is a necessity to calculate the body temperature in mass gathering places. the gps tracking system in collaboration with the population density helps in identifying and locating densely populated areas. the aim is to develop an automatic contactless thermometer system to work in such an environment where the system can be deployed in identifying critically ill people. the proposed work is automated to initiate the functioning of the thermometer system by gathering the location identification of the densely populated area with the help of the gps tracking system, and the ir signals of the contactless thermometer that provide an accurate measurement of the body temperature. as an outcome, the proposed system will help in identifying red alert areas, in which the population is affected with fever in order to isolate and prevent the general public from entering. fig. 2. the hardware circuit diagram of the non-contact ir thermometer. fig. 3. the timing diagram of the ir temperature measurement module. ii. literature review globally, health centers have uploaded covid-19 strains long ago and researchers and scientists are reverse-engineering the strains to find the solution [6]. research institutions collect data regarding temperature, location, test results, and personal details to predict the future consequences using machine learning algorithms. a. smart ir thermometers companies are focused on developing smart iot thermometers. real-time trackability is very crucial. to provide compliance with non-contact temperature measurements, it is necessary to calculate the effective efficiency of the black body and the difference in temperature between the workplace and the point or object in which the contact temperature is set [7]. effective recreation can be calculated by applying the theory of evolution or by adjusting the temperature. the latter method seems to be difficult to use, as long as the black hole is cleaned. engineering, technology & applied science research vol. 11, no. 2, 2021, 7006-7010 7008 www.etasr.com al-shammari et al.: development of an automatic contactless thermometer alert system based on … b. health-internet of things (h-iot) considering the impact of the 2019 pandemic, it is natural that many contact tracing and self-assessment mobile applications have already been developed, such as the aarogya setu app1 of the indian government. health organizations like apollo have developed chatbots for analyzing the symptoms. health iot devices typically belong to two broad types, personal h-iot devices and clinical h-iot devices [8, 9]. fig. 4. flow chart of the automatic test equipment. fig. 5. the voice broadcast circuit. iii. methodology in figure 4, the data flow between the modules of the proposed technique is presented. in the first step, the noncontact mode of operation is selected. in step two, we get the information from the source using sensors. if the reading received from the sensor is within the acceptable range, then the reading temperature is processed for future decision making. else, the system is switched to contact mode to get the temperature, thus always making sure that acceptable accurate temperature is displayed on the display unit. switching between the possible modes is only made based on the format of the data received from the sensor and the acceptable range of the received data. the circuit diagram is presented in figure 5 with complete details. iv. experimental setup and results the circuit unit is simulated on the proteus platform, where the pcb board is designed and built after simulation. the mcu download system and other components are mounted on the pcb board [9]. the temperature of the object is usually simultaneously measured by a mercury thermometer and with a non-contact ir thermometer, time is measured by the length of the clock, temperature is set at 25 0 c to 48 0 c. the results of the measurements are: temperature error is less than 0.1 0 c, measurement time is about 5s with an ir contact thermometer. the measurements are accompanied with a voice message transmission, and lcd display of temperature and time. in general, the measured data are very accurate. a screenshot of the experimental work is presented in figure 6. the display unit ir with the vbc is presented in figure 7. when a temperature of an object below 25 0 c is detected with the ir contact thermometer, a buzzer alarm and a voice transmission take place. object temperature at 25 0 c ~ 48 0 c is accompanied with voice transmission and lcd display of the temperature and time. temperature above 48 0 c is accompanied with a buzzer alarm, and a voice transmission. the data from the sensors are fed into the circuit and the outcome is obtained from the display component shown in figure 7. to estimate the performance of the experimental setup, the collected data (temperature, gps attributes) from the sensors are stored in an engineering, technology & applied science research vol. 11, no. 2, 2021, 7006-7010 7009 www.etasr.com al-shammari et al.: development of an automatic contactless thermometer alert system based on … excel sheet. the corresponding output label (message to be displayed) for each input is included to establish the train data with the help of human radiologists for diagnosis. in order to test the experimental setup, new data instances are used (test data) and the output is stored in the same sheet. the decision tree model is constructed using the trained dataset [10]. the evaluation parameters used to estimate the performance of the model constructed are shown in table i. fig. 6. matlab experimental setup. fig. 7. display unit interface. table i. evaluation parameters parameters formula accuracy (a) tp+tn a= total misclassification rate (mcr) fp+fn mcr= total recall (r) tp r= actualtrue precision (p) tp p= predictedtrue prevalence (pv) actualtrue pv= total f score (fs) r×p fs=2× r+p tp: true positive, tn: true negative, fp: false positive, fn: false negative in figure 8, the x-axis represents the evaluation metric used in estimating the performance of the experiment carried and in the y-axis the performance of the experiment is shown on a scale of 0 to 1. the experiment carried out in the present research work is reliable and proved to be robust with classification accuracy a=0.96. the present experimental setup and its performance are compared with the results of the similar research carried out in [12], in which, the recorded temperature is ±0.2°c accurate. the reason for achieving such accuracy is because of the metal cap attached to the thermopile sensor. the present circuit is designed to have ±0.5 trueness (p), which is better than the design of [11]. the provision of switching between contactless and contact modes allows much better precision in the current design. the gps and population density values are used in identifying the crowded areas. the aim of the proposed work is to keep the average temperature 36.5-37.5°c in the tested locations. the latitude and longitude of the locations help to give alert messages to people in problematic areas in order to maintain their social distance. fig. 8. accuracy plot of the experimental work. v. conlcusions and future work advancement in technology and infrastructure will give us the cure to covid-19 and its fellow strains. automated testing and gps-based geofencing will provide trackability on large scale. the gps tracking system in collaboration with the population density help in identifying and locating the densely populated areas. the proposed system is aimed to develop an automatic contact-less thermometer system to work in such an environment where the system can be deployed in identifying critically ill people. the advantage of the proposed model is that it uses gps coordinates and population density values towards identifying the most crowded areas. the aim of the proposed work is to keep the average temperature between 36.5 and 37.5°c in the tested locations. the latitude and longitude details of the locations allow sending alert messages in order to maintain social distance. the limitation of the product designed in the present research work is that its contactless mode has not been implemented yet. regarding future work, we would like to extend our work in adding a metal cap to the thermopile sensor towards achieving better accuracy. engineering, technology & applied science research vol. 11, no. 2, 2021, 7006-7010 7010 www.etasr.com al-shammari et al.: development of an automatic contactless thermometer alert system based on … table ii. characteristics of the dataset name of the area (india) latitude longitude density level population area (m 2 ) density value average temperature of the area (°c) alert message (text) coimbatore 11.0168 76.9558 low 190 7516 0.0252 36.6 temperature is normal coimbatore 11.0168 76.9558 low 239 13,200 0.10176 36.6 temperature is normal bangalore 12.9716 77.5946 low 670 32,666 0.0205 36.7 temperature is normal bangalore 12.9716 77.5946 low 189 90,100 0.0012 37.4 temperature is normal coimbatore 11.0168 76.9558 high 165 5501 0.03 37.4 temperature is unusually high coimbatore 11.0168 76.9558 high 208 6890 0.0303 37.9 temperature is unusually high coimbatore 11.0168 76.9558 high 260 9634 0.0304 38.2 temperature is unusually high bangalore 12.9716 77.5946 high 259 6890 0.0303 38.3 temperature is unusually high acknowledgment this research has been funded by the scientific research deanship of the university of ha’il, project number covid1908. references [1] r. maddison and c. ni mhurchu, “global positioning system: a new opportunity in physical activity measurement,” international journal of behavioral nutrition and physical activity, vol. 6, no. 1, nov. 2009, art. no. 73, https://doi.org/10.1186/1479-5868-6-73. [2] f. abulude, a. akinnusotu, and a. adeyemi, “global positioning system and it’s wide applications,” continental journal of information technology, vol. 9, no. 1, pp. 22–32, oct. 2015, https://doi.org/10.5707/ cjit.2015.9.1.22.32. [3] “population density: definition, formula & examples video & lesson transcript,” study.com. https://study.com/academy/lesson/populationdensity-definition-formula-examples.html (accessed mar. 21, 2021). [4] j. f. mcdonald, “econometric studies of urban population density: a survey,” journal of urban economics, vol. 26, no. 3, pp. 361–385, nov. 1989, https://doi.org/10.1016/0094-1190(89)90009-0. [5] j.-h. min, n. gelo, and h. jo, “non-contact and real-time dynamic displacement monitoring using smartphone technologies,” life cycle reliability and safety engineering, vol. 4, no. 2, pp. 40–51, may 2015. [6] t. m. fernández-caramés and p. fraga-lamas, “towards the internet of smart clothing: a review on iot wearables and garments for creating intelligent connected e-textiles,” electronics, vol. 7, no. 12, p. 405, dec. 2018, https://doi.org/10.3390/electronics7120405. [7] p. f. paradis and w. rhim, “non-contact measurements of thermophysical properties of titanium at high temperature,” journal of chemical thermodynamics, vol. 32, no. 1, pp. 123–133, mar. 1999. [8] v. siva brahmaiah, b. rajkiran, and s. pradeep, “an intellectual dual axis efficient solar tracking system by using iot integrated controller,” ssrn, https://dx.doi.org/10.2139/ssrn.3554005. [9] s. k. kumaravel et al., “investigation on the impacts of covid-19 quarantine on society and environment: preventive measures and supportive technologies,” 3 biotech, vol. 10, no. 9, sep. 2020, art. no. 393, https://doi.org/10.1007/s13205-020-02382-3. [10] s. m. basha and d. s. rajput, “chapter 9 survey on evaluating the performance of machine learning algorithms: past contributions and future roadmap,” in deep learning and parallel computing environment for bioengineering systems, a. k. sangaiah, ed. academic press, 2019, pp. 153–164, https://doi.org/10.1016/b978-0-12-8167182.00016-6. [11] e. moisello, m. vaiana, m. e. castagna, g. bruno, p. malcovati, and e. bonizzoni, “an integrated micromachined thermopile sensor with a chopper interface circuit for contact-less temperature measurements,” ieee transactions on circuits and systems i: regular papers, vol. 66, no. 9, pp. 3402–3413, sep. 2019, https://doi.org/ 10.1109/tcsi.2019.2928717. [12] b. trstenjak, d. donko, and z. avdagic, “adaptable web prediction framework for disease prediction based on the hybrid case based reasoning model,” engineering, technology & applied science research, vol. 6, no. 6, pp. 1212–1216, dec. 2016, https://doi.org/ 10.48084/etasr.753. authors profile naif khalaf al-shammari academic qualifications: 1993 b.s., meng, ksu, rating (4.25/5), 1999 m.s., meng, ksu, rating (4.56), 2011 phd, beng, birmingham university, uk. professional experience: 1994-2000 saudi electric company, 2001-2010 sultan b.a al saud foundation. 2010-to date: university of hail research interests rehabilitation engineering robotics & control. scientific areas: mechanisms design, biomechanical systems and bio/nano-robotics, dual-arm & flexible manipulator dynamics, smart materials, and structure mechatronics. husam almansour is a distinguished doctor in nursing education and leadership and management programs at the university of hail. he worked as the head of the health management department and as a vice-dean for quality and development of the faculty of public health & health informatics. he has been inclined with research focusing on practice and education. syed muzamil basha completed his phd at vit university, vellore, india in 2020. his current research interests include bigdata analytics, blockchain management, and internet of things. he has more than 30 publications, which include 21 research papers, and 7 conference papers, and 6 book chapters. he is an editor of 4 textbooks. he conducted guest lectures in various engineering colleges in india. he received an award for his scientific contribution from vit in 2018. microsoft word 24-2854_s_etasr_v9_n4_pp4448-4451 engineering, technology & applied science research vol. 9, no. 4, 2019, 4448-4451 4448 www.etasr.com gasmi et al.: determination of fractured rock’s representative elementary volume by a numerical … determination of fractured rock’s representative elementary volume by a numerical simulation method hatem gasmi college of engineering, university of hail, hail, saudi arabia and university of tunis el-manar, enit, tunisia gasmi_hatem@yahoo.fr mabrouk touahmia college of engineering, university of hail hail, saudi arabia touahmia@hotmail.com ahmed torchani college of engineering, university of hail, hail, saudi arabia and university of tunis, ensit, lisier laboratory, tunisia tochahm@yahoo.fr essaieb hamdi university of tunis el-manar, enit, tunisia essaieb@yahoo.fr attia boudjemline college of engineering, university of hail, hail saudi arabia a.boudjemline@uoh.edu.sa abstract—the present study aims at developing a numerical program called dissim which can analyze the homogenization of rock massifs using a new subroutine which calculates representative elementary volume (rev). the dissim methodology consists of two steps. the first step involves the modeling of the fractured network in order to provide a surface simulation that represents the real fracture of the examined front. the second step is to numerically model the wave propagation through the simulated fracture network while characterizing the attenuation of vibrations due to the effect of discontinuities. this part allows us to determine in particular the wave propagation velocity through the fractured mass, from which we can determine the homogenized young's modulus. however, after extensive bibliographic research, it was realized that a third step appeared to be necessary. in fact, it is necessary to look for a representative elementary volume on which we apply the proposed homogenization method. two types of the representative elementary volume are proposed in this article, the geometric rev and the mechanical rev. the presentation of these two types of rev and the dissim methodology are detailed in this paper. then, this methodology was applied to the study of a real case. the present research provides a method allowing the calculation of both types of rev for fissured rocks. the case study yielded comparable results between the mechanical rev and the geometric rev, which is compatible with previous research studies. keywords-representative elementary volume; dissim methodology; homogenization; fractured rock; simulated fracture network i. introduction the examination of a representative elementary volume (rev) is the first step necessary for the homogenization of a studied rock mass. it is a matter of determining a sufficiently large medium with respect to the size of the heterogeneities. rev represents the size from which the homogenized magnitudes (mechanical, hydraulic, geometric, etc.) characterizing the heterogeneous medium become constant or their fluctuations become negligible. different types of rev have been defined, like the hydraulic rev in [1-3]. authors in [4] presented and analyzed the existence of a rev in a porous medium in which two fluids of different natures circulate. the mechanical rev has been studied in [5, 6] by different numerical homogenization methods. the geometric rev has been the subject of [7]. other types such as the thermal rev [8] and the rev of the initial stresses, are also studied mainly for the massifs located at important depths. three-dimensional (3d) fracture network is generated in [9] using field data and applied particle flow code (pfc) to determine the effect of the representative elementary volume size. other studies [10, 11] used numerical modeling based on baecher's model [12] to determine rev. a combination of the procedures developed in [13, 14] and monte carlo simulation is implemented in [11] to create a large number of fracture network models to statistically represent the bedrock and analyze rev. it should be noted that knowing the size of rev makes it possible to analyze rock masses more precisely. indeed, the results of the fracture networks simulation and numerical homogenization can only be applied to faithfully represent the real rock mass if the size of the simulation domain is greater than or equal to the rev’s size. for this reason, the numerical method of homogenization dissim [15, 16] requires a new step for the rev. therefore, two rev types of have been chosen to be computed: the geometrical rev and the mechanical rev, in order to have more accuracy in the choice of the simulation surface of the homogenized rock mass. corresponding author: hatem gasmi engineering, technology & applied science research vol. 9, no. 4, 2019, 4448-4451 4449 www.etasr.com gasmi et al.: determination of fractured rock’s representative elementary volume by a numerical … ii. methodology a. geometric rev method the method used is to look for the smallest square whose center coincides with the center of the initial domain beyond which the value of the considered parameter does not change [7] (figure 1). fig. 1. finding the size of the geometric rev: centered square of increasing size the geometric rev’s calculation is based on the average spacing value between fractures. it is defined as the size of the domain beyond which the mean spacing between fractures remains constant. as for the mean spacing, its calculation requires special analysis. two spacings are determined in two different directions: espvert in the vertical direction and esphorz in the horizontal direction. the calculation steps are: • according to the two considered directions, several parallel and equidistant sampling lines are considered. • the number of fractures intercepting each line is calculated. • the average spacing on each line is calculated by dividing the length of the sampling line by the number of fractures. • the mean values of the two spacings, espvert and esphorz, of all sampling lines in the vertical direction and the horizontal direction respectively, are calculated using (1): / / espvert divert pvert esphorz dihorz phorz =      =  ∑ ∑ (1) where, pvert and phorz are respectively the number of sampling lines in the vertical direction and the horizontal direction, and divert and dihorz are the vertical and horizontal spacings on each line. b. search for the mechanical rev concerning the mechanical rev, and for each examined front, dissim can determine the equivalent young's modulus by increasing the size of the simulated surface. given the stochastic nature of the simulations from dissim program, 20 simulations can be performed. the average value obtained from the 20 simulations is taken as the young's modulus value. the rev size is that of the simulation surface from which the young's modulus becomes constant. iii. numerical development of dissim program to apply the proposed rev research methodology, a subroutine has been developed which consists of different modules as follow: • createhdr: in this module, successive domains are created from the initially simulated surface. after choosing the initial surface in the dissim module, the present subroutine creates centered squares of increasing surface starting with a domain of size 4m until reaching the surface of the initial domain, with a step of 1m. the fracturing data for each created domain are saved in text files named hdr_x with x being the size of the domain in question. • calculesp: this module is used in the search of the geometric rev based on the calculation of the average spacing between fractures. for each size domain x, the module starts by reading the existing fracture data in the square in question from file hdr_x. then, parallel and equidistant sampling lines (equidistance=1m) in both vertical and horizontal directions are created. for each sampling line, the average spacing between the fractures intercepting this line is calculated. the module will give as results on average vertical spacing and an average horizontal spacing for each domain. these results are recorded in a text file marked named resesp. • calculem: this module is used to find the mechanical rev based on the young’s modulus (em) calculation. similar to the preceding module, and for each size domain x, the data of the network of discontinuities existing in the domain considered are read from the hdr_x file. subsequently, the wave propagation procedure is repeated by calling each time the modules mesh, propag and calculation developed in [16], in order to calculate the em for each created surface. finally, the results generated by this calculation are saved in a text file called res. iv. real case study in order to complete the numerical homogenization of the studied fronts, it is necessary to calculate their rev. a detailed example about the research of geometric rev and mechanical rev of the f13 front of the el alto quarry (madrid, spain) was presented in [16]. a. field mapping campaigns using the scanline sampling method the discontinuity survey method applied on the study front is the scanline sampling method of the international society for rock mechanics (isrm). for each line, the parameters for any discontinuity through the scanline are systematically noted, namely, its location relative to a chosen reference (x), length, dip direction counted from the north axis, and dip angle engineering, technology & applied science research vol. 9, no. 4, 2019, 4448-4451 4450 www.etasr.com gasmi et al.: determination of fractured rock’s representative elementary volume by a numerical … measured from the horizontal plane. the field mapping campaigns of the f13 bench front are shown in table i. table i. results of the field mapping campaigns using the scanline sampling method (f13 bench front) front # line # direction (°) discontinuity x (cm) dip direction (°) dip angle (°) length (cm) f13 1 65 1 345 65 70 700 2 70 75 510 600 3 43 63 620 400 4 125 75 790 600 5 15 67 850 500 6 95 88 1110 300 7 101 90 1170 300 8 262 82 1250 100 9 235 76 1320 600 10 20 82 1410 500 11 215 82 1570 200 2 45 1 55 72 1650 300 2 255 85 1700 200 3 135 74 2020 600 4 35 85 2050 700 5 25 75 2130 500 6 50 85 2230 400 7 82 75 2400 300 8 74 64 2520 100 9 45 55 2630 500 10 15 67 3060 500 11 315 85 3160 500 12 137 85 20 300 13 132 84 30 700 3 60 1 5 79 320 600 2 35 73 330 500 3 98 69 360 200 4 326 80 460 400 5 326 80 490 400 6 107 75 510 500 7 82 65 540 200 8 82 65 560 200 9 82 65 600 200 4 285 1 32 74 180 300 2 69 54 520 500 3 55 52 610 300 4 55 52 650 300 5 332 85 1140 600 6 55 64 1510 500 7 333 88 1730 200 8 55 72 1650 300 9 255 85 1700 200 10 135 74 2020 600 15 35 85 2050 700 b. geometric rev for domains of size ranging from 4m to 20m and with a step of 1m, the average spacing is calculated according to the domain size (table ii) for both sounding directions (vertical and horizontal). the variation in vertical and horizontal mean spacing is shown in figure 2. it has been noticed that, for a size greater than 10m, the fluctuations of the value of the mean spacing become negligible in both directions as well as for the case of the average value which reaches a constant value of about 0.04m. from this result, the size of the geometrical rev was estimated at 10m. it has also been observed that for sizes greater than 17m, the average spacing starts to grow. this increase represents a perfectly explainable edge effect which schematizes a certain margin of error due to the absence of a few fractures, some of which exist inside the massif, but whose centers exist outside the domain. in this zone, the fracture density is lower which induces an increase in average spacing. table ii. spacing values by domain size domain size (m) esp vertical (m) esp horizontal (m) esp mean (m) 4 0.024 0.034 0.029 5 0.0268 0.0360 0.0314 6 0.0270 0.0367 0.0318 7 0.0282 0.0372 0.0327 8 0.0294 0.0382 0.0338 9 0.0302 0.0398 0.0350 10 0.0304 0.0404 0.0354 11 0.0306 0.0403 0.0355 12 0.0306 0.0404 0.0355 13 0.0307 0.0401 0.0354 14 0.0312 0.0401 0.0357 15 0.0314 0.0409 0.0361 16 0.0315 0.0411 0.0363 17 0.0333 0.0454 0.0393 18 0.0370 0.0461 0.0416 19 0.0376 0.0473 0.0425 20 0.0402 0.0525 0.0464 fig. 2. variation of vertical, horizontal and mean spacing of fractures as a function of domain size c. mechanical rev the parameter chosen in the search for the mechanical rev is the young's modulus of the rock mass. in the case of the f13 front, the mean value of the young's modulus is calculated for each domain whose size varies between 4m and 20m with a pitch of 1m. it should be noted that the maximum domain size can be increased if the rev is not reached within the proposed range. table iii presents the results of the calculation of the mechanical rev for the f13 front. it includes the value of the average young's modulus for each domain. this average value is calculated on the basis of 20 simulations carried out for each domain. the variation of the young's modulus as a function of the domain size is shown in figure 3. similar to the spacing calculation, it has been observed that for a size greater than 11m, the fluctuations of young's modulus become negligible. this parameter reaches a constant value of approximately 4.1gpa. based on this result, the size of the mechanical rev has been estimated at 11m. according to the literature, as long engineering, technology & applied science research vol. 9, no. 4, 2019, 4448-4451 4451 www.etasr.com gasmi et al.: determination of fractured rock’s representative elementary volume by a numerical … as the mechanical properties of the rock and the joints do not vary in the field, the geometrical rev and the mechanical rev are equivalent. table iii. average values of young’s modulus domain size(m) em (gpa) 4 1.05 5 1.46 6 1.89 7 2.35 8 2.78 9 3.20 10 3.67 11 4.14 12 4.10 13 4.11 14 4.16 15 4.14 16 4.12 17 4.08 18 4.50 19 4.58 20 4.70 fig. 3. value of the equivalent young's modulus according to domain size v. conclusion a numerical program called dissim has been developed. this tool, programmed under matlab environment, uses the isrm methodology to develop useful information on the structure of a rock mass. in general, the following results were obtained: • in order to push the analysis to the response of the rock mass with respect to the blast-induced propagation of variation, a subroutine was added to dissim to calculate the representative elemental volume of the studied mass. it consists of two modules: the first one to search for the mechanical rev and the second for the geometric rev. • to validate the numerical tool, the working methodology has been applied to real mass cases whose fracturing is quite complicated. it has been noted that the estimated geometric rev and mechanical rev are of comparable size. this is consistent with the findings of [7, 17]. • the size of the rev is estimated at 11m for the f13 front. this size is retained for the remaining of the homogenization calculation for this front. acknowledgment the present work was undertaken within the research project (no. 160717), funded by the deanship of scientific research, at the university of hail. references [1] j. c. s. long, j. s. remer, c. r. wilson, p. a. withespoon, “porous media equivalents for networks of discontinuous fractures”, water ressources research, vol. 18, no. 3, pp. 645-658, 1982 [2] a. pouya, a. courtois, “definition de la permeabilite equivalente des massifs fractures par des methodes d‘homogeneisation”, comptes rendus geoscience, vol. 334, no. 13, pp. 975-979, 2002 (in french) [3] a. pouya, “tenseurs de permeabilite equivalente d‘un domaine heterogene fini”, comptes rendus geoscience,vol. 337, no. 6, pp. 581588, 2005 (in french) [4] l. zhang, l. xia q. c. yu, “determining the rev for fracture rock mass based on seepage theory”, geofluids, vol. 2017, article id: 4129240, 2017 [5] k. b. min, l. jing, “numerical determination of the equivalent elastic compliance tensor for fractured rock masses using the distinct element method”, international journal of rock mechanics and mining sciences,vol. 40, no. 6, pp. 795-816, 2003 [6] l. xia, y. zheng, q. yu, “estimation of the rev size for blockiness of fractured rock masses”, computers and geotechnics, vol. 76, pp. 83-92, 2016 [7] m. chalhoub, a. pouya, “a geometrical approach to estimate the mechanical rev of a fractured rock mass”, 1st euro mediterranean symposium on advances on geomaterials and structures, hammamet, tunisia, may 3-5, 2006 [8] k. b. min, j. lee, o. stephansson, “implications of thermally-induced fracture slip and permeability change on the long-term performance of a deep geological repository”, international journal of rock mechanics and mining sciences, vol. 61, pp. 275-288, 2013 [9] m. pierce, p. cundall, d. potyondy, d. m. ivars, “a synthetic rock mass model for jointed rock”, in: rock mechanics: meeting society's challenges and demands, vol. 1, pp. 341-349, taylor & francis group, 2007 [10] w. s. dershowitz, h. h. einstein, “characterizing rock joint geometry with joint system models”, rock mechanics and rock engineering, vol. 21, pp. 21-51, 1988 [11] w. zhang, j. p. chen, c. liu, r. huang, m. li, y. zhang, “determination of geometrical and structural representative volume elements at the baihetan dam site”, rock mechanics and rock engineering, vol. 45, pp. 409-419, 2012 [12] g. b. baecher, n. a. lanney, h. h. einstein, “statistical description of rock properties and sampling”, 18th u.s. symposium on rock mechanics, colorado, usa, june 22-24, 1977 [13] j. chen, “3-d network numerical modeling technique for random discontinuities of rock mass”, chinese journal of geotechnical engineering, vol. 23, no. 4, pp. 397-402, 2001 [14] j. chen, b. f. shi, q. wang, “study on the dominant orientations of random fractures of fractured rock masses”, chinese journal of rock mechanics and engineering, vol. 24, no. 2, pp. 241-245, 2005 [15] h. gasmi, s. yahyaoui, e. hamdi, “a new tool for homogenization of jointed rock masses using wave propagation analysis”, 10th international symposium on rock fragmentation by blasting, new delhi, india, november 26-29, 2012 [16] h. gasmi, e. hamdi, n. b. romdhane, “a numerical homogenization of jointed rock masses using wave propagation simulation”, rock mechanics and rock engineering, vol. 47, no. 4, pp. 1393-1409, 2014 [17] k. esmaieli, j. hadjigeorgiou, m. grenon, “estimating geometrical and mechanical rev based on synthetic rock mass models at brunswick mine”, international journal of rock mechanics and mining sciences, vol. 47, no. 6, pp. 915-926, 2010 microsoft word etasr_v11_n1_pp6674-6679 engineering, technology & applied science research vol. 11, no. 1, 2021, 6674-6679 6674 www.etasr.com ullah et al.: seismic evaluation of the rc moment frame structure using the shake table seismic evaluation of the rc moment frame structure using the shake table hanif ullah department of civil engineering university of engineering and technology, peshawar peshawar, pakistan engrhanifullah@uetpeshawar.edu.pk muhammad rizwan department of civil engineering university of engineering and technology, peshawar peshawar, pakistan mrizwan@uetpeshawar.edu.pk muhammad fahad department of civil engineering university of engineering and technology, peshawar peshawar, pakistan fahadkhan@uetpeshawar.edu.pk syed azmat ali shah centre of disaster preparedness and management university of peshawar peshawar, pakistan engrazmatalishah@uop.edu.pk abstract-this paper presents the findings of an experimental investigation on a reinforced concrete frame structure (ordinary moment resistant frame). the test model was subjected to lateral excitation employing the 1994 northridge earthquake accelerogram. the reinforced concrete test model was fabricated in 1:3 reduced scale acquiring dimensional similarities. the utilized ingredient mix ratio was 1:1.65:1.75 and the water to binder ratio was 0.47. the dynamic characteristics (natural frequency and elastic viscous damping) were calculated using the free vibration record. story shear, drift, and displacement profiles were drawn using multiple excitation records along with damage patterns and capacity curves. the natural frequency of 2.47hz was calculated for the test specimen, which is equivalent to 1.41hz for the prototype. structural damping (elastic viscous) of 12.36% was calculated for the prototype. keywords-shake table testing; inter-story drift; story displacement; story shear; damage mechanism i. introduction the construction growth rate of reinforced concrete (rc) buildings is globally increasing. rc construction is primarily used in high raised and multi-story buildings such as hospitals, schools, and residential projects [1]. shake table testing is used to investigate the performance of both full and reduced scale test models. seismic response parameters, dynamic characteristics, and damage behavior can be examined for the test model if subjecting it to lateral loads on a shake table [2, 3]. the evaluation of dynamic characteristics and response parameters is important in seismic analysis and design of structures [4-6]. dynamic characteristics and response parameters of a 3d panel system were explored in [7], where the test specimen was scaled down as per the available payload capacity of the shake table. this work fabricated a reduced scale model of a typical prototype in pakistan for evaluating its response under lateral loads. in general, construction/design flaws comprise of poorer quality of concrete (low compressive strength), joints lacking ties, reduced flexural reinforcements in beam and column members, spacing of shear reinforcement larger than those specified in code, and avoiding seismic hooks [3, 8]. structures built with those deficiencies in high seismic zones are adversely affected by seismicity, leading to disastrous failures and consequent human and economic losses [9-11]. during model construction, concrete cylinders were also fabricated for evaluating compressive strength. this study was carried on a reduced scale reinforced concrete frame structure, subjected to lateral loads using a shake table. the model was first subjected to free vibration on the shake table (jerks) for the assessment of its dynamic characteristics (fundamental vibration period and structural damping), as in previous research studies [12]. the free vibration test was followed by dynamic testing using multiple runs of low to moderate and then sever excitations, i.e. from 5% to 100% of the 1994 northridge earthquake accelerogram. the time history of the 1994 northridge earthquake and some of its features were produced in detail [13]. the seismic assessment of rc frame structures using shake table reveals the viability of model configuration and material selection and checks the responses of other under-designed and code incompliant specimens [14-16]. ii. fabrication of the test specimen the test model is a representation of the typical prototype (two storys, one bay in the xand two in the y-direction) in pakistan. the plan view of the prototype is shown in figure 1. the middle frame was considered to have one bay and two storys as shown in figure 2. high-grade reinforcement steel (astm, a615, grade 60) was used. in the superstructure, the deformed bars i.e., ø4mm (#1) and ø7mm (#2) were used as required by the dimensional analysis, as the model was fabricated on a reduced scale [17]. the fabricated rc test specimen was identical to the typical frame (prototype) structure [18]. the beams were 304.8×457.2mm (12×18in), corresponding author: muhammad rizwan engineering, technology & applied science research vol. 11, no. 1, 2021, 6674-6679 6675 www.etasr.com ullah et al.: seismic evaluation of the rc moment frame structure using the shake table reinforced with 2ø20mm (2#6) top/bottom main/longitudinal bars, and ø10mm (#3) stirrups provided at 229mm center-tocenter distance. columns of the frame had dimensions of 304.8×304.8mm, were reinforced with 8ø20mm (8#6) main/longitudinal reinforcement and provisioned with ø10mm (#3) stirrups provided at 229mm center-to-center distance. the fabricated test specimen was lacking lateral ties in the beamcolumn joint [19]. the reinforcement and geometric detailing of the frame under consideration were identical to those of model-5 previously evaluated in [18, 20, 21]. the corresponding structural detailing for the test specimen is shown in figures 2 and 3. it is worth mentioning that during the construction of each story, three standard concrete cylinders were also fabricated for compressive strength evaluation as shown in figure 4. fig. 1. prototype plan configuration. fig. 2. prototype elevation and structural detailing. fig. 3. beam and column section detailing (prototype). five displacement transducers and five accelerometers were installed at appropriate locations on the model to record the displacement and acceleration response. similitude scale factors were used in data analysis for converting the parameters in respect of the prototype [22]. story shear, drift, and displacement profiles were plotted for each story in each run, as in [23]. the displacement versus base shear curve was also plotted to reveal the deformation capacity of the test specimen. the fabricated cylinders were tested using a universal testing machine. the average compressive strength for the concrete was calculated as 29.27mpa. fig. 4. standard concrete cylinders. table i. test runs load tons (kip) area mm 2 (in 2 ) strength mpa (ksi) average mpa (ksi) 58.4 (128.48) 18248.99 (28.29) 31.37 (4.55) 29.27 (4.25) 60.2 (132.44) 18248.99 (28.29) 32.34 (4.69) 52.4 (115.28) 18248.99 (28.29) 28.15 (4.08) 57 (125.40) 18248.99 (28.29) 30.62 (4.44) 47.5 (104.50) 18248.99 (28.29) 25.52 (3.70) 51.4 (113.08) 18248.99 (28.29) 27.61 (4.01) iii. experimental scheme a. shake table the test specimen was subjected to lateral loads on the shake table test available at the earthquake engineering centre, university of engineering and technology, peshawar, pakistan as shown in figure 5. some recent studies on the response of an rc model subjected to lateral loads were also used [19, 24]. b. instrumentation after anchoring the model on the shake table, transducers and accelerometers were installed at various locations. one accelerometer was installed at the center of the pad of the model and one at the right/left corner through the centerline of each slab. similarly, displacement transducers were installed on the reference frame at an appropriate location. details of instrumentation are shown in figure 5. fig. 5. instrumentation plan of the test specimen. engineering, technology & applied science research vol. 11, no. 1, 2021, 6674-6679 6676 www.etasr.com ullah et al.: seismic evaluation of the rc moment frame structure using the shake table c. time history and testing protocol the accelerogram of the 1994 northridge earthquake (figure 6), was utilized for dynamic simulation of the test model having a pga of 0.57g. fig. 6. acceleration time history (northridge 1994) the testing protocol, shown in table ii, comprised of free vibration and multiple excitations (dynamic runs). the purpose of multiple excitations was to simulate the specimen from low to moderate and then severe (disastrous) shaking. in each run, damages were also examined to notice the adequacy of the ordinary moment resistant frame (omrf) structure under the lateral loads on the shake table. table ii. test runs time history intensity 1994 northridge free vibration self-check (jerks) 5% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% iv. results a. data analysis seismosignal was used for the filtering and base-line correction of the data recorded in each run, as employed in [18, 25, 26]. after base-line correction and noise removal the corrected data were analyzed using microsoft excel for the calculation of dynamic characteristics, story shear, inter-story drift, displacement profile, etc. deformation versus base shear curve was also plotted using multiple run records. b. dynamic characteristics recorded data were used to evaluate the dynamic characteristics, story shear, drift, and displacement profile. the fundamental frequency was calculated as 2.47hz (0.41s) for the test specimen, as shown in figure 7. this indicates the prototype fundamental duration of vibration calculated using a similitude factor of: √3� 0.41 � 0.71 fig. 7. fundamental frequency of the test specimen. elastic viscous damping was calculated using the decay function proposed used in [27]: ζ = � �� � ln�a�/a�� where ζ is the coefficient of elastic-viscous structural damping, a1 is the peak amplitude of displacement at the reference point 1, an is the peak amplitude after n cycles at the reference point, and n the number of cycles between the considered peaks. the measured damping based on the last two cycles of displacement response is shown in figure 8. the structural damping measured was 12.36% for the frame. fig. 8. free vibration test for calculation of damping. c. inter-story shear the inter-story and base shear was measured using the records from multiple runs. the stiffer the structural system, the higher is the amount of shear and moment it absorbs. the base shear increased while subjecting the model to moderate and then sever intensity excitations in comparison to low intensity runs. this means that the base shear demand is high in case of sever shaking. the observed base and story shear are shown in figures 9, 10, 11, and 12 for some selected runs. fig. 9. 20% excitation of the 1994 northridge earthquake. d. inter-story drift profile inter-story drift was calculated while normalizing the story displacement at story levels. drift increased from low to engineering, technology & applied science research vol. 11, no. 1, 2021, 6674-6679 6677 www.etasr.com ullah et al.: seismic evaluation of the rc moment frame structure using the shake table moderate and then high as shaking intensity increased from 5% to 100%. both positive and negative drifts were calculated for all runs. the profiles are shown in figures 13-16 for some selected runs. a drift value greater than 2.5% indicates increased danger, while drift greater than 10% means the overall collapse of the structure. fig. 10. 30% excitation of the 1994 northridge earthquake. fig. 11. 80% excitation of the 1994 northridge earthquake. fig. 12. 100% excitation of the 1994 northridge earthquake. fig. 13. 20% excitation of the 1994 northridge earthquake. fig. 14. 30% excitation of the 1994 northridge earthquake. fig. 15. 80% excitation of the 1994 northridge earthquake. fig. 16. 100% excitation of the 1994 northridge earthquake. e. inter-story displacement profile multiple records of dynamic excitations were analyzed and processed for story displacement profiles. both in negative and positive direction, the displacement profiles were plotted as shown in figures 17-20 for some selected runs. it can be observed that high-intensity shaking caused large lateral displacement on the model. fig. 17. 20% excitation of the 1994 northridge earthquake. fig. 18. 30% excitation of the 1994 northridge earthquake. fig. 19. 80% excitation of the 1994 northridge earthquake. engineering, technology & applied science research vol. 11, no. 1, 2021, 6674-6679 6678 www.etasr.com ullah et al.: seismic evaluation of the rc moment frame structure using the shake table fig. 20. 100% excitation of the 1994 northridge earthquake. f. capacity curve the capacity curve [28-30] is plotted in figure 21. the idealized elastic-plastic curve using the energy balance equation was also drawn to pinpoint the equivalent value for ultimate displacement and the corresponding base shear, as used in [30]. fig. 21. capacity curve of the tested specimen under shake table testing. the details of the top floor displacement and the corresponding base shear are given in table iii for various intensity excitations of the 1994 northridge earthquake. table iii. displacement and base shear run level displacement mm (in) base shear kn (kip) self-check-1o 23.47 (0.92) 66.06 (14.85) self-check-1a 48.35 (1.90) 100 (22.48) self-check-1b 63.35 (2.94) 111.7 (25.11) self-check 1 95.16 (3.75) 131.14 (29.48) 50% 121.59 (4.79) 148.72 (33.44) 60% 141.46 (5.57) 159.95 (35.96) 90% 167.18 (6.58) 169.34 (38.07) 100-1% 173.26 (6.82) 167.68 (37.70) 100-2% 177.94 (7.00) 167.61 (37.68) fig. 22. vertical and horizontal flexural cracks in in-plane beam. g. damage mechanism no damages and cracks were noticed during low-intensity runs. upon moderate-intensity runs, cracks were produced in the beams at the ground and first floor. during the sever excitation, the existing cracks were further aggravated. figures 22-24 show a few cracks and damages marked. figure 25 shows the spalling of concrete from the peripheral beamcolumn joint along with minor damages. fig. 23. distribution of cracks beam (in-plane). fig. 24. flexural cracks at the top end of a column. fig. 25. spalling of concrete. v. conclusion this work presented the seismic response evaluation of rc moment resisting frame structures on 1/3 scale reduced model via shake table testing. the response of the test model under uni-directional lateral excitations was obtained in terms of dynamic characteristics profiles for inter-story shear, and displacement drift. damage mechanism and prototype model capacity curves were also obtained. the following findings were noticed: • the calculated natural period of vibration and elasticviscous damping for the prototype were 0.71s and 12.36% respectively. • the base and inter-story shear were higher in the highintensity excitation runs in contrast to low-intensity excitations. • it was also evident that the calculated story displacement and drift were within limits. the highest drift noted was engineering, technology & applied science research vol. 11, no. 1, 2021, 6674-6679 6679 www.etasr.com ullah et al.: seismic evaluation of the rc moment frame structure using the shake table less than 2.5%. moreover, in high intensity runs, displacement and drift were higher than moderate and lowintensity runs. • the ultimate floor displacement of 177.94mm and the base shear of 152.406kn for the 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[30] r. a. hakim, m. s. a. alama, and s. a. ashour, "seismic assessment of an rc building using pushover analysis," engineering, technology & applied science research, vol. 4, no. 3, pp. 631–635, jun. 2014, https://doi.org/10.48084/etasr.428. microsoft word etasr_v13_n4_pp11197-11203 engineering, technology & applied science research vol. 13, no. 4, 2023, 11197-11203 11197 www.etasr.com alsharif et al.: ids in iot using machine learning and blockchain ids in iot using machine learning and blockchain nada abdu alsharif department of information technology, college of computer and information sciences, majmaah university, saudi arabia nadaabdu120@email.com (corresponding author) shailendra mishra department of information technology, college of computer and information sciences, majmaah university, saudi arabia s.mishra@mu.edu.sa mohammed alshehri department of information technology, college of computer and information sciences, majmaah university, saudi arabia ma.alshehri@mu.edu.sa received: 27 april 2023 | revised: 17 may 2023 and 22 may 2023 | accepted: 30 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5992 abstract the rise of iot devices has brought forth an urgent need for enhanced security and privacy measures, as iot devices are vulnerable to cyber-attacks that compromise the security and privacy of users. traditional security measures do not provide adequate protection for such devices. this study aimed to investigate the use of machine learning and blockchain to improve the security and privacy of iot devices, creating an intrusion detection system powered by machine learning algorithms and using blockchain to encrypt interactions between iot devices. the performance of the whole system and different machine learning algorithms was evaluated on an iot network using simulated attack data, achieving a detection accuracy of 99.9% when using random forrest, demonstrating its effectiveness in detecting attacks on iot networks. furthermore, this study showed that blockchain technology could improve security and privacy by providing a tamper-proof decentralized communication system. keywords-iot; blockchain; cyber security; neural networks; ids; machine learning i. introduction the iot is a cutting-edge innovation with explosive growth, enormous influence, and great promise. iot refers to a network of devices that share data to enable new applications. iot devices exist in a variety of shapes and sizes, ranging from low-power equipment to smart objects. using iot, processes can be automated, saving time and money. instruments, cameras, and other iot devices frequently collect data that are then transmitted to a server for evaluation and tracking. the quality of the information stored on the server should be maintained in a way to prevent malicious attempts to modify the data, while other individuals and systems must always have access to the data [1]. the expansion of iot networks has led to a growth in the number of iot devices, with an estimated increase from 7.74 in 2019 to 25.44 billion in 2030. the fundamental issue with these gadgets is that security is generally not taken into consideration, as the login and password are often not modified during deployment. so, iot devices have become the primary target of attackers, as they attempt to breach them to launch distributed denial-of-service (ddos) attacks or use them as botnets to steal data [2]. this is evident from the estimated 105 million attacks on iot devices in the first half of 2019. various authentication methods, architectural designs, and algorithms have been proposed that take into account the resource constraints of iot devices [3-4]. iot networks are frequently linked to cloud computing and data centers. as iot devices typically generate a large amount of data, various algorithms are used to extract important information and automate processes. machine learning (ml) techniques are also used to create intrusion detection systems (idss). data from iot devices are often transferred to servers where they are stored before being examined [5]. typically, data should be kept in a way that protects their integrity and thwarts hostile attempts to alter them while being constantly accessible to other users and systems. data can be stored securely using blockchain (bc) [3]. the possibility of combining ml methods and bc approaches to address cyber engineering, technology & applied science research vol. 13, no. 4, 2023, 11197-11203 11198 www.etasr.com alsharif et al.: ids in iot using machine learning and blockchain risks in the iot area is a new concept that warrants further investigation. security and privacy are interconnected, and privacy is a collection of rules that vary depending on the application [5]. bc is made up of a series of linked blocks. the hash code of the preceding block is included in each new block when inserted. the header of the block includes the timestamp, the preceding block's hash, the block's hash code, and additional data. transactions make up the body of the block, which contains most of the bc data [6]. bc has attracted a lot of interest in addressing security issues in numerous systems, including banking, voting, education, etc. [7]. although the use of bc in iot systems has numerous benefits, such as decentralization, security improvement, tractability, and immutability, its implementation presents some difficulties. in [8], some of these issues were described when using bc with iot, such as storage, scalability, and vulnerabilities. corrupted data saved in bc is one of the vulnerability problems, due to the immutability of bc. thus, corrupted data must be detected before being transferred and stored in the bc. such corrupted data typically originate from infected devices. however, since bc must contain a substantial amount of data and must be scalable, iot uses a proof-of-authority consensus process. in contrast to the proof-of-work approach, this algorithm does not require additional computing to answer a mathematical problem [9]. it is crucial to identify the challenges and threats that these systems face and the potential consequences if they are not addressed. the distributed and resource-constrained nature of iot systems presents significant challenges in detecting and preventing attacks. attackers are becoming more sophisticated, making it easy to bypass traditional security measures, and the generation of massive amounts of data from iot devices raises privacy and security risks. the consequences of failing to address these challenges could be severe, including unauthorized access to sensitive data, disruption of critical services, financial losses, and damage to the reputation of organizations that deploy iot systems [10]. to address these challenges, innovative solutions, such as the combination of ml and bc techniques, can significantly improve the effectiveness and efficiency of idss in iot. such solutions could help mitigate the potential consequences of security breaches by providing more robust and effective security measures [11]. the network architecture is constructed for a reputation transfer mechanism, adopted for the reputation value performance analysis system. usually, the network architecture uses low-power ieee 802.11 wi-fi for data communication [12]. effective internet communication is structured with a monitoring system, cloud computing, a server, and a database management system. the network server is connected through a firewall and accepts details, while operations are processed through virtual servers and data centers [13]. traditional security measures face challenges in detecting and preventing attacks due to the distributed and resource-constrained nature of iot systems. to address these challenges, innovative solutions are needed, such as the combination of ml and bc technology [14]. a proof-of-authority process can be used to ensure scalability and efficient data handling, as this algorithm eliminates the need for additional computing to answer a mathematical problem compared to the proof-of-work approach. several studies explored the potential benefits and drawbacks of using ml and bc in idss for iot and aimed to assess their effectiveness in improving security and privacy. the objectives included comparing the performance of ml and blockchain-based ids with traditional approaches, suggesting viable solutions to security and privacy vulnerabilities, evaluating the impact of adversarial attacks on ml algorithms, and assessing the effectiveness of combining ml and bc with other security methods [15]. this study aims to contribute to the development of a more secure and reliable iot ecosystem while addressing potential security and privacy concerns that may arise. this study aims to assess the effectiveness of using ml and bc for ids in iot devices. the main purpose was to examine the benefits and drawbacks of using ml and bc in ids for iot, as well as potential anonymity and safety risks. the primary objectives are to:  compare the performance of ml and bc in ids for iot devices with traditional ids approaches.  identify and suggest viable solutions to the security and privacy vulnerabilities raised by the use of ml and bc in ids for iot.  examine the possible impact of adversarial attacks on ml algorithms and find techniques to defend against such attacks.  assess the impact of combining ml and bc with other security methods, such as encryption and access control, in the development of holistic security solutions for iot systems.  contribute to the development of a more secure and reliable iot ecosystem by exploring the potential of using ml and bc in ids, while also addressing potential security and privacy concerns that may arise. ii. literature review several studies explored the challenges and vulnerabilities in iot systems, such as the lack of security measures and the susceptibility of devices to attacks. in [16], a widespread ids was proposed that used fog computing to detect ddos attacks against edge nodes in bc-based iot networks. the system's efficacy was assessed using an actual iot-based dataset that included current assaults in bc-based iot networks. random forest (rf) and xgboost trained on dispersed fog nodes were used to measure performance. xgboost beat rf in binary attacks, whereas rf exceeded xgboost in terms of multiattack detection. furthermore, compared to xgboost, rf needed less time for instruction or testing on dispersed fog nodes. in [17], pattern recognition, ai, and bc were examined to address iot security challenges, highlighting the security concerns that can be handled using them and the research obstacles that must be addressed. in [18], a random subspace learning knn was used to protect against forged commands aiming at manipulating an industrial control process, and a bcengineering, technology & applied science research vol. 13, no. 4, 2023, 11197-11203 11199 www.etasr.com alsharif et al.: ids in iot using machine learning and blockchain based integrity checking system (bics) was used to prevent misrouting attacks that alter the openflow rules of sdnenabled industrial iot systems. in [19], an ids based on neural network clustering was proposed to help administrators identify and reduce the risk of attacks in the early stages, reducing power consumption. the rp protocol has a clear objective and enables real-time applications to conserve energy while ensuring security. increasing the number of online applications that require protection against different risks, the demand for security will only increase. an ml system was proposed to address the nonlinear identity problem, detect faults, and reconstruct the system. to detect and classify malicious attacks on network integrity and node power consumption in a wireless sensor network, a self-organizing map could be trained to monitor the network using a learning technique and identify any nodes that behave abnormally. in [20], the possible uses and limitations of distributed ledger technology were explored in domains that interact with social impacts, including social justice and concerns. there is a research gap that lies in the security issues related to ids in the iot when using ml and bc. while ml and bc offer potential benefits in enhancing the security and privacy of iot devices, there are security concerns that need to be addressed to ensure the effectiveness of ids. one specific security challenge is the potential for adversarial attacks on ml algorithms. adversaries can manipulate the input data to cause misclassification or other errors in the ml model. this can lead to ids failing to detect intrusions or flag benign behavior as malicious. techniques such as adversarial training and input sanitization can be employed to mitigate these attacks and improve the robustness of the ml model. previous studies have shown that ml algorithms can effectively detect anomalous behavior in iot devices, making them suitable for ids applications. a major challenge is that ml algorithms require large amounts of data to train effectively. this can be a problem in the context of iot, as devices may have limited processing and storage capabilities. furthermore, ml algorithms may be vulnerable to attacks that can be used to fool the algorithm into making incorrect predictions [21]. another challenge is to develop a system that can efficiently and securely store the large amounts of data required for the ml algorithms to work effectively. additionally, more research is needed on how to effectively integrate ml algorithms with bc in the context of iot [22]. future research should focus on developing efficient and secure data storage systems and explore ways to integrate ml algorithms with bc in iot [23]. iii. research methodology a. system design the proposed system was designed to improve the security of iot devices using ml and bc to detect and prevent intrusions and preserve the integrity of the data generated by these devices. the system consists of four main components: iot devices, an ids, bc nodes, and the bc network. iot devices are responsible for collecting data from the environment and sending it to the ids. the ids is the first line of defense against intrusions, and its primary function is to identify any compromised devices and remove any corrupt data. the ids was powered by ml algorithms to detect unusual patterns in the data generated by iot devices. this allows the ids to distinguish normal and abnormal data and identify devices that are compromised or behave suspiciously. when the ids has filtered the regular data, they are forwarded to the bc nodes. these nodes encrypt the data and send them to the bc network. the bc network is public, accepts signed data from the bc nodes, and creates a block containing the data. the bc network ensures that data are authentic and irrevocable and provides a decentralized architecture for iot devices, improving data preservation security. bc networks are in charge of validating the data and ensuring that only legitimate data is uploaded to the bc network. this is achieved by using cryptography, such as cryptographic algorithms and sha256. the bc servers are also in the position of safeguarding the bc network by verifying new blocks and keeping the network safe. the suggested solution for intrusion prevention in iot intends to improve iot device security by identifying and blocking intrusions and protecting the integrity of data generated by these devices. fig. 1. system design. engineering, technology & applied science research vol. 13, no. 4, 2023, 11197-11203 11200 www.etasr.com alsharif et al.: ids in iot using machine learning and blockchain b. proposed ids using ml and bc (ids-mlbc) an ids can employ a variety of ways to identify assaults in iot networks. for example, the signature-based strategy identifies attacks based on certain characteristics or patterns in network traffic. signature-based intrusion detection systems are excellent at identifying attacks with attack patterns, but they may fail to detect new or undiscovered malware assaults because their structures or signatures are not yet recognized. anomaly-based techniques were developed to alleviate this restriction using ml algorithms to provide a reliable activity model. any traffic that does not match this model is deemed suspicious and labeled as a possible attack. as they do not rely on existing signatures, anomaly-based ids can identify fresh or undiscovered malware threats. furthermore, as ml-based algorithms may be taught on a variety of applications and hardware configurations, they offer higher generalization features. the initial component of the platform are the iot devices that collect data and transfer them to the ids for analysis. the ids is responsible for identifying infected devices and removing damaged data. various ml methods were chosen for this procedure, based on their prominence and time efficiency. the proposed framework offers several advantages over traditional security measures. first, the use of ml algorithms allows the detection of compromised devices with high accuracy and efficiency, minimizing false positives and negatives. second, the use of bc improves the security of data storage in a decentralized manner, making it more resistant to attacks. finally, the use of feature selection techniques allows for the identification of the most important features to detect compromised devices, improving the efficiency of the ids. c. ids algorithm the ids algorithm consists of the following steps:  step 1: collect data from iot devices.  step 2: check if the device is compromised using an mlbased ids. if the device is compromised: filter corrupted data. else: sign data using public key cryptography.  step 3: add signed data to bc nodes.  step 4: train a machine learning model using relevant features to detect compromised devices.  step 5: use the trained model to predict if a device is compromised based on collected data.  step 6: if the reputation value (rv) equals 0 to n: create a new transaction (nt) with an attached reputation value: nt(rv).  step 7: if rv equals rv-1, terminate.  step 8: validate the block for nt(rv).  step 9: verify all values of the transaction.  step 10: if nt(rv) is greater than 1: insert a new transaction nt(rv).  step 11: end. iv. experimental setup a. setup for investigation this model was implemented in jupyter notebook format, along with the code used to obtain the results. the model was implemented in python [21]. the following steps were used to implement the ml-based ids in iot:  collect and preprocess the dataset: this step involved collecting data from iot devices and pre-processing it to remove any noise or outliers. the pre-processed data were then split into training and testing sets.  design the neural network architecture: this step involved selecting the appropriate neural network architecture, such as a feedforward or a convolutional neural network. the number of layers and nodes in each layer were also determined in this step.  train the neural network: this step involved using the training set to train the neural network. the weights and biases of the network were adjusted during this process to minimize the error between the predicted and actual output.  evaluate the neural network: this step involved evaluating the performance of the trained neural network on the testing set. metrics such as accuracy, precision, recall, and f1score can be used to evaluate the performance. b. machine learning for ids 1) dataset nsl-kdd is a network intrusion detection dataset, which is an improvement over the original kdd cup '99 dataset. the nsl-kdd dataset has been modified to remove redundant records and balance the number of records in each category. it is a widely used dataset in studies related to network idss [24]. the nsl-kdd dataset contains various features related to network traffic, such as the number of bytes and packets transmitted, the protocol used, and the source and destination ip addresses. it also contains various attack categories, including denial of service (dos), probe, remote to local (r2l), and user to root (u2r). 2) model evaluation and validations the accuracy, precision, recall, and f1-score metrics were used. accuracy measures correctly classified instances, while precision and recall measure true positives and false negatives, respectively. the f1-score is the harmonic mean of precision and recall and provides a more balanced measure of performance. 3) machine learning the validation procedure involves training the model on a training set, evaluating its performance on a separate testing set using appropriate evaluation metrics, and potentially engineering, technology & applied science research vol. 13, no. 4, 2023, 11197-11203 11201 www.etasr.com alsharif et al.: ids in iot using machine learning and blockchain employing additional validation techniques to ensure the reliability and effectiveness of the developed models. linear regression (lr) is a simple and commonly used method for predictive modeling and works by finding a linear relationship between the independent and dependent variables and then using it to make predictions. table i. the nsl kdd dataset dataset number of records total normal dos probe u2r r2l kddtrain+20% 25192 13449 (53%) 9234 (37%) 2289 (9.16%) 11 (0.04%) 209 (0.8%) kddtrain+ 125973 67343 (53%) 45927 (37%) 11656 (9.11%) 52 (0.04%) 995 (0.85%) kddtest+ 22544 9711 (43%) 7458 (33%) 2421 (11%) 200 (0.9%) 2654 (12.1%) fig. 2. lr result. fig. 3. knn result. the k-nearest neighbors (knn) is a non-parametric ml algorithm that can be used for classification and works by finding the k closest data points to a given input and using the majority vote or averaging their output values to make a prediction. the decision tree (dt) is a popular ml algorithm for both classification and regression that uses a flowchart-like structure to represent different decisions and their possible consequences. random forest (rf) is an ensemble learning algorithm that uses multiple decision trees to improve the accuracy and robustness of predictions. it works by training multiple decision trees on random subsets of the data and then combining their outputs to make a final prediction. support vector machines (svm) is a powerful ml algorithm for classification and regression problems that works by finding the optimal hyperplane that separates the different classes of data points in a high-dimensional space. fig. 4. dt result. fig. 5. rf result. the model consisted of five densely connected layers with different numbers of neurons, nonlinear activation functions, and dropout regularization to prevent overfitting. the first layer had 64 neurons, followed by two more hidden layers with 128 and 512 neurons, respectively. all these layers have the rectified linear unit (relu) as the activation function. the output layer had a single neuron, which used the sigmoid activation function to produce a binary classification result. in addition, the model used l1l2, l2, and activity regularization techniques to reduce overfitting, which are commonly used for this reason. l1l2 regularization applies both l1 and l2 regularizations to the model, whereas l2 regularization adds engineering, technology & applied science research vol. 13, no. 4, 2023, 11197-11203 11202 www.etasr.com alsharif et al.: ids in iot using machine learning and blockchain the square of the weights to the loss function, and activity regularization adds a penalty to the activation values to encourage the network to produce more sparse representations. overall, this model is a powerful tool for binary classification problems, as it can learn complex patterns from the data and produce accurate predictions on unseen data. fig. 6. svm result. v. results to evaluate the performance of the proposed ml and bcbased ids, several models were trained and tested on an iot traffic dataset. table ii presents the results of the comparison. table ii. machine learning model comparisons. model accuracy recall precision lr 87.6% 91.80% 83.81% knn 99.05% 98.73% 99.22% naïve bayes 91.80% 89.47% 92.62% svm 97.48% 96.70% 97.85% dt 99.90% 99.98% 99.84% rf 99.99% 99.99% 99.99% nn 97.53% 97% 97% fig. 7. the accuracy of the models. the lr model had an accuracy of 87.60%, knn had 99.05%, nb had 91.80%, svm had 97.48%, dt had 99.90%, rf had 99.99%, and nn had 97.53%. for lr, the precision was 83.81% and recall was 91.80%. similarly, knn had a precision of 99.22% and recall of 98.73%, nb had a precision of 92.62% and recall of 89.47%, svm had a precision of 97.85% and recall of 96.70%, dt had a precision of 99.84% and recall of 99.98%, rf had a precision of 99.99% and recall of 99.99%, and nn had a precision of 97% and recall of 97%. figure 7 illustrates the accuracy of the models. vi. discussion the results of using rf for intrusion detection in iot systems are impressive, with a 99.9% accuracy score. this highlights the potential of this ml algorithm to improve the security of iot systems by detecting and preventing intrusions. the challenge for an ml-based ids is the potential for data poisoning attacks, where attackers inject malicious data into the training dataset to manipulate the behavior of the ml model. data poisoning attacks can also compromise the integrity and reliability of the system by inducing false positives or negatives. to mitigate these threats, a range of countermeasures can be employed, including data sanitization and validation, model robustness testing, and model interpretability and transparency. in addition, the integration of blockchain technology can enhance the security and privacy of ml-based ids by providing a decentralized and tamper-proof data management framework. the rf model achieved higher accuracy than the nn models from previous studies, as the rf is an ensemble of dts which are relatively simple models that are easy to train and interpret. by combining many dts, the rf model can capture complex patterns in the data without overfitting, which can lead to high accuracy. table iii. results comparison with other studies study method accuracy [17] k-means + rf and deep learning 85% [18] dnn binary 96% [19] dsste method 82% this study rf 99.99% fig. 8. rf features. the use of ml and blockchain technology in iot security can provide effective solutions to detect and prevent intrusions. however, the security and privacy threats associated with these technologies need to be carefully considered and addressed through a comprehensive and holistic approach that takes advantage of the strengths of different countermeasures and technologies. the adoption of hybrid approaches that combine engineering, technology & applied science research vol. 13, no. 4, 2023, 11197-11203 11203 www.etasr.com alsharif et al.: ids in iot using machine learning and blockchain ml algorithms with blockchain-based data management and access control mechanisms can provide a robust and effective solution to iot security challenges. future plans involve exploring different ml algorithms, evaluating using diverse datasets, enhancing robustness against adversarial attacks, addressing scalability and resource constraints, and further integrating bc technology. these steps will contribute to advancing the progress of the research and addressing the limitations to improve the effectiveness and practicality of mlbased intrusion detection in iot systems. vii. conclusion and future work the rise of iot devices has led to concerns about their security. one potential solution to these issues is the integration of ml and bc. this study compared various approaches and recommended the use of the random forest algorithm for intrusion detection in iot systems. the security of iot systems can be improved by combining ml algorithms with bc-based data management and access control mechanisms,. the proposed algorithm achieved an accuracy of 99.99%, highlighting the potential of ml to improve iot security. this study suggested several potential directions for future research. one possibility is to explore new techniques and approaches to enhance the development of ml algorithms for intrusion detection in iot systems. furthermore, it is important to evaluate the performance of different ml algorithms and bcbased solutions under real-world conditions to test their effectiveness. in the future, further studies could investigate the development of ml algorithms for intrusion detection and prevention in iot systems. although the random forest algorithm achieved high accuracy, new techniques and approaches can be explored to improve the performance and efficiency of ids. references [1] m. anwer, s. m. khan, m. u. farooq, and waseemullah, "attack detection in iot using machine learning," engineering, technology 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[24] t. su, h. sun, j. zhu, s. wang, and y. li, "bat: deep learning methods on network intrusion detection using nsl-kdd dataset," ieee access, vol. 8, pp. 29575–29585, 2020, https://doi.org/10.1109/ access.2020.2972627. microsoft word 4-2468_s_ca engineering, technology & applied science research vol. 9, no. 1, 2019, 3696-3698 3696 www.etasr.com irfan & almufadi: investigation of mechanical properties of shale rock in qassim region, saudi arabia investigation of mechanical properties of shale rock in qassim region, saudi arabia mohammad a. irfan department of mechanical engineering university of engineering and technology peshawar, pakistan mairfan@uetpeshawar.edu.pk fahad a. almufadi college of engineering qassim university saudi arabia almufadi@qec.edu.sa abstract—an investigation into the mechanical properties of shale rock from qassim province, saudi arabia is presented in this paper. uniaxial compression test, schmidt hammer test and porosity estimation were carried out. regarding the compression test, it was found that the strength ranged from 1.98mpa to 8mpa and the strain ranged from 0.53% to 2.5%. regarding the schmidt hammer test, it was found that the rebound values ranged from 22.4 to 25. the measurements of volumetric porosity indicated that the porosity in the shale rock ranged between 19.12% and 24.31%. all the values determined in this project match well with the published values of other studies about shale rock. keywords-shale rock; mechanical properties; qassim province; saudi arabia i. introduction shale oil and gas production from organic rich shale formations is a growing area of technical interest in oil and gas exploration. long horizontal wells with hydraulic fracturing are required to bring economic production from shale gas reservoirs. since crack propagation in hydraulic fracturing occurs under high strain rates, it is important to understand the fracture behavior of shale rock and its mechanical properties. the properties of shale rock that are needed in order to be able to design the hydraulic fracturing systems include: compressive strength, hardness, porosity, modulus of elasticity, poisson’s ratio, fracture toughness and permeability. rocks in general can be classified as: igneous rocks, sedimentary rocks, and metamorphic rocks. sedimentary rocks are made when products of weathering are subjected to transportation by water, winds or deposition and subsequently are compacted or consolidated. some examples are sandstone, shale, conglomerate, breccias, limestone, and coal. minerals forming sedimentary rocks are kaolinite, illite, smectite, hematite, rutile, corundum and so on. shale is basically a sedimentary rock with fine grains, composed of mud which is a mixture of flakes of clay minerals and small particles of other minerals, mostly quartz and calcite. numerous experimental and theoretical investigations have demonstrated how mechanical properties in sedimentary rocks are affected by porosity [1], clay content [2], overburden stress and pore fluid [3]. further understanding needs to be developed on how these parameters control rock strength. the aim of this paper is to test the mechanical properties of saudi shale rock from qassim province, under static loading. rock samples were taken from shale formations in qassim region, saudi arabia. uniaxial compression test, schmidt hammer test and porosity estimation were carried out. ii. literature review a. uniaxial compression test of shale rock weak rocks are defined by their ultimate compressive strength (ucs) in the range of 0.25 to 25mpa [4]. a good strength limit for weak rocks may be 20mpa because rocks weaker than this behave differently when sheared [5]. sedimentary rocks such as sandstone, siltstone, shale, claystone or mudstone, clay-shale fall under the classification of weak rocks [6, 7]. the prime factor affecting the strength of weak rocks is porosity. commonly, high porosity gives low strength and vice versa. table i summarizes some available strength data for sandstone and shale. it can be seen that higher porosity leads to weak compressive strength. table i. compressive strength as related to porosity reference location porosity % compressive strength (mpa) [5] kidderminster (uk) ~31 2 to 3 [8] bringelly shale, australia 7% to 14% 2.4 to 49 b. schmidt hammer test schmidt hammer test is commonly used for testing different rocks and has a strong correlation with ucs through numerous empirical equations. schmidt hammer rebound (r) values were directly used in the analysis and were not converted to ucs, since there is no standard conversion designated for shale. table ii shows the range of r values for sevier and rome shale [9]. table ii. shale rock compressive strength estimation [9] type of shale schmidt hammer rebound (r) sevier shale 30 rome shale 38 corresponding author: m. a. irfan engineering, technology & applied science research vol. 9, no. 1, 2019, 3696-3698 3697 www.etasr.com irfan & almufadi: investigation of mechanical properties of shale rock in qassim region, saudi arabia c. porosity porosity is defined as the fraction of a rock occupied by pores. it is a static property which can be measured by various methods in the absence of fluid flow. to find effective porosity fluid flow is required to ascertain whether the pores are interconnected. table iii presents some data on average porosity. nearly all the measurements were made at room temperature and pressure of 1 atmosphere [10]. table iii. average porosity for shale rock [10] title average porosity (ф) shale (near ponca city, oklahoma) 42.5% shale (eastern venezuela) 33.5% shale (los manueles field, venezuela) 20.0% shale (ponca city and garber areas, oklahoma) 17.0% weston shale (bonner springs, kansas) 15.8% chanute shale (independence, kansas) 14.9% iii. materials and methods shale rock samples were collected from a local cement quarry in qassim, saudi arabia. a total of 40 samples were obtained for initial testing. a. specimens preparation the cutting of samples was completed in the civil engineering lab at qassim university, using its sample preparation machine. it took five days to complete prepare the specimens to finally obtain only 20 proper samples out of 40. figure 1 shows the shale samples before they were cut into cubical shapes. the specimens were cut as 50mm×50mm×50mm cubes as per astm c 109/c 109m. there may be some errors in the dimensions due to the difficulty in precision cutting of soft rocks. also, there is a maximum expected dimension error of ±2mm. fig. 1. samples before cutting iv. results and discussion a. uniaxial compression test the laboratory uniaxial compressive strength is the standard strength parameter of intact rock material. an mts universal tensile testing machine used with capacity of 25kn was used. table iv shows the results of the compression test. the average strength of the 4 samples used is 2.5mpa. table iv also shows the strain values of the 4 samples. the maximum is 2.5% for sample 3 and the minimum is 0.91% for sample 1, while the average is 1.46%. it is important to compare the results with previous ones, to observe and discuss their differences. table v represents the uniaxial compressive strength of shale rock and its associated porosity, from [5], in comparison with qassim shale results investigated in this paper. the average porosity of qassim shale was 22.54%. the average ucs of qassim shale was 2.5mpa which is well within the range of internationally published values as shown in table v. table iv. tensile test summary sample no. strength (mpa) strain (%) 1 2.13 0.91 2 2.38 1.26 3 3.53 2.5 4 1.98 1.16 table v. results comparison reference location porosity % compressive strength (mpa) [5] kidderminster (uk) ~31 2 to 3 [8] bringelly shale, australia 7% to 14% 2.4 to 49 current study qassim, saudi arabia 19% to 24% 1.98 to 3.53 b. schmidt hammer test three samples were tested by schmidt hammer. the dimensions of the samples were 50mm×50mm×50mm. an ntype schmidt hammer with an impact energy of 2.2n.m was used to measure rock hardness. table vi shows pictures of the three samples before and after the test. it also shows the rebound and strength values obtained. the maximum rebound value was in sample 2, where sample 3 had the minimum value. note that the empirical relation used to estimate the compressive strength in [11] could not be valid for the specimens used in this test. table vi. schmidt hammer test results name before test after test rebound value (r) s h -2 0 1 6 -0 1 23.5 s h -2 0 1 6 -0 2 25 s h -2 0 1 6 -0 3 22.4 tables vii-viii show the results of this study in comparison with previously published results [9]. engineering, technology & applied science research vol. 9, no. 1, 2019, 3696-3698 3698 www.etasr.com irfan & almufadi: investigation of mechanical properties of shale rock in qassim region, saudi arabia table vii. results comparison with sevier shale [9] sample number of current study absolute difference of schmidt hammer rebound value (r) difference of schmidt hammer rebound value (%) sh-2016-01 6.5 21 sh-2016-02 5 16 sh-2016-03 7.6 25 table viii. results comparison with rome shale [9] sample number of current study absolute difference of schmidt hammer rebound value (r) difference of schmidt hammer rebound value (%) sh-2016-01 14.5 38 sh-2016-02 13 34 sh-2016-03 15.6 41 c. determination of porosity mathematically, porosity can be defined by (1): �������� = ф = �� � = � ��� � (1) where ф: porosity (%), vb: bulk volume (cm 3 ), vp: pore volume (cm 3 ), and vm: matrix volume (grain volume) (cm 3 ). vb of the sample was measured by the volumetric displacement method. vm was measured by crushing the sample to grain size and immersing it in a container filled with water. substituting the results in (1) we have the results shown in table ix: table ix. summary of results sample no. porosity (ф) 1 19.12% 2 24.15% 3 24.31% table x shows the porosity results comparison of shale rock in current study and in [10]. it can be seen that porosity measured values lie within the range of other published values. table x. comparison with [10] title average ф[10] qassim average ф percent difference shale (near ponca city, oklahoma) 42.5% 22.53% +20.03% shale (eastern venezuela) 33.5% +10.03% shales (los manueles field, venezuela) 20% -2.53% shale (ponca city and garber areas, oklahoma.) 17% -5.53% weston shale (bonner springs, kansas) 15.8% -6.73% chanute shale (independence, kansas) 14.9% -7.63% v. conclusion and future work uniaxial compressive strength was tested for 4 different samples, ranged from 1.98mpa to 5mpa and with an average of 2.5mpa, while the strain ranged between 0.91% and 2.5% and had an average of 1.46%. the schmidt hammer test results found that the rebound values ranged from 22.4 to 25. displacement method was used to determine the qassim shale rock porosity, the results were 19.12%, 24.15% and 24.31% and the average porosity was 22.53%. the samples for this study were taken from a cement quarry. in future, samples can be derived from the drilling core, because that would give more meaningful results for shale gas exploration. another suggestion is to calculate shale rock’s modulus of elasticity and poisson's ratio. schmidt hammer can be done with a lighter ltype schmidt hammer, which has impact energy 0.735n.m. in addition, impact tests can also be conducted. acknowledgement authors would like to thank undergraduate students suhail a. aswailem, abdurehman s. alquba and ahmed m. alhasan for conducting the experiments as a part of their senior project. references [1] m. r. wyllie, a. r. gregory, g. h. f. gardner, “an experimental investigation of factors affecting elastic wave velocities in porous media”, geophysics, vol. 23, pp. 459-493, 1957 [2] d. han, a. nur, d. morgan, “effect of porosity and clay content on wave velocity in sandstones”, geophysics, vol. 51, pp. 2093-2017, 1986 [3] m. s. king, “static and dynamic elastic properties of rocks from the canadian shield”, international journal of rock mechanics and mining sciences & geomechanics abstracts, vol. 20, no. 5, pp. 237-241, 1983 [4] r. ulusay, the isrm suggested methods for rock characterization, testing and monitoring: 2007-2014, springer, switzerland, 2015 [5] l. dobereiner, m. h. de freitas, “geotechnical properties of weak sandstones”, geotechnique, vol. 36, pp. 79-94, 1986 [6] j. c. jaeger, n. g. w. cook, r.w. zimmerman, fundamentals of rock mechanics, blackwell publishing, 2007 [7] s. klein, “an approach to the classification of weak rock for tunnel projects”, 2001 rapid excavation and tunneling conference, san diego, usa, june 11-13, 2001 [8] w. ezzat, engineering performance of bringelly shale, phd thesis, university of sydney, 2005 [9] a. nandi, c. m. liutkus, m. j. whitelaw, “geotechnical characterization of sevier and rome shale, east tennessee”, 43rd u.s. rock mechanics symposium and 4th u.s. –canada rock mechanics symposium, asheville, usa, june 28-july 1, 2009 [10] g. e. manger, porosity and bulk density of sedimentary rocks, us government printing office, 1963 [11] f. i. shalabi, e. j. cording, o. h. al-hattamleh, “estimation of rock engineering properties using hardness tests”, engineering geology, vol. 90, no. 3-4, pp. 138-147, 2007 authors profile mohammad a. irfan did his phd in mechanical engineering from case western reserve university, cleveland, oh, usa in 1998. following his phd he worked for 2 years in the us industry. his work was related to the design of industrial burners. he has been awarded with the fulbright postdoctoral fellowship in 2008. during his post doc he conducted research on reducing porosity in aluminum die castings. he joined qassim university, in 2010. currently he is working as a professor of mechanical engineering at the university of engineering and technology, peshawar, pakistan. fahad a. almufadi did his phd from ohio university, usa in 2004. he joined qassim university, saudi arabia in 2009 where he was in charge of different academic and administration positions starting with mechanical engineering department head, then vice dean and currently he is the dean of the engineering college. microsoft word 27-2256_s-corrected date.doc engineering, technology & applied science research vol. 8, no. 5, 2018, 3450-3455 3450 www.etasr.com perisic et al.: frequency locked loop based on the time nonrecursive processing frequency locked loop based on the time nonrecursive processing djurdje m. perisic faculty of information technology, slobomir p university (spu), slobomir, republic of srpska, bih djurdje@beotel.rs vera petrovic school of electrical and computer engineering of applied studies, belgrade, serbia vera.petrovic@viser.edu.rs branko kovacevic school of electrical engineering, university of belgrade, beograd, serbia kovacevic_b@etf.rs abstract—this paper describes one new approach to frequency locked loop (fll), which is based on the time non-recursive processing of input periods. system parameters are defined by the ratio of frequencies. the conditions, under which the described system can have the properties of a fll, are analyzed. all math analyses were made by the use of z transform approach. it was shown that fll is extremely fast and that it is suitable for usage in different predicting, tracking and modulation applications, for the measurements of frequency and for other applications. the fll realization in the technique of standard integrated circuits is described. the oscilloscope picture, made on the realized 8 bit model, is presented. analysis in frequency domain was made using matlab tools. keywords-digital circuits; fll; pll; pulse circuits i. introduction time non-recursive time processing fll (tnp fll) described in this paper calculates and generates the output period using measurements and processing of the input periods only. the terms “non-recursive” and “recursive” are borrowed from the theory of digital filters. actually, finite impulse response (fir) digital filters calculate the next output using only input samples, without taking in account previous filter outputs. such processing was called “non-recursive”. infinite impulse response (iir) digital filters use in calculations both input samples and previous outputs as well. this kind of processing was called “recursive”. in [1-10], to describe different applications, recursive processing was used. this means that the output period is calculated using input and output periods. some use time differences between them, but they obviously include partly both periods in the processing. this actually means that all described algorithms in [1-10] function as feedback systems and they can possess the properties either of phase locked loop (pll) or fll. unlike the described algorithms in [1-10], this approach of fll is an open loop system. from the aspect of the algorithm used, it functions similarly to an fir digital filter. although digital filters process amplitude samples of the input signal, and tnp fll uses periods of an input signal, it is very useful to understand the relationship between these two physically different systems in order to utilize, as much as possible, power digital filter theory and software tools in further development and application of tnp fll. the theory and techniques for developing tnp fll are basically very similar to the demonstrated ones in [1-10]. the applicability of this approach is very wide. frequency multiplier is described in [1]. time shifters are described in [2, 3] and time/phase shifting in [4]. trp pll and trp fll for noise rejection are described in [57]. a wide range of tracking and prediction applications is described in [5, 6, 8]. most of the algorithms described in [110] are suitable for usage in software form. such a software predictor is described in [9]. very complex systems, consisting of a lot of subsystems, can also function as flls, whose realization is based on the same technique [10]. articles and books [11-17] are used as theoretical base, for electronics implementation and for the development necessities. ii. mathematical description of fll the general case of an input signal sin and an output signal sop of fll is shown in figure 1. the time difference τk is used instead of the phase difference. the periods tik and tok, as well as the time difference τk, occur at discrete times t0, t1, …tk, tk+1, which are defined by the falling edges of the pulses of sop in figure 1. the main recursive equation describing the functioning of fll is presented by (1), where α and b are the system parameters. the natural relations between variables, which come out from figure 1, are given by (2) and (3): 2 1k k k to a ti b ti + + += ⋅ ⋅ (1) 1k k k k to tiτ τ + = + − (2) 2 1 1 1k k k k to tiτ τ + + + + = + − (3) fig. 1. time relation between variables. note that (3) is just (2), shifted for one step. equation (3) engineering, technology & applied science research vol. 8, no. 5, 2018, 3450-3455 3451 www.etasr.com perisic et al.: frequency locked loop based on the time nonrecursive processing will be taken in account for the simulation of fll. according to (1) and (2), fll has two output discrete variables, which describe the behaviour of fll in terms of tik. the output variables are to(k+1)=f[ti(k)] and τ(k+1)=f[ti(k)]. to analyze the conditions under which the described system possesses the properties of fll, the z transforms of (1) and (2) are presented in (4) and (5) respectively, where to1, to0 and τ0 are the initial values of tok and τk. note that, according to (1), to1=bti0. substituting to1=bti0 into (4), to(z) was found and presented in (6). substituting to(z) from (6) into (5), τ(z) was calculated and presented in (7). note that, in order to shorter the mathematical procedure, (7) is reached taking in account that the relation between the system parameters must be α+b=1, shown later on, in (12). two transfer functions, which describe fll, can be now recognized. the first one is hto(z), shown in (8), which describes the behaviour of the output period in terms of the input period. the second one hτ(z), shown in (9), describes the behaviour of time difference in terms of the input period. 2 2 1 0 0z to( z ) zto z to ati ( z ) zbti( z ) zbti− − = + − (4) 0 z ( z ) z ( z ) to( z ) ti ( z )τ τ τ− = + − (5) 02 ( a zb ) to( z ) ti ( z ) to z + = + (6) 0 0 2 1 1 to zz ( b ) ( z ) ti ( z ) z z τ τ +− − = − + − (7) 2to to( z ) ( a zb ) h ( z ) ti ( z ) z + = = (8) 2 1( z ) z ( b ) h ( z ) ti ( z ) z τ τ − − = = − (9) iii. analysιs of fll properties it is necessary now to investigate the conditions under which the described system possess the properties of fll or pll. let us remember that a fll generates the output pulse rate whose frequency tends to reach the frequency of the input pulse rate during the transient state. fll is in the stable state when the output frequency becomes either equal or in certain pre-defined relation to the input frequency. fll does not care about the phase difference between input and output signals. fll regulates only the frequency of the output signal. the phase difference of fll depends on the initial conditions and fll parameters. unlike fll, pll regulates both frequency and phase difference between input and output signals at the same time. in most applications, classical pll tends to equalize both frequency and phase of input and output signals. however, taking into account results in [2, 3], the phase difference of time recursive pll between input and output signals can be regulated by the system parameters. this phase difference can take any value, but it does not depend on the initial conditions of the variables. generally, some of time recursive plls can control the phase difference between input and output by the system parameters. note that thereby, the phase difference does not depend on the initial conditions. otherwise the system would represent fll. the step analysis is the most suitable approach for the investigation of the properties of the system described. let us suppose that the step input is ti(k)=ti=constant. substituting the z transform of ti(k) i.e. ti(z)=tiz/(z-1) into (6) and using the final value theorem, it is possible to find the final value of the output period to∞=limto(k) if k→∞, using to(z): 1 lim[( 1) ( )] ( ) z to z to z ti a b ∞ → = − = + (10) substituting ti(z)=ti·z/(z-1) into (7) and using the final value theorem, it is possible to find the final value of the time difference τ∞=limτ(k) if k→∞, using τ(z): 1 0 0 lim[( 1) ( )] ( 2) z z z ti b toτ τ τ ∞ → = − = − + + (11) it can be concluded, according to (10), that the described system can possess the properties of a fll, if the system parameters satisfy (12). note that if (12) is satisfied, to∞=ti, i.e. for stable fll, the output frequency is equal to the input frequency. equation (11) confirms that the system possesses the properties of fll, since τ∞ depends on the initial conditions. it comes out that the system does not possess the properties of a pll. 1a b+ = (12) it is interesting to analyze, whether fll is able to track the ramp input. to estimate this, it is necessary to determine well known velocity error kv, providing that the input period is the ramp function ti(k)=tiv(k)=ck, where c is a time constant. note that ti(z)=tiv(z)=z(c·k)=cz/(z-1) 2 . generally, velocity error kv =lim[tov(k)-tiv(k)] for k→∞. one more suitable expression for velocity error is kv =limtiv(k)[hto(k)-1] for k→∞. using the condition (12), the final value theorem and hto(z) given by (8), kv is calculated and shown in (13). according to (13), fll is able to track the velocity input with the constant error. however, if b=2 (α=1-b=-1), kv=0, i.e. fll tracks the velocity input without any error. 1 lim{( 1) ( )[ ( ) 1]} ( 2) v v to z k z ti z h z c b → = − − = − (13) let us now determine the behaviour of τv(k) for the velocity input, if k→∞. taking in account b=2 and α=-1, and using the final value theorem, τv∞=lim τv(k)k→∞ is calculated using τv(z) and shown in (14). the expression τv(z) is found out by substitution of ti(z)=tiv(z)=cz/(z-1) 2 in (7): 1 0 0 lim[( 1) ( )] v v z z z c toτ τ τ ∞ → = − = − + + (14) according to (14), τv∞ is a constant. besides the initial conditions to0 and τ0, τv∞ depend on the time constant c, which is the slope of the ramp input function. it is worth checking whether fll is able to track the acceleration input function ti(k)=tia(k)=ck 2 . note that, in this case, ti(z)=tia(z)=z(ck 2 )=cz(z+1)/(z-1) 3 . it is necessary to calculate now the acceleration error ka=lim[toa(k)-tia(k)], for k→∞. one more suitable expression for ka is ka=limtia(k)[hto(k)-1] for k→∞. taking in account the values b=2 and α=-1, then using the final value theorem and hto(z) given by (8), ka is calculated in (15). according to (15), fll is able to track the acceleration input, but with the constant time error ka =-2c: engineering, technology & applied science research vol. 8, no. 5, 2018, 3450-3455 3452 www.etasr.com perisic et al.: frequency locked loop based on the time nonrecursive processing 11 1 2a a to zk lim{( z )ti ( z )[ h ( z ) ]} c→= − − = − ⋅ (15) iv. realization of fll according to the above analysis, fll possesses powerful tracking performances for α=-1 and b=2. if we substitute these values into (1), it will be transformed into (16). if we now multiply, at the same time, all of its members by clock frequency fc, (16) will be transformed into (17). the functional scheme of fll, which comes out from (17), is presented in figure 2. according to (17), the input period tik is measured by clock with frequency fc, the input period tik+1 is measured by clock with frequency 2fc and the output period tok+2 is generated by clock with frequency fc. fll consists of a recursive calculation model (rcm) and a programmable period generator (ppg). rcm calculates nb in binary form, according to the right part of (17), and ppg generates the output period in the next step. ppg is described in [2-4]. 12 2 ++ +−= kkk titito (16) 12 2 ++ ⋅+⋅−=⋅ kckckc tiftiftof (17) let us remember that ppg is based on the up-down counter and that the output period to of sop is to=nd·tc. nd is the decimal value of binary code nb and tc is the clock period, i.e. tc=1/fc. for the realization of rcm, presented in figure 2, the technique in [1-10] was used. however, there are always differences in realization of any two rcms. the differences are conditioned by the dissimilarity of the algorithms used. the real time functioning of fll is presented in figure 3. fig. 2. functional scheme of fll. fig. 3. the loop is in the stable state and to is equal to ti. the oscilloscope picture is made on the realized 8-bit fll. the voltage waveforms were taken when the fll was in stable state. for this purpose, step input was chosen ti=0.1ms (fin=1/ti=10khz), α=-1 and b=2. clock frequency corresponding to parameter α was fc=110khz. clock frequency corresponding to parameter b was 2fc =220khz. the ratio ti/tc =fc/fin=110khz/10khz=11. this ratio can be noticed in figure 3. as it can be seen, the output period is locked to the input period. the precision of locking depends on the ratio between the input period ti and the clock period tc=1/fc. greater ratio ti/tc provides more precise locking. however, grater ratio of ti/tc requires greater capacity of all fll parts. note also that, in case that a fast dynamic input function is fed into fll, like for instance a ramp function or an acceleration function, the capacity of fll must be great enough to calculate the greatest output period which may appear within the transient state. time differenceτ∞, which corresponds to stable fll in figure 3, is not zero. this is consistent with the properties of any fll. time difference τ∞ has random value, because it depends on the initial conditions, according to (11). v. applications of fll in this chapter some of the applications of fll will be considered. besides the above analysis, these considerations will be supported by the simulation of fll operations. the simulations are to demonstrate the tracking performances of fll, to prove the mathematical analysis, to discover additional properties and possible efficient applications of fll, and to enable better insight into the procedure and the physical meaning of the described variables. all discrete values in simulations were merged to form continuous curves. note that all variables in the following figures were presented in time units. the time unit can be, µsec, msec or any other, but assuming the same time units for ti, to, τ and c, it was more suitable to use just “time unit” or abbreviated “t.u” in the text. it was more convenient to omit the indication t.u in diagrams. all simulations were performed using (1)-(3). the simulations of to(k) and τ(k) for the step input tik=10t.u, are shown in figure 4(a). all values for three cases of different parameters α and b, initial conditions and final values are shown in figure 4(a). the system parameters satisfy (12) in all cases and consequently, the output periods reached input periods. according to (11), using the parameter values and the initial conditions presented in figure 4(a), τ1∞ can be calculated as: τ1∞=ti(b-2)+to0+τ0=10(0.1-2)+3+0=-16t.u. this result agrees with the simulated τ1∞. in the same way, it can be calculated that τ2∞=-4t.u, and τ3∞=6t.u. note that calculated values τ2∞, and τ3∞ also agree with the simulated τ2∞, and τ3∞ presented in figure 4(a). these simulation results prove the correctness of the mathematical description and step analysis. the real time relation between sin, sop and τk, for simulated case nr. 2, is shown in figure 4(b). for the stable fll, period to∞=ti=10t.u and τ∞=-4t.u. note that fll is very fast. it takes only two steps to reach the stable state. fig. 4. (a) transition states of fll for the step input and different system parameters. (b) real time presentation of sin, sop and τk for the simulated case nr 2. all transient states are finished in two steps. (a) (b) engineering, technology & applied science research vol. 8, no. 5, 2018, 3450-3455 3453 www.etasr.com perisic et al.: frequency locked loop based on the time nonrecursive processing the simulations of to(k), kv and τ(k) for the velocity input tik=(10+4· k)t.u, are shown in figure 5. the values for two cases of different parameters α and b, initial conditions and final values are shown in figure 5. the case nr. 1 corresponds to the condition α+b=1. according to (13), kv1=c(b-2)=4(0.22)=-7.2t.u. this calculated result agrees with kv1. the case nr. 2 matches both, the previous one α+b=1 and the additional conditions b=2 and α=-1. according to (13), kv2=c(b-2)=0.0t.u. this result also agrees with kv2 simulation result, proving the previous conclusion. so if b=2 (α=1-b=-1), kv=0, i.e. fll tracks the velocity input without any error. finally, according to (14), τ2∞=-c+to0+τ0=-4+8+3=7t.u. this result agrees with the simulated τ2∞. all simulated values kv1, kv2, τ2∞ agree with the calculated ones by (13) and (14). the identity of analytical and simulation results proves the correctness of the entire theoretical approach, as well as the validity of the obtained results. even for the ramp input, demonstrated in figure 5, fll takes only two steps to reach stable state. fig. 5. simulation of the input and output variables in the tracking of the velocity function. all transient states are finished in two steps. the simulations of to(k), ka and τ(k) for the acceleration input tik=(10+4·k 2 ) t.u, are shown in figure 6. the values for two cases of different parameters α and b, initial conditions and the final values are shown. note that the parameters α and b and the initial conditions are the same as those in figure 5, so comparison between them is available. the case nr. 1 corresponds to the condition α+b=1 and the case nr. 2, satisfies both conditions, α+b=1 and b=2, α=-1. it can be seen that, for the case nr. 2, the output period to2 is able to track even the acceleration function, but with constant error ka2. fig. 6. simulation of the input and output variables in the tracking of the acceleration function. all transient states are finished in two steps. according to (15), ka2=-2· c=-2· 4=-8t.u. this result agrees with the simulated ka2 in figure 6. the acceleration error ka1, for case nr. 1, tends to minus infinity in figure 6. that means fll is not able to track the acceleration function if the parameters do not satisfy the conditions b=2, α=-1. time difference τ2∞ also tends to minus infinity in figure 7. simulations showed that, providing that α+b=1, fll is very fast. it always reaches stable state after only two steps, no matter if the input function was a step function, a velocity function or an acceleration function. no fll or pll, described in [1-10], possesses this property. from a practical point of view, this means that this fll is very suitable for tracking and predicting applications, as well as for other applications which require very short transition time. vi. analysis of fll in frequency domain analysis of fll in frequency domain should expend knowledge of its properties. for this purpose, matlab commands, devoted to digital filter design, were used. since fll is described by two transfer functions hto(z) and hτ(z), shown in (8) and (9), using matlab command freqz, frequency responses in the regain (0, pi) [rad], from both transfer functions, are generated for α=-1 and b=2 and presented in figures 7(a) and 7(b) respectively. the frequency responses consist of magnitude and phase responses. the sampling frequency fs=200hz corresponds to the region (0, 2pi) [rad], so that fs/2=100hz, covers the region (0, pi). regarding figure 7, time presentations of ti and to as well as the spectrums of ti, to and τ, shown in figure 8, will be used. the input signal is the input period ti, presented in figure 8(a), as ti(k+1)=10+6·sin[(2pi/fs)·fm·k)]. it can be considered as a constant period of 10t.u., which is modulated by samples of sinus signal, whose amplitude is 6t.u. and frequency fm=10hz. fig. 7. (a) frequency responses hto(z). (b) frequency responses hτ(z) the number of time steps is chosen to be k=200=fs. the angular sampling step is ws=2pi/200 [rad]. since 200 frequency sampled steps covers region of one period, (0, 2pi), it means the sampling rate will be 20 samples/period. this provides sufficiently good resolution of ti in figure 8(a) for this analysis. fll generates the output to, which is calculated according to (1), (2) and (3). note that to exactly tracks ti with delay of one step. matlab commands fft and stem are used for the generation of the spectrums of ti, to and τ in figure (a) (b) engineering, technology & applied science research vol. 8, no. 5, 2018, 3450-3455 3454 www.etasr.com perisic et al.: frequency locked loop based on the time nonrecursive processing 8(b). these spectrums present the absolute values of amplitudes, covering the whole region (0, 2pi) [rad]. they appear as positive values in the symmetric second half (pi, 2pi) [rad]. the constant of 10t.u as a part of the input signal ti(k+1), corresponds to zero frequency component. this constant appears as very strong amplitude with the frequency of 0hz in ti and to spectrums. besides the constant of 10t.u., ti(k+1) consist of the sinusoidal signal, whose frequency amplitude can be seen in the spectrums of ti, to and τ at 10hz. time amplitude of to spectrum at 0hz is practically the same as in spectrum of ti, because fll attenuation, shown in figure 7(a) for hto, is 0 [db] at 0hz. however the time amplitude at 10hz is slightly amplified at the output to, because the magnitude, at figure 7(a), for hto, is about 0.9[db]. according to figure 8(b), the amplitude of the input sinus signal at 10hz is about 560t.u. and in the spectrum of τ, this component amounts about 200t.u. if we express this attenuation in db, it gives 20log(200/560)~-8.6db. this corresponds to attenuation of -8.6db, as shown in figure 7(b). unlike the very strong amplitude at 0hz in the spectrum of to, this component completely disappeared in the spectrum of τ in figure 8(b), because fll attenuation, shown in figure 7(b), for hτ(z), is about -42db at 0hz. this fact means that the width of time difference τ contains the input sinus signal, but without the zero frequency component. however, according to (11), τ depends on the initial conditions too. the difference between two adjacent τ, i.e. τk+1-τk, will eliminate the initial conditions, since their influence is the same in every τ, if fll is in the stable state. the demodulated input sinus signal, without input period and all other influences is shown as τk+1-τk in figure 9. the agreements between time and frequency presentations of fll input and output signals, confirm the correctness of the presented analysis. fig. 8. (a) time presentation of ti and to. (b) spectrums of ti, to and τ fig. 9. demodulated input sinus signal in time domain vii. conclusion this paper is closely related to the recently published articles in [1-10]. due to the fact that this fll version is based on measurement and processing of input periods only, it is simpler for the realization in comparison to those described in [1-10]. at the same time, it takes fll only two steps to reach stable state for any kind of input. it was shown that this fll can be very efficiently used for step tracking, ramp and acceleration functions. it is especially suitable for applications which require fast fll with very short transient time. this fll is scalable to the very strict requirements in the fields of tracking and predicting. although tnp fll and the digital filter represent different types of systems, since the former is based on time processing and the latter is based on processing of amplitudes, this study showed that matlab tools devoted to the design of fir digital filters, can be used to analyze the tnp fll in the frequency domain. all it takes is to understand the physical aspects of the whole process and to identify the meanings of tnp fll variables in matlab. using matlab, wide options for new analyses and new applications of tnp fll emerged. one as such is described in this article, where tnp fll is used as a demodulator. acknowledgement this article was supported by the ministry of science and technology of the republic of serbia within the project iii 47016. references [1] d. m. perisic, a. zoric, z. gavric, “a frequency multiplier based on the time recursive processing”, engineering, technology & applied science research, vol. 7, no. 6, pp. 2104-2108, 2017 [2] d. m. perisic, m. perisic, s. rankov, “phase shifter based on a recursive phase locked loop of the second order”, revue roumaine des sciences techniques–serie electrotechnique et energetique, vol. 59, no. 4, pp. 391-400, 2014 [3] d. m. perisic, a. zoric, d. babic, d. d. perisic, “recursive pll of the first order”, przeglad elektrotechniczny (electrical review), vol. 89, no. 7, pp. 50-53, 2013 [4] d. m. perisic, m. bojovic, “application of time recursive processing for the development of the time/phase shifter”, engineering, technology & applied science research, vol. 7, no. 3, pp. 1582-1587, 2017 [5] d. m. perisic, m. bojovic, “multipurpose time recursive pll”, revue roumaine des sciences techniques–serie electrotechnique et energetique, vol. 61, no. 3, pp. 283-288, 2016 [6] d. m. perisic, a. zoric, m. perisic, d. mitic, “analysis and application of fll based on the processing of the input and output periods”, automatika, vol. 57, pp. 230-238, 2016 [7] d. m. perisic, m. perisic, d. mitic, m. vasic, “time recursive frequency locked loop for the tracking applications”, revue roumaine des sciences techniques–serie electrotechnique et energetique, vol. 60, no. 2, pp. 195-203, 2015 [8] d. m. perisic, a. zoric, m. perisic, v. arsenovic, l. lazic, “recursive pll based on the measurement and processing of time”, electronics and electrical engineering, vol. 20, no. 5, pp. 33-36, 2014 [9] d. m. perisic, a. zoric, d. babic, d. d. perisic, “decoding and prediction of energy state in consumption control”, revue roumaine des sciences techniques–serie electrotechnique et energetique, vol. 58, no. 3, pp. 263-272, 2013 [10] d. m. perisic, a. zoric, s. obradovic, s. spalevic, “application of frequency locked loop in consumption peak load control”, przeglad (a) (b) engineering, technology & applied science research vol. 8, no. 5, 2018, 3450-3455 3455 www.etasr.com perisic et al.: frequency locked loop based on the time nonrecursive processing elektrotechniczny (electrical review), vol. 88, no. 1b, pp. 264-267, 2012 [11] r. n. dean, a. k. rane, “a digital frequency-locked loop system for capacitance measurement”, ieee transactions on instrumentation and measurement, vol. 62, no. 4, pp. 777-784, 2013 [12] h. e. taheri, “a 4-4.8ghz adaptive bandwidth, adaptive jitter phase locked loop”, engineering, technology & applied science research, vol. 7, no. 2, pp. 1473-1477, 2017 [13] d. jovcic, “phase locked loop system for facts”, ieee transactions on power systems, vol. 18, no. 3, pp. 2116-2124, 2003 [14] g. bianchi, phase-locked loop synthesizer simulation, mcgraw hill professional, 2005 [15] d. abramovich, “phase-locked loops: a control centric tutorial”, ieee 2002 american control conference, anchorage, usa, may 8-10, 2002 [16] r. vich, z transform theory and application (mathematics and applications), springer, 1987 [17] d. b. tablot, frequency acquisition techniques for phase locked loops, wiley-ieee press, 2012 microsoft word 19-2291_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3405-3410 3405 www.etasr.com hussain et al.: analysis of d2d communication system over κ-µ shadowed fading channel analysis of d2d communication system over κ-µ shadowed fading channel zakir hussain national university of computer and emerging sciences (nuces), karachi, pakistan asim ur rehman khan national university of computer and emerging sciences (nuces), karachi, pakistan haider mehdi national university of computer and emerging sciences (nuces), karachi, pakistan s. m. atif saleem national university of computer and emerging sciences (nuces), karachi, pakistan abstract—outage performance of a device-to-device (d2d) communication system in the presence of co-channel interference (cci) is analyzed in this paper. channels for the d2d and cci signals are assumed to be κ-µ shadowed faded. maximal ratio combining (mrc) and selection combining (sc) techniques are considered to combat fading conditions. characteristic function (cf) expression of the d2d system in the presence of cci is presented. outage probability and success probability expressions are presented for the mrc and sc schemes. these outage probability and success probability expressions are functions of various cci, path-loss and channel fading parameters. with the help of numerical results, effects of cci on the performance of d2d communication system under different channel fading and path-loss conditions are discussed. keywords-co-channel interference; d2d communication; κ-µ shadowed distribution; maximal ratio combining; selection combining; outage probability i. introduction the continuous development of technology and ever increasing number of connected devices has boosted the requirement of high data rates for efficient communication. device-to-device (d2d) communication system has emerged as a promising solution for this problem. d2d communication system is one of the most important standards of the 5 th generation (5g) cellular communication system that permits the communication of nearby devices directly bypassing the base station (bs) [1]. d2d communication system can improve data rate and bandwidth efficiency. it can also offload the base station, and it is power efficient communication for the user equipment [2-3]. many d2d communication devices coexisting with other wireless devices are competing for limited bandwidth recourses, which may lead to the co-channel interference (cci) problem. therefore, the effects of cci must be taken into account while analyzing the performance of d2d communication systems [4-5]. the aim of this paper is to analyze the outage and success probabilities of a d2d communication system in an interference limited scenario. outage performance of a full duplex d2d system over a rayleigh fading channel is studied in [6]. authors in [7], studied outage performance of d2d communication system over a rayleigh fading channel in the presence of interference. success probability performance of d2d communication system over rician fading channel is studied and analyzed in [8]. in [9], authors analyzed the success probability performance of d2d communication system over a rayleigh fading channel. the main objective of this work is to analyze the outage and success probabilities of a d2d communication system affected by several co-channel interferers over a κ-µ shadowed fading channel. the interference signals are assumed to originate from any wireless device in the system with which proper coordination is either lost or interrupted. the κ-µ shadowed fading channel is considered for both desired d2d and cci signals. the κ-µ shadowed fading distribution is a versatile model with a mathematically tractable form [10]. the κ-µ shadowed fading distribution can model rayleigh, rician, one-side gaussian, and rician shadowed fading distributions. maximal ratio combining (mrc) and selection combining (sc) techniques are incorporated to tackle the fading conditions. outage probability and success probability expressions based on the characteristic function (cf) expressions for the mrc and sc cases are presented. these outage probability and success probability expressions are functions of various channel fading, shadowing, path-loss and interference conditions. ii. system model the d2d communication model consists of a pair of d2d enabled devices communicating with each other directly. the system model is shown in figure 1. there are n co-channel interferers in the system. the d2d and cci signals are assumed to be independent and non-identically distributed. the cci sources are considered to be situated at different distances from the receiver of the d2d pair. the κ-µ shadowed fading channel is assumed for both desired d2d and cci signals. the probability density function (pdf) of κ-µ shadowed fading distribution is [11]: ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1 1 2 1 1 1 1 , , z m z m m z e z f z f m mm µ κ µµ µ µ µ κ µ κ κ µ µκµ µκ + − − ω  + + = ×   + ωγ ω +   where 1f1(.) is the confluent hypergeometric function of first kind [12]. the signal modeled by κ-µ shadowed fading distribution is considered to contain clusters of multipath engineering, technology & applied science research vol. 8, no. 5, 2018, 3405-3410 3406 www.etasr.com hussain et al.: analysis of d2d communication system over κ-µ shadowed fading channel signals. each cluster has a dominant component and that component can fluctuate randomly due to shadowing. µ denotes the number of clusters, κ is the ratio of sum of powers of dominant components to the sum of powers of all the scattered components, m is the shadowing parameter and ω is related to the average power. a simplified path-loss model is also considered [13]. mrc and sc based diversity techniques with m branches are incorporated to combat fading conditions. fig. 1. d2d system layout considered d2d device n th interference distance between desired d2d devices x distance between n th interference and the desired d2d pair’s receiver yn desired d2d communication signal n th interference signal a. mrc scheme the signal-to-interference power ratio (sir) at the output of m branches mrc combiner is: 2 0 1, 2 0, , 1 n n u m d lu ld mrc vn i n i n nv n n x p h s x s y p y β − = − =      =        ∑ ∑ (1) in (1), pd is the power of the d2d signal, x is the distance between d2d devices, u is the path-loss exponent ( )2 5u≤ ≤ for the d2d signal, x0 is the reference distance and hl is an independent κ-µ shadowed fading variable in the l th diversity branch. similarly, the power of the n th co-channel interferer is pi,n which is located at a distance yn from the d2d receiver, y0,n is the reference distance, vn is the path-loss exponent of the n th co-channel interferer and βn is an independent κ-µ shadowed fading variable of the n th co-channel interferer. the performance of a wireless communication system is assessed by computing the outage probability. the outage probability pout is defined as the probability that the instantaneous sir of the system drops below threshold r. the outage probability is: ( ), ,prout mrc i d mrcp rs s= > (2) where pr(.) denotes the probability. using the expression given in (2), a decision variable ϕ is defined as: ,i d mrc rs sϕ = − (3) for an acceptable quality of a desired d2d received signal, the value of φ has to be negative. otherwise, outage will occur. mathematically, outage acceptable transmission 0 0 ϕ >  ≤ (4) to get the expression of the outage probability, a characteristic function (cf) based approach is considered here. with the help of [11], the cf of the decision variable ϕ is: ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1 1 n n n n l l l l m n nn m n n n m m ll m l l l w ja c x j t ja b z j µ ϕ µ µ µ ω φ ω ω ω ω − = − =  −  = ×  − −   +    − +  ∏ ∏ (5) where: ( )1 , n nm n n n n n n n n m a m µ µ κ µ κ  − +    =     ω +    ( )1 , n n n n n w c µ κ+ = ω n n n n n n m x w mµ κ   =   +  , ( ) ( ) 2 0, , n n v n n i n v n y c rp y − = , ( )1 l l m l l l l l l l l m a m µ µ κ µ κ  − +    =     ω +    , ( ) 1l l l l l t b µ κ+ = ω , l l l l l l m z t mµ κ   =   +  , 2 0 u l d u x b p x − = , [ ]n ne βω = and [ ]l le hω = . based on (4) and (5), the outage probability of the d2d communication system can be obtained by using the formula: 0 1 1 2 out im( ( )) p d ϕϕ ω ω π ω ∞ = + ∫ where im(.) is the imaginary part of the cf of the decision variable φ. the outage probability of mrc based d2d communication system is given in (6). in (6), ( )1 1tan tann n n n n n m m x w ω ω θ µ− −     = − −        and ( ) 1 1tan tanl l l l l l m m t z ω ω ψ µ − −     = − −        . the success probability is defined as the probability for which the sir of a system excides a fixed threshold r. ps of mrc based d2d communication system is given in (7). engineering, technology & applied science research vol. 8, no. 5, 2018, 3405-3410 3407 www.etasr.com hussain et al.: analysis of d2d communication system over κ-µ shadowed fading channel ( ) ( ) ( ) ( ) ( ) ( ) 2 2 2 22 2 1 , 1 10 2 2 2 22 2 sin 1 1 1 2 n n l l n n l l n m m n lm n n l nn l s sc m m l n n l n l w ta a p d c b x z µ µ µ µ θ ψ ω ω ω π ω ω ω − − ∞ = = =        +   + +       = − + ×     − −        + +         ∑ ∏ ∏∫ (6) ( ) ( ) ( ) ( ) ( ) ( ) 2 2 2 22 2 1 1 , 1 10 2 2 2 22 2 sin 1 1 2 n n l l n n l l n m m m n ln m n l n ln l s mrc m m n ln l n l w ta a p d c b x z µ µ µ µ θ ψ ω ω ω π ω ω ω ∞ = = = = − −      +  + +      = −      − −       + +       ∑ ∑ ∏ ∏∫ (7) b. selection combining for the d2d communication system with sc diversity technique, the sir of the l th diversity branch is: 2 0 , 2 0, , 1 n n u d lu d sc l vn i n i n nv n n x p h s x s y p y β − − − =      =         ∑ (8) the outage probability for a sc diversity based d2d communication system is: ( ), ,prout sc i d sc maxp rs s −= > (9) where ( ), , 1, , maxd sc max d sc l l m s s− − = = … . a decision variable θ is defined as: outage acceptable transmission 0 0 > θ  ≤ (10) based on (9) and (10), the outage probability and success probability expressions of sc diversity based d2d communication system are given in (11) and (12) respectively. ( ) ( ) ( ) ( ) ( ) ( ) 2 2 2 22 2 1 , 1 10 2 2 2 22 2 sin 1 1 2 n n l l n n l l n m m n lm n n l nn l out sc m m l n n l n l w ta a p d c b x z µ µ µ µ θ ψ ω ω ω π ω ω ω − − ∞ = = =        +   + +       = + ×     − −        + +         ∑ ∏ ∏∫ (11) ( ) ( ) ( ) ( ) ( ) ( ) 2 2 2 22 2 1 , 1 10 2 2 2 22 2 sin 1 1 1 2 n n l l n n l l n m m n lm n n l nn l s sc m m l n n l n l w ta a p d c b x z µ µ µ µ θ ψ ω ω ω π ω ω ω − − ∞ = = =        +   + +       = − + ×     − −        + +         ∑ ∏ ∏∫ (12) iii. numerical results in this section, numerical results are discussed based on the expressions presented above. the reference distances x0, yn,0 are considered to be 1m. outage threshold r is fixed at 10dbm. in figure 2, the number of diversity branches m is considered to be 3 for both sc and mrc. the values of signal power of the desired d2d signal pd, path-loss exponent u, shadowing parameter ml, parameters µl and κl are assumed to be 20dbm, 3.2, {4, 1, 2}, {1, 2, 3} and {2.7, 3.7, 1.7}, respectively. for cci signals, the values of signal power pi,n, path-loss exponents vn, distances between interferers and the receiver of d2d pair yn, shadowing parameters mn, parameters µn, and κn, and number of interferers n are considered to be {19.59, 19.03, 18.14, 19.35, 19.3}, {3, 3.2, 3.4, 3, 2.5}, {20, 30, 25, 15, 30} meters, {3, 2, 1, 4, 4}, {1, 2, 2, 1, 3}, {2.7, 3.7, 2.7, 2.7, 2.7} and 5, respectively. it can be observed that mrc outperforms sc. furthermore, as the desired d2d devices move away from each other outage performance degrades. it is due to increase in path-loss effects. fig. 2. outage performance comparison of mrc and sc scheme engineering, technology & applied science research vol. 8, no. 5, 2018, 3405-3410 3408 www.etasr.com hussain et al.: analysis of d2d communication system over κ-µ shadowed fading channel figure 3 shows the outage performance with mrc diversity based d2d communication system for various m. the values of pd and u are assumed to be 20dbm and 3.3, respectively. the values of ml, µl and κl for m=2 are set to be {4, 1}, {1, 2}, {2.7, 3.7}, for m=3 the values of ml, µl and κl are {4, 1, 2}, {1, 2, 3}, {2.7, 3.7, 1.7} and for m=4 the values of ml, µl and κl are {4, 1, 2, 2}, {1, 2, 3, 2}, {2.7, 3.7, 1.7, 1}, respectively. for the interference signals, parameters pi,n, vn, yn, n, mn, µn and κn are fixed at {19.59, 19.03, 18.14, 19.35, 19.3}, {3, 3.2, 3.4, 3, 2.5}, {20, 30, 25, 15, 30} meters, 5, {3, 2, 1, 4, 4}, {1, 2, 2, 1, 3}, {2.7, 3.7, 2.7, 2.7, 2.7}, respectively. from the figure, it can be observed that by increasing the number of diversity branches, the outage performance of the system improves. fig. 3. outage performance with varying number of diversity branches outage performance with varying fading parameter values of the d2d signal µl is shown in figure 4. mrc diversity scheme is considered. the values of pd, u, m, ml and κl are fixed at 20dbm, 3.4, 3, {3, 1, 2} and {2.7, 3.7, 1.7}, respectively. for the interference signals, parameters pi,n, vn, yn, n, mn, µn and κn are considered to be {19.59, 19.03, 18.14, 19.35, 19.3}, {3, 3.2, 3.4, 3, 2.5}, {20, 30, 25, 15, 30} meters, 5, {3, 2, 1, 4, 4}, {1, 2, 2, 1, 3}, {2.7, 3.7, 2.7, 2.7, 2.7}, respectively. it can be observed that as the values of fading parameter µl are increased, the outage performance of d2d system is improved. fig. 4. outage performance with various values of µl of the d2d signal outage performance with varying shadowing parameter values of the interference signal mn is shown in figure 5. mrc diversity scheme is considered. the values of pd, u, m, ml, µl and κl are fixed at 20dbm, 3.4, 3, {3, 1, 2}, {3, 4, 5} and {2.7, 3.7, 1.7}, respectively. for cci signals, values of pi,n, vn, yn, n, µn and κn are assumed to be {19.59, 19.03, 18.14, 19.35, 19.3}, {3, 3.2, 3.4, 3, 2.5}, {20, 30, 25, 15, 30} meters, 5, {1, 2, 2, 1, 3}, {2.7, 3.7, 2.7, 2.7, 2.7}, respectively. it is observed that slight change in the outage performance of the system occurs when the interference shadowing conditions are changed. therefore, outage performance is mostly insensitive to the variations of cci shadowing conditions. fig. 5. outage performance with various values of interference shadowing parameters. outage performance with varying values of interference signal µn is shown in figure 6. mrc diversity scheme is incorporated. the values of x, u, m, ml, µl and κl are fixed at 20m, 3.3, 3, {4, 1, 2}, {1, 2, 3} and {2.7, 3.7, 1.7}, respectively. for the interference signals, parameters pi,n, vn, yn, n, mn and κn the values are fixed at {19.59, 19.03, 18.14, 19.35, 19.3}, {3, 3.2, 3.4, 3, 2.5}, {20, 30, 25, 15, 30} meters, 5, {3, 2, 1, 4, 4}, {2.7, 3.7, 2.7, 2.7, 2.7}, respectively. the value of r is 10dbm. from the figure, it is observed that the outage performance of the d2d system is largely insensitive to the varying values of interference parameter µn. fig. 6. outage performance with various values of µn of cci p o u t p o u t 17 18 19 20 21 22 pd (dbm) 10 -8 10 -7 10 -6 10 -5 10 -4 p o u t µn=[1, 2, 3, 1, 3] µn=[2, 3, 4, 2, 5] µn=[3, 4, 5, 3, 6] µn=[4, 5, 6, 4, 7] engineering, technology & applied science research vol. 8, no. 5, 2018, 3405-3410 3409 www.etasr.com hussain et al.: analysis of d2d communication system over κ-µ shadowed fading channel outage performance with varying path-loss exponent values of d2d signal u is shown in figure 7. sc diversity scheme is incorporated. the values of x, m, ml, µl and κl are fixed at 25m, 3, {4, 1, 2}, {1, 2, 3} and {2.7, 3.7, 1.7}, respectively. for cci signals, parameters pi,n, vn, yn, n, mn, µn and κn the are assumed to be {19.59, 19.03, 18.14, 19.35, 19.3}, {3, 3.2, 3.4, 3, 2.5}, {20, 30, 25, 15, 30} meters, 5, {3, 2, 1, 4, 4}, {1, 2, 2, 1, 3}, {2.7, 3.7, 2.7, 2.7, 2.7}, respectively. it is clear from the figure that outage performance degrades as the path-loss exponent values of the d2d signal is increased. it is due to degradation of the sir due to path-loss effects. outage performance with varying shadowing parameter values of the d2d signal ml is shown in figure 8. mrc diversity scheme is considered. the values of pd, u, m, µl and κl are fixed at 20dbm, 3.2, 3, {1, 2, 3} and {2.7, 3.7, 1.7}, respectively. for cci signals, values of pi,n, vn, yn, n, µn and κn are assumed to be {19.59, 19.03, 18.14, 19.35, 19.3}, {3, 3.2, 3.4, 3, 2.5}, {20, 30, 25, 15, 30} meters, 5, {1, 2, 2, 1, 3}, {2.7, 3.7, 2.7, 2.7, 2.7}, respectively. it is observed that the outage performance of d2d communication system improves with increasing values of the shadowing parameter of d2d signal ml. it is because of improved shadowing conditions of d2d signal’s channel with increase in values of shadowing parameter ml. fig. 7. outage performance with various path-loss exponent values of d2d signal fig. 8. outage performance with varying values of shadowing parameter of d2d signal. success probability performance of d2d communication system varying path-loss exponent values of interference signal vn is shown in figure 9. sc diversity scheme is considered. the values of pd, u, m, ml, µl and κl are fixed at 20dbm, 3.9, 3, {1, 2, 3}, {1, 2, 3} and {2.7, 3.7, 1.7}, respectively. for the interference signals, parameters pi,n, yn, n, mn, µn and κn are fixed at {19.59, 19.03, 18.14, 19.35, 19.3}, {3, 3.2, 3.4, 3, 2.5}, {20, 30, 25, 15, 30} meters, 5, {3, 2, 1, 4, 4}, {1, 2, 2, 1, 3}, {2.7, 3.7, 2.7, 2.7, 2.7}, respectively. it is observed that for higher path-loss exponent values of interference signals success the probability of the d2d system is high. it is due to weakening of the cci signals at the receiver of the desired d2d pair. this is because of path-loss effects. the success probability performance with varying distances yn is shown in figure 10. mrc diversity scheme is assumed. the values of x, u, m, ml, µl and κl are fixed at 30m, 3.3, 3, {4, 1, 2}, {1, 2, 3} and {2.7, 3.7, 1.7}, respectively. for interference signals, parameters pi,n, vn, n, mn, µn and κn are fixed at {19.59, 19.03, 18.14, 19.35, 19.3}, {2.5, 2.7, 3, 3.3, 2.8}, 5, {3, 2, 1, 4, 4}, {1, 2, 2, 1, 3}, {2.7, 3.5, 4.1, 3.2, 3.6}, respectively. it is clear that as the interferers move away from the desired d2d receiver, success probability performance of the system improves. it is because as the interferers move away from the d2d receiver, interference signals weaken at the d2d receiver side. it is due to path-loss effects. fig. 9. success probability performance with various path-loss exponent values of interference signal fig. 10. success probability performance with varying distances yn 20 20.5 21 21.5 22 22.5 23 pd (dbm) 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 p o u t u=3.0 u=3.3 u=3.6 20 22 24 26 28 30 x (meters) 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 p o u t ml=[4, 1, 2] ml=[5, 2, 3] ml=[6, 3, 4] p s 13 14 15 16 17 18 pd (dbm) 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 p s yn=[18, 30, 25, 15, 20] yn=[20, 35, 30, 20, 25] engineering, technology & applied science research vol. 8, no. 5, 2018, 3405-3410 3410 www.etasr.com hussain et al.: analysis of d2d communication system over κ-µ shadowed fading channel iv. conclusions outage and success probabilities of a d2d communication system over κ-µ shadowed faded channels have been analyzed. effects of cci on the performances were also considered. mrc and sc based diversity techniques are considered to mitigate fading conditions. the d2d and cci signals are assumed to be independent and non-identically distributed. the interferers are assumed to be present at different distances from the receiver of the considered d2d pair. outage probability and success probability expressions are presented based on a cf based approach. these outage probability and success probability expressions are functions of interference, channel fading and shadowing, and path-loss parameters. from the numerical results, it was observed that the fading, shadowing, path-loss and cci affect the performance of the d2d system. it was also observed that d2d communication system performance is largely insensitive to the channel conditions of the interferers. references [1] h. h. esmat, m. m. elmesalawy, i. i. ibrahim, “adaptive resource sharing algorithm for device-to-device communications underlaying cellular networks”, ieee communications letters, vol. 20, no. 3, pp. 530-533, 2016 [2] y. j. chun, s. l. cotton, h. s. dhillon, a. ghrayeb, m. o. hasna, “a stochastic geometric analysis of device-to-device communications operating over generalized fading channels”, ieee transactions on wireless communications, vol. 16, no. 7, pp. 4151-4165, 2017 [3] w. song, y. zhao, w. zhuang, “stable device pairing for collaborative data dissemination with device-to-device communications”, ieee internet of things journal, vol. 5, no. 2, pp. 1251-1264, 2018 [4] k. yang, s. martin, c. xing, j. wu, r. fan, “energy-efficient power control for 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schemes”, ieee 26th annual international symposium on personal, indoor, and mobile radio communications, hong kong, china, august 30 – september 2, 2015 [10] s. l. cotton, “human body shadowing in cellular device-to-device communications: channel modeling using the shadowed κ-µ fading model”, ieee journal on selected areas in communications, vol. 33, no. 1, pp. 111-119, 2015 [11] j. f. paris, “statistical characterization of κ-µ shadowed fading”, ieee transactions on vehicular technology, vol. 63, no. 2, pp. 518-526, 2014 [12] i. s. gradshteyn, i. m. ryzhik, table of integrals, series, and products, 7th ed, academic press, 2007 [13] a. goldsmith, wireless communications, cambridge university press, 2005 microsoft word etasr_v11_n1_pp6745-6751 engineering, technology & applied science research vol. 11, no. 1, 2021, 6745-6751 6745 www.etasr.com geetha et al.: optimized deep learning for enhanced trade-off in differentially private learning optimized deep learning for enhanced trade-off in differentially private learning p. geetha department of cse cambridge institute of technology bengaluru, india geetharaghuraj@gmail.com chandrakant naikodi department of studies and research in computer science davangere university bengaluru, india nadhachandra@gmail.com l. suresh department of cse cambridge institute of technology bengaluru, india suriakls@gmail.com abstract-privacy and data analytics are two conflicting domains that have gained interest due to the advancements of technology in the big data era. organizations in sectors such as finance, healthcare, and e-commerce take advantage of the data collected, to help them enable innovative decision making and analysis. what is sidelined is the fact that the collected data have associated private data of the individuals involved, and may be exploited and used for unjustified purposes. defending privacy and performing useful analytics are two sides of the same coin, and hence achieving a good balance between these is a challenging scenario. this paper proposes an optimized differentially private deep learning mechanism that enhances the trade-off between the conflicting objectives of privacy, accuracy, and performance. the goal of this paper is to provide an optimal solution that gives a quantifiable trade-off between these contradictory objectives. keywords-privacy; optimization; pareto-optimal; analytics i. introduction nowadays, privacy is a tough bargain. with the onset of digitization, online activities are on the rise and so is the increase in the risk of private information disclosure. online services like shopping, trading, banking, and entertainment are sources of data collection that include sensitive information of the people involved. while not all these services target at the exploitation of personal information, certain applications use them to their benefit. for instance, online browsing information of people is utilized for providing personalized recommendations as a part of the marketing strategy. in healthcare, sensitive information such as disease conditions are used for research and analysis which in turn may be helpful for diagnostic research. such usage scenarios can be extended to many fields. to safeguard privacy, data transformation methods are employed, which protect sensitive information, while still enabling useful analytics. this is easier said than done, since privacy defense and effective analysis conflict each other. given the size of big data, the challenge becomes even bigger, rendering it a multi-objective perspective. a privacy preserving analytic system should be able to balance the multiple criteria of privacy-utility-performance. numerous privacy mechanisms have been proposed that manage privacy preserving analytics for big data. they revolve around privacy algorithms namely k-anonymity [1] and its variants of kanonymity and l-diversity [2]. k-anonymity methods apply data transformation techniques that make the data unidentifiable. in approaches based on k-anonymity, k determines the degree of anonymity and hence the choice of k is an important decision. optimizing k can pave the way for better privacy, but at the cost of degradation in data utility. moreover, optimization approaches have the added limitation of performance overhead. with anonymization, a compromise solution is acceptable, provided preference is given to one of the objectives and this is attributed to the practical setting of the application. more recently, there has been a growing interest in the mathematical foundation provided by the privacy algorithm called differential privacy [3]. the core algorithm is specifically εdifferential privacy, after which relaxed variants have been proposed [4]. companies such as google [5] and apple [5] have used the algorithm for protecting the privacy of their customers, thereby ensuring that they see only a transformed form of the original data. the basic notion of the algorithm is to protect private information of a user, irrespective of the user’s participation or non-participation in data analysis. while the algorithm has been strongly recommended for privacy protection [5], only an equally stronger learning mechanism can provide worthwhile analytical results. ii. paper contribution deep learning [6] with differential privacy is a recently emergent domain that has many research applications in the corresponding author: p. geetha engineering, technology & applied science research vol. 11, no. 1, 2021, 6745-6751 6746 www.etasr.com geetha et al.: optimized deep learning for enhanced trade-off in differentially private learning field of privacy preserving analysis. specifically, the most likely developments in the domain may be: • optimizing epsilon for trade-off benefit. • developing an efficient learning technique to balance tradeoff. • extending trade-off beyond privacy and quality of data analysis. the core idea of the current paper is based on bridging the afore-mentioned research gap in differentially private learning. this paper is targeted at the second and third of the above cases. the main contributions of the paper are: • firstly, given the strong mathematical background of differential privacy, an optimized deep learning architecture is developed that enhances the efficiency of differentially private learning through effective hyperparameter optimization. • secondly, an attempt is made to consider privacy preserving analytics from the performance perspective and the triple trade-off between privacy, utility and performance is enhanced in comparison to the existing techniques. • thirdly, a single optimum solution for the problem is identified by adapting a prototypical decision-making strategy which is challenging in any multi-objective problem scenario. iii. background differential privacy [3, 7] is a notable algorithm used in the field of privacy preserving analysis. it was proposed in 2006 [3] and has been proven to provide strong mathematical guarantees for efficiently quantifying privacy. the key element behind the working of the algorithm is that the analysis of any dataset is not affected by the participation or non-participation of an individual. alternately, it conveys the theory that information about any individual learnt from the data, remains effectively the same before and after analysis. mathematically defining, the algorithm works by adding noise to data. the addition of random noise distorts data, thereby biasing the outcome of the analysis and preserving privacy. it is based on the probabilistic theory and promises that sensitive information of individuals in data is not affected by its use in any type of study. the most popular use of the algorithm is ε-differential privacy [3] in which epsilon (ε) defines a bound on the privacy loss. it can be used to formally quantify privacy loss and is used as the basis for effective analytics. • definition a randomized algorithm a gives ε-differential privacy if for all data sets d′ and d′′ that have a difference of one instance, and for any s⊆ range (a), (1) stands [3]: �� ���� ∈� �� ���� �∈�� � ���� (1) in (1), the datasets d′ and d′′ follow the constraint ||d′ d′′|| � 1 and epsilon is a positive real number, which quantifies privacy loss with change in data. iv. mathematical problem formulation the mathematical problem formulation is conceived as a multi-objective optimization problem and will be alternately referred to as multi-attribute or multi-criteria problem in the rest of this paper. a. mathematical modeling of the proposed model consider m as the vector space of decision variables. let p(m) and u(m) represent the objective functions to be maximized. mathematically, the problem can be formulated as: max�.�.�∈�� �!�, #�!�$ (2) where p(m) and u(m) represent the privacy and utility of the system respectively. in the context of differential privacy, the problem is re-defined as: argmax'()*+�+'(�!,-., /00$ (3) where, !,-. 1 �� ���� ∈� �� ���� �∈�� � ���� (4) /00�-,, 0� 1 2 34 ∗ 100 (5) where ni is the overall number of instances and c is the number of correctly classified instances. b. pareto-optimality when resolving a multi-attribute optimization problem, a solution that simultaneously achieves all objectives is not possible, since maximizing/minimizing one objective degrades the other. consider a set of solutions 8 1 �9'::::;, 9<::::;, 9=::::;, … … 9?::::;$ to a multi-attribute problem. a solution 9'::::; ∈ @ is said to be better than another solution 9<::::; ∈ @ if it satisfies the following condition: a4�9'::::;� b a4�9<::::;�∀, ∈ �1,2,3…�$ (6) fig. 1. visualization of the pareto-optimal front. such a set s is called a pareto-optimal set [8], in which all solutions are possible candidates for becoming an optimal solution, but one cannot dominate the other, without degrading one of the objectives involved. pareto-optimality is a common occurrence in multi-objective optimization problems. figure 2 shows the general occurrence of pareto-optimality in a twodimensional euclidean space. engineering, technology & applied science research vol. 11, no. 1, 2021, 6745-6751 6747 www.etasr.com geetha et al.: optimized deep learning for enhanced trade-off in differentially private learning v. design methodology this section describes the scheme of the proposed system. a differential privacy-based optimized deep learning neural network architecture for implementing privacy preserving learning is suggested. this approach addresses the twin challenges of privacy loss and efficiency of the learning technique. deep learning frameworks for differential privacy are gaining importance for privacy preserving analytics. an appropriate blend of these techniques will be able to provide robust solutions for the problem of privacy preserving learning, primarily due to two reasons. firstly, differential privacy is an algorithm that can provide strict data privacy guarantee. thus, analysis on private data must incorporate complex learning architectures whose outcome can quantitatively substantiate data privacy guarantee. hence this methodology develops a bayesian optimized deep neural network architecture for private learning with accounting of epsilon that determines the privacy assurance offered by the model. a. overview of system architecture a deep neural network is trained on differentially private data, and the intended learning task is classification analysis. the model topology initiates with an embedding layer to handle the categorical parameters of the input data. the transformed input is reshaped, and layers are concatenated before passing to the dense layer. the topology then alternates between dense and normalization layers. each dense layer has 1000 units. batch normalization is carried out to stabilize the output structure. this architecture is considered as the standard learner. in the standard learner, these neural net parameters are chosen arbitrarily and they are fixed as the reference model against which the optimized variant will be compared. since these parameters determine the strength of the learning process, a good combination of the parameters provides significant performance improvement. specifically, in deep learning parlance, these parameters are known as hyperparameters [7]. hyperparameter values have a deciding role in the learning process. selecting optimal values for the hyperparameters is called hyperparameter optimization [7, 9]. fine-tuning of the hyperparameters of the model can allow the privacy-utilityperformance trade-off in a quantitatively principled fashion. in this work, the proposed architecture with tuned hyperparameters is referred to as dpbodl (differentially private bayesian optimized deep learner). the design of the system is shown in figure 3. b. hyperparameter optimization methods such as grid search and random search [7], search the entire space of available parameters to arrive at optimal values. these methods are costly and training a model using them is challenging. the use of genetic algorithms [10] for efficient optimization has also been reported. bayesian optimization [7] reduces the time required for the parameter search which in turn limits the model training time, because only a selected set of parameters are chosen for a subsequent iteration, resulting in a search space which has the local optimal values from the previous evaluations. in this way, the method can efficiently select the global optimal hyperparameter set when the search terminates. fig. 2. dpbodl-design. although the hyperparameterized approach for non-private models has been used [11, 12], experimenting its efficiency for private deep learning models has far-reaching research possibilities. the proposed dpbodl exploits this possibility. c. steps for optimizing the deep learner let hq be the initial hyperparameter search space and acc the classification accuracy. let f���33 �g, hi be the objective function of the differentially private deep neural network (dpdnn) with x as the input space. • step 1: initialize the search space with default hyperparameters to be tuned. they are chosen randomly at stage one of the iteration. the search space consists of the hyperparameter set : hq = {learning rate, number of iterations, batch size, number of dense layers, number of dense nodes, number of input nodes, decay function}. • step 2: if function values follow a gaussian distribution, the optimization function is defined as: j00 1 f���33 �g, hi (7) hkl� 1 argmaxmnf���33 �g,hi o (8) • step 3: calculate the maximum a posteriori hypothesis of the set of hyperparameters �j00|hkl� . the optimizer selects the hyperparameters that maximize the accuracy of the deep learner. vi. experimental setup the deep learning model is trained and hyperparametrized using tensorflow core 2.0 [13]. for the purpose of experimental evaluation, two different types of tabular data varying in size and dimension have been selected. the adult and diabetes datasets adapted from the uci data repository [14] engineering, technology & applied science research vol. 11, no. 1, 2021, 6745-6751 6748 www.etasr.com geetha et al.: optimized deep learning for enhanced trade-off in differentially private learning are used. adult data are chosen since they are the de-facto benchmark for privacy related studies. the dataset provides 14 inputs that are a combination of categorical, numerical, and ordinal types. the target variable requires classification of data into two salaried classes, those belonging to "less than 50k" group and another belonging to the "greater than 50k" group. diabetes dataset has 20 attributes containing categorical and numerical data with around 200,000 instances with presence /absence of disease condition as the target. for both the datasets, the optimization ranges of the different hyperparameters considered are shown in table i. table i. fine-tuned hyperparameters tuned hyperparameters range of values learning rate <1e-4 ,1e-1> batch size <1,28> number of dense layers <1,5> number of dense nodes <1,28> no of input nodes <1,512> decay function adam decay activation function <relu,sigmoid> vii. evaluation in this section, the performance of dpbodl is compared with the standard deep learner's. epsilon, accuracy, and execution time were noted for both learners. the tabulation (table ii and table iii) shows the values of epsilon, accuracy, and execution time for adult and diabetes datasets respectively. the graphs in figures 3 and 4 show the comparison of results between the standard learner and dpbodl for the two datasets. maximizing the privacy and the utility of the analysis in the current context involves minimizing epsilon and maximizing the classification accuracy. the standard learner’s performance for the two datasets is shown in figure 3. epsilon degrades with increasing accuracy and execution time ranges up to 600s. the dpbodl’s performance is shown in figure 4. the dpbodl achieves enhanced trade-off in comparison with the standard learner with reference to epsilon and accuracy. while dpbodl gives epsilon values ranging between <0.78, 5.34> for adult and <0.87, 8.34> for diabetes, it is apparent that the standard model’s learning initiates with larger values for epsilon in the range <5, 11>. similarly, the enhanced learning speed of the optimized learner is due to the optimization of the number of epochs for the training of the model. it can be observed that, on average, 3-6 epochs are required to give an accuracy of approximately 80% .on the other hand, the standard learner requires at least 10 epochs to give a starting accuracy of 80%. essentially, dpbodl’s enhanced performance is attributed to efficient hyperparameter optimization. (a) (b) (c) (d) fig. 3. privacy-utility performance analysis-standard learner. table ii. trade-off results-standard learner epochs adult data diabetes data epsilon classification accuracy execution time (s) epsilon classification accuracy execution time (s) 10 5.68 0.81 61.2 4.36 0.76 65.2 30 6.23 0.82 102.3 5.11 0.772 112.3 50 6.59 0.83 150.3 6.78 0.778 167.3 70 7.21 0.87 253.25 6.923 0.79 292.33 90 7.86 0.87 310.32 7.23 0.81 320.32 110 8.3 0.8723 340.89 7.89 0.822 348.77 130 10.21 0.8756 412.12 8.23 0.83 467.82 150 11.19 0.879 490.11 8.45 0.842 590.71 170 11.56 0.8792 509.12 9.23 0.84 599.42 engineering, technology & applied science research vol. 11, no. 1, 2021, 6745-6751 6749 www.etasr.com geetha et al.: optimized deep learning for enhanced trade-off in differentially private learning table iii. trade-off results-dpbodl epochs adult data diabetes data epsilon classification accuracy execution time (s) epsilon classification accuracy execution time (s) 1 0.783 0.84 3.2 0.87 0.82 4.8 2 0.891 0.84 4.89 0.899 0.84 5.89 3 0.923 0.842 6.312 0.91 0.83 7.314 4 1.02 0.853 7.89 1.56 0.843 9.89 5 1.15 0.86 8.21 3.78 0.87 10.26 6 2.25 0.87 8.29 5.25 0.88 12.29 7 3.523 0.892 9.35 6.23 0.881 13.37 8 4.563 0.89 9.783 7.563 0.892 14.78 9 5.34 0.89 10.56 8.34 0.897 15.723 (a) (b) (c) (d) fig. 4. privacy-utility performance analysisdpbodl. viii. comparative analysis this section compares the proposed dpbodl mechanism with the state-of-the-art techniques for privacy preserving analytics. for the purpose of comparative analysis, three different techniques have been chosen, namely bayesian optimized diff private pareto (bo-dpareto)[9], privacy preserving deep learning (ppdl)[10], and linear regressiondiff private convex optimization (lr-dpco) [15]. both ppdl and bo-dparteo have been chosen for the comparative study for two reasons. primarily, these approaches use deep learning for privacy preserving learning. secondly, tabular data for analysis are used, in comparison to many other approaches, which predominantly use image data. lr-dpco uses shallow learning [16], but the algorithm’s results are equivalent to many deep learning approaches and including them here ensures a fair comparison. the graph in figure 5 shows the comparative performance between the present prevailing techniques and dpbodl. ppdl is able to minimize epsilon, but at the cost of decline in classification accuracy. for epsilon values in the range <10 -2 , 10 -1 >, ppdl achieves about 63% classification accuracy. as epsilon is compromised (larger values of epsilon), accuracy improves. bo-dpareto and lr-dpco have classification accuracies of 75-80% for epsilon range <10 -2 , 10>. minimizing privacy as low as 10 -2 in the existing techniques causes a corresponding reduction in the accuracy of the analysis. therefore, when considering the epsilon-accuracy compromise, dpbodl approach balances it efficiently, without severely affecting analysis accuracy, and hence is achievable in a practical scenario. it can be argued that the technique gives a fair compromise between the two objectives. lower epsilon ranges give accuracy of about 80% for both datasets, and it can be noticed that analysis accuracy stabilizes thereafter. for values of epsilon greater than 1, a higher accuracy (85-90%) is achieved with dpbodl, whereas the known state-of-the-art approaches achieve an average accuracy of only 85%. hence the hyperparameter optimization of the deep learner has resulted in achieving a good balance between privacy and utility. fig. 5. comparative analysis. engineering, technology & applied science research vol. 11, no. 1, 2021, 6745-6751 6750 www.etasr.com geetha et al.: optimized deep learning for enhanced trade-off in differentially private learning as far as computational efficiency is concerned a straight comparison between dpbodl and the afore-mentioned algorithms is unreasonable, since they differ by factors such as data size, dimension, and dynamics. hence its computational efficiency is compared with the standard deep learner. dpbodl performs well in comparison to the standard learner as shown in figure 6. the comparison shows that the number of epochs required to train a standard learner is much higher than its optimized variant. so, it can be perceived from the comparative analysis that the proposed approach has been able to provide a reasonable performance trade-off. fig. 6. performance comparison. the next section discusses the achieved privacy-utility trade-off in detail by considering the pareto-front generated by the approach and the extent to which the approach generates optimal solutions. ix. statistical estimation of optimal privacyutility trade-off this section makes a statistical assessment of dpbodl's results and computes an optimal privacy-utility trade-off. while selecting an optimal solution, the execution efficiency of the model is considered independent from these primary objectives, but the model does not overlook computational efficiency in the process of identifying a compromising solution. from the objective space consisting of a set of optimal solutions, as shown by the pareto-front in figure 7, an optimal solution is identified. the statistical analysis is carried out for the adult dataset. the utopian method [8] is employed to determine this optimum point. it is a decision-making strategy, which involves determining the near optimal <epsilon, accuracy> pair by comparing all data points to the ideal point called utopian point. let the conflicting objective functions in the current setting be defined as p(m) and u(m) (defined in section iv) .while p(m) determines privacy measured by epsilon, u(m) indicates the utility measured by the accuracy of classification analysis. the objective is to maximize both privacy and utility. maximizing privacy in the context of differential privacy involves achieving smaller values of epsilon, while maximizing accuracy of analysis. the objective space is shown as a scatter plot in figure 7. the plane shows the relationship between data points. the utopian point is positioned at (0.783, 89) indicating the ideal values for epsilon and classification accuracy. after estimating the distance measures of all points from the utopian point, the closest one is chosen as the final optimal solution, justifying the ideal trade-off between the objectives of the problem. the results of this calculation are shown in table iv. in this problem setting, a point with an epsilon value of 0.783 with corresponding classification accuracy of 84% is found to be the closest. table v shows the comparison in trade-off between the existing and the proposed technique. the {epsilon, accuracy} pair shows enhanced trade-off in comparison to the existing techniques. computational efficiency has been experimented only by ppdl, and results show that dpbodl is executed in a reduced number of epochs in comparison with ppdl for a corresponding epsilon value. table iv. statistical estimation of otpimum trade-off epsilon classification accuracy distance measure 0.783 0.84 0.063 0.891 0.84 0.1212023102 0.923 0.842 0.149939988 1.02 0.853 0.2413379373 1.15 0.86 0.3694766569 2.25 0.87 1.468180166 3.523 0.89 2.741001642 4.563 0.892 3.781000132 5.34 0.893 4.558 fig. 7. optimal trade-off computation. table v. trade-off comparison privacy technique/ learning technique algorithms optimal trade-off (epsilon, accuracy %) performance (average number of epochs) differential privacy/ deep learning proposed dpbodl (0.783,84) 3-8 existing bodpareto (0.7,79) ppdl (0.7,63) 10 x. conclusions in this paper, an optimization of deep learning technique for differentially private learning is proposed. conceptualizing private learning as a multi-objective optimization problem, the proposed method aims to find an enhanced privacy-utilityperformance trade-off for private learning. although it is challenging to find a single optimal solution, that is engineering, technology & applied science research vol. 11, no. 1, 2021, 6745-6751 6751 www.etasr.com geetha et al.: optimized deep learning for enhanced trade-off in differentially private learning mathematically best, for a multi-objective problem, the proposed method substantiates this trade-off by employing an appropriate decision-making approach. firstly, various tradeoff solutions are generated with the optimized learner. for a decision to be made with reference to the optimum point, pareto-optimal decision-making is done. the results show that the trade-off achieved is a quantifiable enhancement over the existing techniques. the proposed method has also considered execution efficiency which was not experimented by many of the existing techniques. references [1] l. sweeney, "achieving k-anonymity privacy protection using generalization and suppression," international journal of uncertainty, fuzziness and knowledge-based systems, vol. 10, no. 5, pp. 571–588, oct. 2002, https://doi.org/10.1142/s021848850200165x. 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[14] d. dua and c. graff, uci machine learning repository. irvine, ca, usa: university of california, school of information and computer science, 2019. [15] r. iyengar, j. p. near, d. song, o. thakkar, a. thakurta, and l. wang, "towards practical differentially private convex optimization," in 2019 ieee symposium on security and privacy (sp), san francisco, ca, usa, may 2019, pp. 299–316, https://doi.org/10.1109/sp.2019. 00001. [16] t. handhayani, j. hendryli, and l. hiryanto, "comparison of shallow and deep learning models for classification of lasem batik patterns," in 2017 1st international conference on informatics and computational sciences (icicos), semarang, indonesia, nov. 2017, pp. 11–16, https://doi.org/10.1109/icicos.2017.8276330. microsoft word 28-3271_s_etasr_v10_n1_pp5247-5250 engineering, technology & applied science research vol. 10, no. 1, 2020, 5247-5250 5247 www.etasr.com shaikh: financial mismanagement: a leading cause of time and cost overrun in mega construction … financial mismanagement: a leading cause of time and cost overrun in mega construction projects in pakistan fazal ali shaikh department of economics university of sindh, pakistan fazal_110_shaikh@hotmail.com abstract—one important and well-known issue for the majority of construction projects such as buildings, roads, bridges, airports and many more projects all over the world is time and cost overrun. project pricing and time period delay are also major issues. the current investigation is taking into consideration the mega construction projects in the provinces of pakistan, looking into various components controlling and dominating time and cost overrun. a total of 29 factors were identified from literature work and one questionnaire was designed and distributed among 160 respondents. all collected data were analyzed by the average index method. factors having value more than 3.6 were selected as main factors of cost and time overrun, and five factors were revealed to surpass this barrier. time and cost overrun are of the leading financial mismanagement issues of the economy of pakistan. this study will be helpful for stakeholders to control both cost and time overrun in the mega construction projects of pakistan. keywords-cost overrun; time overrun, pakistan; finance management; factors i. introduction in an emergent state such as pakistan, numerous mega projects have been completed or are under construction with the prop up from the government. cost and time surplus had provoked lags and debts, for the parties involved in many new projects, as in numerous fresh construction projects [1]. it is important for all parties who are concerned in the construction of a project to finish it within the agreed time and budget without compromising the quality of the work [2]. the construction industries of almost every asian country suffer from several major drawbacks despite the rapidity of the project development. pakistan is one of the countries facing these problems. these drawbacks are low quality and productivity, cost surplus, low construction ravage administration, time overrun, and low protection achievements [3-6]. cost overrun has a main burden on the whole development of a country [7]. it was discussed [8] that these factors were inadequate events for any construction project to be completed at the predicted price and time. additional considerations [9-11] emphasize on different approaches of particular concerns amongst construction project partners, i.e. contractors, customers, financial consultants and government organizations. one of the main economic pillars of pakistan is its construction industry. due to this, a study on the factors of time and cost overrun is essential, obligatory, noteworthy, and important. factors of cost and time overrun were identified on particular previous projects. thus, the main aim of this review is to look at the components causing time and cost overrun during construction, particularly on mega projects in all provinces of pakistan and to identify the most important factors/causes. ii. time and cost overrun there are three important components in measuring the achievement of construction projects. these components are time, price, and quantity of the entire project. the above mentioned factors are implanted during project life-cycle: preparation/planning, execution, and relinquish phase. it was not easy to assemble the necessities set up for every factor, as nearly all contractors were unable to complete the work on time. this results in an extra financial plan in order to carry out project completion [12-14]. some hazard components upset project period and cost planning, for instance casualties, cost variations, short or poor materials, and bad climate circumstances [15]. the main factors of these issues will be elaborated and discussed below. a. causes of constructing project’s time overrun changes made in designs, labor issues, scarce preparation, and resource shortage are the most important components in a project's time overrun. for instance, the components that affect time and price in projects in indonesia [8] are shown in table i. according to [16], there are two cause categories in delaying project construction: internal and external causes. there are four parties involved in internal causes: owners/clients, designers, contractors, and consultants. in comparison to internal causes, the external causes include the government, material suppliers, and weather conditions. table ii shows the factors affecting time and cost overrun according to [17]. in pakistan, it has been found that deprived place management, construction blunder, delivery delay, and requirement of goods supply management were the main components creating delays in construction projects [18]. proprietors’ monetary concerns are another cause of time overrun. authors in [19] reported that corresponding author: fazal ali shaikh engineering, technology & applied science research vol. 10, no. 1, 2020, 5247-5250 5248 www.etasr.com shaikh: financial mismanagement: a leading cause of time and cost overrun in mega construction … from consultant’s opinion, unskilled or lack of management and the dearth of expert’s acquaintance and skills were the main reasons for time and price overrun. table i. components affecting cost and time management [8] time and cost controls time controls cost controls environment restrictions buildability material prices knowledge of project site labor output precise quantity accurate prediction level of planning lift-off equipment production rate material estimated accuracy project experience equipment availability material availability type weather conditions technicians precision experience of local regulations availability of trained labor project restrictions table ii. components affecting cost and time management [17] category factors owner financial issues of finished work owner interruptions delay in taking decisions unrealistic imposed contract duration selection of sub-contractor poor planning contractor improper planning construction method subcontractor site management inexperienced contractor mistakes during construction financial issues faced by contractor materials material shortage material specification changes delay in the supply of material labor-equipment labor productivity labor supply equipment failure consultant contract management delay for approval of work quality control document preparation poor supervision contractual relationships disputes communication gap external weather effects other site problems changes in regularity b. effects of construction project’s cost overrun authors in [8, 19, 20] reported the following components in cost surplus: design modifications, unskilled and unfinished preparation, doubtful climate conditions, and abnormality and deviation in the cost of project resources. in addition to this, a listing of serious factors like incomplete design at the tendering phase, design alterations at the request of the proprietor, lack of money for the setting up and supervising at the beginning after the contract signing, defective besmirch and location settings, alterations made during construction, transportation charges owing to place locality, and lack of cost information at the development stage. other critical factors which are usually ignored are suspension in transmission of data to the builders during project suspensions, practical deterioration during the design period, obligation demands, customary constructive design advancement at the beginning of construction, uncertainty by the probing team in giving final results, limitations in estimate deviations and extra work, breaching and failures of bulk materials, etc. the main events that affect cost are changes in climate, inflation on prices, inexact material assessment, complications and difficulties of the scheme, builder’s incapability to understand the environmental issues, and lack of knowledge of the ruling set of laws [8]. moreover, authors in [21] studied the budget overrun components in community subdivision schemes establishing that the rise in cost was caused by incompetent original assessments, design delays, modification in opportunities, and inaccuracies. they pointed ten major components causing cost overrun of building projects: • construction setback due to limited scheme preparation, setting up and execution at the starting phase. • inconsistency and unreliability of the suppliers of unrefined resources including types of equipment etc. • modifications of the scheme’s capacity. • release of money, overseas exchange, and elements linked by incomplete accessories. • judgments made by the establishment and breakdown of precise regulating departments’ and sections. • incorrect and unsuitable location. • technical lack of skill and ability and penniless managerial composition. • labor instability. • natural calamities. • lack of experience in finding technical consultants, insufficiency of distant association accords. authors in [22] reported 26 components of cost overrun during the edifice of underground water projects in ghana, collected from consumers, contractors, and consultants. from the approach of contractors and consultants, the top factor that increased cost was difficulties in getting monthly expenditure from agencies. on the other hand, the owners’ perception of the project was that contractor management was the most important component affecting cost. in spite of the difference between their viewpoints, they all have agreed upon the ranking of these factors. iii. methodology this study considers the quantitative process toward assessing the project manager’s approach over the components affecting time and cost overrun in building projects. the designed questionnaire was established on the recognized components towards reaching the major ones which affect time and price overrun for building projects as in [8]. the questionnaire provided every participant the chance to spot those variables which he/she thought as probable to add to cost engineering, technology & applied science research vol. 10, no. 1, 2020, 5247-5250 5249 www.etasr.com shaikh: financial mismanagement: a leading cause of time and cost overrun in mega construction … overrun in a likert scale ranging from strongly agree to strongly disagree. afterwards, on an ordinal scale consisting of high (3), medium (2), or low (1), the members graded the density of recurrence of every factor. in this study, the mean value was calculated of each factor and factors having a mean value of more than 3.6 were identified as dominant factors of cost and time overrun in mega projects in pakistan. iv. results and discussion as mentioned above, a questionnaire was circulated for the evaluation of cost and time overrun in mega projects of pakistan. in total, 160 questionnaires were handed over to project managers, construction managers, and engineers with a 75% response rate of 120 answered questionnaires which deemed adequate because it satisfies the minimum sample requirement for the population [23]. the respondents were highly qualified and experienced. table iii. response summary response rate questions total percentage distributed 160 100% received and processed 120 75% non-returned 40 25% a. time overrun the collected data were graded according to the mean value of each factor. a total of 11 main factors had mean value more than 3.6 and were considered as major factors of time overrun. the summary of the analysis is shown in table iv. table iv. time overrun factors in pakistan mega projects factor mean value rank financial problems faced by contractor 4.871 1 fluctuation in price of materials 4.712 2 poor supervision 4.607 3 poor project management 4.419 4 weather conditions 4.318 5 owner interference 4.127 6 wrong method of construction 4.092 7 political approach in projects 3.873 8 poor estimation 3.801 9 delay in inspection 3.735 10 frequent design changes 3.634 11 b. cost overrun the collected data were analyzed and their mean values were calculated. table v. cost overrun factors in pakistan mega projects factor mean value rank design faults 4.570 1 improper investigation at site 4.491 2 political approach 4.370 3 financial crisis 4.301 4 weather conditions 4.267 5 inexperienced contractor 4.187 6 poor supervision 4.097 7 wrong method of construction 3.871 8 shortage of skilled labor 3.838 9 owner interference 3.781 10 delay in approval 3.670 11 a total of 11 factors had a mean value larger than 3.6 and were identified as dominant. from table v we can see that “financial problems faced by contractor” was found as the main critical factor. v. conclusion the initial discussion in the research work at hand involved a literature study considering construction time overrun and cost overrun. twenty-nine factors of time and cost overrun in mega projects were recognized from the literature review. the dominant factors of cost and time overrun were acknowledged. eleven factors were identified as dominant for each category. five main factors were found to be common in causing time and cost overrun in mega projects of pakistan. these identified main factors are financial issues, weather conditions, political approach, design changes, and owner interference. this work is expected to offer an improved approach in conveying construction projects by 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cost overruns in construction of groundwater projects in a developing countries; ghana as a case study”, international journal of project management, vol. 21, no. 5, pp. 321-326, 2003 [22] s. sohu, a. h. abdullah, s. nagapan, n. a. memon, r. yunus, m. f. hasmori, “causative factors of cost overrun in building projects of pakistan”, international journal of integrated engineering, vol. 10, no. 9, pp. 23-27, 2018 microsoft word etasr_v13_n3_pp10994-10999 engineering, technology & applied science research vol. 13, no. 3, 2023, 10994-10999 10994 www.etasr.com al-snaie: design and testing of a radiofrequency ellipsoidal helmholtz coil in contrast with a … design and testing of a radiofrequency ellipsoidal helmholtz coil in contrast with a circular pair for nuclear magnetic resonance khalid al-snaie department of electrical engineering, college of engineering, imam mohammad ibn saud islamic university, saudi arabia kalsnaie@imamu.edu.sa (corresponding author) received: 11 april 2023 | revised: 27 april 2023 | accepted: 5 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5945 abstract the design and testing of a helmholtz prototype probe with a relatively homogeneous radiofrequency field that can be used for mri are presented in this paper. it consists of two coaxial separately tuned ellipsoidal rings of wire in a symmetric arrangement. the developed ellipsoidal structure is tested experimentally in free space and is compared with the results obtained with an equivalent circular standard helmholtz coil. complete electrical modeling of the coils taking into account all couplings (inductive and capacitive) is studied. the proposed ellipsoidal helmholtz coil provides better performance in terms of field homogeneity, efficiency, and quality factor. the width of the lobe at 10% for the ellipsoidal coil is 20% bigger. moreover, a significant improvement in the quality factor is observed in free space. also, the efficiency is increased by 37%. finally, the signal to noise ratio (snr) of the ellipsoidal coil is higher than that of the circular coil. keywords-mri; nmr; radio frequency; rf coil; ellipsoidal configuration; b1 homogeneity i. introduction magnetic resonance imaging (mri) is a non-invasive imaging technique that does not use harmful radiation, unlike other imaging modalities. mri is based on the phenomenon of nuclear magnetic resonance (nmr), a phenomenon independently discovered by two research teams [1, 2]. nmr exploits the resonant behavior exhibited by certain materials when placed in a strong magnetic field. these materials selectively absorb electromagnetic energy at a frequency specific to their constituent cores and which varies with the strength of the externally applied static magnetic field. the absorption of electromagnetic energy positions moves the nuclei of the materials in a state of resonance, after which they return to their original state of thermodynamic equilibrium through a process known as relaxation with release of energy. in addition, there are a host of tissue-specific properties that interact with applied magnetic fields, the two most important of which are relaxation longitudinal (spin-lattice) and transverse relaxation mechanisms (spin-lattice). the use of signal coding techniques based on a spatial arrangement of magnetic field gradients allows obtaining information on the internal structure of biological samples. this information carried by the energy emitted by biological tissues, constitutes the basis of the mri imaging modality [3-5]. in mri, the need to make coils with the most uniform radiofrequency (rf) field b1 is necessary, hence the use of volume rf coils. among these volume coils, there are the "birdcage" type coils, with several types of operation and structures. they give good results, but they still have some drawbacks and constraints related to their construction. indeed, the realization of this type of coils becomes complex because the most homogeneous rf field is obtained with a high number of bars, moreover, the excessive metal mass constituting the base rings of the coils loops out to be a seat of foucault induced currents and causes disturbances during the switching of the gradients and visible trailing phenomena on the images. moreover, the homogeneity of the b1 field and the quality factor depend on the symmetry of the coil, hence the need for more precision at the manufacturing level [6-8]. in the case of simpler coils, such as helmholtz coils which generate a field b1 along the axis of the coil, the improvement in the homogeneity of the field is clearly greater. thus, unlike "birdcage" type coils, the optimization of the structure in the absence of periodicity is very significant [7-9]. the main objective of this paper is the design and testing of circular and ellipsoidal helmholtz coils that can produce a relatively, high electromagnetic field homogeneity to be used for nmr applications. engineering, technology & applied science research vol. 13, no. 3, 2023, 10994-10999 10995 www.etasr.com al-snaie: design and testing of a radiofrequency ellipsoidal helmholtz coil in contrast with a … ii. calculation of the b1 magnetic field this section is devoted to the calculation of the field produced by the circular and ellipsoidal structures. the objective is to obtain an rf induction b1 of better homogeneity so as to produce a homogeneous field of order 2 in the optimum case. the structure has a reduced dimension compared to the wavelength, so it is possible to apply the law of biot-savart and the principle of superposition to obtain the total field [9] on their axis [10]. the magnetic field of a circular loop of n turns whose plane of the coil is centered at z=+r/2 (field b1(z)), is written [11-12] as: b���� = µ� �� ��������� � �� �� (1) while the magnetic field of a loop of n turns whose plane of the coil is centered at y= -r/2 (field b2(z)), is: b ��� = µ� �� ��������� � �� �� (2) the field on the axis of a circular helmholtz coil is the combination of the two previous magnetic fields, the superposition theorem which is validated by the linearity of maxwell's equations gives the total field: b������������ = b���� + b ��� (3) we proceed by similarity with a structure consisting of two ellipsoidal loops, as shown in figure 1. each single loop has a semi-axial dimension x1 and y1. fig. 1. helmholtz structure with elliptic loops. to analyze this situation, a formula for the field produced around the origin (x = y = z = 0) by any loop traversed by a current i and of declination with respect to oz is proposed [13-14]: b� � = �"µ� #� $%& ×'∑ ) ��,��cos � ./ .0 �12� ) �cos3�4 (4) where pnm(cosα) are the associated legendre polynomials and pn(cosα) are the legendre polynomials. for the field on the oz axis, pn(cosθ) =1, and r = z, and the previous equation becomes: b� � = �"µ� #� $%& '∑ ) ��,��cos � ./ .0 ��2� 4 (5) the total field is the sum of the elementary inductions. it is possible to use the first terms of development. thus an appropriate spacing of the two loops allows a better homogeneity of the magnetic field with a cancellation of derivatives of order two of the field b1 along the axis oz and fortuitously the derivative of order four is relatively weak. for this, the two loops must be positioned at an azimuthal angle of 0.734 rad (about 42°). there is a unique solution for which the second order derivative of the field b1 is zero. for this optimal structure (eopt), the secondary geometric data are shown in table i. table i. parameters of the ellipsoidal coil primary axis a (cm) secondary axis b (cm) α (rad/deg) 3.042 2.459 0.734/42.09 the eccentricity of the ellipsoid is: 5 = 61 − �9�:�� = 0.587 (6) the value of the magnetic field at any point in the space is the sum of the fields created at this point by each of the single ellipsoidal loops and the approximated expression is [15-16]: b� = µ� :9 @ a b� c�de�c�f�gdh��� �9���i�����j:���i���� + b� c�de�c�f�gfh��� �9���i�����j:� ��i����k(7) with: l�m� = n √1 − m sin 3r�0 s3 (8) iii. comparison of the b1 field homogeneity the performance in terms of homogeneity of the b1 field of the ellipsoidal helmholtz coil (he) are compared with a circular helmholtz coil (hc) of the same radial size (diameter d equal to 5cm). figure 2 shows the simulation of the theoretical curves of the normalized magnetic induction b1z produced along the axis oz by both coils. fig. 2. profiles along the oz axis (in m) of the normalized induction (coils: hc, he). engineering, technology & applied science research vol. 13, no. 3, 2023, 10994-10999 10996 www.etasr.com al-snaie: design and testing of a radiofrequency ellipsoidal helmholtz coil in contrast with a … thus, the theoretical width (absolute or relative) of the profiles can be calculated at 1% and 10% of the maximum. the values are presented in table ii. table ii. profile width for both coils configuration profile width at 1% profile width at 10% circular hc 2.31 3.83 ellipsoidal he 2.92 4.44 compared to the reference hc, the lobe width at 10% of the ellipsoidal coil is increased by 12%. this increase is also greater (20%) for lobe width at 1%. the performance stated above is very general and does not in fact depend on the size of the coil. indeed, it suffices to apply a simple scale factor compared to the circular and ellipsoidal prototypes to obtain coils of greater or lesser size. iv. electrical modeling in this section, the complete electrical modeling of the structures, considering all couplings, is investigated. the complete electrical modeling of the coils is necessary to explain their operation and thereby demonstrate their feasibility. the general electrical model for the developed structures is represented schematically in figure 3. fig. 3. general electrical model for the developed structures. because of the symmetry, the input impedance z can be expressed as [17-19]: tu.vwux� uyzu[�\iu�x t�.vw�x� uyz�[�\iu�x ] (9) the two electrically isolated loops are characterized by a set of two equations with two unknowns (i1 and i2): � � ^�_� �`^�_� �` � � � a�a � = �00� (10) in fact, two resonance modes are distinguished: a co-current mode with a symmetric behaviour i1 = i2, which is the mode of interest, and a counter-current mode with non-symmetric behaviour i1 = −i2 (gradient mode). in co-current mode, the system of (10) comes down to a single equation [20]: ba� + ^�_� �`a = 0 (11) equation (10) corresponds to the resonance equation: �c� + _� �` − �d = 0 (12) if the coupling coefficient k is introduced (m12 = k l1), the resonance equation (12) becomes: efc� + m� jc�c g` = 1 (13) equation (13) has a positive real solution [21]: #� = � @6d �wu�hu�jwuw�� (14) for the counter-current mode (i1 = −i2), the value of frequency is: # = � @6d �wu�hu�jwuw�� (15) the two resonance modes are located on either side of the resonance frequency f0 (f0 = 1/(lc) and they are all the more distant as the coupling is strong. a representation of the input impedance amplitude ze is given in figure 4. fig. 4. theoretical curve of the input impedance of two identical tuned circuits. the current ratio is given by the secondary circuit equation, which is [22]: u � = �\ixt (16) when there are no losses at the resonance frequency f1 of the first mode z=jx=−jmω and consequently i2/i1=+1, the mode is co-current. for the mode at frequency f2, a change of sign takes place, so z = jx = + jmω and the mode is counter current (i2/i1= −1). in the case of low losses or high quality factor, i.e. q0 = rlω0 >> 1 [23], these two modes retain their characteristics in terms of frequencies and currents, while the impedances at resonance remain low [24]. the simulation allowed observing the variations of the currents and their relationship (figure 5). the two loops are tuned to the same frequency f0 = 105mhz, with k=0.05, l = 117.6nh, c = 19.47pf, r = 0.41ω, and quality factor q0 = 189. it can be seen that at fo, the transfer of power from the primary to the secondary coil is optimal. this is a particularity of the inductive coupling which is widely used in rf [25-26]. for the other frequencies f1 and f2, the currents i1 and i2 have a maximum value and the difference between the two modes remains at the phase level. engineering, technology & applied science research vol. 13, no. 3, 2023, 10994-10999 10997 www.etasr.com al-snaie: design and testing of a radiofrequency ellipsoidal helmholtz coil in contrast with a … fig. 5. i1 and i2 variation curves and their ratio. v. experimental results a. prototype dimensions the results of the experimental tests obtained with the developed coils are presented in this section. an ellipsoidal helmholtz coil and a circular helmholtz coil were built for mri (h1) at 100.241mhz. to facilitate comparisons, they have the same radial size d=5cm. the precise dimensions of the coils are given in table iii. figure 6 shows a photography of both developed coils. the diameter of the wire constituting the loops is 1mm. table iii. coil dimensions coils loop diameter distance between loops circular helmholtz 5cm 2.5cm ellipsoidal helmholtz a=3cm, b=2.4cm 3.1cm fig. 6. circular and ellipsoidal helmholtz coils. b. tuning and matching of the coils each loop of the coil was tuned at the same self-resonance frequency f0, higher than the resonance frequency of the coil. by predetermination of f0, an empty preset of the coil can be accomplished. fine tuning of the coil at the working frequency f1 is then performed if necessary [27]. using the hp 4195a network analyzer, we were able to obtain the variation of the magnitude and the phase in air without load of the input impedance seen by a test loop in terms of frequency as shown for the ellipsoidal coil in figure 7. fig. 7. curve of the input impedance of the ellipsoidal coil seen by a test loop. at resonance frequency f1, there is almost the same value for the first mode and a small error for the second mode. at f2, the difference is around 3% for the circular coil hc and around 1% for the ellipsoidal coil he. the matching of the coils was carried out without load using a coupling loop (inductive coupling). the position of the coupling loop relatively to the coil determines the optimal distance to get an impedance of 50ω for the matching [28]. this is approximately 1.9cm for the hc (1.99cm in theory, this corresponds to an error of 5%) and 2.7cm for the he (2.56cm in theory, corresponding to an error of 6%). this matching technique allows optimal energy transfer between the coils and the transmission and reception system. it should be noted that the matching and tuning of the coils depend on the nature of the sample and therefore adjustments should be considered for any new load. c. testing the coils without load off-field (in-air) tests were performed for both hc and he coils. thus, in the absence of a sample, relative field measurements along the axis of the coils were carried out using a small measurement loop connected to the hp 4195a network analyzer, and comparative readings of the intensity profile of the magnetic field b1 were established as shown in figure 8. the experimental curves of the normalized magnetic induction produced along the oz axis by both coils are given in figure 9. fig. 8. axial profiles in terms of distance (cm) for coils he and hc. engineering, technology & applied science research vol. 13, no. 3, 2023, 10994-10999 10998 www.etasr.com al-snaie: design and testing of a radiofrequency ellipsoidal helmholtz coil in contrast with a … fig. 9. axial profiles in terms of distance (cm) for coils he and hc. the obtained b1 field profiles along the axis for the two coils (figure 8) are in good agreement with the theoretical predictions of figure 2. compared to the hc (reference coil), the width at 10% of the lobe is 1.32 times greater for the ellipsoidal coil, which is comparable to the theoretical predictions. another positive point for the ellipsoidal coil, its efficiency is better. indeed, at identical absorbed power, the field emitted in the center is on average about 20% higher than that produced by the he coil. moreover, the quality factor of the ellipsoidal coil has also an interesting increment of 32%. vi. conclusion the design and testing of two prototype probes for mri comprising two circular and ellipsoidal free elements was presented. the two loops are correctly spaced and connected directly in series to a tuning capacitor. a complete electrical modeling of the coils taking into account all couplings (inductive and capacitive) was investigated. for a given resonant frequency, a predetermination of the tuning frequency of the tuned circuits is carried out, as well as the calculation of the associated tuning capacitors. at the practical level, the prototypes built are in fact of the same radial dimensions to facilitate comparisons. thus, compared to the reference circular helmholtz coil, 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[28] h. fujita, t. zheng, x. yang, m. j. finnerty, and s. handa, "rf surface receive array coils: the art of an lc circuit," journal of magnetic resonance imaging, vol. 38, no. 1, pp. 12–25, 2013, https://doi.org/ 10.1002/jmri.24159. microsoft word etasr_v11_n3_pp7177-7180 engineering, technology & applied science research vol. 11, no. 3, 2021, 7177-7180 7177 www.etasr.com khan et al.: recommendations for the implementation of iso 9001:2015 in the manufacturing industry … recommendations for the implementation of iso 9001:2015 in the manufacturing industry of pakistan zohaib khan faculty of mechanical and manufacturing engineering universiti tun hussein onn malaysia batu pahat, johor, malaysia yusri bin yusof faculty of mechanical and manufacturing engineering universiti tun hussein onn malaysia batu pahat, johor, malaysia nor haslinda binti abass faculty of civil engineering and built environment universiti tun hussein onn malaysia batu pahat, johor, malaysia maznah binti illyas ahmed faculty of mechanical and manufacturing engineering universiti tun hussein onn malaysia batu pahat, johor, malaysia qadir bakhsh jamali department of mechanical engineering quaid-e-awam university of engineering science & technology nawabshah sindh, pakistan abstract-iso 9001:2015 is known as the highest quality management standard, enhancing customer and company satisfaction. while the manufacturing industry is playing a vital role in pakistan’s gdp, the implementation of iso 9001:2015 is not widespread. this study aims to examine the factors that hinder the implementation of iso 9001:2015 in pakistan’s manufacturing industry and recommend suggestions to overcome them. an in-depth literature review identified 32 general factors that hinder the implementation of iso 9001:2015. a structured questionnaire was designed and distributed to 135 respondents to examine the factors hindering the implementation of iso 9001:2015 in pakistan’s manufacturing industry. the gathered data were analyzed using the average index formula, and 8 significant factors were identified. these factors were used in the design of a semi-structured questionnaire distributed among high qualified and experienced respondents working in top managerial posts of manufacturing industries in pakistan. the collected data were analyzed using content analysis. the findings can be helpful in the determination of recommendations regarding the implementation of iso 9001:2015 in the manufacturing industries of pakistan. keywords-recommendations; manufacturing industry; iso 9001:2015; significant factors i. introduction iso 9001 is based on seven quality administration standards. these standards and codes are elementary convictions, imperatives, norms, and values that form a foundation that ultimately leads firms, companies, and organizations to performance enhancement. before, on iso 9001:2008, the principles were based on 8 quality administration standards, and later they were decreased to the seven quality executive code standards [1, 2]. the previous iso 9001 edition referred to "products" which encompassed every kind of product, while the definition "purchasing" was altered to "control of externally provided processes, products, and services". so, the organizations that subcontract these functions or processes can ensure that their external suppliers comply with the definitions of the administration system [3]. the fundamental model could be interpreted as an organization or a company incorporating the new processes or implementing the new iso standard. the pdca cycle proposes a test preparation process that guides companies or organizations during changes or problem-solving procedures. the pdca cycle includes test data and feedback [4]. the major parts of this sequence involve numerical procedure control strategies in the production process, simplifying quality enhancement. the pdca cycle was applied by japanese industrial engineers with enormous success. for instance, the toyota production system (tps) is partially associated with pdca scientific schemes and quality control [5]. in underdeveloped countries, fewer organizations are certified by iso 9001 in comparison to the developed countries. as north american and european countries demand trustworthy infrastructure for the iso 9001 list and registration, uncompliant organizations cannot access these markets [6]. in many countries, the production sector has an important and vibrant position [7], while unsteadiness in the production division may cause turbulence on the whole economy. several studies investigated the business sector in numerous, developing and developed, countries. previous studies reported that although there is significant literature on the iso 9001, only a few publications highlighted the problems, the issues, and the challenges of the iso 9001, especially in the developing countries [8, 9]. besides, progress in the implementation of iso 9001 has been noticed in middle east countries among numerous groups of companies in the united arab emirates, kuwait, lebanon, qatar, and oman, while pakistani companies are trying to incorporate the codes and the standards to obtain the official certification. experimental research was carried out in egypt, by selecting a sample of industrial organizations to explore the critical aspects of the application process of iso 9001 [10]. the study highlighted the problems arising during the application of iso 9001 principles, the administration body's actions to apply corresponding author: zohaib khan (engr_zohaib@hotmail.com) engineering, technology & applied science research vol. 11, no. 3, 2021, 7177-7180 7178 www.etasr.com khan et al.: recommendations for the implementation of iso 9001:2015 in the manufacturing industry … them successfully, and reported the necessity to alter the organizational system to conform. hence, the employees’ confrontation during the implementation of the standards was the most momentous issue faced. furthermore, 11 probable elements that influence the application of iso 9001 were recommended. the responders were requested to rate the intensity to which every dimension influenced them, and the scale ranged from "very helpful" to "not helpful at all". thus, by investigating the outcomes, it was shown that the main advantageous elements in the successful application of iso 9001:2015 were the commitment from apex supervision, the devotion of the company’s in-house auditor, the well-designed system of the procedures, and the support from the mother organization or the partner. a study conducted on iso 9001 certified goods and manufacturing companies in pakistan reported 8 prominent difficulties during the procedure [11]. another study reported the following significant aspects that assist the iso 9001 implementation in pakistan: a well-organized process system, the commitment of higher management to the goal, and the useful views from domestic auditors [12]. moreover, the major problems connected to the standards' application were the requirements to change the prevailing systems, the uncertainty reported by the employees concerning the alteration, and the lack of understanding and respect to the iso principles illustrated by all departments. furthermore, several problems and issues concerning the function of the quality structure factors in the pakistani manufacturing field were reported, such as the inspiration for the registration, the cost of the official iso certification and the training plans, the quality guidelines, the registration companies, the iso advantages, and the formal auditing. ii. research methodology the main objective of this study was to identify the significant factors which hinder the implementation of iso 9001:2015 in the manufacturing industry of pakistan and determine recommendations to overcome them. an in-depth literature review was conducted which identified 32 common factors that hinder the implementation of iso 9001:2015 in the manufacturing industry worldwide. a structured questionnaire was designed and developed based on the identified common factors shown in table i. the questionnaire was distributed among 130 experienced respondents who were working in the manufacturing industry of pakistan. the respondent's experience profile is shown in figure 1. fig. 1. respondents' experience. table i. factors hindering iso 9001 implementation factors hindering iso implementation 1 2 3 4 5 1 absence of iso 9001 certification 2 unwillingness to change organizational culture 3 inflating the size of documents 4 unwillingness to change work system 5 weak interdepartmental relationship 6 management involvement 7 insufficient knowledge in quality 8 insufficient employee training 9 training to top management by industries 10 insufficient knowledge in quality 11 insufficient human resources 12 shortage of financial resources 13 iso requirements as unrealistic 14 absence of consulting boards 15 difficult to implement iso 16 employee resistance 17 top management involvement 18 leadership from top management of company 19 accountability in industry 20 action orientation by industry 21 credibility of the industry 22 collaboration among industries 23 technology resources in the company 24 big quality standards 25 complexity in industries 26 rules & regulations 27 training of staff 28 previous record of quality 29 inspection and testing 30 unavailability of quality manuals 31 employees behavior 32 corrective and preventive action the gathered data were statistically analyzed using the average index formula. factors having an average score of more than 3.6 were marked as significant factors that hinder the implementation of iso 9001:2015 in the manufacturing industry of pakistan [13]. these factors are shown in table ii. table ii. list of significant factors no significant factors ai score ranking 01 absence of iso 9001 certification 4.874 01 02 unavailability of quality manuals 4.764 02 03 training of staff 4.697 03 04 top management involvement 4.518 04 05 employees behavior 4.473 05 06 management involvement 4.197 06 07 rules and regulations 3.954 07 08 difficult for implementation of iso 3.879 08 after identifying the significant factors, a semi-structured questionnaire was developed and distributed to 50 top managerial respondents to investigate recommendations for each significant factor hindering the implementation of iso engineering, technology & applied science research vol. 11, no. 3, 2021, 7177-7180 7179 www.etasr.com khan et al.: recommendations for the implementation of iso 9001:2015 in the manufacturing industry … 9001:2015 in pakistan's manufacturing industry. the academic qualification of the selected respondents is shown in figure 2. gathered data from the semi-structured questionnaire were analyzed using content analysis. content analysis is a research method involving a thorough inspection of human conversation and a systematic, objective, quantitative analysis of human characteristics. after revising the collected data of every aspect that may be relevant, the coding frame was developed [14]. fig. 2. respondents' academic qualification. iii. data analysis and results cronbach's alpha measures the internal consistency or reliability of survey data, and it was utilized to evaluate the reliability of the data set using spss v27. as cronbach's alpha was measured at 0.914, it was reliable to proceed further [15]. eight significant factors were found to hinder the implementation of iso 9001:2015 in the manufacturing industry of pakistan. content analysis revealed some recommendations and suggestions to counteract those hindering factors, as shown in table iii. table iii. recommendations for significant factors factor recommendations frequency 1 1. iso certification should be clear 47 2. process of iso certification should be explained 45 3. owner should be informed of iso certification 42 2 1. quality manuals should be available easily 48 2. quality manuals should be explained 45 3. quality manuals should be revised 41 3 1. training of staff 48 2. staff should be informed of iso 9001 benefits 45 3. training should be done regularly 41 4 1. top management should be involved in iso 9001 certification 48 2. brief should be given for advantages of iso 9001 46 3. top management should be given examples of iso 9001 certified industries 43 5 1. employess should be informed of iso 9001 advantages 49 2. employees should follow the standards of iso 9001 46 3. employees should be trained on iso-9001 44 6 1. iso certification training should be given to management 48 2. management should be informed of iso 9001 advantages 45 3. quality manuals should be revised 41 7 1. rules and regulations should be informed to all staff 48 2. policies of iso 9001 should be easily understood 45 3. training should be done regularly 41 8 1.clear concept of iso 9001 should be explained 48 2. implementation procedure of iso 9001 should be made easy 46 3.top management should be informed on the advantages of iso-9001 43 fig. 3. significant factors hindering the implementation of iso (with ai score). iv. conclusion iso certification plays an important role in any country's gdp development. the implementation of iso 9001:2015 in pakistan's manufacturing industry is a serious concern. eight significant factors were found to hinder the implementation of iso 9001:2015 in pakistan's manufacturing industry. recommendations and suggestions were pointed out by the qualified and experienced professionals of pakistan's manufacturing industry. the proposed suggestions for the engineering, technology & applied science research vol. 11, no. 3, 2021, 7177-7180 7180 www.etasr.com khan et al.: recommendations for the implementation of iso 9001:2015 in the manufacturing industry … implementation of iso 9001-2015 include training to employees and administrative staff, and informing the top management of the advantages of iso implementation. this study will be helpful for the implementation of iso 9001-2015 in the manufacturing industry of pakistan. references [1] m. m. chhikara, d. m. s. narwal, and m. p. dahiya, "implementation of six sigma in indian manufacturing industries," international journal of advance research, ideas and innovations in technology, vol. 3, no. 1, pp. 22–30, feb. 2017. 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[6] h. latan, c. j. chiappetta jabbour, a. b. lopes de sousa jabbour, p. de camargo fiorini, and c. foropon, "innovative efforts of iso 9001certified manufacturing firms: evidence of links between determinants of innovation, continuous innovation and firm performance," international journal of production economics, vol. 223, may 2020, art. no. 107526, https://doi.org/10.1016/j.ijpe.2019.107526. [7] n. s. siddharthan and k. narayanan, eds., innovation and global competitiveness: case of india’s manufacturing sector, 1st ed. new york, ny, usa: routledge, 2018. [8] a. s. a. al-mijrab, m. e. elgharib, and m. a. al-griw, "critical success factors of iso/iec 17025 implementation within arabic countries: a case study of libyan research centres and laboratories (lrcl)," presented at the 23rd international conference on iso & tqm 23-icit, zhuhai, china, may 2019. 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[13] s. sohu, a. h. abdullah, s. nagapan, t. a. rind, and a. a. jhatial, "controlling measures for cost overrun causes in highway projects of sindh province," engineering, technology & applied science research, vol. 9, no. 3, pp. 4276–4280, jun. 2019, https://doi.org/10.48084/ etasr.2749. [14] g. durak et al., "content analysis of master theses and dissertations based on action research," journal of education and training studies, vol. 4, no. 12, pp. 71–80, nov. 2016, https://doi.org/10.11114/ jets.v4i12.1906. [15] s. sohu, a. h. abdullah, s. nagapan, a. a. jhatial, k. ullah, and i. a. bhatti, "significant mitigation measures for critical factors of cost overrun in highway projects of pakistan," engineering, technology & applied science research, vol. 8, no. 2, pp. 2770–2774, apr. 2018, https://doi.org/10.48084/etasr.1916. microsoft word 374-ce.doc etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 526-531 526 www.etasr.com sekkel and meghachou: the effect of displacement mode of rigid retaining walls on shearing bands … the effect of displacement mode of rigid retaining walls on shearing bands by active earth pressure abdelkrim sekkel moulay tahar university dept. civil engineering & hydraulic fac. technology labo. (l.g.c.e) saida, algeria sekkel.abdelkrim@univ-saida.dz mourad meghachou djillali liabes university dept. civil engineering fac. technology labo. (l.g.c.e) sidi bel-abbes, algeria mourad_meghachou@univ-sba.dz abstract —this work treats the physical modeling of failure mechanisms by active earth pressure. this last is developed by retaining wall movement. a lot of research showed that wall displacement has a significant effect on active earth pressure. a good comprehension of active earth pressure phenomenon and its failure mechanisms help us to better conceive retaining walls. the conception of a small-scale model allowed the realization of active earth pressure tests, while displacing the mobile wall toward the outside of the massif. the studied material is that of schneebeli; light two-dimensional material made of cylindrical plastic rollers, simulating granular non-cohesive soil. the evolution of shearing zones under continuous and discontinuous displacement modes of mobile walls by correlation pictures allows the investigation of the localization of deformations and failure mechanisms. keywordssmall-scale model; active earth pressure; continuous mode; discontinuous mode; shearing band. i. introduction earth pressure problems are always encountered in retaining structures such as retaining walls, sheet pile bulkheads, cofferdams, bridge abutments, basement walls of buildings etc. evaluation of earth pressure is of practical significance for the design of these retaining structures and it is a key research subject in soil mechanics and geotechnical engineering. although results of full-scale model tests are more trustworthy, the costs to conduct such tests are very high. scale model is a powerful tool for the verification of the earth pressure theory and the investigation of the mechanism of earth pressure. a lot of research on small-scale model was carried out by terzaghi into 1934 which is a big step in the history of the earth pressure study [1]. the results obtained showed that wall displacement has a significant effect on earth pressure. the earth pressure distribution on rigid retaining walls rotating about the base through field full-scale tests has been investigated [2]. a model of retaining wall has been developed in order to study the effect of wall displacement mode on earth pressure distribution [3]. the effect of the angle of inclination of the wall on the pressure of the grounds has also been studied [4]. despite intense theoretical and experimental researches for more than 200 years, there remain considerable discrepancies between theoretical solutions and experimental results, due to the complexity of deformation field in granular bodies near the wall caused by the localization of the deformations (which is a fundamental phenomenon of granular material behavior). the localizations can appear single or multiple, depending upon initial and boundary conditions. they can be plane or curved. in shearing zones, pronounced grains rotations [5-8] and large strain gradients [9] are observed. the thickness of shear localizations depends on various factors such as: mean grain diameter [9, 7, 10-12], pressure level [10, 13], initial void ratio [7, 13], direction of deformation [11], grains roughness and grain size distribution [7, 10, 11]. coulomb [14] indicated for the first time, the occurrence of shear zone during earth pressure tests. darwin [15] illustrated that the explanation of the behavior of the granular bodies during earth pressure is not possible without taking into account shear localization. several comprehensive experimental studies on earth pressure in sand were carried out between 1962 and 1974. during this period, a number of researchers [16-24] carried out experiments on the active and passive failure of dry sand deforming under plane strain conditions. the type of wall movement (passive wall translation) [18], active wall rotation about its top [22], passive wall rotation about its top [16, 17, 22], active wall rotation about its bottom [23, 24], passive wall rotation about its bottom [20, 21], wall roughness [17, 24], wall flexibility (rigid wall and flexible wall) [24], initial density of sand (dense and loose) [17, 22], and influences of surcharge, were studied. the evolution of shear localization in sand was recognized by using the radiographic technique which is able to detect density changes. different modes of shear zone during passive and active earth pressure tests depend mainly on the type of wall motion and surcharge. in passive tests with rigid walls rotating about the top, one or two curved shear zones were obtained in sand. multiple curved shear zones of a similar shape were observed during tests with a wall rotating about the bottom. they occurred at the wall top and propagated towards the free boundary. during tests with translating rigid walls, slightly curved shear zones starting to form from the wall bottom, and secondary radial shear zones appears at the wall top. in active tests with rigid walls, nearly parallel straight zones or a mesh of etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 526-531 527 www.etasr.com sekkel and meghachou: the effect of displacement mode of rigid retaining walls on shearing bands … intersecting parallel zones close to the wall (wall rotating around the bottom) or a single curved zone (wall rotating around the top) were observed. the details of these along with radiographs can be found in [25]. numerical calculations [26, 27] revealed that the pattern of shear zones were easier to observe when a non-associated model of coulomb-mohr without dilatancy was assumed. the study carried out by tejchman [28] with a uniform distribution of the initial index of the initial void ratio in sand showed that the calculated deformation field with a wall rotating around the bottom (passive and active case) was different from the experimental one [20, 23]. further, this study showed that the geometry of calculated shear zones was influenced by the size of the sand specimen and its initial void ratio. the pattern of the induced shear zones was created also in the case of loose sand continuously subject to contractancy. this paper wants to answer the following question: how shear zones will evolve when modifying the wall displacement mode? will they follow logic evolution or random diffusion? wall movement is translating in the x-x plane in continuous and discontinuous mode. so that the problem is mathematically determined, it is necessary to also set the boundary conditions on the two borders, free face and screen. the study will be related to horizontal free face not surcharged and vertical smooth wall, and this, for all tests. the studied material is that of schneebeli; light twodimensional material made up of dense rearrangement of cylindrical plastic rollers, simulating granular soil non-cohesive (dense sand). ii. experimental program description of active earth pressure was concretized by suitable experimental study. if one of assumptions theories of states ultimate equilibrium is that of a two-dimensional massif, this assumption cannot be ignored during any experimental work. the use of correlation pictures (kisdef-7d software), allows qualitative visualization and especially the quantification of fields displacement evolution and those of plane objects deformations which will remain plane after transformation process. the principle of method consists in comparing two digital images. a first recording of granular soil surface is taken before deformation, whereas a second is taken after deformation [29]. the design of a small-scale model could as well as possible correspond to physical reality, which remains nevertheless very complex. it is thus a question of studying a physical phenomenon on a reduced dimensional reproduction in smallscale model [30]. a. modeling of granular soil the studied granular soil is represented by schneebeli material which is used in various experimental approaches [5, 31]. schneebeli in 1957 showed that problems in soil mechanics with a granular non-cohesive material can be reduced to two dimensions [32]. the analogy consists in replacing a non-cohesive soil by a stacking of cylindrical, twodimensional rollers. a lot of biaxial tests were carried out with cylindrical rollers made by dural [32-35] (dural or duraluminium is an alloy of aluminum and copper used in aeronautics because of its great strength and its more weak density that steel), rubber [36], pvc [37-40] and steel [41]. all tests showed that the material behavior is identical to dense sand. the material studied in this paper, consisted of light plastic cylindrical rollers accumulation (eighteen thousand rollers), as shown in figure 1, cut out carefully showing the following characteristics: • light massif, dry density, γd= 3,5 kn/m 3 , grain density γs= 9 kn/m 3 with plasticine, its cohesion is null and its natural friction angle ϕ=10°. • indeformable rollers within sight of the actions applied thus simulating incompressible grains. the initially cylindrical rollers remain cylindrical after a process of transformation; • those rearrangements confer on granular soil a dense configuration. • length and diameter are respectively (70x2) in mm. fig. 1. dense configuration of plastic cylindrical rollers rollers have an intrinsic porosity which is not held in account in our estimate. this is justified by the assumption of rollers incompressibility compared to implemented solicitations. b. design of a small-scale model figure 2 illustrates experimental small-scale model. dimensions for the length, width and depth are respectively 800 mm, 500 mm and 100 mm. thus, a displacement wall of 30 mm is relatively low compared to the length justify a semiinfinite massif. shear bands, when propagated, are not blocked by any other side wall. the 100 mm depth is sufficient to allow filling under the best stability conditions with rollers witch occupied a volume of (550x250x70) mm 3 . etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 526-531 528 www.etasr.com sekkel and meghachou: the effect of displacement mode of rigid retaining walls on shearing bands … fig. 2. experimental small-scale model (ref : 01-dpb-040404) c. tests process tests are carried in aim of qualitative comparison of rupture evolution between two displacement modes of rigid retaining wall known as continuous and discontinuous. continuous mode describes wall displacement in an uninterrupted manner during all test process whereas discontinuous mode describes wall displacement marked by regular stops. tests are structured as follows: • wall displacement in continuous mode: mobile wall carried out a translation in the x-x plane at constant speed of 0,22 mm/s without interruption in time during tests process. photographs are taken in a continuous way during all transformation process. total displacement of mobile wall is 30 mm. • wall displacement in discontinuous mode: analog with continuous mode, however the mobile wall marks an interval of stop and a downtime; interval of stop is estimated at 0,75 mm when at the downtime, it is 3 seconds, and then the wall starts again. • after each test, rollers are rearranged and compacted to eliminate dilatancy zones to have the same initial density. the depth must be maintained within 250 mm. for each mode of wall displacement, the tests are repeated five (5) times by taking photographs with steps identical to tests preceding them. • a post treatment by the software of correlation pictures kisdef-7d allows the quantification and shearing bands evolution for studied modes. d. result analysis by correlation pictures the treatment of active earth pressure tests is done by kisdef-7d and it focuses in small deformations analysis by correlation pictures process. digital pictures materializing transformations states are introduced into the software’s database. domain analysis is defined by the operator; it is subdivided in quadrilaterals by a virtual grid of 10x10 pixels on the initial image (see figure 3). deformed grid is found by comparing gray levels for each couple of pictures treated with high accuracy (10 -8 pixels or 0,19x10 -8 mm). it should be noted that picture resolution (see figure 4) is 3264x1836 pixels. its confer ratio mm/pixel of 0,19.3264 pixels correspond at 620 mm in actual size. 620 mm/3264 pixels=0,19 thus 1pixel=0,19mm. fig. 3. definition of quadrilaterals (10x10) pixels fig. 4. ratio mm/pixel e. analysis mode and scale effect representation shearing band is evolutionary for increment displacement and its research requires choosing an incremental type analysis. therefore, photograph couples will be analyzed in incremental way i.e. (1-2), (2-3), (3-4), (49-50)… etc (see figure 5). regarding scale effect representation, the software has two alternatives: local scale and total scale. local scale proposes min and max values of maximum shearing for each analyzed couple, therefore varies from couple to couple. total scale, proposes min and max values of maximum shearing for all analyzed couples. all tests in continuous and discontinuous mode will show fluctuations in shearing bands intensities during transformation process, which will be visible only in local scale, as shown in figure 5. therefore, local scale will be adopted for each treated couple, as a total scale on all pictures couples will not allow observation of shear bands localization. on analysis 49 treating photographs 49 and 50 in continuous mode, shearing band evolution is definitely clearer on left figure (local scale), that on right figure (total scale). the same parameters are valid for discontinuous mode. a) local scale b) total scale fig. 5. scale effect representation on localization shearing band: analyze 49/49 between photographs 49 and 50: maximum shearing etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 526-531 529 www.etasr.com sekkel and meghachou: the effect of displacement mode of rigid retaining walls on shearing bands … f. evolution of shearing bands in continuous and discontinuous mode a question however arises: “how shearing bands will evolve by modifying wall displacement mode? will they follow logic evolution or random diffusion?” figure 6 represents failure evolution of granular soil following active earth pressure by shearing bands. a comparison between the two modes makes it possible to observe rupture evolution during transformation process. continuous mode discontinuous mode fig. 6. shearing bands evolution in continuous and discontinuous mode when a granular soil is solicited in active earth pressure, a localization of deformation appears by shearing bands. dilatancy phenomenon for dense soils is inevitable. the relative grain slips modify their rearrangement and the triangular configuration (dense state) become square (loose state) localized in the shearing band. density distribution is not homogeneous (low in shearing band). when we continue to solicit soil in active earth pressure, it is similar to starting from an initial configuration with a heterogeneous distribution density, therefore slip is favored in the low density zone. if the process is reiterated, the deformation localization will settle more and more in the area in question. however, for continuous mode displacement, in active earth pressure equivalent to a discontinuous sum of displacement mode, shearing bands propagation follows a diffusion logic letting multi mechanisms of failure appear (see figure 6, labels 1-4). g. shearing bands evolution before and after each stop of wall movement figure 7 illustrates shearing bands evolution for discontinuous mode displacement before and after each stop of mobile walls. results are expressed in maximum shearing. discontinuous mode a b c d e f fig. 7. evolution of shearing bands before and after stop of wall movement as shown in figure 7a, at stop of wall movement, an equilibrium state is created in granular soil. with movement wall resuming, shearing band appears clearly (figure 7b) and continues (figure 7c). at time of second stop, a new equilibrium state is created with an heterogeneous density configuration (figures 7d-7e). the last figure is spectacular; its shows the reappearance of shearing band exactly at the same place where it had disappeared when preceding wall movement had stopped. h. repeatability for results validation, six repeatability tests are carried out under same conditions and lead to the same conclusions, as shown in figure 8. 1 2 4 3 etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 526-531 530 www.etasr.com sekkel and meghachou: the effect of displacement mode of rigid retaining walls on shearing bands … continuous mode discontinuous mode a) test 2 b) test 3 c) test 4 d) test 5 e) test 6 fig. 8. tests validation tests results expressed in maximum shearing intensity during discontinuous mode, (on the right of figure 8) clearly show the preponderance of shearing band, while results on the left for continuous mode represent a disturbance of massif, governed by multiple shearing bands accompanied by parallel bands (figure 8c, label 5), as well as perpendicular bands (figure 8b-8c-8d-8e, labels 6-9). the difference is clearly shown. iii. conclusion at the last of this work, we arrive at the following conclusions: • realization of small-scale model simulating a granular soil subjected to active earth pressure made it possible to often highlight the evolution of deformations localization by shearing bands • during the tests known as discontinuous, shearing bands evolution in dense massif favored dilatancy phenomenon, governs by low density in sheared zone. with the resumption of wall movement, the starter of a new shearing band is favored in sheared zone which is the least dense of the massif. this results strong deformation localization. • with each stop of wall movement, an equilibrium state is created with a heterogeneous density configuration. with each resuming of wall movement, granular soil is solicited again and shearing band reappears exactly at the same place where it had disappeared at time of stop preceding wall movement. • during tests known as continuous, shearing bands evolution follows logic diffusion letting appear strong disturbance governed by several shearing bands translating multi-mechanisms of failure. • it was shown through this paper that failure evolution is significantly affected by displacement mode of mobile wall. the qualitative study shows a clear difference between continuous and discontinuous mode. this difference can be thorough in prospect while varying the interval of stop, the downtime as well as displacement speed of rigid retaining wall. references [1] k., terzaghi, "large retaining wall tests", engineering news record vol. 112, pp. 136-140, 1934 [2] m. matsuo, s. kenmochi, h. yagi, “experimental study on earth pressure of retaining wall by field tests”, soils and foundations, vol. 18, no. 3, pp. 27–41, 1978 [3] m. a. sherif, y. s. fang, r. 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leśniewska, z. mróz, “study of evolution of shear band systems in sand retained by flexible wall”, international journal for numerical and analytical methods in geomechanics, vol. 25, no. 9, pp. 909–932, 2001 [27] d. leśniewska, z. mróz, “shear bands in soil deformation processes”, in: bifurcations and instabilities in geomechanics (j. labuz and a. drescher, eds.), swets and zeitlinger, pp. 109–119, 2003 [28] j. tejchman, “patterns of shear zones in granular materials within a polar hypoplastic continuum”, acta mechanica, vol. 155, no. 1–2, pp. 71–95, 2002 [29] p. vacher, s. dumoulin, f. morestin, s. mguil-touchal, “bidimensional strain measurement using digital images”, journal of mechanical engineering science, vol. 213, no. 8, pp. 811-817, 1999 [30] f. darve, “manuel de rhéologie des géomatériaux”, edition de l’association amicale des ingénieurs anciens elèves de l’ecole nationale des ponts et chaussées, 1987 [31] j. lanier, p. c. bonnet, “experimental study of displacements and rotations of grains in 2d-granular media”, meeting tc13, comitee on mechanics of granular materials (issmfe), birmingham, 1993 [32] g. schneebeli, “une mécanique pour les terres sans cohésion”, compte rendus des séances de l'académie des sciences. paris, vol. 243, pp. 2647-2673, 1956 [33] c. coulet, “etude du profil optimal des murs-voiles de soutenement”, thèse, lyon : insa de lyon, 1977 [34] r. albert, a. houy, j. raud, g. verdier, “etude à l’aide de modèles réduits de datardeaux massifs”, proc. of 5 congrès européen, madrid, vol. 1, pp. 231-239, 1972 [35] j. verdeyen, v. roisin, “sollicitation des écrans souples de soutènement”, in : proc. of 5 congrès int. , paris, vol. 1, pp. 422-426, 1961 [36] m. oda, j. konichi, s. nemat-nasser, “experimental micromechanical evaluation of the strength of granular materials: effects of particle rolling”, in. : jenkins and satake eds. mechanics of granular materials: new models and constitutive relations, pp. 21-30, 1983 [37] r. gourves, m. mezghani “micromécanique des milieux granulaires, approche expérimentale utilisant le modèle de schneebeli”, revue française de géotechnique, vol. 42, pp. 23-34, 1988 [38] h. joer, j. lanier, j. desrues, e. flavigny, “1γ2ɛ: a new shear apparatus to study the behavior of granular materials”, geotechnical testing journal, vol. 15, no 2, pp. 129-137, 1992 [39] g. tratapel, “contribution à l'étude du comportement mécanique d'un milieu analogique bidimensionnel”, thèse: génie civil : université scientifique et médicale et l'institut national polytechnique de grenoble, 1977 [40] a. misra, h. jiang, “measured kinematic fields in the biaxial shear of granular materials”, computers and geotechnics, vol. 20, no. 3-4, pp. 267-285, 1997 [41] r. kastner, “excavations profondes en site urbain”, thèse génie civil, lyon : insa de lyon, 1982 engineering, technology & applied science research vol. 7, no. 6, 2017, 2132-2138 2132 www.etasr.com masoumi kazraji et al.: fuzzy predictive force control (fpfc) for speed sensorless control … fuzzy predictive force control (fpfc) for speed sensorless control of single-side linear induction motor s. masoumi kazraji dept. of electrical and computer engineering university of tabriz tabriz, iran m. r. feyzi dept. of electrical and computer engineering university of tabriz tabriz, iran m. b. bannae sharifian dept. of electrical and computer engineering university of tabriz tabriz, iran s. tohidi dept. of electrical and computer engineering university of tabriz tabriz, iran abstract—in this paper a model fuzzy predictive force control (fpfc) for the speed sensorless control of a single-side linear induction motor (slim) is proposed. the main purpose of of predictive control is minimizing the difference between the future output and reference values. this control method has a lower force ripple and a higher convergence speed in comparison to conventional predictive force control (cpfc). in this paper, cpfc and fpfc are applied to a linear induction motor and their results are compared. the results show that this control method has better performance in comparison to the conventional predictive control method. keywords-linear induction motor(lim); predictive force control (pfc); fuzzy logic; estimation; speed control i. introduction linear induction motors (lims) have several advantages such as the lack of need of interface mechanical tools, low mechanical losses, high starting force, and simple and strong structure. these motors are widely used in automation systems and industrial applications such as transportation systems, conveyor drives, electromagnetic launchers, and the transfer of containers in container terminals. among the different linear induction motors, the single-side linear induction motor receives more attention due to its simpler structure and higher endurance [1, 2]. linear induction motors receive a lot of attention in transportation systems since they produce direct force without transforming the rotation energy to transition energy. the main characteristics of linear induction motors with electromagnetic excitation in transportation systems include: thrust force, speed, vertical force, efficiency, power factor, and airgap flux density.the appropriate control of characteristics such as force, ripple, and speed convergence of is necessary to obtain a satisfactory operation in transportation systems [3, 4]. several lim modeling methods have been proposed. an lim model based on electrical design with the consideration of the end, the edge, and the skin effects has been investigated in [5]. usual design parameters can be found in [6] dynamic lim models have been investigated in [7-10]. in [7] and [8], a dynamic model based on the structural elements (width and the depth of slots), secondary thickness, and the number of turns is presented. among the different control methods, model predictive force control (mpfc) has received increased attention as an effective method [11, 12]. pfc directly predicts the considered variables such as force and stator flux. with the calculation of the effect of each possible voltage vector, a force error and minimum flux is selected as the best voltage vector. therefore, it is clear that the mpfc selected vector is more precise and more effective in comparison with dfc. in addition, the flexibility of mpfc allows the control to include non-linear factors and to apply the limitations of the control variables. in mpfc, a cost function is usually defined based on the errors of torque amplitude and flux, but in order to have a satisfactory operation, there is a need for an appropriate weight function. however, tuning the weight function is not easy due to the lack of a theoretical design method. in [13], an empirical method for achieving appropriate weight coefficients has been investigated. in [14], a precise discrete time state-space model for induction motors has been discussed and a current restriction in the cost function has been placed for the prevention of over current. according to [15] and [16], although mptc acts more precisely and more effectively in selecting the voltage vector (in comparison with dtc), applying the selected voltage vector without the tuning coefficient is not optimum. in dtc, the placement of the zero voltage vector along with the active voltage vector in the control period can help in regulating the voltage appropriately and precisely [17]. in [18], minimizing principles of the torque ripple for the calculation of the optimum weight coefficient have been introduced, but the equation of the optimum weight coefficient is complicated and the parameters depend on each other. ii. mathematical model of lim in order to obtain the lim model in a d-q reference frame, first the stator voltage equation should be introduced [2, 10]:    dsdrdsrdssds dt d iiqfriru  (1) engineering, technology & applied science research vol. 7, no. 6, 2017, 2132-2138 2133 www.etasr.com masoumi kazraji et al.: fuzzy predictive force control (fpfc) for speed sensorless control … qsqssqs dt d iru  (2) the equations of the secondary voltage in the direction of dq are as follows:    dr r dr r qr r ds dr dr d u r i r f q i i dt           (3) qrdrrqrrqr dt d iru     (4)   q e qf q  1 (5) rrm rp rll vl q /)( /   (6) where, rs and rr, ls and lr, lp and vr, p and τ are primary and secondary resistance, primary and secondary inductances, primary long and linear speed, pole number and pole pitch respectively, and lm is the magnetic inductance. f(q) has been used to take the end effect of lim into account in (5). moreover, f(q) has been used to provide the end effect on the magnetic factor of lim in the simulation model. the vectors of the stator flux and the secondary sheet flux are calculated from the current and the measured inductance in (7)-(10). the equations of the linkage flux are as follows:    1ds s ds m ds drl i l f q i i     (7)  qrqsmqssqs iilil  (8)    1dr r dr m ds drl i l f q i i     (9)  qrqsmqrrqr iilil  (10) the electromagnetic force of the lim is estimated by (11) and then (12) is calculated. the thrust force is calculated as follows:  dsqsqsdse iipf    22 3 (11)                        qsds r r qsdr mr m e ii qf qf l l i qfll qflp f 1 1 22 3 2    (12) the above equations have been used to simulate lim. iii. fuzzy model predictive force control the general control diagram for the proposed fpfc is shown in figure 1. it can be seen that the reference of the force has been produced by an external speed control loop and the reference of the stator flux amplitude has been kept stable since the operation of the flux weakening has not been considered in this paper. the information and the details about this control diagram are provided below. a. estimation of the flux and force the precise estimation of flux and force is essential for the satisfactory operation of the fpfc. in this paper, a full-order observer has been applied at low speed range due to high precision. the precision of the estimation and the robustness of the observer are increased against the changes of the motor parameters with the introduction of stator current error feedback. the mathematical model of the observer based on the lim model in (1) is:  ss iigbuxa dt xd ˆˆ ˆ  (13) in the above equation,  tssix ̂ˆˆ  are the variables of the estimation state. pi 2-level voltage source inverter lim fpfc cost function mininmazation pulse gen. uopt , t optfe ref fe k+2 is k ѱs k+2 ѱs ref ωr k us k vr ref vr fig. 1. control diagram of the fpfc.        rlb b g / 2 (14) in the above equation 2 1 ( )s r ml l l    and b is the negative stable gain. this method of displacing the poles increases the convergence and the stability of the observer especially at low speeds and it is easy to be applied. b. fuzzy logic control fuzzy logic controller is suitable especially for complex or nonlinear systems. figure 2 shows the structure of the fuzzy controller used in this paper. asshown, the inputs of the fuzzy controller are the error signal and its derivative and the output is the reference value which is applied to the system.the input and output membership functions are normalized values. thus, determining correct values for k1, k2 and k3 is essential. figure 3 shows a three dimension inputs-output diagram. in this paper, the triangular membership function is used due to its simplicity and efficiency [19]. engineering, technology & applied science research vol. 7, no. 6, 2017, 2132-2138 2134 www.etasr.com masoumi kazraji et al.: fuzzy predictive force control (fpfc) for speed sensorless control … fig. 2. the structure of the fuzzy controller. -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 -0.5 0 0.5 ece o fig. 3. three dimension inputs-output diagram c. the selection of the vector in the conventional mpfcs [20], the stator flux and the electromagnetic force have been predicted as the primary states by the predictive model with is(k) and ψs(k) variables at the moment of k+1. the aim is to make the stator flux and the force follow their references. in other words, the error between the estimated flux and force with their reference values has to be minimized. this takes the form of a cost function which is provided as follows:      4,3,2,1 1ˆ1ˆ   i kkkffj is ref sie ref e  (15) in the proposed fpfc, in order to determine the sign of the force and the stator flux, a weight coefficient of the stator flux, kψ is selected as follows: n sn f k   (16) in the above equation, fn is the nominal force, and ψsn is the stator flux amplitude. it should be noted that the kψ weight coefficient in (16) is only used as a starting point for tuning and the final practical amount of kψ is larger than (16), which was shown in [21]. the current of the stator is not directly used in the conventional mpfc cost function. the prediction of stator current is eliminated in order to decrease the complexity. to predict the force at the k+1th moment without the prediction of the stator current , the following equations are employed: 3 ( 1) ( 1) ( ) 2 2 e s s p f k k i k        (17)     ( ) 1 ( ) ( ) s r s sc r sc s r sc r r r sc s i k r l f j f i k r f l j l f k             (18) in the above equations, isλ(k) has been calculated based on the variables of the kth moment. iv. simulation and experimental results a. simulation results the simulation was conducted in matlab/simulink. the results of [22] have been used for comparison. the flowchart of the algorithm is shown in figure 4. the parameters are provided in table i. the reference of the stator flux is 0.9 wb, which is lower than the nominal amount in order to prevent saturation. the kψ weight coefficient in the weight function is only used to regulate the parameters of fpfc. the tuning has been carried for the selection of the most appropriate kψ. however, the selection of a weight coefficient is still a new issue and is usually determined intuitively [22]. the final amount of the kψ weight coefficient is 50 in this paper, which has been applied based on a comprehensive simulation. full oreder observer & time delay compensation duty ratio calculation force and flux prediction cost function gi (fe, ѱs) gi<g i++ i=6 uopt, topt end g= gi uopt=ui topt=ti u(k-1) is(k+1) isλ(k+1) ѱs(k+1) ѱsi(k+2) ui,ti fei(k+2) yesno yes no isλ(k+1) fig. 4. flowchart of the proposed mpfc method with the consideration of time-delay engineering, technology & applied science research vol. 7, no. 6, 2017, 2132-2138 2135 www.etasr.com masoumi kazraji et al.: fuzzy predictive force control (fpfc) for speed sensorless control … figure 5 shows the responses of the steady state simulation at step-function speed of 1.5 to 0.4 m/s, with rated load of 50n for cpfc, fpfc. from top to the bottom, the curves in figure 5 show (a) the electromagnetic force, (b) the amplitude of the stator flux and (c) the one phase stator current for cpfc and fpfc respectively. it can be seen that cpfc has a relatively large force ripple and large current harmonics in comparison with fpfc. in cpfc the unregulated force ripple appears in the stator flux. this issue emerges because the selected voltage vector is not long-lasting when determined proportionally to a separate duty. the proposed fpfc provides a more stable operation in terms of force ripple, flux and harmonics of stator current which confirms the positive effect of the tuning coefficient. 0 0.5 1 1.5 2 2.5 3 3.5 4 -1000 -500 0 500 time(s) f or ce ( n ) reference real 1.8 2.2 0 40 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 time(s) la nd a s ( w b) reference real 1.8 2.2 0.9 0 0.5 1 1.5 2 2.5 3 3.5 4 -1000 -500 0 500 time(s) f or ce (n ) 0 4 -50 0 50 reference real 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 time(s) l an da s( w b) reference real 1.98 2 0.88 0.9 0.92 0 0.5 1 1.5 2 2.5 3 3.5 4 -8 -4 0 4 8 time(s) ia ( a ) 0 0.5 1 1.5 2 2.5 3 3.5 4 -4 -2 0 2 4 6 8 time(s) ia ( a ) -4 4 fig. 5. the responses of the steady state simulation at step-function speed of 1.5 to 0.4 m/s, with rated load for cpfc and fpfc respectively: (a) electromagnetic force, (b) stator flux, (c) phase current the stable states responses, at the speed in which they are higher than the nominal load, are shown in figure 6. it can be seen that the fpfc shows a better operation in force ripple and flux and has fewer current harmonics. figures 7 and 8 show motor speed response waveform, for cpfc and fpfc, in high and low speeds. it is seen that in the fpfc method, the response speed of the motor has a shorter rise time than the cpfc. as shown, fpfc method can be adapted over the reference value in less time than cpfc, which is a confirmation of the proper operation of the proposed mpfc method. b. experimental results real-time hardware-in-the-loop (hil) simulation is an effectual technique for advanced measurements that provides a link between simulation and real conditions. in the hil simulation, real hardware of the investigated system is not accessible and thus emulated hardware is employed. (a) (b) (c) engineering, technology & applied science research vol. 7, no. 6, 2017, 2132-2138 2136 www.etasr.com masoumi kazraji et al.: fuzzy predictive force control (fpfc) for speed sensorless control … table i. lim and inverter parameters values parameter ----linear induction motor 8.5 kw rated power 290 v rated voltage 5 m/s rated speed 4.8 a rated curren 3 pole pairs 69 mh primary leakage inductance (lls)  0 mh secondary leakage inductance (llr) 200 mh magnetizing resistance (lm) 10.6 ω primary resistance (rs) 30 ω secondary resistance (rr) 20 kg moving mass (m) ----inverter 460 v dc-link voltage (u) 0 0.5 1 1.5 2 2.5 3 3.5 4 -1000 -500 0 500 time(s) f or ce ( n ) 2.5 2.51 20 80 0 0.3 -400 600 reference real 0 0.5 1 1.5 2 2.5 3 3.5 4 -1000 -500 0 500 time(s) f or ce (n ) 0 4 -100 100 reference real (a) 0 0.5 1 1.5 2 2.5 3 3.5 4 -8 -4 0 4 8 time(s) ia ( a ) 0 0.5 1 1.5 2 2.5 3 3.5 4 -5 0 5 time(s) ia ( a ) (b) fig. 6. the responses of the steady state simulation at step-function speed of 6 to 1 m/s, with rated load for cpfc and fpfc respectively: (a) electromagnetic force, (b) phase current 0 0.5 1 1.5 2 2.5 3 3.5 4 0 1 4 6 8 time(s) s pe ed ( m /s ) reference real 0 0.5 1 1.5 2 2.5 3 3.5 4 0 1 4 6 8 time(s) s pe ed ( m /s ) reference real fig. 7. the response speed of the motor, for cpfc and fpfc respectively, in high speed. 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 time(s) s pe ed (m /s ) reference real 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 time(s) s p ee d (m /s ) reference real fig. 8. the response speed of the motor, for cpfc and fpfc respectively, in low speed. in order to get a real-time based hil simulation, the matlab/real-time windows target toolbox was employed and the performance of the proposed fpfc of the lim was clarified using the approach in [23, 24]. figures 9(a) and 9(b) show the illustrative diagram and experimental layout of the real-time hil method. the vector control scheme with speed estimator is employed on an ezdspf2812 board. the lim dynamic model and the nonlinear inverter model described in [10], were simulated on a host pc. thus, the host pc is employed as a lim and inverter emulator. the real-time control commands of the dsp board are applied to the host pc as digital control signals using an advantech pci 1711 card located on pc bus. the analog/digital feedback signals are returned to the dsp board and subsequently processed to get control commands. furthermore, an interface board is employed for sending data from the dsp board to the engineering, technology & applied science research vol. 7, no. 6, 2017, 2132-2138 2137 www.etasr.com masoumi kazraji et al.: fuzzy predictive force control (fpfc) for speed sensorless control … oscilloscope. in fact, in the experimental testing, the host pc (lim emulator) is switched with the lim and inverter board. therefore, the real-time property of experimental testing is maintained. figures 10 and 11, show the results from the realtime hil method for motor speed response waveform, for cpfc, fpfc, in high and low speeds. it is seen that in the fpfc method, the response speed of the motor has a shorter rise time than the cpfc. fpfc method can be adapted in less time than the other methods over the reference value, which is a confirmation of the proper operation of the proposed fpfc. figure 12 demonstrates the results from the real-time hil method for electromagnetic force, for methods cpfc and fpfc. it can be seen that cpfc has a relatively large force ripple and large current harmonics in comparison to fpfc. the proposed fpfc shows the most stable operation in the force ripple which confirms the effect of tuning coefficient during the selection of the best vector. fig. 9. real-time hil structure (a) schematic diagram (b) experimental layout. fig. 10. the response speed of the motor in high speed, for cpfc and mpfc respectively, (hil method). fig. 11. the motor response speed, for cpfc and fpfc respectively in low speed (hil method). fig. 12. the response electromagnetic force of the motor, for cpfc and fpfc ii respectively, in high speed (hil method) v. conclusion the conventional pfc has a relatively high force ripple due to the limited number of voltage vectors in the two-level invertor and the lack of tuning flux coefficient in the stable state. in order to decrease force ripple, the tuning coefficient of the flux in fpfc for the linear induction motor has been used in low speed systems. in the optimized fpfc, the voltage vector is selected first based on the minimizing of the weight function and then the selected vector is calculated. from the aspect of error minimizing of the thrust force and flux, a better methodology was proposed. simulation and experimental tests were used to validate the proposed methodology. a comparative investigation was carried out between the proposed fpfc and the cpfc. in the proposed method, an (a) (b) engineering, technology & applied science research vol. 7, no. 6, 2017, 2132-2138 2138 www.etasr.com masoumi kazraji et al.: fuzzy predictive force control (fpfc) for speed sensorless control … improved operation of force and flux can be seen at different speeds, with or without load force, especially within the low speed range. in the meantime, the fast dynamic response in the cpfc has been maintained. references [1] i. boldea, s. a nasar, “linear electric actuators and generators”, ieee international conference on electric machines and drives record, pp. ma1/1.1-ma1/1.5, 1997 [2] i. boldea, linear electric machines, drives, and maglevs handbook, crc press, 2013 [3] r. hellinger, p. mnich, “linear motor-powered transportation: history, present status, and future outlook,” proceedings of the ieee, vol. 97, no. 11, pp. 1892-1900, 2009 [4] l. yan, “the linear motor powered transportation development and application in china,” proceedings of the ieee, vol. 97, no. 11, pp. 1872-1880, 2009 [5] i. boldea, s. a. nasar, linear electric actuators and generators, cambridge, u.k.: cambridge university press, 1997 [6] i. boldea, s. a. nasar, linear electric motors, englewood cliffs, nj, usa: prentice-hall, 1987 [7] f. alonge, m. cirrincione, m. pucci, a. sferlazza, “input–output feedback linearizing control of linear induction motor taking into consideration the end-effects. part i: theoretical analysis”, control engineering practice, vol. 36, pp. 133-141, 2015 [8] f. alonge, m. cirrincione, m. pucci, a. sferlazza, “input–output feedback linearizing control of linear induction motor taking into consideration the end-effects. part ii: simulation and experimental results”, control engineering practice, vol. 36, pp. 142-150, 2015 [9] t. t. overboom, j. p. c. smeets, j. w. jansen, e. lomonova, “decoupled control of thrust and normal force in a double-layer singlesided linear induction motor”, mechatronics, vol. 23, no. 2, pp. 213221, 2013 [10] g. kang, k. nam, “field-oriented control scheme for linear induction motor with the end effect”, iee proceedings electric power applications, vol. 152, no. 6, pp. 1565–1572, 2005 [11] s. masoumi kazraji, m. b. bannae sharifian, “direct thrust force and flux control of a pm-linear synchronous motor using fuzzy slidingmode observer”, advances in electrical and electronic engineering, vol. 13, no.1, pp. 1-9, 2015 [12] c. a. rojas, j. rodriguez, f. villarroel, j. r. espinoza, c. a. silva, m. trincado, “predictive torque and flux control without weighting factors”, ieee transactions on industrial electronics, vol. 60, no. 2, pp. 681– 690, 2013 [13] y. zhang, w. xie, z. li, y. zhang, “model predictive direct power control of a pwm rectifier with duty cycle optimization”, ieee transactions on power electronics, vol. 28, no. 11, pp. 5343–5351, 2013 [14] s. a. davari, d. a. khaburi, r. kennel, “an improved fcs–mpc algorithm for an induction motor with an imposed optimized weighting factor”, ieee transactions on power electronics, vol. 27, no. 3, pp. 1540–1551, 2012 [15] c. a. rojas, j. rodriguez, f. villarroel, j. r. espinoza, c. a. silva, m. trincado, “predictive torque and flux control without weighting factors”, ieee transactions on industrial electronics, vol. 60, no. 2, pp. 681– 690, 2013 [16] t. geyer, “computationally efficient model predictive direct torque control”, ieee transactions on power electronics, vol. 26, no. 10, pp. 2804–2816, 2011 [17] s. a. davari, d. a. khaburi, r. kennel, “an improved fcs–mpc algorithm for an induction motor with an imposed optimized weighting factor”, ieee transactions on power electronics, vol. 27, no. 3, pp. 1540–1551, 2012 [18] y. zhang, h. yang, “torque ripple reduction of model predictive torque control of induction motor drives”, ieee energy conversion congress and exposition, pp. 1176–1183, 2013 [19] m. hosein holakooie, m. ojaghi, a. taheri, ”full-order luenberger observer based on fuzzy-logic control for sensorless field-oriented control of a single-sided linear induction motor“, isa transactions, vol. 60, pp. 96-108, 2016 [20] j. rodriguez, p. cortes, predictive control of power converters and electrical drives, new york, , usa: wiley-ieee press, 2012 [21] c. lascu, a. trzynadlowski, “combining the principles of sliding mode, direct torque control, and space vector modulation in a high performance sensorless ac drive”, ieee transactions on industry applications, vol. 40, no. 1, pp. 170-177, 2004 [22] h. miranda, p. cortes, j. i. yuz, j. rodriguez, “predictive torque control of induction machines based on state-space models ieee transactions on industrial electronics, vol. 56, no. 6, pp. 1916–1924, 2009 [23] j. h. jung, “real-time and power hardware-in-the-loop simulation of pem fuel cell stack system”, journal of power electronics, vol. 11, no. 2, pp. 202-210, 2011 [24] c. s. edrington, o. vodyakho, b. a. hacker, “development of a unified research platform for plug-in hybrid electrical vehicle integration analysis utilizing the power hardware-in-the-loop concept”, journal of power electronics, vol. 11, no. 4, pp. 471-478, 2011 authors profile saeed masoumi kazraji was born in tehran, iran in 1989. he received the b.sc. degree from the sbzevar university of tarbiat moallem, mashhad, iran in 2011 and the m.sc. degree from university of tabriz, tabriz, iran in 2013, both in electrical power engineering. he is currently pursuing the ph.d. program at the universityof tabriz. his research interests include drive and motion control of electric machines, machine design and power electronic converters. mohammad reza feyzi received the b.sc. (hons.) and m.sc. (hons.) degrees in electrical engineering from the university of tabriz, tabriz, iran, in 1973 and 1975, respectively., and the ph.d. degree in electrical engineering from the university of adelaide, adelaide, australia in 1997. he worked with the university of tabriz from 1975 to 1993. soon after his graduation from the university of adelaide, he resumed working at the university of tabriz, where he is currently a professor at the department of power engineering. he is proficient in using two commercial finite elements softwares, such as “ansys” and “vectorfields.” his research interests are design, and analysis of electrical machines using finite element methods. mohammad bagher bannae sharifian studied electrical power engineering at the university of tabriz, tabriz, iran. he received the b.sc. and m.sc. degrees in 1989 and 1992 respectively from the university of tabriz. in 1992 he joined the electrical engineering department of the university of tabriz as a lecturer. he received the ph.d. degree in electrical engineering from the same university in 2000. in 2000 he rejoined the electrical power department of the faculty of electrical and computer engineering of the same university as an assistant professor. he is currently a professor of the mentioned department. his research interests are in the areas of design, modeling and analysis of electrical machines, transformers, linear electric motors, and electric and hybrid electric vehicle drives. sajjad tohidi was born in meshkin shahr, iran, in 1984. he received the b.sc. degree from iran university of science and technology, tehran, iran, in 2006, and m.sc. and ph.d degree in 2008 and 2012 respectively from sharif university of technology (sut), tehran, iran. he was on sabbatical at durham university, durham, u.k., and university of cambridge, cambridge, u.k., in 2011. he is currently an assistant professor in the department of power engineering of the university of tabriz. his research interests include power systems dynamics, electrical machines, and wind power generation. microsoft word 05-investigation-2.doc etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 315-319 315 www.etasr.com olutoge et al: investigation of the strength properties of palm kernel shell ash concrete investigation of the strength properties of palm kernel shell ash concrete dr. festus a. olutoge dept. of civil engineering university of ibadan, nigeria fa.olutoge@mail.ui.edu.ng habeeb a. quadri dept. of civil engineering university of ibadan, nigeria dejiquadry@yahoo.com oladipupo s. olafusi dept. of civil engineering university of ibadan, nigeria olafusidipo@yahoo.com abstract: many researchers have studied the use of agro-waste ashes as constituents in concrete. these agro-waste ashes are siliceous or aluminosiliceous materials that, in finely divided form and in the presence of moisture, chemically react with the calcium hydroxide released by the hydration of portland cement to form calcium silicate hydrate and other cementitious compounds. palm kernel shell ash (pksa) is a by-product in palm oil mills. this ash has pozzolanic properties that enables it as a partial replacement for cement but also plays an important role in the strength and durability of concrete. the use of palm kernel shell ash (pksa) as a partial replacement for cement in concrete is investigated. the objective of this paper is to alleviate the increasing challenges of scarcity and high cost of construction materials used by the construction industry in nigeria and africa in general, by reducing the volume of cement usage in concrete works. collected pksa was dried and sieved through a 45um sieve. the fineness of the pksa was checked by sieving through 45um sieve. the chemical properties of the ash are examined whereas physical and mechanical properties of varying percentage of pksa cement concrete and 100% cement concrete of mix 1:2:4 and 0.5 water-cement ratios are examined and compared. a total of 72 concrete cubes of size 150 × 150 × 150 mm³ with different volume percentages of pksa to portland cement in the order 0:100, 10:90 and 30:70 and mix ratio of 1:2:4 were cast and their physical and mechanical properties were tested at 7, 14, 21 and 28 days time. although the compressive strength of pksa concrete did not exceed that of opc, compressive strength tests showed that 10% of the pksa in replacement for cement was 22.8 n/mm 2 at 28 days; which was quite satisfactory with no compromise in compressive strength requirements for concrete mix ratios 1:2:4. this research showed that the use of pksa as a partial replacement for cement in concrete, at lower volume of replacement, will enhance the reduction of cement usage in concretes, thereby reducing the production cost. this research was carried out at the university of ibadan, ibadan, nigeria. keywords: agro-wastes; concrete; ordinary portland cement; palm kernel shell ash (pksa); compressive strength notations the following abbreviations are used in this paper: astm american society for testing and materials opc ordinary portland cement pksa palm kernel shell ash i. introduction concrete is the most versatile heterogeneous construction material and the impetus of infrastructural development of any nation [1]. concrete is a composite inert material comprising of a binder course (e.g. cement), mineral filler (body) or aggregates and water [2]. concrete is one of the oldest manufactured construction materials used in construction of various structures around the world. the cost of concrete and other construction materials in nigeria is currently so high that the majority of individuals find it difficult to afford, with the exception of government, industrial and business corporations. there had been calls from several government quarters on means to reduce the cost of civil engineering construction works by adopting cheap locally available engineering materials. the nigerian building and road research institute (nbrri) was established in order to fulfill this mandate. ordinary portland cement (opc) is acknowledged as the major construction material throughout the world. the production rate is approximately 2.1 billion tonnes per year, and is expected to grow exponentially to about 3.5 billion tonnes per year by 2015 [3]. according to adepegba [4] the annual cement requirement in nigeria is about 8.2 million tonnes and only 4.6 million tonnes of portland cement are produced locally. the balance of 3.6 million tonnes or more is imported. if alternative cheap cement can be produced locally the demand for portland cement will reduce and ultimately reduce the cost. the search for suitable local materials to manufacture pozzolana cement was therefore intensified and one of the discoveries was that of palm bunch wastes [4]. most of the increase in cement demand will be met by the use of supplementary cementing materials, in order to reduce the green gas emission [5]. industrial wastes, such as blast furnace slag, fly ash and silica fume are being used as supplementary cement replacement materials and, recently, agricultural waste are also being used as pozzolanic materials in concretes, such as palm oil fuel ash (pofa), silica from rice husk and rice husk ash [6]. when pozzolanic materials are incorporated to concrete, the silica present in these materials reacts with the ca (oh)2 released during the hydration of cement and forms additional calcium silicate hydrate (c-s-h), etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 315-319 316 www.etasr.com olutoge et al: investigation of the strength properties of palm kernel shell ash concrete which improves durability and the mechanical properties of concrete [7]. pksa has the potential to be used as a construction material. it is a by-product in palm oil mills. after palm oil is extracted from the palm oil fruit, both palm oil husk and palm oil shell are burned as fuel in the boiler of palm oil mill. generally, after combustion; about 5% pksa by weight of solid wastes is produced [8]. the ash produced sometimes varies in tone of color from whitish grey to darker shade based on the carbon content in it. in other words, the physical characteristic of pksa is very much influenced by the operating system in the palm oil factory. utilization of pksa is minimal and unmanageable while its quantity increases annually and most of the pksa are disposed as waste in landfills causing environmental problems [9]. to solve the energy problems, solid wastes from palm oil residue are used as fuel to produce steam for electricity generation. after burning, an ash by-product is produced. as a solution to the disposal problem of the ash derived from palm oil, research studies have been carried out to examine the feasibility of using the ash as cement replacement materials [10]. the objective of this paper is to study the potential of pksa as partial replacement for cement in concrete, the effects of increasing the volume of pksa replacements on the compressive strength of concrete and the extent to which the pksa can partially replace cement in concrete. ii. test details a. specimen preparation pksa used in this study was collected from a local palm oil processing factory at abedo village via moniya in akinyele local government area of ibadan, oyo state. already dried palm kernel shell was collected. it was burnt and grinded into fine ash particles (pksa). the pksa was sieved through 45um sieve in order to remove any foreign material and bigger size ash particles; and only the fine ashes which pass through 45um sieve were collected (which is available abundantly locally). the chemical analysis of the pksa samples was further carried out in a chemistry laboratory to examine its chemical constituent. the fine aggregate used was sharp sand. granite was used as coarse aggregate. b. mix proportions of concrete specimens the proportioning by weight was used in this research. the cement-aggregates ratio used in this work was 1:2:4. pksa were used to replace opc at dosage levels of 10% and 30% replacement by weight of binder. the mix proportions used were as calculated below: no. of cubes per batch=24 (i.e. six cubes each for ages 7, 14, 21 and 28 days tests) note: batch implies control mix (0% pksa replacement), 10% pksa replacement and 30% pksa replacement size of each cube = 150 mm×150 mm×150 mm vol. of cube = 150 3 = 3.375×10 -3 m 3 vol. of 24 cubes = 24×3.375×10 -3 = 0.081 m 3 to cater for wastage, it was factored by 1.2 vol. of the batch = 0.081×1.2=0.0972 m 3 the ratio used in this research is 1:2:4 = cement: sand: coarse aggregate cement = 1/7 vol of cement needed = (1/7)×0.0972 m 3 = 0.0138858 m 3 standard weight of concrete = 2400 kg/m 3 therefore: weight of cement in one batch =2400×0.0138858 = 33.33 kg ≅ 34 kg vol. of sand=(2/7)×0.0972 m 3 = 0.027774 m 3 weight of sand = 2400×0.0277714 = 66.65 kg ≅ 67kg vol. of coarse aggregate = (4/7)×0.0972 m 3 = 0.0555429 m 3 weight of coarse aggregate = 2400×0.0555429=133.30 kg ≅ 134 kg the water to binder ratio adopted in the course of this research was 0.5 and this was used to calculate the amount or weight of water required per batch. weight of water = 0.5×weight of binder (cement) = 0.5×34 kg = 17 kg based on the calculations above, the mix design of concrete in table i below was generated. table i. mix design of concrete constituent materials control 0% pksa 10% pksa 30% cement (kg) 34.0 30.6 23.8 pksa (kg) 0.0 3.4 10.2 fine aggregate (kg) 67.0 67.0 67.0 coarse aggregates (kg) 134.0 134.0 134.0 water/binder ratio 0.5 0.5 0.5 total water (kg) 17.0 17.0 17.0 iii. test procedure twenty four (24) cubes each were cast for opc as a control mix, opc replaced with 10% and 30% of pksa 45um, making a total of seventy two (72) cubes. all freshly cast specimens were left in the moulds for 24 hours before being demoulded and then cured in water until it was time to be tested as shown in figures 1 and 2. since the numbers of molds required were many, wooden moulds of size 150×150×150 mm were made to cast the entire specimen in one day. the weights of the cubes were examined prior to crushing so as to etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 315-319 317 www.etasr.com olutoge et al: investigation of the strength properties of palm kernel shell ash concrete determine their densities as shown in figure 3. compressive test was conducted at ages of 7, 14, 21, 28 days as shown in figure 4. iv. results and discussion figure 1 shows the pksa concrete cubes while setting, figure 2 shows the curing process of the cubes, figure 3 shows the weighing process to determine the density of the cubes while figure 4 shows the compressive strength testing process. table ii shows the details of the chemical properties of the pksa; table iii shows the detailed densities of the concrete samples, while table iv shows the results of the compressive strength test. fig. 1. pksa concretes while setting fig. 2. pksa concretes in a curing basin fig. 3. weighing process to determine densities of concrete samples fig. 4. compressive strength test table ii. particle sieve analysis of pksa sieve size (mm) % passing 0.600 100 0.425 99.9 0.300 97.5 0.212 83.3 0.150 49.8 0.075 33.5 0.045 31.3 table iii. specific gravity of pksa sample weight (g) test a (g) test b (g) w1 w2 w3 w4 28.20 51.30 97.90 85.40 31.70 55.90 103.10 88.90 gs 2.18 2.41 )}23()14/{( 12 wwwwwwgs −−−−= 2 41.218.2 + =gsaverage 30.2295.2 ≅=gs etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 315-319 318 www.etasr.com olutoge et al: investigation of the strength properties of palm kernel shell ash concrete table iv. chemical properties of pksa chemical composition (%) opc pksa sio2 22.13 54.810 al2o3 3.74 11.4 fe2o3 2.97 0.362 cao 63.36 8.786 mgo 2.58 6.108 k2o 0.52 6.254 true density (g/cm3) 2.97 2.60 table v. density of the cubes (× 10 3 kg/m 3 ) 7 days 14 days 21 days 28 days 0% pksa content (control) 2.53 2.57 2.62 2.64 10% pksa content 2.44 2.52 2.55 2.59 30% pksa content 2.46 2.47 2.49 2.52 table vi. characteristic strength of the cubes (n/mm 2 ) 7 days 14days 21days 28days 0% pksa content (control) 14.59 18.08 21.11 26.80 10% pksa content 11.41 16.22 17.33 22.80 30% pksa content 8.76 13.00 15.40 18.44 2.3 2.35 2.4 2.45 2.5 2.55 2.6 2.65 2.7 7 days 14 days 21 days 28 days 30% pksa content 10% pksa content 0% pksa content (control) fig. 5. densities (x10 3 kg/m³) of various pksa contents 0 5 10 15 20 25 30 7days 14 days 21 days 28 days 0% pksa content (control 10% pksa content 30% pksa content fig. 6. compressive strengths of various pksa contents v. sample properties the pksa collected were grayish in color. the main constituents of the pksa are silicon (as sio 2 ), aluminum (as al 2 o 3 ), and iron oxide (as fe 2 o 3 ). the total amount of sio 2 , al 2 o 3 and fe 2 o 3 present in pksa is 66.572% which is more than the minimum required (50% min.) specified by [11], for type c ash; while its calcium oxide (cao) content is about 8.786%; as shown in table ii. the specific gravity of the pksa was gotten to be 2.30; which was less than that of the opc of 3.15. this means a considerable greater volume of cementitious materials will result from mass replacement for cement. water absorption, initial and final setting time of the pksa concrete took longer time than opc concrete, which implies that the presence of pksa increases the water absorption and setting time of concrete. therefore the higher the pksa content in concrete, the longer the water absorption and setting time. this is so because, the factors that influence setting time of concretes are the volume of portland cement, water requirement, temperature of the concrete and the reactivity of the pozzolan. however, pksa concretes do not absorb water as fast as opc concretes; thereby retarding hydration processes in the pksa concrete (pksa concretes retain water for a longer period before it starts to dry up slowly). table iii revealed that the density decreased with increasing percentage of pksa and increased with curing age (i.e. the more the ash content in the concrete, the lower the density and the density also increases with curing age). this is because density is a reflection of weight; as concretes gain strength and weight with curing age due to hydration process; so pksa concretes are lighter than opc concretes due to its slow strength and weight development and the volume of portland cement in the concretes determines the porosity and the degree of compaction of the concrete. table iv revealed that 10% pksa concrete at 28 days was 22.80 n/mm² meets the minimum required strength of concrete at 28 days; while the slow development of strength which is an important characteristic of pozzolans could be responsible for the 28 days strength of 30% pksa concrete which was 18.44 n/mm². the rate of strength development also depends on the volume of cement replacement. however, they tend to gain more strength over a longer period of time beyond 28 days because concretes made with pozzolans are generally stronger, harder and more durable. this research was limited to a 28 th day examination. it is recommended that subsequent research should examine 90days strength tests and/or use concrete accelerators which increase hydration processes thereby influencing strength at 28days. vi. conclusion based on the findings from this study, the following conclusions can be arrived at; 1. pksa contains all the main chemical constituents of cement though in varying quantities compared to that etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 315-319 319 www.etasr.com olutoge et al: investigation of the strength properties of palm kernel shell ash concrete of opc; this means it will be a good replacement if the right percentage is used. 2. the use of pksa as a partial replacement for cement exhibits a lower water absorption rate and slower setting time of concrete. 3. concrete strengths increases with curing age and decreases with increasing percentage of pksa replacement in concrete. 4. the use of pksa will reduce the volume of cement used in concrete, thereby reducing the cost of concrete production. 5. the use of pksa will minimize the environmental issues arising from the disposal of palm kernel wastes. vii. recommendation 1. subsequent studies on concretes with the replacement of cement with pksa should be allowed to cure for 90 days, by which pozzolanic activity of ash is believed to have been concluded. 2. reduced cost of construction arising from the use of locally available agricultural waste materials such as pksa will enhance infrastructural developments. references [1] o. s. olafusi, f. a. olutoge, “strength properties of corn cob ash concrete”, journal of emerging trends in engineering and applied sciences, vol. 3, no. 2, pp. 297-301, 2012 [2] v. o. oyenuga, simplified reinforced concrete design, astros limited, lagos, nigeria, 2001 [3] s. j. coutinho, “the combined benefits of cpf and rha in improving the durability of concrete structures. cement and concrete composites”, cement and concrete composites, vol. 25, no. 1, pp. 51–59, 2003 [4] d. adepegba, “pozzolanic activity of palm bunch wastes” materials and structures/materiaux et constructions, vol. 22, pp. 220-224, 1989 [5] a. bentur, “cementitious materials – nine millennia and a new century: past, present, and future”, journal of materials in civil engineering, vol. 14, no. 1, pp. 2-22, 2002 [6] g. r. de sensale, “strength development of concrete with rice-husk ash”, cement and concrete composites, vol. 28, no. 2, pp. 158-160, 2006 [7] s. igarashi, a. watanabe, m. kawamura, “evaluation of capillary pore size characteristics in high-strength concrete at early ages”, cement and concrete research, vol. 35, no. 3, pp. 513-519, 2005 [8] k. m. abdullah, w. hussin, f. zakaria, r. muhamad, z. abdul hamid, “pofa: a potential partial cement replacement material in aerated concrete” proceedings of the 6th asia-pacific structural engineering and construction conference (apsec 2006), kuala lumpur, malaysia, 5-6 september, 2006 [9] w. tanqchirapat, t. saeting, c. jaturapitakkul, k. kiattikomol, a. siripanichgorn, “use of waste ash from palm oil industry in concrete”, waste management, vol. 27, no. 1, pp. 81-88, 2007. [10] j. -h. tay, k. -y. show, “use of ash derived from oil-palm waste incineration as a cement replacement material”, journal of resources, conservation and recycling, vol.13, no. 1, pp. 27-36, 1995 [11] astm designation: c 618 standard specification for fly ash and raw or calcined natural pozzolan for use as mineral admixture in portland cement concrete, annual book of astm standards, american society for testing and materials, 1994 microsoft word etasr_v13_n4_pp11248-11252 engineering, technology & applied science research vol. 13, no. 4, 2023, 11248-11252 11248 www.etasr.com ramesh & sathiamoorthy: a deep learning grading classification of diabetic retinopathy on retinal … a deep learning grading classification of diabetic retinopathy on retinal fundus images with bio-inspired optimization radhakrishnan ramesh department of computer application, government arts and science college for women, india radha.esh@gmail.com (corresponding author) selvarajan sathiamoorthy annamalai university pg extension centre, india ks_sathia@yahoo.com received: 11 may 2023 | revised: 25 may 2023 and 5 june 2023 | accepted: 6 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6033 abstract diabetic retinopathy (dr) is considered the major cause of impaired vision for diabetic patients, particularly in developing counties. treatment includes maintaining the patient’s present grade of vision as the illness can be irreparable. initial recognition of dr is highly important to effectively sustain the vision of the patients. the main problem in dr recognition is that the manual diagnosis procedure consumes time, effort, and money and also includes an ophthalmologist’s analysis of retinal fundus imaging. machine learning (ml)-related medical image analysis is proven to be capable of evaluating retinal fundus images, and by using deep learning (dl) techniques. the current research presents an automated dr detection method by utilizing the glowworm swarm optimization (gso) with deep learning (adr-gsodl) approach on retinal fundus images. the main aim of the adr-gsodl technique relies on the recognizing and classifying process of dr in retinal fundus images. to obtain this, the introduced adr-gsodl method enforces median filtering (mf) as a pre-processing step. besides, the adr-gsodl technique utilizes the nasnetlarge method for deriving the gso, and feature vectors are applied for parameter tuning. for the dr classification process, the variational autoencoder (vae) technique is exploited. the supremacy of the adr-gsodl approach was confirmed by a comparative simulation study. keywords-diabetic retinopathy (dr); dr screening; fundus images; deep learning; metaheuristics i. introduction diabetic retinopathy (dr) is a complication of diabetes instigated by diabetes mellitus in which the glucose will block the blood vessels that feed the eye, leading to fluids or blood leakage and swelling that can cause serious eye injury [1]. the detrimental vision impairment due to dr befalls primarily if there is swelling in the retina. the estimated population that suffers from vision loss, whether severe or mild, due to trachoma, glaucoma, and dr, is 11 million [2]. to evade problems related to chronic diseases, namely diabetes, initial identification is crucial. abnormal development of blood vessels in the retina has an effective consequence of dr, which may cause bleeding or scarring from retina and subsequent blindness [3]. universally, dr accounts for nearly 2.6% of impaired vision cases. the period a person suffered from diabetics, high blood pressure readings, and high haemoglobin are regarded as the most high-risk elements linked with dr growth [4]. regular screening is the most used diagnostic tool to ensure that dr is diagnosed at a primary phase. dr detection usually includes an examination by physician of retinal images for the appearance and shape of distinct kinds of lesions [5]. retinal fundus image analysis is useful in medical processing [6]. diseases such as dr, macular degeneration, hypertension, and atherosclerosis could modify the morphology of the arteries, generating modifications in their branching angle, diameter, and tortuosity [7]. manual segmentation of retinal vascular ailments is a time-consuming and skilldemanding process. the initial diagnosis of dr plays an important role in the prevention of blindness. henceforth, doctors prescribe annual retinal screening tests [8]. remarkably, such retina scans are utilized for detecting diabetes, though this demands the judgment of ophthalmologists, which may take time. in the detection of dr, dl methods have illustrated better performance, with a high accuracy level that differentiates them from other methods [9]. certainly, dl could not cover concealed components in images that clinical experts would never see. due to their capacity in training and feature extractions in discriminating among many classes, convolutional neural networks (cnns) are the most employed dl method in the health care sector [10]. often, the engineering, technology & applied science research vol. 13, no. 4, 2023, 11248-11252 11249 www.etasr.com ramesh & sathiamoorthy: a deep learning grading classification of diabetic retinopathy on retinal … use of the transfer learning (tl) method simplified the process of retraining deep neural network (dnn) reliably and speed. this research presents an automated dr detection method using the dso with dl (adr-gsodl) approach on retinal fundus imaging. the main aim of the adr-gsodl technique relies in the recognition and classification process of dr in retinal fundus imaging. to obtain this, the adr-gsodl method enforces median filtering (mf) as a pre-processing step. besides, the adr-gsodl technique also utilizes the nasnetlarge method for deriving the gso and feature vectors are applied in the parameter tuning process. for the dr classification process, the vae technique is exploited. to illustrate the advanced performance of the adr-gsodl approach, comparative simulation analysis is executed. ii. literature review authors in [11] introduced cad techniques that use the dl results for image recognition. this method relies on a deep residual cnn to derive biased factors with no previous convolution images transforming to accentuate specific structures or to improve the image qualities. authors in [12] developed the quantum tl (qtl) algorithm to achieve dr diagnosis. qtl is a hybrid integration of quantum computing and traditional tl. authors in [13] explored ways to utilize deeper tl for the diagnoses of dr through oct images. the authors retrain the present dl model for these tasks and investigate how a retrained method could be enhanced. they demonstrate that utilizing an improved pre-training module as a feature extractor and training a traditional classification on this feature is an efficient method to identify dr through oct images. authors in [14] developed a novel two-phase architecture for the classification of automated dr. initially, the authors used two different u-net architectures for blood vessel (bv) and optic disc (od) segmentation during the preprocessing. next, the improved retinal imaging afterward the extraction of od and bv are applied as the input of tloriented vggnet architecture that implements dr diagnosis by recognizing retinal biomarkers namely exudates (ex), microaneurysm (ma), and haemorrhages (hm). authors in [15] introduced a learning-based model for the classification and segmentation of dr lesioning. the pre-training xception module was applied for the deep factor extracting process in the segmenting stage. the derived feature was given to deeplabv3 for semantic segmentation. for segmentation training, a study was conducted for the selection of optimum hyperparameters that the presented method resulted in the evaluation stage. the multiple classification method is proposed for extracting features through fc matmul layers of pool-10 of the squeeze-net and efficient-net-b0. in [16], automated detection of severity of dr using cnn with a tl technique was developed to assist the diagnosis method. a comparison of distinct cnn frameworks like inceptionresnet-v2 and resnet was performed by the quadratic weighted kappa metric. iii. the proposed model in this research, we introduce the adr-gsodl technique for dr classification on retinal fundus imaging. the adrgsodl technique intends to recognize and classify of dr in retinal fundus imaging. it follows a sequence of procedures, namely mf noise removing process, nasnetlarge feature extractor, gso parameter tuning process, and vae classification process. figure 1 demonstrates the adr-gsodl block diagram model. fig. 1. block diagram of the adr-gsodl. a. feature extraction the adr-gsodl technique utilizes nasnetlarge approach for the derivation of featuring vectors. the nasnetlarge networking contains encoding, decoding, and classifying layers [17]. there are 2 important variances related to segnet which utilizes the pre-trained vgg16 infrastructure to encoder. the nasnetlarge-decoder net utilizes the primary 414 layers of nasnetlarge net (i.e. a highly trained network to imagenet classification) as encoding to decompose the image. it employs the pre-trained weighted network and then retrains it with new data for appropriating nasnetlarge as the database can be different from imagenet. furthermore, the decryption is different and there is no pool index. the nasnetlarge net will produce comprehensive decoded datasets. the appropriately decoded upsample has its input feature mapping with max-pool layers. all blocks initiate with upsampling which would extend the relu, feature mapping, and convolutional layer. after that, a batch normalization layer is used. the primary decrypted data were closer to the final encrypted data generating a multichannel feature map, in a way analogous to segnet. b. hyperparameter tuning in this work, the gso algorithm is enforced for this process. in gso, a glowworm (gw) has a luciferin value and decisions are made on a local level [18]. the luciferin value relies upon its location and objective function. the superior the location of the gw, the brighter it is (i.e. has more luciferin) than its neighbors. �� �� � 1� � �1 ��� ��� � �� ����� (1) for the gw �, the ���� characterizes its luciferin value. this value decay constant is represented as and ranges from 0 to 1. the enhancement fraction of luciferin is denoted as �, ������� provides the objective function at the existing location �� of gw �. then, the gw � will explore the adjacent area to find the neighbors with maximum luciferin values by employing the following rule: engineering, technology & applied science research vol. 13, no. 4, 2023, 11248-11252 11250 www.etasr.com ramesh & sathiamoorthy: a deep learning grading classification of diabetic retinopathy on retinal … ���� ��� if ���������� < !"� ��� and �& ��� > �� ��� (2) where � indicates the gw closer to the � �ℎ gw , ���� represents the set of neighboring gws, ����������indicates the euclidean distance, !"��� provides the local decision range of the � �ℎ gw, and the luciferin levels of gws � and � are denoted by ���� and ����, respectively. the better neighboring gw from the neighboring set is chosen by evaluating the probability of each gw: )!*+�+�,��-�� � ./�0�1.2�0� ∑ .45672 �0�1.2�0� (3) the location of a gw is attuned according to the location of a better neighboring gw and is evaluated by: �� �� � 1� � �� ��� � � 8/�0�182�0� 9�:0;<=>2? (4) where � > 0 indicates the step size of the movement of a gw. the decision range !"� ��� is evaluated as follows: !"� �� � 1� � min b!:, maxd0, !"� ��� � e��f |�� ���|�hi (5) where !: indicates the radial sensor range constant, e represents the model constant, and �j restricts the neighborhood numbers. c. vae-based dr detection for dr classification process, the vae model is utilized in this work. vae belongs to the family of generative mechanisms and bears massive similarities to ae with respect to the design [19]. these mechanisms consist of an encoder (inference or recognition method) and a decoder that is called the generative mechanism. one more similarity among these two is that they try to recreate input datasets while learning from latent vectors. a difference among these two is that vae’s latent space is constant, because the encoder does not output an encoder vector of length �, 0 mean, and 1 standard deviation (sd). the mean vector aims to control the center position of the encoding input, while the sd vector aims to control the region where the encoding could differ. because the encoding is randomly generated, the decoder also exposes itself to encoding variations. the vae encoder will learn a map kl ��|m� from the input n� with covariance * o�n� � and mean p�n� � vectors of the latent variable. vae assumes data augmenting while considering that the latent variable � follows a uniform distribution (0, 1). the decoder should trial from the latent dispersion given as output through encoder because it no more results a latent depiction � as in ae. the vae decoder would learn a map )q �|� from � latent illustration to the dispersion parameter of the training dataset x. for generating realtime samples for the decoder and to avoid overfitting, the log probability of input dataset log ���m�� , should be maximized. a uniform dispersion has identity covariance matrices that denote that the covariance among the latent variables is 0 and they are not dependent. therefore, the vae learns the distribution of training dataset ��m� with encoder kl ��|m�, decoder )q �m|��, and latent dispersion ���� and can be trained by means of the objective function (6): maxl,u,*v���m�� ≈ maxl,u xyz��|[� d,*v�)u�m|���h �\. �kl��|m�|]����� (6) whereas ^, _ denote the parameters of the encoder and decoder, respectively and �\. characterizes the kl divergence amongst two likelihood distributions. iv. results and discussion the presented adr-gsodl method is investigated using the dr database from kaggle [20]. the database holds 35126 instances with 5-class labelling as represented in table i. the presented modes are simulated by utilizing the python 3.6.5 tool on an i5-8600k pc, with geforce 1050ti 4gb, 16 and 250 gb ram and ssd, and 1tb hdd. the parameter setup is: learning rate: 0.01, epoch count: 50, batch size: 5, dropout rate: 0.5, and activation function: relu. table i. dataset details label dr class number of samples 0-dr no 25810 1-dr mild 2443 2-dr moderate 5292 3-dr severe 873 4-dr proliferative 708 total no. of instances 35126 the confusion matrices of the adr-gsodl approach are shown in figure 2. in the 80% of the dataset (training –tr), the adr-gsodl approach has classified 20434, 1878, 4202, 625, and 492 samples into dr of l0, l1, l2, l3 and l4 class, respectively. on 20% the dataset (testing-ts), the adrgsodl technique has classified 5148, 493, 996, 165, and 112 samples into dr of l0, l0, l1, l2, l3 and l4 class. in the same manner, on 70% tr, the adr-gsodl technique categorized 17875, 1585, 3590, 590, and 475 samples into dr of l0, l1, l2, l3 and l4 class. table ii reports a comprehensive dr classifying of the results of the adrgsodl approach on 80 and 20% of tr and ts. on 80% tr, it is notified that the adr-gsodl method has gained average ���`a of 99.33%, ����a of 93.92%, ����a of 99.46%, �:=bf> of 94.06%, and npv of 99.30%. besides, on 20% ts, the adr-gsodl technique has obtained average ���`a of 99.36%, ����a of 94.64%, ����a of 99.51%, �:=bf> of 94.38%, and npv of 99.29%. table ii. dr classifying outcome of the adrgsodl for 80% and 20% tr and ts class accuy sensy specy fscore npv training phase (80%) dr-0 99.04 99.13 98.80 99.34 97.62 dr-1 99.38 97.00 99.55 95.55 99.78 dr-2 99.21 98.20 99.39 97.43 99.68 dr-3 99.55 90.71 99.77 90.84 99.77 dr-4 99.48 84.54 99.80 87.16 99.67 average 99.33 93.92 99.46 94.06 99.30 testing phase (20%) dr-0 99.06 99.08 99.02 99.36 97.42 dr-1 99.40 97.24 99.57 95.91 99.78 dr-2 99.23 98.32 99.38 97.36 99.72 dr-3 99.56 89.67 99.82 91.41 99.72 dr-4 99.56 88.89 99.75 87.84 99.80 average 99.36 94.64 99.51 94.38 99.29 engineering, technology & applied science research vol. 13, no. 4, 2023, 11248-11252 11251 www.etasr.com ramesh & sathiamoorthy: a deep learning grading classification of diabetic retinopathy on retinal … table iii illustrates the comprehensive dr classifying output of the adr-gsodl method on 70 and 30% of tr and ts, respectively. on the tr, the adr-gsodl methodology acquired average ���`a of 99.23%, ����a of 95.45%, ����a of 99.47%, �:=bf> of 92.94%, and npv of 99.15%. besides, on the ts the adr-gsodl method achieved average ���`a of 99.26%, ����a of 95.57%, ����a of 99.50%, �:=bf> of 92.51%, and npv of 99.20%. fig. 2. confusion matrix of adr-gsodl method (a-b) 80:20 tr and ts and (c-d) 70:30 tr and ts data. table iii. dr classifying outcome of the adrgsodl for 70% and 30% tr and ts class accuy sensy specy fscore npv training phase (70%) dr-0 98.97 98.88 99.20 99.29 96.97 dr-1 99.31 94.01 99.70 94.91 99.56 dr-2 99.19 97.37 99.51 97.30 99.54 dr-3 99.59 94.40 99.73 92.19 99.85 dr-4 99.09 92.59 99.23 80.99 99.84 average 99.23 95.45 99.47 92.94 99.15 testing phase (30%) dr-0 99.04 98.97 99.25 99.34 97.21 dr-1 99.38 94.45 99.76 95.65 99.57 dr-2 99.20 97.13 99.57 97.38 99.49 dr-3 99.61 93.95 99.75 91.91 99.85 dr-4 99.04 93.33 99.15 78.28 99.87 average 99.26 95.57 99.50 92.51 99.20 the training and validation accuracy, cd;== and e�;== , respectively, reached by the adr-gsodl approach under trial data are shown in figure 3. the simulating values illustrated that the adr-gsodl approach has attained greater cd;== and e�;== values. seemingly the e�;== is greater than cd;== . fig. 3. cd;== and e�;== of the adr-gsodl method. to verify the enhanced performance of the adr-gsodl method, a comprehensive relative study was conducted and its results are given in table iv. it is noticed that the alexnet model fails to achieve effectual outcomes the output specified that the resnet-50 and resnet-101 approaches have performed less satisfactory, in contrast with the vgg-16 and inception v3 approaches. the adr-gsodl approach achieved the optimum performance with ���`a of 99.26%, ����a of 95.57%, and ����a of 99.50%. thus, the adr-gsodl model can be considered an effective tool for the dr grading process. v. conclusion in this study, the novel adr-gsodl model to classify dr on retinal fundus imaging is presented. the main aim of the adr-gsodl model is in the classification and recognition of dr in retinal fundus images. to obtain this, the adr-gsodl technique applied the mf approach as a pre-processing step. also, the adr-gsodl technique utilizes the nasnetlarge model to derive feature vectors, whereas gso algorithm is applied for the tuning process. for dr classification, the vae method is considered. to exhibit the enhanced adr-gsodl performance, a widespread simulation analysis was performed and the comparison study assured the supremacy of the adrgsodl technique. in the future, the computation complexity of the proposed model can be examined. in addition, the proposed model can be tested on large scale datasets. references [1] i. kandel and m. castelli, "transfer learning with convolutional neural networks for diabetic retinopathy image classification. a review," applied sciences, vol. 10, no. 6, jan. 2020, art. no. 2021, https://doi.org/ 10.3390/app10062021. 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[20] "diabetic retinopathy detection," kaggle, 2015. https://kaggle.com/ competitions/diabetic-retinopathy-detection. engineering, technology & applied science research vol. 8, no. 4, 2018, 3203-3208 3203 www.etasr.com smyrlis et al.: constrained k-means classification constrained k-means classification panagiotis n. smyrlis department of informatics and telecommunications engineering university of western macedonia kozani, greece pan.smyrlis@gmail.com dimosthenis c. tsouros department of informatics and telecommunications engineering university of western macedonia kozani, greece dtsouros@uowm.gr markos g. tsipouras department of informatics and telecommunications engineering university of western macedonia kozani, greece mtsipouras@uowm.gr abstract—classification-via-clustering (cvc) is a widely used method, using a clustering procedure to perform classification tasks. in this paper, a novel k-means-based cvc algorithm is presented, analysed and evaluated. two additional techniques are employed to reduce the effects of the limitations of k-means. a hypercube of constraints is defined for each centroid and weights are acquired for each attribute of each class, for the use of a weighted euclidean distance as a similarity criterion in the clustering procedure. experiments are made with 42 well–known classification datasets. the experimental results demonstrate that the proposed algorithm outperforms cvc with simple k-means. keywords-classification-via-clustering; k-means; supervised learning i. introduction data science and especially data mining [1] is a rapidly evolving field with the extraction of valuable knowledge out of large accumulated information being a major challenge. recent technological progress has led to the creation of large datasets to all scientific areas. thus, developing methodologies which discover knowledge out of raw data is now many researchers' common concern. supervised learning methods are an important part of machine learning and data mining, referring to the task of learning from labeled training data, with classification being the most common. many sophisticated classification algorithms have been proposed in the literature, each exploiting the data in a different way, such as artificial neural networks [2], bayesian classifiers [3], rule based classifiers [4, 5], decision trees [6, 7] and ensemble classifiers [8]. a widely used method is classification-viaclustering (cvc) [9-14]. the latter involves a clustering technique, in order to group data into clusters, mapped to the classes. instances are assigned to the clusters or classes according to some criterion (depending on the clustering algorithm used). the most known algorithm in clustering is kmeans [15, 16], which is computationally light. its low complexity makes it suitable to use in big data analysis for clustering and classification. it is referred to a clustering procedure which pattern for each cluster is a centroid. as a similarity criterion, a sort of distance is used (most commonly the squared euclidean). according to that criterion, each data is assigned to the proper cluster and the centroids are then recalculated given the updated cluster. this algorithm is widely used in cvc, where the clusters are matched to classes. copkmeans [17] is a variation of k-means, using background knowledge in terms of data-level constraints. this includes two kinds of constraints, must-link and cannot-link, defining whether a data must or must not be in a cluster, neither of which can be violated in order to assign a data point to a cluster. so, if a cluster includes a data-point which must be in the same cluster with another, the latter must be assigned to that cluster. also, if two data-points are parts of a cannot-link constraint, they cannot be in the same cluster. in the same manner, another technique proposes an extended set of the above set of constraints [18]. must-link and cannot-link constraints remain, and two more are examined. the latter are based on calculating the maximum distance that two datapoints in the same cluster and the minimum distance that two data-points in different clusters must have. another approach is constrained k-means [19], which includes cluster-level constraints; each cluster has a constraint which is a threshold of the minimum number of data to contain. so, the final centroids are specified when all the clusters contain the desired amount of data. a different method of finding the k centroids is global k-means [20], where the problem is solved incrementally. an iterative procedure begins solving the problem initially for one centroid and each iteration adds one centroid to the solution until the k centroids are found. “fast global k-means” [20] tries to accelerate the above procedure. instead of solving the k-centroids' problem given the k-1 solution, tries to calculate the error reduction from inserting the new centroid. the calculated error is used as a threshold on the next execution of k-means. a different approach is “fuzzy c-means” algorithm [21], with each datum fractionally belonging to all clusters and contributing to all centroids' update. in this work, a k-means based cvc algorithm is presented, introducing the use of constraints for the centroids movement and a weighted euclidean distance as a similarity criterion. the proposed algorithm is evaluated with 42 well known datasets from the uci machine learning repository [22]. the 10-fold cross-validation [23] is employed and classification accuracy, average sensitivity and average precision [24] are used as metrics of interest. experimental results demonstrate that the proposed algorithm considerably outperforms cvc with simple k-means. ii. cvc with simple k-means clustering is a method of finding subgroups within observations. the most known clustering algorithm used for engineering, technology & applied science research vol. 8, no. 4, 2018, 3203-3208 3204 www.etasr.com smyrlis et al.: constrained k-means classification cvc is k-means, which divides the instances of a dataset into clusters. since the number of clusters to be extracted is predefined, k-means can be easily used in classification by setting k to be equal or greater than the number of classes and mapping each cluster to a specific class. in k-means based cvc, is usually set equal to the number of classes . kmeans forms the clusters using the training set. each cluster is mapped to the appropriate class using the labels of the training data. the majority class of the instances of each cluster is assigned to it. in the classification process, the unlabeled instances are assigned to the closest centroid of the clusters formed in the previous step. the formulation of the clusters using k-means algorithm is summarized in the following simple k-means algorithm: input: dt (dt: the training set) output: m (m: the means (centroids)) 1: t=0; 2: initialize randomly the c means m1 t,…,mc t; 3: do 4: c=assigninstances(dt, m t); 5: mt+1=updatemeans(c); 6: t++; 7: while mt!=mt-1 8: return mt; k-means consists of three main steps. at first, the means are initialized randomly (line 2). next, the algorithm assigns the training instances to the “nearest”' mean's cluster (line 4) and updates the means to the centroid of the formulated cluster (line 5). to assign each instance , = 1, . . . , , to a cluster, the squared euclidean distance , = 1, . . . , , from each mean is calculated, as shown in (1). = ∑ ( , − , ) (1) where is the number of attributes. after the calculation of the squared euclidean distance, the instance is assigned to the cluster where ≤ for every ∈ 1, . . . , . the third step of k-means is the recalculation of each mean to be the centroid of all the instances currently in the cluster: , = (∑ ∈ , )/| | , (2) | | is the size of the cluster, in other words the number of instances that are assigned to it. in k-means, if (the number of clusters) and (the number of attributes) are fixed, the problem can be exactly solved in time ( ), where is the number of instances to be clustered [25]. the k-means algorithm has some limitations and weaknesses [26 28] that influence negatively its classification results. first of all, the random initialization of the centroids affects significantly the formation of the cluster-classses. furthermore, due to clustering task small classes may be dominated by bigger classes, so the grouping may demarcate the bigger class instances into 2 separate classes and include the instances of the small class to one of the bigger clusters. moreover, the presence of noise outliers in the dataset can affect the cluster pulling its centroid to a ’bad’ position. another factor that should be taken into account is the distance criterion for the assignation of each instance to a centroid. in cvc, each class may have a difference standard deviation in each attribute than the other classes, thus each attribute may have different contribution in the classification. iii. constrained k-means classification algorithm constrained k-means classification (c-k-means), a novel cvc algorithm, is proposed in this work. the algorithm is designed so as to address the limitations and weaknesses mentioned above. as classification is a supervised learning technique, background knowledge is used efficiently to extract the model. two main alterations to k-means are proposed to use background knowledge: (i) application of constraints to the initialization and update of the centoids, (ii) weighted euclidean distance fuction employment. the training data are used to acquire constraints for each centroid and the weights for each attribute and class. since each hypercube of constraints is generated based on data from a single class, each centroid inherits the class of the respective hypercube. the clustering procedure and the formulation of the clusters takes place in the test data rather than the training set. this helps us to better classify the testing instances, not only using the distance from each observation from the centroids, but also updating the centroids to the test set clusters formation. a. description of c-k-means the model produced during the training procedure includes a hypercube of each class and the weights for each attribute and each class. the algorithm takes as input a training dataset with attributes and classes and a hypercube is defined for each class by calculating minimum and maximum bounds for each attribute: , = , − ∗ , (3) , = , + ∗ , (4) with , being the average value of the attribute ( ∈[1, ]) of the instances belonging to the class ( ∈ [1, ]), and , the respective standard deviation. the minimum and maximum bounds are , and , , respectively and is a parameter defining the relaxation of these bounds. the bounds are used to limit the movement of the centroids and so the cluster formation. the weights are used to facilitate a weighted euclidean distance calculation as a similarity criterion to the clusters during clustering procedure. the concept includes the estimation of the standard deviation of each class’ features in order to define an importance factor for that to be used in the similarity criterion. the calculation of the weights is given by the following formula: , = 1 − ,, , (5) with , being the calculated weight, , being the standard deviation of the attribute ( ∈ [1, ]) of the observations belonging to the class ( ∈ [1, ]), and , , , the respective maximum and minimum values. the weights are then normalized: , = ,∑ , (6) after the acquisition of the hypercube of constraints and the weights, the algorithm is ready for the cvc of the unlabeled engineering, technology & applied science research vol. 8, no. 4, 2018, 3203-3208 3205 www.etasr.com smyrlis et al.: constrained k-means classification instances. k-means algorithm is applied as follows: initialization step: the initial k centroids are generated randomly within the hypercubes, with one centroid in each hypercube ( = ). thus: , ≤ , ≤ , (7) where , is the centroid value of class in attribute . assignment step: in this step, the weighted euclidean distance is employed as similarity criterion, with each observation assigned to the closest centroid. weighted euclidean distance is calculated as follows: = ∑ , ∗ ( , − , ) (8) update step: if during this procedure, a centroid is to be positioned outside the class hypercube of constraints (in which is initilly created), then it is forced to the bound values, i.e. if the value is less than its class , , then it is set to , , and the same applies if it is greater than the respective , . after the convergence of the clustering procedure, each instance is classified to the class of the cluster of the centroid that it was assigned in the last iteration. iv. experimental results and discussion to set up the experimental procedure, the discussed algorithm is implemented using c++. the relaxation parameter in (3) and (4), is experimentally set to 0.1. also, all attributes of the datasets are normalized. in order to evaluate the proposed algorithm, a comparative study with cvc with simple k-means took place and classification accuracy, average sensitivity and average precision performance metrics are extracted. for that purpose, weka software [29] was employed, where the respective results for cvc with simple kmeans were obtained. the number of clusters is set equal to the number of classes of each dataset. both algorithms are tested with 42 datasets from the uci machine learning repository, with various characteristics. the datasets, number of attributes and instances are presented in table i (the number of attributes does not include the class). classification accuracy, average sensitivity and average precision are obtained for each dataset; all results are shown in table ii. the differences per dataset are illustrated in figures 1, 2 and 3 for the classification accuracy, average sensitivity and average precision, respectively. the diagrams were created as follows: the result obtained with simple k-means was subtracted by the respective c-k-means result (for each dataset) and then the results were sorted in a descending order. the experimental study was based on an extremely large selection of classification datasets (42), including all classification datasets reported as “most popular” in the website, and several other well-known datasets. the main exclusion criterion was that no missing values should exist, since dealing with missing values is outside the scope of this study. the datasets have a number of attributes ranging from 4 to 255 and number of instances ranging from 83 to 45211, with 8 datasets having less than 200 instances, 20 having 200 to 1000 instances, 10 having 1000 to 5000 instances and 4 having more than 5000 instances. table i. datasets information # dataset attributes instances 1 abalone 8 4177 2 balance scale 4 625 3 bank full 17 45211 4 banknote 4 1372 5 blood transfusion 4 748 6 breast cancer (wdbc) 32 569 7 breast cancer (winscon) 9 699 8 breast_tissue 9 106 9 cardiotocography 21 2126 10 contraceptive 9 1473 11 dermatology 34 366 12 ecoli 7 336 13 fertility diagnosis 9 100 14 firm teacher 19 10800 15 glass 9 214 16 gps 6 163 17 ionosphere 34 351 18 iris 4 150 19 messidor features 18 1151 20 occupancy detection 7 20560 21 optdigit 64 1797 22 parkinson disease 22 195 23 parkinson speech 26 1239 24 pendigits 16 10992 25 pima indian 8 768 26 seeds 7 210 27 semeion 255 477 28 sonar 60 208 29 spect heart 22 267 30 spectf heart 44 267 31 statlog aust credit 14 690 32 statlog german credit 24 1000 33 statlog heart 13 270 34 statlog img seg 19 810 35 statlog sat image 36 2000 36 thyroid disease new 5 215 37 urban 147 168 38 vertebral column 3c 6 310 39 waveform 21 5000 40 wine 13 178 41 yeast 8 1484 42 zoo 16 83 for all experiments, the classification accuracy results per fold were obtained and a paired 10-fold cross validated t-test [30] was performed, in order to examine the statistical importance of the differences, with 95% confidence interval of 95%. in table ii, all datasets with statistically important difference are marked with a bullet in the right. the results presented in table ii indicate that the proposed approach is superior in terms of classification accuracy: the proposed algorithm outperforms the traditional k-means based cvc to all 42 datasets with the difference ranging from 1.14% to 43.22%. more detailed, the difference in 11 datasets is up to 5%, in 13 it ranges from 5% to 15%, while in another 10 datasets it’s between 15% and 25% and in the remaining 8 datasets it is over 25%. accuracy differences for all datasets are illustrated in figure 1. regarding the average sensitivity res k32 15 sur 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 we sim kins app engineerin www.etasr sults, once aga -means to all .16%. in 7 dat %, in 12 datas rpassed 25%. table ii. dataset abalone balance scale banknote ● blood transfusi breast cance (winsconsin breast cancer (w breast_tissue cardiotocograph contraceptive dermatology ecoli ● fertility diagno firm teacher glass gps ● ionosphere ● iris messidor featu optdigit ● parkinson disea parkinson spee pima indian seeds semeion ● sonar ● spect heart spectf hear statlog aust cre statlog germ credit ● statlog hear statlog img se statlog sat imag thyroid disea new ● urban ● vertebral column 3c ● waveform ● wine yeast ● zoo ● bank full ● occupancy detection ● pendigits ● average despite the ere observed mple k-means -means classi stances from proach. all se ng, technology r.com ain the propos datasets. the tasets it was be sets it was betw classifica classifica accura kmeans c m 50.73% 52 e ● 55.52% 68 ● 57.43% 85 ion ● 59.09% 66 er n) 95.71% 96 wdbc) 92.62% 93 ● 41.51% 60 hy ● 34.20% 54 e ● 37.54% 47 ● 71.86% 97 52.98% 79 sis ● 44.00% 68 r ● 55.56% 98 40.19% 45 66.87% 82 ● 70.94% 75 84.00% 93 ures 52.74% 57 74.80% 90 ase ● 58.46% 76 ech 57.78% 60 ● 64.84% 70 88.57% 91 58.07% 82 54.33% 73 t 62.55% 67 rt 64.04% 66 edit ● 76.81% 85 an 59.40% 70 rt 77.04% 80 eg ● 57.90% 85 ge ● 67.30% 78 ase 85.12% 94 60.12% 73 ● 44.19% 74 ● 49.94% 81 94.38% 96 36.86% 50 69.88% 92 ● 56.78% 71 y ● 62.16% 87 70.87% 82 62.28% 76 smaller max where c-k-m s with a bigger fication mana each class (i ensitivity resul y & applied sci sed algorithm difference ran elow 5%, in 1 ween 15% and ation-via-cluste ation acy avera sensitiv c-kmeans kmeans m 2.21% 50.90% 5 8.64% 51.43% 7 5.57% 57.70% 8 6.44% 49.20% 6 6.85% 94.85% 9 3.85% 91.05% 9 0.38% 45.02% 5 4.99% 38.32% 6 7.39% 37.77% 4 7.81% 75.67% 9 9.76% 49.99% 6 8.00% 50.40% 6 8.78% 65.80% 9 5.33% 40.27% 5 2.82% 65.15% 8 5.21% 71.40% 7 3.33% 87.30% 9 7.41% 51.85% 5 0.76% 75.81% 9 6.41% 70.50% 7 0.02% 57.35% 6 0.96% 60.55% 7 1.43% 88.57% 9 2.18% 58.14% 8 3.56% 54.35% 7 7.42% 60.65% 6 6.29% 50.00% 7 5.65% 78.55% 8 0.40% 52.50% 6 0.37% 77.15% 8 5.06% 62.81% 8 8.15% 66.55% 7 4.42% 72.80% 8 3.21% 63.36% 7 4.52% 41.52% 7 1.20% 49.97% 8 6.63% 95.30% 9 0.27% 37.93% 5 2.77% 65.06% 8 1.93% 52.10% 7 7.99% 68.60% 8 2.94% 71.51% 8 6.41% 61.67% 7 imum differe means was fo r difference. t aged to class in average) t lts are also giv ience research outperforms s nges from 1.9 7 it was from d 25%, while ering results age vity aver precis c-kmeans kmeans 53.54% 52.57% 5 73.93% 55.03% 7 84.92% 57.60% 8 67.16% 49.35% 6 96.81% 95.60% 9 93.28% 93.15% 9 58.62% 50.40% 6 64.02% 34.30% 5 49.47% 37.60% 4 97.55% 84.45% 9 61.79% 52.19% 5 60.23% 50.20% 5 97.96% 58.80% 9 51.96% 29.32% 5 81.66% 71.05% 8 76.48% 69.85% 7 93.33% 88.70% 9 57.42% 52.00% 5 90.76% 76.24% 9 77.34% 66.25% 7 60.04% 57.25% 5 72.33% 60.90% 7 91.43% 88.90% 9 81.95% 59.35% 8 73.08% 54.35% 7 67.42% 61.05% 6 78.77% 37.85% 6 86.30% 76.90% 8 69.71% 52.45% 6 80.83% 76.85% 8 85.79% 63.16% 8 77.59% 68.18% 7 87.62% 86.47% 9 74.44% 64.74% 7 73.22% 43.17% 7 81.11% 50.07% 8 97.18% 94.20% 9 57.24% 34.00% 4 84.85% 60.17% 8 71.64% 50.90% 5 89.36% 63.25% 8 82.93% 72.54% 8 76.44% 61.60% 7 nce, more da ound to outpe his indicates th sify correctly than the tradi ven in figure 2 h v simple 6% to 5% to in 6 it age sion c-kmeans 50.84% 71.66% 85.85% 62.75% 96.28% 93.53% 61.40% 53.60% 48.41% 97.55% 57.77% 54.96% 97.62% 52.39% 87.05% 74.46% 93.38% 57.39% 91.13% 71.54% 59.85% 70.33% 91.38% 82.61% 73.68% 67.81% 68.97% 85.91% 67.19% 80.46% 85.72% 77.36% 97.53% 74.47% 72.23% 84.63% 96.43% 48.65% 87.94% 59.80% 82.48% 83.20% 75.45% atasets erform hat cmore itional 2. the last deta trad whi pre 10 bett whe abo than clas with algo fold diff to resu acc clas vol. 8, no. 4, 20 s t metric, avera ail in table i ditional cvc. ile one datase sented slightly datasets were ter up to 5%, ere the differe ove 25%. here n the tradition ss actually bel h higher dif orithm are obs d cross vali ference in clas 30 out of 42 ults, alongside curacy confir ssification is s fig. 1 fig. 2. fig. 3. 018, 3203-3208 smyrlis et al.: c age precision, i. again, the the difference et was found y better precisi e found where , 18 where it ence was from e is shown tha nal one in ter longs to that c fferences to served accordi dated t-test ssification accu 2 datasets. av e with the trm in a ve uperior to k-m 1. accuracy d average sensitiv average precisi 8 constrained k-m is illustrated proposed app e ranges from where the tr ion (+1.73%). e c-k-means was better fr m 15% to 25% at the proposed rms of if wha class. once ag the benefit ing to this met revealed th uracy was stat verage sensitiv -test validatio ersatile way means based c differences for all vity differences fo ion differences for 3206 means classific in figure 3 a proach outperf m 0.38% to 38. raditional appr on the other h classification rom 5% to 15 and 6 where i d approach is b at is classified gain, more dat for the prop tric. the paire hat the nume tistically signif vity and prec on in classific that c-k-m cvc. datasets or all datasets r all datasets cation and in forms .82%, roach hand, n was 5%, 8 it was better d in a tasets posed ed 10erical ficant cision cation means engineering, technology & applied science research vol. 8, no. 4, 2018, 3203-3208 3207 www.etasr.com smyrlis et al.: constrained k-means classification v. conclusions in this study, a novel cvc algorithm, based on k-means clustering is proposed. the algorithms include two major modifications compared to the k-means, being (i) the use of a hypercube of constraints for each centroid extracted from the information of the training data, and (ii) the use weights for each attribute and each class along with the weighted euclidean distance as a similarity criterion for the clustering procedure. an initial effort on this direction can be found in [31]. since classification is a supervised learning method, the performance can be assessed by the classification rate, i.e. the number of successes and failures of the model. reducing the number of misclassifications is very important regardless of which clustering algorithm or which variation of k-means is used in cvc, an efficient use of the background knowledge is required to succeed. the introduction of constrains in the centroids initialization and update based on background knowledge, which is the main idea of the proposed algorithm, contributes to this direction. in the c-k-means, both training (mainly associated with classification) and clustering are used, since by training the class hypercubes and attribute weights are obtained, and clustering is used for moving the centroids inside the hypercubes. thus, the principal idea is to use the background knowledge to limit the solutions inside a predefined space (i.e. the hypercubes) and then follow an unsupervised technique to fine tune this solutions (by allowing the centroids to be updated but forcing them to remain inside the hypercube). experimental results were obtained using 42 datasets from the uci machine learning repository, with various number of attributes and instances. 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n. giannakeas, a. t. tzallas, p. manousou, “automated collagen proportional area extraction in liver biopsy images using a novel classification-via-clustering algorithm”, ieee 30th international symposium on computer-based medical systems (cbms), greece, june 22-24, 2017 microsoft word etasr_v11_n1_pp6752-6759 engineering, technology & applied science research vol. 11, no. 1, 2021, 6752-6759 6752 www.etasr.com maamri et al.: capitalization of the operating experience of a company for sustainable improvement capitalization of the operating experience of a company for sustainable improvement the case of the etrag foundry, constantine, algeria nadira maamri transport engineering department university of constantine 1 constantine, algeria nadira_maamri@yahoo.fr mohamed benidir transport engineering department university of constantine 1 constantine, algeria mcbenidir@yahoo.fr rachid chaib transport engineering department university of constantine 1 constantine, algeria r3chaib@yahoo.fr ion verzea department of engineering and management gheorghe asachi technical university of iasi iasi, romania iverzea@tuiasi.ro abstract-today, the adaptation to the effects of changing behavior and attitudes of algerian companies has become a necessity. the current work aims to provide real-time information drawn from the field involvement with the use of performance indicators, in order to have a global vision of the general situation of the company. this allows for fulfilling functions such as awareness, guidance, decision support, and strategic planning. these indicators form a key data synthesis that affects all areas of the company's affairs. based on these indicators, a manager could have a better view of the business. consequently, he could act effectively to correct the errors that have been revealed or continue in increasing the company's development. this article describes the progress of management practices improvement in a foundry of the etrag company while relying on employee involvement. through this work, the necessary preventive measures are established in the occupational environment ensuring the health and safety of employees. thus, the well-being of the employees and the improvement of the working conditions can be assessed. the proposed work methodology consists of two components: the survey results obtained through a questionnaire in order to quantify the most exposed to risks and its intersection employees with the solutions proposed by the same employees. this approach aims at optimizing processes, instill a culture to the effects of changing attitudes and behaviors, to spread the culture of continuous and sustainable progress within a company, to ensure a good workplace atmosphere, and to have a respectful attitude towards employees. keywords-indicators; performance; health; safety; sustainability; strategic planning and decision support; gemba walks i. introduction adaptation to the effects of changing behavior and attitudes has today become a necessity and an essential step in preserving the employee’s safety and business sustainability. the adaptation involves changes in behavior, management style, and governance [1]. the adaptation tools aim to improve the knowledge and understanding of issues and outcomes or even to support decision-making and engagement in a process of continuous improvement [2]. continuous improvement culture could not be sustained if managers and employees are not deeply involved in the process, which is known as a key role in a successful lean implementation [3]. hence, in order to develop and maintain a competitive advantage, a company must be efficient in its operations [4, 5]. this can only be done by establishing a list of performance indicators to give the manager an overall view of the state of occupational health and safety [6-8]. these performance indicators form the key data synthesis of the company [9]. based on these indicators, the manager may quickly know if his business is going well or not. thus, managing to provide information that offers a real time global vision on the general situation of the company based on field participation allows the company to accomplish functions such as awareness, guidance, decision support, and occupational health and safety strategy planning. these indicators represent a real dashboard that provides concrete and operational information for all companies [10, 11]. in the future, the performance improvement will become a daily concern which should be established as a common culture for all companies. ii. problematic over the years, the corporate performance issue and its measurement have become a recurring theme. it is true that in a highly competitive world, regular evaluation is crucial to ensure that things are going right in a company, provided of course that the right actions have been implemented at the right time and that there are adequate means to achieve the set goals. corresponding author: nadira maamri engineering, technology & applied science research vol. 11, no. 1, 2021, 6752-6759 6753 www.etasr.com maamri et al.: capitalization of the operating experience of a company for sustainable improvement consequently, adaptation to the effects of change involves changes in behavior, management methods, and governance, while making the best use of the available resources, including employees. thus, the review is conducted by the people involved in the activity. as a result, the employees’ involvement in identifying problems and solving them is of paramount importance in the process of continuous improvement [12]. in fact, people confronted on a daily basis with the reality of the field are the best to report problems and to propose solutions [13]. this can serve as a motivation form which leads towards productivity [14]. they can contribute greatly to the continuous improvement cycle by feeding the processes of new knowledge from the field of accumulated experience. this allows highlighting the company’s elements that perform well in real time. in order to get closer to this perfection state, it is possible to use some tools like the gemba walk, the most basic element of lean leadership which describes the cooperation of employees and leaders in their mutual striving for perfection [13]. gemba means the "real place" and is often referred to as the place where value added activities occur and allow leadership identifying inadequate management systems [15-17]. it inspires the finding of ways to improve processes by seeking the help of the employees [18]. it is therefore important that they feel confident and are encouraged to make proposals and implement changes. in addition, the more the employees become accustomed to solving problems, the easier it will be for them to react to future unpredictable situations. thus preserving the company's sustainability and even being more responsive to the changes imposed by the circumstances. the gemba walk tool promotes a measurement culture that aims to understand the best strategy to achieve a given goal [19]. thus, teamwork and information exchange can be promoted while appealing to the collective intelligence and experience to enrich the proposals for solutions [20]. once the information collection has been completed, the manager is simply asked to make a precise analysis, by putting in place the necessary corrective measures and ensure the follow-up between the regular gemba walk sessions. this approach is a part of the continuous improvement logic, with the objectives of boosting performance and ensuring the sustainability of the company. iii. case study: the etrag foundry, constantine, algeria the motor-tractor complex etrag is an economical public company ("complex motors tractors spa" (epe / cmt spa)), producing thermal engines and agricultural tractors, located in the industrial area of oued hamimine-khroub district of constantine, algeria [22]. it was created to meet the growing needs of the national market in agricultural tractors and spare parts and to contribute to the mechanization of national agriculture, with the following objectives: • the manufacturing and development of agricultural tractors and spare parts. the foundry manufactures and sells agricultural tractors from 68hp to 100hp of 2 and 4wd. • subcontracting in the activities of foundry, blacksmithing, boiler making, mechanical machining, heat treatment, and tool manufacturing. • after-sales service and renovation of tractors. among the most important of these workshops, from the health and safety at work point of view, is the foundry workshop, the study field (figure 1). the latter represents a major challenge, with its working atmosphere (dust and smoke) and activities nature. this building generates the highest accident risk and occupational diseases (silicosis and cancer). fig. 1. the proposed assessment model of the work environment. iv. the analysis approach the main objective of this work has been to use the gemba tool in order to assess the overall work environment process by involving everyone touching the process to answer a questionnaire in order to have a clear view of the situation and existing problems which may help in taking appropriate decisions and improve management practices [21]. a healthy enterprise is an organization where managers and staff are working together to design a health-promoting work environment [22]. any risk assessment process is doomed to fail without the participation of all stakeholders. this approach aims at optimizing processes, instill a safe culture and spread the culture of continuous and sustainable progress within the company [23]. another goal is to change workers and managers' awareness of this issue and suggest ways to improve it. the work environment assessment’ model consists of the following steps: • assessment of the working environment and identification of weak points and sources of risk at the foundry using a questionnaire addressed to all employees working in the foundry. • processing of the questionnaire results. • the obtained survey results are cross-checked with the solutions proposed by the same employees. study area delimitation technical performances managerial performances human resources analysis of performances assessment of the work environment critical points proposition of solutions succe ssss actions and improvements yes no human resources engineering, technology & applied science research vol. 11, no. 1, 2021, 6752-6759 6754 www.etasr.com maamri et al.: capitalization of the operating experience of a company for sustainable improvement • the intervention of the manager to adjust his strategy, correct the errors that have been revealed and refocus on priorities. the survey used in this work is a single questionnaire administered face-to-face to the employees. this technique is classified as one of three major methods to study psychosociological facts in order to gather information to understand and explain them [24]. it consists of well-formed questions to get essential information about the working environment, especially the health risks diffused through the workshop. the questions should highlight the problems and improvement zones on the workplace. the questions focus on the organization characteristics, the communication, the workstation, the working environment, and the risks generated in each activity of the foundry. several simple questions were asked about each theme. the answers are often of yes or no type. the number of employees that responded positively to this survey was 99 out of 146, which represents a rate of 67%. v. survey results the results were processed with the statistical package for social science (spss). a. organizational results the goal of the organizational survey is to build a strategy developed in consultation with employees in a perspective of continuous improvement. it is a fundamental element of the occupational conditions that allow any organization to be competitive. henceforth, it is the reference frame by which any company ensures the continuity of its activities. fig. 2. organizational survey results. according to the obtained results shown in figure 2, it can be found that 60.6% of employees are not satisfied with their working conditions, because of the bad working atmosphere, the lack of staff, and the workload. the latter is associated with practice performance [25]. more than half of the workers say that training is insufficient. in addition, 80% of employees find that working conditions are deteriorating from one year to another, which is the most important point to be corrected urgently: a new management strategy is therefore required. b. material conditions survey its objective is the improvement of the conditions and life quality at work given its importance and its crucial role in the companies which favours the well-being of the workers and the productivity success, see figure 3. fig. 3. the investigation results of material conditions. most employees declared that ppe and handling equipment are available and adequate, which is a very strong point for the company. meanwhile, the employees complain about the lighting and the ventilation system in the foundry. these negative points should be resolved since the physical environment plays a key role. c. communication survey its objective is to set up a reliable information system that can measure in a sustainable manner the dynamics set up at the organization and constitute a dashboard concerning the management of actions. communication is an essential link in any sustainable development process and requires the implementation of an open, permanent and balanced communication strategy. the relationship between the administration and the workers is considered insufficient as there is a lack of information and motivation. working conditions can lead to internal conflicts. as we can see in figure 4, 66% of employees report inadequate internal communication, 60% of them say that the instructions are contradictory, and more than 14% have conflicts with the line manager. coherence and consistency among the various structures and systems, hence "structural conflict" should be avoided [26]. as a conclusion, we may say that internal communication is insufficient in the foundry. in the context of gemba, the leader uses communication to connect with the employee and assess failures and errors of processes [18]. to gain a dynamic and profitable company, the communication between the employees and the managers is a very important factor. strong corporate identity ensures that all internal and external communication is coherent and consistent engineering, technology & applied science research vol. 11, no. 1, 2021, 6752-6759 6755 www.etasr.com maamri et al.: capitalization of the operating experience of a company for sustainable improvement [27]. in the future, the company should review its communication system and activate the implementation of an open, permanent, and balanced communication strategy. fig. 4. communication survey results. d. workstation survey its goal is to gain a good understanding of everyone's role in the company's strategy, with a clear perception of its added value and sense of purpose. in everyday life, prevention of risky behavior must be carried out. it is necessary to be attentive to weak signals and to avoid the so-called "toxic" management behaviors. many toxic managers succeed by achieving short-term goals, but at the same time they may damage the organization by creating a negative environment impacting on the dependent variables of increased turnover, high absenteeism, and low productivity [28]. fig. 5. workstation survey results. in figure 5 we can see the results of the workstation survey. it can be seen that most employees are not satisfied with their jobs. it was found that 56.6% of workers want to change job and 70% of them are not satisfied with their payment, the most common problem in most previous studies [29, 30]. this explains the non-compatibility of studies and training with the desired job by the employee. in addition, with an information deficit of 83% at the workplace this is the most negative point and must be resolved urgently. sufficient information and knowledge sharing makes a big difference on an enterprise. knowledge sharing is most important because the more stronger the knowledge sharing of an organization is, the greater degree of effectiveness the organizational will have [14, 31]. e. occupational health and safety survey its goal is to achieve a more human atmosphere at work, where trust in everyone is strong, and going to work becomes a pleasure. it shows a better performance of the company. the survey results can be seen in figure 6. fig. 6. occupational health and safety survey results. the majority (71%) of the employees report that follow-up and medical treatment is always available. meanwhile, no employee is secure from illness and work-related accidents, which shows that more work is needed to improve safety conditions and well-being at work, hence a risk assessment is required. this justifies the adoption of technical and organizational measures, mainly in the area of management, information and staff participation. for the improvement of the health and safety of employees, every company must engage in a continuous improvement process [2] and manage each existing risk [33]. f. spider chart of working conditions in order to obtain an overall view of the general situation of the company, all the obtained results are reported on a rating grid represented in the form of a spider chart. the results (figure 7) clearly show that standard management practices are insufficient. in general, the assessment of the occupational environment is insufficient since all components are in the 25-50% range, which requires an emergency action plan for the safeguarding and sustainability of the company. it can be noted that the organizational component is insufficient (32%) and requires some improvements. the other components change positively engineering, technology & applied science research vol. 11, no. 1, 2021, 6752-6759 6756 www.etasr.com maamri et al.: capitalization of the operating experience of a company for sustainable improvement in favour of improvement, given that the material and workstation components are considered acceptable. this result is a strong advocacy for a holistic approach in which safety is an essential aspect, but is only a part of a broader prevention and promotion policy for health and wellbeing at work. the approach initiated by this study aims at providing tangible demonstration elements in the positive approach of sustainable and continuous improvement.this approach can be extended to other sectors of industrial activity with different parameters. fig. 7. the assessment representation of working conditions. g. solutions proposed by the employees the employees were asked to propose candidate solutions that could improve the working environment (feeling of being listened and of participating in the decision). the results are listed in figure 8. fig. 8. survey results showing the employees involved in suggesting improvement solutions. more than half of the employees have proposals to improve the current situation. the most important thing is that the proposed solutions were helpful to the company. given the difference in the intellectual levels of the employees, we tried to group together similar propositions and we classified them in order of quotations, with the employee number that proposed each item in parentheses. the results are: • repair of the ventilation system (54) • lighting enhancement (52) • arrangement of break times (44) • organization of periodic medical check-ups for employees (38) • the creation of a committee for the health and safety service and working conditions (35) • improvement of working conditions (35) • cleaning and maintenance of work premises (35) • facilitation of internal communication and the link between the workers and the administration (34) • reduction of the retirement age and increase of the workforce (32) • organization of training for the employees (31) • the establishment of protection and prevention means (26) • repairing or renewal of machines (25) • restructuring of the workshop (25) • maintenance of tools and work machines (25) • the application of regulations (21) vi. discussion, conclusion, and recomandations the study outcomes are a reflection of people's reality in their workplace. henceforth, any assessment of the occupational environment is doomed to failure without the participation of all the actors and in particular the employees which are directly involved in the activity. more concretely, the study findings will allow better assessing of the action relevance of the executing agencies and will also increase their effectiveness through the objectives definition and adapted priorities to current concerns. this qualitative assessment represents a valuable gauge of the company's activity and helps anticipating and correcting dangerous situations. in order to develop a global performance approach, a permanent discussion between the strategic and operational spaces and in particular the employees will be way far helpful as it offers a great added value and provides necessary data. experiments and feedback show that this is a collective and long-term learning. generally, the information synthesis will allow the decision-makers to correct the mistakes and to continue and increase the enterprise development. by proper evaluation of the business activity, the best decisions to maximize the employee’s performance can be made. they not only allow knowing in detail the efficiency of the business, but they also provide usefull informations about the quality of services of each workshop and each activity. in conclusion, the following points are recommended: • the use of management tools to reorganize work. the organization of work includes many aspects, such as work pace, workload, number of people performing a job (staffing levels), workhours, and duration and number of engineering, technology & applied science research vol. 11, no. 1, 2021, 6752-6759 6757 www.etasr.com maamri et al.: capitalization of the operating experience of a company for sustainable improvement rest breaks, which arerelevant to avoiding workload and reaching the assigned goals. • any company willing to develop and maintain a competitive advantage and to be efficient in the way it operates, must base its actions on concrete and operational information drawn from the occupational environment. • knowledge sources should be managed in order to facilitate access, knowledge reuse, and the circulation of information. sufficient information must be provided to workers along with motivation and encouragement of co-operation between employees. encouraging employees to be autonomous and responsible allows them to find positive work environment. • integrate all elements of a safety program such as training, into a single management system that is owned by line management. adapt workstations to employees, taking into account their health status and the division of tasks according to the hierarchical framework and competence of the workers, and encourage them to participate in safety efforts, where the safety is everyone’s responsibility. improve the compliance with laws and regulations. • promote internal communication between the various levels and functions of the organization as well as external communication. plan the communication to provide a space of exchange to enhance safety culture and solve existing problems. finally, in order to maintain a competitive advantage, every company should allow constant discussion and open dialogue between strategic and operational areas, particularly employees. these valued strategies offer a great added value and provide data from the field. henceforth, any action plan should be taking into account the solutions proposed by the employees. appendix the questionnaire on the working conditions in the foundry age: …….. years of experience:………. organization 1do you consider your working conditions? good average bad 2main reasons for dissatisfaction (several possible): workload too important moral pressure bad working atmosphere trainning insufficient number of workers too complex tools 3evolution of your working conditions the last 3 years: improved are the same have degraded material conditions: 4is the material, tool, machine fit to your task and safety? : yes no 5are there any means of personal protection (ppe)? yes no 6if yes, which? helmet anti noise safety shoes gloves glasses mask 7are there any means of handling? yes no 8how do you consider the lighting in your job post: sufficient insufficient 9is there a ventilation system in your workstation? yes no management / communication 10-the number of meetings with your line manager: sufficient insufficient 11the trust that your line manager gives you: sufficient insufficient 12internal communication of your direction: sufficient insufficient 13do you often receive contradictory instructions? yes no 14when you have a problem can you talk about it: yes no if so, to whom?................................. 15do you consider that your line manager assumes his responsibilities?: yes no 16are you in conflict with your line manager?: often sometimes never 17are you in conflict with your colleagues? often sometimes never 18if yes, do you think that conflicts are generated by working conditions? yes no your job 19does your position correspond to your skills? yes no 20do you value your job as fulfilling? yes no 21do you feel that you learn by working? yes no 22do you have useful information for your tasks? yes no 23do your working hours suit you? yes no specify why: ……………………………………………………………………… 24is your remuneration appropriate for you? yes no 25is the division of tasks right? engineering, technology & applied science research vol. 11, no. 1, 2021, 6752-6759 6758 www.etasr.com maamri et al.: capitalization of the operating experience of a company for sustainable improvement yes no 26would you like to change job? yes no your health 27are you able to reconcile your private life with your professional life? yes no 28have your working conditions affected your health? yes no 29if so, how? fatigue sleep disorder stress vertigo pathology irritation to the eyes kidney insufficiency corneal tms redness headache edema diabetes vision disorder hypertension or hypotension auditory issues 30have you had any medical treatment on this subject? yes no 31have you ever had a thermal burn? yes no 32have you ever dropped down? yes no 33if so, what happened to you? contusions intorts injury fracture 34have you ever had an electrification accident? yes no 35was there any fatal accident? yes no if yes what 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[32] n. maamri, c. rachid, m. benidir, and i. verzea, "the assessment of the sound environment in the workplace: a lever for work quality and safety," recent journal, vol. 20, pp. 5–13, mar. 2019, https://doi.org/10.31926/recent.2019.57.005. microsoft word etasr_v10_n6_pp6488-6493 engineering, technology & applied science research vol. 10, no. 6, 2020, 6488-6493 6488 www.etasr.com anh & quyen: optimal speed profile determination with fixed trip time in the electric train … optimal speed profile determination with fixed trip time in the electric train operation of the cat linhha dong metro line based on pontryagin's maximum principle an thi hoai thu anh department of electrical engineering university of transport and communications hanoi, vietnam htanh.ktd@utc.edu.vn nguyen van quyen department of applied mechanics hanoi university of science and technology hanoi, vietnam quyen.nguyenvan@hust.edu.vn abstractthe significant energy consumption for railway electric transportation operation poses a great challenge in outlining saving energy solutions. speed profile optimization based on optimal control theory is one of the most common methods to improve energy efficiency without the railway infrastructure investment costs. the paper proposes an optimization method based on pontryagin's maximum principle (pmp), not only to find optimal switching points in three operation phases: accelerating, coasting, braking, and from these switching points being able to determine the optimal speed profile, but also to ensure fixed-trip time. in order to determine trip time abiding by the scheduled timetables by applying nonlinear programming puts the lagrange multiplier λ in the objective function regarded as a time constraint condition. the correctness and energy effectiveness of this method have been verified by the simulation results with data collected from the electrified trains of the cat linh-ha dong metro line in vietnam. the saving energy levels are compared in three scenarios: electrified train operation tracking the original speed profile (energy consumption of the route: 144.64kwh), train operation tracking the optimal speed profile without fixed-trip time (energy consumption of the route: 129.18kwh), and train operation tracking the optimal speed profile and fixed trip time (energy consumption of the route: 132.99kwh) in an effort to give some useful choices for operating metro lines. keywords-metro system; energy-saving; energy-efficient operation methodology; timetable optimization i. introduction with the worldwide booming of urbanization, people face the increased carbon emission problem and the traffic congestion to affect their quality of live. under these circumstances, the urban railway systems play a key role in removing the harmful effects of urban mobility due to their advantages such as large passenger capacity, safety, and less environmental pollution [1, 2]. metro lines in the big cities of vietnam are under construction or expansion with a total rout length of about 500km. however, the traction system of metro trains consumes a huge proportion of energy [3], so it is vital to find some solutions to minimize the total energy consumption of the railway transportation system. among numerous energy saving solutions, speed profile optimization which reduces energy consumption without investing into infrastructure has attracted attention. there are two known methods of speed optimization: the mathematical and optimal theory and computational intelligence [4]. authors in [5-9] systematically researched optimal strategies using mathematical approaches and the optimal theory to propose control laws to detect the optimal switching points and to find the optimal speed profile whereas authors in [10] attempted to solve the problem of optimal control by applying the pontryagin's maximum principle (pmp). authors in [11] used pmp to find a set of optimal controls, the control switching graphs, and complementary conditions of optimality. authors in [12] applied three optimization algorithms (colony optimization algorithm, dynamic programming, genetic algorithm (ga)) to search for the optimal speed trajectory, while authors in [13] applied the ant colony algorithm to find an optimal power profile to save energy. authors in [14] designed the speed profile giving guarantees of running time and saving energy consumption. authors in [15] designed the train operation speed profiles for an automatic train operation system (ato) to select the optimal speed profiles with reduced energy consumption. authors in [16] designed a decentralized train traffic management system (dtms) which not only possessed good automatic train control (atc) operation, but also saved a significant amount of running time. authors in [17] used ga and authors in [18] utilized artificial neural networks (anns) and ga to determine the optimal coasting point. authors in [19] dealt with speed profile optimization using pontryagin's maximum principle (pmp) and achieved energy-saving but did not guarantee fixed running time in the cat linh ha dong metro line in vietnam. in this paper, pmp is also chosen to determine optimal speed profile, and also ensure fixed trip time thanks to the corresponding author: an thi hoai thu anh engineering, technology & applied science research vol. 10, no. 6, 2020, 6488-6493 6489 www.etasr.com anh & quyen: optimal speed profile determination with fixed trip time in the electric train … lagrange multiplier λ being put into the objective function regarding the cat linh ha dong metro line. the simulation results with three diffirent seniories showed the effectiveness of pmp optimal control method in saving energy of train operation without any changes of infrustructure or facilities. ii. motion model of the train the train is regarded as a particle and kinematic equation that can be represented by the following continuous space model [20, 21]: 0 ( ) ( ) ( ) ( ) tr br grad dx v dt dv mv f v f v w v f x dx  =  = − − − (1) where , , ,v t x m represent train speed (m/s), operation time (s), train position (m), full load translating mass of train (tones) and 0 , , , tr br grad f f w f are traction, electrical braking, resistance, and gradient resistance forces applied on the train. based on the curves of tr f and br f given by the manufacturers [21], the least square method is utilized to find the equivalent polynomials. the maximum traction and maximum braking forces corresponding to the speed v are: 3 252.5 10 0.007 (32 80) 0.66 2 13.2 (0 32 . ) 8 35 tr v f vv v v −  ≤ ≤= + − ⋅ + ⋅ < ≤ − (2) 14.7 (0 65) 0.254 31.21 (65 75) 0.2027 27.36 (75 80) br v f v v v v  ≤ ≤= − + < ≤ − + < ≤ (3) the forces acting on the train in which the resistance force comprises of the air resistance, the friction resistance can be seen in [21]. the basic resistance 0 w can be calculated by the davis formula [22]: 20 0 w w a bv cv m = = + + (4) where , ,a b c are the coefficients of train resistances. the gradient force grad f caused by the slope of the road is: sin grad f mg α= (5) where ,g α are the gravity acceleration and the rail track slope respectively. iii. speed profile optimality analysis based on pmp and energy consumption depending on the distance between stations, a train operates in three or four phases. for short distances, the train runs in three phases: accelerating, coasting, and braking. forces acting on a train in operation modes are different. the tractive force acts during the accelerating and cruising processes, the basic resistance force acts during all processes, while the braking force acts during the breaking process. a. problem formulation the motion of a train along a track can be rewritten by the state equations: 0 1 ( ) ( ) ( ) ( ) tr tr br br grad dt dx v dv v u f v u f v w v f x dx  = = − − − (6) where , tr br u u are the defined traction and braking control variables of train, both of which are restrained by: [0,1] tr u ∈ , [0,1] br u ∈ , and ftr, fbr, fgrad are the traction force applied at the wheels, the braking force, and the gradient force acting on the train. therefore, the boundary conditions are given by: (0) 0, ( ) 0, (0) 0 0 ( ) ( ),0 ( ) ,0 v v x t v x v x t x t x x  = = =  ≤ ≤ ≤ ≤ ≤ ≤ (7) where ( )v x is the maximum allowable speed, x is the terminal of the train operation, ),(0) (v xv are the speed at the beginning and at the end of the route, t is the duration of the trip which is also given by the timetable. the objective is to minimize the train's operation energy consumption as the train runs from location 0x = to x x= in time t by controlling the traction force, while ignoring electric braking force since regenerative braking energy is not recovered. the objective function is written as: 0 ( ) min x tr tr j u f v dx tλ = + →  ∫ (8) where ( ) ( ) actual demand t t x t x= − , and λ is an unknown lagrange multiplier. given: 0 ( ) x actual dx t x v =∫ (9) finding the value of the lagrange multiplier is to deliver the required running time ( ) demand t x , while actual t is the actual running time of the train. therefore the objective function is: 0 ( ) min x tr tr j u f v dx v λ  = + →    ∫ (10) b. solution to find the optimal solutions of an objective function by pmp is equivalent to maximize its hamiltonian equation. based on (6), (8), a hamilton function is formed as: engineering, technology & applied science research vol. 10, no. 6, 2020, 6488-6493 6490 www.etasr.com anh & quyen: optimal speed profile determination with fixed trip time in the electric train … 1 0 2 1 ( ) ( ) ( ) ( ) ( ) tr tr tr tr br br grad h u f v p v v u f v u f v w v f x p v λ =− − +  − − −  +     (11) where 1 2 ,p p are adjoint variables. the adjoint variable differential equations are reformed: 1 0 dp h dx t ∂ =− = ∂ (12) 2 12 2 2 02 2 0 1 ( ) ( ) ( ) ( ) tr tr tr tr br br grad tr br tr br dp fh u p dx v v v v p u f v u f v w v f x v p f f w u u v v v v λ∂∂ =− = − + ∂ ∂  + − − −    ∂ ∂ ∂ − − − ∂ ∂ ∂   (13) defining: 2 p p v = , so 2 1 dpdp dv p dx v dx dx   = −     (14) given: 0 ( ) ( ) ( ) ( ) tr tr br br grad u f v u f v w v f xdv dx v − − = (15) we get: 1 0 ( 1) ( ) tr tr br br grad p h p u f pu f p w f v v λ = − − − + − + (16) the hamiltonian function is maximized by the following values of tr u and br u [19]: 1 1 0 0 1 (0,1) 1 (0,1) 0 0 1 1 0 tr br tr br tr br u if p u if p u if p and u if p u if p u if p   = > = < <    ∈ = ∈ =     = < = <    (17) from the above analysis, five optimal control laws are designed: • full power (fp): 1, 0 tr br u u= = when 1p> • partial power (pp): [0,1] tr u ∈ , 0 br u = when 1p = • coasting (c): 0, 0 tr br u u= = when 0 1p< < • full braking (fb): 0, 1 tr br u u= = when 0p< • partial braking (pb): 0 tr u = , [0,1] br u ∈ when 0p = substituting (13) and (15) in (14) leads to finding the differential equation for ( )p x : 1 0 3 3 (1 ) ( ) ( ) ( ) tr tr br br pdp p p p u f v u f v w v dx v v v v v λ− ′ ′ ′= + + − − (18) from (12), 1 p is easily chosen to be 0. 1) full power mode with 1, 0, 1, br tr p u u> = = finding accelerating time a t and accelerating distance a x can be done by using (18). we get: 1 0 3 3 (1 ) ( ) ( ) tr ppdp p f v w v dx v v v v λ− ′ ′= + − − (19) from (6) we find the differential equations to determine , a a x t : 0 0 ( ) ( ) ( ) 1 ( ) ( ) ( ) tr tr grad tr tr grad dx v dv u f v w v f x dt dv u f v w v f x  = − −  =− − − (20) with initial conditions: ( ) ( )0 0, 0 0x t= = . 2) partial power mode with 1, 0, 0 1 br tr p u u= = < < and using equation: 1 0 3 3 1 ( ) 0 p w v v v v λ′ − − = (21) where h v -hold speed is chosen previously and 1 p is 0, we get: 2 0 v wλ ′= (22) therefore: 2 ( 2 )v b cvλ = + (23) if λ is chosen previously, we can solve (23) to find the hold-speed h v 3) coasting mode the conditions 0, 0,0 1 tr br u u p= = < < are applied. the coasting speed b v is calculated as [4, 23]: ( ) ( ) h b h v v v ψ ϕ = ′ (24) where 2 0 0 ( ), ( )v w v v w vϕ ψ ′= ⋅ = ⋅ . from (6) we find the differential equations to determine , cc x t : engineering, technology & applied science research vol. 10, no. 6, 2020, 6488-6493 6491 www.etasr.com anh & quyen: optimal speed profile determination with fixed trip time in the electric train … 0 0 ( ) ( ) 1 ( ) ( ) grad grad dx v dv w v f x dt dv w v f x  = − −  =− + (25) with ( ) ( ); a ah ht v v t x v v x= = = = . 4) full braking mode the conditions 0, 1, 0 tr br u u p= = < are applied. using (18) we can find braking time and braking distance: 1 0 3 3 ( ) ( ) br pdp p p f v w v dx v v v v λ ′ ′= + − − (26) from (6) we get the differential equations: 2 0 0 ( ) ( ) ( ) ( ) 1 ( ) ( ) ( ) ( ) br br sc grad sc br br grad dx v dv v u f v v w v p t v f x dt dv p t u f v w v f x v  = − ⋅ − ⋅ + − ⋅  = − + − (27) with ( ) ( ), b b b bt v v t x v v x= = = = . iv. simulation results comparison for various scenarios the simulations are based on the data of cat linh-ha dong metro line. there are 12 stations, 1 depot, and 6 traction substations. the simulation results are performed for the first cat linh station to the 12th yen nghia station in a route which is 13km in length [18]. the full load translating mass is 246.7ton and 8 electrical traction motors are used. david’s coefficients of train’s resistance are: 21.19 10a −= ⋅ , 32.56 10b −= ⋅ , 41.54 10c −= ⋅ . assessing the levels of energy savings follow 3 scenarios: energy consumption with original speed profile with fixed trip time, energy consumption with optimal speed profile with fixed trip time, and energy consumption with optimal speed profile but with trip time which is less by 1s in each station. the goal of different simulation scenarios is to give diversified operation choices regarding energy saving for different metro lines. fig. 1. comparison of optimal and original speed profile without fixedtrip time. the results and their comparison for the optimal speed profile and the original speed profile vs distance without fixedtrip time can be seen in figure 1. the results and their comparison for the optimal and original time profile vs distance without fixed-trip time can be seen in figure 2. the results and their comparison for optimal and original speed profile vs distance with fixed-trip time can be seen in figure 3 and for optimal and original time profile vs distance with fixed-trip time can be seen in figure 4. fig. 2. comparison of optimal original time profile without fixed-trip time. fig. 3. comparison of optimal and original speed profile with fixed-trip time. fig. 4. comparison of optimal original time profile with fixed-trip time. regarding track conditions and constraints, the speed from a station to another station is different: the slowest speed is 53km/h and the highest is 73km/h, which means that the speed is always lower than the limit of 80km/h. the optimal trip time is longer approximately by 1s. it was also shown that along with optimal switching points change, so do the optimal engineering, technology & applied science research vol. 10, no. 6, 2020, 6488-6493 6492 www.etasr.com anh & quyen: optimal speed profile determination with fixed trip time in the electric train … accelerating, coasting, and braking distances. table i demonstrates that the percentage of total energy saving is up to 11.96% (practical energy consumption is 144.64kwh, while optimal energy consumption obtains 129.18kwh). table i. comparison results of the energy consumption with non-fixed trip time inter-station length distance (m) original trip time (s) practical energy consumption (kwh) optimal trip time (s) optimal energy consumption (kwh) energy saving (%) cat linh-la thanh 931 88 8.31 88.81 7.31 13.68 la thanhthai ha 902 78 10.20 78.83 9.08 12.33 thai halang 1076 91 10.20 91.85 9.60 6.25 lang-vnu 1248 103 11.73 103.82 10.37 13.11 vnuring road 3 1010 79 13.41 79.8 11.78 13.84 ring road 3thanh xuan 1480 104 16.75 104.85 15.44 8.48 thanh xuanha dong bs 1121 86 13.85 86.82 12.26 12.97 ha dong bsbv ha dong 1324 97 15.74 97.83 13.80 14.06 bv ha dong-la khe 1110 84 14.30 84.77 12.77 11.98 la khe-van khe 1428 101 16.75 101.86 15.15 10.56 van kheyen nghia 1032 81 13.40 81.82 11.62 15.32 total energy consumption 144.64 129.18 11.96 table ii. comparison results of the energy consumption with fixed-trip time inter-station length distance (m) trip time (s) practical energy consumption (kwh) optimal energy consumption (kwh) energy saving (%) cat linh-la thanh 931 88 8.31 7.50 9.75 la thanh-thai ha 902 78 10.20 9.40 7.84 thai ha-lang 1076 91 10.20 9.86 3.33 lang-vnu 1248 103 11.73 10.60 9.63 vnuring road 3 1010 79 13.41 12.23 8.80 ring road 3thanh xuan 1480 104 16.75 15.82 5.55 thanh xuanha dong bs 1121 86 13.85 12.66 8.59 ha dong bsbv ha dong 1324 97 15.74 14.17 9.97 bv ha dongla khe 1110 84 14.30 13.18 7.83 la khe-van khe 1428 101 16.75 15.53 7.28 van khe-yen nghia 1032 81 13.40 12.04 10.15 total energy consumption 144.64 132.99 8.7 figures 3, 4 and table ii indicate that the optimal speed profile with fixed running time complied with the scheduled timetable and the saving energy level is 8.7% (the practical energy consumption is 144.64kwh, while the optimal energy consumption is 132.99kwh). v. conclusion the simulation results by applying pmp to find the optimal speed profile with and without fixed trip time for the 12 stations of the cat linh ha dong metro line operating in three phases (accelerating, coasting, and braking) showed a saving energy percentage varying from 8.7% to 11.96% in comparison with the original speed profile. this research contributes to the modes of ato. if the metro line is going to conduct surveys on the train timetable, it may be able to choose the optimal speed profile with longer trip time, and reduce the dwelling time because this speed profile saves energy to a level up to 11.96%. if the 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[23] n. t. hai, "evaluation of effect pontryagin’s maximum principle for optimal control train by criteria of energy save," in 2010 international symposium on computer, communication, control and automation (3ca), tainan, taiwan, may 2010, vol. 1, pp. 363–366, https://doi.org/10.1109/3ca.2010.5533807. engineering, technology & applied science research vol. 8, no. 6, 2018, 3640-3645 3640 www.etasr.com sunar & cetin: an experimental study on boron carbide reinforced open cell aluminum foams … an experimental study on boron carbide reinforced open cell aluminum foams produced via infiltration technique talha sunar faculty of technology department of manufacturing engineering karabuk university karabuk, turkey talhasunar@karabuk.edu.tr melik cetin faculty of technology department of manufacturing engineering karabuk university karabuk, turkey mcetin@karabuk.edu.tr abstract—light structures and parts are very effective for new engineering applications. their considerably low densities, high energy absorption capabilities, and desirable mechanical properties make them useful for particularly automotive, defense and aerospace industries. besides these positive properties, it is known that the production and processing of cellular materials is very tough and worth the effort. recently, with advances in new technologies like 3d printing or selective laser melting, now different types of cellular materials can be produced. but manufacturing of metallic foams via casting especially replication or infiltration method is fairly an economic method when compared with other methods. in this study, vacuum-gas infiltration set-up was used to produce b4c reinforced aluminum foams. the mentioned method involves the addition of space holder materials and a dissolution technique to remove them after solidification of the metal. as space holder materials nacl particles were selected and mixed with b4c powders to produce b4c reinforced a360 aluminum foam. by changing the weight ratio of b4c particles, the alteration of properties like porosity, compression strength, and energy absorption capacity was investigated. additionally, computer tomography views were obtained to see and interpret the microstructures of the foams. compression tests were carried out to evaluate the mechanical behavior of the foams under static loading. the porosities of samples obtained as between 65-75%. the compressive strength increased with rising relative density. keywords-cellular materials; aluminum foam; space holders; replication i. introduction cellular materials and foams have attractive mechanical and physical properties like low density, high stiffness and thermal conductivity. these properties make them sufficient for advanced engineering applications. generally, foam kind materials are characterized by their cell structures. there are two types of metal foam materials: open cell and closed cell metal foams. open and closed cell metal foams have various definitions, but basically if the cells connect through open faces, so the gas phase is infinite, the foam can be defined as open celled. otherwise, when the cell faces are closed and connected to their neighbors they can be defined as closed cells. the cell structure depends on the production method [1]. there are numerous manufacturing methods to produce metal foams [1, 2]. the main difference between the production methods is the physical state of the main material which is processed. porous metals can be formed from the initial state of liquid or solid metal [2]. the production method for this study is determined as replication or infiltration method which can be classified as foaming from liquid state. the casting of metals and alloys around the space holder material is a convenient and economical way to obtain metallic foams or cellular parts [3, 4]. the pore size and porosity can be controlled by modifying the process parameters like space holder particles (shape, size, material etc.), process pressure and method of infiltration [5, 6]. the infiltration process benefits from the melting point difference between the main metal and space holder materials. for example, in this study the melting temperature of a360 is 650⁰-760⁰ [7] while the melting temperature of sodium chloride is 801⁰ [8]. to infiltrate aluminum into the sodium chloride space holder particles is required to melt aluminum at a temperature below the melting point of nacl and apply pressure. the first study producing aluminum sponge from nacl particles was carried out in 1961 [9]. authors replicated molten aluminum into the sintered nacl preform. the porosity and compression strength values of aluminum sponges were reported as 60%-63% and 20-30mpa respectively. in another study the porosity range for aluminum sponges was reported as 55%-67% [3]. authors in [6], applied cold isostatically pressing to 400µm nacl particles and produced replicated foams which had 15-25% (75-85% porosity) relative densities. there are studies dealing with foaming of different main materials such as copper and magnesium using nacl space holder particles. copper foam was successfully produced with the use of nacl particles via sintering-dissolution process and the resulting porosities were reported as 59.5%-71.3% [10]. in [11], a replication casting device was developed and mg and mg alloys with melting points lower than 950⁰ were manufactured. open celled pure mg and mg-10wt%al foams were produced with porosities of 70% and 67% respectively engineering, technology & applied science research vol. 8, no. 6, 2018, 3640-3645 3641 www.etasr.com sunar & cetin: an experimental study on boron carbide reinforced open cell aluminum foams … [11]. other studies focused on the effects of cell shape and morphology to the mechanical behaviors of cellular metals and metallic foams. open celled 6061 aluminum metal foam with different densities (5%-10%) characterized the compression. density was reported as the primary variable controlling strength. the cell size was referred as it has insignificant influence [12]. recent papers concentrated on cell geometry of lightweight structures. the mechanical properties of different honeycomb structures with the same relative density were investigated using finite element analysis. cell geometry and arrangement highly affect the compression behavior and energy absorption capacity [13]. selective laser melting was also used to produce lightweight similar-to foam steel structure with spherical porosity. different cell arrangements applied, and samples had average porosities between 70.1%-72.5%. as a result, shape geometry considerably affects compression properties [14]. authors in [15, 16] dealt with the addition of ceramic particles into aluminum foams. tib2 particles have been added to al-tih2 compact to produce composite foam via powder metallurgy route. when compared with the al foams, composite foams showed higher proof stress and absorbed more energy [15]. the mechanical properties of b4c reinforced alsi7 foams produced powder metallurgy route were also investigated. it was reported that energy absorption values rise with increments in relative density and b4c content. authors in [16] reported that b4c reinforced foams have approximately 28% higher bending strength compared to unreinforced foams. metal foams can be reinforced with other particles to improve their physical and mechanical properties. moreover, making this enhancement with an economic fabrication technique provides higher efficiency. authors in [17] report that the higher production costs of metallic porous materials limits their application area. thus, there is a good demand of cost-effective production methods that can correspond to the physical and mechanical properties for advanced industrial applications. in infiltration method, commonly nacl particles are used as space holder particles, but, to the best of our knowledge, there is not a study considering the effects of ceramic particle addition into the space holder media. thus, in this study, a360 aluminum is foamed with the addition of different ratios of b4c (0%-5%) into the nacl space holder media. structure and microstructure were analyzed by ct and sem&xrd. the effects of b4c to the porosity, compression strength and energy absorption behaviors were investigated. ii. experimental study for many lightweight applications aluminum or magnesium are preferred because of their physical, mechanical and chemical properties like corrosion resistivity. in this study a360 (alsi10mg) aluminum alloy was used as the main material. the metallic foam samples were produced using nacl space holder particles with size range of 1.8mm-2.8mm. b4c powders (325 mesh) were used for reinforcement particles for the projected metal foams. the contents of the a360 are given in table i. a. infiltration process infiltration process can be expressed as casting around space holder materials. cellular structure can be obtained by removing the space holder materials. this process is also known as replication [18]. infiltration of aluminum was carried out into an atmosphere controlled mold. the mold has been manufactured from 304 series steel in dimensions of 225mm length, 101mm external diameter and 5mm wall thickness. table i. spectral analysis results and commercial data of a360 cast alloy elements si fe cu mn mg zn ni ti commercial data 9-10 0.5 0.1 0.4 0.3 0.1 0.1 0.1 spectral analysis 9.86 0.42 0.08 0.41 0.38 0.09 0.1 0.15 to obtain standard main test material, pre-casting process was carried out and aluminum cylinder blocks 90mm in diameter and 50mm in length, were produced. a constant volume of space holder materials and aluminum block were placed into the mold. b4c particles were added and mixed with the nacl space holder particles. to compare the effects of ceramic addition on strength, three samples were produced without ceramic addition. the mold was placed in a furnace set to 720⁰. before infiltration, vacuum process was applied to the mold in order to avoid oxidation by removing the air from the mold. the temperature and vacuum pressure were kept constant during melting. the next step after melting was to initiate infiltration with the help of pressure. argon gas used to supply constant 2 bar pressure to press aluminum [19]. cooling was performed at room temperature. several conventional operations such as cutting and turning were carried out to get uniform shape before the dissolution process of space holder particles. with the aim of removing the space holder particles from the main material, dissolution process was performed inside 2 liter water tanks at temperature of 90⁰ for 1 hour. a magnetic stirrer hot plate was utilized for better dissolution performance. beside that, to improve solubility, after half an hour the water was refreshed. with this technique, b4c reinforced foams were produced with 14 different weight ratios of b4c: 0.25%, 0.5%, 0.75%, 1%, 1.25%, 1.5%, 1.75%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% and 5%. the samples were named with respect to their ceramic content, e.g. f1.75 represents foam sample which is manufactured with 1.75% b4c content. figure 1 shows a metal block and the resulting foam sample. fig. 1. aluminum block and resulting foam sample. b. compression tests to investigate the effects of b4c reinforcement to the compression behavior of the foam, compression tests were carried out with the following test parameters: test specimens had dimensions of 80mm length and 50mm diameter. the crosshead speed was determined as 0.005s-1. all parameters engineering, technology & applied science research vol. 8, no. 6, 2018, 3640-3645 3642 www.etasr.com sunar & cetin: an experimental study on boron carbide reinforced open cell aluminum foams … were selected as compatible with the standard of iso 13314 compression test for porous and cellular metals [20]. zwick/roell 600kn mechanical test machine has been used for compression tests. each test was repeated three times and the mean values were extracted to provide experimental accuracy. the standard iso 13314 provides the definition and application of basic terms for mechanical test results for cellular materials such as first maximum stress, plateau stress 𝜎𝑝𝑙, plateau end 𝜎𝑝𝑙𝑒 and absorbed energy w. plateau stress values were calculated as the average of the stress data between 20% and 30% compressive strain range on the stress-strain curve. plateau end estimated the stress value as 1.3 times greater of the plateau stress. the energy absorptions of the samples were computed as the area under stress-strain curve up to the plastic strain of 50%. both data analysis and calculations were performed in accordance with the standard. c. porosity and microstructure investigations the foam samples formed cubical shapes and sandpapered to perform basic metallography examination. micro-structural investigation of the foam surfaces was performed using carl zeiss ultra plus scanning electron microscope (sem) supplied with an energy dispersive spectrometer (eds, bruker x flash 6/10). cell walls and truss sections were viewed and mapping images were taken to observe element distributions. component identification was carried out using rigaku ultima iv xrd test machine with cu ka radiation (λ:1.54a) and scanning speed of 3⁰min. diffraction patterns were generated with 2 theta (bragg angle) between 10⁰ and 90⁰. the density of foam samples derived from their weights and volumes [10]. equation (1) gives the porosity: 𝑃 = (1 − 𝜌𝑝 𝜌𝑏⁄ ) × 100 (1) where p is the porosity of the foam, 𝜌𝑝 is the density of porous or foam material 𝜌𝑏 is density of bulk material. the fraction of 𝜌𝑝 𝜌𝑏⁄ is defined as the relative density of the foam [21]. iii. results and discussion a. structure and porosity of the samples al foam resulting samples were defined as open celled when computer tomography images were examined. the sample foams did not have uniformly shaped space holder particles. thus, it was not possible to refer constant average cell size. the space holder material dimensions varied between 1.8mm–2.8mm. aluminum foams were scanned with the 3d computer tomography device and 3d geometric data were obtained. figure 2 shows the alloy (without b4c) foam sample’s 3d and section views. results show that the samples had homogenous pore distributions. the produced metal foam samples had different porosities, approximately in the range of 65%-75% agreeing with similar studies. several papers reported porosity range between 55%-67% (81% when nacl was pre-sintered). maximum porosities obtained were limited and below 80% [3, 22]. figure 10 shows the mean porosity values for different samples. when the porosity results were analyzed, there was seen a complex effect of b4c on porosity. less porous structure was obtained when the b4c content was in the range of 0.25%-2%. the lowest porosity value was 63% and was observed in the sample f0.5. sem and edx investigations were done on the truss faces and cell walls. figure 3 illustrates the combination area of cell wall and the truss section. edx/eds analysis showed that boron and carbon were highly placed at the cell wall for all the samples. these phenomena can be understood because b4c particles were mixed with nacl particles so it's clear that the cell wall would have more ceramic content. the resulting images of the samples which were mixed with higher ratio of b4c showed more obvious boron and carbon content according to figures 47. the point analysis showed the same trend. figure 8 shows the results of point analysis fom different samples. xrd diffraction pattern graph is shown in figure 9. xrd analysis results showed that there are b4c (~32⁰ and ~38⁰) and al3bc (~ 44⁰) compounds. fig. 2. computer tomography images of a360 foam sample. fig. 3. eds mapping images for the region of combination cell walls and truss faces of f.175 sample. b. mechanical behaviour of the foams to investigate the effects of b4c reinforcement on the compression behavior of the foams, compression tests were carried out. the compressing test procedure and the test results are shown in figure 10 and table ii. mean data were extracted from the original 3 data series. the sample f0.5 which was reinforced with 0.5% b4c had better mechanical properties from the other series (see figure 10). engineering, technology & applied science research vol. 8, no. 6, 2018, 3640-3645 3643 www.etasr.com sunar & cetin: an experimental study on boron carbide reinforced open cell aluminum foams … fig. 4. eds mapping images of cell wall of f0 sample. fig. 5. eds mapping images of cell wall of f0.5 sample. fig. 6. eds mapping images of cell wall of f1.75 sample. fig. 7. eds mapping images of cell wall of f5 sample. fig. 8. eds analysis of cell walls of the samples: (a) f0, (b) f0.5, (c) f1.75 and (d) f5. fig. 9. xrd diffraction pattern graph of foam samples. fig. 10. compression test results with the porosities of the foam samples. engineering, technology & applied science research vol. 8, no. 6, 2018, 3640-3645 3644 www.etasr.com sunar & cetin: an experimental study on boron carbide reinforced open cell aluminum foams … when compression test results were analyzed, f0.5 had 21.2mpa first maximum stress and 19.45mpa plateau stress. f0.75 showed the second highest results with values of 18.61mpa first maximum stress and 15.15mpa plateau stress. the mechanical behavior of metallic foams differs, depending on several factors such as the properties of base metal, relative density, pore size and heterogeneity [16, 23]. the compressive properties increase consistently with increasing relative density [6]. by raising the relative density compression the curve slides vertically because of greater strength [24]. in this study, porosity is an important parameter for mechanical properties. except minimal increments, both first maximum stress and plateau stress values showed decreasing trend with the addition of b4c to the nacl media. higher b4c addition into the nacl media caused less compressive strength. table ii. compressive test results data of foam samples samples first max strength [mpa] plateau stress [mpa] plateau end [mpa] absorbed energy [kj/m3] f0 9.224 7.830±2.3 10.179 3107 f0.25 15.664 12.195±.8 15.854 5938 f0.5 21.196 19.448±1.8 25.283 7310 f0.75 18.614 15.155±4.9 19.702 5017 f1 16.05 14.144±3.5 18.387 3938 f1.25 13.028 11.105±1.1 14.437 5129 f1.5 14.596 11.230±2.4 14.598 2628 f1.75 9.23 8.486±2 11.032 2815 f2 10.767 10.407±2.3 13.530 3908 f2.5 8.133 6.229±2.2 8.098 2176 f3.0 9.4 6.745±1.2 8.768 2939 f3.5 6.511 6.4±1.7 8.320 2525 f4.0 4.021 3.594±1.3 4.672 1397 f4.5 7.022 6.362±0.9 8.271 2422 f5 4.52 3.624±2.6 4.711 1602 iv. conclusions an experimental study was conducted on the replication of b4c reinforced a360 aluminum foams. fourteen different series of aluminum foam were manufactured successfully. the outcomes of this study are concluded as follows: metal foams were open celled and the pores were distributed homogeneously. the pore shapes were not uniform because of the natural complex forms of space holder particles. thus, cell sizes ranged between 1.8mm and 2.8mm. the porosity of the acquired metal foams was between 65%-75%. the effect of b4c on the porosity was not proportional. in the range of 0.25%-2% b4c content, the porosities of the foams were lower. on the other hand, a360 aluminum foam (without ceramic addition) and the foams produced with higher than 2% b4c reinforcement showed higher porosity values. b4c particles were distributed mostly at the cell walls. xrd analysis results showed that there were b4c and al3bc compounds. the compressive properties of metallic foams increase consistently with increasing relative density. the sample f0.5 had the lowest porosity and showed the best mechanical properties. first maximum stress and plateau stress values decreased with the addition of b4c. acknowledgment authors would like to thank karabuk university coordinatorship of research projects (bap) and the scientific and technological research council of turkey (tubitak) for their financial support for this study (project numbers are kbubap-17-dr-051 and 215m233 respectively). references [1] l. j. gibson, m. f. ashby, cellular solids, pergamon press ltd., cambridge, 1997 [2] j. banhart, “manufacture, characterization and application of cellular metals and metal foams”, progress in materials science, vol. 46, no. 6, pp. 562-563, 2001 [3] j. banhart, “properties and applications of cast aluminum sponges”, advanced engineering materials, vol. 2, no. 4, pp. 188-194, 2000 [4] r. goodall, a. mortensen, “microcellular aluminum? child’s play!”, advanced engineering materials, vol. 9, no. 11, pp. 951-954, 2007 [5] s. b. pimiento, m. e. hernandez-rojas, m. e. palomar-pardave, “processing and characterization of open-cell aluminum foams obtained through infiltration processes”, procedia material science, vol. 9, pp. 54-61, 2015 [6] j. f. despois, 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mechanical testing of metals, ductility testing, compression test for porous and cellular metals, international organization for standardization, 2011 [21] j. a. liu, f. gao, y. q. rao, c. l. wu, y. liu, “compressive properties of aluminum foams produced by replication route using spheroidal calcium chloride as space holder”, materials transactions, vol. 55, no. 12, pp. 1906-1908, 2014 [22] c. san marchi, a. mortensen, handbook of cellular metals production, processing, applications, pp. 44-56, wiley-vch, 2002 [23] u. ramamurty, a. paul, “variability in mechanical properties of a metal foam”, acta materialia, vol. 52, no. 4, pp. 869-876, 2004 [24] q. fabrizio, a. boschetto, l. rovatti, l. santo, “replication casting of open-cell alsi7mg0.3 foams”, materials letters, vol. 65, no. 17-18, pp. 2558-2561, 2011 microsoft word 20-2457_s engineering, technology & applied science research vol. 9, no. 1, 2019, 3770-3773 3770 www.etasr.com palconit & abundo: transitioning to green maritime transportation in philippines: mapping of … transitioning to green maritime transportation in philippines: mapping of potential sites for electric ferry operations eleonor v. palconit engineering graduate program, school of engineering, university of san carlos (usc), talamban, cebu city, philippines, and school of engineering and architecture, ateneo de davao university, davao city, philippines philippines evpalconit@addu.edu.ph michael lochinvar s. abundo engineering graduate program, school of engineering, university of san carlos (usc), talamban, cebu city, philippines, and programme integration manager, rolls-royce@ntu corporate lab, nanyang technological university, singapore michael.abundu@ntu.edu.sg abstract—philippine maritime industry is considered as a vital component in achieving inclusive growth and socio-economic progress. philippines has been known as one of the susceptible to the impact of climate change countries, and generally the changing climate hampers its economic development. the government committed to reduce carbon emissions to 70% by 2030 during the 2015 paris climate conference. this study aims to map the potential sites and vessels for electric ferry operation for transitioning to green maritime transportation in philippines. at present there are 83 ports and 110 ferries in the country with 33670 registered vessels as of december 2017. it was identified that the 9201 vessels with 10≥grt≥3 will be used for electrification as a kickoff in implementing electric ferry since these vessels are feasible for retrofitting the electric system. implementing green energy sources in the country’s marine transportation will reduce co2 emission by 22.09% in the transport sector. keywords-transitioning; green energy source; electric ferry; co2 emission i. introduction energy security, sustainability, pollution and climate change impact are among the major challenges the world is facing nowadays [1]. the need of energy has been increased with population growth and the advancement of technology. finding and exploiting new energy sources has become a very important topic globally [2]. a sharp increase occurred in the usage of renewable energy in the past decade because of the re promotion to make energy more secure in response to the consumer needs and to the climate change impact which became essential in transitioning to a sustainable future [3]. the transition of energy in different sectors, particularly in the transportation sector faces challenges regarding sustainability [4]. but because the renewable energy availability is now coupled with innovative technology, the energy transition to maritime sector is very possible nowadays. furthermore, transitioning to green maritime transportation contributes to solve the problem in co2 emissions and reduces the dependency on fossil fuels. maritime petroleum dependency resulted to a consumption of about five million barrels per day which is equivalent to 1gt of co2 emissions annually [5], bringing the shipping industry into a great pressure to reduce environmental impact in co2 emissions which is projected to increase 50-250% by 2050 [6]. this industry is one of the stakeholders in the environmental issues, but still a better alternative among other transportation means. still, the european union and united nation framework convention (unfccc) regulate emissions in all sectors and the international maritime organization (imo) is working on the regulation of the emission in shipping industry [7]. imo works towards developing a comprehensive regime aimed to protect the environment from pollution caused by ships [8]. with the transition to renewable energy sources, the maritime sector might achieve the aim of reducing carbon emissions or even eliminate them in the near future [9]. philippine maritime industry is considered as one of the vital components of the country’s economy. there is a major infrastructure connecting philippine islands and the country to global commerce and trade [10]. philippines have been known as one of the susceptible countries to the impact of climate change, only in 2013, a typhoon resulted to the loss of 7,000 lives. the changing climate might hamper the economic development of the country, so the philippine government committed, during the 2015 paris climate conference, to reduce carbon emissions coming from energy, transport, waste, forestry and industry sectors by 70% by 2030, even though the country is one of the lowest co2 emitting countries in the world [11]. with that envision, the philippine government needs to implement policies to ensure the provision of the ecosystem and green services to address the ghg emission and environmental degradation [12]. the government decision to reduce carbon emissions and environmental degradation brings us to the aim of this study of paving the way of transitioning to green maritime transportation in philippines: mapping of potential sites for electric ferry operations. the transition to green energy sources will serve as an example to solve the corresponding author: e. v. palconit engineering, technology & applied science research vol. 9, no. 1, 2019, 3770-3773 3771 www.etasr.com palconit & abundo: transitioning to green maritime transportation in philippines: mapping of … energy security, sustainability, pollution and climate change impact that the country is currently experiencing. ii. e-ferry: new paradigm in aiming green source transition in maritime sector, eferry concept was derived for transporting goods and passengers. ferry electrification in europe emerged because of the coupling of environment considerations with new battery innovations and the increasing fuel prices in order to address the urgent need of reducing the increasing european co2 emissions from waterborne transportation [5]. the electric ferry was considered in navigating close to the coast of the cinque terre natural park in transporting passengers for its noiseless and slow boating that allows transforming a connection route to a touristic journey in a wonderful natural site without impacting with the local environment [13]. it is worth remembering the advantages of using green energy sources in the maritime transport sector. it reduces emissions in air and water, the energy source can be obtained directly from renewable resources like the sun or the wind, and it has a strong reduction in noise [13]. another eco-friendly electric propulsion boat aiming to have zero emissions was used for public transport in lake trasimeno. the boat is powered by lithium-ion batteries that can be charged at any harbor visit [14]. iii. potentiality for e-ferry in philippines a. philippine ports and sites philippines is an archipelago, with a total land area of 299,404km 2 having three major island groups namely luzon, visayas and mindanao, with large mountainous terrains, narrow coastal plains and interior valleys and plains. philippines covers water area of 2.2 million km 2 , of which 12% equivalent to 267,000km 2 are coastal water and 88% (1.934 million km 2 ) are oceanic water. philippines has a total discontinuous coast line approximately 32,400km with 80% of provinces and 65% of cities and municipalities sharing the coast [15]. in philippines, there are 8 gulfs, 7 seas and 10 straits. all ports used for maritime transportation are managed by the philippine port authority (ppa). this agency monitors not only ports but also the ferry terminals. at present there are 83 ports and 110 ferry terminals in the country [16]. existing ferries and small boats are potentially useful to electric maritime transport sector in philippines. fig. 1. registered domestic vessels in philippines b. philippine vessel/ferry all maritime transportation, particularly domestic vessels are registered in the government agency under the maritime industry authority (marina) philippines. as of december 2017, there are 33670 vessels registered in the country with different service types as illustrated in figure 1 [17]. figure 2 shows the breakdown of different service types of vessels in the three major islands in philippines. these vessels help the economy improve and increase the quality of life. however, they contribute to the increase in the co2 emissions and depletion of fossil fuels. fig. 2. registered vessel per island group data coming from the marina philippine were analyzed, to derive potential vessels for electric ferry in maritime transport sector. table i displays the 9201 vessels that have 10≥grt≥3 and are potentially useful for electric propulsion in philippines. for instance, in mindanao, such ferryboats are the ones that operate in davao to paradise samal beach resort. the resort has 12 ferryboats operating in the area. each boat operates 16 times a day for six days in a week. the operator uses 16l of diesel fuel that cost 800 php per day. one liter of diesel fuel contributes a 2.68kg of co2 in the environment. figure 3 shows the co2 emissions of one ferryboat operating in the island. if all the registered ferryboats shown in table i use the same fuel consumption (16l/day), the total co2 emission is 5.184mt in a period of 8 years as shown in figure 5 and it serves as an indicator that philippines need to address the co2 caused by transportation in maritime sector by advocating green energy sources for ferryboat operation. table i. potential vessels for use of green energy place of registry no. of registered boats with 10≥grt≥3 luzon 5226 visayas 2190 mindanao 1785 iv. significance of transitioning to green maritime transportation philippines is a minor emitter of greenhouse gases (ghg), but still needs to address the problem as the country is one of the signatories of the 1992 united nation framework convention on climate change (unfccc) and its kyoto protocol [18]. the country is the 4th asean co2 emitter with engineering, technology & applied science research vol. 9, no. 1, 2019, 3770-3773 3772 www.etasr.com palconit & abundo: transitioning to green maritime transportation in philippines: mapping of … 8% of the total global co2 emissions from 1990 to 2014 which grew 4% annually during this period. denr passed laws concerning climate change and one of them is the ra 9513 which is the promotion of the development of renewable energy resources [19]. data from the department of energy (doe) showed an annual average of 69mt from 2000 to 2014 co2 emissions which mainly derives from electricity generation (41%) and transportation (34%) [19]. this study focuses on water transportation or maritime transport, aiming to reduce co2 in this sector. as shown in figure 1, there are 33670 vessels registered in the country with different service types, and 9201 vessels were put into consideration as being suitable for converting into electric ferryboats. electrifying these vessels will reduce co2 emissions under maritime by 5.18424mt in a period of 8 years. transitioning to green energy is also significant because is meeting the aims of reducing 70% carbon emissions by 2030, helping to solve the energy security, sustainability, pollution and climate change impact that the country is currently experiencing. fig. 3. co2 emissions of one ferryboat fig. 4. co2 emissions per island v. environmental impact over the cost of electric ferryboat as part of the carbon cycle, co2 is a natural part of the atmosphere [19]. but, activities like fossil fuel combustion, especially in the transportation which is one of the primary ghg emission sources, are contributing to the climate change. electrification of some, if not all, vessels will reduce co2 emissions. the cost of converting the existing ferryboats comes into consideration. table ii shows the costs of converting diesel ferries to electric ones. the total cost is $19582.03 for one ferry and the total reduction of co2 emissions in a period of 8 years is 547.9155tons. if all 9201 potential ferryboats in philippines were converted to electric ferries, the reduction of the carbon would be 5.18424mt in 8 years. some co2 is absorbed in the ocean: from the 7 billion tons of co2 released into the atmosphere per year, the ocean takes 2 billion tons, causing an increase of 26% in the concentration of the hydrogen ions, which decreases the ph by 0.1 [20]. co2 reduction also results to saving the marine life ecosystem by not reducing the seawater ph level. table ii. cost over enviromental impact capital cost diesel co2 (tons)/year year diesel operating cost electric operating cost annual savings diesel co2* co2 from manufacturing batteries (leadacid)* co2 emission reduction* 1 $ 6889 $ 3583 $ 3305 15.65 0.43 15.22 2 $ 13778 $ 7166 $ 6611 31.30 0.86 30.44 3 $ 20667 $ 10750 $ 9916 46.95 1.29 45.66 4 $ 27556 $ 14333 $ 13222 62.60 1.73 60.88 5 $ 34445 $ 17917 $ 16527 78.26 2.16 76.10 6 $ 41334 $ 21500 $19833 93.91 2.59 91.32 7 $ 48223 $ 25084 $ 23138 109.56 3.02 106.54 8 $ 55112 $ 28667 $ 26444 125.21 3.45 121.76 * tons/year vi. conclusion transitioning to green energy sources in philippines is a great help to counter climate change. philippines is not one of the major co2 emitters in the world, but it is still ranked 4th among asian countries. that’s why the government looked to solve the problem of co2 emissions. this study considers the marine transportation sector which happens to contribute to 34% of co2 emissions of the transportation sector. furthermore, this research contributes in identifying the potential sites and vessels for electric ferry operation in philippines. with 33670 vessels registered in the country as of december 2017, it is concluded that 9201 vessels can be electrified. a boat with 10≥grt≥3 travelling 2.13h per day at minimum, consumes 16l of fossil fuels. converting this boat will reduce co2 emissions by 15.65tons per year. if green energy sources in the marine transportation will be implemented in all 9201 vessels, the co2 emissions will be reduced by 22.09% in the transportation sector, preventing the increase of ocean acidification and solving the energy security, pollution and climate change impact. acknowledgement the authors are grateful for the scholarship grant given by the department of science and technology (dost) engineering research and development for technology (erdt), ateneo de davao university for the support from the faculty development funds. references [1] a. garcia-olivares, j. sole, o. osychenko, “transportation in a 100% renewable energy system”, energy conversion and management, vol. 158, pp. 266-285, 2018 [2] y. a. kaplan, “overview of wind energy in the world and assessment of current wind energy policies in turkey”, renewable and sustainable energy reviews, vol. 43, pp. 562-568, 2015 engineering, technology & applied science research vol. 9, no. 1, 2019, 3770-3773 3773 www.etasr.com palconit & abundo: transitioning to green maritime transportation in philippines: mapping of … [3] n. vidadili, e. suleymanov, c. bulut, c. mahmudlu, “transition to renewable energy and sustainable energy development in azerbaijan”, renewable and sustainable energy reviews, vol. 80, pp. 1153-1161, 2017 [4] d. f. dominkovic, i. bacekovic, a. s. pedersen, g. krajacic, “the future of transportation in sustainable energy systems: opportunities and barriers in a clean energy transition”, renewable and sustainable energy reviews, vol. 82, pp. 1823-1838, 2018 [5] e. gagatsi, t. estrup, a. halatsis, “exploring the potentials of electrical waterborne transport in europe: the e-ferry concept”, transportation research procedia, vol. 14, pp. 1571-1580, 2016 [6] r. d. geertsma, r. r. negenborn, k. visser, j. j. hopman, “design and control of hybrid power and propulsion systems for smart ships: a review of developments”, applied energy, vol. 194, pp. 30-54, 2017 [7] s. sherbaz, w. duan, “propeller efficiency options for green ship”, 9th international bhurban conference on applied sciences & technology, islamabad, pakistan, january 9-12, 2012 [8] j. prpic-orsic, o. m. faltinsen, m. valcic, “development strategies for greener shipping”, elmar 2014, zadar, croatia, september 10-12, 2014 [9] m. lange, g. page, v. cummins, “governance challenges of marine renewable energy developments in the u.s. – creating the enabling conditions for successful project development”, marine policy, vol. 90, pp. 37-46, 2018 [10] tesda, the philippine maritime industry through the years, tesda, 2017 [11] https://data.worldbank.org/indicator/en.atm.co2e.pc [12] m. mogato, “philippines aims to cut carbon by 70 percent by 2030, if it gets help”, available at: https://www.reuters.com/article/usclimatechange-summit-philippines/philippines-aims-to-cut-carbon-by70-percent-by-2030-if-it-gets-help-iduskcn0rw0kn20151002, 2015 [13] m. bianucci, s. merlino, m. ferrando, l. baruzzo, “the optimal hybrid/electric ferry for the liguria natural parks”, oceans 2015 genova, genoa, italy, may 18-21, 2015 [14] g. s. spagnolo, d. papalilo, a. martocchia, “eco friendly electric propulsion boat”, 10th international conference on environment and electrical engineering, rome, italy, may 8-11, 2011 [15] government of the philippines, the philippines’ initial national communication on climate change, 1999 [16] ppa, list of ports covered in ppa statistics, ppa, 2016 [17] maritime industry authority, “list of philippines registered vessels as of december 2017”, marina, 2017 [18] ttpi inc, cpi energy phils. inc, “a strategic approach to climate change in the philippines”, ttpi inc, cpi energy phils. inc, 2010 [19] e. m. nejar, “feasibility of imposing a tax on the emissions of carbon dioxide in the philippines”, ntrc tax research journal, vol. 28, no. 3. pp. 15-38, 2016 [20] m. briffa, k. de la haye, p. l. munday, “high co2 and marine animal behaviour : potential mechanisms and ecological consequences”, marine pollution bulletin, vol. 64, no. 8, pp. 1519-1528, 2012 microsoft word 09-3223_s_etasr_v10_n1_pp5148-5152 engineering, technology & applied science research vol. 10, no. 1, 2020, 5148-5152 5148 www.etasr.com soomro et al.: eplaodv: energy priority and link aware ad-hoc on-demand distance vector … eplaodv: energy priority and link aware ad-hoc on-demand distance vector routing protocol for post-disaster communication networks mohammad ali soomro quaid-e-awam university of engineering, science and technology, sindh, pakistan mohammadalisoomro23@gmail.com mohammad ibrahim channa quaid-e-awam university of engineering, science and technology, sindh, pakistan ibrahim.channa@gmail.com zahid hussain quaid-e-awam university of engineering, science and technology, sindh, pakistan zhussain@quest.edu.pk mukhtiar ahmed quaid-e-awam university of engineering, science and technology, sindh, pakistan mukhtiar.a@gmail.com abstract—in mobile ad-hoc networks (manets) the major issue between nodes for data transfer is link quality. the majority of the manet routing protocols try to maintain the link quality between nodes but still need improvement. this paper focuses on link quality between nodes in an ad hoc network in emergency scenarios through the design of the energy priority and link aware ad-hoc on-demand distance vector (eplaodv) routing protocol. eplaodv improves the link quality between nodes through snr. for performance analysis, the ns2.35 network simulator was used. simulation time and traffic load were the major simulation parameters. from the simulation results, it is observed that eplaodv performs better than aodv. keywords-mobility; snr; eplaodv; link-quality; lifetime i. introduction many users use wireless communication devices or channels for the exchange of information. in an manet, mobile nodes are connected through wireless links. an manet lacks pre-deployed infrastructure for environment monitoring and disaster scenarios [1-3]. rf frequencies are used from mobile nodes to flood data packets from source to destination nodes. an manet has flexible and dynamic topology. in dynamic topology, the nodes of the network frequently move with different speeds within the transmission range. nodes may join or leave the network thus changing its topology. node mobility is a main cause of frequent link failure. to prolong network lifetime and to get maximum throughput, manets use reactive, proactive and hybrid routing protocols to discover shortest, stable, and efficient routes. the reactive routing protocols aodv [4], dsr [5] and tora [6] are on demand routing protocols which discover routes when required, avoid traffic congestion, reduce routing overhead, minimize end-to-end delay, and reduce traffic collision [7]. generally, manet nodes have battery constraints. in a network, the nodes with very low energy level are disconnected. to discover a route, the conventional aodv routing protocol does not consider the fairness of node energy consumption. manets are used in various real time applications such as environment monitoring control, air traffic control, in battle fields, and in many emergency scenarios like major accidents and disaster relief operations [8]. in real time scenarios, where the replacement or recharging of batteries is almost not possible, the lifetime of the network is important. to prolong the network lifetime link various energy efficient and link aware routing protocols have been proposed. these routing protocols avoid link failures and consider less node energy consumption [9-12], although the current status in maximizing network lifetime still needs improvement. in disaster-affected areas, the telecommunication infrastructures are seriously damaged or even collapsed. manets can be deployed in critical areas to carry out the rescue operations. rescue workers or first responders are equipped with mobile devices to share important information about operations at the disaster site. the first responders share videos, make voice calls and send text messages to their supervisors to inform about the situation in the area. wireless communication is used to support the operational analysis of disaster response. to avoid communication interruption among the rescue works, and to reduce the losses of infrastructure and human lives, critical information travels through high powered nodes or stable links. the proposed energy, priority and link aware ad hoc on demand distance vector (eplaodv) routing protocol discovers energy efficient and link aware routes from source to destination for the exchange of critical information in disaster operations. ii. literature review manet routing protocols are used to discover routes from source to destination. node mobility and unfair consumption of corresponding author: mohammad ali soomro engineering, technology & applied science research vol. 10, no. 1, 2020, 5148-5152 5149 www.etasr.com soomro et al.: eplaodv: energy priority and link aware ad-hoc on-demand distance vector … node energy and frequent link failure are inherent in an manet, which causes routing overhead and end-to-end delay. conventional aodv reactive routing protocol does not consider link stability and energy consumption, while energy consumption is the main issue of manets. different routing protocols based on the node energy consumption and link quality parameters to prolong network life time, have been proposed. authors in [13] proposed maodv routing protocol which is based on aodv. the algorithm considers two parameters, node energy level and node distance. the distances among the nodes are measured and a node with a good energy level and with small distances is considered in route selection. maodv selects an energy efficient route in which all nodes possess good energy level. this protocol consumes less energy and maximizes packet delivery ratio and network lifetime. in [14], authors suggested a local repair method to avoid link breakage. the protocol takes preemptive measures based on the residual energy, and uses three state modes to avoid link failure: normal, selfish, and sleep. the algorithm selects stable and energy efficient routes. it minimizes routing overheads by avoiding link breakages and maximizes network lifetime. authors in [15] proposed the energy efficient routing protocol ad-hoc on-demand distance vector energy aware (aodvea) which utilizes a min-max algorithm to take routing decisions. a node must have a minimum remaining energy to participate in route selection. the algorithm computes the minimum remaining energy of all possible routes. to prolong the network lifetime and minimize end-to-end delay, the protocol selects the path having maximum value of minimum remaining energy. authors in [16] proposed the dynamic energy ad-hoc on-demand distance vector (de-aodv) routing protocol. route selection is based on node energy level. the node energy level is compared with a threshold. a node having more energy is selected in a route. to avoid link failures, the algorithm provides external batteries to the nodes with less energy. the protocol maximizes the network lifetime by minimizing energy consumption. authors in [17] suggested a new method to improve link quality. the suggested method is based on ant colony optimization (aco) algorithm. the algorithm considers received signal strength (rss) as a link quality parameter. the protocol selects nodes in a route that have stable links with good rss values. the protocol minimizes routing overhead and node energy consumption by avoiding link failure. authors in [18] proposed the route stability and energy aware (rsea)-aodv routing protocol, which considers rss, drain rate of nodes, remaining energy, and delay as route metrics to select a stable route. in the route discovery process, these parameters are compared with respective thresholds. a less congested node, having good energy level and good rss values is selected in an energy efficient and stable route. the protocol minimizes energy consumption, end-to-end delay and maximizes network lifetime and packet delivery ratio. iii. the proposed eplaodv in the proposed eplaodv routing protocol, the discovered routes are based on traffic priority, node energy, and link quality. the rreq and rrep control packets are modified by adding new priority fields. high priority 0 is assigned to time critical traffic for exchange of information in the form of voice and video. low priority 1 is assigned to normal traffic for the exchange of information in the form of text and data. when the source node wants to discover a route to a destination, it sets the traffic priority in the rreq control packet and broadcasts it to all its neighbors. in the following section the route discovery process is discussed in detail. a. route discovery assume that node ns is the source and node nd is the destination, as shown in figure 1. the source node initiates route discovery process, ns assigns a traffic priority 0 in the rreq control packet, and broadcasts rreq packets to neighbor nodes n1, n3, and n5. the intermediate nodes n1, n3 and n5 compare their residual energy with the energy threshold the. if their residual energy is greater than the, they make a reverse path entry and broadcast rreq packets to their neighbors. if any node among n1, n3 or n5 has a residual energy level lower than threshold the, it drops the rreq packet. assuming that these nodes have sufficient residual energy level, node n1 rebroadcasts the rreq packet to node n2, which does not accept the packet due to its insufficient energy level. similarly, node n3 rebroadcasts rreq packet to node n4 and node n5 rebroadcasts rreq packet to node n6. this process is continued until rreq packet reaches the destination. fig. 1. broadcasting of rreq packet in time critical traffic when the rreq control packet reaches the destination node nd, it updates the priority field in the rrep control packets for assigning traffic priority, and the rrep packets are unicast to nodes n4 and n7. when nodes n4, and n7 receive the rrep packets, they check their traffic priority value, and their own residual energy and signal-to-noise ratio (snr) value. if the rrep packet contains priority value of 0, the nodes assume that the route is going to be established for high priority traffic, otherwise low priority traffic is established. intermediate nodes do not accept any rrep control packet until they check their node energy level and snr value. if the residual energy of node n4 and n7 is greater than the, and the snr value of node n4 or n7 is greater than thsnro, then node n4 unicasts the rrep packet to nodes n3 and node n7 unicasts rrep packet to node n6. if node n4 or n7 have residual energy level lower than the and less snr than thsnro, they drop the rrep packet. node n5 drops rrep control packet due to insufficient energy or insufficient snr value. this discovery process continues until rrep control packet reaches the source node ns. finally, node n3 unicasts the rrep packet to the source node ns and the route ns − n3 − n4 − nd is established as shown in figure 2. to engineering, technology & applied science research vol. 10, no. 1, 2020, 5148-5152 5150 www.etasr.com soomro et al.: eplaodv: energy priority and link aware ad-hoc on-demand distance vector … discover low priority routes, priority 1 is assigned in rreq and rrep control packets and the same steps are taken in route discovery process to establish energy efficient and stable routes. once the route has been established, the source node forwards data packets to the destination node. fig. 2. unicasting of rrep control packet b. eplaodv algorithm in table i, the route setup process of the eplaodv protocol is described. table i. algorithm 1: eplaodv route setup steps description 1. let ns denote the source node and nd denote the destination node. 2. let n represent the set of intermediate nodes between ns and nd, where n={n0,n1, n2,……., nm} and ni represent the current node. 3. let nie represent the residual energy level of the current node. 4. let snri+1,i represent the snr for node ni+1 to node ni 5. let thsnr0 represent the snr threshold for real time traffic 6. let thsnr1 represent the snr threshold for normal traffic 7. node ns sets the traffic priority value in the priority field in the rreq packet and broadcasts to its neighbors. 8. node ni receives the rreq packet, where ni є n. 9. for every node ni in the forward route, where ni є n { if (ni!= nd) then { ni checks its nie if (nie <the) then { ni drops the rreq packet else ni makes reverse route entry for ns and forwards rreq to its neighbors }}} 10. if (ni= nd) then { ni replicates the traffic priority value from the rreq packet into the priority field in the rrep packet and forwards the rrep to its neighbors } 11. for every node ni in the reverse route, where ni є n if ((ni!= ns) && (priority = 0)) then {ni checks its nie and snr i+1,i if (nie >the) && (snr i+1,i >= th snr0 ) then { ni drops the rrep packet else ni makes forward route entry for nd and forwards the rrep to its neighbors }} if ((ni!= ns) && (priority = 1)) then { ni checks its nie and snr i+1,i if (nie >the) && (snr i+1,i >= th snr1 ) then {ni drops the rrep packet else ni makes forward route entry for nd and forwards rrep to its neighbors }}} 12. if (ni= ns) then { ni makes forward route entry for nd and starts sending data packets to nd. } iv. performance analysis the proposed eplaodv routing protocol is implemented in the open source network simulator ns2 [19]. the simulator helps in evaluating the performance of manet routing protocols. the proposed eplaodv is compared with aodv. to measure the performance of the proposed eplaodv routing protocol, we run different emergency scenarios (simulation) in ns2 environment with varying traffic load and simulation time. the simulation results show that the proposed eplaodv performs better than the original aodv. the simulation parameters are presented in table ii. table ii. ns2 simulation parameters parameters rating mac layer ieee 802.11 coverage area 1000m×1000m antenna type omni directional routing protocols aodv, epaodv number of nodes 50 packet size 512 bytes mobility models random waypoint traffic type cbr initial energy 30j buffer size 50 topology flat-grid simulation time 1000s the simulation results are benchmarked with aodv routing protocol with keeping in mind that energy performance is crucial in manets because node mobility drains the energy of the node. results show that the proposed eplaodv controls the node mobility in efficient way and prolongs the energy of the node as compared to aodv. figure 3 shows the simulation results of packet delivery ratio versus simulation time. eplaodv and aodv are compared for high and low priority traffic. initially at 200s the packet delivery ratio is less because less number of data packets are generated , and less packets are reaching their destination. as the simulation time increases, packet delivery ratio also increases. in conclusion, eplaodv performs better for high priority and low priority traffic. figure 4 shows the simulation results of routing overhead versus simulation time for proposed eplaodv and aodv. as the simulation time increases, eplaodv selects more stable routes on the basis of link quality. the protocol generates less number of control packets, which causes less routing overhead. it can be seen that eplaodv performs better than aodv. fig. 3. packet delivery ratio vs. simulation time engineering, technology & applied science research vol. 10, no. 1, 2020, 5148-5152 5151 www.etasr.com soomro et al.: eplaodv: energy priority and link aware ad-hoc on-demand distance vector … fig. 4. routing overhead vs. simulation time figure 5 shows the simulation results of network energy consumption versus simulation time for the proposed eplaodv and aodv. initially at 200s, the network consumes less energy. as the simulation time increases, eplaodv generates more control and data packets, causing more energy consumption. eplaodv discovers energy efficient and stable routes, which minimizes the flooding of control packets and energy consumption. figure 6 shows the simulation results of end-to-end delay versus simulation time. the proposed eplaodv and aodv are compared for both high priority traffic and low priority traffic. initially, at 200s the end-to-end delay is maximum, because more packets are generated, due to congestion or link breakage. as the simulation time of the network increases, end-to-end delay decreases, because eplaodv selects stable paths based on link quality which helps avoiding link breakage and congested traffic. the proposed eplaodv performs better for both high priority and low priority traffic. fig. 5. consumed energy vs. simulation time fig. 6. end-to-end delay vs. simulation time figure 7 shows the simulation results of packet delivery ratio versus traffic load for high and low priority traffic. initially, the packet delivery ratio is maximum. as the traffic load increases, the network becomes more congested, which reduces packet delivery ratio. the proposed protocol eplaodv performs better than aodv in both cases. fig. 7. packet delivery ratio vs. traffic load figure 8 shows the simulation results of routing overhead versus traffic load. initially the routing overhead of the network minimizes. as the traffic load increases, the congestion of the network also increases, which causes link breakage and increased routing overhead. again, the proposed eplaodv routing protocol performs better than aodv. fig. 8. routing overhead vs. traffic load figure 9 shows the simulation results of network energy consumption versus traffic load. initially, with minimum traffic load, the energy consumption of the network is reduced. as the traffic load increases, the network becomes more congested. aodv routing protocol generates more control and data packets, causing more energy consumption. the proposed eplaodv protocol reduces the broadcasting of control packets, in order to minimize energy consumption. the proposed eplaodv routing protocol performs better than aodv. figure 10 shows the simulation results of end-to-end delay versus traffic load. eplaodv and aodv are compared for both high and low priority traffic. initially, with minimum traffic load, end-to-end delay is reduced. as the traffic load increases, the congestion of the network also increases, which causes more end-to-end delay. the proposed eplaodv performs better for both cases of high priority and low priority traffic. engineering, technology & applied science research vol. 10, no. 1, 2020, 5148-5152 5152 www.etasr.com soomro et al.: eplaodv: energy priority and link aware ad-hoc on-demand distance vector … fig. 9. consumed energy vs. traffic load fig. 10. end-to-end delay vs. traffic load v. conclusion an energy, link and traffic aware extension of aodv routing protocol named eplaodv is introduced in this paper. the eplaodv selects energy efficient and link aware routes for time critical and normal traffic. some emergency scenarios have been simulated by varying simulation time and network traffic load. the simulation results show that the proposed scheme performs better than the traditional aodv for real time and textual data in terms of packet delivery ratio, energy consumption, routing overhead, and end-to-end delay for all simulated scenarios. references [1] w. li, b. jia, q. li, j. wang, “an energy efficient and lifetime aware routing protocol in ad hoc networks”, international conference on algorithms and architectures for parallel processing, guangzhou, china, november 15-17, 2018 [2] v. b. kute, m. u. kharat, “analysis of quality of service for the aomdv routing protocol”, engineering, technology & applied science research, vol. 3, no. 1, pp. 359-362, 2013 [3] i. alameri, “manets and internet of things: the development of a data routing algorithm”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2604-2608, 2018 [4] c. perkins, e. m. belding-royer, s. das, “ad hoc on-demand distance vector (aodv) routing”, available at: https://tools.ietf.org/html/rfc3561, 2003 [5] f. maan, n. mazhar, “manet routing protocols vs mobility models: a performance evaluation”, 2011 third international conference on ubiquitous and future networks, dalian, china, june 15-17, 2011 [6] a. k. gupta, h. sadawarti, a. k. verma, “performance analysis of aodv, dsr & tora routing protocols”, international journal of engineering and technology, vol. 2, no. 2, pp. 226-231, 2010 [7] m. kaur, m. k. sharma, “energy efficient routing protocol for manet”, in: ambient communications and computer systems, pp. 201212, springer, 2018 [8] n. nissar, n. naja, a. jamali, “a review and a new approach to reduce routing overhead in manets”, wireless networks, vol. 21, no. 4, pp. 1119-1139, 2015 [9] s. jamali, l. rezaei, s. j. gudakahriz, “an energy-efficient routing protocol for manets: a particle swarm optimization approach”, journal of applied research and technology, vol. 11, no. 6, pp. 803-812, 2013 [10] c. 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aodv enhancement”, 5th international conference on intelligent systems, modelling and simulation, langkawi, malaysia, january 2729, 2014 [15] n. ket, s. hippargi, “modified aodv energy aware routing for optimized performance in mobile ad-hoc networks”, international conference on wireless communications, signal processing and networking, chennai, india, march 23-25, 2016 [16] j. deepa, j. sutha, “a new energy based power aware routing method for manets”, in: cluster computing, springer, 2018 [17] v. balaji, v. duraisamy, “improved aodv based on link quality metrics”, international journal of advances in engineering & technology, vol. 5, no. 1, pp. 269-275, 2012 [18] r. kumar, m. gupta, “route stability and energy aware based aodv in manet”, international conference on high performance computing and applications, bhubaneswar, india, december 22-24, 2014 [19] t. issariyakul, e. hossain, introduction to network simulator 2 (ns2), springer, 2009 microsoft word 14-3245_s_etasr_v10_n1_pp5175-5179 engineering, technology & applied science research vol. 10, no. 1, 2020, 5175-5179 5175 www.etasr.com abuelgasim & yusof: high speed mobility management performance in a real lte scenario high speed mobility management performance in a real lte scenario ahmed abdelsalam m. kheir abuelgasim school of electrical engineering universiti teknologi malaysia johor, malaysia ahmedkhair22@gmail.com kamaludin mohamad yusof school of electrical engineering universiti teknologi malaysia johor, malaysia kamalmy@utm.my abstract—this paper discusses the mobility management for high-speed users, which is a crucial challenge for all mobile operators, especially when users are moving vertically across different network technologies. mobility, also known as seamless connectivity, is directly influencing the quality of service (qos). mobility management-handover (ho) performance was evaluated by field measurements of a long term evolution (lte) network of a mobile operator in the middle east. drive test measurements were used to analyze the results of different high-speed scenarios. user equipment (ue) with high speed of 80-140km/h causes a high risk of failure of seamless connectivity as the ho procedure timing is longer than for ue with smaller speed. ho failure and call drop may occur when ue is moving with high speed across two adjacent cells in highways. during measurements, ho failure occurred when ue speed was 140km/h, and ho preparation timing increased when ue speed increased. keywords−mobility management; handover; heterogeneous network; user equipment (ue); speed; field measurement i. introduction the most important objective that differentiates cellular technologies is data demand. the design of applications for users mobile users, is a demanding task for mobile telecom operators while continuous communication is constantly required. mobile operators need to improve user-friendly connectivity, while the challenge of mobility will boom in the future. in a mobile telecom network, user equipment (ue) locations continue to change depending on user behavior, and this ue mobility should be supervised through the mobile network so that incoming calls are delivered to the ues. mobility creates handover (ho) as a result of ue moving from one place to another. the ho should be completed regardless of the network access technology. operators may also need to seamlessly combine several technologies that deliver unlimited content to customers in a global environment where fourthgeneration (4g) or long-term evolution (lte) networks and beyond are beginning to spread. to deliver “seamless” interoperability and convergence between these heterogeneous systems, the integration of unique wireless network technology is needed, and therefore the use of vertical handover (vho) methods is required [1]. ho, also known as handoff, occurs when a mobile station (ms) travels through one or more cellular cells and connects to a new cell while disconnecting from the source cellular cell. ho can be classified according to unique classifications. if the ho is within identical wireless access technologies, it is called horizontal handover, while the handover known as vertical handover occurs among separate wireless access techniques. ho decisions can be made using several techniques such as fuzzy logic and machine learning to overcome the mobility challenges and reduce the rate of ho failures and delay. moreover, to optimize the cellular network, hybrid algorithms of ho decisions can use tree methodology to learn the coverage of cells, and predict if the ho is necessary to be done [2, 3]. the lte platform allows mobility, according to the 3rd generation partnership project (3gpp), for low user speeds from 0 to 15km/h and faster user speeds from 15 to 120km/h. mobility at speeds ranging from 120km/h to 350km/h (or up to 500km/h based on the range of frequencies), will effect ho and performance (i.e. interruption time) will be lower than or equal to that given in the circuit switch (cs) domain handover [4]. the lte must minimize delay and packet loss in voice transmission to fulfill this intention and assure reliability in high-speed data transmission circumstances. heterogeneous wireless networks can incorporate various radio access technologies such as global system for mobile (gsm), general packet radio service (gprs), high speed packet access (hspa), universal mobile telecommunications system (umts), or lte. the vital promise of interconnecting these heterogeneous networks is to improve efficiency by achieving high data rates and supporting high-quality video, streaming, and multi-casting [5]. it is also identified as a network made of a mixture of high-power and low-power stations, some of which are configured with limited access, while others may lack wired backhaul. heterogeneous networks are networks that use a combination of classical macrocells, pico, femto, or relay nodes. in addition to possibly having a hybrid of closed and open user access, this type of networks is described by clear variations in the transmission power used by different network nodes. in practice, such power differences position the low-power nodes (pico, femto, and relay) at a disadvantage over the high-power nodes (macrocells). a heterogeneous network requests higher frequencies relying on the relationship between cell radius size and frequency. mmwaves have been recently introduced in corresponding author ahmed abdelsalam m. kheir abuelgasim engineering, technology & applied science research vol. 10, no. 1, 2020, 5175-5179 5176 www.etasr.com abuelgasim & yusof: high speed mobility management performance in a real lte scenario international mobile telecommunications (imt) and are identified as above 6ghz, due to the strong demand for extremely high bandwidth (up to 1ghz) and high data volumes, mainly in crowded urban areas. high frequencies above 6ghz are essential to be used in imt [6]. ii. literature review most of the researches addressed here are using received signal strength and ue speed as main criteria in the ho procedure. along with signal strength, some researchers combine additional parameters to get more mobility efficiency, such as signal quality, ue speed, available bandwidth, and spectrum of cells to reduce ho failure, call drop, ho delay, and improve overall ho performance and qos. in [7], authors showed the importance of signal strength using a ho scheme to assess system results in terms of several hos, the period between two subsequent hos, and sinr uplink. the ho based on the analysis of signal strength was explored at varying ue speeds from 3 to 120km/h. the primary goal of the study was to reduce the overall number of hos by increasing time-totrigger (ttt) and reducing an average of sinr. furthermore, based on the results of the measurement ho bandwidth, the margin for distinct ue speeds has been evaluated. the study was concentrated on the influence of signal strength using a system performance evaluation algorithm. authors in [8] assessed ho effectiveness when implementing different ttt approaches in the lte scheme. the proposed study intended to decrease ping-pong ho, yet due to delay in the ho, ttt may trigger radio link failure (rlf). two procedures were used to achieve optimal ho: the adaptive technique reached by flexibility choice of the ttt value for each ue velocity depending on an rlf rate of 2% and the grouping technique accomplished by categorizing ue velocities into three groups and applying the right ttt value to each range. if the sinr in the serving cell becomes stronger than in the target cell, then the ho will never be practiced, and this occurrence will be marked as “leaving the event”. ue expected velocity sets of 3, 15, 30, 60 and 120km/h over macro-macro ho and macro-pico ho. the rlf rate increases as a consequence and ping-pong declines as ue velocity increases. the rlf rate remains stable when the ttt value exceeds 5120ms, but when the ue speed is 120 km/h, the rlf increases. on the other hand, at 120km/h ue speed, the ping-pong reduces. authors in [9] also explored the impact of high-speed mobility on three handover algorithms’ output in lte. they used the a3 rsrp event with varying ue speed ranges (0-3km/h, 4-60km/h, 60-120km/h and over 120km/h). power budget handover is an efficient algorithm that utilizes two parameters to create ho decisions since it uses ttt and the handover margin (hom). hom is a variable representing the boundary for the signal strength difference between the serving cell and the target cell. the signal strength of the target cell must be larger than the signal strength of the serving cell plus the ho margin, therefore, the enodeb can consider the handover of ue. by stopping the handover trigger within a certain moment, the ttt is used to prevent ping-pong so that the ho procedure is done only after ttt is fulfilled. the ue measures the signal strength that includes antenna gain, route loss, and fast fading average along with bandwidth measurement in received signal strength based ttt. the signal strength is measured periodically, while the variations between the reference signal received power (rsrp) serving and the target cell are incorporated in the integrator handover algorithm using infinite impulse response (iir) filter, and the ho is made according to the triggering situation between the variations between the rsrp values. to assess the impact of mobility in the above three schemes, ue roams across the network at 3, 30, 60, 120 and 170km/h randomly chosen speeds. the efficiency was evaluated at every speed. the increase in speed in the range of 60-120km/h had a mildly stronger performance, and when the speed exceeded 120km/h, the algorithm worked best with a 120db snr. in [10], field measurement was used in two separate zones (urban and highway) to analyze mobility efficiency and timing of ho in both slow and high velocity environments. the researchers estimated both ho preparation time and ho execution time, most likely equivalent to the interruption time of ho. regarding ho timing, other key performance indicators (kpis) such as intra number, inter-site handover, amount of rlfs, and ho failure rate were mentioned. during the drive tests, the proposed algorithm utilized rsrp and ue velocity as the primary parameter. before the ho command measurement 1800mhz ho was initiated using the a3 event where rsrp, ttt, and offsets were used. three values of ttt were used (320, 1024, and 1280ms). larger ttt values tend to postpone hos, while shorth ttt values result in quicker and more aggressive hos. the amount of ho rises during high speed, and the use of mobility robustness optimization (mro) decreases ho failures. the average duration of the ho process was 77ms at a standard velocity in the town, whereas it lasts for 65 and 69ms at a speed of 80 and 100km/h respectively on the highway. the average time of ho interruption was between 24 and 29ms. however, occasional cases of delays greater than 100ms were reported. iii. high-speed mobility challenges at present, a cellular network consists of both new and old technology because when new technology standards are released and are commercially launched, not all of the cellular networks and legacy technology will be replaced at once. in other words, the cellular system works with different technologies, which means differences between network, e.g. the spectrum or cell size of each technology might be different. also, the mobility between different cellular technologies might be different, therefore, heterogeneous networks (hetnets) which may consist of 3g, lte-4g and future generation (5g), are introduced to fill the customers’ needs of high coverage, reliability, seamless connectivity, and high qos. heterogeneous networks are very congested with ues and personal digital assistants (pdas). they are very complicated and therefore more challenges must be addressed. mobility and spectrum limitation are the most challenging topics for the hetnets and upcoming mobile generations. all mobile carriers around the world are fighting to hold enough spectrum to be able to serve their customers and provide services within different technologies. moreover, many regulatory bodies around the world have already started to allocate spectrum via auctions, resulting in driving costs to very high level, thus mobile operators have to utilize the allocated spectrum properly. having successful hos is considered a big challenge engineering, technology & applied science research vol. 10, no. 1, 2020, 5175-5179 5177 www.etasr.com abuelgasim & yusof: high speed mobility management performance in a real lte scenario when the ue moves vertically between different technologies in a hetnet. mobility in a hetnet is considered a critical component that directly impacts mobile network qos in terms of ho, call drop percentage, and seamless connectivity. ho delay is one of the major hetnet challenges when cells have different radius sizes. highway mobility is considered as a most annoying issue for mobile operators because the high speed of the ue (which may reach 120-140 km/h which is the maximum speed limit for most countries [11, 12]). in such cases, mobile operators have to consider the ue velocity in ho preparation. also, the inter-site distance between two adjacent cells in a highway should be included in the measurements. therefore, ho delay due to additional required measurements is another challenge for high-speed mobility. figure 1 illustrates an ue moving with high speed between two adjacent cells. fig. 1. high-speed ue in an lte network iv. handover procedure and timing the lte ho procedure can be seen in figure 1 of [10]. ue is configured to do measurements periodically, and the measurement report period is set by the operator (3ms in most operators). these measurement reports are sent to the serving cell where ue has been currently serving. once a measurement report has been sent by the ue to the source cell that decides to handover, the origin cell sends a request for ho to the destination cell that selects whether or not the ue can be handed over to the cell depending on the control of admission. then the acknowledgment of the ho request is communicated to the source cell to verify that the new cell can accommodate the ue. additionally, the handover command, also known as the reconfigure message for radio resource control (rrc) connection, is sent to ue to indicate that ho is going to take place. therefore, the ho preparation time is defined as the elapsed time between the moment of a measurement report and the moment when the ue receives rrc connection reconfigure message. then, the ue is disconnected from the serving cell and initiates the synchronization procedure with the new cell, the data communication is paused and restored when the complete message is obtained with the handover setup or rrc connection reconfiguration. therefore, the ho interruption time is defined as the time interval between both rrc messages. ho interruption time is also known as ho execution time or accomplishment time. however, authors in [13] declared that the data interruption time during the ho is slightly longer than the ho execution time as the target cell begins scheduling the data for the ue after the ho configuration message is broadcasted. the overall ho time can be defined as the time interval between the instant when the ue directs the measurement reports and the instant when data is restored for the ue. v. measurements handover field measurements have been performed for a telecom operator cellular network using drive test tool and were analyzed by the use of actix software. drive test measurements were performed on a highway between two cities. drive tests were undertaken in various ues for speeds ranging from 80km/h to 140km/h. the samsung galaxy s8 terminal was used in the measurement and was categorized as category 16. ues were lte capable, supporting speeds up to 800mbps, 256 qam modulation, 4x20mhz carrier aggregation (ca), and were able to work with the 1800mhz band. lte cells were configured to operate in both timedivision-duplex (tdd) and frequency-division-duplex (fdd) modes using separated ports to ensure compatibility to both tdd and fdd ue types. nokia bts site manager was used to get lte cell setup where enb carrier frequency was 1870mhz for downlink and 1775mhz for uplink, both operating with 20mhz of bandwidth. the cell was using 4x4 mimo, and no virtual antenna mapping technique was used. measurements were conducted in both directions between a and b which can be defined as the starting point and ending point respectively. the measurement results were analyzed to extract crucial parameters such as reference signal received power (rsrp), reference signal received quality (rsrq), cell id, and rrc connection configuration messages. vi. experimental results a. coverage area the cell coverage measured during the driving test ranges from 0.4km and 0.7km, to 2.8km for lte cells on the same highway at separate places. fig. 2. the observated high-density area of the city (screenshot from google earth, © 2018 google, image © 2019 maxar technologies, image © 2019 cnes/airubus) engineering, technology & applied science research vol. 10, no. 1, 2020, 5175-5179 5178 www.etasr.com abuelgasim & yusof: high speed mobility management performance in a real lte scenario low power cells were used by a mobile operator in the downtown zone where high capacity and seamless service are required in a high-density region, whereas cell power rises towards the highway that runs outside the city where the lowdensity zone is located, so the cell transmission range is also improved. in the city's high-density region, the reported cell coverage was 400m and 700m, while a low-density region it was assessed at 2800m. figures 2 and 3 show the observation area during the drive test in the direction from the city toward outside it. fig. 3. the observated low-density area (screenshot from google earth, © 2018 google, image © 2019 maxar technologies, image © 2019 cnes/airubus) b. rrc message analysis or measurement report analysis based on rrc message analysis, the ue is configured to send measurement reports periodically. rsrp, rsrq, and neighboring cells are included in these reports. the measurements of rsrp and rsrq are used to trigger hos from the serving to the target cell. figures 4 and 5 show the rsrp and rsrq during the measurement report for ue speed of 140km/h. the rsrp value where the ho must be conducted is set by the mobile operator to be within -94dbm and -102dbm based on the field measurement, therefore, optimization robustness is used at the network. fig. 4. rsrp measurements when ue speed is 140km/h (screenshot from google earth, © 2018 google, image © 2019 maxar technologies, image © 2019 cnes/airubus) the measured rsrp value is set within the range of -80dbm and -105dbm and the rsrp ho value to a bit higher value in order to keep qos in a high level and avoid call drops, although call drops occurred during our test when ue speed was 140km/h. figure 6 clearly shows that there is a failure in rsrp value when it varies against ho time, resulting in a call drop. the figure illustrates the rsrp of the serving cell before and after the ho. fig. 5. rsrq measurements when user equipment (ue) speed is 140 km/h (screenshot from google earth, © 2018 google, image © 2019 maxar technologies, image © 2019 cnes/airubus) fig. 6. rsrp variation when user equipment (ue) speed is 140km/h c. ho events and timing during measurements during the driving test, the number of frequent hos increases when the ue’s velocity increases, however, using high power cells helps reducing ho numbers as cell coverage is wider than small cells in the city center. frequent hos are experienced during the drive tests with ue speed between 100and 140km/h. in the driving test, the direction and location of the selected sites play a significant part. an inter-frequency ho has been recorded when ue rides from the city with 140km/h velocity, whereas the received signal strength has been much better when the ue velocity is higher than 140km/h, with the ue driving toward the city and is closer to site location. ho timing was analyzed from the measurement engineering, technology & applied science research vol. 10, no. 1, 2020, 5175-5179 5179 www.etasr.com abuelgasim & yusof: high speed mobility management performance in a real lte scenario results and it was observed that the ho preparation time increases as ue speed increases. moreover, the ho execution time is slightly faster than the ho preparation time. also, the experienced ho time values on the highway are mostly higher than in the city. figure 7 illustrates the change of the ho timing with ue velocity. the x-axis illustrates user speed (km/h) while the y-axis illustrates measurement time (s). fig. 7. ho timing vs ue velocity vii. conclusion in this paper, high-speed mobility performance and ho timing were investigated through drive test measurements for a real situation in a mobile operator's lte network. high-speed mobility was performed for various ue speeds ranging from 80km/h to 140km/h. field measurements were analyzed when ue speed was 140km/h. the results show that the ue speed directly influences mobility management lte and hence the qos. moreover, the analyzed results show that ho preparation time increases when ue speed increases, and ho execution time is slightly faster than ho preparation time. the overall ho time was found to be below 1s for high-speed ue. traffic, safety, and real-time applications are directly affected by ho delay which is higher on highways. refefences [1] j. marquez-barja, c. t. calafate, j. c. cano, p. manzoni, “an overview of vertical handover techniques: algorithms, protocols and tools”, computer communications, vol. 34, no. 8, pp. 985–997, 2011 [2] n. c. eli-chukwu, j. m. aloh, c. o. ezeagwu, “a systematic review of artificial intelligence applications in cellular networks”, engineering, technology & applied science research, vol. 9, no. 4, pp. 4504-4510, 2019 [3] m. k. hassan, a. babiker, m. b. m. amien, m. hamad, “sla management for virtual machine live migration using machine learning with modified kernel and statistical approach”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2459–2463, 2018 [4] 3gpp/etsi, (tr 25.913mike) universal mobile telecommunications system (umts); lte; requirements for evolved utra (e-utra) and evolved utran (e-utran), 3gpp tr 25.913 version 9.0.0 release 9, etsi, 2010 [5] m. zekri, b. jouaber, d. zeghlache, “a review on mobility management and vertical handover solutions over heterogeneous wireless networks”, computer communications, vol. 35, no. 17, pp. 2055–2068, 2012 [6] itu, the technical feasibility of imt in the bands above 6 ghz, technical report rep. itu-r m.2376-0, itu, 2015 [7] m. anas, f. d. calabrese, p. e. mogensen, c. rosa, k. i. pedersen, “performance evaluation of received signal strength based hard handover for utran lte”, ieee 65th vehicular technology conference, dublin, ireland, april 22-25, 2007 [8] y. lee, b. shin, j. lim, d. hong, “effects of time-to-trigger parameter on handover performance in son-based lte systems”, 2010 16th asiapacific conference on communications, auckland, new zealand, october 31-november 3, 2010 [9] m. o. osifeko, a. a. okubanjo, o. r. abolade, o. k. oyetola, a. o. oyedeji, o. i. sanusi, “evaluating the effect of mobility speed on the performance of three handover algorithms in long term evolution networks”, journal of applied sciences and environmental management, vol. 22, no. 4, pp. 503-506, 2018 [10] l. c. gimenez, m. c. cascino, m. stefan, k. i. pedersen, a. f. cattoni, “mobility performance in slow-and high-speed lte real scenarios”, ieee 83th vehicular technology conference, nanjing, china, may 1518, 2016 [11] b. katz, j. ma, h. rigdon, k. sykes, z. huang, k. raboy, synthesis of variable speed limit signs, federal highway administration, 2017 [12] a. merwaday, i. guvenc, “handover count based velocity estimation and mobility state detection in dense hetnets”, ieee transactions on wireless communications, vol. 15, no. 7, pp. 4673-4688, 2016 [13] s. barbera, k. i. pedersen, c. rosa, p. h. michaelsen, f. frederiksen, s. shah, a. baumgartner, “synchronized rach-less handover solution for lte heterogeneous networks”, 2015 international symposium on wireless communication systems, brussels, belgium, august 25-28, 2015 engineering, technology & applied science research vol. 8, no. 1, 2018, 2485-2492 2485 www.etasr.com soomro et al.: single pile settlement and load transfer mechanism due to excavation in silty clay single pile settlement and load transfer mechanism due to excavation in silty clay mukhtiar ali soomro kiran fatima memon mohsin ali soomro department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan eng.soomro@gmail.com department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan kiranf893@gmail.com department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan drmohsin@quest.edu.pk asad memon manthar ali keerio department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan asadmemon10@hotmail.com department of civil engineering quaid-e-awam university engineering, science & technology larkana, pakistan mantharali99@quest.edu.pk abstract—in densely built areas, development of underground transportation system often involves excavations for basement construction and cut-and-cover tunnels which are sometimes inevitable to be constructed adjacent to existing piled foundations. in order to gain new insights into single pile responses (i.e. settlement and load transfer mechanism) to an adjacent excavation in saturated silty clay, a three-dimensional coupledconsolidation numerical analysis is conducted in this study. an advanced hypoplasticity (clay) constitutive model with small-strain stiffness was adopted. a linear increase in pile settlement was observed due to excavation-induced stress release. this is because part of the pile is placed within the boundaries of a major influence zone due to excavation-induced ground movement. based on a settlement criterion, apparent loss of pile‘s capacity is 14%. a maximum bending moment of about 350 knm is induced in the pile with the maximum deflection of 28 mm. in addition, mobilisation of shear strength at the pile-soil interface was found to be a key factor governing pile-soil-excavation interaction. during excavation, a downward load-transfer mechanism in the piles can be identified. keywords-excavation; pile; silty clay; numerical modelling i. introduction the development of underground space induces ground movements and stress release in the surrounding soil that may affect existing structures. owing to the inherent lack of surface space in congested urban areas, deep excavation for basements and cut-and-cover tunnels are inevitably constructed adjacent to existing pile foundations often supporting high-rise buildings [1-2]. thus, it is important for designers to estimate potential damage to existing piles resulting from nearby deep excavations. most of the earlier researchers estimated the buildings settlement and tilting considering wall movements and ground surface settlement trough using empirical approaches. the performance of pile group depends on the stress state in the soil and surrounding sub-surface soil movements [3]. in addition, deep excavation in soft clay induces negative excess pore water pressure [4] which induces long term pile group settlement with the dissipation of excess pore water pressure. therefore, it is essential to investigate the pile group response mechanism adjacent to deep excavation in soft soil. authors in [1, 2] reported case studies in granular soil and alluvium residual soil respectively. they demonstrated that lateral soil movements due to excavation can be detrimental to nearby existing piles. in both reported case studies, pile toe level was much deeper than the excavation level and they reported only the lateral pile behavior. apart from field monitoring, a number of centrifuge tests were also conducted to investigate the response of single pile [5] and pile group in soft kaolin clay [6]. they concluded that the induced bending moment and lateral pile deflection were highly influenced by the distance from the wall and pile head condition. in studies, lateral response of end bearing piles without initial applied load was reported. in reality, pile group in soft clay behave as floating pile group and subjected to initial applied load from superstructure. in the presence of initial applied load, soil surrounding the pile group experiences higher stress level before the commencement of adjacent excavation. authors in [7-8] conducted centrifuge tests to investigate the effects of an unpropped excavation on the behaviours of nearby single piles and pile groups in dry dense toyoura sand. it was found that the distance from the pile to the retaining wall and pile head engineering, technology & applied science research vol. 8, no. 1, 2018, 2485-2492 2486 www.etasr.com soomro et al.: single pile settlement and load transfer mechanism due to excavation in silty clay conditions had a large influence on the induced pile bending moment and lateral deflection. authors in [9] reported the results of three centrifuge tests which were carried out to study the effects of a multipropped deep excavation in-flight on the behaviour of single piles in dry toyoura sand. piles were laterally restrained in terms of rotation and deflection right at or above ground surface in the three different tests. it was concluded that lateral restraints imposed on the pile head have a significant influence on induced pile bending moment. induced bending moment due to excavation can exceed the pile bending capacity. authors in [10] developed design charts to compute the lateral behaviour of a single pile adjacent to deep excavation in soft ground. they performed two staged analysis considering plane strain conditions and linear elastic soil model. similar work was conducted in [11] in which authors used finite element method. in both these studies lateral response of single pile was investigated. the settlement behavior of pile and development of excess pore water pressure and consolidation settlement were not investigated. authors in [12] proposed an analytical method to investigate reduction of capacity and increase in settlement of nearby pile during excavation. it was reported that pile settlement due to excavation depends on the percentages of end bearing and shaft friction of the pile, the soil movement pattern, and the distribution of the maximum shaft friction with depth. however, shaft resistance in these methods is calculated on the assumption that horizontal stress acting on the piles does not change during excavation. this assumption may not be valid and the pile settlement may be underestimated using the preceding methods, leading to a non-conservative prediction. most of the previous studies focused on the lateral response of single pile foundation. the vertical response of floating pile group combined with working load adjacent to deep excavation in soft clay has not been studied. moreover, in soft clay progressive change in excess pore water pressure with time and consolidation settlement of pile group were not investigated. it is well recognised that the stress-strain relationship of soils is highly nonlinear even at very small strain. the stiffness of most soils decreases as strain increases and depends on the recent stress or strain history of the soil [13-14]. owing to nonlinear soil behaviour, an excavation can cause reduction to the ground stiffness. therefore, it is vital to investigate the pile responses to adjacent excavation in silty clay. to obtain a satisfactory numerical model of the single pile responses to excavation-induced stress relief, the analysis must take account of the small strain non-linearity of soil. in view of the aforementioned issues, this study aims at investigating the settlement and load transfer mechanism of an existing single pile due to an adjacent excavation in saturated silty clay. to achieve these objectives, a three-dimensional coupledconsolidation numerical modelling was carried out. settlement, axial load distribution along the pile, stress changes and excessive pore pressure generation during excavation are reported and discussed. ii. three-dimensional coupled consolidation analysis to gain new insights into single pile responses to a nearby multipropped excavation in saturated silty clay, this study conducts a three-dimensional coupled consolidation numerical analysis. figure 1(a) shows the elevation view of the configuration of numerical simulation in which a multipropped excavation was carried out adjacent to a single pile. the final depth of the excavation (he) was 10 m. the embedded length (lp) and diameter (dp) of the pile were 18 m and 0.8 m, respectively. the modelled pile represents a cylindrical reinforced concrete (grade 40, reinforcement ratio = 1) with a bending moment capacity of 800 knm. the clear distance between diaphragm wall and the pile was 3.0 m (0.3he). the excavation was supported by 0.6m thick diaphragm wall. the ratio of wall penetration depth to excavation depth is typically 0.5-2 in engineering practice [15-16], and thus a value of 0.5 was adopted in this study. the retaining wall was supported by three levels of props, at 1.0, 4.0 and 7.0 m depth. the props were modelled as soft with axial rigidity of 81 × 103 knm [15]. horizontal spacing of props was 10 m. ground water table working load (1073 kn) existing single pile silty clay prop 1 (1.0 m) prop 2 (4.0 m) prop 3 (7.0 m) p la n e o f sy m m et ry excavation level 1 (3.0 m) excavation level 2 (7.0 m) formation level (10.0 m) embedded length = 18 m diameter = 0.8 m diaphragm wall thickness = 0.6 m depth = 14.0 m 6.0 m (a) monitoring section 50m 20m p la ne o f sy m m et ry 0.6 m thick diaphragm wall existing single pile prop prop 10m 6m (b) fig. 1. configuration of the numerical run (a) elevation, (b) plan view it is worth noting that, in reality, high-rise buildings are unlikely to be built on a single pile. this hypothesised study is a virtual case [3, 17-18]. this simplification is made to understand the settlement and load transfer mechanism clearly. figure 1(b) illustrates the plan view of the configuration of the numerical simulation. the length of the excavation is 12 m. due to symmetry, only half of the excavation was simulated. a monitoring section was selected at the transverse centreline of the excavation. in addition to this simulation, a pile load test (l) was conducted numerically in “greenfield” conditions (i.e., without excavation) to obtain the ultimate capacity of the pile in silty clay. based on this, the working load was then calculated with a factor of safety of 3.0. the obtained working load was applied to the pile in the analysis simulating excavation. engineering, technology & applied science research vol. 8, no. 1, 2018, 2485-2492 2487 www.etasr.com soomro et al.: single pile settlement and load transfer mechanism due to excavation in silty clay a. finite element mesh and boundary conditions figure 2 shows an isometric view of a finite element mesh used to analyze the soil-pile-excavation problem. the size of the mesh for each numerical runs is 50 m × 20 m × 40 m. these dimensions were sufficiently large to minimize boundary effects in the numerical simulation as further increment of the dimensions of the finite element mesh did not lead to any change in the computed results. regarding the element size in the mesh, it is found that further halving of the adopted mesh size only leads to a change of computed results of no more than 0.2%, suggesting the mesh is sufficiently fine. eight-noded hexahedral brick elements were used to model the soil, the pile and the diaphragm wall, while two-noded truss elements were adopted to model the props. roller and pin supports were applied to the vertical sides and the base of the mesh, respectively. therefore, movements normal to the vertical boundaries and in all directions of the base were restrained. the water table was assumed to be at ground surface. initially, the pore water pressure distribution was assumed to be hydrostatic. free drainage was allowed at the top boundary of the mesh. the excavation process was simulated by deactivating soil elements inside excavation zone. in the meantime, the truss elements representing the props were activated. single p ile diap hragm wall props pin support roller sup port fig. 2. three dimensional finite element mesh and boundary conditions b. constitutive model and model parameters used in finite element analysis the basic hypoplastic model was developed to capture the non-linear behavior (upon monotonic loading at medium to large-strain levels) of granular materials [19-20]. the basic model consists of five parameters (n, λ*, κ*, φc and r) . parameters n and λ* define the position and the slope of the isotropic normal compression line in the ln(1+e) versus lnp’ plane [21], e is the void ratio and p’ is mean effective stress. the parameter κ* defines the slope of the isotropic unloading line in the same plane. φc is the critical state friction angle and the parameter r controls the large strain shear modulus. to account for the strain-dependency and path-dependency of the soil stiffness (at small strains), authors in [22] further improved the basic hypoplastic model by incorporating the concept of intergranular strain. the intergranular strain concept requires five additional parameters (r, βr, χ, mt and mr): r controlling the size of the elastic range, βr and χ controlling the rate of stiffness degradation. the parameters mt and mr control the initial shear modulus upon 180° and 90° strain path reversal, respectively. in this hypothesised study, the parameters for silty clay were adopted the ones in [23]. all the model parameters for silty clay reported in [23] are summarised in table i. the coefficient of lateral earth pressure at rest, ko is estimated in [24] by the following equation:      sin0 sin1 ocrk (1) table i. model parameters of silty clay [23] description value effective angle of shearing resistance at critical state: ’ 33o parameter controlling the slope of the isotropic normal compression line in the ln(1 + e) versus lnp plane, * 0.103 parameter controlling the slope of the isotropic normal compression line in the ln(1 + e) versus lnp plane, * 0.015 parameter controlling the position of the isotropic normal compression line in the ln(1 +e) versus lnp plane, n 1.31 parameter controlling the shear stiffness at mediumto largestrain levels, r 0.3 parameter controlling initial shear modulus upon 180 strain path reversal, mr 12 parameter controlling initial shear modulus upon 90 strain path reversal, mt 12 size of elastic range, r 2×10-5 parameter controlling the rate of degradation of the stiffness with strainr 0.09 parameter controlling degradation rate of stiffness with strain 0.7 initial void ratio, e 0.7 dry density (kn/m3) 1615 coefficient of permeability, k (m/s) 1×10-9 the concrete pile, the diaphragm wall and the props were assumed to be linear elastic with young's modulus of 35 gpa and poisson's ratio of 0.25. the wall thickness was taken as 0.60 m. the concrete unit weight was taken as 24 kn/m3. the parameters for the piles and the diaphragm wall are summarized in table ii. table ii. concrete parameters adopted in finite element analysis description value young's modulus, e 35 gpa poisson's ratio,  0.3 density,  2400 kg/m3 c. numerical modelling procedure each numerical analysis is modeled according to the following steps: step 1: set up the initial boundary and initial stress conditions (i.e., static stress conditions with varying k0 with depth). engineering, technology & applied science research vol. 8, no. 1, 2018, 2485-2492 2488 www.etasr.com soomro et al.: single pile settlement and load transfer mechanism due to excavation in silty clay step 2: activate the brick elements representing single pile (modeled as “wished-in-place”). step 3: apply the working load (determined from numerical pile load test) on the pile. step 4: allow excess pore pressure, which generated in result of the application of working load on the pile, to dissipate. step 5: activate the brick elements representing the diaphragm wall. step 6: staged multipropped excavation was simulated as described above. after excavating to 3 m depth, the first level of props was installed at 1 m below the ground surface. soil was then excavated to 7 m below the ground surface, followed by installation of the second level of props at 4 m depth. finally, excavation was extended to the target level of 10 m depth with installation of third level of props at 7 m. iii. interpretation of computed results a. determination of working load for the pile the objective of this parametric study was to investigate single pile load responses to an adjacent excavation. prior to the simulation of the excavation, it was necessary to determine the ultimate axial load carrying capacity of the pile group. the working load can then be obtained using a factor of safety (fos) of 3.0. therefore, a numerical pile load test was carried out on a different finite element mesh to obtain the load settlement relationship and the capacity of the single pile without excavation. the load applied on the pile was gradually increased to 4 mn over a period of 24 h. the resulting pile load-displacement curve for the simulated pile is shown in figure 3. the ultimate axial load capacity was determined based on a displacement-based failure criterion in [25]. this failure criterion is expressed as follows: ,max 1 0.045 2 h p ph p p p p l d a e    (2) where δph,max is the maximum pile head movement which defines the ultimate load, ph is the pile head load, lp is the pile length, ep is the pile shaft elastic modulus, ap is the crosssectional area of the pile, and dp is the pile diameter. based on the failure criterion, the ultimate bearing capacity of 3.22 mn was calculated. with a factor of safety (fos) of 3.0, the working load was determined to be 1.07 mn. owing to the applied working load, the pile settled by 0.7% dp (figure 3). b. progressive pile settlement and apparent loss of the pile capacity during excavation figure 4 shows the incremental settlement (sp) of the pile with different excavation stages. construction stages of the excavation are indicated by the depth h the ground surface. sp and h are normalized by the pile diameter (dp) and the final excavation depth (he), respectively. the measured induced pile settlement due to excavation in centrifuge modeling reported in [9] is also shown for comparison. the centrifuge test was carried out to investigate the effects of a multipropped deep excavation (final depth of excavation= 8 m in prototype) inflight on the behavior of single pile (diameter of the pile= 1.25 m in prototype) in dry toyoura sand (i.e., dr= 70%). the embedded depth of the pile and clear distance between the pile and model wall is 20 m and 3 m, respectively. a linear increase in sp of the pile was observed with the first two excavation stages (h/he=0.7). however, the pile settled at increased rate due to subsequent excavation stage (h/he=1.0). this may be attributed to two reasons. first, owing to reduction of shaft resistance due to excavation induced stress release, the pile had to settle substantially to further mobilize end-bearing (explained below). second, the most part of the pile is placed within the boundaries of a major influence zone due to excavation-induced ground movement. similar settlement characteristics of a single pile due to excavation observed from the centrifuge test reported in [9]. as expected, induced settlement of the single pile in medium dense sand was less than that of single pile in stiff clay. this is because the sand stiffness is higher than that of clay. the induced pile settlement due to excavation was 9.5 mm (1.2% dp). fig. 3. computed load settlement curve from the pile load test without excavation total pile settlement (including settlement due to working load and excavation) was 15.1 mm (1.9% pile diameter). this value satisfies a reliability-based serviceability criterion (56 mm), which was developed based on 95 composite (reinforced concrete and steel) buildings subjected to settlement. this conclusion may not be applicable to scenarios in which the ground conditions or excavation depth are different from those adopted in this study. considering pile capacity is often interpreted as using settlement criteria, and pile settlement due to excavation may be correlated with an apparent loss of pile capacity (alpc). therefore, the excavation induced settlement can be regarded as an additional load on the pile head. in this study, settlement of the pile due to the applied working load (before excavation) was about 0.7% dp (5.6 mm) (see figure 3). the excavation resulted in an additional pile settlement of 1.2% engineering, technology & applied science research vol. 8, no. 1, 2018, 2485-2492 2489 www.etasr.com soomro et al.: single pile settlement and load transfer mechanism due to excavation in silty clay dp (9.5 mm). with this additional settlement, the pile behaved as if it were loaded by an additional axial force of 1.0 mn on the pile cap (based on load settlement curve shown in figure 3). the additional load accounts for 31% of the ultimate pile capacity of the pile (based on the failure criterion presented in [26]). in other words, alpc of 31% was due excavation. it should be noted that the reduction of pile capacity does not mean that the ultimate load capacity is physically reduced due to the excavation. it instead indicates the violation of the serviceability limit state of the pile as a result of the excavation-induced pile settlement and designers should take measures to control or mitigate this adverse effect. c. computed ground deformation mechanism and deviatoric strain figure 5 shows computed incremental displacement vectors due to excavation. computed incremental shear strain that the excavation induced stress released is also superimposed in the figure. it can be observed that soil on the retained side moved towards the excavation, whereas the soil underneath the excavation heaved upwards due to vertical stress relief inside the exaction zone. furthermore, it can be seen that excavationinduced ground movement is mainly bounded by a wedge at an angle of 450 drawn from the wall toe. in addition to ground movement, significant shear strain (up to 1.44%) is also developed extending nearly at 450 from the wall toe. it can be seen that two-thirds of the pile shaft (0 ≤z/lp ≤0.67) are located inside and pile toe is located outside the sliding wedge zone of ground movement. because the two-thirds of the pile shaft are affected by the ground movement due to excavation induced stress release, shaft resistance decreased. to maintain equilibrium, the pile had to settle resulting in increment in endbearing. on the other hand, the pile toe is located within the region where shear strain is developed. as illustrated, the presence of the pile increases further the soil shear strain near the pile toe, as more end-bearing has to be mobilised to support vertical load transferred from the pile shaft to the pile toe after excavation. d. changes in axial load distribution figure 6 illustrates the axial force distribution along the pile with normalised depth (z/lp) below the ground surface during excavation. the axial load distribution before excavation (after applying the working load) is also included in the figure as a reference. before excavation, the pile carried approximately 70% of the working load (1073 kn) with its shaft resistance and the remainder with its end-bearing resistance. it can be observed that excavation-induced reduction in normal stresses to the pile shaft and downward soil movement caused an increase in axial load along the entire length of the pile at different excavation stages. at the end of the first excavation stage, the maximum increment in the axial force (14% of that at working load) was computed at z/lp = 0.43, which is above the formation level. by inspecting the axial load distribution after the first excavation stage, it is observed that along the upper portion of the pile (z/lp ≥0.2), the shaft resistance decreases to zero. consequently, the load transferred to the lower portion of the pile. to maintain equilibrium, the pile had to settle (see figure 5) to further mobilise the end-bearing and shaft resistance along the lower portion (z/lp>0.2). as the excavation reached at final depth, it caused a further reduction of the normal stresses to the pile shaft. consequently, soil settled more than the pile resulting in negative skin friction (nsf) along the upper portion of the pile (0 ≤ z/lp ≤ 0.6). this suggests that this portion of the pile is subjected to “dragload” by the surrounding soil. this caused the pile to settle more than that due to pervious excavation stages (see figure 6). to maintain vertical equilibrium of the pile, the soil surrounding the lower part of the pile (z/lp>0.6) resisted its settlement by mobilising positive skin friction (psf) at the pile-soil interface and end-bearing resistance at the toe of the pile. owing to end of the excavation, the end-bearing increased to 74%. fig. 4. computed (this study) and measured ([9]) normalised pile head settlement during excavation % mm e x ca v at io n 45o sliding wedge zone of ground movement fig. 5. computed incremental ground movement and shear strain at the excavation end. e. mobilised shaft resistance during excavation to substantiate the previous discussion, the mobilized shaft resistance in the pile after the application of the working load (before the excavation) and the excavation is shown in figure 7. in the figure, the depth below the ground surface (z) is engineering, technology & applied science research vol. 8, no. 1, 2018, 2485-2492 2490 www.etasr.com soomro et al.: single pile settlement and load transfer mechanism due to excavation in silty clay normalized by the pile length (lp). the computed average mobilized unit shaft resistance f(z) at various depths was calculated based on the following equation:    z f f z s z    (3) where δf is the difference between the computed axial loads at two consecutive depths, δz is the vertical distance between the two consecutive depths, and s is the perimeter of the pile. as expected, after the application of the working load, the positive shaft resistance (soil supporting the pile) is mobilized along the entire length of the pile. the mobilized positive shaft resistance increased along pile depth with maximum shaft resistance of 31 kpa near the pile toe. it can be seen from the figure that as excavation depth increases, mobilized shaft resistance decreased above the formation level (z/lp<0.5). on the completion of the excavation (h/he=1.0), the mobilized shaft resistance at the upper portion of the pile (z/lp<0.5) decreased to negative and increased below formation level (0.5<z/lp<1.0). this caused negative skin friction (nsf) mobilization at the upper part of the pile shaft (z/lp<0.5) due to stress release and soil movement as mentioned above. this implies that this portion of the pile is “dragged” down by the surrounding soil, which settles due to excavation. to maintain vertical equilibrium of the pile, the soil surrounding the upper part of the pile resists from settling, by mobilizing psf at the soil–pile interface. the neutral plane, where the zero shaft resistance is mobilized, is located at a depth of z/lp= 0.45 (above formation level). this location is consistent with the depth where the maximum axial load was induced. consequently the load was transferred to the lower part of the pile. to support the applied working load and “dragload” resulting from nsf, the pile settled substantially to mobilize its end-bearing resistance. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 n o rm al is ed p il e d ep th (z /l p) axial force: kn at working load (before excavation) excavation stage 1 (h/he = 0.3) excavation stage 2 (h/he = 0.7) end of excavation (h/he = 1.0) excavation stage 1 (h/he = 0.3) excavation stage 2 (h/he = 0.7) end of excavation (h/he = 1.0) formation level fig. 6. axial force with normalized depth 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -30 -20 -10 0 10 20 30 40 50 60 70 n o rm al is ed p il e d ep th (z /l p) mobilised shaft resistance: kpa at working load (before excavation) excavation stage 1 (h/he = 0.3) excavation stage 2 (h/he = 0.7) end of excavation (h/he = 1.0) excavation stage 1 (h/he = 0.3) excavation stage 2 (h/he = 0.7) end of excavation (h/he = 1.0) formation level fig. 7. mobilized shaft resistance along the pile length at various stages of excavation f. changes in normal stresses to the pile shaft during excavation it is well recognized that the mobilized shaft resistance of a pile is related to the normal stresses to the pile shaft, interface friction angle between pile and soil and relative pile–soil displacement. to further elaborate the changes in mobilised shaft resistance along the pile length, normal stresses to the pile was extracted. figure 8 shows changes in normal stresses to the pile shaft at different excavation stages. it can be observed that normal stresses to the pile shaft decreased with increment of excavation depth. the maximum reduction in normal stresses of 43 kpa occurred at z/lp=0.5 after completion of excavation (h/he=1.0) and, as mentioned above, the shaft resistance decreased. as a result, to support the constant load applied on the pile head, the load borne by the shaft transferred to the pile toe. this led to increase stresses under the pile toe. g. excavation-induced bending moment and lateral deflection along the pile figure 9 illustrates the induced bending moment along the pile with excavation. a positive bending moment means that tensile stress was induced along the pile shaft facing the exaction. since there was no rigid constraint at the pile head, no bending moment was induced at/near the head of the pile at any stage of excavation. it can be observed that after first excavation stage (h/he=0.3) negative bending moment induced along the pile length between z/lp= 0.25 and z/lp= 0.95. however, as excavation depth increases, positive bending moment induced in the pile. this is because the pile was subjected to lateral soil movement towards the excavation resulting from significant stress release (see figure 8). the maximum positive bending moment (350 knm) was induced in the pile at z/lp=0.43 near formation level. on the other hand negligible bending moment was induced near the pile toe. this was because the excavation-induced soil movement (see figure engineering, technology & applied science research vol. 8, no. 1, 2018, 2485-2492 2491 www.etasr.com soomro et al.: single pile settlement and load transfer mechanism due to excavation in silty clay 5) and stress release (see figure 8) near the pile toe was insignificant. 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 20 40 60 80 100 120 140 160 180 200 220 240 260 n o rm al is ed p il e d ep th (z /l p) normal stress on pile: kpa at working load (before excavation) excavation stage 1 (h/he = 0.3) excavation stage 2 (h/he = 0.7) end of excavation (h/he = 1.0) excavation stage 1 (h/he = 0.3) excavation stage 2 (h/he = 0.7) end of excavation (h/he = 1.0) pile ground surface forma tion level wall p1 p2 p3 fig. 8. changes in normal stress acting on the pile during excavation 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -200 -150 -100 -50 0 50 100 150 200 250 300 350 400 450 500 n o rm al is ed p il e d ep th (z /l p) induced bending moment: knm excavation stage 1 (h/he = 0.3) excavation stage 2 (h/he = 0.7) end of excavation (h/he = 1.0) excavation stage 1 (h/he = 0.3) excavation stage 2 (h/he = 0.7) end of excavation (h/he = 1.0) formation level fig. 9. excavation-induced bending moment along the pile length figure 10 shows the computed pile lateral deflection during the excavation stages. pile deflection toward the excavation is taken as the positive direction. owing to horizontal stress release due to excavation and inward ground movement towards the excavation, the positive pile deflection occurred along the pile shaft. the magnitude of the pile deflection increased with excavation stages. significant deflection of the pile occurred due to second (h/he=0.7) and third (h/he=1.0) excavation stages. the maximum deflection of about 29 mm was observed at z/lp=0.3 after excavation. since the pile head was not constrained, pile head deflected (with maximum deflection of 27 mm after completion of the excavation) towards the excavation. this is consistent with the result of excavation-induced bending moment (i.e. zero bending moment at the pile head). 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 n o rm al is ed p il e d ep th (z /l p) pile deflection: mm excavation stage 1 (h/he = 0.3) excavation stage 2 (h/he = 0.7) end of excavation (h/he = 1.0) excavation stage 1 (h/he = 0.3) excavation stage 2 (h/he = 0.7) end of excavation (h/he = 1.0) formation level fig. 10. lateral deflection of the pile due to excavation iv. summary and conclusions this study reports a 3d coupled consolidation numerical analysis investigating single pile responses to an adjacent excavation in saturated silty clay. based on the ground conditions and geometry, the following conclusions can be drawn.  owing to the stiffness degradation of the clay surrounding the pile as a result of excavation-induced stress release and shear strain, the third excavation stage caused larger settlement than the first two stages. the final amount of induced settlement of the pile is 1.2% of the pile diameter. based on the displacement-failure load criterion proposed in [26], the apparent loss of the capacity of the pile is 31%.  as far as load transfer mechanism along the pile is concerned, excavation-induced soil movement due to stress release mobilised negative shaft friction (nsf) at the upper part of the pile. consequently, a downward load transfer is observed along the pile, further mobilising the pile endbearing.  the normal stresses to the pile shaft decreased with increment of excavation depth. the maximum reduction in normal stresses of 43 kpa occurred at z/lp=0.5 (i.e. above formation level) after completion of excavation. consequently, the shaft resistance decreased.  the excavation induced the largest bending moment at z/lp=0.43 near formation level. however, the maximum deflection of about 29 mm was observed at z/lp=0.3 (i.e. above formation level) after the completion of the excavation. engineering, technology & applied science research vol. 8, no. 1, 2018, 2485-2492 2492 www.etasr.com soomro et al.: single pile settlement and load transfer mechanism due to excavation in silty clay references [1] r. j. finno, s. a. lawrence, n. f. allawh, i. s. harahap, “analysis of performance of pile groups adjacent to deep excavation”, journal of geotechnical and geoenvironmental engineering, vol. 117, no. 6, pp. 934-955, 1991 [2] a. 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“k0-ocr relationships in soils”, journal of geotechnical engineering, vol. 108, no. 6, pp. 851–872, 1982 [25] c. w. w. ng, t. l. y. yau, j. h. m. li, w. h. tang, “new failure load criterion for large diameter bored piles in weathered geomaterials”, journal of geotechnical and geoenvironmental engineering, vol. 127, no. 6, pp. 488-498, 2001 [26] l. m. zhang, a. m. y. ng, “probabilistic limiting tolerable displacements for serviceability limit state design of foundations”, geotechnique, vol. 55, no. 2, pp. 151-161, 2005 microsoft word etasr_v11_n3_pp7125-7129 engineering, technology & applied science research vol. 11, no. 3, 2021, 7125-7129 7125 www.etasr.com almerjad: development of an ethernet-based portable embedded isolated ecg system development of an ethernet-based portable embedded isolated ecg system ali s. almejrad department of clinical laboratory sciences faculty of applied medical sciences university of hail hail, saudi arabia a.almejrad@uoh.edu.sa abstract-patient monitoring is an important issue in the medical field, requiring planning, effort, and time. one of the challenges that physicians, nurses, paramedics, and emergency medical technicians face is the shortage of specialized medical equipment and staff with the ability to measure, display, store, and transmit the vital signs of patients for remote diagnosis under critical conditions. therefore, and based on our evaluation for such needs, our main research objective was to develop a new system to enable these professionals to perform such monitoring functions with a higher level of safety, performance, and time effectiveness with reduced cost. an advanced, integrated, effortless, and portable system was developed, which is capable to measure, monitor, display, store, and transmit data related to the electrocardiography (ecg) signal along with its derivatives, such as the heart rate using a hybrid system that combines hardware and software. keywords-ecg; biomedical instrumentation; embedded system; medical isolation i. introduction electrocardiography (ecg) [1] is an interpretation of the electrical activity of the heart, detected by electrodes attached to the surface of the skin and recorded by a device, external to the body. detection is conducted in the form of tiny rises and falls in the voltage between two electrodes placed at the sides of the heart. the display looks like a wavy line either on a screen or on paper. the electrodes are standardly applied on the four extremities and the chest surface. the display indicates the overall rhythm of the heart and weaknesses in different parts of the heart. the ecg device detects and amplifies the small electrical changes on the skin that are caused when the heart muscle depolarizes during each heartbeat. it provides information on the condition and performance of the heart. ecg is one of the vital signs monitored in many medical and intensive care procedures. any deviation from the normal in a particular electrocardiogram is indicative of a possible heart disorder. any ecg instrument is provided with an alert mechanism that warns the medical staff of any abnormal changes detected in the cardiac function. ecg equipment has been developed over the years [2]. digital hardware programmable logic was used to develop an ecg system in late '60s [3] and computer based ecg systems came into use in many hospitals [4, 5]. wireless and digital technologies have been used to develop ecg home monitoring and telehealth systems [6-8]. to reduce size and cost, embedded technology has been used in portable medical systems [9-11]. cardiovascular diseases (cvds) are one of the leading mortality causes accounting for 31% of deaths worldwide [12]. in saudi arabia and in the gulf countries, cvds are becoming a major health concern as being contributing to more than 45% of total deaths [13]. this percentage increases in rural areas where the healthcare is provided in primary health centers with shortage of specialized medical equipment and staff. the most affected people with cvd are elderly and adults with low income. patients of cvds need emergency care as soon as they occur. our case study is the hail region in the north of saudi arabia, having a high number of rural villages (59). the goal of our research, based on our evaluation of the needs of the primary health centers (phcs), is to develop a new system with the required features to enable healthcare professionals to perform monitoring functions with higher safety, performance, and time effectiveness with reduced cost using embedded technology and advanced signal processing that can be used remotely via the virtual instrumentation (vi) technology. this system should also overcome the lack of expert physicians in rural regions or some urban clinics or health centers, who can be consulted remotely in real-time if needed. the proposed dedicated new system consists of a low cost computer, with a developed portable device connected via ethernet, and dedicated developed software (national instruments inc.). the graphical user interface (gui) vi system has been designed for easy measurement and analysis. in addition, it provides a user-friendly interface and the ability for advanced analysis of the acquired ecg signals using advanced signal processing techniques in time and frequency domains to help accurately diagnose such events at early stages without the need for consultation except from very critical situations. the proposed integrated, effortless, and portable system measures, monitors, displays, stores, and transmits data related to the ecg signal along with its derivatives. the system is planned to have the capability to easily process, control, and send the resulted signal through the ethernet technology. corresponding author: ali s. almejrad engineering, technology & applied science research vol. 11, no. 3, 2021, 7125-7129 7126 www.etasr.com almerjad: development of an ethernet-based portable embedded isolated ecg system ii. system development a. hardware the block diagram shown in figure 1 consists of four stages: pre-amplification (surge arrester and low pass filter), amplification (ecg amplifier), controlling (µc, eeprom, and jtag), and interfacing (usb to rs232 converter, serial to ethernet convertor, power adaptor and power modules). fig. 1. system block diagram. the elements of the system are: • surge arrester: it consists of a resistor and a gas discharge tube. it is used to prevent the circuit from high level defibrillation voltage (6000v) by reducing it into nearly 120v. • electro magnetic interference (emi) filter: it is built inside the ecg amplifier. • low pass filter: it is used to filter the weakly resulted ecg signal to become suited to processing, conditioning, and displaying. the ecg amplifier has 10 input leads: ll, rl, ra, la, v1, v2 ,v3, v4, v5, and v6 with 3 power pens of −2.5v, 2.5v analog voltage, and 3.3v digital voltage. • serial peripheral interface (spi): it is a protocol that allows bidirectional communication between the ecg amplifier and the microcontroller. • microcontroller (µc): it is used to represent the controlling stage after the end of the previous pre-amplification and amplification stages. the microcontroller is programmed in c language. the microcontroller will convert the rs232 serial interface into the spi. • jtag: it is linked with a bidirectional linker with the µc and it is represented by a connector for the purpose of µc programming. • electrical erased programmable read only memory (eeprom): it is used for the temporary storage of data before receiving a server request of transmitting these data by the µc. it has a bidirectional linking with the µc because it is available for both writing and reading, even though it is called read only memory (rom). • digital isolator: it is represented by a small power transformer and it is used for the isolation of the transmitting and receiving buses between the computer interface region and the patient interface region. • power module isolated: it consists of power regulators distributed through two stages, the first stage converts the 5vd power module output into 5v and -5v output while the second stage converts the 5v primary output into 2.5v and 3.3vd secondary output and the −5v primary output into −2.5v secondary output. • transmit (tx) switch: it is used to switch between the input from ethernet and the input from the usb controller (figure 2). fig. 2. the tx switch. • usb to rs232 converter: it is used to convert the usb bus into the rs232 serial interface bus that is connected to the digital isolator. • power module: it is one of the two input voltage sources. it converts the 6v input from the adapter into 5v and 3.3v (digital voltage). it is actually a low power transformer. • serial to ethernet converter: it is used to convert the signal bus (rs232) which comes from the power module into ethernet signal. our system has the ability to choose between two alternative input sources, the electrical adaptor and the usb adaptor. we can classify the components of our system into two classes: isolated part components (patient-side components) and non-isolated part components (computer-side components). it is a high-safe system because it offers a safe protection to the patient by using a main digital isolator that separates the non-isolated from the isolated parts. it also offers circuit protection from the high defibrillation voltage (6000v) by reducing it into a much lower voltage (120v) by using the surge arrester. b. software to control the developed hardware, a graphical program has been developed in labview [14]. the graphical user interface (gui) is termed as virtual instrument (vi) because its appearance and operation imitates physical instruments. labview contains a comprehensive set of tools for acquiring, analyzing, displaying, and storing data. labview is used to communicate with hardware for data acquisition via ports such as gpib, rs232 and rs485. the front panel in figure 3 shows 9 leads of normal ecg signals while the front panel in figure 4 shows normal ecg with a red indicator detecting that the v1 lead is off. heart rate derivation from the ecg is conducted as shown in the block diagram in figure 5. engineering, technology & applied science research vol. 11, no. 3, 2021, 7125-7129 7127 www.etasr.com almerjad: development of an ethernet-based portable embedded isolated ecg system fig. 3. normal ecg signal. fig. 4. normal ecg with a red indicator alerting that the v1 lead is off. fig. 5. vi block diagram. wavelet-based peak detection is applied. the peaks in an ecg signal indicate the rhythm of the heart. typically, one lead of an ecg signal (such as lead ii) consists of 5 peaks and valleys. the first positive deflection is referred to as the p wave. the duration between the q and s waves is called the qrs duration and indicates the ventricular condition. the peaks in ecg signals usually are corrupted by environment noise and cannot be detected properly by traditional curvingfitting methods. the wavelet-based peak detection method is naturally immune to noise and can detect both sharp and mild peaks/valleys accurately. the wavelet-based method also is less affected by trends in the signal. this item uses the wa multiscale peak detection vi to detect the peaks in an ecg signal and computes the qrs duration as shown in the block diagram in figure 6. fig. 6. ecg qrst complex detection block diagram. iii. results and discussion to test the developed system we did various tests using a patient simulator for normal (figure 7) and abnormal cases (figures 8-10). a. normal case fig. 7. normal ecg signal. b. abnormal cases 1) tachycardia the heart rate is controlled by electrical signals sent across heart tissues. tachycardia [15] occurs when an abnormality in the heart produces rapid electrical signals. in some cases, tachycardia may cause no symptoms or complications. however, tachycardias can seriously disrupt normal heart function, increase the risk of stroke, or cause sudden cardiac arrest or death. treatments may help control a rapid heartbeat or manage diseases contributing to tachycardia. a healthy adult heart normally beats 60 to 100 times a minute when a person is at rest. if you have tachycardia the rate in the upper chambers or lower chambers of the heart, or both, are increased significantly as shown in figure 8. 2) atrial flutter atrial flutter (afl) [15] is an abnormal heart rhythm that occurs in the atria of the heart. when it first occurs, it is usually associated with a fast heart rate or tachycardia (beats over 100 engineering, technology & applied science research vol. 11, no. 3, 2021, 7125-7129 7128 www.etasr.com almerjad: development of an ethernet-based portable embedded isolated ecg system per minute), and falls into the category of supra-ventricular tachycardia's as shown in figure 9. fig. 8. tachycardia. fig. 9. atrial flutter. while this rhythm occurs most often in individuals with cvds such as hypertension, coronary artery disease, and cardiomyopathy, it may occur spontaneously in people with otherwise normal hearts. it is typically not a stable rhythm, and frequently degenerates into atrial fibrillation. rarely, it persists for months to years. atrial flutter is usually well tolerated initially (a high heart rate is for most people just a normal response to exercise), however, people with other underlying heart diseases or poor exercise tolerance may rapidly develop symptoms, which can include shortness of breath, chest pains, lightheadedness or dizziness, nausea and, in some patients, nervousness and feelings of impending doom. prolonged fast flutter may lead to decompensation with loss of normal heart function (heart failure). this may manifest as effort intolerance (exertional breathlessness), nocturnal breathlessness, or swelling of the legs or abdomen. 3) ventricular fibrillation ventricular fibrillation (v-fib or vf) [15] is a condition in which there is uncoordinated contraction of the cardiac muscle of the ventricles in the heart, making them quiver rather than contract properly as shown in figure 10. ventricular fibrillation is a medical emergency and the most commonly identified arrhythmia in cardiac arrest patients. while there is activity, it is undetectable by palpation (feeling) at major pulse points of the carotid and femoral arteries especially by the layperson. such an arrhythmia is only confirmed by ecg. vf is a medical emergency that requires prompt basic life support interventions because should the arrhythmia continue for more than a few seconds, it will likely degenerate further into a systole ("flat line"). the condition results in cardiogenic shock, cessation of effective blood circulation, and sudden cardiac death (scd) will result in a matter of minutes. fig. 10. ventricular fibrillation. c. the realized system the main designed and developed embedded isolated ecg system board with size of 75mm×75mm is shown in figure 11. fig. 11. the developed main embedded isolated ecg system board. iv. conclusion the developed ecg system development stages consist of designing the board, creating the layout, fabricating the printed circuit board, and assembling the components, in order to get the final system. the developed system has the capability to acquire different ecg signals from different sites on the body, protect the patient at this side, amplify the acquired signal, control it, transfer it from an isolated safely system's part engineering, technology & applied science research vol. 11, no. 3, 2021, 7125-7129 7129 www.etasr.com almerjad: development of an ethernet-based portable embedded isolated ecg system (patient-end part) to a non-isolated one (computer-end part) with perfect isolation. a gui was built for displaying the acquired signals using the labview program with the properties of displaying 9 ecg leads simultaneously or any selected specific lead and storing and transferring them through the ethernet. the presence of physicians, nurses, and paramedics in the phcs and private clinics ensures the developed system to be of low cost, small, portable, safe, biocompatible, effective, precise, simple, and durable. the system will be applied and validated in future work after saudi food and drug authority approval. acknowledgement the author would like to thank the university of hail, kingdom of saudi arabia. references [1] p. kligfield et al., "recommendations for the standardization and interpretation of the electrocardiogram: part i: the electrocardiogram and its technology: a scientific statement from the american heart association electrocardiography and arrhythmias committee, council on clinical cardiology; the american college of cardiology foundation; and the heart rhythm society: endorsed by the international society for computerized electrocardiology," circulation, vol. 115, no. 10, pp. 1306–1324, mar. 2007, https://doi.org/10.1161/ circulationaha.106.180200. [2] w. einthoven, "the string galvanometer and the human electrocardiogram," in knaw, proceedings, amsterdam , netherlands, 1904, vol. 6, pp. 107–115. [3] a. rosado, m. bataller, j. f. guerrero, j. calpe, j. v. francés, and j. r. magdalena, "high performance hardware correlation coefficient assessment using programmable logic for ecg signals," microprocessors and microsystems, vol. 27, no. 1, pp. 33–39, feb. 2003, https://doi.org/10.1016/s0141-9331(02)00083-2. [4] a. c. zoric and s. s. ilic, "pc-based system for electrocardiography and data acquisition," in ℡ siks 2005 2005 uth international conference on telecommunication in modernsatellite, cable and broadcasting services, nis, serbia, sep. 2005, vol. 2, pp. 619–622, https://doi.org/10.1109/℡sks.2005.1572189. [5] a. josko and r. j. rak, "effective simulation of signals for testing ecg analyzer," ieee transactions on instrumentation and measurement, vol. 54, no. 3, pp. 1019–1024, jun. 2005, https://doi.org/10.1109/tim.2005. 847350. [6] s. korsakas et al., "the mobile ecg and motion activity monitoring system for home care patients," in 2006 computers in cardiology, the mobile ecg and motion activity monitoring system for home care patient, sep. 2006, pp. 833–836. [7] f. bagheri, n. ghafarnia, and f. bahrami, "electrocardiogram (ecg) signal modeling and noise reduction using hopfield neural networks," engineering, technology & applied science research, vol. 3, no. 1, pp. 345–348, feb. 2013, https://doi.org/10.48084/etasr.243. [8] k. h. hii, v. narayanamurthy, and f. samsuri, "ecg noise reduction with the use of the ant lion optimizer algorithm," engineering, technology & applied science research, vol. 9, no. 4, pp. 4525–4529, aug. 2019, https://doi.org/10.48084/etasr.2766. [9] s. kara, s. kemaloğlu, and ş. kirbaş, "low-cost compact ecg with graphic lcd and phonocardiogram system design," journal of medical systems, vol. 30, no. 3, pp. 205–209, jun. 2006, https://doi.org/ 10.1007/s10916-005-7989-6. [10] a. s. almejrad, "a single supply standard 8051 microcontroller based medical k-grade isolation ecg module with graphics lcd," in 2012 second international conference on intelligent system design and engineering application, sanya, china, jan. 2012, pp. 1184–1187, https://doi.org/10.1109/isdea.2012.584. [11] a. s. almejrad, "design of an intelligent system for speech monitoring and treatment of low and excessive vocal intensity," artificial life and robotics, vol. 15, no. 3, pp. 320–324, sep. 2010, https://doi.org/10.1007/ s10015-010-0816-5. [12] "cardiovascular diseases (cvds)," who, may 2017. https://www. who.int/news-room/fact-sheets/detail/cardiovascular-diseases-(cvds) (accessed apr. 20, 2021). [13] n. aljefree and f. ahmed, "prevalence of cardiovascular disease and associated risk factors among adult population in the gulf region: a systematic review," advances in public health, vol. 2015, jan. 2015, art. no. e235101, https://doi.org/10.1155/2015/235101. [14] g. w. johnson, labview graphical programming: practical applications in instrumentation and control/book and disk. new york, ny, usa: mcgraw-hill, 1994. [15] b. s. m. macc and t. k. md, chou’s electrocardiography in clinical practice: adult and pediatric, 6th edition. philadelphia, pa, usa: saunders, 2008. authors profile ali s. almejrad received the b.sc. with 1 st honor in electrical engineering from king saud university, saudi arabia, m.sc. in bioengineering from strathclyde university, uk in 1987 and 1990 respectively and the ph.d. in medical engineering from the university of edinburgh, uk, in 1996. he is currently an associate professor of medical engineering and instrumentation in clinical laboratory sciences at the college of applied medical sciences, university of hail, saudi arabia. his research interests include the development of biomedical instrumentation and intelligent systems for health care using advanced technologies. he is a member of ieee and ipem microsoft word 4-2269_s1 engineering, technology & applied science research vol. 8, no. 6, 2018, 3512-3514 3512 www.etasr.com chopra et al.: improving translation quality by using ensemble approach improving translation quality by using ensemble approach deepti chopra department of computer science banasthali university newai, india deeptichopra11@yahoo.co.in nisheeth joshi department of computer science banasthali university newai, india jnisheeth@banasthali.in iti mathur department of computer science banasthali university newai, india mathur.iti@rediffmail.com abstract—machine translation (mt) has been a topic of great research during the last sixty years, but, improving its quality is still considered an open problem. in the current paper, we will discuss improvements in mt quality by the use of the ensemble approach. we performed mt from english to hindi using 6 mt different engines described in this paper. we found that the quality of mt is improved by using a combination of various approaches as compared to the simple baseline approach for performing mt from source to target text. keywords-machine translation; named entity translation; natural language processing; source text rewriting i. introduction machine translation is a natural language processing (nlp) application. it is defined as the process of conversion of text from one language to another and is still considered an open problem. tasks related to mt began soon after the world war ii, when translation was performed with the help of electronic bilingual dictionaries and manually designed lexical rules [1]. to make advancements in the field of mt, us government established a committee called automatic language processing advisory committee (alpac). alpac members concluded that mt was not very accurate, and was more expensive than human translation. so, they suggested investing in basic research in nlp. recently, more powerful computers were developed that could handle the huge amount of the mt related data. today, when we look back into past, we may realize that the alpac report led to progress in the field of nlp in the long term. several nlp based resources have been developed and helped developers to solve mt based problems. today, a large number of companies and institutions have been motivated by the profitability of mt as a business and this has led them to invest in mt based projects. ii. classification of mt systems on the basis of degree of human interaction, mt systems can be classified into three types [2]: (a) machine-aided human translation (maht), (b) human-aided machine translation (hamt) and (c) fully automatic machine translation (famt). maht is implemented by many commercial systems. famt systems are mostly free and can be found on the internet. according to the levels of linguistic analysis, mt may be classified into three types: (a) direct, (b) transfer and (c) interlingua. the levels of linguistic analysis can be seen in [3]. in direct approach, phrase by phrase or word by word translation takes place without undergoing any other additional representation [4]. the advantage of direct mt approach is that translation can be understood with little effort. its disadvantages are that it can be built only for specific language pairs and it is expensive to build in case of multilingual scenarios. also, some of the meanings of the source text might get lost in translation when using it. example based mt (ebmt) systems and statistical mt (smt) systems are based on direct approach. in ebmt systems, bilingual corpus or parallel texts are used. they are implemented using case based reasoning methodology of machine learning. statistical machine translation (smt) systems make use of bayes decision rule and statistical decision theory in order to reduce the number of decision errors. rule based mt (rbmt) systems are based on transfer based approach. rbmt systems can either be syntactic transfer based mt systems or semantic transfer based mt systems, in which the source text is firstly converted to source abstract representation which is then converted to target abstract representation using linguistic rules. the target abstract representation is then finally transformed into target text. in syntactic transfer based systems, source parse tree is constructed from the source text which is then transformed into target parse tree. the target parse tree is then converted into target sentence. in semantic transfer based mt systems, the source text is converted into source semantic abstract representation which is then converted into target semantic abstract representation. target semantic abstract representation is then transformed to syntactic structure which is finally converted to target text. an advantage of transfer based approach is that it can handle ambiguities that are transferred from one language to another. one disadvantage of the transfer based approach is that the original meaning of the source text may get lost during translation. in interlingua based mt systems, a language independent based abstract representation is constructed from the source sentence which is then converted to target sentence. source sentences in different languages having the same meaning have the same abstract representation in interlingua based mt systems. this minimizes transfer generation burden. engineering, technology & applied science research vol. 8, no. 6, 2018, 3512-3514 3513 www.etasr.com chopra et al.: improving translation quality by using ensemble approach iii. problems in mt regarding indian languages indian languages are free word order and morphologically rich languages. some of the problems faced in mt in indian languages are presented below. a. complex sentences are not translated correctly source sentences that are complex are usually translated incorrectly. for example, consider this source text: “the taj mahal is one of the wonders of the world located on the south bank of the yamuna river in the indian city of agra”. the above mentioned complex source text can be simplified or rewritten to obtain the following simplified source text: “the taj mahal is one of the wonders of the world. it is located on the south bank of the yamuna river in the indian city of agra”. b. named entities are not identified correctly. named entity recognition (ner) should be performed prior to mt. so, that named entities are correctly identified and spelled (translated or transliterated) correctly. iv. methodology mt systems are constructed using different combinations of ensemble techniques that include classifier based approach, source text rewriting and named entity translation. mt systems that we have designed are summarized in table i. table i. mt systems for english to hindi translation engine no. scheme m1 english-hindi baseline system m2 classifier based approach incorporated in english-hindi smt m3 source text rewriting approach incorporated in english-hindi smt m4 english name entity translation system incorporated in englishhindi smt m5 classifier based approach coupled with english name entity translation system and incorporated in english-hindi smt m6 source text rewriting approach coupled with english name entity translation system and incorporated in english-hindi smt we have used a testing file consisting of 1100 sentences in english. in m4, named entity recognition using stanford ner is used to detect named entities from the english text. these named entities are translated into hindi and sentences comprising of named entities in hindi and non-named entities in english are produced. these english-hindi mixed sentences are sent to statistical mt for complete translation into hindi. in m6, at first, sentence reordering is performed using classifier based approach. these reordered sentences are sent to stanford ner for named entity recognition. these named entities are translated into hindi and then complete translation into hindi is performed using statistical mt. for human evaluation, we used heval evaluation metric [5]. the language linguistic features that have been included in human evaluation metrics are: • translation of gender and number of nouns. • translation of tense in the sentence. • translation of voice in the sentence. • identification of proper noun(s). • use of adjectives and adverbs corresponding to nouns and verbs. • selection of proper words/synonyms (lexical choice). • sequence of phrases and clauses in the translation. • use of punctuation marks in the translation. • fluency of translated text and translator’s proficiency. • maintaining the semantics of the source sentence in the translation. • evaluating the translation of source sentence (with respect to syntax and intended meaning). in order to assess the quality of translation, a five point scale is employed as shown in table ii. table ii. description of 5 point scale in human evaluation score meaning 4 ideal 3 perfect 2 acceptable 1 partially acceptable 0 not acceptable the overall score is computed for all the linguistic features using (1): overall score = ∑ ���� �� ��� ������� �∗(����� ��.�� ������� �� �������!) (1) this score is also compared with adequacy and fluency score. adequacy and fluency are represented in tables iii and iv respectively. table iii. description of adequacy on 5 point scale score meaning 5 complete information 4 most information 3 much information 2 little information 1 none table iv. description of fluency on 5 point scale score meaning 5 ideal 4 good 3 non native 2 disfluent 1 incomprehensible v. results we have used 1100 sentences for the mentioned 6 mt engines and these sentences were distributed among 10 documents having 110 sentences each. the combined document total score for all 6 mt engines is shown in table v. the value in bold represents the highest overall score attained by the mt engine. out of 10 documents, m6 has attained the highest overall score in 8 documents. the overall accuracy of mt systems is shown in figure 1. m6 has attained the highest overall accuracy of 0.913. engineering, technology & applied science research vol. 8, no. 6, 2018, 3512-3514 3514 www.etasr.com chopra et al.: improving translation quality by using ensemble approach table v. document wise overall score of mt engines m1 m2 m3 m4 m5 m6 doc 1 0.42456 0.53451 0.79728 0.67322 0.8027 0.91302 doc 2 0.47223 0.64324 0.8685 0.6827 0.79626 0.87742 doc 3 0.45623 0.57187 0.8732 0.64068 0.7837 0.89334 doc 4 0.54163 0.65432 0.88698 0.7396 0.80064 0.8899 doc 5 0.43274 0.57435 0.89732 0.73058 0.8045 0.91114 doc 6 0.56847 0.62341 0.96182 0.74444 0.84218 0.96932 doc 7 0.57324 0.62156 0.95778 0.71096 0.8334 0.91216 doc 8 0.54628 0.68942 0.9392 0.73568 0.84058 0.9183 doc 9 0.53404 0.75842 0.92698 0.7437 0.84706 0.9294 doc 10 0.54231 0.74351 0.93215 0.72451 0.82568 0.91245 fig. 1. overall mt systems accuracy. vi. conclusion in this research paper, we showed that using ensemble techniques, the quality of english to hindi mt improves. we have designed 6 mt systems and performed our experiment on 1100 english sentences. the mt engine designed using source text rewriting approach coupled with english name entity translation system and incorporated in english-hindi smt has shown the highest overall accuracy of 0.913. references [1] r. srivastava, r. a. bhat, “transliteration systems across indian languages using parallel corpora”, 27th pacific asia conference on language, information, and computation, pp. 390-398, taiwan, november 21-24, 2013 [2] v. h. yngve, “the machine and the man”, mechanical translation, vol. 1, no. 2, pp. 20-22, 1954 [3] b. vauquois, “a survey of formal grammars and algorithms for recognition and transformation in machine translation”, ifip congress (2), vol. 68, pp. 1114-1122, uk, august 5-10, 1968 [4] w. weaver, “translation”, in: machine translation of languages, pp. 15-23, 1955 [5] n. joshi, i. mathur, h. darbari, a. kumar, “heval: yet another human evaluation metric”, international journal on natural language computing, vol. 2, no. 5, pp. 21-36, 2013 0,509173 0,641461 0,904121 0,712607 0,81767 0,912645 0 0,2 0,4 0,6 0,8 1 1 2 3 4 5 6 o v e ra ll a c c u ra c y mt engines microsoft word etasr_v11_n3_pp7181-7186 engineering, technology & applied science research vol. 11, no. 3, 2021, 7181-7186 7181 www.etasr.com mecieb et al.: convective heat transfer during melting in a solar lhtes convective heat transfer during melting in a solar lhtes fatima zohra mecieb laboratory of reactive systems and materials university djillali liabes of sidi bel abbes sidi bel abbes, algeria fatima.mecieb@univ-sba.dz francisco garcía bermejo thermal and fluid engineering department polytechnic university of cartagena cartagena, spain pacoaitpaco@gmail.com juan pedro solano fernández thermal and fluid engineering department polytechnic university of cartagena cartagena, spain juanp.solano@upct.es samir laouedj laboratory of reactive systems and materials university djillali liabes of sidi bel abbes sidi bel abbes, algeria s.laouedj@gmail.com abstract-melting combined with natural convection in a shell and latent heat thermal energy storage (lhtes) tube driven by a solar collector was analyzed numerically in the present work. this work's particularity lies in the fact that the htf temperature varies at each moment following the solar irradiance curve. a program (udf) has been developed and integrated into ansys to meet this requirement. the use of this coupling strategy allows obtaining realistic unsteady lhtes results. several numerical investigations were carried out to analyze the effect of the heat sources' power on the accumulator's performance. the obtained results show that natural convection considerably influences the heat transfer as well as the melting kinetics of the phase change material (pcm). besides, the results show that increasing the heat transfer fluid's thermal load can increase the melting rate of the pcm and the stored energy and reduce the entire melting time. keywords-natural convection; solar coupling; pcm melting i. introduction among the wide variety of renewable energy sources, solar energy is the largest one and simultaneously an example of a time-variable energy source that is mismatched with the needs of use. energy storage is the most appropriate way to overcome these inadequacies. although there are several storage systems, latent heat storage using phase change material (pcm) has clear advantages over others: a greater density of energy storage and a relatively constant storage temperature. however, these materials present many problems because of their low thermal conductivity. improving heat transfer by developing a useful heat exchanger device in the latent heat thermal energy storage (lhtes) unit is a solution to the pcm's low thermal conductivity problem. this calls for a powerful knowledge of the heat transfer in the lhtes process. the absence of comprehension of heat transfer modes during the phase change is an issue frequently mentioned in the literature. potential heat transfer mechanisms are convection, conduction, or a mixture of both. therefore, the question which mode dominates at different melting levels has been discussed for decades [1, 2]. some authors thought that conduction took an essential part in phase transition operations [3, 4]. however, several researchers have reported that natural convection, especially during melting, is the essential heat transfer mode in phase transformation. among the first works carried out in this context, we can cite the experimental work in [5, 6] as well as the numerical simulations in [7, 8] that proved that natural convection could have a powerful impact on the rate of heat transfer and the form of the melting front. later, authors in [9] developed a scale theory and identified the boundaries of the different regimes of the heat transfer mechanisms present in the melting of pcm in a laterally heated square enclosure. the research results demonstrated that the conduction heat transfer mechanism is dominant in the melting process's initial phases. the natural convection induced by the buoyancy of the liquid is intensified as melting progresses. they mentioned the existence of a transition region between these two. several recent experimental and computational studies have shown that a mixture of conduction and convection is the heat transfer mechanism in an lhtes system [10–14]. as discussed above, the work concentrating on heat transfer with a fixed hot wall temperature in a basic lhtes device configuration was substantially different from the actual situation where the hot source's temperature is not constant. thus, this paper focuses on pcm's heat transfer mechanics during the charging processes in the horizontal cylindrical shell-and-tubes lhtes system driven by a solar collector in which the temperature of the htf changes every moment during the day according to a journal solar irradiation curve. corresponding author: fatima zohra mecieb engineering, technology & applied science research vol. 11, no. 3, 2021, 7181-7186 7182 www.etasr.com mecieb et al.: convective heat transfer during melting in a solar lhtes ii. numerical simulation a. physical model figure 1 shows a schematic illustration of a horizontal shell and tubes lhtes unit. the designed lhtes unit consists mainly of 12 stainless steel tubes with a 17.2mm diameter and a thickness of 2.31mm. the heat transfer fluid flows in series through the inner tubes, and the pcm is uniformly distributed on the shell side. fig. 1. characteristic dimensions of the geometry. the enthalpy-porosity method developed in [15] is employed in modeling and simulating the phase change process. in this method, the enthalpy h is written as the sum of the sensible enthalpy hsensible and the latent enthalpy hlatent. � � ������� � � ����� (1) with: ������� � � � �� � ��. ������� (2) the latent heat enthalpy can vary between zero (for a solid) and hl∆ (for a liquid). � ����� � ��.∆�� (3) the liquid fraction lf can be defined as: � �� � 0�� � 1�� � ��� !"#$% �"#&%#$% �� !"#$% '( � ) ��* �+,�� ) � �-,�+,���* �+,� ) � ) � �-,�+,� (4) the correct characterization of material properties is one of the essential parts of performing simulations. the construction material of the accumulator is steel, whose characteristics are presented in table i. table i. steel properties properties values density [kg/m 3 ] 8030 specific heat [j/kg. k] 502.48 thermal conductivity [w/m.k] 16 the other material to be defined in the system is the paraffin rt70hc, with a melting point around 70°c. this paraffin is used as phase change material, storing the installation's solar collector's absorbed thermal energy. the principal reason for choosing paraffin wax is that its melting temperature conforms with the htf temperature coming from the solar collectors at medium temperatures. this material has been analyzed and detailed correlations of the material's descriptive parameters have been provided in [16]. the melting and solidification temperatures of the paraffin and the latent thermal energy must be added to these correlations. ��* �+,� � 66.76 °c � �-,�+,� � 78.85 °c δ�� � 244970 j/kg note that paraffin should be treated as a fluid that is initially in a solid-state. b. initial and boundary conditions a two-dimensional domain is considered saving computational cost. since there is no depth, there will be no htf flow, and the boundary condition "convective heat transfer" is applied to the tubes' wall. therefore, only the "free stream temperature" is considered. a udf is employed to ensure the three-dimensional aspect of the solution by calculating the outlet temperature of each tube using the following equation: �*,� � =>?> @ab.cd@ab ��� (5) where tin is the output temperature of the previous tube and q & is the heat that the pcm absorbed from the htf at the current time which is calculated by: e> � ����. fg��� h �ij (6) the heat transfer coefficient int h between water and the internal tubes' walls is calculated in the udf according to [17] by the following equations: ���� � klm n@abm (7) klm � op q⁄ sot��uvvvsw uxuy.zop q⁄ s[ \⁄ gw \ ]⁄ �uj (8) the correlation is valid for 0.5<pr<2000 and 3000<re<5.10 6 . the friction factor f is calculated by: ^ � o1.58_`ab h 3.28s�y (9) initially, the solid pcm is at a temperature of 295 o k. the htf flow rate in tubes is 1.84l/min with reynold number re=3,089,37. the heat in (6) is exploited to update the htf temperature at the outlet of one tube (9) that corresponds to the boundary condition (inlet) temperature of the next tube. since a series flow is adopted, the fluid will flow from one tube to the other by gradually decreasing the temperature. at each time step, a different fluid temperature would be imposed for each tube, which implies calculating the solution in each of them. the accumulator will be directly connected to a solar collector (figure 2), with an efficiency given by (10), (11) and an absorption surface of acol=3.03m 2 . engineering, technology & applied science research vol. 11, no. 3, 2021, 7181-7186 7183 www.etasr.com mecieb et al.: convective heat transfer during melting in a solar lhtes d � 0.514 h 1.158.�e* h 0.005.f.�e* y (10) with: �e* � g�cg�#h���j f⁄ (11) fig. 2. schematic diagram of the primary circuit of the installation. as a general rule, under ideal conditions (without cloud interference), solar radiation can be expressed by a positive sinusoidal function whose period corresponds to the duration of the day. according to the murcia region's climatic data (in the south of spain), 3 solar curves can be formed depending on the period (winter, mixed, and summer). the heat is ideally absorbed by the solar collector per unit area, g. f � 270.i1 h jkl m n.�uqvvvop (12) f � 392.i1 h jkl m n.�yuvvvop (13) f � 480.i1 h jkl m n.�yzvvvop (14) the progressive rise of the accumulator fluid inlet temperature, as a function of the irradiation dynamics involved in (12)-(14), drives the storage of thermal energy in the pcm accumulator through a solar coupling algorithm programmed in the udf. equation (15) gets the temperature at the solar collector's output at each moment: �cg�!%q � �cg�#h ecg�. r> s�p. ��s�p (15) with: ecg� � fcg�.f. d (16) the resulting temperature of the htf at the solar collector outlet will be specified at the storage system inlet. the solar coupling scheme will update the heat-transfer fluid's temperature at each moment, considering the solar radiation using the algorithm described above. c. numerical procedure considering the shell-and-tube lhtes design, hexahedron quad and map elements are adopted to discretize the pcm domain. the cells near the inner tube are refined to get accurately the velocity and temperature gradients. the secondorder discretization scheme is used for the momentum and energy equations' spatial discretization to have higher accuracy in the solution. a pressure-velocity coupling by the algorithm simplec is applied in this calculation, with a modification of the under-relaxation factors. the following simplifications are applied to the 2d model: • the liquid paraffin and the heat transfer fluid are incompressible newtonian fluids. • pcm is assumed to be isotropic and homogeneous and the volumetric expansion of pcm during melting is neglected. in the present simulation, the boundary condition by convective heat transfer and the strategies followed for the coupling of the solar curve by udf represent the fundamental basis for this accumulator's modeling. the system's performances are analyzed by modifying the thermal load of the htf through varying the irradiance curve according to the climatic conditions. iii. validation the simulation results are compared with the experimental data from [16] to verify the actual numerical simulations. the comparison of measured irradiation and liquid fraction and the simulation results for the cases of a sunny day of may 31, 2019 are shown in figure 3. a reasonable agreement can be seen between the numerical and the experimental results (with a maximum liquid fraction absolute error of 0.1812), confirming the combined enthalpy porosity and natural convection model's feasibility in the present investigation. iv. results and discussion a. comparison of conduction and conduction-convection models figures 4 and 5 show the temperature and liquid fraction contours in the storage tank's paraffin, whose heat is supplied by two solar collectors for a winter curve. the melting process is simulated using a convection and conduction model and a pure conduction model. as illustrated in figure 4(a), the temperature contours are symmetrical along the horizontal and vertical axes. the conduction heat transfer mechanism could interpret that. the phase change material temperature is monitored by the energy absorbed from the htf by the pcm. thermal energy is transmitted from the hot paraffin to the adjacent layer of cold paraffin. the temperature at one location in the accumulator could remain stable or increase depending on the two energy transfer processes' rates. the total heat transfer rate in the conduction model seems to be the same in all directions. the melting front in the radial direction passes from the tube wall to the shell's internal surface at the same velocity (figure 5(a)). nevertheless, the results found from the convection-conduction model are distinct. figure 4(b) displays the temperature contours through the melting phase. the pcm temperature varies considerably in the vertical axis at distinct moments during the melting process. in the convectionconduction model, heat transfer from the tube surface to the pcm proceeds the conduction just before pcm begins to melt. as the paraffin melts, a thin liquid film forms between the tubes' outer wall and the solid pcm and natural convection begins to occur. as the molten area expands, the convection gets more significant, and the interface front moves quicker (figure 5(b)). engineering, technology & applied science research vol. 11, no. 3, 2021, 7181-7186 7184 www.etasr.com mecieb et al.: convective heat transfer during melting in a solar lhtes fig. 3. irradiance and pcm liquid fraction by current numerical model in comparison with the experimental resutls of [16]. as shown in error! reference source not found.(b), the liquid pcm increases and progressively occupies the storage tank's upper section due to buoyancy. in the top zone of the accumulator, pcm takes less time to melt than the bottom. this result is compatible with that reported in [16]. (a) (b) 11 am 12 am 2 pm fig. 4. temperature contours: (a) conduction model, (b) convectionconduction model. b. nusselt number. nusselt identifies the relationship between convective and conductive heat transmission. it is expressed according to (17): kl � tu!hv.mn (17) the convection coefficient on this lhtes side hconv is such that: �e*�w� � ->#�xy# ��x�,{|}# (18) (a) (b) 11 am 12 am 2 pm fig. 5. liquid fraction contours: (a) conduction model, (b) convectionconduction model. at each moment, only the fluid portion (liquid) of the pcm is considered getting an average pcm liquid temperature value, �x�,wc~� . figure 6 shows the solution obtained for the simulations using different solar curves. the nusselt number is represented as a function of dimensionless time θ, which is given by: � � ^k.��b (19) the temporal evolution of the nusselt number is represented as a function of different heat transfer regimes (figure 6): • a pure conduction regime for θ>0 (corresponding to zone i). as the temperature gradient initially has significant values due to the increased tube wall temperature, the nusselt number decreases quickly within the initial melting step. the weak heat transfer, distinguished by a monotonous drop of the nusselt number, is the particularity of this conduction regime. engineering, technology & applied science research vol. 11, no. 3, 2021, 7181-7186 7185 www.etasr.com mecieb et al.: convective heat transfer during melting in a solar lhtes • a mixed convection-conduction regime for 0.017≤θ≤0.043 (corresponding to zone ii) where the conduction process is gradually replaced by convection. one crucial finding associated with convection melting is that the impact of natural convection ascends with θ [9]. • a convection-dominated regime for θ>0.043 (corresponding to zone iii). within the asymptotic limit of θ, we can get the simplified nu law ∼ ra1/4 [9]. the plateau at ra 1/4 refers to pure convective heat transfer and is shown in figure 6 for 0.043<θ<0.11. besides, the average nusselt number between the heated tubes and the pcm liquid zone is relatively independent of time in the convectiondominated regime. therefore, the convection-dominated regime is also known as the "quasi-steady" regime. • the numerical results indicate a decrease of nu in the ultimate phase (θ>0.11) when the liquid pcm fills the majority of the accumulator (lf>0.8) (corresponding to zone iv). stratification dominates in this advanced evolution of the melting process. fig. 6. nusselt number according to θ. v. conclusion a paraffin melting process has been carried out in a tubeand-shell lhtes integrated with a solar collector. the results can be summarized as follows: • in the convection-conduction model's temperature field, the rise in temperature in the shell's upper zone was faster than in the low zone, whereas in the conduction model, there was a simultaneous rise in temperature at the shell's top and bottom. the convection-conduction model better interprets the heat transfer mechanism during pcm melting. • the performance of the lhtes in summer conditions is higher than in mixed and winter conditions, but the pcm engineering, technology & applied science research vol. 11, no. 3, 2021, 7181-7186 7186 www.etasr.com mecieb et al.: convective heat transfer during melting in a solar lhtes temperature exceeds 100°c, which must be avoided to prevent pcm degradation. • the melting of the complete paraffin passes via 4 regimes, and each regime has its own nusselt number. the relation between the nusselt number and dimensionless time initially indicates a significant drop (conduction), a transition (conduction and convection), a plateau (convection), and, eventually, a gradual decrease towards the disappearance of the solid (stratification). nomenclature d diameter (m) cp specific heat capacity (j·kg -1 ·k -1 ) fo fourier number, ^k � ∝.� m\ ∆hl latent heat (j·kg −1 ) k thermal conductivity (w·m -1 ·k -1 ) m& mass flow (kg·h -1 ) pr prendtl number t température (k) t average temperature (k) tw wall temperature (k) ste stefan number, ��b = cd.∆� ∆s� t time (s) α thermal diffusivity (m 2 .·s -1 ) µ viscosity, kg·m -1 ·s -1 ρ density (kg·m -3 ) references [1] h. hu and s. a. argyropoulos, "mathematical modelling of solidification and melting: a review," modelling and simulation in materials science and engineering, vol. 4, no. 4, pp. 371–396, jul. 1996, https://doi.org/10.1088/0965-0393/4/4/004. [2] y. dutil, d. r. rousse, n. b. salah, s. lassue, and l. zalewski, "a review on phase-change materials: mathematical modeling and simulations," renewable and sustainable energy reviews, vol. 15, no. 1, pp. 112–130, jan. 2011, https://doi.org/10.1016/j.rser.2010.06.011. [3] n. b. khedher, "numerical study of the thermal behavior of a composite phase change material (pcm) room," engineering, technology & applied science research, vol. 8, no. 2, pp. 2663–2667, apr. 2018, https://doi.org/10.48084/etasr.1824. [4] z. tan, k. m. lim, and b. c. khoo, "an adaptive mesh redistribution method for the incompressible mixture flows using phase-field model," journal of computational physics, vol. 225, no. 1, pp. 1137–1158, jul. 2007, https://doi.org/10.1016/j.jcp.2007.01.019. [5] e. m. sparrow, s. v. patankar, and s. ramadhyani, "analysis of melting in the presence of natural convection in the melt region," journal of heat transfer, vol. 99, no. 4, pp. 520–526, nov. 1977, https://doi.org/10.1115/1.3450736. [6] c. benard, d. gobin, and f. martinez, "melting in rectangular enclosures: experiments and numerical simulations," journal of heat transfer, vol. 107, no. 4, pp. 794–803, nov. 1985, https://doi.org/ 10.1115/1.3247506. [7] h. rieger, u. projahn, m. bareiss, and h. beer, "heat transfer during melting inside a horizontal tube," journal of heat transfer, vol. 105, no. 2, pp. 226–234, may 1983, https://doi.org/10.1115/1.3245567. [8] m. okada, "analysis of heat transfer during melting from a vertical wall," international journal of heat and mass transfer, vol. 27, no. 11, pp. 2057–2066, nov. 1984, https://doi.org/10.1016/0017-9310(84) 90192-3. [9] p. jany and a. bejan, "scaling theory of melting with natural convection in an enclosure," international journal of heat and mass transfer, vol. 31, no. 6, pp. 1221–1235, jun. 1988, https://doi.org/10.1016/00179310(88)90065-8. [10] x. sun, y. chu, y. mo, s. fan, and s. liao, "experimental investigations on the heat transfer of melting phase change material (pcm)," energy procedia, vol. 152, pp. 186–191, oct. 2018, https://doi.org/10.1016/j.egypro.2018.09.079. [11] a. memon, g. mishra, and a. k. gupta, "buoyancy-driven melting and heat transfer around a horizontal cylinder in square enclosure filled with phase change material," applied thermal engineering, vol. 181, nov. 2020, art. no. 115990, https://doi.org/10.1016/j.applthermaleng.2020. 115990. [12] n. mallya and s. haussener, "buoyancy-driven melting and solidification heat transfer analysis in encapsulated phase change materials," international journal of heat and mass transfer, vol. 164, jan. 2021, art. no. 120525, https://doi.org/10.1016/j.ijheatmasstransfer. 2020.120525. [13] a. s. soliman, s. zhu, l. xu, j. dong, and p. cheng, "numerical simulation and experimental verification of constrained melting of phase change material in cylindrical enclosure subjected to a constant heat flux," journal of energy storage, vol. 35, mar. 2021, art. no. 102312, https://doi.org/10.1016/j.est.2021.102312. [14] m. a. aichouni, n. f. alshammari, n. b. khedher, and m. aichouni, "experimental evaluation of nano-enhanced phase change materials in a finned storage unit," engineering, technology & applied science research, vol. 10, no. 3, pp. 5814–5818, jun. 2020, https://doi.org/ 10.48084/etasr.3616. [15] v. r. voller and c. prakash, "a fixed grid numerical modelling methodology for convection-diffusion mushy region phase-change problems," international journal of heat and mass transfer, vol. 30, no. 8, pp. 1709–1719, aug. 1987, https://doi.org/10.1016/00179310(87)90317-6. [16] a. egea, j. p. solano, j. pérez-garcía, and a. garcía, "solar-driven melting dynamics in a shell and tube thermal energy store: an experimental analysis," renewable energy, vol. 154, pp. 1044–1052, jul. 2020, https://doi.org/10.1016/j.renene.2020.03.078. [17] f. p. incropera, d. p. dewitt, t. l. bergman, and a. s. lavine, fundamentals of heat and mass transfer, 6th ed. hoboken, nj, usa: john wiley & sons, 2006. microsoft word etasr_v10_n6_pp6456-6461 engineering, technology & applied science research vol. 10, no. 6, 2020, 6456-6461 6456 www.etasr.com lahcene et al.: the effect of geometric parameters on the performance of solar chimney … the effect of geometric parameters on the performance of solar chimney: a numerical and experimental study abdelkader lahcene laboratory of materials and reactive systems djillali liabes university of sidi bel abbes sidi bel abbes, algeria lhkader@yahoo.fr abdel yllah benazza laboratory of materials and reactive systems djillali liabes university of sidi bel abbes sidi bel abbes, algeria abdel_benazza@yahoo.fr mohamed benguediab laboratory of materials and reactive systems djillali liabes university of sidi bel abbes sidi bel abbes, algeria benguediab_m@yahoo.fr abstract-a numerical and experimental study of the geometric parameters of the solar chimney on the aerodynamic and thermal behavior of the air flow is presented in this paper. several configurations were proposed in order to optimize the most efficient geometric one. mass conservation, continuity, and energy equations are solved by the finite volume method. the increase in the radius of the collector and the inclination angle of the roof of the collector contributes favorably to the flow velocity to reach its maximum below the level of the tower, whereas it is inversely proportional to the height of the collector (space: ground-roof). this hangs up the height and the opening of the chimney generates a significant relaxation between the glue and the exit, from where important velocity is recorded at the level of the glue. a good correlation between the experimental and the simulation results is observed. keywords-solar chimney; natural convection; collector; finish volume; opening angle;inclination i. introduction exploitation and consumption of fossil fuels have a considerable impact on the environment, emitting carbon dioxide (co2), a greenhouse gas largely responsible for climate change, whereas the overexploitation of their reserves will lead to their depletion. these causes have led the research to develop and exploit renewable energy sources. among these alternative energy sources, solar energy is virtually inexhaustible. several studies on solar energy exploitation have been carried out, such as the study and simulation of solar flux on the walls of buildings in adrar (algeria) [1] and the effect of hydronic solar heaters for the algerian climate [2]. the solar tower or solar chimney is a solar energy generating installation that uses solar radiation to increase the internal energy of the air entering a system. the solar energy received by the air through the collector will be transformed into kinetic energy and then into electricity by a suitable turbine. the solar tower is suitable for countries with strong solar radiation or sunshine. it has three main parts, namely the collector, the chimney, and the turbine. the adaptability of solar energy for a given application depends on the performance of the solar chimney. understanding the fundamental mechanisms governing the operation of the chimney allows the mastery of all the extrinsic or intrinsic parameters entering into the energy transfer process in order to optimize its performance. solar chimneys have been studied by many researchers. leonardo da vinci made sketches of a solar tower called a smoke outlet [3]. the idea of using a solar chimney for the production of electricity was first developed in 1903 [4]. this concept was taken up by günther [5] in 1931 who gave a detailed description and the authors in [6] developed and implemented this project. the first prototype was made in 1982 in manzanares, spain. from there a series of theoretical studies continued, which developed theoretical models of solar chimneys by deriving the yield and mullett performance data [7]. several theoretical and experimental studies relating to the determination of the profile of the velocity and the temperature inside the chimney as a function of height, angle of inclination, temperature of the ambient air, and intensity of solar radiation were carried out. authors in [8] modeled the heat transfer and the air flow in the ccs with the hypothesis of a laminar flow in natural convection. authors in [9, 10] studied numerically the natural laminar convection and permanent air in a solar chimney. authors in [11] aimed at the development of an analytical and numerical model making possible to describe the performance of solar chimneys. authors in [12] developed a numerical model to simulate the performance of a stack solar power plant in different regions of iran. authors in [13] made a thermal development of the laminar flow with hydrodynamic corresponding author: mohamed benguediab engineering, technology & applied science research vol. 10, no. 6, 2020, 6456-6461 6457 www.etasr.com lahcene et al.: the effect of geometric parameters on the performance of solar chimney … development of a viscoplastic fluid (bingham fluid) between two plane plates. this analysis showed the effect of the inertia and the rheological behavior of the fluid on the velocity fields, pressure and temperature. authors in [14] developed a mathematical model which described the flow rate and the performance evaluation of the solar chimney with different functional and geometric configurations. the effect of the slope on the flow out of the stack was studied by authors in [15], which showed that the absorption is optimal, for an angle of inclination varying between 40° and 60°. the processes of heat transfer and efficiency of natural ventilation driven by a solar chimney have been studied in [16]. authors in [17] published a review of the main characteristics of chimney solar power plants. authors in [4-6] carried out several studies on the optimization of various parameters such the height of the chimney and the angle of inclination of the collector. in the present study, a combination of the variation of three geometric parameters (chimney height, inclination angle of the collector and inclination angle of the chimney) is made in order to obtain the optimal values of the performance of the solar chimney. this work aims to optimize the geometric parameters of the chimney in order to obtain an efficient configuration. several configurations are studied numerically and experimentally. ii. simulation a. geometry the creation of the chimney geometry is based on three two-dimensional elements (surfaces) on the (x, y) plane. the collector is a horizontal rectangle with a length (radius rcoll) of 12m and a width (height hcoll) of 0.8m, the collector has a junction with the chimney by a converging elbow of radius 0.8m. the chimney is a vertical rectangle with a length (height hch) of 12m and a width of 0.8m. figure 1 represents the geometric parameters of the studied chimney. the adopted mathematical model is established using the following simplifying assumptions: the flow is two-dimensional and the system admits an axis of symmetry, the flow is turbulent, the considered fluid is assumed to be viscous and newtonian, and obeys boussinesq's approximation. the properties of the fluid are assumed to be constant and with no heat source. fig. 1. geometry of the studied solar chimney. b. numerical procedure the numerical calculation is based on the finite volume discretization of the transport equations on a 2-d structured mesh. the variables are stored in a non-shifted mesh (collocated) via the interpolation of rhie [18]. the pressure correction is performed using the simple algorithm. the generation of the mesh is an adapted 2-d mesh that is structured, monoblock and curvilinear of the bodyfitted type. mesh dependence was investigated using different numbers of mesh before attaching to a 32×376 mesh (figure 2). fig. 2. boundary conditions. iii. experimental part in this part, a prototype of a solar fireplace inspired by prototypes from france and iran was designed (figure 3). the effect of the geometric parameters of the solar chimney on the temperature and the air flow velocity were studied. the measurements were carried out during may, where the atmospheric disturbances are caused by the wind and the passage of clouds, during a period going from 10:20 a.m. to 3:05 p.m. readings were taken every 15 minutes. three geometrical configurations have been tested. the different configurations are given in table i. fig. 3. the experimental prototype, made in our laboratory. table i. geometrical configurations configuration dimensions of the prototype chimney height (mm) inclination α= 12.7° for collector height (mm) 1 665 155 2 1835 155 3 1835 120 engineering, technology & applied science research vol. 10, no. 6, 2020, 6456-6461 6458 www.etasr.com lahcene et al.: the effect of geometric parameters on the performance of solar chimney … iv. results and discussion a. numerical results the influence of the opening angle of the tower, the angle of inclination of the collector, the height of the tower, the height of the collector and the radius of the collector on the flow rate and the maximum flow velocity have been studied. 1) influence of the opening angle of the chimney figures 4 and 5 represent the iso-velocity for different values of the opening angle α for a collector radius of 15m and 20m. it should be noted that the velocity intensity and the position of its focus vary according to the angle α. the velocity in the chimney increases as the radius of the collector and the opening angle increase. fig. 4. iso-velocity contours for different opening angles α and for a collector radius of 15m. fig. 5. iso-velocity contours for different opening angles α and for a collector radius of 20m. fig. 6. flow variation as a function of the opening angle of chimney α for different collector radius values. the quantitative aspect of these results is illustrated by figures 6 and 7 where a significant increase in the maximum velocity and the flow can be noticed. this can be explained by the increase in the heat exchange surface (large collector radius) and as a result the increase in air temperature, therefore significant buoyancy. fig. 7. velocity variation as a function of the opening angle of chimney α for different collector radius values. 2) influence of the collector inclination angle figures 8 and 9 represent the iso-velocity for different angle openings for collector inclination angle β=0 and β=3°. fig. 8. iso-velocity contours for different opening angles α and collector inclination angle β=0. fig. 9. iso-velocity contours for different opening angles α and collector inclination angle β=3°. it is noted that as the angle of inclination β of the collector roof increases, the velocity through the system increases to a engineering, technology & applied science research vol. 10, no. 6, 2020, 6456-6461 6459 www.etasr.com lahcene et al.: the effect of geometric parameters on the performance of solar chimney … maximum at the foot of the tower. increasing the angle β decreases the phenomenon of recirculation of the flow at the inlet of the collector. the opening of the chimney generates significant relaxation between the neck and the outlet, where the high velocity is recorded at the neck. these results are quantitatively illustrated by figures 10 and 11 showing respectively the variations of the flow rate and the maximum velocity as functions of the opening angle. fig. 10. comparison between the variation of flow as a function of α for β=0°. fig. 11. comparison between the variation of velocity as a function of α for β=0°. b. experimental results three different configurations were tried in order to study the temperature and velocity variations (see table ii). an arduino system was used, which consists of placing digital temperature and velocity sensors in different parts of the chimney, as shown in figure 12. fig. 12. aeras of temperature and velocity readings. table ii. studied geometric parameters configuration dimensions of the prototype chimney height (mm) collector height (mm) inclination 1 665 155 12.7 2 1835 155 12.7 3 1835 120 14.47 1) temperature variation as a function of time figures 13-15 give the temperature variation as a function of time in different areas of the solar chimney. temperatures are measured at points a, b, c, for the three chimney configurations defined in table ii. fig. 13. variation of temperature as a function of time in areas a, b, c for configuration 1. fig. 14. variation of temperature as a function of time in areas a, b, c for configuration 2. fig. 15. variation of temperature as a function of time in areas a, b, c for configuration 3. a gradual increase is noticed in the temperature in the collector (inlet-outlet), due to the greenhouse effect below the collector roof. a slight difference between the temperature at engineering, technology & applied science research vol. 10, no. 6, 2020, 6456-6461 6460 www.etasr.com lahcene et al.: the effect of geometric parameters on the performance of solar chimney … point b and at point c was also noticed. this difference can be explained by heat losses due to the vortex and the poor insulation at the neck. the temperature in the chimney recorded at point d is lower than that recorded at point c. this decrease is the consequence of the transformation of thermal energy into kinetic energy (thermosiphon phenomenon). 2) velocity variation as a function of time the effect of the geometric parameters on the variation of velocity in the chimney was studied in two zones of the chimney: bc and dc. the variation of the velocity in these zones for configurations 1-3 is given in figures 16-18. fig. 16. variation of velocity as a function of time in zones bc and dc for configuration 1. fig. 17. variation of velocity as a function of time in zones bc and dc for configuration 2. fig. 18. variation of velocity as a function of time in zones bc and dc for configuration 3. we can see that this variation differs from case to case and from area to area. for the first configuration, there is not a large difference between the maximum and minimum velocity values in the two zones (figure 16). the values recorded in the dc zone are 0.4171m/s for maximum velocity and 0.1245m/s for minimum velocity. in the bc zone the recorded values are 0.4108m/s and 0.1447m/s respectively. for the second configuration, there is a notable difference in the values recorded in the two zones (figure 17).the maximum and minimum values recorded in the dc zone are 0.7206m/s and 0.1191m/s. on the other hand, the maximum and minimum values in the bc zone are 0.7832m/s and 0.3863m/s. note that despite the fact that the ambient temperature of the configuration is lower than that prevailing in the first configuration, the flow velocity values are two times those of the first configuration. there is a positive effect on the performance due to the height of the chimney. this evolution can be explained by the fact that when the height increases, the thermosiphon phenomenon becomes more important. the effect of the inclination of the collector is studied in the third configuration, with the same chimney height and by modifying the height of the inlet of the collector (figure 18). it is noted that the velocity gradient is greater than the one recorded in the second configuration. the inclination of the manifold positively contributes to the variation of velocity in the chimney. in this configuration, the maximum and minimum values recorded were 0.8321m/s and 0.2704m/s for the dc zone. on the other hand, in the bc zone, the values were 0.7013m/s and 0.4063m/s respectively. v. conclusion the main aim of this study was to investigate the effect of the geometric parameters of the solar chimney on the aerodynamic and thermal behavior of the air flow. the work was split into two parts: the first part was a numerical simulation of the air flow in the chimney under the effect of variation of the opening radius of the chimney and the inclination of the manifold. it has been shown that these two parameters have an important influence on the flow rate and therefore on the efficiency of the solar chimney. in the second part, a prototype was made. the effects of the height of the chimney and the tilt of the header on the velocity and temperature of the air in the chimney were studied. the obtained results allowed us to validate the numerical results and predict the most suitable area for the location of the turbine. acknowledgment this work was carried out in the laboratory of materials and reactive systems of djillali liabes university of sidi bel abbes which is sponsored by the direction of scientific and technological research (dgrst algeria). references [1] a. oudrane, b. aour, b. zeghmati, x. chesneau, and h. massaoud, “study and simulation of the density of the incident solar flux on the walls of a building in adrar, algeria,” engineering, technology & applied science research, vol. 7, no. 5, pp. 1940–1945, oct. 2017, https://doi.org/10.48084/etasr.1337. [2] i. zeghib and a. chaker, “efficiency of a solar hydronic space heating system under the algerian climate,” engineering, technology & applied science research, vol. 6, no. 6, pp. 1274–1279, dec. 2016, https://doi.org/10.48084/etasr.875. engineering, technology & applied science research vol. 10, no. 6, 2020, 6456-6461 6461 www.etasr.com lahcene et al.: the effect of geometric parameters on the performance of solar chimney … [3] r. wengenmayr and t. bührke, eds., renewable energy: sustainable energy concepts for the future, 1st ed. weinheim, germany: wileyvch, 2008. [4] i. cabanyes, “las chimeneas solares (solar chimneys),” la ernergia eléctrica, 1903. [5] h. günther, in hundert jahren die künftige energieversorgung der welt, 1st ed. kosmos, 1931. [6] j. schlaich et al., “the solar chimney-transferability of results from the manzanares solar chimney plant to larger scale-plants,” schlaich bergermann und partner ces, stuttgart, germany, 1995. [7] l. b. mullett, “the solar chimney—overall efficiency, design and performance,” international journal of ambient energy, vol. 8, no. 1, pp. 35–40, jan. 1987, https://doi.org/10.1080/01430750.1987.9675512. [8] t. chergui, s. larbi, and a. bouhdjar, “thermo-hydrodynamic aspect analysis of flows in solar chimney power plants—a case study,” renewable and sustainable energy reviews, vol. 14, no. 5, pp. 1410– 1418, jun. 2010, https://doi.org/10.1016/j.rser.2010.01.017. [9] t. tayebi and d. mahfoud, “numerical simulation of natural convection in a solar chimney,” international journal of renewable energy research, vol. 2, no. 4, pp. 712–717, dec. 2012. [10] t. tayebi and m. djezzar, “numerical analysis of flows in a solar chimney power plant with a curved junction,” international journal of energy science, vol. 3, no. 4, pp. 280–286, aug. 2013. [11] m. a. dos s. bernardes, a. voß, and g. weinrebe, “thermal and technical analyses of solar chimneys,” solar energy, vol. 75, no. 6, pp. 511–524, dec. 2003, https://doi.org/10.1016/j.solener.2003.09.012. [12] a. asnaghi and s. m. ladjevardi, “solar chimney power plant performance in iran,” renewable and sustainable energy reviews, vol. 16, no. 5, pp. 3383–3390, jun. 2012, https://doi.org/10.1016/ j.rser.2012.02.017. [13] a. boualit, n. zeraibi, s. boualit, and m. amoura, “thermal development of the laminar flow of a bingham fluid between two plane plates with viscous dissipation,” international journal of thermal sciences, vol. 50, no. 1, pp. 36–43, jan. 2011, https://doi.org/ 10.1016/j.ijthermalsci.2010.09.005. [14] a. kasaeian, m. ghalamchi, and m. ghalamchi, “simulation and optimization of geometric parameters of a solar chimney in tehran,” energy conversion and management, vol. 83, pp. 28–34, jul. 2014, https://doi.org/10.1016/j.enconman.2014.03.042. [15] j. mathur, n. k. bansal, s. mathur, m. jain, and anupma, “experimental investigations on solar chimney for room ventilation,” solar energy, vol. 80, no. 8, pp. 927–935, aug. 2006, https://doi.org/10.1016/j.solener.2005.08.008. [16] a. li, p. jones, p. zhao, and l. wang, “heat transfer and natural ventilation airflow rates from single-sided heated solar chimney for buildings,” journal of asian architecture and building engineering, vol. 3, no. 2, pp. 233–238, nov. 2004, https://doi.org/10. 3130/jaabe.3.233. [17] x. zhou, f. wang, and r. m. ochieng, “a review of solar chimney power technology,” renewable and sustainable energy reviews, vol. 14, no. 8, pp. 2315–2338, oct. 2010, https://doi.org/10.1016/ j.rser.2010.04.018. [18] c. m. rhie and w. l. chow, “numerical study of the turbulent flow past an airfoil with trailing edge separation,” aiaa journal, vol. 21, no. 11, pp. 1525–1532, nov. 1983, https://doi.org/10.2514/3.8284. microsoft word 36-3826_s_etasr_v10_n5_pp6362-6367 engineering, technology & applied science research vol. 10, no. 5, 2020, 6362-6367 6362 www.etasr.com almalaq & matin: two-switch high gain non-isolated cuk converter two-switch high gain non-isolated cuk converter yasser almalaq electrical engineering department university of hail hail, saudi arabia yasseram1107@hotmail.com mohammad matin department of electrical & computer engineering university of denver denver, usa mohammad.matin@du.edu abstract−this paper introduces a two-switch high gain nonisolated cuk converter which can be used as a high gain dc-dc converter in renewable energy, such as photovoltaic and fuel cell, applications because their output is low. as the conventional, the proposed cuk converter provides negative output voltage but with a higher voltage in magnitude. the main advantage of the proposed converter is having lower voltage stress with the ability to maintain a higher voltage gain. by combining a switchedinductor and a switched-capacitor into the conventional cuk converter, the proposed cuk converter has the ability to reach 13 times the input voltage for a duty cycle d of 0.75. also, by attaching more switched-inductors to the proposed cuk converter, more voltage gain can be achieved. a complete theoretical analysis of the continuous conduction mode (ccm) of the proposed cuk converter is presented and the key aspects of the circuit design have been derived. also, a comparison in terms of voltage gain and voltage stress between the proposed cuk converter and cuk converters using other techniques is presented. the proposed cuk converter has been designed for 100w rated power, -152v output voltage, 50khz switching frequency, and 75% duty cycle. the presented converter is simulated in matlab/simulink and the results are discussed. keywords-cuk converter; dc-dc converters; photovoltaic; switched-inductor; switched-capacitor i. introduction due to the expected depletion of the traditional energy sources, the world pays growing attention to alternative ones [1]. nowadays, most attention goes to the photovoltaic (pv) energy source because it is a pollution free, stable system, and has continuous reduction in cost [2]. the price of a pv panel went from $4.90/wpk in 1998 down to $1.28/wpk in 2011 which means 74% reduction. pv systems are used today in many applications, such as water pumping, battery charging, home power supply, etc. [3-5]. figure 1 shows a block diagram of a typical sustainable energy system, which is composed of renewable energy sources, a high step-up dc-dc converter, a dc grid, and an inverter for ac applications. usually, the rated voltage of renewable energy sources, such as pv and fuel cell, is at low level, and thus, a high gain dc-dc converter is required. generally, the most commonly used topology to supply high output voltage is the conventional boost converter. however, when the conventional boost converter is operated at a high output voltage, the duty cycle will become unity. this will lead to induce high current ripple, low efficiency, and result in severe reverse-recovery as well as high electro magnetic interference (emi) problems [6-8]. many high stepup dc-dc converters have been proposed and are utilized in renewable energy applications [9-16]. fig. 1. a typical renewable energy source system. in this paper, the main aim was to design a dc-dc converter with high voltage gain and low voltage stress on the main semiconductor switch. this was done by integrating both the switched-inductor and the switched-capacitor techniques into the conventional cuk converter. the cuk converter has many advantages over other non-isolated converters, such as having non-pulsating input and output currents, low output voltage ripple, and good steady-state performance [17-19]. ii. power circuit a mosfet, a diode, a capacitor, and an inductor have been added to the conventional cuk converter to maintain high voltage gain and low voltage stress in order to form the proposed cuk converter as shown in figure 2. a mosfet and an inductor are added to form the switched-inductor in which the two inductors are charged in parallel when the two mosfets are on, and they get discharged in series when the two mosfets are off. moreover, the diode and the capacitor are added to perform the switched-capacitor in which the two capacitors are discharged in series when the two mosfets are on, and they get charged in parallel when the two mosfets are off. iii. modes of operation the proposed cuk converter is analyzed in continuous conduction mode (ccm). the operation of the proposed converter is that either both the mosfets are simultaneously on or off. thus, two modes of operation exist. corresponding author: yasser almalaq engineering, technology & applied science research vol. 10, no. 5, 2020, 6362-6367 6363 www.etasr.com almalaq & matin: two-switch high gain non-isolated cuk converter fig. 2. the proposed cuk converter. a. on-mode when the two mosfets s1 and s2 are simultaneously conducting, the two inductors l1 and l2 of the switchedinductor are charged in parallel by the input supply voltage vin. the current direction is shown in figure 3. also, the two diodes d1 and d2 are reversed-biased, and therefore the two capacitors c1 and c2 get discharged in series. the load is supplied by the input voltage vin and the discharged energy from the two capacitors c1 and c2. fig. 3. the proposed cuk converter in on-mode. b. off-mode when the two mosfets are simultaneously not conducting, the two inductors of the switched-inductor are discharged in series. the current direction is shown in figure 4. fig. 4. proposed cuk converter in on-mode in off-mode. also, the two diodes are forward-biased, and therefore the two capacitors are charged in parallel. the load is supplied by the input voltage vin and the discharged energy from the two inductors. the switching diagram of the steady-state waveforms with enlarged variations in ccm of the proposed cuk converter is shown in figure 5. fig. 5. main steady-state waveforms of proposed cuk converter. iv. circuit analysis to simplify the analysis, it is assumed that the proposed cuk converter is operating in steady-state. likewise, the following assumptions are made: all components are ideal (100% efficiency), the input voltage vin is pure dc, and all capacitors c1, c2, and cout are sized to have a relatively small voltage ripple at a switching frequency (f). when the two mosfets s1 and s2 are on, the voltage across the inductors l1, l2, and lout are expressed in (1) and (2) (c1=c2=c): v�� � v�� � v�� (1) v�� � v�� � 2v �v��� (2) where vc stands for the voltage across capacitors c1 and c2. when the two mosfets s1 and s2 are off, the voltages across the inductors l1, l2, and lout are expressed in (3) and (4): v�� � v�� � ������ � (3) v�� � v �v��� (4) engineering, technology & applied science research vol. 10, no. 5, 2020, 6362-6367 6364 www.etasr.com almalaq & matin: two-switch high gain non-isolated cuk converter the expressions in (5) and (6) can be obtained by applying the volt-second method to the inductors l1, l2, and lout: v��d �� ������ � ��1 �d� � 0 (5) �v�� �2v �v����d ��v �v�����1 �d� � 0 (6) from (5), the voltage across c1 and c2 is expressed in (7): v � �� !� ���!� v�� (7) by substituting (7) into (6), the ideal voltage gain in ccm for the proposed cuk converter is expressed in (8): m # � �� ��� � $��$� � �� %!� ���!� (8) the output inductor average current i�� can be considered equal to the output average current iout. therefore, (9) is obtained from (8). i�� � i��� � ���!� �� %!� i�� (9) also, the input inductor currents can be obtained in (11) by using (10). i�� � '2i�� � i�� (d �i��1 �d� (10) i� � i�� � i�� � �� !� �� %!� i�� � �� !�)� �� %!���� (11) the voltage stress across the two diodes d1 and d2 are expressed in (12): v!� � v!� � � ���!�v�� (12) the voltage stresses across the two mosfets are expressed in (13): v*� � v*� � � ���!� v�� (13) the peak-to-peak variation in input inductor’s currents (∆i��� � ∆i�� � ∆i��) is expressed in (14): ∆i��� � ∆i�� � ∆i�� � !-��� ��� � !��� .��� (14) the peak-to-peak variation in output inductor’s current ∆i�� is expressed in (15) ∆i�� � !-���� ������ � �� � !���� ������ � .�� (15) the peak-to-peak variation in capacitor’s voltage ∆v is expressed in (16). ∆v � !-$� � !)� #��0���. (16) v. circuit extensions more switched-inductors can be attached to the proposed cuk converter instead of the single inductors at the input side. this will lead to increase the voltage gain ratio even more. also, to reduce the size of magnetic components, the inductors can be integrated into one magnetic core. a. attaching more switched-inductors in order to increase the voltage gain even more, the single inductors at the input side of the proposed cuk converter can be replaced with a switched-inductor. in this case, the voltage gain reaches above 23 when d=0.75. the power circuit is shown in figure 6. the voltage gain can be expressed as: m # � �� ��� � d ��1 �d� �� %!����!� (17) fig. 6. more switched-inductors attached. b. coupled inductors actually, all the inductors presented in the last section share the same value of inductance and have the same operation condition. therefore, to reduce the size of magnetic components, the inductors can be integrated into one magnetic core as shown in figure 7. fig. 7. magnetic components integration. vi. comparison analysis in table i, a comparison can be seen between the proposed cuk converter, the single-switch cuk converter [20], the hybrid switched-capacitor cuk converter [21], the three-switch cuk converter [22], and the conventional cuk converter in terms of voltage gain, voltage stress, and number of components. the voltage gain and the voltage stress are graphically represented in figures 8 and 9 respectively. as can be seen in figure 8, the highest voltage gain can be accomplished by the proposed cuk engineering, technology & applied science research vol. 10, no. 5, 2020, 6362-6367 6365 www.etasr.com almalaq & matin: two-switch high gain non-isolated cuk converter converter. however, the converter having the lowest voltage gain is the conventional cuk converter. as can be seen in figure 9, the converter having the highest voltage stress is the conventional cuk converter. on the other hand, the lowest voltage stress can be maintained using the proposed cuk converter. therefore, the proposed cuk converter is suitable for applications requiring higher voltage gain with lower voltage stress. table i. proposed and other cuk converters comparison cuk converters gain (mccm) switches count diodes count capacitors count inductors count proposed �1 � 3d� �1 � d� 2 2 3 2 single-switch [20] 2 �1 � d� 1 3 3 1 hybrid sc [21] �1 � d� �1 � d� 1 2 3 2 three-switch [22] 1 �1 � d� 1 2 2 1 conventional d �1 � d� 1 1 2 2 fig. 8. voltage gain comparison. fig. 9. normalized voltage stress comparison on active switches. vii. simulation verification and discussion a prototype 12/-152v design is developed in matlab/simulink to verify the performance of the proposed cuk converter. a simulink prototype has been designed in matlab as shown in figure 10. the simulation specifications of the proposed cuk converter are 12v input voltage, -152v output voltage, 100w rated power, 50khz switching frequency, and 75% duty cycle. detailed parameter values are shown in table ii. the voltage stress and current stress across the two mosfets s1 and s2 are 47v and 5a respectively. the voltage stress and current stress waveforms are shown in figure 11. figure 12 shows the voltage waveforms of diodes d1 and d2 which each one has a voltage stress of -90v. diodes d1 and d2 are reversed biased when the two mosfets s1 and s2 are on, and they are forward-biased when the two mosfets s1 and s2 are off. the voltage waveform of the two capacitors c1 and c2 is shown in figure 13. the current waveforms of the three inductors l1, l2, and lout are shown in figure 14. fig. 10. simulink model of the proposed cuk converter. table ii. design specifications of the proposed cuk converter parameter value input voltage (v��) 12v output voltage (v���) -152v rated power (p���) 100w switching frequency (f) 50khz duty cycle (d) 75% inductors (l�, l�, and l���) 600µh capacitors (c� and c�) 22µf load (r��67) 230ω fig. 11. voltage and current waveforms across mosfets s1 and s2. engineering, technology & applied science research vol. 10, no. 5, 2020, 6362-6367 6366 www.etasr.com almalaq & matin: two-switch high gain non-isolated cuk converter fig. 12. voltage waveform across diodes d1 and d2. fig. 13. voltage waveform across capacitors c1 and c2. fig. 14. current waveforms across inductors l1 and l2. finally, the input voltage vin (12v), the output voltage vout (-152v), and the output power pout (100w) waveforms are shown in figure 15. the efficiency of the proposed cuk converter is calculated as the output power increase as shown in figure 16. the highest efficiency is 92% when the output power is 180w. when the input voltage is increased, the efficiency of the proposed cuk converter is increased because the input current decreases, and therefore, the conduction losses on switches get reduced. fig. 15. waveforms of vin, vout, and pout. fig. 16. efficiency curve as a function of the output power. viii. conclusion a 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[22] dongyan zhou, a. pietkiewicz, and s. cuk, “a three-switch highvoltage converter,” ieee transactions on power electronics, vol. 14, no. 1, pp. 177–183, jan. 1999, doi: 10.1109/63.737606. microsoft word 3-rounian.doc engineering, technology & applied science research vol. 4, no. 1, 2014, 576-580 576 www.etasr.com rooniyan: the effect of confluence angle on flow pattern at a rectangular open-channel the effect of confluence angle on the flow pattern at a rectangular open-channel firooz rooniyan department of civil engineering islamic azad university, ahar branch ahar, iran pirooz.rounia@gmail.com abstract—flow connection in channels is a phenomenon which frequently happens in rivers, water and drainage channels and urban sewage systems. the phenomenon appears to be more complex in rivers than in channels, especially at the y-junction bed joint that causes erosion and sedimentation at some areas resulting to morphological changes. flow behavior at the channel junction area depends on variables such as channel geometry, discharge ratio, tributary width and y-junction connection angle of the channel, bed level changes at the bed joint, flow characteristic at the bed joint upstream and flow froude number in different sections. in this research, fluent numerical model and junction angles of 30o, 45o & 60o are used to analyze and evaluate the effect of channel junction geometry on the flow pattern and the flow separation zone dimensions in different ratios of flow discharge (upstream channel discharge to total discharge of the flow). results for two ratios of flow discharge are represented. results are in agreement with earlier studies and it is shown that the change of the channel crossing angle affects the flow pattern in the main channel and also that the dimensions of the created separation zone in the main channel become larger when the crossing angle increases. this phenomenon can also be observed when the flow discharge ratio is lower. analysis showed that the least dimension of the separation zone will be at the crossing angle of 45o . keywordsflow pattern; transverse channel; y-junction; rectangular channel; fluent numerical model i. introduction one of the flows which leaves important effects on river and channels bed i.e. erosion, scour and sedimentation is the so called transverse flow, which in fact is formed as the result of the collision of two flows with similar or different characteristic. various parameters affect the flow pattern in transverse channels and thus analysis may be difficult. these parameters include geometric parameters (channel form, channel dimensions, angle between main and tributary channel) and hydraulic parameters (froude number of flow, discharge ratio in main and tributary channel). taylor [1] was the first to analyze flow issues in transverse channels. by analyzing momentum equation he represented an equation to obtain flow depth ratio in upstream and downstream channels. hsu at el. [2] represented an equation to obtain flow depth ratio by solving of energy and momentum equations. they also analyzed transverse channels with the angles of 30o, 45o & 60o . weber et al. [3] tested flow patterns at 90o transverse channels. the data evaluated by weber and his colleagues were in the form of three dimensional speeds along with speed and flow depth variations. these data provided an equivalent bed for validity measurement of mathematical models. ramamurthy et al. [4] studied flow characteristics at the confluence of a rectangular open channel of 90o including equal width and they also analyzed the flow pattern at the confluence of channels by using three dimensional turbulence models and evaluated their results by using lab data. lab data confirmed the accuracy of their three dimensional turbulence model. nania et al. [5] perform a lab study on subcritical flows at the four-way intersection with equal width and two inflows and two outflows. results indicated that there is a linear relation between five dimensionless parameters which include the inflow ratio, the outflow ratio, the inflow froude number in one direction and the outflow depth ratio. they also represented an acceptable prognosis about flow distribution at a channel junction. ghobadian [6] analyzed the effect of downstream water level changes on the secondary flow pattern at the confluence of a rectangular open channel and showed that it is possible to simulate the transverse flow by using a three dimensional model. qohari [7] analyzed the flow pattern at the 90o junction by using fluent and lab models and resulted that the fluent numerical model had the capability to simulate the flow dynamic at channels junction and also that the simulation of the secondary flow at the junction of 90o was satisfying and that there was a correlation between the results. ii. materials and methods in this article, the effect of two important parameters is analyzed. simulation for all represented flow ratios is shown in table i and for cross sections of x*= 5.5 to x*= 8.38 are shown in figure 1. three junction angles of 30, 45 and 60 were employed for the two parameters i.e. channel junction angle and flow discharge ratio. lines of longitudinal and latitudinal flow near the bed and flow level were done only for two discharge ratios of q*=0.083 and q*=0.917. nowadays, developing and applying three dimensional mathematical models at river engineering is very popular although the engineering, technology & applied science research vol. 4, no. 1, 2014, 576-580 577 www.etasr.com rooniyan: the effect of confluence angle on flow pattern at a rectangular open-channel accuracy of developed models has always to be confirmed. however, considering the expenses related to lab instruments and the limitations of measuring machines, it is easy to understand why the application of numerical models has increasing in hydrology. the fluent 6.3.26 software is used in this article. table i. lab data specifications for flow at junctions qm(m 3/sec) 0.014 0.042 0.071 0.099 0.127 0.156 qb(m 3/sec) 0.156 0.127 0.099 0.071 0.042 0.014 q*=qm/(qm+qb) 0.083 0.25 0.417 0.583 0.75 0.917 iii. governing equations governing equations on motion of viscous incompressible fluid in the condition of turbulence are expressed by navier stokes equations. the cohesion equation (conservation of mass) and the momentum equation (conservation of momentum) are: 0i i u x    (1) and 1 ( ) i ji i ij i i i u uu p g t x x x               (2) in which, ui denotes the velocity component in the direction of xi, p is the total pressure, ρ is the fluid’s density, gi is the gravity acceleration in the direction of xi and τij is the stress tensor responsible of the effect of the turbulence eddy. fluent is a two or three dimensional analysis software of flow which is able to model fluid flow and heat transfer in complex geometries by using cohesion equations and navierstokes. this software is written in c and uses the constrained volume method. all flow analyses are performed in the steady condition and the simple algorithm is used to couple velocity and pressure. fig. 1. different flow velocity measurement at channel. the breaching method of momentum equations, the loss of turbulent kinematical energy and reynolds stresses have been selected as two order modern methods and the breaching method of pressure equation is selected as a standard method. also k-ω is selected as a turbulent method and the equivalent grillage is considered in the area under viscous area and near the wall. field geometry is provided using gambit 2.3.16 software. the distance of the first node at the under-viscous area is considered 1mm and gradually by going far from the bank, the distance of the nodes becomes larger and the become coarser. iv. results a. flow longitudinal velocity lines flow velocity lines at the xy plate for the three junction angles (i.e. 30, 45, 60) and for flow near the level (z*=0.278) and near the bed (z*=0.014) is depicted in figures 2 to 7. these diagrams have been drawn for the maximum discharge ratio of flow (q*=0.197) and the minimum discharge ratio of flow (q*=0.083) as shown in table i. it was observed that the combination of main and tributary channel flow resulted in the formation of a secondary flow which is affected by the flow discharge ratio and the junction angle. this secondary flow is completely three-dimensional and turbulent. this issue can be mostly observed in the junction of 45o and 60o and for a discharge ratio of q*=0.083 (figures 4 and 6). velocity lines for different junction angles get closer to the left bank near the level and closer to right bank near the bed. this issue occurs due to the flow momentum difference at the level in comparison with the bed, and this causes the flow separation zone dimensions at the level to become larger compared to the ones at the bed. tables iv and v verify this claim. the separation zone is observed in all simulations and for other flow discharge ratios. in case of a discharge ratio of q*=0.917 (high main channel discharge), a turbulence mostly extend into the tributary channel which causes the formation of a separation zone in the left bank of the tributary channel (figure 9), and decrease the dimensions of the separation zone at the main channel. this occurs because of the high momentum of the main channel. b. parametric study of junction angle effect on flow profile in this section, a parametric study of flow junction angle effect analyses is performed on the separation zone dimensions at the main channel downstream. therefore, three junction angles of 30o, 45o & 60o have been evaluated. all six ratios of flow regarding the model and the effect of the junction angle on the separation zone dimensions have been analyzed for each angle. model outlets show that the separation zone occurs in all discharge ratios for all three junction angles. also that it reaches its minimum value at the junction of 45o and in both ratios of flow at the bed and level. engineering, technology & applied science research vol. 4, no. 1, 2014, 576-580 578 www.etasr.com rooniyan: the effect of confluence angle on flow pattern at a rectangular open-channel fig. 2. streamlines at 30°junction for q*=0.083 near water surface and flow bottom. fig. 3. streamlines at 30°junction for q*=0.917 near water surface and flow bottom. fig. 4. streamlines at 45°junction for q*=0.083 near water surface and flow bottom. fig. 5. streamlines at 45°junction for q*=0.917 near water surface and flow bottom. fig. 6. streamlines at 60°junction for q*=0.083 near water surface and flow bottom. fig. 7. streamlines at 60°junction for q*=0.917 near water surface and flow bottom. engineering, technology & applied science research vol. 4, no. 1, 2014, 576-580 579 www.etasr.com rooniyan: the effect of confluence angle on flow pattern at a rectangular open-channel this phenomenon can be observed by in the represented values in tables iv and v for the dimensions of the created rotational zone in the main channel. in this table, the separation zone length and width at the channel of 45o for the flow ratio q*= 0.083 is equal to 0.09 and 0.012 at the bed, and at the level is equal to 1.3 and 0.1 and for the flow ratio of q*= 0.917 it is equal to 0.007 and 0.003 at the bed and equal to 0.14 and 0.005 at the level. by comparing these values with other values in tables iv and v the following can be noticed:  the separation zone at the junction of 45o is smaller than the other angles.  the flow separation zone of this junction angle is small. also, by increasing the flow ratio from 0.083 to 0.917 the separations zone dimensions become smaller. by referring to figures 4 and 6, it can be noticed that at a flow ratio of q*=0.083 and for junction angles of 45o and 60o, a turbulent zone is formed at the left of the main channel with longitudinal velocity vectors being in this area. analysis indicates that the dimensions of turbulence at 45o junction have a decreasing trend in comparison to the 60o junction and that at any of these junctions’ turbulent zone dimensions decrease from bed to level (figure 8). dimensions of turbulence for two angles which verifies this fact is represented in table (2). table ii. dimensions of turbulent in main channel no. q*=qm/(qm+qb) junction angle bottom (z*) distance to channel (l*) zone length (d*) zone width 1 0.083 60 0.014 1.1 0.29 2 0.083 60 0.278 0.48 0.08 3 0.083 60 0.014 1.7 0.32 4 0.083 60 0.278 1.6 0.15 in addition outlets indicate a separation zone inside the tributary channel near the left bank at the junction of 45° and 60° for flow ratio of q*=0.917 which this zone was not observed in 30° angle. this is because of high flow discharge in main channel which causes some part of created turbulent in main channel extend into tributary channel and from turbulent zone in tributary channel. by comparing table (3) values that indicate dimensions of turbulent zone in tributary channel, it can be resulted that dimensions of this zone at the junction of 45° than the junction of 60° has increasing trend regarding length but decreasing trend in the respect of width. also it was observed that created separation zone dimensions decrease from bed to level for a specified junction angle. as shown in figures 2 to 7, for a specific junction angle increased flow discharge ratio relates to decreased flow separation zone dimensions. another result is that a change of junction angle and flow ratio will cause the flow separation zone in the main channel to be displaced. a decrease of the junction angle or an increase of the discharge ratio, will cause it to be inclined towards the right bank and at the bed, in comparison to the level, it becomes closer to the right bank. fig. 8. separation zone in tributary channel at 60°junction for q*=0.083 near water surface and flow bottom. fig. 9. separation zone in tributary channel at 60°junction for q*=0.917 near water surface and flow bottom. engineering, technology & applied science research vol. 4, no. 1, 2014, 576-580 580 www.etasr.com rooniyan: the effect of confluence angle on flow pattern at a rectangular open-channel table iii. dimensions of the separation zone in the tributary channel no. q*=qm/(qm+qb) junction angle bottom (z*) distance to channel (l*) zone length (d*) zone width 1 0.917 60 0.014 0.7 0.2 2 0.917 60 0.278 0.3 0.1 3 0.917 60 0.014 1.13 0.43 4 0.917 60 0.278 0.07 0.13 table iv. dimensions of the roller zone for q*=0.083 and q*=0.917 near the flow bottom. no. q*=qm/(qm+qb) junction angle bottom (z*) distance to channel (l*) zone length (d*) zone width 1 0.083 60 0.014 1.25 0.0625 2 0.917 60 0.014 0.047 0.005 3 0.083 45 0.014 0.09 0.012 4 0.917 45 0.014 0.007 0.003 5 0.083 30 0.014 0.7 0.025 6 0.917 30 0.014 0.022 0.004 table v. dimensions of the roller zone for q*=0.083 and q*=0.917 near the water surface no. q*=qm/(qm+qb) junction angle bottom (z*) distance to channel (l*) zone length (d*) zone width 1 0.083 60 0.278 1.9 0.175 2 0.917 60 0.278 0.3 0.013 3 0.083 45 0.278 1.3 0.1 4 0.917 45 0.278 0.14 0.005 5 0.083 30 0.278 1.45 0.1 6 0.917 30 0.278 0.46 0.02 v. conclusion in this article, flow profile and flow separation zone dimensions at three junction angles of 30°, 45° and 60° for flow ratio of q*=0.083 and q*=0.917 have been investigated by using a fluent numerical model. formation of the flow rotational zone and turbulence are simulated fairly good and the following results are obtained:  for a discharge ratio of q*=0.917 in the case that main channel discharge is high, created turbulence will be drawn mostly into the tributary channel and will decrease the separation zone dimensions in the main channel and also cause another separation zone in the tributary channel due to the high momentum of the main channel.  in a specific junction angle and constant flow ratio, separation zone dimensions increase from bed to level.  simulation indicate that flow separation zone occurs at any of the six discharge ratios and for all junction angles and at the junction of 45° it reaches the minimum value for both flow ratios.  flow separation zone dimensions at the downstream of the main channel decrease with the increase of flow discharge ratio for a specific junction angle.  for a discharge ratio of q*=0.083 and at the junction angle of 45° and 60°, a turbulent zone is formed at the left side of the main channel, created by the high momentum of tributary channel. analysis indicate that turbulence dimensions are larger at the junction of 45° than at the junction of 60° and that turbulence dimensions decrease from bed to level at both junctions. also longitudinal velocity vectors are negative in this area.  for a specific discharge ratio and with an increase of junction angle, separation zone dimensions increase, a process observable at level and near the bed.  obtained results showed that the angle of 45o has the least effect on the main channel flow compared to the two angles and that this angle can be considered as an optimum angle at channel junctions. references [1] e. h. taylor, “flow characteristics at rectangular open-channel junctions”, transactions of the american society of civil engineers, vol. 109, pp. 893–902, 1944 [2] c. c. hsu, f. s. wu, w. j. lee, “flow at 90° equal-width open-channel junction”, asce journal of hydraulic engineering, vol. 124, no. 2, pp. 186–191, 1998 [3] l. j. weber, e. d. shumate, n. mawer, “experiments on flow at a 90° open channel junction”, asce journal of hydraulic engineering, vol. 127, no. 55, pp. 340–350, 2001 [ 4 ] a. s. ramamurthy, j . qu, d. vo, “numerical and e xperimental study of dividing open-channel flows”, asce journal of hydraulic engineering, vol. 133, no. 10, pp. 1135-1144, 2007 [5] l. s. nania, m. gomez, j. dolz, p. comas, j. pomares, “experimental study of subcritical dividing flow in an equal-width, fourbranch junction”, asce journal of hydraulic engineering, vol. 137, no. 10, pp. 1298-1305, 2011 [6] r. ghobadian, “analysis of tailwater surface level on secondary flow profile at rectangular open-channel junction by 3-d cfd model”, 4th national congress of civil eng., tehran university, tehran, iran, 2010 [7] s. gohari, “lab comparison of flow pattern between diversion and cross flow”, 9th civil eng. national congress, may 8-10, esfahan university of technology, esfahan, iran, 2012 microsoft word 15-2536_s engineering, technology & applied science research vol. 9, no. 2, 2019, 3949-3954 3949 www.etasr.com alfaraidy & azzam: residential buildings thermal performance to comply with the energy … residential buildings thermal performance to comply with the energy conservation code of saudi arabia faris a. alfaraidy northern border university arar, saudi arabia falfaraidy@gmail.com salah azzam northern border university arar, saudi arabia salah.alazzam@gmail.com abstract—about half of the total generated electricity in saudi arabia (sa) is consumed for the air conditioning of residential buildings. to reduce this burden on the economy as outlined by the country's 2030 vision, the implementation of the saudi energy conservation code (sbc602) needs to be enforced. this code divided ksa into three climate zones with maximum overall heat transfer coefficients. this study aims to facilitate the use of thermal insulation by analyzing optimum thermal insulation thickness for each zone and calculate the payback period of initial insulation costs. three cities were selected to represent the three climate zones, riyadh, arar, and turaif. the codecompliant thermal insulation thickness is calculated using these variables: thermal properties of three insulation materials, overall heat transfer coefficients, and three insulated wall structures. it is concluded that external insulation and finish system utilizing polyurethane is the most feasible option with the best thermal performance. polyurethane thicknesses are ranging from 45mm to 65mm, wall widths are ranging from 250mm to 320mm, while the overall costs are ranging from 20.02 to 24.57 us$/m 2 . this system is used to conduct a comparison between energy-efficient-building and base-case-building in terms of cooling loads and electrical consumption using hourlyanalysis-program (hap) with international weather data. the simulated annual savings in energy consumption for the three zones are 67.4%, 66.56%, and 67.91%. the economic analysis shows promising payback years, which are 3.1, 3.9, and 4.3 for zone one, zone two and zone three respectively. keywords-energy efficiency code; thermal insulation; residential buildings i. introduction the demand for electricity is growing rapidly in sa due to increase in population and building construction. it grew 33% over the last 5 years [1]. even before the 2030 vision, which outlined the future for sa beyond oil and gas, the government considered an imperative strategy to lower carbon economy and energy efficiency as a major topic for all decisions related to the increase in demand for fuel and feedstock [2]. it is estimated that 2.32 million new houses are to be built by 2020 in order to meet the demands of the growing population [3]. buildings are the largest energy consumer, with 50.36% of total consumption in 2016 [4]. furthermore, the consumption in governmental and commercial sectors makes total building consumption in residential, commercial and governmental sectors about 80.6%. table i shows the total share of building sector among other sectors. table i. electricity consumption in sa (2016) annual (103gwh) share in total % residential 144 50.4 80.6 commercial 47 16.4 government 39 13.8 industrial 45 15.8 19.4 others 10 3.7 total 286 100 100 in developing buildings in sa, the appropriate selection of construction materials would reduce energy consumption for cooling load by 59% [5]. a substantial saving in annual energy subsidies can be achieved by the government if it promotes energy efficiency investments and incentives [6]. author in [7] found that the payback periods for riyadh city were 2.3-2.7 years for polystyrene and 2-2.5 for polyurethane. a recent study showed that air conditioning has the largest segment of power consumption [8]. the statistics on this issue indicate that 60% of the monthly consumption is caused by air conditioning. author in [9] studied the electrical consumption relation with the climate zones of sa. in riyadh city (climate zone 1) the ac consumption is 70%, in tabuk (climate zone 2) the ac consumption is 63% and in abha (climate zone 3) the ac consumption is 49%. therefore, sa has developed regulations regarding building energy efficiency to achieve energy efficient buildings which became mandatory in 2010 [10]. this code was formulated based on the international energy efficiency code (2003) and the american society of heating, refrigerating, and air-conditioning engineers (ashrae). hence, saudi standard metrology and quality organization issued standard no. 28793/2014 thermal transmittance values for residential buildings [11]. a. research problem more than 71% of the residential buildings in sa are not energy efficient and lack the use of thermal insulation [12]. sa is a hot area and most of its terrain consists of arid desert or corresponding author: faris a. alfaraidy engineering, technology & applied science research vol. 9, no. 2, 2019, 3949-3954 3950 www.etasr.com alfaraidy & azzam: residential buildings thermal performance to comply with the energy … barren landforms. therefore there is an extensive use of air conditioning in buildings. interviews with concerned people in the region, like contractors, design engineers, consultants, officials, etc. showed that the reason behind the lack of thermal insulation is mainly its high initial cost, while some interviewers pointed out their lack of knowledge regarding the right architectural installation of thermal insulation. this study aims at facilitating the use of thermal insulation as outlined by sbc602 and to study economic feasibility and energy savings. b. hourly analysis program (hap) it is common to use cooling degree-days to estimate the annual thermal loads as the summation of temperature differences between the building exterior and interior temperatures. as a building's base temperature typically varies throughout the year, the accuracy of degree-days method was very ambiguous and therefore not helpful to energy experts who need robust tools and clear guidance. finally, the combined effect of these problems leads to low accuracy in degree-day calculations. computer based programs are recently used to design heating ventilation and air conditioning (hvac) systems and simulate their energy consumption. hvac presents accurate and reliable methods for engineers and planners. for instance, authors in [13] conducted computer simulations and energy performance studies for a typical residential building and prevalent conditions in the gulf region. one of these computer programs is hourly analysis program (hap). hvac loads are designed using hap to calculate thermal loads and to simulate energy consumption. it uses ashrae-endorsed heat transfer method using detailed 8,760 hour by-hour simulation techniques for energy analysis. it computes hourly cooling loads based on simulated outside temperatures and used historical temperatures logs for many years to give relatively accurate estimation of annual energy consumption. besides, it calculates all heat gains including internal heat gains. it requires scheduling on hourly basis the occupancy of people inside the building, schedules for lighting and home appliances. c. design weather data for the purposes of sbc 602, saudi arabia is divided into 3 climate zones. the selected cities represent those zones (table ii). weather design data for the 3 cities were obtained from ashrae climatic design conditions [14]. annual cooling and enthalpy design conditions, design dry bulb and wet bulb temperatures have been obtained for the 3 cities. table ii. selected cities representing the climatic zones city region climate zone riyadh southern region i arar northern region ii turaif northern region iii d. international weather for energy calculations (iwec 2) the weather data for the three cities are derived from ashrae data base. integrated surface hourly (ish) weather data were archived at the usa national climatic data center. for the selected cities, the ish database contains 12 years of hourly loggings of dry-bulb temperature, wet pulp temperatures and solar radiation [15]. e. base-case building a typical residential building is studied in each of the three cities. most buildings are poorly energy efficient and lack the use of thermal insulation. building's details were used as inputs for later examination using hap for building hvac design and simulation. these details included building drawings, elevations, building structure, external walls and thermal insulations. the base-case building characteristics including architectural and hvac status are summarized in table iii. table iii. energy conservation requirements of sbc 602 item energy efficient building base-case building general front elevation facing south west, rectangular shape, low height building consisting of two floors, 300m 2 area, floor to floor height 3.5m occupancy 7 people wall and roof u wall: 0.342/0.387/0.453 for zones 1, 2,3 2.180 roof: 0.202/0.238/0.273 for zones 1 ,2 ,3 2.449 door u 2.839 for all zones 5.3 window overall u 2.668 for all zones 5.048 window type aluminum frame with thermal breaks or pvc aluminum frame internal shading vertical blinds/drapes closed weave light color. drapes-open weave – medium glass type double glazed with 12mm air space 6mm single glass external color light medium shgc for all zones ≤ 0.25 0.5 sri light color with sri≥50 medium color sri=25 water absorption for insulation materials ≤0.3% na continuous insulation continuous across all building envelope na ventilation 54.5l/s same infiltration in fenestration ≤1.5l/s/m 2 same infiltration in foors ≤2.5l/s/m 2 same lighting power density 10w/m 2 ground floor, 6 w/m 2 first floor same equipment power density 2.0kw ground floor,1.0kw first floor same vertical fenestration area ≤25% of the wall area no restriction eer eer≥11 no restriction u: overall heat transfer coefficient (w/m 2 .ok), shgc: solar heat gain coefficient, sri: surface reflectance index, eer: minimum energy efficiency ratio, f. building energy conservation requirements (sbc 602) saudi building code energy conservation requirements sbc 602 has minimum performance for the design of energyefficient buildings and structures. these requirements address the design of energy-efficient building envelopes. the minimum performance requirements for energy efficient buildings in comparison with the base case building are summarized in table iii. ii. architectural installation of thermal insulation a. wall structure i: double wall system (dws) dws requires the constructing of external wall besides the internal wall, while thermal insulation is inserted in the wall cavity. hollow concrete blocks are conventional architectural engineering, technology & applied science research vol. 9, no. 2, 2019, 3949-3954 3951 www.etasr.com alfaraidy & azzam: residential buildings thermal performance to comply with the energy … style in the region with external finish of decorative profile painting as shown in figure 1. fig. 1. wall type i: dws b. wall structure ii: external insulation and finish system (eifs) in this wall type, insulation materials are installed on the external wall surface and cladded by mechanical means as illustrated in figure 2. many cladding materials may be used like stone, marble, granite, ceramics and fiber cement boards. the use of fiber cement board in external insulation system might be applied according to [16]. in this regard, the fiber cement board should be free of asbestos [17], strong, flat and flexible board composed of portland cement, refined ores and reinforced cellulose fiber as main materials. fig. 2. wall type ii: eifs eifs should be compliant with international standards and specifications related to surface roughness, density, moisture movement, bending strength, impact resistance, shrinkage and expansion and resistance to fungus growth [18]. also, it should be compliant with safety standards and fire resistant for 2 hours of fire for interior or exterior wall system with no failure [19]. c. wall structure iii: internal insulation and finish system (iifs) in this system, the thermal insulation material is installed on the interior part of the wall. it uses fiber cement boards to build the internal partition while insulation material is installed behind it using mechanical fixing. the main difference between eifs and iifs is that iifs usually has thermal bridges in the roof slabs and the columns that are installed inside the building will restrict the selection of insulation material to be highly fire resistant like rock wool as shown in figure 3. fig. 3. wall type iii: iifs iii. design hvac loads and energy consumption a. program input data a brief summary of input data consisting of weather data, heat transfer coefficient for wall structure, roofs, windows, doors, fenestration, ventilation, and infiltration, is listed in table iv. table iv. basic assumption data for energy efficient building for hap 4.9 weather data arar sau_arar_403570_iw2.csv turaif sau_turaif_403560_iw2 riyadh sau_riyadh obs(oap)_404380_iw2 indoor conditions summer dry bulb temperature 24.0 ° summer relative humidity 50% winter dry bulb temperature 21.0 °c winter relative humidity 30% ventilation requirements occupant ventilation 2.5l/s/person floor ventilation requirements 0.30l/(s×m²) overhead lighting recessed (vented) 10.00w/m² ballast multiplier 0.87 occupancy latent heat: 7.0 people 133.3w/person sensible heat: 7.0 people 86.5w/person infiltration 0.5 ach (air volume change per hour) 151.5l/s floor type total floor u-value 1.500w/(m²×°k) exposed perimeter 80.0m edge insulation r-value 0.40 (m²×°k)/w supply fan 1721l/s window, double glass 12mm air space frame pvc/vinyl vertical blinds u: 2.594w/m²×°k frame: wood/vertical blinds / roller shades light translucent/drapes closed weave light. u: 2.67w/m²×°k frame: aluminum with thermal breaks vertical blinds u: 2.371w/m²×°k b. calculation of minimum thermal insulation thickness to comply with sbc 602 a basic heat transfer equation is formulated to determine an overall heat transfer coefficient (uoverall) for walls, roofs, windows and doors. this equation aims to find the overall heat transfer coefficient for building's envelope: engineering, technology & applied science research vol. 9, no. 2, 2019, 3949-3954 3952 www.etasr.com alfaraidy & azzam: residential buildings thermal performance to comply with the energy … uoverall = �� ����∑ ���� ��� � � ��� (1) where k is the thermal conductivity of the material (w/m·k), xi is the thickness of material in composite wall i (m), he is the individual convection heat transfer coefficient for outside air film (w/m 2 ·k), hi is the individual convection heat transfer coefficient for inside air film (w/m 2 ·k), and n is the wall layer number. the wall insulation thickness and roof insulation thickness can be calculated by (2) and (3) respectively: ( ) ( ) ( ) 1 1 1 1. / – / ]/[w w o n i iw c e i i odt k u h h x k=− − −= ∑ (2) ( ) ( ) ( ) 1 t 1 1 1 [ ]. / – / /   r r r co n i ide i e i k u h x k h − = = − −∑ (3) where tw is the minimum wall insulation thickness in compliance with the code, kw is the thermal conductivity of the wall insulation material, tr is the minimum insulation thickness for roof in compliance with the code, kr the thermal conductivity of the roof insulation material, uw-code is the wall overall heat transfer coefficient (w/m 2 .k) as defined by sbc 602 (table iv), ur-code is the wall overall heat transfer coefficient (w/m 2 .k) as defined by sbc 602 (table iv). three insulation materials are selected for this study for their thermal performance and availability in the market. their physical and thermal properties are listed in table v. table v. properties and costs of insulation materials material polystyrene polyurethane rockwool use wall roof wall roof wall roof cost * (sar/m³) 385 415 400 440 400 460 thermal conductivity k (w/m.k) 0.029 0.028 0.02 0.02 0.04 0.04 specific heat (j/kg) 1280 1280 1590 1590 840 840 density (kg/m³) 26-28 32-35 28 35 100 150 appearance rigid boards rigid boards bats *sar= 1 us$/3.75 (conversion rate of november 2018) iv. results and discussion figures 4-9 show the weather design and simulation for the three studied cities. the simulated annual temperature profiles, dry bulb and wet pulp are shown in figures 4-6. the simulated solar profiles and maximum solar heat gains are shown in figures 7-9. fig. 4. hap annual simulated temperature profile for riyadh (zone 1) fig. 5. hap annual simulated temperature profile for arar (zone 2) fig. 6. hap annual simulated temperature profile for turaif (zone 3) fig. 7. hap simulated solar profile for riyadh (zone 1), weather file iwec2 sau_riyadh-obs (oap)_404380_iw2 fig. 8. hap simulated solar profile for arar (zone 2), weather file iwec2 sau_arar_403570_iw2.csv fig. 9. hap simulated solar profile for turaif (zone 3), weather file iwec2: sau_turaif_403560_iw2 three insulation materials were used: extruded polystyrene (pls), polyurethane (plu) and rock wool (rw). minimum 0 100 200 300 400 500 600 700 800 900 1000 s o la r f lu x ( w /m ² ) day of year 8 1 6 2 4 3 2 4 0 4 8 5 6 6 4 7 2 8 0 8 8 9 6 1 0 4 1 1 2 1 2 0 1 2 8 1 3 6 1 4 4 1 5 2 1 6 0 1 6 8 1 7 6 1 8 4 1 9 2 2 0 0 2 0 8 2 1 6 2 2 4 2 3 2 2 4 0 2 4 8 2 5 6 2 6 4 2 7 2 2 8 0 2 8 8 2 9 6 3 0 4 3 1 2 3 2 0 3 2 8 3 3 6 3 4 4 3 5 2 3 6 0 beam solar on horiz. total solar on horiz. engineering, technology & applied science research vol. 9, no. 2, 2019, 3949-3954 3953 www.etasr.com alfaraidy & azzam: residential buildings thermal performance to comply with the energy … insulation thickness is calculated based on the overall heat transfer coefficient for wall and roof structures using (1)-(3). three wall structures were studied to install thermal insulation: dws, eifs, and iifs as shown in table vi and figures 10 and 11. table vi. minimum thermal insulation thickness* climate zone zone 1 zone 2 zone 3 pls dws 70 60 50 eifs/iifs 80 70 60 roof 130 110 100 plu dws 60 50 40 eifs/iifs 65 55 45 roof 100 85 75 rw dws 100 85 70 eifs/iifs 110 90 80 roof 185 155 135 *(mm), in compliance with sbc602 the analysis of thermal insulation thicknesses that are compliant with sbc 602 for the three climatic zones shows that plu has the minimum thickness as shown in figure 10. its thicknesses for dws are 60mm, 50mm, 40mm for zones 1, 2 and 3 respectively, while its thicknesses for eifs/iifs are 65mm, 55mm and 45mm. in roof thermal insulation, plu shows minimum thickness of about 100mm, 85mm, and 75mm for zones 1, 2 and 3 respectively, as shown in figure 11. further calculation is conducted to compute the overall costs of installing the insulation material within the wall structure. the thermal insulation costs including material and labor are generated based on 2018 average market prices and previous experience (table vii). fig. 10. minimum wall insulation thickness in compliance with sbc602 in all zones, eifs and iifs systems show the lowest overall cost utilizing plu as insulation material. dws has the highest cost for the three zones compared to eifs/iifs. also, considering the overall wall thickness, dws has the highest wall thickness ranging from 390mm to 460mm for all cases, while the eifs/iifs thickness ranges from 250mm to 320mm. the system of eifs with plu as insulation material has the lowest cost option with the best thermal efficiency and hence this system has been used for lateral examination by hap. the designed hvac loads for base-case building and energy efficient building show a considerable saving in thermal loads due to using thermal insulation and other measures. the loads for the base case building, designed hvac (w/m 2 ) for each zone are 167.7, 153.1 and 141.9 respectively. for the energy efficient building, the designed hvac (w/m2) are 60.4, 58.3 and 45.8 for each zone. the saving percentage for z1, z2 and z3 is: 65.6%, 61.8% and 67.7% respectively. details of hvac loads for the three zones are presented in figure 12. hvac monthly simulated consumptions for base case building and energy efficient building are presented in figure 13, while the saving in installed hvac capacity and saving in hvac annual consumption are illustrated in figure 14. a simple economic calculation is made to compute the average payback period for the system that costs the least (i.e eifs & plu) based on assumption interest rate of 3%, lifetime of 20 years, and 2018 material prices. the results range from 3.3 to 4.2 years for the three zones as presented in figure 15. fig. 11. minimum roof insulation thickness in compliance with sbc602 table vii. overall costs dws, us$/m 2 eifs/iifs, us$/m 2 pls zone 1 32.49 28.32 zone 2 29.41 25.24 zone 3 27.49 23.32 plu zone 1 28.72 24.57 zone 2 26.15 21.99 zone 3 24.18 20.02 rw zone 1 43.78 39.65 zone 2 38.74 33.56 zone 3 34.98 30.2 fig. 12. designed hvac loads for base-case and energy efficient building fig. 13. simulated monthly hvac consumption per building m 2 for basecase and energy efficient building engineering, technology & applied science research vol. 9, no. 2, 2019, 3949-3954 3954 www.etasr.com alfaraidy & azzam: residential buildings thermal performance to comply with the energy … fig. 14. saving percentage in hvac installed capacities and annual consumption for base-case and energy efficient building fig. 15. pay-back period for plu on eifs wall structure v. conclusions it is concluded that eifs is the most appropriate method of architectural installation of thermal insulation, meeting the minimum requirements of the energy efficiency code in terms of continuous insulation for the building envelope and elimination of thermal bridges. when studying different insulation materials, polyurethane was found the most cost effective while having high thermal efficiency. eifs utilizing plu is used by hap for a comparison study between base-case and energy efficient buildings. hvac loads and annual energy consumption were designed and simulated and the savings were calculated and listed. also, the payback periods were calculated for the three climatic zones of sa. eifs utilizing plu is selected for economic analysis and shows a promising payback period (form 3.3 to 4.2 years). this would encourage the community for extensive use of thermal insulation in buildings. further study is recommended for retrofitting of existing (un-insulated) buildings to calculate the cost of converting to energy efficient buildings. in special cases, when retrofitting existing buildings built with highly expensive external finish like granite, marble or even natural stone, the iifs is recommended but with single restriction to use rw as insulation material, since it has high fire resistance. in this case the insulation cost would be considerably high: 39.65 us$/m 2 , 33.56 us$/m 2 , and 30.2 us$/m 2 for zones 1, 2, and 3 respectively. acknowledgment authors gratefully acknowledge the approval and the support of this research study by the grant no. 461-eng-20161-6-f from the deanship of scientific research at the northern border university, arar, saudi arabia. references [1] electricity & cogeneration regularity authority, annual report, 2017 [2] ksa vision 2030, www.vision2030.gov.sa [3] m. a. mujeebu, o. alshamrani, “prospects of energy conservation and management in buildings – the saudi arabian scenario versus global trends”, renewable and sustainable energy reviews, vol. 58, pp. 16471663, 2016 [4] general authority of statistics, economic indicators, available at: https://www.stats.gov.sa/en/node/10127 [5] w. j. a. lasker, the impact of construction and building materials on energy consumption on saudi residential buildings, phd thesis, heriot watt university, 2015 [6] f. yucel, e. aricioglu, o. ucan, “energy consumption and economic growth nexus: evidence from developed countries in europe”, international journal of energy economics and policy, vol. 4, no. 3, pp. 411-419, 2014 [7] e. h. ahmad, “cost analysis and thickness optimization of thermal insulation materials used in residential buildings in saudi arabia”, the 6th saudi engineering conference, dhahran, saudi arabia, december, 2002 [8] saudi electricity company, optimal use of air conditioner report, 2015 [9] a. h. m. khair-el-din, “energy conservation and its implication for architectural design and town planning in the hot-arid areas of saudi arabia and the gulf states”, solar and wind technology, vol. 7, no. 23, pp. 131-138, 1990 [10] national building codes committee, saudi building code energy conservation requirements sbc 602, 2016 [11] saso standard 28793/2014 (thermal transmittance values), saudi standards, metrology and quality organization (saso), 2014 [12] saudi energy efiiciency center, report of energy sectors, 2017 [13] i. a. al-mofeez, m. y. numan, k. a. alshaibani, f. a. al-maziad, “review of typical vs. synthesized energy modeling weather files”, journal of renewable and sustainable energy, vol. 4, no. 1, p. 012702, 2012 [14] ashrae, design weather data, 2017 [15] ashrae, iwecii international weather data for energy calculation version 2, 2017 [16] saso, astm e2110, standard terminology for exterior insulation and finish systems (eifs), saudi standards, metrology and quality organization (saso), 2011 [17] saso, astm c1154, standard terminology for non-asbestos fiberreinforced cement products) saudi standards, metrology and quality organization (saso), 2012 [18] astm c1186-08, standard specification for flat fiber-cement sheets, astm international, 2016 [19] british standards (bs) 476-7:1997, fire tests on building materials and structures. method of test to determine the classification of the surface spread of flame of products, 1997 microsoft word etasr_v11_n2_pp7011-7017 engineering, technology & applied science research vol. 11, no. 2, 2021, 7011-7017 7011 www.etasr.com kasmi & hassam: comparative study between fuzzy logic and interval type-2 fuzzy logic … comparative study between fuzzy logic and interval type-2 fuzzy logic controllers for the trajectory planning of a mobile robot boucetta kasmi department of electronics laboratory of intelligent systems university ferhat abbas setif 1 setif, algeria boucetta.kasmi@univ-setif.dz abdelouaheb hassam department of electronics laboratory of intelligent systems university ferhat abbas setif 1 setif, algeria abdelhassam@univ-setif.dz abstract-in this study, fuzzy logic (fl) and interval type-2 fl (it-2fl) controllers were applied to a mobile robot in order to determine which method facilitates navigation and enables the robot to overcome real-world uncertainties and track an optimal trajectory in a very short time. the robot under consideration is a non-holonomic unicycle mobile robot, represented by a kinematic model, evolving in two different environments. the first environment is barrier-free, and moving the robot from an initial to a target position requires the introduction of a single action module. subsequently, the same problem was approached in an environment closer to reality, with objects hindering the robot's movement. this case requires another controller, called obstacle avoidance. this system allows the robot to reach autonomously a well-defined target by avoiding collision with obstacles. the robustness of the structures of the defined controllers is tested in matlab simulations of the studied controllers. the results show that the it-2fl controller performs better than the fl controller. keywords-interval type-2 fuzzy logic (it2-fl); fuzzy logic (fl); mobile robot; non-holonomic; obstacle avoidance; trajectory planning i. introduction a mobile robot is generally equipped with perception and decision-making capabilities and actions that allow it to navigate safely and successfully in a given environment and to follow a desired trajectory. this objective is achieved without or with a reduced human intervention [1]. today, independent mobile robots are increasingly used in many applications, such as service tasks, agriculture, handling of nuclear waste, and in space industry [2]. the developments of sensors, microprocessors, and control technology have enabled mobile robots to perform very complex tasks. today, the main challenge regarding mobile robots is the development of intelligent navigation systems [3]. navigation is of great importance, since virtually every task requires the robot to travel between different positions by tracking a desired trajectory while being able to localize itself and plan its future movements without human assistance [4] in order to accomplish the defined task [5]. therefore, once the trajectory of the robot in a complex environment is determined, it must be capable of following it [6]. the generated trajectory must take into account the environmental and kinematic constraints of the moving object [7-8]. to tackle these difficulties and to enable a large number of parameters to be managed, a new control strategy is proposed, which is broken down into weakly coupled units whose interactions are limited and perfectly controlled in a distributed manner. the purpose is to develop robots that can move safely in unstructured environments, despite any unforeseen changes. the main problem of navigation of mobile robots can be broken down into three sub-problems: reaching the target, avoiding obstacles, and tracking an optimal trajectory in a very short time. to reach the target, we can indicate the trajectory to the robot by employing stable techniques based on the search for optimal trajectories. however, since the environments are rarely predictable, it makes little sense to provide the robot with a planned trajectory. obstacle avoidance has often been solved by using local information, perceived by the robot via its sensors. initially, research has focused on solving the obstacle avoidance problem by presenting it as a high-level control component of hierarchical robotic systems. thus, the problem arose as a trajectory planning where the controller at the low level leads the robot towards its final destination while avoiding the surrounding obstacles using the trajectory found at the high level. the main objective of this paper is the tracking of an optimal trajectory in a very short time, which is the third subproblem. a comparative study of fuzzy logic (fl) and interval type-2 fl (it-2fl) controllers was conducted in order to assess their performance. the robot under consideration is a non-holonomic unicycle mobile robot, represented by a kinematic model. ii. modeling of a mobile robot the differential mobile robot is a platform with two motorized wheels (figure 1), mounted on the same axis and controlled independently while having in addition a free front corresponding author: boucetta kasmi engineering, technology & applied science research vol. 11, no. 2, 2021, 7011-7017 7012 www.etasr.com kasmi & hassam: comparative study between fuzzy logic and interval type-2 fuzzy logic … wheel [7]. the simplified hypotheses considered for modeling are: • the ground wheel contact is a contact point. • the rolling of each wheel is done without slipping. the generalized coordinates of the system are given by [ , , , , ] t r l q x y θ ϕ ϕ= where [x, y] are the cartesian coordinates of the mobile robot, θ is its orientation measured from the x-axis and ,r lϕ ϕ are the angular positions of the right and left wheel respectively [2, 3]. fig. 1. the unicycle-type mobile robot under study. iii. kinematic model of the mobile robot the kinematic model of the mobile robot can be written as [3]: cos( ) cos( ) 2 2 sin( ) sin( ) 2 2 2 2 1 0 0 1 r l r l r r x r r y q r r b b θ θ θ θ ϕ θ ϕ ϕ ϕ                   = = =   −                     & & & && & & & (1) by introducing the following control inputs: 1 1 1 1 r l vb r ϕ ϕ ω       =     −     & & equation (1) may be written as: cos( ) 0 sin( ) 0 0 1 x y v θ θ ω θ            = +               & & & (2) 2 2 2 2 r l r r v r r b b ϕ ϕω       =         −    & & (3) where v and ω are respectively the linear and angular velocities of the mobile robot and 2b and r represent respectively the radius of the wheels and the distance between them. the non-holonomic constraint is represented in a simple mathematical form [3]: cos( ) sin( ) 0x yθ θ− =& & (4) equation (4) implies that a perfect tracking is achievable only if the reference trajectories are feasible for the physical platform. iv. localization of a mobile robot one of the fundamental problems of autonomous mobile robotics is the locationing of the robot during its movement. in fact, to locate a mobile robot is to determine, in a given work reference, its position and its orientation, in order to accomplish the control structure that is based on these data. a. presentation of the odometry the odometry allows determining the position and the orientation of a mobile robot navigating on a plane ground, with respect to the reference mark, which is the robot’s mark in its initial configuration. this technique is based on the integration of the elementary motions of the wheels measured by means of incremental encoders. b. the odometry for the localization of a mobile robot this locomotion system is very popular for indoor robots because of its maneuverability and ease of operation. in this case, the displacement d∆ and the elementary rotation θ∆ of the robot model in the plane can be expressed as a function of the elementary displacements of the right and left wheels respectively r d∆ and l d∆ , by [13, 14]: 2 r ld d d ∆ + ∆ ∆ = (5) 2 r ld d b θ ∆ − ∆ ∆ = (6) where ( , , )k k kx y θ is the configuration of the robot at the instant k, and ( , )k kd θ∆ ∆ the components of the elementary displacement measured between instants k and k+1. the elementary rotation at time k+1 is: 1k k kθ θ θ+ = + ∆ (7) these very simple formulas are obtained by considering that the robot moves in a straight line kd∆ in the direction defined by kθ , and then makes a rotation on site of kθ∆ : 1 cos( ) 2 k k k k kx x d θ θ+ ∆ = +∆ + (8) engineering, technology & applied science research vol. 11, no. 2, 2021, 7011-7017 7013 www.etasr.com kasmi & hassam: comparative study between fuzzy logic and interval type-2 fuzzy logic … 1 sin( ) 2 k k k k ky y d θ θ+ ∆ = + ∆ + (9) this robot control was applied in both fl and it-2fl strategies. fig. 2. the odometry applied to the mobile robot. v. structure of the fl controller a classic fuzzy controller consists of a fuzzification interface, a rule base, an inference system, and a defuzzification interface [15-21]. the structure of an fl system is illustrated in figure 3. fig. 3. structure of an fl system. in our work, the fuzzy controller (fl and it-2fl) has 4 triangular-shaped membership functions for the robot-target distance, 7 membership functions for the variation of the robottarget angle and an interval-type of fuzzy sets for the linear velocity and angular velocity output for it-2flc. the output variables for flc are 4 triangular-shaped membership functions for linear velocity and 7 triangular-shaped membership functions for the angular velocity. vi. the proposed navigation system the movement of the unicycle robot is carried out on a flat ground and the position of the robot can be expressed at every moment according to its kinematic model (x, y, θ ). when meeting obstacles or walls, the relevant decision is made by two controllers. figure 4 shows the structure of the system, consisting of a free navigation controller and an obstacle avoidance controller [8-10]. a. implementation of the free navigation controller if we take a mobile robot operating in a non-binding environment, then the optimal path from an initial configuration to a final situation would naturally be a straight line joining the two situations (figure 5) [8, 11, 12]. fig. 4. structure of the proposed navigation system. fig. 5. the mobile robot in a free environment. 1) input variables for the robot-target distance d (m), we have chosen 4 membership functions (figure 6): very near (vn), near (nr), far (f), and very far (vf) distributed over the discourse universe [0, 30]. for the entry θ (rad), the robot-target angle has 7 membership functions that are associated (figure 7): negative big (nb), negative medium (nm), negative small (ns), zero (z), positive small (ps), positive medium (pm), and positive big (pb) distributed over the discourse universe [-3, 3]. fig. 6. the membership functions of the input variable distance d. fig. 7. the membership functions of the input variable θ. 2) output variables for the linear velocity v (m/s), 4 intervals were chosen: very slow (vs), slow (s), fast (f), and very fast (vf) distributed over the discourse universe [0, 0.2]. engineering, technology & applied science research vol. 11, no. 2, 2021, 7011-7017 7014 www.etasr.com kasmi & hassam: comparative study between fuzzy logic and interval type-2 fuzzy logic … the angular velocity ω (rad) has seven (7) intervals: negative big (nb), negative medium (nm), negative small (ns), zero (z), positive small (ps), positive medium (pm) and positive big (pb), distributed over the discourse universe [-0.8, 0.8]. 3) representation of input variables the membership functions of the triangular input variables are shown in figures 8, 9. fig. 8. the membership functions of the input variable d in matlab toolbox. fig. 9. the membership functions of the input variable θ in matlab toolbox. 4) the rule of the free navigation controller table i. the rule base of the free navigation controller orientation θ distance d vn n f vf nb vs, pb vs, pb s, pb s, pm nm vs, pm vs, ps s, ps f, ps ns vs, s s, ps f, ps f,ps z vs, z s, z f, z v, fz ps vs, ns s, ns f, ns vf, ns pm vs, nm vs, nm f, nm f, ns pb vs, nb vs, nb s, nb s, nb the rule base of the free navigation controller is the following: rule 1: if d is vn and θ is nb then v is vs and ω is pb rule 2: if d is vn and θ is nm then v is vs and ω is pm ………………………………………………. rule 28: if d is vf and θ is pb then v is s and ω is nm we applied these rules of the free navigation controller in both fl and it-2fl strategies. b. implementation of the obstacle avoidance controller in the case where the robot moves close to an obstacle, another fuzzy controller is used to avoid the obstacle and steer the robot away from obd using the navigation controller. figure 10 shows the configuration of the robot in the obstacle area [12, 14, 20]. fig. 10. the mobile robot in an environment with an obstacle. the obstacle avoidance controller that we used has two input variables: robot-obstacle distance and robot-obstacle angle ( obd and φ) respectively and two output variables: robot linear velocity v and angular velocity ω. 1) the membership functions of the input variables for flc fig. 11. the membership functions of the input variable dob. fig. 12. the membership functions of the input variable φ. engineering, technology & applied science research vol. 11, no. 2, 2021, 7011-7017 7015 www.etasr.com kasmi & hassam: comparative study between fuzzy logic and interval type-2 fuzzy logic … 2) the membership functions of the input variables for it2flc fig. 13. the membership functions of the input variable dob in matlab toolbox. fig. 14. the membership functions of the input variable φ in matlab toolbox. 3) the rule base of the obstacle avoidance controller table ii. the rule base of the obstacle avoidance controller orientation φ the obstacle distance dob vn n f vf nb vs, pm vs, pm s, pm s, pm nm vs, pm vs, ps s, ps f, ps ns vs, ps s, ps f, ps f,ps z vs, pm s, ns f, ps vf, ps ps vs, nm s, ns f, ns vf, ns pm vs, nm vs, nm f, ns f, ns pb vs, nb vs, nb s, nb s, nb the rule base of the obstacle avoidance controller is the following: rule 1: if ob d is vn and ϕ is nb then v is vs and ω is pm rule 2: if obd is vn and ϕ is nm then v is vs and ω is pm ………………………………………………. rule 28: if ob d is vf and ϕ is pb then v is s and ω is nb we applied these rules of the obstacle avoidance controller in both the fl and it-2fl strategies. vii. simulation results to compare the control and planning performances of fl and it2-fl controllers, simulations were conducted and analyzed with matlab fuzzy logic toolbox r2014a. a. trajectory without obstacles from figure 15, we notice that from its initial position, ( i x =2.5 and i y =4.5, θ =45°) the mobile robot could reach the target whose coordinates are (xf =7, yf =−1). in figures 16 and 17 we can see the velocity and the angular velocity of the mobile robot. from the obtained results, we notice that the mobile robot adopts the following behavior: when the robottarget angle is large, the angular velocity is high, whereas the linear velocity is small. once the robot-target angle becomes zero, the linear velocity reaches its maximum. the latter gradually decreases by canceling once the target is reached. fig. 15. attraction to the target: barrier-free environment. fig. 16. the velocity of the mobile robot. b. obstacle avoidance from figure 18 we can see how the mobile robot reached the target (xf =6, yf =7) from its initial position ( ix =3 and i y =8, θ =−45°). -2-2-2-2 0000 2222 4444 6666 8888 -2-2-2-2 -1-1-1-1 0000 1111 2222 3333 4444 5555 6666 7777 8888 x( m)x( m)x( m)x( m) y ( m ) y ( m ) y ( m ) y ( m ) it2-flc flc 0000 100100100100 200200200200 300300300300 400400400400 5 005 005 005 00 6 006 006 006 00 7 007 007 007 00 0. 020. 020. 020. 02 0 .0 250 .0 250 .0 250 .0 25 0. 030. 030. 030. 03 0 .0 350 .0 350 .0 350 .0 35 0. 040. 040. 040. 04 0 .0 450 .0 450 .0 450 .0 45 0. 050. 050. 050. 05 0 .0 550 .0 550 .0 550 .0 55 0. 060. 060. 060. 06 time(s) t h e v e lo c it y (m /s ) f lcf lcf lcf lc it 2 -f lcit 2 -f lcit 2 -f lcit 2 -f lc engineering, technology & applied science research vol. 11, no. 2, 2021, 7011-7017 7016 www.etasr.com kasmi & hassam: comparative study between fuzzy logic and interval type-2 fuzzy logic … fig. 17. the angular velocity of the mobile robot. fig. 18. convergence towards the target by flc in the presence of obstacles. fig. 19. convergence towards the target by it-2flc in the presence of obstacles. we can highlight from the above results that the it-2fl sets can be quite useful when considering the control of a mobile robot. it was shown in depth that the proposed it2-fl controller is more efficient in terms of saving time, smooth trajectory, and optimal distance than its fl counterpart. viii. conclusion in this paper, movement control methods of a wheeled mobile robot were studied. to achieve this control target, we have designed the fl and it-2fl controllers and simulated the mobile robot movement from an initial to a desired position in different environment configurations, with and without obstacles. the proposed fuzzy control exploits the interactive variables between the mobile robot and the unknown environment to generate the robot’s velocity and steering, which makes it possible to bring the mobile robot towards the target while avoiding any obstacles present in this environment. fig. 20. the velocity of the mobile robot in the presence of obstacles. fig. 21. the angular velocity of the mobile robot in the presence of obstacles. in order to test the applicability of the it-2flc system, we compared its performance with that of an fl controller. the it-2flc offers better results than its fl counterpart in environments with obstacles. the main characteristic of the it2flc sets is its ability to handle uncertainties more efficiently than flc. this is made possible because a larger number of parameters and more freedom degrees are available in the it2flc sets. references [1] p. gil, y. mezouar, m. vincze, and j. a. corrales, "robotic perception of the sight and touch to interact with environments," journal of sensors, vol. 2016, dec. 2016, art. no. e1751205, https://doi.org/ 10.1155/2016/1751205. 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[21] h. a. hagras, "a hierarchical type-2 fuzzy logic control architecture for autonomous mobile robots," ieee transactions on fuzzy systems, vol. 12, no. 4, pp. 524–539, aug. 2004, https://doi.org/10.1109/tfuzz. 2004.832538. microsoft word etasr_v11_n2_pp7018-7022 engineering, technology & applied science research vol. 11, no. 2, 2021, 7018-7022 7018 www.etasr.com hashmi: a novel drone-based search and rescue system using bluetooth low energy technology a novel drone-based search and rescue system using bluetooth low energy technology anas m. hashmi department of electrical and electronic engineering university of jeddah jeddah, saudi arabia ahashmi@uj.edu.sa abstract-drones are widely known for their mobility and ease of use and represent a significant technological breakthrough with various applications. in this paper, a novel inexpensive search and rescue (sar)-based approach for application in indoor environments is presented. the usage of bluetooth low energy (ble) has been evaluated with respect to other technologies and a conceptual view of the complete setup has been presented. besides the cost of the drone and the locator devices, the other hardware is relatively inexpensive costing only a fraction of a us dollar. the system is believed to cover a wide area in a small-time frame ranging a few minutes, for instance, a 3600m 2 surface area could be scanned in less than 5 minutes. the system is tested by attaching a ble device in the payload to evaluate the presence of target beacons. potential upgrades in the system are also proposed, including design modifications for outdoor use and the application in locating missing objects. this system can confidently replace search parties dealing with missing children in public places or venues, with minimal human interaction while bearing the potential for complete automation. keywords-ble; wearable electronics; uavs; localization i. introduction during the last decade, the usage of unmanned aerial vehicles (uavs) has risen exponentially [1]. it is estimated that the global market share of multi-rotor drones is expected to reach $36.9 billion by 2022 from $6.8 billion in 2016 [2]. drones are directly or indirectly used as an effective tool in agriculture, industrial maintenance, logistics, military, entertainment, and traffic control [3, 4]. in most of the aforementioned applications, drones have proven to be an effective replacement of the existing technologies, mainly in terms of cost maintenance, time, training, and automation. one of the most significant applications of uavs lies in the domain of search and rescue (sar)-based missions. usually, such operations are performed in conventional matters, which are time consuming and costly [5]. for example, a successful 19day rescue operation in july 2020 to locate two hikers lost in new zealand cost the new zealand authorities over 80k nzd ($57.8k) [6]. using an autonomous uav would potentially cut the cost and time of a sar operation by 70% in comparison with classic operations [7]. typically, drone-based sar operations are carried out manually by continuously monitoring live transmitted broadcast imagery through technologies, such as the first-person view (fpv). some advances in the automation of the search process have been implemented which involve ai-based protocols to identify pre-trained objects or shapes, or face recognition. in confined places, such as events held at parks, theatres, or concerts, parents or guardians that lose their children usually seek the assistance of a dedicated lost child office to locate them. the proposed uav system can potentially help in such cases or in similar cases regarding elder patients (e.g. patients with alzheimer’s or autism). the search process in these cases can often be costly and time consuming or may involve the risk of a child/patient leaving the dedicated event area [8]. this paper discusses a novel inexpensive approach of utilizing multirotor drones as a sar tool whereby it scans passive pre-defined passive receivers. this device overcomes the characteristic challenges of events being held in large venues, allowing object/person finding applications. potential future upgrades for transforming the system to form a completely autonomous decision support system tool for event management may even be possible. moreover, these developments may be uploaded to upgrade the system for open space usage with certain limitations. ii. existing technology there are various existing drone-based sar applications and these attempts have been featured to be utilized in various types of technologies as described in the existing literature. table i enlists some common technologies used in a typical sar operation. as shown in table i, most of the technologies are focused on searching wireless radio activities emitted by target mobile phones. however, usually minors and individuals with special needs are not expected to carry mobile phones, therefore technology dependent on mobile phones may be difficult to implement in such cases. other technologies achieve this task by different means which include live streaming footage, qr codes, or audio signals. cellular network-based systems received enormous attention when it comes to sar application due to the increased network coverage and enhanced communication capabilities, including the rapid expansion of 5g networks [16, 17]. corresponding author: anas m. hashmi engineering, technology & applied science research vol. 11, no. 2, 2021, 7018-7022 7019 www.etasr.com hashmi: a novel drone-based search and rescue system using bluetooth low energy technology table i. selected existing sar drone-based application s product technology features drawbacks ref. altigator ir thermal imaging manual inspection of live footage. manual inspction requires additional human power, thermal cameras can be expensive. [9] intelligent drone navigation for sar operations computer vision qr codes are used for indoor localization. uses gps for localization, difficult to operate indoors [10] sardo mobile network and ir cameras locates a mobile phone in 3 minutes in an open field. mobile network-based solution, requires a phone carried by the target [11] slam 3d map generation from stitching still images compares movement between two frames of the images. images are difficult to be evaluated in crowded environemnts [12] mobnet mobile phones searches for mobile phones, signal of trapped people. mobile network-based solution, requires a phone carried by the target [13] guideloc wireless signals from mobile phones localization system uses target guiding technology based on region division. mobile network-based solution, requires a phone carried by the target [14] audio-based sar with a drone drone-embedded sound source localization estimates the time difference of arrival (tdoa) of sound waves in a microphone pair in addition to the angle of arrival. difficult to operate in crowded environments due to various sources of sound [15] the possibility of utilizing electronic id tags, such as bluetooth low energy (ble) devices has been explored. we believe that featuring such inexpensive tags will make the task less complex and more achievable comparing to the methods proposed in table i. iii. concept and methodology the concept of the design is to re-design the drone payload in order to be able to carry the required electronics and means of communication for accurate identification of the id tags. in order to design the system appropriately, various elements of the design have been investigated. a. id tags the id tags are an important element of the process of development since they act as the primary point of communication. tags should communicate with the host once close proximity is detected, and may be operated actively or passively. they should feature reliable operation, rapid response, inexpensive price tag, reasonable energy consumption, lightweight arrangement, and acceptable communication range. if the total weight of those tags is low, they can be manufactured as wearable electronics. the recent advances in the development of short to medium range wireless technologies provided multiple options for the uav designed in this study. there are various communication protocols meeting the aforementioned criteria, which are enlisted in table ii [18, 19]. referring to table ii, it can be seen that the ble technology features have low cost, low weight, moderate communication range, and relatively low energy consumption. conventional bluetooth has stable connection, reasonable price, and moderate ipv6 communication energy overhead with a slow data transfer rate. as the name suggests, ble is designed to optimize power consumption compared to the classic bluetooth, while maintaining a similar protocol stack profile. usually ble devices are powered by a single coin battery that lasts up to two years. it was found that ble consumes very little energy compared to competing low-energy communication technology, such as zigbee [20]. it uses a 2.4ghz ism band with 2mhz channel spacing, and is governed by ieee 802.11 and ieee 802.15 standard protocols [21]. the low energy operation of ble is achieved by the potential trade off of the following features: • communication channels: instead of using multiple channels for discovery or connections, only 3 broadcasting channels would be used. • memory: only a few bytes are featured with ble, while additional memory would require additional hardware, increasing the chances of current leakage. • data packets: ble sends shorter data packets which results in fewer calibration iterations drawing less leakage current. • sleep time: classic bluetooth takes over 100ms for waking from sleep, transmitting a data packet, and then going to sleep mode, while ble performs this process 15 times faster. this will reduce scanning time for ble saving more battery, especially if small data segments are broadcast. table ii. existing sar drone-based technolo gies technology cost weight range energy consumption radio frequency identification (rfid) very low low read range of 100m, unidirectional passive near field communication (nfc) very low low 10cm, bidirectional very low or passive bluetooth medium low 100m (class dependent), bidirectional medium (class dependent) ble low low 10-50m, bidirectional very low wifi high high 100m high zigbee moderate low 10-20m low ble operates in star network topology where the nodes can be configured as slaves connected to a single master, or a master connected to multiple slaves. the master scans the designated channels to search for slave devices. once a device is discovered, synchronous connection is established between them resulting in the change of state of activity mode from ‘sleep’ to ‘wake up’. another option would be to set the slave devices to sleep mode by default to save energy [22]. engineering, technology & applied science research vol. 11, no. 2, 2021, 7018-7022 7020 www.etasr.com hashmi: a novel drone-based search and rescue system using bluetooth low energy technology b. data transmission and positioning data are transmitted in ble using two service profiles, namely find me profile (fmp) and proximity profile (pxp), which take into consideration the slave/master (target/locator) positions. as the name suggests, fmp makes the localization of devices a significantly straightforward process. the target seeks the search command broadcast by the locator. once the message is delivered, the target device is triggered, usually in the form of an audio signal or other alert mechanisms. on the other hand, pxp detects any drop in the connection with the target or initiates a connection with a different locator. this profile is effective only if a connection is initiated. other available protocols found in the domain of consumer-based electronics include the ibeacon which operates between preprogrammed manufacturer’s devices. in terms of internal hardware arrangements in ble devices, one point to consider is the directionality of their chip antennas, which are characterized by non-isotropic radiation. this is significantly challenging to mitigate due to the size of the additional antenna. there are various fundamental concepts when considering the positioning of ble devices. the simplest approach of positioning is determining if both the target and the locator are within the radio coverage range, while providing a binary decision about their presence within that range [23]. in order to determine the distance between devices in free space, the following equation that relates distance (d) and the received signal strength indicator (rssi) was utilized. � � 20�rssi � (1) where is an offset based on the maximum rssi of the locator. the equation could also be used to determine the lateration based on multiple locators. unlike outdoors, the indoor environment usually exhibits multipath effect due to the presence of obstacles that may vary in form and arrangement. this significantly worsens the approximation taken into consideration in (1). however, the utilization of the time-offlight (tof) approach has proven to produce more accurate results in indoor locations. unfortunately, tof estimation requires additional electronics (e.g. oscillators) which increase power consumption and cost. it is also important to note that since the locator is fixed in a moving station (i.e. drone), the angulation process may be ignored. in the same context, it is highly challenging to utilize fingerprinting which identifies the pre-recorded target rssi values of both the target and locator, since they tend to exhibit continuous change in their locations. c. locator movement and beacon analysis one of the most challenging issues when attempting to locate the target in indoor environments is the multipath propagation effect. this issue can worsen if several devices are available in a confined space and moving objects are present. usually, no accurate rssi model in case of indoor environments is available and a rather simplistic way of estimation involves the use of tof values. therefore, a worstcase scenario should be taken into consideration when planning such a system. in some commercial applications, such as the ibeacon, it is recommended that the advertising signal intervals should be set below 100ms, when the tag is operated by a coin cell battery for maximizing the battery life to a few months. in addition, when the intervals are set just below 1000ms the battery may last up to 3 years [23]. ble devices continuously broadcast their data packets with a unique identifier known as the universally unique identifier (uuid). this uuid acts as a network mac address for the manufactured chipset and consists of 128-bits, with a 48-bit mandatory advertiser address. for ble target finder, an opensource program, raspberry pi 3 ble sniffer was used [24]. this code allows the detection of various compatible devices from different manufacturers, with all data being analyzed in a dedicated dashboard. while initiating the software, a signal search interval of 200ms was set. the advertising signal interval was set to 500ms, so that the target could operate confidently using a coin cell battery for one full year. in figure 1, we see the raspberry pi (locator) attached to a drone payload for locating advertising channels. fig. 1. basic arrangement of target localization with scan and synchonization with the advertising beacons. iv. experimental setup and route planner for route estimation purposes, the maximum bluetooth coverage radius was assumed to be 10m. to ensure that all targets in the designated search zone are discoverable and that their discoverability is enhanced, the detection range was reduced to 5m. moreover, the drone should fly in intervals whereby the movement was paused for 1000ms for each 5m flown. this interval of inactivity ensures that the locator exhibited at least 4 iterations of advertising signals broadcast by the target. for doubling the chances of discovery, each drone’s vertical/horizontal straight parallel route should have a separation of <5m. raw experimental data are shown in table iii. table iii. raw experimental d ata flight duration wind speed agl route length stop mode 5m vertical movement: 12×55m = 660m horizontal lines: 11×5m = 55m total route: 715m 1000ms every 5m flown 0m/s (indoor) for demonstration purposes, the exhibition hall dhahran expo, located in dhahran, saudi arabia and covering a surface engineering, technology & applied science research vol. 11, no. 2, 2021, 7018-7022 7021 www.etasr.com hashmi: a novel drone-based search and rescue system using bluetooth low energy technology area of 3600m 2 (60m×60m), was chosen [25]. to estimate the planned route, an open-source code named reinforcement learning for autonomous navigation for uavs [26] was used. this code was designed to implement reinforcement learning algorithms for autonomous navigation of drones in indoor environments. figure 2 shows the exhibition hall and the planned route using predefined hall edges. the total horizontal route of the drone was 60m×12m=720m 2 , with an additional 5m×11m=55m 2 surface area of horizontal connecting lines, which makes the total route approximately around 775m 2 . considering the average speed of the drone to be 6.7ms -1 (15mph), the total area can be covered in around 115s, with an additional 1s per 5m taken into consideration. it would take a total of 227s to completely evaluate the whole area of 3600m 2 . (a) (b) fig. 2. (a) a raw image of hall #3 in dhahran expo, dhahran, saudi arabia. (b) raw image processed using planned routing with the aid of opensource code named reinforcement learning for autonomous navigation for uavs. the triangle on the left-hand side demonstrates the drone’s starting point, while the traingle on the right is suggestive of the end point of the flight. the dashed lines demonstrate the main path of vertical movement, and the solid lines represent the path of the horizontal flight. a. accuracy and operationality in order to ensure the maximum accuracy of the system, repeated movements may be performed. once the target is located, the movement of the drone is locked around this area, while it continuously performs search operations in its proximity. if the connection drops, the drone should potentially move in a spiral path to reconnect with the target. the rssi value could be taken into consideration when determining the static positioning of the drone. the proposed model was validated by using a ble device as a target moving backward and forward from the host. the signal loss was evaluated to ensure scan signal being continuously broadcast within the expected bluetooth range. b. potential applications the technological development reported in this study may be used in applications involved in locating objects or persons in halls or exhibitions. this development is easy to implement, since the ble target devices require inexpensive hardware. ble devices could come in different forms, such as wristbands, keychains, tags, pins, each costing less than one us dollar. therefore, the tool shows promising potential for commercialization. one potential upgrade of this application would be its outdoors potential use. in that case, uploading a suggested route plan with details of streets or landmarks may be pertinent. a swarm drone technology may be applied to cover a wider area. v. conclusions a ble-based sar system with indoor applications was proposed which potentially could be applied to locate lost individuals. the proposed ble-based, cell-battery powered device has a year-long operational durability, and bears relatively inexpensive electronic tags in convenient packaging such as a wristband or a keychain. the drone is able to scan an indoor area of 3600m 2 with high accuracy in just below 5 minutes. this time can be further minimized with tradeoff with battery lifetime. this system can be used for additional purposes such as event management and enhanced localization capability based on beacons from target or high-density spots based on attendees’ mobile signals. dedicated ai-based software was utilized in order to estimate the uav route. this system could be upgraded for outdoor operations using swarm technology. references [1] s. maharana, "commercial drones," international journal of advances in science engineering and technology, vol. 5, no. 1 suppl. is. 3, pp. 96–101, mar. 2017. 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[26] m. liaq and y. byun, "autonomous uav navigation using reinforcement learning," international journal of machine learning and computing, vol. 9, no. 6, pp. 756–761, dec. 2019, https://doi.org/ 10.18178/ijmlc.2019.9.6.869. microsoft word 21-review-10-2470_s_bibliografiki engineering, technology & applied science research vol. 9, no. 1, 2019, 3778-3781 3778 www.etasr.com mohammed & ki-seong: chirplet transform in ultrasonic non-destructive testing and structural … chirplet transform in ultrasonic non-destructive testing and structural health monitoring: a review m. s. mohammed nuclear engineering department king abdulaziz university jeddah, saudi arabia mshmohamad@kau.edu.sa kim ki-seong department of mechanical design engineering chonnam national university yeosu, republic of korea sngkim@chonnam.ac.kr abstract—ultrasonic non-destructive testing signal can be decomposed into a set of chirplet signals, which makes the chirplet transform a fitting ultrasonic signal analysis and processing method. moreover, compared to wavelet transform, short-time fourier transform and gabor transform, chirplet transform is a comprehensive signal approximation method, nevertheless, the former methods gained more popularity in the ultrasonic signal processing research. in this paper, the principles of the chirplet transform are explained with a simplified presentation and the studies that used the transform in ultrasonic non-destructive testing and in structural health monitoring are reviewed to expose the existing applications and motivate the research in the potential ones. keywords-chirplet tranform; ultrasonic; guided wave; ndt; structural health monitoring i. introduction non-destructive testing (ndt) methods [1, 2] are used to examine the integrity of engineering materials and structures without altering them or affecting their serviceability. ultrasonic testing [3, 4] is an important ndt method, in which a transducer sends an ultrasound pulse into the material under test, and the reflected or transmitted echo is received, processed and analyzed to provide useful information about the material’s properties or about the presence of flaws and their sizes, locations, and severity. besides conventional ultrasonic testing, ultrasonic guided wave inspection is established in the ndt applications. it uses lamb waves that are guided by the boundaries to propagate along the structure in order to evaluate its condition. the guided wave inspection in structural health monitoring (shm) is carried out by an installed network of sensors, a processor, and an algorithm to instantaneously provide damage prognosis [5]. the usefulness of the received ultrasonic ndt echo signals can be challenged by the noise from several sources including the material’s grain structure and by the limited resolution ability of the measurement system when the echo signals are overlapped due to the small space between the reflectors (interfaces or material flaws). in guided waves inspection, multimodal and dispersion constrain the analysis of the received signals. if the defect is located close to another reflector, it can be only detected if the reflected echo is resolved. the measurement system capabilities can be reinforced by using digital signal processing (dsp) to recover the useful and critical information masked by the poor quality of the signal. dsp methods such as wiener deconvolution, spectral extrapolation, and minimum variance deconvolution have been used to enhance the time resolution of ultrasonic signals [6-9]. artificial neural networks have been used for flaws’ recognition and classification [10, 11]. furthermore, many techniques have been proven effective in improving the signal-to-noise ratio (snr) such as time averaging, matched filters, low-pass filters, high-pass filters, and band-pass filters, wavelet transform, and adaptive filters. examples of noise reduction methods are reported in [12-15]. guided waves signals in ndt and shm applications are often processed using time-frequency analysis methods [16-18]. chirplet transform is a signal approximation method that can provide inclusive solutions for flaw detection and characterization, nevertheless it is not as popular as other methods in the ultrasonic ndt and shm signal processing research. the objective of this paper is to review the principles of chirplet transform, discuss the relevant research papers in ultrasonic ndt and shm signal processing to expose existing applications, and motivate the research in potential ones. ii. chirplet transform chirplet transform was introduced in [19-21]. its basis functions are derivable in time-frequency domain, while the derivation of the basis functions of the wavelet transform and short-time fourier transform (stft) are limited to the time domain, therefore the chirplet transform is a generalization of both former transforms. furthermore, chirplet transform has more degrees of freedom than the wavelet transform, which allows the transform to identify up to eight signal parameters depending on the mother chirplet, and the application. also, since the sinusoids are subsets of the chirplet, gabor transform can be regarded as a special case of the chirplet transform. chirplet analysis has been successfully applied to radar detection of moving objects in oceans, outperforming doppler radar methods. authors in [22] extended their work to address issues pertaining to the large number of parameters identified by their method and introduced an improved one that selects an adapted set of bases using the expectation maximization. the new method was named adaptive chirplet transform. corresponding author: kim ki-seong engineering, technology & applied science research vol. 9, no. 1, 2019, 3778-3781 3779 www.etasr.com mohammed & ki-seong: chirplet transform in ultrasonic non-destructive testing and structural … iii. application of chirplet transform to conventional ultrasonic testing the first application of the chirplet transform to ultrasonic ndt signals was the echo signal’s parameter estimation [23, 24] which was an extension of an earlier work that used maximum likelihood estimation (mle) principles to calculate amplitude, arrival time, center frequency, bandwidth, phase, and chirp rate [25, 26]. the selection of the chirplet transform assumed that ultrasonic echoes are composed of a superposition of chirplet echoes, so the close similarity between the analyzing chirplet and measured ultrasonic signals offers optimal representation. the chirplet transform has been used to represent the ultrasonic signal in the time-frequency domain decomposing it into a linear combination of gaussian chirplets and then iteratively apply parameter estimation algorithm to each identified echo by applying a windowing strategy to segregate the individual echoes. the flowchart of the signal processing procedure and the equations for the echo parameter estimations based on the solutions of the chirplet transform are presented in [24]. the application of the transform via windowing is challenged by the design requirements of the window as the width should be small enough to limit the amount of noise during signal estimation but it should be wide enough to contain the required signal’s information. moreover, the performance can be deteriorated when closely-spaced reflectors are present. the method is comprehensive and advantageous because it calculates the parameters necessary to characterize the physical properties of the reflectors (flaws or materials’ interface) and can be used for applications like target detection, data compression, deconvolution, object classification, velocity measurement, and ranging systems. the performance of the method was compared to another signal processing method, the empirical mode decomposition (emd) coupled with hilbert transform [27]. the chirplet-based method performed better in the case of signals with interfering and overlapped chirplets. the performance demonstration of the above applications was carried out by inspecting a steel block with a flat-bottom-hole in a contact pulse-echo mode using a 5mhz probe. the same method was applied to analyze and estimate ultrasonic echoes in the testing of reverberant multilayered materials, which is an important and challenging application that examines the thin planner defects, disbonding, and lamination [28]. the estimated parameters were used to classify the ultrasonic echoes and calculate the physical properties of a layered structure such as layer thickness. the performance demonstration was carried out by inspecting a steel block with a flat-bottom-hole in an immersion testing setup using a 10mhz probe. the waveform acquired for the experimental verification of the method had high snr and well-resolved echoes. the chirplet transform is suitable to play role in noise suppression and resolution enhancement in the inspection of composite and bonded materials. iv. application of chirplet transform to ultrasonic lamb waves in ndt and shm the frequency content of the dispersive signal is timevarying, so using a time-frequency representation like the chirplet transform is suited for signal processing of the dispersive curves and defect’s echoes identification. authors in [29] introduced the chirplet transform to the signal processing of guided waves. they analyzed the theoretical time-frequency resolution of the transform in the dispersive waves. the application of the transform to the measured signals revealed that it is better than the stft in the analysis of dispersive waves because the time-frequency tiling of the chirplet transform is adapted to the dispersion characteristics. furthermore, an adaptive method was developed to simplify the analysis of the dispersion relationships of the measured signals. the research in [29] paved the way for the application of the transform to guided waves. authors in [30] proved that a model-based chirplet transform method was effective in determining the energy distribution of the dispersive lamb waves. the rayleigh-lamb equations have been used to model the dispersion relationship and an adaptive method to calculate the frequency of the modes. the proposed method was used to address the inconsistency of the standard transform solution with the theoretical solution in the case of dispersive curves intersection. many researchers have proposed variant chirplet transform algorithms to address the complexity problem due to the number of dimensions of the standard transform. one method used to simplify the computation and interpretation is the matching pursuit [31], which was used to implement the chirplet transform for the application to shm guided waves in isotropic plate structures using the pulse-echo testing method [32]. the trace resulting from the difference between the measured and a reference signal is processed using matching pursuit algorithm to calculate the time-frequency centers, chirp rate and energies of the signal. the matching pursuit is applied continuously until the energies of the signal atoms are 10% or lower of the first extracted atom. the frequency centers that do not belong to the excited bandwidth are discarded and the damage status of the structure is evaluated based on the calculated energies. the processing is carried on with mode correlation using the determined chirp rates, and the parameters of the identified modes are used to locate and characterize the defects. authors regarded this version of the chirplet transform better than the conventional methods in resolving the multimodal reflections, robust in noisy signals, and computationally efficient. future works promised by the authors were the application of the method to the guided wave inspection of the composite structures and revisiting the adopted assumption of point-scatterer, however no related research was found in the relevant literature. recently, chirplet matching pursuit has been presented to evaluate the damage in aerospace structures. the method utilizes a library of simulated damage signals generated by varying damage parameters of crack length, depth, and orientation [33]. the successful applications of the chirplet transform in the guided wave inspection motivated researchers to seek further solutions by employing this method. an adaptive algorithm based on chirplet transform has been introduced to evaluate its merits for dispersive mode analysis and calculate the mode displacement ratios and attenuation of lamb waves in [34]. the algorithm, which considered 5dimensional parameters of the chirplet transform, uses basis functions designed to suit the dispersion relation of each mode. engineering, technology & applied science research vol. 9, no. 1, 2019, 3778-3781 3780 www.etasr.com mohammed & ki-seong: chirplet transform in ultrasonic non-destructive testing and structural … a windowing technique was used to average the energy contents that belong to all points of the dispersive curves. the method offered advantages over the stft in resolving the modes and extracting the required information. the limitations of sensitivity to noise, parameter uncertainties, and the need for accurate prior knowledge about the material properties and geometry demand research to improve the robustness of the method for this application. another contribution to ultrasonic guided wave signal processing was brought by the authors in [35] who modified an algorithm that presented a spare representation of the signal using chirplets [36] to develop a chirplet mode decomposition technique for the separation of individual modes in a multimodal torsional signals measured in the magnetostrictive guided wave inspection of pipelines. to ease the implementation, authors replaced an mle equation of those of [36] with a procedure that estimates the chirp rate and duration, uses the estimates to locate the chirp in time and frequency, re-estimates form a local measure, and uses the quasi-newton procedure to find the closest local maximum of the likelihood function. this algorithm is a novel and reliable estimator for the parameters of multicomponent signals. the use of the procedure allows a precise calculation of the group velocity, amplitude, and modal energies, which are used to calculate the reflection coefficients, which are in turn used for defect sizing. the research results have been applied to the detection and characterization of pipe defects using torsional guided waves [37, 38]. an approach for resolution improvement and image fusion was developed in [39]. it comprises adaptive chirplet transform, vold-kalman filter, and a method for image fusion. the adaptive chirplet transform role in the method was to identify the signal components and estimate the instantaneous frequencies. the vold-kalman filter was used as a time-varying filter to use signal parameters, calculated by the adaptive chirplet transform to extract the time-domain waveforms reflected from the defects. investigating alternative methods to the vold-kalman filter and comparing the performances can be a space for development in the use of adaptive chirplet transform in lamb wave applications. v. conclusions the review revealed that the amount of research on ultrasonic ndt and shm signal processing does not match the versatility and inclusiveness offered by the transform. the various variants of the chirplet transform are qualified to provide more and additional robust and effective solutions. various implementations of the chirplet transform were successfully applied to ultrasonic signal processing, with most applications targeting the improvement of the dispersive curves’ resolution in ultrasonic guided wave ndt and shm applications. published studies were reviewed to show the research progress since the transform was first applied to ultrasonic ndt and shm, the areas of application, its advantages, and to briefly highlight the potential openings for further 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w. c. karl, “sparse representations with chirplets via maximum likelihood estimation”, ieee transactions on signal processing, vol. 48, pp. 42-53, 2000 [37] c. y. kim, k. j. park, “characterization of pipe defects in torsional guided waves using chirplet transform”, transactions of the korean society for noise and vibration engineering, vol. 24, no. 8, pp. 636– 642, 2014 [38] y. w. kim, k.j. park, “application of chirplet transform for detecting axial cracks in pipes using torsional guided modes”, insight-nondestructive testing and condition monitoring, vol. 59, no. 3, pp. 138143, 2017 [39] l. zeng, m. zhao, j. lin, w. wu, “waveform separation and image fusion for lamb waves inspection resolution improvement”, ndt & e international, vol. 79, pp. 17-29, 2016 engineering, technology & applied science research vol. 8, no. 6, 2018, 3598-3602 3598 www.etasr.com alghamdi: computerised information security using texture based fuzzy cryptosystem computerised information security using texture based fuzzy cryptosystem abdulrahman abdullah alghamdi college of computer science and it, shaqra university, saudi arabia alghamdia@su.edu.sa abstract—the main objective of this study is to form a unique and economical steganographic technique for digital pictures employed for secret transmission using texture and fuzzy logic. this technique is employed to embed data in the carrier image and to extract the hidden message within the same carrier image. initially, fuzzification, which transforms the carrier and the secret image into numerous bitplanes, is completed. pixel number calculation is completed in the original image. then, feature extraction is completed in the secret image. finally, pixel merging follows within the sender region by assigning white and black pixels in the original image and in the secret image. pixel numbers and texture features are extracted and can be used as a key for retrieving the embedded image from the receiver. this modified approach can be applied in various images. experimental results reveal that this method will hide and retrieve the secret messages in a carrier accurately. keywords-information security; fuzzy logic; texture features; carrier image; secret image; steganography i. introduction maintaining secrecy and security of confidential data over the internet and cloud is very important. cryptography and steganography are techniques which can be used together to maintain security and secrecy of highly confidential data over the computing environment. steganography is the method of providing information security for secret images by inserting the message in other messages (carrier images). the proposed methodology provides more than one level of security since it combines value and texture features of all the pixels present in the entire image. steganography is finalized with numerous enhancements in medium and within the secret pictures. data hidden in images are most commonly used as input [2, 3]. in this case, the medium which is concealing the data is a picture. the picture will be outlined as a two-dimension coordinate function f(x,y), where x and y represent the coordinates, and f the intensity [1]. during this process, the picture is considered as a matrix of two dimensions. regarding the proposed methodology, the text that is to be embedded in a picture is a grey image. embedding will be done by the application of fuzzy rules on the region merging process. the embedded text will be retrieved simply by the receiver who is aware of the defuzzification method. the most significant part this methodology is that it can be used by any end user. this technique only concentrates on the image’s ability of carrying hidden data. ii. literature survey many techniques for information hiding were proposed in [4-6, 8-10, 11-15, 18, 20]. authors in [16, 17] proposed a method for information hiding. they tried to hide the data using a domain supported fuzzy logic-based methodology. the benefit of this methodology is that it is computationally less complicated compared to existing data hiding strategies. however, the information which is to be hided is sensitive in nature and it's easy to be destroyed by creating a little amendment within the overall data and by dynamical with none explicit visibility. author in [4] proposed a methodology for the replacement of data in an image. secret information is hidden as an image by employing a fuzzy based method and cryptography technique which creates minimum distortion within the entire image which ends up in a high quality stego image. the main advantages of this methodology are that it yields a better rate in embedding information and it improves overall security. authors in [18] designed a strategy supported by the mix of a hybrid fuzzy c-means formula and svm for proposing steganography. their model creates an activity such that the key messages are convertible. authors in [3] developed a replacement schema for steganography by least bit technique for utilizing the hybrid-based edge detector technique. their technique uses a combination of character detection methodology and edge detection algorithms supporting fuzzy logic. this methodology overcomes the existing methods of steganalysis systems. it additionally generates prime quality stego pictures. every steganography-based technique has its own disadvantages. authors in [12] worked on the various disadvantages of already used steganography systems. authors in [7] elaborated three kinds of steganographic attacks: in hardiness, in presentation, and in interpretation. most of the prevailing works used threshold based algorithms, fuzzy c means algorithms, and neural networks-based algorithms. also, it has been observed that most of the existing methods show less accuracy in hiding images with more information. therefore, a new methodology to embed secret messages in a carrier image more effectively is necessary. engineering, technology & applied science research vol. 8, no. 6, 2018, 3598-3602 3599 www.etasr.com alghamdi: computerised information security using texture based fuzzy cryptosystem iii. proposed methodology a combination of texture and fuzzy logic-based pixel merging methodology is proposed for embedding information as an image into a carrier image. this combination makes an effective process of steganography, while the quantity of the secret information can be augmented. the proposed methodology is a combination of processing biplanes, texture features of an image and fuzzy rules applied to both original and secret images. the proposed architecture is shown in figure 1. fig. 1. architecture of the proposed method a. steganographic image generation the planned technique consists of the subsequent steps: • grey scale original and secret images are considered as input pictures. • the algorithm counts the amount of black and white pixels in each input picture. • input pictures are separated into four monochrome pictures in order to get the bit values from every bitplane. • the bit pair representing the background is referred to as “lower nibble” and the remaining pair of bits that represents the foreground image is referred as “upper nibble”. • pixel merging is completed within the sender area by distributing the white and black pixels to the first image using fuzzy logic by scrutinizing the pixels in the original and secret image. it conjointly calculates pixel range from both images. • textural features are additionally calculated for the complete images starting from the first pixel. this process is employed to generate the key for encrypting the hidden image. • finally, the obtained area of pixels comprises the steganographic image. b. fuzzification fixing the values of one set of crisp value to a different fuzzy set of qualitative illustration is termed as fuzzification. in several fuzzy strategies like fuzzy based process, fuzzy cmeans and fuzzy based reasoning, intensity transformation of values towards various numerals is processed in the initial stage. in the current study, the fuzzification method is the formation of four bitplanes as shown in figures 2(a), 2(b) and 2(c). the input could be a monochrome image which contains black and white pixels. c. pixel number calculation pixel number is computed in order to find the place in the original image where a pixel of the secret image can be incorporated. it is used for decoding the secret message from stego image. d. feature extraction texture provides some necessary information concerning the structural arrangement of varied surfaces in an image. texture features accustomed in a unit area can classify the different types of pixels in an image. grey level co-occurrence matrix (glcm) options are calculated for the image border regions. for this, features such as correlation, energy, contrast, homogeneity are calculated. e. description of the glcm features in this method, gray level co-occurrence matrix properties like entropy, energy, contrast and homogeneity are computed. the four glcm properties used in this method are: 1) energy the energy returns the sum of the squared elements in glcm. the energy ‘e’ can be calculated by using (1): ∑ 𝑝(𝑖, 𝑗)2𝑖,𝑗 (1) 2) homogeneity homogeneity is a value that counts the closeness of the elements in the glcm to the its diagonal. homogeneity ‘h’ is computed by using (2): ∑ 𝑝(𝑖,𝑗) 1+|𝑖−𝑗|𝑖,𝑗 (2) 3) contrast contrast computes the intensity between a pixel and its neighbors for the entire image. the contrast ‘co’ of a pixel can be computes as: 𝐶𝑜 = ∑ |1 − 𝑗|2𝑖,𝑗 𝑝(𝑖, 𝑗) (3) 4) correlation correlation computes how a pixel is correlated to its neighbor for the entire image. the correlation ‘cr’of an image can be calculated by (4): ∑ (𝑖−µ𝑗)(𝑗−µ𝑗)𝑃(𝑖,𝑗) 𝜎𝑖 𝜎𝑗 𝑖,𝑗 (4) these features are calculated for the pixels present in the original image and in the secret image. an intruder who intends to modify the hidden data can’t predict or calculate the feature values of the image. this ensures that the information cannot be deciphered by intruders. engineering, technology & applied science research vol. 8, no. 6, 2018, 3598-3602 3600 www.etasr.com alghamdi: computerised information security using texture based fuzzy cryptosystem original image bitplane-1 bitplane-2 bitplane-3 bitplane-4 (a) original image bitplane-1 bitplane-2 bitplane-3 bitplane-4 (b) original secret image bitplane-1 bitplane-2 bitplane-3 bitplane-4 (c) fig. 2. fuzzification of (a) a real world original image, (b) a matlab database image (© m.i.t.) and (c) a secret information image and their bit planes f. fuzzy rules for pixel merging pixel merging is the method of merging two or more pixels, and here it is completed with the support of fuzzy rules. four rules where set for this method. this method compares the pixels of original and secret image and hides the key image in the original image. all the fuzzy rules begin the iteration from the initial pixel of the original and secret image. • fuzzy rule 1: if the pixel in original image (o) is black (b) and the pixel in secret image (s) is white (w) then, go to the next pixel of the original image. • fuzzy rule 2: if the pixel in o is w and the pixel in s is b then, calculate the pixel number and correlation value of the entire pixels of the original image. then merge the pixel of s with the one of o. after merging, go to the next pixel in both images. • fuzzy rule 3: if the pixel in o is w and the pixel in s is b, then go to the next pixel in s. • fuzzy rule 4: if the pixel in o is b and the pixel in s is b, then go to the next pixel in both original and secret image. g. encoding the message the pixel number of the original image combined with the feature values are the key which is given to the receiver. the receiver will extract the hidden data from the original image by distinction of the proper pixel and by subtracting the texture feature values from it. since the pixels combined with the texture feature values are taken into account as a key for extracting the hidden data, this method is considered as secure in comparison with different existing steganographic techniques. iv. results and discussion this methodology uses matlab. the results were obtained by giving the input image along with the carrier image. from the obtained results, it can be noted that the carrier and also the output stego image were indistinguishable visually as shown in figure 3. the efficiency of this technique is decided from the peak signal to noise ratio (psnr) and the mean square error (mse). mse and the psnr are the metrics used for scrutinizing the quality of a picture. in general the quality of the processed image is high when the psnr is high. low mse means then the error between the processed and the original image is low. these parameters are outlined as: 𝑃𝑆𝑁𝑅 = 10 𝑙𝑜𝑔10(𝑅 2/𝑀𝑆𝐸 ) (5) where, m and n are the number of rows and columns in the input images. the msc value is calculated by using (6): engineering, technology & applied science research vol. 8, no. 6, 2018, 3598-3602 3601 www.etasr.com alghamdi: computerised information security using texture based fuzzy cryptosystem 𝑀𝑆𝐸 = ∑ [𝐼1(𝑚,𝑛)− 𝐼2(𝑚,𝑛)] 2 𝑀,𝑁 𝑀∗𝑁 (6) table i presents the accuracy obtained from the psnr and mse values for a few sample data as secret original images. the projected methodology is compared with lsb based steganography technique [4] and the existing method described in [19]. results ascertained that the proposed technique offers higher performance than the lsb and the existing technique. fig. 3. results of the original and stegano image for real world and database images table i. accuracy based on psnr and msc image psnr (existing method) mse (existing method) psnr (lsb based method) mse (lsb based method) psnr (proposed method) mse (proposed method) image 1 53.0288 0.1176 52.1268 0.1184 57.1268 0.1044 image 2 59.0198 0.1084 57.0918 0.1390 62.0918 0.0190 image 3 61.1187 0.2217 61.0435 0.2306 62.0435 0.1106 image 4 57.0198 0.1196 54.0211 0.1293 54.4101 0.0293 image 5 58.0139 0.2164 56.9131 0.2142 59.8731 0.1142 v. conclusion a modified steganographic technique is proposed in order to insert a secret message in a carrier image. the proposed technique can obtain better results than the lsb based and existing steganographic techniques regarding the quantity and the size of the hidden message. this methodology performs well in terms of required time to retrieve the hidden data from the carrier image. the obtained results reveal that this methodology offers better results in concealing a large number of pixels in an image. this methodology offers improved efficiency and accuracy when compared to the existing methods. it additionally offers extra since the texture features of the original and the secret image are combined. the performance of the proposed method can be revealed by the higher psnr and lower mse values for different images. references [1] r. c. gonzalez, r. e. woods, digital image processing, pearson, 2008 [2] n. f. johnson, s. jajodia, “steganalysis: the investigation of hidden information”, ieee information technology conference, information environment for the future, syracuse, new york, usa, september 3, 1998 [3] i. avcibas, n. d. memon, b. sankur, “steganalysis based on image quality metrics”, ieee fourth workshop on multimedia signal processing, cannes, france, october 3-5, 2001 [4] a. s. abdullah, “text hiding based on hue content in hsv color space”, international journal of emerging trends & technology in computer science, vol. 4, no. 2, pp. 170-173, 2015 [5] z. k. al-ani, a. a. zaidan, b. b. zaidan, h. o. alanazi, “overview: main fundamentals for steganography”, computer engineering, vol. 2, pp. 158-165, 2010 [6] f. a. p. petitcolas, r. j. anderson, m. g. kuhn, “information hiding-a survey”, proceedings of the ieee, special issue on protection of multimedia content, vol. 87, no. 7, pp. 1062-1078, 1999 engineering, technology & applied science research vol. 8, no. 6, 2018, 3598-3602 3602 www.etasr.com alghamdi: computerised information security using texture based fuzzy cryptosystem [7] s. craver, b. l. yeo, m. yeung, “technical trials and legal tribulations”, communications of the a.c.m., vol. 41, no. 7, pp. 44-54, 1998 [8] r. j. anderson, f. a. p. petitcolas, “on the limits of steganography”, ieee journal on selected areas in communications, vol. 16, pp. 474481, 1998 [9] a. cheddad, j. condell, k. curran, p. mc kevitt, “digital image steganography: survey and analysis of current methods”, signal processing, vol. 90, pp. 727-752, 2010 [10] n. f. johnson, s. jajodia, “exploring steganography: seeing the unseen”, computer, vol. 31, no. 2, pp. 26-34, 1998 [11] w. bender, w. butera, d. gruhl, r. hwang, f. j. paiz, s. pogreb, “applications for data hiding”, ibm systems journal, vol. 39, no. 3-4, pp. 547-568, 2000 [12] f. a. p. petitcolas, “introduction to information hiding”, in: information hiding techniques for steganography and digital watermarking, artech house, inc., norwood, 2000 [13] s. g. miaou, c. m. hsu, y. s. tsai, h. m. chao, “a secure data hiding technique with heterogeneous data-combining capability for electronic patient records”, 22nd annual international conference of the ieee engineering in medicine and biology society, chicago, usa, july 2328, 2000 [14] fujitsu ltd., tackling new challenges, annual report 2007, fujitsu ltd., 2007 [15] n. provos, p. honeyman, “hide and seek: an introduction to steganography”, ieee security and privacy, vol. 99, no. 3, pp. 32-44, 2003 [16] f. khursheed, a. h. mir, “fuzzy logic-based data hiding”, proceeding of cyber security, cyber crime, and cyber forensics, department of electronics and communication, national institute of technology, srinagar, india, 2009 [17] a. h. mir, “fuzzy entropy based interactive enhancement of radiographic images”, journal of medical engineering and technology, vol. 31, no. 3, pp. 220-231, 2007 [18] v. k. munirajan, e. cole, s. ring, “transform domain steganography detection using fuzzy inference systems”, ieee sixth international symposium on multimedia software engineering, miami, usa, december 13-15, 2004 [19] a. a. alghamdi, “computerized steganographic technique using fuzzy logic”, international journal of advanced computer science and applications, vol. 9, no. 3, pp. 155-159, 2018 [20] a. a. alghamdi, “information security using steganographic method: genetic algorithm and texture features”, indian journal of science and technology, vol. 11, no. 34, pp. 1-6, 2018 microsoft word 36-3188_s1_etasr_v9_n6_pp5066-5073 engineering, technology & applied science research vol. 9, no. 6, 2019, 5066-5073 5066 www.etasr.com hassan & izzet: experimental and numerical comparison of reinforced concrete gable roof beams … experimental and numerical comparison of reinforced concrete gable roof beams with openings of different configurations maryam abdul jabbar hassan department of civil engineering college of engineering university of baghdad baghdad, iraq maryemaj123@gmail.com amer farouk izzet department of civil engineering college of engineering university of baghdad baghdad, iraq amer.f@coeng.uobaghdad.edu.iq abstract—this paper demonstrates an experimental and numerical study aimed at comparing the influence of openings of different configurations on the flexural behavior of reinforced concrete gable roof beams. the experimental program consisted of testing six simply supported gable beams subjected to midpoint concentrated load. the variable which has been investigated in this work was opening's configuration (quadrilateral or circular) with the same upper and lower chords depth. the results indicate improvement in the beams’ flexural behavior when circular openings were used compared with that of quadrilateral openings, represented by an increase in ultimate load capacity and a decrease in deflection at the service limit. also, there was an enhancement in the ductility and rigidity of the beams. the results of the tested beams were verified by a nonlinear finite element program, abaqus (2018). comparisons are presented and good agreement is shown between the predictions of the finite element analysis and the experimental results in terms of failure loads and load-deflection relations. keywords-reinforced concrete gable roof beam; opening's configuration; chords; numerical analysis i. introduction the presence of openings in gable beams has many advantages such as flexibility, easier handling, and, most importantly, reduced overall weight. furthermore, concrete has relatively low material cost, good high fire resistance, and low maintenance cost, therefore reinforced concrete gable beams can be used as a good alternative option instead of steel sections to support warehouse roofs, industrial buildings, and airplane hangars. but the insertion of openings in a solid beam directly affects beam behavior resulting in a more complicated behavior as the openings would essentially cause a sudden drop in the beam cross section dimensions. at the same time, the corners of the openings would be subjected to a high concentration of stress that could result in extensive cracking which is inadmissible from both esthetic and durability points of view. in addition, the presence of the openings would reduce the overall stiffness of the beam, which may result in extreme deflections under service loads. the design of these beams therefore, requires special treatment to control the crack width and to avoid probable early failure of the beam [1, 2]. researches on the reinforced concrete beams with openings began in the early ‘60s [3-5]. extensive study has been carried out in [6] on concrete beams with large openings using nonlinear finite element analysis and taking into consideration assumptions for the geometric constraints. the results show that openings near the supports can be used to perform detailed calculations for shear force distribution in both chords. in [7], the influence of circular openings on the structural performance of concrete beams was examined by testing 9 perforated normal strength concrete beams and 5 perforated high strength concrete beams, in addition to a reference solid normal strength concrete beam under two-point loads. the main findings were that both ultimate strength reduction and cracking pattern were magnified in the normal concrete beams, when the opening’s diameter exceeded the one-third of the beam's depth. the diameter and the opening place were the main parameters affecting the strength of the beam. three-dimensional finite element model that can capture the flexural performance of concrete beams with one rectangular opening was proposed in [8]. a thorough validation was undertaken using several models including one rectangular transverse opening showing a good agreement between numerical and experimental results. the main investigated variables to understand their effect on the structural response of the member were: concrete compressive strength, reinforcement ratio, and opening dimensions. the numerical solution showed that the ultimate strength of the beam and the post-cracking stiffness rise with the increase of concrete compressive strength, or increase of bottom reinforcement amount and decrease with increasing opening size. in [9], a new theory of nonlinear three-dimensional elastic damage to simulate reinforced concrete elements was proposed. more attention was paid to simulate perforated reinforced concrete beams’ nonlinear behavior based on thermodynamic basis. the developed theoretical approach considers nonlinear elastic behavior and concrete materials’ deteriorated state. to validate corresponding author: maryam abdul jabbar hassan engineering, technology & applied science research vol. 9, no. 6, 2019, 5066-5073 5067 www.etasr.com hassan & izzet: experimental and numerical comparison of reinforced concrete gable roof beams … the suggested model, a comparison was made with experimental results and a good agreement was reached. in [10], a numerical investigation of the effects of circularshaped openings on the performance of reinforced concrete beams with finite element method (fem) has been suggested. the finite element package ansys 14.0 was used to simulate simply supported concrete beams with circular openings having different diameters at various positions. seven models were numerically replicated with ansys. the main finding was that the location of the opening has a significant effect on the behavior of the model. locating the opening near the supports resulted in dropping of the maximum strength capacity of the model by 32% in respect to the solid beam with less significant influence on the maximum strength when the circular-shaped opening was located at the center of the span. in [11], a numerical study explored the structural behavior of reinforced concrete beams with circular openings via finite element method using abaqus. the main variables were opening size and location. seven beams were tested under three-point loading. the results showed that an increase of the opening size decreases the ultimate strength of the beam and increases its maximum deflection. placing of the opening in the shear zone decreased the ultimate strength by about 26% and 36% and increased maximum deflection by about 4% and 22% compared to the reference beam. on the other hand, for beams with the opening located in the flexure zone, the ultimate strength was decreased by about 6% and 13% and the maximum deflection was increased by about 1.5% and 19.7%. therefore, the optimum location for the openings in the reinforced concrete beam was found to be the flexural zone. ii. experimental program the experimental program of this study was executed by manufacturing and testing 6 simply supported reinforced concrete gable roof beams under monotonic static loading at mid span until failure. the studied variable was the opening's configuration (quadrilateral or circular) with the same upper and lower chords depth [12]. a. specimen details the test specimens, including the reference beam without openings (solid) and the other 5 beams with eight (quadrilateral or circular) openings, had an overall length of 3000mm, width of 100mm, and height 400mm at the center and 250mm at the ends as exhibited in table i. all beams had the same details of reinforcement as shown in figure 1. the beams were tested with an overall clear span of 2800mm. the specimens were divided into three groups (a, b, and c). these groups were classified as mentioned, according to the variable that have been used in this study (table i). b. material properties normal concrete has been used to cast the beams. the properties of concrete (compressive strength, splitting tensile strength, and modulus of elasticity) were determined using cylindrical steel molds (with 150 and 300mm diameter and height respectively). the diameters of used steel reinforcement bars were: 4, 6, 12mm and the properties of the average yield, ultimate stresses, and modulus of elasticity were determined according to the standard tests of steel reinforcements bars. the properties of normal concrete and steel reinforcements used in this work are given in table ii. (a) (b) (c) (d) (e) (f) fig. 1. details of beam specimens (all dimensions are in mm): (a) beam gb, (b) beam gth8, (c) beam gt8, (d) beam gp8, (e) beam gc1, (f) beam gc2 c. setup and testing procedure figure 2 exhibits a schematic shape of the test setup. the test rig frame dimensions were 5.45m width and 3.00m height. the beams were simply supported by steel rollers with a thick steel plate. the left one was welded to the beneath bearing plate to simulate hinge support whereas the other one was not. in the case of beams with multi openings, the applying load is preferred to be on the post nodes. to eliminate the difference in load due to the difference in openings’ size and locations, the load was applied on a thick 100mm×100mm bearing steel plate positioned at the tapered crest end of the gable beam which was flatted horizontally. a hydraulic jack of 50ton capacity was used to apply load on the beams. the applied load was controlled by using a load cell with a digital load reader. the engineering, technology & applied science research vol. 9, no. 6, 2019, 5066-5073 5068 www.etasr.com hassan & izzet: experimental and numerical comparison of reinforced concrete gable roof beams … load was applied with an increment of 2kn. dial gauges were used for measuring the vertical deflections at a distance of 150mm from support and at mid-span. also the longitudinal generated strain at the surface of the concrete and reinforcing steel bar due to the applied loads was measured by strain gauges. the beams were loaded up to failure, the deflection and generated strains were measured, the propagation of cracks was marked and the crack widths measured at different load levels. table i. details of the tested beams lower chord height (mm) upper chord height (mm) total area of openings (mm 2 ) number of openings shape of openings beam mark group -------------------------gb ref. beam 75 75 234000 8 trapezoidal gth8 a 75 75 184200 8 circular gc1 100 100 174000 8 trapezoidal gt8 b 100 100 128000 8 circular gc2 100 100 151000 8 trapezoidal with inclined posts gp8 c 100 100 128000 8 circular gc2 table ii. material properties modulus of elasticity (gpa) ultimate tensile strength (mpa) compressive strength (mpa) yield stress (mpa) diameter (mm) material 27 3.5 31 ----------concrete 200 567 -----370 4 steel 200 629 -----550 6 200 677 -----600 12 table iii. test results crack and failure mode decreasing ratio of pu% 2 decreasing ratio of total volume % 1 ultimate load pu (kn) pcr (kn) beam mark group flexural tension failure ----------90 18 gb ref. beam flexural tension failure and beamtype failure around openings 14.67 23.82 76.8 14 gth8 a flexural tension failure and beamtype failure around openings 9.44 8.35 81.5 14 gc1 flexural tension failure and beamtype failure around openings 10.89 17.71 80.2 14 gt8 b flexural tension failure and beamtype failure around openings 4.44 13.03 86 14 gc2 flexural tension failure and beamtype failure around openings 6.89 15.37 83.8 18 gp8 c flexural tension failure and beamtype failure around openings 4.44 13.03 86 14 gc2 (1) decreasing ratio of total volume related to reference beam gb (2) fig. 2. test setup iii. experimental results and discussion a. cracking, failure loads, and mode of failure first cracking load is known as the applied load at crack appearance in the tension zone of the beam. it was recorded experimentally as the first observed crack by a microscope. the test showed that the first crack load of the solid beam (reference beam) was 18kn while it ranged from 14 to 18kn for the beams with openings. so, it can be concluded that the insertion of openings had a little effect on cracking formation. results exhibit that the presence of openings in a gable roof beam reduces its ultimate load capacity, due to sudden drop in the beam’s cross section dimensions. it can be noticed that the decreasing ratio of ultimate strength ranged between (4.44%14.67%) related to the reference beam which can be considered comparatively little. this might be attributed to the efficient design represented by sufficient quantity of reinforcements and engineering, technology & applied science research vol. 9, no. 6, 2019, 5066-5073 5069 www.etasr.com hassan & izzet: experimental and numerical comparison of reinforced concrete gable roof beams … using short stirrups in the top and bottom chords to prevent frame-type shear failure [2]. conversely, the experiments indicated that the reference beam (gb) failed in the tensioncontrolled flexural mode after the yielding of tension steel. a limited number of diagonal cracks in the vicinity of supports did not influence the failure. the beams with openings failed in the tension-controlled flexural mode due to the formation of several flexural cracks in the tension zone and finally crushing of concrete near the loading point. the type of cracks at the corners of the openings was beam-type failure [2], and it can be observed that cracks at the corner of openings did not cause clear reduction in the load-carrying capacity of the beam. table iii indicates loads and modes of failure, while figure 3 shows the crack patterns of the tested beams. (a) (b) (c) (d) (e) (f) fig. 3. crack patterns: (a) beam gb, (b) beam gth8, (c) beam gt8, (d) beam gp8, (e) beam gc1, (f) beam gc2 b. load-deflection relationship mid-span deflection at different loading stages (20, 50kn, and ultimate load) are summarized in table iv and figure 4. results exhibit that the insertion of openings in a reinforced concrete beam usually increases its deflection due to the abrupt change in the cross-sectional dimensions which leads to reduced stiffness of the beam and thus causes excessive deflection. the increasing ratio of ultimate mid span deflection ranged between 42.32% and 56.85%. figure 4 demonstrates the deflection response due to the applied load for groups a, b, and c. the results indicate an increase in ultimate load capacity for beams with circular openings compared to beams with quadrilateral openings and the increase ratios were: 6.1% for beam gc1 related to beam gth8 (group a), 7.23% for beam gc2 related to beam gt8 (group b), and 2.6% for beam gc2 related to beam gp8 (group c). on other hand, the deflections at different loading stages are: 1) at 20kn lload • group a: the deflection for beam gc1 is less than the deflection of beam gth8 by 22.61%. • group b: the deflection for beam gc2 is less than the deflection of beam gt8 by 15.52%. • group c: the deflection for beam gc2 is less than the deflection of beam gp8 by 3.41%. 2) at 50kn load • group a: the deflection for beam gc1 is less than the deflection of beam gth8 by 18.3%. • group b: the deflection for beam gc2 is less than the deflection of beam gt8 by 16.9%. • group c: the deflection for beam gc2 is less than the deflection of beam gp8 by 11.66%. 3) at ultimate load • group a: the deflection for beam gc1 is less than the deflection of beam gth8 by 1.8%. • group b: the deflection for beam gc2 is higher than the deflection of beam gt8 by 6.82%. • group c: the deflection for beam gc2 is slightly higher than the deflection of beam gp8 by only 0.3%. the results clarified that circular openings improve the ultimate load carrying capacity and flexural behavior, in comparison with quadrilateral openings, because the nature of the circular configuration reduces the possible stress concentration around the opening. also the total area of circular openings is smaller as clarified in table iii. c. ductility and rigidity ductility index (µ) is mostly defined as the ability of the beam to sustain additional deformation before failure. mathematically it is the ratio of mid-span deflection at 85% of ultimate load to that at yielding of the tension reinforcement [13]. this value is tabulated in table v, in addition to the rigidity value (k) which corresponds to the initial slope of the engineering, technology & applied science research vol. 9, no. 6, 2019, 5066-5073 5070 www.etasr.com hassan & izzet: experimental and numerical comparison of reinforced concrete gable roof beams … load-deflection curves (figure 4). according to table v, the highest values of µ are recorded for beams with circular openings (gc1 and gc2) which significantly exceeded the reference beam. also, the increasing number of openings led to decrease µ values, the reason might be the energy absorption capacity of the beam with circular openings which significantly exceeded the energy absorption capacities of solid beam and of the beam with quadrilateral openings. on the other hand, the provision of openings results in significant reduction of the rigidity of a beam. table v indicates that the beams with quadrilateral openings had smaller rigidities compared to the beams with circular openings. this can be primarily attributed to the smaller total area of circular openings. reduction in the stresses due to the lack of sharp corners in circular openings may have resulted in a more rigid flexural behavior in theses beams. table iv. deflection at various loading stages of the tested beams at pu (kn) at 50kn at 20kn beam mark group increasing ratio of deflection% * deflection (mm) increasing ratio of deflection% * deflection (mm) increasing ratio of deflection% * deflection (mm) ----16.80 ----7.93 ----2.62 gb ref. beam 56.85 26.35 42.88 11.33 40.08 3.67 gth8 a 54.05 25.88 16.77 9.26 8.40 2.84 gc1 42.32 23.91 32.16 10.48 27.86 3.35 gt8 b 52.02 25.54 9.84 8.71 8.02 2.83 gc2 51.55 25.46 24.34 9.86 11.83 2.93 gp8 c 52.02 25.54 9.84 8.71 8.02 2.83 gc2 table v. ductility and rigidity of the tested beams rigidity (kn/m) deformation ductility, µ beam mark group ����� ����� �� k μ���� μ���� �� µ ∆yielding ∆0.850f pult 1.00 9.26 1.00 2.85 4.57 13.01 gb ref. beam 0.54 4.96 1.04 2.96 5.87 17.38 gth8 a 0.86 8.00 1.2 3.41 4.11 14.00 gc1 0.74 6.83 0.87 2.48 6.39 15.88 gt8 b 0.92 8.48 1.18 3.35 4.26 14.28 gc2 0.79 7.27 0.89 2.55 5.57 14.20 gp8 c 0.92 8.48 1.18 3.35 4.26 14.28 gc2 fig. 4. load-mid span deflection relationships engineering, technology & applied science research vol. 9, no. 6, 2019, 5066-5073 5071 www.etasr.com hassan & izzet: experimental and numerical comparison of reinforced concrete gable roof beams … iv. finite element modeling a. element types, boundary, and loading conditions the characters of the finite elements types used in modeling each of the tested beams by abaqus program are summarized in table vi. each element type in the present model has been used to represent a specified constituent of each of the tested beams [14]. table vi. description of the used elements beam components family element characteristics concrete and bearing steel plates 3d stress c3d8r: an 8-node linear brick, reduced integration, hourglass control steel reinforcing bars (long. top, long. bottom, and shear reinforcement) truss t3d2: a 2-node linear 3-d truss in order to avoid stress concentration at supports and loading point, steel plates with dimensions of 100mm×100mm×20 mm were added (full contact element with full bond between bearing plates and the specimen). the simple support at the left side of the beam has been modeled as a hinge by constraining a single line of bearing plate nodes over the width of the beam soffit in the xand y-directions support (i.e. ux=uy=0) while allowing rotation about the x–axis. the other support has been modeled as a roller by constraining the y-direction (uy=0) and allowing longitudinal displacements and rotations about the x–plane axis. the load was applied as a distributed pressure on the loading plate, the applied boundary and loading conditions are shown in figure 5. fig. 5. boundary and loading conditions used in the analysis b. reinforcement, meshing and analysis of the model the reinforcement is assumed to be fully embedded into concrete. the general view of the numerical model of reinforcement is displayed in figure 6. fig. 6. numerical reinforcement model the aggregates used in the experimental work had a maximum size of 10mm. since the macro-scale behavior of concrete depends on the aggregate size, the mesh size needed to be greater than the maximum aggregate size [15] for accurate results, therefore a mesh size of 25mm with an aspect ratio of 1 was chosen for the analysis. the meshed model is demonstrated in figure 7. abaqus software allows selecting the kind of analysis required to perform the model with specifying step increment (automatic step increment or fixed step increment). each analysis step in abaqus is divided into several increments. the type of analysis used depends on the loading conditions and response you wish to detect. the presented model, static analysis type and fixed step increment are utilized. fig. 7. numerical meshed model v. result comparison a. failure loads and ultimate deflection table vii shows a comparison between the failure loads and mid-span deflection obtained from the finite element models and from the experimental work at failure stage for all beams under static test [12]. a good agreement was obtained between ultimate loads and deflection of numerical models and experimentally tested beams, where the value of the average for ( �)/( �)� � was 1.03, whilst the value of the average for w��/w� � was 0.95, therefore the finite element analysis can be considered a good tool to describe the flexural behavior of the tested beams. table vii. comparison of failure load and mid-span deflection group beam mark failure load (kn) (((( ����))))��������/(/(/(/( ����))))���� ���� mid-span deflection (mm) wwww��������/w/w/w/w���� ���� (((( ����))))�������� (((( ����))))���� ���� wwww�������� wwww���� ���� ref. beam gth8 81.97 76.8 1.07 24.66 26.35 0.94 a gt8 83.13 80.2 1.04 20.83 23.91 0.87 gc1 84.72 81.5 1.04 27.04 25.88 1.04 b gt8 83.13 80.2 1.04 20.83 23.91 0.87 gc2 87.13 86 1.01 25.88 25.54 1.01 c gp8 85.20 83.8 1.02 23.72 25.46 0.93 gc2 87.13 86 1.01 25.88 25.54 1.01 mean 1.03 mean 0.95 engineering, technology & applied science research vol. 9, no. 6, 2019, 5066-5073 5072 www.etasr.com hassan & izzet: experimental and numerical comparison of reinforced concrete gable roof beams … fig. 8. predicted and experimental load-mid span deflection relations b. load-deflection relationship the results found from the fe analysis for the load versus deflection relation for static analysis models are compared with the experimental results in figure 8. it can be observed that the behavior of load-deflection curves obtained from fe analysis is slightly higher than the real experimental work. in other words, the numerical models were stiffer than the experimental data in both linear and nonlinear regions. this is not strange since the finite element method deals with the model member as a rigid body, which is more stiff and stronger than the actual body, and also due to the assumed perfect bond between concrete and steel reinforcement, but anyhow there was a good agreement between them. vi. conclusions provision of openings in a gable roof reduces their weight which and can be cast in place or manufactured in precast factories and transmitted to be used as supporting members for long span roofs. so, the provision of openings in a gable beam offers several advantages such as lightweight, ease of handling and erection, and geometric flexibility. based on the current study the following can be concluded: • using circular openings instead of quadrilateral ones improves flexural behavior of the beams represented by an increase in ultimate load capacity and decrease in deflection at service limit. also it increases both ductility and rigidity. • using of inclined posts for openings instead of vertical ones has been instrumental in improving flexural behavior and reducing the difference between them and beams with circular openings in terms of maximum load capacity, deflection and rigidity. • finite element analysis with abaqus (2018) software was used to validate the results of the tested beams. comparisons were presented and good agreement was shown between the predictions of the finite element model and the experimental results in terms of failure loads and load-deflection relations. • the average ratio of ultimate loads and deflection of numerical models to the experimentally tested beams was 1.03 and 0.95, respectively. therefore, finite element analysis can be considered a good tool to describe the flexural behavior of the tested beams. references [1] m. a. mansur, k. h. tan, concrete beams with openings: analysis and design, crc press, 1999 [2] v. n. baykov, e. e seagal, reinforced concrete structures, stroyizdat, 1991 [3] s. a. salam, “beams with openings under different stress conditions”, in: proceedings of the 3rd conference on our world in concrete and structures, ci premier, 1977 [4] m. a. mansur, k. h. tan, s. l. lee, “design method for reinforced concrete beams with large openings”, journal proceedings, vol. 82, no. 4, 1985 [5] m. a. mansur, y. f. lee, k. h. tan, s. l. lee, “tests on rc continuous beams with openings”, journal of structural engineering, vol. 117, no. 6, pp. 1593-1606, 1991 [6] s. ehmann, m. schnellenbach-held, “behaviour and design of reinforced concrete beams with large openings”, in: fracture mechanics of concrete structures, pp. 903-909, swets & zeitlinger, 2001 engineering, technology & applied science research vol. 9, no. 6, 2019, 5066-5073 5073 www.etasr.com hassan & izzet: experimental and numerical comparison of reinforced concrete gable roof beams … [7] j. v. amiri, m. h. alibygie, “effect of small circular opening on the shear and flexural behavior and ultimate strength of reinforced concrete beams using normal and high strength concrete”, 13th world conference on earthquake engineering, vancouver, canada, paper no. 3239, august 1-6, 2004 [8] a. s. al-shaarbaf, n. a. m. j. al-bayati, d. i. a. al-kaisy, “nonlinear finite element analysis of reinforced concrete beams with large opening under flexure”, engineering and technology journal, vol. 25, no. 2, pp. 210-228, 2007 [9] h. madkour, k. ahmed, “three-dimensional modelling for reinforced concrete beams with openings based on nonlinear elastic-damage theory”, journal of engineering sciences, vol. 35, no. 1, pp. 9-27, 2007 [10] n. h. saksena, p. g. patel, “effects of the circular openings on the behavior of concrete beams without additional reinforcement in opening region using fem method”, international journal of advanced engineering technology, vol. 4, no. 2, 2013 [11] a. a. f. shubbar, h. alwan, e. y. phur, j. mcloughlin, a. al-khaykan, “studying the structural behavior of rc beams with circular openings of different sizes and locations using fe method”, world academy of science, engineering and technology, international journal of structural and construction engineering, vol. 11, no. 7, pp. 849-852, 2017 [12] m. a. j. hassan, a. f. izzet, “serviceability of reinforced concrete gable roof beams with openings under static loads”, engineering, technology & applied science research, vol. 9, no. 5, pp. 4813-4817, 2019 [13] b. aykac, i. kalkan, s. aykac, y. e. egriboz, “flexural behavior of rc beams with regular square or circular web openings”, engineering structures, vol. 56, pp. 2165-2174, 2013 [14] abaqus/standard user’s manual, hibbitt, karlson and sorensen, inc., 2018 [15] fib, model code for concrete structures, john wiley & sons, 2010 engineering, technology & applied science research vol. 8, no. 3, 2018, 2937-2942 2937 www.etasr.com benmoussa et al.: outlining a model of an intelligent decision support system based on multi agents outlining a model of an intelligent decision support system based on multi agents nezha benmoussa signals, distributed systems and artificial intelligence laboratory (ssdia) enset, university hassan ii mohammedia, morocco meryem fakhouri amr signals, distributed systems and artificial intelligence laboratory (ssdia) enset, university hassan ii mohammedia, morocco souad ahriz signals, distributed systems and artificial intelligence laboratory (ssdia) enset, university hassan ii mohammedia, morocco khalifa mansouri signals, distributed systems and artificial intelligence laboratory (ssdia) enset, university hassan ii mohammedia, morocco elhossein illoussamen signals, distributed systems and artificial intelligence laboratory (ssdia) enset, university hassan ii mohammedia, morocco abstract—performance optimization has become a necessity for the survival of enterprises as emerging technologies continue to impact them. to achieve this goal, decision making, a complex process which depends on big data and human issues, must be effective. as enterprises are being subjected to a multi-faceted pressure, they must ensure the optimization of their performance. this article investigates an intelligent decision support system (idss) based on multi agent systems (mas). our contribution consists in developing an intelligent model with an idss mas approach that can detect and evaluate changes in both the external environment and the enterprise itself. this model is an adequate management tool for optimal and sustainable performance and offers real-time analytical, prospecting and optimization methods. keywords-decision making; performance; value creation; mas; idss i. introduction strategic decisions are the result of a complex process and they often refer to the complexity degree of decision-making issues and the environment in which an enterprise/company operates. for authors in [1], it refers to important decisions, in terms of actions taken to resources committed and jurisprudence. according to [2], there are decisions that especially focus on external environment. a decision is not always easy to take and in order to overcome the unexpected risks to manage, leaders seek to always be more effective when it comes to decision support tools usage. according to [3] decision support is considered as a science based on three assumptions: (a) postulate of reality: to have information and especially knowledge, (b) postulate of the decision-makers: act as a power actor according to the objectives set and the resources available and (c) postulate of the optimum i.e. optimize the decision. this basis principle is conditioned, in general, by various factors including environment changes and technological growth. nowadays with the digital transformation in the field of information systems, no enterprise can escape the use of new technologies that greatly facilitate data processing and sharing. in fact, more and more specialized software offers the possibility of carefully analyzing the data for a reliable result that will allow a quick and efficient decision-making. virtualization has become, therefore, an important tool enabling companies to be more responsive thanks to the different production and management applications. thus, artificial intelligence has no privacy for companies because it has integrated most of their functions and has become a means of data sharing, performance measurement and optimal decision-making thanks to the combination of human and artificial intelligence. indeed, in a highly competitive environment, enterprises seek to meet market demands and are constantly in need of solutions that enable them to be effectively reactive to the environment for greater competitiveness. the distributed decision process is an effective means of sharing, prevention and decision-making. the proposed model, an intelligent decision support system (idss) based on multi agent systems (mas), is part of computer intelligence and therefore business intelligence (bi). it would enable the enterprise to collect, model and report data to provide decision support for driving and optimizing decision-making. a. performance according to [4], performance is an encrypted result from the perspective of classification (in relation to oneself, improve performance / or compared to others). long-term performance has been reduced to its financial dimension. thus, a successful company is one that must reach the desired, by the shareholders, profitability and/or generate a certain level of engineering, technology & applied science research vol. 8, no. 3, 2018, 2937-2942 2938 www.etasr.com benmoussa et al.: outlining a model of an intelligent decision support system based on multi agents profit, or hold market share that preserves its sustainability [5]. performance is the ability of an enterprise to exploit its environment in the acquisition of scarce resources essential to its operation [6]. some authors equate performance with efficiency, ability or competitiveness, productivity, success and excellence [7]. the traditional definition of performance derives through a composition of efficiency and effectiveness [8]. according to [9], effectiveness is evaluated in relation with specific objectives of the company and the degree of result achievement and is likely to be attached to the notion of mission as it is a measurable result to be achieved. efficiency can be defined as the sum of outputs achieved (results achieved) by inputs units (means) engaged. the concept of performance can be defined in different ways. it means completion and it is also treated as competitiveness, effectiveness, efficiency and productivity. commonly, the four other meanings are: • the capacity of the potential of the natural or legal person’s “skills and strategy”. • the processes used to achieve the desired results, “tools”. • the results of actions measured against an endogenous or exogenous reference. • the quantitative and qualitative indicators and success defined objectives for example satisfaction, action plan, cost and time. moreover, the performance's dimensions define four complementary levels related to each other which a manager can follow to set a good strategy: financial results, customer satisfaction, efficient internal processes and organizational system. with the help of an expert system, this performance can be comprehensive and will ensure effective management in all situations. we can deduce that performance occupies a very important place in enterprises. it is their main ambition and also the key business process. in [10], performance is the ability to achieve a minimum of meeting the expectations of strategic customers and optimal benefit. these are the three types of performance: • organizational: a structure seeking to minimize the transactions. • social: social effects of structure’s activity are such that have ways of preventing and managing conflicts and they motivate and involve more staff. • economic or financial: structure achieves profitability. the challenge for enterprises is to improve and optimize their performance through effective decisions. thus, the implementation of a management decision system is a value creation lever that allows them to achieve effectiveness and efficiency in the actions. b. the intelligent dss called “system computerized decision support” (dss: decision support system) or “interactive system decision support” or “system of intelligent decision support”, idss is an integrated computer system, designed especially for decision-making and especially aimed at company leaders. idss is one of the management information system elements. it differs from the information system, since its main function is to provide not only information, but the analytical tools for decision making. it consists of programs, one or more databases, internal or external, and a knowledge database. it works with a language and a modeling program that enables leaders to study different assumptions for planning and evaluating the consequences. one of the first introductions of management decision systems (mds) or dss was in [11]. these systems provide decision makers with an aid in the decision-making even in complex and unstructured situations. they became effective at the end of the 70s when the various operational decision support tools have emerged and took the name of interactive dss. the intelligent dss is a computer system to help decision makers that deal with semi-structured problems [12-15]. according to [16], a dss is an automated information system, interactive, flexible, adaptable and specifically developed to help solve an unstructured decision problem and improve decision making. powered by potentially all financial applications, commercial and administrative, of the enterprise, idss is a tool of observation and description that will enable managers to monitor activity, detect and alert management reshape the strategy to the needs of the company and its environment. however, it provides no explanation or commentary but using dashboards, reporting, and a mas approach, the data is easily interpreted, processed and shared. c. multi agent systems (mas) multi agent systems have been the subject of some studies and have been treated differently [17-19]. the concept of fuzzy logic was introduced in [20], not only as a control methodology but also as a way to process data based on authorizing the use of membership in a small group instead of making use of membership in a cluster group. in the field of artificial intelligence, mas reduce the complexity of solving a problem by dividing the necessary knowledge into subsets, combining an independent intelligent agent to each of these subsets and coordinating the activity of these agents [21]. a multi agent system is a system consisting of agents. these agents each in its own turn, have internal interactions and are also related to the external environment. an agent is an autonomous computer system or program capable of carrying out independent actions. [20]. agents need to cooperate with each other, to have harmony amongst themselves and to carry out interactive conversation in order to have successful internal communication. a multi agent system or distributed artificial intelligence is, therefore, a set of it processes composed of several agents sharing resources and communicating with each other [22]. this communication is provided by different protocols and message types. thus, the mechanisms of the agents’ decisions are related to perceptions, representations and actions by all agents that cooperate to achieve a common task or a negotiation between those whose interests are different [23]. in [24], an agent is a “computational entity” as a computer program or a robot, which can be seen as perceiving and acting independently on its environment. this is an automatic autonomy since its behavior depends on the program and experience. development and implementation of dss continues to hold great promise for improving decision maker's 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of the e reporting gorithm clarifi ansformation in fig f the sequen the chronol ents constituti hich details t agram in figu fferent system ent that is resp mpany’s kpis ng, technology r.com sformation of business intell e olap cube for the dash fies the examp nto kpis. fig. 2. id g. 3. technica fig. 4. model ce diagram of ogical process ng the idss m the overview ure 5 represe m factors. agen ponsible for th s. subsequent y & applied sci benmous data. in the se ligence enterp s and data ma hboards resti ple of data c dss mas model al solution of ids idss mas algo f idss mas s of the diffe mas model is of the softw ents the intera nt 1 expresses he analysis an tly these kpis ience research ssa et al.: outli econd phase, w prise edition) f arts. finally, w itution. this collection and l s mas orithm erent interactio s illustrated fig ware engineer action betwee a need to the nd translation s are transmit h v ining a model o we use for the we use draft d their ons of gure 5 r. the en the e main of the tted to the extr the per dev c. age resu effe mea requ tran that rep to t bef bui resp sum cen wil app him of belo diff d. reen imp lim pro rich use coll vol. 8, no. 3, 20 of an intelligen db agent in raction, loadin execution of rforms the dw velopment of d fig. methodology we consider ents and trans ult of these in ective decision ans. these k quests the etl nsformation of t will be use orts using the the dwh agen fore informing ld his learnin ponse from t mmarizing the ntral agent will l be exploite propriate profil m with an appr the contributi ow the dwh ferent characte disscussion it solutions h ngineering or provement ap mits. these are ocess developm h repository an ers, our idss lection and pr 018, 2937-2942 nt decision supp a sql query ng and transfor f these queries wh design t dashboards and . 5. sequence y expressed nee slators connec nteractions is ns concerning kpis are passe l agent to tran f collected dat d as a basis dashboard ag nt who will us g the etl agen ng system. o the etl agen feedback of l record this d d by his infe le of the consu ropriate respon ion of the id h and data min eristics of each have high pote restructuring pproach. each still the subje ment or its sub nd data minin s sma mod rocessing, but 2 pport system ba y form and wi rmation of dat s by the etl task that wil d reports. diagram of idss eds that require cted to the pr the kpis all g human resou ed to the db nslate by extra ta. subsequen for developin gent. the latte e this data in h nt which will a once the db nt, it informs the previous a data in his know erence engine umer agent an nse to his nee dss mas m ning process b h. ential for proc strategies thr h process ha ect of research bstitution. if th ng makes know del will not also the prepa 2940 ased on multi a ill be translate ta collected thr l agent. the l be the bas s mas e data collectio rincipal agent. ow the makin urces and ma b agent. the action, loading ntly dwh is a ng dashboards er sends a feed his knowledge also use this da agent receiv the central agents. in turn wledge base w e to determine d therefore pro d. for a clear model, we com by highlightin cess optimizati rough a contin as advantages that leads eith he dwh is a wledge availab only enable aration of data agents ed by rough agent sis of on by . the ng of aterial latter g and a task s and dback e base ata to ves a agent n, the which e the ovide view mpare ng the ion in nuous s and her to datable to data a and engineering, technology & applied science research vol. 8, no. 3, 2018, 2937-2942 2941 www.etasr.com benmoussa et al.: outlining a model of an intelligent decision support system based on multi agents the selection of adequate knowledge for effective decisionmaking. in addition, it can also offer various decisions that can help the manager. the following comparative study shows the characteristics of dwh, data mining and our idss mas model whose functionalities are varied and intelligent compared to the first two processes, especially in terms of interactions of multi agents in real time and assistance to improve the decision-making. table ii presents a comparison between the two main systems used for decision making and our idss mas model. through this comparative study, we can conclude that the proposed idss mas model has several advantages over dwh and data mining, especially the coupling between the decision model and the mas which allows task division and multiple targeted interactions offering reliable data and subsequently accurate indicators improving the decision-making system. table ii. data warehouse, data mining and idss mas model comparison criteria data warehouse data mining idss mass problem definition x x data gathering x x selection of the analysis model x study results x x formalization and distribution x x identifying needs x x data modeling x x data deployment x x x expression of needs by agent x translation requirements by the central agent kpi x viewing reports and dashboard in real time x receiving and processing needs by each agent x specific role and independent task by agent x help to improve the decisionmaking process x possibility of adding a decision agent x iii. conclusion in this article, we presented different performance concepts and the proposed idss model that has a significant impact on the management of enterprises in general and on decisionmaking in particular. our study also provided a comparison between different systems such as data warehouse, data mining and our idss mas model to emphasize its advantages that are data analysis, sharing of real-time knowledge and above decision support. indeed, the general interest of this analysis is to guide decision-makers towards intelligent tools of decision support in a complex and evolving system for more efficiency and competitiveness. we deduce, therefore, that artificial intelligence can drive and optimize the performance of enterprises through different systems with human reflections and intelligences. indeed, the integration and popularization of the idss mas model will certainly contribute to the efficiency of the decision-making process of enterprises for optimal, balanced and sustainable performance. it will avoid long consultations, possible update constraints and will allow the management of the unforeseen by the realization of an in-depth diagnosis, real time sharing of knowledge and the performance evaluation for future optimization. finally, our cross readings have shown that in the educational field, despite the implementation of different platforms, universities do not have yet artificial intelligence at the decision-making level. for this reason our perspective is to implement the idss mas model in order to validate it and integrate it into academic institutions for real-time data sharing between stakeholders and effective decision-making through precise indicators concerning both the administrative component, that requires flexibility and rapid implementation, and the offered student training and skills that meet the needs of the market. references [1] h. mintzberg, d. raisinghani, a. theoret, “the structure of “unstructured” decision processes”, administrative science quarterly,vol. 21, no. 2, pp. 246-275, 1976 [2] h. i. anssof, corporate strategy, mcgraw hill, new york, 1965 [3] b. roy, d. bouyssou, “aide multicritère à la décisionméthodes et cas”, economica, paris, 1993 (in french) [4] t. quach, k. oanh, “une perspective de recherche sur la performance dans l'organisation”, 23e colloque annuel du conseil canadien des pme et de l'entrepreneuriat, trois-rivières, 2006 (in frenc) [5] i. missaoui, “valeur et performance des systèmes d'information”, cahier de charge n°5, cigref université paris-sud 11, paris, 2009 (in french) [6] m. bouamama, “nouveaux défis du système de mesure de la performance : cas des tableaux de bord”, gestion et management. université de bordeaux, 2015 (in french) [7] f. nwamen, “impact des technologies de l’information et de la communication sur la performance commerciale des entreprises”, revue des sciences de gestion, no. 218, pp. 111-126, 2006(in french) [8] p. amans, s. rascol-boutard, “la performance entre construit social et indicateur simplifié”, finance contrôle et stratégie, vol. 11, no. 3, pp. 45-63, 2008 (in french) [9] m. gervais, contrôle de gestion, economica, 2005 (in french) [10] a. bourguignon, “peut-on définir la performance?”, revue française de comptabilité, no. 269, pp. 61-66, 1995 (in french) [11] m. s. scott-morton, management decision system, 1971 [12] p. g. w. keen, m. scott-morton, “decision support systems : an oragnizational perspective”, addisonwesley publighing, 1978 [13] r. h. spargue , e carlson, building effective support systems, prentice-hall, inc, englewood cliffs, 1982 [14] p. n. finlay, introducing decision support systems, ncc blackwell, 19889 [15] a. r. probst, “les systèmes d’aide à la décision : rôle, structure et évolution”, gestion-revue in ternationale de gestion, vol. 9, no. 4, pp. 13-19, 1984 [16] e. turban, decision support and expert systems: managerial perspectives, macmillan library reference, 1990 [17] s. shamshirband, n. badrul anuar, m. l. mat kiah, a. patel, “an appraisal and design of a multi-agent system based cooperative wireless intrusion detection computational intelligence technique”, engineering applications of artificial intelligence, vol. 26, no. 9, pp. 2105-2127, 2013 [18] s. shamshirband, a. patel, n. badrul anuar, m. l. mat kiah, a. abraham, “cooperative game theoretic approach using fuzzy q-learning for detecting and preventing intrusions in wireless sensor networks”, engineering applications of artificial intelligence, vol. 32. pages 228241, 2014 [19] a. jahangirzadeh, s. shamshirband, s. aghabozorgi, s. akib, h. basser, n. badrul anuar, m. l. mat kiah, “a cooperative expert based support engineering, technology & applied science research vol. 8, no. 3, 2018, 2937-2942 2942 www.etasr.com benmoussa et al.: outlining a model of an intelligent decision support system based on multi agents vector regression (co-esvr) system to determine collar dimensions around bridge pier”, neurocomputing, vol. 140, pp. 172-184, 2014 [20] s. shamshirband, s. kalantari, z. bakhshandeh, “designing a smart multi-agent system based on fuzzy logic to improve the gas consumption pattern”, scientific research and essays, vol. 5, no. 6, pp. 592-605, 2010 [21] j. ferber, les systèmes multi agents vers une intelligence collective, intereditions, paris, 1995 (in french) [22] b. nachet, a. adla, “an agent-based distributed collaborative decision support system”, intelligent decision technologies various forms of intelligence, vol. 8, no. 1, pp. 15-34, 2014 [23] n. bakhta, modèle multi-agents pour la conception d’un siad collective, phd thesis, université d’oran, 2014, (in french) [24] g. weiss, multiagent systems, mit press, 2013 [25] s. h. chan, q. song, s. sarker, r. david plumleed, “decision support system (dss) use and decision performance: dss motivation and its antecedents”, information & management, vol. 54, no. 7, pp. 934-947, 2017 microsoft word etasr_v13_n4_pp11146-11152 engineering, technology & applied science research vol. 13, no. 4, 2023, 11146-11152 11146 www.etasr.com amritraj & mishra: fatigue performance of rib-to-deck double-sided weld joint of orthotropic steel … fatigue performance of rib-to-deck doublesided weld joint of orthotropic steel deck on plate girder railway bridges radha krishna amritraj department of civil engineering, nit patna, india radhaa.phd19.ce@nitp.ac.in (corresponding author) shambhu sharan mishra department of civil engineering, nit patna, india ssmishra@nitp.ac.in received: 27 april 2023 | revised: 10 may 2023 | accepted: 17 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5994 abstract this research work presents the stress behavior of rib-deck weld joints in orthotropic steel deck (osd) railway bridges. it is essential to determine the most vulnerable load mode of the wheels for fatigue failure of osd bridges and to improve the fatigue resistance of the welded rib-deck connection. fatigue performance largely depends on the weld stress. double-sided welds for rib-deck welds improve fatigue performance. the fatigue behavior of the rib-deck double-sided weld joint has been compared with the single-sided one. this study used abaqus software to create the global shell model and the solid submodel of the osd. the results of the structural stress-based finite element analysis indicated that when the center line of the front axle pair of a locomotive coincides with the center line of the midspan of the bridge, the most severe loading condition occurs. the rib near the main girder experiences the maximum structural stress in the weld toe of the rib-deck joint. moreover, the rib-deck double-sided weld joints have 43.7% less structural stress compared to single-sided weld joints at the root of the weld, and this improves the performance during fatigue of osds. keywords-orthotropic steel deck; rib-to-deck weld joint; double-sided weld; structural stress method; train load i. introduction orthotropic steel decks (osd) are widely used in largespan cable-suspension and -stayed bridges, as they have proven to be a better alternative to the most used steel plate girder railway bridges, from the view of fatigue strength, multi-tracks, high speed, and heavy freight trains. an osd bridge consists of a structural steel deck plate that is stiffened longitudinally, while transverse stiffeners may be optional. osds provide numerous benefits such as low dead weight, substantial loadcarrying capacity, and the ability to be built modularly on-site [1-3]. compared to standard steel plate-girder bridges, the low dead weight features of osds translate into considerable steel tonnage savings of up to 50% [4]. in general, osd bridges are complex structures with many weld connections. therefore, the strength and life of osds are mostly determined by fatigue and fracture of the weld connections and factors such as stress concentrations, the thickness of connecting plates, weld penetration, crack location at the rib-deck weld joints, and position of wheel loads [5-6]. wheel loads applied directly to the osd are the predominant factor that leads to fatigue cracks [7-8]. the most vulnerable fatigue cracks in osd bridges subjected to wheel loads are located in the rib-deck weld connection [4, 6-10]. figure 1 shows the rib-deck weld joints of osds that are prone to four distinct kinds of fatigue cracks, namely toe-deck (type 1), root-deck (type 2), toe-rib (type 3), and root-weld (type 4) [4, 10-12]. fig. 1. rib-deck weld joints. in [4], the structural stress behavior of the rib-deck weld joints of osd models was studied numerically, showing that the toe-deck cracking into the deck plate was the dominant among four crack types. in [13], the fatigue behavior of the engineering, technology & applied science research vol. 13, no. 4, 2023, 11146-11152 11147 www.etasr.com amritraj & mishra: fatigue performance of rib-to-deck double-sided weld joint of orthotropic steel … most prone to fatigue cracking rib-deck weld joints in osds was experimentally investigated, showing that after the beginning of a crack at the weld toe on the bottom surface of the deck plates, it propagates longitudinally till the crack tips reach the deck edges. then, the fatigue crack spreads through the thickness of the deck plate causing a noticeable fatigue crack to appear on the upper surface of the deck plate. several lab tests and numerical investigations have been conducted to improve fatigue performance and study the structural behavior of rib-deck weld joints in osd bridges. in [12], the fatigue capabilities of singleand double-sided weld joints in osd rib decks were studied, taking into account both vehicle load and residual stress. the results showed that the most fatigue-critical segment of the rib-deck single-sided weld joint was in the weld root, while in the double-sided weld joint, it was the outer weld toe. double-sided weld joints in osds can minimize the probability of fatigue cracks in the weld root compared to single-sided ones. in [14], an experimental and numerical investigation was conducted on the fatigue behavior of osd singleand double-side weld joints, concluding that fatigue failure of the single-sided weld joint occurs in the root of the weld, while all the double-sided weld joint samples failed inside the weld toe. in [15], a fatigue test was carried out on singleand double-sided rib-deck weld joints, recommending the latter in osd weld joints. in general, most osds belong to long-span cable-stayed or suspension bridge box girders. the feasibility of osds in short-span bridges still needs to be investigated for improved fatigue life compared to other types of traditional bridges, such as plate girder bridges. in the indian continent, most railway bridges consist of plate girders with rcc decks. an rcc deck has a high deadweight and requires more time to construct along with a lot of formwork compared to an osd. therefore, using osd on a short-span railway bridge may be a good option in place of an rcc deck. the indian short-span steel plate girder welded type railway bridges are of lengths 12.2, 18.3, 19.4, and 24.4m. this study investigated the span length of 12.2m, consisting of two main plate girders and an osd placed over them as a replacement for the rcc deck. ii. structural stress method the structural stress method based on fracture mechanics and the paris law was introduced in [14-16] for fatigue life estimation. the structural stress method to predict fatigue performance is insensitive to mesh size and is used to study the fatigue performance of marine pipelines, pressure vessels, and orthotropic steel bridge elements. the internal stress at the toe in the weld along the through-thickness direction is separated into normal stress σx and shear stress in the plane τxy. normal stress is easily subdivided into membrane stress σm and bending stress σb, based on the forces and moments in equilibria. the vertical shear stress τm is formed by condensing the in-plane shear stress. however, the impact of the shear stress is usually neglected, considering that it would not significantly affect the growth of fatigue cracks. the addition of membrane stress σm and bending stress σb defines the structural stress, as given in (1-3) [4, 17]. abaqus software was used to perform the 3dimensional finite element (fe) analysis on the model shown in figure 2. an 8-node linear brick solid element c3d8r in abaqus was used. to resolve the line forces and line moments corresponding to the middle plane of the deck plate, the forces of nodes (nforc) from the elements located on either side of the line were entered into the equation of matrix form [4, 9]. then, the structural stress corresponding to each node along the weld line, shown as a dashed line in figure 2(b), can be evaluated. the nodal forces are used to obtain membrane stress σm, bending stress σb, and structural stress σs using (1-3). �� � � � ∑ �� � � (1) �� � � � ∑ �� � � � ��� � �/2� (2) �� � �� � �� (3) where fi is the nodal force, and t is the thickness of the plate. fig. 2. the 3d solid element model in structural stress calculation. a. master s-n curve parameter in [16], a two-stage crack propagation model was proposed based on an equivalent structural stress parameter obtained using fracture mechanics fundamentals and integrating various data from plate joint fatigue analysis into a narrow-band master s-n curve. with only one curve, the master s-n curve has been used to predict the fatigue characteristics of multiple kinds of weld joints [4, 18]. the impact of stress intensity on the area of concern, the base metal thickness, and several loading modes were recognized in the master s-n curve. the standard deviation of the s-n curve σ was 0.246. taking into account the impact of the deck plate thickness t, the stress ratio r (4), the loading mode parameter ι(r) 1/m (5), and the structural stress range δσs, the equivalent structural stress range δss can be given by (6) [4, 18]. the parameter m for the growth of fatigue cracks, used in (5), was taken as 3.6. the fatigue life n of the deck to rib welded joints can be determined by (7), considering the s-n curve parameters h and cd as shown in table i [4, 18]. � � |�� ||��|�|�� | (4) ���� � � � 0.0011� � � 0.0767� % � 0.0988� ( � 0.0946� * � 0.0221� + � 0.014� � 1.2223 (5) ∆.� � ∆�/ � � 0��/ �∙2�3��/� (6) engineering, technology & applied science research vol. 13, no. 4, 2023, 11146-11152 11148 www.etasr.com amritraj & mishra: fatigue performance of rib-to-deck double-sided weld joint of orthotropic steel … 5 � 6∆7/89 : �/; (7) table i. master s-n curve parameters statistical basis <= > mean 19930.2 -0.32 +2σ (upper 95%) 28626.5 -2σ (lower 95%) 13875.8 +3σ (upper 99%) 31796.1 -3σ (lower 99%) 12492.6 iii. validation of the method numerical computations wereas carried out based on structural stress to investigate the fatigue performance of an osd, using the loadings, shape, and sizes of [4] to compare results. two load cases are considered: load case-i and load case-ii. the load case-ii is critical when studying the fatigue performance of osds. the osd model was 1000 mm long and 400 mm wide. the deck plate, rib thickness, and rib height were 16, 8, and 300 mm. the model was loaded with a 20 kn load, applied eccentrically above the rib-deck junction on the deck surface in a patch area of 250×250 mm. figure 3 shows geometry, loading, material properties, and boundary conditions [4]. the fe model was discretized using an 8-node c3d8r solid element, available in abaqus 2019 [19-22]. fig. 3. dimensional details and loading condition of the model. fig. 4. structural stress along the weld line at the rib-deck joint. figure 4 shows the structural stress results obtained using abaqus 2019 [21] and fe-safe 2019 [23]. structural stresses were obtained for the deck toe (type 1) and the root (type 2) cracks. the structural stress values obtained along the weld line of the fe model were close to [4] with only a 3% difference that can be treated as admissible. iv. fe modeling of the bridge deck a fe model was developed to study the structural behavior of rib-deck weld joints of a full-span osd railway bridge. stresses on the deck plate at the toe and root of the rib-deck welded joints were calculated using a fracture mechanics-based structural stress method [13-16]. abaqus [21] and fe-safe [23] were used to develop the numerical fe model and calculate the structural stress, respectively. figure 5 shows the geometry of the cross-section of the osd model and the weld. fig. 5. dimensional details of (a) the cross-section of the full-span bridge, (b) single-sided weld, and (c) double-sided weld. engineering, technology & applied science research vol. 13, no. 4, 2023, 11146-11152 11149 www.etasr.com amritraj & mishra: fatigue performance of rib-to-deck double-sided weld joint of orthotropic steel … the linear elastic material properties of e350 steel, having young's modulus of elasticity 2×10 5 mpa and poisson's ratio of 0.3, were considered for the model. the global shell model of the considered osd had 4 diaphragms and 3 u-ribs, as shown in figure 6(a). the span length and width of the bridge deck were 12.2 and 1.9 m, respectively. a solid sub-model was simulated using the sub-modeling techniques in abaqus from the full-span model. boundary conditions of the sub-model were pre-assigned in abaqus from the nodal displacements of the global model. figure 6(b) shows the details of the solid submodel. the lateral and longitudinal lengths of the osd submodel were kept at 600 and 3600 mm respectively. shellto-solid coupling features in abaqus were used to connect the global model shell element (s4r) and sub-model solid element (c3d8r). the contact surfaces at the weld joint in the solid sub-model were connected by tie constraints. the number of elements in the global shell model, and the solid sub-model of singleand double-sided welds were 195500, 32640, and 40800, respectively. (a) (b) fig. 6. fe simulation of (a) global shell-model and (b) solid sub-model. a. loadings in this investigation, the axle loads of a 25-ton indian freight locomotive (train type-7) were considered. according to [24], the length of the sleeper is 2750 mm, the cross-section is 250×250 mm, and the thickness of the ballast layer is 400 mm. a uniform load intensity of 0.294 n/mm 2 on the patch area of the deck surface 450×1900 mm 2 was considered for all models. the longitudinal loading positions were taken as follows: (i) load case i (lc-i): with the front axle of the locomotive at the midspan of the bridge (ii) load case ii (lc-ii): with the center line of the pair of the front axles at the midspan of the bridge, and (iii) load case iii (lc-iii): with the center line of the locomotive at the midspan of the bridge. figure 7 shows the loading conditions. fig. 7. loading conditions: (a) longitudinal load positions and (b) constant transverse loading (in mm). v. results and discussion this study focused only on the structural stress at the toe and root of the rib-deck weld joints of the considered osd. load movement along the bridge was established using a dload user subroutine for abaqus, developed in fortran. the loading begins when the leading wheels touch the second diaphragm and lasts until the back wheel departs the third diaphragm. depending on the global shell model, stress distribution curves were obtained along the weld line in the ribdeck weld joints under different loading conditions. the structural stress calculation procedure was described in section ii. figure 8 shows the variation in structural stress of three different single-sided rib-deck weld joints of the osd shown in figure 5, under the three-axle load positions shown in figure 7. figures 8 (a)-(b) show the stress variation of the toe and root at joint 1 for the three loading conditions. similarly, figures 8 (c)(d) show the stress variation of the toe and root for joint 2, and figures 8 (e)-(f) show the stress variation of the toe and root for joint 3 of the weld along the weld line. engineering, technology & applied science research vol. 13, no. 4, 2023, 11146-11152 11150 www.etasr.com amritraj & mishra: fatigue performance of rib-to-deck double-sided weld joint of orthotropic steel … fig. 8. stress histogram of single-sided weld joints: (a) outside weld toe at joint 1, (b) outside weld root at joint 1. (c) outside weld toe at joint 2, (d) outside weld root at joint 2, (e) outside weld toe at joint 3, and (f) outside weld root at joint 3 for different loading positions. in the single-sided weld, at joint 1, under lc-ii, the maximum tensile structural stress arises in the toe and root of the rib-deck weld in each cycle, and it is the most critical loading position from the view of fatigue of the weld details. at joints 2 and 3, under lc-ii, the structural stresses were compressive in nature at the toe and root of the weld. under lc-ii loading conditions, the fatigue-prone weld part was the weld toe joint 1 on the rib just near the main girder of the bridge. the fatigue lives of joints 1, 2, and 3 in the case of single-sided welds were also determined using (7). the fatigue life of joints 1, 2, and 3 were 9.9×10 9 , 3.14×10 15 , and infinite life cycles, respectively. the results for single-sided weld joints showed that only joint 1 experiences maximum stress, while joints 2 and 3 experience negative stresses (compression). therefore, further stress and fatigue analyses were performed only for joint 1. figure 9, shows the stress variation for joint 1 in the rib-deck double-sided weld for the outside toe and root under the three loading conditions. in the double-sided weld, at joint 1, under lc-ii, the structural stress was maximum at the outside toe of the weld. the fatigue life of joint 1 was also determined in the case of double-sided welds using (7) and was found to be 1.7×10 12 . figure 10 compares the structural stresses for singleand double-sided weld joints. figure 10 shows that the maximum structural stress at the root of the double-sided rib-deck weld was 7.65 mpa, which is 43.7% less than the maximum stress at the root of the single-sided rib-deck weld under lc-ii, which was 13.58 mpa. the stress on the deck plate at the doublesided weld toe was 22.49 mpa and at the single-sided weld toe was 22.31 mpa, which were approximately the same. a similar trend of results was found in [11-13]. as a result, according to the findings of stress analysis, the osd's double-sided weld rib-deck joints can significantly reduce the possibility of rootweld fatigue failure. fig. 9. stress histogram of double-sided weld at joint 1: (a) outer weld toe, and (b) outer weld root. engineering, technology & applied science research vol. 13, no. 4, 2023, 11146-11152 11151 www.etasr.com amritraj & mishra: fatigue performance of rib-to-deck double-sided weld joint of orthotropic steel … fig. 10. comparison of structural stress of weld joints under lc-ii. the novelty of this research work is the intuition of an osd on one-section steel plate girders to support railway tracks, especially in the region of curves or congestion. a railway short-span bridge consisting of an osd on a one-section plate girder is a new idea that will carry multiple tracks. the stiffening of the osd has been proposed with u-ribs having double-sided rib-deck weld joints. most studies focused on osds containing single-sided rib-deck welded joints. this analyzed fatigue stress for double-sided welds for the rib-deck connection. moreover, a larger loading patch area was considered according to the dispersion allowed in european standards [25-27], in contrast to the smaller patch area of highway bridges. vi. conclusions the rib-deck weld joints in an osd are considered to dictate the fatigue efficiency of the deck. this study carried out an analytical investigation on rib-deck weld joints of a fullspan osd on a steel plate girder bridge. the fatigue performances of rib-deck singleand double-sided weld joints of osds for the most severe indian locomotive axle loading positions were analyzed and compared. the fracture mechanics-based structural stress method was used to evaluate the stresses in the weld joints. the strength and fatigue life of the rib-deck double-sided weld joints were investigated and compared with the single-sided ones. the conclusions are as follows:  the maximum stress in the root of the double-sided ribdeck weld was observed to be reduced compared to the stress at the corresponding point in the single-sided one. the maximum stress of 7.65 mpa in the root of the doublesided rib-deck weld was 43.7% lower than the maximum stress of 13.58 mpa in the single-sided one. therefore, there is an improvement in the fatigue performance of osd.  no changes in stresses at the toe of the weld connecting the deck plate were found regardless of whether the rib-deck weld is singleor double-sided. the structural stress on the deck plate at the double-sided weld toe was 22.49 mpa and at the single-sided one was 22.31 mpa, which is approximately the same.  the most severe loading position for singleand doublesided weld joints in osds is the lc-ii, which is with the center line of the front axle pair of the locomotive at the midspan of the bridge deck. lc-ii yields the highest structural stress in the rib weld, which is nearest to the main girder. 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[28] y. kambouz, m. benguediab, and b. bouchouicha, "numerical analysis of crack progress in different areas of a friction stir welded bead for an 5251 h14 aluminum alloy specimen," engineering, technology & applied science research, vol. 4, no. 1, pp. 581–586, feb. 2014, https://doi.org/10.48084/etasr.381. microsoft word etasr_v13_n3_pp11006-11010 engineering, technology & applied science research vol. 13, no. 3, 2023, 11006-11010 11006 www.etasr.com danh & ky: optimization of technological parameters when plasma nitriding the gear working surface optimization of technological parameters when plasma nitriding the gear working surface bui thanh danh faculty of mechanical engineering, university of transport and communications, vietnam danhdaiduong@utc.edu.vn le hong ky vinh long university of technology education, vietnam kylh@vlute.edu.vn (corresponding author) received: 12 april 2023 | revised: 1 may 2023 and 4 may 2023 | accepted: 6 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5946 abstract this paper presents the results of optimizing the technological parameters when plasma nitriding the gear working surface. 27 experiments were carried out on an h4580 eltrolab instrument to obtain a working surface hardness database table, and the minitab statistical software was used to process the experimental results. a regression equation was identified to analyze the influence of temperature, time, and gas permeation concentration on the hardness of the working surface. an analysis of variance (anova) showed that all these nitriding parameters influence the regression equation. the results showed that the permeation temperature tl has the greatest influence on the hardness, while the permeation time h and the first gas permeation concentration g1 had less influence. an optimal set of technological parameters was established, where the permeation temperature was tl=550°c, permeation time was h=8h, and the first gas permeation concentration was g1=4l/h. experiments were carried out using this set of optimal parameters to evaluate the microstructure and the depth of the hardening layer of the part surface. finally, this study presented the whole process for the permeation and plasma nitriding of 18xгt steel. keywords-permeation temperature; permeation time; gas permeation concentration; working surface hardness; plasma nitriding; regression i. introduction plasma nitriding is widely used in steel machine parts [1-2], as it can control the white layer making it very suitable for creating products with high-quality requirements [3-5]. the permeation process is carried out at low pressure in a vacuum furnace with a mixture of h2, n2, ch4, and ar gases [1, 3-4, 67]. these gases are ionized under high voltage, creating a plasma. nitrogen ions are accelerated during the collision of the plasma with the sample. this ion bombardment heats, cleans, and forms a hard layer with good wear resistance, increasing fatigue strength [7]. in recent years, many studies have been conducted on the nitriding process model, but it is generally not enough to predict the influence of the parameters on the quality of the permeable layer [3-5, 9-13]. in [9], wagner's generalized common model was used to analyze the permeable layer formation and use it in plasma nitriding experiments. the parabolic curve in the proposed predictive models shows the increase in nitrogen content in the permeable layer and the diffusion area in plasma nitriding [5, 9]. in [14], a numerical simulation model was presented for the nitride layer growth and nitrogen distribution in the ε, γ', and α phases during plasma nitriding of low-carbon steel. the results showed that the nitride layers consist of ε, γ', and α phases and that the thickness of these phases follows a parabolic pattern. in [9], a numerical model of nitrogen diffusion in low-carbon steel was presented, showing that diffusion depended on nitrogen concentration and that the thickness of the permeable layers was the square root of the nitriding time at 843°k (570°c). in [15], a nitriding process model for low-carbon steel was investigated, performing gas nitriding using nh3-h2 gas permeation. a simple model was designed to predict the thickness of the nitride layers in pure iron, built using a kinetic model derived from fick’s second law. several studies attempted to predict and evaluate the distribution of nitrogen concentrations and nitride compounds formed during pure iron nitriding and the depth of the nitrogen diffusion area after plasma nitriding [3, 8, 16]. as the plasma power increases, the maximum adhesion values change, reaching 80mpa when the plasma power approaches 80kw [11]. in [12], the influence of plasma nitriding technology parameters on the deformation of hypoid gears was investigated, using blue light technology with a non-contact measuring device to determine the deformation after plasma nitriding. engineering, technology & applied science research vol. 13, no. 3, 2023, 11006-11010 11007 www.etasr.com danh & ky: optimization of technological parameters when plasma nitriding the gear working surface there is a lack of studies on plasma nitriding for parts made of 18xгt alloy steel (equivalent to sae 5120) [2, 6, 12, 17]. this study used an eltropul permeation furnace with a premade plasma pulse source with stable plasma flow in all cases and easily penetrating details with complex geometries. along with mathematical statistics tools and minitab software, methods such as edas, marcos, topsis, moora, and piv [11-13, 18-25] were used to design and process the experimental data of this study. ii. experimental process the plasma nitriding sample consists of passive hypoid gear teeth, machined from alloy steel 18xгt according to the russian standards (equivalent to sae 5120) [2, 6, 17], having a chemical composition of (%): c: 0.17 – 0.23; si: 0.17 – 0.37; mn: 0.8 – 1.1; p: < 0.035; s: < 0.035; cr: 1 – 1.3; ni: < 0.3; ti: 0.03 – 0.09; cu: < 0.3; n: < 0.008) [2]. the gear was hardened to achieve a hardness ranging from 34-36hrc, equivalent to 336-354hv of the vickers hardness measurement, and then each tooth was cut apart by the wire cutting method, in order from 1 to 27, as shown in figure 1. (a) (b) fig. 1. sample preparation: (a) hypoid gear pairs after machining, (b) plasma nitriding samples cut from hypoid gears. according to the jis z 2244-2009 standard, a control sample of the same material was included in addition to the experimental sample when conducting each experiment. an h4580 eltrolab was used to perform programmable plasma nitriding, and the following parameters could be set when programming [5]: number of hours executed in each step of the program h, number of minutes executed in each step of the program m, pressure p (in pascals), permeation temperature tl ( o c), temperature rise rate of the furnace over time tg ( o c/min), furnace wall temperature tw ( o c), temperature rise rate of the furnace wall over time wg ( o c/min), voltage v (v), pulse duration pd (μs), number of pulse repetitions pr (μs), gas flow 1 g1 (l/h), gas flow 2 g2 (l/h), gas flow 3 g3 (ml/h), and gas flow 4 g4 (l/h). the permeation process with samples of the same material and size changes little the permeation temperature tl, so the voltage v and pressure p were fixed [1, 11, 26]. the temperature rise rate of the part over time tg, furnace wall temperature tw, and temperature rise rate of the furnace wall over time wg depend on permeation temperature tl and permeation time h. gas permeation flows g1, g2, g3, and g4 are proportional to each other [26]. according to the requirements for selecting input factors, the experimental variables of temperature tl, permeation time h, and first gas permeation concentration g1 were selected. the remaining factors remained unchanged. a total of 27 experiments were planned and the program to control the permeation process was set on the h4580 eltrolab software. as the depth of the plasma nitriding layer on the surface of the experimental sample was very thin (μm), the microscopic hardness was tested using the vickers hardness measurement method (hv) according to the jis z 2244-2009 standard with an fm-700e. table i shows the experimental results. table i. experimental results trial permeation time h (h) permeation temperature tl ( o c) gas flow 1 g1 (l/h) hardness, h (hv) 1 4 510 4 632.0 2 4 510 6 644.2 3 4 510 8 654.1 4 4 530 4 670.7 5 4 530 6 676.2 6 4 530 8 678.8 7 4 550 4 699.9 8 4 550 6 700.4 9 4 550 8 694.2 10 6 510 4 638.1 11 6 510 6 641.3 12 6 510 8 653.5 13 6 530 4 670.6 14 6 530 6 677.9 15 6 530 8 676.4 16 6 550 4 703.1 17 6 550 6 701.5 18 6 550 8 693.9 19 8 510 4 652.7 20 8 510 6 652.7 21 8 510 8 659.7 22 8 530 4 684.8 23 8 530 6 681.4 24 8 530 8 684.3 25 8 550 4 717.0 26 8 550 6 706.1 27 8 550 8 701.9 iii. results and discussions an analysis of variance (anova) was carried out on the regression equation results, to remove the parameters that do not affect them [11, 14, 16-24]. the regression equation for hardness h can be written as follows: � � �2726 � 6.44 ℎ � 10.52 �� � 87.17 � � 1.090 ℎ� �0.00776 ��� � 0.690 ℎ � �1 � 0.1552 �� � �1 (1) figure 2 and regression show that tl has the greatest influence on hardness, while h and g1 have less. in figure 2, the effect of h is parabolic, starting from a level (0), reaches a minimum, and finally approaches the maximum value of 685hv in the level area (+1) of the planning. the effect of tf is almost linear, starting at 645hv and reaching a maximum value of about 700hv. the effect of g1 is linear, starting from engineering, technology & applied science research vol. 13, no. 3, 2023, 11006-11010 11008 www.etasr.com danh & ky: optimization of technological parameters when plasma nitriding the gear working surface the minimum value at level (-1) and reaching the maximum value at level (+1). fig. 2. the influence of parameters on hardness. figure 3 shows a plot of the standardized effects of parameters on the hardness of the working surface. tl has the greatest influence on hardness, followed by h, while g1 has the lowest influence. the interaction between tl, g1, and h greatly affects the hardness of the surface. these results are consistent with the theoretical basis of the first and second fick laws since the temperature is the main factor that strongly influences the coefficients and diffusion. maximal optimization was carried out with the following boundary conditions: max �������� : 4 ! ℎ ! 8510 ! �� ! 5504 ! �1 ! 8 providing the results shown in table ii. fig. 3. standardized effects of variables for hardness. table ii. optimization results using boundary conditions solution h tl g1 hardness fit 1 8 550 4 715.876 the maximum optimization value of stiffness in the planning area was 715.876 at h=8h, tl=550°c, and g1=4l/h. experiments were carried out using the optimal set of parameters to evaluate the microstructure and hardening layer depth of the detailed surface. figure 4 shows the optimization analysis chart. fig. 4. optimization analysis chart. figure 5 shows the microstructure image, indicating that the surface of the test sample corresponds to the materials of the part with a clear, permeable layer. the ε and γ' phases are the white layers that can be seen when etching and taking photos through a microscope. the microscopic organization includes carbides and nitrites distributed in ferrite. fig. 5. microstructure of the plasma nitriding layer. phase ε has a needle shape, as shown by the chemical composition analysis of the permeable layer, using the sem/edx (line-scan) method in figure 6. the microscopic examination showed carbide and nitrite distributed in ferrite and perclite. the microscopic hardness to the penetration depth was measured on a cross-section through the permeable layer and at intervals. surface hardness was high and decreased when depth increased up to 350μm, where it remained constant, corresponding to the hardness of the base metal (340hv). the %n content can be determined by the thickness of the phases ε, λ, and α and the depth of the permeable layer. figure 8 shows the edx analysis results, illustrating that the %n content on the surface was high (10.68%n), but the deeper into the interior, the lower it was. engineering, technology & applied science research vol. 13, no. 3, 2023, 11006-11010 11009 www.etasr.com danh & ky: optimization of technological parameters when plasma nitriding the gear working surface fig. 6. sem image (x8000). fig. 7. hardness distribution with the depth of penetration. figure 9 shows the edx analysis at one location of the sample, while figure 10 shows the nitriding process of hypoid gear pairs using the optimal parameters. except for the optimal set of the examined parameters, the remaining parameters were fixed when conducting experiments. fig. 8. nitrogen composition according to penetration depth. the process of plasma nitriding can be summarized as follows:  clean the details to be absorbed  check the permeation equipment system (electrical, air conduction, cooling)  fix the details and put into the furnace box (make sure the details are installed tightly, do not move during the infiltration process)  the power is closed under high voltage and low pressure to heat for the first time until it reaches approximately 250300 0 c. this temperature is then maintained to activate the surface. after about 2.5h, the temperature should raise at a rate of 100°c/min (second heating phase) until the permeation temperature reaches 550 0 c. the end of the 8hour permeation period is the auto-cooling period, as shown in figure 10. fig. 9. edx analysis at one location on the sample. fig. 10. plasma nitriding technology process of hypoid gear pairs. iv. conclusions this study identified a regression equation as the basis for analyzing the influence of temperature, time, and gas concentration on the hardness of the working surface of a gear. the results of the analysis showed that the permeability temperature tl had the greatest influence on hardness, followed by the permeation time h and the gas concentration g1. the interaction between infiltration temperature tl, gas permeation concentration g1, and permeation time h also affects surface hardness, but to a different extent. engineering, technology & applied science research vol. 13, no. 3, 2023, 11006-11010 11010 www.etasr.com danh & ky: optimization of technological parameters when plasma nitriding the gear working surface the results of this study were completely consistent with the theoretical basis of the first and second fick laws. the maximum optimization value of stiffness in the planning area was 715,876, using h=8h, tl=550°c, and g1=4l/h. experiments were carried out using these parameters to evaluate the microorganism and the depth of the hardening layer of the surface. the control program for the permeation process and the plasma nitriding technology process of hypoid gear pairs made of 18xгt steel were proposed. the proposed optimized set of technological parameters can be used when plasma nitriding various machine parts made of 18xгt or equivalent materials to get an optimal result. references [1] d. pye, practical nitriding and ferritic nitrocarburizing. ohio, usa: asm international, 2003. 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[26] j. c. díaz-guillén et al., "surface properties of fe4n compounds layer on aisi 4340 steel modified by pulsed plasma nitriding," journal of materials science & technology, vol. 29, no. 3, pp. 287–290, mar. 2013, https://doi.org/10.1016/j.jmst.2013.01.017. microsoft word 4-selvam-ed.doc etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 549-551 549 www.etasr.com selvam: a circuit for the square root of the sum of two squared voltages using an ic lm311… a circuit for the square root of the sum of two squared voltages using an ic lm311 open collector comparator k. c. selvam department of electrical engineering indian institute of technology, madras -36, india kcselvam@ee.iitm.ac.in abstract  a circuit which accepts two input dc voltages v1 and v2 and provides an output dc voltage vo equal to the square root of the sum of the two squared voltages of v1 and v2, using an lm311 open collector comparator based single quadrant time division multiplier is described in this paper. keywordsgenerator; comparator; integrator; square rooter; adder i. introduction a circuit for the square root of the sum of two squared voltages is often needed in instrumentation and control systems, particularly in phase sensitive detectors [1] which play an important role in impedance measurements and power measurements. this circuit is used in the construction of signal-envelope circuits, diversity combiner circuits, radiometer circuits and in other applications in which the powers of separate waveforms have to be added. stern and lerner described one circuit [2] in which they used a piecewise-linear network employing resistors and diodes. a different approach employing operational amplifiers, an lm 311 open collector comparator and switches is described here. the principle of the time division multiplier [3-5] is used here in a simplified way. ii. circuit analysis the proposed circuit diagram is shown in figure 1. a sawtooth wave, marked as vs in figure 1, of peak value vt is generated by the opamps oa1, oa2 and the switch s1. let us assume that at start, the charge and hence voltage at the output terminal of opamp oa1 is zero. since the inverting terminal of the opamp oa1 is at virtual ground, the current through r1, namely vt/r1 amps, would flow through and charge the capacitor c1. during the capacitor being charged (till the output of oa1 reaches a voltage level of vt) the output of opamp oa2, configured to work as a comparator, will be at the low state and switch s1 is kept open (off). as soon as the output of oa1 crosses the level of vt, say after a time period t, the output of comparator oa2 goes high and the switch s1 is closed (on). the switch s1 would then short the capacitor c1 and hence vs drops to zero volts. after a very short delay time td, required for the capacitor to discharge to zero volts, the comparator output returns to low and switch s1 is opened, thus allowing c1 to resume charging. this cycle, therefore, repeats itself at a period (t+td). the waveforms at cardinal points in the circuit are shown in figure 2. the output of the integrator oa1 will be 1 ( ) 1 1 1 1 vt vs t vtdt t r c r c   (1) from the waveforms shown in figure 2 and the fact that at t=t, vs(t) = vt: 1 1 vt vt t r c  1 1t r c (2) the sawtooth wave vs is compared with one input voltage v1 using the lm311 comparator comp1. the lm311 comparator has the characteristic that if the –ve input is greater than +ve input voltage, its output goes to low (pin no 1 has to be grounded). when the +ve input voltage is greater than the –ve input voltage, its output goes to the voltage at the other end of its pull up resistor rp connected at the output [6]. hence the output vp1 of the comparator is a rectangular pulse waveform with a maximum value of the input applied voltage v1 as shown in figure 2. the on time of the pulse waveforms vp1 is given by: 1 1 v ton t vt  (3) the average value of vp1 will be 1 1vw v dt t   21 1 1 v v ton t vt   similarly, 22v vx vt  etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 549-551 550 www.etasr.com selvam: a circuit for the square root of the sum of two squared voltages using an ic lm311… . 2vo vy vt  vz vx vw   2 21 2v v vz vt    if r3=r4=r and r5>>r and considering kcl for node ‘j’ in the circuit of figure 1, we get: 1 2i i , vy vz , 2 2 21 2vo v v vt vt   , 2 2 21 2vo v v  2 21 2vo v v  (4) thus the output voltage is the square root of sum of two (v1 and v2) squared voltages. iii. experimental results the circuit shown in figure 1 was tested in our laboratory. lm 324 ic was used for oa1-oa8. cd 4053 ic is used for the switch s1. lm 311 ics were used for comp1-comp3. rp=1.2 kω, r1=1.2 mω and c1 = 10 nf. a voltage of ±7.5 v was chosen for the power supply. the test results are shown in figures 3 and 4. the accuracy of the circuit strongly depends upon the sharpness and linearity of the sawtooth waveform. the offset voltage of all the opamps used may cause a little error in the output and hence it must be adjusted to zero. the small variations in the voltage vt will cause an error at the output, hence a stable precision reference voltage must be used as vt. however, small variations in the power supply will not affect the performance of the circuit at all. -vt vt v1 v2 gnd gnd vo -vz gnd gnd gnd gnd c r c1 s1 r1 + comp2 + comp3 + oa 4 vp2 rp + oa 6 + oa 3 vp1+ comp1 vs r2vx c r + oa 7 vyr c r3 i1 + oa 5 r2 r4 i2 j rp + oa 8 + oa 2 vp r2vw rp + oa 1 r5 fig. 1. circuit diagram for the square root of the sum of two squared voltages etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 549-551 551 www.etasr.com selvam: a circuit for the square root of the sum of two squared voltages using an ic lm311… tt td t on1 t on2t on2 td t on1 v1 vt vs vp vp1 v1 v2 +vcc -vcc v2 vp2 output of integrator oa 1 output of comparator oa 2 output of comparator comp1 output of comparator comp2 fig. 2. associated waveforms of figure 1 fig. 3. test results for vt = 4v, v1 = 2.5v fig. 4. test results for vt = 4v, v2 = 2.5v acknowledgement the author is highly indebted to prof. s. srinivasan, prof. dr. enakshi bhattacharya, prof. dr. v. jagadeesh kumar, prof. dr. sridharan and dr. bharath bhikkaji, department of electrical engineering, indian institute of technology, madras, for their constant encouragement throughout the work. he also thanks mrs. latha selvam for circuit drawing and discussions. references [1] h. o. modi, v. j. kumar, p. sankaran, “feedback compensated synchronous and multiplier type phase sensitive detectors”, ieee transactions on instrumentation and measurement, vol. 40, no. 3, pp. 646-649, 1991 [2] t. e. stern, r. m. lerner,”a circuit for the square root of the sum of the squares”, proceedings of the ieee, vol. 51, no. 4, pp. 593-596, 1963 [3] m. tomata, y. sugiyamma, k. yamaguchi, “an electronic multiplier for accurate power measurements”, ieee transactions on instrumentation and measurement, vol. 17, no. 4, pp. 245-251, 1968 [4] t. s. rathore, b. b. bhattacharyya, “a new type of analog multiplier”, ieee trans on industrial electronics, vol ie-31, no. 3, pp. 268-271, 1984. [5] j. greg johnson, “analysis of the modified tomata-sugiyamayamaguchi multiplier”, ieee transactions on instrumentation and measurement, vol. 33, no. 1, pp. 11-16, 1984 [6] national semiconductor corporation, cmos data book, 1982 authors profile k.c. selvam was born on 2nd april 1968 in krishnagiri district of tamil nadu state, india. he graduated from the institution of electronics and telecommunication engineers, (iete) new delhi, india in 1994. he has published more than 15 research papers in various national and international journals. he got the best paper award by iete in 1996. at present he is working as technical staff in the department of electrical engineering, indian institute of technology, madras, india. his research interests focus on measurements and instrumentation systems. microsoft word 18-3762_s1_etasr_v10_n5_pp6242-6248 engineering, technology & applied science research vol. 10, no. 5, 2020, 6242-6248 6242 www.etasr.com khand & kalhoro: testing and validating delone and maclean is model: erp system success in … testing and validating delone and maclean is model: erp system success in higher education institutions of pakistan zahid hussain khand department of computer science sukkur iba university sukkur, pakistan zahid@iba-suk.edu.pk muhammad ramzan kalhoro department of business administration sukkur iba university sukkur, pakistan ramzan.kalhoro@iba-suk.edu.pk abstract−the universities in pakistan have recently started replacing their old legacy systems with erp systems which are commonly used in business organizations to gain a competitive edge over competitors. the higher education commission (hec) has implemented erps systems at eight different universities of pakistan. hec has invested a huge amount of money to facilitate the integration, customization, and implementation of erp systems in these universities. previous studies have mainly focused on critical success factors (csfs) and risk factors of erp systems. this study intends to empirically measure the support of erp systems in teaching processes. delone and mclean model of information systems (is) success is one of the most commonly used models cited in is literature. in this study, delone and mclean model was applied at a university level analysis to access the impact of erp in higher educational institutions and their support in the improvement of academic processes. hypotheses were tested on the research model using empirical data collected from 230 respondents, including students and faculty at two selected universities, with the use of a questionnaire. the data were analyzed by structural equation modeling. the model was empirically tested and the findings showed that use and user satisfaction effected most net benefits. information quality, system quality and service quality accounted for 42.6% effect in use. whereas, information quality, system quality, service quality and use accounted for 46.5% variance in user satisfaction. keywords-higher education; enterprise resource planning (erp) system; delone and mclean is model i. introduction the term erp (enterprise resource planning) was coined in early 1990s. an erp is a multi-module application software package, which tightly integrates data and business processes for sharing information in an organization [1]. higher educational institutions have implemented erp systems to automate and customize their business processes, which include student records, admissions, student finances, and most common academic and administrative services [2]. erp systems are implemented in higher education to improve the performance and the efficiency of the organization to cope with the changing environment. despite that erp promises to benefit the organizations and even though it is a substantial capital investment, it is not necessarily the case that all erp systems implementations have successful outcomes. in response to that demand, higher education institutions in pakistan have started implementing erp systems to gain a competitive edge over the competitors and enhance the efficiency in the processes. erp has automated and integrated the key processes related to academic and administrative services [3]. the higher education commission (hec) of pakistan has invested a significant amount of funding to facilitate the customization and implementation of erps in eight selected universities (dow university of health sciences, karachi (duhs), university of engineering and technology, peshawar (uet), quaid-e-azam university, islamabad (qau), islamia university, bahawalpur (iub), balochistan university of information technology and management sciences, quetta (buitems), university of punjab, lahore (pu), sukkur institute of business administration (siba), and institute of business administration (iba), karachi) as a pilot run in the country. although there are many studies on the implementation of erp systems in business, less research has been reported on the impact of erp systems in higher education. in pakistan, some small-scale research has focused on the implementation and efficiency issues of the erp systems, which suggests that there might be a lack of research in the evaluation of erp systems in the university environment [4, 5]. the reported research in the contextual areas mainly identified the critical success factors (csfs) for the effective implementation of erp systems [1, 6]. the current research study intends to measure the post implementation impact of an erp system in higher education institutions, focusing on the improvement in the academic and administrative processes [7]. the main reasons that higher education institutions (heis) are implementing erp systems are the needs to replace the legacy manual systems (traditional manual systems), to improve customer service, to increase the transparency in the processes, and to enhance operating efficiency [1, 8]. the current study evaluates the impacts of erp systems at the end user level where the actual benefits and impacts can be measured. the results of the study can be used by the hec and corresponding author: zahid hussain khand engineering, technology & applied science research vol. 10, no. 5, 2020, 6242-6248 6243 www.etasr.com khand & kalhoro: testing and validating delone and maclean is model: erp system success in … heis to inform further expansion of the erp systems to other universities in pakistan. in particular, this research aims is to explore the impact of erp implementation in higher education institutions in pakistan to improve the academic and administrative processes [5]. erp implementation in heis is different from business organizations because they have different environments and conditions. the erp systems are used by the heis to support faculty and students in the fulfillment of a variety of academic needs [5]. to create a high level impact of the research study, the results would be shared with higher education leadership for making decisions regarding the implementation of erp in different heis of pakistan in the future [9]. ii. literature review an erp system is the most widely accepted option for universities that seek to gain a competitive edge and increase their efficiency and transparency through the integration of all information flowing through the different departments [10, 11]. despite this perceived positive impact of the erp system in heis, implementation and integration is considered to be a costly and complex solution [12]. this has led to the need to evaluate the system from a stakeholder’s and technical perspective [13]. most previous research studies on similar topics are related to pre or post implementation issues related to the stakeholder’s perspective or the technical input [14]. few studies have reported on the csfs related to the implementation of the erp system life cycle, or on the academic advantage that the system implementation might foster. there is not a common agreement in which csfs are most important, but most studies suggest that the issues related to top-management support, technical support, user training, education level of the users and organizational culture are important factors in a successful erp system implementation [12, 15, 16]. there are a few studies that have reported the success ratio of the erp systems implementation in higher education and analyze the factors and reasons of failure of such systems. authors in [17] reported that the failure rate at the implementation stage is 40% to 60%. however different researchers have different definitions of failure. the critical failure factors reported in literature are high turnover of project team, over-reliance on heavy customizations, poor consultant effectiveness, poor it infrastructure [10, 17, 19], and poor expected return on investment (roi) [18]. the studies reported in the literature tested and validated the erp success factors using different theoretical information system (is) models [12, 15, 16]. however, different theoretical models to measure is success, have been reported such as: the technology acceptance model (tam), the technologyorganization-environment (toe) framework, the delone and mclean model and the diffusion of innovation (doi). each is success model has strengths and weaknesses. the research studies reported that is success models were used on their own or sometimes in combination with others to measure erp success in organizations. the literature review did not find any research work that studied the impact of erps in heis with particular emphasis on the support on academic processes and higher education leadership decision-making. there are a few studies that measure the efficiency of the erps in the context of higher education institutions of pakistan. authors in [6] proposed a conceptual model based on few suggested changes in the d&m model. the research study also analyzed the success and failure of the erp systems implemented in eight universities in pakistan based on four csfs. authors in [20] conducted a similar research study to evaluate the performance of erp in saudi universities. the results showed that system’s quality and service quality have positive impact on the stakeholders’ performance. authors in [21] studied the impact of erp systems in higher education. the study developed an is successful model based on the key ideas of tam, ttf, and d&m models. the findings indicated that system quality, task technology fit, and information quality are the key factors that lead to better end-user performance. author [7] investigated the success of erp in pakistan with end-user perspective and identified csfs such as top management support, effective project management, clear goals and objectives, selection of erp systems and data accuracy. authors in [22] measured the effectiveness of erp systems in the corporate sector. the research combined the d&m and tam models and the findings suggested that the performance of the employees can be enhanced through high quality erp usage. it can be seen that there is a noticeable research gap in this area [20]. a. research model and hypotheses the delone and mclean is success model is the most widely cited model in is literature [23, 24]. authors in [25] stated that the model is important in is success measurement because it provides a classification of all the evaluation measures that have been reported in is success measurement in the literature. the model identifies potential stakeholders and suggests the way the different constructs interact with each other. the model proposes six dimensions: system quality, information quality, use, user satisfaction, individual impact and organizational impact. the original model is shown in [26] (figure 1), which depicts that system quality and information quality have direct effect on system usage and user satisfaction. this means that if the users are comfortable with the system functionality and quality of service they are likely to use the system. however, the proposed erp success model is based on different is theories in the context of erp implementation in heis. the model is selected after extensive literature review on is success models [27]. many empirical studies have been reported regarding is success measurement based on the d&m model [25, 28]. b. is success variable categories an is is defined as a set of components that are integrated and interconnected to collect, process, store, and distribute information to support decision making and supervision [29, 30]. iss have six dimensions of success, erp system quality, erp information quality, erp service quality, erp use, erp user satisfaction, and erp net benefits [26]. 1) system quality in the proposed model, system quality focuses on the erp’s characteristics system quality is defined as a set of constructs related to the is that determine its quality. these engineering, technology & applied science research vol. 10, no. 5, 2020, 6242-6248 6244 www.etasr.com khand & kalhoro: testing and validating delone and maclean is model: erp system success in … characteristics include: system reliability, ease to learn, ease of use, productivity, flexibility, and integration with other systems [26, 29, 31, 32]. 2) information quality information quality is the degree to which information presents the required benefits. the information quality is measured as the output of the is [30]. these constructs are refined from the literature and include, availability, timelines, relevant, accuracy, appropriateness, concise representation, and interpretability [26, 29, 31, 32]. 3) service quality service quality is a set of characteristics related to services submitted by the is to the customer which include service reliability, support, assurance, empathy, and security. service quality is considered as the overall support offered by the provider of the is by ensuring that it can be applied in the proper way [26, 29, 31, 32]. 4) use is the extent to which the end-users use the result presented by the iss. the measures of the use are defined from the literature and include the degree of system use, responsiveness, adaptability, and effectiveness [26, 29, 31, 32]. 5) user satisfaction user satisfaction is the response of the recipient after using the is [30]. it is associated with attitudes toward is which include system availability, robustness, task achievement, productivity and efficiency [26, 29, 31, 32]. 6) net benefits net benefits are the benefits obtained after using the is. they may be individual or collective. they are a measure for the positive and negative impacts of the is on all persons and groups effected with is. net benefits can be identified with a set of constructs that includes cost saving, expanded markets, incremental additional sale, reduced search cost and time saving [26, 29, 31, 32]. the current study will look into the impact of the erp systems and their components as suggested above, to provide support in academic processes and management in decisionmaking. thus, the following nine hypotheses will be tested in the erp context: • h1: there is a positive relationship between information quality and system use. • h2: there is a positive relationship between system quality and system use. • h3: there is a positive relationship between service quality and system use. • h4: there is a positive relationship between information quality and user satisfaction. • h5: there is a positive relationship between system quality and user satisfaction. • h6: there is a positive relationship between service quality and user satisfaction. • h7: there is a positive relationship between system use and user satisfaction. • h8: there is a positive relationship between system use and perceived net benefits. • h9: there is a positive relationship between user satisfaction and perceived net benefits. fig. 1. research framework. iii. data collection a survey questionnaire was used to collect the quantitative data from the target population. the targeted population for the collection of data was students, faculty members, and the heads of the academic departments. the majority of the respondents were already ict literate, so they were easily accessible through email correspondence. the questionnaires were designed using the online tool survey monkey and were sent to the respondents through an invitation email. invitations were sent to 500 respondents (300 students and 200 faculty members). in response to that, 232 students and 141 faculty members filled the questionnaires giving a response rate of 74.6%. after data cleanup, 230 questionnaires were retained for data analysis. iv. data analysis structural equation modeling (sem) was used to test the established relationships. for that, this study used the partial least squares (pls) method by using smart pls 3.2.7 software [33]. this method utilizes the bootstrapping processes proposed in [34, 35] to underline the level of significance for loadings and path coefficients for the established relationships. the pls path modeling method is carried out in two steps (measurement model and structural model). a. demographic information of the respondents the respondent’s demographic information can be seen in table i. b. measurement model before testing the established relationships, the suitability of the measurement model was assessed based on reliability, convergent validity, and discriminant validity. the reliability was inspected with composite reliability (cr) values. table ii indicates that all scores relating to cr range from 0.809 to 0.885, which are higher than the criterion of 0.7, fulfilling the required level [34]. engineering, technology & applied science research vol. 10, no. 5, 2020, 6242-6248 6245 www.etasr.com khand & kalhoro: testing and validating delone and maclean is model: erp system success in … table i. demographic information variables category frequency (%) gender male 196 85.22 female 34 14.78 age 21 25 25 10.87 25 30 59 25.65 30 40 83 36.09 40 45 48 20.87 45 50 10 4.35 above 50 5 2.17 education higher secondary (12 years of education) 35 15.22 undergraduate (16 years of education) 55 23.91 graduate ms/mphil (18 years of education) 88 38.26 phd 52 22.61 university iba karachi 26 11.3 sukkur iba university 204 88.7 department business administration 98 42.6 computer science 38 16.5 electrical engineering 35 15.2 mathematics 15 6.5 education 23 10.0 other 21 9.1 use of erp system once a day 37 16.1 several times a day 90 39.1 once in a week 39 17.0 several times in a week 64 27.8 table ii. measurement model items model construct measurement item loading cr ave information quality(iq) iq1 0.678 0.834 0.46 iq2 0.749 iq3 0.688 iq4 0.756 iq5 0.668 iq6 0.499 net benefits (nb) nb1 0.635 0.863 0.476 nb2 0.673 nb3 0.728 nb4 0.753 nb5 0.735 nb6 0.696 nb7 0.595 service quality (srq) srq1 0.781 0.859 0.605 srq2 0.758 srq3 0.825 srq4 0.744 system quality (sq) sq1 0.584 0.847 0.483 sq2 0.766 sq3 0.775 sq4 0.689 sq5 0.691 sq6 0.644 use (u) u1 0.850 0.885 0.719 u2 0.863 u3 0.831 user satisfaction (us) us1 0.585 0.809 0.378 us2 0.663 us3 0.546 us4 0.598 us5 0.647 us6 0.620 us7 0.635 note: cr = composite reliability, ave = average variance extracted moreover, using item loadings tested convergent validity and the ave criteria. the results shown in table ii imply that the loading values of all the items are higher than the 0.5 threshold, indicating that the study has achieved scale validity. the values of ave of two variables (service quality and use) exceeded the recommended value (0.5) suggesting that convergent validity is at acceptance level. however, ave values of three constructs (system quality, information quality and net benefit) ranged from 0.46 to 0.483, which are near the threshold value of 0.5, whereas the ave value of one construct (user satisfaction) is 0.378. table ii shows the result of discriminant validity. it was examined using the square root of the average variance extracted criteria suggested in [36], according to which, the square root of the ave should be greater than cross-correlations within construct and correlation with other constructs in the model. all the values of square root of ave of all constructs except one (net benefit) shown in table iii surpassed the inter-construct correlations coefficient, suggesting that discriminant validity is acceptable. table iii. discriminant validity variables iq nb srq sq u us information quality 0.67 net benefit 0.55 0.69 service quality 0.72 0.64 0.77 system quality 0.72 0.59 0.66 0.69 use 0.56 0.60 0.61 0.56 0.84 user satisfaction 0.60 0.78 0.63 0.56 0.50 0.61 note: values in the diagonal represent the square root of the average variance extracted. c. structural equation model fig. 2. pls output. with the achievement of adequate validity and reliability for the measurement model of the study, the proposed structural model with established relationships was estimated by applying 500 iterations of the bootstrapping technique. table iv and figure 2 show the results of the hypotheses testing. the results indicate that information quality had not significant impact on use (h1 rejected, �=0.141, � � 0.1� but had significant influence on user satisfaction (h4 supported, �=0.22, � 0.05). service quality exerted significant impact on both use and user satisfaction at � 0.01. therefore, h3 and h6 were accepted (�=0.36 and �=0.321 respectively). engineering, technology & applied science research vol. 10, no. 5, 2020, 6242-6248 6246 www.etasr.com khand & kalhoro: testing and validating delone and maclean is model: erp system success in … moreover, system quality exerted significant influence on use (�=0.224, � 0.01�, but had not significant effect on user satisfaction (�=0.12, � � 0.1�, thus h5 was rejected and h2 was supported. additionally, use had exerted significant impact on both net benefit and user satisfaction at � 0.01 and � 0.1 respectively. hence, h8 and h7 were supported (�=0.282 and �=0.12, respectively). table iv. hypotheses testing results estimate std error t-value p-value iq ���� u 0.14 0.09 1.559 0.120 iq ���� us 0.22 0.10 2.154 0.032 srq ���� u 0.36 0.07 5.166 0.000 srq ���� us 0.32 0.074 4.358 0.000 sq ���� u 0.22 0.074 3.026 0.003 sq ���� us 0.12 0.081 1.478 0.140 u ���� nb 0.28 0.045 6.194 0.000 u ���� us 0.12 0.07 1.72 0.086 us ���� nb 0.64 0.04 15.62 0.00 user satisfaction had significant influence on net benefits ( � =0.642, � 0.01� , indicating that h9 was supported. overall, the results show that use and user satisfaction accounted for 67.5% variance in net benefit. information quality, system quality, and service quality accounted for 42.6% variance in use and information quality, system quality, service quality and use accounted for 46.5% variance in user satisfaction. table v indicates that information quality, system quality, service quality, use, and user satisfaction show significant total effects on the net benefits being all significant at p<0.01. furthermore, the total effect of user satisfaction on net benefits is stronger than use. likewise, among all quality related constructs, service quality shows strongest total effect (0.335) on net benefits. table v. total effects estimate std error t-value p-value iq ���� nb 0.19 0.07 2.66 0.00 srq ���� nb 0.33 0.05 6.24 0.00 sq ���� nb 0.15 0.05 2.77 0.00 u ���� nb 0.35 0.06 5.84 0.00 us ���� nb 0.64 0.04 15.62 0.00 v. conclusion and future work the current study presents and validates a model of erp system success based on an updated d&m is success model [25] with six success measures that are information quality, system quality, service quality, use, user satisfaction and net benefits. except for the link between is and use and a link between system quality and user satisfaction all other hypothesized relationships between the six erp success variables were significantly or marginally supported by the data [29]. the study recommends more research in this area and finding more variables that have impact on system use and user satisfaction. the current study has a few limitations that could be addressed in the future. first, measuring the impact of erp systems in higher education with d&m is success model is a new research area. the is success model can be respecified with more variables related with the erp context. second, the empirical measurement sample size and the number of universities may be increased to make the findings more generalized. third, future research may be done with longitudinal evidence that could enhance our understanding to replicate the current study with respect to time and long-term usage. appendix aquestionnaire section-a demographic information 1. are you using the campus management solution (cms) system at the university? ( ) yes ( ) no 2. name of the university: ( ) iba, karachi ( ) sukkur iba university. 3. department: ( ) business administration ( ) computer science ( ) electrical engineering ( ) mathematics ( ) education ( ) other 4. how long have you been using enterprise resource planning (erp) in your university? ( ) months ( ) years 5. gender: ( ) male ( ) female 6. age: ( ) less than 21 ( ) 21 and below 25 years ( ) 25 and below 30 years ( ) 30 and below 40 years ( ) 40 and below 45 years ( ) 45 and below 50 years ( ) 50 years and above 7. education: please specify the highest qualification you have attained: ( ) higher secondary school certificate (12 years of education) ( ) undergraduate (16 years of education) ( ) graduate ms/mphil (18 years of education) ( ) doctoral phd 8. how often do you use the system: ( ) once a day ( ) several times a day ( ) once in a week ( ) several times in a week section-b please rate to what extent you agree or disagree with each statement below by clicking the most appropriate number of the scales provided. please click only one option for each statement given below. system quality information quality is measured in terms of ease-of-use, functionality, reliability, flexibility, data quality, portability, etc. engineering, technology & applied science research vol. 10, no. 5, 2020, 6242-6248 6247 www.etasr.com khand & kalhoro: testing and validating delone and maclean is model: erp system success in … 1. the campus management solution (cms) system is easy to use. 2. the cms is effective in providing instant access to information required. 3. the cms system streamlines the best academic practices in the university. 4. the cms supports me in completing my academic related tasks efficiently. 5. the cms is effective in providing accurate information about student attendance and grades. 6. the cms provides complete attendance automation by effectively sending sms and email alerts to students. information quality information quality is measured in terms of accuracy, timeliness, completeness, relevance, and consistency. 7. the cms system effectively provides me with relevant information. 8. the information required is easily accessible in the cms system. 9. the cms system is easy to learn. 10. the cms user interface can easily be configured to my personal requirements. 11. i think that my data in the cms is safe from unauthorized access. 12. the cms effectively generates text and email alerts if someone tries to enter my account unauthorized. service quality service quality is used to measures reliability, responsiveness, assurance, and empathy. 12. the cms system provides reliable information. 13. the information in cms is easily searchable. 14. the cms provides a smooth flow of information regarding the academic calendar, assignments and announcements of results. 15. the cms provides access to grades, attendance, fee status, exam schedule and announcements of results related to students. impact of erp 16. 17. the cms improves the academic processes in the university. 18. the cms system effectively combines the student data from different departments of the university. 17. 19. the cms provides me single login id that improves the information integration between different systems of the university. user satisfaction 20. the cms helps in sharing the scholarship related data of students with potential donors. 21. the cms helps me in getting updated information about my attendance and grades on regular basis. 22. the cms gives students a chance to provide course evaluations in each semester. 23. the feedback given by students in the course evaluations has helped to improve classroom teaching. 24. the cms/erp self-service automates many processes related with students (visibility of semester results, course registration and financial matters). 25. i received adequate cms related trainings during my studies to perform my academic tasks on system effectively. 26. it is easy to get required support from it support team whenever required. net benefits 27. it is useful that the cms manages classroom information and analytical reports of the student grades and attendance. 28. the cms helps me to improve my academic performance by receiving sms alerts on attendance and grades. 29. the cms provides a chance to students to provide feedback on the courses offered in a semester. 30. the cms improves the internal communication within the university (students, faculty and administration). 31. the cms effectively provides chance to register or drop in different courses in a semester through self-service module as compared from what we had before. 32. the cms provides a chance to students to provide feedback at the end of a semester about their overall experience regarding classroom teaching/learning for courses offered in a semester. 33. the cms provides grades related information, which may help students to monitor their progress during the semester. 34. are there any additional comments about your experiences with cms/erp? references [1] a. abugabah and l. sanzogni, “enterprise resource planning (erp) system in higher education: a literature review and implications,” international journal of computer and systems engineering, vol. 4, no. 11, pp. 2120–2124, nov. 2010. 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[20] m. althonayan and a. papazafeiropoulou, “evaluating the performance on erp systems in king saud university (ksu): a stakeholders’ perspective,” in 2013 46th hawaii international conference on system sciences, jan. 2013, pp. 4074–4083, doi: 10.1109/hicss.2013.210. [21] a. abugabah, l. sanzogni, and o. alfarraj, “evaluating the impact of erp systems in higher education,” the international journal of information and learning technology, vol. 32, no. 1, pp. 45–64, jan. 2015, doi: 10.1108/ijilt-10-2013-0058. [22] r. n. lodhi, m. abdullah, and a. shahzad, “an empirical investigation of the effectiveness of erp quality: evidence from corporate sector of pakistan,” journal of quality & technology management, vol. 12, no. 2, pp. 71–88, dec. 2016. [23] s. petter, w. delone, and e. mclean, “measuring information systems success: models, dimensions, measures, and interrelationships,” european journal of information systems, vol. 17, no. 3, pp. 236–263, jun. 2008, doi: 10.1057/ejis.2008.15. 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[online]. available: https://www.techrepublic.com/resource-library/ whitepapers/measuring-erp-system-success-a-respecification-of-thedelone-and-mclean-s-is-success-model/. [32] p. a. e. serumaga-zake, “the role of user satisfaction in implementing a business intelligence system,” sa journal of information management, vol. 19, no. 1, p. 8, feb. 2017, doi: 10.4102/sajim .v19i1.736. [33] c. m. ringle, s. wende, and j. m. becker, smartpls 3. boenningstedt, germany: smartpls gmbh, 2015. [34] j. f. hair, m. sarstedt, c. m. ringle, and j. a. mena, “an assessment of the use of partial least squares structural equation modeling in marketing research,” journal of the academy of marketing science, vol. 40, no. 3, pp. 414–433, may 2012, doi: 10.1007/s11747-011-0261-6. 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[36] c. fornell and d. f. larcker, “evaluating structural equation models with unobservable variables and measurement error,” journal of marketing research, vol. 18, no. 1, pp. 39–50, 1981, doi: 10.2307/3151312. microsoft word 25-2298_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3439-3444 3439 www.etasr.com naim & mahara: fuel substitution for energy saving fuel substitution for energy saving a case study of foundry plant iram naim department of polymer and process engineering indian institute of technology, roorkee roorkee, u.k. india iram.naim03cs@gmail.com tripti mahara department of polymer and process engineering indian institute of technology, roorkee roorkee, u.k. india triptimahara@gmail.com abstract—foundry based organizations consume significant amounts of energy for producing their final products. recently, techno-commercial and environmental factors have started triggering change from fossil fuels to cleaner ones. in this paper, factors acting as driving forces for migration from one fuel to another in order to improve energy efficiency, including various performance parameters in support of environment preservation, have been identified. focus is also given to challenges which encounter during fuel switching. a new framework has been applied that can be used for fuel switching in manufacturing organizations. a real case of switching from three types of fuels to a single fuel has been studied and the outcomes are evaluated. analysis related to energy consumption before and after fuel switching with respect to corresponding production data have been performed. keywords-foundry industry; natural gas; energy consumption; energy efficiency; fuel switching; public sector organization; calorific values; fund saving; castings; liquid fuels i. introduction foundry [1] is one of the most energy-intensive industry sectors due to its energy-oriented manufacturing processes. india holds a significant share of foundries worldwide. there are around 47,000 casting units globally, out of which approximately 4,500 units are in india. according to [2], world casting production was 104.1 million metric tons in 2015. the share of china alone was reported to be 44% whereas india and usa together hold 20% of global casting production. major foundry clusters of india are located at batala, jalandhar, ludhiana, agra, pune, kolhapur, sholapur, rajkot, mumbai, ahmedabad, belgaum, coimbatore, chennai, hyderabad, howrah, kolkata, indore, chennai, faridabad, gurgaon etc. [3]. a huge amount of energy is consumed in foundry plants, thus requiring maximization of energy efficiency, i.e. using less energy for performing a desired task or service [4]. in india, bee (bureau of energy efficiency) [5], a statutory body formed by the government of india issues energy efficiency measures in industrial fields. in casting process, melting of a material is the most energy intensive process, thus, the need of having energy efficient casting processes emerges [6]. recently the focus of foundries is shifting towards coke less furnaces, in particular, induction furnaces [7]. organizations are using various types of fuels like furnace oil, light diesel oil (ldo), high-speed diesel (hsd), liquefied petroleum gas (lpg) and natural gas (ng) in furnaces for carrying out heat treatment procedures. selection and switching of appropriate fuel is an essential decision for improving energy efficiency and fuel economy. energy audit is one of the effective tools suggested to industries in order to identify and improve energy performance [8]. this paper provides identification of potential measures for energy efficiency through fuel switching. in this paper a framework has been proposed that identifies the impact of utilization of various fuels for foundry industries. importance of fuel switching in foundry industry a. this industry, being energy intensive, has a huge potential for improving energy efficiency. improving energy performance of an enterprise will directly reduce energy costs and improve profitability. consideration of an efficient fuel over existing ones is a vital aspect and will help in achieving energy efficiency with a great impact. motivation b. global warming is taking place because of the uncontrolled use of energy sources. carbon emissions are an important factor adversely affecting the environment. there is a strong need worldwide to reduce carbon emissions and improve energy efficiency. improvement of energy performance not only leads to saving of natural reserves, but also serves the purpose of reducing carbon emissions. the fact that energy efficiency has a broader sense in terms of global warming and environment, motivates towards the use of environmental friendly fuels and for improvement in energy efficiency through fuel switching. our contribution c. this paper analyzes the demand of fuel switching in casting industries if they are not working with energy efficient fuels. in this paper a new framework for fuel switching has been established. the framework will help the casting manufacturing enterprises to recognize the performance of existing fuel as well as the opportunities for improving energy performance through fuel switching to an efficient and clean fuel. the contribution of energy efficiency exclusively from fuel switching has been studied. the framework is validated through the case study of a maharatna public sector company of india, cffp, bhel haridwar. engineering, technology & applied science research vol. 8, no. 5, 2018, 3439-3444 3440 www.etasr.com naim & mahara: fuel substitution for energy saving ii. related work related work is divided into two parts. the first part is concerned with energy efficiency measures in the foundry field and the second part includes various studies of fuel switching in different domains. energy efficiency measures in the foundry field a. in [9], authors suggested the use of cleaner technologies in foundry based industry. in [10], authors dealt with the reduction of hazardous waste (hw) in several industries. a study of developing countries for providing resource efficient gains is shown in [11]. in [12], highlighted limitations for sri lanka for cleaner technologies in foundry industries were researched. author in [13] elaborated energy efficiency practices and energy-efficient technologies for iron and steel plants. authors in [14] suggested the reduction in specific energy use irrespective of payback period in iron and steel industry for 2020 over 2010. energy efficiency scenarios are shown in [15] for economic energy saving opportunities of iron and steel industry of india for the duration from 2010 to 2030. authors in [16] outlined a case study of the existing melting techniques in a steel foundry. authors in [17] focused on the measures for improving energy efficiency in an aluminum foundry. fuel switching in different domains b. fuel switching replaces inefficient fuels with cleaner and economical alternatives. the work in [18] is a part of a wider study to measure resource depletion using its environmental and economic impacts for the case of natural gas. in [19] large emission reductions were seen for conversions from oil and gas boilers to a biomass based system. authors in [20] showed that the main policy is to reduce the demand for firewood and to mitigate environmental degradation. authors in [21] show a comparative model of four options, namely biogas, solar energy, heat pump and imported heat. research gap and problem identification c. in foundry sector the research work done is mainly about the improvement in energy efficiency of melting processes, whether it is scrap charging, use of insulation material, control of temperature or other operational improvements. at the best of our knowledge there is a lack in the available literature regarding energy efficiency improvements in foundry with the help of fuel switching. it is evident that fuel switching is an important aspect of energy saving. this paper provides a unique framework for fuel switching in organizations especially for foundry industries to improve their energy performance. iii. framework for fuel switching in foundries in this section, we present the framework developed for the switching from old existing fuel to an energy efficient fuel. the framework has five major components, shown in figure 1. study of reference system with existing fuel a. in this phase, the details of the existing system in the organization have to be identified. all types of fuels under existing scenario are to be listed. the fuel consumption can also be recorded with respect to production. the energy saving opportunities for higher energy consumption processes through fuel switching are to be identified through the following processes: • analysis of actual energy consumption of various equipment and comparative assessment with standard similar equipment. • setting targets along with action plans for achieving the identified opportunities in the switching of fuel. • identification of environmental, legal and other obligations as applicable for existing fuel. fig. 1. frame work for fuel switching -list all production shops and activities involving fuel consumption -identify all fuel types used and check their contribution -identify the production spots that consume most fuel -identify heat content of existing fuel -identify transportation system of existing fuel -identify procurement means of existing fuel. -investment requirements -budget availability -interest of top management -identify the possible alternative fuel -establish previous fuel consumption and production for existing and alternate fuel -bring existing and alternative fuel to same platform by converting into the same energy unit -compare alternate and existing fuel prices -check heat/energy content of alternate and existing fuels -analyze the environmental impact of alternate and existing fuels -check consumption rate for both fuels -compare the ease of transportation of both fuels study of reference system with existing fuel factors for migration towards efficient fuel challenges encountered during switching fuel switching process analysis and decision making for fuel switching engineering, technology & applied science research vol. 8, no. 5, 2018, 3439-3444 3441 www.etasr.com naim & mahara: fuel substitution for energy saving factors for migration towards efficient fuel b. this is the phase of framework that will help in decision making for switching of fuel. the activities at this stage are as below: • calculation of sec (specific energy consumption) based on production data and consumed fuel data. • calculation of savings that may result due to reduction in energy consumption achieved from the switching. challenges encountered during switching. c. investments will be needed for making changes in the existing infrastructure, to make it compatible with alternate fuel. the availability of sufficient infrastructure and its management is needed in order to switch smoothly from one fuel to another, which should be ensured at this stage. fuel switching process d. in this stage, first of all the enterprise has to explore all the possible alternate fuels available in the market that may replace the existing ones. care should be taken while selecting alternate fuel as the selection should require minimum changes in the existing infrastructure. fuel consumption of existing and possible alternate fuel is to be calculated. analysis and decision making for fuel switching e. this phase focuses on the analysis and comparison between the existing and alternate fuel. the final decision of fuel switching can be taken based on the results. the heat content of both fuels is to be compared along with the consumption rate with respect to per unit production. the initial investment cost is to be compared with savings that will occur due to substitution of old fuel. iv. case study: cffp, bhel this paper presents the case study of central foundry forge plant (cffp), bhel, hardwar for migration of their fuels namely, ldo, hsd, and lpg to a single fuel, i.e. natural gas. we studied the manufacturing processes and the energy consumption of the cffp. the enterprise is engaged in the manufacturing of heavy weight casting and forgings in various steel grades. in its quest to improve energy performance, cffp has recently got certification for energy management system standard, iso-50001 [22]. along with this, it is an iso-9001 [23], iso-14001 [24] and ohsas-18001 [25] certified company. apart from producing components for various other applications, components are produced mainly in four steel grades namely, plain carbon grade, alloy steel grade, stainless steel and supercritical grade steel [26]. study of reference system with existing fuel a. in this phase, analysis on the energy consumption pattern of cffp has taken place. until recently, cffp was consuming energy in various forms (ldo, hsd, lpg and electricity) for its operations. handling and use of these fuels were proving to be inefficient and involved environmental and safety hazards. the consumption of liquid fuels and lpg in cffp was mainly for furnaces, cutting operations, boilers and pre-heating of ladles for molten steel. the operations and interactions of these sectors are represented in figure 2. fig. 2. interaction of various shops and operations in cffp plant factors for migration towards efficient fuel b. the migration of an organization from liquid fuels to natural gas may be caused by many driving forces. some of these factors regarding cffp, are described below: • natural gas is cleaner fuel than ldo/hsd. it emits less pollution during combustion [27]. the amount of co2 emitted during combustion per billion btu of natural gas is 117000 while 164000 units are emitted by the burning of one billion btus of ldo [28]. • spreading of oil (hsd or ldo) at workplaces results in hazardous conditions that might lead to an accident while this problem does not exist in natural gas and provides higher safety at the workplace. • in liquid fuel, two types of air supply, primary and secondary are required. primary air is required for atomization and secondary air serves the purpose of combustion [29]. thus the electricity required to supply primary air through blowers driven by electric motors is saved. • moreover, due to the primary and secondary air supply in furnaces, the excess air is much higher in oil fired furnaces and boilers. increase in the quantum of air input to any furnace increases the quantum of flue gasses resulting into a corresponding increase in heat loss to the atmosphere. • in winters, ldo being a high viscosity fuel gets more viscous and sticky [30]. thus, heating is required for ldo for making it suitable for transportation. • transportation of liquid fuel is done either by rail or by road and many times its arrival delays due to unpredictable and uncontrollable reasons. on the other hand, natural gas is transmitted through underground pipelines without any interruption. challenges encountered during switching c. although there might be a need to switch from a traditional final product -scrap steel collection -melting of steel -pouring liquid steel into moulds mould preparation -collection of liquid metal in mould and solidification -heat treatment -cutting, welding and gouging for defect removal -receiving black job -chipping, cutting, boring and milling for final finishing steel melting shop steel foundry light foundry final product machine shop mould preparation -collection of liquid metal in mould and solidification -heat treatment -cutting, welding and gouging for defect removal engineering, technology & applied science research vol. 8, no. 5, 2018, 3439-3444 3442 www.etasr.com naim & mahara: fuel substitution for energy saving fuel to a new one, this conversion may not be simple. some of the major challenges that can be occur during the switching are: • the time of completion required for conversion usually poses the most critical factor, as all the equipment cannot be closed simultaneously in the plant, affecting production activities. so there is always a trade-off between how many types of equipment can be taken up for fuel switching in different phases. • appropriate scheduling and budgeting are required for fuel switching that should include target production, equipment availability, criticality of jobs, and other relevant parameters. fuel switching process d. in order to compare the energy consumption, we have considered the production of foundry shops of cffp for the last four years and the corresponding fuel consumed for the respective production of castings. the main steps to perform the switching of fuel are: • collection of yearly production data. analysis of energy consumed from various types of fuels. • conversion of fuel consumption according to calorific values or any other common unit for comparison. • calculation of sec and yearly comparison of sec. • calculation of fund saving (if any) due to sec reduction. in this case study of fuel switching, the major work is changing the combustion system including pipelines, air supply system, and control system for regulation of fuel and air, and burners that are compatible with new fuel. the activities performed for the evaluation of performance are: 1) collection of yearwise production data before the financial year 2012-2013 the enterprise was using only liquid fuels for manufacturing products. the conversion of fuel in cffp started in 2012-2013 and natural gas completely replaced old liquid fuel by 2015-2016. the enterprise production for these years is shown in table i: table i. production data financial year casting production (mt) 2012-13 5716 2013-14 5807 2014-15 5792 2015-16 5212 2) analysis of energy consumed from various types of fuels in this section, energy data in various forms related to both foundry shops has been analyzed for the last four years. the combined total energy consumption for both foundry shops along with combined production outcome is shown in table ii. 3) conversion of fuel consumption to calorific values the calorific values of all the fuels used (ldo, hsd, lpg or natural gas) are different and in order to compare these fuels and further energy performance, the consumption of various forms of fuels are converted to the same unit based on their calorific values. as the contribution of electricity does not alter the foundry operations and requires a fixed amount of electricity, therefore, to precisely evaluate the variation of other fuel with respect to production, electricity is excluded from the calculations of energy consumption for production operation. the details of calorific values for all the fuels used for conversion and calculated million kilo-calories (mn-kcal) are shown in table iii. table ii. energy consumption form of energy 2012-13 2013-14 2014-15 2015-16 power (10 5 kwh) 49.28 52.67 49.56 41.62 ldo/hsd (10 3 liters) 3872 2601 127 0 lpg (metric tones) 989 26.1 4.14 0 natural gas (10 5 scm) 4.27 27.44 45.03 37.01 production (mt) 5716 5807 5792 5212 table iii. fuel conversion into calorific values fuel type in base unit of consumption equivalent kcal equivalent mn-kcal ldo/hsd 1 litre=11700 1 litre=11700/10 6 lpg 1 ton=11300 1 ton=11300/10 6 natural gas 1 scm=9880 1 scm=9880/10 6 4) calculation of sec and yearwise sec comparison the efficient working of the enterprise or its energy performance can be compared by comparing the yearwise sec per unit of turnover. sec is defined as the ratio of total energy consumed to the total units of production or turnover: sec=total energy consumed/total turnover the consumption of various fuels by the organization in mn-kcal for the compared four years with casting production is shown in table iv. table iv. sec per year financial year energy consumption (mn-kcal) casting production (mt) sec (mn-kcal/mt) 2012-13 60696.86 5716 10.62 2013-14 57837.35 5808 9.96 2014-15 46022.32 5792 7.95 2015-16 36565.88 5212 7.01 analysis and decision making for fuel switching. e. in this phase, the sec for old fuels used before switching and natural gas used after switching are compared. it has been noticed that there is a significant reduction in sec by the use of natural gas. the percentage share of various types of energy consumed by the enterprise during the financial years starting from 2012-13 to 2015-16 has been analyzed and represented in figures 3 and 4. the details of energy consumption before and after fuel conversion are described below. 1) before switching figure 3 shows the distribution of energy for 2012-13. during this financial year, ldo/hsd had the main share in energy consumption with a percentage of 69.76% of total energy consumption. the electricity consumption was 6.53% of total energy consumed whereas lpg and natural gas had engineering, technology & applied science research vol. 8, no. 5, 2018, 3439-3444 3443 www.etasr.com naim & mahara: fuel substitution for energy saving 17.21% and 6.49% respectively. for the financial year 2013-14 (figure 4), the share of ldo/hsd decreased to 48.79%, electricity was at 7.26 %, whereas natural gas share increased to 43.46% and lpg was not consumed. fig. 3. fuel consumption in 2012-13 fig. 4. fuel consumption in 2013-14 2) after switching in 2014-15 (figure 5), natural gas had the largest share in energy consumption, contributing around 88.47% of total energy, the electricity consumption was 8.48% and the use of ldo/hsd was limited to only 2.95%. during 2015-16 (figure 6), the natural gas had completely replaced all other fuels and has contributed 91.08% in total energy consumption, while the share of electricity was 8.92 %. fig. 5. fuel consumption in 2014-15 fig. 6. fuel consumption in 2015-16 3) evaluation of performance on the basis of sec figure 7 shows that the sec decreased by the increase in the use of natural gas. for the time period from 2012-13 to 2015-16, the sec fallen from 10mn-kcal to around 7mnkcal per ton of turnover. fig. 7. specific energy consumption 4) fund savings due to reduction in sec savings compared to the base year 2012-13 have been estimated. in case the enterprise had not used natural gas and consumed the old fuel, the specific consumption was bound to remain almost equal to that of the year 2012-13. but with the increased use of natural gas over the years, sec reduced. the sec for the year 21012-13 was 10.62mn-kcal per metric ton and this value for 2013-14 was 9.96mn-kcal per metric ton. the difference came out to be 0.66mn-kcal per metric ton. the significance of this is that for manufacturing each metric ton of production output, the enterprise saved 0.66mn-kcal. the actual saving of natural gas in the year 2013-14 is computed by multiplying the difference of sec with the turnover of the year 2103-14 and dividing it by its calorific value. the result will give the physical quantum of the natural gas saved. thus, cffp saved 387984scm of natural gas in 2013-14. by considering the rate of natural gas approximately to rs. 25 per scm, it gives the actual monetary saving of rs. 97·10 5 for 2013-14 alone. the savings for the other years have been worked out in a similar way and are listed in table v. table v. savings due to sec reduction year saving in sec with respect to 2012-13 savings in mn-kcal savings of natural gas in scm approx. savings** 2013-14 0.66mn-kcal* 3833.28 387984 rs. 97·10 5 2014-15 2.67mn-kcal* 15464.64 1565247 rs. 391·10 5 2015-16 3.61mn-kcal* 18815.32 1904385 rs. 476·10 5 * per mt of turnover. ** considering rs. 25 per scm of natural gas. v. conclusion in this paper, conversion from various fuels to natural gas has been analyzed. factors acting as driving forces and challenges for switching of fuels have been defined. it is evident from the case study that the use of natural gas in replacement of three fuels, namely ldo, hsd and lpg by cffp has resulted in significantly lower consumption of energy identical production. natural gas has been found to be cheaper, cleaner and more energy efficient fuel for the foundry under consideration. this improvement of energy efficiency directly reduced the enterprise’s energy bills and also saved a significant quantity of natural reserves which were to be consumed if natural gas was not used. thus, the current paper electricity ldo/hsd natural gas lpg electricity ldo/hsd natural gas lpg 48.79% 43.46% 7.26%0.5% electricity ldo/hsd natural gas88.47% 8.48% 2.95% electricity natural gas 91.08% 8.92% 0 2 4 6 8 10 12 2012-13 2013-14 2014-15 2015-16 specific energy consumption 6.53% 69.76% 6.49% 17.21% engineering, technology & applied science research vol. 8, no. 5, 2018, 3439-3444 3444 www.etasr.com naim & mahara: fuel substitution for energy saving serves as a guide to foundry enterprises to review the use of existing fuel and explore the possibility of fuel switch. references e. p. degarmo, j. t. black, r. a. kohser, b. e. klamecki, materials [1] and process in manufacturing, prentice hall, 1997 brief profile of indian foundry industry, available at: [2] http://www.foundryinfo-india.org/profile_of_indian.aspx, 2018 bee, iip and mb associates, best practice guide foundry sector of [3] india, available at: http://www.iipnetwork.org/india_foundry _best_practice_guide.pdf2, 2012 h. zhang, f. qiu, q. wei, l. tong, x. ye, y. cheng, “economic [4] development and energy efficiency in jilin province, china”, journal of geographical sciences, vol. 24, no. 5, pp. 875-888, 2014 bureau of energy efficiency, https://www.beeindia.gov.in [5] s. kalpakjian, s. schmid, manufacturing, engineering and technology, [6] pearson, 2006 m. a. laughton, m. g. say, electrical engineer's reference book, [7] newnes, 2002 bee, energy management and audit, available at: https://www. [8] beeindia.gov.in/sites/default/files/1ch3.pdf, 2001 p. pal, g. sethi, a. nath, s. swami, “towards cleaner technologies in [9] small and micro enterprises: a process-based case study of foundry industry in india”, journal of cleaner production, vol. 16, no. 12, pp. 1264-1274, 2008 r. lilja, s. liukkonen, “industrial hazardous wastes in finland–trends [10] related to the waste prevention goal”, journal of cleaner production, vol. 16, no. 3, pp. 343-349, 2008 p. l. daniels, “technology revolutions and social development: [11] prospects for a green technoeconomic paradigm in lower income countries”, international journal of social economics, vol. 32, no. 5, pp. 454-482, 2005 p. d. wijayatunga, k. siriwardena, w. j. l. s. fernando, r. m. [12] shrestha, r. a. attalage, “strategies to overcome barriers for cleaner generation technologies in small developing power systems: sri lanka case study”, energy conversion and management, vol. 47, no. 9, pp. 1179-1191, 2006 e. worrell, “advanced technologies and energy efficiency in the iron [13] and steel industry in china”, energy for sustainable development, vol. 2, no. 4, pp. 27-40, 1995 j. a. moya, g. n. pardo, “the potential for improvements in energy [14] efficiency and co2 emissions in the eu27 iron and steel industry under different payback periods”, journal of cleaner production, vol. 52, pp. 71-83, 2013 w. r. morrow, a. hasanbeigi, j. sathaye, t. xu, assessment of energy [15] efficiency improvement and co2 emission reduction potentials in india's cement and iron & steel industries”, journal of cleaner production,vol. 65, pp. 131-141, 2014 c. prabhakar, g. l. datta, r. markandeya, “improvements in energy [16] efficiency in alloy steel foundry”, indian foundry journal, vol. 61, no. 7, pp. 21-27, 2015 k. p. dwivedi, s. singh, a. sharma, s. prakash, “improving energy [17] efficiency in aluminum foundry”, indian foundry journal, vol. 61, no. 7, pp. 28-32. 2015 s. rimos, a. f. a. hoadley, d. j. brennan, “determining the economic [18] consequences of natural gas substitution”, energy conversion and management,vol. 85, pp. 709-717, 2014 a. joelsson, l. gustavsson, “energy efficiency measures and conversion [19] of fossil fuel boiler systems in a detached house”, energy efficiency, vol. 3, no. 3, pp. 223-236, 2010 m. chambwera, h. folmer, “fuel switching in harare: an almost ideal [20] demand system approach”, energy policy, vol. 35, no. 4, pp. 25382548, 2007 s. rudra, l. rosendahl, “techno-economic analysis of a local district [21] heating plant under fuel flexibility and performan”, energy efficiency, vol. 10, no. 3, pp. 613-624, 2017 international organization for standardization, iso 50001 quality [22] management, iso, 2015 international organization for standardization, iso 90001 energy [23] management, iso, 2011 international organization for standardization, iso 14001 [24] environmental management, iso, 2015 bsi group, ohsas 18001 occupational health and safety [25] management certification, bsi, 2007 bhel, annual report, bhel, 2016 [26] bee, fuels and combustion, available at: http://www.em-[27] ea.org/guide%20books/book-2/2.1%20fuels%20and%20combustion.pdf natural gas supply association, natural gas and the environment, [28] available at: naturalgas.org/environment/naturalgas, 2013 b. jenkins, p. mullinger, industrial and process furnaces: principles, [29] design and operation, butterworth-heinemann, 2011 s. chapman, t. g. cowling, d. burnett, the mathematical theory of [30] non-uniform gases: an account of the kinetic theory of viscosity, thermal conduction and diffusion in gases, cambridge university press, 1990 microsoft word 33-3786_s_etasr_v10_n5_pp6344-6348 engineering, technology & applied science research vol. 10, no. 5, 2020, 6344-6348 6344 www.etasr.com shaaban: the effects of marble dust on the rheological and mechanical properties of shotcrete the effects of marble dust on the rheological and mechanical properties of shotcrete mostafa shaaban civil engineering department giza higher institute for engineering and technology giza, egypt mostafa.shaaban@gei.edu.eg abstract−recycling industrial waste materials has become an environmental and economic necessity. the utilization of these materials to develop concrete contributes not only to their disposal, but also to the preservation of the environment. this study attempted to evaluate the properties of sprayed concrete with marble dust (md) as partial replacement of concrete components. for this purpose two series of concrete mixtures were prepared: the first series included six mixtures containing md as cement replacement with percentages of 5%, 10%, 15%, 20%, 25%, and 30% by weight, the second series included six mixtures containing 5%, 10%, 15%, 20%, 25%, and 30% of md as replacement for sand. also, conventional concrete mixture with 100% cement and 100% sand was produced as control mixture. rheological and mechanical properties as pumpability, build-up thickness, rebound percentage, adhesion strength, and compressive and tensile strength were studied. in general, the results indicate that use of md improves shotcreting as an application and shotcrete’s performance. keywords-sprayed concrete; marble dust; spraybility; strength; rebound ratio; shotcrete i. introduction shotcrete, also referred to as sprayed concrete or spraycrete, is defined as concrete shooted through a hose at high velocity and pneumatically projected onto a surface [1] or as concrete produced with basic mix and projected pneumatically from nozzle into place to produce a dense homogeneous layer [2]. efnarc defines it as a concrete mix projected pneumatically into a surface to produce a homogeneous and dense mass [3]. this concrete is used for repairs of concrete buildings, underground concrete reservoirs, lining of tunnels, and rapid concrete construction. in order to produce shotcrete, two steps have to be carried out: the fresh concrete must first be pumped, and then shot, so the ideal shotcrete mix should have suitable pumpability, and sprayability, in addition to proper strength. pumpability (i.e. the mobility and stability of concrete under pressure) is measured by standard tests such as the slump test. it is recommended that concrete should possess slump higher than 50mm [4]. sprayability incorporates parameters such as the ability of shotcrete to stick to itself (cohesion) without segregation, to adhere to a surface (adhesion), and to be buildup in thick sections and concrete ricochets off the impacted surface (rebound). when concerning strength, shotcrete should have a compressive strength higher than 30mpa, whereas, for permanent tunnel lining, a compressive strength of at least 40mpa is required [5]. shotcrete should have bond or adhesion strength of 0.5 to 1.0mpa [3] in order to stick to the sprayed surface. marble dust (md) is a solid waste material generated from marble processing and can be used as a cement or fine aggregate replacement material in concrete admixures. authors in [6, 7] studied the effect of sand replacement with different levels of md on concrete properties. they observed that the replacement of sand with 15% md results in compressive strength increment. authors in [8] examined the concrete properties containing 0%, 5%, 10%, and 20% of md as cement substitution. attractive outcomes were achieved for substitution proportions of up to 10%. authors in [9] reported that the replacement cement by md in a percentage up to 5% could be secure, without unfavorable impact on the bond properties of cement in concrete. authors in [10] reported that concrete mechanical properties rise with 15% md substitution. authors in [11] investigated the properties of fresh and hardened concrete containing 0, 5, 10, 15, and 20% of tile and marble powders. the results indicate that using 2.5% marble powder +2.5% tile powder led to increase the compressive and tensile strengths by 8.9% and 8.3% respectively. authors in [12] studied the effects of sand replacement with 0%, 25%, 50%, 75%, and 100% of mp on the mechanical properties of concrete. they reported that substituting sand with 50% mp increased the compressive and flexural strengths by 13.52% and 35.54% respectively. although many studies have examined the utilization of md as a replacement material for sand or cement, however none focused on the effects of md on the rheological and mechanical properties of shotcrete, properties as pumpability, build-up thickness, rebound percentage compressive strength, tensile strength, and adhesion or bond strength. so, this study aims to study the md effects on the aforementioned properties of fresh and hardened shotcrete. ii. research methodology a. materials used natural dolomite with 2.65 specific gravity and 10mm nominal size was used as coarse aggregate in all concrete mixtures, while natural sand was used as fine aggregate. the corresponding author: mostafa shaaban engineering, technology & applied science research vol. 10, no. 5, 2020, 6344-6348 6345 www.etasr.com shaaban: the effects of marble dust on the rheological and mechanical properties of shotcrete fine and coarse aggregates satisfied the astm c33/c33-m [13] specifications. cemi-42.5n ordinary portland cement complying with astm c150/c150-m [14] was used in all mixtures with different proportions. locally available md with a specific gravity of 2.27 and particle size finer than 80µm which was prepared according to [15] was used as cement replacement, while md with particle size ranging between 0.075 to 2mm (figure 1) was used as sand replacement, in six mixtures with percentages of 5%, 10%, 15%, 20%, 25%, and 30% for each case. potable water complying with astm c1602/c1602m-18 [16] was used in concrete mixing and curing. viscocrete sc that meets astm c494 type f [17] was used as a superplasticizer in 1% percentage. fig. 1. particle size distribution for coarse and fine aggregates. b. mixing and specimen preparation the material proportions were estimated based on aci 506.4r-94 [18]. the quantities of concrete ingredients are given in table i. the materials were mixed in an electric mixer, then concrete specimens were prepared for testing the hardened properties as follows: plywood molds of 1000mm×1000mm were used. the molds were positioned vertically, and fresh concrete was sprayed in 150mm thickness under the same conditions. the samples were cured until extraction. the tests of compressive strength were conducted according to [19] on drilled cores taken from the prepared test panel. the samples’ diameter was at least 50mm and the height/diameter ratio ranged between 1.0 to 2.0. the samples required to perform tensile and adhesion tests were cored in accordance with [20]. table i. concrete mix proportions (kg/m3) replacem.% opc md water c. agg. f. agg. hrwr sand md control mix (0% md) 0% 400 0 160 1080 600 0 4 replacement of cement with md 5% 380 20 160 1080 600 0 4 10% 360 40 160 1080 600 0 4 15% 340 60 160 1080 600 0 4 20% 320 80 160 1080 600 0 4 25% 300 100 160 1080 600 0 4 30% 280 120 160 1080 600 0 4 replacement of sand with md 5% 400 0 160 1080 570 30 4 10% 400 0 160 1080 540 60 4 15% 400 0 160 1080 510 90 4 20% 400 0 160 1080 480 120 4 25% 400 0 160 1080 450 150 4 30% 400 0 160 1080 420 180 4 c. testing procedure 1) rheological properties the rheological properties or flow properties of shotcrete such as pumpability (i.e. mobility and stability under pressure), build-up thickness, and rebound percentage were measured according to the corresponding standards as illustrated below. • pumpability: this characteristic was measured by the slump test. the slump test was conducted according to astm c143 [21] and the test results were compared with the recommendations of aci 304.2r-17 [4]. • build-up thickness: to measure build-up thickness, the test procedure presented in jsce-f 563-2005 [22] was followed. • rebound percentage: to measure rebound percentage, the test procedure of jsce-f 563-2005 [22] was followed. 2) mechanical properties • compressive and tensile strength tests were conducted according to astm c 1604/c1604m [23] at 7 and 28 days. • the adhesion strength test was performed according to astm c882 [24] at 28 days. iii. results and discussion a. slump the influence of md on concrete slump at different replacement percentages is shown in figure 2. in general, the value of slump decreases as the md level increases whether it is used as a replacement to cement or sand. the results indicate that the slump of mixtures containing md as a replacement for cement is less than that of the 0% md mixture. this decrease in slump value is caused by the reduced flowability due to the increase of the concrete viscosity resulting from the use of md [25]. also, the results in figure 2 show that the use of md as a sand replacement results in a decrease of slump up to 40%, in comparison with the control mixture. this behavior may be related to the fineness of md which is higher than that of cement. as the particle fineness increases, the concrete water demand increases and consequently reduces concrete slump. studies have shown that the slump of the concrete mixtures is negatively influenced by the md substitution and this effect occurs at greater substitution levels (beyond 15%) [26]. fig. 2. slump values of concrete mixtures. engineering, technology & applied science research vol. 10, no. 5, 2020, 6344-6348 6346 www.etasr.com shaaban: the effects of marble dust on the rheological and mechanical properties of shotcrete b. build-up thickness figure 3 shows the variation in the build-up thickness of concrete mixtures comparing to the build-up thickness of the control mix. the results indicate that the use of md as a cement replacement material results in a slightly decrease of the buildup thickness ranging between 1.3% and 4.59%, with the maximum increase obtained for 30% md. also, figure 3 indicates that the mixtures containing md as a sand replacement have values of build-up thickness higher than the build-up thickness of the control mixt, due to that md particles are finer than sand particles and the cohesive nature of md is higher than sand’s [27]. fig. 3. build-up thickness of concrete mixtures. c. rebound percentage figure 4 presents the results obtained for different mixtures shot under the same conditions (spray distance and angle). increase of the rebound percentage due to the replacement of cement were observed, while mixtures containing md as sand replacement had rebound percentages lower than that of the control mix. these results can be explained by the role that cohesion plays in rebound reduction. the md is more cohesive than natural sand, so consequently, increasing md against the percentage of sand results in a lower rebound amount [27]. fig. 4. rebound percentage of concrete mixtures. d. adhesion strength figure 5 shows the results of the adhesion strength test for all mixtures at the age of 28 days. the results clarify that replacement of cement with md causes decrease in the adhesion strength. on the other hand, the use of md as sand replacement led to adhesion strength increase. for the same md replacement levels, the decrease of adhesion strength in the case of cement replacement is higher than the obtained increase in the case of sand replacement. fig. 5. adhesion strength of concrete mixtures at 28 days. e. compressive strength figure 6 demonstrates the effect of md as cement or sand replacement on 7and 28-day compressive strength tests. at the age of 7 days, the mixtures containing md as cement replacement at all replacement levels exhibit decreased compressive strength in comparison with the control mix (0% md) with percentages ranging between 5.4% for 5% md and 23.4% for 30% md. the results at the age of 28 days follow the same behavior but with smaller decrease, ranging between 4.9% for replacement level of 5% md and 23% for 30% md. it is noticeable that the replacement of cement with md led to a decrease in compressive strength. this decrease occurs because md does not have pozzolanic properties [28-30]. the obtained test results at the age of 7 days of mixtures containing md as sand replacement show increased compressive strength in comparison with the control mix (0% md). also, the results at 28 days indicate that the mixtures with md as sand replacement have increased compressive strength. in general, it can be reported that the partial replacement of sand with md causes a significant rise in compressive strength, a result of the filler effect of md. this result is agreement with the findings in [26, 31]. fig. 6. compressive strength at 7 and 28 days. 0% 5% 10% 15% 20% 25% 30% 0% 5% 10% 15% 20% 25% 30% 0% 5% 10% 15% 20% 25% 30% 0% 5% 10% 15% 20% 25% 30% engineering, technology & applied science research vol. 10, no. 5, 2020, 6344-6348 6347 www.etasr.com shaaban: the effects of marble dust on the rheological and mechanical properties of shotcrete f. tensile strength figure 7 shows the results of tensile strength tests of all concrete mixes at 7 and 28 days. tensile strength at 7 days clarifies that the use of md as cement replacement causes a decrease in tensile strength ranging between 11.3% and 29.3%. the results of 28 days indicate that the use of md as a cement replacement results in decrease of the tensile strength between 4.8% and 23%. the results at the age of 7 days show that the strength of concrete mixtures with md as sand replacement is higher increases by 7.2%-45%. at 28 days, the tensile strength increases by 11%-37.2%. fig. 7. tensile strength at 7 and 28 days. iv. conclusions based on the experimental results, the next conclusions can be drawn: • concrete mixtures containing md as cement or sand replacement with percentages from 5% to 30% have slump values lower than the control mixture (0% md), but still higher than 50mm, which means that these mixtures fulfill the shotcrete requirements reported in [4]. • the use of md as sand replacement with a percentage of 5% up to 30% has a positive effect on the rebound percentage of shotcrete. all mixtures have rebound percentages less than the control mix, while using md as cement replacement at any percentage led to a slight increase of the rebound percentage. • all concrete mixtures with 5% to 30% md as cement replacement have build-up thickness less than the build-up thickness of the control mix (370mm). mixtures with md as sand replacement have build-up thickness higher than the build-up thickness of the control mix. • the compressive strength of the mixtures containing md as cement replacement at the age of 28 days is less than that of the control mix but still higher than 30mpa (with the exclusion of 30% replacement) which meets the shotcrete requirements [5]. all mixtures containing md as sand replacement have compressive strength higher than that of the control mix and more than 40mpa so these mixtures are suitable for permanent tunnel lining, where compressive strength of at least 40mpa is required [5]. • the adhesion strength of mixtures containing md as sand replacement is higher than the adhesion strength of the control mixture, while the adhesion strength of mixtures containing md as cement replacement is less than that of the control mixture. concluding, a mixture containing 5% md as cement replacement appears to be most suitable to be used as shotcrete. references [1] aci 506r, guide to shotcrete. farmington hills, mi: american concrete institute, 2016. 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[31] p. a. shirule, a. rahman, and r. d. gupta, “partial replacement of cement with marble dust powder,” international journal of advanced engineering research and studies, vol. 1, no. 3, pp. 175–177, apr. 2012. engineering, technology & applied science research vol. 8, no. 2, 2018, 2640-2645 2640 www.etasr.com shrivastav et al.: performance analysis of transient current limiters in a distribution system performance analysis of transient current limiters in a distribution system alok kumar shrivastav electrical engineering dpt techno india batanagar kolkata, india alok5497@gmail.com pradip kumar sadhu electrical engineering dpt indian institute of technology (ism) dhanbad jharkhand, india pradip_sadhu@yahoo.co.in ankur ganguly electrical engineering dpt techno india batanagar kolkata, india anksjc2002@yahoo.com abstract—in this study, a simple, but effective method is presented for the limitation of the y-yg transformers transient current. one of the main privileges of this method is its simple topology. it does not need any control circuit or measurement unit. the method is based on a three-phase thyristor bridge with a low resistance reactor. since the number of thyristors is minimized, the voltage ripple, electrical losses and the malfunction probability owing to device failure are decreased considerably. the proposed method is simulated and validated by matlab simulation and conventional methods test results. it is shown that the proposed configuration is effective for the transient current limitation of y-yg transformers keywordstransient current limiter; tcl; stability analysis; fast fourier transform; fft; harmonic restraint, error analysis i. introduction nowadays power systems have been commonly operated with the maximum possible capacity and closer to their stability boundaries due to various reasons such as rapid increase in electricity demand and deregulation of electricity markets. this decreases the power system marginal security in case of instabilities. under such circumstances, when a circuit breaker is charged, a high transient current flows for a little time until normal flux conditions are established. during most practical system conditions, this transient current’s value is high. this transient current, rich in all harmonics, has been found to cause wide raging disturbances in power system and power supplies [1]. in recent years, some solutions have been recommended to overcome the problem with diode bridge-dc reactors and voltage source pwm converters. in addition, a control strategy has been proposed for the assessment of sapfs (shunt active power filters), based on the lyapunov control theory, defines a stable operating region for the interfaced converter during the integration time with the utility grid [2]. authors in [3] developed a wye-delta multi-function balance transformer based power quality control systems (mbt-pqcs). in [5], authors formulated the indirect matrix converter (imc)-based unified power quality conditioner topology for a photovoltaic (pv) system for solving the power quality functionalities. in [6], an exhaustive simulation model based on mathematical model of a three-phase, shunt active power filter has been developed. in [9], the performance of the transformer magnetic flux under phase-hop condition is investigated and compared with different operating conditions using finite elements. these methods have some drawbacks like voltage drop, while they need bypass resistance, additional control circuits and switching devices. in [10], two different types of measurement equipment are presented comparatively for power quality assessment. in [12], shunt compensation based power quality enhancement is shown. however, the controller stability is not discussed in any of the available research methods. this paper’s objective is to investigate stable and harmonic free, transient current limiters (tcls). in this context, two different types of tcls based three-phase converter were proposed, twelve pulse and six-pulse. the first stage had presented the mathematical and simulation considerations of transients that occur during closing of circuit breaker and energizing of transformer and the second stage address the comparative loom of stability and the total harmonic distortion (thd) between twelve-pulse and six-pulse converter based three-phase thyristor bridge system. ii. series tcl for three-phase y-yg transformer transient current in circuit breaker results from any abrupt change in the magnetizing voltage. the transient current waveform consists of a large and long lasting ac component and harmonics [16]. the tcl, has a low resistance coil in order to gain better results. the series tcl connected to threephase breaker and primary side of three single-phase transformers operates in two modes, charging mode and discharging mode [16]. the present mathematical statement in charging mode is composed, as takes after [16]. ( / ) 1 2 2) 2 2 2 2 ( ) sin( ) ( ) ( sin( ) ( ) ( ) r l t tf tf vvp i t e wt rr wl vvp wt rr wl                 (1) where tclp rrr  (rp is the resistance in the primary side of the transformer and rtcl is the reactor resistance), l=lp+ltcl+lm (lp is the leakage spillage inductance in the essential side of the transformer and ltcl is the reactor engineering, technology & applied science research vol. 8, no. 2, 2018, 2640-2645 2641 www.etasr.com shrivastav et al.: performance analysis of transient current limiters in a distribution system inductance and lm is the charging inductance of the transformer), vtf is the forward thyristor voltage drop and vp is the crest plentifulness of the utility voltage. fig. 1. three single phase tcl connected in series with y-yg transformer iii. ppoposed tcl as shown in [16] the transient current of the three-stage transformer can be controlled by utilizing twelve thyristors of the arrangement tcl. through these thyristors, considerable current of the loaded transformers flows. therefore, they are costly as well as unstable. hence, to make the system stable and harmonics free, a modified circuit is proposed which is shown in figure 2 [16]. fig. 2. proposed tcl connected to y-yg transformer iv. charging mode according to figure 3, the coil in comparison by neglecting r1 and l1 is communicated as, charging method of conducting coil [7] and can be written as follows: 1 1 1 1 sin( 30) 2 2 2 2 ll p p tf tcl tcl di v wt r i l dt di d v l r i dt dt         (2) differentiating (2) leads to the following equation: 1 1 2 2 1 1 2 2 sin( 30) 2 2 2 ll p p tcl tcl di wv wt r i l dt d i di d l r dtdt dt        (3) fig. 3. coil charging mode it is clear that      1 m ci t i t i t  (4) ccir dt d   (5) and * m mm m di did d l dt di dt dt     (6) utilizing (4), (5) and (6) the accompanying comparison can be represented as 1 2 3 4( ) sin( ) ft gt m m m mi t i e i e i wt i     dt d l r dt di r dt d m c c   1 2 2 (7) supplanting (7) in (3), we get (8) 2 2 1 1 1 2 2 1 1 cos( 30) 2 2 2( ) ll p p tcl c tcl c m di d i d i wv wt r l l dt dt dt rdi di d r r dt dt l dt         (8) comparing (2) with (8) can be revised in the accompanying structure ewtdci dt di b dt id a  )sin(1 1 2 1 2  (9) where c tclp m r ll la   2 mtclp c tclp m lll r rr lb 22) 2 (    2 p tclc r r  2 2 2 2( ) c m ll c r l w d v r   engineering, technology & applied science research vol. 8, no. 2, 2018, 2640-2645 2642 www.etasr.com shrivastav et al.: performance analysis of transient current limiters in a distribution system 2 30 cos tf ll e v v d         using laplace transform, (9) can be rewritten, as follows 2 ' 2 2 ( ( ) (0) (0)) ( ( ) (0)) ( ) sin( ) cos( ) a s i s si i b si s i ci s s w e d ss w            (10) consequently               2 2 2 2 2 2 2 sin coss i s d d s as bs c s as bs c e s as bs c                 (11) utilizing the inverse laplace transform, the transient current somewhere around 0 and t/4 can be dictated by the accompanying equation. 1 2 3 4( ) sin( ) ft gt m m m mi t i e i e i wt i     (12) where 1 2 2 2 2 ( ) c o s ( ) ( ) ( ) ( ) ( ) ( m e d f s i n d w i f f g f g f w f g f w              2 2 2 2 2 sin( ) cos( ) ( ) ( )( ) ( )( ) m e dg dw i g g f g f g w g f g w                        23243 )22()(4 2 wwfggfw wd im 4m e i gf  2 4 2 b b a c f a     2 4 2 b b a c g a     3 2 4 2 3 2 (2 2 ) cos( ) (2 ( )) sin( ) cos( ) 4 ( ) (2 2 ) w fg w w f g w f g wfg w           as given in (12), the charging mode somewhere around 0 and t/4 comprises of two exponential and one sinusoidal segment. since f and g are negative, these two exponential parts will tend to decay. v. stability analysis the performance and stability analysis of the process under investigation are carried out using the simulated model that is formulated based on the physical properties of the real process. figures 4 to 8, illustrate the impact of tcl on voltage stability of grid-connected photovoltaic system by conventional linear stability analysis tools like bode, nyquist and nichols chart. a. bode plot analysis this method is very helpful for determining the stability of a system. it is a logarithmic plot, so they collapse a wide range of frequencies on the horizontal axis and a wide range of gains on the vertical axis into a completely viewable plot. from (11) bode analysis is done to check the stability of the system shown in figures 1-2. result shows that the preceding system is unstable but the modified system shown in the figure 2 is stable considering the same gain margin and other parameters are also constant. fig. 4. bode diagram for line current stability of figure 1 fig. 5. bode diagram for line current stability of figure 2 b. nyquist plot analysis this is a parametric plot of a frequency response obtained from (11), used for assessing the stability of the system shown in figures 1-2. in, nyquist plot, if tgh contour does not encircle the critical point and the open loop system doesn’t possess any open loop pole at the right half of s-plane then the system is stable. figures 6-7 illustrate the stability of the model presented in figures 1-2. c. nichols plot analysis in this method, derived from (11), considering constantmagnitude loci and constant phase-angle loci in the logmagnitude versus phase diagram. the magnitude in db monotonically decreases with increase in frequency. a engineering, technology & applied science research vol. 8, no. 2, 2018, 2640-2645 2643 www.etasr.com shrivastav et al.: performance analysis of transient current limiters in a distribution system comparative stability analysis of figure 1–2 is shown, which implicates the results shown in figure 8 is unstable and figure 9 is stable considering the same value of gain margin. fig. 6. nyquist diagram for line current stability of figure 1 fig. 7. nyquist diagram for line current stability of figure 2 vi. total harmonic distortion analysis in this paper, fast fourier transform (fft) method has been applied for harmonic assessment in single-phase signals of figure 1 and figure 2. by this fundamental technique, the amplitude and phase angle of harmonic components can be individually determined. the results show that the proposed tcl circuit shown in figure 2 is more efficient than the system shown in figure 1. figures 10-11 show the fft output and thd analysis for 50 and 60hz for tcl systems in figures 1 and 2 respectively. fig. 8. nichols diagram for line current stability of figure 1 fig. 9. nichols diagram for line current stability of figure 2 vii. results and discussion the simulations are carried out in matlab. the comparative analysis and simulation parameters are given in tables ii-iii. figures 4–5, figures 6–7 and figures 8-9 show the close loop stability of the system shown in figure 1 and figure 2 using conventional methods such as bode, nyquist and nichols. as shown in figures 4, 6 and 8, the close loop system becomes unstable without using modified tcl or it can be stable using the conventional tcl as shown in figures 5, 7 and 9. figure 10 (a)-(c) shows the harmonic distortion of figure 1 at different frequency. figure 11 (a)-(c) illustrates the harmonic analysis for the transformer current using conventional tcl shown in figure 2. a comparison of these figures shows that using the proposed tcl results in the reduction of the thd amplitude. the system harmonic parameters up to sixteenth order with and without using the proposed tcl are listed in table i. this test verifies the effectiveness of the proposed tcl for limiting the unwanted harmonics. the results show that the transient current has been limited significantly, which will downsize the nominal values of all circuit elements owing to the new current scale. evidently, this is gained in the cost of adding the tcl. engineering, technology & applied science research vol. 8, no. 2, 2018, 2640-2645 2644 www.etasr.com shrivastav et al.: performance analysis of transient current limiters in a distribution system (a) (b) (c) fig. 10. (a) fft output, (b) thd analysis at 50hz, (c) thd analysis at 60hz for tcl system shown in figure 1 table i. comparative parameter analysis parameters figure2 figure3 sampling time 5.49369e-007 s 6.56117e-007 s samples per cycle 30337.8 25402 total harmonic distortion (thd) 28.65% 0.19% maxm frequency used for thd calculation 910020.00 hz 761940.00 hz table ii. simulation parameters parameters value parameter value rp 0.65ω ltcl 0.8h r1 0.05ω rtcl 0.03ω lp 0.0025h vtf 10v l1 0.001h ω 314.15 lm 0.9h s 20 mva rc 2000ω vll 2000(vrms) (a) (b) (c) fig. 11. (a) fft output, (b) thd analysis at 50hz, (c) thd analysis at 60hz for tcl system shown in figure 2 table iii. comparison of system stability and harmonic analysis with available techniques system analysis stability analysis thd analysis proposed method system stable 0.19% [4] n.a 4.05% [5] n.a 4.3% [2] n.a 16.5% [3] n.a 22.3% [6] n.a 30.8% viii. conclusions in this paper, a comparative study between two efficient tcls, based on a three-phase thyristor bridge system for the mitigation of transient occurs during the closing of circuit breaker and charging of transformer has been proposed. the main advantage of the proposed limiter is that it can automatically provide high impedance to restrain the transient current phenomenon and it will not cause distortion in the steady-state load voltage or current waveforms. the proposed tcl has a simple topology, does not need any controlling engineering, technology & applied science research vol. 8, no. 2, 2018, 2640-2645 2645 www.etasr.com shrivastav et al.: performance analysis of transient current limiters in a distribution system circuit and uses fewer thyristors than other tcls. in addition, it gives a stable output, lower voltage drop, ripple, and lower harmonic distortion for transformers. the simulation results show the effectiveness of the proposed tcl. moreover, this technique is shown to be effective in stability analysis of power systems in distribution area. references [1] m. tarafdar hagh, m. abapour, “dc reactor type transformer inrush current limiter”, iet electric power applications, vol.1 no. 5, pp. 808-814, 2007 [2] m. mehrasa, e. pouresmaeil, s. zabihi, e. m. g. rodrigues, j. p. s. catalao, “a control strategy for the stable operation of shunt active power filters in power grids”, energy, vol. 96, pp. 325-334, 2016 [3] s. hu, z. zhang, b. xie, m. chen, a. kubis, “a wye-delta multifunction balance transformer based power quality control system for single-phase power supply system”, ieee conference on 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m. m. hussain, m. s. habeeb, s. suraya, “neutral point clamped based active power filter for power quality improvement”, international conference on electrical, electronics, signals, communication and optimization, visakhapatnam, india, january 2425, 2015 [13] j. h. brunke, k. j. frohlich, “elimination of transformer inrush currents by controlled switching – part i: theoretical considerations”, ieee transactions on power delivery, vol, 16, no.2, pp. 276–280, 2001 [14] t. hoshino, k. m. salim, a. kawasaki, i. muta, t. nakamura, m. yamada, “design of 6.6 kv, 100 a saturated dc reactor type superconducting fault current limiter”, ieee transactions on applied superconductivity, vol, 13, no.2, pp. 2012–2015, 2003 [15] k. l. lian, b. k. perkins, p. w. lehn, “harmonic analysis of a threephase diode bridge rectifier based on sampled-data model”, ieee transactions on power delivery, vol. 23, no. 2, pp. 1088–1096, 2008 [16] a. kumar shrivastav, p. kumar sadhu, a. ganguly, n. pal, “a novel transient fault current limiter based on three phase thyristor bridge for y-yg transformer” international journal of power electronics and drive systems, vol. 6, no. 4, pp.747–758, 2015 [17] x. n. lin, p. liu, “the ultra-saturation phenomenon of loaded transformer energisation and its impacts on differential protection”, ieee transactions on power delivery, vol. 20, no. 2, pp. 1265–1272, 2005 [18] a. k. al-khalifah, e. f. al-saadany, “investigation of magnetizing inrush current in a single-phase transformer”, ieee large engineering systems conference on power engineering, halifax, canada, pp. 165171, july 26-28, 2006 [19] y. cui, s. abdulsalam, s. chen, w. xu, “a sequential phase energization technique for transformer inrush current reduction – part i: simulation and experimental results”, ieee power engineering society general meeting, denver, usa, vol. 1, pp. 535, june 6-10, 2004 microsoft word 42_98-perspectives_3274_s__etasr_v10_n2_pp5576-5580 engineering, technology & applied science research vol. 10, no. 2, 2020, 5576-5580 5576 www.etasr.com javed et al.: perspectives of heat stroke shield: an iot based solution for the detection and … perspectives perspectives of heat stroke shield: an iot based solution for the detection and preliminary treatment of heat stroke sadia javed department of computer science and software engineering jinnah university for women karachi, pakistan sadi0921@gmail.com samia ghazala department of computer science and software engineering jinnah university for women karachi, pakistan samia_ghazala@yahoo.com ummay faseeha department of computer science and software engineering jinnah university for women karachi, pakistan uf_uit@yahoo.com abstract—heat stroke is considered a major problem in karachi, with a considerable number of people recorded as victims each year. the proposed internet-of-things (iot) based heat stroke shield works under heat stroke conditions, depending on a heat index value (atmospheric temperature and humidity). the system comprises of a wristband, a hardware kit and an alert system which can pre-notify a wearer regarding his body parameter readings. moreover, the system can also work as a problem solver, in heat stroke condition, by showering water on the victim. in both cases, an alert will also be generated to the wearer’s caretakers with his gps location. keywords-internet-of-things; gsm module; heat stroke; wearable i. introduction global warming consists of a constant and continuous rise in the temperature of earth’s atmosphere [1]. among its many catastrophic impacts, this rise in temperature has been an evident cause of heat waves [2]. continuous temperatures above 32oc for three days is an obvious condition of heat wave [3]. it is a prevalent natural climatic hazard with perceptible impacts on the humans and biophysical systems and is considered to be a global and constantly growing problem. heat wave cycle repeats on a yearly basis normally in summer season with symptoms such as heat stress, heat exhaustion and heat stroke. people who work in the sun continuously suffer from sun stroke because of the excessive heat accumulated in their body due to the continuous exposure. also, elders, specifically those with circulatory diseases are most vulnerable to heat stroke [4]. children are also considered to be a high risk group to face heat exhaustion and heat stroke related problems. pakistan has been a victim of heat waves [5]. the heat waves are common in pre-monsoon months (april-june) in the plains of the country. in june 2015, the southern part of pakistan was affected by a severe heat wave in which temperature raised above 45°c. reported mortalities were due to suffocation, dehydration and heat strokes [6]. the death toll for this year rose noticeably to about 1200 individuals, resulting in a stateof-emergency being declared at all public hospitals and morgues. from 2015 onwards, people face extreme weather conditions each year and a noticeable number of individuals get affected. densely populated cities are more vulnerable to negative impacts of heat waves in pakistan [7, 8]. karachi is one of the most heat stroke affected cities of pakistan. the sea breeze moderates the city’s climate as it is located on the coast of the arabian sea. due to the sea breeze a low-pressure system generates in the ocean which may lead to a spike in temperature. it causes the body temperature to increase and affects the nervous system rapidly [9] resulting in death or permanent organ damage or disability if not properly treated on time. furthermore, global climate change makes summers even hotter. this weather fluctuation impact gets worse due to the insufficient functioning of the weather forecast system [10]. to deal with the heat stroke problem, an iot based prototype is discussed in this paper which is using sensors to measure certain parameters like body temperature, oxygen level, and heat index (atmospheric temperature and humidity). wearing the proposed wristband, heat stroke can be detected in advance, on the basis of these parameters, in children, elderly, and adults. a hardware kit, specifically for bedridden or on a wheel chair patients, is also integrated with the wristband for sprinkling water vapors on the heat stroke victim. ii. related work new technological advancements in the field of communications, specifically in mobile network and sensor technology, are further improving the channels and removing the existing obstacles [11]. a new technological era of internet of things (iot) is emerging rapidly and many vendors are constructing sensor enabled devices which follow the open standards allowing these devices to be integrated with any type of system, i.e. inventory management systems, customer corresponding author: sadia javed engineering, technology & applied science research vol. 10, no. 2, 2020, 5576-5580 5577 www.etasr.com javed et al.: perspectives of heat stroke shield: an iot based solution for the detection and … support systems, business intelligence, and health care applications [12]. data acquisition, analysis and processing have become more convenient and transparent with the support of iot. health services are also actively taking part by providing information on time [13]. in iot based healthcare systems, a patient/victim can not only be monitored remotely but an automated cure can be provided as first aid in case of an emergency. a model which is efficiently dealing with real time data for the health care system by taking advantage of iot is proposed in [14]. similarly, a number of wearable physiological monitoring systems has been developed focusing mainly on the heat illness of astronauts, athletes, firefighters, and soldiers. these systems comprise of an array of sensors that can be assimilated with clothes/wearables to continuously sense the physical parameters of the wearer and keep track of his/her health status effectively [15]. similar systems have been proposed for treating heat exhaustion or heat stroke. in [16], heat stress monitoring is done by a flexible bluetooth based self-adhesive patch which is attached on the chest of the patient. it analyzes heat illness by monitoring certain body parameters. a heat illness monitoring system for firefighters is proposed in [17], which uses a wearable shirt integrated with sensors to analyze temperature, humidity, and heart rate. the low energy wireless protocol zigbee is used for sending the information to the remote device. another zigbee based wearable device is proposed in [18] which is worn on the wrist and the finger of a person (athlete or infant). it is used to check heart rate and temperature of the wearer and an alert message is sent to the caretakers if the parameters reach a certain threshold. temperature and heart rate sensors fabricated on gloves are used to detect heat stroke conditions. a smart watch uses body temperature for the prediction of heat stroke in [19] with water intake also monitored by the system. a gprs and wifi based system is discussed in [20] which is mainly focusing on the detection of the presence of humans, especially children, inside locked cars. heat stroke is monitored by temperature sensor and an alert is generated to the owner of the car in case of emergency. likewise, a bluetooth/gprs based system is proposed to address heat stroke in [21], in which an accelerometer sensor is used to detect user movement. the movement detection beyond a certain defined threshold will result in alarm generation. nontechnical solutions to control body temperature in case of heat exertion are discussed in [22]. body temperature can be dropped by 0.35oc /min if the patient is immersed in cold water at 2oc while the temperature decreasing rate in an air-conditioned rooms is only around 0.05oc. alternatively, applying ice packs or crushed ice can also be used to lower body temperature up to a certain limit [23, 24]. these methods can work efficiently with excertional heat strokes. in the case of non-exertional heat strokes, air blow with water spray can bring gradual change in the body temperature up to 0.31oc/min [25]. table i. comparison of different heat stress monitoring systems heat stress monitoring system communication technology hardware body parameters analyzed target audience system alert flexible self-adhesive patch type system for professional heat stress monitoring [16] bluetooth self-adhesive patch ecg, body temperature, humidity, 2-axis acceleration heat stress victim of any age group no wearable system for heat stress monitoring in firefighting applications [17] zigbee wearable shirt temperature, humidity, heart rate, firefighters no a zigbee-based wearable physiological parameters monitoring system [18] zigbee wristband, finger clip heart rate, temperature athlete or infant yes heat stroke detection system based in iot [15] tcp/ip hang glove heart rate, temperature children, elderly people, adults of productive age yes heatwatch [19] bluetooth smart watch, smartphone body temperature, water intake all age groups no affordable system for alerting, monitoring and controlling heat stroke inside vehicles [20] gprs/wifi smart vehicle temperature sensor, presence detection, location children yes minimizing heatstroke incidents for young children left inside vehicles [21] bluetooth/ gprs estimate beacon device movement detection children yes iii. proposed system design a. controling element the arduino nano comprises of an atmega328p microcontroller bearing the same features as arduino uno with compact size and 8 analog ports (a0-a7) and 11 general purpose digital ports (d2-d12). the small size and advanced features of arduino prove it to be an appropriate choice for wearable devices [26-31]. arduino ide platform is used to program the controller as per the desired features of the proposed system. it processes the information received from the sensors and sends the information through the wireless medium to the android application used by the caretaker and the designed kit simultaneously, in case of emergency for treatment from the adverse effects of heat waves. the proposed system works on an iot concept to provide connectivity between the wearable device and the mobile application without human intervention. b. sensors for parameters’ intuiting a heat stroke can be harmful if the patient is not treated urgently due to the rise in body temperature (greater than 40.0°c). therefore, in this proposed system, real time data of the following parameters will be sensed by respective sensors:  body temperature  blood oxygen level  heat index (comprised of environmental temperature and humidity) a body temperature sensor is connected with the analog input pin, a heat index sensor with a digital input pin and a engineering, technology & applied science research vol. 10, no. 2, 2020, 5576-5580 5578 www.etasr.com javed et al.: perspectives of heat stroke shield: an iot based solution for the detection and … blood oxygen sensor with another analog input pin of the arduino to analyze and compare received data with the saved information. all the sensors are embedded in the wearable device. 1) human body temperature sensor humans are effected by heat stroke majorly due to the change in body temperature with respect to change in environmental temperature and humidity level. environmental temperature and humidity level are collectively called heat index [32]. therefore, the proposed system is focused on human body temperature in comparison with external weather conditions. mlx90614 sensor is a non-contact infrared thermometer connected at a digital input of the arduino embed in the wrist band and measures the infrared radiation emitted from the human body. the purpose of the controller is to absorb infrared radiation from the body and convert it to heat. the heat is converted into electrical energy, which is communicated to a detector to determine the temperature of the body. the normal range of human body temperature is between 37-38°c, when heat index reading is between 27-32°c. therefore, the effected person or the caretaker must be cautious and have to take some measures to drop body temperature. however, if the temperature of the human body raises from 3940°c at heat indexbetween 32-41°c, then the person needs extreme attention because these symptoms of heatstroke can be lethal and the patient’s body temperature must drop quickly. in the proposed solution, mlx90614 sensor is used for the continuous monitoring of the human body temperature along with the other parameters such as heat index and oxygen level. table ii. heat stoke and environmental parameter effects heat index (°c) body temperature (°c) oxygen level (mm hg) observation 27-32 37-38 75-73 caution 32-41 39-40 72-70 extreme caution 41-54 41-42 69-65 danger over 54 above 42 less than 65 extreme danger 2) heat index heat index is used to measure apparent temperature or feellike temperature. therefore, the proposed system focuses on environmental temperature and humidity along with other parameters. an sht75 sensor is used to sense environment temperature and humidity levels. it consists of a capacitive element which measures relative humidity and a band gap sensor which measures temperature. the sensor is connected with an analog pin of the controller and gives the results in digital form. ther output of sht75 will be compared with the output of the mlx90614 sensor and spo2 sensor to get the actual impact of heat wave on human body. 3) light-based spo2 sensor in the proposed idea, spo2 is used to sense the oxygen level of the human body, it is a clamp-like device which is connected to the input of the arduino in a wrist band. minorrays of light pass through the blood in the wrist, measuring the amount of oxygen through the changes of light absorption in oxygenated or deoxygenated blood. c. communication technology long range wireless connectivity is required for the uninterupted flow of sensed data in the case of an emergency. therefore, a gsm/gprs module is used for sending alert messages to the registered number of the caretaker. the gsm module is heplful to mentain long range wireless communication between the caretake and the wearer. it is the most suitable device for iot applications because of its size and features of text messaging, phone calling, and accessing the internet through gprs. however, gprs services will not be used to avoid the additional penetration of harmful rays in human body. iv. implementation the methodology of the proposed system is shown in figure 1 in which environmental parameters (heat index) along with human body temperature and oxygen level are the main areas of concern in case of extreme weather conditions. therefore, the decision of sending alert or activation of the showering kit will be depending upon the parameters discussed in table i. the proposed system will be composed of two modules. the first module is based on a wearable wristband which is used while the user is in mobility as shown in figure 2. figure 3 shows the second module comprised of a wristband along with a showering kit for immobilized persons. fig. 1. data flow of the proposed system the wristband in both modules is designed with embedded sensors. mlx90614, spo2 and sht75 sensors are used to monitor heat index, body temperature, and oxygen level respectively. the working of the wristband will start with the sensing of the value of heat index (hi). if the hi value is greater than 32°c, it is considered an indication of extreme caution for heat stroke. to examine accurately, the processing unit will immediately check body temperature and oxygen level. if the body temperature increases to 39°c or above and the oxygen level decrease below 70mm hg, then it is engineering, technology & applied science research vol. 10, no. 2, 2020, 5576-5580 5579 www.etasr.com javed et al.: perspectives of heat stroke shield: an iot based solution for the detection and … considered a certain condition of heat stroke and the gsm module placed on the wristband will send an alert message to the caretaker. if the wearer also wants to keep track of his fluctuating condition, he can also get alert on his mobile device and can take precautionary measures himself. this is considered to be an obvious advantage of this setup. fig. 2. proposed system module 1: wearable wrist band fig. 3. proposed system module 2: wristband along with showering kit the same setup followed by a water showering kit will be used as a second module. this device will be designed especially for patients. in addition to generate an alert from wristband to the caretaker, a bluetooth enabled showering kit will also start working on the same values of monitored parameters. kit will shower water vapors on the heat stroke victim progressively until the caretaker handles the condition of the patient. this will act like first aids for the patient when no one is nearby to take care of him in a case of an emergency. the second module is covering both features of the system, i.e. monitoring and treating. v. test case a solution is proposed for addressing heat stroke by measuring body temperature and oxygen level of an elder adult. figure 4 shows the prototype of the system. a site in karachi has been selected for experiment in the extreme weather of june, 2019. the observed heat index and body temperature were 43.2°c and 39.2°c respectively. the system successfully generated an alert message to caretaker’s contact number fed already in the application. vi. conclusion and future work the proposed system is an attempt to address cataclysmic situations of heat stroke. the wristband contains sensors for continous measurement of crucial parameters like body temperature, oxygen level, and heat index, and it can also send alert messages to the caretakers in a case of an emergency. this is beneficial for all age groups and for persons engaged in different outdoor activities. the integrating hardware kit with wristband, especifically working for debridden patients and elderly people, is used to provide first aid as well. architecture and simple design corroborate to make it an afforable and easily implementable system. in the future, more parameters like pulse rate and sweating can be monitored considering other illnesses or diseases. fig. 4. the prototype of the proposed system references [1] t. p. hughes, j. t. kerry, s. k. wilson, “global warming and recurrent mass bleaching of corals”, nature, vol. 543, pp. 373–377, 2017 [2] m. s. nashwan, s. shahid, “spatial distribution of unidirectional trends in climate and weather extremes in nile river basin”, theoretical and applied climatology, vol. 137, pp. 1181–1199, 2019 [3] m. akbar baig, s. waheed, a. mian, e. hussain, “unforgiving heat wave deaths in the largest metropolitan city of pakistan: lessons learned”, eurasian journal of emergency medicine, vol. 14, pp. 209– 210, 2015 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arduino and cloud service”, engineering, technology & applied science research, vol. 8, no. 4, pp. 3238–3242, 2018 [32] p. o. antonio, c. m. rocio, r. vicente, b. carolina, b. boris, “heat stroke detection system based in iot”, ieee second ecuador technical chapters meeting, salinas, ecuador, october 16-20, 2018 microsoft word etasr_v11_n1_pp6632-6636 engineering, technology & applied science research vol. 11, no. 1, 2021, 6632-6636 6632 www.etasr.com zaini: image segmentation to secure lsb2 data steganography image segmentation to secure lsb2 data steganography hatim ghazi zaini department of computer engineering taif university taif, saudi arabia h.zaini@tu.edu.sa abstract-a digital color image usually has a high resolution, thus its size is good enough and the image can be used as a covering (holding) image to hide secrete messages (short and long). the methods commonly used for data steganography, e.g. lsb and lsb2 are not secure, so in this paper, a method of securing the lsb2 method is proposed. the proposed method is based on wavelet packet decomposition. the levels of decomposition will be kept in secret and one of the resulting segments will be used as a covering segment. mse, psnr, hiding time, and extraction time will be experimentally analyzed to prove that the proposed method is capable of handling the process of hiding secret messages, either sort or long. keywords-steganography; lsb2; mse; psnr; hiding time; extraction time; wpt; decomposition level; segment; security i. introduction data steganography [1-3] is the process of hiding secret data into covering data. the covering data must be large enough in order to be capable to hide the secret data [4-5]. data steganography [6-7] must provide the following important features [8]: • the changes in the holding data must not affect them while the concealment process result must not be visible to the naked eye [2]. • the mean square error (mse) [9] between the original covering data and the holding data must very small and close to zero. • the peak signal-to-noise ratio (psnr) [10-11] between the original covering data and the holding data must very big in order to keep the quality of the holding data high. • the secret data hiding time must be minimal. • the secret data extraction time must be minimal. • the hiding method must be secure and the process of hacking must be very complicated. • the method must be simple to implement. • the method must be capable of hiding secret data of various sizes (short and long messages). one of the most common types of data that can be used to hide confidential messages is digital color images for the following reasons [12-15]: • the wide spread use of digital images. • the sheer volume of covering data that a digital image provides [16, 17]. • the ease of digital image processing [18-19]. • the possibility of reshaping the image before the process of masking data. • the possibility of using a section of the image to implement the concealment process [20]. ii. hiding data methods one of the most popular methods of data hiding is the least significant bit (lsb) method which requires 8 bytes from the holding image to hide one character from the secret message. the lsb2 method is a modification of the lsb but it doubles the capacity of hiding by using 4 bytes from the covering image to hide one character from the secret message. the least two significant bits are used to hold data from the secret message as shown in table i. the lsb2 adds minor changes to the covering image, ranging from +3 to -3. these changes in the pixel colors cannot be noticed by the human eye. the process of data hiding and data extracting using the lsb2 method is very simple, figure 1 shows the process of hiding, while figure 2 shows the process of data extracting. table i. hiding a=65 d=01000001b 155 142 133 120 covering bytes 10011011 10001110 10000101 01111000 binary 10011001 10001100 10000100 01111001 holding byte (binary) 153 140 132 121 holding bytes the lsb2 method adds minor changes to the covering image. these changes cannot be noticed by the human eyes, thus this method keeps the holding image very close to the covering one, and minimizes mse and maximizes psnr between the covering and the holding images. as we can see in figures 3 and 4, the histograms of the two images are very close to other. corresponding author: hatim ghazi zaini engineering, technology & applied science research vol. 11, no. 1, 2021, 6632-6636 6633 www.etasr.com zaini: image segmentation to secure lsb2 data steganography fig. 1. the data hiding process. fig. 2. the data extraction process fig. 3. covering image. fig. 4. the same image holding a 50 byte character message. iii. aim of the study lsb2 is a method of secret data is an easy-to-implement and quick-to-perform way, but one of its main flaws is its lack of security in the data-stripping device, due to its ease of penetration from non-authorized parties. accordingly, the aim of this research is to update this method by strengthening it with the required protection operations and thus to prevent intruders from the possibility of obtaining or knowing the secret messages included in the digital image, provided that the advantages of the concealment method are preserved and without negatively affecting the efficiency of the method. iv. research method the hiding process is going to be implemented in four phases. the information in the first two phases must be kept confidential in order to secure the data. • color image rearrangement. the color channels are rearranged, then the color image 3d matrix is reshaped into a one row matrix. the reshaping can be done either rowwise or column-wise. • row matrix decomposition. the principles of wavelet packet tree decomposition [21, 22] are used to decompose the image row matrix. in this phase, we have to select the number of levels needed to divide the image into segments, and then we have to select the segment [23] where we must hide the secret massage (figure 5). • the lsb2 method of data hiding is applied. • the holding image is rearranged back. the extraction process will be implemented in 3 phases. • image rearrangement: here we have to use the information used in the hiding process. • after we get the number of decomposition levels and the segment number, image decomposition is applied. • the lsb2 method to extract the message from the selected segment is applied. fig. 5. the diagram of the proposed method. v. results and discussion twelve images were processed, and each of them was rearranged by replacing the color channels from red, green, and blue to blue, red, and green. each image matrix was reshaped from 3d form to 1d column-wise. the number of the selected decomposition levels was defined as 7, and segment 6 was selected for message hiding. figure 6 shows the segments of one image. engineering, technology & applied science research vol. 11, no. 1, 2021, 6632-6636 6634 www.etasr.com zaini: image segmentation to secure lsb2 data steganography fig. 6. image (with small size ) 1 segments. table ii. segment sizes image# segment size(byte) s1 s2 s3 s4 s5 s6 s7 1 2358 2358 4715 9429 18857 37713 75425 2 1219 1219 2437 4874 9747 19494 38988 3 8100 8100 16200 32400 64800 129600 259200 4 80325 80325 160650 321300 642600 1285200 2570400 5 67598 67598 135195 270389 540777 1081553 2163105 6 1911 1911 3821 7642 15284 30567 61133 7 8100 8100 16200 32400 64800 129600 259200 8 2359 2359 4718 9436 18872 37744 75488 9 2359 2359 4718 9436 18872 37744 75488 10 2365 2365 4730 9460 18920 37839 75677 11 29532 29532 59063 118125 236250 472500 945000 12 95614 95614 191227 382454 764907 1529814 3059628 table iii. segment locations # of colors starting column starting row segment 6 size (byte) image # 3 37 113 37713 1 3 38 1 19494 2 3 90 1 129600 3 3 267 803 1285200 4 3 245 245 1081553 5 3 41 41 30567 6 3 90 1 129600 7 3 45 137 37744 8 3 45 137 37744 9 3 50 50 37839 10 3 150 1 472500 11 3 286 1 1529814 12 the obtained segments for each image are of different sizes and locations and when the decomposition level changes the segments, their sizes, and their locations also changed. tables ii and iii show the image segment information after applying 7 image decomposition levels. segment 6 was chosen in each color image and a message with a length of 50 characters was selected and hided in each covering image. table iv shows the obtained experimental results. we can notice the following facts: • the quality of the holding images is very high, the mse value is very low, while the values of psnr are very high. • the hiding and extraction times are minimal. • increasing the image size leads to increased psnr values as shown in figure 7. • if the size of one segment does not meet the message length, we can use more segments. • it is very difficult to know the segment number and the segment size without knowing the decomposition levels. table iv. hiding a 50 character message in segment 6 of each image image # resolution (pixel) size (byte) mse psnr hiding time (s) extraction time (s) 1 151×333 150849 0.0024 171.2046 0.00015 0.00012 2 152×171 77976 0.0050 163.7287 0.0010 0.0010 3 360×480 518400 0.00079282 182.2244 0.0010 0.0010 4 1071×1600 5140800 0.000077420 205.4879 0.0030 0.0025 5 981×1470 4326210 0.000096389 203.2964 0.0020 0.0020 6 165×247 122265 0.0031 168.4323 0.0012 0.0012 7 360×480 518400 0.00081790 181.9130 0.0010 0.0010 8 183×275 150975 0.0022 172.0226 0.0010 0.0010 9 183×275 150975 0.0025 170.8047 0.0010 0.0010 10 201×251 151353 0.0029 169.1633 0.0010 0.0010 11 600×1050 1890000 0.00019365 196.3198 0.0025 0.0025 12 1144×1783 6119256 0.000062426 207.6406 0.0030 0.0030 fig. 7. psnr as a function of image size. fig. 8. covering image and histograms. figures 8 and 9 show the covering and the holding images in image #12, with message size = 331776. table v shows the obtained results after hiding messages with various sizes in segment 6. from table v we can conclude the following: engineering, technology & applied science research vol. 11, no. 1, 2021, 6632-6636 6635 www.etasr.com zaini: image segmentation to secure lsb2 data steganography • the mse values remain low and the psnr values remain high even after hiding long-length messages. • the quality of the holding image is close to the quality of the covering image. • increasing the message length will lead to decreasing psnr as shown in figure 10. • increasing message length will lead to increased hiding time as shown in figure 11. • increasing message length will lead to rapidly increasing extraction time, as shown in figure 12. fig. 9. holding image and histograms (big size image). table v. hiding various messages in image 12, segment 6 message size (bytes) mse psnr hiding time (s) extraction time (s) 162 0.00025036 193.7515 0.0040 0.000120 324 0.00047963 187.2502 0.0060 0.001000 648 0.00097087 180.1985 0.0090 0.0040 1296 0.0020 173.2242 0.0150 0.0080 2592 0.0039 166.3545 0.0260 0.0240 5184 0.0078 159.3298 0.0510 0.0700 10368 0.0155 152.4668 0.1000 0.2660 20736 0.0311 145.5429 0.2020 0.6040 41472 0.0620 138.6369 0.4340 1.2770 82944 0.1247 131.6397 0.9130 3.5160 165888 0.2489 124.7307 1.5750 11.5300 331776 0.4981 117.7943 3.0810 43.4310 fig. 10. psnr vs message length. fig. 11. hiding time vs message length. fig. 12. extraction time vs message length. the obtained experimental results showed that the proposed method can be recommended to be used instead of the lsb2 method, because it can add a security level without affecting the efficiency and capacity of the lsb2 method. from the obtained results we can see that the quality parameters are better when we use images with big sizes. vi. conclusion in this paper, a secure lsb2 method of data steganography was proposed, implemented, and analyzed. the obtained experimental results showed that selecting the image rearrangement method, the number of decomposition levels, and a segment number will increase the security level of 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[15] a. a. moustafa and z. a. alqadi, "a practical approach of selecting the edge detector parameters to achieve a good edge map of the gray image," journal of computer science, vol. 5, no. 5, pp. 355–362, may 2009, https://doi.org/10.3844/jcssp.2009.355.362. [16] m. dwairi, z. alqadi, a. abujazar, and r. abu zneit, "optimized truecolor image processing," world applied sciences journal, vol. 8, no. 10, pp. 1175–1182, nov. 2010. [17] j. al azzeh, b. zahran, z. alqadi, b. ayyoub, and m. abu zaher, "a novel zero-error method to create a secret tag for an image," journal of theoretical and applied information technology, vol. 96, no. 13, pp. 4081–4091, jul. 2018. [18] z. a. a. alqadi, m. k. a. zalata, and g. m. qaryouti, "comparative analysis of color image steganography," international journal of computer science and mobile computing, vol. 5, no. 11, pp. 37–43, nov. 2016. 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[25] a. y. hindi, m. o. dwairi, and z. a. alqadi, "a novel technique for data steganography," engineering, technology & applied science research, vol. 9, no. 6, pp. 4942–4945, dec. 2019, https://doi.org/ 10.48084/etasr.2955. microsoft word rohani-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 216-220 216 www.etasr.com rohani et al: design of multi-layer optical fibers with ring refractive index… design of multi-layer optical fibers with ring refractive index to reduce dispersion and increase bandwidth in broadband optical networks mahmood seifouri shahid rajaee teacher training university, faculty of ece lavizan, tehran, iran mahmood.seifouri@srttu.edu mohammad mehdi karkhanehchi razi university, faculty of engineering kermanshah, iran mkarkhanehchi@razi.ac.ir sohran rohani shahid rajaee teacher training university, faculty of ece lavizan, tehran, iran shoran_rohani@yahoo.com abstract— the main goal in this paper is to design single-mode optical fibers for dwdm networks, which are used today in rapid communications. these networks require low dispersion in a wide range of wavelengths. so, in this paper, multi-layer optical fibers with low dispersion value and flat dispersion slope in wavelength range of (1.5-1.6µm) are designed, using optimization algorithms. keywordssingle-mode fiber; dispersion; dispersion slope; optimization algorithm. i. introduction triple-clad single-mode fibers have gain significant attention because of the perfect transmission properties that can be achieved by adjusting the multi-parameters [1–3]. a tripleclad fiber was firstly studied by cozens and boucouvalas as an optical coupler for sensing [4]. dispersion curves for a particular coaxial structure were theoretically obtained with the resonance technique [5] and later by the solution of the transcendental equation [6]. in this paper, previous work reported in [5] is extended and the study is focused on the chromatic dispersion coefficient and the chromatic dispersion slope, and the design of triple-clad optical fibers with very low chromatic dispersion value and flat chromatic dispersion slope. a type of large effective area fibers with ring index profiles is proposed. the effects made by the geometric parameters and optical parameters on the waveguide dispersion and cutoff characteristics of low order modes have been analyzed in detail. the calculated results indicate that the waveguide dispersion during single-mode propagation can be controlled by changing the optical and geometrical parameters. this means that it is possible to a obtain dispersion-flattened fiber with large effective-area along a region of wavelengths in wii type single-mode fibers [7]. the dispersion is optimized using a differential evolution (de) algorithm. any similar structure can be optimized and controlled with this design. in section 2, a theoretical method to model the fiber structure and to obtain dispersion and dispersion slope in triple-clad fibers is investigated. ii. theoretical modeling of fiber structure refractive index for wii structure is presented in figure 1. refractive index of each layer is as follows:        <→ <<→ <<→ <<→ ,, ,, ,, ,0, 4 3 2 1 rcn crbn bran arn (1) where r is the position vector of fiber radius. optical parameters are defined as: , 23 31 1 nn nn r − − = (2) , 23 42 2 nn nn r − − = (3) , 4 41 2 4 2 4 2 1 n nn n nn − ≈ − =∆ (4) etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 216-220 217 www.etasr.com rohani et al: design of multi-layer optical fibers with ring refractive index… geometric parameters are defined as follows [8]: c a q c b p == , (5) fig. 1. refractive index structure in the wii fiber[8]. another parameter considered as a geometric parameter is the fiber core radius a, in the first layer. other parameters are as follows: , 2 4 2 10 nnakv −= (6) ,1 2 1 2 4 2 1 2 4 2 0       −= − −      = v u nn n k b b (7) where v is the normalized frequency, b is the normalized propagation constant [8] and r is the radial position. according to the effective refractive index given by 0 k n eff β = where β is the longitudinal propagation constant of guided mode and 0 k is the wave number in free space, the structure of wii-type can be divided into two regions, which are shown in figure 1. according to the wave equation, the boundary conditions of electromagnetic field and under the lp approximation, the characteristic equations in regions (ii)–(iii) can be as described in (14) and (15), and the parameters in these matrices are defined as follow: , 22 1 2 01 β−= nkau (8) , 2 3 2 0 2 2 nkbu −= β (9) , 22 3 2 03 β−= nkbu (10) , 2 2 2 0 2 3 nkaw −= β (11) , 2 4 2 0 2 4 nkcw −= β (12) , 1 , 1 , 3 ' 32 ' 23 ' 3 u p uu p uw q p w === (13) ( ) 1 uj m ( ) 3 wi m − ( ) 3 wk m − 0 0 0 0 ( )' 3 wi m ( )' 3 wk m ( ) 3 uj m − ( ) 3 uy m − 0 0 0 0 ( ) 3 uj m ( ) 3 uy m ( ) 4 wk m − ( ) 1 ' 1 uju m ( ) 3 ' 3 wiw m − ( ) 3 ' 3 wkw m − 0 0 0 0 ( )' 3 '' 3 wiw m ( )' 3 '' 3 wkw m ( ) 3 ' 3 uju m − ( ) 3 ' 3 uyu m − 0 0 0 0 ( )' 3 '' 3 uju m ( )' 3 '' 3 uyu m ( ) 4 ' 4 wkw m − =0, ( ),, 34 wiinnn eff << (14) etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 216-220 218 www.etasr.com rohani et al: design of multi-layer optical fibers with ring refractive index… ( ) 1 uj m ( ) 3 wi m − ( ) 3 wk m − 0 0 0 0 ( )' 3 wi m ( )' 3 wk m ( ) 2 ui m − ( ) 2 uk m − 0 0 0 0 ( )' 2 ui m ( )' 2 uk m ( ) 4 wk m − ( ) 1 ' 1 uju m ( ) 3 ' 3 wiw m − ( ) 3 ' 3 wkw m − 0 0 0 0 ( )' 3 '' 3 wiw m ( )' 3 '' 3 wkw m ( ) 2 ' 2 uiu m − ( ) 2 ' 2 uku m − 0 0 0 0 ( )' 2 '' 2 uiu m ( )' 2 '' 2 uku m ( ) 4 ' 4 wkw m − =0, ( ),, 13 wiinnn eff << (15) where mmmm ijky ,,, are the bessel and modified bessel functions. dispersion and dispersion slope of monomode fiber are expressed in (17) and (18) respectively [9]: ( ) ( ) ,1 2 2 4 2 4 2 dv vbd v c n dv vbd d nd c d λλ λ ∆ −    ∆+−= (16) ( ) ( ) ( ) ( ) ( ) ,2 2 1 1 1 2 2 2 4 2 2 2 2 4 3 3 2 2 4 2 4 2 3 4 3 dv vbd v d �d c dv vbd v c � dv vbd v c n dv vbd d nd cdv vbd d nd c s λ λλ λλ λ ∆ +      ∆ +      ∆ +    ∆+−    ∆+−= (17) where ,4 44 λ λ d dn n� −= is the group index of outer cladding. 4 � and       2 4 2 4 , λλ d nd d dn represent the material dispersion of pure silica, which can be calculated by the sellmeier formula [5]. in order to acquire the dispersion and dispersion slope of a mono-mode fiber, it is necessary to compute ( ) dv vbd ، ( ) 2 2 dv vbd v and ( ) 3 3 2 dv vbd v , which represent the waveguide dispersion. deducing from (7), we obtain [10]: ( ) ,211 11 2 1             −      += dv du v u v u dv vbd (18) ( ) ,22 2 1 2 1 2 11 2 2 dv ud u v u dv du dv vbd v −      −−= (19) ( ) ,6 26 11 2 1 2 3 1 3 1 11 3 3 2       −− −−      −−= v u dv du dv ud v dv ud uv v u dv du dv vbd v (20) iii. design and optimizing dispersion and dispersion slope curves in multi-layer fibers and specially wii fiber, dispersion depends on optical and geometrical parameters. optimization algorithms are employed to design optical fibers with minimal dispersion and the desired optical and geometrical parameters. in this section, we employ de optimization algorithm to design a fiber with low dispersion value and flat dispersion slope. a similar approach employing genetic algorithms to improve dispersion can be found in [8]. a de algorithm cost function (cf) is considered in different ranges of wavelengths. a gaussian function for the de algorithm weight function is considered. ( )∑ ×= max min ,. λ λ λ diapersionwfc (22) ( ) ( ) , 2 exp 2 2 0         − = σ λλ λw (23) etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 216-220 219 www.etasr.com rohani et al: design of multi-layer optical fibers with ring refractive index… fig. 2. gaussian weight function curve applied to the cost function. figure 2 represents the gaussian weight function curve applied to the cost function. due to the importance of mµ55.1 in telecommunications networks, the wavelength interval between ( )mµ6.15.1 − was chosen, and it was attempted to shift the dispersion at this interval to zero dispersion wavelength. iv. simulations and results the dispersion optimization operations are chosen in ( )mµ6.15.1 − wavelength range. de algorithm results with ( ) ( )1 1.22 8, 2 1.6 8sigma e sigma e= − = − and ( ) ,8787.23 == esigma with various optical and geometrical parameters are represented in table 1. the dispersion and dispersion slope curves related to these tables are depicted in figures 3 and 4 respectively. table i. geometrical and optical parameters obtained from the de algorithm geometrical and optical parameters obtained from the de algorithm with: parameters sigma(1)=1.22e-8 sigma(2)=1.26e-8 sigma(3)=2.787e-8 1 r 3.15264670 3.09483016 3. 27005336 2 r -0.92721549 -0.93197766 -0. 96152876 ( )ma µ 2.52132231 2.51136893 2. 51245195 ∆ 55637852e-3 54855381e-3 53750754e-3 p 0.76817297 0.73308432 0. 72238260 q 0.25397348 0.23099590 0. 22219703 fig. 3. dispersion curves in different sigmas, with shifted optimal wavelength. fig. 4. dispersion slope curves in different sigmas in correlation to table(1) etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 216-220 220 www.etasr.com rohani et al: design of multi-layer optical fibers with ring refractive index… according to the results and dispersion curves obtained, we can easily see how dispersion wavelength is shifting towards zero dispersion wavelength. also we can get minimum dispersion with desired sigma value and consequently shift the bandwidth to maximum desired value ( )mµ1.0 in this wavelength range. figures 5 and 6 show the dispersion and dispersion slope curves respectively for sigma=2.6e-8. according to the dispersion slope curve in wavelength range ( )mµ6.15.1 − , we can conclude that in this modeling, dispersion slope is almost flat. fig. 5. dispersion curve in sigma=2.6e-8. fig. 6. dispersion slope curve in sigma=2.6e-8. dispersion value in figure 5 at mµ55.1 , equals to nmkmps //4345.0 which is negligible to the increased bandwidth. it is also shown that the dispersion slope is flat in this bandwidth. the results obtained here, compared with previous research [7-10] show remarkable improvement both in terms of dispersion and the amount of bandwidth obtained through optimization in dwdm networks. v. conclusion in this paper, we presented the design of multi-layer optical fibers with wide bandwidth, low dispersion and flat dispersion slope. calculations show that with increasing distance between two points with zero dispersion, increased dispersion values are achieved. the main purpose of this paper is not to reduce the dispersion dramatically, but to optimize the bandwidth. therefore, the optimization range of the wavelength is selected so as to increase the bandwidth and not to adversely effect the dispersion. this research, not only provides a novel fiber with flat dispersion, but also gives the basic principle behind the design of any fiber with any desired dispersion curve using appropriate optimization algorithms together with the desired cost function. acknowledgment this project was financially supported by the iranian telecommunications research center. references [1] y. li, c. hussey, t. briks, “triple-clad single-mode fibers for dispersion shifting”, journal of lightwave technology, vol. 11, no. 11, pp. 1812-1819, 1993 [2] p. tosin, w. luthe, h. weber, “triple-clad fibers for lasers and amplifiers”, conference on lasers and electro-optics europetechnical digest, p. 44, 1998 [3] h. hattori, a. safaai-jazi, “fiber designs with significantly reduced nonlinearity for very long distance transmission”, applied optics, vol. 37, no. 15, pp. 3190-3197, 1998 [4] j. cozens, a. boucouvalas, “coaxial optical couplers”, electronic letters, vol. 18, no. 13, pp. 138-40, 1982 [5] a. ghatak, k. thyagarajan, introduction to fiber optics, cambridge university press, 2002 [6] g. p. agrawal, fiber-optic communication systems, john wiley & sons. inc. 3 rd ed, 2002 [7] k. kawano, t. kitoh, introduction to optical waveguides analysis, john wiley & sons, 2001 [8] x. tian, x. zhang, “dispersion-flattened design of the large effective-area single-mode fibers with ring index profiles”, optics communications, vol. 230, no. 1-3, pp. 105-113, 2004 [9] a. rostami, s. makouei, advances in solid state circuit technologies: a novel multiclad single mode optical fibers for broadband optical networks (chapter 7), isbn: 978-953-307-086-5, intech, 2010 [10] m. savadi-oskouei, s. makouei, a. rostami, z. d. koozeh kanani, “proposal for optical fiber designs with ultrahigh effective area and small bending loss applicable to long haul communications”, applied optics, vol. 46, no. 25, pp. 6330-6339, 2007 microsoft word etasr_v11_n3_pp7187-7190 engineering, technology & applied science research vol. 11, no. 3, 2021, 7187-7190 7187 www.etasr.com minh et al.: electromagnetic torque analysis of srm 12/8 by rotor/stator pole angle electromagnetic torque analysis of srm 12/8 by rotor/stator pole angle dinh bui minh school of electrical engineering hanoi university of science and technology hanoi, vietnam linh dinh hai school of electrical engineering hanoi university of science and technology and college of electromechanical and civil engineering vietnam national university of forestry hanoi, vietnam tuan le anh hanoi university of industry hanoi, vietnam vuong dang quoc school of electrical engineering hanoi university of science and technology hanoi, vietnam . abstract—this paper presents the harmonic torque reduction by the different rotor pole angles of a three-phase 12/8 switched reluctance motor via an analytical model and simulation method. improving torque performance by stator and rotor angles was applied for three-phase switched reluctance motor at stator pole/rotor pole ratios of 6/4, 8/12, 18/12, and 24/18. the average torque and the torque ripple effect by stator and rotor pole embrace have been recently studied in many projects. due to the fact that leakage flux, flux density, and inductance are affected by the stator and rotor pole angles non-linear and linear leakage flux curves occur. many stator and rotor pole angle combinations for the three-phase switched reluctance motor have already been done via a finite element method. in this paper, turn-on and turnoff angles will be figured based on stator and rotor pole embraces. keywords-switched reluctance motor (srm); pole arcs; torque; finite element method (fem) i. introduction nowadays, the switched reluctance motor (srm) is considered as the most appropriate candidate to drive small scale electric vehicles due to advantages such as its simple construction, wide constant power regions, and effective torque speed characteristics. the srms have been applied in various fields [1-5]. a convenient design of the srm has a significant importance for an efficient performance of the motor. some design parameters must be considered such as the number of phases, stator pole arc, air gap thickness, and other srm geometry elements. the effect of the srm geometry on the motor performance has been examined thoroughly. in [6], the influence of pole embrace has been investigated on the performance of the srm by the finite element method (fem) with stator and rotor pole embraces changing from 0.2 to 0.5. according to the highest average torque and lowest torque ripple, the proper pole embraces have been selected for the optimum design of the srm [7-9]. ii. electromagnetic torque analysis the rotor and stator pole arc angles are a critical part in the design of the srms. the rotor pole arc (βr) must be equal or greater than the stator pole arc (βs), because the number of rotor poles is less than the number of stator poles (βs ≤ βr). when the βs is smaller than the step angle, then none of the phases can have rising inductance slope. the rotor pole angle should be greater than the sum of stator and rotor pole arcs [10]: �� � ��; �� � �� � �� � ; min���, ��� � �� �. � (1) fig. 1. cross-section of a three-phase srm 12/8 βr equal to (a) 15 0 , (b) 18 0 , (c) 20 0 , (d) 22 0 for βs=15 0 , 15 0 , 15 0 , and 12 0 respectively. corresponding author: dinh bui minh (dinh.buiminh@hust.edu.vn) engineering, technology & applied science research vol. 11, no. 3, 2021, 7187-7190 7188 www.etasr.com minh et al.: electromagnetic torque analysis of srm 12/8 by rotor/stator pole angle the initial size l is estimated from the output power and torque with speed of 1500rpm. with an initial assumption for the l and with respect to the average torque proportionality with ld 2 , the values of l and d have been calculated via the analytical method. the three phase srms 12/8 with rotor angle (15 0 ÷ 22 0 ) are listed in table i. table i. technical parameters of srm 12/8 technical parameters value units stator poles 12 stator pole angle 15 degrees stator lam dia 140 mm stator bore 90 mm stator pole depth 15 mm stator duct layers 2 rotor pole angle 15, 18, 20, 22 degrees rotor slot depth 11 mm airgap 0.3 mm number strands in hand 9 phases 3 turns per phase 12 power 1200 w speed 1500 rpm torque 12 n.m rotor pole τr (360/nr=360/8) 45 degrees stator pole τr (360/ns=360/12) 30 degrees the static torque curves (�� � have been implemented with fem with current ranging from 0 to 50a depending on the rotor angle, i.e.: �� � �� �� ����, ��� (2) the rotor embrace ratio as and stator embrace ratio ar are determined by: !� � "#$# , !� � "� $� (3) in order to maximize the static electromagnetic torque, the stator embrace angle values of 0.45, 0.5, 0.55, 0.6, or 13.5 0 , 15 0 , 16.5 0 , 18 0 have been applied to the finite element simulation to get the static torque, and the rotor angle is verified from 0 to 45 0 as shown in figure 2. fig. 2. the static torque curves and rotor position stator pole embrace for rotor embrace of 0.4. the static torque curves have been also evaluated with rotor embrace ratio of 0.5 and stator pole embrace values of 0.45, 0.5, 0.55, 0.6 or 13.5 0 , 15 0 , 16.5 0 , 18 0 . the stator pole embrace is changed from 0.45 to 0.6 with 0.05 steps for constant rotor pole embrace of 0.5 as shown in figure 3. it is obtained that the combination of 0.40 rotor pole and 0.5 stator pole embraces produces the highest peak output torque which is 31.046nm. besides, the combination of stator and rotor pole embraces at 0.40 value has the minimum output torque which is 30.920nm. fig. 3. the static torque curves and rotor position stator pole embrace for rotor embrace of 0.5. the stator pole embrace is changed from 0.45 to 0.6 with steps of 0.05 for a constant of 0.40 rotor pole embrace depicted in figure 3. it is seen that the combination of 0.5 rotor pole and 0.50 stator pole embraces produces the highest peak output torque which is 31.191nm. in the same way, the combination of stator pole embrace and 0.50 rotor pole embrace has the minimum output torque which is 31.094nm. as can be seen from the results, while the highest output torque is obtained by the combination of 0.40 rotor pole and 0.5 stator pole embraces, the lowest output torque is obtained by the combination of 0.6 rotor pole and 0.6 stator pole embraces. according to these combinations, the optimum values of pole arcs stator/rotor can be selected for better motor design. the average torque is calculated and the best combination of stator and rotor pole embrace can be selected for optimum analysis. the results on the effect of pole embrace are given in figure 4 for different combinations of the stator and rotor pole embraces. fig. 4. average torque vs rotor embrace. engineering, technology & applied science research vol. 11, no. 3, 2021, 7187-7190 7189 www.etasr.com minh et al.: electromagnetic torque analysis of srm 12/8 by rotor/stator pole angle figure 5 shows the average torque and torque ripple, and the embarce stator for various values of the embrace rotor. the average torque is maximum or on top of the curve (as=0.5) at rotor pole arc ar=0.3. with the 4 rotor poles and 6 srm stator poles, the rotor/stator pitches are 45/30 degrees. thus, the rotor embrace ar=0.3 is 30 mechanical degrees and the stator embrace is ar=0.5. this means that the rotor pole angle and stator angle have the same value of 15 degrees. the electromagnetic torques with different rotor and stator embraces are presented in table ii. from those results, the best combination of as=0.3 and ar=0.5 is selected to verify the dynamic torque performance. fig. 5. torque ripple/average torque rate vs rotor embrace. table ii. average torque (nm). ar as=0.2 as=0.3 as=0.4 as=0.5 as=0.6 0.2 12.09608 18.2667 20.69018 19.97587 17.31098 0.3 10.9917 17.04873 21.39854 22.89821 21.54776 0.4 8.411142 12.35922 16.03515 19.25603 21.00559 0.5 4.228949 7.167675 10.4344 13.63371 16.0756 0.6 1.233799 3.079451 5.558719 8.299413 10.63121 0.7 0.150363 0.761016 2.154871 4.085025 5.991545 iii. dynamic simulation and experimental results the finite element model has been presented to validate the dynamic torque of 1500rpm and phase current i=50a. the turn on and turn off angles are determined in (4). the torque curve plot is depicted in figure 6. the torque ripple ranges from 5 to 9n.m. % �&' � (&' � )���*����&++ � (&++ � )���*��� � , � (4) the dynamic torque and efficiency with different rotor and stator angles are compared in table iii. the srm 12/8 with βs=15 0 , βr=18 0 is the maximum average torque and minimum torque ripple. the harmonic torque of srm 12/8 is classified with multiples of 3 oders such as 3 th , 6 th , 9 th , 12 th and 15 th because the srm 12/8 has 3 phases in stator and 4 coils/phase (figure 7). the total torque of srm 12/8 can be calculated by 3 th , 6 th , 9 th , 12 th and 15 th . the 3 th harmonic component is still significant on the torque ripple. therefore, this study will investigate different stator and rotor embrace angles on the harmonic torque and total torque. fig. 6. dynamic torque curve at 1500rpm. table iii. srm 12/8 electromagnetic performance comparison parameters unit 15 0 /15 0 15 0 /16.5 0 15 0 /18 0 15 0 /20 0 maximum possible torque nm 8.466 8.6722 8.6466 8.5649 average torque nm 7.642 8.0111 8.1424 7.9893 average torque nm 7.496 7.9467 8.159 8.1269 torque ripple nm 4.223 1.9376 1.9682 2.4121 torque ripple [%] % 57.93 23.812 23.958 29.622 electromagnetic power w 916.1 1022.5 1032.4 1023.3 input power w 1092 1198.8 1207.6 1195.1 output power w 872.7 976.22 985.65 976.53 total losses (on load) w 219.4 222.55 221.99 218.59 system efficiency % 79.91 81.435 81.618 81.71 shaft torque nm 6.945 7.7685 7.8435 7.771 fig. 7. harmonic torque. the dynamic torque test bench installation for srm 12/8 and permanent magnet generator in the torque transduce is shown in figure 8. the torque sensor tm300 is connected to pc to get the data during testing. fig. 8. dynamic torque test bench. the speed and torque values with different time steps are presented in figure 9. in the time interval from 1s to 5s, the engineering, technology & applied science research vol. 11, no. 3, 2021, 7187-7190 7190 www.etasr.com minh et al.: electromagnetic torque analysis of srm 12/8 by rotor/stator pole angle speed and torque are very stablized and vary trivially. however, torque ripple appears in the begining time (0.02s). these values are also recorded in starting stage and constant speed. the dynamic torque with different rotor positions is shown in figure 10. the values on the torque at stator 15 and rotor 22 reach approximately 10nm. fig. 9. dynamic speed (top) and torque (bottom). fig. 10. dynamic torque with differnt rotor positions. iv. conclusion the current paper has developed stator and rotor embrace/pitch influenced on the average torque and torque ripples via fem [10, 11]. for high speed of the srm, the control method is single voltage or current pulse because the magnetic circuit is saturated. thus, it is difficult for chopping current to apply and the phase current cannot reach reference values. the electromagnetic design will help improving torque and current controller. the static torque curves have been also evaluated by the fem. this paper also demonstrates a method to improve and design the srms in practice. references [1] r. m. azhagar and a. kavitha, "effect of rotor geometry on peak and average torque of direct drive external-rotor synchronous reluctance motor (ex-r synrm) in comparison with switched reluctance motor for low speed domestic application," in 2017 ieee international magnetics conference (intermag), dublin, uk, apr. 2017, pp. 1–2, https://doi.org/10.1109/intmag.2017.8007641. [2] j. han, b. ge, k. zhang, y. wang, and c. wang, "influence of control and structure parameters on the starting performance of a 12/8 pole switched reluctance motor," energies, vol. 13, no. 14, jan. 2020, art. no. 3744, https://doi.org/10.3390/en13143744. [3] n. k. sheth and k. r. rajagopal, "optimum pole arcs for a switched reluctance motor for higher torque with reduced ripple," ieee transactions on magnetics, vol. 39, no. 5, pp. 3214–3216, sep. 2003, https://doi.org/10.1109/tmag.2003.816151. [4] m. yildirim and h. kurum, "influence of poles embrace on in-wheel switched reluctance motor design," in 2018 ieee 18th international power electronics and motion control conference (pemc), budapest, hungary, aug. 2018, pp. 562–567, https://doi.org/10.1109/epepemc. 2018.8521859. [5] a. tap, l. xheladini, t. asan, m. imeryuz, m. yilmaz, and l. t. ergene, "effects of the rotor design parameters on the torque production of a pmasynrm for washing machine applications," in 2017 international conference on optimization of electrical and electronic equipment (optim) 2017 intl aegean conference on electrical machines and power electronics (acemp), brasov, romania, may 2017, pp. 370–375, https://doi.org/10.1109/optim.2017.7974998. [6] r. krishnan, switched reluctance motor drives: modeling, simulation, analysis, design, and applications, 1st ed. boca raton, fl, usa: crc press, 2001. [7] z. yueying, y. chuantian, y. yuan, w. weiyan, and z. chengwen, "design and optimisation of an in-wheel switched reluctance motor for electric vehicles," iet intelligent transport systems, vol. 13, no. 1, jan. 2019. [8] a. siadatan, m. roohisankestani, and s. farhangian, "design and simulation of a new switched reluctance motor with changes in the shape of stator and rotor in order to reduce torque ripple and comparison with the conventional motor," in 2018 international symposium on power electronics, electrical drives, automation and motion (speedam), amalfi, italy, jun. 2018, pp. 353–358, https://doi.org/10.1109/speedam.2018.8445245. [9] o. m. al-barbarawi, "improving performance of the braking process, and analysis torque-speed characteristics of the induction motor," engineering, technology & applied science research, vol. 8, no. 6, pp. 3585–3591, dec. 2018, https://doi.org/10.48084/etasr.2325. [10] v. d. quoc, "robust correction procedure for accurate thin shell models via a perturbation technique," engineering, technology & applied science research, vol. 10, no. 3, pp. 5832–5836, jun. 2020, https://doi.org/10.48084/etasr.3615. [11] v. d. quoc, "accurate magnetic shell approximations with magnetostatic finite element formulations by a subdomain approach," engineering, technology & applied science research, vol. 10, no. 4, pp. 5953–5957, aug. 2020, https://doi.org/10.48084/etasr.3678. microsoft word etasr_v11_n2_pp6979-6985 engineering, technology & applied science research vol. 11, no. 2, 2021, 6979-6985 6979 www.etasr.com "kazi & khan: dyte: an effective routing protocol for vanet in urban scenarios" dyte: an effective routing protocol for vanet in urban scenarios abdul karim kazi ned university of engineering and technology karachi, pakistan karimkazi@neduet.edu.pk shariq mahmood khan ned university of engineering and technology karachi, pakistan shariq@neduet.edu.pk abstract-a vehicular ad-hoc network (vanet) is a subclass of wireless ad-hoc networks, widely used in on-road vehicles and roadside equipment, having applications in various areas including passenger safety, smart traffic solutions, and connectivity on vehicles the vanet is the backbone of the intelligent transport system (its) that establishes connectivity between vehicles through a wireless medium. when it comes to the communication between high-speed vehicles there is the challenge of dynamic mobility. in order to provide a higher packet delivery ratio (pdr) and increase the throughput, a new routing protocol called dynamic trilateral enrolment (dyte) is introduced which chooses a dynamic trilateral zone to find the destination vehicle by allowing only relevant nodes to participate in the communication process using the location coordinates of the source and destination nodes. the proposed routing protocol is compared with ad-hoc on-demand distance vector (aodv), ad-hoc on-demand multipath distance vector (aomdv), and dynamic source routing (dsr), and the results show a remarkable improvement in reducing the network routing load (nrl) and in increasing the pdr and throughput of the network. dyte has performed more efficiently in terms of pdr (23% approximately), throughput (26% approximately) and drastically minimized the nrl by a factor of almost 3. keywords-vehicular ad-hoc networks; location aided routing; trilateral zone; broadcast storm i. introduction vehicular ad-hoc networks (vanets) are becoming quite popular because nowadays fast moving vehicles are able to communicate with each other and on-road equipment [1]. the network topology in a vanet changes rapidly as it consists of fast moving nodes. a vanet is considered to be an opposite option for the development of its [2]. a vanet is a specialized type of mobile ad-hoc network (manet), through which vehicular communication can take place in urban and highway scenarios. many applications such as security, information services, accident alarm, road safety and traffic managements are associated with vanets. the speed of the vehicle is the major factor which affects the communication process due to which rapid changes in network topology occur, so the selection of the intermediate vehicle is very crucial. a typical vanet scenario is depicted in figure 1 where communication can take place between vehicle-tovehicle (v-2-v), vehicle-to-infrastructure (v-2-i) and hybrid (either v-2-v or v-2-i) [3]. in a vanet, routing protocols are generalized in five categories [4]: ad-hoc based, cluster-based, position-based, broadcast-based, and geocast-based routing. position-based routing protocols use geographical coordinates from the global positioning system (gps). they also use digital maps to obtain road information. low overhead and its effectiveness for rapidly moving nodes are the key advantages of location-based routing protocols. geocast-based routing protocols basically limit the area of transmission in a specific portion by identifying the next hop using the node's position. information related to the position and speed of the node help to decrease overhead packets and to increase pdr [5]. fig. 1. a vanet scenario. location aided routing (lar) is based on the exact gps location of the destination node [6, 7]. in [8], an advancement of lar that works on the principle of choosing next-hop with minimum angle difference to the straight line between source and destination node to reduce the packet overhead is reported. in [9], two strategies are opted for the transmission of packets while selecting the next-hop, greedy forwarding strategy chooses the closest node with respect to the destination and perimeter forwarding strategy is opted whenever the distance between the forwarding and the target node is closer than the distance to the destination of its neighbors. in [10], the lifespan of the node is calculated using the speed and position in order to get the time for the node’s availability within the transmission range. greedy perimeter coordinator routing (gpcr) is also a position-based routing protocol which differs from the gpsr because it does not rely on the static global map [11]. corresponding author: abdul karim kazi engineering, technology & applied science research vol. 11, no. 2, 2021, 6979-6985 6980 www.etasr.com "kazi & khan: dyte: an effective routing protocol for vanet in urban scenarios" in dsr [12], a complete list of nodes in sequence is attached in the packet header therefore network overhead is increased. aodv [13] is a reactive and loop-free routing protocol which is still considered relevant [14-16]. an optimization in aodv is proposed in [17] by formulating route weight. the improved aodv (iaodv) is proposed in [18] for dense networks and focuses on forwarding timely and accurate information to nodes by keeping a list of all one hop nodes as a backup route. multiple routing path is accumulated during the route discovery phase by aomdv [19] from source to destination node to get an uninterrupted communication in case of failure of the primary path. a variant of the aomdv protocol is the speed direction aodv (sd-aodv) [20], in which the parameters of speed and direction are included in the hop count field during the process of route establishment. in [21], data transfer rate is optimized using signal-to-noise ratio (snr), improving link quality and minimizing energy consumption. a reactive routing protocol is proposed in [22] that minimizes the routing load by selecting reliable routes during the route discovery phase. an upgraded version of tora was introduced in [23] where only highly reliable discovered links are used. in errrp [24], the disconnection of routes is minimized by the reliability factor (rf) which is based on route expiration time (ret) and hop count. higher rf value routes are selected as reliable paths. roadside service discovery protocol (rsdp) [25] proposed an application layer beaconing-based protocol to address the problem of service discovery upon request. velocity-aided routing protocol [26] works on the principle of predicting the moving behavior of mobile nodes. the possible trajectory of the destination node is predicted on the basis of its position and velocity information and determines the packet forwarding region. the incorporation of mobility characteristics in the routing enhances its performance and makes it more adaptive. ant colony optimization (aco) algorithms [27, 28] extract the optimal routing information by selecting the best available path among the available routes or by finding an alternate route in case of route failure. aco algorithms successfully reduce link failures by applying the above strategies. an improved genetic algorithm-based route optimization technique (igarot) [29] is implemented by considering road anomalies resulting in prompt notification by road maintenance agencies of persistent road conditions through v2i communication. using an iterative k-means algorithm, igarot generates clusters into two nonoverlapping groups and then updates the size of the successful cluster using likelihood metric in the initial population size. overhead reduction was achieved in [30] by forwarding the location of the destination to every generated rreq packet. efficient routing protocol (erp) [31] minimizes the unnecessary broadcast in the network by finding the minimum set of vehicles for backbone communication that act as forwarders and only those nodes will be having the responsibility to broadcast. using the gps system, the selection process of the next forwarding node is based on the lesser distance to destination node in geopps [32]. due to network topology dependence, not every node is needed to calculate the optimal path. a large number of rreqs leads to frequent change in topology, and thus impede the transmission of information packets. also excessive requests might cause congestion and ultimately packet loss. in [33], efficiency is achieved by selecting a carrier group of vehicles to relay the data packet to the destination. this group maintains the vehicle information only in those streets that are indispensable in reaching the destination. it is observed that the problem of broadcast storm during the route finding phase still needs to be addressed. therefore, in order to address that issue a routing protocol is proposed in this paper which not only minimizes the routing overhead but also increases the efficiency of the overall network. the proposed routing protocol is influenced by the above mentioned protocols. it uses the vehicles' positions and limits the transmission in a specific zone. extensive simulations have been carried out in the ns2 simulator. node mobility has been generated by the simulation of urban mobility (sumo) whereas real environment of the traffic was generated by openstreetmap. ii. the proposed routing protocol much research has been being carried out to improve the efficiency of routing protocols in vanets. densely populated networks with excessive number of nodes and their scalability issue have drawn much attention. a novel approach is proposed in this work to increase throughput and pdr and to decrease the overhead packet count. the route discovery is initiated from the source by sending route request packets to all neighbors. the neighbor nodes subsequently forward the route request to their respective neighbors. the process continues until the packet reaches its destination. the route reply packet confirms the route establishment. in the proposed protocol, initially the source node generates a trilateral zone using the destination vehicle's last known position where the destination vehicle could reside and makes a list of nodes which lie inside that zone. information about the list of nodes is added to the rreq packet header which is sent to the neighbors. each neighbor who receives the rreq packet checks the list of nodes. if its information related to the trilateral membership is present in that list, then it can participate, otherwise the packet will be dropped. the receiving node checks whether the packet targets its own vehicle. if not, it then calculates a new trilateral zone using the updated position of the destination vehicle and adds that information in its new rreq packet. the process continues until the destination node is reached. the proposed protocol avoids unnecessary rreqs, thus efficient usage of bandwidth is achieved during route discovery. a. dyte – the algorithm the proposed protocol (dyte) combines the power of position-based routing and geocast-based routing protocol because it uses the coordinates of the vehicles and limits the packet request in a limited trilateral zone. in figure 2, an area is shown where the trilateral zone is extracted as a zone of interest and the remaining area (red colored) is excluded. engineering, technology & applied science research vol. 11, no. 2, 2021, 6979-6985 6981 www.etasr.com "kazi & khan: dyte: an effective routing protocol for vanet in urban scenarios" fig. 2. a trilateral zone example. the sequence of steps to be taken is (figure 3): • get source and destination location through gps. • calculate the trilateral zone where the broadcast of packets is going to be accepted. • add the list of nodes to the rreq packet. • each node that receives the rreq packet will examine the list to identify its trilateral zone’s membership. • only if the receiving vehicle (destination/intermediate) lies within the trilateral zone, it can process it further. else, the packet will be dropped. • if the request received by a vehicle lies within the trilateral zone, it checks whether that packet was destined to it. if it does not, it will create a new list of trilateral zone’s membership to forward the packet but with a newly calculated list of members. • the above steps are repeated until the destination node is reached. b. creation of trilateral zone when an intermediate node receives the request, it checks whether the packet is generated by its own vehicle in order to avoid looping. the request can be seen initially by every neighbor node that lies within the wireless transmission range but the rreq packet header contains the special array field that consists of a list of nodes which are allowed to take part in the rreq process. to create a trilateral zone, we used source and destination vehicle’s gps coordinates to find the slope (1) of the straight line between the source (sx, sy) and destination (dx, dy) vehicle. y y x x d -s∆y m= = ∆x d -s (1) the distance between source and destination nodes is calculated by (2): 2 2 x x y y dist= (d -s ) +(d -s ) (2) after calculating the slope and distance, the perpendicular slope is calculated by (3): perpendicular 1 m = m (3) fig. 3. flowchart of the lgorithm. c. trilateral enrolment identification process the next step is to identify whether the receiving node exists within the trilateral zone. to find out that a given node can participate in rreq flooding, consider the trilateral zone, as shown in figure 4, where the coordinates of a, b, c and an arbitrary node p are given as (ax , ay), (bx , by), (cx , cy) and (px , py) respectively. in order to allow the node to get the enrolment for the rreq forwarding process, dyte goes through calculating the area and sub areas for each node. the area of the trilateral zone (triangle abc) as shown in figure 4 is calculated by: x y y x y y x y y | a × (b -c )+b × (c –a )+c × (a -b )| 2 total area = (4) the sub area #1 of the trilateral zone (triangle pab) is calculated by: 2 |)b-(a×p+)a–(p×b+)p-(b×a| yyxyyxyyx 1 = area sub (5) engineering, technology & applied science research vol. 11, no. 2, 2021, 6979-6985 6982 www.etasr.com "kazi & khan: dyte: an effective routing protocol for vanet in urban scenarios" the sub area #2 of the trilateral zone (triangle pbc) is calculated by: 2 |)b-(p×c+)p–(c×b+)c-(b×p| yyxyyxyyx 2 = area sub (6) the sub area #3 of the trilateral zone (triangle pac) is calculated by: 2 |)p-(a×c+)a–(c×p+)c-(p×a| yyxyyxyyx 3 = area sub (7) fig. 4. coordinates of a trilateral zone of an arbitrary point p. d. forwarding path and request / reply process in dyte each participating node during the phase of rreq discovery sets up a special entry called reverse route which contains the ip address of the source node, a sequence number along with hop counts to the source node, and the ip address of the neighbor from which the rreq was obtained. since no information should be kept in forever in the routing table, a timer variable called lifetime is associated with the reverse route so that if the route entry is not used for the specified allocated time, then the information will be wiped off from the table to minimize the routing overhead. routing loops are handled by the sequence numbers with source node information in order to check the freshness of the rreqs of the unicasted response of the rrep back to the node. broadcasting of a route request within a trilateral zone is permitted again only when an intermediate node gets out of contact, because disconnection of the intermediate node will make the destination node inaccessible. the rrep packet contains the information of the source and the ip address of the destination. if the destination node is able to reply, then it resets the hop count information and the sequence number and lifetime are also updated in the rrep packet. in case the intermediate node is able to reply, then the hop count will be updated as per the intermediate node's distance to the destination node along with the destination sequence number information and the time validity of routes is calculated within the routing table. a forwarding path is stored in the routing table when the rrep packet is received by an intermediate node. this path entrance contains the neighbor's ip address from which the rrep is received, the ip address of the destination and the hop counts to the destination. to obtain the distance of the destination, the receiving node increases the value in the hop count by one and also associates this entry with the lifetime. the associated lifetime gets updated whenever the route is used and is deleted when the route is not used within the specified time limit. an rrep can be received from multiple neighbors for a similar destination. in that case the rrep which is received first will be considered and the alternative rreps are only used if they contain information with smaller hop count or if the destination sequence number is greater to ensure quick and updated routing. in other words, after receiving the first rrep, the source node will begin the data transmission process and if it discovers, at a later stage, a better route, then the routing information will be updated and a different path will be taken for data transmission. iii. simulation and results network simulation was performed on ns-2 simulator [34]. for mobility simulation within urban environment, sumo [35] was used. figure 5(a) shows the simulation plot which is an original image containing a map portion of karachi extracted from openstreetmap [36] whereas figure 5(b) is the network animation within the ns-2 simulator and figure 5(c) is the converted map using sumo. the performance of the proposed protocol is compared with the performance of other popular routing protocols (aodv, aomdv, and dsr). the metrics considered for comparison are pdr, network routing load (overhead), and throughput. to avoid the possibility of fluctuations in simulations, the presented results are the average of multiple simulations. the network is considered from moderate to highly-dense and random distribution of nodes was incorporated. the simulation parameters are given in table i. table i. simulation parameters parameter value mobility manhattan channel type wireless antenna omni directional model two ray ground no. of vehicles 50, 100, 150, 200, 250 simulation area 2500×2000m 2 simulation time 100s routing protocols aodv, aomdv, dsr, dyte speed range 50–100km/h transmission zone 250m connection type udp traffic type cbr packet rate 4 per second in figure 6, the nrl is depicted which can be defined as the proportion between the number of packets generated by each node and the number of packets successfully transmitted to the destination nodes. since only relevant packets are allowed to get transmitted over the network, improvement is achieved by the proposed dyte protocol. figure 7 represents the pdr which is defined as the ratio of data packets that are successfully received at the destination with the number of data packets generated at the source node. the nodes enrolled in the trilateral zone are the most favorable to transmit the request to the destination, therefore the results are improved. figure 8 depicts the throughput of the network which is the cumulative engineering, technology & applied science research vol. 11, no. 2, 2021, 6979-6985 6983 www.etasr.com "kazi & khan: dyte: an effective routing protocol for vanet in urban scenarios" number of packets transmitted successfully to the destination over the entire simulation. the comparison shows a direct relation between the number of nodes and the number of delivered packets to the destination node, reflecting a higher throughput. (a) (b) (c) fig. 5. (a) the map of a part of karachi, (b) network animation in ns-2, (c) sumo map conversion. fig. 6. nrl against node density. fig. 7. pdr against node density. fig. 8. throughput against node density. fig. 9. dropped packet ratio against node density. figure 9 shows the dropped packet ratio which is a reciprocal of pdr, since pdr is increased therefore it is quite understandable that the dropped packet ratio is decreased. the request packets are controlled before sending the actual data to minimize the unnecessary overhead. it is conclusive that minimizing the unnecessary route request within the network actually lowers the burden on the overall network. since only expected and reachable nodes can participate in the route request phase, nrl is minimized, the chance of reaching the packet to the destination is increased, and therefore pdr is increased. iv. conclusion a novel way of limiting the request zone for the effective communication is presented in this paper with focus given in engineering, technology & applied science research vol. 11, no. 2, 2021, 6979-6985 6984 www.etasr.com "kazi & khan: dyte: an effective routing protocol for vanet in urban scenarios" essential parameters such as nrl, throughput, and pdr. the main challenge in vanets is designing routing protocols for dynamic topology along with the consideration of mobility. the proposed routing protocol dyte uses the location of the vehicles and limits the area of communication. the results have shown that dyte is not only efficient in increasing the pdr and throughput but also greatly minimized the nrl. dyte has been found to have better performance than aodv, aomdv, and dsr in vanets. acknowlegement the research reported in this study was conducted at the ned university of engineering and technology (neduet) and is funded by most (ministry of science and technology). references [1] y. kim and i. kim, "security issues in vehicular networks," in the international conference on information networking, bangkok, thailand, jan. 2013, pp. 468–472, https://doi.org/10.1109/ icoin.2013.6496424. 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[36] j. thebault-spieker, b. hecht, and l. terveen, "geographic biases are ‘born, not made’: exploring contributors’ spatiotemporal behavior in openstreetmap," in proceedings of the 2018 acm conference on supporting groupwork, new york, ny, usa, jan. 2018, pp. 71–82, https://doi.org/10.1145/3148330.3148350. microsoft word 43-3717_setasr_v10_n4_pp6147-6151 engineering, technology & applied science research vol. 10, no. 4, 2020, 6147-6151 6147 www.etasr.com touahmia et al.: creep performance of geosynthetic reinforcements creep performance of geosynthetic reinforcements mabrouk touahmia civil engineering department university of hail hail, saudi arabia m.touahmia@uoh.edu.sa hatem gasmi civil engineering department university of hail hail, saudi arabia h.gasmi@uoh.edu.sa mohamed ahmed said architectural engineering department university of hail hail, saudi arabia mo.said@uoh.edu.sa abstract−most geosynthetic materials exhibit rheological properties that lead to creep strain response when subjected to sustained loads, and consequently it is necessary to evaluate their long-term creep deformation before any real application. this paper presents the results of sustained loading tests conducted on large-scale geogrid soil reinforcement. the purpose of these laboratory tests was to identify the appropriate design parameters for geosynthetic-reinforced systems. the results of these tests demonstrate the continuous creep deformation characteristic of geogrid materials under constant sustained loading. the increase in the applied load led to a continuous increase in the amount and rate of the geogrid creep deformation. the data analysis method used in this investigation enabled the possibility of predicting the load-deformation-time behavior and the ultimate load of geosynthetic reinforcements. keywords-soil reinforcement; geosynthetics; geogrid; creep i. introduction the use of geosynthetic materials has increased significantly over the last three decades in different geotechnical aspects such as retaining walls, slops’ stability, pavements, and railway embankments. their applications have proven to offer cost-effective and environmentally friendly solutions to many unstable ground problems where the use of conventional construction methods would be limited or considerably expensive. however, identification of the design parameters for geosynthetic reinforcements is complicated when compared to conventional materials. it requires the designer to have a good understanding of the material loadstrain and strength behavior and the changes in this behavior with time, temperature, and loading conditions. it is recognized that geosynthetic materials display rheological properties that exhibit creep strains and stress relaxation response when subjected to axial constant loads. such phenomena may influence the long-term behavior of the geosynthetic reinforcement and can cause potential damage to the corresponding structural system [1-2]. creep, defined as the time-dependent increase in the geosynthetic accumulative strain resulting from a constant applied load, is considered one of the most important properties that should be properly estimated and integrated in the design process of geosyntheticreinforced structures [3-4]. the mechanics of creep is not completely understood. creep may be simply described as the phenomenon that occurs when the geosynthetic reinforcement held under sustained load continues to deform with time increase. standard laboratory creep tests were developed to compute the tensile strength and elongation parameters of geosynthetics in isolation [5-6]. similarly, in-soil creep tests were also performed using special equipment in an attempt to better simulate the effect of soil confinement on the creep behavior of geosynthetics [7-9]. however, the results of these tests were somewhat inconclusive and until now there is a lack of a thorough understanding of the time-dependent response of geosynthetic soil reinforcements due to the absence of comprehensive and conclusive studies. more recently, numerous constitutive models have been developed to simulate the load-strain-time behavior of geosynthetic materials. the majority of these models have been applied for in isolation geogrids and geotextiles [10-11]. moreover, several sophisticated finite element codes have been developed to simulate the response of geosynthetic materials to different loading and environmental conditions in order to provide appropriate design parameters for geosynthetic-reinforced soil systems [12-14]. this paper presents the results of sustained loading tests carried out on sr2 tensar geogrid reinforcements. the purpose of these large scale laboratory tests is to examine the loadstrain-time response of geosynthetic reinforcements in order to develop design parameters for geosynthetic reinforced systems. ii. test equipment, materials, and procedure a. equipment and materials figure 1 shows the experimental pullout apparatus used in this study. it consists of a rigid sand container of 4.0×0.3×0.3m inside dimensions, a loading system to apply static axial loads to the reinforcement and a confining pressure system to apply surcharge pressures of up to 300kpa (figure 2). it was designed corresponding author: mabrouk touahmia engineering, technology & applied science research vol. 10, no. 4, 2020, 6147-6151 6148 www.etasr.com touahmia et al.: creep performance of geosynthetic reinforcements according to the recommendation of astm d6706-01 [15] which prescribes the standard method for computing the pullout resistance of geosynthetic reinforcements. fig. 1. pull-out apparatus. fig. 2. schematic view of the test apparatus. the experimental apparatus permits for the testing of different types of soil reinforcing materials and the application of different values of axial loads and surcharge pressure on the reinforcement. the load was applied to the reinforcement by adding incremental dead weights to the load hanger situated at the rear end of the sand container. the confining stress was applied to the top of the reinforced soil sample via a pressure plate loaded through a water bag and connected to an air compressor. the pullout device was equipped with a number of dial gauges and load cells to compute the applied load, confining pressure and reinforcement movement. the geogrid specimen was placed in the middle of the soil mass and was connected to the loading system with a special clamp as shown in figure 3. more details about the experimental apparatus can be found in [16]. fig. 3. pull-out apparatus. the reinforcement used in testing is formed by cutting tensar sr2 geogrid into a row of two ribs in width and 35 bars length (approximately 4m). physical and mechanical properties of the geogrid are taken from manufactures’ data and are shown in figure 4 and table i. the distribution of axial strain in the geogrid was measured using axial movement gauges provided at different locations along the reinforcement. the applied load levels were expressed as a percentage of the index load (pur) of the geogrid, defined as the ultimate rupture load of an identical geogrid in air (figure 5). fig. 4. geogrid (sr2) dimensional properties. table i. geogrid (sr2) physical properties geogrid properties mean values product width (sl) 100mm transverse bar width (dth) 12.69mm maximum transverse bar thickness (dtv) 4.56mm minimum transverse bar thickness (dtv ) 4.36mm rib width (dlh) 5.72mm rib thickness (dlv) 1.34mm number of ribs 44/m mass per unit area 972g/m 2 0 1 2 3 4 0 10 20 30 40 50 60 a p p li e d l o a ds , (k g ) extension, (mm) index load (pur) = 3.2 kn longitudinal direction specimen size: 4 bars x 2 ribs fig. 5. geogrid material tensile strength. the soil used in this study was a uniformly graded sand of medium size with the properties given in table ii. the sand samples were prepared in the pullout box by raining method to an average and repeated medium bulk density of 1.59mg/m 3 . table ii. soil properties parameter mean value uniformity coefficient, cu 1. 9 specific gravity of solids, gs 2. 67 friction angle, φ ( o ) 39.4 max/min densities, ρmax/ρmin (mg/m 3 ) 1.78/1.42 max/min void ratios, emax/emin 0.872/0.491 engineering, technology & applied science research vol. 10, no. 4, 2020, 6147-6151 6149 www.etasr.com touahmia et al.: creep performance of geosynthetic reinforcements b. test procedure two series of sustained loading tests, short-term and longterm tests, were conducted throughout this investigation. the test procedure included 4 steps: (i) formation of the sand bed, (ii) placement of the geogrid reinforcement, (iii) application of the surcharge confining pressure, and (iv) application of the static load. these tests were performed under very small variation in temperature to reduce its effect on the test results. the temperature recorded during the tests was 18±1 o c. silicone grease was smeared on the container inside walls in a thin layer to minimize the friction effect and ensure uniform distribution of the normal stress all over the soil mass. after the preparation of the experimental arrangement the test started by monitoring the surcharge pressure and applying gradual sustained loads to the reinforcement. iii. results and discussion a series of sustained loading tests were conducted to obtain the load-strain-time characteristics of the geogrid reinforcement. the tests involved monitoring the normal stress first and then applying the axial load to the reinforcement incrementally. in all these tests the normal pressure was kept constant at 100kpa during the pullout process. in the short-term test series, a loading increment of 5% pur was applied every 60min during which the creep deformations of the geogrid were recorded at 1, 2, 5, 10, 20, 40 and 60min. for the longterm tests, the sustained loads were held for a period of 2000h and the creep strains of the geogrid were recorded each hour. the data collected during each test included the measurements of axial pullout loads and creep strains of the geogrid reinforcement with time. figure 6 shows the total displacement of the geogrid versus time data in which the sustained loads were incrementally increased every 60min. it can be seen that there is a significant increase in the geogrid creep displacement with time increase and this is more apparent at high loading increments. the test results clearly demonstrate the continuous extension characteristic of the geogrid reinforcement when subjected to sustained load as shown in figure 7. this deformation was mainly close to the point of load application which consisted only of an extension of the front part of the geogrid. to illustrate further the effect of time on the creep behavior of the geogrid, the above data are re-plotted in a semilog form. figure 8 shows the creep deformation-log time relationships for the 35 bar length geogrid reinforcement under 100kpa confining stress. both the instantaneous displacement and the creep displacement are given for a series of loading levels over a period of 1h. these curves demonstrate the effect of time on the deformation of the geogrid under sustained loading. it can be seen that for most of the loading levels, the relationship between creep displacement and time when plotted on a semi-log scale produces approximately straight lines the slope of which, defined as the creep coefficient, increases with the increase of load increment. this finding is somewhat in contrast with the result of the creep rate which showed no dependency of the stress levels. however, both plots indicated clearly the effect of time on the creep behavior of the geogrid material. the relationships between creep rate and time are shown in figure 9 in a log-log scale. the visual impression from these plots is that at any constant applied load the creep rate decreases linearly with time giving approximately same slopes. 0 5 10 15 20 25 30 35 180 240 300 360 420 480 c re e p d is p la c e m e n t, ( m m ) time, (min) 20%pur 40%pur 35%pur 30%pur 25%pur confining pressure = 100 kpa fig. 6. load-creep-time relationships. 0 5 10 15 20 25 30 35 0 10 20 30 40 50 60 c re e p d is p la c e m e n t, ( m m ) time, (min) 20%pur 25%pur 30%pur 35%pur 40%pur conf ining pressure = 100 kpa fig. 7. creep displacement-time relationships. 0 5 10 15 20 25 30 35 1 10 100 c re e p d is p la c e m e n t, ( m m ) log time, (min) 20%pur 25%pur 30%pur 35%pur 40%pur conf ining pressure = 100 kpa fig. 8. creep displacement-log time relationships. for additional examination of the stress-strain-time effects on the geogrid behavior, a “long-term” creep test series was undertaken. two sustained loads, namely 25% pur and 35% pur, were chosen to be held for a duration of 2000h while the creep deformation of the geogrid was recorded at specified time intervals. throughout these tests the surcharge stress was engineering, technology & applied science research vol. 10, no. 4, 2020, 6147-6151 6150 www.etasr.com touahmia et al.: creep performance of geosynthetic reinforcements kept constant at 100 kpa. figure 10 shows the creep strain of the geogrid reinforcement against log time. 0.01 0.1 1 10 1 10 100 c re e p r a te , (m m /s ) log time, (min) 20%pur 25%pur 30%pur 35%pur 40%pur confining pressure = 100 kpa fig. 9. creep rate-log time relationships. 0 5 10 15 20 25 30 1 10 100 1000 10000 c re e p d is p la ce m e n t, ( m m ) log time, (hrs) 25%pur 35%pur confining pressure = 100 kpa fig. 10. long-term creep behavior of the geogrid. it can be clearly noted from these diagrams that the increase in the applied sustained load leads to a continuous increase in the amount and rate of the geogrid deformation. a remarkable aspect is that the rate of the deformation-log time diagrams remained almost steady during the first weeks and then started to decrease. this result indicates that retaining the load constant for long periods may lead to significant creep deformations of the geogrid materials. similar observations were also reported by the authors of [17] in their centrifuge study performed to investigate the time-dependent behavior of geotextile-reinforced soil walls. their test results indicated considerable time-dependent deformations of the geotextile reinforcement during the long-term tests. it is evident from this analysis that the use of geosynthetics as soil reinforcements may not play a significant role in the long-term stability of reinforced soil structures. in order to estimate the ultimate load of the geogrid reinforcement, the short-term sustained loading tests were analyzed in accordance with the recommendations of the german code of practice din 4125 [18] for permanent anchorage in loose stone. this code recommends a method to estimate the future creep displacement of an anchor and predict its ultimate and safe working loads. according to this standard, the general relationship between creep displacement and time is an exponential function which gives a straight line when plotted to a semi-log scale. for each load increment a graph is plotted between the creep displacement and log-time and the slope of the creep curve, defined as the stabilization coefficient (α), is calculated. the values of α are then plotted against the applied loads and the value of the critical load is identified as that load at which there is a bend in the α-load relationship. figure 11 shows the creep coefficient-load relationship of the geogrid under 100kpa surcharge pressure. as can be seen, the value of the critical load corresponds to the load at which a bend in the plot α-load starts. this method of analysis may provide the possibility of predicting the ultimate load of geosynthetics by taking into consideration their long-term creep characteristic. 0 0 .5 1 1 .5 2 2 .5 0 1 0 2 0 3 0 4 0 5 0 c re e p c o e ff ic ie n t, a l o a d , (% pu r) u ltim a te lo ad = 3 0 % pur c o n f in ing p r essu re = 1 0 0 k pa fig. 11. prediction of the ultimate load. iv. conclusion this study investigated the creep behavior and performance of geosynthetic soil-reinforcements. a series of pullout tests were conducted on geogrid reinforcements embedded in uniformly graded sand and subjected to a constant vertical confining pressure. the results obtained from this experimental and analytical investigation demonstrate that the identification of the appropriate design parameters for geosynthetic reinforcement requires a thorough examination of the loadstrain and strength behavior of the material, as well as the change in this behavior with time and load levels. the analysis method used in this investigation enabled the possibility of predicting the load-deformation-time behavior of the geogrid material and the estimation of its ultimate load. the tests’ results indicated that maintaining the applied load constant for long periods results in a continuous creep deformation of the geogrid reinforcement without cessation. it is clear from these findings that geosynthetic reinforcing materials may play a significant role in the long-term stability of reinforced-soil structures and, therefore, care is required in ensuring that appropriate factors of safety are applied to control the resulting creep deformation of geosynthetic-reinforce structures. acknowledgment this research was funded by the deanship of scientific research at the university of hail, saudi arabia, under grant no. 0160735. engineering, technology & applied science research vol. 10, no. 4, 2020, 6147-6151 6151 www.etasr.com touahmia et al.: creep performance of geosynthetic reinforcements references [1] a. sawicki, “a basis for modelling creep and stress relaxation behaviour of geogrids,” geosynthetics international, vol. 5, no. 6, pp. 637–645, jan. 1998, doi: 10.1680/gein.5.0139. 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[6] astm d6637 / d6637m-15, standard test method for determining tensile properties of geogrids by the single or multi-rib tensile method,. west conshohocken, pa: astm international, 2015. [7] j. g. zornberg, b. r. byler, and j. w. knudsen, “creep of geotextiles using time–temperature superposition methods,” journal of geotechnical and geoenvironmental engineering, vol. 130, no. 11, pp. 1158–1168, nov. 2004, doi: 10.1061/(asce)10900241(2004)130:11(1158). [8] c. j. f. p. jones and d. clarke, “the residual strength of geosynthetic reinforcement subjected to accelerated creep testing and simulated seismic events,” geotextiles and geomembranes, vol. 25, no. 3, pp. 155–169, jun. 2007, doi: 10.1016/j.geotexmem.2006.12.004. [9] f. franca and b. bueno, “creep behavior of geosynthetics using confined-accelerated tests,” geosynthetics international, vol. 18, pp. 242–254, oct. 2011, doi: 10.1680/gein.2011.18.5.242. 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[18] din 4125, “ground anchorages: design, construction and testing: deutsche norm,” beuth verlag, 1990 microsoft word etasr_v11_n3_pp7152-7157 engineering, technology & applied science research vol. 11, no. 3, 2021, 7152-7157 7152 www.etasr.com alameri et al.: assessing the risk level of the challenges faced in construction projects assessing the risk level of the challenges faced in construction projects abdulla alameri faculty of business and technology management, universiti tun hussein onn malaysia (uthm) johor, malaysia ahmed s. a. marey alhammadi faculty of business and technology management, universiti tun hussein onn malaysia (uthm) johor, malaysia aftab hameed memon department of civil engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan ismail abdul rahman faculty of civil and environmental engineering universiti tun hussein onn malaysia (uthm) johor, malaysia nur ain ngah nasaruddin faculty of civil and environmental engineering, universiti tun hussein onn malaysia (uthm) johor, malaysia abstract-the failure of construction projects could be attributed to several challenges that emerged during the construction process. nine major challenges were uncovered from the literature: resource allocation, time, cost, quality, safety, project complexity, changes, uncertainties, and communication. a survey was carried out among professionals having a minimum of 10 years of experience in the construction industry to identify the occurrence and severity of these challenges. a total of 117 responses were analyzed and plotted on a risk matrix. the mean values indicated that time, cost, and quality are the top three challenges faced in construction projects, while the risk matrix revealed that all challenges are high-risk challenges. thus, the professionals should consider suitable measures to address these challenges for improving a project’s performance. keywords-construction industry; construction challenges; risk; risk matrix; malaysia i. introduction the construction industry is considered a key industry in a country’s development and contributes 18% of the worldwide gdp [1]. the construction industry is referred to as vibrant due to uncertainties in technology, budgets, and development processes [2]. the operations of the construction industry require sufficient labor force, skills and commitment, and effective manpower organization [3]. conventionally, the performance of a construction project is assessed based on three parameters i.e. time, incurred cost, and quality [4-6]. other studies have stated that the performance also includes safety as an additional criterion [7-9]. once the project size becomes larger it is becoming more challenging, especially during the implementation stage and thus it will likely disrupt the targeted performance [10]. to deal with this challenge, specific skills, expertise, experience, and knowledge are needed to avoid any potential project overruns [11]. several approaches have been introduced to address these challenges, and leadership is one of them [12]. failure or success of construction projects highly depends on the ability to handle challenges that emerge along with the construction processes. for this, the knowledge of the challenges occurring in construction projects is essential. this study aims to investigate the various challenges faced in construction projects and to assess the level of risk for each of them. ii. identification of construction challenges challenges are inevitable in a construction project and impact its performance. these challenges may emanate from improper communication among the staff, low quality workmanship, and insufficient amount of materials available [13]. moreover, the organizational drawbacks and the incapability to deal with critical situations also fuel these challenges [14]. this study investigated the constraints faced by construction leaders to keep the project well organized and running smoothly, ensuring its successful completion. in [15] the challenges were classified into construction issues and peripheral pressures. in [16] the challenges were classified into 4 categories: engineering, human development, managerial and political, and sustainability challenges. seven construction management challenges were pointed out in [17]. financial constraints and awareness & knowledge were identified as two major challenges of the construction field in [18]. in [19], three project challenges were pointed out: late approvals, sudden changes of rules, and non-uniform compliance. in [20], the challenges in construction practices were abridged to resource allocation, scheduling and budget management, meeting the quality and safety standards, maintaining complexity, organization management, change management, risk and uncertainties management, and communication system. in [21], the challenges were classified into resource management, risks and uncertainties, support from top management, and restraint of budget. in [22], uncertainty, bad worker attitude, financing matters, contractor selection, and adoption of the latest technology and advanced techniques were pointed out as major construction challenges. corresponding author: aftab hameed memon (aftabm78@hotmail.com) engineering, technology & applied science research vol. 11, no. 3, 2021, 7152-7157 7153 www.etasr.com alameri et al.: assessing the risk level of the challenges faced in construction projects moreover, claim challenges are faced by every contractor in the construction project [23]. a literature review highlighted the nine common challenges faced in construction works shown in table i. table i. challenges faced in construction projects challenges in construction projects references resource allocation [24-29] time [30-33] cost [33-38] quality [39, 40] safety [41, 42] project complexity [43, 44] changes [45, 46] uncertainties [24, 47-49] communication [50-52] a. resource allocation construction activities depend on the availability of resources [53]. resource management is essential to achieve the success of any project [54]. resources in the construction project usually consist of labor, materials, machines, and money [55]. the success of infrastructure and megaprojects needs a high amount of financial and human resources [56]. resources should be properly allocated due to limited availability and high demands in the construction industry, while all resources are equally important. construction materials typically contribute about 40-45% to the total cost of a project [57, 58]. hence, appropriate planning is crucial to ensure the timely availability of adequate and suitable materials [59]. planning the construction project manpower is important for determining the size of the project workforce, organizing into functional groups, and hiring suitable manpower [58, 59]. construction machinery contributes about 20-30% to a project’s cost, with additional costs for maintenance, repair, and operation. resource planning also ensures the availability of adequate and suitable equipment [59]. b. time construction time is a major concern, as each project has a predetermined period with a definable beginning and an identifiable end. inefficient time management increases a project’s cost, spoils a company’s reputation, and reduces construction productivity [55]. c. cost the construction process is capital intensive due to the large amounts incurred at every project stage [29]. the cost of labor, materials, equipment, professional fees, and total profit are major components of a project’s cost. cost management can be affected by capital shortages, impractical profit margin, high debits, and improper management of resources [37]. besides, cost escalation is also a ubiquitous issue faced in construction projects [60]. d. quality quality is defined as meeting the legal, aesthetic, and functional requirements of a project [61]. quality problems cause delays and cost overruns. effective quality management increases product quality, improves workmanship and efficiency, decreases wastage, and increases profit [62]. quality is an essential consideration in selecting the proper contractor for any project [63]. e. safety safety is a major concern in the success of the construction industry, especially when considering work-related accidents [64]. safety measures account for 1-2% of the total contract cost in a construction project [58]. safety management issues in a construction site depend on workers’ attitudes [65]. f. project complexity project complexity involves the employment of individuals from different organizations and combinations of technology [66]. project complexity has a direct relation with uncertainty in the term of its element [67]. g. changes a change in a construction project is an alteration or a modification in the pre-existing conditions, assumptions, or requirements [68]. it occurs when the scope of work differs from the scope of the work outlined in the contract documents [69]. changes in construction affect delivery time and cost significantly [69-70]. h. uncertainties uncertainty is the chance of any event with a genuinely unknown probability distribution [71]. the ambiguity of a project’s uncertainty is considered a threat to construction performance [72]. managing uncertainties involves risk and opportunities, where the activities and processes could become worse or better than planned [73]. i. communication previous studies indicated that over 50% of construction projects were unsuccessful due to poor or insufficient communication [74]. the complex communication environment in large or mega construction projects requires frequently changing sets of relationships [50]. iii. data collection and analysis this study performed a quantitative survey on the perceptions of various professionals engaged in handling construction projects. it aimed to uncover the possible challenges in the construction industry and identify their respective level of risk. professionals’ perceptions were collected utilizing a structured questionnaire. data analysis involved statistical methods using mean score calculation with the formula adopted by [75]: � = ∑(�) � (1) where m is the mean, x are the individual data points, and n is the sample size (number of the data points). the risk level of the challenges was assessed based on the risk matrix. a risk matrix is a tool to assess the risk level using a graphical representation based on two axes: the level of severity and occurrence. a 5-point scale was used for each axis, as shown in table ii: 1-very low, 2-low, 3-moderate, 4high, and 5-very high. the factors could be classified based on engineering, technology & applied science research vol. 11, no. 3, 2021, 7152-7157 7154 www.etasr.com alameri et al.: assessing the risk level of the challenges faced in construction projects risk level or using a risk matrix where the factors are placed based on occurrence and severity levels and assessed accordingly. this study utilized the risk matrix to assess the risk category of construction’s challenges. based on the two parameters and the scale, the drawn risk matrix can be seen in figure 1 [76]. table ii. measurement scale scale level of severity frequency of occurrence/likelihood 1 very low (vl) very low (vl) 2 low (l) low (l) 3 moderate (m) moderate (m) 4 high (h) high (h) 5 very high (vh) very high (vh) fig. 1. risk matrix. the risk matrix is divided into three zones: • green zone: risks are of low level and can be ignored. • yellow zone: risks are of moderate importance and should be controlled. • red zone: risks are of critical importance. these are the top priorities and close attention should be paid. iv. results and discussion a total of 117 completed questionnaires were collected throughout peninsular malaysia. data collection was performed through an in-person/site visit (face-to-face) approach. fig. 2. respondents’ experience. initially, an appointment was set with the respondents to participate in a telephone interview and an e-mail survey. on the agreed date, the respondents were approached and a short briefing was given about the study’s purpose and the contents of the questionnaire. the survey was completed in 3 months. the respondents were professionals with experience in several project types and sizes. a summary of the respondents’ project experience and size is shown in figures 2 and 3 respectively. fig. 3. size of the projects participated. respondents’ experience is a very crucial parameter as they could provide better judgment on the challenges and the required leadership characteristics due to their long-time involvement. from figure 2, it can be noted that the minimum experience of the respondents was 10 years while 38 respondents were working for more than 20 years in the construction industry. this indicates that the participants were capable enough to provide insight views of the problems faced in construction. the respondents were handling projects of several sizes. the minimum size of the projects handled by respondents was rm 10 million, while the majority was engaged in projects with more than rm 200 million contracts. collected questionnaires were checked for reliability to assess their consistency. cronbach's alpha value was computed to check the internal consistency, which ranges from 0 and 1, where 1 means that the data are highly reliable and valid while 0 means the opposite [77]. in this study, cronbach’s alpha value of data for severity level was found at 0.851, and the same for occurrence level was found as 0.844. as these values are higher than 0.6, they are deemed suitable for further analysis as suggested in [78]. the mean values of the responses on the occurrence and severity levels of construction challenges were calculated, and the results are shown in table iii. from table iii, it can be observed that time challenge is the most commonly occurring and severe challenge in construction projects of malaysia, as it was also shown in [79]. the second major challenge was the cost of the construction project. cost is a very serious issue and is given the highest priority by the owners and subsidizers. many researchers have emphasized that cost must be given a high priority. quality was reported as the third major challenge from the occurrence point of view, while from the severity perspective it was reported as fourth. engineering, technology & applied science research vol. 11, no. 3, 2021, 7152-7157 7155 www.etasr.com alameri et al.: assessing the risk level of the challenges faced in construction projects on the contrary, the practitioners reported safety as the fourth and third major challenge from the occurrence and severity aspects respectively. the mean values of all challenges were plotted on a risk matrix, as shown in figure 4. table iii. level of occurrence and severity of the challenges s. no challenges in handling the construction projects frequency of occurrence level of severity 1 time 3.67 3.48 2 cost 3.51 3.29 3 quality 3.44 3.19 4 safety 3.33 3.24 5 resources allocation 3.29 3.09 6 changes 3.19 3.08 7 uncertainties 3.15 3.06 8 project complexity 3.03 2.84 9 communication 3.13 2.83 fig. 4. risk level of the challenges. figure 4 illustrates the 9 challenges marked with "x" on the risk matrix. since all marks are located in the red zone/region, it indicates that all challenges belong to the high-risk category. the challenges need to be addressed carefully by the construction leaders during the implementation of a project. hence, appropriate measures should be considered to handle these challenges successfully. one of the appropriate ways for controlling these challenges is effective leadership. leadership can be used effectively by adopting several characteristics such as imparting information effectively, knowledgeable, work according to the plan, setting priorities, and willingness to take responsibility 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[80] n. a. nasaruddin, i. a. rahman, and m. m. jaber, "pls-sem model of leadership characteristics facing challenges in malaysia construction industry," international journal of engineering & technology, vol. 7, pp. 620–624, 2018. engineering, technology & applied science research vol. 8, no. 4, 2018, 3162-3167 3162 www.etasr.com ahmad et al.: forecasting parameter estimates: a modeling approach using exponential … forecasting parameter estimates: a modeling approach using exponential and linear regression w. m. a. w. ahmad school of dental sciences universiti sains malaysia, malaysia wmamir@usm.my r. a. a. rohim universiti sains malaysia malaysia adawiyah5350@yahoo.com n. h. ismail universiti sains malaysia malaysia noorhuda@usm.my abstract-this paper supplies a calculation method for the parameter estimates of an exponential equation through sas algorithm. the aim of this paper is to investigate the efficiency of the gained parameter estimates through the forecasting performance. the proposed calculation method can provide a very useful technique to develop an exponential equation with better accuracy performance. this research paper illustrates a sample of the data obtained from the established study, which characterize the proliferative capacity of mesenchymal stem cells. this paper also provides the specific algorithm for the parameter estimates. keywords-exponential; sas algorithm; parameter estimates i. introduction regression analysis is a statistical methodology that uses the relationship between two or more quantitative variables in a way that one variable can be predicted from the other, or others. this methodology is widely used in business, social, behavioral and biological sciences, including agriculture and fishery research [1]. for example, fish weight at harvest can be predicted by utilizing the relationship between fish weights and other growth affecting factors like water temperature, dissolved oxygen, and free carbon dioxide. there are other situations in a fishery where relationships among variables can be exploited through regression analysis [1]. regression analysis serves three major purposes: (1) description, (2) control and (3) prediction. we frequently use equations to summarize or describe data. regression analysis is helpful in developing such equations. for example, we may collect a considerable amount of fish growth data and a data on a number of biotic and abiotic factors and a regression model would probably be a much more convenient and useful summary of those data than a table or a graph. besides prediction, regression models may be used for control purposes. a cause and effect relationship may not be necessary if the equation is to be used only for prediction [2]. a functional relationship between two variables is expressed by a mathematical formula. if x denotes the independent variable and y the dependent variables, a functional relationship is of the form  xfy  . given a particular value of x, the function indicates the corresponding value of y. a statistical relation, unlike a function, is not a perfect one. in general, the observations for a statistical relation do not fall directly on the relationship’s curve. depending on the nature of the relationship between x and y, regression approach may be classified into two categories, linear regression and nonlinear regression models. the models that are linear in these parameters are known as linear models, whereas in nonlinear models parameters show nonlinearity. linear models are generally satisfactory approximations for most regression applications. there are occasions, however, when an empirically indicated or a theoretically justified nonlinear model is more appropriate [3]. a. linear regression linear regression is used to study the linear relationship between a dependent variable y and one or more independent variables x. the dependent variable y must be continuous, while the independent variables may be either continuous, binary, or categorical. the initial judgment of a possible relationship between two continuous variables should always be made on the basis of a scatter plot (scatter graph). this type of plot will show whether the relationship is linear or nonlinear. performing a linear regression makes sense only if the relationship is linear. other methods must be employed to study nonlinear relationships [4]. a model with more than predictor variables is a straightforward one. the model can be stated as follows: iεxββy i10i  (1) where iy is the value of the response variable in the i th trial, β0 and β1 are parameters xi is a known constant, namely the ith value of the predictor variable and εi is a random error term with mean zero and variance σ2 and their covariance is zero [5]. b. history of the exponential function the exponential is one of the most significant and widely occurring functions. in biology, it may depict the growth of bacteria or animal populations, the reduction of the number of bacteria in response to a sterilization process, the development of a tumor or the absorption or elimination of a drug. exponential growth cannot go on forever because of limitations of nutrients, etc. knowledge of the exponential function makes it more comfortable to understand birth and death rates, even when they are not perpetual. in physics, the exponential function describes the disintegration of radioactive nuclei, the engineering, technology & applied science research vol. 8, no. 4, 2018, 3162-3167 3163 www.etasr.com ahmad et al.: forecasting parameter estimates: a modeling approach using exponential … emission of light by atoms, the assimilation of light as it passes through matter, the change of voltage or current in some electrical circuits, the variance of temperature with time as a warm object cools, and the rate of some chemical reactions [1]. although the exponential distribution provides a simple, elegant and closed form solution to many problems, it does not offer a reasonable parametric fit for some practical applications where the underlying failure rates are nonconstant, presenting monotone shapes. recently, in the procedure of overcoming such problems, new categories of examples were introduced based on adjustments of the exponential distribution. authors in [6] offered a generalized exponential distribution, which can hold data with increasing and decreasing failure rate function. authors in [7] ushered in the exponential geometric distribution with decreasing failure rate, authors in [8] proposed a twoparameter distribution known as exponential-poisson distribution, which takes in a decreasing failure rate and authors in [3] proposed another modification of the exponential distribution with decreasing failure rate function this model is inferred in a complementary risk scenario [9] where the lifetime associated with particular danger is not evident, rather we observe just the maximum lifetime value among all risks . c. exponential growth exponential growth is often used to model the growth of organism populations in a resource-rich environment. here “resource-rich” means that there is abudance of food and other resources necessary for the population to grow. for example, the initial growth of a cell bacteria in a mouth is often modeled as exponential. the justification for this model is that the rate at which a population of organisms grows should be proportional to their number, assuming that the organisms reproduce at a constant rate. for example, if you double the size of a population, then this should precisely double the rate at which the population bears an offspring, and should, therefore, double the rate at which the size of the population increases. what this means is that the population a of a given organism in a resource-rich environment should satisfy the differential equation ax, dx da  where x is some constant that depends on the rate of reproduction. thus the population grows exponentially bx 0 eaa  this model predicts that the population a will grow indefinitely, which cannot be true in any real situation. eventually, any population will run out of resources such as food or space to grow. however, the exponential model often gives fairly accurate results in cases where the short-term growth of a population is not inhibited by limited resources[10]. d. interpreting r2 r2 is frequently defined as the proportion of variance of the response that is predictable (or explained) from the regressor variables, that is the variability explained by the model. a low value of r2 can suggest that the assumptions of linear regression are not satisfied. plots and diagnostics will substantiate this suspicion. ii. materials and methods we used the data which characterize the proliferative capacity of mesenchymal stem cells. the data are composed of two variables which are the days of the culture (x) and population doubling level (lny). first, we bootstrap the data in order to increase the sample size and also to optimize the parameter estimates. then, we estimate the parameters through the exponential curve fitting and transform the nonlinear model into a linear form. this would bring a linear equation form. from the equation, we estimate the value of the independent variable (x) and fit the data with robust weighted regression by cauchy, robust fair weighted regression and robust weighted regression by huber. then a covariate-dependent variable is used to examine the differences in performance of the model suitability. a. the algorithm of exponential calculation the algorithm showed below is the way of inserting data in sas algorithm and the way of calculating the bootstrapping method.  data in sas format. the name of the dataset is given as cell_growth. the data consist of two variables x and ln y data cell_growth; input x y lny; cards; 0.00 38.00 3.64 5.00 39.31 3.67 8.00 39.74 3.68 10.00 40.98 3.71 13.00 43.10 3.76 17.00 45.78 3.82 20.00 49.15 3.89 22.00 49.90 3.91 24.00 53.98 3.99 28.00 57.46 4.05 31.00 61.03 4.11 34.00 63.80 4.16 37.00 65.52 4.18 40.00 68.54 4.23 44.00 72.62 4.29 47.00 75.42 4.32 50.00 79.38 4.37 53.00 83.31 4.42 ; run;  adding bootstrapping algorithm to the methodology building. cell_growth data were bootstrapped two times with resampling. the following procedure was given in sas syntax as follows. the new data which are generated by the sas procedure will be named as booted. the produce data in the study will be print through the print procedure.  we also add the syntax of ‘ods rtf file='abc.rtf' style=journal’ in the sas language in order to get the output in microsoft word format. %macro bootstrap(data=_last_, booted=booted, boots=2,   b.   engineerin www.etasr seed=1234); data &boote pickobs = int et &data poi replicate= i+1; if i> n*&boot run; %mend boot ods rtf file='ab %bootstrap(da run; proc print data run; proc sql this procedur and views. sa the syntax b sum of squa through the fitness of th value. title “corre proc sql; select css(y) in cell_growth; quit; title “expon ods graphics/im proc nlin data= parameters a= model y = a * ods output est run; proc sql; select n.nval sse.nvalue1 1 sse/&cor n * log(sse/n) summexp as n where n.labe sse.label1=“ quit; the syntax of of calculatio calculation r syntax is give title “regre /* robust r procrobustreg model lny = x output out=rob run; calculation r the full synt /* robust (w title “robus procrobustreg model lny = x ng, technology r.com ed; t(ranuni(&se int = pickobs n =int(i/n)+1; ts then stop tstrap; bc.rtf' style=jour ata= cell_growth a=booted; is a procedure re to adjust, r as will create below shows ares and the e syntax provi he parameter ected sum o nto :correct nential para magename=“ex = booted plots= =1 b=0; * exp(b*x); tsummary=sum lue1 as n, 1 as sse, rrected_su ) + 2*2 as aic n el1=“observatio “objective”; of regression m on regression bas en as follows. ession”; regression * method=mm da / diagnostics le bout r=resid sr= regression bas tax is given as weighted) h st (weighted method=m(wf= / diagnostics le y & applied sci eed)*n)+1; nobs = n; ; rnal; h, boots=2); e developed in retrieve and re e the output in the calculatio exponential p ded, we are a through the r of squares”; ted_sum_of_ ameter est xponentialfit”; fit; mmexp; um_of_squar from summexp ons used” and modeling bas sed on robust */ ata=booted; everage; =stdres; sed on robust follows. huber */ d) huber”; =huber(c=1.345 everage; ience research ahmad et al.: f n sql. we ca eport data in the form of ta on of the cor arameter estim able to measu r-square and ; _squaresy fr imates”; resy as rsqua p as sse, sed on four ty regression. th t (weighted) h )) data=booted; h v forecasting pa an use tables ables. rrected mates. ure the d aic rom are, ypes he full huber.   in gen pro mo than sign the a. vol. 8, no. 4, 20 arameter estima output out=rob run; calculation re the full synta /* robust (w title “robust procrobustreg m model lny = x / output out=rob run; calculation re full syntax is /* robust (w title “robust procrobustreg m model lny = x / output out=rob run; ods rtf close; the syntax of microsoft w nerated in the m the results fo ocedures is giv del predicts th n 0.05, and thi nificantly pred data. figure 1 result for exp source df model 2 error 34 total 36 018, 3162-3167 ates: a modelin out r=resid sr=s egression base ax is given as f weighted) c t (weighted method=m(wf= / diagnostics lev out r=resid sr=s egression base given as follow weighted) fa t (weighted method=m(wf= / diagnostics lev out r=resid sr=s f “ods rtf close word. this m microsoft wor iii. or the first mo ven in tables he dependent v is indicates tha dicts the outco 1, indicates the ponential fit fig. 1. the table i. sum of squares 100489 43.3029 100533 7 ng approach u stdres; ed on robust ( follows. auchy */ d) cauchy”; cauchy(c=2.385 verage; stdres; ed on robust (w ws. air */ d) fair”; fair(c=1.4)) dat verage; stdres; e” gives an ord means that th rd format. results odel without i i and ii. tabl variable well. at, overall, the ome variable a e fit plot for ln e fit plot for y vs x anova mean square 50244 1.273 3164 using exponent (weighted) cau 5)) data=booted weighted) fair a=booted; der to close th he output wil involving weig le i shows tha the p-value i e model statisti and is a good f ny. x f value appr pr>f 39450.4 <.000 tial … uchy. d; r. the he file ll be ghted at the s less ically fit for ox f 01 it c ta var exp exp wh go b. the tra can dep val ta c. reg wh engineerin www.etasr t parameter a b from table i y 9735.35 model (2) ca can be written      3.58 ln y ln ln y   table iii giv able iii, the r riation in the plained by the plained, which hich is the sm od model is th n 36 result for ro figure 2 sho e original dat ansformed data n write an exp y 572.3ln  the r-squa pendent variab lue of aic is g able v. result for ro figure 3 giv gression. from hich is weighte ng, technology r.com table ii. pa estimate a st 35.9735 0.0160 0 ii, we can writ xe 0160.05 an be transform as follows  35.9735 0. 827 0.0160x   ves the inform r-square value dependent var e regression m h is very large mallest value a he one that has table iii. sse r43.302936 0. obust regressi ws the fit plot ta, while in a. table iv sh ponential mode x0162.09  are value indi ble. in this cas given as 28.24 fig. 2. obust (weighte ves the plot m the table vi ed by huber as y & applied sci arameter estima approx td. error ap co 0.2564 35. 0.000219 0.0 te an exponent med into a lin 0160x mation of exp indicates how riable or varia model. in this e. the aic val among all pro s minimum ai exponential fi -square 988339 10 ion t for lny vs x. this section hows the param el as: icates the tot se, 78.94 can b 4. detailed info fit plot for lny ed) huber for lny vs x i, we can write s: ience research ahmad et al.: f ates pproximate 95% onfidence limits .4525 36.494 0155 0.016 tial model as (2) near form by ta ponential fit. w much of the ability of the d case, 97.98 c lue is about 10 oposed metho ic value. it aic 0.64925 previously we we are usin meter estimate (3) tal variation i be explained an formation is giv x for huber r e a robust regre h v forecasting pa % s 45 64 aking, from e total data is can be 0.649, ods. a e used ng the es. we in the nd the ven in robust ession valu para inte s d. wei a ro vol. 8, no. 4, 20 arameter estima y 5799.3ln  from the robu ue of r-squar t ameter df e ercept 1 x 1 cale 0 ta result fo in figure 4 ighted by cau obust regressio y 5798.3ln  018, 3162-3167 ates: a modelin x0160.09 ust regression re is 0.9577 an fig. 3. f table iv. par paramete estimate std. erro 3.5729 0.008 0.0162 0.000 0.0282 able v. par goodn statistic r-square aicr bicr deviance for robust (we the result o uchy is plotted on which is we x0160.08 fig. 4. f 7 ng approach u which is weig nd aic value is fit plot for lny rameter estima er estimates . or 95% confidenc limits 87 3.554 3.5 03 0.016 0.0 rameter estimat ess-of-fit value 0.7894 28.2413 32.9392 0.0205 eighted) cauch of robust reg d. from table eighted by hub fit plot for lny 3165 using exponent (4) ghted by hube s given as 24.3 ates ce chisquare c 590 168673 017 2383.2 tion hy gression whic viii, we can ber as follows (5) tial … er, the 3544. pr > chi.sq. <0001 <0001 ch is write 37 see par int s pa in e. we of engineerin www.etasr the value of 7.98. a robu ems not to be a table vi. rameter df e tercept 1 x 1 scale 1 table vii. table viii. arameter df e ntercept 1 x 1 scale 1 table ix. result f below is the e can write a f r-square is 0 y 580.3ln  ng, technology r.com f r-square is 0 ust regression a good proced parameter es paramet estimate std erro 3.5799 0.00 0.0160 0.00 0.0335 parameter es goodn statistic r-square aicr bicr deviance parameter est paramet estimate std. error 3.5798 0.008 0 0.0160 0.000 3 0.0336 parameter est goodn statistic r-square aicr bicr deviance for robust (w result of fair fair robust reg .9616 and aic x0160.003 fig. 5. y & applied sci 0.4797 and ai which is we dure for the for stimates for hu ter estimates d. or 95% confiden limits 76 3.5651 3. 03 0.0154 0. stimates for hu ness-of-fit value e 0.9577 24.3544 29.2774 e 0.0249 timates for cau ter estimates r 95% confidence limits 8 3.564 2 3.59 5 0 0.015 4 0.01 6 timates for cau ness-of-fit value 0.4797 377.9854 383.0731 0.4252 weighted) fair robust regress ression is give c value is give fit plot for lny ience research ahmad et al.: f ic value is giv eighted by c recasting. uber regression nce chisquare 594 222668 016 2807.09 uber regression uchy regression chisquare c 201478 <0 2540.99 <0 uchy regression sion. from tab en in (6). the en 12.309. (6) h v forecasting pa ven as cauchy n pr > chisq. <.0001 <.0001 n n pr > chisq. 0.0001 0.0001 n ble x, value para inte s f. met thei ex r ro r par also thro cell ro (ta rob rob ove be e sho wei high fit i oth out to ana pro calc the com vol. 8, no. 4, 20 arameter estima table x. ameter df e ercept 1 3 x 1 0 cale 1 0 table xi. method comp table xii sh thods. we sum ir parameter es table parameter estimates xponential fit robust regression robust huber obust cauchy robust fair iv. the main ob ameter estima o to find the b ough modelin l doubling d obustreg. i able xii): (i) bust (weighted bust (weighted erview of the a employed. fro ows a very goo ighted by fai hest r2 and th is the best me er methods fit liers through t delete them f alysis once aga oposed model culation with e exponential mpared to the o 018, 3162-3167 ates: a modelin parameter es paramete stimate std. error 3.5803 0.0086 0.0160 0.0003 0.0336 parameter es goodn statistic r-square aicr bicr deviance parison hows the com mmarized the stimates. xii. paramete mode y 9735.35 or in a linea  y 5827.3ln  y 5729.3ln  y 5799.3ln  y 5798.3ln  y 5803.3ln  . discussio bjective of th ate between se best calculatio ng techniques. data by usin in this paper, f exponential d) huber (iv) d) fair. this pa above mention om the results, od fitting resu ir techniques he lowest aic ethod, followe t the model po the output. th from the set ain. to keep th , it is neces some improve l fit reveals other proposed 7 ng approach u stimates for fa er estimates 95% confidence limits 6 3.563 3.5 0.015 0.0 stimates for fa ess-of-fit value 0.9616 12.3093 17.8695 0.0121 mparison of output of the er estimates co el r xe 0160.05 ar form x0160.0 0 x0162.0 0 x0160.0 0 x0160.0 0 x0160.0 0 on and concl his research i everal propose on which can we have giv ng proc n five different m fit (ii) robu ) robust (wei aper provides ned different t , we can see th ult, followed by . both meth c. this indicat ed by robust f oorly. this m he best way to of data and he efficiency a ssary to have ements of the the findings d methods. 3166 using exponent air regression e chisquare c 97 171908 < 016 2162.9 < air regression the five diff gained model omparison -square a .988339 1.06 0.7894 282 0.9577 243 0.4797 3.77 0.9616 123 lusion is to compare ed calculations represent the ven an examp nlin and p methods were ust regression ighted) cauch only a prelim techniques tha hat the expone y robust regre hods produced tes that expone fair regression may be due to o handle outli then rerun to and accuracy o e a good wa proposed stra s more expl tial … pr > chisq. <0.0001 <0.0001 ferent l with aic 64.925 2.413 3.544 79.854 3.093 e the s and e data ple of proc used n (iii) hy (v) minary at can ent fit ession d the ential . the some ers is o the of the ay of ategy. licitly engineering, technology & applied science research vol. 8, no. 4, 2018, 3162-3167 3167 www.etasr.com ahmad et al.: forecasting parameter estimates: a modeling approach using exponential … acknowledgment authors would like to express their gratitude to universiti sains malaysia for providing the research funding (grant no.1001/ppsg/8012278, school of dental sciences, universiti sains malaysia). references [1] n. r. draper, h. smith, applied regression analysis, wiley eastern, 1998 [2] r. j. tallarida, r. b. murray. exponential growth,and decay, manual of pharmacologic calculations, springer, 1987 [3] r. tahmasbi, s. rezaei, “a two-parameter lifetime distribution with decreasing failure rate”, computational statistics & data analysis,vol. 52, no. 8, pp. 3889-390, 2008 [4] a. schneider, g. hommel, m. blettner, “linear regression analysis”, deutsches arzteblatt international, vol. 107, no. 44, pp. 776-82, 2010 [5] d. c. montgomery, e. peck, g. vining, introduction to linear regression analysis, 3rd edition, john wiley and sons, 2003 [6] r. gupta, d. kundu, “generalized exponential distributions”, australian and new zealand journal of statistics, vol. 41, no. 2, pp. 173-188, 1999 [7] k. adamidis, s. loukas, “a lifetime distribution with decreasing failure rate”, statistics & probability letters, vol. 39, no. 1, pp. 35-42,1998 [8] d. kus, “a new lifetime distribution distributions”, computational statistics and data analysis, vol. 11, no. 9, pp. 4497-4509, 2007 [9] f. louzada-neto, “poly hazard regression models for lifetime data”, biometric,vol. 55, no. 4, pp. 1281-1285, 1999 [10] j. u. kreft, g. booth, j. w. t. wimpenny, “bacsim, a simulator for individual-based modeling of bacterial colony growth”, microbiology, vol. 144, no. 12, pp. 3275-3287, 1998 microsoft word 25-3246_s1 engineering, technology & applied science research vol. 10, no. 1, 2020, 5233-5236 5233 www.etasr.com madani et al.: experimental study of electric and dielectric behavior of pvc composites experimental study of electric and dielectric behavior of pvc composites lakhdar madani department of electrical engineering dac hr laboratory ferhat abbas setif i university setif, algeria madani_lakhdar10@yahoo.fr kamel salim belkhir department of electrical engineering lepci laboratory ferhat abbas setif i university setif, algeria ksbelkhir@univ-setif.dz saad belkhiat department of electrical engineering dac hr laboratory ferhat abbas setif i university setif, algeria belsa_set@yahoo.fr abstract—polyvinyl chloride (pvc) is usually used as insulation in electrical engineering, mainly as cable insulation sheaths. a method for improving pvc’s dielectric properties, reducing the effects of uv ageing, is the use of pvc films doped in alumina and titanium dioxide. this research investigated the influence of alumina and titanium dioxide (al2o3/tio2) to the dielectric properties of pvc. four pvc samples were examined using an rlc impedance analyzer. fourier transform infrared (ftir) spectroscopy was utilized on the sample’s surfaces, exploring the chemical stability of the tested materials. in addition, the volume resistivity and average breakdown voltage of each sample was examined. doping al2o3/tio2 into pvc improved its dielectric properties and volume resistivity, while adding more ceramic decreased volume resistivity. furthermore, the addition of al2o3/tio2 caused a significant enhancement in voltage breakdown strength. keywords-pvc; composite; alumina; titanium dioxide; al2o3/tio2 doped pvc; breakdown voltage i. introduction in recent years, nanotechnology has been used in the synthesis of various types of polymer nanocomposites and in understanding their physical and chemical properties [1-5]. the presence of nanoparticles in polymers improves their mechanical, electrical and chemical properties. polymers doped with metal oxide nanoparticles have been studied as alternative materials for electrical applications, especially in underground and transmission cables [6-7]. many polymers have been proved as suitable matrices in the development of composite structures, due to their ease of production and processing, good adhesion with reinforcing elements, resistance to corrosive environment, and occasionally ductile electrical performance. polyvinyl chlorides (pvcs) are polymers used as electrical insulating materials in both industrial and communication applications. due to its excellent dielectric strength, low dielectric permittivity, low loss factor and thermomechanical behavior, pvc has been used for a long time as an electrical insulator in distribution [8]. its compression behavior was studied in [9], where the dielectric reaction in the frequency range of 20hz–1ghz of polymeric insulating materials, such as pvc, polytetrafluoroethylene (ptfe) and high-density polyethylene (hdpe) was evaluated. furthermore, it is recognized that inorganic fillers, such as tio2, zno, and al2o3 particles, can be used as ultraviolet (uv) light screening agents in a pvc matrix [10, 11]. the inorganic fillers can absorb or reflect uv light, forming a barrier between the polymer and the light source. researchers in [12] focused on the space charge characteristics of epoxy resin and its nano-mgo composites. it was found that specimens with 3wt%~5wt% nano-mgo accumulate less space charge, while the 1wt% nanocomposites accumulate the most. surface modification and characterization of tio2 nanoparticles and their roles in thermal, mechanical, and accelerated aging behavior of foamed wheat straw fiber/polypropylene composites were studied in [13]. the antiaging properties of polymer resins are influenced by the dispersion of inorganic fillers in the matrix. the inorganic fillers can effectively absorb or reflect uv light when they are uniformly dispersed in the polymer matrix, while agglomerated inorganic fillers result in many defects [15, 16]. this paper studies the dielectric properties of the al2o3/tio2 composite based pvc. four pvc samples, a pure sample and three doped with al2o3/tio2, were examined, studying the effect of doping in permittivity, loss index, chemical stability, volume resistivity and average breakdown voltage. ii. experimental method the structure of the studied samples is given in table i. the basic component was the pvc resin used in the algerian industry (type h3000), mixed with an antioxidant (bariumzinc) to assure thermal stability, dicumyl peroxide as linking agent lubrificant, and dop (di-octyle phatalate-99.5%) plasticizer from zhengzhou p&b chemical co ltd. four types of samples, standard pvc without additives and al2o3/tio2doped pvc were examined, in conformity with [17]. table i. content of pvc al2o3/tio2 composites samples 1 2 3 4 polymer (pvc) 100% 90% 90% 80% al2o3 0% 10% 0% 10% tio2 0% 0% 10% 10% the preparation was mixed in a two-roll mixer for 5 minutes at 160°c. the samples were prepared as sheets of corresponding author: kamel salim belkhir engineering, technology & applied science research vol. 10, no. 1, 2020, 5233-5236 5234 www.etasr.com madani et al.: experimental study of electric and dielectric behavior of pvc composites predetermined thickness. the sheets were cut into 10cm×10cm squares with 0.6mm thickness. the apparatus used for the dielectric response was an rlc (wayne kerr, type 6420), using a range up to 10mhz. the samples were then introduced between two plane copper electrodes. afterwards, the capacitor representing the sample was submitted to an alternating electric field of 1v/m. dielectric loss factor tgδ, relative permittivity εr and loss index (ε'') were measured, with the measurement error being ±0.05%. the volume resistivity of the pvc nanocomposites was measured using the bridge method, at room temperature (figure 1). tests on the voltage breakdown of the samples were performed, using weibull’s method, in conformity with [18]. fig. 1. measuring circuit of the volume resistivity iii. experimental results a. doping effect on permittivity figure 2 shows the permittivity for frequencies in the range 0-1khz on the four samples of different doping types and rates. it was noticed that the dielectric constant varies, depending on the frequency and the percentage of doping and that the permittivity of the ferroelectric ceramic (al2o3, tio2) doped pvc rises in comparison with the standard sample. ferroelectric ceramics, such as al2o3 and tio2, are known for their high permittivity [19-20]. in figure 2 permittivity increases gradually, between 3.2-7.3 at 50hz and between 2.86 at 1khz) as a function of the type of additive content. three zones were observed in each curve. in the first zone (0-300hz), εr reaches a local maximum value of 7.2 for samples 3 and 4 and 6.2 for sample 2. moreover, doped samples have a small peak at 47hz. the second zone, in the range of 300-600hz, is turbulent and has two peaks, and all curves gradually decrease to minimum values at 400hz, while in the range of 400-500hz εr rises rapidly, reaching a maximum value at 500hz. finally, in the third zone, at frequencies greater than 600hz, εr slowly decreases and stabilizes. b. doping effect on loss index figure 3 shows the progress of loss index (ε''), for doped and standard samples as a function of frequency. it is observed that there are also three zones in each curve. in the first zone, between 0 and 300hz, an important peak appears at around 50hz for sample 4 and at 35hz for the other samples. after that, all curves vary slowly until 300hz. the second zone, (300-600hz), is turbulent as after the minimum at 300hz a new peak is appearing at 350, 370, 380 and 410 hz for samples 4, 2, 1 and 3 respectively. finally, at the third zone, after 600hz, all curves have little variation. fig. 2. permittivity (εr) of standard and al2o3/tio2 doped pvc samples fig. 3. loss index of standard and al2o3/tio2 doped pvc samples c. fourier transform infrared (ftir) spectroscopy ftir spectroscopy results are shown in figure 4. at first, it is noted that the infrared spectrum of the four samples with and without doping have slight variation and broad resemblance on the following characteristic bands: a peak at the area of 1000cm -1 shows the existence of the c-c bond (sp3). two wide bands centered at about 1440 and 1370cm -1 respectively characterize the symmetrical and ch3 asymmetric deformation vibrations. the intense band around 700cm -1 is assigned to the swings of (ch2)n, when n≥4 whereas that noted to 620cm -1 is due to the vibration of the c-cl bond. concerning the standard pvc sample, three bands are revealed, between 2970 and 2820cm -1 , assigned to the symmetric and asymmetric elongation vibrations of the c-h bonds, ch2 and ch3 groups at the end of pvc chains. an adsorption of -oh groups appears engineering, technology & applied science research vol. 10, no. 1, 2020, 5233-5236 5235 www.etasr.com madani et al.: experimental study of electric and dielectric behavior of pvc composites between 3300 and 3665cm -1 , corresponding to the elongation of the chemisorb hydroxyl groups at the level of the surface adsorption sites, as well as to the contribution of the dissociated and molecularly adsorbed hydroxyl groups. in addition, the infrared spectrum of the pvc sample doped with 10% tio2 and 0% al2o3 showed an intensive and wide band at 430900cm -1 , corresponding to a strong ti-o and ti linkage elongation vibration. the presence of a band at 1630cm -1 is attributed to the adsorption on the surface of tio2. the peaks that appeared at 785 and 586cm -1 , and their absence in the ftir spectrum of pure pvc, represent the al-o bond. fig. 4. ftir results for standard and al2o3/tio2 doped pvc samples d. volume resistivity and average breakdown voltage table ιι shows the measurements of volume resistivity and average breakdown with and without doping. standard pvc had the maximum resistivity. the tio2 doped samples, had much smaller resistivity values than the other samples. on the other hand, the tio2 doped samples had the minimum average breakdown voltages, which was lower than the breakdown voltage in standard pvc samples. table ii. volume resistivity and average breakdown voltage sample number 1 2 3 4 volume resistivity (10 14 ωm 2 /m) 8.7975 6.11672 1.5853 1.8370 average breakdown voltage (kv) 21.008 24.2 15.2 17.575 iv. discussion usually, εr and tgδ depend on the physical, chemical and structural variations of insulators during service. novel polymeric composites containing ceramic powders have been utilized in order to improve insulators’ performance [8, 19-22]. after the doping process in the samples a broadening of the peak in the bf region occurs [23] (figures 2 and 3). a peak appears in the curve of the dielectric constant and in parallel an inflection in the curve of the loss index under around 50hz. moreover, a second peak, more resolved in the dielectric constant and an inflection in loss index curves, has been recorded around 500hz as indicated in [24]. however, as the tio2 or al2o3 content increases the dielectric constant increases. the peak of the most intense relaxation, occurring in the low-frequency region, seems to be depending on the content of ceramics and on the accumulation of charges at the interface between the sample and electrodes, such as those indicated in [22, 24], because of the interfacial polarization (ip) expected at this frequency. ftir spectroscopy indicates the presence of ketones and esters [19, 22] in the 1713.6cm -1 and 1740cm -l respectively. in this work, εr increased and tgδ decreased when the nano-filler content increased. the volume resistivity decreased with increasing ceramic content. comparing the ceramic doped samples, increasing the nanofiller content increased εr and decreased tgδ. this is explained as reducing of space charge, due to the capturing behavior of the ceramics, in the pvc matrix [25]. the main carriers present were attributed to free ions from the ingredients used in the polymerization reaction of pvc, such as the stabilizer, as well as the ingredients in the plasticizer itself. as the samples of this work were elaborated in the same conditions as in [5], one plausible explanation for the increase of εr with nano-filler content can be the conductivity of batio3 nano-particles incorporated in the inter-granular interfaces of pvc. the electric conductivity decreased as ceramic content increased. this can be explained as reducing of space charge, due to the capturing behavior of the ceramics, in the pvc matrix [26]. the recorded breakdown strength value of sample 2 is higher than standard pvc’s, but samples 3 and 4 fall short. the variation of the breakdown strength values depends on the ceramic content, as they tend to decrease by increasing ceramic content up to some practical limit [27-28]. it was well shown that, void defects and electromechanical stress produced cracks, which play an important role in the injected electrons from the electrodes gaining sufficient energy which increases the probability of macromolecule ionization and further initiation of electron avalanche. this process accelerates the rising of conducting channels and the final breakdown [29-31]. furthermore, the increasing interface domains, due to the dispersion of nps, increase the number of the trapped charge carriers, which plays a role in reducing carrier mobility and delays the final breakdown [29]. al2o3 makes possible to stabilize the volume values and to improve the resistance values in the pvc matrix, on the basis of the insertion of the alumina [12, 27-28, 32]. on the other hand, tio2 has an inverse effect on the pvc matrix. v. conclusion this study investigated the effects of al2o3/tio2 doping in pvc’s dielectric properties. moreover, electrical breakdown tests were carried out on standard and doped pvc samples, in order to examine the influence of tio2 and al2o3 on the behavior of these insulators. the results showed that pvc reveals a degree of dielectric relaxation and higher losses in the frequency range of 20hz-1khz. ftir spectroscopy showed changes in the plasticizer or pigment of pvc. moreover, a change in the transmittance peak with the change in doping al2o3-tio2 in the polymer nanocomposites was revealed. this engineering, technology & applied science research vol. 10, no. 1, 2020, 5233-5236 5236 www.etasr.com madani et al.: experimental study of electric and dielectric behavior of pvc composites explains the increased compatibility, in chemical composition, between polymer and nanoparticles. these results indicate that the presence of al2o3/tio2 nano-particles does not exert any influence on the structure of the pvc, and show that ceramics as fillers improved its dielectric properties. νano-al2o3/tio2 particles reflect uv light, which can destroy the pvc chain, restraining dehydrochlorination and the simultaneous oxidation reactions. additionally, the segmental motion of polymer chains and a hopping mechanism is revealed, which contributes equally in coupled form for ion transportation in the pvc/al2o3-tio2 nanocomposites. this study shows that a well dispersed ceramic in the 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synthesis and characterization of poly(styrene)-block-poly(acrylic acid) and … synthesis and characterization of poly(styrene)block-poly(acrylic acid) and organoclay based hybrid composite materials sajid haleem soomro institute of chemistry, shah abdul latif university, khairpur, pakistan sajidsoomro80@gmail.com muhammad sanaullah institute of geology, university of the punjab, lahore, pakistan sana.ullah.geo@pu.edu.pk noor zaman national center of excellence in analytical chemistry, university of sindh, jamshoro, pakistan noorzamanshar@yahoo.com a. q. laghari dpt. of chemical engineering, mehran university of engineering & technology, jamshoro, pakistan engrchemi@gmail.com nabi bux jalbani dpt. of chemical engineering, quaid-e-awam university of engineering, science and technology, pakistan n.bux@quest.edu.pk kamran mirza institute of geology, university of the punjab lahore, pakistan kamran.geo@pu.edu.pk ejaz ahmed abbasi institute of geology, university of azad jammu and kashmir, muzaffarabad, ajk, pakistan ejazahmed990@gmail.com abstract—polystyrene (ps) and polyacrylic acid (paa) are organic and synthetic polymers. generally, a composite needs a matrix and reinforcement. montmorillonite (mmt) is used as reinforcement to form a hybrid matrix by ultra-sonication. block polymers of ps and paa were first synthesized and then hybrid nanocomposite material of synthesized block polymeric matrix was fabricated by incorporating organoclay as reinforcement through 6 and 12 hours of ultra-sonication. the characterizations of the hybrid nanocomposite material were done by uv-visible and infrared (ir) spectroscopy, which confirm the successful synthesis of ps and paa block polymer. the uv-visible spectroscopic measurements revealed that hybrid composite material is different from ps-block-paa and that absorbance increases on increasing concentration. after successful ultrasonication the hybrid composite is analyzed through scan electron microscopy (sem) regarding surface morphology, distribution, uniformity, porosity, matrix compatibility, and matrix reinforcements. sonication (for 6 hours) demonstrates a heterogeneous porous surface and an increase in roughness and porosity of surface morphology at different optical zooms. keywords-poly(acrylic acid); poly(styrene); block polymer; montmorillonite (mmt); exfoliation i. introduction a polymeric composite material is made out of two distinct parts, network and filler. it is also called fortification or dispersed stage [1, 2]. it might come in the form of strands (fibers), sheets or particles. however, sometimes extra mixtures are utilized. the properties of composites depend on size, shape, orientation, relative amount, distribution of particles, constituent phase, and geometry of dispersed phase [3]. the dispersed medium is liable for further structure improvement. in order to improve the interaction between filler and matrix, compatibilizers can be added which have expressive effect on material cohesion and properties. due to their unique advantages composite materials are used in various technical applications [4]. the combination of synthetic or natural inorganic filler makes up polymer matrix composites (pmcs). pmcs comprise resins as matrix. metal matrix composites (mmcs) can enhance properties like tensile strength, yield stress and high impact resistance. mmcs usually are alloys of al and mg using silicon carbide fibers [5]. polymers have been with us and other species from the beginning, they formulate the basic building blocks of life [6]. polymers like polyethylene, ps, plastics and nylon are obtained by synthetic methods. the polymeric products are widely abundant in nature [7, 8]. nano scale structuring material has unique properties. the physical and chemical properties of nano scale materials significantly differ from the ones at large scale. filler alternative additive nanoparticles utilized within polymers for different impacts are an expanded investment [9]. regarding physical structure, nanofillers might be characterized into their substance nature, yet they are arranged in view of the particle states. constituents have at least one dimension in the nanometer scale [10]. the collaboration amongst nanoclays and polymers can deliver two sorts of nanocomposites. the primary type possess intercalated nanocomposites, which are framed because of the infiltration of polymer chains between the layers of the clay, shaping a multilayer structure with rotating layers of polymer and clay [11]. ii. materials and methods it is logical to investigate spectrum and quantum properties regarding ionized electronic conduction of fabricated high subengineering, technology & applied science research vol. 8, no. 5, 2018, 3411-3415 3412 www.etasr.com soomro et al.: synthesis and characterization of poly(styrene)-block-poly(acrylic acid) and … atomic weight novel composite and nanocomposite materials. it is fundamental to acquire and investigate optical and quantum analysis with expanded ultraviolet and close infrared spectroscopy. the hybrid composite material of polystyreneblock-polyacrylic acid (ps-b-paa) is characterized by ft-ir, sem and uv-visible spectrophotometer. analyses are done in order to know the shifting of functional groups and main bond vibrations and to accumulate and confirm the nano-fabrication. a. uv-visible spectroscopy uv-visible spectroscopy is a valuable apparatus to scan the natural atoms that incorporate in saturated and unsaturated compounds like aromatic compound, alkanes, alkenes, alkynes, ketones and aldehydes for various distinct wavelengths. it delivers change from pre-synthesis to post-synthesis [13]. b. ft-ir spectroscopy polymers and composite materials would be also examined by ft-ir spectroscopy. the limitation and utilitarian of instrument is in terms of vibrational frequencies of single wavelength to various wavelengths of polymers and composite materials. bonding and circulation of polymerized and copolymerized monomeric units in chains is done with the aid of hydrogen bonding [15]. all the inner and outer composition can be revealed by the ft-ir technique. the created crosslinked and polymer and nano-composite blocks are identified in terms of wave numbers and bands of vibrations. c. scanning electron microscopy (sem) sem is a helpful system to examine the surface morphology of a composite material. sem runs through a pc program, the pictures of sem are seen on crts arranged at electronic reassure in addition to efi pictures [16]. d. ultra sonication ultra sonication is a process which converts electrical signals into physical vibrations. ultra sonication is mostly done by sonicator devices which work on a mechanism in which sound waves are converted into mechanical waves. sonication has various impacts on physical and chemical properties. sonication can be utilized to speed disintegration, by breaking intermolecular associations. it is particularly helpful when it isn't attainable to mix the given substance, as with nmr tubes [12]. e. centrifuge a centrifuge is deployed for the detachment of particles of matter whether it is solid, liquid or gas. a centrifuge works on the application of centrifugal force for the sedimentations of heterogeneous mixture. it is a device for isolating particles from a solution as indicated by their size, shape, thickness, density, medium consistency, and rotor speed. in a mixture, particles whose thickness is higher than that of the dissolvable sink and particles that are lighter than it glide to the top. the more prominent the distinction in density, the speedier they move. if there is no distinction in thickness (isopycnic conditions), the particles remain steady [14]. f. chemicals and reagents following chemicals were utilized without sterilization. refined water was utilized for arrangement of tests. • polystyrene 99% pure • poly acrylic acid 99% pure • mmt nanoclay • tetra hydrofuran (thf) (solvent) 98% g. synthesis of ps-b-paa \ mmt clay composite for the synthesis of ps-b-paa and mmt clay based hybrid composite materials, 3g of ps were dissolved in 30ml of thf and were shaken till the viscous nature of solution increased. ten ml from the resulting solution were mixed with 10ml of paa and the mixture was sonicate for 30 minutes to form the block polymer of ps-paa. the appearance of light brownish color justifies the reaction proceedings. after careful monitoring we added 1g of mmt clay in the brownish colored solution under continuous stirring for 1 hour. the solution was sonicated for 6h to 12h. in spite of the fact that the specimens were gathered for different hours (3, 6, 9 and 12 hours), to get an even checked trial contrasts and for successful incorporation 6 hours and 12 hours ultra-sonicated arrangements were sufficient to indicate clear nanofabrication. after ultrasonication the color consistently changes to white colored solid as well as white viscous solution formed that came about because of development of composite via reinforcement and matrix. the nanocomposite hybrid material changes its properties and behavior with the designed structure. it was additionally affirmed with the assistance of ft-ir and sem results. iii. results and discussion a. spectrophotomteric study & uv-visible measurement the qualitative studies of ps–paa and their hybrid composite material by incorporation of mmt organoclay, were studied by uv-visible spectroscopy which gives strong indication for the successful incorporation of organoclay in the matrix. the pure block copolymer of ps–paa was scaned in 300nm-700nm and its maximum absorbace was found at 479nm. after, the different solutions of composite material i.e, 10%, 20%, 30%, 40%, and 50% were scanned at 479nm to determine absorbance. it was found that the absorbance increases with the increase of concenration, almost in linear relation, except minute deviation observed due to expected impurities during the preperation of the solutions. the results are depicted in table i. results show that absorbance increases with the increase of concentration of hybrid composite material (figure 1). this indicates the formation of hybrid composite material between block copolymer of ps–paa and organoclay. hybrid composite material should differ from its polymer matrix and on increasing concentration the absorbance should increase in linear relationship. table i. ps-paa concentration and absorbance concentration % of hcm absorbance λmax 10% 0.769 479nm 20% 0.834 30% 0.918 40% 1.091 50% 1.423 pure block co-polymer ps-paa 1.178 engineering, technology & applied science research vol. 8, no. 5, 2018, 3411-3415 3413 www.etasr.com soomro et al.: synthesis and characterization of poly(styrene)-block-poly(acrylic acid) and … uv-visible spectroscopy results b. ft-ir of ps-b-paa ft-ir spectrum of ps-b-paa shows peak at 2985cm-1 for ch3 symmetric stretch vibrations (figure 2). the peak at 1721cm-1 corresponds to c=o stretching, confirming the presence of paa which was initially present in paa at 1696cm-1 and c=c aromatic peaks in phenyl ring of polystyrene were initially present at 1601cm-1-1458cm-1 which was shifted to 1640cm-1-1451 cm-1. this confirms that both characteristic peaks of acrylic and styrene are present in the block of composite material. there also exist c-o for carboxylic acid at 1275cm-1-1175cm-1 and the broadening of peaks at >3000cm-1 justifies the presence of h-bonding. ft-ir spectrum of ps-b-paa c. ft-ir of 6 hour sonicated hybrid composite ftir spectrum was recorded after 6 hours sonication of the hybrid composite. the spectrum shows the characteristic peak at 1031cm-1 for si-o stretching of tetrahedral silicate layers of the surface modified clay. the appearance of this peak shows that polymeric chains are separated due to the incorporation of nano clay. this can also be justified by the significant decrease in the intensity of si-o. the peaks at 2925cm-1-2850cm-1 are for -ch asymmetric and symmetric stretching respectively, while the peak at 1703cm-1 for c=o stretching shows the existence of paa. this confirms the configuration of nanocomposites (figure 3). ft-ir of 6 hour sonicated hybrid composite d. ft-ir of 12 hour sonicated hybrid composite after 12 hour sonication of hybrid composite, ftir shows difference in the peak positions. the peaks at 2915cm-1 and 2853cm-1 are for sp2 and sp3 c-h stretch and the peak at 1707cm-1 for c=o stretching. the peak at 1015cm-1 is attributed to si-o stretching of mmt. the peak of mmt is still visible in the hybrid composite; showing that mmt has been dispersed in the polymeric matrix. as the hybrid composite was prepared through sonication, mmt has not been intercalated in the polymer matrix but rather exfoliated (figures 4 and 5). ft-ir of 12 hour sonicated hybrid composite comparative ft-ir of block polymer ps-paa & 6 hour sonicated hybrid composite material e. ir characterization of composite material comparative the appearance of peak at 1031cm-1 is attributed to si-o bond, which is a characteristic peak for organoclay. the successful incorporation of organoclay can be seen by observing the decrease in h-bonding. the two layers of block are strongly merged with h-bonding. after incorporation of organoclay between two layers of block, an obvious decrease in h-bonding is observed. f. sem analysis of ps-paa hybrid composite (6-hour ultra-sonication) sem study of ps-paa hybrid composite incorporated with mmt reveals that the morphology of hybrid composite material shows porous surface. circulation and position of lattices over the surface show the unjumbled spines with somewhat rocky shape (figure 6). it further reports the nanofabrication with reference to the successful incorporation of organoclay over the composite material with different interfacial faces and edges. g. sem analysis of ps-paa hybrid composite (12-hour ultra-sonication) sem study of ps-paa hybrid composite material engineering, technology & applied science research vol. 8, no. 5, 2018, 3411-3415 3414 www.etasr.com soomro et al.: synthesis and characterization of poly(styrene)-block-poly(acrylic acid) and … incorporated with organoclay reveals that the morphology of hybrid composite material shows porous surface. circulation and position of lattices over the surface are like inside curved concaves with phase separation as shown in figure 7. sem images of organoclay and 6-hour ultra-sonicated ps-paa composite material sem images of 12-hour ultra-sonicated ps-paa hybrid composite material h. sem analysis comparative surface morphology declares the even distribution of organoclay (mmt) with ps-b-paa composite material. sem shows the phase separation and permeable surface of the hybrid composite material. mmt has diffusive properties at elevated temperatures. the material turns out to be significantly more grounded because of expanded support. to synthesize the composite material, filaments and layers of mmt are evenly adsorbed with help from the ultrasonic bath. organic polymers with physically blended mmt have circulation, similarity of lattices with unjumbled spines and some-what rocky shape while, after 12 hours they show the inside curved concaves. with the assistance of sem we decipher the morphological examinations at various optical zooms. the novel composite materials should be analyzed with sem to elucidate the surface morphology, porosity, transport and network similitude which had been refined successfully. sem pictures show permeable and penetrable surfaces (figure8). sem pictures disentangle the morphological surface territories and the physical adsorption occurring through the shedding between the layers of block copolymer and mmt organoclay. (a) (b) comparative 6-hour (a), and 12-hour (b) sem analysis of hybrid composite iv. conclusions polymeric composite materials of ps-b-paa ultrasonicated with mmt had been combined through 6-hour and 12-hour ultrasonication at various interims. the composite material was subjected to uv-visible to confirm the finished structure. the antecedents and novel composite materials were studied by infrared and sem techniques. the ft-ir spectrum confirms the incorporation of organoclay in the polymeric structure of ps and paa with mmt. sem pictures deciphered the surface morphology, porosity, circulation and similarity of framework and support in it, which had been accomplished effectively. references [1] f. j. doucet, c. schneider, s. j. bones, a. kretchmer, i. moss, p. tekely, c. exley, “the formation of hydroxyaluminosilicates of geochemical and biological significance”, geochimica et cosmochimica acta, vol. 65, no. 15, pp. 2461-2467, 2001 [2] a. j. erwin, w. xu, h. he, k. matyjaszewski, v. v. tsukruk, “linear and star poly (ionic liquid) assemblies, surface monolayers and multilayers”, langmuir,vol. 33, no. 13, pp. 3187-3199, 2017 [3] c. liu, h. qin, p. t. mather, “review of progress in shape-memory polymers”, journal of materials chemistry, vol. 17, no. 16, pp. 15431558, 2007 [4] c. sanchez, p. belleville, m. popall, l. nicole, “applications of advanced hybrid organic–inorganic nanomaterials from laboratory to market”, chemical society reviews, vol. 40, no. 2, pp. 696-753, 2011 [5] h. buhl, advanced aerospace materials, springer-verlag, 2012 [6] z. spitalsky, d. tasis, k. papagelis, c. galiotis, “carbon nanotube– polymer composites: chemistry, processing, mechanical and electrical properties”, progress in polymer science, vol. 35, no. 3, pp. 357-401, 2010 [7] r. n. boyd, “introduction”, in: stardust, supernovae and the molecules of life, springer science & business media, 2012 [8] c. e. carraher jr, carraher's polymer chemistry, crc press, 2010 [9] q. chaudhry, l. castle, r. watkins, nanotechnologies in food, rsc publishing, 2017 engineering, technology & applied science research vol. 8, no. 5, 2018, 3411-3415 3415 www.etasr.com soomro et al.: synthesis and characterization of poly(styrene)-block-poly(acrylic acid) and … [10] m. zebarjadi, g. joshi, g. zhu, b. yu, a. minnich, y. lan, x. wang, m. dresselhaus, z. ren, g. chen, “power factor enhancement by modulation doping in bulk nanocomposites”, nano letters, vol. 11, no. 6, pp. 2225-2230, 2011 [11] d. rawtani, y. k. agrawal, “multifarious applications of halloysite nanotubes: a review”, reviews on advanced materials science, vol. 30, no. 3, pp. 282-295, 2012 [12] k. n. prasad, b. yang, m. zhao, n. ruenroengklin, y. jiang, “application of ultrasonication or high ‐ pressure extraction of flavonoids from litchi fruit pericarp”, journal of food process engineering, vol. 32, no. 6 , pp. 828-843, 2009 [13] s. q. xie, j. wan, b. r. lu, y. sun, y. chen, x. p. qu, r. liu, “a nanoimprint lithography for fabricating su-8 gratings for near-infrared to deep-uv application”, microelectronic engineering, vol. 85, no. 5, pp. 914-917, 2008 [14] j. yang, s. z. he, l. q. wang, “dynamic balancing of a centrifuge: application to a dual-rotor system with very little speed difference”, modal analysis, vol. 10, no. 7, pp. 1029-1040, 2004 [15] j. lamontagne, p. dumas, v. mouillet, j. kister, “comparison by fourier transform infrared (ftir) spectroscopy of different ageing techniques: application to road bitumens”, fuel, vol. 80, no. 4, pp. 483488, 2001 [16] j. meng, “understanding cultural influence on price perception: empirical insights from a sem application”, journal of product & brand management, vol. 20, no. 7, pp. 526-540, 2011 microsoft word 10-2463_s1 engineering, technology & applied science research vol. 9, no. 2, 2019, 3918-3923 3918 www.etasr.com hung et al.: analyzing the dynamic characteristics of milling tool using finite element method … analyzing the dynamic characteristics of milling tool using finite element method and receptance coupling method jui-pin hung graduate institute of precision manufacturing national chin-yi university of technology taichung, taiwan hungjp@ncut.edu.tw wei-zhu lin graduate institute of precision manufacturing national chin-yi university of technology taichung, taiwan weijun@itri.org.tw kung-da wu graduate institute of precision manufacturing national chin-yi university of technology taichung, taiwan ffi85236@hotmail.com wei-cheng shih graduate institute of precision manufacturing national chin-yi university of technology taichung, taiwan z91150@hotmail.com abstract—this study aims to investigate the dynamic characteristics of a milling machine with different head stocks by using finite element (fe) method and receptance coupling analysis (rca). for this purpose, five full finite element machine models, including vertical column, reformed head stock and feeding mechanism were created. with these models, the tool point frequency response functions were directly predicted. another approach was the application of the receptance coupling method, in which the frequency response of the assembly milling tool was calculated from the receptance components of the individual substructures through the coupling operation with the interfaces of the feeding mechanism. results show that a whole machine model with reformed stock has superior dynamic behavior when compared with the original design, by an increment of 10% in the dynamic stiffness. the receptance coupling method was verified to show an accurate prediction of the frequency response functions of the spindle tool when compared with the results obtained from the full fe models. overall, the proposed methodology can help the designer to efficiently and accurately develop the machine tool structure with excellent mechanical performance. keywords-frequency response function; receptance coupling analysis method; spindle tooling system i. introduction virtual machine tool technology has been widely used in the design of innovative machine tools of various configurations [1]. basically, the kernel of the virtual machine tools was developed based on the integration of kinematics, structural dynamics, machining mechanics and the motion control of the machining dynamic system, which can help the designer to evaluate the motion precision and machining performance by means of implementation of the structural optimization and virtual machining into virtual machine tool technology [2, 3]. on other hand, the machining performance could be affected by poor situations due to the tool chattering during chip generation process. as a well-recognized fact, the machining performance is determined by the frequency characteristics of the machine tool structure and the dynamics of the cutting process [4-8], while the dynamic behavior of a machine tool system is determined by the machine frame structure, feeding and guiding system, and the spindle-tool holder-tool module, in particular the interaction of the vibration coupled with fundamental modes of the machine tool structure [9-10]. in general, improvement of the dynamic characteristics can be achieved in an easier way through the optimization of the feeding system with different specifications, instead of the modification of the machine frame structures. the main components and their properties that affect the static and dynamic characteristics of the milling tool system have been clarified, including the machine frame structure, linear components, feeding mechanism configuration, and spindle tool holder/tool modulus. besides, detail considerations of the selection of the spindle tool unit and the linear components in feeding mechanism are important for the design of a milling machine system with the desired performance [11, 12]. in an attempt to propose the improvement strategy of the machine tool system by maximizing machining stability, different approaches were developed for machine manufacturing to improve machine productivity and energy efficiency. the strategies include the use of new materials for the constructions of machine structures and design methodologies for machine frame configurations [13-17]. optimization criteria of the machine tool design have been carried out by incorporating the dynamics of machine tool with the consideration of machining stability in process [18]. corresponding author: j. p. hung engineering, technology & applied science research vol. 9, no. 2, 2019, 3918-3923 3919 www.etasr.com hung et al.: analyzing the dynamic characteristics of milling tool using finite element method … on the other hand, at design phase, the prediction of dynamic behavior of the spindle tooling system can be a complicated task when considering the change of the machine frame structure or structure configuration or the change of the linear components specifications. a number of significant developments have been completed to improve the tool and holder modeling techniques and understand the contact stiffness and damping behavior at connecting joints [19-26]. for example, authors in [20, 21] implemented the receptance coupling theory of structural dynamics by using experimentally obtained spindle–holder dynamics and analytically obtained tool dynamics for the prediction of the frequency response functions (frfs). authors in [23] and [24] also analyzed the effects on the frfs of spindle-holder and tool-holder interfaces respectively and suggested a fast and accurate approach for the identification of connection parameters. authors in [25] investigated the influence of overhang length of cutter on the frequency responses of spindle tool based on the receptance coupling operation method. the aim of this study is to investigate the effect of reformed spindle head stock on the dynamic performance of a machine tooling system by fe method. besides, considering analysis efficiency, frequency based coupling method was employed to predict the tool point frfs by coupling the feeding mechanism between head stock and the vertical column structure. through this investigation, the influence of the design configuration and specification of spindle tool unit can be clarified. also, the enhancement of the dynamic characteristics of machine tool before and after improvement can be quantified effectively. it is believed that the proposed methodology can help manufacturesr to develop a machine tool structure with excellent mechanical performance. ii. finite element modeling of a milling machine a. model description figure 1 illustrates the main components of a vertical milling machine, which includes a vertical column structure, spindle head stock, feeding mechanism and spindle tool module. to evaluate the dynamic behaviors of the milling machine, a three dimensional cad model was created by using solidworks software and then imported into the ansys workbench software to perform the simulation. the fem machine structure is shown in figure 1. each structural component of the system was meshed using an eight-node hexahedron and ten-node tetrahedral elements in a total of 130,850 elements and 451,533 nodes. regarding the linear components in the feeding mechanism of the spindle head stock, the ball screw and the linear guide modulus were included in the fe model since they demonstrated affecting the mechanical behaviors of the spindle heads [9, 10]. following the modeling method [9], the rolling interfaces between rolling balls and raceways were simulated as surface-surface contact elements with adequate contact stiffness. in this study, the rigidity of the linear guides is rated as 1000n/µm and 3000n/µm in horizontal and vertical directions respectively. the material properties of the structure components are ρ=7860kg/m3, young’s modulus e=200gpa and poisson’s ratio µ=0.3. modal and harmonic analysis were respectively conducted to assess the vibration modal shapes and frequency response functions. in fe governing equation for harmonic analysis, a modal damping ratio of 2.5 % was assumed for spindle dominant vibration mode. the frequency responses can then be predicted by applying a unit force at the end of the tool holder of the spindle. fig. 1. solid model and fe model of the vertical spindle tool system b. vibration modes and frequency response function according to the results of modal and harmonic analysis, the fundamental vibration modes of the vertical column spindle tool are illustrated in figure 2. these modes are associated with the vibration of the machine frame structure. for example, the first mode at about 43hz is the twisting vibration of the vertical structure about the z axis and the second mode around 107hz is associated with the yawing vibration of the spindle head, which may cause a great deformation of the spindle tool. the fourth mode is the yawing motion of the spindle head stock on the vertical column about the y axis. figure 3 shows the frequency response function of the spindle tool subjected to unit force at spindle nose, which is expressed in terms of the dynamic compliance at the tool end as a function of frequency. the frequencies ranging from 0 to 500hz are mainly dominated by the structure vibrations. it is also found that maximum compliance occurs at mode 1 and 2 around 43 and 107hz. the maximum compliance is about 0.285um/n and the maximum negative real part is about 0.14um/n. fig. 2. fundamental modal shapes of vertical spindle tool system. engineering, technology & applied science research vol. 9, no. 2, 2019, 3918-3923 3920 www.etasr.com hung et al.: analyzing the dynamic characteristics of milling tool using finite element method … fig. 3. frequency response function of the vertical spindle tool system c. structure effect of spindle head stock 1) reformed head stocks following the analysis results of the whole milling machine, the structure geometry of the spindle head was redesigned to enhance the stiffness of the spindle tool. the head stocks are shown in figure 4 with different stiffened ribs of different size. the weights of the 5 head stocks are listed in table i. to examine the effect of the spindle head structure on the dynamic compliances, 4 fe models of the milling machine with different reformed head stock were respectively created following the previous method. harmonic analysis was conducted on each whole machine model to assess the frfs for comparison. fig. 4. reformed head stocks with different stiffened ribs of different size. table i. head stocks comparison spindle head stock model weight (kg) original model i 272 stiffened model ii 308 stiffened model iii 298 stiffened model iv 297 stiffened model v 308 2) frfs predicted by full fe models the tool point frfs predicted from the vertical spindle tool model with different head stocks are illustrated in figure 5. as observed, the spindle tool shows similar vibration behaviors with two dominant modes at lower frequency ranges although it is equipped with head stocks of different design. as mentioned above, the first mode around 43hz is mainly the twisting vibration of the head stock and vertical column about the z axis. so it was found not to vary when the head stock changed. however, the second mode around 102-107hz is the yawing vibration of the head stock, which is related to the yawing motion of the linear guides on the vertical column [9]. it is noted that the frequency and compliance of this mode vary due to the change of the head stock. this clearly implies the effect of the spindle stock on the dominant vibration of the vertical spindle head. maximum compliances of the five spindle tool models are 0.287um/n at 107hz (original stock i), 0.263um/n at 103hz (stock ii), 0.259um/n at 105hz (stock iii), 0.270um/n at 103hz (stock iv) and 0.267um/n at 102hz (stock v), respectively. actually, differences in the frequency and compliance among these spindle tool systems are not so apparent, but the spindle with third stock indeed improve the structure performance, about 10% increment in the dynamic stiffness compared with the original one. as shown in figure 5, there are two vibration modes with significant amplitudes around 43hz and 107hz, in which the one at 107hz was selected as the base for evaluation of the machining stability since it is associated with the yawing vibration of spindle head and both frequency and amplitude are affected to different extent by the reformed head. according to machining mechanics [7], the machining stability is determined by the maximum value of negative real part of the frf. therefore, the difference of the machining stability of spindle tool with different head stocks can be assessed by comparing the real parts of the frfs. based on the real part of the predicted frfs, the machining stability of the milling tool can be expected to be increased by about 10% when the head stock is reformed to the third design from original one. fig. 5. predicted tool point frequency response functions of vertical spindle tool models with different head stocks. iii. frf prediction by rsca a. basic theory of receptance coupling method (rca) in this section, receptance coupling substructure analysis method (rcsa) was used to predict the frfs of the spindle tool with different head stocks, instead of the fe prediction with whole machine models. the vertical column and the feeding mechanism remained in the structure, only the spindle engineering, technology & applied science research vol. 9, no. 2, 2019, 3918-3923 3921 www.etasr.com hung et al.: analyzing the dynamic characteristics of milling tool using finite element method … head was reformed with stiffened ribs on stock housing. the vertical column spindle tool system (assembled structure ab) can be regarded as an assemble of the spindle head (substructure a) and the vertical column (substructure b) coupled by linear guide modules (joints) as shown in figure 6. fig. 6. schematic of the coupling of substructures, vertical column and spindle head stock. for substructure a, the relationship between the displacements of points 1, a2 and forces f1, fa2 can be expressed as: � ������ � � ��� ��� ��� ��� � �� ���� (1) where x1 and xa2 are the displacements at point 1 and a2 on substructure a. f1 and fa2 are the forces applied at point 1 and a2. ha11 and ha12 are the responses of the point 1 due to the excitation at point 1 and point 2 respectively. so the term haij represents the response of the point i caused by the excitation at point j, normally called the compliance function of the substructure a. for substructure b, the relationship between the displacement of point b2 and force fb2 is: �� �� � � ����� �� (2) where xb2 is the displacement at point b2 on substructure b. fb2 is force applied at point b2. hb22 represents the compliance function of the substructure b. when substructure a is combined with substructure b, we have: f2= fa2+fb2 ， x2= xa2= xb2 (3) the displacement of point 1 caused by force f1 can be obtained as follows: ��� � ���� � ��� � ���� ��� � ��� �� ��� (4) where h2=ha22+hb22 represents the coupled term of the substructure a and substructure b, and g11 is the frequency response function of the assembled structure due to the excitation f1. actually, the displacement components measured at each point on the substructures or assembled structure include the linear translation displacement (x) and the angular displacement (θ), which are caused by the force (f1) and moment (m1), respectively. the generalized relationship between the displacement vector ���� and force vector ���� can be expressed as follows: ���� � � x� θ� �;���� � ��� �� (5) taking the head stock (substructure a) as an example, we have the following expressions: [ ]             =       =       1 1 a1 1 1 1 m f pana laha m f θ x 1111 1111 11ha (6) 1 1 11 1 1 11 1 1 11 1 1 11 ;;, m ap f an m x al f x ah θθ ==== (7) where [ ]11ah represents the frequency responses matrix or component receptance matrix of substructure a. similar expressions are valid for the vertical column (substructure b) and the vertical spindle tool system (assembled structure ab). since the vertical column and spindle head stock are assembled together by the feeding mechanism, there is an elastic bonding between the two substructures. also, it is noted that the linear guide modules show important influences on the dynamic characteristics of the milling machine [9]. considering this elastic joint, the coupled effect should be included in (4) through the interface characteristics matrix [26]: �!"� � � !#$ �%&'#$ !($ �%&'($ !#) �%&'#) !() �%&'() (8) where kxf, kθf, kxm and kθm are the normal and rotational stiffness of the interface against the transverse force and moment. cxf ,cθf ,cxm and cθm are the damping coefficients of the interface associated with the normal and rotational degree of freedom, respectively. b. coupling operation of frfs the receptance compliance matrices of spindle head stock and vertical column can be respectively expressed as below: [ ] 1,2ji, ha ijij ijij ij =      = pana laha [ ]       = 2222 2222 hb pbnb lbhb 22 (9) direct or cross compliance components in receptance matrix such as haij and laij can be obtained by conducting harmonic analysis on the fe model of spindle unit and head stocks. these components are then used to derive naij and paij by finite difference approach [20]. figure 7 shows the frfs of the ha11 and la11, in which ha11 is the displacement of the spindle nose under the excitation force f1 and la11 is the displacement at mounted position of linear guides with vertical column under the moment m1 applied at the end point of tool holder respectively. it is noted that the reformed head stocks with different stiffened ribs have different structure characteristics. figure 8 shows the frfs of the hb22 and lb22, representing the displacements of the vertical column under the excitation force f2 and moment m2 applied at joints respectively. engineering, technology & applied science research vol. 9, no. 2, 2019, 3918-3923 3922 www.etasr.com hung et al.: analyzing the dynamic characteristics of milling tool using finite element method … fig. 7. frequency reponse functions of the head stocks (ha11 and la11) fig. 8. frequency reponse functions of the vertical column (hb22 and lb22) according to (4) and (8), the frequency response function at the spindle nose of the whole vertical spindle tool system can be predicted as follows: { } { } ( ) -1 -11 11 s 1 x k f 12 22 22 21bha ha ha h ha              = ⋅ + + ⋅               (10) as noted in (10), the interface characteristic matrix [ks] is the required parameter for the coupling operation. for this, the compliance matrices associated with the vertical spindle tool system with original head stock were input to the operation algorithm and hence the interface properties were identified by inverse coupling operation. c. frf comparison by fem and rcsa figure 9 illustrates the frequency response functions predicted by the whole machine models and calculated by rcsa. it can be found that for milling machines with different reformed head stocks, the frfs calculated by rcsa agree well with the fe predictions for whole machine models. fig. 9. comparison of the frfs predicted by the whole machine model and calculated by receptance coupling method. it is observed that for the first mode, the predictions of the compliance and frequency by the two approaches are almost the same, irrespective of the type of the reformed head stocks. this is due to the fact that this mode is affected by the linear feeding mechanism. however, for the second mode, there is a slight difference in the predicted frfs of the 5 machine models between the two methods, with maximum difference of 3.5%. this shows the reformed head stock has a slight influence on the interface characteristics of the coupling joints at the feeding mechanism, causing the prediction errors in coupling operation. overall, the results of the above analysis indicate that the rcsa in prediction of the frfs of the assembled structure is an efficient and accurate way in determining the structure performance when attempting to reform the machine tool at design stage. engineering, technology & applied science research vol. 9, no. 2, 2019, 3918-3923 3923 www.etasr.com hung et al.: analyzing the dynamic characteristics of milling tool using finite element method … iv. conclusion in this study, the dynamic characteristics of the spindle tool system were analyzed by employing a full fe model of the machine frame structure and spindle tool unit. the effect of the reformed spindle head stock was also examined through rcsa. the results show that appropriate reformed stocks indeed improve the structure performance, showing about 10% increment in dynamic stiffness or 10% reduction in dynamic compliance when compared with the original stock. according to the machining mechanics, the machining stability is determined by the maximum value of negative real part of the frf. based on the predicted frfs, the machining stability of the milling tool can be appropriately increased by reforming the head stock with stiffened ribs. additionally, rcsa was employed to calculate the frequency responses of the reformed spindle tool system based on the receptance components of vertical column and head stocks by introducing the interface characteristics into coupling operation. as a whole, the proposed methods were verified to show an accurate prediction of the frfs of the spindle tool for the improvement of the structure configuration. acknowledgment authors gratefully acknowledge the support provided by the national science council in taiwan through project number most105-2221-e-167-006. references [1] y. altintas, c. brecher, m. weck, s. witt, “virtual machine tool”, cirp annals, manufacturing technology, vol. 54, no. 2, pp. 115-138, 2005 [2] r. 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“modeling and identification of tool holder–spindle interface dynamics”, international journal of machine tools and manufacture, vol. 47, no. 9, pp. 13331341, 2007 [23] k. ahmadi, h. ahmadian, “modelling machine tool dynamics using a distributed parameter tool–holder joint interface”, international journal of machine tools and manufacture, vol. 47, no. 12-13, pp. 1916-1928, 2002 [24] e. budak, a. erturk, h. n. ozguven, “a modeling approach for analysis and improvement of spindle-holder-tool assembly dynamics”, cirp annals – manufacturing technology, vol. 55, no. 1, pp. 369-372, 2006 [25] x. j. xuan, z. h. haung, k. d. wu, j. p. hung, “prediction of the frequency response function of a tool holder-tool assembly based on receptance coupling method”, engineering, technology & applied science research, vol. 8, no. 6, pp. 3555-3560, 2018 [26] a. erturk, h. n. ozguven, e. budak, “analytical modeling of spindle– tool dynamics on machine tools using timoshenko beam model and receptance coupling for the prediction of tool point frf”, international journal of machine tools and manufacture, vol. 46. no. 15, pp. 19011912, 2006 microsoft word 7-2472_s_ca engineering, technology & applied science research vol. 9, no. 1, 2019, 3711-3714 3711 www.etasr.com jakhrani et al.: appraisal of climatic conditions for potential solar energy applications in nawabshah … appraisal of climatic conditions for potential solar energy applications in nawabshah and quetta cities abdul qayoom jakhrani department of chemical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan aqunimas@hotmail.com abdul rehman jatoi department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan arjatoi@quest.edu.pk muhammad moosa jakhrani department of electrical engineering, indus university, karachi, pakistan moosajakhrani@gmail.com abdul nasir laghari department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan mashaalnasirlaghari@gmail.com shakeel ahmed kamboh department of mathematics and statistics, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan shakeel.maths@yahoo.com abstract—this study was conducted to appraise climatic conditions for potential applications of solar energy units in nawabshah and quetta cities. for that, twenty two annual monthly average data of insolation on horizontal surface, at various slopes on titled surface, air temperature, earth skin temperature was acquired and evaluated through the statistical package for the social sciences software. it is discovered from the study that quetta is a more promising place for installation of solar energy applications as compared to nawabshah as it receives more solar radiations and less air temperature. keywords-air temperature; insolation; solar systems; climatic conditions i. introduction climate change influences severely the weather patterns of various countries by reducing precipitation or increasing temperatures [1]. a rise of 0.6°c-1.0°c in average temperature in coastal areas of pakistan has been reported since early 1900s [2]. it is important to mention that pakistan experienced a rise in temperature of around 0.47°c during 1960-2010 [1]. power sector is more susceptible to extreme weather conditions, predominantly electricity supply and demand [3]. currently, pakistan is confronting stern energy crisis and power failures [4]. the level of electricity dearth has jumped up to about 5000mw, which is being compensated by increasing load shedding from 8 to 14 hours per day. industrial development has also been slowed down having a negative impact on the economy of the country [3]. also, the provision of energy amenities needs to be extended to distant areas. alternative methods of providing energy at home could be arranged to supply uninterrupted power to these areas [4, 5]. this goal can be achieved by utilizing solar energy. solar energy is wholly dependent on climate conditions of the area and there are many climatic zones in pakistan [4, 6, 7]. the variety of climatic zones has profound effect on the availability of solar energy. climatic divisions of pakistan include highland, lowland, coastal and arid climates. even the division of climatic zones does not indicate accurately the same conditions throughout the zone as there are variants in rainfall, temperature, humidity etc. in similar climatic zones [8, 9]. nawabshah city is located almost at the geographical center of sindh province. the climate of nawabshah is hot to exceptionally hot during summer and cold and foggy during winter [10]. the highest temperatures in the city are typically climbing above 50°c from may to august. on may 26, 2010, the air temperature reached up to 52°c, which was the highest temperature ever recorded in nawabshah. on january 7, 2011, the temperature in the city dropped to 4°c. quetta city is the capital of balochistan province bordering along afghanistan [11]. the climate of quetta is dry and arid, and temperature variants significantly between winter and summer. it is hot in summers and mild to extreme cold in winter [12]. the highest observed temperature is around 42°c and the lowest -18.3°c [1]. to analyze the link between electricity consumption and climatic variables requires appropriateness of climate for any particular application. this work is an attempt to compare the weather variability on solar energy applications of nawabshah and quetta cities. ii. materials and methods comparison of nawabshah (26.3°n and 68.4°e), sindh and quetta (30.1°n and 67.0°e), balochistan weather parameters was made to realize their influence on solar energy application [10, 12, 13]. the meteorological data of both locations were acquired from [14]. the methodology adopted for the data comparison is given in table i. the appraisal was made with the help of spss software. corresponding author: a. q. jakhrani engineering, technology & applied science research vol. 9, no. 1, 2019, 3711-3714 3712 www.etasr.com jakhrani et al.: appraisal of climatic conditions for potential solar energy applications in nawabshah … table i. satellite data acquisition [10, 15] effect range type of database nasa sse 6 level global data inputs gewex/srb, 3 + isccp satellite, clouds + ncar, reanalysis length of data 1983–2005 time resolution 3-h spatial resolution 1 arc-degree x 1 arc-degree insolation satellite model diffuse part of radiation diffuse radiation model tilted surface (diffuse model) retscreen model iii. results and discussions annual monthly average insolation on horizontal and tilted surfaces is shown in figure 1. monthly average yearly insolation on horizontal surface was found to be 5.24kwh/m 2 /d in nawabshah [16] and 5.57kwh/m 2 /d in quetta. maximum value of insolation was recorded in may with 6.42kwh/m 2 /d in nawabshah and minimum in december with 3.75kwh/m 2 /d, whereas, in quetta, maximum insolation was recorded in june with 7.6kwh/m 2 /d and minimum in december with 3.3kwh/m 2 /d. similarly, monthly average minimum insolation on tilted surface was recorded as 4.68kwh/m 2 /d in nawabshah and 4.97kwh/m 2 /d in quetta. maximum value of insolation in nawabshah was recorded in may with 5.97kwh/m 2 /d and minimum in december with 3.34kwh/m 2 /d, while, maximum insolation in quetta was recorded in june with 6.82kwh/m 2 /d and minimum in december with 2.66kwh/m 2 /d. it is found that both monthly average and minimum insolation values on a horizontal and tilted surface were 6% more in quetta than in nawabshah. fig. 1 monthly average insolation on a horizontal surface and minimum on tilted surface. the average monthly insolation on tilted surface at different slopes for nawabshah and for quetta is shown in figures 2 and 3 respectively. at slope ±15° of the latitude of the location, the insolation was in between maximum and minimum values. the average monthly radiation incident on an equator-pointed tilted surface at optimum slopes for both locations is given in figure 4. it is concluded that quetta receives approximately 9% more annual monthly average solar radiations than nawabshah at optimum slope. in order to consider only worst and best situations at optimum slopes for both locations, monthly minimum average and maximum average radiations were considered and are illustrated in figure 5. it was found that quetta receives 7% more minimum radiation and 10% more maximum radiation than nawabshah. fig. 2 monthly average insolation on tilted surface at different slopes at nawabshah. fig. 3 monthly average insolation on tilted surface at different slopes at quetta. fig. 4 monthly average insolation on an equator-pointed tilted surface at optimum slope. monthly average yearly mean insolation on all slopes for both locations is illustrated in figure 6. it was found that both locations receive minimum amount of insolation at 0° slope and maximum at optimum slope. it was found that quetta receives 6% more minimum radiation at 0°, and 9% more maximum radiation at optimum slope than nawabshah. it has engineering, technology & applied science research vol. 9, no. 1, 2019, 3711-3714 3713 www.etasr.com jakhrani et al.: appraisal of climatic conditions for potential solar energy applications in nawabshah … been found that both locations could get maximum insolation at optimum slope. monthly average and yearly optimum slopes of both locations are depicted in figure 7. fig. 5 monthly averaged minimum and maximum insolation on tilted surface. fig. 6 monthly average yearly insolation on tilted surface. fig. 7 monthly average optimum slope for solar system mountings. it was found that optimum slopes of both locations are almost 2° less than that of their latitude. for example, nawabshah is located on 26.24°n latitude and its optimum average slope for solar system installations is 24.7°, while quetta is located on 30.25°n and its optimum slope is 38.3°. however, maximum slope of 53° was determined for nawabshah in december, and 57° for quetta in december. similarly, 0° was required for nawabshah from may to july, whereas, 0° slope from june to july is best for quetta. temperature is also an important parameter, after solar radiation, for the installation of solar systems, as it has negative relationship with the power output or efficiency of solar photovoltaic systems. therefore, monthly minimum and maximum average temperature of both locations are illustrated in figure 8. monthly average minimum yearly mean was found 20.7°c for nawabshah and 12°c for quetta, whereas, monthly average maximum yearly mean was 32.6°c for nawabshah and 23.9°c for quetta. monthly average air and earth skin temperature of both locations are illustrated in figure 9. monthly average mean air temperature was found 26.3°c for nawabshah and 18.0°c for quetta, whereas, monthly average mean earth skin temperature was 29.7°c for nawabshah and 21.5°c for quetta. it was found that quetta has 46% less average temperature and 38% less earth skin temperature than nawabshah. it is concluded from the study that quetta is a more favorable place for the installation of solar systems as it receives more solar radiation and has less air temperature. fig. 8 monthly average minimum and maximum air temperature. fig. 9 monthly average air and earth skin temperature. iv. conclusions monthly average insolation on horizontal surface was found to be 5.24kwh/m 2 /d in nawabshah and 5.57kwh/m 2 /d in quetta. monthly average insolation was found maximum at the optimum slope for both locations with 5.87kwh/m 2 /d for nawabshah and 6.38kwh/m 2 /d for quetta, whereas, minimum insolation was 5.18kwh/m 2 /d and 5.51kwh/m 2 /d for nawabshah and quetta respectively at 0° slope. it was found that the optimum slopes of both locations are almost 2° less engineering, technology & applied science research vol. 9, no. 1, 2019, 3711-3714 3714 www.etasr.com jakhrani et al.: appraisal of climatic conditions for potential solar energy applications in nawabshah … than their respective latitudes. however, maximum slope of 53° was determined for nawabshah and 57° for quetta. similarly, a minimum slope of 0° was required for both cities. the hottest month at nawabshah was observed to be may and the coldest was january, whereas, the hottest month at quetta was june and the coldest was january. it is found that quetta receives 6% more insolation on horizontal surface, and 9% more insolation at optimum slope than nawabshah. quetta also gets 6% more minimum radiation at 0°, and 9% more maximum radiation at the optimum slope than nawabshah. moreover, quetta has 72% less minimum temperature and 36% less maximum temperature than nawabshah. quetta also has 46% less average temperature and 38% less earth skin temperature than nawabshah. it is thus concluded that quetta is a more promising place for the installation of solar systems as it receives more solar radiations and less air temperature. references [1] i. h. durrani, s. adnan, m. ahmad, s. m. khair, e. kakar, “observed long-term climatic variability and its impacts on the ground water level of quetta alluvial”, iranian journal of science and technology, transactions a: science, vol. 42, no. 2, pp. 589-600, 2018 [2] m. j. iqbal, j. quamar, “measuring temperature variability of five major cities of pakistan”, arabian journal of geosciences, vol. 4, no. 3-4, pp. 595-606, 2011 [3] m. ali, m. j. iqbal, m. sharif, “relationship between extreme temperature and electricity demand in pakistan”, international journal of energy and environmental engineering, vol. 4, no. 1, pp. 1-7, 2013 [4] p. h. shaikh, f. shaikh, m. mirani, “solar energy: topographical asset for pakistan”, applied solar energy, vol. 49, no. 1, pp. 49-53, 2013 [5] a. q. jakhrani, a. k. othman, a. r. h. rigit, s. r. samo, “comparison of solar photovoltaic module temperature models”, world applied sciences journal, vol. 14, pp. 1-8, 2011 [6] a. q. jakhrani, a. k. othman, a. r. h. rigit, s. r. samo, “assessment of solar and wind energy resources at five typical locations in sarawak”, journal of energy and environment, vol. 4, no. 1, pp. 1-6, 2013 [7] a. q. jakhrani, s. r. samo, a. r. h. rigit, s. a. kamboh, “selection of models for calculation of incident solar radiation on tilted surfaces”, world applied sciences journal, vol. 22, no. 9, pp. 1334-1343, 2013 [8] s. bhakta, v. mukherjee, b. shaw, “techno-economic analysis of standalone photovoltaic/wind hybrid system for application in isolated hamlets of north-east india”, journal of renewable and sustainable energy, vol. 7, no. 2, pp. 1-15, 2015 [9] k. n. shukla, s. rangnekar, k. sudhakar, “comparative study of isotropic and anisotropic sky models to estimate solar radiation incident on tilted surface: a case study for bhopal, india”, energy reports, vol. 1, pp. 96-103, 2015 [10] a. q. jakhrani, a. r. h. rigit, m. m. jakhrani, s. a. channa, “comparative analysis of weather parameters at two locations for viability of solar energy systems”, quaid-e-awam university research journal of engineering, science & technology, vol. 14, no. 2, pp. 6468, 2015 [11] a. s. khan, s. d. khan, d. m. kakar, “land subsidence and declining water resources in quetta valley, pakistan”, environmental earth sciences, vol. 70, no. 6, pp. 2719-2727, 2013 [12] unicef, district development profile quetta, planning & development department, government of balochistan in collaboration with unicef, 2011 [13] m. ismail, a. alam, a. r. masud, m. hussain, h. rasheed, “optimal configuration of hybrid renewable energy system for remote areas of balochistan”, 17th ieee international multi topic conference, karachi, pakistan, december 9-10, 2014 [14] nasa, nasa surface meteorology and solar energy, available at: https://eosweb.larc.nasa.gov/sse/ [15] a. angelis-dimakis, m. biberacher, j. dominguez, g. fiorese, s. gadocha, e. gnansounou, m. robba, “methods and tools to evaluate the availability of renewable energy sources”, renewable and sustainable energy reviews, vol. 15, no. 2, pp. 1182-1200, 2011 [16] h. maammeur, a. hamidat, l. loukarfi, m. missoum, k. abdeladim, t. nacer, “performance investigation of grid-connected pv systems for family farms: case study of north-west of algeria”, renewable and sustainable energy reviews, vol. 78, pp. 1208-1220, 2017 microsoft word etasr_v13_n4_pp11235-11241 engineering, technology & applied science research vol. 13, no. 4, 2023, 11235-11241 11235 www.etasr.com alshehri et al: the efficacy of the strategy planning process criteria based on the fuzzy analytical … the efficacy of the strategy planning process criteria based on the fuzzy analytical hierarchy process reema alshehri department of computer science and artificial intelligence, college of computer science and engineering, university of jeddah, saudi arabia ralshehri0289.stu@uj.edu.sa (corresponding author) nahla aljojo information system and information technology department, college of computer science and engineering, university of jeddah, saudi arabia nmaljojo@uj.edu.sa areej alshutayri department of computer science and artificial intelligence, college of computer science and engineering, university of jeddah, saudi arabia aoalshutayri@uj.edu.sa ahmed alrashedi human resource department, business college, university of jeddah, saudi arabia akalrashde@uj.edu.sa abdullah alghoson information system and information technology department, college of computer science and engineering, university of jeddah, saudi arabia alghoson@uj.edu.sa azida zainol department of software engineering, college of business, technology and engineering, sheffield hallam university, united kingdom a.zainol@shu.ac.uk received: 11 may 2023 | revised: 27 may 2023 | accepted: 1 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6034 abstract this study investigated the strategic planning procedure used by the university of jeddah to determine which of its efficacy criteria are the most significant for future development. a university's performance is founded on its ability to capitalize on its specialization and set of skills obtained through meticulous planning and development and involves setting goals using analysis tools to compare options and prioritize constructs. evaluation approaches to strategic planning lack adaptability and durability. thus, a high-level deductive instrument that aggregates trade-offs and prioritizes the most essential aspects is needed. this study used the fuzzy analytical hierarchical procedure (fahp) to examine whether the university of jeddah's strategy formulation process improves strategy and planning. this study defined the objectives and criteria, established pairwise comparisons based on the owners of the strategic plan and the faculty and administration questionnaire responses, assigned weights to each criterion, verified their consistency, and ranked them in importance order. this study showed that fahp can help groups make strategic planning decisions in universities. engineering, technology & applied science research vol. 13, no. 4, 2023, 11235-11241 11236 www.etasr.com alshehri et al: the efficacy of the strategy planning process criteria based on the fuzzy analytical … keywords-fuzzy analytical hierarchy process (fahp); mcdm; university ranking; decision making; planning i. introduction universities want always to maximize the utilization of their specialties and competencies [1]. multi-criteria decisionmaking (mcdm) is crucial in achieving a long-term competitive edge in staff selection [2]. the fuzzy analytical hierarchy process (fahp) provides a more accurate definition of this type of process than the old ahp [3]. fahp is widely used in education for evaluation [4-9]. organizational decisionmaking and problem-solving can benefit from consensus-based strategic planning. like any approach, although it presents some challenges and restrictions on the time and effort required to solicit opinions from a wide range of interested parties, it can organize productive dialogue and ultimately establish consensus. competing ideas and interests at play can slow down the decision-making and execution processes, as they can make it difficult to accommodate and reconcile divergent opinions when members' interests are at odds or when there is an imbalance of power. this can result in judgments that aren't as strong as they could be and that don't adequately address the requirements and goals of all parties. the five strategic objectives of the university of jeddah are to improve the work and study conditions, provide an integrated learning journey based on excellence in teaching and research, empower distinctive individuals, improve the quality of its services and outputs, and confirm its leadership in many areas [10]. measuring the effectiveness of the techniques used to help people make decisions is crucial [11], as it could allow the development of a structured model designed to assist decisionmakers and selected specialists in dealing with complex problems, achieving consensus, and making the best decisions possible [12]. a hierarchical organization of the components of the problem is needed to analyze them objectively [13-14]. fahp is a modern analytical approach that employs a fuzzy number triangle to evaluate the values of criteria, making it an excellent method in mcdm that provides clear answers in paired matrices. fahp has been used in a variety of decisionmaking contexts due to its ability to classify the relative relevance of criteria that must be evaluated in stages [15-16]. pairwise comparison scales are based on triangular fuzzy numbers (tfn) [17-18], and fahp consists of a set of three values, such as a1, a2, and a3, representing the smallest, the most promising, and the greatest values, respectively [16]. this study aimed to evaluate the effectiveness of the strategic planning process of the university of jeddah by using fahp to identify key factors that influence its effectiveness and help it to achieve its strategic goals. as a result, this study aimed to investigate the factors influencing the effectiveness of the university of jeddah's strategic planning process, identify efficient tools for evaluating important criteria, and determine the most effective criteria. the fahp was used to assign numerical values to the twelve e-learning roadblocks and establish an order of dominance [19]. the main contributions of this study are:  to set a research goal to evaluate the efficiency of laboratory construction in higher education institutions and use its characteristics and fahp to create a system and model to do so.  to describe the key success factors of the criteria of the strategic planning process based on a fuzzy analytical hierarchy, considering the success of previous studies that used similar approaches [20]. many previous studies also followed this footprint to establish their findings [21-32]. a cause-and-effect diagram was used to identify and organize the causes and sub-causes of poor performance in a hospital and create a hierarchy using information obtained from experts, staff, and patients in [34]. the fahp method, which employs human cognition and judgment power based on knowledge and experience, was applied and used for decision-making to prioritize the major and sub-causes as potential improvement project topics. due to limited resources, the priorities corresponding to each major cause and sub-cause can be used to decide on the improvement of projects and their order. ii. methodology a. defining criteria and objectives the primary focus of this study was the application of a methodology that takes into account more than one criteria. this would make it much simpler to determine which of the significant effectiveness criteria have the greatest influence on achieving the university of jeddah's process of making important decisions according to its strategic planning. the criteria used were the main criteria and the subcriteria determined by the department of strategic planning and realization of the kingdom's vision 2030 which are accessible through the website of the university of jeddah. b. selection of experts and their opinions this study conducted a survey using a questionnaire to obtain the feedback of faculty members, administrators, and officials of the university of jeddah's strategic plan to carry out pairwise comparisons, finding out which aspects of the criteria and subcriteria are more important and how they differ from one another. the survey questionnaire was constructed using straight weights, such as agree, strongly agree, neutral, disagree, and strongly disagree, and there were a total of 61 responses. c. triangular fuzzy numbers the opinions are presented as tfn to represent uncertainty or ambiguity [6], as it is more effective to describe. tfn comes in the format a~= (l, m, u) and is defined as low, medium, and high, as shown in (1) [32]. table i shows the linguistic scale and the corresponding crisp value (1-9) for the fuzzy triangular scale. �� ��� = � �� � , 1 ≤ � ≤ �� � � , � ≤ � ≤ �0, otherwise (1) engineering, technology & applied science research vol. 13, no. 4, 2023, 11235-11241 11237 www.etasr.com alshehri et al: the efficacy of the strategy planning process criteria based on the fuzzy analytical … table i. linguistic terms and the corresponding triangular fuzzy numbers scale e definition tfn 1 equally important (eq. imp.) (1,1,1) ) 3 weakly important (w. imp.) (2,3,4) 5 fairly important (f. imp.) (4,5,6) 7 strongly important (s. imp.) (6,7,8) 9 absolutely important (a. imp.) (9,9,9) 2 the intermittent values between two adjacent scales (1,2,3) 4 (3,4,5) 6 (5,6,7) 8 (7,8,9) d. pairwise comparison matrix with triangular fuzzy elements equation (2) shows the fuzzy pairwise comparison matrix, related to the data obtained using the fahp linguistic variable scale given in table ii. �� = �� !" #$×$ = & �1,1,1� �'�(, ��(, ��(� ⋯ �'�$, ��$ , ��$��'(�, �(�, �(�� �1,1,1� ⋯ �'($, �($ , �($ �⋮ ⋮ ⋮�'$�, �$�, �$�� �'$( , �$(, �$( � �1,1,1� + (2) where: �� !" # = �'!" , �!" , �!" # = �� !" # � = , 1�"! , 1�"! , 1'"!, ., / = 1, ⋯ 0; ≠ / table ii. pairwise comparison matrix for decision-making criteria criteria c.1 c.2 c.3 c.4 c.5 c.6 c.7 c.1 1,1,1 1,1,1 1,2,3 1,1,1 1,2,3 1,1,1 1,2,3 c.2 1,1,1 1,1,1 1/3,1/2,1/1 1,1,1 1,1,1 1,1,1 1,1,1 c.3 1/3,1/2,1/1 1,2,3 1,1,1 1,1,1 1,2,3 1,1,1 1,2,3 c.4 1,1,1 1,1,1 1,1,1 1,1,1 1,1,1 1,1,1 1,1,1 c.5 1/3,1/2,1/1 1,1,1 1/3,1/2,1/1 1,1,1 1,1,1 1,1,1 1,1,1 c.6 1,1,1 1,1,1 1,1,1 1,1,1 1,1,1 1,1,1 1,1,1 c.7 1/3,1/2,1/1 1,1,1 1/3,1/2,1/1 1,1,1 1,1,1 1,1,1 1,1,1 e. defuzzification of the obtained matrices the defuzzification of all matrix elements was performed to facilitate the determination of the consistency ratio for each pairwise comparison using [33]: 345!67 = �8�9:9��; (3) table iii shows the de-fuzzification of the matrix's elements. table iii. de-fuzzified matrix decision-making criteria criteria c.1 c.2 c.3 c.4 c.5 c.6 c.7 c.1 1 1 2 1 2 1 2 c.2 1 1 0.5 1 1 1 1 c.3 0.5 2 1 1 2 1 2 c.4 1 1 1 1 1 1 1 c.5 0.5 1 0.5 1 1 1 1 c.6 1 1 1 1 1 1 1 c.7 0.5 1 0.5 1 1 1 1 f. checking the consistency ratio (cr) after estimating the importance of the criteria, the consistency ratio (cr) of the obtained matrix was checked using: <= = �>?@a $��$ �� (4) <b = cded (5) where λmax is the maximum eigenvalue, n is the number of criteria, and ri is the average random index. a cr of 0.1 (10%) was set to judge the stability of the opinions in the matrix. the lower the cr is than 0.1 shows more stability and noncontradiction, but when it crosses 0.1, the opinions should be rejected and returned to the questionnaire stage. table iv. ratio index n 1 2 3 4 5 6 7 8 9 ri 0 0 0.58 0.9 1-12 1.24 1.32 1.41 1.45 iii. results and discussion this study presented a significant criterion that was taken into account during the strategic planning process at the university of jeddah. the seven primary criteria that should be included in the strategic plan for the university of jeddah were determined, as well as their dimensions (sub-criteria), and the fahp was used to determine the order in which the criteria should be ranked. table v provides a summary of the weights of the criteria derived from pairwise comparisons and the rankings for the subcriteria that were considered. to calculate the general weight, for example, c1=0.167×0.185, where 0.185 represents the weight of the main criteria and 0.167 is the local weight of the sub-criterion, the general weights of all listed criteria were determined and the results showed that c 1.1 was classified as the most important factor that affects the performance of the university's strategic planning process. table vi shows a list of the criteria in priority order. this study established the objectives and criteria necessary to carry out the fahp study, which is an effective method in mcdm because it gives clear results in pairwise matrices. fahp uses tfn to evaluate the criteria values and make pairwise comparisons based on the questionnaire responses from the strategic plan's owners and the university of jeddah faculty and administration. it is vital to define and assign weights to each criterion before determining whether or not they are consistent and placing them in the order of significance. based on these findings, fahp may prove to be an advantageous tool for the strategic planning needs of student organizations. engineering, technology & applied science research vol. 13, no. 4, 2023, 11235-11241 11238 www.etasr.com alshehri et al: the efficacy of the strategy planning process criteria based on the fuzzy analytical … table v. determined global ranks of the criteria. main criteria weight ranking subcriteria local weight of subcriteria local rank global weight of criteria global rank c 1 0.185 1 c 1.1 0.167 1 0.0308 1 c 1.2 0.104 7 0.0192 26 c 1.3 0.138 5 0.0256 8 c 1.4 0.167 2 0.0308 2 c 1.5 0.141 4 0.0260 6 c 1.6 0.132 6 0.0244 13 c 1.7 0.151 3 0.0279 3 c 2 0.128 5 c 2.1 0.142 3 0.0181 29 c 2.2 0.142 4 0.0181 30 c 2.3 0.156 1 0.0199 18 c 2.4 0.142 5 0.0181 31 c 2.5 0.144 2 0.0184 28 c 2.6 0.131 7 0.0167 41 c 2.7 0.142 6 0.0181 32 c 3 0.174 2 c 3.1 0.142 3 0.0247 9 c 3.2 0.142 4 0.0247 10 c 3.3 0.155 1 0.0269 4 c 3.4 0.142 5 0.0247 11 c 3.5 0.121 7 0.0210 15 c 3.6 0.155 2 0.0269 5 c 3.7 0.142 6 0.0247 12 c 4 0.138 3 c 4.1 0.142 3 0.0195 19 c 4.2 0.155 1 0.0213 16 c 4.3 0.142 4 0.0195 20 c 4.4 0.121 7 0.0166 45 c 4.5 0.155 2 0.0213 17 c 4.6 0.142 5 0.0195 21 c 4.7 0.142 6 0.0195 22 c 5 0.119 6 c 5.1 0.13 5 0.0154 47 c 5.2 0.141 2 0.0167 42 c 5.3 0.141 3 0.0167 43 c 5.4 0.187 1 0.0222 14 c 5.5 0.13 6 0.0154 48 c 5.6 0.13 7 0.0154 49 c 5.7 0.141 4 0.0167 44 c 6 0.138 4 c 6.1 0.187 1 0.0258 7 c 6.2 0.13 5 0.0179 33 c 6.3 0.141 2 0.0194 23 c 6.4 0.13 6 0.0179 34 c 6.5 0.13 7 0.0179 35 c 6.6 0.141 3 0.0194 24 c 6.7 0.141 4 0.0194 25 c 7 0.119 7 c 7.1 0.131 3 0.0155 46 c 7.2 0.143 2 0.0170 36 c 7.3 0.143 2 0.0170 37 c 7.4 0.143 2 0.0170 38 c 7.5 0.143 2 0.0170 39 c 7.6 0.143 2 0.0170 40 c 7.7 0.156 1 0.0185 27 the implications of this study depend on the analysis of the criteria. the "local weight of sub-criteria" and the "global weight of criteria" both investigate the actual circumstances. the weights indicate that the most important decision criterion is "providing qualitative programs to keep ahead of local, regional, and worldwide developments", indicating the improvement of people's lives through the provision of college programs that have been verified for their quality level and meet the requirements of the labor market. it is also essential to establish a unique learning and research environment to maintain and improve the number of academics and scientists, although local gatherings, beneficial friendships, and common objectives and views are also components of essential concerns. despite this, high-tech decision-support tools related to the rules of good governance are essential for a productive academic culture, in addition to encouraging the growth of new firms, young people, and creative endeavors. the predictions of strategic planning using fahp are subjected to several biases, assumptions, limits, and problems. one of the most crucial is that the power of the study could be compromised due to insufficient sample size or lack of representation. a not representative sampling of the population being studied may introduce bias and lack of generalizability, as the criteria and options considered may potentially be subject to bias. fahp is founded on the availability and quality engineering, technology & applied science research vol. 13, no. 4, 2023, 11235-11241 11239 www.etasr.com alshehri et al: the efficacy of the strategy planning process criteria based on the fuzzy analytical … of data. erroneous judgments and forecasts may be made based on incomplete, out-of-date, or unreliable data. acquiring accurate and thorough data is a time-consuming and arduous process, and it can be difficult or controversial to put fahp estimates and strategic objectives into action. adoption of strategies could be hampered by the reluctance to change. strategic planning may need to be adjusted as a result of stakeholders' openness to change, resource constraints, administrative hurdles, or unanticipated events. strategic planning that incorporates a comprehensive fahp analysis requires a substantial investment of resources and expertise, and the depth of the analysis can be constrained by available resources. it is essential to communicate limitations, as researchers can more realistically evaluate results and suggestions if they are aware of and take into account any biases, assumptions, and constraints. this study also pinpoints areas for further study and improvement within the strategic framework of the university of jeddah and other higher education institutions. table vi. list of criteria in priority order code criteria rank c 1.1 providing qualitative programs to keep abreast of local, regional, and global updates 1 c 1.4 supporting job opportunities for university graduates by making fruitful partnerships with relevant authorities 2 c 1.7 activating field training and experiential learning activities in the work environment 3 c 3.3 enabling the students to train on practice community activities related to national issues 4 c 3.6 establishing training centers to provide advanced programs and courses for all segments of society 5 c 1.5 adopting and nurturing talented and outstanding people through specialized quality programs and services 6 c 6.1 develop programs to attract talented people and create the appropriate environment to develop their skills 7 c 1.3 continuous evaluation to measure the level of development of university program outputs 8 c 3.1 building diverse cooperation and partnership relationships with community institutions and business organizations 9 c 3.2 providing society with its needs with the qualified human resources commensurate with the future development of the professions 10 c 3.4 linking the university with productive institutions in a reciprocal social and developmental relationship 11 c 3.7 exchanging the dissemination of the fruitful participatory culture between the university and the community 12 c 1.6 designing specialized programs to qualify students with special needs 13 c 5.4 achieving credibility, transparency, and commitment to defined policies and stated promises 14 c 3.5 employing the university's possibilities for community development and parallel activities 15 c 4.2 upgrade the level of information security in the university's electronic work system 16 c 4.5 use of data and information effectively to predict crises and solve problems 17 c 2.3 directing scientific research and graduate programs toward areas that serve national issues 18 c 4.1 develop data and information management systems to serve workflow in all fields 19 c 4.3 establishing information centers that contribute to decision-making and performing tasks effectively 20 c 4.6 provide programs and modern technologies that help in the provision and development of academic programs 21 c 4.7 integrating electronic services for all sectors of the university in all fields 22 c 6.3 sponsoring business incubators for small projects to motivate individuals and community development 23 c 6.6 building strategic partnerships that support innovation and creativity and provide pioneering programs for entrepreneurship 24 c 6.7 developing talents and creating creativity by creating an environment that incubates ideas and innovations 25 c 1.2 develop faculty members, curricula, and educational methods according to international standards 26 c 7.7 increasing financial returns and university revenues by providing opportunities to enroll in its paid academic programs 27 c 2.5 attracting researchers and scientists to produce and invest in advanced knowledge 28 c 2.1 supporting and motivating distinguished scientific research and regional and international publication 29 c 2.2 encouraging the formation of scientific teams and specialized research groups 30 c 2.4 establishing scientific and medical research centers that contribute to sustainable local development 31 c 2.7 employing the results of applied research in the flourishing of the knowledge economy 32 c 6.2 developing the capabilities of faculty members to discover the talents and abilities of students and ways to enhance them 33 c 6.4 supporting the creative abilities and skills of university employees according to international standards 34 c 6.5 providing an environment that enhances creativity and innovation in the technical industries and entrepreneurship 35 c 7.2 supporting projects and initiatives that contribute to the development of the university's resources 36 c 7.3 legalization of public spending and reducing wastage to achieve fiscal balance 37 c 7.4 sustainability of university services by conducting periodic maintenance on its properties and facilities 38 c 7.5 involving the private sector in investing in the various sectors of the university 39 c 7.6 diversifying sources of self-financing by establishing scientific and medical endowments 40 c 2.6 increasing investment in the field of scientific research by establishing effective partnerships with the government and private sectors 41 c 5.2 determining academic, administrative, and financial priorities and references according to regulations that ensure no conflict of interest 42 c 5.3 improving the degree of satisfaction of the beneficiaries of the university services; finding solutions to obstacles and procedural problems 43 c 5.7 establishing effective oversight mechanisms for the university sectors to promote a culture of accountability and accounting 44 c 4.4 improving data and information analysis systems to invest in opportunities and interact with challenges 45 c 7.1 initialization appropriate opportunities for investment in the university's facilities and services 46 c 5.1 restructuring of administrative systems and processes to raise the productivity of academic, administrative, and financial performance 47 c 5.5 evaluate the performance of various practices according to global performance indicators updated periodically 48 c 5.6 distributing the university’s available resources to different sectors and activities according to specific criteria 49 engineering, technology & applied science research vol. 13, no. 4, 2023, 11235-11241 11240 www.etasr.com alshehri et al: the efficacy of the strategy planning process criteria based on the fuzzy analytical … strategic planning by fahp has its flaws, assumptions, restrictions, and problems. an essential problem is the small size and lack of representation of the sample. the capacity to generalize and avoid bias toward particular concepts or groups may be compromised by the lack of suitable size or representational sampling, as there is a potential for bias in the evaluation of criteria and options. fahp relies on access to high-quality data. conclusions and predictions based on inaccurate, out-of-date, or otherwise unreliable information should be treated with caution. it takes a lot of time and effort to collect reliable information that is useful for strategic planning. furthermore, putting fahp projections and longterm plans into action could prove difficult or divisive. adoption of a new strategy may be slowed by resistance to change. the adaptability of stakeholders, the scarcity of available resources, bureaucratic roadblocks, and unanticipated events are all factors that could affect strategic planning. a lack of resources could prevent an in-depth investigation. limits should be communicated. researchers can realistically assess the results and proposals of the study after being aware of these limitations, biases, and assumptions. opportunities for further study and improvement are also highlighted, all within the context of the institution's strategic plan. in conclusion, it is essential to diversify programs, endowments, and educational offerings to ensure the continued viability of the program over the long run. it is also very crucial to have a high-quality updating program that promotes scientific research and publication both regionally and globally, to develop a variety of community and business connections, in addition to adding value to the workflow. iv. conclusion this study used the fahp method as a multicriteria tool for decision-making, given its ability to enable a systematic examination of trade-offs. as a result, it was able to identify the 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[36] m. a. akbar et al., "prioritization based taxonomy of devops challenges using fuzzy ahp analysis," ieee access, vol. 8, pp. 202487–202507, 2020, https://doi.org/10.1109/access.2020.3035880. microsoft word 23-3801_s_etasr_v10_n5_pp6270-6275 engineering, technology & applied science research vol. 10, no. 5, 2020, 6270-6275 6270 www.etasr.com more & mishra: enhanced-pca based dimensionality reduction and feature selection for real-time … enhanced-pca based dimensionality reduction and feature selection for real-time network threat detection pournima more department of computer science and engineering koneru lakshmaiah education foundation vaddeswaram, andhra pradesh, india pournima.more1@gmail.com pragnyaban mishra department of computer science and engineering koneru lakshmaiah education foundation vaddeswaram, andhra pradesh, india pragnyaban@kluniversity.in abstract-with the rise of the data amount being collected and exchanged over networks, the threat of cyber-attacks has also increased significantly. timely and accurate detection of any intrusion activity in networks has become a crucial task. while manual moderation and programmed logic have been used for this purpose, the use of machine learning algorithms for superior pattern mapping is desired. the system logs in a network tend to include many parameters, and not all of them provide indications of an impending network threat. the selection of the right features is thus important for achieving better results. there is a need for accurate mapping of high dimension features to low dimension intermediate representations while retaining crucial information. in this paper, an approach for feature reduction and selection when working on network threat detection is proposed. this approach modifies the traditional principal component analysis (pca) algorithm by working on its shortcomings and by minimizing false detection rates. specifically, work has been done upon the calculation of symmetric uncertainty and subsequent sorting of features. the performance of the proposed approach is evaluated on four standard-sized datasets that are collected using the microsoft sysmon real-time log collection tool. the proposed method is found to be better than the standard pca and fast methods for data reduction. the proposed approach makes a strong case as a dimensionality reduction and feature selection technique for reducing time complexity and minimizing false detection rates when operating on real-time data. keywords-principal component analysis; fast clustering; dimensionality reduction; machine learning; network security i. introduction and related work network security is of utmost importance, especially for companies or foundations. any security breach will be characterized by a pattern in the network logs preceding the attack and these patterns, if detected accurately, can help diverting major mishaps [1]. previous approaches have relied upon the use of security intelligence and management systems (siems) coupled with manual moderation for scanning network threats. siems are associated with security operations center (soc) to whom they report these threats [23]. they conform to the laws on risks and regulation criteria and make use of predefined rules for catching any network breach or incident response (ir). however, similar to manual moderation, there are certain limitations in the use of siems. they operate on a static set of vulnerability rules and hence are not able to detect any trends of a novel attack. further, they are associated with an operational overhead and hence come up short when working with real-time data. the performance of socs has worsened over the years and they are no longer sufficient when working with large scale networks. machine learning algorithms help in deriving rules and making accurate predictions even on previously unseen data. the behavioral features of the system logs can be used for attack detection. however, the system logs consist of many parameters and not all of them contribute to the detection of network threats. previously, methods like principal component analysis (pca) and fast clustering have been used for eliminating the redundant features from high dimensional data [3, 4]. while pca focuses on the derivation of a set of orthogonal eigen vectors, fast clustering focuses on an efficient but less effective grouping of features. in this paper, an approach for dimensionality reduction and feature selection is proposed which ameliorates the shortcomings of the pca algorithm and improves the performance of the system. specifically, fast and pca approaches were combined in a novel way and subsequently machine learning algorithms were used for detecting anomalies that deviate from normal configurations, hence predicting possible threats to the system. the main contributions in this paper are: • the formulation of a new approach for dimensionality reduction and feature selection that improves standard conventional approaches. • the combination of fast and pca algorithms in a unique manner for efficient, yet effective dimension mapping. • a network threat detection approach that has better performance than the previous approaches when working on a real-time data set. there has been ample work in the past on anomaly detection on unseen data [5-9]. most of this work can be segregated into three types based on their nature: statistical, corresponding author: pournima more engineering, technology & applied science research vol. 10, no. 5, 2020, 6270-6275 6271 www.etasr.com more & mishra: enhanced-pca based dimensionality reduction and feature selection for real-time … distance, and density-based techniques. each of these three methods has some shortcomings. statistical methods often assume univariate distribution which is most often not true with real-world data. distance-based methods struggle with overlapping data, while density-based methods may be useful but are computationally very expensive. authors in [10] proposed a primitive regression method to detect the presence of unauthorized users masquerading as registered users by comparing their activity to the previous actions from those accounts. various unsupervised learning algorithms have been applied, however, most of them have huge memory requirements [2, 11]. clustering has been used [12-14], but incorrect grouping would lead to higher risk of false negatives. as a result, dimensionality reduction becomes a crucial part of the process and thus the majority of approaches have focused on the use of pca for this task [3, 15]. pca aims to derive new variables, called main components (pcs) as linear input variable combinations so that a few of the new variables reflect the overall variation between the input variables. authors in [19, 20] provide a network intrusion prevention approach that tackles the problem of controlling high computer network traffic and the time pressure to handle security threats. they use the techniques of multivariate analytics, including clustering and pca to identify classes in the observed data. the use of pca is appealing due to its statistical consistency, faster inference, and effective computation [11]. yet there has been valid criticism in its use for network intrusion detection due to several reasons like struggle with rare class labels, exponential complexity, etc. [4, 7]. examples of this are [18, 19] where a combination of recorded variation and the screen-plot process were used for selecting the key components which may be risky as some anomaly amongst lesser-known components may be ignored. the existence of unusual data from regular operations is seen in [20] where the criteria of choosing components for pca remain unanswered. a large number of variables could be reported to explain network traffic behavior [21]. for example, authors in [22] assume a certain expectation for collection methods for the variable. typically, every input variable has a non-zero factor on all pcs. however, in practice, it is common that the majority of the component loadings is close to zero [23] and is of less practical significance. recently there have been proposals of some hybrid approaches [24-26] but they have a higher training and inference cost, with increased complexity. wormhole attacks have been tackled using separate routing [27] but the method does not work in structured log data. while synthetic oversampling and under sampling approaches may work well on text data [28], they are often detrimental to structured network log data. hence it can be seen that there is a need for improving the shortcomings of the previous methods and come up with a more accurate and efficient solution. ii. proposed methodology in this paper, we work upon an enhanced feature selection and reduction technique that ameliorates the shortcomings of the previous approaches. the diagrammatic representation of the proposed algorithm is shown in figure 1. the phases on the algorithm are defined in the following subsections. fig. 1. diagrammatic representation of the proposed algorithm. a. log files and feature extraction the microsoft sysmon log process collection tool was utilized for extracting the logs from the given system. these logs are collected in real-time and have a certain number of input attributes associated with them. these attributes are described in detail below. the data features are stored together in a matrix format for subsequent processing. b. calculation of symmetric uncertainty symmetric uncertainty (su) is used to obtain the selection of features by calculating the fitness of the features between the feature and the target class. symmetric uncertainty is defined as: 2*gain( | ) su( , ) ( ) ( ) x y x y h x h y = + (1) where gain(x|y) is the amount by which the entropy of the variable y decreases. h(x) is the entropy of a discrete random variable x. if the prior probability of each element of x is p(x), then h(x) can be calculated as: h��� � �∑ p� � log p� ��∈� (2) the entropy value takes care of any associated bias amongst the features with large values and also normalizes them to a range of [0, 1]. an su value of 1 indicates that the information value of the one variable is fully represented by the other, whereas a 0 value of su(x, y) indicates that x and y are independent variables. such mathematical representation also helps normalizing continuous features to a discrete form. these su values are used for the calculation of the eigenvalues and the eigenvectors. engineering, technology & applied science research vol. 10, no. 5, 2020, 6270-6275 6272 www.etasr.com more & mishra: enhanced-pca based dimensionality reduction and feature selection for real-time … c. eigenvalues and eigenvectors eigenvalues are used to calculate the dependency of features and their correlation with the class values. the eigenvector with the highest uniqueness is considered as the most characteristic feature implying the highest variance [4]. similarly, the second most unique vector is considered as the second characteristic principal variable with information retention. in this way, the top n eigenvectors are calculated and represented using a co-occurrence matrix. n indicates the higher contribution rate amongst all the eigenvectors. if m is a n×n matrix, then v is considered as the eigenvector of m if: m ×v = λ (3) where λ is the eigenvalue associated with v. for the given eigenvector v of m, given a scalar a: a aλ× =m v v (4) n different eigenvectors can always be chosen such that they collectively account for a unit length: 2 2 1 ... 1 n v v+ + = (5) the n eigenvectors are always orthogonal to each other. thus, they can be used as the basis for the formulation of a new n-dimensional vector space. it is crucial to analyze the security of information from different unknown sources or attacks [10]. a fixed policy can never detect new different threats that are created. this examination can be done on different network trees. once the fast calculations of su are done, the representation of the method is done by us using the pca method. a multidimensional hyperspace is hard to visualize. the key objectives of the unsupervised learning approaches are to minimize dimensionality, ranking all identifications based on a composite index, and clustering related identifications based on multivariate attributes together. since it is difficult to imagine a multidimensional space, pca is used to scale down the dimensionality of multivariate parameters into three dimensions. in this paper, pca is used for multivariate analysis. the data set can be represented as a matrix x with n rows and m columns, the sample rows, and the attribute columns. some multivariate methods presume a structure, while others separate the cases into classes trying to figure out the structure of data. the former is a case of supervised learning while the latter indicates unsupervised learning. in pca, the interrelated multivariate parameters are mapped to a set of non-related components, each expressing a distinct linear combination of the main variables. the nonrelated components extracted are the pcs and are predicted from the covariance matrix's main variables' ownership. pca aims to obtain providence and minimum dimensionality by extracting the smallest number of pcs that account for most of the variation in the main multivariate information and summarizing the data with minimum information loss. the variance of an attribute is defined as: )1( )( )var( 1 2 1 − − = ∑ = n xx a n i i (6) in this method, the last principal component score needs to be zero. all the given variables are scattered on a hyper plane. if there is any update in the interrelations, there may be an extension of the information outside the hyper plane. this is reflected in the updates of the principal component scores that were previously zero. nil scores are the most sensitive to updates in the interrelations. the main component scores are powerful in observing any updates to the information. pca performs normal data circulation by selecting a suitable orthogonal coordinate. the range of the main rectangular factor scores is more suitable for expressing normal data distribution than those of the sensed and actuated initial orthogonal coordinates. d. threshold calculations after the eigenvectors are calculated, they are sorted in descending order and the feature class mean value is calculated. this value is used for deciding the threshold value for obtaining the features. the following algorithm indicates the entire process followed by the enhanced pca algorithm. input: input attribute matrix x ∈ x1, x2,...,xn, output y, threshold t output: reduced representation s 1. for each xi in x do 2. calculate h(xi) 3. calculate su(xi,y) 4. calculate variance(xi) 5. endfor 6. sort all variances in descending order 7. calculate eigenvalues λ1, λ2,…. λn 8. calculate subsequent v ∈ v1; v2; ::; vn 9. for each vi in v do 10. if vi > t do 11. s.append(vi) 12. endif 13. endfor 14. return s iii. dataset description for evaluation using a real-time dataset, data were collected from logged data using the microsoft sysmon data collector tool [30]. it provides the information of certain parameters present in the network, considered as the input variables for the network intrusion detection task. for a more generalized evaluation and elimination of bias, we collect four different sets of data each of varying sizes. the individual sizes of each of the dataset are: • dataset 1: 1000 • dataset 2: 1200 • dataset 3: 800 • dataset 4: 361 the total dataset size accounts for 3361 samples. each of the datasets is split into a training set and a testing set in a 3:2 ratio. for every sample in the dataset, there are 22 variables engineering, technology & applied science research vol. 10, no. 5, 2020, 6270-6275 6273 www.etasr.com more & mishra: enhanced-pca based dimensionality reduction and feature selection for real-time … associated with it indicating the corresponding configuration. these variables are described in table i. table i. description of the input attributes parameter description process name 1. name of the process login time login time with 8 segmentations, three hours each: 2. 12pm-3pm 3. 3pm-6pm 4. 6pm-9pm ............. 9. 9am-12pm browsing history 10. urls being browsed (if any) network transfer 11. uploading 12. downloading days of the week 13. current day frequency 14. no. of executed processes spam mail keywords 15. credit card 16. loan 17. offer 18. monsoon 19. sale 20. winning 21. money 22.prize iv. results and discussion the obtained results are presented on two different levels: the output of the dimensionality reduction and the obtained performance on task-specific performance metrics. while the output variables received by the dimensionality reduction algorithm can be variable, we judge their effectiveness by comparing the results with those obtained by the models that use other dimensionality reduction methods. table ii indicates the output variables determined by the proposed approach to be deemed most important and relevant to the task in hand. the threshold was set to 66% and thus the total number of variables was reduced to 15. table ii. output parameters derived by the proposed algorithm parameter no. output parameter name 1 name of the process 9 9am-12pm 3 3pm-6pm 11 uploading 7 3am-6am 15 credit card 5 9pm-12pm 17 offer 2 12pm-3pm 10 browsing history 6 12am-3am 12 downloading 21 money 19 sale 16 loan the performance of the proposed approach is evaluated with two different metrics: accuracy and inference time. these are defined in (7) and (8): accuracy= ��: �� ��������� ��������� � !���� "�� � #�: �� � !���� (7) inference time = $%&'(&' – $)*(&' (8) inference or prediction time is defined as the amount of time required for the system to output the prediction for a given input set. it is found by subtracting the time frame when the input was given from the time frame when the output was predicted. the results of the proposed approach for each of the four datasets for the three methods (fast, pca and enhanced pca) are compared. the accuracy obtained for the three approaches is shown in table iii. it can be seen that the proposed approach has outperformed the standard approaches and has a healthy growth over the use of the normal pca approach. in table iv the evaluation of the tested methods in terms of inference time is shown. it can be seen that while the proposed approach is not the best regarding inference time, it still performs better than the pca algorithm. while the fast algorithm has faster inference time, the proposed approach is better in terms of accuracy, which is more important in the case of network intrusion detection systems. the graphical comparison of the three approaches in terms of accuracy and inference time is shown in figures 2-3. thus our proposed approach has been able to get the right mix of effectiveness and efficiency. table iii. accuracy (%) of the tested algorithms dataset fast pca enhanced pca (proposed) dataset 1 90 87 92 dataset 2 90 88 92 dataset 3 88 88 89 dataset 4 94 90 96 table iv. inference time (ms) dataset fast pca enhanced pca (proposed) dataset 1 350 420 370 dataset 2 360 530 380 dataset 3 350 440 430 dataset 4 270 315 260 fig. 2. accuracy comparison. v. conclusion in this paper, a new approach was presented for the dimensionality reduction and the subsequent prediction of any intrusion threats to a network system. we were able to minimize time complexity and false detection rates, especially on a real-time data set. engineering, technology & applied science research vol. 10, no. 5, 2020, 6270-6275 6274 www.etasr.com more & mishra: enhanced-pca based dimensionality reduction and feature selection for real-time … fig. 3. inference time comparison. the proposed approach derived inspiration from the traditional pca algorithm but ameliorated its shortcomings and improved further its performance. specifically, we made use of symmetric uncertainty, entropy, and associated factors to boost the working of the feature selection pca algorithm. the sysmon tool was used for the collection of data. the performance of the proposed approach was evaluated on four different datasets and was compared with the standard pca and fast approaches. the proposed approach was found to be more accurate while possessing a satisfactory inference time. an increment of over 2% was observed in terms of accuracy as compared to the standard approach. the reduction time was faster than the regular pca approach by more than 15% in all cases. the proposed approach was proved to be a more preferred method than the previous approaches. future work in this domain includes working upon other machine learning algorithms to couple with the dimensionality reduction method for enhanced results. other preprocessing methods can also be used so that the initial variables are made 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[30] m. russinovich and t. garnier, “sysmon v11.11,” jul. 15, 2020. https://docs.microsoft.com/en-us/sysinternals/downloads/sysmon (accessed sep. 12, 2020). microsoft word 32-2354_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3541-3544 3541 www.etasr.com latreche et al: implementation of mppt algorithm and supervision of shading on photovoltaic module implementation of mppt algorithm and supervision of shading on photovoltaic module samia latreche automatic laboratory, electrical engineering department, ferhat abbas setif university 1, (ufas1), setif, algeria ksamia2002@yahoo.fr abd essalam badoud automatic laboratory, electrical engineering department, ferhat abbas setif university 1, (ufas1), setif, algeria badoudabde@yahoo.fr mabrouk khemliche automatic laboratory, electrical engineering department, ferhat abbas setif university 1, (ufas1), setif, algeria mabroukkhemliche@univ-setif.dz abstract—this paper presents an implementation of mppt (maximum power point tracking) algorithm based on real-time measurements and on model-based simulation. for the supervision of a photovoltaic module, different cases of shading are used. attention was given on advanced control for the supervision of a photovoltaic system according to the need to maximize energy output. experimental results verified the performance and the feasibility of the proposed system. keywords-implementation; simulation; supervision; mppt algorithm; photovoltaic; shading i. introduction fossil fuel energy causes a lot of concerns, from global warming and air pollution, to the issue of their limited reserves [1]. solar energy is a green and renewable energy source. it has been widely exploited in grid-connected systems, in pv pumps and in stand-alone systems. in most systems pv modules are required to be connected in series to form pv panels. pv applications can be classified into two broad categories: the stand-alone and the grid-connected systems. a stand-alone system is widely used in remote places where access to electricity is not viable. the stand-alone configuration can provide well regulated load voltage but the reliability of power supply cannot be guaranteed. this enables the overall pv panel to obtain high input voltage producing high output power to justify the use of mppt control [2]. increasing the efficiency of solar cell is an open issue. different kinds of solar cells have been designed and introduced. the solar panel, the most essential part of a photovoltaic system, converts solar to electrical energy, having nonlinear i/v characteristic curves. modeling of photovoltaic system predicts the system’s electrical behavior in various environmental and load conditions. a pv generation system should operate at its maximum power point (mpp) to increase system efficiency [3]. therefore, mpp tracking is very crucial for pv power generation systems, their optimum use is to operate at mpp as much as possible. since the earliest mppt methods published in 1960s, we can count over than fifteen mppt methods [4, 5]. they can be classified according to the research process of mpp into direct and indirect methods [6]. indirect methods, like short circuit and open circuit methods need a prior evaluation of the pv panel. they are based on mathematical relationships which are not valid for all operating meteorological conditions. so, they cannot obtain exactly the maximum power of pv module at any irradiance and cell temperature. direct methods operate at every meteorological condition. the most used methods are perturb and observe (p&o), incremental conductance (inc) [7], and fuzzy logic (fl) based mppt. some direct mppt methods can be classified according to the variable being tracked. mppt algorithms with fixed step and with variable step can be differentiated. classifications can be built based on implementation simplicity, energy efficiency, convergence speed, sensors required and cost effectiveness. these criteria are often dependent to each other, and make the choice of mppt method more difficult [8-10]. ii. proposed method the proposed scheme of the controller is shown in figure 1. it is composed of an array of photovoltaic modules (s×p) composed of s cells in series connection and p cells in parallel connection, depending on the power system. the buck-boost dc/dc converters use mppt for the pv array in order to extract the maximum available power from them. lead-acid battery is used to store the energy, to regulate the dc-bus voltage through a reversible current dc/dc converter and to supply the motor pump at the low solar irradiance conditions. iii. analysis of the pv system the solar cell is the basic unit of the pv modules which converts photons directly into electrical energy. a solar cell is generally represented by a circuit diagram [11] as shown in figure 2. the one diode model is commonly used for modeling cells of crystalline silicon technology. the equivalent electric circuit comprises a current source, two resistors, and a singlediode. the one-diode model contains five parameters which describe the pv cell properties. the voltage current relationship that can be deduced using the equivalent circuit results in a transcendental equation [12]. the modeling of the pv power supply system is the initial stage that must precede all sizing simulation applications. pv system’s modeling is quite complex. several models are proposed for modeling the different components of a stand-alone pv system [13]. these engineering, technology & applied science research vol. 8, no. 6, 2018, 3541-3544 3542 www.etasr.com latreche et al: implementation of mppt algorithm and supervision of shading on photovoltaic module are based on analytical models or numerical simulations. other methods are based on software simulations using [14, 15]. automatic data acquisition systems are currently used for both monitoring the system performance and control of its operation. the obtained information can be used to evaluate the plant efficiency during long periods and to optimize future systems in terms of performance and reliability. these systems are based on the use of microcontroller and microprocessor for pv applications [16]. fig. 1. photovoltaic system fig. 2. equivalent electrical circuit of photovoltaic cell iv. mppt control pv modules are known to be nonlinear, and there is one operation point where the pv string generates maximum power. one of the problems in the pv systems is that the amount of electric power by the pv arrays is always changing along with the weather conditions. an mppt control strategy, which has quickly response characteristics and is able to make good use of the electric power generated in any weather, is needed to solve this problem. the most commonly used mppt algorithm is the p&o, due to its ease of implementation in its basic form [17]: we assume that the pv module operates at a given point, which is outside the mpp, it is perturbed by ∆v=v(n)-v(n-1), and the change in the power ∆p=p(n)-p(n-1) is measured. if ∆p>0, the operation point has approached mpp, and the next perturbation must take place in the same direction as the previous one. if ∆p<0, the system has moved away from the mpp and, consequently, the next perturbation must be performed in the opposite direction. v. validation of the algorithm the proposed algorithm was validated by simulink in two different situations (figure 3), assuming the presence of the proposed control system and its absence. in both cases the module output power was evaluated in order to perform a subsequent comparison. during the tests, the pv module was submitted to constant temperature and solar irradiance conditions. during the test, a dc/dc converter was connected between the module and the load without controller. in this case the pv module was connected to the generic impedance. under these conditions, the output power is always less than 800w, as can be seen in figure 4. in the latter test the same conditions were maintained, but the mppt control was properly inserted. in this case the output power is always greater than 850w as can be seen in figure 5. fig. 3. simulink model for perturbation and observation mppt fig. 4. output power without mppt fig. 5. output power with mppt vi. implementation of the mppt algorithm figure 6 describes the electrical circuit implemented in proteus software. the pv array was simulated with two solar energy cases a and b (details in table i). table i. simulation datasheet cases solar irradiance (mw/cm 2 ) mpp power (w) mpp voltage (v) mpp current (a) a 65.357 102.648 27.315 7.750 b 24.982 42.610 32.280 2.640 engineering, technology & applied science research vol. 8, no. 6, 2018, 3541-3544 3543 www.etasr.com latreche et al: implementation of mppt algorithm and supervision of shading on photovoltaic module fig. 6. electrical scheme in proteus figures 7 and 8 represent respectively i/v and p/v curves under two different cases at 65°c. the pv array gives 150w maximum power, 43.5v open-circuit voltage and 4.75a closecircuit current at 1kw/m 2 solar energy under 25°c. solar energy is changed from a to b. however, this part is needed to run only when the environmental conditions are changing. it can be executed with low sampling rate. fig. 7. the i/v curve under the cases a and b at 65°c fig. 8. the p/v curve under the cases a and b at 65°c vii. supervision of pv module shading the model of the complex system is reduced without requiring much computational resources and is suitable for operating in real-time, in order to verify the effectiveness of the system developed under various partial shadow conditions (figure 9). (a) without shading (b) with one cell partially shadowed (c) two cells with the same area shadowed (d) with two cells entirely shadowed fig. 9. measured and simulated i/v characteristics of the pv module viii. conclusions due to the age of the module used, its behavior is not identical to the datasheet. the environmental conditions for the simulation have been adjusted in order to create the same shortcircuit current and open-circuit voltage to the measurement. q1 irfz44n 6 /7 2 u3 tc4421 r1 3.3k r2 1k ip+ 1/2 ip3/4 viout 7 vcc 8 gnd 5 filter 6 u1 acs712elctr-05b-t c4 0.1uf c5 0.01uf 3 2 1 4 1 1 u4:a lm324 r3 100k r4 100k r7 3.3k r6 1k ra0/an0 2 ra1/an1 3 ra2/an2/vref-/cvref 4 ra3/an3/vref+ 5 ra4/t0cki/c1out/rcv 6 ra5/an4/ss/lvdin/c2out 7 ra6/osc2/clko 14 osc1/clki 13 rb0/an12/int0/flt0/sdi/sda 33 rb1/an10/int1/sck/scl 34 rb2/an8/int2/vmo 35 rb3/an9/ccp2/vpo 36 rb4/an11/kbi0/csspp 37 rb5/kbi1/pgm 38 rb6/kbi2/pgc 39 rb7/kbi3/pgd 40 rc0/t1oso/t1cki 15 rc1/t1osi/ccp2/uoe 16 rc2/ccp1/p1a 17 vusb 18 rc4/d-/vm 23 rc5/d+/vp 24 rc6/tx/ck 25 rc7/rx/dt/sdo 26 rd0/spp0 19 rd1/spp1 20 rd2/spp2 21 rd3/spp3 22 rd4/spp4 27 rd5/spp5/p1b 28 rd6/spp6/p1c 29 rd7/spp7/p1d 30 re0/an5/ck1spp 8 re1/an6/ck2spp 9 re2/an7/oespp 10 re3/mclr/vpp 1 u2 pic18f4550 u 2 (r a 3 ) d 7 1 4 d 6 1 3 d 5 1 2 d 4 1 1 d 3 1 0 d 2 9 d 1 8 d 0 7 e 6 r w 5 r s 4 v s s 1 v d d 2 v e e 3 lcd1 lm044l 5 6 % rv1 1k rv1(2) x1 crystal c1 15pf c2 15pf +5v l1 100uh bat1 12v a b c d r5 150ohm r3(1) c4(1) r d 7 rd7 r d 6 rd6 r d 5 r d 4 rd5 rd4 rd1 rd0 r d 1 r d 0 u3 u 3 i i v e ve v s v s d d v v 1 1 c6 100uf c3 220uf c7 1000pf d1 10bq015 engineering, technology & applied science research vol. 8, no. 6, 2018, 3541-3544 3544 www.etasr.com latreche et al: implementation of mppt algorithm and supervision of shading on photovoltaic module the pv module gives 150w maximum power, 43.5v opencircuit voltage and 4.75a short-circuit current at 1kw/m 2 solar energy under 25°c. an advanced control of the photovoltaic system, in normal or in shadow weather conditions has been realized. experimental and simulation results were compared in order to confirm the established mppt control. experimental measurements of voltage and pv power of mppt method were conducted under step changing irradiance. the obtained experimental curves are identical to the simulation ones. all results have been achieved while modeling all systems in simulink and writing all models in matlab code. the studied schemes include the pv plant model, the estimator parameters, the reference model block and the supervision system control. the block mppt is necessary to track the maximum power point and to establish the reference voltage in input. it is based on the p&o algorithm, which step by step researches the point where the first order derivative is zero. the experimental results are quite satisfactory, showing the effectiveness of the proposed control in improving the power quality and the reliability of the power supply. acknowledgment authors gratefully thank the university ferhat abbas of sétif (ufas) for the financial support of this study. references [1] m. dimitropoulou, d. pylarinos, k. siderakis, e. thalassinakis, m. danikas, “comparative pollution field measurements on outdoor insulators of different material and design”, engineering, technology & applied science research, vol. 5, no. 2, pp. 764-774, 2015 [2] m. a. eltawil, z. zhao, “grid-connected photovoltaic power systems: technical and potential problems–a review”, renewable sustainable energy review, vol. 14, no. 1, pp. 112-129, 2010 [3] a. kargarnejad, m. taherbaneh, a. h. kashefi, “a new fuzzy-based maximum power point tracker for a solar panel based on datasheet values”, international journal of photoenergy, vol. 2013, article id 960510, 2013 [4] j. a. r. hernanz, j. j. c. martin, i. z. belver, j. l. lesaka, e. z. guerrero, e. p. perez, “modeling of photovoltaic module”, international conference on renewable energies and power quality, granada, spain, march 23-25, 2010 [5] t. esram, p. l. chapman, “comparison of photovoltaic array maximum power point tracking techniques”, ieee transactions on energy conversion,vol. 22, no. 2, pp. 439-449, 2007 [6] a. m. kassem, “mppt control design and performance improvements of a pv generator powered dc motor-pump system based on artificial neural networks”, international journal of electrical power energy system, vol. 43, no. 1, pp. 90-98, 2012 [7] g. farivar, b. asaei, m. a. rezaei, “a novel analytical solution for the pv-arrays maximum power point tracking problem”, 2010 ieee international conference on power and energy, kuala lumpur, malaysia, november 29-december 1, 2010 [8] m. a. ozcelik, a. s. yilmaz, “modification of the incremental conductance algorithm in grid connected photovoltaic systems”, revue roumaine des sciences techniques-serie electrotechnique et energetique, vol. 61, no. 2, pp. 164-168, 2016 [9] a. al nabulsi, r. dhaouadi, “efficiency optimization of a dsp-based standalone pv system using fuzzy logic and dual-mppt control”, ieee transactions on industrial informatics, vol. 8, no. 3, pp. 573-584, 2012 [10] a. attou, a. massoum, m. chadli, “comparison study of two tracking methods for photovoltaic systems”, revue roumaine des sciences techniques-serie electrotechnique et energetique, vol. 60, no. 2, pp. 205-214, 2015 [11] m. a. g. de brito, l. galotto, l. p. sampaio, g. de a. e melo, c. a. canesin, “evaluation of the main mppt techniques for photovoltaic applications”, ieee transactions on industrial electronics, vol. 60, no. 3, pp. 1156-1167, 2013 [12] h. patel, v. agarwal, “matlab based modelling to study the effects of partial shading on pv array characteristics”, ieee transactions on energy conversion, vol. 23, no. 1, pp. 302-310, 2008 [13] h. kawamura, k. naka, n. yonekura, s. yamanaka, h. kawamura, h. ohno, k. naito, “simulation of i/v characteristics of a pv module with shaded pv cells”, solar energy materials and solar cells, vol. 75, no. 3-4, 75, pp. 613-621, 2003 [14] j. n. ross, t. markvart, w. he, “modeling battery-charge regulation for a stand-alone photovoltaic system”, solar energy, vol. 69, pp. 181-190, 2000 [15] a. d. hansen, p. sorensen, l. h. hansen, h. binder, models for a stand-alone pv system, dtu library, 2000 [16] l. castaner, s. silvestre, modeling photovoltaic systems using pspice, john willy & sons, 2002 [17] e. koutroulis, k. kalaitzakis, “development of an integrated dataacquisition system for renewable energy systems monitoring”, renewable energy, vol. 28, pp. 139-152, 2003 microsoft word rev-1-25-2392_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3668-3672 3668 www. etasr. com nazari-sharabian et al: climate change and eutrophication: a short review climate change and eutrophication: a short review abstract—water resources are vital not only for human beings but essentially all ecosystems. human health is at risk if clean drinking water becomes contaminated. water is also essential for agriculture, manufacturing, energy production and other diverse uses. therefore, a changing climate and its potential effects put more pressure on water resources. climate change may cause increased water demand as a result of rising temperatures and evaporation while decreasing water availability. on the other hand, extreme events as a result of climate change can increase surface runoff and flooding, deteriorating water quality as well. one effect is water eutrophication, which occurs when high concentrations of nutrients, such as nitrogen and phosphorus, are present in the water. nutrients come from different sources including agriculture, wastewater, stormwater, and fossil fuel combustion. algal blooms can cause many problems, such as deoxygenation and water toxicity, ultimately disrupting normal ecosystem functioning. in this paper, we investigate the potential impacts of climatic factors affecting water eutrophication, how these factors are projected to change in the future, and what their projected potential impacts will be. keywords-climate change; water quality; eutrophication i. introduction the planet is getting warmer as an impact of exponentially increasing anthropogenic greenhouse gas emissions, especially co2. according to the fifth assessment report of the intergovernmental panel on climate change (ipcc), the global average surface temperature has undergone a warming of 0.85°c (0.65 to 1.06) from 1880 to 2012, proving that global warming is occurring [1]. a warmer climate will affect the hydrological cycle and change atmospheric and meteorological properties such as precipitation patterns, atmospheric water vapor and evaporation [2-4], and consequently impact water quality by intensifying many forms of water pollution [5-7]. one form of water pollution is water eutrophication, which occurs when high concentrations of nutrients, such as nitrogen and phosphorus, are present in the water. in recent years, specific concerns about the impacts of climate change on water eutrophication, which causes global environmental challenges regarding the management of water resources, have been raised [8-15]. the fifth global environment outlook (geo-5) reports that more than 40% of water bodies all around the world suffer from different levels of eutrophication [16]. the reason for this phenomenon is an important issue of great concern is its potential consequences, threatening the reliable supply of drinking water [17-19]. the terminology and application of trophic development of freshwaters date back to the early twentieth century. the consequences of anthropogenic-induced eutrophication of freshwaters did not become evident until the 1940s and 1950s as public concern over the severity of surface water deterioration became evident and triggered expanding scientific interest. scientists debated which nutrient is primarily responsible for limiting productivity in lakes and rivers, an issue known as limiting nutrient controversy, and they ultimately agreed that phosphorus (p) is the key element in controlling eutrophication. [20]. algal blooms in water bodies are a sign of eutrophication that indicates the presence of high concentrations of phosphorus and nitrogen. algal blooms can form anoxic environments in the water and consequently deteriorate water quality [10, 15, 21]. predictions indicate that with rising concentrations of atmospheric co2, the occurrence of algae blooms will likely increase [22, 23]. recent anthropogenic changes, such as urban, agricultural, and industrial development, have accelerated the progress of nutrient over-enrichment, leading to eutrophication in water bodies [24-26]. undesirable symptoms of eutrophication primarily occur during the plant growing season (spring and summer), when low flow, high water residence times, sufficient light levels and high water temperature promote rapid algal growth. during the growing season, the eutrophication risk mainly originates from point discharges, a major source of high concentrations of dissolved, bioavailable phosphorus fractions. at times when diffuse agricultural runoff contributions are relatively low, phosphorus concentrations from point sources become even higher in the receiving water bodies, as a result of reduced effluent dilution [27]. the trophic state in flowing waters depends mainly on phosphorus and nitrogen levels. hydraulic flushing of nutrients, light limitation, and water velocity are essential in controlling algal growth. this suggests that rivers or riverine lakes with short retention times (<3 days) will show different effects compared to those with long retention times (>3 days) [28]. climate change can, directly and indirectly, affect eutrophication, as a result of interactions between meteorological factors and nutrient availability [24, 29]. the mohammad nazari-sharabian department of civil and environmental engineering and construction, university of nevada, las vegas, las vegas, usa nazarish@unlv. nevada. edu sajjad ahmad department of civil and environmental engineering and construction, university of nevada las vegas, las vegas, usa sajjad. ahmad@unlv. edu moses karakouzian department of civil and environmental engineering and construction, university of nevada las vegas, las vegas, usa mkar@unlv. nevada. edu engineering, technology & applied science research vol. 8, no. 6, 2018, 3668-3672 3669 www. etasr. com nazari-sharabian et al: climate change and eutrophication: a short review existing literature shows that sensitive factors to climate change such as water temperature, precipitation, wind, and solar radiation can affect trophic conditions in water bodies. therefore, to maintain water resources availability and safety, it is crucial to investigate the impacts of climate change on water quality in water resources. this paper briefly summarizes the potential impacts of climate change on the occurrence of eutrophication in water resources. ii. climate change effects a. temperature regarding climate change, many factors are considered in order to predict how future global warming will occur. in this case, the amount of future greenhouse gas emissions is a key variable. two different emissions scenarios, including rcp2.6 (low emissions scenario) and rcp8.5 (high emissions scenario), show that by the end of the 21st century, the global surface temperature is expected to increase by 0.3°c-1.7°c and 2.6°c-4.8°c under rcp2.6, and rcp8.5, respectively [30]. temperature is an important environmental factor that influences chemical and physical properties in water ecosystems such as ph, salinity, solubility, and diffusion rates, and can consequently affect water eutrophication potential [31, 32]. air temperature and temperature in water bodies are in close equilibrium. hence one of the immediate reactions to climate change is expected to be alterations in river and lake water temperatures [22, 33-35]. when water temperature and nutrient concentrations increase, algae growth is stimulated, leading to water eutrophication and algal blooms. as concentrations of phosphorous and nitrogen increase in lakes, rivers and estuaries, cyanobacteria become increasingly dominant. cyanobacteria are a group of bacteria that grow in any type of water (fresh, brackish, or marine) and use sunlight to create food and survive. because of their color, they are commonly known as “blue-green algae”. they grow quickly and bloom in warm, nutrient-rich environments. water bodies experiencing frequent blooms of cyanobacteria show properties that can impact water quality as well as the health of the surrounding environment [36, 37]. once the water temperature rises above 25°c, the growth of cyanobacteria accelerates [32, 38-40]. similarly, warmer temperatures could also stimulate earlier and more extended periods of potential algal blooms, as the immediate direct effect of a warmer environment [31, 41, 42]. moreover, warmer temperatures will affect nutrient loadings from soil and sediment, which can ultimately impact the trophic status of water [43]. as the inflow to a reservoir gets warmer as a result of higher temperature, the water column will stratify more intensely, decreasing nutrient availability in the surface water. in this case, cyanobacteria will obtain nutrients from deeper depths and accelerate nutrient release in water [44, 45]. higher temperatures will accelerate microbial activity in sediments at the bottom of lakes and rivers. in this case, the release rate of internal phosphorus will increase, and will contribute to a significant portion of the total nutrient load in the water [46]. in addition, higher water temperatures will reduce the degradation coefficients of water and decrease its self-purification capacity [10]. therefore, under climate change conditions, the release of nutrient loadings from internal sources could still make water eutrophic, even if external sources of nutrients, such as waste discharge and non-point pollution are restrained [47]. moreover, when the surface water gets warmer, water viscosity will decrease, and as a result, nutrient diffusion will increase towards the surface. in this situation, larger phytoplankton (photosynthesizing microscopic biotic organisms that inhabit the upper sunlit layer of almost all oceans and bodies of fresh water on earth) will sink, and cyanobacteria will become more abundant [38, 48, 49]. as a summary, increasing air temperature will increase water temperature and deteriorate water quality conditions by accelerating the eutrophication process in water bodies, which can cause environmental and health-related issues [23, 26, 46]. b. precipitation besides the temperature effects, the change in hydrological regimes is also a consequence of climate change. as the temperature is predicted to rise, precipitation will not change uniformly [30]. under the rcp2.6 and rcp8.5 scenarios, climate model mean projections for 2081-2100 compared to 1986-2005 indicate that annual mean precipitation will increase mostly around the equatorial pacific and some high-latitude areas. however, projections show that mean precipitation is likely to decrease in certain mid-latitude and subtropical regions, although some increase in mean precipitation in many mid-latitude regions is also likely to occur under the same scenario. therefore, in areas with projected higher precipitation, it is possible that intense extreme precipitation events will occur and cause more erosion and resuspension of sediments, ultimately resulting in higher concentrations of sediments and nutrients in receiving water bodies [24, 48]. furthermore, these extreme events will increase contaminant discharge and affect non-point pollution by mobilizing them over land and increasing nutrient concentrations in receiving water bodies, consequently degrading water quality. [49, 5153]. less precipitation can also increase the risk of eutrophication by lowering minimum flows. in this case, less water volume will be available for dilution of pollutants. as a result, increased concentration of contaminants can cause deoxygenation, by lowering dissolved oxygen concentration (do) and increasing biochemical oxygen demand (bod). consequently, the risk of eutrophication, especially in water bodies with limited re-aeration capacity, will be increased [24, 54]. therefore, under climate change conditions and due to the alteration of regional precipitation patterns, water bodies are exposed to greater nutrient loads, which can ultimately lead to water quality deterioration. c. wind the wind will also be affected by climate change, and will have direct and indirect impacts on water resources [39]. authors in [50] used general circulation models, under the a2 emission scenario, to predict the wind speed in different regions in 2050. modeling results showed that across the boreal regions of the northern hemisphere, including canada, tropical and subtropical regions, northern europe, and central and south america, stronger surface wind speeds will occur in 2050, while decreasing wind speeds were predicted for southern europe, east and south asia, and much of the west coast of south america. the direct effects of wind refer to engineering, technology & applied science research vol. 8, no. 6, 2018, 3668-3672 3670 www. etasr. com nazari-sharabian et al: climate change and eutrophication: a short review blowing of algae from the water surface to the lakeshore or river banks and influencing these regions by forming algal blooms and changing environmental conditions. the indirect effect is the disturbance caused by the wind, which can circulate the water and mix different layers of the water column. this circulation enhances the mixture of nutrients and accelerates the release of nutrients from sediments [55]. also, as the air temperature rises, wind mixes the warmer upper layers of water with the colder lower layers, which can speed up the volatilization, migration, and transformation of pollutants [9]. authors in [56] used different sediment resuspension models to simulate nutrient distributions in the wind-dominated salton sea in the united states, which is highly eutrophic. they concluded that sediment resuspension, which induces both particulate and dissolved forms of nutrients, is the critical factor in nutrient cycling of the sea. therefore, higher wind speeds will accelerate sediment resuspension, contaminant circulation, and finally exacerbate trophic conditions. moreover, authors in [57] studied the taihu lake in china, which has experienced periods of severe eutrophication in the past. model results, which coupled the biological processes and hydrodynamics in the lake, showed that temporal variations of eutrophication have high dependencies on meteorological forces. on the other hand, intense and high-speed winds can also restrain the formation of algal blooms by dissipating them and weakening their aggregation [58]. therefore, the wind will have direct and indirect impacts on water trophic conditions, but it does not act as a single decisive operator, and mostly influences eutrophication along with other meteorological factors. d. solar radiation global warming and solar radiation have mutual connections [59]. as an important source of energy, solar radiation plays a crucial role in photosynthesis in different ecosystems and is an essential factor for the growth of phytoplankton and other aquatic species. therefore, the photosynthesis efficiency is dependent upon the temporal and spatial variations of solar radiation. sufficient sunlight increases water temperature and the presence of nutrients altogether provide suitable conditions for the growth of algae and phytoplankton, finally resulting in water eutrophication [22]. solar radiation affects a wide range of living organisms, by penetrating aquatic systems and acting as the energy source for plant photosynthesis. if plants do not receive sufficient amounts of sunlight, they take up oxygen from the water, and do depletion will occur. under anaerobic conditions, phosphorus release from sediments can cause water eutrophication [60, 61]. algae distribution is also dependent on the intensity of solar radiation received at different depths. however, increased sunlight will not necessarily cause more algae growth. there is a maximum growth rate for algae, in which beyond this threshold, the growth rate will decrease [62, 63]. authors in [62] projected uv-b radiation at the earth’s surface from 1960 to 2100. although the global temperature is slated to rise until 2100, results of uv-b predictions showed that radiation change at different latitudes will alter differently. projected uv-b radiation compared with 1980 levels, showed increasing trends at 60˝ to 90˝ southern latitude (more than 20% increase), and decreasing trends at 60˝ to 90˝ northern latitude (around 10% decrease). e. summary besides the effects of temperature, precipitation, wind and solar radiation alteration, an increasing population, rapid urban development, and lack of land use planning continually contribute to the degradation of the environment and water resources. figure 1 summarizes the impacts of climate change on water eutrophication. climate change factors air temperature precipitation wind speed solar radiation human activities direct effects indirect effects water temperature, ph, solubility, viscosity growth and reproduction of algae accumulation of phytoplankton ecosystem degredation self-purification capacity microbial activities water viscosity and nutrient diffusion stratification release and transport of internal nutrients change of hydrological regimes uneven distribution of water resources water cycle water level water quality runoff degradation coefficients extreme events, droughts, flood, etc. water pollution water quality degredation nutrient release water stability aggregation of algae mixing of nutrients formation of blooms migration of pollutants photosynthesis sunlight degradation and intensity transparency light respiration phototoxicity dissolved oxygen algae growth pollution discharges external nutrient loads eutrophication fig. 1. the interaction among climate change factors and eutrophication. engineering, technology & applied science research vol. 8, no. 6, 2018, 3668-3672 3671 www. etasr. com nazari-sharabian et al: climate change and eutrophication: a short review iii. conclusion in this paper the effects of climate change on meteorological parameters such as temperature, precipitation, wind, and solar radiation were reviewed, and their potential impacts on water quality, especially eutrophication, were investigated. based on the available literature and historical, scientific evidence, a changing climate will lead to degradation of water quality. the recent anthropogenic climate change will also amplify deterioration of trophic conditions in water resources, by changing the internal and external nutrient loadings, as an impact of global temperature rise, changing precipitation patterns, and altering wind speed and solar radiation intensity. therefore, maintaining our invaluable water resources in a changing climate is a big and significant challenge for the policymakers today, and deserves considerable attention for the sake of future generations. references [1] ipcc, ipcc working group i contribution to the ipcc fifth assessment report (ar5): the physical science basis, ipcc, 2013 [2] ipcc, climate change 2007: the physical science basis, cambridge university press, 2007 [3] ipcc, managing the risks of extreme events and disasters to advance climate change adaptation, cambridge university press, 2012 [4] t. g. huntington, “evidence for intensification of the global water cycle: review and synthesis”, journal of hydrology, vol. 319, no. 1-4, pp. 83-95, 2006 [5] r. deus, 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engineering mehran university of engineering and technology, pakistan sami.qureshi@faculty.muet.edu.pk abstract-service life modeling of reinforced concrete structures in a chloride environment is mainly performed without considering the loading effects. different loading effects can produce different service life results. this study presents a theoretical framework for the modeling of the service life of reinforced concrete structures in a chloride environment using loading factors, showing that, depending on the loading nature (either compression or tension), different diffusion results could be obtained. this paper also highlights various approaches to service life modeling, such as the deterministic, probabilistic, and semi-probabilistic, which consider different ways to estimate the service life of reinforced concrete structures in chloride environments. the importance of various distributions for the input parameters in the chloride ingress modeling was examined. the proposed framework includes a procedure to estimate the probability of concrete failure in chloride environments. keywords-concrete durability; service life design; service life framework; chloride ingress i. introduction service life modeling, in terms of durability, is performed to estimate the service life and performance of reinforced concrete structures. a structure's performance is defined as its capacity to meet the target service time for its intended performance. service life modeling estimates the residual life and is needed to apply any repair and maintenance strategies. several studies have been conducted for modeling the estimation of service life [1-6], presenting various frameworks. in [7], a framework for the degradation of concrete was presented, highlighting the importance of the deterministic, probabilistic, and semi-probabilistic approaches, and the importance of cover thickness, concrete strength, cement type, and water to cement ratio. a detailed study for the chloride ingress parameters was conducted in [6], providing a procedure of using input parameters for the service life modeling of chloride ion ingress. in [8], the service life of concrete was quantified by a reliability index, utilizing the probabilistic method to consider the distribution laws of input parameters. authors in [9] reported that the initiation period starts with the exposure of structure and ends with the de-passivation of reinforcement. in [2], a probabilistic model was presented and validated with data collected from two projects. the results showed that the chloride ingress process involved great uncertainties and randomness in material input parameters and structure's geometry. the proposed model was validated through a parametric analysis, finding the influences of diffusion co-efficient do, surface chloride concentration cs, age factor m, cover depth x, and chloride threshold cth. authors in [10] reported that the degrading state of an aging concrete structure could be updated for reliability purposes. authors in [11] reported that the level of reliability for service life design was generally unclear, proposing that the criteria should be based on long-term experience. in [12], the factors influencing the chloride transport mechanism such as diffusion coefficient, surface chloride ion concentration, and drying and wetting regimes were analyzed, while the results showed that diffusion coefficient, drying, and wetting influenced the maximum transmission depth. in [4], the deterministic approach to analyze service life was reported to fail due to uncertainties on input parameters, while a probabilistic model was proposed and developed. probabilistic methods including uncertainty parameters for input parameters were presented in [3], considering the sensitivity of the corrosion probability to different parameters and a durable design concrete cover as the most important parameter. a probabilistic model including uncertainties arising from the loadbearing capacity of reinforced concrete structures was proposed in [5]. durability extension and service life predictions were reported to be important in [1], as corrosion has many consequences such as cracking and spalling of concrete, as well as losses of bond strength in crosssectional areas of steel. in [6], an in-depth study was presented on the use of the concrete diffusion coefficient. the durability properties of fuel ash concrete and metakaolin concrete were studied in [13] and [14] respectively. this study aims to develop a framework for the chloride diffusion in concrete, considering the loading effect using semi-probabilistic and probabilistic analysis. corresponding author: amjad ali pathan engineering, technology & applied science research vol. 11, no. 1, 2021, 6806-6809 6807 www.etasr.com pathan et al.: a theoretical framework for service life prediction of reinforced concrete structures … ii. chloride ingress modeling the estimation of chloride content in concrete requires a deep study of the input parameters for service life modeling. the following equation was used in [5] for the probabilistic analysis: ���, �� = � 1 − erf � � �√�� �� (1) the chloride diffusion coefficient d for an aging factor m is given by: ���� = �� � �� � � � (2) a. service life modeling service life modeling is essential to apply repair and maintenance strategies for existing and enhancing the durability of new structures. service life modeling can be performed in three different ways: deterministic, probabilistic, or semi-probabilistic. table i shows a comparison of these three approaches in terms of complexity and table ii summarizes the three approaches. table i. service life modeling approaches approach obtained results procedures deterministic over-estimated simple probabilistic balanced-estimated complex semi-probabilistic under-estimated semi-complex table ii. service life modeling approaches summarization approach values c(x,t) cth deterministic mean (µ) mean (µ) probabilistic mean (µ) and standard deviation (σ) mean (µ) and standard deviation (σ) semiprobabilistic mean (µ) and standard deviation (σ) mean (µ) b. deterministic in this approach, the values of variables are considered deterministic, and the approach can be conducted as a discrete or continuous overtime study. the deterministic approach considers average values, such as µ, taken as input parameters, and the calculation procedure is simple. the disadvantage of this approach consists of not considering the variation and scatter of input parameters. c. probabilistic in this approach, the input parameters are defined using distributions. the selection of the distribution depends on available data, previous conducted studies, and designer's experience. this approach uses load and resistance concepts in general. the input parameters for load are taken as c(x,t) as defined in (1) and (2). cth input values are obtained from the average and standard deviation of available data or previous studies. τhis procedure gives acceptable results, despite its complexity. the designer's experience in selecting input parameters plays an important role, as an incorrect selection could result in over or under-estimated results. d. semi-probabilistic in the semi-probabilistic approach, the input parameters for c(x,t) are defined using distributions, while cth values are considered as a deterministic uniform value without any variation or scatter in resistance. iii. loading factors real concrete members perform differently under different loading conditions in experimental tests. load causes strain in the members, as shown in table iii. a column under loading conditions causes negative strain increasing tortuosity, while a beam under tense causes positive strain lowering tortuosity. in general, parapet walls do not experience any loading and their tortuosity levels are normal. table iv shows an example of various members’ nature in a bridge structure. a bridge deck experiences both compressive and tensile forces, a column remains under tensile forces, a pier remains under compressive forces, and a deck beam remains under both compressive and tensile forces. table iii. members under load and nature of strains concrete members strain levels example tortuosity level (�) compression members negative columns higher tension members positive beams lower normal members neutral parapet walls normal table iv. examples for compression and tensile members in a bridge structure compression members tension members comments bridge deck ✓ ✓ varies due to the stress level along the deck bridge columns ✓ loading causes compressive strain bridge piers ✓ loading causes compressive strain bridge deck beams ✓ ✓ varies due to the stress level along the length a. compression members service life modeling for compression members, such as the columns in a bridge, may differ from normal concrete under no loading. members under compression generally develop shrinkage stress, increasing concrete's compactness by filling micro-pores. in such cases, a reduction in diffusion can be observed. so instead of assuming do as a constant value, a reduced do can be used. the revised values for do are shown in table v. table v. loading factors compression members tension members revise do for compressive strain, so: �� �� !� = �� − 1.1 �� for loading value 0.4 times the limit state value �� �� !� = �� − 1.2 �� for loading value of 0.5 times the limit state value revise do for tensile strain, so: �� �� !� = �� + 1.2 �� for loading value 0.4 times the limit state value �� �� !� = �� + 1.4 �� for loading value 0.5 times the limit state value engineering, technology & applied science research vol. 11, no. 1, 2021, 6806-6809 6808 www.etasr.com pathan et al.: a theoretical framework for service life prediction of reinforced concrete structures … b. tension members tension members in a structure are subjected to stresses that cause strains, defined by: & = '.( (3) where ( is stress, e is the modulus of elasticity, and & is the strain. this strain is a measure of expansion in concrete members, producing micro-cracks that accelerate the diffusion process within the concrete body. c. normal members in normal members, dο with aging factors could be considered as normal. so, a revised diffusion coefficient (d) is needed for service life modeling. iv. durability parameters and their probability distributions probabilistic and semi-probabilistic analyses require a probability distribution, which is obtained from large data. the analysis is performed after deciding on the shape of the curve to be developed from large data. this also depends on designer's experience. table vi shows various distributions used in several studies, and in the present study. table vi. parameters and load parameter reference [2] [4] [9] [11] present study do log normal log normal normal log normal normal co log normal log normal deterministic log normal normal cs log normal ---------normal m beta ---normal ---normal α normal ---------normal x normal normal --- log normal normal cth normal ---deterministic log normal normal c(x,t) ---uniform beta ---normal v. service life modeling framework design service life modeling can be performed utilizing various simple or complex approaches, as can be seen in figure 1. analysis can be performed based on the design level. for instance, a deterministic approach may be followed during the design of a new structure, as it produces a quick result. later, a semi-probabilistic analysis could be performed. a probabilistic analysis could be performed when detailed information for service life and maintenance is needed, requiring large datasets and experience. vi. understanding the probability of failure the probability of failure is a common region between both probability density functions (pdfs) of c(x, t) and cτη, as seen in figure 2. this is based on the concept of load and resistance, as a failure occurs when the load value exceeds resistance. figure 2 shows the resistance of concrete in terms of its chloride uptake capacity, which is a theoretical chloride content cth. the load is described by chloride content on depth x over time t written as c(x, t). so, a failure occurs when c(x, t) overlaps the region of cτη. fig. 1. flow chart of service life modeling. fig. 2. domains of failure and success. vii. durability performance and cost effect concrete's durability performance is directly related to costeffectiveness, as more durable concrete structures reduce service life cost. similarly, concrete's poor performance results in earlier demolition of structures raising the overall cost. enhanced service life can be achieved for new and existing structures by applying a repair strategy before major failures. the design framework includes all necessary parameters for service life modeling. the load effect has a major contribution to the analysis, as concrete performs differently depending on loads' nature. based on the loads' nature (i.e. compression (columns) and tension (beams)), different results can be obtained. table vii shows various levels of durability designs and their effect on cost. durability performance is enhanced by the use of high strength concrete with cementitious materials having chloride binding properties and aggregates with low porosity. sustainability involves economic considerations, as extending service reduces the total cost of construction and maintenance. engineering, technology & applied science research vol. 11, no. 1, 2021, 6806-6809 6809 www.etasr.com pathan et al.: a theoretical framework for service life prediction of reinforced concrete structures … table vii. enhancing durability performance criteria enhancing durability effect on initial cost service life cost resistance using conventional materials, ordinary portland cement (opc), and aggregates low low capacity cementitious additives such as fly ash, slag, silica, and metakaolin are are added to the concrete more more performance high-performance materials are used in concrete such as opc with fly ash and silica fume high high service life corrosion initiation corrosion inhibitors are used high high service life corrosion propagation cathode protection measures are applied high high service life corrosion cracking additional measures are applied, such as sealing of cracks and protection of anode and cathode high high sustainability high strength concrete with low porosity aggregate is used very high very high viii. conclusion this study highlighted the importance of the deterministic, probabilistic, and semi-probabilistic approaches for service life modeling, which give different levels of analysis. the probabilistic analysis is more complex, as it involves a lot of computational stages. a theoretical framework for service life modeling was presented considering the loading factors, while the loading effect on chloride ingress was ignored. theoretically, it was shown that coefficient d can be applied based on the loads' nature corrections in diffusion. moreover, it was shown that the diffusion process in concrete is not as straightforward as using (2), but using time steps the chloride content inside the concrete volume increases raising tortuosity and reducing chloride's ingress. previous studies proposed various distributions for the input parameters of service life modeling. concrete's performance level can be enhanced by using various high-performance materials, such as opc with fly ash and silica fume, for sustainable concrete with aggregates with low porosity. this study's results can be concluded as: • better performance of concrete structures reduces their service life costs. the service life can be estimated based on the level of analysis. • service life can be estimated based on deterministic, semiprobabilistic, or probabilistic modeling. probability distributions have been proposed for various parameters. • chloride diffusion in concrete is a time-dependent 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[14] a. saand, m. a. keerio, and d. k. bangwar, "effect of soorh metakaolin on concrete compressive strength and durability," engineering, technology & applied science research, vol. 7, no. 6, pp. 2210–2214, dec. 2017, https://doi.org/10.48084/etasr.1494. microsoft word 37-3655_s_etasr_v10_n4_pp6102-6108 engineering, technology & applied science research vol. 10, no. 2, 2020, 6102-6108 6102 www.etasr.com khalid & wu: supporting scholarly search by query expansion and citation analysis supporting scholarly search by query expansion and citation analysis shah khalid school of computer science and communication engineering, jiangsu university, china and nust, islamabad, pakistan shahkhalid@ujs.edu.cn shengli wu school of computer science and communication engineering jiangsu university, china swu@ujs.edu.cn abstract−published scholarly articles have increased exponentially in recent years. this growth has brought challenges for academic researchers in locating the most relevant papers in their fields of interest. the reasons for this vary. there is the fundamental problem of synonymy and polysemy, the query terms might be too short, thus making it difficult to distinguish between papers. also, a new researcher has limited knowledge and often is not sure about what she is looking for until the results are displayed. these issues obstruct scholarly retrieval systems in locating highly relevant publications for a given search query. researchers seek to tackle these issues. however, the user's intent cannot be addressed entirely by introducing a direct information retrieval technique. in this paper, a novel approach is proposed, which combines query expansion and citation analysis for supporting the scholarly search. it is a two-stage academic search process. upon receiving the initial search query, in the first stage, the retrieval system provides a ranked list of results. in the second stage, the highest-scoring term frequency– inverse document frequency (tf-idf) terms are obtained from a few top-ranked papers for query expansion behind the scene. in both stages, citation analysis is used in further refining the quality of the academic search. the originality of the approach lies in the combined exploitation of both query expansion by pseudo relevance feedback and citation networks analysis that may bring the most relevant papers to the top of the search results list. the approach is evaluated on the acl dataset. the experimental results reveal that the technique is effective and robust for locating relevant papers regarding normalized discounted cumulative gain (ndcg), precision, and recall. keywords-academic search; query expansion; citation analysis; pseudo relevance feedback; user relevance feedback i. introduction the rate in publications is about 2.5 million per year [1]. this large increase in the number of scholarly publications makes finding relevant papers with a few keyword query a challenging task [2]. this can be caused by several reasons: first, the problem of synonym and polysemy [3, 4], i.e. the query terms submitted, can be related to multiple topics due to which the search results list may not contain the intended papers. second, the query terms can be too short making hard to discover what papers the user wants. this may be a matter of habit: searchers usually formulate very short queries (e.g. the average size of query terms is 2.4 words [5, 6]). third, a new researcher has limited knowledge and often is not sure about what is looking for until the results are displayed. even if searchers know what they are looking for, they are unable to formulate the search query for increasing accuracy and completeness of the search results. these issues obstruct scholarly retrieval systems in locating highly relevant publications for a given search query. to deal with these issues, a lot of research has been done in recent years, and the output has been presented in different styles, including research papers [7], books [8, 9], doctoral dissertations [10, 11], test collections [12], retrieval evaluation events [13], etc. to the best of our knowledge, no technique has been investigated that uses both query expansion (qe) by prf and citation analysis in scholarly search. in this study, we emphasize the use of qe methods by prf and citation analysis to support academic searchers in finding the most relevant papers on their queries. in our recent research work, we incorporated qe by considering user's relevance feedback with citation analysis [7]. it was assumed that a user's search query if expanded by considering interesting terms from the initial few top-ranked results as pseudo relevance feedback (prf) besides the citation graph may provide better performance [7]. now we believe that this assumption may support academic searchers faster because the system does not wait for the user feedback. in this paper, we look at pseudo relevance feedback (prf)-based qe methods in greater detail. prf-based qe technique augments the original user's query with terms generated from the initially retrieved results list. this technique has advantages and disadvantages. one of its main benefits is that it performs qe without the user's interaction. in contrast, scholarly retrieval systems also inherit the fundamental issues of search engines, i.e. at first the initial retrieval list may be a mixture of papers about different subjects and documents. second, document retrieval systems normally provide a long list of documents ranked by their relevance to the user's query. to address these issues while expanding the original query, we utilize citation analysis and the concept of interesting terms from a top few papers [7]. in summary, the key contributions of this paper include: (1) we formulated the index to facilitate the design of qe by prf and the results in re-ranking strategies. (2) we developed an algorithm that uses qe (prf) and citation analysis in corresponding author:shengli wu engineering, technology & applied science research vol. 10, no. 2, 2020, 6102-6108 6103 www.etasr.com khalid & wu: supporting scholarly search by query expansion and citation analysis extracting and weighting qe terms. (3) we evaluated the proposed framework on the acl data set using standard evaluation metrics, i.e. ndcg, recall, and precision, to demonstrate the comparative analysis. ii. related work note that here we will not concentrate on the well-known text retrieval models such as bm25, vsm, jaccard index, ngram string matching, etc, since the information about these models are easily available, and they rely on word matches. the aim of this study is to investigate how qe by prf and citation graph may support academic searchers [2]. for this only the recent relevant literature in the domain of scholarly retrieval systems was taken into account in order to demonstrate our proposed technique. sofia search is a well-known example in the domain of academic search for identifying relevant articles [14], which starts from the initial set of papers and follows both the in-links and out-links of the papers repeatedly up to a given depth or when a desired numbers of candidates is found. however, in the growing rate of research papers, the use of sofia search is limited. it needs seed papers while all the in-links and out-links are not equally relevant [15]. most of the approaches that use citation graphs do so in combination with content-based approaches. examples include academic search engines such as google scholar, pubmed, and citeseerx which use the links between scholarly articles provided by citation network analysis for documents ranking. cb method processes the textual content of the papers, which can be title, abstract, keywords, and main content. the text-based methods weigh the relevant articles by the frequency and position of the terms in the article. based on the term weight, several techniques have been developed to estimate the relatedness of articles. pubmed is a popular scholarly retrieval system, primarily designed for biomedical literature [16]. it is maintained by the us ncbi (national center for biotechnology information) with over 28 million articles. it reflects many factors of the scholarly article for indexing and retrieval including (a) stemming, (b) number of terms in the article (tf), (c) position of terms (i.e. title, abstract, body-content), (d) weight of the terms in the article, and (e) key terms of the article in a domain-specific database (e.g. mesh database). recently, pubmed enriched its search architecture by considering two stages. in the first stage, it retrieves articles that match a user query using standard information retrieval (ir) weighting function bm25. in the second stage, it re-ranks the top 500 articles using learning to rank (l2r) method. web search query is an integral part of the ir, and it is generally accepted that searchers habitually pose short queries to search engines [5, 6]. many research works have shown the effectiveness of qe by adding new words to original queries [7, 18]. authors in [19] proposed synonym weighting strategies for biomedical retrieval. they took into account ‘gene synonym qe’ in biomedical information retrieval and presented the effectiveness of the technique in retrieving relevant information from biomedical literature. likewise, article retrieval for precision medicine (artpm) has recently been proposed for relevant article retrieval using query formulation and expansion [20]. in artpm, the searcher has to specify a query consisting of the disease, contextual medical condition, and genetic mutation. it then uses several external resources to formulate and extend a query for effective article retrieval. several other approaches have been practiced to make scholarly search engines more effective [14, 16, 21-24]. among these, the explicit semantic ranking (esr) is a wellknown and recent representative approach that uses knowledge graph embedding in ranking scholarly documents [24]. it uses semantic scholar corpus, query log, and freebase for building an academic knowledge graph. its knowledge graph considers concept entities and their descriptions, context correlations, relationships with authors and venues, and embedding trained from the graph structure. it uses l2r to query and represent documents (as entities in the knowledge graph) in the embedding space. another popular approach is to transform the concept of keywords into key queries [22]. key phrases are extracted from input documents for formatting key quires with the objective of finding more relevant documents. liu introduced another technique called ccse (core content similarity estimation) for retrieving scholarly articles with similar core content [16]. for a given article, ccse recommends those articles that share similar core content terms with it. it has two interesting features: (1) it works on article titles and abstracts only, which are freely available on the web and (2) it improves inter-article relation estimation by considering the core contents of the article, which include the research goal, background (problem description), and conclusion of the article. recently, we used qe through urf and citation networks analysis for relevant retrieval of scholarly articles [7]. however, to the best of our knowledge, until now no published effort has investigated the use both qe by prf and citation analysis for academic search in identifying relevant papers. iii. proposed framework the proposed technique enhances academic search not only by qe via prf but by performing citation analysis while ranking scholarly articles. the citation network analysis can play a vital role in identifying influential papers [25]. figure 1 demonstrates how the qe works in our proposed approach. fig. 1. the proposed qe model. we have used bm25 similarity measure and citation analysis for selecting an initial set of retrieved documents, which is more efficient than the traditionally used cosine similarity measure. engineering, technology & applied science research vol. 10, no. 2, 2020, 6102-6108 6104 www.etasr.com khalid & wu: supporting scholarly search by query expansion and citation analysis to construct the terms pool, as shown in figure 1, we first retrieve several top documents from the first retrieved document set for the query using a matching function and citation analysis. once the top relevant documents are retrieved, all the unique terms of top documents are selected to form a term pool or candidate term set. the terms are ranked by the tf-idf scoring scheme to rank the terms based on their appropriateness for qe. the following subsections illustrate the proposed approach. a. indexing formulation index formulation parses the document collection into indices so that retrieval can be done accordingly. we used the solr v7.2 ir platform for indexing and retrieval. solr tokenizes the free text in the target document collection to index tokens and passes through a term pipeline, which removes stop words and performs stemming to the indexing terms. a predefined list of stop words and stemming algorithms have been configured in solr schema to carry out all the steps in the pipeline. the tokens obtained after the term pipeline were used to generate indices. the document indexing is designed in a way to consider both qe via prf and citation analysis, i.e. the indexing scheme keeps paper citation network record for feeding into citation networks analyzer to utilize it in the strategic ranking of the proposed approach. b. structural overview this section demonstrates the pictorial flow of the way the system refines the final results set by considering citation networks analysis besides qe in article ranking. identifying the most cited papers using citation networks by means of the ranking algorithm has gained considerable attention [7]. citation network is a graph model gp = (p, e), consisting of nodes (p) and edges (e). here, p is the set of nodes representing papers p= {p1, p2, p3… pn}, and e is the set of edges e= {eij, 1 ≤ i ≤ n, 1 ≤ j ≤ n, i 6= j} that represent the links between papers. for example, if pi cites pj, then there should be an edge eij in between pi and pj. this edge/citation or formal reference shows a conversation between the paper's authors and exists when a published article cites an external source. citation network codifies scholarly conversation and plays a vital role in ranking scholarly articles [2]. this conversation appears in each published article as a pointer to other published views under consideration in footnotes, endnotes, or bibliographies for several aims. for instance, if some authors want to contradict the arguments of another author, they will cite the works where those arguments appear. likewise, if other authors rely on the conclusions of someone else's work or his previous work, they will cite it accordingly. the proposed framework uses citation analysis along with the bm25 retrieval model while computing the base-weight of articles for a given user query. the schema-independent view of how the system works is visually presented in figure 1. in figure 2, relevant and irrelevant papers to the user's query are indicated by red and blue rectangles respectively. the experimental analysis presented below reveals that qe by prf and citation analysis can support academic searchers in a more nuanced way with a little computational overhead. the original titles of the documents with interesting terms to the user query are explicated in figure 2 as a general retrieval scenario. the following section explains the way the proposed approach considers and expands the original query. fig. 2. general retrieval scenario. c. prf documents selection for query expansion query expansion (qe) methods mainly depend on feedback documents and extracted interesting terms from those documents. the documents used by prf query expansion methods might not be all relevant. without loss of generality, relevant documents contain relevant terms to the query, and those terms are useful in finding more relevant documents when added to the query. however, non-relevant documents may contain noisy terms that are not relevant to the query, and choosing those noisy terms for qe will not help in finding more relevant documents, but it will fetch irrelevant documents instead. thus, it is crucial to accept proper feedback documents and feedback terms for qe. selecting feedback documents in the qe process for scholarly document retrieval was first described in [26]. in the process of choosing good feedback documents, our classification module as a local qe method [27] adjusts the query relatively to the documents that match by considering the query and the related documents in the form of term frequency and inverse document frequency (tf–idf). this approach selects the interesting terms from the title and abstract of a few top articles as a prf from the first round search results list. the selected papers are then processed in rocchio style [28] to revise the search query using the tf-idf score of the top k words from title and abstract. in this way, the revised query and citation analysis are utilized to produce the final results list. d. why prf? it has been proved that urf-based techniques are better than prf-based techniques for scholarly document retrieval [29, 30], but they require the cost of human interaction. in our recent work [7], we utilized urf besides citation analysis for supporting the scholarly search. in this paper, we take into account the advantage of prf-based techniques, as they are engineering, technology & applied science research vol. 10, no. 2, 2020, 6102-6108 6105 www.etasr.com khalid & wu: supporting scholarly search by query expansion and citation analysis fully automated and do not require expensive outside inputs in the retrieval process while still performing well in ir. in the prf technique, the system assumes the top n documents retrieved in the initial run to be highly relevant and fetches the terms in those documents for qe. in our system, qe via prf is applied to all the runs by altering the solr unsupervised feedback qe plugin with the configuration of 20 terms from the top 3 documents retrieved in the initial run for adjusting the query. e. query expansion/formulation in the qe process, the terms having the highest tf-idf are called interesting terms. the approach extracts these terms from the first results. both of these mechanisms can be implemented as solr plugins [31] by using the rocchio algorithm. in our experiment, we employ the top 20 interesting terms after normalization in query reformulation through the solr request handler. our local-based qe procedure proceeds as follows: first, the base query is run for initial retrieval. the result is a ranked list of articles from the acl collection, in descending order of predicted relevance. from this ranked list, we define the top-ranked r articles as the relevant set, sr ={a0, a1, ..., ar}, each term ai appears in a document sr and in the reference section of the relevant papers after the citation networks analysis. this extraction creates an extended list of candidate terms, and their frequencies can then be used for qe weighting. a weighted query is then built with those top terms, and this query is combined with the original one to retrieve the final set of documents using citation network analysis. in our experiment, we take r=3 and consider the top 20 terms for qe. f. results re-ranking after qe using citation analysis after the retrieval results have been obtained from solr, a re-ranking technique was applied to the results with the expectation of boosting the system performance by adjusting the order of the retrieved documents. in this technique, a rearranging methodology was employed based on the availability of the desired terms in the retrieval results using citation analysis. besides citation analysis, the interesting terms are the deciding factors for determining a document’s relevancy. based on these conditions, a module is designed to rearrange the ordered list in such a way that the documents having the highest tf-idf besides citation analysis were given a higher relevance score. a description of the approach is described below. g. the materialization of the framework and algorithm the framework implements the above-mentioned task in three steps represented by three processing flow-lines, shown at the bottom of figure 3. blue arrows indicate the preprocessing, including information and citation extraction/ parsing of the research articles. the green lines show the actual search flow, i.e. how the approach performs initial retrieval. the brown lines represent qe and final retrieval. the system extracts interesting terms for qe from the top-three papers keeping in view both tf-idf and citation score. interesting terms are the ones having the highest tf-idf, which is the most widely used technique for keyword extraction [32]. the system runs the revised query in the background for generating the final results list. fig. 3. flow diagram of the proposed approach. 1) metadata and citation networks extraction the system pre-processes the corpus to extract metadata (e.g. authors, publisher, date, incites, out-cites), to construct citation networks, and to fragment papers into different desired fields (title, abstract, and content). the extracted data are then indexed in a multi-core architecture for efficient retrieval. 2) base weight computation, qe via prf and citation analysis in the second step, the framework computes the base weight of each paper for the initial query using bm25 and citation analyzer in terms of different indexed fields. the approach is described in the algorithm in figure 4. fig. 4. the retrieval algorithm. the algorithm shown in figure 4 is the main algorithm that implements the proposed technique. it calls procedure 1 in line engineering, technology & applied science research vol. 10, no. 2, 2020, 6102-6108 6106 www.etasr.com khalid & wu: supporting scholarly search by query expansion and citation analysis 1 for the initial search query to retrieve the first set of search results. procedure-1 computes the bm25 score of all the papers against the initial search query, which is combined with the citation analysis score to compute the final base weight of the candidate papers and ranks the initial search results in steps 614). the formula used in line 12 in procedure 1 computes paper score pr of each paper pi, in which d is a parameter usually set to 0.85 and n is the total number of research papers in the citation network, i.e. the set of all the nodes which inlink to paper pi. win(pi, pj) is the score of the link (pi, pj) that is estimated based on the number of incites of paper pi and the number of incites of all reference papers of paper pj. in line 2, the system selects the top 3 papers behind the scene for the qe process. in line 3, it uses these selected relevant results in selecting the most interesting terms as the revised query terms, i.e. used in qe for further processing. the algorithm, once again, calls procedure 1 in line 4 to compute the base weights of all the newly matched candidate papers against the revised query. based on the newly computed scores, the search results are re-ranked to the user in step-17. to demonstrate how the proposed approach work, we present an example-query in figure 5: let q be the search query “natural language processing technique.” this initial query is represented by a list of terms {i.e. q1, q2… qn}, and c is the list-of-candidate terms for qe, represented by {c1, c2 … ck}. the initial set of c is selected out of all of the terms in the first m (a parameter to be set) selected papers, which include all terms found in the selected papers. the list of candidate terms c is then extended by all the terms that appear in the selected documents. fig. 5. example query. for qe, we devise a simple approach inspired by rocchio's relevance feedback method [33]. an inverted index implementing bm25 is used initially to retrieve a ranked list of documents matching the original query. this list of documents acts as a data source for qe. our inverted collection index allows accessing the tf-idf weights of terms. the tf-idf weights of every term (word) in the n top-ranked documents are summed up, and the terms are sorted by their accumulated weight. finally, the first k terms of the sorted list are added to the original query. figure 5 demonstrates the general retrieval and qe scenario of the proposed approach by considering the prf with citation networks analysis. the first part of figure 5 displays a few top-ranked papers from the initial retrieval after posing the query q. the figure has four types of information: the user query, paper id, title, and relevance score. the relevance score is displayed here from the human evaluators to demonstrate the effectiveness of the proposed approach. the top-ranked papers of the initial query are considered for qe, from which several terms are extracted. the new, expanded query is then re-run on the collection for the results set. this demonstrates that the proposed qe algorithm increases the precision of the scholarly retrieval system. as we see, the final retrieval has comparatively relevant papers because the documents which include the interesting terms, are listed at the top of the search results list. the following subsections describe the experimental methodology, and the data set used, the results, and performance comparison. iv. experimental set up and results the dataset consists of 23058 papers, 17695 authors, and 121137 citations, indexed in solr [34]. for the evaluation, we use standard evaluation measures shown in table i. for recall, we took into account the assumption described in [22] that a human would often not consider many more than the top-50 results of a single query. a. dataset and query formulation the acl anthology network (aan) [35, 36] dataset is used for the experimentation of the proposed technique. it is an ir dataset having 23058 research papers from the acl anthology. the articles are from the field of computational linguistics. some of the statistics of the data set are given in table i. table i. some of the acl dataset statistics item value papers 23,058 authors 17,695 venue 350 we evaluated the proposed approach on 60 queries (associated with each subject area following the method to capture the logic of underspecified queries to evaluate the effectiveness of the system accordingly). these queries were structured and formulated for experimental analysis with the help of three ph.d. students, because the users' satisfaction can only be measured based on the experience of real users. b. evaluation criteria generally, for the relevance judgments of scholarly search systems, two different methods are used. the first method considers the reference list of the paper as ground truth to check that if the system can re-identify them or not. in the second method, the scholars' relevance judgments are taken into account. the first method is rather prejudiced toward citation networks analysis, but it does not address the use case we have in mind. therefore, we adopted the second method and involved users to check the system's relevance. engineering, technology & applied science research vol. 10, no. 2, 2020, 6102-6108 6107 www.etasr.com khalid & wu: supporting scholarly search by query expansion and citation analysis c. performance comparison we used a four-point scale for measuring ndcg: 3 for highly relevant, 2 for relevant, 1 for marginally relevant, and 0 for non-relevant. moreover, as recall needs to have expected relevant papers and can be computed on any k, therefore, we took the hypothesis that a researcher would often not consider more than the top 40 related papers for a given single query. we compared the proposed technique’s results with urf’s (our previous technique) [7] and bm25’s. to have a closer look and investigate the generalizability, we present the precision, recall, and ndcg results and graph of the three models in table ii and figure 6. table ii. performance comparison method p@5 p@10 p@20 r@15 ndcg@10 bm25 0.7148 0.6728 0.6335 0.2045 0.6812 urf 0.7600 0.7508 0.71 0.23 0.72231 prf 0.7534 0.7345 0.7074 0.2213 0.7115 fig. 6. performance comparison. the participants assessed the results using the 4-point scale. each participant evaluated the proposed technique for 20 different input queries. for each query, the top 20 results were checked, i.e. in total each participant evaluated about 400 papers. the papers suggested by bm25, urf [7], and our proposed prf approach vary. out of all the evaluated papers, approximately 34% of the results were found highly relevant, 22% relevant, 19% marginally relevant, and 25% not relevant at all to the given input papers. the ndcg@10, precision@5, 10 20, and recall@15 of the proposed framework are presented in the fourth row of table ii. the results show that qe via prf, along with a citation analyzer, improve precision, recall, and ndcg in all the cases. overall, the graph in figure 6 shows that the proposed technique can refine scholarly search effectively as compared to no query expansion (bm25). the urf [7] provides better results because the human can select more relevant results for qe. the benefits of the prf approach includes saving computing resources and less human intervention. since it assumes that the top papers returned by the initial user query are relevant, interesting terms are extracted from the top-ranked papers from the initial results to formulate a new query for a second retrieval cycle. d. microscopic analysis in this section, we evaluate the performance of the proposed technique at the query level. the analysis is given in figure 7, which illustrates the fact that for good ndcg, the precision rate can be obtained at the top 5 and 10 results with the integration of both citation analysis and qe via prf. the blue line in figure 6 dominates the other line fluctuations. the precision rate at the top 5 results is higher for both the retrieval approaches and close in performance at the top 20. overall, the microscopic analysis reveals our hypothesis that the incorporation of qe through prf and citation network analysis can support academic searchers in today’s colossal expansion of academic literature. fig. 7. microscopic analysis. finally, the approach is statistically more significant than the qe approach. the approach has a performance penalty: the query is executed twice. however, this can be partially mitigated through the intelligent cache, while it is known that the academic searchers usually spend more time in query reformulation to obtain the intended results [16]. both figures 6 and 7 show that the framework can provide more relevant papers for academic searchers at the top of the result list. we believe that our proposed approach is effective, and the integration of citation analysis and qe in the scholarly retrieval model can obtain comparatively more relevant papers. v. conclusion scholarly search engines attempt to reduce the manual efforts of researchers when searching for relevant papers. however, the huge expansion and the complexity of the academic web makes it a very hot and challenging area of research. in this paper, a new technique has been presented that uses query expansion (qe) via pseudo relevance feedback (prf) and citation analysis for supporting the scholarly search. the experiments were evaluated by standard evaluation metrics that demonstrate the usefulness of the proposed technique. the framework uses qe via prf and citation network analysis and is capable of filtering and ranking relevant papers in the retrieval model and can help scholars locate relevant papers in scholarly published documents. the experimental results engineering, technology & applied science research vol. 10, no. 2, 2020, 6102-6108 6108 www.etasr.com khalid & wu: supporting scholarly search by query expansion and citation 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[36] a. a. jbara and d. r. radev, “the acl anthology network corpus as a resource for nlp-based bibliometrics,” 2013. g. w. furnas, t. k. landauer, l. m. gomez, and s. t. dumais, “the vocabulary problem in human-system communication,” communications of the acm, vol. 30, no. 11, pp. 964–971, nov. 1987, doi: 10.1145/32206.32212. microsoft word 16-1944_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3387-3391 3387 www.etasr.com khan et al.: an outlook of ozone air pollution through comparative analysis of artificial … an outlook of ozone air pollution through comparative analysis of artificial neural network, regression, and sensitivity models jam shahzaib khan department of civil engineering quaid e awam university of science and technology, nawabshah, pakistan jam_shahzaib@hotmail.com salim khoso department of civil engineering quaid e awam university of science and technology, nawabshah, pakistan engr.salimkhoso@gmail.com zafar iqbal faculty of civil engineering universiti teknologi malaysia, malaysia zafar.thalvi@gmail.com samiullah sohu department of civil engineering quaid e awam university of science and technology, nawabshah, pakistan sohoosamiullah@gmaiol.com manthar ali keerio department of civil engineering quaid e awam university of science and technology, nawabhshah, pakistan mantharali99@quest.edu.pk abstract—air pollution and atmospheric ozone can cause damages to human health and to the environment. this study explores the potential approach of the artificial neural network (ann) model and compares it with a regression model for predicting ozone concentration using different parameters and functions measured by the climate prediction center of us national weather service. in addition, this study has compared the economic viability of ann and other measuring methods. results showed that the ann-based model exhibited better performance. such model types can be beneficial to government agencies. by predicting ozone concentration government agencies can take preventive measures to avoid significant health effects, protect local populations, and help preserve a sustainable environment. keywords-ozone pollution; environment; sustainability i. introduction ozone is a reactive gas, considered a subsidiary pollutant as it is not discharged directly into the atmosphere. ozone is observed in two different regions of the atmosphere, ground level ozone (“bad ozone”) in troposphere and “good ozone” in stratosphere, both with the same chemical composition of o3. ozone at stratosphere protects from harmful sun rays and troposphere ozone is the main component of smog [1], caused by automobile emissions, especially in urban areas. ozone is formed by the chemical processes of oxides of nitrogen (nox) and volatile organic compounds (vocs) in the presence of sunlight. the ozone concentration in urban areas is relatively high compared to rural areas, and it rises in the morning, reaches its peak in the afternoon, and decreases at night time [2]. us environmental protection agency (usepa) has set standards called air quality index (aqi) for ozone (table i) [3]. table i. usepa aqi standards for ozone health concern levels value meaning good 0 to 50 air quality is considered satisfactory and air pollution poses little or no risk. moderate 51 to 100 air quality is acceptable, however, for some pollutants there may be moderate health concern for a very small number of people who are unusually sensitive to air pollution. unhealthy for sensitive groups 101 to 150 members of sensitive groups may experience health effects. the general public is not likely to be affected. unhealthy 151 to 200 everyone may begin to experience health effects. members of sensitive groups may experience more serious health effects. very unhealthy 201 to 300 health warnings of emergency conditions. the entire population is likely to be affected. hazardous 301 to 500 health alert: everyone may experience serious health effects. the ozone concentration significantly depends upon the atmospheric temperature, uv index, and emissions from different sources. usepa has defined the overall percentage of the different sources of emission. figures 1 and 2 show the sources of nox and voc in mississippi state [4]. ozone affects lungs, causes asthma and lung cancer [5]. the extent of respiratory illness depends on various factors such as concentration and duration of exposure, climate characteristics, individual sensitivity, preexistent respiratory diseases, and socioeconomic status [6, 7]. this study aims to predict ozone for jackson, mississippi. jackson is the largest urban area in mississippi with a population of 173,514. data engineering, technology & applied science research vol. 8, no. 5, 2018, 3387-3391 3388 www.etasr.com khan et al.: an outlook of ozone air pollution through comparative analysis of artificial … were collected from the climate prediction center of the national weather service [8], and were used in an ann to predict ozone and to find out the correlation between some variables. from the daily measured ozone data, the average was taken to observe the trend of the ozone pollution. as shown in figure 3 a comparison to the aqi shows very unhealthy and hazardous level of health concerns [8]. fig. 1. nox sources in mississipi. fig. 2. voc sources in mississipi. fig. 3. average of daily ozone of jackson, ms-2014 ii. ann model development an ann model was developed based on the available data. initially, ann architecture was developed and used data from 2010 to 2014. these data were given numbers to identify the intensity of the uv index based on the number of each day of each year. however, some data was missing. due to the large number of data sets available, it has been decided to remove the missing data sets in order to maintain accuracy. the model architecture was developed in order to work as a computational model using neuronets [9]. anns are often used as a black-box model and show any continuous function to discretional accuracy, where the number of nodes is large [10]. in the model development, dependent and independent categories were found and formed in the required ann format. data was also classified as training, testing, and validation sets. correlation and regression were carried out to determine the correspondence between the variables involved. in the first phase, the ann was set to run on training and testing data sets to obtain the required hidden nodes and training iterations for the optimal model. for the next phase, the best network obtained from the previous phase, was verified on the database validation sets. the best performing network obtained from the previous phase has been then retrained on all available patterns in the database in order to account for all information embodied in the database. this retraining provides reliable prediction and better accuracy. research studies carried out using this approach had shown that the train-all stage is recommended to obtain a better performing model [11]. iii. ann model architecture data considered in this study was taken from the climate prediction center of national weather service. additional data of air operation was taken from federal aviation authority, usa (faa) [12]. the data was then organized for utilization by the ann. in this case, the database was set to include seven dependent variables and one independent variable as listed below: 1. independent variables: • day • clear sky uvi • cloudy sky uvi • cloud transmission “percent probability clear” • solar zenith angle “percent probability scattered” • aerosol transmission “percent probability broken” • air operation data of jackson, ms 2. dependent variable: • total ozone concentration measured ozone was based on 5 inputs: clear sky uvi, cloudy sky uvi, cloud transmission, solar zenith angle, and aerosol transmission. in this study, air operation (flights operated at jackson international airport) was also used as an input to identify the impact of air operation on the ozone pollution. the ann model was developed and selected based on statistical accuracy measures such as maximum values of coefficient of determination (r 2 ), averagedsquared-error (ase) and minimum values of mean absolute relative error (mare). collectively, 1059 data sets were used for the ann modeling, namely 479 for training, 232 for testing, 232 for validation, and 116 were kept for true validation. data was used for training and testing in order to obtain the optimal network. in this case, optimum network was achieved using 2 hidden nodes at 20,000 iterations. accuracy statistics found on the optimum network were mare-tr (mare on training data)=0.329%, mare-ts (mare on testing data)=0.318%, r 2 -tr=0.997, r 2 -ts=0.997, ase-tr=0.000034 and ase-ts=0.000032. figures 4-7 show the comparison of train, test, validate and train-all modeling stages respectively. these graphs engineering, technology & applied science research vol. 8, no. 5, 2018, 3387-3391 3389 www.etasr.com khan et al.: an outlook of ozone air pollution through comparative analysis of artificial … show the best prediction models obtained for all modeling stages. fig. 4. training predicted results versus measured values for ozone concentration. fig. 5. testing predicted results versus measured values. fig. 6. validation predicted results versus measured values. fig. 7. train-all predicted results versus measured values. iv. regression model regression model has been developed using microsoft excel data analysis toolkit. while developing the required linear regression prediction model, all 1059 data sets were used. same input and output variables with the ann model were used. linear regression approach was used, and the following regression equation was developed: ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 11125.86 0.03 27.77 2.07 0.19 5.50 123.87 0.01 q day clear sky uvi cloudy sky uvi cloud transmission solar zenith angle aerosol transmission air operation data = − + − −+ + + − + − + + (1) from the linear regression model, it can be observed that aerosol transmission has a very high impact in the output. on the other hand, the clear sky uvi is placing moderate impact on output, while the air operation data of jackson does not have any significant impact. the developed linear regression model produced a statistical accuracy measure r 2 of 0.79 with standard error of 13.29. in comparison, an r 2 value as 0.998 was obtained via the developed ann model. this translates to about 25% increase in prediction accuracy when compared to the regression model. the regression model comparison graph is shown in figure 8. as can be noted, a wider cloud is shown in figure 8 in contrast to the very thin cloud depicted in figures 4-7. fig. 8. regression model predicted results versus measured values v. sensitivity analysis sensitivity analysis is a systematic study of the behavior of the model that reacts over ranges in the variation of inputs and parameters [1]. it can be used to understand whether the predicted model behavior is constant under all parameters or it is changing with respect to change of independent variables. the basic objective of research was to identify the factors affecting ozone concentration and to develop an appropriate model for predicting ozone levels of urban areas of jackson, mississippi based on the uvi index data and air operation data. from the correlation matrix, it was observed that some of the independent input variables were highly correlated, namely day, clear sky uvi, cloudy sky uvi, cloud transmission, solar zenith angle. therefore, sensitivity analysis was not carried out on these variables. aerosol transmission and air operation were the only two independent input variables found to have the least correlation values. therefore, sensitivity analysis was carried for these two variables by keeping all other variables constant. accordingly, ann output vs. aerosol transmission and air operation sensitivity plots were obtained as shown in figures 9 and 10, respectively. it can be observed that both variables do not impact on ozone concentration levels. fig. 9. sensitivity analysis of aerosol transmission on ozone concentration. vi. results discussion results obtained from ann and regression models clearly depict the performance and accuracy of both models. the comparison of the prediction accuracy measures (table engineering, technology & applied science research vol. 8, no. 5, 2018, 3387-3391 3390 www.etasr.com khan et al.: an outlook of ozone air pollution through comparative analysis of artificial … ii) shows that the ann model excels. sensitivity analysis indicates that there is no impact found on the ozone levels from prevailing values of aerosol transmission and/or air operation. however, ann model implicates that the coefficient of determination has apparently the same value. thus, train, test, validate and train-all stages of ann also speculate that data is smooth. ase and mare show that there is very little error between observed and predicted values. fig. 10. sensitivity analysis of air operation table ii. ann results training data testing data validation data train-all data mare-tr= 0.329% mare-ts= 0.318% mare-val= 0.304% mare-trall= 0.287% ase-tr= 0.000034 ase-ts= 0.000032 ase-val= 0.000032 ase-trall= 0.000029 r 2 -tr= 0.9978 r 2 -ts=0.9976 r 2 -val=0.9977 r 2 -trall=0.998 a microsoft excel interface (based on developed ann prediction models) was developed to project the ozone concentration levels from a given set of input variables to facilitate the prediction process (figure 11). fig. 11. excel interface application screen shot. it is worth noting that two ann models were implemented in the interface where model 1 is based on training, testing and validation stages only, and model 2 is based on the train-all data. the prediction accuracy of model 2 is expected to be higher than that obtained from model 1. however, since both models yield very high prediction accuracy, the difference in this case will be minimal. both models are included in the interface in order to enable the user to assess the predicted values from two different perspectives. it is worth noting that both models have similar architecture of 2 hidden nodes and similar number of connection weights. however, the values of the connection weights are different because training data sets for each model are different. vii. economical analysis there are many ways of measuring ozone in the atmosphere, such as aircrafts, high altitude balloons, satellites, and on ground instruments [13]. table iii shows the relative equipment, cost, expertise and accuracy for atmospheric ozone measurements. table iii. comparison of equipment for ozone measuring [14] equipment cost (approx.) us $ training and skills needed review spectrophotometer dobson spectrophoto meter 100,000 training: dobson/brewer for global observations: 2 weeks. dobson training is available on a space limited basis at soohk brewer maintenance requires high technical abilities. new instruments are not currently available commercially. brewer spectrophoto meter 100,000 calibrations are required every 12 years and are available commercially. m-124 filter ozonometer 15,000 new instruments are not currently available commercially. ozonesondes one balloon flight package 600 to 800 to prepare and conduct an ozone sounding, one technician with some experience in meteorological instrumentation and training in simple chemical laboratory handling is required. to perform an ozone sounding, pre and post flight operations take about 8 hours. training for performing an ozone sounding will take from 2 to 4 weeks at a sounding site. na ground station equipment costs 30,000 na surface ozone uv ozone monitor with data system 15,000 personnel: station operator: half a day per week. training: operator for station instrument: one week various annual costs including inlet filters and instrument repairs when required: about 300/year network standard 15,000 table iii implies that the various methods used to measure ozone air pollution cost much more than the ann calculating technique. anns have been widely used in various sectors and have played a vital role in modernizing computer assisted techniques by handling large data sets and predicting with quite small error. viii. conclusion and recommendations in this study, ann approach was used to predict, compare and verify ozone concentration at jackson, mississippi. ann-based models were observed to perform engineering, technology & applied science research vol. 8, no. 5, 2018, 3387-3391 3391 www.etasr.com khan et al.: an outlook of ozone air pollution through comparative analysis of artificial … better than linear regression model. this research also illustrated the economic viability of all models for calculating and measuring ozone in the atmosphere. the developed models can be beneficial (via the use of a user friendly interface) to government agencies and other stakeholders. by predicting ozone concentration, government agencies can take preventive measures. this study can also be extended further by including additional input variables such as vmt (vehicle miles travel) and emissions from the industry within the jackson region that might impact the ozone concentration levels. references [1] s. cordiner, r. baciocchi, m. attina, “a sensitivity analysis of ozone formation to ambient air composition by means of photochemical models”, water, air soil pollution: focus, vol. 2, no. 5-6, pp. 573–85, 2002 [2] b. j. bloomer, j. w. stehr, c. a. piety, r. j. salawitch, r. r. dickerson, “observed relationships of ozone air pollution with temperature and emissions”, geophysical research letters, vol. 36, no. 9, 2009 [3] us environmental protection agency, air quality index basics, available at: https://airnow.gov/index.cfm?action=aqibasics.aqi (accessed april 12, 2017) [4] us epa office of air quality planning and standards, national emissions inventory 2016, available at: https://www3.epa.gov/cgibin/broker?_service=data&_debug=0&_program=dataprog.state_1.sa s&pol=nox&stfips=28 (accessed april 12, 2017) [5] r. b. devlin, w. f. mcdonnell, r. mann, s. becker, d. e. house, d. schreinemachers, h. s. koren, “exposure of humans to ambient levels of ozone for 6.6 hours causes cellular and biochemical changes in the lung”, american journal of respiratory cell and molecular biology, vol. 4, no. 1, pp. 72–81, 1991 [6] m. kampa, e. castanas, “human health effects of air pollution”, environmental pollution, vol. 151, no. 2, pp. 362-367, 2007 [7] environmental protection agency (epa), ozone pollution 2016, available at https://www.epa.gov/ozone-pollution (accessed april 12, 2017) [8] nws, climate prediction center, uv index: annual time series, available at: http://www.cpc.ncep.noaa.gov/products/stratosphere/ uv_index/uv_annual.shtml (accessed april 12, 2017) [9] y. najjar, x. zhang, “characterizing the 3d stress-strain behavior of sandy soils: a neuro-mechanistic approach”, in: numerical methods in geotechnical engineering, pp. 43–57, crc press, 2000 [10] m. manngard, j. kronqvist, j. m. boling, “structural learning in artificial neural networks using sparse optimization”, neurocomputing, vol. 272, pp. 660-667, 2018 [11] h. yasarer, y. najjar, “development of a mix-design based rapid chloride permeability assessment model using neuronets”, 2011 international joint conference on neural networks, san jose, usa, july 31august 5, 201 [12] faa. air traffic activity system (atads): airport operations 2014, available at: https://aspm.faa.gov/opsnet/sys/airport.asp (accessed april 12, 2017) [13] d. w. fahey, m. i. hegglin, “how is ozone measured in the atmosphere?”, in: twenty questions and answers about the ozone layer: 2010 update, world meteorological organization, 2010 [14] world meteorological organization, global atmosphere watch, global atmosphere watch measurements guide, gaw report no. 143, wmo, 2001 microsoft word etasr_v10_n6_pp6542-6548 engineering, technology & applied science research vol. 10, no. 6, 2020, 6542-6548 6542 www.etasr.com tavassoli et al.: integrated preventive maintenance scheduling model with redundancy for cutting … integrated preventive maintenance scheduling model with redundancy for cutting tools on a single machine leyla sadat tavassoli department of industrial manufacturing and systems engineering university of texas at arlington arlington, tx, usa leylasadat.tavassoli@mavs.uta.edu nahal sakhavand department of industrial manufacturing and systems engineering university of texas at arlington arlington, tx, usa nahal.sakhavand@mavs.uta.edu seyed sajjad fazeli department of industrial and system engineering wayne state university detroit, mi, usa sajjad.fazeli@wayne.edu abstract-in this paper, we present an integrated multi-objective framework of a single machine for a single cutting tool problem. our maintenance policy is based on performing minimal repairs in case of a minor failure and preventive maintenance (pm) to avoid a major failure that results in the replacement of the tool. this framework allows simultaneous optimization of the two conflicting time and cost objectives. a redundant system is proposed as a part of the model to assist the production line under a major failure. in addition, the tool’s preventive maintenance time is synchronized with the completion of the machine tool’s work cycle to reduce the machine’s set-up time. the model was optimized using a customized non-dominated sorting genetic algorithm (nsga-ii). an experimental study based on real-market data was conducted and the results were compared with the ones obtained from classical methods. keywords-maintenance scheduling; preventive maintenance; redundancy; non-dominated sorting genetic algorithm; multiobjective optimization; time and cost trade-off i. introduction addressing the trade-off between time and cost brings forth several challenges. notably, any change in the time schedule has an impact on project cost and ultimate profit. this is reflected in the efficiency of the tools and machines in the production line. cutting tools are widely used in almost all lines of industrial systems. however, due to their constant use they are subjected to gradual depreciation and/or severe damages. these complications attribute to the costs of storage and procurement as well as the production disruption during operation. in order to reconcile these challenges, it is necessary to consider the system characteristics before implementing the production process. in a manufacturing system, all the equipment parts, including machines and tools, have an estimated lifetime. in order to prevent the line from going idle as a result of an unexpected minor or major breakdown of a piece of equipment, a common approach is to incorporate preventive maintenance (pm) as proposed in [1, 2] using linear programming algorithms. pm is regularly performed to decrease the likelihood of system failure under two alternatives. a repair action allows the equipment to be operable again or a replacement to a new tool. for a comprehensive review on integrated maintenance and production planning models, we refer the enthusiastic reader to [3]. in general, there is a possibility of an excessive amount of time to repair a tool in addition to the fact that replacement with a new element might not always be to the best profit interest. therefore, pm actions alone may not be as effective in planning decisions. another technique to improve system performance, is to use redundancy in the processing operation [4]. the redundant system is designed to automatically take over the equipment operation if a failure occurs. some works have considered a joint redundancy and maintenance strategy optimization [5]. this model determines the optimal redundancy levels in addition to the minimal repair simultaneously. while there are clear advantages of incorporating pm and redundant systems (e.g. reduction in time and cost of failures), these systems can create other difficulties such as extra operational costs. in an optimal pm scheduling process, there is an essential role in resource and planning management to meet the conflicting user-driven requirements. the objective of such a system is to minimize the time between the essential pm actions and the corresponding cost. although in a competitive environment minimizing time and cost is less likely to happen simultaneously, an optimal trade-off between time and cost is corresponding author: leyla sadat tavassoli engineering, technology & applied science research vol. 10, no. 6, 2020, 6542-6548 6543 www.etasr.com tavassoli et al.: integrated preventive maintenance scheduling model with redundancy for cutting … achievable. time and cost trade-off models have long been addressed using traditional exact optimization algorithms where the cost function is linear [6–9] or nonlinear [10]. in several works, these problems have been formulated using dynamic programming [11]. however, given the np-hard nature of the trade-off problems, using exact algorithms may become computationally intractable for large-size nonlinear problems. in order to improve the computational performance over the exact algorithms, several works suggest near-optimal heuristics such as genetic algorithms (ga) [12-14], simulated annealing (sa) [15], and ant colony optimization (aco) [16]. in all of these models, the problem is considered as a single objective time and cost trade-off. alternatively, time and cost trade-off problems can be formulated as multi-objective models. in conventional multi-objective optimization problems, weighted lp and nlp algorithms yield a single optimal point based on the random or fixed weights [17, 18]. in singleobjective optimization models and multi-objective problems, the endeavor is to find a set of optimal solutions for conflicting objectives which are not necessarily superior corresponding to all objectives, called the non-dominated pareto optimal solutions [19-21]. utilizing evolutionary algorithms such as non-dominated sorting genetic algorithm (nsga) [22-25], multi-colony aco (moaco) [26], and multi-objective particle swarm optimization (mopso) [27, 28], establishes a set of solutions which are subject to decision-makers’ selection from the optimum. although single-objective maintenance scheduling problems have been broadly addressed in the literature, the number of studies on multi-objective maintenance problems is quite limited. authors in [29] use goal programming to solve the pm and replacement scheduling problem while suggesting heuristic solution procedures for large-scale problems. for large-scale multi-objective maintenance scheduling problems, nsga is commonly used in search heuristics to optimize these problems based on operators of biologically inspired principles like mutation and crossover. using ga, we can obtain optimal maintenance actions for the multi-objective maintenance scheduling problem of deteriorating structures. authors in [14] proposed a bi-objective model for electromechanical products where they considered soft and hard failure as well as an imperfect pm approach. their goal was to maximize the availability and minimize the cost of the system. in terms of solution methodology, they considered nsga-ii with the single mutation and crossover operators. compared with the literature, the main contributions of this paper are: • we propose an integrated multi-objective preventive maintenance scheduling for a cutting tool system on a single machine with redundancy that captures the existing time and cost trade-off. our model inherits the merits of providing a more realistic set of solutions which are tested for a large-scale case study. • our model provides a well-suited customized redundancy option to decide which tools require a redundant system to assist the production line in addition when conducting pm actions. • we present an innovative customized crossover and mutation operators in the nsga-ii algorithm and we contrast our set of pareto front solutions with conventional nsga-ii algorithms. our numerical results attest the faster convergence of our modified nsga-ii algorithm over the techniques used in the literature. ii. problem description in order to formulate our scheduling problem, we begin by stating the following assumptions. a. minor failure problem let us consider an operating cutting tool assembled on a machine. as soon as a minor failure occurs, we perform minimal repair so that the tool is in an operable status again. in this case the tool’s useful life does not change. generally, tools’ life deteriorates with time which necessitates regular tools inspection to replace the tool or perform a minimal repair. to address this, we schedule reoccurring pm actions to avoid unpredictable failures which affect the efficiency of the production line. in this case, the tool’s age is reset. in our problem, as a part of the optimization process, we would like to minimize the process time of pm actions which leads to an optimized cost and time of the process. b. major failure problem from time to time, cutting tools are subjected to major failures in the middle of a cycle. these failures are caused by either human error or a tool life depreciation which leads to complete tool breakage. in order to keep the production line active, a new replacement tool needs to be available. however, inventory and holding equipment is costly. therefore, in addition to scheduling pm actions in a timely manner, including redundant systems can have a significant impact on a cost-effective and time-saving system performance. c. setup time pm actions implementation entails stopping the machine tool and extracting the cutting tool out of it. if pm actions do not take place at the end of the machine’s cycle time, we have to interrupt the machine in the middle of the cutting operation. after pm actions are performed, the machine requires to be set up again. we define a penalty indicator for the setup time in the middle of the production process which we tend to minimize in our objective function. d. the integrated problem in the cutting process, in addition to performing pm actions in case of a minor failure, we consider a redundant system in the form of a backup when a major failure occurs. moreover, as a part of our objective, we minimize the setup time after each process disruption. in the next section, the full model formulation is provided. iii. problem formulation our formulation is inspired by [30]. the failure rates for minor and major failures are determined as: engineering, technology & applied science research vol. 10, no. 6, 2020, 6542-6548 6544 www.etasr.com tavassoli et al.: integrated preventive maintenance scheduling model with redundancy for cutting … 1 1 1 ( ) ( ) ( ) y f y r y f y ∞ = ∫ (1a) ����� � ��� � ��� ��� (1b) where f1(y) and f2(y) are the probability density functions for minor and major failure variables. let zt , t ∈ � be 1 if pm actions are performed before time t and 0 otherwise. we can formulate the effective age of the cutting tool as: �� � �1 � �������� � �� ∀� ∈ � (2) equation (2) suggests that when zt = 0, no pm action is applied before time t. therefore, the tool’s current age is its age at the previous time period t-1 in addition to some period length denoted by l. on the other hand, if pm actions are performed on the tool before t, its age is reset and the tool is considered as new. next, we present the maintenance costs which consist of the expected cost of minimal repair (cmr) and the cost of pm (cpm) for each tool. �� � ∑ �"� #�$� �� � ��% �����&�'()*'( ∀+ ∈ , (3a) we can immediately write the cycle time for pm actions as: �� � ∑ �"� #�$� �� � ��% �����&�'()*'( ∀+ ∈ , (3b) where tpm and tmr are the process time for pm actions and minimal repair which are considered as continuous variables. if a major failure occurs, the production line will be stopped until the tool is replaced. most of the equations described here can be applied to every cutting tool i ∈ i. we will explicitly mention when this is not the case. we denote the penalty associated with the major failure by cf1 and define it as: �-� � ��,�.�� �����&�� � ��'()*'( (4a) where cm is defined as the cost of production of machine tool per time and ti and ct are the idle time of the machine due to a major failure and cost of replacing a broken tool with a new one respectively. the time it takes for replacing the tool can be computed as: �-� � �, �����d��'()*'( (4b) we define b to be 1 if the redundant system is applied and 0 otherwise. when redundancy is considered in the process, the major failure occurrence penalty is defined as in (5a) which is the cost of applying a redundant system denoted by crs in addition to ct. �-� � �%0 � �� (5a) in this case, we assume that the process time of replacing the tool is ignored as it does not affect the overall production time as a result of a backup system which results to: �-� � 0 (5b� consequently, (6a) and (6b) construe the cost and time penalty functions respectively. let tset be the machine setup time after being interrupted in the middle of its cycle time to conduct pm. we note that if the process time of the pm actions is equal to a coefficient of the cycle time of the machine tool, �� = 0, which results in no time penalty. the cost penalty function can be interpreted in a similar manner. �456'7� � ∑ ��tset�.#�$� (6a) �456'7� � ∑ ���<=�#�$� (6b) where �� can be computed as: >� � 1 ⇔ ∄a ∈ b: a d cycle �+i= � �"� (7a) >� � 0 ⇔ ∃a ∈ b: a d cycle �+i= � �"� (7b) our cost and time objective functions can be formulated as: min cost=k �� � ��� �.� � βmcf�,m �p $��1 � q ��-�, � �r56'7� , (8a) min time=k �� � q �-�, � �1 � q ��-�, �p $��r56'7� , (8b) where q is binary ∀+ ∈ , and tpmi ≥ 0 ∀+ ∈ ,, where , is the set of cutting tools in the process. iv. methodology on a production basis, we often use a lot of cutting tools in the process which affects the decisions about time and cost of pm actions and redundant systems inclusion. to mitigate the computational difficulties of solving the resulting large scale problem due to the non-linear objective functions, we apply a modified nsga-ii heuristic algorithm. we apply these modifications in the crossover and mutation operators which allow a faster convergence. we ultimately assess our solutions by introducing an index penalty in the algorithm. a. initialization before creating the crossover and mutation operators, we require maintaining a diverse population of the candidate solutions which we refer to as chromosome strings. for starters, we generate 100 random solution alternatives. for each of our two variables of q and tpmi, we assign a row which is extended for each tool i. figure 1 demonstrates one set out of the randomly generated 100 solutions. fig. 1. a chromosome string of set of candidate solutions. b. mutation we define 3 mutation operators where we generate the parents using the roulette wheel selection. we design the first mutation operator to change the value of a random β cell picked from its row. in order to address the possibility of finding better optimal solutions whether redundancy is applied or not, the proposed operator switches the values of the cell from 0 to 1 or from 1 to 0. our second operator picks a cell engineering, technology & applied science research vol. 10, no. 6, 2020, 6542-6548 6545 www.etasr.com tavassoli et al.: integrated preventive maintenance scheduling model with redundancy for cutting … from the second row of the chromosome string. this operator sums the value of the cell with a random number x in order to avoid selecting local solutions. the third operator is set to select solutions of the second row with the minimum penalty. c. crossover for our experiment, we consider two crossover operators where the first one generates a parent using roulette wheel selection. it then switches two randomly selected parents and creates two offspring. the second operator generates uniformly distributed solutions in the pareto front. in this approach, the operator chooses consecutive parents from the pareto front which maximize the crowding distance. we use the following equations to create new solution candidates. ��s � �� � �1 � t���� � ��� (9a� ��s � �� � t��� � ��� (9b) where 0 ≤ λ ≤ 1 and ��s and ��s are the updated new cell values. d. non-dominated sorting to sort the solutions, we use the convexity crowding distance method. for every chromosome we have: & � w xy �z��[xy\]^�xy\_y ` $6 (10) where a6�b� is the nth objective function and a6.'z and a6. 6 are the maximum and minimum values of the n th objective function value. g is the closest value obtained to the considered objective value. e. penalty algorithm as explained above, we consider a penalty for each pm action that requires disturbing the production line in the middle of its cycle. in order to find the number of each solution's penalty α, we conduct a penalty algorithm which is illustrated in figure 2. fig. 2. penalty function algorithm. f. numerical example for the computational experiments, we used real data collected from [31]. in our numerical experiment, we consider 6 cutting tools which perform machining operation on an aluminum part. using a vertical milling machine, it produces 10000 parts with a cost of $2.5 per minute. we consider the idle time of the machine tool in case of a major failure to be one complete shift of 8 hours and the cycle time of the machine tool to be 375 seconds. figure 1 demonstrates the time and cost of pm for each cutting tool. we note that the cost and time of pm actions are assumed under screw and tool replacement after a breakage. v. numerical result a. results for modified-nsga-ii vs. nsga-ii we initialize the algorithm by randomly generating a population of 100. the number of the initial population and the solutions provided by mutation and crossover differ based on their importance. table i demonstrates the population for each operator. table i. pm cost and time results tool #1 tool #2 tool #3 tool #4 tool #5 tool #6 cpr ($) 12 47 14 25 23 17 cmr ($) 12 9 8 7 8 7 tpr (min) 4 5 4 6 4 4 tmr (min) 4 2 2 2 2 2 table ii. algorithm specifications and population algorithm specification number of produced population primary population 100 mutation type1 30 mutation type2 30 mutation type3 30 crossover 1 30 crossover 2 30 in order to assess the performance of our modified nsgaii algorithm, we define a reference based on 100 best candidate solutions obtained by the modified nsga-ii, nsga-ii with redundancy, and nsga-ii without redundancy, each replicated 10 times. we conduct the experiment using matlab platform on a windows-based server with 16 gb ram. our case study is based on a real data-set. figure 3 contrasts the pareto front results for the three algorithms. it can be seen that the modified nsga-ii provides a wider range of nondominated optimal solutions. to provide better intuition on how the implemented algorithms perform, the detailed results are exhibited in table iii. each replication was run for 100 iterations. we observe that due to the computational complexity of the modified nsga-ii, it takes relatively more time to solve each replication. moreover, since we incorporated a mutation operator that seeks candidate solutions with no penalties, there are fewer solutions with penalty for the modified nsga-ii than for nsga-ii with and without redundancy. applying our mutation operators select solutions with no penalty in our proposed nsga-ii. however, there is no such operator incorporated to generate these solutions and may randomly select these solutions. we also notice that engineering, technology & applied science research vol. 10, no. 6, 2020, 6542-6548 6546 www.etasr.com tavassoli et al.: integrated preventive maintenance scheduling model with redundancy for cutting … nsga-ii with redundancy provides better computational performance confirming the effectiveness of including redundancy in the system. the results of the comparison between the nsga-ii and the modified nsga-ii can be seen in table iii. table iii. results for nsga-ii and modified nsga-ii time penalty nns no. iteration modifiednsga2 nsga2 modifiednsga2 nsga2 modifiednsga2 nsga2 without the redundant system with the redundant system without the redundant system with the redundant system without the redundant system with the redundant system 1 100 128.6 94.2 86.5 131.4 161.2 178.5 0 19 1 2 100 134.3 87.8 87.2 116.0 176.4 150.6 0 0 6 3 100 127.2 88.1 88.5 74.0 115.5 142.5 13 8 5 4 100 127.0 88.0 88.6 125.8 177.1 167.3 0 1 5 5 100 126.8 100.2 90.0 68.7 171.7 160.3 2 0 0 6 100 128.2 113.2 87.4 75.6 156.3 157.3 31 4 4 7 100 128.2 87.8 87.4 68.2 167.5 120.6 15 0 14 8 100 126.0 86.5 87.3 119.1 121.7 159.4 1 14 7 9 100 129.8 86.0 88.1 92.7 136.2 183.2 7 6 20 10 100 128.0 85.9 87.9 97.2 163.7 156.8 1 0 2 ave. 128.4 91.8 87.9 96.8 154.7 157.6 7 5.2 6.4 std. dev. 2.20 8.31 0.92 23.44 21.25 16.86 9.59 6.35 5.85 inverted generated distance delta index spacing metric no. iteration modifiednsga2 nsga2 modifiednsga2 nsga2 modifiednsga2 nsga2 without the redundant system with the redundant system without the redundant system with the redundant system without the redundant system with the redundant system 1 100 268990 670680 1782100 4618 2499 465 185 796 291 2 100 107210 651130 1772100 4974 3051 478 237 704 278 3 100 82140 656510 1774300 5716 3118 583 332 204 362 4 100 252240 601480 1782100 4606 3368 249 232 1273 83 5 100 130800 675760 1777100 5296 2706 607 258 479 572 6 100 81027 600140 1765000 5600 2221 332 184 695 202 7 100 119160 677110 1785900 5153 3214 257 248 429 143 8 100 177600 639400 1779800 5609 3163 414 241 354 249 9 100 160170 677310 1771300 3978 2551 195 212 515 74 10 100 50396 674010 1784400 6373 3401 442 225 483 396 ave. 142970 652353 1777410 5192 2929 402 235 593 265 std. dev. 68860 28442 6324 649 384 133 39 281 145 fig. 3. optimal pareto front for nsga-ii vs modified nsga-ii. b. inverted generated distance this approach is designed to evaluate the diversity of the optimal solutions computed by: ,cd � ∑ e�f,r�g∈h∗|r∗| (11) where p is a set of non-dominated solutions obtained by the algorithm and "∗ is the set of uniformly distributed points in a true pareto front. &�k, "� is the minimum euclidean distance between k and the points in ". in table iii, we observe that modified nsga-ii provides far less igd numbers over the other nsga-ii algorithms across all the replications which prove the significant effectiveness of the algorithm in finding the optimal solutions. c. delta index in this approach, we examine the distribution of the pareto front considering the following equation: l�<� � w |e_�em||n|�� |n|�� $� (12) where di is the euclidean distance of two consecutive solutions of the pareto front with s optimal solutions and &̅ is the average distance. the less the delta is, the more uniformly the pareto front will be distributed. however, the range of pareto front solutions affect the delta index as is demonstrated in table iii. since the modified nsga-ii selects a wider range of solutions engineering, technology & applied science research vol. 10, no. 6, 2020, 6542-6548 6547 www.etasr.com tavassoli et al.: integrated preventive maintenance scheduling model with redundancy for cutting … in the pareto front, its index is more than other reported indices for nsga-ii algorithms. d. spacing metrics in this technique, we opt for analyzing the uniformity between the pareto front and the reference solutions which can be computed as in (13): 0"�<� � p �|q|�� w �&̅ � & �� |n| $� (13) where & is the minimum distance of optimal solution i from the reference point and &̅ is defined as the average distance for s optimal solutions. notice that the spacing metrics across all the replications for modified nsga-ii are less than nsga-ii with and without redundancy which suggests better uniformity to reference solutions. vi. conclusion in this study, we developed an integrated multi-objective preventive maintenance scheduling model for a single machine cutting tool system with the option of redundancy in one framework. redundancy performs as a backup and major failure safe system. our model optimizes the redundancy requirements and the time duration of the pm process. we propose a modified genetic algorithm with customized mutation and crossover operators which allow finding a better pareto front compared to the existing algorithms. we implemented our experiments on a case study drawn from real data. our results confirm the better performance of the modified nsga-ii algorithm which suggests that evolutionary algorithms alone do not necessarily provide more viable optimal solutions and require customized operators for better computational efficiency. moreover, integrating the pm process with redundancy outperforms the conventional models by providing more realistic solutions. furthermore, defining the appropriate mutation and crossover operators in ga avoids selecting local optima which improves significantly the convergence. analyzing pm process times provides valuable information to manufacturing companies in order to determine meticulous planning and scheduling decisions. in addition, these industries have the privilege of economic justification for applying redundancy in the production line before implementing the project, not to mention the ability to design, produce and procure their products based on customers’ priorities and demand requirements. utilizing the modified nsga-ii, one can consider more objective functions such as the quality of roughness amount of the cutting surface as well as machine energy consumption or labor requirements in order to provide better scheduling results. for future work, the incorporation of the pm 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[31] "products," sumitomo electric hardmetal. https://www.sumitool.com/ en/products/ (accessed dec. 04, 2020). microsoft word etasr_v11_n3_pp7075-7078 engineering, technology & applied science research vol. 11, no. 3, 2021, 7075-7078 7075 www.etasr.com mero & machuve: the usability testing of ssaat, a bioinformatic web application for dna analysis … the usability testing of ssaat, a bioinformatic web application for dna analysis at a nucleotide level victor mero school of computational and communication science and engineering nelson mandela african institution of science and technology (nm-aist) arusha, tanzania merov@nm-aist.ac.tz dina machuve school of computational and communication science and engineering nelson mandela african institution of science and technology (nm-aist) arusha, tanzania dina.machuve@nm-aist.ac.tz abstract—sanger sequencing remains the cornerstone method for deoxyribonucleic acid (dna) sequencing due to its high accuracy in targeting smaller genomic regions in a larger number of samples. the analysis of sanger sequence dna data requires powerful and intelligent software tools. most of the preferred tools are proprietary licensed tools that offer a user-friendly interface and have many features, however, their affordability, especially to individual scientists or students, is limited. on the other hand, a few free and open-source licensed tools are available but have limited features. this study focuses on the usability testing of the developed sanger sequence automatic analysis tool (ssaat), a free and open-source web tool for sanger sequence analysis. usability tests were conducted with potential users and the results demonstrate that the participants were able to use the tool easily and accomplish the test tasks at the given time. moreover, the participants were excited with the easy-to-use interface and agreed that most users could use the tool with no need for technical assistance. however, the participants also identified some issues that require more development effort. keywords—sanger sequence; usability; bioinformatics; web tool i. introduction a. background sanger sequencing technique is one of the most famous methods used for determining nucleotide sequences in dna [1], due to its high sequencing accuracy compared to the next generation sequencing (ngs) technologies and its efficiency in sequencing short fragments of dna, ranging from 200 base pairs (bp) to around 1,000 bp. sanger sequencing is extensively used to the fields of functional and comparative genomics, evolutionary genetics, and complex disease research. particularly, the method was employed in sequencing the first human genome in 2000 [2]. the sanger sequencing process is composed of a pipeline from the dna extraction to the generation of a chromatogram which is stored as a file called ab1. this process can be seen in [3]. the sanger sequencing quality relies on the "base calling quality", i.e. the relative certainty with which the nucleo-bases are determined [2]. assessing the base-calling accuracy is usually performed using the visual inspection of the sequence trace chromatogram. most often, proprietary software like clc genomics workbench (qiagen), seqman (dnastar), etc. are preferred due to their user-friendly interfaces and the features they provide. nevertheless, some free open-source software tools for sanger sequence analysis exist. phred was among the earliest base-calling software tools reported to have less error rate than the abi machine software [4-6]. however, phred was developed as an open-source resource but it is not freely available [7]. tracy on the other hand is a free opensource tool for sanger sequence analysis that performs basecalling and other tasks including sequence alignment, assembly, and deconvolution of sanger chromatogram trace files, all in a command-line interface [8]. moreover, sangerseqr [9], automated sanger analysis pipeline (asap) [10], and seqtrace [7] are also reported open-source tools for performing sanger sequence data analysis but have limited graphical user interface and cross-platform capabilities. some web tools are also available including indelligent, child, and mixed sequence reader they are limited to a single feature usage [11-13]. the sanger sequence automatic analysis tool (ssaat), unlike the aforementioned tools, was developed as a web-based tool to eliminate the cross-platform issues while providing an easy-to-use interface and more dna analysis features. b. usability usability refers to how easily a user of a specific product or design can use it to accomplish the intended goals effectively, efficiently, and acceptably [14]. in the field of human-computer interaction, usability is defined as a way to remove all possible frustrations that users may experience when using a product or design. on the other hand, usability evaluation refers to a method used in the central design to assess a product or design by testing it with a group of representative users [15], and a platform for users to give direct feedback and corresponding author: victor mero engineering, technology & applied science research vol. 11, no. 3, 2021, 7075-7078 7076 www.etasr.com mero & machuve: the usability testing of ssaat, a bioinformatic web application for dna analysis … recommendations [16]. usability is a result of the basic quality components which are learnability, efficiency, memorability, error tolerance, and satisfaction [17]. there are several methods for testing products and among them, usability testing and heuristic evaluation have been the most appropriate ones [18]. heuristic evaluation is mostly done by professionals who use generally accepted guidelines to evaluate the usability of the product through demos and report issues. in contrast, usability testing recruits users to evaluate a particular product's usability through their feedback after interacting with it [18]. the current study aims to explore the usability of ssaat, which was developed as a user-friendly web tool for analyzing sanger sequence data at the nucleotide level. the study focused on the task completion rates, the meantime to complete tasks, and system usability. ii. materials and methods a. ssaat tool description ssaat was created to provide an easy-to-use interface for molecular biologists to perform sanger sequence dna analysis. ssaat reads the dna input files, performs basecalling, and provides chromatogram visualization, dna sequence alignment, and polymorphism detection, and delivers a structured report of the analysis. the flow diagram of ssaat (figure 1) illustrates the working flow of the tool. fig. 1. flow diagram of ssaat. ssaat utilizes a web-based interface that allows the molecular biologist to perform dna analysis in a user-friendly graphical interface and also enables working in cross-platform environments. one important element in accomplishing the goals of ssaat is to ensure that its design satisfies the needs of the users and is flexible to handle the continued evolution of this emerging area. b. usability testing methodology in this study, both qualitative and quantitative methods were used to capture user interactivity with the web tool. qualitative data were collected through a likert scale questionnaire while quantitative data, such as total users who were able to complete all the tasks, total complete tasks, complete task time, etc., were also collected. the testing session was designed in a way that each participant performed all the tasks and summative assessment was done to examine and evaluate participants’ insights. the study aimed at capturing the indicating factors of usability such as learnability, efficiency, usefulness, and satisfaction through the conducted test session. 1) participants and duration a total of 15 individuals participated in the usability test sessions. based on previous studies, 5-20 participants are a valid sample for usability testing [19]. the first 3 participants were scheduled on the first day and were regarded as a pilot for the next sessions. the testing sessions were conducted for 5 days (3 participants per day). the duration for each session was 60 minutes and after every session, a break period of 60 minutes was given. the session duration was based on previous studies on usability which suggest that 60-90 minutes time is valid for test sessions [19]. during the testing sessions, the moderator provided a brief overview of the test session and requested the participants to fill in a pre-test questionnaire in order to collect the general data. the participants then read the task instructions and began to perform the tasks on the tool using a web browser. as soon as the participants completed all the tasks, the moderator requested the participants to rate the web tool (ssaat) using the likert scale questionnaire. this was done as a post-test session in order to find out more information about the overall usability of the web tool. 2) tasks table i presents the results of the tasks that were obtained during the test sessions. each participant was required to attempt the tasks and the moderator observed the time of completion and participant’s behavior while attempting the tasks. table i. summary of usability test results by task code tasks baseline time (min)/estimated time (min) mean time (min) completion rate (%) task 1 identify the use of the web tool. 3/5 0.56 100 task 2 file upload, view the sequence quality, and download the extracted sequence as a fasta file. 3/5 4 87 task 3 navigate to chromatogram viewer, trim the 5’ end 50 base and trim 3’ end 100 base and download the chromatogram as a pdf file. 7/10 7.3 73 task 4 upload a reference sequence and calculate the global/local sequence alignment with the previously uploaded file as a primary sequence. 7/10 9 60 task 5 generate a report with sequence detail, chromatogram quality score plot, and sequence alignment results. 3/5 3.1 73 engineering, technology & applied science research vol. 11, no. 3, 2021, 7075-7078 7077 www.etasr.com mero & machuve: the usability testing of ssaat, a bioinformatic web application for dna analysis … iii. results and discussion a. participant characteristics among the 15 participants, there were 7 masters and three phd students in life sciences, 3 molecular biologists, and 2 bioinformaticians. eight were women and 7 were men, aged between 21 to 47 years old. all the participants claimed to use the internet daily. none of the participants received formal training or had the chance to review a user guide before participating in the usability test. b. task completion rate results all participants successfully completed task 1 marking a 100% completion rate. task 2 was completed by 87% of the participants. among the long duration tasks, task 3 scored 73% completion rate, while task 4 scored 60% completion rate, and task 5 was successfully completed by the 73% of the participants. the task definitions, completion rate, and mean time are illustrated in table i. c. mean time to complete task results the moderator recorded the task execution time for each participant. the allocated time for each task ranged from 5 to 10 minutes where simple tasks were allocated with less time and lengthy tasks with more. task 1 had the shortest completion time with a mean time of 0.56 minutes. this was followed by task 5 and task 2, with times of 3.1 minutes and 4 minutes respectively. task 3 and task 4 were the longest to complete with mean times of 7.3 minutes and 9 minutes respectively. the overall completion time ranged from 0.56 to 9 minutes, with a commonly recorded time of less than 5 minutes for the majority of tasks. d. system usability survey results during the post-testing session, the participants were asked to rate the web tool to capture the general usability aspects of the ssaat. the detailed results are shown in table ii. the measurements which were captured from participants’ post-test questionnaires included: • its ease of use • if the users would prefer to use the web tool • its learnability • if assistance from technical personnel was required • system functionality integrations • if the participants would recommend the tool to a colleague the majority of the participants (86.67%) agreed that the web tool was easy to use. additionally, most participants (93%) reported that they would prefer to work with the web tool often. regardless of the higher scores of participants agreeing that the tool was easy to use, 40% of them agreed that technical assistance was needed to operate the tool effectively. more than half of the participants agreed that the integrated features were functioning well. lastly, the majority of participants reported that they would recommend the tool to a colleague. e. discussion the usability of ssaat a bioinformatic tool for dna analysis at the nucleotide level was assessed in this study. our findings suggest that ssaat is easy and learnable, and even new users may be able to use the tool without prior exposure or technical assistance and accomplish the required tasks at a given time. the participants identified a number of possible improvements to the tool such as the addition of batch processing capabilities, trace file editing, and connection to remote dna databases. however, the mentioned suggestions would require more development effort and time, therefore we plan to work on them in the future versions. other modifications such as the suggested lighter interface background colors and the creation of a user guide with some visual illustrations were easier and more straightforward to implement. table ii. system usability survey results statement response frequency "the web tool is user friendly" strongly agree agree neutral 5 (33.33%) 8 (53.33%) 2 (13.33%) "i would like to use web tool often" strongly agree agree neutral 4 (26.67%) 10 (66.67%) 1 (6.67%) "i think most of the users will be able to use the web tool fast" strongly agree agree neutral disagree 4 (26.67%) 8 (53.33%) 1 (6.67%) 2 (13.33%) "i will not need technical assistance to be able to use the web tool" agree neutral disagree strongly disagree 7 (46.67%) 2 (13.33%) 4 (26.67%) 2 (13.33%) "i think the web tool units/parts are well integrated" strongly agree agree neutral disagree 4 (26.67%) 6 (40%) 4 (26.67%) 1 (6.67%) "i will recommend this web tool to my colleagues" strongly agree agree neutral 4 (26.67%) 9 (60%) 2 (13.33%) iv. conclusion the primary focus of this study was to examine the usability of the developed ssaat tool. this is an attempt towards eliminating the barriers to the availability of free and user-friendly software for sanger sequence dna analysis. the usability assessment results suggest that most of the users will be able to use the web tool without assistance. this is a good indicator that the tool is easy to use and hence most of the users are likely to often use it in their work and would probably recommend it to their colleagues. the participants in this usability study encountered several minor usability issues while using the prototype of this web tool. to ensure the effective use of ssaat, the issues identified during the usability testing sessions will be addressed in the upcoming version of the tool and the analysis results will affect the future development. usability evaluations are invaluable to the success of technology in an emerging area, especially in a complex domain such as genetics. engineering, technology & applied science research vol. 11, no. 3, 2021, 7075-7078 7078 www.etasr.com mero & machuve: the usability testing of ssaat, a bioinformatic web application for dna analysis … acknowledgement the authors would like to acknowledge the support from the bioinformatics unit at the beca-ilri hub in nairobi kenya and cocse laboratory at nm-aist in arusha tanzania. references [1] j. shendure et al., "dna sequencing at 40: past, present and future," nature, vol. 550, no. 7676, pp. 345–353, oct. 2017, https://doi.org/ 10.1038/nature24286. 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[7] b. j. stucky, "seqtrace: a graphical tool for rapidly processing dna sequencing chromatograms," journal of biomolecular techniques : jbt, vol. 23, no. 3, pp. 90–93, sep. 2012, https://doi.org/10.7171/jbt.122303-004. [8] t. rausch, m. h.-y. fritz, a. untergasser, and v. benes, "tracy: basecalling, alignment, assembly and deconvolution of sanger chromatogram trace files," bmc genomics, vol. 21, no. 1, mar. 2020, art. no. 230, https://doi.org/10.1186/s12864-020-6635-8. [9] j. t. hill and b. demarest, sangerseqr: tools for sanger sequencing data in r. bioconductor version: release (3.12), 2021. [10] a. singh and p. bhatia, "automated sanger analysis pipeline (asap): a tool for rapidly analyzing sanger sequencing data with minimum user interference," journal of biomolecular techniques : jbt, vol. 27, no. 4, pp. 129–131, dec. 2016, https://doi.org/10.7171/jbt.16-2704-005. [11] c.-t. chang et al., "mixed sequence reader: a program for analyzing dna sequences with heterozygous base calling," the scientific world journal, vol. 2012, jun. 2012, art. no. e365104, https://doi.org/10.1100/ 2012/365104. [12] d. a. dmitriev and r. a. rakitov, "decoding of superimposed traces produced by direct sequencing of heterozygous indels," plos computational biology, vol. 4, no. 7, 2008, art. no. e1000113, https://doi.org/10.1371/journal.pcbi.1000113. [13] i. zhidkov, r. cohen, n. geifman, d. mishmar, and e. rubin, "child: a new tool for detecting low-abundance insertions and deletions in standard sequence traces," nucleic acids research, vol. 39, no. 7, apr. 2011, art. no. e47, https://doi.org/10.1093/nar/gkq1354. [14] m. shitkova, j. holler, t. heide, n. clever, and j. becker, "towards usability guidelines for mobile websites and applications," in wirtschaftsinformatik proceedings, mar. 2015. [15] p. t. koziokas, n. d. tselikas, and g. s. tselikis, "usability testing of mobile applications: web vs. hybrid apps," in proceedings of the 21st pan-hellenic conference on informatics, new york, ny, usa, sep. 2017, art. no. 55, https://doi.org/10.1145/3139367.3139410. [16] j. r. bergstrom and a. schall, eds., eye tracking in user experience design, 1st ed. amsterdam , netherlands; boston, ma, usa: morgan kaufmann, 2014. [17] e. folmer and j. bosch, "architecting for usability: a survey," journal of systems and software, vol. 70, no. 1, pp. 61–78, feb. 2004, https://doi.org/10.1016/s0164-1212(02)00159-0. [18] a. fernandez, e. insfran, and s. abrahão, "usability evaluation methods for the web: a systematic mapping study," information and software technology, vol. 53, no. 8, pp. 789–817, aug. 2011, https://doi.org/ 10.1016/j.infsof.2011.02.007. [19] j. nielsen, "usability for the massesjus," journal of usability studies, vol. 1, no. 1, pp. 2–3, nov. 2005. microsoft word 13-3190_s_etasr_v9_n6_pp4937-4941 engineering, technology & applied science research vol. 9, no. 6, 2019, 4937-4941 4937 www.etasr.com alshammari: assessment of reliability and quality performance using the impact of shortfall … assessment of reliability and quality performance using the impact of shortfall generation capacity index on power systems badr m. alshammari department of electrical engineering, college of engineering university of hail, hail, saudi arabia bms.alshammari@uoh.edu.sa abstract—this paper presents a novel practical technique developed and applied for assessment of reliability and quality in real-life power systems. system-wide integrated performance indices are capable of addressing and revealing areas of deficiencies and bottlenecks as well as shortfalls in the composite generation-transmission-demand structure of large-scale power grids. the new evaluation methodology offers a general and comprehensive framework to assess the harmony and compatibility of generation capacities, transmission and required demand in a power system. the technique used in this paper is evaluated by the shortfall generation capacity index which is based on three dimensions introduced to represent the relationship between certain system generation capacity and demand. also, practical applications to the saudi power grid are presented for demonstration purposes. keywords-shortfall; reliability; quality; assessment; power systems i. introduction the issues of service reliability and system quality have risen to a high priority on the agenda of electric power companies. in this regard, many power utilities are concerned about the continuous increase in system demand along with the growing limitations on generation and transmission, facility expansion due to financial constraints, environmental concerns, etc. power system components are divided into two main categories, namely, the generating equipment and the transmission equipment. definitions for this equipment were prepared and presented in a number of the ieee committee reports [1-4]. in general a component is a piece of equipment or a group of items which is viewed as an entity and is not subdivided during reliability analysis. the main generating components are the boiler installation (single or multiple), common header system, turbine, generator, and boiler. transmission lines and transformers are considered as the main transmission components. the other components are either considered as associated with or external to the major components. a number of factors determine when a detailed component model is needed in a reliability analysis. the size and structure of the network are two important factors. power system cost-effectiveness, security, adequacy, and reliability analyses have evolved over the years from mere theoretical topics of limited interest to a vital branch in utility business during the current competitive market, tight economy and the “do the best with what you have” concept [5-8]. the novel technique utilizes a basic linear programming formulation, which offers a general and comprehensive framework to assess the harmony and compatibility of generation and demand in a power system. using the developed methodology, integrated system reliability evaluation and quality assessment can be performed globally on the whole system or locally on parts of the power grid. it can be applied to the system under normal operation or subject to contingencies with certain or random occurrences [9-11].the methodology presented in this paper has been implemented in the form of efficient computerized algorithms which analyze the network structure, generation and load balance and evaluate various composite system performance quality indices such as the generation shortfalls capacity index. the investigated reliability and quality measurements are not only useful for the design of flexible power supply reliability for various customers but also beneficial to the long-term system capacity expansion planning of electric power systems [12-17].the current work constitutes a new research in system reliability assessment where the derived system-wide performance quality indices are capable of addressing and revealing areas of shortfall and bottlenecks as well as redundancies in the composite generation-demand structure of large-scale power grids. ii. power system quality assessment a. performance quality framework the novel framework applied in this paper is based on [18], in which three metaphors (dimensions) were introduced to represent the relationship between a certain system generation capacity and the demand. these metaphors relate to the following demand fulfillment issues: • need of capacity for demand fulfillment • existence of capacity (availability for demand fulfillment) • ability of capacity to reach the demand corresponding author: badr m al-shammari engineering, technology & applied science research vol. 9, no. 6, 2019, 4937-4941 4938 www.etasr.com alshammari: assessment of reliability and quality performance using the impact of shortfall … ( ) pppp 0ppp 0ppp p p pa ppp tttt ggg lll g l t tgl n 1 = l , , , = such that and , respect towith = f minimize l ≤≤ ≤≤ ≤≤       ∑ p l the first dimension defines whether or not the capacity is needed, the second defines whether or not it exists, and the last one defines whether or not it can satisfy the demand. the eight possible combinations associated with the 0/1 (yes/no) values of the three dimensions would, in turn, define a set of powerful system-wide performance quality measures, namely: • utilized: a given capacity is said to be utilized if it is needed (for demand fulfillment), if it exists, can if it can reach the demand. • bottled: a given capacity is said to be bottled if it is needed (for demand fulfillment) and exists, but cannot reach the demand. • shortfall: a given capacity is said to be shortfall if it is needed (for demand fulfillment) and, anyhow, does not exist and can reach the demand. • deficit: a given capacity is said to be deficit if it is needed (for demand fulfillment) but, however, does not exist and cannot reach the demand. • surplus: a given capacity is said to be surplus if it is not needed (for demand fulfillment) although it exists and can reach the demand. • redundant: a given capacity is said to be redundant if it is not needed although it exists but, anyhow, cannot reach the demand. • spared: a given capacity is said to be spared if it is not needed and, anyhow, does not exist although it can reach the demand. • saved: a given capacity is said to be saved if it is not needed and, anyhow, does not exist and cannot reach the demand. we note here that the above performance quality measures are associated with different combinations (topples) of the three quality dimensions, namely, “existence”, “need” and “ability to reach the demand”. the corresponding quality state of a given capacity can be represented by a three-value expression of either a “yes/no” or “1/0” type indicating the true/false value associated with each quality metaphor. the evaluation of the above quality indices requires the knowledge of the following data types for the demand and various system facilities: • the value of the demand required to be supplied. • the value of generation capacity as well as the maximum site capacity (the limit of potential increase in existing generation capacity). • the value of transmission capacity. • the linear program formulation. in the computational scheme of [18], the integrated system quality assessment is performed via solving a master linear programming problem [19] in which a feasible power flow is established which minimizes the total system non-served load subject to capacity limits and flow equations. the master linear program, which utilizes the network bus incidence matrix a, is formulated as: (1) in the above master linear program,pt is the vector of nt elements representing transmission branch capacities, plis the vector of nl elements of peak bus loads, and pg is the vector of ng elements representing generator capacities. also, in the above master linear program (1), pl, pg, and pt are nl, ng and nt column vectors representing the actual load bus powers (measured outward), generator bus powers (measured inwards), and transmission line powers (measured as per the network bus incidence matrix a) respectively. the solution of the above linear program provides a more realistic (less conservative) flow pattern in view of the fact that when the load curtailments are anticipated, all system generation resources would be re-dispatched in a way which minimizes such load cuts. the feasible flow pattern established from the master linear program is then used to evaluate various integrated system quality indices through a set of closely related sub-problems. b. implementation mechanisms for real life power systems with practical sizes, the quality indices cannot be evaluated by inspection. an appropriate computerized scheme is needed in order to properly evaluate various quality indices according to their stated definitions. the master linear program presented before forms the base for analyzing and evaluating quality indices, for example the load supply reliability can be evaluated as follows: lnsl=load not-served at load bus (l)= (1) l lp p− lns= total system load not-served= (1) 1 ln l l l p p = −∑ where the bus loads at the solution of the master linear program are termed as (1) lp , and pl denotes the solution load value at bus (l). on the other hand, generation quality indices are defined in terms of the previously defined “1/0” states indicating the engineering, technology & applied science research vol. 9, no. 6, 2019, 4937-4941 4939 www.etasr.com alshammari: assessment of reliability and quality performance using the impact of shortfall … {needed, exists, can-reach} true/false values associated with each quality dimension. we shall use the symbol qgijk to indicate the generation quality index state. also, in the following expressions, we shall use min {x, y,...,z} to indicate the minimum of x, y,..., z. the notation <x> will be used to denote max {0, x}, that is the maximum of x and zero (= x if x> 0, or 0 otherwise). for example, the utilized generation capacity index (qg111≡{needed, exists, can reach}) is given by: ��111 = ∑ ��( )��� (2) the bottled generation capacity index(qg110≡{needed, exists, cannot reach}) is given by: ��110 = ���{[∑ ������ − ∑ ��( )], [��� ∑ ���{0,(��� − ��( ))}]}��� (3) the surplus generation capacity (qg011≡{not needed, exists, can reach}) is calculated as: ��011 = ���{[��� {0, (∑ ��� − ∑ ���)}], [���{0, (∑ �� − ∑ ���)}]}��� ��� ��� ��� (4) where the generation output values pg are calculated at the solution of the linear program with open limits on the loads. the above reliability and quality indices (2)-(4)only require knowing the available generation capacity and the value of required demand. on the other hand, to evaluate the energy shortfall index depends on the inspection of the capacity of transmission lines along with knowing the available generation capacity and the required demand. therefore, the shortfall generation capacity index (qg101≡ {needed, does not exist, reach}) is given by: ��101 = 0 ,�ℎ!"! ∑ ���#� ≤ ∑ ����� (5) ��101 = ��� %∑ �� &��� − ∑ ����� ∑ �'�(' − ∑ �'�(' ∑ ����� − ∑ ����� ,�ℎ!"! ) ∑ ����� > ∑ ����� ∑ ���+� − ∑ �� = 0��� (6) ��101 = 0 ,�ℎ!"! ∑ ����� ≤ ∑ �'�(' (7) ��101 = ��� )∑ �'�(' − ∑ ������ ∑ ����� − ∑ ������ , �ℎ!"! ,. -/ ∑ �� ��� > ∑ ����� ∑ ���+� − ∑ �� ≠ 0��� [∑ ����� − ∑ ����� ] ≤ [∑ ��&��� − ∑ ����� ] ∑ ���+� ≤ ∑ �'�(' (8) ��101 = 0 , �ℎ!"! ,. -/ ∑ �� ��� > ∑ ����� ∑ ���+� − ∑ �� ≠ 0��� [∑ ����� − ∑ ����� ] ≤ [∑ ��&��� − ∑ ����� ] ∑ ���+� > ∑ �'�1' (9) ��101 = ��� )∑ �'�(' − ∑ ������ ∑ ��&��� − ∑ ������ , �ℎ!"! ,. -/ ∑ �� ��� > ∑ ����� ∑ ���+� − ∑ �� ≠ 0��� [∑ ����� − ∑ ����� ] > [∑ ��&��� − ∑ ����� ] ∑ ���+� ≤ ∑ �'�(' (10) where: ��� = required value of the load. �� = actual value of the load. ��& = sit capacity of generation. ��� = available capacity of generation. �� = actual capacity of generation.��� = available capacity of generation. �� = actual capacity of generation. �'� = capacity of transmission lines. �' = actual flow in transmission lines. iii. example of quality andreliabilitydimensions consider the 4-bus system of figure 1. all load, flow and capacity values are in mw. note that the generation and transmission element capacities shown in figure 1 are for illustration purposes only and may not reflect the actual element values. for this simple system, the quality and reliability indices can be evaluated as shown in table i. fig. 1. a 4-bus sample power system table i. quality and reliability indicesfor the sample system index qg111 qg110 qg101 qg011 lns value 85 15 15 0 30 iv. applications to sec power system in a recently completed industry supported study, applications were conducted on a practical power system comprising of a portion of the interconnected saudi power grid. the power system consists of two main regions, namely the central region and the eastern region. the two systems are interconnected through two 380kv and one 230kv doublecircuit lines. one zone is identified in the present analysis, hail zone. in this application, four reliability and quality performance indices were considered, namely the system load not-served (lns), utilized generation capacity (qg111), the bottled generation capacity (qg110), and the shortfall generation capacity (qg101).the system model used for hail network zone is shown in figure 2. table ii outlines the network data in terms of generation and transmission facilities as well as system loads. figures 3 and 4 summarize the results of the reliability and performance quality measures applied to the hail network power system for various system status (isolated or connected) of the hail zone. in particular, figures 3-4, depict the variation of the variation of quality indices (qg111, qg110, and qg101) with the required load level of the hail isolated and interconnected network respectively. the results reveal several important observations. for example, the obtained results for the isolated network scenario of hail zone (figure 3) show that the shortfall generation capacity (qg101) is non-zero even for relatively low generation levels as it decreases continuously from 350mw to reach 0mw when the generation level is 653mw. this problem is clearly mitigated in the interconnected network scenario of hail zone (figure 4), where generation support from qassim zone becomes available. engineering, technology & applied science research vol. 9, no. 6, 2019, 4937-4941 4940 www.etasr.com alshammari: assessment of reliability and quality performance using the impact of shortfall … fig. 2. single-line diagram of sec – hail zone table ii. generation, transmission and loads of hail network state isolated interconnected generators value 593.63 1393.6 number 9 10 transmissions number 68 69 loads value 655.3 655.3 number 46 46 fig. 3. variation of qg111, qg110 and qg101 with the variation of available generator capacity levels of the hail interconnected network bottled generation capacity (qg110) stays at zero value for all available generation capacity levels up to 594mw where it starts to increase slowly to reach saturation, due to limitations of transmission lines, at about 11mw when the available generation capacity level is 653mw. it is also noted from figure 3 that the utilized generation capacity (qg111) starts at 300mw and increases continuously with the available generation capacity levels until it saturates at 644mw when the available generation capacity is 653mw. for the hail interconnected network the results of figure 4 show that the bottled generation capacity (qg110) remains at zero value for all available generation capacity levels (supplied fully). on the same regard, the utilized generation capacity (qg111) stays constant (nominal load) for all available generation capacity levels. fig. 4. variation of qg111, qg110 and qg101 with the variation of available generator capacity levels of the hail isolated network v. conclusions this paper presents a major extension to a previously published work by developing a theory and formulas for computing the expected values of different system reliability and performance quality indices. the reliability and performance quality indices, when evaluated at a given load level and a certain scenario of available generation and transmission capacities, would provide indications on system performance only for such a particular system condition (snapshot). based on the solution of the basic linear program described in this paper, a more realistic (less conservative) flow pattern can be established. the more realistic nature of such a flow pattern comes from the fact that when the load curtailments are anticipated, all system generation resources would be redispatched in a way which minimizes such load cuts. this work constitutes a new line of research in system reliability assessment where the derived system-wide performance quality indices are capable of addressing and revealing areas of shortfall and bottlenecks as well as redundancies in the composite generation-demand structure of large-scale power grids. examples of such very important quality measures is the shortfall generation capacity(qg101), which is needed(for demand fulfillment) and, anyhow, does not exist and can reach the demand. the practical applications presented in the paper have demonstrated the powerful features of the adopted approach and its suitability for large-scale system implementations. the, under investigation, hail network contains 10 generators, 69 branches (transmission lines, underground cables, and power transformers), and 46 loads. acknowledgment this work was supported by the university of hail. references [1] ieee committee report, “proposed definitions of terms of reporting and analyzing outages of generating equipment”, ieee transactions on power apparatus and systems, vol. pas-85, pp. 390-393, 1966 9030 8911 8913 8914 8912 8916 8901 8902 8903 8919 8904 8915 8918 8917 8921 8922 8920 7910 7905 7903 7904 7912 7914 7901 7906 7908 7909 7907 7902 7911 7915 7913 7916 7917 7918 ~ ~ ~ 2×20 2×20 2×5 2×15 1×10 6×60mw 2×8 2×18 = 36 mw 4×20 2×80 2×40 2×90 3×20 2×8 2×15 2×5 2×5 2×5 3×20 2×8 2×8 2×10 3×100 2×5 2×8 2×20 2×10 2×20 2×15 2×400 2×60 2×20 2×20 2×20 2×20 2×20 \\ \\ \\ \\ \\ \\ \\ hail network 2×5 2×5 2×5 2×5 2×5 2×5 2×5 2×5 2×5 2×5 2×10 2×5 2×5 2×5 2×5 200 300 400 500 600 700 800 900 0 200 400 p g [mw] q g1 0 1 [ m w ] 200 300 400 500 600 700 800 900 0 10 20 p g [mw] q g1 1 0 [ m w ] 200 300 400 500 600 700 800 900 0 500 1000 p g [mw] q g 1 1 1 [ m w ] 600 800 1000 1200 1400 1600 1800 2000 2200 0 5 10 p g [mw] q g1 0 1 [ m w ] 600 800 1000 1200 1400 1600 1800 2000 2200 0 5 10 p g [mw] q g1 1 0 [ m w ] 600 800 1000 1200 1400 1600 1800 2000 2200 640 650 660 p g [mw] q g 1 1 1 [ m w ] engineering, technology & applied science research vol. 9, no. 6, 2019, 4937-4941 4941 www.etasr.com alshammari: assessment of reliability and quality performance using the impact of shortfall … [2] ieee committee report, “proposed definitions of terms of reporting and analyzing outages of electrical transmission and distribution facilities and interruptions”, ieee transactions on power apparatus and systems, vol. pas-87, pp. 1318-1323, 1968 [3] ieee committee report, “definitions of customers and load reliability indices for evaluating electric power system performance. paper a75 588-4”, ieee pes summer meeting, san francisco, usa, july 20-25, 1975 [4] h. f lester, “power system: functional reliability more than component reliability is key in serving customers”, ieee spectrum, vol. 18, pp. 5859, 1981 [5] m. el-kady, m. el-sobki, n. sinha,“reliability evaluation for optimally operated largeelectric power systems”, ieee transactions on reliability, vol. r35-1, pp. 41-47, 1986 [6] s. torre, a. conejo, j. contreras,“transmission expansion planning in electricity markets”, ieee transactions on power systems, vol. 23, no. 1,pp. 238-248, 2008 [7] m. el-kady, m. el-sobki, n. sinha,“loss of load probability evaluation based on realtime emergency dispatch”, canadian electrical engineering journal, vol. 10, pp. 57-61, 1985 [8] m. a. el-kady, b.m. alshammari, “a practical framework for reliability and quality assessment of power systems”, energy and power engineering, vol. 3, no. 4, pp. 499-507, 2011 [9] j. choi, t. mount, r. thomas, “transmission expansion planning using contingency criteria”, ieee transactions on power systems, vol. 22, no. 4, pp. 2249–2261, 2007 [10] p. jirutitijaroen, c. singh, “reliability constrained multi-area adequacy planning using stochastic programming with sample-average approximations”, ieee transactions on power systems, vol. 23, no. 2, pp. 405-513, 2008 [11] r. billinton, d. huang, “effects of load forecast uncertainty on bulk electric system reliability evaluation”, ieee transactions on power systems, vol. 23, no. 2, pp. 418-425, 2008 [12] o. kahouli, b. alshammari, k. sebaa, m. jebali, h. hadj abdallah “type-2 fuzzy logic controller based pss for large scale power systems stability”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3380-3386, 2018 [13] s. perez-londono, g. olivar-tost, j. j. mora-florez, “online determination of voltage stability weak areas for situational awareness improvement”, electric power systems research, vol. 145, pp. 112– 121, 2017 [14] s. poudel, z. ni, w. sun, “electrical distance approach for searching vulnerable branches during contingencies”, ieee transactions on smart grid, vol. 9, no. 4, pp. 3373–3382, 2018 [15] m. de jong, g. papaefthymiou, p. palensky, “a framework for incorporation of infeed uncertainty in power system risk-based security assessment”, ieee transactions on power systems, vol. 33,no. 1, pp. 613–621, 2018 [16] f. jandan,s. khokhar, z. memon, s. shah, “wavelet based simulation and analysis of single and multiple power quality disturbances”, engineering, technology & applied science research, vol. 2, no. 2, pp. 3909-3914, 2019 [17] j. chakravorty, j. saraswat, v. bhatia, “modeling a distributed power flow controller with a pem fuel cell for power quality improvement”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2585-2589, 2018 [18] b. m. alshammari, m. a. el-kady, y. a. al-turki, “power system performance quality indices”, european transactions on electrical power, vol. 21, no. 5, pp. 1704–1710, 2011 [19] p. e. gill, w. murray, m. h. wright, practical optimization, emerald, 1982 engineering, technology & applied science research vol. 8, no. 4, 2018, 3130-3134 3130 www.etasr.com ahmad et al.: developing a new dimension of an applied exponential model: application… developing a new dimension of an applied exponential model: application in biological sciences w. m. a. w. ahmad school of dental sciences universiti sains malaysia, malaysia r. a. a. rohim universiti sains malaysia malaysia y. norhayati universiti sains malaysia malaysia n. a. aleng school of informatics and applied mathematics universiti malaysia terengganu malaysia z. ali school of mathematical sciences universiti sains malaysia malaysia abstract—modeling of exponential growth or decay is a nonlinear regression technique. in the real world, the exponential growth is often used to model population growth while the exponential decay is often used to a model declining population or a decreasing size. in this study, we try to improve the performance of exponential growth by adding bootstrap and fuzzy techniques. this gives us the option to perform analysis even when there is not enough data. the aim of the current work is to develop a new dimension of an applied exponential analysis with improved results. the suggested method was tested and applied to biological data. the gathered data was compared by measuring the average width of the predicted interval using least squares method and fuzzy method. the result shows that the average width of the predicted interval using least squares method was 0.522 while using fuzzy method was 0.082. this indicated the superiority of the fuzzy regression methodology. besides that, this paper provides the algorithm for the prediction of cell growth and inferences. keywords-bootstrap; exponential growth; fuzzy regression; exponent decay; nonlinear regression i. introduction the exponential function is one of the most important and widely occurring functions in physics and biology [1]. the exponential distribution has many applications in biology. examples of the exponential application include the bacteria growth time and the decay time of bacterial pathogens with constant failure rates. exponent distribution of an event is the probability of the event occurring in the next small time interval which does not vary through time, and time between events has a poisson distribution. the exponential growth or decay follows a function n which changes with time in such a way that the change δn in n during a short time interval δt is proportional to n and to δt, as δn=kδt, rearranging this equation, we obtain: n k n t    (1) therefore, the constant of proportionality k can be seen by rearranging equation (1). then, we obtain k=(δn/n)/δt. the constant k is then the fractional change (δn/n) in n per unit time δt. the dimension of k is (time) 1 [2]. ii. statistical theory and methodology the linear regression model is a powerful method for modeling and forecasting, especially in conventional regression analysis. for modeling purposes, data should be crisp and should follow a normal assumption, this will lead to better significant results [3]. in the current study, an exponential model was applied after transforming the data to a linear model with mathematical programming by assuming that the dependent variables were crisp while the independent variable was a symmetric fuzzy number. this paper provides an algorithm for the exponential growth model using cell cultured dataset. the basic analysis is to transform the nonlinear equation into a linear form. after transforming into linear regression, we will obtain an equation in the form of y=β0+β1x1+ε. we transformed the nonlinear equation in order to get better results and better significant inferences. the random error term is added to make the model probabilistic rather than deterministic. the value of the coefficient βι determines the contribution of the independent variables and β0 is the y-intercept [3, 4]. to be more accurate, a fuzzy regression can be rearranged as 110 xzzy  (2) where the explanatory variables xi are assumed to be precise. however, according to (2), response variable y is not crisp but is instead fuzzy in nature. for the fuzzy approach, zi are engineering, technology & applied science research vol. 8, no. 4, 2018, 3130-3134 3131 www.etasr.com ahmad et al.: developing a new dimension of an applied exponential model: application… assumed symmetric fuzzy numbers which can be presented by the interval. zi can be expressed as a fuzzy set given by  1w1c1 a,az where ica is the center and iwa is radius or associated vagueness. this reflects the confidence in the regression coefficients around ica in terms of symmetric triangular membership function. so, the relationship is also considered to be fuzzy. this  w1c1i a,az can be written as  r1l11 a,az  with w1c1l1 aaa  and w1c1r1 aaa  . in fuzzy regression methodology, parameters are estimated by minimizing total vagueness in the model. using  1w1c1 a,az , we can write the fuzzy regression as  0w0c a,ay xa,a 1w1c  (3) data collection main algorithm : algorithm of an exponential with combining fuzzy method end process \*using secondary data*\ interpret the output performing exponential growth or decay to estimate the parameter adding bootstrapping to the main algorithm \*methodology building for bootstrap and this methodology will be add to the main algorithm*\ \* main methodology *\ \*performing an analysis*\ \*obtained an output*\ \*finish*\ fig. 1. flowchart of the integrated exponential calculation. thus this can be written as 1j1c0cjc xaay  then it can be written straightly as jw 0w 1w 1jy a a x  . as jwy represents radius and so cannot be negative, therefore on the right-hand side of the equation 1j1w0wjw xaay  , absolute values of ijx are taken. suppose there are m data points, each comprising of   row1na  vector. the parameters zi are estimated by minimizing the quantity, which is the total vagueness of the model-data set combination, subject to the constraint that each data point must fall within the estimated value of response variable. this can be visualized as the following linear programming problem, minimized   m 0w 1w 1j j 1 a a x   and subject to:     0c 1c 1j 0w 1w 1j ja a x a a x y        0c 1c 1j 0w 1w 1j ja a x a a x y    and 0aiw  . a simple procedure is commonly used to solve the linear programming problem [5]. the present data is a sample of the results obtained from [6] which characterize the proliferative capacity of mesenchymal stem cells. the data are composed of two variables which are the days of culture (x) and population doubling level (y) – see table i. table i. x and y description variable description x a total number of time (days) between each cell passage. y population doubling level is the proportion of cells count at 80% confluency over the original number of cells seeded. a. exponential growth transforming to linear form exponential growth formula and exponential decay formula are given by bxy ae . the procedure to transform the growth and decay formula into a linear form follows. the equation for the linear form for exponential growth is given by (4): ln ln( ) ln( ) ln( ) ln(a) bx bx y ae a e bx     (4) b. calculations of an exponential cell growth using sas algorithm  first step: data for exponential cell growth should enter in sas algorithm as follows. data cell_growth; input x y lny; datalines; 0.00 38.00 3.64 5.00 39.31 3.67 8.00 39.74 3.68 10.00 40.98 3.71 13.00 43.10 3.76 17.00 45.78 3.82 20.00 59.15 3.89 22.00 49.90 3.91 24.00 53.98 3.99 28.00 57.46 4.05 31.00 61.03 4.11 34.00 63.80 4.16 37.00 65.52 4.18 40.00 68.54 4.23 44.00 72.62 4.29 47.00 75.42 4.32 50.00 79.38 4.37 53.00 83.31 4.42 ; run;  second step: adding bootstrapping to the calculation. the following algorithm calculates the data using a bootstrap method and prints out the data. %macro bootstrap(data=_last_, booted=booted, boots=2, seed=1234); data &booted; pickobs = int(ranuni(&seed)*n)+1; set &data point = pickobs nobs = n; replicate=int(i/n)+1;   c. sum t p par exp at obt mo engineerin www.etasr i+1; if i > n*&bo run; %mend bo ods rtf file='a %bootstrap(d run; proc print da run; third step: equation. t parameters a title “expon ods graphics proc nlin dat parameters a model y = a ods output e run; fourth step according to proc reg data model lny=x run; ods rtf close; parameter e the sas ou mmary of the table ii. parameter es a 35 b 0 the obtained y e97.35 exponential rameter estim ponential grow the certain po tain ln (35.97y ln ln 3.5827y  so the param 3.5827 lny std error   the upper li odel are compu ng, technology r.com oots then st otstrap; abc.rtf' style=j data= cell_gr ata=booted; estimating th the algorithm according to th nential equatio / imagename a=booted plot a=1 b=-1; *exp(b*x); stsummary=su p: estimating o the transform a=booted; x; estimation for utput for the pa output follows parameter e timate appr std er 5.9723 0.256 .0160 0.0002 d equation is g x016.0 growth formu mation, we ob wth equation w oint ˆ 35.97y  0.016735 ) (xe ln 78 0.0160 x meter estimatio   78 0.0160 0.2566 0.0 x  imits of predic uted using (7) y & applied sci top; ournal; rowth, boots=2 he parameters m below is he data. on”; = “exponentia s=fit; ummexp; the linear f m bootstrap dat exponential c arameter estim s. stimate of an e ox rror approxim 66 35.4509 219 0.0155 iven by (5): ula is given by btain (6). usin we can estimat 0.0167 xe . takin (35.9735) (ln e on and standard 000219 ction interval : ience research ahmad et al.: d 2); s of an expon used to est al equation”; form of regre ta. cell growth mation follows xponential equ mate 95% confid limits 36.4937 0.0164 (5) y bxy ae . ng the equati te the growth o ng a logarithm 0.016 )x  d error are giv (6) for the expon h v developing a n nential timate ession s. the uation ence after ion of of cell m, we ven as nential ln ln y y and mo ln y ln y d. (fl be sum esti vol. 8, no. 4, 20 new dimension    3.58278 3.83938 y y    d the lower lim del are compu    3.58278 3.32618 y y    f calculation o growth the algorithm ls) for expone visualized b mmarizes the imates. ods rtf file='ab 018, 3130-3134 n of an applied      0.2566 0 0.016219    mits of predic uted using (8):     0.2566 0 0.015781    fig. 2. the pl fig. 3. fit d of fuzzy leas m below calc ential growth. by the follow e optimizatio abc.rtf' style=jo 4 d exponential m  0.0160 0.000 x  ction interval f .0160 0.0002 x  lot of an exponent diagnostic for lny t squares(fls culates the fu the full set wing program on results fo ournal; 3132 model: applicat 0219 x (7) for the expone 219 x (8) tial y. s) for expone uzzy least sq of calculation mming. table or the param tion… ential ential quares ns can e iii meter engineerin www.etasr proc nlp; min y; decvar a0c a0 bounds a0w> lincon a0c+1 lincon a0c+5 lincon a0c+2 lincon a0c+5 lincon a0c+1 lincon a0c+5 lincon a0c+0 lincon a0c+5 lincon a0c+2 lincon a0c+8 lincon a0c+0 lincon a0c+2 lincon a0c+5 lincon a0c+5 lincon a0c+5 lincon a0c+4 lincon a0c+2 lincon a0c+2 lincon a0c+1 lincon a0c+2 lincon a0c+1 lincon a0c+2 lincon a0c+1 lincon a0c+2 lincon a0c+8 lincon a0c+3 lincon a0c+0 lincon a0c+2 lincon a0c+5 lincon a0c+1 lincon a0c+4 lincon a0c+8 lincon a0c+8 lincon a0c+2 lincon a0c+3 lincon a0c+4 lincon a0c+1 lincon a0c+5 lincon a0c+2 lincon a0c+5 lincon a0c+1 lincon a0c+5 lincon a0c+0 lincon a0c+5 lincon a0c+2 lincon a0c+8 lincon a0c+0 lincon a0c+2 lincon a0c+5 lincon a0c+5 lincon a0c+5 lincon a0c+4 lincon a0c+2 lincon a0c+2 lincon a0c+1 lincon a0c+2 ng, technology r.com 0w a1c a1w; >=0, a1w>=0; 13*a1c-a0w-13 5*a1c-a0w-5*a 20*a1c-a0w-20 5*a1c-a0w-5*a 13*a1c-a0w-13 5*a1c-a0w-5*a 0*a1c-a0w-0*a 5*a1c-a0w-5*a 24*a1c-a0w-24 8*a1c-a0w-8*a 0*a1c-a0w-0*a 24*a1c-a0w-24 5*a1c-a0w-5*a 50*a1c-a0w-50 53*a1c-a0w-53 40*a1c-a0w-40 22*a1c-a0w-22 20*a1c-a0w-20 17*a1c-a0w-17 28*a1c-a0w-28 17*a1c-a0w-17 20*a1c-a0w-20 13*a1c-a0w-13 22*a1c-a0w-22 8*a1c-a0w-8*a 37*a1c-a0w-37 0*a1c-a0w-0*a 28*a1c-a0w-28 50*a1c-a0w-50 13*a1c-a0w-13 44*a1c-a0w-44 8*a1c-a0w-8*a 8*a1c-a0w-8*a 28*a1c-a0w-28 34*a1c-a0w-34 40*a1c-a0w-40 13*a1c+a0w+1 5*a1c+a0w+5* 20*a1c+a0w+2 5*a1c+a0w+5* 13*a1c+a0w+1 5*a1c+a0w+5* 0*a1c+a0w+0* 5*a1c+a0w+5* 24*a1c+a0w+2 8*a1c+a0w+8* 0*a1c+a0w+0* 24*a1c+a0w+2 5*a1c+a0w+5* 50*a1c+a0w+5 53*a1c+a0w+5 40*a1c+a0w+4 22*a1c+a0w+2 20*a1c+a0w+2 17*a1c+a0w+1 28*a1c+a0w+2 y & applied sci 3*a1w<=3.76; a1w<=3.67; 0*a1w<=3.89; a1w<=3.67; 3*a1w<=3.76; a1w<=3.67; a1w<=3.64; a1w<=3.67; 4*a1w<=3.99; a1w<=3.68; a1w<=3.64; 4*a1w<=3.99; a1w<=3.67; 0*a1w<=4.37; 3*a1w<=4.42; 0*a1w<=4.23; 2*a1w<=3.91; 0*a1w<=3.89; 7*a1w<=3.82; 8*a1w<=4.05; 7*a1w<=3.82; 0*a1w<=3.89; 3*a1w<=3.76; 2*a1w<=3.91; a1w<=3.68; 7*a1w<=4.18; a1w<=3.64; 8*a1w<=4.05; 0*a1w<=4.37; 3*a1w<=3.76; 4*a1w<=4.29; a1w<=3.68; a1w<=3.68; 8*a1w<=4.05; 4*a1w<=4.16; 0*a1w<=4.23; 13*a1w>=3.76 *a1w>=3.67; 20*a1w>=3.89 *a1w>=3.67; 13*a1w>=3.76 *a1w>=3.67; *a1w>=3.64; *a1w>=3.67; 24*a1w>=3.99 *a1w>=3.68; *a1w>=3.64; 24*a1w>=3.99 *a1w>=3.67; 50*a1w>=4.37 53*a1w>=4.42 40*a1w>=4.23 22*a1w>=3.91 20*a1w>=3.89 17*a1w>=3.82 28*a1w>=4.05 ience research ahmad et al.: d ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; 6; 9; 6; 9; 9; 7; 2; 3; 1; 9; 2; 5; h v developing a n e. a0w upp the and mo cap hig was vol. 8, no. 4, 20 new dimension lincon a0c+17 lincon a0c+20 lincon a0c+13 lincon a0c+22 lincon a0c+8* lincon a0c+37 lincon a0c+0* lincon a0c+28 lincon a0c+50 lincon a0c+13 lincon a0c+44 lincon a0c+8* lincon a0c+8* lincon a0c+28 lincon a0c+34 lincon a0c+40 y= a0w*36+7 run; ods rtf close; parameter es cell growth parameter w=0.041176, a per prediction equation as fo   ln 3.598 0.015 ln 3.6400 y y    d the lower lim del is compute   3.5 0.0 3.55 l yn lny    table iv sh pable of handli hly correlated s found to be 018, 3130-3134 n of an applied 7*a1c+a0w+1 0*a1c+a0w+2 3*a1c+a0w+1 2*a1c+a0w+2 *a1c+a0w+8* 7*a1c+a0w+3 *a1c+a0w+0* 8*a1c+a0w+2 0*a1c+a0w+5 3*a1c+a0w+1 4*a1c+a0w+4 *a1c+a0w+8* *a1c+a0w+8* 8*a1c+a0w+2 4*a1c+a0w+3 0*a1c+a0w+4 727*a1w; fig. 4. stimation for f estimates a1c=0.015294 limit for expo ollows: 824 0.04117 294 0.00000 00 0.015294x    mit of predict ed using the eq 598824 0.041 015294 0.000 57648 0.0152    hows that fuz ing situations d. from this t 0.522, while 4 d exponential m 7*a1w>=3.82 0*a1w>=3.89 3*a1w>=3.76 2*a1w>=3.91 a1w>=3.68; 7*a1w>=4.18 a1w>=3.64; 8*a1w>=4.05 0*a1w>=4.37 3*a1w>=3.76 44*a1w>=4.29 a1w>=3.68; a1w>=3.68; 8*a1w>=4.05 4*a1w>=4.16 40*a1w>=4.23 plot lny vs x fuzzy least sq are given: 4 and a1w=0.0 onential model   76 00 x x tion interval f quation:   1176 0000 294 x x zzy regression in which pred table, the ave the one for f 3133 model: applicat 2; 9; 6; ; 8; 5; 7; 6; 9; 5; 6; ; quare exponen a0c=3.598 000000. the f l is computed u (9) for the expone (10) n methodolog dictor variable erage width fo fr was only 0 tion… ntial 8824, fuzzy using ential gy is es are 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residual for lny optimization r dient objective function 0 36.000000 0 727.000000 value of o width for fitted method of fu  (lp) up 1, 2,..., 36 i i i  ower of width predictio ry and discus explanation f otstrap appro near regressio the algorithm e programmin on result. fuzz curacy model ence on the re ussed zadeh's o the least squ estimates of model. they c better perform wledgment press their gra ng the resear ool of dental s erences manual of phar nger, 1981 ience research ahmad et al.: d fuzzy regre results active bou constrai lower b objective function=1.48 regression mod uzzy regression (   36 1 3 0.082 i i width    on, up upper of width p ssion for the altern ach to expon on procedure m is to provid ng of data an zy model and l compared t esult can be se extension prin uares method. ften lead to oncluded that mance compar atitude to univ rch funding ( sciences, univ rmacologic calcu h v developing a n ession und int bc 23529412 dels (fr) 36 prediction native nential using de the nalysis d crisp to the een in nciple they better fuzzy red to versiti (grant versity ulations [2] [3] [4] [5] [6] [7] vol. 8, no. 4, 20 new dimension a. a bartlett, vol. 14, no. 7, w. m. a. w. a ruhaya, a. zal regression mo biostatistics”, i vol. 12, no. 18 t. h. d. ngo, c regression an analysis, orlan h. ghosh, s. w agriculture usin (iasri), 2001 ν. yusop, p. waddington, “i from rat bone stem cells inte r. korner, w. extended class estimates”, info 018, 3130-3134 n of an applied “the exponential pp. 393-401, 197 ahmad, a. nor a lila., b. adam, z odeling using international jou 8, pp. 7853-7856, c. a. la puente, c nalysis”, sas gl ndo, usa, paper 3 wadhwa, applicat ng sas, indian a battersby, a. a isolation and char marrow and the rnational, vol. 20 nather, “linear r sical estimates, ormation sciences 4 d exponential m l function-part i” 76 azlida, d.yosza, . syerrina, “appl sas: an alt urnal of applied 2017 c. a. “the steps lobal forum 201 333-2012, april 2 tion of fuzzy regr agricultural stati lraies, a. j. slo racterization of m endosteal niche: 018, article id 68 regression with r best linear est s,vol. 109, no. 13134 model: applicat ”, the physics t a. h. nurfadhli lied exponential g ternative metho engineering res to follow in a m 12: statistics and 22-25, 2012 ression methodol stics research in oan, r. moseley, mesenchymal stem a comparative s 869128, 2018 andom fuzzy var timates, least s -4, pp. 95-118, 19 tion… teacher ina, h. growth od of search, multiple d data logy in nstitute , r. j. m cells study”, riables: squares 998 microsoft word etasr_v13_n4_pp11326-11331 engineering, technology & applied science research vol. 13, no. 4, 2023, 11326-11331 11326 www.etasr.com kumar & kumar: stability analysis of fgcnt beams with imperfections stability analysis of fgcnt beams with imperfections pranav kumar department of civil engineering, national institute of technology patna, india pranavk.phd18.ce@nitp.ac.in (corresponding author) ajay kumar department of civil engineering, national institute of technology delhi, india sajaydce@gmail.com received: 12 april 2023 | revised: 10 may 2023 and 16 may 2023 | accepted: 25 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5949 abstract functionally graded carbon nanotube (fg cnt) reinforced curved beams are being used nowadays in different structural applications due to their properties although they have stability issues due to geometric imperfections that affect the load-bearing capacity of the beam and residual strength, hence a geometric imperfection is being introduced as a hollow trapezoidal layer is incorporated in the curved beam design to get better strength. hence a new frictional endo-stratified thermal model is proposed to analyze the frictional effect between interface layers with the help of elastic and plastic deformation of the curved beam. thus, analysis is done in abaqus using a finite element model to determine the stability due to frictional characteristics. the proposed design is giving better results than existing designs with higher specific gravity and tensile strength. keywords-functionally graded cnt; reinforced curved beams; friction behavior; delamination; thermal behavior i. introduction functionally graded materials (fgms) are being developed as a tough contender to replace existing laminated composites and isotropic materials [1]. this is primarily due to inherent properties like thermal and flexural resistance and continuity, which eliminates abrupt transitions between distinct materials, which can cause problems like inter-laminar stresses, delamination, or cracking in multi-layer systems [2]. in terms of characteristics, this compositional diversity improves the system's thermal and mechanical performance. elasticity, density, heat conduction, and other properties of fgm structures can be produced in a variety of ways to meet different needs. beams, plates, and shells have all been used extensively in various types of engineering structures as fundamental components [3]. the beam element is one of the most useful and widely used elements in skeletal structures. many researchers have become increasingly interested in analyzing the nonlinear behavior of structures in recent years. geometric imperfections in engineering structures, such as beams and plates, are unavoidable during the manufacturing process due to a variety of production and environmental factors [4]. hence the thermal stability of beams due to friction are concentrated and analyzed in this study to enhance its stability. the main contribution provided by this paper is that, the frictional endo-stratified thermal model is an effective method for determining the thermal characteristics of functionally graded reinforced curved beams. this model involves identifying the frictional behavior of the various layers in the beam, and can be used to accurately predict the thermal performance of the structure. ii. literature review authors in [5] presented a study of the effect of an applied methodology on out-of-plane interlaminar strength characterization. additionally, the mechanical behavior of three carbon fiber-reinforced thermoplastic composites was compared using the curved beam strength test. data evaluated using different standards gave statistically significantly different results. further tests on the coupon with tpc matrix are planned for the future in order to expand the material database. based on these tests, a material will be selected that could replace the thermosetting materials used in aircraft structures for interior panels. authors in [6] discussed the existing literature on the area of application, stability, and free vibration analysis of fgm structures conducted by some recent research studies and to provide a comprehensive overview of the development, application, different numerical representation of materials, demonstrating procedures and arrangement technique and solution method of fgm rectangular plate. to expand the thermal analysis of various structures, including nonlinear effects, detailed research must be conducted. authors in [7] investigated the nonlinear stability of the functionally graded porous (fgp) cylinder reinforced by graphene nanofiller (gnf). engineering, technology & applied science research vol. 13, no. 4, 2023, 11326-11331 11327 www.etasr.com kumar & kumar: stability analysis of fgcnt beams with imperfections authors in [8] proposed a unified and generic numerical modeling approach that accounts for both the intra and interlaminar damage modes in stiffened cfrp panels. a 3d finite element based progressive damage model (pdm) is proposed to simulate the collapse behavior of the single blade stiffened composite (ssc) cfrp panels with and without embedded debonding defects under uniaxial compression loading. a userdefined material subroutine based on 3d hashin failure criteria was developed in abaqus to study the evolution of intralaminar damages in the ssc panel. the stability response and collapse load results obtained using the proposed pdm were compared with the experimental observations. authors in [11] performed fiber-optic-based internal strain measurement and evaluated the residual deformation of l-shaped parts with interlaminar resin layers. through thickness cure shrinkage strain at the corner part was relaxed and the spring-in angle decreased by holding the parts at the cure temperature, indicating that viscoelasticity of the thermoplastic particles is important. viscoelastic finite element analysis supported this finding and indicated that the effect of inter-laminar toughened layers on the residual deformation should be considered to optimize curing processes. in [5], a material was selected that could replace the thermosetting materials used in aircraft structures for interior panels. in [6], detailed research was conducted to expand the thermal analysis of various structures, including nonlinear effects. authors in [7] reported that more detailed modeling of inter-laminar resin layers for quantitative comparison between experiments and simulation, and development of a method to reduce variations in residual deformation are required. the result of the numerical examples showed that changes in the stiffness of the elastic support have a significant effect on the displacement response of the beam. this is being studied in [14]. in this paper, we studied the stochastic iso-geometric analysis (siga) for a functionally graded plate under random loads with the assumption that random loads are a homogeneous gaussian random field in the plate plane. the coefficient of variation of the deflection in the center of the plate predicted by siga was validated with the results of monte carlo simulation in [15]. this work is carried out to evaluate the effects of nanoparticle addition on the penetration and wear resistance of polyethylene at different temperatures (22.8 and 40 °c). a low volume of fractions of carbon nanotubes and nanoclays (0.5 wt.%) were embedded separately into the blend of polymeric materials to improve their mechanical properties, mainly wear and penetration resistance [16]. a homogenization strategy must be used to reduce the complicated heterogeneous microstructure of fgms to examine them properly [17]. iii. stability enhancement for geometrically imperfect fg cntr curved beams affected by frictional behavior fgcnt have geometric imperfections that influence their buckling behavior and strength. with the help of this research, a unique design of induced imperfect hollow trapezoidal layer is incorporated to get better result for the residual strength of the fgcnt reinforced curved beam. hence a novel frictional endo-stratified thermal model was used to analyze the thermal behavior due to the inter laminar frictional effect caused by the delamination between the induced imperfect hollow trapezoidal layer and the adjacent layer of the geometrically imperfect stacked foliate and is modeled using frictional effects due to elastic and plastic deformation of the curved beam at the peak and the trough, respectively, hence determining the thermal characteristics effectively. figure 1 exhibits the block diagram of the proposed stability analysis and enhancement model in which thermal characteristics were analyzed with the determination of frictional effects on the surface of the curved beam. to further enhance the stability of the curved beam, the interaction among the molecules in fgcnt has been analyzed with the kinetic molecular theory for intermolecular forces with the consideration of the strength bearing capacity of the fgcnt. fig. 1. overall architecture of proposed model. a. the frictional endo-stratified thermal model in the frictional endo-stratified thermal model, the frictional effect is considered during the analysis of thermal behavior in the curved beam, introducing an imperfect hollow trapezoidal layer in the design. a mixture of cnts and polymeric matrix, blended based on the volume proportion of constituents makes up the fg cnt reinforcement curved beam. the volume fraction of carbon nanotubes in the fg cnt reinforcement curved beam mixture is dispersed in the thickness direction according to the (ud), (fg x), (fg v), (fg k), and (fg o) functions. figure 2 illustrates the various intermolecular positions of the fgcnt in a curved beam. the volume fraction of cnt (�� ) under various functions is given in (1): �� ��� � ⎩⎪ ⎪⎨ ⎪⎪ ⎧ ���∗4����∗ �|�|� � ����∗ �1 � ��� � ���⋀∗ �1 � ��� � 2����∗ �1 � �|�|� � (1) engineering, technology & applied science research vol. 13, no. 4, 2023, 11326-11331 11328 www.etasr.com kumar & kumar: stability analysis of fgcnt beams with imperfections where � ∗is the total volume fraction of cnt, given by: � � !� ""#�$%&� ' � � ∗ (2) where )* is the mass density of the matrix and ) and +, are the mass density and mass fraction of the cnt, respectively. the rule for fgcnt is based on the condition provided in (3): 1 � �� ��� � �* (3) where �� ��� and �* are the effective volume fractions of cnts in position y along the thickness direction and the matrix mixture. the expanded rule of mixture is used to express the mixture of fg cnt reinforced curved beams and the definition of its mechanical properties as a function of � is expressed by: -% � .%-%/ �� � -*�* (4) where the yong's moduli of cnts are represented by the parameter -% . -* stands for the cnt matrix's elastic moduli. the efficiency parameter .% is included to account for the scale-dependent material properties of cnts. by comparing the elastic moduli that are discovered by molecular dynamic simulations and the law of mixture, it is feasible to estimate the efficiency parameters. it is possible to characterize the material properties of fg cnts reinforced curved beam as a function of y for different distributions of cnts in the thickness directions by incorporating (1) and (3) into (4). when the produced equivalent stresses in fg cnts reinforced curved beam exceed its yield limit, the ductile metallic component primarily yields the fg structure plastically. consequently, (5) is an expression for the multi-linear hardening elastoplastic material properties of fg in fg cnts reinforced curved beam throughout thickness: -��� � 0� 1!231!2#� -*�* � -/ �/ 4 / 0� 1!231!2#� �* � �/ 4 (5) where -/ denotes the elastic modulus of the ceramic phase, and 6� and ℎ* represents the yield limit and tangent modulus of the metallic phase, respectively. the ratio of stress to strain transfer is represented by 8. fig. 2. cnt distribution in fg reinforcement curved beams. b. the finite element model a finite element model is constructed in abaqus to analyze the thermal behavior due to frictional and inter molecular characteristics constituting the stability of the beam. to perform finite element analysis, initially the geometry of fgcnt reinforced curved beams is introduced by incorporating hallow trapezoidal layers and stability has been analyzed in this model with the consideration of friction and molecular interaction. the finite element algorithm uses the pre-processed data obtained from the geometry of fgcnt as input to generate and solve a scheme of linear or nonlinear equations. during the fem process, the detailing friction effect and stresses at various points across the model are calculated with a typical presentation of colored outlines displaying the stress levels on the model. the elastic stresses and strains were examined using the functionally graded cnt model, which included deformations and von mises stresses. the stress caused by the loading distribution was calculated using the elastic von mises stress. this parameter integrates the three main stresses to determine the plastic deformation in metals: 69 � %� :�6;< � 6* �� � �6* � 6=�� � �6= � 6;< ��> ? @ (6) where 6;< , 6* , and 6= are the principal stresses in hollow trapezoidal coordinates. to determine the effect of the friction on the curved beam, initially the volume fraction of fgcnt in various distributions was analyzed and then the material property was calculated. coulomb’s friction law is applied to determine the frictional behavior of the interface layers due to elastoplastic deformation. also, using finite element exploration, the peak and trough thermal stability of a geometrically imperfect curved beam containing functionally graded cnts is determined. fg cnts reinforced curved beams were subjected to the kinetic molecular theory of intermolecular forces to analyze the molecular interactions and the strength bearing capacity of the curved beam with various distributions of fgcnt reinforced composites. the steps used in the fem are: step 1: create the geometry of the curved beam with fgcnt reinforced composite. step 2: define the material characteristics of the fgcnt. step 3: assign appropriate material attributes to various distributions of fgcnt. step 4: create an element section and assign it to each element involved when determining the curved beam parameters including the volume fraction of cnt. step 5: make an element instance. step 6: create analysis stages for the friction effect and molecular interaction. step 7: apply the corresponding neumann boundary conditions by providing dynamic load and energy constraints. the normal derivative at the boundary must be zero or a constant according to the neumann boundary condition. in the context of a heat diffusion problem, zero normal derivative denotes an adiabatic boundary when the boundary is a plane normal to an axis, such as the x axis. at the boundary, the flux engineering, technology & applied science research vol. 13, no. 4, 2023, 11326-11331 11329 www.etasr.com kumar & kumar: stability analysis of fgcnt beams with imperfections of conduction heat is zero, assuming that there is no bending moment on the free ends of the curved beam. step 8: use the element's quadratic meshing to its full potential. step 9: create a job and submit it for consideration. step 10: result visualization. these steps were performed to simulate the curved beam model with mesh characteristics and functionally graded cnt reinforced composite. then, stability analysis of the curved beam was performed to evaluate the enhancement of the residual strength of the curved beam while considering the thermal characteristics. iv. results and discussion this section details the implementation findings as well as the performance of the proposed curved beam design along with a comparative study to guarantee that this proposed design outperforms the existing ones. a. simulation output and performance evaluation this section of the research paper presents the simulation results and performance metrics of the proposed curved beam design. the performance of the proposed design was evaluated using various metrics, including elastic stress, strain, path points, and von mises stress. the results are provided and analyzed. fig. 3. von-mises stress in an fg cnt reinforced curved beam. fig. 4. von mises stress of an fg cnt reinforced curved beam. figure 3 represents the von-mises stress of the fg cnts reinforced curved beam with a hollow trapezoidal layer. the sudden increase and decrease of stresses in fg cnt reinforced curved beams have an impact on the strength bearing capacity. the maximum von-mises stress obtained was +3.9791 e&b , with a step time of 1.00 and a deformation scale factor of +1.636e&c�. the von mises stress of the fg cnt reinforced curved beam with hollow trapezoidal layer is shown in figure 4. the maximum and the minimum obtained stress are 3 e&d at 17.5 mm and -0.6 e&d at 25 mm. as a result, the true distance along the path increases from 0.5 to 25 mm whereas the stress level varies non-linearly. the stress obtained after analyzing the thermal characteristics based on the frictional effect in terms of time is shown in figure 5. in thermal analysis, pressure, von misses stress, and strain increase as load pressure rises. furthermore, when the true length along the path increases, the stress determined along the path points in terms of time decreases to an average of 75%. the yield stress and total deformation of the fg cnts reinforced curved beam rise as the stress decreases. fig. 5. stress in terms of time function. b. comparison analysis to assess the effectiveness of the proposed fg cnt reinforced curved beam design, a comparison was made with existing designs, such as poly phenyl sulfide (pps), polyether-ether-ketone (peek), and poly-aryl-ether-ketone (paek) [5, 13]. the comparison was made in terms of various properties, including specific gravity (g/cm 3 ), melt temperature (°c), tensile strength (mpa), tensile modulus (gpa), elongation yield (%), and flexural strength (mpa). the purpose of this comparison was to determine how the proposed design performs compared to the existing designs and to identify any potential areas for improvement. fig. 6. specific gravity comparison. engineering, technology & applied science research vol. 13, no. 4, 2023, 11326-11331 11330 www.etasr.com kumar & kumar: stability analysis of fgcnt beams with imperfections figure 6 depicts the specific gravity comparison of the proposed fg cnts reinforced curved beam design with the existing pps, peek, and paek. it is noted that the proposed design has a high specific gravity of 1.45 g/cm 3 , whereas pps, peek, and paek have a low specific gravity of 1.35, 1.30, and 1.40 g/cm 3 . hence the proposed design has a high specific gravity whereas peek has a low specific gravity. fig. 7. comparison of tensile strength. figure 7 depicts the tensile strength (mpa) comparison of proposed fg cnts reinforced curved beam design with the existing designs such as pps, peek, and paek. it is noted that the proposed design has a high tensile strength of 98 mpa due to the introduction of hollow trapezoidal layer and with the consideration of frictional effect in thermal analysis whereas the existing techniques such as pps, peek, and paek have a low tensile strength of 90.5, 97, and 95 mpa. hence, the proposed design has a high tensile strength whereas pps has a low tensile strength. overall, the proposed fg cnts reinforced curved beam design has the better von mises stress and maximum stress for molecular level interaction as 5.5 e&d. also, friction coefficient up to 1.5 and stress of 51,000 mpa were provided for the determination of thermal characteristics. the proposed design has a high specific gravity of 1.45 g/cm 3 , a melt temperature of 360°c, and a tensile strength of 98 mpa, which overperform the pps, peek, and paek. v. conclusion this research paper presents a study on improving the stability of imperfect functionally graded carbon nanotube reinforced curved beams by incorporating a hollow trapezoidal layer design. the design was able to improve the tensile strength of the fg cnts up to 98 mpa. 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[17] p. kumar and a. kumar, "stability analysis of imperfect functionally graded cnts reinforced curved beams," mechanics based design of structures and machines, sep. 2022, https://doi.org/10.1080/15397734. 2022.2116340. microsoft word 22-2420_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3603-3608 3603 www.etasr.com pehlivan et al: modeling and validation of 2-dof rail vehicle model based on electro–mechanical… modeling and validation of 2-dof rail vehicle model based on electro–mechanical analogy theory using theoretical and experimental methods fatih pehlivan faculty of engineering department of mechanical engineering karabuk university karabuk, turkey fatihpehlivan@karabuk.edu.tr cihan mizrak faculty of engineering department of mechatronic engineering karabuk university karabuk, turkey cihanmizrak@karabuk.edu.tr ismail esen faculty of engineering department of mechanical engineering karabuk university karabuk, turkey iesen@karabuk.edu.tr abstract—this paper presents theoretical and experimental results on modeling and simulation of two degrees of freedom rail vehicle by using electro-mechanical similarity theory. in this study, the equations of motion were derived using newton’s second law of motion and then mechanical and equivalent electrical circuits were obtained with the help of a free body diagram. a schema in simulink allowing analyzing of the behavior of the primary and secondary suspension was created. in order to verify the electrical model, transfer function and schema were developed in simulink. the simulation results were compared with the experimental data and the comparison showed that the results of the mechanical experiments were close to the simulation results, but the electrical results showed better periodic behavior. keywords-electro-mechanical analogy; equivalent electrical circuit; modeling; simulation; simulink; vehicle; suspension i. introduction urban and intercity transportation have been provided by highways in many countries and so issues regarding traffic congestion, traffic accidents and increasing transportation cost are emerging. in developed countries, railway transport systems are preferred for either urban or intercity transportation because of the fact that they are one of the safest and the most economical transport modes [1–3]. recently the demand for railway transport systems has increased globally. the most crucial effect determining the driving safety and ride comfort is vehicle vibrations caused by dynamic forces occurring during movement. it was shown that during movement, vibrations occur due to dynamic forces usually caused by wheel-rail interaction [4–7]. this vertical oscillation of the rail vehicle can be minimized by optimizing spring stiffness and damping coefficient of the shock absorber as shown in [8, 9]. models with various degrees of freedom (dof) were examined to determine the dynamic behavior of the rail vehicles in [10]. authors in [7] realized dynamic solutions of rail vehicles from single-dof to multi-dof and also worked on rail-wheel contact problems. authors in [11] studied the dynamic behavior of two degrees of freedom (2-dof) wagon models under random vibrations. authors in [12] designed the vehicle suspension system of the quarter vehicle model in matlab/simulink and msc-adams and compared the results. the mathematical model of the system was created using the state space model and the vibration of the system was investigated by the unit step input function. authors in [13] studied the mathematical modeling and simulation of a quartercar with two dof. the state space mathematical model of the system was derived using newton's second law of motion and free-body diagram. afterwards, the performance of the system was examined with matlab/simulink. passive, semi-active and active suspension systems have been tested with unit step input function. authors in [14] studied the effect of spring and damping coefficients on acceleration and deflection using matlab/simulink. authors in [15] aimed to improve driving comfort and road handling. authors in [16] modeled a wagon moving on a bridge considered to be an elastic beam and done some calculations in terms of vibration and acoustics. they also calculated the response of the harmonic force that comes from the bridge and the rail. authors in [17] studied the responses of the contact force and displacement caused by wheel-rail interaction. analysis of the 5-dof quarter-rail model supported by a 3-layer rail system was examined by using the equations of motion of vehicle and rail. most of the studies performed regarding rail vehicles have been related to keeping the vehicle vibrations at optimum level. in this paper, vehicle vibrations were studied, however, results were achieved by creating not only mechanical prototypes but also their equivalent electrical circuits. experimental data obtained from the mechanical mechanism or the equivalent electrical circuit were compared with the simulation results. ii. model of the system a. mathematical model of the 2-dof rail vehicle in order to constitute the mathematical model of the rail vehicle, it is beneficial to understand the quarter, half and full car models which are widely used in the literature due to their similarity with the models of rail vehicles. the modeled 2-dof engineering, technology & applied science research vol. 8, no. 6, 2018, 3603-3608 3604 www.etasr.com pehlivan et al: modeling and validation of 2-dof rail vehicle model based on electro–mechanical… rail vehicle shown in figure 1(a), consists of two masses: m1 is the mass representing the rail vehicle body or wagon and m2 is the mass representing the bogie system. k1 and b1 are the stiffness and damping coefficients of the secondary suspension respectively, k2 and b2 are the stiffness and damping coefficients of the primary suspension respectively, x1 and x2 are the vertical displacements of the rail vehicle body and the bogie system respectively and y is rail excitation as shown in [18–20]. d’alembert’s principle was used to draw the freebody diagram of this system shown in figure 1(b). (a) (b) fig. 1. (a) the 2-dof rail vehicle model. (b) vehicle free body diagram. accordingly, the equations for the vertical motion of the rail vehicle body and the bogie system are obtained by (1) and (2): ����� � ���� ��� � � � �� � ����� 0 (1) ���� � ���� ��� � � �������� � ��� � ��� � � � �� � ����� 0 (2) b. mechanical and equivalent electrical circuit substituting values in (3), (4) and (5), the force representation for the 2-dof rail vehicle can be written as: ��� � ��� � ��� 0 (3) ��� � ��� � ��� � ��� � ��� 0 (4) �� � ��� � ��� 0 (5) the mechanical circuit of the system is obtained using (3), (4) and (5) as shown in figure 2. fig. 2. the mechanical circuit of the modeled rail vehicle with 2 dof. mechanical systems have one excitation source (force), while electrical systems have two excitation sources (voltage difference and current). in this sense, mechanical systems have two different electrical counterparts. the first similarity theory developed to find the first electrical charge is obtained by using the force-voltage difference similarity and the kirchoff voltage law (kvl). to find the other electrical counterpart, the second theory of similarity is established, the force-flow similarity and the kirchoff current law (kcl) are used [21]. the electrical responses of the mechanical elements in both theories are obtained by (6)-(8) which are generated using kirchoff's laws and are shown in table i: ���� �� ��� � ���� � � � ������ (6) ���� � ������� � !��� � � " � !����� (7) !��� # �$����� � $��� % � � & � ������ (8) table i. analogous quantities mechanical quantity electrical quantity (1st similarity theory) electrical quantity (2nd similarity theory) force (f) voltage (v) current (i) velocity (v) current (i) voltage (v) mass (m) inductance (l) capacitance (c) friction (b) resistance (r) inverse resistance (1/r) spring constant (k) inverse capacitance (1/c) inverse inductance (1/l) here, the second theory is selected to be applied to the modeled 2-dof rail vehicle. according to the velocity-voltage similarity or the second similarity theory, the connections in parallel or serial of the mechanical circuit will be the same for the electrical system and so the electrical equivalent circuit of the rail vehicle is obtained by using the mechanical circuit of the system shown in figure 2. the obtained circuit illustrated in figure 3, and consists of two capacitances: c1 is mass representing rail vehicle body or wagon and c2 is mass representing the bogie system. l1 and r1 are the inductance and resistance stiffness and damping coefficients of secondary suspension respectively, l2 and r2 are the stiffness and damping coefficients of primary suspension respectively, and v is the excitation voltage. fig. 3. the mechanical circuit of the modeled 2-dof rail vehicle. c. theoretical methods in order to check the theoretical implementations of the system, a crank-connecting rod mechanism is considered for a harmonic rail excitation in the design of the mechanical system because it is simple and the most fundamental mechanism to transform the rotary motion to translational motion or vice versa [22]. the trigonometric method is used for the kinematic analysis and the velocity of the wheel is calculated for the rail excitation as shown in the following equations: � cos * �+ cos , (9) engineering, technology & applied science research vol. 8, no. 6, 2018, 3603-3608 3605 www.etasr.com pehlivan et al: modeling and validation of 2-dof rail vehicle model based on electro–mechanical… cos , -1 � sin� , (10) 123 4 % 123 5 6 (11) cos , 71 � 8%6 9 � sin� * (12) � cos * �+71 � 8%6 9 � sin� * (13) � cos * �7+� � +� 8%6 9 � sin� * (14) � � * sin * � ��� :-+� � ; � � sin� *< (15) � � * sin * � :=5 >�%� 123 �5<�-?�=>�%� 123� 5 (16) the 2-dof rail vehicle consists of three main parts representing rail actuator, rail vehicle body and bogie system. they are separately designed and assembled together with other parts such as suspension, step motor, linear bearing etc. figure 4 shows the assembly view of the designed parts of the objective rail vehicle. fig. 4. the designed 2-dof rail vehicle. d. transfer function of the designed system taking the laplace transformation of (1) and (2), either the connection between the rail vehicle body and bogie system or the connection between the bogie system and the rail actuator are found as in the following equations. equation (23) gives the transfer function of the 2-dof rail vehicle: ��@��a� � ��@��a� � �a@��a� � �a@��a� ��a�@��a� (17) @��a� b��c �d��cd�� ��cd�� e @��a� (18) ��fg�a� � @��a�h � �afg�a� � @��a�h��f@��a� � @��a�h � �af@� �a� � @��a�h ��a�@��a� (19) � �a � ���g�a� � � �a � ���@��a� f��a� �� � � ��a � ��� � ���h@� �a� (20) � �a � ���g�a� � � �a � ���@��a� f��a� � � � � ��a � ��� � ���h b��c �d��cd�� ��cd�� e @��a� (21) j��c� k�c� ����c�d����� d�����cd�� �� ������cld�m�cnd�o�c�d�"�cd���� (22) where: p �� � � �� � � �� �, q ���� � � � � ���� � ����, and # ��� � ��� r�a� j��c�k�c� j� �c� k �c� s (23) e. mathematical model of the system in matlab simulink simulink offers a graphical solution for modeling, simulating and analyzing dynamic systems over customizable blocks and tool library [23]. a simulink model of the system is created using the mathematical model obtained through (1) and (2) as shown in figure 6. f. result of the theoretical methods in matlab simulink in order to verify the electrical model, a transfer function and a model were developed in simulink as shown in figure 5. the results were obtained by using (16) for the rail excitation and the system parameters shown in table ii. figure 7 shows the vertical displacement of the rail vehicle body with time and it is seen that the transfer function and the simulink model of the mechanical system have one-to-one correspondence with the electrical model of the system. iii. experimental study experiments were conducted to validate both mechanical and electrical approaches. the 2-dof rail vehicle model prototype was created. the theoretical study and the parameters shown in table ii were used in simulations to compare the experimental results with the theoretical ones. fig. 5. matlab representation of the electrical model, the transfer function and the simulink model of the system engineering, technology & applied science research vol. 8, no. 6, 2018, 3603-3608 3606 www.etasr.com pehlivan et al: modeling and validation of 2-dof rail vehicle model based on electro–mechanical… fig. 6. mathematical model of the system in simulink. table ii. parameter values used in the 2-dof rail vehicle parameters values mass of the rail vehicle body or wagon, m1 0,794kg damping coefficients of secondary suspension, b1 57,53n.s/m stiffness of secondary suspension, k1 400n/m mass of the bogie system, m2 0,748kg damping coefficients of primary suspension, b2 57,53n.s/m stiffness of primary suspension, k2 400n/m crank length, r 0,025m connecting rod length, l 0,084m engine speed, * 74rpm fig. 7. verification of the electrical model of the system by using the transfer function and the simulink model. a. mechanical test rig the design of the experimental prototype, which comprises the primary and secondary suspension mechanisms and the excitation mechanism, is shown in figure 8. aluminum shock absorbers, stepper motor and its drive module, control card, chromium rods, linear bearings, rod holders, power supply and vibration datalogger were used in the design. the parts representing the rail excitation, the bogie and the wagon were made up of particle board. it was preferred because it is lighter than all other metals, including aluminum and is more rigid than composite or plastic. mechanical vibration experiments were performed on the prototype rail vehicle test rig shown in figure 9. in the mechanical test rig, a stepper motor controls the rail excitation by using a crank-connecting rod mechanism and the bottom particle board which is below the primary suspension and provides the excitation as velocity to the system. in this way, both primary and secondary suspensions start to move and acceleration of the wagon which is the top particle board is taken with vibration datalogger mounted to the wagon. (a) (b) fig. 8. (a) crank-connecting rod mechanism, (b) kinematic analysis. fig. 9. mechanical test rig engineering, technology & applied science research vol. 8, no. 6, 2018, 3603-3608 3607 www.etasr.com pehlivan et al: modeling and validation of 2-dof rail vehicle model based on electro–mechanical… b. electrical test rig to verify the theoretical study and the designed and manufactured prototype of the 2-dof mechanical rail vehicle model, it is necessary to establish the equivalent electrical test rig of the system. for this purpose, the first step is to create voltage representing the rail excitation. an arbitrary voltage generator can supply the existing excitation because of the fact that it can produce periodic signals as the rail excitation in the mechanical test rig. an aa tech awg-1020 function generator was used in the experiments. the current excitation signal was generated as shown in figure 10 via easywave software and was sent to the voltage generator. fig. 10. the electrical excitation signal for convenience, the electrical parameters were selected such that the ratio of electrical parameters and their representing mechanical parameters be 1:100, which means 1kg corresponds to 0.01f etc. the parameter values are shown in table iii. except for the inductance element, all values shown in table iii were obtained with elements available in the market. in this study, two inductance elements having values of 250mh were needed. an inductor of this value is difficult to find on the market and it is obtained by wrapping copper wire on ferrite [24]. the number of turns is calculated by using (24): s 7 &mt (24) where l is the desired inductance value and al is the magnetic conductivity. the magnetic conductivity of the ferrite used to wrap the copper wire is 24700x10 -9 h. the electrical experiments were performed on the created electrical circuit shown in figure 11. using the gw instek gds-1102-u digital oscilloscope, the voltage values on the capacitor (c1), which is the electrical equivalent of the wagon, were measured and transferred to the freewave software and experimental data were obtained. table iii. parameter values used in the 2-dof rail vehicle equivalent parameter used values wagon mass, c1 capacitor 0,008f damping coefficients of secondary suspension, r1 resistor 1,7424ω stiffness of secondary suspension, l1 inductor 0,25h mass of the bogie system, c2 capacitor 0,0075f damping coefficients of primary suspension, r2 resistor 1,7424ω stiffness of primary suspension, l2 inductor 0,25h fig. 11. electrical equivalent circuit set up iv. results to compare the experimental results with the theoretical mechanical and electrical approach, a series of simulations were conducted in matlab. the vertical vibrations obtained from the mechanical experiment (figure 12) and the vertical vibrations obtained from the electrical experiment (figure 13) were compared with the simulation results. fig. 12. mechanical experiment and theoretical results comparison of vibration values of the rail vehicle model (a) first and (b) second experiment. fig. 13. electrical experiment and theoretical results comparison of vibration values of the rail vehicle model (a) first and (b) second experiment. engineering, technology & applied science research vol. 8, no. 6, 2018, 3603-3608 3608 www.etasr.com pehlivan et al: modeling and validation of 2-dof rail vehicle model based on electro–mechanical… both experimental methods were applied two times and the sampling duration was 6s in each experiment. when the rootmean-square (rms) values of the vertical vibrations obtained from the mechanical test rig, the equivalent electrical test rig and the theoretical model were compared to each other, it was seen that the mechanical test rig and the theoretical methods had the same results by a maximum error of 9.23% as shown in table iv. on the other hand, the maximum error was 25.71% when the equivalent electrical test rig was compared with the theoretical methods as shown in table v. table iv. rms-theoriticalvalue result comparison mechanical test rig rms values error mechanical test rig (1st experiment) 1,084 6,47% mechanical test rig (2nd experiment) 1,266 9,23% theoretical method 1,159 table v. rms-theoritical value comparison-equivalent electrical test rig rms values error equivalent electrical test rig (1st experiment) 0,11717 25,71% equivalent electrical test rig (2nd experiment) 0,12749 19,17% theoretical method 0,15773 v. conclusion two-dof rail vehicle has been studied and modeled by mechanical test rig, its equivalent electrical circuit and theoretical methods. both the mechanical test rig and its equivalent electrical circuit were validated by simulations and both methods were found to be capable of determining the vertical vibrations of both bogie and wagon. the mechanical test rig rms results are closer to the simulation results in comparison with the electrical circuit, but the electrical results show better periodic behavior. 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environment and urban planning istanbul, turkey halilibrahimpolat34@gmail.com abstract—developmental stages of construction technologies in turkey followed various methods and showed differences in practice up to 20th century when the first examples of earlyperiod reinforced concrete structures was created. following the late 18th century, when traditional construction techniques were applied to new masses and building types, the use of modern bricks in vertical carrier elements together with the means of the 19th century was followed by an increase in masonry construction types of building structures. the paper emphasizes in the effects of traditional construction techniques applied with brick, steel, concrete materials on construction technology in turkey. traditional construction techniques are classified and detailed evaluations are made on the design principles of the buildings with historical characteristics. keywords-construction technology; brick arc floor; ferroconcrete; early reinforced concrete structures i. introduction the 20th century modern architectural theme is a complex area and can be diverted differently depending on where the researcher is standing [1]. it had become inevitable for the ottoman state to be exposed to influences at the point of architectural and engineering applications and to incorporate domestic and imported ideas into the framework of westernization starting from the tanzimat (the political reforms made in the ottoman state) years. this relationship has affected construction elements, constructive behavior, facade applications, material usage and carrier system selection. in this context, with the help of both architectural and engineering terminology, an eye was kept on the construction techniques used in the past between the westernization period architecture that started to take effect in the ottoman empire since the second half of the 19th century and the early reinforced concrete technology that lasted until the 1940s. in the late 19th century, mainly due to large fires, the building materials were transferred from the wooden material to the masonry system consisting of stone and bricks. in this paper, developmental stages of construction technology are discussed in the context of purely carrier systems. it is attempted to establish a classification proposal from the written and visual documents about certain special buildings by determining which types of vertical and horizontal elements are used for tensile stress and bending loads. the basic nuance in this classification is based on the composite construction technology (masonry+brick arch floor, framework+brick arch floor, ferroconcrete, reinforced concrete, etc). studied structures have been confined to istanbul, the locomotive of the westernization phenomenon in turkey. the mentioned buildings consist of monumental structures as well as structures registered in the state inventory and private properties. in [2], the author set out from the early 18th century traditional construction techniques, based on the process leading up to the westernization period when making his classification. he gave examples from the wooden skeletal systems. he narrated the development of masonry (stone and brick) from the middle of the 18th century and talked about the horizontally brick arch floor technique which gave its first yields in the late 19th century. at the beginning of the 20th century, the steel skeleton system was used in vertical and horizontal directions. in the same period, the steel and concrete together with ferroconcrete construction technology had been integrated into the new buildings and finally the reinforced concrete structure system was used in all structural elements. the classification method used in [2] is the cause of the path of the article. starting from the late 19th century, stacked masonry is chosen as the starting point of the horizontal voltaic laying system, where composite construction technology was dominant. the process continued until the first examples of the horizontal and vertical reinforced concrete system. according to this study, reaching up to the first decade of the young republic of turkey, the divisions of the construction technology used are:  masonry + brick arch floor  masonry + steel frame + brick arch floor  steel frame + brick arch floor  ferroconcrete  steel frame + reinforced concrete  masonry + reinforced concrete  reinforced concrete engineering, technology & applied science research vol. 7, no. 5, 2017, 1909-1913 1910 www.etasr.com polat: a classification study on the development stages of construction … given this classification, one must consider the intricate approaches in the selection of the bearing systems in some buildings, the direction of the progress of the technology in restoration, where especially the flooring systems and masonry walls transformed into reinforced concrete columns. steel column reinforcements were also made in the structures where ferroconcrete technology was used. but however, the classification is based on the original carrier system. it is difficult to talk about a unification in the architectural context between the periods of the destruction of the ottoman state and the establishment of the republic of turkey. while studying the structure, it can be seen that the architects and engineers of this period used mixed systems. for example there are buildings which are of vertical masonry, horizontally brick arch floor, while steel beams and concrete, which is ferroconcrete system, can be found in the load bearing system of the building. hence, the method of classification of each structure can be based on one’s conviction. the time scope of this classification extends from the last quarter of the 19th century to the first quarter of the 20th century (approximately 50 years) and is limited to istanbul, with more than 200 structures having been researched. ii. classification of construction technologies beyoglu-karakoy, galata, tepebasi, historical peninsula in eminonu, sirkeci, gulhane, beyazit, sisli, tesvikiye, bomonti, besiktas, akaretler, kadikoy, haydarpasa and moda stand out as the new architectural point of view and a reflection of production technologies in istanbul, which tends to be westernized. the data of structures ranging from single-floor to 10 floor buildings, which were built in this period is further investigated. the usual number of floors studied varied between 3 and 4. it has been concluded that the original architectural and structural system of approximately 25% of the structures is changed by restoration. it is determined that the private property concrete structures, which were built especially in the early years of turkish republic have been demolished. this practice has sprung up the old structures which are built in the brick arch floor and ferroconcrete system. the current function of the majority of the buildings is commercial, educational, residential and hotels. in karakoy french architect alexandre vallaury, in yildiz italian raimondo d'aronco, in the historical peninsula architect kemalettin bey who are the pioneers of the first national architecture movement and vedat tek who has worked on new construction technologies, are authorized by the state in the construction of many buildings. there is a transitive between the years when these construction technologies were used and of the years left to be used. at the same time, the criterion applied for ranking is determined by the behavior and variability of the production technologies. a. masonry + brick arch floor in the last quarter of the 19th century brick and steel, which are mass production based materials, started to be used as composite building materials, leaving behind wood which has a low fire resistance and stone which has a high labor cost. so, the brick arch floor is only used as horizontal load bearings. brick arch floor is a type of slab where approximately 0.500.60 m small brick vaults are placed between parallel steel beams [3]. the brick arch floors running in the horizontal direction provide load transfer to the vertical walls which are vertical load bearings. the transfer is by means of steel beams. it is thought that the first building that was built in istanbul with this construction technique was the macka silahhane (1873-1875) [4]. the brick arch floor of the building which functions as istanbul technical university macka campus was transformed into reinforced concrete floors in 1955. besides, the german consulate, cicek pasaji, akaretler, balikli greek hospital, pera palas otel and italian salesiani school are among the most known examples of this building technology. bomonti brewery administration building and boiling oven building (1920-1924) are among the latest and most important structures that were built in masonry + brick arch floor system [5]. b. masonry + steel frame + brick arch floor buildings built in this technology are located in galata along bankalar caddesi and gumruk road. in particular, it has been found that steel profiles are used in addition to the vertical load bearing wall at the elevator sections and at the central points of the structures. the most well-known example is omer abed han designed by alexandre vallaury in karakoy [6]. the 5-floor building, which was built in 1902, now functions as a business center (figure 1) [7]. fig. 1. omer abed han (on pervitich maps and at present) c. steel frame + brick arch floor in ottoman architecture, iron was not used as a loadbearing element alone, but as an auxiliary element that only supports the principal elements carrying loads [8]. on the other hand, in the vertical direction, only the steel beam was used instead of the masonry wall. the first known example is the 6floor british marines hospital (1901-1904) located in galata [9]. the most popular example of this building technology can be said to be haydarpasa train station which is one of the symbols of istanbul. the building was built in german 'new renaissance’ style between 1906 and 1908 and it was built on gigantic steel beams, brick arch flooring being used as a horizontal load transfer element (figure 2). bostanci pier and tunel (metro) han, built in the first quarter of the 20th century, are also examples of this construction technique [10] engineering, technology & applied science research vol. 7, no. 5, 2017, 1909-1913 1911 www.etasr.com polat: a classification study on the development stages of construction … d. ferroconcrete at the beginning of the 20th century, masonry (stone and brick) materials were inadequate for the design of large and monumental structures. also, a new material was needed instead of the steel due to its high cost at the time in question. concrete was the material produced as a result of this need. however, there are some drawbacks of concrete being a standalone building element. because concrete is a structural element which is resistant to pressure (ductile) but cannot show resistance against tensile stresses that can cause brittle fracture. for this reason, the discovered ferroconcrete technology takes as principle the joint placing with steel beams (bending strength) and concrete (compressive strength). and it is considered as an important construction technology accelerating the transition process to reinforced concrete construction technique. in this system, the horizontal loads are transferred to the vertical elements with the aid of ferroconcrete beams by closing the spaces above and by using an improved form of the brick arch floor technique. eminonu post and telegraph building (1905, architect vedat tek) and galata customs buildings warehouses (1907-1910) are examples of early ferroconcrete applications [11]. vedat tek’s defter-i hakani building (1908), nemlizade tobacco warehouse (1912) and liman han (1912) on which demolition decision is taken due to laying 3° towards the sea in sirkeci are the extant products of ferroconcrete technology. in addition, assicurazioni generali han (1909-1923) and wiener bankverein (karakoy ziraat bank, 1911-1912) by the architect giulio mongeri are built with ferroconcrete system. central rihtim han (1912-1914), which is one of the symbols of galata, was destroyed under the name of repair and conversion to hotel, due to galataport project during the days of this study (figure 3). e. steel frame + reinforced concrete in the ferroconcrete construction technique, concrete and steel work as composite building elements. in the 2nd machinery and boiler houses between silahtaraga power plant buildings in alibeykoy, a construction system where vertically oriented concrete beams are placed separately with heavy steel beams is used. second engine house (1921) was built in steel cage columns sitting on a reinforced concrete foundation plate of 0.70 m. the foundation plaque is strengthened by reinforced concrete foundation pile of 7.3 m length and 0.25/0.25 m crosssection [12]. second boiler house (1929) is constructed of a reinforced concrete plate on which the metal structure is placed and columns under it (figure 4). f. masonry + reinforced concrete this construction technology is not a composite technique like steel frame + reinforced concrete. the vertical masonry is formed by placing reinforced concrete plates on the masonry wall. also, it is consisted of reinforced concrete columns which are articulated in the wall in the wall’s direction. in the years when the reinforced concrete systems which are designed in the mixed model have become widespread and they are found in kadikoy, fatih and sisli. the majority of the samples which are built between 1930 and 1938 such as prof. dr. ahmet agaoglu house [13] (figure 5), eczaci nazim malkoc house [14], a house at feneryolu [15], the behcet unmeric house [16], did not reach the todays time. g. reinforced concrete the discovery of concrete is based on the need for a combination of concrete with high compressive strength and steel that meets tensile stresses. it was the american t. hyatt that first brought the idea of using concrete and steel together in the event of bending. in 1901 auquste and gustave perret performed the first application of the reinforced concrete skeletal system. shortly after the discovery of the reinforced concrete building element, the first yields were revealed in the saint antoine church (1906-1911) and apartments (19061912) on istiklal avenue (figure 6). these constructions designed by architects giulio mongeri and eduardo de nari were recorded as the first concrete example of the ottoman period [17]. the columns in the building, the beams that connect them to each other, arches and vaults which covers roof are all built as reinforced concrete [18]. until the 1930s, the monumental buildings in reinforced concrete technology structures which were generally handled by the state were in hospital, pier, factory and apartment buildings functions. seyr-i sefain building (1912), moda pier (1915) and nemlizade tobacco warehouse (1925) by vedat tek [19], harikzedegan apartments (1919-1922) by kemalettin bey, sureyya opera house (1924-1927) by a. and g. perret are among the main examples (figure 7) [20]. many apartment buildings belonging to private property, which represent republican era istanbul architecture, were constructed with reinforced concrete construction technology between 1930 and 1940. unique apartment buildings by the famous architects such as abidin mortas, zeki sayar, sedad hakki eldem, t. cubukciyan ve ekrem hakki ayverdi were located in gumussuyu, nisantasi, bahariye where the people have high educational level [21]. most of these constructions are designed with a beam-column frame structure. however, unfortunately a considerable number of these buildings have been destroyed before they reached the present day. dervis bey apartment (6 floors, in cihangir, 1930-1932), bosfor apartment (10 floors, in gumussuyu, 1930-1932), sevket bey apartment (5 floors, in fatih, 19301933), rontgen apartment (5 floors, in bahariye, 1930 -1933), seza apartment (5th floor, in muhurdar, 1930-1933), halit ziya bey apartment (5th floor, in cemberlitas, 1930-1934), dr. ziya zeren house (4th floor, in bahariye, 1930-1935) which are in the city's memory as qualified constructions was demolished and replaced with new buildings. tahir khan, which was built in 1934, is one of the early republican concrete structures built in karakoy, gumruk caddesi. the architect vedat tek structure, which is composed of 6 floors, is now abandoned (figure 8). fig. 2. haydarpasa train station engineering, technology & applied science research vol. 7, no. 5, 2017, 1909-1913 1912 www.etasr.com polat: a classification study on the development stages of construction … fig. 3. the rihtim han center fig. 4. silahtaraga electric power plant, 2nd engine house fig. 5. prof. dr. ahmet agaoglu house fig. 6. sant'antoine church and its apartments fig. 7. harikzedegan apartments (at present and on pervitich maps) fig. 8. tahir han there are still standing buildings which are symbolizing the early years of the young republic of turkey, especially in the beyoglu and sisli regions. istiklal, ceylan, pertev and cumhuriyet apartments in gumussuyu, tuten apartment in ayaspasa, melek apartment in nisantasi and gevrek apartment in talimhane are trying to move to next generations even if they are under the threat of construction by contractors who want to make investments there. iii. conclusion and evaluation a variety of construction techniques is visible in buildings in istanbul, depicting the technological and cultural changes throughout the ages. a classification of the different techniques could prove valuable for contemporary architectural orientations and for the preservation of originality in possible restoration works. in this paper, the classification carried out was based on load bearing system. the vast majority of the buildings considered are state monumental buildings. the classification scheme followed can not be absolutely accurate as it is not always easy to define the load-bearing system of every structure. further, restoration works have also an impact on the load-bearing system used. however, it offers a useful road-map for classifying different structures and understanding the architectural history of istanbul. references [1] s. o. gur, s. durmus, “tarihyazimina bir kayit dusmek”, yapi no 425, pp. 74-80, 2017 [2] u. yergun, batililasma donemi mimarisinde, yapim teknolojisindeki degisim ve gelisim, yildiz technical university institute of science, phd thesis, istanbul, 2002 [3] m. sozen, u. tanyeli, “sanat kavram ve terimleri sozlugu”, remzi press, istanbul, pp. 317-318, 2014 [4] http://www.tas-istanbul.com/portfolio-view/macka-silahhanesi/ [5] g. tanyeli, d. ikiz, “istanbul'da bir endustriyel miras ornegi: bomonti bira fabrikasi”, turkiye bilimer akademisi, 7, 2009 [6] m. s. akpolat, fransiz kokenli levanten mimar alexandre vallaury, hacettepe university institute of social science, phd thesis, ankara, 1991 [7] j. pervititich, sigorta haritalarinda istanbul, tarih vakfi yurt press, axa oyak, istanbul, 2003 [8] u. tanyeli, osmanli mimarliginda demirin strukturel kullanimi (15-18 y.y.), istanbul technical university institute of science, phd thesis, istanbul, 1996 [9] s. genim, panorama istanbul 1955, masa press, istanbul, 2017 [10] c. kiziltug, tunel (1875-1990), istanbul, 1990 [11] t. uzun, gec osmanlierken cumhuriyet donemi mimarlik pratiginde bilgi ve yapim teknolojileri degisimi erken betonarme istanbul ornekleri: 1906-1930, yildiz technical university institute of science, istanbul, 2008 engineering, technology & applied science research vol. 7, no. 5, 2017, 1909-1913 1913 www.etasr.com polat: a classification study on the development stages of construction … [12] s. y. brangar, silahtaraga elektrik santrali’nin korunmasi ve yeniden kullanimina yonelik oneriler, yildiz technical university institute of science, msc thesis, istanbul, 2004 [13] anonim, macka’da profesor ahmet. agaoglu evi, arkitekt journal, 1011, istanbul, 1938 [14] a. mortas, “eczaci nazim malkoc evi”, arkitekt journal, 4, istanbul, 1937 [15] a. denktas, “feneryolu’nda bir ev”, arkitekt journal, 9, istanbul, 1937 [16] n. akatay, “behcet unmeric evi “, arkitekt journal, 1-2, istanbul, 1939 [17] c. can, p. girardelli, “beyoglu’nda bir latin aniti”, yasayan cizgiler sant’antoine kilisesi mimari cizimler sergisi, yapi kredi culrural center, istanbul, 1996 [18] c. can, istanbul'da 19. yuzyil batili ve levanten mimarlarin yapilari ve koruma sorunlari, yildiz technical university institute of science, phd thesis, istanbul, 1993 [19] h. pilehvarian, “moda iskelesi”, mimarlik dekorasyon, sayi: 97, istanbul, 1997 [20] y. yavuz, birinci ulusal mimarlik donemi ve mimar a. kemalettin bey, istanbul technical university institute of science, phd thesis, istanbul, 1981 [21] d. ozakbas, cumhuriyet donemi (1923-1940) istanbul mimarisi, mimar sinan guzel sanatlar university institute of social sciences, msc thesis, istanbul, 2007 microsoft word 19-3275_s_etasr_v10_n1_pp5201-5204 engineering, technology & applied science research vol. 10, no. 2, 2020, 5201-5204 5201 www.etasr.com elmansouri et al.: the immersion corrosion resistance of shot peening and mao applied on … the immersion corrosion resistance of shot peening and mao applied on az31−0.5% la sheets galal elmansouri metallurgical and materials engineering department karabuk university karabuk, turkey galal_mansouri@yahoo.com hayrettin ahlatci metallurgical and materials engineering department karabuk university karabuk, turkey hahlatci@karabuk.edu.tr ismail hakki kara metallurgical and materials engineering department karabuk university karabuk, turkey ihakkikara@karabuk.edu.tr yunus turen metallurgical and materials engineering department karabuk university karabuk, turkey yturen@karabuk.edu.tr abstract—in this study, the effect of shot peening (sp) and micro arc oxidation (mao) process on the corrosion resistance of 0.5% la with added az31 mg alloy, hot rolled at different rolling speeds, was investigated. it was found that the surface of the rolled material at a rolling speed of 4.7m/min had higher surface smoothness values than the one rolled at 10m/min. it was observed that the corrosion rate changed in the first 40 of 168 hours. in the following hours, the corrosion rate showed different results according to the initial microstructure properties of the base materials. initially, pore size was the dominant factor determining corrosion resistance, although, after coating, the corrosion rate was affected by the twins formed, based on rolling speed, which enhanced the corrosion rate between 48 and 168 hours. keyword-shot peening; micro arc oxidation; az31; la; hot rolling; corrosion resistance i. introduction mg alloys attract attention especially from the automotive and aerospace industries due to their low density and high strength [1]. hcp (hexagonal package structure) reduces the easy forming of mg alloys and weakens the competitiveness of sheet mg products [2]. it is known that rare earth elements increase the formability of az31 mg alloy [3]. on the other hand, the corrosion resistance of mg alloys is poor and coating and alloying in order to improve corrosion resistance are quite popular [4-5]. moreover, it is desired to improve the mechanical properties of mg alloys by creating tension on the surface of the material by processes such as shot peening (sp) [6]. in addition, the micro arc oxidation (mao) process improves corrosion resistance perfectly [7]. az31 mg alloys which have been treated with only sp or mao have been reported [4-6]. the aim of this study is to improve the corrosion resistance of az31 mg alloy metal sheets by addition of la as well as sp and mao applications. in addition, the effect of rolling speed and rolling parameters on the final result was investigated. ii. experimental study az31 mg alloys containing 0.5 la (%wt.) were produced by using low pressure gravity die casting method. the composition of the produced material, determined by an xrf machine, was 3.11%wt al, 1.06%wt zn, 0.23%wt mn, and 0.54%wt la. in an argon gas protected environment, pure mg alloys were allowed to melt at 750°c for 1 hour and then the la-mg master alloy was added to the ladle and alloyed. in sf6co2 blended protective atmosphere, the alloy was transferred with 2atm pressure to a stainless steel 36x36x200mm mold which was heated at 350°c. billets with dimensions 36x12x80mm were cut from the billets left to cool in the molds to be used in the homogenization process before rolling. the surfaces of the billets were homogenized for 24 hours at 400°c and were sanded with 800 sanding sheets before rolling. before rolling the specimens were heat treated at 400°c for 30min. the samples were rolled at 400°c. the thickness of billets reduced from 12mm to 2mm in 5 passes and they were allowed to cool in air after the last pass. the rolling parameters were 15% cross-sectional redultion per pass and the rolling speeds were 4.7m/min and 10m/min. the used rollers of the rolling stand were from stainless steel with a diameter of 110mm. no lubricant was used in the rolling process. the sp process was carried out for 20min with tab company ball sp machine by using z850 metal balls on the sheet materials which were previously sanded with 1200 grit by giving maximum 8bar air pressure according to aisi 1070 standard. after the sp process, the surface of the samples was cleaned with alcohol and dried. micro arc oxidation process followed: 25x25x12mm samples previously sanded up and cleaned with ultrasonic cleaning device were immersed in 4g/lt sodium silicate, 1g/lt potassium hydroxide and 3g/lt disodium hydrogen phosphate containing 4lt pure water medium under 85ma/cm 2 current corresponding author: hayrettin ahlatci engineering, technology & applied science research vol. 10, no. 2, 2020, 5201-5204 5202 www.etasr.com elmansouri et al.: the immersion corrosion resistance of shot peening and mao applied on … density and 250hz frequency for 5min. immersion corrosion test in 3.5% nacl solution was applied to the 2mm sheets for 168 hours. after the corrosion test, the corrosion waste of the samples were extracted using chromic acid solution and then dried with alcohol and the weight loss was measured using 0.0001 precision balance machine. microstructure images of the samples were taken before and after the corrosion test by sem (carl zeiss ultra plus gemini fesem). in addition, information was obtained about thesecondary phases by using xrd (rigaku ultima iv). the surface smoothness of the samples was measured according to the iso 1997 standard (mitutoya surftest sv-2100m4). iii. results and disussion a. microstructure results as shown in figure 1, the base metal of az31-0.5 la alloys rolled at 4.7m/min had twins dominated microstructure and bigger sized secondary phases shaped as globular, although the rolled at 10m/min speed specimen includes dynamic recrystallization grains and finer secondary phases distributed mostly continuously on grain boundaries. as shown in figure 2, surface morphology and cross-sectional images of the samples after mao treatment are different. however, the typical coating properties of the mao process were obtained, for example, from islets of different sizes and micropores of different diameters formed on these islets. melting and rapid solidification during mao ensure that the pores are circular. at a rolling speed of 4.7m/min, the extruded sample has smaller diameter micropores, which are more dense in the islets. the rolled material at 10m/ min has larger pores with larger diameters, but they are distributed less on the islets. fig. 1. sem images of base metals rolled at 4.7 and 10m/min (a) (b) fig. 2. sem images of surface and cross-section of materials rolled at: (a) 4.7m/min, (b) 10m/min the images taken show us that the rolled material at 4.7m/min is coated non-uniformly. the coating is more uniform at 10m/min. the xrd results of the rolled material at a rolling speed of 4.7m/min coated with mao are given in figure 3. it is seen that the coating contains mgo and mgal2o4 phases. fig. 3. xrd paterns of mao coated material rolled at 4.7m/min b. surface smoothness as can be seen from figure 4, the surface images of the samples after coating are similar. however, surface smoothness was found to be lower in the material rolled at 10m/min. 3.46 2.32 (a) (b) fig. 4. surface properties of the examined materials at: (a) 4.7m/min, (b) 10m/min c. corrosion test immersion test results are shown in figure 5. the corrosion rate of the rolled material at the rolling speed of 10m/min for the first 40 hours is faster than that of 4.7m/min, but afterwards, the corrosion rate increased more in the 4.7m/min sample. the corrosion rate of the first 40 hours is under the influence of the coating. however, the corrosion rate was influenced by the properties of the base material in the following hours. firstly, the relationship between corrosion rate and mao coating was determined by the diameter and the number of pores of the coating. the more the pores or the -20,0 0,0 20,0 0,0 1,0 2,0 -20,0 0,0 20,0 0,0 1,0 2,0 engineering, technology & applied science research vol. 10, no. 2, 2020, 5201-5204 5203 www.etasr.com elmansouri et al.: the immersion corrosion resistance of shot peening and mao applied on … larger the diameter, the faster the corrosion tendency. it is believed that the large diameter pores of the rolled material at 10m/min cause a high corrosion rate in the first 40 hours [8]. the corrosion attacks find a way to enter inside the coating due to the pores formed during mao resulting in destruction of the coating layer. on the other hand, the degrading of coating firstly occurs in the porous/outer layer and after that the degrading encounters with the barrier/inner layer which is denser than the porous layer, wherein the corrosion rate is changed by the time of immersion. as seen in figure 5, the 4.7m/min rolled sample had the most liner line, although the 10m/min rolled sample includes decreasing corrosion rate till 120 hours. the dense inner layer is the main determiner of the corrosion rate of the coating under increasing corrosion attacks with increasing immersion time [9]. however, it is known that the rolled materials at high speeds contain fewer twins and more recrystallized grains. it is reported that twinning adversely affects the corrosion resistance due to their different stress zones. however, the fact is that the recrystallized grains contain more grain boundaries and less dislocation density contributes to corrosion resistance [10]. the reason why corrosion resistance is weaker after 40 hours in the material with 4.7m/min rolling speed may be attributed to this. fig. 5. corrosion rates of samples that were corroded for 168 hours in 3.5% nacl d. after corrosion after the corrosion test, pictures and sem images were taken from the surfaces of the materials and are exhibited in figure 6. as it can be seen from the macro pictures and the sem images, it is understood that the rolled material with a rolling speed of 4.7m/min has deeper and wider corrosion pits. as can be seen from figure 7, mg, o and al elements remain in the coating material. however, as it progresses towards the base material, mg becomes more dominant. during corrosion, oxidation occurs on the surface of the material and forms a compound with al and mg. iv. conclusion corrosion resistance of az31mg alloy with 0.5% la was higher in the first 40 hours at of 4.7m/min rolling speed compared to the rolled material at 10m/min due to the size of micro pores which is narrower at 4.7m/min. the following hours, the corrosion rate of 4.7m/min deteriorated by the twins dominated microstructure. (a) (b) fig. 6. sem investigations after the corrosion test, (a) 4.7m/min, (b) 10m/min fig. 7. linear eds analysis from section to base material after corrosion test for the 4.7 sp-mao sample references [1] x. liu, b. w. zhu, c. xie, j. zhang, c. p. tang, y. q. chen, “twinning, dynamic recrystallization, and crack in az31 magnesium alloy during high strain rate plane strain compression across a wide temperature”, materials science and engineering: a, vol. 733, pp. 98107, 2018 [2] j. b. zhang, l. b. tong, c. xu, z. h. jiang, l. r. cheng, s. kamado, h. j. zhang, “influence of ca-ce/la synergistic alloying on the microstructure and mechanical properties of extruded mg–zn alloy”, materials science and engineering: a, vol. 708, pp. 11-20, 2017 [3] i. h. kara, h. ahlatci, y. turen, y. sun, “microstructure and corrosion properties of lanthanum-added az31 mg alloys”, arabian journal of geosciences, vol. 11, no. 18, article id 535, 2018 [4] d. sreekanth, n. rameshbabu, k. venkateswarlu, “effect of various additives on morphology and corrosion behavior of ceramic coatings developed on az31 magnesium alloy by plasma electrolytic oxidation”, ceramics international,vol. 38, no. 6, pp. 4607-4615, 2012 [5] y. du, m. zheng, x. qiao, w. peng, b. jiang, “effect of la addition on the microstructure and mechanical properties of mg–6 wt% zn alloys”, materials science and engineering: a, vol. 673, pp. 47-54, 2016 [6] m. mhaede, f. pastore, b. hadzima, “influence of shot peening on corrosion properties of biocompatible magnesium alloy az31 coated by dicalcium phosphate dihydrate (dcpd)”, materials science and engineering: c,vol. 39, pp. 330-335, 2014 engineering, technology & applied science research vol. 10, no. 2, 2020, 5201-5204 5204 www.etasr.com elmansouri et al.: the immersion corrosion resistance of shot peening and mao applied on … [7] v. ezhilselvi, j. nithin, j. n. balaraju, s. subramanian, “the influence of current density on the morphology and corrosion properties of mao coatings on az31b magnesium alloy”, surface and coatings technology, vol. 288, pp. 221-229, 2016 [8] a. keyvani, m. zamani, a. fattah-alhosseini, s. h. nourbakhsh, m. bahamirian, “microstructure and corrosion resistance of mao coatings on az31 magnesium”, materials research express, vol. 5, article id 086510, 2018 [9] k. dong, y. song, d. shan, e. h. han, “corrosion behavior of a selfsealing pore micro-arc oxidation film on am60 magnesium alloy”, corrosion science,vol. 100, pp. 275–283, 2015 [10] f. guo, d. zhang, x. yang, l. jiang, s. chai, f. pan, “influence of rolling speed on microstructure and mechanical properties of az31 mg alloy rolled by large strain hot rolling”, materials science and engineering: a,vol. 607, pp. 383-389, 2014 author profiles galal elmansouri was born in 1972 in triboli and obtained his bsc degree from libya. presently, he is phd student in the department of metallurgical and materials engineering, faculty of engineering, karabuk university, turkey. ismail hakki kara is a research assistant at karabuk university, turkey. he obtained his bsc degree from the department of metallurgical and material engineering, itu, istanbul, turkey, in 2012. his research interests include welding technology, p91 and p92 steels, microstructure characterization, sem, microscopy, and magnesium alloys. hayrettin ahlatci, was born in 1969 in karabuk and obtained his bsc degree from the department of metallurgical and material engineering, istanbul technical university (itu), turkey, in 1994. he started his academic career as a research assistant at karaelmas university in zonguldak, turkey. he completed his msc and phd degrees at the institute of science at itu. presently, he is associate professor in the department of metallurgical and materials engineering, faculty of engineering, karabuk university, turkey. yunus turen was born in 1965 in karabuk and obtained his bsc degree from the department of metallurgical and material engineering, gazi university, turkey, in 1999. presently, he is an associate professor in the department of metallurgical and materials engineering, faculty of engineering, karabuk university, turkey. microsoft word 31-3789_s_etasr_v10_n5_pp6330-6334 engineering, technology & applied science research vol. 10, no. 5, 2020, 6330-6334 6330 www.etasr.com alnaimat: the geometrical effect on the von mises stress on ball and socket artificial discs the geometrical effect on the von mises stress on ball and socket artificial discs feras adnan alnaimat medical engineering department faculty of engineering al-ahliyya amman university al-saro, al-salt, amman, jordan f.alnaimat@ammanu.edu.jo abstract-wear has been considered as a major issue for ball and socket artificial discs. this paper studies the effects of ball radius and radial clearance of the artificial disc on the von mises stresses. different material combinations, used in artificial discs, are compared. fea simulation using solidworks has been conducted for different disk geometries. the highest von mises stress was 714mpa for 10mm radius metal against metal design. the lowest von mises stress was 14.8mpa for 16mm radius of the uhmwpe/cocr material combination, which exhibited the lowest von mises stresses for all the radii of the ball and socket articulation. considering radial clearance, the lowest von mises stress was 14.8mpa for 0.015mm clearance of the uhmwpe/cocr combination. the highest von mises stress of 100.8mpa with a radial clearance of 0.25mm was recorded for the same combination. there is a strong relation between the von mises stress and the geometry of the ball and socket of the artificial disc. keywords-fea; von mises stress; radial clearance; artificial disc; artificial joint i. introduction intervertebral discs are majorly responsible for back motions [1]. there are 24 discs in the spine which have the same shape but different sizes [2]. intervertebral discs lose their mechanical ability of holding compression loads and giving the required motion without causing pain when they get degenerated [3]. artificial discs have been introduced to relieve disc pain and to restore the required mechanical motion [4]. ball and socket articulation idea came from artificial hips and has been widely used to design artificial discs [5]. one of the major problems articulation joints face is the wear particles resulting from the friction between the ball and socket artificial joints [6-8]. these wear particles migrate to the surrounding tissues causing inflammation response and toxicity [9]. researchers have been trying to use different material combinations such as metal against metal, metal against polymers and ceramic against ceramic to solve this problem [10]. others tried to understand the link between the geometry of the ball and socket and the lubrication regime [11-15]. one of the main effects of increasing the radius of the ball is that it is increasing the range of motion for the implant for flexion, extension and lateral bending. in addition, the force facing the facet joint was lower with the larger radius of the ball for all motions [16]. other studies showed that increasing the radius of the ball has a direct effect on the lubricant film thickness enhancing the lubrication regime of the implant [17]. it has been noticed that the film thickness decreases with increasing radial clearance of the ball and socket artificial joint [15, 17]. choosing the right geometry of the ball and socket could improve the artificial joints lubrication regime and reduce the wear and friction generated from the articulation between them [18]. there is a direct relationship between the wear and the contact stress. it was found that the wear increases with higher contact stress [19]. there is a direct relationship between the von mises and contact stresses as the contact stress increases when the von mises stress increases [20]. maximum distortion energy was obtained by studying the strain energy that develops at a material point [21]. in this study, different geometries with different materials and the stresses these designs face are studied with the use of simulation software. bs iso 21534:2009 [22] suggests that different material combinations could be used in joint replacement. the aim of this study is to compare the different geometrical designs of the ball and socket artificial discs on von mises stresses and to study the effect of the different material combinations on the stresses these geometrical designs face. ii. methodology and materials a. methods different artificial disc geometrical designs have been simulated using solidworks (dassault systèmes solidworks corp., massachusetts, usa). the focus of changing the geometry was to use different radii for the balls and sockets. seven radii for the ball and socket were chosen with radial clearance of 0.015mm. this radial clearance has been chosen after comparing different radial clearances with solidworks simulation tool. some of these ball and socket radii were similar to the design geometries used in the market. each design consisted of a socket and a ball. the ball part was designed with different radii, such as 10, 11, 12, 13, 14, 15 and 16mm. different ball radii in the 5-20mm range have been simulated in [23]. the socket part was designed with the same geometry of the ball but adding to each radius a radial clearance of 0.15mm. a static solid model using solidworks corresponding author: feras adnan alnaimat engineering, technology & applied science research vol. 10, no. 5, 2020, 6330-6334 6331 www.etasr.com alnaimat: the geometrical effect on the von mises stress on ball and socket artificial discs with tetrahedral solid elements was used to simulate the finite element analysis of the models with different geometries. the total number of nodes for the different geometries varied between 74913 and 78765. figure 1 shows the ball part design before assembly and simulation. an axial force of 2000n was applied on the upper plate of the socket. it is the maximum force that can be applied according to the standard iso 181921:2011 [24]. the ball and socket artificial disc was fixed from the bottom plate of the ball as the loads come axially from above [24], as shown in figure 4. figure 2 shows the fine mesh of the ball and socket artificial disc with 78765 tetrahedral solid elements used in the simulation. (a) (b) (c) fig. 1. (a) ball part and (b) socket part of the artificial disc. (c) the artificial disc assembly. fig. 2. mesh of the ball and socket artificial disc assembly. b. materials cobalt-28 chromium-6 molybdenum (cocr) alloy castings that are used in implants were used in this simulation. the cocr against cocr has been used in maverick and kinefelx artificial discs [25, 26]. uhmwpe was used as the socket part of the artificial disc implant. the uhmwpe against cocr combination have been used in multiple artificial discs such as charite and prodisc artificial discs [27, 28]. polyether ether ketone (peek) against peek combination has been used to produce nunec artificial discs [29, 30]. metal against metal materials were designed and simulated using a cocr socket against a cocr ball. other models were designed and simulated using polymer against metal materials and uhmwpe socket against cocr ball. polymer against polymer materials were designed and simulated using peek socket against peek ball. the materials’ mechanical properties are listed in table i. table i. materials mechanical properties [31-33] mechanical properties cocr uhmwpe peek yield strength (pa) 4.5×10 8 2.3×107 9.3×107 tensile strength (pa) 2.35×10 8 5.3×107 1.1×108 elastic modulus (pa) 2.11×10 11 7.25×108 4×109 poisson's ratio (pa) 0.31 0.46 0.36 mass density (kg/m3) 8900 930 1300 shear modulus (pa) 8.8×1010 3.2×108 1.425×109 iii. results and discussion a. results the results of the fea simulation showed that, as expected, the ball and socket had the highest von mises stress on the edges of the socket (figure 3). the highest von mises stress was 14.8mpa on the edges of the uhmwpe socket and the lowest stress was 0.04mpa for the same combination. the design with the 16mm radius of the ball and socket showed a von mises stress lower than the yield stress of the uhmwpe used in the simulation of the artificial disc. the von mises stress gradually reduced by moving away from the edges of the socket and increased again when reaching the lowest point of the concave part of the socket reaching around 11mpa, as shown in figure 3. fig. 3. the von mises stress of the uhmwpe socket with 16.015mm radius after fea simulation. figure 4 shows the fea simulation of the ball and socket artificial disc assembly. the uhmwpe socket faces most of the high stresses. the highest stresses on the ball part were engineering, technology & applied science research vol. 10, no. 5, 2020, 6330-6334 6332 www.etasr.com alnaimat: the geometrical effect on the von mises stress on ball and socket artificial discs caused by the edges of the socket in direct contact, where the von mises stresses were between 5mpa and 10mpa. fig. 4. fea simulation of the uhmwpe socket against a cocr ball with 16mm radius. the von mises stresses were different for the cocr socket against cocr ball in which the socket did not face a lot of stresses on the top edges of the socket like the uhmwpe socket. the stresses were concentrated on the top center of the socket and this could be due to the higher 450 mpa yield strength of the cocr used in this study. fig. 5. fea simulation of the cocr socket against a cocr ball with 14mm radius. the highest von mises stress was 714mpa for the 10mm radius ball and the socket metal against metal design. the lowest von mises stress for the same material combination but with a larger radius of 16mm was 153.4mpa, as shown in figure 6. for the peek against peek combination, the highest von mises stress was 682mpa for the 10mm radius and the lowest was 24mpa for the 16mm radius design. the highest von mises stress for the uhmwpe against cocr combination was 44mpa for the 10mm radius and the lowest was 14.8mpa for the 16mm radius. it was noticed that the von mises stress reduced when the ball and socket radius was increased for all material combinations. the contact stress showed nearly the same trend as the von mises stress. they both showed a decrease with the increment of the ball radius (figure 7). radial clearance is a factor well-known for affecting the lubrication regime in any ball and socket artificial joint. this study showed that the radial clearance had an effect on the von mises stress as well, as shown in figure 8. it was noticed that by increasing the radial clearance, the von mises increased for the 16mm socket to reach about 100mpa in the uhmwpe against cocr combination. the lowest von mises stress of 14.8mpa was for a radial clearance of 0.015mm for the same combination. fig. 6. von mises stress of the different geometries and material combinations. fig. 7. contact stress of the different geometries and material combinations. fig. 8. radial clearance effect on the von mises stresses facing the 16mm radius socket for the uhmwpe against cocr combination. b. discussion ball and socket artificial disc simulations showed that the maximum von mises stress occurred on the edges of the contact between the ball and socket. it is suggested by the engineering, technology & applied science research vol. 10, no. 5, 2020, 6330-6334 6333 www.etasr.com alnaimat: the geometrical effect on the von mises stress on ball and socket artificial discs results that any design for the ball and socket must be curved on the contact edges. the blue area on the concave part of the socket in figures 3 and 7 was due to the 0.015mm radial clearance applied on the design of the socket. the uhmwpe socket showed higher von mises stresses than the cocr ball as was expected due to the higher yield modulus of the cocr mentioned in table i. in this kind of articulation, it is most likely that the wear particles will be from the uhmwpe [34]. there is a direct relationship between wear volume, contact stress, and von mises stress [19, 20]. this study investigated the way the von mises stress is applied on artificial joints of different material combinations and the effect of radial clearance on the artificial joint using fea simulation, instead of mathematical calculations [11, 15]. these stresses are important to be analyzed and understood in depth as they can affect the facial joints at the treated level by increasing the force these joints face [35, 36]. the uhmwpe against cocr combination had the lowest von mises stresses for all designs. peek against peek combination had higher von mises stresses than uhmwpe against cocr. the highest von mises stresses occurred for the cocr against cocr combination, which was expected [37]. in addition, the highest friction coefficient for the different combinations was for cocr against cocr and the lowest for uhmwpe against cocr [38]. larger radii of the ball and socket artificial discs showed a lower von mises stress for all material combinations, as shown in figure 5. also, it has been shown that a larger radius of the ball and socket artificial disc will help reduce the resulting wear [15, 39, 40]. in this aspect, there is a sharp contrast with the previous published theoretical results in which the wear and friction increase with the decrease of ball radius [18, 31]. it has been noticed from figures 3 and 7 that the highest stresses were applied on the edges of the socket. this would cause them to wear more than the rest of the socket. improving the design to make it curvier would have an impact in reducing the von mises stress. maverick is one of the artificial discs which have a design of curved edges of the socket part [25]. the radial clearance had a direct effect on the von mises stress. increasing the radial clearance caused increment on the von mises stress, as shown in figure 8. the benefit of the radial clearance is that it enhances the lubrication film thickness between the ball and socket. however, it could increase the von mises stress of the implant. authors in [15] found that by decreasing the radial clearance of the ball the fluid film thickness will be increased and this will cause a fluid film lubrication regime. authors in [41] reported similar results stating that there is a direct relation between the radial clearance and the lubrication regime in which decreasing the radial clearance will increase the film thickness of the lubricant. iv. conclusion it has been found that there is a relationship between the von mises stress and the ball radius of the artificial joints. the uhmwpe against cocr compilation had the lowest von mises stress values for all radii. in addition, there is a strong relation between the radial clearance of the socket and the von mises stresses facing the articulation. the conclusions of this study are: • von mises stress was the highest with 714mpa for the 10mm radius ball and socket metal against metal combination. • the lowest von mises stress was 14.8mpa for the 16mm radius for the uhmwpe against cocr combination. • there is a strong relationship between the von mises stresses and the radius of the ball and socket artificial discs. • the von mises stresses increase with the increment of the radial clearance of the socket part. • uhmwpe against cocr combination showed the lowest von mises 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[41] i. j. udofia and z. m. jin, “elastohydrodynamic lubrication analysis of metal-on-metal hip-resurfacing prostheses,” journal of biomechanics, vol. 36, no. 4, pp. 537–544, apr. 2003, doi: 10.1016/s0021-9290 (02)00422-0. engineering, technology & applied science research vol. 8, no. 1, 2018, 2433-2437 2433 www.etasr.com shahmohammadi: the impact of total quality management on the effectiveness of educational … the impact of total quality management on the effectiveness of educational programs of karaj first grade high schools nayereh shahmohammadi organization for educational research and planning (oerp) ministry of education tehran, iran nsh_teh@yahoo.com abstract—this study aimed to explore the role of total quality management (tqm) in educational programs of first grade high schools in karaj city. the target population included all high school teachers of the academic year 2015-2016. sample population of 324 persons was selected by random cluster sampling. a questionnaire was used to measure the variables in the study. content validity of the questionnaire was confirmed by experts. the reliability of the questionnaire was estimated to be 0.89 by cronbach's alpha coefficient. t-test was used to analyze the data. the results showed that tqm and each of its dimensions affect the effectiveness of training programs and courses in junior high schools in the city of karaj. keyword-total quality management; effectiveness; training; quality; education; analysis i. introduction enterprise development depends on the promotion of knowledge, skills, and insights of employees. as a tool for development, education meets the needs of organizations. sustainable development in different dimensions depends on education, its quality, continuity and effectiveness [1, 2]. the improvement of human resources through education in general and high quality and effective in-service training in particular is the most effective means to create harmony between employees and organizations [3]. authors in [4] argue that educational effectiveness depends largely on teachers’ effectiveness. the educational effectiveness of teachers should be evaluated based on the behavior and learning of students. the theoretical and research literature indicate that the major obstacles of educational programs which have reduced the efficiency and effectiveness of education over the years are associated with educational programs themselves. in [5], factors such as lack of skilled labor, lack of participation of education stakeholders in program designing, lack of evaluation in educational system, and not using evaluation results to reform educational process affected the effectiveness of training programs are reported. education management experts consider total quality management (tqm) as an important tool for the reconstruction of the educational system and for increasing its effectiveness [6]. tqm consists of many components including leadership, data analysis, benchmarking, quality strategic planning, human resources development, products and services quality assurance, and customer satisfaction [7]. there are many studies on the application of tqm on educational systems. in [8] it was found that there was significant relationship between tqm application in schools and leading teachers by principals, helping students, constructive relations with parents, skill evaluation and school administration. authors in [9] defined that the application of tqm in education has a strategic and systematic approach that includes seven steps. authors in [10] claimed that four major principles of tqm have not been considered properly. authors in a similar study [6] found that there is a significant and positive correlation between the deployment of tqm and effectiveness. in [11], the attitudes of professors, students, and teachers (from preschool to high school) toward the role, appropriateness, and application of tqm in education were evaluated. the findings showed that teachers have less resistance to implement it than other groups. author in [12] studied the implementation of tqm in new jersey schools. he identified five factors which help to implement tqm in organizations: 1) efforts should be based on the improvement process, 2) quality should be identified and defined by customers, 3) everyone must be involved in decision-making, 4) decision must be made based on data and results, and 5) a long-term commitment should be created by top management. the necessity of tqm, as an important factor for effectiveness of training programs, is more important than ever. this study aims to investigate the impact of tqm on the effectiveness of training programs of first grade high school in karaj in order to help practitioners and stakeholders to consider tqm and control continuously its indicators to identify the key factors for strengthening the effectiveness of training programs and provide grounds for improving them. ii. methodology this study applied a descriptive survey. it assessed the perspective of teachers about the quality and effectiveness of training programs considering quality management. the population consisted of all first grade high school teachers in karaj in 2015-2016 (n=2073). using cochran's formula and engineering, technology & applied science research vol. 8, no. 1, 2018, 2433-2437 2434 www.etasr.com shahmohammadi: the impact of total quality management on the effectiveness of educational … random cluster sampling method, 324 teachers were selected as participants. moghimi’s tqm evaluation questionnaire [13] was used as research tool. it included 39 questions which evaluated the impact of each of the eight tqm dimensions, shown in table i, on the effectiveness of educational programs from the teachers’ perspective. questionnaire’s content validity was confirmed by 12 experts. to determine the reliability of the questionnaire, it was distributed among 30 subjects. using cronbach’s alpha, the reliability was determined to be 0.89 (table ii). the descriptive (frequency, percentage, mean, and standard deviation) and inferential (kolmogorov smirnoff to assess the normality of population, one sample t-test) statistics were used for data analyzing. table i. questionnaire dimensions questions dimension 1 to 4 support and leadership 5 to 11 strategic planning 12 to 17 customer orientation 18 to 23 staff identification and training of 24 to 29 empowerment of employees and teamwork 30 to 33 quality measurement and analysis 34 to 36 quality assurance 37 to 39 outcomes of efficiency and quality improvement table ii. reliability of questionnaire reliability coefficient dimension row 0.84 support and leadership 1 0.75 strategic planning 2 0.81 customer orientation 3 0.91 identification and training of staff 4 0.82 empowerment of employees and teamwork 5 0.84 quality measurement and analysis 6 0.80 quality assurance 7 0.75 outcomes of efficiency and quality improvement 8 0.89 total quality management 9 iii. findings using descriptive statistics, the demographic characteristics (gender, age, education, and work experience) of participants were investigated. these characteristic are shown in table iii. before testing the study hypotheses, the normality of data frequency distribution was investigated using kolmogorovsmirnoff’s goodness of fit test. results are presented in table iv. as shown, all data have a normal distribution and the parametric statistics may be used for analysis. therefore, the one-sample t-test was used to test the main hypothesis (tqm) and consequent sub-hypotheses. main hypothesis: tqm has impact on the effectiveness of first grade high school educational programs in karaj. according to table v, the mean score of impact of tqm on the effectiveness of first grade high school educational programs in karaj is 3.23. the calculated t is larger than the critical t=8.47. therefore, the impact of tqm on the effectiveness of first grade high school educational programs in karaj is statistically significant. this is consistent with findings in [8], where author found that there was a significant relationship between applying tqm in schools and principal leadership, appropriate behavior of teachers, helping of students, constructive relations with parents, evaluation skills, and management of affairs. schools that use tqm pay special attention to students, teachers, and meet their needs and demands. in these schools, all employees including teachers and students are in good terms and staff members are involved in enriching and improving school’s quality. improvement of all school elements and factors is performed based on principles of tqm [7]. table iii. participants demographic characteristics demographic variable frequency percentage gender men 189 58.3 women 135 41.7 educational degree associate degree 51 15.7 bachelor degree 182 56.2 master degree and above 91 28.1 work experience (years) 1 to 5 32 9.9 6 to 10 83 25.6 11 to 15 88 27.2 16 to 20 81 25 21 and above 40 12.3 age 20 to 30 55 17 31 to 0 146 45.1 41 to 50 105 32.4 51 and above 18 5.6 table iv. kolmogorov-smirnoff’s test dimension frequency kolmogorovsmirnoff’s test significance level 1 support and leadership 324 1.17 0.106 2 strategic planning 324 0.824 0.429 3 customer orientation 324 0.920 0.298 4 staff identification and training 324 0.576 0.638 5 empowerment of employees and teamwork 324 0.813 0.492 6 quality measurement and analysis 324 1.22 0.097 7 quality assurance 324 1.02 0.154 8 outcomes of efficiency and quality improvement 324 0.793 0.572 first sub-hypothesis: support and leadership of senior management dimension of tqm has impact on the effectiveness of first grade high school educational programs in karaj. according to table vi, the mean score of impact of support and leadership of senior management dimension of tqm is 3.16. the calculated t (3.52) is larger than the critical t. therefore, the impact of support and leadership of senior management dimension of tqm is statistically significant. engineering, technology & applied science research vol. 8, no. 1, 2018, 2433-2437 2435 www.etasr.com shahmohammadi: the impact of total quality management on the effectiveness of educational … this is consistent with findings in [6] where author found that there is significant relationship between managers' knowledge of tqm and teachers’ effectiveness. findings also showed that the more managers support these programs, the more schools will naturally try to provide better programs to students [14]. the support is an effective component to achieve and improve the quality of education [15]. second sub-hypothesis: strategic planning dimension of tqm has impact on the effectiveness of first grade high school educational programs in karaj. according to table vii, the mean score of impact of strategic planning dimension of tqm is 3.16. the calculated t is larger than the critical. therefore, the impact of strategic planning dimension of tqm is statistically significant. this is consistent with findings in [6, 8]. when the schools consider the necessity of strategic planning, the individuals or organizations involved in planning should be identified, the planning steps should be described and the needed resources should be specified. staff will perform better and have more motivation to work and the educational programs will be more effective. schools should adjust their direction based on strategic planning and changing environment, because strategic planning improves performance and meets the needs of a changing environment [16]. table v. one sample t-test of tqm’s role on the effectiveness of educational programs component average assumed mean sd t df p total quality management on educational program effectiveness 3.23 3 0.491 8.47 323 0 table vi. one sample t-test on tqm’s support and leadership of senior management dimension on the effectiveness of educational programs component average assumed mean sd t df p support and leadership on educational programs effectiveness 3.16 3 0.862 3.52 323 0 table vii. one sample t-test on tqm’s strategic planning dimension on the effectiveness of educational programs component average assumed mean sd t df p strategic planning dimension on educational program effectiveness 3.16 3 0.863 3.52 323 0 third sub-hypothesis: customer-orientation dimension of tqm has impacts on the effectiveness of first grade high school educational programs in karaj. according to table viii, the mean score of the impact of customer-orientation dimension of tqm on effectiveness is 3.29. the calculated t (5.38) is larger than the critical t. therefore, the impact of customer-orientation dimension of tqm on effectiveness is statistically significant. one of the ways for educational institutions, especially schools to differentiate their services from other organizations is providing continuously high quality programs, considering total quality [17]. total quality management in classroom aims to involve students in continually improving skills and learning processes, encourage them to take responsibility of their own learning, and promote their ability at all learning levels based on concrete objectives. meanwhile, tqm tries to turn the students, parents, and staff to active, automated, effective, and critical thinkers, in order for the school services to meet the community needs [18]. table viii. one sample t-test on tqm’s customer orientation dimension on the effectiveness of educational programs component average assumed mean sd t df p customer orientation dimension on educational program effectiveness 3.29 3 0.989 5.38 323 0 fourth sub-hypothesis: training of staff dimension of tqm has impact on the effectiveness of first grade high school educational programs in karaj. according to table ix, the mean score of the impact of training of staff dimension of tqm on effectiveness is 3.12. the calculated t (2.24) is larger than the critical t, therefore, the impact of training of staff dimension of tqm is statistically significant. this is consistent with findings in [6, 8]. it indicates that the planning for improving the quality of education makes learning enjoyable. the inclusion of quality in education means continuous changing and commitment [13]. in other words, high quality educational programs have an important influence on increasing organizational commitment and avoiding waste of knowledge and skills. staff considers training as an important factor in their professional development [19]. fifth sub-hypothesis: the employees’ empowerment and teamwork dimension of tqm has impact on the effectiveness of first grade high school educational programs in karaj. according to table x, the mean score of impact of this dimension of tqm is 3.38. the calculated t (6.44) is larger than the critical t. therefore, the impact of employees’ empowerment and teamwork dimension of tqm is statistically significant. in other words, high capability managers and teachers perform well and successfully and improve the organization's activities. in fact, the empowerment is one of the factors affecting quality and effectiveness of educational programs. managers and employees may provide better education if they have the ability to do their jobs, show competence and ability to work, and have sufficient engineering, technology & applied science research vol. 8, no. 1, 2018, 2433-2437 2436 www.etasr.com shahmohammadi: the impact of total quality management on the effectiveness of educational … proficiency. as a result, training programs will have better quality [8]. table ix. one sample t-test on tqm’s identification and training of staff dimension on the effectiveness of educational programs component average assumed mean sd t df p identification and training of staff dimension on educational program effectiveness 3.12 3 1.02 2.24 323 0.025 table x. one sample t-test on the mployees’ empowerment and teamwork dimension of tqm on the effectiveness of educational programs component average assumed mean sd t df p employees’ empowerment and teamwork dimension on the educational program effectiveness 3.38 3 1.07 6.44 323 0.000 sixth sub-hypothesis: quality measurement and analysis dimension of tqm has impact on the effectiveness of first grade high school educational programs in karaj. according to table xi, the mean score of impact of quality measurement and analysis dimension of tqm is 3.13. the calculated t (2.84) is larger than the critical. therefore, the impact of quality measurement and analysis dimension of tqm is statistically significant. quality measurement and analysis in schools is one of the factors which improve the quality of educational programs. as a control tool, it improves the performance of human resources. the impact of evaluation systems on organizational improvement and excellence gets more evident when the organization tries to conduct planned changes. quality measurement and analysis aim to promote human resources in all aspects and cause employees to know their weaknesses, perform the organizational works well and successfully, and improve the organization's activities. this, makes individuals to have sufficient proficiency [6]. seventh sub-hypothesis: the quality insurance dimension of tqm has impact on the effectiveness of first grade high school educational programs in karaj. according to table xii, the mean score of the impact of the quality insurance dimension of tqm is 3.29. the calculated t (4.39) is larger than the critical t. therefore, the impact of this dimension is statistically significant. when teachers have good teaching skills, teach with enthusiasm and interest, use practical tests for measuring and evaluating students, behave fairly to students, involve all students in educational activities and help students in solving their problems and weaknesses, the school will have high quality training programs [17]. table xi. one sample t-test on the quality measurement and analysis dimension of tqm on the effectiveness of educational programs component average assumed mean sd t df p quality measurement and analysis dimension on the educational program effectiveness 3.13 3 0.875 2.84 323 0.005 table xii. one sample t-test on the quality insurance dimension of tqm on the effectiveness of educational programs component average assumed mean sd t df p quality insurance dimension on educational programs effectiveness 3.29 3 1.19 4.39 323 0 eighth sub-hypothesis: the productivity and quality improvement dimension of tqm has impacts on the effectiveness of first grade high school educational programs in karaj. according to table xiii, the mean score of this dimension is 3.30. the calculated t (5.3) is larger than the critical t. therefore, the impact of this dimension is statistically significant. high quality education in schools means that the teachers perform school work and teaching well and successfully, use the experiences of others to improve their teaching practices, pay more attention to student problems, involve students in solving problems in classroom and pay attention to all students in classroom. under this condition, students may learn better [20]. table xiii. one sample t-test on the productivity and quality improvement dimension of tqm on the effectiveness of educational programs component average assumed mean sd t df p productivity and quality improvement dimension on educational program effectiveness 3.30 3 1.03 5.3 323 0 iv. conclusion this study explored the role of tqm in the educational programs of first grade high schools in karaj city. the target population included all high school teachers of the academic year 2015-2016. a suitable and reliable questionnaire was used to measure the variables in the study. result analysis showed that tqm and each of its dimensions affect the effectiveness of training programs and courses in junior high schools in the city engineering, technology & applied science research vol. 8, no. 1, 2018, 2433-2437 2437 www.etasr.com shahmohammadi: the impact of total quality management on the effectiveness of educational … of karaj. the impact of each tqm dimension was documented and discussed. acknowledgment author would like to express her gratitude to all teachers in karaj city who cooperated with her while conducting this study. references [1] a. youzbashi, factors affecting the effectiveness of training courses in naftiran intertrade company, msc thesis, department of psychology and education, tehran university, 2010 [2] s. sahney, d. k. banwet, s. karunes, “an integrated framework for quality in education: application of quality function deployment, interpretive structural modelling and path analysis”, total quality management & business excellence, vol. 17, no. 2, pp. 265-285, 2006 [3] f. saadati tabar, satisfaction of beneficiaries from in-service training in development and renovation organization in iran, msc thesis, school of management, tehran university,2012 [4] g. j. anderson, fundamentals of educational research, psychology press, 1998 [5] m. b. akbari sari, assessing vocational training needs of agricultural educators in training centers in mazandaran, msc thesis, faculty of psychology and educational sciences, 2010 [6] f. mahmoudi khatoonabad, awareness and adoption of managers from total quality management (tqm) and its relation to effectiveness from vocational teachers' views in karaj, msc thesis, faculty of management and economics, pnu, 2011 [7] m. abzari, a. yazdkhasti, “total quality management in education”, sixth international conference of quality managers, tehran, iran, june, 2005 [8] r. jahanian, “the relationship between total quality management and effectiveness of managers in tehran secondary schools”, journal of management and leadership, vol. 3, no. 13, 2010 [9] m. moghadam yousef, m. ali, j. reza, “the role of exclusive quality management in the advancement of training quality in i.r.i. police university”, danesh-e-entezami, vol. 10, no. 3-4, pp. 181204, 2009 [10] r. hoveyda, a. siyadat, m. es'haghian, “comparing viewpoints of faculty members and students about application of measures of total quality management (tqm) in education process in isfahan university”, journal of tqm, pp. 29-46, 2008 [11] d. tomas, h. david, “educator attitudes towards the appropriateness of total quality of management in education”, dissertation abstracts international, vol. 56, no. 8, pp. 43-58, 1995 [12] j. macdonald, total quality management in a week, hodder & stoughton, 1998 [13] m. moghimi, management & organization, research approach, terme publishing, 2002 [14] k. abeli, “experiences of organizations effectiveness and assessing it in enterprises in iran (weaknsses and solutions)”, 1st international conference of education administrators, 2009 [15] h. abtahi, s. abesi, empowering employees research and training, institute of management, 2007 [16] a. namavaran, a. manafi, “increasing the effectiveness of programs and educational 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www.etasr.com eli-chukwu et al.: a systematic review of artificial intelligence applications in cellular networks a systematic review of artificial intelligence applications in cellular networks ngozi clara eli-chukwu department of electrical & electronics engineering, alex ekwueme federal university, ndufu alike, ebonyi, nigeria ngozieli@gmail.com j. m. aloh department of electrical & electronics engineering, alex ekwueme federal university, ndufu alike, ebonyi, nigeria joedreams4u@yahoo.com christopher ogwugwuam ezeagwu department of electrical & electronics engineering, nnamdi azikiwe university, awka, nigeria ogwugwuamezeagwu@gmail.com abstract—mobile technology has made communication easier and faster. people communicate in a matter of picoseconds, with little or no inhibition, regardless of their distance or location. mobile networks are rapidly expanding all over the world. the demand led to the evolution of different technologies to meet with traffic challenges. challenges are still evident as the cellular network system faces dynamic and chaotic behavior that needs to be resolved intelligently without human intervention. the current paper presents the state of the art of artificial intelligence (ai) in enhancing the performance of cellular networks. this paper summarizes the ai concept and reviews its applications in cellular network design, operations, and optimization. a special focus is laid on the advantages and disadvantages of ai application and a holistic study of the challenges is undertaken in order to give new research directions. keywords-artificial intelligence; cellular network; network design; operations; optimization; network management i. introduction the telecommunication industry is witnessing an explosion as the demand for its services and applications is geometrically increasing. facing the challenges associated with this tremendous rise led to the evolution of different technologies: second generation, third generation, fourth generation and the future fifth generation networks and beyond. the 3g supports high data rates of about 14.0mbps and 5.8mbps for downlink and uplink respectively while the 4g has an estimated peak rate of about 100mbps [1]. the massive increase in the usage of devices and communication between machines which are internet dependant is expected to put pressure on the recent 4g technology. it is envisaged that there will be over a thousand times increase in network traffic because of the increaesd demand [2]. to tackle this in future networks, the system and network drivers need to get smarter and more automated. system automation in a radio network is realizable through ai [2]. the ai can be applied in different layers of cellular network architecture: antenna design, network management, vendor-operator service level of agreement, etc. ii. the need for ai in a cellular network ai is an autonomous system with the capacity to learn, reason, take decisions and solve problems [3]. it is a system with the capacity to act relatively like a human [4, 5]. the artificial in the intelligence is derived from the fact that the autonomous system is not human, but human will design, train the system (in a supervised and/or unsupervised manner) to think, reason and take decisions in solving real-world problems. its action is beyond the input/output of a computer system. in an artificially intelligent system, the human mind is mimicked by the system that learns the environment and solves the problem [2]. an ai system has the capacity to identify, predict, and execute tasks [6]. the acquired data can be studied over time and used in predicting future network behavior while they are also deployed in resolving network challenges [6]. to enhance the performance of a cellular network, the overall life cycle of cellular network planning, design, operation, implementation, and maintenance need to be embedded in the ai system, starting from network planning [7]. in this study, four intelligent agent tools were considered: artificial neural networks (ann), fuzzy network (fn), re-enforced learning and case-based reasoning (cbr). iii. ai in cellular network design the performance of a cellular network system depends on system design. cellular network designs consider various parameters that measure overall network performance. as the cellular and pc worlds collide with wireless lans and internet-based packet data, new networking approaches will support the integration of voice and data on the composite infrastructure of cellular base stations (bss) and ethernet-based wireless access points [8]. when designing a cellular network that will carry a multitude of traffic, it is essential to consider different parameters and/or different requirements, such as different mobility parameters or quality-of-service requirements. in such situations, it may be cost-effective to build many cellular infrastructures, each serving a particular traffic type. the network resources (e.g. radio channels) are then divided [9]. authors in [10] proposed a design that improves only cellular network dependability using neural networks. this research uses simulations to train and validate the neural network. a wide range of traffic scenarios were studied and sensitivity analysis was performed to determine a reliable solution to improve availability, reliability, maintainability, and survivability of the network. authors in [11] proposed designing a system that considers radio resource management (rrm) parameters using fuzzy logic corresponding author: ngozi clara eli-chukwu engineering, technology & applied science research vol. 9, no. 4, 2019, 4504-4510 4505 www.etasr.com eli-chukwu et al.: a systematic review of artificial intelligence applications in cellular networks controllers to improve cellular network performance. the proposed design uses fuzzy logic controllers to improve network call admission. the drawback of the proposed design is that it does not improve cellular service retainability. authors in [12] proposed an appropriate model for cooperative and cross-layer design that uses cognitive radio and multi-hop network to reduce extended mobility management challenges. although the proposed cross-layer design improved network service retainability, it fell short in service availability, accessibility, and integrity. authors in [13] proposed a cellular network system that considers handover as a parameter for improving network performance using fuzzy controlling [13]. authors in [14] used cell individual offset (cio) to manage a handover algorithm that increases the network capacity by 9%. they also proposed admission control for wcdma/wlan heterogeneous network with multimedia traffic. the proposed design uses the fuzzy q-learning admission control (fqac) system managed by the minimax theorem to estimate call admission request time. the fqac design achieved lower blocking probabilities and reduced handoff rate by 20%. authors in [15] proposed a hybrid cognitive engine for improving coverage in a 3g wireless network. the proposed hybrid system uses case-based reasoning and decision tree algorithm to learn the coverage of a cell, predicts if handover is necessary and determines policy patterns to improve 3g network coverage. authors in [16] proposed a vertical handover decision algorithm in 4g heterogeneous wireless networks. although the vertical handover decision (vhd) algorithm allows seamless roaming of network technologies, it does not impact service accessibility. in [17], authors provided an efficient radio access technology selection for the next generation wireless networks. their proposed system uses fuzzy logic controllers, genetic algorithm (ga), particle swarm optimization and multi-criteria decision-making methods for radio access decision making. the algorithm performs better than the radio resource management algorithm and provides highest user satisfaction. authors in [18] proposed an artificial neural network algorithm that reduces handoff latency. the proposed algorithm combines multiple attribute decision making and artificial neural network to determine if a handoff is a necessary by comparing the values of the devices’ bit rate, cost of transmitting specified data bytes and the rssi. the neural network based algorithm significantly reduces handoff latency. authors in [19] proposed a cac scheme for multimedia applications based on fuzzy logic. the proposed scheme is called fuzzy admission control for multimedia applications (mfac). the design comprises of fuzzy qos controller (fqc) and fuzzy congestion controller (fcc). mfac improved the call admission rate by reducing system congestion. designing a system that improves integral channel allocation algorithms in cellular communication systems enabling multimedia qos services was proposed in [20]. the proposed design used dynamic channel assignment algorithms to provide the requested capacity for the preferred service, supported data and video (video viewing, video conference) transmission with quality of service (qos) by reducing signal interference reported by the cnr and cnir. this design will fail in network accessibility as it was not considered. authors in [21] proposed an intelligent agent that uses case-based reasoning to control radio resource allocation and congestion control. in [21], a congestion pattern in wcdma was extensively studied and embedded in a cbr with their respective solutions, such that when the system anticipates congestion, the cbr searches the case library to get a matching solution. recently, authors in [22] saw system fault as a major draw-back in effective qos delivery and they proposed a design that uses fuzzy reasoning in communication network fault diagnosis. the proposed design processes network alarms into fuzzy network alarm that is compatible with fuzzy reasoning. in this way, the root alarm can be located more quickly and accurately. more recently, authors in [23] studied the use of ai to perform handoff in cellular network design when they proposed an intelligent handoff algorithm to enhance the quality of service in high altitude platforms using neural networks. the research design combines high altitude platforms and terrestrial system in a handoff algorithm to improve signal coverage in a cellular network. it was found that hand-off rate and blocking rate are greatly improved using anns for handoff decision. authors in [24] proposed a secure-aware call admission control scheme for wireless cellular networks using fuzzy logic. the proposed secure-aware cac scheme uses fuzzy logic to improve call admission rate. elastic call admission control using fuzzy logic in virtualized cloud radio base stations was proposed in [25]. the proposed design uses fuzzy logic in c-ran to run an intelligent elastic cac scheme. in this scheme, the bs resources are consolidated to the cloud by using virtualization technology and dynamically provisioned using the elasticity concept of cloud computing in accordance with traffic demands. simulations showed that the proposed cac algorithm has high call acceptance rate compared to conventional cac. authors in [26] proposed a new hybrid prediction model that optimizes handoff delay and predicts the next location of the mobile station. the proposed architecture uses a gps integrated sim for ms location and a prediction server embedded in the bsc to assign the mobile station to a non-congested bs amongst the btss under its control. the design focuses on service accessibility. service retainability and integrity are major drawbacks of the design. table i summarizes the above mentioned techniques and implementations with their advantages and disadvantages. iv. ai in cellular network operations in wcdma, the traffic exhibits high fluctuations in time and over space, thus incurring energy waste [27]. during crowded events, cellular networks face voice and data traffic volumes that are often orders of magnitude higher than what they face during routine days. despite the use of portable bss for temporarily increasing communication capacity and free wi-fi access points for offloading internet traffic from cellular base stations, crowded events still present significant challenges for cellular network operators looking to reduce dropped call events and improve internet speeds [28]. designing an intelligent agent to manage the operations of a cellular network will improve the overall quality of service. authors in [29] proposed a mobility management design that incorporates fuzzy logic for a heterogeneous ip environment. engineering, technology & applied science research vol. 9, no. 4, 2019, 4504-4510 4506 www.etasr.com eli-chukwu et al.: a systematic review of artificial intelligence applications in cellular networks table i. ai in cellular networks design reference ai technique advantages disadvantages [10] ann network availability, reliability, maintainability, and survivability. accessibility and retainability were not considered. [11] fuzzy logic controller (flc) improved service admission control. no improvement in traffic capacity. traffic retainability was not considered. [12] cognitive radio (cr) satisfactory performance in mobility management availability, accessibility, integrity and retainability were not considered [13] flc improved the network capacity by 9%. it only solves current capacity problems and cannot be deployed when there is additional network load. [14] fqac and nfis improves and manages network accessibility. restricted to network service accessibility. some service requests are still rejected. [15] cr, decision tree (dt) and cbr improvement in signal coverage. signal quality and other relevant kpis used to assess the network were not discussed. [16] vhd allows seamless roaming of network technologies. only considered retainability. [17] flc and ga easy network access and high user satistisfaction. kpis such as speech quality and handover were not studied. [18] multiple attribute decision making algorithm and ann manages handoff number and reduces handoff latency. will surely fail in availability, accessibility and integrity. [19] mfac, fqc, and fcc improved call admission rate by reducing system congestion. qos and service retainability were not considered. [20] dynamic channel assignment (dca) improved qos by reducing interference. no work was done on network accessibility. [21] cbr reduces congestion during cellular network traffic session. case matching and learning process are slow. [22] fuzzy reasoning algorithm detects the root cause of cellular network alarm quickly and accurately. it does not fix the detected alarm. [23] ann reduced network blocking rate did not consider qos. the blocking performance is limited to handoff cases. [24] fuzzy logic (fl) and fcacs improved call admission rate. limited number of subscribers. system capacity was not consider. [25] fl high call acceptance rate no considerations for dropping probabilities. [26] gps/sim detection algorithm improves service accessiblity service retainability and integrity. the proposed design uses a fuzzy inference method to process a multi-criteria vertical handover decision metrics. a vertical handover decision algorithm to decode a handover is necessary. although the design recorded improvement in the system mobility it never handled the case of service accessibility. authors in [30] proposed a gsm mobile station location using reference stations and anns based on the measurements of radio signal strength from a number of neighbouring base stations (antennas) and estimation of the mobile station position using trained ann models. an improved version of the positioning back-propagation (bp) ann multi-level perceptron (mlp) model that improves positioning accuracy and an extension of the mlp primary ann model by introducing correctional factors were obtained from a number of reference stations. authors in [27] proposed a traffic-driven power saving in operational 3g cellular networks. a profile-based approach to green cellular infrastructure was proposed. bs traffic and approximate network-wide energy proportionality were studied using nonload-adaptive base stations. the proposed scheme yields up to 53% energy saving in a dense large city and 23% in a sparse, mid-sized city. authors in [31] proposed an adaptive multicriteria vertical handoff decision algorithm for radio heterogeneous network. the algorithm is made up of the fuzzy interference system that adopts crucial criteria of vertical handoff and the modified elman nn for predicting the number of users. although it improves subscribers’ mobility, service accessibility remains a problem. a knowledge-based model for analyzing gsm network performance was proposed in [32]. the research analyzed gsm network performance using quadratic programming to estimate gsm parameters. the parameter estimates were used to find the input-output variable pairs involved in the most severe performance degradations. authors in [33] proposed a case-based reasoning agent for resource management in 3g networks. the research presented a new method of balancing traffic load in mobile cellular networks by using cbr to learn traffic patterns at periods of congestion. the obtained traffic patterns were then used to control co-operating semi-smart antennas to optimize the radio coverage, hence minimizing the effects of congestion. the scheme is restricted to curbing congestion which is not up to 25% of 3g challenges. authors in [34] proposed performance analysis of call admission control in a wcdma system with adaptive multi-class traffic based on fl. the fuzzy cac scheme considers the mobility information of the new user requesting connection and already existing users, the type of service request (real time or non-real time), and the load factor which is calculated from the intra-cell interference and the inter-cell interference at the base station. the qos requirement of the non-real time traffic is reduced to accommodate a higher number of real-time traffic users to improve the performance of the admission control scheme. although the fuzzy based cac scheme performs better than the fixed cac schemes without fuzzy in terms of new call blocking and handoff call dropping probabilities, it requires longer time to access the network. authors in [35] proposed advanced analysis methods for 3g cellular networks. they presented an algorithm called selforganizing map (som) together with a conventional clustering method for simplified network analysis. engineering, technology & applied science research vol. 9, no. 4, 2019, 4504-4510 4507 www.etasr.com eli-chukwu et al.: a systematic review of artificial intelligence applications in cellular networks table ii. ai in cellular network operation reference ai technique advantages disadvantages [29] fl handover management. limited kpis were discussed. [30] ann, bp, mlp swift and accurate reporting of radio signal strength and mobile station location takes time to train the data and no kpi was discussed. [27] bs profile-based approach saved energy up to 53% and 23% in dense-large and mid-large cities. does not discuss subscribers’ interest. [28] fuzzy logic quantitative decision algorithm (fqda) impoved service availability and accessibility. the rate of service retainability was not discussed. [31] adaptive multicriteria vertical handoff (amvho), fis, and modified elman nn (menn) improved handoff accuracy. accessibility and retainability were not discussed. [32] quadratic programming (qp) effective estimation of gsm parameters. it does not improve the estimated parameters. [33] cbr minimizes congestion. it will fail with time as population is always on the rise. [34] fl better network accessibility and resource management. poor signal quality will affect the performance of the system. [35] ann, som better network performance analysis, fast and efficient troubleshooting only spots-out but does not solve network problems. [36] cell-zooming algorithm reduces energy consumption. cellular network kpis were not captured. [37] mecp cost reduction in cellular network operation. qos and overall user satisfaction was not considered. [38] fuzzy topsis rise in handover success rate. very few quality of service kpis were considered. the algorithms help in visualizing and classifying similarly behaving cells. thus, it is easier for a human expert to discern different states of the network with respect to the cells. authors in [36] presented a proposal on cell zooming for cost-efficient green cellular networks. they introduced a concept of cell zooming, which adaptively adjusts the cell size according to traffic load, user requirements, and channel conditions. centralized and distributed cell zooming algorithms were developed, and simulation results show that the proposed algorithms can reduce energy consumption. authors in [28] proposed a context aware fuzzy rule based vertical handoff decision strategy for heterogeneous wireless networks. they proposed a qos aware fuzzy rule based vertical handoff mechanism using fuzzy logic quantitative decision algorithm (fqda) to run handoff decision criteria to choose which network to handover among different available networks. the qos parameters considered are available bandwidth, end-toend delay, jitter, and bit error rate (ber). authors in [37] proposed minimizing energy cost by dynamic switching (on/off) the bss in cellular network operations. the proposed scheme uses an algorithm to solve the minimum energy cost problem (mecp) in two steps. the simulation results show that the proposed scheme can achieve significant energy cost reduction of the cellular network, but the qos and overall user satisfaction were not considered. authors in [38] proposed a traffic prediction based power saving in cellular networks using a machine learning method. the research exploits a machine learning method to estimate the bs traffic and proposes a bs sleeping strategy based on predicted traffic for power saving in the cellular network. network traffic was analyzed in terms of temporal influence, spatial influence, and event influence. a multi-view learning model that predicts network traffic load, learns the traffic in multi-views and combines the results, was proposed and developed. the traffic prediction algorithm improves about 40% the state-of-the-art machine learning methods and yields about 10% more energy saving and less device damage than the competitors in the simulated environment. table ii lists the above mentioned techniques and implementations with their advantages and disadvantages. v. ai in cellular network optimization in a wireless cooperative cellular data network with a bs and many users in which the subscribers have the ability to relay information for each other to improve overall network performance, optimization of physical-layer transmission strategies can be done efficiently. for a wireless network operating in a frequency-selective slow-fading environment, the choices of a relay node, relay strategy, and the allocation of power and bandwidth for each user are important design parameters to be optimized [39]. for wireless cellular and ad hoc networks with qos constraints, allocation of network resources to optimize sir, maximize throughput and minimize delay is really necessary [40]. for small cell technology to significantly increase the capacity of tower-based cellular networks, mobile users will need to be actively pushed onto the more lightly loaded tiers (corresponding to, e.g., pico and femto-cells), even if they offer a lower instantaneous sinr than the macro-cell base station (bs). optimizing a function of the long-term rate for each user requires (in general) a massive utility maximization problem over all the sinrs and bs loads [41]. authors in [42] proposed an analyzing mobile radio access network using som. they presented a model of the network using state vectors with parameters from all mobile cells or a general one cell model trained by utilizing one cell state vector from all cells. authors in [43] proposed cellular network optimization through automated bs placement and dimensioning for network planning. authors in [44] proposed a system the uses fuzzy inference to improve tcp congestion control over wireless networks. the system uses environmental variables available to tcp implementations to feed a fuzzy inference system that classifies packet loss due to congestion or wireless problem without sacrificing the end-to-end reliability of tcp. authors in [45] proposed an optimization approach that accesses network selection based on fl and ga. the research presented a general scheme to solve the access network selection (ans) problem in a heterogeneous wireless engineering, technology & applied science research vol. 9, no. 4, 2019, 4504-4510 4508 www.etasr.com eli-chukwu et al.: a systematic review of artificial intelligence applications in cellular networks network (hwn). a combination of fl and ga were used to give the proposed scheme the required scalability, flexibility, and simplicity. authors in [46] proposed a condition monitoring of 3g cellular networks through competitive neural models. the proposed scheme uses frequency sensitive competitive learning, som and neural-gas (ng) algorithm to evaluate the overall condition of a cellular system and discover abnormal conditions. the system performs well in cellular network snag detection but fails in corrections. authors in [47] proposed an adjustment of a fuzzy logic controller for is-ho parameters. performance assessment was carried out by implementing the flc and is-ho algorithms in a dynamic network simulator including gsm and umts radio access technologies. the results showed a significant reduction in blocked call rates. system flaws include accessibility, integrity, and qos in general. authors in [48] studied handover as a major parameter in cellular network optimization and they proposed an automatic link balancing using fl control of the handover parameter. the research presents a novel selfoptimization algorithm based on fl control. taking into consideration measurements gathered from the network, the fuzzy logic controller balances continuously the individual link gain and the network gain. although the system increased the capacity by 23%, the qos was negatively affected as the system only optimizes service accessibility. authors in [49] proposed an evolvable fl system utilizing ga for handoff management in a heterogeneous wireless network. authors in [50] proposed optimization of load balancing using fuzzy qlearning for next-generation wireless networks. an flc optimized by the fuzzy q-learning algorithm was proposed for the load balancing problem, with the aim of decreasing call blocking in congested cells, while at the same time restricting call dropping in neighbouring cells according to the network policy. results show that the optimized flc provides a notable reduction in call blocking while preserving call dropping under the operator constraints. the system does not improve retainability as it does to accessibility. authors in [51] proposed adaptive neuro-fuzzy inference models for speech and video quality prediction in real-world mobile communication networks. the research optimizes speech and video quality parameters using fuzzy inference models. table iii lists the above mentioned techniques and implementations with their advantages and disadvantages. vi. challenges a. design telecommunication operators are facing the challenge of deploying umts. the target of having to meet users’ expectations, tight budget constraints, and governmental regulations slow network design and implementation. careful dimensioning of the radio access infrastructure plays an essential role in achieving these targets [52]. deployment of cellular networks involves substantial capital investment. competition motivates service providers to minimize the cost while maintaining qos [53]. cell planning (cp) is the most important phase in the life cycle of a cellular system as it determines the operational expenditure (opex), capital expenditure (capex), and the long-term performance of the system [54]. table iii. ai in cellular network optimization reference ai technique advantages disadvantages [42] som effective data handling. handled data do no improve network performance. [43] fuzzy expert system (fes) improvement in the signal coverage and traffic capacity with minimal interference. has not been tested in urban areas. [44] fl reduces packet losses caused by network congestion. other packet loss causes were not considered. [45] fl and ga flexible, scalable, capable of reducing block call rate. it will fail in reducing dropped call rate. [46] som and ng ability to detect network snags. unable to correct the detected network snags. [47] flc significant reduction in blocked call rate. network accessed after an unknown number of trials [48] flc improved handover and capacity by 23% does not consider signal quality as an optimization parameter [49] fl and ga improvements on signal coverage and data rates signal quality and data throughput latency performance are a major drawback [50] flc reduces call blocking and stabilizes cell load balancing does not impact on dropped call rate and radio environment [51] neuro-fuzzy estimates and predicts speech and video quality does not improve network signal quality b. operation with the ever-growing demand of data applications, traditional cellular networks face the challenge of providing enhanced system capacity, extended cell coverage, and improved minimum throughput in a cost-effective manner. wireless relay stations, especially when operating in halfduplex operation, make it possible without incurring high site acquisition and backhaul costs. design of wireless relay stations faces the challenges of providing backward compatibility, minimizing complexity, and maximizing efficiency [55]. mobile communications are increasingly contributing to global energy consumption. at the network level, the potential for reducing energy consumption is in the layout of networks and their management, that take into account slowly changing daily load patterns, and highly dynamic traffic fluctuations [56]. the operation of cellular network infrastructure incurs significant electrical energy consumption. reducing this consumption is not only a matter of showing environmental responsibility but also of substantially reducing operational expenditures [57]. the operation of mobile networks is a complex task with the networks serving a large number of users with voice and data services, containing extensive sets of elements, generating extensive amounts of measurement data and being controlled by a large number of parameters. a major objective is to ease engineering, technology & applied science research vol. 9, no. 4, 2019, 4504-4510 4509 www.etasr.com eli-chukwu et al.: a systematic review of artificial intelligence applications in cellular networks the operation of mobile networks by introducing advanced monitoring and automated optimization methods [58]. c. optimization in cellular network optimization, coverage and capacity planning remain the major challenges and should be addressed simultaneously [59]. optimization is necessary for cellular network activities as it will trigger maximum efficiency. network snags such as blocked or dropped calls, poor signal coverage and quality, and insufficient bandwidth force the devices to reduce the audio bandwidth or even ban access, or slow down response times for data downloading, continue to make network optimization inevitable. vii. future work designing a cellular network that uses an ai system that intelligently sorts and uses hopping sequence numbers and broadcasts control channel re-assignment will reduce blocked and dropped calls and will improve qos. the system should also be able to reduce cell transmit power and promote optimal cell utility. this is very essential as the 4g network falls back to gsm/umt network during circuit switch services. viii. conclusion application of ai in cellular network design, operation, and optimization aims at improving qos in a cellular network. the increase in the number of mobile users and the overwhelming demand of offered services by the network providers affect the network qos and a high demand for optimization emerges. engineers need to ensure that key performance benchmarks are met. in this paper, an extensive review of the current ai applications has been performed and their advantages, disadvantages, challenges, and future scopes were presented. deploying ai in the telecommunications field improves the overall qos. improvements have been noticed in key performance indicators (kpis) such as blocked call rate, dropped call rate, handover success rate, signal coverage and quality, latency and data throughput, but on individual kpi bases. to telecommunication operators and users, the system to be deployed should be cost-effective and possess primary capabilities to access the network and retain network services. as such, the expert system and ai agents should be costeffective and improve network service accessibility and retainability. new research should be focused on these areas: • designing a cost-effective communication paradigm that is ai driven in network design, operation, and management. • designing an ai system that uses hopping sequence number and broadcast control channel re-assignment to reduce blocked and dropped calls, and improve qos. references [1] s. singh, p. kumar, “challenges and prospects of wireless network in 4g”, international journal of computer applications, vol. 133, no. 11, pp. 1-5, 2016 [2] d. banupriya, pandi, s. preetha, r. r. prathisha, “a study on use of artificial intelligence 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springer, 2014 microsoft word etasr_v11_n2_pp7029-7032 engineering, technology & applied science research vol. 11, no. 2, 2021, 7029-7032 7029 www.etasr.com khoso et al.: a microservice-based system for industrial internet of things in fog-cloud … a microservice-based system for industrial internet of things in fog-cloud assisted network fida hussain khoso department of basic science dawood university of engineering & technology karachi, pakistan fidahussain.khoso@duet.edu.pk abdullah lakhan computer science and it department benazir bhutto shaheed university karachi, pakistan abdullahrazalakhan@gmail.com aijaz ahmed arain department of computer science quaid-e-awam university of engineering, science and technology nawabshah, pakistan aijaz@quest.edu.pk m. ali soomro department of computer systems engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan kalakot2@gmail.com shah zaman nizamani department of information technology quaid-e-awam university of engineering, science and technology nawabshah, pakistan hahzaman@quest.edu.pk kelash kanwar department of electronic engineering quaid-e-awam university of engineering science and technology nawabshah, pakistan kelashkanwar@quest.edu.pk abstract-nowadays, the usage of the industrial internet of things (iiot) in practical applications has increased. the primary utilization is a fog cloud network, which offers different services, such as network and remote edges, at different places. existing studies implemented the service-oriented architecture (soa) based on the fog-cloud network to run iiot applications, such as e-healthcare, e-agriculture, renewable energy, etc. however, due to the applications' monolithic property, issues like failures, security, and cost factors occur, e.g. the failure of one service in soa affects monolithic applications' performance in the system. with this motivation, this study suggests a microservice-based system to deal with the cost, security, and failure risks of iiot applications in the fog-cloud system. the study improves the existing soa systems for e-healthcare, eagriculture, and renewable energy and minimizes the applications' overall cost. the performance evaluation shows that the devised systems outperform the existing soa system in terms of failure, cost, and the deadline for all applications. keywords-iiot; security; e-healthcare; soa; microservice i. introduction real world applications of the digital transformation of technologies such as the industrial internet of things (iiot) posses many advantages [1]. such applications belong to the eagriculture, e-healthcare, e-transport, e-servicing, and augmented fields [2]. cloud computing is an incipient archetype which offers services based on service-oriented architecture (soa) [3]. generally, soa comprises of different services which are monolithically managed by one centralized component [4]. soa architecture capabilities extend to the fog computing, edge computing, and cloudlet data center to efficiently execute time and latency-sensitive applications [5]. however, fault tolerance, security, and cost of services in soa architecture depend directly upon the centralized controller. for instance, if any specific service fails or is attacked, then the impact and cost will affect the entire system [6]. the microservice-based system is an innovative solution which offers autonomous service to run iiot applications. each microservice executes its application independently, and service failure has no impact on the other services during the process. all microservices are communicating with each other via an rest api. the generalization is a standard interface that exploits the rest api to create cross-platform for all microservices to run one application. each application requires many microservices to run its tasks. for instance in e-health applications, blood pressure, heartbeat, and ecg tasks each require one microservice for execution [7]. however, a microservice-based system for iiot has not been developed yet. the current study extends the existing iiot work [7] with new suggestions that improve the handling of cost, security, and failure issues of the system in fog-cloud networks. the current work is a survey paper. however, it proposes a solution corresponding author: abdullah lakhan engineering, technology & applied science research vol. 11, no. 2, 2021, 7029-7032 7030 www.etasr.com khoso et al.: a microservice-based system for industrial internet of things in fog-cloud … for those systems to improve applications' cost and security mechanisms. the paper makes the following contributions to the existing systems: it discusses the general iiot process based on the microservices system. it also discusses industry automation based on microservices with cost and security constraints and e-healthcare services based on microservices connected with the distributed fog-cloud network. generally, all systems exploit microservice systems in a fog-cloud network with deadline, cost, security, and fault-tolerant constraints. the study solves the offloading and scheduling problems for the considered systems. ii. related work authors in [1] suggested the soa aware framework to solve the iiot mechanism issue of e-agriculture applications in a fog cloud network. the goal was to minimize the end to end latency of the applications. however, they did not consider the security and fault-tolerance of the applications. fault-tolerant aware soa is discussed in [2]. the goal was to minimize the failure risks and exploit the primary backup method to handle any soa architecture failure. however, it consumed much more resources and had high cost during the process. the security-aware framework [3] handles application-level security in soa architecture. applications can offload tasks with secure data in the distributed network, however the authors did not consider failures and network and cloud security mechanisms. a hybrid security-aware system based on soa architecture was suggested in [4]. the goal was to protect data from denial of service and brute force attacks to iiot applications. the security and failure aware centralized soa systems for monolithic and coarse-grained applications were studied in [5]. the objective was to improve resource utilization and minimize the application cost. however, the centralized control could fail anytime, and this would affect the entire system in the network. cost-efficient offloading for healthcare applications based on soa architecture by considering security and deadlines was investigated in [6]. all considered applications are monolithic and fine-grained and run their tasks distinctly under their deadline. soa architecture offers services based on an rpc model where users are treated as thin clients and servers as thick clients. however, still the centralized failure of any service affects the entire system. an e-agriculture and a body area sensor aware network based on soa architecture was suggested and studied in [7, 8]. the goal was to optimize the service process with minimum end to end latency of the applications while offering 24/7 services with the robot and faultless services. however, there are many issues in the system. the soa architecture selects the services from a published pool for consumer and producer and a hacker can publish services and quickly become part of soa monolithic architecture. the container and function aware iiot solutions were suggested in [9, 10] to handle the offloading and scheduling problem's transient failure and security issues. these studies achieved better results as compared to soa architecture. however, the proposed systems have not matured yet for all kinds of iiot applications. all reviewed studies proposed systems for iiot based on the soa and container function mechanisms. many of them considered different constraints such as security, failure, cost, and latency. however, failure in service due to hacking or resource-imbalance will impact the overall system performance. the suggested process was very costly and consumed a lot of resources. with the motivations mentioned earlier, this paper suggests microservice aware different iiot system to minimize failure risk, cost, and security and meet the deadline of applications. iii. the proposed solution the study proposes a different system based on microservice architecture instead of soa in order to improve cost, failure, and security risk of the applications. fig. 1. microservice based fog-cloud system. cloud computing is a distributed service provider which offers services at different rates to run any application on the network. fog computing is an extension of cloud computing which brings cloud resources at the end of a wireless network. the main advantage of fog computing is the reduction of the end to end latency of an application. this study complements the existing architecture [15-24] which is based on soa. the work creates a system which consists of three layers such as user-end, fog end and cloud end as shown in figure 1. the user-end is connected with different computer systems that offload their data to the fog server via communication channels for further processing. the fog servers are located at the edge of the network and have short distance and minimum end to end latency during submission or offloading. the basic mechanism design is based on the remote process call which is a popular method allowing the communication channels between users and serves via stud and skeleton objects. the renewable iiot aware network performs different tasks such as monitoring temperature, humidity, weather, etc. sensors which require microservices to run and save their data in the cloud as shown in figure 1. generally, these are real-time tasks, engineering, technology & applied science research vol. 11, no. 2, 2021, 7029-7032 7031 www.etasr.com khoso et al.: a microservice-based system for industrial internet of things in fog-cloud … working 24/7 and generating big data to the fog system. due to the time sensitive and security sensitive data, the initial process will be done on the fog servers. after that, for persistent saving, the fog node offloads all data to the cloud for further big data analytics. the high volume of data with various types and speed will be easily managed by the rich resource cloud computing. a body-area network is connected with different sensors for blood pressure, heartbeat, ecg, and online monitoring tasks at the user level. all tasks offload their data to the fog node which applies computation by using a unique microservice to run each task under its deadline. big data are generated by the tasks to be offloaded to the remote cloud for further analyzing. the main advantage of the system is that the failure of one microservice will not affect the entire system because they all are working isolated to each other. another advantage is that microservices have execution charges. if one microservice fails it will not charge for anything until and unless a task is finished without completing its execution. the fault-isolation, security, and autonomous execution make this system more efficient and intelligent in comparison with all the existing soa architectures. this system selects microservices from the published pool which is publically available with different charges and time-slots. however, the considered system is smart, if one microservice fails, the system will select another without any violation of task deadlines. iv. performance evaluation the performance evaluation was conducted by implementing the edgex foundry microservice and soa architecture to run all iiot applications. we conducted the experiment in different cases as shown in tables i-iii. table i summarizes the security methods at the user level only and the execution cost of the applications. table ii summarizes the study of the failure mechanisms in the case only one system failure and determines the execution cost of the applications. table iii shows the results of the comparison based on deadline methods at the application level only and the execution cost of the applications. the overall service cost of security of the monolithic applications based on soa architecture became high during the process due to the centralized handling of all components. however, microservices had low cost because they are run inside a container and charged for their execution instead of the resource provisioning of soa which charged for all applications. the primary backup and check pointing always required a lot of resources in soa architecture. if one node fails, it may transfer a task from a service to another node. this improves the overall performance of the applications, but with high cost. the bottom line is that users pay for the failure costs for their applications. generally, fog-cloud applications co-operatively work together to achieve the goals of the applications. however, due to the monolithic architecture, if a centralized component fails or is attacked, it needs a lot of time to restart. in this way, the deadline of and the overall performance of the applications will be degraded. the deadline of applications directly depends upon execution time and the availability of resources. the cost of the applications by combining both failure and security becomes high when iiot uses the soa architecture (table iv). the monolithic applications need a lot of resources for their execution. however, the isolated microservice-based system works efficiently for all iiot in the fog-cloud network. table i. security mechanisms reference security cost application [1, 2] rsa 10$ monolithic [3, 4] rsa 20$ monolithic [5, 6] md5 17$ monolithic [7, 8] sha 23$ monolithic [9, 10] crc32 27$ coarse-grained proposed rsa 2$ fine-grained table ii. failure mechanisms reference fail cost application [1, 2] primary backup 10$ monolithic [3, 4] primary backup 20$ monolithic [5, 6] check pointing 17$ monolithic [7, 8] check pointing 23$ monolithic [9, 10] check pointing 27$ coarse-grained proposed isolated 2$ fine-grained table iii. deadline reference deadline cost application [1, 2] missed 40$ monolithic [3, 4] missed 70$ monolithic [5, 6] average 88$ monolithic [7, 8] reached 75$ monolithic [9, 10] reached 99$ coarse-grained proposed reached 23$ fine-grained table iv. overall soa and microservice system performance ref. security cost fail applications [1, 2] no 100$ no e-agriculture [3, 4] yes 200$ no e-agriculture [5, 6] no 150$ yes e-health [7, 8] yes 300$ yes e-health [9, 10] yes 500$ yes industry automation proposed yes 30, 50, 70$ yes all v. conclusion this study suggests the microservice based system for iiot applications instead of the soa architecture in order to minimize cost, failure effects, and risk. simulation results show that the proposed microservice based system can enhance the performance of the applications in comparison with the 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[24] f. yang, y. zhang, b. lv, and w. dai, "a task-oriented automatic microservice deployment method for industrial edge applications," in iecon 2020 the 46th annual conference of the ieee industrial electronics society, singapore, oct. 2020, pp. 2149–2154, https://doi.org/10.1109/iecon43393.2020.9254447. microsoft word 01-yahaya.doc etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 76-83 76 www.etasr.com yahaya et al: comparative assessment of gate drive control schemes in high frequency converter comparative assessment of gate drive control schemes in high frequency converter n. z. yahaya power & energy system research cluster universiti teknologi petronas bandar seri iskandar 31750 perak, malaysia norzaihar_yahaya@petronas.com.my k. m. begam electronic material & devices research cluster universiti teknologi petronas bandar seri iskandar 31750 perak, malaysia mumtajbegam@petronas.com.my m. awan electronic material & devices research cluster universiti teknologi petronas bandar seri iskandar 31750 perak, malaysia abstract—several gate drive control schemes are simulated and the results show that the fixed duty ratio (fdr) can help drive synchronous rectifier buck converter (srbc) correctly with low dead time and hence reduce body diode conduction loss. even though fdr is prone to cross-conduction effects, the design is simple. apart from that, adaptive gate delay (agd) and predictive gate delay (pgd) control schemes have also shown high level of efficiency. however, agd generates more losses. this makes pgd preferable in achieving a highly efficient converter of more than 82 % in spite of the advantage in fdr and agd schemes. keywords-gate drive control; high frequency; pspice simulation; synchronous rectifier buck converter i. introduction many control schemes in gate driver for dc-dc converters have been introduced back in the 1990s. they include digital and also analog controls. in 1997, pulse based dead time, td compensator (pbdtc) was introduced [1] where the switching times were modified to compensate td so that output voltage, vo can be properly controlled in magnitude. in addition, it can adjust symmetric pulse width modulator (pwm) pulses to correct voltage distortion. this replicates the fixed delay implementation. some other literatures have discussed different methods in details [2, 3]. on the other hand, in recent development, several analog techniques have been developed to ensure “break before make” operation. they are the fixed “dead time” or fixed duty ratio (fdr), adaptive gate delay (agd) and predictive gate delay (pgd). each of them has its own characteristics, advantages and drawbacks which provide information for the suitability and cost effective gate driver design. a. fixed duty ratio (fdr) fixed duty ratio is the first pwm controller for synchronous rectifier buck converter (srbc) circuit. the advantage of this technique is that it has a simple control circuit with lower voltage stress [4, 5]. however, this scheme requires the td to be provided long enough to cover the entire applications so that no cross conduction will occur. a lengthy td would reduce the converter efficiency by allowing the body diode to conduct. fig. 1. switch node waveform of srbc figure 1 shows typical switch-node voltage waveform of srbc. it shows the relative effects of fdr and agd control schemes on body diode conduction time, tbd. theoretically, fdr scheme in general, produces a longer tbd eventually reducing the channel conduction time. however, a precise timing control could solve this issue. during tbd, the inductor current, ilo will flow from ground through the body diode of switch s2 and lo resulting the voltage drop across body diode which leads to the reduction in the efficiency of power conversion [6]. fig. 2. block diagram of fdr scheme with srbc etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 76-83 77 www.etasr.com yahaya et al: comparative assessment of gate drive control schemes in high frequency converter figure 2 shows the block diagram of fdr control circuit integrated with srbc circuit. the input signal produced by the driver circuit has td application between switches. in addition, the efficiency of fdr technique also varies with different type of mosfets’ ambient temperature and with lot-to-lot variation of the td delay during manufacturing [7]. b. adaptive gate delay (agd) figure 3 shows the adaptive gate delay (agd) control scheme. this second generation gate driver control scheme was introduced to overcome the limitation in the fdr. it uses a control loop that includes a digital delay line where it senses the drain to source voltage, vds of the s2 and adjusts the digital delay line according to the amount of delay that should be applied to turn on s2. consequently, s2 is turned on only when the switch node voltage equals to zero [8]. fig. 3. adaptive gate delay control scheme the advantage of using this control scheme is that the adjustment of the delay can be made adaptively according to the type of mosfet used. however, there is a disadvantage that comes from this control scheme. the variation of body diode conduction time interval may not easy to predict. this is due to the logic components used as the feedback circuit. each of the components has its own propagation delay which may indirectly increase the td between the pulses. c. predictive gate delay (pgd) since both fdr and agd schemes have limitations, the predictive gate delay (pgd) control scheme was then introduced. it is a combination of a predictive circuit integrated with pwm where it has the ability to vary the td from time to time according to the feedback signal. the predictive time is shown in figure 4. here, the next td, td[n+1] can be predicted and minimized based on the feedback. pgd uses feedback loop as shown in figure 5 in order to reduce the td until it reaches near zero [9]. the predictive circuit will sense a signal (it can be in the form of voltage or current) from the srbc circuit. table i shows the summary of all three gate driver control schemes for srbc circuits. even though fdr is not suitable, it has the simplest configuration and easy to drive the srbc. the only issue is that the td has to be provided longer. however, this is not true since simulation results proved otherwise [10], the details of which are presented in results and discussions section. the data in the table gives the advantages and disadvantages of different control schemes so that the choice of the design can easily be made based on cost, component count and simplicity. fig. 4. predictive timing fig. 5. pgd scheme block diagram table i. advantages and disadvantages of gate drive control schemes fixed duty ratio adaptive gate delay predictive gate delay constant, pre-set delays for turn-off to turn-on intervals simple in design efficiency varies with mosfet types and ambient temperature need to make delay long enough to cover entire application. variable delays based on volatage sensed on current switching cycle uses state information from power stage to control turn-on of two gate drivers and set td increases body diode conduction time caused by delay in cross coupling loops unable to compensate for delay to charge mosfet gate to threshold level difficult to determine whether s2 is off uses information from current switching cycle to adjust delays to be used in next cycle can prevent body diode from being forward biased and hence cross conduction increases power savings when mosfet is turned on minimizes reverse recovery loss in s1 body diode. tight layout regulation requirement ii. methodology in this part of work, dual-channel function generators are again used to fix the pulse widths and td of q1 to q4 switches for fixed duty ratio (fdr) scheme to proposed dual-channel resonant gate drive (rgd) circuit as shown in figure 6 [10]. on the other hand, a set of combinational discrete components and transistor-transistor logic (ttl) gates are employed for the generation of adaptive gate delay (agd) and predictive gate vo vin lo co ro vds,s2 high side pulse high side mosfet (s1) low side mosfet (s2) s1 on delay s2 on delay td[n] td[n+1] low side pulse sensed signal (v or i) next switching cycle pwm predictive circuit etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 76-83 78 www.etasr.com yahaya et al: comparative assessment of gate drive control schemes in high frequency converter delay (pgd) schemes. all three schemes are compared to determine the effectiveness in terms of switching loss, output power distribution, body diode conduction loss and efficiency of the converter. figure 7 and figure 8 show the proposed agd and pgd schemes respectively. fig. 6. proposed dual-channel gate drive circuit fig. 7. proposed adaptive gate delay scheme the digital control block is included in the agd scheme for the proposed srbc circuit shown in figure 7. in this scheme, s1 is applied with a fixed pwm signal. s2 switch is actually controlled by the scheme. here, the node switch voltage is first captured and compared with the reference voltage, vref. the digital clock will then be fed to the and gate so that when the clock triggers with input 1, s2 switch will not turn on until node voltage is zero. the td is measured along side with the body diode conduction time of s2. as a result, the conduction loss, pco-d, body diode conduction loss, pbd and total switching loss, psw can be calculated. the digital delay line settings are shown in table ii. table ii. digital delay line settings parameters value delay (ns) 340 on time (ns) 645 off time (ns) 355 start value 0 opposite value 1 fig. 8. proposed predictive gate delay scheme on the other hand, in pgd control scheme as shown in fig 8, the pwm technique using comparator is used where an equal pulse width will be generated from the comparison between the triangular waveform, vtri and a reference voltage, vref. the comparator will produce an output voltage each time vtri goes above vref. in this work, the pulse width will be varied by adjusting vref in between 0.2 v and 0.8 v, to find out the capability of td reduction in srbc circuit. a b d c pwm delay controller vsource vout high side pulse low side pulse fig. 9. block diagram of pgd control scheme ro lo co cr lr s2 cx cs ls s1 vp1 and not vp2 vref vin switch node voltage, v s2 s1 vin cr lr cx co ro lo cs ls vtri vref rg v1 v7 v4 v2 vpulse vin vo da vp1 vp2 vp3 vp4 d1 d2 d3 d4 l1 l2 ca s1 s2 vs q1 q2 q3 q4 etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 76-83 79 www.etasr.com yahaya et al: comparative assessment of gate drive control schemes in high frequency converter the block diagram of the pgd is shown in figure 9. note that it is constructed from several circuits constituting pwm circuit (a), delay controller circuit (b), circuit to sense the body diode conduction (c), and srbc circuit (d). the pwm circuit (a) will generate the pulse that is used to turn on and off the mosfet. the high side pulse will directly be used to drive s1. the low side pulse will be the input of the delay controller (b) before it drives the s2. circuit (c) will perform the feedback operation and generate output signal to the delay controller. the operating details of block b and c are described below. delay controller circuit the delay controller circuit will adjust the low side pulse before the output drives the s2. the adjustment is based on the prediction concept where the width of the pulse will be adjusted by the controller according to the feedback signal it receives. from figure 10, the d[n] pulse is currently turned on the s2. during this turn-on period, the feedback circuit will sense the conduction at s2 due to the inductive load and it will generate a signal to the delay controller. based on this signal, the controller will make an adjustment for the next pulse, d[n+1] so that the dead time, td[n+1] for next switching cycle can be minimized while preventing the cross conduction. fig. 10. adjustment of pulse width using delay controller the adjustment made by the controller can be either to maximize or minimize the pulse width. note that the dead time for td[n+1] is adjusted by the delay controller. the adjustment of the pulse width can be done by varying the reference voltage, vref. so, the delay controller will be fed to the reference voltage. it has the ability to vary the reference voltage according to the received input from the feedback circuit. figure 11 illustrates how the pulse width can be adjusted based on the feedback circuit. fig. 11. operation of delay controller this is a circuit which the feedback operation is performed. the output generated from this circuit will be used as the input for the delay controller. during the high side pulse transition from high to low, the comparator will sense the vds of s2. if body diode conduction is detected, the comparator will generate high output and the delay controller will reduce the delay of low side pulse for the next switching cycle. if the comparator output generates a low output, the delay controller will increase the delay for the next switching cycle of s2. as long as the srbc operates, this shifting process will continuously occur to avoid the cross conduction while ensuring the td delay introduced is small. the feedback circuit will be received by the delay controller. based on the signal received, the delay controller will adjust the vref. since the width of the pulse generated depends on the comparison between the vtri and vref, the variation in vref will change the td between the pulses accordingly. the parameter setting for vtri and vref are given in table iii and table iv respectively. using the required frequency of 1 mhz, the frequency of the vtri must also be same. as previously mentioned, the duty ratio, d of s1 is determined to be 20 %. table iii. parameter settings for vtri parameters value max voltage, v1 0 min voltage, v0 1 rise time, tr 0.5 µs fall time, tf 0.5 µs table iv. parameter settings for vpulse parameters value max voltage, v1 5 v min voltage, v0 0 v rise time, tr 5 ns fall time, tf 5 ns time delay, td 893 ns pulse width, pw 200 ns time taken for a complete cycle, per 1 µs the steady-state simulation analysis is repeated with different vref values in order to investigate the effect in td on srbc circuit’s performance. the study on the pco-d – pbd and td – tbd relationships with respect to vref are also carried out in addition to switching related losses in the converter. iii. results and discussions fdr, agd and pgd control schemes are investigated to determine the feasibility in the reduction of srbc’s switching loss. in fdr scheme, the proposed dual-channel gate driver is applied directly to the converter. as for agd and pgd control schemes, each of them is configured to connect the gate terminals of q4 and s2 respectively. then, the simulated results are compared and analyzed. delay controller td[n] td[n+1] td[n] td[n+1] d[n] d[n] d[n+1] d[n+1] vref feedback circuit delay controller comparator etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 76-83 80 www.etasr.com yahaya et al: comparative assessment of gate drive control schemes in high frequency converter a. comparison between fdr and agd control schemes table v shows the comparison in the analysis of fdr and agd circuit operations. the initial study concentrates on the agd scheme which was applied directly to the gate terminal of q4 (agd-q4) in the proposed rgd circuit as shown in figure 12 below. it is found that the implementation of agd-q4 does not show significant improvement in srbc except for the vo compared to fdr. when agd-q4 is used, this adds up the s2 body diode conduction time caused by the delay in cross coupling loops during td detections in q3-q4 and s1-s2. as a result, s2 will take a longer time to conduct. moreover, the proposed agd-q4 scheme requires a precise control on gate charge compensation delay of the switch. otherwise, this may result in higher switching loss as measured of 2.52 w, which is more than 7 % higher than fdr. the switching power loss is measured to be higher in agds2 as shown in figure 7 compared to agd-q4 (figure 12). this is due to the impact of cx in the converter which prolongs the detection of td by the controller and hence reduces the efficiency. when comparing with fdr, their switching losses have increased by more than 7 % and 24 % respectively. therefore, this clearly indicates that using the proposed dual-channel rgd may help solve issues related to td, reduce conduction loss to 68.30 mw and hence switching loss. in other words, by applying the digital delay control directly to s2 will not give much advantage in converter performance. this is the remarkable finding where the proposed stand-alone dualchannel rgd network can generate better loss savings in the converter. fig. 12. rgd circuit with agd control at q4 switch table v. fdr, agd-q4 and agd-s2 analysis for d = 20 % parameters analyzed fdr agd-q4 % ∆ to fdr agd-s2 % ∆ to fdr vo (v) 10.18 10.41 2.21 10.27 0.88 ilo (a) 1.51 1.27 15.89 1.28 15.23 tbd (ns) 24 27 11.11 28 14.28 pco-d (mw) 68.30 86.90 21.40 87.40 21.85 pbd (mw) 25.73 26.11 1.46 28.62 10.10 psw (w) 2.33 2.52 7.54 3.09 24.6 b. fdr and pgd control schemes the simulation of pgd control scheme is carried out based on the variation of vref as shown in figure 8 and it is applied directly to the gate of s2 (pgd-s2) in the proposed srbc circuit through delay controller. the simulation data are presented in table vi. from the variation of vref in the pgd-s2 control block, the srbc switching losses in both s1 and s2 are measured. as vref is decreased from 0.8 v to 0.27 v, all parameter values except ilo reduces with respect to td. then once vref is below 0.27 v, the results are no longer valid since td is negative. it is also found that low switching losses lie between 0.27 v and 0.3 v. if vref is applied with less than 0.27 v, the pulses will overlap each other and lead to crossconduction. a high vref yields a greater output voltage which is favorable in the design but the body diode conduction loss will increase resulting in high total switching loss in the circuit. 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.32 0.34 0.36 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 dead time (t d ) body diode conduction time (t b d ) reference voltage (v) d e a d t im e ( n s) -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 b o d y d io d e c o n d u c tio n t im e (n s) fig. 13. relationship between td and tbd vs vref fig. 14. body diode conduction time at vref of 0.29 v agd q4 etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 76-83 81 www.etasr.com yahaya et al: comparative assessment of gate drive control schemes in high frequency converter table vi. switching loss measurement adopting pgd-s2 control scheme for d = 20 % vref (v) vo (v) ilo (a) td (ns) tbd (ns) pco�d (mw) pbd (mw) psw,s1 (w) psw,s2 (w) psw,total (w) 0.8 11.60 1.12 260 350 103.90 109.0 1.64 1.03 2.88 0.6 11.23 1.25 170 220 115.65 77.0 1.96 1.42 3.34 0.4 10.23 1.31 66 82.5 92.51 54.9 1.42 1.25 2.82 0.35 10.41 1.48 40 48 81.15 48.8 1.61 1.20 2.94 0.33 10.35 1.50 27 33 71.24 36.8 1.56 1.15 2.82 0.3 10.24 1.52 15 24 68.27 24.6 1.16 1.10 2.35 0.29 10.22 1.53 10 25 67.27 24.0 1.17 1.09 2.35 0.285 10.11 1.54 4 24 62.43 23.5 1.15 1.10 2.33 0.28 10.07 1.56 0 24 61.89 23.7 1.18 1.11 2.38 0.27 10.02 1.58 0 27 60.25 23.2 1.20 1.15 2.43 0.26 10.95 1.29 -7.5 28 59.57 28.5 1.28 1.90 3.26 0.25 11.89 0.98 -11 32 66.93 30.7 1.32 2.35 3.76 0.2 12.38 0.64 -34 46 71.68 33.1 1.56 3.10 4.76 figure 13 explains that the tbd increases linearly with td starting from vref at 0.27 v. the faster free-wheeling ilo flows into the body diodes during td, the lower power loss in the converter will be. for instance, at vref = 0.29 v, the tbd is measured 25 ns with 0.75 v overshoot indicating the duration of on-state conduction of body diode as shown in figure 14. therefore, tbd has to be minimized and this can be realized by reducing td. however, due to the fact that td cannot be negative, the best applicable vref is 0.28 v to achieve the lowest tbd. in figure 15, the pco-d and pbd losses are minimum at vref = 0.27 v. here, when vref is less than 0.27 v or greater than 0.3 v, these losses will increase. it is also seen in the figure that the mosfet’s conduction loss is slightly higher at vref = 0.3 v due to the presence of td = 15 ns. the role of the controller is to minimize the td for the lowest possible pco-d by detecting it before s2 can be turned on. however, this is valid only if td is positive. the tbd is slightly higher at vref = 0.27 v compared to 0.3 v because the high possibility of cross-conduction. the next study looks at the application of pgd control scheme to the q4-switch (pgd-q4) of the proposed dualchannel rgd circuit. the process in determining the srbc switching losses is similar to the pgd-s2 implementation. table vii gives the comparative assessments between pgd-q4 and pgd-s2 for vref = 0.27 v and td = 0 ns. 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.32 0.34 0.36 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 c onduction l oss b ody d iode c onduction l oss r eference v oltage (v ) c o n d u c ti o n l o ss ( m w ) 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 b o d y d io d e c o n d u c tio n l o ss (m w ) fig. 15. relationship between pco-d and pbd vs vref table vii. comparison of pgd-q4 and pgd-s2 for vref = 0.27 v, d = 20 % and td = 0 ns parameters analyzed pgd-q4 pgd-s2 % ∆ vo (v) 10.20 10.02 1.76 ilo (a) 1.56 1.58 1.27 tbd (ns) 26 27 3.70 pco-d (mw) 62.30 60.25 3.29 pbd (mw) 23.65 23.20 1.90 psw,s1 (w) 1.25 1.20 4.00 psw,s2 (w) 1.18 1.15 2.54 psw,total (w) 2.52 2.43 3.57 table vii reveals the impact on utilizing the rgd network with pgd control block. the pco-d is seen slightly higher in pgd-q4 scheme of 62.30 mw which gives a reduction in 3.29 % compared to pgd-s2. also, since the td is assumed to be zero at vref = 0.27 v, ideally, pbd can be minimized. however, this will slightly increase tbd compared to vref at 0.3 v and hence shoots up s1 switching loss. in spite of this drawback, the pgd controller is still able to control and adjust s2 gate signal and maintain pco-d and pbd losses at low levels. by introducing a small interval of 15 ns td as given in table viii, the issue in signal overlapping can be avoided. in fact, the pgd controller can have a longer safe time margin to detect the td before vgs,s2 can be turned on. the application of non-zero td may in turn give rise to higher pco-d and pbd. remarkably, s1 switching loss is reduced compared to vref at 0.27 v leading to lower total switching loss for a shorter duration in tbd. etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 76-83 82 www.etasr.com yahaya et al: comparative assessment of gate drive control schemes in high frequency converter table viii. comparison of fdr and pgd-s2 at vref = 0.3 v for d = 20 % and td = 15 ns parameters analyzed fdr pgd-s2 % ∆ vo (v) 10.18 10.24 0.59 ilo (a) 1.51 1.52 0.65 tbd (ns) 24 24 pco-d (mw) 68.30 68.27 0.04 pbd (mw) 25.73 24.60 4.39 psw,s1 (w) 1.14 1.16 1.72 psw,s2 (w) 1.10 1.10 psw,total (w) 2.33 2.35 0.85 in addition, the use of the proposed dual-channel rgd (fdr) circuit can also be considered as an independent gate drive control option to bias s1 and s2 gates. the total switching loss in fdr is only 0.85 % lower than pgd-s2. however, pwm signals have to be generated with precise control to avoid cross conduction even though it is known for its simplicity. from the evaluation, pgd-s2 is found to be the best option for the gate drive control mechanism. apparently all simulation results have indicated positive remarks and brought to successful analyses in the comparison of different pgd driving techniques with the fdr scheme. c. efficiency comparison the efficiency is measured based on the proposed srbc circuit with fixed load and input values. the gate drive control schemes: agd and pgd are applied to q4 and s2 respectively in each case. it is observed in figure 16 that the use of pgd control scheme gives a higher efficiency of more than 82 % at ilo of 1.5 a compared to agd and fdr. in addition, the application of agd-q4 produces better efficiency compared to agd-s2 by only 2 % because rgd helps control vgs,q4 turn-on for the generation of s2 pulses. this indicates the necessity of having gate drive circuit in srbc. however, pgd control scheme does not require any intermediate rgd circuit to achieve high efficiency. the application of pgd-s2 can reduce the switching loss effectively as s2 gate can intelligently be adjusted and controlled with respect to the detection of td in the circuit. 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 77 78 79 80 81 82 83 84 85 86 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.40.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.40.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.40.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 efficiency fdr efficiency agd-q 4 efficiency agd-s 2 load current, i l o (a) efficiency pgd-s 2 efficiency pgd-q 4 fig. 16. efficiency of gate drive control schemes vs ilo for ds1 = 20 %, ds2 = 75 % and td = 15 ns on proposed srbc circuit in fdr scheme, the driving pulses given to q1-q4 switches can be precisely controlled by independent pwm generators. it is found that fdr scheme can also manage to cap the efficiency high of 83 % which is comparable to pgd-s2 implementation. due to its simplicity, it can be considered since the complemented signals generated at the gates of s1 and s2 are easy to control and monitor in accordance with any design requirements. conclusion as pgd scheme is concerned, the total switching loss has improved slightly by 1 % compared to the fdr scheme which indicates the feasibility of the design. however, pgd is not easy to be implemented. it has been proven in the work that fdr can manage to sustain a low value of body diode conduction time even though there is a risk in shoot-through current due to its simplicity in design. the agd and pgd schemes are beneficial to improve the gate driving loss but the design is complex. comparatively, fdr scheme is easy to apply and eventually gives better advantages in converter’s performance. therefore, the stand-alone fdr control or a direct implementation of pgd-s2 scheme can be chosen as an easy alternative in the design of high frequency srbc circuit. acknowledgment the authors would like to thank universiti teknologi petronas, for providing financial support in publishing this work. references [1] d. leggate, r. j. kerkman, “pulse-based dead-time compensator for pwm voltage inverters” in ieee 21 st int. conf. ind. electron., contr. and instr., usa, vol. 1, pp. 474 481, 1995. [2] k. yamamoto, k. shinohara, h. ohga, “effect of parasitic capacitance of power device on output voltage deviation during switching deadtime in voltage-fed pwm inverter” in proc. power conv. conf., japan, vol. 2, pp. 777 782, 1997. [3] c. jung-soo, y. ji-yong, l. seung-won, k. young-seok “a novel dead time minimization algorithm of the pwm inverter” in ieee 34 th annu. meet. ind. app. conf., vol. 4, pp. 2188 2193, 1999. [4] t. y. ahn, h. j. kim, k. harada, “fixed frequency, fixed duty ratio controlled forward zvs-mrc using a saturable core” in ieee of 24 th annu. power electron. spec. conf., pp. 551-557, 1993. [5] t.y. ahn, h.j. kim, k. harada, “fixed frequency forward zvs-mrc using a saturable core” in 15 th int. telecom. energy conf., vol. 1, pp. 334-340, 1993. [6] a. chapuis, m. hill, “adaptive delay control circuit for switched mode power supply”, u. s. patent 6958592 b2, 2005. [7] s. mappus, “predictive gate drive boost synchronous dc/dc power converter efficiency” app. rep. texas instruments slua281, 2003. [8] m. l. chiang, l. c. fu, "adaptive control of switched systems with application to hvac system” in ieee int. conf. contr. applications, pp 367 372, 2007 [9] j. s. brown, “method and apparatus for intelligently setting dead time”, u. s. patent: 7098640 b2, 2006. [10] n. z. yahaya, k. m. begam, m. awan “design and simulation of an effective gate drive scheme for soft-switched synchronous buck converter” in ieee 3rd asia int. conf. mod. & sim., pp. 751 – 756, 2009. e ff ic ie n c y ( % ) etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 76-83 83 www.etasr.com yahaya et al: comparative assessment of gate drive control schemes in high frequency converter authors profile 8or zaihar yahaya was born in lumut, malaysia. he went to the university of missouri-kansas city, usa to study electronics. he graduated with bsc in electrical engineering in 1996. after that he served 5 years in the industry in malaysia. in 2002, he was awarded his msc in microelectronics from the university of newcastle upon tyne, uk. he received his phd from the universiti teknologi petronas, malaysia in 2011. his main teaching/research areas are the study of power electronics switching converters and analog power devices. k. m. begam graduated in physics from the madras university, india in 1982. after graduation, she joined the post-graduate course in physics with electronics specialization and received her masters degree from the bharathidasan university, india in 1984. then she was working in various capacities at the p.s.n.a. college of engg. & tech., affiliated to anna university for 17 years. she came to malaysia in the year 2000 and obtained her doctorate from the multimedia university for her work on solid state devices. currently, she is attached with the university teknologi petronas as an associate professor in the department of electrical and electronic engr. her research interest is in lithium-ion batteries, hybrid power sources, solid state devices, and semiconductor sensors. m. awan received the b app sc from usm, penang, malaysia, in 1980, the msc (e) from university of new brunswick, fredericton. canada, 1984, and the ph.d from university of southampton, england, 1991. he had worked as test engineer at intel technology, penang, prior to the post graduate study. he is an associate professor at the department of electrical and electronic engineering, usm, until 2003. currently, he is an associate professor at the electrical and electronic engineering, universiti teknologi petronas, malaysia. he research interests include the design and implementation and verification of low power analog rf circuits and digital ics. engineering, technology & applied science research vol. 9, no. 1, 2019, 3818-3821 3818 www.etasr.com oad et al.: impact of long-term loading on reinforced concrete beams made with … impact of long-term loading on reinforced concrete beams made with partial replacement of coarse aggregates with recycled aggregates from old concrete mahboob oad department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan engrmahboob04@gmail.com abdul hafeez buller department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan engrabdulhafeezbuller@gmail.com bashir ahmed memon department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan basher_m@hotmail.com noor ahmed memon department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan nahmedmemon@gmail.com abstract—this research work presents an experimental evaluation of the effect of sustained loading on reinforced concrete beams made with 50% replacement of natural coarse aggregates with aggregates from old concrete. a total of 9 rc beams were cast, 6 with natural coarse aggregates and 3 with recycled concrete aggregates. all beams were cured for 28 days in standard fashion. among the first batch, 3 beams were used to test under short term loading till failure. an application of 50% of short-term loading followed on all beams assembled on purpose made frames. all beams were monitored for deflection, strain, and cracking. both deflection and strain remained within limits. crack monitoring revealed maximum crack width 0.5 mm. after six months of sustained load, beams were removed from the frames and tested in universal load testing machine with central point load till failure. the load-deflection pattern of all beams was observed to be almost similar and 22.12% higher in recycled concrete beams than all-natural aggregate beams. the results show promising use of recycled concrete aggregates in new concrete subjected to sustained loading. keywords-recycled concrete aggregates; green concrete; longterm loading; flexural strength i. introduction concrete is one of the most common and versatile materials used around the globe. demolishing of old concrete structures generates huge amounts of waste. dealing with this waste particularly in areas where dumping space is less or unavailable is a serious problem, and dumping this waste raises several environmental issues. one of the prominent aspects of dealing with this waste is by reusing it in new concrete leading to production of green concrete. several components of the demolishing waste have been used in new concrete as replacements of fine and coarse aggregates. the bulk amount of demolishing waste is concrete and can effectively be used as coarse aggregates. old concrete has been studied by several scholars as partial or full replacement of coarse aggregates in new concrete. in this regard, author in [1] presented a review on the recent developments about the use of recycled aggregates and summarized its use, limitations and the state-ofthe-art achieved in recent years. fresh and hardened properties of new concrete with coarse aggregates from old concrete under short term loading have also been studied, although the scatter in reported results shows that still a lot of work is required to be done in this field to improve the confidence in the use of this material. on the other hand, structures during service life are applied with sustained loading / long term loading. creep, shrinkage and deflection due to long term loading are important parameters which generate and redefine the stresses in reinforced concrete members thus need to be studied to ensure proper design and thus proper functioning of the reinforced concrete members. in this regard, authors in [2] determined creep and shrinkage of concrete with recycled coarse aggregates. they used 0.5 and 0.65 water-cement ratio with 0%, 20%, 50% and 100% dosage of recycled aggregates to study the proposed parameters for 1000 days. they observed that both parameters increased with increased dosage of recycled aggregates. also, different behavior was recorded due to the use of pre-saturated coarse aggregates. finally, numerical expression was developed to predict shrinkage and creep coefficients at early age and internal curing effect. in [4], the same authors used the same parameters to study long-term deflection. flexural capacity of reinforced concrete beams with recycled concrete aggregates has been studied in [7, 9]. authors studied the combined effect of corroded steel and sustained loading on the flexural performance of reinforced concrete beams. authors in [10] conducted experimental work to check the long-term behavior of frc (polymer and glass fibers) flexural beams under corresponding author: m. oad engineering, technology & applied science research vol. 9, no. 1, 2019, 3818-3821 3819 www.etasr.com oad et al.: impact of long-term loading on reinforced concrete beams made with … sustained load. in [11], authors used glass polymer bonded to tension face of reinforced concrete beams to check flexural behavior. based on the outcome of their studies it is observed that recycled aggregate concrete is valuable as structural material. deflection due to long term loading has been studied in [3] considering normal and high-strength concrete and by taking into compressive strength, compressive zone reinforcement and dimension of reinforced concrete beams. authors in [5] also studied it by using bayesian analysis as a more improved technique than probabilistic prediction. authors in [14] used 0%, 30% and 100% replacement of natural coarse aggregates and w/c ratios of 0.35, 0.45 and 0.6 and aggregate to cement ratios of 3, 4.5 and 6 to study the same. authors in [15] checked long-term deformation in recycled aggregate concrete due to creep and shrinkage. authors in [6] used recycled aggregates and high-volume fly ash to study long-term deflection, creep and shrinkage of reinforced concrete beams. almost all above-mentioned studies reported increase in deformation due to the increase in dosage of recycled aggregates. effects of long-term deformation on creep, shrinkage and other properties of concrete are also evident from the results. a comparison of the results shows that recycled concrete aggregates can be used in new concrete. refinement of relevant provisions of bs8110 and eurocode 2 for tension stiffening decay with time were addressed in [12] and revisions for behavior modeling were proposed. a collective study of pore size distribution and mechanical properties was done in [13] with the use of recycled aggregates from different sources. based on the test results of 5-year cured concrete samples, authors concluded that there is good correlation between porosity and strength of the concrete. authors in [17] studied the long-term deflection and flexural behavior of rc beams with recycled aggregates under sustained loading for more than 1 year. they compared the experimental results and based on their observations they proposed a modified equation to predict the long-term deflection of reinforced concrete beams with recycled aggregates. the output of the proposed equation showed good agreement with the experimental results. authors in [16] researched regarding the mortar attached to old concrete aggregates and introduced the residual-mortar-factor to existing aci and ceb methods for calculating creep and drying shrinkage. they observed that with the proposed technique creep and drying shrinkage are lower compared to their conventional counterpart. authors in [18] developed formulas to compute long-term deflection of cracked reinforced concrete beams. they assumed all important parameters along with stress in steel in accordance with experimental tensile stress in steel. the output of the proposed function was compared with 217 reinforced concrete beams from the literature under sustained loading and showed good agreement between the two sets. from the above discussion of relevant literature, it is evident that more work is required in the field to develop the confidence in using recycled concrete aggregates. therefore, this paper presents laboratory testing of reinforced concrete beams made with 50% replacement of natural coarse aggregates with recycled old concrete under 6-month loading. specimen details, testing and results are given in relevant sections. comparison of the results shows that concrete with recycled aggregates from old concrete performs well after 6 months of sustained loading. ii. model description and testing large blocks of old demolished concrete were collected from a 40 year old demolished school. these large blocks were manually hammered to approximate size of 20mm (figure 1). after screening of the obtained material for debris, organic compounds, mortar pieces and cracked particles, sieve analysis was done in standard fashion to obtain well graded material. in parallel, sieve analysis of natural coarse aggregates was also done. the comparison of grading of both aggregates is given in figure 2. fig. 1. old concrete fig. 2. gradation of coarse aggregates using ordinary portland cement, hill sand, natural coarse aggregates and coarse aggregates from old concrete, 3 reinforced concrete beams with 50% replacement of natural coarse aggregates were prepared. in addition, 6 reinforced concrete beams with all-natural coarse aggregates were also prepared and used as control specimens. for preparation of all the beams 1:2:4 mix was adopted. water-cement ratio of 0.5 was used for the preparation of control specimens, whereas, water cement ratio of 0.6 was used to cast the proposed beams. increased water-cement ratio was used to keep the same workability of concrete in both cases. for all beams, dimensions were kept the same and equal to 1875mm×150mm×300mm. 2#4 bars were used in both tension and compression zones with #3 bars as stirrups at 150mm center to center throughout the length of beam. after casting in standard manner, all the beams were cured in water for 28 engineering, technology & applied science research vol. 9, no. 1, 2019, 3818-3821 3820 www.etasr.com oad et al.: impact of long-term loading on reinforced concrete beams made with … days. reinforced concrete beams made up of all-natural aggregates are termed as nb1, nb2 and nb3. whereas, notation of rb1, rb2 and rb3 is used for the beam cast with 50% recycled concrete aggregates. after the elapse of curing time, 3 beams made of all-natural aggregates were tested in universal load testing machine to determine the maximum load carrying capacity. the average of the 3 specimens was 74.022kn. pads were applied on the remaining reinforced concrete beams in center location with 25mm center to center along the depth of beams for strain measurement. then the beams were mounted on purpose made frames to test for long term loading (figure 3) one-point load at center. dial gauges were fixed at center location below the beams to measure deflection. 50% of the load obtained from short-term load testing was applied on each beam by means of screw jack and load cell system. deflection, strain and cracking were monitored on a daily basis for all beams. under sustained loading, deflection and strain values were measured on daily basis. the maximum values of deflection and average of all 11 readings of strain at the end of 6 months are given in table i. fig. 3. reinforced concrete beams for testing under long term loading. table i. deflection and strain after 6 months loading parameter nb1 nb2 nb3 rb1 rb2 rb3 deflection (mm) 1.97 2.04 2.11 2.10 2.22 2.15 strain (×10-3) 2.31 2.36 2.38 2.43 2.45 2.41 iii. results and discussion all parameters discussed earlier were monitored on daily basis and analyzed. weekly and final values of the parameters were recorded. the increasing trend of deflection and strain confirms the normal behavior of the beams. maximum deflection among all 6 beams was recorded for rb2 and was equal to 2.22mm at the end of the 6-month loading. the same beam also showed maximum strain equal to 0.00245. maximum deflection and strain values of all beams are shown in figures 4 and 5. the values obtained are within the allowable limits of the parameters of aci-318-95 provisions. during sustained loading, cracking in the beams was observed and marked and measured. weekly marking of cracks in all beams is shown in figure 7. although figure 7 shows a closed exaggerated view of the beams, yet it was observed and recorded that the maximum crack width was equal to 0.5mm, which confirms minor cracks under sustained loads thus better utilization of demolished aggregates form old concrete in new concrete. fig. 4. maximum deflection fig. 5. maximum strain fig. 6. load vs deflection fig. 7. crack monitoring in beams under sustained loading engineering, technology & applied science research vol. 9, no. 1, 2019, 3818-3821 3821 www.etasr.com oad et al.: impact of long-term loading on reinforced concrete beams made with … after 6 months of sustained loading, load on the beams was removed and all the beams were tested under central point load till failure in a universal load testing machine. during the testing, deflection was recorded at regular intervals. the loaddeflection behavior of all beams is shown in figure 6. it may be observed from this figure that the pattern of deflection increase is the same in all beams, however the reinforced recycled concrete aggregate beams exhibited more deflection compared to reinforced natural aggregate beams. the maximum deflection observed in reinforced recycled aggregate beams is equal to 11.65mm which is 22.12% higher than the maximum deflection observed in reinforced natural aggregate beams. both recycled concrete aggregate and natural aggregate beams exhibited shear failure, showing proper functioning of the rca beams under loading. based on the above findings it is concluded that recycled concrete aggregates can comfortably be used in new concrete subjected to sustained loads up to six months. iv. conclusions based on the findings of this research work, the following conclusions are made: • deflection and strain of reinforced concrete beams having partial replacement of natural aggregates with recycled concrete aggregate and all-natural aggregates are within allowable limits of aci-318-95. • reinforced rca beams exhibited higher deflection and strain than reinforced natural aggregate beams. • during sustained loading cracks were monitored and crack width was evaluated. maximum crack width recorded is 0.5mm. • after 6 months of sustained loading, beam testing till failure shows almost similar deflection trends. • at peak load values, shear failure in all beams is observed. therefore, it is concluded that coarse aggregates from old demolished concrete can be used in new concrete subjected to sustained loading without compromising its properties. references [1] b. a. memon, “recent development on use of demolished concrete as coarse aggregates”, international journal of emerging technology and innovative engineering, vol. 2, no. 1, pp. 1-11, 2016 [2] s. seara-paz, b. gonzalez-fonteboa, f. martinez-abella, i. gonzaleztaboada, “time-dependent behavior of structural concrete made with recycled coarse aggregates. creep and shrinkage”, construction and building materials, vol. 122, pp. 95-109, 2016 [3] h. m. muthana, “long-term deflections for normal and high strength reinforced concrete beams”, journal of babylon university/engineering scineces, vol. 20, no. 1, 2012 [4] s. seara-paz, b. gonzalez-fonteboa, f. martinez-abella, d. carrolopez, “long-term performance of reinforced concrete beams with recycled coarse aggregates”, construction and building materials, vol. 176, pp. 593-607 2018 [5] b. han, t. y. xiang, h. b. xie, “a bayesian inference framework for predicting the long-term deflection of concrete structures caused by creep and shrinkage”, engineering structures, vol. 142, pp. 46-55, 2017 [6] n. tosic, s. marinkovic, n. pecic, i. ignjatovic, j. dragas, “long-term behavior of reinforced beams made with natural or recycledaggregate concrete and high-volume fly ash concrete”, construction and building materials, vol. 176, pp. 344-358, 2018 [7] w. p. zhang, h. f. zhang, x. l. gu, w. liu, “structural behavior of corroded reinforced concrete beams under sustained loading”, construction and building materials, vol. 174, pp. 675-683, 2018 [8] a. r mari, j. m. bairan, n. duarte, “long-term deflections in cracked reinforced concrete flexural members”, engineering structures, vol. 32, no. 3, pp. 829-842, 2010 [9] a. lapako, r. grygo, “long-term deformations of recycled aggregate concrete (rac) beams made of recycled aggregates”, 10th international conference on modern building materials, structures and techniques, vilnius lithuania, may 19-21, 2010 [10] e. vasanelli, f. micelli, m. a. aiello, g. plizzari, “long-term behavior of frc flexural beams under sustained load”, engineering structures, vol. 56, pp. 1858-1867, 2013 [11] s. h. kim, k. b. han, k. s. kim, s. k. park, “stress-strain and deflection relationship of rc beam bonded with frps under sustained load”, composites part b: engineering, vol. 40, no. 4, pp. 292-304, 2009 [12] a .w. beeby, r. h. scott, a. e. k. jones, “revised code provisions for long-term deflection calculations”, proceedings of the institution of civil engineers, structures & buildings, vol. 158, no. 1, pp. 71-75, 2005 [13] s. c. kou, c. s. poon, m. etxeberria, “influence of recycled aggregates on long-term mechanical properties and pore size distribution of concrete”, cement and concrete composites, vol. 33, no. 2, pp. 286-291, 2011 [14] v. w. y. tam, d. kotrayothar, j. xiao, “long-term deformation behaviour of recycled aggregate concrete”, construction and building materials, vol. 100, pp. 262-272, 2015 [15] a. domingo, c. lazaro, f. l. gayarre, m. a. serrano, c. lopez-colina, “long-term deformations by creep and shrinkage in recycledaggregate concrete”, materials and structures, vol. 43, no. 8, pp. 1147–1160, 2010 [16] g. fathifazl, a. g. razaqpur, o. b. isgor, a. abbas, b. fournier, s. foo, “creep and drying shrinkage characteristics of concrete producedwith coarse recycled concrete aggregate”, cement and concrete composites, vol. 33, no. 10, pp. 1026-1037, 2011 [17] w. c. choi, h. d. yun, “long-term deflection and flexural behavior of reinforced concrete beams with recycled aggregates”, materials & design, vol. 51, pp. 742-750, 2013 microsoft word 3-2152_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3316-3320 3316 www.etasr.com abbasi et al.: impact of a single spoiler on scouring depth status beneath a river crossing inclined … impact of a single spoiler on scouring depth status beneath a river crossing inclined pipeline saeed abbasi department of civil engineering university of zanjan zanjan, iran abbasi.saeed@znu.ac.ir maryam masoomi department of civil engineering university of zanjan zanjan, iran m.masoomi@znu.ac.ir seyyed aliasghar arjmandi department of civil engineering university of zanjan zanjan, iran arjmandi@znu.ac.ir abstract—deep river crossing pipelines utilized to carry fluids are often placed upon the sand bed. placement of pipe on the non-smooth bed would result in the production of some local gaps beneath the pipe. asymmetric scouring is one of the main reasons for pipe underwater failures which are significant in pipeline management. so, in designing pipelines, knowing the interaction between pipelines and bed, and predicting the scour depth with respect to the pipe distance from the bed is significant to ensure that the pipe will finally deposit on the bed. numerical models have been developed for predicting the balance depth of scouring beneath the pipelines. in this paper, the impact of pipe orientation on maximum scour depth beneath the pipelines is investigated. to do this, a pipe is modeled with various angles with the flow. to manage the local scouring, some spoilers are placed and modeled upon some pipes too. also, in order to know the effects of placement of a pipe at various distances from the bed, the impact of placement of each pipe at a distance of 0.2d, 0.4d and 0.6d is investigated as well. to model the pipe with and without a spoiler, the finite element model flow-3d is utilized and the results show good accordance with previous experimental studies and proof the current model’s precision in predicting the scour depth. results show that in the placement of the pipe in angles not investigated before and also with the installing of a spoiler, the scour process has a reverse ratio with the distance which would result in full deposition of the pipe on the bed. the least scour depth belongs to the condition in which the pipe has a 130° angle with the side wall. keywords-flow-3d; pipeline; pipe orientation; pipe with spoiler; scouring i. introduction submerged pipes are significant parts of water conveying systems, wastewater networks, and oil transmitting lines. sediment movement under the pipes is very important because failure of these pipes would cause huge costs and damages on the environment. the local scouring at the river is investigated in [1]. during the water transmission around a pipe situated at the flow path, collide of the streamlines to an obstacle would produce several vortices around the pipe. the vortices move the sediment particles until a small void is produced beneath the pipe which causes tunnel erosion [2]. scouring of the soil under the pipe might suspend a part of the pipe in the water and if the free span of the pipe is big enough, it would result to vibration resonance and might lead to pipe failure. so it is essential to assess the scouring depth to be able to make an exact and secure design. preparing a spoiler on the pipe is a method to accelerate the pipe self-interring (figure 1). fig. 1. pipe on the flow path: up: with spoiler, down: without spoiler several researches have been performed on scouring phenomena around a pipeline. in these studies, the pipe is placed perpendicular to the flow path, while it is not always possible to install the pipe perpendicular to the flow path. authors in [3] showed that for the pipe with a spoiler the selfinterring process is ten times faster than that for a pipe with no spoiler. author in [4] investigated the scouring around a horizontal cylinder under various reynolds numbers (re), various shields parameters (θ) and various distances from the bed and introduced two small vortices on pipe upstream and downstream. author in [5] showed that the scour depth could be considered as a function of froude number and the free distance between the pipe and the bed. author in [6, 7], experimentally investigated the impact of spoiler and its orientation on a pipe subjected to wave and a one-way flow. he showed that the installation of spoiler would accelerate the under pipe scouring (tunnel erosion) and also increase the erosion on downstream and its depth. authors in [8] investigated the scouring under the pipe experimentally and studied the impact of froude and reynolds numbers on it. author in [9] studied the flow and scouring beneath the pipe engineering, technology & applied science research vol. 8, no. 5, 2018, 3316-3320 3317 www.etasr.com abbasi et al.: impact of a single spoiler on scouring depth status beneath a river crossing inclined … utilizing k-ε turbulence model using taylor-galerkin fem method. authors in [10] showed that a standing spoiler considerably increases the upstream pressure, reduces the downstream pressure and causes a downward force. authors in [11, 12] showed that the k-ω turbulence model is more adaptive than k-ε and a special case of les turbulence models. authors in [13] investigated numerically the scouring beneath the pipe under one-way flow and wave. authors in [14, 15] investigated numerically the scouring under the pipe with spoiler and its impact on flow characteristics. authors in [16] studied the hydrodynamic effects of a horizontal spoiler on the flow around a pipe and concluded that the length of 1-1.5 times the pipe diameter for the spoiler is optimum. authors in [1] investigated a river crossing inclined pipeline experimentally and authors in [17] modeled the flow around a cylinder over a scoured bed. despite that experimental models are accurate and suitable for scour depth estimation, some limitations such as costs, scaling, data acquiring and also some benefits of the numerical methods such as flexibility and considerable improvement of their potentials, have expanded the use of numerical simulations. in this paper, the impact of spoiler installation on an inclined river crossing pipeline on local scour depth is numerically investigated. also, in addition to the spoiler presence, effects of bed-pipeline distance are included in this paper which was not studied in [1]. ii. governing equations the governing equations are continuity and momentum equations. to include the sediment effects, some changes are applied to these equations. the continuity and momentum equations are presented in (1)-(5): ( ) ( ) ( ) xf x y z dif sor ua v ua r ua ua r r t x y z x ρρ ρ ρ ρ ξ ∂ ∂ ∂ ∂ + + + + = + ∂ ∂ ∂ ∂ (1) 2 yx x sorf z vaua ua rv wa r t x y z xc ρ ξ ρρ ∂∂ ∂∂ + + + + = ∂ ∂ ∂ ∂ (2) 2 1 1 ( ) y x y z f f sor x x x w s f a vu u u u ua va r wa t v x y z xv p r g f b u u u x v ξ δ ρ ρ  ∂ ∂ ∂ ∂ + + + −  ∂ ∂ ∂ ∂  ∂ = − + + + − − − − ∂ � (3) 1 1 ( ) ( ) y x y z f f sor y y y w s f a uvu v v v ua va r wa t v x y z xv rp r g f b u u u y v ξ δ ρ ρ  ∂ ∂ ∂ ∂ + + + −  ∂ ∂ ∂ ∂  ∂ = − + + + − − − − ∂ � (4) 1 1 ( ) x y z f sor z z z w s f u w w w ua va r wa t v x y z rp g f b u u u z v δ ρ ρ  ∂ ∂ ∂ ∂ + + +  ∂ ∂ ∂ ∂  ∂ = − + + + − − − − ∂ � (5) .( ) 0 f f v auf t ∂ + ∇ = ∂ (6) where vf is the proportion of open volume to the flow, ρ is the fluid density and rsor is the spring function. the fluid particle movement equations in three directions are navier-stocks equations with an additional term. also, ax, ay, and az are volume ratios, gx, gy and gz are gravitational accelerations, fx, fy and fz are viscosity accelerations and bx, by and bz are dissipations in porous media in x, y and z directions respectively. equation (6) is the vof equation in which a is mean flow cross-sectional area, u is mean flow velocity in x, y and z directions and f is fluid volume function. in flow-3d, two methods, vof (to model the performance of the fluid at the open boundary with air) and favor (to model the rigid volumes and surfaces such as geometric boundaries) are used to model the interactions [18]. a. the k-ω model the k-ω turbulence model is a two-equation model which uses two partial differential equations with two variables of k and ω. the first variable (k) is turbulent kinetic energy and the second one (ω) is dispersion characteristic velocity [19, 20]. the related equations of this model are presented in (7-9). t k ν ω = (7) ( )* *ij ij t j j j j uk k k u k t x x x x τ β ω ν σ ν  ∂∂ ∂ ∂ ∂ + = − + +  ∂ ∂ ∂ ∂ ∂   (8) ( )2ij ij t j j j j u u t x k x x x ω ω ω ω α τ βω ν σν  ∂∂ ∂ ∂ ∂ + = − + +  ∂ ∂ ∂ ∂ ∂   (9) where * * * 5 3 9 1 1 , , , , , 9 40 100 2 2 kα β β σ σ ε β ω= = = = = = b. dimensional analysis the effective parameters in local scouring beneath the pipeline in a channel are flow conditions, sediments characteristics and pipe shape [1, 8]. the relation between the mentioned parameters can be written as: 50 ( , , , , , , , , , ) s s f d f v y g d s d e sρ ρ= (10) where ds is scouring balance depth, ρ is flow density, ρs is sediment density, ν is kinematic viscosity, y is flow depth, g is gravitational acceleration, d50 is mean particle size, sf is energy line slope, d is pipe diameter, e is bed-pipe distance and s is the spoiler length. utilizing the buckingham’s π theorem and neglecting the reynolds number effects, we get: *50( , , , , , , )s d d d e s fr y y y y y ψ τ θ= (11) in which fr is froude number, τ* is shields parameter and θ is the angle of pipe orientation. iii. the numerical solution, analytical domain in this paper, the experimental work of [21] for a fixed pipe is used to validate the model. in the experimental work, the width of the flume is 0.5m, the pipe diameter is 0.032m, the flow velocity is 0.255m/s, sediment particle mean size is 0.38mm and the shields parameter is evaluated as 0.039. in the numerical model, the k-ω turbulence model is used; the pipe is placed at a distance of 10d from the beginning and at various distances from the bed. the depth of flow is 0.40m and two nested mesh of 10mm and 5mm are utilized for the outer and engineering, technology & applied science research vol. 8, no. 5, 2018, 3316-3320 3318 www.etasr.com abbasi et al.: impact of a single spoiler on scouring depth status beneath a river crossing inclined … inner domain (around the pipe) respectively. figure 2 shows the analytical domain. fig. 2. analytical domain with respect to the orientation angle, the pipe and flow can be at three situations: 1) perpendicular to the river, 2) parallel to the flow, and 3) inclined crossing [22]. in this paper, an inclined pipe with angles of 90°, 100°, 110°, 120° and 130° at various bed-pipe distances is investigated. figure 3 shows the inclined pipe and table i represents the numerical model's layout. fig. 3. inclined pipe on the flow path table i. numerical models layout pipe angle θ (deg.) bed-pipe distance 0.2d 0.4d 0.6d pipe without spoiler 90° a1 b1 c1 100° a2 b2 c2 110° a3 b3 c3 120° a4 b4 c4 130° a5 b5 c5 pipe with spoiler 90° a6 b6 c6 100° a7 b7 c7 110° a8 b8 c8 120° a9 b9 c9 130° a10 b10 c10 a. boundary conditions nested mesh was used to model the flow in this study. to apply the boundary conditions, the specified velocity was applied to the inlet boundary. the outflow is used for the outlet boundary and the symmetry is applied to the upper boundary. for the other borders, the wall boundary condition was utilized. these boundary conditions are shown in figure 4. b. validation the results of an experimental work in [21] show that the balance depth of scouring beneath a pipe was 1.34cm. the result of numerical simulation was 1.39cm which shows a good accordance with the experimental work. the relative error is 3.73% which shows a good precision of numerical simulation under a submerged pipe. comparison of numerical and experimental work and balance reaching process for the numerical model are shown in table ii and figure 5 respectively. fig. 4. the boundary conditions table ii. numerical and experimental result comparison error % scouring depth (cm) 3.73% 1.34 experimental [21] 1.39 numerical (flow-3d) fig. 5. balance reaching process for the scouring under the pipe, numerical model validation iv. results and discussion a. results for pipe placement without spoiler at various bed-pipe distances to investigate the impact of pipe inclined placement on the flow path, the following characteristics were applied to the numerical model: pipe diameter=0.032m, water velocity =0.255m/s, sediment particle mean size d50=0.38mm, channel width=0.5m and shields parameter=0.039. the pipe was oriented at 90°, 100°, 110°, 120° and 130° measured from the side wall (figure 3). to investigate the bed-pipe distance effects, the pipe was placed at distances of 0.2d, 0.4d and 0.6d of the bed. table iii. maximum depth of scouring beneath the pipe w/o spoiler bed-pipe distance (cm) pipe angle ys=0.6d ys=0.4d ys=0.2d 0.88 1.29 1.39 90° 1.06 1.34 1.40 100° 1.03 1.34 1.41 110° 0.84 1.29 1.34 120° 0.75 1.02 1.15 130° figures 7-9 show the simulation results for various distances and orientations. the asymmetric scouring under the pipe in figure 6 is caused by flow turn, affecting the flow by the walls, vortex pattern change and their expansion path deviation. this asymmetry scouring decreases by increasing the bed-pipe distance because of bed-pipe interaction reduction. engineering, technology & applied science research vol. 8, no. 5, 2018, 3316-3320 3319 www.etasr.com abbasi et al.: impact of a single spoiler on scouring depth status beneath a river crossing inclined … fig. 6. numerical simulation sample result, scouring hole beneath inclined pipe, θ=130° fig. 7. scouring beneath the inclined pipe, e/d=0.2 fig. 8. scouring beneath the inclined pipe, e/d=0.4 fig. 9. scouring beneath the inclined pipe, e/d=0.6 b. with spoiler to investigate the impact of spoiler installation around the pipe [23], an 1cm length spoiler was installed on top of the pipe and the pipe and spoiler were subjected to the flow. the scouring results of this configuration on orientations of 90°, 100°, 110°, 120° and 130° are presented in figures 7-9 and table iv. these results show that installation of the spoilers has increased the depth of scouring compared to a similar situation without spoiler. the spoiler changes the flow and pressure distribution around the pipe and increases the pressure at the rear [10]. also, results indicate that the scouring depth decreases as the bed-pipe distances increase. figure 10 shows the scouring progress for the submerged pipe with and without spoiler for e/d=0.2. it is evident that the scouring progress in case of utilizing a spoiler is more consistent and continuous which helps the pipe in the self-interring process. table iv. maximum scouring depth with spoiler bed-pipe distance (cm) pipe angle ys=0.6d ys=0.4d ys=0.2d 1.73 1.84 1.95 90° 1.60 1.85 1.92 100° 1.80 1.89 2.03 110° 1.77 1.89 2.00 120° 1.35 1.66 1.91 130° fig. 10. scouring progress beneath the inclined pipes, e/d=0.2 v. summary and conclusions in this paper, the effectiveness of a single spoiler on scouring depth reduction beneath a river crossing inclined pipeline at various bed-pipe distances was investigated numerically. main conclusions are: • as the scouring depth at the validation model has a balance time of 140s, the simulation time was selected to be 350s for all models. • considering the results, the least scouring belongs to the pipe in 130° orientation and the depth of scouring in orientations of 90°, 100°, 110° and 120° is more by 2.09%, 0.52%, 6.28% and 7% respectively. the scouring hole is symmetric when the pipes angle is 90° while the scouring hole for the pipe at 100°, 110°, 120° and 130° is asymmetric. according to the results, the maximum depth of scouring occurs next to the wall in which the pipe angle deflects the flow and the pressure varies upstream and downstream. sediment transport to the pipes downstream is because of the uplift pressure beneath the pipe and also the pipe orientation. the scouring starts somewhere upstream and slightly travels towards the pipe. • maximum scouring depth occurs at the first stages of scouring process. also, when the bed-pipe distance is more than zero, the scouring starts immediately after the simulation starts, because no time is needed for the piping phenomenon. so the sediment particles under the pipe start their travel immediately after the flow beginning. for angles of 120° and 130°, the scouring depth balance occurs engineering, technology & applied science research vol. 8, no. 5, 2018, 3316-3320 3320 www.etasr.com abbasi et al.: impact of a single spoiler on scouring depth status beneath a river crossing inclined … more rapidly and the variation chart extends with fewer slopes. also, the scouring depth is less than in other orientations. this is because of less resistance of pipe against the flow. • placement of the pipe at distances of 0.2d, 0.4d and 0.6d from the bed increases the horizontal distance of deepest scouring hole location from the pipe center. according to tables iii and iv, the bed-pipe distance at five distinct states of orientations has a similar impact on all pipes which proofs the reverse relation of bed-pipe distance with scouring depth. it is seen that the scouring depth decreases with increase in the bed-pipe distance which happens because of the pipe influence reduction on the bed at greater bed-pipe distances. • spoiler installation increases the scour depth and extension. the flow rate increases between the pipe and river bed which results to increasing scour depth under the pipe with a spoiler. • the influence of pipe on the bed scouring depth reduces with an increment of bed-pipe distance at the case of pipe with spoiler and the maximum scouring depths reduce. references [1] h. m. azamathulla, m. a. m. yusoff, z. a hasan, “scour below submerged skewed pipeline”, journal of hydrology, vol. 509, pp. 615620, 2014 [2] e. w. bijker, w. leeuwestein, “interaction between pipelines and the seabed under influence of waves and currents”, in: seabed mechanics, springer, dordrecht, 1984 [3] c. h. hulsbergen, r. bijker, “effect of spoilers on submarine pipeline stability”, offshore technology conference, houston, usa, may 1-4, 1989 [4] y. mao, the interaction between a pipeline and an erodible bed, phd thesis, technical university of denmark, 1986 [5] j. a. maza, introduction to river engineering, advanced course on water resources management, universita italiana per stranieri, 1987 [6] y. m. chiew, “effect of spoilers on scour at submarine pipelines”, journal of hydraulic engineering, vol. 118, no. 9, pp. 1311-1317, 1992 [7] y. m. chiew, “effect of spoilers on wave-induced scour at submarine pipelines”, journal of waterway, port, coastal, and ocean engineering, vol. 119, no. 4, pp. 417-428, 1993 [8] a. t. moncada-m., j. aguirre-pe, “scour below pipeline in river crossings”, journal of hydraulic engineering, vol. 125, no. 9, pp. 953958, 1999 [9] b. brors, “numerical modeling of flow and scour at pipelines”, journal of hydraulic engineering, vol. 125, no. 5, pp. 511-523, 1999 [10] l. cheng, l. w. chew, “modeling of flow around a near-bed pipeline with a spoiler”, ocean engineering, vol. 30, pp. 1595-1611, 2003 [11] d. liang, l cheng, f. li, “numerical modeling of flow and scour below a pipeline in currents: part ii. scour simulation”, coastal engineering, vol. 52, pp. 43-62, 2005 [12] d. f. liang, l. cheng, “numerical modeling of flow and scour below a pipeline in currents: part i, flow simulation”, coastal engineering, vol. 52, pp.25-42, 2005 [13] y. zhang, m. zhao, k. c. s. kwok, m. m. liu, “computational fluid dynamics–discrete element method analysis of the onset of scour around subsea 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models”, aiaa journal, vol. 26, pp. 1299-1310, 1988 [20] d. c. wilcox, “formulation of the k–ω turbulence model revisited”, aiaa journal, vol. 46, pp. 2823-2838, 2008 [21] f. p. gao, b. yang, y. x. wu, s. m. yan, “steady current induced seabed scour around a vibrating pipeline”, applied ocean research vol. 28, no. 5, pp. 291-298, 2006 [22] q. deng, l. li, y. zhang, “an analysis of river washout influence and protective measures of long-distance gas and oil pipelines”, international conference on pipelines and trenchless technology, wuhan, china, october 19-22, 2012 [23] x. ruan, b. shi, l. yang, z. zhang, “an experimental study on scour around the submarine pipeline with spoilers under wave conditions”, ieee 2011 international conference on remote sensing, environment and transportation engineering, nanjing, china, june 24-26, 2011 microsoft word etasr_v10_n6_pp6494-6499 engineering, technology & applied science research vol. 10, no. 6, 2020, 6494-6499 6494 www.etasr.com priyadarshini & panigrahi: optimal allocation of synchrophasor units in the distribution network … optimal allocation of synchrophasor units in the distribution network considering maximum redundancy subhashree priyadarshini school of electrical engineering kalinga institute of industrial technology deemed to be university bhubaneswar, india subhashre9@rediffmail.com chinmoy kumar panigrahi school of electrical engineering kalinga institute of industrial technology deemed to be university bhubaneswar, india panigrahichinmoy@gmail.com abstract-phasor measurement unit (pmu) is a smart measuring device commonly used in wide-area monitoring systems. it provides the synchronized phasor values and the magnitudes of voltages and currents in real-time for the proper state calculation of the electrical network in a common time reference frame. but in order to avoid unnecessary placements, minimize installation cost, and due to the lack of communication facilities at the substations, the placing of pmus at every location is not possible. therefore several optimization techniques have been developed to solve the optimal pmu placement (opp) problem. the opp problem aims to reduce the number of pmus by achieving a completely observable network. many solutions to the opp problem have been proposed for the transmission networks with the use of conventional and heuristic-based approaches, but very few for distribution networks. in this paper, the binary grey wolf optimization (bgwo) algorithm is proposed to solve the opp problem considering the measurement redundancy (mr) to achieve complete observability of the distribution network. finally, case studies have been done by implementing the proposed algorithm on different ieee test feeders such as the ieee -13, -33, -37, and -123 node feeder systems. the obtained results are compared with previous studies to verify the feasibility and efficiency of the proposed technique. keywords-binary grey wolf optimization; measurement redundancy; observability; optimal pmu placement; phasor measurement unit i. introduction proper monitoring, control, and protection of a power system can only be possible with complete observability of the entire network. a completely observable system provides accurate control and protection schemes for the secure and reliable operation of the electrical network. the invention of the synchrophasor unit or phasor measurement unit (pmu) has made it possible by providing real-time measurements of the voltage and the current signals [1, 2]. the measurements obtained from pmus are accurate and time-stamped as they are connected with the global positioning system (gps). the installation of pmu at different bus locations monitors the whole network by providing an accurate state estimation of each bus, but it is not possible to place pmus at each bus as the installation includes the high cost of pmu devices along with its communication infrastructure and the data handling capacity. this leads to the optimal pmu placement problem. therefore, the basic objective of the opp problem is to optimize the pmu numbers to a minimum value by achieving the complete observability criterion. many researchers have solved this opp problem by using both traditional as well as heuristic optimization algorithms. heuristic methods are capable of solving the placement problem in small and large networks with less computational time as compared to the traditional methods. the most common traditional approach is the integer linear programming (ilp). a binary ilp (bilp) method is implemented in [3] to find minimum pmus for the opp problem in the distribution network considering the topology changes. similarly, the bilp is implemented in [4] to solve the placement problem of pmus with the consideration of communication links for the distributed state estimation in the distribution network. a hybrid ilp-based method is proposed in [5] to solve the opp problem for the distribution network by finding all the possible solutions with observability. a heuristic binary-based particle swarm optimization (bpso) algorithm is proposed in [6] to minimize the pmu number and maximize redundancy. the proposed method was implemented in a transmission network. another improved bpso has been proposed in [7] to find minimum pmus with complete observability. the observability analysis was done by the state estimation of each bus in the network. authors in [8] developed a new genetic algorithm (ga) to solve the pmu placement issue to achieve a complete observable and secure system. a non-dominated sorting ga was proposed to place pmus optimally as well as to maximize the redundancy for ieee 39 and 118 test bus transmission network in [9]. ant colony optimization was implemented in [10] to minimize the pmus by achieving maximum redundancy under normal and contingency conditions. an artificial bee colony optimization (abc) algorithm was implemented in [11] to find minimum pmus in the presence of conventional flow measurements and zero injection buses. a multi-objective problem was solved for opp using a binary-based gravitational search algorithm (gsa) in [12]. the binary jaya optimization was implemented corresponding author: subhashree priyadarshini engineering, technology & applied science research vol. 10, no. 6, 2020, 6494-6499 6495 www.etasr.com priyadarshini & panigrahi: optimal allocation of synchrophasor units in the distribution network … to minimize the pmu numbers with complete network observability in [13]. this approach was only implemented in ieee standard transmission networks. the recursive tabu search (rts) method was proposed to reduce the pmu devices by using numerical based observability analysis in [14]. the proposed method was only tested on the ieee test bus transmission networks. teaching-learning based optimization has been suggested in [15] to find the minimum pmus required for the monitoring of the transmission network. all these traditional and heuristic approaches have been implemented in transmission networks. only the traditional approaches were used for solving the opp in the distribution network. in this paper, a binary-based grey wolf optimization technique is developed to minimize the pmus with complete observability and to maximize the measurement redundancy for distribution networks. ii. problem formulation the opp problem is defined as the minimization of the number of pmus required for monitoring the electrical network. in this paper, the purpose of solving the opp problem is to reduce the number of pmus in the distribution system. as a result, the overall installation cost can be minimized. the concept of maximum measurement redundancy is also considered in the opp problem with complete observability in the objective function. hence, the objective function j(z) for the distribution network can be expressed as [16]: ��� ���� � ∑ � �� � � ���� � �′����� � �′�� � ������� subject to �′ ∙ � � � (1) where nd is the total number of nodes in the feeder, w1 and w2 are the weight parameters, nob is the total number of observable nodes in the system, and zi is the element of binary decision vector (z) which denotes the pmu placement at the ith node and it can be defined as follows: � � �1,�" #�$ is placed at node �0,otherwise (2) a’ is the binary connectivity matrix derived from the connection of each node in a distribution network. ��′�454��, 6� � 7 1,if node � � node 61,if node � �s connected to 60,otherwise (3) �45� � 91 1 1… ……….<�= unit vector (4) � � 9�����= … …… ���<�5��� (5) the entries of each element in the m vector are defined as the connectivity of each node plus one. for example, node 2 in figure 1 is connected with 3 branches. therefore the maximum value of node 2 is 4 {3 for the connected branches (node 1, node 3, and node 4) and 1 for the node itself}. hence the values of each element are set to be more than the actual connections. in (5), the minimization of the difference between the desired value (m) and the actual value (obtained from pmu placement) is nothing but the maximization of measurement redundancy. the placement set with a minimum mr value will give the best placement result. fig. 1. basic diagram of a 5 node feeder network. a completely observable electrical network is defined when all the nodes are directly or indirectly monitored by the installed pmus [17]. therefore, the pmu measurement method is divided into two categories. the first one is the direct measurement method and the second one is the indirect measurement method. the node at which a pmu is placed can directly monitor that node and also the connected nodes to it. hence, it is known as the direct measurement method. in indirect measurement, kirchhoff’s law is used to calculate the unknown current value and the voltage value of the nodes. based upon these two laws, observability rules are developed and expressed as: rule 1: a node with a known voltage value along with its current value gives the unknown voltage value of the other end node. rule 2: if the voltage values of two connected nodes are known, then the current that flows between them can be calculated by using ohm’s law and kcl. in this work, the solution for the placement problem is solved by considering the normal operating condition and single pmu loss. a. single pmu loss single pmu loss is an important contingency during which the monitoring of the entire network can be affected. therefore, to avoid such problems in the distribution system, each node should be observed by at least two pmus for the continuation of proper monitoring and control of the entire network [18]. hence the unit vector in (4) can be modified as: �45� � 92 2 2… ……….<� (6) b. measurement redundancy (mr) the measurement redundancy calculation is necessary for every opp solution set for the secure and quality operation of the electrical network. since the proposed bgwo technique is a meta-heuristic based approach, multiple placement sets will be obtained with an equal number of minimum pmus to achieve a completely observable system. therefore, the calculation of the bus observability index (boi) and the complete system observability index (csoi) are required to maximize the redundancy [19]. boi represents the total number of times each node is observed from the opp solution set, whereas csoi is the summation of all the bois calculated for each node in the distribution network. the highest csoi value yields a better placement location for the pmu installation. in this paper, the mr concept is considered to evaluate and compare the best placement sets obtained from the proposed and previously developed techniques. the expressions for boi and csoi are given in (7) and (8): engineering, technology & applied science research vol. 10, no. 6, 2020, 6494-6499 6496 www.etasr.com priyadarshini & panigrahi: optimal allocation of synchrophasor units in the distribution network … ?@a � �′ ∙ � (7) bc@a � ∑ ?@a �� � (8) iii. binary grey wolf technique grey wolf optimization (gwo) is a newly developed population-based meta-heuristic technique influenced by the organizational structure and hunting nature of grey wolves [20]. here, the binary-based gwo technique is proposed to solve the opp problem along with maximum redundancy for the distribution system. the grey wolf family mainly consists of four different kinds of members, starting with the head of the group commonly known as the alpha wolf (α), which is the leader of the family and responsible for the decision making. the next member is known as the beta wolf (β). it follows the order of the alpha wolf and commands the other wolves. the third kind is known as the delta wolf (δ) which follows the commands given by the alpha and beta wolves. the last member of the group is the omega wolf (ω). the omega wolves are dominated by all the above three types of wolves. the hunting activity of grey wolves follows three basic steps. the first step is the tracking of the desired prey, the next step is the encircling of the prey, and the last step is harassing and attacking the prey. mathematically, the hunting process of the prey starts with the alpha (α), beta (β), and delta (δ) wolves, while the omega (ω) wolves only follow the instructions provided by the three leaders and update their positions according to them. the following mathematical equations describe the encircling behavior of the grey wolves [20]. d � eb fgh �i�j � g �i�e and g�i � 1� � kgh�i� � � ∙ dl (9) where x represents the position of the grey wolf, xp represents the position of the prey and t presents the current iteration. the co-efficient vector parameters, a and c, can be determined by: � � 2m ∙ n� � m & b � 2 ∙ n� (10) m � 2 � 2 o p�qrst (11) where a is a linearly decreasing component from 2 to 0, t is the current iteration, tmax is the maximum number of iterations, and r1 and r2 are two random values between 0 and 1. when the searching and tracking of the prey location is completed by the alpha, beta, and delta wolves, they lead the omega wolves to surround the prey. by assuming the prey location, the best three solutions are stored for updating the position of the other grey wolves in the group. the equation for updating the grey wolf position is: g�i � 1� � ouvw uxwuy= t (12) where each position of x1, x2, and x3 can be updated as: zg� � |g\ � �� ∙ d\|g� � eg] � �� ∙ d]eg= � |g^ � �= ∙ d^| (13) zd\ � |b� ∙ g\ � g|d] � eb� ∙ g] � ged^ � |b= ∙ g^ � g| (14) the binary conversion of the grey wolf technique can be obtained by the sigmoid conversion of the position vectors presented in [21]. the updated position of the grey wolves in the binary format can be represented by:. g�i � 1� � �1,�" c_ � n=0,otherwise (15) where r3 is a random number in [0,1] and sf represents the sigmoid function and can be written as: c_ � �� w `abc d�e ofvgfxgfyy de.hti (16) the flowchart of the proposed bgwo technique is presented in figure 2 and the steps to find the optimal pmus along with their placement locations are explained below: step 1: initialize the total population of the grey wolves, the maximum number of iterations (max_iter), and a & c parameters. step 2: then randomly initialize the position of pmus and calculate the objective function value for each alpha wolf solution. step 3: update the three searching agents and compute xα, xβ, and xδ using (13). step 4: update the position of each wolf with (15) after converting it into binary form. step 5: repeat step 2 to step 4 up to the max_iter. finally, the xα gives the optimal pmu numbers along with its optimal positions. fig. 2. flowchart of the proposed bgwo for the opp problem. engineering, technology & applied science research vol. 10, no. 6, 2020, 6494-6499 6497 www.etasr.com priyadarshini & panigrahi: optimal allocation of synchrophasor units in the distribution network … iv. results and discussion the proposed bgwo was implemented on several ieee test node feeders including ieee -13, -33, -37, and -123 node systems to solve the pmu placement problem using the matlab 2019 version. the proposed technique is simulated considering two conditions: under normal operation and under a single pmu loss. in this paper the channel limit is considered to be fixed for the optimal placement of pmus and it is based on the maximum branches connected to a node in the feeder network. therefore the maximum channel limit is set to 5 for all the test feeders except the ieee 33 node test feeder where the maximum channel is considered as 4. the value of each parameter used in the simulation is given in table i. table ii shows the minimum pmus required for the solution of the opp problem along with their locations and csoi value. the results obtained under normal operating conditions satisfy the observability criterion. the results show that a total of 6 pmus are required for the ieee 13 system. the basic structure of the network is given in figure 3. table i. values of considered parameters parameters values population taken 50 to 200 maximum iteration number 300 weight value for the measurement redundancy (w1) [18] 0.01 weight value for the number of observable nodes (w2) [18] -2 table ii. results of the opp problem with csoi value under normal operation test node feeders pmu locations csoi optimal number of pmus ieee-13 3,4,5,8,9,10 23 6 3,4,6,8,9,10 22 2,4,5,8,9,10 22 2,4,5,8,9,11 21 2,4,6,8,9,11 20 ieee-33 2,4,8,11,14,17,21,24,26,29,32 34 11 2,5,8,11,14,17,21,24,27,29,32 34 2,5,8,11,14,17,21,24,27,30,32 34 2,5,8,11,14,17,21,24,26,29,32 34 2,5,8,11,14,17,21,24,27,30,33 33 ieee-37 2,3,6,9,12,15,19,22,28,30,33,35 47 12 1,3,6,9,12,15,19,22,28,30,33,35 46 2,3,6,9,12,15,19,22,29,30,33,35 46 1,3,6,9,12,15,19,22,29,30,33,35 45 ieee123 1,3,5,8,14,15,19,21,23,25,27,30,31,36, 38,40,42,45,47,51,53,55,58,60,63,65,67 ,70,74,76,78,82,84,87,89,91,93,95,97, 100,103,106,108,110,113 162 45 1,3,5,8,14,15,19,21,23,25,27,30,31,36, 38,40,42,45,47,51,52,55,58,60,63,65,67 ,70,72,74,78,82,84,87,89,91,93,95,97, 100,103, 106,108,110,113 162 for the ieee 33 test node feeder as shown in figure 4, 4 sets of placement locations have been obtained with a maximum csoi of 34 by reducing the number of pmus to 11. similarly, 12 pmus with a maximum of 47 csoi have been obtained for the ieee 37 node system (figure 5). to verify the efficiency, a large size ieee 123 test node feeder network has also been considered. the ieee 123 test feeder has 123 nodes containing several switches. here, there are 119 nodes in the network and the basic topology is given in figure 6. the proposed technique has given 45 pmus obtained with a maximum csoi limit of 162 by solving the opp problem. the convergence graphs of all the four test feeders are shown in figure 7 over a maximum of 300 iterations. fig. 3. schematic diagram of the ieee 13 node test feeder. fig. 4. schematic diagram of the ieee 33 node test feeder. fig. 5. schematic diagram of the ieee 37 node test feeder. fig. 6. schematic diagram of the ieee 123 node test feeder. engineering, technology & applied science research vol. 10, no. 6, 2020, 6494-6499 6498 www.etasr.com priyadarshini & panigrahi: optimal allocation of synchrophasor units in the distribution network … fig. 7. convergence graph of all the ieee test node feeders under normal condition. the opp solutions under a single pmu loss are given in table iii. it can be observed that the numbers of pmus in this case are increasing twice than the normal operating condition except for the ieee 13 node system. the condition to maintain complete observability during the single pmu loss is to observe each node by two pmus. therefore, in order to ensure that the feeder networks remain observable, the obtained results are quite larger than the normal condition. for the ieee-13 node test feeder, the number of pmus obtained is the same as the total number of nodes in the system. any further reduction in the obtained solution fails to satisfy the full observability criterion. therefore it is not included in the tabulation. but except the ieee-13 system all other feeder networks have given smaller numbers of pmus. table iii. results of the opp problem with csoi values under a single pmu loss test node feeders optimal number of pmus csoi ieee-33 24 70 ieee-37 31 90 ieee-123 97 282 a comparative analysis of the opp solution between the proposed approach and previously developed methods is presented in table iv. it has been observed that only the conventional method is implemented to solve the placement problem for the distribution network. as these methods have the disadvantage of finding local minima for large networks, it is therefore advised to opt for heuristic methods over conventional methods. from the comparison, it has been observed that the number of pmus obtained from the proposed method is similar, but the csoi values are different. the results have either equal or higher csoi value. the computational time obtained from each feeder network is given in table v and the convergence plots are shown in figure 8. table iv. comparative results under normal operation methods test feeders with their csoi ieee-13 ieee-33 ieee-37 ieee-123 proposed 6 (23) 11 (34) 12 (47) 45 (162) binary ilp [3] 11 (na) binary ilp [4] 11 (na) 45 (na) hybrid ilp [5] 11 (34) 45 (162) linear programming [22] 6 (16) 12 (43) 48 (148) ilp [23] 17 (na) fig. 8. convergence graphs for the ieee-33, -37, and -123 feeder networks under a single pmu loss condition. table v. computational time test node feeders normal operating condition (s) single pmu loss (s) ieee-13 1.76 1eee-33 2.23 2.31 ieee-37 2.38 2.55 ieee-123 27.42 27.71 these solutions are consistent when compared with the prior studies. hence, it has been proved that the proposed metaheuristic based technique is capable to solve the pmu placement problem while achieving full observability with maximum measurement redundancy for the distribution network. v. conclusion a binary gwo 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[23] v. tran, h. zhang, and v. nguyen, "optimal pmu placement in multiconfiguration power distribution networks," in proceedings of the 2016 4th international conference on electrical & electronics engineering and computer science (iceeecs 2016), dec. 2016, pp. 508–514, https://doi.org/10.2991/iceeecs-16.2016.104. engineering, technology & applied science research vol. 7, no. 2, 2017, 1460-1463 1460 www.etasr.com pakdel and jalilzadeh: a novel neutral point clamped full-bridge topology for transformerless… a novel neutral point clamped full-bridge topology for transformerless photovoltaic grid-connected inverters majid pakdel department of electrical engineering university of zanjan zanjan, iran pakdel@znu.ac.ir saeid jalilzadeh department of electrical engineering university of zanjan zanjan, iran jalilzadeh@znu.ac.ir abstract—this paper presents a novel neutral point clamped fullbridge topology for transformerless photovoltaic grid-tied inverters. transformerless grid-connected inverters have been used widely in recent years since they offer higher efficiency and lower costs. ground leakage current suppression is the main issue which should be considered carefully in transformerless photovoltaic grid-connected inverters. among different methods used to decline ground leakage current, neutral point clamped (npc) topologies are considered more useful and effective. in npc topologies, the short-circuited output voltage at the freewheeling period is clamped to the middle of the dc bus voltage. therefore, the common-mode voltage (cm) will be constant at the whole switching period. various npc topologies such as h6 [1], hb-zvr [2], oh5 [3], and pn-npc [4] have been proposed. in this paper, a novel npc topology is proposed which has lower power losses and higher efficiency over previous topologies. furthermore, the proposed npc topology exhibits a similar ground leakage current with the pn-npc topology. the proposed npc topology is analyzed theoretically using simulation studies and an experimental prototype is provided to verify theoretical analysis and simulation studies. keywords-common-mode voltage (cmv); grid-connected inverter; ground leakage current; neutral point clamped (npc) topology; photovoltaic (pv) generation system i. introduction due to the limit reservation of fossil fuels such as oil, coal, gas, etc. tendency to exploiting of renewable energy resources such as solar and wind energies have been growing rapidly worldwide. with recent reduction in prices of photovoltaic (pv) array modules and due to the excessive advancement of power electronics devices and technologies, grid-connected pv inverters have been playing an important role in distributed generation systems. most of pv grid-connected inverters are designed with galvanic isolation using a bulky low frequency transformer connected to the grid voltage. nevertheless of not flowing ground leakage current in a grid-tied inverter with the galvanic isolation, however, the total price and space required to the grid-connected inverter will be very high as well as its efficiency will be very low. to overcome these drawbacks, transformerless grid-tied inverters have been introduced. among the different methods used to decline ground leakage current, neutral point clamped (npc) topologies are considered more useful and effective. in npc topologies, the short circuited output voltage at the freewheeling period is clamped to the middle of the dc bus voltage. therefore, the commonmode voltage (cm) will be constant at the whole switching period. various npc topologies such as h6 [1], hb-zvr [2], oh5 [3], and pn-npc [4] have been proposed. various topologies have been proposed for the reduction of ground leakage current in transformerless grid-tied inverters [5-19]. in this paper, a novel npc topology is proposed which has lower power losses and higher efficiency over previous topologies. furthermore, the proposed npc topology exhibits similar ground leakage current with the pn-npc topology. the proposed npc topology is analyzed theoretically using simulation studies and an experimental prototype is provided to verify theoretical and simulation studies. the main disadvantage of a transformerless grid-tied inverter is that ground leakage current is produced because of commonmode voltage variations in switching periods. the common-mode and differential-mode in a transformerless gridtied inverter are defined as follows [6]: )vv(v bnancm  2 1 (1) bnandm vvv  (2) therefore, we have the following equations [6]: dmcman vvv  2 1 (3) dmcmbn vvv  2 1 (4) furthermore, using the thevenin’s theorem, the commonmode (cm) voltage equivalent circuit which produces the ground leakage current can be constructed, from which the total cm voltage is calculated as follows [6]: )( 2 ab abdm cmtcm ll llv vv    (5) engineering, technology & applied science research vol. 7, no. 2, 2017, 1460-1463 1461 www.etasr.com pakdel and jalilzadeh: a novel neutral point clamped full-bridge topology for transformerless… usually, la = lb, therefore, the following relation is satisfied: .)( 2 1 constvvvv bnancmtcm  (6) leakage current standard according to vde 0126-1-1 is depicted in table i. table i. leakage current standard according to vde 0126-1-1 leakage current value (ma) disconnection time (s) 30 0.3 60 0.15 100 0.04 ii. neutral point clamped full-bridge topologies in neutral point clamped (npc) full-bridge topologies, the short circuited output voltage at freewheeling period is clamped to the middle of the dc bus voltage. therefore, the commonmode (cm) voltage will be constant in the whole switching period. the h6 [1] topology consists of two switches and a bidirectional branch with a capacitive divider and two diodes which clamp the cm voltage to the half of input dc voltage. in this topology, the leakage current suppression is only dependent to the turn on speed of clamping diodes. a main drawback of this topology is its higher conducting losses. since, the inductor current flows through four switches in active mode. another npc full-bridge topology with ac bypass is the hb-zvr topology [2]. in this topology, the short circuited output voltage at the freewheeling period is clamped to the middle of the dc bus voltage using a diode rectifier and a bidirectional switch. to prevent short circuiting of the lower capacitor in the capacitive divider, a diode is added. neutral point clamping condition is provided by short circuiting of inverter output in freewheeling period. the main drawback of this topology is that clamping using a diode is done when the freewheeling voltage is greater than the middle point of input dc bus. therefore, the variations of cm voltage in reverse condition will happen. in case of the oh5 topology [3], the main disadvantage of this topology is that the inductor current flows through three switches in active mode; therefore, there will be more conducting losses. the last npc topology is the pn-npc topology [4]. in this topology, two switching cells i.e. positive neutral point clamped (p-npc) cell and negative neutral point clamped (n-npc) are combined to make the pnnpc topology. the operation principle of pn-npc topology is similar to h6 topology. the cm voltage is kept constant at half of the input dc voltage. the main drawback of this topology is the existence of high number of switches and higher conductive losses since, in the worst condition the inductor current flows through four switches in the active mode. iii. proposed neutral point clamped full-bridge topology a variant npc full-bridge topology with its modulation strategy is proposed in this paper. the proposed topology and the control circuit for generating the drive signals are illustrated in figures 1 and 2. the main idea is clamping the short circuit output voltage at the freewheeling period to the middle of the dc input voltage. the control and modulation strategy for triggering the power switches is as follows: during the positive half cycle, the power switches q1 and q4 are turned on and turned off with switching frequency (q2, q3 and q5 are off). when both q1 and q4 are turned off, the power switch q6 is turned on and vice versa i.e. while q1 and q4 are turned on, q6 is turned off (with the switching frequency). fig. 1. proposed single phase transformerless npc topology fig. 2. control and modulation circuit of proposed npc topology therefore, in active mode (during positive half cycle) the current flows in the route q1-l1-vg-l2-q4. during the freewheeling period, the current flows in the route q6-l1-vgl2-d5. as a result, the cm voltage is clamped to the half of the dc input voltage. therefore the ground leakage current is decreased significantly. during the negative half cycle, the power switches q2 and q3 are turned on and turned off with switching frequency (q1, q4 and q6 are off). when both q2 and q3 are turned off, the power switch q5 is turned on and vice versa i.e. while q2 and q3 are turned on, q5 is turned off (with switching frequency). therefore, in active mode (during negative half cycle) the current flows in the route q3-l2-vgl1-q2. during the freewheeling period, the current flows in the route q5-l2-vg-l1-d6. as a result, the cm voltage is clamped to the half of input dc voltage. therefore, the ground leakage current is declined significantly. the analysis of the cm equivalent circuit for the proposed topology to obtain the cm voltage which is defined in (6) as the sum of output terminal voltages to the npc, the following relation is satisfied: engineering, technology & applied science research vol. 7, no. 2, 2017, 1460-1463 1462 www.etasr.com pakdel and jalilzadeh: a novel neutral point clamped full-bridge topology for transformerless… az bz cm v +v v = (7) 2 the cm voltage related to the positive, negative and neutral vectors can be portrayed as follows: bz dc dcaz cm v +0 vv +v positive: v = = = (8) 2 2 2 bz dc dc dcaz cm (9) v /2+v /2 vv +v neutral: v = = = 2 2 2 bz dc dcaz cm (10) 0+v vv +v negative:v = = = 2 2 2 as illustrated in equations (8) to (10), the cm voltage remains constant in different switching conditions. therefore, a very small ground leakage current should be expected to flow through pv stray capacitors. iv. simulation results the proposed topology and control strategy were tested by simulation analysis with the parameters illustrated in table ii. load current, the voltage measured between the grid terminal and ground (leakage voltage) and the leakage current are shown in figures 3-5 respectively. as shown, the load current is very close to a sinusoidal waveform which leads to a low dv/dt. it means that the leakage current will be low as depicted in the figure 5. therefore, the maximum leakage current is below 100 ma that comply with the standard din vde 01261-1 as pointed in table i. v. experimental results an experimental prototype of the proposed grid tied inverter was made and its operation was tested as depicted in figure 6. the inverter output voltage and its ground leakage current are shown in figure 7. as illustrated in figure 7, the ground leakage peak current same as the simulation result is below 100 ma that comply with the standard din vde 01261-1 mentioned in table i. vi. conclusion a novel neutral point clamped full-bridge topology was proposed for transformerless photovoltaic grid-tied inverters. transformerless grid-connected inverters have been using widely nowadays since, they offer higher efficiency and lower economic cost. ground leakage current suppression is the main issue that should be considered in transformerless photovoltaic grid-connected inverters. different methods have been employed to reduce ground leakage current in grid tied inverters. neutral point clamped (npc) topologies are considered more useful and effective. in npc topologies, the short-circuited output voltage at the freewheeling period is clamped to the middle of the dc bus voltage. therefore, the common-mode voltage (cm) will be constant at the whole switching period resulting to a very small ground leakage current. the proposed npc topology exhibits a similar ground leakage current with the pn-npc topology. the proposed npc topology was tested using simulation studies and an experimental prototype was also implemented to verify the results. table ii. simulation circuit parameters circuit parameters values c1 10 µf c2 10 µf l1 2.2 µh l2 2.2 µh c3 4.7 µf rg 1 ohm cpv 1 nf fsw 50 khz fig. 3. load current fig. 4. leakage voltage fig. 5. leakage current engineering, technology & applied science research vol. 7, no. 2, 2017, 1460-1463 1463 www.etasr.com pakdel and jalilzadeh: a novel neutral point clamped full-bridge topology for transformerless… fig. 6. experimental setup for the proposed grid tied inverter fig. 7. inverter output voltage and its ground leakage current references [1] r. gonzalez, j. lopez, p. sanchis, l. marroyo, “transformerless inverter for single-phase photovoltaic systems”, ieee transactions on power electronics, vol. 22, no. 10, pp. 693-697, 2007 [2] t. kerekes, r. teodorescu, p. rodríguez, g. vázquez, e. aldabas, “a new high-efficiency single-phase transformerless pv inverter topology”, ieee transactions on industrial electronics, vol. 58, no. 1, pp. 184191, 2011 [3] h. xiao, s. xie, y. chen, r. huang, “an optimized transformerless photovoltaic grid-connected inverter”, ieee transactions on industrial electronics, vol. 58, no. 5, pp. 1887-1895, 2011 [4] l. zhang, k. sun, l. feng, h. wu, y. xing, “a family of neutral point clamped full-bridge topologies for transformerless photovoltaic grid-tied inverters”, ieee transactions on power electronics, vol. 28, no. 2, pp. 730-739, 2013 [5] d. barater, e. lorenzani, c. concari, g. franceschini, g. buticchi, “recent advances in single-phase transformerless photovoltaic inverters”, iet renewable power generation, vol. 10, no. 2, pp. 260273, 2016 [6] m. islam, s. mekhilef, m. hasan, “single phase transformerless inverter topologies for grid-tied photovoltaic system: a review”, renewable and sustainable energy reviews, vol. 45, pp. 69-86, 2015 [7] m. victor, f. greizer, s. bremicker, u. hübler, “method of converting a direct current voltage from a source of direct current voltage, more specifically from a photovoltaic source of direct current voltage, into a alternating current voltage”, u.s. patent 7,411,802, 2008 [8] s. christoph, k. jurgen, “inverter for transforming a dc voltage into an ac current or an ac voltage”, europe patent 1, no. 369, p. 985, 2003 [9] w. yu, j. s. j. lai, h. qian, c. hutchens, “high-efficiency mosfet inverter with h6-type configuration for photovoltaic nonisolated acmodule applications”, ieee transactions on power electronics, vol. 26, no. 4, pp. 1253-1260, 2011 [10] b. yang, w. li, y. gu, w. cui, x. he, “improved transformerless inverter with common-mode leakage current elimination for a photovoltaic grid-connected power system”, ieee transactions on power electronics, vol. 27, no. 2, pp. 752-762, 2012 [11] b. gu, j. dominic, j. s. lai, c. l. chen, t. labella, b. chen, “high reliability and efficiency single-phase transformerless inverter for gridconnected photovoltaic systems”, ieee transactions on power electronics, vol. 28, no. 5, pp. 2235-2245, 2013 [12] s. bremicker, f. greizer, m. victor, “inverter, more specifically for photovoltaic plants”, u.s. patent 7.843,714, 2010 [13] m. xu, l. zhang, y. xing, l. feng, “a novel h6-type transformerless inverter for grid-connected photovoltaic application”, 7th ieee conference on industrial electronics and applications (iciea), pp. 5863, 2012 [14] j. wang, b. ji, j. zhao, j. yu, “from h4, h5 to h6—standardization of full-bridge single phase photovoltaic inverter topologies without ground leakage current issue”, ieee energy conversion congress and exposition (ecce), pp. 2419-2425, 2012 [15] j. m. shen, h. l. jou, j. c. wu, “novel transformerless grid-connected power converter with negative grounding for photovoltaic generation system», ieee transactions on power electronics, vol. 27, no. 4, pp. 1818-1829, 2012 [16] d. dong, f. luo, d. boroyevich, p. mattavelli, “leakage current reduction in a single-phase bidirectional ac–dc full-bridge inverter”, ieee transactions on power electronics, vol. 27, no. 10, pp. 4281-4291, 2012 [17] l. zhang, k. sun, y. xing, m. xing, “h6 transformerless full-bridge pv grid-tied inverters”, ieee transactions on power electronics, vol. 29, no. 3, pp. 1229-1238, 2014 [18] w. cui, b. yang, y. zhao, w. li, x. he, “a novel single-phase transformerless grid-connected inverter”, 37th annual conference on ieee industrial electronics society, pp. 1126-1130, 2011 [19] s. v. araujo, p. zacharias, b. sahan, “novel grid-connected nonisolated converters for photovoltaic systems with grounded generator», ieee power electronics specialists conference, pp. 58-65, june, 2008 microsoft word 4-416-ce.doc engineering, technology & applied science research vol. 4, no. 2, 2014, 612-617 612 www.etasr.com habibi et al.: modeling a small punch testing device modeling a small punch testing device samir habibi djillali liabes university of sidi bel abbes, algeria habibismr@yahoo.com abdelkader ziadi university center of ain témouchent, algeria ziadiaek@yahoo.com abdelkader megueni djillali liabes university of sidi bel abbes, algeria habibismr@yahoo.com abstract— a small punch test of a sample in miniature is implemented in order to estimate the ultimate load of crmov ductile steel. the objective of this study is to model the ultimate tensile strength and ultimate load indentation according to the geometrical parameters of the spt using experimental data. a comparison of the model obtained with the two models (european code of practice and method of norris and parker) allows the design and dimensioning of an indentation device that meets the practical constraints. implemented as a matlab program, allows the investigation of new combinations of test variables. keywords-small punch test; experiments design; constraints; modeling i. introduction the small punch test (spt) is a method considered in practice as non-destructive because of the very small size of the specimen used [1-4]. the need to test components without compromising the performance of the overall system (e.g. thermal or nuclear power plants), or the need to reduce the size of the area tested (e.g. heat affected zones, coating materials, etc.) makes the characterization through conventional mechanical tests virtually impossible [4-6]. spt miniature tests consists of a specimen (0.25 to 0.50 mm thick and 3 to 10 mm in size) which is punched by a ball (usually 1 mm diameter to 2.5 mm) [7]. among the previous studies on the impact of different factors of spt, the normative method of european practice [8] refers to using the ratio of the tensile stress on the maximum load of the indenter as a function of specimen thickness, diameter of the sphere indenter and the lower die of indenter. the norris and parker approach [9] was based on the three variables of the indentation device. due to the lack of an experimental standard specifying the conditions and parameters chosen for the design of the necessary equipment, we mention the values of the three variables frequently cited in international publications which are (4, 2.5, 0.5) [10-13], (4-5, 2.5, 0.5) [1315], (3.8, 2.54, 0.5) [16] and (1.5, 1, 0.25) [17-18]. the dimensions of spt devices commonly used are shown in table i. however certain technical constraints linking variables should be considered (e.g. the diameter of the lower die is greater than the diameter of the sphere to indent and thickness of the sample) [9]. it is thus attempted in this paper to perform an optimization of the search space by fixing a gap of 0.5*e-3 between the compared models taking into account the intervals of variables and their constraint expression by a mathematical algorithm associated with a certain experiment. at first, the experimental setup is presented. then, we proceed to develop a full factorial design on the ductile steel studied. finally, based on a comparative study, an optimization of the geometric variables of the spherical indentation device is presented. ii. experimental procedure the spt device is adapted to a universal testing machine (instron model 5582) equipped with a load cell of 20 kn with calibrated tests. the test is performed to control the movement at a speed of 0.2 mm/min. a video extensometer is used to determine the load-displacement curve (f-d). the indenting tool comprises of a rigid lower die and a threaded upper die and both matrices are perforated to allow the passage of the punch, in order for the specimen to be deformed until rupture, using a ball head punch (1 or 2.5 mm in diameter, respectively for the two types of specimens required) as shown in figure 1. specimens routinely used in this test are of square shape (10x10 mm2) and 0.5 mm thick or 3 mm discs 0.25 mm thick (specimens commonly used in transmission electron microscopy). four nuances of ductile steel specimens of crmov are used in this study. fig. 1. schematic illustration of the dies used in the spt apparatus. the probable maximum deformation is limited by the diameter of the lower die. some researchers suggest that the dimensions of the lower hole should satisfy the following expression: 2a d t  (1) engineering, technology & applied science research vol. 4, no. 2, 2014, 612-617 613 www.etasr.com habibi et al.: modeling a small punch testing device according to the literature, the design of indentation device must comply with (1) for limiting the frictional forces resulting from the contact between the specimen and the lower die. table i. common geometric dimensions of spt devices pastille d =3 mm square specimen 10 10 mm2 pastille d = 8 mm pastille d= 6.40mm a = 2*r 1.5 4-5 4.0 3.80 d= 2*p 1.0 2.5 2.5 2.50 t 0.10-0.25 0.5 0.5 0.5 iii. modeling of the device through experimental design in order to acquire a mathematical model, the response σm/pmax, which characterizes the behavior of the phenomenon studied according to factors r, p, t should be expressed. the high level (+1) and down (-1) of each factor are shown in table ii. processing results are obtained using multiple linear regression and variance analysis [18] as shown in table iii. a full factorial design (order 23) is performed by estimating the coefficients of the model using yates algorithm [20]. the results are shown in table iv. table ii. choice of levels of factors table iii. indication of responses maxm p p r t tests 3.25 0.5 0.75 0.2 1 1.30 0.5 0.75 0.5 2 3.96 0.5 2 0.2 3 1.58 0.5 2 0.5 4 1.08 1.25 0.75 0.2 5 0.43 1.25 0.75 0.5 6 1.32 1.25 2 0.2 7 0.53 1.25 2 0.5 8 table iv. presentation of design of experiment 23 ytest x1.x3 x2. x3 x1.x2 x3 x2 x1 average tests 3.25 +1 +1 +1 -1 -1 -1 +1 1 1.30 -1 +1 -1 -1 -1 +1 +1 2 3.96 +1 -1 -1 -1 +1 -1 +1 3 1.58 -1 -1 +1 -1 +1 +1 +1 4 1.08 -1 -1 +1 +1 -1 -1 +1 5 0.43 +1 -1 -1 +1 -1 +1 +1 6 1.32 -1 +1 -1 +1 +1 -1 +1 7 0.53 +1 +1 +1 +1 +1 +1 +1 8 8 8 8 8 divisor a13 = 0.360 a23 = 0.082 a12 = 0.070 a3= 0.84 a2= 0.16 a1= 0.72 a0 = 1.68 effects we then obtain the model coefficients and the average effects of factors x1, x2, x3 calculated. the polynomial model is written as: 0 . . . . . .i i ij i j ijk i j ky a a x a x x a x x x      (2) the treatment of the experimental design is to estimate the coefficients of the mathematical model p and n residues using the method of least squares. so the model of the studied system is expressed as follows: max 1.682 0.721. 0.164. 0.842. 0.070. . 0.082 . 0.360. .m t r p t r r p t p p         (3) a. validation of the model the estimate of the mathematical model requires the calculation of the differences between the measured and the calculated values for each test by the following formula: m a x m a x ( ) ( )m mi i c a lc u lée p p     (4) residues responses are shown in table v. table v. estimate of residues 1 2 3 4 5 1 mechanical ratio observed predicted obs-pred conf.int (±) 2 1 3.25 3.28625 -0.0362499 1.21863 3 2 1.3 1.26375 0.0362499 1.21863 4 3 3.96 3.92375 0.0362499 1.21863 5 4 1.58 1.61625 -0.0362499 1.21863 6 5 1.08 1.04375 0.0362504 1.21863 7 6 0.43 0.46625 -0.0362502 1.21863 8 7 1.32 1.35625 -0.0362498 1.21863 9 8 0.53 0.49375 0.0362497 1.21863 10 n=8 q2 = 0.940 cond. no.= 1.0000 11 df=1 r2 = 0.999 y-miss = 0 12 r2adj. = 0.993 rsd = 0.1025 13 conf. lev.= 0.95 deviations residues explains the good dispersion of the points which means that the model obtained is acceptable. b. significance test of the model coefficients [21] an estimator of the common variance of the residuals is obtained. this estimator is given by: 2 21 is e n p    (5) where n is the number of experiments and p is the number of coefficients in the mathematical model. for the estimation and significance of the effects of coefficients, the student's t test was applied. 1) descriptive quality model: the coefficient of determination of descriptive quality r2 is 2 0.999r  (6) level (-1) (+1) type symbols and units factors 0.20 0.50 quantitatif t (mm) thickness 0.75 2.00 quantitatif r (mm) lower die 0.50 1.25 quantitatif p (mm) punch engineering, technology & applied science research vol. 4, no. 2, 2014, 612-617 614 www.etasr.com habibi et al.: modeling a small punch testing device 2) quality of predictive model: the coefficient q2 predictive quality of the model is 2 0.940q  (7). thus, the mathematical model is acceptable and allows prediction responses. figure 2 highlights the predominance of the role of the spherical indent size factor (p) that appears larger than the others in the histogram of the contributions of different factors. thus, we can see that the indent factor (p) and thickness (t) explain 70% of the variation. both factors explained the 70% of the variation of the response. the contribution of the diameter of the lower die is hidden due to the small value of 07.41%. fig. 2. histogram of the three factors and their combined contributions. 3) graphical analysis of results: the graphical analysis of the results is shown in figure 3. the blue zone, that is the lower part of the graph, corresponds to minor influence parameters. the slight variation of the response does not exceed 0.95 mm-2. despite the magnitude of the radius of the indent (1.25 mm), the effect of the size of the matrix lower than 0.8 mm is not significant. all areas (yellow, orange and red) is in the form of a "triangle" with a pointed head which is a critical point, where all the data points converge to. this means that the behavior of the studied material passes another different state thereof, (a plastic deformation or rupture). we also note that the response variation in this area is even greater compared to the previous case, as we arrive to a maximum ratio of 2.75 mm-2, which comes from the interaction of two parameters , i.e. the increase of the radius of the matrix up to 2 mm and of the radius of the lower indent of at least 0.55 mm . same conclusion is drawn for the next area (greater variation, maximum ratio of 2.49 mm-2, which comes from the interaction of two parameters , i.e. the increase the radius of the matrix up to 1.6 mm and the decrease of the thickness of the sample of at least 0.2 mm). (a) (b) (c) fig. 3. contours response (iso-response) versus r, p, t (a) response vs (r,p); (b) response vs (r,t); (c) response vs (p,t). the analysis of the third curve shows that the simultaneous reduction of both parameters allows us to note that the variation of the response is inversely proportional, that is to say, the simultaneous decrease in the thickness and radius of the indent can generate a maximum increase in the response that reaches 3.27 mm-2 for a thickness of 0.25 mm and an indent radius of 0.6 mm. it is clear that a simultaneous increase in the thickness and the indent radius results to the variation of the response being alternative and unstable. we found that, for a constant thickness, the increase in the radius of the indent causes decreased response. for an indent constant radius, increasing the thickness leads to an increase in the response. indeed, the simultaneous increase in both parameters results in a compensation between them, one decreases and the other increases the response, which explains the curvature areas. iv. optimization of admissible domain values (r, p, t) for which the absolute value of the difference noted res1 between the model proposed by experience (r1) and the model of the european code (r2) (and res2 between r1 and norris and parker model r3) is less than 0.5*e-3 (three near significant numbers). values are determined (r, p, t) in order to acquire res1 and res2 less than 0.5*e-3 (three near significant numbers) and that satisfy all the constraints to determine the permissible range. the constraint linking the combination of factors (r, p, t) is: r p t  (8) the research areas of the variables (r, p, t) are: 0 . 7 5 2 0 . 5 0 1 . 2 5 0 . 2 0 0 . 5 0 r p t             (9) a program in matlab was developed for calculating the permissible range. variable input arguments are respectively n and eps meaning the number of intervals of the variables (r, p, t) and the error imposed (eps=0.5*e-3). for fixed n, we have engineering, technology & applied science research vol. 4, no. 2, 2014, 612-617 615 www.etasr.com habibi et al.: modeling a small punch testing device (n +1)3 combinations of variables recorded in the output argument. the ultimate tensile stress and ultimate load were related to sample thickness, punch diameter, and die clearance by r1, r2, r3 expressing respectively the following three models studied: ● the model built by experience level: 1 1.682 0.721. 0.164. 0.842. 0.070. . 0.082. . 0.360. .r t r p t r r p t p       (10) ● the model expressed by the european code of practice 0.2 1.22 3.33. . .r r r t (11) where ksp: factor dimensional correlation with ksp = 1 [2, 10]. ● the model expressed by norris and š.d. j.d.parker 1 3 . ( 3 . 2 2 0 . 9 1 . 8 0 . 5 6 ) r t d a t     (12) v. results and discussion the calculation program gave the numerical results shown in tables vi and vii and the corresponding curves (figures 4 and 5). the variation curves (figures: 4 (a, b, c)) factors (r, p, t) depending on n intervals (n > = 40) define the research areas of the three variables as follows: 1 . 2 1 6 2 . 0 0 0 . 7 1 6 1 . 2 5 0 . 4 2 2 0 . 5 0 r p t             (13) similarly, the variation curves (figures: 5 (a, b, c)) delimit spaces more reduced following research: 1 . 1 5 8 2 . 0 0 0 . 7 3 6 1 . 2 5 0 . 2 9 7 0 . 5 0 r p t             (14) the results obtained by matlab show the convergence of the curves (figures 4 and 5) for n=35. the results of the models studied coincides with the third significant numeral. for practical experimental considerations, we propose a clearance die between 0.025 and 0.25. table vi. comparison between design experiments and european code of practice n rmin rmax pmin pmax tmin tmax 5 1.75 2 0.95 1.1 0.44 0.44 10 1.722 1.722 0.833 1 1.3 1.433 15 1.8 2 0.8 0.9 0.5 0.5 20 1.3 1.9 0.8 1 0.4 0.5 25 0.854 2 0.8125 1.25 0.425 0.475 30 1.267 1.957 0.733 1.172 0.427 0.5 35 1.265 2 0.72 1.25 0.429 0.5 40 1.23 2 0.73 1.25 0.423 0.5 45 1.261 2 0.756 1.25 0.425 0.5 50 1.286 2 0.729 1.25 0.426 0.5 55 1.259 2 0.722 1.25 0.422 0.5 60 1.216 2 0.716 1.25 0.424 0.5 65 1.238 2 0.734 1.25 0.425 0.5 70 1.239 2 0.717 1.25 0.426 0.5 table vii. comparison between design experiments and model of norris and parker (a) (b) (c) fig. 4. comparison of design of experiments and european code of practice (a) rmax, rmin vs n; (b) pmax, pmin vs n; (c) tmax, tmin vs n. n rmin rmax pmin pmax tmin tmax 5 2 2 1.1 1.1 0.44 0.44 10 1.305 1.305 1 1 0.3 0.3 15 1.38 2 1.1 1.1 0.38 0.44 20 1.276 2 0.776 1.21 0.31 0.5 25 1.167 2 0.781 1.25 0.312 0.5 30 1.224 1.914 0.784 1.25 0.303 0.458 35 1.338 2 0.83 1.25 0.297 0.491 40 1.167 2 0.788 1.25 0.3 0.5 45 1.233 2 0.756 1.25 0.302 0.5 50 1.158 2 0.749 1.25 0.298 0.5 55 1.167 2 0.736 1.25 0.3 0.5 60 1.174 2 0.754 1.25 0.297 0.5 65 1.16 2 0.746 1.25 0.298 0.5 70 1.167 2 0.739 1.25 0.3 0.5 engineering, technology & applied science research vol. 4, no. 2, 2014, 612-617 616 www.etasr.com habibi et al.: modeling a small punch testing device (a) (b) (c) fig. 5. comparison of design of experiments and norris and parker (a) rmax, rmin vs n; (b) pmax pmin vs n; (c) tmax, tmin vs n. vi. conclusion this work has enabled the modeling of small punch test through an experimental approach combined with the development of a computer program, based on the comparison of the models obtained with two previous models that served as references. the permissible ranges of the variables (r, p, t) proposed by the previous models were verified. a set of combinations of the variables r, p, t cited for numerous industrial application possibilities are given in tables viii and ix listed in the annex. references [1] g. e. lucas, g. r. odette, 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d’expériences, dunod, 2006 [20] m. pillet, les plans d’expérience par la méthode taguchi, editions d’organisation, 2001 [21] o. gaudoin, principes et méthodes statistiques, ensimag2ème année, inp grenoble, 2009 engineering, technology & applied science research vol. 4, no. 2, 2014, 612-617 617 www.etasr.com habibi et al.: modeling a small punch testing device annex table viii. combinations of test variables (plan of experience / european code of practice) r p t p + t abs( r1-r2) 1.326923076923077e+000 8.269230769230769e-001 4.5384615384+61538e-001 1.280769230769231e+000 4.464491361105827e-004 1.358974358974359e+000 8.846153846153846e-001 4.384615384615385e-001 1.323076923076923e+000 4.076666387792249e-004 1.455128205128205e+000 8.461538461538462e-001 4.538461538461538e-001 1.300000000000000e+000 4.714400510807959e-004 1.455128205128205e+000 9.038461538461539e-001 4.384615384615385e-001 1.342307692307692e+000 1.596450758211132e-004 1.487179487179487e+000 7.692307692307692e-001 4.846153846153846e-001 1.253846153846154e+000 3.588561039836735e-004 1.487179487179487e+000 1.038461538461538e+00 4.230769230769231e-001 1.461538461538462e+000 4.558314209741621e-004 1.519230769230769e+000 8.076923076923077e-001 4.692307692307692e-001 1.276923076923077e+000 4.024617061731961e-004 1.519230769230769e+000 9.615384615384616e-001 4.307692307692308e-001 1.392307692307692e+000 3.143993290599667e-006 1.551282051282051e+000 8.846153846153846e-001 4.461538461538461e-001 1.330769230769231e+000 3.469995577822793e-004 1.583333333333334e+000 9.807692307692308e-001 4.307692307692308e-001 1.411538461538462e+000 3.927997191666144e-005 1.615384615384615e+000 7.500000000000000e-001 5.000000000000000e-001 1.250000000000000e+000 4.242916498056193e-004 1.615384615384615e+000 8.653846153846154e-001 4.538461538461538e-001 1.319230769230769e+000 2.209377108854937e-004 1.647435897435897e+000 1.000000000000000e+000 4.307692307692308e-001 1.430769230769231e+000 4.173562455133117e-004 1.647435897435897e+000 1.173076923076923e+000 4.384615384615385e-001 1.611538461538462e+000 4.271211662808527e-004 1.679487179487180e+000 1.019230769230769e+000 4.307692307692308e-001 1.450000000000000e+000 1.129971355298132e-004 1.679487179487180e+000 1.096153846153846e+000 4.307692307692308e-001 1.526923076923077e+000 3.540596929840767e-004 1.711538461538462e+000 1.038461538461538e+000 4.307692307692308e-001 1.469230769230769e+000 4.455852458427057e-004 1.711538461538462e+000 1.057692307692308e+000 4.307692307692308e-001 1.488461538461539e+000 1.982211015507662e-004 1.711538461538462e+000 1.153846153846154e+000 4.384615384615385e-001 1.592307692307692e+000 4.047499885332373e-004 1.743589743589744e+000 1.192307692307692e+000 4.461538461538461e-001 1.638461538461538e+000 1.789344656100145e-004 1.807692307692308e+000 1.134615384615385e+000 4.384615384615385e-001 1.573076923076923e+000 1.563375008113432e-004 1.807692307692308e+000 1.211538461538462e+000 4.538461538461538e-001 1.665384615384616e+000 4.001535792800270e-004 1.839743589743590e+000 1.173076923076923e+000 4.461538461538461e-001 1.619230769230769e+000 4.849589176273428e-004 1.871794871794872e+000 1.230769230769231e+000 4.615384615384615e-001 1.692307692307692e+000 1.200892572432721e-004 1.903846153846154e+000 1.250000000000000e+000 4.692307692307692e-001 1.719230769230769e+000 4.290393902528500e-005 table ix. combinations of test variables (plan of experience / model norris and parker) r p t p + t abs( r1-r2) 1.262820512820513e+000 9.038461538461539e-001 3.230769230769231e-001 1.226923076923077e+000 3.019030383411003e-004 1.262820512820513e+000 9.230769230769231e-001 3.153846153846154e-001 1.238461538461539e+000 4.085191353456752e-004 1.423076923076923e+000 8.269230769230769e-001 4.461538461538461e-001 1.273076923076923e+000 1.508640411858053e-004 1.455128205128205e+000 1.038461538461538e+000 3.153846153846154e-001 1.353846153846154e+000 8.555087374340076e-005 1.455128205128205e+000 1.076923076923077e+000 3.076923076923077e-001 1.384615384615385e+000 4.378066387181745e-004 1.487179487179487e+000 1.115384615384615e+000 3.076923076923077e-001 1.423076923076923e+000 1.441483062560867e-004 1.551282051282051e+000 1.134615384615385e+000 3.153846153846154e-001 1.450000000000000e+000 3.931497210469814e-004 1.615384615384615e+000 1.153846153846154e+000 3.230769230769231e-001 1.476923076923077e+000 3.210561946248580e-004 1.615384615384615e+000 1.250000000000000e+000 3.230769230769231e-001 1.573076923076923e+000 3.118853190887672e-004 1.647435897435897e+000 1.134615384615385e+000 3.307692307692308e-001 1.465384615384615e+000 4.213653606355283e-005 1.679487179487180e+000 1.192307692307692e+000 3.307692307692308e-001 1.523076923076923e+000 4.685962219056483e-004 1.679487179487180e+000 1.211538461538462e+000 3.307692307692308e-001 1.542307692307692e+000 6.442938899375861e-005 1.679487179487180e+000 1.230769230769231e+000 3.307692307692308e-001 1.561538461538462e+000 2.718541483529569e-004 1.711538461538462e+000 1.115384615384615e+000 3.461538461538462e-001 1.461538461538462e+000 2.638983263698602e-004 1.743589743589744e+000 1.153846153846154e+000 3.461538461538462e-001 1.500000000000000e+000 3.247063243844162e-004 microsoft word etasr_v11_n2_pp6919-6929 engineering, technology & applied science research vol. 11, no. 2, 2021, 6919-6929 6919 www.etasr.com muhirwa et al.: markov chain monte carlo analysis of the variable-volume exothermic model for … markov chain monte carlo analysis of the variablevolume exothermic model for a continuously stirred tank reactor jean pierre muhirwa department of applied mathematics and computational science (amcs), nelson mandela african institution of science and technology tanzania (nm-aist) arusha, tanzania and department of mathematics, university of rwanda, college of science and technology (ur-cst), kigali, rwanda muhirwaj@nm-aist.ac.tz isambi sailon mbalawata research department african institute for mathematical sciences (aims) kigali, rwanda imbalawata@nexteinstein.org verdiana grace masanja department of applied mathematics and computational science (amcs) nelson mandela african institution of science and technology tanzania (nm-aist) arusha, tanzania verdiana.masanja@nm-aist.ac.tz abstract-in this paper, a variable-volume continuously stirred tank reactor (cstr) deterministic exothermic model has been formulated based on the reynold transport theorem. the numerical analysis of the formulated model and the identifiability of its physical parameters are done by using the least squares and the delayed-rejection adaptive metropolis (dram) method. the least square estimates provide the prior information for the dram method. the overall numerical results show that the model gives an insight in describing the dynamics of cstr processes, and 14 parameters of the cstr are well identified through dram convergence diagnostic tests, such as trace, scatter, autocorrelation, histograms, and marginal density plots. global sensitivity analysis was further performed, by using the partial rank correlation coefficients obtained from the latin hypercube sampling method, in order to study and quantify the impact of estimated parameters, uncertainties on the model outputs. the results showed that 7 among the 14 estimated model parameters are very sensitive to the model outcomes and so those parameters need to be handled and treated carefully. keywords-parameter identifiability; variable volume; exothermic; cstr; rtt; mcmc; dram i. introduction during the past decades, continuously stirred tank reactors (cstrs) have gained research momentum as important industrial and chemical production tools. for controlling the reactors, various methods have been proposed to tackle the complexity and the non-linearity operational behaviors that are present in the tank reactor during the production processes [1-6]. discussions about cstrs seem to be broad and range from general to specific purposes. for example, mathematical modeling and numerical simulations of two-phases which are gas-liquid flow in the cstr can be found in [7] and the fokker-plank equation was applied for a two-state stochastic cstr system in [8]. in [9], the robust feedback linearization of an isothermal cstr was conducted by using the mixed sensitivity synthesis and iteration approaches in the presence of uncertainties. a one state variable, temperature, of a non-isothermal cstr was analyzed by using proportional integral derivative (pid) and fuzzy logic controllers, and the results from simulations and temperature control show that fuzzy logic can be adopted as a good controller of the process compared with the pid controller [10, 17]. the effects of hydrodynamic shear on biogas production in the cstr using the metzner-otto method were analyzed and discussed in [11]. the bayesian approach was used in [12] as the sorption parameter identifiability tool. the research outputs showed that the bayesian inference is a more preferable method for the analysis of cstr experiments as per numerical identifiability as well as the sorption parameter identifiability. the efficient azo dye color identification in the cstr with the built-in bio-electrochemical system was developed for azo dye alizarin yellow r (ayr) which in turn can help in wastewater treatment [13]. authors in [14] investigated the performance of cstr as bioreactor for producing biohydrogen from water melon waste in the anaerobic digester. the lyapunov-based stochastic non-linear model predictive control was used in [15] to shape the state probability density functions in the cstr with the exothermic reaction k a b→ , where � is the reaction rate, � is the reactant and � is the product. the corresponding author: jean pierre muhirwa engineering, technology & applied science research vol. 11, no. 2, 2021, 6919-6929 6920 www.etasr.com muhirwa et al.: markov chain monte carlo analysis of the variable-volume exothermic model for … luenberger fuzzy observer with and without sliding modes, the walcott-zak fuzzy observer, and the utkin fuzzy observer were adopted and used as fault detection sensors of the cstr in [16]. a two state cstr stochastic model was studied and analyzed in [18] by using the approximate expectation maximization (aem) and bayesian algorithms. it was revealed that the bayesian algorithm is an effective method to be applied on the cstr's stochastic model since it provided more accurate parameter estimates compared with aem, and it is even more applicable for an unknown system with a small number of data sets. authors in [19] used monod and haldane kinetics methods to perform the stability analysis of a system that models the formation of biofilms inside the cstr during the waste-water treatment process. even though both methods performed well, still the monod kinetics provided biofilms formation in a shorter time compared to the opponent method. the effect of operating conditions on the cstr's performance with a saponification experiment was conducted in [20] and the results showed that the increase in conversion scale may depend on the increase in cstr's volume. the neural network approach was used in [21] in order to identify the dynamics of two states, namely the temperature and the concentration of the cstr's model, and reasonable and precise results were obtained. three-dimensional computational fluids dynamics (cfd) simulations were carried out [22] in order to identify the flow behaviors in the cstr. authors in [23] used the cascade control strategy to control the temperature of the exothermic cstr with a cooling jacket. the stability analysis of the system was investigated with the routh-hurwitz and argand diagram techniques. as a result, the cascade control was pointed out to be an efficient control method for the cstr processes. a modified cstr model for the neutralization process was studied and analyzed in [24]. this model has been used to assess the effects of strong acid (hcl) and strong base (naoh) on the flow rates of ionic concentrations [24]. firstorder and higher-order sliding mode observer methods were used in [25] in order to design and estimate states and unknown inputs of the cstr, and it was shown that higher-order sliding modes may be adopted to reduce the noise into the system compared with the first-order sliding mode. parameter estimation of non-linear chemical and biological processes with non-measured variables from a number of data sets was performed in [26] using the bayesian approach. furthermore, a mathematical model and simulation of reactors with the production experiment of hexane from benzene were conducted in [27] and the numerical investigation of phenol oxidation from waste-water inside a reactor was carried out in [28]. nonparametric and non-linear stochastic dynamical model along with the behavior analysis of a class of the single state isothermal cstr was also studied and analyzed in [29]. the adaptive method with recursive identification and the polynomial synthesis with placement of poles were applied on the cstr system to determine its dynamics, however this method provided inappropriate control responses and overshoots [30]. the problem of characterizing the global dynamics of a single state non-linear stochastic cstr system was addressed in [29] using the fokker-plank as the state probability distribution function, but the study of a several-state non-linear stochastic system is paramount as recommended in this article. in the same way, different types of reactors and types of reactions in the chemical engineering processes are widely defined, explained and described in [31]. the modeling and control of the cstr were also conducted based on a mixed logical dynamical model which resulted in a satisfactory performance of the tank [32]. in [33], the general model of the cstr was developed and the transient behavior for irreversible non-linear polymerization process in the cstr was studied and analyzed. chemical process hazards, causes and proposed measures of safety of batch and semi-batch processes were discussed in [34]. the dynamical behavior of the cstr through a single first order reaction was researched and analyzed in [35]. the limitations of cstrs' performance due to cooling jacket dynamics with both open and closed loops are well explained and discussed in [36]. authors in [37] performed multivariate character and stability analysis of irreversible exothermic cstrs. the signal flow diagram and the equilibrium states were determined by taking into consideration the first and the second-order reactions. often, the volume is treated as a constant [4, 25, 38, 39], however, in reality the tanks may expand and lead to variable volume. moreover, the parameters are randomly assumed and the estimation of physical parameters that are very influential in the system variation using mcmc methods is lagging behind. it is with these reasons this paper aims to treat the cstr volume as a variable and identify 14 cstr physical parameters. ii. model formulation the assumptions on the parameters and physical properties inside and outside the tank have been considered during model formulation and are adopted from [25, 38-40], except for the volume which is considered to be a variable. to depict the problem, the cstr dynamics are schematically illustrated using the cstr and the reynold transport theorem (rtt) diagrams. a. assumptions the cstrs under investigation assume perfect mixing to avoid spatial gradients of velocity, temperature, concentration and of other properties of the mixture. • the cstrs assume non-viscous liquid and gas phases which are frequently supplied in it and a static mixer which makes the shaft work produced by the stirring process to be negligible. • no pressure drop is taking place in the cstrs, i.e. cstrs work at a constant pressure. • kinetic energy, potential energy, and other forms of external energy are infinitesimally small compared to the heat exchange and the heat from the chemical reactions. • the wall is isolated and its temperature is negligible. only the heat exchange is channelled through the designed area. • the cstrs assume the volume variation. • the cstrs assume density � and specific heat capacitiy �� to be constants. engineering, technology & applied science research vol. 11, no. 2, 2021, 6919-6929 6921 www.etasr.com muhirwa et al.: markov chain monte carlo analysis of the variable-volume exothermic model for … • since there is negligible external stress acting on the system, it is assumed that there is also a negligible momentum on the system. b. formulation based on schematic diagrams presented in figures 1 and 2, considering the above listed assumptions, and according to the transport phenomena, mass and energy conservation, the variable-volume exothermic cstr model formulated is given by the system of equations (1): 1 1 ( ) 0 1 1 ( ) * 0 , ( ) , ( ) ( ) , ( ) ( ) , mean mean in c in out e r t t in e r t t c in p p c c c c c c c c p dv f f dt dc f c c k e c dt v dt f h k e c ua t t t t dt v c v c dt f ua t t t t dt v v c ρ ρ ρ − − − −  = −   = − −   − − = − + −   − = − +  (1) where vis the tank volume, fin = f is the feeding velocity, fout is the outlet velocity, cin is the feeding concentration, c is the mixture concentration, e is the activation energy, t is the temperature of the tank, tin is the feeding temperature, tmean is the reference temperature, h * is the reaction enthalpy, ρ is the density, cp is the heat capacity, u is the heat transfer coefficient, a is the cross-sectional area, tc is the cooling temperature, fc is the cooling velocity, vc is the jacket volume, inc t is the feeding coolant temperature, ρc is the coolant density, cp c is the jacket's heat capacity, and � � � � � � �� � �� � ����� � is the arrhenius equation [41], with � being the gas law constant and � the pre-arrhenius frequency factor. fig. 1. schematic diagram that describes the dynamics of cstr. fig. 2. schematic illustration of the rtt. iii. materials and methods a. markov chain monte carlo method the markov chain monte carlo (mcmc) is a numerical analysis method used as a statistical and bayesian technique to identify the complex ordinary differential equations' parameters that fit the dynamics of chemical and biological models [4244]. in this paper, the dram method is used to estimate 14 parameters of the model (1). the bayesian inference, qualified to be a very powerful statistical technique, has been widely used to identify the model's parameters � which are obtained after evaluating the parameters' posterior density ���/ ���,�� ,…,��"�, where ��� ,�� ,…, ��" are the measurement points of the chemical process. for the model (1), � � #$%&',$, � ,(,)*+,-,. ∗ ,�,��,0,�,$1, 21,�1,��34 and �� � �2, �,),)5�. further, the mcmc method is a sampling technique that combines monte carlo integration and markov chains [45]. the overall implementation process starts from proposing a suitable distribution, called proposal distribution, and drawing samples from it [46]. the proposal distribution sometimes depends on the present value to form the chain, which in turn is considered as a markov chain. the acceptance or rejection mechanisms are employed in the simulation to rectify the trial proposal distribution which ends up with the target distribution. in the end, a simulated chain of parameters (drawn samples, �6,�7,…,�" ) can be used to approximate the intractable integral (distribution), as: (#8���/ ���,�� ,…, �"�4 9 6 " ∑ 8��; " ;<6 � where (#8���/ ���,�� ,…,�"�4is the expectation and 8��;� is the density function. the metropolis algorithm, metropolis hastings, hamiltonian monte carlo, gibbs sampler, reversible jump monte carlo, metropolis adjusted langevin, slice sampling, multiple try metropolis, and delayed rejection metropolis are among the most used mcmc algorithms [47, 48]. however, the method considered in this paper is the dram, presented in algorithm 1 since it has the desirable feature of tuning the reliable proposal distribution without defining it manually [45, 46]. this method overcomes the tedious task of trial and error of tuning the suitable proposal distribution that may appear in the metropolis-hastings technique [49]. in this case, the gaussian distribution is mostly used as a proposal distribution. for a startup, mcmc needs the initial parameter values and a proposal distribution. the dram method is used to propose a distribution and its initial parameter values are computed using the classical least square method. the details of the numerical results obtained from the least squares and the mcmc methods are well explained and discussed in section iv. b. least squares method the model in (1) is a system of time dependent differential equations of the form: =>? =' @��, �a,b;c � 0 where � is the number of state variable and �� is the vector of engineering, technology & applied science research vol. 11, no. 2, 2021, 6919-6929 6922 www.etasr.com muhirwa et al.: markov chain monte carlo analysis of the variable-volume exothermic model for … state variables. for the model (1), � � 4, b; is the discrete time sampling, and �� � �2, �, ), )5 ), �a is the set of parameters of the model to be identified, where f � 1,2, . . . ,14. so, in this paper, the 14 parameters to be identified are: �a = [$%&' , $ , � , (, )*+,, .∗ , �, ��, 0, �, $1 , 21, �1 , ��3 ] the least squares method one of the classical optimization methods with the purpose of minimizing the sum of squared residuals. to obtain the residuals, a predictive model is described as: j�; = k@��;, �a , b; c + m�; where j�; represents the observations, k@��; , �a , b; c are the solutions of the model (1) at time b; starting from a fixed set of parameters � , and m�; is the residual term. the sum of squared residuals function is obtained by taking the sum of squares of m�; : n.n. � � ∑ �m�;� 7 � ∑ �j�; − * ;<6 * ;<6 k@��;, �a, b; c)7 hence, the least square method searches the best fitting parameters that minimize the n. n. � taken as the likelihood function. thus, the fitting set of parameters �a can be obtained after solving (2): p�q.q.r� pst � 0 ≡ p(∑ (v?w�wx� �y@>?w ,st,'w c) pst = 0 (2) simultaneously. almost all chemical processes are intractable and complex due to their non-linearity behaviors. in fact, stepping back to the model (1) with 14 parameters of interest, if we could manually solve (2), we would end up with solving 14 nonlinear equations simultaneously, which is a complicated task. as a simplification, the numerical simulations become a usual way of solving the problem. c. delayed adaptive markov chain monte carlo in this paper, the delayed-rejection adaptive metropolis (dram) algorithm is used for the parameter identifiability of the deterministic variable-volume exothermic cstr model described in (1). the dram algorithm is chosen since it combines and utilizes both the delayed-rejection (dr) and the adaptive metropolis (am) methods to efficiently improve and speed-up the computation process for a slow-start adaptation. the inputs of the algorithm are the initial values of the parameters and all of them are the least square optimal parameter values shown in table ii. the proposed distribution which is a gaussian with mean 0 and standard deviation σ taken as the initial covariance matrix, σ � 6 [\]t ^a , has been used, where j is the length of model’s parameters to be estimated, and _a � _a×a which is an f × f identity matrix. 1) algorithm 1: dram draw the initial point � , from initial distribution � ���. set an initial non-adaptive period a and initial covariance matrix σ . for b � 1, 2, … perform the following: (i) sample a current point �c from the proposal distribution d(�c/�;�6 ) (ii) compute the acceptance probability using: e@�;�6 , �cc = min �1, �(� c/��� , �� , … , ��" )d(�;�6 / �c� ���;�6/��� , �� , … , ��" )d(�c/�;�6 )) (iii) acceptance/rejection rule by setting: �; = h �c, b8 i < e@�;�6, �cc kℎ�m� i~n�0, 1) �;�6, obℎ�mkbp�. (iv) if q ≪ b (or after every q 's iterations), then update the covariance matrix by using: σ; � �ot�� , �6, … , �; ) + u_= where _= is an v × v identity matrix and u is a small positive number that makes the matrix σ; to be non-singular [46, 52, 53]. (v) i ← i+1 table i. variables, constants, and parameters values parameters and variables symbol unit physical meaning values source �; wxyz x{| x} feeding concentration 316.8 [50] � wxyz x{| x} initial concentration 316.8 [50] � wxyz x{| x} mixture concentration state variable simulated );~ feeding temperature 298.35 [50] ) ~ initial temperature 298.35 [50] ) ~ mixture temperature state variable simulated .∗ w��z wxyz enthalpy -1004.3×10 3 [50] )1� k initial cool temperature 288.15 [50] )1w� ~ feeding cool temperature 293 [38] )1 ~ jacket temperature state variable simulated � w� ~ wxyz gas constant 8.314 [50] 2 x } initial tank volume 100 [51] 2 x} tank volume state variable simulated ( w� wxyz activation energy 0.5 [50] )*+,~ reference temp 298.15 [50] �� w��z ~ w� heat capacity 4186 [50] 0 w� ~ x{| x� heat transfer coefficient 100000 assumed $1 x} x{| cooling velocity 46.5×10 -6 [50] 21 x} jacket volume 50×10 -6 [50] �1 w� x} density of the coolant 1000 [51] ��3 w��z ~ w� heat capacity of jacket 4186 [50] $%&' m� min outlet velocity 130×10 -6 [50] $ m� min feeding velocity 130×10 -2 assumed � min -1 pre-arrhenius factor 0.9 [50] � kg m� density 1000 [51] � m7 area 0.015 [50] engineering, technology & applied science research vol. 11, no. 2, 2021, 6919-6929 6923 www.etasr.com muhirwa et al.: markov chain monte carlo analysis of the variable-volume exothermic model for … iv. numerical analysis of the model and discussion the formulated model (1) is solved numerically by the 4's order runge-kutta method which is the ode45 solver available in matlab r2016b software package. the parameter identifiability is done using the least squares and mcmc. a. numerical simulations due to lack of actual information (real data) about the system, the model (1) is simulated by using literature and assumed values (table i), the discrete sampling time points are 100, and 100×4 numerical solutions of the model j�; presented in (1) are obtained. the numerical results from the subplot 1 of figure 3 reveal that the volume of tank reactor increases from 100m 3 to approximately 126m 3 and this is an indication of having non-constant flow rates of reactants due change at both the inlets and outlets. fig. 3. numerical solutions of the model. figure 3 also shows that the reactants are consumed inside the reacting tank as its concentration approaches zero, which means the complete mixing and at the same time symbolizes a non-partial conversion of reactants into products that may lead to time residence distribution analysis as one of the inconveniences of cstrs. along this process, there is a covering cooling jacket that communicates with the reacting tank through a designed cross-sectional area of 0.015m 2 to cool down the rising temperature inside the reacting tank. the covering cooling jacket contains the substance whose temperature is initially lower than the starting temperature of the reacting tank to disable the explosion of the reaction. during this process, the temperature of the reacting tank rises from 298.35k to its operating working temperature that is373.48k. meanwhile, the cooling temperature of the covering cooling jacket also rises from its initial temperature 288.15k until it reaches 363.14k. as a result, if this scenario is selected to be a piloting tank, then all the simulated information and the working conditions that are described above have to be taken into consideration quantitatively. b. least square results the deterministic variable-volume exothermic cstr model presented in (1) has been numerically analyzed by using the least square method and 14 parameters of the model were optimized from the noisy measurements of the system. the noisy measurements are obtained after corrupting the obtained empirical data with gaussian noise of 0.05 standard deviation. the obtained results are presented in figure 4, and the 14 estimated parameters and their corresponding initial values are also presented in table ii. according to the results, all parameters relatively converge to their corresponding initial values and the measurements fit the exothermic cstr model as can be viewed from fitted state variables shown in figure 4. fig. 4. least square fitting model. we can see that the measurements fit the model well as parameters vary. c. markov chain monte carlo results the initial values for the mcmc are estimated using the least squares method. since we have fourteen parameters to be estimated, a sample consisting of 100,000 ×14 parameters has been generated during simulations and the method has been adapted 100 times. also the initialized covariance matrix of mcmc is chosen to be σ � 6 [\]�\`�\ √6� . details of the mcmc results are discussed by the following mcmc diagnostic tests. 1) mcmc diagnostics the identifiability of the model parameters is mainly based on the convergence of the mcmc. there are several statistical and graphical convergence tests for the mcmc methods [5457]. in this paper, we use the common statistical inference and graphical analyses of the trace (time series plots), scatter plots, autocorrelation plots, histograms, and the marginal density distributions for each drawn sample of the parameters to identify the model and diagnose the convergence of the generated mcmc samples. 2) trace plots one way to analyze the convergence of the mcmc is to check the mixing of the generated sample of posteriors through trace plots. if the generated chain of posteriors becomes stationary for several initial values, and there are no obvious spikes, it is an indication of having a good mixing which is a good sign of convergence. in figure 5 we can see that the mixing of samples is very good so the chain converges, and the 14 sampled values of posteriors are the means (centers) of the samples. engineering, technology & applied science research vol. 11, no. 2, 2021, 6919-6929 6924 www.etasr.com muhirwa et al.: markov chain monte carlo analysis of the variable-volume exothermic model for … table ii. the statistical inference on the estimated parameters by using the least square and mcmc methods param lsq and mcmc estimates initial values lsq estim mcmc posterior mean mcmc posterior median cred interv std mcerr tau geweke kurtosis skewness $%&' 130×10 -6 130.016×10 -6 130.015×10 -6 130.016×10 -6 [130.015×10 -6 , 130.016×10 -6 ] 7.32 ×10 -8 1.0633×10 -9 41.003 0.99994 2.9626 -0.0630 $ 130×10-2 130.09×10-2 129.971139×10-2 129.9704569×10-2 [129.9705396×10 -2 , 129.9716882×10 -2 ] 0.00093 3.9735×10 -5 62.713 0.99997 3.0915 -0.0225 � 0.9 0.900553 0.900592376 0.900596750 [0.900586482, 0.900598270] 0.000951 2.2856×10 -5 50.329 0.99994 3.0930 -0.0016 ( 0.5 0.493183 0.493486288 0.493470050 [0.493480384, 0.493492191] 0.0009525 1.7754×10 -5 46.313 0.9985 3.1854 0.0934 )*+,298.15 298.147 298.151888471 298.151879315 [298.151882554, 298.151894388] 0.00095466 1.9926×10 -5 58.812 1 3.0988 -0.0220 .∗ -1004.3×103 1026.03×103 -1028032.32 9702401 -1028032.329 677610 [-1028032.32970, -1028032.3296 966452] 0.00095973 3.2217×10 -5 57.28 1 3.1340 0.0125 � 1000 1017.16 1026.121280804 1026.121304498 [1026.121274963, 1026.121286644] 0.00094236 2.9081×10 -5 59.644 1 3.0811 -0.0299 �� 4186 4231.14 4217.368624072 4217.368601824 [4217.368617960, 4217.368630185] 0.00098619 2.1133×10 -5 48 1 3.3398 0.0578 0 100,000 100681 100098.50255273 8 100098.502551528 [100098.502547056, 100098.502558419] 0.00091663 4.2388×10 -5 69.113 1 3.2362 0.0790 � 0.015 0.0151979 0.014959065 0.014962113 [0.014953136, 0.014964995] 0.00095668 3.0706×10 -5 53.978 0.99458 3.0965 -0.0279 $1 46.5×10 -6 46.7705×10 -6 74.7936×10 -5 62.4641×10 -5 [74.4298×10-5, 75.1574×10-5] 0.00058698 3.7635×10-5 85.568 0.21093 3.9661 1.0355 21 50×10 -6 49.6872×10 -6 76.2673×10 -5 63.7067×10 -5 [75.8967×10-5, 76.6379××10-5] 0.00059791 3.2879×10-5 69.882 0.41264 3.8227 1.0014 �1 1000 987.751 994.859555082 994.859566589 [994.859549347, 994.859560817] 0.00092534 2.464×10 -5 63.819 1 3.2461 0.0145 ��3 4186 4134.6 4163.918586616 4163.918608754 [4163.918580689, 4163.918592542] 0.00095621 1.7679×10 -5 45.604 1 3.0466 -0.0150 note: param=parameters, lsq=least squares, estim=estimates, cred interv=credible interval, std=standard deviation, mcerr=mcmc error fig. 5. the trace plots of the samples. 3) scatter plots (pairs) a poor convergence of mcmc method inventively leads to high correlation between estimated parameters. since there are 14 parameters to be identified, then there are 91 scatter plots which we need to investigate if there are strong correlations between them. figure 6 shows the scatter plots for the first 10 sampled parameters equivalent to 45 scatter plots and how these posterior samples correlate to each other. we observe that there is no high correlation between the pairs of the estimated parameters and so the parameters of the model (1) are adequately identified. 4) autocorrelation plots figure 7 determines and examines the correlation between consecutive samples during posteriors chain sampling. we can see that the coefficients of autocorrelation functions of all generated samples (x-axis) tend to zero as the number of lags (y-axis) increases and get stationary around zero after 100 lags. that is an indication of having a good mix. 5) marginal distribution (density) of the sampled parameters another diagnostic test is to plot the posteriors density distributions. normally for better mixing we expect the distributions of all density estimations to follow a gaussian distribution. figure 8 depicts how density distributions of all estimated parameters follow gaussian distribution and their values are taken as means of distributions. engineering, technology & applied science research vol. 11, no. 2, 2021, 6919-6929 6925 www.etasr.com muhirwa et al.: markov chain monte carlo analysis of the variable-volume exothermic model for … fig. 6. the scatter plots of pairs of sampled parameters. we can see that none of the parameters #$%&', $, � ,(, )*+,-,. ∗ , �,��, 0, �4 is correlated to the others because there are no correlation patterns observed. fig. 7. autocorrelation plots of the sampled parameters. fig. 8. the marginal density distribution of the sampled parameters. engineering, technology & applied science research vol. 11, no. 2, 2021, 6919-6929 6926 www.etasr.com muhirwa et al.: markov chain monte carlo analysis of the variable-volume exothermic model for … fig. 9. histograms of the 14 sampled parameters. fig. 10. parameter prccs' plot for the model outputs. 6) histograms of the sampled parameters from figure 9, we can see that almost all parameter values follow the normal distribution. the mcmc's convergence tends to be bad for $1 and 21. however, the other 12 parameters are fine. this could be caused by different and uncertain reasons. it may stem from either the complexity of the model, the little information about their mean values, or the method itself has failed to sample well these two parameters from the proposed distribution. the results in table ii show that almost all parameters converge to their initial values and posterior means are within their credible intervals. we can see that the posterior means and posterior medians are nearly equal. we can in addition observe that the markov chain errors and the standard deviation of the model parameters are significantly small which shows that the method performed well in identifying the best estimates. the computed autocorrelation time (tau) values are small with the significance of having independence in sampling the successive posteriors as well as the convergence of the method. all geweke values are almost 1, except 0.21093 for $1 and 0.41264 for 21 with the indication of having non-stationary means values by default for the start (10%) and the end (50%) of sampling of these two parameters. in reality, the skewness and kurtosis values for the gaussian distribution are approximately expected to be 0 and 3 respectively. so, the skewness and kurtosis values for the obtained samples show that only $1 and 21 values are somehow skewed in the right hand side and do not incorporate the exact features of the gaussian distribution. d. global sensitivity analysis to quantify the uncertainty effects of estimated parameters on the model outputs, we performed global sensitivity analysis by using latin hypercube sampling method. this method computes the partial rank correlation coefficients (prccs) and determines which parameters are globally very sensitive to the model. prccs values vary between -1 and +1 with high sensitivity index for values approaching ±1 and low sensitivity index for values which are far from ± 1. the prccs values are graphically displayed in figure 10 and their results can be seen in table iii. from figure 10, we observe that the 1 st parameter significantly and negatively affects the model volume outputs. the increase in that parameter decreases the volume. from subplot 2, the 3 rd parameter, which is � , has high negative effect on the concentration outputs of the model. the increase engineering, technology & applied science research vol. 11, no. 2, 2021, 6919-6929 6927 www.etasr.com muhirwa et al.: markov chain monte carlo analysis of the variable-volume exothermic model for … of the temperature profiles positively depends on the increase in the 6 th , 7 th and 8 th parameter values whereas the increase of the 8 th and 10 th parameter values decreases and increases the cooling temperature profiles respectively. so, in total there are 7 identified parameters that may have a great impact on the model response and their values are represented by (*) in table iii. table iii. prcc results parameter partial rank correlation coefficient values for each variable � � � �� $%&' −0.9847 �∗) 0.2545 −0.0479 −0.0429 $ −0.0269 0.4127 0.1482 −0.0119 � −0.1060 −0.7418 �∗) 0.0302 −0.0761 ( 0.0070 0.3054 −0.0743 −0.0973 )*+,−0.1713 −0.0515 −0.2141 0.0032 .∗ 0.0813 −0.1444 0.6114�∗) −0.3979 � 0.0819 −0.3102 0.5000(∗) −0.2924 �� −0.0345 −0.2137 0.6391(∗) −0.5186(∗) 0 0.0232 −0.0547 −0.1470 0.4348 � −0.0091 0.0298 −0.2086 0.5232(∗) $1 0.1761 −0.2802 0.0415 −0.3810 21 0.0038 −0.0401 −0.1139 0.1187 �1 0.0928 −0.0246 0.1285 −0.2502 ��3 −0.0655 −0.2189 0.0294 −0.3894 v. conclusion this paper focused on the mathematical formulation of the deterministic variable-volume exothermic cstr model, and its numerical simulations were tested to supplement the theoretical results as applications using literature values. the identifiability of the parameters required real system measurements, but due to the absence of real data, the system measurements were simulated, i.e. the numerical solutions were empirical data corrupted with gaussian noise with a standard deviation of 0.05. the identifiability of the physical parameters of the formulated model was numerically carried out by using the least squares and dram. the least square estimates converged to the literature values and were treated as prior information for the dram method. the 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[61] z. prokopova and r. prokop, "modelling and simulation of chemical industrial reactors," in 23rd european conference on modelling and simulation, madrid, spain, jun. 2009, pp. 378–383. microsoft word etasr_v11_n2_pp6949-6955 engineering, technology & applied science research vol. 11, no. 2, 2021, 6949-6955 6949 www.etasr.com junejo et al.: classification of voltage sag propagation under double line to ground fault on a low … classification of voltage sag propagation under double line to ground fault on a low voltage distribution power network abdul khalique junejo department of electrical engineering quaid-e-awam university of engineering, science and technology, nawabshah, pakistan ak.junejo@quest.edu.pk mohsin ali koondhar department of electrical engineering quaid-e-awam university of engineering, science and technology, nawabshah, pakistan engr.mohsinkoondhar@quest.edu.pk munwar ayaz memon department of electrical engineering quaid-e-awam university of engineering, science and technology, nawabshah, pakistan engr.mam@quest.edu.pk irfan ali channa department of automation beijing university of chemical technology beijing, china irfanali@mail.buct.edu.cn syed abid ali shah bukhari department of electrical engineering quaid-e-awam university of engineering, science and technology larkana, pakistan abidshah@quest.edu.pk abstract-the key issue of the voltage-sag propagation on the different types of winding connections for the low voltage transformer in the distribution power network is considered in this study. the issues of voltage sag propagation depend upon the type of the asymmetrical fault and the connection of the transformer windings. in this paper, the double line to ground fault is adopted for the voltage sag characterization. the depiction of the sage propagation is an outcome of the zero sequence components. voltage sag propagation detection can be used to improve the power quality of the system. the obtained results reveal the characteristics of the voltage drop propagation from the primary to the secondary winding of the transformer throughout different connection. the implemented method will help analyze the power quality (pq) problem in terms of voltage sag of the distributed transmission networks of the power system. keywords-voltage sag; power quality; double line to ground fault i. introduction power quality (pq) is an important issue in electrical systems [1]. due to the existence of symmetric faults in the transformer windings, the sinking of the distribution network will deviate from the waveform of the power supply voltage, which depends on the nominal sine waveform and the nominal frequency [2, 3]. many industrial and home customers often have equipment that is sensitive to electrical interference [4]. therefore, it is important to understand the quality of the supplied power [5, 6]. if sufficient power supply voltage is not provided, electrical appliances may or may not be sued at all. end users have increased their awareness of voltage quality and challenge network operators to obtain appropriate information and provide them with better power supply quality [3]. nowadays, pq has become a major aspect of the power distribution system (pds), due to reasons such as the presence of sensitive and nonlinear loads in the distribution system [7, 8]. the main problem is the quality of energy in terms of voltage constancy in the pds. voltage sag, defined as a sharp decrease in the amplitude of the supply voltage, is a pq problem that can cause loss of susceptible loads in the pds. in recent years, many defects due to low voltage, such as electrical equipment failure, production line loss, and complete equipment failure, have been studied [9-12]. the voltage sag defined by ieee is the decrease of the rms voltage value between 0.1 and 0.9pu [10]. voltage sag can interfere with the operation of sensitive equipment. these circumstances may lead to huge cost-effective fatalities by disturbing the industrial manufacture process [13, 14]. ii. discription and system modeling the variation in voltage, current, or frequency may cause equipment failure/malfunction. according to ieee 1159-1995 standard, the sag reduces the voltage between 0.1 to 0.9pu. as corresponding author: mohsin ali koondhar engineering, technology & applied science research vol. 11, no. 2, 2021, 6949-6955 6950 www.etasr.com junejo et al.: classification of voltage sag propagation under double line to ground fault on a low … shown in figure 1, the rms at the power frequency ranges from 0.5 to 1 minute. figure 2 shows a one line schematic diagram power network with two buses. if a bus failure occurs, the voltage on the primary transformer would be in a fault state, and on the other hand, on the secondary of the transformer has not a zero level of the voltage. it can be said that voltage sag can propagate from primary to secondary. duration t2-t1 magnitude time (sec) 1.0 vthr vsag m a g n it u d e (p .u ) t1 t2 fig. 1. sag voltage discription. b b load g fault fig. 2. one line diagram of the power system. a. simulink model of the distribution network for voltage sag propagation this study aims to classify the voltage sag propagation under double line to ground fault on a low voltage distribution power network. the power system has four stages: generation, transmission, distribution, and utilization. in the model shown in figure 3, one distribution feeder of 11kv from the feeder voltage has been sent to the load side and between them there is transformer. when fault occurs on the primary side of the transformer, the voltage will sag at the primary side and also propagate on the secondary side depending on various factors, i.e. fault type, winding connection, winding impedance, and fault impedance. voltage sag was measured with a measurement block and calculated from the sequence analyzer on the primary and secondary side of transformer. 1) three phase source block this block is formed in simulink where three phase voltage displaced with reference degree is present. here, 11kv voltage is selected and reference angle is selected. 2) voltage current measurement block this block is formed where the three phase of voltage and current are measured and shown with a connected scope. 3) three phase fault block this block is formed where the fault type (line to ground fault, double line fault, double lone to ground fault, and three phase faults) is selected. fig. 3. the matlab/simulink model for the classification of voltage sag propagation of the distribution network. 4) rms voltage block this block measures the rms value. 5) two winding transformer in this block, winding connections are selected with suitable winding resistance and inductance. 6) rlc load block in this block, active and reactive powers are selected. engineering, technology & applied science research vol. 11, no. 2, 2021, 6949-6955 6951 www.etasr.com junejo et al.: classification of voltage sag propagation under double line to ground fault on a low … 7) sequence analyzer block in this block, sequence component values and phase angles are measured and shown. the discrete time (5 e-5) solver is used in the simulink model. b. modeling for sequence analyzer's symmetrical and unsymmetrical faults in a power system, two kinds of faults occur, due to a variety of reasons, namely the symmetrical and the unsymmetrical faults. in symmetrical faults, all phases are short circuited, so all phases have the same amount of voltage, i.e. zero or maximum. in an unsymmetrical fault, two phases are short circuited with one another or to the ground: line to line, phase to line, and phase-phase to ground faults (ll, lg, and lll). c. sequence components fault calculation may be conducted with the sequence components. there are three sequence components (positive, negative, and zero sequence components) used in the analysis of the power system's faults and its stability. the sequence components are used to analyze the voltage sag propagation under unsymmetrical faults. 1) positive sequence components positive sequence components have the same magnitude and displaced phase angle as the normal phase voltage or current, as shown in figure 4. 2) negative sequence components negative sequence components have the same magnitude but opposite phase displacement with normal phase voltage or current as shown in figure 5. fig. 4. positive sequence components. fig. 5. negative sequence components. 3) zero sequence components zero sequence components have the same magnitude and angle as shown in figure 6. fig. 6. zero sequence components. d. phase voltages calculation by sequence components in a three phase system va, vb, and vc are the three phase voltages displaced at 00, 1200 and 2400or-1200. equations (1)(3) [15] describe the system: �� = �� + �� + �� (1) �� = � � �� + ��� + �� (2) � = ��� + � � �� + �� (3) fig. 7. a three phase vector. iii. results and discussion in this section, the simulink sequence analyzer is used to display the simulation results. in this article, the different types of the connection of the three-phase transformers are considered and the voltage sag propagation on the distribution power network under double line to ground fault is analyzed. sequence components (positive and zero components) are implemented to characterize the voltage sag. when the fault appears on the power system, then the voltage sag also occurs on each side of the transformer, but due to the transformer winding connection, the voltage sag will expand. voltage sag analysis is performed by changing the fault resistance on the primary side of the transformer to monitor the propagation voltage on the secondary side by modifying the fault resistance, selecting double line to ground fault for voltage sag analysis, and selecting start-delta connection for comparative analysis. engineering, technology & applied science research vol. 11, no. 2, 2021, 6949-6955 6952 www.etasr.com junejo et al.: classification of voltage sag propagation under double line to ground fault on a low … a. llg fault with y-y connection in this section, the llg with y-y connection of the transformer is used to test the voltage sag propagation on the power network. when an llg fault takes place in the power network, voltage sag emerges on the primary and secondary sides, as shown in figures 8 and 9. it can be clearly seen from the rms value waveform that when a fault occurs on the primary to the secondary side of the transformer, then the voltage drop can appear as a different rms value. the rms values under llg fault with different types of transformer connection were simulated in the matlab model by using the phase sequence analyzer (table i). table i. sag voltage on the primary and secondary of t/f with y-y connection t/f primary side t/f secondary side va1=0.333∠−1.3 va1=0.332∠−4.059 va2=0.333∠−121.28 va2=0.3325∠−124.09 va0=0.332∠−120.11 va0= 0 va = 0 va= 0.332∠−64 vb = 0 vb=0.332∠−64 vc = 0.99∠119.17 vc = 0.66∠115.92 fig. 8. sag voltage at the primary side by using y-y connection. fig. 9. sag voltage at the secondary side by using y-y connection. b. llg fault with y-delta connection when a llg fault occurs in the power network, voltage sag would come out on both sides of the transformer as illustrated in figures 10-11. the rms value waveforms obviously state that once the primary side of the transformer fails, at different rms values, the voltage sag of the transformer will drop to the secondary side. this is simulated in the model and can be passed. the phase sequence analyzer performs the calculations, as shown in table ii. c. llg fault with yg-yg connection llg fault with yg-yg connection is considered in this section. when a llg fault takes place in the distribution network, there will be voltage sag on the primary and secondary sides as shown in figures 12-13. table ii. primary and secondary of t/f on y-d connection voltage sag t/f primary side t/f secondary side va1=0.333∠−1.3 va1=0.332∠−34.05 va2=0.333∠−121.28 va2=0.3325∠−94.039 va0=0.3321∠−120.11 va0= 0 va = 0 va = 0.57∠-64 vb = 0 vb=0 vc = 0.99∠ 119.17 vc=0.57∠ 115.98 fig. 10. y-d connection sag voltage at the primary side. fig. 11. y-d connection sag voltage at the secondary side. fig. 12. yg-yg connection sag voltage at the primary side. fig. 13. yg-yg connection sag voltage at the secondary side. from the rms value waveform, it is observed that when the primary of the transformer fails, at different rms value, the engineering, technology & applied science research vol. 11, no. 2, 2021, 6949-6955 6953 www.etasr.com junejo et al.: classification of voltage sag propagation under double line to ground fault on a low … voltage sag of the transformer will also drop to the secondary side. the phase sequence analyzer performance is shown in table iii. table iii. primary and secondary of t/f on yg-yg connection voltage sag t/f primary side t/f secondary side va1 = 0.333∠-1.3 va1= 0.332∠−4.25 va2= 0.333∠−121.28 va2= 0.332∠−124.23 va0 = 0.3321∠120.11 va0= 0.332∠-117.15 va = 0 va= 0 vb = 0 vb=0 vc = 0.99∠119.17 vc= 0.99∠116.2 d. llg with yg-delta connection following, the llg with yg-delta connection has been tested for voltage sag propagation. when an llg fault occurs, the voltage sag on the primary and secondary would appear on the transformer. it can be observed from the waveform of the rms values in figures 14-15 that when the primary of the transformer is under fault condition, then the voltage sags would be dropped to the secondary side of the transformer at different rms values. table iv represents the voltage sags on both sides of the transformer under phase sequence analyzer performance. table iv. primary and secondary of t/f on yg-d connection voltage sag t/f primary side t/f secondary side va1=0.333∠−1.3 va1=0.332∠−34.05 va2=0.333∠−121.28 va2=0.3325∠−94.039 va0=0.3321∠120.11 va0= 0 va = 0 va= 0.57∠-67 vb = 0 vb=0 vc = 0.99∠119.17 vc=0.57∠115.98 fig. 14. yg-delta connection sag voltage at the primary side. fig. 15. yg-delta connection sag voltage at the secondary side. e. double line to ground fault with delta-star connection the rms values of an llg fault are shown in figures 1617. the voltage sags on the primary and secondary sides are again calculated with the sequence analyzer in the matlab model. the calculated rms values are shown in table v. fig. 16. d-y connection sag voltage at the primary side. fig. 17. d-y connection sag voltage at the secondary side. table v. primary and secondary of t/f on d-y connection voltage sag t/f primary side t/f secondary side va1=0.333∠−1.3 va1=0.332∠25.945 va2=0.333∠−121.28 va2=0.3325∠−154 va0=0.3321∠120.11 va0= 0 va = 0 va= 0 vb = 0 vb=0.57∠ -64 vc = 0.99∠119.17 vc=0.57∠115.98 f. double line to ground fault with delta-delta connection the rms values of an llg fault are shown in figures 1819. the voltage sags on the primary and secondary sides are again calculated with the sequence analyzer in the matlab model. the calculated rms values are shown in table vi. table vi. primary and secondary of t/f on d-d connection coltage sag t/f primary side t/f secondary side va1=0.333∠−1.3 va1=0.332∠ -4.059 va2=0.333∠−121.28 va2=0.3325∠−124.09 va0=0.3321∠120.11 va0= 0 va = 0 va= 0.332<-64 vb = 0 vb= 0.332 ∠ -64 vc = 0.99∠199.17 vc = 0.66∠115.92 g. llg fault with d-yg connection the rms values of an llg fault are shown in figures 2021. the voltage sags on the primary and secondary sides are engineering, technology & applied science research vol. 11, no. 2, 2021, 6949-6955 6954 www.etasr.com junejo et al.: classification of voltage sag propagation under double line to ground fault on a low … again calculated with the sequence analyzer in the matlab model. the calculated rms values are shown in table vii. fig. 18. d-d connection sag voltage at the primary side. fig. 19. d-d connection sag voltage at the secondary side. table vii. primary and secondary of t/f on d-yg connection voltage sag t/f primary side t/f secondary side va1=0.333∠−1.3 va1=0.332∠ 25.945 va2=0.333∠−121.28 va2=0.3325∠−154 va0=0.3321∠120.11 va0= 0 va = 0 va= 0 vb = 0 vb= 0.57 ∠ -64 vc = 0.99∠119.17 vc=0.57∠115.98 fig. 20. d-yg connection sag voltage at the primary side. fig. 21. d-yg connection sag voltage at the secondary side. iv. conclusion this paper conducts in-depth research on the voltage sag propagation under double line to ground fault (llg) with different transformer connections, which are used for lowvoltage in distribution power networks. the results have been acquired with the use of the sequence analyzer. the obtained results show the voltage sag classification, which propagates from the primary to the secondary of the transformer. the voltage sag characterizations are important in order to check the power quality under fault condition of the distribution network. this study's results may be found helpful when designing proper protection schemes and ways to improve the voltage sag under fault conditions at 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[14] s. s. rao, switchgear protection and power systems, 13th ed. delhi, india: khanna publishers, 2008. author profiles abdul khalique junejo was born in larkana, sindh, pakistan in 1989. he received his b.e. and m.e. from the electrical engineering department of the quaid-e-awam university of engineering, science and technology, pakistan in 2011 and 2015 respectively. he is currently working towards his phd in the school of electrical and electronics engineering at the state key laboratory of advanced electromagnetic engineering in huazhong university of science and technology, wuhan, china. he is currently employed as an assistant professor in the quaid-e-awam university of engineering, science and technology. he has served as a reviewer for various ieee journals. his research interests include sliding mode control, direct torque control, model predictive control, and sensorless control methods for permanent magnet synchronous machines, induction machines, and linear induction machines and drives. mohsin ali koondhar was born in nawabshah, sindh, pakistan in 1985. he received his b.e. and m.e. from the electrical engineering department of the quaid-e-awam university of engineering, science and technology in 2007 and 2016 respectively. he is currently employed as a lecturer in the quaid-e-awam university of engineering, science and technology. he has served as a reviewer for iet generation, transmission & distribution journal. his research interests include the control of dc and ac machines, renewable energy, and programmable logic controllers. munwar ayaz memon was born at bhiria, pakistan in 1987. he received his b.e and m.e from quaid-e-awam university of engineering science and technology and nowadays is working as an assistant professor at the department of electrical engineering at the quaid-e-awam university of engineering, science and technology. he is currently pursuing his ph.d. in electrical engineering from the same university. his fields of interest are power systems, power quality, and renewable energy systems. he is an author/co-author of 8 publications. he is a member of pakistan's engineering council. irfan ali channa was born at nawabshah, pakistan. he received his b.e and m.e from the electrical engineering department of the quaid-eawam university of engineering, science and technology in 2011 and 2015 respectively. he is currently enrolled as a ph.d. student in beijing university of chemical technology, china. his fields of interest are power systems, power quality, signal processing, and ai. syed abid ali shah was born in 1983 in sukkur sindh-pakistan. he received the b.e in electrical engineering from quaid-e-awam university of engineering, science and technology in 2009, his m.e in electrical power engineering from mehran university, pakistan in 2015, and his ph.d. from aston university, uk in 2019. he has successfully completed the associate fellowship from the higher education academy, uk. he is an assistant professor at the quaid-e-awam university of engineering. his research interests include the design and optimization of electrical machines and drives and analyzing of special machines. he is a registered engineer of pakistan engineering council and a member of ieee and iet of uk and ireland section. microsoft word 31-3719l_s_etasr_v10_n4_pp6062-6067 engineering, technology & applied science research vol. 10, no. 4, 2020, 6062-6067 6062 www.etasr.com boudjemline et al.: surface quality of ti-6al-4v titanium alloy parts machined by laser cutting surface quality of ti-6al-4v titanium alloy parts machined by laser cutting attia boudjemline college of engineering, university of hai’l hail, kingdom of saudi arabia a_boudjemline@hotmail.com mohamed boujelbene college of engineering university of hai’l hail, kingdom of saudi arabia mboujelbene@yahoo.fr emin bayraktar lismma, supméca – institut supérieur de mécanique de paris paris, france emin.bayraktar@supmeca.fr abstract-this paper investigates high power co2 laser cutting of 5mm-thick ti-6al-4v titanium alloy sheets, aiming to evaluate the effects of various laser cutting parameters on surface roughness. using multiple linear regression, a mathematical model based on experimental data was proposed to predict the maximum height of the surface sz as a function of two laser cutting parameters, namely cutting speed and assist-gas pressure. the adequacy of the proposed model was validated by analysis of variance (anova). experimental data were compared with the model’s data to verify the capability of the proposed model. the results indicated that, for fixed laser power, cutting speed is the predominant cutting parameter that affects the maximum height of surface roughness. keywords-laser cutting; titanium alloy; cutting speed; gas pressure; maximum height of surface roughness i. introduction titanium alloys, including ti-6al-4v, are characterized by good mechanical and chemical properties such as high tensile strength and toughness, excellent resistance to corrosion and oxidation, light weight, resistance to extreme temperatures, and high strength-to-weight ratio. as a result, they are increasingly used in aerospace, spacecraft, automotive, biomedical, chemical and petrochemical, offshore oil and gas, water desalination, and power generation industries [1-8]. to overcome the difficulties encountered when using traditional machining techniques with super alloys, such as titanium alloys, engineering workshops resort to non-conventional techniques. these include electrical discharge machining (edm), ultrasonic machining (usm), abrasive water jet machining (awjm) and laser machining (lm) [5, 9-10]. laser cutting is a thermal-cutting process using a laser to cut materials, typically used in industrial manufacturing applications. this is achieved by focusing a high-power, coherent, and monochromatic laser beam, having a wavelength ranging from ultra-violet to infrared, onto the surface of a workpiece. laser beam’s energy is absorbed by the workpiece, resulting in rapid increase of material’s temperature at the focused spot. the temperature is so high that, depending on the material’s characteristics and beam’s intensity, the material melts or vaporizes and may undergo chemical transformation, and is then removed using an assist gas at high pressure [1119]. surface roughness of materials and mechanical components plays an important role in determining their characteristics and performance for the intended applications. therefore, it is crucial to quantify the roughness of finished materials and parts in order to ensure high quality and performance of the product [11, 20-29]. the quality of laser cutting, such as surface roughness, depends on many parameters such as thermal and optical properties of the material, laser power, cutting speed, type and pressure of the assist gas [13-14, 16, 22]. the effects of laser cutting parameters on the topographic quality of different metals have been the subject of many studies. for example, researchers in [30] used nd:yag laser to cut stainless steel sheets finding that in cw mode the surface became smoother as cutting speed increased. the surface roughness of ti-6al-4v cut with a pulsed nd:yag laser was investigated in [13] as a function of cutting speed, gas pressure, pulse width and pulse frequency, by employing an artificial neural network (ann) approach to successfully model and optimize surface roughness. authors in [31] studied the effect of cutting speed and assist-gas pressure on the roughness of the cut edge. their work showed that surface roughness decreased as both cutting speed and gas pressure increased, whereas roughness was higher at the lower part of the cuts. this study used line parameters, as they are more appropriate for analyzing the 3d surface. the investigated parameter was the maximum height of the surface sz, defined as the peak-to-valley height over an areal measurement, as established in iso 25178-2 standard. the maximum height of the surface was investigated as a function of two laser cutting parameters, cutting speed and assist-gas pressure. subsequently, an analytical model was developed using multiple linear regression and anova analyses to predict the variation of sz as a function of these parameters. ii. experimental procedure a. experimental conditions in order to investigate the effects of laser cutting, small ti alloy samples were cut from 5mm-thick sheets using an amada as 4000 e /co2 laser sheet metal cutting machine, (figure 1), in cw mode, and nitrogen as assist-gas. tables i and ii list the chemical composition and the mechanical properties of the alloy. this work examined two laser cutting factors, namely cutting speed v (mm/min) and assist-gas pressure p (bar), at a fixed laser power of 2kw. three levels were specified for each factor, as shown in table iii. corresponding author: attia boudjemline engineering, technology & applied science research vol. 10, no. 4, 2020, 6062-6067 6063 www.etasr.com boudjemline et al.: surface quality of ti-6al-4v titanium alloy parts machined by laser cutting fig. 1. the laser cutting machine amada as 4000 e. table i. chemical composition of ti-6al-4v (%) ti balance al 6 v 4 fe 0.3 o 0.2 c 0.08 n 0.05 h 0.01 table ii. basic mechanical properties of ti-6al-4v hardness (hrc) 36 density (g/cm³) 4.43 modulus e (mpa) 910 elongation (%) 0.7 tensile strength (mpa) 1000 thermal conductivity (w/mk) 7.3 table iii. important process parameters and their levels factors levels level 1 level 2 level 3 cutting speed: v (mm/min) 480 1440 2400 gas pressure: p (bar) 2 8 14 b. experimental design using full factorial design one of the most commonly used experimental designs in manufacturing is the full factorial at 2 and 3-levels. in these designs, all possible combinations of factors (input or process variables) are used in order to fully and systematically investigate their impact and significance level on the output of the studied process. a full factorial design was adopted in this study resulting in 9 experiments with different factors and levels. iii. experimental results the surface roughness sz of the 9 specimens was measured using a 3d optical surface roughness profilometer (3dsurfascan from somicronic, seen in figure 2), and data were analyzed with mountainsmap software program. it should be noted that one new sample was used for each experiment, and the reported sz value was the average of three measurements taken from the middle of the sample. the effects of cutting speed v and assist-gas pressure p on the maximum height of surface roughness sz are illustrated in figures 3 and 4 respectively. figure 3 shows that sz decreased as v increased from 480 to 2400mm/min at a laser power of 2kw, for three fixed values of p: 2, 8 and 14bar. the smallest value of sz was obtained at the highest speed. figure 4 shows that as gas pressure p increased, sz almost remained unchanged. note that smallest values of sz were obtained for the highest speed regardless of pressure. both figures indicate that the effect of gas pressure was minimal within the chosen value ranges. fig. 2. the 3d-surfascan optical profilometer. fig. 3. sz as a function of v for three values of p. fig. 4. sz as a function of p for three values of v. the decrease of roughness as speed increases is in agreement with the results obtained in [22] for ti-6al-4v, in [27] for carbon steel, in [31] for ti-6al-4v, in [32] for aisi316l stainless steel, and in [33] for astm stainless steel 304. in addition, in [34], 304 stainless steel showed at first a relatively rapid drop in roughness, which slowed as v increased indicating a possible plateau. moreover, a drop in roughness with an increase in cutting speed of austenitic stainless steel was reported in [30], attributing it to the fact that at high speed there was not enough time for heat diffusion and formation of wider grooves. contrary to this, in [35] it was showed, for 316l stainless steel, that roughness had an initial rapid increase as v increased, which levelled off at higher speeds. in [36], an almost constant value of roughness for certain values of cutting engineering, technology & applied science research vol. 10, no. 4, 2020, 6062-6067 6064 www.etasr.com boudjemline et al.: surface quality of ti-6al-4v titanium alloy parts machined by laser cutting speed and an increase when the speed increased further was reported for 4130 stainless steel. this was explained by the possibility that speed may have reached an optimum value at which the roughness was minimum, noticing that this optimum value of v is also the value at which the frequency of striations started to increase, implying that roughness is strongly related to striations. the initial slight increase and then levelling off of sz with an increase in p that was obtained is consistent with the results described in [33], where the roughness of 304 stainless steel increased as gas pressure increased. likewise, authors in [30] also reported a small increase in roughness with an increase of pressure for austenitic stainless steel, explaining it by the increase in mechanical force due to the high pressure exerted on the molten material, which produced large peaks and valleys. the opposite was observed in [34] where the roughness of 304 stainless steel decreased slightly when p increased and then levelled off, indicating a negligible contribution of p. similar results were also obtained in [31]. as the laser beam moves forward, the heated/molten material is affected by the convective cooling effect of the gas flow. this effect becomes relatively more pronouced as gas pressure increases [11, 37]. moreover, the drag force exerted by gas on the molten metal increased as v increased. the combination of these two effects may have contributed to the small increase in sz when p increased. further increase in pressure may not increase the cooling effect, thus contributing less to the roughness change. the apparent agreement and disagreement of the results from this work with other studies show the interaction complexity of the process parameters and workpiece properties involved in laser cutting. the comparison is further complicated by the fact that the parameter value ranges are different. in this context, the results from the current investigation shed light on some aspects of laser cutting of metals and ti-6al-4v in particular. hence, this work constitutes a positive contribution to the ongoing effort of better understanding this manufacturing process. iv. mathematical modeling of surface roughness a mathematical model, which approximates the surface roughness of ti-6al-4v alloy as a function of the cutting speed and assist-gas pressure was developed. linear regression analysis was used to achieve this goal. subsequently, anova was performed to estimate the level of significance of each factor’s contribution to the regression model, considering only individual variables. statistical analysis was conducted with the statistical software package minitab. a. normality test linear regression and anova require a normal distribution of data. to this effect, a normal probability plot was generated, shown in figure 5. as it is depicted, the residuals fall approximately along a diagonal straight line, indicating that data do not deviate severely from a normal distribution [38]. fig. 5. normality test of maximum surface roughness parameter sz. b. regression analysis the validity of the model equation obtained by regression analysis is based on the assumption that the residuals or error terms are constant with a mean of zero [39].these assumptions were tested by plotting the residuals versus the produced fitted values, as depicted in the top right plot in figure 6, showing that the residuals are randomly scattered around zero, and not forming any clusters or distinct patterns, suggesting that the errors have constant variance. in addition, the top left normal probability plot shows that the plotted points follow nearly a diagonal straight line, suggesting that the errors are almost normally distributed. furthermore, the histogram in the bottom left plot shows no evidence in residuals’ deviation from normality. finally, the bottom right plot represents the residuals against the order in which data were collected, showing that there is no pattern, and they are scattered uniformly around 0, indicating that the error terms are independent from one another and the regression assumptions are satisfied [39-42]. fig. 6. residual plots resulting from multiple linear regression analysis of the effects of v and p on sz. based on these assumptions, multiple linear regression analysis was carried out at a 95% level of confidence. the first order linear equation resulting from the linear regression is: �� � 71.627 0.010146� � 0.0794 � � (1) where, sz is measured in µm, v in mm/min and p in bars. the model described by (1) shows clearly that an increase in v will lead to a decrease in surface roughness, while an increase in p will increase it. model’s goodness of fit is measured by the 210-1-2 99 90 50 10 1 n 9 ad 0.260 p-value 0.616 standardized residual p e r c e n t 7065605550 2 1 0 -1 -2 fitted value s ta n d a r d iz e d r e s id u a l 210-1-2 3 2 1 0 standardized residual f r e q u e n c y 987654321 2 1 0 -1 -2 observation order s ta n d a r d iz e d r e s id u a l engineering, technology & applied science research vol. 10, no. 4, 2020, 6062-6067 6065 www.etasr.com boudjemline et al.: surface quality of ti-6al-4v titanium alloy parts machined by laser cutting coefficient of determination r2. the value obtained from regression analysis, as seen in table iv, indicates that 99.33% of the variability in the surface roughness is associated with the input parameters values. hence, the high value of r2 justifies the validity of the model. table iv. regression model summary s r 2 (%) r 2 (adj. %) press r 2 (pred. %) 0.801300 99.33 99.11 7.66013 98.67 as noted in table v, p-values, at a 95% level of confidence for v, are much lower than 0.05. this indicates that v plays a significant role and has a strong effect on sz. however, p-value for p is 0.195, implying that, within the used range of values for p, there is not enough evidence to conclude that the assistgas pressure has an effect on roughness. the variance inflation factor (vif) for the two parameters is 1, implying the absence of multicollinearity [38, 40]. table v. coefficients of the regression analysis at 95% level of confidence term coef. se coef. 95% ci tvalue pvalue vif constant 71.627 0.709 (69.892, 73.361) 101.06 0.000 v (mm/min) −0.010146 0.000341 (−0.010980, −0.009312) −29.77 0.000 1.0 p (bar) 0.0794 0.0545 (−0.0540, 0.2129) 1.46 0.195 1.0 c. analysis of variance (anova) once the linear model was generated, anova was used to determine the level of significance of each parameter’s contribution to surface roughness. the results of this analysis are displayed in table vi. table vi. anova for multiple linear regression model source df seq ss contribution (%) adj ss adj ms f-value p-value regression 2 570.569 99.33 570.569 285.284 444.31 0.000 v (mm/min) 1 569.206 99.09 569.206 569.206 886.50 0.000 p (bar) 1 1.363 0.24 1.363 1.363 2.12 0.195 error 6 3.852 0.67 3.852 0.642 total 8 574.421 100.0 in addition to the p-values, the table also shows that the contribution of v (99.09%) is much higher than that of p (0.24%). this confirms that v is the dominant factor. based on the results presented above, it is concluded that the regression model given by (1) is statistically significant with a value of r2 equal to 99.33%. both experimental and predicted values of maximum surface roughness for the 9 samples are plotted in figure 7. it can be noted that model’s results are very close to the experimental ones. d. interaction plots the interaction plots in figure 8 show that all plots’ lines are almost parallel. this indicates that the relationship between each parameter and surface roughness is independent from the other. it is worth mentioning that lines corresponding to assistgas pressure are nearly parallel to the x-axis, meaning that within these value ranges this parameter had little effect on roughness. fig. 7. comparison between experimental and predicted data for maximum surface roughness. fig. 8. interaction plot showing the effects of cutting speed v and assistgas pressure p on surface roughness sz. e. contour plots contour plots representing sz against v and p are depicted in figure 9 to determine the optimum working zone. fig. 9. contour plot of surface roughness sz versus cutting speed v and assist-gas pressure p. 70 65 60 55 50 148224001440480 70 65 60 55 50 v (mm/min) p (bar) 480 1440 2400 v (mm/min) 2 8 14 p (bar) interaction plot for sz data means p (bar) v ( m m /m in ) 1412108642 2250 2000 1750 1500 1250 1000 750 500 > – – – – – < 48 48 52 52 56 56 60 60 64 64 68 68 sz contour plot of sz vs v and p engineering, technology & applied science research vol. 10, no. 4, 2020, 6062-6067 6066 www.etasr.com boudjemline et al.: surface quality of ti-6al-4v titanium alloy parts machined by laser cutting it is inferred that, for a fixed laser power of 2kw the desired working zone lies between 2250 and 2400mm/min, for assist-gas pressure between 12 and 14bar. v. conclusion this study investigated the effects of laser cutting parameters, namely cutting speed v and assist-gas pressure p, at a fixed laser power, on the maximum height of the surface roughness sz of ti-6al-4v titanium alloy sheets. using experimental data, a mathematical model was developed to provide the relationship between the surface roughness and the laser cutting parameters. to accomplish this task, multiple linear regression analysis was employed, followed by anova to validate the model. within the used control parameters’ value ranges, the salient conclusions of this experimental study are: • cutting speed is the dominant factor affecting surface roughness. increasing it leads to roughness decrease. • assist-gas pressure has no significant effect on surface roughness. • a simple first-order regression model using the two laser cutting parameters was developed. its goodness of fit r2 was 99.33%, confirming its adequacy. • the model’s anova showed that the effect of gas pressure is almost insignificant contributing only 0.24% to surface roughness compared to cutting speed with 99.09%. • excellent agreement between the experimental and predicted results was obtained. • this model can be deployed during manufacturing to choose the right values of cutting parameters in order to achieve the desired surface quality, leading to a reduction in machining time and cost. acknowledgment the authors would like to thank the deanship of scientific research at the university of hail, for funding this work under project no. 0160857. references [1] k. gupta and r. f. laubscher, “sustainable 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[42] d. c. montgomery, e. a. peck, and g. g. vining, introduction to linear regression analysis, 5th ed. hoboken, nj, usa: john wiley & sons, 2012. engineering, technology & applied science research vol. 8, no. 6, 2018, 3619-3623 3619 www.etasr.com laarem & merbouha: chaos suppression using genetically optimized pid control of the 4-d novel… chaos suppression using genetically optimized pid control of the 4-d novel hyperchaotic vaidyanathan system guessas laarem department of electronics university ferhat abbas setif 1 setif, algeria l_guessas@univ-setif.dz abiza merbouha department of electronics university ferhat abbas setif 1 setif, algeria liali87@yahoo.fr abstract—in this paper, a dynamical analysis of the novel hyperchaotic system with four parameters is presented. genetically optimized proportional integral and derivative (pid) controllers were designed and applied for the chaos suppression of the 4-d novel hyperchaotic system, by varying the genetic algorithms (ga) options to view the impact factor on the optimized pid controllers. the use of the final optimized pid controllers ensures less time of convergence and fast speed chaos suppression. keywords-hyperchaos; chaos suppression; pid control; optimization; genetic algorithm i. introduction the study of chaotic and hyper chaotic attractors arising in nonlinear dynamical systems has received much attention as it has potential applications in many branches of science and engineering. chaotic systems are characterized as nonlinear dynamical systems, are irregular, aperiodic, unpredictable and have sensitive dependence on the initial conditions [1-4]. a hyperchaotic system is mathematically defined as a chaotic system having more than one positive lyapunov exponents implying that its dynamics are expended simultaneously in many different directions. thus, a hyperchaotic system has more complex dynamical behaviors than a chaotic system [5]. there are many well-known hyperchaotic systems [6-10] and the 4-d novel hyperchaotic vaidyanathan system [11]. pid control, in which parameters are optimized by genetic algorithm, is used in chaos suppression and synchronization for chaotic and hyper chaotic systems [11-16]. in this paper, the qualitative properties of the novel hyperchaotic system are described. the lyapunov exponents of the system are having two positive signs showing that the system is hyperchaotic. ii. dynamical analysis of the novel 4-d hyperchaotic system in this work, the vaidyanathan novel hyperchaotic system is described by (1) [7]: �̇� = 𝑓 (𝑋) = { �̇� = 𝑎 (𝑦 − 𝑥) + 𝑤 �̇� = 𝑐𝑦 − 𝑥𝑧 �̇� = 𝑥𝑦 – 𝑏𝑧 + 𝑦 �̇� = 𝑥𝑧 + 𝑟𝑤 (1) where 𝑥,𝑦,𝑧,𝑤 are the variable states, and 𝑎,𝑏,𝑐,𝑟 are positive constant parameters. in this work, we show that the system (1) is hyperchaotic when we take parameters as: a = 39, b = 3, c = 22, r = 1 (2) for numerical simulations, we take the initial values of the hyperchaotic system as: x(0)=0.2, y(0)=0.2 z(0)=0.2, w(0)=0.2 (3) figures 1, 2 show the 3-d projections of the novel 4-d hyperchaotic system (1) on (x, y, z), (x, y, w) space projections, respectively. fig. 1. 3-d projection of the novel 4-d hyperchaotic system on (x, y, z) space. a. equilibrium points the equilibrium points of the novel hyperchaotic system (1) are obtained by solving (4) [11]: �̇� = 𝑓 (𝑋) = 0 (4) engineering, technology & applied science research vol. 8, no. 6, 2018, 3619-3623 3620 www.etasr.com laarem & merbouha: chaos suppression using genetically optimized pid control of the 4-d novel… the parameter values are taken as in the hyperchaotic case (2), and are found as: e0 = [ 0 0 0 0 ] e1 = [ 7.6394 14.4163 41.5161 −264.2990 ]e2 = [ −8 .6394 −16.3034 41.5161 298.8957 ] (5) fig. 2. 3-d projection of the novel 4-d hyperchaotic system on (x, y, w) space. b. the lyapunov exponents the lyapunov exponents of the system (1) are numerically determined as: l1=1.0623, l2=0.2952 l3=0, l4=-20.1063 (6) since there are two positive lyapunov exponents in (3), it is clear that the 4-d system (1) is hyperchaotic. c. the kaplan-yorke dimension the kaplan-yorke dimension of the 4-d hyperchaotic system (1) is derived as in (7): 𝐷𝐾𝑌 = 3 + 𝐿_1+𝐿_2+𝐿_3+𝐿_4 |𝐿4| = 3.0675 (7) which is fractional as is in [1]. iii. genetically optimized pid control of the system. control of nonlinear systems is difficult in the absence of a systematic procedure as is available for linear systems. many techniques are limited in their application to a special class of systems. here again, more commonly available methods are heuristic in nature and the genetic algorithm can reduce the arbitrariness in the design of a controller to a great extent. however, even if a model of the nonlinear system is available, no systematic and generally applicable control theory is available for the design of controllers for nonlinear systems. the best-known controllers used in industrial control processes are proportional-integral derivative (pid) controllers because of their simple structure and robust performance in a wide range of operating conditions. in the past decades, control theory has gone through major developments. advanced and intelligent control algorithms have been developed in [18-20]. however, the pid-type controller remains the most popular in industry. reasons for this are the simplicity of this control law and its few tuning parameters. hundreds of tools, methods and theories are available for this purpose. however, finding the appropriate parameters for the pid controller is still a difficult task, so in practice control engineers still often use trial-and-error for the tuning process. pid control consists of three types of control, proportional, integral and derivative control. pid controller algorithm can be implemented in many forms but they are mostly used in feedback loops in [11-16]. a simple diagram illustrating the schematic of the pid controller can be seen in figure 3 [11, 15], where: 𝑢𝑖 = 𝐾𝑝𝑒𝑖 + 𝐾𝐼 ∫ ∫𝑒𝑖(𝜏)𝑑𝜏 𝑡 0 − 𝐾𝐷 𝑑𝑒𝑖 𝑑𝑡 , 𝑖 = 𝑥,𝑦,𝑧,𝑤 (8) where 𝑢𝑖 is the output pid controller, 𝑒𝑖 is the error signal, and 𝐾 𝑃, 𝐾𝐼, 𝐾 𝐷 are the proportional, integral and, the derivative gains respectively. fig. 3. schematic of the pid control the proportional controller output uses a “proportion” of the system error to control the system. however, this introduces an offset (static) error into the system. the integral controller output is proportional to the amount of time there is an error present in the system. the integral action removes the offset introduced by the proportional control but introduces a phase lag into the system. the derivative controller output is proportional to the rate of change of the error. derivative control is used to reduce or eliminate overshoot and introduces a phase lead action that removes the phase lag introduced by the integral action. the effective pid controller’s parameters 𝐾𝑃 , 𝐾𝐼 , 𝐾 𝐷 are optimized using genetic algorithms. genetic algorithm (ga) is a stochastic global search method that mimics the process of natural evolution [18-20]. it starts with no knowledge of the correct solution and depends entirely on responses from its environment and evolution operators (i.e. reproduction, crossover and mutation) to arrive at the best solution. by starting at several independent points and searching in parallel, the algorithm avoids local minima and converging to sub optimal solutions. iv. genetic algorithm stages there are three main stages of a (ga), known as reproduction, crossover and mutation (figure 4). • reproduction: just like in natural evolution, an example of a common selection technique is the “roulette wheel” selection method. • crossover: once the selection process is complete, the crossover algorithm is initiated. the simplest crossover engineering, technology & applied science research vol. 8, no. 6, 2018, 3619-3623 3621 www.etasr.com laarem & merbouha: chaos suppression using genetically optimized pid control of the 4-d novel… technique is the single point crossover. • selection: using selection and crossover on their own will generate an amount of different strings. if there is not enough diversity in the initial strings, the ga may converge on sub-optimum strings due to a bad choice of initial population. this problem may be overcome by the introduction of a mutation operator into the ga. • mutation: mutation is the occasional random alteration of a value of a string position. the probability of mutation is normally low around 0.1% 0.01%. once a string is selected for mutation, a randomly chosen element of the string is changed or ‘mutated’. fig. 4. the ga process the steps in creating and implementing a ga are: [19] • generate an initial, random population of a fixed size of individuals. • evaluate their fitness. • select the fittest members of the population. • reproduce using a probabilistic method (e.g., roulette wheel). • implement crossover operation on the reproduced chromosomes. • execute mutation operation with low probability. • repeat step 2 until a predefined convergence criterion is met. • the convergence criterion of a ga is a user-specified condition i.e. the maximum number of generations or when the string fitness value exceeds a certain threshold. the hyper chaotic system with the pid controllers is described as in (9): �̇� = 𝑓 (𝑋) = { �̇� = 𝑎 (𝑦 − 𝑥) + 𝑤 + 𝑢𝑥 �̇� = 𝑐𝑦 − 𝑥𝑧 + 𝑢𝑦 �̇� = 𝑥𝑦 – 𝑏𝑧 + 𝑦 + 𝑢𝑧 �̇� = 𝑥𝑧 + 𝑟𝑤 + 𝑢𝑤 (9) where: ui = kpei + ki ∫ ∫ei(τ)dτ t 0 − kd dei dt , i = x,y,z,w (10) since this work is using ga to optimize the gains of the pid controller, there are going to be three strings assigned to each member of the population, these members will be comprised of a 𝐾𝑃 , 𝐾𝐼 , 𝐾 𝐷 in (10). each string will be evaluated throughout the course of the ga, real (floating point) numbers will be used to encode the population. the three terms are entered into the ga application in simulink via the declaration of a three-row, between -0.2 and 0.2 which is called the initial range, the controlled system is given a step input and the error is assessed using an appropriate error performance criterion i.e. e = e0 − x (11) where e = [ ex ey ez ew ] , e0 = [ 0 0 0 0 ], x = [ x y z w ] (12) the chromosome is assigned an overall fitness value according to the magnitude of the error, the smaller the error the larger is the fitness value. a. ga options: • variable bounds matrix=[-0.2,0.2], • population size=80 individuals, • number of generations=100, • selection function=stochastic uniform, • crossover fraction=0.8, • mutation function=default function, • stopping criteria=error performance criterion or the maximum number of generations, in order to evaluate the pid values chosen by ga, the objective function is written based on error performance criterion: fobj = ∑absei (13) the objective function (13) is designed as the sum absolute error which gets the absolute value of the error to remove negative error components. this kind of error performance criteria is good for simulation studies. the best population may be plotted to give an insight into how ga converged to its final values. table i shows the pid gain values of the best solution for the 4-d novel hyperchaotic system. for numerical simulations of the system, we take the parameter values of (2) and the initial conditions of (3). figure 5 represents the converged states to the equilibrium point, figure 6 shows 3-d projection (𝑥,𝑦,𝑧) space of chaos suppression, and figure 7 shows the action control of the output of the pid optimized by the ga. engineering, technology & applied science research vol. 8, no. 6, 2018, 3619-3623 3622 www.etasr.com laarem & merbouha: chaos suppression using genetically optimized pid control of the 4-d novel… table i. optimized pid gain values pid controller kp ki kd ux 0.8736 0.9530 -1.0075 uy -1.1834 0.8585 2.9629 uz 1.4453 0.1727 -1.7600 uw 2.5530 0.0005 2.8930 fig. 5. time-history of converged states (control in action at 0.8s) fig. 6. time-history of chaos suppression errors. fig. 7. action control of the pid optimized by the ga b. impact factor of the ga options on the optimized pid controllers. genetic algorithm is typically characterized by three options. to get the optimum pid controllers, two of them remain fixed while the third option varies. let ex, ex1, ex2 the errors for the state 𝑥 for the three bounds respectively. 1) the initial range variable the crossover and the mutation probability are kept fixed. variable bounds matrix=[-0.2;0.2], [-0.5;0.5], [-0.8;0.8], crossover fraction=0.8, mutation function=default function. table ii show the best pid optimized for the bounds matrix [0.8;0.8]. table ii. pid gain values, bounds matrix= [-08;0.8] pid controller kp ki kd ux 4.015 10.044 -3.437 uy -1.94 7.084 5.959 uz 2.306 1.131 -8.61 uw 10.119 0.002 11.846 figure 8 represents the time history of chaos suppression errors for the state 𝑥, the best one is for the bound [-0.8;0.8], the time of convergence is typically small. fig. 8. time-history of chaos suppression errors. 2) fixed crossover fraction variable, bounds matrix and mutation probability. the best bound matrix [-0.8;0.8] and the same probability mutation default function are used while the crossover rate varies (0.6;0.4;0.8). table iii represents the best pid optimized for crossover rate=0.6. the time of convergence is typically small (control in action at 0.08s) (figure 9). table iii. pid gain values crossover rate=0.6 pid controller kp ki kd ux -3.643 4.438 -11.021 uy 2.007 17.038 7.866 uz 16.364 2.53 -11.973 uw 12.339 0.001 16.909 fig. 9. time-history of chaos suppression errors. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 time(seconde) v a ri a ti o n o f s ta te s i n t im e x y z w 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 time(seconde) v a ri a ti o n o f e rr o rs i n t im e ex ey ez ew 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -14 -12 -10 -8 -6 -4 -2 0 2 time(seconde) va ria tio n of a ct io ns c on tr ol in t im e ux uy uz uw 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 time(seconde) va ria tio n of e rr or s in t im e ex ex1 ex2 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 time(seconde) va ria tio n of e rr or s in t im e ex ex1 ex2 engineering, technology & applied science research vol. 8, no. 6, 2018, 3619-3623 3623 www.etasr.com laarem & merbouha: chaos suppression using genetically optimized pid control of the 4-d novel… 3) fixed mutation probability variable, bounds matrix and crossover. the best of the bound matrix [-0.8;0.8] and crossover rate=0.6 are used, while the probability mutation default function varies according to the gaussian and adaptive feasible function. table iv gives the best pid values. table iv. pid values, gaussian function pid controller kp ki kd ux 5.8108 8.9852 -11.8140 uy 2.7394 9.8449 14.7133 uz 9.4557 -0.0000 -11.7124 uw 15.4197 11.3442 21.3892 mutation probability=gaussian function, the time of convergence is typically small (control in action at 0.10s). figure 10 shows the chaos suppression. fig. 10. time-history of chaos suppression errors. v. conclusion in this paper, a novel hyperchaotic system was described and its qualitative properties were discussed. lyapunov exponents were calculated to prove that the system is hyperchaotic. chaos suppression was done by the use of pid controller’s gains which were optimized by the use of ga. after varying ga options, i.e. the initial range of the controller’s gains, the crossover rate and the mutation function, in order to view their impact factor on the optimized pid controllers, the optimum controller was the one with the smallest time for chaos suppression. it was shown that the best controller had bound matrix [-0.8;0.8], crossover rate=0.6 and mutation probability=default function with control in action at 0.08s. references [1] s. vaidyanathan, c. volos, advances and applications in chaotic systems, springer, berlin, 2016 [2] a. t. azar, s. vaidyanathan, advances in chaos theory and intelligent control, springer, berlin, 2016 [3] e. n. lorenz, “deterministic non-periodic flows”, journal of the atmospheric sciences, vol. 20, no. 2, pp. 130-141, 1963 [4] o. e. rossler, “an equation for continuous chaos”, physics letters a, vol. 57, pp. 397-398, 1976 [5] v. dobrushkin, applied differential equations, crc press, 2015 [6] q. jia, “hyperchaos generated from the lorenz chaotic system and its control”, physics letters a, vol. 366, pp. 217-222, 2007 [7] o. s.ojoniyi, a. n. njah, “a 5d hyperchaotic sprott b system with coexisting hidden attractors”, chaos, solitons & fractals, vol. 87, pp. 172-181, 2016 [8] q. yang, m. bai, “a new 5d hyperchaotic system based on modified generalized lorenz system”, nonlinear dynamics, vol. 88, no. 1, pp. 189-221, 2017 [9] y. li, w. k. s. tang, g. chen, “generating hyperchaos via state feedback control”, international journal of bifurcation and chaos, vol. 15, no. 10, pp. 3367-3375, 2005 [10] w. fa-qiang, l. chong-xin, “hyperchaos evolved from the liu chaotic system”, chinese physics, vol. 15, no. 5, pp. 963-968, 2006 [11] k. rajagopal, l. guessas, s. vaidyanathan, a. karthikeyan, a. srinivasan, “dynamical analysis and fpga implementation of a novel hyperchaotic system and its synchronization using adaptive sliding mode control and genetically optimized pid control”, mathematical problems in engineering, vol. 2017, article id 7307452, 2017 [12] a. karthikeyan, k. rajagopal, “chaos control in fractional order smart grid with adaptive sliding mode control and genetically optimized pid control and its fpga implementation”, complexity, vol. 2017, article id 3815146, 2017 [13] a. jayachitra, r. vinodha, “genetic algorithm based pid controller tuning approach for continuous stirred tank reactor”, advances in artificial intelligence, vol. 2014, article id 791230, 2014 [14] d. davendra, i. zelinka, r. senkerik, “chaos driven evolutionary algorithms for the task of pid control”, computers and mathematics with applications, vol. 60, no. 4, pp. 1088-1104, 2010 [15] l. guessas, k. benmahammed, “adaptive backstepping and pid optimized by genetic algorithm in control of chaotic systems”, international journal of innovative computing, information and control, vol. 7, no. 6, pp. 5299-5312, 2011 [16] w. d. chang, “pid control for chaotic synchronization using particle swarm optimization chaos”, solitons & fractals, vol. 39, no. 2, pp. 910-917, 2009 [17] h. k. khalil, nonlinear systems, pearson education, new york, 2002 [18] r. l. haupt, s. e. haupt, practical genetic algorithms, wiley, new york, 2004 [19] d. e. goldberg, genetic algorithms in search, optimization& machine learning, addison-wesley, 1989 [20] q. wang, p. spronck, r. tracht, “an overview of genetic algorithms applied to control engineering problems”, second international conference on machine learning and cybernetics, xi’an, china, november 5, 2003 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 time(seconde) va ria tio n of e rr or s in t im e ex ex1 ex2 https://www.sciencedirect.com/science/article/pii/s0960077916301291#! https://www.sciencedirect.com/science/article/pii/s0960077916301291#! https://www.sciencedirect.com/science/journal/09600779 https://www.sciencedirect.com/science/journal/09600779/87/supp/c mailto:qgyang@scut.edu.cn https://link.springer.com/journal/11071 https://www.hindawi.com/86481565/ https://www.hindawi.com/76320658/ http://www.sciencedirect.com/science/article/pii/s0960077907001592#! microsoft word etasr_v13_n4_pp11459-11465 engineering, technology & applied science research vol. 13, no. 4, 2023, 11459-11465 11459 www.etasr.com nasri: numerical simulation of a efficient solar-powered ventilation system numerical simulation of a efficient solarpowered ventilation system faouzi nasri mechanical engineering department, college of engineering, university of bisha, bisha, saudi arabia fnasri@ub.edu.sa (corresponding author) received: 13 may 2023 | revised: 7 june 2023 | accepted: 21 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6038 abstract the objective of this study is to conduct a numerical analysis of a small-scale solar ventilation-air conditioning system operating under the meteorological conditions of bisha, saudi arabia. the primary objective of the proposed system is to provide sustainable and comfortable thermal conditions. to achieve this objective, the system recovers the heat wasted by the solar ventilation process and reuses it to power the desiccant dehumidification process. the solar chimney features a lateral (vertical) wall design, and a comparative performance investigation of two solar chimney designs (conventional vs original) is conducted. mathematical models of the ventilated room and solar chimney are developed, and numerical simulations are carried out to evaluate the performance of each solar chimney design. the study aims to assess the ability of each design to maintain indoor thermal comfort through the analysis of air distribution temperature and air streamlines. the results of the performance comparison revealed that the proposed solar chimney design outperformed the conventional design in terms of thermal and ventilation performance. the proposed solar chimney design, with its lateral (vertical) wall, was also found to be more effective in maintaining indoor thermal comfort than the conventional design. the simulations showed that the proposed design produced a more uniform air distribution temperature within the ventilated room, resulting in improved comfort levels. additionally, the proposed design was found to have a more efficient airflow pattern, with fewer areas of stagnant airflow. these results suggest that the proposed solar ventilation-air conditioning system has the potential to provide sustainable and comfortable thermal conditions in small-scale buildings. keywords-solar chimney; ventilation; mathematical modeling; numerical simulation i. introduction changes in operating conditions, such as flow rate, porosity, and inlet air temperature, have a significant impact on the amount of mass and heat transfer that occurs during sorption phenomena between the air and adsorbent medium. to design an efficient dehumidification system, it is essential to accurately determine the influence of the initial moisture content of the adsorbent. recent literature has explored this topic and offers several interesting works that examine the influence of operating conditions on mass and heat transfer. authors in [1] investigated the impact of rotational speed on the performance of the desiccant wheel, which was characterized by the dehumidification effectiveness, dehumidification coefficient of performance, and sensible energy ratio. they also examined the influence of process air temperature and humidity inlets, regeneration air temperature, and the mass flow rate ratio of regeneration and process air on the optimal rotational velocity of the desiccant wheel. the authors discovered that the optimal rotational velocity for maximizing the dehumidification performance of the desiccant wheel ranged from 5 to 10 revolutions per hour, depending on the specific operating conditions. additionally, they observed that the sensible energy ratio increased monotonically with an increase in the rotational velocity. authors in [2] attempted to determine the optimal angle for achieving maximum airflow through natural ventilation in a solar chimney. they developed a model that allowed for the consideration of various parameters such as air velocity and temperature variation within the chimney. authors in [3] used numerical analysis to investigate the temperature of the internal air in a solar greenhouse. they found that the temperature varied depending on several factors, including climate conditions, location, number of covers, and the shape of the greenhouse. it was also suggested that roofs could be utilized to generate electricity. authors in [4] devised and analyzed a solar chimney system in a residential building that included a humidification and dehumidification desalination unit. the design aimed to facilitate ventilation and fresh water production through desalination. authors in [5] proposed a solar energy-powered air conditioning system that utilized a façade acting as a solar chimney. the system used the heat from the solar chimney to facilitate the dehumidification process and drive an adsorption chiller. authors in [6] conducted a numerical investigation on the effect of the inclination angle of the solar chimney and simulated the variation of the ventilation rate for different angles. they found engineering, technology & applied science research vol. 13, no. 4, 2023, 11459-11465 11460 www.etasr.com nasri: numerical simulation of a efficient solar-powered ventilation system that an inclination angle of 45° to 70° was optimal for a latitude of 28.4°. authors in [7] examined the impact of meteorological conditions on the daily incident solar flux on the facades of a building in the adrar region of south algeria. authors in [8] carried out a theoretical study of a vertical facade solar chimney. authors in [9-10] developed correlations to estimate a new pair of independent effectiveness parameters for desiccant wheels and investigated the influence of atmospheric pressure on heat and mass transfer within the wheels. authors in [11] proposed a solar hybrid system for water desalination, air conditioning, and electricity production. authors in [12] conducted a numerical and experimental study of a solar chimney and found that ambient air velocities greater than 2 m/s improved the air velocity in the ducts. authors in [13] performed experiments on solar chimney thermal performance for natural ventilation and observed the impact of the pressure difference between input and output on the air velocity. authors in [14] investigated the thermal comfort in a building obtained through a solar chimney in cold weather and found that indoor thermal comfort was maintained even with low solar intensity and ambient temperature. authors in [15] compared different configurations of solar chimneys to determine the most efficient one. authors in [16] investigated the solar energy potential and carried out an economic study of a 5 kw rooftop photovoltaic system in botswana. many researchers have proposed hybrid systems for air conditioning, electricity production, and desalination. in this work, a proposed design of the studied system will be developed. the governing equations are presented and the results are discussed. ii. problement statment in figure 1, the design proposal involves linking solar ventilation and solar desiccant air-conditioning. the coupling of these two systems is achieved by harnessing the waste heat generated by the solar ventilation system and using it to drive the desiccant dehumidification process. the conditioned room is naturally ventilated by a wall-mounted solar chimney that is oriented towards the south, and is also conditioned through a solar desiccant air-conditioning system. fig. 1. the proposed approach for a solar-powered ventilation-air conditioning system design. to maintain a room temperature of 25°c, the proposed system utilizes a wall-mounted solar chimney that uses the greenhouse effect to heat up the air gap and create a pressure difference. this drives the hot air from the conditioned room outlet towards the regeneration part of the rotary desiccant wheel (rdw), allowing for desorption of the adsorbent in the rdw. in situations where the regeneration air is not hot enough, such as during night time, cloudy days, early morning, or late evening, an auxiliary heater (ah) and blower (av) may be used to heat and drive the air from the chimney outlet. the system also incorporates a renewal inlet air (i-air) that is first drawn from outside, filtered through f1, and then dehumidified using the desiccant in the adsorption part of the rdw. if the renewal inlet air (i-air) has low relative humidity and is already dry, there is no requirement for dehumidification, and the rotary desiccant wheel (rdw) can be bypassed. the renewal dehumidified air and room air are then mixed to obtain the process air, which is cooled through the water-air radiator (heat exchanger). the cooled process air is then filtered through f2 and injected into the conditioned room. solar energy is harnessed using photovoltaic panels oriented towards the south to generate electricity to power all the electrical components of the proposed design, including blowers, auxiliary blower, desiccant wheel mechanical rotation, and possibly an auxiliary heater. the room to be ventilated has two openings, one providing direct access to fresh air intake, and the other used to release stale air to the solar chimney. the continuity equation, the momentum equations along the x and y axis and the energy conservation equation are stated as follows: continuity equation: ( ) ( ) 0 u v x y       (1) xand y-momentum:     ( ) ( ) 1 1 1 2 3 t t u u v u p u x y x x x u k y y x                                     (2)      0 ( ) ( ) 1 1 1 2 3 t t uv vv p v x y y x x v k g t t y y y                                       (3) energy conservation equation:     1 pr pr 1 pr pr t t t t ut vt t x y x x t y y                                  (4) the equations governing the transport of turbulent kinetic energy (k) and turbulent energy dissipation (ε) are fundamental equations used in turbulent fluid mechanics. the equations are typically expressed below. turbulent kinetic energy:       1 pr 1 1 pr t k t k b k uk vk k x y x x k g g y y                                         (5) engineering, technology & applied science research vol. 13, no. 4, 2023, 11459-11465 11461 www.etasr.com nasri: numerical simulation of a efficient solar-powered ventilation system turbulence dissipation:       2 1 3 2 1 1 pr pr t t k b u v x y x x y y c g c g c k k                                                          (6) with 1 c  , 2c  and 3c  values of 1.44, 1.92, and 0.09, respectively, and are empirical constants [17], prk and pr are the turbulent prandtl numbers for the variables k and ε having values of 1.0 and 1.3, respectively [13], and k g indicates the gradients in mean velocity, are the turbulent prandtl numbers for the variables: 2 3 ji i i k t ij j i j j uu u u g k x x x x                  (7) where b g represents the production of the turbulent kinetic energy due to the buoyancy: pr t b i t i t g g x      (8) equations (1)-(8) are numerically implemented to assess the air temperature distribution and the air streamlines in the conditioned room. the proposed solar chimney consists of two key components: a tunnel and a collector (absorber and glass cover). when creating an energy model for the solar chimney, several necessary hypotheses are taken into account, including:  the absorber is uniformly heated: it is assumed that the absorber is heated uniformly by the sun's radiation, which allows for simplified calculations.  the solar collector is facing south: the solar collector is assumed to be oriented towards the south, and the influence of the sun's azimuth angle fluctuation is neglected. this simplifies the calculations but may not accurately represent the actual solar radiation that the collector receives.  the impact of the turbine on the airflow turbulence is disregarded: it is assumed that the airflow through the solar chimney is steady, and the impact of the turbine on airflow turbulence is ignored. this simplifies the analysis but may not represent the actual airflow behavior.  airflow resistance losses are ignored: the losses due to air flow resistance are disregarded, which may not represent the actual pressure drop through the solar chimney. energy balance equation for the glass cover:         , , , , .gls rd gls sky gls sky cv gls top gls amb cv gls f gls f rd gls abs gls abs i h t t h t t h t t h t t              (9) energy balance equation for the absorber:      , , gls gls abs b abs b cv abs f abs f rd abs gls abs gls i u t t h t t h t t            (10) energy balance equation for the air flow in the collector:       , , , f p f f r cv gls f f gls cv abs f f abs m c t t s h t t h t t            ɺ (11) axial mean air temperature equation: ,out ,in (1 ) f f f t t t    (12) where is a constant that is suggested to be 0.74 [19]. the heat transfer coefficients involved in (9)-(11) can be found in [18]. the air temperature at the entrance of the regeneration portion of the rotating desiccant wheel is obtained numerically using (9)–(12). iii. numerical results and discussion figure 2 depicts the evolution of realistic solar irradiance on june 1 and july 15, 2022, from 07:00 to 18:00. parabolic trends of solar irradiance are imposed by the sun path. on june 1 st , 2022, the solar irradiance starts with 240 w/m 2 at 07:00 to reach 800 w/m 2 at 13:00 and finally falls to 470 w/m 2 at 18:00. on july 15 th , 2022, the solar irradiance starts with 330 w/m 2 at 07:00 to reach 910 w/m 2 at 12:00-13:00 and finally falls to 480 w/m 2 at 18:00. based on figure 3, the evolution of the realistic ambient temperature on june 1 and july 15, 2022, from 07:00 to 18:00, can be described as follows: on june 1st, 2022: the ambient temperature starts at 27°c at 07:00 and rises rapidly to 39°c at 13:00. after 13:00, the temperature begins to decrease slowly and falls to 32°c at 18:00. on july 15 th , 2022: the ambient temperature starts at 29°c at 07:00 and increases rapidly to 42°c at 14:30. after 14:30, the temperature begins to drop slowly and falls to 39°c by 18:00. fig. 2. solar irradiance on june 1 and july 15, 2022. figures 4-6 provide important information regarding the thermal performance of the solar chimney. specifically, these figures depict the inlet chimney air temperature, as well as the minimum and maximum required regeneration air temperature. this information allows for an assessment of the appropriateness of the outlet chimney air temperature in relation to the thermal performance of the solar chimney. engineering, technology & applied science research vol. 13, no. 4, 2023, 11459-11465 11462 www.etasr.com nasri: numerical simulation of a efficient solar-powered ventilation system fig. 3. simulation study of the realistic ambient temperatures on june 1 and july 15, 2022. figure 4 provides important information regarding the evolution of the outlet chimney air temperature on june 1 st and july 15 th , 2022, from 07:00 to 18:00. the figure indicates that the glass transmittance, chimney air gap, and chimney area were set to 0.799, 5 mm, and 3×3 m² respectively. according to the figure, the outlet chimney air temperature becomes appropriate as regeneration air from 08:30 on june 1, 2022, and from 09:30 to 17:00 on july 15, 2022. this suggests that the solar ventilation system is effective in providing the required ventilation and cooling during these periods, as well as providing hot air for the dehumidification stage of the active desiccant air conditioning system. it is important to note that the periods lasting from 08:30-09:30 to 18:00 are the most critical periods when the solar ventilation as passive airconditioning and active desiccant air conditioning system are required to maintain the desired room temperature. during these periods, the outlet chimney air temperature is appropriate, which indicates that the solar ventilation system is operating efficiently and effectively. fig. 4. numerical analysis of the outlet chimney air temperature in the solar ventilation system, june 1st and july 15th, 2022. fig. 5. numerical analysis of the impact of the chimney air gap on the outlet chimney air temperature in the solar ventilation system on june 1 and july 15, 2022 in bisha, saudi arabia. engineering, technology & applied science research vol. 13, no. 4, 2023, 11459-11465 11463 www.etasr.com nasri: numerical simulation of a efficient solar-powered ventilation system fig. 6. numerical analysis of the impact of the chimney area on the outlet chimney air temperature in the solar ventilation system, on june 1 and july 15, 2022 in bisha, saudi arabia. fig. 7. desorption evolution in the solar chimney system. fig. 8. the impact of chimney air gap on the desorption rate in the solar chimney system. figure 5 provides information regarding the effect of chimney air gap on the thermal performance of the solar chimney in terms of outlet air temperature. the chimney air gap was varied from 5 mm to 7 mm during the two engineering, technology & applied science research vol. 13, no. 4, 2023, 11459-11465 11464 www.etasr.com nasri: numerical simulation of a efficient solar-powered ventilation system investigation days: june 1 and july 15, 2022. the glass transmittance and chimney area were set to 0.799 and 3×3 m², respectively. according to figure 5, on june 1 st , 2022, increasing the chimney air gap from 5 mm to 7 mm resulted in a drastic reduction in the outlet chimney air temperature. the maximum air temperature reduction recorded was in the order of 14°c (from 75°c to 61°c), and the outlet chimney air temperature became totally outside the appropriate range of the required regeneration air temperature. this reduction in the outlet chimney air temperature is expected since increasing the chimney air gap reduces the air flow, leading to reduced heating and ventilation effectiveness. figure 6 provides information regarding the effect of chimney area on the thermal performance of the solar chimney in terms of outlet air temperature. the chimney area was varied from 3×3 m² to 3.1×3.1 m² for the same study period. the glass transmittance and chimney air gap were set to 0.799 and 5 mm, respectively. according to figure 6, on june 1 st , 2022, increasing the chimney area from 3×3 m² to 3.1×3.1 m² induced a moderate increase in the outlet chimney air temperature, which became more and more within the appropriate range of the required regeneration air temperature. the maximum air temperature increase recorded was in the order of 4°c (from 75°c to 79°c). on july 15 th , 2022, increasing the chimney area from 3×3 m² to 3.1×3.1 m² induced a moderate increase in the outlet chimney air temperature but led to a slight exceeding of the outlet chimney air temperature evolution outside the appropriate range of the required regeneration air temperature. the maximum air temperature increase recorded was in the order of 5°c (from 84°c to 89°c). this increase in the outlet chimney air temperature is expected since increasing the chimney area enhances the heat transfer between the absorber and the air. overall, the results suggest that a chimney area in the order of 3×3 m² is appropriate to achieve an acceptable thermal performance in terms of hot air regeneration for the desiccant medium within the dehumidification stage. however, a chimney area around 3.1×3.1 m² should be avoided when solar irradiance and ambient temperature are highly intense because it can lead to a slight exceeding of the outlet chimney air temperature outside the appropriate range of the required regeneration air temperature. it is important to note that the appropriate chimney area can vary depending on various factors such as the climate, the solar irradiance, and the size of the conditioned room. therefore, it is recommended to perform a thorough analysis and simulation under different operating conditions to determine the optimal chimney area for a specific application. overall, figure 6 provides important information about the effect of chimney area on the thermal performance of the solar chimney and can be used to optimize the system's operation to maintain a comfortable room temperature while minimizing energy consumption. figure 7 principally depicts the evolution of the desiccant moisture content within the dehumidification stage on june 1 and july 15, 2022 from 07:00 to 18:00. the glass transmittance, the chimney air gap and the chimney area are set at 0.799, 5 mm and 3×3 m², respectively. the desiccant desorption rate becomes slightly more pronounced when the regeneration air temperature increases by 9°, from 75°c to 84°c. the moisture content drops below 0.01 kg (h2o)/kg (dry desiccant) from 900 s and 1100 s for a regeneration air temperature around 84°c to 75°c respectively. it can be concluded that even if the increase in regeneration air temperature is important, the increase in desiccant desorption rate remains not significant. figure 8 provides information regarding the effect of the chimney air gap on the rate of desiccant desorption during the dehumidification stage. the chimney air gap changed from 5 to 7 mm during the two inquiry days. the chimney area and glass transmittance were set as 33 m² and 0.799 m², respectively. according to figure 8, on june 1 st , 2022, the increment of the chimney air gap from 5 mm to 7 mm resulted in a moderate decline in the desiccant desorption rate. for regeneration air temperatures ranging from around 75°c to 61°c, the moisture content decreased to less than 0.01 kg (h2o)/kg (dry desiccant) in the 1100 s and 1700 s, respectively. on july 15, 2022, increasing the chimney air gap from 5 mm to 7 mm also resulted in a moderate decline in the desiccant desorption rate. from 900 s and 1400 s, with a regeneration air temperature ranging from 84°c to 68°c, respectively, the moisture content fell below 0.01 kg (h2o)/kg (dry desiccant). overall, the results suggest that increasing the chimney air gap from 5 mm to 7 mm can lead to a moderate decline in the rate of desiccant desorption during the dehumidification stage. however, the reduction in the desiccant desorption rate is still within an acceptable range, and the moisture content falls below the required level for dry desiccant. it is important to note that the appropriate chimney air gap can vary depending on various factors such as the climate, solar irradiance, and the size of the conditioned room. therefore, it is recommended to perform a thorough analysis and simulation under different operating conditions to determine the optimal chimney air gap for a specific application. overall, figure 8 provides important information about the effect of chimney air gap on the rate of desiccant desorption during the dehumidification stage and can be used to optimize the system's operation to maintain a comfortable room temperature while minimizing energy consumption. iv. conclusions a new solar chimney design with a lateral (vertical) portion is proposed to provide winter mode thermal comfort in a ventilated room. the objective of this study was to conduct a numerical analysis of the thermal and ventilation capabilities of a small-scale hybrid solar ventilation-air conditioning system during two summer days in bisha, saudi arabia. the results of this study will help the optimization of the design of the solar chimney and improving its performance. to further enhance the sustainability of the suggested design, future technological investigations can be undertaken to examine the coupling between solar ventilation and photovoltaic electricity generation. the integration of these two systems can increase the overall energy efficiency of the building and reduce its carbon footprint. additionally, experimental studies of the suggested hybrid design, alone or in combination with photovoltaic electricity generation, can be engineering, technology & applied science research vol. 13, no. 4, 2023, 11459-11465 11465 www.etasr.com nasri: numerical simulation of a efficient solar-powered ventilation system carried out to validate the results of the numerical analysis and identify any potential areas for improvement. overall, the proposed solar chimney design with a lateral (vertical) portion has the potential to provide winter mode thermal comfort in a ventilated room while also reducing energy consumption and carbon emissions. further research and development in this area can lead to the creation of more sustainable and energy-efficient buildings. acknowledgement the authors are thankful to the deanship of scientific research at university of bisha for supporting this work. references [1] g. angrisani, c. roselli, and m. sasso, "effect of rotational speed on the performances of a desiccant wheel," applied energy, vol. 104, pp. 268– 275, apr. 2013, https://doi.org/10.1016/j.apenergy.2012.10.051. 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[19] c. li, y. goswami, and e. stefanakos, "solar assisted sea water desalination: a review," renewable and sustainable energy reviews, vol. 19, pp. 136–163, mar. 2013, https://doi.org/10.1016/j.rser.2012. 04.059. microsoft word 23-3247_s engineering, technology & applied science research vol. 10, no. 1, 2020, 5221-5227 5221 www.etasr.com khouni & hemsas: nonlinear system identification using uncoupled state multi-model approach nonlinear system identification using uncoupled state multi-model approach: application to the pcb soldering system sofiane khouni department of electrical engineering ferhat abbas setif 1 university setif, algeria sofiane.khouni@cevital.com kamel eddine hemsas department of electrical engineering ferhat abbas setif 1 university setif, algeria hemsas_ke_dz@univ-setif.dz abstract—multi-model approach is an adapted tool of modeling nonlinear systems. the underlying idea is to simplify the complex nature of the system to be studied by decomposing it into simple (linear) sub-systems, in order to simplify the study (stability, control law, surveillance, etc.). this technique allows us to extend the application of linear systems methodology to nonlinear systems. this paper presents nonlinear system identification using an uncoupled state multi-model applied to a printed circuit boards (pcb) soldering system. precision, simplicity, and fidelity of the obtained results show the effectiveness of the used algorithm to identify, model, and write down as simple subsystems, a complex black box system. keywords-nonlinear system; identification; uncoupled state; multi-model; profile modeling i. introduction physical systems are often complex and difficult to model. the aim of control law synthesis and/or system diagnosis is to call for a modeling phase which allows obtaining a faithful representation of the behavior of the considered system. this representation must be sufficiently accurate and simple at the same time. a nonlinear model is more suitable to offer a good representation for most real processes, compared to a linear model that remains valid only over a rather restricted area of the operating space or around a balance point. the performance of the linear model declines by moving away from it and the search for a more suitable, often nonlinear model becomes necessary. unfortunately, the use of a nonlinear model in different contexts (identification, estimation, control, and diagnosis) becomes more difficult and more delicate than a linear model, and, on the other hand, the analysis techniques of a linear time invariant (lti) model have been widely developed, which is not the case for nonlinear systems. the mathematical structure that can solve the problem mentioned above, while keeping the mathematical simplicity of the lti models, is a global approach, called multi-model. the multimodel is a universal approximation approach for nonlinear systems. it allows us to extend the use of techniques adapted to linear systems on nonlinear systems. the multi-model approach is based on the idea of decomposing the complex nonlinear system into a finite number l of linear sub-models �� valid in operating areas. the output of each sub-model �� is put into action through an interpolation mechanism (weighting functions) which ensures the transition from one sub-model �� to another. the overall behavior of the nonlinear system is thus approximated by taking into account the contribution of each sub-model. there are two types of multi-model systems, depending on the way of interconnection between the sub models, namely the coupled state multi-model or takagi sugeno fuzzy model [1], and the uncoupled state multi-model [2]. nonlinear system identification using coupled state multimodel approach has been extensively studied [3-6]. on the other hand, a few works suggest an identification procedure based on an uncoupled multi-model structure [7, 8]. however, the field of electronic card (pcbs) manufacturing has recently grown significantly, due to the fact that the different areas of contemporary life require the presence of these boards in various domestic appliances. the manufacturers of these devices demand that these pcbs must be of high quality and without problems to ensure the reliability and the safety of their devices. this objective can only be achieved by ensuring the manufacturing quality of pcbs in its various phases, including soldering. thus, soldering system monitoring in the dedicated “industrial oven” has become a necessity to ensure the quality and durability of the pcb soldering. this complex system can only be monitored after developing its mathematical model. so, in this paper, the decoupled multi-model method is used to model a real-world industrial complex system which is a soldering system of pcb into an off-line oven (“profile” system). ii. multi-models throughout this paper, we will designate sampled variable ���� as the value of the variable ���� at time � = �.�� where �� is the sampling period. thus, the global output of the sampled time multi-model ���� is defined by: ���� = ������������� � ��� (1) where �� are the weighting functions that ensure the switching between sub-models. they are associated with each operating corresponding author: sofiane khouni engineering, technology & applied science research vol. 10, no. 1, 2020, 5221-5227 5222 www.etasr.com khouni & hemsas: nonlinear system identification using uncoupled state multi-model approach area, and are chosen to verify the convex sum properties: �������� = 1 � ��� et 0 � �������� � 1, ∀� = 1…�, ∀� (2) ���� is the vector of decision or indexing variables of weighting functions ��. these decision variables can be measurable state variables or input or output, or a combination of these variables, � is the sub-model’s number. the contribution of each sub-model ����� depends on its weighting function ��������. �� is obtained from the normalization of the activation functions �� for each sub-model: �������� !�"�#��∑ %�"�#��&%'( (3) these activation functions �� can be triangular, trapezoidal, gaussian or sigmoidal. iii. multi-model structures depending on the coupling or interconnection nature of the local sub-models used to generate the global output of the multi-model, two large families are used: coupled state and one uncoupled state multi-models. a. coupled state multi-models (takagi-sugeno) also called unique state or takagi-sugeno multi-models [1], they operate with sub-models sharing the same state vector )���. the sampled state representation for this multi-model is given by [9]: *)���+1� ,�)����+-�.���+/�)�� +1� ��������)���+1��������� ��������0�)������� (4) where �� satisfy the defined convexity conditions in (2), ) ∈ 23 is the state vector, . ∈ 24 the input vector, � ∈ 25 the output vector, � the indexation variables vector of weighting functions ��. b. uncoupled state multi-models (filev) in this type of multi-model, the sub-models are uncoupled [2], i.e. each sub-model has its own state vector )����, so the dimensions and complexity of the sub-models vary. the sampled state representation for this multi-model is given by [8, 10]: 6)���+1� ,�)����+-�.���+/������ 0�)�������� ����������������� (5) where �� satisfy the defined convexity conditions in (2), )� ∈ 23! is the state vector of the ith sub-model, . ∈ 24 is the input vector, � ∈ 25 the output vector, � the indexation variables vector of multi-model obtaining methods. it is suitable to note that the outputs ����� of the sub-models are “artificial modeling signals” used only to describe the nonlinear behavior of the real system. these signals, inaccessible to measurement and devoid of any physical sense, are connected to the real system only by their weighted sum [8]. iv. multi-model obtaining methods a nonlinear system is given by the following general state and input-output relations: 7)�� +1� 8�)���,.�������� 9�)���,.���� (6) the objective of multi-model modeling is to simplify the complex nonlinear functions 8�.� and 9�.�. on the other hand, modeling a nonlinear system by a multi-model amounts to defining these parameters, i.e. ,�,-�,0� and /� with parameters of the weighting functions of the sub-models in (4) and (5). three well-known methods to obtain these parameters are: • linearization around operating points [9, 11, 12]. • transformation by nonlinear sectors [11, 13]. • parametric identification [5, 7, 8, 14]. v. parametric identification of uncoupled state multi-model the identification of a multi-model concerns the search of an optimal structure and the estimation of the parameters of the weighting functions and of the local models. this method can be applicable if only the measurements of the inputs and outputs of the system (with no mathematical model or black box) are available [5], by searching or imposing the structure of the multi-model that is the input/output behavior, without interest in obtaining a knowledge model who describes its internal behavior (phenomenological), the global representation of the identification method is illustrated in figure 1. fig. 1. multi-model identification there are two steps in obtaining a multi-model identification: • determination of the structure → partitioning of the inputoutput data which leads to: determining the number of local models, choosing the decision variables, and realizing the partitioning of the space and determining the parameters of the weighting functions. • identifying sub-model parameters using an iterative approach. a. problem formulation a sampled time uncoupled multi-model and function of an unknown parameter vector :, is in the form: 6)��� + 1� ,��;<�)���,;<�+-��;<�.��� + /��;<������ 0��;<�)���,;<� ���� ������������,;<����� (7) where: engineering, technology & applied science research vol. 10, no. 1, 2020, 5221-5227 5223 www.etasr.com khouni & hemsas: nonlinear system identification using uncoupled state multi-model approach ;<: are the parameters of the sub-model i in the form of a column vector of dimension =� . for the purposes of the identification procedure, all parameters of the sub-models are grouped together in a single augmented column vector θ, where: : >:� :? ⋯ :� ⋯ :�abcccccccdcccccccefghigjkjlm jnhokp� ∑q! r:� >:�,� … :�,q … :�,q!ar (8) =�: stands for the parameter’s number in sub-model i. :�,q: is the qth parameter in sub-model i, it is a scalar to identify. thus, the problem of identification is summarized as follows: the weighting functions ��(.) are fixed, and from the input .(�) and the measured output ��(�) (of a miso or siso system), : is the parameter vector of the multi-model must be identified. b. implementation of identification the sub-model parameter identification is done by minimizing a criterion which presents the difference between the measured output (original system) and the estimated output (the multi-model). most often the criterion used is of a quadratic form: st(:) = �? u?(�,:) v w�� u(�,:) = �(�,:)− ��(�) (9) where �(�) is the multi-model output, ��(�) the measured output of the nonlinear system and y is the measurement number. the criterion st in (9) is a global one. it is used if we want to obtain a behavioral multi-model in a global way. it is also possible to use a local criterion if we want to obtain a multimodel that favours a good match between the local behavior of sub-models and of the nonlinear system in each operating zone. the local criterion is given by: s�(:) = ∑ ∑ ����(�)����(�,:)− ��(�)�? vw������ (10) where ��(�) is the ith sub-model output. it is also possible to combine two criterions in a single mixed criterion of the form: sz(:) = [st + (1 − [)s�, 0 ≤ [ ≤ 1 (11) the parametric estimation procedure of the parameter vector : is done iteratively, with each iteration approximating the optimal solution of the vector :. this procedure is implemented by using the gauss-newton algorithm. the updating of the parameter vector at each iteration \ is obtained from the following recurring formula: :(\ + 1) = :(\)− ](:)^�_(:) (12) where :(\) is the parameter vector at iteration n, θ(n+1) the same vector at the following iteration, 2 ( ) ( ) j h θ θ θ θ τ ∂ = ∂ ∂ is the hessian matrix, ( ) ( ) j g θ θ θ ∂ = ∂ is the gradient vector, and s is a global, local, or mixed criterion. the computation of the gradient vector _ and the hessian matrix ] is based on the computation of the sensitivity functions of the multi-model output with respect to the parameters of each sub-model. in order to ensure and improve the convergence of (12) the following marquardt formula is recommended [15]: :(\ + 1) = :(\)− ∆(\)(](:) + a(\)b)^�_(:) (13) where: ∆(\): the relaxation coefficient of the iteration \, with ∆(\) ≤ 1,∀\, and a(\): the regularisation parameter, a(1) is chosen near zero, i.e.: a(1) ≈ 0. 1) computation of gradient vector _t the gradient vector _t is calculated by derivation of the global criterion in (9) with respect to the parameters vector: _(:) = def(g)dg = dh(i∑ ji(w,g )kl'( m dg _(:) = ∑ u(�,: )dn(w,g)dgvw�� (14) with : dn(w,g) dg = ∑ ����(�)�dn!(w,g)dg���� (15) the term ( , ) i y k θ θ ∂ ∂ represents the sensitivity functions of the 1 st order of the i th output with respect to the parameter vector : of the multi-model. 2) computation of hessian matrix hg it is obtained directly from the gradient by derivation with respect to the parameter vector: ]t(:) = dief(g)dgdgo _(:) ]t(:) = ∑ u(�)p →r din(w,g) dgdgo vw�� +∑ dn(w,g)dgvw�� dn(w,g)dgo (16) u(�) is negligible under the assumption that the error tends to zero, in this case the hessian matrix becomes: ]t(:) = dief(g)dgdgo ≈ ∑ dn(w,g)dgvw�� dn(w,g)dgo (17) 3) computation of sensitivity functions dn!(w,g) dgs,t = du!(g) dgs,t )�(�,:) + 0�(:) dv!(w,g) dgs,t (18) where: i: is the index of the i th sub-model, p: the index of the p th parameter vector of the p th sub-model, q: the q th parameter in :5 vector, and: dv!(w,g) dgs,t = dw!(g) dgs,t )�(�,:) + ,�(:) dv!(w,g) dgs,t +dx!(g)dgs,t .(�)+ dy!(g) dgs,t , � = 2,3,… (19) engineering, technology & applied science research vol. 10, no. 1, 2020, 5221-5227 5224 www.etasr.com khouni & hemsas: nonlinear system identification using uncoupled state multi-model approach 4) parametric identification algorithm for a multi-model figure 2 summarizes the steps constituting the algorithm of the parametric identification described above. fig. 2. parametric identification algorithm for a multi-model vi. application a. system description 1) smt process smt (surface mounted technology) means: surface mounted technology of the electronic components on the pcb, in other words, non through the whole component but placed on the surface of the pcb. this process is carried out within a production line of pcb. the placement of the smd (surface mounted device) is done by special machines called pick and place machines who place the smd on blank boards. the pcb and smd will be soldered automatically by passing through an industrial in-line reflow dedicated oven. the high heat inside the reflow oven melts the alloys contained in the paste to weld the components already mounted on the pcb. fig. 3. in-line industrial reflow oven (dual-lane 14×2 zones) in smt line this operation, (soldering board in a reflow oven), is divided into 4 steps: • preheating: increases the temperature of the components and solder paste. • drying: time for the flux to act and evaporate completely. • reflow: fusion of the solder paste and rise to the maximum temperature which must be the melting temperature. • cooling. the variation of the temperature is studied and regulated very strictly so that the soldering is of good quality. 2) profile a “profile” is a graph that represents the temperature of the pcb soldering in the reflow oven, i.e. represents the variation of the temperature as a function of time t°(t) during this operation. this function depends mainly on the solder paste and the product to be manufactured. the variation of the temperature in a profile passes through the four steps mentioned above: preheating, drying, reflow and cooling. the general form of the profile is illustrated in figure 4. fig. 4. general form of the profile 3) system description: “profile of forced convection oven hysc co-81” this type of oven (figure 5) belongs to the family of desktop reflow ovens or single-zone off-line reflow ovens. it can be used off-line, and has the advantage of being simple (mono-zone) as opposed to the multi-zone reflow oven (figure 3), which makes its modeling possible in the context of multimodels. this oven is composed of a single phase thermoelectric actuator (heating resistor), an ssr (solid static relay) which supplies the electrical power to the thermoelectric actuator, and an electronic controller that regulates the power of the ssr. the most important specifications of this oven are [16]: • temperature: max=250°c. • controller: digital pid controller. • heater: sheath heater. • heating : convection (forced by fans). engineering, technology & applied science research vol. 10, no. 1, 2020, 5221-5227 5225 www.etasr.com khouni & hemsas: nonlinear system identification using uncoupled state multi-model approach • electric requirements: 220vac, 50/60hz. • power consumption: 1600w. fig. 5. industrial forced convection oven hysc co-81 the profile of this oven can be considered as an automated siso (single in-single out) system, the input is the average power supplied by the ssr (power transformer), and the output is the profile itself, as shown in figure 6. fig. 6. reflow oven system scheme heat (energy) generated by the heating resistor and produced by the electrical power, is propagated by the phenomenon of forced convection by fans. the temperature in this case (the profile) is that of the paste solder measured by a temperature probe installed in a special device called profiler, which is connected to the pc for data collection (t°(t)). the formula that relates the average power dissipated in the heaters over a period �| (cycle time of the ssr) and the cyclic rate α is: }~�� = [ ���� i � (20) where r is the resistance. the input }~�� in one pcb soldering cycle is represented in figure 7. fig. 7. system input (average power) note that the pcb soldering cycle for this measurement is 315s. the measured output ��(�) or the profile is represented by figure 8 (in the same soldering cycle). fig. 8. system output (profile) the general formula linking the input .(�) = }4�n(�), the state vector �(�) and the measured output ��(�) = �°(�) of this system is: ��(�) = 9(�,.� (21) note that the nonlinear function 9 is unknown, so we are facing an identification problem. b. multi-model modeling since there is no mathematical relation or equation linking the input and the output, we will use identification to obtain the parameters of the sub-models. the first step is the partitioning of the operating space and the choice of the parameters of the weighting functions. for simplifying reasons, it has been assumed that the partitioning and the parameters of the weighting functions are known. the operating space is divided into five zones, which means that we would consider five submodels and five weighting functions. the activation functions used for the normalization of the weighting functions are chosen to be gaussian. note that this partitioning is not unique. the decision variable is the measured output of the system, �(�) = ��(�). each activation function �� of a sub-model i, of centre �� and of dispersion coefficient � (which is assumed to be common for all sub-models) is of the following form: ����(�)� = �^� �(�)��!� � i (22) the weighting function ����(�)� of a sub-model i is given by figure 9, in which we see that the weighting functions are highly mixed, this choice is appropriate for the global parametric estimation method. the degrees of the five submodels are respectively: 1, 1, 2, 2, 1. this arbitrary choice is based on the form of the measured output ��(�), which depends on the complexity of the five operating areas. hence, the form of the five sub-models is: 7)�(� + 1� ,��;<�)����+-��;<�.���+/��;<������ 0��;<�)���� (23) � 1. .5 engineering, technology & applied science research vol. 10, no. 1, 2020, 5221-5227 5226 www.etasr.com khouni & hemsas: nonlinear system identification using uncoupled state multi-model approach where: ,� = �� , -� ��, /� ��, 0� ��, ��,��,��,�� are scalars, and ;< >�� �� �� ��a� for i=1, 2 and 5, ��,�..�, ��,�..?, ��,�..?, ��,�..? are scalars, and ;< >��,� ��,? ��,� ��,� ��,� ��,? ��,� ��,? ��,� ��,?a� for � 3 and 4. fig. 9. weighting functions (highly mixed) the application of the identification algorithm gives us the following results, with ��…� being sub-model parameters: �� ∶ �,� �� 0.0283; -� �� 0.0496 /� �� 0.1469; 0� �� 1.0102 ¢ �? ∶ �,? �? 0.0843; -? �? x0.0228/? �? 0.3911; 0? �? 1.0637 ¢ �� ∶ 6,� ¤ 0.4707 0.52910.4501 0.5300 ¥; -� ¤ 0.1536x0.1334¥ /� ¤0.72990.7297¥; 0� �� >1.3740 1.2510a¦ �� ∶ 6,� ¤ 0.9863 0.09280.0021 0.0084 ¥; -� ¤x0.00680.0701 ¥ /� ¤ 1.0738x0.0000¥; 0� �� >1.5572 x0.0340a¦ �� ∶ �,� �� 0.9967; -� �� 0.0001 /� �� 1.0641; 0� �� 1.5994 ¢ the five sub-models �� are exhibited in figure 10. fig. 10. the five sub-models �� the global multi-model output is represented in figure 11. fig. 11. global multi-model output c. multi-model precision the precision of a multi-model is described by two performance indices, the first being the mse (mean square error) given by: §�¨ = �v∑ ���(�)− �(�)� ?vw�� (24) the second is the vaf (variance accounted for) given in percentage. the evaluation of the vaf allows, in the general case, to compare two matrices. the vaf is equal to 100% if the two matrices § and §© are identical. otherwise, the vaf varies between 0% and 100%. it is defined by: ª,« = maxh1x �~¯�z^z©��~¯�z©� ,0m°100% (25) where m is the measured data matrix and §© the estimated data matrix (the multi-model in our case). in the obtained multimodel, mse=0.0727, and vaf=99.998%. figure 12 gathers the measured output (profile) and the estimated output (multimodel) in the same view, allowing the precision of the applied multi-model identification to be shown. fig. 12. the multi-model identification precision vii. conclusion the multi-model is a high precision global approximation approach for nonlinear systems. its principle is “divide and rule”, i.e. it eliminates the complexity of a nonlinear system by decomposing it into a finite number of simple (linear) subsystems that are easy to manipulate. the output of each submodel contributes through an interpolation mechanism (weighting functions) which ensures the transition from one sub-model to another. the overall behavior of the nonlinear engineering, technology & applied science research vol. 10, no. 1, 2020, 5221-5227 5227 www.etasr.com khouni & hemsas: nonlinear system identification using uncoupled state multi-model approach system is thus approximated by taking into account the contribution of each sub-model. the major advantage of this approach is to extend the application of the methods developed for linear systems to nonlinear systems. depending on the nature of the coupling of the local sub-models associated with the different zones of operation, two large multi-model families are utilized, global state multi-models whose sub-models share the same operating space and uncoupled state multi-models where each sub-model has its own state vector. to obtain these multi-models, three main methods are noted: linearization around operating points, transformation into nonlinear sectors, and parametric identification, which has been presented in detail in this paper for uncoupled state multi-model. despite its difficulty in terms of identification, this type of multi-model has the advantage of being simple to study in particular for monitoring and diagnosis. the uncoupled state multi-model identification method was applied to an off-line pcb soldering system profile. the obtained precision was described by mse=0.0727 and vaf=99.998%. these two performance indices clearly show the efficiency and the accuracy of this method. the profile of an off-line and single-zone oven (figure 5) was modeled as a single nonlinear system. in the case of online ovens (figure 3) of several heating and cooling zones, which are used for all production lines because of their reliability and capacity (up to 15pcbs at the same time every 3 minutes), the profile is more complicated and a factor of several parameters and variables. in this case it can be considered as an automated switching system or hds (hybrid dynamical system), where each mode is modeled by a multimodel. references [1] t. takagi, m. sugeno, “fuzzy identification of systems and its applications to modelling and control”, ieee transactions on systems, man and cybernetics, vol. 15, no. 1, pp. 116–132, 1985 [2] d. filev, “fuzzy modeling of complex systems”, international journal of approximate reasoning, vol. 5 no. 3, pp. 281–290, 1991 [3] t. a. johansen, b. a. foss, “non linear local model representation for adaptive systems”, singapore international conference on intelligent control and instrumentation, singapore, february 17-21, 1992 [4] t. a. johansen, b. a. foss, “constructing narmax using armax”, international journal of control, vol. 58, no. 5, pp. 1125–1153, 1993 [5] k. gasso, identification des systemes dynamiques non-lineaires: approche multi-modele, phd thesis, national polytechnic institute of lorraine, 2000 (in french) [6] j. k. gugaliya, r. d. gudi, s. lakshminarayanan, “multi-model decomposition of nonlinear dynamics using a fuzzy-cart approach”, journal of process control, vol. 15, no. 4, pp. 417–434, 2005 [7] h. elaggoune, m. benouaret, m. messaadia, “modeling and fault diagnosis sensor by multi-model approach”, 10th international confernece on conception and integrated production, tanger, morroco, december 2-4, 2015 [8] r. orjuela, b. marx, j. ragot, d. maquin, “nonlinear system identification using heterogeneous multiple models”, international journal of applied mathematics and computer science, vol. 23, no. 1, pp. 103-105, 2013 [9] z. lendek, t. m. guerra, r. babuska, b. de schutter, stability analysis and nonlinear observer design using takagi-sugeno fuzzy models, springer-verlag, 2010 [10] h. bedoui, a. kedher, k. ben othman, “fault detection and isolation for an uncertain takagi-sugeno fuzzy system using the interval approach”, in: handbook of research on advanced intelligent control engineering and automation. igi global, 2015 [11] k. tanaka, h. o. wang, fuzzy control systems design and analysis: a linear matrix inequality approach, john wiley & sons, 2001 [12] a. akhenak, conception d’observateurs non lin´eaires par approche multimod`ele: application au diagnostic, phd thesis, national polytechnic institute of lorraine, 2004 (in french) [13] m. chadli, p. borne, multiple models approach in automation: takagisugeno fuzzy systems, john wiley & sons, 2012 [14] r. isermann, m. munchhof, identification of dynamic systems: an introduction with applications, springer-verlag, 2011 [15] d. w. marquardt, “an algorithm for least-squares estimation of nonlinear parameters”, journal of the society for industrial and applied mathematics, vol. 11, no. 2, pp. 431–441, 1963 [16] http://www.hysc.co.kr/wp/item/forced-convection-oven/#tab-id-2 microsoft word 8-2360_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3530-3535 3530 www.etasr.com kumar et al.: an efficient power control technique for high-frequency resonant inverter in … an efficient power control technique for highfrequency resonant inverter in induction heating system anand kumar department of electrical engineering indian institute of technology (indian school of mines) dhanbad, india anand.2016dr0084@ee.ism.ac.in debayan sarkar department of electrical engineering indian institute of technology (indian school of mines) dhanbad, india debayan.17dr000423@ee.ism.ac.in pradip kumar sadhu department of electrical engineering indian institute of technology (indian school of mines) dhanbad, india pradip@iitism.ac.in abstract—an efficacious and reliable power control technique has been developed which can be used to regulate the output power of a high-frequency full bridge series resonant inverter (hf-fbsri) in an induction heating (ih) system. in this paper, a modified buck-boost converter is presented to control the dc link/bus voltage which maintains the ih system under resonant mode and optimizes the performance of the ih system. controlled dc link/bus voltage has been applied to this hf fbsri to control the average output power in the ih system. using this aimed control technique, a wide range of output powers has been controlled and consistent performance of the ih system has been achieved. zvs switching technique has been used to reduce the switching losses. varying average power has been obtained at different duty cycles ranging from 0.2 to 0.8 with variable dc link voltage and it has been corroborated using psim environment for an ih system rated at 5500w. keywords-induction heating (ih) system; dc link voltage; duty cycle; fbsri; series resonance i. introduction today’s era reveals that the uses of induction heating (ih) technology are increasing in industrial and domestic applications [1]. the benefits of using this technology are its high efficiency, less heating time, accurate heating pattern, safety and cost-effectiveness. due to these unique merits, ih technology became one of the most promising methods to attain high heating performance for development in the field of high frequency (hf) inverter and its control technique [2]. ih technology can be defined as an electrical and contactless process in which workpiece/object is heated with the help of eddy current, generated by hf alternating flux/current [3]. actually this hf alternating flux links with the workpiece and generates eddy current. due to this eddy current, the workpiece placed inside the ih coil gets heated by the joule principle. generally, to generate hf current, an hf resonant inverter is used like the full bridge series resonant inverter (fbsri) [4-5], half bridge-sri [6], single switch topology [7], class –d [13] and so on. the demerit of resonant converters is the occurence of switching and power losses across semiconductor switches. zero voltage switching (zvs) and zero current switching (zcs) techniques are used to mitigate these losses [8]. in the current work, fbsri has been applied with zvs condition. apart from that, various power control techniques have been developed for resonant converter topologies [2]. in the resonant inverter, output power could be varied in two ways. one is by employing variable dc link voltage to the resonant inverter and another is by manipulating the time period of pulses. out of these two techniques, pulse width modulation (pwm) technique is employed for manipulating output power. some of the control techniques for a resonant inverter used for ih applications are: frequency modulation technique [9], phase shift [10], pulse density modulation [11, 16], asymmetrical duty cycle [12] and square wave [12]. these methods are not able to maintain the ih system under resonant mode. due to this, the performance of the ih system decreases and switching losses become more significant [12]. it has been seen in frequency modulation technique that while varying frequency the current and power through resonant tank diminish. regarding the elimination of the aforementioned disadvantages, variable dc link voltage method is proposed in this work which has been done by a modified buck-boost dc-dc converter. in this paper, controlled output power has been achieved using modified buck boost dc-dc converter. the main advantage of dc-link voltage control technique through a dcdc converter is that, it protects from the electromagnetic disruptions at the input side of the ih system. this electromagnetic disruption is generated through a high frequency component (i.e. generated at the output side) which tries to superimpose on the input side. in this paper, additionally ls and cs have been used to eliminate this hf component in the input side of fbsri. this proposed control technique can be applied in both industrial and domestic ih applications. ii. proposed classical ih system based on modified buck boost converter the block diagram of the proposed classical ih system is shown in figure 1. in this figure, ac supply (230v, 50hz as engineering, technology & applied science research vol. 8, no. 6, 2018, 3530-3535 3531 www.etasr.com kumar et al.: an efficient power control technique for high-frequency resonant inverter in … per indian standards) has been applied to the full bridge diode rectifier which converts alternating current (ac) to direct current (dc) with ripple content. after rectification, filter inductor (lf) and capacitor (cf) have been used for mitigating the ripple content in dc voltage. later, this pure dc supply has been applied to the modified buck-boost dc-dc converter which is used to regulate dc-link voltage (vdcl). now this variable dc–link voltage has been applied to a full bridge series resonant inverter (fbsri) through a filter composed of ls and cs that eliminates high frequency components [4]. this fbsri generates hf ac current which flows through the ih coil. due to this, hf alternating flux generated across the coil, links with the metallic object and thus creates eddy current inside the object which is to be heated. due to joule’s law of heating effect, the metallic object that is placed inside the ih coil gets gradually heated. fig. 1. block diagram of the proposed hf induction heating system in this paper, the heat intensity in the object is being controlled by controlling the output power of fbsri. this has been done through the modified buck boost converter topology which controls the dc link voltage that is finally applied to the fbsri as shown in figure 1. the circuit configuration of modifed buck boost converter is shown in figure 2, where lbb and cbb are the buck boost inductor and capacitor respectively. unlike the conventional buck boost converter, the modified buck boost converter allows both input and output voltage to be of the same polarity. switches m1 and m2 are turned on and off simultaneously. when both switches are turned on, lbb stores the energy and when the switches are turned off, lbb supplies energy to the load through a path incorporating both diodes, d1 and d2. fig. 2. modified buck boost converter lbb and cbb have been evaluated by (1)-(2): sl dcl bb fi dv l ∆ − = )1( (1) so o bb fv di c ∆ = (2) where, vdcl is the dc link voltage, d is the duty cycle, ∆il and ∆vo are the changes in current and voltage respectively and fs is the switching frequency of the modified buck boost converter. the controlled output of the modified buck boost converter is fed to fbsri. the circuit configuration for fbsri is shown in figure 3 [17-18]. an fbsri generally consists of four hf semiconductor switches (i.e. mosfets, gto, igbts) with an anti-parallel diode. due to the switching of two switches at the same time in one leg, a quasi-square waveform is generated. commonly, mosfets and igbts are the first choices for the resonant inverter in ih applications. in fbsri, the ih coil and its load have been modeled as a series combination of req and leq [14-15]. ceq is the resonating capacitor connected in series to create series resonance condition for analyzing the electrical behavior of the practical ih system. generally, resonant inverter operates at the resonant frequency fr. but in practical cases, switching frequency fs of the fbsri must be greater or less than resonant frequency fr to reduce switching losses. in this work, fbsri has been incorporated with zvs condition. fig. 3. circuit configuration of fbsri a. mathematical analysis of the proposed control technique in this part, a brief description of the proposed power control technique has been presented. from figure 1 it can be seen that the buck boost converter has been connected to control the output power of fbsri. the proposed power control technique has been validated by the use of the following mathematical equations. let vd is the average dc output voltage of bridge rectifier, vdcl is the average dc link voltage, and d is the duty cycle. so: π = md v v 2 (3) where vm is the maximum input voltage and ( ) ( )tvtvv mddcl ω− π =ω−= cos1 2 cos1 (4) now the output voltage of the buck boost converter i.e. vbb can be written as: ( ) d d t v d d vv m dclbb − ×ω− π = − = 1 cos1 2 1 (5) equation (5) reveals that vbb can be controlled by varying duty cycle. let vo be the output voltage of fbsri and its first harmonic amplitude can be defined as: α π = cos 4 1 bbvv (6) φ = ω +ω+=ω cos 1 )( eq eq eqeq r cj ljrjz (7) engineering, technology & applied science research vol. 8, no. 6, 2018, 3530-3535 3532 www.etasr.com kumar et al.: an efficient power control technique for high-frequency resonant inverter in … where φ is the phase angle between voltage and current while the proposed fbsri operates at resonant frequency (fr). due to this, voltage and current will be in the same phase. owing to this α=φ is assumed for further analysis. α =ω∴ cos )( eqr jz (8) fundamental output current, i1 and output power of fbsri can be expressed as: α π = ω = 211 cos 4 )( eq bb r v jz v i (9) 2 4 41 2 2 2 16 8 22 bb bb eq eq eq eq i v v p r r cos cos r r α α π π   = = =    (10) from (10) it can be concluded that output power can be controlled by varying buck boost output voltage vbb. iii. ih load electrical modeling and frequency response analysis a. electrical modeling of ih load to analyze the electrical behavior of the classical ih system, the electrical modeling of ih load is needed. the electrical modeling of ih load can be explained with the help of a transformer equivalent circuit representation because ih system works on the principle of electromagnetic induction between the ih coil (which acts as a primary winding) and the load (which will act as a secondary winding) [19-20]. the electrical equivalent circuit of ih load is shown in figure 4. in this figure, lp and ls are the self-inductances in the primary and secondary side respectively. m is the mutual inductance of transformer equivalent circuit. rl is the resistance of the object to be heated which is placed inside the ih coil. fig. 4. transformer model/equivalent circuit of ih load req and leq can be calculated by: 12 psp vmijlj =ω+ω (11) 0)( 21 =+ω+ω slsp irljmij (12) rearranging (11) and (12), we get (13):         ω+ −ω+ ω+ ω+ ω = 222 222 222 2 ( 1 1 sl spslp sl l p p lr mlllrl j lr mr i v (13) on identifying the real and imaginary part in (13), the values of req and leq can be found as: 222 sl l eq lr mr r ω+ ω = (14) 222 22 sl s peq lr ml ll ω+ ω −= (15) the exact equivalent circuit of the ih system is shown in figure 5 where req and leq are connected in series. additionally, a capacitor is connected in series to create the resonance condition shown in figure 3. fig. 5. the equivalent circuit of ih load/series rlc circuit b. frequency response analysis of ih load it is already mentioned that, ih load is modeled as a series connection of req, leq, and ceq. the voltage gain of the equivalent circuit shown in figure 5 is used for frequency analysis. here vs is the input voltage for the resonant tank and vout is the output voltage across resistance that has been taken for calculation of gain. the voltage gain equivalent circuit shown in figure 5 can be defined as: eq eqeq eq eq eqeq eq in o sc slr r sc slrsi sir sv sv sg 1 ) 1 )(( )( )( )( )( ++ = ++ == (16) putting s=jω in (16): 1 1 1 eqo s s in s eq s eq s eq s eq eq s eq eq rv ( j ) g( j ) v ( j ) r j l j c j l j r c r ω ω ω ω ω ω ω ∴ = = + + = + − (17) where ωs is the switching frequency of the fbsri. resonant frequency and quality factor of series req, leq and ceq are defined as: eqeq r cl 1 =ω , eq eqr r l q ω = (18)       µ −µ+ =       ω ω − ω ω + =ω∴ 1 1 1 1 1 )( jqjq jg s r r s s (19) 2 2 1 1 1 s g( j ) q ω µ µ =    + −       (20) where s r ω µ ω = . engineering, technology & applied science research vol. 8, no. 6, 2018, 3530-3535 3533 www.etasr.com kumar et al.: an efficient power control technique for high-frequency resonant inverter in … the magnitude plot for the different values of quality factor in (20) is shown in figure 6. from figure 6, it can be concluded that, as the quality factor increases, the selectivity for the resonant frequency increases, thereby maximizing power transfer occurs from source to load. it can be observed that maximum output power and maximum gain g(jω) i.e. 1 could be obtained at the resonant frequency. by varying resonant frequency, the output power of fbsri could be varied but it disturbs the quality factor of the resonant tank. so the characteristic of req, leq, and ceq tank becomes selectively poor, thereby yielding poor regulation of the output power. due to this, the switching frequency is kept fixed and near to resonant frequency. the switching frequency and quality factor for the fbsri are calculated from (18). fig. 6. frequency response curve of req, leq, and ceq series circuit iv. simulated model and results a 5kw classical ih system based on the buck boost converter has been proposed and corroborated with psim. design parameters and their values are given in table i. figure 7 shows the simulated model of the proposed classical ih system. in this work, a modified buck boost converter has been designed to control the output power of fbsri. this modified buck boost converter has been designed to generate a regulated dc link output voltage vbb between 8v and 124.71v corresponding to duty cycle 0 2 0 8. d . .≤ ≤ this variable vbb is fed to fbsri. thus, a wide range of values of the controlled output power across ih load is achieved through fbsri. table i. designed parameters and their values designed parameters values input ac voltage (vr.m.s) 230v, 50hz switching frequency (fs) for fb-sri 25khz filter inductance (lf) 1mh filter capacitance (cf) 250mf buck boost inductor (lbb) 320.5uh buck boost capacitor (cbb) 2.49mf resonating capacitor (ceq) 0.8uf equivalent inductance (leq) 52.7uh equivalent resistance (req) 5ω hf filter inductance (ls) 25uh hf filter capacitor (cs) 5uf maximum r.m.s output power (pout) 5500w figures 8(a) to 8(d) show the simulated waveforms of voltages and currents with regulated vbb at different duty cycles d across req, leq, and ceq. figures 8(a) and 8(b) show the buck operating mode while figures 8(c) and 8(d) show the boost operating mode of the modified buck boost converter with the input of 30v dc link voltage (vdcl). thus, variable dc-link voltage (vdcl) has been obtained using modified buck boost converter. non smoothing inductor (ls) and capacitor (cs) have been used to mitigate hf component at the dc link voltage. the switching frequency for the buck boost converter has been kept at 30khz along with the variable duty cycle but for fbsri, switching frequency fs and duty cycle α of pwm have been kept at 25khz and 50% respectively. fig. 7. simulation model of the proposed classical ih system (a) at duty cycle d=0.2 (b) at duty cycle d=0.4 (c) at duty cycle d=0.6 (d) at duty cycle d=0.8 fig. 8. simulated results across ih load at different duty cycles. engineering, technology & applied science research vol. 8, no. 6, 2018, 3530-3535 3534 www.etasr.com kumar et al.: an efficient power control technique for high-frequency resonant inverter in … fbsri operates at the resonant frequency fr and is calculated by: 1 r eq eq l c ω = (21) 6 6 1 1 25khz 2 2 527 10 0 8 10 r eq eq f l c . .π π − − = = ≈ × × × (22) pulse density modulation (pdm) controller has been used to generate pulses for the fbsri as shown in figures 9(a) and 9(b). table ii shows the variation of output power pout of the fbsri with respect to variable duty cycle α. here, cosθ (power factor) has been assumed as unity for the calculation of output power because the proposed fbsri works on the resonant frequency. the graph between average output power pout versus duty cycle α is shown in figure 10 which validates the linear relationship between pout and α. from this figure, it can be concluded that as the duty cycle increases, output average power increases. thus, simulation results show that the proposed ih system is more efficient and reliable. table ii. output power vs duty cycle (α) vbb(v) vo (v) io (a) po(avg)=vo*io (w) 0.2 7.82 6.54 0.88 5.75 0.4 20.86 17.42 2.34 40.76 0.6 46.90 39.24 5.27 206.79 0.8 124.71 104.17 14.01 1459.42 (a) (b) fig. 9. (a) pdm controller and (b) its pulses v. conclusions an efficient output power control technique has been implemented for the classical ih system which controls the dc link voltage and it has been verified in psim environment. the heating effect of this proposed ih system can be varied by using variable average output power of 5.5kw. owing to this, whatever the requirements of power/heat, it can be regulated up to its rated power. this fbsri transfers the maximum amount of current because it is resonating in nature. this dc link voltage control technique can be applied to both domestic and industrial induction heating (ih) applications. fig. 10. output power (pout) vs duty cycle (α) references [1] o. lucia, p. maussion, e. j. dede, j. m. burdio, “induction heating technology and its applications: past developments, current technology, and future challenges”, ieee transactions on industrial electronics, vol. 61, no. 5, pp. 2509-2520, 2014 [2] a. kumar, m. sadhu, n. das, p. k. sadhu, d. roy, a. ganguly, “a survey on high-frequency inverter and their power control techniques for induction heating applications”, journal of power technologies, vol. 97, no. 3, pp. 201-213, 2017 [3] s. lupi, “survey on induction heating development in italy”, third ieee history of electro-technology conference, pavia, italy, september 5-7, 2012 [4] a. dominguez, l. a. barrangan, j. i. artigas, a. otin, i. urriza, d. navarro, “reduced-order models of series resonant inverters in induction heating applications”, ieee transactions on power electronics, vol. 32, no. 3, pp. 2300-2311, 2017 [5] n. yongyuth, p. viriya, k. matsuse, “analysis of a full-bridge inverter for induction heating using asymmetrical phase-shift control under zvs and non-zvs operation”, 7th international conference on power electronics and drive systems, bangkok, thailand, november 27-30, 2007 [6] h. sarnago, o. lucia, a. mediano, j. m. burdio, “analytical model of the half-bridge series resonant inverter for improved power conversion efficiency and performance”, ieee transactions on power electronics, vol. 30, no. 8, pp. 4128-4143, 2015 [7] a. shenkman, b. axelrod, y. berkovich, “improved modification of the single-switch ac-ac converter for induction heating applications”, iee proceedings-electric power applications, vol. 151, no. 1, pp. 1-4, 2004 [8] c. m. wang, h. j. chiu, d. r. chen, “novel zero-current-switching (zcs) pwm converters”, iee proceedings-electric power applications, vol. 152, no. 2, pp. 407-415, 2005 [9] f. forest, s. faucher, j. y. gaspard, d. montloup, j. j. huselstien, c. joubert, “frequency-synchronized resonant converters for the supply of multiwinding coils in induction cooking appliances”, ieee transactions on industrial electronics, vol. 54, no. 1, pp. 441-452, 2007 [10] c. carratero, o. lucia, j. acero, j. m. burdio, “phase-shift control of dual half-bridge inverter feeding coupled loads for induction heating purposes”, electronics letters, vol. 47, no. 11, pp. 670-671, 2011 [11] v. esteve, e. s. kilders, j. jordan, e. j. dede, c. cases, e. maset, j. b. ejea, a. ferreres, “improving the efficiency of igbt series-resonant inverters using pulse density modulation”, ieee transactions on industrial electronics, vol. 58, no. 3, pp. 979-987, 2011 [12] b. meziane, h. zeroug, “comprehensive power control performance investigations of resonant inverter for induction heating surface hardening”, ieee transactions on industrial electronics, vol. 63, no. 11, pp. 6086-6096, 2016 [13] h. sarnago, o. lucia, a. mediano, j. m. burdio, “class d/de dualmode-operation resonant converter for improved-efficiency domestic induction heating system”, ieee transaction on power electronics, vol. 28, no. 3, pp. 1274-1285, 2013 engineering, technology & applied science research vol. 8, no. 6, 2018, 3530-3535 3535 www.etasr.com kumar et al.: an efficient power control technique for high-frequency resonant inverter in … [14] j. acero, c. carretero, r. alonso, j. m. burdio, “quantitative evaluation of induction efficiency in domestic induction heating applications”, ieee transactions on magnetics, vol. 49, no. 4, pp. 1382-1389, 2013 [15] c. carretero, o. lucia, j. acero, r. alonso, j. m burdio, “frequencydependent modelling of domestic induction heating using numerical methods for accurate time-domain simulation”, iet power electronics, vol. 5, no. 8, pp. 1291-1297, 2012 [16] v. esteve, j. jordan, e. s. kilders, e. j. dede, e. maset, j. b. ejea, a. ferreres, “enhanced pulse density modulated power control for high frequency induction heating inverters”, ieee transactions on industrial electronics, vol. 62, no. 11, pp. 6905-6914, 2015 [17] v. esteve, j. jordan, e. s. kilders, e. j. dede, e. maset, j. b. ejea, a. ferreres, “improving the reliability of series resonant inverters for induction heating applications”, ieee transactions on industrial electronics, vol. 61, no. 5, pp. 2564-2572, 2014 [18] o. fernandez, j. delgado, f. martinez, j. correa, m. heras, “design and implementation of a 120 a resonant inverter for induction furnace”, ieee international autumn meeting on power, electronics, and computing, mexico city, mexico, november 13-15, 2013 [19] n. a. ahmed, “high-frequency soft-switching ac conversion circuit with dual pwm/pdm control strategies for high-power ih applications”, ieee transactions on industrial electronics, vol. 58, no. 4, pp. 1440-1448, 2011 [20] b. patidar, m. m. hussain, s. k. jha, b. dikshit, a. sharma, “modelling and experimental demonstration of a litz coil-based high-temperature induction heating system for melting application”, iet electric power applications, vol. 12, no. 2, pp. 161-168, 2018 authors profile anand kumar was born in bokaro, jharkhand, india in 1991. he received his b.e degree in electrical and electronics engineering from the rajiv gandhi technological university, bhopal, madhya pradesh, india in 2012 and m.e degree in power electronics (electrical engineering) from birla institute of technology, mesra, ranchi, india in 2014. he served as an assistant professor in department of electrical engineering at guru gobind singh educational society technical campus (ggsestc), kandra, bokaro, india. he is presently pursuing ph.d in department of electrical engineering at indian institute of technology (indian school of mines), dhanbad, india. his research interest includes power electronics converters, high frequency resonant converter, direct ac-ac converters, applications of resonant converter in domestic as well as industrial induction heating systems. at present he is engaged in research work on “analysis and power control technique in high frequency inverter in induction heating system”. debayan sarkar was born in kharagpur, west bengal, india in 1992. he received his b.tech degree in electrical engineering & m.tech degree in power systems from department of electrical engineering, national institute of technology, durgapur, india in the year 2015 & 2017 respectively. presently, he is pursuing his ph.d under the guidance of prof. p. k. sadhu, department of electrical engineering, indian institute of technology (indian school of mines), dhanbad, india. his research interests include maximum power extraction from bipv and roof integrated pv systems, solar photovoltaic power generation techniques, dc-dc power electronics converter topologies, iot in electrical engineering applications, monitoring and analysis of dielectric strength of transformer oil & high voltage engineering. presently, he is engaged in a research work entitled, “maximum power extraction approach from building integrated photovoltaic's (bipv)”. pradip kumar sadhu received his b.e., m.e. and ph.d. (engineering) degrees in electrical engineering from jadavpur university, west bengal, india. he is presently working as a professor and as the head of the department of electrical engineering of the indian institute of technology (indian school of mines), dhanbad, india. he has a total of 30 years of experience including 18 years of teaching and research plus 12 years in the industry. he has four granted patents and twenty seven patents that are under process. he has several journal and conference publications at national and international levels. he is the principal investigator of few government funded projects. his current research interest includes power electronics applications, the application of high frequency converters, energy efficient devices, energy efficient drives, computer aided power system analysis, condition monitoring, lighting and communication systems for underground coal mines. microsoft word 39-3193_s1_etasr_v9_n6_pp5088-5092 engineering, technology & applied science research vol. 9, no. 6, 2019, 5088-5092 5088 www.etasr.com samad et al.: performance evaluation of learning classifiers of children emotions using feature … performance evaluation of learning classifiers of children emotions using feature combinations in the presence of noise abdul samad department of computer science hamdard university karachi, pakistan asamad23@gmail.com aqeel-ur-rehman department of computer science hamdard university karachi, pakistan aqeelrehman1972@gmail.com syed abbas ali department of computer & information systems engineering, ned university of engineering & technology, pakistan saaj@neduet.edu.pk abstract—recognition of emotion-based utterances from speech has been produced in a number of languages and utilized in various applications. this paper makes use of the spoken utterances corpus recorded in urdu with different emotions of normal and special children. in this paper, the performance of learning classifiers is evaluated with prosodic and spectral features. at the same time, their combinations considering children with autism spectrum disorder (asd) as noise in terms of classification accuracy has also been discussed. the experimental results reveal that the prosodic features show significant classification accuracy in comparison with the spectral features for asd children with different classifiers, whereas combinations of prosodic features show substantial accuracy for asd children with j48 and rotation forest classifiers. pitch and formant express considerable classification accuracy with mfcc and lpcc for special (asd) children with different classifiers. keywords-spoken utterances; special children; learning classifiers; noise; features i. introduction and related work in the modern era of human-computer interaction, emotional speech recognition is a field of vast concern. ser has a great influence on human behavior and is a key point to build relations. different emotions have their own characteristics that make it memorable in their own way [1]. furthermore, “emochildru” has been introduced [2] as the first child emotion database created to recognize speech and voice emotions from children’s behavior. two child emotional speech examination probes are reported in the context of the corpus: grown-up audience members and programmed listeners. automatic classification results are fundamentally the same as human discernment, despite the fact that the precision is underneath 55 % for both, demonstrating the trouble of child emotion recognition from speech under natural conditions. to improve the state of people with asd, a few cal procedures have been executed. authors in [3] depict the investigation of fluctuated cal strategies actualized to enhance the everyday life states of such individuals. furthermore, the authors briefed about the cal strategies involved in various applications improving correspondence, behavioral and social abilities of such special children. in [4], it was noticed that it is not easy to observe mental and emotional conditions in autism spectrum conditions (asc) aspects. a technique was proposed to recognize their speech in [5] independently from the speaker. in this technique, mel & bark scale, equivalent rectangular bandwidth in filter space along with gamma toned features were utilized at the front end, whereas at the back end, fuzzy c means (fcm), multivariate hidden markov models (mhmm) and vector quantization (vq) approaches were applied. individual words and short sentences in tamil language were used to evaluate the performance by three variants. the data of two speakers were tested against the features of eight speakers. a prominent real situational database was organized in [6] to detect fear thorough the feature classifier “interjection” through speech in extreme emotional and real world emergencies. mfccs along with support vector machine with variant interjections were utilized to categorize speech emotions. in [7], urdu language has been taken to recognize emotions from primary age children. the authors used 3 different prosodic features with 5 different classifiers and four emotions. they reported that j-48 classifier achieved the highest accuracy. a profound architecture was utilized in [8], which uses a convolutional network for extricating space shared highlights and a long short-term memory network for arranging emotions utilizing space particular features. a complete cross-corpora exploration of different avenues regarding various speech emotions areas uncovers that transferable features give increases extending from 4.3% to 18.4% in speech emotions recognition. the fundamental of deep neural networks (dnns) is to perceive human emotions from a speech signal. mel-frequency cepstral coefficient (mfcc) is selected as a one of the frequently used speech features from crude sound information. in next step, dnn nourished the extricated speech features to prepare the system. also, a hand crafted database was presented improving the utilization of the system [9]. the work-related recognition, classification, emotion detection children with asd is still an open topic of research, while researchers are now more concerned to help these children by making them realize the emotions in the real world. under this scope, an autism-based game “emotify” has been developed [10]. it comprises two levels of difficulty and attempts to teach children about neutral, anger, sadness and happiness emotions. corresponding author: abdul samad engineering, technology & applied science research vol. 9, no. 6, 2019, 5088-5092 5089 www.etasr.com samad et al.: performance evaluation of learning classifiers of children emotions using feature … at the second level, children are helped in expressing their feelings which would be evaluated and examined. machine learning approaches are exploited to develop a multilingual emotion recognition system. this paper evaluates the performance of learning classifiers when dealing with prosodic and spectral features and their combinations considering special (asd) children as noise in terms of classification accuracy. ii. learning classifiers and features in daily routine conversations the prosodic features play a vital role [11]. the parameters used in expressing the speech to perceive the feelings of users are speech rate, length, pitch, formant, intensity, mel frequency cepstrum coefficient (mfcc) and lpcc [12]. two spectral features and three prosodic features (intensity, pitch, and formant) and their potential combinations are utilized in this research. • pitch: pitch and frequency are correlated. the analysis of every speech frame is obtained by their statistical values throughout the sample. these values [13] depict the clear picture of properties of audio parameters. • intensity: intensity demonstrates the prosodic feature encoding and the emotion based spoken utterance expressions [12]. • formant: formant is a critical recurrence segment of speech which gives quantifiable results of the consonants and vowels of the speech signal [12]. four learning classifiers were used in the experimental framework. the evaluation of the performance of these classifiers regards spectral and prosodic features and their combinations. the comprehensive description of the learning classifiers can be found in [14]. the classifiers are: • j48: a family of decision tree algorithms used to figure the feature vector for different examples. the classes for the recently produced events are being learned on the basis of the training examples. with the support of tree grouping calculation the elementary dispersion of the information is successfully justifiable [15]. • multi-layer perceptron (mlp): a class of deep artificial neural network that contains three layers at minimum. the first is the input layer while the last one is the output layer. the middle is a hidden layer and different mlps can have various numbers of invisible layers [16]. • rotation forest: rotation forest [15] eliminates randomly any subsets of classes, performs bootstrap on the remaining data and finally performs pca and establishes free decision trees. • logit boost classifier: boosting [16] works on the principal that a set of weak learners can be used to create a strong classifier. logit boost provides higher weights for misclassified classifiers. iii. corpus collection and recording specification the corpus has been collected from both categories of children (normal and with asd) in urdu and it comprises of 200 samples, equally divided for both cases. as per the research methodology, asd children have been considered as noise in the experimental framework. the recording specification has been considered in standard conditions with signal-to-noise ratio ≥ 45db. microsoft windows 7 sound recorder has been utilized to record the emotion based spoken utterances of normal and special (asd) children. the configuration is 16 bit, mono, pcm with a testing rate of 48khz with microphone hazard and awareness of 54db±2db and 2.2w separately, 3.5mm mash stereo and link length of 1.8m. the choice of a spoken utterance incorporated these qualities a) semantically impartial, b) simple to investigate, c) reliable with any circumstance exhibited, and d) having comparable importance for every dialect. the sentence was: ― “mujhe khelna hai” or “i have to play”. iv. experimental results and discussion the performance of learning classifiers is evaluated in the experimental framework for normal and special children making use of prosodic and spectral features and their combinations on spoken utterances recorded in urdu. the corpus collection comprises of 200 spoken utterance samples in different emotions equally distributed in normal and special children. the experimental framework further classifies inter and intra feature combinations with four different classifiers (logit boost, mlp, j48 and rotation forest) with the following feature configurations: 1) separate prosodic and spectral features, 2) combinations of all three prosodic features (intensity, formant, and pitch) with two spectral features (lpcc and mfcc). the objective of the proposed framework is to identify the behavior of the four classifiers in a single feature or different combinations of spectral and prosodic features on spoken utterances of special (asd) and normal children in terms of classification accuracy. the experimental results for both corpuses taken from normal and special (asdtreated as noise) children in urdu follow. a. prosodic features pitch demonstrates great precision in portraying the states of children under all four classifiers while classifying special children more precisely than normal children (table i). the classification accuracy of rotation forest with prosodic feature pitch for asd (noisy) children spoken utterances was significantly better than the accuracy of the other classifiers. intensity also shows good classification accuracy for asd children for all classifiers except from rotation forest. all learning classifiers demonstrate higher classification accuracy with formant for asd children in comparison with normal children b. spectral features mfcc has significant accuracy with mlp and logit boost classifier in case of normal children, on the other hand, only rotation forest shows considerable classification accuracy for asd children. lpcc has very good accuracy only from logit boost classifier in both normal and special children. the outcome demonstrates that in any study of lpcc the logit boost classifier ought to be utilized. engineering, technology & applied science research vol. 9, no. 6, 2019, 5088-5092 5090 www.etasr.com samad et al.: performance evaluation of learning classifiers of children emotions using feature … fig. 1. prosodic features table i. classification accuracy for prosodic features feature classifier asd children classification accuracy (%) normal children classification accuracy (%) intensity mlp 81.3 65.6 logit boost 81.5 90.5 rotation forest 76.5 64.5 j48 81.3 65.6 pitch mlp 80 71.4 logit boost 93.8 72 rotation forest 94.4 76.7 j48 80 71.4 formants mlp 50 11 logit boost 90 78.6 rotation forest 99 63.2 j48 98 60 table ii. classification accuracy for spectral features features classifier asd children classification accuracy (%) normal children classification accuracy (%) mfcc mlp 64.7 85.7 logit boost 64.7 85.7 rotation forest 83.3 61.1 j48 10 50 lpcc mlp 50 10 logit boost 84.6 62.9 rotation forest 9 50 j48 11 50 fig. 2. spectral features c. inter combination of prosodic and spectral features the prosodic feature pitch shows significant accuracy with the combination of two other prosodic features. in combination with intensity, pitch illustrates considerable classification accuracy with logit boost and j48 for asd (special) children. pitch with formant performs well in classifying special (asd) children with all classifiers except logit boost. in combination with intensity and formants, mlp and rotation forest show significant classification accuracy in comparison with the other two classifiers for asd children. j48 has comparable accuracy in classifying special and normal children. fig. 3. inter and intra combinations of features d. intra combination of prosodic and spectral features in intensity-mfcc, mlp performs better in classifying the normal children, while logit boost is considerably good in engineering, technology & applied science research vol. 9, no. 6, 2019, 5088-5092 5091 www.etasr.com samad et al.: performance evaluation of learning classifiers of children emotions using feature … classifying noisy spoken utterances for special children. in this case, rotation forest and j48 are performing averagely. similarly, in intensity-lpcc combination, the mlp is good and accurate. nevertheless, logit boost more accurately classifies the normal children’s spoken utterances. rotation forest and j48 perform averagely. table iii. classification accuracy for prosodic and spectral features feature combination classifier asd children classification accuracy (%) normal children classification accuracy (%) pitch, intensity mlp 88 91.3 logit boost 90 88 rotation forest 87.5 87.5 j48 80 71.4 pitch, formant mlp 90.5 81.5 logit boost 88 91.3 rotation forest 90.9 84.6 j48 98 60 intensity, formant mlp 85.7 77.8 logit boost 92 95.7 rotation forest 89.5 76 j48 88.3 88.3 mfcc, lpcc mlp 56.5 56 logit boost 93.8 71.9 rotation forest 98 57.1 j48 11 50 pitch, mfcc mlp 95.2 85.2 logit boost 77.8 85.7 rotation forest 94.7 79.3 j48 92.3 65.7 pitch, lpcc mlp 84.2 72.4 logit boost 89.5 75.9 rotation forest 85.7 77.8 j48 92.3 65.7 intensity, mfcc mlp 98 80 logit boost 82.1 95 rotation forest 94.4 76.7 j48 69.7 93.3 intensity, lpcc mlp 80.8 86.4 logit boost 87 84 rotation forest 85.7 77.8 j48 69.7 93.3 formant, mfcc mlp 53.5 80 logit boost 98.4 75 rotation forest 98 57.1 j48 97 60 formants, lpcc mlp 46.4 45 logit boost 94.1 74.2 rotation forest 97 61.5 j48 98 60 table iii provides the results of the learning classifiers with combinations of prosodic and spectral features for classifying the noisy spoken utterances in terms of classification accuracy. the most significant results can be observed of the combination of lpcc with pitch and formant in classifying the noisy (special children) utterances, whereas, pitch and formant with mfcc also show substantial classification accuracy for special (noisy) children. other combinations such as intensity and lpcc and intensity with mfcc also provide considerable results in classification. v. conclusion in this paper, the performance of learning classifiers has been evaluated considering prosodic and spectral features and their combinations for children with asd in terms of classification accuracy. the experimental frame comprises four different classifiers with different inter and intra combinations of prosodic and spectral features. the experiments were conducted on a sample of 200 individuals equally taken from normal and children with asd which were considered as noise. the conclusions of the experimental results are: • the spectral features show significant classification accuracy with prosodic features (pitch & formant) with rotation forest and j48 classifiers. • separate analysis of the spectral and prosodic features reveals that the classification accuracy of prosodic features is considerably better than of spectral features. • the intra feature combinations of spectral features with pitch and formant demonstrate better classification accuracy for different classifiers. the authors are now focusing on developing an experimental framework to perform the same methodology with different emotions for evaluating the performance of classifiers to special children (asd) in terms of classification accuracy. references [1] s. ramakrishnan, “recognition of emotion from speech: a review”, in: speech enhancement, modeling and recognition algorithms and applications, pp. 121-137, intech, 2012 [2] e. lyakso, o. frolova, e. dmitrieva, a. grigorev, h. kaya, a. a. salah, a. karpov, “emochildru: emotional child russian speech corpus”, lecture notes in computer science, vol. 9319, springer, cham, 2015 [3] s. dewan, a. singh, l. singh, s. gautam, “role of emotion recognition in computive assistive learning for autistic person”, indian journal of science and technology, vol. 9, no. 48, 2016 [4] o. golan, y. sinai-gavrilov, s. baron-cohen, “the cambridge mindreading face-voice battery for children (cam-c) complex emotion recognition in children with and without autism spectrum conditions”, molecular autism, vol. 6, no. 1, article id 22, 2015 [5] r. arunachalam, revathi, “a strategic approach to recognize the speech of the children with hearing impairment different sets of features and models”, in: multimedia tools and applications, springer, 2019 [6] s. a. yoon, g. son, s. kwon, “fear emotion classification in speech by acoustic and behavioral cues”, multimedia tools and applications, vol. 78, no. 2, pp. 2345-2366, 2019 [7] s. khan, s. a. ali, j. sallar, “analysis of children’s prosodic features using emotion based utterances in urdu language”, engineering, technology & applied science research, vol. 8, no. 3, pp. 2954-2957, 2018 engineering, technology & applied science research vol. 9, no. 6, 2019, 5088-5092 5092 www.etasr.com samad et al.: performance evaluation of learning classifiers of children emotions using feature … [8] a. marczewski, a. veloso, n. ziviani, “learning transferable features for speech emotion recognition”, thematic workshops of acm multimedia, mountain view, usa, october 23-27, 2017 [9] m. f. alghifari, t. s. gunawan, m. kartiwi, “speech emotion recognition using deep feedforward neural network”, indonesian journal of electrical engineering and computer science, vol. 10, no. 2, pp. 554-561, 2018 [10] a. rouhi, m. spitale, f. catania, g. cosentino, m. gelsomini, f. garzotto, “emotify: emotional game for children with autism spectrum disorder based-on machine learning”, 24th international conference on intelligent user interfaces companion, new york, usa, march 16-20, 2019 [11] k. s. rao, s. g. koolagudi, emotion recognition using speech features, springer, 2013 [12] p. shen, c. zhou, x. chen, “automatic speech emotion recognition using support vector machine”, international conference on electronic, mechanical engineering and information technology, harbin, china, august 12-14, ieee 2011 [13] a. s. utane, s. l. nalbalwar, “emotion recognition through speech”, 2nd national conference on innovative paradigms in engineering & technology, nagpur, maharashtra, india, february 17, 2013 [14] s. a. ali, s. zehra, m. khan, f. wahab, “development and analysis of speech emotion corpus using prosodic features for cross linguistic”, international journal of scientific & engineering research, vol. 4, no. 1, pp. 1-8, 2013 [15] s. a. ali, a. khan, n. bashir, “analyzing the impact of prosodic feature (pitch) on learning classifiers for speech emotion corpus”, international journal of information technology and computer science, vol. 2, pp. 54-59, 2015 [16] m. swain, a. routray, p. kabisatpathy, “databases features and classifiers for speech emotion recognition: a review”, international journal of speech technology, vol. 21, no. 1, pp. 93-120, 2018 microsoft word etasr_v10_n6_pp6557-6562 engineering, technology & applied science research vol. 10, no. 6, 2020, 6557-6562 6557 www.etasr.com alotaibi & alotaibi: design of a planar tri-band notch uwb antenna for x-band, wlan, and wimax design of a planar tri-band notch uwb antenna for x-band, wlan, and wimax sattam alotaibi department of electrical engineering taif university taif, saudi arabia srotaibi@tu.edu.sa abdullah alhumaidi alotaibi department of science and technology taif university taif, saudi arabia a.alhumaidi@tu.edu.sa abstract-in this work, a new ultra-wideband (uwb) antenna design with 2.08ghz to 12ghz impedance bandwidth and tripleband specifications is presented. the proposed antenna is formed by a truncated square patch, a partial ground plane, and a 50ω microstrip line. three different types of slots were used in order to induce notched bands. a c-shaped slot is etched on the radiating patch to obtain a notched band in 3.31-4.21ghz for wimax. an inverted u-shaped slot in the micro-strip line induces a second notched band in order to reduce the interference with the wlan [5.04-6.81ghz]. finally, two inverted l-shaped slots around the micro-ribbon line on the ground plane allow the x-band [9.13 to 10.75ghz]. the antenna has dimensions of 32×28×1.6mm 3 . the ansoft software (hfss) was used to simulate the proposed structure. the simulation results are in good agreement with the measurement results. the antenna shows an omnidirectional radiation pattern. keywords-uwb antenna; notched band; wimax; wlan; x band i. introduction the demand for higher data rates is increasing, and the available frequency bands are becoming scarce [1]. to meet the requirements, ultra-wideband (uwb) antenna technology (3.1ghz-10.6ghz) seems to be an effective solution. uwb technology has advantages such as the ease of manufacture, the small size, and the large bandwidth [2-3]. this bandwidth is mainly due to the fact that uwb communications use extremely narrow pulses for transmitter and receiver communication. the most popular antennas used for uwb applications are printed monopole antennas which are easily integrated with different kinds of integrated circuits like monolithic microwave ones [4, 5]. however, it should be borne in mind that the use of the uwb band frequency can be the cause of interference in applications using neighboring frequencies such as wlan or wimax applications [6-7]. to avoid this, it is necessary to ensure, generally during manufacture, that the developed antenna operates on a frequency interval whose limits can be chosen by the manufacturer. one way to do this is to modify the antenna structure. the slot insertion method is the best known method for obtaining a frequency band rejected in the uwb antenna. indeed, the presence of slots in the patches and/or the ground plane [8-11], in the parasitic elements [12-13], or in the supply line [14-15] are effective techniques used for making a notched strip. for a given element, the shape and the dimensions of the slot allow fixing the frequency of the notch band. usually, the slot dimensions depend on the wavelength λ on which the rejected band is centered, and is chosen to be equal to about λ/2 or λ/4 depending on the position and shape of the slot. in [16], two frequencies (3.5ghz and 10.5ghz) were obtained when using a u slot on the radiating element. in the ground plane, the insertion of an l-shaped slot also generated a notch centered at the frequency of 5.5ghz. the bandwidth of this structure is established between 2.8ghz and 12ghz. in [17], a micro strip line-fed monopole antenna has been developed. the designed antenna (size 30×30mm 2 ) was modified to keep the band rejection at the level of a local wireless network. for this, inverted u and π slots as well as two u-grooves in the radiating patch were used. to satisfy the need for wireless technologies, the use of uwb notch band antennas is necessary [18-19]. in this work, a 32×28×1.6mm 3 triple band square patch antenna with a fr4 substrate (permittivity 4.4) was studied with an obtained bandwidth of 2.08ghz-12ghz. the tri-band specifications were achieved through engraving a c-shaped slot in the radiating patch, an inverted u-shaped slot in the microstrip line, and an inverted l-shaped slot around the microribbon line in the ground plane. ii. design procedure all the simulations presented in this work have been performed with ansoft's hfss simulation software which allows simulating finite and limited ground planes. as shown in figure 1 and table i, the proposed antenna is made up of a 2.99mm×10.75mm microstrip feed line. the length and width of the microstrip line were chosen taking into account that the nature of the substrate and its thickness directly influence the characteristics of the microstrip feed line. with the fr4_epoxy substrate (εr=4.4, thickness=1.6mm), the dimensions we used allow the microstrip feed line to have a characteristic impedance of 50ω over a very wide frequency band. the antenna is in the form of a rectangular patch with partial ground plane. the two lower corners of the radiating element were cut to improve the band width. the dimensions of the truncated corners are 2.5×5.625mm 2 . corresponding author: a. alhumaidi alotaibi engineering, technology & applied science research vol. 10, no. 6, 2020, 6557-6562 6558 www.etasr.com alotaibi & alotaibi: design of a planar tri-band notch uwb antenna for x-band, wlan, and wimax fig. 1. diagram of the antenna. table i. dimensions of the proposed antenna (mm) parameter �� �� �� � �� value (mm) 32 28 10.7 1.6 14 parameter �� �� �� �� �� �� �� value (mm) 14 10.7 2.9 2.5 5.625 c shaped slot inverted u-shaped slot pair of inverted lshaped slots � �� �� � �� �� �� �� �� �� 10 3.5 2.5 1 6 2 0.25 3.5 4 0.25 as shown in figure 2, this modification of the geometry of the radiating element directly influences the appearance of the return loss spectrum. after truncating the corners, we note that the antenna has a better adaptation compared to the base antenna of the same frequency band. a minimum reflection coefficient of -27db at a frequency close to 8.5ghz is obtained for this antenna. it is also noted that the minimum in the vicinity of the 4ghz frequency is accentuated with respect to the case of the base antenna. fig. 2. the s11 of the proposed and the conventional antenna. a. first notched band as mentioned above, the presence of slots in the different elements of the antenna allows the appearance of notch at given frequencies. the arrangement of these slots, their shape and their dimensions allow control of the frequencies of the notches. to have a rejection of the wimax band, and to obtain a first notched band in the range 3.31ghz-4.21ghz, a c-shape slot is introduced (figure 3) in the radiative element [2, 4, 19-21]. to get satisfactory results and highlight the influence of each parameter, the thickness of the slit t1 and the position in the patch noted by pf1 vary while the length remains unchanged (proportional to the rejected frequency). as a first step, the position of the slot remains unchanged, and the values of the thickness t1 vary (25×10 -5 m, 50×10 -5 m, 100×10 5 m, 150×10 -5 m, and 200×10 -5 m). fig. 3. geometry of the antenna: l1= 10mm, l2= 3.5mm, l3= 3mm, t1=1mm. the return loss s11 spectra (figure 4) correspond to different values of t1. the antenna presents a good adaptation in the studied frequency band, with a reflection coefficient of around -10db, except in the bands [3.5, 4.5ghz] and [9.5, 11.5ghz] where the reflection coefficient is slightly above -10db. a minimum reflection coefficient varying from -20db to -47.5db, depending on the used values of t1, is observed between 8ghz and 9ghz. fig. 4. evolution of the return loss spectra for different values of t1. figure 5 shows the simulated vswr of the proposed antenna. an adequate choice of parameters associated to the c slot allowed us to obtain the desired band according to (1) and (2): fnotch= � ������� (1) εeff= ���� � (2) where l represents the length of form c and εeff the substrate dielectric constant. it is evident from the simulation results of engineering, technology & applied science research vol. 10, no. 6, 2020, 6557-6562 6559 www.etasr.com alotaibi & alotaibi: design of a planar tri-band notch uwb antenna for x-band, wlan, and wimax the vswr, that the antenna is well suited (vswr <= 2) in the band [2.0ghz, 12.0ghz] except for the band bands [3.2ghz, 4.0ghz] where vswr > 2 with a vswr = 9 obtained in the vicinity of 3.8ghz. fig. 5. the antenna vswr. b. second notched band due to the wide frequency range of uwb technology, it is essential to avoid interference with wlan technology in order to reduce its impact on the uwb system. in order to obtain a second notched band in the range 5.04ghz-6.81ghz, a second slot was embedded in the micro-strip line [22-24]. the inverted u shape of this slot (figure 6) has the following characteristics: the λc/4 length chosen for this slot allows the rejection of the band centered at fc=5.5ghz. the other geometric parameters are not modified comparing to the base antenna's. fig. 6. insertion of the second slot for wlan rejection. to analyze the influence of the parameters of the slot, the thickness of the slot t2 and the position in the patch noted by pf2 varied, whereas the length of the slot was kept unchanged. in the first step, the position of the slot remained fixed, and the thickness values varied (25×10 -5 m, 50×10 -5 m, 75×10 -5 m, 100×10 -5 m, and 125×10 -5 m). figure 7 shows the evolution of the return loss s11 according to the slot thickness variation. a clear evolution of the frequency and value of the minima can be observed. fig. 7. s11 versus the variation of the thickness t2. by adjusting the main parameters, the length of this slot is chosen to be 13.5mm. the desired rejected wlan band is accomplished, and the antenna is well suited as shown in figure 8. fig. 8. vswr spectra with u-shaped slot. c. third notched band another type of slot was used to attenuate interference signals over the frequency range of 9.13 to10.75ghz for the xband, an inverted l-shaped slot (pf3) is etched around the micro-ribbon line on the ground plane [25-27]. the geometry of the obtained antenna is shown in figure 9. the total length of the slot is 8.5mm, or about λc/4 when considering the frequency fc=10ghz which corresponds to the center of the rejected band. no modifications were made to the other antenna parameters. the position of the pf3 varied whereas the thickness of the slot remained fixed. the position pf3 was calculated according to the center of the ground plane. according to the evolution of the shape of spectra in figure 10, corresponding to different positions of the slot, it can be seen clearly that when the slot moves upwardly [28], the mismatching band shifts to lower frequencies with an increase of the antenna bandwidth. at the position pf3=0mm the antenna is adapted in the band [3.1ghz, 10.6ghz] with the rejection of the central frequency band of 10ghz [9.33ghz, 10.54 ghz]. the band we wanted to reject was obtained by adjusting the parameters of l6 and l7 (figure 11). engineering, technology & applied science research vol. 10, no. 6, 2020, 6557-6562 6560 www.etasr.com alotaibi & alotaibi: design of a planar tri-band notch uwb antenna for x-band, wlan, and wimax fig. 9. geometry of the proposed antenna: l6=2.5mm, l7=6mm, t3=0.5mm. fig. 10. variation of the position pf3. fig. 11. vswr spectrum of the antenna after inserting an l-shaped slot. iii. results and discussion the vswr spectrum of the proposed uwb antenna is presented in figure 12. we notice a bandwidth ranging from 2.08ghz to 12ghz, which covers the frequency band of the uwb. the three notched bands are: 3.28 to 3.91ghz (vswr=8 at 3.59ghz), 4.9 to 7.15ghz (vswr=7.73 at 5.18ghz) and 9.21 to 10.94ghz (vswr=5 at 10.27ghz). figure 13 shows the antenna radiation directional dependence obtained at three different frequencies. these patterns are omnidirectional at the considered frequencies. on the other hand, there is a deterioration of the radiation pattern at the 10ghz frequency. fig. 12. triple-band-notched vswr spectrum of the proposed antenna. (a) (b) (c) fig. 13. radiation patterns corresponding to three different frequencies. the antenna current distributions at the three frequencies are shown in figure 14. we can observe that for frequencies engineering, technology & applied science research vol. 10, no. 6, 2020, 6557-6562 6561 www.etasr.com alotaibi & alotaibi: design of a planar tri-band notch uwb antenna for x-band, wlan, and wimax 5.18ghz and 10.27ghz, the surface currents are localized on the feed line. on the other hand, at 3.59ghz, the surface currents increase in the patch around the slot. (a) (b) (c) fig. 14. antenna surface current distribution associated to the frequencies of (a) 3.59ghz, (b) 5.18ghz, and (c) 10.27ghz. to validate the design of our notched triple band uwb antenna, we have manufactured (figure 15) and tested it in an anechoic chamber (figure 16). fig. 15. photo of the manufactured tri-band uwb antenna. (a) (b) fig. 16. photos of the measurement procedure. the numerically obtained results of the reflection coefficients with those obtained experimentally are represented in figure 17. the comparison of the two curves shows a good agreement between the experimental and the simulation results. fig. 17. comparison of simulated and measured s11. iv. conclusion a new ultra-wideband planar antenna with triple band notch characteristics is proposed in this work. the first notch at 3.59ghz is achieved by inserting a c-shaped slot in the radiating patch, the second notch at 5.18ghz is realized by etching a u-shaped slot in the micro-strip line, and the third engineering, technology & applied science research vol. 10, no. 6, 2020, 6557-6562 6562 www.etasr.com alotaibi & alotaibi: design of a planar tri-band notch uwb antenna for x-band, wlan, and wimax notch at 10.27ghz is accomplished by using an l-shaped slot on the ground plane. an almost 10ghz large operating band frequency is obtained (2.08ghz-12ghz) with three rejected bands (3.28-3.91ghz, 4.9-7.15ghz, and 9.21-10.94ghz). it also presents an omnidirectional radiation pattern which allows minimizing the interference from technologies such as wimax, wlan and applications in the x band. acknowledgment the authors would like to thank the deanship of scientific research at taif university for funding this work through the daem research support program, project no. 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[28] h. lee, y. jang, j. kim, and j. choi, "wideband monopole antenna with wlan (2.4 ghz/5 ghz) dual band-stop function," microwave and optical technology letters, vol. 50, no. 6, pp. 1646–1649, 2008, https://doi.org/10.1002/mop.23467. microsoft word 2-599-ed.doc engineering, technology & applied science research vol. 5, no. 6, 2015, 876-884 876 www.etasr.com jadeja et al.: an investigation on the performance of random pwm controlled converters an investigation on the performance of random pwm controlled converters rajendrasinh jadeja department of electrical engineering marwadi education foundation’s group of institutions rajkot, india rajendrasinh.jadeja@ marwadieducation.edu.in amit dilipkumar ved research scholar, school of engineering, r.k. university, rajkot, india amitved_1999@yahoo.co.uk siddharthsingh k. chauhan department of electrical engineering marwadi education foundation’s group of institutions rajkot, india siddharthsingh.chauhan@ marwadieducation.edu.in abstract— this paper provides an insight on various random pulse width modulation techniques and their effect on spreading the harmonic spectrum for various applications like drives, hybrid electric vehicles and renewable energy sources, for two level as well as three level inverter. acoustic noise reduction, electromagnetic interference conducted and torque ripple are obvious advantages of random pulse width modulation (pwm). pwm converters with multilevel topology can meet with global quality standards for power supplies. the random pwm technique provides additional advantages. among others, it may be implemented to achieve switching loss equalization in power switches for cascaded h-bridge multilevel inverters. this paper provides in depth understanding for different random pwm techniques and their applications. keywords-random pwm, random svpwm, multilevel inverter, drives i. introduction with the increased penetration of automation due to advancements in power semiconducting devices and processors like dsp, fpga, cpld etc., power electronic converters have found numerous applications in different fields. this has led to topological advancements in power electronic converters, with multi-level converter being one of them. effective control of power electronic converters has emerged as a challenge. these converters use modulation techniques such as selective harmonic elimination (she) or high switching frequency pulse width modulation (pwm). she pwm technique utilizes a low frequency switching and hence can reduce switching losses. by selecting proper angles using advanced artificial intelligence techniques, it is possible to reduce lower order harmonics without affecting the fundamental component. however, this technique will also result to an increased switching frequency. for unbalanced load 3phase 4 leg neutral point clamped inverters the she pwm [1] and she pulse width amplitude modulation is proposed [2]. selective harmonic mitigation (shm) is combined with she to provide a better harmonic control [3]. however, she is limited to offline calculations and multicarrier techniques are also been worked upon [4]. various pwm techniques have been implemented for the control of these converters. pwm techniques are classified as current controlled pwm and voltage controlled pwm. these pwm techniques are also categorized as either carrier based or carrierless pwm schemes. for carrier based pwm schemes, a typical harmonics spectrum exhibits prominent harmonics around the carrier frequency. this results to the generation of acoustic noise at these frequencies by the machines controlled by such schemes. also, it is better to have a distribution of harmonic energy over a wide frequency spectrum as compared to the energy being concentrated at few frequencies. this is achieved by carrierless pwm scheme. random pwm schemes also achieve spreading of the energy spectrum by randomly switching, random switching frequency and random pulse position [5]. for random pwm schemes research till now has mostly focus on a carrier based implementation. however, space vector (carrierless) based random pwm techniques which results in better dc bus voltage utilization and easier digital implementation is also gaining popularity. with increasing requirements of power electronic converter application at higher power levels (especially grid connected systems), implementation of multilevel converters is also continuously increasing. this paper is focused on investigating the performance for various random pwm schemes based two-level and multi-level inverter systems. ii. different random pwm (rpwm) techniques [6-45] various pwm techniques are depicted in figure 1. acoustic switching noise gets remarkably reduced by increasing the carrier frequency above 18 khz, however, that increases the switching losses in the inverter and decreases operating efficiency. an inverter with random pwm has an advantage of spread and continuously dispersed output harmonic spectra [6]. a. random carrier frequency (rcf-pwm) [7] the method is based on a random selection of the carrier frequency for each carrier period. the only requirement for rcf-pwm is to maintain the volt-second balance during a carrier period, ensuring that the fundamental frequency component is not affected by the randomization. engineering, technology & applied science research vol. 5, no. 6, 2015, 876-884 877 www.etasr.com jadeja et al.: an investigation on the performance of random pwm controlled converters fig. 1 random pwm techniques. fig. 2 random carrier frequency pwm the random carrier pwm technique uses two different triangular carriers as depicted in figure 2. one is of required frequency and the other is 180 degree phase shifted. the selection of the carrier among these carriers is done by a random bit generated. that is, if ‘1’ is the output carrier 1 (basic) is selected as carrier 2 (180° shifted). the selection is done for ever carrier cycle and the selected carrier is compared with the reference sinusoidal waveform. the pseudo random carrier modulation scheme is most commonly used for the random triangular frequency generation. here, the random triangular frequency is achieved in the range of 3 khz. space vector based random carrier frequency scheme and switching pulse generation is shown in figure 3 fig. 3 random carrier frequency, svm generated vector and switching pulse generation 1) random switching frequency (rsf) [8] random switching frequency has a similarity with random pulse duration. here the switching period is changed in every cycle and pulse period is placed at the beginning of switching cycle, i.e. the problem of randomization is minimized by randomly varying the switching period for a limited interval in the control loop as shown in figure 4. a reference number or slope of triangular wave is varied in between a min and a max value randomly for all phases. however, it is difficult to select random frequency for real time applications,. in the majority of applications, sampling and pwm periods need to be synchronized. random sample rate puts limitation on code size. space vector based scheme requires either switching interval per cycle or sub cycle interval equivalent to 60 degrees are to be randomized. this applies a limitation on the interval for which frequency can be varied. fig. 4 random switching frequency (rsf) 2) dithered sigma delta modulator (dsdm) based rpwm switching scheme [9-23] delta sigma modulation is an oversampling method where sampling frequency is much above the frequency mentioned by nyquist criteria. here analog input is converted to digital output same as in an analog to digital controller (adc). as shown in figure 5(a) the addition of a 1-bit random sequence to the lsb of the input signal, results in suppression of harmonic spikes in dithered sigma delta modulation (dsdm). the dithered sigma-delta modulation (dsdm) scheme has a sigma delta modulator (sdm) and a random dither generator as component can be realized with simple hardware and software algorithms. as shown in figure 5(b) random dither generation constitutes of random magnitude adjustment where in for every sampling period a random number is generated and subtracted by a bias as well as a sign discriminator which decides the application of dither [9]. there are two types of sdm, depending upon the position of random dither generator and quantizer viz. space-dither sdm (sdsdm). space-dither sdm (sdsdm) scheme employs quantizer being fed from a random dither generator in sdm while in time-dither sdm (tdsdm) the quantizer feeds the output to random dither generator. harmonics spikes at multiples of switching frequency are reduced by using a sigma delta modulator where switching frequency is varied randomly using a vector quantization technique [10]. dsdm scheme is easy to implement due to less arithmetic operations and limited use of times. harmonic spread factor is also engineering, technology & applied science research vol. 5, no. 6, 2015, 876-884 878 www.etasr.com jadeja et al.: an investigation on the performance of random pwm controlled converters comparable in the case of dsdm and rsvpwm [11-22]. a 2nd ordered space dithered sdpwm is investigated in [23]. fig 5. (a) block diagram of sdm scheme, (b) random dither generator b. fixed career frequencyrandom pwm (fcf-rpwm) [24-38] in this method, the switching period is fixed and pulse position is varied randomly. these methods portray a good closed loop response. figure 6 shows the control block of fcfrpwm which can be implemented with open loop or closed loop. control block calculates the reference voltage vector in αβ plane. svm block will estimate and compare values for pwm. ff_rpwm block will randomize active vectors and zero vectors in the given modulation period. duty ratios are converted to compare values for generating random pwm output required by vsc block. fig. 6 fcf–rpwm in open & closed loop the fcf-rpwm methods, even though easy to synchronize with the control algorithm suffer from problems like current sampling, calculation overhead and spreading effectiveness. the ollowing methods of fcf-rpwm are finding many applications in adjustable speed drives. 1) random lead-lag modulation (rll)[24-25] with regular sampling, output cycle frequency is equally divided into equal switching intervals. at constant frequency the pulse position in all 3 phases, is either originating at the beginning of the switching interval (leading-edge modulation) or at its trailing edge (lagging-edge modulation) [24] as shown in figure 7. trailing edge modulated pulse width is used in lead mode, whereas leading-edge modulated pulse width is used in lag mode. average switching frequency is decided to provide the optimum solution for switching losses as well as quality of output current. the random number generator decides leading and lagging edge modulation. advantage of the scheme is a requirement of single bit random generator for randomization [25]. sampling of current produces problems and use of anti-aliasing filter becomes necessary. fig. 7 random lead-lag modulation (rll) 2) random displacement of the pulse centre (rcd) [26] in this method the pulses are mutually center-aligned at constant frequency as in space vector modulation (svm), but the common pulse center is displaced by a small amount randomly (trand1,) from the middle of the period [26]. at high (modulation index) mi values, displacement becomes very small. variation of rcd pwm is available as the dual zero rcd, where for mi>0.8 (1 1 1) is regarded as zero vector and for mi<0.8 (000) is considered as zero vector. this helps to overcome issues with high mi values and provides randomization effect in a whole range of mi. figure 8 shows pwm technique applied to two phase pwm. fig. 8 (a) centre allign svpwm (b) rcdpwm 3) random pulse position pwm (rpp) [25-28] the central idea is that the average output voltage over an interval is not dependent on pulse position. methodology implements randomization of pulse position of one phase, pulse position of remaining phase is randomized as per previous (a) (b) (a) engineering, technology & applied science research vol. 5, no. 6, 2015, 876-884 879 www.etasr.com jadeja et al.: an investigation on the performance of random pwm controlled converters phase in sequence. rpp pwm can be implemented by time intervals of zero states controlled randomly within a switching cycle. rll is considered as a case of rpp. here pulses can be placed anywhere randomly within switching interval [28]. rpp strategy cannot generate desired ideal noise spectra, though the harmonic clusters of power spectra for fixed switching intervals are less dominant and distributed in a better manner as compared to the deterministic vector pwm technique [25]. 4) random distribution of the zero voltage vector (rzd) [24] phase voltages are not altered by the duration of zero voltage vector in a three-phase, three-wire system. this point is employed in the random distribution of the zero voltage vectors at constant frequency. random distribution of zero vectors limits maximum pulse change and becomes difficult at high mi values. control strategy and required vector distribution are shown in figure 9. (a) (b) fig. 9 (a). random zero-vector distribution (b) random zero-vector distribution 5) random phase shift pwm (rps) here random phase shift time is applied randomly at constant frequency. figure 10 shows rps technique output waveform, where trp is the random phase shift time in the positive half-cycle, and trn is the random phase shift time for the negative half-cycle. at each half cycle both trp and trn are altered randomly. in this method, the phase shift is varied randomly, keeping the switching frequency constant. for the rps scheme, there is a random variation of phase shift keeping switching frequency constant. it has the advantage of reducing acoustic noise emissions generated by the pwm inverter. the phase shift of the fundamental component for each half-cycle controls, discrete harmonic components of the inverter output voltage. 6) variable delay random pwm (vd-rpwm) [30] in this method a random delay is introduced at the trailing edge of next pwm output cycle. figure 11 shows the process for the calculation of switching time and random delay. random delay is a product of sample period and the normalized random number. obviously maximum delay will be produced with random number equal to 1. here switching period is varied randomly in between min switching period to double the value of sampling period that implements variable delay random pwm [30]. to ‐‐‐‐‐ 2 to trp trn fig. 10 timing waveform of rps scheme fig. 11 block diagram for computation of delays and switching period 7) asymmetric carrier random pwm (ac-rpwm) [3132] this scheme can be considered as a kind of rcf-pwm in which the new voltage vector is updated with a constant frequency. a different frequency is used to generate the voltage vector in the rising time period and falling time period. the scheme works well for both low and high mi values. the method selects a random time length for falling edge as well as rising edge for every modulation period, varying randomly time length of the active vector region as shown in figure 12. fig. 12 ac-rpwm, 1st modulation time has symmetrical carrier and in 2nd modulation time it has asymmetric carrier 8) separately randomized pulse position (srp) [33] pulses are placed randomly in switching interval as shown in figure 13. as there is full possibility to place pulse engineering, technology & applied science research vol. 5, no. 6, 2015, 876-884 880 www.etasr.com jadeja et al.: an investigation on the performance of random pwm controlled converters anywhere, a control for full range of mi is possible, as far as switching sequence is maintained. calculation of duty ratio is done using space vector modulation, with each pulse located randomly. as pulse can be positioned randomly, harmonic spectrum is more flattened as compared to conventional methods. so, svm based duty ratio calculation is followed by random positioning of pulse to realize srp-pwm [33] ts ts ts ts ea eb ec fig. 13 srp-pwm 9) fractal based space vector pwm [34-38] fractals are known as never ending patters made by repeating simple patterns by recursion and feedbacks. svm representation of multi-level inverters have inherent fractal structure. fractal approach can reduce the complexity in computation for sector identification and switching vector determination in svpwm. the position of the reference vector in a given sector can be found by fractal methods. the basic pattern in the fractal base unit is a triangle comprised by three adjacent inverter voltage space vectors as shown in figure 14 for 2-level, 3-level and 5-level inverter. in multilevel inverter, for higher level, each sector is divided into triangles and smaller sub triangles. triangularization helps to implement this technique for any level of mli [34]. for multi-level inverter, the number of sectors increases as the number of level increases. it is very complex to identify the location of reference vectors in the sector. 2-level inverter has 6 sectors, 3level inverter has 24 sectors. if we take 60° coordinate system, fractal calculations can be avoided for 5-level inverter having 96 sectors [35-38]. the sector identification algorithm used in this method with reverse mapping technique does not require memory crunchy lookup tables. the inverter switching states for a sector are generated along with sector identification. this provides optimum switching of the vectors [35]. a04 a05 iii iii iv v vi a01 a02a03 a06 a00 fig. 14 2-level, 3-level and 5-level svpwm c. hybrid random pwm or dual random pwm [39-43] with a view to gain advantage of better performance for the different modulation index (mi) values including over modulation region or to reduce the complexity of computation, the hybrid or dual random pwm methods are proposed. here an attempt is made to maximize the advantages of various pwm schemes. a hybrid random pwm using dithered pulse position and zero vector position are suggested, simulated with complex calculations [39]. hybrid scheme is also given by [40] using random pulse position and random career frequency pwm [5]. lead lag random bit and random triangular carrier are used in [41-42]. time for zero voltage is randomized to get better result with direct torque control (dtc) for drives [43]. d. random svpwm [44-45] spwm converters have sideband harmonics and carrier acting as source of electromagnetic noise and pollution by common mode and differential mode noise. the random pwm inverter has low weight, volume, filtering and has better emi/emc. lower switching losses are useful to improve battery efficiency and reduced switching losses. svm is digitally better implementable and has a higher output. fixed frequency svm also has high harmonics in switching frequency this can be spread by using random space vector pwm (rsvpwm). three types of random svpwm are suggested, random zero vector distribution pwm (rzdpwm), random pulse position pwm (rpppwm) and random switching frequency pwm (rsfpwm) [44]. mathematically random svpwm is similar to traditional svpwm and so existing methods for capacitor voltage balancing can be modified to reduce switching harmonics [45]. iii. random pwm controlled two -level inverters [46-59] output current of two-level inverters has a square wave with limited power range. it is rich with harmonics. the twolevel 3-phase voltage source inverter (vsc) is considered as a mature technology and has become an industrial standard. the alternative topology to the vsc is the current source converter (csc), well suited for medium-voltage industrial applications with voltage waveforms having high quality required. various authors have also implemented random pwm techniques for multilevel inverter, keeping methodologies adopted for 2-level [46-58]. c. guoqiang, w. zhihong, z. yuan, and z. junwei realized random space vector pulse width modulation methods based on infineon tricore tc1767/tc1797 like rsfpwm, rpppwm, rzdpwm and hybrid random pwm is involving various combinations of three listed herewith [59]. the ac-rpwm technique is found appropriate for applications like heating, ventilation and air conditioning (hvac) [31]. iv. random pwm controlled three-level inverters [60-74] multilevel inverters provide nearly sinusoidal output and achieve higher power output. this allows the use of renewable energy sources such as pv, wind, fuel cells to be easily interfaced with mli for medium voltage, high power drives, distributed energy sources and hybrid electric vehicles. topology itself helps in reducing harmonics. multilevel inverters are replacing conventional two-level inverters due to reduced dv/dt stresses, common mode voltages, and lower harmonic distortion. 3-level rpwm in comparing to 2-level rpwm schemes has the advantages of low switching frequency, low continuous noise and low undesirable low-order engineering, technology & applied science research vol. 5, no. 6, 2015, 876-884 881 www.etasr.com jadeja et al.: an investigation on the performance of random pwm controlled converters harmonics, making it suitable for high voltage inverter application such as motor drives, active filters and power conditioning [60-62]. different conventional topologies like neutral point clamped (npc), cascaded h-bridge (chb), and flying capacitor (fc) along with pwm strategies reported, are reviewed in [63]. novel topologies are report for mli in form of crossover switches cell (csc) for renewable energy sources and pinned mid-points multilevel inverter for high voltage applications [64-65]. in [60-61] the authors compared random pwm technique for 2-level and 3-level. their observations include that the fundamental component is found to be smaller in the 3-level rpwm scheme than in the 2-level rpwm scheme. both 2-level and 3-level have a similar discrete spectral characteristic, however the 3-level has smaller continuous noise as compared to the 2-level. this advantage of the better power spectrum comes at the cost of a relatively higher switching frequency for specified sampling frequency [66]. t. ramanathan et al. [67] utilized pseudo random carrier modulation technique for chb mli. jacob and baiju [65-66] applied space vector quantized dsdm technique for 3-level inverter to reduce harmonic noise to chb mli supplying power to induction motor drive. in [54] the authors implemented space vector based random pwm for 3-level inverter for any topology. in [50] the authors pointed out that the fixed frequency scheme has limitation in the form of the dependency of randomization on the duration of active vectors. in [70] the authors used combined dsdm based random pwm scheme. artificial intelligence tools like fuzzy logic, genetic algorithm, etc., are also utilized to randomize the pwm output. in [71], the authors used clonal selection algorithm, a technique based on ga applied for 3-level pwm inverter for optimization. in [72], the authors implemented random frequency based space vector pwm method and introduced wavelet transformation for better harmonic response. in [74], randomized-svm application is also extended to hybrid electrical vehicle (hev). a. applications of random pwm [75-100] random pwm finds extensive application in lv and mv motor drives to reduce acoustic noise, electromagnetic interference, and harmonics at multiple of switching frequency, also it helps to flatten the power density spectrum [75-80]. motor drives on board are increasing for electric, hybrid and fuel cell based vehicles. to decrease current ripple, switching loss and auto adjust to load characteristics along with other advantages very crucial for the consumer that is acoustic noise and electromagnetic noise make the random pwm better choice for application in automobiles [81-87]. shunt active power filter is used to improve power quality issues like current harmonics and power factor for power system with nonlinear load. with random pwm, apf response can be improved without adding any cost [88-93]. present scenario for inverter used with renewable energy sources: pwm techniques are used with mosfet/igbt while for high power scr/gto is required which can be controlled with suitable firing and commutation control. another way by which we can use mosfet/igbt for medium or high power application is to go for multilevel inverter (mli) [94-97]. grid connected pwm converters used to control power for various applications including renewable energy sources are reported [99]. use of svpwm is reported in 3-level npc inverter [100]. v. analysis of research work carried out with random pwm and random svpwm literature reveals the extensive usage of random pwm techniques in various applications. in order to further validate the research interest year by year refer to figure 15. figure 16 indicates that the research for random pwm is dominated by the field of drives, motor control and low power applications. fig 15. papers published year wise for random pwm fig. 16 papers reporting random pwm viii. conclusion this paper presents a critical review of random pwm techniques and their applications. the random pwm technique is found to reduce harmonics in particular at a multiple of switching frequency. the technique has proved its advantages in drives especially through reduction of acoustic noise, mechanical vibration, torque ripple and current harmonics. the advantage of rpwm technique in reducing emi conducted to the source is discussed. drives, hevs, active power filters have proved to provide better performance with the random pwm technique. harmonic power remains unchanged with the randomizing technique, but can reduce the peaks at multiple of switching frequency and can reduce harmonic content in the current waveform. the effect of randomizing for inverters connected with renewable sources using bundled multilevel technique with the advantage of lower switching frequency, spreaded noise and low lower harmonics needs to be worked on, as renewable energy sources are preferred to address issues of pollution, energy security cost, etc. hence there is a research gap for the issue of harmonic mitigation in grid connected systems by application of random svpwm technique for multilevel inverters. engineering, technology & applied science research vol. 5, no. 6, 2015, 876-884 882 www.etasr.com jadeja et al.: an investigation on the performance of random pwm controlled converters references [1] m. sharifzade, h. vahedi, a. sheikholeslami, h. ghoreishy, k. alhaddad, "selective harmonic elimination modulation technique applied on four-leg npc," in isie 2014-23rd ieee international symposium on industrial electronics, pp. 2163-2168, turkey, 2014 [2] m. sharifzade, h. vahedi, a. sheikholeslami, h. ghoreyshi, k. alhaddad, "modified selective harmonic elimination employed in four-leg npc inverters," in iecon 2014-40th annual conference of the ieee industrial electronics society, pp. 5196-5201, 2014 [3] m. sharifzadeh, h. vahedi, a. sheikholeslami, p.-a. labbé, k. alhaddad, "hybrid shm-she modulation technique for four-leg npc inverter with dc capacitors 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often utilized in technical analyses for identifying and evaluating patterns that could be utilized to achieve profits in trading. although technical analysis utilizing various measures has been proven to be helpful for forecasting and predicting price trends, its utilization in formulating trading orders and rules in an automated system is complex due to the indeterminate nature of the rules. moreover, it is hard to define a specific combination of technical measures that identify better trading rules and points, since stocks might be affected by different external factors. thus, it is important to incorporate investors’ sentiments in forecasting operations, considering dynamically the varying stock behavior. this paper presents a sentiment aware stock forecasting model using a log bilinear (lbl) model for learning short term stock market sentiment patterns, and a recurrent neural network (rnn) for learning long-term stock market sentiment patterns. the sentiment aware stock price forecasting (saspf) model achieves a much superior performance compared to standard deep learning based stock price forecasting models. keywords-sentiment analysis; data mining; machine learning; social networking platform; stock price forecasting; time series i. introduction analyzing and forecasting future stock prices has attracted much research interest. success in stock trading totally relies on determining the right time to sell or buy stocks. however, predicting accurate stock prices is a very challenging task due to the congenitally noisy environment and the high volatility of price variations [1]. stock price movement is related to a number of elements including government policies, organization’s performance, inflation rates and economic environment. technical analysis examines the variations of a stock through mathematical formulas and charts, called technical indicators, aiming to discover patterns that could be utilized for profitable gains in trading, and it is a usual approach in financial engineering for stock market prediction [1]. despite the advances in technical analysis, it is difficult to accurately predict stock prices and trading points in financial markets, mostly because of the volatile investors’ sentiments during uncertainties. authors in [2] proclaimed that the stock market is very efficient and trading prices totally reflect the available data, which is referred as the efficient market hypothesis (emh), while fundamental or technical analysis would not lead to profit that is consistently over-average for investors. nonetheless, not all researchers agree with emh [3], as some conventional methods in financial economics proclaim that stock markets have anomalies [4-5]. most studies use technical analysis, which includes older stock volumes and prices, in order to demonstrate trading profits and predict future stock market prices [6]. research studies focused on discovering native parameters, mostly used web data such as social networking services (sns) [7], investor’s sentiments [8], news articles [9], or search engines [10], and explained that search query frequencies and investors’ sentiments from sns platforms provide vital information for predicting upcoming stock prices, especially during global uncertainties such as the recent covid-19 pandemic. initially, during december 2019 to march 2020 covid-19 cases were significantly high in the republic of china affecting its stock market. due to the rigid expenditure on rents, wages, and bank interests the stability of the banking system was affected and small-medium sized organizations were significantly impacted as the chinese stock index nearly dropped by 8% on february 3 rd [11-13]. on the other side, reliance industries limited (ril) stock prices were continuously growing as facebook and google obtained certain percentage of its stake during the covid-19 pandemic. during the previous years, researchers mostly focused on volatility modeling, evaluated as the standard deviation of an asset’s return, showing the variability in finance time series (fts) data [14], which play a crucial role in effective stock forecasting. extensive surveys were carried out showing limitations of the existing machine learning (ml) based stock forecasting models, based on random forest, neural networks, and support vector machines, as they proved inefficient in highly volatile market behaviors. furthermore, in order to confront the dynamic nature of stock markets, a number of deep learning models such as rnns with gated recurrent and long-short term memories, convolutional neural networks (cnn), deep neural networks (dnn), and general adversary networks (gan) [15] have been presented. neural networks and reinforcement learning (rl) methods are the most widely utilized ml methods [16, 17]. existing deep learning models have limitations, as although they are efficient in modeling long-term market sentiment behaviors they do not detect shortterm market sentiment behaviors. modern ml methods have been adapted in various domains such as speech recognition, corresponding author: uma prashant gurav engineering, technology & applied science research vol. 10, no. 5, 2020, 6356-6161 6357 www.etasr.com gurav & kotrappa: sentiment aware stock price forecasting using the sa-rnn-lbl learning model image classification, and natural language processing, and they are designed using either rnns or cnns [18]. long short term memory (lstm) [19-22] networks outperform random forests and dnns. in [23], an rl method was presented using rnn architecture for addressing gradient descent problems during the training process. correspondingly, in [15] a forecasting error loss and direction prediction accuracy method was proposed, noting that generative adversalial (ga) training can be used to integrate the loss parameter for acquiring the long-term outcomes. the gan-fd used cnn and lstm [2426] for predicting more accurately stock prices. nonetheless, it failed to get a good learning tradeoff performance of modeling both short and long-term market behavioral contexts. therefore, the gan-fd suffers considerably when market’s behaviors are high volatile in nature, while market’s short-term and long term sentiment pattern is not considered [15]. ii. the sentiment aware stock price forecasting model (saspf) the highly dynamic stock forecasting environment during the pandemic requires the modeling of both short and longterm sentiment behaviors of the market. to the best of our knowledge, no prior work has considered capturing market sentiment in dynamic manner for forecasting stock price. this paper presents a sentiment aware stock price forecasting (saspf) model combining short and long term sentiment features. at first, a sentiment analysis was carried out on review datasets, marked it as “-1” for negative, “0” for neutral and “1” for positive sentiment. this sentiment forecast data were added to the stock information datasets and trained using a sentiment aware stock forecasting model. the model was built utilizing both an rnn and an lbl. the rnn was used for detecting long-term market features, while the lbl was used for detecting short-term features. the main contributions of this paper are: • a sentiment aware rnn-lbl (sa-rnn-lbl) learning model is presented for forecasting stock prices considering dynamically varying stock sentiment. • the sa-rnn-lbl model can capture both short-term and long-term market sentiment features more efficiently. • the sa-rnn-lbl model can obtain multiple market sentiment behaviors within short-term context for current trading sessions. thus, it can predict the stock value fluctuation time more efficiently and can be used for forecasting the price of short sells. • the experimental outcome shows the proposed sentiment aware rnn-lbl based stock forecasting model attain better rmsre and dpa performance than existing [15] deep learning based stock price forecasting model. high-quality one-step forecasting provides significant information for risk assessment and management in trading environments, especially during pandemics. this work aims to forecast the price fluctuation of individual stocks or the market index one step ahead, using historical data and market sentiments derived from tweets. a. mathematical formulation this problem can be mathematically formalized as follows: �� represents a set of basic indicators including sentiment parameters and � denotes the closing price of a stock for 1minute intervals at time �, described as: � = 1,2,. . . ,� (1) given the historical basic indicators, � is described as: � = {� ,��, . . . ,��} (2) the closing price � is described as: � = {� ,��, . . . ,��} (3) the goal is to predict the closing price ��� for the next minute considering the market sentiment factor. lets consider a set of stock market and set of stock within stock market as follows: �{� ,��,…}, (4) � = {� ,��,…} (5) this work considers stock market environment, which is composed of following stock volatility behavior such as: � = {� ,��,��,�� } (6) similarly, in the stock performance pattern there exist: � = {� ,��,�� } (7) behaviors. the final task is to predict the future price of a particular stock in a stock market using the sentiment aware stock price forecasting methodology. b. sentiment analysis tool for predicting market sentiments from tweet data the sentiment analysis model detects and marks market sentiments having positive (1), neutral (0), and negative (-1) polarity. however, using a state-of-art sentiment analyzer tool is bulky in nature and induces high computation overhead. for addressing this problem, a sentiment analysis method by employing partial text entailment (pte) was utilized. the pte is used for grouping similar tweets by measuring the semantic similarities among different tweets. this aided in improving the speed of market sentiment prediction, meeting the real-time requirements of stock forecasting models. c. model’s description this section presents the sentiment aware stock market pattern analysis model by learning both short and long-term behaviors using lbl and rnn respectively similar to the lstm model. the rnn model is composed of a set of input layers, multiple hidden layers, and an output layer. the activation parameters of the hidden layers are obtained as: �ℓ� = ����ℓ� +!"#ℓ�$ (8) where, �ℓ� ∈ &' depicts the hidden illustration of stock �at time instance (i.e., position) ℓ in a series, and "#ℓ� ∈ &' depicts the illustration of the ℓ�( input stock of a particular stock market �. the activation function (af) is represented by �)�* engineering, technology & applied science research vol. 10, no. 5, 2020, 6356-6161 6358 www.etasr.com gurav & kotrappa: sentiment aware stock price forecasting using the sa-rnn-lbl learning model and the transition matrix (tm) of the present stock is represented as: ! ∈ &' (9) while the previous status is represented as: + ∈ &'. (10) where ! can obtain stock’s present volatility (i.e. behavior pattern) and � can propagate time series signals. equation (8) is executed iteratively to obtain or compute the status of each time instance in a time series sequence. the rnn is composed of multiple hidden layers. hidden layer information is dynamic in nature with respect to stock market behavior sequence where the pattern is repetitive. thus, the rnn faces problems in learning short-term patterns in a stock market behavior sequence. for addressing this limitation, an lbl was appended with a single linear hidden layer, and it can be considered as a deterministic model. using lbl for stock market behavior forecasting, the absolute forecasting representation of time sequence is constructed based on stock market score/price input and tms at each time instance. the next time instance is a linear forecasting, described as: �ℓ� � ∑ !-"#ℓ.-� ,/0 -12 (11) where !∈ &3∗3 depicts the tm for the respective time instance in a stock market score behavior sequence and / is the number of elements modeled in a time sequence. each position in the time sequence is modeled with a precise tm. in general, lbl finds difficulties in efficiently learning long-term contexts in stock market behavior sequence. furthermore, the market behaves dynamically depending on market sentiments (i.e. the moods of customers and investors). thus, it is important to capture such information into stock price forecasting. thus the proposed method considers sentiment aware matrices for obtaining feature sets of various aspects of sentiments. thus, for the respective stock market � at ℓ (i.e. hidden description) is computed as: �ℓ� � ��ℓ� ∑ !-5�ℓ.-� 6ℓ.-� ,/0 -12 (12) where 5�ℓ.-� ∈ &3∗3 are sentiment aware tms with respect to the -�(stock of a stock market �. the cold start problem is overcome by assuming �2� � 72. it should be noted that if any change in sentiments is detected, the proposed method can obtain underlying feature sets of different sentiments exhibited in past sessions. however, the existing stock forecasting model in general doesn’t consider session variance between features, playing a significant role in improving prediction accuracies. this happens because short-term market sentiment variance plays a significant part in future buying or selling of stocks compared to long-term market sentiment information. thus, this work improves the previous rnn-lbl model by incorporating time based sentiment feature variance information, modeling a sentiment aware rnn-lbl model. the sentiment aware rnn-lbl stock market forecasting model is shown in figure 1. considering the respective stock market 7, the position 8 is established using: 9:; � �9:0<; ∑ =>?@0>?.a@ bc?.d@ ,<0 e12 (13) where f:; represents current time, f:0 ; represents time information of each stock of each layer of the model, and =>?@0>?.a@ is the time-specific tm of sentiment session variation f:0 ; g f:; . the time-specific tms aid in collecting time specific sentiment pattern features with respect to recent tweet information. considering these, (13) is updated as: 9:; � �92; ∑ =>?@0>?.a@ bc?.d@:0 e12 , (14) where 9:; � 72 with respect to the initial status of the respective stock within the stock market environment. for obtaining the varying sentiment nature of stock market with respect to different time intervals, this work established sentiment aware tms in the model, described by: 9:; � �9:0<; ∑ =>?@0>?.a@ hi?.j@ bc?.d@:0 e12 . (15) finally, the prediction of whether a stock 7 will exhibit certain patterns or sentiments k with respect to stock l at successive position 8 1 is calculated by: m;,:� ,i,c � )�:;*nhibc � )9:; 7;*nhibc. (16) where oℓ� is the current sentiment of the stock market � with respect to session instance ℓ, with static hidden and dynamic feature illustration being 7� ∈ &3 and �ℓ�, respectively. fig. 1. the architecture of the sentiment aware rnn-lbl model. in order to learn exclusive possible time variances in a continuous manner, it is important to establish large sized timespecific tms, but this introduces over-fitting issues. this problem can be addressed by dividing time variance into equal windows. this model estimates transitional matrices of lower and upper limits of time windows/bins, utilizing linear interpolation of entire time variance in time windows, in order to establish the corresponding tms. experiments were conducted in order to evaluate the outcome of the proposed saspf model and are described below. engineering, technology & applied science research vol. 10, no. 5, 2020, 6356-6161 6359 www.etasr.com gurav & kotrappa: sentiment aware stock price forecasting using the sa-rnn-lbl learning model iii. results and discussion this section presents the performance evaluation of the proposed saspf model over other prediction models. the gan-fd model [15] was chosen for comparison as it achieved much better results than existing lstm based stock forecasting methods [21, 24-28], as investors’ sentiments are considered as a major contributing parameter. fig. 2. results obtained for sentiment index (positive, negative, neutral and compound). the proposed saspf model was implemented using python. the dataset for evaluating sentiments was obtained from public available sources [29-31]. this work evaluated performance using the same datasets used by gan-fd [15]. data were composed of 244 trading points ranging from january 1 to december 31 st 2016. more detailed description of the dataset used can be obtained from [15], while it can be downloaded from [32]. direction prediction accuracy (dpa) and root mean squared relative error (rmsre) were used for performance evaluation. the 80% of the data was used for training, while the remaining 20% was used for testing. experiments were conducted for different stocks considering time �, a forecasting was performed for the next time interval � +1 using the proposed learning methods. the total time interval for the forecasting was �2. the actual stock value is �� and the forecasted value is �p�. a. rmsre performance evaluation this section evaluated the rmsre’s performance achieved by saspf model over existing deep learning stock price forecasting methods. the rmsre metric was computed as: qrsqt = u �v ∑ w xpyza0xyza xyza [ ��v �1 (17) a low rmsre value indicates that forecasting is good (i.e. it defines it is as closer to the actual stock price). the rmsre outcomes of the saspf model and existing deep learning based stock price forecasting methods are shown in table i. the graphical representations of rmsre performance achieved by saspf and existing deep learning based stock price forecasting methods are shown in figure 3. table i. rmsre performance comparison method used rmsre lstm-fd 0.0197 gan-fd 0.00885 rnn-lbl 0.00675 saspf 0.005465 fig. 3. rmsre performance of saspf model and existing deep learning based stock price forecasting methods. the results showed that the average rmsre performance achieved by lstm-fd, gan-fd, rnn-lbl, and saspf was 0.0197, 0.00885, 0.00675, and 0.005465, respectively. the rnn-lbl model had lower rmsre by 65.736% and 23.73% over lstm-fd and gan-fd, respectively. similarly, the saspf model had lower rmsre by 72.41%, 38.59% and 19.48% over lstm-fd gan-fd and rnn-lbl models, respectively. the results show that saspf model achieves much superior rmsre performance than the existing deep learning based stock price forecasting models. in order to further evaluate the performance of the saspf model, a performance evaluation was performed under highly dynamic and volatile environments. for evaluating such scenarios, this work considered the evaluation using the reliance jio communication stock and a corresponding tweet dataset obtained from yahoo finance [30] and yahoo news [31] datasets, respectively. the stock price forecasting performance was evaluated between march 1 st and june 30 th 2020. the rmsre performance achieved considering the sentiment index is shown in figure 4. the results show that rnn-lbl and saspf model achieves an rmsre of 0.0085 and 0.0059, respectively. saspf had improved forecasting performance by 30.59% over rnn-lbl considering stock market sentiments. thus, saspf can work really well under highly dynamic and volatile environments such as the covid19 pandemic scenario. fig. 4. comparitive analysis of saspf and rnn-lbl models in terms of rmsre rmsre :comparitive analysis of rnn-lbl and saspf engineering, technology & applied science research vol. 10, no. 5, 2020, 6356-6161 6360 www.etasr.com gurav & kotrappa: sentiment aware stock price forecasting using the sa-rnn-lbl learning model b. dpa performance evaluation this section evaluated the dpa performance achieved by the saspf model over existing deep learning stock price forecasting methods. the higher value of dpa describes higher revenue for the investor. the dpa metric is computed as: \]^ = 22�v ∑ _�, �v �1 (18) where: _� � `1 9�)��� g��*�� p�� g��$ a 0 0 c�defl9be (19) the dpa outcomes of the saspf and existing deep learning based stock price forecasting methods are shown in table ii, while the graphical representation of the results is shown in figure 5. table ii. dpa performance method used dpa lstm-fd 0.6423 gan-fd 0.68585 rnn-lbl 0.7822 saspf 0.80305 fig. 5. dpa performance of saspf and existing stock forecasting methods. the results showed that the average dpa performance achieved by lstm-fd, gan-fg, rnn-lbl, and saspf model was 0.6423, 0.68585, 0.7822, and 0.80805, respectively. the rnn-lbl model had better dpa performance by 17.88% and 12.32% over lstm-fd and gan-fd. similarly, the saspf model had better dpa performance by 20.51%, 15.123%, and 3.2% over lstm-fd, gan-fd, and rnn-lbl model, respectively. the saspf model achieves superior dpa performance than the existing deep learning based stock price forecasting models. furthermore, in order to evaluate the saspf model’s performance under highly dynamic and volatile environments, the model was evaluated using reliance jio communication stock and corresponding tweet datasets obtained from [30, 31]. its stock price forecasting performance was evaluated with data between march 1 st and june 30 th of 2020. the dpa performance achieved considering the sentiment index is shown in figure 6. the results show that the saspf and rnn-lbl achieved dpas of 0.0085 and 0.0059 respectively. the saspf had better forecasting performance by 18.26% over the rnn-lbl when considering stock market sentiments. thus, saspf can work really well under highly dynamic and volatile environments such as the covid-19 pandemic scenario, providing better profits for an investor. fig. 6. comparitive analysis of saspf and rnn-lbl models in terms of dpa. iv. conclusion predicting stock prices is a challenging task, especially when considering external fluctuating factors such as a pandemic situation, since stock markets are volatile in nature as user sentiments, behaviors, and patterns vary over time. during the pandemic situation some stocks such as oil price fell, and contrarily the stock prices of gold and mobile communication sector increased significantly. thus, it is important to capture market sentiments in order to design a better forecasting model. very few researches integrated market sentiments into stock prices forecasting models. in order to predict better profits, reduce forecasting errors, and achieve higher returns for short sell, this paper presented a sentiment aware stock price forecasting model. the saspf divides the current session into multiple bins and compares them to establish stock behavior patterns. results showed the saspf improved forecasting 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[32] “wind financial terminal – chinese stock dataset.” https://www.wind. com.cn (accessed jul. 30, 2020). engineering, technology & applied science research vol. 9, no. 1, 2019, 3734-3738 3734 www.etasr.com nedelchev & kolev: synthesis of planar filters using defected ground structure miniaturized hairpin … synthesis of planar filters using defected ground structure miniaturized hairpin resonators marin nedelchev radiocommunication and videotechnologies dept. faculty of telecommunications technical university sofia sofia, bulgaria mnedelchev@tu-sofia.bg aleksandar kolev radiocommunication and videotechnologies dept. faculty of telecommunications technical university sofia sofia, bulgaria alex.n.kolev@gmail.com abstract—this paper presents an effective technique to suppress the spurious passbands in planar filters by using defected ground structure (dgs) resonators etched in the ground plane. the proposed miniaturized hairpin dgs slot resonator is researched in terms of its resonance frequency, corresponding coupling topologies, and filter design. the resonator and the topologies of coupled dgs resonators are simulated in a fullwave electromagnetic (em) simulator. using a curve-fitting technique, useful design formulas are proposed for filter synthesis. using the synthesis procedure, a 3rd order filter design is simulated, manufactured and measured. the insertion loss of -3db in the passband of 280mhz is observed, while the suppression of the spurious passbands up to 12ghz is more than 24db. keywords-microstrip; defected ground resonator; coupling coefficient; slot line filter deisgn i. introduction bandpass filters used in modern microwave communication systems have to comply with very strict requirements about their performance, size and volume. the manufacturing process of such filters must be technologically easy to produce and adjust. many compact microstrip resonators are reported in [110]. the introduction of etched slots in the ground plane of a microstrip line adds degrees of freedom in the design and synthesis of microstrip filters. these are also known as defected ground structures (dgs). they can be periodic or non-periodic disturbances in the ground plane of the microstrip line. their shape can be adopted from microstrip resonators [1] and appears to be dual to them. this encourages the development of new topologies of planar filters with special specifications. the use of half wave square open loop and miniaturized hairpin resonators as dgs is researched in-depth in [5-8]. a combination of microstrip resonators and dgs resonators are used in [8] as building elements of planar filters. both applications of slot resonators are a promising way of adding additional degrees of freedom in filter design. the use of dgs resonators can solve a serious problem in filter design the small gap that is required between coupled lines in order to achieve strong coupling. one of the problems encountered in the design of wideband and ultra-wideband filters is the physical realization of very small gaps between coupled resonators. the manufacturing tolerances and the precision of the manufacturing process associated with realization of small gaps affect the frequency response of the designed filter. by utilizing different shaped slots in the ground plane of the microstrip line – dgs [1-3, 5-8], it is possible to enhance the coupling coefficient. this paper researches miniaturized hairpin dgs resonator and the coupling structures formed by placing two resonators close to each other. the resonance frequency of the dgs resonator is investigated and a design formula is proposed. the main topologies of coupled dgs resonators are researched and based on the simulation results, simple formulas are proposed using a curve fitting technique. a three-resonator filter is synthesized, simulated, produced and measured in order to verify the design equations. there is a good agreement between theoretical, simulated and measured results. ii. miniaturized hairpin dgs resonator all the simulations and design procedures in this paper are performed in ansys electromagnetics suite v.17.2 for a fr-4 dielectric substrate with εr=4.4, 1.5mm height and loss tangent tgδ=0.02. the miniaturized hairpin microstrip resonator is proposed and its synthesis method is described in [1, 3]. the resonator consists of a main slot line loaded with two parallelcoupled slots with a small gap between them. the etched resonator is symmetrical around the axis and the open end is in the middle of the main line. the magnetic field is concentrated in the coupled lines and the electric field is at its maximum near the open end of the resonator. based on the field distribution there are three main coupling topologies that can be realized, namely electric, magnetic and mixed coupling. the occupied area of a miniaturized hairpin dgs resonator is less than the conventional hairpin or slow wave resonators. this makes the miniaturized hairpin dgs resonator suitable for devices working in the lower microwave bands, where the physical dimensions of the transmission lines are relatively large and miniaturization is not possible. another advantage of the dgs resonator is its rectangular form, which allows its usage in the design of canonical and pseudo-elliptic filters with cross coupling. corresponding author: m. nedelchev engineering, technology & applied science research vol. 9, no. 1, 2019, 3734-3738 3735 www.etasr.com nedelchev & kolev: synthesis of planar filters using defected ground structure miniaturized hairpin … coupled slot lines can be used for altering the resonant frequency of the resonator. the dimensions of the resonator tuned to central frequency f0=2.4gzh are shown in figure 1. the main slot’s width is w=2.8mm which equals the width of a 50ω microstrip line for the used substrate. figure 2 shows the dependence between the length of the coupled lines 𝑝 and the first resonant frequency of the resonator, obtained with fullwave electromagnetic simulations. following the simulation results, the resonance frequency of the dgs resonator is easily tuned by adding or removing metal to the ground plane. using a curve fitting technique, a useful expression is derived for the length of the coupled arms: 𝑝 = 103.8𝑒 −0.9858𝑓0[𝐺𝐻𝑧], [𝑚𝑚] (1) the accuracy of (1) compared to the electromagnetic simulations is better than 2.5% and prevents errors caused by a wrong read of the graphic results shown in figure 2. fig. 1. dimensions of the dgs resonator tuned to f0=2.4gzh fig. 2. dependence of the resonant frequency of the coupled lines length iii. coupling coefficients and external quality factor simulations as described in [2], the coupling coefficient for synchronously tuned resonators can be calculated by finding the eigenfrequencies of even (𝑓𝑒 ) and odd (𝑓)𝑜 mode associated with coupling between a pair overcoupled resonators. 𝑘 = 𝑓𝑒 2−𝑓𝑜 2 𝑓𝑒 2+𝑓𝑜 2 (2) a finite element method (fem) based fullwave em simulator is used to identify the resonance frequencies in the response [2]. figure 3 shows the coupling topologies used to evaluate the coupling coefficients and the external quality factor. the miniaturized hairpin slot resonators are dual to the miniaturized hairpin resonators and the electromagnetic field is inversely distributed in it. the magnetic field has a maximum value in the connection point of the coupled lines with the transmission line and the electric field has a maximum value in the center of the main slot line. (a) (b) (c) (d) fig. 3. coupling topologies of miniaturized hairpin dgs resonators: (a) electric, (b) magnetic, (c) mixed, (d) external quality factor there are three main types of coupling topologies – electric, magnetic and mixed. the electric coupling is shown on figure 3(a), where the electric field has a maximum and dominates over the magnetic field. in this configuration the sign of the coupling coefficient is negative and can be used for cross coupled filters. on figure 3(b) the magnetic coupling is shown. in this configuration, the magnetic field is dominant and the sign of the coupling coefficient is positive. the mixed coupling is shown on figure 3(c). in this case neither the electric nor the magnetic field is dominant. when a microstrip filter is being synthesized, an important point is the determination of the gap between the coupled resonators with respect to the value of the coupling coefficient calculated from the approximation. three main approaches exist to determine the separation between the resonators: analytic formulas [2], approximate formulas from curve fitting [8] and extraction from em simulations [2, 3]. using (2) and em simulation of the coupling structures, which are weekly coupled to a 50ω microstrip feed line the coupling coefficients are extracted. figures 4-6 show the coupling coefficients for the three types of coupling as a function of the distance between the resonators s. using a curve fitting method, the following dependences are derived for design purposes: for electric coupling : 𝑠𝑒 = 6.88𝑒 −40.36𝑀𝑒 (3) for magnetic coupling: 𝑠𝑚 = 12.36𝑒 −18.45𝑀𝑚 (4) for mixed coupling: 𝑠𝑚𝑖𝑥 = 13.05𝑒 −28.73𝑀𝑚𝑖𝑥 (5) engineering, technology & applied science research vol. 9, no. 1, 2019, 3734-3738 3736 www.etasr.com nedelchev & kolev: synthesis of planar filters using defected ground structure miniaturized hairpin … fig. 4. coupling coefficient as function of the separation between the resonators for the electric coupling fig. 5. coupling coefficeint as function of the separation between the resonators for the magnetic coupling fig. 6. dependance of thecoupling coefficient as a function of the separation between the resonators for the mixed coupling by using (3)-(5) it is easy to compute the separation between the coupled lines with accuracy better than 5% compared to the em simulations. the external quality factor defines the position of the input/output lines. in the case of miniaturized hairpin slot resonators, the external quality factor is realized by a 50ω microstrip line on the top layer of the substrate (figure 3(d)). the dependence of the external quality factor as a function of the linear position of the microstrip line is shown on figure 7. the input/output microstrip line influences the resonance frequency of the slot resonator and shits it towards lower frequencies. this effect must be compensated while the filter is being designed by reducing the length of the coupled lines of the input/output resonators. because the feed line is placed on the top layer of the substrate, input/output lines can overlap the slot resonators. the external quality factor changes its value at a very high rate when the microstrip line is placed near the dgs resonator. fig. 7. dependance of the external coupling as a function of the position of the input/output microtrip line iv. bandpass filter synthesis, simulations and measurements the proposed topologies of coupled resonators and the formulas for the coupling coefficients can be verified by designing a three-resonator chebyshev filter. the required coupling coefficients must be computed by using the standard technique described in [2]: 𝑀𝑛,𝑛+1 = 𝐹𝐵𝑊 √𝑔𝑛𝑔𝑛+1 (6) where 𝐹𝐵𝑊 is the fractional bandwidth and 𝑔𝑛 , 𝑛 = 0,1,2,3 are the values of the elements of the lowpass filter prototype. different sources of precomputed values for the elements for different pass band ripple can be found. the current filter is designed for center frequency f0=2400mhz, bandwidth δf=200mhz and return loss in the pass band rl=-20db. the values for the coupling coefficients are m12=m23=0.086 and the external quality factor is qe=25.92. the gaps between the resonators are s12=s23=1.13mm and the overlapping between the input/output line and slot resonator is d=-1.25mm. ansys electromagnetics suite v.17.2 is used to simulate the filter in its planar simulator. the topology of the simulated filter is shown on figure 8 and the results are shown on figures 10 and 11. the simulated filter has a bandwidth of 280mhz and the coupling between the resonators appears to be stronger than designed. due to the effect of the input/output lines on the first and third resonators frequency response the length of the coupled lines has to be reduced by 0.6mm in order to achieve the desired frequency. from figure 10 it is seen that the filter has no spurious pass band response up to 12ghz. the minimum suppression of the out of bandpass is -23db, while the maximum suppression is below -45db. the designed filter was produced using standard pcb manufacturing technology on a fr-4 substrate with 1.5mm thickness and 0.035mm copper foil (figure 11). on figure 12 the simulated and measured frequency responses for the 𝑠11 and 𝑠21 in narrowband are both shown. the measurements were performed on a 2 port network analyzer pna-x n5242b. there is good agreement between the simulated and the measured results. engineering, technology & applied science research vol. 9, no. 1, 2019, 3734-3738 3737 www.etasr.com nedelchev & kolev: synthesis of planar filters using defected ground structure miniaturized hairpin … fig. 8. topology of the synthesized three resonator chebyshev filter fig. 9. simulated narrowband frequency response of the synthesized filter. fig. 10. simulated wideband frequency response of the synthesized filter (a) (b) fig. 11. fabricated pcb of the synthesized three resonator chebyshev filter: (a) top layer, (b) bottom layer the measured bandwidth of the filter is 287mhz, while the insertion loss in the passband is -2.79db. the maximum value of the reflection coefficient in the passband is -20db, which corresponds to 0.1db ripple of the transmission coefficient. the measured center frequency of the filter is 2.35ghz. figure 13 shows the wideband frequency response of the simulated and measured filter. the measured suppression of the spurious passbands is lower than -24db as predicted in the filter simulations. fig. 12. measured and simulated narrowband freqeuncy response of the synthesized filter fig. 13. measured and simulated wideband freqeuncy response of the synthesized filter v. conclusion a design of a dgs resonator and its corresponding coupling structures are presented in this paper. topologies of coupled dgs resonators are researched and the use of curve fitting technique designed formulas is proposed. a three resonator filter is synthesized, simulated and produced in order to verify the design equations. a good agreement between the simulated, theoretical and measured results is observed. the proposed dgs resonators can be used in the design of microstrip filters in the ism band on 2.4ghz. acknowledgement this work has been supported by the research grant no – 182пд0011-07 with the scientific research center – technical university of sofia. references [1] m. makimoto, s. yamashita, microwave resonators and filters for wireless communication, theory design and applications, springer, 2001 [2] j. hong, m. j lancaster, microstrip filters for rf/microwave applications, john wiley and sons, 2001 engineering, technology & applied science research vol. 9, no. 1, 2019, 3734-3738 3738 www.etasr.com nedelchev & kolev: synthesis of planar filters using defected ground structure miniaturized hairpin … [3] r. garg, i. bahl, m. bozzi, microstrip lines and slotlines, artech house 2013 [4] h. j. chen, t. h. huang, c. s. chang, l. s. chen, n. f. wang, y. h. wang, m. p. houng, “a novel cross-shape dgs applied to design ultra-wide stopband low-pass filters,” ieee microwave and wireless component letters, vol. 16, no. 5, pp. 252–254, 2006 [5] a. abdel-rahman, a. r. ali, s. amari, a. s. omar, “compact bandpass filters using defected ground structure (dgs) coupled resonators”, 2005 ieee mtt-s international microwave symposium digest, long beach, usa, june 12-17, 2005 [6] p. singh, r. tomar, p. bhartia, “the use of defected ground structures in designing microstrip filters with enhanced performance characteristics”, procedia technology, vol. 17, pp. 58-64, 2014 [7] a. r. ali, a. abdel-rahman, s. amari, a. s. omar, “direct and crosscoupled resonator filters using defected ground structure (dgs) resonators”. 2005 european microwave conference, paris, france, october 4-6, 2005 [8] p. vagner, m. kasal, “a novel bandpass filter using a combination of open-loop defected ground structure and half-wavelength microstrip resonators”, radioengineering, vol. 19, no. 3, pp. 392-396, 2010 [9] s. k. parui, s. das, “a new defected ground structure for different microstrip circuit applications”, radioengineering vol. 16, no 1, pp. 16-16, 2007 [10] d. j. woo, t. k. lee, “suppression of harmonics in wilkinson power divider using dual-band rejection by asymmetric dgs”, ieee transactions on microwave theory and techniques, vol. 53, no. 6, pp. 2139-2144, 2005 microsoft word etasr_v11_n2_pp6943-6948 engineering, technology & applied science research vol. 11, no. 2, 2021, 6943-6948 6943 www.etasr.com bouziane et al.: investigation of swirl stabilized ch4 air flame with varied hydrogen content by using … investigation of swirl stabilized ch4 air flame with varied hydrogen content by using computational fluid dynamics (cfd) to study the temperature field and flame shape a. bouziane laboratory of materials and reactive systems (lmsr) faculty of technology university of djillali liabes sidi bel abbes, algeria abouziane@yahoo.fr a. alami renewable energies department saad dahlab blida university 1 blida, algeria alami.ahmed@univ-blida.dz m. zaitri laboratory of gas combustion and environment university of sciences and technology of oran oran, algeria zaitri_mohammed@yahoo.fr b. bouchame laboratory of mechanics of structures and solids (lmss) faculty of technology university of djillali liabes sidi bel abbes, algeria boucham1@yahoo.com m. bouchetara laboratory of gas combustion and environment university of sciences and technology of oran oran, algeria mbouchetara@hotmail.com abstract-in the current paper, numerical simulations of the combustion of turbulent ch4-h2 are presented employing the standard k-epsilon and the rng k-epsilon for turbulence closure. the fr-ed concept is carried out to account for chemistry/ turbulence interaction. the hydrogen content is varied in the fuel stream from 0% to 100%. the numerical solutions are validated by comparison with corresponding experimental data from the combustion laboratory of the university of milan. the flow is directed radially outward. this method of fuel injection has been already been explored experimentally. the results show that the structure of the flame is described reasonably and both standard k-ɛ and rng kɛ models can predict the flame shape. the general aspect of the temperature profiles is well predicted. the temperature profiles are indicating a different trend between ch4 and ch4/h2 fuel mixtures. keywords-rng k-epsilon; swirl; hydrogen; cfd; ch4 i. introduction lean combustion emerges as a potential and an advantageous concept to attain efficiently the combustion process and control nox emissions in power-generation gas turbines [1–3]. the best approach to obtain a stable lean flame is to add a highly reactive fuel to a traditional hydrocarbon fuel. due to its high chemical reactivity, hydrogen could be used as a useful fuel addition to enhance the combustion of natural gas. the use of hydrogen in blended fuel can be a good option regarding combustion characteristics, such as extending the lean flammability limits [4, 5] and the environmental advantages by decreasing the emissions [6]. the research on the combustion of ng–h2 fuel mixtures is open and growing. studies [5, 7-9] on ng–h2 hybrid flame stability behavior are at the center of attention. authors in [10-11] conducted an experimental investigation on laminar lpg-h2 jet diffusion flame and ng-h2 turbulent flame respectively and affirmed that a very small fluctuation in the visible flame length, in up to 20% of hydrogen addition, enhances the flame length when higher hydrogen concentrations are injected. in the other hand, different investigations [5, 7, 8, 12, 13] were undertaken on the height of the blue cone and pointed out the influence of hydrogen injection in the increment of the combustion rate, the reduction of co, co2 and hc emissions, and the extension of the stable lean limit of natural gas burner [1, 9-12, 14-16]. authors in [17] developed an experimental investigation in optically accessible propane/ hydrogen burner and found that corresponding author: a. bouziane engineering, technology & applied science research vol. 11, no. 2, 2021, 6943-6948 6944 www.etasr.com bouziane et al.: investigation of swirl stabilized ch4 air flame with varied hydrogen content by using … the flame pattern of the hydrogen is of a weak turbulent flame [18]. a significant reduction in both co emissions and soot concentration with hydrogen addition was reported in [4, 11, 12] when turbulent jet diffusion flame was characterized. authors in [19-21] report an increase in flame adiabatic temperature and a reduction in flame thickness. authors in [15] investigated the counterflow of ng/h2–air partially premixed flame numerically and experimentally. they stated that the influence of prompt nox was important in the total nox formation. one of the purposes of this paper is to support certain theories and assumptions drawn from experiments in swirl flames. the goal was to obtain qualitatively correct predictions. this work focuses on the numerical simulation of turbulent flames utilizing well known turbulence and combustion models [22, 23]. leaner flames due to the hydrogen addition with different various hydrogen-hydrocarbon mixtures lead to thermodiffusive instabilities which have an impact on flame propagation and stability [24, 25]. more details are needed about the interaction of these types of flames with turbulence in practical devices (swirl-stabilized burner). a better understanding of the fuel improvement on the fundamental flame properties is critical to the development of combustion systems and the role of hydrogen on these systems appears to be an important parameter. the goal of the current study is the investigation of flame behavior by the use of numerical simulations with the rans model to treat turbulence coupling (the standard /rng k-epsilon ) and the fr-ed model to represent the turbulence/chemistry interactions. for this purpose, the effect of hydrogen addition in methane flames has been examined by modeling a swirl-stabilized combustor in radial injection. the aim is to give more information on the influence of hydrogen enrichment on the ch4 flame properties and a comparison is presented between the experimental results and the numerical solutions by considering a flame shape, temperature field, and velocity vectors. ii. numerical methodology the conservation equations governing reactive flows solved by code fluent [26] are mass, momentum, species, and energy using several models described with finite volume methods [27]. the schematic of the partially premixed swirlstabilized burner configuration can be seen in [5]. the grid is shown in figure 1. the geometry is open to atmospheric pressure and the meshing of all computational domain examined in this work was set up with gambit [24]. the meshing is non-uniform, with a fine meshing in zones of great interest. the numerical simulations carried out in this study were generated using a segregated, implicit solver. the coupled equations were solved with second-order accuracy in time and momentum, continuity, and turbulence parameters. the algorithms presto and simple were respectively used for the pressure interpolation and for the coupling of pressure and velocity. a uniform velocity profile was assumed for the inlet conditions, and the inlet turbulence intensity was set to 11%. at the inlet, the boundary conditions were validated by the experiments. theoretically, zero gradient condition is taken at the outlet boundary. these boundary conditions can be listed as follows: inlet, outlet, and wall boundary conditions. the do model was used to calculate the radiating heat transfer of the unconfined flames [28]. the experimental apparatus is a laboratory scale swirl burner [5]. it consists of two concentric pipes with the annulus (outer radius, rb = 18mm) supplying the central pipe (rint = 7.5mm) injecting the fuel mixtures (swirled air). the fuel mixture is radially injected into the swirled air stream through 8 circular holes. the holes are distributed on the circumferential section located 3mm upstream from the exit of the burner. fig. 1. numerical grid of the burner/furnace system. iii. turbulence model to solve the turbulence problem, the two equation-based rans standard k-ɛ turbulence model was used [29]. it is a semi-empirical turbulence model based on isotropic eddyviscosity hypotheses. the rng k-ɛ model is considered as a new version of the k-ɛ family of turbulence models. it is derived by a statistical technique called renormalization group method [30]. iv. results and discussion a. flame shape the consequence of hydrogen addition is studied using cfd and compared against measurement data [31, 32]. streamlines were obtained by two-dimensional (2-d) piv measurements, in a region located immediately downstream of the exit throat of the burner. flame imaging of the spontaneous flame emission is used to gain a general understanding (see figure 2(a)). we can see the simulation plot from the right side. although these diagnostics provide a somewhat different view of the flame, they provide complementary information. in general, the simulated image of the investigated flame (100% ch4) shows a very similar shape compared to the experimental ones, typical of high swirl processes in transverse injection. the comparison shows that standard k-ɛ is slightly overpredicted at most locations whereas the rng k-ɛ model results are quite good [33]. figure 2(a) shows the sudden expansion nozzle at the lower part of the combustion chamber and two locations of high product formation rates are located: one is on centerline in an upside-down v-shape, which can also be clearly seen in the photo of the flame in the experiment and the second in red color indicates a high product formation rate, which means an area with high chemical reaction production rates. the use of finite-rate-eddy dissipation model generates a reaction at the mixing zone. engineering, technology & applied science research vol. 11, no. 2, 2021, 6943-6948 6945 www.etasr.com bouziane et al.: investigation of swirl stabilized ch4 air flame with varied hydrogen content by using … (a) 100% ch4 40% h2+60% ch4 80% h2 + 20% ch4 100% h2 (b) 100% ch4 40% h2+60% ch4 80% h2 + 20% ch4 100% h2 fig. 2. flame shape and position comparison of the simulation (right) and the flame photo from the experiment (left): (a) standard k-ɛ model, (b) rng k-ɛ model. the experimental reaction takes place at the center of the zone where a strong inner recirculation zone appears, whereas reaction occurs with a certain delay, when simulation is considered. the impact of the different percentage of h2 blending to the ch4–air flame on the global flame characteristics is shown in figure 2 (different flame shapes and positions). (a) (b) (c) (d) (e) (f) fig. 3. radial distribution of mean temperature: (a) rng k-ɛ 50% ch4 50% h2, (b) standard k-ɛ 50% ch4 50% h2, (c) rng k-ɛ 20% ch4 80% h2, (d) standard k-ɛ 20% ch4 80% h2, (e) rng k-ɛ 100% ch4, and (f) standard k-ɛ 100% ch4. engineering, technology & applied science research vol. 11, no. 2, 2021, 6943-6948 6946 www.etasr.com bouziane et al.: investigation of swirl stabilized ch4 air flame with varied hydrogen content by using … it can be observed both from the experiments and the numerical simulation that the structure of the flame, i.e. central recirculation zone shape, changes with h2 addition. enhances in h2 concentration in the mixture increase the axial velocity and decreases the size and strength of the recirculation region. similar behavior was reported in [34]. b. temperature field to provide more information in this section, the computational solutions were compared with the measurements. to examine the role of turbulence closure models, the same configuration was modeled using the standard k-ɛ and rng k ɛ turbulence models. the mean temperature profiles are shown in figure 3, reporting a different trend between ng and h2/ng fuel mixtures. isothermal 100% ch4 fig. 4. experiment (left) and simulation (right) velocity vectors. (a) (b) fig. 5. velocity fluctuations. comparison of the experimental data and simulation results: (a)100 % ch4, (b) 20% ch4 + 80% h2 flame. the calculated temperature profiles are in agreement with the experimental results. when moving on radial direction, the numerical simulation agrees well with the trend of the experimental data. the calculated temperature indicating the existence of the hot area of the flame and then finally to the limit which assigns to the recirculation zone. the temperature profiles can be split in into three separate areas as reported in figures 5 and 6. the same results were obtained in [35]. the highest temperature shows that the flame takes place in the inner recirculation zone. when burning 100% ng, the peak temperature of the flame is quite close to 1150k, while its experimental value is estimated as 1250k. the peak temperature of the 80% h2 flame increases to about 1800k, as we seen in the experiment [31, 32]. an unexpected temperature value is determined by the cfd when the k-e model is considered. at the periphery, a region characterized by quite uniform temperature values is established. this is related with the formation of a corner recirculating flow induced by the radial expansion of the air stream and by the wall confinement. this model succeeds to predict the hot zone of the flame while over predict the calculated temperature. when r = 0.05m, the model agrees with the experimental results. on the other hand, a good agreement is obtained when the rng kɛ model is used. the rng k-ɛ model results are in good accordance with the experimental measurements, and are comparable to the results obtained with the k-ɛ model, despite the lack of accounting for non-isotropic turbulent shear stresses expected in the swirling flow. it can be observed that the predicted radial profiles of temperature of the two models are reasonable at most of the axial locations. c. mean flow fields to provide more information on the nature of the flow, we focus our solutions on the behavior of this type of flame by showing the existence of the central recirculation zone (crz). the numerical solution shows an open swirl flow core. the figure points out a more closed form with a small but strong recirculation region. the reaction zone estimated by simulation is not located on the axis as indicated by the measurements. the dynamic flow field is affected greatly by the combustion that redefines a velocity distribution. this discrepancy is mainly the result of shortcoming of the turbulence model which might overestimate the decay of turbulence intensity for these swirling flames. undercombustion regime (figure 4), in a region located immediately in the exit of the burner clearly indicates the existence of a crz. the width of the crz is smaller than under when burning 100% ng. similar behavior was reported in [29]. as the h2 percentage increases, the above regions reduce in size and move closer to the reactant outlet. when burning 100% ng, the axial flow fields by introducing velocity vectors obtained by the simulation are more large than the 80% h2 flame. another important parameter describing the flow field, is the velocity fluctuations (figure 5). both results show an increase of the intensity a few mm downstream of the respective flame zone. a crz can be found, where the axial velocity is smaller than zero. this recirculation increases the flow divergence in the combustion chamber. in general, the numerical solutions agree well with the experimental results engineering, technology & applied science research vol. 11, no. 2, 2021, 6943-6948 6947 www.etasr.com bouziane et al.: investigation of swirl stabilized ch4 air flame with varied hydrogen content by using … (100% methane flame), but we failed to predict the inner recirculation zone with precision. v. conclusion numerical simulations of a turbulent (ch4-h2)/air flame were conducted in this study. the h2 percentage varied in the mixture from 0% to 100%. the numerical investigation involved simulations employing the standard k-ɛ and the rng k-ɛ for turbulence closure. the fr-ed model is used to represent the turbulence/chemistry interactions. numerical solutions were compared to experimental measurements which were used for model validation. the results show that the structure of the flame is described reasonably in both standard k-ɛ and rng k-ɛ models which can predict satisfactorily the flame shape with the rng k-ɛ model providing better performance than the k-e model. from the flame simulations, the hydrogen addition alters considerably the global flame characteristics by different flame shapes and flame positions. it can be observed from the experiments and the simulations that the structure of the flame varies with hydrogen blending. in general, the temperature data were well represented. the rng k-ɛ model consistently demonstrated superiority over the standard k-ɛ turbulence model. the dynamic flow field is affected greatly by the combustion. a region located immediately downstream of the exit throat of the burner clearly indicates the existence of a crz. under combustion conditions the width of the crz is smaller than under when burning 100% ng. it was concluded that the use of a 2d axial symmetric grid is a promising toolbox for modeling turbulent combustion and can be used for predicting the operating conditions of complex industrial furnaces. nomenclature �� mass fraction of a particular reactant � ��,� � stoichiometric coefficient for reactant in reaction ��,�: �� stoichiometric coefficient for product in reaction n number of chemical species in the system � ,� molecular weight of species � ,� molecular weight of species� � ,� molecular weight of a particular reactant � k/ε large-eddy mixing time scale � empirical constant equal to 4.0 � empirical constant equal to 0.5. α thermal diffusivity [m 2 . s1 ] β thermal expansion coefficient [k -1 ] φ solid volume fraction ɵ dimensionless temperature µ dynamic 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[26] g. solero, a. coghe, and g. scribano, "influence of natural gas injection procedure in a swirl burner," in 7th mediterranean combustion symposium, sardinia, italy, sep. 2011. [27] m. r. lecic, a. s. cocic, and s. m. cantrak, "original measuring and calibration equipment for investigation of turbulent swirling flow in circular pipe," experimental techniques, vol. 38, no. 3, pp. 54–62, may 2014, https://doi.org/10.1111/j.1747-1567.2012.00812.x. [28] b. e. launder, lectures in mathematical models of turbulence. london, new york: academic press, 1972. [29] v. yakhot and s. a. orszag, "renormalization group analysis of turbulence. i. basic theory," journal of scientific computing, vol. 1, no. 1, pp. 3–51, mar. 1986, https://doi.org/10.1007/bf01061452. [30] f. cozzi, a. olivani, and a. coghe, "combustion of ng + h2 fuel mixtures in a partially premixed swirlburner," presented at the third european combustion meeting ecm 2007, 2007. [31] a. olivani, f. cozzi, g. solero and a. coghe, "analysis of the environmental impact of a swirl burner:hydrogen and natural gas mixture feeding," presented at the 28th meeting of the italian section of the combustion institute, 2005 [32] j. f. widmann, s. r. charagundla, and c. presser, benchmark experimental database for multiphase combustion model input and validation: characterization of the inlet combustion air. gaithersburg, md, usa: national institute of standards and technology, 1999. [33] m. w. eldeen, m. a. taemah, and w. m. el-maghalany, "influence of swirl intensity and blended methane-hydrogen on gas turbine combustion characteristics," international journal of engineering research & technology, vol. 7, no. 7, pp. 405–412, 2018. [34] a. frassoldati, s. frigerio, e. colombo, f. inzoli, and t. faravelli, "determination of nox emissions from strong swirling confined flames with an integrated cfd-based procedure," chemical engineering science, vol. 60, no. 11, pp. 2851–2869, jun. 2005, https://doi.org/10.1016/j.ces.2004.12.038. engineering, technology & applied science research vol. 7, no. 6, 2017, 2282-2287 2282 www.etasr.com polat: analysis of a frame-shear wall concrete structure by using base isolation and evaluation … analysis of a frame-shear wall concrete structure by using base isolation and evaluation of structuresoil interaction halil ibrahim polat ministry of environment and urbanization istanbul, turkey halilibrahimpolat34@gmail.com abstract—a base isolation system is a type of earthquakeresistant structure design approach based on the principle of reducing a structure’s earthquake response rather than increasing the structure’s earthquake resistance capacity. seismic base isolated structures have the ability to make large displacements relative to the level of insulation elements. this means that a large structure performs very small displacements between floors during an earthquake and exhibits a rigid body behavior. at this point, the earthquake forces acting on the structure decrease along with the floors. in this article a school building composed of frame-shear wall is resolved primarily with the traditional fixed base structure system, mode shapes are found and periods are obtained. for earthquake response analysis, earthquake loads are distributed to the floors using the equivalent seismic load method and structural elements experiencing capacity problems are found. then, using the earthquake record, larger failure of cross sections and capacity problems are obtained compared to the first method. in the second stage, the same structure is dissolved again by placing the lead core rubber base isolators between the base and the vertical structural members. the periods of structures under earthquake load have increased significantly by utilizing base isolation, as a result of that spectral accelerations decreased. thus, large decreases in the shear forces acting to the structure are determined and failures of cross sections are removed. keywords-base isolation; construction-soil interaction; time history analysis i. introduction one of the areas of interest of building and geotechnical earthquake engineering is the examination of the extent of damage occurred due to loads caused by lateral effects such as earthquakes and winds, the developing of suggestions against destructive effects and sustaining the relationship between the ground and the structure. in this context, it can be considered that the ground-structure interaction is the basic argument of the structural analysis calculations, especially the selection of the load-bearing system. in traditional building design, the strengthening of the bearing system, in order to provide a significant seismic performance, leads to a rather rigid behavior. the choice of such a load-bearing system causes the structures to be subjected to more lateral forces and to shear loads. in this approach, the consumption of the seismic energy transferred through the structural ground is mainly due to the plastic hinges. therefore, this means accepting the possible damage on the structure. recently, the consumption of this energy is taken into consideration by means of some damping systems. these systems find use a method called base isolation. during the earthquake, the earth movement spreads in every direction in wave form and when it reaches a structure, starts shaking its foundation which shakes the load bearing system. effects of inertia forces in the cross sections of the bearing system elements occur. prevention of structure vibration by separating the foundation from the bearing system is the main idea of earthquake base insulation [1]. the strengthening of the load bearing system, in classical built-in structure design, increases the stiffness of the structure and results in augmenting structure’s strength. on the other hand, base isolation is a kind of earthquake resistant structural design approach that focuses on the principle of reducing the response to earthquake rather than increasing the structure’s resistance. in other words, the structures provide rigid body behavior, especially during large magnitude earthquakes, and structural constraints remain within elastic limits. thus, a large part of the earthquake energy is consumed by the seismic isolator system and additional damping devices at the isolation level. so, a small portion of the earthquake energy is transmitted to the structure (figure 1). fig. 1. behaviour of fixed base structure and seismically base isolated structure during the earthquake engineering, technology & applied science research vol. 7, no. 6, 2017, 2282-2287 2283 www.etasr.com polat: analysis of a frame-shear wall concrete structure by using base isolation and evaluation … a structure with a seismic isolation system can exhibit almost rigid superstructure behaviour in an earthquake motion as well as the flexibility needed to reduce floor accelerations with the isolation zone of large displacements. in this context, it has the rigidity required to reduce the relative floor displacements. during the first dynamic mode of the structures in which the base insulation systems are applied, the displacement is only at the isolation level. the top modes producing displacement are orthogonal to the first mode and hence the ground motion. participation of these upper modes to the motion is very low (figure 2) [2]. fig. 2. seismic isolator base displacement at base level the effective resonance period of a structure is usually between 0.1 and 1.0 second. this period also includes the dominant period of many violent earthquakes [3]. since the elastic first vibration periods of the seismic base insulated structures are considerably larger than the fixed base construction, the elastic first vibration periods are enlarged (figure 3), it is provided to move away from the resonance zone, at which earthquake is very dangerous for structures. thus, the magnitude of ground acceleration is prevented by the structure [4]. fig. 3. a typical design spectrum the basic characteristics that a seismic isolator system should have are [5]:  low enough horizontal stiffness  high vertical stiffness (to allow the weight of the superstructure to be transported without deterioration)  enough damping (for a possible resonance condition)  back-centering effect (to return to pre-move position)  anti-collapse system  sufficient strength against tensile loads (in case of tensile strength) the seismic insulation elements are placed on the foundation in structures that have no basement or in the lower, middle or upper sections of column and curtain elements in structures with basement [6, 7]. in this study, a kind of leadcore rubber isolator in spherical form is used. the insulator is formed by joining the natural rubber layers with low damping with the help of steel reinforcement plates and by placing the cylindrical lead core in the middle. lead material is a crystallized material that can temporarily change its form below the pour point. on the other hand, rubber has the effect of corrective force which restores the system to its original state and maintain its elastic characteristics. lead-core is forced to change the plastic shape by the effect of the shear forces transmitted by the steel plates. in this context, the energy expenditure mechanism of lead-core rubber isolators is related to the elasto-plastic behaviour of rubber and lead [6]. natural rubber isolations have many advantages:  simple production  easy modelling  bearings mechanical behavior of is not affected by speed, temperature and aging over time [8]. ii. existing system analysis with the help of the etabs program, an existing 3-storey (consisting of ground floor + 2 typical floors) school building with a reinforced concrete curtain-framed load bearing system, with 21,60 x 14,35 m dimensions, storey height: 3.00 m is analyzed and its results are tried to be evaluated [9]. fig. 4. floor plan and section of the curtain-frame structure the thickness of all curtains is 25 cm. there are three types of column sections available (table i). the largest beam dimension in the structure is 35x70 and the smallest is 25x40 (table ii). also, there are three types of floor slabs of 12, 15 and 18 cm. table i. column sections according to floors floor sz02sz05 sz03-sz04-sz10-sz11sz12-sz14-sz15-sz16 sz06-sz07sz08-sz09 s102-s205 s103-s104-s110-s111-s112-s114-s115-s116 s106-s107s108-s109 s202 s205 s203-s204-s210-s211s212-s214-s215-s216 s206-s207s208-s209 g 25x50 30x50 50x35 1 25x50 30x50 50x35 2 25x50 30x50 50x30 engineering, technology & applied science research vol. 7, no. 6, 2017, 2282-2287 2284 www.etasr.com polat: analysis of a frame-shear wall concrete structure by using base isolation and evaluation … table ii. beam sections according to floors floor k101-k102k103-k110k111 k112-k114k115-k126k127 k104-k108k109-k118k119 k121-k122k123-k124k125 k105 k106-k107 k117 k201-k202k203-k210k211 k212-k214k215-k226k227 k204-k208k209-k218k219 k221-k222k223-k224k225 k205 k206-k207 k217 k301-k302k303-k310k311 k312-k314k315-k326k327 k304-k308k309-k318k319 k321-k322k323-k324k325 k305 k306-k307 k317 g 30x70 25x50 25x40 35x70 25x70 1 30x70 25x50 25x40 35x70 25x70 2 30x70 25x50 25x40 35x70 25x70 c14 concrete and csi non-ribbed steel are used in the construction. cross section and material selection of all structural elements have been made according to the existing axle system. movable and constant load distributions are provided and the bearings are defined (figure 5). fig. 5. building plan and three-dimensional view as a result of the analysis, the natural vibration periods of the building are determined. according to this; the 1st mode of the building is in the y direction and 0.2165 s. (figure 6). the second mode of construction is 0.1447 s in the z direction. the third mode is 0.110 s in the x direction (figures 7 and 8). fig. 6. 1st mode (t1y = 0.2165 s) fig. 7. 2nd mode shape (t1z = 0.1447 s) fig. 8. 3rd mode shape (t1x = 0.1110 s.) after the mode shapes are obtained, the shear wall-frame system is analyzed by linear equivalent seismic load method. in the second phase, nonlinear analysis is performed in time domain by using the data, including east-west and north-south directional components, recorded at 1999 marmara earthquake in duzce meteorology station. after these two analyses were completed, the base isolation is added to the fixed-base system, and the system is re-solved in the time domain and all three cases are compared (cross section insufficiencies, period, mode shapes, etc.). a. earthquake analysis by equivalent seismic load method (current system) equivalent seismic load method (eslm) and lateral seismic loads are defined at floor alignments with ± 0.05 eccentricity. building earthquake parameters:  effective ground acceleration coefficient: a0 = 0.40 (1st degree earthquake region)  significance coefficient of the building: i = 1.4 (school building)  spectrum characteristic period: ta = 0.15, tb = 0.60 (z3 soil class)  load bearing system behavior coefficient: r = 4 (ductility level normal system) [10] engineering, technology & applied science research vol. 7, no. 6, 2017, 2282-2287 2285 www.etasr.com polat: analysis of a frame-shear wall concrete structure by using base isolation and evaluation … a total of 21 load combinations are defined. according to the analysis made by reflecting the parameters of the eslm, none of the columns belonging to the structure are found to be inadequate in cross section. as seen in table iii, the capacity has been exceeded at the bending of p3 shear-wall in the 1st floor (ground floor). in addition, as shown in table iv, the p2 shear-wall in the 1st and 2nd storeys, and the p3 shear-wall in the 1st storey have capacity problem (figure 9). fig. 9. capacity problems in shear walls in eslm table iii. capacity problems in shear walls in eslm shear-walls 1st floor 1st floor 1st floor p2 p2 p3 b. earthquake analysis with time history method (current system) the current system model has been solved with time history method without any changes in material characteristics and cross sections. acceleration records of 1999 marmara earthquake recorded at duzce meteorology station are utilized (figures 10 and 11). the time period is 0.005 s, the maximum acceleration value is 3.73 m/s2 for east-west and 3.14 m/s2 for north-south. according to the analysis results, in all three floors, shear-walls are found to be inadequate (table iv). in vertical load bearings, 15 of the 42 existing columns are found to be inadequate (table v). table iv. capacity problems in shear-wall elements in the time definition area shear-walls 1st floor 2nd floor 3rd floor p1 p1 p2 p2 p3 table v. columns exceeding the capacity ratio limit columns 1st floor 2nd floor 3rd floor sz02 s102 s202 sz05 sz07 s107 s207 sz10 s110 s210 sz11 sz12 sz14 s114 sz15 fig. 10. düzce north-south acceleration recording chart fig. 11. düzce east-west acceleration recording chart iii. system analysis of base isolations the analysis is renewed by placing the base isolation in the base-column junction of the present school building, which consists of shear wall-frame. dis b type lead core rubber isolator manufactured by dynamic isolation systems company is used for the base isolation material. the characteristic of this isolator is shown in table vi. table vi. characteristic features of dis b type isolator total weight of isolation element 8.3404 kn effective rigidity for vertical direction 2.468.654,085 kn/m (linear) effective rigidity for horizontal direction 1.180,926 kn/m (linear) effective rigidity for horizontal direction 6.808,12 kn/m (nonlinear) yield strength 127,03 kn the ratio of post-yield strength to pre-yield strength 0,1 the linear and nonlinear damping of the isolator and the yield strength assignments are performed and the results are shown in figure 12 [11]. the natural vibration frequency of the isolated structure has now been determined. according to this, the 1st mode of the building is 1.7407 s in the z direction (torsional direction) (figure 13). the second mode is 1.6550 s engineering, technology & applied science research vol. 7, no. 6, 2017, 2282-2287 2286 www.etasr.com polat: analysis of a frame-shear wall concrete structure by using base isolation and evaluation … in the y direction (figure 14). the third mode is 1.6458 s in the x direction. (figure 15). fig. 12. assign screen for characteristics of dis b type isolator fig. 13. 1st mode of isolator system with (t1z = 1.7407 s.) fig. 14. 2nd mode of isolator system with (t1y=1.6550s.) iv. earthquake analysis with base isolator in time history method the existing system with base isolation has also been solved in nonlinear time history method. as a result of the analysis made on the basis of the acceleration records in figures 10 and 11, it is seen that all the sections are sufficient in contrast to the current situation and no capacity problem is encountered. the 1st period of the classical analysis is 0.2165 s in the y direction . while the 1st period of the base isolated system is in the direction of z (torsion direction) and equal to1.7407 s. fig. 15. 3rd mode of isolator system with (t1x=1.6458s.) v. conclusion and evaluation according to the nonlinear time history method it is seen that the cross sectional insufficiency is more than eslm. for this reason, the application of the base isolation is made on the basis of the time history method in the context of the “safety engineering principle”. with the assignment of dis b type lead-core rubber isolator, the analysis is revised and compiled as shown in table vii. according to this, it has been seen that with the base isolation application, the natural periods increased from about 8 to 16 times for all three directions compared to the fixed-base building. as a result, the spectral acceleration decreased in the base isolation system and decrease in the shear forces is observed. in addition, during the reflected earthquake, there is a very small displacement between the floors, rigid body behaviour and the deformations remained especially at the isolator level. table vii. comparative period table shear wall-frame system fixed-base system t1x t1y t1z 0.111 0.2165 0.1447 base isolation system 1.6458 1.655 1.7407 the results of the analysis of the generated system are summarized in table viii. a capacity problem occurred in some shear walls in fixed-base structure with the solution of eslm. in the results of the earthquake calculations using the nonlinear time-history method, bending capacity in almost all column and shear wall sections is found to be inadequate. on the other hand, it is seen that there is no capacity problem in the insufficient sections of the structural system components. as a result, seismic isolator systems have proven that the structure can be dimensioned for smaller loads during the design of a engineering, technology & applied science research vol. 7, no. 6, 2017, 2282-2287 2287 www.etasr.com polat: analysis of a frame-shear wall concrete structure by using base isolation and evaluation … new structure. it is thought that the application area of base isolation should be increased as an alternative solution method in order to construct more secure structures in regions where settlement density is clustered on the north anatolian fault line. table viii. comparative capacity table structural elements exceeding capacity fixed bearing solution with equivalent seismic load method fixed bearing solution with time history method base isolator solution with time history method 1st floor 2nd floor 3rd floor 1st floor 2nd floor 3rd floor 1st floor 2nd floor 3rd floor sz02 s102 s202 sz05 sz07 s107 s207 sz10 s110 s210 sz11 sz12 sz14 s114 sz15 p1 p1 p2 p2 p2 p2 p3 p3 references [1] z. celep, n. kumbasar, deprem muhendisligine giris ve depreme dayanikli yapi tasarimi, beta publisher, 2004 [2] http://www.mafiamax.com/2012/06/evim-depreme-dayanikli-mi.html, 2017 [3] s. pinarbasi, u. akyuz, “sismik izolasyon ve elastomerik yastik deneyleri”, imo teknik dergi, vol. 237, pp. 3581-3598, 2005 [4] r. pekgokgoz, deprem yukleri altindaki yapi davranisinin yari-aktif akiskanli sonumleyiciler ve sismik taban yalitim sistemleri kullanilarak bulanik mantik yontemi ile kontrolu, phd thesis, institute of science, istanbul technical university, 2005 [5] j. m. kelly, “seismic isolation as an innovative approach for the protection of engineered structures”, 11th european conference on earthquake engineering, pp. 338, 1998 [6] www.arfen.com.tr, 2017 [7] www.erseteknoloji.com, 2017 [8] h. turker, taban izolasyonu ile klasik guçlendirme arasinda bir maliyet karsilastirilmasi, msc thesis, institute of science, istanbul technical university, 2003 [9] h. i. polat, perde-cerceve ve cercevelerden olusan yapilarin taban izolatorleri kullanilarak analizi ve degerlendirilmesi, msc thesis, institute of science, istanbul technical university, 2007 [10] ministry of environment and urban planning, deprem bolgelerinde yapilacak yapilar hakkinda yonetmelik, bayindirlik ve iskan bakanligi, 2007 [11] g. ozmen, e. orakdogen,k. darilmaz, orneklerle etabs, birsen yayinevi, 2005 microsoft word 8-2474_s engineering, technology & applied science research vol. 9, no. 1, 2019, 3715-3720 3715 www.etasr.com badri-koohi et al.: optimizing number and locations of alternative-fuel stations using … optimizing number and locations of alternativefuel stations using a multi-criteria approach babak badri-koohi grado department of industrial and systems engineering, virginia tech, blacksburg, va, usa babakbk@vt.edu reza tavakkoli-moghaddam school of industrial engineering, college of engineering, university of tehran, tehran, iran tavakkoli@ut.ac.ir mahnaz asghari grado department of industrial and systems engineering, virginia tech, blacksburg, va, usa mahnaz@vt.edu abstract—the transition to alternative fuels is obligatory due to the finite amount of available fossil fuels and their rising prices. however, the transition cannot be done unless enough infrastructure exists. a very important infrastructure is the fueling station. as establishing alternative-fuel stations is expensive, the problem of finding the optimal number and locations of initial alternative-fuel stations emerges and it is investigated in this paper. a mixed-integer linear programming (milp) formulation is proposed to minimize the costs using net present value (npv) technique. the proposed formulation considers the criteria of the two most common models in the literature for such a problem, namely p-median model and flow refueling location model (frlm). a decision support system is developed for the users to be able to control the parameter values and run different scenarios. for case study purposes, the method is used to find the optimal number and locations of the alternative-fuel stations in the city of chicago. some data wrangling techniques are used to overcome the inability of the method to solve very large-scale problems. keywords-continuous location problem; multi-criteria decision making; alternative-fuel stations; mixed-integer linear programming; optimization; chicago transportation network i. introduction since it is estimated that oil and gas resources will come to an end by the next 200 years, the use of alternative fuels such as hydrogen [1, 2], electricity [3], and natural gas [4] instead of gasoline and diesel is sensible. hence, there’s a growing interest in vehicles powered by alternative fuels. research has pointed out the significant impact that constructing refueling stations has on the promotion of alternative fuels [5-9]. many researchers and industry representatives addressed the whichcomes-first issue regarding alternative fuel (alt-fuel) stations and vehicles [10]. in [11] the which-comes-first question involving refueling stations and vehicles is stated to be like the “chicken-and-egg” dilemma. the research asserts that optimizing the location of refueling stations is inevitable to maximize the potential for consumers to use alt-fuel vehicles, especially in the early steps of transition to an alternative fuel. whether existence of refueling stations leads to the appeal for alternative fuels or vice versa, it is evident that the establishment of fuel stations and the optimization of their location are crucial. optimization techniques have long been used in supply chain design, logistics, and supply chain planning problems [12-16]. the use of optimization methods for finding optimal locations especially in energy application area has also been investigated in [17-19]. various mathematical models are specifically proposed in the literature for optimally locating fuel stations. some have addressed the problem with a pmedian model which is a commonly used location-allocation model whose objective is to minimize the total distance traveled from demand nodes to a given number p of facilities by optimally locating the facilities and allocating the demand nodes to them [20, 21]. it has been used in [22-24] to optimally locate alt-fuel stations close to where people live since consumers usually prefer to refuel near their homes, according to empirical studies [3, 25]. the p-median model was first applied to fuel stations in [26] as an objective in a multiobjective programming model for relocating existing gas stations. authors in [9] developed the “fuel travel-back” approach whose structure is very much like the p-median model. in this approach, however, nodes are weighted by the quantity of fuel consumed on road segments passing through them instead of population. moreover, travel time between nodes is considered instead of distance. vehicle-miles traveled (vmt) data is used in this approach for minimizing total travel time for all the fuel (in gallon-minutes) needed to travel from everywhere to the nearest fueling station. the advantage of this approach is that it only needs road network data and population data that are easily accessible in gis format from a variety of sources. there is another approach that tries to locate fuel stations on high-traffic routes. for example, a second criterion that maximizes traffic flows on the roads that have fuel stations is considered in [26] along with the p-median criterion. a similar approach is proposed in [1] considering only high-traffic roads (with at least 20,000 passing vehicles per day). the logic behind this approach is that drivers usually refuel on their way to somewhere else and do not deviate much from their route to refuel. the criteria considered in [27] are a hybrid of the first two types, maximizing the population on covered links. corresponding author: babak badri-koohi engineering, technology & applied science research vol. 9, no. 1, 2019, 3715-3720 3716 www.etasr.com badri-koohi et al.: optimizing number and locations of alternative-fuel stations using … however, the same trips by the same drivers are counted more than once in traffic-count or vmt methods if the trip travels multiple links, even if drivers might refuel only once. so, this approach could locate stations on several segments of a hightraffic freeway. another approach for locating refueling stations was originally named flow-capturing location model [28] and later termed as the flow-intercepting location model (film) [29], that maximizes passing traffic flows without counting the traffic multiple times. since the flows on paths across a network representing the routes people travel are considered as the demand in these models in substitute for population (pmedian models) and road traffics (traffic-count models), these models are classified as path-based or flow demand models. locating facilities in such a way that the number of trips captured or intercepted (i.e. there is a facility anywhere along its path) is maximized is the main criterion in film. the film is supporting the idea that drivers refuel along their ways to somewhere else rather than making trips for the sole reason of refueling and each flow intercepted is counted only once in the standard film, regardless of the number of existing stations in its route. the first problem with film is that the model needs a matrix of precise traffic flows from origins to destinations, namely “trip table” data that may not be accessible for all regions and is more complicated than population data. the other problem with this model is that, it considers a path intercepted if it passes by at least one fuel station regardless of the limited driving range of vehicles and the need for multiple times of refueling in longer inter-city trips to complete the path without running out of fuel. given that electric vehicles and hydrogen-powered vehicles suffer from limited energy storage capabilities, the flow refueling location model (frlm) was developed [30] to address this critical problem. in the frlm, a flow is considered refueled or intercepted only if there are stations along the path in such a way that drivers can complete their round trip via the path without running out of fuel, given the limited driving range of their vehicles. the frlm aims at maximizing the number of trips that can be potentially refueled by a given number of stations and it has been applied to realworld networks in florida [31] and arizona [32]. maximizing trip-miles instead of trips [31], considering stations with limited capacities [11, 33], and considering locations along arcs [34] are some of the extensions to this model. another advantage of the frlm is that it also performs better with the p-median model’s objective than the p-median model does with the frlm’s objective. however, the frlm has two major problems. first, it locates stations far from people’s homes. hence, the long distances may cause some people not to have access to any refueling station, thereby not being able to use alt-fuel vehicles. this reduces the robustness of the locations. next, the model requires the flow data of all origin-destination pairs considering all possible combinations of stations which can capture a route. thus, the applicability of the model is disputable. another refueling-station-location model is proposed in [35] based on a set covering mixed-integer programming formulation and vehicle routing concept. the proposed technique only requires a matrix of origin-destination data that is usually very accessible. however, the study suffers from not considering flows of traffic as a crucial factor in its model. building a true multi-objective model to tradeoff between the flow-refueling and the p-median objectives is proposed as the next logical step to solve the problem in the future work section of many research studies (e.g. [11]). a multi-objective model allows different decision-makers to increase or decrease the weights on these objectives. for example, covering most of the major regions could be more important for governmental decision-makers, while maximizing the profit could be more vital for the decision-makers in the private sector. ii. problem definition based on what is mentioned above, a multi-criteria model for locating alt-fuel stations in a region considering the pmedian objective while considering traffic flows and construction costs of stations was developed. the model tries to locate stations close to people’s homes and close to the traffic flows at the same time while constructing as fewer stations as possible. in all the models mentioned above, the number of stations is considered determined. but, the question is how this number can be determined. since constructing alt-fuel stations is very costly, covering as much of the consumers’ demand for fuel as possible while constructing the minimum number of stations possible is essential. although several studies have independently addressed the general questions of how many refueling stations are needed and where the optimal locations for stations are, the literature has been mostly silent on how to tradeoff between the location of stations and the sufficient number of hydrogen stations. in this research, a multi-criteria mathematical model is formulated to minimize the total costs of constructing stations and the costs of the fuels used for all commutes with the purpose of refueling using the simple npv (net present value) technique of engineering economics. this formulation can find the optimal locations while optimizing the number of stations. moreover, candidate sites for stations in the literature are mostly considered discrete. however, it is very difficult to find all the candidate sites over the whole city in a big city like tehran. even by finding all candidate sites, we will have many binary variables which can make the problem harder to be solved optimally in a reasonable time. furthermore, by considering a few of them as candidate sites, the problem of missing some parts of the solution space may occur. therefore, the solution space for candidate sites is considered continuous in this paper. this makes the problem similar to a continuous location problem (weber location problem). for taking into account traffic flows in the model, the most common method in the literature is using all origindestination pairs, but finding all these pairs is very difficult for big cities like tehran. also, it is somehow impossible in places where gis (geographic information system) is not deployed widely. to face the problem, we proposed using flow nodes like population nodes. for example, when there is a route (highway) about 40 kilometers long, it can be divided into two or more nodes with 20 kilometers or less length. then, some weights proportionate to the traffic flow of the centers of these nodes can be assigned to them. average daily traffic (adt) data for cities conveys the same information. population nodes engineering, technology & applied science research vol. 9, no. 1, 2019, 3715-3720 3717 www.etasr.com badri-koohi et al.: optimizing number and locations of alternative-fuel stations using … can be determined similarly from census block population data. we can ignore population nodes with very low population and flow nodes with very low traffic flows. iii. mathematical formulation a multi-criteria milp (mixed-integer linear programming) mathematical formulation is proposed below to solve the problem of finding the optimal number and locations of alt-fuel stations. some of the characteristics of the problem are listed below: • there can be at most i alt-fuel stations. • there is a set of j nodes for traffic flows determined beforehand. • the flow of each flow node is deterministic. • there is a set of k nodes for population distribution determined beforehand. • population of each population node is deterministic. • construction of each station costs c1 dollars. • t equal to 30 years is the time horizon for using newlyconstructed stations. • there is an inflation rate equal to 15% for alternative fuels’ prices and depreciation equal to 10% for all costs. • distance metric is assumed to be rectilinear (1-norm). this norm seems more reasonable than the euclidean distance function (2-norm) since mostly in a network of streets of a city, there is no direct way from somewhere to somewhere else, but rectilinear way. • total population tp and total number of cars tc in the region are deterministic. so, the average number of cars per person is tc/tp (tc divided by tp). • traveling from an origin to a station for refueling requires consumption of some fuel. the cost of the fuel burned per unit of distance c2 is deterministic. • rj is considered as the radius of the identified node j. • the vehicle range is assumed 100km per full refueling. so, each flow will travel for 2*rj kilometers and in each 100km, the vehicle needs refueling, hence 2*rj/100 (2 times rj divided by 100) in the formulation. • candidate space for stations is considered continuous. • some weights w1, w2 and w3 are assigned to each objective function in order for the decision-maker to control the policy. sum of the weights had better be equal to one. a. notations 1) indices • i=1,…, i index for stations • j=1,…, j index for flow nodes • k = 1,…, k index for population nodes 2) parameters • w1, w2, w3 weights for objective functions • c1, c2 costs • fj flow of node j • pk population of node k • tc total number of cars • tp total population • fxj, pxk x-coordinates of flow node j and pop node k • fyj, pyk y-coordinates of flow node j and pop node k • m1, m2 sufficiently large numbers 3) variables • xi x-coordinate of location of station i • yi y-coordinate of location of station i • fdj distance of flow node j from the nearest station • pdk distance of pop node k from the nearest station • fsij 1, if station i is the closest station to flow node j; 0, otherwise • psij 1, if station i is the closest station to pop node j; 0, otherwise • si 1, if station i is open; 0, otherwise • fxaij absolute horizontal distance of station i and flow node j • pxaij absolute horizontal distance of station i and pop node j • fybij absolute vertical distance of station i and flow node j • pybij absolute vertical distance of station i and pop node j iv. model � ! " = #$%$ ∑ '( + #* + $,$../01 $,$../ 2 %* ∑ 34 + *56 $..24 374 + (1) #8 + $,$../01 $,$../ 2 %* ∑ + 9: 9;2 <= 37== >. ?. 3@a(4 + 3bc(4 ≤ 374 + e1 − 3'(4g�$ ∀ , i (2) <@a(= + <bc((= ≤ <7= + j1 − <'(=k�$ ∀ , l (3) ∑ 3'(44 + ∑ <'(== ≤ '(�* ∀ (4) ∑ '(4( = 1 ∀i (5) ∑ '(=( = 1 ∀l (6) engineering, technology & applied science research vol. 9, no. 1, 2019, 3715-3720 3718 www.etasr.com badri-koohi et al.: optimizing number and locations of alternative-fuel stations using … @( − 3@4 ≤ 3@a(4 ∀ , i (7) 3@4 − @( ≤ 3@a(4 ∀ , i (8) @( − <@= ≤ <@a(= ∀ , l (9) <@= − @( ≤ <@a(= ∀ , l (10) b( − 3b4 ≤ 3bc(4 ∀ , i (11) 3b4 − b( ≤ 3bc(4 ∀ , i (12) b( − <b= ≤ <bc(= ∀ , l (13) <b= − b( ≤ <bc(= ∀ , l (14) 3@a(4, 3bc(4 m 0 ∀ , i (15) <@a(=, <bc(= m 0 ∀ , l (16) @(, b( m 0 ∀ (17) 374 m 0 ∀i (18) <7= m 0 ∀l (19) 3'(4 m 0 ∀ , i (20) <'(= m 0 ∀ , l (21) '(4 m 0 ∀ (22) equation (1) represents the objective function and is comprised of three parts for three different objectives. all three different objectives are transformed to cost functions for being able to be summed up. constraints (2), (3), (18) and (19) define the values of fdij and pdik which are the minimum of the distances between nodes and stations. constraints (4), (5), (6) and (22) indicate whether a station must be constructed or not. constraints (7)-(14) are substitutes for absolute term in rectilinear distance function to make the model linear. constraints (2), (3), (15) and (16) define the values of fxaij, fybij, pxaik, pybik, xi and yi. v. case study to examine the capability of our model, we applied it on a real case study in the united states. we considered chicago, il as our case study and found the optimal locations for alternative fuel stations in this city. we obtained chicago’s census block population data, which contains 46291 blocks [45]. these data include latitudes and longitudes of the vertices of the census blocks along with the population of the blocks. we also obtained average daily traffic count data, which contain 1279 traffic nodes [46]. the data for traffic nodes include the latitudes and longitudes of the nodes representing streets and roads along with the average daily number of vehicles passing through those streets and roads. a. data wrangling some process has been performed on the data so that they become usable in the formulation. the means of the latitudes and longitudes of the vertices of each census block were calculated and considered as the latitude and longitude of the population node representing the whole block. the locations of the population and traffic nodes were represented in the geographic coordinate system using latitudes and longitudes. the proposed method, however, requires the data to be in the two-dimensional (2d) euclidean coordinate system. therefore, we projected our location data to a 2d coordinate system. @ = o ∗ % ∗ eqr! − qr!stug ∗ vr' j% ∗ qa?k b = o ∗ % ∗ eqa? − qa?stug where r=6371000 is an approximation of earth’s radius at the equator in meters and c=π/180 is the coefficient for converting degree centigrade to gradian. since the majority of nodes in this case study could hinder the ability of our proposed method to find the optimal solution in a reasonable amount of time, we used k-means clustering algorithm to cluster our population nodes and traffic nodes to 20 node clusters. in this algorithm, the total population in each cluster is equal to the aggregate population of the nodes in the cluster and the total traffic in each cluster is equal to the aggregate traffic of the nodes in that cluster. vi. computational results we coded the formulation in python and solved the case study using ibm ilog cplex 12.7 solver. based on that, we developed a decision support system (dss) where the user can control objectives’ weights w1, w2, and w3, cost coefficients c1, c2, and ac, and the maximum number of stations. the dss visualizes data and optimal solutions in the map of chicago in html format. the following assumptions were made for the formulation to solve the case study: w1=0.4, w2=0.5 , w3=0.1, c1=1000000$, c2=30$, ac=(tc/tp)=0.125. in all following figures, population clusters, traffic flow clusters, and optimal locations of alt-fuel stations are shown in green, blue, and red circles, respectively. for maximum number of stations greater than or equal to 4, the dss decides to open 4 stations as shown in figure 1. fig. 1. optimal locations for maximum number of stations>=4 the size of population and traffic flow clusters are proportionate to the population and traffic volumes. the results engineering, technology & applied science research vol. 9, no. 1, 2019, 3715-3720 3719 www.etasr.com badri-koohi et al.: optimizing number and locations of alternative-fuel stations using … for maximum number of stations equal to 1, 2, and 3 are shown in figure 2. if the cost parameter c2 is increased to 300$ and the maximum number of stations is assumed to be 10, the dss decides to open 10 stations as shown in figure 3. fig. 2. optimal locations for maximum number of stations equal to 1, 2, and 3 from left to right. fig. 3. optimal locations for c2=300$ and maximum number of stations equal to 10 vii. conclusions a mathematical modeling approach was proposed in this paper for determining the optimal number and locations of alternative-fuel stations. net present value technique of engineering economics was used in this multi-criteria model. a decision support system using data wrangling techniques was developed in python based on the proposed approach. the decision support system uses ibm ilog cplex solver to solve the mixed-integer linear programming formulation. the approach is tested on a case study in chicago city. the results highlight the effectiveness of the approach. they also point out the flexibility of the approach based on the decision makers’ wills. however, this flexibility comes with a price and that price is the high dependency of the results on the parameter values. as a perspective for future 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www.etasr.com anuradha & najumnissa: classification of dementia in eeg with a two-layered feed forward … classification of dementia in eeg with a twolayered feed forward artificial neural network g. anuradha department of ece bsa crescent institute of science and technology chennai, india bhavanandhi@yahoo.com d. najumnissa jamal department of eie bsa crescent institute of science and technology chennai, india najumnissa.d@crescent.education abstract—dementia has become a global public health issue. the current study is focused on diagnosing dementia with electro encephalography (eeg). the detection of the advancement of the disease is carried out by detecting the abnormal behavior in eeg measurements. assessment and evaluation of eeg abnormalities is conducted for all the subjects in order to detect dementia. eeg feature analysis, namely dominant frequency, dominant frequency variability, and frequency prevalence, is done for abnormal and normal subjects and the results are compared. for dementia with lewy bodies, in 85% of the epochs, the dominant frequency is present in the delta range whereas for normal subjects it lies in the alpha range. the dominant frequency variability in 75% of the epochs is above 4hz for dementia with lewy bodies, and in normal subjects at 72% of the epochs, the dominant frequency variability is less than 2hz. it is observed that these features are sufficient to diagnose dementia with lewy bodies. the classification of lewy body dementia is done by using a feed-forward artificial neural network which proved to have a 94.4% classification accuracy. the classification with the proposed feed-forward neural network has better accuracy, sensitivity, and specificity than the already known methods. keywords-lewy body dementia; eeg; dementia; neural network; dominant frequency i. introduction the term dementia refers to a syndrome that causes a decline in cognitive functions, mainly the person’s memory and intelligence, due to the death of brain cells. different types of dementia have their own characteristic features. in alzheimer's disease, the pathology involves the reduction of neurons which help in stimulating cortex and hippocampus regions, deposits in blood vessels, and formation of amyloid plaques [1]. an intermediate stage called mild cognitive impairment was found between the normal cognitive and dementia. subjects in this stage are not demented but exhibit a decline in memory beyond that expected at their age and education [2, 3]. mild cognitive impairment is an earlier stage, which may progress to dementia [4]. psychometric predictors and clinical evaluation in elderly subjects can predict mild cognitive impairment [5]. mild cognitive impairment and dementia can be detected using eeg biomarkers [6-8]. mini mental state examination (mmse), clinical dementia rating (cdr), and global deterioration scale (gds) are the subjective measures used to evaluate the early stages of mild dementia [3, 4, 11]. alzheimer’s disease (ad) is the most common form of dementia [9, 10]. in ad patients, the decrease in consistency of fast rhythms and shift of power spectrum to lower frequencies, are the abnormalities in eeg signals [13]. the second most common dementia is vascular dementia (vad) [14]. vad is caused by the ischemic brain lesions due to cardiovascular pathology resulting in decline of the cognitive functions [1517]. another type of dementia, lewy body dementia (lbd) is characterized by lewy bodies with large old plaques. fronto temporal dementia (ftd) might occur in middle aged people and is characterized by the degeneration of prefrontal and anterior temporal cortex associated with personality changes and changes in social conduct [18]. parkinsonism consists of problems in motor nerves namely, resting tremor, rigidity and freezing [19]. finding a biomarker to detect dementia at an earlier stage is a major challenge. the biomarker should detect the neuropathological processes caused by dementia to help the effective treatment of the disease [10]. eeg can function as such a biomarker to identify those physiological and pathological conditions. eeg in addition to functioning as a diagnosis tool also differentiates the stages of dementia [20]. the reduced cost and non-invasiveness of the eeg electrodes makes it suitable for detecting dementia and its progression [10, 11]. the challenges in an eeg biomarker are the accurate and early detection of the disease [6]. the identification of different stages of dementia and the precise detection is made possible by eeg [21]. slowing of eeg dominant posterior rhythm frequency and reduced alpha and beta activities are observed in visual characteristics of ad. reductions in mean frequency and alpha and beta power are observed in the analysis of eeg signals of ad patients, in earlier stages of dementia [4]. mild dementia is characterized by an increase in theta activity and severe dementia by a decrease in beta activity [22, 23]. resting state eyes-closed eeg recording is used to assess the progression from mild to severe ad. the stage of mild cognitive impairment is characterized by increase in delta power and decrease in alpha and beta power [24]. early stages of lbd show reduction in cognitive functions like attention, problem solving, and visuospatial skills. changes in cognitive corresponding author: g.anuradha engineering, technology & applied science research vol. 11, no. 3, 2021, 7135-7139 7136 www.etasr.com anuradha & najumnissa: classification of dementia in eeg with a two-layered feed forward … function and parkinsonism are the characteristic features that differentiate dlb from ad and other dementias [25]. lbd and ad are distinguished in early stages by quantitative analysis on the eeg signal. the dominant frequency of ad patients were in alpha range, in greater than 60% of the epochs and dominant frequency variability in ad was less than 1.6hz whereas lbd patients had dominant frequency variability greater than 4hz [26-28]. in our present study, classification of lbd and control (normal) subjects is achieved with the help of a feed forward neural network with features extracted in the frequency domain [33]. this paper aims in finding whether these abnormalities are present in the eeg and whether these can help in the detection and classification of dementia to improve diagnostic accuracy. ii. materials and methods the proposed method consists of eeg acquisition, preprocessing, feature extraction, and classification as shown in figure 1. eeg recording was done with subjects awake, relaxed, and with eyes closed. the sampling rate was 173.6hz. two-second long epochs were chosen for analysis [28, 33]. a total of 12 abnormal and 18 normal eeg records were obtained. fast fourier transform (fft), ���� was performed for the eeg time series ���� . spectral amplitude � was evaluated for each epoch, with being the number of epochs. the frequency at which � is maximum, among all epochs is the dominant frequency value � . the mean dominant frequency (mdf) of all epochs was found. dominant frequency range (dfr), the range of maximum and minimum value of � , dominant frequency variability (dfv), the variation of the dominant frequency, i.e. the difference between the maximum and minimum value of � , frequency prevalence (fp) which indicates the existence of a frequency � in alpha, theta, or delta range were evaluated. the above features are extracted from the preprocessed signal which is applied for classification to the feed forward neural network as normal and demented signals. in the proposed method, levenberg algorithm is used to update the weights of the feed forward neural network. fig. 1. flow chart of the proposed method. machine learning algorithms learn from the past experience and provide optimized performance criteria. the most important aspect of a learning algorithm is its accuracy. statistical learning techniques are developed and compared using pattern recognition which is one of the key aspects of artificial intelligence. linear discriminant analysis (lda) and neural networks, support vector machine (svm) [29, 30], linear support vector machine (lsvm), balanced communication-avoiding support vector machine (bcasvm) [32], and levenberga algorithm [33] are some of the available classifiers. in the proposed method, accuracy, i.e. the differentiation of subjects with lbd from normal subjects, sensitivity which determines lbd correctly, and specificity which determines the healthy subjects correctly, were obtained with a twolayered feed forward neural network. simulation of the above study is done using the eeg data obtained from the bonn data base [32]. iii. results and discussion analysis of dominant frequency (df), mdf, dfr, dfv, and fp in both normal and abnormal eegs was conducted. table i shows the features extracted from 12 abnormal eegs. for every subject, the maximum df among all epochs was chosen. it is observed that, the df in almost all subjects, except subject 9, falls in the delta range. mdf is present in the delta range in all the analyzed subjects. the dfrs of subjects 2, 4, and 8 fall completely in the delta range. the dfv of 50% of the subjects is present in the delta and theta range. above 80% of the subjects have fp in the delta range. from the feature analysis of abnormal subjects, it is found that, the mdf of all the epochs is found to be greater than 0.9hz and the dfv is greater than 4hz in 75% of epochs which confirms lbd similar to pattern 4 [27]. table i. features of ldb s.no df (hz) mdf (hz) dfr (hz) dfv (hz) fp (%) 1 1.3 1.0 0-4.4 4.0 d=90 t=10 2 3.3 0.9 0-3.3 3.0 d=100 3 0.6 1.6 0-11.5 12.0 d=90 a=10 4 0.6 1.0 0.3-2.0 2.0 d=100 5 1.3 1.6 0-5-7.0 6.0 d=80 t=20 6 0.3 1.4 0.0-11.8 12.0 d=80 a=20 7 0.3 3.5 0.3-11.1 11.0 d=73 a=27 8 1.0 1.29 0.3-3.0 3.0 d=100 9 10.8 2.9 0.0-11.8 12.0 d=80 a=20 10 0.6 2.2 0.3-11.5 12.0 d=90 a=10 11 0.339 4.0 0.0-11.5 11.5 d=58 a=42 12 0.339 4.2 0.33-12.2 11.86 d=67 a=33 d: delta 1-3.9hz ,t: theta 4-5.5hz, a: alpha 8-12hz table ii shows the features extracted from normal eegs. it is observed that, the df in more than the 80% subjects falls in the alpha range. mdf is present in alpha range 80% of the analyzed subjects. the df range of 83% of the subjects falls in the delta range. the dfv of 80% of the subjects is present in the delta range. above 70% of the subjects have fp in the alpha range. figure 2 shows the comparison of the df for lbd and normal subjects. the df for lbd is present in the 85% of the epochs in delta range, between 0.3hz and 3.3 hz. the df of subject 9 alone falls in the alpha (10.8hz) in lbd, whereas subjects, except 3, 15, and 16, exhibit df in alpha, between 10hz and 11hz. the 85% of the epochs in normal subjects have df in the alpha range. engineering, technology & applied science research vol. 11, no. 3, 2021, 7135-7139 7137 www.etasr.com anuradha & najumnissa: classification of dementia in eeg with a two-layered feed forward … table ii. features of normal subjects s.no df (hz) mdf (hz) dfr(hz) dfv(hz) fp (%) 1 10.5 3.2 0.0-10.5 10.5 d=75 a=25 2 11.0 11.0 11.0-12.0 1.0 a=100 3 14.0 14.0 12.0-14.0 2.0 a=100 4 11.0 11.5 11.0-12.0 1.0 d=25 a=75 5 11.0 11.5 11.0-12.0 1.0 d=100 6 10.8 11.0 10.5-11.0 1.02 a=100 7 11.0 11.29 11.0-12.0 1.0 a=100 8 11.0 11.25 11.0-12.0 1.0 d=75 a=25 9 11.0 11.13 11.0-12.0 1.0 a=100 10 11.0 11.55 11.0-12.0 1.0 a=100 11 11.0 11.61 11.0-12.0 1.0 a=100 12 11.0 11.5 11.0-12.0 1.0 d=8 a=92 13 11 10 9-11 2 d=8 a=92 14 11 11 11-12 1 d=25 a=75 15 15 13 10-16 6 a=100 16 14 14 8-15 7 a=100 17 11 11.5 11-12 1 a=100 18 11 11.5 11-12 1 a=100 d: delta 1-3.9hz ,t: theta 4-5.5hz, a: alpha 8-12hz fig. 2. df of lbd and normal subjects. the calculated mdf for lbd and normal subjects is shown in figure 3. all the normal subjects, except 1, 3, 15, and 16, have mdf in alpha, between 11hz and 12hz, whereas in lbd, the mdf falls in the delta range of 0.9hz and 3.5 hz in subjects 1 to 10 and theta range of 4hz and 4.2hz in subjects 11 and 12 respectively. fig. 3. mdf of lbd and normal subjects. figure 4 shows the comparison of dfv for subjects with lbd and normal subjects. in 75% of the epochs, dfv above 4hz is observed in dementia and in normal subjects 83% of the epochs have dfv less than 2hz. all lbd subjects, except 2, 4, and 8, have dfv above 4hz. all normal subjects, except 1, 15, and 16, have dfv less than 2hz. the calculated fp for lbd and normal subjects is shown in figure 5. more than 80% of the epochs in lbd have fp in the delta range [24], whereas for normal subjects 80% of the epochs are in the alpha range. it is therefore found that eeg abnormalities can function as a marker for the detection of lbd. fig. 4. dfv for lbd and normal subjects. fig. 5. fp for lbd and normal subjects. iv. classification the extracted features df, mdf, and dfv were utilized in a feed forward neural network implemented in matlab. levenberg algorithm was used to update the weights of the neural network. accuracy, sensitivity, and specificity were used to evaluate the classification performance. these parameters are calculated as: accuracy � ����� ����������� (1) sensitivity � �� ��� �� (2) specificity � �� ����� (3) where tp, tn, fp, fn stand for the true positive, true negative, false positive and false negative classifications respectively. the confusion matrix evaluates the overall performance of a classification method. accuracy, sensitivity, and specificity of each feature are obtained from the confusion matrix. figure 6 shows the confusion matrix obtained for classification using the feature dfv. accuracy of 88.9%, sensitivity of 83.3%, and specificity of 100% were achieved. figure 7 shows the confusion matrix obtained for classification using df, with accuracy of 94.4%, sensitivity of 90.9%, and specificity of 100% achieved. figure 8 shows the confusion matrix obtained for mdf. the acquired accuracy, sensitivity, and specificity were 94.4%, 88.9% and 100% respectively. table iii shows the accuracy, sensitivity, and specificity using the classifiers spectral svm, decision tree with fourier coefficients, and svm with spectral peak [30, 35, 36]. the classifier performance is poor in fourier coefficients with decision tree, where the accuracy, sensitivity and specificity are less than 75%, whereas spectral svm shows good classifier performance, with accuracy of 86%, sensitivity of 88% and engineering, technology & applied science research vol. 11, no. 3, 2021, 7135-7139 7138 www.etasr.com anuradha & najumnissa: classification of dementia in eeg with a two-layered feed forward … specificity of 84%. the accuracy, sensitivity, and specificity of the proposed feed forward neural network classifier with features like mdf, dfv and df obtained from the confusion matrix is shown in table iv. fig. 6. confusion matrix for dfv. fig. 7. confusion matrix for df. fig. 8. confusion matrix for mdf. table iii. accuracy, sensitivity, and specificity of other classifiers feature accuracy (%) sensitivity (%) specificity (%) spectral svm 86 88 84 fourier coefficients with decision tree 72.2 72.2 59.4 spectral peak svm 79.9 83.2 76.4 table iv. accuracy, sensitivity, and specificity of the nn classifier feature accuracy (%) sensitivity (%) specificity (%) nn with mdf 94.4 88.9 100 nn with dfv 88.9 83.3 100 nn with df 94.4 90.9 100 the highest percentage of sensitivity of the proposed classifier is 90.9% with the df feature. the specificity obtained for the proposed classifier is 100% for mdf, dfv, and df, while the accuracy is 94.4% in both mdf and df. hence, df produces better results when compared to the other features, mdf and dfv. this type of classification method with a two-layered feed forward nn using dominant frequency feature gives better sensitivity, specificity, and accuracy when compared with other existing methods. v. conclusion in this study, eeg analysis was performed on both abnormal and healthy subjects. dominant frequency analysis was 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[38] m. b. ayed, "balanced communication-avoiding support vector machine when detecting epilepsy based on eeg signals," engineering, technology & applied science research, vol. 10, no. 6, pp. 6462–6468, dec. 2020, https://doi.org/10.48084/etasr.3878. microsoft word 3-594-ed.doc engineering, technology & applied science research vol. 5, no. 5, 2015, 860-863 860 www.etasr.com al-qaisi et al.: evaluation of e-commerce website functionality using a mamdani fuzzy system evaluation of e-commerce website functionality using a mamdani fuzzy system l. al-qaisi a. mesleh a. al-qaisi a. sharadqh b. zahran j. alkasassbeh m. olaimat the world islamic sciences & education university amman, jordan laila.qaisi@ gmail.com computer engineering dpt, al-balqa applied university, amman, jordan wadood@ fet.edu.jo communication technology engineering dpt, al-balqa applied university, amman, jordan aws.alqaisi@ bau.edu.jo computer engineering dpt, al-balqa applied university, amman, jordan dr.ahmed.shara dqah@ bau.edu.jo computer engineering dpt, al-balqa applied university, amman, jordan zahranb@ bau.edu.jo electrical engineering dpt, al-balqa applied university, amman, jordan jawdat1983@ bau.edu.jo communication technology engineering dpt, al-balqa applied university, amman, jordan olaimat@ bau.edu.jo abstract— the majority of leader companies are running their businesses using online e-commerce websites. these e-commerce websites are becoming significant revenue drivers and major retailers. hence, it is critical to evaluate the functionality of these websites which are expected to support growing business needs. the evaluation of the functionality of e-commerce websites is not a straightforward process due to the many constraints and standards that should be considered. fuzzy logic is a powerful technique used in modeling impreciseness and uncertainties. this paper proposes a mamdani fuzzy system that evaluates the functionality of e-commerce websites over different parameters: accuracy, flexibility, client support, and availability of product information. experimental results provide positive relations between accuracy and flexibility on the functionality of ecommerce websites. keywords--commerce websites; mamdani fuzzy system; websites functionality i. introduction the use of internet affects the world of business in various aspects. international trend goes towards using e-media in conducting many business functions, through easy to use websites (especially for multinational companies). nowadays, multinational companies focus on having such portals and websites to serve their customer needs and to simplify procedures of purchasing their products. ecommerce gains attention as it helps in achieving better price, improved quality and customer satisfaction with lower costs. this attention is growing as more facilities are introduced in the field [1]. many researchers have conducted various studies focusing on websites characteristics. these characteristics influence clients’ impression of the companies’ portals. for clients, any company website represents a connection tool between them and the company and affects their behavior, beliefs and intentions. also, companies are much aware of the power of word of mouth (wom) which has a great impact on their reputation especially with the current increased usage of social networking portals [2]. in [3], authors concluded that many commercial websites characteristics such as precise information, loading speeds, interactivities, graphics, colors, accessibility and ease of usage are well studied. however, less focus is paid to the firm’s interactivity with clients via their websites. it’s important for any organization to assess their ecommerce website to improve their services and to achieve their goals as well as getting competitive among their peers [4]. most of working companies across the world has already adopted e-commerce and has created online websites [5]. also, researchers in the field of e-commerce have agreed on the increased use of internet in commercializing products [3]. moreover, the demand of customers of online shopping to get the desired products in an easy and quality guaranteed way has been increased rapidly. it is obvious that the internet and information technology (it) revolution has created a new business environment which differs from the previous ones and has motivated the need to establish an effective measurement for e-commerce websites’ quality. it is also clear that the majority of previous studies on the quality of e-commerce websites and their characteristics have failed to address the direct relation between functionality and quality of e-commerce websites. many researches have adopted the theory of fuzzy sets and expert systems in various applications including e-commerce. many of the fuzzy expert systems that are used in e-commerce applications focused on models that assessed security, trust and privacy aspects of ecommerce websites [6-9]. some researcher also studied the quality of e-commerce websites [10-13]. however, the quality of e-commerce has not been studied separately. this paper proposes a mamdani type of fuzzy system to assess eengineering, technology & applied science research vol. 5, no. 5, 2015, 860-863 861 www.etasr.com al-qaisi et al.: evaluation of e-commerce website functionality using a mamdani fuzzy system commerce website functionalities and their role in ecommerce website quality. in [14], the authors constructed a model to evaluate the quality of e-commerce websites depending on several aspects such as the usability, conceptual reliability and representation reliability. in their study, the degree of functionality is logically found to be an effective factor on quality of any website. hence, it affects an e-commerce website’s quality as well as it plays vital role in its performance. in [9], the authors described a fuzzy system which allows users to encode knowledge needed for specialists’ thinking to solve complex problems such as assessing the functionality of an e-commerce website. furthermore, in [12], the authors found that assessment process is neither familiar with normal peoples’ logic nor traditional boolean logic and they introduced a fuzzy expert system. in [15], the author discussed the characteristics of online shopping websites from 2006 to 2011. nevertheless, he did not investigate the functionality factor. this paper fills the gap of assessing e-commerce website functionalities and their role in e-commerce websites’ quality using mamdani fuzzy system. the theory of fuzzy logic is based on the concept of relative graded membership, as inspired by the processes of human perception and cognition [16]. fuzzy logic usually deals with information arising from computational models, that is, uncertain, imprecise, vague, partially true, or without sharp boundaries. fuzzy logic is considered extremely useful for a wide range of applications such as facial pattern recognition, air conditioners, washing machines, vacuum cleaners, antiskid braking systems, transmission systems, control of subway systems and unmanned helicopters, knowledge-based systems for multiobjective optimization of power systems, weather forecasting systems, models for new product pricing or project risk assessment, medical diagnosis and treatment plans, consumer electronics, image processing and stock trading [16]. ii. the proposed mamdani fuzzy system figure 1 illustrates the general steps of implementing the proposed mamdani fuzzy system model to assess e-commerce websites’ functionalities and their role in e-commerce websites’ quality [17-19]: • the problem of assessing e-commerce website functionalities is described. • four linguistic variables (fuzzy logic operating parameters) are chosen for input parameters namely: accuracy, flexibility, client support and availability of product information. one linguistic variable is chosen for output namely functionality. • a fuzzy set and membership functions for each linguistic variable are set based on initial knowledge and modified several times during tuning stages. • the linguistic ranges and values for the linguistic variables are specified (see table 1). moreover, the membership functions and the associated values for each parameter are initialized in fig.2-4. • the rules for the fuzzy logic system are constructed that use input membership values as weighting factors to determine their influence on the fuzzy output set. some of these rules are: rule 1: (accuracy==low) | (flexibility==low) => (functionality = weak) rule 2: (accuracy==moderate) | (flexibility== moderate) => (functionality = moderate) rule 3: (accuracy==high) | (flexibility==strong) => (functionality = strong) rule 4: (client support==low) & (availability of product information==low) => (functionality = weak) rule 5: (client support==moderate) & (availability of product information== moderate) => (functionality =moderate) rule 6: (client support==high) & (availability of product information==high) => (functionality = strong) • the parameters of the fuzzy system (such as the number of membership functions and their shapes, linguistic variables ranges and values) and fuzzy rules undergo through a tuning stage that modifies them several times before getting stabilized. • the fuzzy model is coded and ready to be tested. a mamdani fuzzy method is used to infer the proposed model. • the inference process begins with the fuzzification stage which coverts crisp inputs to fuzzy values. • the fuzzy values are projected into the fuzzy rules. • the outputs of each rule are combined using min-max method. • the aggregated fuzzy output is defuzzified using fuzzy centroid method. • finally, the results of functionality of the e-commerce website are evaluated. fig. 1. steps of designing the mandani fuzzy system engineering, technology & applied science research vol. 5, no. 5, 2015, 860-863 862 www.etasr.com al-qaisi et al.: evaluation of e-commerce website functionality using a mamdani fuzzy system table i. ranges and values for the linguistic variables. linguistic values notation normalized numerical ranges low l 0 – 0.4 moderate m 0.3 – 0.7 accuracy high h 0.65-1 low l 0 – 0.4 moderate m 0.3 – 0.7 flexibility strong s 0.65-1 low l 0 – 0.4 moderate m 0.3 – 0.7 client support high h 0.65-1 low l 0 – 0.4 moderate m 0.3 – 0.7 availability of products high h 0.65-1 weak w 0 – 0.4 moderate m 0.3 – 0.7 functionality strong s 0.5 – 1 iii. results the proposed mamdani fuzzy system was coded using matlab which offers a fuzzy logic toolbox. figure 2 shows the effect of accuracy on the functionality of e-commerce websites. in figure 2, it is clear that functionality is lowest when accuracy is minimum. however, functionality is most excellent when accuracy is maximum. it is clear that functionality is stable when the accuracy is between 5 and 10 (averaged values). moreover, figure 3 shows that the functionality of e-commerce websites increases as flexibility is increasing. figure 4a shows the effect of accuracy combined with client support on functionality of e-commerce websites. figure 4b shows the effect of accuracy combined with product information. from figure 4, it can be concluded that client support and availability of product information have low effect on the functionality of e-commerce website. figure 5a shows the effect of flexibility combined with client support. figure 5b shows the effect of flexibility combined with the availability of product information on the functionality of e-commerce website. from figure 5, it can be concluded that the flexibility combined with client support/availability of product information has low effect on the functionality of e-commerce websites. finally, figure 6 plots the surface diagram of our proposed mamdani fuzzy system and describes the flexibility effect on the accuracy combined with the flexibility effect on the functionality of e-commerce websites. it can be concluded from figure 9 that the functionality is lowest at low accuracy and flexibility levels. on the other hand, the functionality is highest at the maximum levels of accuracy. it can be concluded that the surface graph in figure 6 indicates a positive effect between the degree of accuracy, the flexibility and the functionality of e-commerce websites. furthermore, other functionality values vary when changing the accuracy and flexibility. fig. 2. accuracy effect on e-commerce websites functionality fig. 3. flexibility effect on e-commerce websites functionality (a) (b) fig. 4. effect of accuracy combined with (a) client support and (b) availability of product information on functionality of e-commerce websites. it should be noted that the other dimensions in (a) and (b) are the client support and the availability of product support respectively engineering, technology & applied science research vol. 5, no. 5, 2015, 860-863 863 www.etasr.com al-qaisi et al.: evaluation of e-commerce website functionality using a mamdani fuzzy system (a) (b) fig. 5. effect of flexibility combined with client support and availability of product information on functionality of e-commerce websites. note that the other dimensions in (a) and (b) are the client support and the availability of product support respectively fig. 6. plot of surface that shows the effect of accuracy combined with flexibility on functionality of e-commerce websites iv. conclusion many researchers have authored various studies focusing on websites characteristics. these characteristics influence clients’ impression of the companies’ portals. as increased functionality has a positive effect on the quality of an ecommerce website, we implemented and tested a mamdani fuzzy system that evaluates the effect of accuracy, flexibility, product availability and client support on the functionality of e-commerce websites. it was concluded that accuracy and flexibility are the most effective variables regarding the functionality of an e-commerce website. the availability of product information and client support however had fixed effect on functionality. references [1] s. mariotti, f. sgobbi, “alternative paths for the growth of ecommerce”, futures, vol. 33, no. 2, pp. 109-125, 2001 [2] c. chan, p. swatman, “management and business issues for b2b ecommerce implementation”, 35th hawaii international conference on system sciences, pp. 3083-3093, big island, hawaii, january 7-10, 2002 [3] b. hernández, j. jiménez, m. josé martín, “key website factors in ebusiness strategy”, international journal of information management, vol. 29, no. 5, pp. 362-371, 2009 [4] l. mich, m. franch, l. gaio, “evaluating and designing web site quality”, ieee multimedia, vol. 10, no. 1, pp. 34-43, 2003 [5] d. sui, d. rejeski, “environmental impacts of the emerging digital economy: the e-for-environment e-commerce?”, environmental management, vol. 29, no. 2, pp. 155-163, 2002 [6] n. griffiths, k. chao, m. younas, “fuzzy trust for peer-to-peer systems”, 26th ieee international conference on distributed computing systems workshops, lisboa, portugal, july 04-07, 2006 [7] x. xiu-yan, “a fuzzy cluster model for evaluating ecommerce trust”, 4th international conference on management of e-commerce and e-government, pp. 60-64, chengdu,  china, october 23-24, 2010 [8] o. signore, “a comprehensive model for web sites quality”, 7th ieee international symposium on web site evolution, pp. 30-36, budapest, hungary, september 26, 2005 [9] f. akhter, d. hobbs, z. maamar, “a fuzzy logic-based system for assessing the level of business-to-consumer (b2c) trust in electronic commerce”, expert systems with applications, vol. 28, no. 4, pp. 623628, 2005 [10] j. zhang, x. guo, “trust evaluation model based on fuzzy logic for c2c e-commerce”, 1st international symposium on information engineering and electronic commerce, pp. 403-407, ternopil, ukraine, may 16-17, 2009 [11] m. nilashi, k. bagherifard, o. ibrahim, n. janahmdi, m. barisami, “an application expert system for evaluating effective factors on trust in b2c websites”, engineering, vol. 3, no. 11, pp. 1063-1071, 2011 [12] h. liu., s. zhang, s. zhang, “fuzzy expert system based intelligent website assessment system”, ieee 10th international conference on computer and information technology (cit 2010), pp. 432-437, bradford, united kingdom, june 29-july 1, 2010 [13] f. kong, h. liu, “applying fuzzy analytic hierarchy process to evaluate success factors of e-commerce” , international journal of information and systems sciences, vol. 1, no. 3-4, pp. 406-412, 2005 [14] a. albuquerque, a. belchior, “e-commerce website quality evaluation”, 28th euromicro conference, pp. 294–300, dortmund, germany, september 4-6, 2002 [15] s. cebi, “a quality evaluation model for the design quality of online shopping websites”, electronic commerce research and applications, vol. 12, no. 2, pp. 124-135, 2013 [16] h. singh, m. gupta, t. meitzler, z. hou, k. garg, a. solo, l. zadeh, “real-life applications of fuzzy logic”, advances in fuzzy systems, vol. 2013, article id 581879, 2013 [17] g. klir, b. yuan, fuzzy sets and fuzzy logic: theory and applications, prentice hall, 1995 [18] l. zadeh, “fuzzy sets”, information and control, vol. 8, no. 3, pp. 338353, 1965 [19] l. zadeh, “is there a need for fuzzy logic?”, information sciences, vol. 3, no. 3, pp. 2751-2779, 2008 microsoft word etasr_v11_n3_pp7158-7171 engineering, technology & applied science research vol. 11, no. 3, 2021, 7158-7171 7158 www.etasr.com alatawi et al.: a new model for enhancing student portal usage in saudi arabia universities a new model for enhancing student portal usage in saudi arabia universities salem suliman t. alatawi school of computing universiti teknologi malaysia johor, malaysia salem.net1@hotmail.com suraya miskon azman hashim international business school, universiti teknologi malaysia johor, malaysia suraya@utm.my norris syed abdullah azman hashim international business school, universiti teknologi malaysia johor, malaysia norris@utm.my fahad ghabban college of computer science and engineering taibah university medina, saudi arabia fghaban@taibahu.edu.sa faisal saeed college of computer science and engineering taibah university medina, saudi arabia fsaeed@taibahu.edu.sa ibrahim alfadli college of computer science and engineering taibah university medina, saudi arabia ialfadli@taibahu.edu.sa omair ameerbakhsh college of computer science and engineering taibah university medina, saudi arabia oameerbakhsh@taibahu.edu.sa abstract-portals are gateways that provide users with the information they need from different sources and display it on a single page. it is important to see that universities utilize the resources and services provided by their student portals. with the rapid development of information and communication technology (ict), the ministry of education in saudi arabia aims to develop and improve student portals by providing highquality teaching services through the university portal systems. this paper discusses the importance of student portal usage in saudi arabian universities and investigates the factors that influence the utilization of student portals as perceived by the students of the saudi universities. based on these factors, a model is proposed which identifies students’ expectations about the saudi university portals. a quantitative methodology was employed to develop the model. the results revealed that 8 out of 10 factors of the model are significant and positively affect student portal usage. the enhancement of student portals based on the identified significant factors will assist the universities to increase their utilization and their provided services. keywords-university portal; higher education; e-services; elearning; quality of service; utilization of student portals; ict i. introduction high-quality web portals are critical to commercial and non-commercial organizations [1, 2]. a portal is defined as a general knowledge management system that helps companies to share, reuse, create or exchange information [3]. a university portal provides its users a specialized view that matches their needs and meets their software and hardware requirements. to build a university portal that is updated regularly with the latest information and can accommodate additional services is a significant challenge [4]. the main concern is to build a portal that controls, coordinates, interacts and takes feedbacks from customers (visitors, staff and students). the ministry of higher education in saudi arabia works close with saudi universities to improve the quality of higher education in order to ensure that university graduates have skills and learning outcomes in line with the international standards and job market requirements. despite the good information and communication technology (ict) infrastructure in saudi universities, the usage of university student portals remains low [5]. according to [6], a big challenge that saudi universities face is the lack of awareness regarding the use of ict among students, faculty members, and administrative staff. many universities in saudi arabia spend generously on ict, but this expenditure does not lead to significant improvements in the usage of ict services. many universities have adequate ict infrastructure, but they do not use it effectively [7]. higher education institutions, particularly universities in developed countries, are heavily involved in portals which have become an essential tool for service delivery and communication between faculty members, administrative staff, and, most important, students [8]. several studies have been conducted in saudi arabia on the importance and usage of university student portals. authors in [9] showed that the official university portal for king abdulaziz university is well-below the expected standard. the study corresponding author: salem suliman t. alatawi engineering, technology & applied science research vol. 11, no. 3, 2021, 7158-7171 7159 www.etasr.com alatawi et al.: a new model for enhancing student portal usage in saudi arabia universities claims that king abdul-aziz university’s portal does not match the standards of design, content, user support, and navigation and the undergraduate students are dissatisfied with it [10]. the aim of [10] was to explore usability problems within saudi university websites in comparison with the uk university websites by applying the sus methods and thinking aloud method to measure the usability of the websites. the results illustrated that saudi students faced various usability problems related with satisfaction, integration, and confidence. the author in [2] evaluated the edugate, an online academic portal of king saud university and problems were found concerning its design and content. these problems reduced the usage of the portal and dissatisfied academic staff. the author in [11] revealed that saudi university portals need to focus on their content to meet the needs of staff and students and to increase their level of usage. furthermore, authors in [12] revealed that the score for using king khalid university’s website is 53.5 while the average industry score of using a website is 65. this indicates that there are problems impeding the effectiveness and efficiency of the university portal resulting in minimal usage. given the above background, this study investigates the factors that affect students’ usage of their university portal by proposing a model that meets student expectations and increases their satisfaction. this model will help the universities to communicate more efficiently with their students. ii. related work web portals are general knowledge management systems that help institutions to share, reuse, create, or exchange information or knowledge [3]. portals have been employed increasingly to manage the communication between different stakeholders in an organization or initiative. educational web portals have become more responsive and turned out to be very dynamically based on the demands and the requirements of the varying academic community. the communication between teachers and students is often conducted through these websites and even more these days due to the covid 19 pandemic. these portals actually integrate the application, content, and information together in order to help the end users. university student portals provide customers with a specialized view that matches their needs and meets their software and hardware requirements. the understanding of the users’ needs is a key element in the student portal usage. it mainly includes four important things, namely the accessibility standards, page layout, graphic design, and, most important, content design [13]. therefore, the main concern of the university is to build a portal that is able to control, coordinate, and receive feedback from the users (visitors, staff, and students). such input contributes to developing a portal that will meet the expectations of end-users and the industry standards [2, 13]. king saud university and king abdul-aziz university are among the top five universities of saudi arabia [14, 15]. authors in [14] indicated that information technology infrastructure is a key success factor that increases students’ confidence in using saudi university portals. as such, the author in [15] recommended updating the information of the portals, e-services, and redesigning in order to increase their use. he examined the attitudes of faculty members towards the use of virtual learning portals in teaching language programs at major saudi universities. authors in [16] evaluated and compared the awareness and the level of the use of portals among the students of the al-jouf university. the study concluded that the undergraduate students of the university lack the necessary information skills needed to meet their academic and research requirements in order to continue to use the portal. authors in [17] examined different factors that affect the use of the university portals and determined the level of the use of e-learning portals in saudi arabia while they compared the results with the results from studies conducted in other countries. it was revealed that the technical infrastructure of the portal, instructor knowledge of the use of portal technologies, and student knowledge of using computer systems are important to the success and increase of the usage of the portal. the author in [18] conducted a comprehensive literature study to identify the current state of using the health information systems’ portals in saudi arabia. the findings revealed that factors such as: design, privacy, and efficiency affect portal usage. author in [19] examined the current situation of king abdulaziz university portal content and proposed a content strategy, which can help the university to solve portal content issues and encourage users to use it. also, this study recommended examining the students' perceptions regarding the use of the portal. the author in [20] examined the level of the use of academic portals by the staff of alqassim university in saudi arabia. the results showed that the academic staff members lack awareness about the use of the available services in the portal. this study revealed that there is a need to increase the level of usage by training the academic members on how to use the services of the portal. authors in [21] examined the level of use of university portals by identifying the factors that influence lecturers to use it. the result revealed that there are some issues such as: navigation, response time, minimum download time, and portal accessibility. this study recommended university decision makers and web designers to take into consideration these issues in order to increase the level of portal’s usage. the author in [22] examined students' attitudes towards using electronic information resources of the library portal at princess nora university in saudi arabia. the results revealed that the management should attempt to decrease the gap between student attitudes and their use in order to increase the portal usage. in addition, authors in [10] examined the level of usage of the portal of the king abdulaziz university among undergraduate students. it was found that students were dissatisfied with the portal. the study recommended the improvement of the level of the portal usage by solving the problems the students face. in spite of the advancements being made in the domain of mobile portals in saudi arabia, there are aspects that present obstacles in the progress. for instance, authors in [23] ascertained several limitations related to mobile learning in saudi arabia, limitations related to processing performance, memory size, battery life, user interface, and the existence of various platforms. other concerns encompass the availability of dependable and inexpensive web access from home, because the it security in saudi universities makes it difficult for students who are away from campus to access the university engineering, technology & applied science research vol. 11, no. 3, 2021, 7158-7171 7160 www.etasr.com alatawi et al.: a new model for enhancing student portal usage in saudi arabia universities systems. the author in [24] highlighted the substandard wireless network and technical concerns. utilizing mobile phones for education would render likely issues regarding the hardware specifications of the devices involved: small screen sizes, inadequate input options, small battery life, inadequate memory capacity, and inadequate video quality [26, 27]. based on these limitations, this study focuses on student web portals in saudi arabia universities. social cognitive theory (sct), which is regarded as a very powerful theory related to human behavior, was utilized. the sct was applied for investigating computer utilization in [28, 29]. the nature of the proposed model along with its theory allowed its extension to the acceptance and usage of web portals. the sct was regarded as the base model because: first, the constructs that were used in the model represented the variables that were analyzed as the factors responsible for improving the web portals. second, since the sct was a relatively less-represented model in the adoption of the web portals, it was important to investigate its performance and application in the existing context. finally, this model included all the appropriate and vital constructs that helped in understanding the behavior of an individual. according to [25], user behavior is an important key to enhance and continue using a website. in addition, user behavior and perceived enjoyment on websites are important factors regarding the increase of its usage [26]. also, the consideration of user behavior provides useful guidelines for designers to deliver the optimum website design. according to [32], student behavior is the most important key factor to improve the use of an educational portal. therefore, understanding students’ expectations has significant influence on their performance and increases user satisfaction [33, 34]. based on the previous studies, it was found that there are issues regarding the usage of portals of saudi arabia universities. these issues decrease the student portals usage and make the students dissatisfied with them. therefore, this study will investigate the factors that prevent the undergraduate students from using the university student portals. iii. materials and methods a. population and study context this study uses the quantitative approach to achieve its objectives by investigating the importance of student portals and the most important factors that affect students to use the portals of saudi universities. the collected data were from 399 participants and were gathered from students of four different universities, namely the university of tabuk, taibah university, taif university, and king faisal university, which are located in different states of saudi arabia. also, the study used the pls algorithm in smartpls3 to analyze the collected data. b. factor selection method five databases were used, namely sciencedirect, taylor & francis, springer, emerald, and google scholar to determine the importance of student portals and the most important factors which affect the students’ usage. moreover, this study attempts to investigate the importance of student portals among students based on their attitude in order to increase their performance. there are works indicating the importance of studying personal and organizational factors to enhance users’ performance. the factors that enhance academic staff in nigeria to use itc in the library were examined in [59]. the findings of the study revealed that organization factors are the most important. organization factors include the lack of ict strategy and the lack of commitment by the institutional management. according to [60], personal and behavioral factors are key success factors in improving the performance of employees. it is essential to examine the impact of personal, behavioral, and organizational factors on the academic staff in universities in order to improve the performance of research productivity [61]. personal factors, such as the level of skills for using ict, are important. therefore, this study identified the factors that affect students’ use of the university portals by using microsoft excel to extract and filter the factors from previous studies. this approach consisted of four steps namely, search for suitable factors, filtering factors, naming three classification categories, and classifying the factors into these categories. fig. 1. factor derivation process. firstly, 54 papers were reviewed. twenty eight papers were found that were related to this study domain. from these included papers, 151 factors were identified. in the second step, the researchers filtered all identified factors to determine the included and excluded factors. in this step, the researchers identified 127 included sub-factors and excluded 24 factors. at the third step, the researchers extracted and classified the identified 127 subfactors and factors into 3 categories, namely environmental, personal, and behavioral. then, the researchers divided each category’s sub-factors into the main factor. in the fourth step, the researchers identified the main factors related to each category. regarding the environmental category, the researchers found that there are 8 main factors related with it. these factors are: information quality (iq), availability of content (aoc), interaction (i), navigation (n), design (d), portal service quality (psq), user satisfaction (us), and portal user support (pus). the personal category consists of 1 main factor namely efficiency (e), and the behavioral category also consists of 1 main factor namely user intention (ui), as shown in figure 1. engineering, technology & applied science research vol. 11, no. 3, 2021, 7158-7171 7161 www.etasr.com alatawi et al.: a new model for enhancing student portal usage in saudi arabia universities 1) environmental factors environmental factors refer to the degree an individual trusts the technical and organizational infrastructure that should exist and the level of support for using the system [27] or the availability of technological and external resources of the organization such as money, time, and effort needed to ease the performance of a specific behavior. a) user satisfaction in information technology, user satisfaction of web portals has been studied extensively. authors in [28, 36] studied the direct influence of competing resources, user satisfaction, and the voluntariness on the portal usage. it has been used as a surrogate measure for the effectiveness of information systems [29]. user satisfaction is defined as the degree of successful interaction between users and the information system [30]. authors in [31] described satisfaction as the degree of the comparison of the expectations with the perceived performance. the first hypothesis regarding user satisfaction is: • ha1: us positively affects students’ use of the student portal. b) information quality information quality is the quality of the information system output that reflects user needs such as accuracy, content, format and timing [33], which is critical to user acceptance [33]. iq can predict consumer satisfaction [34]. accordingly, providing a high-quality student portal will help provide innovative services to students. the assumption made regarding information quality is: • ha2: iq positively affects students' use of the student portal. c) interaction according to [35], interaction refers to the ease by which users can interact with the input and output of the system and their ability to learn through it. human-computer interaction is vital to improving user performance [36]. better humancomputer interaction provides good learning systems to create portals that are easy to use and increases user satisfaction [35]. as such, interaction helps improving student portal usage. • ha3: interaction positively affects students’ use of the student portal. d) availability of content aoc can affect students’ usage of the university portal [37]. educational and non-educational services provided in the portal, such as online library services, email services, lecturer evaluation, and registration services are the key areas. the student portal should facilitate the accessibility to all services and be flexible, quick, and allow users to perform their tasks efficiently [38]. the students will be more satisfied when they get more available content. • ha4: aoc positively affects students’ use of the student portal. e) portal service quality authors in [39] defined psq as the support from the information technology department concerning the user system. psq is also defined as the level of customers’ expectations with the degree of the services delivered via the user information system [40]. according to [41], psq can be determined within the context of e-services as a portal that is responsive, available, accessible, and flexible. therefore, psq is a key determinant of use and user satisfaction about the eservices provided in a portal [42]. • ha5: psq positively affects students’ use of the student portal. f) design portal design is considered an important factor that determines the usage of any online portal [43]. portals through simple user interface design provide services and information that users need [44]. so, a student portal should include design features that help students enjoy their visit, which will lead to increased activity [45, 46]. • ha6: design positively affects students’ use of the student portal. g) navigation navigation is a significant factor in using web portals [47]. users should be able to move through portal links without getting lost. the ease of navigation is a critical component of portal usage [48]. therefore, the definition of navigation refers to the ease of finding what the user wants in the portal [49]. the navigation hyperlinks should be available and must work properly [50]. • ha7: navigation positively affects students’ use of the student portal. h) user support us is the ability of the it department to provide users with assistance when needed [51]. moreover, because an academic portal is usually complex and needs qualified staff, it is necessary to have online us tools such as online chatting services provided via an instant messenger to help users resolve problems should they arise [28]. • ha8: us positively affects students’ use of the student portal. figure 2 presents the environmental factors which affect the students’ use of a portal. 2) personal factors this study suggests that the personal factors have a significant impact on the students’ use of the portal. moreover, personal factor efficiency refers to the judgements of people on their capabilities to organize and implement the required courses of action to achieve the required action [52]. a) efficiency a student portal is a good learning environment that helps students increase their abilities to learn [38]. efficiency is a kind of self-evaluation that can assist the understanding of human behavior and its performance in specified tasks [53]. even though student portals offer good information, their engineering, technology & applied science research vol. 11, no. 3, 2021, 7158-7171 7162 www.etasr.com alatawi et al.: a new model for enhancing student portal usage in saudi arabia universities efficiency will decrease if the students’ ability does not meet the expectations [54]. the students’ ability to use the portal is vital for them to achieve their needs, as shown in figure 3. • hb1: efficiency positively affects students with using the students’ portal. 3) behavioral factors authors in [55] defined ui as the degree by which a person can formulate clear plans to perform a determined future behaviour (figure 4). a) user intention ui is defined by the individual’s behavioral intention and, in turn, the behavioral intentions are a function of an individual’s attitude to the behavior. this is suggested by the theory of reasoned action (tra). the attitude towards a type of behavior is defined by a person’s feelings toward that action and can be negative or positive [56]. authors in [57] stated that behavioral intention is an important independent variable that predicts the actual use. similarly, authors in [58] stated that behavioral intention is likely to be linked with the actual usage. • hc1: ui positively affects user with using the students’ portal. fig. 2. environmental factors. fig. 3. personal factors. fig. 4. behavioral factors. c. survey instruments in this study, a questionnaire-based survey method was adopted and used to collect study data and test the hypotheses. the method includes data collection, data analysis, and report writing. authors in [62] identified the questionnaire as recording the respondents’ opinions on specific topic as a preformulated set of questions. using a questionnaire method is efficient, less expensive, and less time-consuming compared to other methods such as interviews and observation. the goal of the developed data collection survey instruments was to measure the validity and reliability of each factor in the model. according to [63], the developing of data collection survey instruments includes three steps: defining the constructs and content domain, generating and judging measurement items, and constructing studies to develop and refine the scale. the first step in data collection is to define each construct definition in the model. the importance in a theory to identify the construct definition and its domain was also highlighted, and conducting a comprehensive literature review to determine them was recommended. therefore, the authors of this study did a thorough literature review and defined each construct in the model based on the content domain of the study. the second step of generating and judging measurement items follows. in addition, using the existing literature is considered a good scientific method to determine the items of the study [63]. therefore, the authors of the current paper identified the items from previous studies that are related to this domain. d. face and content validity assessment in this step, the researchers measured the face and content validity of the measurement items [64]. according to [65], via referring to the literature or an expert, content and face validity can be achieved. a content and face validity form to test the validity of the selected measurement items was developed based on the validity form in [66]. the validity form consists of the research title, a short description of the research, the goal of this form, construct definitions, and items choice type. the items include three types of choice, perfect match (maintain items as it is), moderate match (maintain item but some refining is needed), and poor match (remove item) as shown in appendix c. the researchers distributed the validation form to 9 experts as shown in table i. the researchers invited experts from different disciplines to examine whether the items of each construct represent the construct’s definition. some items were changed and deleted based on the experts’ comments and feedback. table i. experts' profiles university department/school area of expertise universiti teknologi malaysia school of computing 1 expert in information systems, ecommerce, m-commerce. universiti teknologi malaysia azman hashim international business school 1 expert in information systems, it project management, information system planning. taibah university community college 2 experts in information systems and computer science. taibah university faculty of computer science and information systems 5 experts in information system and computer science, educational technology, e-learning. e. data analysis tools to analyze the data, partial least square (pls) technique of structural equation modeling (sem) was used. by applying pls-sem, we were able to examine the measurement and the structural process of the proposed model. pls-sem is considered as a data analysis tool that validates predictive models [73]. smartpls software tool is appropriate for small sizes of data [73]. in this study, a two-type assessment to engineering, technology & applied science research vol. 11, no. 3, 2021, 7158-7171 7163 www.etasr.com alatawi et al.: a new model for enhancing student portal usage in saudi arabia universities analyze the data has been applied by using smartpls v.3. the first assessment is the measurement model, which is accomplished by the assessment of indicator reliability, internal consistency, convergent validity, and discriminate validity. the second assessment is the structural model, which is used to assess path analysis hypotheses testing by examining the size and significance of the path coefficient and coefficient determination [73]. iv. results and discussion this study examines the importance of student portal usage in saudi universities by examining the most important factors affecting students’ use of these portals. ten factors were identified, 8 of which with a positive impact on students’ usage of the student portal while the other 2 factors had no effect. these factors were divided into 3 main categories, namely environmental, personal, and behavioral. these 3 categories have three primary hypotheses. furthermore, each primary hypothesis includes a sub-hypothesis depending on how many factors belong to each category in order to investigate the relationship between the constructs. a. demographic background as mentioned above, the study was conducted in 4 universities, in different states of saudi arabia. the total number of participants was 399. the distribution of the participants’ gender indicates that the highest percentage of participants were female (n=295, 73%), while males were n=104, 26.1%. regarding the participants’ age distribution, 299 participants (75%) were aged between 18 and 24 years, 50 participants (12.5%) were in the range of 25 and 29 years, and the same number and percentage were more than 30 years old (50 participants, 12.5%). the distribution of participants in the selected universities is: university of tabuk n=77, 19.3%, taibah university n=131, 32.8%, taif university n=91, 22.8%, and king faisal university n=100, 25.1%. as for the participants’ experience in using computer and internet, 51 participants (13%) had less than 1 year of experience, 57 participants 14.2% had 1 to 3 years, 67 participants 16.7% had 3 to 5 years, 103 participants 25.8% had 5 to 10 years, and 121 participants 30.3% had more than 10 years of experience. two hundred and thirty (27.6%) participants had good computer skills, 154 participants had excellent computer skills (38.6%), and 15 had low computer skills (3.8%). most (218) participants had excellent internet skills (54.6%), 171 had good internet skills (42.9%), and 10 had low internet skills (2.5%). b. data analysis this study used the pls algorithm in smartpls3 to identify the reliability and validity of the study items. measurement and structural models were used to measure the study model and hypotheses. the measurement model examines the constructs and their items. it also determines the degree to which the indicators measure the construct. the structural model evaluated the reliability and validity of the measurement model, determined the measurement of each item and concluded that all are reflective items. authors in [67] summarize the standard criteria tests used to evaluate the measurement model. cronbach’s alpha and composite reliability (cr) of 0.60 or greater are accepted. the average variance extracted (ave) is another criterion for the assessment of the measurement model, and its accepted value is 0.5 or greater. as shown in table ii, the criteria of the measurement model of all construct items meet the standard criteria. figure 5 presents the study measurement model. table ii. the criteria of the measurement model types of analysis test name standard criteria reliability of internal consistency cronbach’s alpha ≥ 0.6 acceptable composite reliability ≥ 0.6 acceptable convergent validity factor loading ≥0.7 acceptable ave ≥ 0.5 acceptable discriminant validity cross loading the outer loading of each construct should be more than the cross loading of the next constructs 1) reliability of internal consistency the reliability of internal consistency of the constructs was the first indicator that was evaluated. moreover, composite reliability test and cronbach’s alpha test were used. cronbach’s alpha is a convenient test that uses inter-correlations to estimate the reliability indicator variables. the second test composites reliability which is considered another measure for the reliability of internal consistency that takes into consideration the different outer loading of indicator variables. cronbach’s alpha and composite reliability should be more than or equal to 0.60 for each construct [73]. as shown in table iii, the result of both tests indicated the reliability of internal consistency. table iii. reliability of internal consistency 2) convergent validity according to [67], the convergent validity indicates the degree of which alternative procedures for the same construct are correlated positively. in this regard, there are two tests: the ave and outer loadings of indicators that should be taken into account in this stage to evaluate the convergent validity of the constructs. outer loading value should be 0.7 and above [67]. the ave value for each construct should be 0.5 and above [67-69] as shown in table iv. 3) discriminant validity discriminant validity is defined the as the degree of which a specific construct is different from others [73]. cross loadings is the first measure to evaluate the discriminant validity indicators. the outer loadings indicators should be greater than construct name constuct code cronbach's alpha composite reliability availability of content aoc 0.952 0.959 design d 0.954 0.961 efficiency e 0.929 0.945 interaction i 0.922 0.939 information quality iq 0.892 0.921 navigation n 0.916 0.947 portal service quality psq 0.953 0.962 portal user support pus 0.967 0.972 student portal usage spu 0.942 0.954 user intention ui 0.933 0.946 user satisfaction us 0.964 0.97 engineering, technology & applied science research vol. 11, no. 3, 2021, 7158-7171 7164 www.etasr.com alatawi et al.: a new model for enhancing student portal usage in saudi arabia universities any of its correlations to other constructs (see appendix a). fornell-larcker is the second measure to evaluate discriminant validity. it compares the square root of the ave values with the construct correlations. fornell-larcker criterion determines whether the ave is bigger than the squared construct correlation with the other constructs [67]. the fornell-larcker results satisfy the criterion (appendix b). table iv. convergent validity tests independent variable items loading ave iq iq1 0.804 0.699 iq2 0.847 iq3 0.9 iq4 0.842 iq5 0.783 aoc aoc2 0.811 0.724 aoc3 0.775 aoc4 0.879 aoc5 0.864 aoc6 0.836 aoc7 0.852 aoc8 0.883 aoc9 0.862 aoc11 0.888 i i2 0.785 0.721 i3 0.842 i5 0.897 i6 0.86 i7 0.842 i8 0.864 n n1 0.916 0.856 n3 0.94 n4 0.92 d d2 0.805 0.733 d3 0.871 d4 0.862 d8 0.871 d9 0.842 d10 0.859 d11 0.882 d12 0.846 d14 0.867 e e1 0.764 0.741 e2 0.867 e3 0.888 e4 0.868 e5 0.909 e6 0.861 ui ui1 0.788 0.715 ui2 0.846 ui3 0.837 ui4 0.889 ui5 0.869 ui6 0.852 ui7 0.833 psq psq2 0.878 0.783 psq3 0.758 psq4 0.906 psq5 0.883 psq6 0.915 psq7 0.928 psq8 0.918 pus pus1 0.843 0.815 pus2 0.889 pus3 0.919 pus4 0.915 pus5 0.922 pus6 0.905 pus7 0.91 pus8 0.918 us us1 0.872 0.822 us2 0.923 us3 0.935 us4 0.904 us5 0.926 us6 0.895 us7 0.891 4) goodness of fit (gof) gof is a global fit measure [70]. it is the geometric mean of both the ave and the average of r 2 of the endogenous variables [71]. the calculation formula of gof is: 2 _ _____ gof r ave= × (1) the criteria to determine whether gof values are no fit, small, medium, or large to be considered as global valid pls model [72] are shown in table v. table v. goodness of fit ≤ 0.1 no fit 0.1 to 0.25 small 0.25 to 0.36 medium ≥ 0.36 large the value of the gof of this study is 0.771, which means the gof model of this study is large enough to be considered of sufficient global pls model validity. the next stage examines the hypotheses of this study using the structural model. this stage tests the predictive capability of the model and the relationship between the constructs. the path coefficients of the structural model are determined after the collinearity assessment, which represents the relationship of the hypotheses among the structural model constructs. the standardized values of the path coefficients are between –1 and +1. if the path coefficients are close to 1, it means that there is a strong and statistically significant positive relationship among the constructs. if the path coefficients are close to 0, then the relationship between the constructs is considered weak [68]. in this study, the one-tailed test was used because the relationships of the hypotheses are positive and direct. the critical values and p-values for one-tailed tests are 1.28 (with significance level=10%), 1.65 (with significance level=5%), and 2.33 (with significance level=1%) [67] as shown in table vi. figure 6 presents the path coefficients of the structural model using smartpls3. table vi. path relationships analysis test standard path relationship p value * < 0.10 ** <0.05 *** < 0.01 t value >1.28 level of significance =10% >1.96 level of significance = 5% >2.33 level of significance = 1% engineering, technology & applied science research vol. 11, no. 3, 2021, 7158-7171 7165 www.etasr.com alatawi et al.: a new model for enhancing student portal usage in saudi arabia universities fig. 5. study measurement model. fig. 6. path coefficients of the structural model. table vii. results of hypothesis testing factor path t value p value significant level decision aoc → sp 1.33 0.092 * supported d → sp 1.828 0.034 ** supported e → sp 3.666 0 *** supported i → sp 2.918 0.002 *** supported iq → sp 0.436 0.331 ns not supported n → sp 0.272 0.393 ns not supported psq → sp 2.232 0.013 *** supported pus → sp 4.709 0 *** supported ui → sp 2.915 0.002 *** supported us → sp 1.953 0.025 ** supported the result of hypotheses testing shows that most of the hypotheses are significant. moreover, by using a bootstrapping test in smart-pls, the result shows that 8 out of 10 hypotheses are significant. table vii presents the results of hypotheses testing. as presented above, this study has 10 hypotheses. ha1 stated that us has a significant and positive affect on students’ use of the student portal. previous studies indicated that the satisfaction of users will provide a surrogate which is significant to the critical product of the existing or new information system [30]. us is in terms of the use of the system and the acceptance of the portal, which is important in measuring the success of the information system [73]. therefore, in this study, us about the portal is considered significant based on preliminary studies and the final result of data collection which reveals that there is a positive relationship between us and the use of the student portal (tvalue=1.953, p-value=0.018). saudi universities should take engineering, technology & applied science research vol. 11, no. 3, 2021, 7158-7171 7166 www.etasr.com alatawi et al.: a new model for enhancing student portal usage in saudi arabia universities into account the us when they improve their portals based on their students’ needs and demands. ha2 states that iq has a positive effect on students’ use of the student portal. according to [38], iq is the output quality of an information system, which reflects dimensions such as content, accuracy, timing, and format. it is an important factor because providing high-quality information to users in a university student portal can help in delivering innovative services to students. the results show a negative relationship between iq and the use of the students’ portal (t-value=0.436, p-value=0.331) because the student portal does not create new information nor meet students’ needs based on students’ point of view. however, the quality of the information provided on the portal should meet the students’ needs. thus, universities in saudi arabia have to improve their student portals based on their students’ needs and demands. ha3 states that interaction has a positive and significant effect on students’ use of the student portal. authors in [35] defined interaction as the ease by which users interact with the input and output of the system and their ability to learn through it. interaction is one of the main factors that contribute to positive learning outcomes in a learning environment [74]. the findings of this study reveal that there is a positive relationship between interaction and using the student portal (tvalue=2.918, p-value=0.002). thus, interaction is considered an important indicator that can help improve student portal usage. ha4 states that the aoc has a positive effect on students’ use of the student portal [37]. this is shaped by the educational and non-educational services provided in the portal, such as online library services, email services, lecturer evaluation, and registration services. a student portal should facilitate easy access to all services and be flexible, quick, and allow users to perform their tasks [38]. the findings of this study showed that there is a positive relationship between the availability of content and the usage of the student portals (t-value=1.33, pvalue=0.092). thus, the aoc will help saudi universities to improve their student portals based on their students’ demands and expectations. ha5 states that psq has a significant and positive effect on students’ use of the student portal. the author in [40] defined psq as a measure of the level of customers’ expectations with how well the information system offers services to users. service quality within the context of the portal can be determined by prompt, responsive, available, accessible, and flexible e-services [41]. therefore, psq is a key determinant for the use and us about e-services provided via a portal [42]. the result of this study reveals a positive relationship between psq and the use of a students’ portal (t-value=2.232, pvalue=0.013). thus, psq is a significant indicator that can help saudi universities improve their student portals. ha6 states that portal design has a significant and positive effect on the use of the student portal. according to [75], university student portals are designed to make the member’s experience with the portal as personalized as possible. the design features that attract users and increase their satisfaction include enjoyment, excitement, participation, and charm [45]. design can motivate them to participate and promote excitement to enjoy while visiting the website. therefore, student portal design features that help students to enjoy their visit lead to increased activity [46]. this study reveals that there is a positive relationship between design and use of the students' portal (t-value=1.828, p-value=0.034). thus, the portal design is paramount to improving student portal usage. ha7 states that navigation has a positive effect on students’ use of the student portal. usually, a navigation bar offers the main tasks of the website [76]. according to [47], navigation is a significant factor in learning the web portal. users should be able to move through portal links without getting lost. the ease of navigation is a critical component of portal usage [48]. the result of this study shows that there is a negative relationship between navigation and use of portals (t-value=0.272, pvalue=0.393) which means that navigation is not regarded as an essential predictor for the use of a student portal from the viewpoint of students. anyhow, the student portal navigation does not attract students or meet their needs, so it will be useful for saudi universities to improve it, provide more links that students need in their study, and make the portal easier to use and easier to find the necessary information. ha8 states that pus has a significant and positive effect on students’ use of the student portal. authors in [51] define user support as the ability of the it department to assist users when needed. moreover, because an academic portal is usually complex and needs qualified staff, it is necessary to have online user support tools to help the users [28]. students (users) should be given specified training and user support, to increase the ease of use and learnability to effectively and efficiently fulfil a specified range of task scenarios on the web portal while management achieves their economic and global attainments [77]. this study reveals that there is a positive relationship between pus and the use of the student portals (tvalue=4.709, p-value=0). hypothesis hb1 states that efficiency has a significant and positive effect on students’ use of the student portal. as a personal factor, efficiency is defined as the judgements of people on their capabilities to organize and implement the required courses of action to achieve a required goal [52]. efficiency was shown to be an important indicator that determines the actual behavior of a person [78]. furthermore, the student portal is a good learning environment [38]. even though student portals offer good information, their efficiency will decrease if the student ability does not meet the suitable level [54]. this study reveals that there is a positive relationship between the efficiency factor and the use of students’ portals (t-value=3.666, p-value=0). the last hypothesis is that ui has a significant impact on students’ use of the student portal. moreover, as a behavioral factor, ui is defined as a person’s ability to formulate clear plans to perform a determined future behaviour [55]. many factors might affect students’ behavioral intention to use the student portal. behavioral intention predicts or at least is linked with the actual usage [57, 58]. this study revealed that there is a positive relationship between ui and using the students’ portal (t-value=2.915, p-value=0.002). engineering, technology & applied science research vol. 11, no. 3, 2021, 7158-7171 7167 www.etasr.com alatawi et al.: a new model for enhancing student portal usage in saudi arabia universities this study developed and validated a model based on data collected via a survey of students in 4 saudi universities. smartpls3 was used to analyze the data. the findings indicate that 8 out of 10 considered factors are significant and have a positive effect on student portal usage. these factors are user satisfaction, design, availability of content, user intention, efficiency, portal user support, portal service quality, and interaction. on the other hand, information quality and navigation had no significant effect on portal usage. the model was able to discover students’ expectations about the portals of saudi universities, so it can help them to imrove their students’ portal usage. figure 7, presents the model of this study along with the significance results. fig. 7. the model of this study. the model of this study has established the context of what students need to use the university portals. this model recommends university management and it departments to provide an appropriate electronic e-service and suitable ict environment that support the portal users. the model of this study also identified the most important factors that affect the students to use the portals. by taking into account these factors in the portal development process, universities can improve their portals. in addition, this study is one of the few studies that provide the factors that help universities build suitable electronic systems to develop and improve their university portal usage. v. conclusion and future work this study studied the importance of student portals by investigating the most important factors that attract undergraduate students in saudi universities to use them. the authors divided the identified factors into environmental, personal, and behavioral. each category included sub-factors. the environmental category included 8, the personal category included 1, and the behavioral category also included 1. this study found that the 3 categories positively affect students’ portal usage. moreover, the 10 hypotheses regarding the factors and their results presented the relationship between independent variables and the dependent variable, which indicates that ui, d, aoc, ui, e, pus, psq, and i have a positive effect on students’ use of the student portal. on the other hand, iq and n do not have a significant effect on students’ portal usage. future work can investigate these factors from other perspectives, such as the academic and administrative staff point of views. this study was conducted on undergraduate students in saudi arabia universities. future work can extend and consider postgraduate students. this study can be considered a good start for researchers to investigate more on the usage of electronic resources and ict in university portals to improve the needs of other university users. appendix a cross loadings of discriminant validity aoc d e i iq n psq pus spu ui us aoc2 0.811 0.611 0.593 0.605 0.592 0.662 0.658 0.511 0.58 0.581 0.63 aoc3 0.775 0.512 0.526 0.667 0.528 0.543 0.543 0.426 0.553 0.552 0.503 aoc4 0.879 0.589 0.591 0.666 0.598 0.701 0.621 0.531 0.603 0.58 0.605 aoc5 0.864 0.626 0.625 0.638 0.533 0.669 0.645 0.585 0.602 0.638 0.64 aoc6 0.836 0.623 0.578 0.616 0.503 0.611 0.596 0.535 0.568 0.585 0.617 aoc7 0.852 0.655 0.604 0.672 0.553 0.657 0.61 0.535 0.573 0.607 0.607 aoc8 0.883 0.662 0.625 0.681 0.571 0.723 0.654 0.586 0.623 0.608 0.657 aoc9 0.862 0.648 0.648 0.689 0.597 0.663 0.629 0.619 0.667 0.666 0.65 aoc11 0.888 0.645 0.633 0.655 0.556 0.712 0.656 0.619 0.616 0.676 0.669 d2 0.598 0.805 0.592 0.611 0.464 0.591 0.601 0.555 0.544 0.614 0.609 d3 0.645 0.871 0.671 0.641 0.538 0.658 0.652 0.616 0.603 0.672 0.68 d4 0.614 0.862 0.627 0.633 0.503 0.63 0.662 0.573 0.584 0.653 0.687 d8 0.692 0.871 0.664 0.679 0.514 0.681 0.727 0.593 0.591 0.688 0.735 d9 0.55 0.842 0.611 0.565 0.455 0.566 0.62 0.571 0.562 0.659 0.64 d10 0.615 0.859 0.65 0.631 0.56 0.635 0.636 0.616 0.631 0.688 0.637 d11 0.633 0.882 0.661 0.632 0.49 0.671 0.669 0.59 0.602 0.698 0.681 d12 0.666 0.846 0.686 0.642 0.472 0.679 0.663 0.638 0.587 0.629 0.677 d14 0.6 0.867 0.679 0.612 0.431 0.666 0.692 0.623 0.594 0.677 0.72 e1 0.541 0.605 0.764 0.561 0.498 0.573 0.599 0.635 0.645 0.649 0.611 e2 0.628 0.677 0.867 0.602 0.443 0.647 0.755 0.723 0.69 0.658 0.787 e3 0.635 0.697 0.888 0.63 0.509 0.659 0.7 0.73 0.7 0.675 0.75 e4 0.619 0.618 0.868 0.582 0.436 0.561 0.677 0.726 0.718 0.666 0.739 e5 0.647 0.683 0.909 0.629 0.49 0.657 0.754 0.746 0.731 0.708 0.805 e6 0.592 0.637 0.861 0.582 0.501 0.594 0.645 0.736 0.742 0.704 0.69 i2 0.62 0.585 0.521 0.785 0.514 0.565 0.589 0.51 0.537 0.607 0.544 i3 0.606 0.57 0.519 0.842 0.558 0.591 0.536 0.474 0.612 0.613 0.535 i5 0.69 0.619 0.58 0.897 0.53 0.679 0.601 0.527 0.615 0.652 0.579 i6 0.62 0.608 0.587 0.86 0.543 0.69 0.578 0.549 0.589 0.59 0.58 i7 0.667 0.659 0.636 0.842 0.495 0.732 0.637 0.597 0.66 0.629 0.623 i8 0.711 0.683 0.68 0.864 0.518 0.728 0.691 0.59 0.653 0.645 0.663 iq1 0.575 0.501 0.508 0.535 0.804 0.489 0.493 0.478 0.523 0.523 0.49 iq2 0.546 0.442 0.436 0.499 0.847 0.434 0.408 0.376 0.428 0.47 0.406 iq3 0.594 0.522 0.505 0.541 0.9 0.498 0.483 0.444 0.495 0.534 0.47 iq4 0.518 0.459 0.46 0.502 0.842 0.449 0.42 0.399 0.465 0.479 0.418 iq5 0.505 0.472 0.399 0.505 0.783 0.367 0.4 0.381 0.396 0.489 0.372 n1 0.714 0.69 0.653 0.722 0.527 0.916 0.667 0.595 0.642 0.653 0.657 n3 0.716 0.677 0.658 0.74 0.498 0.94 0.683 0.612 0.663 0.643 0.664 n4 0.729 0.717 0.674 0.719 0.473 0.92 0.696 0.624 0.633 0.671 0.669 psq2 0.676 0.7 0.731 0.678 0.478 0.711 0.878 0.621 0.675 0.738 0.792 psq3 0.574 0.642 0.635 0.632 0.498 0.572 0.758 0.62 0.7 0.702 0.661 psq4 0.656 0.681 0.703 0.651 0.46 0.661 0.906 0.641 0.663 0.676 0.798 psq5 0.66 0.685 0.684 0.617 0.477 0.649 0.883 0.605 0.619 0.647 0.772 psq6 0.644 0.656 0.701 0.599 0.451 0.622 0.915 0.615 0.638 0.663 0.803 psq7 0.658 0.686 0.742 0.625 0.446 0.676 0.928 0.642 0.67 0.68 0.827 psq8 0.668 0.698 0.751 0.609 0.468 0.661 0.918 0.648 0.664 0.669 0.845 pus1 0.615 0.633 0.746 0.551 0.47 0.608 0.622 0.843 0.714 0.634 0.679 pus2 0.638 0.634 0.768 0.622 0.481 0.624 0.644 0.889 0.771 0.679 0.682 pus3 0.578 0.654 0.759 0.585 0.431 0.595 0.64 0.919 0.728 0.661 0.693 pus4 0.576 0.618 0.752 0.563 0.445 0.568 0.634 0.915 0.716 0.647 0.656 pus5 0.606 0.654 0.791 0.609 0.472 0.623 0.675 0.922 0.769 0.694 0.714 pus6 0.543 0.654 0.745 0.549 0.413 0.562 0.648 0.905 0.7 0.628 0.7 pus7 0.551 0.584 0.712 0.556 0.428 0.586 0.621 0.91 0.743 0.651 0.649 pus8 0.575 0.608 0.743 0.575 0.474 0.593 0.652 0.918 0.747 0.637 0.675 spu1 0.647 0.625 0.737 0.65 0.504 0.653 0.656 0.717 0.889 0.685 0.657 spu2 0.647 0.599 0.726 0.648 0.487 0.643 0.649 0.709 0.897 0.678 0.633 spu3 0.55 0.542 0.662 0.584 0.468 0.535 0.578 0.674 0.876 0.629 0.562 engineering, technology & applied science research vol. 11, no. 3, 2021, 7158-7171 7168 www.etasr.com alatawi et al.: a new model for enhancing student portal usage in saudi arabia universities spu4 0.553 0.556 0.649 0.611 0.487 0.547 0.598 0.662 0.863 0.653 0.575 spu5 0.657 0.642 0.768 0.645 0.493 0.634 0.724 0.768 0.884 0.697 0.728 spu6 0.654 0.656 0.771 0.668 0.498 0.659 0.738 0.768 0.875 0.722 0.728 ui1 0.641 0.724 0.692 0.607 0.455 0.663 0.755 0.612 0.615 0.788 0.768 ui2 0.665 0.708 0.684 0.638 0.486 0.686 0.709 0.63 0.638 0.846 0.727 ui3 0.515 0.565 0.598 0.566 0.478 0.511 0.547 0.555 0.636 0.837 0.55 ui4 0.643 0.72 0.701 0.687 0.528 0.632 0.687 0.639 0.697 0.889 0.687 ui5 0.594 0.629 0.662 0.608 0.538 0.553 0.624 0.601 0.652 0.869 0.614 ui6 0.588 0.621 0.668 0.602 0.517 0.579 0.655 0.643 0.689 0.852 0.646 ui7 0.612 0.629 0.65 0.632 0.537 0.573 0.607 0.61 0.631 0.833 0.622 us1 0.688 0.753 0.748 0.637 0.481 0.692 0.795 0.651 0.661 0.711 0.872 us2 0.67 0.703 0.764 0.615 0.465 0.638 0.833 0.68 0.681 0.697 0.923 us3 0.709 0.742 0.783 0.669 0.499 0.701 0.822 0.665 0.671 0.715 0.935 us4 0.643 0.689 0.768 0.639 0.465 0.657 0.801 0.715 0.683 0.694 0.904 us5 0.658 0.735 0.766 0.634 0.463 0.65 0.802 0.682 0.653 0.724 0.926 us6 0.627 0.692 0.779 0.592 0.459 0.609 0.794 0.68 0.631 0.694 0.895 us7 0.638 0.685 0.785 0.613 0.471 0.602 0.795 0.709 0.708 0.706 0.891 appendix b fornell-larcker of discriminant validity aoc d e i iq n psq pus spu ui us aoc 0.851 d 0.729 0.856 e 0.71 0.759 0.861 i 0.77 0.733 0.694 0.849 iq 0.658 0.575 0.557 0.619 0.836 n 0.778 0.75 0.715 0.785 0.54 0.925 psq 0.734 0.769 0.801 0.714 0.531 0.737 0.885 pus 0.649 0.698 0.833 0.639 0.501 0.66 0.711 0.903 spu 0.705 0.688 0.819 0.722 0.556 0.698 0.75 0.816 0.881 ui 0.719 0.776 0.786 0.733 0.599 0.708 0.774 0.725 0.771 0.846 appendix c the questionnaire please answer the following questions by choosing the correct information representing your demographic. 1.your gender: (male/female) 2.your age: (18 24 years/25 29 years/ more than 30) 3.your university name: (taibah university/ taif university/ king faisal university/ university of tabuk) 4. years of experience using computer and internet: (less than 1 year/1 3 years/3 5 years/5 10 years/ more than 10 years) 5. computer skills: (low/good/ excellent) 6. internet skills: (low/good/ excellent) b. for the following questions, please rate your perception with regard to your experience in using student portals. (possible choices: strongly disagree, disagree, neutral, agree, strongly agree) 1. information quality (iq): refers to the system’s output value, as perceived by the users. i believe that the easy to understand information on the student portal encourages me to use the portal. i believe the student portal provides accurate information to me as a student. i believe the information displayed on the student portal is useful to me as a student. i believe the student portal provides information related to my study needs. i believe the rich information available on the student portal attracts me to use the portal. 2.availability of content (aoc): refers to the availability of portal content and services which provide to student in their portal. i believe that if the availability of information content in the student portal meets my needs, it will encourage me to use the portal. i believe that if online discussions were available in the student portal, that would help me increase my interaction with the portal. the availability of online course catalogues in the student portal will help me in my study. i believe that if the student portal provides complete information about the university and the various events, it will attract me to use it. i believe having contact information such as phone number, fax number, e-mail, and postal address in the portal is helpful to me as a student. i believe that giving feedback and facilitated question forms in the student portal will increase the interaction with the portal. i believe that if a help facility was provided in the student portal, that will make the portal more usable. i believe that if the student portal provides e-mail services to students will help me interact with the portal administration. i believe that if the student portal contains an e-learning material service, will make my materials easy to access on the portal. 3. interaction (i): refers to the interaction between the students, instructors, and the portal services. i believe that the interaction in the student portal enhances the effectiveness of my academic decisions as a student. i believe that the interaction in the student portal enhances my productivity in my academic life as a student. i believe that if the student portal makes online discussion tasks easy to use, will increase my interaction with it. i believe the interaction allows me to share experiences with other students in the portal. i believe the instructor can encourage students to increase their interaction with the student portal. i believe interactive feedback between students and teachers in the student portal will encourage both of them to use it. 4.navigation (n): assesses whether a portal includes tools (i.e. navigation menu, internal search facility) and links which facilitate users'navigation. i believe that if all links are working in my student portal, that will make it more interesting to use i believe that if the internal search is effective in the student portal, that will help me in my study. i believe that if the internal search is working in the student portal, that will help me to use it. 5. design (d): refers to the visual attractiveness of the portal design, the appropriate design of a portal pages and the appropriate use of images, fonts, colors in the portal design. i believe that if the images in the student portal are interesting, that will increase my satisfaction of the portal i believe that if there are consistent colors throughout the student portal, that will make the portal more attractive. i believe that if the student portal menu design is consistent, that will make it more interesting to use. i believe that if the content text is simple in the student portal, that will make the portal easier to use. i believe that if the layout of the student portal is very simple, that will make the portal more attractive. i believe that if the alignment of the header on each page is consistent in the student portal, that will make it more attractive. i believe that if all pages have proper headings, that will make the portal more interesting to use. engineering, technology & applied science research vol. 11, no. 3, 2021, 7158-7171 7169 www.etasr.com alatawi et al.: a new model for enhancing student portal usage in saudi arabia universities i believe that if consistent language is used throughout the student portal, that will make the portal easier to use. i believe that the design makes pleasurable for students to use the student portal services. 6. user intention (ui): refers to the behavioral of user intention to use the student portal services. i believe that if the portal services are worthwhile for students, that will make me use the portal more. if i get good services, i will use the student portal many times per week. i plan to use the student portal very often in the future. if the student portal is enjoyable, i intend to use it in the future. i intend to use the student portal to conduct university related study tasks. i predict i will use the student portal in the future. if i get to use the student portal, i intend to use all of its services. 7. portal service quality (psq): refers to the users evaluation that the service they are receiving from the portal is the service they expect. i believe the services offered in the student portal should be reliable. i believe the services offered in the student portal save my time. i believe the pages should respond fast when i use the portal services. i believe the student portal should provide sufficient information to achieve my tasks. i believe the student portal should be flexible to use. i believe the services offered in the student portal should be comprehensive for all student needs. i believe the student portal should provide up-to-date information. 8. user satisfaction (us): refers to student satisfaction about the provided services. if the quality of information provided through the student portal is good, i will feel satisfied. if the quality of the student portal system is good, i will feel satisfied. if the services offered in the student portal meet my needs, that will increase my satisfaction with the portal. i believe that if the student portal is enjoyable, it will make me satisfied. if the services offered by the student portal are suited to my needs, that will make me satisfied. i believe the services offered by the student portal should be easy to use. i believe that if the process of using the student portal is pleasant, that will make me satisfied. 9. efficiency (e): mean users have the ability to organize and perform the actions on the portal in order to achieve their tasks. i have the ability to download programs and use student portal services. i believe the student portal services should be easy to use. i believe that if the information in the student portal is interesting to me, it should be obtained with minimal effort. i believe that if i find that anyone can use the student portal easily, that will encourage me to use the portal. i believe that if i can easily navigate the student portal, that will help me to find what i need easily. i believe the student portal serves its purpose by producing good services. 10 portal user support (pus): the degree to which the usersupport departments are willing to serve the users and provide them with the required services. i believe the portal loads its pages quickly if user support provides high internet speed. i believe the user support will help users by providing training in the use of the student portal. i believe the user support will help users by providing quick responses to their service requests. i believe the user support will help users by providing correct information. i believe the user support will help users by providing different browsers where portal pages work. i believe the user support will help users by providing a help desk. i believe the user support will help users by providing feedback forms. 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[78] j. c. roca, c.-m. chiu, and f. j. martinez, "understanding e-learning continuance intention: an extension of the technology acceptance model," international journal of human-computer studies, vol. 64, no. 8, pp. 683–696, aug. 2006, https://doi.org/10.1016/j.ijhcs.2006.01.003. microsoft word etasr_v11_n4_pp7522-7530 engineering, technology & applied science research vol. 11, no. 4, 2021, 7522-7530 7522 www.etasr.com doan et al.: a novel fuzzy logic based load frequency control for multi-area interconnected power … a novel fuzzy logic based load frequency control for multi-area interconnected power systems diem-vuong doan faculty of control and automation electric power university hanoi, vietnam vuongdd@epu.edu.vn khoat nguyen faculty of control and automation electric power university hanoi, vietnam nkn.research@gmail.com quang-vinh thai institute of information technology vietnam academy of science and technology hanoi, vietnam tqvinh@ioit.ac.vn abstract—this study focuses on designing an effective intelligent control method to stabilize the net frequency against load variations in multi-control-area interconnected power systems. conventional controllers (e.g. integral, pi, and pid) achieve only poor control performance with high overshoots and long settling times. they could be replaced with intelligent regulators that can update controller parameters for better control quality. the control strategy is based on fuzzy logic, which is one of the most effective intelligent strategies and can be a perfect substitute for such conventional controllers when dealing with network frequency stability problems. this paper proposes a kind of fuzzy logic controller based on the pid principle with a 49-rule set suitable to completely solve the problem of load frequency control in a two-area thermal power system. such a novel pidlike fuzzy logic controller with modified scaling factors can be applied in various practical scenarios of an interconnected power system, namely varying load change conditions, changing system parameters in the range of ±50%, and considering governor dead-band (gdb) along with generation rate constraint (grc) nonlinearities and time delay. through the simulation results implemented in matlab/simulink software, this study demonstrates the effectiveness and feasibility of the proposed fuzzy logic controller over several counterparts in dealing with the load-frequency control of a practical interconnected power system considering the aforesaid conditions. keywords-load frequency control (lfc); fuzzy-pid controller; pid controller; uncertainties; nonlinearities i. introduction due to the random change of load in a power system, electrical energy varies continuously. this affects the system's operating frequency, leading to a deviation of the network frequency from the nominal value. a modern power system network has several control areas. for the stable operation of power subsystems, the total generation of each control area must match with the total load demand plus associated system losses, regulate system frequency, and exchange tie-line power accordingly. this is defined as the load frequency control (lfc) or automatic generation control (agc), which plays an important role in power system operation and control. the lfc strategy aims to continuously monitor the system frequency and the tie-line power. it also calculates net changes of these two parameters from their nominal values, which is known as area control error (ace), in order to control the valve settings of prime movers with a goal of forcing ace signals to acceptable values. considered to be a crucial part of agc, the lfc strategy drives ace signals to desirable values, meaning both frequency and tie-line power deviations should be treated to be near zero with allowable tolerance. there are several reports regarding the lfc problem. in [1], the authors designed a fuzzy-pi controller to control the load frequency for a six-area power system with non-reheat turbines. authors in [2] proposed a pid hierarchical frequency controller for four-area interconnection power systems. the control structure used pid controller to prevent grc from generating. the author in [3] proposed the optimal sliding control method h∞ load frequency (smlfc) for power system with time delay. in [4], a fuzzy controller was proposed to find the optimal parameters for the pid frequency controller of a three-area power system. in [5], a neural controller was proposed, designed to automatically and continuously adjust the parameters of the pid controller according to the change of the control error area. in [6], the control plant under consideration was a three-area electric power system composed of wind, heat, and hydraulic turbines. the authors gave control methods that were considered to be advanced, such as pid, fopid, fpid, and ffopid, which were designed based on itae objective function. in [7], the method used was a hybrid controller hpso-ps for two-area power systems without heat recovery, each with two generators. in [8], a model predictive controller (mpc) was used to control a multi-connected power system with four areas and eight generators. in [9], the corresponding author: khoat nguyen engineering, technology & applied science research vol. 11, no. 4, 2021, 7522-7530 7523 www.etasr.com doan et al.: a novel fuzzy logic based load frequency control for multi-area interconnected power … qogwo algorithm was used to optimize the parameters of the pid controller based on the itae objective function. in [10], the coa algorithm was used to optimize the parameters of the piadf controller. the controller was used to control the load frequency for a multi-connection system with two nonrecovery areas, two multi-generator areas, and three multi generator hydrogen turbine areas. in [11], the authors proposed the t-smc sliding controller for a two-area power system with wind turbines. in [12], the authors studied a virtual inertial controller to stabilize the frequency in a two-area power system with wind and solar renewable energy supplies. in [13], fractional order proportional-integral-derivative (fopid) and tilted-integral-derivative (tid) controllers were applied in the design of lfc for a two-area diverse-unit power system. tuneable parameters were adjusted via an improved particle swarm optimization algorithm which was powered by chaotic parameters and a crossover operator to find a globally optimal solution. in [14], a novel evolution (mde) algorithm optimized fuzzy pid controller was proposed for the lfc of a two-area power system. in order to stabilize the frequency in an interconnected power system, many problems arising in the system affect its control quality. these include devices with nonlinear system components such as: gdb (governor dead band), grc (generation rate constraint), time delay in the system, changes of parameters of electrical equipment, and varying operating loading conditions. all the above factors make the system unstable, leading to fluctuations of the operating frequency. the frequency change affects greatly the devices in the system: • most ac motors run at speeds that are directly related to frequency. the speed and induced electro motive force (emf) may vary because of the change of frequency of the power circuit. • when operating at frequencies below 49.5hz some types of steam turbine certain rotor states undergo excessive vibration. • the change in frequency can cause maloperation of power converters by producing harmonics. • for power stations running in parallel it is necessary that the frequency of the network must remain constant for the synchronization of generators. • many devices connected to the grid will only work properly when the input frequency is within a certain range. • the inductances of the inductive elements (e.g. transformers) are chosen based on the switching frequency. changes in the frequency will cause disturbances in the output and may even cause the supply’s control system to become unstable the traditional pid controller, controller parameters are not updated when the system encounters the above problems. therefore, the fuzzy pid controller [15] is studied in this paper to solve the load frequency control problem. although they do not have an apparent structure of pid controllers, fuzzy logic controllers are considered to be nonlinear pid controllers with parameters that can be determined on-line based on the error signal and its time derivative. the response results of the system are compared with the genetic algorithm tuned pi (ga-pi) [16], bacterial foraging optimization algorithm tuned pi (bfoa pi) [16], bfoa-pso optimized pi controller [17], fuzzy pi controller [18], and fractional pid (fpid) [19]. ii. interconnected power system modeling each interconnected power system consists of several subsystems called control areas. a control area should be considered as a power station including several elements, namely governor, turbine, load, and generator. these elements are connected to be the core of a power plant. their mathematical models are described below. a. speed governor model a typical model of governors is depicted in figure 1 [1]. this model can be mathematically expressed as: 1 1 ( ) ( ( ) ( )) 1 p s p s f sg c st rg ∆ = ∆ − + (1) where r is the speed regulation of the governor, tg is the time constant of the speed the governor. 1 1 g st+ 1 r + ( ) c p s∆ ( )f s∆ ( ) g p s∆ fig. 1. speed governor model. b. thermal turbine models thermal turbines are widely used in power plants. technically, they are classified into two types: non-reheat and reheat turbines. the non-reheat model is shown in figure 2. the following expression is obtained: 1 1 g ( ) ( ) ( ) t g t stch s p s p s = + = (2) where tch is the non –reheat time constant. 1 1 ch st+ ( ) g p s∆ ( ) t p s∆ fig. 2. non – reheat turbine model. the reheat turbine model is presented in figure 3 and the mathematical model in (3). 1 2 ( ) 1 g ( ) ( ) ( ) t g f t shp rh t t t s t t sch rh ch rh s p s p s + = + + + = (3) engineering, technology & applied science research vol. 11, no. 4, 2021, 7522-7530 7524 www.etasr.com doan et al.: a novel fuzzy logic based load frequency control for multi-area interconnected power … where trh and fhp are the low pressure reheat time constant and the high pressure stage respectively. ( ) g p s∆ ( )tp s∆1 2 ( ) 1 f t s hp rh t t s t t s ch rh ch rh + + + + fig. 3. reheat turbine model. c. generator load model equation (4) is obtained from the block diagram in figure 4: 1 f( ) ( ( ) ( ))s p s p s t dms d ∆ = ∆ − ∆ + (4) where m is the inertia constant of the generator and d is the load damping constant. 1 ms d+ (s) t p∆ (s) d p∆ (s)f∆ fig. 4. generator – load model. figure 5 shows the block diagram of a two-area interconnected power system with gdb and grc. the system is represented by the state space shown in appendix a. fig. 5. block diagram of a two-area interconnected non-reheat thermal– reheat thermal power system with grc and grc. the control objectives of the lfc in a multi-area interconnected power system are mainly to control the frequency variation, ace, and tie-line power deviation in the areas towards zero while the system has many nonlinear, uncertain components and varying operating load conditions. iii. design of the fuzzy-pid controller the fuzzy pid controller studied in this paper is compared in terms of control quality with other controllers to prove its superiority. the pid controller [15] is characterized by 3 parameters: kp, kd, and ki. assuming that kp and kd are always in the range [kpmin, kpmax] and [kdmin, kdmax], it is reasonable to define the following equations: ' ( ) / ( ) min max min k k k k p p p p p k = − − (5) ' ( ) / ( ) dmin dmax dmin k k k k d d k = − − (6) i d t tα= (7) 2 / t / ( ) i p d p d k k k tα α= = (8) min max 0.32 0.6 p u p u k k k k = = (9) dmin dmax 0.08 t 0.15 u u u u k k k k t = = (10) where u k and u t are, respectively, the gain and the period of the oscillation at the stability limit under p-control. fig. 6. the structure of the control area #i using different controllers. pid controller system fuzzy caculate kp caculate kd caculate ki ace ace∆ ' kp 'kd α fig. 7. the structure of the fuzzy – pid controller. the fuzzy controller designed with ace and ∆ace inputs has the membership functions presented in figures 8-10 and tables i-iii. the outputs of the fuzzy set are ' p k , ' d k and α. fig. 8. membership function of ace and ∆ace engineering, technology & applied science research vol. 11, no. 4, 2021, 7522-7530 7525 www.etasr.com doan et al.: a novel fuzzy logic based load frequency control for multi-area interconnected power … fig. 9. membership function of kp', kd'. fig. 10. membership function of α. table i. fuzzy rule for kp' ∆ace nb nm ns zo ps pm pb ace nb s s s s s s s nm b b s s s b b ns b b b s b b b zo b b b b b b b ps b b b s b b b pm b b s s s b b pb s s s s s s s table ii. fuzzy rule for kd' ∆ace nb nm ns zo ps pm pb ace nb b b b b b b b nm s b b b b b s ns s s b b b s s zo s s s b s s s ps s s b b b s s pm s b b b b b s pb b b b b b b b table iii. fuzzy rule for a ∆ace nb nm ns zo ps pm pb ace nb 2 2 2 2 2 2 2 nm 3 3 2 2 2 3 3 ns 4 3 3 2 3 3 4 zo 5 4 3 3 3 4 5 ps 4 3 3 2 3 3 4 pm 3 3 2 2 2 3 3 pb 2 2 2 2 2 2 2 from (5), (6) and (8) the following equations can be deduced: ' max min min ( ) p p p p p k k k k k= − + (11) ' dmax min min ( ) d d d d k k k k k= − + (12) 2 / ( ) i p d k k tα= (13) the above factors will be applied when running the pid – like fuzzy logic controller in dealing with the load frequency control of an interconnected power system. iv. case studies this section presents numerical simulations implemented in matlab/simulink considering numerous perspectives to demonstrate the proposed control strategy. the simulation scenarios describe a system encountered with nonlinearities, variation of different load types, uncertainties, and time delay. the system parameters used in the simulations are described in the appendix (table vi). the proposed controller is compared with ga pi [16], bfoa pi [16], bfoa-pso optimized pi [17], fuzzy pi [18], and fpid [19] controllers to verify its control quality. a. performance comparison under step load, pulse load, random load, and sinusoidal load disturbances. in a power system, the electrical energy at the power supply is taken from generators and imported energy sources. the electrical energy is supplied to consumers, production plants, energy for export, or is lost on the transmission line. when the supplied electrical energy is greater than the consumed energy, the system frequency will increase, otherwise, it will decrease. in fact, due to the large changes of the load, the frequency of the system changes continuously affecting the equipment in the system such as: ac motors, tranformers, steam turbines, etc. the types of load disturbance are shown in figure 11. • step load disturbance : 0.03 (pu) 1 2 p p d d ∆ =∆ = . • pulse load disturbance: 0.03(pu) 1 2 p p d d ∆ =∆ = , period: 40s, and pulse width: 10%. • random load disturbance: 0.03 (pu) 1 2 p p d d ∆ =∆ = , sample time: 40s. • sinusoidal load disturbance: 0.03sin(0.0628 ) 1 2 p p t d d ∆ =∆ = fig. 11. load disturbance types. engineering, technology & applied science research vol. 11, no. 4, 2021, 7522-7530 7526 www.etasr.com doan et al.: a novel fuzzy logic based load frequency control for multi-area interconnected power … the proposed fuzzy pid controller was compared with ga pi [16], bfoa pi [16], bfoa-pso optimized pi controller [17], fuzzy pi [18], and fpid [19] controllers and the results are shown in table iv. we see that minimum itae value and minimum settling time in frequency deviations are obtained with the fuzzy pid controller. (a) (b) fig. 12. dynamic responses to the step load disturbance in two areas: (a) ∆f1, (b) ∆f2. the step load disturbance in two areas and the system dynamic response are shown in figure 12 along with the simulation results of the tested controllers on the same power system. critical analysis of the dynamic responses clearly reveals that significant improvement is observed with the proposed fuzzy pid controller. table iv. comparative performance of error and settling time under step load disturbances techniques/parameters itae settling ts (s) ∆f1 ∆f2 fpid [19] 12.07 40.01 40.67 ga pi [16] 7.16 17.89 19.01 bfoa pi [16] 7.01 19.14 24.26 bfoa pso pi [17] 5.08 12.80 16.98 fuzzy pi [18] 3.44 13.11 11.07 fuzzy pid 0.84 6.02 5.83 the expression for the itae objective function is: ( ). .1 2 0 t sim itae f f p t dt tie = ∆ + ∆ + ∆∫ (14) (a) (b) fig. 13. dynamic responses to the pulse load disturbance in two areas: (a) ∆f1, (b) ∆f2. the simulation results shown in figures 12-15 show that the output response of the frequency difference of the two areas has a settling time of about 7 to 10s, the overshoot is very low and the frequency oscillation does not exist when using the proposed fuzzy – pid controller. these results prove the optimality of the proposed controller. in this section, when the system faces different types of load disturbances, the undesirable effects will be minimized under the active capability of the suggested controller. b. system simulations considering nonlinear system components and uncertainty parameters it is a fact that nonlinear components such as gdb and grc along with the uncertainties of parameters are highly suitable for practical control systems. a real interconnected power system must naturally include such components. nonlinearities, gdb and grc, may concern directly the operation of the power system. in the meantime, the uncertainties regarding the variation of system parameters as illustrated in table v obviously affect the stability of the power system. in this subsection, these undesired effects will be minimized under the positive influence of the proposed pidlike fuzzy logic controller. engineering, technology & applied science research vol. 11, no. 4, 2021, 7522-7530 7527 www.etasr.com doan et al.: a novel fuzzy logic based load frequency control for multi-area interconnected power … (a) (b) fig. 14. dynamic responses to the random load disturbance in two areas: (a) ∆f1, (b) ∆f2. (a) (b) fig. 15. dynamic responses to the sinusoidal load disturbance in two areas: (a) ∆f1, (b) ∆f2. simulation results when embedding nonlinearities and uncertainties are exhibited in table v and figure 16. as can be seen, the negative influences of these variations are successfully limited. both the frequency and tie-line power deviations are still rejected with good control performance, i.e. low overshoots and short settling times. these results demonstrate the robustness of the proposed fuzzy logic-based load-frequency controller. table v. parameter variations tg1 0.1 ± 0.1*50% tg2 0.2 ± 0.1*50% m1 10 ± 0.1*50% d1 1 ± 1*50% m2 10 ± 0.1*50% d2 1 ± 1*50% grc 5% gdb 5% (a) (b) fig. 16. dynamic responses to the step load disturbance in two areas (with uncertainty parameters): (a) ∆f1, (b) ∆f2. c. performance comparison with time – delay = 0.2s and 0.03 1 2 p p d d ∆ =∆ = (step load) time delay is another crucial parameter affecting the operation of a power system. long time delay may be detrimental to system stability and may degrade system performance. from figure 17, it is obvious that the damping characteristics obtained by the proposed fuzzy – pid controller are the best among the results. engineering, technology & applied science research vol. 11, no. 4, 2021, 7522-7530 7528 www.etasr.com doan et al.: a novel fuzzy logic based load frequency control for multi-area interconnected power … (a) (b) fig. 17. dynamic responses to the step load disturbance in two areas (with time delay): (a) ∆f1, (b) ∆f2. v. conclusion and further work in this paper, a comparative evaluation has been performed to examine the effectiveness of the proposed fuzzy –pid controller. in order to provide realistic results, the proposed and five known controllers, namely the fpid, ga pi, bfoa pi, and the fuzzy pi controllers were validated on a two-area thermal unit power system in which the physical constraints of the grc, gdb, and uncertainty have been taken into consideration. a rule-based scheme for gain scheduling of the pid controller is proposed for process control. the new scheme utilizes fuzzy rules and reasoning to determine the controller parameters and the pid controller generates the control signal. comparative dynamic performance evaluations have been carried out under step, pulse, sinusoidal, and random load perturbation patterns. the results demonstrate that the fuzzy – pid controller achieves much better dynamic performance (largest minimum damping ratio, smallest iate value, smallest overshoots, and smallest settling times of the area frequency oscillations). it is confirmed that the proposed fuzzy – pid controller outperforms many existing counterparts such as the fpid, ga pi, bfoa pi, bfoa pso pi, and fuzzypi controller in stabilizing the system. future work will focus on finding a new method to determine significant factors, namely kpmin, kpmax, kdmin and kdmax. in this context, an effective optimization method should be taken into account. appendix description of a two-area interconnected power system in a state-space form state variables: 1 1 2 1 3 1 54 2 2 6 2 7 2 8 9 1(1,2) 10 2 x f x p x p t g x f x p x p t r x p x p x ace dt g tie x ace dt = ∆ = ∆ = ∆ = ∆ = ∆ = ∆ = ∆ = ∆ = ∫ = ∫ control inputs: , 1 2 u u disturbance inputs: , 1 1 2 2 d p d p l l = ∆ = ∆ the state vector ‘x’ (10×1), control vector ‘u’ (2×1), and the disturbance vector ‘d’ (2×1) are: fig. 18. block diagram of a two-area interconnected non-reheat thermal– reheat thermal power system used to find the state – space of the system. engineering, technology & applied science research vol. 11, no. 4, 2021, 7522-7530 7529 www.etasr.com doan et al.: a novel fuzzy logic based load frequency control for multi-area interconnected power … 5 71 2 3 4 6 8 9 10 1 1 2 2 x x x x x x x x x x x u d u d u d  =       = =           1 -11 0 0 0 0 0 0 0 1 1 1 -1 1 0 0 0 0 0 0 0 0 1 1 -1 -1 0 0 0 0 0 0 0 0 1 1 1 1 12 0 0 0 0 0 0 0 2 2 2 -1 -1 0 0 0 0 0 0 0 2 2 -1 1 0 0 0 0 0 0 0 0 2 2 -1 -1 0 0 0 0 0 0 0 0 2 2 2 2 0 0 -2 0 0 0 0 0 0 12 12 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 1 0 0 2 d m m m tch tch r t t g g d m m m f fa hp hp t t t t rh rh ch ch t t ch ch r t t g g t t b b π π =                                                    0 0 0 0 1 0 1 0 0 0 0 0 0 1 0 2 0 0 0 0 0 0 t g b t g                   =                      -1 0 1 0 0 0 0 -1 0 2 0 0 0 0 0 0 0 0 0 0 0 0 m m                   γ =                     parameters of a two-area interconnected power system table vi. the parameters of the two areas [19] area with non reheat turbine value area with reheat turbine value m1 (p.u.s) 10 m2 (p.u.s) 10 d1 (p.u./hz) 1 d2 (p.u./hz) 1 tch1 (s) 0.3 tch2 (s) 0.3 tg1 (s) 0.1 tg2 (s) 0.2 r1 (hz/p.u.) 0.05 r2 (hz/p.u.) 0.05 b1 (p.u./hz) 21 b2 (p.u./hz) 21 t1 (p.u./rad.) 22.6 t2 (p.u./rad.) 22.6 fhp 0.3 trh (s) 7 references [1] n. 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[19] s. a. taher, m. hajiakbari fini, and s. falahati aliabadi, "fractional order pid controller design for lfc in electric power systems using imperialist competitive algorithm," ain shams engineering journal, vol. 5, no. 1, pp. 121–135, mar. 2014, https://doi.org/10.1016/j.asej.2013. 07.006. microsoft word etasr_v11_n1_pp6626-6631 engineering, technology & applied science research vol. 11, no. 1, 2021, 6626-6631 6626 www.etasr.com pathan et al.: a multivariable twin-rotor system control design a multivariable twin-rotor system control design erum pathan department of electrical power engineering universiti tun hussein onn malaysia johor, malaysia erumasad79@gmail.com muhammad kashif aslam electrical engineering department comsats university islamabad, pakistan kashif_aslam11@yahoo.com haider arshad department of electrical power engineering university tun hussein onn malaysia johor, malaysia haiderarshadkhan@gmail.com mubashir hayat khan department of electrical power engineering university tun hussein onn malaysia johor, malaysia mubashir.uthm@gmail.com muhammad asad substation automation engineer ng csd-c, saudi electricity company riyadh, saudi arabia csd_sec@yahoo.com muhammad imran rabani department of electrical contracting & maintenance xervon saudi arabia imran.shafaat@xervon-me.com abstract—this paper presents the design of a multi-input multioutput (mimo) pid controller for a twin-rotor mimo system. a multivariable control system consisting of two loops is designed for a non-linear system with two inputs and two outputs. the designed controllers have been tested on a simulated model with different possibilities and real-time results were taken. the designed pid controller efficiently controls the loops of the system and does not suffer from any process interactions. the results indicate that the performance of the pid controllers is excellent and both the transient and the steady-state enactment are adequate. the yaw and pitch rotor’s real-time responses are almost the same as the desired ones. keywords-pid controller; mimo; non-linear system i. introduction helicopters have been widely used for fast or immediate transports like medical emergencies, personal use, crime prevention, traffic conditioning, fire detection, etc. [1]. the twin rotor mimo system (trms) can be related to the helicopters in many aspects, e.g. the complex structure, nonlinearity, and cross coupling rotors' behavior. the trms due to the coupling effect suffers from many issues regarding the transversal vibration in beam. many studies have been carried out to handle this issue by providing mathematical models representing unbalanced external forces. the implementation of the discrete time model has attracted attention [2, 3]. for a complex system, an adaptive controller was designed [4, 5] and implemented in order to get the desired output of the uncertain system and the errors were successfully tracked by the adaptive self-tuning control scheme. adaptive natured control motivation led the authors in [6, 7] to compute a mathematical model of trms which is based on the adaptive control principle and the on-line identifier armax model. the two multivariable adaptive controllers were implemented into the system and compared with the fixed gain pid controller. the controllers showed very good results in error tracking with self-tuning control (stc) having external disturbances. a robust technique was used in [8, 9]. a fuzzy integral sliding controller was utilized in the vertical subsystem and on the horizontal plant a fuzzy sliding controller was implemented to track the errors. in [10-12], a particle swam optimization (pso)-based control technique was implemented to a trms with a pid controller that helped tune the pid controller at optimal point. pso-based controller with pid was also used in [11] with the addition of a compensator. although the compensator-based technique tracked the errors efficiently, the overall system was very complex to implement. an autonomous adaptive controller implemented with the pid controller to mitigate the oscillation errors was proposed in [13] to control trms. the comparison results showed that the autonomous adaptive controller with frictional order pid was more suitable than the integral order pid controller. a predictive control approach used for wind turbine speed control was presented in [14] and an optimizated control of the hydraulic actuator was presented in [15] with pid controllers by minimizing integral time. a multivariable pid controller was proposed in [16-18] with the ability to operate autonomously and the yaw and pitch angle were efficiently controlled. linear parameter varying (lpv) modeling [19] implements a control technique to the trms that takes care of the errors [18]. this controller performs well with fast corresponding author: erum pathan engineering, technology & applied science research vol. 11, no. 1, 2021, 6626-6631 6627 www.etasr.com pathan et al.: a multivariable twin-rotor system control design response, but having the design complexity as its main drawback of its implementation. a self-tuned online parameter estimation-based controller was designed in [20] for the trms kit and its simulation results were compared with real time data. the online estimation-based self-tuned adaptive controller needs to have real time data and varying parameters’ exact computation. the arx model was utilized to design the online estimation-based controller in almost all the cases. this paper presents the design of a multi-input multioutput (mimo) pid controller for a twin rotor mimo system. a multivariable control that consists of two loops for a nonlinear system with two inputs and two outputs was designed. the designed controller was tested on a simulated model and the results were compared with real data. the designed pid controller efficiently controls the loops of the system and does not suffer from any process interactions. ii. twin rotor mimo system model a basic trms model (tmrs-33-220) is illustrated in figure 1. the system is standing with the help of a tower, arranged in such a way that the model exhibits its rotary motion. the model can move in two directions, vertically and horizontally and the motion of the free-fall beam generates force. the beam pivoted on the tower is attached via bearings. these bearings allow the free movement in the vertical and horizontal direction within some limitations [21] (it cannot move freely up to 360o). if the beam is locked, the model cannot roll. two rotors are also attached on end points of the free-fall beam. the ends are categorized as the main and tail rotors. fig. 1. the trms model. fig. 2. block diagram of the trms. the mathematical model of the trms is quite complex and difficult to implement. for convenience, the overall model is separated in small units for decoupling [22]. the overall model is divided into six parts as shown in figure 2. the sub model load+ dc motor has ωy and ωp as inputs. the aerodynamic rotor block has the ωy and ωp as inputs and its outputs are aerodynamic torques jp, jy jp,a. the last blocks are the mechanics of the tail and main rotors. their outputs are azimuth angles ψres,y and ψres,p. the first order differential equation expresses the dynamics of the propeller sub system. the simplification of the trms can be made by two point mass system. iii. the proposed controller design for the trms model, the motion of the system can be described in terms of main and tail rotors as shown in (1)-(2): 2 ( ) 1 [( )cos sin ] ( )sin2 2 v y b v y v v v v v ds l s f k dt g x y z x y z ω λ φ φ λ φ = − + − − − + + (1) pr p v v v j s j ω λ = + (2) where v s is the angular momentum around the horizontal plane (in the vertical plane). b s , is the balance scale, and v v d dt φ λ= ( )cosh p b h p v h h ds l s f k dt ω φ λ= − (3) where cos h yr y v h h s j j ω φ λ + = ⇒ 2 2 cos sin cos h yr y v h v v s j p q r ω φ λ φ φ + = + + (4) where h s is the angular momentum around the vertical plane of the beam (in the horizontal plane), jpr is the moment of inertia (in the dc motor tail propeller subsystem), jyr is the moment of inertia (in the dc motor main propeller subsystem), and ωy and ωp describe the system’s velocity for nonlinear system’s output voltage. figure 3 shows the block diagram which mathematically can be expressed as: 1 ( )vv vv v yr dd d d dt t = − + ( ) y v vv p dω = (5) 1 ( )hh hh h pr dd d d dt t = − + p ω = )( hhh dp (6) where yr t and pr t are main and tail rotor propeller system time constants. engineering, technology & applied science research vol. 11, no. 1, 2021, 6626-6631 6628 www.etasr.com pathan et al.: a multivariable twin-rotor system control design fig. 3. block diagram. the pid controllers combine the advantages of the individual p, i, and d controllers. the above system structure is composed of two summing points. their function is to determine the error signal which is the difference between the set point and the measured variable. the error signal is amplified via a proportional amplifier and again by integral and derivative amplifiers. secondly, the additions of the outputs from the amplifiers are also carried out by the summing points. the three term function can be expressed as: 0 (0) t g out g g g i g g d de p k e k k e dt k k p dt = + + +∫ (7) three term controllers were connected in series and in parallel. when these three controllers were connected in parallel, the pid controller is considered to be non-interacting. in this situation, the interaction of the proportional control action with the integral and derivative control action is neglected. most of the pid controllers are available in serial or interaction configuration. due to the interaction fact, the derivative precedes the proportional controller by 90o. the pid control model is discussed in detail below. a. pid controller model the simulation model of the pid controller for the main rotor is shown in figure 4. figure 5 shows the tail rotor configuration. their parameters are given in tables i and ii respectively. fig. 4. main-rotor controller. fig. 5. tail-rotor controller. table i. main and tail rotor parameters parameter value moment of inertia 6.8e-2kgm2 torque c1 (psi) 6e -3nm torque c2 (psi) 1e -3nm static characteristics d1,c1 0.0134,0.0924 parameter kgy 0.05s/rad movement of gravity mgy 0.32nm table ii. tail rotor parameters parameters values moment of inertia 2e-2kgm2 torque c1 (psi) 1e -1nm torque c2 (psi) 1e -3nm static characteristics d2,c2 0.01,0.09 fig. 6. simulation model for pitch and yaw rotor trms system with pid controllers. engineering, technology & applied science research vol. 11, no. 1, 2021, 6626-6631 6629 www.etasr.com pathan et al.: a multivariable twin-rotor system control design b. trms model the simulation model of the trms with overall connections and control methodology is given in figure6. iv. simulation results and discussion the simulation results for the pitch rotor pid controller with kg, kd and ki being the proportional, derivative and integral parameters having values 09, 09, 07 respectively are given in figure 7. the simulation results for yaw rotor pid controller with kg, kd, and ki having values 02, 10, 02 respectively are given in figure 8. fig. 7. pitch pid controller simulation. fig. 8. yaw pid controller simulation. the plots of tail and main rotor are given in figures 9 and 10 respectively. figure 9 shows the desired and actual yaw angle in the time interval 0-100s. the designed behavior of the yaw angle for the trms versus time is presented with different line patterns for desired and actual position. it can be seen that there is no major difference. figure 10 shows the desired and actual pitch angle during the time interval 0-100s. the designed behavior of the yaw angle for the trms versus time is presented with different line patterns for the desired and actual positions. again, the pattern lines are almost the same. fig. 9. yaw rotor responses. fig. 10. pitch rotor responses. fig. 11. simulation results of yaw and pitch rotors with pid controller. engineering, technology & applied science research vol. 11, no. 1, 2021, 6626-6631 6630 www.etasr.com pathan et al.: a multivariable twin-rotor system control design figures 11 and 12 show the response of the trms system. the plot between angle in radians and during 0-100s describes the behavior of the pitch angle response. in both figures, the plot shows that the desired and the actual results do not have much difference. so, the controller results are considered satisfactory. fig. 12. real time results of yaw and pitch rotors with pid controller. v. conclusion this paper presents a mimo pid controller designed for a twin rotor system. a non-linear system based design with two inputs and outputs accurately tracks the errors. the performance indices of the simulation results are satisfying and the design simplicity of the control is a major advantage. both 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[22] x. yang, j. cui, d. lao, d. li, and j. chen, "input shaping enhanced active disturbance rejection control for a twin rotor multi-input multioutput system (trms)," isa transactions, vol. 62, pp. 287–298, may 2016, https://doi.org/10.1016/j.isatra.2016.02.001. engineering, technology & applied science research vol. 8, no. 2, 2018, 2809-2813 2809 www.etasr.com ebrahim et al.: a performance comparative analysis of block based compressive sensing and line … a performance comparative analysis of block based compressive sensing and line based compressive sensing mansoor ebrahim department of computer science iqra university karachi, pakistan mebrahim@iqra.edu.pk syed hasan adil department of computer science iqra university karachi, pakistan hasan.adil@iqra.edu.pk daniyal nawaz department of computer science iqra university karachi, pakistan daniyal.nawaz@iqra.edu.pk abstract—compressive sensing (cs) is an innovative idea that has opened new areas for viable communication of correlated data. in this paper, a comparative performance analysis of two different variants of compressive sensing i.e. block based compressive sensing (bcs) and line based compressive censing (lcs) schemes is performed for natural images. the idea is to evaluate which variant performs better in terms of reconstruction quality and provides easy initial solution. the experimental analysis demonstrates that lcs scheme can enhance the image reconstruction at lower subrates by 0.5 db to 2.5 db, when compared to the bcs scheme. keywords-compressive sensing; block based approach; line based approach; reconstruction; image i. introduction compressive sensing (cs) is one of the latest techniques that have achieved popularity recently and is applied to various imaging applications [1], such as magnetic resonance imaging (mri) [2, 3] and seismic identification [4]. cs [5, 6] idea is to express a signal (image/video) with sample estimation rate much lower than that of the nyquist rate which is essential for the recovery of the signal. one of the innovative of this is the single-pixel camera [1] that openly condenses the sampling and amount of data that will be transmitted, but increases the difficulty of recovering the original signal. in other words, the recovery of the original signal from small number of sample measurements is difficult. numerous earlier researches have already examined the utilization of cs in image compression [3-8]. many researchers concentrated their work on proposing how natural images can be compressed utilizing cs and the recovery of the encoded signal (image) from such little estimation. in cs we concentrate mostly towards discrete signs instead of constant time space signals. in addition, compressive sensing of natural images is exposed to few issues such as computationally complex reconstruction algorithm and requirement of large memory to store the random sampling operator φ. in order to encounter the aforementioned issue different approaches were developed i.e. block based compressive sensing and line based compressive sensing. the block-based approach is far more developed and widely employed as compared to the newly developed line based approach to reduce of the computationally complexity of cs scheme [9-14]. such methodologies value cs because (i) block/line based estimation is more convenient for applications where the sample image data don't need to be encoded completely in a block/line form until the point when the estimation of the whole image is completed, (ii) the application and capacity of the estimation operator are straightforward, (iii) the individual handling of each block/line of image data brings about simple initial solution with considerably quick and better recovery process. in this paper, a performance comparison of two different variants of compressive sensing i.e. block based compressive sensing and line based compressive sensing for images is performed. the purpose is to find out which variant works best to solve the issues related to cs. the variants are evaluated based on computational complexity and reconstruction quality at various subrates for different test image datasets. in addition, block based and line based approaches are also compared at various block/line sizes to validate the effectiveness of each scheme. the paper is structured as follows. the fundamentals of the cs along with block based and line based approaches are presented in section ii. section iii presents and discusses the simulation results. section iv concludes the paper. ii. theory of compressive sensing the cs theory [5] states that a sparse (original or some transform domain) signal can be completely recovered from a number of samples below than that stated by the nyquist theorem. the cs scheme efficiently eases the computational prerequisites, for example, memory, processing power, and transmission data transfer capacity at the encoder by relating signal acquirement and dimensionality reduction into a distinct stage. cs is effective in two circumstances. when direct measurements of a high-resolution signal are hard to attain and when multiple high-resolution signals are complex to encode. in literature, cs is a standard and isn’t stated for any particular signal other than underlying sparsity assumptions. cs permits great prospect of signal reconstruction by utilizing least amount of unsystematic measurements, as long as the signal/image is spa sch me red me tra as fig me vec ma ma est x= by com can the cs sim sig sam iss ma a. the red div sep con sam enc ma app bri pri rec pro engineerin www.etasr arse and inc hemes, in c easurements r ducing the com consider a easurementsis ansformation d shown in figu y=φ·x g. 1. compres asurement matrix x∈rn and y ctor respectiv atrix φ is orth atrix. in addi timation is no =φ-1 y is ill-po cs ought to mpleted by ta n be expressedx argmin however, mo eoretical and a s requires a multaneously gnals difficult mpled signals sue, various res ainly 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34.6 2.23 2.5 0.25 0.3 30.89 32.0 33.16 34.5 2.27 2.4 ower subrates, e adequate to c image dataset ure variations f the reconstru ned from bcs 2. it can be no prove the disto d using the ng the empha that reconstru ements looks m struction of opoly image usin ine … ncode 3 69 87 8 3 89 03 4 3 1 57 47 3 66 98 2 3 07 65 8 3 07 51 44 , it is create ts are . the ucted s and oticed orting bcs asized uction much bcs g bcs fig bc blo sen and app 1d [1] [2] [3] [4] [5] [6] [7] [8] [9] [10 [11 [12 [13 engineerin www.etasr g. 9. visual re cs and lcs encod this article ock based com nsing for diffe d sizes. the e proach perfor db to 3db at va m. f. duarte, kelly, r. g. sampling”, iee 2008 m. lustig, d. sensing mri” 72-82, 2008 m. lustig, d. l compressed se medicine, vol w. tang, j. m seismic data r d. l. dono information th e. j. candes, m ieee signal pr a. chambolle minimization a no. 2, pp. 167m. a. t. figue sparse reconst inverse probl processing, vo l. gan, “bl international c 403–406, july 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agedb/dbroot/ster hihewa, “distribu international con w), melbourne, a 2813 sensing and li ge block compr isual sensor netw communication 5 “total variation ents”, in: handbo ger, pp. 17-31, 20 d compressive s ld, 2017 ion regularization mpressive sensing sing tasks: applic sity, usa, 2013 bined depth and r society confere york, usa, pp. ereo depth maps nference on com a, vol. 1, pp. 19 anuary 12, 2014 reo_image uted video coding nference on multi australia, pp. 32 ine … ressive work”, ns, and image ook of 005 ensing n with g, msc ations, outlier nce on 2394using mputer 95-202, , from g based imedia 25-330, engineering, technology & applied science research vol. 8, no. 1, 2018, 2452-2458 2452 www.etasr.com nouaiti et al.: experimental implementation of a low-cost single phase five-level inverter for … experimental implementation of a low-cost single phase five-level inverter for autonomous pv system applications without batteries ayoub nouaiti abdallah saad abdelouahed mesbahi mohamed khafallah laboratory of energy and electrical systems (lese) superior national school of electricity and mechanical (ensem) university of hassan ii casablanca casablanca, morocco laboratory of energy and electrical systems (lese) superior national school of electricity and mechanical (ensem) university of hassan ii casablanca casablanca, morocco laboratory of energy and electrical systems (lese) superior national school of electricity and mechanical (ensem) university of hassan ii casablanca casablanca, morocco laboratory of energy and electrical systems (lese) superior national school of electricity and mechanical (ensem) university of hassan ii casablanca casablanca, morocco abstract—this paper presents the design and the implementation of a low-cost single phase five-level inverter for photovoltaic applications. the proposed multilevel inverter is composed of a simple boost converter, a switched-capacitor converter, and an h-bridge converter. an efficient control method which associates a closed-loop regulation method with a simple maximum power point tracking (mppt) method is applied in order to allow the proposed multilevel inverter to transfer power energy from solar panels to autonomous load with no storage batteries. an experimental prototype of this inverter is fabricated at the laboratory and tested with a digital control system. obtained results confirm the simplicity and the performance of the proposed photovoltaic system. keywords-multilevel inverter; boost converter; switched capacitor converter; mppt; pv i. introduction power inverters are mostly used in photovoltaic systems to convert the dc power energy from solar panels to an ac form while respecting the standard criteria for voltage, frequency, and total harmonic distortion (thd). classical power inverters structures present many problems such as high switching losses, high level of thd, output filters with high sizes [1]. multilevel inverters present many advantages compared to classical ones [2]. classical multilevel inverters are systematized in three categories: flying capacitor, neutral point clamped inverter, and cascaded h-bridge inverter [3]. several structures of multilevel inverters can be deduced from these categories by using, hybrid, symmetric, and asymmetric adjustment [4]. from hybrid adjustment, an important structure is derived: the switched-capacitor converter (scc) used in two ways: either as a step-up converter or as a multilevel converter tied with classical inverters to get multi-level ac waveforms [5]. non-isolated dc-dc converters such as classical boost converters (bc) are frequently used between solar panels and multilevel converters structures for low and medium powerlevels applications in order to increase the used dc-bus voltage. these converters are chosen for their simplicity, low manufacturing cost, and low weight [6]. this paper presents the design and experimental test of a simple single phase five-level inverter for photovoltaic (pv) system applications. an efficient control method which incorporates an mppt method with a closed-loop regulation method is used. the key part of this inverter is the scc which is used to tie a bc with a classical h-bridge converter (hbc). by utilizing this structure, the duty cycle of the control signal of the bc will be smaller, thus reducing the switching losses across its power switch, the total number of power switches with their gate-drivers power supply is reduced compared to conventional multilevel inverters. the proposed inverter is tested experimentally under industrial values of voltage and frequency by feeding power energy from solar panels to a 130w single phase induction motor driving a water pump. ii. description of the proposed multilevel inverter the topology of the proposed pv multilevel inverter is shown in figure 1. it’s composed of a single dc voltage source from solar panels (vpv), a dc-dc bc circuit, a dc-ac fivelevel converter (flc) circuit, and an ac single-phase load. fig. 1. topology of the pv multilevel inverter. engineering, technology & applied science research vol. 8, no. 1, 2018, 2452-2458 2453 www.etasr.com nouaiti et al.: experimental implementation of a low-cost single phase five-level inverter for … a. dc-dc boost converter circuit the bc is used to increase the input voltage vpv to a specified output voltage vb by controlling the switch sa with a pwm signal [6]. the expression of the output voltage vb from this converter is: )d1( vpv vb   (1) where d is the duty cycle of the pwm signal. b. dc-ac five-level converter circuit the proposed dc-ac flc circuit is composed of an scc tied with an hbc. the scc is used to deliver an output voltage (vdc-bus) two times greater than the input voltage vb (from the bc) by controlling the power switches sb and sc with complementary pulses [5, 7], while the hbc is used to convert the generated dc-bus voltage to an ac voltage. the scc operates in two modes:  charge mode: the switch sb is on; the switch sc is off. the diode d2 is forward biased. in this mode, the capacitor cs is charged by vb. the expression of the dc-bus voltage is: vb=vcs=bus-vdc (2)  discharge mode: the switch sc is on; the switch sb is off. the diode d2 is reversely biased. in this mode, the capacitor cs is discharged. by considering the value of vcs from (2), the new expression of the dcbus voltage is: 2vb=vcs+vb=bus-vdc (3) table i resumes the switching states of the power switches of the dc-ac flc circuit. table i. switching states of the power switches switching states vac q1 q2 q3 q4 sb sc on off on off off on +2vb on off on off on off +vb off on on off off off 0 on off off on off off 0 off on off on on off -vb off on off on off on -2vb the scc has two important aspects in the proposed inverter. the first aspect is to tie the used bc with the hbc by using a small duty cycle (d), while the second is to deliver a special dc-bus voltage to the hbc in order to get output ac voltage with five-levels, because if the inverter is composed just of a bc and an hbc which is the classical topology. the bc will operate with high duty cycle, and the hbc will deliver just an output ac voltage with two or three levels. in order to obtain the gate pulses of the power switches used in the dcac flc circuit by considering the switching states shown in table i, a simple modulation technique (pwm) is applied (figure 2). it consists of comparing a reference rectified sinusoidal signal (ref) with frequency of 50hz with two identical high-frequency triangular carrier signals (carr1 and carr2) [8]. fig. 2. used pwm method with the gate pulses, and generated output ac voltage. by adjusting the modulation index (mi) (4) of the used pwm method, the rms value of the output ac voltage is controlled. ac2 am mi  (4) where ac and am are respectively the amplitude of the carrier signals and the reference signal. iii. control method for autonomous pv system application without batteries in pv systems, mppt methods are used to extract maximum power energy available across solar panels under all climatic conditions. in this paper, the used mppt method is perturb and observe (p&o) [9], the flowchart of which is shown in figure 3. simplicity and easy implementation are important advantages of this method. in the case of autonomous pv system application with no storage batteries, the application of the chosen mppt method on the bc circuit will allow the studied system to deliver maximum power energy to the loads. however, the output voltage of the bc will change depending on the climatic conditions. in order to fix a nominal voltage that the bc never exceeds, a closed loop regulation control system will be added with the mppt method. figure 4 shows the flowchart of the proposed control method, and figure 5 shows its application with the studied inverter. bc is controlled to deliver an output voltage vb which will never exceed a limit (vb-ref), and the dc-ac flc is controlled with a fixed mi. as a result, the rms value of the output ac voltage will also never exceed a limit. engineering, technology & applied science research vol. 8, no. 1, 2018, 2452-2458 2454 www.etasr.com nouaiti et al.: experimental implementation of a low-cost single phase five-level inverter for … fig. 3. flowchart of the “p&o” method fig. 4. flowchart of the proposed control strategy. fig. 5. the proposed control strategy with the studied pv system. in order to interpret the operation of the pv system with the proposed control method, the autonomous ac load is selected to utilize specific power energy (pn) under an ac voltage with a specific rms value when the output voltage of the bc is equal to vb-ref. regulation mode: when maximum power energy across solar panels (pmax) is higher than pn, the pv system starts working with the mppt until the voltage vb is greater than or equal to vb-ref, at this time, the control method switches from the mppt mode to the regulation mode, as shown in figure 4. in this case, the bc is controlled with the signal am2, this signal is generated with the help of two pi regulators: the first pi regulator minimizes the error between the sensed voltage vb and vb-ref, and the second pi minimizes the error between the generated reference current ipv-ref from the first pi and the sensed current ipv, as shown in figure 5 [10]. mppt mode: when pmax is lower than pn, the voltage vb will never overtake vb-ref; the bc is controlled with the signal am1, this signal is generated by a pi regulator that minimizes the error between vmpp-ref from the mppt block and vpv, as shown in figure 5 [11]. another act of this pi regulator is to make the response faster of the mppt block to any sudden and quick variation of climatic conditions. from the descriptions above, the selected signal (am1 or am2) will be compared to a high-frequency triangular signal in order to deliver the pwm signal with the appropriate duty cycle for the bc, as shown in figure 5. iv. experimental results the proposed multilevel inverter is designed and fabricated at the laboratory for a rated power of 250w, as shown in figure 6. two microcontrollers are used as digital control system. the first one is used to control the bc, and the second one is used to control the dc-ac flc. two voltage sensors are used for measuring vpv and vb. two current sensors are used for measuring ipv and the output current of the bc. the power switches sa, sb, q2, and q3 have a common source with the ground of the input dc voltage (figure 1). a common power supply for the gate-drivers is used. table ii resumes values of the used components with their costs. in order to test the robustness of the proposed control method implemented on the microcontrollers, the mppt method and the regulation method are tested separately before using them in one program. the regulation method (figure 5) is implemented on the microcontroller n° 1 using two digital pi regulators. vb-ref is set to 168v. figure 7 shows the used test bench. a digital oscilloscope (do) is used to record the experimental results, it contains two channel for measuring (ch1 and ch4). fig. 6. fabricated prototype of the photovoltaic multilevel inverter. engineering, technology & applied science research vol. 8, no. 1, 2018, 2452-2458 2455 www.etasr.com nouaiti et al.: experimental implementation of a low-cost single phase five-level inverter for … table ii. costs of components components no. of items parameters (250w) costs (€) (250w) switch sa 1 spw47n60c3 3.713 (with gate driver) switches(sb, sc, q1, q2, q3, and q4) 6 stp10nc50 6*2.938 (with gate drivers) inductor l 1 6mh 24.00 capacitors (cb and cs) 2 750uf/450v 2*4.60 diodes (d1 and d2) 2 byt12p 2*1.59 fig. 7. the test bench used to validate the regulation program. a. validation of the regulation method two tests are used to validate the regulation method program. test1: the load is constant with a rated power of 80w and the input voltage (vin) is variable. figure 8 and 9 show the regulated output voltage vb with the variation of the input voltage from 63v to 33v and from 33v to 63v respectively. test2: the input voltage vin is fixed at 63v and the load is variable (the rated power changes between 50w and 170w). figures 10 and 11 show the regulated output voltage vb with the variation of the output current from 0.25a to 1a and from 1a to 0.25a respectively. from test1 and test 2, the output voltage vb is regulated at 168v despite the variation of the input voltage and the load proving the robustness of the implemented digital regulation program. fig. 8. regulated output voltage vb (ch1) and input voltage (ch4) fig. 9. regulated output voltage vb (ch1) and input voltage (ch4) fig. 10. regulated output voltage vb (ch1) and output current (ch4) fig. 11. regulated output voltage vb (ch1) and output current (ch4) fig. 12. the test bench used to validate the mppt program. engineering, technology & applied science research vol. 8, no. 1, 2018, 2452-2458 2456 www.etasr.com nouaiti et al.: experimental implementation of a low-cost single phase five-level inverter for … fig. 13. regulated voltage vin (ch1) and input current iin (ch4). b. mppt validation the mppt method shown in figure 5 is implemented on the microcontroller n° 1 using a digital pi regulator. the load is constant with a rated power of 200w. the objective of this test is to stabilize the input voltage from a variable dc source at a chosen vmpp-ref (59v) and extract the maximum current (3a). figure 12 shows the used test bench, and figure 13 shows the obtained input voltage vin with the delivered maximum current. the mppt program stabilizes the input voltage from 63v to 59v fast, and the input current oscillates around the maximum value (3a) prooving proves the robustness of the implemented digital mppt program. c. mppt and regulation validation the mppt and the regulation method are implemented in one program inside the microcontroller n° 1 using the condition shown in figure 4. figure 14 shows the used test bench. fig. 14. the test bench used to validate the mppt program with the regulation program. in this test, two cases are discussed: case1 (regulation mode): the maximum power energy from the variable dc source (pmax-dc) under 59v (vmppref) is 177w for this; the system is tested with a 130w rated power (pn) load. vb-ref is set to 168v. figure 15 shows the values of the output voltage vb stored in microsoft excel in real time using plx-daq software, and figure 16 shows the variation of the output voltage vb and the variation of the input voltage vin in the do. fig. 15. recorded output voltage vb. fig. 16. output voltage vb (ch1) and input voltage vin (ch4). from figures 15 and 16, the system starts with mppt program. input voltage is equal to vmpp-ref (59v) and the voltage vb increases. when the voltage vb is equal to 168v (vb-ref) the program switches from mppt to regulation mode. the voltage vb is regulated at 168v and the input voltage changes to 63v. case2 (mppt mode): the system is tested firstly with a load where its rated power pn is 130w, which means that the voltage vb will take the same values as seen in case1. after some time, the rated power pn is changed suddenly to 200w. figure 17 shows the variation of the output voltage vb and the variation of the input voltage vin under this test. from figure 17, when pn changes from 130w to 200w, the voltage vb decreases, the program switches from regulation mode to mppt mode and the input voltage changes from 63v to 59v (vmpp-ref). in this case, the voltage vb increases again but never exceeds vb-ref (168v) because pn is greater than pmax-dc. fig. 17. output voltage vb (ch1) and input voltage vin (ch4). engineering, technology & applied science research vol. 8, no. 1, 2018, 2452-2458 2457 www.etasr.com nouaiti et al.: experimental implementation of a low-cost single phase five-level inverter for … d. full pv system test the full pv system (figure 5) is tested with a 130w single phase induction motor driving a water pump. two solar panels (240wp for each one) are used as a dc source for the pv system (figure 18). the pwm method of the dc-ac flc is programmed inside the microcontroller n° 2 with a fixed mi of 0.92 and a switching frequency of 2 khz (frequency of carr signals), the output frequency is set to 50hz, and the vb-ref of the bc is fixed to 168v. from these parameters, the rms value of the output ac voltage will be limited to 220v. the full pv system is tested under optimal climatic conditions. the system starts with mppt program and when the voltage vb reaches vb-ref, the control system switches to regulation mode. obtained voltage vb is similar to the results presented in figures 15-16. figure 19 resumes all results obtained when the motor is running under regulation mode. from these results the scc delivers a dc-bus voltage which begins from 168v and ends at 336v repeated at each half period (0.01s), the output ac voltage has a shape with five levels obtained by converting the staircase waveform of the dc-bus voltage to an alternative form with the hbc, the rms value of this ac voltage is 220v (50hz), the output ac current is sinusoidal without using filters, and its rms value is 1.22a, the fft spectrum shows that the even harmonics are absent, the first important odd harmonics (3rd and 5th) are very low and the other odd harmonics are moved to the high frequency. the implemented digital control method provides the possibility to benefit from both mppt and regulation advantages because the use of mppt method alone without batteries the problem of overvoltage can happen at the output terminal of the bc when pmax from solar panels becomes greater than pn of the load. also, the use of regulation method alone will pose the problem of over-currents from solar panels which can reach the shortcircuit values (isc) when pmax becomes less than pn. fig. 18. the two solar panels installed at the laboratory roof with the full pv system. v. conclusion an experimental test of a low-cost single phase five-level inverter for pv system applications was presented. a switched capacitor converter is used in this photovoltaic inverter to tie a classical boost converter with an h-bridge converter in order to use a small duty cycle for high voltage applications, and also to ameliorate the output ac voltage waveform to get five levels. the thd of the output ac waveforms is very low without using filters. the proposed control method is used to extract maximum power energy from solar panels and regulate voltage and current without using batteries. the proposed pv system was tested with industrial values of voltage and frequency (220v, 50hz). this multilevel inverter is able to supply power energy from solar panels to the industrial machines such as induction motors used in pv pumping systems. the future scope of this work is to increase the rated power of this photovoltaic multilevel inverter (1kw) and to use a dsp card as a digital control system. fig. 19. (a) dc-bus voltage; (b) output ac voltage (ch1) and output ac curent (ch4); (c) the fft spectrum of the output ac voltage (ch1) and output ac current (ch4) ; (d) zoom of the fft spectrum of the output ac voltage (ch1) and output ac current (ch4) . engineering, technology & applied science research vol. 8, no. 1, 2018, 2452-2458 2458 www.etasr.com nouaiti et al.: experimental implementation of a low-cost single phase five-level inverter for … references [1] u. b. tayab, m. a. al humayun, “modeling and analysis of a cascaded battery-boost multilevel inverter using different switching angle arrangement techniques”, engineering, technology & applied science research, vol. 7, no. 2, pp. 1450–1454, 2017 [2] a. nouaiti, a. saad, a. mesbahi, m. khafallah, m. reddak, “single phase seven-level inverter for pv solar pumping system”, international renewable and sustainable energy conference, pp. 474–478, 2016 [3] k. k. gupta, a. ranjan, p. bhatnagar, l. k. sahu, s. jain, “multilevel inverter topologies with reduced device count: a review”, ieee transactions on power electronics, vol. 31, no. 1, pp. 135–151, 2016 [4] n. prabaharan, k. palanisamy, “a comprehensive review on reduced switch multilevel inverter topologies, modulation techniques and applications”, renewable and sustainable energy reviews, vol. 76, pp. 1248–1282, 2017 [5] r. barzegarkhoo, h. m. kojabadi, e. zamiry, n. vosoughi, l. chang, “generalized structure for a single phase switched-capacitor multilevel inverter using a new multiple dc link producer with reduced number of switches”, ieee transactions on power electronics, vol. 31, no. 8, pp. 5604–5617, 2016 [6] m. forouzesh, y. p. siwakoti, s. a. gorji, f. blaabjerg, b. lehman, “step-up dc-dc converters: a comprehensive review of voltageboosting techniques, topologies, and applications”, ieee transactions on power electronics, vol. 32, no. 12, pp. 9143–9178, 2017 [7] a. nouaiti, a. saad, a. mesbahi, m. khafallah, “implementation of a single phase switched-capacitor nine-level inverter for pv system applications with selective harmonic elimination”, international journal of computer applications, vol. 168, no. 7, pp. 9–15, 2017 [8] m. a. sayed, m. ahmed, m. g. elsheikh, m. orabi, “pwm control techniques for single-phase multilevel inverter based controlled dc cells”, journal of power electronics, vol. 16, no. 2, pp. 498-511, 2016 [9] n. karami, n. moubayed, r. outbib, “general review and classification of different mppt techniques”, renewable and sustainable energy reviews, vol. 68, pp. 1–18, 2017 [10] o. ellabban, o. hegazy, j. v. mierlo, p. lataire, “dual loop digital control design and implementation of a dsp based high power boost converter in fuel cell electric vehicle”, 12th international conference on optimization of electrical and electronic equipment, 2010, pp. 610– 617, 2010 [11] l. qin, s. xie, c. yang, m. hu, s. luo, “design method of input voltage robust pi controller for pv interface converter”, international conference on renewable power generation, pp. 1–6, 2015 engineering, technology & applied science research vol. 8, no. 4, 2018, 3135-3140 3135 www.etasr.com ahmad et al.: statistical modeling via bootstrapping and weighted techniques based on variances statistical modeling via bootstrapping and weighted techniques based on variances an oral health case study w. m. a. w. ahmad school of dental sciences universiti sains malaysia malaysia wmamir@usm.my n. a. aleng school of informatics and applied mathematics, universiti malaysia terengganu, malaysia azlida_aleng@umt.edu.my z. ali school of mathematical sciences universiti sains malaysia malaysia zalila_ali@usm.my m. s. m. ibrahim school of dental sciences universiti sains malaysia malaysia shafiqmat786@gmail.com abstract—multiple logistic regression is a methodology of handling dependent variables with a binary outcome. this method is becoming increasingly widespread as a statistical technique that represents a discrete probability model. many studies have focused on the application but less on the methodology building. this study aims to provide an applied method for multiple logistic regression which is called modified bayesian logistic regression modeling as an alternative technique for logistic regression analysis that focuses on a combination of the bootstrap method using sas macro and weighted techniques based on variances using sas algorithm. data on oral cancer were applied to illustrate a real scenario of oral health data. this data will be applied to the multiple logistic regression algorithm and modified bayesian logistic regression. results from both cases are strongly supported by clinical studies. through the proposed algorithm, the researcher will have an option whether to analyze the data with the usual or an alternative method. final results indicate that the modified procedure can provide more efficient results especially for the case which involves statistical inferences. keywords-multiple logistic regression; bootstrap; bayesian and weighted techniques i. introduction the logistic regression, analyzes the relationship between multiple independent variables and categorical dependent variables [1]. the multiple logistic response functions is exp( ) 1 exp( ) xe y x           β β where x β β x β x 0 1 1 p-1 p-1     β  x β β x β x 0 1 i1 p-1 i, p-1     β  β 111 xxβ i112 x xβ p 1 i,p 1p 1                                        β x x i  p 1p 1 p 1 the multiple logistic regression models can, therefore, be stated as follows: yi are independent bernoulli random variables with expected values e{yi}=πi where:   exp( ) 1 exp( ) xie yi i xi     β β  . the x observations are considered to be constants. alternatively, if the x variables are random  ie y is viewed as a conditional mean, given the values of xi1+xi2+…+xi,p-1. a. bootstrapping, weighted techniques and bayesian approach with sas authors in [2] introduced the bootstrap method which emphasizes on an empirical density function (edf). the basic concept of bootstrap is that it is initiated with an original sample which is taken from the studied population. the second step is to copy the original sample a number of times in order to create a pseudo-population. then, it draws several samples considering random sampling approach thus providing a new comprehensive sample from the original sample. it stores the new set of data from the original dataset and creates a new distribution for further analysis [2, 3]. the bayesian analysis involves the posterior distribution. in the stage of bayesian estimation procedures, the posterior distribution will play an important role especially in statistical inferential. while running the analysis the summary statistics for the posterior distribution samples are produced by default. the sas statements of outpost provide an option that saves the samples in the sas data set for further processing. proc genmod procedure fits generalized linear models with bayesian methods (considering bayesian estimation procedures) with a normal error term [4]. in sas programming procedure, the seed option is to maintain reproducibility. by default, the uniform prior is a flat prior with a distribution that reflects ignorance of the location of the parameter. its placing an equal likelihood for all possible values which regression coefficients can take. proc genmod also produces convergence diagnostics where ods graphics is enabled in sas statements which provides a section of assessing markov chain convergence diagnostics and their interpretation [5]. engineering, technology & applied science research vol. 8, no. 4, 2018, 3135-3140 3136 www.etasr.com ahmad et al.: statistical modeling via bootstrapping and weighted techniques based on variances weighting is a very important technique which involves adjusting data to reflect dissimilarities in the number of population units that represent each respondent [6]. there are several techniques that can be used as a weighted method like weighted by mean, standard deviation or variances to apply to the model according to the sample population of interest. moreover, a weighted technique allows assigning different weights to the different cases in data analysis. the aim of the weighted method is to correct the skewness and to make the sample more representative of a true population. ii. methodology: algorithm building and results we used secondary oral medical data which involved 23 oral cancer patients from universiti sains malaysia (usm). the selected variables are nerve invasion (nerv_inv), gender (gen), betel quid (bet), tumour site (tum_site) and tumour size (tum_size). to explore the underlying association between nerve invasion and the selected explanatory variables, a set of the regression model is fitted in this section. let us define the following dichotomous variables for the model: yij=0 has not nerve invasion and yij=1 has nerve invasion. the proposed model is given in equation form as follows:         ..... β β gender β betel quid 0 1 2 β tumour site β tumour size εij43        b x ij (1) then the logistic regression model for (1) is given as:                   ˆp 1 | exp( ) 1 exp( ) i i 0 1 2 3 4 0 1 2 3 4 y x β β gender β betel quid β tumour site β tumour size β β gender β betel quid β tumour site β tumour size                             1 1 exp β β gender β betel quid0 1 2 β tumour site3 β tumour size4                                then we obtain (2) as follows:           1 ˆp 1 | 1 exp β β gender0 1 β betel quid2 y xi i β tumour site3 β tumour size4                                          (2) the estimated model for our case is given in (2). before we apply the equation there are two main steps needed to be done which are bootstrapping and weight data. a. multiple logistic regression modeling on nerve invasion  cancer cell data should be entered as follows in sas algorithm to calculate the multiple logistic regressions.. data cancer; input nerv_inv gen bet tum_site tum_size ; datalines; 0 0 0 1 1 0 1 0 2 0 0 1 0 2 0 0 1 0 2 0 0 1 0 3 0 0 1 0 2 0 0 1 0 3 0 0 0 0 2 0 1 0 1 1 1 0 0 0 4 0 0 0 1 1 1 1 0 1 3 1 0 0 1 4 0 0 0 1 1 0 0 0 1 1 1 0 0 0 2 0 0 1 0 4 0 0 0 0 2 0 0 1 0 2 0 0 1 0 2 0 1 0 1 2 0 1 1 0 2 0 1 0 0 4 0 ; run; ods rtf file='abc.rtf' style=journal;  run the analysis using multiple logistic regression. below is the syntax of multiple logistic regression. /* run the logistic regression through proc logistic*/ ods graphics on; proc logistic descending data=cancer; model nerv_inv(event='1') = gen bet tum_site tum_size / rsquare expb lackfit; roc 'gen bet tum_site tum_size ' gen bet tum_site tum_size ; run; ods graphics off; ods rtf close; b. results: using multiple logistic regression modeling on nerve invasion in figure 1 and table i the results of using the above syntax are shown. none of the variables in the list is significant. the area under the roc curve is 0.70556. the model can accurately discriminate 71.0% of the cases (it significantly discriminates more than half of the cases). c. modified multiple bayesian logistic regression on nerve invasion  adding bootstrapping to the calculation. the following syntax calculates the data using a bootstrap method and prints them out: %macro bootstrap (data=_last_, booted=booted, boots=4, seed=1234); data &booted; pickobs = int(ranuni(&seed)*n)+1; /* this procedure is randomly select an integer from 1 to n*/ tel bse loo ob  engineerin www.etasr set &data po ls sas to re ervation in & op through the replicate=int /* and saves i+1; if i > n*& b /* this proc servation have run; %mend boot ta parameter intercept gen bet tum_site tum_size logistic regr data cancer; input nerv_i datalines; 0 0 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0 1 0 0 0 1 0 1 0 0 0 0 0 1 1 0 1 0 0 1 0 0 1 0 0 1 0 0 0 ng, technology r.com oint = pickobs ad value pick data, when th e data step fore t(i/n)+1; number of cur boots then stop edure stop wi e been created tstrap; fig. 1. able i. ma estimate -3.2222 -0.1454 0.9728 0.5295 1.2608 ression using b nv gen bet tu 0 1 1 0 2 0 0 2 0 0 2 0 0 3 0 0 2 0 1 3 0 0 2 0 1 1 1 0 4 0 1 1 1 1 3 1 1 4 0 1 1 0 1 1 1 0 2 0 y & applied sci ahma nobs = n; /*t kobs, nobs se he point optio ever*/ rrent bootstrap p; ill leave data d*/ roc curve aximum likehood standard er 2.1179 1.5915 1.4332 0.5908 1.6022 hosmer and l bootstrap and w um_site tum_ ience research ad et al.: statist this procedure ets n to numb on is used sa p*/ set when n*& d estimates rror pr>ch 0.128 0.927 0.497 0.370 0.431 lemeshow goodness-o chi-square pr>chisq weighted samp _size ; v tical modeling v e point ber of s will &boots hisq 82 72 73 01 14 of-fit test 4.6580 q 0.4590 ple.    dist      vol. 8, no. 4, 20 via bootstrappi 0 1 0 0 0 0 0 1 0 0 1 0 1 0 1 1 1 0 1 0 0 ; run; ods rtf file='ab the syntax fo % bootstrap(d run; the syntax fo proc print dat run; the syntax fo residuals proc genmod class nerv_in model nerv t=binomial lin output out=ps run; compute the data data_ner set pseudo_da absresid=abs( sqresid=residu run a regress variables to g proc genmod model absresi output out=da run; compute the data data_ner set data_nerve varians_weigh label varians_ do the weigh estimated var proc genmod weight varian model nerv_i dist=binomial link=logit; run; ods graphics o run the logis logistic. proc logistic d plots= effect p weight varian model nerv_i 018, 3135-3140 ing and weight 0 4 0 0 2 0 0 2 0 0 2 0 2 0 0 2 0 0 4 0 bc.rtf' style=jo or generating a data= cancer, b or bootstrappin ta=booted; or logistic reg data= booted nv; v_inv = gen nk=logit; seudo_data re absolute and s rve_invasion1; ata; (residual); ual**2; sion with the ab et the estimate data=data_ner id = gen bet t ata_nerve_inva weights using rve_invasion; e_invasion; ht=1/varians_h _weight = "we hted least squ iances data=data_ne ns_weight; inv = gen bet l on; tic regression descending da plots= roc(id= ns_weight; inv(event='1') 0 ted techniques ournal; a bootstrap sam boots=4); ng data printing gression and b descending; n bet tum_ eschi=residual; squared residu ; absolute residu ed standard de rve_invasion1 tum_site tum asion p=varian g the estimated hat; eights using sq ares using the erve_invasion; t tum_site tum with weighted ata=data_nerve =prob); = gen bet tu 3137 based on vari mple g bootstrap to ge _site tum_si ; uals uals vs. indepen eviation ; m_size; ns_hat; d variances quared residual e weights from ; m_size / d data through e_invasion um_site iances et the ize / ndent ls"; m the h proc  d. th sig suf con tra exa bas ma exa hig engineerin www.etasr tum_size / r roc 'gen bet tum_size ; run; run the logis genmod. proc genmod weight varian model nerv_ dist=binomia link=logit; bayes nbi=10 out=posterior run; ods graphics ods rtf close; results: mod on nerve inv the area und he model can gnificantly disc table i parameter intercept gen bet tum_site tum_size a converged fficiently acc nvergence by ace plot for e amination), no sed on conver arkov chain h amination of gh-density reg ng, technology r.com square expb la tum_site tum stic regression d data=data_ne ns_weight; _inv = gen be al 000 nmc=1000 r; off; ; dified multiple vasion der the curve accurately dis criminates mo ii. maximum estimate 1.9942 1.3686 -1.6603 -0.1978 -0.3001 fig. 2. d markov cha cording to t visualization c ach variable ot just the one rgence markov has stabilized the trace plot gion of the y & applied sci ahma ackfit; m_size ' gen b n with weighte erve_invasion et tum_site tu 00 thin=2 seed e bayesian log of roc (fi scriminate 78. re than half of m likehood para standard error 1.5181 1.1029 0.9156 0.4045 1.0968 hosmer and l roc curve ain explored th the distributi can also be ex (assess conve es of interest. i v chains. figur with a good t. the sample target distribu ience research ad et al.: statist bet tum_site ed data through descending; um_size/ d=1 gistic regress gure 2) is 0.7 5% of the cas f the cases). ameter estimate r pr > chisq 0.1890 0.2146 0.0698 0.6248 0.7844 lemeshow goodness-o chi-square pr>chisq he parameter ion. besides xamined throug ergence with inference shou res 3 to 6 show d mixing by es stay close ution (conver v tical modeling v h proc sion 78556. ses (it es of-fit test 4.9294 q 0.2946 space that, gh the visual uld be w that visual to the rgence look stab e. met bay met app sign sup inv mas bete was not sign valu resu vol. 8, no. 4, 20 via bootstrappi ks good and bilized). comparison o modified mul table iii sh thods, multipl yesian logisti thod’s result pear to be mo nificant. this pported in [7] asion were fou sk zone of the el quid indepe s the same wit related to the nificant associ ue. this show ults by fixing 018, 3135-3140 ing and weight d consistent fig. 3. trac fig. 4. trace fig. 5. trac fig. 6. trac of the multiple ltiple bayesian hows the sum le logistic reg ic regression is improved. ore significant study signifi ] in which th und in male se e face. autho endently contri th our finding e dependent va iation with ner ws that the alte g the p-value 0 ted techniques in paramete ce plot for gender e plot for betel qu ce plot tumour site ce plot tumour siz e logistic reg n logistic reg mmary of the gression and . as expect gender and t at p<0.25, w icance factor he skin tumo exual orientati ors in [8-10] f ibutes to the ri gs. moreover, ariable also ap rve invasion w ernative metho and the roc 3138 based on vari ers and they r uid e ze gression with gression mode e results for modified mu ted, the mod betel quid fa which is clini on gender is rs with perin ion, in the high found that che isk of cancer w the factor whi ppears to have with non-signif od can improv c curve. figu iances y are el both ultiple dified actors ically s also neural h-risk ewing which ich is a not ficant ve the ure 7 sho (ob (ob the bu se res inf pat on tak dem suc reg reg p     ord sam the me mo pro ner eff me bet we engineerin www.etasr ows that the btained from btained from m p b t t this paper e e first of whi ilding with b cond is the ou search. in o fluencing the tients. accord factors that a king betel monstrates tw ch relationship gression we ob  p 1 | 1 exp y xi i β              and second gression:  ˆ1 | 1 exp 0.1 y xi i β0              this propose dinary multipl mple size. thi e previous one iv. d the objectiv ethod for m odification on ocedure, we c rve invasion (f fectiveness of ethods is the tter results. t eighted techn ng, technology r.com increased are multiple log modified multi parameter e intercept gender betel quid tumour site tumour size iii. co examined and ch is the met ootstrap weig utput gained a our study, th nerve invasio ding to table are related to g quid β2=-1. wo different te ps. at first, b btained the res   ˆ 0.1454 0.5295 β gen0 tumour     d, the modifie   1.3686 1978 gender tumour site  ed method can le logistic reg s method prod e. discussion an e of this resea multiple logis the programm can determine for the case of f calculation b primary focus the combined niques and y & applied sci ahma ea under curv gistic regressio iple bayesian t multiple logisti estimate st -3.2222 -0.1454 0.9728 0.5295 1.2608 onclusion focused on tw thodology bas ghted data by s a new findin he potential on among ora ii, nerve inva gender β1=1.13 6603, p<0.2 echniques that by using the sult as follows:     0.9728 1.2608 nder b r site t   ed bayesian     * 1.6603 0.3001 r bet e tum   n be alternativ gression in th duces better re nd recommen arch is to deve stics regressi ming calculati the associate f oral study). o y combining s, which lead d calculation bootstrap ap ience research ad et al.: statist e equals to 0 on) and to 0 logistic regres table iii. r ic regression tandard error 2.1179 1.5915 1.4332 0.5908 1.6022 wo main sectio sed on algorit using varian ng for the app variables w al health prob asion may dep 3686, p<0.25 25. this pa t can be used multiple logi :   betel quid tumour size    multiple logi   1 *tel quid mour size    vely applied to he case of sm sults compare ndations elop an alterna ion with so ion. through ed factors for on top of that, several statist ds to significan method betw pproach show v tical modeling v 0.7056 0.7855 ssion). the mea results compari sig. value 0.1282 0.9272 0.4973 0.3701 0.4314 chi-square 4.6580 pr > chisq 0.4590 ons, thm nces. plied were lem pend and aper d to istic 1 istic 1 o an mall d to ative ome this the the tical ntly ween wed im ii th im th a s a th vol. 8, no. 4, 20 via bootstrappi e position of asuring of the ison of the two modified mu estimate 1.9942 1.3686 -1.6603 -0.1978 -0.3001 mprovement o i. table i show he modified mprovement in fig. 7. in table ii he dependent also estimate t quare. this pr and gave better he decision 018, 3135-3140 ing and weight the roc on model and ov methods ultiple bayesian l standard 1.518 1.102 0.915 0.404 1.096 hosmer and le of the results w ws the standar calculation. n the results. comparison of i, factors whic variable show the precise od romising meth r results for th maker. ther 0 ted techniques the graph ref verall test perfo logistic regress error sig. v 1 0.18 9 0.21 6 0.06 5 0.62 8 0.78 chi-square pr > chisq emeshow goodness-of*significant at p which can be s rd calculation both tabl f roc curve of th ch are clinical w their true as dd ratio based hod lead to a s he decision ma refore, in or 3139 based on vari flects the accu ormance. sion value 890 146* 698* 248 844 e 4.9294 q 0.2946 fit test p < 0.25 seen in tables and table ii s les shown he two methods lly associated ssociation. we on the wald successful res aking especiall rder to keep iances uracy i and shows some with e can d chiearch ly for p the engineering, technology & applied science research vol. 8, no. 4, 2018, 3135-3140 3140 www.etasr.com ahmad et al.: statistical modeling via bootstrapping and weighted techniques based on variances effectiveness of the results, it is necessary to have a good way of calculation with some improvement of the proposed strategy. the approached method can have a better predicting result in future for the decision making. in this paper, the algorithms have a good potential to determine the potential factors that lead to oral cancer. some recommendations are raised in the following study findings:  there is a need to explore more on the methodology improvement in order to optimize the gained output. this could include a higher level of a combination of theoretical, methodology building and computation which may lead to higher precision and accuracy of the results.  performance measurements can be taken into consideration when measuring quality of the recommended algorithms. this knowledge will empower researchers and serve as a roadmap to improve future studies. acknowledgment authors would like to express their gratitude to universiti sains malaysia for providing the research funding (grant no.1001/ppsg/8012278, school of dental sciences, universiti sains malaysia). references [1] d. w. hosmer, s. lemeshow, r. x. sturdivant, applied logistic regression, 3rd ed, john wiley & sons, 2013 [2] b. efron, r. j. tibshirani, an introduction to the bootstrap, chapman and hall/crc, 1993 [3] g. e. higgins, “statistical significance testing: the bootstrapping method and an application to self-control theory”, the southwest journal of criminal justice, vol. 2, no. 1, pp. 54-76, 2005 [4] a. gelman, j. b carlin, h. s. stern, d. b. rubin, bayesian data analysis, chapman and hall/crc, 2004 [5] m. stokes, f. chen, f. gunes, “an introduction to bayesian analysis with sas/stat software”, sas global forum 2014 conference, washington dc, usa, paper sas400-2014, march 23-26, 2014 [6] j. mickey, s. greenland, “the impact of confounder-selection criteria on effect estimation”, american journal of epidemiology, vol. 129, no. 1, pp 125-137, 1989 [7] i. leibovitch, s. c. huilgol, d. selva, s. richards, r. paver, “basal cell carcinoma treated with mohs surgery in australia iii. perineural invasion”, journal of the american academy of dermatology, vol. 53, no. 3, pp. 458-463, 2005 [8] c. t. liao, c. j. tung-chieh, h. m. wang, i. h. chen, c. y. lin, t. m. chen, l. l. hsieh, a. j. cheng, “telomerase as an independent prognostic factor in head and neck squamous cell carcinoma”, head & neck, vol. 26, no. 6, pp. 504–512, 2004 [9] c. t. liao, j. t. chang, h. m. wang, s. h. ng, c. hsueh, l. y. lee, c. h. lin, i. h. chen, s. f. huang, a. j. cheng, t. c. yen, “analysis of risk factors predictive of local tumor control in oral cavity cancer”, annals of surgical oncology, vol. 15, no. 3, pp. 915–922, 2008 [10] c. t. liao, c. j. kang, j. t. chang, h. m. wang, s. h. ng, c. hsueh, l. y. lee, c. h. lin, a. j. cheng, i. h. chen, s. f. huang, t.c. yen, “survival of second and multiple primary tumors in patients with oral cavity squamous cell carcinoma in the betel quid chewing area”, oral oncology, vol. 43, no. 8, pp. 811–819, 2007 microsoft word etasr_v11_n1_pp6645-6649 engineering, technology & applied science research vol. 11, no. 1, 2021, 6645-6649 6645 www.etasr.com mahdi & mohammed: experimental and numerical analysis of bubble distribution influence in … experimental and numerical analysis of bubbles distribution influence in bubbledeck slab under harmonic load effect ali sabah mahdi department of civil engineering university of baghdad baghdad, iraq ali.sabah@esraa.edu.iq shatha dheyaa mohammed department of civil engineering university of baghdad baghdad, iraq shatha.dh@coeng.uobaghdad.edu.iq abstract-reducing a structure’s self-weight is the main goal and a major challenge for most civil constructions, especially in tall buildings and earthquake-affected buildings. one of the most adopted techniques to reduce the self-weight of concrete structures is applying voids in certain positions through the structure, just like a voided slab or bubbledeck slab. this research aims to study, experimentally and theoretically, the structural behavior of bubbledeck reinforced concrete slabs under the effect of harmonic load. tow-way bubbledeck slab of 2500mm×2500m×200mm dimensions and uniformly distributed bubbles of 120mm diameter and 160mm spacing c/c was tested experimentally under the effect of harmonic load. numerical analysis was also performed with the abaqus software. the results of the adopted numerical model were in acceptable agreement with the experimental results. the numerical analysis presented by the bubbles distribution effect was carried out for the bubbledeck two-way slab under the effect of harmonic load through the evaluated numerical model. two cases were considered in which the distribution kept the critical positions of the slab free from the bubbles. the results proved that bubbles distribution significantly affected the structural behavior. keywords-distribution of bubbles; resonance frequencies i. introduction a concrete slab is usually a horizontal flat plate with parallel top and bottom surfaces. generally, slabs are supported by reinforced concrete beams (commonly, it is cast monolithically with slabs), by reinforced concrete walls, by masonry walls, by structural steel members, directly by columns, or continuously by ground [1]. bubbledeck is a construction technology adopted in many industrial projects nowadays [2]. it was invented by jorgen bruenig in the 1990s, who developed the first biaxial hollow slab (known as bubbledeck now) [3]. bubbledeck slab system uses recycled plastic hollow balls to eliminate concrete that has no significant structural effect from the solid slab so that the slab self-weight can be reduced to a significant extent (30% to 50%), thus reducing the loads transferred to the whole building [3]. the dynamic load is a load that changes in its magnitude, direction, and position with time. structures are usually subjected to at least one type of dynamic load during their service life. when an applied load varies as a sine or a cosine function, it is termed as harmonic loading. the vibration developed by an unbalanced rotating machine, the vertical motion of an automobile on a sinusoidal road surface, and a tall chimney’s oscillations due to vortex shedding in a steady wind are all examples of harmonic motion [4]. ii. literature review authors in [5] carried out a theoretical study about the structural behavior of bubbledeck slab. the solid slab was modeled as pure concrete thick shells, while the bubbledeck slab was modeled as a layered shell. bubbledeck slab was modeled with three layers, two (top and thin bottom) layers of standard concrete, and one intermediate rectangular layer of hollow spheres made from recycled high-density poly ethylene (hdpe). ten kn live loads were applied upon both types of models. the results of the finite element analysis were compatible with the primary analysis and the experimental results. it was found that the bending stresses of bubbledeck slab were smaller than that of the solid slab by 6.43%. bubbledeck slab deflection was greater than that of the solid slab by 5.88% due to the descent of the slab stiffness caused by the presence of the hollow portion. the analysis results also showed that bubbledeck slab’s shear resistance was 60% that of the same thickness’s solid slab. vertical reinforcement can be provided to solve this problem. the self-weight of the bubbledeck slab was found to be the 35% of the solid slab. authors in [6] studied the effects of a moving harmonic load on beams with different boundary conditions. several parameters were considered such as support type, excitation frequency, and speed of the harmonic load. all the beams under study were homogeneous, isotropic, and initially at rest. all of them were subjected to concentrated harmonic forces of constant amplitudes. iii. finite element analysis integrodifferential equations and partial differential equations have been recognized to be better solved by the finite element method (fem). therefore, fem has become the numerical method most preferred in solving many corresponding authors: ali sabah mahdi, shatha dheyaa mohammed engineering, technology & applied science research vol. 11, no. 1, 2021, 6645-6649 6646 www.etasr.com mahdi & mohammed: experimental and numerical analysis of bubble distribution influence in … engineering and applied science field problems. since fem needs a minimal amount of training and versatile computer programs, it became more recommended for solving different practical problems [7]. during the last three decades, rapid development in computer-aided and finite element techniques provided an economical solution to perform many accepted 3d structural analyses. to investigate the overall behavior and analysis of the bubbledeck slab, the finite element software abaqus/cae 6.14.1/2019, was utilized. abaqus is a suite of engineering simulation programs that depends on fem [9]. it can solve problems that include various types of simple linear analysis and the most challenging nonlinear simulations [8]. for the performed modeling, three parts were necessary to be generated. the first part represented the bubbledeck slab that was modeled with a tetrahedral element. the second part was the steel-reinforcement which was modeled as wires. the third part was the steel support that was modeled as a solid sweep. the details of these parts are shown in figures 1-3. after creating the specimen parts, the material properties were defined and suitable interaction ways between all specimen’s components were selected. an assembly module process was considered to perform the achieved model geometry by creating part instances, then sample proportions were placed in the global coordinate system, as shown in figure 4. along the contact surface between the steel support and the concrete slab, tie interaction was applied. the steel support surface was considered as a master surface while the concrete surface was the slave. for interface conditions between the steel reinforcement and concrete, embedded interaction was considered. fig. 1. modeling of the bubbledeck slab. fig. 2. model of the reinforced steel. to simulate the experimental conditions of the harmonic load in fea, a harmonic load of characteristics compatible with that of the experimental test was applied on the mid surface (figure 5). the considered mesh size was 20mm for all the parts of the model, while the adopted element types included tetrahedron, truss, and quad-dominated elements for the bubbledeck slab, steel-reinforcement and steel support respectively as shown in figures 6-8. fig. 3. modeling of steel support. fig. 4. assembly model of the bubbledeck slab. fig. 5. harmonic load application. fig. 6. bubbledeck slab meshing. engineering, technology & applied science research vol. 11, no. 1, 2021, 6645-6649 6647 www.etasr.com mahdi & mohammed: experimental and numerical analysis of bubble distribution influence in … fig. 7. steel reinforcement meshing. fig. 8. steel support meshing. iv. numerical application and discussion a. verification of the finite element model for verification purposes, a comparison between the experimental and the numerical results was considered for only one specimen (model i – figure 9 and table i). fig. 9. verification model. table i. details of the adopted parametric study specimen bubble diameter (mm) spacing between bubbles c/c (mm) s (mm) number of bubbles volume reduction (%) model i 120 160 290 169 15.6 model ii 140 270 160 15 model iii 150 290 the harmonic load of various frequencies was applied upon the experimental specimen. data were recorded with a laser indicator and an ultra-sonic piezo device to measure the vertical vibration and the applied harmonic load of the different frequencies. the adopted dynamic load in this study is harmonic (figures 10-11). fig. 10. experimental harmonic load. fig. 11. test set-up. generally, the mathematical formula of this load consists of two main parts. the first characterizes the amplitude of the harmonic load (2���� �) while the second represents the sine wave (sin ���� [10]: �� � 2���� � ��� ���� (1) where �� is the induced harmonic dynamic load (n), � is the eccentric rotating mass (kg), e is the eccentric distance (m), and �� is the operating frequency of the machine (hz). table ii shows the details of the considered cases of the harmonic load. table ii. amplitude of the harmonic load. operating frequency (hz) amplitude (kn) 5 13.90 6 20.02 7 27.24 8 35.58 9 45.04 10 55.60 15 125.10 20 222.40 25 347.50 engineering, technology & applied science research vol. 11, no. 1, 2021, 6645-6649 6648 www.etasr.com mahdi & mohammed: experimental and numerical analysis of bubble distribution influence in … the build-up numerical model’s evaluation process under dynamic load was established to compare the maximum amplitude response as illustrated in table iii. the verification process showed that when the fea outputs regarding vibration amplitude were compared with the experimental results, they improved the validity and significantly of the adopted finite element model. the difference percentage for model i was 8.3%. table iii. experimental and fea result comparison for maximum amplitude under harmonic load frequency (hz) maximum amplitude (mm) error (%) experimental fea 5 1.1 1.05 4.5 6 1.2 1.12 6.67 7 1.3 1.2 7.69 8 1.2 1.1 8.3 9 0.85 0.8 5.9 10 0.8 0.78 2.5 15 0.6 0.57 5 20 0.45 0.43 4.4 25 0.35 0.33 5.7 b. parametric study an investigation study was conducted ,that considered the bubbles arrangement influence on the structural behavior of bubbledeck slab in dynamic states. the specimen in model i was selected to characterize the uniform bubbles arrangement case where the bubbles number was 169 (figure 9). this slab was analyzed experimentally and theoretically. this study includes two bubbles arrangements, both of the same bubbles diameter and concrete volume reduction, and with different bubbles distributions as shown in table i. the main difference in bubbles distribution between the specimens in model ii and model iii is the adopted clear distance from the fixed-end supports to the adjacent bubbles’ first raw. the specimen in model ii was designed to have such bubble arrangement that the first raw of the bubbles was far from the fixed support by 270mm while this distance was enlarged in model iii to 290mm. the distance between the bubbles was selected to be compatible with [11]. since the adopted concrete volume reductions were less than 20%, the traditional slab design can be adopted for bubbledeck slab [11]. the slab was designed to carry a uniform distribution load of 120ton. fig. 12. adopted bubbles distributions (model ii and model iii). on the other hand, no bubbles were allocated in the middle part of these specimens. the center area of a square shape was selected to be solid with a side length of 1.14 and 0.48m for model ii and model iii respectively (figure 12). it is well known that for a fixed-end slab, the critical position can be presented at central and fixed-end locations (maximum moment generation). hence, providing a solid section in these locations will modify the structural behavior of the bubbledeck slab. c. dissociation in this part of the numerical analysis, the harmonic load’s effect upon the bubbledeck slab of the adopted bubbles arrangement was inspected. the investigation comprised of studying the dynamic response concerning the natural frequencies and the deflection time history. table iv illustrates the natural frequencies of the three studied bubbles distribution models. the outcomes improved the achieved modification regarding the gained natural frequencies. model ii specimen was characterized by optimum distribution with a modification percentage reaching 19.6%, 24.4%, and 23.8% respectively for the three considered modes. this refers to the enhancement of the dynamic characteristics (stiffness and mass) that were attained by the redistribution of bubbles. figure 13 shows the layout of the first three considered modes. (a) (b) (c) fig. 13. modes of harmonic load: (a) mode i, (b) mode ii, (c) mode iii. the results of this analysis indicated that model ii specimen was the most strong under the effect of harmonic engineering, technology & applied science research vol. 11, no. 1, 2021, 6645-6649 6649 www.etasr.com mahdi & mohammed: experimental and numerical analysis of bubble distribution influence in … load. the maximum response of this specimen was not more than 0.5mm, while the specimen of uniform bubbles distribution (model i) reached 1.0mm for the first 0.2s of loading time. moreover, it was also clear that load time duration significantly affected the strength reduction during the load time (figure 14 and table v). table iv. natural frequencies modes natural frequencies (hz) modification % model i model ii model iii model ii model iii mode i 6.7 8.01 7.9 19.6 17.9 mode ii 12.6 15.68 15.1 24.4 19.8 mode iii 18.38 22.76 21.8 23.8 18.6 table v. variation in the vibration amplitude models vibration amplitude (mm) 1st cycle 2nd cycle 3rd cycle 4th cycle 5th cycle 6th cycle 7th cycle mode i 0.91 1.16 1.23 1.29 1.38 1.46 1.56 mode ii 0.5 0.25 0.42 0.24 0.39 0.28 0.35 mode iii 0.69 0.79 0.91 1.02 1.15 1.26 1.36 fig. 14. vibration-time history for the adopted models. v. conclusion after comparing the experimental and theoretical studies to ensure that the bubbledeck slab’s modeling is adequate, nonlinear finite element analysis was carried out using the abaqus/standard 2019 to analyze the two-way bubbledeck slabs adopted in the current study. after a satisfying agreement between the experimental and the theoretical results, the analysis of the tested bubbledeck slabs with some important parametric studies was also conducted, and the following points were deducted: • the constituent materials, the element type for concrete and reinforcing steel, and the modeling of the connection between the specimen parts and the support adopted in the numerical analysis are in good agreement with the experimental work. • according to the considered parametric study, the bubbles distribution was highly affected upon the dynamic response of the bubbledeck slab. references [1] a. nilson, d. darwin, and c. dolan, design of concrete structures, 14th ed. boston, ma, usa: mcgraw-hill education, 2009. [2] b. g. bhade and s. m. barelikar, "an experimental study on two-way bubble deck slab with spherical hollow balls," international journal of recent scientific research, vol. 7, no. 6, pp. 11621–11626, jun. 2016. [3] m. pandey and m. srivastava, "analysis of bubble deck slab design by finite element method," international journal of science technology & engineering, vol. 2, no. 11, pp. 599–606, may 2016. [4] r. w. clough and j. penzien, dynamics of structures, subsequent edition. new york, ny, usa: mcgraw-hill college, 1975. [5] p. p. teja, p. v. kumar, s. anusha, c. mounika, and p. saha, "structural behavior of bubble deck slab," in ieee-international conference on advances in engineering, science and management (icaesm -2012), nagapattinam, tamil nadu, india, mar. 2012, pp. 383–388. [6] m. abu-hilal and m. mohsen, "the vibration of beams with general boundary conditions due to a moving harmonic load," journal of sound and vibration, vol. 232, no. 4, pp. 703–717, may 2000, https://doi.org/ 10.1006/jsvi.1999.2771. [7] n.-h. kim, introduction to nonlinear finite element analysis. new york, ny, usa: springer, 2014. [8] "getting started with abaqus: interactive edition (6.10)," abacus 6.10. http://130.149.89.49:2080/v6.10/books/gsa/default.htm?startat=ch01s02. html (accessed dec. 20, 2020). [9] abaqus analysis user’s guide volume iv: elements. waltham, ma, usa: dassault systemes, 2014. [10] b. m. das and g. v. ramana, principles of soil dynamics, 2nd ed. stamford, ct, usa: cl engineering, 2010. [11] "bubbledeck voided flat slab technical manual & documents." bubbledeck, jun. 2008. engineering, technology & applied science research vol. 8, no. 5, 2018, 3416-3420 3416 www.etasr.com ndje et al.: dynamic matrix control and tuning parameters analysis for a dc motor system control dynamic matrix control and tuning parameters analysis for a dc motor system control martial ndje national school of agro-industrial sciences university of ngaoundere ngaoundere, cameroon ndjemartial@gmail.com jean maurice nyobe yome faculty of industrial engineering university of douala douala, cameroon nyobeyome@yahoo.fr alexandre teplaira boum higher technical teachers training college university of buea kumba, cameroon boumat2002@yahoo.fr laurent bitjoka national school of agro-industrial sciences university of ngaoundere ngaoundere, cameroon lbitjoka@univ-ndere.cm jean claude kamgang national school of agro-industrial sciences university of ngaoundere ngaoundere, cameroon jckamgang@gmail.com abstract—model predictive control (mpc) in system control industry overrides the challenges of conventional controllers in controlling complex systems. however, for efficient control, it is essential to find the best combination of parameter values. in this paper, we present the implementation of a multivariable dynamic matrix control (dmc) algorithm. an industrial system consisting of a dc motor, coupled to a mechanical load, the assembly associated with an electronic speed variator was considered to test the implemented dmc controller. dmc’s tuning parameter analysis on the manipulated inputs and their variations on the controlled outputs was performed. results guarantee that efficient control was presented. keywords-model predictive control (mpc); dynamic matrix control (dmc); tuning parameters; dc motor control i. introduction advances in the system control industry have led engineers to develop robust controllers with higher performance than conventional ones (lqr, imc, pid) [1-3]. dmc is a subset of the mpc algorithms that refers to a class of computer control algorithms that use an explicit process model to predict the future response of a system [4, 5]. the ability of this controller to drive multivariable, non-linear and constrained systems, and its ease of tuning gives it a prominent place in industrial processes [6-9]. however, the best combination of controller parameter values that ensures efficient tuning has often been very difficult to find [8, 10-12] because of the effect of each of these parameters on the controller's control signals and system outputs [9, 10]. in this paper, in addition to the simulation, we propose a dmc’s tuning parameter analysis approach for efficient tuning. figure 1 presents the principle of the moving horizon of [13], which is at the heart of any mpc algorithm. ii. dmc algorithm dmc [14] is part of the first generation of mpc, consisting of algorithms that provide a systematic means of controlling systems more efficiently while count multivariable cases, for which the step responses of the system are used as a predictive model [4, 15]. for a given system, let the value of step response at each sample time be   ,2,1 ,  iitaai and n the length of the horizon of the system model, then  tnaaa 1 is called the predictive model of the system. choosing the length of the control horizon as m and the length of optimal horizon as p, the dynamic matrix of dmc can be written according to (1). 1 1 1 0 m p p m a a a a a a + é ù ê ú ê ú ê ú ê ú = ê ú ê ú ê ú ê ú ê ú ë û      (1) for a multiple input–multiple output (mimo) system with nu inputs and ny outputs, any input-output i-j pair can be represented by a matrix aij of coefficients ia in every way similar to (1) so that the complete system is finally represented by a mimo dynamic matrix of control aij composed of elementary matrices according to (2): fig. 1. principle of the moving horizon of model predictive control. engineering, technology & applied science research vol. 8, no. 5, 2018, 3416-3420 3417 www.etasr.com ndje et al.: dynamic matrix control and tuning parameters analysis for a dc motor system control            nyny nu aa aa a 11 11   (2) at time k, assume the control input increment is  kum . by using dynamic matrix a, it can be obtained that      kuakyky mpopm  ~~ , where  ky pm~ represents the predictive outputs at future under the control of increment  kum , and  ky po~ the predictive outputs at future when  kum =0. for dmc, the vector  ky po~ can be obtained by shifting the predictive vector output at the last time instant ahead one step. the online optimization problem of the dmc controller without constraints can be formulated according to:         22 21 ~ wmwpmp kukykkjmin   (3) where j is the cost function to minimize compared to the control law  kum ,  kp is the reference at time k, w1 and w2 are the weight matrices of output errors and control input increments respectively. authors in [16] point out that the dmc is a least-squares optimization problem with a quadratic performance objective and penalty on manipulated variable variations. thus, the problem of (3) can be written in the form of (4): ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1 1 2 2 11 2 1 t t m t t m m m min j k a u k e k w w a u k e k u kw w u k d d d d = é ùé ùê ú+ ´ê úë ûê ú ê úé ù+ +ê úê úë ûë û (4) where  1ke represent the predicted future errors between the predicted outputs and the practical outputs. by solving the optimization problem (3), dmc controller can obtain the solution vector. the details of the derivation of (4) to search the mimo optimal control law of dmc can be found in [16, 17], where the solution (5) is found.     )1(111211   kewwawawwaku tttttm (5) it should be noted that only the first element of the control law of (5)  ku is sent to the plant. then, the vector of the future system outputs predicted by the predictive model is written according to (6):      kuakyky nn  01 ~~ (6) since there are always model errors or unknown disturbances for practical applications, the dmc will adjust the predicted outputs of (6) based on the practical outputs  1ky . the error vector between the predicted outputs and the practical outputs is written according to (7): ( ) ( ) ( )11 1 1e k y k y k k+ = + + (7) choosing the adjustment coefficient vector h, the adjusted predictive vector is written according to (8): ( ) ( ) ( ) 1 1 h 1 cor n y k y k e k+ = +  (8) at time k+1, the whole procedure mentioned above is repeated. figure 2 presents the diagram of dmc's general principle. figure 3 presents the key building steps of the mimo dmc algorithm without constraints.  ( )u k ( )u k ( )y k p 1 ny ( )e k   cory 1 1 1 i z 1 ny fig. 2. block diagram of dmc's general principle. begin calculate the step response coefficients ( ) of system build the dynamic matrix of control a calculate the vector of predicted future errors e(k+1) calculate the vector of future control signals u(k+1) send future control signals to the real system and the model approximated system end 60 ?k yes initialization: set the initial parameters retrieve future responses of the real system y(k + 1) and the approximated system for updates calculate the vector of control law δu(k) a calculate the vector of predicted future outputs calculate the vector of predicted future outputs k=k+1 corrected to the next sample  kyn1 ~  1~ kycor  1~1 ky fig. 3. flowchart of mimo dmc algorithm without constraints. iii. system model to test our dmc controller algorithm, the dc motor system of [18] was considered. in this system, the separately engineering, technology & applied science research vol. 8, no. 5, 2018, 3416-3420 3418 www.etasr.com ndje et al.: dynamic matrix control and tuning parameters analysis for a dc motor system control excited dc motor system drives a load and the assembly is coupled to an electronic variator speed drive. previously used models of the dc motor to test control algorithms [19-24] were unrealistic and limited to electromechanical models. in the model of [18], the electromechanical model is associated with an electronic speed variator, consisting of a simple chopper which allows the whole system to function in the first quadrant (q1) of the couple-speed plane. the principle of operation of the whole system is illustrated in figure 4. the system parameter values taken into account in simulations are given in table i. fig. 4. operating principle of the system. table i. design specifications of the dc motor system symbol system parameter value uα supply voltage 24v rα armature circuit resistance 2 lα armature circuit inductance 0.5h ke voltage constant 0.1vs/rad km torque constant 0.1nm/a kf viscous friction 0.2nms j total moment of inertia 0.02kgm2 the discrete average state model of the system is given by (9) with a sampling step of t=0.1 s: ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1 1 2 2 1 1 2 2 0 3656 0 2516 2 38821 0 0101 0 6676 3 98301 1 0 0 1 . . . . . . x k u k x k u k y k x k y k x k ìé ù é ùé ù é ùï -+ïê ú ê úê ú ê úï = +ïê ú ê úê ú ê úï -+ê ú ê úï ê ú ê úï ë û ë ûë û ë ûíé ù é ùé ùïïê ú ê úê úï =ïê ú ê úê úïê ú ê úê úï ë ûë û ë ûïî (9) it is then a mimo 2×2 linear time invariant (lti) state space model of the dc motor system, where the manipulated inputs (u1) and (u2) are respectively the load-resisting torque (tr) and the duty cycle of the electronic speed converter (d). the controlled outputs (y1) and (y2) are respectively the armature current (i) and the motor angular speed (). the problem is to use the duty cycle of the chopper and the resistive torque of the load to control the rotational speed and the induced current of the motor. iv. analysis of dmc tuning parameters the mimo 2×2 dmc controller program presented in this paper has been developed in matlab with simulation time of 6s. in this program, the references of the induced current and the angular speed of the motor are respectively 10a and 60rad/s. the effects of the dmc tuning parameters are analyzed on the manipulated inputs and their variations, and on the controlled outputs of the plant. a. effect of prediction horizon (p) figure 5 shows the dmc simulation results obtained at different values of prediction horizon while keeping the other parameters constant according to table ii. we find that the controlled outputs of the plant (figures 5(a) and 5(b)) are faster for the lower values of p [2]. however, large control actions (figures 5(c)-5(f)) are required. this makes it possible to compensate for the uncertainties of the model of our system. thus, the prediction horizon must be consistent with the response time of the process [16]. table ii. effect of prediction horizon (p). parameter value model horizon (n) 60 prediction horizon (p) 3, 6, 10 control horizon (m) 1 error weight matrix (w1) 1 control weight matrix (w2) 0 fig. 5. effect of prediction horizon p: (a) and (b) controlled outputs, (c) and (d) manipulated inputs, (e) and f) variations of manipulated inputs. b. effet of control horizon (m) figure 6 shows the dmc simulation results obtained at different values of control horizon m while keeping the other parameters constant according to table iii. table iii. effect of control horizon (m). parameter value model horizon (n) 60 prediction horizon (p) 3 control horizon (m) 1, 2 error weight matrix (w1) 1 control weight matrix (w2) 0 we find that the controlled outputs of the plant (figures 6(a) and (b)) are slow for the low values of control horizon (m=1), with control actions (figures 6(c)-6(f)) soft and progressive, while m=2 produces fast responses but with raw control actions. the controller becomes more sensitive to engineering, technology & applied science research vol. 8, no. 5, 2018, 3416-3420 3419 www.etasr.com ndje et al.: dynamic matrix control and tuning parameters analysis for a dc motor system control external noise for large values of the control horizon. thus, the large values of the control horizon are not recommended for our system. fig. 6. effect of control horizon m: (a) and (b) controlled outputs, (c) and (d) manipulated inputs, (e) and (f) variations of manipulated inputs. c. effect of model horizon (n) figure 7 shows the dmc simulation results obtained at different values of model horizon while keeping the other parameters constant according to table iv. we find that the controlled outputs (figures 7(a) and 8(b)), the manipulated inputs (figures 7(c) and 7(d)) and the manipulated input variations (figures 7(e) and (f)) of the system are partially unstable for n=20 and n=40. however, they become perfectly stable for n=60. thus, the model horizon must be chosen such that the dynamics of the system are sufficiently captured by the controller. in general, large model horizons are recommended [25, 26]. table iv. effect of model horizon (n). parameter value model horizon (n) 20, 40, 60 prediction horizon (p) 3 control horizon (m) 1 error weight matrix (w1) 1 control weight matrix (w2) 0 d. effect of error weight matrix w1 and control weight matrix w2 figure 8 shows the dmc simulation results obtained at different values of the control weight matrix when the weight matrix of the error is set to w1=1. the other parameters stay constant according to table v. we find that the responses of the system (figure 8(a) and 8(b)) are faster for the lower values of w2 with progressive control signals (figures 8(c) and 8(d)). however, there is a lot of contact on control variations (figures 8(e) and 8(f)). thus, error and control weight matrices are the most important dmc parameters and must be used to control the rise time of responses, and to produce progressive responses to control variations [10, 16]. fig. 7. effect of model horizon n: (a) and (b) controlled outputs, (c) and (d) manipulated inputs, (e) and (f) variations of manipulated inputs. table v. effect of error weight matrix (w2). parameter value model horizon (n) 60 prediction horizon (p) 3 control horizon (m) 1 error weight matrix (w1) 1 control weight matrix (w2) 1, 8, 15 fig. 8. effect of error weight matrix w1 and control weight matrix w2: (a) and (b) controlled outputs, (c) and (d) manipulated inputs, (e) and (f) variations of manipulated inputs. v. dmc controller results in response to an efficient tuning from the previous analysis of the effects of the dmc's parameters, a set of parameter values that guarantees efficient tuning of the implemented dmc controller is proposed (table vi). the simulation results of the mimo dmc in response to this setting are shown in figure 9. the results of figures 9(a) and 9(b) show that the controlled outputs follow their respective setpoints, while the manipulated inputs (figures 9(c) and 9(d)) and their variations (figures 9(e) and 9(f)) provide smooth and progressive control actions. thus, for our system, the prediction horizon must be consistent with the response time of the process [16]. engineering, technology & applied science research vol. 8, no. 5, 2018, 3416-3420 3420 www.etasr.com ndje et al.: dynamic matrix control and tuning parameters analysis for a dc motor system control table vi. optimal values of the dmc parameters. parameter value model horizon (n) 60 prediction horizon (p) 3 control horizon (m) 1 error weight matrix (w1) 1 control weight matrix (w2) 0 fig. 9. mimo dmc controller results for an efficient tuning: (a) and (b) controlled outputs, (c) and (d) manipulated inputs, (e) and (f) variations of manipulated inputs. vi. conclusions in this paper, mimo dmc algorithm applied to control speed and current of a dc motor system has been implemented. an approach to analyze the effect of each tuning parameter and its variations on manipulated inputs and on controlled outputs has been presented. obtained results showed that the combination of the values of dmc tuning parameters such as prediction horizon (p), control horizon (m), model horizon (n), error and control weight matrices (w1) and (w2), which guarantees efficient control can be found through an individual and systematic analysis of the influence of each of these parameters on the outputs of the controller and the system. in this way, the mimo dmc controller algorithm drives the outputs of the plant to their desired setpoints. references [1] a. t. boum, “observer based and quadratic dynamic matrix control of a fluid catalytic cracking unit: a comparison study”, international journal of computer applications, vol. 80, no. 3, pp. 1-8, 2013 [2] j. m. lopez-guede, b. fernandez-gauna, m. grana, f. oterino, “on the influence of the prediction horizon in dynamic matrix control”, international journal of control, vol. 3, no. 1, pp. 22-30, 2013 [3] e. f. camacho, c. bordons, model predictive control in the process industry, springer science & business media, 2012 [4] s. joe qin, t. a. badgwell, “a survey of industrial model predictive control technology”, control engineering practice, vol. 11, no. 7, pp. 733-764, 2003 [5] j. richalet, a. rault, j. testud, j. papon, “model predictive heuristic control: applications to industrial processes”, automatica, vol. 14, no. 5, pp. 413-428, 1978 [6] n. vatsa, tuning parameters of dynamic matrix control, phd thesis, national institute of technology rourkela, india, 2011 [7] g. m. de almeida, m. a. de s. l. cuadro, r. p. p. amarai, j. l. f. salles, “optimal tuning parameters of the dynamic matrix predictive controller with ant colony optimization”, 11th ieee/ias international conference on industry applications, juiz de fora, brazil, december 710, 2014 [8] p. bagheri, a. k. sedigh, “robust tuning of dynamic matrix controllers for first order plus dead time models”, applied mathematical modelling, vol. 39, no. 22, pp. 7017-7031, 2015 [9] a. s. yamashita, a. c. zanin, d. odloak, “tuning of model predictive control with multi-objective optimization”, brazilian journal of chemical engineering, vol. 33, 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engineering trends and technology, vol. 4, no. 6, pp. 2600-2602, 2013 [16] r. shridhar, d. j. cooper, “a novel tuning strategy for multivariable model predictive control”, isa transactions, vol. 36, no. 4, pp. 273280, 1998 [17] c. r. cutler, dynamic matrix control, an optimal multivariable control algorithm with constraints, phd thesis, university of houston, usa, 1983 [18] l. bitjoka, m. ndje, a. t. boum, j. song-manguelle, “implementation of quadratic dynamic matrix control on arduino due arm cortex-m3 microcontroller board”, journal of engineering technology, vol. 6, no. 2, pp. 682-695, 2017 [19] a. a. kheriji, f. bouani, m. ksouri, m. b. ahmed, “a microcontroller implementation of model predictive control”, international journal of electrical and information engineering, vol. 5, no. 5, pp. 600-606, 2011 [20] a. k. abbes, f. bouani, m. ksouri, “a microcontroller implementation of constrained model predictive control”, international journal of computer, electrical, automation, control and information engineering, vol. 5, no. 8, pp. 878-885, 2011 [21] c. ekaputri, a. syaichu-rohman, “model predictive control (mpc) design and implementation using algorithm-3 on board spartan 6 fpga sp605 evaluation kit”, ieee 3rd international conference on instrumentation control and automation, ungasan, indonesia, august 28-30, 2013 [22] l. malouche, a. k. abbes, f. bouani, “automatic model predictive control implementation in a high-performance microcontroller”, ieee 12th international multi-conference on systems, signals & devices, mahdia, tunisia, march 16-19, 2015 [23] r. nagarajan, s. sathishkumar, s. deepika, g. keerthana, j. k. kiruthika, r. nandhini, “implementation of chopper fed speed control of separately excited dc motor using pi controller”, international journal of engineering and computer science, vol. 6, no. 3, pp. 2063120633, 2017 [24] v. h. haji, c. a. monje, “fractional-order pid control of a chopper-fed dc motor drive using a novel firefly algorithm with dynamic control mechanism”, soft computing, vol. 22, no. 18, pp. 6135-6146, 2018 [25] s. li, k. y. lim, d. g. fisher, “a state space formulation for model predictive control”, aiche journal, vol. 35, no. 2, pp. 241-249, 1989 [26] e. f. camacho, c. bordons, model predictive control, springer-verlag, 1998 microsoft word 40-2794_setasr_v9_n3_pp4287-4291 engineering, technology & applied science research vol. 9, no. 3, 2019, 4287-4291 4287 www.etasr.com alsuwaiket et al.: formulating module assessment for improved academic performance predictability … formulating module assessment for improved academic performance predictability in higher education mohammed alsuwaiket department of computer science, loughborough university, loughborough, leicestershire, uk m.alsuwaiket@lboro.ac.uk anas h. blasi department of computer information systems, mutah university, karak, jordan ablasi1@mutah.edu.jo ra'fat al-msie'deen department of computer information systems, mutah university, karak, jordan rafatalmsiedeen@mutah.edu.jo abstract—the choice of an effective student assessment method is an issue of interest in higher education. various studies [1] have shown that students tend to get higher marks when assessed through coursework-based assessment methods which include either modules that are fully assessed through coursework or a mixture of coursework and examinations than assessed by examination alone. there are a large number of educational data mining (edm) studies that pre-process data through conventional data mining processes including data preparation process, but they are using transcript data as they stand without looking at examination and coursework results weighting which could affect prediction accuracy. this paper proposes a different data preparation process through investigating more than 230,000 student records in order to prepare students’ marks based on the assessment methods of enrolled modules. the data have been processed through different stages in order to extract a categorical factor through which students’ module marks are refined during the data preparation process. the results of this work show that students’ final marks should not be isolated from the nature of the enrolled module’s assessment methods. they must rather be investigated thoroughly and considered during edm’s data pre-processing phases. more generally, it is concluded that educational data should not be prepared in the same way as other data types due to differences as data sources, applications, and types of errors in them. therefore, an attribute, coursework assessment ratio (car), is proposed to be used in order to take the different modules’ assessment methods into account while preparing student transcript data. the effect of car on prediction process using the random forest classification technique has been investigated. it is shown that considering car as an attribute increases the accuracy of predicting students’ second-year averages based on their first-year results. keywords-edm; data mining; higher education; machine learning; module assessment i. introduction although educational data have been recorded and analyzed from educational software for a long time, only recently has this process been formed into a new field, educational data mining (edm). the edm process converts raw data from educational systems into useful information that could potentially have a great impact on educational research and practice [1]. additionally, edm uses a wide range of methods to analyze data, including, but not limited to, supervised and unsupervised model induction, parameter estimation, relationship mining, etc. [2, 3]. during the last few decades, the use of coursework-based module assessment increased in the uk and other countries due to various educational arguments. additionally, it appears to be that students prefer the assessment to be based on either coursework alone or by a mix of both coursework and exams because these types of assessments tend to yield higher marks than exam-based assessment alone [4]. the increased adoption of courseworkbased assessment has contributed to an increase over time in the marks on individual modules and in the proportion of good degrees across entire programmes [5]. accurate and fair student assessment is an issue of concern in higher education (he). changes in the use of different assessment methods have given rise to an increasing number of universities shifting from traditional exam-based to continuous assessment throughout the semester (coursework-based) [6]. coursework-based assessment methods differ from exam-based assessment methods where knowledge or skill is tested for a very specific period of time. moreover, it has been widely acknowledged that the chosen assessment method will determine the style and content of student learning and skill acquisition [6]. coursework marks are a better predictor of long-term learning of course content than are exams [7]. nonetheless, it appears to be that none of the studies in the edm research field reflected the assessment method used in modules on the final marks. so, this paper aims to pre-process students’ transcript data differently, extract a factor from the assessment method and use it to refine student marks again to ensure more accuracy prior to processing them by using the edm techniques. ii. assessment methods in higher education regardless the inabilities to absolutely ensure student learning through different assessment methods, assessment is still an essential tool through which teachers influence the ways students respond to courses. on the other hand, there are clear steers from uk government towards coursework-based corresponding author: anas h. blasi engineering, technology & applied science research vol. 9, no. 3, 2019, 4287-4291 4288 www.etasr.com alsuwaiket et al.: formulating module assessment for improved academic performance predictability … assessment focused on employability that should apply across all degree subjects [8]. however, other studies show that not all assessment methods suit different programmes or even courses [9]. thus, student assessment methods in he can be generally divided into two main categories: exam-based assessments, which include different forms such as closed and open book examinations, essay-type exams, multiple choice exams, etc. and coursework-based assessments, which include research projects, assignments, etc. different studies proved that students tend to gain higher marks from coursework-based assignments than they do from examinations [4]. authors in [10] found that combining exam-based and coursework-based assessment methods produced up to 12% higher average marks than did examinations alone. as a result, this paper tries to take into account the different assessment methods of universities’ modules and their effect on the students’ academic performance, and also formulates the differences in assessment methods into a new attribute that can be part of further data mining processes. iii. student transcript data in this study, 4662 modules with different assessment methods that were collected from a uk university, are investigated. basic average calculations of module marks in various departments (business, computer science, math, electrical and computer systems engineering, civil engineering, and mechanical engineering) are calculated for students taking modules with exam-based, coursework-based or a mixture of both assessment methods. a simple t-test was applied on the data (table i) in order to measure the difference between means of each pair of variables. results show that there is a statistically significant difference between the exambased and coursework-based assessments (with 95% confidence level (which equates to declaring statistical significance at the p<0.05 level, a t-value of -5.06 and a pvalue of 0.001). table i. average marks based on assessment method department student number average module mark of students exam-based assessment courseworkbased assessment mixed assessment business 54960 59.77 60.83 60.01 civil engineering 34892 58.78 63.74 60.70 computer science 19800 58.18 64.40 58.87 electronic and computer systems engineering 13740 59.55 63.26 57.00 math 24152 61.59 66.00 61.17 mechanical engineering 31385 58.80 64.26 60.24 applying the t-test to measure the significance of difference between each pair of variables ex-cw, ex-mix, and cw-mix assessment methods results in table ii. as shown in table ii, the p-value of the t-test between the fields: exam-based and coursework-based assessments (0.002) and both exam and coursework-based assessments, and coursework-based assessment (0.004) is less than 0.05, which indicates the statistical significant difference between these assessment methods. on the other hand, there seems to be no statistical significant difference between the exam-based assessment and the mixture of both exam and coursework assessment methods, since the p-value was 0.749 which is greater than 0.05. table ii. p-values of t-test assessment method p-value t-value exam and coursework 0.002 -4.5 mixed and exam 0.749 0.39 mixed and coursework 0.004 -3.99 throughout the literature, module assessment methods in he have been investigated. various studies such as [4] show that students tend to get higher marks when assessed using coursework than when assessed using exam-based assessment. table i shows that this study initially does not contradict with previous studies, by confirming that students who are assessed using coursework tend to get higher marks than those who are assessed using exams or a mixture of both coursework and exams. the next section explains educational data used and their attributes before processing the data and applying data mining techniques. a. understanding student transcript data student transcript data were collected, and they consisted of files with hundreds of thousands of records. the standard dm practice suggests that the data in these files had to be first understood, then cleaned, and finally the most significant factors had to be highlighted in order to further process these data using edm techniques. normally, educational data are discrete, i.e. either numeric or categorical data, and noise-free. the lack of noise in educational data is due to the fact that there are not measured. they are either collected automatically or checked carefully [8]. on the other hand, missing data values exist usually in the cases where students – for example skip answering a given questionnaire or in other cases where teachers skip checking attendance. humans normally do this type of errors, referred as data entry errors [11]. the investigated data represent around 230,823 student records representing 19,886 students in a total of six departments of a uk university. each one of these department data sheets contains a number of student records. for each record, a number of attributes that represent a student’s academic accomplishments during three levels (preparatory, 1 st , and 2 nd levels) are divided as: • student-related attributes: these attributes highlight the status of the students, including: (i) module mark: student’s mark in a certain module, (ii) exam mark: the mark achieved by a student on the exam-based assessment part, and (iii) cswk mark: the mark achieved by a student on the coursework-based assessment part. • module-related attributes: a group of attributes that describe a certain module and its characteristics including: coursework weighting (cww): alternatively, this attribute indicates the ratio of coursework-based assessment to the total mark of a module. engineering, technology & applied science research vol. 9, no. 3, 2019, 4287-4291 4289 www.etasr.com alsuwaiket et al.: formulating module assessment for improved academic performance predictability … for each module, the values of these two attributes complement each other to reach maximum total mark (i.e., 100). for example, if the exam weighting for a certain module is 75, the coursework weighting must be 25 in order to reach 100, and so on. for each department, different ratios between exam weighting and coursework weighting will be described in detail. b. causes of errors in educational data prior to storing educational data, they are normally processed by the involvement of human interaction, or computation, or both. sources of errors in databases are categorized into four main types: data entry errors, measurement errors, distillation errors, and data integration errors [11]. as mentioned before, since educational data are not measured using instruments, the errors are caused by humans (i.e. through data entry errors) so these data have minimum, or zero noise compared to other non-educational data types. the following section will present the pre-processed students’ transcript data in a different way in order to increase the data mining accuracy by extracting a new factor from the assessment method and use it to refine student marks to ensure more accuracy prior to processing them using edm. iv. coursework assessment ratio (car) in order to refine student’s marks based on modules’ assessment methods, the data have been processed through various stages. each of these stages enhances the data in terms of readability by statistical software and ability to extract knowledge easily. the first step is to categorize the cw to ex ratios. the categorization algorithm relies on the number of classes the ratio between cw to ex weighting can have based on ratios of cw to ex the original data have. namely, each department has its own classification of cw to ex weighting ratios. car represents the ratio of cw weighting for each module, which by default will reflect the ratio of ex weighting. table iii shows the different classes: table iii. classes of cw to ex weighting ratios model assessment method cw 0 10 15 20 25 30 35 40 45 50 55 60 65 66 70 75 100 business � � � � � � � � � � ceng � � � � � � � � � � cs � � � � � � � � � � � � ecseng � � � � � � � � � � � � math � � � � � � � � � meng � � � � � � � � � � table iii shows that there is no department that shares the same ratio classes with the other departments, i.e. each department has its own unique ratios between cw to ex. thus, filling the missing values in the table is not a solution since doing so yields incorrect data. this research considers the department with the greatest number of classes to start with, and then generalizes the findings on the other departments while bearing in mind the change of ratios. two departments have 12 complete ratios (the cs and ecseng departments). in this paper, the cs department was chosen for further processing. v. refining students marks based on car in order to obtain the relation between the student’s module mark and car which represents the cww to exw ratios, simple quadratic regression was used. regression analysis is being used to infer relationships between the independent (car) and dependent (refined module mark) variables. the variable of cw ratio was used, since the simple quadratic regression is more suitable for one variable relation. the choice of choosing quadratic over linear is based on the r-squared (coefficient of determination): when the r-squared is higher, then the model fits data more. for the case of quadratic regression, the coefficient is 2.90%, which is higher than in the linear model (2.77%). by applying simple quadratic regression on the data with car as a variable for module mark as a response, we achieved the following fitted regression line: rmm=mm-12.77(car)+5.873(car) 2 (1) where rmm is the refined module mark after fitting and mm is the current module mark. by applying (1) on student transcript data of the cs department, an additional field will be added which contains the rmm for each student at the department. rmms are selfexplained when referring to table i that compares the average module marks for student attending modules according to different assessment methods. the more the percentage of cww, the more the added marks to mm, and vice versa. any edm that considers student marks with different assessment methods should consider adding a sub-process within the data pre-processing phase that takes into account the difference between those assessment methods. figure 1 shows the addition of sub-processes 2-5 on raw students’ module marks. the task of these sub-processes is to take the differences in assessment methods into account. these sub-processes are utilized because applying conventional dm processes on educational data may not produce accurate results. fig. 1. refining students’ module marks sub-process vi. the effect of car on dm’s prediction accuracy in order to verify the effect of the newly constructed variable, prediction of a student’s third year average mark using his first and second year’s average was compared to engineering, technology & applied science research vol. 9, no. 3, 2019, 4287-4291 4290 www.etasr.com alsuwaiket et al.: formulating module assessment for improved academic performance predictability … predicted third year’s average using first and second year’s average and the newly constructed variable, car. this comparison may highlight how accurate the prediction process can be by adding new attributes that reflect the nature of the module. orange canvas tool is a simple data analysis tool with clever data visualization and interactive data exploration for rapid qualitative analysis with clean visualizations. moreover, there are many prediction techniques which can be investigated using the orange data mining tool, but one of the most popular technique that could be used is random forest [12]. the random forest was used in this study to evaluate the role of car in increasing the prediction accuracy. the data of 406 undergraduate students of the computer science department included their first, second and third years’ average marks, and their average car for all years. the comparison was done including and excluding car as an input attribute. figures 3 and 4 show the confusion matrices of the comparisons and how car affected the accuracy of predicting students’ third year average marks. table iv. predicting third year’s average from first and second year’s excluding car prediction c o r r e c t c la ss fail first lower second pass third upper second fail 0 1 3 0 5 3 12 first 0 36 0 0 0 37 73 lower second 0 0 0 0 6 31 47 pass 0 0 0 0 0 3 3 third 0 0 8 0 9 13 30 upper second 0 5 4 0 0 110 119 0 42 25 0 20 197 284 table v. predicting third year’s average from first and second year’s including car as an attribute prediction c o r r e c t c la ss fail first lower second pass third upper second fail 3 2 6 0 0 2 13 first 0 59 0 0 0 23 82 lower second 0 4 16 0 0 26 46 pass 0 0 1 0 0 2 3 third 1 1 14 0 0 9 25 upper second 0 12 4 0 0 99 115 4 78 41 0 0 161 284 the roc (receiver operating characteristics) curve has been introduced to evaluate ranking performance of machine learning algorithms [13]. author in [14] has compared popular machine learning algorithms using the area under the curve (auc) that represents the proportion of false positive rate covered by the curve of true positive rate and found that auc exhibits several desirable properties compared to classification accuracy (ca). table v shows an enhancement on the prediction probabilities for each of the mark classes (fail, pass, third, lower second, upper second, and first classes) compared to probabilities of prediction shown in table iv. the random forest scored the highest auc when car was considered (table v) with auc value of 0.9304 and 0.0696 error rate. the auc represents the proportion of false positive rate covered by the curve of true positive rate. in other words, the bigger the area of the curve, the more items are classified successfully as presumed, and with the increase of auc, the mean profit difference also increases. when car was excluded as an input (table iv), the auc was lower with value 0.9073 and the error rate was 0.0927. vii. results and discussion this study shows that the pre-processing phase of educational data should include additional sub-phases that deal, not only with noise or missing data, but also with data refinement so as to cope with differences between various educational systems and their data. therefore, the attribute car was constructed in order to take the different modules’ assessment methods into account while preparing student transcript data. the effect of car on the prediction process using random forest classification was investigated and applied on the equation of rmm. it was shown that considering rmm increases the accuracy of predicting students’ marks. by refining students’ marks, they either increase or decrease depending on the ratio between cww to exw for each student during his study. for instance, by considering a student x as an example, the student had enrolled in 32 modules during his/her study at the department of cs. nineteen out of 32 modules are 100% exam-based assessed modules, 7 are assessed by a mixture of coursework and examination, while only 6 modules are 100% assessed by coursework only. despite that the majority of the modules are assessed through examination only, which means that the student gets no extra marks compared with coursework-based modules, the rest of the modules give the student extra marks and hence add to his overall average. in numbers, 19 modules have 0 car value, which means that rmm=mm. on the other hand, the rest of the modules have values of car ranging from 0.1 to 1, which means that the rmm is always less than mm for those courses. this decrement in the marks is due to the fact that students get higher marks in modules that are assessed by coursework or mixture of coursework and examinations. therefore, to balance the module marks and the overall average, the formula decrements the module marks by varying percentage depending on the cww to exw to ratios. table vi engineering, technology & applied science research vol. 9, no. 3, 2019, 4287-4291 4291 www.etasr.com alsuwaiket et al.: formulating module assessment for improved academic performance predictability … shows the differences in module marks and overall average for the example student. table vi. refining student x marks based on enrolled modules’ assessment methods average mm average rmm 19 exam-based modules 48.6 48.6 6 coursework-based modules 60.3 52.7 7 mixed ex and cw modules 60.4 58.3 total 32 modules 56.4 53.2 by following the procedure in figure 1 on a real student’s marks, table vi shows that rmm remains unchanged for the student when the assessment method of the enrolled modules is purely exam-based. alternatively, when the assessment method of the enrolled modules is purely coursework-based, the rmm is refined down on average 7.6 compared to mm. finally, a mixture of ex and cw based modules yields less refinement of the rmm (2.1 marks) compared to mm for the same student. this means that student in the example who is taking 32 modules of different types may have his average marks refined down by 3.2 when applying the proposed procedure. upon deriving car and examining its effect on students’ marks, random forest prediction technique was used to validate the enhancement on auc. it was shown that by including mar as an input for predicting students’ third year from their first and second years, auc was enhanced from 0.9073 to 0.9304. the derived car enhances the predictability of students’ third year marks from their first two years, which means that additional preparation steps, such as this paper’s module mark refinement based on modules’ assessment methods, are required on the student transcript data prior to applying dm techniques for improved predictability. additionally, the findings of this paper will be generalized in different departments and universities that may have various assessment methods, in other words, the refinement procedure should be considered as a sub-process within the edm data pre-processing phase when dealing with different modules and their marks. viii. conclusions and future work during the last few decades, there has been an increased interest in coursework-based assessment in the uk and other countries due to various educational and personal arguments such as its learning effectiveness, the lack of time limits and stress, etc. this increased interest led to discovering that students who are assessed by coursework tend to achieve higher marks than those who are assessed by examinations in the same modules. however, it seems that no studies have considered this increase in marks in the data pre-processing phase. more generally, this led to a conclusion that applying conventional dm processes on educational data may not produce accurate results. in this paper, a model that refines students’ marks based on enrolled modules’ assessment methods has been proposed. the model represents a subprocess through which module assessment methods are considered for further processing using a new attribute that reflects the ratio of coursework weightings. the key to refine students’ marks is to develop a ratio that represents the ratio of cw weighting for each module, which by default will reflect the ratio of ex weighting. this ratio, coursework assessment ratio (car), has been extracted using simple quadratic regression on the mm (module marks) variable. based on car values, rmm (refined module marks) were calculated and compared to the original mm. although this increase on marks was proved in literature and throughout this research, none of the previous studies considered this increase as a feedback to the data pre-processing phase of the edm, which has mostly been following conventional dm pre-processing methods while neglecting the differences between the types of data being processed. therefore, it is vital to consider this feedback generation for edm pre-processing phase. this means that the formulation of the relation between car and the current mm should be part of the edm pre-processing phase. this study investigated the effect of car on the prediction process using random forest classification technique. it was shown that considering car as an attribute increases the accuracy of predicting students’ third year averages based on their first and second year’s averages. for future work, the predictability of individual module results based on their assessment method and further investigation into the group course work can be applied to improve predictability. references [1] c. romero, s. ventura, m. pechenizkiy, r. baker, handbook of educational data mining, chapman & hall, 2010 [2] r. s. j. d. baker, k. yacef, “the state of educational data mining in 2009: a review and future visions”, journal of educational data mining, vol. 1, no. 1, pp. 3-16, 2009 [3] c. romero, s. ventura, “educational data mining: a survey from 1995 to 2005”, expert systems with applications, vol. 33, no. 1, pp. 135-146, 2007 [4] j. t. e. richardson, “coursework versus examinations in end-of-module assessment: a literature review”, assessment & evaluation in higher education, vol. 40, no. 3, 2015 [5] p. bridges, a. cooper, p. evanson, c. haines, d. jenkins, d. scurry, h. woolf, m. yorke, “coursework marks high, examination marks low: discuss”, assessment & evaluation in higher education, vol. 27, no. 1, 2002 [6] j. heywood, assessment in higher education: student learning, teaching, programmes and institutions, jessica kingsley, 2000 [7] g. gibbs, c. simpson, “conditions under which assessment supports students’ learning”, in: learning and teaching in higher education, vol. 1, pp. 3-31, university of gloucestershire, 2005 [8] r. dearing, higher education in the learning society: main report, national committee of inquiry into higher education, 1997 [9] g. gibbs, “using assessment strategically to change the way students learn”, from assessment matters in higher education,vol. 4, pp. 41-53, 1999 [10] p. e. morris, c. fritz, “conscientiousness and procrastination predict academic coursework marks rather than examination performance”, learning and individual differences, vol. 39, pp. 193-198, 2015 [11] j. m. hellerstein, quantitative data cleaning for large databases, united nations economic commission for europe, 2008 [12] r. asif, s. hina, s. i. haque, “predicting student academic performance using data mining methods”, international journal of computer science and network security, vol. 17, no. 5, pp. 187-191, 2017 [13] r. kohavi, f. provost, “glossary of terms”, machine learning, vol. 30, no. 2, pp. 271-274, 1998 [14] a. p. bradley, “the use of the area under the roc carve in the evaluation of machine learning algorithms”, pattern recognition, vol. 30, no. 7, pp. 1145-1159, 1997 microsoft word etasr_v11_n2_pp7068 engineering, technology & applied science research vol. 11, no. 2, 2021, 7068 7068 www.etasr.com marar et al.: erratum and addendum: "mandible bone osteoporosis detection using cone-beam ..." erratum and addendum: "mandible bone osteoporosis detection using cone-beam computed tomography" rasha f. abu marar department of computer science faculty of information technology middle east university amman, jordan ramarar82@gmail.com diaa m. uliyan department of information computer science college of computer science and engineering university of hai’l hai’l, saudi arabia d.uliyan@uoh.edu.sa hamza a. al-sewadi department of computer science faculty of information technology middle east university amman, jordan hsewadi@meu.edu.jo the authors would like to clarify that [1] is the original source of a figure that was included in our previously published manuscript as figure 7 [2]. although a reference to [1] was provided in [2], a direct reference was not inserted in the image caption. the image is reshown here as figure 1 for convenience. we would like to thank dr e. klintström, the copyright holder, for agreeing to the reuse of the figure. fig. 1. the above figure was included as fig. 7 in [2] with the following caption: "the figure bone structure parameters. (a) trabecular nodes, (b) trabecular termini, (c) trabecular separation, (d) trabecular spacing, and (e) trabecular thickness." the authors of [2] wish to clarify that the source of this figure is [1]. references [1] e. klintström, "image analysis for trabecular bone properties on conebeam ct data," linköping university medical dissertations no. 1594, department of medical and health sciences, linköping university, sweden, linköping, 2017. [2] r. f. a. marar, d. m. uliyan, and h. a. al-sewadi, "mandible bone osteoporosis detection using cone-beam computed tomography," engineering, technology & applied science research, vol. 10, no. 4, pp. 6027–6033, aug. 2020, https://doi.org/10.48084/etasr.3637. microsoft word etasr_v11_n3_pp7201-7206 engineering, technology & applied science research vol. 11, no. 3, 2021, 7201-7206 7201 www.etasr.com nguyen & le: day-ahead coordinated operation of a wind-storage system considering wind forecast … day-ahead coordinated operation of a wind-storage system considering wind forecast uncertainty nhi thi ai nguyen faculty of electrical engineering the university of danang university of science and technology danang, vietnam ntanhi@dut.udn.vn dinh duong le faculty of electrical engineering the university of danang university of science and technology danang, vietnam ldduong@dut.udn.vn abstract-this paper proposes an optimal operation for coordinated battery energy storage (bes) and wind generation in a day-ahead market under wind uncertainty. a comprehensive ac optimal power flow (ac opf) model was established to incorporate wind and storage into a power system. to take into account wind forecast uncertainty, preprocessing technique, time series model, and fast forward selection method were applied for scenario generation and reduction processes. tests were performed on a modified ieee 14-bus system and the results show that the use of bess is an alternative to guarantee a more efficient and flexible operation of wind power plants. keywords-ac opf; battery energy storage (bes); operation; wind; uncertainty i. introduction wind energy has gained considerable interest globally during the last decades due to the increased environment concern. the overall capacity of wind turbines installed worldwide by the end of 2019 reached 650.8gw, according to statistics by the world wind energy association (wwea). in 2019, 59,667mw were added, substantially more than the 50,252mw of 2018. the sum of the wind turbines installed by the end of 2019 can cover more than 6% of global electricity demand [1]. unfortunately, wind power output is well documented for its variable and non-dispatchable nature. the output of a wind turbine depends on wind speed, which varies daily and seasonally. thus, the high penetration level of wind generation brings new challenges to the power system. from the operational aspect, it is essential to find a solution regarding the provision of controllability to wind generation, improving power quality of grid-connected wind farms and hence, facilitating higher wind installation capacity. energy storage systems (esss) can be an economically favorable option to mitigate the variability of renewable generation. esss can be used by system operators for reliability improvement, ancillary services, and transmission congestion relief [2-4]. for wind power producers, esss are utilized in capacity firming and energy time shifting [5]. in electricity markets, storage systems can take advantage of price difference and gain profits for wind power plant using energy arbitrage. wind power output is usually high during night-time and low at daytime, whereas electricity demand and price are usually low at night and get higher during daytime. if wind energy is stored during lowprice periods and is discharged back to the supply load at highprice periods, higher profit can be obtained. energy storage can benefit by providing other services to the grid, but energy arbitrage is by far the largest business opportunity. the cooperation strategy of a wind-storage system is substantially important in achieving optimal tradeoff between operation cost and profit. this operation problem is challenging due to the stochastic behavior of wind power output. the issue of coupling operation of wind and storage has been extensively studied with regard to operation and planning aspects [6-13]. authors in [9] presented a dynamic programming algorithm employed to determine optimal energy exchange with the market for a specified scheduling period, taking into account transmission constraints. in [10], research was conducted to analyze the possibility of coupling wind and storage systems for time-shifting application, reducing grid congestions and making renewables more controllable on grid operator side. authors in [11] investigate the problem of planning and operation of a combined wind-storage system. specifically, a procedure is proposed, aiming to determine an hourly operation schedule of the combined system. in [12], a joint planning problem is established for transmission congestion and wind curtailment, including wind power installed capacity and location, transmission network expansion, and ess locating and sizing. the problem was formulated into a linearized milp model. an optimized output strategy of wind storage system is formulated in [13]. the storage is shown to effectively improve the efficiency of the wind farm while reducing wind power output fluctuations. there are many publications discussing the incorporation of an energy storage system in day-ahead market. in [14], a deterministic centralized unit commitment problem is proposed to optimally schedule storage operation in power systems with high wind penetration. authors in [15] formulate an optimal joint bidding problem of wind hydro system under deterministic scenarios of wind generation, and illustrate its solution with a simple three-reservoir cascade. in addition to those deterministic formulations, wind uncertainty has also been dealt with, applying scenario-based stochastic programming [16-20]. authors in [16] present a stochastic unit commitment model with energy storage and obtained a reduced corresponding author: dinh duong le engineering, technology & applied science research vol. 11, no. 3, 2021, 7201-7206 7202 www.etasr.com nguyen & le: day-ahead coordinated operation of a wind-storage system considering wind forecast … system constraint violation in the n-1 analysis. authors in [17] adopt a scenario-based stochastic unit commitment model to address uncertainties of renewables and demands in evaluating the reserves provided by esss and generators. the problem is solved using the progressive hedging algorithm with heuristic approaches. in [18], a stochastic unit commitment model with ess and wind for system scheduling at day-ahead and realtime stages is proposed. a stochastic unit commitment model is presented in [19] for optimal energy and reserve bids in systems with high wind penetration. in [20], a stochastic battery arbitrage model for day-ahead and real-time prices is proposed. authors in [21] formulated a robust unit commitment model with pumped hydro storage units. this approach models the randomness using an uncertainty set to protect the system against worstcase scenarios. most previous studies explored the value of storage systems with wind generation in day-ahead market, either using deterministic models [11, 14, 15, 22-23] or focusing on price uncertainties [24-26]. however, with the increasing level of wind energy integration, the variable nature of wind should be examined in any optimization model. therefore, in this paper, we establish a day-ahead optimal dispatch model of windstorage system while taking into account wind power uncertainties. this is implemented by formulating an ac opf model with bes and wind integration and applying wind uncertainty modeling techniques, including preprocessing technique, time series model, and fast forward selection method. the model focuses on the use of bes to time-shift wind energy to higher price periods, i.e. arbitrage, which is a particularly important service that energy storage systems can provide in day-ahead energy markets. this model is an effective tool for wind farm operators to determine the optimal day-ahead operating strategies of wind-storage systems under wind uncertainties. extensive tests were performed on a modified ieee 14-bus system. ii. wind uncertainty modeling in this section an approach to capture wind uncertainty is presented. combined preprocessing technique and time series analysis are used to build a model representing the uncertainty associated with wind speed. taken as an example, three-year measured hourly wind speed values of a real wind farm (rated at 85mw) in italy, are used. wind speed is usually not stationary with distinct diurnal and seasonal patterns [27] while a time series model such as auto-regressive moving average (arma) requires stationary data. to handle this issue, we adopt preprocessing techniques [27]. after that we make use of the process described in detail in [28] to build the arma model for the obtained stationary data. by sampling from the resulting time series model, the set of 10,000 hourly wind speed scenarios for day-ahead operation is generated as in figure 1. equal probability is assigned to each scenario of the set. to capture the uncertainty, a large number of scenarios should be generated, leading to increased complexity and computational burden. in this research, the fast forward selection approach [29] was used to select a limited number of representative scenarios for the set. figure 2 depicts 10 selected wind speed scenarios. for determining an optimal operation for coordinated bes and wind generation in a day-ahead market, wind power data are necessary. for this purpose, an aggregate power curve for the entire wind farm is needed to map wind speed scenarios into wind power scenarios. in this paper, we make use of the method of bins [27, 30, 31] using wind powerwind speed pairs at the wind farm to obtain the aggregate power curve as in figure 3. using the power curve, 10 representative wind power scenarios are obtained from 10 representative wind speed scenarios as shown in figure 4. fig. 1. wind speed scenarios. fig. 2. representative wind speed scenarios. fig. 3. estimated power curve. fig. 4. representative wind power scenarios. engineering, technology & applied science research vol. 11, no. 3, 2021, 7201-7206 7203 www.etasr.com nguyen & le: day-ahead coordinated operation of a wind-storage system considering wind forecast … iii. the ac opf model a. objective function the problem is formulated into an ac opf model with an optimization goal of minimizing total system operating cost, which includes generating cost of all generating units and bes operation cost. ��� ∑ ∑ ���, � ��, �, ��� � ��, � �, ���� ���� ������ � ∑ ∑ ���,� �,���� � ���,� ��,���� �!������� (1) where �, ��� is real power generating at bus i and period t, ��,���� is the charging power of bes at bus i and period t, �,���� is the discharging power of bes at bus i and period t, ��, ; ��, ; ��, are the cost coefficients of generating unit at bus i, ���,�; ��,�are the cost coefficients for charging and discharging power of bes at bus j, ng is the number of generating units, ns the number of bess, and t is the optimization time horizon. b. system constraints the objective function must fulfill the following network constraints: • power balance: �, ��� � #, ��� � �, ��� � ��, ��� $ % ��� ∑ %&���'( &cos ,��� � -&���. � / &sin ,��� ��2&�� -&���.3 (2) 4�, ��� � 4#, ��� � 4�, ��� � 4��, ��� $ % ��� ∑ %&���'( &sin ,��� � -&���. � / &cos ,��� ��2&�� -&���.3 (3) where 4�, ��� is the reactive power generating at bus i and period t, #, ��� is the real load power at bus i and period t, 4#, ��� is the reactive load power at bus i and period t, 4�, ��� is the reactive discharging power of bes bus i and period t, 4��, ��� is the reactive charging power of bes at bus i and period t, % ��� is the magnitude of voltage at bus i and period t, %&��� the magnitude of voltage at bus k and period t, ��� the angle of voltage at bus i and period t, -&��� the angle of voltage at bus k, period t, ( & the line conductance of branch ik, / & the line susceptance of branch ik, and nb the total system bus number. • voltage magnitude limits: % ,5 6 7 % ��� 7 % ,589 (4) where % ,5 6 is the lower limit and % ,589 is the upper limit for voltage bus i. • generator power limits: �, :5 6 7 �, ��� 7 �, :589 (5) 4�, :5 6 7 4�, ��� 7 4�, :589 (6) where �, :5 6, �, :589 are the active and 4�, :5 6, 4�, :589 the reactive generating power limits. • branch current limits: ; ���� 7 ; �,589 (7) ;� ��� 7 ;� ,589 (8) where ; ���� is the magnitude of current flowing from i to j, in period t, ;� ��� the magnitude of current flowing from bus j to bus i, in period t, and ; �,589, ;� ,589 the current limits. c. bes constraints • energy balance: / ��� $ / :���� � �<�� ��, ��� � �, ���/<� δ� (9) where / ��� is the energy level of bes at bus i in period t, / :���� the energy level of bes at bus i in period � � 1, <�� the charging efficiency, <� the discharging efficiency, and ∆t the time interval between two consecutive periods. • charging/discharging power limits: �, :5 6 7 �, ��� 7 @ ,589 (10) ��, :5 6 7 ��, ��� 7 @ ,589 (11) where @ ,589 is the power rating of bes at bus i and ��, :5 6, �, :5 6 the minimum charging/discharging power of bes at bus i. • ess energy limits: / ,5 6 7 / ��� 7 / ,589 (12) where / ,5 6 is the minimum energy limit of bes at bus i and / ,589 the energy rating of bes at bus i. iv. the proposed approach the overall procedure for the proposed approach is described in figure 5, where ab is the number of representative wind power scenarios. according to this procedure, wind data are first preprocessed to create wind power scenarios. these wind scenarios and load data will be the input of the ac opf model which optimizes the operation of wind-storage systems. the model is run for all wind scenarios and the obtained results will be the optimal dispatching schedules for the systems. fig. 5. overall procedure of the proposed approach. engineering, technology & applied science research vol. 11, no. 3, 2021, 7201-7206 7204 www.etasr.com nguyen & le: day-ahead coordinated operation of a wind-storage system considering wind forecast … v. tests and results in this section, a case study is carried out on a modified ieee 14-bus network (figure 6), with a wind-storage system located at bus 6. the bes is used for energy arbitrage. it is charged from both wind and conventional sources during low price periods and discharged at peak price hours. the wind farm has an installed capacity of 85mw, accounting for 40% wind penetration level. there are 4 conventional generators, at buses 1, 2, 3, and 8, with total capacity of 292.4mw. the typical load per day, with peak value of 212mw, is calculated through statistical average data. wind scenarios are generated as described in section ii. the optimization horizon is 24h. simulations are performed for both deterministic and scenariobased cases, using matlab 2016a, on a pc with intel core i7 – 3.4ghz cpu and 8.0gb of memory. first, a base case is run with bes parameters as shown in table i and wind penetration level of 40% to obtain optimal day-ahead operating schedules of the wind-storage system. then, in order to show the effect of wind uncertainties on optimization results, sensitivity analysis is performed on bes capacities with different wind penetration levels in both deterministic and scenario-based cases. the energy arbitrage profits of the system are also calculated for all wind penetration levels. table i. bes parameters cdef [mw] gdef [mwh] hij hk 80 200 0.85 0.85 fig. 6. the modified ieee 14-bus system. as a result, the optimal output of wind storage system in a typical day can be observed in figure 7. as can be seen in this figure, the available wind generation in a single day is negatively correlated to the market price. however, with the use of bes, the actual wind-storage system output is made to positively follow market prices. accordingly, less power is generated during low-price hours (from 12 to 16), instead, more power is generated at peak-price periods (hours 7, 8 and 18 to 21). figure 8 presents the storage system operation. as can be seen, the bes has a large possibility of charging during valley hours to store more power and transfer that to peak hours for energy arbitrage. this operation effectively follows system market prices. fig. 7. the output of wind-storage system in a typical day. the optimal day-ahead power dispatches of bes in deterministic and scenario-based cases are shown in figure 9. this figure shows that bes operation follows the market price trend in all wind scenarios, thus effectively supports wind generation. fig. 8. bes operation. fig. 9. bes optimal day-ahead power dispatch. in order to see the impact of wind uncertainty on storage capacities, sensitivity analysis was performed. wind penetration level varied from 20% to 50% and the rest was kept to the same level as in the base case. deterministic and scenario-based models were run. the simulation results are shown in figure 10. it is seen that wind uncertainty has a high impact on bes capacities. for example, at 40% wind engineering, technology & applied science research vol. 11, no. 3, 2021, 7201-7206 7205 www.etasr.com nguyen & le: day-ahead coordinated operation of a wind-storage system considering wind forecast … penetration level, a bes capacity of approximately 45mw and 130mwh is required for the deterministic case while a bes capacity of about 59mw and 150mwh is found in the scenario-based case. besides, wind penetration level leads to increasing bes capacities. table ii shows the energy arbitrage profit of wind-storage system at different wind penetration levels, with and without bes. this table shows the obvious benefit of using energy storage systems along with a wind farm for energy arbitrage. in addition, considerably higher profits are gained for the wind-storage system with higher wind penetration levels. fig. 10. bes capacities. table ii. wind–storage system energy arbitrage profit [$] wind penetration [%] 20 25 30 35 40 45 50 no bes 7.14 x 10q 8.75 x 10q 1.028 x 10u 1.056 x 10u 1.058 x 10u 1.028 x 10u 7.68 x 10q with bes 7.24 x 10q 8.95 x 10q 1.064 x 10u 1.215 x 10u 1.362 x 10u 1.517 x 10u 1.644 x 10u vi. conclusions in this paper, a model was developed to simulate the bes operation for energy arbitrage in power systems with high wind integration. the problem was formulated into an ac opf model. wind uncertainty was taken into account by applying generation and reduction techniques. tests were carried out on a modified ieee 14-bus system and day-ahead optimal operation schedule for wind-storage system was obtained. the simulation results show that the use of bes with wind generation can significantly improve profit for wind farm operators, especially at high wind penetration level. furthermore, when considering wind uncertainty, higher capacities of bes are noted for the system as compared with deterministic cases, which means wind uncertainty should be examined in any optimization model with wind penetration. acknowledgment this research was funded by the ministry 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[online]. available: https://www.osti.gov/biblio/983731. microsoft word etasr_7-1_1429-1436.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1429-1435 1429 www.etasr.com rohani et al.: sensitivity analysis of workspace conflicts according to changing geometric conditions sensitivity analysis of workspace conflicts according to changing geometric conditions mohammad rohani faculty of civil engineering semnan university seman, iran m.rohani@ students.semnan.ac.ir gholamali shafabakhsh faculty of civil engineering semnan university seman, iran shafabakhsh@ semnan.ac.ir abdolhosein haddad faculty of civil engineering semnan university seman, iran ahadad@ semnan.ac.ir ehsan asnaashari faculty of civil engineering alaodole semnani institute seman, iran asnaashari.ehsan@ gmail.com abstract—workspace conflicts and building components can happen in different forms and both permanently and temporarily. these spatial clashes affect the work process and deplete the project process. geometric clash detection system of 4d simulation tools can identify the number of clashes for construction resources in the worksite to improve workflow planning. in the present research, building components and their corresponding workspaces were simulated, based on the schedule and activities, using a visual simulation tool. first, the total daily volumes of workspace were calculated according to the activities' schedule and compared by the available space in order to determine the critical days for the project. then, the number of time-based conflicts were examined and analyzed for building components and resources among activities and by different tolerance distances. the main objective of this study was to evaluate the sensitivity analysis of clash numbers based on the geometrical conditions in different statuses (inflexible, semiflexible and flexible) to assist the planner for detecting real conflicts. the results show that the tolerance distance of 0.2 to 1 meter for the clashes of workspace and the building components and 0.2 to 2 meters for the clashes of workspaces with each other to provide realistic results of actual construction operation conflicts. by the help of this methodology, the project planners are able to identify and prioritize the effective conflicts on the work process in comparison to the clashes resulted from iteration or minor design inaccuracy. keywords-building components; construction workspace; geometrical clashes; tolerance distance i. introduction time and cost management without investigating the required workspace for the execution of activities would not only be unrealistic, but also they can have additional consequences on projects costs. the required space for activities like the required resources for implementing activities, must be managed by planning and scheduling. the lack of the management for the required space for activities by conventional planning and scheduling techniques leads to the time-space conflicts [1], in which the required space of one activity is interrupted with the space required by another activity or workspace. in this regard, multi-dimensional cad models significantly help in identifying and resolving this conflict [2, 3], however, some problems are prevented from achievement. the first issue in developing these models is related to the capability of dynamic presentation [4, 5]. as the project site location is a dynamic one, each of the construction activities have their own workspace that are reformed by time. an activity can occupy different spaces in different stages of construction [6]. actually a simple 3d form in visual simulation of process cannot be used to present the workspace dynamics of the construction activities [7]. usually, "3d cad" models are used as the occupied space by building components and put other required workspaces aside. as a result, the cad models are not able to present realistic visualization of construction process [5]. therefore, the planners and project managers should collect and integrate the fragmented time and space information from different sources to display the project workspaces and the workflow of construction operation manually [8]. on the other hand, the progress of other fields such as information technology has affected the development of engineering and construction tools. this development has caused building information modelling (bim) to be one of the encouraging developments in architecture, engineering and construction (aec) sector [9, 10]. by bim based tools, visualization and simulation technologies and project management knowledge, the project planning and controlling can be performed with a better perspective and the information gaps of the projects that have huge financial and time consequences can be solved [11]. the construction industry needs a workspace model, in which the building components and the spaces required by working teams are merged, but this is not possible without the consideration of workspace details. despite the dynamism and changes of the workspaces required for activities over a period of time, these spaces still follow a distinct evolutionary process in most construction activities [6]. an ideal 4d construction planning system should be capable of dynamic presentation and be able to model and present dynamic elements and components acceptably [9, 12]. this study, providing the space for one day of work performance engineering, technology & applied science research vol. 7, no. 1, 2017, 1429-1435 1430 www.etasr.com rohani et al.: sensitivity analysis of workspace conflicts according to changing geometric conditions and simulation based on time to enable the planners for understanding of the real conditions of work progress and possible clashes of them. different types of clashes and their intervals can help planners in identification and prioritization of the important conflicts [13]. ii. research methodology this investigation is initiated by converting 2d drawings of buildings to 3d building components in a design software. next, the workspaces of one day's work which is correspond with each of the building components were designed and generated in the form of 3d volumes based on construction resources analysis. by using bim based tools (4d cad software) like naviswork manage [14], 3d volumes corresponding with the workspaces of resources (temporary appearance) and building components (permanent appearance) were visualized and simulated based on the schedule. the workspaces were designed according to the building component axis and for one day segments and the volumes were automatically estimated. the total amount of workspaces required for working teams and construction resources were estimated based on a schedule on a daily basis. then, this estimated daily volumes were compared to the total available space of each floor (level) to determine the days with critical space. finally, the time-based simulation is assessed in hard mode and with specific different distances to compare and analyze the resulted clashes in different intervals. these volume clashes have occurred between activities and in three general types: building components and workspaces, building components with each other and workspaces with each other. this system is of great help to the identification of clashes and appropriate intervals for any kind of clashes. in this way, the planners are able to identify and detect the effective workspace conflicts on the work process from the clashes resulted from iteration or design inaccuracy. iii. the quantity of workspaces by analyzing the construction resources, the required workspace for each of the activities is calculated and designed. considering that in the case study of 12 defined activities, only 9 activities were active. the space properties for each of the building components are estimated based on the square meter and meter length of the drawings and 3d volumes automatically and are presented in table i. also, the workspace volumes for the activities resources are specified in the mentioned table in total and in average. these volumes were created by automatic estimation of spaces in google sketchup software, in which all of the specifications of the considered component is inserted. table i. table of quantities and volumes of building components and workspace activity name & no. duration component quantity (m2 & ml) average of component (m2 & ml) workspace (m3) daily average of workspace (m3) 1.project total 60 2372 2. basement structure 0 0 0 3. external wall 15 418.2 27.9 1743.3 116.2 4. windows frames 12 1032 129 1009.8 84.2 5. interior wall 12 316.3 26.4 1640 136.7 6. gypsum plastering 12 480.8 40.1 790.8 65.9 7. concrete base 8 678 84.8 1882 235.3 8. ceramic tile 25 678 27.1 2404.8 96.2 9.fan coil unit & piping 5 53.4 10.7 555.9 111.2 10. cable tray 3 87 29 631.5 210.5 11.fabric-mate ceiling 18 678 37.7 3640.3 202.2 considering that the examined case study of this research is in floor level and the available space of construction is specified and limited, the volumes of construction resources are placed daily and base on schedule to determine the required space of each day. the volumes of the designed workspace are compiled daily base on schedule to determine the required space of the construction resources for each day and compare with the maximum available space [15] ( (1)). the available space of each floor level for each day is 2372 cubic meters that is much higher than the maximum required space of the projects days. total space required for each day is varied from 50 to 584 cubic meters and it was at its highest level from day 37th up to day 42th (table ii). also, the maximum required space is for the 40th day with 584 cubic meters that is lower than the available space of each level (floor) and it has worked, but the final number of spatial clashes is determined by 4d simulation. available space ≥ daily required (needed) space (1) iv. development of workspace for construction resources the most important factor in spatial formation and shaping is the final building component and the linear axis of these elements. the geometrical transparent volumes correspond to workspaces were formed along these lines and in the two dynamic and static categories [16]. the dynamic and static workspaces were created in parallel with components lines and in coordination with its development (figure 1). on the other side, the classification of the construction methods is a great help in organizing and configuration of the workspaces in the worksite [17]. therefore, geometric volumes were generated for activities in each day of project by utilizing resource analysis, construction methods classification and the building components axis. engineering, technology & applied science research vol. 7, no. 1, 2017, 1429-1435 1431 www.etasr.com rohani et al.: sensitivity analysis of workspace conflicts according to changing geometric conditions table ii. total daily and schedule based required volumes of the construction resources days no. act. 3 act. 4 act. 5 act. 6 act. 7 act. 8 act. 9 act. 10 act. 11 daily required space (m3) day1 99 99 day2 125 125 day3 161 161 day4 160 160 day5 123 83 206 day6 99 85 184 day7 110 85 195 day8 99 83 182 day9 111 83 195 day10 111 84 195 day11 115 85 200 day12 111 85 196 day13 111 85 212 408 day14 99 85 170 354 day15 107 83 94 285 day16 84 121 205 day17 146 146 day18 149 149 day19 142 142 day20 149 149 day21 96 96 day22 131 131 day23 110 110 day24 119 119 day25 61 81 230 372 day26 58 117 234 409 day27 50 110 168 328 day28 74 143 217 day29 51 106 157 day30 50 50 day31 60 60 day32 61 61 day33 88 88 day34 90 90 day35 88 219 306 day36 60 242 81 382 day37 236 111 194 541 day38 252 83 202 537 day39 252 78 193 522 day40 228 151 204 584 day41 246 86 151 482 day42 207 65 156 429 day43 86 216 303 day44 94 241 334 day45 121 276 397 day46 94 286 380 day47 94 207 301 day48 121 233 354 day49 94 152 245 day50 90 144 235 day51 117 191 308 day52 90 214 305 day53 57 186 243 day54 134 193 327 day55 83 83 day56 79 79 day57 80 80 day58 94 94 day59 128 128 day60 96 96 engineering, technology & applied science research vol. 7, no. 1, 2017, 1429-1435 1432 www.etasr.com rohani et al.: sensitivity analysis of workspace conflicts according to changing geometric conditions fig. 1. the development of workspaces based on the building components axis in this method, the spaces of building components were utilized separately from the workspaces of construction resources and their nature were different in terms of appearance. therefore, they should be categorized in different groups in order to simulate activities in a correct way. two kinds of activities can be defined in visual simulation software for appearance. these types of appearance in the simulation model should be in accordance with the nature of construction activities and their correspond resources. these definitions of the activities determine the way in which the volumes corresponding the activities appear in visual simulation software. considering the micro level of the case study defined for the activities and the construction resources, both the permanent (construct) and temporary activities are applied. building components are of construct type during the simulation and were attributed to the corresponding activities with all of the volumes (3d components) that were permanent from the time of appearance to the end of simulation. this group includes building components and elements such as doors, windows, floors, walls and so on. the appearance of these activities in the beginning of the activity is as transparent volumes with green color and in the end of the activity the final 3d model of the building component appears and remains to the end. because of breaking the building components down to one day's building components, these components were added daily and based on the schedule to the volumes and remain. 3d components related to the workspace were in temporary state and only appear in the time of activity performance in simulation. temporary activities were corresponding to the construction resources in three categories of materials, machinery or equipment and manpower. for each of the resources, an attributed space was designed that covered the main resource in the form of transparent and geometric volumes. the workspace of the construction resource was defined to produce the building components of one day and it is appeared daily and continuously besides building components and is hidden in the end of that day. actually, after the construction of one day's workspace were hidden and then the corresponding volumes with 3d building components were appeared and remained to the end. v. conflict analysis of building components and construction resources the most fundamental issue in the workspace planning is the dynamism and mobility of the available workspace. first, because different sub-contractors and working-teams occupy workspace in a similar way and lead to spatial conflicts. second, the building components change the available space of the activity and generally these spaces become more restricted by the project progresses[18]. for instance, by constructing of interior walls, the available space of floor has changed and divided to smaller parts for other activities. the experienced planners consider the availability of workspaces based on the personal view in the projects, but it is not according to specific principles and mechanism. a distinctive feature of the construction projects which distinguishes it from other sector is the changing of workspace by passing time. while the spatial configuration of the manufacturing in factory has an emphasis in the equipment’s layout and remains permanent and static in the space production [8]. the time-based conflicts creates integration of time-based simulation by clash detection method. actually, permanent and temporary 3d volumes were appeared and disappeared based on the timeline of activities and on the specific location. two or more volumes corresponding to the workspace and building components can occupy a specific space simultaneously and create clashes that lead to workspace conflicts. launching the time-based clash detection examines the clashes automatically during the construction operation. therefore, each clash is recorded and identified together with its time, coordination and the clash distance to enables the user for analyzing the project space situation. generally, the methods of detecting spatial clashes for the activities are in two forms. the first choice is the cross section method (hard) in which a test for the detection of geometric cross clash among volumes is conducted. in this case, a negligible distance is defined for the clash, so if the geometric clash distance is more than that distance, then a conflict is recorded. the second option is called the tolerable permission, in which a distance between two volumes is defined and any distance less than that is unpermitted. if the distance between two geometric volumes is more than the determined distance by the user, no spatial conflicts are recorded. for instance, facility pipes need space as insulation around them, which requires a minimum distance between these two volumes. in this regard, the three types of clashes were compared and analyzed using the hard mode and in various distances. a. inflexible conflicts (3d components against each other) the clashes of building components with each other occur in conditions that the design is problematic and the permanent components are located and occupied in the same location [16]. these clashes are not investigated based on time and should be examined toughly and with geometric crosses, without any permitted distance. in a context that the 3d geometric models were derived from 2d space drawings and positioned on the specific axis from different disciplines, it is possible that occurs conflicts[19]. this problem can arise from some reasons such engineering, technology & applied science research vol. 7, no. 1, 2017, 1429-1435 1433 www.etasr.com rohani et al.: sensitivity analysis of workspace conflicts according to changing geometric conditions as miscalculations or the lack of awareness of other discipline changes. in such cases, the design issue should be removed from all activities of projects and no clashes are acceptable. in the modeling of this research, nine activities were derived from three architectural, mechanical and electrical disciplines and based of 2d drawings. then, these 2d construction documents were imported to google sketchup software to make the 3d models. these building components were examined in hard geometric clash detection with zero acceptable clash range, and the number of 316 geometric and design clashes were identified. by changing the acceptable distance of the clashes from 0 to 0.3 meter, the quantity of clashes reached from 316 to zero. the first case of clash in design was between dropped ceiling and interior dry walls which is shown in figure 2. also, the graph of clash quantity changes is presented in table iii with its acceptable changing range. in fact, the accuracy of the modeling contains 30 cm error which is not an acceptable distance for engineering design and multi-discipline layouts. according to the statistics, only 7.3% of the clashes (23 cases) have been continued in more than 0.1 meters, and were mainly caused by the vertical items like dry wall with suspended ceiling. the large number of remained clashes (92.3%) were related to minor errors in the volume design that have not a great impact on the construction operation and can be resolved easily by design modifications. table iii. sensitivy analysis of inflexible conflicts in different distance intervals 3d components against 3d components (hard type of clash detective on non-time-liner simulation) tolerance distance (m) 0.3 0.25 0.20 0.10 0.00 clash numbers 0 10 14 23 316 percent 0% 3.2% 4.4% 7.3% 100% b. semi-flexible conflicts (3d components against 3d workspaces) by the project progression and the creation of permanent building elements based on the schedule, the available workspace is affected especially in micro level construction. in fact, by the creation of building components, the workspace of the activities are restricted and new obstacles are created for the dynamic space of the construction resources. actually, the dynamic volumes of the construction resources that correspond to the workspaces may have clashes with static building elements. although, according to the construction requirements and the execution nature of activities, dependency and delays between these activities must be considered correctly and at the beginning of the planning by experts' planners, so that they do not prevent each other's operation. but the building component development can restrict the upcoming activity resources' workspace. for example, the activity of constructing the interior wall causes the breakdown of the floor space and the delay in construction of the next activities' space. these limitations do not make the other activities' execution and construction impossible, but make more difficulties and hinders for the movement of materials and human resources. so, minimizing these kind of clashes can be very effective by itself. the changing of these clashes according to tolerance distance are depicted in table iv. as it can be seen, only the building components of the three activities of 3, 5 and 6 had clashes with the other construction workspaces with the distance of more than 0.1 meters. as predicted, most of the clashes were related to the construction of internal walls that occurred for distances up to 3 meters. after that, the building components of the external brick-laying activities and plastering that cover the surrounding operations of floor have made the most conflicts with other workspaces. the other clashes between 0 to 0.2 meter distances can resolved by increasing the accuracy of design and decreasing the overlap of the volumes. this minor interferences were negligible and they do not prevent the progress of the construction operation because of their slight quantity between the resource clashes (dynamic volumes) and permanent building components (static volumes). one of the examples of these spatial conflicts is presented in figure 3. as shown in this figure, the 3d building components of dry wall have space conflict with 3d workspace of ceramic tiling activity. this clash was detected in visual simulation in wide ranges of tolerance distance. c. flexible conflicts (3d workspaces with each other) the challenges of time-space conflicts analysis in construction projects include 3d spatial and temporal conflict detection. the temporary dimension of the time-space conflicts indicates that the spatial conflict detection among activities must include 3d geometric clashes in specific time intervals that shows the time aspect of these conflicts [13]. in addition, many kinds of time-space conflicts can occur between the activities and the quantity and intensity of them are varied. one simple 3d shape cannot be used to present the dynamism of the workspace in construction activities. in this regard, this study by breaking down the volumes related to the construction resources and assigning daily activities to them caused the dynamic and real presentation of work flow development. the activities related to the workspace volumes mutually were examined with other activities' workspace volumes in the visual simulation software to specify the spatial clashes. the geometric clash detection were performed in visual simulation software to record the cross section volumes corresponding to the workspaces with each other in the hard type and in the permitted distances of 0 to 3.5 meters. this test is presented in table iv. from the information analysis and the visualization of clashes it can be concluded that in the range of 0 to 0.1 meters, the quantity of clashes are decreased to 49%, which was mainly for the repeated or minor overlaps of the workspace. the conflicts of this range can be solved by a slight review and design of the spatial volumes. on the other hand, the clashes would not much change and in the real conditions it would be led to serious conflicts in the range of 0.1 to 2 meters. in this interval, the clashes have reached from 32 to 18 and they are mostly related to the workspace of the three activities of 3, 6 and 8 construction activities resources. the maximum workspace clashes are related to the ceramic flooring activity (8) which has conflicts with other workspaces such as fabricating of the suspended ceiling. engineering, technology & applied science research vol. 7, no. 1, 2017, 1429-1435 1434 www.etasr.com rohani et al.: sensitivity analysis of workspace conflicts according to changing geometric conditions table iv. sensitivy analysis of flexible conflicts in different distance intervals 3d workspaces against 3d workspaces (time-liner hard conservative) tolerance distance (m) 3.5 3 2.5 2 1.5 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 act.3 clashes 0 2 2 3 3 4 4 5 7 7 7 7 7 7 7 10 act.4 clashes 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 act.6 clashes 0 0 0 0 1 2 2 2 2 3 3 3 3 3 3 4 act.7 clashes 0 0 0 0 1 2 2 2 2 2 2 2 2 2 2 2 act.8 clashes 0 0 6 14 14 15 16 16 16 16 17 18 18 18 25 58 act.9 clashes 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 act.10 clashes 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 total clash numbers 0 3 9 18 20 24 25 26 28 30 31 32 32 32 39 76 percent 0% 4% 12% 24% 26% 32% 33% 34% 37% 39% 41% 42% 42% 42% 51% 100% in 2 to 3 meters ranges, the number of conflicts decreased completely and reached to zero and does not provide an appropriate interval for the serious consideration of the workspace clashes. the clashes of workspaces with each other are temporary, related to time dimension and instead they are depended on the dynamic resources and can be solved by different strategies. one of the examples of these spatial conflicts is presented in figure 4. as shown in this figure, the 3d workspaces required for installation of cable tray have time-space conflict with 3d workspace of plumping fan coil activity. this clash was detected in visual simulation in almost all ranges of tolerance distance which demonstrates its necessity situation. fig. 2. a sample of building components design clashes vi. results and findings the number of conflicts were explored in three states of flexible, semi-flexible and rigid with clash ranges from 0 to 3.5 meters. the highest number of clashes was shown as 100% and the condition without any clashes was considered as 0% (figure 5). although in design clashes no permitted intervals were acceptable, but the main and the most important clashes that can be examined and be effective in the design process were related to 0.1 meters and further. the semi-flexible clashes between dynamic construction resources (workspaces) and static building components showed that the 0.2 to 1 meter intervals had a great impact on the project progression and must be solved. the clashes of flexible workspace with each other in 0.2 to 2 meter intervals were consistent and caused by the operation inconsistencies. in this interval, the number of conflicts were close and it is essential to solve them by using of conflict resolution strategies. fig. 3. a sample of flexible spatial conflict for workspaces. fig. 4. a sample of flexible spatial conflict for workspaces vii. conclusion in the present study, the relation between the numbers of clashes in different modes according to the geometric condition was examined. to achieve this goal, after analyzing the 3d components of interior wall 3d workspaces of ceramic tilling 3d workspaces of cable tray 3d workspaces of fan coil 3d components of interior wall 3d components of fabric-mate ceiling engineering, technology & applied science research vol. 7, no. 1, 2017, 1429-1435 1435 www.etasr.com rohani et al.: sensitivity analysis of workspace conflicts according to changing geometric conditions construction activities and calculating the corresponding volume quantities for resources in each day, the building component and resource spaces were defined permanently and temporarily. the corresponding geometric volumes with these spaces were formed and generated in the 3d shape using building component axis and its daily quantity. then, these 3d volumes were linked to the correspond activities in the timeline to visual simulation software. the 4d cad model was simulated based on time in three statuses of building components with each other, workspaces with each other and the combination of workspaces and building components. then, the time-based clashes of each category by different permitted distances were examined to determine the way of changing the number of clashes based on this condition changing. this system effectively helps designers and planners in finding the permitted range of volume clashes and can identify the clashes that affect the project progression and delay the project work flow. fig. 5. the percent of clashes in three different modes and based on different permitted intervals references [1] a. mahalingam, r. kashyap, c. mahajan, “an evaluation of the applicability of 4d cad on construction projects”. automation in construction. vol. 19, no. 2, pp. 148-159, 2010 [2] h. moon, n. dawood, l. kang, “development of workspace conflict visualization system using 4d object of work schedule”. advanced engineering informatics. vol. 28, no. 1, pp. 50-65, 2014 [3] b. koo, m. fischer, “feasibility study of 4d cad in commercial construction”. journal of construction engineering and management. vol. 126, no. 4, pp. 251-260, 2000 [4] b. akinci, k. tantisevi, e. ergen, “assessment of the capabilities of a commercial 4d cad system to visualize equipment space requirements on construction sites”, construction research congress. p. 1-7, 2003 [5] k. tantisevi, b. akinci, “automated generation of workspace requirements of mobile crane operations to support conflict detection”, automation in construction, vol. 16, no. 3, pp. 262-276, 2007 [6] x. su, a spatial temporal information model for construction planning, purdue university, 2013 [7] h. j. wang, j. p. zhang, k. w. a. chau, “4d dynamic management for construction planning and resource utilization”, automation in construction, vol. 13, no. 5, pp. 575-589, 2004 [8] g. winch, s. north, “critical space analysis”, journal of construction engineering and management, vol. 132, no. 5, pp. 473-481, 2006 [9] t. hartmann, j. gao, m. fischer, “areas of application for 3d and 4d models on construction projects”. journal of construction engineering and management, vol. 134, no. 10, pp. 776-785, 2008 [10] m. rohani, g. shafabakhsh, a. haddad, e. asnaashari, “operation planning of concrete box girder bridge by 4d cad visualization techniques”, international journal of civil, environmental, structural, construction and architectural engineering. vol. 10, no. 6, pp. 790796, 2016 [11] v. c. dixit. “4d modeling: adding a new dimension to cpm scheduling”, aace international transactions, 2007 [12] d. heesom, an analytical system for space planning on construction sites, university of wolverhampton, 2004 [13] b. akinci, m. fischen, r. levitt, r. carlson, “formalization and automation of time-space conflict analysis”, journal of computing in civil engineering, vol. 16, no. 2, pp. 124-134, 2002 [14] r. morkos, j. macedo, m. fischer, c. somu, “quantifying effects of specific 4d tool functionalities on 4d modeling productivity”, proceedings of the cib w78, beirut, lebanon, 2012 [15] w. thabet, y. beliveau, “modeling work space to schedule repetitive floors in multistory buildings”, journal of construction engineering and management, vol. 120, no. 1, pp. 96-116, 1994 [16] i. chen wu, y. chang chiu, “4d workspace conflict detection and analysis system”, conference on construction applications of virtual reality, 2010 [17] m. rohani, m. fan, c. yu, “advanced visualization and simulation techniques for modern construction management”, indoor and built environment, vol. 23, no. 5, pp. 665-674, 2014 [18] m. kassem, n. dawood, r. chavada, “construction workspace management within an industry foundation class-compliant 4d tool”. automation in construction. vol. 5, no. 2, pp. 42-58, 2015 [19] d. riley, “the role of 4d modeling in trade sequencing and production planning”, construction congress vi, pp. 1029-1034, 2000 engineering, technology & applied science research vol. 9, no. 1, 2019, 3826-3831 3826 www.etasr.com oad et al.: effect of water-cement ratio on flexural strength of rc beams made with … effect of water-cement ratio on flexural strength of rc beams made with partial replacement of coarse aggregates with coarse aggregates from old concrete mahboob oad department of civil engineering, quaide-awam university engineering, science & technology, pakistan engrmahboob04@gmail.com abdul hafeez buller department of civil engineering, quaide-awam university engineering, science & technology, pakistan ah.buller@quest.edu.pk bashir ahmed memon department of civil engineering, quaide-awam university engineering, science & technology, pakistan masher_m@hotmail.com noor ahmed memon department of civil engineering, quaide-awam university engineering, science & technology, pakistan nahmedmemon@gmail.com zaheer ahmed tunio department of civil engineering, quaide-awam university engineering, science & technology, pakistan zaheerahmedtunio@gmail.com muneeb ayoob memon department of civil engineering, quaide-awam university engineering, science & technology, pakistan engr.muneebmemon@gmail.com abstract—this research paper presents an experimental evaluation of the effect of water-cement ratio on the flexural strength of reinforced concrete beams made with 50% replacement of coarse aggregates with recycled concrete aggregates (rca). 72 reinforced concrete beams were cast using 0.54, 0.6, 0.65 and 0.70 water-cement ratio. in each ratio, 12 beams were cast using rca and 3 beams were cast using allnatural coarse aggregates (nca). beams were cured for 7 and 28 days. after curing, all beams were tested with central point load in a universal load testing machine. from the obtained results, it is observed that the maximum reduction in flexural strength of rca beams is about 28% when compared to the 0.54 w/c ratio beams of the same group and 31.75% in comparison to nca beams cast with same w/c ratio. the maximum deflection and average strain in beams remained within limits. the observed cracking pattern shows shear failure of all beams. keywords-recycled concrete aggregates; green concrete; reinforced concrete; beams; flexural strength; water/cement ratio i. introduction demolishing of old structures generates huge amounts of demolishing waste. proper management of this waste is essential. for a long time, dumping of this waste in landfills was the main practice. research on this issue led to the utilization of useable materials in new constructions. a big percentage of this waste is old concrete which can be used as coarse aggregates in new concrete. this technique not only solves, to some extent, the management issue of demolished waste and paves the way to save the natural coarse aggregates but also can lead to financial benefit of the new construction. to this end, different researchers remained engaged in exploring the possibilities of utilization of this waste by conducting research to understand the behavior of this material [1-6]. authors in [8] conducted research on reinforced concrete beams made by 50% replacement of natural coarse aggregates with aggregates from old concrete to study its flexural behavior. the results show good flexural behavior correlation with the one from reinforced concrete beams of the same size and steel reinforcement made with 100% natural coarse aggregates (normal concrete). authors in [17-18] presented flexural stress-strain behavior of reinforced concrete beams made with recycled concrete aggregates for normal and rich mix concretes. they used 7and 28-day curing. they recorded 8.8% and 2.59% reduction in flexural strength of the proposed beams for normal and rich mix beams respectively. water-cement (w/c) ratio plays a vital role in concrete mix to ensure the workability which in turn ensures the proper strength of reinforced concrete. it is a general observation that on old concrete as coarse aggregates water absorption is higher than that of normal coarse aggregates [7]. this demand of higher w/c ratio in concrete mix using old concrete as coarse aggregates to make the new concrete workable to the extent corresponding author: m. oad engineering, technology & applied science research vol. 9, no. 1, 2019, 3826-3831 3827 www.etasr.com oad et al.: effect of water-cement ratio on flexural strength of rc beams made with … that it does not give rise to bleeding or honeycombing. in a research to study the effect of different w/c ratios on sulphate resisting concrete, authors in [9] used four different ratios ranging from 0.45 to 0.75. they concluded that lean mixes and compression members were affected more than rich mixes and flexural members respectively. they also observed that concrete mix with w/c ratio more than 0.55 was affected more when exposed to sulphate attack. on the study of the effect of w/c ratio on portland cement, author in [10] studied the effect of different w/c ratios with negerian grande 42.5 opc. he used w/c ratio ranging from 0.5 to 0.6 with increment of 0.05 to produce normal concrete in 9 batches. he also used 2 different sizes of 19mm and 12.5mm washed gravel. he concluded that only concrete mix with 19mm washed gravel and 0.5 w/c ratio obtained marginally higher flexural strength than the standard value. he also observed that although the flexural strength of the above-mentioned mix remained within the range of standard values yet, the tensile strength of the same mix remained less than standard values. towards the research on lateritic concrete and the effects of w/c ratio on it, authors in [11] conducted experimental work to study the effects of w/c ratio on the workability and compressive strength of concrete and lateritic concrete. they used w/c ratio in the range of 0.55– 0.8 and curing periods of 7 and 28 days. they observed decrease in compressive strength of concrete when w/c ratio was more than 0.65. based on the experimental results of slump and compressive strength, they concluded that lateritic concrete is not as suitable and workable as normal concrete. in [12], authors conducted experimental work to evaluate the modulus of rupture of concrete with different w/c ratios. they used 15 prototype beams with different w/c ratios. after curing of 28 days, the test results showed that optimum flexural strength was obtained with w/c ratio of 0.58 beyond which they observed significant reduction in flexural strength. therefore, they concluded that 0.58 is the optimum w/c ratio to obtain maximum flexural strength of concrete prototype beams. authors in [13] conducted experimental study using m20 concrete to check the effect of water type i.e. tap water, waste water, well water, bore well water and mineral water on the compressive strength of concrete. they cast 150mm cubes and cured them for 7 and 28 days. after curing, they tested the cubes. based on the obtained results, they concluded that there was no significant variation in concrete compressive strength. although it is surprising that they used waste water, the results show no countable variation in the compressive strength results. authors in [14] researched the effect of water ratio on portland cement pastes. they used w/c ratio in the range of 0.19 to 0.5 to prepare cement pastes and studied their composition and morphology. they concluded that lower w/c ratio gave rise to crack propagation and lowered compressive strength. finding alternatives of cementitious products is an active research area. authors in [15] studied the effect of w/c ratio on the mechanical properties of blended cement containing bottom ash and limestone. they used 10% of both limestone and bottom ash with 0.35–0.55 w/c ratio to study the compressive and flexural strength of cement mortar specimens cured for 2, 7, 28 and 60 days. test results showed that both compressive and flexural strength were same to the ones of control concrete specimens at w/c ratio of 0.4 but they reduced with increase in w/c ratio untill it reached 0.5. they attributed this phenomenon to the pozzolanic reaction of the cement. based on the test results they concluded that at 28 days curing, both flexural and compressive strength of the proposed product went higher than the control specimens. they also concluded that as w/c ratio increased beyond 0.4 to 0.5 both blended cement and ordinary cement gave higher values of compressive and flexural strength. this shows the validity of the use of the proposed product in concrete mix. authors in [16] conducted research to study the effect of w/c ratio and cement content on the properties of fresh concrete without admixtures using 8 different mortar mixes. based on the test results they developed relationships for fresh concrete without admixtures. the experimental and analytical research remains active on the subject matter, but the scatter of results and, in a few cases, the unavailability of data, proves that more research is required to build confidence for the use of concrete made with partial replacement of coarse aggregates with old concrete. this motivated the current research. this paper presents the effect of w/c ratio on the flexural strength of reinforced concrete beams made with 50% replacement of natural coarse aggregates with coarse aggregates from demolished concrete. selection of 50% replacement is based on the outcome of the authors’ research presented in [7]. to achieve the proposed task, four different water cement ratios i.e. 0.54, 0.6, 0.65 and 0.7 were used to study the effect of w/c ratio on the flexural strength of rc beams made with partial replacement of natural coarse aggregates with recyclable aggregates. in each value of w/c ratio, 18 reinforced concrete beams were prepared. these beams were prepared in two groups. in the first group, 12 beams were cast using 50% replacement of natural coarse aggregates with recycled aggregates from old concrete and 6 beams with all-natural coarse aggregates. concrete ingredients for all w/c ratios were batched using 1:2:4 mix with weight batching process. in all beams ordinary portland cement, hill sand, 50% natural crushed coarse aggregates of size up to 25mmand and 50% recycled aggregates from old concrete of size up to 25mm as coarse aggregates were used. 50% of these beams were cured for 7 days and 50% were cured for 28 days. water curing in standard manner was used. old concrete in the shape of large blocks was collected from demolished, approximately 60-year-old reinforced concrete buildings. the large blocks of old concrete were hammered down to the required size. screening of the small particles was done to separate and discard the cracked particles. sieving was done to obtain aggregates of size up to 25mm in standard manner. to reinforce the beams 2#4 deformed bars were used both in tension and compression zones with #3 stirrups at 150mm center to center distance. the dimension of all used beams was 150mm×150mm×900mm. after curing, all beams were tested in a universal testing machine with central point load as per astm c-293. the obtained results are presented, analyzed and compared with the ones from the control specimens. analysis of the results shows that old concrete as coarse aggregates can be used in new concrete without much loss of flexural strength. the outcome of this research work is a landmark in understanding the effect of different w/c ratios on the flexural strength of reinforced concrete beams. this research work used four water cement ratios with commonly used concrete mix ratio. however, more w/c ratios and concrete mix ratios with engineering, technology & applied science research vol. 9, no. 1, 2019, 3826-3831 3828 www.etasr.com oad et al.: effect of water-cement ratio on flexural strength of rc beams made with … old concrete from different sources may be used to refine the results. ii. model description and testing this work aims to evaluate the effects of w/c ratio on the flexural strength of reinforced concrete beams made by 50% replacement of natural coarse aggregates with old concrete. to achieve this purpose, a total of 72 reinforced concrete beams were prepared. the old concrete was collected from nawabshah city. the old concrete, collected in shape of large blocks, comes from a school building about 60 years old. the large concrete blocks were hammered down to size approximately equal to 25mm. due to the age and hammering action on large blocks, smaller pieces might have been cracked. the cracked particles should be week and may produce weaker concrete specimens. therefore, the material was screened to separate and discard the cracked particles. sieving was then performed in standard way to get aggregates of size up to 25mm. sieving of natural coarse aggregates was also performed in a similar fashion. the comparison of the gradation of both coarse aggregates is shown in figure 1. the size of all beams is kept the same and equal to 150mm×150mm×900mm (figure 2). ordinary portland cement, hill sand, crushed natural coarse aggregates and old concrete as coarse aggregates in 50% proportion were then batched using batching weight method. four different w/c ratios i.e. 0.54, 0.6, 0.65 and 0.7 were used to prepare the reinforced concrete beams. under normal conditions the commonly used concrete mix is 1:2:4 therefore it is selected in this research work. to reinforce the beams, deformed bars were used. 2#4 bars were used in both tension and compression zones respectively. to provide shear reinforcement in beams, #3 bars at 150mm center to center were used. for each value of w/c ratio mentioned above, 12 beams were cast using 50% replacement of natural coarse aggregates with old concrete. 50% of these beams were cured for 7 and 50% for 28 days respectively. water curing in standard manner was adopted. fig. 1. gradation of coarse aggregates fig. 2. beam dimensions and reinforcement to compare the results of the proposed beams, 24 reinforced beams with 100% natural coarse aggregates were also prepared with the same size and reinforcements. similar to the procedure adopted for the proposed beams, these beams were cast and cured, but in each group the number of beams was restricted to 3. table i gives details for all the beams. after the elapse of curing time, all the beams were tested in a universal load testing machine with central point load in accordance with astm c-293. figure 3 shows the loading arrangement of a typical beam. during the testing, load, deflection and strain were observed at regular intervals. also, cracking in beams was observed and recorded. flexural strength was then computed numerically from the recorded load. the average values of the above-mentioned parameters are given in tables ii and iii for 7and 28-day cured beams. table i. details of the reinforced concrete beams group w/c ratio % rca number of beams reinforcement 7-day curing 28-day curing top & bottom zone stirrups g54 0.54 50 6 6 2#4 #3 @ 150mm c/c 0 3 3 2#4 #3 @ 150mm c/c g60 0.60 50 6 6 2#4 #3 @ 150mm c/c 0 3 3 2#4 #3 @ 150mm c/c g65 0.65 50 6 6 2#4 #3 @ 150mm c/c 0 3 3 2#4 #3 @ 150mm c/c g70 0.70 50 6 6 2#4 #3 @ 150mm c/c 0 3 3 2#4 #3 @ 150mm c/c table ii. 7-day cured beams w/c ratio 50% rca 0% rca flexural strength strain deflection flexural strength strain deflection 0.54 24.342 0.00270 4.405 25.873 0.00279 3.957 0.60 22.254 0.00275 3.909 24.141 0.00246 3.709 0.65 20.118 0.00225 5.233 22.441 0.00218 4.633 0.70 18.783 0.00225 5.818 21.147 0.00215 5.250 table iii. 28-day cured beams w/c ratio 50% rca 0% rca flexural strength strain deflection flexural strength strain deflection 0.54 28.15 0.00230 4.37 29.70 0.00218 3.73 0.60 26.25 0.00227 4.22 28.07 0.00245 3.86 0.65 23.44 0.00233 4.76 25.05 0.00215 4.26 0.70 20.27 0.00231 4.91 21.84 0.00215 4.39 fig. 3. loading arrangement iii. results and discussion the results of load testing were analyzed for maximum values of proposed parameters. it was observed that for the same w/c ratio the difference remained within 15%. numerically computed flexural strength vs strain is plotted in figures 4 to 7 for 7and 28-day cured beams of 0.54, 0.60, 0.65 and 0.70 w/c ratios respectively. engineering, technology & applied science research vol. 9, no. 1, 2019, 3826-3831 3829 www.etasr.com oad et al.: effect of water-cement ratio on flexural strength of rc beams made with … (a) (b) fig. 4. flexural strength vs strain for w/c ratio=0.54. (a) 7-day curing, (b) 28-day curing. (a) (b) fig. 5. flexural strength vs strain for w/c ratio=0.60. (a) 7-day curing, (b) 28-day curing. it is observed that the pattern of the graphs remained similar within the w/c ratio. peak values of rca beams exhibited lower maximum flexural strength and higher strain than nca beams. it was also observed that with increase in w/c ratio (i.e. 0.65 and 0.70), strain fluctuated at higher values of flexural strength, but the peak values of strain for all beams remained within limits. the similar trend of flexural strength and strain is observed in both rca and nca beams. maximum values of deflection (tables ii and iii) remained within the limits of approximate maximum deflection except for 3 values of 7-day cured beams. out of these, 7-day cured beams of 0.65 w/c ratio exhibited 4.66% higher deflection, and both rca and nca beams of 0.7 w/c ratio exhibited 5% and 16.36% higher values. this may be due to their higher w/c ratio and early age of concrete because deflection of 28-day cured beams of same w/c ratio remained within limits. (a) (b) fig. 6. flexural strength vs strain for w/c ratio=0.65. (a) 7-day curing, (b) 28-day curing. flexural strength vs w/c ratio is plotted in figure 8 for 7 and 28 days of curing. from figure 8, it is observed that the residual flexural strength of 7-day cured rca beams in comparison to the rca beams of 0.54 w/c ratio is 91.42%. 82.34% and 68.47% for beams made with 0.60, 0.65 and 0.70 w/c ratio respectively. similar trend of reduction of flexural strength with increase in w/c ratio is observed for 7-day cured nca beams with minimum of 6.7% and maximum of 18.27% loss in flexural strength. while comparing 7-day cured rca beams with 7-day cured nca beams keeping w/c ratio of 0.54 of nca beams as base measure, it is observed that the reduction of flexural strength is 94.43%, 86.01%, 77.75% and 72.59% for w/c ratios of 0.54, 0.60, 0.65 and 0.70 respectively. similar to 7-day cured beams, 28-day cured rca beams exhibited 93.25%, 83.27% and 72.01% residual flexural strength for rca beams of w/c ratio equal to 0.60, 0.65 and 0.70 respectively. same cadre nca beams also exhibited reduction in flexural strength of 5.49% minimum and 28.79% maximum. keeping nca beams with w/c ratio equal to 0.54 as base measure, residual flexural strength of rca beams is recorded as 94.78%, 88.38%, 78.92% and 68.25% for w/c ratios equal to 0.54, 0.60, 0.65 and 0.70 respectively. engineering, technology & applied science research vol. 9, no. 1, 2019, 3826-3831 3830 www.etasr.com oad et al.: effect of water-cement ratio on flexural strength of rc beams made with … (a) (b) fig. 7. flexural strength vs strain for w/c ratio=0.70. (a) 7-day curing, (b) 28-day curing (a) (b) fig. 8. flexural strength vs w/c ratio: (a) 7-day curing, (b) 28-day curing first crack, cracking pattern and cracks at failure were also recorded (figure 9). it is clearly observed that the failure mode of the beams is shear failure and is in line with the failure mode of nca beams. from the above discussion it is evident that increase in w/c ratio leads to reduction in flexural strength of both nca and rca beams. however, the maximum reduction in flexural strength of rca beams with w/c ratio equal to 0.70 is recorded as about 28% in comparison to rca beams of 0.54 w/c ratio. the same in comparison to nca beams of 0.54 w/c ratio is equal to 31.75%. therefore, it is concluded that although increase in w/c ratio improves the workability of concrete, it affects flexural strength leading to early failure of the beams. however, it is worth noting that the reduction in flexural strength is independent of the type of coarse aggregate. this infers the viability of the usage of the rca in concrete. fig. 9. cracking in beams iv. conclusion use of recycled old concrete as coarse aggregates in new concrete and the effects of water-cement ratio on its flexural strength are combined and studied experimentally in this research paper. the dosage of rca is kept 50% in all beams. 48 proposed beams were cast using 0.54, 0.60, 0.65 and 0.70 w/c ratios. in addition, 24 nca beams with 6 beams of each w/c ratio were cast to compare the results. half beams in each w/c ratio were cured for 7 and half for 28 days. all beams were then tested in a universal load testing machine with central point loading. from the obtained results it is observed that rca can be used in new concrete as deflection, strain, cracking pattern are in good agreement with nca beams for all considered w/c ratios. the results also revealed that flexural strength of the proposed beams reduced with increase in w/c ratio. the maximum strength reduction of proposed beams in comparison to nca beams made with 0.54 w/c ratio is equal to 31.75%. whereas, 26.46% reduction in flexural strength of nca beams with 0.7 w/c ratio in comparison to the same group of beams of 0.54 w/c ratio was noted. therefore, the strength reduction for the highest w/c ratio considered in this research work is within 5%. references [1] c. thomas. j. setien, j. a. polanco, “structural recycled aggregate concrete made with precast wastes”, construction and building materials, vol. 114, pp. 536-546, 2016 [2] s. omary, e. ghorbel, g. wardeh, “relationships between recycled concrete aggregates characteristics and recycled aggregates concretes properties”, construction and building materials, vol. 108, pp. 163-174, 2016 [3] p. kathirvel, s. r. m. kaliyaperumal, “influence of recycled concrete aggregates on the flexural properties of reinforced alkali activated slag concrete”, construction and building materials, vol. 102, pp. 51-58, 2016 [4] b. a. memon, “recent development on use of demolished concrete as coarse aggregates”, international journal of emerging technology and innovative engineering, vol. 2, no. 1, pp. 1-11, 2016 [5] s. tanwani, b. a. memon, “tensile strength of concrete cylinders made by partial replacement of natural coarse aggregates with coarse aggregates from old concrete”, international journal of emerging technology and innovative engineering, vol. 1, no. 4, pp. 1-10, 2015 [6] a. a. bhatti, b. a. memon, “strength, deflection and cracking behavior of concrete slab using demolished concrete as coarse aggregates”, international journal of engineering sciences & research technology, vol. 3, no. 6, pp. 492-506, 2014 [7] m. oad, b. a. memon, “compressive strength of concrete cylinders using coarse aggregates from old concrete”, 1st national conference engineering, technology & applied science research vol. 9, no. 1, 2019, 3826-3831 3831 www.etasr.com oad et al.: effect of water-cement ratio on flexural strength of rc beams made with … on civil engineering (ncce 2013-14)-(modern trends and advancements), muscat, oman, april 28-29, 2014 [8] b. a. memon, g. s. bhatti, “flexural behavior of beam made by partial replacement of natural aggregates with coarse aggregates from old concrete”, international journal of engineering sciences & research technology, vol. 3, no. 5, pp. 52-61, 2014 [9] a. saeed, s. faisal, “effect of different mix ratios and water cement ratios on sulphate attack on concrete”, 30th conference on our world in concrete structures, singapore, august 23-24, 2005 [10] a. isaac, “effects of using 0.5, 0.55 and 0.6 water cement ratio separately with nigerian grade 42.5r portland cement”, international journal of science, technology and society, vol. 4, no. 6, pp. 80-88, 2016 [11] o. alawode, o. i. idowu, “effects of water cement ratios on the compressive strength and workability of concrete and lateritic concrete mixes”, the pacific journal of science and technology, vol. 12, no. 2, pp. 99-105, 2011 [12] d. o. onwuka, c. t. awodiji, s. u. onwuka, “investigation of the effect of water cement ratio on the modulus of rupture of concrete”, international journal of engineering and computer science, vol. 4, no. 7, 2015 [13] r. a. more, s. k. dubey, “effect of different types of water on compressive strength of concrete”, international journal on emerging technologies, vol. 5, no. 2, pp. 40-50, 2014 [14] t. slamecka, f. skvara, “the effect of water ratio on microstructure and composition of the hydration products of portland cement pastes”, ceramics, vol. 46, no. 4, pp. 152-158, 2002 [15] o. o. olubajo, a. o. osha, u. a. el nafaty, h. a. adamu, “effect of water cement ratio on the mechanical properties of blended cement containing ash and limestone”, civil and environmental research, vol. 6, no. 12, pp. 1-10, 2014 [16] k. marar, o. eren, “effect of cement content and water cement ratio on fresh concrete properties without admixtures”, international journal of physical sciences, vol. 6, no. 4, pp. 5752-5765, 2011 [17] m. oad, a. h. buller, b. a. memon, n. a. memon, “flexural stressstrain behavior of rc beams made with partial replacement of coarse aggregates with coarse aggregates from old concrete part-1,ratio 1:2:4”, engineering, technology & applied science research, vol. 8, no. 3, pp. 3048-3053, 2018 [18] m. oad, a. h. buller, b. a. memon, n. a. memon, s. sohu, “flexural stress-strain behavior of rc beams made with partial replacement of coarse aggregates with coarse aggregates from old concrete part-2: 1:2:4 ratio”, engineering, technology & applied science research, vol. 8, no. 5, pp. 3338-3343, 2018 microsoft word 33-3507_s_etasr_v10_n3_pp5784-5789 engineering, technology & applied science research vol. 10, no. 3, 2020, 5784-5789 5784 www.etasr.com mahessar et al.: impact of encroachment and hyderabad city effluents on pinyari canal impact of encroachment and hyderabad city effluents on pinyari canal ali asghar mahessar sindh barrages improvement project irrigation department, government of sindh karachi, pakistan abdul latif qureshi uspcas-w mehran university of engineering and technology jamshoro, pakistan ashafaque pathan department of civil engineering mehran university of engineering and technology jamshoro, pakistan kamran ansari uspcas-w mehran university of engineering and technology jamshoro, sindh, pakistan kishan chand mukwana department of energy and environment engineering quaid-e-awam university of engineering, science and technology, nawabshah, pakistan shafi muhammad kori department of civil engineering mehran university of engineering and technology jamshoro, pakistan abstract—pinyari canal off-takes from the left bank of kotri barrage with a design discharge of 13,636 cusecs which passes through the ridge of hyderabad city along with new fuleli canal and akram wah on its left side. its water is used for irrigation, agriculture, industrial, domestic, and drinking purposes in hyderabad and sajawal districts in sindh. this canal is nonperennial. water is being released with low discharge only for drinking purposes during the dry season and with full supply in the wet season. the global water quality issue reflects the major impact of socioeconomic development and population growth changes on freshwater resources including canals and rivers. this paper presents the impact of untreated wastewater disposal to the canal. the practice of disposing of untreated effluents has created serious health and environmental problems for the locals. the statistical and geospatial tool gis has been used for the assessment of water quality with visualization of wastewater behavior in the canal. the results of the statistical analysis showed that ph was within the permissible limits but electric conductivity (ec), total dissolved solids (tds), sodium (na), and hardness exceed them. the water quality index of the samples rated from very poor to unsuitable for drinking, hence, canal water is unfit for domestic use or drinking purposes. keywords-waterborne diseases; hyderabad city; solid waste; wastewater; gis; statistics i. introduction globally, freshwater resources are depleting and their quality is deteriorating due to over exploitation. effluents from various sources are discharged into freshwater bodies and rivers creating potential risks for public health [1, 2]. furthermore, the growing population with economic development poses a pressure on the available limited freshwater resources. waste disposal has created critical problems to the environment [3, 4]. the water quality of the rivers in pakistan has been degraded due to wastewater discharge [5, 6]. the rivers and canals have directly been contaminated from industrial and urban waste of major cities [7]. the discharge of wastewater from the industries is most alarming in rivers, canals, and drains irrespective of wastewater treatment. karachi, sialkot, faislabad and lahore cities are major contributors of pollution into fresh water bodies [8]. polluted water from urban and industrial sources has been disposed to urban peripheral canals. hence, municipal, domestic, industrial, and agricultural waste, animal manure, etc. are dumped directly to canals [9]. sewage water is added to canals by different sources of drains which affects directly their water quality [10, 11]. the consumption of contaminated fresh canal water poses negative impacts on public health and agro-environment [12]. the reuse of wastewater has a potential in industrializing countries as being cost-effective for industries where secondary effluents are readily available for reuse [13]. annually, about 1.8 million people die from waterborne diseases from the consumption of contaminated water [14, 16] and frequent attacks of diarrhea caused by bad water quality can leave a child more vulnerable to illness [6]. recent studies indicate that the various water quality parameters of pakistan drinking water do not meet the standards of pakistan and who [15]. various researchers have indicated that fresh water quality in several countries is not in accordance with who standards [17]. however, the introduction of remote sensing technology and of the geographical information system (gis) has made easy to integrate various metadata for assessment of water quality and gave a powerful tool for mapping and assessing water quantity and quality, flood management, and precipitation assessment corresponding author: ali asghar mahessar (amahessar@yahoo.com) engineering, technology & applied science research vol. 10, no. 3, 2020, 5784-5789 5785 www.etasr.com mahessar et al.: impact of encroachment and hyderabad city effluents on pinyari canal [18, 19]. the remote sense is a useful tool to classify lc and lu changes with various datasets. meanwhile, the water quality index (wqi) which is used globally for water quality assessment is the most operative model for management and evaluation of surface and groundwater quality [14, 20]. thus, the aim of this study is to explore the eco-chemical status of water quality of the pinyari canal which is degraded by the disposal of effluents from hyderabad city and the encroached canal banks area. ii. study area hyderabad city is located at the left side of indus river and its population is about 1.5 million residing in the urban area comprised on talukas such as qasimabad, latifabad, cantonment, and hyderabad city as shown in figure 1(a). this dense populated city has a drainage system with wastewater treatment plants but no safe disposal points, thus the wastewater of the entire city is directly or indirectly disposed to the canals. the wastewater treatment plants are almost dysfunctional and not in accordance with modern technology. water samples were collected at different wastewater disposal locations as shown in table i and figure 1(b). this study has been conducted considering encroachment, dumping of solid waste, disposal of waste water into canals from the head regulator of the canal to hosri town covering a distance of 30km as shown in figure 2. (a) (b) fig. 1. (a) study area, (b) disposal and sample collection locations iii. materials and methods a. sampling a survey was conducted in the study area regarding encroachment (i.e. the existence of illegal permanent buildings such as households, farms or factories), major disposal locations from the city, and industrial units. figure 2 shows the encroached left and right banks of the canal with houses, huts, ranches, and farms with high density. the solid waste and wastewater is directly dumped to the canal. there are many major and small inlets for wastewater disposal to the canal at locations such as the deplai colony wastewater pumping station, the jacob wastewater pumping station, the wastewater of khawja colony, the outfall structure at kari mori bridge, the outfall structure just upstream the railway line, and the darya khan pumping station (figure 2). samples were collected and preserved in an icebox in 4 o c. nitric acid (hno3) was added to the sampling bottles in quantities sufficient to lower the ph of the sample to just about 2, to stabilize the concentration of total and dissolved metals for a maximum of 28 days. standard sample transfer procedures were followed to avoid confusion in sample identification, including labeling and safe transportation to laboratory. the collected samples were sent to the hi tech laboratory of the sindh university, for further analysis. table i. sample collection locations sample # latitude longitude location 1 25°.44339 68°.37372 hur camp pumping station wastewater dumping into the canal 2 25°.43706 68°.38622 wastewater of khawaja colony 3 25°.40994 68°.38989 wastewater dumping from the central jail area into the canal. 4 25°.42556 68°.37939 hala road bridge 5 25°.43178 68°.38383 wastewater into the canal, just d/s of kari mori 6 25°.415 68°.39122 wastewater into the canal just d/s of preatabad bridge 7 25°.41822 68°.39539 wastewater into the canal near the preatabad bridge 8 25°.40456 68°.41522 wastewater coming from urban areas 9 25°.414 68°.41389 wastewater to the canal, near kachhi paro 10 25°.40517 68°.41078 wastewater u/s of the railway bridge 11 25°.39333 68°.41267 draya khan pumping station 12 25°.39372 68°.41256 darya khan pumping station 13 25°.40517 68°.41078 waste effluents at railway bridge 14 25°.42261 68°.38033 slaughterhouse, liaquatabad 15 25°.41922 68°.400 kari mori bridge b. water quality index (wqi) wqi is an indicator of water suitability for drinking and surmises many parameters [21]. the equation of wqi is: 1 n i i qwi w q= ×∑ (1) where qi is the i th wq parameter, wi is the weight associated with this parameter, and n is the total number of wq parameters. the classification of water samples according to the wqi is shown in table ii. table ii. wqi ratings wqi value rating 0 25 excellent 25 50 good 50 75 poor 75 100 very poor > 100 unsuitable for drinking engineering, technology & applied science research vol. 10, no. 3, 2020, 5784-5789 5786 www.etasr.com mahessar et al.: impact of encroachment and hyderabad city effluents on pinyari canal (a) (b) (c) fig. 2. solid waste dumping and wastewater disposal to the pinyari canal iv. results and discussion a. solidwaste dumping besides the problem of wastewater discharging, a huge volume of solid waste is dumped to the canal. solid waste dumping locations along the canal were observed during the survey at hala road bridge, kari mori bridge, downstream of the pretabad bridge, adjacent to the slaughterhouse, and at the railway bridge. the estimated quantity of solid waste on the canal embankments is about 15-20 tons per day (figure 2). b. buffaloe farms (bfs) on the banks of pinyari canal many bfs were spotted during sampling, i.e. 4 on the left side of the canal just upstream of the bypass bridge, each farm with 15 to 40 buffaloes and 6 bfs on the right side of the canal just upstream of the bypass bridge, with 10-35 buffaloes, 8 bfs on the left side of the canal between the bypass road bridge and hala road bridge, with 10-25 buffaloes, and 10 bfs between the bypass road bridge and the hala road bridge with 10-30 buffaloes on the right side of the canal (figure 2). the manure and the other waste of the farms are directly disposed to the canal. c. city wastewater • deeplai colony wastewater pumping station is discharging its wastewater into the canal at rd 14+00 and has a capacity of about 7.8 million gallons per day. • pumping station at jacob ponds is pumping wastewater at rd 16+00 through a delivery pipe with 18’’ diameter. • wastewater of khawja/mubark colony discharges wastewater into the canal at rd 17+00 and 18+00 by pipes and the estimated disposal water is about 0.6 million gallons per day. • outfall structures at kari mori bridge. the effluent of vast area of market and hirabad area is being discharged through these inlets at rd 24+00. an open channel of 6’×6’ just downstream of kari mori bridge is discharging 10 to 15 cusecs of untreated wastewater. • slaughterhouse: the wastewater of the liaquat colony and the slaughterhouse is being disposed of at rd 25+00. the main slaughterhouse is situated downstream of pretabad bridge on the right bank which is a covered large area in which an estimated number of 1500 animals are being slaughtered every day. the remains and the blood are directly dumped to the canal. • outfall structure upstream of railway bridge: the main outfall structure and pumping station on the right side of the canal and near the railway bridge has been constructed by hyderabad development authority (hda) for discharging wastewater at rd 28+00. • darya khan pumping station: darya khan wastewater outfall and pumping station is situated at rd 40+00 on the right side of the canal has been constructed by hda and receives untreated wastewater of hyderabad site area. during the dry season when there is not water available in the canal, the wastewater is being discharged through gravitational flow, whereas during the full supply flow in canal the wastewater is discharged through pumping. there are 17 main and about 20 small locations inlets on the left side of the canal from where the untreated wastewater generated from small industries and municipal areas is being discharged. there are 20 main and many small inlets at the right side of the canal from where the untreated wastewater is being discharged. the total estimated discharge of untreated wastewater (industrial & municipal) into the canal is about 90 million gallons per day. d. canal wastewater sample analysis the collected samples were analyzed at the hi tech laboratory of sindh university. the results are shown in table ii and are discussed below. engineering, technology & applied science research vol. 10, no. 3, 2020, 5784-5789 5787 www.etasr.com mahessar et al.: impact of encroachment and hyderabad city effluents on pinyari canal 1) ph it is a measure of the acidic or basic (alkaline) nature of a solution. a ph ranging from 6.5 to 8.5 is suitable for aquatic life. it was observed after analyzing of the samples that the values of all samples ranged from 6.5 to 7.3, hence ph is within the permissible limits of neqs (table iii). figure 3 exhibits the geospatial distribution of ph using gis. fig. 3. spatial distribution of ph with gis 2) electrical conductivity (ec) the ec of the collected samples exceeds the permissible limit of neqs (680µs/cm). the ec ranged from 760µs/cm to 13700µs/cm. the highest value (13700µs/cm) was found at location sw-1 because of wastewater that mostly comes from the domestic and saline pond area. 3) total dissolved solids (tds) the tds values of the collected samples are higher than the permissible limits of neqs. the sample s-1 had the higher tds value. figure 5 exhibits the geospatial distribution of tds and its red color indcates high concentration of wastewater. 4) hardness the hardness of all samples was higher than the limits of neqs. the highest value was found in water sample 1 as shown in table iii. the hardness of the collected samples varied from 120 to 760mg/l. fig. 4. spatial distribution of tds with gis 5) nitrate the values of the collected samples shows that nitrate varied from 0.14 to 16mg/l. nitrate level below 0.5mg/l seems to have no effect on warm water fish. water with nitrate levels exceeding 1.0mg/l should not be used. 6) sodium (na) the values of analyzed samples are within the permissible limit of neqs except sample no. 14 due to the industrial unit waste. these units mostly comprise of textile, soap, paper, etc. industries, which require large quantities of sodium. 7) potassium (k) the analyzed result shows that the values of potassium varied from 24 to 120mg/l. the value of sample 13 was higher than the permissible limit. table iii. water sample parameter values sample # ph ec tds hco3 hardness do nitrate na k mg (µs/cm) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) 1 7 13700 8768 800 1140 1.95 2.05 95 120 49.2 2 6.9 3100 1984 400 330 0.29 0.14 92.3 38 40.5 3 6.9 760 486 110 120 0.44 5.9 50 14 17 4 7.5 4180 2675 360 410 0.56 bdl 92 101 44.4 5 6.7 1124 719 110 120 0.34 1.85 80 50.6 24.6 6 6.5 1013 648 120 130 0.45 0.435 60 25.2 20 7 6.7 1290 826 180 150 0.34 1.425 90 37.5 40 8 7.3 3300 2112 490 250 0.21 0.064 90.4 76.7 23.2 9 7.3 1233 789 210 130 0.32 9.65 80 35.2 19 10 6.6 1550 992 240 120 0.2 1.2 81.3 34.5 25.8 11 7.2 1080 691 216 130 0.22 21.2 80 31.3 25.2 12 7 1908 1220 250 210 bdl 4.85 86.3 48.9 25.7 13 7 3480 2227 300 260 bdl 1.4 92 51 42 14 6.9 3270 2138 320 760 0.8 12.2 340 24 52 15 6.6 1488 1932 285 360 3.2 16 116 26 46 engineering, technology & applied science research vol. 10, no. 3, 2020, 5784-5789 5788 www.etasr.com mahessar et al.: impact of encroachment and hyderabad city effluents on pinyari canal 8) magnesium (mg) the values of the analyzed samples vary from 23.2 to 49.2mg/l. the maximum value found at sample 1. magnesium is a nutritionally essential metal that can be responsible for adverse health effects due to deficiency or excess. e. wqi analysis the water quality of the study area calculated by wqi indicates that the water of most of the samples is unsuitable for drinking. the computed wqi values range from 81 to 410 as shown in table iv. thus, the quality of the canal water varies from very poor to unsuitable for consumption. the overall view of the wqi of the study area signifies its deteriorated water quality. hence, the canal water is unfit for drinking during low discharge. the physicochemical parameter values of the collected samples reveal that 100% of the ec and tds values and 70% of the k values were found higher than the permissible limits, while ph na, hardness, nitrate, and mg are close to the permissible limits. however, wqi indicates the water from very poor to unsuitable for drinking the result indicates that the canal is receiving different category of effluents, e.g. domestic, industrial, farming, etc. which undermine its own and ground water quality, having repercussions in agriculture, livestock, and soil while degrading the environment. there is a need to follow the iso-14000 standard for the protection of environment from degradation. this can be achieved by adopting state-of-the-art primary and secondary wastewater treatments at tertiary level and along with the encroachment removal from the canal banks [23]. furthermore, the use of gis tools for monitoring of wastewater dumping sites and canal water quality is proven useful. table iv. wqi rating sample # latitude longitude wqi 1 25°.44339 68°.37372 403 2 25°.43706 68°.38622 372 3 25°.40994 68°.38989 209 4 25°.42556 68°.37939 410 5 25°.43178 68°.38383 316 6 25°.415 68°.39122 228 7 25°.41822 68°.39539 352 8 25°.40456 68°.41522 389 9 25°.414 68°.41389 344 10 25°.40517 68°.41078 71 11 25°.39333 68°.41267 355 12 25°.39372 68°.41256 81 13 25°.40517 68°.41078 86 14 25°.42261 68°.38033 294 15 25°.41922 68°.400 101 v. conclusions the statistical analysis of physicochemical parameters showed that ph was within permissible limits, ec and tds exceeded the permissible limits and hardness, k, na, and mg were almost within the permissible limits. nevertheless the water quality index showed that the water quality of the collected samples ranged from very poor to unsuitable for drinking. the effluents discharged into the fresh canal water pose serious threats to public health, aquatic life, livestock, agriculture, soil, and ground water. their negative impact on water may be addressed by installing primary and secondary tertiary treatment with trickling effect and oxidation ponds before it is too late [9]. it is further suggested that research studies on surface and ground water quality should continue in the area to assess canal water quality as a result of multiple categories of wastewater from different sources [1, 9, 22]. acknowledgment the authors wish to thank the irrigation department for providing its facilities. references [1] a. a. mahessar, s. qureshi, a. l. qureshi, k. ansari, g. h. dars, “impact of the 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etasr_v10_n6_pp6403-6409 engineering, technology & applied science research vol. 10, no. 6, 2020, 6403-6409 6403 www.etasr.com kumar & dhull: genetic algorithm based optimization of uniform circular array genetic algorithm based optimization of uniform circular array vinod kumar department of ece guru jambheshwar university of science & technology hissar, india vinodspec@yahoo.co.in sanjeev kumar dhull department of ece guru jambheshwar university of science & technology hissar, india sanjeevdhull2011@yahoo.com abstract-signal estimation at the antenna is a major challenge of the antenna array structure because the received signals have different directions. therefore, in this paper, a genetic algorithm (ga) is applied to the uniform circular array for the optimization of array structure in regard to its geometry. on the optimized array structure, four different algorithms (estimation of signal parameter via rotational invariance technique – esprit, first order forward prediction fofp, beamscan, and multiple signal classification music) have been implemented in order to estimate the signal direction accurately with quick estimation time. the accuracy has been calculated with root mean square error (rmse) indices. from the experimental analysis, it has been found that the performance of the esprit algorithm is better than the others in terms of accuracy and estimation time. keywords-computational complexity; fofp; genetic algorithm; rmse; uniform circular array i. introduction when an incoming signal wave is detected and measured at a sensor array, it is processed and information is extracted from it (e.g.: direction of arrival doa). the algorithms that are used to find doa in the antenna array are generally used in wireless communication systems to increase the system capacity and the throughput of the wireless network. the antenna array consists of several antennas for finding the direction of incident waves and suppressing interference signals. the estimation problem is of significant importance in the array signal processing. parameter estimation is an area where research is conducted for performance improvement. a major topic of interest is the accurate discovery of the signal direction. sensor array field processing is an area for research focused in accurate signal estimation. as improvements in the geometry of the antenna array occur, the doa estimation approach will become an important part of smart antenna systems. the antenna array collects data from all the elements and then combines them for spatial information and detects the incoming signal direction based on signal processing algorithms. the main aim of the antenna array is to find the signal directions from signals that come from different directions. the estimation of the signal may be obtained with the help of the array’s geometry and doa algorithms. doa estimation is an interesting field and many doa algorithms were proposed including spatial spectrum estimation. the first method based on the spatial spectrum was proposed in [1]. this method is used for estimating the direction of the incoming signal by computing and observing the spatial spectrum. after that, a local maxima point is decided. author in [2] presented a new method based on minimum variance distortionless response (mvdr). this mvdr is used to conduct spectrum estimation with the help of maximum likelihood (ml) method [3] which maximizes the log-likelihood function among a set of arrays. in [4] a subspace based algorithm was proposed which scans all the angles between the signal subspace and noise subspace. author in [5] improves the solution ability of the music algorithm and gives good estimation results by introducing a variant of music algorithm. authors in [6] propose a new algorithm named esprit which has higher computation efficiency. authors in [7-8] proposed the weighted subspace fitting method for better estimation results. authors in [9] proposed a new method for the signal estimation in two dimensions. authors in [10] improved the music algorithm. authors in [11] gave an improvement in the static performance of the music algorithm. authors in [12] proposed a new scheme for the increase of resolution ability of the music algorithm. authors in [13] gave advancement in the esprit algorithm for two dimensions. table i gives the detailed description of the existing doa algorithms. these algorithms are based on spectral search and subspace methods. table i. different doa algorithms algorithm comments bartlett [1] estimate doa by computing spatial spectrum and finalizing local maxima. the noise signal is excluded. mvdr [2] spectrum estimation with maximum likelihood method. music [4] scans all the angles from signal and noise subspace. esprit [6] increased computation efficiency with the help of two identical sub arrays. weighted subspace fitting [7-8] unified approach for signal estimation. music [14] discussion on maximum likelihood and cramor rao bound music [9] a method for signal detection on two dimensions. music [11] static performance of music algorithm. music [12] improved the resolution ability of music algorithm root music [5] does not find the spectral peaks, it solves the rooting problem of a polynomial with good resolution ability. corresponding author: vinod kumar engineering, technology & applied science research vol. 10, no. 6, 2020, 6403-6409 6404 www.etasr.com kumar & dhull: genetic algorithm based optimization of uniform circular array ii. estimation of signal parameters via rotational invariance techniques authors in [6] proposed an algorithm named estimation of signal parameter via rotational invariance technique (esprit) for doa estimation. in esprit, array doublets are used and formed by n/2 pairs which further form a displacement vector, where n is the number of array elements. the starting two elements of the doublet are separated and grouped to make two n/2 sub arrays. the vectors x and y are the data vectors corresponding to each of the sub arrays. the output of the sub arrays x and y can be expressed as: 1 ( ) 0 [ ] [ ] ( ) [ ] r x k i k i k i x n s n a v nθ − = = +∑ (1) k 1 ( )2 sin 1 [ ] [ ] ( ) [ ] r yj k i k i k i y n s n e a v n πδ θ θ − = = +∑ (2) where similar notation has been used and δ is the displacement magnitude in wavelengths. the estimated angle by esprit algorithm is relative to the displacement vector. the output of sub arrays, x and y, in matrix form is given as: ( )x n n nx as v= + (3) ( )y n n ny a s vϕ= + (4) the matrix φ is a diagonal r×r matrix where the diagonal elements are: 0 1 1{exp( 2 sin ),exp( 2 sin ),....exp( 2 sin )}rj j jπδ θ πδ θ πδ θ − the phase delay may be represented by the complex exponentials between the r signals and the doublet pair. the data vectors may be concatenated from sub arrays to make a single 2n-2 data vector like: n n b n n x z a s y   = =    (5) ( ) ( ) , x n b n y n va a v a vϕ    = =         (6) the columns of ab occupy the signal subspace of the new array. let vs be the column matrix depending upon the signal subspace and zn, ab. vs is related with r×r transformation t and can be written as: s bv a t= (7) and can be portioned as follows: x s y e at v e a tϕ     = =       (8) from this step, a will be equal to ex, ey, and have the same range. the rank r of matrix exy is: [ ]xy x ye e e= (9) to find the r×2r rank r matrix having null space of exy to form the matrix f is written as: [ ]x y x x y y x ye e f e f e f atf a tfϕ= + = + (10) assuming ψ is: 1 [ ]x yf fψ −= − (11) by reshuffling the above equations, we get: x ye eψ = (12) now, by substituting we get: 1 1 at a t at t a t tψ ϕ ψ ϕ ψ ϕ− −= ⇒ = ⇒ = (13) the given equations mean that the eigenvalues of ψ are the same as the diagonal elements of φ. once the eigenvalues λ of φ have been calculated, the angle of arrival is calculated as: 2 sin kj k e πδ θλ = (14) arg( ) arcsin 2 k k λ θ πδ   =     (15) if a is the full rank matrix, then the eigenvalues of the matrix ψ are the diagonal elements of φ and the eigenvectors of ψ are the columns of t. practically, the signal subspace is not known exactly, the only estimate is taken from sample covariance matrix rxx or from a sub space tracking algorithm. therefore, exψ=εy will not be exactly satisfied and we will have to resort to a least square solution to compute ψ. the least square process assumes that the columns in ex are known exactly whereas the data in ey are noisy. if the assumption that ex and ey are equally noisy is made, then the total least square criteria is used to solve to above problem with better results. iii. optimization using genetic algorithm the genetic algorithm (ga) is a population search algorithm inspired by the evolutionary process of natural selection [15]. ga is a simple algorithm that has been proven to be very powerful and widely applicable. the algorithm arrives at a solution by performing operations on a population of solutions referred to as chromosomes over several iterations, which are referred to as generations. the operations used are borrowed from genetic concepts such as mutation, reproduction, fitness, etc. the algorithm uses fitness evaluation to rank solutions and randomness in creating new generations of solutions in order to promote diversity. authors in [16] used the ga to optimize the relative position in an antenna system. authors in [17] used the ga in a linear array with infinite snr in order to extract the amplitude and doa of various signals. authors in [18] introduced the use of ga in ml based parameter and spatial spectrum estimation. authors in [19] introduced a new refined ga for accurate and reliable doa estimation with the help of a sensor array based on the ml function. authors in [20] introduced a new genetic based estimation method with the help of fourth order cumulant. a new genetic firefly hybrid algorithm based on the neural network was designed in [21] for finding the best position in engineering, technology & applied science research vol. 10, no. 6, 2020, 6403-6409 6405 www.etasr.com kumar & dhull: genetic algorithm based optimization of uniform circular array the data cube. a new algorithm was designed in[22] for finding the best path in all the clusters based on the generalized travelling salesman problem. this algorithm was based on the minimum cost tour within a clustered set of cities. the application of ga on beam forming of correlated and uncorrelated static sources was discussed. when the target is moving in cdma systems by knowing the spreading code, the lms algorithm received the signal at zero rates. the snr was as low as -9db for uncorrelated static sources but when the signals were correlated, the lms gave unstable beam forming. hence, ga gives good results for all sources which are static with good error rate [23]. authors in [24] proposed a multiple source localization method for doa estimation at each sensor mode. the ga based proposed algorithm was compared with conventional sequential search techniques. the computational load and inter node communication burden was reduced, so the algorithm was considered suitable for use in it based applications having large numbers of sensor nodes and sources. the ga is most commonly used as an optimization algorithm and has efficiently solved various optimization problems across many disciplines in proficient manners. alternating projection maximum likelihood, stimulated annealing grid based search, and data based grid search are used in the ga. the ga has widely been used in the doa estimation by using the spatial spectrum estimation. the ml technique gives an optimal solution when compared to other methods. based on the likelihood function, the ml is superior to other techniques [3, 14, 25]. a new optimized array structure for doa estimation was designed which can estimate both azimuth and elevation angles. the array is designed with the help of the ga that has as a fitness function the optimization of the array structure. the array aperture size increases when the number of elements in the array is increased. after that, various doa algorithms have been applied to the proposed structure and simulation results were obtained. the proposed array was compared with other arrays in terms of rmse of azimuth and elevation angles. a. structure of the new optimized array based on the ga, the proposed design array structure is given in figures 1 and 2. in this structure, the population size is taken as 100 with 1000 iterations and a randomly generated initial array structure of 10 elements on the xy plane. the signal generated from various directions is received at each array element and combined to produce the output. fig. 1. optimum configuration with number of iterations=1. the optimized new array structure is formed and the total spacing between array elements is 314.1593 for 10 array elements and 157.0796 for 20 array elements. total spacing reduces when the number of array elements increases along with the complexity of the structure. the formed structure is the optimized structure that can be used to detect the signal in two dimensions. the optimized structure is designed with the help of ga after several iterations. fig. 2. the purposed array structure of 20 elements. b. steps involved in array optimization figure 3 gives the flowchart of the used algorithm. the steps involved in the optimization of the array are: input: config (pq, distance, cost function), population, crossover 90%, and mutation 10%, iterations for number of iterations for population selection cost( config) ==> mse ==> small mse 10% crossover= offsprings are created in hope of producing better config mutation =changing the configuration pq in hope of producing better config population for next iteration end end fig. 3. flowchart of the matlab code. 0 1 2 3 4 5 6 7 8 9 10 array spacing 1 2 3 4 5 6 7 8 9 10 total spacing between array's elements (mm) = 188.7047, iteration = 1 0 125 250 375 500 array spacing 0 125 250 375 500 total spacing between array elements= 157.0796 mm engineering, technology & applied science research vol. 10, no. 6, 2020, 6403-6409 6406 www.etasr.com kumar & dhull: genetic algorithm based optimization of uniform circular array c. execution time of doa estimation algorithms in terms of execution time (the time taken by the algorithm to estimate the signal), the esprit algorithm requires the least time when compared to the other algorithms, as can be seen in figure 4. fig. 4. execution time of algorithms on the proposed configuration. in the optimized array, we have applied simulations of various doa algorithms in order to compare their performance in terms of execution time. the simulation results are obtained with different signal directions at various angles. figures 4-9 give the simulation results of the different doa algorithms on the optimized array structure. figure 4 gives the simulation results of the different algorithms in terms of execution time. it is evident that the esprit algorithm shows better results than the other algorithms. figures 5 and 6 show the simulation results of the esprit and beam-forming algorithm at different angles (60°, 80°, 90°, 100°, 120°). the angles are accurately estimated through the esprit algorithm but the estimation through beam-forming is poor. also, in figures 7-9 (estimation through music, fofa, and capon algorithms) the estimation is accurate and clear. the simulation results of the discussed algorithms depend on the number of sources, the number of antenna elements, the spacing between the elements, and the snr. when the number of sources is bigger than the antenna elements, it is difficult to estimate the signal directions. when there are more of antenna elements, the obtained results are better. the spacing between the elements is taken as 0.5λ. fig. 5. esprit histogram corresponding to 5 signals directions. fig. 6. beam-forming spatial spectrum corresponding to 5 signals. fig. 7. music spatial spectrum corresponding to 5 signals. fig. 8. fofp spatial spectrum corresponding to 5 signals. d. comparison with existing arrays the proposed array is compared with circular, rectangular, concentric, and iasa arrays in terms of rmse of azimuth and elevation angles. the results of the ga based array have been observed to be better when compared with the other arrays. figures 9-21 give the detailed comparison and show that the rmse of the proposed design offers better results. figures 1011 depict the azimuth and elevation angle comparison with rmse of the proposed ga based array. the circular array is compared with the ga based array in figure 10. the result shows that the rmse of the ga based array is lower for both azimuth and elevation angles. execution time of algorithms esprit beam forming music fofp 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0 20 40 60 80 100 120 140 160 180 angle° 0 1 2 3 4 5 6 7 8 9 10 esprit histogram 0 20 40 60 80 100 120 140 160 180 angle° 0 5 10 15 20 25 beamforming spatial spectrum 0 20 40 60 80 100 120 140 160 180 angle° 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 music algorithm spatial spectrum 0 20 40 60 80 100 120 140 160 180 angle° 0 20 40 60 80 100 120 140 first-order forward prediction algorithm spatial spectrum engineering, technology & applied science research vol. 10, no. 6, 2020, 6403-6409 6407 www.etasr.com kumar & dhull: genetic algorithm based optimization of uniform circular array figures 12 and 13 show the azimuth and elevation angle comparison with rmse of the proposed ga based array with the rectangular array. the result shows that the rmse of the ga based array is lower for both angles. figures 14 and 15 show the comparison results of azimuth and elevation angle with rmse of the proposed ga based array with the concentric array. the result shows that the rmse of the ga based array is lower for both angles. figures 16 and 17 illustrate the comparison of azimuth and elevation angle with rmse of the proposed ga based array with the iasa array. the result shows that the rmse of the ga based array is lower for both angles. fig. 9. capon algorithm spatial spectrum corresponding to 5 signals. fig. 10. rmse of the azimuth angles of circular and ga based arrays. fig. 11. rmse of the elevation angle of circular and ga based arrays. fig. 12. rmse of the azimuth angle of rectangular and ga based arrays. fig. 13. rmse of the elevation angle of rectangular and ga based arrays. fig. 14. rmse of the azimuth angle of concentric and ga based arrays. fig. 15. rmse of the elevation angle of concentric and ga based arrays. 0 20 40 60 80 100 120 140 160 180 angle° 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 capon algorithm spatial spectrum -10 -5 0 5 10 15 20 25 30 snr 0 0.01 0.02 0.03 0.04 0.05 0.06 rmse v s snr of azimuth angle circular array ga based array -10 -5 0 5 10 15 20 25 30 snr 0 0.005 0.01 0.015 0.02 0.025 0.03 rmse v s snr of elev ation angle circular array ga based array -10 -5 0 5 10 15 20 25 30 snr 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 rmse v s snr of azimuth angle rectangular array ga based array -10 -5 0 5 10 15 20 25 30 snr 0 0.005 0.01 0.015 0.02 0.025 0.03 rmse v s snr of elev ation angle rectangular array ga based array -10 -5 0 5 10 15 20 25 30 snr 0 0.01 0.02 0.03 0.04 0.05 0.06 rmse v s snr of azimuth angle cocentric ring array ga based array engineering, technology & applied science research vol. 10, no. 6, 2020, 6403-6409 6408 www.etasr.com kumar & dhull: genetic algorithm based optimization of uniform circular array fig. 16. rmse of the azimuth angle of iasa and ga based arrays. fig. 17. rmse of the elevation angle of iasa and ga based arrays. fig. 18. rmse error of the azimuth angle of circular, rectangular, concentric, and iasa arrays. figures 18 and 19 show the azimuth and elevation angle comparison with rmse of the four arrays. the result shows that the rmse of the iasa array is lower for both azimuth and elevation angles. figures 20 and 21 show the azimuth and elevation angle comparison with rmse of the proposed ga based array with all the considered existing arrays. the result shows that the rmse of the ga based array is lower for both azimuth and elevation angles. this type of ga based array is generally used in the communication field for the estimation of the signal and radar and sonar field for signal estimation. the only limitation of this type of optimized ga based array is that it basically estimates the signal direction of static targets. concluding, this optimized array structure detects the signal accurately in terms of rmse. fig. 19. rmse of the elevation angles of circular, rectangular, concentric, and iasa arrays. fig. 20. rmse error of the azimuth angle of circular, rectangular, concentric, iasa, and ga based arrays. fig. 21. rmse error of the elevation angle of circular, rectangular, concentric, iasa, and ga based arrays. iv. conclusions the doa of signal estimation is a major concern for the communication technologist. the proposed geometry for doa estimation aims to meet the estimation accuracy requirements. the simulation results of the proposed configuration show that the ga based array with esprit algorithm has better estimation accuracy among all four proposed doa estimation -10 -5 0 5 10 15 20 25 30 snr 0 0.01 0.02 0.03 0.04 0.05 0.06 rmse v s snr of azimuth angle iasa array ga based array -10 -5 0 5 10 15 20 25 30 snr 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 rmse v s snr of elev ation angle iasa array ga based array -10 -5 0 5 10 15 20 25 30 snr 0 0.01 0.02 0.03 0.04 0.05 0.06 rmse v s snr of azimuth angle circular array rectangular array cocentric ring array iasa array -10 -5 0 5 10 15 20 25 30 snr 0 0.005 0.01 0.015 0.02 0.025 0.03 rmse v s snr of elev ation angle circular array rectangular array cocentric ring array iasa array -10 -5 0 5 10 15 20 25 30 snr 0 0.01 0.02 0.03 0.04 0.05 0.06 rmse v s snr of azimuth angle circular array 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[22] h. jafarzadeh, n. moradinasab, and m. elyasi, “an enhanced genetic algorithm for the generalized traveling salesman problem,” engineering, technology & applied science research, vol. 7, no. 6, pp. 2260–2265, dec. 2017, https://doi.org/10.48084/etasr.1570. [23] d. burgos, r. lemos, h. silva, j. kunzler, and e. flôres, “adaptive beamforming for moving targets using genetic algorithms,” ingeniería, vol. 21, no. 2, aug. 2016, https://doi.org/ 10.1109/wea.2015.7370139. [24] y. zhang and y. i. wu, “multiple sources localization by the wsn using the direction-of-arrivals classified by the genetic algorithm,” ieee access, vol. 7, pp. 173626–173635, 2019, https://doi.org/10.1109/ access.2019.2956825. [25] i. ziskind and m. wax, “maximum likelihood localization of multiple sources by alternating projection,” ieee transactions on acoustics, speech, and signal processing, vol. 36, no. 10, pp. 1553–1560, oct. 1988, https://doi.org/10.1109/29.7543. authors profile vinod kumar is presently working in the department of electronics & communication engineering, guru jambheshwar university of science & technology, hisar, india. he is pursuing his ph.d. from the same department. his research area of speclization is array signal processing. sanjeev kumar dhull received his bachelor of engineering (ece) from mangalore university, mangalore, in 1996, his m.tech. from punjab university chandigarh, in 2004 and his ph.d. from guru jambheshwar university of science and technology (gjus&t), hisar, in 2013. he joined gjus&t as an assistant professor in 2006 and became an associate professor in 2013 and professor in 2018. his research interests include adaptive signal processing and speech processing. microsoft word etasr_v10_n6_pp6521-6525 engineering, technology & applied science research vol. 10, no. 6, 2020, 6521-6525 6521 www.etasr.com nethravathi et al.: structuring natural language to query language: a review structuring natural language to query language: a review b. nethravathi department of information science and engineering jss academy of technical education, bangalore karnataka, india nethravathi.sai@gmail.com g. amitha department of information science and engineering jss academy of technical education, bangalore karnataka, india amithagk98@gmail.com anusha saruka department of information science and engineering jss academy of technical education, bangalore karnataka, india anushasaruka21@gmail.com t. p. bharath department of information science and engineering jss academy of technical education, bangalore karnataka, india bharathtp.1js16is018@gmail.com setu suyagya department of information science and engineering jss academy of technical education, bangalore karnataka, india setu.suyagya@gmail.com abstract-sql (structured query language) is a structured language for specialized purposes used to communicate with the data stored in a database management system. it uses dynamic and sophisticated query commands for processing and controlling data in a database, which can become an obstacle for users with no previous experience. in order to address this constraint, we have analyzed the existing models in natural language processing, which convert a native-language query into an sql query. thus, any novice user can use the sql program and eliminate the need to generate any complex queries. this work is a detailed survey of the existing literature. keywords-structured query language; natural language processing; query i. introduction structured data are useless without the use of a data management system. such a system makes the information organized making easier the communication between it and its users. in order to communicate effectively, one must have complete knowledge of database languages such as the structured query language (sql), converting natural language queries in machine-translated queries. although sql was developed primarily for commercial users, even the most capable ones find difficulties in creating queries, due to the large amount of data required to fully define a modern database. a common solution to overcome these barriers is the addition of natural language databases. this enables novice users to submit their queries in any language to access the required information. ii. literature survey natural language in databases allows users to have easy approach to access the data, without the knowledge of a query language. the system in [1] is an idea driven program consisting of local language queries of natural language. a two-part approach has been proposed: the natural language query (nlq) is translated into the object query language (oql) first and then the query is converted to sql. the twostep approach will allow the users to physically extract data from the semantics of the question, which gives physical independence. in addition, ontologies that provide rich semantics, are missing from the related schema. the system achieves 100% accuracy on the mas and geo function, and 99% accuracy on the fin load factor used for complex ontology. in addition, athena gains 87.2%, 88.3%, and 88.9% recall in the geo, mas, and fin activities. natural language interface to database (nlidb) has problems regarding language (language similarity) and domain behavior. the actual problem with nlidbs is sequential translation. stack exchange data explorer is a website that can be used to train the natural methods of internal information. it is reported [2] that it promotes basic results in small hand-held manuals. although the sql output can occasionally be ineffective and is hardly a desirable sql query, the results are encouraging. the main aim of data centers is allowing business analysts to make superior accord. technology has grown and repositories have proved to be increasingly useful. because of this, more data are being incremented to datasets and their corresponding author: b. nethravathi engineering, technology & applied science research vol. 10, no. 6, 2020, 6521-6525 6522 www.etasr.com nethravathi et al.: structuring natural language to query language: a review schemas become more compound. these systems tend to make inefficient match for incompetent users who need answers to unexpected crude questions. an important solution is to use a graph pattern similar to an algorithm which uses a metadata database model. actions with original data show that soda [3] generates queries with high preciseness, and makes it way easier to use devices that store abundant data. the main aim of soda is to generate sql statements built on simple keywords using the algorithm’s graphical pattern. the experiments show that queries that are performed with great accuracy are reminiscent of handwritten queries. the key issue of soda is that it can confuse the definition of words when it comes to the association and inheritance relations between adjacent tables. in addition, soda allows reducing the noises' power in the data or schema and the quality of data issues by upgrading the appropriate graph or by broadening the graph algorithm. banks [4] is a program that provides search based on keywords in databases. boards enables novice users to get access to data or extract information from a database without any sql or programming knowledge. the banks models depend on graphs and are connected by links inserted by an external button. questions are used as focus trees to connect keywords in the generated sql query. combining browsing and keyword identification for related information, banks allows inexperienced users to query and browse a database easily. boards dramatically reduces the effort involved in publishing web-related information and making it searchable. the approach in [5] promises accuracy, completeness and preciseness of a nli. their model could be improvised to analyze a broad spectrum of questions in analytical and theoretical sense. the highlight of this approach is the use of the max-flow algorithm which collects solutions and also disregards those solutions that disobey semantic constraints. the proposed technology in [6] addresses challenges like the lack of good visual interactive tools and the fact that nlidbs have still not made sufficient progress into practical and commercial products. this model has a considerable leverage on dnn models as the core of its nl interface system. sqlnet [7] generates sql queries from natural language with no reinforcement learning. it tends to cater challenges like issues of sequence-to-sequence models with respect to different queries with similar outputs. it is mainly designed to be universal, in such a way that each and every sql query can be generated. the proposed system is known to have employed a sequence-to-set model in order to generate sql queries when the order is insignificant. this model has shed light on novel solutions to problems on structural generation. the proposed system in [8] mainly aimed at solving the problem of insufficient schema or query knowledge of users by slimming down the number of all possible cogent predicates for a particular question in hand. a semantic parser that could scale to freebase rather depending on annotated logical forms was trained. this work interacted successfully with different streams of work, one of which involved learning models of semantics and another which involved connecting natural language and open domain databases. the proposed system for "conversion of natural language query to sql query" allows a novice user to use text or speech to retrieve data. also, provides an additional feature where the user can insert, update or delete data from the database. the text or speech is processed in succession. this system uses four main steps to convert a natural language query to an accurate sql query (tokenization, lexical analysis, syntactic analysis, and semantic analysis) [4]. the system in [9] enables the novice user to input queries in hindi. this system uses analyzers such as word group analyzer morphological analyzer, which excerpts the keyword out of the query. it then uses a pattern matching formula to categorize the keyword. a domainspecific dictionary is used to retrieve the semantics. to each of these keywords, sql grammar is mapped and a proper syntactic query is generated. the proposed technique in [10] uses simple natural language (english) that has basic pos such as verbs, nouns, adjectives, and adverbs, which are translated into an sql query. this is followed by a preprocessing step which involves processes such as tokenization, tagging pos, and stemming. then, it is processed with semantic disambiguation by categorizing the words based on their domain and replacing them with corresponding sql keywords. then these keywords are clubbed into proper syntax and a query is generated. the proposed system in [11] mainly focuses on eliminating the difficulties of matching natural language to sql queries. the main adversities faced in this conversion are join path inference and keyword mapping. keyword word mapping involves retrieving candidate mappings, scoring, and pruning, ranking configurations. join path inference mainly deals with joins between the schema: since the users won’t be aware of the internal structure of the schema, they won’t know their connectivity. so, join path inference involves generating join paths, scoring join paths, and self-joins. authors in [12] propose a novel, fully automated method for producing sql queries from the input given in natural language. their method first creates a query sketch or partial query of the input using standard nlp procedures. this sketch is then passed to a typedirected program which generates a complete sql query. to further improve accuracy, this method performs fault localization when there is an error and database repair knacks to improve the original sketch. these steps are repeated in a confidence driven refinement loop and the top results are presented to the user. authors in [13] aimed to reconnect the void between natural language and query language with nominal domain knowledge. neural networks were used to encode and decode the input parameters and their machine representations. this method is described in two models: sequence-to-sequence and sequence-to-tree. the method has two steps, an encoder to convert the natural language input to vector representation and to form a proper sql query using a decoder from this vector. it also includes an attention layer which enables the model to learn soft alignments between inputs and outputs and present a way to handle rare mentions of entities and numbers. this approach demonstrates the same or better performance with similar models though it doesn’t use representation specific features. authors in [14] proposed an improved semantic parser named scissor that generates a sophisticated meaning representation language from a natural language sentence. their approach uses two target meaning representation languages (mrls). they have created a semantic parsing framework that constructs a semantically engineering, technology & applied science research vol. 10, no. 6, 2020, 6521-6525 6523 www.etasr.com nethravathi et al.: structuring natural language to query language: a review augmented parse tree (sapt) and uses a recursive procedure to construct meaning representations (mrs) for each node. the experimental results demonstrate that this approach produces more accurate mrs than several previous methods. a detailed representation of the reviewed existing work is depicted in table i. table i. detailed analysis ref. defined problems conclusion and future work [1] understanding the semantics of the query is a challenging task in the development of nlidbs. it is an improvement of the previous attempts at the utilization of database schemas as the skeleton of the system. it provides physical independence, by separating logical and physical schemas. future work: extend athena to include natural language dialogue capabilities and to handle self-join queries through nesting [2] linguistic uncertainties, domain inflexibility, non availability of model benchmarks in data driven methods which lead to additional complexity. this design is the first large corpus for data driven neural natural language interfaces to databases and has succeeded in training an e2e nlidb using sequence to sequence model. a future scope is the implementation of a stacked decoder to generate a query sketch. [3] high complexity of data-warehouses which clashes with non-tech users. uses relationships of inheritance to eliminate the ambiguity in the meaning of words. future work: debate the effects of the usage of dbpedia for pairing keyword queries against numerous synonyms found by the model. [4] a substantial increase in the number of online database users. failure of previous attempts at introducing simple query languages. successful implementation using servlets, javadatabase connectivity to an existing universal database of ibm. with proper parameter settings, the system in most cases outputs the more initiative solutions before the less initiative ones. [5] need of more nlis, low accuracy of previous nlis, and people unwilling to switch over to nlis from previous interfaces this is supposedly the first formal fulfilment of soundness and completeness of a natural language interface. their method could be extended to include large classes of questions. [6] lack of good visual interactive tools for databases, non availability of commercial and practical nlidbs. this approach makes an adequate use of dnn models as the core of its natural language interface system. future scope: to enable users to incrementally generate queries in a chatbot-like interface, where the system can question the user for clarifications and use prediction tasks. [7] issues of sequence-to-sequence model regarding different queries with identical output. previous methods of reinforcement learning only bring about a small increment in performance. employs a seq2set model to form sql queries with no order, and a column attention mechanism, which can further improve the model’s execution and efficiency. this approach shines new light on innovative solutions to structural generation problems with no order. [8] reducing the large number of logical implications for a given natural language input. this model intersects with two other techniques: the first includes attaining knowledge about models of semantics influenced by denotations or interactions with the external factors and the second involves connecting nls and open-domain dbs. [9] strict syntax and complexity of sql queries. inability of novice users to use sql efficiently. this model enables users to use english language to retrieve data from a database, thus eliminates any requirement to have knowledge about any complex query language. [10] addition of natural language interfaces to databases has become promising. lack of nlis in indian languages. successfully generates sql queries from hindi sentences. it makes use of a morphological analyzer and a word group analyzer to obtain and mark keywords. this model uses domainoriented dictionaries to determine the keyword type. in the future, this approach can be improved to a multilingual system. [11] aims to make the conversion from natural language to query language automatic and to put more emphasis on requirement specification. aims to increase the performance of query generation from natural language queries by preventing ambiguities in meaning of words. the future scope of this approach is to extract oo data from software specification. [12] the semantic difference between an nl query and relevant data is an overbearing problem in the creation of nlis to databases. the performance of existing nlis is improved by this method using information in the sql query log of a data structure. future scope: to research the influence of additional data in the sql query log such as user sessions [13] lack of knowledge about forming correct queries. importance of familiarity with the database schema in order to retrieve data. the parse-synthesize-repair loop approach can be instantiated with multiple different settings to generate programs from an nl. [14] high dependency on advanced vocabulary, custom made templates, and language specific features which are either representation or domain-specific outperforms older approaches despite not having domain or representation specific features. this model can also be applied to similar structured prediction problems such as constituency parsing. [15] shallow analysis in previously used semantic methods. by developing a state-of-the-art statistical parsing model containing semantic data, it is able to have syntactic and semantic clues to develop a robust interpretation that supports the creation of complete formal meaning representations. engineering, technology & applied science research vol. 10, no. 6, 2020, 6521-6525 6524 www.etasr.com nethravathi et al.: structuring natural language to query language: a review iii. methodology the solution to the major challenge of removing the middle layer hurdles discussed above is nlidbs. there are several inter-related domains to serve this purpose, some of which are [15]: • natural language processing • database implementation style • compiler design there are mainly two known options for converting natural language to sql [15]: • semantic parsing: the given input is translated to a standard not generalized format which depends on several factors such as the quality of lexicons, realm representationspecific features, etc. • neural networks: instead of using hard coded rules, this method relies on self-improvising and cognitive techniques to drive the task of conversion. the next important step is obtaining data from dbms. two paths can be considered [16]: • keyword-based methods: although comprehensibility is an advantage, processing large sentences can be difficult. • structured query method: this method is expressive and powerful but complex to use. it is challenging to meet the requirements because converting the natural language input into a query of schema structure is a complex task. one proposed solution is nalir (natural language interface working with rdbms) [15]. another perspective to cater to the challenge of nl input conversion is with respect to a graph database system [16]. this perspective most importantly fairs well to carry out computations when there are inter-related data. unlike a conventional rdbms, this system is entirely structured on inter-relationships between data by treating them not as a schema structure but as data, just like other values. there are four main steps involved in the conversion of natural language input to sql queries [18-25]. a. tokenization tokenization is the process of demarcating and classifying all possible sections of a string of input characters. the tokens that result from this process are then passed on to some other form of processing. this step can be considered as a sub-task of the parsing input. tokenization is followed by parsing. from this point, the data that are already interpreted may be loaded into respective data structures for further interpretation, compiling or general use. b. parsing the challenges that need to considered while parsing are [17]: • dependences of some intermediate representations on the database language. • domain-dependent syntactic parsing. • no/lack of any improvement in the waiting-time translating already processed input. there are two types of syntactic rules to be followed to parse an nl query in the proposed system [17], where the nl query is first syntactically parsed and then evaluated against dbms using machine learning. these two types of rules are: • rules that link only non-terminal symbols (non-leaf nodes). • rules that link only terminal symbols (leaf nodes). natural language query definitions [17], is a system proposed to represent all classes of logically interpreted natural language queries, as a solution to minimize the waiting-time for translating the already translated input. c. lexical analysis the next step in the process of conversion of a nl query is lexical analysis. this step involves analyzing a stream of characters into a lexicon token sequence which is further fed to the parser. this process can be seen as a rough equivalent of splitting text written in a natural language into a sequence consisting of words and punctuation symbols. although tokenization can be handled by the parser, we bother with tokenization to make the parser simpler and ensure that it is decoupled from the character encoding which is used for the source code. d. syntactic analysis the main task involved in this step is analyzing the syntactic structure of the program and its components and to check for errors. this step ensures that the dictionary of table names, keywords, and attributes is maintained. every tokenized word is mapped with the respective attributes in the maintained dictionary. it is passed onto the next step for further analysis. e. semantic analysis semantic analysis essentially ensures that the statements and declarations of a program are correct in the semantic sense. this makes sure that their meaning is consistent with the control structures and data types. this step involves: • label checking: ensures that the label references in a program exist. • type checking: ensures that the data types are used in consistence with their definition. • flow control checking: ensures that the control 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beam-column connection; haunch; bracket; damper; crane i. introduction a structure must be designed and constructed to safely resist the applied loads. the forces applied to a building must be transferred through its structural framework to the building foundation and the supporting ground. this applies to both vertical forces caused by building self-weight and occupancy loads, and the lateral forces caused by winds and earthquakes. to provide a stable structure, the design of the structural framework should provide a complete load path capable of transferring loads from their point of origin to the load-resisting elements. the building must also be designed to resist the overturning effects caused by the lateral forces. steel structures should be stiff enough to control the drift to prevent structural damage and also must have sufficient ductility to prevent collapse caused by deformation. portal framed steel structures are the most common type of industrial buildings. they are very efficient and economical when used for single-story buildings provided that the design details are cost effective and the design parameters and assumptions are well chosen. the major components of a portal frame building are a series of parallel portal shaped frames as the major framing elements. each frame is rigid and resists horizontal lateral forces and gravity loads in the plane off the frame by flexural action in the beams and columns. beam-to-column connection is a conventional rigid connection in steel moment resisting frame. the columns are generally larger than the rafters because the rafters are haunched near the columns to cater for the peak bending moments at the columns. for the eaves of the portal frame, bolted connections are mostly used of the form shown in figure 1. a haunch can be created by welding a “cutting” to the rafter to increase its depth locally and to make the connection design more efficient. the cutting is often made from the same steel section as the rafter. in some cases, the column and the haunched part of the beam are constructed as one unit and the constant depth part of the beam is bolted using an end plate connection. fig. 1. steel framed structure with haunches at eave and ridge in the design of rafters and columns in portal frames the selection of the member sizes may be governed by the ultimate or strength limit state, or by limiting deflections in serviceability limit state. to obtain an economical rafter design, it is important to ensure that the design bending strength is as close as possible to the section capacity which for many sections will be the plastic moment capacity. this capacity is usually achieved by the use of adequate restraints such as fly braces to restrain the inside rafter and lateral column flanges laterally. rafters are subjected to high bending moments in the plane of the frames which vary from a maximum “hogging” moment at the junction with the column to a minimum sagging moment close to apex. haunches are used at eaves and apex connections and made from the same sections of beams with a height that equals the depth of frame’s beam and a length equal to 10% of frame’s span as shown in figure 2. in this study, a proposed system using friction dampers called ring springs as bracing system is used to allow a more efficient design, both statically and dynamically. corresponding author: nagui william bishay-girges engineering, technology & applied science research vol. 10, no. 1, 2020, 5126-5131 5127 www.etasr.com bishay-girges: improved steel beam-column connections in industrial structures (a) (b) fig. 2. (a) eave connection with haunch, (b) prototype of rafter with build-up haunch ii. beam-to-column connections the detailing of frame connections is probably the most important part of structural design and undoubtedly requires more experience to achieve both sound and economical solutions than does member sizing. rigid connections transfer significant moments to the columns and are assumed to undergo negligible deformations. rigid connections are necessary in sway frames for stability and also contribute in resisting lateral loads. in high-rise and slender structures stiffness requirements may warrant the use of rigid connections. according to their stiffness values, connections can be classified as pinned, fully rigid, or semi-rigid. pinned connections should transmit the internal forces without developing significant bending moments which could affect the connected structural elements. a fully rigid connection presents a high rotational stiffness while semi-rigid connections do not satisfy the criteria for fully rigid or pinned connections [20]. according to the bending moment resistance, a full-strength connection develops a larger capable bending moment than the plastic capable bending moments of the connected elements. thus, yielding will appear in the weakest structural member connected in the joint [21]. generally, full strength beam-to-column connections are designed to ensure the plastic hinge formation in the connection or in the beam, thus avoiding plastic deformation is fulfilled by varying the connection components characteristic. although there are many technical solutions for moment resistant connections, the most frequently used type is the end plate connection with bolts or welding the beam directly to the column. all components of this connection can influence its behavior: the end plate type (exact, extended, or extended with stiffeners), end plate thickness, bolts diameter, the compression or tension stiffeners on the web panel of the column, and the shear stiffeners on the web panel of the column as shown in figure 3. (a) (b) (c) fig. 3. rigid beam-to-column connections: (a) flushed short end plate and haunch beam-column connection, (b) connection prototype, and (c) extended end plate and section a-a moment connections are designed to transfer bending moments, shear forces and sometimes normal forces. the design strength and stiffness of a moment connection are defined in relation to the strength and stiffness of the connected members. the design strength of a moment connection may be full-strength (i.e. the moment capacity of the connection is equal to or large than the capacity of the connected member) or partial-strength (i.e. the moment capacity of the connection is less than that of the connected member). similarly, the stiffness of a moment connection can be rigid or semi-rigid compared to the stiffness of the connected member. the rotation capacity of the structure may be provided by either the connection or the connected member. deformation capacity is usually provided by plastic deformation of one or more components. if the strength of the connection clearly exceeds the strength of one of the connected members, the designer can rely on the deformation capacity coming from the connected, e.g. the formation of a plastic hinge in the beam. after the mechanical properties of all components have been determined, the various components can be assembled to determine the strength, stiffness, and deformation capacity of the whole connection. the bending moment of the beam is primarily taken by the flanges in the form of tension and compression forces. the bending moment of the column is also resolved as a force couple. stiffeners help in distributing the forces in the engineering, technology & applied science research vol. 10, no. 1, 2020, 5126-5131 5128 www.etasr.com bishay-girges: improved steel beam-column connections in industrial structures connection zone and in avoiding local repture, crushing or buckling of the beam web. iii. previous research considerable research has been carried out to improve the beam column connections in resisting the applied loads and deflections [2-14]. a different method of a steel yielding damper in the beam-to-column connections relying on the combination of slit damper and t-stud is proposed in [2] as shown in figure 4, with an aim to increase energy dissipation capacity and stiffness and to reduce lateral damage on the structure. the purpose of this method is to develop a connector which works as a key energy-absorbing device in beam-to column joints. the idea of combining a t-stud and steel slit dampers is utilized and a damper is formed via embedding slit segments within the flange of the connector. it is expected that plastic deformation to be concentrated on connectors, while the main structural components remain elastic. fig. 4. t-stud connection another research in developing the beam to column connections used cast high-strength steel brackets that fastened to each beam flange and bolted to the column flange as shown in figure 5 [3]. the brackets are proportional to develop the full moment capacity of the beam and can be either welded or bolted to the beam flange. when subjected to large lateral deformation, the connection forces yield and plastic hinge formation occurs in the beam, beyond the tip of the brackets and away from the column face. fig. 5. bolted bracket and typical connection authors in [4] presented beam to column connections equipped with super elastic shape memory alloy tendons as recentering elements and shear tabs or web hourglass steel pins as supplementary energy dissipating and shear resisting components (figure 6). connecting the beam web to the column flange, shear tabs can help transfer shear force from the beam to the column. moreover, friction between shear tab and beam web can enhance the energy dissipation capacity of the connection. (a) (b) fig. 6. (a) typical tendon connection, (b) beam-to-column connection with shape alloy tendons connections incorporating shape memory alloy tendons outside the beam flanges feature a significantly higher amount of moment capacity and initial stiffness as this configuration provides a longer lever arm for the tendon-bearing force couple. changes in the amount of resisting forces produced by the energy dissipating devices could greatly affect the cycle behavior of the connection in terms of strength, stiffness, energy dissipation and recentering ability. the sliding hinge joint (shj) connection [5] is a low damage alternative to the traditional beam column welded connections of the moment resisting steel frame (mrsfs). the sliding hinge joint connection is intended to behave as a rigid beam-column connection under the serviceability limit state (sls) condition. under the uls condition, the shj is expected to allow large beam to column inelastic relative rotation through stable sliding in its key energy dissipating components i.e. the asymmetric friction connections (afcs). fig. 7. the sliding hing joint connection (shj) engineering, technology & applied science research vol. 10, no. 1, 2020, 5126-5131 5129 www.etasr.com bishay-girges: improved steel beam-column connections in industrial structures the afcs are located at the bottom web and bottom flange bolt groups as shown in figure 7. a top flange plate is bolted to the beam top flange, and the shj point of rotation is where this top flange plate is pinned to the column. the moment-relative rotation behavior of the shj is dependent on and schematically similar to the afc force-displacement behavior. when subjected to an increasing bending moment, the shj initially behaves like a rigid beam-column connection until the moment in the beam end exceeds the frictional resistance of the bottom web and bottom flange. when this occurs, the beam rotates relatively to the column about the point of rotation, through sliding in the afcs while dissipating energy through friction sliding. the main benefits to the shj are isolating the floor slab to limit additional demands to the beam, column, and slab under inelastic rotations; and confining yielding to the bolts. iv. proposed beam column connection system this study produces a new system that can be used to connect beams and rafters to steel columns in industrial steel buildings subject to a combination of gravity and lateral loads [18]. this system is used for the large span steel frames [16-19] required haunches in the eaves to increase the capacity of the beam section to resist the large bending moment at the eave in the steel frame [20, 21]. the haunch in the eave of the frame can be replaced by a damper device that can produce damping forces to reduce bending moment, thereby reducing the cross section of the rafter with haunch as shown in figure 8. the damper is fixed at the bottom flange of the beam or rafter by using a couple of plates welded to the beam and column flanges. the device can be relatively small and in the same configuration to the bottom flange of the haunch. stiffeners may be used in the beam and column webs at the location the damper is connected. the end plate is not needed to extend more than the height of the beam rafter. fig. 8. beam-column connection with damper the damper device that can be used in this case is the ring spring damper. this passive control system provides a selfcentering friction mechanism. the damper consists of inner and outer rings that have tapered mating surfaces. under the application of axial compression load, the wedge action of the taper faces causes the inner elements to radially contract and the outer elements to radially expand, allowing axial deflection as shown in figure 9. this sliding action between mating elements results in a large amount of energy being absorbed in overcoming the friction forces. when applying load to a preloaded system, sufficient force must be applied to the ring springs for the motion to proceed along the stiffness path from point 0 to point 1. that force is to overcome frictional resistance before sliding action within the ring spring commences. this gives rise to an elastic stiffness between points 0 and 1. as load is increased, displacement continues between points 1-2. during the next phase of displacement unloading proceeds between points 2-3 and then continue to point 4, returning to the origin. this motion is repeated when the direction of the loading / unloading is reversed as shown in figure 10. (a) (b) (c) fig. 9. ring springs damper properties: (a) ring spring prototype, (b) loaded ring springs fully compacted, (c) deflection of friction springs fig. 10. double acting hysteresis diagram of ring spring dampers to illustrate the benefits of the proposed system in reducing the bending moment at the eave connection, a 25m span with 6m eave height is used for a steel frame applied to a vertical load equals to 20kn/m. the cross section of both steel columns and rafter was selected to be universal steel section 360ub50. as shown in figure 11, the maximum bending moment at the eaves of the frame is equal to 795kn.m [15]. the shown bending moment is obtained without using haunch at the eaves of the frame. in conventional steel structures, in order to resist large values of bending moment, the rafter should be provided by a haunch at the eaves to increase the leaver arm of the rafter and section capacity. by adding haunches in the eave engineering, technology & applied science research vol. 10, no. 1, 2020, 5126-5131 5130 www.etasr.com bishay-girges: improved steel beam-column connections in industrial structures connection, the additional stiffness of the haunches will change the horizontal reaction which in turn will influence the eave and ridge moments. the percentage increase in bending moment in eave connections ranges from 2 to 3%. in this case, the eave bending moment will be equal to 815kn.m. with the proposed system using dampers at the eaves to produce control forces to resist the applied loads, the bending moment of the beam rafter is reduced significantly. figure 12 shows the bending moment for the frame structure using damper devices rather than haunches in the eaves. the force produced in the damper is 100kn and the bending moment at the eave reduced to 272kn decreasing to 65%. in this case, the 360ub50 section is a cable to resist the reduced bending moment without increase the section of the beam rafter by using haunch. fig. 11. bending moment of the steel frame without haunch fig. 12. bending moment of the steel frame with the proposed damper v. crace brackets in industrial buildings bridge cranes are used for handling in large workshops and storage and industrial buildings, usually working under the roof, and if necessary, in the open. they move by two parallel rails placed along the length of the hall. the main parts are the bridge and the driving winch, which moves along the bridge. fig. 13. industrial trussed frame structure with crane the crane bridge moves on the rails and the driving winch carts move across the bridge to transport from one place to another within the working range of the crane as shown in figure 13. in industrial buildings with crane, the crane girders are supported either on brackets connected to columns of uniform section or on stepped columns. brackets are used for lighter crane loads as shown in figure 14, and the stepped columns for heavy cane loads. the proposed system can also be used in industrial buildings with cranes. due to the significant impact of the wheel load of the moving crane on the crane rail, a haunch connected to the bracket is required to resist the vertical and horizontal applied load. the haunch of the bracket is fixed to the steel frame column by a steel plate using high tensile steel bolts welded to the bracket. instead of using the steel haunch, the damper device is installed on the column-bracket as a control system to reduce the impact of the applied load and enables the bracket section to carry the load. the damper device is installed under the crane bracket as shown in figure 15. figure 16 shows the difference between the bending moment of the frame without and with the damper devices. the reduction in the bending moment of the frame is about 23%. the advantages of using the proposed system are the easy installing to the crane bracket and the effective reduction of the internal straining forces in frame structure. fig. 14. support bracket connection fig. 15. crane bracket with damper and haunch (a) (b) fig. 16. bending moment diagram (a) without damper system at the crane bracket, (b) with damper system at the crane bracket engineering, technology & applied science research vol. 10, no. 1, 2020, 5126-5131 5131 www.etasr.com bishay-girges: improved steel beam-column connections in industrial structures the results of the numerical analysis showed that the proposed system improves beam-column connection behavior either at the eaves or at the crane bracket column connections. vi. conclusion this study describes an improvement of the steel beam-tocolumn connections in frame industrial buildings. the beamcolumn connection is considered and acts as the main load resisting system in the structural design. several previous researches in developing beam-to-column were presented and different connection forms were shown. in conventional connections, haunches are used to increase the capacity of the steel beam to resist the applied loads. an alternative system to the conventional connection using dampers is proposed. friction ring spring dampers are attached beneath the bottom flange of the beams and fixed to the flange of the column rather than increasing the depth of the cross section of the beams by haunches. the proposed system can be used at the critical connections of the steel frame such as the eave and crane bracket connections of the high values of the bending moments. dampers are used to produce the control system to reduce the bending moment of the applied load on the frame sections. the proposed system offers advantages such as: a) simplified installing to the bottom of the beams and columns, b) the possibility of increasing the control system produced by the damper to reduce the bending moment. with the proposed system there is no need to increase the depth of the beam height by welding haunches of cutoff of the beam section and increase the end steel plate to resist the high bending moment at the critical connections. in order to assess the behavior of the proposed system in industrial buildings, the model of a steel frame without and with the system was carried in microstran [11] and analyzed. two analysis groups with the dampers at eaves and bracket column connections were investigated. the percentage of reduction in the bending moment varied between 65% and 23% in eave and crane bracket connections respectively. the structure behavior was evaluated and the results indicated that the bending moments at the critical connections have been significantly reduced by the installation of the proposed system. acknowledgements the author wishes to express his gratitude to professor athol j. carr for his suggestions and help. references [1] new zealand standard, as/nzs 1170.2 (2002): structural design actions, part 2: wind actions, new zealand standard, 2002 [2] k. bayat, b. shekatehband, “seismic performance of beam to column connections with t-shaped slit damper”, thin-walled structures, vol. 141, pp. 28-46, 2019 [3] p. p. cordova, r. o. hamburger, “steel connections: proprietary or public domain?”, modern steel construction, vol. 10, pp. 24-31, 2011 [4] m. a. farmani, m. ghassemieh, “steel beam-to-column connections equipped with sma tendons and energy dissipating devices including shear tabs or web hourglass pins”, journal of constructional steel research, vol. 135, pp. 30-48, 2017 [5] s. rambormozian, g. c. clifton, g. a. macrae, h. h. khoo, “the sliding hinge joint: final steps towards on optimum low damage seismic-resistant steel system”, key engineering materials, vol. 763, pp.751-760, 2018 [6] t. j. mander, g. w. rodgers, j. g. chase, j. b. mander, g. a. macrae, r. p. dhakal, “damage avoidance design steel beam-column moment connection using high-force-to-volume dissipators”, journal of structural engineering, vol. 135, no. 11, pp. 1390-1396, 2009 [7] g. machae, c. clifton, “low damage design of steel structures”, steel innovations 2013 workshop, christchurch, new zealand, february 2122, 2013 [8] j. m. fisher, design guide 7 industrial buildings: roofs to anchor rods, american institute of steel construction, 2005 [9] c. christopoulos, a. filiatrault, c. m. uang, b. folz, “posttensioned energy dissipating connections for moment-resisting steel frames”, journal of structural engineering, vol. 128, no. 9, pp. 1111-1120, 2002 [10] s. r. mirghaderi, m. d. renani, “the rigid seismic connection of continuous beams to column”, journal of constructional steel research, vol. 64, no. 12, pp. 1516-1529, 2008 [11] j. m. ricles, r. sauce, m. m. garlock, c. zheo, “posttensioned seismicresistant connections for steel frames”, journal of structural engineering, vol. 127, no. 2, pp. 113-121, 2001 [12] c. c. chou, y. c. wang, j. h. chen “seismic design and behavior of post-tensioned steel connections including effects of a composite slab”, engineering structures, vol. 30, no. 11, pp. 3014-3023, 2008 [13] j. n. arlekar, c. v. r. murty, “improved truss model for design of welded steel moment-resisting frame connections”, journal of structural engineering, vol. 130, no. 3, pp. 498-510, 2004 [14] m. wolski, j. m. ricles, r. sause, “experimental study of a selfcentering beam-column connection with bottom flange friction device”, journal of structural engineering, vol. 135, no. 5, pp. 479-488, 2009 [15] microstran leading-edge software for structural engineers, product data sheet, bentley [16] p. h. sarjou, n. shabakhty, “effect of the improved pall friction damper on the seismic response of steel frames”, engineering, technology & applied science research, vol. 7, no. 4, pp. 1833-1837, 2017 [17] g. xu, m. yamanari, “performance of steel frame with linkage system under earthquake excitation”, engineering, technology & applied science research, vol. 9, no. 1, pp. 3795-3801, 2019 [18] n. w. b. girges, “an alternative system for eccentrically braced frames resisting lateral loads”, engineering, technology & applied science research, vol. 9, no. 3, pp. 4281-4286, 2019 [19] a. williams, steel structural design for lateral and vertical forces, mc graw hill, second edition, 2016 [20] s. t. woolcook, s. kitipornchai, m. a.bradford, design of portal frame building, australian institute of steel construction, third edition, 1999 [21] b. e. gorenc, r. tinyou, a. a. syam, steel designers’ handbook, unsw press, eighth edition, 2012 engineering, technology & applied science research vol. 9, no. 1, 2019, 3774-3777 3774 www.etasr.com chughtai: circuit design for thermal compensation of avalanche photodiode circuit design for thermal compensation of avalanche photodiode muhammad tajammal chughtai department of electrical engineering, college of engineering university of hail, hail, saudi arabia mt.chughtai@uoh.edu.sa abstract—it has been observed that the breakdown voltage of the avalanche photodiode (apd) changes with the change in the ambient temperature. this situation may result in a poorer signal to noise ratio and sometimes to permanent damage to the apd. in order to overcome these problems, various considerations may be taken into account, including maintaining the temperature of the apd permanently or the design of a bias system, which would be self-adjusting according to any changes in the temperature. the latter technique was adopted and the design of a bias supply is presented in this article. keywords-apd; thermal adjustment; optoelectronics i. introduction avalanche photodiodes (apds) are a good solution to the situations where very week signal is expected [1]. over the years, researchers have developed various techniques in modeling and manufacture of apds. authors in [2] suggested a new technique towards etching of epitaxial layer in an apd. authors in [3] developed a technique for temperature tracking using temperature sensors for si photodiode. authors in [4] studied and reported the dependence of apds’ temporal stability on a range of temperature variations. authors in [5] also presented a study on photodiodes’ dependence on temperature variations. diverse approaches have been adapted by researchers in the field of optoelectronics to come up with a range of promising solutions in relation to photodiodes. embedded version of photodiodes in technical textiles has been reported in [6]. apds have been known for their sensitivity towards changes in the ambient temperature, their operating point keeps shifting i.e. with increase in the temperature their operating point shifts away from the original breakdown point, which results in less sensitivity and reduced amplitude of the signal output. on the other hand, a drop in the temperature will shift the breakdown point to a lesser value, which may result in increased sensitivity and enhanced multiplication noise, which may eventually result into a permanent damage to the apd [7]. a study on apd in relation to its performance in extreme variations of temperature environment was conducted in [8]. the remedy to these problems is thought to be in the form of a temperature compensated bias system, which is capable of keeping track of any changes in the ambient temperature and hence providing a higher safety to the apd. a self calibrating photo detector at room temperature while operating it in dual mode has been reported in [9]. authors in [10] discussed on the variety of parameters related to pin photodiodes from the point of view of its manufacturing and physics involved. authors in [11] developed a 3d structure version of inp/ingap apd and claimed low noise factor figures. ii. various suggested methods to maintain the multiplication factor to keep the multiplication factor constant for a constant level of input signal it is necessary for the reverse bias voltage fed to the apd to track any changes in the temperature otherwise, changes in the temperature of the apd may cause the breakdown voltage of the apd to excess or the apd may give a signal of lower amplitude than desired. if the applied voltage exceeds the breakdown voltage (as a result of decrease in temperature), a permanent damage to the apd may occur. additionally, a rise in temperature will shift the breakdown point, leading to a signal of a lower than desired amplitude. three most common solutions to this problem are: (i) constant current operation, (ii) maintenance of the temperature of the apd at a constant level, and (iii) bias the apd using a temperature compensated power supply. a constant current power supply scheme can be seen in [12] along with the derived formulas to compensate the temperature variations and hence devised methods to stabilize the operating the operation of an apd. two types of temperature coefficients γ and β were used, where γ represents the change in multiplication factor due to temperature variation while the apd is biased under constant voltage condition and β describes the change in avalanche voltage with respect to temperature when the apd is operating under constant multiplication factor. multiplication factor (m) is related to ionization rate (α) as: 1 − 𝑀−1 = ∫ 𝛼 𝑑𝑥 (1) the solution of this integral has been suggested in terms of width of avalanche region in [15]. one method of temperature compensation can be achieved by ensuring that the voltage of the apd tracks any temperature change by using another apd to produce a reference voltage signal [13]. the second method mentioned above, causes condensation on the apd window and hence a poorer response and need to clean the window. the third method of stabilizer and apd is to design a circuit using temperature sensing components, as shown in figure 1. corresponding author: muhammad tajammal chughtai engineering, technology & applied science research vol. 9, no. 1, 2019, 3774-3777 3775 www.etasr.com chughtai: circuit design for thermal compensation of avalanche photodiode fig. 1. schematic of temperature compensated bias supply for apd. usually, temperature sensing components produce a current signal which varies with any change in temperature. this output current may be converted to a voltage using an operational amplifier, configured as a current to voltage converter. the output of this op-amp can then be fed to a summing amplifier in a non-inverting configuration, thereby summing the voltage with the negative value from a conventional high voltage power supply and a reference voltage. the resultant output is used to control the base current of the bias control transistor. iii. design considerations the apd used for this design study was an nec model ndl-1202, the temperature coefficient β for this particular apd is 1×10-1%ºc [14]. in order to convert this temperature coefficient into a voltage variation (volts/ºc) (1) is used: 𝛽 𝑉𝐵𝑅 = 1 × 10−1 × 100 (1) where  is temperature coefficient of the apd in volts/ºc and vbr is the reverse breakdown voltage of the apd. the value of vbr for this case is 213.5v, so that (1) yielded [7]: 𝛽 = 213.5 mv ℃⁄ . (2) the circuit for a temperature compensated power supply for an apd is illustrated in figure 1, a step by step design and analysis of the circuit follows. a. step-1 a constant voltage reference of -6.8v was obtained using a precision reference diode package lm329. this constant reference voltage was then supplied to the temperature sensor ic ad590, which has a temperature coefficient of 1a/ºk. b. step-2 consider the combination of the temperature sensor ici and the operational amplifier a1. the total current generated by ic1 for a rise of t kelvin degrees in the temperature will be tx10-6 a. hence, the current i supplied by the temperature sensor for a rise of t will be: 𝐼 = 𝑇 × 10−6 a k⁄ . (3) therefore, the voltage at the output of the op-amp a1 with feedback resister r1 can be expressed as: 𝑇 × 10−6 = 𝑉1 𝑅1 ⁄ . (4) thus, the voltage change v1 becomes: 𝑉1 = 𝑅1 × 𝑇 × 10 −6 v (4) c. step-3 the operational amplifier a2 was used in a summing amplifier configuration so that it added all three voltages applied at its inputs to produce the output vo. this output vo was supplied at the base of an npn transistor q1, through a resistor. transistor q1 was configured so that the smaller the voltage signal at its base, the lower was the conduction between its collector and emitter. when conducting, the transistor produced a flow of current between its collector and emitter of q1. in turn, this caused the +hv point to float, hence, a variation in the hv point at the output could be observed. kirchhoff’s law states that, at any point in an electrical circuit, the algebraic sum of the currents meeting at that point is zero. therefore, the current equation according to kirchhoff’s law at the input of a2 can be written as. 𝑉𝑟𝑒𝑓 𝑅2 + 𝑉𝐵 𝑅4 + 𝑉1 𝑅3 = 0 (5) however, substituting the value of v1 from (4) in (5) we have: 𝑉𝑟𝑒𝑓 𝑅2 + 𝑉𝐵 𝑅4 + 𝑇 ×𝑅1×10 −6 𝑅3 = 0 (6) differentiating (6), with respect to t leads to: 𝑑𝑉𝐵 𝑑𝑇 = − 𝑅1 × 𝑅4 × 10 −6 𝑅3 (7) putting up 𝑑𝑉𝐵 𝑑𝑇 = 𝛽, (7) becomes: 𝛽 = − 𝑅1 × 𝑅4 ×10 −6 𝑅3 (8) which gives the value for the temperature coefficient 𝛽 of the apd. substituting this value into (5) gives: 𝑉𝐵 = − 𝑉𝑟𝑒𝑓 × 𝑅4 𝑅2 + 𝑇 × 𝛽 (9) the values for the resistors r2, r3 and r4 can be calculated by solving (5), (8) and (9) simultaneously. iv. practical implementation from the data provided with the apd, the reverse breakdown voltage of the particular apd under consideration was found to be 213.50v and, according to this value, the temperature coefficient was 213.50mv/k. in order to calculate the appropriate values of the various resistors to be used in the circuit, this voltage value must be substituted into (2) using r1=20kω. this yields: − 213.5 × 10−3 = 20𝑘 × 𝑅4 𝑅3 × 10−6 thus, 𝑅4 𝑅3 = 213.5 20 = 10.675 (10) leading to the value r4=11r3. since it was already required that the apd should operate at a temperature of 300k (i.e, approximating to a normal room temperature), this implied that the following values were already fixed: engineering, technology & applied science research vol. 9, no. 1, 2019, 3774-3777 3776 www.etasr.com chughtai: circuit design for thermal compensation of avalanche photodiode t=300ok, β=−213.5mv/ ok, r1=20×10 3ω inserting these values in (9) led to a value for the reversed breakdown voltage: 𝑉𝐵 = − 𝑉𝑟𝑒𝑓 𝑅4 𝑅2 − 64.05 (10) furthermore, it was required to operate the apd at a reverse breakdown voltage value of vb=−212.5v, so that the avalanche noise was at optimum level. therefore − 212.5 + 64.05 = −𝑉𝑟𝑒𝑓 𝑅4 𝑅2 (11) but vref = 5 volts ∴ 𝑅4 𝑅2 = 29.69 assuming that r2=100kω, (10) yields: 𝑅4 = 1000k (29.69) = 2969k ≈ 3mω 𝑅3 = 3m 10.675 = 281kω inserting these design values for r1, r2, r3 and r4 into the circuit design, satisfactory performance of the temperature compensated power supply for the apd was obtained. however, to set the value of the temperature coefficient precisely, it was decided to insert a variable resistor instead of a fixed value for r2. this could then be adjusted until the required output value for bias voltage was obtained. apart from the present application, the implementation of calculations may also be employed to temperature sensitive environment and systems such as shop-floor gauging, altimeter temperature correction and other sensor temperature compensations. v. results and conclusion application of the circuit under consideration was applied to bias an apd which have been used at the receiving end of a laser doppler anemometer (lda) system in back scatter mode. since in backscatter mode the signal intensity is far lower compared to forward scatter, the necessity of using an apd arose. regarding apd’s performance with respect to thermal changes the application of such circuit became compulsory so that reasonable amplitude of the signal could be maintained. the circuit for temperature compensation of the apd was implemented and assembled on a double-sided printed circuit board, according to the design values of the components calculated above (figure 2). tests were carried out to the designed circuit by applying different load conditions to hv power supply. for such cases it is very common to pick up noise by oscilloscope probes. in this case, ripple was also observed, an average pk-pk value of 15.35mv and an rms value of 3.30mv at a frequency of 50hz were observed. tests on hv supply were carried out by employing a range of loads having values ∞, 1m, 10k and 47kω. results in terms of noise frequency in hz and ac noise level were collected and are presented in table i. in order to measure the variation in the circuit performance for changes in the ambient temperature, the temperature sensing semi-conductor element and a thermocouple were both mounted on the same heat sink. fig. 2. pcb sharing thermal compensation circuit. table i. load results load resistance (ω) noise (hz) ac noise level (vp-p) ∞ 192k 0.003 1m 50 -0.034 10k 100 0.195 47k 100 0.462 the thermocouple was used to monitor the temperature variations directly. the heat sink itself was coiled around by a 1m long high resistance eureka wire for heating purposes. the two ends of this wire were attached to a variable current power supply, so that it could be heated, thereby raising the temperature of the heat sink, and varying the amplitude of the signal from the temperature sensing element to the high voltage (hv) circuit. the variation in the output voltage from the circuit was observed. the output of the high voltage power supply was attached to a voltage ratio divider unit, which helped reduce the high voltage to an appropriate level which could be supplied to an analogue to digital converter card fitted inside a personal computer. the arrangement used can be seen in [5]. a number of observations were taken for different heat sink temperatures, with data being collected in the temperature range of 20-77 ºc. the results shown in figure 3 confirm that the output signal of the hv power supply circuit follows a reasonably linear behavior in accordance with temperature variations. fig. 3. performance profile of designed circuit. such deviations from linear behavior may be caused by the non-linear behavior of components used to construct the engineering, technology & applied science research vol. 9, no. 1, 2019, 3774-3777 3777 www.etasr.com chughtai: circuit design for thermal compensation of avalanche photodiode temperature compensation circuit. the design methodology and calculations mentioned above are versatile and can easily be used in applications where variation of temperature becomes problematic to the operation of a system. this may be carried out by considering appropriate values of temperature coefficients and other discrete component values depending upon power requirement. references [1] j. w. gardener, micro sensors: principles and applications, joηn wiley & sons, 1995 [2] a. k. budtolae, t. n. grishina, p. e. khakuashev i. v. chinareva, “formation of guard ring of avalanche photodiode based on the ingaas/inpheterostructure”, journal of communications technology and electronics, vol. 62, no. 9, pp. 1078-1082, 2017 [3] e. borreguero, c. k. tang, j. gran, a. p. aglio j. c. acosta, “preliminary results of feasibility of self-calibration of silicon pn photodiodes at room temperature using temperature sensors”, optica pura y aplicada, vol. 51, pp. 1-8, 2018 [4] s. abdullah, c. h. tan, x. zhou, s. zhang, l. pinel, j. s. ng, “investigation of temperature and temporal stability of algaassb avalanche photodiodes”, optics express, vol. 25, no. 26, pp. 3361033616, 2017 [5] m. t. chughtai, “temperature compensated bias supply circuit for photodiodes”, przeglad elektrotechniczny, vol. 94, no. 10, pp. 207-209, 2018 [6] a. satharasinghe, t. hughes-riley, t. dias, “photodiodes embedded within electronic textiles”, scientific reports, vol. 8, no. 1, pp. 1-13, 2018 [7] b. woodward, a. oliviero, cabling: the complete guide to copper and fiber-optic networking, sybex, 2009 [8] t. y. chuan, r. chandrasekara, c. cheng, a. ling, “silicon avalanche photodiode operation and lifetime analysis for small satellites”, optics express, vol. 21, pp. 16946-16954, 2013 [9] m. u. nordsveen, c. k. tang, j. gran, “demonstration of a dual-mode si detector as a self-calibratingdevice at roomtemperature”, optics express, vol. 25, pp. 8459-8469, 2017 [10] e. fossum, r. hondongwa, b. donald, “a review of the pinned photodiode for ccd and cmos image sensors”, ieee journal of the electron devices society, vol. 2, no. 3, pp. 33-43, 2014 [11] z. wu, j. guo, y. li, y. zhao, “low-noise 3-d avalanche photodiodes”, ieee photonics journal, vol. 8, no. 4, pp. 1-10, 2016 [12] k. nishida, m. nakajima, “temperature dependence and stabilization of avalanche photodiodes”, review of scientific instruments, vol. 43, no. 9, pp. 1345-1350, 1972 [13] d. renker, “properties of avalanche photodiodes for applications in high energy physics, astrophysics and medical imaging”, nuclear instruments and methods in physics research section a: accelerators, spectrometers, detectors and associated equipment, vol. 486, no. 1-2, pp. 164-169, 1974 [14] k. kiya, t. hayashi, “direct current method for extremely weak optical signal detection using avalanche photodiodes”, journal of spectroscopic society of japan, vol. 33, no. 2, pp. 78-85, 1984 [15] r. hall, “temperature coefficient of the breakdown voltage of silicon pn junction”, international journal of electronics, vol. 22, no. 6, pp. 513-519, 1967 https://link.springer.com/journal/11487 https://link.springer.com/journal/11487 https://link.springer.com/journal/11487/62/9/page/1 https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-26-33610&origin=search https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-26-33610&origin=search microsoft word 02-salem-ed2.doc etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 114-120 114 www.etasr.com gouda et al: a study of k-factor power transformer characteristics by modeling simulation a study of k-factor power transformer characteristics by modeling simulation o. e. gouda electric power and machines dpt cairo university cairo, egypt osama241@hotamail.com g. m. amer high institute of technology benha university benha, egypt ghada.amer@bhit.bu.edu.eg w. a. a. salem high institute of technology benha university benha, egypt. walid.attia@bhit.bu.edu.eg abstract— harmonic currents generated by nonlinear loads can cause overheating and premature failure in power transformers. k-factor transformers are specially designed to accommodate harmonic currents and offer protection against overheating caused by harmonics. they minimize harmonic current loss and have an additional thermal capacity of known limits. according to ieee c57-110, the winding eddy current losses are considered proportional to the harmonic current squared times its harmonic number. k-factor is only an indicative value and the authors' main objective in this paper is to study the effect of harmonics on oil filled transformer and to simulate harmonic behavior using matlab simulink. a case study is simulated in order to investigate k-factor values with pumping loads, with and without the use of harmonic filters. results are compared with measured values. keywords-component; k-factor transformers; harmonics filter; total harmonic distortion i. introduction in recent years, there has been an increased concern about the effects of nonlinear loads on electric power systems [1]. harmonic currents adversely affect virtually every component in the power system, creating additional dielectric, thermal, and/or mechanical stresses [2]. the harmonic currents flowing through the power system impedances result in harmonic voltage drops which are observed as voltage distortions. severe voltage distortions may occur when the power system's inductive and capacitive reactance’s happen to be equal (parallel resonance) at one of the nonlinear load's significant harmonic current frequencies (typically the 5th, 7th, 11th or 13th harmonic) [2-5]. even without resonance, harmonic currents cause losses in normal power system components. wiring experiences additional heating beyond the normal i 2 r, due to skin and proximity effects. harmonics also cause over heating of the neutral conductor due to the additive nature of triple harmonics (3rd, 9th, 15th, etc.) on three phase four wire systems serving nonlinear loads with line-to-neutral connections [6, 7]. with transformers, harmonic load currents cause additional heating, primarily in the form of additional winding eddy current losses. ieee c57.110, provides methods to de-rate a transformer for any given harmonic load profile [8]. k-factor transformers are specifically designed to accommodate harmonic currents and they have an additional thermal capacity of known limits, allowing operation up to nameplate capacity without de-rating. ii. k-factor transformers k-factor rating is optionally applied to a transformer, indicating its suitability for use with loads that draw non sinusoidal currents. the k-factor is given by the following equation [6, 9]. max 2 2 1 ( ) h h h k factor i h pu = = − = ∑ (1) where: h= harmonic number, ih = the fraction of total rms load current at harmonic number h k-factor rated transformers have not been evaluated for use with harmonic loads where the rms current of any singular harmonic greater than the tenth harmonic is greater than 1/h of the fundamental rms current. a. relationship between k-factor and harmonic loss factor the definition of the k-factor by the underwriter’s laboratory (ul) [10] is based on using the transformer rated current in the calculation of per unit current in the previous equation. substituting the rated current for the k-factor gives: max max 2 2 2 2 2 1 1 1 ( ) h h h h h hr r i k factor h i h i i = = = = − = =∑ ∑ (2) where: h is the harmonic order, ih is the rms current at harmonic “h” (amperes), ir is the rms fundamental current under rated frequency and rated load conditions (amperes). the relationship of the harmonic loss factor and the ul kfactor [11-13] is given by: max 2 1 2 ( ) h h h hl r i k factor f i = = − = ∑ (3) the harmonic loss factor is a function of the harmonic current distribution and is independent of the relative magnitude. the ul k-factor is dependent on both the magnitude and the distribution of the harmonic current. for a etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 114-120 115 www.etasr.com gouda et al: a study of k-factor power transformer characteristics by modeling simulation set of harmonic load current measurements, the calculation of the ul k-factor is dependent on the transformer rated secondary current. for a new transformer with harmonic currents specified as per unit of the rated transformer secondary current, the k-factor and harmonic loss factor have the same numerical values. the numerical value of the k-factor equals the numerical value of the harmonic loss factor only when the square root of the sum of the harmonic currents squared equals the rated secondary current of the transformer [14, 15]. b. standard transformers k-factor ratings the standard k-factor transformer ratings and typical loads are given in table i [10]. table i. k-factor transformer ratings load k-factor incandescent lighting (with no solid state dimmers) electric resistance heating (with no solid state heat controls) motors (without solid state drives) control transformers/electromagnetic control devices motor-generators (without solid state drives) k-1 k-1 k-1 k-1 k-1 electric-discharge lighting ups w/optional input filtering induction heating equipment welders plc’s and solid state controls (other than variable speed drives) k-4 k-4 k-4 k-4 k-4 telecommunications equipment ups without input filtering multi-wire receptacle circuits in general care areas of health care, facilities and classrooms of schools, etc. multi-wire receptacle circuits supplying inspection or testing equipment on an assembly or production line k-13 k-13 k-13 k-13 mainframe computer loads solid state motor drives (variable speed drives) multi-wire receptacle circuits in critical care areas and operating/recovery rooms of hospitals k-20 k-20 k-20 multi-wire receptacle circuits in industrial, medical, and educational laboratories. multi-wire receptacle circuits in commercial office spaces small mainframes (mini and micro) k-30 k-30 k-30 other loads identified as producing very high amounts of harmonics (especially in higher orders) k-40 k-factor transformers are designed to be operated fully loaded with any harmonic load having a k-factor equal to or less than its k-rating. for example, a k-13 transformer can be fully loaded with any harmonic load having a k-factor up to k13. if the load has a k-factor greater than 13, then the transformer cannot be safely operated at full load and would require de-rating [16]. for k-factor transformers, ul also requires that the neutral terminal and connections be sized to accommodate twice the rated phase conductor size (double the minimum neutral capacity) of standard transformers. standard transformers, i.e. those not marked with a k-factor rating, may have some tolerance to nonlinear loading [16], but their capability is unknown to the user and is not certified by a third party such as ul. currently, marking a transformer with a k-factor rating is not required by ul. iii. case study the toshka pumping station was constructed between 1998 and 2003. it is literally the largest state project in egypt. located along the shores of the nasser lake, which was created by the construction of the famous, aswan dam, this pumping station is a project in which hitachi, ltd. installed 21 large vertical centrifugal volute pumps with the capacity to draw 29 million cubic meters of water per day and supply it to the desert area. about 2,250 square kilometers of land are to be greened through this project [17, 18]. a view of the toshka pumping station is illustrated in figure 1. fig. 1. toshka pumping station a. description of toshka pumping station the pumping station, which is located at the intake basin, will accommodate (in the final stage) 24 variable speed pumps with a total capacity of 288mw (24 x 12mw) and a total discharge of 400 m 3 /s (24 x 16.7m 3 /s). the static suction head is 56m. the pumping station dimensions are 145 x 60 x 45m (l x h x w). the electrical supply to the plant is secured via a 220/11kv substation in toshka and an 11 kv bus duct, which were also supplied by abb in a separate contract under the toshka project. figure 2 represents the single line diagram of 220kv substation to 11kv toshka pump station. fig. 2. connection between aswan connection substation and toshka pumping station b. measurement technique the harmonics measurement location is shown in figure 3, the point of common coupling is the most important point of etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 114-120 116 www.etasr.com gouda et al: a study of k-factor power transformer characteristics by modeling simulation harmonics measurement, and it is located on the output of the 66/11 kv, 25mva transformers. measurements of the harmonic currents and k-factor calculations for toshka pumping station without harmonic filter are shown in table ii and with harmonic filter are shown in table iii. the measurements are carried out on phase b. from the measurement values it is shown that the k-factor for the system without harmonic filter is equal to 5.436679, whereas the kfactor for the system with harmonic filter is equal to 1.200575, which means that he use of the harmonic filter decreases the selected k-factor transformer ratings almost five times. table ii. harmonics measurement without filter h ih% fund ih ih = ih / irms h 2 *(i h) 2 1 100 1 0.996924891 0.993859237 3 2.5591 0.025591 0.025512305 0.005857899 5 6.8061 0.068061 0.067851705 0.115096347 7 2.263 0.02263 0.02256041 0.024939633 9 0.12456 0.0012456 0.00124177 0.000124901 11 1.4063 0.014063 0.014019755 0.023782976 13 1.3018 0.013018 0.012977968 0.028464274 15 0.05778 9 0.0005778 9 0.000576113 7.46789e-05 17 0.09951 4 0.0009951 4 0.00099208 0.00028444 19 0.08968 6 0.0008968 6 0.000894102 0.00028859 21 0.05123 3 0.0005123 3 0.000510755 0.000115044 23 0.20088 0.0020088 0.002002623 0.002121553 25 0.07366 9 0.0007366 9 0.000734425 0.000337112 27 0.05600 2 0.0005600 2 0.000558298 0.000227227 29 0.04900 7 0.0004900 7 0.000488563 0.000200741 31 0.09088 2 0.0009088 2 0.000906025 0.000788867 33 0.04416 6 0.0004416 6 0.000440302 0.00021112 35 0.05046 9 0.0005046 9 0.000503138 0.000310106 37 0.05041 1 0.0005041 1 0.00050256 0.000345763 39 0.04367 2 0.0004367 2 0.000435377 0.00028831 41 0.03704 6 0.0003704 6 0.000369321 0.000229285 43 0.04254 5 0.0004254 5 0.000424142 0.000332628 45 0.04760 5 0.0004760 5 0.000474586 0.000456095 47 0.07259 6 0.0007259 6 0.000723728 0.001157034 49 0.05342 9 0.000534 0.000532647 0.000681194 ∑ = 1.200575 fig. 3. single line diagram of toshka pimping station table iii. harmonics measurement with filter h ih% fund ih ih = ih / irms h 2 *(i h) 2 1 100 1 0.996197 0.992408 3 0.36702 0.0036702 0.003656 0.00012 5 0.45481 0.0045481 0.004531 0.000513 7 0.68039 0.0068039 0.006778 0.002251 9 0.30952 0.0030952 0.003083 0.00077 11 0.011008 0.00011008 0.00011 1.46e-06 13 5.501 0.05501 0.054801 0.507528 15 0.12257 0.0012257 0.001221 0.000335 17 0.19933 0.0019933 0.001986 0.00114 19 0.26443 0.0026443 0.002634 0.002505 21 0.19914 0.0019914 0.001984 0.001736 23 4.4975 0.044975 0.044804 1.061911 25 3.1756 0.031756 0.031635 0.625492 27 0.14193 0.0014193 0.001414 0.001457 29 0.21729 0.0021729 0.002165 0.003941 31 0.21076 0.0021076 0.0021 0.004236 33 0.15327 0.0015327 0.001527 0.002539 35 2.6503 0.026503 0.026402 0.853918 37 2.0062 0.020062 0.019986 0.546817 39 0.13907 0.0013907 0.001385 0.002919 41 0.21042 0.0021042 0.002096 0.007386 43 0.17302 0.0017302 0.001724 0.005493 45 0.12539 0.0012539 0.001249 0.00316 47 1.4933 0.014933 0.014876 0.488855 49 1.1575 0.011575 0.011531 0.319245 ∑ k= 5.436679 etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 114-120 117 www.etasr.com gouda et al: a study of k-factor power transformer characteristics by modeling simulation c. modeling of toshka pumping station toshka pumping station consists of four groups and each group contains six synchronous motors. the simulation model is consisted of the aswan connection station 132/220 kv, two transmission lines 220 kv (distance 276km), two transformers 125mva, 220/66 kv and two transformers 25mva, 66/11kv. figure 4 shows the model of the pumping station, transmission lines and the power transformers. figure 5 shows the control and drive circuits for the synchronous motor. d. results the modeling results are obtained on the output of the 66/11kv, 25 mva transformer for the following two cases case (1) without using harmonics filter: figures 6-9 show voltage and current (phase and 3-phase) at low tension of 25mva 66/11kv transformer. figures 10-11 show the frequency response characteristics without harmonic filter for voltage and current respectively. the harmonics of currents and voltages are listed in table iv. the 5th, 7th and 11th harmonics exceeded the limits recommended by ieee-519 [9] fig. 4. modeling of toshka pumping station, transmission lines and the power transformers fig. 5. control and drive circuit for the synchronous motor etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 114-120 118 www.etasr.com gouda et al: a study of k-factor power transformer characteristics by modeling simulation 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 -1.5 -1 -0.5 0 0.5 1 1.5 x 10 4 time (s) p h a s e v o lt a g e ( v ) fig. 6. phase voltage at low tension side of 25mva 66/11kv transformer without harmonic filter 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 -1.5 -1 -0.5 0 0.5 1 1.5 x 10 4 time (s) p h a s e s v o lt a g e ( v ) fig. 7. 3-phase voltage at low tension side of 25mva 66/11kv transformer without harmonic filter 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 -4000 -2000 0 2000 4000 6000 8000 10000 time (s) p h a s e c u rr e n t (a ) fig. 8. phase current at low tension side of 25mva 66/11kv transformer (without harmonic filter) 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 -8000 -6000 -4000 -2000 0 2000 4000 6000 8000 10000 time (s) p h a s e s c u rr e n t (a ) fig. 9. 3-phase current at low tension side of 25mva 66/11kv transformer without harmonic filter table iv. thd for voltage and current without using filter harmonic order harmonic voltage % if harmonic current % if 3 1.72 2.92 5 9.29 41.11 7 11.49 11.29 11 6.17 3.53 thd 17.64 % 42.93 % 0 0.05 0.1 0.15 0.2 -1 -0.5 0 0.5 1 x 10 4selected signal: 10 cycles. fft window (in red): 1 cycles time (s) 0 200 400 600 800 1000 0 20 40 60 80 100 frequency (hz) fundamental (50hz) = 9296 , thd= 17.64% m a g ( % o f f u n d a m e n ta l) fig. 10. voltage and frequency response characteristics without harmonic filter 0 0.05 0.1 0.15 0.2 -2000 0 2000 4000 6000 8000 selected signal: 10 cycles. fft window (in red): 1 cycles time (s) 0 200 400 600 800 1000 0 20 40 60 80 100 frequency (hz) fundamental (50hz) = 2116 , thd= 42.93% m a g ( % o f f u n d a m e n ta l) fig. 11. current and frequency response characteristics without harmonic filter case (2) by using harmonics filter figures 12-13 show 3-phase voltage and current at low tension of 25mva 66/11kv transformer respectively with harmonic filter. figures 14-15 show the frequency response characteristics when using harmonic filter for voltage and etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 114-120 119 www.etasr.com gouda et al: a study of k-factor power transformer characteristics by modeling simulation current respectively. the total harmonic distortion for current and voltage with and without the use of the harmonic filter is listed in table v. the calculated k-factor for the simulated model with and without harmonic filter is shown in table v. the k-factor without the use of the harmonic filter is 5.1497 which is five times greater than the k-factor calculated when using the harmonic filter. therefore, when a harmonic filter is employed, the k-factor rating used is k1 or k4 whereas a kfactor rating of k7 is used when a harmonic filter is not employed. the k-factor calculated from the measured values taken from the station is approximately equal to the calculated values of the simulated model. 0 0.05 0.1 0.15 0.2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 x 10 4 time (s) p h a s e s v o lt a g e ( v ) fig. 12. 3-phase voltage at low tension side of 25mva 66/11kv transformer with harmonic filter 0 0.02 0.04 0.06 0.08 0.1 0.12 -3 -2 -1 0 1 2 3 x 10 time (s) 3 -p h a s e c u rr e n t (k a ) fig. 13. 3-phase current at low tension side of 25mva 66/11kv transformer with harmonic filter 0 0.05 0.1 0.15 0.2 -1 -0.5 0 0.5 1 x 10 4selected signal: 10 cycles. fft window (in red): 1 cycles time (s) 0 200 400 600 800 1000 0 20 40 60 80 100 frequency (hz) fundamental (50hz) = 1.143e+004 , thd= 4.42% m a g ( % o f f u n d a m e n ta l) fig. 14. voltage and frequency response characteristics with harmonic filter 0 0.05 0.1 0.15 0.2 -2 0 2 x 10 4selected signal: 10 cycles. fft window (in red): 1 cycles time (s) 0 200 400 600 800 1000 0 20 40 60 80 100 frequency (hz) fundamental (50hz) = 2.467e+004 , thd= 2.47% m a g ( % o f f u n d a m e n ta l) fig. 15. current and frequency response characteristics with harmonic filter table v. k-factor and thd for voltage and current without harmonic filter with harmonic filter thdu% thdi% thdu% thdi% 17.64 42.93 4.42 2.47 ieee-519 recommended limit 5% 5% k-factor from measured values 5.436679 1.200575 k-factor from modeling 5.1497 1.0147 iv. conclusion in this paper a study of k-factor power transformer characteristics is presented. a case study (toshka pumping station) is simulated with the use of matlab simulink. the total harmonics distortion at the output of 25mva, 66/11kv transformer with and without harmonic filter is calculated. measured harmonics current and calculated k-factors with and without filters are in agreement with the results obtained by the suggested model. references [1] i. daut, h. s. syafruddin, h. haziah “the effects of harmonic components on transformer losses of sinusoidal source supplying nonlinear loads”, american journal of applied sciences, vol. 3, no. 12, pp. 2131-2133, 2006. [2] r. n. jayasinghe, “power system harmonic effects on distribution transformers and new design considerations for k-factor transformers” iee sri lanka annual sessions, 2003. [3] i. a. maswood, “harmonics, sources, effects and mitigation techniques” second intl. conf. on electrical and computer engineering, icece, dhaka, bangladeh, 2002. [4] t. m salih, “the effect of the harmonic components upon transformer active losses in case of (non) sinusoidal sources and (non) linear loads”, ieee international conference on industrial technology, vol. 2, 2000. [5] g. w. massey, “estimation methods for power system harmonic effects on power distribution transformers”, ieee trans. industry appl., vol. 30, no. 2, pp. 485 – 489, 1994. [6] computer business equipment manufacturers association (cbema) “three-phase power source overloading caused by small computers and electronic office equipment”, esc-3 information letter, 1987. etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 114-120 120 www.etasr.com gouda et al: a study of k-factor power transformer characteristics by modeling simulation [7] t. m gruzs, "a survey of neutral currents in three-phase computer power systems", ieee trans. on industry applications, vol. 26, no.4, pp. 719 – 725, 1990. [8] ansi/ieee c57.110 “recommended practice for establishing transformer capability when supplying non-sinusoidal load currents”, 1998. [9] ieee standard, 519 “recommended practices and requirements for harmonic control in electrical power systems”, 1992 [10] underwriters laboratories, ul1561 “proposed requirements and proposed effective dates for the first edition of the standard for dry-type general purpose and power transformers”, santa clara ca, 1991. [11] d. yildirim, e. f. fuchs, “measured transformer de-rating & comparison with harmonic loss factor (fhl) approach”, ieee transactions on power delivery, vol. 15, no. 1, pp. 186 – 191, 2000. [12] s. n. makarov, a. e. emanuel, “corrected harmonic loss factor for transformers supplying non-sinusoidal load currents”, 9th international conference on harmonics and quality of power, vol. 1, pp. 87 – 90, 2000. [13] tao shun, xiao xiangning, “comparing transformer de-rating computed using the harmonic loss factor fhl and k-factor”, 3rd international conference on electric utility deregulation and restructuring and power technologies, pp. 1631 – 1634, nanjing china, 2008. [14] http://www.federalpacific.com/university/kfactor/kfactor.html [15] copper development association, “harmonics, transformers and kfactors”, cda publication 144, 2000. [16] http://www.powertransformer.us/federalpacifickfactor transformers.htm [17] n. m. abdelsalam, m. m. abdelaziz, “toshka project electrical power demand”, 12th international water technology conference, iwtc12 pp. 503 517, alexandria, egypt, 2008. [18] consulting services for the south of egypt development project, "water management plan", technical assistance for toshka project, vol. 3, 2004. microsoft word 2-ntuli.doc engineering, technology & applied science research vol. 4, no. 1, 2014, 570-575 570 www.etasr.com ntuli and allopi: impact of inadequate experience and skill on the construction sector in kwazulu… impact of inadequate experience and skill on the construction sector in kwazulu-natal, south africa bonga ntuli water business unit royal haskoningdhv (pty) ltd pietermaritzburg, south africa bonga.ntuli@rhdhv.com dr dhiren allopi department of civil engineering & surveying durban university of technology durban, south africa allopid@dut.ac.za abstract—civil engineering contractors encounter serious challenges in order to sustain their businesses, especially in a weak economic climate. a certain level of construction experience, expertise and training are required to manage a sustainable construction company. the construction industry development board (cidb) was established in 2000 as a statutory body to provide leadership to stakeholders and stimulate sustainable growth, reform and improvement of the construction sector for effective infrastructure delivery and improvement of construction skills. the objectives of this research were to investigate challenges faced by civil engineering contractors whilst making their enterprises sustainable. contractors’ views were presented at “construction indaba 2011” held on 1–2 june 2011 and hosted by ethekwini municipality’s business support, tourism and markets in durban kwazulu-natal. discussion and findings revealed to a skills’ shortage in the construction section and underlined the need for continuous training of the contractors’ employees. the south african government in conjunction with all stakeholders should develop and implement contractor programs to address the lack of technical and management skills in the construction sector. keywords: construction; development; training; survey; seda; cidb; smme; ssustainable construction firms i. introduction a sustainable construction industry is critical to the economy of south africa. in 1999 the construction industry contributed approximately 35% of the total gross domestic fixed investment and employed 230,000 employees [1]. the south african public sector expenditures regarding infrastructure works is the main contributor to the growth of the construction sector [2]. as a result, the south african government has identified that to achieve overall economic benefit, the development of construction enterprises needs further attention. during the early 1990’s in south africa, there was a general decline in the workload handled by the construction sector. this was a result of the scale down of heavy infrastructure projects because of the government shifting focus to housing and other related projects, mainly as an effort to meet the needs of the previously disadvantaged communities. this trend was confirmed by [3] in the western cape province where the value of tenders awarded dropped from r 518 million (1994) to r 120 million (1995) during the january to may period. in october 1995, three well-established civil engineering contractors in western cape went insolvent. in the survey and studies conducted, insolvency causal factors associated with insolvencies in general construction firms were identified [4-5]. these factors could be broadly classified into the categories of operational management, environmental, strategic, personal, cost overruns and various technological factors. economic factors are noteworthy, but are often perceived as being external to a firms’ operation. therefore firms may fail to recognize that their impact may lead to the termination of their operation. the construction industry has certain distinct characteristics that are susceptible to failure [6–9]. these are:  trading within a high uncertain environment e.g. uncertain ground conditions, unpredictable weather and labor availability  the necessity to price a product before it is produced.  the contractors have to make assumptions relating to: the likely duration of the project, adequacy conditions, uncertainty in bad weather and other contingencies [10].  competitive tendering as a means of pricing.  the low fixed capital requirements for market entry, which result to an over capacitated market.  ease of entry into the civil construction industry given the lack in legislation, stating who may or may not build. the most prominent cause of insolvency results from inadequate cash resources and the failure to convince creditors for cash availability [6, 7]. even profitable firms could be forced into liquidation because the demand of payment of outstanding accounts could not be met at a critical time, considering the fact that the assets may be tied in long-term investments [7]. furthermore, capital is often required to engineering, technology & applied science research vol. 4, no. 1, 2014, 570-575 571 www.etasr.com ntuli and allopi: impact of inadequate experience and skill on the construction sector in kwazulu… smoothen out the strains on the cash flows resulting from the occurrence of cost and uncertainty [6]. escalating material prices coupled with high interest rates have forced the management of construction firms to focus on the control of cash flow as being critical to its survival [7]. moreover the terms of payment stipulated in the contractual conditions and the escalation formulae (on contracts with escalation) require a great deal of expertise to apply, coupled with the task of ensuring promptness in the submission and payment of bills to ensure that the cash flow situation is controlled and improved (i.e. preventing the erosion of profit). capital is critical for a company to grow, given that at a certain point in time its fund requirement will exceed its fund generation. the financing of construction projects may be external and internal to an organization. internal sources include the contractor’s retained earnings from previous projects or investments and depreciation income obtained through depreciating assets, thus through their sale. external sources include bank loans and other financing mechanisms. these may be short or long term. good management implies an awareness of all factors making up a successful business, namely: good strategy, marketing, pricing and financial control. financial mismanagement and management incompetence have been cited among the attributes that lead to the prominence of construction failures [4, 11]. there need to be training amongst entrepreneurs on matters relating to financial management such as bookkeeping, tax planning, budgeting and cash flow management. additionally, the lack of management information also contributes to the failure of businesses. the use of financial ratios and inter-firm comparisons have been cited as the most useful tools in providing management information which measure the overall effectiveness of any business [11]. furthermore, management information permits managers to monitor, measure and evaluate the performance of the company at certain time intervals, with the attainment of an improvement of profitability in view ii. skill shortages within the construction industry according to the state of skills document compiled by the department of labour of the south african government [12], there was a growth in the size of the country’s economically active population, from 10 million in 1997 to 15.9 million in 2002. this represents a growth rate of over 50%. during the same period the number of employed people has increased, from 8.7 to 11.4 million. the most striking feature over this period has been the increase in the number of unemployed – from 2.5 million in 1997 to 4.8 million in 2002 (see figure 1). fig. 1 economically active, employed and unemployed in south africa, 1997 – 2002 source: september 2002 household surveys and labour force surveys, statistics, south africa. the unemployed represent an important target group for the national skills development strategy. it is vital that their skills be upgraded in order to facilitate their transition into active employment and life-long learning and to grow the skill pool from which employers can recruit. figures on the characteristics of the unemployed by educational level and population group are shown in table i. the table illustrates the ongoing legacy of apartheid in that africans are nearly seven times more likely to be unemployed than any other population group. africans also constitute the largest number of those who have less than a grade 12 or matric qualification, with african women exceeding men slightly in this category. but there are over 1 million people who are unemployed and who do have a grade 12/matric or equivalent qualification. this represents an under-utilized human potential and is likely to be associated with high social costs that go with this exclusion. table i. educational profile of the unemployed by population group and gender (000s) african other male female total male female total total male total female total total* 1965 2248 4213 194 329 623 2259 2577 4836 none 80 88 168 – – – 83 94 77 <grade 12/matric 1312 1417 2729 165 177 342 1490 1618 3108 grade 12/matric or equivalent 494 608 1102 93 104 197 591 715 1306 >grade 12/matric 70 122 192 – – – 81 136 217 * figures may not add up to total due to rounding and other statistical manipulations. source: labour force survey, statistics, south africa, september 2002. engineering, technology & applied science research vol. 4, no. 1, 2014, 570-575 572 www.etasr.com ntuli and allopi: impact of inadequate experience and skill on the construction sector in kwazulu… it is important to note that youth unemployment continues to be a striking feature of the south african labor market. those in the 15 to 34 years age group make up the vast majority of the unemployed – the chances of being unemployed are three times higher for this age group, as reflected in figure 2 . moreover, most unemployed youths are african, with over 3 million in the 15 to 34 years age group compared to 411,000 for white, indian and coloured youth. fig. 2 unemployment by age group source: statistics sa, labour force survey, statistics, south africa, september 2002. the employed are an equally important target group for skills development, particularly through the work of the sector education and training authorities (setas). a significant labor market indicator for skills development is the current and changing skill level of those in employment. of the 11.03 million workers employed in the south african economy:  6.7% had no educational qualifications  51.9% had an educational attainment below grade 12/matric  25.1% had a grade 12/ matric  the remaining 15.2% had achieved a qualification level above grade 12/matric. if these figures are examined by gender, they reveal that qualification differences between men and women are small (see table ii):  7% of employed women have no qualifications, compared to a figure of 6% for men  employed men with grade 12/matric make up 26% of the total employed men, compared with 24% for women  there are slightly more women in employment with a qualification higher than a grade 12/matric, a 17% share, compared to 14% for men. when examined by population group, some important issues emerge from table ii:  9% of employed africans have no qualification compared with 1% of whites, indians and colored  29% of african workers have achieved a grade 12/matric level qualification or higher compared with 64% for white, indian and colored workers. these differences in the qualification level for africans compared to other workers, pose an important challenge for linking of skills development to equity considerations in the workplace. it is encouraging to note, however, that the number of africans with grade 12/matric and higher qualifications has been growing between 1997 and 2002 (see table iii). table ii. educational qualifications of the workforce by population group and gender (000s) african other male female total male female total total male total female total total* 4028 3208 7236 2156 1632 3788 6184 4840 11024 none 343 337 680 41 20 61 384 357 741 <grade 12/matric 2 521 1932 4453 745 528 1273 3266 2460 5726 grade 12/matric or equivalent 785 512 1297 808 657 1465 1593 1169 2762 >grade 12/matric 326 404 730 539 412 951 865 816 1681 * figures may not add up to total due to rounding and other statistical manipulations. source: statistics sa, labour force survey, september 2002. table iii. changes in the qualification of the workforce by population group (000s) none less than matric matric post matric african other african other african other african other 1997 642 66 3310 1195 880 1121 536 828 1998 762 66 3683 1127 887 1251 578 952 1999 667 75 4105 1299 1061 1274 667 1008 2000 803 55 5172 1288 1184 1057 729 1233 2001 801 52 5120 1240 1260 1240 763 2394 2002 680 61 4394 1194 1250 1368 837 2493 source: statistics sa, household surveys and labour force surveys, september 2002 engineering, technology & applied science research vol. 4, no. 1, 2014, 570-575 573 www.etasr.com ntuli and allopi: impact of inadequate experience and skill on the construction sector in kwazulu… clearly, past historical imbalances are being addressed through education and training, although significantly more progress needs to be made before a parity of qualification levels is achieved between the different population groups in the workforce. the south african government has put emphasis to transforming the sector to allow the participation of emerging and small contractors but this was not properly regulated as most of these contractors did not have the experience and skills to operate sustainable construction firms. exacerbating this problem is the inadequate investment skills development across all levels in the sector, despite sufficient funding available from the construction education and training authority (ceta) and specific deficiencies include inadequate recognition of prior learning and work place training. the construction industry development board (cidb) was established in 2000 as a statutory body to provide leadership to stakeholders and to stimulate sustainable growth, reform and improvement of the construction sector for effective delivery and the industry’s enhanced role in the country’s economy. cidb’s regulations were implemented after 2003 and are continuously improving the sector’s growth. the cidb has realized that a vibrant and successful construction industry is only possible if those employed within it, have the required skills and competency to function effectively in their roles. investing in appropriate suitable training is vital and leads to improvements in productivity and, in the long term, to cost savings. training should lead to qualifications recognized by the industry and the enablement of employees to demonstrate the level of attainment and competence reached. the operation of the cidb is the start of a long process. in order to realize tangible results in terms of performance improvement and prospects for the construction industry, several issues need attention. the cidb should formulate long term plans for developing the industry [13]. there should be supported by comprehensive reviews of the state of the industry and its concerns and imperatives [14]. one of the most important resources is people. skill shortage and development remains a pressing concern in south africa and the construction sector is no exception [15]. with an increasing number of small-to-medium-size-enterprises (smme) emerging in the construction sector, it becomes increasingly challenging for authorities to regulate the level of skills and training of the community’s construction force [13]. added to this is a lack of management level where a shortage of skilled project managers often has significant consequences for projects and businesses. while management skills are important areas of focus, the industry needs to invest in training from the bottom all the way to the top. naturally, the quality of the company’s employees is also reflected in the quality of the service they provide. this proves partially challenging for the construction sector where smme make for a significant part, skill development is integral to the sustainable growth and where smaller companies developed within the industry lack the required resources to provide employees with the needed development and training opportunities [14] a. discussion in order to obtain the necessary information on the subject, the following are considered:  findings from the “construction indaba 2011” held on the 1st and 2nd of june 2011 hosted by ethekwini municipality’s business support, tourism and markets in durban, kwazulu–natal, south africa. the municipality invited construction contractors with a cidb grading of level 2 or more. the conference had speakers from different stakeholders sharing information and knowledge to empower contractors to become self sustainable entities whilst guiding them through the industry’s most common challenges and factors that impact negatively on their business. furthermore it furnished the opinion of the owners discussed at workshops in the conference of the causes which may have led to business failure or stifled growth.  conclusion and recommendations based on the outcome of discussions with the civil engineering contractors. b. findings the “construction indaba 2011” was attended by 276 construction company representatives from various parts of kwazulu–natal. the target group was contractors registered with cidb level two grading or more. the level two grading contractors have the capacity to undertaken construction work over the value of r 200,000. the program had various speakers from government department, construction mentors and financial institutions. initially the study was going to be based on a questionnaire but after evaluating the target group, it was clear that the level of the questionnaire was going to be a challenge for most contractors since over 80% of them uses english as a second language. the interaction at the four workshops was conducted in isizulu to the benefit of the contractors. using isizulu to conduct discussions made it comfortable for contractors to express their challenges with great emotions. the attendees were later divided into four groups according to the numbers they received during registration in order to discuss the challenges they face on their daily business activities. the following were the main challenges highlighted:  human resource development  lack of understanding tendering process  late payments affecting business cash flow  corruption in the industry  procurement policies not fully understood by contractors  lack of knowledge to develop business plans for their businesses  securing of work  lack of understanding of the cidb’s role in the industry engineering, technology & applied science research vol. 4, no. 1, 2014, 570-575 574 www.etasr.com ntuli and allopi: impact of inadequate experience and skill on the construction sector in kwazulu…  lack of operational and managerial skills amongst contractors  under pricing  lack of understanding of the general conditions of contracts  encourage established contractors to subcontract work to smaller contractors – partnering approach  improve transparency in the circulation of tender opportunities especially on invited tenders  establish a forum where they can share experiences. it was noted during the group sessions that there was a negative feedback and a dissatisfaction regarding the way the industry treats them as stakeholders. the groups felt their concerns are currently inadequately addressed to assist them to grow as contractors. the discussions revealed that the main concerns related to operational and financial management challenges although corruption was raised prominently as one of the main limiting factors for the sustainability of their businesses [15]. they felt that no matter how many resources are made available to assist them, it’s pointless if work is only awarded to undeserving contractors. c. success story: mentorship and business incubationmodel a representative from the seda (small enterprise development agency) construction incubator shared some experience regarding one of their contractor development program at the conference. the program was established in 2006 as a government funded contractor development incubator under the banner of a ring fence incubator program called seda technology program. the core business is to develop emerging contractors through the infusion of both technical and business administration skills that are aligned with the introduction of technology in order to enhance the efficiency and efficient management of their businesses. the incubator provides support to selected participants for a period of 3 years by which time each the emerging contractor should have advanced by at least one financial level above its entry point on the cidb register and should be capable of operating unassisted in the open market. in the development of the program, the ethos of the mission and vision is carried forward by means of an appropriate approach towards mentorship. the success and failure of the organization is determined by the quality of its product and the directing market forces that it influences. there is constant interaction with incubates through workshops as guidance to those who have limited knowledge of the workings of the construction industry. incubates are taken through from tender to completion stages. to this end the program has supported about 63 contractors with a success rate of 95% of contractors who remained in the program for the full duration of three years. d. a typical participants in the seda contractor program velile business enterprise is a general building construction company owned and managed by florence malinga. she joined the program in february 2007 as a grade 3 gb. since then velile has been showing growth as contractor and as business. before getting involved in construction projects, florence malinga was a clothing designer for many years. when she started operating as a sole proprietor in 2000 her first project (with engineering municipality) had a budget in the region of r 2000 to r 3000, and she grew to a point where she concentrated more into plumbing contracts with better projects amounting to r 127,000 by 2002.velile business enterprise was then registered as a cc. it worked with various government departments like public works and housing. velile has been renovating municipality hostels in durban, south africa for two and a half years. most of these hostels were renovated and changed to flats for residential dwelling of the community. during 2007, velile renovated more than 40 flats and even more during 2008 and this was due to the high level of performance and the displayed quality. this led to velile being awarded more work every year which led to its growth as a business and also regarding its cidb grading. velile business enterprise reached 6 grades of growth and acquired a project exceeding r 20,000,000 e. conclusion the new breed of novice contractors is flooding the market with the hope of success. however, the south african culture and its linguistic diversity must be taken into consideration in any research study, in particular when it involves the construction industry, as it posses as one of the ethnic work forces in the country. the lack of construction education appears to be one of the major hurdles for small enterprises. many of the new entrants into the construction sector, have little construction related education and/or poor english skills but these individual are still allowed to set up construction companies. at the “construction indaba 2011” all participants expressed the desire to learn and retrain. it appeared that current education strategies are not designed to accommodate such people. new strategies need to be applied and different learning styles need to be properly managed by educators and researchers with tangible knowledge of the deficiencies and the needs of the industry. the outcry from the contractors indicates that the influence of the government is substantial in assisting the construction industry to develop. the government’s role as a major client for engineering contractors combined with its role in creating, maintaining and initializing a conducive environment whether this is defined as business education or in other terms. industry stakeholders need to develop well researched development programs in conjunction with academia. the attitude towards each other needs to change to achieve a engineering, technology & applied science research vol. 4, no. 1, 2014, 570-575 575 www.etasr.com ntuli and allopi: impact of inadequate experience and skill on the construction sector in kwazulu… common goal: the design of contractor development programs which relate to the needs of the construction industry. research needs construction industry if construction programs are to survive in tertiary institutions [16]. f. recommendations given the identification of education and training, skills development and human resource development in general, a further possible parameter in the form of development should be included. the industry should also endeavor to:  realize 100% educational mentoring and training.  increase the amount of research and development especially on oral training programs to individuals with less academic background.  engender a partnering approach to improve collaboration among stakeholder within the construction sector  influence government’s policies relating to the construction industry. references [1] department of public works, “creating an enabling environment for reconstruction, growth and development in the construction industry”, white paper for public works, pretoria, south africa, 1999 [2] s. dlugwana, x. nxumalo, s. van huyssteen, p. d. rwelamila,c. noyana, “development and implementation of the south african construction excellence model (sacem)”, first international conference on construction in the 21st century, florida, usa, 2002 [3] e. symon, “crisis in the cape”, the civil engineering contractor, vol. 30, no. 2, pp. 7-11, 1995 [4] a. henry, “an investigation into factors associated with insolvencies in the building firms”, b.sc. dissertation, university of cape town, 1994. [5] p. d. rwelamila, l. lobelo, “factors associated with insolvencies amongst civil engineering contractors in south africa”, rics construction and building research conference (cobra '97), pp. 282298, portsmouth, united kingdom, 1997 [6] h. ren, “risk management in construction cost and inflation”, d.sc. thesis, university of reading, 1992 [7] a. r. jach, “cash flow forecasting for the contractor”, b.sc. dissertation, university of cape town, 1985 [8] r. kangari, “business failure in the construction industry”, journal of construction engineering and management, no.114, no. 2, pp. 172-190, 1988 [9] r. davis, construction insolvency, sweet & maxwell ltd, united kingdom, 2011 [10] a. e. olusegun, a. o. michael, “abandonment of construction projects in nigeria: causes and effects”, journal of emerging trends in economics and management sciences, vol. 2, no. 2, pp. 142–145, 2011. [11] j. j. potgieter, a. b. frank, ratio analysis and inter-firm comparisons as a means of providing management information in the small business sector, university of zululand, south africa, 1990 [12] department of labour, state of skills in south africa for formulation of the national skills development strategy, government, pretoria, 2003 [13] f. calldo, “skills shortage in south africa: the facts and what is being done”, solidarity research department, 2007 [14] w. franck, “addressing skills shortage in the built environment”, biz community news, johannesburg, south africa, march 2013. [15] w. shakantu, c. chiocha, “corruption in the construction industry: the case of malawi”, cobra 2009: cape town, south africa, 10–11 september 2009 [16] construction industry development board (cidb), “baseline study of provincial contractor development programs: review of the contractor development programs towards an ncdp monitoring and evaluation system”. [online], available from www.cidb.org.za (accessed: 07 april 2012) authors profile bonga ntuli holds a bachelor’s degree in technology – civil engineering and he is currently studying towards his masters degree in technology (civil engineering) at the durban university of technology. he is registered with the engineering council of south africa as a professional engineering technologist (prtech eng) and is a member of the south african institute of civil engineers (msaice). he has experience in sanitation and water engineering projects in all phases of water infrastructure ranging from feasibility studies including financial analysis, preliminary and detail designing. he has been involved in contract management of public works community based projects and projects mentoring emerging contractors. he is currently employed at royal haskoningdhv (sa) as a director of advisory group for the water business unit in kwazulu-natal, south africa and is responsible for both commercial and technical performance of the water business unit. prof dhiren allopi is the associate professor/director in the department of civil engineering and surveying at the durban university of technology. he has five qualifications from four different tertiary institutions including a doctorate degree in civil engineering. prof allopi has over 33 years of combined industrial and academic experience mainly in the field of geotechnical, traffic and transportation engineering. he has over 70 conference proceedings and journal papers to his credit. he is professionally registered with the engineering council of south africa and is a fellow member of the south african institute of civil engineering. he has lectured to diploma and degree students and is currently supervising ten postgraduate students mainly in the field of traffic and transportation engineering. microsoft word etasr_v11_n4_pp7442-7445 engineering, technology & applied science research vol. 11, no. 4, 2021, 7442-7445 7442 www.etasr.com syarif & tjaronge: a comparison of organic cement made from recycled waste material and … a comparison of organic cement made from recycled waste material and portland cement muhammad syarif department of architecture muhammadiyah university of makassar makassar, indonesia m. wihardi tjaronge department of civil engineering hasanuddin university makassar, indonesia abstract—organic cement is an environmentally friendly alternative to portland cement which is acquired by recycled organic waste and mediterranean soil. waste management is a global problem. the physical characteristic test results of the organic cement show that the weight test of fresh organic concrete is 2081kg/m³ and the dry weight of concrete is 2032kg/m³ which are smaller than portland cement concrete's which are 2525kg/m³ and 2405 kg/m³ respectively. the fineness of alternative cement grains that passed the 200 mesh sieve is 56%, which is more than portland cement's which is 52%. the solid weight of alternative cement is 1200kg/m 3 whereas the solid weight of portland cement is 1250kg/m 3 . keywords-bleeding; finenes; mediterranean soil; organic cement; organic waste i. introduction this study aims to develop previous experimental research which can be found in [1]. organic cement is the latest alternative to portland cement and is made through organic waste recycling and mediterranean soil substitution of portland cement [2]. the necessity of building materials needs to be addressed by researching the utilization of recycling waste to obtain alternative building materials [3]. gradually, high waste volume has a negative impact on the environment, so handling of waste is necessary. urban waste management in indonesia is a real problem as population growth has an impact on the amount of produced waste and the occurrence of degradation problems that have the potential to cause social conflict to the communities [4, 5]. the high growth of waste volume coincides with high population growth rate. therefore, the waste management problem can be considered as a global problem. in [6], it was shown that handling of organic waste through the combustion process with the furnace at 700°c will provide materials such as: 69.7% caco3, 12.1% kcl, 3% sio2, 8.1% fe and 3% al2, while shellfish ash contains 100% caco3 [6]. along with economic growth, per capita garbage production will continue to increase. it is predicted to reach 1.2kg/person/day for urban areas and 0.55kg/person/day for rural areas by 2030. in indonesia, organic waste is a major component of waste. the proportion of organic waste ranges between 34 and 70% which is 20-30% higher than most countries in europe [7]. mediterranean soil is a soil formed from weathering of sedimentary rock and limestone. this type of soil contains a considerable amount of carbonate and compounds of iron, water, aluminum, along with some organic materials [8]. additional mineral components are called reactive supplemental minerals and contribute to the hydration process. other additions include natural pozzolans and microsilica/silica fume [9]. the highest tensile strength in 14-day-old concrete with the addition of 5% bagasse ash is 6.221mpa representing an increase of 2.45% [10]. the increase in cement growth is still influenced by the high level of private sector development and the high demand for housing [11]. a cement that contains mineral elements as a substitute for portland cement is known as composite cement, mixed cement or alternative cement. the additional mineral is reactive and contributes to the hydration process. the use of saturated fly ash is one way to reduce high exposure in the process of hydration to the density of cement in concrete [12, 13]. the use of alternative sources for the manufacture of cement developed in japan produced ecocement made from municipal waste ash through incineration as a substitute for some of the main raw materials containing 50% of cement raw materials such as mud waste [14]. to create an eco-semen csa clinker, the appropriate starting raw material needs to be burned at a maximum temperature of 1200-1300°c. reuse of waste materials in the form of phosphogypsum will reduce the temperature and duration of the combustion process. large-scale eco-cement making can be done in conventional rotary kilns used for portland cement and producing chemical cement mineralization [15]. ii. research methodology characteristic testing was performed on the organic cement. the tests included bleeding test, air content test, fineness test, normal consistency test, and unit weight test. the references to the test method come from the american society for testing and materials (astm) which include: astm c 188-95 for granular fineness/density tests [16], astm c 232-99 for fresh concrete bleeding test [17], and astm c 231-03 for air content of freshly mixed concrete [18]. they are normative references that are considered very relevant in the process of testing the physical properties of cement. corresponding author: muhammad syarif (muhsyarif00@gmail.com) engineering, technology & applied science research vol. 11, no. 4, 2021, 7442-7445 7443 www.etasr.com syarif & tjaronge: a comparison of organic cement made from recycled waste material and … iii. results and discussion a. air content the obtained results of air content test can be seen in table i. in this stud y, the air content value of fresh concrete was calculated b y using an organic cement test sample and the results were compared with the ones of fresh concrete of p ortland cement. figure 1 shows the measuring percentage process of the air content value of fresh concrete in both organic cement concrete and portland cement concrete samples. (a) (b) fig. 1. measuring process of air content. table i. air content results organic cement concrete portland cement concrete test concrete volume (m 3 ) 0.0016 0.0016 correction factor reading 1% 1% reading result 3.2% 2.9% air content of reading result 2.2% 1.9% air content for 1 m 3 (prediction) 13.75% 11.88% b. bleeding the amount of water bleeding is shown in table ii. a organic cement concrete cylinder with a weight of 3.33kg has a water-bleeding value of 0.04ml/cm², so the prediction of water-bleeding for 1m 3 of organic cement concrete is 23.88ml/cm 3 . meanwhile, for concrete that utilizes portland cement the weight of the same cylinder was 3.36kg with a water-bleeding value of 0.05ml/cm² and the prediction for 1m³ was 31.83ml/cm 3 . testing of water-bleeding volume of cylinder concrete is calculated b y [17]: bleeding = v / a ( ml/cm²) (1) where v is the water-bleeding volume of the test specimen (ml) and a is the surface area of the test specimen (cm²). figure 2(a) shows the process of taking and measuring water bleeding. figure 2(b) shows a graph of the amount of water bleeding to the cylinder concrete weight between an organic cement cylinder concrete with a portland cement cylinder concrete. table ii. bleed ing test results organic cement portland cement test specimen weight (kg) 3.33 3.36 cylinder volume (m 3 ) 0.0016 0.0016 test specimen area (cm 2 ) 78.53 78.53 test specimen bleeding v (ml) 3 4 v / a (ml/cm²) 0.04 0.05 prediction of bleeding in 1m³ concrete (ml/cm 3 ) 23.88 31.83 (a) (b) fig. 2. (a) bleeding measurement process, (b) amount of water bleeding graph. c. fineness and density the more fine the cement, the wider the surface of the grains, and the compacting with water will be faster and will require larger amount of water. the value of material fineness for organic cement which passes the 200 mesh sieve is 56% with solid weight of 1200kg/m 3 , while for portland cement, it is 52% with solid weight of 1250kg/m 3 . fineness and density tests in this research refer to the formulation in [16]. figure 3 shows the fineness of the organic cement and portland cement concretes whereas figure 4 shows the process of the fineness test. the calculation formula of fineness percentage is: � � × 100 % = � � � � × 100 % (2) where d is the weight restrained on each sieve, b is the sample weight. the density test result of organic cement is 3.05gr/ml while for portland cement is 3.15gr/ml. this density greatly affects the proportion of the cement use in the mixture. figure 5 shows the density test process of organic and portland cements. engineering, technology & applied science research vol. 11, no. 4, 2021, 7442-7445 7444 www.etasr.com syarif & tjaronge: a comparison of organic cement made from recycled waste material and … (a) (b) fig. 3. (a) organic cement with density of 3.05gr/ml, (b) portland cement with density of 3.15 gr/ml. fig. 4. fineness test process. the density calculation formula used in this research is : density = �� � � �� ��� � �� � �� � × d (3) where v1 is the first reading of bottle scale, v2 the second reading, and d denoted the content weight of distilled water which is 1gr/cm 3 . fig. 5. density test of organic cement. d. unit weight the unit weight of fresh concrete using organic cement is 2081kg/m³ with its dry weight being 2032kg/m³, while, for portland cement, the unit weight of fresh concrete is 2525kg/m³ with 2405kg/m³ dry weight. the unit weight test results are shown in table iii. the weight of a concrete cylinder using organic cement and of the cylinder using portland cement are shown in f igure 6(a) whereas in figure 6b the concrete cylinders' condition at 28 days can be seen. (a) (b) fig. 6. weight and temperature measurement of (a) organic cement concrete, (b) portland cement concrete. table iii. un it weight test results organic cement portland cement cylinder mold weight (kg) 6.20 6.20 test specimen weight (kg) 9.53-6.20 = 3.33 10.24-6.20 = 4.04 cylinder volume (m³) 0.0016 0.0016 fresh concrete weight (kg/m³) 3.33/0.0016 = 2081 4.04/0.0016 = 2525 dry concrete weight at 28 days (kg/m³) 3.25/0.0016 = 2031 3.85/0.0016 = 2406 iv. conclusions in this paper, the physical properties of organic cement were tested in the form of granular fineness/density, unit weight of dry and fresh concrete, and bleeding and the results were compared with the ones regarding portland cement. organic cement has been found to indicate similarities in physical properties with portland cement, whereas organic cement has also been able to bind and contain amorphous pozzolanic materials. to achieve improved binding and better resilience, further research is required as a process of seeking the feasibility of organic cement into an alternative of portland cement. references [1] m. syarif, v. sampebulu’, m. wihardi tjaronge, and nasruddin, "characteristic of compressive and tensile strength using the organic cement compare with portland cement," case studies in construction materials, vol. 9, dec. 2018, art. no. e00172, https://doi.org/10.1016/ j.cscm.2018.e00172. [2] m. syarif, "a study of cement made from recycled gerbage materials compared with portland cement," presented at the third international cenference on sustainable infrastructure and built environment (sibe2017), bandung, indonesia, sep. 2017. [3] m. syarif, "karakteristik sampah organik dan tanah mediteran menjadi semen organik," presented at the konferensi nasional teknik sipil 11 (konteks-11), jakarta, indonesia, oct. 2017. engineering, technology & applied science research vol. 11, no. 4, 2021, 7442-7445 7445 www.etasr.com syarif & tjaronge: a comparison of organic cement made from recycled waste material and … [4] r. p. mahyudin, "kajian permasalahan pengelolaan sampah dan dampak lingkungan di tpa (tempat pemrosesan akhir)," jukung (jurnal teknik lingkungan), vol. 3, no. 1, pp. 66–74, apr. 2017, https://doi.org/10.20527/ jukung.v3i1.3201. [5] i. w. widiarti, "pengelolaan sampah berbasis zero waste skala rumah tangga secara mandiri," jurnal sains & teknologi lingkungan, vol. 4, no. 2, pp. 101–113, jun. 2012, https://doi.org/10.20885/jstl.vol4.iss2.art4. [6] f. a. syafnijal and d. sawitri, "studi eksperimental pembuatan ekosemen dari abu sampah dan cangkang kerang sebagai bahan alternatif pengganti semen," jurnal teknik its, vol. 2, no. 2, pp. d162–d165, aug. 2013, https://doi.org/10.12962/j23373539.v2i2.4287. [7] a. s. alisjahbana et al., "indonesia climate change sectoral roadmape (iccsr)," republic of indonesia, indonesia, synthesis report, dec. 2009. [8] a. maulana, fungsi tanah mediteran bagi kehidupan. 2016. [9] w. b. nicholas, understanding cement, low concrete strenght, ten potential cement-related causes. uk: copyright whd microanalysis consultan ltd, 2014. [10] g. p. rompas, j. d. pangouw, r. pandaleke, and j. b. mangare, "pengaruh pemanfaatan abu ampas tebu sebagai subtitusi parsial semen dalam campuran beton ditinjau terhadap kuat tarik lentur dan modulus elastisitas," jurnal sipil statik, vol. 1, no. 2, pp. 82–89, jan. 2013. [11] r. r. nur, f. d. hartanti, and j. p. sutikno, "studi awal desain pabrik semen portland dengan waste paper sludge ash sebagai bahan baku alternatif," jurnal teknik its, vol. 4, no. 2, pp. f164–f168, 2015, https://doi.org/10.12962/j23373539.v4i2.9868. [12] v. sampebulu, "influence of high temperatures on the workability of fresh ready-mixed concrete," journal of engineering and technological sciences, vol. 44, no. 1, pp. 21–32, 2012, https://doi.org/10.5614/itbj.eng. sci.2012.44.1.2. [13] v. sampebulu’, "increase on strengths of hot weather concrete by selfcuring of wet porous aggregate," civil engineering dimension, vol. 14, no. 2, pp. 92–99, sep. 2012, https://doi.org/10.9744/ced.14.2.92-99. [14] s. hanehara, "eco-cement and eco-concrete environmentally compatible cement and concrete technology," in jci/kci international joint seminar, kyonju, south korea, jan. 2001, vol. 1. [15] n. ukrainczyk, n. mihelj, and j. sipusic, "calcium sulfoaluminate ecocement from industrial waste," chemical and biochemical engineering quarterly, vol. 26, no. 1, pp. 83–93, oct. 2011. [16] c01 committee, "test method for density of hydraulic cement," astm international. https://doi.org/10.1520/c0188-95. [17] c09 committee, "test methods for bleeding of concrete," astm international. https://doi.org/10.1520/c0232-99. [18] c09 committee, "test method for air content of freshly mixed concrete by the pressure method," astm international. https://doi.org/10.1520/ c0231_c0231m-17a. microsoft word etasr_v10_n6_pp6389-6392 engineering, technology & applied science research vol. 10, no. 6, 2020, 6389-6392 6389 www.etasr.com phan & nguyen: elastic and deformation characteristics of mswi bottom ash for road construction elastic and deformation characteristics of mswi bottom ash for road construction van tien phan faculty of construction vinh university vinh city, vietnam vantienkxd@vinhuni.edu.vn thi thu hien nguyen faculty of construction vinh university vinh city, vietnam thuhien.tvna@gmail.com abstract-bottom ash from municipal solid waste incineration (mswi) is a typical granular material resulting from the incineration of domestic waste. it is mainly used in road engineering substituting traditional natural aggregates. as the characterization of the mechanical behavior is essential, the work presented in this paper pursues the study of the elastic and deformation characteristics of bottom ash, in particular young’s modulus and poisson’s ratio. from the consolidated-drained triaxial test data, it was possible to extract fundamental material parameters about the samples, including their young’s modulus e0.2 and e50, its poisson’s ratio ν, and its maximum deviatoric stress peak. these parameters were then used in computer models to predict how the bottom ash will behave in a largerscale engineering application. furthermore, the mechanical behavior of bottom ash related to road construction’s loading condition, especially the secant modulus, was detailed. keywords-bottom ash; municipal solid waste; incineration; triaxial test i. introduction waste management has become a major preoccupation of federal and state agencies. it consists mainly of construction waste, fly ash and bottom ash [1-11]. bottom ash from municipal solid waste incineration (mswi) is the solid residue from the combustion of municipal waste. it consists mainly of silica and alumina, limestone, lime, water, salt, heavy metals and unburned wastes [6, 12-14]. they are granular materials, potentially recoverable for engineering works, especially in road construction [1, 12-18]. in france, about 3 million tons of bottom ash are produced annually [2, 19]. in recent years, bottom ash is either used in road engineering (84%) or is disposed in non-hazardous waste facilities (16%) [17]. in france, after treatment, bottom ash is classified into three categories according to its physical and chemical characteristics as defined in [17]. the use of bottom ash is highly regulated: its use must be safe for the environment, must meet standards, and requires a thorough knowledge of the material. this study aims to study the elastic and deformation characteristics of bottom ash. the triaxial testing method is described, and then the basic parameters of bottom ash (elastic and volumetric parameters) are calculated. these results are discussed by analyzing and simulating the corresponding formula of schanz and vermeer [20]. ii. materials and methods a. materials the studied bottom ash came from a platform of waste recycling based in fretin, near lille, owned by the préfernord company. this bottom ash was taken from the factory, after having undergone a sorting (removal of ferrous elements, aluminum and heavy elements). it is a bottom ash type v1 or v2, which can be used in public works such as trench backfill or sub-layer of pavement, in place of finer materials such as sand or gravel. b. triaxial test two sets, a and b, of consolidated-drained triaxial tests were performed (table i). the two porewater pressures pw corresponding to tests a and b are, respectively, pw=200kpa and pw=400kpa. in both tests, the effective confining pressure varied from 100 to 400kpa, corresponding to a total confining stress ranging from 300 to 600kpa for test a and 500 to 800kpa for test b. the principles of the tests are in accordance to the french standard nf p 94-074. table i. triaxial test conditions tests porewater pressure pw (kpa) confining pressure ��(kpa) effective confining pressure ��� (kpa) a1 200 300 100 a2 200 400 200 a3 200 500 300 a4 200 600 400 b1 400 500 100 b2 400 600 200 b3 400 700 300 b4 400 800 400 the triaxial test is a standardized test. a cylindrical sample of the material is placed in a membrane and subjected to a confining stress σ3 and an axial stress σ1. the experimental methodology is described below. 1) saturation at first, bottom ash compact samples were made. for this, a water content of 12.5% (water content corresponding to the modified proctor optimum determined by our framing) was corresponding author: van tien phan engineering, technology & applied science research vol. 10, no. 6, 2020, 6389-6392 6390 www.etasr.com phan & nguyen: elastic and deformation characteristics of mswi bottom ash for road construction poured in bottom ash. this mixture was compacted with the modified proctor compactor set with european standard en 13286-2 [21], what corresponds to filling the cylindrical mold proctor (117.5mm height, 101.5mm diameter) in 5 layers, each compacted by 25 strokes of modified proctor in order to obtain a surface as flat as possible. then, the sample was placed around two protective latex membranes with a striated plastic film between (figure 1). fig. 1. sample on its base, with and without protective membranes. the tightness of this system was ensured with four rubber seals and then the sample was set up in the triaxial apparatus (figure 2). triaxial tests were conducted with fully saturated samples. the saturation was handmade. sample degassing was performed by creating an updraft from bottom to top with two cruets: one was filled with water and was connected to the bottom of the sample, the other was empty and connected to the upper part of the sample, with a radial pressure of σ3=20kpa. saturation cycles were performed with those two cruets, until there were no more visible air bubbles, and a volume of 40ml of sample output was collected. this was followed by a saturation with two gds which continued for 400min. fig. 2. overview of the triaxial test. that finished saturation was checked by calculating the skempton coefficient b=∆u/∆σ3. this coefficient is an indicator of advanced saturation. it has to be larger than 0.9 to indicate a successful saturation. 2) consolidation the consolidation step was then launched for 800min. it was performed with cell pressure σ3=400kpa (or σ3=600kpa for test type b) and back pressure uw=200kpa (or uw=400kpa for test type b). the initial effective confining stress remains p’=200kpa. 3) shear when consolidation was finished, the shearing of the samples started. cell pressure was 400kpa and 600kpa and back pressure was 200kpa and 400kpa for test types a and b respectively and were kept constant during this step. an axial stress deviator was applied on the upper part of the sample until the axial strain reached ε1=14%. c. calculation of the basic parameters of bottom ash there are three elastic parameters: the initial young's modulus e0.2, the sequent stiffness e50, and the maximum deviatoric stress qpeak. in addition, volume parameters such as the poisson’s ratio v were determined. the determination of young modulus value concerns the calculation of settlement [22]. when a value of young modulus is quoted for civil engineering aggregates, it is usually the secant modulus that is specified [23]. the secant modulus e is obtained from the initial slope of the deviator curve (q, ε1) at 0.2 % of axial strain or at 50 % of the maximum deviator stress as illustrated in figure 3. this range (e0.2, e50) is a common range of working stress in actual foundation problems. it depends on the case: either of e0.2 or e50 may be chosen, but in practice e50 is often preferred [1, 24]. deviator stress is the difference between the axial and confining stresses in a triaxial test. failure stress is the maximum deviator stress qpeak. fig. 3. determination of secant moduli and maximum deviator stress. the poisson ratio � is the ratio transverse strain to axial strain of a loaded specimen. it is obtained from the initial slope of the volumetric strain curve (εv, ε1) (figure 4), using (1): � � �� � � � 1� (1) fig. 4. determination of poisson’s ratio. engineering, technology & applied science research vol. 10, no. 6, 2020, 6389-6392 6391 www.etasr.com phan & nguyen: elastic and deformation characteristics of mswi bottom ash for road construction d. formula of schanz and vermeer the formula of schanz and vermeer [20] for dense and clean sand is: ��� ���� � 500� ��� ���� (2) where e50 is the secant modulus obtained from the initial slope of the deviator curve at 50% of the maximum deviator stress, pref=100kpa, and ��′ is the effective confining pressure. iii. results and discussion a. triaxial test curves the response for consolidated-drained triaxial tests is shown in figures 5 and 6. on these figures, the deviator stress q=(σ1-σ3) and the volumetric strain εv are plotted versus the axial strain ε1. for both tests a and b, the curves of the deviator stress evolution are quite similar in terms of trend and quantitative results (figure 5). the first phase is almost linear up to 70% of the peak deviator stress qpeak followed by the second non-linear phase up to the peak deviator stress. there is a final phase where the curves tend towards a level characterized by a residual deviator stress. in figure 6, the strain curves show an initial phase of contraction followed by a phase of dilatancy for large strains. for large strains without localization phenomenon, it can be assumed that all the curves tend towards a horizontal asymptote (critical). these responses indicate that the mechanical behavior of bottom ash is similar to that of dense sand [3, 15, 25, 26]. fig. 5. evolution of deviator stress in the triaxial tests. fig. 6. evolution of volumetric strain in the triaxial tests. b. basic parameters of bottom ash the obtained basic parameters of bottom ash are reported in table ii. the elastic behavior of the studied bottom ash is close to the elastic behavior of sand and gravel (e for sand: 5080mpa, for gravel: 100-200mpa), which are typical materials used for constructions embankments, road bases, and sub-bases [16]. values are similar to those of [4] for the bottom ash from the préfernord company, however this bottom ash was obtained 3 years earlier. the obtained values of secant moduli indicate that bottom ash exhibits good resistance capacity to deformation. the difference between e0.2 and e50 indicates that the first phase of the deviator curve is nonlinear. table ii. elastic and deformation characteristics test (σ1-σ3)max (kpa) e0.2 (mpa) e50 (mpa) υ a1 1215 75.33 42.56 0.243 a2 2283 83.02 70.01 0.235 a3 2463 87.23 73.22 0.206 a4 3090 92.47 79.82 0.197 b1 1357 72.56 48.71 0.217 b2 2073 78.89 63.56 0.224 b3 2707 86.35 69.51 0.212 b4 3179 94.85 81.90 0.180 both secant moduli e0.2 and e50 increase with maximum deviator stress qpeak. the relationships between these parametersis nearly linear, expressed as: e0.2 = 12.73 qpeak+ 55388 (kpa) (3) e50 = 18.81 qpeak + 22985 (kpa) (4) on the other hand, the poisson ratio (table ii) does not change much according to the effective confining pressure. the obtained poisson ratios are similar to those of sand [27]. c. application of the formula of schanz and vermeer tables iii-iv present the comparison between the secant modulus of this study and [4, 20]. the errors between the obtained and predicted secant moduli are rather high, so the formula of schanz and vermeer is not applicable for bottom ash. table iii. values of secant modulus e50 (mpa) σ3’ (kpa) tests a tests b [20] [3-4] 100 42.56 48.71 50 60 200 70.01 63.56 70.71 69 300 73.22 69.51 86.60 91 400 79.82 81.90 100 136 table iv. errors between obtained and predicted secant modulus values σ3’ (kpa) tests a tests b [3-4] 100 -14.88 -2.58 20 200 -0.99 -10.11 -2.42 300 -15.45 -19.74 5.08 400 -20.18 -18.10 36 engineering, technology & applied science research vol. 10, no. 6, 2020, 6389-6392 6392 www.etasr.com phan & nguyen: elastic and deformation characteristics of mswi bottom ash for road construction iv. conclusions the elastic and deformation characteristics for road construction of mswi bottom ash were studied in this paper. these characteristics were compared to those of construction materials and of other bottom ash reports. one prediction of young’s modulus of bottom ash was analyzed. the main conclusions of this study are: • the triaxial tests curves showed that the mechanical behavior of bottom ash is similar to that of dense sand. • the basic parameters of bottom ash are close to those of sand and gravel, which are typical materials used for construction embankments, road bases, and sub-bases. • the obtained values of secant moduli indicate that bottom ash exhibits good resistance capacity to deformation. • the formula of schanz and vermeer [20] was simulated to predict secant modulus e50 of bottom ash. moreover the error was relatively high, showing that this formula is not applicable for bottom ash. references [1] ademe and brgm, mâchefers d’incinérations des ordures ménagères états de l’art et perspectives: états de l’art et perspectives. paris: dunod, 2008. 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[24] t. l. nguyen, “etude expérimentale de la loi d’écoulement de matériaux anisotropes tranverses,” ph.d. dissertation, école nationale des ponts et chaussées, 2008. [25] b. m. das and k. sobhan, principles of geotechnical engineering, 8th ed. cengage learning, 2012. [26] m. r. b. cox, “the influence of grain shape on dilatancy,” ph.d. dissertation, university of arizona, tucson, az, 2008. [27] g. ranjan and a. s. r. rao, basic and applied soil mechanics, 2nd ed. new delhi, india: new age international, 2000. engineering, technology & applied science research vol. 8, no. 1, 2018, 2417-2421 2417 www.etasr.com touahmia: identification of risk factors influencing road traffic accidents identification of risk factors influencing road traffic accidents mabrouk touahmia department of civil engineering college of engineering, university of hail hail, saudi arabia m.touahmia@uoh.edu.sa abstract—road traffic accidents (rtas) are becoming a major problem around the world, incurring enormous losses of human and economic resources. recent reports from the world health organization (who) reveal that each year more than 1.25 million people are killed and 50 million are injured in road traffic accidents worldwide. in saudi arabia, statistics show that at least one traffic accident occurs every minute, causing up to 7,000 deaths and over 39,000 injuries annually. in this study, the main causes of rats in the province of hail are examined. the data was collected through the use of a survey which was developed to evaluate the effect of influencing parameters on rta rate. the results show that 67% of rtas result from human factors, 29% from road conditions and 4% from vehicle defects. excessive speed and violation of traffic rules and regulations were found to be the main causes of rats. low rates of compliance with speed limit signs and seat-belt regulations were also observed. these findings highlight the need of strengthening effective traffic law enforcement alongside with improving traffic safety and raising public awareness. keywords-road traffic accidents; regulations; rtas; survey; traffic; speeding i. introduction road traffic accidents (rtas) are increasingly being recognized as one of the greatest public health issues, incurring heavy losses of human resources along with severe socioeconomic costs worldwide. everyday, thousands of people are killed and injured on roads across the world. the world health organization (who) estimated that over 1.25 million deaths and 50 million injuries occur worldwide due to road crashes each year. statistics anticipate rtas to be the third among fifteen more often causes of death by 2020 [1]. studies performed worldwide have shown that developing countries represent 67% of world rta fatalities although they own only 11% of the vehicle fleet [2]. the increased rate of motor vehicle crashes worldwide has been attributed to the increased motorization of urban population. in saudi arabia, with its rapid expansion of road construction and increase in the number of vehicles, the rates of road accidents have increased dramatically. over the past two decades, the traffic division of the saudi ministry of interior has recorded more than 4 million road accidents 7% of which resulted in permanent disabilities [3]. an average of 19 deaths occurs daily in saudi arabia, which represents the country’s principal cause of death in adult males, aged 16 to 36, giving a rate of 23.3 traffic accident fatalities per 100,000 population [3-4]. the economic losses due to rtas in saudi arabia were estimated to exceed 6 billion us dollars annually, in addition to other health and social impacts due to injuries [5]. despite the fact that saudi arabia has a high rate of traffic accidents, relatively little literature about this problem has been produced. previous studies observed that saudi arabia has a higher rate of rats occurrence than other developing countries with comparable vehicle ownership levels [6-7]. excessive speed and violation of traffic laws and regulations were found to be the main causes of rtas in saudi arabia [8-12]. the causes of rats are complex and involve the interaction of a combination of factors that include road users, the vehicle, roadway, environment and the way they interact [13-14]. acquiring knowledge of the risk factors that contribute to road traffic crashes is important in formulating the priorities of action plans and interventions that can reduce the risks associated with those factors. it is generally recognised that a multi-disciplinary approach is essentially needed in understanding the main causations of rats and providing better and appropriate solutions. the aim of this research is to identify the contributing factors affecting road traffic accidents in the province of hail, saudi arabia. it is expected that the findings of the study will contribute to raising public awareness and designing policies for road safety planning in the kingdom of saudi arabia and other similar countries. ii. survey development to meet the objectives of this study a structured and comprehensive survey was developed based on an extensive literature to collect the necessary data for analysis. the methodology employed was based on both qualitative and quantitative methodologies. the questionnaire contains 39 items of different types such as, likert-scale type, multiple answers, single answer, and open questions and includes detailed information on the survey participants, their driving behavior and practices, their knowledge and awareness of engineering, technology & applied science research vol. 8, no. 1, 2018, 2417-2421 2418 www.etasr.com touahmia: identification of risk factors influencing road traffic accidents traffic laws and regulations, their assessment of road conditions and the interactions between these factors. the survey was designed to allow the researchers to identify the most profound difficulties and traffic safety problems that road users face. it is also designed to serve the researchers to identify the level of adherence and understanding of traffic regulations of the individual being interviewed. in addition, the questionnaire was designed to allow the researchers to provide measures of the traffic experience, knowledge, perception, attitude, traffic safety and road conditions. the data was collected through the questionnaire which is composed of four main sections namely: the first section includes general information about the participants, the second section evaluates the driving attitudes and practices of participants, the third section assesses knowledge and awareness of participants about traffic laws and regulations, and the fourth section assesses traffic safety rules awareness of the participants. the survey allows identifying the most thoughtful difficulties and trafficking safety problems that road users face in hail. it also provides an evaluation of the traffic experience, awareness, attitude, traffic safety and road conditions and allows identifying the level of understanding and compliance with traffic regulations of the participants. iii. data processing more than 500 questionnaires were distributed randomly to a sample of people living in hail. the total number of completed and returned questionnaires was 208 giving a rate of 41.6%. the collected data was analyzed by the statistical package spss, which was extensively used to produce different statistical tables of varying kinds, and in simple statistical computations. a discussion is provided on the importance of data considerations, particularly with respect to discrepancies existing in accident-casualty data from different sources. iv. results and discussion the results of the survey show that the respondents are mainly students falling within the age group of 19 to 29 years as illustrated in figure 1. when asked about the insurance, 60% of the respondents answered having insurance, either full or third party coverage, while 40% of them mentioned not having an insurance as shown in figure 2. as far as the driving license is concerned, 76% of the survey respondents mentioned possessing a driving license, while a relatively high percentage of them (24%) reported not having driving license as shown in figure 3. the durations of the survey participants driving licenses are shown in figure 4. it is worth noting that 94% of the unlicensed respondents are high school students, aged less than 18 years old who drive on a daily basis. this result highlights the need for a strict driving license policy to enhance current measures against unlicensed driving, particularly in the area of enforcement practices. unlicensed drivers represent a serious danger within the drivers’ community due to the fact they have not undergone appropriate training and testing and may, therefore, be deficient in some aspects of the knowledge, awareness and skills required to drive safely. furthermore, drivers who are unauthorized may have less incentive to comply with road traffic regulations and laws. driving without a valid license remains a serious problem in many countries despite ongoing improvement in traffic law enforcement practices. a survey in the usa has shown that approximately 20% of fatal crashes involves at least one driver who does not possess a valid license at the time of the crash [15-16]. in 2000, it was estimated that there were around 7,000 crashes (11,000 casualties) in uk involving drivers subsequently prosecuted for unlicensed driving [17]. in australia, unlicensed drivers represent over 5% of the drivers involved in fatal crashes [18]. fig. 1. age breackdown of the respondents. fig. 2. rate of insurance coverage of the participants. fig. 3. rate of licensed-unlicensed driving. engineering, technology & applied science research vol. 8, no. 1, 2018, 2417-2421 2419 www.etasr.com touahmia: identification of risk factors influencing road traffic accidents when asked about their knowledge about traffic laws and regulations, approximately 23% of the participants reported having very good/good levels, 65% mentioned they have moderate level and 14% indicate having weak/very weak knowledge about traffic regulations. figure 5 illustrates the participants’ levels of knowledge on traffic regulations. similar studies were reported by other researchers [19-20]. this result emphasizes the need for more training and education campaigns concerning the importance and benefits of traffic laws and regulations. fig. 4. durations of the respondents’ driving licenses. fig. 5. respondents knowledge of traffic regulations. a further analysis of the questionnaire data showed that 63% of the participants experienced rats at least once in the past as shown in figure 6. human factors are the leading contributing factor in any rats study including this one. data indicated that 67% of the accidents resulted from human errors, 29% from road defects and 4% from vehicle conditions as illustrated in figure 7. approximately two thirds of the respondents reported not complying with the speed limit signs and they often drive faster than the speed limits in urban roads and highways as shown in figure 8. this result reflects the lack of awareness among a large number of respondents concerning the danger and consequences of non-compliance with speed limit regulations. the survey data indicate that excessive speeding is the main cause of road crashes among the human causes of accidents. fig. 6. rate of involvement in rats. fig. 7. main causes of rats. fig. 8. rate of compliance with speed limit regulations. this result is consistent with previous studies [3,4, 7-9] which pointed out that the majority of traffic accidents in saudi arabia are directly related to human characteristics and errors, while road safety and vehicle's condition contributed to only 20% of the accidents. it is worth noting that approximately one third of the accidents are caused by road conditions as reported by the participants. although there are many variables that can lead to rats, roadway’s conditions like pavement quality, shoulders, visibility, signals, lane marking, traffic control engineering, technology & applied science research vol. 8, no. 1, 2018, 2417-2421 2420 www.etasr.com touahmia: identification of risk factors influencing road traffic accidents devices and intersections, can be considered as major potential factors in reducing rats. data from the safety section of the survey show that only 34% of the respondents comply with seat-belts use whilst driving as shown in figure 9. a further examination of the respondents’ reasons for not using seat-belts while driving showed that 54% claims not doing so due to discomfort, 16% to forgetfulness, 14% to carelessness and 6% to uselessness. however, when asked about the importance of wearing a seatbelt, 96% of the respondents mentioned they are convinced of its significance in saving lives and reducing severity of road crash injuries. this result emphasizes the need for more public awareness campaigns as well as effective laws enforcement to raise divers’ compliance with seat-belts use. fig. 9. rate of compliance with seat-belt regulations. v. conclusion rats are a leading cause of death and injury in saudi arabia, resulting in significant social and economic costs. in this study, the main causes of rats in the province of hail are analyzed. the data was collected through the use of a survey which was developed based on literature. the surveyquestionnaire consisted of four sections, namely, participants’ general information, driving attitude and practice, traffic regulation knowledge and traffic safety awareness. the results show that 63% of the participants experienced road crashes at least once in the past, where 67% of these accidents are caused by human errors, 29% by road conditions and 4% by vehicle defects. data analysis indicates that excessive speeding is the main cause of road crashes. although most of the participants reported having a good to moderate knowledge and understanding of road traffic laws and regulations, low rates of compliance with speed limit signs and seat-belts use were observed. in general, it can be concluded that further efforts should be undertaken for setting and enforcing effective traffic laws and road safety legislations alongside with promoting public awareness on traffic safety. the issue of improving the quality of roads and all related traffic safety equipments is also a critical factor of reducing rats. acknowledgment this research was funded by the deanship of scientific research at the university of hail, saudi arabia, under contract e012-ce. the author would like to extend his gratitude to the deanship of scientific research and to the college of engineering at the university of hail for providing all facilitations required for this research. references [1] world health organization, global status report on road safety 2015, 2015 [2] a. a. galal, “traffic accidents and road safety management: a comparative analysis and evaluation in industrial, developing and richdeveloping countries”, 29th southern african transport conference, pp. 530-540, 2010 [3] f. a. mansuri, a. h. al-zalabani, m. m. zalat, r. i. qabshawi, “road safety and road traffic accidents in saudi arabia: a systematic review of existing evidence”, saudi medical journal, vol. 36, no. 4, pp. 418–424, 2015 [4] e. s. gharaibeh, a. m. abu abdo, “assessment of traffic safety and awareness among youth in al-ahsa region, saudi arabia”, journal of emerging trends in engineering and applied sciences, vol. 2, no. 2, pp. 210-215, 2011 [5] a. j. al-saif, prediction of traffic accidents in gcc, solutions, and the role of al-shura council in addressing that, saudi arabia as a model, king fahd national library, 2010 [6] a. bener, f. m. abu-zidan, a. k. bensiali, a. a. k. al-mulla, k. s. jadaan, “strategy to improve road safety in developing countries”, saudi medical journal, vol. 24, no. 6, pp. 603–608, 2003 [7] s. f. ansari, a. m. mandoorah, k. moutaery, “causes and effects of road traffic accidents in saudi arabia”, public health, vol. 114, no. 1, pp. 37-39, 2000 [8] s. ramisetty-mikler, a. almakadma, “attitudes and behaviors towards risky driving among adolescents in saudi arabia”, international journal of pediatrics and adolescent medicine, vol. 3, no. 2, pp. 55-63, 2016 [9] y. a. al-turki, “how can saudi arabia use the decade of action for road safety to catalyse road traffic injury prevention policy and interventions?”, international journal of injury control and safety promotion, vol. 21, no. 4, pp. 397-402, 2013 [10] t. usman, l. fu, f. miranda-moreno, “quantifying safety benefit of winter road maintenance: accident frequency modelling”, accident analysis & prevention, vol. 42, no. 6 pp. 1878–1887, 2010 [11] a. s. al-ghamdi, “analysis of traffic accidents at urban intersections in riyadh”, accident analysis & prevention, vol. 35, no. 5, pp. 717724, 2003 [12] j. t. wong, y. s. chung, “investigating driving styles and their connections to speeding and accident experience”, journal of the eastern asia society for transportation studies, vol. 8, pp. 1944-1958, 2010 [13] m. h. khan, i. ahmed, n. zia, t. s. babar, t. s. and k. s. babar, “road traffic accidents: study of risk factors”, professional medicine journal, vol. 14, no. 2, pp. 323-327, 2007 [14] d. eisenberg, “the mixed effects of precipitation on traffic crashes”, accident analysis and prevention”, vol. 36, no. 4, pp. 637–647, 2004 [15] r. a. scopotz, c. e. hatch, b. h. delucia, k.a. tays, “unlicensed to kill”, aaa, foundation for traffic safety, 2003 [16] c. l. hanna, d. m. taylor, m. a. sheppard, l. laflamme, “fatal crashes involving young unlicensed drivers in the u.s”, journal of safety research, vol. 37, no. 4, 385-393, 2005 [17] uk department of transport research, unlicensed driving, report no. 4, 2003 [18] b. watson, “a survey of unlicensed driving offenders”, road safety research, policing & education conference, pp. 181-190, 2004 engineering, technology & applied science research vol. 8, no. 1, 2018, 2417-2421 2421 www.etasr.com touahmia: identification of risk factors influencing road traffic accidents [19] r. a. al-naggar, k. al-jashamy, “knowledge, attitude and practice towards road traffic regulations among university students, malaysia”, international medical journal malaysia, vol. 9, no. 2, pp: 29-34, 2010 [20] y. m. al-khaldi, “attitude and practice towards road traffic regulations among students of health sciences college in aseer region”, journal of family & community medicine, vol. 13, no. 3, pp.109-13, 2006 microsoft word pawar-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 5, 2012, 281-284 281 www.etasr.com pawar and poddar: car black box with speed control in desired areas for collision avoidance car black box with speed control in desired areas for collision avoidance dheeraj pawar electronics and telecommunication atharva college of engineering, university of mumbai mumbai, india dheeraj304@yahoo.com pushpak poddar electronics and telecommunication atharva college of engineering, university of mumbai mumbai, india pushpak.poddar@gmail.com abstract— this paper presents an advanced step to the concept of car black-box in developing a comprehensive vehicle safety system which would not only record the video and audio, but also try to prevent a possible collision by limiting the speed of the vehicle in accident-prone areas. in case of an accident, the time and location (co-ordinates) is sent through gsm to a preset number for immediate rescue and treatment. recorded data can also be used for forensics, revealing the problems that caused the accident and give manufacturer an idea for improvement. so the motto is to develop an embedded integrated system consisting of a microcontroller, a power supply unit, sensors, memory, a motor driver unit and a gps/gsm modem. keywordsblack-box; gsm; collision avoidance; speed-control i. introduction the black-box is a digital video-audio event data recorder. the concept is similar to the “black box” data recorders on airplanes. it records all the information, like speed & temperature of the cabin/engine, time and location, before and after the accidents so that it can be used to analyze the accident accordingly. it includes a web-camera, a microphone, a realtime clock, and other electronic components, all controlled by a microprocessor with embedded software and fully selfcontained in a tiny, rugged black box that installs unobtrusively on the dash board [1]. benefits customers receive are accurate, real time, easy to interpret data, a tamperproof system, and additional security. other benefits include being able to see what the driver could see, hear, and feel in a crash. the user interface is very simple and has been designed to minimize driver distractions. a green indicator light shows that the system is armed and ready to capture an event. as soon as a collision is detected automatically, the indicator light will turn red and start recording all the relevant data during a pre-defined period before and after the accident. the black-box is modified accordingly so that the system is triggered automatically as soon as abnormal readings are detected by the sensors and is prioritized as shown in table i. collection of audio and video can take place by a camera which can be easily stored in a flash memory/sd card. captured video and audio is date and time-stamped and can be downloaded to a laptop computer or vcr for viewing and/or long-term storage. events can be displayed immediately on a television or camcorder, thus offering great ease for viewing recorded information. for more efficiency, the data recorded will get refreshed on every start of the vehicle for managing the limited data storage capacity, unless an accident has taken place. table i. priority order for triggering of black-box priority event 1 crash 2 erratic driving 3 manual button the applications of car black-box include: 1. better crash research that may produce improved driver education programs, safer road designs and improve highway safety. 2. collision data for research, data to improve vehicle design internally and externally 3. to not only record the relevant data, but also try and prevent a possible collision by limiting the speed of the vehicle in accident-prone areas. 4. wireless communication by transmission of alert message in the event of a collision alongwith the time and location co-ordinates through gsm ii. car black box system architecture the in vehicle based car black-box consists of a microcontroller 89s52 core of the family 8051 embedded system used widely in the industry with an arm processor. a web camera and a microphone is present for video and audio recording. the gsm/gps module is also connected to the processor. figure 1 shows the entire architecture of the car black-box [1-7]. the data from infrared sensors are given to an encoder converting it from parallel to serial and transmitted wirelessly via a transmitter module. inside the car, the data is received by etasr engineering, technology & applied science research vol. 2, �o. 5, 2012, 281-284 282 www.etasr.com pawar and poddar: car black box with speed control in desired areas for collision avoidance a receiver module and a decoder converts it back again from serial to parallel to give it to the microcontroller. the accident switch is a circuitry which senses abnormal readings and triggers the system. various sensors such as the temperature and speed sensor are converted from analog to digital and given to the microcontroller. depending on various inputs given and bi-directional connectivity with the arm processor, the 89s52 controller takes decisions and varies output given to the motor driver assembly which is in direct contact with the motors of the car. the microcontroller not only recognizes the crash through the interrupt pin connected with the accident switch when car collision is detected, but also moves the data of the memory buffer to the sd card. the recording camera comprises of cmos sensors having advantages like low power consumption, small size, direct digital output and simple design compared to traditional ones. the gps (global positioning system) continuously tracks the vehicle’s position and keeps record of accurate time. the sd card used was selected keeping in mind newly emerging audio video consumer electronic devices. it can support easy interface allowing a pc to be connected without any special devices making it more portable. fig. 1. block diagram of car black-box iii. working of speed control in desired areas the assembly for this section consists of ir sensors which immediately detect the entry of vehicle in an accident prone zone. as soon as the same happens they send a level high signal which is transmitted wirelessly via the transmitter module. in the next stage, via the receiver module, data are given to the 89s52 microcontroller, which understands the presence of car in the accident zone and hence by pre defined logic it gives signal to the motor driver circuitry to control the speed of the vehicle at demarcated locations. as seen in figure 2, as soon as the car enters a predefined zone, e.g. a school as shown, it gets detected by sensors (marked with red dots) and after immediate signal transmission to the microcontroller inside the car, the speed is instantly brought to a preset level, reducing the chances of any accidents taking place. fig. 2. speed control dramatization iv. hardware details hardware details are depicted in figures 3-7. the specific microcontroller was chosen due to various advantages. it’s a low-power, high-performance 8-bit microcontroller with 8k bytes of in-system programmable flash memory. the on-chip flash allows the program memory to be reprogrammed insystem or by a conventional nonvolatile memory programmer. the atmel at89s52 is a powerful controller which provides a highly-flexible and cost-effective solution to our project. it is also the most easily available one. the ir sensor unit comprises of ir led’s which emit high intensity red light out of the sensor unit. if the light finds an obstacle in its path it is reflected back and this light it is received by the photo transistor. the reflected signal falls on the photo transistor. this ray excites the base of the transistor and switches the transistor on. fig. 3. working logic of ir sensors the comparator compares the two voltages and switches its output to indicate which is larger. we are using lm358 ic as a comparator. the non inverting input terminal of comparator is given an input signal detected by photo transistor while the inverting input terminal is given a reference voltage with the help of potentiometer. the comparator is used in non inverting mode i.e. when voltage falls below reference voltage, the output becomes low. on pin 3 i.e. non inverting terminal of etasr engineering, technology & applied science research vol. 2, �o. 5, 2012, 281-284 283 www.etasr.com pawar and poddar: car black box with speed control in desired areas for collision avoidance comparator the voltage is maintained above the reference voltage. due to which, the output is initially high. the light emitted by the led falls on the photo diode. the voltage at pin 3 of op-amp goes low. hence the output will go low. when the sensor is on the white surface the photo diode receives light and turns on and voltage at non-inverting input terminal decreases. hence the output becomes low. whereas when the sensor is on the black surface no light is received by photo transistor and it remains off. so the voltage at non inverting input of op-amp is greater than that of reference voltage at inverting input. so the output of comparator goes high. the encoder section is a series of cmos lsis for remote control system applications. they are capable of encoding information which consists of n address bits and 12_n data bits. each address/data input can be set to one of the two logic states. fig. 4. encoder and decoder assembly the programmed addresses/ data are transmitted together with the header bits via an rf or an infrared transmission medium upon receipt of a trigger signal. the capability to select a te trigger on the ht12e or a data trigger on the ht12a further enhances the application flexibility of the 212 series of encoders. on the other hand the decoders receive serial addresses and data from a programmed 212 series of encoders that are transmitted by a carrier using an rf or an ir transmission medium. they compare the serial input data three times continuously with their local addresses. if no error or unmatched codes are found, the input data codes are decoded and then transferred to the output pins. the vt pin also goes high to indicate a valid transmission. the 212 series of decoders are capable of decoding information that consists of n bits of address and 12_n bits of data. of this series, the ht12d is arranged to provide 8 address bits and 4 data bits, and ht12f is used to decode 12 bits of address information the microcontroller receives the code for left, right, up, down from arm processor at port 1. it checks the code and accordingly provides the data on port 0 to motor of the car. to drive the motor we have used the l298 motor driver ic. two motors on the left side of the car are connected in parallel combination & other two on the right side are connected in parallel combination with respect to the motor driver circuit. the l298 motor driver has 4 inputs to control the motion of the motors and two enable inputs which are used for switching the motors on and off. to control the speed of the motors a pwm waveform with variable duty cycle is applied to the enable pins. rapidly switching the voltage between vs and gnd gives an effective voltage between vs and gnd whose value depends on the duty cycle of pwm. 100% duty cycle corresponds to voltage equal to vs, 50% corresponds to 0.5vs and so on. the 1n4004 diodes are used to prevent back emf of the motors from disturbing the remaining circuit. many circuits use l293d for motor control, l298 is chosen here as it has current capacity of 2a per channel at 45v compared to 0.6a at 36v of a l293d. l298 on the other hand also works happily at 16v without a heat sink, though it is always better to use one. the embedded software used is executed by 89s52. the software is designed in assembler by keil software using c language in hex [6]. the data recording starts as soon as the accident switch is triggered and the code is compiled to set the proper baud rate so that all the data is updated every second. fig. 5. working of motor driver l298 fig. 6. pcb design of microcontroller and receiver section etasr engineering, technology & applied science research vol. 2, �o. 5, 2012, 281-284 284 www.etasr.com pawar and poddar: car black box with speed control in desired areas for collision avoidance fig. 7. pcb design of motor driver section v. conclusion in this paper we present the design of a car black box. we have successfully implemented the embedded system which gave good results and expected functioning. the data can be retrieved as required with great ease. the initial testing was done with connection to a pc instead of an arm processor for simplicity on trial purposes and later on the actual platform. acknowledgement the authors thank the authorities and professors of atharva college of engineering, university of mumbai for their support throughout the research work. references [1] song jie, li na-na, chen ji-lin, dong yong-feng, zhao zheng, “design and implementation of intelligent transportation system based on gprs and bluetooth hybrid model”, ical2008. ieee international conference on automation and logistics, pp. 1381-1385, china, 2008 [2] i. papapanagiotou, d. toumpakaris, jungwon lee, m. devetsikiotis, “a survey on next generation mobile wimax networks: objectives, features and technical challenges”, ieee communications surveys & tutorials, vol. 11, no. 4, pp. 3-18, 2009 [3] g. q. maguire, f. reichert, m. t. smith, “a multiport mobile internetrouter”, ieee 44th vehicular technology conference, vol. 3, pp. 14351439, 1994 [4] eunryung lee, jung wook lee, jeongho son, “osek/vdx-based gateway for car black-box”, icce 2011, ieee international conference on consumer electronics, pp. 521-522, usa, 2011 [5] kenneth ayala, the 8051 microcontroller, penram , india ,1995 . [6] yashavanth kenetkar, let us c, bpb publication, 2002 [7] myke predko, programming customizing 8051 microcontroller, mcgraw hill, new york, 1999. authors profile dheeraj pawar is a final year engineering student pursuing the bachelor of engineering degree from atharva college of engineering affiliated to the university of mumbai. his areas of interest include microprocessors and wireless technology. pushpak poddar is a final year engineering student pursuing the bachelor of engineering degree from atharva college of engineering affiliated to the university of mumbai. microsoft word etasr_v11_n2_pp6993-7000 engineering, technology & applied science research vol. 11, no. 2, 2021, 6993-7000 6993 www.etasr.com chatti & hadoussa: factors affecting the adoption of e-learning technology by students during the … factors affecting the adoption of e-learning technology by students during the covid-19 quarantine period: the application of the utaut model houcine chatti dar al uloom university riyadh, saudi arabia houcine@dau.edu.sa slim hadoussa brest business school brest, france slim.hadoussa@brest-bs.com abstract-the adoption of e-learning technology has become a major challenge for many academic institutions during the covid-19 pandemic. more and more institutions are questioning the success of adopting this technology and are seeking to understand their adoption process. the objective of the current research work is to study the factors affecting the intent of saudi university students to adopt online technologies during the covid-19 pandemic. based on the information technology adoption model, utaut, a research model was designed and validated by combining the factorial analysis method with simple linear regression analysis. the study revealed four key factors that had significant and positive effects on users' intent to use online technology, including the perceived usefulness, perceived ease of use, teacher influence, university management commitment, and availability of student technical assistance. keywords-covid-19; utaut; e-learning i. introduction the covid-19 pandemic has disrupted education in a unprecedented scale. as of march 16, 2020, 777 million pupils and students had been forced to leave their school or university in a total of 100 countries, with 85 governments closing schools nationally and 15 others imposing school closures at local levels [1]. in saudi arabia, the decision to close schools and universities was taken early, on march 9, 2020 almost a week after the appearance of the first case of covid-19 in the kingdom. the saudi government, through its ministry of education (moe), ensured that educational activities were not interrupted, adopting the concept of distant learning very effectively. in fact, the moe provides a 5-way integrated system (ranging from electronic portals to youtube channels) that takes into account the contrasting technical capabilities of the students and which can be adapted to their daily schedule. universities have also adopted distant learning with their students, with each university using its respective channel/portal, which has resulted in undisrupted teaching cycle and final exam schedules. thus, the use of new technologies has become essential to mitigate the impact of closure of academic institutions. to this end, distance learning is offered as an alternative that guarantees pedagogical continuity. education and classroom teaching have changed radically with the rise of e-learning. the crisis of covid-19 pushed educational institutions to make greater use of online technology or start using e-learning systems for course continuity. institutions use many technologies such as teaching and learning programs or even social media. in saudi arabia, most universities turn to online education through various applications such as zoom, blackboard, lms and teams [2]. e-learning generally refers to the use of computer network technology and electronic media to deliver and transfer knowledge for educational purposes [3]. in addition, e-learning assists students to get access to different online courses, scientific databases, and learning tools [4]. e-learning is generally considered as an important educational source for improving the effectiveness and efficiency of learning services, because of its availability, low cost, ease of use, and interactive nature [5]. furthermore, e-learning systems help to capitalize knowledge and coach students. e-learning systems have several functionalities that can be useful in the learning process. they allow sms sending and supporti the learning activity on a laptop or mobile device. students can easily integrate the learning content into their mobile devices since they can easily connect to mobile or wi-fi networks. elearning is thus seen as the process of using electronic technologies to access learning material in a non-traditional way [3, 6]. in other words, e-learning refers to the provision, organization and management of educational activities, such as student registration, exams, assignments, course descriptions, lesson plans, messages, syllabus, core course material, etc. within a remote system. [7]. since the success of the e-learning system depends on the willingness and acceptance of students to use it [3, 8], rejection of the use of this online technology may hinder the realization of the expected benefits [9]. nonacceptance makes the implementation or adoption of this technology a failure and a waste of money for academic institutions [10]. the research on this topic is still in its infancy, as students' views are not well studied [11]. exploring the corresponding author: houcine chatti engineering, technology & applied science research vol. 11, no. 2, 2021, 6993-7000 6994 www.etasr.com chatti & hadoussa: factors affecting the adoption of e-learning technology by students during the … adoption of e-learning technology can lead universities to understand better the needs of their students and manage more efficiently such educational systems that are widely diffused due to covid-19 crisis [12]. to date, little work has been attempted in analyzing the use of e-learning systems during the covid-19 pandemic. this research aims to investigate the main factors affecting the use of e-learning systems during the covid-19 pandemic in saudi arabia. the process of adopting online technology involves two major activities that are carried out sequentially: initiation and implementation [13]. during the initiation stage, the academic institution becomes aware of the e-learning system, forms an attitude towards it, and evaluates the innovation. initiation includes the activities of researching information, conceptualizing, and planning for adoption of this technology [14]. initiation includes, the stages of awareness, consideration, and intention. at the end of this stage, a decision on whether to adopt or reject the technology is made. authors in [15] adhere to this two-stage vision by considering that the adoption process includes adoption and implementation. an organization adopts an innovation when it decides to allocate resources to it. the implementation stage includes the development and installation activities that take place when the organization begins to use the innovation [16]. however, the process of setting up the e-learning system begins without a real awareness of the different stakeholders in the system: students, teachers, and administration. in other words, the initiation stage is only cursory. as a result, the question of acceptance of this innovation arises, particularly for students. the utaut technology acceptance model is, a framework for studying the question under research. ii. theoretical framework a. theories of technology acceptance behavioral theories about people's intentions have provided the theoretical basis for the development of models of technology adoption and acceptance [17]. these include the theory of reasoned action, the theory of planned behavior, and the technological acceptance model (tam). the theory of reasoned action [18] aims to predict and understand the behavior of individuals. it claims that the behavior (adoption of a technology) of any individual is reflected and directly influenced by his or her intention to achieve it, the latter being determined by two variables: attitudes and subjective norms. these two determinants of behavioral intention are in turn influenced respectively by beliefs about the consequences of the behavior and normative beliefs about a given behavior. the theory of planned behavior [19] is an extension of the theory of reasoned action. this theory adds a third determinant to the two determinants of the theory of reasoned action, namely the perceived control of the behavior or what is also called the perceived ability to carry out the behavior. it is based on the idea that individuals make rational use of available information to construct intention when faced with a behavioral decision [19]. in addition, the concept of perceived control of behavior stems from external and internal factors that facilitate the achievement of a given behavior, as well as the individual's perception of his or her personal effectiveness in achieving that behavior. in addition, two other variables explain this concept. these are control beliefs and facilitating conditions, which refer to an individual's assessment of the importance and availability of resources or an environment conducive to the achievement of the behavior. built from the theories of social psychology, particularly the theory of reasoned action, the tam is specifically concerned with the acceptability behavior of ict. the tam offers a perspective for understanding problems related not only to the adoption and use of information systems, but also to the appropriation of information systems by users. the main objective of this model is to predict the acceptance of an information system and, above all, to evaluate the impact of various external factors on internal beliefs, attitudes, and intentions of its users. the amt postulates that the actual use of a technology depends on the intention to use it and considers that this intention is influenced by the perceived usefulness and ease of use. the perceived usefulness is defined as the degree to which an individual believes that the use of a particular system could improve job performance [20]. it is therefore a function of the degree to which a technology is seen as advantageous and beneficial by its users. perceived ease of use, on the other hand, refers to the degree to which an individual believes that the use of a particular system can reduce effort [20]. it refers to the degree to which an individual believes that the use of a system will not require "much" cognitive effort. the specificity of amt in relation to ict, the accuracy of the determinants it proposes, and the precision of the measures [21], make it the most widely used model in the areas of ict adoption and acceptance [17]. the listed models focus on individual ict acceptance by predicting usage intent for icts that are already implemented. this study focuses on a context in which the technology is already implemented and used by individuals. thus, to answer the research question, the unified model theory of individual technology acceptance (utaut), which is considered to be the most recent and unifying theory, will be adopted in this study. utaut uses the essential elements of previously established models [21]. it is tested and empirically validated by longitudinal and cross-sectional studies on technology adoption in different contexts [22-26]. the utaut model [21] is a synthesized and comprehensive theory, which takes up the theories of acceptance of technologies in use, the variables whose validity and predictive power have been shown to be significant. compared to previously established acceptance models, utaut is considered [24] the best account for technology adoption, use, and acceptance. utaut postulates that the actual use of a technology is a function of the intention to use it, which in turn is influenced by determinants such as the expected performance, expected effort, social influence, and enabling conditions. moreover, unlike previous models, this model integrates new categories of moderating variables that vary the influence of the determining variables on the intention to use. these are: gender, age, experience of use, and whether the use is compulsory or voluntary. b. research model design the main objective of this work is to determine the factors that influence the acceptance of e-learning technology in the saudi academic community. the selection of the determinants of acceptance used in this research is heavily influenced by the engineering, technology & applied science research vol. 11, no. 2, 2021, 6993-7000 6995 www.etasr.com chatti & hadoussa: factors affecting the adoption of e-learning technology by students during the … utaut model [21, 27]. utaut has the advantages of (1) being a general model belonging to the set of theoretical models that have been developed to explain human adoption behavior and (2) having a high number of constructs, which gives it great explanatory power for the intention to use a technology. four independent variables define the model of [21], namely the perceived ease of use, the perceived utility, social influences, and facilitating conditions. four moderating variables (age, gender, experience, and mandatory or voluntary use), moderate the influence of the explanatory variables in the intention to adopt the technology. some authors consider that when the technology integrates with the individual's old tasks, and is therefore compatible with existing values, it can be recognized as useful and can influence the intention to use. this is why we have also considered, in this modeling effort the construct "compatibility with existing values" [28], also called task-technology compatibility [26], as an (independent) explanatory variable for the intention to adopt e-learning technology. finally, the variables explaining the intention to use and actual use of the utaut were grouped into a single variable called intention to adopt e-learning technology. for the present study we will not retain the moderator variables. thus, we have: a (dependent) explanatory variable: intention to adopt, and the (independent) explanatory variables: perceived usefulness, ease of use, social influences and facilitating conditions (figure 1). fig. 1. the research model. 1) perceived usefulness perceived usefulness is the degree to which an individual believes that using a system would help him or her achieve gains in job performance [21]. it has been shown by several studies to be a very significant determinant in explaining the intention to adopt a technology [21, 29]. indeed, e-learning technology can only be adopted if the students perceive gains in terms of efficiency, speed, and performance in the execution of tasks. the variable "perceived usefulness" is therefore understood as the perception of the usefulness of e-learning technology. theoretical models of technology adoption (tam, utaut) and the work of several researchers have confirmed that the perceived usefulness of a technology promotes its adoption and use. based on the empirical research in [21, 29] we assume that: h1: the perceived usefulness of e-learning technologies by students in performing their tasks positively influences their intention to adopt them. 2) perceived ease-of-use the perceived ease of use is seen as a direct determinant of the intent to adopt [26]. this variable is defined as the intensity with which an individual believes that the use of a particular system will occur without difficulty or additional effort [21]. thus, the likelihood that there is an intention to use the elearning technology is all the greater as long as the appropriation and learning process is easy to understand and use [26]. in other words, this variable explains the extent to which an individual believes that the organizational and technical infrastructure exists to support the use of the system [30]. the following hypothesis is therefore adopted: h2: the perceived ease of use of e-learning technologies by students positively influences their intention to adopt them. 3) social influences social influences are defined as an individual's perception that most people who are important to him or her think he or she should or should not engage in the behavior in question [18]. in other words, they include the role of people who are important to the individual and who exert some influence on his/her behavior [25]. prior to utaut, several technology acceptance [28, 31, 32] models showed that this "social influence" variable also called subjective norms or social factors exerted a significant influence on technology use. in our study, this social influence variable is measured separately by three constructs drawn from research using different models such as the gam [31], the gam2 [3]: influence of colleagues, influence of the hierarchical superior, and expected professional valorization. thus, we postulate that: h3.1: colleagues' use of e-learning technologies influences students' adoption intentions. h3.2: the commitment of the line manager (teacher) to the use of e-learning technologies for teaching influences the positively the students' adoption intention. 4) facilitating conditions enabling conditions refer to the extent to which an individual believes that an organizational and technical infrastructure exists to support the use of the system [21]. this variable is generally assessed through management involvement and the availability of technical assistance [33]. organizational support or the involvement of leaders, which have been described as agents of change [34], is presented as a determining factor in the process of adopting a technology within an organization [21]. we suggest the following hypotheses: h4.1: the involvement of university management positively influences students' intention to adopt online technologies. h4.2: the availability of technical assistance within the university positively influences the intention of students to adopt online technologies. engineering, technology & applied science research vol. 11, no. 2, 2021, 6993-7000 6996 www.etasr.com chatti & hadoussa: factors affecting the adoption of e-learning technology by students during the … iii. methodological framework a. study population the data were collected through a distributed by email questionnaire. our study population consisted of students from a saudi business school. out of the 120 contacted students, 87 (55.3% male and 44.7% female) answered the questionnaire. they were asked about the way they used to attend online classes, which indicated that 95% of the students used cell phones and 5% laptops. b. questionnaire construction the questionnaire consisted of two parts, demographic data and a 20 item questionnaire on a 5-point lickert scale ranging from 1 for strongly disagree to 5 for strongly agree. spss software was used to test the reliability and validity of the scales and to apply multiple regression analysis on the collected data. for its construction, the guidelines of [25, 3538] on the determinants of e-learning adoption and on the determinants of pedagogical integration of ict by university teachers were followed. the items selected for each variable are summarized in table i. c. methods of analysis for the processing of the collected data during the survey, two types of analysis were opted. at first, a principal component factor analysis was performed to test the validity and reliability of the measurement scales. then simple linear regression was used to test the research hypotheses. this method is widely used to explain or predict a variable to be explained based on one or more explanatory variables [39]. these analyses and statistical treatments were performed using the spss version 25.0. table i. measured items in the research constructs variables items perceived usefulness puse1 the use of e-learning systems helps me to perform my learning tasks in a better way. puse2 the use of online learning systems helps me to better follow my courses. puse3 using e-learning systems can improve my level of interaction with my teachers and classmates. puse4 using e-learning systems can improve the effectiveness of my learning. perceived ease-of-use peas1 it would be easy for me to learn how to use the e-learning system recommended by the university. peas2 i find the e-learning system recommended by the university easy to use. peas3 i may have difficulties in using the e-learning system recommended by the university. peas4 it would be easy for me to become competent in the use of the learning system. classmate influence cinf1 my classmates help me use the e-learning system. cinf2 i interact with my classmates on the use of e-learning systems. teacher influence tinf1 my teacher explicitly supports my use of e-learning systems. tinf2 my professor is convinced of the advantages of the e-learning systems. top management tman1 the university management is particularly interested in the use of the e-learning system. tman2 the use of the e-learning system is strongly encouraged by the university management. tman3 the management of the university is actively involved in the implementation of the e-learning system. technical assistance tass1 the members of the it department are always available to help those who need to tass2 the university has an it department with technicians ready to help me in case of need. tass3 the necessary instructions for a better use of the e-learning system are available for me. intention to adopt bint1 i have decided to adopt the e-learning system recommended by the university. bint2 i decided to attend the online course bint3 during this pandemic, i think it is good to use the e-learning system in courses. iv. result presentation and discussion a. purification of measurement scales there is a question of verifying the unidimensionality of the constructs and the internal coherence of the different scales of measurement. to do so, principal components factorial analysis was performed and the coefficient of cronbach's alpha was calculated [40]. the analysis of the results of the onedimensionality test of the measurement scales shows that the vast majority of our constructions present a cronbach's alpha greater than 0.8, which is widely acceptable in the literature. these values show and attest to the existence of internal consistency between the scale items. the constructs are therefore reliable for testing the research hypotheses. b. testing the validity of the model hypotheses the obtained results, presented in table ii, show that the perceived usefulness and the perceived ease of use positively influence the intent to adopt. thus the hypotheses h1 (β=0.93, p<0.01), h2 (β=0.95, p<0.01) are verified. in addition, the hypothesis h3.1 (β=-0.06, p>0.1) is rejected while h3.2 (β=0.32, p<0.01) is accepted. finally, the two constructs of the facilitation condition variable, management involvement and availability of technical assistance, both positively influence the intention to adopt the technology. the hypotheses h4.1 (β=0.33, p<0.01) and h4.2 (β=0.59, p<0.01) are therefore verified. c. discussion 1) the impact of perceived usefulness on the intent to adopt online learning technology the results of the analysis show that perceived usefulness has a significant influence on adoption intention. these results are consistent with those of [20, 41]. the significance of this perceived utility variable in our study shows that for students, the online learning system supports the teacher-student relationship and promotes the learning activity. students appear to believe that a learning system improves the effectiveness of engineering, technology & applied science research vol. 11, no. 2, 2021, 6993-7000 6997 www.etasr.com chatti & hadoussa: factors affecting the adoption of e-learning technology by students during the … their learning, allowing them to visualize and follow their course and to interact more easily with teachers. usefulness is perceived by the fact that an e-learning system would be a real platform for students to continue to attend their course and complete their assignments without any constraints. the students consider these platforms as real tools for communication, content publication (knowledge sharing), technology monitoring, etc. the respondents are therefore aware of the contributions of e-learning systems to learning activities. table ii. variable purification in the research model construits items quality of representation eigenvalues explained variance cumulative variance cronbach's alpha perceived usefulness puse 1 0.788 2.076 62.28% 62.28% 0.872 puse 2 0.789 puse 3 0.921 puse 4 0.834 perceived ease-of-use peas 1 0.701 3.150 65.11% 65.11% 0.801 peas 2 0.698 peas 3 0.744 peas 4 0.786 classmate influence cinf 1 0.651 2.795 55.01% 55.01% 0.891 cinf 2 0.569 teacher influence tinf 1 0.734 1.918 71.11% 71.11% 0.863 tinf 2 0.781 top management tman 1 0.901 2.823 74.16% 74.16% 0.857 tman 2 0.878 tman 3 0.865 technical assistance tass 1 0.689 2.350 59.19% 59.19% 0.901 tass 2 0.707 tass 3 0.819 intention to adopt bint 1 0.780 2.090 70.35% 70.35% 0.874 bint 2 0.865 bint 3 0.897 table iii. testing the validity of the hypotheses construits items hypotheses r2 β f perceived usefulness, intention to adopt puse, inta h1 0.91 0.93,*** 4.125, *** perceived ease-of-use, intention to adopt peas, bint h2 0.93 0.95,*** 0.97, *** classmate influences, intention to adopt cinf, bint h3.1 0.79 -0.06 -1.00 teacher influence, intention to adopt tinf, bint h3.2 0.81 0.32,*** 7.61, *** top management, intention to adopt tman, bint h4.1 0.83 0.33,*** 0.59, *** technical assistance, intention to adopt tass, bint h4.2 0.73 0.59,*** 7.28, *** *p<0.10, **p<0.05, ***p<0.01 2) the impact of perceived ease of use on the intention to adopt an e-learning system the results showed that there was a significant and direct relationship between these two variables. the influence of the perceived ease of use on the intent to adopt e-learning systems was found to be very significant and positive in this research. these findings are consistent with the results in [20, 21, 41], where authors assume that the more the student sees the use of e-learning systems in the learning activity as effortless, the greater the intention to adopt will be. perceived ease of use, a logical consequence of personal experience in using such a technology, which itself has created a kind of attachment to elearning systems, favors the willingness to use it. thus, the results obtained can be explained by: • the fact that, for respondents, this is not a new and unknown technology, but rather a technology that they are used to practice in a personal and sometimes playful way (social media). almost 80% of the respondents used social media to communicate with each other. the majority of them were fairly accustomed to these platforms. • the availability of training material on the use of online learning systems and web 2.0 platforms at the university and on the internet for free. 3) the impact of social influences on the intention to adopt the e-learning system in most studies of technology adoption in workplaces [21, 25], the influence of classmates and of the teacher has been considered the as a "social influence". these studies have shown that each of these constructs has a significant influence on technology adoption. our results showed that only one of the starting constructs of the social influence variable exerts an influence on the adoption of e-learning systems. only the teacher influence construct that emerged during the treatment was found to significantly influence the intention to adopt elearning systems. these results call for several comments: • we note the absence of a significant impact of peer influence on the intention to adopt e-learning systems. based on the results, we conclude that in the context of our survey, the students to whom our respondents belonged did not have "early" adopters [41] who could encourage them engineering, technology & applied science research vol. 11, no. 2, 2021, 6993-7000 6998 www.etasr.com chatti & hadoussa: factors affecting the adoption of e-learning technology by students during the … to use e-learning systems for their learning practices. we could also assume that in a period of confinement, contact is virtually absent and the use of these platforms does not require great skill or ability to motivate students to seek help from their colleagues. • our study showed the presence of a causal link between the variable influence of teachers and the intention to adopt elearning systems. this suggests that according to the surveyed students, the adoption of e-learning systems is a function of teacher encouragement. teachers encourage their students to adopt e-learning systems because they are convinced of the benefits that the learning activity can derive from their implementation. teachers help students to solve many technical problems and answer many of their questions regarding the use of these platforms. teachers post all course material on these platforms and even conduct online exams. they do not give students a choice about whether or not to use these platforms. 4) the impact of facilitation conditions on the intention to adopt the e-learning system both constructs of the facilitation condition variable of management involvement and the availability of technical assistance were found to significantly influence the intention of adoption of e-learning systems by the sampled students. these results are consistent with several previous studies [29, 33]. the involvement of university management is necessary to improve student commitment and motivation to adopt such systems. senior management commitment refers to a concept well identified, through work on information systems, as a determinant of successful it acceptance [42]. under the impetus of a policy of presence and support from management, students are obliged to align themselves with management's guidelines for distance education and to become more involved in the use of these platforms. we can therefore consider that the respondents are aware that despite the significant benefits of elearning systems, management support is necessary for the successful adoption of these platforms. the meaning of the availability of technical assistance is simply explained by the fact that despite a certain willingness on the part of the students, if there is no technical infrastructure, or if it is not adequate and there is no high speed internet connection, there can be no claim of adopting e-learning systems. thus, the presence of computer equipment, internet connection, and technical assistance, as well as the establishment of a training policy, if necessary, to accompany the adoption of e-learning systems is essential for the respondents. v. conclusion within covid-19 context, online education and e-learning has emerged at many universities as a modern educational model and changed radically the previous traditional learning concept. to avoid the spread of the virus and enhance the social distancing among students, many saudi universities and high schools implement and adopt different online educational systems to ensure course continuity. this research focuses on identifying the factors that determine e-learning system adoption by students at a saudi business school. the study adopts the utaut theory [21] to develop a conceptual model which was tested through a quantitative methodology by an online survey (87 students). the most important outcome of this research was the confirmation of the importance of factors determining the acceptance and the adoption of an e-learning system. the results show that the main determining factors are: the perceived usefulness, the perceived ease of use, teacher influence, involvement of university management, and the availability of technical assistance. this research demonstrates that if students perceive the usefulness of e-learning systems with their learning tasks, they will be more inclined to adopt such a system. this result can be useful to higher education managers that focus on enhancing awareness-raising actions regarding the benefits and opportunities that e-learning systems can provide. such policies would encourage the e-learning system adoption by students and would enhance the success of the online educational transition. this awareness can be done, for example, through offers of continuing education and/or short awareness meetings. moreover, the results suggest that early awareness rising among students by the school management is vital for the adoption of e-learning systems. the use of e-learning systems is relatively new at many higher educational institutions. therefore, like any technological innovation, it faces difficulties in its launching. the e-learning system makes learners struggle with their habits, which sometimes leads to a reaction of rejection or at best, mistrust. this is apparent both in the appreciation of the usefulness of the system and its ease of use. this feeling could be also increased by the anxiety expressed by many students due to the general negative atmosphere that exists due to the lockdown. the role of management is essential in this case to facilitate the development of a positive attitude towards e-learning systems. furthermore, the role of the academic staff is crucial to enhance the adoption and the creation of an attractive atmosphere that encourages students to not only virtually assist but also to interact during the online courses’ sessions. the availability of technical assistance was also found to be a very significant influence on the intent to adopt e-learning systems. since a technology can only be used if the technological infrastructure is available, it is essential to strengthen the it infrastructure in general and the broadband internet connection. many students have the importance of being technically assisted, especially when they encounter a technical problem during the course’s online session. the insights obtained by this study could be helpful for both academics and practitioners interested on e-learning adoption at the educational sector. thus, this research helps educational managers to establish effective policies towards elearning system use that may ensure the education continuity during the covid-19 pandemic and would enhance the knowledge transfer quality [3, 43]. however, this research has some limitations. although the results are valid, the tested sample is limited to only one saudi business school. it would be interesting in a future study to consider other higher institutions specialized in different fields with a larger number of students. also, the sampling method could be enriched by taking consideration of the field’ differences that exist between students coming from different backgrounds. a future study could also compare the performances of the public and the engineering, technology & applied science research vol. 11, no. 2, 2021, 6993-7000 6999 www.etasr.com chatti & hadoussa: factors affecting the adoption of e-learning technology by students during the … private educational sector. moreover, the current study did not consider the emotional situation, stress, and anxiety caused by the covid-19 atmosphere that was expressed by many students during the survey and that could possibly impact the adoption of the e-learning system. in addition, the current study is limited to the students' point of view that could be different from the academic staff's. these different additional studies and data could be very valuable for exploring and understanding some causal relationships in the conceptual model and to enhance the results interpretation. this study attempts to offer a positive and optimistic perspective regarding the online educational student experience in the context of saudi higher education system. the digital transformation of the higher education sector will continue to change educational practices and learning methods. future studies could be conducted in this sense and explore the impact of e-learning systems on knowledge sharing and capitalization. acknowledgement the authors wish to thank the deanship of graduate studies and scientific research at dar al uloom university for the support and funding of this study. references [1] "covid-19 educational disruption and response," unesco, mar. 24, 2020. https://en.unesco.org/news/covid-19-educational-disruption-andresponse (accessed mar. 17, 2021).2 kingdom of saudi arabia ministry of education. https://www.moe.gov.sa/en/pages/default.aspx (accessed mar. 17, 2021). 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[43] h. louati and s. hadoussa, "study of social media impacts on social capital and employee performance – evidence from tunisia telecom," journal of decision systems, feb. 2021, https://doi.org/10.1080/ 12460125.2021.1872142. microsoft word etasr_v11_n1_pp6714-6718 engineering, technology & applied science research vol. 11, no. 1, 2021, 6714-6718 6714 www.etasr.com ahmed et al.: experimental analysis and control of a wind-generator system through a dc-dc boost … experimental analysis and control of a windgenerator system through a dc-dc boost converter for extremum seeking tarique ahmed department of electrical engineering mehran university of engineering and technology, szab campus khairpur mir’s, pakistan tariqahmed3940@gmail.com mazhar hussain baloch department of electrical engineering mehran university of engineering and technology, szab campus khairpur mir’s, pakistan mazhar.hussain08ele@gmail.com noman khan department of electrical engineering mehran university of engineering and technology, szab campus khairpur mir’s, pakistan nomankhan@muetkhp.edu.pk gul mehr department of electrical engineering balochistan university of information technology, engineering and management sciences, quetta, pakistan mehrbuitms@gmail.com baqir ali mirjat department of electrical engineering mehran university of engineering and technology szab campus, khairpur mir’s, pakistan baqirali@muetkhp.edu.pk yasir aftab memon department of mechanical engineering mehran university of engineering and technology szab campus, khairpur mir’s, pakistan yasiraftab@muetkhp.edu.pk abstract-the advancement in technology has significantly improved the living standard, having a direct impact on the quality of life, at the cost of ever-increasing energy demand. renewable energy resources such as the wind energy conversion system (wecs) provide variable power generation. the current paper presents the results of the experimental analysis on the control of the wind-generator system based on scig through a dc/dc boost converter for extremum powerseeking. since the squirrel cage induction generator (scig) is widely used in wind industries for power generation, their performance will be compared. the proposed system can operate either on a variable or at a nearly constant speed, with higher load capacity, while its power consumption is comparatively lower. the research will enhance the wind power at different wind speeds, to acquire the extremum power point tracking system from the wind power energy system by using two different machines. keywords-wind power energy; extremum power tracker; dc/dc converters; scig i. introduction most countries face problems when using conventional sources such as coal, natural gas, and oil for the generation of energy, due to the imminent depletion of non-renewable resources and ecological problems. due to environmental problems, such as the global warming and the greenhouse effect, there is an increasing attention on renewable sources of energy. wind power energy is an obtainable renewable energy source, it is clean, and practically infinite [1] and is the most prominent source of energy for power generation [2]. several studies have being carried out to regulate the way extremum wind power can be taken from the wind energy power generation system [3]. in figure 1, we can see the increasing trend of the year-wise global cumulative capacity (gw) [3]. fig. 1. globally wind power cumulative capacity (data taken from [3]). the energy sector of pakistan has improved significantly in 2020, but still faces a shortage of 6gw [4]. due to the energy deficit, the industrialized and commercial segments utilize diesel generators, while residential consumers are using uninterrupted power supply (ups) units which increase the operating cost [5]. the pakistan meteorological department (pmd) has carried out a detailed study of the wind energy potential of the coastal regions of pakistan [6], allowing us to recognize possible exploitable windy regions [7], e.g. the shore regions of sindh have a better potential for wind power energy than the shore regions of baluchistan [8]. the candidate regions occupy 9700km 2 in sindh. a potential capacity of this corresponding author: mazhar hussain baloch engineering, technology & applied science research vol. 11, no. 1, 2021, 6714-6718 6715 www.etasr.com ahmed et al.: experimental analysis and control of a wind-generator system through a dc-dc boost … cumulative wind power energy in the mentioned region is around 43,000mw [9]. by considering the limitations of the utilization of the region, it is estimated that the exploitable potential of electric power generation in this area is approximately 11,000mw [10]. this research study uses variable speed for wind power systems which has numerous benefits associated with constant speed wind power energy scheme, such as producing extremum wind power energy from the network and developing small mechanical stress by improving the efficiency and quality of the energy. the current paper presents the results of experimental analysis on the control of a wind generator system based on squirrel-cage induction generators (scigs), through a dc/dc converter for extreme energy seeking. the scigs are generators of frequent use at the industrial level, they are cheap, and can operate at different, constant or variable, speeds, with great load capacity, and their energy consumption is comparatively low. the objective is the acquisition of extremum wind power at different wind speeds and the implementation of the dc/dc boost converter for extremum seeking control. ii. the proposed experimental setup the block diagram of figure 2 shows the scig, which is driven through a prime mover. at the coupling of the prime mover and the scig, the rpm of the generator is measured by a tachometer. fig. 2. flowchart of the proposed setup. the excitation of scig is controlled by the excitation capacitance and feeds the rectifier. after that the observation of generated power with and without booster at variable wind speed is compared using dummy load. iii. wind generation modeling characteristic equations the output power from the wind turbine is expressed as [11]: �� � 0.5�� �λ, ������ (1) where � � 1.25��/�� is the density of the wind, r represents the turbine blade length, �� is the speed of wind, � � 0.3 to 0.5 is the power coefficient, the pitch angle is represented by (supposing zero degrees at zone-ii), and λ is the tip speed ration described as ([12]): λ � �� ! (2) where " is the rotor speed of wind generator in rad/sec. the relationship between turbine power and wind power is defined as [13]: �# � $#"# � �λ, ��� (3) � � �0.73�151 &��' �� ( 13.645+ , -!.!'/0.00�1 23 (4) the output power of the wind generator system is driven from (1)-(4) and defined by the wind speed, as calculated from [14]: �# � 55.155�4 !��' ( 0.09+ ,-!.!'/0.00�1 23 (5) the power of the wind turbine system at the speed of the wind turbine is shown in figure 3 by using (5). it is clearly visible that the power of wind turbine changes with respect to the speed of wind turbine which depends on wind speed. the graph shows that the 3 rd order curve gives maximum power generated by a wind turbine at different wind speeds [15]. fig. 3. wind turbine power curve. iv. experimental model design the experimental model for the wind generation system is shown in figure 4. the wind energy conversion system consists of a 3-phase sinusoidal voltage which is inverted to dc voltage through a rectifier. our main objective is to generate and control the extremum power from the wind generation engineering, technology & applied science research vol. 11, no. 1, 2021, 6714-6718 6716 www.etasr.com ahmed et al.: experimental analysis and control of a wind-generator system through a dc-dc boost … system through dc-dc converters by changing their duty cycle at the dc side. the experimental circuit diagram for the dc-dc boost converter is shown in figure 5. fig. 4. experimental circuit without booster. fig. 5. experimental circuit with booster. v. experimental setup the experimental model of wind energy conversion system (wecs) requires a wind channel, which is normally assembled to generate controlled wind speed to run a wind energy conversion system. however, it is expensive and space challenging. a software simulator is simple but with many restrictions. the best way to use the characteristics of the wind turbine is by using an engine generator (mg) –set, in which the engine is functioned and controlled to re-produce the wind energy converter system scheme at variable wind speeds. through a comprehensive study, the mg set was used as a prime mover for the wecs. the scig was used for power generation at variable wind speed. a permanent magnet dc machine was used as a wind turbine emulator to analyze the non-linear behavior of the wind turbine. in this experimental setup, the motor works at varying speed in order to examine the generated output power from the scig with and without dcdc boost converters. our main objective is to acquire the maximum wind power at different wind speeds, through the dc/dc boost converter for extremum power-seeking. the experimental models without and with the booster based on dcdc boost converter are shown in figures 6 and 7 respectively. initially, the wind energy power system was operated without dc-dc boost converters, connected to the rectified output of a scig to calculate output parameters such as voltage, current, and power under variable speed conditions. the resistive load was used as an imaginary load to take continuous power measurements for generator output analysis. to acquire extremum power, the modified output of the wind generator system was fed to the dc-dc booster, which consists of a single mosfet while the capacitor values calculated from primary to secondary are 470µf, 450v, 680µf, and 450v respectively. the rated value of the output inductor is 1.8mh, 2.5a, with a switching frequency of about 240khz (table i). the efficiency of the system's response to the proposed controller scheme based on boost converters impulse converter was confirmed by a different duty cycle. fig. 6. experimental model without booster. fig. 7. experimental model with booster. vi. results and discussion the results were extracted at variable wind speed of the prime mover and different time intervals in order to analyze the wind turbine system output by using scig. the permanent magnet direct current machine was used as the prime mover. the scig was coupled with a wind turbine channel and was operating at variable wind speeds. in the experimental model of wecs, it is important to observe parameters like current, voltage, and power at varying wind speed. the without-booster scheme was applied to the wind generator system. the scig operated at variable wind speed and the generated power was measured at different time intervals. the speed (rpm) response with respect to time is shown in figure 8, which shows that the speed of the generator increases with respect to time as the speed in rpm is increased: from 4 to 6s it gets from 400 to 600rpm and from 10 to 12s from 1000 to 1100rpm. the main objective is to analyze the output power without a booster at different wind speeds to observe the power (w) vs speed (rpm). figure 9 shows the speed vs power graph, in which the generation of wind power ranges from 600rpm to 1000rpm and reaches 105.9w when the speed of wind turbine reaches 1150rpm. secondly, in the experimental model, the generated power was observed at variable wind speed with a booster applied to the wind generator system output. the scig engineering, technology & applied science research vol. 11, no. 1, 2021, 6714-6718 6717 www.etasr.com ahmed et al.: experimental analysis and control of a wind-generator system through a dc-dc boost … was operated at different wind speeds and its output power was measured at different time intervals. our main objective was to analyze the output power with booster at different wind speeds. the extremum power was achieved by varying the duty cycle with the help of the pwm method, as a pulse feed to the gate of mosfet used in dc-dc boost converters. figure 10 shows the power with respect to turbine speed. the power generation was 105w at 1000rpm, and the generation increased to 144w at 1150rpm. the duty cycle and wind speed changed in order to extract the maximum power by varying the point of energy conversion. in this experimental setup, the duty cycle changed from 10% to 16.60% as shown in figure 11. table i. equipment description list of equipment descriptions and model no power supply power electronics universal supply model no:aep1/ev prime mover (dcpmsg) 2500rpm, type em-3330-1a 180v dc, 2.7a, 0.4kw, s/n:201 3-phase scig 0.3kw,1420/1670rpm type: em-3330-3c 3-phase, 220v, 1.4a, 50/60hz, s/n:201 tachometer tachometer 20713 a excitation capacitors (cap) 15µf ±5% 350-400 vac 3-phase rectifier aql5010-5a booster capacitor 1:470µf,450v capacitor 2:680µf,450v inductor:1.8mh 5a diode:fr305 mosfet measuring instruments oscilloscope, model:dl:10282 digital oscilloscope gw instek gds-2074 laptop pc: toshiba fig. 8. wind speed response with time. fig. 9. power response without booster at variable wind speed. fig. 10. power response with booster at variable wind speed. fig. 11. power response at varying duty cycle. vii. without vs with booster result comparison the experimental results are summarized in figure 12. the configuration without booster generated power from setup at different wind speed is 105.9w at 1100rpm but at the same time, the extraction of the maximum power by using the dc-dc booster is 144w at 1100rpm. fig. 12. power response with and without booster at varying wind speed. viii. conclusion the current paper presents an experimental setup for a wecs based on scig through dc-dc converters for extremum power-seeking. the advantage of this model is that it generates the power at variable speed from the wind energy system, due to this the variable speed wind energy generator system faces engineering, technology & applied science research vol. 11, no. 1, 2021, 6714-6718 6718 www.etasr.com ahmed et al.: experimental analysis and control of a wind-generator system through a dc-dc boost … the least pressure on different varying factors like gear or shaft of the system. the dc-dc boost converters are independent of the speed of the wind. the proposed experimental model characterized the generated output power from the wind generator system. the dc-dc converters provide extremum power at the grid end by changing the duty cycle connected with the rectifier. the proposed experimental setup can be adjusted efficiently to the current wind energy system at varying speed, in the minimum wind speed area. the dc-dc converters provide maximum power at the end of the grid by changing the duty cycle connected to the rectifier. references [1] m. h. baloch, g. s. kaloi, and z. a. memon, "current scenario of the wind energy in pakistan challenges and future perspectives: a case study," energy reports, vol. 2, pp. 201–210, nov. 2016, https://doi.org/ 10.1016/j.egyr.2016.08.002. 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[14] k. s. belkhir, "intelligent maximum power tracking control for a wind energy system based on magnetic gear generator," engineering, technology & applied science research, vol. 9, no. 4, pp. 4329–4333, aug. 2019, https://doi.org/10.48084/etasr.2851. [15] s. mahesar et al., "power management of a stand-alone hybrid (wind/solar/battery) energy system: an experimental investigation," international journal of advanced computer science and applications, vol. 9, no. 6, 2018, https://doi.org/10.14569/ijacsa.2018.090631. microsoft word etasr_v11_n4_pp7430-7435 engineering, technology & applied science research vol. 11, no. 4, 2021, 7430-7435 7430 www.etasr.com ghaly et al: design and simulation of an 8-lead electrical capacitance tomographic system for flow … design and simulation of an 8-lead electrical capacitance tomographic system for flow imaging sidi m. ahmed ghaly electrical engineering department college of engineering imam mohammad ibn saud islamic university (imsiu) riyadh, saudi arabia sidiahmedghaly@gmail.com khalid al snaie electrical engineering department college of engineering imam mohammad ibn saud islamic university (imsiu) riyadh, saudi arabia kalsnaie@imamu.edu.sa mohammad obaidullah khan electrical engineering department college of engineering imam mohammad ibn saud islamic university (imsiu) riyadh, saudi arabia dearkhan@gmail.com mohamed y. shalaby electrical engineering department college of engineering imam mohammad ibn saud islamic university (imsiu) riyadh, saudi arabia shalaby88@gmail.com majdi taha oraiqat electrical engineering department college of engineering imam mohammad ibn saud islamic university (imsiu) riyadh, saudi arabia dr.majdi.taha@gmail.com abstract-electrical capacitance tomography (ect) is a method for determining the dielectric permittivity distribution inside an object from measurements of external capacitance. the technique differs from conventional tomographic methods in which high-resolution images are formed from slices of the material. the measuring electrodes, which are metal plates, must be large enough to give a measurable change in capacitance. the main objective of this paper is the implementation and simulation of 8 external electrode ect systems in order to increase the quality of reconstructed permittivity images while preserving the simplicity of design and to fulfil the demand for real-time process tomography. a complete sensor model was developed to improve the accuracy of the forward validation, especially the validation of measured data from neighbouring electrodes. a prototype ect sensor with high sensitivity was designed that can be applied to all materials which have low electrical conductivity. the capacitance between different electrode pairs is calculated for some typical permittivity distributions based on labview and matlab. the obtained capacitance data can be used to reconstruct images. the sensitivity distributions for the ect sensors with different number of electrodes were analyzed. preliminary tests were performed and the developed prototype showed good performance. the developed concept contributes to the study and comprehension of the ect systems that can be used for the monitoring of oil-gas flow. keywords-electrical capacitance tomography; permitivity; labview; simulation; electrode i. introduction to monitor and diagnose the internal dynamics of a gas/liquid flow mechani1sm system in industrial process, one of the most widely used imaging techniques is the electrical capacitance tomography (ect) system [1-4] which is an economical, non-interrupting, fast responding imaging scheme. it can generate real-time images, generally with a speed that reaches 100 frames per second. different experimental outcomes demonstrated that the water-in-liquid ratio (wlr) and gas volume fraction (gvf) in an oil-gas-water flow can be roughly calculated or measured by the ect with suitable algorithms [5]. to get high-speed imaging along with quantitative measurements of a multi-phase flow system is a challenging demand in petroleum industry hydraulic applications. this can also be used in detecting corrosion, leakage, or to monitor the dynamics of the liquid in the petroleum/gas underwater/underground pipeline network [6-7]. ect can be employed to investigate the distribution of spatial permittivity within a defined region of interest generally in the interior of a closed pipe. it works on the principle of measuring the capacitances between electrodes located outside of the specimen portion in the region of investigation. generally, it can be a hollow pipe carrying a liquid or gas. the data achieved from the electrodes are processed to reconstruct the internal image of the pipe. the essential components of a typical ect system are: a set of multi-electrode sensors, data retrieving or acquisition system, and an image reconstruction system [8-9]. if a sensor uses n electrodes for capacitance measurements, there will be 1 2n( n )/− unique electrode pairs and thus 1 2n( n ) /− independent capacitance measurements. 1 2m n( n ) /= − (1) for instance, as illustrated in figure 1, an 8-electrode sensor needs 28 independent measurements of electrode pairs 1-2, 1-3, ..., 1-8, 2-3, 2-4, ..., 2-8, ..., up to 7-8. corresponding author: sidi m. a. ghaly engineering, technology & applied science research vol. 11, no. 4, 2021, 7430-7435 7431 www.etasr.com ghaly et al: design and simulation of an 8-lead electrical capacitance tomographic system for flow … fig. 1. cross section of a typical 8-electode sensing system. usually the ect systems use directly the "raw" capacitance data achieved from the sensor to reconstruct images using linear back-projection (lbp), iterative, or neural network algorithms. the lbp algorithm is a commonly used popular method due to its simplicity and high rate of image reconstruction. an lbp image is obtained by superimposing the sensor sensitivity maps (i.e. the sensitivity distributions) for all electrode pairs after weighting by the corresponding measured changes in normalized capacitance [10-11]. this process can be expressed by the mathematical relations given below: ���� � ∑ ∑ λ�� ��� � � ��� � ��� ��� ∑ ∑ ��� � � ��� � ��� ��� (2) λ�� � ��� � ���� � ��� � ���� � (3) where n is the number of electrodes in an ect sensor, x(p) is the fraction of high permittivity material in the p th pixel, s is the sensitivity of electrode pair i-j at the p th pixel, ��� � and ��� � are the capacitances of the electrode pair i-j when the sensor is filled with high and low permittivity materials, and ��� � is the "raw" measured capacitance of electrode pair i-j. this paper focuses on the simulation and design of a prototype ect sensor, which is used for the measurement of the independent capacitance values. the resolution and sensitivity of an ect sensor are defined by the number of external electrodes. therefore, an 8-electrode ect prototype which is widely used in industrial applications is developed in this paper. the developed prototype is simulated in labview [12-14] with low and high permittivity materials (air and rod) with permittivity values of 1 and 80 respectively. the developed sensor is used for image reconstruction from the permittivity distribution which is obtained from independent capacitance measurements. a preliminary test is realized with the prototype for the measurement of the independent capacitance values. ii. electrical modeling of the ect sensor without radial screen the ect sensor considered in this article has 8 external electrodes without radial screens as illustrated in figure 1. these electrodes can be installed with a flexible printed circuit board (pcb) to a greater precision, both in size and in position, than the copper sheet electrodes that use the radial screens. without radial screens, the external capacitances are to be considered because they are no longer negligible. the measured capacitance of one pair of electrodes cm, can be modeled as the combination of an internal capacitance cx, two pipe wall capacitances cw1, cw2, an external capacitance cex, and two stray capacitances cs1, cs2 as illustrated in figure 2 [15-16]. (a) (b) fig. 2. electrical model of the 8-electode sensing system without radial screen: a) model with all capacitances, b) simplified model. considering figure 2, the equivalent capacitance cm can be calculated and measured by the relation: w x m ex w x c c c c c c = + + (4) the unknown capacitances cex, cw, and cx can be found by filling a material of known relative permittivity εr1 into the sensor. this step is repeated with another material of known relative permittivity, say εr2, e.g. air. thereby, after finding cex and cw, the internal capacitance with any fluid available inside the region of interest in the pvc pipe can be obtained from the raw capacitance measured by (4). hence, it can be rearranged as [17-18]: w m ex x w m x c (c c ) c c c c − = − − (5) iii. simulations and results of the ect sensor without radial screen to evaluate the ect sensor without radial screen model, a cylindrical ect sensor of 84cm diameter with 8 external electrodes of l0cm length without radial screens (as shown in figure 1) is employed. it is calibrated with two materials of known permittivity values, air (ε = 1) and a 0.9cm in diameter rod (ε = 8). the prototype simulation data that are the raw capacitance measurements for all electrode pairs, first with the sensor unfilled and then with the rod positioned in the center of the sensor, are obtained by means of the ect system parameters. these two sets of raw capacitance measurement data with respect to low and high permittivity are shown in tables i and ii respectively. from these measured data, 28 pipe wall capacitances and 28 internal capacitances for air were calculated using (4) and (5). these calculated data show that similar electrode pairs have similar pipe wall capacitance values. all pipe wall capacitances for adjacent electrode pairs are around 400pf, and those of the opposing electrode pairs are around 20pf. as expected, the pipe wall capacitances of adjacent electrode pairs are much larger than those of the other electrode pairs. engineering, technology & applied science research vol. 11, no. 4, 2021, 7430-7435 7432 www.etasr.com ghaly et al: design and simulation of an 8-lead electrical capacitance tomographic system for flow … table i. raw capacitance (pf) data measured with low permittivity electrode detection electrode 8 7 6 5 4 3 2 1 362 29 18 11 17 30 370 2 420 29 18 11 17 31 3 422 30 17 12 18 4 427 29 18 12 5 388 30 17 6 419 30 7 397 table ii. raw capacitance (pf) data measured with high permittivity electrode detection electrode 8 7 6 5 4 3 2 1 420 21 22 24 28 48 407 2 435 21 22 24 29 47 3 434 22 23 25 30 4 413 21 22 23 5 422 21 22 6 436 21 7 431 iv. simulation results and discussion in an ect system the number of sensitivity maps equals to the independent capacitance measurements [3]. each matrix represents the capacitance value of the electrode when the pipe is full with high or low permittivity material. the sensitivity distribution si,j(k) for the electrode pair i, j can be described as: ��,� � ��⋅� � ���⋅� ��⋅� � ���⋅� ! "��" (6) where ��⋅� � is the inter electrode capacitance, ��⋅� # is the inter electrode capacitance measurement when the sensor area is completely filled with low permittivity material, ��⋅� � is the inter electrode capacitance measurement when the sensor is full with high permittivity material, and $� and $# are the permittivity values for the high and low permittivity materials respectively. the sensitivity map can be calculated by the sensor, by placing a plastic probe inside the sensing area as shown in figure 3. fig. 3. total sensitivity map of the 8-electrode ect system. the sensitivity matrix defines the change in the measured capacitance between electrodes when the dielectric constant varies inside the sensor and the distribution of the electric field when one electrode is connected to a potential v and all the other electrodes are connected to the ground. this shows that the field is strongest close to the exciting electrode and the equi-potential lines inside the sensor. the corresponding lines of the electric field are shown in figure 4. fig. 4. illustration of the electric field intensity pattern corresponding to sensitivity. the change in measured capacitance (sensitivity) between any two electrodes caused by an object with a given permittivity varies depending on where the object is placed (near the walls or the center of the vessel). these data are saved in the sensitivity map text file which is used to develop images of the ect system by reading the sensitivity map and manipulating the image gray level values accordingly. the field sensitivity distribution of electrode pair i,j is defined as [12]: s = ei.ej.da (7) where ei is the electric field within the specimen sensor when one electrode of the pair i is electrified or powered as a source electrode and ej is the electric field when the electrode j is electrified or powered as a source electrode. to obtain the sensitivity distributions, rotation transformations are further employed in the image domain (the center of the vessel is the center of rotation). mathematical models have been built to describe such a typical ect sensor. using this model, the internal capacitances of two materials with known permittivity (air and rod) and, as appropriate, the pipe wall and/or external capacitances are calculated from the system simulation parameters. the models allow "raw" capacitance measurements to be converted to the internal capacitances before their use in the image reconstruction process. instead of using the raw simulation data, the equivalent relative permittivity values as defined by: ε% & � �' . �) . (8) equation (8) can be used for image reconstruction. for example, a variation of the lbp image reconstruction technique can be used to produce images showing the quantitative distribution. in this technique, the equivalent relative permittivity is expressed by: ε��� � ∑ ∑ ε�� ��� � � ��� � ��� ��� ∑ ∑ ��� � � ��� � ��� ��� (9) engineering, technology & applied science research vol. 11, no. 4, 2021, 7430-7435 7433 www.etasr.com ghaly et al: design and simulation of an 8-lead electrical capacitance tomographic system for flow … ε�� � �*+,/�.+, (10) where ε(p) is the relative permittivity value of the p th pixel, and εij is the equivalent relative permittivity of the material between the electrode pair i,j. the permittivity distribution of both materials is obtained as a series of normalized pixels located on a 32×32 square pixel grid. as the sensor cross-section is circular, the simulated contour is projected onto the square grid containing 1024 pixels. some of the pixels will lie outside the vessel circumference and the image is therefore formed from those pixels that lie inside the vessel. figure 5 shows the simulated contour for the permittivity distribution of both materials where the circular image is constructed using the available 1024 pixels. a typical frame of the model for image generation and display using labview is illustrated in figure 6. the image of the permittivity distribution is represented with an appropriate color scale to indicate the normalized pixel permittivity. the lower permittivity material (air) used is shown in blue, while the higher permittivity material is shown in red. fig. 5. illustration of the permittivity distribution represented with an appropriate color scale to indicate the normalized pixel permittivity. v. design and prelimenary test in this part, we present the preliminary measurements obtained with the developed prototype (8-electrode ect sensor). we conducted tests in the air using a function generator and a digital storage oscilloscope. gain measurements (normalized capacitance values) of each electrode were carried out and were compared with those found in simulation. fig. 6. diagram of image generation subvi and diagram of image display subvi. a. design requirements there are some reasons that determine the electrode location. if the tube wall is made up of dielectric material, the electrodes can be installed inside or outside it, but if the wall is conductive there is only one choice to design the electrode location (external electrode), but because the proposed design is employing dielectric material, the electrodes are put outside the pipe, as it is easier to design. the number of electrodes depends on capacitance value, circuit complexity, and data acquisition speed. if more electrodes are used, they provide a better image, but they are difficult to be measured. mostly, the number of electrodes used is 12 or 8 (in this paper we chose 8). a guard electrode is required to improve the measurement sensitivity, to prevent the electric field from reaching the ground and the end of the measuring electrode. they must be used if the length of measuring electrodes is less than approximately twice the sensor diameter. finally, it is important to add a discharge resistor. in order to avoid the static charge and the damage of a measuring sensor, the resistor must be connected between each electrode and driven guard and earth. typically, the value of the resistance is 1mω. if the capacitance values of inter-electrodes are around 1pf, an earthed screen is required around the electrodes to avoid unwanted or external signal. a photo of the typically developed prototype is shown in figure 8. fig. 7. normalized capacitance values obtained with preliminary tests and simulations. engineering, technology & applied science research vol. 11, no. 4, 2021, 7430-7435 7434 www.etasr.com ghaly et al: design and simulation of an 8-lead electrical capacitance tomographic system for flow … fig. 8. the developed prototype. b. measurements a photo of the gain measuring of each electrode is presented in figure 9. for this measurement, each electrode’s gain with respect to its neighboring electrode is performed. an input of 10v peak to peak signal is applied from an arbitrary function generator, and the output taken from each and every electrode is measured on digital storage oscilloscope. since the sensor is symmetrical, there are 3 values of capacitances (c1-2, c1-3, and c1-4) instead of the 28 values whatever the sensor is either filled with a material or not. fig. 9. illustration of gain measurement of ect sensor electrodes. from the results shown in figure 7, it can be seen that the gain for neighboring electrodes is higher than that of distant electrodes. these values of gain were simulated and measured with the sensor containing air and should be risen if any other material with different dielectric is inside the prototype. also, an asymmetrical capacitance distribution has observed since the use of a pcb copper foil with the join between electrodes 1 and 8 and small errors in the inter-electrode opening provide large errors in capacitance values between electrodes. table iii gives the designed lengths and measurements. vi. conclusion and future scope in this paper, the proposed mechanism is illustrated with the help of the powerful software tool labview. it was shown by the simulations that the internal condition of a closed object can be detected by an internal image taken by means of determining the dielectric permittivity distribution inside from measurements of the external capacitance. simulations were performed to get the values of capacitance from high and low permittivity for 8 electrode ect systems and the results illustrate the feasibility of such simulations for generating a 2d image reconstruction. table iii. design ed length s and measurements type length (cm) width or diameter (cm) pipe 30 15m electrodes 6 45 driven guards 8 45 earthed screen 4 along the diameter of the pipe with the existing technology, image data can be captured at 100 frames per second for a 12-electrode sensor and displayed on-line. for the proposed 8-electrode sensor, this image capture rate is drastically increased up to roughly 200 to 300 frames per second as the number of capacitance measurements is reduced. a typical hardware of the ect system with 8 outer electrodes covering a cylindrical tube of 15cm diameter with adjustable length, proper resolution and reasonable sensitivity was developed and simulated. this system is being employed with 8 electrodes, so 28 capacitance values were measured, collected, and analyzed in order to get the required image of the fluid flowing inside the tube. in the future, the developed prototype ect senor can be employed for the monitoring of oil or gas transportation or supply by means of underground/sea pipeline system or in a refinery plant. acknowledgement this project was funded by the national plan for sciences, technology and innovation (maarifah) – king abdulaziz city for science and technology – the kingdom of saudi arabia, award number (14-ele741-08). references [1] s. m. huang, a. b. plaskowski, c. g. xie, and m. s. beck, "tomographic imaging of two-component flow using capacitance sensors," journal of physics e: scientific instruments, vol. 22, no. 3, pp. 173–177, mar. 1989, https://doi.org/10.1088/0022-3735/22/3/009. 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[18] s. m. a. ghaly and s. al-sowayan, "a high b1 field homogeneity generation using free element elliptical four-coil system," american journal of applied sciences, vol. 11, no. 4, pp. 534-540, feb. 2014, https://doi.org/10.3844/ajassp.2014.534.540. engineering, technology & applied science research vol. 8, no. 5, 2018, 3366-3368 3666 www.etasr.com detho et al.: proposed remedies to prevent road traffic accidents (rtas) on highways in pakistan proposed remedies to prevent road traffic accidents (rtas) on highways in pakistan amir detho department of energy & environment engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan aamir_detho@yahoo.com saleem raza samo department of energy & environment engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan sfaizsamo@yahoo.com kishan chand mukwana department of energy & environment engineering, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan mukwana_99@yahoo.com imdad ali memon department of mechanical engineering quaid-e-awam university of engineering, science & technology, nawabshah, pakistan engineerimdad@yahoo.com umair ahmed rajput department of mechanical engineering quaid-e-awam university of engineering, science & technology, nawabshah, pakistan engr.umair@quest.edu.pk abstract—in pakistan, the number of roads and highways is increasing along with the number of road traffic accidents (rtas). many researchers attempted to collect data of rtas and to investigate their causes. keeping those causes and reasons for rtas in mind, remedies to prevent rtas on the highways in pakistan are proposed to make the roads and highways safer for traveling. keywords-causes of rtas; road traffic accidents (rtas); proposed remedies i. introduction in most rtas in pakistan, the main cause is the negligence of drivers, although mechanical faults and road deficiencies play major roles in accident occurrences. the highways were initially used as feeder to the railways in pakistan, but nowadays, they serve not only travellers but also agricultural producers, users and suppliers. agricultural products supply main markets and are linked to larger inland markets all over the country by the karachi port. highways present phenomenal increase in length, from 249,972km in 2000-01 to 263,356km by 2015‐16 and in the number of vehicles from 4,701,600, in 2000-01 to 17,317,600 in 2015-16 [1]. generally highways are of single or double lane. the maintenance and construction of roads are under the state government and national highway department. ii. previous research summary for this work, extensive literature survey was carried out to determine the findings in the area of rta causes. authors in [2] took data from pakistan bureau of statistics to fit linear, quadratic, cubic, logarithmic, inverse, exponential growth, logistic-curve and compound models for prediction. data is summarized in table i. authors in [3] state that road studies and road safety learning is very necessary for the road user. they propose the introduction of road safety for pre schooling students through animal world stories. elementary (primary) and middle level students must be aware and give a proper guidance about the sidewalk, road signs etc. higher level students must be able to learn about defensive driving, breaking distance, alcohol hazards and reaction times. random alcoholic blood concentration tests must be conducted along the road sides. it is concluded that the adoption of strict rules and regulations, more comprehensive rules and traffic controlling devices are essential. public transport drivers should have basic first aid training. rtas are globally the 8th leading cause of death and, according to who, rtas will become the 3rd cause of death by the year 2020, if not controlled properly [4, 13]. the available data is not trustworthy due to under reporting, however, rtas are one of the leading causes of death and injury worldwide. author in [5] states that huge losses due to road accidents were reported in tanzania, something that urged the government to take measures, however, the road accidents still kept increasing. a research was conducted, in a survey form to investigate the possible reasons of the road accidents. in the survey, participants were asked their opinion regarding the reasons of rtas. it was identified that driver mistakes were the main reason of the accidents. it was concluded that drivers should be better trained before they acquire their license. rtas cause not only economic losses but also intangible consequences such as pain, grief etc. [6]. the increasing number of vehicles is the one of the major causes of rtas. for reducing the impact of road accidents, many safety programs have been organized. authors in [6] concluded that for reducing rta number, safety programs of developed countries should be implemented. a little amount of research has been conducted on rtas in india, which is the second-largest engineering, technology & applied science research vol. 8, no. 5, 2018, 3366-3368 3667 www.etasr.com detho et al.: proposed remedies to prevent road traffic accidents (rtas) on highways in pakistan populated country in the world. to make the policies (regarding prevention of the road accidents) workable and effective, the safety plan must be based on local research and evidence. these plans must be designed to suit the local environment and circumstances [7]. flow complexity on highways is the main reason for rtas. it is estimated that 12 persons (in 100 accidents) were killed in 2011, whereas 7 persons were killed (in 100 accidents) in 2001. because of damaged roads in rural areas, road accidents are likely to happen [8]. author in [9] reports that in 2010, 10 rtas in every minute have been reported and one death caused by rtas occurred every 4 minutes. he concluded that it is difficult for the government to solve this problem alone. authors in [10] state that the abrupt increment in the number of vehicles on the same infrastructures is the major cause of the increased highway accidents in kerala. authors in [11], with the help of the geographic information system (gis), identified rta “black spots”. author in [12] collected data of the road accidents in kerala from 2010 to 2016. he found that 12 deaths occur per 100 accidents in 2016. nowadays, road traffic safety has become an issue of major concern. in pakistan, population increases along with traffic control problems. rta related fatalities and injuries have great impact on the socioeconomic development. according to world health organization [13], each year an estimated 1.2 millions of people lose their lives and around 50 millions get injured due to rtas worldwide. rtas are caused by technical faults, dangerous driving, bad weather, road design and signage. however, in terms of automobile technology, safety has been achieved at a certain level. our research group conducted a two-year survey on hyderabad-karachi highway in terms of traffic accidents, loss of lives and vehicles, and rta causes [14]. results revealed that careless driving is the major cause of rtas on the motorway. data regarding loss of human lives and damaged vehicles in rtas due to different reasons are summarized in table ii. table i. road traffic accidents during 2006 2016 year number of accidents accidents persons vehicles involved fatal non-fatal killed injured 2006-07 10466 4535 5931 5465 12875 11481 2007-08 10466 4610 5856 5615 12096 11456 2008-09 9496 4145 5351 4907 11037 10322 2009-10 9747 4378 5369 5280 11173 10496 2010-11 9723 4280 5443 5271 11383 10822 2011-12 9140 3966 5174 4758 10145 9986 2012-13 8988 3884 5104 4719 9710 9876 2013-14 8359 3500 4859 4348 9777 9423 2014-15 7865 3214 4651 3954 9661 8949 2015-16 9100 3591 5509 4448 11544 10636 table ii. casualties, damages and rta causes [14] year damages totals causes careless driving tire burst brake failure road condition pedestrian crossing 2015 deaths 56 27 16 9 3 1 injuries 170 90 36 28 16 0 vehicles 141 93 19 20 4 5 2016 deaths 53 19 7 14 13 0 injuries 123 50 24 22 24 3 vehicles 110 52 12 15 30 1 iii. proposed remedies to prevent rtas rtas not only take human lives and damage properties but also can lead to social problems. it is important to prevent or at least minimize rtas. keeping in mind this and the rta causes, the following are the proposed remedies to prevent/minimize rtas in pakistan.  it is necessary to provide proper education to drivers and proper driving habits should be enforced.  the process of issuing driving licenses must be tough and the license should be issued after proper examinations.  in the presence of bad road conditions, appropriate sign boards should be erected along the highways.  vehicles not in a good condition should not be allowed to enter motorways.  the roads should be maintained properly. the black spots (where repeated accidents have happened) should be looked into for proposing possible remedial measures.  a nationwide campaign should be launched to educate and warn people about traffic laws. regular inspections should be made necessary for new and existing roads.  over speeding offenders should stop being conveniently ignored by the enforcing agencies.  commercial vehicles should be road worthy and a system of banning the entry of such vehicles in bad shape should be implemented.  a proper check should be done regarding all safety aspects before allowing rickshas on highways.  while designing new highways, proper attention should be given on facilities for pedestrian and handicapped people.  immediate legislation should be undertaken without any delay.  authorities and parents should discourage underage kids from driving.  it is quite difficult to drive in night time due to the head lights of vehicles coming from the opposite side. therefore it is highly recommended to divide the lanes by walls of sufficient height or vegetation.  to stops animals, fences along the road should be erected.  motorcyclists, bicyclists and bull/donkey/horse carts should be prohibited from entering highways.  sign boards and traffic signals must be provided wherever it is necessary.  every highway should be made to have three lanes in each direction. on two lanes would be sufficient for roads.  one of the major causes of rtas in pakistan highways is that goods are transported on trucks and trailers. to prevent these from running on roads, the railway system should be improved. engineering, technology & applied science research vol. 8, no. 5, 2018, 3366-3368 3668 www.etasr.com detho et al.: proposed remedies to prevent road traffic accidents (rtas) on highways in pakistan  it should be mandatory for trucks and tractors to have lights behind the trolleys. iv. summary and conclusions based on literature and data review, some remedy measures were proposed to prevent rtas on highways and roads. references [1] pakistan economic survey, available at: http://121.52.153.178:8080 /xmlui/handle/123456789/14893 [2] m. imran, j. a. nasir, “road taffic accidents, prediction in pakistan”, the professional medical journal, vol. 22, no. 6, pp. 705-709, 2015 [3] n. jha, d. k. srinivasa, g. roy, s. jagdish, “epidemiological study of road traffic accident cases: a study from south india”, indian journal of community medicine, vol. 29, no. 1, pp. 20-24, 2004 [4] g. al-haji, road safety development index: theory, philosophy and practice, phd thesis, linkoping university of technology, 2007 [5] r. r. akkarro, “peoples opinion on the causes of road accidents in selected places of tanzania”, european journal of social sciences, vol. 9, no. 4, pp. 615-626, 2009 [6] b. b. pillai, j. kurian, “causes and consequences of road accidents in kerala”, international journal of research in it & management, vol. 1, pp. 83-95, 2011 [7] m. m. ruikar, “national statistics on road traffic accidents in india”, journal of orthopedics, traumatology and rehabilitation ,vol. 6, no.1, pp. 1-6, 2013 [8] b. v. sreekumar, v. sreedevi, “impact of road accidents in kerala during 2001 to 2011-a case study”, vol. 6, no. 1, pp. 51-57, 2014 [9] d. pawan, “road safety and accident prevention in india”, international journal of advanced engineering technology, vol. 5, no. 2, pp. 64-68, 2014 [10] b. b. pillai, g. d. singh, “scenario of road accidents in kerala and its ill effects”, international journal in management and social science,vol. 3, no. 3, pp. 559-567, 2015 [11] l. isen, a. shibu, m. s. saran, “identification and analysis of black spots using geographic information system”, international journal of innovative research in science, engineering & technology,vol. 2, no. 1, pp. 131-139, 2013 [12] a. chand, “a case study of raod accidents in kerala during 2010 to 2016”, international journal of innovative research in science, engineering & technology, vol. 6, no. 4, pp. 199-203, 2017 [13] world health organization (who), word report on road traffic injury preventation: summary, who, 2004 [14] a. detho, s. r. samo, k. c. mukwana, k. a. samo, a. a. siyal, “evaluation of road traffic accidents (rtas) on hyderabad karachi m-9 motorway section”, engineering, technology & applied science research, vol. 8, no. 3, pp. 2875-2878, 2018 microsoft word etasr_v11_n2_pp6956-6964 engineering, technology & applied science research vol. 11, no. 2, 2021, 6956-6964 6956 www.etasr.com çamur et al.: a techno-economic comparative study of a grid-connected residential rooftop pv panel a techno-economic comparative study of a gridconnected residential rooftop pv panel the case study of nahr el-bared, lebanon hüseyin çamur department of mechanical engineering engineering faculty near east university nicosia, cyprus huseyin.camur@neu.edu.tr youssef kassem department of mechanical engineering engineering faculty near east university nicosia, cyprus yousseuf.kassem@neu.edu.tr ebaa alessi department of mechanical engineering engineering faculty near east university nicosia cyprus ibaa_a88@hotmail.com abstract—lebanon suffers from daily electricity shortages. the country has paid much attention to renewable energy sources, particularly solar, to gradually replace conventional energy. installing a photovoltaic (pv) system becomes increasingly attractive for residential consumers due to the rising electricity tariff rates while it reduces the dependency on domestic power generators. no known study has dealt with the investigation of potential grid-connected rooftop pv systems with various suntracking modes and pv technologies in nahr el-bared, lebanon. consequently, the main objective of the current paper is to investigate the feasibility of a 5kw grid-connected pv system of various technologies (mono-crystalline silicon and polycrystalline silicon) and sun-tracking modes including fixed tilt and 2-axis systems for rooftop households in lebanon. the nahr el-bared camp was the case study was of the paper. retscreen expert software was used to evaluate the techno-economic performance of the proposed systems. the results show that the annual electrical energy from a fixed 5kw pv panel tilted at an optimal angle ranged from 8564.47kwh to 8776.81kwh, while the annual electrical energy from the pv tracking system was within the range of 11511.67-12100.92kwh. this amount of energy output would contribute significantly to reduce the energy shortage in the country. a typical household was selected to establish a load profile and load supply during both grid availability and outage periods. the highest energy consumption that can be covered by the pv systems was recorded during the spring and summer seasons. also, the average energy production cost ranged from 0.0239 to 0.0243$/kwh for all the proposed systems. it was concluded that a 5kw grid-connected rooftop pv system could be economically justifiable. finally, this study tried to increase the awareness about utilizing pv sun-tracking systems and the feasibility of small-scale grid-connected rooftop pv systems in the selected regions. the results of this research can help investors in the energy and building sectors. keywords-lebanon; nahr el-bared camp; rooftop pv system; grid-connected; retscreen i. introduction energy is an indispensable need, which, until quite recently, was met with the consumption of conventional fossil fuels. however, the use of fossil fuels has polluted the environment and led to climate change mainly due to greenhouse gas emissions [1]. the environmental problems resulting from the increasing consumption of fossil fuels have encouraged scientific researchers to search for alternative sources of energy that would affect less the environment [2, 3]. many researchers found that renewable energy sources, like solar and wind, play a significant role in reducing greenhouse gas (ghg) emissions. for instance, authors in [4] concluded that the utilizing of solar thermal energy provided an important step towards sustainable zero-emission production in the industry. authors in [5] found that renewable energy sources have a high potential for providing an increasing share of future energy growth without increasing ghg emissions. authors in [6] reported that the production of electricity with the use of solar systems can protect the environment. recently, solar power has been considered as a potential, economically viable, and environment friendly energy source. authors in [7] evaluated the solar energy potential in pakistan based on data from 58 meteorological stations covering the whole country. the results indicated that in an area of 100m 2 , 45 mw to 83 mw power per month may be generated in the southern punjab, sindh, and balochistan regions. authors in [8] compared the potential of utilizing wind energy and solar energy as power sources for a small household in three urban regions in northern cyprus. the results showed that the selected regions have huge solar corresponding author: youssef kassem engineering, technology & applied science research vol. 11, no. 2, 2021, 6956-6964 6957 www.etasr.com çamur et al.: a techno-economic comparative study of a grid-connected residential rooftop pv panel potential compared to the wind energy potential. authors in [9] studied the feasibility of a 12mw grid-connected wind/pv project in two regions of northern cyprus. the results indicated that the selected regions have a high potential compared to wind energy. authors in [10] evaluated a technoeconomic analysis of a 50mw wind/pv system in various locations in libya. the results showed that a solar pv plant project was more economical than a wind farm. authors in [11] reported that the production of electricity using solar systems would have a great material impact on the lives of low-income households as compared to their high-income counterparts in united states. authors in [12] investigated the feasibility of a 10mw grid-connected pv system at different locations in libya. the results indicated that the proposed system offered the best solution for generating electricity in libya. lebanon suffers from problems in the electricity sector. generally, electricity cuts range from 3 to 13 hours per day, depending on the area. as a result, families are forced to pay two electricity bills: one to the electricity provider of lebanon (electricite du liban-edl) for the energy it provides, and another for generators, in which many families have to invest in order to ensure continuous access to electricity. moreover, the electric rationing, has returned at a high rate due. presently, the demand is estimated to be more than 3458mw, while the current capacity is around 2000mw. besides, the cost of generating electricity is high. with peak time electricity demand of about 3458mw, which is probably less than its real size, the edl only provides a part of this demand, and the remaining demand is met through private diesel generators, illegally connected to low voltage distribution networks. most of the households depend on this source despite its very high prices and its low capacity. the potential for utilizing wind and solar energy in lebanon has been investigated in [13-22]. authors in [13] investigated the feasibility of 100mw gridconnected wind/solar systems in the rayak region. the results indicated that wind power was more efficient than solar power in the selected region. authors in [17] investigated the potential of wind energy at 3 coastal regions of lebanon. the results showed that small-scale wind turbines offered high wind potential when compared to other types of wind turbines. similar results were found in [18, 19]. furthermore, according to the solar atlas map, the global horizontal irradiation (ghi) and direct normal irradiation (dni) values vary from 1600kwh/m 2 to 2000kwh/m 2 and 1700w/m 2 to 2200w/m 2 , respectively. based on the values of ghi and dni, it is concluded that the country has high solar resources, being categorized as good, excellent, or outstanding according to solar potential classes [23]. the coastal regions have lesser values of ghi and dni compared to other regions based on the solar atlas map. according to the wind atlas map, the mean wind speed and wind power density are within the range of 2.53m/s and 25-75w/m 2 , respectively at a height of 10m in coastal regions. therefore, it can be concluded that the country has a huge solar energy potential compared to wind energy. the conclusions after reviewing the previous studies are: • lebanon has a huge solar energy potential when compared to wind energy. • solar power systems can reduce fossil fuel consumption and co2 emissions. • no scientific studies proposed small-scale grid-connected rooftop pv solar power systems to meet the electricity demand of households in nahr el-bared. • to the best of our knowledge, no studies investigated the economic feasibility of small-scale pv systems with various sun-tracking systems (fixed-tilt and two-axis tracking systems) in lebanon. thus, there is a of literature discussing the performance of rooftop pv systems in lebanon. also, according to [13], citizens rely on domestic power generators or small home generators during the periods of power outage, adding financial burdens to the citizens. furthermore, none of the reviewed studies addresses the case of nahr el-bared in lebanon. according to united nations relief and works agency in 2018, the total energy generated from the generators in the nahr el-bared is found to be about 80mwh/day. therefore, grid-connected pv systems can be an attractive solution to reduce electricity consumption, dependence on utility power, and increase electricity generation from renewable energy sources for residential electricity users. furthermore, household rooftop pv systems will create significant savings in the cost of electricity bills. additionally, such systems can help the edl to reduce fossil fuel consumption and make electricity available throughout the day. consequently, the study aims to investigate the techno-economic and environmental sustainability of rooftop pv systems in nahr el-bared. to achieve this, the nasa's database has been utilized as a source of meteorological information. sun-tracking systems, including fixed tilt and 2-axis systems, are investigated in this study. moreover, numerous economic indices including net present value, payback period, annual life cycle savings, internal rate of return, and the levelized cost of energy have been taken into consideration as measure of performance indicators for the proposed projects. to this aim, retscreen software was used in the present study. the proposed system can provide valuable inputs for the development of new policies and innovative solutions for the pv market growth in the country. ii. materials and methods the solar energy potential in the selected region in the northern part of lebanon is discussed based on nasa's average monthly global solar radiation and air temperature. besides, the grid-connected rooftop pv system is investigated as a solution for the electricity crisis with the use of the retscreen software. figure 1 shows the methodology used in this study. a. study area and data nahr el-bared camp is one of the largest palestinian camps in the northern part of lebanon, located near tripoli and near the mediterranean sea at 34°30'28.19"n latitude and 35°57'23.99"e longitude. from a topographic perspective, the highest and lowest average elevation reach 27m and 12m above the sea level respectively. the area of the old camp is estimated to be about 2km². according to united nations relief and works agency (2018), nahr el-bared camp is divided in two engineering, technology & applied science research vol. 11, no. 2, 2021, 6956-6964 6958 www.etasr.com çamur et al.: a techno-economic comparative study of a grid-connected residential rooftop pv panel camps, the old camp with an average apartment area of 78m 2 and total built residential area of 360000m 2 and the new camp with an average household area of 150m 2 and total built area of 300000m 2 . several studies evaluated the solar energy potential in different locations using the nasa database [24, 25]. moreover, the nasa database showed good agreement with the measured data of global solar irradiation of previous studies [25-27]. therefore, the monthly nasa database is utilized in the current study to investigate the potential of solar energy in the selected region. fig. 1. the flowchart of the analysis steps of the current study. b. design of the pv power system for the proposed small-scale grid-connected pv system, mono-si-cs6x-300m and poly-si cs6x-310p were selected which are manufactured by canadian solar. table i summarizes the specifications of the selected modules. the total number of modules and the area required for the proposed system are 17 modules and 33m 2 . the description method of designing a solar pv system is available in [10, 13, 25]. power generating factor (pgf): ��� � ������ � (1) energy demand (ed): �� � � �� (2) solar pv energy required (spver): �� �� � ��� � ��� (3) pv module sizing: ���� � �������� (4) ���� � �������� (5) inverter sizing (is:) �� � ��� � �� (6) where si is solar irradiance, sh is the sunshine hours, stci is standard test condition irradiance, ecal is the energy consumption of all loads, twpr is total watt peak rating, pgf is panel generation factor, pvms is pv module size, pvopr is pv output power rating, fs is the factor of safety, per is peak energy requirements, els is energy lost in the system and the factor of safety is 1.3. moreover, one inverter with 6kw capacity and 97.9% efficiency is used to convert the dc into ac and feed it directly to the grid (table ii). engineering, technology & applied science research vol. 11, no. 2, 2021, 6956-6964 6959 www.etasr.com çamur et al.: a techno-economic comparative study of a grid-connected residential rooftop pv panel table i. pv module specification item specification module technology mono-si poly-si manufacturer canadian solar model mono-si cs6x-300m poly-si cs6x-310p nominal power [w] 300 310 open-circuit voltage [v] 45 44.9 short-circuit current [a] 8.74 9.08 voltage at point of maximum power [v] 36.5 36.4 current at point of maximum power [a] 8.22 8.52 module area [m2] 1.919 1.918 efficiency [%] 15.63 16.16 warranty [year] 25 25 cost [usd/wdc] 0.83 0.8 table ii. specifications o f the selected inverto r input dc parameters value mpp voltage range vdc (at 25°c / at 50°c) 850v-1425v/1275v min. input voltage vdc,min / start voltage vdc,start 778v/878v max. input voltage vdc, max 1500v max. input current idc, max (at 25°c / at 50°c) 3000a / 2700a max. short-circuit current rating 4300a output dc parameters value nominal ac power at cosφ =1 (at 25°c / at 40°c / at 50°c) 2500kva/2350kva/2250kva nominal ac power at cosφ =0.8 (at 25°c / at 40°c / at 50°c) 2000kw/1880kw/1800kw nominal ac iac, nom = max. output current iac, max 2624a c. economic analysis software like retscreen and homer are used to estimate the economic indicators for financial analysis. several researchers have utilized retscreen to investigate the feasibility of a grid-connected pv system [8, 10]. in the present study, 6 economic indicators, namely npv, lcoe, irr, sp, ep, and alcs are estimated using retscreen. also, the ghg emission reduction, energy production, and the capacity factor (cf) for the proposed systems are determined using retscreen. net present value (npv): ��� � ∑ !"#$%&!'()* (7) levelized cost of energy (lcoe): � +� � ,-. 01 20,3 045% 671537.5, 01 56523%72738 95(5%:35; 045% 3<5 671537.5 (8) internal rate of return (irr): + � ∑ !"#$���&!'()* (9) simple payback (sp): �� � =��> ?!?@$ abcb$ de$ fgfh=> i&k$ lm?nh (10) equity payback (ep): �� � ∑ ('()* (11) annual life cycle savings (alcs): �� � � '��o @p#= o "oq@&rs (12) ghg reduction cost (grc): �� � tu �∆fgf (13) benefit-cost ratio (b-c): w − � '��$"#=1y& "#=1y&�z (14) capacity factor (cf)): � � �im[��\]^* (15) where �0-3 is the energy generated per year, � is the installed capacity, n is the project life in years, ( is the after-tax cash flow in year n, r is the discount rate, c is the total initial cost of the project, _; is the debt ratio, b is the total benefit of the project, �� is the incentives and grants, 5(35% is the annual energy savings or income, :``: is the annual capacity savings or income, �� is the annual renewable energy (re) production credit income, ��� is the ghg reduction income, 0&a is the yearly operation and maintenance costs incurred by the clean energy project, %-56 is the annual cost of fuel, which is zero for renewable projects, and ∆��� is the annual ghg emission reduction. iii. results and discussion a. monthly solar radiation it is well known that the performance of pv modules is influenced by several climate parameters including the meteorological factors of the specific location, and solar irradiance is one of the most essential among them. several studies utilized various simulation tools to assess the performance simulation of small-scale grid-connected rooftop pv systems. authors in [28] assessed the feasibility of a 6.4kw grid-connected rooftop pv system in ujjain, india by using 4 simulation tools. the results indicated that pv*sol is an easy, fast, and reliable software tool for the simulation of the solar pv system in the selected region. authors in [29] investigated the performance of a 1mw grid-connected rooftop pv system in an educational institute in india using 3 simulation tools and the actual data and the pvgis has the lowest average mean bias error and average normalized mean bias error compared to the other two tools (pvsyst and pvwatt). in this paper, the performance of the developed pv systems is estimated by 2 simulation tools, pvgis and retscreen. with the pvgis (figure 2), the highest solar radiation was recorded in july with a value of 246.892kwh/m 2 while the minimum was obtained in december with a value of 76.211kwh/m 2 . in the retscreen simulation tool, the highest value of solar radiation was recorded in july (250.48kwh/m 2 ) as shown in figure 2. moreover, it was found the annual solar radiation is 1941 kwh/m 2 and 2010kwh/m 2 , given by pvgis and retscreen engineering, technology & applied science research vol. 11, no. 2, 2021, 6956-6964 6960 www.etasr.com çamur et al.: a techno-economic comparative study of a grid-connected residential rooftop pv panel respectively. it is noticed that the pvgis and retscreen almost give the same annual value of solar radiation. authors in [25] found that the estimated values of solar radiation, obtained from pvgis and retscreen, are close to the actual data. based on the value of solar radiation at the selected location, it was found that the solar source of nahr el-bared is categorized as excellent (class 5) according to [23]. therefore, this region is suitable for installing a pv system. fig. 2. average monthly solar radiation at the studied location. b. electricity generation and capacity factor the optimum slope angle and azimuth angle for the fixedtilt system are estimated with the photovoltaic geographical information system (pvgis) simulation tool. several scientific studies have used pvgis to find the slope angle and azimuth angle for pv systems [30, 31]. generally, the pvgis provides the optimum slop and azimuth angles that give the maximum annual global solar radiation for a specific location. the slop and azimuth angles for the selected study were estimated to be 30 ° and -3 ° respectively. the economic feasibility of the developed system is investigated with retscreen. according to [32, 33], solar radiation and the number of clear sunny days are important factors that affect the annual energy exported to the grid by the panel and the capacity factor (cf). table iii shows the monthly and annual electricity generation (eg) and cf of the proposed systems. for the fixed-tilt system, it is found that the total annual value of eg is 8564.47kwh for mono-si and 8776.81kwh for poly-si. the total annual eg for the two-axis tracking system is within the range of 11511.67kwh (mono-si) to 12100.92kwh (poly-si). the maximum value of eg is recorded in july for all the proposed systems. it can be concluded that the amount of output power could be increased from 34% to 37% by a two-axis tracking system. furthermore, it is found that the cf values of both systems vary from 19.01% to 26.43% for the fixed-tilt and twoaxis sun-tracking systems. these observations can be supported by the findings of other researchers who analyzed the feasibility of grid-connected pv systems. for instance, authors in [34] found that the cf of the proposed pv system in oman was within the range of 16-23%. authors in [35] found that the value of cf of grid-connected pv systems with different suntracking modes was within the range of 17.54-27.42%. authors in [35, 36] concluded that the use of the two-axis instead of the fixed-tilt option significantly increases the generated electricity. therefore, it can be concluded that the value gotten from the present study for the selected location is compatible with the acceptable values. consequently, it is technically sustainable to build a grid-connected rooftop pv system in nahr el-bared. table iii. electricity generation in kwh and capacity factor for the developed systems month fixed-tilt axis two-axis mono-si poly-si mono-si poly-si jan. 514.14 526.89 663.81 680.27 feb. 549.70 563.33 663.81 700.90 mar. 726.28 744.29 663.81 963.47 apr. 778.32 797.61 1015.02 1040.19 may 861.40 882.76 1261.22 1292.49 jun. 853.38 874.54 1293.29 1325.35 jul. 864.42 885.85 1296.47 1328.61 aug. 852.87 874.02 1246.95 1277.86 sep. 805.77 825.75 1083.05 1109.90 oct. 718.62 736.43 970.07 994.12 nov. 562.21 576.15 730.92 749.05 dec. 477.36 489.19 623.25 638.70 annual [kwh] 8564.47 8776.81 11511.67 12100.92 cf [%] 19.17 19.01 26.43 26.21 c. performance of the proposed systems the performance of the aforementioned sun-tracking systems was evaluated by the estimation of the economic and environmental factors for each system. in this study, the financial parameters (table iv) inflation rate, discount rate, reinvestment rate, debt ratio, debt interest rate, were considered as input variables for the estimated economic indicators assumed based on [10, 13, 25, 35, 37-40]. in the present study, the system cost is around $5261 and $5243 for mono-si and poly-si fixed-tilt and $7365 and $7347 for mono-si and polysi two-axis tracking systems which are estimated based on recent market data in the country and are consistent with the cost prices available in the literature. in general, the net present value of any investment project can be defined as the difference between the present value of cash inflows and outflows of the project [41]. therefore, it is clear that in order to calculate the net present value, there must be a discount rate based on which the cash flows associated with the investment are deducted [42, 43]. therefore, it can be concluded that the difficulty in determining the discount rate that is used as a basis for calculating the net present value has an impact on the investment decision. additionally, the average credit interest rate can be used as the discount rate, or the interest rate on project loans can be considered as the discount rate [44]. there is an inverse relationship between the discount rate and the current value of the project, which means that choosing a discount rate is very important [45]. the debt ratio is the financial ratio used to assess and measure the leverage of an entity over the relationship between total debt (long-term debt and short-term debt) and total assets [46]. if the ratio is higher than 1, this means that the total liabilities are higher than the total assets, which means that the facility's leverage is high and it faces more financial risks. if the ratio is less than 1, then this means that the total liabilities are less than the assets, which means that the facility is financially sound. besides, highinterest rates lead to an increase in the future value of the project as the period of investment leads to a future value increase. the results regarding the economic performance of the 5kw grid-connected rooftop pv system for all the developed pv systems are summarized in table v. the obtained results show that the value of npv for the proposed systems is positive and makes the project to be financially and engineering, technology & applied science research vol. 11, no. 2, 2021, 6956-6964 6961 www.etasr.com çamur et al.: a techno-economic comparative study of a grid-connected residential rooftop pv panel economically feasible [24, 35]. also, it is found that the proposed projects in the selected location are economically acceptable based on the internal rate of return, which is a measure of a project’s profitability [24, 47]. it is observed that the developed pv project has the longest value of ep of 3.2 years for mono-si and the lowest one for poly-si system with a value of 3.1 years. for the fixed-tilt system, the sp values are 6.14 years and 5.97 years for mono-si and poly-si respectively. for the two-axis tracking modes, the sp values are 6.24 and 6.07 years respectively for mono-si and poly-si. the results indicate that the pv projects in the region make financial sense. table iv. financial parameters factor unit value inflation rate % 2.5 discount rate % 0 reinvestment rate % 9 project life year 25 debt ratio % 50 debt interest rate % 0 debt term year 20 electricity export escalation rate % 5 table v. economic perfo rman ce –current study parameters fixed-tilt axis two-axis mono-si poly-si mono-si poly-si irr [%] 15.99 16.14 15.92 16.05 sp [year] 6.14 5.97 6.24 6.07 ep [year] 3.21 3.12 3.26 3.17 npv [$] 37658.51 38740.63 51809.73 53294.87 alcs p$/year] 1506.34 1549.63 2072.39 2131.79 npv [$] -248.79 -249.75 -248.26 -249.20 lcoe [$/kwh] 0.0246 0.0239 0.0249 0.0243 performance [%] 82.63 81.90 91.62 93.16 table vi. economic performan ce comparison ref. country size/ load tracking mode lcoe [$/kwh] [8]a northern cyprus 6.4kw fixed tilt 0.0194-0.0199 [10]a libya 5kw fixed tilt 0.0307-0.0270 [38]a norway 2.07kw fixed tilt 0.149-11.632 [48]b india 6kw fixed tilt 2.944 two-axis adjustment tracking 3.165 [49]c nigeria 1kw two-axis continuous tracking 0.299 [50]a jordan 7.98kw fixed tilt 0.097 two-axis continuous tracking 0.122 [51]b india 5.19 kwh/d fixed tilt 0.226-0.287 two-axis continuous tracking 0.523-0.732 [52]a spain 1kw fixed tilt 0.075 two-axis continuous tracking 0.109 [53]c iraq 4kw fixed tilt 0.09 [54]a europe 4kw fixed tilt 0.120-0.390 [55]a indonesia 3kwp fixed tilt 0.09 [56]a iraq 5kw fixed tilt 0.078 cs lebanon 5kw fixed tilt 0.0239-0.0246 two-axis continuous tracking 0.0243-0.0246 cs: current study, a: grid-connected pv system, b: stand-alone pv with micro wt hybrid power system, c: stand-alone pv system the lowest value of lcoe is found for poly-si systems as shown in table v. the lcoe value of the proposed projects is compared with the existing value of small-scale pv systems in the literature. table vi summarizes the economic analysis of solar projects with various tracking modes in different countries. it is found that the lcoe values of the proposed systems are within the range of the maximum (3.165$/kwh) and minimum (0.0199$/kwh) of lcoe values obtained from the literature. it is noticed that the value of lcoe is slightly increased by 4.23% when the two-axis system is used. this increment of lcoe is primarily due to the high cost of the twoaxis system. the developed systems provide a very good insight into the economic viability of the project for all regions. additionally, the obtained results demonstrated that the development of the proposed 5kw pv power system is economically acceptable due to the obtained favorable economic results. d. the case of a solar pv system for household electricity generation this section aims to evaluate the techno-economic performance of 5kw grid-connected pv systems for rooftop pv systems. designing the electrical load is an essential part of this section. the energy demand (�60:; ) of the considering household can be estimated by [57]: �60:; � ∑ �cdc�c'ab[?ei@fc)# (16) where �c is the rated power of the j-th kind of household appliance (kw), nj is the number of the j-th kind of household appliances, �c is the used hours per day of the j-th kind of household appliance (h/day) and ncategory is the category number of household appliances. according to [58, 59], lighting, tv, air conditioning, refrigerator, electric cooker, washing machine, water heater, and small power appliances are the most important energyconsuming household devices. in this case, the chosen house is equipped with efficient appliances. the characteristics of this house are: • room number: three rooms. • lighting: rooms, kitchen, toilet, bathroom, courtyard, and corridor. • appliances: refrigerator, tv, water heater, computer, laptop, washing machine, air conditioner, and fan. the total energy consumption for the chosen house is estimated as 20kwh/day. as mentioned previously, the total annual energy generating from both pv systems is varied from 8564.47kwh to 8776.81kwh and 11511.67kwh to 12100.92kwh for fixed-tilt and two-axis tracking systems, respectively. figure 3 shows the energy consumption covered by the proposed pv systems and grid for each month. it is observed that around 13% out of the total energy consumption is covered by the grid and the remaining is supplied by a fixed-tilt pv system, which is about 87% for the winter season. this is due to a heavy electrical load connected in the system like a water heater. for the rest of the year, the pv systems could cover all engineering, technology & applied science research vol. 11, no. 2, 2021, 6956-6964 6962 www.etasr.com çamur et al.: a techno-economic comparative study of a grid-connected residential rooftop pv panel the energy consumption. also, due to the length of the day that depends on sun altitude, the geographical latitude of the location, declination angle of the sun, and hour angle, the amount of energy production from the pv system will be increased. (a) (b) (c) (d) fig. 3. monthly variation of energy generation and energy consumption. iv. limitations and conclusions due to rising electricity tariff rates and the potential reduction of the dependency on domestic power generators in lebanon, installing pv systems has become increasingly attractive for residential consumers, a trend that is supported by the reviewed studies. before starting the main conclusions in the present study, it is essential to acknowledge the limitations of this work. first, the financial parameters were assumed based on historical values in the literature. second, the influence of various parameters such as dust, irradiation intensity, air temperature, and relative humidity were neglected due to limitations of the retscreen software. third, the cost of the proposed projects was estimated based on the existing costs in the literature. the findings from the present study showed that the annual value of solar radiation for the selected region is 2010kwh/m 2 . based on annual global solar irradiation, the analysis indicates that the selected region in lebanon has a potential for the distribution of pv power systems in residential applications. moreover, the annual energy output showed that the 5kw grid-connected pv system in nahr el-bared was within the range of 8564.47-8776.81kwh and 11511.6712100.92kwh respectively when fixed tilt and two-tracking systems have been used. based on this analysis, it was found that the highest energy consumption that can be covered by pv systems is recorded in spring and summer seasons. the average energy production cost ranged in 0.02390.0249$/kwh for all the proposed systems. the electricity price depends on the amount of energy consumption, i.e. the energy cost calculation starts from 0.025$/kwh for energy consumption of 0-100kwh, 0.04$/kwh for 100-300kwh, 0.0584$/kwh for 300-400kwh, 0.0875$/kwh for 400500kwh, and 0.146$/kwh over 500kwh. therefore, the energy production cost of the proposed systems is competitive with the electricity tariffs. furthermore, it was found that the difference between the energy production cost from a fixed-tilt system and from a two-axis tracking system is lower than 2%. it can be concluded that a 5kw grid-connected pv tracking system is economically justifiable. the results of this paper demonstrate that a small-scale grid-connected rooftop pv system in the nahr el-bared has the potential to solve the electricity issue in the area, reduce the consumption of fossil fuels and environmental pollution by minimizing the emissions of co2. the present study tried to increase the awareness about utilizing pv sun-tracking systems and the feasibility of small-scale grid-connected rooftop pv systems in the studied region. the results of this research can help the investors in the energy and building sectors and accelerate an informed transition towards a more sustainable future. acknowledgments the authors would like to thank the faculty of engineering and especially the mechanical engineering department at near east university for their support and encouragement. references [1] f. chermat, m. khemliche, a. e. badoud, and s. latreche, "technoeconomic feasibility study of investigation of renewable energy system for rural electrification in south algeria," engineering, technology & applied science research, vol. 8, no. 5, pp. 3421–3426, oct. 2018, https://doi.org/10.48084/etasr.2253. 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the use of credit cards, has resulted in the emergence of new security flaws that pose threats to customers and enterprises worldwide. e-commerce and other forms of online monetary transactions have become essential in the manufacturing and service sectors, propelling the global economy. the widespread and dependent connectivity of mobile payment systems using credit card transactions presents chances for fraud, risk, and security breaches. in light of the importance of accurately predicting fraud incidents through payment procedures, this study investigated the credit card payment methods used for movie tickets, using the machine learning logistic regression method to analyze and predict such incidents. this study used a dataset from cinema ticket credit card transactions made in two days of september 2013 by european cardholders, including 284,807 transactions out of which 492 were fraudulent purchases. the results of the proposed method showed a prediction accuracy of 99%, proving its high prediction performance. keywords-fraud prediction; movie theater; credit card; machine learning i. introduction credit card frauds have a negative impact not just on customers, but also on businesses [1]. along with the rise in the popularity of credit card use and online transactions, there is also an increase in fraudulent activity. therefore, it is vital to detect fraudulent use of credit cards to prevent monetary losses and preserve the personal and financial data of consumers [2]. identifying fraudulent activity on credit cards can be accomplished using several methods from various angles. rule-based systems or machine learning algorithms can examine patterns of normal behavior and identify deviations from the norm [3]. trust is another issue that needs to be addressed in terms of credit card concerns [4]. payment systems are the engine that drives e-commerce business, and a substantial amount of trust and security in cutting-edge technology is necessary [5]. furthermore, it is not unusual for mobile users to switch to new solutions, adjust their payment routines, and encounter other types of security challenges [6-7]. this study used a machine learning model to predict fraudulent activity in credit card payment transactions. today, electronic payment methods are increasingly growing and are increasingly vital and convenient [8-9]. several studies have shown that phone-based payments are a crucial and necessary addition to the available payment retail [10]. electronic payment systems are particularly vulnerable to fraud and cyber security breaches since they store sensitive consumer information such as id, card number, card name, purchase history, and more [11]. because of all these interconnected factors, it is essential to examine the problem of credit card fraud from a variety of perspectives to determine how it can be resolved. this study also considered other dimensions associated with electronic payment operations to detect unusual or suspicious behaviors, taking into account additional facets related to electronic payment operations, such as the geographic location of transactions. for instance, if a credit card is used unexpectedly multiple times in a short period, this could be indicative of fraudulent activity [12-13]. another aspect lies in the analysis of user behavior to identify any unique patterns that may emerge. when a user suddenly starts making large transactions or uses his card at irregular times, this may be an indication of fraudulent activity [14]. machine learning is one of the most important fields in this sector and currently depends on algorithms that can boost an organization's productivity and performance. there are four distinct methodologies of machine learning: supervised, unsupervised, semi-supervised, and reinforced learning [1518]. this study used logistic regression (lr) as a classification algorithm to assign the data to a discrete set of classes. lr resembles the linear regression model, however, it uses a more complex cost function called sigmoid function or logistic function rather than a linear one [19]. lr is a method for making predictions and its outcomes are converted into engineering, technology & applied science research vol. 13, no. 3, 2023, 10941-10945 10942 www.etasr.com alshutayri: fraud prediction in movie theater credit card transactions using machine learning probability values. to limit the cost function to values between 0 and 1, an lr hypothesis must be taken into account. as a result, linear functions are unable to adequately describe this because they can have a value that is either more than 1 or less than 0, both of which are prohibited by the lr hypothesis [19]. when using a classification strategy, lr is applied to the observations of the discrete classes involved, operating on the principle of probability and employing the predictive analysis on the provided scenarios. to accurately estimate the necessary probabilities, the sigmoid function converts any real values between 0 and 1 by: �(�) = � ��� ( ) (1) to validate the hypothesis and ensure its consistency with the expected assumption, the value of the hypothesis must fall somewhere between 0 and 1 by: ℎ�( ) = � ��� (������) (2) when the prediction function is applied to the classifier, the classifier will provide values based on a set of outputs on probability. this establishes the decision boundaries with a selected threshold value. the accuracy of the optimized model is represented by the cost function after it has been optimized to provide the least amount of inaccuracy: �� � � ∑ (ℎ� )�� (�)� − (� (�))����� (3) gradient descent is used to reduce the cost values using: �� ≔ �� −∝ ∑ (ℎ�)�� (�)� − (� (�))�� (�)� ��� (4) several previous studies used lr for detection and prediction. the need to apply security in e-commerce in a highly effective way creates the concepts of asset protection, security prediction, and vulnerability detection to save end users and resources that can be exploited. lr was a vital component in the development of deep and machine-learning models on the google cloud platform [20]. similarly, lr was used to forecast student performance in community colleges [21]. in [22], a road crash zone was modeled using lr to determine the nature of the accidents and the types of people that were involved. in a similar vein, a privacy-protecting lrbased diagnosis method for digital healthcare was presented in [23]. the effectiveness of machine-learning rl for tomography processing was shown in [24]. in [25], lr and a survival model were used in russian exports. in [26], an intelligent categorization of coal structure was presented, using multinomial lr. in [27], lr was effectively used in nursing. in [28], a prediction model for clinical applications was developed using lr, showing its feasibility. in [29], an sk-tree method to detect malicious events on a portion of a publicly available dataset achieved an auroc score of 98%. in [19], several machine learning algorithms were investigated to detect and analyze frauds in online transactions with a european credit card dataset, proposing a novel fraud detection method to stream transaction data by analyzing the old transaction details of customers and extracting behavioral patterns. the study in [30] focused on fraud events in real-world transactions, using and evaluating a series of machine learning algorithms, such as vector machine, naive bayes, k-nearest neighbor, and lr. in [31], a credit card fraud detection system was presented using machine learning algorithms that included the modeling of the dataset. the past credit card transactions were modeled with data considered as fraud, and this model was used to define if a new transaction is fraud. this study showed that fraud detection is a classification problem and focused on preprocessing and analyzing datasets using different anomaly detection algorithms, such as local outlier factor and isolation forest, on a principal component analysis (pca)-transformed credit card transaction dataset. pca reduced the feature dimensionality [32] and kept the most effective features to improve the prediction process [33]. the above-mentioned studies in the e-commerce security domain used different machine learning algorithms to examine which fit best to their datasets and provide the best accuracy scores. in other words, these studies show the importance of carefully choosing machine learning algorithms that are compatible with the underlying dataset and have the best accuracy performance. ii. methodology this study focused on applying machine-learning algorithms to predict credit card fraud transactions in movie theaters. figure 1 shows the flow chart of the proposed method. fig. 1. the flow diagram of the proposed method. lr was used to make the predictions, leading to successful results. these two approaches were combined into one. as a consequence, the procedure started with the construction of the model, followed by the collection and preprocessing of the dataset. then, the model was trained and tested for its engineering, technology & applied science research vol. 13, no. 3, 2023, 10941-10945 10943 www.etasr.com alshutayri: fraud prediction in movie theater credit card transactions using machine learning prediction accuracy. the most important phase of this method was the generation and mapping of credit card fraud incidents in movie theater transactions. the study began by isolating movie theater credit card transactions, from all the credit card transactions contained in the dataset. in the end, only the dataset for credit card payments of movie tickets was selected for the best-fit test, which was followed by the import and cleaning of the data, their division into training and test sets, and finally using the machine-learning lr algorithm to determine the best-fit for making predictions. the necessary data were collected from kaggle [34], as shown in table i, which contains a total of 284,807 transactions and 492 fraudulent transactions that took place in two days in september 2013 by european cardholders. the dataset has a huge imbalance, as the positive class (frauds) accounts for only 0.172% of all transactions. the features of the dataset were represented by a number value (v1-v28). the pca method was used, and "time" and "amount" were the only unchanged features. the "time" feature saves the number of seconds that elapsed between the first and each subsequent transaction, for each subsequent transaction in the dataset. the "class" feature is the response variable, assigned the value of 1 in the event of fraud and 0 in all other cases, whereas "amount" denotes the total amount of the transaction. this study selected only transactions that involved purchasing a ticket and additional services for a cinema. the data include not just numerical values, but also a description and a "label". table i. the sample dataset generated from the credit fraud investigation time v1 v2 v3 v27 v28 amount class 0 -1.35981 -0.07278 2.536347 … 0.133558 -0.02105 149.62 0 0 1.191857 0.266151 0.16648 … -0.00898 0.014724 2.69 0 1 -1.35835 -1.34016 1.773209 … -0.05535 -0.05975 378.66 0 1 -0.96627 -0.18523 1.792993 … 0.062723 0.061458 123.5 0 2 -1.15823 0.877737 1.548718 … 0.219422 0.215153 69.99 0 2 -0.42597 0.960523 1.141109 … 0.253844 0.08108 3.67 0 4 1.229658 0.141004 0.045371 … 0.034507 0.005168 4.99 0 7 -0.64427 1.417964 1.07438 … -1.20692 -1.08534 40.8 0 7 -0.89429 0.286157 -0.11319 … 0.011747 0.142404 93.2 0 9 -0.33826 1.119593 1.044367 … 0.246219 0.083076 3.68 0 10 1.449044 -1.17634 0.91386 … 0.04285 0.016253 7.8 0 ⋮ ⋮ ⋮ ⋮ … ⋮ ⋮ ⋮ ⋮ 172782 0.219529 0.881246 -0.63589 … 0.131507 0.081265 5.49 0 172783 -1.77513 -0.00424 1.189786 … 0.181205 0.215243 24.05 0 172784 2.03956 -0.17523 -1.19683 … 0.454379 0.130308 79.99 0 172785 0.120316 0.931005 -0.54601 … -0.08083 -0.07507 2.68 0 172786 -11.8811 10.07178 -9.83478 … 0.21794 0.068803 2.69 0 172787 -0.73279 -0.05508 2.03503 … 0.943651 0.823731 0.77 0 172788 1.919565 -0.30125 -3.24964 … 0.068472 -0.05353 24.79 0 172788 -0.24044 0.530483 0.70251 … 0.004455 -0.02656 67.88 0 172792 -0.53341 -0.18973 0.703337 … 0.108821 0.104533 10 0 iii. experimental analysis and presentation of the results figure 2 shows the particular processes to import the dataset and initialize the fraud variable. fig. 2. experimental import and initialization of the fraud variable. python, pandas, and scikit-learn were used to develop the proposed method. in the first stage, the dataset was loaded using pandas, and the value of the fraud variable was initialized to 0 or 1, based on the dataset. in the second step, the test sample was defined, and the algorithm was applied using scikit-learn, as shown in figure 3. in the third phase, lr was used to perform the classification, and then the accuracy of the model was assessed, as shown in figure 4. the variable x is independent and denotes the credit card transactions, while the variable y is dependent and denotes the class of the transaction or the fraud flag. figure 4 shows the results of the proposed method, indicating an accuracy of 0.9988. fig. 3. selecting the sk-learn algorithm, importing the model, and defining the test sample. engineering, technology & applied science research vol. 13, no. 3, 2023, 10941-10945 10944 www.etasr.com alshutayri: fraud prediction in movie theater credit card transactions using machine learning fig. 4. calling the predict function, applying classification, and checking accuracy. the accuracy results of this study were compared with similar studies that used lr to detect fraudulent credit card transactions, as shown in table ii. the study in [35] used a credit card transaction dataset from the uci machine learning data repository to detect frauds in credit card transactions, while studies [36-38] used the same dataset as this study. all these studies used the lr method to achieve high accuracy and predictive performance, regardless of their individual approaches. this study achieved the best prediction performance result. table ii. comparative prediction performance study algorithm accuracy [35] logistic regression 77.97% [36] logistic regression 99.26% [37] logistic regression 91.20% [38] logistic regression 74.65% this study logistic regression 99.88% iv. conclusion the results of this study indicate that the implementation of a machine learning approach is imperative for the detection and prevention of fraudulent activities within payment operations. this study proposed the use of a logistic regression model to investigate fraudulent credit card transactions, using a machine learning approach to analyze various credit card payment methods for purchasing movie tickets. the raw data were divided into training and testing samples. the use of historical data to accurately predict future outcomes is a significant impetus for the extensive implementation of machine learning in various sectors. this study showcased the impact of the widespread adoption of digital financial transactions, particularly those involving credit cards, on the emergence of novel security risks that pose a threat to businesses and customers worldwide. the emergence of e-commerce and other electronic forms of monetary transactions has a crucial role in the production and service sectors, thereby promoting the advancement of the worldwide economy. the study was initiated based on the acknowledgment that, despite their widespread use, mobile credit card payment systems present opportunities for fraudulent activities, potential hazards, and security violations across all industries due to their ubiquitous and interdependent connectivity. this study investigated credit card transactions related to cinema ticket purchases to detect potentially fraudulent activities. the application of logistic regression machine learning provided an accurate prediction. the dataset used in this study 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[38] m. v. krishna and j. praveenchandar, "comparative analysis of credit card fraud detection using logistic regression with random forest towards an increase in accuracy of prediction," in 2022 international conference on edge computing and applications (icecaa), tamilnadu, india, jul. 2022, pp. 1097–1101, https://doi.org/ 10.1109/icecaa55415.2022.9936488. engineering, technology & applied science research vol. 8, no. 6, 2018, 3624-3630 3624 www.etasr.com farid et al: perspectives of water level measurement in plastic pipes using wideband horn antenna perspectives of water level measurement in plastic pipes using wideband horn antenna zahid farid department of electrical engineering, university of science and technology, bannu, pakistan zahidfarid@ustb.edu.pk zeeshan najam the ultimate engineering enterprises ltd, islamabad, pakistan shaani75@hotmail.com m. y. ali khan department of electrical engineering, gomal university d.i.khan, dera ismail khan, pakistan myousafak@gu.edu.pk sheeraz ahmed department of computer science, iqra national university, peshawar, pakistan sheerazahmed306@gmail.com sarah akhtar department of physics, federal urdu university of arts sciences & technology, karachi, pakistan sara@fuuast.edu.pk abstract—this paper is concerned with the investigation of a possible working principle of a microwave sensor for the measurement of water levels in plastic pipes. according to the research, most current sensors for water level measurement require an unobstructed path from the sensor in the water and therefore, the integrity of the pipes, in which water flows, will be compromised. the proposed sensor will work at microwave frequencies to measure the flow in the pipes from the outside. this would be non-invasive and non-intrusive. a beam of microwave energy from an antenna is directed towards a water surface within a pipe and the reflection due to the surface of the water will be isolated and knowledge of the pipe dimensions and properties will allow the depth of water to be calculated. knowledge of the pipe drop may also allow flow to be estimated. it is observed that at microwave frequencies the reflection from the surface of the water is many times greater than the reflection from the surface of a typical plastic pipe. keywords-pvc pipe; cst; antenna and return loss i. introduction wter usage of water is commonly monitored by water meter installation. if there are no meters, users are billed a constant amount of charge irrespective of the amount of water they consume. this situation causes not only a deficit to the country's revenue of the recourse but also extra charges in some cases at the consumer level. so, there is a need of a monitoring system which could give us continuous information about the water usage at any level. with the advancement of electronic measurement and control systems, this problem can be solved by providing a microwave sensor which could be installed on pvc pipes having continuous water flow. pulse, phase difference and doppler methods along with pressure sensing are four popular ways of electronic distance measuring [1]. these all offer possible situations for the water sensor. measuring the time between transmission and reception of a pulse transmitted by a transmitter, the distance can be calculated as: 2d=c∆tꞌ=c(tr-te) (1) where d is the distance between instrument and target, c is the light velocity in the medium, tr is the pulse flight time, te is the time of pulse departure. it can be seen that the accuracy of the distance measurements depends on the accuracy of flight time measurement. an accuracy of 0.1nsec is equivalent to an accuracy of 15mm. for example a 150mm diameter pipe would require a 2nsec delay before a pulse reflected from the bottom side of a pipe should be seen. for the transmitter, the narrower the impulse transmitted the better the resolution of the target that will be achieved. however, narrow pulses in time tend to larger bandwidths in frequency. therefore, pulse method distance measurement systems are required to be broadband. it turns out that the broader the bandwidth of the measuring device, the better the resolution in the accuracy of the measurement. in the phase difference method, distances are measured by measuring the phase difference of continuous waves. light waves and radio waves are used as carrier waves in this technique. a modulated signal on the carrier wave is transmitted from the transmitter towards the reflector and back to the electronic distance measurement (edm) device, where it is picked up by the receiver. it is at the receiver where the phases of transmitted and received signals are compared and phase lead is calculated. phase comparison only gives us the lead time. a time equivalent to the number of full cycles elapsed during the flight of a specific signal has to be added to obtain the total time of flight ∆tꞌ. ∆tꞌ=m.t*+∆t (2) where m is the integral number of full wavelengths over the measuring path, 𝑡∗ is the elapsed time for one full cycle of the engineering, technology & applied science research vol. 8, no. 6, 2018, 3624-3630 3625 www.etasr.com farid et al: perspectives of water level measurement in plastic pipes using wideband horn antenna modulation signal. the phase difference method can be implemented in a narrow band form. the level of accuracy depends on the frequency of the carrier used and the level to which the phase difference between the transmitted and received waveforms can be resolved. the most popular technique for electronic distance measurement is a doppler system consisting of a microwave transmitter and receiver. the principle behind the technique is that the instrument moves with a speed of v towards the reflecting surface which is placed at a distance d from the instrument. the surface of the target reflects the transmitted signal and is captured by the receiver. the emitted frequency is expressed as: ft=v/ƛ (3) where v is velocity of light and λ is the wavelength of the emitted radiation. the frequency which arrives at the reflecting surface is: fs=(c+v)/ƛ (4) where v is the speed of the instrument, relative to the reflecting surface. at the receiver the received frequency is given by: fr=(c+2v)/ƛ (5) the doppler frequency𝑓𝐷can be achieved by subtracting 𝑓𝑇 from fr: fd=fr-ft=(c+2v)/ƛ-v/ƛ=2v/ƛ (6) the procedure for measuring the doppler frequency depends on the type of waves used. for radio waves it is measured by counting the cycles of the doppler signal per second. equation (6) can be written as: v=½fsƛ (7) the distance travelled by the instrument between time t1and t2 is: d12=∫ 1 2 𝑓𝑠ƛ 𝑡2 𝑡1 (8) close inspection of (8) shows that for a stationary system this equation yields the fundamental wavelength which is equivalent to the phase difference method for distance measurement. this system is narrow band. such a system could also be used to measure perturbations on the surface of water in a pipe. principle of microwave reflections has been used in tumor and breast cancer detection [2-5] in the medical field, and in analyzing rubber containing iron particles [6], mineral treatment processes [7], high accuracy microwave ranging system [8], electronic distance measurements [9] and most importantly cable fault detection [10, 11] in the industrial field. the proposed technique is to isolate the reflection coefficient, s11 (db), of a wideband antenna held on the top of flowing water inside a pvc pipe. for this, it is necessary to study the behavior of the reflected signal from a planar normal surface and is best illustrated using the example of time domain step reflection. in figure 1 we see an abstracted version of the measurement scenario. transmitter and antenna have been replaced with an oscilloscope. the air way between the antenna and the pipe is represented by a section of transmission line and the pipe and water are represented as a device under test. fig. 1. a block diagram of a reflectometer the step generator produces a positive-going incident wave that is applied to the device under test via a transmission line. the step travels along the transmission line at the velocity of propagation of the light. if the load impedance of dut is equal to the characteristic impedance of the line, no wave is reflected and all that will be seen on the oscilloscope is the incident voltage step recorded as the wave passes the point on the line monitored by the oscilloscope as shown in figure 2. if there is a mismatch at the dut then a part of the incident wave will be reflected back and the wave form on the oscilloscope will embed some of the incident and reflect wave as shown in figure 3. fig. 2. oscilloscope display of when there is no mismatch, er=0 fig. 3. oscilloscope display when there is any mismatch, er≠0 the reflected wave is readily identified since it is separated in time from the incident wave. this time is also valuable in determining the length of the transmission system from the monitoring point to the mismatch. letting d denote this length: d=vp×t/2 (9) where vp is the propagation velocity and t is is transit time from monitoring point to the mismatch and back again. one of the advantages of time domain reflection (tdr) is its ability to handle cases involving more than one discontinuities. if we look at the example in figure 4, it can be seen that there are more than one impedance mismatches occurring in this system. fig. 4. cable with more than one discontinuities engineering, technology & applied science research vol. 8, no. 6, 2018, 3624-3630 3626 www.etasr.com farid et al: perspectives of water level measurement in plastic pipes using wideband horn antenna ρ1, ρ2 are the reflection co-efficients given by: 0 0 1 0 0 ' ' z z z z  − = + (10) 0 2 0 ' l ' l z z z z  − = + (11) if we consider that 0 0 ' l z z z  then the display which will appear on the oscilloscope will be like the one shown in figure 5. the important point here to note is that as we go further down the cable, the measurement accuracy goes down. in our case of measurements, for determining the height of water inside the pipe, the electromagnetic waves will propagate in air with a propagation velocity approximately equal to 3x108m/sec. figure 6 shows the transmission line equivalent circuit for the water measurement device. fig. 5. oscilloscope display for a cable with multiple discontinuities fig. 6. transmission line equivalent circuit for the water measurement device here z stands for impedance, pus stands for pipe upper surface and pbs stands for pipe bottom surface. in the model we can assume that the impedances in order of magnitude are likely to be zwater, zantenna (including connectors), zsoil, zpipesurface. a layer model with approximate thicknesses and dielectric properties of pipe, water, soil and air is shown in table i. note that it is assumed that there are no magnetic materials in the system. in this system, water would have the largest reflection followed by soil. note the soil below the pipe could be treated with iron or salt to increase its reflection/mismatch thereby providing a calibration surface for the system. however, any conductive surface below the pipe may increase the number and magnitude of echoes into the system. table i. layer model impedance permittivity 0≤z≤1m air 1 5×10-3 pvc ≈2-4 0≤z≤150-3m air2 1 150×10-3m–air2 water ≈55-90 5×10-3m pvc ≈2-4 0≤z≤-∞ soil ≈10-40 ii. simulations and experimental results a. distance measurement inferred from reflections from the metal surface. the purpose of these experiments is to determine the relative level of reflected energy that could be available to a time of flight measurement system from the normal surface of water within a pvc pipe. in the system a transducer emits a wave towards the pipe. at the surface of the pipe the wave is partially reflected, partially absorbed and partially transmitted. this happens again at the boundary between the pipe material and the air in the pipe, again at the surface between the air in the pipe and any water in the pipe, again at the boundary between the water and the lower inner surface of the pipe and finally at the boundary between the pvc and the soil under the pipe. according to [10] and the properties of air, pvc, water and soil at microwave frequencies, the air-water boundary will reflect the largest proportion of energy whilst transmitting the least. the pipe wall is planar along its long axis and curved at right angles to its long axis. however, for the initial measurements the pipe wall can be represented by a planar sheet of pvc with suitable thickness. if the sheet is large when compared to the wavelength, unwanted scattering from the non normal axis of the pipe and diffractions from the edges of either the pipe or the planar sheet will be avoided. at first, the system consisting of a measurement unit, an antenna and a pipe with water is represented by a sheet of polyvinyl chloride (pvc) of large extent above a copper sheet. the copper sheet represents an ideal reflector and the pvc sheet the top surface of the pipe. large planer surfaces also allow avoidance of problems with orientation and non perpendicular reflections. the system was first modeled in cst. in the model a plane wave was used for excitation. this scenario used an impulse and is therefore a representative of the pulse distance measurement system. two plates of 250mmx250mmx3mm (pvc and copper) were spaced 1m from one another and excited by plane wave 0.2m away and an output point was set at a distance of 0.8m away from the pvc plate. this experiment is shown in figure 7. fig. 7. plane wave illuminations of pvc and copper plates with 1m distance the results after simulation are shown in figure 8. according to the results the first reflection is from the pvc plate which occurred at 3.202nsec. here it should be explained that this time is the total time from excitation point to the surface of pvc plate and then back to the output point shown in figure 8. this time equates to a distance of 0.961m. the measured distance is 0.985m, therefore there is a 2.43% error. similarly for the copper plate, the reflection occurred at 9.912nsec which equates to a distance of 2.974m. the actual distance was 2.997m having a 2.3% error. one point here to be noted is that the speed of light in all these measurements was chosen to be 3x108m/sec. the errors in the measurement can be reduced by taking the actual speed of light, which is 2.998x108m/sec. this experiment shows that a sensor would be possible and indicates that a return from a copper plate has approximately 12 times the magnitude of a return from the engineering, technology & applied science research vol. 8, no. 6, 2018, 3624-3630 3627 www.etasr.com farid et al: perspectives of water level measurement in plastic pipes using wideband horn antenna pvc sheet. the experiment also shows that returns 1m apart lead to a time difference of approximately 8nsec. from this we can assume that for a 150mm diameter pipe, the time difference between the returns is likely to be: 8×10-9[1/0.15]=1.2nsec. this means that if the receiver started 2nsec before the first pulse arrived and run for 4nsec all the required data would be captured. fig. 8. the time domain representation of the reflections from a copper plate behind a pvc sheet. water was added in the next simulation (figure 9). note that whilst we can reasonably assume materials and conditions of the pipe to be constant, we cannot assume the conditions of materials of the surface below the pipe. one way to create repeatable conditions would be to cover the bottom face of the pipe with a good conductor such as copper foil. the next simulation therefore contains a conductive copper plate beyond the water. the results are shown in figure 10. fig. 9. water and air between two pvc sheets terminated by a copper plate short circuit fig. 10. the time domain response of several levels of water between two pvc plates truncated by a copper plate in this case the gate of the experiment was reduced from 1m to 0.5m. it can be seen that the first return is the top of the pipe and its amplitude does not change for no water, 100mm of water and 1mm of water. this reassures that this is a single reflection rather than several reflections merged together. the water surface produces good returns at both 100mm and 1mm. the return at 100mm water is distinct from the metal plate. the return at 1mm is not distinct from the metal plate. in figure 11 the return from metal plate is constant in time. these results also show multiple reflections in time as energy is reflected to and from each boundary in the system. the periodicity of these reflections indicates that the plates are large enough to avoid significant diffractions at their edges and that the copper plate terminates the gate effectively. one important point here to note is that if copper plate was not backing the whole structure we would have a minute reflection for from the end pvc plate. for this purpose a small amendment was made with the structure in figure 10 by eliminating the copper plate from behind so that the whole of the transmitted wave is absorbed and not reflected. the results for this case are shown in figure 11. in this case a 1mm height water did not give any reflection but the reflections from the surface of 100mm height water and front end pvc plate remained fixed in time. fig. 11. time domain representation of reflections from different levels of water between pvc plates a 1m long with 0.2m radius pvc pipe, having different levels of water was also simulated in cst micro stripes (figure 12). a plane wave excitation was given from the top. the results for no water and almost half full water pipe are shown in figure 13. simulations suggest that in general the returns from the pipe are less than those from planar experiments. this is most likely due to the scattering caused by the curved surface of the pipe. this may mean that the polarization of the incident wave may be used to maximize the return or minimize the scattering or both. the two traces in figure 14 show an empty pipe (red trace) and a pipe that is half full (black trace). the red trace shows only reflections from the upper and lower surfaces of the pipe. the black trace shows the reflection from the upper surface of the pipe and a significant return from the surface of the water in the pipe. all the responses are within the time frame of 4nsec. copper sheet absence (conductive foil at the lower outer of the pipe) significantly reduced reflections and therefore cleared up the trace for peak detection. engineering, technology & applied science research vol. 8, no. 6, 2018, 3624-3630 3628 www.etasr.com farid et al: perspectives of water level measurement in plastic pipes using wideband horn antenna fig. 12. simulation of 1m long pvc pipe having different levels of water fig. 13. simulation results for 1m pvc pipe with different levels of water b. experimental results for static water in a tank the aim of this experiment was to measure the reflections from the surface of water only. the experiment is shown in figure 14. fig. 14. layout of the experimental rig for measuring reflections from the surface of static water the reflection coefficient of the horn antenna was measured for the empty tank and tank having different levels of water (16mm, 32mm and 48mm). a large container was used in order to avoid any reflections from the edges. in front of the horn no metallic objects were allowed, however there may have been metal in the floor. the instrument used was rhodes and schwarz r&s zvl13 [11], which was able to produce results in time domain. the instrument’s bandwidth was 9khz to 13.6ghz. the results are shown in figure 15 which shows that the peaks for the four scenarios are distinct. there is a great deal of noise in the results indicating a metal plate or bars in the floor below the experiment. the dynamic range of the measurements is ≈10db. the range of the measurements is less than 2nsec. fig. 15. reflections of water levels inside a plastic tank c. experimental results for static water inside a pipe a pvc pipe having an external diameter of 11cm was used with and without water. at first some water inside the pipe was made static by closing both sides of the pipe. the reflection coefficient was again measured for the empty pipe and then for the pipe having some water inside it. the setup is shown in figure 16. at first the challenge was to find out the reflection of electromagnetic waves coming from the upper and lower ends of the pipe. for this, a sheet of copper foil was selected to be put on the lower and upper ends of the pipe. measurements were performed for a frequency span of 9khz to 13.6ghz for the empty pipe. the purpose of these measurements was to find the reflections coming from the lower and upper surfaces of the pipe. results are given in figure 17. once the reflections from the upper and lower end of the pipe were found, another set of measurements was performed to find out the effects of water inside the pipe and the results are shown in figures 18 and 19. in these figures, front means front end of the pvc pipe and bottom means bottom end of the same pipe. the difference in the curves of figures 18 and 19 is caused by the presence of a metal plate beneath the pipe during the measurements of figure 19. fig. 16. layout of the experimental rig for water to flow inside the pipe fig. 17. reflections of the upper and lower surfaces of a pipe and from a metallic surface placed beneath the pipe engineering, technology & applied science research vol. 8, no. 6, 2018, 3624-3630 3629 www.etasr.com farid et al: perspectives of water level measurement in plastic pipes using wideband horn antenna fig. 18. reflections from the surface of water inside a pipe with a copper plate beneath fig. 19. reflections from the surface of water inside a pipe d. experimental results for flowing water with different heights inside the sewerage pipe the aim of these experiments was to measure the reflections of flowing water inside a pipe. to allow water flow, the pipe was arranged with a 2 degree slope. this arrangement means that the antenna was slightly off the perpendicular. however, an initial test (not shown here) suggests that the degree of movement of the main beam did not have a significant effect. for these experiments, some arrangements were made to achieve variable and smooth flows. a submersible water pump was placed inside a water reservoir which could push water through a small pipe (black) to the start of the main pipe (brown). a valve separate from the motor was used in order to have two different water levels in the main pipe. these levels were approximately 9mm and 21mm high. the results for these flowing water levels inside the pipe are shown in figures 20 and 21. in these figures “with water” (a)(g) represent seven different measurements for flowing water at 9mm and 21mm heights inside the pvc pipe, to check the repeatability of the measurements. fig. 20. reflections from the surface of 21mm flowing water inside a pipe fig. 21. reflections from the surface of 9mm flowing water inside a pipe the next step was to transform these time domain results into distance domain, which was done and the results are shown in figures 22 and 23. it has to be remembered that the pipe diameter “d” was approximately 110mm. fig. 22. distance domain analysis of the results in time domain for 21mm water flowing inside a pipe fig. 23. distance domain analysis of the results in time domain for 9mm water flowing inside a pipe iii. mathematical analysis the location of the peak of the reflections from the upper end of the pipe, d1 equals to 756mm. the location of the peak of the reflections from lower end of the pipe, d2 equals to 977mm. the difference between these two should give a distance twice as big as the diameter of the pipe. d1–d2=2d=>977–756=221mm which is nearly double the diameter of the pipe. similarly the locations of the peaks of the reflections from the surfaces of the 9mm and 21mm high water inside the pipe were found to be at 10.5mm and 18.5mm respectively. engineering, technology & applied science research vol. 8, no. 6, 2018, 3624-3630 3630 www.etasr.com farid et al: perspectives of water level measurement in plastic pipes using wideband horn antenna iv. conclusions this paper presented analysis, simulations, and measurements relating to the feasibility and principles of a device to measure water levels inside pvc piping using microwaves. simulations showed that for a solution, measured results would need to be obtained during a time window between 2ns and 10ns dependent on the distance of the transducer from the target. simulations showed that in the absence of noise and with a large bandwidth, water surface could be resolved to within a few mm with an accuracy of approximately 97%. the top surface as well as the lower surface of the pipe could be detected. the concept of gating was introduced here whereby the only period of time of interest is twice the time taken for the pulse energy to illuminate the surface of the water in the pipe. an idealized version of the system was modeled using a state of the art electromagnetic simulation package. the model consisted of a pvc sheet in front of a copper plate with water at varying levels and without water. the simulated results yielded some useful facts. the time of flight measurements could be easily translated into distance and the error was less than 4%. the reflection form the water surface was approximately 12 times larger than the reflection from the pipe surface. the reflection form the pipe surface was unaffected by the level of water in the pipe. the main period of interest in the measurements lasted 4ns. the experimental measurements gave the following points as worth noting: • all four water heights had distinct peaks. • reflections from below the floor caused many standing waves indicating that gating would be required for both pulse and phase type emd systems. • the period of interest is less than 2nsec which is consistent with the model. • even with a possible metalized floor it was difficult to determine a fixed point in time/space for the bottom of the water container. based upon the obtained results it is apparent that a device of the type described here is entirely feasible. references [1] j. m. rueger, electronic distance measurement: an introduction vol. 4, springer, berlin-heidelberg-new york, 1996 [2] e. c. fear, x. li, s. c. hagness, m. a. stuchly, “confocal microwave imaging for breast cancer detection: localization of tumors in three dimensions”, ieee transactions on biomedical engineering, vol. 49, no. 8, pp. 812-822, 2002 [3] e. fear, m. stuchly, “microwave detection of breast cancer”, ieee transactions on microwave theory and techniques, vol. 48, no. 11, pp. 1854-1863, 2000 [4] h. zhang, s. y. tan, h. s. tan, “a novel method for microwave breast cancer detection”, 2008 asia-pacific microwave conference, macau, china, december 16-20, 2008 [5] u. weinstein, a. bernstein, e. cohen, microwave monitoring of heart function, u.s. patent us 2011/o130800 a1, 2016 [6] s. s. kim, s. t. kim, y. c. yoon, k.s. lee, “magnetic, dielectric, and microwave absorbing properties of iron particles dispersed in rubber matrix in gigahertz frequencies”, journal of applied physics, vol. 97, no. 10, pp. 10f905-1-10f905-3, 2005 [7] k. e. haque, “microwave energy for mineral treatment processes-a brief review”, international journal of mineral processing, vol. 57, no. 1, pp. 1-24, 1999 [8] g. s. woods, d. l. maskell, m. v. mahoney, “a high accuracy microwave ranging system for industrial applications”, ieee transactions on instrumentation and measurement, vol. 42, no. 4, pp. 812-816, 1993 [9] m. i. khattak, m. shafi, g. ahmad, n. ullah, m. saleem, “effects of the span of the calibrating frequency scan on resolution of microwave electronic distance measurements”, technical journal, taxila, pakistan vol. 19 no. 4, pp. 30-33, 2014 [10] q. shi, o. kanoun, “wire fault diagnosis in the frequency domain by impedance spectroscopy”, ieee transactions on instrumentation and measurement, vol. 64, no. 8, pp. 2179-2187, 2015 [11] q. shi, u. troltzsch, o. kanoun, “analysis of the parameters of a lossy coaxial cable for cable fault location”, eighth international multiconference on systems, signals & devices, sousse, tunisia, march 212-25, 2011 engineering, technology & applied science research vol. 9, no. 1, 2019, 3836-3845 3836 www.etasr.com gopal et al.: swarm optimization-based modified selective harmonic elimination pwm technique … swarm optimization-based modified selective harmonic elimination pwm technique application in symmetrical h-bridge type multilevel inverters yatindra gopal department of electrical engineering, rajasthan technical university, kota, india ygopal.phd@rtu.ac.in kaibalya prasad panda department of electrical engineering, national institute of technology, meghalaya, india kaibalyapanda@nitm.ac.in dinesh birla department of electrical engineering, rajasthan technical university, kota, india birlartu2@gmail.com mahendra lalwani department of electrical engineering, rajasthan technical university, kota, india mlalwani.ee@gmail.com abstract—the problem of elimination of harmonics and the need of a large number of switches in multilevel inverters (mlis) have been a hot topic of research over the last decades. in this paper, a new variant swarm optimization (so) based selective harmonic elimination (she) technique is described to minimize harmonics in mlis, which is a complex optimization problem involving nonlinear transcendental equation. optimum switching angles are calculated by the proposed algorithms considering minimum total harmonic distortion (thd) and the best results are taken for controlling the operation of mlis. the performance of the proposed algorithm is compared with the genetic algorithm (ga). conventional mlis have some disadvantages such as the requirement of a large number of circuit components, complex control, and voltage balancing problems. a novel seven-level reduced switch multilevel inverter (rs mli) is proposed in this paper to recoup the need of a large number of switches. matlab/simulink software is used for the simulation of two symmetrical topologies, i.e., a seven-level cascaded h-bridge multilevel inverter (chb mli) and a seven-level (rs mli). simulation results are validated by developing a prototype of both mlis. the enhancement of the output voltage waveform confirms the effectiveness of the proposed so she approach. keywords-swarm optimization; selective harmonic elimination; multilevel inverter; cascaded h-bridge multilevel inverter; genetic algorithm; reduced switch multilevel inverter; selected harmonic elimination; total harmonic distortion; modulation index i. introduction nowadays many industrial drives require high or medium power for their operation and some require high power with medium voltage. recently [1, 2], multilevel inverters are evolving as an alternative in high output power and medium voltage applications. mli consists of many power semiconductor switches and a number of voltage sources, allowing integration of renewable energy sources with it [3-6]. mli produces a staircase voltage output thus reducing the thd as the output waveform in close proximity to sinusoidal waveform [7-9]. as the number of level increases, harmonic distortion reduces more, but not without increasing the cost and complicacy. mlis are generally categorized into three types: diode clamped mli (dc mli) [10], flying capacitor mli (fc mli) [11], and chb mli. dc mli requires a large number of diodes, fc mli requires voltage balancing of more capacitors and thereby has augmented cost. chb mli is more advantageous in respect to low dv/dt stress, less emi noise and less thd than the other types [12, 13]. chb mli is made up of a series connected separate single phase bridge inverters, which operate with separate dc voltage source. this paper presents the design of a single phase seven-level cascaded hbridge mli using 12 switches aiming to reduce lower order harmonics which produce staircase voltage output waveform. the output voltage waveform is not purely sinusoidal, and it contains a number of odd order harmonics. the higher order harmonics can be easily reduced by using filters, but the lower order dominant harmonics are difficult to reduce. authors in [14-16] explained different methods to reduce harmonics using pulse width modulation (pwm) and selected harmonic elimination (she) method. lower-order harmonics are dominant in nature and complete elimination of these harmonics is not possible using conventional pwm techniques. she or programmed pwm technique [17] approach is thus used to eliminate specific order harmonics by calculating optimal switching angles. switching angles are calculated by solving transcendental non-linear equations. iterative techniques such as newton-raphson (nr) method [18] and mathematical resultant theory method [19] suffer from many disadvantages in doing so. the former approach fails at a good initial guess and results in only a few sets of solution. the degree of polynomial becomes large when the later approach is applied to higher level asymmetrical mlis as the number of harmonics to be eliminated increases. active harmonic elimination method [20] is another combinational approach of nr and resultant theory method for eliminating any number of specific harmonics. this method doesn’t suggest finding all possible solutions for the infeasible modulation index. evolutionary algorithms have been further developed to overcome shortcomings of conventional methods. ga was an early developed stochastic algorithm that dealt with the she problem widely used in the literature [21, 29]. particle swarm corresponding author: y. gopal mailto:kaibalyapanda@nitm.ac.in mailto:birlartu2@gmail.com mailto:birlartu2@gmail.com engineering, technology & applied science research vol. 9, no. 1, 2019, 3836-3845 3837 www.etasr.com gopal et al.: swarm optimization-based modified selective harmonic elimination pwm technique … optimization (pso) [22, 23, 32] is another such bio-inspired algorithm mostly used to eliminate harmonics in mlis. however, for complex multi-minima functions, pso fails to locate global optima and also reduces the speed of convergence [22]. a hybrid ga-pso approach considering thd as a fitness function has been successfully demonstrated for chb mli in [7]. authors in [24] report an analytical solution for harmonic elimination using bee algorithm for a symmetrical seven-level mli and proved its superiority over ga. the low-order 5th and 7th harmonics are effectively suppressed assuming constant magnitude of dc sources. however, the magnitude of the dc source can be fluctuating when mli is used in applications such as drives, renewable energy sources, and facts devices. in such cases, new expression needs to be considered which leads to a complex calculation of switching angles for each set of modulation index. in this regard, a new group of optimal harmonic minimization techniques has been investigated in [25-27] considering variable dc-link voltage. an analytical solution for thd minimization using online switching angle calculation for equal voltage sources has been suggested in [19]. in [28], an online switching angle calculation approach using artificial neural networks has been discussed considering unequal dc sources. however, equal values of dc sources are considered in the present study and a novel optimization approach is developed to deal with the she problem. in this paper, advanced she technique was utilized in order to reduce specific lower order harmonics, such as the 5th and the 7th, from the output voltage. the technique solves different non-linear equations and gives best optimized results. furthermore, this paper reports the development of a reduced switch seven-level mli (rs mli) topology which uses 7 switches and requires less number of driver circuits. rs mli produces the same voltage output as chb mli and involves less expenditure. calculation of thd as an optimization problem is also described. ga [29, 30] and so she approach are applied to solve non-linear equations for reducing thd. also, a comparison study drawn between ga and so she approach is provided. the calculated so she data are used for developing simulation models and hardware design. the proposed topology is validated by comparing the results obtained from the simulation and the experimental model. ii. cascaded h-bridge mli topology (chb mli) for a single phase 7-level chb mli, the structure is shown in figure 1(a). in this circuit, each voltage source is connected in cascade with other voltage sources via 3 h-bridge circuits. each h-bridge consists of 4 power semiconductor switches which produce 3 level outputs, i.e., +vdc, 0 or -vdc [13]. at any instant of time, (nl-1) numbers of switches are in the current path in a chb mli, which incurs more conduction loss. the final voltage in the +ve half cycle is +3vdc and in –ve half cycle is -3vdc. the number of levels in an nl-level mli is given by 2ndc+1, where ndc denotes the number of dc sources used. output voltage waveform pattern for the 7-level chb mli is shown in figure 1(b). the overall output voltage of mli is given by v=vdc1+vdc2+vdc3. in this paper, all three voltage levels are taken equal, i.e. vdc1=vdc2=vdc3=vdc. in figure 1(b), 1  , 2  , and 3  are three switching angles needed to be calculated by solving non-linear equations to minimize thd. (a) (b) fig. 1. (a) structure of single phase seven-level chb mli, (b) output voltage waveform of single phase seven-level mli iii. proposed reduced switch mli the number of switches in mli defines cost, circuit size, reliability and complexity. so the key element in designing a mli is the number of required switches against the required voltage level. to construct the same output obtained as in a seven-level chb mli, a new circuit topology has been developed with a reduced number of switches without increasing the number of h-bridges. figure 2(a) shows the proposed mli structure and figure 2(b) shows the proposed mli output voltage waveform with corresponding switching states. the h-bridge switches (or polarity generation switches) operate at low switching frequency whereas the level generation switches t1-t3 operate at high switching frequency. hence, a cost effective solution is to choose low switching power components for the h-bridge and high switching power components for the level generation. in comparison to a chb mli the required number of switches in rs mli is smaller. in chb mli 12 switches are used, whereas only 7 switches with 2 discrete diodes are used in design of rs mli. the working principle of rs mli is summarized in the following modes: engineering, technology & applied science research vol. 9, no. 1, 2019, 3836-3845 3838 www.etasr.com gopal et al.: swarm optimization-based modified selective harmonic elimination pwm technique … • mode a: when t1 is on, current flows through the two diodes, both h-bridge switches s1 and s2. so, voltage output is +vdc across the load (figure 3(a)). similarly when s3 and s4 are switched on, voltage output is -vdc. • mode b: in this mode, switch t2 is made on. current flows through diode d2, and switches s1 and s2. so, output voltage is +2vdc across the load (figure 3(b)). similarly when s3 and s4 are switched on, voltage output is -2vdc. • mode c: when t3 is on, this mode of operation starts. current flows through switches s1 and s2, so voltage output is +3vdc across the load. diodes d1 and d2 are reverse biased (figure 3(c)). similarly when s3 and s4 are switched on, voltage output is -3vdc. • mode d: both s1 and s3 or s2 and s4 are on in this mode. switches t1, t2 and t3 are in off state. voltage output obtained across the load is zero (figure 3(d)). the switching scheme of rs mli is depicted in table i. output voltage obtained from a rs mli with corresponding switching states has been depicted in figure 2. although the output voltage is the same, the switching stress in rs mli is less and the voltage profile can be improved by proper control. (a) (b) fig. 2. (a) structure of single phase seven-level rsmli, (b) output voltage waveform with corresponding switching states a. comparison of conventional and proposed mli topology in this section the proposed mli topology is been compared with the conventional chb mli, dc mli, and fc mli. for generating nl output voltage levels, the proposed rs mli requires only (nl+7)/2 switches (nsw), whereas conventional mli topologies need 2(nl-1) per phase switches. table i. swithcing scheme of seven-levl rs mli switching state t1 t2 t3 s1 s2 s3 s4 d1 d2 +3vdc 0 0 1 1 1 0 0   +2vdc 0 1 0 1 1 0 0  ✓ +vdc 1 0 0 1 1 0 0 ✓ ✓ 0 0 0 0 1 0 1 0   0 0 0 0 0 1 0 1   -vdc 1 0 0 0 0 1 1 ✓ ✓ -2vdc 0 1 0 0 0 1 1  ✓ -3vdc 0 0 1 0 0 1 1   (a) (b) (c) (d) fig. 3. operation of proposed rs mli for generating positive output voltage levels: (a) mode a, (b) mode b, (c) mode c, (d) mode d engineering, technology & applied science research vol. 9, no. 1, 2019, 3836-3845 3839 www.etasr.com gopal et al.: swarm optimization-based modified selective harmonic elimination pwm technique … as shown in figure 4(a), the proposed inverter requires fewer switches to realize nl voltage levels at the output. it is important to note that the required number of driver circuits (ndriver) is the same as nsw for all aforementioned topologies. figure 4(b) compares the number of dc voltage sources with the aforementioned mli topologies. for realizing nl voltage levels, chb mli and the proposed topology needs (nl-1)/2 dc voltage sources, whereas dc mli and fc mli topologies need only 1 dc source with (nl-1) dc bus capacitors. however, the proposed topology doesn’t need any clamping diodes or clamping capacitors similar to a chb mli. but, dc mli needs (nl-1)×(nl-2) extra clamping diodes per phase and fc mli needs (nl-1)×(nl-2)/2 clamping capacitors per phase. (a) (b) (c) fig. 4. comparison of the proposed rs mli with the conventional topologies: (a) number of semiconductor switches against the number of voltage levels, (b) number of dc voltage sources against the number of voltage levels, (c) gc variation against the number of voltage levels another comparison index, gc is taken from the viewpoint of volume, size, and cost of the mli. the coefficient gc can be defined as: c dc sw driver vr g n n n n=    (1) figure 4(c) shows the variation of the coefficient gc with respect to nl voltage levels. the chb mli topology has very high value of gc as compared to the dc mli and fc mli topologies. the proposed rs mli topology has lower gc coefficient than chb mli topology. this signifies that the size and overall cost in designing the rs mli are smaller than the conventional and other h-bridge based mli topologies. here, the required number of clamping diodes and clamping capacitors are not taken into account when calculating gc. so, it is much lower for dc mli and fc mli topologies. but, practically the overall cost of dc mli and fc mli topologies is more than the one of the other mentioned topologies due to the presence of additional clamping diodes and capacitors. b. comparison of proposed mli with recently developed well-known mli topologies the comparison presented above is extended for the recently developed mli topologies, mli 1 [1], mli 2 [29], mli 3 [7], mli 4 [2], mli 5 [34], mli 6 [36] in terms of number of dc sources (ndc), number of switches (nsw), number of diodes (nd), number of capacitors (nc), and number of transformers (ntr). mli 1 and 2 require the same number of components, whereas the switch count has been reduced in mli 3, but the total number of components is the same as in mli 1 and 2 due to the addition of discrete diodes and capacitors. in this regard, mli 4 requires less components than the afore-mentioned topologies. furthermore, a few transformer-based topologies are also developed, such as mli 5 which uses single dc source but also a transformer for producing 7 levels. other single dc source mlis reported in [33, 35, 36] utilize fewer semiconductor switches, smaller total number of components, and thus are superior among the discussed topologies with regard to cost and volume. but, as mli 6 consists of a capacitor, thus for higher voltage level application, capacitor voltage balancing may be a measure issue in such an mli. the requirement of components for a 7level rs mli is summarized in table ii. although the proposed topology requires a number of dc sources which increases as the voltage level increases, this can be of use in multiple renewable energy source based applications. table ii. proposed rs mli well known 7-level mli topologies comparison mli topologies ndc nsw nd nc ntr total mli 1 [1] 3 10 0 0 0 13 mli 2 [29] 3 10 0 0 0 13 mli 3 [7] 1 8 2 2 0 13 mli 4 [2] 3 8 0 0 0 11 mli 5 [34] 1 8 0 0 1 10 mli 6 [36] 1 6 0 1 0 8 proposed rs mli 3 7 2 0 0 12 iv. thd calculation using optimization algorithm as described above, the she technique is currently being prominently used to synthesize output voltage of multilevel inverters. the configuration showed in figures 1(a) and 2(a) produces similar patterns of output voltage. in the output voltage waveform the positive half cycle is equal to the negative half cycle, i.e. quarter wave symmetrical output. the output voltage waveform shown in figure 2(b) can be expressed in fourier series as: 1 (t) sin( ) cos( ) n n n n n v v n b n   = = + (2) engineering, technology & applied science research vol. 9, no. 1, 2019, 3836-3845 3840 www.etasr.com gopal et al.: swarm optimization-based modified selective harmonic elimination pwm technique … the even order harmonics automatically get canceled due to quarter wave symmetry, i.e. bn=0 for all n. so the new equation of output voltage becomes: 1 (t) sin( )  = =  n n n v v n (3) the amplitude n v can be expressed in terms of fourier series with  varies in the range of 0 to π/2: 1 2 3 4 (cos cos cos )    = + +dc n v v n n n n (4) the three switching angles 1  , 2  , and 3  and the fundamental component of output voltage are controlled using the modulation index. the dominant lower order harmonics need to be eliminated from the output phase voltage. accordingly, the three non-liner equations for the solution of the problem are taken in this work as: 1 1 2 3 5 1 2 3 7 1 2 3 4 (cos cos cos ) 4 (cos 5 cos 5 cos 5 ) 0 5 4 (cos 7 cos 7 cos 7 ) 0 7             = + + = = + + = = + + = dc dc dc v v m v v v v (5) where, (4 ) f dc v m v  = , modulation index = / dc m m n= , ndc is the number of dc sources, and fv is the required value of fundamental voltage. fifth and 7th order harmonics are targeted for elimination by solving the above non-linear equations. the solution of these equations leads to discontinuity for the certain modulation index. so, the non-linear equations of the she problem are solved as an optimization problem. conventional technique uses nr method to solve the above problem which involves more computation time and complicated mathematical calculations. in order to reduce this, so she is developed which solves the objective function at optimal value of switching angles. the suitable fitness function is chosen to eliminate 5th and 7th order harmonics at different value of switching angle and to satisfy the fundamental component as under: 1 5 71 * ( )  + = − +    dc dc dc dc v v v ff m h n v n v (6) subject to the condition that: 1 2 3 0 2        (7) to obtain the least thd with feasible modulation index the whole term in (6) is multiplied with a factor 1/h. the fundamental value and the targeted 5th and 7th order harmonics are kept within 1% (i.e., h=0.01) error limit. to check the quality of voltage waveform, thd can be defined and calculated as: 1 2 2 2 21 1 thd (%) ( ) 100  =   =      k k v v (8) where k v is the voltage of particular harmonics. v. genetic algorithm ga [29, 30] is a method of random search process used to find approximate solutions of optimization problems. it is a local search technique inspired by biological evolution. the evolution starts from a random initial population and repeatedly modifies the solution in each generation. over a successive generation, multiple individuals (switching angle) are selected from the current population and are used in the next iteration of the algorithm until it reaches an optimal solution. ga uses three main rules in each step to create the next generation of the current population, which contributes for the desired results to select the population. crossover and mutation are used to simulate the natural reproduction and mutation. in crossover, selected individuals are combined and swapped to produce new offspring. with a continuous number of generations and a large population in each generation, the algorithm optimizes a set of solutions of the problem. it computes the different values of the three switching angles to obtain the minimum ff keeping the harmonics within the limit. the ga toolbox is an inbuilt graphical user interface that allows using ga in matlab environment without working at the command line [17]. the ga toolbox results are shown in figure 5. results obtained from ga are summarized in table iii. to use the ga toolbox, the following information should be entered. • fitness function: the fitness function as given in (6) has been entered in the form @ff, where ff.m is a program file that computes the fitness function. • no of variables: the length of input vector to the fitness function is entered. the three switching angles are considered as variables. • constraint function for the problems can be specified in the constraints panel of toolbox. boundary variables can be specified as well. population size, initial population and display command are set in the options panel. fig. 5. best fitness and no. of variables obtained using ga engineering, technology & applied science research vol. 9, no. 1, 2019, 3836-3845 3841 www.etasr.com gopal et al.: swarm optimization-based modified selective harmonic elimination pwm technique … table iii. results obtained from ga results obtained from ga generation count obtained switching angles (in degree) mean fitness best fitness 100 α1 α2 α3 0.133 0.088 12.56 49.69 56.89 vi. so she technique a new variant swarm optimization based algorithm called so she is analyzed in this paper. the theory of so she has been influenced from the same phenomenon as pso, i.e., bird flocking in which it helps the swarm or particle (bird) in dodging from predators. similar to the conventional pso algorithm, so she has a cognitive and a social behavior component. both these components are composed of best and worst values, but pso considers only the best value in successive iterations. including both best and worst values enhances the swarm’s ability to follow the best possible solution. the particles progress in the search space with certain velocities and may reach a best or worst solution. the best and worst positions are stored in the memory as good and bad experience components respectively. the food location is modeled as the best solution point and a predator is modeled as the worst position [31, 32, 37]. the new velocity-position update equation in so she model is accordingly modified by (9) and (10) for ith particle in d dimensional space as: 𝑉𝑖𝑗 𝑟+1 = 𝛿 𝑟 𝑣𝑖𝑗 𝑟 + 𝐶1𝑅1(𝑃𝑏𝑖𝑗 𝑟 − 𝑃𝑖𝑗 𝑟 ) + 𝐶2𝑅2(𝑃𝑤𝑖𝑗 𝑟 − 𝑃𝑖𝑗 𝑟 ) + 𝐶3𝑅3(𝐺𝑏𝑗 𝑟 − 𝑃𝑖𝑗 𝑟 ) + 𝐶4𝑅4(𝐺𝑤𝑗 𝑟 − 𝑃𝑖𝑗 𝑟 ) (9) 𝑃𝑖𝑗 𝑟+1 = 𝑃𝑖𝑗 𝑟 + 𝑉𝑖𝑗 𝑟+1 (10) where i=1, 2, …., n; j=1, 2, …., d; r is the iteration number and r+1 index denotes the next iteration, 𝛿 is the inertia weight which can be defined as: 𝛿 = (𝛿𝑚𝑎𝑥 − 𝛿𝑚𝑖𝑛 ) × 𝑖𝑡𝑒𝑟𝑚 − 𝑖𝑡𝑒𝑟 𝑖𝑡𝑒𝑟𝑚 + 𝛿𝑚𝑖𝑛 (11) where 𝑖𝑡𝑒𝑟𝑚 is the maximum number of allowable iterations and iter is the current iteration. 𝛿𝑚𝑎𝑥 is set to 0.9 and 𝛿𝑚𝑖𝑛 is 0.4. vii. so she algorithm for fitness evaluation • initialization: initialize modulation index (m), size of population, maximum number of iteration (itermax) and the acceleration coefficients 𝐶1, 𝐶2, 𝐶3 and 𝐶4. the acceleration coefficients’ values are set to 1.5, 0.55, 1.75 and 0.35 respectively. 𝑅1to 𝑅4 are random numbers between [0, 1]. randomly create a set of the three switching angles. • fitness function (ff) evaluation: evaluate the ff for each of the switching angles. • the initial positions until iteration r are considered as the local best position of each particle, i.e., 𝑃𝑏𝑖 𝑟 and the global best position 𝐺𝑏𝑟 is the minimum value of the ff. similarly, the final positions are considered as the local worst position, i.e., 𝑃𝑤𝑖 𝑟 and the global worst position 𝐺𝑤 𝑟 is the maximum value of ff. • condition check: switching angles must satisfy the feasibility criteria that they lie between 0 to π/2 as in (7). • updating velocity and position: in this step the particles follow a velocity and position update rule given in (9) and (10). new best and worst values are stored in the memory. iteration continues in the same way until the counter reaches the maximum set value and the new positions of the particles are then calculated. • termination: if the iteration count reaches the maximum set value then calculate the fitness function by varying the m from 0 to 1, otherwise repeat the updating procedure. viii. ga proposed so she algorithm comparison the behaviors of ga and so she algorithm are compared and it is observed that both algorithms converge with acceptable solutions for different modulation indices. figure 6(a) shows the variation of switching angles obtained using so she for different m. the switching angles satisfy the condition (7). the thd obtained using both algorithms against m is plotted in figure 6(b) taking a population size of 100 individuals. lesser thd is obtained at full range of m using so she as compared to ga. this as well signifies that so she converges to a better solution than ga. thd decreases with increase in m, which satisfies the operational principle of mlis. figure 6(c) shows the harmonic profile versus the m obtained using the so she algorithm. (a) (b) (c) fig. 6. (a) switching angles obtained using so she, (b) comparison of thd (%) against m for ga and so she, (c) low order harmonics profile against m. the 3rd harmonic is as high as expected at the whole range of m. keeping in mind future applications of the algorithm to 3 engineering, technology & applied science research vol. 9, no. 1, 2019, 3836-3845 3842 www.etasr.com gopal et al.: swarm optimization-based modified selective harmonic elimination pwm technique … phase systems, triple harmonic content is not chosen to be eliminated in this paper. triple harmonics are absent in line to line voltage of a 3 phase balanced system. 5th and 7th harmonics are nearly zero at almost all values of m which shows the effectiveness of the proposed so she algorithm. furthermore, to prove the robustness of the algorithm, a test is conducted in matlab environment on an intel(r) core (tm), i5, 2.60 ghz processor taking computational time and attained objective value into consideration when all other conditions are kept unchanged. with 100 individuals per population, both algorithms run 20 times and the results are tabulated at 0.5, 0.7 and 0.9 modulation indices. table iv shows the best objective value and corresponding computational times for 50, 150 & 300 iterations. the comparison in table iv summarizes that under the same conditions, so she always converges faster than ga and also approaches to a better solution. table iv. ga and so she behavior comparison m iteration=50 iteration=150 iteration=300 ga so she ga so she ga so she best objective value in 20 runs, in % 0.5 18.7894 17.95 13.919 13.729 8.9312 6.8966 0.7 15.5441 14.8122 11.127 8.1018 6.1201 4.1911 0.9 13.9921 11.1216 6.1132 5.1101 4.0319 3.0113 computational time, in sec. 0.5 99 77 141 134 197 173 0.7 89 69 136 133 191 173 0.9 83 65 132 129 196 168 population=100 ix. simulation and hardware results in order to validate the proposed mli topology, simulations have been carried out using matlab/simulink for the sevenlevel chb mli and rs mli. the value of all three dc sources is taken equal to 35v and the frequency of output voltage is assumed to be 50hz. a series resistive-inductive load of 100ω 150mh is taken in both cases. the calculated switching angles using so she algorithm at 0.91 modulation index (table iv) are applied to the simulation and experimental models. the so she programming code run integrated to the simulation model and results are obtained. a. simulation of chb mli insulated gate bipolar transistors (igbts) are considered as switching devices for simulation and hardware design of sevenlevel chb mlis. required pwm signals for one switch of each h-bridge (t1, t5 and t9) are shown in figure 7(a). figures 7(b) and 7(c) show the simulated output voltage and current waveform, respectively, of a seven-level chb mli. the output voltage results in very small thd of 14.33% are shown in figure 7(d). b. simulation of rs mli four igbts and three mosfets with two discrete diodes were used for designing a seven-level rs mli. generated pwm signals for the level generation switches t1, t2 and t3 are shown in figure 8(a). the simulated output voltage and current waveform of seven-level rs mli are shown in figures 8(b) and 8(c). the fft analysis of the output voltage waveform is shown in figure 8(d). it is observed that the 5th and 7th order harmonics are nearly 0.01% and 0.025%, respectively which is negligible. a comparison of mli topologies described in this study has been presented in table v. (a) (b) (c) (d) fig. 7. simulation results obtained for seven-level chb mli: (a) pwm signals for switches t1, t5, and t9, (b) output voltage waveform, (c) output current waveform, (d) fft analysis of load voltage table v. comparison of mli topologies different topology 7-level chbmli 7-level rsmli no.of switches 12 [2(nl-1)] 7 [(nl+7)/2] switching loss more less switching angle * 1  =16.5° for h-bridge 1 for t1 switches s1 and s2 are continuously on for +ve half cycle (0°-180°) switches s3 and s4 are continuously on for -ve half cycle (180°-360°) 2  =26.2° for h-bridge 2 for t2 3  =41.8° for h-bridge 3 for t3 thd (in %) 14.33 11.84 * using so she at m=0.91 (°) c. hardware design of chb mli the simulation results are validated by a prototype laboratory setup of seven-level chb mli with three isolated dc sources, each of constant voltage 25v. gate pulse for the switches is generated using an atmega16 microcontroller. a series resistive-inductive load of 80ω 50mh is used. the components used for the hardware design of the seven-level chb mli are given in table vi. figure 9(a) shows the pwm pulses for the switches t1, t5, and t9. the feasible switching angles at m=0.91 given in table iv are calculated offline using so she algorithm, and were programmed into the microcontroller using winavr programmer. engineering, technology & applied science research vol. 9, no. 1, 2019, 3836-3845 3843 www.etasr.com gopal et al.: swarm optimization-based modified selective harmonic elimination pwm technique … (a) (b) (c) (d) fig. 8. simulation results obtained for seven-level rs mli: (a) pwm signals for level generation switches t1, t2, and t3, (b) output voltage waveform, (c) output current waveform, (d) fft analysis of load voltage tlp250 opto-coupler was used as driver and for the isolation. all waveforms were acquired using tektronix tps2014b digital storage oscilloscope (dso) and postprocessed using matlab to obtain the harmonic spectrum. figure 9(b) shows the staircase 7-level output. the sinusoidal output current is shown in figure 9(c). figure 9(d) shows the harmonic spectrum, in this case the value of thd is 14.91%. table vi. 7-level chb mli: components used for components/parameters specification power switches (igbt) fga25n120 driver tlp250 processor atmega 16 microcontroller isolated dc supply 25v nominal frequency 50hz linear r-l load (0-100)ω, 50mh d. hardware design of rs mli a 7-level rs mli setup is developed consisting of 4 igbts and 3 mosfets. similar setup as for chb mli is developed and the output is obtained across the rl load. the components used for design of rs mli are given in table vii. figure 10(a) shows the pwm signal for h-bridge s1 and the level generation switches t1, t2, and t3. the offline calculated switching angles are programmed into the atmega16 microcontroller using a burner circuit. the generated pulses drive the power semiconductor switches. output voltage and current obtained for the proposed rs mli across a rl load (80ω, 50mh) is shown in figures 10(b) and 10(c). the fft analysis of the voltage waveform obtained is shown in figure 10(d). it is evident from the results that the proposed seven-level rs mli has better performance, less requirements of components, and low %thd compared to the seven-level chb mli. (a) (b) (c) (d) fig. 9. experimental results for 7-level chb mli: (a) pwm signals for switches t1, t5, and t9 (y-axis 20v/div, x-axis 2ms/div), (b) output voltage waveform (y-axis 50v/div, x-axis 1ms/div), (c) output current waveform (yaxis 1a/div, x-axis 1ms/div), (d) fft analysis of load voltage table vii. 7-level rs mli: components used components/parameters specification power switches (mosfet & igbt) irfp250 & fga25n120 diode rhrp840 driver tlp250 processor atmega 16 microcontroller isolated dc supply 25v nominal frequency 50hz linear r-l load (0-100)ω, 50mh x. conclusion in this paper, a new rs mli topology using reduced switch count was presented and compared with the conventional chb mli topology. the total number of switches is nearly halved when compared to the chb mli topology. so, switching loss is expected to be reduced drastically while the cost is minimized. engineering, technology & applied science research vol. 9, no. 1, 2019, 3836-3845 3844 www.etasr.com gopal et al.: swarm optimization-based modified selective harmonic elimination pwm technique … (a) (b) (c) (d) fig. 10. experimental results obtained for 7-level rs mli: (a) pwm signals for polarity generation switch s1, level generation switches t1, t2, and t3 (y-axis 20v/div, x-axis 2ms/div), (b) output voltage waveform (y-axis 50v/div, x-axis 1ms/div), (c) output current waveform (y-axis 1a/div, x-axis 1ms/div), (d) fft analysis of load voltage for the proposed rs mli, a total number of (nl+3)/2 switches including discrete diodes are in the current path at any time whereas (nl-1) switches are in the current path for the chb mli. this indicates that the conduction loss and voltage drop are also less for the proposed mli when compared to a chb mli. a comparison in view of cost, size and volume is also drawn among seven-level mli types. novel so she algorithm is used to determine the optimum switching angles for selectively eliminating voltage harmonics as detailed in the ff. a delineative analysis 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“real-time implementation of a packed ucell seven-level inverter with low switching frequency voltage regulator”, ieee transactions on power electronics, vol. 31, no. 8, pp. 5967–5973, 2015 [37] k. p. panda, g. panda, “application of swarm optimisation-based modified algorithm for selective harmonic elimination in reduced switch count multilevel inverter”, iet power electronics, vol. 11, no. 8, pp. 1472-1482, 2018 microsoft word nai_etasr_v10_n6_pp6526-6532 engineering, technology & applied science research vol. 10, no. 6, 2020, 6526-6532 6526 www.etasr.com zouari et al.: a comparative study of computer-aided engineering techniques for robot arm … a comparative study of computer-aided engineering techniques for robot arm applications lilia zouari ces laboratory sfax university, tunisia lilia.zouari@gmail.com slim chtourou college of engineering, electrical department king faisal university, saudi arabia slim.chtourou@ieee.org mossaad ben ayed alghat college of science and humanities al majmaah university, saudi arabia and university of sfax, sfax tunisia tunisiamm.ayed@mu.edu.sa shaya a. alshaya department of computer science majmaah university majmaah, saudi arabia shaya@mu.edu.sa abstract-as systems become increasingly complex, their simulation techniques have to be more accurate and enhanced. despite the wide use of robotic arms in industries, they still encompass a wide number of complexities. the control of a flexible robot arm driven by a brushless dc motor (bdcm) for tracking problems is a great challenge, not only for its complex algorithms but also for its verification process. robotic systems are designed heterogeneously by combining continuous and event discrete models. therefore, computer-aided engineering tools have to be enhanced in order to support the verification of the control algorithms. ensuring definite and rapid simulations is a challenging task for robotic application systems. although control strategies can be tested using the matlab/simulink environment to assess their performance, their verification at a low-level still remains a very difficult task. this paper studies different simulation techniques based on model in the loop (mil), hardware in the loop (hil), and hardware software in the loop (hsil) on a flexible robot arm driven by bdcm in order to overcome each method's limits, focusing on performance and cost and simulation time reduction. the hsil achieves the highest accuracy and speed than mil and hil and provides reusability and portability of the control unit compared to the other techniques. keywordscontrol; robot arm; brushless dc motor; model in the toop; hardware in the loop; hardware software in the loop i. introduction robots’ control driven by bdcm has achieved an interesting breakthrough recently [1-2]. the utilization of bdcms is widely spread due to their independence of bearings and brushes, providing them a long survival time, robustness, energy efficiency, and implementation simplicity [3-7]. authors in [8] utilized bdcm in robotics to benefit from its advantages, such as the execution time decrease of control algorithms. they showed that this was a great advantage, especially when looking for robot manipulators either in the industry performing repetitive tasks, or in service robots performing manipulation tasks. nevertheless, despite the progress in this field, there is still an urgent need to minimize cost and time for certain robotic applications [9-13]. robotic systems still require many improvements in design, accuracy, and real-time processing. on the other hand, computer-aided design methods have to be up to date in order to support the complexity and the needs of these systems. this challenge is the main subject of this paper, as it attempts to evaluate the control algorithm performance for a flexible robot arm with one freedom degree using model in the loop (mil), hardware in the loop (hil), and hardware software in the loop (hsil) [14] simulation techniques. the more complex is a control algorithm, the longer simulation time it requires. hence, the design of accurate and rapid simulations is a great challenge for robotic systems, as the need for high performance and available real-time systems has increased their complexity. the design of these complex systems requires an efficient simulation tool for verification, ensuring high performance in less time. hil appends the sincere device in the verification process. this may enhance the test capacity, diminish conceit time and predict the environment interaction. despite its pertinence, compounding variant architecture conceits and protocols at the same time is a complex mission [15]. in [16], an environment to verify and test the hardware via hil was presented and integrated in matlab/simulink. the simulation model was synchronized via real-time communication, and logic control was performed by simulink. authors in [17] presented a technique to test real time embedded systems via hil, benefiting from high-level architecture (hla) for interoperability and synchronization of heterogeneous architectures. their proposed test used ptolemy to verify the patterns operating in hardware and their correspondent ptolemy developed reference patterns in realtime. this approach developed further performers in ptolemy to integrate it in an hla and to interface the software in the hardware under verification. as substantiation of concept, it was applied on a navigation algorithm for a mobile robot. corresponding author: mossaad ben ayed engineering, technology & applied science research vol. 10, no. 6, 2020, 6526-6532 6527 www.etasr.com zouari et al.: a comparative study of computer-aided engineering techniques for robot arm … every data collected by the sensors and the reactions were transmitted in real-time to ptolemy performing the check in the face of a reference model. this allowed multiple computation models to be exploited as reference models, in order to checkout multiple hardware architectures synchronously based on hla [17]. in [18], a distributed co-simulation environment to integrate virtual components was introduced. the cosimulation used a modified hla nominated as distributed cosimulation backbone, which was the standard to exchange data, claiming specific appeals to run-time infrastructure functions. in general, the operation was similar to high-level architecture. similarly, other works used hil to test embedded systems, whereas they were restrained to a restricted set of models and devices, with specific architectures and computation models making the integration harder. in contrast, in [17] the co-simulation was performed for homogeneous models only. unfortunately, these models lack any easy extensions for integration with heterogeneous systems, and their adaptation to diverse hardware platforms, synchronization and communication protocols require much effort. authors in [19] attempted to support synchronization and heterogeneity by involving different computation patterns and integrating realtime hardware devices in ptolemy using high-level architecture. this was an improvement to the integration of several instances of ptolemy to improve performance without hil [20]. in [21], ptolemy was integrated with hardware devices for testing excluding real-time constraints. however, test integration of embedded systems with hil via ptolemy and high-level architecture has not been found. nowadays, designing complex systems requires tools and methods that allow verification and simulation in a practical and efficient way [22]. the use of different modeling and simulation tools during a unique design flow is a very common procedure. however, the integration of hybrid systems is not easy, as there is no guarantee that continuous and discrete systems that work smoothly when separated, will work well when combined [23]. this paper studies the development and evaluation of different verification techniques, based on highlevel architecture, for a flexible robot arm driven by bdcm. to reach this goal, a verification environment for the control of the robot system is necessary. therefore, at first, the mil simulation based on matlab/simulink was used. then, its results were compared with the results of hil and hsil, in order to feature a high performance and short-time method for heterogeneous and complex embedded robot systems. this approach of co-simulation was expected to allow the synchronization between heterogeneous models, such as continuous and discrete models, integrating different simulators. ii. problem formulation and control strategy this section describes the control strategy associated to the bdcm and the flexible robot arm. a. bdcm control the dc voltage ensuring power over the three arms in highand low-level was conventionally provided by an ac-dc converter which was easily achievable through batteries. in line with [24], it was assumed that the insulated-gate bipolar transistors (igbts) and the diodes constituting the inverter were ideal switches, in order to simplify the brushless motorconventional inverter association formulation. the voltages of the bdcm's three phases, van, vbn, and vcn were expressed as functions of s1-6 signals, characterizing the igbts of the three arms state. the bdcm phase voltages a, b, and c were determined considering the signals combinations s1-6. each functioning sequence was divided into motor sub-sequence during which the power was transmitted from the battery to the motor stator phases through two igbts, and a generator subsequence resulting in a power recovery that was returned to the battery through two diodes. the igbts conduction outbreak was ensured by the hysteresis current controllers. the principle of the hysteresis controller was to maintain the real current within a centered given width band around the reference current iref . figure 1 shows the flowchart of the bdcm control. fig. 1. flowchart of bdcm control. b. flexible robot arm control the proposed design focused on a flexible robot arm with one degree of freedom. most similar robots use an actuator brushless motor. the flexible robot arm based on bdcm provides fast, precise movements, and excellent dynamic response with a high dynamic and torque performance. the use of a transmission system is essential for the flexible robot arm. figure 2 describes the flowchart of the flexible robot arm control. iii. verification techniques the choice of the verification technique of the developed digital systems is a very important task. any verification technique should be based on two essential requirements. at first, the existence of a software simulation tool is essential to monitor the performance and avoid potential risk scenarios in real tests. additionally, the provision of a hardware simulation tool is imperative to verify its functionality and measure its performance under realistic conditions. the following section engineering, technology & applied science research vol. 10, no. 6, 2020, 6526-6532 6528 www.etasr.com zouari et al.: a comparative study of computer-aided engineering techniques for robot arm … presents the three verification techniques used for the control of the flexible robot arm driven by bdcm. fig. 2. flowchart of flexible robot arm control. a. mil simulation technique the simulation approach for dynamic systems analysis is a vital step in all robotics studies. for this reason, the scheme of the closed-loop robot manipulator control was modeled using simulink as shown in figure 3. fig. 3. flexible robot arm control using mil. machine-converter associations were particularly involved in this, study since these systems are quite complex, nonlinear, presenting multiple time scales with very small time constants, and variables depending on the operating point. within a perspective to implement the control algorithms for brushless motors driving the robot arm, special focus was given on studying and checking the dynamic performance of this robot in matlab/simulink environment. this model uses the electrical and mechanical equations and quantities already developed from the considered bdcm, and this section focuses on the implementation of the control strategy, adopting the dynamic model of the robot with the determined controller parameters. b. hil simulation technique there is an increased interest in using electrical drives and power electronics in the control of a large variety of different applications, particularly in the robotic field. however, authors in [25, 26] recommended a serious consideration of the design and strict control of electrical drives and power electronics to validate their control strategies. therefore, hil and rapid prototyping methods are described as a deep layer of verification that is required after the software simulation. hil simulators were essentially used for the verification of complex electromechanical systems such as industrial robots [27]. hil simulations always performed the real-time simulation of the system including actuator and sensor models. furthermore, theoretical considerations have been reported along with simulation results related to differences and the evaluation of approaches [28]. this technique has multiple advantages [27]: • during the initial design phases, the platform is not always available to perform real tests. • cost and simulation time will be reduced. • in the presence of system uncertainties during the initial phases of the design, hil is the safest simulation technique to avoid all scenarios risks and dangerous situations. • the verification flexibility can be automated and reproducible. simulink/matlab provides hil by performing cosimulation between the fpga board and the quartus ii software design [27, 29-33]. hil simulation is used to achieve the control strategy of the flexible robot arm, and ensures the verification of the effectiveness of controllers in a repeatable and cost-effective way [29, 31]. the steps required to perform the verification of the controller’s accuracy according to the hil [30-33], are: • step 1: provide the model of the controllers based on the dsp builder blocks in the simulink/matlab environment. • step 2: compile the design based on the signal compiler. compilation creates a compiled quartus ii project presented in figure 4. the compilation procedure (figure 5) comprises of four steps. the closed-loop flexible robot arm control driven by bdcm is described using the dsp builder tool to perform the hil simulation based on the altera de2 board, as shown in figure 6. • step 3: select the adequate configuration of the hil interface and program the fpga board, as shown in figures 7 and 8. after finishing all these steps, the verification of the controllers' efficiency is performed through simulation with matlab/simulink and an altera fpga board. however, despite the provided modeling language and the hil multiple advantages, this verification technique is not suitable for hardware/software co-design. one of the contributions of this paper is to deal with hil weaknesses by developing a new standard target based on the fpga board [29, 33]. shortcomings could be resumed as: • only a few targets are supported. • lack of reuse and portability: the model associated with the control unit (cu) target block set decreases reusability and portability. • unchangeable hw: the hw is created based on the generated code that prevents the modification of hw architecture. engineering, technology & applied science research vol. 10, no. 6, 2020, 6526-6532 6529 www.etasr.com zouari et al.: a comparative study of computer-aided engineering techniques for robot arm … • waste of time: when the model related to the cu changes, the hil technique platform requires to be performed again. c. hsil co-simulation technique in line with [29], the control part was an embedded system defined by sw and hw components. each part had to be aware of the other part's characteristics to obtain optimized components. the most adequate strategy was the co-design, since it was expected to develop hw/sw components concurrently. the main idea was to set the hsil to overcome its limits, as it was recommended in [29, 32-33]. the described method could improve hil, having the following advantages: • expanding the hil to attend the co-design strategy. • the s-function can be integrated into the simulink block to perform specific communication with the fpga board. this is a very powerful way to extend the capabilities of simulink, guaranteeing reusability and portability. • without modifying the architecture, the cu modification and verification is enabled. the main advantage of the proposed method is the synchronization mechanism that ensures the relationship between the simulink/matlab simulator and the hw architecture emulated on the fpga board. the aim of the flexible robot manipulator control design was to verify the cus. the model had a speed controller, a torque controller, and current controllers were considered as sw applications. three steps were crucial for the implementation of the controller units [29-30,34]: • target architecture: the verification needs several tools to satisfy continuous and discrete models. the discrete model was implemented on the altera de2-70 fpga board, using the quartus ii, niosii ides. matlab was used for the continuous model. • synchronization block integration: this block ensures communication and synchronization between the matlab/simulink simulator and the target architecture described in s-function block. the endpoints related to the synchronization interface represent the input signals of the continuous model. when an activation signal is triggered, the synchronization block ensures a context switch to the board by sending a data packet. upon resuming execution, the data packet read by the interface synchronization defines the next activation time. • simulation results: the signals' update events were not periodic, so the simulation was performed using the synchronization scheme. iv. experiments figures 4 and 5 represent the design in the matlab/simulink environment associated to the mil and hil techniques respectively. controllers were replaced with the hil block, and the control algorithm was computed on the board. the hil technique was performed using the dsp builder tool provided by matlab/simulink. figure 6 shows the different characteristics mounted. a cyclone version of fpga was used, based on architecture done in quartus ii (bdcm dspbuilder was the file architecture). as shown in figure 6, the compilation passed through four steps: analyze, synthesis, fitter, and program. figures 7 and 8 describe hil technique's parameters. fig. 4. flexible robot arm control using dsp builder blocks. fig. 5. flexible robot arm control using hil. fig. 6. compilation using the dsp builder. the simulation results for the three techniques, mil using simulink, hil using dsp builder tools and altera fpga board, and the hsil using s-function and niosii were compared. the implementation steps of the hsil techniques are described in [33]. figures 9-11 show speed evolution, position, speed and position error, and the control law respectively using mil, hil, and hsil techniques. however, as the curves in the mil and hsil are similar, only the curves using mil are presented. as it can be observed, the flexible robot arm followed the desired trajectory with a tiny static error rate, confirming the robustness of the controllers orienting the flexible robot arm to the desired position respecting a definite speed. moreover, when the desired final position is reached, the engineering, technology & applied science research vol. 10, no. 6, 2020, 6526-6532 6530 www.etasr.com zouari et al.: a comparative study of computer-aided engineering techniques for robot arm … electromagnetic torque is equal to the load torque. in addition, it would be worth noting that the controllers applied on a flexible robot arm driven by the bdcm yielded an acceptable performance using all techniques. therefore, the desired speeds and accelerations were reached. fig. 7. selection of the hil configuration. fig. 8. the interface of the hil program. table i shows the simulation time for the hysteresis, pid, and torque controllers and all systems using mil, hil, and hsil techniques. table i shows that: • the output signals obtained using hil have an error compared to the output signals using mil and hsil. at first, this error was not expected as the same control algorithm was used in both cases. after a deep research it was concluded that this error happened due to the insufficient memory of the fpga board. this lack of memory led to data corruption which affected the computation results. • satisfactory performance is obtained to achieve the desired speeds and positions at a lower cost. • the presence of a precision loss using hil compared to simulation results using mil, due to the high sampling time. this caused the failure to get all the points for more accuracy, while it allowed having a faster system. fig. 9. speed and position. fig. 10. speed error and position error. fig. 11. control law. table i. simulation time parts simulation with mil (s) simulation with hil (s) simulation with hsil (s) hysteresis controller 48 12 6 torque controller 16 4 2 pid controller 24 6 3 flexible robot arm control 8424 2107 1053.5 after verifying the control algorithm of the flexible robot arm driven by a bdcm using mil, the hil verification results engineering, technology & applied science research vol. 10, no. 6, 2020, 6526-6532 6531 www.etasr.com zouari et al.: a comparative study of computer-aided engineering techniques for robot arm … were closer to the real case. this could enable a faster run of verification scenarios than with the software simulation. following the previously described design methods, hil simulation was much faster and more confident than software simulation. in addition, the refinement of the development and the rapidity of the control strategy were continued by the combination of the hsil co-simulation, as it benefited from each technique's advantages. these results proved that hil simulation was 4 times faster than software simulation. furthermore, the hsil simulation was twice faster than the hil simulation, proving that hsil is the best verification method. v. conclusion this paper aimed to evaluate three computer-aided engineering techniques in robotic systems, focusing on a bdcm control fitted to a flexible robot arm and simulating in matlab/simulink environment via verification methods. the model and the control of the bdcm-inverter flexible robot arm were presented. then, different control strategies such as a speed controller, a torque controller and a hysteresis controller for controlling currents were described. mil, hil, and hsil simulations were studied and analyzed, showing the hsil's benefits. according to simulation results 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[34] m. b. ayed, f. bouchhima, and m. abid, "codis+: co-simulation environment for heterogeneous systems," journal of control engineering and applied informatics, vol. 20, no. 1, pp. 98-107, mar. 2018. engineering, technology & applied science research vol. 8, no. 5, 2018, 3445-3449 3445 www.etasr.com balamurugan et al.: optimal allocation of dstatcom in distribution network using whale … optimal allocation of dstatcom in distribution network using whale optimization algorithm p. balamurugan department of electrical and electronics engineering, saveetha school of engineering, saveetha institute of medical and technical sciences, chennai, india mrbalap@gmail.com t. yuvaraj department of electrical and electronics engineering, saveetha school of engineering, saveetha institute of medical and technical sciences, chennai, india yuvaraj4252@gmail.com p. muthukannan department of electrical and electronics engineering, saveetha school of engineering, saveetha institute of medical and technical sciences, chennai, india muthukannan@saveetha.com abstract—this paper deals with a new approach implemented to decrease power losses and improve voltage profile in distribution networks using distribution static compensator (dstatcom). dstatcom location can be determined by the voltage stability index (vsi) and sizing can be identified by nature inspired, recently developed whale optimization algorithm (woa). to check efficacy, the proposed technique is tested on two standard buses: indian rural electrification 28-bus and ieee 69-bus distribution systems. obtained results show that optimal allocation of dstatcom effectively reduces power losses and improves voltage profile. keywords-whale optimization algorithm (woa); voltage stability index (vsi); distribution static compensator (dstatcom); radial distribution system (rds) i. indroduction high r/x ratio in distribution networks causes poor power quality in a distribution system [1]. its major drawbacks are voltage drop, lagging power factor and instability. these issues create large power losses, poor voltage profile and create network security problems in rural distribution network (rds). in total power generation 10–13% is consumed as losses in distribution [2–6]. aforesaid problems can be resolved by adequate reactive power injection in the distribution system. the reactive power can be injected in the rds with the help of compensating devices. so, compensating devices are essential in the distribution system to decrease power losses and increase the voltages between buses [7]. the majorly of compensating devices used in the rds are shunt capacitors, regulators, upfc, sssc, and dstatcom [8]. dstatcoms have many advantages over other compensating devices, like low power losses, less harmonic production, compact size and low cost. in addition, they will not create any operation problems like resonance or harmonics [9]. a dstatcom consists of a shunt connected voltage source converter (vsc) which is capable, by compensating the bus voltage, to provide enhanced power factor and reactive power compensation in the rds. a new strategy can be designed for determining the location and size of dstatcom to reduce system power loss, improve voltage profile, power factor, load balancing and power quality, free from distribution line overloading, enhance system stability, decrease pollutant emissions, and increase system efficiency [10]. several optimization techniques and compensating devises have been introduced to reduce power loss in the distribution side via optimal dstatcom placement: immune algorithm (ia), differential evolution algorithm (dea), particle swarm optimization (pso), genetic algorithm (ga), bat algorithm (ba), harmony search algorithm (hsa) [7–13]. whale optimization algorithm (woa) has not yet been utilized for finding the location of dstatcom in the rds. in this work dststcom is introduced for reducing total power loss in rds by using the woa. this proposed optimization algorithm is developed on the activities and performance behavior of the whales. woa is effectively utilized for finding the optimal size and location of the dstatcom in a distribution network. this biological based algorithm effectively reduces the exploration area. this method is tested on standard 28-bus and 69-bus test systems by considering minimization loss and voltage stability enhancement. obtained results by woa are compared with the results taken from ia and ga. when compared to these existing algorithms, woa effectively reduces losses and increases voltage stability. ii. problem formulation newton–raphson, gauss-seidal and fast decoupled are a few classical load flow methods, which are not suitable in identifying the line flows and voltages in distribution networks because of the high resistance by reactance ratio (r/x) of the distribution system. so, the forward-backward sweep distribution load flow is used in the present work to solve the load flow [15]. at node t, the equivalent injected current is specified as: = (1) by applying kirchhoff’s current law amongst the buses t and t+1 in line section, the branch current is set as: , = + (2) engineering, technology & applied science research vol. 8, no. 5, 2018, 3445-3449 3446 www.etasr.com balamurugan et al.: optimal allocation of dstatcom in distribution network using whale … by the usage of bus injected in the direction of branch current matrix (bibc), (2) is resulted into matrix format: | | = | || | (3) for calculation of voltage at buses t+1, kirchhoff’s voltage law is employed and the equation is specified as: = − , , + , (4) in the middle of line section buses t and t+1, the real reactive power loss will be computed as: ( , ) = , ,, ∗ , (5) ( , ) = , ,, ∗ , (6) total power loss in the system is calculated by summing up of all losses in every line section: = ∑ ( , , ) (7) a. objective function objective function’s mathematical formulation is stated as: min(f)=min( ) (8) where , is the total power loss of the radial distribution system. b. constraints additional inequality constraints are also considered for this problem. these are: 1) voltage deviation limit: ≤ | | ≤ (9) where are the minimum and maximum voltage limits at bus t, respectively. 2) reactive power compensation: 1 2 min max( ) ( ) ( ), ,.....,dstatcom t dstatcom t dstatcom tq q qt nb   (10) where min ( )dstatcom tq and max ( )dstatcom tq are the minimum and maximum reactive power limits at bus t, respectively. c. voltage stability index in order to discover the node, vsi is used. at each node, voltage stability is calculated with the aid of (11). the less significance vsi node will be the appropriate locality for the employment of dstatcom [16]. to avoid the probabilities of voltage collapse, vsi will be maximized. ( + 1) = | | − 4 , ∗ −, ∗ −4 , + ∗ + | | (11) iii. whale optimization algorithm woa is a biological based optimization algorithm which is developed on humpback x behavior of whales. certain brain cells of whales and human beings are similar. the special behavior of whales in search for food is called bubble-net feeding method. the searching method is based on creating bubbles by encircling or through a ‘9’-shaped path. this behavior of searching is derived mathematically by two phases [17]: a. searching and encircling prey searching prey can be modeled by (12) and (13), where variables a and c are coefficient vectors denoted as in (14) and (15): = | . − | (12) ( + 1) = − . (13) = 2. . − (14) = 2. (15) where α is linearly decreasing from 2 to 0 and r is a random number between [0, 1]. = | . ∗( ) − ( )| (16) ( + 1)= ∗( ) − . (17) if a≥1, searching prey, denoted by (12) and (23), otherwise encircling prey, by shrinking mechanism denoted by (16) and (17), are used, where t is the current iteration, x is the position vector and x* is the best value of the position vector so far. b. spirally updating position position updating is denoted by (18): 0 5 1 2 5 *( ). , .( ) . .cos *( ), bl x t a d if px t d e l x t if p             (18) where p is a random number between [0, 1], l is between [-1, 1] and b is constant for describing the spiral shape [18]. c. proposed work implementation woa approach to reduce power losses and enhance voltage profile by placing dstatcom optimally in the network is described by the following steps:  step 1: set load data and bus data.  step 2: estimate the total power loss, vsi and bus voltages using forward–backward sweep method.  step 3: read line and load data of the system and solve the feeder-line flow for the system using load flow method.  step 4: find the best dstatcom locations using vsi.  step 5: set the population/solutions itmax=100, number of dstatcom locations d=1, dstatcom min=20, dstatcom max=2000  step 6: generate the population of dstatcom sizes randomly using : engineering, technology & applied science research vol. 8, no. 5, 2018, 3445-3449 3447 www.etasr.com balamurugan et al.: optimal allocation of dstatcom in distribution network using whale … population=(dstmax−dstmin)×rand()+dstmin where dstmax and dstmin are minimum and maximum limits of dstatcom sizes.  step 7: find power losses for generated population.  step 8: current best solution is dstatcom values with low losses.  step 9: whales position can be updated through (13) – (15)  step 10: from updated population, losses can be determined, by load flow method.  step 11: if acquired losses are less, then substitute with current best solution or else repeat step 9.  step 12: display the results if maximum iterations number is reached. iv. results and discussion in this paper, woa is implemented for 28-bus and 69-bus systems. in these test systems, three different cases are analyzed to show the effectiveness of the proposed method as shown in tables i and ii, namely a system without dstatcom, system with single dstatcom, and system with multiple dstatcoms. to show the advantage of woa, the simulation results of woa are matched with the ones from other existing optimization methods. the results produced by woa are better than the ones acquired with other optimization methods. a. 28-bus indian rural distribution network to evaluate the capability of the proposed method in real time systems, an 11kv, 28-bus rural indian distribution system has been taken and tested. the network is radial in nature with 28 buses and the substation linked at first bus as displayed in figure 1. essential load and bus data of power lines are taken from [19]. fig. 1. one line diagram of 28-bus indian distribution network 1) case (i) system without dstatcom the initial power losses without using any dstatcom in the radial network are 68.88kw. performance analysis of the 28-bus test system in terms of power losses and voltage stability index with and without dstatcom are displayed in table i. 2) case (ii) system with single dstatcom. by this process, the 7th bus is designated as an optimal dstatcom installation and the optimal place of this location can be designed through woa. the power losses are reduced to 36.89kw from 68.88kw and the voltage profile is greatly improved. the least bus voltage is obtained by placing single dstatcom is 0.9472p.u. 3) case (iii) system with multiple dstatcoms by this process, two dstatcoms are optimally placed and sized at 7th and 12th bus. from table i, it is observed that power loss reduction and voltage stability enhancement are high in multiple dstatcom placement compared with single dstatcom placement. power losses are reduced to 33.75kw and the vsi is improved to 0.8035p.u with multiple dstatcom placement. also the minimum bus voltage enhanced from 0.9123p.u to 0.9495p.u. figure 2 shows the voltage profile improvement of 28-bus with and without single and multiple dstatcom placement. the voltage profile is greatly improved with the placement of multiple dstatcom’s compared to single dstatcom placement. we did not compare the proposed method with existing ones, since there is no work available with dstatcom placement for 28-bus system in the related literature. table i. 28-bus test system performance analysis proposed method case (i): without compensation ploss (kw) 68.88 cvd 1.7975 vsimin (p.u) 0.6927 vmin (p.u) 0.9123 case (ii): with single dstatcom size in kvar (location) 580 (7) ploss (kw) 36.89 % ploss reduction 46.44 total cvd 0.3093 vsimin (p.u) 0.7999 vmin (p.u) 0.9472 case (iii): with multiple dstatcoms size in kw (location) 480 (7), 230 (12) ploss (kw) 33.75 % ploss reduction 51 tvd 0.2076 vsimin (p.u) 0.8035 vmin (p.u) 0.9495 fig. 2. voltage profile improvement of 28-bus b. ieee 69–bus distribution network to evaluate woa in a high level system, an 11 kv, ieee 69-bus has been taken and tested. the required load and bus 5 10 15 20 25 0.85 0.9 0.95 1 bus number v m in (p .u ) voltage profile improvement of 28-bus system without dstatcom with single dstatcom with multiple dstatcoms engineering, technology & applied science research vol. 8, no. 5, 2018, 3445-3449 3448 www.etasr.com balamurugan et al.: optimal allocation of dstatcom in distribution network using whale … data of power lines are taken from [9]. the real and reactive load are 3801kw and 2694.6kvar and the base values are 100mva, 12.66kv. the real and reactive power losses of the base case are 225kw and 102.2kvar. the one line diagram of ieee 69-bus is depicted in figure 3. performance analysis of the ieee 69-bus test system with and without compensation in terms of power losses, kvar, vsi, and voltage profile is shown in table ii. fig. 3. one line diagram of ieee 69-bus table ii. 69-bus test system performance analysis proposed method ia [9] ga [9] case (i): without compensation ploss (kw) 225 225 225 total cvd 0.7327 0.7327 0.7327 vsimin(p.u) 0.6822 0.6822 0.6822 vmin(p.u) 0.9090 0.9090 0.9090 case (ii): with single dstatcom size in kvar (location) 1300 (61) 1704 (61) 1928 (61) ploss (kw) 151.09 157.50 165.43 % ploss reduction 32.84 30 26.47 total cvd 0.5162 ------------ vsimin (p.u) 0.7584 0.7561 0.7534 vmin (p.u) 0.9389 0.9353 0.9380 case (iii): with multiple dstatcoms size in kw (location) 350 (17), 1250 (61) ---- ploss (kw) 146.34 ---- % ploss reduction 34.96 ---- total cvd 0.5011 ---- vsimin (p.u) 0.7630 ---- vmin (p.u) 0.9417 ---- 1) case (i) system without dstatcom the initial power loss without any compensation is 225kw. 2) case (ii) system with single dstatcom. in this process, the 61st bus is designated for optimal dstatcom installation using vsi and the optimal placing of this location can be designed through woa. the real power loss in this case is reduced to 151.09kw. the minimum bus voltage obtained from this case is 0.9299p.u. 3) case (iii) system with multiple dstatcoms in this test case, dstatcoms are optimally placed and sized at 17th, and 61th buses. from table ii, it is observed that power loss reduction and voltage stability enhancement are high in multiple dstatcom placement compared with single dstatcom placement. the power loss is reduced to 34.96kw which is high compared with case (ii). the stability value of the system is improved from 0.6822p.u to 0.7630p.u. to show its effectiveness, the proposed woa is compared with ia and ga [9]. it could be concluded that the proposed woa gives better loss reduction, stability improvement and voltage enhancement compared with existing algorithms. fig. 4. voltage profile improvement of 69-bus system v. conclusion whale optimization algorithm has been implemented and tested in indian 28-bus and ieee 69-bus radial distribution systems. to find the optimal location of the dstatcom, vsi method was used. to find optimal size of dstatcom, woa was used. the power loss was reduced and voltage profile was improved. the proposed method resulted in better power loss reduction and improved the voltage profile than other existing techniques. hence, the proposed method can be implemented for any distribution system to reduce power loss and enhance voltage profile. references [1] t. yuvaraj, k. ravi, k. r. devabalaji, “dstatcom allocation in the radial distribution network with different stability indices using bat algorithm”, ain shams engineering journal, vol. 8, no. 3, pp. 391-403, 2017 [2] t. yuvaraj, k. ravi, k. r. devabalaji, “optimal allocation of dg and dstatcom in radial distribution system using cuckoo search optimization algorithm”, modelling and simulation in engineering, vol. 2017, article id 2857926, 2017 [3] k. somsai, t. kulworawanichpong, “modeling, simulation and control of d-statcom using atp/emtp”, ieee 13th international conference on harmonics and quality of power, wollongong, nsw, australia, september 28 – october 1, 2008 [4] c. sumpavakup, t. kulworawanichpong, “distribution voltage regulation under three-phase fault by using d-statcom”, international journal of electrical and computer engineering, vol. 2, no. 11, pp. 2492-2496, 2008 [5] b. m. repalle, k. m. rosalina, n. p. kumar, “fuzzy logic based optimal location and sizing of dstatcom in radial distribution systems”, international journal of advanced technology in engineering and science, vol. 2, no. 8, pp. 122-129, 2014 [6] g. ledwich, a. ghosh, “a flexible dstatcom operating in voltage or current control mode”, iee proceedings-generation, transmission and distribution, vol. 149, no. 2, pp. 215-224, 2002 [7] i. wasiak, r. mienski, r. pawelek, p. gburczyk, “application of dstatcom compensators for mitigation of power quality disturbances 10 20 30 40 50 60 0.9 0.95 1 1.05 bus number v m in (p .u ) voltage profile improvement of 69-bus system without dstatcom with single dstatcom with 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novel fruit fly algorithm”, journal of advanced research in dynamical and control systems, no. 8 (special), pp. 1470-1478, 2018 [16] y. thangaraj, r. kuppan, “multi-objective simultaneous placement of dg and dstatcom using novel lightning search algorithm”, journal of applied research and technology, vol. 15, no. 5, pp. 477-491, 2017 [17] s. mirjalili, a. lewis, “the whale optimization algorithm”, advances in engineering software, vol. 95, pp. 51-67, 2016 [18] d. b. prakash, c. lakshminarayana, “optimal siting of capacitors in radial distribution network using whale optimization algorithm”, alexandria engineering journal, vol. 56, no. 4, pp. 499-509, 2017 [19] s. gupta, g. brar, “an efficient ga method for optimal capacitor placement in radial distribution system”, acta electrotehnica, vol. 51, no. 4, pp. 243-247, 2010 microsoft word etasr_v11_n1_pp6781-6786 engineering, technology & applied science research vol. 11, no. 1, 2021, 6781-6786 6781 www.etasr.com mustafa et al.: experimental investigation and control of a hybrid (pv-wind) energy power system experimental investigation and control of a hybrid (pv-wind) energy power system. ghulam mustafa department of electrical engineering mehran university of engineering and technology khairpur mir’s, pakistan gm_petarian@yahoo.com mazhar hussain baloch department of electrical engineering mehran university of engineering and technology khairpur mir’s, pakistan mazhar.hussain08ele@gmail.com sajid hussain qazi department of electrical engineering mehran university of engineering and technology khairpur mir’s, pakistan sajidhussain@muetkhp.edu.pk sohaib tahir department of electrical and computer engineering comsats university islamabad sahiwal campus, pakistan sohaibchauhdary@hotmail.com noman khan department of electrical engineering mehran university of engineering and technology khairpur mir’s, pakistan nomankhan@muetkhp.edu.pk baqir ali mirjat department of electrical engineering mehran university of engineering and technology khairpur mir’s, pakistan baqirali@muetkhp.edu.pk abstract-the most essential infrastructure of today’s modern civilization is the energy system. a new energy revolution is ongoing worldwide in understanding the affordability, reliability, and sustainability of energy supply. one of the major challenges and opportunities considered in this energy revolution is the integration of the energy system. the varying dynamics of renewable energy production and the environmental conditions between the different energy sources are the major reasons for this challenge. wind and solar energies are considered the best renewable sources and the foremost substitute sources for power generation. these energies are playing a vital role as alternates of nuclear energy and fossil fuels. electricity is generated through wind energy conversion systems and photovoltaic (pv) cells. these technologies are clean and environmentally friendlier than non-renewable energies. a hybrid pv-wind generation system is more effective and consistent than a single-source system because the solar system cannot work at night or in cloudy weather while the wind speed is variable. the current study proposes an experimental-based analysis. the hardware used is the squirrel cage induction generator (scig) and solar panels. a boost converter is added for maximum power point tracking (mppt) at variable wind speed and available sunlight. keywords—wecs; pv cells; scig; mppt i. introduction wind and solar energy are the most favorable renewable energy sources due to their low cost of energy production. many studies have considered only one of these energy sources (solar or wind), which has disadvantages. wind speed variations disturb the generated power through wecs, whereas the power produced through pvs is affected by the deviation in solar radiation and varying temperature. hybrid solar/wind generation is much more effective and consistent, because the solar system cannot work at night or in cloudy weather and wind speed is varying with time and season. moreover, usually low winds flow on sunny days when solar generation works with higher efficiency [1]. for achieving maximum power, dc/dc converters are used in systems [2-7]. dual input recommendations are given in [2] in order to get maximum power by using buck/buck boost converters for solar and wind systems. the grid connection of a hybrid system based on solar/fuel and cell/wind was suggested in [3]. another configuration of multi input booster was proposed for hybrid solar/wind generation systems in [8]. in [1], pmsg machines were utilized for the wind turbine and two dc/dc converters were used for wind and solar energy, whereas in the proposed work, a scig machine is used for the wind turbine, to get maximum power and two separate boost converters are used for the wind generator and the pv system. in the proposed model, the characteristic of wind energy conversion system, exhibits maximum power of 3kw and the pv module characteristic exhibits maximum generated power of 44.71w. ii. proposed hybrid system configuration this hybrid system is an assemblage of scig based wecs, pv and super capacitor connected mppt-based boost converters separately at the output of wecs and solar as displayed in figure 1. the converter is easily controlled by varying the duty cycle with high efficiency and minimum corresponding author: mazhar hussain baloch engineering, technology & applied science research vol. 11, no. 1, 2021, 6781-6786 6782 www.etasr.com mustafa et al.: experimental investigation and control of a hybrid (pv-wind) energy power system power variability. the output of both boost converters is connected to a mutual dc bus bar. fig. 1. diagram of the proposed hybrid system. a. maximum power point tracking algorithm the algorithm used in this model is p&o (perturbation and observation). it is easy to device, low-cost, and simple. the flow chart of p&o mppt is shown in figure 2. the scheme constantly perturbs the operative voltage after equating the output power with its earlier value. fig. 2. p&o flow chart. b. characteristics of the wecs generator model in the impacted area on the turbine, the power produced is articulated as [9]: �� � 0.5� � � , ��²��³ (1) where the co-efficient of power is cp=0.3-0.59, vω is the speed of wind, β is the pitch angle for zone-2 supposing 0°, ρ=1.25kg/m³, and λ is speed ratio of tip and can defined by: � ��� (2) here, ω is denoted as the rotor speed of the wind generator. wind power and the turbine power relations are expressed as: �� � ���� � �� ,���� (3) equation (4) illustrates wind generator’s turbine power captured by the wind turbine system. cp is the performance coefficient, � is free wind speed and ω is the turbine's angular speed. � � �0.73�151 !��� �� " 13 ⋅ 635% & ! ��� ��'(.(()* '! (4) the turbine power of the wind generator taken by the turbine system is defined by the wind speed given in (4)-(7), whereas the speed of the wind turbine is expressed as in [10, 11]. equation (5) expresses the power of the wind turbine versus its speed, where p is mechanical power, ρ is air density, and a is the turbine swept area. �� � 55 ⋅ 155�+ ,��-. �� " 0.09exp& ,��� " 0.003* '! (5) figure 3 shows the speed of the wind turbine versus the wind turbine power expressed from (5), where vw is wind velocity. it should be noted that at different wind speeds, the turbine power changes with respect to the speed of turbine. figure 3 shows that the turbine power varies at differed wind speeds. the maximum power moves on a 3rd order curve, which shows the maximum power produced by the turbine at each wind speed. fig. 3. turbine power versus turbine speed. c. wind generator system’s controller model through a rectifier wind-generator system, the three-phase ac voltage is inverted to dc voltage (vin) by back electromagnetic force. this review mainly consists on maximum power tracking control performed by the varying duty cycle of the dc-dc boost converter to the dc side. figure 4 shows the generator control of the dc-dc equivalent circuit. the input voltage adjusted through voltage/current is controlled by the dc-dc boost converter. as a control variable of the duty cycle, the speed of the generator is varied with respect to the turbine in the same proportion. engineering, technology & applied science research vol. 11, no. 1, 2021, 6781-6786 6783 www.etasr.com mustafa et al.: experimental investigation and control of a hybrid (pv-wind) energy power system fig. 4. circuit diagram with the dc-dc booster converter. d. pv cell modeling an equivalent circuit of a single pv cell can be shown by applying a source of current, two resistors, and a diode. the model of the pv cell with the single diode is shown in figure 5, and its description in table i. fig. 5. equivalent circuit of the pv cell. the pv cell equation for v-i characteristic is expressed as: 3 � 3�4 " 35 " 367 (6) � 3�4'89:;<=> ?@abc��d8�e�f'!g' hijke kel (7) where: 3m9 � 3n9 & oconpq* ) &rstua v ! onpq " ! oc w* (8) 3�7 � x39y z [3��\ " 298�_ (9) table i. pv module parameters parameter variable values maximum power pm 260w output tolerance ±3% maximum voltage vm 30.82v maximum current im 8.44a open circuit voltage voc 36.97v short circuit current isc 8.94a reference solar irradiation sref 1000w/m 2 reference temperature tref 25 o c nominal operating cell temperature tnoct 45±2℃ e. super-capacitor it comprises of two actuated carbon electrodes, which are electrically shielded by an absorbent separator. the current accumulators permit current transferring to the external terminals. the entire system is saturated with electrolyte permitting the ion transportation between both electrodes. low internal resistance is a property of the super-capacitor. there is contact resistance in the electrode between the current collector and carbon particles, with increase to the non-significant resistance values given by electrode [12-14]. there are many advantages of super-capacitors for hybrid systems where energy storage devices are needed. the use of these capacitors as secondary power systems allows them to respond quickly during the high load demand. these capacitors have lower time constant than the conventional electrochemical generators (perhaps release charge in a few seconds). moreover, these capacitors have the ability to deliver bulk power in a very short time. due to the lack of electrochemical response at the electrodes, the super-capacitors are considered to be used for stability as storage devices [13]. the equivalent model of the super-capacitor is shown in figure 6. equation (10) gives the expression of vsc of the voltage of the super-capacitor in relation with the internal resistance rsc and the current isc of the super-capacitor as: �9y � �1 " a9y39y � mebceb " a9y39c (10) fig. 6. equivalent model of the super-capacitor. for the proposed hybrid system, the super-capacitor is used for storage and stability and is connected to the dc bus. the capacitor bank is shown in figure 7 and the parameters of the super-capacitor are given in table ii. fig. 7. super capacitor bank. table ii. parameters of the super-capacitor characteristic value rated capacitance (total) 2.640mf measured capacitance (total) 2.376mf absolute maximum voltage 450v rated capacitance of individual cells 0.22mf number of cells 12 temperature 105°c iii. experimental model and analysis to study the factual and tangible status, the real setup of the wind and solar energy conversion system is required, which is mostly set up to generate simulated controlled wind speed to engineering, technology & applied science research vol. 11, no. 1, 2021, 6781-6786 6784 www.etasr.com mustafa et al.: experimental investigation and control of a hybrid (pv-wind) energy power system operate the wecs and extract solar energy, which requires high cost and big area. a simpler way is software simulation, but it has limitations for real-time investigation. the best way is to follow the wind turbine norms by using a motorgenerator (mg) setup, where a motor replicates the wind turbine sketch under varying wind speed and a pv panel with artificial generated irradiation represents the solar setup. table iii. equipment and too l list with description equipment name description prime mover (dc permanent magnet machine) 180vdc, 2.7a, 0.4kw, 2500rpm. type:em-3330-1a, s/n: 201 3 phase squirrel motor (scig) 3-phase, 220v,1.4a, 50/60hz, 0.3kw,1420/1670rpm. type:em33303c s/n: 201 solarppanel maximum power 260w tachometer tachometer 20713a rectifier (for 3phase) pe-5310-5a measuring instrument company yalong: yl195 company rohde & schwarz rth1002 load (resistor) 3.3kω (variable) capacitor (excitation cap) 10uf ±5%, 350-400vac super capacitor bank 2.640mf, 450v power supply power electronics universal supplymod: aep-1/ev booster capacitor : 470uf 450v*3 inductor: 1.8mh 5adiode: fr205 digital oscilloscope gwinstek gds-2074a, 60mhz fig. 8. experimental model setup for the hybrid power system. after ample study, an mg set was taken as a prototype for wecs based entirely on the experimental model. a squirrel cage induction motor machine generated power and a permanent magnet dc machine was chosen to emulate the wind turbine in order to investigate the wind turbine non-linear performance. for the analysis of the output power of scig, the motor operated at variable speed. the aim is to experimentally investigate and control the hybrid power system, which is based on wecs and pv through mppt. the model setup is shown in figure 8. the wecs was operated with a dc-dc converter connected to the scig rectified output. the pv was operated with a dc-dc converter connected to the panel output in order to analyze output factors, i.e. power, voltage, and current. to get the succeeding power values a resistive load was connected as dummy load. iv. results and discussion the experimental results of the hybrid wind/pv power system under different scenarios and conditions are discussed below. figure 9 shows the bus bar output voltages when both sources are available and on (hybrid state). maximum output voltage of 320v is generated by the hybrid system on the bus bar by maintaining the common bus voltage and figure 10 shows the output current of the hybrid system (0.408a). figure 11 shows the maximum output power (130.56w) generated by the proposed hybrid system when maintaining common bus power sharing. fig. 9. bus bar output voltage. fig. 10. hybrid output current. fig. 11. hybrid output power. figure 12 shows the voltages before and after the boost converter with respect to generator speed (rpm), when wecs us on and pv is off. it is clearly shown from the output results that at 37s a high rectified output voltage of 280v is generated while out of the dc/dc boost converter the output voltage received is 340v. the speed of the generator was 660rpm when these maximum voltages were recorded. so the voltages of wecs before boost converter was augmented by engineering, technology & applied science research vol. 11, no. 1, 2021, 6781-6786 6785 www.etasr.com mustafa et al.: experimental investigation and control of a hybrid (pv-wind) energy power system 21% by using the designed boost converter, working on the principle of p&o algorithm. fig. 12. output voltages before and after boost w.r.t speed. figure 13 shows the voltage before and after the boost converter along with the power after the boost converter (44.71w). it is clearly shown from the output results that at 31s, the maximum generated output voltage of the solar panel is 34v while at out of dc/dc boost converter the output voltage received is 324v. the voltage of the solar source before the boost converter is maximized by using the designed buck-boost converter working on the principles of genetic algorithm. the results are summarized in table iv. fig. 13. pv output vs boost converter output. table iv. result summary hybrid pv-wind power system s.no. wind rpm pv irradiation voltage power 1 on 660 off n/a 340 100.3 2 off n/a on 9.164 324 44.71 3 on 621 on 9.164 320 130.56 v. conclusion the achieved experimental results show the below mentioned conclusions, which can be extracted from this study. at present, standalone wind and pv systems are globally supported on a relatively large-scale but are not able to give consistence energy. the hybrid system based on wind/pv is a smart scheme for the utilization of the emergent substitute and renewable sources of energy. this study shows a hybrid wecs/pv system connected to a dc bus with mppt. the analysis and results of the proposed experimental model signified the output power produced by the hybrid scheme which can supply continuous power with improved consistency in comparison with a single power source system. the results of the system in three different conditions were analyzed. • when the wecs system was on and the pv was off, the characteristic of wind energy conversion system, exhibited maximum power of 100.3w. • when the wecs system was off and the pv was on, the pv module characteristic exhibited maximum power of 44.71w. • when both sources were on (hybrid state), the maximum power generated by the hybrid system was 130.56w by maintaining the common bus voltages and power-sharing. the hardware-based experimental model of the hybrid system proved to provide fruitful results under varying environmental conditions. in the proposed model, two boost converters are separately used for pv and wind having mppt functions. the converters were based on the p&o and genetic mppt algorithms, which transferred maximum power to the dc bus from the wecs and the pv cell. references [1] s. p. lakshmanrao, c. p. kurian, b. k. singh, and v. athulya jyothi, "simulation and control of dc/dc converter for mppt based hybrid pv/wind power system," international journal of renewable energy research, vol. 4, no. 3, pp. 801–809, sep. 2014. 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[12] a. kadri, h. marzougui, a. aouiti, and f. bacha, "energy management and control strategy for a dfig wind turbine/fuel cell hybrid system with super capacitor storage system," energy, vol. 192, feb. 2020, art. no. 116518, https://doi.org/10.1016/j.energy.2019.116518. [13] o. erdinc, b. vural, and m. uzunoglu, "a wavelet-fuzzy logic based energy management strategy for a fuel cell/battery/ultra-capacitor hybrid vehicular power system," journal of power sources, vol. 194, no. 1, pp. 369–380, oct. 2009, https://doi.org/10.1016/j.jpowsour.2009.04.072. [14] t. r. ayodele, a. s. o. ogunjuyigbe, and b. e. olateju, "improving battery lifetime and reducing life cycle cost of a pv/battery system using supercapacitor for remote agricultural farm power application," journal of renewable and sustainable energy, vol. 10, no. 1, jan. 2018, art. no. 013503, https://doi.org/10.1063/1.4999780. microsoft word etasr_v11_n2_pp6912-6918 engineering, technology & applied science research vol. 11, no. 2, 2021, 6912-6918 6912 www.etasr.com kehili et al.: early detection of neurological diseases using the vot_mean feature early detection of parkinson’s and alzheimer’s diseases using the vot_mean feature ahlem kehili research unit of processing and analysis of electrical and energetic systems faculty of sciences university of tunis el manar tunis,tunisia ahlemkehili@gmail.com karim dabbabi research unit of processing and analysis of electrical and energetic systems faculty of sciences university of tunis el manar tunis, tunisia dabbabikarim@hotmail.com adnen cherif research unit of processing and analysis of electrical and energetic systems faculty of sciences university of tunis el manar tunis, tunisia adenen.2fr@gmail.com abstract-alzheimer’s (ad) and parkinson’s diseases (pd) are tw of the most common neurological diseases in the world. several studies have been conducted on the identification of these diseases using speech and laryngeal disorders. those symptoms can appear even at the early stages of ad and pd, but not in very specific and prominent ways. voice onset time (vot) is an acoustic specification of the stopping consonant that is commonly discussed in studies of phonetic perception. in this study, the vot_mean feature was explored to identify ad and pd early using /pa/, /ka/, and /ta/ syllables for the diadochokinetic task (ddk). vot_mean was calculated as the average of the first and the second vot values (vot_1 and vot_2), corresponding to the second and the penultimate vot measurement cycles. experimental tests were performed on tunisian arabic and spanish databases for the early detection of ad and pd respectively. the results showed a very high significance of vot_mean on the early detection of ad and pd. moreover, the best results were achieved using the xgboost (xgbt) algorithm as a classifier on the vot_mean feature. keywords-alzheimer’s disease (ad); parkinson's disease (pd); early detection; neurological disorders; vot_mean; ddk; tunisian arabic database; spanish database i. introduction associated speech disturbances caused by disturbances in the speech mechanism, particularly in muscle control, are grouped under the single definition called dysarthria. these disturbances result from disorders of the basic motor processes involved in the production of speech [1]. the difficulties in verbal production caused by dysarthria are due to weaknesses of muscle speech, lack of coordination, and paralysis. moreover, dysarthria can cause peripheral and central nervous system damages. these lesions can appear from birth, as in the cases of cerebral palsy and muscular dystrophy, or later in life engendered by different conditions that can disrupt the nervous system, involving injuries, parkinson's disease (pd), cerebral moods, multiple sclerosis, huntington’s disease, etc. the first studies related to the perceptual characteristics of dysarthria were carried in [2-3]. a total of 212 patients having symptoms of joint dysarthria with different neurological disorders, such as parkinsonism, amyotrophic lateral sclerosis, chorea and cerebellar ataxia, bulbar palsy, dystonia, and pseudobulbar palsy were examined, identifying 38 distinct characteristics of speech and categorizing them into seven modalities: articulation, respiration, pitch, prosody, loudness, resonance, and vocal quality. these studies specified the characteristics of each neurogenic group in addition to those shared by more than one. once the perceptual characteristics of each neurogenic group were identified and grouped, the characteristics of dysarthric speech were classified into the following dysarthria types: hyperkinetic, ataxic, unilateral upper motor neuron, mixed and flaccid, and hypokinetic. hypokinetic dysarthria is considered to be one type of dysarthria primarily associated with alterations in the functions of the control circuits of the basal ganglia. these disorders are the iterations that occur between motor and cognitive functions in the hippocampus. hypokinetic dysarthria includes several aetiologies. idiopathic pd is one such prototypical and common disease linked to this type of dysarthria. as the rate value of the estimated prevalence of pd in people aged over 65 years is 1.5%, it is considered to be the second most common neurodegenerative disorder [4], following alzheimer’s disease (ad) [5-6]. moreover, cognitive impairment can be observed in 80% of people with pd [7]. the epidemiological study demonstrated in [8] showed that 80% of the patients with pd developed cognitive impairment, while 50% of them had pd dementia. the risk of developing dementia was higher in people with pd than in healthy ones [9]. additionally, pd dementia contributes to the increased burden of care in addition to morbidity or mortality [10]. thus, it is important to detect early parkinson’s disease dementia (pdd). further studies are needed to identify, evaluate, and distinguish pdd indices from other types of dementia, such as ad. although the discriminating characteristics of pdd were manifested in damage on the executive function from the cognitive function test and problems related to the free recall in the memory test, pd without dementia may have diminished executive functions, such as worsening the verbal fluency [11]. however, problems with memory and executive functions can also be evidenced by ad and other types of cognitive impairments at the early-stage, complicating their distinction based on executive functions. additionally, there may still be a corresponding author: ahlem kehili engineering, technology & applied science research vol. 11, no. 2, 2021, 6912-6918 6913 www.etasr.com kehili et al.: early detection of neurological diseases using the vot_mean feature significant overlap between the cognitive impairments of ad and pd patients, although the former primarily suffer from deterioration of the cortical profile (i.e. memory and ability language) and the latter have defects in the subcortical profile (i.e. executive functions and visuospatial ability) [12]. moreover, similar cognitive disorders have been reported for ad and the 26% of the pdd cases [13]. furthermore, 50% of pd patients without dementia exhibited amyloid accumulation [14], which is a widely known characteristic of ad. it should be noted that greater patient's age and later onset of pd increase the risk of dementia [15]. pd can lead to motor limitations affecting the speech production process causing several disorders, broadly categorized into three main dimensions: linguistic, prearticulatory (resonance and phonatory characteristics), and prelinguistic (prosodic fluctuations and articulatory changes) [16]. in this context, sound production from the physical point of view is referred to prearticulatory, keeping in mind only the characteristics linked to the phonation process at the level of modulations integrated by the vocal tract (such as a resonant structure invariant in time) and phonation. prelinguistic dimension refers to variations in the prosody of speech and is rendered as variations in f0 and intensity, as well as articulatory variations appearing due to changes in the coordination frequency, the position of articulators, and a result of their interconnection with excitement. thus, it mentions the mechanisms of speech production as forms varying in time. the linguistic dimension is linked to changes in the expected acoustic content of speech, mainly due to substitutions and/or repetitions. to sum up, the linguistic dimension is related to the expressive capacities of the language, while the prelinguistic and prearticulatory dimensions are related to the speech [16]. ad involves the whole process of the first pathological variations in the brain before its symptoms manifest as dementia [17]. ad includes patients with dementia, patients with mild cognitive impairment (mci), and asymptomatic persons having positive ad biomarkers [16]. brain variations occur when specific neurons are deteriorated or destroyed. the progression of symptoms varies more quickly when the diagnosis of ad is made at an early stage [17]. language issues are considered as one of the most specific symptoms of ad, which manifest as an unavoidable and direct outcome of cognitive impairment [18]. primary progressive aphasia (ppa), defined as a clinical syndrome specified by a progressive language disorder with a neurogenerative etiology, could be a manifestation mode of several neurodegenerative deficiencies such as ad [19]. communication and language problems are evident in interactions between neurologists and patients, and interactional feedback can be explored to distinguish cognitive difficulties caused by neurodegenerative or functional memory impairments [20]. the use of different linguistic tests has shown poor performance for patients with ad [21], as they have more difficulty in naming tests where they often repeat the same ideas, use simpler forms of speech, and use empty or longer pauses. moreover, people having ad show monotonous prosody and less cohesive, informative, and consistent speech compared to control groups [22]. methods based on the automatic processing of the voice signal from its forms have been recently explored for the detection of neurodegenerative impairments. the traditional and common features of ad detection using voice signals are linear and considered to be the easiest to interpret clinically [23-28]. other innovative and current techniques have explored non-linear features [29]. both types of features are primary indicators of expressive forms of language based on the tasks performed [24]. besides the feature extraction process, where mathematical models and/or statistical analysis are used to quantify the characteristics of speech, there is the classification process based on the exploration of machine learning techniques. different types of classifiers have been constructed to perform the classification procedure, such as artificial neural networks (anns), support vector machines (svms), and k-nearest neighbour (knn). deep learning appears as a more sophisticated learning technique making possible the advance on automatic ad detection from the voice signal. the ddk task is defined as a clinical test explored in the evaluation of the articulatory system's functional capacities [30]. its concept is that motor deficits in vocal abilities of people suffering from pd appear more strongly in circumstances requiring motor execution and planning over long sequences of motor production (i.e. repeating the same sequence several times or in cases where a given fragment appears in a sentence context). correcting pd results leads to simplifying the articulation at the cost of ease of processing [31], indicating important signs on speech production from a motor point of view. fine articulatory precision is required for the ddk test, including the alternating production of syllable sequences, as well as the ability to quickly change articulators between consecutive segments. this is usually performed by asking the patient to produce combinations comprising of a voiceless consonant and vowels with velar, bilabial, and alveolar places of articulation. more precisely, the subjects are usually asked to constantly repeat the sequence of syllables /pa/-/ta/-/ka/ for about 10 seconds as quickly and clearly as possible. this test needs fast movements of the articulators using the soft palate (back of the mouth), the lips (the front), and the lip of the tongue (middle) continuously and sequentially. regardless of its simplicity, this task reveals some signs of the speaker’s ability to assess subphonemic durations or syllable-to-syllable stability and produce the speech at an appropriate rate [31]. the syllable rates of the ddk test are used in this sense to quickly alternate speech movements and assess the patient’s ability [30]. the test was also used to evaluate imprecise consonantal coordination determining the vot, typically measured as the duration between the initial burst and the vowel onset [32]. moreover, in [33], it was proposed that the imprecisions of articulations on stop consonants were mainly due to low-frequency frictional noise or spirantization substituting stop gaps as a consequence of reduced closure. in this sense, the change in vot for voiceless (/p/, /t/, /k/) and voiced (/b/, /d/, /g/) stops was identified as an indicator for the presence of pd [33-37]. furthermore, vot measurements were explored and compared for analyzing the speech production [p, t, k] of bilingual adults. vot values were higher in brazilian portuguese (bp) than in english [38]. in [39], the differences between the vot duration measures engineering, technology & applied science research vol. 11, no. 2, 2021, 6912-6918 6914 www.etasr.com kehili et al.: early detection of neurological diseases using the vot_mean feature were studied in the case of plosive consonants [p, t, k] for 14 bilingual subjects (spanish-english) aged 18-24 years. lower vot values were found for subjects who learned both languages when they were less than 6 years old [40]. in [41], vot measurements were studied in the case of non-voiced plosive sounds [p, t, k] for five bilingual children (english and bp) aged 8-9 years, reporting the following vot values: for english, [p]=40ms, [k]=65ms, and [t]=56ms, while for bp [p]=48ms, [k]=70ms, and [t]=60ms. a few studies were conducted using vot measurements in turkish [42-44], while the vots in lebanese arabic were shorter compared to other languages [45]. this study adopted the vot_mean measure as an indicator to identify pd on a tunisian arabic dataset and ad on a spanish dataset, using different machine learning algorithms and voiceless consonants (/pa/, /ta/, and /ka/) for the ddk task. the measurement of vot_mean was carried out by taking the average value of the second (vot_1) and the penultimate (vot_2) vot measurement cycles. ii. methods and datasets a. methods the proposed method was composed of five phases: feature extraction, feature selection, feature scaling, data distribution, and classification. 1) feature extraction the vot measurements were carried out manually for /pa/, /ta/, and /ka/ syllables by utilizing the praat software. as shown in figure 1, the vot_mean was calculated by averaging the values of vot_1 and vot_2 which corresponded to the second and the penultimate vot measurement cycles. the second cycle of the vot measurement was selected due to the insufficient speech energy of the speaker, during the first vot cycle. the penultimate vot measurement cycle was selected due to its sufficient energy. the time cycle measurement was given in ms. the vot_mean values were consistent with the production of the stop consonant. fig. 1. the extraction of vot_1 and vot_2 using praat software. 2) feature selection in this phase, principal component analysis (pca) was used due to its high performance on feature extraction and feature dimension reduction. this approach was based on the assumption that features with high variance included most of the information relating to certain classes. furthermore, it permitted the conversion of observation groups with correlated variables into smaller groups with linear correlated variables by exploiting an orthogonal transformation. 3) feature scaling this step was applied for the samples remaining after the feature selection. minmax was used as a scaling function to scale the samples between -1 and 1. this phase's objective was to restrict the values of the concerned features in this range, avoiding large variations. thus, the computational cost could be decreased ameliorating the model's performance. 4) data distribution the explored database was split into training and test sets using the python train_test_split function. as shown in table i, 20% of the database was used for testing, while 80% was used for training. this distribution reduced computation time for the first cycles of modeling. table i. information about the explored database data repartition test training number of samples 20% 80% 1024 5) classification after the previous steps, the desired classifiers were selected and applied. many machine learning (ml) algorithms were explored, such as decision tree (dt), knn, xgboost (xgbt), random forest (rf), and multi-layer perceptron (mlp). b. datasets 1) tunisian arabic dataset for alzheimer’s disease the dataset included numerous vocal recordings of male and female individuals of the ad group, where 20 suffered from ad, and 20 were healthy (hc). each group was equally divided between the two sexes. each speaker was requested to pronounce the sequence of syllables /pa/, /ka/, /ta/, or /pataka/ in the tunisian arabic dialect with a comfortable height and intensity. the goal behind the repetition of each syllable was the preservation of high reliability and quality in speech production for each participant. the number of repetitions was linked to the ability of each participant to repeat the requested sequence, so the duration of the recordings differ. all samples were recorded at 16-bit resolution, 22khz sample rate, and saved in wav format. the extracted features were saved in csv format. healthy participants' samples were labeled with "0", whereas participants suffering from ad were marked with "1". the mean age of the participants was 76 years, while its standard deviation was 8.17 years. the youngest and the oldest participants were 61 and 88 years old, respectively. the mean age of the healthy participants was 74.125, while its standard deviation was 5.79. 2) spanish dataset for parkinson’s disease this dataset was composed of voice recordings from 50 people suffering from pd and 50 hc. each group consisted of 25 men and 25 women. all participants were native colombian engineering, technology & applied science research vol. 11, no. 2, 2021, 6912-6918 6915 www.etasr.com kehili et al.: early detection of neurological diseases using the vot_mean feature spanish speakers. women aged between 44-75 years (mean 60.1±7.8), whereas men aged between 33-77 years (mean 62.2±11.2). in hc, women aged between 43-76 years (mean 60.7±7.7), while men aged between 31-86 years (mean 61.2±11.3). it should be noted that the participants suffering from pd did not suffer from any other neurological disease. additionally, all participants were diagnosed and labeled by expert neurologists using the updrs and h&y scales [46]. the samples were recorded at 16-bit resolution and 44.1khz sample rate using a dynamic omnidirectional microphone. 3) data analysis the spss software was utilized for performing multivariate analysis of variance (manova) on the repeated tests of vot_mean data. as shown in table ii, the vot_mean demonstrated a very high significant effect on the ad and pd groups ([f(1, 63)=44.773; p<0.000] and [f(1.296)=94.346; p<0.000], respectively), proving that the ad and hc groups' vot_means differ significantly. the sum and the average of squares of vot_means for inter and intragroups are also presented in table ii. table ii. one way anova for vot_means vot_mean for ad sum of squares ddl average of squares f significance inter-groups 2877.19 1 2877.1 44.77 0.000 intra-groups 3984.24 62 64.2 total 6861.43 63 vot_mean for pd inter-groups 0.006 1 0.006 94.34 0.000 intra-groups 0.019 295 0.000 total 0.25 296 4) evaluation metrics different evaluation metrics were explored for verifying the predictability of the different models. the accuracy and the fmeasure offered the opportunity to measure the capacity of differentiation of one class among others, even if they were unbalanced. nevertheless, accuracy in such a case can lead to misleading results. the precision, sensitivity, and measurement metrics f were expressed as: ��������� = � �� � (1) ����������� = � �� � (2) � − ������� = �×���������×��� !! ������������� !! (3) where tp, fp, and fn represent true positive, false positive, and false negative, respectively. precision and specificity were determined as: "������� = �� � �� �� �� � (4) �#���$����� = � �� � (5) where tn represents true negative. moreover, the matthews correlation coefficient (mcc) was used to prove the quality of the binary classification. this metric was expressed as: �%% = �. �' �. � () �� �*) �� �*) �� �*) �� �* (6) iii. results and discussion a. results table iii shows the results of using different classifiers on the tunisian arabic dataset to detect ad. the best performance in all terms was achieved by xgbt, followed by rf. the xgbt algorithm had 92% precision, 92% accuracy, 92% sensitivity, 92% f1-measure, and 0.84 mcc. the rf algorithm had 90% precision, 90% sensitivity, 90% accuracy, 92% f1-measure, and 0.80 mcc. table iii. results of different classifiers on ad mlp pres (%) sens (%) f1 (%) acc (%) mcc hc 83 86 88 87 0.74 ad 90 88 86 avg 87 87 87 knn hc 86 85 88 88.3 0.77 ad 92 92 89 avg 89 88 88 dt hc 89 80 84 88 0.75 ad 88 95 91 avg 88 88 88 rf hc 89 89 89 90 0.80 ad 90 90 90 avg 90 90 90 xgbt hc 91 91 91 92 0.84 ad 93 93 93 avg 92 92 92 table iv shows the results of using different classifiers on the spanish dataset for detecting pd. the best results were achieved by using the xgbt algorithm on the /ka/ syllable. the xgbt algorithm achieved the best average for precision (92%), followed by rf (88%). regarding accuracy, the best average value was reached by xgbt (92%), followed by the rf (90%). the best sensitivity was achieved by xgbt (92%), followed by rf (90%). concerning the f1, the best average values were achieved by xgbt (92%), followed by rf (87%), while the best mcc was achieved by xgbt (0.88), followed by rf (0.73). overall, it can be concluded that xgbt was the best classifier on both ad and pd, in terms of results. b. discussion this study aimed to examine whether subtle early symptoms of ad and pd exist in the acoustic signal of arabic and spanish speech respectively, by comparing the vot_mean feature between hc, ad, and pd groups. in [47], it was noted that the overall variation in vot production could be revealed in individuals with moderate ad. also, relying on results from various measurements on older people, there was an expectation that people at this stage of ad can show an overall change around the smaller vot values. according to this study's results, the differences in vot_mean values were statistically very significant in people with ad or pd compared to a healthy control group, on both arabic and spanish databases. to the best of our knowledge, no published studies have tested vot_mean measurements in people with ad in arabic languages. nevertheless, some studies have been performed on arabic databases using the vot measure for engineering, technology & applied science research vol. 11, no. 2, 2021, 6912-6918 6916 www.etasr.com kehili et al.: early detection of neurological diseases using the vot_mean feature other tasks, such as testing the impact of contrast on f0 (cf0) caused by consonants in lebanese arabic [48]. testing vot measures on english [48] showed that there was no statistical significance in the differences of people with ad for the early detection of this disease. table iv. results of different classifiers on pd vot_mean /ka/ pre (%) acc (%) sens (%) f1 (%) mcc mlp hc 86 80 93 85 0.58 pd 78 60 71 avg 82 77 78 knn hc 89 80 91 81 0.62 pd 74 70 78 avg 82 80.5 79.5 dt hc 85 84 90 89 0.59 pd 80 61 87 avg 82 76 88 rf hc 88 88 93 91 0.73 pd 88 79 82 avg 88 86 87 xgbt hc 94 92 94 94 0.88 pd 90 89 89 avg 92 92 92 vot_mean /pa/ mlp hc 86 80 90 84 0.56 pd 76 63 71 avg 81 67 77 knn hc 89 88 90 91 0.68 pd 83 75 77 avg 86 83 84 dt hc 82 82 89 86 0.6 pd 80 68 73 avg 81 87 97 rf hc 88 88 94 91 0.71 pd 86 75 80 avg 87 84 85 xgbt hc 92 91 92 93 0.84 pd 90 87 89 avg 91 90 91 vot_mean /ta/ mlp hc 77 75 78 80 0.4 pd 67 71 35 avg 74 74 74 knn hc 77 79 83 80 0.59 pd 82 75 78 avg 79 79 79 dt hc 80 81 89 84 0.61 pd 83 71 77 avg 82 80 81 rf hc 82 83 90 87 0.63 pd 86 70 75 avg 84 80 81 xgbt hc 90 88 90 90 0.73 pd 83 83 83 avg 87 87 87 for early detecting pd in the spanish language, it was found that utilizing the vot_mean measure produced better results using the /ka/ syllable than /ta/ or /pa/. this is in agreement with [49], who proved that the proposed vot was accurate for estimating its limits with the /ka/ syllable for healthy and pd-affected individuals. moreover, the highest discrimination ability (94.4% with the leave-one-out method and 92.2% with the 10-fold cross-validation) was achieved using the pd detection approach proposed in that study with /ka/ syllable. furthermore, good results were obtained on the early detection of ad and pd using the vot_mean measurement, proving that this approach is effective regardless of the languages explored. iv. conclusion this paper studied the early detection of alzheimer’s and parkinson’s diseases using the vot_mean feature of the ddk task. the early detection of ad test was performed on a tunisian arabic dataset using /pa/, /ta/, and /ka/ syllables, and the best results were obtained using the xgbt algorithm (precision=92%, accuracy=92%, sensitivity=92%, f1=92%, mcc=0.84). the early detection of pd test was carried out on a spanish dataset using separately the /pa/, /ta/ and /ka/ syllables, and the best average results (precision=92%, accuracy=92%, sensitivity=92%, f1=92, mcc=0.88) were reached with xgbt on the /ka/ syllable. moreover, the very high significance of the vot_mean feature was noted concerning early detection of ad and pd. future work should test the vot_mean feature on the early detection of pd on arabic databases, as there is no such database to this date. furthermore, the proposed model for pd detection should be tested on other syllables, such as /pata/, /pakata/, etc. regarding the early detection of ad, it is important to test the suggested approach on different language 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otls are bound to happen and thus locating and coping with them is an important aspect of otl’s operation and maintenance. these faults may be of temporary or permanent nature, with certain types of faults progressing over time from the first category to the second. local weather may also have a direct effect on the occurrence of faults resulting to puzzling events. a special category, often complex in nature, is insulator faults. insulators are used in otls to support phase conductors while not allowing current to flow through the tower’s body to the ground. traditional ceramic insulators used materials such as porcelain and glass as insulation, but in the last decades composite insulators with two insulating parts (a glass core/rod and a rubber housing), have also known great use mainly due to their low weight and their capability to withstand pollution. however, they are subjected to certain faults unique to them, such as flashunders. flashunder is a term commonly used lately to describe faults that are related to the rod/housing interface of composite insulators. such faults are rather difficult to locate as the electrical discharge does not create an easily visible trace (as in the case of flashovers) or a permanent mechanical fault (as in the case of brittle fractures). such a fault occurred for the first time in the transmission system of crete in 2019 and this paper follows and discusses the incident and the experience gained. keywordsflashunder; overhead; transmission; line; insulator; power; high voltage; permanent; transient; fault i. introduction overhead transmission lines (otls) are major components of power systems, used in the power transmission part of the system to connect high voltage substations, usually over long distances. their basic components are the conductors (used to carry the high voltage), the supporting structures (used to elevate the conductors at safe distances above the ground, the trees and all other structures), and the insulators that are used to provide electrical isolation and clearance (i.e. safe distance) obviously while also providing mechanical support. overhead ground wires (or earth wires) are also commonly used, suspended above all other components, to provide lightning protection. the types, materials and designs for all these components (as well as for the voltage level used) vary [1-3]. under various circumstances, and due to various causes, the electrical isolation between different conductors or, more commonly, between a conductor and the supporting structure may be bridged and in that case, a fault occurs [2-3]. faults in otls may be of transient or permanent nature. when a fault occurs, it is detected by protection equipment and the line is powered off almost instantly [2-4]. to avoid needlessly powering off the line for large periods of time due to transient faults, protection schemes employ a re-energization (reclosing) strategy [2-4]. a transient line fault is by definition a fault cleared after a small interruption of power and it is the result of factors that are either temporary in nature (e.g. lightning, birds/twigs etc.) or are removed due to the stress induced by the power arc (e.g. a piece of string or wire) [2-4]. the term “permanent fault” on the other hand does not necessarily describe a fault related to a permanent damage. the term includes all faults that are not transient and a further categorization using the term “semi-permanent” is also occasionally used (e.g. in [5-6]). in this paper, just the basic separation in the two main categories is followed, which means that the term “permanent” is also used to describe faults that are sustained long enough to not allow reclosing but are removed in the long term. such faults may be the result of factors that cease to exist after a longer period than the one set for reclosing (e.g. a passing fire [7], an air-borne item eventually carried away or burned out etc.). it should be noted, however, that a transient fault is not to be treated lightly as it may be an indication of an issue likely to re-appear causing new disturbances and/or that builds up and will eventually lead to a permanent fault. also, a possible damage from the power arc and/or the fault’s cause (e.g. a ground fire [7]) may have a direct impact on the lines’ capability to operate correctly in the future. thus, when a transient fault is recorded, the line maintenance crews are called to provide further insight. to that end, several factors are considered (time of fault, weather conditions etc.) to assess the importance of the event and inspections are scheduled. powering off a transmission line may have a significant impact on the power system and huge economical costs (risks aside) and thus the usual first approach is to perform live inspections from the ground to check for any signs revealing the fault’s cause and location as well as any fault-related damages. if nothing is found then the line is kept energized (or, in case of a permanent fault, re-energized). however, the number of events corresponding author: d. pylarinos engineering, technology & applied science research vol. 9, no. 5, 2019, 4851-4858 4852 www.etasr.com pylarinos and pellas: investigation of an insulator flashunder in an 150 kv otl … (along with other data) may be used in the long term to assess the necessity of further improvements in a certain transmission line (or parts of it). it should be noted that the exact location and cause of a line fault is often not easily identified. thus, the faults’ cause may often be misidentified or remain unidentified (e.g. some typical examples in [8]). it should also be noted that just the time needed to reach the indicated area (let alone complete the inspection) may be significant [9]. thus, it is not unusual for operators to re-energize lines even when a nonconclusive inspection report is received. in the same context, it is not illogical for operators to sometimes try to re-energize a line even without an inspection report (e.g. in an emergency situation). such approaches however may lead to a puzzling series of events in the case of insulator faults such as flashunders or pollution induced flashovers (which are generally rare compared to other fault causes [8]). this paper focuses on a flashunder fault experienced earlier this year in the transmission system of crete. it took more than 20 days for the fault to be identified and located. during this time, the fault kept appearing and disappearing creating a confusing profile. the series of events related with the fault (and the attempts to locate it) are thoroughly discussed in this paper, from the otls subsection’s point of view, aiming to add to worldwide experience. ii. flashing over and under a special category of otl faults is the one related to insulators. although insulator faults are easy to deal with in terms of the immediate actions needed to remedy the situation (a simple insulator replacement is usually enough), actually locating the faulted insulator tends to be much more complex. locating was not much of an issue when dealing with traditional ceramic insulators (using glass or porcelain as an insulating material) as a power arc usually meant some broken glass insulators or some clearly visible signs on porcelain insulators in the string. the most complex and well known issue related to traditional ceramic insulators is the accumulation of pollution on their surface that, in the presence of a wetting agent, creates a conductive film [2-3, 10-11]. this procedure may lead to a flashover [2-3, 10-11] but arcing counteracts it and thus an inconsistence performance may be recorded. the ability to suppress the pollution phenomenon along with several other advantages (e.g. low weight) has led to wide installations of the relative new, for otl time frames, composite insulators. composite insulators have two different insulating parts, a core and a housing, and have proved to be able to cope with the pollution phenomenon due to their hydrophobic surface properties [2-3, 10-11]. they still experience flashovers however, mainly caused by other factors (e.g. bird activity, ground fires etc.) [3, 8, 10-11]. they also suffer from another type of fault whose root cause is located in the rod/housing interface, as internal tracking along the core may occur due to moisture ingress [12]. it should be noted that internal defects may also cause tracking through the core [12]. initially, such faults were more frequent due to design imperfections (e.g. filling the rod/housing interface with grease, improper rod material etc. [3, 11]) or mishandling [2-3, 11]. as more experience was gained from manufacturers and linemen, such issues are now considered solved [3] but their traces are still evident in transmission lines already equipped with such insulators (as replacing older insulators precautionally is usually not an option) or in past fault recordings. thus, such faults are still found to be among the top fault causes for composite insulators (a sum up of major surveys can be found in [3, 11-12]). it should be noted however that there are several issues regarding the classification between different organizations, countries and time frames as a result of the absence of strict definitions and also due to the fact that one type of failure may lead to another [3, 11-13]. “flashunder” has surfaced as a term commonly used to describe a bridging discharge conducted under the housing (in contrast to “flashover”) and along or within the core [12]. internal tracking grows in or on the rod until a critical distance is bridged and a flashunder occurs [12]. a flashunder is visibly spotted when traces are ultimately created on the sheath, but the location and size of these traces makes them difficult to spot. on the contrary, a flashover is much more easily spotted as the power arc leaves easily visible traces on the sheds. typical images from worldwide experience can be found in [3, 11-14] whereas additional images from flashed-over and flashed-under insulators removed from service from the transmission system of crete are shown in figure 1. it should also be noted that, similar to the effect arcing has on recessing the pollution flashover process, a flashunder power arc may dry out the moisture from the rod/housing interface thus allowing the line to be re-energized, only to fail again after time or renewed wetting [12]. a b c d fig. 1. visible traces of flashover (discolored sheds) in a-b and flashunder (damaged sheath) in c-d. photos a and b from past faults. photos c and d from the insulator of the incident analyzed in this paper. iii. the transmission system of crete the transmission system of crete operates at a 150kv nominal voltage and it is consisted of 20 substations (three of them attached to powerplants) and the lines that connect them, as shown in figure 2. historically, the coastal growth of the network along with the experienced weather and microclimate, resulted to increased pollution issues, especially to the eastern engineering, technology & applied science research vol. 9, no. 5, 2019, 4851-4858 4853 www.etasr.com pylarinos and pellas: investigation of an insulator flashunder in an 150 kv otl … side of the island (eastern of heraklion) [15-17]. a major program to replace ceramic insulators with composite ones with silicone rubber (sir) housing has been launched in 2004 in order to cope with the problem, with rather satisfying results [15]. it should be noted however that originally, back in the 80s, a prior attempt to use polytetrafluoroethylene (ptfe) composite insulators proved to be a failure due to brittle fracture issues, attributed to poor design of end fittings [16]. this bad experience held back the further installation of composite insulators for a number of years [16]. the first installation of non ptfe composite insulators started in 1993, in a trial basis. as results were encouraging (no problems reported), large scale installation was initiated in 2004, on the longest line of the eastern side and other lines gradually followed [15]. today almost all otls in crete have been equipped with sir composite insulators (with the exception of the far west line connecting chania and kasteli that does not face pollution problems and the line connecting moires and ierapetra which is under refurbishment). the gradual progress, a necessity derived from operational needs, means that insulators from different generations and manufacturers have been installed in the system. they are collectively referred to as sir insulators in this paper, even though variation approaches in design and material (e.g. [11, 18]) may exist. fig. 2. the transmission system of crete (screenshot from google earth. map data: image landsat/copernicus) (yellow triangles: step-down substations, blue squares: step-up substations attached to power plants). the length of all transmission lines in crete today (considering the axes) is approximately 583.5 km (approximately 151 of them are lines carrying two circuits), supported by 1629 towers (mostly lattice ones, with the exception of 20 steel poles). the otl subsection currently employees four linemen, stationed in heraklion, to cover the scheduled inspection and maintenance of the transmission system and also to tend to faults. the same crew also has to tend to the needs of the transmission system of rhodes, another island in eastern greece [9]. the morphology of crete is an added burden as moving from heraklion to the west or the east end of the system means roughly a three hour drive (a six hour drive from one end to the other). these drive times are achieved by following pavement roads and highways and not line routes. actually reaching the towers (or moving from one tower to the next) requires much more relocating time [9] which should be added to the time needed to perform the actual work. iv. transmission line details the transmission line of interest is the one connecting atherinolakos and sitia substations at the far east side of the island of crete as shown in figure 3. it is a single circuit transmission line, approximately 23.24 km long supported by 67 lattice towers (numbered incrementally from south to north). the installation of sir composite insulators in this line started in 2006 [15]. a roughly 3 hour drive from heraklion is needed in order to reach either substation. it should be noted that inspecting thisd line is a tedious task as the line moves over gores and mountainous locations and is subjected to frequent and strong winds. in fact, it is not unusual for the line crew to have to lie down when performing ground inspections in order to be able to maintain a steady view through their binoculars/cameras. fig. 3. the considered transmission line and the location of the fault at tower 29 (screenshot from google earth. image © 2019 cnes/airbus, map data: data sio, noaa, u.s. navy, gebco). v. incident analysis the first fault was recorded on february 16, 2019 (14:20). it was a transient fault (phase c to earth). two linemen were sent to perform ground inspections but nothing was found. at the time, the fault was attributed to bad weather/lightning and was considered a run-of-the-mill fault of this type. however, a new transient fault was recorded a day later (february 17, 05:37) and then again half an hour after that (february 17, 06:07). a new fault occured again 35 minutes later (february 17, 06:42) and this time it was permanent. the readings from the distance relay were consistent that they all were phase c to earth faults with a relatively steady distance around 12.3 km from sitia (roughly in the span between towers 32 and 33). this was a rather unusual and puzzling series of events. a third lineman was added to the crew and the crew performed close range visual inspection (i.e. climbing inspections). the inspections proved fruitless and thus an attempt was made to re-energize the line (february 17, 13:27) but failed. as a response, the line crew foreman (a lineman with over 25 years engineering, technology & applied science research vol. 9, no. 5, 2019, 4851-4858 4854 www.etasr.com pylarinos and pellas: investigation of an insulator flashunder in an 150 kv otl … of experience) was also sent to the location. a climbing inspection was performed again at the next day, but still nothing was found. at this point, suspicions emerged that the fault was not related to the power line at all, but was originated from some other piece of network equipment (e.g. within the gis structure of atherinolakos) or a protection equipment malfunction. to make matters worse, the line protection scheme at atherinolakos suffered from a communication error at the time and thus the possible fault location wasn’t easy to be confirmed or narrowed down. fear of a possible flashunder also emerged. however, the spotless record of composite insulators installed in crete advocated for the opposite. nevertheless the possibility was brought to the attention of the crew and specific instructions to pay extra care to the sheaths were given. in an attempt to acquire more information, the line was divided in two parts by removing the bridging parts in tower 37 (february 18, 11:38). then, the northern part was energized without an issue. the northern part was then taken offline and the bridging parts were reinstalled at tower 37 and removed from another tension tower (tower 24) closer to atherinolakos. the northern part (that this time included tower 29, the actual location of the fault) was again energized without an issue (february 18, 13:58). the part was de-energized, the bridging parts were reinstalled and the line was re-energized without an issue an hour later (february 18, 14:57). at this time, the linecrew had performed several ground and climbing inspections and had found nothing. the behavior of the fault did not suite any of the usual profiles of line related faults experienced by the team and the line had been successfully reenergized. thus, a decision was made to relocate the crew on the western side of the island for scheduled inspection and maintenance works. it should be noted that during that time, a transient fault was recorded on a line at the western side connecting chania to rethymno (february 25, 13:11). however, a new transient fault was recording at the atherinolakos-sitia line on february 26, 08:49. at this time, the line had been energized without issues for more than a week since the previous fault. the fault kept being recorded between the same phase and the earth and roughly at the same distance. still no verification on the distance and thus the location of the fault could be provided from atherinolakos. while the division was still puzzled by the event, yet another fault was recorded almost two hours later (february 26, 10:20) and this time it was a permanent one. it was rapidly decided to relocate the crew to the eastern side. at the same time, a protection crew also prepared to be relocated to atherinolakos to attend to the communication issues and thus provide some additional information. for the two following days (february 27 and 28) the line stayed de-energized while the linecrew did thorough climbing inspections on all towers. photos of insulators that have flashed-under found in the literature (most notably the one in [14]), were handed out to the crew in an attempt to help them visualize the sought traces. again nothing was found. the line was re-energized on march 1, 12:40 without any issues. the following day, it was decided to overload the line and perform an ir inspection, focusing on insulators in an attempt to spot activity and heating under the housing [3, 12, 19]. again, nothing was found. however, a new permanent fault occurred later that night (march 2, 22:10). the next morning an attempt to re-energize the line proved futile (march 3, 08:21). at this point a decision was made to remove again the bridging parts at tower 24 and leave the two parts energized (march 03, 11:06) hoping that soon a new fault would provide a more solid confirmation on the location of the fault (and eliminate the possibility of a malfunction/ protection/substation fault in atherinolakos). some switching was tried in march 04 hoping to re-create the fault but unfortunately, nothing happened for the following 5 days. during this time, the readings from the distance relay in atherinolakos came in and seemed to confirm the readings from sitia, although they expanded the possible location of the fault by approximately 2 km. thus, it was decided to reinstall the bridging parts on tower 24. however, prior to that, the crew conducted yet another climbing inspection on the line. during that inspection, a crew member noticed arc traces on the arcing rings (figures 4-5) of an insulator installed in tower 29 and the fault was finally located (march 08, 13:10). a sum up of the timestamps of the different events and actions is shown in table i. fig. 4. the flashed under insulator with visible arc traces on rings. sheath damage barely visible from this angle and distance. fig. 5. a direct view of the flashed under insulator (red arrow). some conductor parts used for phase transposition are also visible (green arrows). vi. discussion the fault was found in one of the two insulators in a double tension string in tower 29, located 13.73 km away from sitia. towers 28 and 29 are double circuit tension towers with the extra circuit endings being used in a way that facilitates a phase transposition (figure 5), the only one in the cretan transmission system. these towers, known to suffer from strong winds and intense humidity in early mornings, are located at the top of a steep hill (figures 6-7). for all these reasons, and even though the distances recorded from the fault engineering, technology & applied science research vol. 9, no. 5, 2019, 4851-4858 4855 www.etasr.com pylarinos and pellas: investigation of an insulator flashunder in an 150 kv otl … locator in sitia was steadily around 12.3 km (approximately 1.5 km short), extra focus was given to these specific towers as possible fault locations. they were inspected multiple times, by different linemen, from the ground and in close range and also using an ir camera while the line was overloaded. however, the fault could not be spotted. a breakdown of the several reasons for that is provided below. table i. timestamps of events/actions date, time switches comment feb 16, 14:20 a: o-c b: o-c transient fault. two linemen sent for ground inspection (no findings) feb 17, 05:37 a: o-c b: o-c transient fault. feb17, 06:07 a: o-c b: o-c transient fault. feb 17, 06:42 a: o b: o-c-o permanent fault. add third lineman for climbing inspection. feb 17, 13:27 b: c-o inspection ended (no findings). failed attempt to close the cb at b. linecrew foreman added to the crew. feb 17, 13:27 feb 18, 11:38 a:o (remain) b: o (remain) climbing inspection. no findings. bridges at tower 37 removed. feb 18, 11:46 a:o (remain) b: c part (tower 37-b) energized. feb 18, 12:26-13:43 a:o (remain) b: o reinstall bridges at tower 37 and remove bridges at tower 24. feb 18, 13:58 a:o (remain) b: c part (tower 24-b) energized. feb 18, 14:15-14:38 a:o b: o bridges at tower 24 reinstalled. feb 18, 14:57 a: c b: c line re-energized. feb 19-25 a: c (remain) b: c (remain) line crew relocated to the west side of the island. feb 26, 08:49 a: o-c b: o-c transient fault. feb 26, 10:20 a: o-c-o b: o-c-o permanent fault. line crew relocated to the east side. protection crew sent to atherinolakos feb 27-28 a: o (remain) b: o (remain) climbing inspection. no findings. mar 1, 12:40 a: c b: c line re-energized. mar 2, 8:36-13:00 a: c (remain) b: c (remain) line overloaded. ir inspection. no findings. mar 2, 22:10 a: o-c-o b: o-c-o permanent fault. mar 3, 8:21 b: c-o failed attempt to re-energize. mar 3, 9:14-10:30 a: o (remain) b: o (remain) bridges at tower 24 removed. mar 3, 11:06 a: c b: c part (a-tower 24) energized from a. part (tower 24-b) energized from b. mar 8, 08:25 mar 8, 13:10 a: o b: o climbing inspection. mar 8, 13:10 a: o (remain) b: o (remain) fault located at tower 29. mar 8, 13:10 – mar 9, 10:50 a: o (remain) b: o (remain) bridges at tower 24 reinstalled. insulator at tower 29 replaced. mar 9, 11:00 a: c b: c line re-energized. a=atherinolakos, b=sitia, o=open, c=close fig. 6. a view of the location of towers 28 and 29 fig. 7. the location of tower 29 (red circle) on top of a steep hill (screenshot from google earth, map data: google earth) a. lack of signs/traces the first and most important reason is the very nature of the fault. considering the mechanism of a flashunder, it is safe to assume that there were probably no visible signs prior to the fault. even after the first fault(s), the visible traces could be minimal. it probably have taken multiple power arcs to achieve the state shown in figure 1 and figures 8-10. it should be noted that, besides periodical visual inspections, yearly ir inspections (during the summer) were also performed on that tower and although it have been proposed that ir inspection could locate internal tracking and activity under the housing [3, 12, 19], this approach also proved futile in this case. even when ir inspections were performed on march 2 with the line overloaded and with special attention given to any sign of such activity, nothing was found. b. insulator type/design and installation the insulator that suffered the fault was an even shed insulator, installed in a double tensions string. thus, the sheds’ shadows obscured the view of the sheath at most times and angles (figures 8-10). c. location of visible damage on the insulator the location of the sheath damage was on the “outer” side of the insulator, i.e. facing away from the tower, making it difficult to spot from any angle accessible from the tower or the ground (figures 8-10). engineering, technology & applied science research vol. 9, no. 5, 2019, 4851-4858 4856 www.etasr.com pylarinos and pellas: investigation of an insulator flashunder in an 150 kv otl … fig. 8. even from a small distance, the damage is not visible due to the sheds overshadowing the seath fig. 9. the damage visible from close distance and correct angle. fig. 10. views of the flashed under insulator before its removal d. weather data the area around tower 29 is not inhabited. thus, at the time of the incidents, the information regarding the weather came from the cities of sitia and ierapetra (along with inspection information). the location of these cities, next to the substations with the same names, and their relation to the fault location can be seen in figure 3. the weather information did not seem to advocate for the possibility of a weather related fault. this can be more understood when examining the recordings from the closest automatic weather stations of the national observatory of athens network which are located in sitia and ierapetra [20]. their monthly data are easily available through [21] and the rain and wind recordings are depicted in figure 11. fault occurrence could not be correlated with any specific weather condition (e.g. strong wind or heavy rain). the first fault was recorded on feb 16, a day with minor winds that had followed a series of days with much stronger winds. no correlation with rainfall, a factor that may play a role in the flashunder process, could also be established, as faults were recorded on days with no rain in sitia (feb 17, feb 26, mar 2) or ierapetra (feb 16, mar 2) and feb 25 was faultless although intense rain fell on both cities. the micro-climate at tower 29, and especially values with a strong locality factor such as relative humidity (rh), can not accurately be described by the recordings in either ierapetra or sitia (thus the rh measurements are not shown in figure 11). it was known that tower 29, being located at a top of a steep hill, was subjected to intense humidity (fog/mist) in early mornings. the same could be hypothesized for late afternoons. however, even when a possible flashunder was brought to the table as a strong possibility, the time of faults would not back a correlation with high rh values either. the first fault was recorded at midday of feb 16 (at 14:20), the line was reenergized on feb 18 and the next fault was recorded on feb 26 at 08:49. thus, no safe correlation with morning and afternoon fog/humidity could be established. fig. 11. weather data from weather stations in the national observatory of athens network located in sitia and ierapetra. yellow vertical lines indicate the occurrence of fault(s). green lines indicate the re-energization of the line. engineering, technology & applied science research vol. 9, no. 5, 2019, 4851-4858 4857 www.etasr.com pylarinos and pellas: investigation of an insulator flashunder in an 150 kv otl … e. similarity to run-of-the-mill incidents one should keep in mind that transient faults are rather usual in a transmission system and not being able to locate a fault or its cause is also usual. an initial analysis of the 307 faults recorded in the transmission lines of crete from 1994 to 2013 is available in [22]. although, both record keeping and analysis suffer from much of the issues described in [8] (i.e. non uniform record keeping, cause: “unknown”, cause: “under investigation”, misclassification, changes in line configuration etc.) some basic info can be deducted with safety: first of all, faults are mainly transient. only 29 of the 307 faults, less than 10%, were permanent/semi-permanent. the two months where most faults are recorded historically are february and march (figure 12), exactly as in the considered case. faults recorded with causes such as “bad weather”, “rain”, “storm”, “lightning”, “under investigation” and “unknown” are the vast majority of the data. in the particular line in question, only 6 faults had been recorded: two attributed to lightning, three to bad weather and one of unknown origin. in other words, the basic initial profile of this specific fault did not hinted to anything out of the ordinary and certainly did not justify any special action. fig. 12. faults per month as recorded in transmission lines of crete from 1994 to 2013. f. typical inspection procedure not suitted for flashunders the run-of-the-mill inspection procedure proved to have weaknesses in spotting a flashunder. this is however rather logical, as the procedure has been designed (and adjusted) to the faults and issues historically experienced in this particular system, always aiming to achieve the optimum trade off between result/productivity and time/cost. thus, thorough sheath inspection had never been incorporated in inspections. the usual inspections in crete are performed either from the ground using binoculars or by climbing and inspecting from the tower’s body (an ir inspection is also performed annually on tension towers). checking the sheath from all angles (e.g. using mirrors as shown in [14], ladders, cranes etc.) would mean a significant decrease of productivity (and increase in costs) and would have brought zero results for the past 15 years. so, such approaches have justifiably not been incorporated in the inspection procedure. this however means that even if any signs of the problem (e.g. minor sheath damage) were visible prior to the fault (which is rather doubtful), they couldn’t have been spotted. this also means that the infrastructure, experience and tendency for such an approach were missing. in short, it can be assumed that the long successive experience of following a specific walkthrough resulted to a weakness when an unpresented case presented itself. g. practical issues the limited personnel combined with the size of the system and relocation times means that each inspection and each maintenance has to be carefully planned and crew relocating is conducted only when strictly necessary. for example, as mentioned earlier, during the time that the flashunder induced faults appeared in the east, a transient fault also appeared in the west and a line inspection was scheduled to take place also in the west. this means that the otl subsection rarely has the luxury of dedicating extra time and manpower to investigate any single incident further than needed to assure the system’s operation. even more so in case of an incident that originally appeared as a run-of-the-mill transient fault and its profile kept not fitting to any of the “more serious” fault types. it should also be noted that de-energizing this line does not have a direct effect on the system (outages, cutting off wind farms etc.) so faults in this specific line are generally considered of lower priority. besides the otl subsection, similar conditions exist for all other subsections and thus several actions that could offer more information were judged not necessary at the beginning, adding to the overall delay in locating the fault. for example, hedno substation personnel (two persons at the considered period, working on different shifts) were regularly located only in sitia. this means that for one of them to visit the other end of the line (atherinolakos) (even just to read the readings of the distance relay) will mean that both substations have to be left unattended for two hours (as the single-way travel time is approximately one hour) or that the second person has to be called in for overtimes, which is also a decision not to be taken lightly in the current economical context. in addition, when the communication issue with the distance relay in atherinolakos surfaced, all the personnel from the protection, metering & telecom systems section of the division was stationed elsewhere and the relocation of a crew to atherinolakos took some additional faults (and days). h. psychological aspect although earlier ptfe insulators have performed poorly suffering from brittle fracture [16] and flashover [17] faults, the next generation sir composite insulators had an almost spotless record in the cretan power system. the only, rather rare, faults were caused by bird activity (figures 1a and 1b) [15, 23]. this had caused an increased confidence to the personnel regarding the performance and the reliability of the sir insulators. the linemen performing the inspection had never experienced any such phenomenon (i.e. a flashunder that induced line faults without causing brittle fracture). it is also possible that the brittle fracture issues on older ptfe insulators more than 35 years ago [16] had created an erroneous notion that moisture ingress under the sheath would lead straight to brittle fracture faults. even though the possibility of a flashunder that wouldn’t lead to a brittle fracture was communicated to the linemen, it is logical to assume that, engineering, technology & applied science research vol. 9, no. 5, 2019, 4851-4858 4858 www.etasr.com pylarinos and pellas: investigation of an insulator flashunder in an 150 kv otl … subconsciously, they never fully accepted that possibility and thus they were not that prone, in an subconscious level, to perform an as thorough as needed inspection on sheaths. not having solid information on fault location from both distance relays, at least for the first few days, contributed to that by increasing the load of work and also creating doubts about the correctness of the information. the ill-correlation with weather data also contributed as the behavior of the fault didn’t seem to fit any scenario (including a flashunder). vii. conclusion moisture ingress in the rod/housing interface of composite insulators, widely used in transmission lines, may lead to a flashunder, a bridging discharge taking place under the housing and along the core. the discharge may dry the moisture causing a temporary recess while leaving minimal traces on the insulator. this procedure along with the general operating principles of transmission systems may cause a rather difficult to interpret series of events as the fault may keep appearing and disappearing. locating such a fault may prove rather challenging for the otl sections bearing the responsibility to inspect, locate and remedy otl faults. this paper discusses the experience gained from a flashunder incident that occurred in the transmission system of crete in february/march 2019, mainly by following the point of view of otl personnel. the actions taken and the various scenarios considered up until the identification of the fault and the replacement of the faulted insulator are discussed. additional pieces of information, such as historical and weather data, are also considered in order to provide an, as complete as possible, image of the various factors involved in the process. references [1] h. h. farr, transmission line design manual, united states departmentof the interior, 1980 [2] l. l. grigsby (editor), the electric power engineering handbook: electric power generation, transmission and distribution, crcpress taylor and francis group, 2012 [3] k. o. papailiou (editor), overhead lines, cigre green books, springer, 2017 [4] european network of transmission system operators for electricity, best protection practices for hv and ehv ac-transmission systems of entso-e electrical grids, entso-e, 2018 [5] r. k. tajput, a textbook of power system engineering, laxmi publications, 2006 [6] n. veerappan, s. r. krishnamurthy, power system switchgear and protection, s. chand publishing, 2009 [7] cigre wg b2.45, vegetation fire characteristics and the potential impacts on overhead line performance, cigre, 2019 [8] h. f. vosloo, the need for and contents of a life cycle management plan for eskom transmission line servitudes, msc thesis, rand afrikaans university, 2004 [9] d. pylarinos, i. pellas, “incorporating open/free gis and gps software in power transmission line routine work: the case of crete and rhodes”, engineering, technology & applied science research, vol. 7, no. 1, pp. 1316-1322, 2017 [10] cigre wg 33-04, tf 01, a review of current knowledge: polluted insulators, cigre, 1998 [11] k. papailiou, f. schmuck, silicone composite insulators: materials, design, applications, springer, 2013 [12] cigre wg b2.21, assessment of in-service composite insulators by using diagnostic tools, cigre, 2013 [13] electric power research institute, field guide: visual inspection of polymer insulators, 2006 [14] r. gorur, “reviewing modes of insulator failure”, inmr, 2011, available at: http://www.inmr.com/reviewing-modes-of-insulator-failure/ [15] d. pylarinos, k. siderakis, e. koudoumas, e. thalassinakis, “polymer insulators and coatings in the cretan power system. the transmission line case”, 9th mediterranean conference on power generation, transmission distribution and energy conversion, athens, greece, 2-5 november, 2014 [16] s. gubanski, “greek power company evaluates alternatives to combat pollution in transmission system on crete”, inmr, vol. 10, no. 4, 2002 [17] inmr, “greek utility battles pollution affecting island transmission system”, inmr, vol. 15, no. 4, pp. 24-38, 2007 [18] a. sykaras, v. rajini, m. g. danikas, r. sarathi, “a study of sir/epdm mixtures for outdoor insulators”, engineering, technology & applied science research, vol. 7, no. 4, pp. 1737-1740, 2017 [19] cigre wg b2.21, guide for the assessment of composite insulators in the laboratory after their removal from service, cigre, 2011 [20] k. lagouvardos, v. kotroni, a. bezes, i. koletsis, t. kopania, s. lykoudis, n. mazarakis, k. papagiannaki, s. vougioukas, “the automatic weather stations noann network of the national observatory of athens: operation and database”, geoscience data journal, vol. 4, no. 1, pp. 4-16, 2017 [21] database of weather stations of the national observatory of athens, available at: http://meteosearch.meteo.gr/ [22] t. stamatakis, “statistical analysis of faults on 150 kv transmission lines of the power system of crete”, degree thesis, electrical engineering department, technological educational institute of crete, 2014 (in greek) [23] n. mavrikakis, k. siderakis, p. n. mikropoulos, n. katsarakis, “condition assessment of a field-aged 150 kv htv sir suspension insulator following flashover”, ish 19th international symposium on high voltage engineering, pilsen, czech republic, august, 23–28, 2015 microsoft word ogbonnaya-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 402-407 402 www.etasr.com ogbonnaya et al.: effects of greenshipping to the maritime industry effects of greenshipping to the maritime industry ezenwa a. ogbonnaya department of mech/marine engineering, niger delta university, wilberforce island, bayelsa state.nigeria. ezenwaogbonnaya@yahoo.com robert poku department of mech/marine engineering, niger delta university, wilberforce island, bayelsa state.nigeria. robertpoku@yahoo.com emmanuel m. adigio department of mech/marine engineering, niger delta university, wilberforce island, bayelsa state.nigeria. emadigio@yahoo.com abstract—in order to keep focus on the important agenda of sustainability which has lately become an issue of priority, the maritime industry must implement technologies on existing vessels and on those under construction so as to reduce their emissions into the environment. this study examines three potential sources of emission and also identifies a set of emission control measures that are available and could, if fully applied, reduce emission by 19.058%. with the waste heat recovery system, about 2500 kw of energy are saved, thereby increasing the efficiency to 59.11% having about 10.13% gain compared to engines without a waste heat recovery system. it is therefore recommended that the use of waste heat recovery systems should be encouraged on marine vessels to reduce the impact of noxious gasses into the atmosphere. keywordsgreenshipping; maritime industry; exhaust emission control; single pressure waste heat recovery system; exhaust gas waste heat recovery nomenclature bc black carbon xco carbon oxides hc hydrocarbon lcv lower calorific value f m mass flow rate of fuel x�o nitrogen oxides s.f.c specific fuel consumption xso sulphur oxides b w brake power egwhr exhaust gas waste heat recovery seca sulphur emission control area ₦ nigerian naira i. introduction today, ninety percent of the world trade is carried by ship and for the vast majority of this trade, there is little or no transport alternative [1]. ships can carry large quantities of cargo with high efficiency. with the rapid growth of economies of developing nations, e.g. in asia, trading activity is increasing and along with it comes an increase in ship traffic and the need for large ships that are able to carry more cargo. this creates a need for balanced economic growth and also for improving and maintaining the air quality. it is estimated that 2.7% of the global carbon dioxide emission comes from international shipping. it is inevitable that ships contribute to unwanted emissions as they use bunker fuel which contains high level sulphur, ash and nitrogen compound and generate higher emissions than distillate fuel. to make matters worse, they use unrefined fuel, the dirtiest in the market, thus emitting various global warming pollutans which include cox, sox, hcx and nox. these pollutants all contribute to global climate change either directly by acting as agents that trap heat in the atmosphere or indirectly by aiding the creation of additional green house gases (ghg) [2, 3]. exhaust emissions sends out tiny particles which are too small for the human upper respiratory system to filter from the air when we breathe [1]. they go deep into the lungs, where they may cause damage and chemical changes. similarly, the volatile organic compounds (vocs) are not left out. vocs are chemicals that contain organic carbon and they readily evaporate, changing from liquids to gas when exposed to air. vocs may produce health effects if humans are exposed to high enough concentrations of them [4]. lastly equipment such as refrigerators, air conditioners, fire extinguishers etc are also sources of emission. these equipment use fluids in their operations which are toxic and could deplete stratospheric ozone. hence, they also produce ghg which deplete the ozone layer [5]. some existing measures for the reduction of emission from ships are: a. water base control water base control is a measure through which the emission from the diesel engine is reduced by introducing water into the combustion chamber at different stages of the combustion process. this is to reduce the maximum peak combustion temperature and the formation of nox, sox and cox. b. seawater scrubbing technology seawater scrubbing technology utilizes the natural alkalinity of seawater to reduce the sox emission from the exhaust stream [6]. the solid particles are removed from the mixture and the seawater is then returned to the ocean, which is etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 402-407 403 www.etasr.com ogbonnaya et al.: effects of greenshipping to the maritime industry a natural reservoir as it contains high qualities of sulphur. the scrubbing provides an alternative to fuel switching for vessel operators traveling in seca. fuel switching is a simple approach to reduce energy consumption and costs for endusers, as well as curbing carbon emissions [6]. the seawater scrubbing technology has been found to reduce exhaust gas so2 levels by 69-94% from vessels operating on fuel with a sulphur content of 2.5%. c. selective catalytic reduction: the selective catalytic reduction (scr) process is another procedure to reduce the emission of toxic waste gases into the atmosphere. the configuration involves injecting a reagent such as ammonia or urea into the exhaust stream which then passes through a catalyst to achieve about 90% upward reduction of nox [6]. d. exhaust gas scrubber exhaust gas scrubber is used for washing exhaust gas from the engine. with the exhaust scrubbing system, it is possible to reduce the sulphur emissions to a level as low as if low sulphur fuel oil was used [1]. but because low sulphur fuel oil has a significantly higher cost price, it makes good financial sense to use scrubbers to clean off the exhaust gas and thereby continue using heavy fuel oil. dry scrubber uses a catalyst to remove toxic components by chemisorptions or adsorption to their surface. the required contact time is very short and does not depend on the inlet concentration [7]. ii. materials and methods the egwhr system has been found to be a beneficial contributor to the reduction of co2 emissions from ships as well as lowering the fuel cost. one of the ways this can be done is by utilizing the waste heat into electric power [8]. the waste heat recovery system (whrs) consists of an exhaust gas boiler and a supplying steam to a steam turbine. the steam turbine is connected to a generator, and thereby the waste heat is recovered as electrical energy. to obtain the highest electrical production, the optimal solution is to use a dual steam pressure system for exhaust gas recirculation [9]. data were obtained from sulzer engine rlb-66 specification single pressure waste heat recovery system (spwhrs) logbook [10], containing inventory records of monthly energy generation and operational statistics. a. calculations of the mass flow rate of fuel to measure the amount of energy input, the value of mass flow rate of fuel was derived and is used to multiply the calorific value of fuel to get the amount of energy input. 3600 ws.f.c m b f × = (1) f 0.175 12080 m 0.5872 kg / s 3600 × = = b. amount of energy input to system the amount of energy input to the system due to fuel combustion is given as: input f m lcvq = (2) where input q =energy supplied due to combustion of fuel lcv =lower calorific value of fuel =4200 kj/kg f m =mass flow rate of fuel =0.5872 kg/s therefore input q =0.5872 x 4200=24663.33 kw. c. efficiency and cost analysis the efficiency of the main engine is given as e e η input output me = (3) = 24663.33 kw 0.4898 12080 = efficiency of spwhrs is given as: sp me lp me η η η (1 η )0.2337= + − (4) =0.4898 + 0.85(1-0.4898)0.2337 =59.11% where ηlp is the efficiency of the low pressure steam drum. also, the efficiency gained as a result of spwhrs is given as: gain sp me η η η= − (5) gain η =59.11 48.98 =10.13% the energy saved by using spwhrs is given by: energy saved = gain input eη × (6) =0.1013 × 24663.33 kw =2500 kw amount of fuel saved per day for spwhrs is given as: density fuel timee s.f.c m save f ×× = (7) 0.86 2425000.175 m f ×× = = 12209.302 litres per day therefore, the amount of fuel saved per year for spwhrs is: liters saved per year =mf per day x 365=4,456,395.35 lt etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 402-407 404 www.etasr.com ogbonnaya et al.: effects of greenshipping to the maritime industry but if a liter costs ₦ 97.00, then the cost saved is: cost saved per day = ₦ 97 x 12209.30 = ₦ 1,184,302.1. cost saved per year = ₦ 432,270,266.5 however, at normal operating condition without whrs, the amount of fuel used per day will be fuel the ofdensity timees.f.c m normal f ×× = = 120448.821 litres per day the cost of 120448.821 litres per day will be: = ₦ 97 x 120448.821 = ₦ 11,683,535.64 per day. cost of running per year = ₦ 4,264,490,508 per year the cost used to run the spwhrs is: single normal saved c c c= − = ₦ 11,683,535.63− ₦ 1,184,302.1 = ₦ 10,499,233.54 per day the cost used to run the spwhrs per year is single c = ₦ 10,499,233,.54 x 365 = ₦ 3,832,220,240.0 per year. d. percentage decrease of heat transfer to exhaust gas heat transfer to exhaust due to single pressure whrs single pressure normal (saved)single pressure q e e−= = 4700.4 kw percentage heat transfer to exhaust gas ( g % q ) due to spwhrs: ( ) ( ) g sp g sp input % 100 q q e = × g(sp) q % =19.058% the % decrease of heat transfer to exhaust gas ( g % q ) due to spwhrs: %decrease ( g q ) = (29.19 – 19.058)% = 10.132% iii. results and discussion a summary of the calculations obtained between equations 1 to 7 is shown in table i. the analysis covered the areas of efficiency, energy and fuel saving cost, heat transfer and exhaust emission. the calculated savings are based on the spwhrs. the whrs helps in the reduction of the operating cost and the emission rate. the graphs shown in figures 1 to 4 depict how the reductions in emission rates are achieved. comparing the maximum brake power output of 12080 kw and efficiency of 48.98% of the total energy supplied to the combined heat dissipated by charge air cooler, jacket water cooler and exhaust shows that about 51.02% of the total heat supplied was wasted. however, with the installation of the whrs, part of this wasted heat was recovered. table i. summary of the spwhrs s/n items single (whrs) 1 efficiency 59.11% 2 efficiency gain 10.13% 3 energy saved 2,500 kw 4 amount of fuel saved per day 12209.302 litres 5 cost saved per day ₦ 1,184,302.10 6 amount of fuel saved per year for spwhrs 4,456,395.35 litres 7 cost saved per year ₦ 432,270,266.50 8 cost used to run spwhrs per day ₦ 10,499,233.30 9 heat transfer to exhaust 4700.4 kw 10 %heat transfer to exhaust 19.058% 11 %decrease of heat transfer to exhaust 10.132% 12 amount of fuel required to run 12209.320 litres/day a. effiiciency increase with spwhrs the efficiency of the main engine without the whrs is about 48.98% but with the installation of a spwhrs, the efficiency became 59.11% having about 10.13% as compared to engine without waste heat. b. impact of spwhrs on cost in the cost analysis, the input at normal operation is 24663.33 kw with about 120,449 litres of fuel per day is required to run at normal operating condition amounting to ₦11,683,535.64 per day. with the installation of spwhrs about 2500 kw of saved energy is observed. c. c. exhaust gas analysis more so, in the exhaust gas analysis, with the energy input at normal operation of 24663.33 kw, about 29.19% of the total heat input is lost to the atmosphere as exhaust gas. with the installation of the single pressure whrs the exhaust gas to the atmosphere is reduced to 19.058% of the total input energy 1) analysis of �ox emission table ii is a summary of nox emission in terms of water per ship speed and reagent per ship speed. figures 1 and 2 emanated from table 2. the graphs also show that there is an inverse relationship between nox emission versus water per ship speed and nox emission versus reagent per ship speed. this implies that, to reduce nox emission, water per ship speed and reagents per ship speed have to be high. figure 1 shows how injection process is used to reduce the emission of nox as the speed increases. this system reduces the nox formation by 50-60%. figure 2 is the scr process where reagents such as ammonia or urea are injected into the exhaust stream, which then passes through a catalyst to achieve upwards of 90% nox reduction. etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 402-407 405 www.etasr.com ogbonnaya et al.: effects of greenshipping to the maritime industry table ii. summary of x�o emission x�o emission water per ship speed reagent per ship’s speed 8 2000 2000 10 1500 1500 12 1000 1000 14 500 500 16 100 100 fig. 1. rate of x�o emission figure 3 illustrates the impact of seawater scrubbing technology. this technology utilizes the natural alkalinity of seawater to reduce the sox emission from the exhaust stream. this technology has been found to reduce exhaust gas so2 level by 69-94% from vessels operating on fuel with a sulphur content of 2.5%. fig. 2. �ox emission to reagent per ship speed figure 4 shows fuel switching process. this is suitable for vessels operating in regions that are defined as sulphur emission control area under the imo annex vi and have options for complying with the requirement of the regulation. 2) analysis of sox emission table iii is a summary of sox emission in terms of exhaust emission per speed and fuel switching emission per speed. figures 3 and 4 were obtained from table 3 which show the inverse relationship between sox emission and exhaust emission per ship speed and emission per ship speed respectively. this again implies that, to reduce sox emission, ship speed must be increased. table iii. summary of xso emission xso emission exhaust emission per speed fuel switching emission per speed 8 2000 2000 10 1500 1500 12 1000 1000 14 500 500 16 100 100 fig. 3. exhaust emission per speed fig. 4. fuel switching emission per speed 3) cox analysis table iv shows the relationship between the cox emission and the density of air per speed. it is seen that an increase in the density of air per speed will cause a reduction in cox emissions. figure 5 shows the inverse relationship between the cox emission and the density of air per speed. hence, passing the charge air through an air cooler yield great advantage regarding cox emission. etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 402-407 406 www.etasr.com ogbonnaya et al.: effects of greenshipping to the maritime industry table iv. emission rate due to turbocharging. xco emission density of air per speed 8 2000 10 1500 12 1000 14 500 16 100 also, the increase in air density entering the engine ensures that there is complete combustion which creates more power and fewer emissions as shown in figure 5. fig. 5. emission rate due to turbocharging iv. conclusion from the analysis carried out, the whrs reduces the rate of air pollution from the vessel with respect to the number of steam drum and pressure. the rate at which fuel is burnt is reduced and this is based also on the number of steam drum and pressure. this analysis shows that the electrical needs on board can be met with the aid of a turbo generator with all the auxiliary set shut down while running at full load. this is made possible with the spwhrs with about 2500 kw of energy saved to drive the turbo generator to produce electricity. seawater scrubbing technology is the water emulsion technology where emission control yields 1% reduction in nox for 1% concentration of water. more so, the scr process involves the use of reagent which will achieve up to 90% of nox reduction. with the scrubbing system, it is possible to reduce the sulphur emission to a level as low as if low sulphur fuel oil was used. despite the space factor, the maintenance cost and its complexity, the whrs has its advantages as it increases fuel saving, cost saving and also reduces the exhaust gas emission. the use of the above mentioned technologies if fully applied will reduce the emission rate. this implies that turbocharging would also help to reduce exhaust emission from diesel engines used in the maritime industry. therefore, there is a need for environmental protection agencies (epas) at all levels to assist in the enforcement of the above policies. v. recommendations • regulatory authorities all over the world should implement technical and operational measures to reduce global warming and pollution as soon as possible. such measures include speed controls, weather routine, fuel switching and specialized hull coatings. • fleets should begin to implement longer-term measures to reduce global warming and pollution, such as fuel efficient design of new ships and engines created specifically for slow steaming. • epas should find that the carbon dioxide, black carbon, nitrogen oxides and nitrous oxide emissions from ships significantly contribute to climate change and ocean acidification and therefore pose a threat to public health and welfare. • epas should regulate global warming pollutants from ships operating within their various exclusive economic zones. this can be done by setting emission standards and by requiring specific operational procedures, such as speed restrictions. • the imo should set international emission standards to reduce global warming pollutants from the shipping industry. acknowledgements the authors of this work are extremely indebted to mr felix o. akpobome and mr. kuvie a. ejabefio for their help with data collection, manuscript drafting, typesetting and final formatting. references [1] h. o. kristensen, “greenship of the future, co2-neutralised production”, rosendahls, esbjerg, denmark [2] f. van haren, m. kadlec, “focus on diesel exhaust-air quality program: why is diesel exhaust a problem?”, washington state department of ecology, 2009 [3] e. a. ogbonnaya, k. t. johnson, c. u. orji, “reducing the impact of emissions on the environment from gas turbine exhaust”, proceedings of nigerian society of engineers annual general meeting & conference, international conference center, abuja 2010 [4] healthy building network, kaiser permanente, “toxic chemicals in building materials: an overview for health care organizations”, global health and safety initiative-health care without harm, 2008 [5] united nations industrial development organization, “ozone-friendly industrial development. impact and lessons learned. refrigeration and alternative technologies for domestic appliances”, united nations industrial development organization, vienna, 2003 [6] j. o. hellmann, k. aabo, emission control, two-stroke low-speed diesel engines, inst. of diesel and gas turbine engineers, 1997 [7] crystec technology trading gmbh, dry exhaust gas cleaner, semaian technology, https://www.crystec.com/ksicate.htm [8] j. cofala, m. amann, c. heyes, f. wagner, z. klinont, m. posch, w. schopp, l. tarasson, j. e. johnson, c. whall, a. stavrakaki, “analysis of policy measures to reduce ship emissions in the context of the revision of the national emission ceilings directives”, international institute for applied systems analysis, schlossplate 1, laxemburg, austria, 2007 [9] siemens ag, “waste heat recovery (whr) system: generating energy from a ship's exhaust gases”, siemens, industry sector, etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 402-407 407 www.etasr.com ogbonnaya et al.: effects of greenshipping to the maritime industry industry solutions division, hamburg, germany, reference number: iis201009.684e fp, 2010 [10] technical data for sulzer rlb marine diesel engine, “the sulzer rtfl ex common-rail system described,” wärtsilä switzerland ltd, po box 414, ch-8401, winterthur, 2004 engineering, technology & applied science research vol. 8, no. 1, 2018, 2427-2432 2427 www.etasr.com chakamian keshvari et al.: a model for the development οf employees’ learning (career path) … a model for the development οf employees’ learning (career path) in industrial enterprises g. chakamian keshvari j. mohammadi faraz n. safaie s. j. hosseini nedjad industrial management institute tehran, iran allameh tabataba'i university tehran, iran k. n. toosi university of technology tehran, iran k. n. toosi university of technology tehran, iran abstract—the goal of this study is to propose a model for the development of employees' learning (career path) in industrial enterprises. in the research a descriptive-survey method along with field research were used. the statistical population consists of all 110 employees of dana baspar's enterprises. a questionnaire with content verified by 30 experts along with the supervisor and the advisor was employed. related validity of the questionnaires and their stability were 70%, counted by cronbach's alpha, showing a good level of stability. descriptive statistics for demographic data (frequency, standard deviation and mean) and inferential statistics were used. research findings show that the influence of workshop and experimental skills gained by apprenticeship, the effect of training by holding meetings and seminars with experts or experience acquired during work is significant and positive on organizational productivity while the mediation variable of professional skills exists but the influence of classic and academic trainings is not positive and significant on organizational productivity considering the existence of mediation variables. keywords-learning development; career development; job skill; employees; career path; industrial enterprises i. introduction the development of knowledge management and the increasing number of businesses that use modern management opens a new path of knowledge-based performance success, especially important in developing countries such as iran. adapting all business activities to all knowledge management elements at once may prove difficult as well as costly and time consuming. thus, a gradual approach may prove better in helping employees to adapt themselves with modern work culture [1]. when an effective learning strategy is absent, problems such as learning prolongation, financial losses, accidents or even casualties caused by the lack of proficiency and reduced possibility of transmitting job skills are bound to occur. these problems obviously decrease the productivity and profitability [2]. on the other hand, to implement an effective strategy for organizational learning elements like the existence of a cooperative culture in every level and the presence of a capable leader to motivate and guide employees are essential. the results of such a process are however significant as a better working environment is combined with increased productivity. therefore, the final result of this process is to create a vibrant, knowledge-based, fast-paced organization [3]. establishment of compatibility between needs, abilities and potential capabilities of people on one hand, professional needs of organizations on the other are determining each employee’s career path. the management of the progress of such paths is also known as organizational support and includes programs, processes and aids provided by an organization to support and increase the success of its employees in career progression. such activities include a wide range of programs and interventions that compare the employees’ and the organization's needs [4]. among other things, developing job progress path programs provided by the organization result to a feeling of success for the employees [5]. this way, job satisfaction and loyalty will increase which is bound to result higher efficiency. it should be noted that other factors such as consultation, performance estimation and employee development programs may also be provided for that purpose [6]. it is natural for organizations to try to update and develop the skills of their employees and improve the individual, group and organizational learning level. through such programs, the employees are expected to improve their theoretical background as well as their practical expertise, which should also provide increase work motivation [4]. people whose job progress is adapted to their needs and capacities try more to improve their knowledge and skills [7]. thus, if the organization is able to provide two or three job preferences for each employee, they would be more stable in the organization. authors in [8], proposed an example of the relations in job path with the focus on creativity/entrepreneurship, absolute, technical/functional and challenges in one group and with complimentary relationships by using bristow's questionnaire. they claimed that the relation between security /stability and absolute changes is contradictory. authors in [3], presented 5 types of process paths. the success in job progress is divided to two dimensions: objective and subjective [9]. the objective factors of job progress success have observable results such as paying, development and growth in job [10]. but subjective success of job progress is usually presented as the amount of job satisfaction in the job progress [11]. authors in [12, 13] verified the relationship between training and the satisfaction of job progress and had referred to their relation [3]. authors in engineering, technology & applied science research vol. 8, no. 1, 2018, 2427-2432 2428 www.etasr.com chakamian keshvari et al.: a model for the development οf employees’ learning (career path) … [14], found a positive significant relation between organizational support for job progress and the employees' satisfaction of their job progress. according to [15], support, encouragement, training, development and challenging jobs are effectively in relation with the satisfaction of women managers from the job progress. authors in [16], found a strong relationship between the management support and the satisfaction of job path. authors in [17] concluded that the management of job progress functions including estimation, development and training for job progress in the military department, have strong, positive impact on satisfaction in job progress. authors in [18], described several variables as suitable explanations of job progress. ii. research methodology the goal of this research is to propose a model for the development of employees' learning (career path) in industrial enterprises and to verify the relation between the considered variables. therefore, the research type is quantitative and the method is descriptive, correlated and fundamental. data are gathered through a questionnaire and are statistically analyzed. the statistical population consists of all 110 employees of dana baspar's enterprises. the statistical sample is the same with the statistical population, because the population is small. the questionnaire contains two parts: the first part consists of demographic questions such as gender, educational level and age. the second part includes 3 questionnaires (1. effective factors in job progress management 2. job loyalty in the way of progress 3. learning) by profiting likert five point scale (from 1. "absolutely disagree" to 5."absolutely agree") and consists of 55 questions. the first questionnaire has 3 dimensions (job path satisfaction, management attitudes and management support) with 15 questions. the second questionnaire consists of 2 dimensions (scale of mental success in the job path and job loyalty scale). the third questionnaire includes 6 dimensions (academic and classic trainings, professional courses in technical and vocational organizations, experimental skills gained by apprenticeship, training by holding meetings and seminars with experts, online technologies and tutorials) and has 24 questions. the stability was 70%, counted by cronbach's alpha, which is acceptable. also the research validity is confirmed by 30 supervisors of knowledge management and some experts of industrial management institute. iii. findings data analysis of the research consists of two parts: descriptive findings and main findings. for data analyzing, the descriptive statistics are presented at first, verifying the variables. then the inferential findings and the results of the hypotheses are proposed. at the beginning, a sample of 100 persons where chosen as the statistical population and their individual and demographic features were. frequency and its percentage for gender, marital status, age, educational level, work experience, job title, department and income level are shown in table i. table ii shows the descriptive indexes of the variables. the median of classic trainings variable is 2.250 that shows half of the data are less than this amount and the other half is more than it. the standard deviation for this variable is 0.601. it shows that the average amount of variability for classic trainings is about 0.054 around the mean. skewness coefficient of this variable is positive, that means it's skewed to the right and the variables are tending to small values. if the kurtosis coefficient is more than 3, the distribution of the variables is more than normal and the data are around the mean. so it can be conducted that they are not distributed around the mean for the variable of classic trainings. we used a two-step method of structural equations modeling for analyzing the hypotheses. confirmatory factor analysis is done in the first step and if the measurement model is confirmed, we can perform the second step. each latent variable forms a measurement model with the questions that test the same variable. structural equations are sophisticated methods in data analysis: it's a developed linear equation that helps the researcher to measure a set of regression equations at the same time, collect data and enter them to the software package of structural equations. structural equations develop the relation between the variables and have two main parts: measurement model and structural model, which are used for measuring latent and visible variables. they are introduced as one in the software and the final model. the software used in this research for analyzing is smart pls. confirmatory factor analysis (kaiser criterion) confirms that the data is suitable for factor analysis. the value of the statistic changes between 0 and 1. if the sample is suitable, the amount of this statistic should be more than 0.5 [19]. here, the statistic is 0.724, so factor analysis is appropriate. the elemental correlation matrix is an identity matrix. in factor analysis, the correlation between the variables should not be zero, but if the correlation matrix is the same as identity matrix, it means that all the correlation coefficients are zero. if the bartlett's test is significant, it means that the correlation matrix is not identity matrix and there is correlation between the variables and the factor analysis can be done [19]. here, the value of significance is less than 0.05 thus the factor analysis can be used. the results are shown in table iii. considering the value of cronbach's alpha, which is 70%, and according to [20, 21] the suitable fit for measuring models is confirmed. therefore, according to table iv, it can be contacted that the research modes are fitted very well. after the confirmation of the model, we can use and interpret the results of the path analysis in testing the hypotheses. this model shows the amount of correlation of the latent variables that are the conceptual image of the hypotheses in practice and in reality due to the observations and the data gained from the questionnaires. it also confirms how the hypotheses of the research would be rejected or accepted. the verification of the hypotheses with regression and determination coefficients will be discussed and it's results are shown in figure 1 and table v. considering the determination coefficient amounts for the variables of professional skills and organizational productivity shown in table v, that are respectively 0.95 and 0.968, regression models are suitable. engineering, technology & applied science research vol. 8, no. 1, 2018, 2427-2432 2429 www.etasr.com chakamian keshvari et al.: a model for the development οf employees’ learning (career path) … table i. demographic features of the samples variable sub-variable number frequency accumulated percentage gender male 91 91% 91% female 9 9% 100% marital status married 81 81% 81% single 19 19% 100% age 21-24 9 9% 9% 25-29 16 16% 25% 30-34 25 25% 50% 35-39 33 33% 83% 40-44 8 8% 90% 45-49 7 7% 98% more than 50 2 2% 100% educational level under diploma 25 25% 25% diploma 42 42% 67% associate 6 6% 73% bachelor 23 23% 96% master & higher 4 4% 100% work experience 5 years & less 45 45% 45% 6-9 years 19 19% 64% 10-14 years 31 31% 95% 15 years & more 5 5% 100% job title operator 50 50% 50% technician 19 19% 69% supervisor/employee 9 9% 78% expert 9 9% 87% manager 8 8% 95% departement manager 5 5% 100% department production 71 71% 71% quality control 6 6% 77% engenering 3 3% 80% financial & administrative 7 7% 87% trading 11 11% 98% management 2 2% 100% income level less than 1m 3 3% 3% 1-1.5 m 52 52% 55% 1.5-2 m 32 32% 87% 2-2.5 m 7 7% 94% 2.5-3 m 3 3% 97% more than 3 m 3 3% 100% table ii. descriptive statistics of datas variable m ea n m ed ia n s ta n d a rd d ev ia ti o n k u rt o si s s k ew n es s classic trainings 2.297 2.250 0.601 0.054 0.811 technical and vocational trainings 2.065 2.000 0.654 0.367 0.446 apprenticeship method 2.356 2.333 0.648 0.068 0.446 learning by holding meetings with experts 2.264 2.200 0.622 0.014 -0.260 online and tutorial trainings 1.987 2.200 0.824 0.692 -0.084 experimental learning 2.204 2.000 0.633 0.152 -0.006 professional skill 2.386 2.233 0.622 0.080 -0.065 organizational productivity 2.275 2.366 0.727 0.329 -0.0378 table iii. bartlett test 0.24 kaiser criterion 26.205 rotation test bartlett test 0.000 signification level table iv. fit indices index type index amount absolute index 0.664 relative index 0.783 exterior model index 0.825 interior model index 0.906 table v. determination coefficient and moderated determination coefficient determination coefficient moderated determination coefficient organizational productivity 0.950 0.950 professional skills 0.968 0.966 engineering, technology & applied science research vol. 8, no. 1, 2018, 2427-2432 2430 www.etasr.com chakamian keshvari et al.: a model for the development οf employees’ learning (career path) … fig. 1. path coefficients iv. verification in each hypothesis we tried to find the existence of correlation between some variables and professional skill and its correlation with organizational productivity. regarding the second part, as shown in table vi, the p value of professional skills' influence on organizational productivity is less than 0.05 (0.000), and the t value is more than 1.96 (t=218.301>1.96), so it's concluded that the influence of professional skills is significant on organizational productivity. first hypothesis: the influence of classic and academic trainings presented by higher education institutions on organizational productivity is significant with the mediating role of professional skills' variable. according to table vi, the p value of academic and classic trainings on professional skills is more than 0.05 (0.288). the t value for is less than 1.96 (t=1.063<1.96), so we can say that the influence of classic and academic trainings on professional skills is not meaningful to professional skills. as the relation between the influence of classic and academic trainings variable on professional skills, the first hypothesis is rejected. table vi. general model results r el a ti o n p a th c o ef fi ci en t t st a ti st ic s s ig n if ic a ti o n le v el r es u lt first hypothesis classic trainings → professional skills 0.055 1.063 0.288 rejected professional skills → organizational productivity 0.975 218.301 0.000 second hypothesis technical and vocational trainings → professional skills 0.219 1.451 0.147 rejected professional skills → organizational productivity 0.975 218.301 0.000 third hypothesis apprenticeship method → professional skills 0.293 2.369 0.018 accepted professional skills → organizational productivity 0.975 218.301 0.000 fourth hypothesis learning by holding seminars → professional skills 0.171 2.017 0.044 accepted professional skills → organizational productivity 0.975 218.301 0.000 fifth hypothese online and tutorials trainings → perfessional skills 0.293 0.292 0.77 rejected perfessional skills → organizational productivity 0.975 218.301 0.000 sixth hypothese experimental trainings → perfessional skills 0.293 2.584 0.000 accepted perfessional skills → organizational productivity 0.975 218.301 0.000 second hypothesis: the impact of professional courses in technical and vocational organizations on organizational productivity is significant with the mediating role of professional skills' variable. according to table vi, the influence of p value of professional courses in technical and vocational organizations on professional skills is more than 0.05 (0.147). also by considering absolute value of t for each path that is less than 1.96 (t=1.451<1.96), we can say that the influence of professional courses in technical and vocational organizations on professional skills is not significant. as the relation between the influence of professional courses in technical and vocational organizations variable on professional skill, the second hypothesis is rejected. third hypothesis: the influence of workshop and experimental skills that are gained by apprenticeship on organizational productivity is significant with the mediating role of professional skills' variable. the influence of p value of apprenticeship training method is less than 0.05 (0.018). the engineering, technology & applied science research vol. 8, no. 1, 2018, 2427-2432 2431 www.etasr.com chakamian keshvari et al.: a model for the development οf employees’ learning (career path) … absolute value of t is more than 1.96 (t=2.369>1.96), so we can say that the influence of apprenticeship training method on professional skills is significant. as the relation between the influences of apprenticeship training method on professional skill, the second hypothesis is accepted. fourth hypothesis: the impact of the effect of training by holding meetings and seminars with experts on organizational productivity is significant with the mediating role of professional skills' variable. the influence of p value of the effect of training by holding meetings and seminars with experts on professional skills is less than 0.05 (0.044). also by considering absolute value of t for each path that is more than 1.96 (t=2.017>1.96), we can say that the influence of the effect of training by holding meetings and seminars with experts on professional skills is significant. so the fourth hypothesis is accepted. fifth hypotheses: the influence of online technologies and tutorials on organizational productivity is significant with the mediating role of professional skills' variable. the influence of p value of online technologies and tutorial trainings on professional skills is more than 0.05 (0.77). its t value is t=0.292<1.96, so we can say that the influence of online technologies and tutorial trainings on professional skills is not significant. as the relations are not significant, the fifth hypothesis is rejected. sixth hypothesis: the impact of learning by experiencing during work on organizational productivity is significant with the mediating role of professional skills' variable. the influence of p value of the learning by experiencing during work on professional skills is less than 0.05 (0.000) and t=2.377>1.96, so we can say that the influence of learning by experiencing during work is significant. so, the sixth hypothesis is acceptable. v. discussion the main purpose of this study is to propose a model for the development of employees' learning (career path) in industrial enterprises. according to the research findings, the overall results are: • the influence of classic and academic trainings presented by higher education institutions on organizational productivity is not significant with the mediating role of professional skills' variable. regarding the relation between the influence of classic and academic trainings on professional skill, the hypothesis is rejected. • the impact of professional courses in technical and vocational organizations on organizational productivity is not significant with the mediating role of professional skills' variable. regarding the relation between the influence of professional courses in technical and vocational organizations on professional skill, the hypothesis is rejected. • the influence of workshop and experimental skills that are gained by apprenticeship on organizational productivity is significant with the mediating role of professional skills' variable. regarding the relation between the influence of apprenticeship training method on professional skill, the hypothesis is acceptable. • the impact of the effect of training by holding meetings and seminars with experts on organizational productivity is significant with the mediating role of professional skills' variable. so it's concluded that the influence of professional skills is significant on organizational productivity. • the influence of online technologies and tutorials on organizational productivity is not significant with the mediating role of professional skills' variable. • the impact of learning by experiencing during the work on organizational productivity is significant with the mediating role of professional skills variable. considering the results of the research, some suggestions can be proposed. according to the result of the first hypothesis, we have to try to make the academic trainings more compatible with the work environment. also it's necessary to motivate the employees to benefit from their academic teachings to optimize the job processes. considering the results of the second hypothesis, the applied job skills should be increased by providing specialized trainings in technical and vocational organizations. it's also recommended for the employees to be motivated to learn technical and vocational skills in the work environment. according to the third hypothesis result that confirms the influence of workshop and experimental skills that are gained by apprenticeship is significant on organizational productivity with the mediating role of professional skills' variable, we can improve this by increasing personal discipline, and also reduce equipment and device failure through apprenticeship. besides, it's recommended to lead up the concepts of seniority in order to encourage senior employees to institutionalize learning culture by apprenticeship method. based on the fifth hypothesis result that confirm the significance of the effect of training by holding meetings and seminars with experts on organizational productivity with the mediating role of professional skills' variable, the recommendation for development of this hypothesis is achieving the organization's goals, improving employee’s performance, enhancing their creativity, responsibility and personal discipline through holding meetings and seminars with experts. considering the result of the fifth hypothesis, motivating and encouraging employees to increase their knowledge of the job continuously, augmenting the self confidence in performing the tasks is suggested through online technologies and tutorials. finally, considering the sixth hypothesis that says the impact of learning by experiencing meanwhile the work is significant on organizational productivity with the mediating role of professional skills' variable, we recommend asking employees to perform researches about the ways for optimization the organization's progress to achieve job promotion and to be contributed in economic benefits of the organization gained by their innovation and their promotional work for integrating this process. engineering, technology & applied science research vol. 8, no. 1, 2018, 2427-2432 2432 www.etasr.com chakamian keshvari et al.: a model for the development οf employees’ learning (career path) … vi. restrictions the most essential limitations of the current research are the following. time and cost: as the skill-building process is a long-term process, it's results appear after a long time in the form of increasing organizational productivity so it is impossible to evaluate the final results during the project implementation. the high cost of this type of researches which sometimes last long can be an effective obstacle that prevent the researchers to follow-up and continue such projects. human resources and general limits in iran: lack of capable and trained employees depending on the required level of job skills is another preventing factor in skill-building. trust and belief in researches, working relationship between management and staff and also the absence of a secure environment like external threats causing the feeling of job insecurity is another major problem. lack of incentive mechanisms and/or organization's chief’s support and belief. definitely without the support of the leadership of the senior management of the organization, this kind of projects would not be useful and will be just reports or non-functional articles. vii. conclusion the current work focused on a model for the development of employees' learning (career path) in industrial enterprises. a descriptive-survey method along with field research, through a questionnaire, were used. the statistical population consisted of 110 employees of dana baspar's enterprises. descriptive statistics for demographic data (frequency, standard deviation and mean) and inferential statistics are considered. six different hypotheses are investigated and results are discussed. references [1] a. aghaz, a. tarighian, “the impact of optimism mediator on the job progress in relation with the fitness of person and job and the fitness of the person and the organization”, journal of management sciences of iran, vol. 10, no. 37, pp. 79-102, 2015 [2] c. hendry, human resource management. routledge, 2012 [3] a. shahbandar zadeh, e. haji hosseini, “check the perception of employees as the organization’s core capital and assess their progress along the model developed by shine”, 2nd conference of executive management, pp. 1-10, 2011 [4] a. sadeghi mal, “the model for analyzing the efficient variables on talent”, journal of human resource management, imam hussain university, 6th period, no. 4, pp. 67-92, 2014 [5] r. wood, a. bandura, “social cognitive theory of organizational management”, academy of management review, vol. 14, no. 3, pp. 361-84, 1989 [6] s. r. razvan shahrzad, s. b. babak alavi, “job orientations and internal job references of software programmers”, journal of management sciences of iran, vol. 4, no. 16, pp. 55-84, 2009 [7] j. h. greenhaus, a. c. gerard, m. g. veronica, career management, dryden press, 2011 [8] w. b. barclay, j. r. chapman, l. b. brown, underlying factor structure of schein's career anchor model, journal of career assessment, vol 21, no 3, pp. 430-451, 2013 [9] w. mayrhofer, m. meyer, m. schiffinger, a. schmidt, “the influence of family responsibilities, career fields and gender on career success: an empirical study”, journal of managerial psychology, vol. 23, no. 3, pp. 292-323, 2008 [10] h. i. ballout, “career success: the effects of human capital, personenvironment fit and organizational support”, journal of managerial psychology, vol. 22, no. 8, pp. 741-65. 2007 [11] n. dries, r. pepermans, o. carlier, “career success: constructing a multidimensional model”, journal of vocational behavior, vol. 73, no. 2, pp. 254-267, 2008 [12] h. kong, c. catherine, s. haiyan, “from hotel career management to employees’ career satisfaction: the mediating effect of career competency”, international journal of hospitality management, vol. 31, no. 1, pp. 76-85, 2012 [13] m. yap, m. r. holmes, c. a. hannan, w. cukier, “the relationship between diversity training, organizational commitment and career satisfaction”, journal of european industrial training, vol. 34, no. 6, pp. 51938, 2014 [14] b. r. barnett, l. bradley, “the impact of organizational support for career development on career satisfaction”, career development international, vol. 12, no. 7, pp. 617-636, 2009 [15] m. armstrong-stassen, s. cameron, “factors related to the career satisfaction of older managerial and professional women, career development international, vol. 10, no. 3, pp. 203-215, 2015 [16] v. wickramasinghe, m. jayaweera, “impact of career plateau and supervisory support on career satisfaction”, career development international, vol. 15, no. 6, pp. 544-561, 2013 [17] a. rezaian, a. hatami, s. hussain, “the relationship between the management of job progress and the satisfaction of the job path”, journal of military medicine, vol. 10, no. 4, pp. 217-221, 2011 [18] s. sheikh email, s. hezbavi, “proposing a model of effective factors on job path orientation”, journal of human resource management, imam hussain,year 8, no. 8-23, pp. 55-78, 2016 [19] r. i. levin, statistics for management. pearson education india, 2008 [20] j. henseler, c. m. ringle, r. r. sinkovics, “the use of partial least squares path modeling”, book series: advances in international marketing, vol. 20, pp. 277-319, 2009 [21] p. zhang, c. wang, “an empirical study on consumer s perceived value and attitude toward advertising”, 6th global information technology and management world conference, 2005 microsoft word 14-2479_s_etasr_v9_n4_pp4389-4391 engineering, technology & applied science research vol. 9, no. 4, 2019, 4389-4391 4389 www.etasr.com murawwat et al.: energy cycle optimization of mobile phones using ieee 802.16e energy cycle optimization of mobile phones using a sleep cycle optimization algorithm sadia murawwat electrical engineering department lahore college for women university lahore, pakistan hira akash electrical engineering department lahore college for women university lahore, pakistan iqra manzoor electrical engineering department lahore college for women university lahore, pakistan javeria ahmed electrical engineering department lahore college for women university lahore, pakistan abstract—researchers and mobile network operators are dealing with the steep rise in energy consumption of mobile phones. a massive amount of phones are available in the market which are updating services from time to time. the problem lies in their battery drainage in response to the usage of internet-based applications including online streaming, multimedia requests, social networking usage and many more. in this research, a new technique is proposed and evaluated for energy optimization in mobile phones by exploiting the listening cycle of the mobile station (ms) wake-up mode while connected to the base station (bs) that is connected to a mobile network based on ieee 802.16e. an ms cannot communicate with the bs if it is in the sleep mode while the other is in the wake-up mode. service time and sojourn time are assumed to be exponential and based on tdistribution. the confidence interval comes up to 95% for our technique. the relative error is computed between the earlier techniques available and the approximated proposed one. results show that there is a considerable improvement in energy consumption as compared to the other available techniques. keywords-energy optimization; mobile phones; listening interval; relative error i. introduction the growth of broadband wireless access (bwa) technologies is strongly related to the growing incorporation of internet and wireless multimedia applications of mobile phones in a wide variety of every day life’s aspects. worldwide interoperability for microwave access (wimax) standards provide multiple physical layer (phy) and media access control (mac) options and are a group of communication standards based on the ieee 802.16 set of standards. the basic ieee 802.16 was released in 2002 (originally focused on just fixed node stations) [1] and was modified later [2-4] in order to include mobility demands such as low energy consumption and techniques as the sleep mode operation (smo). energy consumption and restoration has been the focusing point of several works [5-11]. the smo technique uses two different modes for each mobile station (ms): the sleep mode and the wake-up mode. the ms falls in the sleep mode when it cannot transmit or receive uplink or downlink traffic to or from the base station (bs), thus saving power, while it switches to wake-up mode when it can transmit or receive from the bs. smo plays an essential role in the minimization of energy consumption of ms in an ieee 802.16e based network. sleep cycle and listening interval are the two main parts of sleep mode while the wake-up mode has respectively the active cycle and the listening interval. in smo, sleep and wake-up mode can be switched from one to another in reference to the traffic arrival rate. when the ms is in wake-up mode and there is no uplink or downlink traffic for bs, it sends a sleep request (slp_rqt) message addressed for bs to initiate sleep mode and waits for approval. if the bs responds positively, then the ms gets to sleep mode for a while and then wakes up temporarily for a small duration. this momentarily wake-up duration is called listening interval. if the bs responds negatively then the ms will remain in wake-up mode. positive response indicates that there is no traffic and the ms can switch mode to wake-up. negative response means that the ms should remain in the sleep mode. sleep request and sleep response messages have some parameters i.e. initial and final sleep window, listening window and start interval of sleep mode. the minimum and maximum sleep intervals are represented as tmin and tmax respectively [12]. ii. the scoa algorithm sleep cycle optimization algorithm (scoa) is the here proposed algorithm for the minimization of energy usage in mobile stations using ieee 802.16e. at first some parameters are initialized, i.e. tmin (sleep interval-minimum), tmax (sleep interval-maximum), l (listening interval), where es and el represent the units of energy consumption per time in sleep cycles and listening cycles respectively. for the optimization of sleep cycle, minimum and maximum sleep and listening intervals are considered as key parameters. sleep cycle is optimized by calculating the jth sleep cycle using (1): corresponding author: sadia murawwat (sadia.murawwat@hotmail.com) engineering, technology & applied science research vol. 9, no. 4, 2019, 4389-4391 4390 www.etasr.com murawwat et al.: energy cycle optimization of mobile phones using ieee 802.16e �� � � 4 ����� � 4����� � ���� ���� � 4����� � ���� (1) in (1), tj represents the jth sleep cycles and j initializes from j=1. this calculation ensures that the sleep cycles are adjusted by increasing four times the time interval to the next sleep cycle as compared to the previous cycle instead of simply increment or doubling the previous sleep cycles. the algorithmic steps are: 1. parameter initialization: j=1, l=1ms, tmin=1ms, tmax=1024ms 2. mode detection 3. if wake-up mode, get tmin, and tmax //else (step 4 ) send sleep request message to bs ms will wait for response from bs if ms gets positive response then it goes to step 4 if ms gets negative response then it goes to step 3 4. if sleep mode, compare values of tmin, and tmax if (tmin<tmax) calculate tj , using (1) tj: tmax else tj=tmax 5: return to step 2 fig. 1. sleep mode operation iii. numerical analysis the mathematical model of scoa using smo of ieee 802.16e is presented in this section. the performance parameter i.e. energy consumption is evaluated by assuming that the frame arrival process follows the poisson distribution with rate λ and service time and sojourn time follow the same distribution with 1/λ. frame arrival rates are recursively calculated for scoa. pr��� � ����� � 1 � pr ��� � ����� (2) where, pr��� � ������ � ��!�"#$% (3) equations (2)-(3) are the poisson distribution equations of sleep mode parameters for data arrival and for no data arrival at ms respectively. iv. energy consumption & confidence interval the energy consumption, e[c] can be determined by adding the es and el to each sleep cycle time [13].the value of el is 100mw in listening interval of wake-up mode and es is assumed to be 10mw. hence, e[c] is recursively calculated using (6): &'() � ∑ pr �+ � , ∑ ��-&. / 0&%�-1� 2�1� (4) &'() � ∑ ��! ∑ �"3$% #45365271� �1 � ��!�"#$%�� ∑ ��-&. / 0&%�-1� (5) &'() � ∑ ��! ∑ �"3$% #45365271� ∑ ��-&. / 0&%�-1� � ∑ ��! ∑ �"3$% #365 ∑ ��-&. / 0&%�-1� 271� (6) a 95% confidence interval of the proposed technique for the ms energy consumption has been calculated using (7), based on t-distribution that provides a predictable range of values with the assumption of α=0.05. in (7), 8̅ represents mean, s is the standard deviation, n is the total sample number, and t_(α⁄2,(v) ) is calculated from the t-table. 8̅ : ;< => ,�@ .√ (7) v. simulation results & comparison the accuracy of the mathematical model is verified through matab simulations. the simulation results demonstrate the dependency relationships between the performance parameters and the frame arrival rate. the performance parameter, i.e. the energy consumption e[c] was measured and compared for different values of tmax. the arrival rate (λ) was considered from 0.01 to 0.02. moreover, ieee 802.16e standard and advanced energy saving mechanism (aesm) [5] approaches were compared with the proposed scoa technique. the energy consumption comparison for the different techniques is summarized in figure 2, where the sleep window-minimum is 1 msec and the sleep window-maximum is 1024 msec. from figure 2 it can be seen that ieee 802.16e drains more energy per frame than scoa due to its unnecessary energy consumption in sleep window because of the big number of sleep cycles. the comparison of the optimized value of energy consumption is shown in table i. it is seen that scoa consumes less energy than ieee 802.16e and aesm. vi. conclusion in this research, sleep cycle optimization algorithm (scoa) based on smo has been compared with the basic ieee 802.16e standard and the aesm approach with the use of matlab. the simulation results of the mathematical model of energy consumption have shown satisfactory results when compared to earlier existing techniques. additionally, the confidence interval and relative error between the proposed technique and the basic standard ieee 802.16e have been calculated. the confidence interval comes up to [1.99903, 1.99976] which shows efficient accuracy. the relative error engineering, technology & applied science research vol. 9, no. 4, 2019, 4389-4391 4391 www.etasr.com murawwat et al.: energy cycle optimization of mobile phones using ieee 802.16e between the standard and the proposed technique is 6.898. concluding, scoa consumes 10%-20% less energy than the existing techniques. fig. 2. simulation of e[c] for different techniques table i. energy consumption comparison frame per unit time (λ) ieee802.16e aesm scoa 0.02 2.004 4.004 0.2509 0.04 1.965 3.925 0.2459 0.06 1.926 3.847 0.241 0.08 1.887 3.771 0.2362 0.1 1.85 3.696 0.2315 0.12 1.813 3.623 0.2269 0.14 1.777 3.551 0.2224 0.16 1.742 3.48 0.218 0.18 1.707 3.411 0.2136 0.2 1.673 3.344 0.2094 references [1] ieee, ieee std 802.16-2001-ieee standard for local and metropolitan area networks part 16: air interface for fixed broadband wireless access systems, ieee, 2002 [2] ieee, ieee std 802.16e-2005-ieee standard for local and metropolitan area networks part 16: air interface for fixed and mobile broadband wireless access systems amendment for physical and medium access control layers for combined fixed and mobile operation in licensed bands, ieee, 2006 [3] ieee, ieee std 802.16e/d6-2005-ieee amendment to ieee standard for local and metropolitan area networks part 16: air interface for fixed broadband wireless access systems physical and medium access control layers for combined fixed and mobile operation in licensed bands, ieee, 2005 [4] ieee, ieee std 802.16e/d5-2004-ieee, amendment to ieee standard for local and metropolitan area networks part 16: air interface for fixed broadband wireless access systems physical and medium access control layers for combined fixed and mobile operation in licensed bands, ieee, 2004 [5] h. j. thontadharya, d. shwetha, m. s. bhat, j. t. devaraju, “effect of idle mode on power saving in mobile wimax network”, international conference on advances in computing, bangalore, india, july 4-6, 2012 [6] y. xiao, “performance analysis of an energy saving mechanism in the ieee 802.16e wireless man”, 3rd ieee consumer communications and networking conference, las vegas, usa, january 8-10, 2006 [7] k. han, s. choi, “performance analysis of sleep mode operation in ieee 802.16e mobile broadband wireless access systems”, 63rd vehicular technology conference, melbourne, australia, may 7-10, 2006 [8] y. zhang, m. fujise, “energy management in the ieee 802.16e mac”, ieee communications letters, vol. 10, no. 4, pp. 311-313, 2006 [9] j. b. seo, s. q. lee, n. h. park, h. w. lee, c. h. cho, “performance analysis of sleep mode operation in ieee 802.16e”, 60th vehicular technology conference, los angeles, usa, september 26-29, 2004 [10] n. h. lee, s. bahk, “mac sleep mode control considering downlink traffic pattern and mobility”,61st vehicular technology conference, stockholm, sweden, may 30-june 1, 2005 [11] y. xiao, “energy saving mechanism in the ieee 802.16e wireless man”, ieee communications letters, vol. 9, no. 7, pp. 595-597, 2005 [12] y. zhang, m. fujise, “energy management in the ieee 802.16e mac”, ieee communications letters, vol. 10, no. 4, pp. 311-313, 2006 [13] y. c. tseng, j. j. chen, y. c. yang, “managing power saving classes in ieee 802.16 wireless mans: a fold-anddemultiplex method”, transactions on mobile computing, vol. 10, no. 9, pp 1237-1247, 2011 engineering, technology & applied science research vol. 7, no. 6, 2017, 2293-2295 2293 www.etasr.com rittidech and rodbumrung: behavior of corrosion of a heat pipe cooling device in a computer behavior of corrosion of a heat pipe cooling device in a computer sampan rittidech heat pipe and thermal tools design research unit faculty of engineering mahasarakham university thailand s.rittidech@hotmail.com anuluk rodbumrung heat pipe and thermal tools design research unit faculty of engineering mahasarakham university thailand a_rodbumrung@hotmail.com abstract—the aim of this study was to perform life testing and to determine the effect of working time on the corrosion of a heat pipe used for cooling in a computer. the heat pipe was made from a copper tube. the heat pipe consists of evaporator and condenser section. it had a specification similar with the use in ordinary computers, the working fluid being distilled water. when the computer starts, the concentration of the copper solution slightly increases. the greater copper concentration was 0.00062 ppm upon 3000-5000 hours of testing. the surface traces of corrosion rises due to the oxidation of the porous material within the working fluid. the test found that oxygen (o) and carbon (c) are component contents. keywords-heat pipe; computer; cooling; corrosion i. introduction the advantage of heat pipe is that it can be used as cooling and heat exchange equipment, as an application for cooling of power electronics or communications devices. the heat pipes are usually made of metal, most common of which is copper and contain a porous material. after some time, corrosion will emerge within the heat pipes and porous materials. the corrosion mechanism of the heat pipe has been studied by many researchers. in [1], authors studied corrosion in a closedloop oscillating heat-pipe with check valves (clohp/cv) when water and ethanol were used as working fluids. they used scanning electron microscopy (sem) and energy dispersive x-ray spectrometry (edx), and found that the characteristics of the corrosion of the internal surface of the clohp/cv were pitted. analysis with atomic absorption spectroscopy (aas) showed that ethanol had a higher concentration of copper particles than water. in [2], authors studied corrosion behavior in copper tube heat pipes with distilled water and ethanol as working fluids. the results of the scanning electron microscope and energy dispersive x-ray spectrometry analysis showed that the corrosion of the heat pipe was uniform. the result of the atomic absorption spectroscopy indicated that the concentration of the copper in the ethanol as working fluid was greater than in the distilled water, and the highest concentration of copper particles in the ethanol was 22.7499 ppm or 0.0409 mg after testing for 3000 h. the concentration of copper was higher when the length of the life test increased due to corrosion of the heat pipe. in [3], authors studied the failure of copper tubes in air conditioning. they found that the copper tube in air conditioning had ant-nest corrosion. the failure of the copper in the air-conditioning units caused the loss of refrigerant. the major causes of failure were moisture and oxygen. the need of studying the mechanisms and forms of corrosion and heat transfer of heat pipes cooling device in desktop computer emerged. to date, no such research has been done. this research will focus on the study of the heat transfer rate of heat pipes and corrosion affecting the use of heat pipe cooling device that uses a central processor unit (cpu ) in a desktop computer. ii. explerimental procedure corrosion occurs on the inner surface of a heat pipe, was made from a copper tube. the heat pipe’s id and od are 4.48 mm and 6 mm respectively. its length 295 mm consisted of an evaporator section of 35 mm, condenser section of 190 mm and an adiabatic section of 70 mm. the wick thickness was 0.24 mm and wick pore 0.5. the heat pipe cooling device for testing is shown in figure 1. the experimental setup and testing tools are shown in figure 2, and the test rig is shown in figure 3. this study consisted of a 4 set desktop computer with a heat pipe cooling device. the evaporator section was embedded in the cpu of the computer and the condenser section transfer heat by a fan system. the durations of testing were 500, 1000, 3000 and 5000 hours. the test heat pipe cooling system was measured with an hour meter, a temperature recorder, and a personal computer. the time was measured using the hour meter kurber model 134, the ambient temperature was kept at 25°c. thermocouples (omega type k) were used to measure the temperature of the condenser sections. all the temperature data were recorded by a data logger (yokogawa dx200) and then transferred to a personal computer. 1) the controlled parameters were:  cpu = 3.5 ghz,  working fluids = di water. 2) the variable parameters were:  heat transfer rate engineering, technology & applied science research vol. 7, no. 6, 2017, 2293-2295 2294 www.etasr.com rittidech and rodbumrung: behavior of corrosion of a heat pipe cooling device in a computer  effect of corrosion of the heat pipe on lifetime 3) specifications  desktop computer  copper tube heat pipe with porous media, consists of fins  fan cooling system embedded to heat pipe system  temperature of cpu varies  fan speed of cooling system varies fig. 1. heat pipe cooling device. fig. 2. experimental set up. iii. results and discussion the cooling device operated under a steady temperature condition for 5000 h. then, there was an examination of the metallographic and preparation of specimens for the study of the inside of the pipe and wick. the composition of the heat pipe with a sintered wick composed of purified dendritic copper (99.97%). the preparation specimens were cut into 10, 3 and 6 mm sections to be tested and analyzed by the sem in order to identify the corrosion on the inside of the tube. the edx identified the composition of the corrosion products from the inner heat pipe and wick. the working fluid within the heat pipe was di water and the analysis of the concentration of the copper solution in the working fluid was done by the aas. the results from the experiment are presented in figures 4, 5 and 6. figure 4 shows the effect of the concentration of the copper solution with corrosion occurred inside the heat pipe. the concentration of the copper solution slightly increases when the computer starts. the greater concentration of the copper is 0.00062 ppm after 3000-5000 hours. this may be due to the fact of the oxidation reaction between the porous material and the working fluid. in any case, from 3000 to 5000 working hours, the concentrations of copper have similar values. fig. 3. test rig. fig. 4. concentration of the copper solution. in figures 5 a-c we see the effect of surface corrosion inside the evaporator section of the heat pipe. after 500 hours, the test found traces of corrosion. porous materials and powders are packed together noticeably. after 1000 hours of testing, the surface traces of corrosion are on the rise due to the oxidation of the porous material by the working fluid, thereby resulting in corrosion spreading up and delivery affecting the structure of spaces of porous structures. after 3000-5000 hours we found uneven traces of corrosion on the surface of the porous material. however, the operating temperature of the heat pipe is not very high. the changing nature of the internal structure of porous materials may see no clear effect of surface corrosion and the inside elements. figures 6 a-c show the corrosion effect on the elemental content inside the evaporator section. the test found oxygen (o) and carbon (c) along with copper (cu). this reaction is caused by corrosion of the internal working fluid. the amount of copper in the evaporator reduces when the test period is increased as we see with test periods of 500 1000 and 3000-5000 hours, although the results did not find any other elements. this explains the process of creating a heat pipe with the removal of non-condensables and the use of water with lead ions as working fluid. deionized water would cause the least corrosion. this will coincide with the results of the analysis from the aas and the characteristics of the porous structure made from sem results of the test period. engineering, technology & applied science research vol. 7, no. 6, 2017, 2293-2295 2295 www.etasr.com rittidech and rodbumrung: behavior of corrosion of a heat pipe cooling device in a computer fig. 5. surface corrosion at (a) 500 hours (b) 1000 hours (c) 3000-5000 hours fig. 6. elemental content at (a) 500, (b) 1000 and(c) 3000-5000 hours iv. conclusions the concentration of the copper solution increases slightly when the computer starts. the greater concentration of the copper is 0.00062 ppm after 3000-5000 hours of testing. the surface traces of corrosion rise due to the oxidation of the porous material within the working fluid, resulting in the spreading up of the corrosion and the affecting of the structure of spaces of porous structures. as for the elemental content of the corrosion inside the evaporator section of the heat pipe, the test found oxygen and carbon as component contents. acknowledgement the authors wish to express their gratitude to the project for higher education research promotion and national research university development and the mahasarakham university for providing the necessary financial aid and the facilities to conduct the research. references [1] s. sangiamsuk, b. bubphachot, s. rittidech, o. watanabe, “corrosion mechanism in a closed-loop oscillating heat-pipe with check valves (clohp/cv)”, anti-corrosion methods and materials, vol.61, no. 5, pp. 293-299, 2014 [2] a. rodbumrung, s. rittidech, b. bubphachot, “corrosion behavior in heat pipe”, advances in mechanical engineering, vol.8, no. 1, pp.1-9, 2016 [3] d. m. bastidas, i. cayuela, j. m. bastidas, “ant-nest corrosion of copper tubing in air-conditioning units”, revista de metalurgia, vol. 42, no. 5, pp. 367-381, 2006 (a) (b) (c) microsoft word 29-2367_s1 engineering, technology & applied science research vol. 8, no. 6, 2018,3631-3639 3631 www.etasr.com abdel-haq et al: investigating the success and the advantages of using erp system in ksa context investigating the success and the advantages of using erp system in ksa context mohammad samir abdel-haq dar al uloom university, saudi arabia mohdsamir@dau.edu.sa houcine chatti dar al uloom university, saudi arabia houcine@dau.edu.sa evan asfoura dar al uloom university, saudi arabia evan@dau.edu.sa abstract—enterprise resource planning (erp) is an important innovation, affecting the business world by generating improvements both tangible and intangible in large companies and small and medium enterprises (sme). this study focuses on the determinants of success and the advantages of the adoption of this technology. to address these points, a comprehensive literature survey was carried out in order to formulate an original research model for erp success evaluation and provide a prospect for it infrastructure and integration. the model, thus suggested and taken within the kingdom of saudi arabia (ksa) context, examines in a systematic approach the relation between the erp acceptance determinants, the effects of the process of erp systems diffusion, and the impacts expected on organizational performance. obtained results underline two key determinants of erp projects success: first, the preponderance of information control and the improvement in the use of competences. the second factor is the quality of team projects, the definition of team’s mission, training, business processes reengineering, user acceptance, top management support and the selection of the erp solution. keywords-erp; it infrastructure; key success factors; erp benefit; systematic approach i. introduction businesses are becoming more and more inclined to adopt integrated management systems. the growing interest in enterprise resource planning (erp) solutions is due to the promise of such systems for both large companies and small and medium enterprises (smes). in the past, this innovation was only possible for very large multinational companies. in 1998, almost 40% of firms with more than $1 trillion in annual revenue implement erp systems [1]. today, this vision is different, the brightest future growth of sales of these systems is at the level of medium-sized companies [2]. most companies that have acquired an erp solution have done so primarily because of their capacity to better respond to the need for change in their business environment [3]. this solution, aimed to integrate application software to be used as a management process transformation machine. it is a fact that the transition to a large-scale erp solution is no longer limited to the acquisition of hardware and software, but the main challenge in implementing an erp solution is change management [4, 5] and knowledge management [36]. in other words, the challenges of implementing an erp are not only technical, they also involve human and organizational aspects. about half of the erp transition projects failed to achieve projected benefits as managers underestimated efforts to invest in change management [6]. well-known companies [7] have failed to implement an erp system. as a result, companies are facing a paradoxical situation: on the one hand, the high potential of gain resulting from the installation of an erp system and, on the other hand, the risks of failure. the broad scope of an erp and the changes in workflows that accompany its implementation increase both risks and expected benefits [8]. in this perspective, which is situated within the paradigm of the contribution of information systems to organizational performance, the objective of this research is to assess the postimplementation evaluation of the adoption success of the erp. the issue is, therefore, part of the theme of the impact of it on organizational performance. this research also tries to evaluate the organizational benefits following the implementation of erp systems and to determine the key success factors of its adoption. ii. theoritical framework the modeling process of the evaluation is carried out in two stages. first, the determinants of success of erp implementation and information systems are clarified, in general. then, the potential benefits of erp implementation in terms of organizational performance are identified. the modeling effort focuses on explaining the effects of spreading erp innovation in terms of organizational performance, through its adoption process. a. determinants of success of erp adoption four distinct categories of success factors for adoption have been identified in [9, 10]: the first category relates to the determinants of success of information systems with factors such as the role of users [11, 12], the availability of appropriate resources and skills, and the presence of a sponsor [13]. the second category relates to the determinants of success that can be extended to software packages. factors such as the general management commitment, and factors related to the implementation process, such as the rigorous management of the project, hardware and software issues, the software selection, or the absence of training support [9, 35]. the third category concerns the specific determinants of the management of the erp implementation project. factors such as communication, recruitment of necessary staff, customer consultation, implementation of a project plan/schedule, engineering, technology & applied science research vol. 8, no. 6, 2018,3631-3639 3632 www.etasr.com abdel-haq et al: investigating the success and the advantages of using erp system in ksa context supervision and feedback at each step and troubleshooting [14], are all important to successfully manage the erp project. the last category of success factors relates to the actual implementation of erp systems. in addition to standard project management factors, information technology projects also require additional success factors because of their impact on an organization's structure and business processes. it should be emphasized that the success of an erp implementation, defined in terms of determining factors, is limited, if its relationship with the organizational and cultural context is ignored [15]. the list of success factors presents a static perspective of success and does not identify the processes by which these factors operate as well as their links or correlations [9]. as a result, factors can be usefully combined with approaches that focus on the broader understanding of contextual and “process” characteristics, to better explain how and why factors and outcomes are related [9, 15]. authors in [16] examined the determinants of successful erp implementation in saudi arabia, and they proposed a conceptual model which was developed based on internal and external factors. the internal factors covered business process reengineering, team competence, project management support, and top management support. the external factors covered vendor support and consultant competency. authors in [17] defined critical success factors (csfs) contributing to the success of erp implementation in saudi arabia. the research identified 13 most important erp csfs, extracted from previous studies in this field. b. evaluation factors of erp impact several studies and numerous examples of companies deal with the success of the erp implementation, process and analyze the post-implementation benefits notably through their impact on business performance [18-22]. authors in [18] summarize the impact of erp. table i explains the taxonomy of benefits across five dimensions. this structure is validated and consolidated in [23]. it constitutes an indispensable contribution, both theoretical and practical, to differentiate the impacts of erp, to be usefully retained in the construction of the theoretical scheme of this research. c. theoretical scheme of research based on the theoretical foundations, a theoretical scheme for evaluating the post-implementation success of erp was developed. this schema is a systemic representation of the evaluation at a given moment of the process of transformation of resources used during implementation. it postulates the existence of a theoretical structure of the concepts mobilized, to study causal relationships between the identified determinants of success and the characteristics of innovation (in terms of advantage technical and enhancement of it infrastructure capabilities) and it application integration, with the success of erp adoption and implementation. this schema is a simplified representation of reality that aims to establish direct and indirect effects of the two explanatory levels (mobilized resources and transformation process) on the level of the benefits derived from the use of an erp. based on this systemic approach, widely used in management science to evaluate it performance and impact [24], the theoretical scheme, shown in figure 1, presents a three-dimensional structure for the levels of analysis. table i. erp benefits [18] dimensions sub dimensions operational cost reduction deadline mitigation improved productivity quality improvement improved customer service management better resource management improved decision-making and planning improved performance strategic support to the growth of the case support to business alliances construction of business innovation construction of cost leaderships generate product differentiation construction of external links (customers and suppliers) expansion on a global scale e-commerce accommodation technology business flexibility for current and future changes cost reduction of t.i increased opportunities for the infrastructure of t.i organizational support for organizational change business learning facilitation “empowerment” common vision construction change of employee behavior employee satisfaction and morale improvement fig. 1. theoretical scheme of determinants of adoption success regarding figure 1, one can see an entry level, characterizing the resources or critical success factors (csf) that were mobilized during the pre-implementation phase of an erp (relating to information systems, software packages, project management). these resources are likely to affect both the implementation of erp and its expected organizational performance. this level of theoretical analysis therefore engineering, technology & applied science research vol. 8, no. 6, 2018,3631-3639 3633 www.etasr.com abdel-haq et al: investigating the success and the advantages of using erp system in ksa context considers the facilitating factors of a complex process (black box) of it acceptance, which aims to efficiently transform the resources mobilized into management results. an intermediate level includes the factors that describe erp implementation, that is, the factors that formalize the complex process of adoption and it integration, as the new organizational is. these are factors that express the effects of the decision to innovate and integrate, through perceptions (in terms of success or failure) of the planning and implementation of the technology [25]. the model uses them, for each of the two mentioned sub-processes (innovation and integration), as “factors of process quality” (fqp) of adoption. an output level describes the success of erp adoption. these factors reflect the impacts of erp (of its adoption and its integration), in terms of the benefits of erp implementation. d. conceptual model and research premise beyond this first exploratory approach and the effort of theoretical structuring, this work aims at proposing an original conceptual model intended to validate the premises of existing relations between the concepts characterizing the three levels of the scheme: the resources mobilized during erp implementation, it infrastructure opportunities, integration and organizational performance. the inclusion of quality factors of process describing the it infrastructure and the integration of applications is a rather new and interesting perspective in understanding the erp adoption process and in understanding its conditions of success. a study of 20 canadian companies focused on the challenges of updating it infrastructure during erp implementation showed that almost 50% of these companies have deployed a new infrastructure to support the requirements of the software package, and they migrated from a “mainframe” architecture to a client/server architecture [26]. this update of the it infrastructure typically leads companies to replace their old critical systems with fully integrated systems [19]. in addition, several studies supported the thesis that system integration is directly related to the performance. the greater the difference between the degree of integration before and after erp implantation, the greater the benefits obtained [27]. the conceptual model (figure 2) presents two kinds of causal relationships between the variables of the three conceptual levels: direct and/or indirect dependency relationships. this paper is limited to studying the existence of three direct causal relationships, which are the subject of premises, between levels 1 and 2 (p1), 2 and 3 (p2), and in level 2 (p3): • p1: the key success factors of an erp implementation directly and positively influence the improvement of the possibilities of the it infrastructure. • p2: improving the possibilities of the it infrastructure directly and positively influences the integration of applications. • p3: application integration directly and positively influences erp implementation benefits. e. methodological framework of research this is an exploratory study [28], the methodological approach is part of the grounded theory method (gtm) approach [29], and advocated as a response to the “rigid positivism” in [30]. due to the specificity of the situation and the research object, it is difficult to fully rely on the results of the work that has been done on it adoption. erp systems are considered both as a major technological innovation and a complex machine of re-engineering having a very important impact on the development and transformation of the company. using directly quantitative methods, without the use of exploratory analysis, to test models that are developed solely from the literature cannot favor the reliability and the actualization of the results generated by this research. it is characterized by a short life cycle where yesterday’s technology is becoming obsolete today. in this research work, the qualitative data collection technique was chosen. focused, non-directive and semi-structured personal interviews were conducted. the choice of this type of interviews seems to achieve the best fit between the degrees of freedom left to the respondent, and the degree of depth of the information sought. fig. 2. the structure of the conceptual model the questions asked are of two distinct types. two open (non-directive) questions aiming to obtain information as freely as possible on the most important critical success factors and the benefits of erp implementation. through these two open questions, the objective was to find “ indications as to the level of information of the person interviewed about what is central in his mind” [31]. underlying questions of open (semidirective) types, aimed at obtaining information on categories of benefits and critical success factors, were developed on the basis of items and constructs identified from [18]. the analysis would then review all the trends from the different underlying issues and confront them later, with the constructs cleared of the main issues in order to infer the most significant variables to remember. for these variables to be definitively retained, it suffices that they are mentioned by more than 50% of the respondents at the level of the main question and also appear in an advanced position in the ranking made on the basis of this question. since the design of the research is a multi-site design, the analysis process consists, initially, in a separate study of each case separately and, in a second step, in an inter-site analysis [32]. the research field is made up of two parts involved in erp projects, namely five erp system suppliers and five industrial companies having had to implement at least four to six modules of an erp software within the last two years. the engineering, technology & applied science research vol. 8, no. 6, 2018,3631-3639 3634 www.etasr.com abdel-haq et al: investigating the success and the advantages of using erp system in ksa context interviewed specialists have experience in consulting several tenders, participating in many erp projects, and have sufficiently experienced the effects on the organization of these it. thus, the main interlocutors, constituting the “theoretical sample” of the analysis, are project managers and general management executives who are deep involved in the implementation of the system and the monitoring of its operation. the expertise of the interviewees helps, in the sociocultural context of ksa companies, to give a specific representation of knowledge concerning the adoption of erp systems and their success. this representation is confronted with a permanent comparison of the manipulated concepts and research variables. iii. results and interpretations a. benefits of implementing an erp system 1) control of information the content analysis of the interviews showed that respondents are unanimous on the control of information as a benefit provided by the erp system. by acquiring an erp solution, business managers seek, in fact, to solve problems related to the fluidity, availability and credibility of information. they are trying to limit the number of speakers and remove the dependency of people to access the information. they want the removal of personal links in the company and obtain full information transparency. 2) operational and management benefits analysis shows improved performance control, cost control, time reduction, improved decision making, improved resource management, improved production management, and productivity as benefits provided by the establishment of an erp system. a) improved performance control according to interviewees, the system significantly improved performance control. it ensures “fairly rigorous activity control based on reliable and instantaneous information, generated in the form of report and dashboard”. the analytic and multidimensional processing capability of the information also allows “a control of the performance by line of business, by product, by customer, by region or by different combinations”. using these reporting and analysis tools, the system improves the anticipation of problems relating, for example, to stock outage, quality deterioration and the overflow of cash facilities granted to customer and/or obtained from suppliers. with the automatic control procedures incorporated in the processes, the system also offers the possibility of “automatic blocking, if a critical threshold is exceeded” and encourages the employees of the company to “carry out their work on time so as not to block the process or be blamed by their colleagues”. b) cost containment according to interviewees, the system has significantly improved cost control. with better information management and control, the system has generated “a certain ease and reliability in the calculation of technical costs, supply costs, commercial costs, and tooling costs”. in this respect, one respondent stated that real-time cost control has led to, among other things, better monitoring of the waste rate and a waste reduction. c) improved decision-making the system improved decision-making in the companies that have implemented it. for them, the control of information, brought by the new system, is at the origin of the improvement of the decision-making. d) time reduction the erp system has also improved time efficiency in the companies that have implemented it. one respondent, pointed out that through some system-calculated indicators, such as the out-of-stock index, his firm was able to achieve a reduction in supply and delivery. e) better resource management the erp system allowed better management of fixed assets, receivables, stocks, etc. for some of the respondents, this improvement depends, in fact, on the degree of use of system functions. one respondent reported that “the system has been able to improve inventory management by minimizing dead stocks, which are usually caused by poor management at the supply and production levels”. f) better production management according to the interviewees, the system has generated a “better management of production” by optimizing production capacity. the management of computer-assisted production “gpao” has led to an improvement in the planning and control of cost prices. this advantage is summarized in: “the production becomes a showcase, we can observe everything we want”. g) improved productivity the interviewed suppliers suggested that there may be a few firms that have achieved an improvement in the level of productivity. they found, in this sense, better quality of the work done by the users of the system. they found “a decrease in the number of errors and an increased speed in carrying out the work”. for some of them, it is the system in general and the self-checking procedures embedded in the processes, which have forced employees to be up-to-date in their work and which have “reduced seizure operations and forgetfulness”. 3) strategic benefits improving customer satisfaction and tracking customers and suppliers are the reported strategic benefits of erp systems. a) better customer satisfaction according to the interviewees, the system has improved the satisfaction of customers. respondents found better client management. for them the system has allowed a better response to customer needs. they note that the system has brought “a reduction in customer response times, a respect of delivery times, better management of rebates, discounts, customer returns and a better study of prices”. the software also contributed to better customer order tracking. for the respondents, the improvement in customer satisfaction is engineering, technology & applied science research vol. 8, no. 6, 2018,3631-3639 3635 www.etasr.com abdel-haq et al: investigating the success and the advantages of using erp system in ksa context essentially due to the different functionalities offered by the system and to the control of the information obtained as a result of its installation. indeed, it is the accessibility of reliable information in real time, which allowed “a better customer follow-up”. b) e-business according to the interviewees, not all companies in saudi arabia use the possibilities of the erp system to improve or establish possible electronic links between the company and its partners. if they have a website, its use is intended, generally, to present the company and its products. in this sense, respondents say that the majority of businesses have a website but virtually no link between the erp system and their websites. however, a link is considered necessary for real-time management of customer and supplier relationships. c) better tracking of customers and suppliers the system has made it possible to better “identify sales and purchasing trends, anticipate customer needs and make decisions regarding procurement, delivery and customer or supplier settlement”. for the interviewees, it is the information provided by the system that has made it possible to have better follow-up of the customers and better monitoring of suppliers (thanks in particular to a module dedicated to the management and monitoring of supplier performance). the system also provides alerts for both customers and suppliers and supports “better negotiation with customers and suppliers. 4) organizational benefits improving the use of skills, employee empowerment, communication and the development of a common language, are some of the benefits of erp systems. a) better use of skills according to respondents, the implementation of an erp system can benefit employees by enabling them to acquire certain management and organizational skills. interviewed companies report that the system has allowed users to improve their “control of tasks, behavior and organization in the work”. the erp system forced employees to be organized by imposing a very specific working method. the system allowed employees to have a better understanding of the interaction of management processes, to “practice management at the international level”, to “get away from routine tasks, to focus on the aspects trades, and move on to analytical tasks”. the system also promoted better use of certain management tools and techniques, such as dashboards, simulation techniques etc. and allowed employees to focus on their tasks. employees will rid of the seizure routine and will move more toward control and analysis operations. in this case, the system has been able to improve the use of the talents and experiences of the employees. this new orientation has, to summarize, “the emergence of hidden skills which some employees had the opportunity to show”. b) empowerment the implementation of an erp system can lead to greater autonomy for employees. the process editor module of the mfg/pro solution, for example, provides each user with the ability to view his schematic workflow on his screen. the user's range of action is thus clearly defined: with a simple click, he can consult and visualize the different tasks to be performed. users are also more autonomous regarding information: “they find all the information they need at their workstation”. c) improved communication respondents say that implementing an erp system can improve communication throughout the company. for them, the system has allowed a certain speed of communication: “the communication is automatic, the system creates a purchase requisition, sends the request for approval to the hierarchical superior, before it is transmitted, then to the general direction for downstream and the service supply for ordering”. this increased improvement in communication and information consolidation is largely due to the interoperability between applications. according to stakeholders, it seems that integration is the source of this improvement in communication. d) the development of a common language the implementation of an erp system standardized nomenclatures and documents. for the interviewees, an integrated system is synonymous with “the same for everyone”, “same order form, same good of exit, same invoice”. the employees speak the same language and share the same notions. respondents consider that the system has allowed the development of a common language, notably through the standardization of work methods, tasks, and business processes. 5) conclusion the exploratory analysis of the erp earnings data collected confirmed several operational, managerial, organizational and strategic benefits (table ii). however, the analysis of the interviews resulting from the control question brought out the control of information and the improvement of the use of skills as the two most important advantages provided by the erp system. these two benefits are mentioned by more than 50% of the respondents. they thus occupy the top two positions in the overall ranking of erp benefits, which are considered central by the respondents. several studies have highlighted the relationship between it adoption and organizational learning [18]. this work has shown that it and application knowledge applications are key factors that facilitate organizational learning. authors in [18] have shown that it supports employee communication, facilitates the flattening of the organizational structure and the empowerment of employees. exploratory analysis has brought out some aspects of this organizational learning. the analysis showed that the implementation of the system and its use can benefit employees by improving the use of certain skills. the concept: “better use of skills” is measured by two variables identified from the exploratory study: “mastering the work to be done” and the “use of certain tools and management techniques”. organizations typically adopt it to improve the quality of information generated by their existing system and to strengthen their control over internal operations [33]. the need for better information can be considered, thus, as being at the origin of the need for integration of data and systems [33]. engineering, technology & applied science research vol. 8, no. 6, 2018,3631-3639 3636 www.etasr.com abdel-haq et al: investigating the success and the advantages of using erp system in ksa context exploratory analysis revealed four indicators or measurement variables of the “information control” concept, namely: availability, security, reliability and access to information. table ii. erp benefits control of information improving the use of skills cost control the reduction of deadlines improved performance control improving the management of resources improvement of production improving productivity improving decision-making improving the use of skills empowerment improved communication the development of a common language improving customer satisfaction improved tracking of customers and suppliers b. determinants of success the project team is an important factor in the successful implementation of an erp system. 1) the quality of the project team analysis of the collected data makes it possible to recognize that the implementation team is composed in most cases of company executives, informant and manager (80% of respondents), erp provider staff (80%), consultant (70%), super user “key users” (50%), who have some control of the work processes of the company and rarely of newly recruited staff on the occasion of the project (30%). the composition of the team shows that there is a combination of both technical and business aspects, both necessary for this type of project. the choice of a balanced team is emphasized by the respondents to meet the technical and business requirements of the project. this project team is generally composed, as almost all respondents indicate, of members with at least a few years’ experience and good professional qualification. the majority of the team members have a university education. professional experience and qualifications are important attributes of project team members. most (80%) of the respondents pointed out that in the majority of cases, team members cannot be assigned to the project on a full-time basis. the time that can be spent by the company's staff assigned to the project team can reach 50% to 70% of their overall time as the assigned staff has responsibilities and obligations regarding day-to-day operations. the full-time assignment of project team members is a feature of the project team. the training of team members is highlighted as an important feature. respondents in all categories are unanimous on this point. training sessions are organized for the benefit of the members of the project team by the supplier's staff. finally, the respondents unanimously underline the importance of the presence of a project manager during erp implementation. for them, the implementation team usually has a project manager with technical and business skills. for the purposes of the project, it knowledge and knowledge of procedures, user and management expectations, and company management rules are necessary for the smooth running of the project. the project leader is qualified by the respondents as a leader without being authoritarian, with charismatic personality, good interlocutor, communicator, conflict manager, good decision-maker and someone who has a sense of consensus. the presence of a project manager in the team is a feature of great importance to the project team. a quality project team is, in short, a well-rounded, experienced team of qualified people who have been trained and who have a skillful project manager. 2) the mission of the project team interviewees unanimously stressed the importance of defining the mission of the project team. an interviewee pointed out that “the supplier usually has a management plan for setting up an erp system. this plan specifies the role of each stakeholder in the mission”. the definition of the mission is integrated at the contract level, in order to set the responsibilities and the right of each party. the mission of the project team is sometimes fixed or documented at the level of the specifications or the contract. 3) the presence of a champion or a sponsor respondents say there may be one or two people who can play a vital role in the project. these people have the role of reinforcing the commitment of staff to the project, anticipate conflicts, prevent financial overflows, facilitate the task of the erp provider, etc. for the respondents, this “champion” has several qualities: he is a good communicator, diplomat, arbitrator, he has the power to easily influence decisions and to intervene, if necessary, with the general management. with the exception of a few cases where the sponsor may be a key user or a member of the project team, the champion usually belongs to the senior management of the organization. the respondents consider a position at the higher hierarchical level as a necessary condition, so that the sponsor plays its full role. in this regard, the sponsor may be the head of the company, a senior executive close to the director, an is director, a management controller, a project manager, etc. 4) users of the erp system the analysis shows that training, user acceptance and user satisfaction are success factors for erp projects. no interviewee mentioned user participation as a key success factor. according to the respondents, the users do not have an essential role in the implantation, and they “have a role only after implantation in optimization or improvement of the use of the system”. their contributions are limited to providing the project team with the information needed for the “needs analysis and parameterization” tasks. in addition, the analysis showed unanimity of interviews on the importance of training users in this type of project. according to respondents, the participation of users in training sessions is necessary for the efficient operation of the software package. this training is generally provided by the staff of the company and more specifically by the project team and/or rarely by the staff of the integrator or the supplier, often performed on all functionalities and modules. moreover, the analysis showed that the users do not easily accept the erp system at the beginning of the project. only one vendor mentioned that user acceptance of the system is necessary for erp success. according to the respondents, “the users think only of their interests, they are not engineering, technology & applied science research vol. 8, no. 6, 2018,3631-3639 3637 www.etasr.com abdel-haq et al: investigating the success and the advantages of using erp system in ksa context convinced of the interest of the erp, since the old system is easier to use”. interviewees find that the difficulties and complexities of the system features make users afraid to use it. one respondent stated, that “users do not easily accept the erp system because of the phobia of the new”. however, the intervention of the general management makes that users begin to accept the system after some time: “users are starting to apologize and defend the system, almost after a few months”. in a similar way, the analysis initially revealed unanimity on the satisfaction of the users as being an important factor for the success of the erp implementation. according to the interviewees, the users are generally satisfied after some time of experimentation with the system and its effective exploitation: “users are only satisfied with the system after six months of operation”. this can be explained by their resistance manifested at the beginning of the project, and by the fact that the information provided by the system does not fully meet their needs. for the interviewees the satisfaction of the users comes, generally, in the ex-post phase of the erp implementation. nonetheless, respondents say that user satisfaction is not complete, since they continue to use manual entry techniques, prepare reports using excel spreadsheets, and maintain old ones. 5) communication analysis showed that users are not kept informed of the progress of the project in a formal way. communication is not considered a key factor in the success of erp projects. according to the respondents, the users “often bathe in vagueness and confusion”. if they are informed about the progress of the project, it is by means of some information flashes and informally. people who are most knowledgeable about the progress of the project often belong to the project team, the general management and the great users. for these stakeholders, regular kick-off meetings are the main source of information. the resulting decisions are formalized in the form of “signed minutes, internal notes, posters, e-mails”, often conveyed informally. 6) project management the exploitation of the collected data makes it possible to recognize that the rigorous management of the project is an important factor in the successful implementation of the erp systems. the definition of objectives and the precision of the fields of application of the project are recognized by the respondents as a key factor of success. according to the respondents, the objectives are defined in the initiation phase of the project. they appear formally “on the specifications or at the level of the call for tenders launched by the company”. the analysis recognizes that preparing a project plan/schedule is a key success factor. the project plan and schedule are designed, generally, in a systematic way. integrator and client collaborate for the overall project planning. together, they design a precise project implementation schedule and specify the objectives of each stage of the project. setting up an erp system requires the use of a project methodology. all interviewees are unanimous on this point. according to them, when the company does not develop a methodology by itself, the providers have and apply their own implementation approach and project management methodology. in coordination with the rest of the project team, integrators (rarely companies) sometimes use project management tools such as ms project. some erp solutions even have integrated project management tools, in this case the "oracle wizard" of the oracle solution. a project with small fields and restricted functionalities is more likely to succeed. none of the interviewed companies mentioned this element of response, whereas nearly 60% of the providers consider that this element is a key factor of potential success. according to respondents, businesses are “afraid to upset all their areas of activity”. they are much more supportive of a step-by-step strategy for implementing the erp system. in summary, rigorous management is a project management which involves the definition of the objectives, the precision of the field, the fixing of a plan, a calendar and the application of a project methodology. 7) control analysis showed that problem-solving (supervision and feedback) is one of the critical factors in successful erp implementation. according to the respondents, many problems can arise during the project: problems of resistance and noninvolvement of a part of the staff, high rotation rates, resignations of key people, unavailability of customer personnel, deadline non-compliances, absence of a procedures manual, slowness of the validation of decisions, etc. these problems are overcome by the “relational” and the intervention of the project manager and/or the general management. for the respondents, the difficulty of defining the needs during the preparation of the specifications and/or during the evaluation test that precedes the acquisition of the system (the providers execute the specifications provided by the company) is at the root of these problems. companies generally exercise tight control over the project's achievements. this interest is justified by: “companies pay for the acquisition and implementation of this system”, and “would like and expect results”. several ways are used for the supervision of the progress of the project, such as: reception pv, project dashboards, activity reports, echoes or feedback from users, etc. supervision is carried out by the project team, the project management team (firm and external consultant) and/or the general management. it is on the basis of the periodic accounts that the project manager and the management will intervene to find suitable solutions. 8) top management analysis showed the importance of the role of senior management in the success of erp projects. important, primordial, strategic, philosophical, stimulating, motivational are terms that often came up by the respondents to describe the role of the general management in the process of implementing an erp system. for the respondents, the management mobilizes the necessary resources (human, material, financial) and ensures the permanent monitoring of the progress of the project. it also intervenes in case of resistance to change or in case of conflict and/or blockage. 9) business process reengineering data mining recognizes that business process reengineering can be seen as a success factor for erp projects. it plays a engineering, technology & applied science research vol. 8, no. 6, 2018,3631-3639 3638 www.etasr.com abdel-haq et al: investigating the success and the advantages of using erp system in ksa context decisive role in obtaining the benefits projected by companies that have adopted an erp system. the analysis showed that the implementation of an erp is usually preceded by identification and modeling of the main business processes of the organization: “the diagnosis often requires the visualization of existing processes”. this visualization supports the implementation of the erp, by identifying the processes to keep, to reject and those to improve in order to increase the performance of the case. these processes can sometimes be modeled using software tools or a modeling tool incorporated into the erp system. the parties involved in this operation may be the project team (client and integrator), the process managers, the key users, or the consultant firms. analysis showed almost unanimity regarding the review of pre-planted business processes. according to the respondents, this reconfiguration aims to respond to the solution desired by the customer and improve the performance of business processes. generally, the “unorganized, unclear and problematic processes” would be reviewed. this operation is usually performed in parallel with the installation of the system, by calling on the services of the integrator or consultants. the analysis also revealed the revision of the content of the functions as a serious element in the success of the implementation of an erp. according to the respondents, the implementation is “an opportunity to review the content of the functions of the employees of the company”. it is considered as a consequence of implementation, which requires the deletion, modification and/or addition of certain tasks. 10) selection of the erp solution the data collected makes it possible to recognize that the selection of an erp solution (the selection of the appropriate software package and the supplier/company relationship) is considered as a key success factor for erp projects. according to the respondents, evaluating erp solutions on the market is a key step in the process of adopting erp innovation. the purpose of this step is to choose the software package that best suits the business processes of the company. in fact, erp solutions differ from one business sector to another and the solution that best fits the needs defined by each company should be chosen. for the purposes of this step, the companies proceed, initially, to the elaboration of specifications based on the analysis of the needs and the offers on the erp software market. “this step can take up to one year and a half”. the evaluation of the selected software packages (preliminary study) is carried out according to several criteria, such as the competence of the erp supplier team and the availability of human resources necessary for the smooth running of the project. finally, the selected software packages are the subject of a demonstration and a real test before the final decision of its acquisition. the purpose of this demonstration is to show mainly whether the erp model can correspond to the management model of the company or not. the careful choice of the appropriate software package can be retained as a useful element for the successful implementation of an erp system. another critical element is the supplier/company relationship. according to the respondents, the presence of a serious and confident relationship between the buyer and the erp supplier is important. companies require the erp provider, in particular, the human resources necessary for the smooth running of the project. they insist on the “competence and availability of the integrating team”. generally, ksa companies use the service of their erp suppliers to help them set up the acquired system. in this case, they are called upon to seek not only the software package that best suits their needs, but also to ensure also the choices of the supplier with the human resources necessary for the proper project completion. the interviewed companies realized, indeed, that quality of the service, know-how, experience and availability of the integrator's team, are necessary for the success of the project. 11) conclusion the exploratory analysis thus confirmed the results of other theoretical studies, highlighting the presence of several success factors relating to erp projects (table iii). the factors in table iii are mentioned by at least 50% of the respondents. they are in the top five ranks in the overall csf ranking, and considered essential by the respondents. the exploratory analysis also highlighted several features of the erp implementation team. all of these distinctive are grouped into two measurement variables distinct from the concept “quality of the project team”, “composition of the project team” and “project team capacity”. table iii. key factors of success the quality of the project team the mission of the project team the presence of a champion or a sponsor user training user acceptance rigorous management of the project control the commitment of the general management business process reengineering selection of the appropriate software package the erp/business provider relationship iv. conclusions this research study aims to provide elements for understanding the success of implementing erp systems in an emerging country context where smes constitute the bulk of the economic fabric. to answer this problem, a theoretical research framework was developed by exploiting theories and models that deal with the success of information systems. two main theories have been mobilized: strategic alignment [34] and diffusion of innovation [13]. various models inherent to it adoption and evaluation were also used [25, 35] to define the theoretical model of this research. this model aims to examine the effect of the relationship between the determinants of success and the characteristics of innovation as well as the integration of it applications on the success of erp adoption, applied to ksa companies, by analyzing the experience of five erp suppliers and five companies having installed such systems. the experience feedback presented in this work helped to consolidate the conceptual model adopted after the theoretical analysis (figure 2). the results of the exploratory study made it possible to specify, relativize and even eliminate a number of elements that were tested in ksa and tended to be considered as central or fundamental. engineering, technology & applied science research vol. 8, no. 6, 2018,3631-3639 3639 www.etasr.com abdel-haq et al: investigating the success and the advantages of using erp system in ksa context references [1] b. caldwell, stein, “beyond erp -new it agenda -a second wave of 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case study method in evaluation research”, evaluation practice, vol. 15, no. 3, pp. 283-290, 1994 [33] d. oliver c. romm, “justifying enterprise resource planning adoption”, journal of information technology, vol. 17, no. 4, pp. 199213, 2002 [34] j. henderson, n. venkatraman, “strategic alignment: leveraging information technology for transforming organizations”, ibm systems journal, vol. 32, pp. 4-16, 1993 [35] e. erturk, j. k. arora, “an exploratory study on the implementation and adoption of erp solutions for businesses”, available at: https://arxiv.org/ftp/arxiv/papers/1701/1701.08329.pdf, 2017 [36] u. jayawickrama, “knowledge prioritisation for erp implementation success: perspectives of clients and implementation partners in uk industries”, industrial management & data systems, vol. 117, no. 7, pp. 1521-1546, 2017 microsoft word 15-3508_s_etasr_v10_n3_pp5668-5673 engineering, technology & applied science research vol. 10, no. 3, 2020, 5668-5673 5668 www.etasr.com alqunun: strength pareto evolutionary algorithm for the dynamic economic emission dispatch … strength pareto evolutionary algorithm for the dynamic economic emission dispatch problem incorporating wind farms and energy storage systems khalid alqunun college of engineering university of hail hail, saudi arabia khalid.alqunun@gmail.com abstract—intermittent and stochastic characteristics of wind energy sources cause many challenges for the existing power networks. one of these challenges is the violation of the energy balance constraint due to the high penetration of wind power. the use of energy storage systems (esss) can facilitate the high penetration of wind power and mitigate the effect of its intermittency. within this context, ess incorporate the dynamic economic emission dispatch (deed) problem. the problem is formulated as a multi-objective problem and the strength pareto evolutionary algorithm (spea) is used for its resolution. simulations were carried out on a well-known ten-unit system and the results show the importance of using esss in reducing the total production cost of electricity and total emissions. keywords-dynamic dispatch; wind energy; energy storage systems; evolutionary algorithm i. introduction due to the energy shortage and the increasing pressure to protect the environment, wind energy is gaining attention. wind is considered a clean energy source and can mitigate the dependence on fossil fuels. however, the random characteristics of the wind speed result in volatility and uncertainty of the wind power output. consequently, high penetration of wind power may cause a negative impact on the system stability and lead to the violation of the energy balance constraint [1]. in fact, once the wind power penetration becomes more than 5% of the total energy production, the power quality will be influenced by the uncertainty of the wind power [2]. therefore, in wind-thermal systems, it is important to allocate perfectly the generation of all units including wind power in order to alleviate wind power curtailment. this problem is referred to as the power dispatch problem. several research works have handled the optimal dispatch for the windthermal systems. the resolutions of such problems have been based on quadratic programming, genetic algorithm (ga) [3], particle swarm optimization (pso) [4], simulated annealing [5], harmony search [6], firefly algorithm [7], chemical reaction optimization [8], etc. the uncertainty of the wind power output is handled with different manners, such as scenario method [9], forecast error method [10], stochastic programming [11], probability theory-based model [12], fuzzy logic [13], and chance constraint model [14]. for example, a chance constraint-based formulation for the dispatch problem was described in [15]. in [16], the intermittent nature of the wind power was described by evaluating its underestimation and overestimation costs and was then incorporated in the wind-based economic emission dispatch problem. the recent trend is directed towards the integration of esss into wind-thermal systems regarding the power dispatch problem. recent studies [17, 18] have demonstrated that esss can decrease operational cost, improve the power system’s reliability, and mitigate the impact of wind power fluctuations. battery energy storage sizing technique has been intensively discussed in [19]. the study explored the relationship between the size of centralized battery storage and operation cost of distributed generation in a microgrid using economic power dispatch. it explained how optimal capacity storage within a specified investment cost and predefined system constraints could provide a significant reduction in operation cost. the battery storage of the study has also created opportunities for the microgrid to trade energy in the electricity market during off-peak times, which increases the benefits of the dispatchable generating units. a technique based on back-propagation neural network and multi-objective pso was proposed in [17] for optimum sitting and sizing of esss in hybrid wind-diesel power networks. in [18], an ess was utilized in the deed problem when intermittency and uncertainty of the wind power is described by a chance constraint. authors in [20] used markov chain to simulate pv and wind power and then applied the pso algorithm to dispatch the thermal units and esss’ outputs. the deed problem aims to find the optimum schedule of power generation in order to minimize simultaneously total production cost and emission of harmful gases. the focus of this paper is to solve the deed problem incorporating wind farms and esss. the main contributions of this study are: corresponding author: khalid alqunun engineering, technology & applied science research vol. 10, no. 3, 2020, 5668-5673 5669 www.etasr.com alqunun: strength pareto evolutionary algorithm for the dynamic economic emission dispatch … • the problem is represented as a multi-objective problem and the spea is used to provide the best solutions. total fuel cost and total emission functions are minimized simultaneously. • to address the uncertainty of the wind power output, the energy balance is converted into a stochastic constraint. • the effectiveness of the proposed method is verified on a ten-unit system and through comparison with other published optimization techniques. the simulation results show that the incorporation of wind power and esss into the deed problem may decrease cost and emissions. ii. mathematical modeling of the problem a. modeling of the wind power for the dispatch problem the uncertainty of the wind power is modeled by a chance constraint and a probability distribution function (pdf) is used to describe the stochastic nature of the wind speed. the weibull pdf given in (1) is proposed to describe the wind speed distribution. the corresponding cumulative distribution function (cdf) is given in (2). ( ) 1 exp k k v k v v f v c c c −      = −           (1) ( ) ( ) 0 1 exp , 0 k v v v v f v f d v c τ τ    = = − − ≥      ∫ (2) where, v is the wind speed. parameters k and c are the shape and scale factors. these parameters depend on the geographical location of the wind source. several techniques such as least squares fit method and method of moments have been suggested to estimate the values of k and c [15]. the probability to have wind power equal to or less than w is given in (3) [18], where, in v , out v and r v are cut-in, cut-out, and rated wind speeds respectively. ( ) ( ) ( ) ( ) 0, 0 1 1 exp pr exp , 0 1, k r in in in r w k out r r w v v w v v w c f w w w v w w c w w <   −          +           − −      = ≤ =                      + − ≤ <         ≥ (3) b. objective functions and constraints the deed problem is formulated as an optimization problem, where the objective functions to be minimized are the total fuel cost ft and the total emission et. these functions are [21]: ( ) ( ){ } 2 , , , 1 1 sin h n it i i i h i i h i i i h h i f a b p c p d e p p = = = + + + −∑∑ (4) ( ) ( ) 2 , , , 1 1 exp h n t i i i h i i h i i i h h i e p p pα β γ η λ = = = + + +∑∑ (5) where ai, bi, ci, di, and ei are cost coefficients and αi , βi , γi , ηi , and λi are emission coefficients. the previous objective functions are optimized under the following constraints: 1) generation limits , , 1,...,ii hip p p i n≤ ≤ = (6) 0 h rw w≤ ≤ (7) 2) ramp rate limits , 1 , down i h i h ip p u− − ≤ (8) , , 1 up i h i h ip p u−− ≤ (9) where downiu and up iu are the prohibited operating zones of unit i. 3) constraints related to the ess the constraints of the ess are described below. equation (10) states the energy conversion. equations (11), (12) and correspond to the limits of charging and discharging powers of the ess and its storage capacity respectively. , , 1 , , , ,s h s h c sc h s h sd h s h sd te e p ch t p dcη η− ∆= + ∆ − (10) ,0 cap sc h scp k e≤ ≤ × (11) ,0 cap sd h sdp k e≤ ≤ × (12) ,0 cap s he e≤ ≤ (13) , , 0s h s hch dc× = (14) where [ ]0,1sck ∈ and [ ]0,1sdk ∈ . 4) energy balance constraint when wind power and esss are integrated into the deed problem, the energy balance constraint can be described by a chance constraint in order to take into account the wind power intermittency. this constraint can be written as: , , , , , , 1 n w d h h i h h sc h s h sd h s h i f p loss p w p ch p dc ζ =    + − − − + ≤     ∑ (15) where hloss is the total losses at hour h. it may be calculated using b-loss formula as given in (16): engineering, technology & applied science research vol. 10, no. 3, 2020, 5668-5673 5670 www.etasr.com alqunun: strength pareto evolutionary algorithm for the dynamic economic emission dispatch … , , , 1 1 1 n n n h i h ij j h oi i h oo i j i loss p b p b p b = = = = + +∑∑ ∑ (16) where bij, boi and boo are the loss-coefficient matrices. iii. proposed algorithm: spea approach spea [21] is an elitist multi-objective evolutionary algorithm. a brief description of the spea is given in this section. for more detailed explanation, the interested reader can be referred to [21]. the main steps of an iteration of spea are: • step 1: generate the initial population 0p with npop individuals, set the external archive 0p′ = ∅ and t=0. • step 2: extract the pareto solutions from tp referred as pareto(pt). • step 3: set ( )t t tp p pareto p′ ′= ∪ . • step 4: set ( )t tp pareto p′ ′= . • step 5: if ( )tsize p n′ ′> , reduce tp′ with the clustering method. • step 6: assign the strength pareto of each individual i from tp′ defined as given in (17), where in is the number of solutions from tp that are dominated by or are equal to the individual i. 1 i i pop n s n = + (17) • step 7: assign the fitness jf of each solution xj from the current population pt as given in the flowing equation: 1j i i j f s= +∑ ≺ (18) • step 8: combine the current population pt and the external archive tp′ . then, use selection, crossover, and mutation operations to generate the new population 1tp+ . • step 9: set t=t+1. • step 10: if maxt t< return to step 2. else the archived members are the pareto optimal solutions. iv. simulation results a. presentation of the ten-unit system in this section, the ten-unit system is used to prove the feasibility of the proposed optimization method for solving the deed problem. all cited operating constraints are considered. the b-loss matrix of the ten-unit system is given in (19). both cost and emissions are optimized individually and simultaneously according to the variation of the power demand ,d hp in mw over a time period of one day, subdivided into 24 time intervals of one hour. unit data are taken from [18]. wind source and ess parameters are as given in [18]. 0.49 0.14 0.15 0.15 0.16 0.17 0.17 0.18 0.19 0.20 0.14 0.45 0.16 0.16 0.17 0.15 0.15 0.16 0.18 0.18 0.15 0.16 0.39 0.10 0.12 0.12 0.14 0.14 0.16 0.16 0.15 0.16 0.10 0.40 0.14 0.10 0.11 0.12 0.14 0.15 0.16 0.17 0.12 0.14 0.35 0.11 0.13 0.13 0. 10 4 b = − 15 0.16 0.17 0.15 0.12 0.10 0.11 0.36 0.12 0.12 0.14 0.15 0.17 0.15 0.14 0.11 0.13 0.12 0.38 0.16 0.16 0.18 0.18 0.16 0.14 0.12 0.13 0.12 0.16 0.40 0.15 0.16 0.19 0.18 0.16 0.14 0.15 0.14 0.16 0.15 0.42 0.19 0.20 0.18 0.16 0.15 0.16 0.15 0.18 0.16 0.19 0.44                                 (19) b. implementation of the proposed method two cases for the ten-unit system are considered in this sub-section. case 1: only thermal units are considered and case 2: with wp and esss. figure 1 shows the convergence of total cost and emissions for case 1, by using the proposed algorithm and the non-dominated sorting genetic algorithm (nsga). convergence is obtained after 100 iterations. figure 2 shows the pareto solutions of the static eed problem where the power demand equals to 1700mw. from figures 1 and 2 it is clear that the proposed method provides better solutions when compared to the nsga. (a) 0 20 40 60 80 100 0.99 1 1.01 1.02 1.03 1.04 1.05 1.06 1.07 x 10 5 iterations c o st ( $ /h ) spea nsga (b) 0 20 40 60 80 100 1.1 1.15 1.2 1.25 1.3 1.35 1.4 x 10 4 iterations e m is si o n ( to n /h ) spea nsga fig. 1. convergence of the objective functions: (a) cost, (b) emissions optimum compromise solutions under these two cases are shown in tables ii and iii respectively. in this study, compromise solutions were obtained using fuzzy theory [23]. it is clear from these two tables that all constraints were taken into account. in addition, the total production cost and the total emission are decreased when the wind energy source and the engineering, technology & applied science research vol. 10, no. 3, 2020, 5668-5673 5671 www.etasr.com alqunun: strength pareto evolutionary algorithm for the dynamic economic emission dispatch … ess are incorporated in the problem. the total production cost and the total emissions are 2530173.68$ and 315022.47ton respectively for the first case and 2357551.22$ and 266882.90ton respectively for the second case. the effect of the use of wind source and ess is shown in figure 3. it is clear that minimum production cost and minimum emissions are clearly reduced when wind power and esss are used. fig. 2. pareto solutions for pd=1700mw table i. comparison with other techniques for case 1 method minimum cost minimum emissions spea 2474311.14 295120.82 nsgaii 2.5168x106 3.1740x105 ibfa 2481733.3 295833.0 it is clear from table i that spea outperforms nsgaii [24] and ibfa [25] for both minimum cost and minimum emissions. (a) 0 5 10 15 20 25 0.4 0.6 0.8 1 1.2 1.4 1.6 x 10 5 hours c o st ( $ ) wind-ess-thermal only thermal units (b) 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5 3 x 10 4 hours e m is si o n ( to n ) wind-ess-thermal only thermal units fig. 3. variation of minimum cost and emission over a single day table ii. best compromise solution for case 1 hour pd,h p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 1 1036 151.87 135.00 93.95 68.72 126.84 132.97 102.84 120.00 80.00 43.58 2 1110 150.81 135.00 80.55 118.72 170.82 144.07 116.73 90.00 71.01 54.74 3 1258 154.10 135.00 141.16 138.64 181.96 151.59 130.00 120.00 79.10 55.00 4 1406 159.01 215.00 174.99 122.99 231.96 160.00 130.00 113.47 80.00 55.00 5 1480 171.29 221.75 188.90 172.99 231.97 157.95 128.43 115.54 78.32 53.17 6 1628 217.44 223.49 262.22 192.82 243.00 160.00 123.34 120.00 80.00 55.00 7 1702 249.44 244.87 271.04 226.46 225.95 160.00 130.00 120.00 80.00 48.65 8 1776 229.28 265.74 281.88 276.46 243.00 159.17 128.73 118.25 79.37 53.30 9 1924 248.81 345.74 312.37 300.00 243.00 160.00 130.00 120.00 80.00 55.00 10 2022 303.44 404.20 340.00 300.00 237.47 153.90 130.00 116.79 75.22 41.20 11 2106 371.77 415.27 340.00 300.00 243.00 139.45 130.00 120.00 80.00 55.00 12 2150 344.53 470.00 340.00 300.00 243.00 160.00 130.00 120.00 80.00 55.00 13 2072 368.93 390.00 340.00 300.00 243.00 160.00 130.00 120.00 80.00 25.00 14 1924 298.98 312.96 299.65 300.00 242.05 159.68 128.90 117.93 80.00 55.00 15 1776 224.60 241.71 295.30 300.00 243.00 159.28 130.00 109.59 78.67 52.78 16 1554 161.81 161.71 265.52 250.00 238.72 160.00 130.00 120.00 55.00 55.00 17 1480 161.2867 165.25 190.72 242.21 242.21 160.00 128.15 120.00 55.00 54.83 18 1628 198.24 155.05 270.72 292.21 243.00 160.00 130.00 120.00 55.00 52.24 19 1776 272.35 235.05 283.41 299.61 235.61 160.00 130.00 116.50 53.27 49.63 20 1972 346.63 315.05 307.59 300.00 243.00 160.00 130.00 120.00 70.28 55.00 21 1924 305.13 308.83 327.88 300.00 230.08 159.72 109.96 119.88 78.89 55.00 22 1628 227.10 228.83 247.88 250.00 243.00 160.00 96.77 120.00 48.89 55.00 23 1332 153.70 148.83 171.15 200.00 193.00 119.83 126.77 120.00 78.89 51.95 24 1184 154.35 135.00 106.67 118.72 163.66 152.62 130.00 119.97 75.46 52.98 total cost ($) 2530173.68 total emission (ton) 315022.47 total losses (mw) 1302.82 engineering, technology & applied science research vol. 10, no. 3, 2020, 5668-5673 5672 www.etasr.com alqunun: strength pareto evolutionary algorithm for the dynamic economic emission dispatch … table iii. best compromise solution for case 2 hour pd,h p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 1 1036 150.00 135.00 73.00 146.30 128.40 71.58 20.00 47.00 80.00 55.00 2 1110 151.76 135.00 73.00 106.41 114.04 118.85 50.00 77.00 80.00 55.00 3 1258 150.00 135.00 153.00 151.77 127.58 151.19 74.11 102.39 50.00 54.29 4 1406 153.20 135.00 181.5 160.99 177.58 160.00 104.11 120.00 80.00 55.00 5 1480 150.00 165.28 170.80 158.21 225.60 136.77 126.35 119.39 78.24 53.41 6 1628 170.39 245.28 250.80 208.21 175.60 160.00 130.00 89.39 80.00 55.00 7 1702 231.92 165.28 284.85 224.68 205.50 160.00 130.00 119.39 60.97 42.45 8 1776 205.52 210.35 299.50 234.68 241.21 159.58 118.97 110.94 80.00 54.01 9 1924 248.74 290.35 278.77 284.68 243.00 160.00 130.00 120.00 80.00 34.62 10 2022 269.46 308.25 340.00 300.00 218.83 152.63 130.00 120.00 80.00 55.00 11 2106 327.73 388.25 340.00 253.67 239.77 156.49 130.00 114.17 71.40 50.83 12 2150 354.75 436.84 340.00 283.32 189.77 160.00 128.74 104.06 73.25 46.40 13 2072 428.66 356.84 313.83 233.32 239.77 146.08 113.72 115.90 45.15 37.55 14 1924 361.14 276.84 233.83 283.32 243.00 124.18 130.00 119.65 75.15 55.00 15 1776 283.53 220.45 154.90 260.62 242.65 159.91 129.79 119.25 79.76 54.80 16 1554 212.65 155.59 158.25 218.29 243.00 160.00 130.00 96.80 49.76 55.00 17 1480 150.00 185.98 172.47 168.29 243.00 133.65 117.49 120.00 55.00 55.00 18 1628 230.00 215.08 246.21 218.29 243.00 160.00 105.13 90.00 25.00 26.69 19 1776 206.54 295.08 294.86 168.29 243.00 144.32 130.00 120.00 55.00 55.00 20 1972 277.98 365.02 336.86 209.69 242.92 156.01 130.00 119.48 51.09 52.15 21 1924 239.14 314.48 301.78 225.77 239.65 155.98 129.80 120.00 79.85 53.83 22 1628 163.96 235.28 221.78 181.93 218.23 160.00 129.13 107.88 78.15 52.49 23 1332 150.00 155.28 144.70 131.93 178.00 126.78 130.00 120.00 80.00 27.41 24 1184 150.00 135.00 156.48 81.93 176.16 76.78 100.00 118.95 58.37 55.00 total cost ($) 2357551.22 total emission (ton) 266882.90 total wind energy (mwh) 1190.94 total ess energy (mwh) 185.05 total losses (mw) 1133.02 v. conclusion during the last decades, the high penetration of wind energy has created difficulties in energy dispatching due to the stochastic availability of wind power. thus it is required to handle these random characteristics of energy sources. in this study, a method based on the spea technique is proposed for solving the deed problem incorporating wind power. in order to avoid the overestimation penalty and underestimation costs, the wind power output is described by a chance constraint. moreover, esss are added to the power network to increase the penetration of the wind energy. the effectiveness of the proposed method is verified on a ten-unit system. simulation results show that the incorporation of ess into the deed problem can decrease clearly cost and emissions. acknowledgment the author would like to thank the deanship of the scientific research of university of hail, saudi arabia for funding and supporting this research under the project (ba1917). nomenclature ( )vf • probability density function (pdf) ( )vf • cumulative distribution function (cdf) v wind speed in m/s ζ threshold tolerance ft total fuel cost in $. et total emission in tons pi,h output power of unit i at hour h p i , pi lower and upper generation limits of unit i ν number of thermal units wh wind power output at hour h in mw es,h stored energy of the ess at hour h psc,h charging power at hour h in mw psd,h discharging power at hour h in mw ηc and ηsd ess charging and discharging 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monitoring system for transboundary foot and mouth disease (fmd) considering the demographic characteristics in gairo, tanzania ahmed kijazi school of computational and communication science and engineering (cocse), nelson mandela african institution of science and technology (nm-aist), arusha, tanzania and mathematics and ict department, college of business education (cbe), dar es salaam, tanzania ahmedk@nm-aist.ac.tz michael kisangiri school of computational and communication science and engineering (cocse) nelson mandela african institution of science and technology (nm-aist) arusha, tanzania kisangiri.michael@nm-aist.ac.tz shubi kaijage school of computational and communication science and engineering (cocse) nelson mandela african institution of science and technology (nm-aist) arusha, tanzania shubi.kaijage@nm-aist.ac.tz gabriel shirima school of life sciences and bio-engineering (lisbe) nelson mandela african institution of science and technology (nm-aist) arusha, tanzania gabriel.shirima@nm-aist.ac.tz abstract-foot and mouth disease (fmd) is present in many countries, including tanzania. gairo is among the districts that frequently face fmd. this study found that the current mechanism for communicating fmd in gairo district suffers from a long chain of information flow that causes delay and insufficient information for fmd control. therefore, this study aimed to explore the implementation of an information system named "monitoring system for transboundary foot and mouth disease," developed purposely to provide a standard platform for communicating fmd between livestock keepers and other stakeholders in the district. the system enables timely sharing of fmd events such as outbreaks, precaution measures, clinical signs, and negative impacts using short message services (sms), unstructured supplementary service data (ussd), and voice calls (robo-calls) through the mobile phones. also, livestock keepers may report fmd outbreaks direct to the system using feature phones. the statistical package for social sciences (spss) was used to analyze data and microsoft visio was used for drawing the system architecture and information flow diagram. finally, the system was implemented using php hypertext processor, jquery, html, json, javascript, mysql, and apache webserver. keywords-voice broadcasting; livestock keepers; fmd events; short message service (sms); robo-calls; unstructured supplementary service data (ussd); zero-grazing (smallholder dairy); agro-pastoralist; pastoralist i. introduction tanzania has the third largest livestock population in africa, with 25 million cattle approximately contributing 7.4% of the national gdp [1]. however, the annual animal production growth rate is low, at 2.2% because of low livestock reproductive rates and the high mortality due to increased disease prevalence [1]. regardless of other diseases, fmd has been given great attention because of its high mortality, especially in calves, its ability to cause a significant loss in milk production and draught animal power, and hinders international trade [2]. fmd is a transboundary disease caused by a virus from the picornaviridae family. the disease affects domestic and wild cloven-hooved animals such as sheep, goats, pigs and buffaloes [3]. there are currently 7 known serotypes of the fmd virus and many more subtypes. type a, o, sat1, sat2 and sat3 serotypes are present in tanzania [4]. fmd is transmitted from one animal to another through direct or indirect contact, e.g. by contact with contaminated inanimate objects (often referred to as fomites). the fmd clinical signs include high fever (up to 42 o ) accompanied by severe depression and inappetence [5]. other clinical signs are the appearance of wounds on the feet and tangle of the animal [5]. the fmd is currently present in asia and africa and in one country in south america [4]. in tanzania, gairo is among the districts that frequently face fmd. since the disease has no cure, immediate information sharing during the outbreaks is mandatory for mitigating the disease [6]. the big challenge in gairo district is the long chain of communication for fmd outbreaks. usually, the ward veterinary officers receive fmd outbreaks from immediate livestock keepers either by routine visits or phone calls. sometimes, the veterinary officers leave unreported cases corresponding author: ahmed kijazi engineering, technology & applied science research vol. 11, no. 4, 2021, 7302-7310 7303 www.etasr.com kijazi et al.: a monitoring system for transboundary foot and mouth disease (fmd) considering … due to the unfriendly terrain that hinders the access to remotely livestock-keeping communities, especially during rainy seasons. normally, the veterinary officer upon receiving the information, reports the incident to the district veterinary officer (dvo) either by phone or by a visit to the dvo’s office. the dvo forwards the information to the directorate of veterinary service (dvs) that has the mandate of uploading data to the global surveillance systems. sometimes, communication breakdown may happen if somebody is irresponsible along the reporting chain. similarly, whenever there is a threat of fmd, the veterinarians use to visit individual livestock keepers to alert them about the disease and precautions measures. therefore, the current reporting mechanism causes delay and insufficient information provision for the control of fmd in gairo district. also, the process of visiting livestock keepers for collecting or giving information is costly and requires the deployment of more veterinarians in order to be more effective. this study explores the implementation of an information system named monitoring system for transboundary foot and mouth disease, which might reduce the communication barriers among livestock stakeholders in the district taking into account the livestock keepers' demographic characteristics. the monitoring system for transboundary fmd is not the first system to monitor animal health. several electronic devices and software systems exist for similar purposes [7-12]. an excellent example of such devices is the cattle monitoring system that uses a wireless network, which monitors cows' body temperature and heartbeat to determine their general health [8]. another system is the cattle health and environment monitoring system that monitors the cattle's body temperature and heartbeat along with the farm's temperature and humidity [12]. the devices are normally attached to the cattle's body. the challenge of these devices is that they provide information only when the cattle have already been affected by the disease. therefore, they are inefficient in controlling fmd, which requires more preventive measures as it has no cure [6]. some countries use surveillance systems for communicating animal disease outbreaks, which replace the paper-based reporting mechanism [9]. however, these information systems depend on the input data from veterinarians, laboratories, and other healthcare providers that act as primary sources of information [4, 10]. the systems contradict other fmd surveillance studies that emphasize livestock keepers as the primary source of outbreak information for early disease detection. on the other hand, a few surveillance systems enable livestock keepers to report disease outbreaks directly to the system but failed to consider the education level and livestock keepers' demographic characteristics on the devices that are mandatory for accessing the system. as a result, livestock keepers access to the system is limited due to the lack of devices and skills. for example, most surveillance systems are web-based and emphasize on smartphones and computers to report disease outbreaks. at the same time, most livestock keepers, especially in developing countries, own feature phones that cannot browse the internet [11]. similarly, the systems communicate the disease outbreaks, precaution measures, clinical signs, and negative impacts through websites, while livestock keepers lack skills and devices for browsing the internet [9,13]. also, few systems are integrated with short message service (sms) alerts for disease outbreaks while many livestock keepers, especially in developing countries, have no formal education and cannot read sms though they own mobile phones[13]. the partial involvement of livestock keepers in fmd control, contributes to the factors affecting the information flow to the existing surveillance systems. therefore, the proposed monitoring system for transboundary fmd is a surveillance system that accommodates the current system deficiencies. the proposed system is similar to other web-based surveillance systems but enhances livestock keepers' interactions through their feature phones. the system allows the following interactions with livestock keepers using their feature phones: (1) it enables them to report fmd events directly to the surveillance system using ussd code and sms, (2) the system maintains fmd awareness to livestock keepers by periodically reminding them of fmd precaution measures, clinical signs, the negative impact, and transmission pathways using sms and voice messages (robo-calls). not only that, livestock keepers may access precaution measures, clinical signs, adverse effects, and transmission pathways of fmd at any time from the system through the ussd menu using their feature phones (figure 4). ii. materials and methods a. description of the study area gairo is a district in the morogoro region, tanzania. it is located between the 36'500e-37'200e latitude and 6'400s5'500s longitude. the reason for selecting gairo district as the study area was the fact that it combines three cattle farming systems (smallholder dairy, agropastoral, and pastoral), high incidences of fmd outbreaks, and accessibility. b. sample size for system requirement gathering demographic information was collected, including mobile phone usage and education level and the overall process of communicating fmd among livestock keepers and other livestock stakeholders was observed. from the 6 selected villages (kilama, chogoali, chakwale, kilimani, gairo town, and ibuti), 180 livestock keepers were interviewed (table i). the interviewees were the head of their families, regardless of gender. the number of households to be interviewed was selected by using the rule of thumb to determine the sample size of households which states that a minimum sample size of 25-30 households is appropriate for a village has 100 to 500 families [14]. to capture the farming systems, all 54 villages in the region were stratified into pastoral, agropastoral and smallholder dairy farmers. thereafter, the 3 groups were listed in the excel sheet, 2 villages were randomly selected from each group for data collection, and 30 households from each village were randomly chosen and interviewed [15]. lastly, a focus group discussion involving 15 veterinarians of 15 wards of gairo district was conducted, and the results were recorded. the focus group was purposely to gather information on the overall process of communicating fmd outbreaks in the district. after that, the statistical package for social sciences (spss) was used to analyze the data and draw the frequency distributions table. finally, the waterfall model was used for the development of the system [16]. the results indicate that there was a long chain of communication for fmd outbreaks in the district. also, the results indicate that 91% of livestock engineering, technology & applied science research vol. 11, no. 4, 2021, 7302-7310 7304 www.etasr.com kijazi et al.: a monitoring system for transboundary foot and mouth disease (fmd) considering … keepers own feature phones, and 9% own smartphones (table i). most livestock keepers used mobile phones to receive voice calls and send and receive smss (table i). about 60% of livestock keepers had primary school education while 33% had no formal education at all. therefore, the study suggests that sms, ussd code, and automatic broadcasting calls (robocalls) may be the best options for communicating fmd events among livestock farmers and other stakeholders in gairo district. technically, sms, ussd, and robo-calls are suitable for those who have primary school level education and above, whereas robo-calls alone will benefit those who have no former knowledge and can't read or write sms messages. however, all the mentioned technologies will satisfy most livestock keepers because the majority owns feature mobile phones. table i. livestock keepers' demographic characteristics variables frequency percentage (%) livestock keepers own mobile phones (n=170) no 27 16 yes 143 84 total 170 100 mobile phone usage (n=143) smartphone 13 9 feature phone 139 91 total 152 100 level of education (n=171) primary school 103 60 secondary school 10 6 university 1 1 no formal education 57 33 total 171 100 mobile phone usage (n=144) sending and receiving sms 114 39 making and receiving calls (including robo-calls) 141 48 surfing the internet 10 3 social networking 11 4 other 19 6 total 295 100 iii. system architecture and working principles the monitoring system for transboundary fmd comprises of several functional blocks that depend on each other to operate (figure 1). the blocks include the fmd awareness maintenance module, fmd incidents/outbreaks reporting module, databases (pdb1, tdb, pdb2), and ussd api. the fmd awareness module is responsible for maintaining fmd awareness to livestock keepers by periodically (with reference to operating system time) broadcasting precaution measures, clinical signs, negative impacts, and fmd transmission pathways in sms and audio format (voice calls) from the permanent database (pdb1). during the sms or audio broadcast, the system calls or sends sms to more than one mobile numbers at once. if a livestock keeper responds to a voice call, the system plays the audio file prior uploaded to the system. the broadcasting time interval for each awareness sms or audio file is specified when uploaded to the surveillance system through the specific menu (figure 7). also, livestock keepers may use the ussd menu (e.g. *150*009#) to access fmd awareness descriptions using mobile phones (figures 1, 2, and 4). the fmd awareness descriptions and the ussd menu were translated into english for readability in this paper. however, in the actual system, the information is in the native (kiswahili) language (figures 3, 4, and 7). on the other hand, the fmd incident/outbreak reporting module enables livestock keepers to report fmd outbreaks to the system using sms or ussd code. the livestock keeper may notify the fmd outbreaks to the system by sending sms indicating the number of fmd suspected cattle to a given mobile phone number. the alternative way is to use the ussd menu. for example, figure 3 shows the livestock keepers' procedure of reporting fmd outbreaks using option number 1 of the ussd menu. once received in the system, the suspected number of cattle is stored in a temporary database (tdb) and labeled as unverified information. the system differentiates the suspected herds from the apparently healthy herds using blue circles, as indicated on the system's disease spatial distribution map (figure 8). the veterinary officers validate the incident by calling and physically visiting the area. if the outbreak report is valid, the number of affected cattle is stored in the permanent database (pdb2) for future use after the veterinarian clicks the "accept cases" button to verify the fmd reported cases page (figures 1, 2, and 6). after that, the system broadcasts sms and voice calls to other livestock keepers, informing the incidents and suggesting precaution measures (figures 1-2). again, the system differentiates the confirmed fmd herds from the apparently healthly herds using red and orange circles on the system's disease spatial distribution map (figure 8). note that, livestock keepers should first be registered to the system to receive or send information. the ussd application user interface (ussd api) connects the fmd incident/outbreak reporting module with the ussd server (figure 1). before implementing the ussd api, one should purchase the ussd service from the provider and configure the callback url after registering and logging in to the ussd server account [17]. the fmd awareness maintenance module, fmd incident/outbreak reporting module, and the ussd api were implemented using php, jquery, html, json, javascript, and mysql, in an apache webserver. the monitoring system for transboundary fmd is also composed of other third-party software and hardware such as voice gateway, sms gateway, voice modems, and sms models that support its operations. voice gateway provides automatic voice call services to the system through the voice modem pool (figure 1) [18, 19]. it acts as a communication interface between the fmd monitoring system and the voice modem pool attached to the server's usb port. the sms gateway provides sms services to the system [20]. the sms modem pool is connected to the sms gateway software for routing sms to the mobile network (figure 1). the sms gateway act as a communication interface between the fmd monitoring system and the sms modem pool attached to the server's usb port. iv. system security procedures for developing a secure web-based information system, such as using parameterized queries when implementing the system login script to avoid sql injection attacks, etc. had been followed during the implementation phase [21]. the livestock keepers should first be registered in engineering, technology & applied science research vol. 11, no. 4, 2021, 7302-7310 7305 www.etasr.com kijazi et al.: a monitoring system for transboundary foot and mouth disease (fmd) considering … the system in order to receive or send information to it. other stakeholders, including veterinarians, have the privilege to register livestock keepers in the system. apart from livestock keepers, different stakeholders may access the system by using their username and password on the login page (figure 8) [22, 23]. the system administrator registers stakeholders by asigning the username and a temporal password that must be changed the first time the user logins into the system. strong password policy [24] has been followed while developing the change password section. only registered stakeholders are allowed to access different parts of the system based on privileges assigned by the system administrator during registration. the server machine was hosted in a room with biometric access for authorized personnel only. voice modem pool (via usb port) sms modem pool (via usb port) network interface card tdb pdb2 fmd incidents/ outbreaks reporting module sms gateway ussd api fmd awareness maintenance module pdb1 voice gateway mobile network on cloud ussd server notations hardware awareness or responses sent to the livestock keepers software livestock keeper reporting fmd incident/outbreak (unverified information) pdb – permanent database tdb temporarily database livestock keepers with feature phone fmd awareness stored in pdb1 internet other stakeholders with computers/smart phone internet verifying fmd outbreaks and uploading fmd awareness descriptions to the system fig. 1. block diagram of the system architecture. v. results figures 3 and 4 are the ussd menu shown on the livestock keeper’s mobile phone after dialling a specific ussd code. the ussd menu allows livestock keepers to report fmd outbreaks or access different fmd awareness descriptions such as transmission pathways, precaution measures, clinical signs, and negative impacts from the server. figure 3 shows a livestock keeper reporting 67 fmd suspected cattle to the system after choosing option number 1 of the ussd menu. upon completing the request, the system stores the 67 cattle to the system for verification purposes (figure 6). veterinarians may use this information to verify the fmd outbreak validity by calling and physically visiting the livestock keeper. later on, veterinarians may either update the number of suspected animals to reflect the actual number of victims or discard the information as invalid (figure 6). figure 4 shows the sms feedback after the livestock keeper requested fmd transmission pathways from the system by selecting option number 2 of the ussd menu. the descriptions were uploaded to the server by other livestock stakeholders, including but not limited to veterinarians, researchers, and research institutions (figure 7). engineering, technology & applied science research vol. 11, no. 4, 2021, 7302-7310 7306 www.etasr.com kijazi et al.: a monitoring system for transboundary foot and mouth disease (fmd) considering … choose reporting method accessing ussd server api querying reported info usb modem receiving sms sms gateway temporary database open ussd menu/sms panel is information valid? permanent database2 discard the information and inform the reporter querying livestock keepers mobile no. from db inform all livestock keepers about the incident/outbreak choose reporting method voice gateway pre-recorded audio file ussdsms no yes usb modem attached to the system sms gateway sms/ automatic phone call sms feature phone livestock keepers incident/outbreak reporting awareness maintenance feature phone livestock keepers permanent database1 choose fmd scenario repeat after every 30 seconds query a particular fmd awareness if(ost-lastbrt<brti) voice yes no f e e d b ac k reporting the fmd incident/outbreak verifying information veterinarian/ laboratories etc verifying fdm outbreaks and uploading fdm awareness descriptions to the system notations ost current operating system time lastbrt last fmd awareness broadcast time brti broadcast time of each fmd awareness r ep e a ti ng t h e p ro ce s s fig. 2. data flow in the system. fig. 3. reporting fmd outbreak using ussd menu. engineering, technology & applied science research vol. 11, no. 4, 2021, 7302-7310 7307 www.etasr.com kijazi et al.: a monitoring system for transboundary foot and mouth disease (fmd) considering … the system accepts name, gender, mobile phone number, cattle shed location (latitude and longitude), age, etc. (figure 5). the system allows access only to registered livestock keepers. the mobile number enables the livestock keeper to communicate with the surveillance system using ussd, voice calls, and sms. also, veterinarians may use the number for management purposes, including calling livestock keepers at any time or after the report of an fmd outbreak for verification. veterinarians may also verify the fmd reported outbreaks to the system after physically visiting the livestock keeper and observing the actual number of cattle suffering from fmd (figure 6). the login page is also the systems’ home page with cattle shed and kraal spatial distribution map generated by the google maps (figure 8). the map indicates the cattle sheds and kraals as circles generated by the system after registering the livestock keeper’s particulars in the system for the first time in line with cattle’s shed and kraal (herbs) location details (latitude and longitude) (figure 5). different colors are used to indicate herds fmd status. for example, the herd appears green when no fmd case is reported by the livestock keeper (an apparently healthly herd). it appears blue when the livestock keeper reports an unverified (unconfirmed) fmd case, red when the reported fmd case is confirmed, and orange when unconfirmed and confirmed cases co-exist in the same herd. otherwise, the status remains green (figure 8). fig. 4. accessing fmd transmission pathways using the ussd menu. fig. 5. livestock keeper’s registration form. engineering, technology & applied science research vol. 11, no. 4, 2021, 7302-7310 7308 www.etasr.com kijazi et al.: a monitoring system for transboundary foot and mouth disease (fmd) considering … fig. 6. verifying fmd reported cases. fig. 7. uploading fmd awareness description to the system. vi. discussion apart from the proposed monitoring system for transboundary fmd, there are many other existing web-based, mobile-based, and integrated (mobile and web-based) systems developed for similar purposes [7, 9, 11, 25-27]. they offer limited access to the local communities, who are the main stakeholders in animal disease reporting since a disease always starts from their cattle [26]. in the case of existing web-based surveillance systems, only the top-level stakeholders such as laboratories, researchers, and international agencies can upload or access disease information to the system because they have the necessary skills and devices [10, 11]. unfortunately, most livestock keepers, especially in developing countries, were excluded from the use of these systems due to the lack of skills and tools to access them (table i). there are also existing mobile-based animal and human health surveillance systems such as the ema-i and afyadata, which collect nearly realtime surveillance data in the local communities’ context [25, 27], but still, they deny livestock keepers the ability to communicate the surveillance data to the respective authorities directly. instead, the organizations utilize veterinarians and community health reporters (chrs) in the livestock-keeping communities to collect the surveillance data for them on behalf of livestock keepers with the use of smartphones. this engineering, technology & applied science research vol. 11, no. 4, 2021, 7302-7310 7309 www.etasr.com kijazi et al.: a monitoring system for transboundary foot and mouth disease (fmd) considering … mechanism of collecting data leaves many unreported cases, especially in the hard-to-reach livestock-keeping communities [26] and requires more veterinarians and chrs in the field in order to be effective and well facilitated. the presented monitoring system for transboundary fmd is designed to cover the existing surveillance systems' deficiencies. the extra integrated ussd and automatic voice call (robo-calls) features in the monitoring system for transboundary fmd provide two-way communication to the server to the local communities that lack internet access. as a result, livestock keepers can access and receive information directly from the server using any mobile phone (feature or smartphone). these features differentiate this system from the rest. the system continuously maintains awareness to livestock keepers by reminding them disease precaution measures, clinical signs, negative impacts, and transmission pathways in sms and robo-calls. also, livestock keepers can access this and any other uploaded information to the server using a ussd menu instead of web browsers. different stakeholders may also access similar information using web-browsers, smartphones, or pcs with internet access like in the other surveillance systems [7, 9, 11, 25-27]. similarly, the system enables livestock keepers to report disease outbreaks through the ussd menu. fig. 8. system login page with cattle’s shed and kraal spatial distribution map. the current study believes that the total involvement of livestock keepers in animal disease surveillance will enhance early disease outbreak detection, reporting, and will provide real-time quality data for fast response to disease epidemics allowing more efficient disease control. also, periodically receiving various fmd events in sms or voice calls increases the fmd awareness of the livestock keepers. policymakers may also use the fmd secondary data in the system for decision-making like in other surveillance systems (figure 8). this study found that 91% of livestock keepers in the gairo district own feature phones (table i), which is comparable with the data from [26]. it was also found that the majority of livestock keepers use mobile phones for calling (48%) and sending sms (39%). the sufficient number of livestock keepers owning feature mobile phones and their calling and sending sms preferences motivated the use of ussd and robocalls services in the proposed monitoring system for transboundary fmd. lastly, the system generates a spatial distribution map of fmd suspected and affected cattle sheds or kraals generated on the home page to determine the disease distribution behavior for a specific period (figure 8), unlike other surveillance systems that generate spatial distribution in regional and country-wise levels. vii. conclusion the proposed monitoring system for transboundary fmd provides a common platform for communicating fmd data among livestock keepers and transmit information across the ladder. adopting the surveillance system will enable fmd awareness maintenance to livestock keeper’s communities, timely sharing of fmd outbreaks, and prompt preparedness and responding to the district's disease epidemics. the system can even be adopted in other endemic livestock diseases. references [1] 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[27] event mobile application (ema-i). rome, italy: fao. microsoft word etasr_v11_n3_pp7257-7261 engineering, technology & applied science research vol. 11, no. 3, 2021, 7257-7261 7257 www.etasr.com raza et al.: harnessing electrical power from hybrid biomass-solid waste energy resources for … harnessing electrical power from hybrid biomasssolid waste energy resources for microgrids in underdeveloped and developing countries abstract-this paper presents an energy plan for harnessing electrical power from hybrid energy resources, including biomass and solid waste, through hybrid technologies for microgrid development to overcome the current energy crisis and provide future sustainable electricity pathways for a developing country. biomass and solid waste were collected from different dumping sites in pakistan and were tested for their calorific value, which was found to be 6519kcal/kg. the total power was calculated based on this calorific value and it was found that there is a potential of total 11,989.5gw of power generation. thus, hybrid energy resources are suitable for harnessing electrical energy through hybrid technologies. different hybrid systems were examined for these resources and the gasification technique is finally proposed as the most suitable method for producing energy from biomass and solid waste resources in pakistan. this technique is also found to be economically feasible for processing all kinds of waste. keywords-biomass; solid waste; electrical power; sustainable development; developing countries; underdeveloped countries i. introduction a developing country may face an exponential growth of population and industrialization, which is resulting in huge requirements of energy. this further leads to the exploitation of fossil fuels, such as domestic coal, natural gas, and oil which are not renewable. the use of fossil fuels poses a threat to the environment and public health in terms of harmful greenhouse gases (ghg) and huge production of waste [1]. the generated municipal solid waste (msw) will globally reach 2200 million tons annually by 2025 which would increase to 2600 million tons by 2030 [2, 3]. sewage sludge produced from industrial and household wastewater treatment produces thousands of tons of solid waste daily [4]. proper treatment of biomass and solid waste is an alternative option for power generation which reduces ecological and social issues [5]. facilitating biomass and solid waste renewable resources for power generation instead of fossil fuels provides better technoeconomic opportunities for pakistan [5]. if biomass and solid waste resources are exploited, the ratio of renewable power generation would be increased from 2% to 27% and would cater for the 56% of local energy needs [6]. the major advantage of biomass and solid waste is that they can be available at any location in contradiction with fossil fuels[6]. there are many biomass and solid waste resources including human waste, msw, food waste, firewood, shrubbery waste, fabrics, paper products, latex, and plastics [7]. the quantity and composition of biomass and solid waste vary greatly depending upon the region and human living standards [7]. there are four major sectors involved in the production of biomass and solid waste in pakistan: agriculture, domestic, industrial, and commercial. easy accessibility to biomass and solid waste resources provides a sustainable option for harnessing electrical power while resolving the issue of inappropriate dumping of biomass and solid waste. biomass and solid waste are considered as the most feasible option for biofuel production and biochemical energy generation [8]. biomass and solid waste are converted into biofuel through thermochemical conversion processes including combustion, gasification, incineration, and pyrolysis [9]. gasification is a suitable option for managing large quantities of biomass and solid waste in pakistan because it produces multiple outputs including heat for commercial purposes, energy for residential purposes, and bio-oils for the chemical industries while it utilizes all types of biomass and solid waste products [10]. the muhammad amir raza department of electrical engineering ned university of engineering and technology karachi, pakistan amir.eed.neduet@gmail.com krishan lal khatri department of electrical engineering ned university of engineering and technology karachi, pakistan engrkrishan@yahoo.com khalid rafique azad jammu and kashmir information technology board muzaffarabad, pakistan khalidrafiquepk@gmail.com abdul sattar saand electrical engineering department quaid-e-awam university of engineering, science and technology, nawabshah, pakistan as-saand@quest.edu.pk corresponding author: muhammad amir raza engineering, technology & applied science research vol. 11, no. 3, 2021, 7257-7261 7258 www.etasr.com raza et al.: harnessing electrical power from hybrid biomass-solid waste energy resources for … incineration techniques, amongst all considered techniques, are responsible for large environmental pollution [10]. economic activities in the developing countries lead to augmented generation of biomass and solid waste. these sources could be used for the generation of electrical energy, bio-oil, and biofuel [11]. the usage of biomass and solid waste is valuable because these sources are available in huge quantities [11]. the type of material and the quantity of generated waste are different in each region as shown in table i. pakistan generates over 64,000tons/day of biomass and solid waste. this material is useful for power generation because it has good calorific value (6.9j/kg) [12]. in the main municipalities, the total production capacity of solid waste is around 712 million tons/year [12]. however, in india, the intermediate and massive populated cities generate a large quantity of waste which is increasing at a rate of 6% every year [13]. the production of biomass at a global level is also high [13]. table i. production capacity of biomass and solid waste in various countries ref country material type production capacity [12] pakistan biomass 46886 million tons/year solid waste 8536 million tons/year [13] india biomass 180 million tons/year solid waste 600 million tons/year [14] europe biomass 205 million tons/year [15] china biomass 850 million tons/year [16] brazil biomass 597 million tons/year the utilization of biomass and solid waste for power generation in pakistan is the focus of this study. however, to overcome the environmental pollution and available energy issue in the country, the research is on the way for converting unused sources into useful sources by using hybrid technologies for the generation of energy and heat. the main aim of the current research is to develop an energy plan for the energy sector of pakistan in order to overcome the energy crisis and identify a future path of electricity supply for sustainable development. this research identifies the quantity and quality of solid waste and biomass resources and it justifies the suitability of harnessing electrical power from them. an experiment was performed in the lab for the final testing of waste pallets and the waste calorific value was identified in order to calculate its total power capacity. furthermore, hybrid technologies were examined and the most suitable technology for hybrid resources was selected. ii. materials and methods a. study area pakistan is located in the north western part of south asia and covers an area of 881,913km 2 with an overall population of 207 million with a growth rate of 2.4% [17]. its neighboring countries are china from the northeastern side, india from the eastern side, iran, and afghanistan from the western side and the arabian sea from the southern side. the growth rate of the gross domestic product (gdp) in pakistan is 5.8% [18] whereas the per capita income is $1641 [18]. if the growth rate of the population continues to increase at a pace of 2.4% then by 2050 the country will become the 4 th largest in the world [18]. the power consumption per capita is around 500kwh which is quite low compared with the global per-capita of power consumption which is around 2603kwh [19]. b. compostion of biomass and solid waste table ii shows the chemical composition criteria of biomass resources through ultimate and proximate analysis on the physicochemical characteristics [20]. these characteristics would help to identify the selectivity and suitability of biomass resources for power generation. the chemical composition of solid waste is quite different from the biomass in the sense that the quality and capacity of solid waste is affected by various factors including the living standards, weather conditions, surrounding region, and financial status. solid waste normally comprises of organic waste, inorganic waste, hazardous waste, paper waste, plastic waste, and textile waste. the waste composition type and percentage is shown in figure 1 [21]. the physicochemical characteristics of solid waste are obtained from ultimate and proximate analysis tests. the ultimate analysis test is used to find the proportion of oxygen, nitrogen, sulphur, carbon, and hydrogen in the total solid waste whereas the proximate analysis test is used to find the fixed carbon, ash, moistness, and volatile matter. the physiochemical characteristics of solid waste are shown in figure 2 [21]. fig. 1. composition type of solid waste in pakistan. c. experimental study of biomass and solid waste samples an experimental setup is designed based on the quartering method as shown in figure 3. initially, 25kg of biomass and 25kg of solid waste were collected from different regions of pakistan. then, manual mixing and cutting were performed and all the waste was gathered at a single place. further, this total waste was divided into 8 sections namely i, ii, iii, iv, v, vi, vii, and viii. these sections were separated into even (ii, iv, vi, and viii) and odd sections (i, iii, v, and vii). even sections were mixed and again separated into two sections namely m and n. similarly, odd section were mixed and separated into two sections namely o and p. then these four sections (m, n, o and p) were mixed diagonally like m & p and n & o and separated into two sections like m & p into y and n & o into z. finally, y and z were mixed for the final sample of analysis. the manual mixing and cutting were performed many times until the weight became 15kg. engineering, technology & applied science research vol. 11, no. 3, 2021, 7257-7261 7259 www.etasr.com raza et al.: harnessing electrical power from hybrid biomass-solid waste energy resources for … table ii. biomass chemical composition [22, 23] sulphur carbon oxygen hydrogen fixed carbon ash volatile matter moisture rice husk 0.02 35.6 59.7 4.5 14.6 26.2 59.2 8.8 straw 0.21 39 35.46 5.73 17.5 10.1 64.43 8.32 bamboo 0.09 50.52 42.80 6.04 16.05 1.95 83.95 6.14 wheat straw 47.9 45.2 6.1 16.5 6.9 76.5 0.1 sugarcane bagasse 0.09 46.6 43.3 5.92 8.30 3.90 82.5 5.25 pine sawdust 0.36 49.79 44.12 6.36 13.91 1.29 82.03 2.77 oat 42.3 40.9 6.3 1.5 7.1 kenaf 0.05 46.71 54.32 6.71 17.18 5.45 73.64 3.73 fig. 2. composition content of solid waste in pakistan. fig. 3. quartering diagram method for waste sampling. d. determination of heating or calorific value the calorific value is highly dependent on the amount of heat produced during the combustion process. the calorific value of the final sample of waste pellets was determined in the laboratory using the gallen kamp ballistic bomb (gkbb) calorimeter. the net calorific value is determined as 6519kcal/kg. however, from other research data, the calorific value ranges from 9mj/kg to 44mj/kg respectively [24]. equations (1) and (2) were used for finding the higher and lower values of calorific of mixed biomass and solid waste pallets [25]. higher calorific value � ∑�� ��.��� �� (1) lower calorific value � ∑�� ��.��� �� (2) where (c.v)l is the lower calorific value in kcal/kg, (c.v)h is the higher calorific value in kcal/kg, qp is the quantity of the specific material in the total waste pallets in kg, and tp is the total waste pallets in kg. e. theoretical power potential of biomass and solid waste the power potential of mixed biomass and solid waste pallets can be calculated by: ep � �c.v�l ! aw ! 1.16 (3) where ep is the energy potential in kwh and aw is the aggregate waste in kg. iii. results and discussion a. net power calculations net power of biomass and solid waste pallets were calculated as follows: the heat of combustion (hoc) was calculated using the total quantity of waste pallets (qwp) and calorific value (cv): hoc � qwp ! cv (4) hoc � 55,422,000,000 ton ! 6,519,000 kcal/ton hoc � 3.61296018 x 1067 kcal the heat output (ho), considering efficiency of 25% [25], was: ho � overall efficiency ! hoc (5) ho � 0.25 ! 3.61296018 x 1067 ho � 9.03240045 x 1069 kcal with 1kwh equal to 860kcal the units generated/annum (uga) are: uga � ho/860 (6) uga � 9.03240045 x 1069/860kcal uga � 105,027,912,209,302.3kwh uga � 105,027,912,209.3023mwh the average load on the system (als) is: als � uga/total hours in a year (7) als � 105,027,912,209.3023mwh /8760h als � 11,989,487.69512584mw this mathematical framework calculated the total power production capacity from the hybrid energy resources based on authentic and realistic data. the available capacity and quality of waste pallets can generate a power of 11,989.5gw. this power capacity can drive the economy of the country at a great extent but there is a need to develop a proper energy harnessing system with sufficient financing and resources. engineering, technology & applied science research vol. 11, no. 3, 2021, 7257-7261 7260 www.etasr.com raza et al.: harnessing electrical power from hybrid biomass-solid waste energy resources for … table iii. technology selection parameters for power generation parameters pyrolysis plasma gasification incineration feedstock solid waste solid waste biomass and solid waste biomass and solid waste variable composition did not accept variable waste did not accept variable waste accept heterogeneous waste of all types little difficult to proceed variable waste product oil, syngas and energy syngas and energy syngas and energy heat and energy operating cost 150$ per tone 120$ per tone 60$ per tone 60$ per tone annual capital cost 1500$ per tone 1300$ per tone 850$ per tone 775$ per tone disposal ash 0.3 tone per feedstock tone bottom ash around 10% less than 1% bottom ash around 5% bottom ash energy production capability 800 kwh per tone 600kwh per tone 800kwh per tone 850 kwh per tone efficiency less than 18% less than 10% 18% to 30% 18% to 25% fig. 4. hybrid energy storage systems for renewable source integration in the microgrid energy management system. b. power generation technology for hybrid resources the gasification technique for power generation is more suitable than the other techniques mentioned in table iii [2629]. the gasification technique accepts all types of waste (biomass and solid waste) for power generation with greater power production efficiency and has the capability of producing less ash. gasification with its hybrid system opens the door for new development in the country because hybrid technologies based on other resources, including wind, solar, and nuclear, coupled with biomass and solid waste resources can provide more energy benefits to the community. c. integration of hybrid biomass-solid waste energy resources in a microgrid most renewable sources are used in microgrids with lower power levels (around 200kw) and are connected with the main bus through power converters [28-31]. these systems are installed near the commercial and industrial sites for meeting the power demand. these systems produce low noise and emissions which ultimately provide reliable power on low cost. the selection of a suitable renewable source is a complex process. this research paper has described a step-wise feasibility study of hybrid biomass and solid waste resource for microgrid development. figure 4 shows the hybrid energy storage systems for hybrid renewable source (biomass/solid waste) integration in the energy management system of a microgrid. the integration of a hybrid energy storage system, distributed energy resources, and distributed loads with a renewable energy ecosystem is called microgrid. a microgrid helps to setup the smart and active electrical grid with the potential to increase the efficiency, reliability, and safety of the system. iv. conclusion this study aims to alleviate the current energy crisis and suggests future electricity pathways to drive the economy of a developing country such as pakistan. an experiment was performed in the lab in order to identify the suitability for power generation of waste pallets collected from different sites of pakistan. the results of this study were examined quantitatively to justify the feasibility of the energy plan. the projected power generation is 11,989.5gw which is sufficient to alleviate the ongoing energy crisis and facilitate the future industrial development in the country. pakistan therefore needs to develop a new policy that is economically feasible and environmentally friendly for longer tenure. hybrid energy resources provide a suitable option through hybrid technologies for microgrid development. engineering, technology & applied science research vol. 11, no. 3, 2021, 7257-7261 7261 www.etasr.com raza et al.: harnessing electrical power from hybrid biomass-solid waste energy resources for … references [1] s. hansen, a. mirkouei, and l. a. diaz, "a comprehensive state-oftechnology review for upgrading bio-oil to renewable or blended hydrocarbon fuels," renewable and sustainable energy reviews, vol. 118, feb. 2020, art. no. 109548, https://doi.org/10.1016/j.rser.2019. 109548. 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[31] bayati, n. bayati, h. r. baghaee, a. hajizadeh, and m. soltani, "localized protection of radial dc microgrids with high penetration of constant power loads," ieee systems journal, pp. 1–12, 2020, https://doi.org/10.1109/jsyst.2020.2998059. engineering, technology & applied science research vol. 7, no. 2, 2017, 1436-1443 1436 www.etasr.com bassi and mobarak: state-space modeling and performance analysis of variable-speed wind turbine… state-space modeling and performance analysis of variable-speed wind turbine based on a model predictive control approach hussain bassi electrical engineering department faculty of engineering king abdulaziz university rabigh, saudi arabia hmbassi@kau.edu.sa youssef mobarak electrical engineering department, faculty of engineering king abdulaziz university, rabigh, saudi arabia & electrical engineering department, faculty of energy engineering, aswan university, egypt ysoliman@kau.edu.sa abstract—advancements in wind energy technologies have led wind turbines from fixed speed to variable speed operation. this paper introduces an innovative version of a variable-speed wind turbine based on a model predictive control (mpc) approach. the proposed approach provides maximum power point tracking (mppt), whose main objective is to capture the maximum wind energy in spite of the variable nature of the wind’s speed. the proposed mpc approach also reduces the constraints of the two main functional parts of the wind turbine: the full load and partial load segments. the pitch angle for full load and the rotating force for the partial load have been fixed concurrently in order to balance power generation as well as to reduce the operations of the pitch angle. a mathematical analysis of the proposed system using state-space approach is introduced. the simulation results using matlab/simulink show that the performance of the wind turbine with the mpc approach is improved compared to the traditional pid controller in both low and high wind speeds. keywords-blades; maximum power point trackers; modeling; predictive control; turbines i. introduction wind energy has known wide research interest over the past years [1-4]. research focuses on various aspects such as reliability [5], system stability, security, low-voltage ridethrough faults, energy profile, current movement, the short circuit flows and responsive power ability [6]. variable-speed wind turbines play a key role in energy harvesting. they enhance energy production and reduce drive train rotations as well as fluctuations in power production [7-9]. design and implementation of the regulation method for wind energy conversion systems (wecs) is a complex process. complexity results from the multi-input multi-output (mimo) systems which consist of robustly attached variables. the nonlinear nature of the input power and the natural hindrances of the system differences also cause difficulties to the regulation design [10-12]. there are several control techniques that have been used to maximize wind turbine efficiency. in the industry, most of the commercial wind turbines are operated by controlling the blade pitch angle. these controllers are divided into main categories; linear and nonlinear. for instance, linear controllers are able to regulate wind turbines using pitch angle control after the system has been linearized. they are also extensively used together with quadratic gaussian or quadratic regulator to control the output power [13-14]. the design process undertaken for the proportional integral derivative (pid) and the proportional integral (pi) has also been examined together with the regulators [15-18]. since wind systems have highly nonlinear characteristics, the performance of the system may be diluted with the operating point diverge from the linearized range. gain scheduling control is another linear technique that has been suggested as a way of introducing the linear features in the power systems. although this technique outperforms pid and pd methods by widening the operation point range, it is limited in terms of the level of performance they offer to the wind turbines with non-linear characteristics [19-23]. model predictive control (mpc) is one of the nonlinear control methods to improve the performance of the wecs that has attracted attention. there are two sub-categories derived within the electrical area of the mpc drives. the first category is based on the advancement of the conventional field-oriented control in which changes are made to the internal current loops [24-26]. it is done with a mpc regulator without removing the modulator. in the second sub-category, the modulator is removed and the mpc controls the inverter [27-30]. a different form of mpc is the model predictive direct torque control (mpdtc). it enhances direct regulation of the torque as well as rotor flux in the machines [31-34]. the computational process of this technique may become tedious if the prediction horizon is extended massively. the mpc technique is a newer version which is responsible for controlling the machines stator currents [35-38]. in this paper, mpc approach is used to create a reasonable pitch angle regulator integrated in a variable speed wind turbine system. mathematics concepts, mimo and wecs are projected. the main objective of this study is to determine and engineering, technology & applied science research vol. 7, no. 2, 2017, 1436-1443 1437 www.etasr.com bassi and mobarak: state-space modeling and performance analysis of variable-speed wind turbine… standardize the apprentice mpc system set in contrast to the pid system. ii. wecs model wecs changes electric energy from kinetic energy through a process where air streams are converted into electric energy. the conversion process takes place when wind causes the blades to rotate which in turn spins the turbines. the spinning rotor drives the machine which then produces electricity. currently, many wind turbines are built on the lateral design and consists of either two or three blades [2]. energy transformation in the wind turbines takes place in four subsystems as illustrated below [4]: • electric generator model: this works together with the basics required for local grid connection. mpc or pid controls the inputs to generator model and pitch actuator system to improve wind turbine efficiency. • aerodynamic model: these are the blades for the turbine. input factor consist of the speed of wind, how fast the rotor spins and the pitch angle. the output on the other hand consists of the rotation of the rotor which in turn produces electricity. • pitch actuator model: this part consists of a mechanical servo that rotates the turbine blades against the wind to regulate the generator rotor speed. • drive train model: involves the speed shafts, the turbine hub, and the speed multiplier. the input in this section constitutes the rotor rotation and speed multiplier which drives the train model. the rotor speed and shaft rotation make up the output. figure 1 shows the wecs model as a three-fundamental system that portrays a standard practice in wecs control. tr and tg are the rotor torque and generator torque input, and ωr and ωg are the revolving speed of the rotor and the generator speed. fig. 1. aerodynamic, mechanical and electrical models of the wecs. wind turbines have evolved form the traditional constant speed to the more efficient variable speed design. there are assumptions that wind turbines which generate levels of energy greater than the recorded speed are not cost effective. the energy curve is divided into three specific areas [10]. area i constitutes mild wind speed lower that the rated power of the turbines, therefore the turbine is operated at the highest possible level. area ii is the transformation area and responsible for reducing the level of noise. lastly, area iii experiences high wind speed and it is where the turbine derives their highest level of power. at this level, the wind turbines are regulated within the limits of the optimal energy. the variablespeed variable-pitch wecs is made up of two operating areas [11]. first, the partial load regime consists of all the different wind speeds and rotors of the wind turbine responsible for achieving the highest level of performance. secondly, the full load regime consists of wind turbines which are run when the speeds level are high or below the vco. the control systems in this area controls the output energy and the speeds of generator based on their expected speed levels. it is known as the ratio of recorded output of energy to the free stream-like power flowing in the same area. the tip speed ratio λ is defined as the speed of the wind turbine at the highest part of the blade to the free stream speed of wind. the speed on the tip of the blade has to reach a certain speed so that the wind turbine can generate maximum energy [10]. utilizing an efficient control technique such as mpc will produce this desirable outcome. the highest output energy released does not flow in the same direction as the highest torque level. both follow different laws with the output energy following the cube law while the torque takes the square law. a. wind turbine aerodynamics system the aerodynamic system converts wind energy into useful mechanical energy. a thorough discussion about wind turbine aerodynamics can be found by reading [16]-[20]. it is important to understand the equations about the torque and how power is captured by the blades. figure 2 illustrates three aspects (wind, energy curve, and responsiveness to wind fluctuations) of capturing wind energy. the energy and torque derived from the wind is shown in the equations below:   2 3w p w 1 p = c λ,β ρπr v 2 (1)  ta 3 2 w 1 t = c λ,β ρπr v 2  (2) where: pw is the extracted power from the wind, ta is the aerodynamic torque of the rotor, ρ is the air density, r is the radius of the blades, vw is the wind velocity, cp is the power coefficient, β is the pitch angle of the rotor blades and ct is the aerodynamic coefficient. fig. 2. block diagram of the aerodynamic wind turbine model cp and ct are nonlinear functions with respect to the tip speed ratio and the pitch angle and have the following relation, cp(λ,β)= λ ct(λ,β). where λ is tip speed ratio which is the ratio between the blade tip speed and the wind speed upstream the rotor and is given as: engineering, technology & applied science research vol. 7, no. 2, 2017, 1436-1443 1438 www.etasr.com bassi and mobarak: state-space modeling and performance analysis of variable-speed wind turbine… r w ω r λ= v (3) where ωr is the rotational speed of the rotor in (rad/s) and vw is effective wind speed (m/s). the blades are designed to ensure the highest energy coefficient outcome at the best speed on the tip speed ratio λopt. the energy coefficient is based on the speed at the tip and will fall under 0≤cp≤0.4. however, it will not be able to attain the maximum value cp-betz, referred to as betz limit, cp<cpbetz=0.593 [18]. the equation below illustrates utmost collected energy and aerodynamic torque of the wind turbine:   2 3max p,max opt w 1 p = c λ ,β ρπr v 2 (4)   5a,max p,max opt3 opt 1 t = c λ ,β ρπr 2λ (5) b. pitch actuator system this is a non-linear system that rotates the wind turbine blades. it is created using the saturation of the amplitude which can be modeled as mathematical dynamic equations [23]. figure 3 demonstrates the first-order system of the actuator. the equation below illustrates the changing performance of the pitch actuator. * 1 1 d                 (6) where: βmin≤ β ≤βmax, βmin *≤β*≤βmax *, β the actual pitch angle (0-45o) with ±10% max and β* the desired pitch angle. after calculating the desired pitch angle, the error in the closed loop has to go through a pitch angle limiter to bound the rate of change on the blades angle which results in increasing the blades lifetime [24]. fig. 3. pitch angle actuator model c. drive train system figure 4 shows the model made up of two mass mechanical models which are connected using a shaft with damping and stiffness coefficients. this shaft can be modeled as a torsion spring connecting two masses [26]. the mechanical model using the motion laws can be described as:   t t s t 1 ω = t k δθ+bδω j  (7) θ=δω (8)  1 1g s g g gear k b t j n              (9) t gδθ=θ -θ (10) g t gear ω δω=ω n (11) d. generator system it is important to model only the generator side converter considering the control system design of the wind turbine. the following equation represents the overall component of the generator torque control action by the generator side for second-order dynamic system:     2 g ng * 2 2 2 g ng ng ng t s ω = t s s +2ξ ω s+ω  (12) where tg * is the command value of the generator torque (wng ≈ 40 r/s) is the natural frequency, and (ξng ≈ 0.7) is the damping ratio. fig. 4. two mass model for the driven train iii. linearized model of wecs according to the rotor, the aerodynamic rotation, non-linear function of wind speed, pitch angle and rotor speed can be formulated into linear equations as below: ( ) ( ) ( )a w r w r v r w w β r wδt =-β ω ,v ,β δw +-β ω ,v ,β δv +-β ω ,v ,β δβ (13) where:             r w r w r w a w r w ω ,v ,β r a v r w ω ,v ,β w a β r w ω ,v ,β δt β ω ,v ,β = | δw δt β ω ,v ,β = | δv δt β ω ,v ,β = | δβ  for state space equation: x=ax+bu+gw  (14) y=cx  (15) where: engineering, technology & applied science research vol. 7, no. 2, 2017, 1436-1443 1439 www.etasr.com bassi and mobarak: state-space modeling and performance analysis of variable-speed wind turbine… r w sh g * * t g w τ t g ]x=[δw δv δt δt δβ u=[δt δβ y=[ δv δp ] ]  then: 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 a 1 1 0 w t t t shsh w sh sh d sh t t g t g r n j j j ndnd n d d k n k j j j j                                            0 1 0 0 0 1 , , 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 v t sh v r g t r j b g and cnd j                                                       equation (13) shows the wind speed model based on (17) [28]. the model consists of tower shadow, rotational sampling and wind shear effects. the working positions are ascertained by the regulatory strategy. however, it has limitations such as energy, rotor, wind speed and pitch angle [32]. equations (14) and (15), increase and assess the various wind speeds. equations (14) and (15) are the linear model of the entire system. the state vector and the regulatory input are the assessed results. the system is described as mimo which has a changing dynamics whenever there is a change of wind speeds. iv. problem description and proposed mpc approach the main task is to regulate the rotor speed of the turbine which will in turn enhance the smoothness in the turbines making them efficient; especially at the limited load regime. the process however has a limitation which occurs during the creation of the regulator. the regulator is able to completely enhance the changed efficiency while at the same time reducing the temporary loads. the outcome indicated that variances existed between two objectives which required a balancing position [34]. the objective of regulation when operating at full load regime is to control the generator resulting energy and equally control the generator at set standards. the greatest limitation at this point is the big percentages of variations in the turbines energy. the percentages are caused by fluctuations in wind speed. the limitation also leads to a fluctuation in the drive train torsion torque as well as output electric power delivered to the grid. this power must be regulated thereby reducing the wecs apparatus and the flicker troubles [36]. ordinary tests on the full load and partial regimes occur when the systems dynamics are not linear and viable variations occur at the operational center. another test occurs when the system has cyclic aerodynamic torque difference and the turbine blades are rotating at three times their speed. this occurrence is known as the rotation sampling effect which is caused by uneven wind. similarly, regulatory systems must identify regulatory goals kept at a certain level when facing limitations. for example, the highest level 1 is based on amplitude, speed pitch servos, generator energy and the speed of the turbines. normally, variable speed and pitch consist of two working areas. the first is undertaken in partial load region with the aim of deriving the highest level of energy by regulating the turbine rotor speed. the second working area is the full load region where regulatory processes are able to alter the resulting energy as well as the speed of the generator at standardized figures. this creates difficulties especially in the wecs design since the mimo system is not linear. in addition, factors such as the stochastic and sustainable differences of the speed of the wind and the restrictions by the system limit must be considered. the model illustrated above provides further complications to the regulatory design process. when assessed in the same level as the fixed speeds wind turbines, the variable speeds wind turbine has greater benefits such as increased production of energy on lower costs [37]. mpc control method can alter, regulate and predict perceptions of predictive models. it can also alter limitations and different weights. when varying scenarios are run on the system, which could either be linear or non-linear, the mpc can assess the regulatory performance. this can be seen in the altering of chemical processes and electromechanical systems. it is most beneficial when used in predictive model and is relevant in deriving regulatory actions by reducing certain functions which are objective. mpc optimization takes into consideration reduction of the variances existing in the predicted and reference parameters. the regulatory attempt is also based on the determined limitations. the mpc takes the following approach: • the expected outputs for the anticipated prospect n, are predicted at each instant, t using the process model. • for k=1, …, n, the predicted outputs y=(t+k(t)) depends on the known values up to instant t (past inputs and outputs) and on the future control signals u=(t+k(t)), for k=0, ...,n-1, are calculated out of the process. • the future control signals set is determined by an enhancing categorization to keep the process as close to the trajectory of the reference w=(t+k). • the reference trajectory can be the set point itself or a close approximation of it. • typically, this standard takes the appearance of a quadratic role of the errors between the predicted output signal and reference trajectory. • the regulatory indication u(t) is taken to the system while the next regulatory indicator calculated the rejected, since the next sampling instant y(t+1) is known and the step 1 is repeated with this new value. engineering, technology & applied science research vol. 7, no. 2, 2017, 1436-1443 1440 www.etasr.com bassi and mobarak: state-space modeling and performance analysis of variable-speed wind turbine… mpc model is vital in the prediction of future outputs arising from current values and expected future regulation action based on general composition as illustrated in figure 5. when using the linear model, over prediction are based on open and compulsory answers. the optimizer allows for the selection of the most beneficial regulation systems hence reducing cost functions. this is carried out by getting the weighted sum of the square predicted inaccuracy as well as square predictable regulatory figures. they are calculated at the high and low predicted possibilities and are known as the regulation perspective. the regulatory perspective allow the reduction allow the reduction in the predicted regulation based on the δu(k+j) for j≥nu. the w(k+j). this signifies the location route over the regulatory perspective n. fig. 5. mpc controller limitations placed on the regulatory indicators, the outputs, and regulatory indicator varying can be included in the following equation: ( ) ( ) ( ) ( )( ) ( ) ( )( ) 2 1 2 2 1 2 u 1 j n ,n ,n = β j y k+j -w k+j + λ j u k+ (16)j -1 unn j n j= = å å if n1, n2 fall at the bottom and highest prediction level on top of the results, then nu is the regulatory possibility, β(j), λ(j) are weighting variables. limitation on the regulatory indicators, results as well as regulatory indicators varying can be included in equation below:       min max min max min max u u k u u u k u y y k y           the outcome of (16) derives the best order of regulation indicators based on the perspective n and at the same time recognizing limitation on (17). the mpc has many benefits such as the ability to control different systems, easy to use on complex systems, and offer prediction even if the outcome is delayed. similarly, it can bring about the predicted results in systems which are closed loop. it can also be used to achieve the best outcomes with recognition of limitations. although the benefits are diverse, it requires skills for anyone to model the system and handle its limitations. the mpc model is more complex as compared to pid since it requires more calculations. v. results and discussions the considered 600 kw turbine system consists of three blades and pitch regulator. the feature of the mpc is an advantage over traditional pid controller including nonlinear control action. it can also reduce the noise, disturbance and parameters variations. the limitations for partial-load and fullload operations with mpc and with pid controllers are similar. they include wind velocity, angular momentum, pitch angle, generator power as well as torque output for 300 seconds. the system parameters are given in the appendix. a. partial-load operation figure 6 shows the results from the reputation exercise conducted for 300 seconds of partial-load wecs process. the outcomes reveal that the mpc and the pid regulators had identical tracing performance as observed in the speed and energy of the generator. this is resulted from the consistency of the return speed from the generator in tracking the maximum point tracking. nevertheless, amounts of these speed and energy variations reduce with the use of the mpc control strategy. therefore, the system has a better performance with mpc approach compared with traditional pid control. b. full-load operation figure 7 shows a duplicate outcome key for an operation that consists of a full load. it is important in examining the strength of the suggested mpc against uncertainties in the parametric. the power production when using the mpc leads to a more even and decreased fluctuation levels in the power output. the value of the decrease on the fluctuation of power production is enabled and enhanced based on the speed variations in the generator when compared to the pid control method as shown in figure 7.since the speed of wind, up to the first 50 seconds, is below the rated value of wind speed (10m/s) as shown in figure 7a. in this period, the pitch angle is forced to level zero and the torque devolved is affected. from 50 to 218 seconds time period, the angle pitch is adjusted in order to extract the maximum power from the wind turbine above the rated wind speed as shown in figure 7d. compared to the pid controller that forces the pitch angle to zero at early time of 218 seconds, the mpc approach enhances the wind power exploitation. table i shows the evaluation of performance in the two systems and this arises because of the sustainable differences in the wg* which follows the mppt. however, the scales of these fluctuations reduce with the utilization of the mpc regulation approach. when the mpc is compared with other methods based on performance, the mpc is vital for either strong or mild wind speeds. table i illustrates average speed in the generator, the average energy, as well as the highest pitch motion. the outcomes from table i indicate captured power shut by union at the mild or strong wind speeds. nevertheless, the highest level of the pitch angle was reduced by the mpc regulator as compared to the pid. the requested method proved most valuable as compared to other methods based on the level of performance. engineering, technology & applied science research vol. 7, no. 2, 2017, 1436-1443 1441 www.etasr.com bassi and mobarak: state-space modeling and performance analysis of variable-speed wind turbine… fig. 6. partial-load operation table i. output parameters for mpc and pid controllers mild wind velocity strong wind velocity item mpc pid mpc pid power output, pu. 0.97 0.73 0.94 0.87 pitch angle, deg. 26 13 34 26 generator speed, pu 0.89 0.81 0.89 0.78 vi. conclusion the main objective of this paper is to examine the variable speed and the pitch turbine regulatory designs of wecs, with the goal of extracting maximum wind energy and enhancing the progress against full load and partial load operation. the paper illustrates how the mpc controller regulates the wind turbine and introduces a system which is dynamic based on its speed, pitch wind turbine as well as limitations in the of the rotation and pitch angle regulator. the system is modeled and simulated using matlab/simulink. the obtained results at partial-load and full-load operations show that the studied system with the proposed mpc approach has a better performance compared to the traditional pid control in terms of speed response and energy extraction. fig. 7. full-load operation acknowledgment this project was funded by the deanship of scientific research (dsr), king abdulaziz university, jeddah, under grant no. (829-236d1435). the authors, therefore, acknowledge with thanks dsr's technical and financial support. engineering, technology & applied science research vol. 7, no. 2, 2017, 1436-1443 1442 www.etasr.com bassi and mobarak: state-space modeling and performance analysis of variable-speed wind turbine… references [1] p. kundur, power systems stability and control, new york: mcgraw hill, 1994 [2] l. wang, model predictive control system design and implementation using matlab, springer australia, 2009 [3] p. c. krause, o. wasynczuk, s. d. sudhoff, analysis of electric machinery and drive systems, hoboken, nj: wiley, 2002 [4] o. anaya-lara, n. jenkins, j. b. ekanayake, p. cartwright, m. hughes, wind energy generation modelling and control, uk: john wiley and sons, 2009 [5] n. a. ahmed, m. miyatake, a. k. al-othman, “hybrid solar photovoltaic/wind turbine energy generation system with voltagebased maximum power point tracking”, electric power components and systems, vol. 37, no. 1, pp. 43–60, 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department of computer science albaha university albaha, saudi arabia meid@bu.edu.sa shaikh abdul hannan department of computer science albaha university albaha, saudi arabia abdulhannan05@gmail.com r. j. ramteke school of computer sciences, kbc north maharashtra university, jalgaon, india rakeshj.ramteke@gmail.com abstract—palm-print and iris biometric traits fusion are implemented in this paper. the region of interest (roi) of a palm is extracted by using the valley detection algorithm and the roi of an iris is extracted based on the neighbor-pixels value algorithm (npva). statistical local binary pattern (slbp) is applied to extract the local features of palm and iris. for enhancing the palm features, a combination of histogram of oriented gradient (hog) and discrete cosine transform (dct) is applied. gabor-zernike moment is used to extract the iris features. this experimentation was carried out in two modes: verification and identification. the euclidean distance is used in the verification system. in the identification system, the fuzzybased classifier was proposed along with built-in classification functions in matlab. casia datasets of palm and iris were used in this research work. the proposed system accuracy was found to be satisfactory. keywords-palm-print; iris; valley detection; slbp; hog; dct; zernike moment; fuzzy classifier i. introduction pattern recognition classifies data based on already gained knowledge [1], it is a process of understanding the class to which an object/pattern belongs. those patterns/objects can be 1d e.g. signals or 2d e.g. images. biometrics is an application of pattern recognition regarding analyzation and measurements of human body characteristics. there are three types of biometrics: physical, behavioral and cognitive. physical biometrics deal with the bodily parts like face, fingerprints, palm etc. behavioral biometrics considers the activities of the body like gait, keystroke, and voice. cognitive biometrics regard every human nervous tissue and its response to signals like electrocardiogram (ecg), electromyogram (emg), electroencephalogram (eeg) and electrodermal response (edr). in this paper, two physical biometrics have been considered (palm-print and iris). iris looks like a ring inside the eye, and it controls the intensity of light entering through the pupil, the radius of the iris is increasing and decreasing according to illumination. there are many features on the iris, such as tiny crypts, nevi anterior border layer collarette, texture features, etc. [2]. in the same person, the right iris has different features than the left. iris is one of the touchless biometrics. the palm is the region on the human hand between the wrist and root-fingers. authors in [3] were the first who described the palm as one type of biometric traits in 1998. biometric systems can be classified into two types: verification and identification. in the verification mode, biometric data are compared against the same data to decide whether it is accepted or rejected. in the identification mode, biometric data is used to identify the id/name of the person. table i explains the difference between the verification and identification in a biometric system. table i. verification vs identification verification identification one to one search one to many searches answer the question “can you prove who you are?” answer the question: “who are you?” id is needed as manually input id is automatically recognized no need for classification classification is required less time for verification more time for identification higher accuracy lower accuracy than verification systems access control, fingerprint in mobile phones attendance systems, face recognition ii. literature review authors in [4] proposed a new method to extract palm features named as the histogram of oriented lines (hol). hol is based on the histogram of oriented gradient (hog) [5] which was proposed in 2005 for human detection. hol is not sensitive to light changing and is used to extract palm lines corresponding author: a. alsubari engineering, technology & applied science research vol. 9, no. 1, 2019, 3807-3813 3808 www.etasr.com alsubari et al.: composite feature extraction and classification for fusion of palm-print and … along with the orientation features. euclidean distance was used in the verification and identification system for the palmprint trait in two databases. in the verification mode, the error rates were computed as 0.31% and 0.64%. in the identification system, the recognition rates were calculated based on the matching samples from the testing templates and were found to be 99.97% and 100%. authors in [6] presented face recognition based on global and local features. in global features, the zernike moment is applied to the output of a gabor filter. for extracting the local features of the face image, hog is applied on the face image. thus, the global and local features were combined for producing a feature vector of the face image. nearest neighbor classification based on the euclidean distance was used for the matching process. the accuracies were 97.8%, 98% and 97.7% in three databases. authors in [7] proposed the magnitudes of the zernike moments for generating the feature vector of the face images. they experimented in 2d and 3d face images. the features were selected on the basis of the order of the zernike moments, so the length of the feature vector varied from 16 to 42. the dataset was divided into 60% for training and 40% for testing. authors used the neural network tools in matlab (nprtool) for the matching process. in the orl database, the highest recognition rate was 99.5% with 36 features by using the radial basis function neural network (rbfnn). in the 3d face database, the best achievement was 99.71% with 42 features by using multilayer perceptron neural network (mlpnn). authors in [8] extracted iris and palm-print features by applying gabor filter with 4 orientations and 3 spatial frequencies. they fused the palm and iris after the features were described by a gabor filter. the output of the gabor filter for the palm and iris images was integrated into a single matrix by using a second level wavelet transform. in other words, second wavelet transform was applied on palm and iris images and the result was combined in one matrix for generating the feature vector. the fusion system accuracy was 99.2% by using the knn classifier. authors in [9] presented a multimodal of iris and palm-print by extracting global features using wavelet transform. haar wavelet transform was used to extract iris features at four levels. for extracting the palm-print features, daubechies wavelet transform was applied at four levels as well. the hamming distance was utilized in the matching phase for the iris modal and palm-print modal separately. authors proposed three different levels of fusion for the iris and palm-print biometric traits: feature level, score level and decision level and they compared the results. at the feature level, the feature vectors of the iris and palm were combined in a single vector for generating a feature vector of the iris and palm-print. in case of the score level fusion, the feature vectors of iris and palm-print were evaluated separately/individually and based on each feature vector score, the decision was made by using a weighted sum-rule. finally, at the decision level, the fusion was based on the error rate from the feature vectors of iris and palm-print. authors in [10] presented the fuzzy rulebased classification for identifying the normal sperm from the abnormal. iii. methodology in this paper, the fusion of palm-print and iris biometric traits were integrated at the feature level as shown in figure 1. the palm is segmented from the rest parts of the hand by using an algorithm from our previous work [11]. iris was localized by using the npva [12]. texture features of iris and palm were extracted by computing the mean and standard deviation of the local binary pattern (lbp). dct and hog were applied together for extracting the palm texture features. gabor filter with 8 orientations and 5 scales was applied on the roi of iris for generating 40 sub-images. then, the zernike moment was applied to each sub-image to generate the feature vector of the iris. the gaussian fuzzy membership function is used as a classifier in the identification system. proposed system for palm-print and iris biometric traits a. pre-processing 1) roi extraction palm roi was extracted by using the valley detection algorithm [13] and thresholding segmentation. the algorithm steps to extract the palm roi are: • the hand-image is binarized to segment the hand object from the background. • valley-points between the fingers are to be detected by using the method in [11]. to detect the valleypoints/reference-points, the four conditions in valley detection algorithm should be satisfied. • from the reference-points, the coordinate system of the palm region is established with the help of the following equations: 𝑃1 = 𝑟 × [cos⁡( 1 2 𝜋 − 𝜃)⁡⁡sin⁡( 1 2 𝜋 − 𝜃)] + rp1⁡ (1) 𝑃2 = 𝑟 × [cos⁡( 1 2 𝜋 + 𝜃)⁡⁡sin⁡( 1 2 𝜋 + 𝜃)] + ⁡rp3 (2) 𝑑 =⁡√(𝑥2 − 𝑥1) 2 + (𝑦2 − 𝑦1) 2 (3) 𝑃3 = 𝑑 × [cos⁡( 1 2 𝜋 + 𝜃)⁡⁡sin⁡( 1 2 𝜋 + 𝜃)] + p1 (4) 𝑃4 = 𝑑 × [cos⁡( 1 2 𝜋 + 𝜃)⁡⁡sin⁡( 1 2 𝜋 + 𝜃)] + p2 (5) where the locations of points p1-p4 and rp1-rp4 are mentioned in figure 2(a), 𝑟 is the radius of around valley-point, 𝑑 is the pixel distance from p1 to p2 and this distance will be engineering, technology & applied science research vol. 9, no. 1, 2019, 3807-3813 3809 www.etasr.com alsubari et al.: composite feature extraction and classification for fusion of palm-print and … the edges-value for roi of the palm region. the slope between p1 and p2 was computed to obtain the angle rotation of the palm image. • the final step is to rotate and extract the palm region to a fixed size image. for extracting the iris region, npva was proposed for calculating the radius and center values of the iris. the npva steps are: • sobel operator was applied to the eye-image to detect the boundaries of the pupil or to detect the inner boundaries of the iris. • dilation operator is applied for connecting the pixel gap in the boundaries. • circle hough transform [14] is applied to find the radius and center of the pupil circle. • for detecting the outer boundaries of the iris, the three neighboring pixels from the pupil boundaries were computed in horizontal-left and horizontal-right as shown in figure 2(b). if those pixels’ intensity values were found to be more than 200 or closer to the white color, then the skipped pixels obtain the iris radius value. after localization of the iris, the pixel intensity values which are close to zero or close to 255 will be avoided and it will be considered as noise (sclera, eyelids and eyelashes). after the iris localization, the iris region is converted into a rectangular form by using the rubber sheet normalization [15]. the dimensionality of iris images was resized to 64×384 and palm images were resized to 64×64. (a) the location of reference and roi points, (b) the direction of computing npva 2) enhancement three enhancement techniques were applied on the roi of the palm: contrast-limited adaptive histogram equalization (clahe) [16], sobel filter and gaussian filter mask. a) clahe this method is based on local histogram equalization (lhe) and has three steps for image enhancing [17]: • divide the image into not overlapping sub-blocks. • each sub-block will be enhanced individually. • for reducing the sub-block artifacts, interpolation operation is applied. b) sobel mask: after enhancing the contrast of palm images by using the clahe, sobel mask is applied for filtering those images and to obtain palm lines and wrinkles. sobel mask filter can be used as feature extraction technique because it is dealing with edges of the image but, in this paper, we considered it in enhancement approach because it shows the palm’s principal lines and wrinkles: 𝐺𝑥 = [ +1 0 −1 +2 0 −2 +1 0 −1 ] ∗ ⁡𝐼𝑚𝑔 (6) 𝐺𝑦 = [ +1 +2 +1 0 0 0 −1 −1 −1 ] ∗ 𝐼𝑚𝑔 (7) where img is the palm image, gx contains the horizontal derivative approximation and gy contains the vertical derivative approximation. in this experiment, the vertical of sobel mask is selected to detect and enhance the features of the palm images [18]. c) gaussian mask the last step in the palm enhancement is to apply a smoothing filter of gaussian for reducing the noise of palm image. histogram equalization (he) is applied on the roi of iris for the enhancing the contrast of the iris pixels. he is distributing the intensity values in the range 0-255. it is a powerful image processing technique. the effect of he on the roi of the iris is shown in figure 3. histogram equalization of iris b. feature extraction the concept of feature extraction in image processing is to convert the matrix (image) into a set of mathematical parameters which will be in vector form (feature vector) or template features. those features can be edges, lines in the palm, minutia in a fingerprint, neighbor pixel-based (lbp features), texture features or shape-based features etc. in this experiment, the texture features of the palm and iris were extracted by using these techniques: 1) slbp lbp was introduced in [19] where it was used as a filter for palm and iris images. lbp is applied in each pixel of an image except the first and last row and column. lbp filter compares the pixel against its 8 neighboring values. if the pixel intensity value of the neighbor is greater than or equal to the central pixel, it will be assigned as 1, otherwise, it will be assigned as 0. from the lbp filter, the output of the previous process will engineering, technology & applied science research vol. 9, no. 1, 2019, 3807-3813 3810 www.etasr.com alsubari et al.: composite feature extraction and classification for fusion of palm-print and … be 8 binary numbers. these will be converted to a decimal number and will be replaced with the center pixel as shown in figure 4. in other words, the central pixel is the threshold value for its neighbor-pixels [20]. lbp filtering for obtaining the slbp, the mean and standard deviation were calculated from the lbp matrix. those values were composted for generating the feature vector of slbp. the mean equation is: 𝑀 = 1 𝑁 ∑ 𝐴𝑖 𝑁 𝑖=1 (8) where the standard deviation equation is: 𝑆 =⁡√ 1 𝑁 ∑ |𝐴𝑖 − 𝑀| 𝑁 𝑖=1 2 (9) slbp method is a common feature extraction technique for palm and iris. because slbp extracts only local features of palm and iris, different methods were adopted to enhance the features of palm and iris. 2) composite of dct and hog dct is an image transform which converts signals/pixels to the frequency domain. dct transforms can be used to extract the edges from the palm image. where the palm has edge features (principal lines and wrinkles etc.), then the hog and dct were proposed to extract the features of the palm. dct is computed with the following equations: 𝑓(𝑎) = w(𝑎)∑ 𝑦(𝑛)𝑐𝑜𝑠 ( 𝜋 2𝑛 (2𝑛 − 1)(𝑎 − 1)) 𝑁 𝑛=1 (10) 𝑤(𝑎) = { 1 √𝑁 , 𝑎 = 1 √ 2 𝑁 , 2 ≤ 𝑎 ≤ 𝑁 (11) where, 𝑎=1,2, 3...n, and n is the length of 𝑦. 𝑎 and 𝑦 are of the same size. 𝑎 and n are indexed from 𝑎=1, n=1 because matlab vectors run from 1. the output of dct is having negative and positive values, so the negative values will be converted into positive values. hog was introduced and proposed in 2005 [5] for the purpose of human detection. in this experiment, hog is used for extracting the texture feature of palm. thus, the combination of dct and hog is proposed for extracting palm features. dct is used to extract the edges from the image, so it was applied in the palm images. after that, hog was applied to the dct output. hog algorithm steps are: • the palm image is divided into cells and blocks, where the cell is 8×8 pixels and the block size is 2×2 cells which means the block size is 16×16 pixels • 50% overlapping was assigned from the next block as shown in figure 5. so, the total number of blocks in each palm image is 7×7=49. • nine directions were selected from the range 0o-180o. the orientations and gradient magnitudes were computed by the following equations: 𝑑𝑥 = 𝐼(𝑥 + 1,𝑦) − 𝐼(𝑥 − 1,𝑦)⁡⁡⁡⁡ (12) 𝑑𝑦 = 𝐼(𝑥,𝑦 + 1) − 𝐼(𝑥,𝑦 − 1)⁡ (13) 𝑚(𝑥,𝑦) = √𝑑𝑥2 + 𝑑𝑦2 (14) • the histograms of each cell with respect to 9 bins direction were computed. total no of features=nb×cb×p (15) where, nb is the total of blocks number in the palm-image, cb is the cells number in each block which are four cells in each block, p is the bins orientation which is assigned by 9. from (14), the total number of hog features are 49×4×9=1764. blocks and cells in the palm image 3) composite of gabor filter and zernike moment the idea behind this technique is to combine the gabor filter with the zernike moments for extracting texture features of an iris image. the combination of zernike moments and gabor filter achieved a satisfactory result in the face and iris traits. 2d gabor filters [22] are widely used in texture analysis, edge detection, feature extraction, etc. in this implementation, the gabor filter was applied on the iris image with respect to 8 orientations and 5 scales, thus 40 sub-images were generated from the gabor filter. therefore, zernike moments [23] technique was applied to each sub-image of iris with different orders and repetitions. four features were selected from each sub-image. the length of the feature vector of this technique is 160. the zernike moments of order n with repetition m is obtained by (16)-(18): 𝑍𝑛𝑚 = 𝑛+1 𝜋 ∑ ∑ 𝑓(𝑥,𝑦)𝑉𝑛𝑚𝑦𝑥 (𝑥,𝑦), x 2 + y2 ≤ 1 (16) where zernike moments 𝑍𝑛𝑚on rotated image have the same magnitudes. therefore, | 𝑍𝑛𝑚 | is the rotation invariance of features. 𝑉𝑛𝑚(𝑥,𝑦) is a zernike polynomial on a unit circle 𝑥2 + 𝑦2 ≤ 1. 𝑉𝑛𝑚(𝑥,𝑦)=𝑉𝑛𝑚(𝜌,𝜃) = 𝑅𝑛𝑚(𝜌)𝑒𝑥𝑝⁡(𝑗𝑚𝜃) (17) engineering, technology & applied science research vol. 9, no. 1, 2019, 3807-3813 3811 www.etasr.com alsubari et al.: composite feature extraction and classification for fusion of palm-print and … 𝑅𝑛𝑚(𝜌) = ∑ (−1) 𝑠 𝑛−|𝑚| 2 𝑠=0 (𝑛−𝑠)! 𝑠!( 𝑛−|𝑚| 2 −𝑠)!( 𝑛−|𝑚| 2 −𝑠)! 𝜌𝑛−2𝑠 (18) where, 𝑛 is a non-negative integer which represents the order of zernike moment and 𝑚 represents the repetition. satisfying the conditions 𝑛 − 𝑚 is even and |⁡𝑚|≤ 𝑛. also 𝜌 = √𝑥2 + 𝑦2 and = 𝑡𝑎𝑛−1 𝑦 𝑥 . c. fusion the fusion is to integrate the palm and iris biometric traits. in this experiment, the fusion was done at the feature level. the feature vectors of iris and palm were composited to generate a single vector. before compositing the vectors, max normalization was adopted for making the values of the vector in the same range [0-1]. the max normalization steps are: • convert the feature vector values into integer values. • find the maximum value of the feature vector of iris and palm. • divide the feature vector with the maximum values of iris and palm respectively. • composite the feature vectors of iris and palm in a single vector. the numbers of extracted features are shown in table ii. table ii. number of features techniques slbp features dct-hog features gabor-zernike moment features fusion features biometric traits palm-print 124 1764 ---1888 iris 124 ----160 284 fusion of palmprint and iris 2172 d. matching the proposed system was evaluated in two different ways, verification and identification. 1) verification the verification mode is a one-to-one system and it is more used than the the identification system. for biometric verification, the matching algorithm was developed based on the euclidean distance. its steps are: • enroll the whole features and labels of the biometric trait in a matrix form respected to their labels/classes. • divide the features into training vectors and testing vector for each person separately. • calculate the euclidean distance between the training vectors to each other for the specific person. then, find the maximum distance value ma. • compute the euclidean distance of the testing vector against the training vectors of the same label and those values are assigned in a different variable me. apply this process for all persons. • if me<ma then it is accepted otherwise it will be rejected. there are two recognition rates obtained from this algorithm. the first rate is the total number of training vectors which are matched with the testing vector. the second recognition rate is the total number of accepted testing vectors. 2) identification a) fuzzy-based classification the feature vectors are classified by using the gaussian fuzzy membership function [21, 24]. this function gives output in the range 0-1. the steps of the algorithm of fuzzy classification based on the gaussian fuzzy membership function are: • enroll all feature vectors of the biometric traits as a matrix. • divide the feature matrix into 50% for training and 50% for testing. • compute mean and standard deviation for each training sample of the specific label separately. 𝜇(𝐻) = ∑𝐻𝑖 𝑛 (19) 𝜎(𝐻) = √ ∑|𝐻𝑖−𝜇| 2 𝑛 (20) where 𝐻 is the features vector and the 𝑛 is the total number or the length of the 𝐻 vector, 𝜇 is the mean or the average of the specific features, 𝜎 is the standard deviation. • apply gaussian fuzzy membership function to the testing samples based on the mean and standard deviation of the training samples: 𝐹(𝐻𝑤) = 𝑒 −(𝐻𝑖−𝜇) 2 2𝜎2 (21) where, 𝑒 is a mathematical constant with approximate value of 2.7183. 𝐻𝑤 is the gaussian fuzzy membership values in the range between 0 and 1, 𝐻𝑖 is the testing vector, 𝜇 and 𝜎 are the mean and the standard deviation respectively. the average of each observation (𝐻𝑤) of the testing vector is stored in another matrix for computing the accuracy. b) built-in classification functions there are many built-in functions in matlab which can be useful for the classification process. in this experiment, 5 builtin classification functions were able to classify the features of the system with different accuracies. these functions are shown in table iii. table iii. built-in classification function in matlab function name description kitcecoc fit a multiclass mode for svm fitcknn fit knn classification model fitcnb fit a naïve bayes classifier fitcensemble fit ensemble classification fitctree fit a classification decision tree iv. implementation and results the algorithms in this paper were developed in matlab. casia-iris and casia-palm databases [25] were used in the implementation. in this experiment, 24 subjects with 8 samples engineering, technology & applied science research vol. 9, no. 1, 2019, 3807-3813 3812 www.etasr.com alsubari et al.: composite feature extraction and classification for fusion of palm-print and … i.e. 8×24=192 samples were selected randomly from each database of casia-palm-print and casia-iris-interval database. the total number of images is 8×24+8×24=384. a. verification results in the verification system, 2 samples were used for testing and the remaining images were used for training. for obtaining the threshold value of matching, the euclidean distance is computed between each sample in the training, and the maximum value is assigned as a threshold value. if the distance between the testing sample and the training sample is smaller than the threshold value, then it is accepted, otherwise it is rejected. the accuracies were calculated by: 𝑇𝑀𝑆𝑇 = 𝐴𝑐𝑐𝑒𝑝𝑡𝑒𝑑⁡𝑇𝑟𝑎𝑖𝑛𝑖𝑛𝑔⁡𝑆𝑎𝑚𝑝𝑙𝑒𝑠 𝑇𝑜𝑡𝑎𝑙⁡𝑜𝑓⁡𝑇𝑟𝑎𝑖𝑛𝑖𝑛𝑔⁡𝑆𝑎𝑚𝑝𝑙𝑒𝑠 × 10 (22) 𝑉𝐴 = 𝐴𝑐𝑐𝑒𝑝𝑡𝑒𝑑⁡𝑇𝑒𝑠𝑡𝑖𝑛𝑔⁡𝑆𝑎𝑚𝑝𝑙𝑒𝑠 𝑇𝑜𝑡𝑎𝑙⁡𝑜𝑓⁡𝑇𝑒𝑠𝑡𝑖𝑛𝑔⁡𝑆𝑎𝑚𝑝𝑙𝑒𝑠 × 100 (23) where 𝑇𝑀𝑆𝑇 is the number of training samples which are matched with the testing samples and va stands for verification accuracy. table iv shows the accuracy of the verification system. iris obtained better accuracy along with less procedure time, while both vas were 100%. table iv. verification results palm iris fusion matching samples 82.29% 93.75% 93.75% time (s) 0.179285s 0.148785s 0.1966s va 100% 100% 100% b. identification results feature vectors of palm and iris biometric traits were classified with the gaussian fuzzy membership function. feature vectors were divided into training and testing groups (50%-50%). mean and standard deviation were computed for the training features and two vectors for each person were stored. the testing vector was evaluated by the gaussian fuzzy membership function with respect to the stored two vectors. as shown in table v and figure 6, the fuzzy-based classification leads to higher accuracy. the highest accuracy (96.87%) of the built-in classification was obtained by kitcecoc function in palm-print recognition system. nevertheless, the fuzzy-based classification obtained 1.05% higher accuracy and less execution time than svm. table v. identification accuracies with comparison classification method and time* palm iris fusion kitcecoc 96.87% (40.4861s) 87.5% (45.6512s) 89.58% (14.856) fitcknn 94.79% (1.08582s) 92.708% (0.41267s) 92.708% (1.906) fitcnb 82.29% (246.5609s) 89.58% (39.4774s) 86.458% (132.042) fitcensemble 50% (106.1933s) 71.875% (29.8159s) 66.66% (122.11) fitctree 34.375% (1.6339s) 55.208% (0.4371s) 31.25% (1.8502) fuzzy-based (proposed method) 97.92% (5.0109s) 93.75% (0.9434s) 98.96% (7.47215s) * classification time (s) results comparison v. conclusion in this paper, comparison between unimodal and multimodal biometrics system based fuzzy classifier was done with matlab. roi of palm and iris were detected and extracted by using valley detection algorithm and nvpa respectively. slbp was the common technique to extract the local features of palm and iris. compared to other methodologies, slbp played a vital role in extracting the local features of iris and palm. the combination of dct and hog was an important step in enhancing texture features. composition of gabor filter and zernike moment played an important role in extracting iris texture features. max normalization was applied to make the feature vectors in the same range and the feature vectors of palm and iris were integrated into a single vector. fuzzy logic led to high accuracy classification in the identification mode. the experiment considered both verification and identification. euclidean distance was used in verification and the accuracy of the system was 100%. in the identification system, fuzzy classifier was used for comparing with the existing built-in classification function in matlab. the highest recognition rate of the multimodal is 98.96% and the approximate time of classification was 7.47s. the recognition rate of this system was found to be satisfactory. references [1] m. n. murty, v. s. devi, “pattern recognition: an algorithm approach”, springer science & business media, 2011 [2] r. p. wildes, “iris recognition: an emerging biometric technology”, proceeding of the ieee, vol. 85, no. 9, pp. 1348-1363, 1997 [3] w. shu, d. zhang, “automated personal identification by palm-print”, optical engineering, vol. 37, no. 8, pp. 2359-2363, 1998 [4] w. jia, r. x. hu, y. k. lei, y. zhao, j. gui, “histogram of oriented lines for palm-print recognition”, ieee transaction on systems, man, and cybernetics: systems, vol. 44, no. 3, pp. 385–395, 2014 [5] n. dalal, b. triggs, “histogram of oriented gradients for human detection”, ieee computer society conference on computer vision and pattern recognition, san diego, usa, june 20-25, 2005 [6] a. fathi, p. alirezazadeh, f. abdali-mohammadi, “a new globalgabor-zernike feature descriptor and its 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identification, msc thesis, university of western australia, 2003 [16] k. zuiderveld, “contrast limited adaptive histogram equalization”, in: graphic gems iv, pp. 474-485, academic press professional, 1994 [17] v. a. bharadi, l. padole, “performance comparison of hybrid wavelet transform-i variants and contrast limited adaptive histogram equalization combination for image enhancement”, ieee fourteenth international conference on wireless and optical communications networks, mumbai, india, february 24-26, 2017 [18] l. hong, y. wan, a. jain, “fingerprint image enhancement: algorithm and performance evaluation”, ieee transactions on pattern analysis and machine intelligence, vol. 20, no. 8, pp. 777-789, 1998 [19] t. ojala , m. pietikainen, t. maenpaa, “multiresolution gray-scale and rotation invariant texture classification with local binary patterns”, ieee transactions on pattern analysis and machine intelligence, vol. 24, no. 7, pp. 971-987, 2002 [20] a. alsubari, d. n. satange, r. j. ramteke, “facial expression recognition using wavelet transform and local binary pattern”, ieee 2nd international conference convergence in technology, mumbai, india, april 7-9, 2017 [21] r. j. ramteke, s. c. mehrotra, “feature extraction based on moment invariants for handwriting recognition”, 2006 ieee conference on cybernetics and intelligent systems, bangkok, thailand, june 7-9, 2006 [22] v. struc, n. pavesic, “the complete gabor-fisher classifier for robust face recognition”, eurasip journal on advances in signal processing, vol. 2010, no. 1, p. 847680, 2010 [23] a. khotanzad, y. h. hong, “invariant image recognition by zernike moments”, ieee transactions on pattern analysis and machine intelligence, vol. 12, no. 5, pp. 489-497, 1990 [24] l. x. wang, j. m. mendel, “fuzzy basis functions, universal approximation, and orthogonal least-squares learning”, ieee transactions on neural networks, vol. 3, no. 5, pp. 807-814, 1992 [25] casia iris image database and casia palm image database, http://biometrics.idealtest.org/ microsoft word etasr_v13_n4_pp11119-11123 engineering, technology & applied science research vol. 13, no. 4, 2023, 11119-11123 11119 www.etasr.com bazuhair & alqahtani: an assessment of testing and conditiong protocol to evaluate asphalt mixtures an assessment of testing and conditiong protocol to evaluate asphalt mixtures rabeea w. bazuhair civil engineering department, college of engineering and islamic architecture, umm al-qura university, saudi arabia rwbazuhair@uqu.edu.sa (corresponding author) majed a. alqahtani civil engineering department, college of engineering and islamic architecture, umm al-qura university, saudi arabia s43980459@st.uqu.edu.sa received: 1 may 2023 | revised: 15 may 2023 | accepted: 17 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6003 abstract asphalt mixtures frequently contain a wide variety of components that may interact. when put into service, they can be damaged due to several factors such as traffic, loading, and environmental impact. thus, it is necessary to predict or simulate the asphalt mixtures’ damage and performance in service utilizing laboratory conditioning protocols and tests. this paper investigates the property measurements themselves and how a mixture test can simultaneously assess oxidation and moisture damage. in this study, three asphalt mixtures are used with different mixture tests such as indirect tensile tension (idt), cantabro mass loss (cml), and hamburg loaded wheel tracking (hlwt). unaged (control) and two laboratory conditions were utilized to simulate the performance of the mixture in service. the result showed that the laboratory conditioning of the combined effects of oxidation and moisture simulates better the asphalt damages in service than laboratory single environment effect conditioning. the cml test is recommended for the evaluation and capture of these combined damage effects. keywords-warm mix asphalt; laboratory conditions; sasobit; rediset lq1200 i. introduction laboratory conditioning is often administered in two ways: oxidative degradation by long-term oven aging (ltoa) and moisture damage through hot water conditioning or freezethaw. authors in [1] acknowledged that little research had been done regarding the aging of asphalt mixes. ltoa procedures spanning from 2 to 8 days at 85 °c have been recommended [1-3]. consequently, the existing aging regimen (aashto r30) was devised with 5 days of ltoa at 85 °c, which is a routinely applied approach to generate oxidative stress on asphalt samples [4-6]. aashto t283 [7] and astm d4867 [8] are the most commonly used moisture conditioning technologies nowadays. t283 involves vacuum saturating compressed samples, undergoing a 16-hour ft cycle before being transferred to a 60 °c water bath for 24 ± 1 hours, whereas d4867 involves vacuum saturating compressed samples immersed in a 60 °c water bath for 24 ± 1 hours and can optionally undergo a 15-hour ft cycle. even though these exact techniques are not universally utilized [5, 9], they are very commonly used to assess moisture susceptibility [4, 10]. the kind of damage caused to compressed asphalt mixture samples is the most interesting part of this research. usually, oxidative and moisture conditioning are studied independently and are evaluated by different mixture tests such as idt, apa, hlwt, and cml [11-17]. many researchers do not consider the impact of one environment’s effects on the other, specifically how prolonged oxidation influences wma resistance to moisture degradation in comparison to hma. several studies investigated moisture damage resistance with the help of aashto t283 and/or hlwt test as a role of oxidative aging durations, generally produced by ltoa [5, 6, 10, 11, 18]. authors in [5] used ltoa to produce oxidative stress for 4 and 8 days at 85 °c and a revamped version of aashto t283 moisture conditioning without integrating the indicated 16-hour curing period and 24-hour storage period. they conducted idt tests on both dry and moist samples prior to ltoa as well as after 4 and 8 days of ltoa to explore variations between the moisture resistance of wma and hma with increased oxidative damage. as discovered in [5], the preliminary tsr of wma was equal to or superior to that of hma and grew higher with rising ltoa periods for wma than for hma. in terms of tensile strength values, hma originally had greater dry and moist tensile strength readings. after 4 days of ltoa, the authors noted that wma dry tensile strength neared hma's, which denotes a convergence of values, but after 8 days, hma and wma demonstrated considerable disparities. the authors gathered wet tensile strength data and revealed that engineering, technology & applied science research vol. 13, no. 4, 2023, 11119-11123 11120 www.etasr.com bazuhair & alqahtani: an assessment of testing and conditiong protocol to evaluate asphalt mixtures wma increased at a higher rate than hma across the aging cycle analyzed by the researchers. extended ltoa is projected to enable wma's wet tensile strength to surpass that of hma. authors in [11] evaluated the aged and unaged moisture sensitivity of five various wma combinations made using asphamin, cecabase, evotherm, rediset, and sasobit. aashto r30 and t283 were used to generate ltoa and moisture conditioning, respectively. the dry and wet tensile strengths and tsr values of the mixes following r30 aging showed that there was minimal variation between the majority of mixtures following ltoa, except the mixture with asphamin [12]. authors in [13] examined the moisture sensitivity of wmas made with sasobit, and evotherm using the sc t 70 (24 hours in 60 °c water) benchmark of south carolina. the researchers identified wet and dry tensile values of the samples preand post-ltoa by using aashto r30. prior to ltoa, the researchers noted the greater values of wet tensile strengths in hma and sasobit in comparison to evotherm. the study showed that ltoa increased the moisture damage resistance of sasobit and evotherm made mixes compared to hma. furthermore, the findings revealed that sc t 70 enhanced the flow resistance in all mixes. authors in [15] evaluated the performance of asphalt mixtures with different additives including titan 7205, styrene-butadienestyrene (sbs) and crumb rubber (cr). the unconditioned and aashto r30 conditioned asphalt mixtures were evaluated and tested utilizing dynamic shear rheometer (dsr) testing, cml, tensile strength ratio (tsr), and idt. the study concluded that titan 7205 would be an alternative additive to be used with hma. authors in [6, 19, 20] utilized the combined effects of oxidation and moisture to evaluate asphalt mixtures. moisture conditioning was conducted in accordance with aashto t283 prior to and post various periods of ltoa [6]. the laboratory mixed laboratory compacted (lmlc) samples of mixes patterns that had undergone long-term aging for 16 weeks at 60 °c were examined through dry and wet idt testing. lmlc samples were conditioned and tested by the hlwt test and wet and dry idt. before performing ltoa, the researchers noted that wma mixes were more moisture susceptible than hma, after aging for 16 weeks at 60 °c or 5 days at 85 °c. also, authors in [19] evaluated asphalt mixture damages utilizing several laboratory conditioning protocols, including single and/or combined environmental effects as well as mixture tests at intermediate temperature. cml and binder tests correlated with each other. however, neither cml nor binder tests did correlate with idt strength. idt testing is sensitive to oxidation damage and was unable to react to laboratory conditioning protocols that considered combined or various environmental effects, i.e. oxidation, moisture, and freeze-thaw. cml had a good ability to detect various environmental effects. in order to evaluate the properties of intermediate temperature mixtures in relation to non-load related environmental effects, cantabro testing was recommended. hundreds of field-aged and laboratory-conditioned specimens in a warm, non-freezing environment with several laboratory conditioning protocols, including single and/or combined environmental effects as well as different mixture and binder tests were evaluated in [20]. asphalt mixture damages in service were investigated and the filed temperature and moisture levels in asphalt mixes were tracked over time and used in the evaluation. the combined effects utilized in this study include 5 days of 85 o c oxidation, 14 days of immersing in 64 o c water, and 1 freeze-thaw cycle. this laboratory conditioning procedure can simulate at least 4 years of field aging while conventional single-mechanism protocols cannot. idt results of field cores showed that st values increase over time until a specific period (around 4 years) and then decrease as the influence of moisture starts to damage the asphalt mixture. also, the hlwt value showed that the rut depth of field cores decreases until a specific long period (around 4 years), and then it begins to increase as the influence of moisture starts to damage the asphalt mixture. the cml results of field aging showed an increase in ml values over time representing that the asphalt mixture deteriorated over time in service. the study recommended that the asphalt industry needs to be more rigorous when evaluating mixes in laboratories and that combined environmental effect conditioning should be taken into account when implementing. ii. material and methods table i shows the gradation of a mix design used in this study. hma, termed as m0, is used as the control mix, while two wma additives are used, sasobit (m1) and rediest lq1200 (m2). the doses of sasobit and rediest lq-1200 additives are 1.5% and 0.5% by weight of the binder, respectively. during the mixing procedures, the oven was set to the approximate plant mixing temperatures of 160 o c for the hma and 140 o c for the two wmas. the samples were conducted with target air voids (va) of 7 ± 1% according to aashto t166. samples with different sizes were produced as required for mixture testing. different mixture tests were utilized including idt, cml, and hlwt. also, different laboratory conditions were used, including unaged, single, or combined effects of oxidation and moisture as described below. a. laboratory conditioning 1) oxidation conditioning oven condition was conducted according to aashto r30. after the mixture samples were prepared, they were placed in an oven (figure 1) at a temperature of 85 °c for 120 ± 0.5 hours. after the conditioning was completed, the oven was turned off and the samples were allowed to cool down to room temperature. 2) combined effects of oxidation and moisture damage conditioning the specimens were initially vacuum saturated to approximately 80% of va according to aasht t166. they were then temporarily stored in room-temperature water until they were transferred to a pre-heated water bath at 64 o c, as shown in figure 2. the specimens were conditioned in the water bath for 14 days and were then allowed to cool to room temperature. finally, the specimens were transferred to the oven for oxidation conditioning as described above. engineering, technology & applied science research vol. 13, no. 4, 2023, 11119-11123 11121 www.etasr.com bazuhair & alqahtani: an assessment of testing and conditiong protocol to evaluate asphalt mixtures table i. properties of the tested mixtures mixture id m0 m1 m2 pg 64-10 64-10 64-10 bitumen (%) 5.6 5.6 5.6 wma none sasobit rediset lq-1200 dosage none 1.5 % binder 0.5 % binder p25mm (%) 100 100 100 p19.0mm (%) 100 100 100 p12.5mm (%) 92.2 92.2 92.2 p9.5mm (%) 86.8 86.8 86.8 p4.75mm (%) 57.2 57.2 57.2 p2.36mm (%) 38.7 38.7 38.7 p1.18mm (%) 24 24 24 p0.60mm (%) 15.6 15.6 15.6 p0.30mm (%) 10 10 10 p1.5mm (%) 7 7 7 p0.075mm (%) 5.4 5.4 5.4 nmas (mm) 12.5 12.5 12.5 gb 1.0 1.0 1.0 gsb 2.7 2.7 2.7 ps 94.4 94.4 94.4 gse 2.8 2.8 2.8 pg = performance graded, wma = warm mix asphalt, pxxx = percentage passing a xxx mm sieve, nmas = nominal maximum aggregate size, gb = specific gravity of asphalt binder, gsb = bulk specific gravity of aggregates, ps= aggregate percentage, gse = effective specific gravity of aggregates, dp = dust percentage fig. 1. oxidation conditioning. fig. 2. moisture conditioning. b. mixture testing 1) cantabro mass loss (cml) testing the specimen size used for cml is 150 mm in diameter and has a height of 115 mm. the samples were placed in a los angeles (la) abrasion drum for 300 rotations at 25 °c without spheres ball (figure 3). the specimen mass was recorded before and after testing. the percentage of mass loss was calculated by: ml = ����� �� × 100 (1) where ml is the percentage of mass loss , m1 is the specimen's mass before testing, and m2 the specimen's mass after testing. fig. 3. cml equipment. 2) testing indirect tensile (idt) testing idt test was conducted on specimens’ with 150 mm diameter and 95 mm height. the test processor is according to aashto t283, where specimens were loaded at 50 mm/min until they failed at 25 °c (figure 4). equation (2) was used to determine tensile strength (st): s = ���×���� �× ×� (2) where pmax is maximum load (n), t is the specimen's thickness (mm), and d is the specimen's diameter (mm). fig. 4. idt equipment. 3) hamburg loaded wheel tracking (hlwt) testing hlwt was conducted according to aashto t324 standards (figure 5). the specimens' size used for hlwt was 150 mm diameter by 63 mm height. hlwt was performed at 20,000 passes (or failure at 12.5 mm rut depth). rut depth (rdhlwt) measurements were taken at 5000, 10000, 15000, and 20000 passes. the key finding of the current study was rdhlwt at 20,000 passes or fails. the samples were immersed in water at 50 °c for 30 ± 1 minutes before and during testing. engineering, technology & applied science research vol. 13, no. 4, 2023, 11119-11123 11122 www.etasr.com bazuhair & alqahtani: an assessment of testing and conditiong protocol to evaluate asphalt mixtures fig. 5. hlwt equipment. iii. test results and discussion table ii summarizes the testing results for mixture tests. the values for a given test method of cml or idt represent an average of 3 samples (table ii). in hlwt tests, 2 specimens were used (referred to as a set) to represent 1 test value, while an average of 3 sets were used to represent the test value in table ii. hlwt was performed at 20,000 passes or failure at 12.5 mm rut depth, where the pass number at which failure was reached is reported. rut depth of hlwt (rdhlwt) measurements were made at 5000, 10000, 15000, and 20000 passes. table ii. mixture tests results. conditi oning mix cml ml (%) idt st (kpa) hlwt 5k 10k 15k 20k p12.5 lc0 m0 6.1 1415 2.55 6.50 10.62 --1 16462 m1 7.6 1602 2.26 4.12 6.42 --1 19492 m2 6.4 1757 3.85 4.11 8.63 --1 14928 lc1 m0 7.3 1711 1.29 2.38 3.39 4.61 --2 m1 11.1 1835 1.44 4.68 5.60 7.25 --2 m2 8.1 2115 1.45 4.13 7.13 --1 18816 lc2 m0 11.6 1073 6.10 10.4 --1 --1 12693 m1 13.1 995 2.57 3.23 7.19 --1 17435 m2 10.4 1174 7.26 --1 --1 --1 9647 lc0 = unaged, lc1 = oxidation, lc2 = combination of oxidation and moisture, --1 test reached rut depth of 12.5 mm before 20k passes, --2 test reached 20k passes. iv. conditioning effects figure 6 illustrates the comparison between the unconditioned control (lc0), and the two-lc (oxidation and combined effects) conditioning. for instance, each point in figure 6 represents 2 cml test specimens, 1 of which was examined before conditioning (lc0), and the other after conditioning (lc1). hlwt test results are represented by the ratio between the depth and the number of passes. the ratio is calculated by dividing the rut depth value by the number of passes. figure 6 illustrates that if the values are above the equality line in the equality plots, this case indicates higher values measured after conditioning. values below the equality line in the equality plots indicate lower values measured after conditioning, and values on the equality line in the equality plots indicate no property change as a result of conditioning. authors in [19] showed that in an oxidation-dominated environment damage, both ml and st values would rise. moisture and/or freeze-thaw dominated environment would result in an increase in ml but a decrease in st or no change at all. combined environment (oxidation-moisture and/or freezethaw) damage might result in the two damage processes canceling each other for st or increasing the ml value as a result of the severity of the condition. authors in [20] showed that the st values of field cores increase over time until a specific period (around 4 years) and then decrease as the influence of moisture damage [20]. the hlwt test showed that the rut depth of the field cores decreases until a specific period (around 4 years) and then it begins to increase as a result of moisture damage. the ml values of field aging increased over time representing that the asphalt mixture deteriorated over time in service. fig. 6. conditioning effects. figure 6(a)-(b) shows that the ml values are above the equality line. the slope in figure 6(b) is higher than the one in figure 6(a) as the severity of laboratory conditioning increases. the st values are shown in figures 6(c) and (d). they are above the equality line for oxidation damage effects (figure 6(c)). in contrast, the st values are below the equality line in the combined environment effects (figure 6(d)) in accordance with the findings in [15, 16]. the hlwt results in figure 6(e)-(f) showed rut depth value below the equality line for oxidation damage, but above the equality line for combined environment damages, in accordance with [16]. the laboratory testing y = 1,3x 0 8 16 0 8 16 l c 1 lc0 cml a) y = 1.2x 0 1500 3000 0 1500 3000 l c 1 lc0 idt c) y = 0.6x 0 0 .0 0 0 8 0 .0 0 1 6 0 0.0008 0.0016 l c 1 lc0 hlwt e) y = 1,7x 0 8 16 0 8 16 l c 2 lc0 cml b) y = 0.7x 0 1500 3000 0 1500 3000 l c 2 lc0 idt d) y = 1.3x 0 0 .0 0 0 8 0 .0 0 1 6 0 0.0008 0.0016 l c 2 lc0 hlwt f) engineering, technology & applied science research vol. 13, no. 4, 2023, 11119-11123 11123 www.etasr.com bazuhair & alqahtani: an assessment of testing and conditiong protocol to evaluate asphalt mixtures results represented in figure 6 confirm previous laboratory and field studies. the combined environment effects condition is more severe than single environment effects (i.e. oxidation or moisture). the effects of oxidation would damage the asphalt mixture in the early life cycle while moisture would influence the asphalt mixture in the long term. v. conclusions this paper investigates the property measurements themselves and how a mixture test can simultaneously assess multiple types of damage, such as damage from oxidation and moisture. the laboratory results demonstrated in this study confirm other laboratory and field studies. the study concluded that laboratory conditioning of the combined effects of oxidation and moisture simulates better the asphalt damage in service than laboratory single environment effect conditioning. to predict or simulate the asphalt mixture damages and performance in service utilizing laboratory combined environment effects conditioning protocols, cml tests would be recommended to evaluate and capture these combined environment effects damage. acknowledgment pan kingdom real estate sapak produced the mixtures. nouryon provided warm mix additive materials. saudi arabia ministry of transport and logistic services facilitated the process of conducting laboratory experiments. individuals deserving special thanks include al-abbas bin ahmed alhazmi, ayman al-howitan, motaz bashiti, and hassan al naqib. references [1] c. a. bell, "summary report on aging of asphalt-aggregate systems," oregon state university, corvallis, or, usa, summary report srosu-a-003a-89-2, 1989. [2] c. a. bell, y. abwahab, m. e. cristi, and d. sosnovske, "selection of laboratory aging procedures for asphalt-aggregate mixtures," national research council, washington, dc, usa, shrp-a-383, 1994. [3] c. a. bell, a. j. wieder, and m. j. fellin, "laboratory aging of asphaltaggregate mixtures: field validation," national research council, washington, dc, usa, shrp-a-390, 1994. [4] l. garcia cucalon, e. kassem, d. n. little, and e. masad, "fundamental evaluation of moisture damage in warm-mix asphalts," road materials and pavement design, vol. 18, no. sup1, pp. 258–283, jan. 2017, https://doi.org/10.1080/14680629.2016.1266765. [5] s. d. diefenderfer and a. hearon, "laboratory evaluation of a warm asphalt technology for use in virginia.," virginia transportation research council, charlottesville, va, usa, fhwa/vtrc 09-r11, 2008. 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[15] h. m. alnaqib and r. w. bazuhair, "evaluation of hma modified with titan polymer," engineering, technology & applied science research, vol. 13, no. 3, pp. 10725–10730, 2023, https://doi.org/10.48084/ etasr.5856. [16] h. m. a. a. kareem and a. h. k. albayati, "the possibility of minimizing rutting distress in asphalt concrete wearing course," engineering, technology & applied science research, vol. 12, no. 1, pp. 8063–8074, feb. 2022, https://doi.org/10.48084/etasr.4669. [17] s. s. almasoudi and a. h. k. albayati, "statistical analysis of component deviation from job mix formula in hot mix asphalt," engineering, technology & applied science research, vol. 12, no. 5, pp. 9295–9301, oct. 2022, https://doi.org/10.48084/etasr.5225. 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[20] r. w. bazuhair, i. l. howard, a. middleton, w. s. jordan, and b. c. cox, "combined effects of oxidation, moisture, and freeze–thaw on asphalt mixtures," transportation research record, vol. 2674, no. 12, pp. 409–424, dec. 2020, https://doi.org/10.1177/0361198120954190. microsoft word selvam-ed.doc etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 278-280 278 www.etasr.com selvam and latha: a novel voltage divider circuit a novel voltage divider circuit k. c. selvam department of electrical engineering indian institute of technology, madras chennai – 600 036, india kcselvam@ee.iitm.ac.in s. latha department of electrical engineering indian institute of technology, madras chennai – 600 036, india latha@ee.iitm.ac.in abstract  a novel analog divider is described in this paper. the circuit enables the division of a dc voltage with another dc voltage. the constant of the division is dependent upon a third dc voltage and a pair of resistors. employing a precision source for the third dc voltage and matched resistors, an acceptable level of accuracy can be obtained. keywords-sawtooth wave; integrator; comparator; analog switches; divider i. introduction a common need arises for taking the ratio of two analog voltages, in many instrumentation and control applications. this operation is usually performed by a log-antilog network configuration [1]. an alternative method that has been proposed in the past is based on fet [2, 3]. the fact that a fet can be used as a voltage dependent resistor, albeit within restricted gate-to-source voltage limits, is exploited in this method. hence, this method is useful only for small voltage levels. a different approach is to convert the input voltages to equivalent frequencies [4], take the ratio of two frequencies using conventional digital techniques, and then produce an output voltage proportional to the period of the ratio-metric signal. this method is applicable only when the numerator voltage varies within a small specified range of values. s. i. liu and j. j. chen developed a scheme [5] in which the analog division was performed with two current feedback op amps, one resistor and two mosfets. n. i. khachab and m. ismail developed another scheme [6] by using one op amp and eight mosfets. carlos a. de la cruz blas and antonio lopez developed a scheme [7] which is based on a cmos translinear loop using a novel biasing scheme that allows class–ab operation. munir a. al – absi proposed a circuit [8] which consists of four mosfets biased in weak inversion. a novel circuit for analog division using only op amps and switches is described in this paper. a feedback amplifier performs the analog division with a two-quadrant multiplier in the feedback path. hence the divider thus obtained is a twoquadrant divider. the proposed analog divider has a better performance, even when the numerator voltage varies over a wide range. ii. circuit analysis the circuit diagram of the proposed analog divider is shown in figure 1. a sawtooth wave is generated by charging a capacitor at a specified rate and then rapidly discharging it with a switch. the sawtooth wave, marked as vs in figure 1, of peak value vr is generated by op amps oa1, oa2 and a switch s1. let us assume that at start, the charge and, hence, the voltage at the output terminal of oa1 is zero. since the inverting terminal of oa1 is at virtual ground, the current through r1, namely vr/r1 amps, would flow through and charge the capacitor c1. during the charging of the capacitor (till the output of oa1 reaches the voltage level of vr) the output of oa2, configured to work as comparator, will be at the low state and switch s1 is kept open (off). as soon as the output of oa1 crosses the level of vr, say after a time period t, the output of comparator oa2 goes high and the switch s1 is closed (on). the switch s1 would then short the capacitor c1 and hence vs would drop to zero volts. during the time period t we have: 1 1 vr vs vrdt t r c = =∫ (1) after a very short delay time td, required for the capacitor to discharge to zero volts, the comparator output returns to low and switch s1 is opened, thus allowing c1 to resume charging. this cycle, therefore, repeats itself at a period (t+td). the waveforms at cardinal points in the circuit of figure 1 are shown in figure 2. from (1) and the fact that at time t=t, vs=vr, we get t=r1c1. oa3, configured to work as comparator, compares the generated sawtooth voltage to the input voltage v1. the output of oa3 would be high (voltage level of +vcc, being the supply voltage) till the sawtooth waveform vs reaches the value v1 and thereafter low within the period t+td. the output of oa3 is also indicated in figure 2 as a pulse train vm. the on time, ton, of this pulse train will be: 1 1 1 1 v v ton t r c vr vr = = (2) etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 278-280 279 www.etasr.com selvam and latha: a novel voltage divider circuit gnd gnd -vr -v2 v1 vo gnd +vr r2 + oa 2 vc s1 r1 + oa 1 c1 c2 s2 + oa 4 + oa 3 r3 i1 r4 i2j + oa 5 r5 vo = v2 v1 __ vr vm vr v1.vo vk _____ vl = vs fig. 1. circuit diagram of proposed analog divider fig. 2. associated waveforms of figure 1 this pulse train controls switch s2. the output of the switch would be a pulse train vk having ton as its on time and amplitude of vo. the output of s2 is given to a low pass filter realized by r2, c2 and oa4. this low pass filter extracts the average voltage of the output of switch s2. the output of oa4 will be: 0 1 ton vl vodt t = ∫ , 1vo v vo vl ton t vr = = (3) here, the integration is done over a period t, but the actual period is (t+td). since t>>td, the error introduced by the approximation would be negligibly small. oa5 sums up the output voltage of oa4 and the second input to the divider, namely, -v2. as shown in figure 1, no input signal current can flow into the inverting terminal of oa5 which is at virtual ground. therefore, at the junction ‘j’, i1=i2, where i1=vl/r3 and i2=v2/r4. if r3=r4 and r5>>r3, then vl=v2 1 2 v vo v vr = , 2 1 v vo vr v = (4) iii. experimental results to check the practical feasibility, the proposed circuit shown in figure 1 was assembled with the following components values: all op amps=op 07 ics. switches s1 and s2 are realized with ic cd4053. r1=200k, c1=470pf, r2=20k, c2=100uf, r3=r4=10k and r5 = 2.2m. first the divisors, namely, the input voltage v1 as well as vr, are fixed and the numerator voltage is varied from zero to full scale. the output was measured and compared with the expected values. the results obtained are given in table i. then the numerator voltage v1 is set and the divisor voltage v2 is varied from zero to full scale and the results are tabulated in table ii. as expected, when the denominator voltage kept at zero, the output vo was at the saturation level. the results indicate practical usefulness of the proposed divider for instrumentation and control applications. it is observed that the accuracy obtained is very much dependent on the t t td t on1 td t on1 v1 vr +vcc +vcc -vcc vo output of integrator oa1 vs output of comparator oa2 vc output of comparator oa3 vm output of switch s2 vk 0 etasr engineering, technology & applied science research vol. 2, no. 5, 2012, 278-280 280 www.etasr.com selvam and latha: a novel voltage divider circuit linearity and sharpness of the sawtooth waveform. offset voltage of all op amps will appear as an error at the output, hence offset should be eliminated by a suitable circuitry. table i. test results for v1=vr = 6v sl no v2 vo volts practical vo volts calculated error % 1 0.556 0.554 0.556 -0.36 2 1.503 1.505 1.503 0.13 3 2.514 2.513 2.514 -0.04 4 3.501 3.500 3.501 -0.03 5 4.506 4.508 4.506 0.04 6 6.012 6.006 6.012 -0.10 table ii. test results for v2=0.43v, vr = 3.915v sl no v1 vo volts practical vo volts calculated error % 1 0.306 5.490 5.501 0.2 2 1.002 1.673 1.680 -0.42 3 2.003 0.840 0.840 0 4 3.004 0.562 0.560 0.29 5 3.505 0.482 0.480 0.41 6 3.910 0.432 0.430 0.47 acknowledgement the authors are highly indebted to prof. dr. enakshi bhattacharys, prof. dr. v. jagadeesh kumar and dr. bharath bhikkaji, electrical engineering department, iit madras for their constant encouragement throughout the work. they also thank mr. mithun for proofreading the manuscript. references [1] j. g. graeme, applications of op amps: third generation techniques, mcgraw hill, 1973 [2] d. ghosh, d. patranabis, “a simple analog divider having independent control of sensitivity and design conditions”, ieee transactions on instrumentation and measurement, vol. 39, no. 3, pp. 522-526, 1990 [3] g. han, e. sanchez-sinencio, “cmos transconductance multipliers; a tutorial”. ieee transactions on circuits and systems ii: analog and digital signal processing, vol. 45, no. 12, pp. 1550-1563, 1998 [4] t. l. laopoulos, c. a. karybakas, “a simple analog division scheme”, ieee transactions on instrumentation and measurement, vol. 40, no. 4, pp. 779-782, 1991 [5] s. -i. liu, j. -j. chen, “realisation of analog divider using current feedback amplifiers”, iee proceedings circuits devices systems, vol. 142, no. 1, pp. 45-48, 1995 [6] n. i. khachab, m. ismail, “mos multiplier/divider cell for analog vlsi”, electronic letters, vol. 25, no. 23, pp. 1550-1552, 1989 [7] c. a. de la blas, a. lopez, “a novel two quadrant mos translinear squarer-divider cell”, ieee international conference on electronics, circuits and systems, pp. 5-8, 2008 [8] munir a. al – absi, “ low-voltage and low–power cmos currentmode divider and 1/x circuit”, ieee international conference on electronic devices, systems and applications (icedsa), pp. 245– 247, 2010 authors profile k.c. selvam was born on 2 nd april 1968 in the krishnagiri district of the tamil nadu state, india. he graduated from the institution of electronics and telecommunication engineers, new delhi, in 1994. he got the best paper award by iete in 1996. at present he is working as technical staff at the department of electrical engineering, indian institute of technology, madras, india. his research interests include measurement and instrumentation systems. s. latha was born on 21 july 1967 in the vilupuram district of the tamil nadu state, india. she obtained a diploma in electronics and communication engineering from the periyar century polytechnic college, vallam, thanjavoor, tamil nadu, india in 1985. at present she is working as technical staff in the department of electrical engineering, indian institute of technology, madras, india. her research interests include microcontroller based digital measuring instruments. microsoft word etasr_v11_n1_pp6740-6744 engineering, technology & applied science research vol. 11, no. 1, 2021, 6740-6744 6740 www.etasr.com belkham et al.: elaboration and physico-chemical characterization of the gibbsite li(oh)3 hybrid … elaboration and physico-chemical characterization of the gibbsite li(oh)3 hybrid material nour-el-houda belkham department of chemical engineering lmpmp laboratory ferhat abbas sétif i university sétif, algeria anisbelkham2002@yahoo.fr djafer benachour department of chemical engineering lmpmp laboratory ferhat abbas sétif i university sétif, algeria bendjafer@univ-setif.dz abedaziz mehamha center of mineral technology and plasturgy quebec, canada amehamha@cegepth.qc.ca abstract-a hybrid material can be defined as a combination of two components of different chemical nature. the combination of a mineral matrix and organic matter has multiple significance. from a chemical point of view, it allows the obtaining of bifunctional materials that combine the chemical properties of their components. the development of new materials with specific properties and nanostructured lamellar double hydroxides (ldhs) has been widely investigated due to their great importance. this study focuses on the development of a hybrid material consisting of a matrix of alumina trihydrate al(oh)3 (gibbsite). previous studies on the synthesis of suspension ldhs by lithium salts intercalation in a gibbsite matrix were examined, while the obtained samples were characterized by different physicochemical methods. keywords-alumina; inorganic compounds; gibbsite; lithiumsalts intercalation; lamellar double hydroxide components i. introduction nanotechnology has been used for synthesizing various polymer nanocomposites and examining their physical and chemical properties [1-3]. the presence of nanoparticles in polymers improves their mechanical, electrical, and chemical properties as it results in bi-functional materials that combine the chemical properties of their components. layered double hydroxides (ldhs) have attracted considerable interest due to their potential applications as selective sorbent medicines [4, 5], precursors for ceramics [6], and nanocomposite materials [7, 8]. crystalline aluminum hydroxides, such as gibbsite, bayerite, and nordstrandite, exhibit properties of intercalation matrices for lithium salts [9-12]. the reaction between aluminum hydroxides and lithium salts is represented by: linx + 2n al(oh)3 + qh2o → �lial2(oh)6]n x.qh2o the most remarkable synthetic procedure is the direct intercalation of lithium salts into crystalline al(oh)3 polymorphs [13, 14]. intercalation of inorganic or organic ions into gibbsite matrices is used for creating li/al ldhs [15-17]. gibbsite is intercalated with lithium cations obtained from various lithium salts, which dehydrate readily giving highly crystalline intercalates. these crystal structures display highly ordered lamellar phases consisting of eclipsed [lial2(oh)6]+ sheets with sandwichlike layers of intercalated anions [17]. li and al-x can be prepared using different synthetic approaches. the products are obtained by the intercalation of lithium cations into the octahedral voids of aluminum hydroxide layers of trihydroxides, having anions and water molecules incorporated between the layers [18]. the compounds consist of layers with [lial2(oh)6]+. xn-anions of [lial2(oh)6]nx or xn-anions and water of [lial2(oh)6]nx.qh2o are located between the layers. therefore a structural study of these intercalation compounds and their synthesis mechanisms is very interesting from both theoretical and practical viewpoints. this study investigates the physicochemical properties of the intercalation of lithium cations and inorganic anions (cl-, no3-) from [lial2(oh)6]nx.qh2o, where x=cl-, no3-, into gibbsite al(oh)3, to examine the structural mechanism leading to the double hydroxide lamellar intercalated compounds. the obtained phases were examined by x-ray diffraction (xrd), infrared spectroscopy (ftir), thermogravimetric analysis (tg/dta), and microscopic (sem) techniques. the results of this paper confirm that the li–al ldh synthesized by this protocol can be compared with the work already published in the synthesis of double lamellar hydroxides [1, 9]. in order to have a good reinforcement between the load and the matrix (already mentioned at the beginning of the introduction), this requires interactions between the organic and inorganic phases. such results open up a new route for the synthesis of nanocomposites using polymeric entities and layered materials [3]. ii. materials and methods a. materials the alumina trihydrate (gibbsite) al(oh)3 powder was supplied by diprochim in algeria, and its chemical composition was defined by the volumetric method. this powder consisted of 61.31% al2o3, 0.64% sio2, 2.42% cao, 0.30% mgo, 0.16% fe2o3, and up to 34% water. the average particle size of this powder was 15µm, with a density of about 3.106g/cm3. two fatty acids were used: palmitic acid c16h32o2 and stearic acid c18h36o2, which had molecular weights of 256.43g/mol and 284.49g/mol respectively. corresponding author: nour-el-houda belkham engineering, technology & applied science research vol. 11, no. 1, 2021, 6740-6744 6741 www.etasr.com belkham et al.: elaboration and physico-chemical characterization of the gibbsite li(oh)3 hybrid … b. synthesis of [lial2(oh)6]nx.qh2o the layered double hydroxide [lial2(oh)6]nx.qh2o was synthesized using the previously reported method [11, 13, 17, 19]. in a standard experiment, the intercalation was achieved by stirring a suspension of gibbsite in an aqueous solution containing a 6-fold molar excess of lithium salts (licl, libr, or lino3) at 90°c for 15h, as shown in figure 1. samples were washed with 5-10ml of deionized water and then dried in an oven at 90°c for 1-2h to give samples of idealized composition. fig. 1. experimental setup of the gibbsite synthesis by lithium salt: 1: hotplate, 2: synthesis balloon, 3: refrigerant, 4: nitrogen gas balloon, 5: sample after filtration. c. anion exchange reactions the intercalated fatty acids were stuffed as follows: 7 moles of [lial2(oh)6]n2ox.qh were added to 4-fold excess of stearic or palmitic acid. the mixture was stirred for 48h at room temperature in a nitrogen atmosphere. after hustle and bustle, the product was isolated by filtration, washed with deionized water, and dried in an oven at room temperature for 48h. d. characterization the layered double hydroxide [lial2(oh)6]nx.qh2o was examined in a siemens d5000 x-ray diffractometer, equipped with a graphite monochromator placed between the sample and the detector. the x-ray source was a copper anticathode (λcukα1 = 1.5406å), while the beam divergence was limited to 0.2°. the diffractograms were recorded between 2° and 70° (90° in some cases) 2θ, using an impact of 2° for mounting in grazing incidence. the infrared spectrum was examined using a nicolet 5700 spectrometer, employing kbr technical dilution (1.5% w/w) on a range of 400-4000cm with a resolution of 2cm. thermogravimetric analysis was carried out on a setaram tg dta 85, from 20 to 850°c with a heating rate of 5°c/min. microscopic studies were carried out with an e3 electroscan sem at 10 to 30kv, which allowed a magnification up to 30,000 times. iii. results and discussion a. x-ray diffractograms of hybrid materials figure 2 shows the intensity/angle graph for raw and calcinated materials. the raw alumina spectrum has two major peaks at 19° and 21°, corresponding to the combination of gibbsite and bayerite phases. the other peaks correspond to structures and monohydrate forms. the calcinated at 300°c material has lower peaks. this is supposed to be the result of smaller crystallite domain sizes due to the stacking disorder of aluminum hydroxide layers. the diffractograms of the gibbsite products, which came from lithium salts intercalation, showed new reflections differing from those of the crystalline gibbsite. figure 3 represents the x-ray diffractograms of the licl salt intercalation in the al(oh)3 structure. the possibility for gibbsite to react with lithium salts has been shown individually [20]. the components' intercalation depended on the al(oh)3 dispersion and the nature of lithium chloride, while it was also limited by the diffusion rate of a layer of the obtained lithium chloride. among the studied lithium halides, licl was more reactive with al(oh)3. this halide showed intercalation between licl and al(oh)3. the peak at about 14° after 15h reaction indicates that gibbsite was transformed into ldh. these reflections of ldh were in agreement with those reported in [17, 21-22]. lithium cations were located in the octahedral voids of the aluminum hydroxide layer. fig. 2. x-ray diffraction (xrd) of crystalline gibbsite and gibbsite calcined at 300°c. fig. 3. x-ray diffraction (xrd) of crystalline gibbsite, gibbsite intercaled by licl, and anionic exchange precursor with fatty acids (stearic acid). engineering, technology & applied science research vol. 11, no. 1, 2021, 6740-6744 6742 www.etasr.com belkham et al.: elaboration and physico-chemical characterization of the gibbsite li(oh)3 hybrid … the chloride anions are opposite to lithium cations, at exactly the midway between the interlayer spaces, in such a way that they are partially lied in the holes of hydroxide ions of the layers. the x-ray diffractograms contained intense reflections with multiple interplanar distances, indicating that the structure of the products was lamellar. analogous studies were performed for [lia12(oh)6]brand [liai2(oh)6]no3-. treatment results of [liai2(oh)6]brand [liai2(oh)6]no3 precursors were similar to those of [liai2(oh)6]c1-. b. thermogravimetric analysis figure 4 shows the differential thermal analysis (dta) thermogram for a gibbsite specimen. as it can be observed, the gibbsite loses most of its structural water by thermal dehydration above 279.23°c with a weight of about 30%. furthermore, the tg-dta curve gradually varies with increasing temperature, indicating that the gibbsite structure changes continually upon heating. this change led to the formation of several transition alumina phases that are alumina of crystallographic structure intermediates between hydrate and alumina α [23, 24]. fig. 4. tg/dta curves of raw gibbsite. the thermal stability of the lithium salt intercalated into gibbsite noted as compounds [lial2(oh)6]x where x={cl, br, no3} was examined by tg/dta measurements between 100800°c, and these results are depicted in figure 5. fig. 5. tga and dtg curves of [lial2(oh)6]cl.h2o precursor. the tg/dta curves exhibit two temperature range regions at 100-300°c and 300-600°c. the tg curve shows that the major weight loss occurred below 300°c. a weight loss of 25% below 250°c happened probably due to the loss of water from the external surface. this weight loss is indicated by the two sharp endothermic peaks seen in the dta curve at 207.78°c and 250.85°c respectively. the second loss of 15% in temperatures between 300 and 600°c was attributed to the interlamellar water molecule and dehydroxylation of metal hydroxide layers [25]. [lial2(oh)6]br.h2o and [lial2(oh)6]no3.h2o samples showed the same trends during the thermal analysis with an almost identical weight loss rate [26]. c. infrared spectroscopy (ftir) all reactions were carried out in a closed reaction vessel with continuous n2 purging. under such conditions, co2 likely does not dissolve into the samples. the ir spectra of the lix/al(oh)3 ldh, as depicted in figure 6, show no co3 characteristics at ∼1400cm−1, indicating no contamination by dissolved carbonate from the air during its synthesis. the ir spectra show the bands of stretching vibrations of oh groups, deformation vibrations of al-oh and water molecules, and stretching vibrations of the al-o bond of the [lial2(oh)6]x ldh [27]. the absorption bands that appear at the 500cm-1 range are attributed to a1-o bond deformation, and a wide strip of binding oh water appears at 3500cm-1. moreover, some bands, especially those observed around 1150cm-1, are identifiable. fig. 6. ir spectra of rough gibbsite and gibbsite intercalated by licl salt. figure 7 shows a band between 3550cm-1 and 3300cm-1, which is attributed to the oh bond elongation. a band appearing at 1650cm-1 corresponds to the oh bond deformation, and the one at 750cm-1 corresponds to the al-oh bond deformation. figure 8 shows the ir spectra of lial2(oh)6]br.h2o, [lial2(oh)6]no3.h2o, and the ldhs exchanged by fatty acids, which were similar. in these spectra, the difference in the intensity decreases. further bands were found at 2920cm-1 corresponding to the c—h bond with asymmetric elongation, at 2850cm-1 corresponding to the c—h symmetric stretching bond, and at 1720cm-1 and 1190cm-1 corresponding to the c=o and the c-o bonds. this analysis revealed the presence of all the characteristic vibration modes engineering, technology & applied science research vol. 11, no. 1, 2021, 6740-6744 6743 www.etasr.com belkham et al.: elaboration and physico-chemical characterization of the gibbsite li(oh)3 hybrid … of the double lamellar hydroxide. furthermore, the absorption bands observed at 3500cm-1 and 1600cm-1 were attributed to hydroxylated layers of the [li-al-cl] ldh vibration modes in the ir spectrum of intercalated ldh, confirming the lix intercalation into the gibbsite. fig. 7. ir spectra of gibbsite intercalated by salt and exchanged by stearic acid. fig. 8. ir spectra of gibbsite intercaled by br, no3 salts and exchanged by stearic and palmitic acid. d. scanning electron microscopy (sem) figure 9 shows images obtained by sem for various raw and synthesized materials to obtain an hdl gibbsite, revealing a difference in their particle morphology. the second loss of 15% in temperatures between 300-600°c is attributed to the interlamellar water molecule and dehydroxylation of metal hydroxide layers [25]. [lial2(oh)6]br.h2o and [lial2(oh)6]no3.h2o samples showed the same trends during the thermal analysis with an almost identical weight loss rate [26]. iv. conclusion this study aimed at the synthesis and the characterization of a gibbsite based double lamellar hydroxide filler, using several characterization techniques (xrd, atg/atd, ftir, and sem). the ftir spectra confirmed the penetration of molecules within these matrices. new absorption bands appeared for the investigated materials, including synthesized and exchanged samples, following the disappearance of the characteristic bands, and a decrease in the absorbance of the corresponding peaks. moreover, the thermogravimetric analysis (tg/dta) proved the high thermal stability of all materials. their calcination at high temperatures resulted only in their dehydration, thus creating several transition phases. the gibbsite seems to intercalate certain lithium salts, while halogen anions intercalate within the gibbsite structure. the crystalline structure indicated that these materials showed lamellar intercalation of [lial2(oh)6]+ cations. the main contribution of the current research is the elaboration of a mineral ceramic by incorporating a fatty acid between its layers, thus facilitating the ceramic-polymer interaction. 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[27] a. j. jacobson, "intercalation reactions of layered compounds," in solid state chemistry, vol. 2: compounds, oxford, new york: oxford university press, 1992, art. no. 182. microsoft word 22-3769_s_etasr_v10_n5_pp6264-6269 engineering, technology & applied science research vol. 10, no. 5, 2020, 6264-6269 6264 www.etasr.com pathan et al.: a robust frequency controller based on linear matrix inequality for a parallel islanded … a robust frequency controller based on linear matrix inequality for a parallel islanded microgrid erum pathan department of electrical power engineering faculty of electrical and electronic engineering university tun hussein onn malaysia johor, malaysia erumasad79@gmail.com shamsul aizam zulkifi department of electrical power engineering faculty of electrical and electronic engineering university tun hussein onn malaysia johor, malaysia aizam@uthm.edu.my haider arshad department of electrical power engineering faculty of electrical and electronic engineering university tun hussein onn malaysia johor, malaysia haiderarshadkhan@gmail.com afarulrazi abu bakar department of electrical power engineering faculty of electrical and electronic engineering university tun hussein onn malaysia johor, malaysia afarul@uthm.edu.my mubashir hayat khan department of electrical power engineering faculty of electrical and electronic engineering university tun hussein onn malaysia johor, malaysia mubashir.uthm@gmail.com muhammad asad substation automation engineer ng csd-c saudi electricity company riyadh, saudia arabia csd_sec@yahoo.com abstract-this paper presents a robust h ∞ control technique for an islanded microgrid in the presence of sudden changes in load conditions. the proposed microgrid scheme consists of a parallel connected inverter with distributed generations. when the load is suddenly changed the frequency deviates from its nominal value. the objective is to design a robust frequency droop controller in order to achieve the frequency at nominal values without using any secondary controller and communication systems while improving power sharing accuracy. small signal modeling of the power system is designed for the formulation of the problem and the h ∞ optimal linear matrix inequality technique is applied in order to achieve the objectives. the proposed controller has been tested with the matlab/ simpowersytem toolbox. keywords-distributed energy resource; linear matrix inequality (lmi) units; robust control i. introduction conventional power systems change as a consequence of the rising fuel cost and global warming. distributed generation (dg) sources are being incorporated to overcome the aforementioned issues. moreover, modern power systems provide increased reliability and alleviate the pressure on power transmission. a cluster of interconnected dgs is known as a microgrid (mg). the mg has been proposed to integrate dgs to the local loads. its primary function is to facilitate the penetration of dgs, and thus enhance the persistence of power supply [1, 2]. the nature of the connected load may be different. it may be of critical or non-critical in nature. however, in any load conditions, the dgs need power converter mechanisms. consequently, inverters and converters are adapted to connect the dgs to the mg. an mg can be operated in grid-connected or islanded mode to provide reliability and power quality. when a mg is operated in gridconnected mode, at the time of operation the voltage and frequency are fixed by the stiff grid and the dc/ac inverters are connected in parallel to the utility grid, whereas in islanded mode, multiple parallel dgs are required to stabilize voltage and frequency [3]. voltage and frequency deviation (from nominal values) because of the mismatch between load and generation may lead to complete failure of the mg. so, a robust control strategy is necessary to be taken into account to resolve this control objective in stand-alone operation [4, 5]. a sudden load change will affect the power sharing between two parallel inverters, and the voltage amplitude and frequency will deviate from their nominal values. in order to avoid this problem, a secondary controller has been proposed to restore such deviations. however, the secondary controller fails the concept of distributed power sharing control whereas the communication also needs to be set up. this communication will increase the cost of operation and the complexity of the system while it will reduce reliability and flexibility. also, such corresponding author: erum pathan engineering, technology & applied science research vol. 10, no. 5, 2020, 6264-6269 6265 www.etasr.com pathan et al.: a robust frequency controller based on linear matrix inequality for a parallel islanded … a system is not easily expanded in remote areas [4, 6]. in order to ensure system’s stability and performance, the robust h∞ control theory is mostly applied to synthesize a h∞ controller by using linear matrix inequality (lmi) technique. it is a robust theoretical powerful tool that can be used directly in finding the optimal solution and therefore reducing the impact of disturbances. the weighted functions are designed properly so they optimally set up the trade-off between robustness and performance in feedback loop. several methods have been applied in order to resolve the mg frequency control issue [7, 8]. controlling of frequency deviation has been studied with the help of techniques such as neural networks, fuzzy logic, and particle swarm optimization (pso) [9]. in the presence of uncertainties, the performance and robustness has also been enhanced by combined pso-based h2/h ∞ [10]. in the traditional techniques the frequency deviation cannot be stabilized in islanded mode when the load is changed. however, the robust control techniques provide effective control synthesis while considering uncertainties and physical constraints [11]. some researchers have also studied robust control systems for mgs. distributed robust controllers have been designed for different renewable sources in islanded mode in [12]. a µ-synthesis robust controller has been designed through iteration technique in [13]. other µ-synthesis robust controller techniques have been discussed in [14] and the h∞ robust controller in [15]. the main contribution of this paper is the proposal of an advanced, control theory-based, robust, h∞, power sharing, non-communication based, controller that restores frequency and improves the accuracy of power sharing, is easy to install, and more reliable without using the secondary existing controller. ii. conventioanl primary, existing secondary and proposed robust h ∞ power sharing controller in islanded mode the first mg layer for control purpose is the primary control, which consists of a combination of the cascaded voltage-current and power sharing controller as given in figure 1. the cascaded controller is for controlling the inner current controller’s signal li and getting the reference signal from the outer voltage controller. the outer voltage controller’s signal is from the cf of the ac mg system, which can obtain the voltage reference from the frequency signal and the amplitude signal by the power controller. the grid-side inverter current and voltage of the filter capacitor are determined to calculate the average power supplied by each distributed power inverter. the power sharing controller can be implemented for calculating the reference voltage and frequency. hence, the power sharing controller uses the non-communication power sharing control technique. the power sharing controller comprises of two equations. one of them is the p-ω equation, which gives the relationship between the dg active power and the pcc frequency level. in power sharing technique, frequency deviations occur when the mg is operated in islanded mode since frequency is dependent on the connected load. therefore, a secondary control layer is used to compensate the frequency deviation issue of the power sharing strategy. the secondary controller transfers the signal of frequency ωsec, which adds offsets to the primary controller through the communication links, as illustrated in figure 1. a synchronous reference frame phase lock loop is implemented to the secondary controller. the basic concept is that the frequency of the output voltage is a global variable in the mg, hence, by controlling the reference angle which extracts the frequency from the pcc, the signal is fed back and compared to the reference signal ω* to generate the error which must be reset by the secondary controller. the delay block is modelled with a 10ms low-pass filter. the point of common coupling voltage and frequency are regulated by the secondary control layer. the proposed h∞ controller is shown with the blue-dashed area in figure 1, where the robust power sharing controller considers the mg frequency and active power. there are two primary problem formulations in this study, which are: • the frequency deviation when the load is suddenly changed, without applying a hierarchical secondary-level communication-based controller. • the accuracy of active power sharing according to dg’s rating. iabc l iabc r gabcl gabcr oabc v pccv labc i oabc v oabc i , , , mg mg mg mg v p qω vsi dc decentralized robust h∞ controller iabc l iabc r gabcl gabcr oabc v labc i oabc v oabc i , , , mg mg mg mg v p qω vsi dc load_1 load_2 s1 s2 ω∗ p&q calcu. i qip v ∗ direct park transf. decentralize d robust h∞ controller cascaded controller inverspark transf odq v ldq i odq v labc i oabc voabci odq v odq i ʃ * idq v iabc v , , , mg mg mg mg v p qω proposed decentralized robust h∞ controller decentralized robust h∞ controller fig. 1. block diagram of the conventional primary controller, existing hierarchical secondary controller, and proposed robust h∞ decentralized power sharing controller. iii. proposed controller via lmi optimisation the standard robust h∞ power sharing controller is configured to achieve the accuracy of power sharing and no frequency deviation. a systematic design procedure is adopted for designing the controller. open-loop block diagram can be engineering, technology & applied science research vol. 10, no. 5, 2020, 6264-6269 6266 www.etasr.com pathan et al.: a robust frequency controller based on linear matrix inequality for a parallel islanded … formulated into a standard configuration by using linear fractional transformation (lft) [15, 16] and building an augmented system model. the complete virtual augmented system model with exogenous input, output, sensed signal, and control signal is illustrated in figure 2, where g(s) is the nominal plant, u is the input of the system control vector and v is the sensed output of the controller that needs to be minimized. ω=[ωo ωmg pmg] t represents a vector of exogenous inputs such as reference signals and disturbances. the external disturbances are unknown, thus they need to be minimized in order to improve the performance specification of the system. ∆z=[z1 z2] t represents the regulated output signals and the [w1 w2] weighted functions are used to shape the control input and achieve good tracking performance. k is the conventional power sharing controller. the goal is to minimize the h∞ norm of the transfer function ∆ω→∆z and replace the conventional power sharing controller with a robust h∞ controller. the main function of the implemented robust h∞ controller is to collect the information from ∆v and generate the control signal ∆u, which antagonizes the influence of ∆ω→∆z, which in turn minimizes the norm from ∆ω→∆z. g(s) controller k(s) 2w 1w augmented plant 1 2 z z z  ∆  i mg mgp ω ω ω ∆ −∆ ∆  ∆ v∆u∆ h ∞ fig. 2. augmented plant. the h∞ controller is h∞(s)=[k(s)]. the linear fractional representation of the overall system is represented in (1): 1 1 2 2 2 2 0 0 0 0 o mg mg z w i z w g w g w g p v hg hg i hg u ω ω              −     =            −       � � � � � � � � � � (1) the control object of p is augmented by the nominal plant with the norm of weighted functions w1, w2 via applying matlab’s hinfsyn and mixsyn algorithms. the robust power sharing controller is based on a lower bandwidth than the inner cascaded controller. therefore, a low-pass butterworth filter at 20hz is chosen for w2 to minimize the sensitivity of frequency, and the control effort can be assured to be within the saturation limits. a weighted function w1, which is the integral gain constant with the diagonal matrix, is chosen. the diagonal values of the matrix are the inverse of the active power dc gain, which adjusts the power set-point of the voltage source inverters in order to minimize the sensitivity of the active power. the input sensitivity is w2=(0.09*f), where f is the second-order discrete butterworth low-pass filter with a cut-off frequency of 20hz. if the range of the frequency is different, the sensitivity and the complementary sensitivity cannot meet the h∞ constraint and system’s response will not be properly stable. the reduced design of the h∞ controller is given as: 3 2 4 3 2 0.0001783 s + 0.1508 s + 59.56 s + 9938 ( ) s + 4.537e05s + 1.029e11 s + 1.168e16 s + 4.029e18 k s = (2) the closed-loop transfer function is represented (3) by lft: ( ) ( ) ( ) ( ) ( ) 1 11 12 22 21 )(zt p s p s k s i p s k s p sω −  = − + (3) the controller k(s) can be chosen by applying h∞ optimal control problems. the main purpose of designing the robust h∞ controller is to minimize the h∞ norm, which is represented as ║tωz║ ∞<1. equation (2) is developed in matlab environment and normhinf was used to calculate the stability of the closed-loop system. the resulting ║tωz║ ∞ is 0.654, which ensures that the closed-loop system is stable. iv. simulation and discussion a model with two parallel dg-based mgs in islanded mode is built in matlab/simulink (figure 3). during the switching from low to medium loads (resistive), time domain response of current and voltage at the point of common coupling, power sharing of mg, voltage, and frequency are analyzed in order to check the effectiveness of the proposed robust h∞ power sharing controller over the secondary hierarchical controller and the conventional decentralized primary power sharing controller. in table i the parameters of the parallel inverter ac mg and the controller can be seen along with the load ratings and switch on-off times. table i. parallel inverter ac mg, controller parameters and load ratings with switch on-off times parameters values parameters values ri=rg 100mω m=n 0.0001 li=lg 1.5mh kpc 5.29 cf 25µf kpv, kiv 0.041, 35 τpll 10ms kpωsec 0.150 pl_1 365w (0–1 s) kiωsec 9kpωsec pl_2 730w (1-2 s) ω 31.415rad/s vdc 700v ωc 2pi10rad/sec a. time domain analysis of voltage/current at the point of common coupling the voltage and current analysis at the point of common coupling (pcc) are given in this section. figures 4 and 5 present the voltage and current responses at the pcc level of the proposed robust h∞ controller, the conventional and the secondary controller-based systems along with the zoomed pictures for clear visualisation. the load current is contributed by the parallel islanded dgs when two different loads are connected. at time 0-1s and using load 365w, the consumed current is nearly 0.73a and the voltage peak is around 311.12v. when the load is slightly changed at 1s, the proper sinusoidal signal continues again. in addition, when a load of 730w is connected at 1-2s, the consumed current is engineering, technology & applied science research vol. 10, no. 5, 2020, 6264-6269 6267 www.etasr.com pathan et al.: a robust frequency controller based on linear matrix inequality for a parallel islanded … approximately 1.457a for the secondary and the proposed robust h∞-based parallel dgs. when the conventional system is observed, there is a slight difference in current and voltage at the pcc. at 0-1s, the current and voltage are approximately 0.699a and 311v respectively, and during the second load at 1-2s, the current and voltage are around 1.4a and 310.2v respectively. there is a spike in the current and the voltage slightly changes, however it is still stable. this shows that smooth transient voltage and current are flowing when the load is suddenly changed, and the parallel islanded system’s behavior is stable. (a) (b) (c) fig. 3. comparison: (a) simulation model, (b) electrical system and existing secondary, (c) conventional and proposed robust h∞. b. time domain analysis of dgs’ sharing power and microgrid power at a second stage, the analysis takes into account the transient behavior of active power sharing of dg1 and dg2 as well as the total mg average power, which are illustrated in figure 6 and figure 7 respectively. engineering, technology & applied science research vol. 10, no. 5, 2020, 6264-6269 6268 www.etasr.com pathan et al.: a robust frequency controller based on linear matrix inequality for a parallel islanded … fig. 4. voltage response at pcc: (a) h∞ voltage at pcc and (a-h) zoomed picture, (b) conventional voltage at pcc and (b-c) zoomed picture, (c) secondary voltage at pcc, and (c-s) zoomed picture. fig. 5. current response at pcc: (a) h∞ current at pcc and (a-h) zoomed picture, (b) conventional current at pcc and (b-c) zoomed picture, (c) secondary current at pcc (c), and (c-s) zoomed picture. fig. 6. active sharing power time domain response (h=robust h∞ control, s=secondary hierarchical control, c=conventional primary hierarchical control). fig. 7. active power time domain response (h=robust h∞ control, s=secondary hierarchical control, c=conventional primary hierarchical control) the proposed controller, the hierarchical primary controller, and the secondary controller change condition under low-to-medium sudden load. the simulation time is 0-1s when a low load of 365w is connected. each dg’s active sharing power is approximately 181.8w in the hierarchical primary conventional controller. meanwhile, the proposed robust h∞ controller and the hierarchical secondary control loop share the active power in each dg at about 182.489w. additionally, when the second medium load of 730w is connected at 1-2s the sharing of each dg’s active power is approximately 364.245w using the conventional hierarchical primary controller. on the other hand, the secondary hierarchical controller and the robust h∞ controller are sharing power at around 365w during low-to-medium load sharing. it can be noticed that the sharing of active power has been improved without using any communication technique in the proposed robust h∞ controller and in the hierarchical secondary controller, though the hierarchical secondary controller has failed the concept of plug-and-play because it requires communication. while the conventional hierarchical primary controller has no communication, the sharing of power is not equal to the ratings of the dgs. figure 7 depicts the active mg power of around 363.6w when using the conventional hierarchical primary controller. when the proposed robust h∞ controller is applied, the power is approximately 365w and is similar to the secondary hierarchical controller at low load. when the load is suddenly switched from low to medium, the mg power using a conventional controller is approximately 728.5w at 1-2s while the proposed robust h∞ controller and the secondary hierarchical communication-based controller have almost similar active mg power of around 730w. c. time domain analysis of frequency restoration this section analyzes the effectiveness of the proposed robust h∞ controller in terms of frequency restoration during sudden low-to-medium load changes. in addition, signals from the secondary communication-based hierarchical controller and the conventional primary decentralized non-communicationbased hierarchical controller are compared with the proposed controllers (figure 8(a)). fig. 8. (a) frequency time domain response, (b) transient frequency response at pcc, and (c) and transient response of sudden load change. figure 8(b) indicates the step response of the conventional, the existing secondary, and the proposed controller. the response under the existing secondary controller frequency is slower by 0.12s in rise time because of processing delay, whereas the proposed robust h∞ controller is demonstrated in fast manner with 0.06s and reaches steady state faster than the existing secondary controller. figure 8(c) indicates that the engineering, technology & applied science research vol. 10, no. 5, 2020, 6264-6269 6269 www.etasr.com pathan et al.: a robust frequency controller based on linear matrix inequality for a parallel islanded … frequency deviates more with sudden load using the conventional primary hierarchical controller at around 49.92hz. transient is also slower than the proposed controller at step time 1-2s. on the other hand, the secondary controller shows a slower rise time of 1.145s with high peak at 1.01s with 40% overshoot and slower steady state level because of processing delay. the proposed robust h∞ controller restores the frequency and retains the nominal frequency during a sudden load change in a faster manner with 1.02s rise time. from the figure, it is clear that the proposed controller’s overshoot is reduced to 6%. the controller efficiency response increased by 95% for reference value tracking. moreover, it has the capability to restore the frequency response faster to nominal value than the conventional and the existing secondary controller. consequently, the proposed robust h∞ controller and the secondary hierarchical loop restore frequency within the specified range given in the respective ieee standard [17]. v. conclusion a systematic designing procedure of robust frequency droop controllers has been presented. the proposed mg consists of parallel connected dc sources with loads which are suddenly changed and the controller shows its robustness to maintain the frequency at its nominal value in very short time in comparison with the secondary hierarchical controller and the conventional controller without using any communication links. all the effective signals are considered here as disturbances and the proper weighted function and proper h∞ controller were designed for achieving the desired objective by using lmi technique. the proposed controller was simulated in matlab and the results were compared with the results of the conventional and the secondary controllers. references [1] r. h. lasseter, “microgrids,” in 2002 ieee power engineering society winter meeting. conference proceedings (cat. no.02ch37309), jan. 2002, vol. 1, pp. 305–308 vol.1, doi: 10.1109/pesw.2002.985003. 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[17] 2030.7-2017 ieee standard for the specification of microgrid controllers. ieee, 2018. microsoft word etasr_v10_n6_pp6462-6468 engineering, technology & applied science research vol. 10, no. 5, 2020, 6462-6468 6462 www.etasr.com ben ayed: balanced communication-avoiding support vector machine when detecting epilepsy … balanced communication-avoiding support vector machine when detecting epilepsy based on eeg signals mossaad ben ayed department of computer science, college of sciences and humanities sciences at alghat majmaah university, saudi arabia and department of computer science, computer and embedded system laboratory sfax university, tunisia mm.ayed@mu.edu.sa abstract—the revolution in technology affects many fields and among them the healthcare system. the application-based computer was developed to help specialists to detect diseases, and to perform some basics operations. in this paper, focus is given on the proposed attempts to detect epilepsy disease (ed). several computer-aided diagnosis (cad) methods were used to provide the brain’s disease status according to signals related to brain activities. these applications achieved acceptable results but still have their limitations. an intelligence cad based on the balanced communication-avoiding support vector machine (bca-svm) is proposed to detect ed using electroencephalogram (eeg) signals. this attempt is implemented on a raspberry pi 4 as a real board to ensure realtime processing. the cad-based on bca-svm achieved an accuracy of 99.8% and the execution time was around 3.2s satisfying the real-time requirement. keywords—healthcare; epilepsy; computer-aided diagnosis; balanced communication-avoiding support vector machine; electroencephalogram (eeg); raspberry pi 4 i. introduction brain disorders such as alzheimer’s and epilepsy disease (ed) [1] are consuming vast resources of the health care system. several methods have been proposed for the automated diagnosis of brain diseases. many computer-aided diagnosis (cad) methods use electroencephalogram (eeg) signals [2], physiological signals [3], or wearable sensors and smartphones [4]. most recent works employ eeg signals instead of other methods due to their accuracy. the eeg is capable to read the brain’s electrical signals generated by neurons measured through the scalp. electroencephalography is the process of measuring the brain’s neural activity as electrical voltage fluctuations along the scalp as a result of the current flowing in the brain’s neurons [5, 6]. the brain’s electrical activity is monitored and recorded, in typical eeg tests, using electrodes that are fixed on the scalp [7]. a brain-computer interface (bci) system enables individuals to communicate through external devices by using their brain's electrical signals in the recording positions of the scalp. this can help to recognize anomalies of frequency patterns or accomplishing several tasks and seems to have many potential applications. this paper highlights the main issues of these methods, taking into account the proposed attempts to detect brain diseases and the fact that several methods based on cad were used to identify ed using eeg signals. this paper contributes by highlighting the deficiency of a huge eeg database and techniques that were used may need a hardware accelerator to reduce the time duration of their applications. ii. literature review traditional medicine is based on visual inspection to recognize features assigned to brain diseases. this kind of inspection suffers from low accuracy while it is timeconsuming. in this section, many related works on recognizing ed based on machine learning techniques supported by different cad tools are presented. authors in [2, 4] attempted to analyze eeg signals in detective and predictive data analytics by applying different intelligent classifiers to identify a range of signals related to brain diseases. authors in [7-9] attempted to detect epilepsy outcome features through the eeg signals with artificial neural networks. in [7], the authors proposed an enhancement of the snn model and reached an accuracy of 92.5%. in [8], the authors followed a wavelet methodology for nonlinear features. then, a levenbergmarquardt backpropagation neural network method was performed, resulting in an accuracy of 96.7%. authors in [9] proposed the use of the multi-spiking neural network technique and the reached accuracy was about 90.7%. authors in [10] analyzed the eeg features according to a multi-spiking neural network with a new supervised learning algorithm. the accuracy is 94.8%, which was better than the result obtained in [9]. authors in [11-17] applied the gaussian mixture model to the eeg signals. an accuracy of 93.1% was reached in [11]. in [12-14], the authors used the support vector machine as the main idea. the wavelet transformer obtained an accuracy of 96.3%, the recurrence quantification analysis achieved an accuracy of 95.6%, and the discrete wavelet transformation an accuracy of 96%. in [15, 16], the authors used fuzzy sugeno corresponding author: mossaad ben ayed engineering, technology & applied science research vol. 10, no. 5, 2020, 6462-6468 6463 www.etasr.com ben ayed: balanced communication-avoiding support vector machine when detecting epilepsy … applied to entropy and higher-order spectra methods. the achieved accuracy was around 98.1% and 99.7%. this method is challenged by its huge need of processing time and hardware resources. in [17], a deep learning methodology was used by applying convolutional neural networks (cnns). the model formed by a 13-layer neural network achieved an accuracy of 88.7%. authors in [18, 19], proposed an epilepsy detection method based on the gaussian mixture model with 93.1% accuracy. authors in [20], used the svm methodology followed by the power spectral density estimation method, with the accuracy not exceeding 93.3%. authors in [21], combined the svm and the tunable q wavelet transformer with 98.6% accuracy. authors in [22], analyzed the eeg features using the k-nearest neighbors (knn) method with 93.5% accuracy. authors in [23] proposed an advanced algorithm for the recognition of seizures based on eeg features. these characteristics are extracted from the signal in temporal domains. a back-propagation neural network (bnn) was used to achieve an accuracy of about 93%. authors in [24] found the eeg frequency by applying a wavelet transformer to the spectral components. then the mixture of expert (me) was performed as a classifier to achieve an accuracy of about 94.5%. authors in [25] achieved an accuracy of about 98.68% when using a decision tree (dt) as a classifier. authors in [26] proposed the use of cross-correlation coefficients to extract statistical features. based on it, the svm classifies the input eeg signal with about 96% accuracy. authors in [27] attempted to improve the recognition accuracy by using the linear discriminant analysis (lda) classifier. but the obtained results showed an accuracy of 91.8% which was inferior to previous attempts. authors in [28] applied the svm to the entropy features associated with the eeg signal with 97.25% accuracy. authors in [29] proposed the local neighbor description pattern (lndp) as a new technique to extract features. this technique was tested by different classifiers including svm, dt, and ann. lndp technique fused with ann had the highest classification accuracy of 98.72%. authors in [30] tried to detect epilepsy using the brain activities measured by the eeg signals. the signals were processed according to the position of electrodes and analyzed with the use of an adaptive mixture of the independent component. a symmetric-weighted scale-invariant local ternary pattern technique was applied to the obtained signals. the achieved features trained a neural network, reaching an accuracy of 99.53%. authors in [31] attempted to overcome the problem of the variability of feature distribution by applying an adaptive median feature baseline correction (am-fbc). this method was followed by the svm. features were defined by a matrix of determinants and a successive decomposition index. the sensitivity was enhanced to achieve 96.6%. a summarization of the most significant studies on brain disorder disease recognition using computer-aided diagnosis can be seen in [32]. table i presents a review of various implemented approaches to automate classification with the use of the eeg signals. the eeg data used by the authors in table i are collected at bonn university, germany [33]. these data recordings were chosen from multi-channel eeg. table i. comparison between techniques used to detect epilepsy disease techniques reference main contribution performances accuracy sensitivity specificity nns [7] an improved snn model for epilepsy and epileptic seizure detection 92.5% [10] a multi-spiking nn with a new supervised learning algorithm 94.8% [8] wavelet chaos methodology, nonlinear features, levenbergmarquardt backpropagation nn 96.7% [9] multi-spiking nn 90.7% [30] three-layered nn 99.53% [23] bnn 93% gaussian mixture model (gmm) [11] nonlinear features 93.1% 92.2% 100% [18] hos features 93.1% 97.7% 92% [19] hos based entropy features 93.1% 89.7% 94.8% svm [20] power spectral density estimation methods 93.3% 98.3% 96.7% [24] wavelet transform 94.5% [12] discrete wavelet transform higher cumulant features 96.3% 100% 97.9% [13] recurrence quantification analysis 95.6% 98.9% 97.8% [14] discrete wavelet transform 96% 96% 99% [26] cross-correlation coefficients 96% [28] entropy features 97.25% [21] tunable q wavelet transform 98.6% [29] (lndp 98.72% [31] adaptive median feature baseline correction 96.6% knn [22] genetic programming 93.5% dt [25] dt 98.68% lda [27] lda 91.8% fuzzy sugeno [15] entropy, higher-order spectra, nonlinear features 99.7% 100% 100% [16] entropy 98.1% 99.4% 100% cnn [17] ten-fold cross-validation strategy, 13-layer deep cnn structure 88.7% 95% 90% engineering, technology & applied science research vol. 10, no. 5, 2020, 6462-6468 6464 www.etasr.com ben ayed: balanced communication-avoiding support vector machine when detecting epilepsy … iii. open challenges this section discusses the results achieved by the above mentioned techniques in detecting brain diseases based on the eeg signal. the discussion is performed considering the reported drawbacks. in the light of this brief review, the eeg signal represents a powerful criterion for the detection of brain diseases. according to the studied disease (seizures, epilepsy, alzheimer’s, etc.), the extraction phase tries to extract data from the eeg signal based on some features related to the specificity of the disease. this phase could be performed to an eeg signal depending on domains. the next phase applies different classifiers to obtain recognition accuracy. the shortcomings related to the recognition of brain diseases based on the eeg signals are: • uncertain accuracy: commonly the obtained accuracy is higher than 90%. most works use the public eeg database in [33]. it is composed of five datasets (a, b, c, d, and e) collected from only 5 participants. therefore, the findings must be implemented in a larger database allowing result generalization. as mentioned above, several studies achieved different accuracy values despite the use of the same classifier and dataset. this can be explained by three reasons: (1) differences in the use of the dataset, (2) the extracted features are not always the same, and (3) difference of domains (time, frequency, and timefrequency). • non-real-time: most previous works implement advanced algorithms for the detection of brain diseases. hence, algorithms were not executed in real-time due to the considerable computation time they demanded. authors in [34] proposed a hardware implementation based on an fpga board to ensure real-time detection. the authors used the svm algorithm and achieved an accuracy of 86%. this result proved the decrease of the performance when implementing the algorithm on board. the need for a cad framework deployed on a hardware board that maintains high accuracy is a necessity. • non-predictive: all previous works do not support disease prediction for a healthy person. as a conclusion, the detection of the epilepsy disease using cad tools still needs improvement in both software and hardware. the accuracy of the recognition had to be improved and the execution time should be decreased to ensure real-time response. these objectives are attained by performing the bca-svm [35] algorithm and by deploying it in a raspberry pi 4 board. in this paper, a system based on the bca-svm method as an intelligent algorithm to recognize the epilepsy disease at an earlier stage is presented. iv. the proposed method the aim of this study is to detect signs related to the ed according to the measured eeg signals. the bca-svm algorithm is applied to the eeg signals. this technique is chosen in order to ensure both speed and accuracy. during the training phase, the model is built through a set of input data. this phase requests an increasing number of processors and a set size which reduces the performance of the algorithm. the prediction phase is the easiest one due to the speedup and the parallel processing. the proposed bca-svm technique follows these steps: (1) preprocessing, (2) feature extraction, (3) classification, and (4) evaluation. a. preprocessing this step aims to normalize the eeg signal. the normalization is important due to the frequency bands associated with the difference of the frequency magnitude. the normalization aims to scale features, while the obtained values are more user-friendly. the filtered/raw values are scaled. the z-score method is used for normalization [32]: ������ = � � (1) where v is the value of the feature to be scaled, m is the mean value of the feature, and s is the standard deviation of the feature. this method is adopted because it manages outliers. secondly, focus was given on augmenting data in the dataset. this goal aims to improve the obtained results of the training. the data augmentation was done with the use of the synthetic minority over-sampling technique. this method provides new samples based on the neighborhood method without re-using the available data. this method provides new samples belonging to the same original distribution. the most common challenge encountered in the ed research is the limited datasets and the limited data included in a dataset. this issue reduces the accuracy of cad tools based on machine learning algorithms. the data augmentation step attempts to increase the amount of data in the dataset. data drawn as a signal are segmented to attain a signal of equal length and associated with the same label as the original data. in our case, the length of the eeg signal is 10s. this process increases the number of available signals in the dataset from 40 to 96. b. feature extraction ed features are determined based on five frequency bands considered as signals of interest. these bands are described by the following restriction: �� �� 0 < � < 4��4�� < � < 8��8�� < � < 12��12�� < � < 30�� 30�� < � < 50�� it is necessary to apply a low pass filter to the signals to remove high frequency components. through these frequency bands, the feature extraction could be defined. in the current study two key features were considered: (1) the fast fourier transform (fft) and (2) the continuous wavelet transform (cw) features. the fft is applied to frequency signals to define the average magnitude related to all fft coefficients. the fast fourier (ff) features are defined according to: �� = ∑ |#$|%&'$(%)' *�' *+' (2) where fs is the starting frequency, fe is the ending frequency associated with i th band, and ck defines the fft coefficients. the computed results of each band correspond to the average engineering, technology & applied science research vol. 10, no. 5, 2020, 6462-6468 6465 www.etasr.com ben ayed: balanced communication-avoiding support vector machine when detecting epilepsy … frequency response. the cw features define the average magnitude of the computed cw transform coefficients: ,= ∑ ∑ ./0,$.%&'$(%)' 2&0(2) 34� 4+53*�' *+'5 (3) where ts is the starting time, te is the ending time, and xj,k are the wavelet coefficients. c. classification in this paper, focus is given on the training phase to overcome the mentioned shortcomings. sequential minimal optimization (smo) classes are introduced to divide the data set and to build the bca-svm kernel. figure 1 describes the proposed technique. fig. 1. the proposed architecture based on bca-svm. the implementation proceeds with the k-means algorithm. this classifier has some shortcomings: (1) k-means partitioning suffers from regularity and balance, (2) k-means is unpredictable because it dependents on data. an improvement is proposed to the k-means by applying the first come first served (fcfs) algorithm. algorithm 1 as shown in figure 2 describes the proposed enhancement. we assume that a clustering center corresponds to a machine node. the goal is to look for the closest center for every sample. the k-means is enhanced when a data center has n/m samples. the algorithm begins with a general definition. then the machine node center and the balanced value are initialized. the treatment part manages data to find the center for each sample. the optimization step is done to improve the achieved result. fig. 2. algorithm 1: k-means/fcfs partiotining. the bca-svm method is the final step of the procedure. it classifies data based on the local learning model. the samples are divided according to different zonal, region, sub-region, and local region. the learning process proceeds as follows: (1) the samples are learned as a sub-region, (2) sub-regions of samples are joined to form a region, (3) the regions are integrated as a zonal of samples. the balanced condition used for prediction is computed under the number of zonals per level. the balanced value corresponds to the result of the number of zonals per level divided by the number of each specific zonal. algorithm 2 (figure 3) details the functionality of the proposed bca-svm algorithm. fig. 3. algorithm 2: bca-svm algorithm. d. evaluation the necessary metrics to measure accurately the prediction and evaluate the classification performance are presented in this section. the validation is used 10 fold. 67789:7; = 1 < =>?=@ a>?a@?=>?=@ (4) where false positive (fp) is the number of non-ed predicted examples, false negative (fn) corresponds to the number of non-detected ed examples, true positive (tp) is the number of correct ed detected examples, and true negative (tn) presents the number of correct non-ed detected examples. the accuracy parameter could be resumed by : 67789:7; = 1 < =bc+� ����de 4 �e a�f� ����de 4 �e?=bc+� ����de 4 �e (5) where false recognition is the number of false classifications and true recognition is the number of correct classifications. sensitivity and specificity are defined as: ghijklkmkl; = a>a>?=@ (6) gnh7kok7kl; = a@a@?=> (7) the evaluation step is finished by implementing the proposed method. for that, the cad framework was deployed into a raspberry pi 4 [34] tied with the eeg device emotiv [37]. this phase is evaluated with regard to processing time, cpu usage, and memory demand. engineering, technology & applied science research vol. 10, no. 5, 2020, 6462-6468 6466 www.etasr.com ben ayed: balanced communication-avoiding support vector machine when detecting epilepsy … v. experimental results in this section, the proposed cad based on the bca-svm method and using the dataset in [33] is verified and the implementation phase is described. a. verification the verification is applied to samples considering ed and healthy (h) cases. the evaluation of the bca-svm method is presented in table ii. the proposed related to the ed cases reached 99.8% accuracy and 100% sensitivity and specificity. nevertheless, the results related with regard to the h cases achieved 95.1% accuracy, 92.6% sensitivity, and 89.9% specificity. the obtained accuracy proves that the proposed bca-svm method gives a reliable decision of the health status of the studied cases. the accuracy covers both tp and tn results. the sensitivity highlights that our method detects consistently the ed. an error of about 8% is computed when considering healthy persons. the specificity defines the rate of cases correctly detected without ed. the achieved performance metrics attaint certain detection of the ed. a comparison between our findings and previous works is presented in table iii. it can be seen that the bca-svm achieves the best results. table ii. classification performance ed h accuracy 99.8% 95.1% sensitivity 100% 92.6% specificity 100% 89.9% table iii. performance comparison reference year accuracy specificity sensitivity [23] 2006 93% [7] 2007 92.5% [8] 2007 96.7% [24] 2007 94.5% [25] 2007 98.68% [9] 2009 90.7% [11] 2009 93.1% 100% 92.2% [18] 2009 93.1% 92% 97.7% [26] 2009 96% [20] 2010 93.3% 96.7% 98.3% [19] 2011 93.1% 94.8% 89.7% [12] 2011 96.3% 97.9% 100% [13] 2011 95.6% 97.8% 98.9% [22] 2011 93.5% [27] 2012 91.8% [15] 2012 99.7% 100% 100% [16] 2012 98.1% 100% 99.4% [14] 2013 96% 99% 96% [10] 2016 94.8% [28] 2016 97.25% [21] 2017 98.6% [29] 2017 98.72% [17] 2018 88.7% 90% 95% [30] 2019 99.53% [31] 2020 96.6% proposed 2020 99.8% 100% 100% most attempts ensure accuracy more than 90%. the diagnosis classifiers can be considered satisfying until the achieved accuracy reaches 100%. rival attempts suffered from the requested processing time. therefore, the validation of the cad framework on board is highly recommended. b. implementation the verified cad has been implemented with the use of the earlobe electrode landmark [38] and a raspberry pi 4 [36]. the eeg signals were recorded according to the international system metrics. measures were taken when the eyes were closed, ensuring the same dynamic process. in the test phase, the record is defined as follows: duration of 120s, 1024hz frequency, and sampling by 256. this implementation aims to provide an accurate device to predict ed. the device has to take into consideration real-time requests. the raspberry pi 4 was connected with the eeg device [37] via bluetooth. the bca-svm was developed using python and run on the raspbian gnu/linux 9 operating system. the raspberry pi 4 was chosen because it runs codes in python, and it provides high-level apis as scikit-learn library [39]. the performance of the proposed device depends on the memory usage, cpu temperature, and cpu average load. the memory resources are defined by memory usage. the requested memory varies between 17 and 24mb. the raspberry pi board provides the needed memory. figures 4-6 present the results related to hardware factors. the cpu temperature curve is highlighted in figure 4. the average temperature was around 66°c. the arm processor did not need a cooling mechanism because the temperature did not exceed 85°c. fig. 4. temporal variation of the cpu temperature. fig. 5. temporal variation of the cpu average load. engineering, technology & applied science research vol. 10, no. 5, 2020, 6462-6468 6467 www.etasr.com ben ayed: balanced communication-avoiding support vector machine when detecting epilepsy … the cpu average load defines the average number of processes loaded by the cpu during the studied period. figure 5 shows the number of loaded processes for 120s. the cpu manages between one and two processes at the same time (the average is about 1.4). an intermediate buffer between the cpu and the primary memory has to be considered to ensure accurate running. the cad tool could be considered as a realtime system. the cpu usage factor defines the occupation status. this factor could shut down the cpu when the occupation rate achieves 100%. figure 6 shows the variation of usage during the 120s period. the cpu usage did not exceed 92% and the average rate was about 83%. all these results related to the architecture factors prove that raspberry pi 4 is sufficient for the ed detection using the bca-svm method. the execution time request by the raspberry pi 4 board is about 3.2s, allowing the conclusion that it obeys the real-time demands. table iv summarizes the hardware performance related to the implementation of the bca-svm method on the raspberry pi 4 board. fig. 6. variation of the cpu usage. table iv. hardware performance hardware features findings average cpu temperature (°c) 66 average cpu load (processes/second) 1.4 average cpu usage (%) 83% the hardware features prove that the used board provides sufficient resources to ensure stable functioning of the cad framework. vi. discussion as mentioned above, the ed detection using the eeg signal faces three major issues: (1) accuracy, (2) real-time response, and (3) prediction. during this attempt, we dealt with the problems of accuracy and real-time response. despite the high accuracy of the previous works, the findings were uncertain because of the small size of the considered dataset. a data augmentation method was proposed based on the synthetic minority over-sampling technique. the obtained accuracy (99.8%) is more significant and solid in comparison with other works. hardware performance is a critical factor in the implementation phase. the requested time to make a decision is around 3.2s. moreover, the proposed method did not need a special hardware board. a raspberry pi 4 board provided sufficient memory size, and cpu speed to perform the framework. this proposed attempt can be extended to recognize other brain diseases such as alzheimer's. the cad tool has to support prediction in order to enhance pre-emptive care. vii. conclusion the main subject of this paper is the detection of the ed. the detection of ed is challenged by increasing reliability and real-time constraints. to obtain 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[39] s. raschka and v. mirjalili, python machine learning second edition: machine learning and deep learning with python, scikit-learn, and tensorflow, 2nd ed. packt publishing, 2017. microsoft word etasr_v11_n3_pp7172-7176 engineering, technology & applied science research vol. 11, no. 3, 2021, 7172-7176 7172 www.etasr.com hassan et al.: an effective combination of textures and wavelet features for facial expression … an effective combination of textures and wavelet features for facial expression recognition syed muhammad hassan department of ai and mathematical sciences smi university karachi, pakistan m.hassan@smiu.edu.pk abdullah alghamdi college of computer science and information systems najran university najran, saudi arabia abdulresearch@hotmail.com abdul hafeez department of software engineering smi university karachi, pakistan ahkhan@smiu.edu.pk mohammad hamdi college of computer science and information systems najran university najran, saudi arabia mahamdi@nu.edu.sa imtiaz hussain department of ai and mathematical sciences smi university karachi, pakistan imtiaz@smiu.edu.pk mesfer alrizq college of computer science and information systems najran university najran, saudi arabia msalrizq@nu.edu.sa abstract—in order to explore the accompanying examination goals for facial expression recognition, a proper combination of classification and adequate feature extraction is necessary. if inadequate features are used, even the best classifier could fail to achieve accurate recognition. in this paper, a new fusion technique for human facial expression recognition is used to accurately recognize human facial expressions. a combination of discrete wavelet features (dwt), local binary pattern (lbp), and histogram of gradients (hog) feature extraction techniques was used to investigate six human emotions. k-nearest neighbors (knn), decision tree (dt), multi-layer perceptron (mlp), and random forest (rf) were chosen for classification. these algorithms were implemented and tested on the static facial expression in wild (swew) dataset which consists of facial expressions of high accuracy. the proposed algorithm exhibited 87% accuracy which is higher than the accuracy of the individual algorithms. keywords-ann; fer; dwt; lbp; hog; k-nearest neighbors i. introduction facial expressions are a way of sentiment expression and non-verbal correspondence. there are various systems that deal with human attitude and point of view recognition. facial expression recognition (fer) transforms is one of the most discussed scientific areas nowadays. this issue is furthermore incredibly noteworthy in human-computer collaboration (hci) [1, 2]. fer is being utilized to provide a description for the mental state of human beings [3]. meanwhile, modifications in the look of photos can occur by disturbances in the pixels. illumination troubles might also occur in indoor or outdoor photos. the exploration indicates those issues and proposes a combination strategy for different accessible highlights that surpasses these issues [4]. ii. literature survey and theoretical framework it is very difficult to identify human facial regions. in order to handle this efficiently, a technique should be implemented to recognize facial indicators. one clause that is vital to know is the dynamic angle on transferring video [5]. lower and top face method extends the spatial pyramid histogram of edges which give 3-dimensional facial acknowledgment. fundamentally in this method, elements are researched for cheerful and pity indicators [6]. lbp and improved local binary pattern have been applied alongside coordinate bunching representation [7]. face recognition using an optimized algorithm chain for both 2d and 3d images gives an accuracy about 96% with svm classifier using lbp and pca. further testing on 2d and 3d images using lbp and pca with ffbpnn (feed forward back propagation neural network) is less effective and efficient as compared to the svm classifier [8]. locality preserving projections (lpps) have been used for manifold systems originated from local binary pattern (lbp) subjects [9]. at first, a pyramid change is utilized to divide the test photographs into different areas. so, the goal pictures are isolated. after this, the elbp is applied upon the little pictures to compute the elbp pyramid and the community photo decided qualities are utilized to the little pictures from awm which can ascertain the importance of the facts they got. corresponding author: syed muhammad hassan engineering, technology & applied science research vol. 11, no. 3, 2021, 7172-7176 7173 www.etasr.com hassan et al.: an effective combination of textures and wavelet features for facial expression … finally, the awelbpp highlight is assembled from the blend of the little elbp pyramid and the awm [10]. support vector machine (svm) has been applied in dispensing boisterous pictures for highlight extraction [11, 12]. background subtraction [13] showed good results by applying background subtraction on real-time feeds. in this work, a model based on gaussian mixture was used for unfolding the pixels of images and the variables of the pattern were calculated with the expectation-maximization (em) algorithm. the shades were also spotted effectively. background subtraction was also very effective and met the requirements of drowning detection. authors in [14] reviewed earlier approaches and tried to cover up the issue of recognizing actions and behaviors and the problem of dealing with a moderate crowded situation with a good modeling technique. the conventional techniques where mixed and a gaussian distribution was used to design the temporal changing of the background pixels in [15]. this has been proven to be insufficient for extremely non-stationary environment. however, the thresholding method with hysteresis dealt with the issue of choosing thresholds in the background subtraction context. stationary cameras have also been used to find drowning persons in swimming pools [6, 17, 18]. in contrast to previous works based on geometrical and 3d mahalanobis distance features, the presented method in [18] captured the temporal and spatial correlation of the swimmers along with color information using the markov random field (mrf) context to give better performance. promising outcomes for drowning detection were achieved using an exclusive functional link net which fused the descriptors of extracted swimmers optimally. an improved descriptor fusion technique associated with the hierarchical technique was proposed in [19]. the current drowning detection techniques can be broadly classified into the vision-based schemes and the systems based on wearable sensors [20-22]. on the other hand, the combination of aerial and underwater cameras to monitor the postures of fer was utilized in [23], whereas the cnn model achieved 99.78% accuracy [24]. an even more successful accuracy level was achieved in learning similarities and dissimilarities among the faces of dataset using fdrenet in [25]. iii. system methodology usually, cameras are present in most areas for security purposes. the already installed cameras can be utilized for the purpose of monitoring and expression detection. so, few critical frames are extracted from the video or can be utilized. a facial expression video is divided into frames to be processed. the image frames extracted from the video are utilized for feature extraction. then, classification is carried out. a. feature extraction the input dataset is very large to be handled and processed. it is supposed to be redundant (enough data, but not abundant information), so, the input dataset will be converted into a reduced depiction set containing features. this set is named as features vector (fv). this process is known as feature extraction. therefore, taking out the prejudiced features from the images enhances the decline of the dimension of the fv by removing the redundancy in images and squeezing the relevant data into the fv to a much smaller size. fig. 1. the flowchart of the proposed method. b. feature extraction via discrete wavelet transform discrete wavelet transform (dwt) is utilized to extract features from an image on various levels of low pass (g), and high pass filtering (h). a signal x is calculated by passing through these series of filters, at first through the low pass filter (g) and then through the high pass (h): ( )[ ] [ ] [ ][ ] * k h n x g n x k g n k ∞ =−∞ = = −∑ (1) the low pass filter (g) and the high pass filter (h) with h cut-off frequency are described by: [ ] [ ] [ ]2low k y n x k g n k ∞ =−∞ = −∑ (2) [ ] [ ] [ ]2high k y n x k h n k ∞ =−∞ = −∑ (3) the wavelet coefficients are the consecutive persistence of the estimate and the detail coefficients. the basic process of features extraction consists of: engineering, technology & applied science research vol. 11, no. 3, 2021, 7172-7176 7174 www.etasr.com hassan et al.: an effective combination of textures and wavelet features for facial expression … • mouldering the image using dwt in n-levels using decimation and filtering to get the detailed coefficients and approximation. • feature extraction using the dwt coefficients output. • the features that were taken out from the dwt coefficients of the images are considered as the input to classifiers because of their operative representation. the algorithmic steps for feature extraction from the dataset are: • step 1: the image data are decomposed into 4 detailed subbands by dwt. • step 2: the coefficients of approximation are further been decomposed by dwt to obtain localized data from the subband of the detailed coefficients of approximation (horizontal, vertical, and diagonal). • step 3: aimed at processing and analyzing, all of the 4 levels detailed coefficients are calculated. • step 4: finally, the features are analyzed and tabulated to be used as the input of the classifier. c. feature extraction via histogram of gradients the histogram of oriented gradients (hog) is the shape of the "function descriptor". the motive behind a feature descriptor is to generalize the item on a way that the same item (in this case a person) produces the same feature descriptor at the same time as considered under specific situations. this makes the class assignment simpler. static facial expressions in the wild (sfew) has been utilized for selecting frames from afew. regarding the block normalization for hog, we consider v as the non-normalized vector containing all histograms in a given block, k v be its k-norm for k =1, 2, and e is some small constant. the normalized factor is defined as: 2 2 2 v f v e = + (4) the dataset covers unconstrained facial expressions, numerous head poses, massive age variety, occlusions, numerous poses, and near actual global illumination. frames had been extracted from afew sequences and were labeled based on the label of the series. typically, sfew includes seven-hundred snapshots which have been classified for six fundamental expressions: anger, disgust, fear, happiness, sadness, and surprise, and were categorized by unbiased labelers. d. feature extraction via local binary pattern (lbp) the lbp method is applied on facial images in order to extract features that may be used to get a degree of similarity. firstly, the pictures have been divided into several blocks. after that, the lbp histogram was calculated for each block. the value of the lbp code of a pixel ( ),c cx y is considered as: ( ) ( ) 1 , 0 , 2 p p p cp r p lbp s g g − = =∑ (5) where ( ) {1, 0}s x x= ∀ ≥ and ( ) {0,otherwise}s x = . the notation ( ), 2p rlbp u is used for the lbp operator, where (p, r) represents the neighborhood, and u2 stands for uniform patterns and labeling all reaming patterns with a single label. the histogram for the image ( )1 ,f x y is defined as: ( ) ( ), { , }, 0,......., 1, i i x y h i f x y i i n= = = −∑ (6) the number of different labels produced by the lbp operator, and i{a} is 1, if a is true and 0 if it is false. further, the image patches whose histograms are to be compared must be normalized in order to get a coherent description: 1 0 i i n j j h n h − = = ∑ (7) then, the block lbp histograms were concatenated into an unmarried vector. the histograms have then been evaluated by using space similarity [16]. moreover, each bin in histograms consists of the variety of its look within the region. lastly, the feature vector is constructed with the useful data by concatenating the community histograms to one massive histogram. iv. results and discussion in this study, the sfew dataset was used for testing, which is close to real world environment, having 300 color images with 6 emotion categories, consisting of 50 pictures each with dimensions of 143×181 pixels. the classes are surprise, fear, anger, sadness, disgust, and happiness represented by su, f, a, s, d, and h respectively. the results were evaluated with assessment metrics, including confusion matrix, precision, recall, and f1 score. to compute the overall precision, we used micro-averages to combine the consequences across the 6 categories. we divided our dataset into 80% training and 20% testing subsets. the sets were fed to the distinctive learning system which utilized algorithms such as k-nearest neighbor (knn), decision tree (dt), multilayer perceptron (mlp), and random forest (rf). our experimental model was divided into four parts. the mentioned machine learning algorithms were applied directly to the first part of the dataset. table i shows the original dataset accuracies. table i. original images without feature extraction algorithm knn dt mlp rf accuracy 27% 14% 22% 32% table ii. lbp feature extraction algorithm knn dt mlp rf accuracy 50% 96% 22% 95% engineering, technology & applied science research vol. 11, no. 3, 2021, 7172-7176 7175 www.etasr.com hassan et al.: an effective combination of textures and wavelet features for facial expression … maximum accuracy was achieve by the rf and was only 32%. then, all algorithm accuracies were computed using dwt, lpb, and hog for the other parts of the dataset (tables ii-iv), and finally combined them and achieved 87% maximum accuracy with mlp and 29% minimum accuracy with knn (table v), which are respectively shown in the confusion matrices of figures 2 and 3. table iii. dwt feature extraction algorithm knn dt mlp rf accuracy 12% 17.5% 36% 21% table iv. hog feature extraction algorithm knn dt mlp rf accuracy 12% 12% 37% 14% table v. combination of lbp, dwt, and hog algorithm knn dt mlp rf accuracy 29% 80% 87% 79% fig. 2. mlp confusion matrix. fig. 3. knn confusion matrix. further, we also calculated some edges of the face generated by dwt, lbp, and hog. the original image is reconstructed using harr dwt techniques. fig. 4. retained energy is 99.40%. fig. 5. hog edges. fig. 6. lbp visualized surprised face. v. conclusion and future work the proposed model combines dwt, hog, and lbp capabilities in a feature extraction technique with system learning algorithms in an excellent way of enhancing the accuracy of facial feature recognition. six facial expressions from the sfew database had been used for training and validation. the results indicated that the accuracy of the use of blended methods is 87%, which is higher from the individual accuracies of the combined algorithms. however, the proposed combination has the issue of generalization which may be addressed in our future work. engineering, technology & applied science research vol. 11, no. 3, 2021, 7172-7176 7176 www.etasr.com hassan et al.: an effective combination of textures and wavelet features for facial expression … fer is one of the most well-known regions in image processing. generally, fer has been given more attention nowadays. the proposed technique gives an exquisite overview of facial recognition methods. the extraction of functions is vital as it decreases the very massive amount of data to only a required set. 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[25] d. virmani, p. girdhar, p. jain, and p. bamdev, "fdrenet: face detection and recognition pipeline," engineering, technology & applied science research, vol. 9, no. 2, pp. 3933–3938, apr. 2019, https://doi.org/ 10.48084/etasr.2492. microsoft word 29-3795_s_etasr_v10_n5_pp6316-6322 engineering, technology & applied science research vol. 10, no. 5, 2020, 6316-6322 6316 www.etasr.com alqunun: optimal unit commitment problem considering stochastic wind energy penetration optimal unit commitment problem considering stochastic wind energy penetration khalid alqunun college of engineering university of ha’il, saudi arabia khalid.alqunun@gmail.com abstract—wind energy has attracted much attention as a clean energy resource with low running cost over the last decade,. however, due to the unpredictable nature of wind speed, the unit commitment (uc) problem including wind power becomes more difficult. therefore, engineers and researchers are required to seek reliable models and techniques to plan the operation of thermal units in presence of wind farms. this paper presents a new attempt to solve the stochastic uc including wind energy sources. in order to achieve this, the problem is modeled as a chance-constrained optimization problem. then, a method based on the here-and-now strategy is used to convert the uncertain power balance constraint into a deterministic constraint. the obtained deterministic problem is modeled using mixed integer programing (mip) on gams interface whereas the ceplex mip solver is employed for its solution. keywords-stochastic optimization; mixed-integer programming; unit commitment; wind energy sources i. introduction a. research background wind power generation has attracted much attention due to the emergence of energy crises and the related environmental issues. thus, engineers and researchers in power systems have encountered new challenges due to the intermittent and stochastic nature of wind power (wp). one of the main challenges is to study the unit commitment (uc) when wind energy sources (wess) are incorporated into the main power network. the uc problem aims to determine which units have to be committed/uncommitted from the economic perspective [1]. the production levels of the committed units must be specified in order to meet the predicted load at a minimum total production cost over a planning horizon varying from one day to one week. in general, most of the operation costs include the start-up and shut-down costs [2]. the minimization of the operation cost is affected by several operating constraints, which can limit the search space. power balance constraint, generation limits, spinning reserve constraints, minimum uptime/down-time constraints, unit initial status, and ramp rate limits of units are the most used constraints in the uc problem formulation [3-4]. the decision variables for the uc problem consist of both states of units, which are based on binary/integer variables (i.e. 1 when the unit is on and 0 when the unit is off) and the output power of the committed units, which are continuous/real variables. for a long time, the uc problem has been mainly formulated as a mixed-integer optimization problem [5-9]. recently, the issues of climate change have begun to be a global concern and some countries have made immediate decisions to decrease their gas emissions [10]. on the other hand, wess are characterized by the lowest generation cost and the largest available energy amongst all renewable energy sources [11]. due to the aforementioned reasons, some countries are committed to using wes. the integration of wes into power grids is usually accompanied by several difficulties, such as the stochastic availability of wind energy [12]. therefore, scientific researches and technological developments, that seek to resolve this kind of problems, are in the process of finding the best solutions. the uc and power dispatch problems are among the most investigated related issues [13-14]. accordingly, the uc problem should be modified in order to consider the uncertain characteristics of the wes in the power balance constraint. b. related work the uc problem has mostly been considered as a nonlinear mixed-integer optimization problem [5]. priority list (pl), an earlier technique for solving the uc problem, has been based on sorting thermal units in a list according to their production costs in an increasing manner [13]. units to be committed are extracted from the list in order to meet the hourly power demand. the pl method seems to be easy and can provide a quick pre-estimation of the optimum solution but it is criticized for its high convergence time and the large required number of units [14]. several other strategies and formulations have been proposed to solve the uc problem such as dynamic programming (dp) [15], lagrangian relaxation (lr) [16-17], benders decomposition (bd) [18-19], mixed-integer linear programming (milp) [20-22], neural networks [23-24], and meta-heuristic techniques [2, 25-28]. however, these strategies have certain limitations [4]. for example, dp-based approaches are considered as impractical for the case of large power networks. compared with the dp method, the lr method is more effective because of its flexibility in managing various types of constraints. however, the coupling constraints are not often met by the dual optimum solution provided by the lr approach. another limitation of the lr method is the sensitivity of the optimum solution of the uc problem to the lagrange multipliers. optimization methods based on the milp approach have also been criticized for their high cpu corresponding author: khalid alqunun engineering, technology & applied science research vol. 10, no. 5, 2020, 6316-6322 6317 www.etasr.com alqunun: optimal unit commitment problem considering stochastic wind energy penetration time especially when the power system is large in size [2]. regarding the meta-heuristic based techniques, despite they can achieve hopeful results when their parameters are well tuned, they are not above criticism. one of their main disadvantages is the requirement of delicate tuning of the optimization algorithm parameters which is a fundamental step to ensure their effectiveness. nowadays, due to the improvements in the mathematical modeling solvers utilized in optimization problems, milpbased models are becoming the most used for solving the uc problem. two main features justified the use of the milp in the modern optimization solvers: (i) the mixed-integer programming (mip) solver provides feasible solutions, and (ii) the level of optimality is controllable [29]. instead of focusing on the optimization algorithm, nowadays solvers require excellent problem modeling. mip solvers like cplex, gurobi and xpress [30] have become quite popular in both academia and industry, especially after the year 2000. in recent years, several works regarded modeling and solving the stochastic uc (suc) including the wess problem. the main contributions of these works are focused in the forecasting methods of wp. as wes is a fluctuating electrical energy source, the forecasts of wind power generation are useful for uc and dispatch problems [31]. in [32], a combined wavelet and time series methods based on short-term forecasting procedure for small farms was presented. an approach using chaos theories for prediction of wind speed and wp was proposed in [33]. other prediction techniques based on artificial intelligence, such as neural networks [34-36], fuzzy logic systems [38] and evolutionary algorithms [38] have been also developed. according to the used methodology, forecasting procedures can be categorized into two categories: physical and statistical approaches. physical approaches, also called deterministic approaches, are based on numerical weather data [39-40]. statistical approaches use a historical data base to estimate the future wind speed and wp at any future time [41]. in recent years, more emphasis has been given to probability density functions (pdfs) to describe the stochastic characteristics of wind speed [42-45]. one of the pioneer works in investigating power generation scheduling with wes is described in [43]. the authors used a stochastic programming approach called here-and-now (hn) strategy to model the stochastic optimization problem. although, it is demonstrated that the impact of the random wp on the power dispatch can be easily evaluated when such a strategy is applied, the production cost has been approximated by a quadratic function. according to [46], the hn strategy is used when the decision must be made even before the first realization of the random variables. the basic idea of this approach is to transform the stochastic problems into equivalent deterministic programs. in hn approach, the decision variables of the stochastic problem are detached from the random variables. furthermore, all uncertain variables are described by chance constraints. pdfs and cumulative distribution functions (cdfs) are used to convert these constraints into deterministic constraints. the weibull distribution function has been widely used to describe the random wind speed and wp characteristics. c. study aims and contribution even though an enormous amount of research work has been conducted on the integration of wp resources into power systems, the uc problem with simultaneous integration of these devices is hardly studied. thus, this study aims to develop an efficient model for the chance-constrained uc (ccuc) problem with both wind turbines and thermal generators, where the violation of the power balance constraint caused by the uncertain output power of the wess is restricted by a user-defined probability. this probability represents the tolerance in which the power balance constraint cannot be satisfied at a given time t. in the problem formulation, all operating constraints and power system losses are considered. the hn strategy, used for modeling the economic dispatch [43] is extended for the ccuc problem formulation. using that strategy, the ccuc problem is converted into a deterministic optimization problem. weibull pdf is employed to describe the wp. the obtained deterministic problem is then implemented in gams interface and the ceplex mip solver is employed for its solution. the effectiveness of the proposed strategy is evaluated on a six-unit system including wind farm. the results are compared with those obtained in other works. ii. deterministic uc problem formulation mostly, the uc problem is formulated as a minimization problem. it aims to meet the load profile over a planned timehorizon with minimum total operating cost subject to several equality and inequality constraints. the decision variables of the problem are the status of each unit which is a binary value and the power output of each online unit which is a continuous variable. a. objective function as given in (1), the principal components of the total operating cost of the thermal units are the fuel cost and the transitional costs which are start-up and shut-down costs [46]: ( ) ( ) ( ) 1 1 1 1 1 1 1 1 t n t n t t t t t t i i i i i i t i t i t n t t t i i i t i c c p u s u u d u u = = = = = =     = + −         + −   ∑∑ ∑∑ ∑∑ (1) the fuel cost of the i-th unit at time t depends on its real output power at the same time and it can be approximated by: ( ) ( ) 2t t t i i i i i i i c p a b p c p= + + (2) where, ai, bi, and ci are the cost coefficients of the i-th unit. n is the number of thermal units, t is the scheduling period in hours, tip is the generation in mw of unit i at time t, t iu is the status of unit i at time t (1 for on and 0 for off), and tis and t id are start-up and shut-down costs of unit i at time t. the start-up cost is the required cost to restart the unit from the off status to the on status. it comprises mainly of the reheating and maintenance costs. that cost depends on the offline duration preceding the start-up. several expressions such as two-valued staircase, linear and exponential-based engineering, technology & applied science research vol. 10, no. 5, 2020, 6316-6322 6318 www.etasr.com alqunun: optimal unit commitment problem considering stochastic wind energy penetration functions have been proposed [4] to describe the start-up cost. the first function adopted in this paper is: , , t d c hi i off i it i t d c ci i off i i s if t t t s s if t t t ≤ + =  > + (3) where his and cis are the hot start-up and cold start-up costs of unit i respectively, , t i offt is the duration in hours for which the unit i is continuously off at time t, and d it and c it are minimum down time and minimum up time in hours of unit i respectively. the transition cost of thermal units from the online status to the offline status may be considered constant and it does not depend on the online duration preceding the shut-down. however, it is often ignored in the uc problem formulations. b. deterministic constraints four operating constraints are taken more frequently into account in the classical uc problem. 1) power balance constraint at each hour t, the total generated power must meet the predicted load t d p plus the total real losses t l p as described by (4): ( ) 1 0 n t t t t i i d l i p u p p = − − =∑ (4) 2) unit limits the output power t i p of the i-th committed unit must be within its lower and upper limits. min maxt i i i p p p≤ ≤ (5) 3) minimum up/down times these constraints signify the minimum required durations for which the de-committed/committed unit can be turned on/off. , t i ont is the duration in hours for which the unit i is continuously on at time t. , , t u i on i t d i off i t t t t >  > (6) 4) spinning reserve constraints spinning reserve is the reserve capacity of all units synchronized on the grid and ready to take load. at each hour t, the spinning reserve constraint is described as: 1 n t t t t i i d i p u p sr = ≥ +∑ (7) where tsr is the system spinning reserve at time t. iii. equivalent chance-constrained uc model the output power of any wes depends on wind speed and the technical characteristics of the turbine. moreover, wind speed is influenced by several factors depending on the geographical location. indeed, wind speed uncertainty may be characterized by probability principles [43]. the incorporation of wes in the uc problem can be described by including new constraints into the classic uc model. these constraints describe the stochastic characteristic of wind speed that obviously influences the output power of the wes. in this study, the following stochastic constraint is included in the ccuc problem formulation: 1 pr i d l n t t t t i p w p p σ =   + ≤ + ≤     ∑ (8) where σ is a user-defined parameter in the range [0,1] that represents the tolerance that power balance constraint cannot be satisfied at a given time t, t dp is the total power demand and t lp is the total system losses calculated using b-loss formula [13]. tw is the output power of the wes at hour t. obviously, power balance constraint (4) is replaced by the following equation, which results from the integration of the wes: ( ) 1 0 n t t t t t i i d l i p u w p p = + − − =∑ (9) the probability distribution has been widely used to describe the stochastic characteristics of wind speed [44]. in this study, the two-parameter weibull pdf described by (10) is proposed to approximate wind speed distribution. the probability to have wind speed equal to or less than v, called cdf is given in (11). ( ) 1 exp k k v k v v f v c c c −      = −           (10) ( ) ( ) 0 1 exp , 0 k v v v v f v f d v c τ τ    = = − − ≥      ∫ (11) where v is the wind speed. parameters k and c are the shape and scale factors which depend on the geographical location of the wind turbine. after predicting wind velocity from the weibull pdf, the output power w of the wind turbine can be determined as: ( ) 0, if orin outw v v v v vφ= = < > (12) ( ) ( ) ifin r in r r in v v w w v v v v v v φ − = = ≤ < − (13) ( ) , ifr r outw v w v v vφ= = ≤ < (14) where in v , out v and r v are cut-in, cut-out, and rated wind speeds respectively. using probability theories and (12)-(14), the probability to have a wes between zero and rated power can be described as [43]: engineering, technology & applied science research vol. 10, no. 5, 2020, 6316-6322 6319 www.etasr.com alqunun: optimal unit commitment problem considering stochastic wind energy penetration ( ) ( )pr 1 1 exp exp w k in k outr f w w w hw v vw c c = ≤     +          = − − + −                 (15) where r in in v v h v − = . from (15), the stochastic constraint given in (8) can be converted into the following deterministic constraint: 1 1 pr n n t t t t t t d l i w d l i i i w p p p f p p p σ = =       ≤ + − = + − ≤        ∑ ∑ (16) iv. implementation of the solving method in order to have minimum fuel cost, the output power of the wind turbine must be maximum as much as possible. however, it is required to make sure that this power meets the constraint in (16). to meet this objective, for each time-horizon t, wind power is increased gradually until constraint (16) is not verified or until the maximum generation of the wind turbine is reached. then, the total generation will be subdivided economically between all thermal units in order to cover the total load power t d p plus the total losses for the same timehorizon minus the suggested wind turbine output w t . the milp is used in this study to model the ccuc problem. in order to apply the milp solvers effectively, nonlinearities must be removed from the problem. therefore, the quadratic form of the fuel cost of thermal units is converted into piecewise linear functions. the ccuc problem is implemented in gams and the ceplex mip solver is employed for its solution. v. case study to test the performance of the proposed strategy in solving the stochastic uc problem incorporating both thermal generation units and wes, two test cases are considered in this study (all system data are taken from http://motor.ece.iit.edu/ data): (a)case 1: 6-bus system without wes and (b) case 2: 6bus system with wes a. case 1: 6-bus system without wes as given in figure 1, the 6-bus system consists of three thermal generating units, seven transmission lines and three loads. fig. 1. the 6-bus system. the generating units and the transmission line characteristics are shown in tables i and ii. the hourly demand is illustrated in table iii. the objective is to deliver the required energy with the minimum operation cost, and assuming wind power is unavailable in this case. the network operator would satisfy the demand whilst taking into consideration the power supply limitations and the transmission line’s constraints. the optimum hourly power supply of the three generating units obtained after the convergence of the optimization algorithm is depicted in figure 2. it is clear that unit 1 supplies the majority of the required demand due to its high capacity and low production cost. table i. unit data unit 1 unit 2 unit 3 pmin (mw) 100 10 10 pmax (mw) 220 200 50 cost coefficients c ($/mw2h) 0.014 0.02 0.086 b ($/mwh) 19.96 23 29.14 a ($) 200 150 50 start-up cost ($) 50 40 0 shut-down cost ($) 100 200 0 minimum up time (h) 4 3 1 minimum down time (h) 4 2 1 ramp up rate (mw/h) 40 30 20 ramp down rate (mw/h) 50 35 20 table ii. line data line from to x (pu) flow limit (mw) 1 1 2 0.17 140 2 1 4 0.258 110 3 2 4 0.197 140 4 5 6 0.14 140 5 3 6 0.018 130 6 2 3 0.037 150 7 4 5 0.037 50 table iii. hourly demand in mw hour demand hour demand 1 170 13 236.1 2 175.19 14 242.18 3 165.15 15 243.6 4 158.67 16 248.86 5 154.73 17 255.79 6 155.06 18 256 7 160.48 19 246.74 8 173.39 20 245.97 9 177.6 21 237.35 10 186.81 22 237.31 11 206.96 23 232.67 12 228.61 24 195.93 fig. 1. power supply in case 1 (without wind power). engineering, technology & applied science research vol. 10, no. 5, 2020, 6316-6322 6320 www.etasr.com alqunun: optimal unit commitment problem considering stochastic wind energy penetration table iv. operation cost ($) of generating units in case 1 time (h) unit 1 unit 2 unit 3 total 1 4010 4010 2 4139.75 4139.75 3 3888.75 3888.75 4 3733.08 3733.08 5 3638.52 3638.52 6 3646.44 3646.44 7 3776.52 3776.52 8 4094.75 4094.75 9 4200 4200 10 4430.25 4430.25 11 4934 4934 12 4975.25 590 350 5915.25 13 4662.5 1110 5772.5 14 4564.5 1350 5914.5 15 4600 1350 5950 16 4668.965 1415.036 6084.001 17 4567.319 1700.928 6268.247 18 4564.239 1709.592 6273.831 19 4678.5 1350 6028.5 20 4659.25 1350 6009.25 21 4443.75 1350 5793.75 22 4442.75 1350 5792.75 23 4451.75 1230 5681.75 24 4408.25 390 4798.25 total 104179.083 16245.556 350 120774.639 unit 1 is committed alone at hours 1-11 since the hourly demand is less than its maximum capacity of 22mw. at hours 1-11, the hourly demand variation does not exceed the ramping limit of unit 1. unit 3 does not have start-up/shut-down costs, while these costs are very high in unit 2. therefore, unit 3 has been specifically turned on at hour 12 with unit 2 to reduce the operation cost. the hourly operation cost is shown in table iv. the operation cost begins with $4010 when unit 1 was only operated at hour 1. however, the operation cost is increased to $6273 at the peak time (hour 18), which represents an increase of 56% in the total cost as compared with hour 1. b. case 2: 6-bus system with wes in this case, the 6-bus system of case 1 with an extra wind farm is used. the wind farm comprises of 50 wess of the same parameters as shown in table v. the hourly availability of wind power in mw of the wind farm is depicted in table vi. for the applicability of the problem, tolerance σ should verify the following inequality [43] which ensures [ ]0.1447,1σ ∈ : ( )pr 0 1w σ= ≤ < (18) table v. wind parameters k c vin vout vr 1.7 15 5 45 15 table vi. hourly wind power in mw hour wind power hour wind power 1 44 13 84 2 70.2 14 80 3 76 15 78 4 82 16 32 5 84 17 4 6 84 18 0 7 100 19 10 8 100 20 0 9 78 21 6 10 64 22 56 11 100 23 82 12 92 24 52 table vii. power supply of the generating units (mw) in case 2 with variable wind tolerance σσσσ = 0.2 σσσσ = 0.25 σσσσ = 0.3 σσσσ = 0.35 hour units pw units 1 to 3 pw units pw units pw 1 2 3 1 2 3 1 2 3 1 164.81 5.19 160.4 9.6 156.13 13.87 151.9 18.1 2 166.92 8.27 159.89 15.3 153.06 22.13 146.32 28.87 3 156.2 8.95 148.59 16.56 141.2 23.95 133.9 31.25 4 149.01 9.66 140.8 17.87 132.83 25.84 124.95 33.72 5 144.84 9.89 136.42 18.31 128.26 26.47 120.19 34.54 6 145.17 9.89 136.75 18.31 128.59 26.47 120.52 34.54 7 148.71 11.77 138.69 21.79 128.97 31.51 119.36 41.12 8 161.62 11.77 151.6 21.79 141.88 31.51 132.27 41.12 9 168.41 9.19 160.6 17 153.02 24.58 145.52 32.08 10 179.27 7.54 172.86 13.95 166.64 20.17 160.49 26.32 11 195.19 11.77 185.17 21.79 175.45 31.51 165.84 41.12 12 217.78 10.83 208.56 20.05 199.62 28.99 190.78 37.83 13 216.21 10 9.89 217.79 18.31 209.63 26.47 201.56 34.54 14 192.76 40 9.42 214.75 10 17.43 216.97 25.21 209.28 32.9 15 184.41 50 9.19 186.6 40 17 219.02 24.58 211.52 32.08 16 195.08 50 3.78 191.88 50 6.98 218.77 10 10 10.09 215.69 10 10 13.17 17 205.3 50 0.49 204.9 50 0.89 214.52 40 1.27 214.13 40 1.66 18 206 50 0 206 50 0 206 50 0 206 50 0 19 195.55 50 1.19 194.55 50 2.19 193.58 50 3.16 192.61 50 4.13 20 195.97 50 0 195.97 50 0 200.97 45 0 200.97 45 0 21 186.63 50 0.72 191.03 45 1.32 215.45 10 10 1.9 214.87 10 10 2.48 22 185.71 45 6.6 215.1 10 12.21 219.66 17.65 214.28 23.03 23 213.01 10 9.66 214.8 17.87 206.83 25.84 198.95 33.72 24 189.8 6.13 184.59 11.34 179.54 16.39 174.54 21.39 engineering, technology & applied science research vol. 10, no. 5, 2020, 6316-6322 6321 www.etasr.com alqunun: optimal unit commitment problem considering stochastic wind energy penetration the problem is solved for various values of the threshold tolerance σ. in this case, σ is changing from 0.2 to 0.35. the injection of wind power has completely changed the power production of the generating units. the impact of wind power (pw) on the supply of the generating units is demonstrated in table vii. it is clear that the penetration rate of wind energy increases if the tolerance increases and vice-versa. the results obtained for the proposed approach are compared with those found for the stochastic security-constrained unit commitment (sscuc) investigated in [46]. from table viii, it is clear that the proposed strategy provides minimum cost when a wind farm is integrated. moreover, if the tolerance increases the production cost decreases thanks to the increase of the wp output. table viii. total production costs method proposed approach sscuc [46] σσσσ = 0.2 σσσσ = 0.25 σσσσ = 0.3 σσσσ = 0.35 total cost ($) 116,203 112,418 108,845 105,415 121,445.015 vi. conclusion due to the high emergence of renewable energy sources in nowadays power grids, it is important to take into account the intermittent characteristics of these sources. a strategy for solving the uc problem comprising uncertain production is proposed in this paper. in order to address the uncertainty of the output of the wes, the power balance constraint is represented as a chance-constraint with a pre-defined probability called tolerance. the stochastic uc problem is reformulated as a deterministic mixed-integer optimization problem. to do so, the hn strategy was used to convert the chance constraint into a deterministic constraint. the applicability of the proposed 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[46] g. haddadian, n. khalili, m. khodayar, and m. shahidehpour, “optimal coordination of variable renewable resources and electric vehicles as distributed storage for energy sustainability,” sustainable energy, grids and networks, vol. 6, pp. 14–24, jun. 2016, doi: 10.1016/ j.segan.2015.12.001. engineering, technology & applied science research vol. 8, no. 2, 2018, 2790-2795 2790 www.etasr.com alghobiri: a comparative analysis of classification algorithms on diverse datasets a comparative analysis of classification algorithms on diverse datasets muhammad alghobiri management information systems department king khalid university, abha saudi arabia abstract—data mining involves the computational process to find patterns from large data sets. classification, one of the main domains of data mining, involves known structure generalizing to apply to a new dataset and predict its class. there are various classification algorithms being used to classify various data sets. they are based on different methods such as probability, decision tree, neural network, nearest neighbor, boolean and fuzzy logic, kernel-based etc. in this paper, we apply three diverse classification algorithms on ten datasets. the datasets have been selected based on their size and/or number and nature of attributes. results have been discussed using some performance evaluation measures like precision, accuracy, f-measure, kappa statistics, mean absolute error, relative absolute error, roc area etc. comparative analysis has been carried out using the performance evaluation measures of accuracy, precision, and fmeasure. we specify features and limitations of the classification algorithms for the diverse nature datasets. keywords-data mining; classification algorithms; diverse; dataset i. introduction due to the evolving of computer science and the fast development and vast usage of world wide web and other electronic data, information extraction is a popular research field. data mining [1, 2] is a significant method to extract information from data. there are various domains of data mining like classification, clustering, anomaly detection, association rule mining, regression, pattern mining, summarization etc. data mining has even further involved in many other studies like text mining, social network mining, influence mining, sentiment mining etc. data mining utilizes the information from existing data to examine the result of a specific problem. it analyzes the data that may have been extracted or gathered from any business. decision makers opt for data mining to take a decision regarding marketing strategies for their products. data mining interferes data into real-life investigation and can be applied to enhance sales, new product promotion, or product deletion. classification [3, 4] is one of the main domains of data mining and has extensively been used for various purposes like decision making, weather forecasting, prediction of customers’ attitude, prediction of various social risk analysis as well as official tasks, prediction of influential bloggers [5-10] etc. a classification process can easily be separated into two main steps. in the first step, a part of data known as training data is used and each row or value of training dataset comprises a set of characteristics. determination of classes is the main target behind classification. the first phase generates the classification model known as classifiers that depict the relationship between characteristics and classes. in the second phase, the classification accuracy of a classification algorithm that has been generated by the first stage is analyzed. there are various classification algorithms, classified into different categories. the category of classification algorithms includes probability based bayesian algorithms, decision tree based algorithms, neural network based algorithms and kernel-based algorithms. most classifiers use probability calculations to make class labels, however, accuracy measure has not been a target. naive bayes and the c4.5 learning algorithm are alike in predictive accuracy [11-13]. ii. related work classification is a very vast domain in data mining, having received a great deal of exploring over the last few decades. a comparison of four classification algorithms (logistic regression, naïve bayes, c4.5 decision tree and nearest neighbor) has been carried out in standard and boosted forms to predict class members for an online community in [14]. the comparison has been evaluated using two performance measures, one is the area under the curve and another is the accuracy in the standard and boosted forms. analysis conducted depicts very significant differences among base classification algorithms. several classification techniques have been empirically compared within the analysis of unbalanced credit scoring data sets. traditional classification techniques such as neural networks, logistic regression and decision trees have been used in order to find the suitability of support vector machines, gradient boosting and random forests for loan default prediction [15]. the use of data mining is also very common in bio-informatics. authors in [27] emphasized on the importance of rule-based decision trees as a classification method. there are two types of nondeterministic rules in decision tables known as inhibitory rules and bounded rules. in the former, we have decisions on one right side while in the later we can have fewer decisions on the right side. two classification algorithms of polynomial time complexity established on deterministic and inhibitory decision rules have been compared. experiments are executed on five practical engineering, technology & applied science research vol. 8, no. 2, 2018, 2790-2795 2791 www.etasr.com alghobiri: a comparative analysis of classification algorithms on diverse datasets data sets from the predictive toxicology domain and mutagenesis. later experiments performed on a dataset of artificial datasets constructed to evaluate the performance of the classifiers on the basis of different parameters [16]. in [17], different logical analysis methods were compared for hypothetical target classification. this study reveals how preprocessing can protect result confidence and compares the results between multi-quantization, fuzzy and boolean techniques. classification algorithms are used for a variety of purposes including spam filtering [18-20], web page ranking calculation for web spam [21], software defect detection [22], text classification [23], music emotion classification [24], feature-based mining of digital images [25], or annual crop classification [26]. the discussion above reveals that all the existing comparative works on classification algorithms have been done on algorithms of the same category. this study is a novel in the sense that algorithms have been selected with a diverse nature and diverse data sets better than those established on deterministic decision rules. iii. research methodology a. selected classification algorithms there are numerous classification algorithms, but we have focused on algorithms of diverse nature, therefore, three different algorithms have been chosen. c4.5 is the famous algorithm that is based on the decision tree algorithm, whereas the naïve bayes is a probabilistic algorithm and the support vector machine algorithm (svm) is a kernel based algorithm. the diversity of the proposed algorithms can lead decisionmaking to confusion, therefore, in the following, a brief description will be introduced. positioning figures and tables decision tree is also known as a statistical classifier used in classification. the decision tree is produced by c4.5. after a tree is built, the c4.5 rule induction program is used to produce a set of rules. trees are shown by c4t and rules by c4r. at each node of the tree, one attribute is efficiently split its example set into subsets. information gain is used for splitting. attribute with top value of normalized information gain is selected to make the decision. the c4.5 algorithm is recursive on the smaller sub-lists. decision tree divides the features of the documents into partitions. splitting of data reduces the chances of errors at every stage. the root node is used to examine the branches of the tree to predict a label for new data [28]. data is trained in less time because of the graphical representation. we can examine it quickly from root to child nodes in which root node depicts the input. to calculate decision tree we need to calculate two type of entropies.  frequency table of one attribute. (d) = ∑ −(pᵢlog₂pᵢ) (1)  frequency table of two attributes. e(t,x) = ∑ p(e)е∊ e(e) (2) gain(t,x) = entropy(t) − entropy(t,x) (3) naïve bayes (nb) it is a probabilistic algorithm, supposing that some features are not relevant to other features. naïve bayes is used for supervised learning methods, parameter estimation for naive bayes models etc. in a practical environment, this classifier performed better than others. different attempts are taken to improve naïve bayes for classification [29]. new text is presented with t* in a document a. it calculates: t ∗= argmax p(a|as) (4) the naïve bayes (nb) classifier uses bayes’ rule: p(t|a) = ( ) ( | )( ) (5) p(a) does not select t*. by supposing conditional independence of features ƒᵢ’ class d, p( | ) is being estimated. training procedure calculates the relative frequency of p(t) and p(ƒᵢ|t). p(t|a) = pɴʙ(t)( ∏ᵐᵢ₌₁p(ƒᵢ|t ⁿᵢ⁽ᵈ⁾) (6) support vector machine (svm) a learning algorithm which is based on the kernel is used in svm. it is used to identify pattern regression analysis and classification and it performs well in text classification. it predicts classes by using training data. svm carries out nonlinear classification efficiently [30]. training points are separated into two categories based on support vectors by using decision surface. svm optimization is calculated as 1 1 1 arg min{ ( ) } n n n i i i i j j j i i j y x x y            (7) ∑ βᵢyᵢⁿ = 0;0 ≤ β ≤ c (8) b. selected datasets ten datasets have been considered. details of each dataset is shown in alphabetical order in table i. contact lenses the examples in the dataset are complete. the attributes are unable to define all the factors affecting the decision. cpu it is used for prediction in numeric form on the basis of instance-based learning with encoding length selection. credit this is a credit related data set which is the largest and consists of 15 attributes and results in whether the credit is positive or negative. iris-discretized a small dataset about iris classification. it is unique in this regard as its values are ranging and given in special characters and unique style. labor this dataset is the most unlike one as the attributes in the dataset are of a unique style. few are having special characters, engineering, technology & applied science research vol. 8, no. 2, 2018, 2790-2795 2792 www.etasr.com alghobiri: a comparative analysis of classification algorithms on diverse datasets few have enumerated values. there are boolean attributes as well. the attributes are mainly related to wages, pension, allowances, assistance, plan, duration period etc. spambase this dataset is concerning spam and is a very large set of attributes in real format. usually based on the frequency of words or characters or case-based sentences in various categories, the attributes can be described as derived values. it is unique as its values are in real format and derived attributes based values. titanic this dataset is related to the famous titanic sinking event and it predicts a person survival level based on its class, age, and gender. vo this dataset is regarding congress voting. it is very interesting in this regard that it has a number of attributes regarding factors influencing voters to vote either for democrats or republicans. table i. datasets name attributes instan ces classes remarks 1 contact lens 4 24 2 values are in nominal form 2 cpu 8 209 1 class is in real values 3 credit 16 490 2 predicts whether positive or negative 4 irisdiscretized 5 150 3 attributes in special characters 5 labor 17 56 2 attributed in special format, real as well as anime 6 spambase 58 4600 2 predicts whether spam or not 7 titanic 3 2202 2 calculates whether individual survived or not 8 vo 17 435 2 political field data from us elections c. software used weka workbench provides the facility of visualizing attributes and algorithms for predictive analysis. it was built in c language, now we found java-based versions only. it supports many tasks related to data mining like clustering, data preprocessing, classification, feature selection, visualization and regression. the arff file consists of two parts: the header and the data section. as the minimum number of attributes in the datasets is 6, thus, this value has been considered as the number of folds for all the algorithms. the following measures are used to find the results of the given classifiers: precision precision is denoted as the ratio of retrieved documents that are relevant to the search. precision = (9) f-measure the f-measure includes both precision and accuracy. it may be considered as the weighted average of both values. f = ∗ ∗ (10) recall recall is also known as the fraction of relevant instances that have been retrieved over the total amount of retrieved instances. recall = (11) mcc mcc is used for measuring the quality of binary classification. it takes into account tp and fp and is generally known as a balanced measure. |mcc| = x /n (12) kappa statistic kappa is the most robust method of measuring inter-rater agreement for a qualitative item. k takes into account the possibility of the agreement occurring by chance k = k = -…(14) (13) iv. results all datasets have been taken in arff file format, which is used in weka [31, 32] for data mining. the four main diverse nature algorithms have been compared twice. exclusively, the datasets have been analyzed extensively as shown in tables iivii below. table ii. comparative result analysis for naïve bayes algorithm dataset accuracy (%) kappa mean absolute error (%) relative absolute error (%) coverage of cases (%) mean -relevant region size (%) contact lens 70.83 0.43 0.25 67.0 100.0 84.72 credit 77.55 0.53 0.23 44.94 87.96 59.49 iris-discretized 94.0 0.91 0.03 7.15 98.66 35.33 labor 92.98 0.84 0.12 26.25 98.24 65.78 spambase 79.28 0.59 0.20 43.45 79.78 50.43 ticdate 84.5 0.16 0.36 144.2 91.41 58.63 titanic 77.87 0.44 0.32 87.83 100.0 99.9 voting 90.11 0.79 0.09 20.95 93.1 53.2 engineering, technology & applied science research vol. 8, no. 2, 2018, 2790-2795 2793 www.etasr.com alghobiri: a comparative analysis of classification algorithms on diverse datasets table iii. weighted average of detailed accuracy results for naïve bayes algorithm dataset accuracy (%) kappa mean absolute error (%) relative absolute error (%) coverage of cases (%) mean -relevant region size (%) contact lens 70.83 0.43 0.25 67.0 100.0 84.72 credit 77.55 0.53 0.23 44.94 87.96 59.49 iris-discretized 94.0 0.91 0.03 7.15 98.66 35.33 labor 92.98 0.84 0.12 26.25 98.24 65.78 spambase 79.28 0.59 0.20 43.45 79.78 50.43 ticdate 84.5 0.16 0.36 144.2 91.41 58.63 titanic 77.87 0.44 0.32 87.83 100.0 99.9 voting 90.11 0.79 0.09 20.95 93.1 53.2 table iv. comparative result analysis for c4.5 algorithm dataset accuracy (%) kappa mean absolute error (%) relative absolute error (%) coverage of cases (%) mean relevant region size (%) contact lens 83.3 0.71 0.15 0.32 91.0 45.0 credit 85.3 0.70 0.18 37.8 96.0 86.0 iris-discretized 94.0 0.91 0.05 13.4 98.0 44.2 labor 57.9 -0.04 0.46 100.0 92.0 93.0 spambase 92.9 0.85 0.08 18.6 94.9 55.9 ticdate 93 -0.01 0.11 100.0 99.9 99.9 titanic 78.9 0.42 0.31 71.3 99.7 96.3 voting 96 0.92 0.06 12.0 98.6 54.8 table v. weighted average of detailed accuracy results for c4.5 algorithm dataset true positive rate false positive rate precision recall f-measure mcc roc area rpc area contact lens 0.83 0.09 0.85 0.83 0.83 0.70 0.84 0.81 credit 0.85 0.15 0.85 0.85 0.85 0.70 0.87 0.83 iris-discretize 0.94 0.03 0.94 0.94 0.94 0.91 0.96 0.90 labor 0.57 0.62 0.53 0.57 0.54 -0.05 0.49 0.55 spambase 0.93 0.078 0.93 0.93 0.93 0.85 0.93 0.91 ticdata 0.94 0.94 0.88 0.94 0.91 -0.06 0.49 0.88 titanic 0.78 0.42 0.82 0.78 0.75 0.50 0.74 0.77 voting 0.96 0.04 0.96 0.96 0.96 0.92 0.97 0.95 table vi. comparative result analysis for svm algorithm dataset accuracy (%) kappa mean absolute error (%) relative absolute error (%) coverage of cases (%) mean relevant region size (%) contact lens 70.8 0.43 0.31 88.32 87.5 66.6 credit 86.3 0.72 0.13 27.6 86.3 50.0 iris-discretized 94 0.91 0.23 53 100 66.6 labor 85.9 0.68 0.14 30.6 85.9 50.0 spambase 90.6 0.79 0.09 20.2 90.4 50.0 ticdate 98.9 0.10 0.98 0.98 98 50.0 titanic 77 0.43 0.22 51 77.6 50.0 voting 96.0 0.91 0.039 8.2 96 50.0 table vii. weighted average of detailed accuracy results for svm algorithm dataset tp rate fp rate precision recall f-measure mcc roc area rpc area contact lens 0.80 0.05 0.80 0.80 0.80 0.74 0.92 0.71 credit 0.86 0.12 0.87 0.86 0.86 0.73 0.86 0.82 iris-discretized 0.94 0.03 0.94 0.94 0.94 0.91 0.96 0.90 labor 0.86 0.19 0.85 0.86 0.85 0.68 0.83 0.80 spambase 0.90 0.12 0.90 0.90 0.90 0.79 0.89 0.86 ticdata 0.98 0.11 0.98 0.98 0.98 0.92 0.89 0.92 titanic 0.77 0.37 0.77 0.77 0.76 0.45 0.70 0.69 voting 0.96 0.04 0.96 0.96 0.96 0.91 0.96 0.94 evi set the use and out on res wit ma log hav hav me pre car and [1] [2] engineerin www.etasr thorough a idence of the t ts. for compa e algorithms o ed classificatio d f-measure. tperforms the accuracy an spectively. fig. 1. fig. 2. classification th the predicti any classificat gic and metho ve applied thr ve worked ex easures like ecision, recall rried out the c d most widely n. m. ramos, appliation of hygrothermal b. bakhshinat data mining a education and 2018 ng, technology r.com v. compa analysis of th three algorithm arative explici only with resp on evaluation the comparat e other classif nd f-measure comparative comparative vi. c n is a main d ion of classes tion algorithm ods. we have ree widely us xtensively and accuracy, k l, f-measure, comparative an y used perform refe j. m. delgado, r f data mining t conditions, sprin tegh, o. r. zaian applications and d information tec y & applied sci arative analy he above ta ms’ effectiven it evaluation, pect to the thr measures of a tive analysis c fication algori are given in e analysis based o analysis based on conclusion domain of data based on exis ms, each estab 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department of software engineering, college of computer sciences and engineering, university of jeddah, saudi arabia wsalmukadi@uj.edu.sa (corresponding author) received: 12 april 2023 | revised: 24 april 2023 | accepted: 26 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5952 abstract this paper presents the design rationale of a color-changing scarf depending on the emotional state it detects. the goal of the design is to associate people to show up their emotional state especially those who have difficulties in expressing their feelings, such as elderly people, children, people with special needs, and people who have to wear a face mask, which covers their facial expression, as it is common during the covid-19 pandemic period. wearing a smart emotional scarf provides a context of the individual's emotional state that might help surrounding people in dealing with them. our design uses a heart rate sensor and a skin sensor to detect and recognize emotional information. the scarf will change its color based on the emotional state it detects (neutral, angry, happy, and sad). an interface allows the provision of emotional data and displays emotional statistics and daily history. we went through a user-centered design process adopting wearable technology guidelines. a proposed prototype of the smart scarf is presented called scarfy. a user evaluation is conducted showing that wearing the scarf with changing colors based on emotional status is a good solution to express feelings with comfort and wearing it might enhance social engagement. keywords-wearable technology; design process; emotion recognition; internet of things (iot) i. introduction wearable technology has evolved along with wearable sensors and textile technologies, and they are now a part of our daily life. in the subject of human-computer interaction, using wearable technology to provide wearers with emotional support has been seen as an essential research question in humancomputer interaction (hci). in addition, to improve one's own emotional health, it is necessary to have an impact on others' emotional state through interactions in a social setting. moreover, in the field of ambient assisted living, people with mild cognitive impairments (mci), alzheimer's disease, or dementia, require supervision in their everyday activities. the need to develop an innovative approach in order to explore ways of working with elder people and their formal and informal caregivers, is emphasized [1]. providing information on both physical and emotional statuses positively affects multiple stakeholders and facilitates communication. today technologies facilitate monitoring and analyzing body data to recognize a person’s feelings and moods. interaction designers face new challenges when designing wearable technology. beyond those of self-emotional awareness and management, other challenges and principles are raised by the design of wearable technology. designers need to adopt a user-centered methodology to find the important touch points with users that help in finding recommendations for tech designers. smart wearable devices are becoming an increasingly important part of the internet of things (iot) technology. smart watches, wrist bands, headsets, and earbuds are some of the wearable technologies developed for different applications. authors in [2] classify the smart wearable devices into major clusters based on their applications: health, sports, daily activity, tracking and localization, and safety. moreover, iot-based wearable technology can be improved further to save human lives by detecting in advance health risk conditions such as heat strokes [3].  the major challenges of wearable iot devices are data resolution of wearable sensors, power consumption, wearability, safety, security, regulation, and privacy [4]. in this paper, an emotion smart scarf called scarfy is presented. scarfy is connected to an led light that can change its color based on the wearer's feelings. the scarf analyzes the wearers' feelings through their vital signs and tries to help them improve their emotional state and facilitate the elucidation of their feelings to others. in addition, the scarf is connected to a mobile application via bluetooth to store the user's current emotional status. the application helps determines the users’ emotional status and tries to predict different emotional statuses over a period. these data can be used in future work to determine user behavior and predict a user's emotional status. we add a new classification to wearable application, "human emotions". during the design process, focus was to both challenges, data resolution of the wearable sensors and wearability.  engineering, technology & applied science research vol. 13, no. 3, 2023, 10870-10874 10871 www.etasr.com almukadi: smart scarf: an iot-based solution for emotion recognition ii. related work a. emotion and technology heart rate variability (hrv) has been used to quantify controlled emotional reactivity [5]. hrv tracks the ebbs and flows of heart rate. a rise in hrv is associated with positive stimuli, while a drop in hrv is associated with negative stimuli. hence, hrv can be used to gauge a person's emotional state. authors in [6] looked for ways to create a wearable display that changes colors quickly. their ambikraf nonemissive analog fabric display was developed using thermochromic inks and incorporated semiconductor peltier junctions. the controller enables the thermochromic ink to display several colors while regulating the temperature in the soft cloth [7]. authors in [2] studied the association between heart rate changes and emotions changes. they considered three emotions: sad, happy, and neutral. the study uses hrv extracted from the ppg signal and analyzes its relationship with feelings. ten characteristics were computed and analyzed in each measurement cycle. the project is similar to the work in this paper by studying the relationship between heart rate changes and emotional changes using electrocardiograms (ecgs). but our project scarfy uses a skin sensor as well and produces a response based on the results. scarfy is also a wearable smart device that can be used by anyone. in our project we will use the same approach to detect emotions based on hrv. b. emotion and therapy throught a smart-scarf authors in [5] looked for ways to affect a user's mood using bodily data. twelve people aged from 20s to 40s were chosen to discuss their emotional experiences. all participants were college students and employees. numerous concepts were discussed before presenting them to the same group of people: a clever hair band, a bracelet, a helmet, a vest, and a scarf. most of the participants opted to wear a scarf since it is less noticeable and could be worn daily. researchers suggested to create a smart-scarf prototype called smiley to help individuals comprehend selfand emotion-consciousness, improve communication, and strengthen social relationships by altering its color. the interaction concept was developed into three scenarios:  self-scenario  one-to-one scenario  one-to-many scenario a wearable device must be flexible, lightweight, pleasing, conductive, and fairly priced. its design considers connecting to a heart rate sensor module, a skin conductance sensor module, a color sensor module, and an ir transceiver to a lilypad arduino. in our project, we will currently focus on the selfscenario. c. emotion and color combination a color-combination emotion model was created in [8]. it was made up of a three-dimensional axis that depicts the parameters soft-hard, light-heavy, and splendid-sober. the color combinations correspond to nine different mood categories. in his work a book of colors, shigenobu kobayashi examined numerous color combinations while making allusions to various emotion adjectives [9]. the primary focus is given on the interior design, which motivated us to investigate how color combinations and emotions relate to one another. table i summarizes the similarities and differences between the related work and our project. table i. related work summary related work difference similarities detect emotions changes using heart rate changes [2] the project depends only on a heart rate sensor and the result is shown in a screen. our project uses both heart rate and skin sensors then produces a response based on the results on a smart wearable device. smilar to our project in the motivation of studying the relationship between heart rate and emotions changes using ecg. emotion therapy through a smartscarf [5] the interaction concept is developed into 3 scenarios: self, one-to-one, and oneto-many. our project will develop the self scenario. create the same wearable device connecting to a heart rate sensor and a skin sensor. user experience on a smart scarf [8] focus is given on enhancing communication between the scarf wearer and the surrounding parties, while our project does not consider the surrounding parties at this stage. a smart wearable is created that will assist people become more conscious of their emotions in a group surroundings while also enhancing good emotions and reducing negative ones iii. design process design wearable technology is beyond combining electronic components with fashionable clothing, however it should concern physical form, electronic components, graphical user interface (gui), physical interface, and embodied product value [10]. furthermore, the design of wearable technology needs to consider the collection of bodily data and their processing, considering some design principles such as comfort, contextual-awareness, affordance customization, ease of use, pleasant, ergonomy, wearability, and fashion [11]. a. user-centered design process we investigated the use of body data to influence a user’s mood and allowing the surrounding environment to be aware of one’s emotional status. with a web survey method, we reached 269 participants to answer a survey of 14 questions and share their emotional experience. all participants were college students and staff members, and their ages ranged from 17 to 45. they were questioned about what their bodies had gone through when being in depressing or exhilarating situations and how do colors affect their emotional experience. collecting data helped us determine the project requirements and specifications. b. biometrics data gathering and analysis the heart, through contraction and diastole, pumps blood to all parts of the body. when blood is pumped into the body, it produces a pulse in the arteries. this pulse represents the engineering, technology & applied science research vol. 13, no. 3, 2023, 10870-10874 10872 www.etasr.com almukadi: smart scarf: an iot-based solution for emotion recognition number of heartbeats. the healthy heart rate for resting adults is 60-80 beats per minute (bpm) [12]. changes in heart rate can be seen with a typical ecg. there are factors that affect the resting heart rate, including heart problems and emotional outbursts. in our project, we focus on the relationship between changes in the heart rate and the emotional state. mccraty [13] observed a clear change in the pattern of the heart's rhythm due to the change in feelings. it was found that negative emotions such as anxiety and anger cause irregular heartbeats, while positive emotions such as sympathy and love produce high heartbeat rhythms. so, we chose the heart rate as one of the indicators to differentiate between emotions in our project. in addition, in terms of identifying human sensations, skin temperature is an effective indicator. the association between stressful work and skin temperature was investigated and it was discovered that when people are stressed, tense, or have other unpleasant feelings, their skin temperature rises [12]. for accurate results of the wearer's emotional state, we considered combining both sensors, heart rate and skin temperature. they can be used to classify the emotional state in 4 categories (neutral, happy, sad, and angry) [14] as shown in table ii. table ii. emotion states according to the heart rate and skin temperature state bpm skin temperature natural 50 80 36.5 37.5 °c happy 90 100 37.5 38 °c sad 80 90 35 36 °c angry 100 120 37 38.5 °c fig. 1. scarfy changes color base on emotional state. our project will adopt the techniques developed in [14]. we will represent the emotional state with different colors as following: white for neutral, red for angry, blue for happy, and yellow for sad (figure 1). c. interface design we chose cotton fabric to design our smart scarf scarfy (figure 2). the main components of the system are: 1. a scarf made of cotton fabric. 2. heart rate max30100 pulse oximeter sensor: is an i2cbased low-power plug-and-play biometric sensor. 3. skin temperature sensor: an infrared thermometer for noncontact temperature measurements hiletgo gy-906 mlx90614esf non-contact infrared. 4. led light strip: ws2812b. 5. bluetooth: hc-05. 6. arduino: an open-source single-board microcontroller appropriate for low budget, small electronics projects. hrv and skin temperature sensors are used to detect scarf wearer's emotions. they are comfortable, inexpensive, and can be easily attached to the scarf. the arduino board is used to read the input data from sensors and control them. the small size, compact design, and advanced features of the arduino make it an appropriate choice for wearable technology [15]. the system architecture demonstrates the position of the two sensors (heart rate and skin temperature). the sensors will sense heart rate and skin temperature and send the data to the arduino, which will collect and analyze them to determine the emotional state. after that, the led color will change based on the current emotional state of the wearer and send the state to the "scarfy" application via bluetooth. the application will send the state to firebase to store the user status and retrieve when needed for open daily/weekly analysis (figure 3). fig. 2. system architecture and design for scarfy. iv. working procedure in order to detect the emotional state and change led color, we adopt the methodology of [14]. the following algorithm describes the working procedure: if the heart sensor between (100 and 120) and skin temperature between 37 38.5 °c then emotional state is "angry" and led = red else if heart sensor between (91 and 100) and skin temperature between 35 36 °c engineering, technology & applied science research vol. 13, no. 3, 2023, 10870-10874 10873 www.etasr.com almukadi: smart scarf: an iot-based solution for emotion recognition then emotional state is "sad" and led = yellow else if heart sensor between (80 and 90) and skin temperature between 37.5 38 °c then emotional state is "happy" and led = green else if heart sensor between (50 and 80) and skin temperature between 36.5 – 37.5 °c then emotional state is "neutral" and led = white fig. 3. system architecture connecting to mobile application. v. user evaluation scarfy was tested on 10 participants aged between 20 and 25. the participants were seated on an empty lab except for the observer and were asked to wear scarfy. first, each user was required to create an account at the scarfy application by entering his email and password and filling up the profile page. after that, the user has to select some preferred activities regarding his emotional status such as: "what activities help you relax? eat an ice cream, watch a movie, read a book, play video games, go on a picnic, and talk to friends." the user’s preferred activities were attached next to user emotional status as a suggestion message to enhance user’s negative mood and maintain good mood (figure 4). subsequently, different movie clips were played with different contents. the contents were intended to affect the emotions of participants. when the participant was watching the clip and scarfy detected changes in the emotional status, the user was prompted to answer an online questionnaire to evaluate the prototype and provide feedback. figure 5 shows two participants wearing scarfy while being in different emotional statuses during watching movie clips with different contents. moreover, the mobile application provides a feature to users that allows them to view their emotional states during the day or the week (figure 6). this feature allows the users to track their emotional states and be aware of which activities affected their emotions negatively or positively. this analysis may be used as raw data for future work. fig. 4. user interface of the sign up page of the scarfy mobile application. fig. 5. participants during the user evaluation session. vi. disscussion and conclusion this paper focuses on the use of wearable technology to provide wearers with emotional support which is an essential research question in the hci field. our evaluation indicates that users were pleased with the smart scarf’s appearance, comfort, and engagement. the smart scarf was proven simple to use while it assists people to track and control their emotions. at the same time, it provides a good channel for people to show their feelings to the surrounding people, thus facilitating communication. however, inaccurate readings may engineering, technology & applied science research vol. 13, no. 3, 2023, 10870-10874 10874 www.etasr.com almukadi: smart scarf: an iot-based solution for emotion recognition result from the limits of skin conductance and heart rate sensors. moreover, not all body emotions could be distinguished by the two sensors alone. fig. 6. daily (left) and weekly (right) emotional state analysis. for future work, we may consider employing a variety of channels, such as breathing and blood pressure pulse, to detect emotions more emotions with more accuracy. moreover, we should address the gender and culture differences in color and privacy. furthermore, we would like to consider the one to one and group scenarios where users who wear scarfy can communicate together via their scarves sharing their emotional states and allow sending messages based on their emotional status. in general, scarfy aims to enhance social bonds and facilitate interaction. the stored emotional data for users may be an opportunity for further artificial intelligent studies. acknowledgment the author would like to thank amal almaabady, bayan bin tahin, ferdous babttat, and manar alsefri for their contribution in implementing the prototype of scarfy during their senior project. references [1] d. schnelle-walka et al., "proceedings of the 1st joint workshop on smart connected and wearable things 2016," iowit, 2016, https://doi.org/10.1145/2876456.2882849. [2] r. rakshit, v. r. reddy, and p. deshpande, "emotion detection and recognition using hrv features derived from photoplethysmogram signals," in proceedings of the 2nd workshop on emotion representations and modelling for companion systems, new york, ny, usa, aug. 2016, art. no. 2, https://doi.org/10.1145/3009960.3009962. [3] f. john dian, r. vahidnia, and a. rahmati, "wearables and the internet of things (iot), applications, opportunities, and challenges: a survey," ieee access, vol. 8, pp. 69200–69211, 2020, https://doi.org/ 10.1109/access.2020.2986329. [4] s. javed, s. ghazala, and u. faseeha, "perspectives of heat stroke shield: an iot based solution for the detection and preliminary treatment of heat stroke," engineering, technology & applied science research, vol. 10, no. 2, pp. 5576–5580, apr. 2020, https://doi.org/ 10.48084/etasr.3274. [5] b. m. appelhans and l. j. luecken, "heart rate variability as an index of regulated emotional responding," review of general psychology, vol. 10, no. 3, pp. 229–240, sep. 2006, https://doi.org/10.1037/10892680.10.3.229. [6] a. dzedzickis, a. kaklauskas, and v. bucinskas, "human emotion recognition: review of sensors and methods," sensors, vol. 20, no. 3, jan. 2020, art. no. 592, https://doi.org/10.3390/s20030592. [7] r. l. peiris, m. j. tharakan, n. fernando, and a. d. chrok, "ambikraf: a nonemissive fabric display for fast changing textile animation," in 2011 ifip 9th international conference on embedded and ubiquitous computing, melbourne, vic, australia, jul. 2011, pp. 221–228, https://doi.org/10.1109/euc.2011.13. [8] y.-j. lee and j. lee, "the development of an emotion model based on colour combinations," international journal of consumer studies, vol. 30, no. 2, pp. 122–136, 2006, https://doi.org/10.1111/j.1470-6431. 2005.00457.x. [9] s. kobayashi, a book of colors: matching colors, combining colors, color designing, color decorating. kodansha, 1987. [10] j. maeda, the laws of simplicity. cambridge, ma, usa: mit press, 2020. [11] v. g. motti and k. caine, "human factors considerations in the design of wearable devices," proceedings of the human factors and ergonomics society annual meeting, vol. 58, no. 1, pp. 1820–1824, sep. 2014, https://doi.org/10.1177/1541931214581381. [12] m. t. quazi, "human emotion recognition using smart sensors," m.s. thesis, massey university, palmerston north, new zealand, 2012. [13] s. xefteris, n. doulamis, v. andronikou, t. varvarigou, and g. cambourakis, "behavioral biometrics in assisted living: a methodology for emotion recognition," engineering, technology & applied science research, vol. 6, no. 4, pp. 1035–1044, aug. 2016, https://doi.org/10.48084/etasr.634. [14] g. kaur and p. s. pandey, "emotion recognition system using iot and machine learning a healthcare application," in proceedings of the 23rd conference of open innovations association fruct, helsinki, uusimaa, fin, aug. 2018, pp. 465–470. [15] s. zafar, g. miraj, r. baloch, d. murtaza, and k. arshad, "an iot based real-time environmental monitoring system using arduino and cloud service," engineering, technology & applied science research, vol. 8, no. 4, pp. 3238–3242, aug. 2018, https://doi.org/10.48084/ etasr.2144. microsoft word 1-603-ed.doc engineering, technology & applied science research vol. 6, no. 1, 2016, 895-905 895 www.etasr.com jadeja et al.: statcom – a preface to power quality in power systems performance statcom – a preface to power quality in power systems performance rajendrasinh jadeja faculty of engineering, marwadi education foundation rajkot, india rajendrasinh.jadeja@ marwadieducation.edu.in shital patel research scholar school of engineering, r. k. university rajkot, india shital_elect@yahoo.com siddharthsingh k. chauhan faculty of engineering, marwadi education foundation rajkot, india siddhartsingh.chauhan@ marwadieducation.edu.in abstract— this paper investigates different types of flexible ac transmission system (facts) controllers with focus on various operational and control aspects of static synchronous compensators (statcom) to different performance characteristics like power transfer capability, voltage regulation, reactive power management, stability limits, power factor improvement etc. in addition, various features related to statcom like converter topologies, reference compensating signal generation schemes, controllers, and generation of switching signals are reviewed. keywords-power quality; statcom; multilevel voltage source converter; harmonic i. introduction electrical power systems are stretching to their operational limits to meet growing demand. an added issue is power quality, as more and more nonlinear loads connect to the grid. several large power swings and outages can be largely attributed to lack of awareness about system condition as well as inadequate understanding of power quality [1-2]. several researchers have tried to address the issues that fall under the term of power quality. even though there is not a strict universal definition, power quality can be considered as a set of various parameters like voltage/current magnitude variation, voltage fluctuation, voltage/current unbalance, harmonic voltage/ current distortion, high frequency voltage noise [3-4]. flexible ac transmission systems (facts) due to their higher controlling capability and quick response have become an area of research with increased interest. many researchers have developed facts controllers to mitigate different power system problems such as voltage unbalance, poor power factor, voltage sag/swell, reactive power compensation, harmonics etc. these controllers are adaptive to various operational conditions and competent to improve the usage of existing installations. this paper provides a thorough review on the topic, focused on static synchronous compensators (statcom). ii. facts controllers –types & performance analysis facts controllers due to their competency in governing the operation of transmission system by control of interdependent system parameters like power flow control, transmission capability, reactive power control, power quality improvement, etc. have become a key area of research. facts controllers were proposed in [5-8]. depending upon the technological advancements facts controllers are segregated into two generations: the first that uses conventional thyristor switched capacitors, reactors tap changing transformers and the second that uses gtos, mosfets, igbts etc. [9-18]. both generations of facts controllers have distinct operating characteristics with the operation of first generation controllers restricted to reactive power control only, whereas the second generation controllers were able to control both active as well as reactive power flow, of the transmission system[19-21]. based on connection with the grid, facts controllers are classified as series shunt and combined controllers. figure 1 depicts statistics of facts controller installed worldwide. performance analysis for different types of facts controllers is presented in table i. fig. 1. facts controller installation worldwide iii. development and research interest of statcom statcom is the original shunt connected controller and falls amongst the facts controllers. in 1976 gyugyi anticipated the idea of power flow control through statcom. as per ieee definition static synchronous compensator is competent to control capacitive or inductive output current independent of system voltage [1]. the entire power flow control is achieved by injection or absorption of controlled reactive power into/from the power system. at the time of lapse in system voltage statcom feeds reactive power engineering, technology & applied science research vol. 6, no. 1, 2016, 895-905 896 www.etasr.com jadeja et al.: statcom – a preface to power quality in power systems performance (capacitive) and during increased system voltage statcom takes up reactive power (inductive) [2]. figure 2 is an indicative of the research work being carried out in the area of statcom applications. it is clearly depicted from figure 2 that most research work has been carried out on the usage of statcom for voltage control in power system. it is shown that statcom application for voltage control in power system has increased in the past decade. this also reflects the extensive utilization of statcom in power system stability and power quality issues. it is also shown that statcom application in renewable energy has also increased significantly. table i. performance analysis of facts controllers svc tcsc tcpst statcom sssc upfc ipfc mva capacity best best good better better better better reactive power control good better better good best best best voltage control best good good best good better better thermal stability good better good good better best best transmission competency good best better good best best best transient stability good best better better best best best investment cost good good better better better best best converter loss better good good better better best best expected operational life best better better best better better better installations till date best best better best better good good future trends better better better best best best best fig. 2. statcom growth (publications in the ieee/iee library) iv. statcom component statcom controllers achieve active as well as reactive power control by injecting current in to the line at the point of common coupling. saha et al, have presented various topologies and control algorithms for statcom [22]. also, the facts program sponsored by electrical power research institute (epri) identifies the significant challenges faced by the facts technology and their proposed solutions [23]. various applications of shunt controllers have been studied and reported in literature [24-25]. controllable reactive power can be generated by all types of dc to ac switching converters (voltage source and current source converters). however due to issues like high conduction losses, additional over voltage protection and higher voltage rating for the semiconductor in current source converter, voltage source converter is popular in power system application like facts controllers, especially statcom. a controlled three phase voltage of power frequency is produced by sequential switching of power semiconductor devices. the power flow either from line to controller or controller to line is due to dc charged capacitor at input side of converter. each output voltage of converter is in phase with line voltage due to small tie reactance linking converter and line. conventionally two-level vsc are used for statcom, however, nowadays multi-level vsc due to its modularity in structure and power handling capability are quickly replacing two-level vscs for statcom [26-39]. a. multilevel voltage source converter topologies for statcom multilevel converters have substituted the traditional converters due to structure modularity and low total harmonic distortion (thd). components required per leg for different multilevel converter topology are listed in table ii. table ii. component per leg of multilevel voltage source converter converter type diode clamp flying capacitor cascaded main switching device (m 1) x 2 (m 1) x 2 (m 1) x 2 main diode (m 1) x 2 (m 1) x 2 (m 1) x 2 dc bus capacitor (m 1) (m 1) (m 1) / 2 balancing capacitor 0 (m 1) x (m 2) /2 0 clamping diode (m 1) x (m 2) 0 0 1) diode clamped multilevel converter extensive number of clamping diode and balancing of dc link voltage are the two major issues that made diode clamped multilevel inverter less popular. diode-clamped converter with virtual vector based modulation [40] and space vector pulse width modulation [41] for dc link voltage balancing algorithm has been proposed with experimental results. dupuis and okou have proposed a novel approach for dc link voltage balancing based on sub-controller [42]. statcom output voltage is supposed to be controlled by: terminal voltage sub-controller, neutral-point sub controller alleviate neutral point and two more auxiliary controllers maintain dc capacitor voltage [42]. a method to find the state space model for a general n-level engineering, technology & applied science research vol. 6, no. 1, 2016, 895-905 897 www.etasr.com jadeja et al.: statcom – a preface to power quality in power systems performance diode clamped converter evaluated with simulation can be found in [43]. voltage balancing between different capacitors with the use of an auxiliary capacitor in diode clamped multilevel converters is discussed and compared with traditional methods [44-45]. a combine diode-clamp cascade multilevel converter topology is suggested, where multilevel principal synthesizes output voltage with sub-harmonic pwm technique [46] and advantage of fewer numbers of clamping diodes helps in cost and size reduction [47]. increased use of power electronics application, wind energy application and solar photovoltaic application, multi-level converters are designed for specific duty cycle, optimal balancing strategy, reduced switching strategy and specific modulation approach [48-54]. 2) flying capacitor multilevel converter with the large amount of energy storage capability during power outage, prevalent real and reactive power flow control and low harmonic content the flying capacitors multilevel converters have been accepted in facts control application. the only difficulty is that the excessive number of storage capacitors complicates converter control for real power transmission and capacitor voltage balancing issue [55-56]. the conventional flying capacitor multilevel converter performance can be improved by replacing the clamping capacitors by a number of series connected half bridge cells which will generate voltage at the converter output [57]. the measurement of voltage and selection of suitable switching states can control harmonic content of generated wave form, switching frequency and load impedance. a closed loop control based on phase shifted spwm strategy with adjustment in switching time of selected switching states or selective harmonic elimination pulse-width modulation control has improved the selfbalancing characteristics of the converter [58-60] and this can be achieved by adding two low frequency switches and capacitors [61]. the combined conventional flying capacitor multilevel converter with two level bridges is proposed in [62] and its soundness is checked with simulation. also semi bridge converter with reduced switch count and free phase leg structure is used for unity power factor application [63]. output voltage vector method for swapping of two switch modes which uses charging current in flying capacitor multilevel inverter is developed and simulation results are derived [64]. the number and size of flying capacitor limits use of converter. as a solution of this converter with multiple duty cycles with modulation technique in direct response to the capacitor voltage is explored [65-66]. a synchronous reference frame control is also broadly used to control power flow and dc bus voltage unbalance. ghias et al. have carried out the simulation for back to back flying capacitor converter with reduced dc bus capacitance [67]. a work has been done on average models in abc and dq0 coordinates which will improve the performance of flying capacitor multi-level converters [6869]. 3) cascaded multilevel converter cascaded-multilevel voltage source converter with separate dc source is proving itself an appealing concept due to its modularity in structure [70-72]. peng et al. have proposed a cascaded 11-level inverter with a control scheme in which swapping pulses p1-p5 at every half cycle makes all dc capacitor voltage equally charged and discharged [73]. instead of using dc voltage source of same magnitude if a dc voltage source of magnitude ratio 1:2:4:8, the traditional 9-level inverter is switched to 31-level inverter [74]. a six stage, 31level converter of 30 kv with minimum step of 2 kv is simulated and tested on hardware of railway power compensators [75]. due to generation of medium/ high voltage capacity directly at converter output allows to eliminate the coupling transformer [76]. while in [77], a cascaded transformer for multi-level converter is suggested. this is the concept where, each level of the converter is transformer connected. this idea works for equal power sharing and losses estimation for multi-level converter. in [78] two structures for 11 kv and 33 kv are proposed with 81 and 27 levels. here two comparative studies are carried out. the one with all cascaded converter of equal size cell and the other with the selection of cell size made on the basis of its dc-link voltage. in terms of their losses results, it is shown that the 27-level, 33 kv converters are superior with equal sized cell while the 81 level, 11 kv converters are good with ternary sequence selection of dc-link voltage. instantaneous power theory for reference current extraction has been executed for multi-level inverter used in wind mill. the approach of the author is to analyze dynamic response of statcom for constant speed wind turbine [79]. modular structure of cascaded multilevel inverter with two full-bridge units in parallel with two halfbridge units with single control loop to control both dc link voltage [80] and to improve power factor [81] has been obtained. the addition of two controllable diodes in each cell to reduce voltage ripple is a novel technique proposed in [82]. multilevel converters made of cascaded cells energy storage systems integrated with conventional topology or with integer/non-integer dc voltage ratio or dynamically varying voltage ratio have made multi-level converter application more attractive [83-86]. a concept of sub-multilevel converter blocks is explored with reduced number of switches and capacitors through experimental result in [87-89]. an asymmetrical 147level converter topology with sub-multi-level arrangement is proposed. the objective of this converter is to improve its’ performance for dvr. together with conventional number of switches at each level, two additional switches between two dc sources are used to generate more number of level in [90]. reference [91] deals with the elimination of dc components of current in coupling transformer secondary due to core saturation issues. authors have proposed two methods to achieve this: either reduce the positive half cycle area by keeping the negative half cycle area constant or reduce the positive half cycle area by increasing the negative half cycle area. experimental results are derived for 154 kv, ±50 mvar, t-statcom. a digital controller parallel to pd and repetitive control is simulated by xu et al. in [92]. to achieve dc link voltage regulation, low thd, redundancy and reductions in cost; modular multilevel converter topologies like single star bridge cells, single delta bridge cells, double star bridge cells etc. for drives and pv solar system are discussed in [93-94]. the multilevel converter topology generally uses the fundamental engineering, technology & applied science research vol. 6, no. 1, 2016, 895-905 898 www.etasr.com jadeja et al.: statcom – a preface to power quality in power systems performance switching frequency modulation method and the high frequency pwm method [95]. an accurately designed switching scheme can further reduce converter losses, size of inductor and dc capacitor. as a harmonic elimination technique, it gives better result compared to other techniques, but its complexity in deciding the parameter rating increases as the levels of the inverter increase [96-98]. reference [99] shows the comparative simulation studies of sine-wave pulse width modulation (spwm) and optimized hybrid phase disposition method (ohpdpwm) to measure the effectiveness of statom control. dc voltage balancing with phase shifted sinusoidal pulse width modulation (ps-spwm) technique for cascaded multilevel converter by means of experimental result is proposed in [100-103]. this scheme helps out to eliminate weighty transformer and reduces converter power loss. sinusoidal pulse width modulation (spwm) with carrier phase-shifting, unipolar phase-shifting, reversing voltage etc. for statcom to reduce thd and switching frequency is discussed in [104-106]. b. controller design for statcom for ease the following section is arranged as;  pole placement controller technique  pi / pid/ pd controller technique  dc-link balancing controller technique  hysteresis band controller technique this however, doesn’t mean that the above mentioned controller techniques are the only solutions. researchers are continuously updating previous concepts by amalgamating existing one. pole placement controller design with two set of controller gain i.e. first gain, by the use of linear matrix inequalities (lmis) to meet design specification and second gain, by the use of zero set to meet overall system voltage control [107], first gain with one modulation index for steady state and second gain with adaptive modulation index for transient [108], combine linear-quadratic regulator (lqr) [109] etc. are discussed for improving the operation of statcom. in the environment of damping power systems oscillations, two controllers which regulate dc voltage and ac voltage using the optimal pole shifting (ops) technique [110] are proposed. also, the same concept but with fixed modulation index (mi) and variable dc capacitor voltage reference is implemented for statcom in [111]. single machine infinite bus and two area four machine system for damping control by the nonlinear matrix inequalities is proposed in [112] with tested closed-loop performance under three phase fault and small signal disturbances. reference [113] has come up with the exact linearization method to transform the nonlinear threedimension equations with proportional integral control. simulation results are derived for statcom operation for three phase ground fault too. a h∞ loop shaping technique [114] for voltage magnitude and angle controller is identified and compared with a pid controller using pole placement method for gain derivation. rule based controller, which utilizes fuzzy logic, bang-bang, root counting theory, selftuning pi with particle swarm optimization etc. are proposed over a fixed parameter pi control to enhance the improved performance of controller [115-117]. behavior of sssc and statcom on single machine infinite bus [118] and svc and statcom with usual lead – lag controller [119] with particle swarm optimization for dynamic stability performance has been proposed. the result proves that the sssc offers fast dynamic recovery amongst all three. an adaptive pi controller is designed to maintain the voltage at point of common coupling for a range of instability. for the intended change in the gain of pi controller a cautious study of previous gain, practical gain and global is done for the algorithm [120-121].a self-tuning statcom with pi controller based on real time data adoption and gain setting with pole placement technique for different loading condition is designed and simulated [122123]. a direct axis current control for any pi, pid or adaptive mechanism is proposed in [124]. simulation results are compared for controller output voltage variations when reactive power demand does not exceed limits and when reactive power demand exceeds them. particle swarm optimization technique for ac/dc voltage regulation, ac/dc damping controller, power system stabilizer on the single bus system with several fault condition with simulation result is investigated in [125]. in [126] transient stability is improved using euler-lagrange method based on passivity, where setting of pi controller kpd=0.01, kid=0.3, kpq=2 and kiq=10 and in [127-128] a back to back statcom based on passivity controller with pwm based rectifier section and multipulse inverter section is proposed. whereas in [129] sliding mode technique is adopted where inner loop performs for switching of vsc and outer loop performs for ac and dc side voltage control. a decoupled controller with pole placement technique having an inverter voltage of 480 v and a reference reactive power of 1000 var is tested for reactive power change up to 5000 var. while doing so the capacitor voltage variation is very small [130]. a various approach supporting zero set technique, additional current feedback, phase-lead compensation, and series passive compensation, shunt active compensation etc. are conceded to study system dynamic [131-135]. in the case of [136] ct behavior is analyzed for cascaded multilevel inverter feedback loop. voltage compensation at far end of line is experimented by 8 kva, 415 v statcom. the results are strongly matched with speculative framework as voltage sag is reduced by 39% for the statcom designed at 25% of rated load [137], while in [138] an attempt to integrate power converter with digital controller equipped with optical interface is described. this local controller is also capable of sensing signal and sending them back to the power converter via a serial port. mohan et al. have worked out the issues related to practical implementation of statcom for voltage regulation through estimation of load conductance with feedback control. they have modeled statcom as an instantaneous reactive current source which controls dc bus voltage with tolerable value of charging and discharging current [139-143]. singh et al. has come up with low thd, 48–pulse, voltage source converter. the uniqueness is achieved by 8 set of double star connected 2–level converter topology. the phase angle difference between two star connections can control reactive power [144]. engineering, technology & applied science research vol. 6, no. 1, 2016, 895-905 899 www.etasr.com jadeja et al.: statcom – a preface to power quality in power systems performance dc capacitor voltage balancing with swapping switching pattern for fixed time period only has been proposed in [145148]. here two series h-bridge five level converter is simulated and tested on prototype. at some instant the swapping of switch may introduce redundant switching loss and phase shift in voltage. this limitation is overshoot by small signal model and dead band controller where controller is designed to work in capacitive, inductive and standby mode with changing frequency of 120 hz [145 –148]. a wide area control technique for 12-bus statcom is proposed in [149] capable of controlling large power disturbance. at the time of operation, the controller generates two signals, one for avr of generator and second for statcom. these will together look up the damping of generator rotor during interruption and restoration too whereas in [150] an automatic gain controller is designed for a gain 0< k≤ 1. stability enhancement with less variation in dc voltage is the key issue while designing a controller. in [151– 154] an attempt to offer the solution for the above said problem via modified invasive weed optimization (miwo) algorithm, back to back statcom or loop-shaping technique is presented. a repetitive controller is endowing with the conventional pi controller to trail or refuse the signal with moderate steady state error. for abrupt changes in load the output of the repetitive controller is constant which offers effectiveness in power factor improvement and dc voltage stabilization [155]. statcom controller based on rl trial and error is designed. the data is monitored online through six layer fuzzy neural network controller [156]. floating of dc voltage is a challenging issue for today’s facts controllers. in [157-161] the focus is on how to improve the drift in voltage for diode clamped multi-level converter by space vector modulation techniques. while managing voltage stability or reactive power compensation, inverter losses and harmonics in a statcom controller is also a question of research. a multilevel inverter with harmonic elimination method is one of the suggested solutions. but these can malpractice with the change in load condition. in [162-164] the authors had put on the concentration on current harmonics due to resonance, dc voltage ripple due to firing angle of each switch, consequence of coupling transformer. also a square-wave controller with current feedback and phase lead compensation is proposed. differential algebra [165] and a loop shaping method with use of hysteresis band are worked out where pre and post comparator shaped to provide a preferred open loop [166-167]. the best input signal is chosen by inspection. here a complex perturbation is used to compute optimal control. a seven level cascaded multilevel converter is design as standalone system or h-bridge building blocks technique for 1.5 mva. this model is capable of handling 4.5 to 30 mva by adding more number of h-bridges [168-169]. in [171], a ±75 kvar, 50 hz, angle-controlled statcom was put up for minute operating rang of angle difference between converter voltage and system voltage. the value of angle is set (1.5°, 1.5°), hence state-space averaging principal provides more accurate results for reactive power compensation [170]. similarly root locus method [171] and dynamic voltage controller configurations with negative sequence component and phase voltage magnitude is suggested for steady state and dynamic stability [172-173]. an adaptive control that counts the ambiguity in the parameter variation is designed and tested for power factor improvement. author has also compared adaptive controller test results with conventional vector control test results which satisfy the performance of statcom in both the case [174-175]. a comparative analysis is conceded for voltage source converter (vsc) in shunt and series connection applications. along with this radial basis function network based vsc is proposed and compared with pi controller based vsc for statcom, sssc and upfc [176177]. high power multipulse, multipoint clamped and chain converter topologies are analyzed on basis of no. of devices, total harmonic distortion, component sizing, capability of voltage control and dc voltage drift. later on, generalized nconverter module for h-bridge is presented which uses voltage and current harmonic component to stabilize the dc capacitor voltage. experiments were executed for two and three modules where second harmonic of line voltage has been adopted for injected component [178-180]. h-bridge cascade multilevel statcom with low voltage and 11 kv power rating hardware has been jointly developed by university of newcastle and restech pty ltd. voltage balancing is done by arranging the dc capacitor voltage in incremental order. this will decide the sequence of phase leg to generate the output based on instantaneous real power flow [181-184]. a nonlinear controller based statcom on multi-machine power system is designed and simulated for three-phase to ground fault at two different nodes [185]. a special purpose statcom for spallation neutron source power beam accelerator at oak ridge national laboratory has been effectively implemented for full rated power [186]. also for regulation of bus voltage a system stabilizer based on statcom is designed on computational optimization approach [187]. ±100 mvar, 132 kv, 48–pulse, 2-level statcom is designed to locate at midpoint of line. the reason behind midpoint location is that it requires only four transformers which further reduces size and cost [188]. in [189] superconducting magnetic energy storage coil is integrated with statcom operation for three phase to ground fault. the operation of the proposed statcom is simulated for voltage control as well as frequency control model. a space vector based 3–zone, 5–zone and 7-zone, pwm technique has been carried out by narayanet al. the proposed work is to reduce current ripple for inverter used in high-tension lines [190]. few converters reported for adjustable speed drives (asds), are also reviewed to analyze their probable application in statcom. a concept of 5-level inverter has been implemented by cascading one 2-level and one 3-level inverters [191]. mahadevan et al. team has suggested phaseshifted dual source matrix converter topology [192] v. conclusion by looking at the number of papers published in recent years, it is easy to conclude that a variety of facts controllers is available for evaluating performance in large power systems. engineering, technology & applied science research vol. 6, no. 1, 2016, 895-905 900 www.etasr.com jadeja et al.: statcom – a preface to power quality in power systems performance the research and development activity to obtain accuracy has adequately crossed the threshold. a trend of having more and more advanced facts controllers is evident. this paper provides 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levi, “a reducedswitch-count five-level inverter with common mode voltage elimination for an open-end winding induction motor drive”, ieee transactions on industrial electronics, vol. 54, no. 4, pp. 2344-2351, 2007 [192] s. mahadevan, s. raju, r. muthu, “elimination of common mode voltage using phase shifted dual source matrix converter with improved modulation index”, the international journal for computation and mathematics in electrical and electronic engineering, vol. 32, no. 6, pp. 2006-2026, 2013 engineering, technology & applied science research vol. 8, no. 5, 2018, 3338-3343 3338 www.etasr.com oad et al.: flexural stress-strain behavior of rc beams made with partial replacement of coarse … flexural stress-strain behavior of rc beams made with partial replacement of coarse aggregates with recyclable concrete aggregate part-2: rich mix mahboob oad department of civil engineering, quaid-e-awam university engineering, science & technology, nawabshah pakistan engrmahboob04@gmail.com abdul hafeez buller department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah pakistan engrabdulhafeezbuller@gmail.com bashir ahmed memon department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah pakistan basher_m@hotmail.com noor ahmed memon department of civil engineering, quaid-e-awam university of engineering, science & technology, nawabshah pakistan nahmedmemon@gmail.com samiullah sohu department of civil engineering, quaid-e-awam university college of engineering, science & technology, larkano, pakistan sohoosamiullah@gmail.com abstract-crowded city centers pose serious problems of infrastructure and associated facilities. construction industry is obliged to opt for vertical construction in place of short height structures in order to meet with the needs. this leads to the generation of huge quantities of demolishing waste whose management is a serious issue. one of its best uses is its utilization in new concrete. concrete is widely used in construction industry. normally 1:2:4 mix is used, but the use of rich mix is also common in columns and elsewhere. therefore, this research work focuses on evaluating the flexural stress-strain behavior of rich concrete mix beams made with 50% replacement of natural coarse aggregates with coarse aggregates from old concrete. a total of 12 reinforced concrete beams 1:1.5:3 ratio mix and 0.54 w/c ratio are prepared in two batches in 0.9mx0.15mx0.15m beams. in the first batch, natural coarse aggregates are replaced in 50% with coarse aggregates from demolished concrete and the second batch contains beams made with all-natural coarse aggregates. to reinforce the beams, 2#4 deformed bars are used in compression and tension zone along with #3 stirrups at 15cm c/c all along the length of the beam. in each batch, half of the beams are cured for 7 days and half for 28 days. after curing, all beams are tested for load, deflection, and strain in a universal load testing machine. all parameters are recorded at regular intervals and cracking and failure patterns are monitored. from obtained results, it is analyzed that the beams presented 11.68% reduction in flexural capacity. cracking pattern and failure mode of the beams is similar to those of the control specimen. keywords-flexural stress; green concrete; old concrete; recycled coarse aggregates; strain i. introduction living space and associated infrastructure congestion in urban areas pose serious problems around the globe. construction industry is forced to opt for vertical constructions particularly for residential purposes in place of short height buildings. therefore, demolishing of short height buildings and construction of higher buildings has become a need of the day, resulting in huge amounts of construction waste. unavailability of landfills to deposit this demolishing waste poses another problem. transportation of this waste to far distances causes loss of time and it is also expensive. proper disposal of this waste is a serious need. the utilization of this waste in new construction as a remedial measure has been proposed and the relevant research is active. this not only helps in waste management efforts but saves natural aggregates. different researchers studied properties of concrete by making use of demolished concrete as partial or full replacement of natural coarse and fine aggregates [2-5]. concrete’s behavior with respect to load-deflection, cracking, ultimate load etc. have been studied. focus has also been made on cleaning and screening of old concrete before using it in new concrete. although the material has successfully been used in pavements, sideways and walkways yet, different proposals based on the research outcomes show wide scatter, giving room for more research. the, already completed, first part of this research focuses on the flexural stress-strain behavior of reinforced concrete beams made by replacing 50% natural coarse aggregates with coarse aggregates from old concrete batched with 1:2:4 mix. engineering, technology & applied science research vol. 8, no. 5, 2018, 3338-3343 3339 www.etasr.com oad et al.: flexural stress-strain behavior of rc beams made with partial replacement of coarse … the selection of 50% replacement is made following the conclusions of [3]. this research work addresses flexural stress-strain behavior of above mentioned beams made with rich mix (1:1.5:3). old concrete from rc buildings / rc members demolished in nawabshah city is collected in the form of large pieces. these large pieces are then hammered down to approximately 25mm size. the smaller objects are then screened and sieved with a 25mm sieve. for the research presented in this paper 6 reinforced concrete beams are prepared using opc, hill sand, natural coarse aggregates and coarse aggregates from old concrete in 50% proportion in 1:1.5:3 mix. to reinforce these beams two #4 bars are used in both tension and compression zone along with #3 deformed bar as stirrups at 15cm c/c from the left to the right end of the beam. six reinforced concrete beams using the same specification, except for 100% natural coarse aggregates, are also prepared (control specimen). in both batches three beams are cured for 7-days and another three for 28-days. normal water curing is adopted. after curing, all beams are tested with central point load up to rupture. load, deflection and strain are recorded at regular intervals during loading process. from the recorded load, flexural stress is computed by using numerical expression. during the loading process, track of cracking pattern and cracking load was recorded for analysis and comparison. obtained results were analyzed, compared and presented in tabular and graphical form. typical and selected images of cracking in beams are also given in relevant sections. it is believed that the results of this research pave way for setting reference for scholars in the field and improve the understanding of using rich mix with 50% replacement of natural coarse aggregates with coarse aggregates from demolished concrete. ii. literature review finding alternative materials for cement, fine and coarse aggregates is an active research area. to this end, the use of demolished concrete in new concrete is also studied but more research is required to make solid conclusions regarding its behavior. recent development on the use of demolished concrete as course aggregate in new concrete in [1] presents the possibilities of using demolished concrete as coarse aggregate. author in [1] discusses the difficulties associated with the use of demolished concrete. he concludes that partial use of demolished concrete as coarse aggregate has very good effect on the strength of the new product. authors in [2] used 50% replacement of natural coarse aggregates with coarse aggregates from demolished concrete. they used mathematical modeling to establish the relationship between the tensile strength and weight of concrete specimen. they compared tensile strength of cylinders made by using 50% replacement by coarse aggregates from demolished concrete and cylinders made by natural coarse aggregates alone. obtained results show 5% loss of tensile strength in comparison to control specimen. authors in [3] used replacement of natural coarse aggregate from 0 to 50% with 5% increment and studied the compressive strength of concrete cylinders. for their research, they used 1:2:4 mix and water cement ratio from 0.45 to 0.6. they tested 54 cylinders made with 100% natural coarse aggregates and 324 cylinders with aggregates from demolished concrete. they altogether tested seven batches of the cylinders in three groups of 7, 14 and 28 day curing. based on the outcome of this testing, they concluded that demolished concrete can be used as an alternative of natural coarse aggregates as they recorded maximum decrease in compressive strength equal to 26% with 50% replacement of natural aggregates. on the use of demolished concrete as partial replacement of coarse aggregates in new concrete, authors in [4] used 50%, 60%, 70% and 80% replacement of natural coarse aggregates in slabs. test results showed that 50% replacement is the optimum as with this replacement they observed only 7.1% reduction in maximum load. they also observed maximum deflection at the slab center equal to 4.4mm which is within the allowable limits of aci 318 [14]. study of flexural behavior of reinforced concrete beams made with partial replacement of natural coarse aggregates with aggregates from demolished concrete was conducted in [5]. authors prepared 30, 36"x6"x6" size beams using 1:2:4 mix and 0.45-0.55w/c ratio along with 4#4 deformed bars and #2 bars as stirrups. authors used 50% to 80% replacement with 10% increment. they used 28-day curing for all beams and performed testing for flexural strength and cracking behavior. from the test results, they recorded 12% as minimum and 26% as maximum reduction in flexural strength. the research outcome also revealed that 88% strength can be obtained using 50% replacement. thus, they concluded that demolished concrete can effectively be used as coarse aggregates in new concrete, particularly in the areas of moderate or low load. authors in [6] studied the flexural strength of concrete beams made with preplaced coarse aggregates with colgrout. they called this new material colcrete. they used colgrout to prepare concrete beams of size 750mmx150mmx150mm in two batches. one with 1:2:4 mix and 0.56w/c ratio and other in 1:3:6 mix with 0.58w/c ratio. they also prepared similar beams with natural coarse aggregates as control specimens. after curing for 28 days all beams were tested for flexural strength. the comparison of the results shows that the performance of colcrete in flexure was better than that of concrete. hence they concluded that the use of colcrete particularly for members predominantly loaded in flexure is more effective than normal concrete. author in [7], studied the feasibility of using recycled concrete for pavement work, with laboratory testing and finite element analysis. laboratory results showed that the compressive strength and modulus of elasticity decreased slightly with increase in percentage of recycled concrete aggregates. using these parameters, finite element analysis was performed to determine the maximum stresses under critical temperature and loading conditions. the obtained results were in good agreement with the theory. authors in [8] conducted research using lateritic sand and quarry dust as fine aggregates to study flexural and tensile strength of concrete. they used variation of 0 to 100% with interval of 25% against quarry dust and prepared samples using 1:1.5:3 mix with 0.65w/c ratio. the samples were cured for 28 days followed by testing for flexural and tensile strength properties. test results showed that both flexural and tensile strengths increased with increase in lateritic percentage. based on the results, they concluded that the mixture of lateritic sand and quarry dust can be used as a replacement of river sand engineering, technology & applied science research vol. 8, no. 5, 2018, 3338-3343 3340 www.etasr.com oad et al.: flexural stress-strain behavior of rc beams made with partial replacement of coarse … without losing much flexural and tensile strength concrete properties compared to normal concrete. authors in [9] studied section stress distortion performance and failure characteristics of beams made with recycled concrete. they prepared beams with 50%, 70% and 100% recycled concrete along with 0.68%, 0.69% and 1.13% steel reinforcement. based on the experimental results, they concluded that the distortion and destruction pattern, cracking moment and ultimate flexural carrying capacity of the beams, in comparison to control beams, was the same, however the beams made with recycled concrete presented more deflection than the control specimens. to study the flexural behavior of reinforced concrete beams strengthened with bfrp bars, authors in [10], conducted experimental work to determine the load-deflection behavior. from the experimental results, they observed that the new material had bonding problem. the deflection of the beams was also larger than that of the control specimens. therefore, they concluded that the bonding problems affect severely the usage of bfrp bars in concrete. flexural behavior of concrete beams using recycled fine aggregate as partial replacement of river sand and steel fibers was evaluated in [11]. authors used various doses of recycled fine aggregates and based on the research outcome they concluded that the use of recycled fine aggregates in structural concrete has promising effect on the strength of the concrete. authors in [12] used 100% replacement of course aggregates with coarse aggregates from demolished concrete to study the load-strain behavior of reinforced concrete beams along with the influence of steel fiber reinforcements. based on the experimental results they observed that addition of steel fibers and recycled aggregates significantly increased the mechanical strength and fracture process in comparison to the control concrete. authors in [13] conducted flexural loading tests on concrete beams made with recycled concrete aggregates. both fine and course aggregates were produced from demolished old concrete. they studied and compared basic concrete properties and load-deflection behavior. based on the test results the conclusion was that the use of demolished concrete as aggregates in the new concrete is possible under the proper design procedures and limits of usage of the aggregates. iii. model and testing reinforced concrete beams of 0.9m length and 0.15mx0.15m cross-section were used. a total of 12 beams were prepared, out of which 6 beams were prepared by replacing 50% natural coarse aggregates with coarse aggregates from old concrete and 6 beams were prepared with 100% natural coarse aggregates. the latter are termed as control specimens and are used for result comparison. large old concrete pieces were collected from demolished concrete structures/reinforced concrete members in the vicinity of nawabshah city. the pieces were then hammered down to maximum size of 25mm. the resulting dust was then sieved with 25mm sieve to match the natural coarse aggregates in use. to provide reinforcement in the beams 2#4 deformed bars were used both in tension and compression zones along with #3 stirrups all along the length of beam at 15cm c/c. ordinary portland cement, fine and coarse aggregates were then batched in 1:1.5:3 proportions with 0.54w/c ratio. a few beams are shown in figure 1. table i presents the beam details. fig. 1. model beams table i. specimen details batch no 1 2 no. of spec: 3 3 3 3 % rca 50 50 0 0 mix ratio 1:1.5:3 1:1.5:3 1:1.5:3 1:1.5:3 w/c ratio 0.54 0.54 0.54 0.54 curing period 7 28 7 28 main steel bottom 2#4 2#4 2#4 2#4 top 2#4 2#4 2#4 2#4 stirrups #3 @ 6" c/c #3 @ 6" c/c #3 @ 6" c/c #3 @ 6" c/c all beams were divided in two batches with 6 beams in each batch. out of these six beams in each batch 3 beams were cured for 7-days and 3 for 28-days. afterwards, the beams were left for air drying followed by installation of dumic pads on one side of beams in three layers with 37.5mm gap between them (figure 5). all the beams were tested in a universal load testing machine, using gradually increasing load at the loading rate of 0.25mpa/s (figure 2). fig. 2. load arrangement during the loading process load, deflection and strain were measured at intervals of 2.5kn. strain was recorded at the same interval for all three locations set for the purpose. the average was then evaluated and recorded for load value. table ii gives the average values of 7-day cured beams of both batches, whereas the same parameters for 28-day cured beams are listed in table iii. iv. results and discussion the beams prepared for this research were tested with gradually increasing central point load in utm until failure. all parameters under consideration were recorded at load intervals of 2.5kn. first crack appearance and associated load were carefully monitored and recorded. figures 3-6 show the first crack in some beams. shear failure of the beams is evident from the above-mentioned figures. the load recorded at regular engineering, technology & applied science research vol. 8, no. 5, 2018, 3338-3343 3341 www.etasr.com oad et al.: flexural stress-strain behavior of rc beams made with partial replacement of coarse … intervals and was used to compute the flexural stress numerically from (1): (1) table ii. average values, 7-day cured beams # beam no max load (n) deflection (mm) flexural stress (n/mm2) strain first crack load (n) 1 rb-1 63361.00 4.15 25.34 0.00321 45002.00 rb-2 rb-3 2 rb-7 71736.33 7.41 28.69 0.00301 55765.67 rb-8 rb-9 % value: 88.32 55.96 88.33 106.57 80.70 % difference: 11.68 44.04 11.67 -6.57 19.30 table iii. average values, 28-day cured beams # beam no max load (n) deflection (mm) flexural stress (n/mm2) strain first crack load (n) 1 rb-4 69694.67 4.97 27.88 0.00325 53372.33 rb-5 rb-6 2 rb-10 71549.33 6.30 28.62 0.00277 48121.33 rb-11 rb-12 % value: 97.41 78.93 97.41 117.15 110.91 % difference: 2.59 21.07 2.59 -17.15 -10.91 fig. 3. cracking in beam fig. 4. beam failure dial readings were recorded. these reading were then converted into strain by multiplying with dial constant. average of obtained strains was computed and recorded for all loading intervals. deflections values for all load intervals except crushing load were also recorded. table iv gives information of maximum values of all parameters for 7-day cured beams made with 50% replacement of natural course aggregates with coarse aggregates from old concrete. similar results are given in table v for 28-day cured beams. table vi and table vii show the results for 7-day and 28-day cured beams made with 100% natural aggregates respectively. fig. 5. beam failure fig. 6. beam failure table iv. 50% rca, 7-day cured beams beam no max load (n) deflection (mm) flexural stress (n/mm2) strain first crack load (n) rb-1 67530 5.13 27.01 0.00335 50000 rb-2 55043 3.28 22.02 0.00314 45000 rb-3 67510 4.03 27.00 0.00314 40006 table v. 50% rca, 28-day cured beams beam no max load (n) deflection (mm) flexural stress (n/mm2) strain first crack load (n) rb-4 67574 4.12 27.03 0.00317 55043 rb-5 67510 5.64 27.00 0.00318 50031 rb-6 74000 5.16 29.60 0.00339 55043 table vi. 0% rca, 7-day cured beams beam no max load (n) deflection (mm) flexural stress (n/mm2) strain first crack load (n) rb-7 71726 7.10 28.69 0.00300 56023 rb-8 71824 7.86 28.73 0.00301 55142 rb-9 71659 7.26 28.66 0.00302 56132 table vii. 0% rca, 28-day cured beams beam no max load (n) deflection (mm) flexural stress (n/mm2) strain first crack load (n) rb-10 71267 6.21 28.51 0.00276 48095 rb-11 71321 6.34 28.53 0.00278 48130 rb-12 72060 6.35 28.82 0.00278 48139 figure 7 shows the flexural stress-strain graphs of beams made with 50% replacement of natural aggregates with coarse aggregates from old concrete. the flexural stress-strain pattern of the three beams is almost the same. it is further observed that except minor differences in strain, all three beams present similar patterns. maximum flexural stress and strain values observed in beam rb-1 are equal to 27.01n/mm2 and 0.00335 engineering, technology & applied science research vol. 8, no. 5, 2018, 3338-3343 3342 www.etasr.com oad et al.: flexural stress-strain behavior of rc beams made with partial replacement of coarse … respectively. the other two beams showed 18.4% and 0.34% less flexural stress. the average flexural stress and strain in all three beams is 25.34n/mm2 and 0.00321 respectively. the deflection in the beams is recorded in the range of 3.28mm– 5.13mm. the highest deflection value is about 2.6% higher than the approximate allowable value as per aci-318 [14]. fig. 7. flexural stress-strain behavior of 7-day cured beams with 50% natural aggregates figure 8 shows the flexural stress vs strain behavior of 28day cured beams made with 50% replacement of natural coarse aggregates with coarse aggregates from old concrete. the average values of flexural stress and strain were 28.69n/mm2 and 0.00301 respectively. the average deflection for these beams is recorded in the range of 4.12mm-5.64mm which is 12.8% higher than the approximate allowable value of aci-318 [14]. the average flexural stress of these beams is about 13.2% higher than those cured for 7 days. the average strain of these beams is about 10.1% lower than those cured for 7 days. figurer 9 and 10 show flexural stress vs strain behavior for 7day cured beams and 28-day cured beams made with 100% natural coarse aggregates respectively. fig. 8. flexural stress-strain behavior of 28-day cured beams with 50% natural aggregates fig. 9. flexural stress-strain behavior of 7-day cured beams with 0% natural aggregates figure 11 gives comparison of control parameters of all 7day cured beams. it is evident that beams made with 50% coarse aggregates from old concrete gained less flexural stress and more strain than control specimens cured for the same time. the maximum values for all parameters under study are given above. it is observed that 7-day cured beams failed at 11.68% less load. the same percentage reduction occurred in flexural stress. however, these beams showed 6.57% less strain than the control specimens. contradictory to theoretical analysis, these beams showed 44.04% more average deflection than the control specimens. it is also observed that the first crack in 7-day cured beams appeared at 19.3% more load than in control specimen. fig. 10. flexural stress-strain behavior of 28-day cured beams with 0% natural aggregates fig. 11. flexural stress-strain behavior of all beams cured for 7-days in figure 12, the comparison of control parameters of all 28-day cured beams is given. beams made with 50% coarse aggregates from old concrete showed 2.59% less flexural stress and 17.15% more strain than control specimens. table iii shows that these beams failed at 2.59% less load. similarly to 7-day cured beams, these beams deflected more than what was theoretically anticipated and deflected up to 21.07% more than control. it is also observed that 28-day cured beams showed first crack at 10.91% less load than the control specimens. figures 13 to 15 show the comparison of peak load, deflection and load at which first crack appeared for both 7 and 28-days cured beams. it is concluded that new rich mix concrete made with 50% partial replacement of natural coarse aggregates with coarse aggregates from old demolished concrete results in good strength, flexural stress, and strain without much compromise on the concrete quality, as it is evident that the loss of flexural stress for 28-day cured beams is only 2.59%. this can be controlled by better screening techniques, control of aggregates size and control of steel percentage. although cracking pattern and load at first crack are in good agreement with the control specimens, yet rich mix beams have showed more deflection than control. this should be addressed properly by tuning steel percentage to bring the deflection in allowable limits. engineering, technology & applied science research vol. 8, no. 5, 2018, 3338-3343 3343 www.etasr.com oad et al.: flexural stress-strain behavior of rc beams made with partial replacement of coarse … fig. 12. flexural stress-strain behavior of all beams cured for 28 days fig. 13. comparison of peak load fig. 14. comparison of average deflection fig. 15. comparison of load at which first crack appeared v. conclusion an experimental study for flexural stress vs strain was done for rich mix (1:1.5:3) concrete using reinforced concrete beams made with 50% replacement of natural coarse aggregates from demolished concrete. result analysis shows that only 11.68% reduction is observed in beams cured for 7 days whereas 28day cured beams showed 2.59% flexural stress reduction. more strain than control is recorded in both groups of beams. cracking pattern for all beams remained in good agreement with control. 7-day and 28-day cured beams presented 44.04% and 21.07% more displacement than control. this parameter should be controlled before using rich mix concrete beams made with partial replacement of coarse aggregates with coarse aggregates from demolished concrete. therefore, it is concluded that further work is required in order to bring the displacement within allowable limits. whereas, strength and flexural stress-strain behavior show that demolished concrete can comfortably be used in rich mix concrete without quality loss of reinforced concrete beams. vi. recomendations it is recommended that more concrete mix ratios, different water cement ratios, and old concrete aggregates from different sources may be used in order to come up with better conclusions. references [1] b. a. memon, “recent development on use of demolished concrete as coarse aggregates”, international journal of emerging technology and innovative engineering, vol. 2, no. 1, pp. 1-11, 2016 [2] s. tanwani, b. a. memon, “relationship between weight and tensile strength of concrete cylinders made by partial replacement of coarse aggregates from old concrete”, international journal of engineering inventions, vol. 5, no. 6, pp. 1-9, 2016 [3] m. oad, b. a. memon, “compressive strength of concrete cylinders using coarse aggregates from old concrete”, 1st national conference on civil engineering (ncce 2013-14) (modern trends and advancements), april 28-29, 2014 [4] a. a. bhatti, b. a. memon, “strength, deflection and cracking behavior of concrete slab using demolished concrete as coarse aggregates”, international journal of engineering sciences & research technology, vol. 3, no. 6, pp. 492-506, 2014 [5] b. a. memon, g. s. bhatti, “lexural behavior of beam made by partial replacement of natural aggregates with coarse aggregates from old concrete”, international journal of engineering sciences & research technology, vol. 3, no. 5, pp. 52-61, 2014 [6] m. o. a. mtallib, a. i. marke, “comparative evaluation of the flexural strength of concrete and colcrete”, nigerian journal of technology, vo. 29, no. 1, pp. 13-22, 2010 [7] p. a. bekoe, concrete containing recycled concrete aggregate for use in concrete pavement”, msc thesis, university of florida, 2009 [8] j. o. ukpata, m. e. ephraim, “flexural and tensile strength properties of concrete using lateritic sand and quarry dust as fine aggregates”, arpn journal of engineering and applied sciences, vol. 7, no. 3, pp. 324-331, 2012 [9] w. bai, b. sun, “experimental study on flexural behavior of recycled coarse aggregate concrete beam”, applied mechanics and materials, vol. 29-32, pp. 543-548, 2010 [10] g. n. yang, b. r. huo, m. x. zheng, “flexural behavior of reinforced concrete beams strengthened with bfrp bars”, international conference on power electronics and energy engineering (peee 2015), hong kong, china, april 19-20, 2015 [11] m. kaarthik, k. subrmanian, “flexural behavior of concrete beams using recycled fine aggregates and steel fibers”, international conference on biological, civil and environmental engineering, dubai, uae, march 17-18, 2014 [12] m. kosior-kazberuk, m. grzywa, “recycled aggregate concrete as material for reinforced concrete structures”, journal of sustainable architecture and civil engineering, vol. 2 no. 7, pp. 60-66, 2014 [13] r. sato, i. maruyama, t. sogabe, m. sogo, “flexural behavior of reinforced recycled concrete beams”, journal of advanced concrete technology, vol. 5, no. 1, pp. 43-61, 2007 [14] aci 318, building code requirement for structural concrete, american concrete institute, 2005 microsoft word 6-2427_s engineering, technology & applied science research vol. 9, no. 1, 2019, 3705-3710 3705 www.etasr.com manafpour & ebrahimnezhadian: investigating the effect of ramp geometry on the flow … investigating the effect of ramp geometry on the flow characteristics around under pressure tunnel aerator using openfoam open source software mohammad manafpour department of civil engineering urmia university urmia, iran m.manafpour@urmia.ac.ir hamzeh ebrahimnezhadian department of civil engineering urmia university urmia, iran h.ebrahimnezhadian@urmia.ac.ir abstract—the flow around the ramp embedded in a pressurized tunnel is divided into various zones downstream of the ramp, including the cavity and the main zone of flow above the shear layer. ramp angle and height are parameters that affect the flow characteristics such as cavity length, velocity, and pressure coefficient immediately downstream of the ramp. in this study, openfoam open source software and rng k-ε turbulence model were used to simulate the flow around the under pressure tunnel ramp. in order to investigate the effect of the ramp geometry on the flow in various relative air discharges 0<β<10, the range of height and the angle of the ramp as 5<θ<20 and 0.1<tr/d<0.4 were developed and simulated. the correlation coefficient between the numerical and experimental results for the relative cavity length is in the range of 0.9377≤ r 2 ≤ 0.9722 that indicates proper agreement between results. the result of the research shows that in both cases of fixed height of ramp and increasing ramp angle, and fixed angle of the ramp and increasing ramp height, the values of the cavity length and maximum turbulence intensity increase, and the minimum pressure values at the cavity zone bed are decreased. but in both cases, the sensitivity of the three mentioned parameters is higher than the ramp height increment. keywords-aerator ramp; pressurized tunnel; rng k-ε turbulence model; openfoam; cavity length i. introduction aeration is known as the most efficient and economical method for prevention of cavitation in high-speed flows over chute spillways [1, 2]. with 8% air near the concrete surface the damage of cavitation attack is completely prevented [3, 4]. surface aeration takes place in spillways but in this way usually not enough air is introduced near the concrete surface [5]. therefore, forced aeration of flow is recommended [6]. aerators, which locally create an air cavity at the lower boundary of the flow, have been found to be an effective and cheap way of promoting air entrainment into the flow. aerators cause the flow to separate from the surface of the spillway and form a nappe. flow behavior on aerator ramps in figure 1 shows the complex interaction between flow turbulent structures, the phenomenon of cavitation, the behavior of the jet in the atmosphere, the air entering the jet, as well as the propagation of bubbles in the downstream of ramps. air will be entrained along the lower surface as well as along the upper surface of the nappe [7]. the entrainment on the lower surface introduces air bubbles near the bed of the spillway for some distance downstream [8, 9]. fig. 1. flow region over typical aerator. in under pressure flow upon ramp aerator embedded in the tunnel floor (figure 2), immediately downstream of the ramp, the flow is two-phased and disturbed. there is no surface aeration and it is divided into the various zones immediately downstream of the ramp, including the cavity zone and the main zone of flow above the shear layer. as flow separates from the trailing edge of the ramp, the lower layers accelerate and small intense eddies form on the lower surface of the nappe which roughens the air-water interface. as turbulence overcomes surface tension, this air will be entrained into the flow. on the other hand, the pressure distribution in the nappe rapidly adjusts itself to near atmospheric conditions, the slip velocity of air bubbles falls and the air bubbles are diffused by turbulence deeper into the core of the nappe. further downstream, more and more air will be entrained into the flow [10]. turbulence plays an important rule here, and higher turbulence levels cause more air entrainment [5, 11]. the introduction of forced air, especially from the bottom of the jet, will increase air concentration near the surface of the concrete. aeration in spillways and under pressure tunnels is usually carried out by aeration systems and by using ramp, groove, and steps. the most common type of aeration can be seen in figure 3. bringing air to the bottom of the jet is carried corresponding author: mohammad manafpour engineering, technology & applied science research vol. 9, no. 1, 2019, 3705-3710 3706 www.etasr.com manafpour & ebrahimnezhadian: investigating the effect of ramp geometry on the flow … out by a duct from the floor. in this way, the flow is completely aerated and despite this air near the floor, the damage caused by cavitation is prevented [12]. fig. 2. flow pattern upon under pressure tunnel ramp. proper recognition of the two-phase flow pattern in under pressure tunnel spillways with and without aeration system is among the studied topics, but because of the complexity of two-phase flows, there is still a need for more studies in this field. many research works have been conducted to find the relationship between the inflows of air through aerators. relative air discharge (β), which is defined as the ratio of air to water discharge, is a function of cavity length, froude number and cavity subpressure. in 1990, a mathematical model based on galzoo's work in 1984 was presented [13]. this model computed the cavity length as well as the airflow and cavity subpressure. based on this model, cavity length directly affected airflow. authors in [4] studied and compared vof and mixture methods during a series of experimental and numerical studies with three-dimensional simulation of aerated flow downstream of ramp aerator in a tunnel under pressure. comparing numerical and experimental results indicated that both methods calculated accurately free water surface and cavity length. air concentration inside the water and the average values of pressure downstream the aerator from the mixture model have less error than the experimental results. authors in [14] examined the effects of flow regime downstream of aerator on entering the air into the flow and preventing damage of cavitation. the results of the experiments showed that the conversion of flow regimes downstream of aerator to each other depends on aerodynamic parameters such as ramp angle, ramp height and slope of tunnel floor. authors in [15] compared laboratory performance of two types of aerator in two different designs. it was found that for tunnel spillways, the shape and size of aerator require special design and tunnel spillways can be protected from cavitation by applying a plan of aerator that increases cavity zone length, air inflow, and the air concentration near the floor. authors in [16] carried out laboratory studies on measuring the pressure fluctuations in downstream of the aerator located in a circular tunnel and studied aerator performance with different geometries. it was found that the use of aerator with small heights for air supply in tunnel duct is more suitable than aerator with high heights from a hydrodynamic point of view. authors in [17] studied the effect of geometric and hydraulic parameters on pressure, cavity length and relative air discharge in the flow around the ramp embedded at the end of the tunnel. it was found that by increasing the relative cross-section of the air inflow, which leads to an increase in the amount of air entering the flow, the cavity length downstream of the ramp and the aeration coefficient of the flow increase. the average cavity pressure also increases significantly with increasing air inflow. authors in [18] experimented in the effect of air injection on the wall pressure in the near field of deflectors placed in a duct. various quantities of air have been injected just downstream of the ramps to form stationary air cavities. the variation of cavity length has been studied as a function of the ratio of the volume of air flow to the water discharge. this study showed how air injection affects the wall pressure field. the effects of aerator ramp geometry on the flow characteristics have been studied, but the effective factor between ramp height and angle is not determined on the flow characteristics. hence, in this study, the flow near the aerator ramp embedded in a under pressure flow in various relative air discharges 0<β<10, angle 5<θ<20 and height 0.1<tr/d<0.4 was developed and simulated, by the use of an open-source numerical model and appropriate turbulence model. the effect of the angle and ramp height on the characteristics of the flow, the minimum values of the pressure at the cavity zone bed, and the maximum turbulent intensity are determined immediately downstream of the ramp. ii. materials and methods a. experimental setup the details of the experimental arrangement are presented in figure 3. the experimental model consists of a horizontal pressurized duct with a square cross section that ramps of perspex of triangular cross section were glued to the duct bottom. four ramps were used. two heights of tr/d=0.1 and 0.2 were used, where tr is the height of the ramp and d is the height of the duct. for each value of tr/d test, two slopes of 5 0 and 10 0 were used. water supply to the duct housing the ramps was from a constant head tank located on the roof of the laboratory. a 0.1m wide and height duct was used with a tank upstream to achieve the desired flow velocities. the modeled aerator consisted of a ramp. dimensions of the aerator are given in table i. the aerator was installed 1m downstream of the channel entrance to allow the turbulent boundary layer to develop completely. a pitot tube was employed to measure flow velocity. air was introduced through nine 10mm diameter holes placed at regular intervals immediately downstream of the ramps [19]. table i. characteristics of the studied ramps tr/d ramp angle (θ) ramp length lr (mm) ramp height tr (mm) ramp 0.1 5 113.4 10 a 0.1 10 56.7 10 b 0.2 5 226.8 20 c 0.2 10 113.4 20 d b. numerical model openfoam software was used to simulate the flow around the aerator ramp embedded in a under pressure duct. c. openfoam the widely known cfd-toolbox “openfoam” (open field operation and manipulation) is a well-designed c++ library that allows numerical simulation of various engineering applications. through its object-orientated structure it is very flexible and can be adjusted to very specific problems. since engineering, technology & applied science research vol. 9, no. 1, 2019, 3705-3710 3707 www.etasr.com manafpour & ebrahimnezhadian: investigating the effect of ramp geometry on the flow … the code is open source, code analysis and manipulation are possible. with its specific data types for describing the pdes and the usage of operator overloading, openfoam allows formulating equations in a way that resembles the mathematical formulation. in contrary to most cfd programs, openfoam is not delivered with a graphical user interface for performing preand post-processing of the simulations [20]. fig. 3. experimental apparatus. the most important difference between openfoam and other computational fluid dynamics commercial software is that in openfoam to create a model in each subcategory, the user must choose a proper solver to project physics. therefore, one of the difficulties of openfoam is the choice of proportional solver. the flow around the under pressure tunnel ramp aerator has a two-phase nature. multiphase flow modeling is performed using three views: 1) volume of fluid, 2) eulerian-lagrangian, and 3) eulerian-eulerian. in openfoam, to analyze multiphase flow problems, various solvers are foreseen. the choice of a suitable solver is the most important part of the simulation in openfoam. a number of multiphase solvers in the openfoam are interfoam, bubblefoam, twophaseeulerfoam and multiphaseeulerfoam. in this study, due to the two-phase nature of the flow and the importance of mixing the two phases, the eulerian-eulerian approach and a solver that has the basis of the twophaseeulerfoam solver were used. necessary development in the solver to increase efficiency in the discussion of the twophase mixing simulations has been done. openfoam was used to simulate the flow around the aerator ramp embedded in a under pressure duct. d. geometry, meshing and boundary conditions in order to construct the geometry of the numerical model, a code was written in fortran. by applying the input data such as the ramp angle and height, the distance to the ramp entrance and the distance from the end of the ramp, the information necessary for constructing geometry from the fortran code was extracted and transferred to the blockmesh environment inside the openfoam. regarding the dimensions of the study area and air bubble diameter, a geometry grid of the numerical model with dimensions of 2mm was prepared. the meshing of the numerical model is shown in figure 4. fig. 4. numerical model meshing. sensitivity analysis of the numerical model was measured relative to the mesh size, and it was found that using a smaller cell size did not affect the accuracy of the calculations. the boundary conditions in the present study include: 1) water inlet: mass flow rate, 2) air inlet: mass flow rate, and 3) outlet: pressure outlet and for all duct walls, a wall boundary condition was used. iii. results and discussion in order to evaluate the performance of a numerical model in the simulation of two-phase flow around an aerator ramp embedded in under pressure duct bed for 4 types of ramps that are presented in table i, numerical and experimental results were compared. the flow near the aerator ramp embedded in a under pressure flow in various values of relative air discharge β, 0≤β≤10, angle θ, 5 o ≤θ≤20 o , and height tr, 0.1≤tr/d≤0.4 were simulated until the effect of θ and tr on the characteristics of the flow, such as the cavity length (lc), the minimum values of the pressure at the cavity zone bed (cpmin) and maximum turbulent intensity (t.i.max) were determined immediately downstream of the ramp. a. verification of numerical results 1) cavity length (lc) after the passing flow through the aerator ramp, in addition to the main zone, cavity zone is formed: two regions are separated by a shear layer between them (figure 5). in figure 6, the comparison between the relative cavity lengths calculated by the numerical model using the two-equation turbulence model rng k-ε and experimental results for cavity formed immediately downstream of four different ramps in the various relative values of β are shown in which lc and tr are the length of the cavity zone and ramp height respectively. according to figure 6, the two-dimensional numerical model in all ramps estimates a cavity length less than the experimental model. the correlation coefficient between the relative cavity length of the numerical and experimental models for forced relative air discharge 2%, 4%, 6% and 8% was 0.9729, 0.9371, 0.946 and 0.966 respectively, which suggests an acceptable simulation of the flow by the numerical model. results for 2% and 8% relative air discharge are presented. fig. 5. cavity in the under pressure duct due to forced air injection. 2) flow velocity the comparison of average velocity distribution profiles between numerical and experimental results for ramp d (tr/d=0.2, θ=10 o , β=2%) is displayed in figure 8, where z is the distance from the end of the ramp and u is the average velocity of the flow equal to 4.1 m/s. the adaptation of numerical and experimental results suggests the proper accuracy of the numerical model in simulating the flow velocity field near the aerator ramp. according to figure 8, the velocity in the direction of flow at the end of the ramp due to the existence of engineering, technology & applied science research vol. 9, no. 1, 2019, 3705-3710 3708 www.etasr.com manafpour & ebrahimnezhadian: investigating the effect of ramp geometry on the flow … the ramp and the decrease of the duct cross section reaches its maximum value. fig. 6. comparison of the cavity length generated by the numerical model, the experimental results, and their correlation. fig. 7. flow velocity profiles for ramp d (tr/d=0.2, θ=10 o ), in section (z/tr: a=-28, b=-0.2, c=2.1, d=6.7, e=15.7). 3) pressure coefficient the dimensionless parameter of pressure coefficient (cp) is defined as the static pressure ratio to the dynamic pressure. in this research, the pressure coefficient is obtained from the relationship cp=p-po/0.5ρu 2 where p is the static pressure of the floor at the desired point, po is the static pressure at the reference point located at the upstream of the ramp, ρ is the water density and u is the average flow velocity. figure 8 shows the variation of the pressure coefficient in the duct floor relative to the distance from the downstream of ramp. the correlation coefficient between the numerical and experimental results for pressure coefficient of the ramp b (tr/d=0.1, θ=10 o ) and forced relative air discharges (β=2%,4%,6%,8%) is in the range of 0.7163<r 2 <0.9167 which emphasizes the accuracy of the numerical model in simulating the flow field. fig. 8. changes in the pressure coefficient in the duct floor relative to the distance from the end of the ramp a (tr/d=0.1, θ=5 o ) and (β=2%, 8%). b. effect of ramp angle and height on cavity length to investigate the effect of the angle and height of ramp on the flow characteristics near the aerator ramp embedded in an under pressure flow in various β, various values of θ (5 o ≤θ≤ 20 o ) and tr (0.1≤ tr/d≤ 0.4) were simulated. the variation process of cavity length in aeration to flow is the same as the variations in the length of recirculation zone of the flow in a non-aeration state. figure 9(a)-(b) shows the effect of increasing tr relative to the fixed θ=5 o and the effect of increasing θ relative to the fixed tr/d=0.1 for various β. according to figure 9, increased intensity of cavity length (lc) in increased tr/d is more than the increase of θ. this suggests greater sensitivity of cavity length to the increase of the ramp's relative height. the cavity length increases with increment of relative air discharge (β ) in both cases. (a) (b) fig. 9. changes in cavity length: (a) ramp height increase relative to fixed ramp angle 5 o , b) ramp angle increase relative to fixed ramp height (tr/d=0.1). in figure 10, variations in the relative air discharges coefficient of flow are presented as a function of cavity length for different ramps. the changes in this function are very close in both quantitative and qualitative terms for ramps of the same height. in other words, the effect of the ramp angle on the aeration coefficient through the relative cavity length is very low (comparing ramp a with b and c with d). while the effect of ramp height on this relationship is high (ramp a comparison with c and b with d). engineering, technology & applied science research vol. 9, no. 1, 2019, 3705-3710 3709 www.etasr.com manafpour & ebrahimnezhadian: investigating the effect of ramp geometry on the flow … fig. 10. air discharges coefficient variation relative to cavity length for different ramps. c. effect of ramp angle on minimum pressure coefficient of the cavity zone bed the effect of increasing relative height and ramp angle on cpmin follows [17] which showed that with increasing ramp height and angle, the local pressure in the whole tunnel, decreases. the effect of increasing relative height and ramp angle on cpmin at the cavity zone created at the downstream of the ramp is shown in figure 12. cpmin values in both cases are reduced and the impact intensity of the cpmin of the ramp height (tr/d) is far greater than ramp angle. therefore, the sensitivity of the minimum pressure coefficient to increasing ramp height is higher than the ramp angle’s. also, by increasing the relative air discharge to the flow, the minimum pressure coefficient value increases, indicating the effect of flow aeration on localized pressure increase over the entire duct. (a) (b) fig. 11. minimum floor pressure of cavity zone variations: a) increasing ramp height for fixed ramp angle 5 o , b) increasing ramp angle for fixed ramps height (tr/d=0.1). d. effect of ramp angle on minimum turbulence intensity of the flow the changes in turbulence intensity due to the increase in relative height and ramp angle in different relative air discharges follow the qualitative process of figure 12. with increasing ramp angle and height, turbulence intensity increases. figure 12 illustrates the effect of increasing height and ramp angle on the maximum turbulence intensity at the downstream of the ramp. results indicate that increasing angle and relative height of the ramp increase the turbulence intensity with the difference that the increase in maximum turbulence rate due to ramp height (tr/d) is higher than the ramp angle increase. also, maximum turbulence intensity was reduced due to an increase in the air flow rate (β). (a) (b) fig. 12. maximum turbulence intensity variation: a) increasing ramp height for fixed ramp angle 5 o , b) increasing ramp angle for fixed ramp height (tr/d=0.1) iv. conclusions this study on the flow field near the aerator ramp of a tunnel under pressure with openfoam produced the following results: the correlation between numerical and experimental results for relative cavity length and relative air discharge of 2%, 4%, 6% and 8%, was 0.9722, 0.9371, 0.946 and 0.966 respectively, which indicates proper agreement between numerical and experimental results and the superiority of the twophaseeulerfoam solver in the simulation of two phase flow. in both cases of fixed ramp height and increasing ramp angle and fixed ramp angle and increasing ramp height, the values of the cavity length and maximum turbulence intensity increase, and the minimum pressure values at the cavity zone bed are reduced. however, with increasing ramp height at fixed ramp angle, the intensity of the increase in the cavity length, maximum turbulence intensity and the reduction of the minimum pressure at the cavity zone bed are greater indicating higher sensitivity to ramp height. by increasing the forced relative air discharge β, minimum pressure coefficient value is increased and maximum turbulence intensity is reduced. references [1] n. l. pinto, “prototype aerator measurements”, in: air entrainment in free-surface flow, pp. 115-130, routledge, 2018 [2] i. r. wood, air entrainment in free-surface flows, crc press, 1991 [3] a. j. peterka, “the effect of entrained air on cavitation pitting. joint meeting paper”, in: proceedings: minnesota international hydraulic convention, pp. 507-518, asce, 1953 [4] j. m. zhang, j. g. chen, w. l. xu, “three-dimensional numerical simulation of aerated flows downstream sudden fall aerator expansion in a tunnel”, journal of hydrodynamics, vol. 23, no. 1, pp. 71-80, 2011 [5] r. w. p. may, p. m. brown, i. r. willoughby, physical and numerical modeling of aerators for dam spillways. hydraulics research report, no. sr 278, wallingford, uk, 1991 [6] h. t. falvey, cavitation in chutes and spillways, us department of the interior, denver, colorado, usa, 1990 [7] h. chanson, “aeration of a free jet above a spillway”, journal of hydraulic research, vol. 29, no. 5, pp. 665-667, 1991 [8] h. chanson, “flow downstream of an aerator. aerator spacing”, journal of hydraulic research, vol. 27, no. 4, pp. 519-536, 1989 engineering, technology & applied science research vol. 9, no. 1, 2019, 3705-3710 3710 www.etasr.com manafpour & ebrahimnezhadian: investigating the effect of ramp geometry on the flow … [9] a. r. zarrati, j. d. hardwick, “mathematical modelling of deaeration zone downstream of aerators”, in: proceedings 26th congress of iahr, london, u.k., vol. 2, pp. 220-225, iahr, 1995 [10] j. attari, a. r., zarrati, “the effect of nappe impact angle on aerator performance”, in: energy and water: sustainable development, pp. 601606, asce, 1997 [11] d. a. ervine, a. r. khan, “turbulence measurements in an air-slot ramp aerator”, 24th iahr world congress, madrid, spain, september 9-13, 1991 [12] h. chanson, “aeration and de-aeration at bottom aeration devices on spillway”, canadian journal of civil engineering, vol. 21, pp. 404-409, 1994 [13] a. t. glazov, “calculation of the air-capturing ability of flow behind an aerator ledge”, hydrotechnical construction, vol. 18, no. 8, pp. 554558, 1984 [14] j. wu, f. ma, h. c. dai, “influence of filling water on air concentration”, journal of hydrodynamics, vol. 23, no. 5, pp. 601-606, 2011 [15] s. p. ruan, j. h. wu, w. w. wu, “hydraulic research of aerators on tunnel spillways”, journal of hydrodynamics, ser. b, vol. 19, no. 3, pp. 330-334, 2007 [16] m. kavianpour, a. toloui, a. s. al-mu'zsoumi, “evaluation of pressure fluctuations in downstream of aerator in lower tunnels of dams with circular sections”, national conference on national hydroelectric power plants, tehran, iran, june 6-7, 2002 [17] v. v. bhosekar, v. y. jothiprakash, p. b. deolaikar, “orifice spillway aerator: hydraulic design”, journal of hydraulic engineering, vol. 138, no. 6, pp. 563-572, 2012 [18] r. narayanan, m. manafpour, m. r. kavianpour, “wall pressure field in the reattaching flow past deflectors, part 2: with air injection”, in: proceedings of the institution of civil engineers-water and maritime engineering, vol. 148. no. 1, pp. 39-45, thomas telford ltd, 2001 [19] m. manafpour, effects of air injection on the flow immediately downstream of deflectors on spillways, phd thesis, manchester university, uk, 2004 [20] h. g. weller, h. jasak, c. fureby, “a tensorial approach to computational continuum mechanics using object-oriented techniques”, journal of computational physics, vol. 12, no. 6, pp. 620-631, 1998 microsoft word etasr_v11_n4_pp7296-7301 engineering, technology & applied science research vol. 11, no. 4, 2021, 7296-7301 7296 www.etasr.com owida et al.: classification of chest x-ray images using wavelet and mfcc features and support … classification of chest x-ray images using wavelet and mfcc features and support vector machine classifier hamza abu owida medical engineering department faculty of engineering al-ahliyya amman university amman, jordan h.abuowida@ammanu.edu.jo amani al-ghraibah medical engineering department faculty of engineering al-ahliyya amman university amman, jordan a.ghraibah@ammanu.edu.jo muneera altayeb electronics and communications engineering department faculty of engineering al-ahliyya amman university amman, jordan m.altayeb@ammanu.edu.jo abstract-the shortage and availability limitation of rt-pcr test kits and is a major concern regarding the covid-19 pandemic. the authorities' intention is to establish steps to control the propagation of the pandemic. however, covid-19 is radiologically diagnosable using x-ray lung images. deep learning methods have achieved cutting-edge performance in medical diagnosis software assistance. in this work, a new diagnostic method for detecting covid-19 disease is implemented using advanced deep learning. effective features were extracted using wavelet analysis and mel frequency cepstral coefficients (mfcc) method, and they used in the classification process using the support vector machine (svm) classifier. a total of 2400 xray images, 1200 of them classified as normal (healthy) and 1200 as covid-19, have been derived from a combination of public data sets to verify the validity of the proposed model. the experimental results obtained an overall accuracy of 98.8% by using five wavelet features, where the classification using mfcc features, mfcc-delta, and mfcc-delta-delta features reached accuracy around 97% on average. the results show that the proposed model has reached the required level of success to be applicable in covid 19 diagnosis. keywords-chest x-ray images; classification of chest diseases; covid-19; feature extraction; support vector machine (svm) i. introduction rarely the danger of disease involved such an extensive amount of our thought as the covid-19 pandemic. the disease's growth, transmission, and increased mortality make the improvement of prevention important. covid-19 virus came to light in december 2019 in wuhan province, china, and the ensuing pandemic influenced most countries with extensive worldwide health, economic, and personal effects [1]. in order to control the disease, identification and early and follow-up quarantine, are important. the early covid-19 diagnosis is significantly crucial. the key tool for the diagnosis of covid-19 disease is actually a reverse transcriptasepolymerase chain reaction (rt-pcr) [2]. currently, the rtpcr test is considered a time consuming and strenuous with complicated manual procedure. moreover, there is a shortage and availability limitation of rt-pcr test kits [3]. therefore, an integrated solution system, which is both rapid and reliable, is urgently needed for covid-19 diagnosis. radiological imaging is an effective and important tool for the detection of covid-19 in addition to the rt-pcr method [4]. medical imaging method is complicated because the radiologist must advertently identify the white spots that contain water and pus, which is time consuming and troublesome. also, a radiologist or doctor may often misdiagnose other conditions including pulmonary tuberculosis as covid-19. for that reason, recently developed artificial intelligence-driven automatic diagnostic systems based on machine and deep learning result in quicker and more reliable covid-19 detection and can be considered as alternatives to manual testing [2-4]. ii. the state of the art automated methods in covid-19 detection there are several studies in the published literature which are based on machine learning applications to detect and diagnose covid-19. these state of the art approaches are based on machine and deep learning approaches by using chest x-ray images. machine and deep learning systems are frequently used to automatically extract specific classification features for the purpose object. authors in [4] established a convolutional neural network (cnn)-based model for corresponding author: hamza abu owida engineering, technology & applied science research vol. 11, no. 4, 2021, 7296-7301 7297 www.etasr.com owida et al.: classification of chest x-ray images using wavelet and mfcc features and support … covid-19 diagnosis. they used 3 different groups of x-ray images, i.e. covid 19, pneumonia, and normal/healthy. the researchers managed to achieve a classification accuracy of 92.6% with images from all groups, while authors in [5] reported 87% accuracy in a similar study. authors in [6] evaluated the performance of different cnns (vgg19, inception, mobilenetv2, xception, and inceptionresnetv2) in covid-19 detection. they used three different groups of xray images comprising of covid 19, pneumonia, and normal and the highest achieved accuracy was 96.78%. authors in [7] built up a bayesian convolutional neural network (bcnn) architecture for covid-19 detection with an accuracy score of 92.9%. authors in [8] developed a cnn model termed as corodet for automatic covid-19 detection by using chest xray images with accuracy of 94.2% for covid, normal, and non-covid viral pneumonia classes [8]. authors in [9] proposed a cnn model, and support vector machine (svm) with the linear kernel function to classify covid-19 and healthy chest x-ray images and reached 94.7% accuracy. authors in [10] developed two cascade networks, semeresnet50 and seme-densenet169, to assess three classes of chest x-ray images: normal, bacterial, and covid-19 pneumonia with 85.6% accuracy score in classification of pneumonia infection. authors in [11] proposed a cnn model and transfer learning for covid-19 detection for 3 classes, normal, bacterial, and covid-19 pneumonia with 95.69% precision by using resnet-50 pretrained model. authors in [12] developed an integrated deep learning model focused on a capsule network and used a four-class dataset of chest x-ray images, achieving 95.17% accuracy. authors in [13] designed a decently pretrained resnet152 architecture using transfer learning for the identification of covid-19 and attained a success rate of 87%. authors in [14] proposed a deep learningbased approach for the diagnosis of covid-19 using x-ray images for infected patients and achieved 95.38% accuracy using the resnet50 architecture with svm classifier. the current study aims to implement a new model for covid-19 disease detection by using advanced deep learning technique. effective features were extracted using wavelet analysis and mel frequency cepstral coefficients (mfcc) method, and in the classification process the svm classifier was utilized. a total of 2400 x-ray images, 1200 normal (healthy) and 1200 covid-19, were derived from a combination of public data sets to verify the validity of the proposed model. with regard to the pandemic outbreak, the proposed study seeks to close the gap between the small number of highly qualified radiologists and the increasing need for chest x-ray interpretation. iii. methodology a. feature extraction covid 19 symptoms can be seen in lungs, both in the peripheral and subpleural areas, particularly in lower lobes and posterior segments. in x-ray images, the appearance and consolidation of bilateral nodular and peripheral ground glass lenses should serve as a warning for radiologists of the potential for covid-19 [15]. however, x-ray image diagnosis and examination of covid-19 symptom consumes time and relies on the existence of medical experts. hence, computer assistance is important in helping the medical staff to detect covid-19 in x-ray images [4]. many methods for extracting features are used in the literature. this study aims to apply methods for detecting covid-19 from x-ray images. these methods are described in detail in the next section. 1) wavelet features in image processing, 2-dimensional discrete wavelet transformation (2d dwt) is a powerful image analysis, denoising, and image segmentation method. when the original image is transformed by low pass and high pass filters in the x and y directions, the 2d dwt is computed. the obtained images are down-sampled to half of the original image dimensions. with high pass and low pass filters, the resulting images are convoluted again. the four sub-band acquired images comprise the approximation coefficient (containing the maximum image information), horizontal, diagonal and vertical image information, and the approximation coefficient (containing the maximum image information) [16, 17]. three image details are being employed to determine the energy of any decomposition level by applying the absolute values for the wavelet coefficients (the highpass images). then the total energy for the three high pass images is computed. five energy values corresponding to each of 5 decomposition levels are extracted. 2) mel frequency cepstral coefficient (mfcc) features mfcc is a very popular and efficient technique for signal processing where the frequency bands are distributed depending on the mel-scale [15, 18]. fig. 1. mfcc feature extraction. this research presents a new purpose of working with mfcc by using it to extract the features of chest x-ray images. the present technique is based on converting the chest x-ray images into one dimensional (1-d) signal and then extracting mfcc, delta-mfcc, and delta-delta mfcc from the converted 1-d signal. the output after applying mfcc is a matrix. in this output matrix the rows represent the corresponding frame numbers and the columns represent the engineering, technology & applied science research vol. 11, no. 4, 2021, 7296-7301 7298 www.etasr.com owida et al.: classification of chest x-ray images using wavelet and mfcc features and support … corresponding feature vector coefficients. classification is performed by using svm. the steps involved in the mfcc feature extraction are summarized in figure 1 [19]. 3) framing and windowing the resulting 1-d signal is a non-stationary signal, therefore analysis should always be performed by blocking the signal into possibly overlapping frames, so that the signal is constant [20]. in this step, the continuous 1-d signal is broken into 60 frames of n=2000 samples, with consecutive frames separated by l=512 samples. the adjacent frames are overlapped by n-l samples, which is around 74.4%. windowing is done by using a hamming window represented by w(n) multiplied by the input signal represented with x(n). the output signal is represented by (1): ����� � ������� � ��, � � 0,… , � � 1 (1) where k is the number of frames and n is the number of samples by which the window is shifted in order to yield the ith frame then taking the dft of the resulting signal [21]. 4) mel-spectrum the resulting spectrum of fourier transformed signal is given as input to a mel-scale filter bank that consists of 24 filters. the coefficients of each short time fourier transform (stft) are multiplied by the corresponding filter gain to know the approximation of the existing energy at each spot with the help of a triangular overlapping window. these energies are also known as the mel spectrum and can be used for calculating the first 13 coefficients using dct. a popular formula to convert f in hertz into ���� is given in (2) [20, 21]: ���� � 2595 log���1 � ����� (2) 5) discrete cosine transform (dct) the dct applied to the transformed mel frequency coefficients produced a set of mfcc capestral coefficients which are usually referred to as stationary features. 6) dynamic mfcc features the cepstral coefficients are usually referred to as static features, since they only contain information from a given frame. the extra information about the temporal dynamics of the signal is obtained by computing the first and second derivatives of the cepstral coefficients. the first-order derivative is called delta coefficients (delta-mfcc), and the second-order derivative is called delta–delta coefficients (delta–delta-mfcc). in this work, 39 features are extracted from each method [22]. figures 2 and 3 show the mfccs coefficients for the normal chest and chest infected with coronavirus. the x-axis represents the number of mfccs extracted from the input signal and the y-axis represents the feature values for each frame. in this work, the first 13 mfcc coefficients were used and the rest were discarded. the lower order coefficients contain most of the information about the overall spectral shape according to the feature values shown in figures 2 and 3. we can observe the difference in mfccs. fig. 2. mfcc features for an infected patient's x-ray chest image. fig. 3. mfcc features for normal patient's x-ray chest image. b. classification the purpose of supervised machine learning is to build a model that makes predictions based on evidence in the presence of uncertainty. the machine learns from the results when adaptive algorithms classify data patterns. the computer improves its prediction performance when exposed to more observations. particularly, a learning algorithm uses a known array of input data and known data responses (classes) and trains a model to provide a reliable prediction of how new data will respond [22, 23]. in this study, the input x-ray image that has covid-19 disease was addressed class 1 and the image without a disease was addressed as class 0. figure 4 shows a simple description of the svm. fig. 4. general description of svm the entire set of input data can indeed be termed as a heterogeneous matrix, since the matrix rows are referred to as observations or instances and ach comprises of various measurements for a subject. matrix columns are defined as predictors or characteristics, which are calculated by each subject [24]. herein, the observations are x-ray images of human chest and the features of each image are set in columns. the data matrix includes one row of features extracted from each image as shown in (3): engineering, technology & applied science research vol. 11, no. 4, 2021, 7296-7301 7299 www.etasr.com owida et al.: classification of chest x-ray images using wavelet and mfcc features and support … �1,1 ⋯ �1,�⋮ ⋱ ⋮� ,1 ⋯ � �$ (3) where n is the number of extracted features and m is the number of images. all supervised learning approaches begin with an input data matrix. the data were arranged in such a way that one observation was made in each row in the feature matrix and one variable or indicator in each column. in this step, each xray image in the data set has been extracted and organized in a matrix for each image, called a data matrix. each row has 5 characteristics related to the 5 wavelet features previously mentioned and another 39 features from each mfcc method. cross-validation is a statistical approach for the computation and comparison of learning algorithms through the division of data into two segments: the first one for model creation and the other for model validation. the essential cross-validation method is a k-fold cross-validation [24, 25]. in this study, a 10fold cross-validation approach was used in which the matlab software randomly divides the data into 10 sets of the same size, and then trains the svm classification on the 9 sets. the previous steps are repeated 10 times and the method incorporates generalization statistics from each fold. c. performance evaluation in this study, x-ray images were used for the diagnosis of covid-19. the total number of chest images used in this work is 2400, of which 1200 are images with covid-19 while the rest are images from normal lungs. the terms used in the confusion matrix (table i) can briefly be described as: true positive (tp): true event system classified as true, true negative (tn): false event classified as false, false positive (fp): false event classified as true, and false negative (fn): true event classified as false [25, 26]. table i. confusion matrix confusion matrix patient case normal abnormal normal tp fp abnormal fn tn accuracy (ac) refers to the probability that the system classification is correct [22, 23]: %& � '( ) '*�'( ) +( ) '* ) +*� ∗ 100 (4) sensitivity (true positive rate (tpr)) and specificity (true negative rate (tnr)) are also calculated from the confusion matrix using (5), and (6) respectively [25, 26]: -./ � 0101)23 (5) -4/ � 0303)21 (6) iv. results in this section, the results of the classification using wavelet features and using mfcc features are presented. as mentioned above, 1200 normal and 1200 coronavirus x-ray images were considered. the data were collected from different publicly accessible datasets, online sources, and published papers. they form the database of covid-19 x-ray images in [27]. a. classification using wavelet features the result confusion matrix of using wavelet features in the classification process is shown in table ii, where the ac is equal to 98.83%, tnr is 99.75%, and tpr is 97.95%. table ii. confusion matrix using wavelet features confusion matrix patient case normal abnormal normal 1197 3 abnormal 25 1175 b. classification using mfcc features this section includes 3 experiments, the first one is classification of the x-ray chest images into normal and corona cases using mfcc features, where the second and the third experiments are accomplished using mfcc-delta and mfccdelta-delta features. 1) mfcc features the result confusion matrix of using mfcc features in the classification process is shown in table iii, where ac is 95.46%, tnr is 94.17%, and tpr is 96.82%. table iii. confusion matrix using mfcc features confusion matrix patient case normal abnormal normal 1128 72 abnormal 37 1163 2) mfcc delta features the result confusion matrix of using mfcc-delta features in the classification process is shown in table iv, where ac is equal to 97.75%, tnr is 97.43%, and tpr is 98.07%. table iv. confusion matrix using mfcc-delta features confusion matrix patient case normal abnormal normal 1169 31 abnormal 23 1177 3) mfcc delta delta features the result confusion matrix of using mfcc-delta-delta features in the classification process is shown in table v, where the ac is 97.83%, tnr is 97.52%, and tpr is 98.15%. table v. confusion matrix using mfcc-delta-delta features confusion matrix patient case normal abnormal normal 1170 30 abnormal 22 1178 c. comparison from the presented results, classifying the x-ray images using wavelet features gave higher accuracy than using the three types of mfcc features. also, mfcc-delta-delta engineering, technology & applied science research vol. 11, no. 4, 2021, 7296-7301 7300 www.etasr.com owida et al.: classification of chest x-ray images using wavelet and mfcc features and support … provided higher accuracy than the other types of mfcc features. the number of features used in the classification process is not necessary to be high, but the type of the method used to extract these features is most important to get higher accuracy. from the results, we found that using only 5 effective features (wavelet features) gave better results than using 39 mfcc features. the consumed computational time in the feature extraction process and classification experiment was about 10 minutes. inspired by the previous research studies, the current work used advanced deep learning techniques to introduce a new model for the detection of covid-19. the extracted effective features using wavelet analysis and mfcc were used with the svm classification technique. a hybrid of public data sets have been used to validate the value of the proposed model by a total of 2400 x-ray images categorized as 1200 normal images and 1200 images of patients infected with covid-19. the proposed method aims to help close the gap between the smaller number of highly trained radiologists and the growing need for chest x-ray interpretation in relation to the pandemic outbreak. v. discussion early diagnosis of the coronavirus condition is significant in order to minimize the probability of pandemic transmission. automated early disease diagnosis can be obtained using radiological images by using artificial intelligence-based image processing approaches. many studies have recently been carried out based on machine learning models for covid-19 detection. mostly, in the present state of the increasing prevalence of covid-19 cases, many researches focus on clinical characteristics. deep learning is a combination of machine learning approaches based primarily on automated image detection and classification. the classification and detection of the purposed object are the dual major objectives in which deep learning is implemented. the progress of machine learning has significant benefits for patient assessment and the improvement of computer-aided systems. table vi summarizes the methods for automatic detection of coronavirus cases where the proposed method for detecting covid-19 using x-ray images is compared with the methods used in previous studies. the model results demonstrated in the present research have been shown to be superior than the ones of earlier researches. in this work, a new diagnostic method for detecting covid-19 disease is implemented using advanced deep learning. effective features were extracted using wavelet analysis and mfcc method, and they were used in the classification process with the svm classifier. in order to test the proposed model, publicly available x-ray images used in previous covid-19 studies were utilized. in the experimental testing of the proposed approach, the highest performing effective properties were selected using the current model. testing results show an ac score of 98.8% achieved using wavelet features and demonstrated that the current proposed model is more successful than earlier studies carried out for the detection of covid-19 using x-ray imaging. the proposed work has several certain limitations. first of all, the network design could be improved to increase the sensitivity or tp rate of covid-19 detection. in the current workflow, if the stage1 model misclassifies a viral pneumonia image as healthy or bacterial pneumonia, the further detection of covid-19 or other viruses completely misses. also, the limited number of covid-19 images makes it more difficult to train the deep learning models from scratch, which is overcome in the current study by using the deep transfer learning method. the present work is carried out with images from kaggle [27]. the work can be extended with a greater number of images of covid-19 form other databases. table vi. result comparison of the proposed model and previous studies study / year methods and models no of classes ac [4] /2020 cnn /covid-net 3 92.6% [5] /2020 cnn/ darkcovid-net 3 87% [6] /2020 deep transfer/ vgg 19 3 96.8% [7] /2020 cnn/resnet50 4 88.39% [8] /2021 cnn/ corodet 3 94.2% [9] /2021 cnn/svm 2 [10] /2021 cascade networks semeresnet50 and semedensenet169 3 85.6% [11] /2020 cnn/ transfer learning 3 95.69% [12] /2020 cnn-based capsule networks 4 95.17% [13] /2020 cnn/resnet152 2 87% [14] /2020 resnet50 and svm 2 95.38% proposed wavelet and mfcc and svm 2 97% vi. conclusion the experimental results show that the proposed application of using wavelet for chest x-ray images feature extraction has very good accuracy, around 98.8%, and hence can be used for application in combination with other techniques such as the mfcc to increase the accuracy rate and to make it more efficient. in future research, a mobile web-based framework is expected to be build that will assist health professionals in their efforts to identify instances of covid-19 as well as other illnesses. furthermore, the studies in this field will be investigated by other ai models and attention modules. references [1] j. f.-w. chan et al., "a familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-to-person transmission: a 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[27] "chest x-ray images (pneumonia)," kaggle. https://kaggle.com/ paultimothymooney/chest-xray-pneumonia (accessed jun. 03, 2021). microsoft word 5-2482_s1 engineering, technology & applied science research vol. 9, no. 2, 2019, 3896-3899 3896 www.etasr.com jawed et al.: impacts of in-accessible and poor public transportation system on urban environment … impacts of in-accessible and poor public transportation system on urban environment: evidence from hyderabad, pakistan aqsa jawed department of city and regional planning, mehran university of engineering and technology, jamshoro, sindh, pakistan geatarchisa@yahoo.com m. a. h. talpur department of city and regional planning, mehran university of engineering and technology, jamshoro, sindh, pakistan aftab.talpur@faculty.muet.edu.pk i. a. chandio department of city and regional planning, mehran university of engineering and technology, jamshoro, sindh, pakistan imtiaz.chandio@faculty.muet.edu.pk p. n. mahesar department of city and regional planning, mehran university of engineering and technology, jamshoro, sindh, pakistan pirah.noor21@gmail.com abstract—city design plays a major role in the way of life of its inhabitants. the growth of urban centers requires careful schemes to ascertain that the quality of life is not adversely influenced. the rate of motorization is increasing in hyderabad, pakistan due to inaccessible public transportation. an efficient public transportation system performs a critical part in sustaining and improving urban welfare by providing access to daily necessities. the basic aim of this study is to discuss the impacts of inaccessible public transportation on urban population, the environmental effect of recent urban transport designs, and the expansion in traffic congestion. landsat images were used to highlight the existing public transportation routes and dynamic and more realistic travel distances and times were measured. data were collected from local households and further frequency analysis was done through spss. the outcome of this research may assist the evolution of a sustainable and accessible transportation system for the urban population. keywords-transportation; sustainability; accessibility; public transport; environmental impact i. introduction urban public transport accessibility in the cities is raised by increasing population growth and spatial expansion [1, 2]. an improved transportation system supports lower transaction costs, permits economies of scale and specialization, widens opportunities, enhances trade, combines marketing and expands the income and welfare of society [3]. according to the 2017 census, hyderabad’s population is 1.733 million, making it the second most urbanized city of sindh after karachi. recent transportation planning techniques generate unfair accessibility distribution and produce safety and environment inequalities while favoring private transportation, whereas local public transports and non-motorized means have been neglected [4]. due to cost, distance, and congestion people face socio spatial “deprivations” which can lead to a decrease in the quality of life [5]. the urban population in pakistan constituted 32.5% of the whole population (135.8 million) in 1998. by 2020, the urban extent of the population is expected to be over 50% of the overall population [6]. an increase in the density of cities causes an increase in the number of personal vehicles and improper planning of routes, due to which transport associated externalities are generated such as increasing congestion, pollution, consumption of nonrenewable assets, and traffic accidents. sustainable transportation systems should be embraced to adjust between the major pillars of sustainable evolution [1, 2]. improved public transport accessibility can be seen as the core objective of transport development [7] because public transport is likely to ease urban regions significantly, with regard to accessibility and sustainability [8]. this study tries to emphasize on urban public transportation problems and their influences on regional designs of evolution, economic practicality, environment, and on the quality of life [8]. authors in [2] recommended a few strategies for the evolution of sustainable urban transportation systems. the approach adopted in this study reflects the accessibility in terms of public transport, including its environmental and social effects. ii. materials and methods a. studied area hyderabad is the former capital of sindh, pakistan and the second largest city of the sindh province. it consists of four talukas, namely hyderabad city, qasimabad, latifabad and corresponding author: a. jawed engineering, technology & applied science research vol. 9, no. 2, 2019, 3896-3899 3897 www.etasr.com jawed et al.: impacts of in-accessible and poor public transportation system on urban environment … hyderabad rural. it is located at 25.24°n and 68.20°e. the city faces many problems, one of which is transportation which emerges as a major one nowadays. figure 1 shows the studied areas which are nasim nagar road, shedigoth and wehdat colony from qasimabad area. fig. 1. studied area b. methodology this study focuses on marking different accessibility problems of public transportation. it is based on a spatial evaluation of the current public transport routes, which is used to examine accessibility issues. analysis of the public transport inaccessibility and its impacts on urban environment can be the origin of important data for regional strategy makers to keep sustainable evolution. landsat images were used to highlight the current public transport routes and traffic flows in the studied areas. accessibility was evaluated in each of the sites. for traffic volume count, various samples were taken at an interval of 5 minutes on major intersections of qasimabad at peak times (1pm-3pm), providing helpful data with regard of the future demands of public transport in the areas and their social and environmental impacts. c. data collection data were gathered through questionnaires on households and traffic volume surveys in order to examine the accessibility issues towards public transport. landsat images were used to evaluate the distances from home to public transport access areas. three sites (shedigoth, nasim nagar road, and wehdat colony) were selected from qasimabad for spatial analysis, where there was eminent usage of public transport, and 30 questionnaires were given to the inhabitants of each. ultimately the reason was to relate recognized ‘transport problems’ to quantifiable information defining the impacts on urban environment. iii. results and discussion figure 2 highlights the overall existing routes of public transport at qasimabad. figure 3 highlights the accessibility problem of the 3 selected sites as the time taken to reach a public transport, which has an obvious effect on total travel time. the blue arrows define the distance from the spatial settlements towards public transport, whereas the red lines show the existing public transport routes, the green dots display the stops of public transports, whereas the red areas are inaccessible by public transport. from figure 3 we can examine the accessibility problem. under normal conditions, the distance of a comfortable walk for most individuals towards public transport stops is 400m [8]. in the studied areas, it takes 765m from shedigoth, 800m from nasim nagar road and 300m from wehdat colony to reach a public transport route. these distances affect the accessibility of people towards public transportation. people take extra time to reach their destination therefore there is a need to extend public transport routes towards these areas to increase accessibility and reduce the usage of private vehicles. fig. 2. existing routes of public transport at qasimabad. screenshots from google earth, map data: © digital globe fig. 3. distance of selected sites towards existing routes of public transport. screenshots from google earth, map data: © digital globe a. impacts of inaccessible and poor public transportation figure 4 shows the respondents’ time to reach public transport and figure 5 shows the time taken to reach a destination via public transportation. the majority of the respondents take more time in public transports because of poor conditions and accessibility as shown in figure 6 which shows that only 28 out of the 90 respondents said that the transport routes are easily accessible. engineering, technology & applied science research vol. 9, no. 2, 2019, 3896-3899 3898 www.etasr.com jawed et al.: impacts of in-accessible and poor public transportation system on urban environment … fig. 4. time taken to reach public transport fig. 5. travel time to reach destination fig. 6. public transport is easily accessible to reach destination the way of transportation used by the respondents of qasimabad taluka to reach their destination is showed in figure 7 which reveals that the majority of population use their own vehicle. one for the main reasons is the poor availability and accessibility of public transportation. figure 8 elaborates the affordability of people of qasimabad taluka regarding the current transportation means they use. the majority of people said that the current mode is unaffordable, so there is an augmented need of reliable and accessible public transport. only 16% of the respondents were satisfied over the current services of public transport while the 84% rest are unsatisfied as shown in figure 9. fig. 7. mode of transportation used fig. 8. affordability towards current mode fig. 9. satisfaction of people regarding existing conditions b. traffic volume count figure 10 shows the traffic volume count at poonam square, in which the total generated trips were 504. out of these trips, 86 trips were generated from poonam square to giddu square, 181 trips were to shahbaz flyover, 75 to qasim square and 162 trips were generated from poonam square to nasim nagar road. the yelow line shows the trips attracted towards poonam square. from a total of 486 trips, 125 trips were attracted from shahbaz flyover to poonam square, 146 trips from giddu square, 144 trips from nasim nagar road, and 101 trips were attracted from qasim square to poonam square. the 5 minute sample result shows that there is heavy traffic congestion at poonam square during peak hours. fig. 10. trips attracted and generated at various locations from poonam chowk. screenshots from google earth, map data: © digital globe fig. 11. trips attracted and generated at various locations from nasim nagar intersection. screenshots from google earth, map data: © digital globe the traffic flow of nasim nagar intersection was surveyed at peak time, and the results are shown in figure 11. from 410 total trips, 95 trips were made from nasim nagar road to ali palace, 104 trips to qasimabad gate, 103 trips to alamdar square and 86 trips were generated from nasim nagar road to engineering, technology & applied science research vol. 9, no. 2, 2019, 3896-3899 3899 www.etasr.com jawed et al.: impacts of in-accessible and poor public transportation system on urban environment … poonam square. the yellow line shows the trips attracted towards nasim nagar road. from a total of 435 trips, 117 were attracted from ali palace, 84 trips from qasimabad, 152 trips from alamdar square, and 104 trips were attracted from poonam square to nasim nagar road. the 5 minute sample result shows that there is heavy traffic congestion at nasim nagar intersection during peak hours. the outcome reveals that there is unplanned public transport provision in the study area. the majority of the respondents (55 out of 90) take 10-15 minutes to reach public transport, a thing that directly affects the travel time to reach destination. the majority of people (57%) use a private mode to reach their destination causing congestion and air pollution, while 84% said that the current mode is unaffordable and 84% are not satisfied with the existing conditions of public transport. iv. conclusion regional sustainability can be attained by adequate public transportation planning. the absence of public transport affects the social and environmental circumstances of the local population. this paper assessed public transport accessibility and its adverse impacts on the urban environment. in doing this, bad performance of public transport was inspected in qasimabad. the result concluded that 57% of the population relied on private vehicles affecting travel time, affordability, accessibility and urban environment. it was seen that the public transport means are poor and inaccessible. development and extension of route facilities are required. public transport access could be improved by increasing coverage of spatial units, considering demographic and socioeconomic factors. besides, due to insufficiencies in the government structure, the public transport strategies are doomed to be unsuccessful. there is no proper planning to bring sustainability in transport planning and evolution projects in growing nations. a part of government rules and regulation authorities were also found to be non-operational which often generates difficulties in carrying progressed assessments and development processes. the system of current transportation planning described in this paper, provides a baseline on the way to develop policy making strategies that can contribute to the development of appropriate urban public transportation. as a recommendation, brt system should be implemented and the proposed public transport infrastructure. references [1] i. a. qureshi, h. lu, s. ye, “urban transportation and equity: a case study of beijing and karachi”, transportation research part a: policy and practice, vol. 42, no. 1, pp. 125-139, 2007 [2] i. a. qureshi, h. lu, “urban transport and sustainable transport strategies: a case study of karachi, pakistan”, tsinghua science and technology, vol. 12, no. 3, pp. 309-317, 2007 [3] m. soomro, d. a. c. maunder, s. cavill, “effective regulation for sustainable public transport in developing countries”, transport policy, vol. 13, no. 3, pp. 177-190, 2006 [4] m. imran, n. low, “sustainable urban transport in pakistan: threats and opportunities”, management of environmental quality: an international journal, vol. 16, no. 5, pp. 505-529, 2009 [5] j. r. e. russel, g. abbas anjum, “public transport and urban development in pakistan”, transport reviews, vol. 17, no. 1, pp. 61-80, 2007 [6] m. a. niedzielski, e. e. boschmann, “travel time and distance as relative accessibility in the journey to work”, annals of the association of american geographers, vol. 104 , no. 6, pp. 1156-1182, 2014 [7] j. cheng, l. bertolini, f. le clercq, “measuring sustainable accessibility”, transportation research record journal of the transportation research board, vol. 2017, pp. 16-25, 2007 [8] a. t. murray, r. davis, r. j. stimson, l. ferreira, “public transportation access”, transportation research part d: transport and environment, vol. 3, no. 5, pp. 319-328, 1998 microsoft word etasr_v11_n5_pp7542-7550 engineering, technology & applied science research vol. 11, no. 5, 2021, 7542-7550 7542 www.etasr.com rezoug et al.: a new optimization approach for a solar tracker based on an inertial measurement unit a new optimization approach for a solar tracker based on an inertial measurement unit mohamed redha rezoug department of electrical engineering university kasdi merbah ouargla ouargla, algeria redha77.rmr@gmail.com djamel taibi department of electrical engineering university kasdi merbah ouargla ouargla, algeria taibi.djamel@yahoo.fr mahdi benaouadj department of electrical engineering university kasdi merbah ouargla ouargla, algeria benaouadjmahdi@gmail.com rachid chenni moderna laboratory university of constantine 1 constantine, algeria rachid.chenni@gmx.fr abstract—improvements and applications of inertial measurement unit (imu) sensors have increased in several areas. they are generally used in equipment that measures orientation, gravitational force, and speed. therefore, in this paper, we worked on improving the performance of imu in an application on solar trackers of the kalman filter. this work illustrates the design of an autonomous device with astronomical control of a photovoltaic (pv) panel, allowing the optimization of the orientation/energy gain ratio. the device is based on two concepts at the same time, the modeling of the solar trajectory adopted by an algorithm which calculates continuously the solar angles (elevation and azimuth) and the approval of these by the imu in order to sweep away any climatic fluctuations and thus allow an almost perfect adjustment relative to the perpendicular axis of the rays. the tracking system is based on two joints controlled by an arduino control board. experiments have shown a better performance of the two-axis device: the net energy gains can be around 34% with an additional 1.1% when the kalman filter is applied. keywords-astronomical control; orientation; energy gain; optimization; inertial measurement unit i. introduction solar trackers are devices that allow the orientation of daylight reflectors regardless of their nature (photovoltaic (pv) solar panels, concentrated solar reflectors, or a lens focused towards the sun). the position of the sun in the sky varies with the seasons (elevation) and the time of day as the sun moves across the sky [1]. most solar powered pieces of equipment serve us best when pointed at the sun [2, 3]. in the literature, we find many works focused on the knowledge of several astronomical and atmospheric quantities, whereas the use of these in algorithms makes the parameters difficult to implement when it comes to simple solar tracking systems [4]. a solar tracker can increase the efficiency of such equipment at any fixed position at the cost of additional system complexity [5-7]. there are many types of solar trackers of varying cost, sophistication, and performance [8, 9]. the accuracy of the solar tracker depends on the application [10-16]. usually, pv systems do not work properly without monitoring, therefore at least one-axis tracking is mandatory [17]. in our work, we tried to structure a new two-axis tracking approach in which we aimed to orient the panel in real time towards the sun, in order to be placed in optimal position in relation to the incidence of solar radiation (perpendicular radiation if possible) because, throughout the day and depending on the season, the position of the sun varies constantly and in a different way, depending on latitude and longitude. first, we modeled the position of the sun by calculating each location on the earth at any time of day and determined the periods of daily sunshine as a function of time and place in order to get maximum benefit from the solar energy. sunrise and sunset are defined as the instants when the upper limb of the sun's disk has just touched the horizon. this corresponds to an altitude of about zero degrees for the sun. the calculation of the position of the sun in our algorithm uses a certain coordinate system where time and location are given as input while the coordinates of the reference ground are given as output and this using a gps sensor responsible for geolocation and timing. real-time adaptation has the effect of substantially increasing the amount of reception and energy output of the pv panel as a second goal in our work by focusing on the layout, use, and angular correction of panel deflection due to the displacement of the sun by special inertial measurement unit (imu) sensors that empower the reading and inform us of all the surface angles of a solar panel in relation to the horizontal and vertical axes of the platform in a 3d aspect. for additional precision, correction by kalman filter was carried out correcting the internal angular error. the correction was made with two actuators which are excited and corresponding author: mohamed redha rezoug engineering, technology & applied science research vol. 11, no. 5, 2021, 7542-7550 7543 www.etasr.com rezoug et al.: a new optimization approach for a solar tracker based on an inertial measurement unit driven by a driver through an arduino card. the experiments have shown better performance of the two-axis device by using imu, especially through the kalman filter, the net energy gains of which prove the efficiency of the proposed system. ii. modeling the path of the sun the position of any celestial object is described in two angles, the azimuth angle and the elevation angle. the elevation angle is the angle of the object above the horizon from the point of observation while the azimuth angle has diverse definitions. figure 1 shows the concept of azimuth (γ) and elevation angles (α). fig. 1. overview of tracking angles. the calculation of the position of the sun in terms of azimuth and elevation angles and the sunshine duration requires the calculation of certain parameters such as local solar time (lst) and local time (lt). the 12:00 hours lst is defined as the highest position of the sun in the sky. lt usually varies from lst due to the eccentricity of earth's orbit and due to human adjustments such as time zones and daylight saving time. a. local standard time meridian the local standard time meridian (lstm) is a reference meridian used for a particular time zone and is similar to the prime meridian which is used for greenwich mean time (gmt) which can be calculated by the following equation: ���� � 15° ��� (1) b. the equation of time the hour lines are the traces of the hourly plane which is perpendicular to the equator on the surface of the dial. the solar time measured and established by a dial is counted on the equator by the daily displacement of the hourly plane of the sun. one hour has passed when the direction of the sun's hourly plane has changed by 15°. the sundial does not take into account the declination of the sun, therefore, whatever the date of the year, the position of the time plane one hour after noon will be the same. thus, 1 pm the time line will be identical for every day of the year. this is the principle of the polar style dials in which the duration of a solar hour is not constant throughout the year. although the variation is minimal, on the order of a few seconds, the essential consequence is that these variations accumulate to form a larger gap. and during the year, the moment of the passage of the sun to the meridian (solar noon) slowly shifts day after day compared to noon which will be indicated by a perfect and regular clock. our clock shows the average time. the annual variation in the difference between solar noon and mean noon is called the equation of time. by definition: ����������� � �������� � �������������� (2) equation (2) is periodic from year to year. it has a maximum of more than 14 minutes at the beginning of february and a minimum of -16 minutes at the beginning of november. it also has an intermediate maximum and minimum. it becomes zero 4 times a year: around april 15, june 15, september 1 and december 24. the exact value of the equation of time can be calculated at any moment with all the precision required by formulas presented in various works of astronomy. there are also simplified formulas and tables sufficient for the needs of gnomonics [18] but with the current power of pcs, it is better to use formulas as exact and complete as possible. it takes a little longer, but at least the calculated values are accurate within a few seconds. the equation of time (in minutes) is an empirical equation that corrects the eccentricity of the earth's orbit and the axial tilt of the earth is: ��� � 9.87sin' 2)* + 7.53cos' )* + 1.5sin' )* (3) where )81( 365 360 −= db , where d is the day of the year (i.e. d = 1 for january 1st, d = 32 for february 1st, etc.). the precise time correction (tc) factor (in minutes) explains the variation in lst in a given time zone due to variations in the longitude of the location in the time zone and also incorporates the eot as in (4). number 4 in the equation shows the number of minutes the earth takes to rotate by one degree. �/ � 4 '�������1� + ����* � ��� (4) the lst can be calculated using (4) and lt as follows: 60 tc ltlst += (5) c. the angles of solar corrections 1) the hour angle (hra) as the first correction angle, the hra presents the conversion of lst to the degrees with which the sun moves across the sky. by definition, the hra is 0° at solar noon. each hour from solar noon corresponds to an angular movement of the sun by 15°. this step of 15° presents the rotation of the earth during one hour. in the morning, the hour angle is negative. 2�� � 15° '��� + 12* (6) 2) declination angle (δ) the declination is the angle that the sun makes at the maximum of its course (solar noon) in relation to the equatorial plane. it varies between -23.45° on december 21 and +23.45° on june 21. for this, it is important to establish an equation relating the position of the sun in relation to the perpendicular engineering, technology & applied science research vol. 11, no. 5, 2021, 7542-7550 7544 www.etasr.com rezoug et al.: a new optimization approach for a solar tracker based on an inertial measurement unit to the plane of the pv module. the declination angle can be calculated by [7]:       + ×= 365 284 2sin45.23 d πδ (7) 3) elevation angle (α) the elevation angle varies throughout the day. it also depends on latitude and date. the maximum elevation angle is an important parameter in the design of pv systems. this angle is measured at solar noon and depends on the angle of latitude and declination. the formula for the maximum elevation angle is: 3 � 90 � 5 + 6 (8) when (8) gives a number greater than 90°, the result is subtracted from 180°. this means that the sun at solar noon is coming from the south, as is typical of the northern hemisphere. 5 is the latitude of the location of interest (with a positive sign for the northern hemisphere and negative for the southern hemisphere) and δ is the declination angle. d. sunrise and sunset in order to calculate the sunrise and sunset for a given location, altitude zeroing must be applied and the altitude equations are reformulated to give: 60coscos sinsin cos 15 1 12 1 tc hsunrise −      × ×− ° −= − δϕ δϕ (9) 60coscos sinsin cos 15 1 12 1 tc hsunset −      × ×− ° += − δϕ δϕ (10) all the calculations mentioned above were developed in the labview environment by the use of command blocks and micro programs. figure 2 shows the overall code for modeling the path of the sun in the form of command frames designated as outputs from an arduino board. this map takes over from correcting the angular deviation (elevation and azimuth) caused by the daily and seasonal variation of the position of the sun. the selected imu is a hmc5883l magnetic field sensor (gyroscope). this module encompasses in a single circuit all the functions necessary for the realization of a complete imu. it integrates three axes for the two elements, the accelerometer and the magnetometer. it simultaneously measures the tracked movement and combines it with perfect synchronization with the clock. with the collaboration of the sensors, it performs an almost absolute position tracking without giving in to external transmission or emission elements. however, the majority of imus are exposed to negative distortion from external magnetic fields which affect the accuracy regardless of their nature. we therefore applied a correction by a kalman filter in order to make the imu more exact. fig. 2. global diagram of the tracking system and the modeling of the trajectory in labview. iii. description of the tracking system the tracking system corrects the angular deviation (elevation and azimuth) due to the apparent movement of the sun. it controls the movement of a pv module on two axes. the first has a 360° rotation capability, it is considered the main support of the whole mechanism. the second has a 90° rotation capability and is responsible for the rotation of the pv. to keep the solar radiation perpendicular to the active surface of the pv module, the automation of the trajectory of the sun is defined thanks to the equations of time translated into programs in labview with the cooperation of the arduino board. the control system is shown schematically in figure 3. it consists of two parts: the operative part and the control part. the operative part has two joints actuated by two jacks. engineering, technology & applied science research vol. 11, no. 5, 2021, 7542-7550 7545 www.etasr.com rezoug et al.: a new optimization approach for a solar tracker based on an inertial measurement unit fig. 3. general description of the system. a. the operative part the design of tracking systems is usually designed by one axis or by two axes. to amplify the energy gain of the pv module, two-axis trackers are the ideal solution. the choice of motors is essential, so we chose motors that have axial encoders in order to know at any time the exact angle of the motors after each movement. a powerful motor rotates 360° and presents the overall support of the module. it is responsible for correcting the azimuth deviation. the weight of the joint does not present any movement constraint on the motor because it is mounted axially on the latter using a bearing. the second motor allows the angular correction of the elevation. these motors are commonly used in the home automation field. b. the order part the control device is essentially based on multisensory technology in order to collect at any time any information that enters directly or indirectly into the calculations of the path of the sun and the angles of deviation which correct the deviation through the equations of time. the electronic imu devices measure and report the specific strength of a body. the angular rate and sometimes the magnetic field surrounding the body and the use of a combination of accelerometers and gyroscopes or magnetometers as criteria of choice led us to use them to optimize the energy gain by orientation of the pv module. for a near-perfect pv initialization, a gyroscope is used. iv. magnetometric sensor model magnetic field measurement is subjected to two types of distortion: hard iron distortion and soft iron distortion. to obtain precise measurements, a mathematical correction of the scale factor, misalignment, and bias errors by a kalman filter is applied to the model matrix. this process involves finding a transformation and bias matrix in order to obtain corrected measurements of the magnetic field. in this algorithm, a bias is applied to the vector of initial magnetometric data (x, y, z coordinates) which is then multiplied by the resulting vector. we then subtract the bias vector from the result as shown in (11). this was done by the intervention of an arduino card in the labview environment. 789:;<=>=?@9:;<=>=?a9:;<=>=?b � c �dd �de �df�ed �ee �ef�fd �fe �ffg hc 8:i:<:j;@:i:<:j;a:i:<:j;g + 7 )k)l)mbn (11) we used intrinsic active rotations of the magnetometer module around the (x, y, z) axes in a three-dimensional plane. we created 3 angles which present respectively pitch, roll, and yaw. we thus obtained 12 probabilities as indicated in figure 4. fig. 4. axial probabilities of the imu on the three-dimensional plane. in its initial position, the magnetometer module coordinate system and the panel coordinate system are aligned with each other. if we want to rotate the axis of the panel, we would perform the three elementary rotations as follows: • rotation by the roll angle around the x axis: o8d � 8p@d � @p cos' ����* + ap sin'����*ad � @p sin'����* � ap cos' ����* (12) • rotation by the pitch angle around the y axis: o8e � 8d cos' q��rs* + ad sin'q��rs*@e � @dae � +8d sin'q��rs* � @d cos' q��rs* (13) • rotation by the yaw angle around the z axis: o8f � 8e cos't�u* + @e sin' t�u*@f � 8e sin' t�u* � @e cos't�u*af � ae (14) the numbering 0 on the x, y, and z coordinates presents the starting point. the numberings 1, 2 and 3 respectively present 3 elementary rotations (the first, the second, and the third). it is possible to return to euler angles [19] from a rotation matrix. the equation varies in correspondence with the order of execution of the elementary rotations of euler angles and the euler angles of tait-bryan [20] which correspond to the order yaw-pitch-roll with corrections by a kalman filter. we integrate (11) to obtain the angles as follows: z y x 180 ° 270 ° 90 ° 0 ° z y x 180 ° 270 ° 90 ° 0 ° z y x 180 ° 270 ° 90 ° 0 ° 1 3 z y x 180 ° 270 ° 90 ° 0 ° 4 2 z x y 180 ° 270 ° 90 ° 0 ° z x y 180 ° 270 ° 90 ° 0 ° z x y 180 ° 270 ° 90 ° 0 ° 5 7 z x y 180 ° 270 ° 90 ° 0 ° 8 6 y x z 180 ° 270 ° 90 ° 0 ° y x z 180 ° 270 ° 90 ° 0 ° y x z 180 ° 270 ° 90 ° 0 ° 9 11 y x z 180 ° 270 ° 90 ° 0 ° 12 1 hmc5883l yaw pitch 180 ° 270 ° 90 ° 0 ° roll horizontal plane engineering, technology & applied science research vol. 11, no. 5, 2021, 7542-7550 7546 www.etasr.com rezoug et al.: a new optimization approach for a solar tracker based on an inertial measurement unit ( )1 21 21 11 11 tan tan2m yaw a m ,m m   = =    (15) v��rs � +sinwd'�fd* � +�sin'�fd* (16) ( )1 32 32 33 33 tan tan2 m roll a m ,m m −  = =    (17) these were deduced using the fact that the magnetometer module rotates back to front and the local field vectors move inward. using this information along with knowing the orientation of the imu allows the formation of a direction cosine matrix which is used to convert the measurements from the imu coordinate frame to the panel coordinate frame. we can present the order of transformations as follows: • turn the angle α +90° around the x axis to align the z axis of the imu with the z axis of the panel support. �d � c1 0 00 0 +10 1 0 gc 1 0 00 cos3 +sin 30 sin 3 cos3 g (18) • -rotate β +90° around the z axis to align the coordinate frames of the imu and the panel support. �e � ccosx sin x 0sin x cosx 00 0 1gc 0 +1 01 0 00 0 1g (19) thus, the complete transformation of the imu into coordinates of the panel support is given by the multiplication of the equation: � � c+sinx sin3 .cosx cos3 .cosxcosx sin 3 .sinx cos3 .sin x0 cos3 +sin 3 g (20) the similarity of movement of the angles of our problematic which is the movement of a pv panel around its axes at the first two angles (yaw and pitch) led us to make a correspondence of the azimuth and elevation angles with the latter. fig. 5. center of circle before calibration and filtering separately, (a) on the χ axis, (b) on the υ axis, (c) on the ζ axis, (d) and (e) on the xyz kernel. figure 5 shows that the center of the circle after hard iron distortions is now at y=100 and x=200. there is therefore a polarization of hard iron on the x axis of 200mg and a polarization of iron hard on the y axis of 100mg. these distortions move the center of the circle away from its original position but preserve its original shape. soft iron distortions on their part distort existing magnetic fields. soft iron distortions are easy to identify in a magnetic output graph because they distort the circular output. the soft iron distortions distort the circle and give it an elliptical shape. an illustration of the magnetometer output with the two distortions on the x and y axes in order can be seen in figure 6. fig. 6. center of circle after calibration and filtering separately (a) on the x axis, (b) on the y axis, (c) on the z axis, (d) and (e) on the xyz kernel. a circle which does not undergo any distortion must be centered on x=0, y=0 and its radius must be equal to the magnitude of the magnetic field. figure 7 shows the application of the kalman filter with block-chained logic under the labview environment. v. general structure of the device the produced system is an autonomous, automatic, and preprogrammed solar tracker based in its design on an arduino mega embedded system which is capable of astronomically resetting the local parameters of a pv installation by geolocation and instantly correcting with a new approach of the imu the angular fluctuations (azimuth and elevation) caused by the displacement of the sun using a preprogrammed algorithm and pulse control in order to minimize the power consumed by the actuators and to increase the luminous flux on the active surface of the panel. usually, imus are used in the field of aeronautics, especially drones. they allow the collaboration with a gps receiver when the gps signals are absent as is the case in tunnels. in order to collect as much information as possible to geolocate a photovoltaic installation, we have chosen the gyneo6m type gps compatible with the master arduino mega card. it can be synchronized with an rtc of our system or operate autonomously. the modeling of the above mentioned path of the sun requires knowledge of a few parameters in order to determine the angles of azimuth and elevation. engineering, technology & applied science research vol. 11, no. 5, 2021, 7542-7550 7547 www.etasr.com rezoug et al.: a new optimization approach for a solar tracker based on an inertial measurement unit fig. 7. application of the kalman filter in labview. fig. 8. general descriptive diagram of the system. an internal clock updates the gps in order to detect the local coordinates as well as the date and the time required in this calculation. the imu works by sensing linear acceleration using the internal accelerometer and the rotation rate using the hmc5883l at each angular correction (azimuth or elevation). so, it is updated with the next angles and the current angles. these data are stored in the arduino in an eeprom to be compared to the angles of the motor encoders to confirm their values and to be used as correction steps through power stages that reposition the equipment. to access the internal parameters that are introduced into the initialization and configuration of the tracking system or the modeling of the trajectory, a touch screen can be used which does this through several actions. figure 8 summarizes the general design of the produced device. a. gps communication modeling the path of the sun requires the intervention of a few quantities. the gy-neo6m uses geolocation by the world geodetic system (wgs 84) which is used in mapping and navigation including satellite navigation systems. the geographic coordinates of the pv system are quantities (latitude, longitude, and time) which define its position on the installation surface. latitude values collected by the system and longitude values are the considered entrances. through two pins of the arduino board (txd1 and rxd1) the gps communicates at a speed of 9600bps. more parameters are shown in table i. table i. technical parameters parameter value power supply 3v / 5v model gps-neo-6m-001 antenna ceramic antenna battery rechargeable battery back-up signal light led light antenna size 25×25mm model size 25.5mm×31.5mm mounting hole 2mm default baud rate 9600 default output compatible with nmea0 b. tactile communication in order to simplify the communication between the user and the arduino and to minimize the use of electronic components (push buttons), a touch screen type (320×240 tft lcd) was used in the constitution of our device. its role is also to display any action applied on the arduino. a multi-screen menu has been created to organize the control and display of the various parameters which can be the measured quantities or different input and output data. the main purpose of this tactile communication is to access the internal parameters of the quantities recorded previously such as the initial variables stored on the arduino eeprom and change them according to our needs. this adjustment is considered as a manual mode (all the quantities are inserted manually without the use of the arduino dated, time longitude latitude temperature unit of measure v and i motor panel gps tft touch screen fashion communication h an d t x / r x support 1 0 encode the master card physical mechanism positioning angle imu magnetometer engineering, technology & applied science research vol. 11, no. 5, 2021, 7542-7550 7548 www.etasr.com rezoug et al.: a new optimization approach for a solar tracker based on an inertial measurement unit sensors). this choice is provided as an emergency solution if auto locate fails. vi. experimental test in order to demonstrate the effectiveness of this new approach, we first carried out a comparison of the results obtained on a fixed module with respect to another module oriented by two axes based on the new approach while correcting the variation related to elevation and azimuth. these two angles are directly linked to the day, night, and seasonal variation under the same operating conditions. a further comparison was made between the results obtained by the technique without and with the kalman filter. these experiments were carried out in a day where the illumination was relatively good with some disturbances in the afternoon in the eastern algeria (ain beida) defined by 35.796 n altitude and 7.393 e longitude with a varied temperature. for a daily correction, a series of successive orders to the equipment at equal intervals during the period of sunshine carries the angular correction of deviation which varies from 1.5 to 2 degrees. the command information is extracted from the database which is calculated by the arduino and stored in the eeprom of its microcontroller. voltage and current measurements were conducted at equal time intervals. the copernicus equation gives us an initial declination of the pv module of 14.81°. the labview environment provides us with graphical interfaces to display the different quantities collected experimentally by the card (current, voltage, and power). the results are shown in figures 9-13. in figures 9-11, we obtained from the labview the responses represented in blue for the measured quantities of a tracking system without kalman filter and in red for those of a fixed system. in figure 9, we see that the oriented system generates a current intensity that exceeds three times the current obtained by the fixed system at the start of the day because the panel has already been initialized in a perpendicular position with respect to the solar rays, so this system stabilizes at a maximum current value. we also notice disturbances caused at the end of the day by a cloud passage. during this time, the fixed system starts with a low current which gradually increases towards the optimal period of sunshine then decreases (knowing that the panel is fixed at a tilt angle of 32°). the current generated by the stationary panel always remains lower than that generated by the oriented panel. this validates the significant influence of irradiation on the current and more precisely that of the angles formed by the rays and the panels. it is always favorable to keep an angle of 90° with the panels for a total absorption of the rays without losses and without refractions which leads us to choose the most precise oriented systems. in figure 10, we see that the voltage supplied by the oriented module at the start of the day is high but decreases regularly due to the influence of the temperature on the voltage of the panel caused by the fact that the active surface of the panel remains perpendicular to solar radiation while the voltage supplied by the fixed module at the start of the day is low and remains constant with some variations and disturbances and exceeds the oriented module a few times. figure 11 shows the power obtained during this day by the two panels which represent the product of the voltage and the current. we notice the effect of the orientation technique on the efficiency which is a gain of 34% in comparison with the fixed system. fig. 9. current-time curves for a fixed and an oriented module. fig. 10. voltage-time curves for a fixed and an oriented module. fig. 11. power-time curves for a fixed and an oriented module. in figure 9, we can see the gain obtained by the tracking system, manifested by the difference between the two schemes. this gain was obtained thanks to the angle detection precision of the imu. this reflects the influence of this technique on the efficiency of a pv panel. to remedy the errors caused by the external magnetic effects on the imu sensors, a kalman filter is applied. in order to show the effect of the latter on the yield, two comparative experimental tests were carried out on a filtered and an unfiltered system during two different days to generalize the results. we plot the curves of the measured quantities (i and v) using labview. figures 12 and 13 show the power plot obtained by the tracking system with (blue) and without (red) the kalman filter. the difference between the plots in the same chart in figures 12 and 13 is respectively a gain of 1.1% and 1.2%. this proves the advantage that this new engineering, technology & applied science research vol. 11, no. 5, 2021, 7542-7550 7549 www.etasr.com rezoug et al.: a new optimization approach for a solar tracker based on an inertial measurement unit technique gains with the application of the kalman filter on the behavior of the imu sensor. in [13], a comparative study between a fixed system and another two-axis oriented system using a 120w pv panel showed an average daily energy gain of 112.5wh. according to the energy aspect and over the same period, we arrived to obtain an average daily energy gain of 403.2wh (since the pv panel used in [13] is 12 times greater than the one opted in the current work). so, the developed new optimization approach for a solar tracker based on an imu is most suitable for twoaxis tracking systems. fig. 12. power curves during the first day. fig. 13. power curves during the second day. vii. conclusion due to the poor performance of fixed panels resulting from the movement of the sun and energy losses, the main goal of the researchers in this field is to track the variant trajectory of the sun and to optimize the techniques used while taking into account the materials. various methods have been employed to remedy this. in the current work, a preprogrammed technique using different equations of time was adopted which includes the use of imu modules. these new components are characterized by their precision of positioning identification along three axes. this helps us to collect more accurate data on the position of the panels and thus to better control them to follow the sun. however, these components operate using magnetic fields and are highly sensitive. they are therefore often influenced by neighboring magnetic fields and end up showing calculation errors, which cause energy losses. to solve this problem, we used an additional corrector, which is the kalman filter. it corrects deviations 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[20] c.-c. wei, y.-c. song, c.-c. chang, and c.-b. lin, "design of a solar tracking system using the brightest region in the sky image sensor," sensors, vol. 16, no. 12, dec. 2016, art. no. 1995, https://doi.org/ 10.3390/s16121995. microsoft word etasr_v10_n6_pp6549-6556 engineering, technology & applied science research vol. 10, no. 6, 2020, 6549-6556 6549 www.etasr.com aktas & esen: state-space modeling and active vibration control of smart flexible cantilever beam … state-space modeling and active vibration control of smart flexible cantilever beam with the use of finite element method kerim gokhan aktas department of mechanical engineering karabuk university karabuk, turkey kerimgokhanaktas@karabuk.edu.tr ismail esen department of mechanical engineering karabuk university karabuk, turkey iesen@karabuk.edu.tr abstract-the aim of this study is to design a linear quadratic regulator (lqr) controller for the active vibration control of a smart flexible cantilever beam. the mathematical model of the smart beam was created on the basis of the euler-bernoulli beam theory and the piezoelectric theory. state-space and finite element models used in the lqr controller design were developed. in the finite element model of the smart beam containing piezoelectric sensors and actuators, the beam was divided into ten finite elements. each element had two nodes and two degrees of freedom were defined for each node, transverse displacement, and rotation. two piezoelectric ceramic lead zirconate titanate (pzt) patches were affixed to the upper and lower surfaces of the beam element as pairs of sensors and actuators. the location of the piezoelectric sensor and actuator pair changed and they were consecutively placed on the fixed part, the middle part, and the free end of the beam. in each case, the design of the lqr controller was made considering the first three dominant vibratory modes of the beam. the effect of the position of the sensor-actuator pair on the beam on the vibration damping capability of the controller was investigated. the best damping performance was found when the sensor-actuator pair was placed at the fixed end. keywords-vibration control; piezoelectric; lqr control; finite element analysis; smart beam i. introduction because of the low resistance of lightweight and flexible structures, vibration problems occur at low frequencies and their control is a major problem. active vibration control systems are preferred because passive methods are considered inadequate in dealing with this problem. one of the most effective solutions of the vibration problem in light and flexible structures is to make them smart using smart materials [1]. piezoelectric materials come to the forefront in smart materials due to advantages such as high sensitivity in sensing and drive, being applicable in a wide frequency range and being supplied in different shapes and sizes. piezoelectric materials have been widely used recently in various areas especially in aviation, flexible robot arms, energy harvesting, and noise and shape control due to their ability to convert mechanical into electrical and electrical into mechanical energy [2-5]. flexible beam elements are distributed parameter systems with infinite degrees of freedom (dof). the active vibration control generally requires a low-order mathematical model of the system containing a limited number of dof [6]. in particular, care must be taken so that the control of low-frequency modes does not affect the stabilization of high-grade modes, since sensors and actuators have limited bandwidth [7, 8]. many techniques have been used to solve this problem, but the most effective is the use of collocated sensors and actuators that work in harmony with each other [9]. vibration can be controlled by different control techniques. the most used control techniques are classical control algorithms such as positive position feedback (ppf), velocity feedback and pid control [10-14]. it is very important to specify the sensor and actuator position optimally to keep the control capability at maximum. otherwise, control spillover and observation spillover may occur, and this will affect the efficiency of the control system [6]. authors in [15] proposed a controller combining ppf and pd control methods to suppress the first three vibration modes of the cantilever plate. authors in [16] used two types of actuators (an inertial and a distributed strain actuator) and two types of controllers (pvf and h∞ control) to suppress the vibration of a fully clamped beam, and found that the best result was obtained with the h∞ controller and a distributed strain actuator. authors in [17] designed a lqr controller based on the independent mode space control techniques. lqr control is one of the methods frequently used in active vibration control [18]. in lqr control, the performance index is minimized with optimum weight matrices. the lqr control provides the optimal response between the response speed and energy required to suppress vibration. [q] and [r] are the most important parameters in keeping the permissible actuator voltage within certain limits while keeping the control performance at maximum level. therefore, the important thing in lqr control is to determine the optimum state weighting matrix [q] and the input weighting matrix [r]. significant research has been done on the determination of weight matrices [19-21]. corresponding author: kerim gokhan aktas engineering, technology & applied science research vol. 10, no. 6, 2020, 6549-6556 6550 www.etasr.com aktas & esen: state-space modeling and active vibration control of smart flexible cantilever beam … in this study, the method of constructing a comprehensive mathematical model including piezoelectric mass and stiffness sensor-actuator and controlling the first three dominant vibration modes of a cantilever beam using the lqr controller are presented. the collocated piezoelectric sensor and actuator pair were placed on various finite elements. this allowed us to examine the effect of the sensor-actuator pair position on the performance of the controller. since piezoelectric actuators have a certain operating voltage range, it is important to keep the actuator voltage within the allowable limits for a realistic control performance. for this reason, unlike most studies in the literature, the necessary actuator voltage was determined while ensuring optimum controller performance. as a result of the simulation study, system response and required actuator voltage were determined. ii. system modeling in this section, the mathematical model of a smart cantilever beam with a piezoelectric collocated sensor and actuator pair is presented. the mathematical model of the smart beam was created on the basis of the euler-bernoulli beam theory. as shown in figures 1 and 2, the beam is divided into 10 finite elements, each element with two nodes and two dof were defined for each node: transverse displacement and rotation ( �� , �� , �� , �� ). the physical and mechanical properties of the beam and pzt patches are given in table i. table i. mechanical and physical properties parameters beam pzt patches length lb=0.25 m lp=0.025 m width w=0.03 m w=0.03 m thickness hb=1.0 mm ha=hs=0.55 mm density ρb=8030 kg/m 3 ρp=7700 kg/m 3 young’s modulus eb=193 gpa ep=68 gpa pzt strain constant d31=125x10 -12 m/v fig. 1. finite element discretization of the smart cantilever beam. fig. 2. beam element and piezoelectric beam element. as shown in figure 2, the section of the beam without the piezoelectric patch is expressed as a beam element, and the section with the piezoelectric patch is expressed as a piezoelectric beam element. in figures 1-2, fext, lb, lb, lp (ls, la), and p represent the external disruptive force applying at the free end of the beam, the length of the entire beam, the length of the beam element, the length of the piezoelectric sensor and of the actuator patch, and the polarization direction. a. modeling of the beam element in the modeling, beam and piezoelectric patches were considered as an euler-bernoulli beam. the governing equations of motion of the smart beam for forced motion can be written as a fourth order partial differential equation [22] : �� �� �, �� � � �� �� �, ���� � ��� (1) where � is the displacement of the beam, � is the mass density, � is the cross-section area, � is the young’s modulus, � is the moment of inertia, and ��� is the external force. in order to obtain the shape functions, the beam displacement function is taken as a cubic displacement function as in (2): � �, �� � ���� � ���� � ��� � �� (2) where �� indicates the total degree of freedom, including displacement and rotation in each element (��, �� , ��, ��). constants ��, ��, ��and �� are obtained by using cantilever beam boundary conditions. substituting the constants ( �� , �� , �� , �� ) in (2), the displacement function can be obtained as: � �, �� � ��� �� … … �� ��� ��������! � ����"� (3) where ��� represents the shape function and �"� represents the nodal displacement vector. the strain energy in bending and bending moment can be found as [23] : # � $ %��&'() *�, + � �� �� ��� (4) using (4), the potential energy is obtained as in (5): # � &,',� $ -�� ���.� *� � &,',� $ �"�/�0��/�0���"�*�1,)1,) � �� �"�/ -�2�2 $ �0��/�0��*�1,) . (5) the kinetic energy can be found as: 3 � 4,5,� $ -� � .� *�1,) � 4,5,� $ �"6�/�0�/1,) �0��"6�*� � �� �"6�/ -�2�2 $ �0�/1,) �0�*�.�"6� (6) where 0� and 0 are the second spatial derivative and the time derivative of the shape function, respectively. total kinetic and potential energy can be found as: # � �� �"�/�72��"� (7) 3 � �� �"6�/�82��"6� (8) using the lagrange equations, the stiffness and mass matrix of each beam element can be written as in (9) and (10): engineering, technology & applied science research vol. 10, no. 6, 2020, 6549-6556 6551 www.etasr.com aktas & esen: state-space modeling and active vibration control of smart flexible cantilever beam … �72� � &,',1,9 :;; ;< 12 6@2 −12 6@26@2 4@2� −6@2 2@2�−12 −6@2 12 −6@26@2 2@2� −6@2 4@2� cdd de (9) �82� � 4,5,1,��) :;; ;< 156 22@2 54 −13@222@2 4@2� 13@2 −3@2�54 13@2 156 −22@2−13@2 −3@2� −22@2 4@2� cdd de (10) b. modeling of the piezoelectric beam element and of the smart beam element similarly, when the piezoelectric patches are considered as euler-bernoulli beam elements, the stiffness and mass matrix of the piezoelectric patches can be obtained as: h7ij � &k 'k1k9 :; ;; < 12 6@i −12 6@i6@i 4@i� −6@i 2@i�−12 −6@i 12 −6@i6@i 2@i� −6@i 4@i� cd dd e (11) h8ij � 4k 5k1k��) :;; ;< 156 22@i 54 −13@i22@i 4@i� 13@i −3@i�54 13@i 156 −22@i−13@i −3@i� −22@i 4@i� cd dd e (12) as shown in figure 2, two piezoelectric patches are bonded to the upper and lower surface of the beam element as a sensor and actuator. this state of the beam is called a smart beam element. the stiffness of a smart beam element can be obtained by the equivalent flexural stiffness method [24] . ����l � �2�2 � 2�n�n (13) with the help of the parallel axis theorem, the moment of inertia of the smart beam element can be obtained as: �n � opk9�� � qℎn spktp,u�� (14) the mass per unit length of the beam element can be found as: �� � q �2ℎ2 � 2�iℎi� (15) where ℎi and ℎ2 represent the thickness of the pzt patch and core beam respectively. the elemental stiffness and mass matrix of the smart beam can be written as: �7v� � &'�wx1y9 :;; ;< 12 6@v −12 6@v6@v 4@v� −6@v 2@v�−12 −6@v 12 −6@v6@v 2@v� −6@v 4@v� cdd de (16) �8v� � 451y��) :;; ;< 156 22@v 54 −13@v22@v 4@v� 13@v −3@v�54 13@v 156 −22@v−13@v −3@v� −22@v 4@v� cdd de (17) iii. piezoelectric constitutive equations piezoelectric materials can be used as both sensors and actuators. if used as an actuator, the piezoelectric patch undergoes mechanical strain when voltage is applied as input (inverse piezoelectric effect). if used as a sensor, the patch generates voltage as an output when mechanical stress is applied to it (direct piezoelectric effect) [25]. when a disruptive external force is applied to the beam, the beam is exposed to vibration. in the vibration damping process, mechanical stress occurs in the beam exposed to vibration, and the patch used as a sensor produces a voltage against this stress. the generated voltage is applied to the controller after the signal conditioning process. after the signal is evaluated, it is applied to the actuator as a control signal. the patch used as actuator undergoes a mechanical strain and suppresses vibration by producing an equal amplitude and an opposite response to vibration. the ieee piezoelectricity standard was taken into account in defining the electromechanical properties of the piezoelectric material and the piezoelectric material is considered to exhibit linear behavior [26]. the electromechanical equations of linear piezoelectric materials can be written as: z� � [��&\� � *���] (18) ]̂ � *��\� � _��`�] (19) where z� , [�� , \� , *�� , �] , ]̂ and _�� represent the strain (m/m), compliance (m 2 /n), stress (n/m 2 ), piezoelectric strain constant (m/v), electric field (v/m), electric displacement (c/m 2 ), and permittivity (f/m). also, the superscripts e and σ represent the constant electric field and the constant voltage. a. sensor equations equation (19) expresses the direct piezoelectric effect and is used to determine the total charge obtained from the pzt sensor. since no extra electric field is given to the sensor, (19) can be written as: ]̂ � *��\� � *��a��z� � b��z� (20) where b�� is the piezoelectric stress/charge constant and a�� is the inverse of compliance (1/[��). the total charge obtained from the sensor layer can be calculated as: c �� � $ ]̂5 *� (21) the charge can be converted to current as: d �� � ef �e � ee $ ^]5 *� � ee $ b��z�5 *� (22) as we know, strain at any point can be found as [23]: z� � − ]g , �g = e� e��, z� = h e� e�� (23) where h is the distance to the neutral axis and i is the radius of curvature. equation (22) can be written as: d(�) = ee $ b��h0�"5 *� = hb��q $ 0�"61k) *� (24) h = (p,� + ℎj) (25) engineering, technology & applied science research vol. 10, no. 6, 2020, 6549-6556 6552 www.etasr.com aktas & esen: state-space modeling and active vibration control of smart flexible cantilever beam … the current obtained from the sensor is converted into voltage with the signal conditioning device. the voltage value obtained is given to the actuator with a suitable control gain: k v(�) = lhb��q $ 0�"61k) *� = ["6 (26) where l is the signal conditioning device gain. this sensor voltage is given as input to the controller and the controller output is multiplied by the controller gain and is given to the actuator. the actuator input voltage can be found as: kj(�) = m = n � kv(�) (27) where n is the control gain. b. actuator equations equation (18) expresses the inverse piezoelectric effect and is used to calculate the total strain. since no extra stress is given to the actuator, (18) can be written as: z� = *���] (28) when an input voltage is applied to the actuator in the polarization direction, the actuator strains in one direction. the stress and electrical field generated in the actuator can be obtained as: �] = op( )pp , \� = �iz� = �i*�� op( )pp (29) where �i and ℎj are the young’s modulus and the thickness of the actuator respectively. as a result of the stress, the bending moment occurs in the beam element. the bending moment in a small cross section can be written as: *+jq = �i�i e� e�� (30) the sum of the moments of the stresses on the x axis relative to the y axis can be written as: +jq = $ h̿\�*h, h̿ = spptp,� t (31) by using (29) and (30), the bending moment can be found as: +jq = �i*��h̿kj(�) (32) the control force applied by the actuator to the beam element can be obtained using (27) and (32): ujq = �i*��qh̅ $ 0�/1k *�kj(�) = wkj(�) (33) where w is a constant vector of size (4×1). iv. equations of motion, state space representation, and model verification a. equations of motion for the smart beam the dynamic equation of a smart beam can be written as: �+�x"yz + �n�x"z = ��� + �q {1 (34) rayleigh proportional damping method is used to include the damping effect in the model. structural damping matrix can be obtained as [27]: a = |+ + }n (35) where a is the damping matrix, | is the mass proportional damping coefficient, and } is the stiffness proportional damping coefficient. in obtaining the damping matrix of the smart beam, | and } coefficients were taken as 0.001 and 0.0001 respectively. +, aand n represent the global mass and the damping and stiffness matrices of each finite element. the mass and stiffness matrices of the entire beam are obtained by combining the local mass and stiffness matrices using the finite element technique. the equation of motion of cantilever beam and sensor output equation can be written as: �+�x"yz + �a�x"6z + �n�x"z = ��� + �jq (36) ~(�) = kv(�) = ["6 (37) in order to examine the dominant first three vibration modes of the system, " = φ* conversion was made and the transition from generalized coordinates to principal coordinates was made [28]. here, φ denotes the modal matrix. using the transformation " = φ*, (36) and (37) can be written as: +φ*y + aφ*6 + nφ* = ��� + �jq (38) ~(�) = kv(�) = [φ*6 (39) by pre-multiplying (38) with φ/ , generalized mass, stiffness and damping matrices can be obtained as: φ/+φ*y + φ/aφ*6 + φ/nφ* = φ/��� + φ/�jq (40) +�*y + a̅*6 + n�* = ���� + ��jq (41) the +� , a̅ and n� matrices are generalized mass, damping matrix, and stiffness matrix respectively, each (3×3) in size. the generalized external force vector ���� is obtained as: ���� = φ/��� = φ/u�(�) (42) where �(�) refers to the external force input to the smart beam. the generalized control force vector is expressed by: ��jq = φ/�jq = φ/wkj(�) (43) b. state space repsentation of the smart beam the state and output equation of a dynamic system can be written as: �6 = �� + �m (44) ~ = a� + ^m (45) where � is the system matrix, � is the input matrix, a is the output matrix, ^ is the direct transmission matrix. �, m and ~ represent the state vector, input vector and output vector respectively. x is used as the state variable to obtain the state equations. the generalized coordinates in (44) can be written in terms of the state variable as follows: �*� = �*�*�*�� = � ������� , h*6j = � *�6*�6*�6 � = � ������� , h*yj = � �6��6��6�� (46) the state space form of the (36) can be written as: engineering, technology & applied science research vol. 10, no. 6, 2020, 6549-6556 6553 www.etasr.com aktas & esen: state-space modeling and active vibration control of smart flexible cantilever beam … +� ��6��6��6�� + a̅ � ������� + n� � ������� = ���� + ��jq (47) the state equation form of (47) can be written as: :; ;; ;<�6��6��6��6��6��6�cd dd de = 0 �−+���n� −+���a̅. :;; ;;< ������������cd ddd e + 0+� ��φ/w. m(�) + � 0+���φ/u� �(�) (48) the sensor voltage can be taken as output and is obtained as: ~(�) = a/�(�) + ^m(�) (49) ~(�) = �0 [φ� ���⋮������ (50) c. model verification before starting the simulation study, the created mathematical model was compared with two previous numerical studies and the results are shown in tables ii and iii. in [28], considering a cantilever beam divided into four finite elements, four different models were created by placing piezoelectric elements in different positions and the dominant first two vibration mode natural frequency values were obtained for each model. these values were compared with the values obtained from the current study in table ii. the mechanical and physical properties of the considered beam are given in [28]. in [29], a bimorph cantilever beam consisting of two piezoelectric pvdf layers divided into five finite elements, was considered and tip displacements were obtained by applying various voltage values in the range of 0-200 v. the dimensions of the pvdf beam are l=100 mm, w=5 mm and h=1 mm. the tip displacement values were compared with the values obtained from the current study in table iii. the mechanical properties of the pvdf layers are given in [29]. table ii. natural frequency comparison model natural frequency (hz) [28] present mode 1 mode 2 mode 1 mode 2 model 1: fixed end 6.66 36.89 6.6581 36.8735 model 2 4.73 27.43 4.7246 27.4143 model 3 3.85 30.52 3.8212 30.2934 model 4: free end 3.16 25.34 3.0433 25.0924 table iii. tip displacement comparison voltage (v) tip displacements (×10 -4 m) [29] present 50 0.1755 0.1736 100 0.3409 0.3377 150 0.5067 0.4991 200 0.6819 0.6706 v. lqr control design lqr control theory is used in active vibration control of smart cantilever beams. the cost function can be written as [30]: � = �� $ (�/c� + m/im)�) *� (51) where [c] and [i] are the positive semi-definite symmetric and positive definite symmetric weighting matrices respectively. larger [c] means that a better control performance is requested from the controller. on the other hand, the meaning of the larger [i] is the reduction of the permissible control effort. using the linear control law, the control input can be found in: m = −n� (52) where n is the feedback control gain which can be obtained as: n = i���/� (53) where � is a algebraic ricatti equation solution of (54): �� + �/� − ��i���/� = 0 (54) once � is calculated, the actuator input voltage can be found with the help of (27). [q] and [r] matrices can be written as: �c��� = ��� 0 0 00 ⋱ 0 000 00 ⋱ 00 ���! (55a) �i��� = ��� 0 0 00 ⋱ 0 000 00 ⋱ 00 ���! (55b) the [c ] and [i ] weighting matrices are obtained using bryson’s method [31]: ��� = s �|��|�p�� t , ��� = s �|��|�p�� t d = 1,2,3, . , 0 (56) in the bryson’s method, in a system with n state variables, the state weight coefficient of each state variable is determined according to the maximum acceptable error amount of that variable (|��|�j�). the determination of the r control weight coefficient depends on the maximum acceptable value of the control signal (|m�|�j�). vi. results and discussion as shown in figure 3, the beam was divided into ten finite elements and the actuator-sensor pair was placed in three different positions to examine the effect of the pair's position on the beam. as a result, three different models were created, and a state space model was obtained for each model. finite element model and lqr controller were programmed in matlab. the maximum acceptable error was 2% and the maximum voltage applied to the actuator was 200v. the feedback control gain n obtained for each model can be written as: �n�� = �−25.3 146.7 −129.2 355.2 95.1 28.6� (57) �n�� = �52.2 434.8 326.6 −426.3 145.9 37.7� (58) engineering, technology & applied science research vol. 10, no. 6, 2020, 6549-6556 6554 www.etasr.com aktas & esen: state-space modeling and active vibration control of smart flexible cantilever beam … �n�� = �53.8 410.4 364.5 a432.1 166.6 42.1� (59) the natural frequencies for the first three vibration modes of the three models are given in table iv. the step responses for the first three vibration modes of the system are given in figures 4-6. (a) (b) (c) fig. 3. position of the pzt sensors. (a) model 1, (b) model 2, (c) model 3. table iv. natural frequencies model natural frequency (rad/s) mode 1 mode 2 mode 3 model 1: fixed end 92.51 569.42 1568.50 model 2 77.92 504.73 1405.32 model 3: free end 68.15 458.34 1326.90 fig. 4. closed loop displacement responses of model 1. fig. 5. closed loop displacement responses of model 2. when table iv and figures 4-6 are examined, it is seen that as the actuator-sensor pair moves from the fixed end to the free end, the stiffness of the system increases depending on the natural frequency and thus the vibration amplitudes and settling time decrease. the required actuator voltage for the vibration control of the three models is shown in figures 7-9. fig. 6. closed loop displacement responses of model 3. fig. 7. maximum actuator voltage requirement of model 1. fig. 8. maximum actuator voltage requirement of model 2. fig. 9. maximum actuator voltage requirement of model 3. the obtained settling time and actuator voltage values, according to the simulation results are shown in table v. 1 2 3 4 5 6 7 8 910 1 2 3 4 5 6 7 8 910 1 2 3 4 5 6 7 8 910 engineering, technology & applied science research vol. 10, no. 6, 2020, 6549-6556 6555 www.etasr.com aktas & esen: state-space modeling and active vibration control of smart flexible cantilever beam … table v. settling time and actuator voltage model settling time (s) maximum voltage (v) model 1: fixed end 2.33 28.05 model 2 3.39 23.12 model 3: free end 4.56 19.88 as seen in table v, the best settling time values were obtained in model 1. although the required actuator voltage in model 1 is higher than that of other models, the difference is not significant when settling time values are considered. vii. conclusion this paper presents the active vibration control of a smart flexible cantilever beam bonded with a collocated pzt actuator and sensor pair. an lqr controller was designed for the control of first three vibration modes of the beam. the natural frequency and tip displacement values obtained to verify the finite element model and equations of motion created within the scope of the study were compared with existing studies in the literature. it has been determined that the natural frequency values are similar with a maximum error rate of 0.98% and the tip displacement values are similar to the 1.66% error rate. the position of the pzt sensor-actuator pair on the beam was changed to optimally determine the sensor-actuator position. as a result of the simulation study, system response, settling time, and required actuator voltage were determined for the first three vibration modes. the simulation results demonstrate that the best vibration damping results were obtained when the pzt actuator and sensor were affixed to the fixed end. references [1] t. c. manjunath and b. bandyopadhyay, “vibration control of a smart structure using periodic output feedback technique,” asian journal of control, vol. 6, no. 1, pp. 74–87, mar. 2004, https://doi.org/10.1111/ j.1934-6093.2004.tb00185.x. 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[31] a. e. bryson and y. c. ho, applied optimal control: optimization, estimation, and control. washington, usa: hemisphere publishing corporation, 1975. microsoft word 44-3727_setasr_v10_n4_pp6152-6160 engineering, technology & applied science research vol. 10, no. 4, 2020, 6152-6160 6152 www.etasr.com ombongi et al.: energy efficient resource allocation in millimeter-wave d2d enabled 5g cellular … energy efficient resource allocation in mmwave d2d enabled 5g cellular networks filbert onkundi ombongi department of electrical engineering pan african university institute for basic sciences, technology and innovation nairobi, kenya heywood ouma absaloms department of electrical and information engineering university of nairobi nairobi, kenya philip langat kibet department of telecommunication and information engineering jomo kenyatta university of agriculture and technology, nairobi, kenya abstract-the current trend has seen the data capacity and traffic density increase due to the increased demand for multimedia services. since this cannot be handled successfully by the current 4g networks, there is a need to integrate the mmwave and the device-to-device (d2d) communication 5g technologies to meet this increased demand and traffic density. however, there is the challenge of increased interference between dense d2d users and cellular users if d2d users are allowed to reuse the resources allocated to cellular users. this degrades the performance of the d2d users in terms of achievable data rate and energy efficiency (ee). the paper formulates a match theoretic resource allocation scheme to maximize the achievable d2d sum rate. in addition, an ee optimization problem is formulated for d2d users by considering the rate and power constraints. the ee optimization problem is solved by the lagrangian dual decomposition method. the algorithms were simulated in matlab and the results were compared to hungarian and heuristic optimization algorithms. the results showed that the match theoretic resource allocation is on average 1.82 times better than the hungarian algorithm. at the same time, the match theoretic resource allocation algorithm increases fairness in resource allocation as it maintains a higher sum rate for low and high-density number of users. the proposed ee optimization algorithm improved the d2d performance by 8.2% compared to the heuristic algorithm. keywords-d2d; energy efficiency; mmwave; matching theory; lagrangian decomposition i. introduction mobile data traffic has been projected to rise over the next 10 years with the number of devices connected to each other and with the cloud reaching 50 billion. this exponential growth in the number of devices brings the challenge of managing the increased capacity required for multimedia communications. despite these shortcomings, the implementation of the 5g technology can enhance coverage, energy efficiency and spectrum usage [1, 2]. this challenge can be solved by deploying device-to-device (d2d) communications which allow proximity users to share content directly without going through the base stations (bss). this also ensures that there is better channel quality and lower transmit power for d2d communication [3, 4]. the integration of millimeter-wave (mmwave) and d2d communication ensures higher data rates, in the order of giga-bits per second, to be realized. the mmwave communication can address the challenge of implementing bandwidth-intensive applications such as interactive gaming and video streaming. the implementation of mmwave d2d networks may not only accomplish higher data rates but also reduce the energy consumption of the network [5]. the main merits of d2d communication is the provision of high data rates, better spectrum efficiency, lower latency, improved energy efficiency, and reduced power consumption. however, in d2d communication networks, there is limited battery life which requires the energy consumption to be taken into consideration in the design of d2d communication networks. therefore, to reap the merits of d2d communication, resource and power allocation, mode selection, and interference control algorithms should be carefully developed to realize the optimal quality of service (qos) guarantee for the cellular users (cus) and d2d user pairs [6]. in this paper, a power control scheme for d2d communication network in the mmwave band is formulated for a single cell with multiple cus and multiple d2d user pairs to improve performance in terms of sum rate and energy efficiency (ee). the ee, defined as the ratio of the achieved data rate (in b/s/hz) and the total energy consumed, is an important metric for the future green 5g communication networks [7]. this study proposes a matching theory based on the gale shapley algorithm and a lagrangian dual decomposition based ee maximization algorithm to allocate spectrum and power to the d2d user pairs and cus in order to determine the optimal transmit power for each device in the network and to maximize sum rate and ee. the contributions of this study are: • the formulation of a match-theoretic d2d solution for sum rate maximization and resource allocation optimization function for mmwave d2d communication, where d2d users share the uplink resources of cellular users. • the formulation of an energy-efficient solution for resource allocation optimization function by considering minimum data rate, interference, and maximum power constraints. • the validation of the proposed algorithm by comparing it with other resource allocation algorithms. corresponding author: filbert onkundi ombongi engineering, technology & applied science research vol. 10, no. 4, 2020, 6152-6160 6153 www.etasr.com ombongi et al.: energy efficient resource allocation in millimeter-wave d2d enabled 5g cellular … ii. related work there are studies which have implemented and analyzed mmwave d2d communication networks by optimizing ee and sum rate. in [8], a multiuser communication system consisting of cellular and d2d pairs was analyzed in order to optimize throughput under interference and transmit power constraints. the formulated nonlinear optimization problem was solved by a heuristic algorithm to obtain sub-optimal results while satisfying the minimum data rate requirement. this study was extended in [9] where a resource allocation for underlay d2d in outdoor mmwave scenario was studied with emphasis on fair distribution of resources in a cell while maximizing spectrum efficiency (se). the power allocation for the d2d users in a single cell was done by applying an iterative water filling algorithm which considered the interference experienced in resource blocks with sub-optimal results being obtained. in [10], the objectives were to maximize the ee and to reduce transmission power. the optimization problem was mathematically formulated as a nonlinear fractional programming problem which was solved by an iterative power allocation algorithm for full duplex relay aided mmwave d2d communication. the study was extended by implementing a modified bottleneck effect elimination power algorithm for transmission power reduction and further improvement on the ee. in [11], a mode selection and resource sharing mechanism was implemented to maximize the sum logarithmic rate in a single cell based on time division duplex (tdd) mmwave cellular network. the resource sharing solution was formulated as a mixed integer programming problem which was remodeled as a convex optimization problem. the lagrangian dual technique was applied to obtain the solution. the adaptive mode selection was proposed after getting the solution of the resource sharing scheme. in [12], an ee maximization method with a trade-off between ee, system sum rate, and outage probability for various qos levels and varying density of cus and d2d pairs was studied. the energy-aware radio resource management scheme was formulated to jointly maximize the achievable rate and the ee of all cus with a minimum qos requirement and maximum input power constraint. the resource optimization problems reformulated to convex subproblems by applying dual decomposition and lagrange multipliers. then the karush kuhn tucker conditions were applied to find the optimal power allocation for microwave and mmwave bss. the optimal power allocation for the microwave bs associated users was determined by multi-level water filling where the water level depended on the beam-level beamwidth for the transmitter and the receiver. the subcarrier allocation problem was solved with the hungarian algorithm obtaining a near optimal solution. the concept of channel inversion was applied in [13] to develop an energy efficient outband d2d communication network in the mmwave band. it considered the effect of sectored antenna models and the number of elements in the uniform linear array antennas for se and ee maximization. the analysis was based on stochastic geometry and the results showed that the ee can be improved by a factor of 23 in a dense user scenario compared to omnidirectional antennas. in [14], a downlink mmwave cellular communication network underlaid with multiple d2d user pairs was studied to optimize the outage probability and ergodic capacity. the nonorthogonal multiple access (noma) was integrated with multi-user mimo in the developed d2d underlaid system model. the simulated model was then compared with the traditional tdma with the results showing that noma had a better performance. an ofdma cellular network with an integrated d2d communication was studied in [15] to optimize device association probability, coverage probability, spectral efficiency, and energy efficiency. the resource allocation scheme considered incorporated distance threshold, device association, antenna radiation pattern, and blockage effects with an out-of-cell interference constraint. the present study formulates a match-theoretic resource allocation scheme for a mmwave d2d communication network to maximize sum rate. it also develops a lagrangian based resource allocation scheme to optimize the energy efficiency of d2d users. the developed mmwave d2d communication model considers the d2d reuse and dedicated modes. this study addresses the challenge of interference and increased energy consumption in 5g d2d networks by developing an energy efficient scheme. the energy efficient optimization algorithm considers the distance of the d2d user pair from the bs, the distance of the cus from the bs, and the maximum transmit power. the sum rate maximization algorithm considers the number of d2d user pairs, the number of resource blocks, and the cell radius variation. iii. system model consider d2d users (dus) operating in dedicated mode for line of sight (los) conditions and cellular reuse mode when the interference threshold set for the d2d link is exceeded in non-los (nlos) conditions, thereby sharing resources with the cus. figure 1 shows a single cell considered in this study which consists of a set of k cus, � � �1,2,3,…, and a set of l du pairs denoted by � � �1,2,3,…,� sharing the available spectrum. when the dus are not communicating due to severe signal blockage, they will shift to the reuse mode by sharing the uplink resources with the cus in the same cell. fig. 1. system model. the bs has n resource blocks (rbs) � �1,2,…,� , each having a bandwidth b for communication. in this case, there are rbs allocated to cus and dus denoted as ��, where a cellular user � ∈ � can transmit with a resource block � ∈ � at a transmit power ��,� with the transmit power engineering, technology & applied science research vol. 10, no. 4, 2020, 6152-6160 6154 www.etasr.com ombongi et al.: energy efficient resource allocation in millimeter-wave d2d enabled 5g cellular … constraint given as ∑ ��,� ≤ ����∈� , where ��� is the transmit power threshold for the cellular device and � denotes a cellular device. in the same way, the d2d user � ∈ ℒ does its transmission with a resource block � ∈ with a transmit power ��,� subject to the d2d user’s own transmit power constraint which is given by ∑ ��,� ≤ ����∈� , with ��� being the transmit power threshold for a d2d device and � denotes the d2d device. in addition, the communication is assumed to use the uplink transmission resources for the cus since the uplink cellular spectrum is lightly loaded in comparison with the downlink cellular spectrum. this implies that the interference originating from the spectrum sharing scheme can only affect the bs side. for a successful resource sharing and optimal power allocation, the cus and the dus must meet certain signal-to-interference-to-noise ratio (sinr) constraints before spectrum sharing is set up. it is also assumed that the number of du pairs l is equal to the number of cus k to attain a stable matching. the channel model takes into consideration the multipath propagation effects, i.e. fast fading, slow fading, and shadowing effect. therefore, the channel gain between the cellular user, �� and the bs can be given as [16]: �,! = ψ#�,!$�,!��,!%& (1) where ψ is a constant value for determining the system parameter, #�,! is fast fading gain, $�,! is slow fading gain, ��,! is the distance between cellular user �� and the bs, and α is the path loss exponent (ple). the channel gain between the du transmitter and receiver �� is denoted as �, the interference link between the du transmitter and receiver �� and the bs has its channel gain as ℎ�,! , the interference link between the cellular user �� and du �� has a channel gain given as ℎ�,�. the spectrum sharing between any du and a cu is made possible when the minimum sinr requirement is satisfied between a du transmitter and receiver or a cu. the additive white gaussian noise power spectral density is assumed for all the cases to be �). the sinr for communication between the du and the bs is: *�� = +,-.,/0,,+0120,,3�4 (2) the sinr for the cellular user and bs communication can be expressed as: *�� = +01.0,5/0,,+,-2,,53�4 (3) the maximum sum rate for the d2d network in reuse mode can then be formulated as: max/0,,,+01,+,∑ ∑ 9�:log>?1 + *��a + b�,� log>(1 + *��)ef�ghi�gh (4) j. l *�� = +,-.,/0,,+,-20,,3�4 ≥ *�,n��� ∀�� ∈ ℒ (5) *�� = +01.0,5/0,,+,-2,,53�4 ≥ *�,n��� ∀�� ∈ � (6) ∑ b�,� ≤ 1, b�,� ∈ �0,1 ∀f,∈f �� ∈ � (7) ∑ b�,� ≤ 1, b�,� ∈ �0,1 ∀�0∈i �� ∈ ℒ (8) ��� ≤ �nqr� , ∀�� ∈ ℒ (9) ��� ≤ �nqr� , ∀�� ∈ � (10) the binary variable b�,� is defined such that b�,� = 1 if the rb of cellular user is shared with a du ��operating on the same rb � otherwise b�,� = 0. the optimization function of (4) incorporates the cus and dus’ interference constraint. the formulated problem is a mixed integer nonlinear problem (minlp) whose objective function is non-convex. this problem is non-convex due to the existence of the interference term in the denominator of the objective function. the complexity of the solution method increases exponentially with the number of dus and sub channels. the sub channel and power allocation variables are coupled together. therefore, the formulated optimization problem will be decomposed into two sub problems where one deals with the sub channel assignment and the other with the power allocation to the receivers. the spectrum assignment and power allocation problems are solved by applying matching theory and lagrangian dual decomposition. a. admission control scheme this scheme is used to determine the admissible pairs which have one cu and one du pair. the membership to the set of these admissible pairs is possible only when both the cus and the dus transmit powers have satisfied the minimum sinr requirements. the equations which govern the admissible sets are given by: *�� = +,-.,/0,,+,-20,,3�4 ≥ *�,n��� *�� = +01.0,5/0,,+,-2,,53�4 ≥ *�,n������ ≤ �nqr� ,��� ≤ �nqr� st u tv (11) b. optimal power allocation for every admissible pair between the cellular users and the d2d user pair, the optimal power allocation is determined. the optimal pair can be expressed by: ?���∗,���∗a = argmax+01,+,-∈yz-[0\ ]?���, ���a (12) with ]?���,���a = 9�:log>?1 + *��a + b�,� log>(1 + *��)e , where yq�n�� is a set containing all the transmission power pairs for the cellular users and d2d pairs. if the function ]?���,���ais defined as ]?���,���a = 9�:log>?1 + *��a + b�,� log>(1 + *��)e, then ]?$���, $���a can be derived such that ]?$���, $���a = 9�:log>?1 +*��a + b�,� log>(1 + *��)e if $ > 1. this implies that, at least one value exists for the transmission power in ?���∗,���∗a which is bounded by the maximum power values. therefore, the function ]?���,���a can be maximized by allowing only one user to transmit at the maximum transmit power value. it has been shown that ]?���,���a is a convex function over either ��� or ��� when the other power value is fixed [17]. c. gale-shapley algorithm for stable matching the sum rate optimization problem is modeled as a one-toone matching game and then a stable marriage is applied to engineering, technology & applied science research vol. 10, no. 4, 2020, 6152-6160 6155 www.etasr.com ombongi et al.: energy efficient resource allocation in millimeter-wave d2d enabled 5g cellular … match the d2d users with the cus and mappings [18]. the gale shapley (gs) algorithm [19] is applied in this stable marriage game to determine a stable solution. a stable matching is defined as a complete matching between a du transmitter and a du receiver that admits no blocking pair. the basis of the gs algorithm is that one du transmitter makes a series of proposals to the other set of cus. this implies that each du transmitter and receiver pair proposes, in order, to cus which are in their preference list and waits for the cus to consider the proposal, but continues if the proposal is rejected. the cu receives the proposal and rejects it, if there is already an existing better proposal, otherwise it holds it for another consideration. the process terminates if all the proposals have been considered and no other request can be made from the d2d pairs. the admissible pairs and the optimal transmit power can be determined after admission and power control. the cellular users’ sum rate is given by 9� log>(1 + *��) during spectrum sharing with d2d users, �� being used to show the ��′j preference over ��. similarly, the d2d user sum rate 9� log>(1 + *��) is used to show the ��′j preference over ��. thus, defining the preference relation for ��, which is between �� with ��` and preference relation for��, which is between �� with ��`. definition 1: the cu �� prefers �� to ��a if the achievable rate of �� is greater than that of ��a , 9� log>?1 + *��a >9� log>?1 + *��̀a which is denoted as b� ≻�0 b�` for �� ∈ � , b�, b�` ∈ d�� , e ≠ ea , where d�� is a set of dus admitted by cu ��. definition 2: the d2d user, b� prefers �� to ��a if 9� log>(1 + *��) >9� log>?1 + *��̀ a which is denoted as �� ≻�, ��a for b� ∈ ℒ , ��,��` ∈ d�� , g ≠ ga , with d�� denoting the set of dus admitted by du b�. the rank which is denoted as (��,b�) shows the position of b� in the ��′j preference list, hℒ�� and rank (b�,��) as the position of �� in b�′j preference list, hℒ��. definition 3: the matching ℳis said to be stable, if there is no blocking pair (��, b�) such that b� ≻�0 ℳ(��) and �� ≻�, ℳ(b�) where ℳ(��) denotes ��′j partner in ℳ and ℳ?b�a represents b�′j partner in ℳ. the matching-theoretic sum rate maximization algorithm is summarized in algorithm 1. algorithm 1: sum rate maximization 1. input: d2d user set, ℒ , cellular user set, �, number of rbs, and number of d2d links, j, �nqr� , �nqr� . begin 2. set, b�,� = 0,∀�� ∈ � k�� ∀�� ∈ ℒ 3. for �� ∈ � ; �� ∈ ℒ 4. if sinr condition is met, then 5. b�,� = 1 6. count how many times a node is chosen 7. for j=1: j do 8��� = jmn(o�,1: ). 9. end 10. for i=1: , do 11. ��� = jmn(o�,1:j) 12. end 13. d2d link, e)with minimum ��q� is selected 14. for i=1: , do 15. if b�,�4 = 1, then 16. rs − �� with minimal ���selected for d2d link-e) 17. maximize u�,�4 by optimizing ���, ��� 18. end 19. end 20. delete du-cu reuse pair already used from the set 21. update , j. 22. go to step 13 till =0 or j =0 23. end d. energy efficiency optimization for d2d user devices the reuse mode is selected and the n th rb is allocated to the �� cu. the nth rb that is allocated to the cu is then reused by the �� d2d pair. the transmit power from the transmitter of the �� d2d pair on the nth rb is denoted as ��,�� . the achieved data rate by the �� d2d users on the nth rb can be given as: u� = v log> w1 + +,,\.,,,+0-.0,,3�4x (13) where v is the bandwidth of the �y2considered rb, �,� is the channel gain between du ��, �,� is the interference channel gain from the �� cu to the �� du pair and �) is the noise power. the total d2d data rate can be denoted as uz which can be given by: uz = ∑ ∑ u���ghf�gh (14) the total radiated power, ��,y� , for the �� d2d pair can be expressed as: ��,y� = ∑ ∑ ��,�� ��ghf�gh (15) where b ∈ ℒ the number of d2d users is, � ∈ is the number of rbs. let {� represent the total power consumption by the device circuitry of all the d2d users under consideration and is independent of the radiated power. the total ee, |}} of the d2d communication pairs can be expresses as: |}} = ~�+,,�3�1 (16) where {�, is the power consumed by the device circuitry. the binary variable b�,� indicates when the resources are allocated to the d2d users, is such that b�,� = 1 when a resource has been allocated to a d2d user and zero otherwise. the ee optimization problem can then be formulated as: max/,,\,+,,\|}} (17) subject to: uz ≥ uz,n��,∀b�,� = 1 (18) ��,�� �,� ≤ �,∀b�,� = 1 (19) engineering, technology & applied science research vol. 10, no. 4, 2020, 6152-6160 6156 www.etasr.com ombongi et al.: energy efficient resource allocation in millimeter-wave d2d enabled 5g cellular … ∑ ∑ ��,�� ��ghf�gh ≤ �nqr� (20) where u�,n�� is the minimum data rate requirement for every d2d pair, � is the interference threshold between the cu and the d2d pair, and �nqr� is the maximum transmit power for every d2d pair transmitter. since the optimization problem has a binary variable, it falls in the category of minlp which is complex to solve. in addition, the fractional energy efficiency optimization problem is a non-convex function. the optimal value of ee for the d2d pairs can be denoted as |∗ and is expressed as: |∗ = max�/,,\,+,,\ ∈� ~�+,,�3�1 (21) where ω is the feasible region of the constraints. the objective function can be transformed by applying the following theorems [20]. theorem 1: the maximum value of ee, |∗ can be attained if and only if: max�/,,\,+,,\ ∈�φ(|) = �uz − |∗?��,y� + {�a� = 0 (22) the equivalent subtractive function can be obtained for the fractional optimization problem by utilizing the fractional programming techniques. the equivalent objective function is convex and can be solved by the lagrange dual decomposition technique. the lagrange dual function can be expressed as: ℒ?��,�� , ,�, �, #a = uz − |?∑ ∑ ��,�� ��ghf�gh + {�a +�?uz − uz,n��a + �?∑ ��,�� �,����� − �a +#?∑ ∑ ��,�� ��ghf�gh − �nqr� a (23) where �,�, # are the lagrange multipliers for the constraints given in (18)-(20). the lagrange dual optimization function can then be formulated as: min�,�,� max+,,\ℒ?��,�� , ,�, �,#a (24) j.l �,�,# ≥ 0 (25) the karush kuhn conditions for the optimization problem given by (22) result in a series of nonlinear equations which are complex to solve. therefore, an efficient numerical iteration method should be proposed to optimally solve the problem in (22). the optimal power allocation to maximize energy efficiency can be determined by taking the first derivative of (23) with respect to ��,�� : �f�+,,\= (h3�).,,,�(�3�)3� ∑ +,,\.0,,�0�, ��� > − ��,�� − ∑ ��,�� �,����� + �) (26) then, equating the first derivative to zero and rearranging gives the optimal power allocation as: ��,��∗ = (h3�) �(�3�)3� ∑ +,,\.0,,�0�, ��� > − ∑ +,,\.0,,�0�, 3�4.,,, (27) this is the solution of the optimization problem given in (23). the values of �,� and # that can minimize the dual objective function (24) can be determined by applying the subgradient method [21, 22]: �(n + 1) = :�(n) −∆?uz − uz,n��ae (28) �(n + 1) = :�(n) − ∆(��,�� �,� − �)e (29) β(n + 1) = :β(n) − ∆(∑ ∑ p�,�� (n) ��gh� gh − p¡¢£� e (30) where n is the iteration index and ∆ is a positive parameter which is the newton decreasing step size. this shows that as the value of n increases, the value of power � converges to some fixed point. the newton decreasing step size ∆ is determined as: ∆= �ℒ¤+,,\,,�,�,�¥ �+,,\-¦ �§ℒ¤+,,\,,�,�,�¥ �(+,,\)§¦ (31) the stopping criteria for the iterative optimization algorithm is determined as: ¨ = © ª«�ℒ¤+,,\ ,,�,�,�¥ �+,,\-¦ ¬ ­® § �§ℒ¤+,,\,,�,�,�¥ �(+,,\)§¦ (32) the energy efficiency optimization problem is solved by algorithm 2. algorithm 2: energy efficiency optimization 1. input: � = 0.001,� = 0.001,# = 0.001 2. while, ¯ℒ?��,�� , ,�,�,#a¯ ≥ ¨ or ° ≤ °nqr 3. repeat 4. find ��,�� using (27) 5. update δ, θ, and β using (28), (29), and (30) respectively 6. until �, � and # converge 7. update |(° + 1) = ~�+,,�3�1 8. update ℒ?��,�� , ,�,�,#a 9. ° = ° + 1 10. end while iv. simulation results and discussion this section presents the simulated results of a mmwave d2d communication network in terms of sum rate and ee performance metrics. the mmwave d2d model illustrated in figure 1 was simulated in matlab version r2018b using the settings given in table i. the simulation procedure starts by drawing a circular single cell with the bs at the center. then, the d2d users and cus are randomly distributed within the cell by a poisson point distribution process for a cell radius of 250m. the users’ admission criteria given in (11) are used to define the selection of users within the network. for the d2d user pairs, an additional criterion of minimum distance between them is defined. for this study, the minimum distance between engineering, technology & applied science research vol. 10, no. 4, 2020, 6152-6160 6157 www.etasr.com ombongi et al.: energy efficient resource allocation in millimeter-wave d2d enabled 5g cellular … a d2d user pair was taken as d0=4m. the energy consumption of the d2d user pairs which consists of the radiated transmission power and the circuit power was determined for maximization of the energy efficiency. the d2d performance analysis is based on the mathematical expressions presented above and the proposed algorithms for los and nlos scenarios. the d2d sum rate for dedicated and reuse modes was simulated by algorithm 1 and the energy efficiency by algorithm 2. the results of the proposed gale shapley and the lagrangian dual decomposition based algorithms were compared to hungarian and heuristic algorithms respectively. the mmwave channel model was modeled with (1) with the parameters ±�, ±� being the path loss exponents for los and nlos conditions. the path loss parameters and shadowing standard deviation in db are based on the new york university (nyu) mmwave model presented in [23]. the mmwave d2d simulation settings such as maximum transmit power and number of resource blocks are based on [24, 25]. table i. simulation parameters parameter notation value maximum radius of the cell r 250m maximum transmit power of du {nqr� 23dbm carrier frequency fc 28ghz noise power (dbm) �) -174 bandwidth per rb b 20mhz system bandwidth w 1ghz number of rbs n 50 sinr threshold, du �� 4db d2d link distance �f 5-50m path loss exponent (ple) ±�,�²³ ±�,��²³ 2 2.92 number of d2d users l 50 fading standard deviation los nlos 5.8db, 8.7db e. sum rate maximization the d2d communication was simulated in matlab with the cue and d2d devices being distributed randomly in a single cell network. figure 2 gives the variation of d2d sum rate when the number of d2d pairs is increased for reuse and dedicated modes in a cell radius of 250m. the d2d communication under los conditions was simulated for dedicated mode where the d2d user pairs operate in a dedicated channel which is free from the interference of the cus. this shows that the d2d deployment as an overlay (outband) to the cellular network in the mmwave band can achieve higher data rates compared to other operating modes. when the d2d users are implemented as an underlay to the cus, the interference between the cus and the d2d user pairs is taken into consideration and reduces the achievable sum rate by the d2d pairs which are reusing the resources already allocated to the cus. the nlos conditions were also considered in the mmwave d2d network scenario. the results showed that the dedicated mode of operation from the d2d user pairs performs well when the number of pairs is less 30 as shown in figure 3. this is because with the densification of the d2d user pairs, the interference which was assumed to be so small for an overlaid implementation starts to increase. this reduces the sum rate attainable for the dedicated mode. fig. 2. sum rate versus number of d2d pairs for los. fig. 3. sum rate versus d2d pairs for nlos. fig. 4. sum rate versus number of d2d pairs. for the reuse mode, since the d2d user pairs are reusing the spectrum resources of the cus, they are able to complete the communication. in this case, the cus might not be encountering the nlos conditions at the same time with the d2d pairs. this is the reason why the implementation of a reliable d2d communication network should incorporate both modes of operation so that in case of poor channel conditions it can able to switch between modes. the comparison of the sum engineering, technology & applied science research vol. 10, no. 4, 2020, 6152-6160 6158 www.etasr.com ombongi et al.: energy efficient resource allocation in millimeter-wave d2d enabled 5g cellular … rate obtained by both the d2d user pairs and cus when the d2d users are operating in the los reuse mode is given in figure 4. the cell radius is maintained at 250m. the figure shows that the d2d achievable sum rate is higher compared to the cus whose resources are reused. the higher data rate for d2d users is beneficial for meeting the high data rate requirements for the mmwave 5g networks. the study also considered the effect of varying cell radius from 100m to 500m as shown in figure 5. the performance in terms of sum rate improved when the radius of the cell was reduced due to the existence of many d2d connections with the radius of 100m offering the best performance. this is very useful when the d2d communication is integrated with pico cells to improve sum rate and ee. in addition, this allows the densification of the d2d user equipment and pico cells for capacity enhancement in 5g networks. fig. 5. sum rate versus cell radius. fig. 6. spectrum efficiency versus transmission power. as shown in [23], the minimum cell radius for femto cells is 10m, for pico cells is 100m, and for micro cells it is 200m. the femto cells are only applied for indoor networks while the pico and micro cells are applied for both outdoor and indoor network scenarios. therefore, the minimum radius used in this study is 100m, which is appropriate for pico cells. the deployment of pico cells is beneficial for d2d implementation as it can serve both indoor and outdoor users. figure 6 shows that the range of a d2d pair from the bs has an impact on the obtained spectrum efficiency. it can be seen that when there is a range reduction, there is an increase of spectrum efficiency up to 25dbm. beyond 25dbm the spectrum efficiency curve remains almost flat due to an interference increase as the transmission power goes beyond 25dbm. f. energy efficiency optimization the energy efficiency for d2d users is presented in figure 7 for various locations of the cus from the bs whose resources are reused by the d2d users. the results show that as the location distance of the d2d user from the bs is increased, the ee is reduced due to the increased path losses and interference. in addition, when the cu location distance from the bs whose resources are reused is increased, the ee improves due to the reduction of interference contribution from the bs which might be communicating to other devices using the same channel. figure 8 shows the variation of ee with the range of d2d users from the bs for different levels of rbs. the performance is better when 500 rbs are used. the use of more rbs reduces the interference experienced by the d2d user devices. fig. 7. energy efficiency versus location of d2d users fig. 8. ee versus number of rbs. engineering, technology & applied science research vol. 10, no. 4, 2020, 6152-6160 6159 www.etasr.com ombongi et al.: energy efficient resource allocation in millimeter-wave d2d enabled 5g cellular … v. performance validation the gale shapley based resource allocation optimization algorithm for sum rate maximization was compared with the hungarian algorithm to validate the achieved performance. this was done by varying the number of d2d pairs. figure 9 shows that the proposed algorithm performs better for any density of d2d users. the hungarian algorithm only performs similarly for high density of d2d users. therefore, the proposed gale-shapley algorithm increases fairness in resource allocation for attaining a higher d2d rate. figure 10 shows the comparison of the ee obtained by varying maximum transmit power. the result shows that the proposed algorithm has an improved performance by an average of 8.2% compared to that of the heuristic algorithm presented in [8]. fig. 9. comparison of optimization algorithms for given numbers of d2d pairs. fig. 10. comparison of the proposed and the heuristic algorithm from [8]. vi. conclusion in this paper, the resource allocation problem was studied for mmwave d2d communication in frequency reuse and cellular mode. the main goal was to optimize the sum rate by applying the matching-theoretic algorithm. in addition, the ee of d2d users was maximized by varying the distance of a d2d transmitter from the bs. the results showed that the gale-shapley algorithm had a performance which was averagely 1.82 times better when compared to the hungarian algorithm. the gale shapley algorithm also ensured fairness in resource allocation for low density and high density scenarios. the hungarian algorithm had a poor performance in the low density d2d user scenario. the spectral efficiency improved with the reduction of the cell radius. this showed that with densification of cells having a radius of between 50-100m, higher sum rates for d2d users can be obtained. the ee was found to decrease with an increase of the distance between the d2d transmitter and the bs due to the increase in path losses for d2d communication in the mmwave band. when the transmission power varied, it was found that the spectrum efficiency increased up to 30dbm and beyond that there was no further increase of the spectrum efficiency. when the ee was compared between the proposed algorithm and the heuristic algorithm from [8], the results 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[24] “[spec] 3gpp tr 36.746 – study on further enhancements to lte device to device (d2d), ue to network relays for internet of things (iot) and wearables – itectec.” https://itectec.com/archive/3gppspecification-tr-36-746/ (accessed aug. 02, 2020). [25] etsi ts 138 101-1 v15.5.0. 5g; nr; user equipment (ue) radio transmission and reception; part 1: range 1 standalone (3gpp ts 38.101-1 version 15.5.0 release 15). sophia antipolis cedex, france: etsi, 2020. [26] w. xiang, k. zheng, and x. s. shen, 5g mobile communications. switzerland: springer, 2016. microsoft word etasr_v11_n2_pp6882-6888 engineering, technology & applied science research vol. 11, no. 2, 2021, 6882-6888 6882 www.etasr.com khan et al.: seamless transition between islanded and grid connected three-phase vsi-based microgrids seamless transition between islanded and grid connected three-phase vsi-based microgrids mubashir hayat khan department of electrical power engineering faculty of electrical and electronic engineering university tun hussein onn malaysia johor, malaysia mubashir.uthm@gmail.com muhammad asad commissioning services devision-central national grid sa saudi arabia csd_sec@yahoo.com amjad ammar qureshi ner engineering & capital projects trafigura nyrstar, australia engr.amjadammar@gmail.com erum pathan electronic engineering department quaid-e-awam university of engineering. science and technology nawabshah, pakistan erumasad79@gmail.com muhammad ahsan sadiq department of electrical engineering university of poonch rawalakot, pakistan engr.ahsan@upr.edu.pk muhammad shahid protection & automation siemens ltd saudi arabia engr.shahid26@gmail.com amanullah khan pathan power and distribution department larsen and toubro saudi arabia llc dammam, saudi arabia amanullahpathan@yahoo.com nadim imtiyaz shaikh construction manager larsen and toubro saudi arabia llc dammam, saudi arabia nahids12@yahoo.com abstract-microgrids (mgs) are the emergent solution to overcome the current electricity demand. the mgs provide the facility to operate in both isolated and grid-connected modes. for both operating modes, distributed generation (dg) inverters are operating under grid forming or grid following control modes. during mode switching, the mg experiences enormous fluctuations, which occur due to the unidirectional islanding event. this paper presents a control strategy by using the modified power control scheme, current controller, and dc linked voltage controller scheme to ensure the operational mode transfer smoothly from the grid-connected to the islanded mode and vice versa. the proposed control scheme is applied to a three-phase distributed energy resource-based mg system with fixed loads. the simulation results validate the effectiveness of the control technique while tested at the point of common coupling and also at the time of mode transfer. keywords-grid forming; grid following; seamless transition; droop control i. introduction microgrids (mgs) provide a promising solution to overcome the electricity shortage in a reliable way. distributed generation (dg) utilized in mgs is pretty common nowadays. dgs like solar, wind, and combined heat power (chp), that are attached to grid connected mode (gcm) or islanded mode (im) protocols with connecting loads have many advantages over the traditional grid [1-2]. although the mgs provide an alternative with bidirectional communication, there are some control issues, particularly regarding power, voltage, and frequency deviations that may occur when the mg changes its operational mode from gcm to im [3-4]. generally, the control schemes in terms of transition are divided into two categories. the first one is the single control scheme for regulating voltage [5-10], which is non-linear theory-based such as the lyapunov-based control. the second one is the control with two schemes with pre-allotted intents [11-16], based on the model predictive control scheme. however, in both control techniques, high computational values and the complexity of the schemes do not allow efficient implementation of the control schemes. on the contrary, linear control schemes are less complicated and can be easily implemented without any complex computational burden [5]. feedback and feed-forward procedures can be a good alternative to make the control structure simple and convincing corresponding author: mubashir hayat khan engineering, technology & applied science research vol. 11, no. 2, 2021, 6882-6888 6883 www.etasr.com khan et al.: seamless transition between islanded and grid connected three-phase vsi-based microgrids with the provision of seamless transition either from gcm to im or im to gcm [17-18]. during the mode transition from grid following to grid-forming mode, frequency deviations may occur which may lead the mg system to instability. moreover, voltage and current errors may also occur during the mode transition, while the voltage during the switching process must follow the ieee standard criteria [19]. a proper synchronization algorithm is needed in order to have smooth switching from one mode to another. switching between modes can be done with the help of an operator or automatically. in the first case, the control of transition intensity can be controlled with the mg functional point’s readjustment. in the second case, unidirectional islanding is used to readjust the operational points of the mg, but faces various issues related to frequency and voltage errors and system stability concerns. in [8-9, 14, 16, 20-23], different solutions have been presented to compensate the errors that occur during transition. most of the control solutions are based on switching, but the droop-based control scheme [8, 19] does not need any kind of switching. this control scheme can be used for the transition from im to gcm or gcm to im. in [5, 9, 16, 21], nonlinear control schemes with adaptive feedback stepping technique have been introduced to solve the voltage frequency deviations and were applied to both operation modes. the model predictive control (mpc) technique [5] is applied to the single phase multi bus inverterbased mg system with automatic tuning functionality for seamless transition. the interaction between different inverter controllers used in the same system still needs to be investigated because during the im, frequency and power sharing errors occur. hence, the damping ratio needs to be improved in this case. in order to achieve smooth operation the frequency deviations are mitigated by utilizing the virtual inertia [23]. virtual synchronous generators (vgss) with droop control are used to improve the dynamic performance of the system. however, active power sharing accuracy is not achieved [24]. if the droop control parameters are selected accurately as per system requirements, the active power sharing errors can be controlled and the control strategy could be more efficient as compared to the control using vgs [25]. the proportional resonant (pr) controller is implemented to mitigate the frequency errors during mode transition in [26]. moreover, phase angle correction with autonomous operation was also ensured in the control scheme. modified pq control technique with tracking v/f controller [27-28] needs constant communication between the im and the main grid. a two separate synchronization compensator-based control system was implemented in [29] to mitigate the voltage and phase angle deviations but the system stability was not ensured. to get an effective mg operation during mode switching, a fast seamless transient control technique should be implemented which will not compromise the permissible standards in terms of power sharing accuracy, voltage, and frequency. this paper presents a control strategy that uses a modified power control scheme, consisting of the current controller and a dc linked voltage controller scheme to ensure the operational mode transfer smoothly from gcm to im transitions and vice versa. the proposed control scheme is applied to a three phase distributed energy resources-based mg system with fix loads. the simulation results validate the effectiveness of the control technique in terms of voltage, frequency, and power sharing behavior at the point of common coupling (pcc) and at the time of mode transfer. ii. microgrid configuration and operation a three phase mg system with three dgs is shown in figure 1. a constant dc source is connected separately to all the dgs. an lcl filter is connected with each dg and the loads are connected to the pcc. all the voltage source inverters (vsis), explored for voltage, power sharing, and frequency, are connected to the main grid with the help of a circuit breaker installed just after the pcc. fig. 1. a microgrid with three dg inverters connected in parallel. a common load is connected to the pcc and the parallel connected inverters can be detached from the main grid for im operation. gcm and im operational modes are further explained below. a. grid connected mode generally the gcm control is implemented in a gridfeeding control scheme. a control structure based on a pi controller with a dq reference frame work is established by using the convention current control structure [30-31]. the current control structure block arrangement is shown in figure 2. fig. 2. current control. b. islanded mode during the im control mode, when a change occurs between frequency and voltage because they are designed separately for load and generation, ultimately the p and q sharing accuracy is decreased [30-31]. it is therefore essential to overcome this mismatch according to the load requirements. in a parallel connected mg system, when multiple dgs are connected in the same network, the load sharing also needs to be equally distributed to all the dgs as per their capacities so the droop characteristics need to be incorporated in the system to cope up with the load sharing issue as shown in figure 3. engineering, technology & applied science research vol. 11, no. 2, 2021, 6882-6888 6884 www.etasr.com khan et al.: seamless transition between islanded and grid connected three-phase vsi-based microgrids fig. 3. voltage control. active and reactive powers are calculated by using lpf with very small cutoff frequency. the block diagram for grid forming is shown in figure 3. the output voltage can be expressed as: ( ) o ref o o v g s v z i= − (1) iii. the proposed control scheme the control loops consists of a droop controller, a current controller, and a linked voltage controller. for these controllers, the control design procedure is given below which is further categorized into gcm and im control schemes. a. modified power control droop control technique provides p-ω and q-f droop control with decentralized and communication free facilities. the active and reactive powers of each inverter are depending on voltage and frequency at the pcc which is managed by conventional droop control in the im mode control scheme. moreover, another pi controller is also applied for ensuring proper tracking of vref. the power calculation mechanism is given in figure 4. fig. 4. active and reactive power calculations. b. current controller higher bandwidth is required in the design of the current controller. it is preferred to get faster response, so low switching frequency is needed. in the closed loop system, the bandwidth is taken 10 times smaller than the switching frequency. the block diagram in figure 5 shows the current controller configuration. the transfer function for the current control strategy is: 1 ( ) ( ). 1 1 1 c inv f f f f g s g s r sl s r sl τ + = + + (2) where τ can be considered as a constant of the pi controller transfer function cg . fig. 5. current controller. c. dc linked voltage controller both side inverter currents are equalized for the voltage dc linked controller before designing the controller: 3dc dc ph phv i i v= (3) where 2 d rms i i= and can be is expressed as: 3 / 2 l dc d dc d dc v l i i k i v − = = (4) and dci relates to the capacitor current which is given as: dc dv idc c dt = (5) so, the basic functionality of the voltage controller is to maintain the voltage. the configuration of the dc linked voltage controller is given in figure 6. fig. 6. dc lined voltage controller. iv. simulation results the validation of the proposed control mechanism for the seamless transition of mgs between the two operational modes was carried out in matlab/simulink. the system specifications are given in table i, and the overall matlab/simulink model is given in figure 11. a. case 1: grid connected mode in the gcm control scheme it is necessary for a mg system to operate in constant pq mode. to attain constant pq, the inverter is operated in dq-reference framework to get current control. in the transformation dq-abc, the observation time scale is very high and so it is preferred to consider the average model to get the voltage at the abc domain. in the gcm mode, engineering, technology & applied science research vol. 11, no. 2, 2021, 6882-6888 6885 www.etasr.com khan et al.: seamless transition between islanded and grid connected three-phase vsi-based microgrids the imbalance occurs due to the generated power and load at the point of connection and the excess power is supplied by the dc bus capacitor. the occurring reduction in the bus voltage due to the supply needs to be maintained again. however, an inner loop is established to balance the dc bus voltage and current controller.when the breaker of the proposed model is closed towards the gcm, the grid connection mode operation is established. in gcm the voltage and frequency at the pcc must always be in a fixed allowable range. as shown in figure 7(a), voltage and frequency are in the permissible range. the frequency is almost constant throughout the operation from t=0 to t=10s. at t=0.8s, voltage maintains the fixed magnitude. the inverter current is successfully tracking the reference current as shown in figure 7(b). the active and reactive powers are shared accurately as shown in figure 7(c) just after some delay at t=0.6s. (a) (b) (c) fig. 7. gcm results: (a) voltage and frequency, (b) reference and inverter currents, (c) active and reactive powers. b. case 2: transition between gcm and im this section shows the results when transition occurs from gcm to im. the pcc voltage and frequency waveform are shown in figure 8(a). at t=5s there is a little deviation which is compansated in a very short time interval. the same happens in the case of deviating frequency. figure 8(b) shows the behavior of the currents. iinverter decreases at t=5s which is cuccessfully tracked by the reference current. figure 8(c) shows the power sharing accuracy of the dg inverters durreng the change in the operational mode. from t=5s the active and reactive powers are shared equally. (a) (b) (c) fig. 8. transition from gcm to im: (a) voltage and frequency, (b) reference and inverter currents, (c) active and reactive powers. (a) (b) (c) fig. 9. im results: (a) voltage and frequency, (b) reference and inverter currents, (c) active and reactive powers. engineering, technology & applied science research vol. 11, no. 2, 2021, 6882-6888 6886 www.etasr.com khan et al.: seamless transition between islanded and grid connected three-phase vsi-based microgrids c. case 3: islanded mode in case 3, the im of the mg is discussed with respect to the behavior of voltage, current, and powers. as shown in figure 9(a), voltage and frequency are in the permissible range. the frequency is constant throughout the simulation and the voltage magnitude is constant just after 0.8s. the inverter current is successfully tracking the reference current as shown in figure 9(b). figure 9(c) shows the pq sharing in im. d. case 4:transition from im to gcm it is shown in figure 10(a) that when the reconnection of the mg from im to gcm takes place, there is a small deviation in the voltage waveform and the frequency shows some deviations before returning to a smooth level just after t=5s. figure 10(b) shows the behavior of the inverter and reference currents which are tracking each other successfully at t=5s. in figure 10(c) the power sharing accuracy of the proposed control scheme is shown when the mg is shifted to gcm from im operation. the results show that the active and reactive powers are shared accurately from t=5s. table i. system parameters parameter value parameter value vdc 400 v load 130 ω,0.22 h fsw 10khz zgrid 0.4+j0.6 ω f 50 hz c 15 µf zl1, zl2 and zl3 0.3+j0.5 ω, 1.3+j2.65 ω & 2.4+j3.54 ω (a) (b) (c) fig. 10. transition from im to gcm: (a) voltage and frequency, (b) reference and inverter currents, (c) active and reactive powers.. fig. 11. matlab/simulink model. v. conclusion in this paper, the transition from gcm to im and vice versa was studied in detail. a simple approach by modifying the power, current, and dc linked voltage controllers was presented. a smooth transfer from one operational mode to another was conducted without affecting the active and reactive power sharing among the dg inverters connected in parallel and the voltage, frequency, reference current, and inverter engineering, technology & applied science research vol. 11, no. 2, 2021, 6882-6888 6887 www.etasr.com khan et al.: seamless transition between islanded and grid connected three-phase vsi-based microgrids current the at the pcc have been explored. the proposed control scheme is applied to a three distributed energy resource system with fixed load. the simulation results validate the effectiveness of the control scheme in terms of voltage, frequency, and power sharing behavior at the pcc and at the time of mode transfer. references [1] p. singh, d. p. kothari, and m. singh, "integration of distributed energy resources," research journal of applied sciences, engineering and technology, vol. 7, no. 1, pp. 91–96, 2014. 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[31] g. shen, d. xu, l. cao, and x. zhu, "an improved control strategy for grid-connected voltage source inverters with an lcl filter," ieee transactions on power electronics, vol. 23, no. 4, pp. 1899–1906, jul. 2008, https://doi.org/10.1109/tpel.2008.924602. microsoft word 45-2810_s1_etasr_v9_n3_pp4310-4314 engineering, technology & applied science research vol. 9, no. 3, 2019, 4310-4314 4310 www.etasr.com oad et al.: farm-based evaluation of sustainable alternative irrigation practices farm-based evaluation of sustainable alternative irrigation practices shamotra jai oad department of civil engineering technology, the benazir bhutto shaheed university of technology and skill development, khairpur mir’s, sindh, pakistan shamotra@bbsutsd.edu.pk hadiqa maqsood us-pakistan center advanced studies of water, mehran university of engineering and technology, jamshoro, sindh, pakistan hadiqamaqsood02@gmail.com abdul latif qureshi us-pakistan center advanced studies of water mehran university of engineering and technology, jamshoro, sindh, pakistan alqureshi.uspcasw@faculty.muet.edu.pk shoaib ahmed department of civil engineering, ned university of engineering and technology, karachi, pakistan shbned@gmail.com imran ali channa professional structural engineer, alliance consultants pvt ltd, karachi, sindh pakistan channaimran99@gmail.com muhammad yousif ali department of civil engineering technology the benazir bhutto shaheed university of technology and skill development, khairpur mir, sindh, pakistan muhammadyousifali@gmail.com abstract—water management is one crucial component of agribusiness and municipal policy. one of the water-oriented dimensions is irrigation. in pakistan, there is a lack of water system planning and water conservation management. this study is an effort to focus on water conservation and optimum crop yield using cost effective irrigation practices. this study is based on the comparative analysis among four irrigation techniques: flood irrigation (conventional), furrow, alternate furrow, and raised bed on wheat crop in order to decide the most efficient irrigation technique on clay loam soil. the wheat crop was cultivated in rabi season from november 2015 to march 2018 on a one-acre area of a local farmer of sajawal district, sindh. randomize complete block design (rcbd) method was used to design and allocate 3 irrigation sub-plots. the results show significance p<0.05 and the efficiency of conserved water by using the furrow irrigation was 25%, alternate furrow 49%, and raised-bed 31% in comparison to conventional methods. furthermore, crop yield indicates that furrow irrigation and raised-bed gave higher yields. the increase in yield was 35% by using raised-bed technique and 20% by furrow irrigation whereas by using alternate irrigation it was 15% in comparison with the conventional method. the soil type is clay loam and saline soil. keywords-water conservation; raised-bed; wheat; sujawal; alternate furrow i. introduction developing countries are focusing on the water scarcity problem in order to secure efficient food production. to secure water resources and have optimum use of water, most countries take measures to conserve these resources and mitigate water shortage problems. irrigation plays a vital role to food production and enhances the economy of a country [1], while most of the population of asian countries is engaged in agriculture. there are various studies on performance evaluation of water and soil for integrated systems to attain efficient irrigation practices. there are various types of irrigation systems: border irrigation, furrow irrigation, flood irrigation, sprinkler irrigation, and drip irrigation. flood and border irrigation are inundating the land. furrow irrigation comes in different types such as alternate furrow, surge, and raised beds. sprinkler and drip are mechanized systems employing further water conservation strategies. there are generally three water sources for irrigation: groundwater, surface water, and non-conventional sources such as treated wastewater and desalinated water. the study area is a farmer in pakistan. the climate of pakistan is mostly semi-arid in lower indus basin making irrigation a vital need for food production. at farm level, most of the irrigation water is lost due to deep percolation and surface runoff. until it reaches the downstream of the region, some water gets wasted due to leakages and line losses. in the most part of the country, farmers divert water to their farm from passing by canals without being charged. the related irrigation department of state government has taken steps to manage water resources from any sort of theft, but due to population increase and damages of infrastructures, they are corresponding author: shamotra jai oad engineering, technology & applied science research vol. 9, no. 3, 2019, 4310-4314 4311 www.etasr.com oad et al.: farm-based evaluation of sustainable alternative irrigation practices not capable of fulfilling the production needs. therefore, to overcome these issues, highly efficient irrigation systems are utilized such as sprinkler and drip. since most of the farmers either can’t afford mechanical means or are unable to handle these advanced systems, they prefer old fashioned, economical irrigation practices like furrow, surge, alternate irrigation, and raised bed [2]. in pakistan, there is a lack of water system planning, management and proper system operation and maintenance. time, quality and financial management are important to achieve optimum economy rate while the agriculture production is based on these factors [3]. authors in [4] used furrow and raised bed techniques and concluded that by adopting these techniques 16.6% more yield was achieved and 50% of the water was conserved. another comparable experiment was performed on crop physiology in seasons 2002-2003 and 2003-2004 [5] between raised-bed planting, furrow irrigation, and conventional free flood irrigation to ameliorate water use efficiency in winter wheat. authors evaluated the techniques by designing varying row distances between furrows, raised bed and conventional flood. authors concluded that by keeping 68cm bed to bed distance gave maximum wheat yield as compared with furrow and conventional irrigation. generally, surface irrigation technique is mostly used (80.9%) followed by sprinkler [6]. another research on the effects of raised bed planting was conducted on irrigated wheat yield, as influenced by using a variety of same crop and row spacing. this research was conducted in northwestern mexico from 1998 to 2005 to check the performance of farmers on how they intern the solar radiations in the gap and reduce their effects between the beds. they found that low density and less row to row spacing gave more yield and reduced by 10% the losses in the raised-bed system [7]. a similar study focusing on water conservation and crop yield was carried out in [8], where researchers examined the effects of continuous planting, furrow irrigation, and raised bed cropping on water content in soil. the research concluded that deficit irrigation system on furrow cropping gives the best yield in north china. authors in [9] designed a framework for assessing technology and management options to reduce water losses. they suggested that a framework is needed in adopting alternative irrigation practices and appropriate management techniques that will reduce water shortage. the wheat crop yield and water use efficiency in sandy loam soil can be improved by using conventional tillage practices [10]. by using the furrow planting technique for wheat crop in loamy soil the yield of wheat enlarged [11]. a study on indo gangetic basin was done to improve water conservation efficiency [12]. authors depicted that indo genetic countries give less crop yield than the potential, due to lack of water resource management. a field experiment was conducted in the tandojam region of pakistan on okra, by using an alternate irrigation practice for water conservation in [13]. it was a comparison between alternative furrow irrigation with conventional irrigation practices. in [14], it was concluded that by using alternative furrow irrigation, crop yield was decreased only to the negligible amount of 7.3%, but crop water productivity was higher with water conservation. ridged furrow irrigation system extracted optimum moisture from soil and achieved more yield (66.1% and 50.4%) as compared to free flood and mini ditch irrigation practices [15]. as compared to the free flood practice, drip irrigation and furrow irrigation methods gave more yield and water use efficiency (wue) for chili pepper crop as compared to basin irrigation method. in afghanistan, farmers prefer furrow irrigation over drip irrigation because it is more economical and easy to maintain [16]. authors in [17] used furrow and raised bed techniques and concluded that by adopting these techniques 16.6% more yield was achieved and 50% of the water was conserved. according to multi criteria analysis, alternative irrigation methods are more suitable for water saving and normal crop yield is obtained [18]. authors in [19] designed a framework for assessing technology and management options to reduce water losses. they suggested that a framework is needed in adopting alternative irrigation practices and appropriate management techniques that will reduce water shortage. authors in [20] did a study on crop water productivity, reviewing 84 articles and concluded that minimum wheat crop water productivity range is 0.6-1.7kg/m 3 ii. materials and methods a. study area and crop the wheat crop was cultivated in a local farm in the village ghullam shah, district sujawal, sindh, pakistan. it is located at latitude and longitude of 24°29’03” and 68°12’41”. the highest temperature observed was 41°c and the lowest was below 19°c, while the average annual rainfall is 48mm. the most cultivated crops are wheat, cotton, sugarcane, rice and mustard. the methodology of this study is focued on field-based analysis for water saving, crop yield, and crop water productivity estimations. it also includes soil and water analysis to determine better irrigation scheduling. a field-based experiment was conducted for three seasons on wheat crop cultivated from november 2015 to march 2018 on clay loam soil. in this study the cultivated crop was rabi season wheat, the root depth of the crop was 110cm and the available soil moisture depletion was 50%. b. experimental design a one-acre field was divided into four sections with each treatment having three replications. treatments were random complete block design (rcbd) system showing different irrigation methods. the adopted irrigation practices are tabulated in table i, which shows their geometrical properties. the practices are coded as: free flood as t1, furrow as t2, alternate furrow as t3, and raised bed as t4. moreover, these irrigation practices are divided into a total of 12 blocks, each block having 23.247m length, 14.33m width and an area of 333.11m 2 . c. irrigation and fertilization process the equipment installed at the field station was cut throat flume and tensiometers. these were determining the crop water requirements at specific times. the field was irrigated by giving soaking dose and the seeds were sowed manually with hand drill when soil was in full moist condition. fifty kg of wheat seed were applied along with 50kg of diammonium phosphate fertilizer ((nh4)2hpo4) at the time of sowing and two bags of urea. the nitrogen fertilizer is more suitable compared to potassium (k) and phosphorous (p), due to its engineering, technology & applied science research vol. 9, no. 3, 2019, 4310-4314 4312 www.etasr.com oad et al.: farm-based evaluation of sustainable alternative irrigation practices ability to dissolve quickly in soil while it cannot contaminate ground water [9]. npks were applied in the form of urea, diammonium phosphate fertilizer and sulfate of potash. all p, k with half n were applied during the land preparation. the remaining half n was split applied with 2nd, 3rd and 4th irrigations. the crop was harvested on march 2018. table i. geometry of the experimental area s r . n o w id th o f fu r r o w /b a s in d e p th o f fu r r o w n o . o f fu r r o w s n o . o f b e d s w id th o f b e d d e p th o f b e d s lo p e o f fu r r o w s t1 14.33 t2 0.304 0.304 23 23 0.305 0.31 0.005 t3 t4 0.38 0.372 15 14 0.610 d. sampling and analysis water samples were collected for quality analysis. the tests consisted of physical and chemical measurements. before determining the physicochemical parameters, all the equipment was calibrated using distilled water. regarding soil, a total of 72 disturbed soil samples were collected using an auger hole at different depths of 0-15cm, 15-30cm, 30-45cm, 45-60cm, 6075cm and 75-90cm to determine soil texture, bulk density and other parameters. water and soil analyses were performed at the drainage and reclamation institute of pakistan (drip), pakistan council of research in water resources (pcrwr), tandojam, pakistan. e. irrigation scheduling the irrigation of wheat crop under furrow, alternate furrow, raised bed irrigation and conventional practice was applied at 21-25 day intervals. the irrigation of wheat crop underneath conventional irrigation technique was based on the farmer’s practices. equation (1) was used to determine crop water requirement [1]: � = ��.���.� �� × × � (1) where r=water requirement, f.c=field capacity (%), m.c=moisture content (%), b=bulk density (g/cm 3 ), and d=depth of root zone (cm). f. irrigation application the irrigation application of each treatment was calculated to obtain the irrigation efficiencies and water productivity. g. crop water requirement crop water requirement was found by: ��� = ��� × �� (2) where eto is the evapotranspiration and kc is crop coefficient. h. crop water productivity crop water productivity (cwp) of raised-bed and conventional irrigation systems was calculated by [1]: ��� = � �� (3) where cwp=water use efficiency (kg/m 3 ), y=yield of crop (kg·ha -1 ), wr=total water consumed (m 3 ha -1 ) . i. water saving the water saving for wheat crop over the conventional irrigation system was calculated as: ���% = ����� �� (4) where, ws=water saving (%), wa=maximum total water used in conventional irrigation system in water application practice (m 3 ), and wb=minimum total water used in the irrigation system in water application practice (m 3 ). iii. results and discussion the results show that the soil was quite saline and local farmers did not have any idea about economical and efficient irrigation practices, because mostly they are uneducated and lack technical skills, therefore they adopt traditional practices. the water analysis gave the results shown in table ii. vanal water was non-saline and non-sodic. the mean ph value of water was 8.4, ec was 1080µscm -1 , tds was 681.8ppm, chloride 5.6, the presence of sodium in water source was 3.2, and the sodium absorption ratio was 3.2. from the experimental results it is clear that the quality of the available water is marginally useable and not too good. table ii. water sample characteristics sample no. ecw (µs cm -1 ) ph tds (ppm) sar 1 1051 8.2 683.15 3.2 2 1100 7.7 700 3.5 3 1085 8.1 670 3.4 4 1095 8.5 680 3.1 5 1065 8.2 675 3.0 soil sample analysis was done before sowing and after harvesting. its purpose was to know soil condition, texture and salinity status. the results concluded that the soil condition was more saline before sowing and after harvesting it was less due to evapotranspiration and soil texture changes from depth to depth. the mean value of soil texture was clay loam (table iii). table iii. soil characteristics parameters unit results t1 t2 t3 t4 ec (µs cm -1 ) 996 867 680 920 ph 8.35 8.4 8.1 8.2 sar 3.4 3.1 3.5 3.8 esp % 3.9 3.4 3.7 3.8 co3 me/l 0.03 nil nil 0.02 hco3 me/l 2 2.7 3 1.6 cl me/l 3 5 4 3.4 ca+ mg me/l 3.6 5 4.10 5.5 na 3.2 6 4.20 3.35 so4 me/l 1.7 3.2 3.3 2.2 table iv shows the water savings per irrigation method. figure 1 shows the field experiment of the applied methods of irrigation. the difference in water application, seepage, and crop growth can be seen. crop water productivity and increase in yield is illustrated in table v. the results show that furrow engineering, technology & applied science research vol. 9, no. 3, 2019, 4310-4314 4313 www.etasr.com oad et al.: farm-based evaluation of sustainable alternative irrigation practices irrigation yield production was 5928kg, for alternate it was 5681.988kg, for raised-bed it was 6669kg, and conventional gave 4940kg. the total day number from sowing to harvest was 123 from november to march. the cwr of the wheat crop was 314mm, determined by using eto and kc values as illustrated in table vi. table iv. water savings and comparison to conventional method method consumption of water for wheat crop (m 3 hec -1 ) water saving (%) t1 4431.18 t2 3328.572 25% t3 2297.0 49% t4 3076.63 31% table v. crop water productivity and increase in yield comparison with conventional irrigation method crop water productivity (mean) (kg m -3 ) increase in yield (%) t1 1.011 t2 2.14 20.0 t3 3 15.0 t4 1.75 35.0 table vi. wheat crop water requirements period eto kc november 4.83 0.35 december 4.0 0.75 january 3.3 1.0 february 4.62 0.85 march 5.33 0.65 average 3.55 0.72 fig. 1. growing stages of wheat crop the study area map was digitized by the arc geographical information system (arc-gis). crop water requirements were calculated with the help of the evapotranspiration data. the monthly data of evapotranspiration of 2015-2018 were collected from the metrological department of karachi, they can also be downloaded from the usgs website. economic analysis was also done. it showed that use of furrow irrigation system is more profitable. the social aspect was also taken into consideration. it was the first time where a local farmer was convinced on the application of furrows, alternative, and raised bed irrigation practices, making it a challenge. the main issue was system monitoring and understanding the methods and their significance. the will of farmers is to be appreciated, however there is a dire need of awareness and acceptability toward non-conventional systems. figure 2 shows the comparative irrigation application under various irrigation modes. graphical representation shows maximum quantity of water about 4000m 3 /hc. τhe alternate furrow irrigation system utilized 51.83% less water as compared to free flood, and furrow and raised-bad irrigation systems utilized equal quantities of water. figure 3 depicts the comparative crop yield for various irrigation practices. raised-bed achieves maximum yield of wheat crop as compared to other irrigation systems. fig. 2. water applied to wheat crop under alternate irrigation practices in comparison with free flood fig. 3. comparative analysis of crop yield statistical analysis was performed to justify the results of yield and water applied by using anova testing. an analysis of variance for significance p<0.05 was used to determine differences between means. the anova test results are illustrated in tables vii and viii. note: the results show that there is a variance between irrigation practices and between groups the anova gives significant result values, i.e. 0.0004, which is less than 0.01 and fcritical is less than f, also showing significance between values. table vii. anova results method conventional furrow alternate furrow raised-bed sum 179.4 134.7 93 124.56 average 29.9 22.46 15.5 20.76 variance 0.156 14.27 52.62 21.35 f 9.62 p-value 0.000387 fcritical 3098 engineering, technology & applied science research vol. 9, no. 3, 2019, 4310-4314 4314 www.etasr.com oad et al.: farm-based evaluation of sustainable alternative irrigation practices table viii. anova results for crop yield method conventional furrow alternate furrow raised-bed sum 500 600 575 675 average 166.7 200 191.7 225 variance 2.33 100 10.57 9.0 f 56 p-value 0,000009 fcritical 4.07 iv. conclusion the area of study for this research is composed of clay loam receiving canal water that is marginally saline but still good for irrigation. the quality of water was marginally useable and its dry bulk density was 1.35gm·cm -3 , the field capacity was 26.5%, and the infiltration rate was 0.18cm·hr -1 . out of the four irrigation practices, on-farm based analysis showed that alternate furrow technique gave most water saving but not enough yield, whereas raised bed method enhanced 26% of yield and conserved 31% more water compared to conventional flood irrigation. anova provides evidence to the results. this concludes that raised bed is the most effective irrigation practice. acknowledgement authors are thankful to the us-pakistan center for advanced studies in water, muet, jamshoro for the financial support and to the drainage and reclamation institute of pakistan (drip), pakistan council of research water resource (pcrwr), tandojam for the laboratory work. references [1] m. m. a. kaisi, j. f. shanahan, irrigation of winter wheat, crop series, 1999 [2] n. dabour, “the role of irrigation in food production and agricultural development in the near east region”, journal of economic cooperation, vol. 23, no. 3, pp. 31-70, 2002 [3] a. darzi-naftchali, h. ritzema, “integrating irrigation and drainage management to sustain agriculture in northern iran”, vol. 10, no. 6, pp. 1-17, 2018 [4] r. a. fischer, k. sayre, i. o. monasterio, “the effect of raised bed planting on irrigated wheat yield as influenced by variety and row spacing”, in: aciar proceedings no. 121, pp. 1-11, australian centre for international agricultural research, 2005 [5] j. m. goncalves, a. p. muga, m. g. horst, l. s. pereira, “furrow irrigation design with multicriteria analysis”, biosystems engineering, vol. 109, no. 4, pp. 266-275, 2011 [6] e. a. holzapfel, m. a. marino, j. chavez-morales, “procedure to select an optimum irrigation method”, journal of irrigation and drainage engineering, vol. 111, no. 4, pp. 319-329, 1985 [7] m. l. jat, r. gupta, y. s. saharawat, r. khosla, “layering precision land leveling and furrow irrigated raised bed planting: productivity and input use efficiency of irrigated bread wheat in indo-gangetic plains”, american journal of plant sciences, vol. 2, no. 4, pp. 578-588, 2011 [8] d. labadarios, z. j. mchiza, n. p. steyn, g. gericke, e. m. maunder, y. d. davids, w. a. parker, “food security in south africa: a review of national surveys”, bulletin of the world health organization, vol. 89, no. 12, pp. 891-899, 2011 [9] d. k. majumdar, irrigation water management principles and practices, prentice hall of india, 2010 [10] g. mishra, h. s. kushwaha, “winter wheat yield and soil physical properties responses to different tillage and irrigation”, european journal of 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“review of measured crop water productivity values for irrigated wheat, rice, cotton and maize”, agricultural water management, vol. 69, no. 2, pp. 115-133, 2004 microsoft word 09-3888_s_etasr_v10_n6_pp6427-6431 engineering, technology & applied science research vol. 10, no. 6, 2020, 6432-6437 6432 www.etasr.com alshammari: teaching-learning-based optimization algorithm for the combined dynamic economic … teaching-learning-based optimization algorithm for the combined dynamic economic environmental dispatch problem badr m. alshammari college of engineering university of ha’il ha’il, saudi arabia abstract-the dynamic economic environmental dispatch problem (deedp) is a major issue in power system control. it aims to find the optimum schedule of the power output of thermal units in order to meet the required load at the lowest cost and emission of harmful gases. several constraints, such as generation limits, valve point loading effects, prohibited operating zones, and ramp rate limits, can be considered. in this paper, a method based on teaching-learning-based optimization (tlbo) is proposed for dealing with the deedp problem where all aforementioned constraints are considered. to investigate the effectiveness of the proposed method for solving this discontinuous and nonlinear problem, the ten-unit system under four cases is used. the obtained results are compared with those obtained by other metaheuristic techniques. the comparison of the simulation results shows that the proposed technique has good performance. keywords-dynamic economic environmental dispatch; teaching-learning-based optimization; prohibited operating zones; ramp rate limits i. introduction with the growing demand for electricity and rising fuel prices, electricity companies are constantly working to ensure continuous and reliable electrical power supply to their customers. in order to achieve this, system operators need to constantly adjust the control variables of power networks. this extremely difficult task is performed by the resolution of the economic dispatch problem (edp), which aims to determine the production levels of all thermal units which guarantee a balance between production and consumption at the lowest cost. unfortunately, today network loads are dynamic, which means that it is required to plan the generation of units in real time to guarantee continuous power balance. the resolution of such dynamic edp problems (dedp), considers the constraints imposed by generator ramp-rate limits (rrl). along with dedp, the emission dispatch problem, which aims to minimize the emissions of fossil fuels, has emerged. the combination of the two problems in one single problem called dynamic economic environmental dispatch problem (deedp) has become attractive. deedp aims to minimize simultaneously the total production cost and the emission of harmful gases. thus, it can be considered as a multi-objective problem with conflicting objective functions [1]. in the past, several operating constraints have been taken into account in the deedp mathematical formulation, such as power balance constraint, valve-point loading effects (vple), prohibited operating zones (poz), and rrls. during the past decades, several techniques have been proposed to solve this kind of problems, including linear programming [2], dynamic programming [3], and gradient algorithms [4]. unfortunately, in these techniques, the cost function has been approximated by quadratic functions and vples have been ignored in the problem formulation. this frequently leads to inexactitude of the optimal solutions. moreover, those techniques may be trapped in local optima due to the non-convex and nonlinear characteristics of the cost function. in recent years, various meta-heuristic techniques have been suggested in the literature to overcome the limitations of the traditional methods. in [1], a differential evolution-based technique has been used to solve the deedp where a fuzzy-based method has been employed to extract the optimal solution. authors in [5] utilized the artificial bee colony algorithm to solve the edp with vples. unfortunately, the environmental impact of thermal units has not been considered. particle swarm optimization (pso) has also been used to solve power dispatch problems [6-8]. basu [9] has solved the deedp by applying the second version of the non-dominated sorting genetic algorithm (nsgaii) proving that such technique may provide promising results. another technique based on ngsaii has been developed in [10] to handle the deedp incorporating poz constraints. an optimization method based on simulated annealing (sa) algorithm has been implemented in [11] in this regard, the cost function has been approximated by a cubic function and the problem has been converted into monoobjective problem by using price penalty factors. within this context, other metaheuristic techniques, such as gravitational search algorithm (gsa) [12], biogeography-based optimization (bbo) [13], bacterial foraging algorithm (bfa) [14], and harmony search (hs) algorithm [15] have been developed and implemented for various complex dispatch problems. the main advantage of the aforementioned techniques is that they expand the entire search space for the optimal solution to avoid getting trapped in a local optimal. in addition, these techniques are not concerned with the nature and the shape of the objective functions. however, the corresponding author: badr m. alshammari engineering, technology & applied science research vol. 10, no. 6, 2020, 6432-6437 6433 www.etasr.com alshammari: teaching-learning-based optimization algorithm for the combined dynamic economic … convergence of most of these techniques depends on their parameters and their computational time is quite large. the teaching-learning-based optimization (tlbo) algorithm [16] is a powerful algorithm which can provide promising results in single objective and multi-objective optimization. it is a population algorithm inspired from the teacher/learner relationship. the tlbo algorithm is based on two basic methods of learning: (i) through the teacher, known as the teacher phase, and (ii) through interaction with other students, called student phase. in this optimization algorithm, a group of students is considered as a population and the different subjects offered to the students are considered to be the feasible solutions and a student's result is considered to be the value of the fitness function [16]. the best solution in the whole population, which corresponds to the best value of the objective function, is assigned to the teacher. it has been shown that tlbo has the advantage of only requiring a few control parameters, such as the number of students in the class and the number of subjects presented for students, for its operation [17, 18]. in this regard, a tlbo-based method is proposed for dealing with the problem of deedp. in the deedp formulation all operating constraints, such as generation limits, energy balance, vples, rrls, and poz constraints are considered. to render the problem more practical, total real power losses are taken into account. to assess the effectiveness of the proposed optimization method, a ten-unit system is employed. the simulation results obtained by the proposed method are compared with other metaheuristic techniques. ii. mathematical formulation of the deedp the deedp is a principal problem in power network operation. it aims to determine the optimum allocation of power outputs of all thermal units to minimize simultaneously the total fuel cost and total emission according to the predicted load demands, over entire dispatch periods generally of one hour. taking vples into account, the total fuel cost can be expressed by: ( ) ( ){ } 2 min 1 1 sin t n t t t t i i i i i i i i i t i c a b p c p d e p p = = = + + + −∑∑ (1) where , , , and are the cost coefficients of unit i, t ip is the output power in mw of unit i at time t, t is the number of hours, and n is the number of units. the second objective function considered in this study, which is the total emission of harmful gases, is described as: ( ) ( ) 2 1 1 exp t n t t t t i i i i i i i i t i e p p pα β γ η λ = = = + + +∑∑ (2) where , , , and are the emission coefficients. in this work, the two objective functions are combined in a single objective function by integrating the price penalty factor. the combined function is: ( )1t t tf c eδ δ λ= + − (3) where ( )0,1randδ = and λ is the average of the price penalty factors of all units. the price penalty factor for unit i can be determined as: max max i i i c e λ = (4) where max ic and max ie are the maximum fuel cost and the maximum emission of unit i respectively. in order to find the optimal pareto solutions, the objective function ft is minimized for various values of δ subject to the constraints (5)-(9). equation (5) describes the power balance constraint where the real power losses t lp at time t are calculated by (10) [19]. as given in (6), the output power of each generator i should be within its lower min ip and upper max ip limits. the rrls of the thermal units are shown in (7) and (8) while pozs constraints are given in (9). 1 0, 1,..., n t t t i d l i p p p t t = − − = =∑ (5) where, t dp is the load at time t. (6) 1t t down i i ip p r − − ≤ (7) 1 upt t i i ip p r −− ≤ (8) where down ir and up ir are the down-ramp and up-ramp limits of unit i. min ,1 ,, 1 max , , 2,..., i t down i i i upt t down i i i k ii k up t i ii z p p p p p p p k z p p p −  ≤ ≤   ∈ ≤ ≤ =   ≤ ≤  (9) where , down i kp and , up i k p are the down and up bounds of poz number k and iz is the number of poz for unit i. 1 1 1 n n n t t t t l i ij j oi i oo i j i p p b p b p b = = = = + +∑∑ ∑ (10) where, , , are the loss coefficients of b-loss matrix. iii. the tlbo algorithm tlbo algorithm, developed in [16], is a population-based optimization algorithm that mimics the teaching and learning phenomenon in a class. it is inspired by the transmission of knowledge from teacher to students and the mutual interaction between classmates. in tlbo algorithm, students in a class ia ib ic id ie iα iβ iγ iη iλ min max , 1,...,≤ ≤ =ti i ip p p i n ijb oib oob engineering, technology & applied science research vol. 10, no. 6, 2020, 6432-6437 6434 www.etasr.com alshammari: teaching-learning-based optimization algorithm for the combined dynamic economic … constitute the population and a student is considered as a feasible solution for the optimization problem. subjects offered to students constitute the decision variables and student’s result is the fitness function evaluated at the feasible solution. tlbo method is divided into two phases which are teacher phase and student phase. a. teacher phase in this phase, the teacher is the main interfering where his job is to improve the knowledge level of learners (students) and helps them to get high grades. however, grades or marks of students depend on teaching quality and student’s quality. for simulation, consider there are ‘n’ subjects offered to npop students. therefore, variable ‘n’ is equivalent to the number of problem design variables and npop is the population, in tlbo algorithm. let k jm be the mean result of learners in a particular subject j where { }1,2, ,j m∈ … , at the k-th teachinglearning cycle ( { }max0,1,2, ,k i∈ … ). since the teacher is the most highly learned and experienced person in the class, thus, he is considered the best learner in the entire population or class. let *k x be the best solution in the entire population at the k-th iteration. the difference between the teacher’s results and the mean result of students in the j-th subject is calculated as [18]: ( )*k k kj j f jd r x t m= − (11) where [ ]0,1r ∈ is a random number. tf is the teaching factor that is selected randomly from { }1,2 . it is used to choose which value of mean should be changed. at the k-th teaching-learning cycle, the i-th feasible solution is updated according to the following expression. , , k k k ij new ij old jx x d= + (12) if , k ij newx gives better results compared to , k ij oldx , it is accepted, otherwise, it is rejected. all accepted solutions will be used as input for the student phase. b. student phase in this phase, students acquire knowledge through mutual interaction. the learning phenomenon is simulated as follows. two feasible solutions, k ux and k vx withu v≠ , are randomly selected from the population. if k ux is better than k vx , then update k vx as given in (14) otherwise update k ux as given in (13). if the new solution is better than the old solution, then, the new solution will be accepted in the population and the old solution will be rejected, otherwise the new solution will be rejected and old solution will be kept in the population. ( ),k k k kuj new uj uj vjx x r x x= + − (13) ( ),k k k kvj new vj vj ujx x r x x= + − (14) the tlbo algorithm’s steps are shown in figure 1. fig. 1. steps of the tlbo algorithm. iv. tlbo algorithm implementation for the deedp to verify the effectiveness of the proposed method in solving the deedp, numerical experiments are carried out employing the ten unit system. the tlbo algorithm was firstly applied for static economic emission dispatch for total demand power of pd=2000mw, and then for the dynamic case. all system data are taken from [20]. in this paper, tlbo and pso algorithms are implemented in matlab r2018b on a pc intel(r) core i7, 1.5ghz, 64 bits. population size and maximum number of iterations are both 200. the b-loss matrix of the studied system is shown in (15). 0.49 0.14 0.15 0.15 0.16 0.17 0.17 0.18 0.19 0.20 0.14 0.45 0.16 0.16 0.17 0.15 0.15 0.16 0.18 0.18 0.15 0.16 0.39 0.10 0.12 0.12 0.14 0.14 0.16 0.16 0.15 0.16 0.10 0.40 0.14 0.10 0.11 0.12 0.14 0.15 0.16 0.17 0.12 0.14 0.35 0.11 0.13 0.13 0. 10 4 b = − 15 0.16 0.17 0.15 0.12 0.10 0.11 0.36 0.12 0.12 0.14 0.15 0.17 0.15 0.14 0.11 0.13 0.12 0.38 0.16 0.16 0.18 0.18 0.16 0.14 0.12 0.13 0.12 0.16 0.40 0.15 0.16 0.19 0.18 0.16 0.14 0.15 0.14 0.16 0.15 0.42 0.19 0.20 0.18 0.16 0.15 0.16 0.15 0.18 0.16 0.19 0.44                                 (15) a. static dispatch the convergence of the objective functions for the proposed algorithm and pso is shown in figure 2. it can be seen that tlbo provides cheaper electricity production and lowest emission compared to pso. in fact, the minimum cost engineering, technology & applied science research vol. 10, no. 6, 2020, 6432-6437 6435 www.etasr.com alshammari: teaching-learning-based optimization algorithm for the combined dynamic economic … and emissions are 132968.93$/h and 18832.63ton/h respectively for the tlbo algorithm and 133088.62$/h and 19054.12ton/h respectively for the pso algorithm. the pareto front generated by the proposed algorithm is shown in figure 3. it is clear that that the pareto solutions are uniformly distributed in the objective space. moreover, figure 3 shows that cost and emissions are conflicting functions. (a) (b) fig. 2. convergence of objective functions for pd=2000mw: (a) cost, (b) emission. fig. 3. pareto solutions for pd=2000mw. b. dynamic dispatch pure dynamic economic dispatch and pure dynamic environmental dispatch are solved separately. then, they are dynamically combined for economic environmental dispatch. table i shows the optimal variation of the generation for dynamic economic dispatch, according to the daily variation of the load ( t dp ). it is clear that the optimal output powers of all units are within their limits. the minimum production cost is 2472116.66$ while the corresponding emission is at its maximum value which is 330411.81ton. the optimum schedule of all system units for the dynamic emission dispatch is depicted in table ii. it can also be seen that output powers of all units are within their limits. the minimum emission is 294153.04ton while the total cost is at its maximum value which is 2594148.32$. table i. dynamic economic dispatch hour p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 1 1036 150.1259 135.5687 73.0000 117.0485 175.4140 126.8733 130.0000 117.5441 20.0000 10.0000 2 1110 150.0664 135.0000 73.0000 108.9781 225.4140 160.0000 130.0000 120.0000 20.0000 10.0000 3 1258 150.2382 135.0000 153.0000 125.7599 223.8123 159.6342 129.5876 119.8081 49.7545 39.8977 4 1406 150.5704 135.0000 206.7431 175.7599 243.0000 159.0079 129.5631 119.0141 79.6457 43.2159 5 1480 150.5888 135.0000 255.5104 225.7599 221.4589 156.7358 130.0000 119.9033 78.9610 45.4764 6 1628 150.2503 135.0000 335.5104 275.7599 243.0000 159.7044 129.6031 119.9085 79.8822 47.4658 7 1702 150.1468 198.5926 331.5975 300.0000 241.5421 160.0000 130.0000 119.9352 79.8647 43.3868 8 1776 210.1460 213.1343 340.0000 300.0000 243.0000 160.0000 130.0000 120.0000 80.0000 38.2598 9 1924 273.4194 293.1343 340.0000 300.0000 243.0000 160.0000 130.0000 120.0000 80.0000 55.0000 10 2022 300.4154 373.1343 340.0000 300.0000 243.0000 160.0000 130.0000 120.0000 80.0000 55.0000 11 2106 315.4490 453.1343 337.4498 300.0000 243.0000 160.0000 130.0000 120.0000 80.0000 55.0000 12 2150 344.5307 470.0000 340.0000 300.0000 243.0000 160.0000 130.0000 120.0000 80.0000 55.0000 13 2072 331.2602 397.3814 340.0000 300.0000 242.9249 159.9539 130.0000 119.9397 79.9670 55.0000 14 1924 251.3135 317.3814 338.7426 300.0000 242.6070 159.6948 129.9303 120.0000 79.9776 54.9429 15 1776 171.7944 237.3814 339.7179 300.0000 242.9101 159.5908 129.9045 118.7763 79.9693 54.4079 16 1554 150.0967 157.3814 296.4912 250.7445 238.3715 159.4043 129.3618 119.6965 53.0343 43.1300 17 1480 150.9007 135.0000 240.7998 242.3687 242.1751 159.6100 129.7144 119.7307 55.0000 44.0521 18 1628 150.3632 174.5376 300.0000 292.3687 242.2373 159.9336 129.4308 119.2750 54.7366 53.3392 19 1776 217.4110 254.5376 300.0000 300.0000 243.0000 160.0000 130.0000 120.0000 55.0000 55.0000 20 1972 284.3186 334.5376 340.0000 300.0000 243.0000 160.0000 130.0000 120.0000 80.0000 55.0000 21 1924 259.9202 309.6601 340.0000 300.0000 243.0000 159.2709 129.8075 119.9798 79.9277 53.0288 22 1628 180.1857 229.9838 291.1958 250.6165 223.4006 159.4022 126.6683 120.0000 51.6945 43.7541 23 1332 150.2720 150.0578 211.4456 201.6378 174.2186 160.0000 130.0000 90.0000 52.0055 44.2729 24 1184 150.5086 135.0000 131.4456 167.0485 175.3310 110.0000 130.0000 120.0000 50.0000 40.0000 cost ($) 2472116.66 emission (ton) 330411.81 c o st ( $ /h ) e m is si o n ( to n /h ) e m is si o n ( to n /h ) t dp engineering, technology & applied science research vol. 10, no. 6, 2020, 6432-6437 6436 www.etasr.com alshammari: teaching-learning-based optimization algorithm for the combined dynamic economic … table ii. dynamic emission dispatch hour p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 1 1036 150.3364 135.2479 88.8628 91.5246 133.1490 133.2677 96.0287 92.6589 79.7478 54.8723 2 1110 150.4649 138.1099 101.9172 99.8572 143.6597 143.8590 105.5614 114.0802 79.9698 55.0000 3 1258 164.2919 166.1639 117.3305 121.6243 172.9143 159.9093 129.7196 120.0000 80.0000 54.9823 4 1406 199.0112 203.9786 147.0126 144.0633 204.0232 159.7183 129.9286 119.9410 79.9646 55.0000 5 1480 216.9388 219.6330 157.4592 163.6519 218.2469 160.0000 129.9633 120.0000 79.9462 55.0000 6 1628 253.4935 255.9774 190.1283 190.7046 242.9276 159.9049 129.9803 119.9825 80.0000 55.0000 7 1702 275.2332 273.7700 209.7002 210.7657 242.8287 160.0000 129.9338 120.0000 79.9196 54.9987 8 1776 291.1351 295.7189 229.4559 232.4257 242.9839 159.8865 130.0000 120.0000 80.0000 54.8400 9 1924 324.3152 326.1564 277.5305 279.7439 243.0000 160.0000 129.9974 119.9869 79.9975 54.9994 10 2022 348.6556 349.0595 321.7455 294.5092 243.0000 160.0000 130.0000 119.9751 80.0000 55.0000 11 2106 383.1823 382.7515 339.9697 299.9955 243.0000 160.0000 130.0000 120.0000 80.0000 54.9992 12 2150 397.8457 425.6329 340.0000 300.0000 241.7596 152.4816 130.0000 120.0000 80.0000 55.0000 13 2072 364.1944 364.2761 339.9983 299.9967 243.0000 159.9968 130.0000 120.0000 79.9960 55.0000 14 1924 327.2057 322.9324 278.8479 278.7852 243.0000 159.9789 130.0000 120.0000 79.9829 55.0000 15 1776 292.5619 292.8412 230.3221 233.2478 242.7153 159.8868 129.8985 119.9561 80.0000 55.0000 16 1554 234.6654 237.5412 181.0347 183.2478 243.0000 160.0000 129.7930 120.0000 55.0000 55.0000 17 1480 224.4285 225.2253 162.6887 164.5307 224.1457 160.0000 129.9327 120.0000 54.9989 55.0000 18 1628 262.2682 260.2198 197.1840 196.3723 242.4237 159.9493 129.8766 119.9320 55.0000 55.0000 19 1776 298.9110 296.1538 240.5298 238.0002 243.0000 159.9865 129.9697 120.0000 54.9945 55.0000 20 1972 337.0679 337.4869 297.2509 287.9121 242.9982 159.9977 129.9953 119.9968 79.9966 54.9965 21 1924 328.1016 326.5158 278.6325 274.7016 243.0000 159.9165 130.0000 119.9709 79.9725 54.9936 22 1628 248.1062 246.5158 198.6325 224.7016 215.3974 159.6594 130.0000 119.9354 79.8864 55.0000 23 1332 176.4330 166.5158 127.4188 174.7016 174.6863 160.0000 129.7901 119.8400 80.0000 54.9865 24 1184 154.0152 155.7069 100.8685 124.7016 168.9035 152.3155 107.1434 110.9206 80.0000 55.0000 cost ($) 2594148.32 emission (ton) 294153.04 table iii. combined economic emission dispatch hour p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 1 1036 150.4594 135.3072 80.0281 120.0864 126.2070 124.4066 129.6379 86.1200 59.2616 44.0814 2 1110 150.0709 135.0000 81.2516 102.8341 167.8358 125.3782 129.3292 116.1200 79.9973 44.7038 3 1258 150.4932 135.0161 138.7766 129.6167 188.9086 160.0000 129.2388 120.0000 79.7994 54.6856 4 1406 154.9053 161.9512 177.1730 179.6167 223.7618 159.9893 129.7067 119.9437 79.9075 54.7681 5 1480 152.9466 217.8705 186.4596 185.1000 236.2579 159.5941 130.0000 119.8567 79.8784 52.1092 6 1628 213.1264 236.4829 260.3624 203.1865 243.0000 136.3359 130.0000 120.0000 80.0000 55.0000 7 1702 227.8217 221.6160 271.7060 246.9217 243.0000 160.0000 129.8277 120.0000 79.9719 55.0000 8 1776 228.2304 242.9587 290.8592 286.3618 242.9531 159.9532 130.0000 119.4716 79.8240 54.3041 9 1924 293.0721 293.5529 340.0000 280.7385 243.0000 160.0000 130.0000 120.0000 80.0000 54.5004 10 2022 306.2281 368.3049 340.0000 300.0000 243.0000 160.0000 129.8569 120.0000 80.0000 54.1663 11 2106 376.6213 389.3073 339.9899 299.9805 242.9987 159.9980 129.9979 119.9977 79.9869 54.9993 12 2150 385.6214 428.8158 340.0000 300.0000 243.0000 160.0000 130.0000 120.0000 80.0000 55.0000 13 2072 361.8808 397.2726 340.0000 300.0000 243.0000 160.0000 130.0000 90.0000 80.0000 55.0000 14 1924 289.4585 317.2726 300.7884 300.0000 243.0000 159.9907 129.6966 119.8300 80.0000 55.0000 15 1776 232.8384 281.4039 276.1673 257.2175 242.9575 159.8950 129.9781 120.0000 79.9478 55.0000 16 1554 153.0008 218.8426 222.2456 241.2300 243.0000 159.9386 130.0000 119.8715 55.0000 55.0000 17 1480 150.1175 217.9193 195.6985 194.4730 243.0000 159.8241 129.9954 119.9426 55.0000 54.0499 18 1628 229.1932 233.6730 207.0696 244.4730 243.0000 160.0000 130.0000 120.0000 55.0000 55.0000 19 1776 257.6630 290.2181 268.7446 256.2676 242.9809 159.9782 130.0000 120.0000 54.9739 54.9997 20 1972 271.6633 347.2125 340.0000 300.0000 243.0000 160.0000 130.0000 120.0000 80.0000 55.0000 21 1924 301.8759 308.5015 297.6986 299.7156 242.8737 159.9440 129.6663 119.8831 79.9622 54.9860 22 1628 222.0018 228.5015 217.6986 249.7616 222.5752 159.8970 129.6350 119.9210 79.9730 47.2841 23 1332 150.2022 148.5746 138.5624 200.3815 223.2994 159.5506 130.0000 89.9210 80.0000 43.5042 24 1184 150.4527 135.1441 73.0000 170.0864 173.2994 127.6795 130.0000 114.8581 80.0000 55.0000 cost ($) 2519909.93 emission (ton) 303338.20 table iii depicts the best compromise solution obtained from the resolution of the combined deedp. fuzzy-based method [9] is employed to extract the optimal best compromise solutions. the total cost is 2519909.93$ which is more than the cost obtained for the pure economic dispatch (2472116.66$) and less than the cost obtained for the pure environmental dispatch (2594148.32$). similarly, the emission is 303338.20ton which is less than the emission obtained for the t dp t dp engineering, technology & applied science research vol. 10, no. 6, 2020, 6432-6437 6437 www.etasr.com alshammari: teaching-learning-based optimization algorithm for the combined dynamic economic … pure economic dispatch (330411.81ton) and more than the emission obtained for the pure environmental dispatch. the comparison results shown in table iv show that the proposed tlbo outperforms pso, improved bacterial foraging algorithm (ibfa), and the second version of the nondominated sorting genetic algorithm (nsgaii) in finding the optimum generation schedule for the deedp. table iv. comparison with other meta-heuristic techniques method minimum cost ($) minimum emission (ton) tlbo 2472116.66 294153.04 pso 2497562.38 301539.82 ibfa [21] 2481733.3 295833.0 nsgaii [10] 2.5168x10 6 3.1740x10 5 v. conclusion in this study, a new metaheuristic called teachinglearning-based optimization (tlbo) algorithm was used for solving the deedp. the problem is described as an optimization problem. the decision variables of the problem are the output powers of units at the hours of a single day. energy balance equation, generation limits, valve point loading effects, prohibited operating zones and ramp rate limits are considered as problem constraints. to assess the effectiveness of the proposed method, the ten-unit system is used. the tlbo is applied for the pure dynamic economic dispatch, the pure dynamic environmental dispatch and the combined dynamic economic environmental dispatch. the obtained results were compared with other techniques proposed recently in the literature, such as pso, ibfa and nsgaii, and it was found that the proposed algorithm outperforms them. references [1] x. jiang, j. zhou, h. wang, and y. zhang, “dynamic environmental economic dispatch using multiobjective differential evolution algorithm with expanded double selection and adaptive random restart,” international journal of electrical power & energy systems, vol. 49, pp. 399–407, jul. 2013, https://doi.org/10.1016/j.ijepes.2013.01.009. 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[21] n. pandit, a. tripathi, s. tapaswi, and m. pandit, “an improved bacterial foraging algorithm for combined static/dynamic environmental economic dispatch,” applied soft computing, vol. 12, no. 11, pp. 3500– 3513, nov. 2012, https://doi.org/10.1016/j.asoc.2012.06.011. engineering, technology & applied science research vol. 8, no. 1, 2018, 2526-2531 2526 www.etasr.com hosseini et al.: an assessment of the impact of information technology on marketing and advertising an assessment of the impact of information technology on marketing and advertising zohre hosseini school of management multimedia university malaysia sara mohammadi faculty of management and economics shahid bahonar university of kerman iran hoda safari school of management multimedia university malaysia abstract—the present study aimed to evaluate the impact of technology on marketing and advertising by using structural equations modeling. to do this, 200 marketing and information technology (it) experts participated in the study. they answered questionnaires regarding it, marketing mix and advertising. for data analysis, structural equations modeling using smartpls were used. the results showed that the effect of it on marketing mix and advertising was positive and significant. the effect of marketing mix on advertising was positive and significant. the indirect effect of it on advertising via marketing mix was therefore positive and significant. totally, the results emphasized the effect of technology on marketing mix and advertising. keywords-technology; mass media; marketing; advertising i. introduction technology is defined as a combination of information equipment, techniques and processes needed to convert the data to output [1]. main technology components like software, hardware, mind mapping software and support network, interact with each other [2]. adopting appropriate technology does not mean the application of the advanced technology, but rather of the most appropriate which is consistent with a country's development objectives and available resources. transfer of technology could be the most useful or useless of transactions and the effective use of transferred technology depends on the recipient country's efforts to adapt [3]. new technologies have a profound impact on structure and production. in recent decades, different systems and management tools have been provided to improve the structures, goals, and strategies [2]. the forms of "market uncertainty" and "uncertainty in technology" are two properties proposed for technology. technological uncertainty refers to doubt about technology achievement and capability to respond to customer needs [4]. hence it is necessary to examine industries and areas changed by technology in order to enhance the chances of success of technology. one of these areas is marketing. marketing is one crucial factor for economy and society. as long as the gap between the producer and the consumer is slight and manufacturer is familiar enough with customers’ needs and interests, there is no need for distribution and marketing agents. moreover, when production is limited, factors like production planning, distribution strategy, marketing system completion etc. are of no concern for the manufacturers. however, in the case of mass production or when manufacturers target global markets and plan to distribute their products in a global scale, a wider range of marketing activities are required to deliver the product to the consumer. in the changing market conditions, it is expected for the existing marketing processes to face transformations and similarly, it is the market condition causing the success of a marketing plan. thus, identifying and analyzing environmental factors such as the impact of new technologies in this field is of great importance. the advertisement phenomenon was first performed through face-to-face verbal messages in the streets. later, books became the most important means of disseminating information and advertisement while religious propaganda was conducted in mosques and minarets, churches, temples, schools and books. progress of science, industry, and modern technology led to new ways of advertising with new equipments and tools [5]. in fact, advertising as a marketing technique plays a considerable role in the transfer of information (about products, services and business) to the consumer. over time, advertising methods have changed due to the coming of new technology. the internet and mobile technology were presented as new advertising media. mobile technology is able to create new markets, change organization competitive vision, create new opportunities and change the status of communication and market structures. considering the above, the question emerges. what are the changes in the marketing and advertising industry imposed by the entrance of new technology? ii. literature review with the arrival of communication technologies, the design of marketing mixture has more or less been altered. basic marketing elements have been fundamentally transformed and continue to do so. a. product mix product packaging and the presenting of product information in the internet reduces the need for physical testing and leads to saving time and money [7]. in e-commerce, acquisition of the customer’s likes and designing products according to customer’s opinion is facilitated [8]. engineering, technology & applied science research vol. 8, no. 1, 2018, 2526-2531 2527 www.etasr.com hosseini et al.: an assessment of the impact of information technology on marketing and advertising b. price mix customers’ quick access to competitors and their capability to quick compare prices, increased price competition between suppliers [10]. also, when it comes to virtual stores design, the lack of opening cost consequently reduces product cost and thus the selling price [8]. c. distribution mix for most buyers, the most important advantage of new technologies like internet is the ease of accessibility of the purchase place. using new technology, home is a place to buy products [8]. in addition, via the internet one manufacturer can remove the distribution networks and get connected to the final customer. a customer can gather information, negotiate with vendors, order products and pay via the internet. these distribution network duties are now in the responsibility of the customer [9]. d. advertisement mix advances of propagation tools have changed data transfer from its most basic form of verbal messages and face to face interaction to e-mail or real time messages. new methods of advertising and marketing use the latest developments in technology to send advertising messages. new technologies have affected advertising in several domains. e. advertisement instruments tv used to be an effective mass media in presenting adds. messages, letters, brochures and e-magazines accessible through the internet are the most recent advertisement instruments in the modern era. f. advertisement content although, information essentially could function as an ad, it must be mentioned that in ads the content of information intends to affect audiences’ attitudes and values. this impact occurs in two ways. as information presentation in the form of specific ads that could introduce new values in the society and create some desire towards the new values while making existing values insignificant. on the other hand, ads reflect the current society values along with individuals’ ideas and desires. for years advertising has been involved more in transferring social values and attitudes and less in the notification of basic information about goods and services [10]. g. effectiveness of advertising one of the most critical features of the internet is its reciprocal nature. when reviewing content of the web, customers can make a mutual relationship and determine how much and what kind of information they require [11]. changing the communication patterns from in-person to group to group and group to individual are two other ad properties. due to new technologies like internet the ad effectiveness and cost are affected. through changing the communication models, efficiency of the ads will considerably increase [11]. iii. research methodology the study method is descriptive (non-experimental) and correlation of structural equations was done by the least partial squares method and the relationship between variables in the causal model [12]. present study applies the partial least squares due to the benefits compared to covariance-based approach. a. participants the participants are marketing and it experts in iran. 220 questionnaires are distributed by purposeful sampling method, of which 207 questionnaires were answered, 7 questionnaires were excluded from the analysis and finally, 200 questionnaires entered the analysis. b. data collection measure to measure it capability, the questionnaire presented in [6] was used. this questionnaire consists of 16 items. 8 relational items, 3 technical capability items and 5 managerial capability items. to measure marketing mix, a researcher-built questionnaire consisting of 14 questions was used. 4 items regarded product, 3 items regarded price, 4 items regarded distribution and 3 items propaganda. another researcher built questionnaire was applied regarding advertisement. this questionnaire consists of 9 items. 3 items regarded content, 3 items tools and 3 items the effectiveness. all questions were answered on a five-item likert scale of strongly disagree (1) to strongly agree (5). iv. results a. measures validity and reliability the measurement test includes the evaluation of reliability (internal consistency) and validity (discriminant validity) of study constructs. to evaluate the reliability of constructs, authors in [13] proposed three criteria: reliability of each of the items, composite reliability of each of the constructs and the average variance extracted. regarding the reliability of each of items, the factor loading is 0.6 and above and in confirmatory factor analysis, it shows the suitability (figures 1, 2, 3). also, the factor loading of items should be significant at the level 0.01 [14]. to calculate t-statistics to determine the significance of factor loading, boot strap (with 500 subsamples) is applied. to evaluate the composite reliability of each of constructs, dillon-goldstein's (ρc) is applied. the acceptable values of ρc should be 0.7 or higher. the third criterion of reliability is the average variance extracted [13], which is recommended to be 0.50 or above [15]. tables i and ii show factor loading, ρc and ave of study variables. these values show suitable reliability of constructs. to evaluate validity or divergent validity, author in [15] recommended that items of a construct should have the highest factor loading on the construct. authors in [14] proposed that the factor loading of each item on the construct should be at least 0.1 higher than the factor loading of the item on other constructs. another criterion indicates that ave square of a construct should be higher than its correlation with other constructs. this shows that the correlation of the construct with its indicators is higher engineering, technology & applied science research vol. 8, no. 1, 2018, 2526-2531 2528 www.etasr.com hosseini et al.: an assessment of the impact of information technology on marketing and advertising than its correlation with other constructs. table iii shows the cross load of items on the study constructs. as shown in table iii, all dimensions have the highest factor loading on their construct, the least distance between the relevant factor loading is higher than 0.1 and the constructs have good validity. table iv shows the results of correlation and second criterion of validity, square ave. table i. factor loading, composite reliability and ave of second order factor analysis of it and advertising item factor loading item factor loading item factor loading item factor loading item factor loading item factor loading managerial 1 0.66 technical 1 0.84 relational 1 0.65 content1 0.81 tool 1 0.83 effect1 0.73 managerial 2 0.75 technical 2 0.87 relational 2 0.65 content2 0.86 tool 2 0.72 effect2 0.86 managerial 3 0.67 technical 3 0.89 relational 3 0.69 content3 0.79 tool 3 0.76 effect3 0.86 managerial 4 0.81 relational 4 0.70 managerial 5 0.74 relational 5 0.72 relational 6 0.78 relational 7 0.76 relational 8 0.67 cronbach’s alpha 0.77 0.83 0.85 0.75 0.76 0.75 ρc 0.85 0.90 0.89 0.86 0.82 0.86 ave 0.53 0.75 0.50 0.67 0.60 0.67 note: all factor loading is significant at the level 0.01 and above table ii. factor loading, composite reliability and ave of second order factor analysis of marketing mix item factor loading item factor loading item factor loading item factor loading product1 0.88 price 1 0.91 distribution 1 0.91 propaganda 1 0.85 product2 0.89 price 2 0.93 distribution 2 0.90 propaganda 1 0.89 product3 0.84 price3 0.90 distribution 3 0.85 propaganda 1 0.82 product4 0.90 distribution 4 0.88 cronbach’s alpha 0.90 0.90 0.91 0.82 ρc 0.93 0.94 0.93 0.89 ave 0.77 0.83 0.78 0.73 note: all factor loading is significant at the level 0.01 and above fig. 1. the second order of factor analysis of it engineering, technology & applied science research vol. 8, no. 1, 2018, 2526-2531 2529 www.etasr.com hosseini et al.: an assessment of the impact of information technology on marketing and advertising fig. 2. the second order of factor analysis of marketing mix fig. 3. the second order of factor analysis of advertising table iii. cross factor loading informational technology mix marketing advertising ave managerial 0.88 0.42 0.47 0.79 relational 0.88 0.56 0.55 technical 0.91 0.50 0.57 distribution 0.51 0.93 0.52 0.85 price 0.55 0.95 0.55 product 0.51 0.92 0.53 propaganda 0.49 0.89 0.46 content 0.54 0.50 0.86 0.77 effectiveness 0.52 0.53 0.90 tool 0.52 0.44 0.88 engineering, technology & applied science research vol. 8, no. 1, 2018, 2526-2531 2530 www.etasr.com hosseini et al.: an assessment of the impact of information technology on marketing and advertising table iv. correlation matrix and square ave of study variables informational technology mix marketing advertising informational technology 0.89 mix marketing 0.56 0.92 advertising 0.60 0.56 0.88 as shown in table iv, the square ave of all study variables is higher than their correlation with other variables. thus, second criterion of divergent validity of study variables is established. in addition, values below the diameter of correlation matrix are reported to evaluate the relationship between the variables. as shown, the correlation coefficient between variables is positive and significant. b. structural εquations μodeling τest to predict advertising, the conceptual model via structural equation modeling is evaluated and based on the study hypotheses and the partial least squares method is used to estimate the model. also, boot strap method (with 300 subsamples) is used to calculate the t-values to determine the significance of path coefficients. figure 4 shows the tested model of the relationship between study variables. as shown, the effect of it on marketing mix and advertising is positive and significant. the effect of marketing mix on advertising is positive and significant. table v shows the estimation of path coefficients and the variance of study variables. the values inside the parentheses are t coefficients. fig. 4. figure 4the tested model of study table v. path coefficients and variance variables path coefficients explained variance on advertising from marketing mix it 0.33** (4.19) 0.41** (5.39) 43% on marketing mix from it 0.56** (8.55) 31% the indirect effect of it on advertising via marketing mix 0.18** (3.76) *p<0.05, **p<0.01 in addition to the indices of table vi, total gof (goodness of fit) index of pls model is used to evaluate the reliability or quality of pls model as general. this index evaluates the total model prediction and whether the tested model is successful in the prediction of endogenous latent variables or not [16]. the present study has achieved gof index 0.55 and the value of fit indicates good fit of the tested model. the present study aimed to evaluate the effect of it on marketing and advertising by structural equations. the results showed that the proposed model has good fit with the study data and can explain 43% variance of advertising and 31% variance of marketing mix. results showed that technology had positive and significant effect on marketing mix and advertising. we can say that the adoption of new technologies, the promotion of it projects, the increase in key commercial technology use, the support in assignment of required resources to implement it strategy, the engineering, technology & applied science research vol. 8, no. 1, 2018, 2526-2531 2531 www.etasr.com hosseini et al.: an assessment of the impact of information technology on marketing and advertising consideration of it training for employees, lead to the improvement of marketing mix and advertising. results showed that marketing mix had positive and significant impact on advertising. we can say that if an organization decides to outperform the rivals, it should have suitable marketing strategies for success. marketing mix provides a set of controllable marketing tools to respond the target market, includes all the tasks a company performs to affect the demand and leads to the advertising improvement. table vi. cv-communality and cv-redundancy of variables study variables q2 (cv-redundancy) cv communality informational technology 0.794 mix marketing 0.266 0.851 advertising 0.249 0.774 v. conclusion recent media technological advances have led to great changes in the contemporary world and new concepts like information technology, explosion of information and information community have been included in world languages. within less than three decades, many outstanding transformations have occurred in the field of mass media. these transformations have also maximized the capacity of data transfer in terms either of information volume or transfer speeds. main concern nowadays is not the lack of information, but rather the way to find strategies to manage and regulate a large bulk of information. all social, political and economic institutions are bound to take big steps and try to adjust with the rapid pace of technological advances. development of communicative technologies in form of satellites, computers, cable tv, video conferences and computer networks have enabled people to access information more rapidly. therefore, it is important to investigate the impact of technology on different parts of the market and marketing. present research findings indicate that the new technology and its entrance into the marketing area have affected different aspects of marketing mix. according to marketing experts, advertising mix is the first part affected by the use of new technologies. the major role of advertising is to introduce a broad range of goods to the public and thus to reinforce the market economy. accordingly the impact of this part of technology as the results and fitness of different aspects of marketing mix show, have influenced other aspects of marketing mix like product, price and distribution. moreover, the results indicate that advertising and its components are affected by the new technologies. the advertising instruments according to the marketing experts have received the highest rate of effect. references [1] m. chatterji, technology transfer in developing countries, st. martin’s press, 1990 [2] m. mahmoudzadeh, managing the future with future technology, iran ιnstitute, 2001 [3] m. larsson, a. wall, c norstrom, i. crnkovic, “technology transfer: why some succeed and some don't”, 2006 international workshop on software technology transfer in software engineering, pp. 23-28, 2006 [4] r. d. stacey, strategic thinking and change management: international ideas on organizational dynamism, translated by mostafa jafari, rasa publication, 2010 [5] t. a. ismail, j. h. ahmad, “public relations vs advertising”, jurnal komunikasi, malaysian journal of communication, vol. 31, no. 2, pp. 117-130, 2015 [6] gary garrison, robin l wakefield, sanghyun kim, the effects of it capabilities and delivery model on cloud computing success and firm performance for cloud supported processes and operations, international journal of information management, vol. 35, no. 4, pp. 377-393, 2015 [7] m. de kare-silver, e-shock 2000: the electronic shopping revolution: strategies for retailers and manufacturers, springer, 1999 [8] h. rahman, l. han, customer satisfaction in e-commerce, a case study of china and bangladesh, msc thesis, university west, 2001 [9] p. timmers, electronic commerce: strategies and models for business to business trading, john willey & sond ltd, 2000 [10] m. hirt, p. willmott, “strategic principles for competing in the digital age”, mckinsey quarterly, vol. 5, no. 1, 2014 [11] d. l. hoffman, t. p. novak, “marketing in hypermedia computer mediated environments: conceptual foundations”, journal of marketing, vol. 60, no. 3, pp.50-68, 1996 [12] w. w. chin, b. l. marcolin, p. r. newsted, “a partial least squares latent variable modelling approach for measuring interaction effects: results from a monte carlo simulation study and an electronic-mail emotion/adoption study”, information systems research, vol. 14, no. 2, pp.189–217, 2003 [13] c. fornell, d. f. larcker, “evaluating structural equations models with unobservable variables and measurement error”, journal of marketing research, vol. 18, no. 1, pp. 39-50, 1981 [14] d. gefen, d. straub, “a practical guide to factorial validity using plsgraph: tutorial and annotated example”, communications of the association for information systems, vol. 16, no. 5, pp. 91–109, 2005 [15] w. w. chin, “commentary: issues and opinion on structural equation modeling”, mis quarterly, vol. 22, no. 1, pp. vii-xvi, 1998 [16] m. seyed abasszadeh, j. amani, h. k. azar, g. pashouy, “an introduction of structural equations modeling by pls method and its application in behavioral sciences”, oroumieh university publication, vol. 2, no. 1, pp. 126-139, 2012 microsoft word 319-863-1-sm-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 516-521 516 www.etasr.com sadeghikia and hodjat-kashani: a two element plasma antenna array a two element plasma antenna array f. sadeghikia aerospace research institute tehran, iran sadeghi_kia@ari.ac.ir f. hodjat-kashani department of electrical engineering iran university of science and technology kashani@iust.ac.ir abstract—this theoretical study presents the characteristics of plasma monopole antennas in the vhf/uhf range using finite difference time domain (fdtd) simulation. results show that more broadband characteristics can be obtained by increasing the diameter of the plasma tube and that the minor lobes diminish in intensity as diameter increases. furthermore, the nulls are replaced by low level radiation. since the collision frequency, which is a function of gas pressure, represents the loss mechanism of plasma, decreasing its value increases the gain and radar cross section (rcs) of the antenna. theoretical modeling shows that at higher plasma frequencies with respect to the signal frequency, the gain and radar cross section of the plasma antenna are high enough and that the impedance curves are altered as the plasma frequency varies. using these preliminary studies, mutual impedance and gain of a broadside array of two parallel side-byside plasma elements is presented. keywords-plasma antenna; radiation pattern; gain; input impedance; surface wave i. introduction plasma antennas represent a completely new class of antennas which employ ionized gas enclosed in a tube as the conducting element of the antenna. operating plasma antennas can transmit and receive through a surface wave driven (swd) plasma column [1-3]. therefore it could be possible for large stacked antennas with improved range precision to replace numerous small antennas, thus decreasing clutter, weight and interface. since plasma antennas have properties quite different from those of metallic conductors, the key plasma parameters should be determined and optimized with respect to the characteristics of antennas. however, there are limited numerical simulations in this regard [4-8]. numerical simulation is a powerful tool to evaluate, with maximum flexibility and minimal cost, the performance of these novel antennas. numerical analysis of a broadside array of two parallel side-by-side, equal in phase, current plasma elements is the subject of this theoretical study. in the first part of this paper, the radiation characteristics of a swd plasma monopole antenna are examined, considering the effects of variations of plasma frequency, collision frequency and radius of the tube on the gain, efficiency, input impedance and radar cross section (rcs) of the antenna, because few studies are reported in this regard [4-5]. further, the primary goals are to investigate efficiently the effects of gas pressure and the excitation power on the performance of a swd plasma antenna and to provide a better understanding of a linear array of plasma elements. these results should provide more insight to construct an effective array of plasma antennas. ii. simulation setup the geometry of the simulated plasma column antenna is illustrated in figure 1. the plasma column is inserted in a metallic box as a ground plane and a copper ring placed around the tube as a coupling sleeve for launching the signal. the length and radius of the column were chosen to be 600 mm and 12 mm respectively and the thickness and height of the coupling sleeve were 3 mm and 30 mm. the surface wave is launched applying an intense field between the coupling sleeve and the metallic box, and the results are reported in [8]. the dimensions of the metallic box were chosen to be 130 250 55 .mm× × the gap between the coupling sleeve and the metallic box is 5 mm. the fdtd problem space is 60 80 200× × cells and the waveform of the source is a modulated gaussian pulse. fig. 1. simulated plasma column antenna. the power flux of the wave in a swd plasma column decreases axially as power is gradually transferred to the discharge [1, 8-10] and the electron density steadily decreases from the launcher which has been shown previously experimentally [1] and theoretically [9]. consequently, the plasma column is axially non uniform and it will result in a non uniform conductivity along the column. this non uniformity of the swd plasma column is considered as a shortcoming and some remedies have been proposed to overcome it [11]. in this etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 516-521 517 www.etasr.com sadeghikia and hodjat-kashani: a two element plasma antenna array investigation, we have considered that the plasma density in the discharge tube remains uniform, which is an ideal condition. there are many different ways to simulate the electromagnetic interaction in plasma. in this case, the direct integration method (di) was used to simulate the isotropic cold plasma with a fixed uniform electron density [12]. in this method, the temporal evolution of plasma state is not taken into account and a weak electromagnetic wave propagates in a previously created plasma [6]. in di method, maxwell's equations are coupled to an auxiliary ordinary differential equation modeling the response of the current density, j, to the field, e as shown in (1)-(3). t h e ∂ ∂ −=×∇ � � 0µ (1) j t e h � � � + ∂ ∂ =×∇ 0ε (2) ej t j p �� � 2 0ωευ =+ ∂ ∂ (3) where e � and h � are the electric (v/m) and magnetic (a/m) fields, respectively, 0 µ is the magnetic permeability (h/m) of free space, 0 ε is the free space permittivity (f/m), υ is the average collision frequency (hz) and j � is the plasma current density (a/m 2 ). for details of the fdtd methodology, the reader is referred to [8, 13-14]. to calculate the rcs of a plasma antenna, we assume an arbitrary incidence and polarization plane wave as: rikj i ere . )ˆsinˆ(cos)( ϕαθα += (4) where α is the polarization angle, i k is the propagation vector given by: )ˆcosˆsinsinˆcos(sin0 zyxkk iiiiii θϕθϕθ ++= (5) and θ̂ and φ̂ are the unit vectors in the spherical coordinate system and ( , ) i i θ φ defines the angle of arrival of the plane wave. in the three dimensional case, the rcs is defined as [15]: 2 22 2 ),,(),,( (4lim),( i ss r e rere rrcs ϕθϕθ πϕθ ϕθ + = ∞→ (6) to validate our fdtd program, rcs of a plasma monopole antenna with fp=70 ghz and collision frequency of 10 ghz is compared with those of cgfft numerical results which were simulated in [7], as shown in figure 2. in this comparison we considered the radius of the plasma column r=5 mm, dielectric constant of plasma tube 3.4 r ε = and thickness of the column as 2 mm. comparison between our fdtd simulation and cgfft result shows close agreement between the two different codes. 1 2 3 4 5 6 7 -40 -30 -20 -10 frequency (ghz) r c s ( d b ) cg-fft method [7] fdtd numerical simulation fig. 2. comparison between rcs of a plasma column antenna with fdtd numerical simulation and cg-fft method results. iii. numerical results and discussion a. the effects of the radius of the plasma column numerical simulation of a plasma antenna, as shown in figure 3, reveals that in a swd plasma monopole antenna, similar to a conventional metallic radiator, one method to widen the acceptable operational bandwidth will be to decrease the rl / ratio [16], where l is the length of the plasma antenna and r is the radius of the tube. it has been observed that for a given length of a plasma column, its impedance variations becomes less sensitive as a function of frequency as rl / decreases. thus, more broadband characteristics can be obtained by increasing the diameter of the plasma tube, similar to metallic conventional antennas. to demonstrate this, in figure 3a, we have plotted, as a function of frequency, the input impedance of plasma monopole antenna with 70/ =rl , 34 and 23. when the plasma frequency is large enough with respect to the excitation frequency, the imaginary part of the input impedance of plasma antenna can be eliminated by making the total length l of the antenna less than 4λ , where λ is the wavelength. this value is approximately 0.18 ,fλ ′ when the plasma frequency is 7500 mhz and rl rl f /1 / + =′ . however, its value increases by increasing the plasma frequency and consequently conductivity of the plasma while for the maximum conductivity this value becomes 0.24 fλ ′ [16]. in figure 3a it is observed that increasing the radius of the column decreases the resistance at the first resonance. the radiation pattern is essentially unaffected by the thickness of the plasma tube in the regions of intense radiation. however, as the radius of the tube increases, the minor lobes diminish in intensity and the nulls are replaced by low level radiation as shown in figure 3b. b. the effects of the collision frequency the collision frequency is a function of pressure and represents the loss mechanism of plasma. it depends on the type of gas and the average number of the particles. there are etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 516-521 518 www.etasr.com sadeghikia and hodjat-kashani: a two element plasma antenna array various kinds of collisions in plasma whereas their evaluation is complicated and is not reported here. readers interested in this subject can refer to [17]. the complex plasma conductivity is stated as: υω ωε ωσ + = j p 2 0 )( (7) where, 2 0 2 /p pf $e mω π ε= = in which pf is the plasma resonant frequency (hz), $ is the electron density (m -3 ), υ is the average collision frequency (hz), 0ε is the free space permittivity (f/m), e and m are the electron charge (c) and mass (kg), respectively. (a) 50 100 150 200 250 -150 -100 -50 0 50 100 150 frequency (mhz) in p u t i m p e d a n c e ( o h m s ) l / r = 70 l / r = 34 l / r = 23 (b) -40 -20 0 20 30 60 90 270 300 330 l / r = 70 l / r = 34 l / r = 23 fig. 3. the effects of the variations of the diameter of plasma tube, in the plasma frequency of 7500 mhz and collision frequency of 400 mhz, on (a) input impedance, (b) radiation pattern when the length of antenna is 3 / 2λ . in a certain plasma frequency the conductivity of the plasma column decreases as the collision frequency increases and it affects all characteristics of a plasma antenna. increasing the collision frequency from 200 mhz to 1000 mhz, in a fixed plasma frequency, decreases the gain of the plasma antenna, as illustrated in figure 4a, which is due to the increased loss in the plasma column. the gain of a plasma monopole antenna, in our case, is less than that of a conventional metallic antenna and their difference increases as frequency increases. this means that at lower lengths plasma antenna operates more effectively than at higher lengths. stealth application of a plasma antenna has high priority over its different applications. numerical investigation of the impact of collision frequency on the rcs of a plasma antenna, as shown in figure 4.b, reveals that rcs reduces with increasing the collision frequency which is due to the reduced conductivity of the antenna. therefore, a larger collision frequency is preferable for the purpose of rcs reduction. it is conceivable to optimize the plasma rcs by controlling the plasma collision frequency for practical applications. in our simulations, the incident plane wave is with 180 , o i θ = 0 , o i φ = 0 o α = . (a) 0.5 1 1.5 -2 0 2 4 6 8 10 antenna length (wavelength) g a in ( d b ) collision = 200 mhz collision = 600mhz collision = 1000mhz metallic antenna (b) 100 200 300 400 500 600 700 800 -15 -10 -5 0 5 10 frequency (mhz) r c s ( d b ) collision = 200mhz collision = 600mhz collision = 1000mhz metallic antenna (c) 100 200 300 400 500 600 700 800 0 20 40 60 80 frequency (mhz) e ff ic ie n c y ( % ) collision = 200 mhz collision = 400 mhz collision = 1000mhz (d) 50 100 150 200 250 300 350 -100 0 100 200 frequency (mhz) i n p u t i m p e d a n c e ( o h m s ) collision = 200 mhz collision = 600 mhz collision = 1000mhz fig. 4. characteristics of a plasma antenna when the plasma frequency is 7500 p f ghz= and at different collision frequencies (a) gain, (b) rcs, (c) efficiency and (d) input impedance. etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 516-521 519 www.etasr.com sadeghikia and hodjat-kashani: a two element plasma antenna array the efficiency of the plasma antennas is a key parameter to evaluate the possibility of using a plasma element instead of a metallic one. the efficiency takes into account the losses at the input terminal and the structure of the antenna and is directly related to plasma conductivity. due to the much lower conductivity of the plasma, at higher collision frequencies the efficiency of the antenna decreases, as shown in figure 4c. it is noted that the radiation pattern of a plasma antenna is essentially unaffected by the variation of the collision frequency. however, as the collision frequency increases, the minor lobes diminish in intensity and the nulls are replaced by low level radiation. when the plasma frequency is small, at low collision frequencies, the input impedance of the antenna has a lot of oscillations which decrease when collision frequency increases. the collision loss of plasma increases the loss of the antenna, resulting in a reduced radiated power and damping the impedance variations. therefore, increasing the collision frequency increases the bandwidth of the plasma antenna. however, the collision frequency does not influence the period of resonance as shown in figure 4d. this may be considered as one of the useful methods which can be used for a dynamic control of an antenna bandwidth by varying the q-factor of the antenna. c. the effects of the plasma frequency measurements of plasma electron number density using langmuir probes have proved that the increase of input rf power at a fixed filling gas pressure increases the plasma density in the column [18, 19] and plasma frequency is a function of plasma density. increasing the plasma frequency in the column increases the conductivity and consequently it causes considerable increment in the values of the gain, rcs and efficiency of a plasma antenna. at higher plasma frequencies with respect to the excitation frequency, the gain and the rcs of a plasma antenna are as high as of a metallic antenna. the variations of the gain, rcs and efficiency of a plasma antenna versus the plasma frequency, in the collision frequency of 400 mhz, are shown in figures 5a-5c. comparison between the radiation patterns of a plasma antenna with 23λ=l at different plasma frequencies with a metallic antenna (figure 5d) shows that in the plasma antenna, the numbers of lobes are increased up to those of a conventional metallic antenna when the plasma frequency increases and also that the radiation pattern finds deeper nulls. at higher plasma frequencies, the radiation pattern becomes more similar to that of a metallic one. furthermore, an interesting phenomenon is observed when 2.5 p f f < . whereas the metallic monopole antenna does not radiate energy along the monopole axis, the plasma antenna radiates thus showing the characteristics of an end fire antenna, as was introduced before in [4] and [20]. this occurs because the radiating source is a surface wave along the column. the plasma column does not carry a current, but a surface wave propagates along the column and reaches its tip. therefore, it contributes the radiation towards the end fire direction, as shown in figure 5d and increasing the collision frequency, increases this property. this narrow cone beam is associated with the least antenna efficiency as was shown in figure 5c (the dotted line where 1500 mhz p f = ), so it is not of practical interest. numerical simulation reveals that the input impedance curves of the antenna, as shown in figure 5e, are altered as the plasma frequency varies. this property can be used to construct dynamically reconfigurable antennas. d. a linear array of two plasma elements essential background for this section is covered in the previous sections and the 'elements' are swd plasma monopole antennas with a radius of 12 mm and a length of 600 mm at the plasma frequency of 7500 mhz and the collision frequency of 400 mhz. a broadside array of two parallel side-by-side, equal in phase current elements has been analyzed numerically. let d be the separation of elements. referring to the arrangement of figure 6a, the mutual resistance 12 r and reactance 12 x of the first resonant frequency of the antenna are presented in figure 6b as a function of the spacing d. moreover, the quantity 11 12 r r+ , which is important in this array calculation is also illustrated, where 11 r is the self impedance of the elements. it is worthy to mention that at the spacing 0.45 0.52d< < between the elements, the total resistance is in its minimum value around 28.5; which is incorporated with the maximum array gain as shown in figure 6c. iv. conclusion numerical simulation of the characteristics of a plasma column antenna, when the plasma density is uniform in the column, has been established in this paper. numerical simulation was validated through comparisons with other investigations. it has been shown that for a fixed excitation power, the variation of gas pressure, which varies the collision frequency, changes antenna characteristics. increasing the collision frequency decreases antenna gain, rcs, efficiency and peak input impedance and it may be considered as one of the useful methods which can be used for a dynamic control of an antenna bandwidth. from the computed numerical results it is clear that increasing the excitation power, which increases the plasma frequency, increases the conductivity and consequently it causes considerable increment in the values of gain, rcs and efficiency of the antenna. moreover, it can be considered as a powerful tool to construct dynamically reconfigurable antennas because the impedance curves are altered as plasma frequency varies. variations of the radii of the plasma column have non negligible effects on the antenna characteristics. increasing the radius of the tube can be considered as a method to widen the acceptable operational bandwidth of the antenna and replacing the nulls in the radiation pattern by low level radiation. finally, we have presented the mutual impedance and gain of a broadside array of two parallel side-by-side, equal in phase current swd plasma monopole antenna and it was concluded that maximum gain will be achieved when the spacing between elements is around 2/λ . etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 516-521 520 www.etasr.com sadeghikia and hodjat-kashani: a two element plasma antenna array (a) 0.5 1 1.5 -40 -30 -20 -10 0 10 antenna length (wavelengths) g a in ( d b ) fp = 1500mhz fp = 3500mhz fp = 7500mhz metallic antenna (b) 0.5 1 1.5 -25 -20 -15 -10 -5 0 5 10 antenna length (wavelengths) r c s ( d b ) fp = 1500mhz fp = 3500mhz fp = 7500mhz metallic antenna (c) 100 200 300 400 500 600 700 0 20 40 60 80 frequency (mhz) e ff ic ie n c y ( % ) fp = 1500 mhz fp = 3500 mhz fp = 7500mhz (d) (e) 50 100 150 200 250 300 350 -200 -100 0 100 200 frequency (mhz) i n p u t im p e d a n c e ( o h m s ) fp = 2500 mhz fp = 6500 mhz fp = 20500 mhz metal antenna fig. 5. the effects of the plasma frequency on the characteristics of a plasma antenna at the collision frequency of 400 mhz: (a) gain, (b) rcs, (c) efficiency, (d) radiation pattern and (e) input impedance. 0 0.2 0.4 0.6 0.8 1 -100 -50 0 50 distance between elements, d/lambda m u tu a l im p e d a n c e ( o h m s ) r12 r11+r12 x12 0.2 0.4 0.6 0.8 1 1.5 2 2.5 3 3.5 4 distance between elements, d/lambda g a in ( d b ) (a) (b) (c) fig. 6. 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“fundamental limitation on excitation of a surface wave on a plasma column”, ieee antennas and propagation society international symposium, texas, usa, vol. 4, pp. 272-275, 2002 microsoft word 07-3250_s_etasr_v10_n1_pp5132-5141 engineering, technology & applied science research vol. 10, no. 2, 2020, 5132-5141 5132 www.etasr.com alamer & soh: design and implementation of a statistical testing framework for a lightweight … design and implementation of a statistical testing framework for a lightweight stream cipher ahmed alamer department of computer science and information technology, school of engineering and mathematical sciences, la trobe university, victoria, australia and department of mathematics, tabuk university, saudi arabia a.alamer@latrobe.edu.au ben soh department of computer science and information technology, school of engineering and mathematical sciences, la trobe university, victoria, australia b.soh@latrobe.edu.au abstract—the shrinking generator (sg) is a popular synchronous, lightweight stream cipher that uses minimal computing power. however, its strengths and weaknesses have not been studied in detail. this paper proposes a statistical testing framework to assess attacks on the sg. the framework consists of a d-monomial test that is adapted to sg by applying the algebraic normal form (anf) representation of boolean functions, a test that uses the maximal degree monomial test to determine whether the anf follows the proper mixing of bit values, and a proposed unique window size (uws) scheme to test the randomness properties of the keystream. the proposed framework shows significant weaknesses in the sg output in terms of dependence between the controlling linear-feedback shift register (lfsr) and non-linearity of the resulting keystream. the maximal degree monomial test provides a better understanding of the optimal points of sg, demonstrating when it is at its best and worst according to the first couple of results. this paper uses uws to illustrate the effect of the lfsr choice on possibly distinguishing attacks on the sg. the results confirm that the proposed uws scheme is a viable measure of the cryptographic strength of a stream cipher. due to the importance of predictability and effective tools, we used neural network models to simulate the input data for the pseudo-random binary sequences. through the calculation of uws, we obtained solid results for the predictions. keywords-stream ciphers; randomness testing; shrinking generator; cryptanalysis i. introduction cryptography is used to transform information from plain text to cipher text and vice versa in order to prevent unauthorized access to information [1, 2]. this paper focuses on symmetric encryption, specifically synchronous stream ciphers, of which the shrinking generator (sg) is an example. the sg functions use two linear-feedback shift registers (lfsrs). lfsra generates the output bits and lfsrb generates the controlling bits. the bit from lfsra is output as part of the keystream whenever the bit from lfsrb is 1, otherwise the output is not selected by the cipher. although some might argue that the sg is an old form of cipher technology, it is significant as a foundation for other variants of ciphers, such as the self-shrinking generator (ssg) [3] and its variations. consequently, the sg is still studied, and its practical advantages continue to be appreciated. for example, researchers recently examined the sg from a cellular automaton point of view [4]. while the study was simplistic in its approach, the sg was nonetheless useful. provided the key is unknown, the only method that can attack the sg is an exhaustive search. the sg continues to attract interest because of its reputation as a standard and a model for enlightening cryptanalysis techniques. lessons learned from the sg can be transferred to the cryptanalysis of other cipher techniques. ii. background the sg is a lightweight stream cipher that uses minimal computing power [5]. it has been applied in various practical settings, such as radio frequency-based identification systems (e.g. in bluetooth protocol) and in microsoft word, excel, etc. this study follows the summarized presentation of the sg in accordance with [6]. the sg was first introduced in [7]. it is composed of two shift registers, namely shift register b (which is used as s in their paper), lfsrs and lfsra. lfsrb is designated as a control register that orchestrates what is produced by lfsra. to illustrate this, {��} represents the bits produced by lfsrb, {��} represents the bits produced by lfsra and {��} is the final output produced by the sequence. thus, the final bit sequence will follow this rule: if ��=1, then ��= ��, else if ��=0, then �� is discarded (i.e. the bit is skipped). prior attacks on the sg were studied in [6, 8–10] among others. this paper presents the lessons learned in subjecting the sg to testing methods that have not been previously applied to it. it relays the newly discovered weaknesses of the sg which may be used to strengthen its succeeding variations. lightweight encryption is important for small devices with limited computation power and is more effective than using the more popular advanced encryption standard (aes), which consumes more computation power [11]. thus, the lightweight encryption algorithm sg and its security flaws are the focus of this study. iii. using the d-monomial test as mentioned above, the sg produces a sequence of ciphertexts in bits dictated by two lfsr registers. for this reason, the sg falls under the category of ciphers defined by boolean functions. these boolean functions may be examined corresponding author: ahmed alamer engineering, technology & applied science research vol. 10, no. 2, 2020, 5132-5141 5133 www.etasr.com alamer & soh: design and implementation of a statistical testing framework for a lightweight … using their algebraic normal form (anf). in 2002, the authors of [12] introduced a d-monomial test that examines the randomness of the anf of boolean functions. many researchers have considered this test as the most appropriate for examining anfs. it has been used to detect the bias found in gate complexities, which can be represented by boolean functions, and it has been extended to stream ciphers using initialisation vectors (ivs) [13]. further, this test has been applied using polynomial description to find monomials of degree d, where � = 1,2,…, per polynomial, to find the weaknesses in several other stream ciphers not dealt with by the sg, such as the ciphers trivium and grain [14]. because the sg is a boolean function that can be expressed in anf, the first hurdle that needs to be cleared by the sg is the dmonomial test, which we have specifically adapted for our purpose of examining the sg. a. our approach to the d-monomial test the treatment of this subject in [13] explains the work of [12] and their own adoptions of the tests. the fundamental idea behind our approach is that each bit of the sg output is viewed as a boolean function of all different key variables (i.e. the initial loading of the lfsr). given a boolean function ��� ⟶ ��, and vector � with �� as an element, we have: ����� = ��⨁���� ⨁…⨁����⨁�����������,…,��. (1) this function can be transformed as: �∧���� = ∑ ����∏ ��#$��%�#∈�'� (2) where �∧ is a multivariate polynomial representation of �. the expression of �∧ is used for convenience in finding the algebraic form of �, as this is generally given in a truth table. this expression of �∧ is comprised of permutations of monomials in ��. this is also based on the original boolean function f. the subjects of this test are these monomials. the d in this test pertains to the number of non-zero bits in the boolean string. it is the hamming weight (i.e. the length of the longest monomial in the anf). practically speaking, this test involves counting the number of �∧���� = 1 with hamming weight �. moreover, the keystream length of the sg is ( = *2+ – 1-�2.���, where / is the degree of (0123, and 4 is the degree of (0125 . this length is not a power of 2, so the largest boolean function we can use is obtained by taking the largest power of 2 less than ( as the length of the truth table. thus, we use: 67#8 = 9:;<��2+ − 1�.2.��> (3) and choose ≤ 67#8 for the boolean representations of the relevant cryptographic bits. in general, �����,…,��� is the boolean function representing the @.a output bit ��@� of the keystream ���, ��,…� of an sg. as the key b = ���,…,��� ranges over ���, the @.a bit of the keystream produces the anf of the boolean function ��. we can then use fast möbius transform to compute it for each � that we choose to represent. as shown in [12], the number of weight d monomials that appear in the anf of a random function has an approximately normal distribution, as follows: c d��*�e-, �� f*�e g (4) the author of [12] proposed h� testing to examine this property based on the null hypothesis that the original boolean function � is not random (i.e. comes from a known distribution). in the context of this study, when we describe the test as passing, this means we can reject h0. for example 1, lfsra corresponds to (�� + � + 1) and lfsrs to (�l + � + 1) as characteristic polynomials. we initialized both lfsrs with all possible values and then used (3), which yielded keystream length 56, which means we had a truth table of length 32. we then used möbius transform to obtain the anf. next, we examined every monomial weight to calculate how many exist per function, and we applied the h� tests. for the algorithm for this test and other monomial tests, see [14], in which these tests to iv-based ciphers using iv were applied. in our case, we used the initial lfsrs’ loading, while authors in [15] performed this test on the ssg, which is a variant of the sg. however, the test had to be adapted because there are two lfsrs in the sg to generate the keystream but only one in the ssg. for the monomial distribution test, we needed to count the number of monomials across all functions. we performed this calculation using the anf representation of the functions. for a particular monomial (say x1x3), we counted how many functions contain that monomial. finally, we compared the monomial count with the expected monomial distribution [14]. in short, the difference between the two tests is that in the �monomial test, we counted the number of monomials with a certain weight for each function. b. our experiments for the d-monomial test to perform this test, we set up all combinations of pairs of primitive lfsrs with relatively prime lengths and applied three different scenarios: • we initialized both lfsrs with all possible random values. • we fixed the control lfsrb with chosen values and varied lfsra with all possible random values. • we fixed the input lfsra with chosen values and varied lfsrb with all possible random values. for each lfsr combination, in each scenario, we created a truth table of the maximal length possible given the applicable keyspace and the limitation form from (3). we performed exhaustive computations for all admissible pairs of primitive lfsrs, and we tested the sg outputs corresponding to lfsrs of combined length up to n=19. as tables ii and iii show, certain bit functions failed the randomness test at 0.01 and 0.05 levels of significance, therefore they have an anf that is far from that expected of a random function. note that for lfsrs of combined length 16–19, we took half of the maximum keystream length possible and therefore half as many ��o because of memory constraints in the computations. the examples in tables ii and iii illustrate the �-monomial test. for the results of this test for sg degrees 7–15 with full keystream output applying (3), we used the ssg results from [15] for engineering, technology & applied science research vol. 10, no. 2, 2020, 5132-5141 5134 www.etasr.com alamer & soh: design and implementation of a statistical testing framework for a lightweight … comparison (see table i, last column). for degrees 16–19, we used half of the keystream outputs and applied (3) (see table ii). by applying the monomial distribution test to the first example, we found that the keystream fails in 16 out of 24 pairs for sg with degree 7, therefore the passing percentage is approximately 33.33%. more extensive results are reported later in this paper for higher degrees. table i. d-monomial test for sg degrees 7–15, with full keystream output using h� test, displayed with ssg results from [15] for comparison sg degree number of lfsrs pairs number of fi fails at α=0.01 total passes passing percentage ssg passing percentage 7 24 768 251 505 67310% 98.6% 8 72 4608 1561 2255 66124% 9 72 9216 3121 4329 66135% 10 216 55296 27847 27359 49640% 11 624 319488 55203 198895 82721% 12 648 663552 339627 206071 48817% 99.8% 13 2520 5160960 2831437 2083684 45137% 14 3840 15728640 7938000 6542587 49531% 99.9% 15 3840 31457280 18213724 13183968 42100% table ii. d-monomial test for sg degrees 16–19, with half of keystream output using h� test sg degree number of lfsrs pairs number of fifififi fails at α=0.01 passing percentage 16 50 409600 198895 51441% 17 50 819200 510001 37744% 18 50 1638400 932719 43071% 19 50 1114112 655568 41158% table iii. exhaustive testing results for maximal monomial test for combined lfsr lengths 7-9 lfsra lfsrb observed with fixed lfsrb observed with fixed lfsra number of functions �� + �� + 1 �l + �� + 1 0 12 32 �l + �� + 1 �� + �� + 1 0 14 32 �l + �� + 1 �� + � + 1 0 14 32 �l + � + 1 �� + �� + 1 0 16 32 �l + �� + 1 �r + �� + 1 0 66 128 �l + �� + 1 �r + �� + 1 0 66 128 �r + �� + 1 �l + � + 1 0 70 128 �r + �� + 1 �l + �� + 1 0 68 128 c. maximal degree monomial test the maximal degree monomial is the monomial where all variables are factors in the term. thus, when taking a binomial function’s anf for variables ��,��,��, the maximal degree monomial will be the term �s������ (�s is the coefficient of the term with maximum weight). this monomial may not be present in an arbitrary anf. it is unlikely to exist if lower degree monomials do not exist, but its existence is an indication of how the anf follows proper mixing of bit values. it is therefore worth testing. here, we followed [14], which demonstrated that the maximal degree monomial may be detected using the reed-muller transform by conducting an xor of all entries in the truth table. the existence of this monomial may be checked by xoring the first keystream bit from the initialisation. we then determined whether this exists in the output of the cipher. see [14] for a full description of this test. the results are presented in table iii and discussed below. d. discussion of d-monomial and maximal degree monomial tests for the higher degrees of 16–19, we chose 50 lfsr pairs and used the first half of the keystream output *2+ – 1-�2.��� bits to derive the maximal boolean function possible, which was then subjected to the �-monomial test. this was done for computational efficiency. table i shows that varying percentages of keystream bits ��, from 18–58%, failed the �monomial test at significance level α=0.01. we also carried out a limited d-monomial test on the ssg for comparison (table i). this exhaustive testing provided further evidence that the sg is much weaker than the ssg. although the data in table ii are not exhaustive, they show that the same kind of failure rates continued for the d-monomial test applied to 16–19 sg degrees at t=0.01 significance level. we performed a maximal degree monomial test for sg degrees 7–15 and presented a chosen sample for lfsr pairs of degrees 7–9. the maximal degree monomial occurred roughly between 37% (12 of 32, indicated by dividing the number in column 4 with column 5) to 54.6% (70 of 128). we observed that if lfsrs (the controlling lfsr) is fixed, the output is linear, and thus no monomial of degree ≥1 appears, which directly rules out the maximal degree monomial. in summary, it is ideal for an sg to have a high degree of monomials because this makes more difficult to guess the boolean function behind it. however, as shown in table i, the percentage of passing samples decreases with higher degrees, meaning that the failure to be random becomes high. conversely, we can keep the degree of the monomials low, which the data show to have a high pass rate, however this has the disadvantage of being computationally easy to break. iv. testing for the unique window size the unique window size (uws) of a keystream is the minimal length w where every observed window of length w in the keystream is unique. an m-sequence (pseudorandom binary sequence) of period 2n-1 is generated by an lfsr of length n. thus, � = *��0�, …,��u − 1�∈ ��� is an arbitrary u -tuple over ���, where 1 ≤ u ≤ then we used the function: 6��� = v2��w @� � ≠ �0,0,…,0� 2��w − 1 y:�y (5) where 6��� denotes the number of times the k-tuple a appears as a ‘window’ *��@�,��@ + 1�,… .��@ + u − 1� of the msequence *��4�-.z�. therefore, it is a count of repetitions of the tuple that appear in the keystream. for an lfsr, the uws is trivially n+1 where is the length of the lfsr. further, if we let the lfsrs in the sg be run for a full period, that is, for *2+ – 1-�2.��� output bits, this corresponded to about twice as many clock cycles, namely �2+ − 1��2. − 1� cycles, since / and 4 were chosen to be relatively prime. this means that the state space is the product of the two state spaces. in the following example, we investigated the uws distribution for the sg. for example 2, lfsra was �� + � + 1 and lfsrb was �l + � + 1 with initial states of 001 and 0001, respectively. the lfsra output was engineering, technology & applied science research vol. 10, no. 2, 2020, 5132-5141 5135 www.etasr.com alamer & soh: design and implementation of a statistical testing framework for a lightweight … 0011101 and the lfsrb output was 000111101011001. therefore, the sg output (keystream) was 11010110101011000100101110011101001100010111101011 100111. next we found the uws, which in this case was 11. we examined the uws for a certain degree (i.e. the total length of the two lfsrs) for sg. for example, for degree 8, we could see that the uws was not well-distributed. there was a large variation in size (table iv). table vi shows the uws computations for the different lfsrs combinations for sg with degree 8. table iv. uws count for sg keystream of degree 8 where the average of uws is 13.25 uws 11 12 13 14 15 16 count 4 6 4 2 6 2 a. uws tests: results, statistical tests and observations we performed exhaustive testing of the uws distribution for the sg keystream using algorithm 1: algorithm 1 uws algorithm given a periodic bit sequence b[i] with period p, the uws algorithm calculates the uws. given: b = periodic bit sequence, p = period of b. calculate: l = minimum subsequence length such that all l-bit subsequences are unique. initialize l with 1. repeat for each bit index, i of b do test for each bit index, j of b greater than i do if l-bit subsequence of b starting at i = l-bit subsequence of b starting at j then increment l continue the next repeat loop end if end for end for until all l-bit subsequence of b are unique. return l authors in [15] introduced general observations, whereas we conducted deeper analysis with more tests and investigations to produce a greater understanding of the sg’s weaknesses based on tests and predictions applied on the uws. figure 1 shows the uws, also called the minimal window size, for degree 20 of the sg. we ran the computations for 70,416 lfsrs pairs. as shown in figure 1, the uws is concentrated between 37 and 41. this means that it is highly likely to be concentrated below approximately 2n, where n is the combined degree of the sg, indicating that a distinguishing attack on sg may be feasible. as shown in [16], uws is a very good indicator of the randomness of a keystream. this relationship is discussed below. to explain the maximum order complexity of a given sequence 1, it is necessary to find the possible shortest fsr that can produce 1. this concept was introduced in [17] in 1990. thus, for 1, the maximum order complexity is equal to 1+l, where : represents the longest s ⊂ s length that can be found twice within s, and that is our uws. the authors of [17] found an approximation of maximum order complexity distribution of a chosen pseudorandom binary sequence. more importantly for our purposes, the uws dependence on the choice of polynomials is an indicator that there might be a possible distinguishing attack based on this variability. of course, the lfsr polynomials are public knowledge, by kerchoff’s principle, and this can be used as a guide in choosing good polynomials from the vast number of choices φ ������ � for degree . if the sg user broke kerchoff’s principles and kept the polynomials secret, as is sometimes ill-advisedly suggested, the investigation of the uws would enable an attacker to mount an attack more efficient than the brute force attack on the polynomials. recall that when the polynomials are kept secret, their degree sequences can be considered a part of the key, squaring the search space for brute force attacks. the uws enables one to search a much more limited set of polynomials. see table v for uws distribution in the sg keystreams of degree 15. fig. 1. uws distribution for degree 20 b. statistical distribution and prediction modeling using easyfit and r software, we confirmed that the uws of degree 20 (uws20) was skewed (see figure 1). in fact, it approximately follows a lognormal distribution, as presented in figure 2. the distribution function of lognormal distribution is given by: c�ln�;_,`� � abcd� �efghi�' 'j' k l√�n (6) given that the sg keystream’s uws exhibits an approximate lognormal distribution, we can follow standard confidence interval information, such as the 68-95-99.7 rule, in determining the range of probable uws values in the keystream by taking the log of uws. using the bartel rank test, cox stuart test, rank test and runs test, we found that the sequence of data (uws20) is a non-random sequence (p<0.001). this indicates that this sequence of data could be predicted using statistical models. we then used several methods to learn about the pattern and predict the sequence, engineering, technology & applied science research vol. 10, no. 2, 2020, 5132-5141 5136 www.etasr.com alamer & soh: design and implementation of a statistical testing framework for a lightweight … namely: 1. generating a theoretical lognormal sequence from the mean and standard deviation of observed data of the same length and comparing the accuracy of prediction, 2. using a linear regression method to predict and check the accuracy of the predicted sequence, and 3. using a non-linear (nonparametric regression) method to predict and check the accuracy of the predicted sequence (including validation and calibration). fig. 2. comparison of cdfs of observed and theoretical distributions, uws20 table v. uws count for sg keystream of degree 15 uws count uws count 24 4 34 48 25 52 35 32 26 112 36 12 27 166 37 20 28 232 38 4 29 168 39 6 30 146 40 4 31 116 42 10 32 92 45 2 33 54 1) method 1 here, we used r software to generate an equal number of observations (70,416) from lognormal distribution using the mean and standard deviation of observed uws20. we then differentiated between observed uws20 and simulated uws20 and compared the accuracy (the difference between the observed and simulated predicted uws20 being 0). the accuracy was 7.8%, which was expected, as uws20 was found to be non-random. hence, a random sequence may not entirely predict the sequence. 2) method 2 we used the linear regression model, where the outcome was uws20 and the explanatory variables were input degree, input weight, control degree, control weight, input polynomial, and control polynomial. each input and control polynomial variables had polynomials of up to 17 degrees and hence produced 17 separate binary variables based on the possible terms in a primitive polynomial of degree 17 (for an sg with degree 20, the highest lfsr degree is 17 and the lowest is 3 for a primitive polynomials combination). step 1 of method 2 was to extract 34 variables from the input and control polynomials and add them to four other independent variables to form a pool of independent variables. in step 2, we ran a simple linear regression model on each of suitable candidates for the multi-variable linear regression model. the input degree was found to be the strongest predictor because it had the highest r-square value and accuracy rate. interestingly, it was highly correlated with the control degree and, as such, the two cannot be put together in the same model. this means that control degree and input degree as variables are correlated, or input degree =�(control degree), so just one of them is necessary. table vi. uws computations for degree 8 with lfrps pairs input lfsra control lfsrb uws �� k � k 1 �r k �� k 1 13 �� k � k 1 �r k �� k 1 15 �� k � k 1 �r k �� k �� k � k 1 11 �� k � k 1 �r k �l k �� k � k 1 14 �� k � k 1 �r k �l k �� k � k 1 12 �� k � k 1 �r k �l k �� k �� k 1 15 �� k �� k 1 �r k �� k 1 15 �� k �� k 1 �r k �� k 1 13 �� k �� k 1 �r k �� k �� k � k 1 15 �� k �� k 1 �r k �l k �� k � k 1 12 �� k �� k 1 �r k �l k �� k � k 1 14 �� k �� k 1 �r k �l k �� k �� k 1 11 �r k �� k 1 �� k � k 1 16 �r k �� k 1 �� k �� k 1 12 �r k �� k 1 �� k � k 1 12 �r k �� k 1 �� k �� k 1 16 �r k �� k �� k � k 1 �� k � k 1 15 �r k �� k �� k � k 1 �� k �� k 1 13 �r k �l k �� k � k 1 �� k � k 1 12 �r k �l k �� k � k 1 �� k �� k 1 11 �r k �l k �� k � k 1 �� k � k 1 11 �r k �l k �� k � k 1 �� k �� k 1 12 �r k �l k �� k �� k 1 �� k � k 1 13 �r k �l k �� k �� k 1 �� k �� k 1 15 in step 3, we calculated and analyzed the multicollinearity among the univariable significant variables to determine which variables had to be discarded from the multi-variable regression model. multicollinearity is defined here as high correlation among explanatory variables, which can be assessed from a matrix of correlation coefficients of the explanatory variables along with p values. we discarded the control degree, input polynomial of degree 14 and control polynomial of degree 17 from the model due to multicollinearity with other covariates. we also checked first order interaction. in step 4, a backward stepwise multi-variable regression model was run with the suitable variables for the prediction of uws20. we could then retain 24 variables (in the model), which were used in our final predictive model. predicted:log(uws20)=3.9541011-inputdegree*0.0121524+ inputweight*0.0005625-controlweight*0.1042675 input1 * 0.0023569 + input11 * 0.0051394 -input12 * 0.0057957 engineering, technology & applied science research vol. 10, no. 2, 2020, 5132-5141 5137 www.etasr.com alamer & soh: design and implementation of a statistical testing framework for a lightweight … input13 * 0.0122590 input17 *0.0106996 + control1 * 0.1060109 + control2 * 0.1035639 +control3 * 0.1034507 + control4 * 0.1062923 + control5 *0.1051447 + control6 * 0.1061192 + control7 * 0.1001495 +control8 * 0.1053034 + control9 * 0.1104407 + control10 *0.1036258 + control11 * 0.1058865 + control12 *0.0999843 + control13 * 0.0953821 + control14 * 0.1055764 + control15 * 0.1042613 + control16 * 0.1049406 input 17 refers to the term of power 17 in the input lfsr and similarly in control 17 (the number indicates the power of term in the given polynomial). using the above model, uws20 can be predicted by inserting the values of the variables in the model. a numerical value must be inserted for numerical variables, with 0 = absence and 1 = presence. this model can be used as a selection tool for the lfsrs pairs by choosing two primitive polynomials and inserting their parameters in the model to see if the uws is high enough for the chosen pairs. in step 5, bootstrap validated bias was used to correct the adjusted r-square and assess the discrimination. calibration graphs were produced to assess the calibration of the model. these were done using the rms package in r. afterwards, we measured the accuracy with respect to the difference of observed and predicted uws20. sensitivity analysis was performed to ensure that the effect of a relatively smaller sample size on prediction capabilities was not detrimental. hence, we randomly selected 50%, 25%, and 10% of the data and performed the above calculations again to check the accuracy and performance of the prediction model. in method 2, the accuracy was approximately 12.1%. however, the accuracy increased from 12.1% to 37.8%, 61.8%, 78.6%, and 87.1% if we allowed the prediction to be within 1 (e.g. observed uws20 was 40, prediction is 39), 2, 3, and 4 degrees of tolerance with observed uws20 respectively. although the bootstrap validated adjusted r-square (0.262) indicated a weak to moderate prediction performance, the calibration graph showed good calibration between the observed and predicted uws20 (see figure 3). 3) method 3 using r software (e.g. np package), we implemented nonparametric regression analysis with the same modeling structure as the multi-variable linear regression model but without any assumptions about the inherent distribution of the observed uws20. unfortunately, method 3 failed to produce better accuracy than the parametric multi-variable linear regression model. thus, we used the multi-variable linear regression model as the final model because it was more powerful than nonparametric regression. c. implications of the uws when coupled with statistical techniques, the uws can be used as a method of sampling to help better comprehend the behavior of a cipher under testing. as discussed, we used regression tools as a support for detecting cipher properties. thus, sophisticated pattern recognition methods may be used for improved prediction. lastly, we considered the given sequence s and what the linear complexity (lc) of an lfsr produces upon it. thus, we analyzed s against uws. both lc and uws must be higher for good security. thus, like lc, uws can be used as a measure of security strength. v. proposed neural network prediction model neural networks (nns) have many everyday applications, but they are principally focused on simulating the ability of neurons in the human brain to process information and data. the human brain consists of nerve cells and neurotransmitters to handle orders and inputs, and a nn follows this structure, processing information and learning from it to predict the outcomes based on inputs (data). an nn functions by employing a flexible algorithm that learns from the available data and produces expectations in response to them [18]. nns have many applications, including climate forecasting [19], stock market prediction [20], music production [21], or even cancer prediction [22]. they may also be applied in the fields of confidentiality and security of information, such as in the selection of keys used for encryption or in pattern recognition [23]. it is important to note that deep nn modeling is still a valid method and is evolving to be used in new areas, as shown in [24] which is an interesting study demonstrating the effectiveness of an nn-based model for investigating a complex system. fig. 3. calibration graph for predicting uws of degree 20 sg a. neural networks and security using the nn model provided by authors in [30] in 1976, it was possible to emulate the method of exchanging secret keys as a means of communicating through an insecure network. especially in cases where a large number of keys are required, the application of nn models allows the study of the most secure ways to handle the exchange of keys using an unsafe engineering, technology & applied science research vol. 10, no. 2, 2020, 5132-5141 5138 www.etasr.com alamer & soh: design and implementation of a statistical testing framework for a lightweight … communication channel [25]. nns have also been implemented to produce a secret key on a public network [26]. it is important to select a design and the appropriate weights for the nn to test and choose the best encryption system and to ensure that the messages are encrypted correctly [27]. to follow up the applied studies of nn models in terms of design and testing of encryption systems as well as measuring their effectiveness and potential problems, see [28]. because there are limited studies on the use of nn models to test the randomization of the binary sequence required for use in an effective cryptosystem, it is important to study the nn as a measurement tool. therefore, an extra step must be added in the implementation of the nn to enhance the desired cryptosystem. b. neural network model implementations given that the pseudorandom binary sequence plays an important role in encryption, the selection of the best binary sequence should be as random as possible to produce a powerful cipher (algorithm) that will generate an attackresistant sequence. therefore, in this study we employed nn models to measure the prediction based on uws to ascertain whether they are able to predict uws. the study succeeded, and the results were very promising, enabling us to measure the strength of the pseudorandom binary sequence, which is predicated on the strength of the algorithm (cipher) produced by it. these results may be applied to other algorithms, thus contributing to the analysis and selection of the best encryption systems. we calculated uws using ec2 for sg and ssg to obtain data for a large number of these algorithms at different degrees (sg and ssg). we sought to verify the validity of the application of nn at the different sg and ssg degrees along with the accuracy of our expectations. to confirm the effectiveness of the models, a high prediction rate exceeding 97% for some degrees and of no less than 90% for the others with negligible mean square errors (mses) is expected. tables vii–ix detail the anticipated results. from this, we conclude that the nn is a more effective tool for prediction than the other statistical methods previously introduced in this study. the mse is a good indicator of the validity of the method used [29] which protects the messages and shows the accuracy of the results by measuring mse. c. nn models and results for sg table vii shows that uws20 comprises three layers with ten, five and two nodes each, exhibiting a learning rate of 0.001 and an mse of 0.0088, which is very low and indicates the effectiveness of the model when applied to uws prediction. there were 6,791 overall training parameters. 56,333 were used as exercise data, representing 80% of the total data. the remaining 20% were used for testing and validating. the effectiveness of the forecast pertains to 94.30% of the total data. by way of another example relating to uws24, we found the effectiveness of the prediction to be 95.42% and the learning rate to be 0.0001 with an mse of 0.0019 and the same number of training parameters. the training dataset was 192,750. d. comparison with self-shrinking generator we found that with a range from uws4 to uws20 in a single model, the number of layers was four with 100, 50, 20, and 10 nodes on each layer, exhibiting a learning rate of 0.0001 with an mse of 0.0012. the training set consisted of 58,232 samples, the validation set of 14,558, total training parameters were 6,591 and the prediction rate was 96.05% (table viii). for uws24, we located the same number of layers, nodes and training parameters and the same learning rate with an mse of 0.0098, with training set equal to 22,1184, with validation set equal to 55,296, and with a prediction rate of 97.01% confirming the efficiency of the models for sg and ssg (tables vii–ix). table vii. sg model results for the new nn models including results for degrees 20, 21, 23, and 24 uws20 model uws21 model uws23 model uws24 model layers 3 4 4 4 number of nodes 10, 5, 2 50, 20, 10, 5 50, 20, 10, 5 50, 20, 10, 5 learning rate 0.0001 0.0010 0.0001 0.0001 mse 0.0088 0.0138 0.0033 0.0019 training set 56333 196502 713395 770997 validation sample 14084 49126 178349 192750 total parameters 6791 6791 6791 6791 prediction percentage 96.01 94.07 95.39 95.42 table viii. ssg model results for the new nn models including results for degrees 4–20, 21 and 22 uws degrees 4-20 uws21 model uws22 model layers 4 4 4 number of nodes 100, 50, 20,10 100, 50, 20,10 100, 50, 20,10 learning rate 0.0001 0.0001 0.0001 mse 0.0012 0.0014 0.0160 training set 58232 67737 96025 validation sample 14558 16935 24007 total parameters 6591 6591 6591 prediction percentage 96.05 96.66 89.61 e. the difference between sg and ssg ssg is another type of cipher derived from sg. however, in ssg, the process of selection and input is conducted using a single primitive polynomial working as an lfsr. in general, this has been found to be more effective in the field of confidentiality. using the same principles as sg, the ssg keystream was used to calculate uws. when applying the nn model, the dependent variable was uws, as it was in sg, and the independent variables were the ssg polynomial degree and the polynomial weight. the results of this prediction can be seen in tables viii and ix. f. nn model design we used a sequential model to define the model layer by layer, and we used a rectified linear unit (relu) for an activation function. our model had four hidden layers, with 100, 50, 10, and 5 nodes and the output layer had 1 node. the loss function was defined as the mse, and the learning rate was 0.0001. the optimization technique was regulated by the ‘adagrad’ optimizer, and the data were fitted to train the model. most of the data refer to sg with uws20 under slight modifications. engineering, technology & applied science research vol. 10, no. 2, 2020, 5132-5141 5139 www.etasr.com alamer & soh: design and implementation of a statistical testing framework for a lightweight … 1) cost function to ascertain whether the model was learning as required, we needed to calculate the mse, which needed to be small to demonstrate that the prediction was close to the actual output data. the smaller the mse, the better the model and the more accurate the prediction. the mathematical equation for the mse is: � �∑ o�� − �� ^ q�� (7) where n is the number of data inputs (simulations), �� is the observed data and �� ^ is the predicted data. table ix. ssg model results for the new nn models including results for degrees 23, 24, and 25 uws23 model uws24 model uws25 model layers 4 4 4 number of nodes 100, 50, 20, 10 100, 50, 20, 10 100, 50, 20, 10 learning rate 0.0001 0.0001 0.0001 mse 0.0046 0.0098 0.0052 training set 285568 221184 1036800 validation sample 71392 55296 259200 total parameters 6591 6591 6591 prediction percentage 90.14 97.01 97.14 2) the rectified linear unit activation function this function is nonlinear and has become popular for use in deep learning. since the data we entered were positive and nonlinear, we achieved the best results using the relu activation function. its advantage is that it is a fast learner and thus reduces the cost of use. we used relu in the inner layers of our models with the following formula: ��� � max��, 0� (8) here, the learning rate must be adjusted to reduce the mse as much as possible. we found a learning rate of 0.0001 to be the optimal setting (see tables vii–ix). the importance of nn for our study lies in its ability to accurately predict uws, which makes it an optimal instrument for measuring randomness in a given binary sequence, which is important in applying effective and safe encryption. this study and its application of nn models paves the way for future applications to measure the validity of the cryptosystems used, evaluate their effectiveness and further develop them. we found that by comparing nn models to study the behavior of the randomized binary sequence, more effective and more efficient predictions could be made than those of the model in the previous section, which used multivariable linear regression (a non-nn-based model). further, the extent and efficiency of the predictions remained high, even though ssg appeared to be more random than sg. this can be seen in the results of the prediction in tables vii–ix, which confirm that nn-based models are effective even in cases of random and discrete data, as in our case. vi. our findings this paper analyzed new weaknesses in the sg, a popular synchronous stream cipher. the first test was the d-monomial test adapted to sg (applied to the anf representation of boolean functions), which showed significant weaknesses in the sg output. we also investigated the dependence between the controlling lfsr and the non-linearity of the resulting keystream. after this, we performed a side test, called the maximal degree monomial test, which is related to the dmonomial test. in the result analysis, we reported a better understanding of the optimal points of the sg, showing when it was at its best and worst. finally, we analyzed the cipher technique using the uws and demonstrated dependencies between the uws and the two lfsr polynomials. the results were assisted by statistical techniques provided by the uws. using the uws, we showed the effect of the lfsr choice on possible distinguishing attacks on the sg. the results confirmed that the uws is a viable measure of cryptographic strength. lastly, the statistical model for the uws model can be used to test the sg pairs, which can help to measure their strength based on their uws so the user can choose the pairs with a higher uws. the �-monomial test showed that the controlling lfsr causes more non-linearity if it has a higher degree than the input lfsr. conversely, using the uws test and modeling, we found that the input lfsr helps the prediction, which confirms that controlling lfsr with higher degree than input lfsr makes better choices. additionally, the most effective elements (in decreasing order) in the model to help the prediction are presented in table x. table x. most effective elements in the prediction model for uws20 variable r square input polynomial term of order 17 0.18 input degree 0.127 control degree 0.127 control weight 0.10 input weight 0.09 input polynomial term of order 12 0.09 input polynomial term of order 13 0.08 input polynomial term of order 14 0.08 input polynomial term of order 15 0.08 input polynomial term of order 16 0.08 as another measure of validity analysis, we modeled uws17, uws18 and uws19 and found similar prediction performance (adjusted r-square) and accuracy. by using 50%, we modeled the data with similar accuracy with an r-square of approximately 26.6%. this means that we can model with less data, which reduces computational complexity. to ensure that every state was unique, we applied the uws to find the minimal length of the sg keystream. doing so, we found that identifying the uws can lead to discovering the lfsr pairs’ weakness, which, in forming the keystream, can in turn lead us to understand which lfsr pairs should be avoided. our research also showed that by using statistical tools along with uws, we can experimentally predict the sg’s behavior. this again illustrates the possible weaknesses in the sg keystream against attacks that may use this measure. finally, we found the possibility of using nn models to predict uws with better effectiveness and promising results compared with the non nn-based models. nn models are an effective measuring instrument for non-lc tests and should be adopted in the field of cryptanalysis more often. engineering, technology & applied science research vol. 10, no. 2, 2020, 5132-5141 5140 www.etasr.com alamer & soh: design and implementation of a statistical testing framework for a lightweight … vii. conclusions the goal of this research was conducting exhaustive experimental testing of some cryptographic security measures applied to the sg. by running complex computations for different sg degrees, it was found that the sg keystream output failed the d-monomial test. thus, it is possible to establish distinguishing attacks on this kind of stream cipher. this test can be applied to other ciphers in different ways, depending on whether it is an iv-based or iv-less cipher. additionally, the controlling lfsr had a greater effect than the input lfsr on the anf non-linearity. this was confirmed by applying the d-monomial test. uws test results can identify the lfsr pairs’ weakness. a weakness can result in vulnerability to attacks, thus the cipher user must pay attention to the lfsr pairs selection. we found that a model of the nn predictor offered highly precise results that contribute to its efficacy as a tool for measuring the extent of pseudorandom binary sequences and, thereby, the strength of the produced encryption systems. the results show that care must be taken when using the sg as a cryptographic technique. first, with a clearer understanding of the sg, analysts can design new attack techniques to mount on the sg. second, the uws can be used to analyze any keystream generated by any cipher. we intend to examine the uws on selected ciphers in the future. we also plan to dig deeper into the mathematical relationship of the uws and lc for specific ciphers. finally, we found that applying the models by implementing the nn gave us superior results compared with a multi-nonlinear regression model (non-nn-based model). acknowledgement the authors would like to thank molla huq for the comments on the statistical modeling, as well the victorian partnership for advanced computing for the use of their supercomputing facilities. in addition, the authors would like to show their appreciation to serdar bostaz for his valuable comments and feedback. references [1] c. paar, j. pelzl, understanding cryptography: a textbook for students and practitioners, springer science & business media, 2009 [2] a. j. menezes, p. c. van oorschot, s. a. vanstone, handbook of applied cryptography, crc press, 1996 [3] w. meier, o. staffelbach, “the self-shrinking generator”, in: communications and cryptography, 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[26] t. godhavari, n. alamelu, r. soundararajan, “cryptography using neural network”, 2005 annual ieee india conference indicon, chennai, india, december 11-13, 2005 [27] e. volna, m. kotyrba, v. kocian, m. janosek, “cryptography based on neural network”, ecms 2012, koblenz, germany, may 29-june 1, 2012 [28] a. el-zoghabi, a. h. yassin, h. h. hussien, “survey report on cryptography based on neural network”, international journal of emerging technology and advanced engineering, vol. 3, no. 12, pp. 456-462, 2013 [29] r. j. rasras, z. a. alqadi, m. r. a. sara, “a methodology based on steganography and cryptography to protect highly secure messages”, engineering, technology & applied science research, vol. 9, no. 1, pp. 3681-3684, 2019 engineering, technology & applied science research vol. 10, no. 2, 2020, 5132-5141 5141 www.etasr.com alamer & soh: design and implementation of a statistical testing framework for a lightweight … [30] w. diffie, m. e. hellman, “new directions in cryptography”, ieee transactions on information theory, vol. 22, no. 6, pp. 644-654, 1976 author profiles ahmed alamer conducted his postgraduate studies at adelaide university (bsc) and qut university (msc degree), majoring in mathematical sciences with a research focus in cryptography. he also graduated with a bsc degree in mathematical sciences from king khalid university. he currently focuses on the applications of mathematics in the field of cryptanalysis and security. he is currently a phd candidate at the department of computer science and computer engineering of la trobe university, where he has published and under-review papers in cryptology, neural networks applications in security, statistical analysis and randomness testing, lightweight cryptosystem design, and cryptanalysis. he has also held a lecturer position at the university of tabuk since 2012 and has organized several workshops in mathematics applications there. ben soh (s’89–m’92–sm’03) received his phd degree in computer science and engineering from la trobe university, melbourne, australia, in 1995. he is currently an associate professor with the department of computer science and computer engineering, la trobe university. he has taught numerous successful phd graduates. he has authored more than 180 peer-reviewed research papers and made significant contributions in various research areas, including fault-tolerant and secure computing and web services. microsoft word 22-2507_s engineering, technology & applied science research vol. 9, no. 1, 2019, 3782-3785 3782 www.etasr.com ugur et al.: friction coefficient and compression behavior of particle reinforced aluminium matrix … friction coefficient and compression behavior of particle reinforced aluminium matrix composites a. ugur mechanical engineering department engineering faculty karabuk university, karabuk, turkey augur@karabuk.edu.tr g. sur mechanical engineering department engineering faculty karabuk university, karabuk, turkey gokhansur@karabuk.edu.tr h. gokkaya mechanical engineering department engineering faculty karabuk university, karabuk, turkey hgokkaya@karabuk.edu.tr n. eltugral metallurgical and materials engineering department engineering faculty karabuk university, karabuk, turkey nurettineltugral@karabuk.edu.tr abstract—metal matrix composites (mmcs) are materials used in a large range of engineering applications. in this paper, the relatively low-cost stir casting is evaluated with the use for silisyum carbite (sic) as reinforcement and al7075 alloy as matrix to produce mmcs with varied reinforcement from 10% to 18%. the produced composites were examined, and their wear behavior was investigated. the results showed that the mechanical properties of the mmcs decrease with the increase of the mass percentage of reinforcement and compression. keywords-metal matrix composites; stir casting; sic; friction coefficient i. introduction aluminum and its alloys play an important role in the production of mmcs. these materials began to be used towards the end of the 20th century, especially in the automotive space and aviation industry. they attract attention due to their specific strength, light weight, heat insulation and high abrasion resistance. composite material production and material properties can be improved by changing the types and amounts of matrix and reinforcement elements [1-3]. today, methods such as infiltration, powder metallurgy, rapid solidification, plasma spray hot stamping [4, 5] and stir casting [6-8] are used on mmc material production. stir method is the most economical and with higher product capacity process for production of mmcs. but, stir casting technique, is difficult to produce a homogenous and stable material due to inherent stir casting problems such as poor wetting, clustering and prosite [9-11]. the mechanical properties of mmcs are affected by the interface bond between the matrix and the reinforcing materials and the load transfer is decreased. authors in [12] studied aluminum alloy 6061 reinforced with al2o3 particles with different mass ratio for the fabrication and characterization of aa 6061/ al2o3 ammc by stir casting process. they found some improvement about micro hardness and ultimate tensile strength in produced samples. al7075 material was used as matrix due to its lightness and relatively high strength. authors in [13] studied 7075 alloy as a matrix with whisker reinforced composites with squeeze casting method for manufacturing superplastic material and succeeded 260% total elongation. authors in [14] used 7075 alloy as a matrix to produce (sic+ti) hybrid composites using squeeze casting method. they successfully produced hybrid composite material with increasing strength due to decreasing ductility. authors in [15] studied 7075 alloy as matrix to produce nano hybrid composites using stir casting and squeeze casting improving the hardness of composites [15]. there are three types of composite reinforcements, long or fibers, finite length fibers and particulates. in our study sic particles are selected as a reinforcement material. authors in [16] used sic particles as reinforcement. as a result the material strength increased along with a loose on ductility. authors in [17] used sic particles as a reinforcement with al6061 matrix composites while investigating wear behavior and sliding speed in different sic ratios. as a result, in increasing sic ratio the wear decreases and friction coefficient increases. authors in [18] used sic as reinforcement with al6063 matrix to produce composites with vacuum molding assisting stir casting method and to investigate the effect of reinforcement ratio and particle size on dry sliding wear. as a result they found optimum tribological behavior on 7.5% reinforcement ratio and 70afs particle size. authors in [19] used sic particles with two different matrix alloys (a536, 6061) and studied reinforcement distribution and wettability improving the wettability of sic. authors in [20] used sic and c nano tubes as reinforcements to the cooper matrix to produce hybrid self-lubricating composites, and investigated their wear and friction behavior. the resulted hybrid composites showed higher tribological behavior than monolithic copper [20]. authors in [21] studied magnesium matrix composites corresponding author: a. ugur engineering, technology & applied science research vol. 9, no. 1, 2019, 3782-3785 3783 www.etasr.com ugur et al.: friction coefficient and compression behavior of particle reinforced aluminium matrix … reinforced with sic particles using semisolid stirring assisted ultrasonic vibration method. they found that the composite mechanical properties mostly depend on grain refinement and particle distribution. authors in [22] produced aluminum matrix composites with al2o3 particles. the product microstructure and its mechanical properties were investigated via extrusion processes. they found that porosity increased by increasing reinforcement ratio and stirring speed and decreased by extrusion process. the samples’ mechanical properties were usually increased. a limited number of studies is available on the development of al7075 aluminum alloy based mmcs by a combination of stir casting method. in this work, different weight percentage of sic particle reinforced al7075 aluminum alloy matrix composites were produced by stir casting. mechanical and microstructural observations between the aluminum alloy and sic were described. ii. experimental procedure al7075/10wt sic, al7075/14wt sic, al7075/18wt sic, composite materials were produced. al7075 was selected as matrix material. the chemical constituents of the material are listed in table i. this alloy contains 2.7% mg which increases wettability. sic particles of 50-100µm in size were used as reinforcement elements. the production work was carried out in a specially prepared stir casting machine (figure 1). chemical composition of al7075 table i. fe si cu mn mg zn cr zi ti rest 0.5 0.5 1.5 0.3 2.7 5.6 0.23 0.25 0.15 al fig. 1 mixing casting machine al7075 was selected as the matrix material, and was heated to 690°c under argon gas, and then the sic reinforcing particles, heated at the same temperature were added in packs. the addition continued for 10 minutes at a rate of 200rpm. during this mixing process the temperature dropped to around 590°c. we may say the study occurred in semi solid state rather than liquid state. after the mixing process, the temperature increased to 720°c to increase the fluidity of the composite material, and then it was poured into a pre heated at 350°c mold. when it was cooled to room temperature, 500g of composite material were produced. a produced test sample is shown in figure 2. samples were cut with a finger milling machine and a precision saw was used to give the same shape. for metallographic observation, they were prepared by grinding through 1000 grit papers followed by polishing with diamond paste. the samples were examined with sem devices. the same samples were prepared as per astm e9 standard for compression testing at room temperature, with 20m/s velocity. to obtain friction coefficient a uts tribometer t10/20 was used. samples were prepared on astm g-33 standard. 20n, 30n, 40n forces were applied on the samples in 200m distance for wear test. fig. 2 sample obtained after casting iii. results and discussion a. friction coefficient the friction coefficients for different test loads and samples are listed in table ii and their graph is shown in figure 3. normally friction coefficient of aluminum steel couples is 0.5-0.6 and increases with the test distance [23]. the result shown in figure 4 is analogous to that. also, an increase in load increases friction coefficient. generally, in low loads composites shown good tribological characteristic [24]. the values obtained from the test were adjusted to a 6th degree curve to reduce noise. the increase in the ratio of the reinforcement element at a load of 40n obtained a lower drag coefficient. friction coefficients increased due to the increase in distance and wear of the contact surface in the material. b. compressive stres composite materials had different mechanical properties according to particle size and matrix alloy. the results of the test are given in figure 4. when the sic reinforcements increasedat room temperature, the strength of the composite material decreases [25, 26]. the 10% sic-containing sample showed a sudden strain drop due to the progression of capillary cracks. it was observed that the increase in the sic ratio caused a decrease in compressive strength due to the fact that the grain size is above 50 microns and porosity occurred in the microstructure during production. different states for the samples. table ii. sample mass% sic method al7075 sic 10 free casting al7075 sic 14 free casting al7075 sic 18 free casting engineering, technology & applied science research vol. 9, no. 1, 2019, 3782-3785 3784 www.etasr.com ugur et al.: friction coefficient and compression behavior of particle reinforced aluminium matrix … fig. 3 friction coefficient: (a) on 40 n load for samples 1-3, (b) on 20n, 30n, 40n laod for 10% sic content composites. fig. 4 compressive stress fig. 5 (a) sem 1-3, (b) xrd samples c. microstractural characterization the microstructure of 14% sic-containg composites by sem is shown in figure 5(a). the microstructure can be counted as having homogenous distribution and interconnection. but at some points porosity is also observed. xrd images give the structure of the particles (figure 5 (b)). the results of spectrum analysis are listed in table iii. contents of xrd spectrum table iii. c o al si cu zn 1 4.49 2.69 44.2 45.3 69.5 3.18 2 2.74 1.17 87.8 0.23 1.64 6.47 3 29.2 0.73 0.48 69.5 0.05 0 iv. conclusions aa7075 alloys reinforced with sic aluminum matrix composites were manufactured by stir casting method. sem figures show the nearly uniform distribution of sic particles in the matrix and a good bonding. some porosity was noticed in the micrograph. the mechanical properties of the aluminum matrix composites change with respect to their sic content. acknowledgment authors wish to acknowledge the help from karabuk university scientific research coordinatorship (project no. kbu-bap-15/1-dr-027). references [1] d. b. miracle, “metal matrix composites from science to technological significance”, composites science and technology, vol. 65, no. 15-16, pp. 2526-2540, 2005 [2] m. m. dave, k. d. kothari, “composite material-aluminium silicon alloy : a review”, indian jopurnal of research, vol. 2, no. 3, pp. 148150, 2013 [3] v. k. lindroos, m. j. talvitie, “recent advances in metal matrix composites”, journal of materials processing technology, vol. 53, no. 1-2, pp. 273-284, 1995 [4] a. demir, n. altinkok, “effect of gas pressure infiltration on microstructure and bending strength of porous al2o3/sic-reinforced aluminium matrix composites”, composites science and technology, vol. 64, no. 13-14, pp. 2067-2074, 2004 [5] t. fiedler, m. a. sulong, v. mathier, i. v. belova, c. younger, g. e. murch, “mechanical properties of aluminium foam derived from infiltration casting of salt dough”, computational materials science, vol. 81, pp. 246-248, 2014 [6] s. naher, d. brabazon, l. looney, “development and assessment of a new quick quench stir caster design for the production of metal matrix composites”, journal of materials processing technology, vol. 166, no. 3, pp. 430-439, 2005 [7] d. r. j. selvam, d. r. i. dinaharan, “synthesis and characterization of al6061-fly ashp-sicp composites by stir casting and compocasting methods”, energy procedia, vol. 34, pp. 637-646, 2013 [8] s. j. abraham, s. c. r. madane, i. dinaharan, l. j. baruch, “development of quartz particulate reinforced aa6063 aluminum matrix composites via friction stir processing”, journal of asian ceramic societies, vol. 4, no. 4, pp. 381-389, 2016 [9] c. g. kang, k. s. yun, “fabrication of metal-matrix composites by the die-casting technique and the evaluation of their mechanical properties”, journal of materials processing technology, vol. 62, no. 1-3, pp. 116– 123, 1996 [10] m. mohammadpour, r. azari khosroshahi, r. taherzadeh mousavian, d. brabazon, “effect of interfacial-active elements addition on the engineering, technology & applied science research vol. 9, no. 1, 2019, 3782-3785 3785 www.etasr.com ugur et al.: friction coefficient and compression behavior of particle reinforced aluminium matrix … incorporation of micron-sized sic particles in molten pure aluminum”, ceramics international, vol. 40, no. 6, pp. 8323-8332, 2014 [11] f. delannay, l. froyen, a. deruyttere, “the wetting of solids by molten metals and its relation to the preparation of metal-matrix composites composites”, journal of materials science, vol. 22, no. 1, pp. 1-16, 1987 [12] b. c. kandpal, j. kumar, h. singh, “fabrication and characterisation of al2o3/aluminium alloy 6061 composites fabricated by stir casting”, materials today: proceedings, vol. 4, no. 2a, pp. 2783-2792, 2017 [13] s. w. lim, y. nishida, “high strain rate superplasticity of s & n , whisker reinforced 7075 alloy matrix”, scripta metallurgica et materialia, vol. 32, no. 11, pp. 1821-1825, 1994 [14] w. chen, y. liu, c. yang, d. zhu, y. li, “(sicp+ti)/7075al hybrid composites with high strength and large plasticity fabricated by squeeze casting”, materials science and engineering: a, vol. 609, pp. 250-254, 2014 [15] c. kannan, r. ramanujam, “comparative study on the mechanical and microstructural characterisation of aa 7075 nano and hybrid nanocomposites produced by stir and squeeze casting”, journal of advanced research, vol. 8, no. 4, pp. 309-319, 2017 [16] s. v. nair, j. k. tien, r. c. bates, “sic-reinforced aluminium metal matrix composites”, international metals reviews, vol. 30, no. 1, pp. 275-290, 1985 [17] r. n. rao, s. das, “effect of sic content and sliding speed on the wear behaviour of aluminium matrix composites”, materials & design, vol. 32, no. 2, pp. 1066-1071, 2011 [18] r. singh, g. singh, “investigations of al-sic amc prepared by vacuum moulding assisted stir casting”, journal of manufacturing processes, vol. 19, pp. 142-147, 2015 [19] w. zhou, z. m. xu, “casting of sic reinforced metal matrix composites”, journal of materials processing technology, vol. 63, no. 1-3, pp. 358-363, 1997 [20] m. r. akbarpour, s. alipour, a. safarzadeh, h. s. kim, “wear and friction behavior of self-lubricating hybrid cu-(sic+xcnt) composites”, composites part b: engineering, vol. 158, pp. 92-101, 2019 [21] m. j. shen, x. j. wang, c. d. li, m. f. zhang, x. s. hu, m. y. zheng, k. wu, “effect of submicron size sic particles on microstructure and mechanical properties of az31b magnesium matrix composites”, materials & design, vol. 54, pp. 436-442, 2014 [22] h. r. ezatpour, m. torabi-parizi, s. a. sajjadi, “microstructure and mechanical properties of extruded al/al2o3 composites fabricated by stir-casting process”, transactions of nonferrous metals society of china, vol. 23, no. 5, pp. 1262-1268, 2013 [23] v. n. tran, s. yang, t. a. phung, “microstructure and properties of cu/tib2wear resistance composite coating on h13 steel prepared by insitu laser cladding”, optics & laser technology, vol. 108, pp. 480-486, 2018 [24] y. zhan, g. zhang, “friction and wear behavior of copper matrix composites reinforced with sic and graphite particles”, tribology letters, vol. 17, no. 1, pp. 91-98, 2004 [25] r. k. gupta, s. p. mehrotra, s. p. gupta, “evaluation and optimization of metal matrix composite strip produced by single roll continuous strip casting method”, materials science and engineering: a, vol. 465, no. 12, pp. 116-123, 2007 [26] a. v pozdniakov, v. s. zolotorevskiy, r. y. barkov, a. lotfy, a. i. bazlov, “microstructure and material characterization of 6063 / b 4 c and 1545k / b 4 c composites produced by two stir casting techniques for nuclear applications”, journal of alloys andcompounds, vol. 664, pp. 317-320, 2016 engineering, technology & applied science research vol. 8, no. 6, 2018, 3545-3549 3545 www.etasr.com mukhtar & nasir: comparative closed vessel firing-ballistic parameters evaluation for development … comparative closed vessel firing-ballistic parameters evaluation for development of base bleed composite solid propellant amir mukhtar school of chemical and materials engineering national university of science and technology islamabad, pakistan amirmukhtar@scme.nust.edu.pk habib nasir school of natural sciences national university of science and technology islamabad, pakistan habibnasir@sns.nust.edu.pk abstract—closed vessel test (cvt) is widely used for the measurement and comparison of ballistic and energetic properties of propellants by the ignition of a specific sample mass in a closed high-pressure vessel. in our research, comparative cvts were performed in a vessel, where an internationally accepted composite propellant base bleed grain sample served as a reference (ref) for recording the standard values of the under investigation propellant composition, in relation to which newly developed samples were characterized. these comparative cvt experiments were performed under chamber volume of 100cm3, sample mass of 10g for all samples and identical ignition system having 1.5g igniter bag of gunpowder. we used closed vessel with working pressure limit of 5000 bars for recording the ballistic parameters of various composite solid propellant samples with reference to a standard sample. it was found that the ref sample at 50% propellant loading recorded mean maximum pressure (pm) of 1040 bars in complete combustion time (tpm) of 120ms and vivacity of 0.038 (1/bar∙s). the measured mean pm was taken as relative force (%) and measured mean vivacity was taken as relative vivacity (%). this data has been used to tune and study the ballistic parameters to develop ammonium perchlorate (ap) and hydroxyl-terminated polybutadiene (htpb) based composite solid propellant (csp) base bleed grain for artillery projectile. keywords-composite propellant; closed vessel i. introduction closed vessel test (cvt) of gun propellants is a technique employed for the experimental evaluation of propellant ballistic parameters at laboratory level [1, 2]. the equipment consists of a vessel made of very high strength steel, equipped with piezoelectrical pressure transducer, outlet valves, special ignition system fitted in breech screw and data acquisition device. tests are mainly used to measure pressure history and pressure maximum of propellants [3]. dynamic firing for testing any propellant is an expensive method so the closed vessel (cv) provides a very safe, quick and economical way for research and development of propellants [4-6]. it involves combustion of a known mass of propellant in a closed chamber of a specific volume. the pressure rises with time inside the vessel, it is measured, recorded and processed by the data acquisition system. recorded p-t data are used to calculate the ballistic parameters including differential pressure (dp/dt), relative force and relative vivacity (quickness) of the propellant [7]. the ballistic assessment of the propellant charge fired in closed vessel is the mean result of its force and value of its vivacity compared to that of the reference or standard propellant. the force is the maximum pressure developed in cv chamber by firing a propellant charge and it is considered as the energy of the propellant. it also indicates that the developed composition is correct [4]. propellant vivacity is defined as the differential pressure (dp/dt) divided by maximum pressure (pm). vivacity is the measure of quickness and efficiency of a propellant to produce energy while undergoing combustion. the development of new propellants with desired properties and the quality control in production of propellants at industrial scale requires the measurement of pressure, vivacity and ballistic properties [8]. comparative tests are also performed in closed vessel where a sample is considered as reference (ref) and the obtained data of other propellant samples are evaluated in comparison to the reference sample. comparative tests are performed in identical conditions including closed chamber capacity, loading conditions, loading density and ignition system. a specific amount of propellant charge is loaded in the cv and fired remotely [9]. range enhancement of artillery shells is a basic need of all modern armies. one out of the many methods to extend the range is employment of base bleed (bb) unit housing a bb composite propellant grain at the base of artillery projectile [10-12]. the projectile travels at supersonic velocity during its flight which creates an under-pressure region at its base which is about 50% of total drag acting on shell body. bb grain inside the bb-unit acts as a gas generator that fills the under pressure zone behind the shell with hot gases and increases the pressure consequently overcoming the base drag giving the projectile increased range [13, 14]. ammonium perchlorate (ap) and hydroxyl-terminated polybutadiene (htpb) based composite solid propellant (csp) is employed as bb grain in the bb unit for large caliber artillery gun projectile. csp contains ap (oxidizer) particles embedded in htpb binder with metal powders like aluminum as fuel [15, 16]. burning rate is the engineering, technology & applied science research vol. 8, no. 6, 2018, 3545-3549 3546 www.etasr.com mukhtar & nasir: comparative closed vessel firing-ballistic parameters evaluation for development … most important characteristic of the csps. the combustion behavior and ballistic performance of the propellants depends upon the oxidizer, burning rate modifiers and fuel type [17-19]. the combustion process is mainly the decomposition of the ap which is a self-sustained process [20]. being at the bottom of the projectile, the bb-unit starts burning as the projectile is fired under high pressure conditions. the bb-grain travels through the bore under high pressure. cvt can be employed for the evaluation and modification of ballistic parameters of bb grain under high pressure conditions [21, 22]. we used for the first time cv firing to record the ballistic parameters of various csp samples with reference to a standard sample for bb unit of 155mm artillery projectile. measured data have been used to tune and study the ballistic parameters in order to develop a composition with required properties. different compositions were developed based on ap and htpb cured with ipdi. cvt was performed by firing three rounds of each sample and the mean values were recorded to study the tuning of ballistic parameters during the development process of bb propellant grain according to the ref sample. ii. experimental a. composite propellant preparation csp samples were synthesized based on htpb binder cum fuel over a solid loading range of 68%-78% including ap as oxidizer. aluminum powder was used to opacify the propellant and for stable combustion. htpb binder and various additives including dioctyl sebacate (dos), 1-(2-methyl) aziridinyl phosphine oxide (mapo), trimethylol propane (tmp) and fe2o3 as plasticizer, bonding agent, crosslinker and burning rate promoter respectively were charged in a horizontal kneading machine for 30min followed by the addition of al powder and ap which is a bimodal mixture of two different partial sizes. after kneading the complete mixture for 40min ipdi was added and mixed for 30min under vacuum. finally, the completely homogenized mixture was poured in teflon coated stainless steel molds and cured in oven at 60°c for 170 hours. propellant compositions developed for this study are given in table i. sem images show that the solid ap particles have been homogeneously mixed and embedded in polyurethane matrix in figure 1. table i. composite propellant formulation sample propellant composition wt. % htpb + additives al (22μm) ap (256μm) ap (130μm) fe2o3 a 28.00 02.00 35.00 35.00 b 26.00 02.00 36.00 36.00 c 24.00 02.00 37.00 37.00 d 22.00 02.00 38.00 38.00 e 20.00 02.00 39.00 39.00 f-1 26.00 02.00 35.80 36.00 0.20 f-2 26.00 02.00 35.60 36.00 0.40 f-3 26.00 02.00 35.40 36.00 0.60 f-4 26.00 02.00 35.20 36.00 0.80 b. high pressure clossed vessel cv is a widely used technique for ballistic evaluation of propellants at laboratory level. it is a safer, quicker and less expensive process instead of field firing with gun when dealing with the research and development of propellants and high energy pyrotechnic materials [4]. a sample of known loading density is test fired in cv of known volume for valuable ballistic performance evaluation [7]. the cv used in this research work is a conventional cv which has chamber volume of 100cm3 with pressure recording range up to 5000bars. the vessel has a loading density of δ=0.20g/cm3 which is the ratio of propellant mass being tested to the volume of cv chamber. the cv is equipped with a pressure block and a firing block. the firing block has a nickel chrome wire soldered to firing terminals and passing through an ignition bag containing 1.50g of gun powder. gun powder bag is initiated by the firing control unit to provide ignition to the propellant sample. pressure block is equipped with high pressure quartz direct measuring pressure transducer type 6203 with maximum recording range of 5000bar. the cv is connected to a kistler charge amplifier type 5018 and an electronic signal acquisition module for p-t data recording. a schematic diagram of cv is shown in figure 2. fig. 1. sem images of prepared csp. fig. 2. high strength steel cv: 1) exhaust valve, 2) vessel station, 3) firing block, 4) ignition electrode, 5) vessel body, 6)vessel rotating arm. c. clossed vessel sample firing method according to the theory of constant volume, loading density is used to calculate the total sample loading mass and required quantity of ignition powder for cvt. the vessel has a loading density of δ=0.20g/cm3 with full loading charge capacity of 20.00g. propellant samples were fired in cv at half loading charge mass of 10g with 1.5g of gun powder ignition bag for all tests. csp is different from gun propellants in geometry and composition, therefore identical square shaped samples were cut and loaded in cv (figure 3). firing control unit gives an electrical pulse to the ignition head which generates thermal impulse to ignite the gun powder bag for initiating the propellant samples in cv chamber. the pressure produced is measured by the piezoelectric pressure transducer which is further amplified and recorded by the data acquisition system. engineering, technology & applied science research vol. 8, no. 6, 2018, 3545-3549 3547 www.etasr.com mukhtar & nasir: comparative closed vessel firing-ballistic parameters evaluation for development … figure 4 shows a schematic diagram of loaded cv ready for test firing. fig. 3. prepared samples for cvt. fig. 4. schematic diagram of cv: 1) coaxial data cable, 2) pressure transducer, 3) vessel wall, 4) igniter sample, 5) vessel chamber, 6) ignition bag, 7) firing block. iii. results and discussion cvt experiments were performed with 10g of sample mass for each sample which is the 50% of loading charge capacity of the vessel. five rounds were test fired for reference and each batch of ap/htpb csp under identical conditions and results were averaged. single fire data are as represented in figure 5. fig. 5. recorded data for single cvt. a. effect of oxidiser/fuel ratio most valuable output from the cvt data acquisition system comes in the form of p-t profile. in the initial phase, five propellant compositions with different bimodal ap content (wt. %) were fired comparatively with the standard ref sample. recorded and calculated values including pm, maximum differential pressure (dp/dt)m, tpm relative force (f) and relative vivacity (v) from first phase of cv firing are reported in table ii. recorded p-t profiles from firings at identical conditions and loading density are plotted in figure 6. recorded data were divided in three parts, the first part is taken from 10%-30% of the maximum recorded pressure and second part at 10%-60% and the final at 10%-80%. the phase of propellant charge combustion used to determine the ballistic parameters of solid composite propellant is taken from 10%-80% and finally the maximum obtained pressure at the end of the complete combustion. the vivacity is taken at 30%-80% of the recorded curve. p-t data are used to calculate dp/dt which is plotted against pressure in figure 7. mean values of vivacity obtained from cv firing data is plotted against p/pm in figure 8. table ii. cvt results phase-i sample pm (bar) tpm (ms) (dp/dt)m (bar/ms) f % v % ref 1040.80 120.00 15.74 100.00 100.00 a 980.09 281.00 14.69 93.40 44.44 b 1043.10 220.00 16.00 100.48 56.13 c 1098.20 178.00 22.58 105.75 70.32 d 1160.60 158.00 26.64 112.25 72.90 e 1218.20 114.00 35.20 114.00 89.68 fig. 6. comparative p-t profile. fig. 7. rate of change of pressure against pressure. in compositions a to e, the composite propellant solid loading of bimodular oxidizer content has been gradually increased and no burning rate modifier has been employed. from figure 6, it is observed that recorded maximum pressure rises along with oxidizer content. this is an obvious result as higher solid loading in composite propellant resulted in the release of higher amount of energy. as the percentage of engineering, technology & applied science research vol. 8, no. 6, 2018, 3545-3549 3548 www.etasr.com mukhtar & nasir: comparative closed vessel firing-ballistic parameters evaluation for development … oxidizer mass increases, the pressure generated increases and the complete combustion time reduces. the quickness or higher rate of regression of burning surface is caused by gradual positive change in oxidizer to fuel (o/f) ratio. it can be observed that the rate of pressure rise is increasing with increase in the oxidizer percentage. this implies that the slope showing rate of change of pressure vs pressure rises with increasing ap loading of composite propellant. fig. 8. vivacity against p/pm. from figure 7 can be observed that the rate of increase of pressure rises with the rise in o/f ratio. it is seen that the slope of dp/dt against p rises with the rise in wt. % of oxidizer content which indicates that the higher the solid loading, the higher is the energy produced. vivacity is the quickness and rate at which energy is released. the higher the vivacity the higher is the rate of regression of burning propellant surface in the high pressure chamber. figure 8 shows the vivacity against p/pm. figures 6-8 show that the change in oxidizer resulted in rise in pressure and quickness. at a fixed o/f ratio we achieved the requisite pressure at slower rate of propellant combustion taking longer time than the ref. with gradual increasing of the o/f ratio the rate of pressure rise increased, taking shorter time for the whole propellant mass to burn (closer to ref). the combustion process grew faster getting closer to ref but pressure rose beyond the standard limit. therefore, the o/f ratio was fixed based on the p-t profile and composition b with requisite force was selected for further development. b. addition of burning rate promoter in the second phase we added the burning rate modifier fe2o3 in chosen composition b for studying the effect on p-t profile, with fixed o/f ratio. fe2o3 was employed to increase the quickness or combustion to shorten the burning time to match that of the ref. the measured values of the experimental results are given in table iii. the recorded and calculated data for p-t, dp/dt against pm and vivacity against p/pm respectively are plotted in figures 9-11. table iii. cvt results phase-ii sample pm (bar) tpm (ms) (dp/dt)m (bar/ms) f% v% ref 1040.80 120.00 15.74 100.00 100.00 f-1 1030.50 131.50 24.69 99.01 91.25 f-2 965.34 126.00 22.77 92.74 95.24 f-3 1011.80 120.50 17.23 97.21 99.58 f-4 1039.70 119.00 16.00 99.89 01.00 p-t profile in figure 9 clearly shows that at a fixed solid loading of ap with bimodular particle distribution, the pressure generated remained within given limits whereas the rate of regression of burning surface changed. the burning rate modifier acts as a burning rate promoter by reducing the temp at which ammonium perchlorate decomposes, consequently the propellant mass combustion grew faster. gradual increasing percentage of fe2o3 at a fixed o/f ratio affected the relative vivacity. the higher rate of regression of burning surface is indirectly observed in figure 10. the rate of change of pressure is higher when compared to the composition without burning rate promoter at the same o/f ratio. this means that the same mass of propellant charge is undergoing combustion process at a faster pace. fig. 9. comparative p-t pofile. fig. 10. rate of change of pressure against pressure. fig. 11. vivacity against p/pm figure 11 represents the comparative vivacity and the relative vivacity increased with increase in the catalyst wt. %. engineering, technology & applied science research vol. 8, no. 6, 2018, 3545-3549 3549 www.etasr.com mukhtar & nasir: comparative closed vessel firing-ballistic parameters evaluation for development … by observing the change in relative vivacity, the final composition f-4 gave acceptable relative force (%) and relative vivacity (%). by comparative firing of newly developed compositions and evaluating the recorded p-t profiles we were able to develop a composition for base bleed composite propellant. the technique is applied to gun propellants and it is very effective in quality control and production of newly developed gun propellants. our research work proves that this technique is very useful for the development and study of composite propellants. iv. 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vol. 10, no. 3, 2020, 5719-5723 5719 www.etasr.com manjunatha et al.: an optimized multilevel inverter topology with symmetrical and asymmetrical dc … an optimized multilevel inverter topology with symmetrical and asymmetrical dc sources for sustainable energy applications b. m. manjunatha department of eee r. g. m. college of engineering and technology nandyal, india manjunath.bmeee@gmail.com s. nagaraja rao department of eee m. s. ramaiah university of applied sciences bengaluru, india raoeee123@gmail.com a. suresh kumar department of eee r. g. m. college of engineering and technology nandyal, india surianisetty@gmail.com k. shaguftha zabeen department of eee r. g. m. college of engineering and technology, nandyal, india shaguftha27@gmail.com sanjay lakshminarayanan department of eee bms institute of technology and management, bangalore, india sanjay.laks@gmail.com a. vishwanath reddy department of eee golden valley integrated campus madanapalli, india vishwa2231@gmail.com abstract—this paper proposes an optimized multi-level inverter (mli) topology with symmetrical and asymmetrical dc sources for sustainable energy applications. the proposed mli has optimized components to reduce size, cost, and installation area in comparison with traditional mlis. it also improves output power quality by reducing harmonics in the stepped output, and hence it can be used for sustainable energy applications with a grid interface. the proposed inverter is equipped with six switching devices, one clamping diode, and two dc sources. it produces a five-level stepped output when using symmetrical dc sources and a seven-level stepped output when using asymmetrical dc sources. in this topology, the six switching devices are divided into two units, namely the level generator and the polarity generator units, the switches used in the level generator are responsible for producing the required number of levels in the form of rectified stepped output and the switches used in the polarity generator are responsible for converting the rectified stepped waveform to stepped ac output. the simulation results verify the operation of the mli when fed with linear load with symmetrical and asymmetrical dc sources, and the experimental output results are presented for validation. keywords-optimal multilevel inverter; symmetrical; asymmetrical; total harmonic distortion i. introduction multi-level inverters (mlis) are popularly used devices for power conversion in grid-connected systems, industrial applications, electric vehicles, uninterruptible power supply (ups) devices, facts devices, etc. mlis are capable of generating an output voltage with near sinusoidal wave shape. in addition, they have features like producing output with reduced total harmonic distortion (thd), reduction in power losses due to the lower switching frequency, reduced dv/dt stress and un-necessity of filters which results in size and cost reduction of the overall inverter [1-4]. the classical topologies of mlis are diode clamped mli or neutral point clamped (np-mli) [5], flying capacitor mli (fc-mli) [6] and cascaded h-bridge mli (ch-mli) [7], and are used in various industrial applications. however, np-mli and fc-mli suffer from limitations compared to ch-mli, limitations such as the larger number of switching devices, the requirement of clamping diodes and capacitors, voltageunbalancing issues across the capacitors etc. due to the simple structure of ch-mli, it can be easily integrated with renewable energy sources. over the last years, research has focused on emerging topologies to overcome the limitations of the conventional mli. ch-mli consists of h-bridges with independent dc sources across each bridge. the magnitude of all voltage sources can be either the same or different. in symmetric ch-mli, the magnitude of all voltages sources will be equal, whereas in asymmetric ch-mli, the magnitude of all voltage will be different [8, 9]. the asymmetric inverters generate more levels in output as compared with symmetric mlis with the same topology or the same number of power electronic switches and sources. therefore, cost, size, complexity, thd, and losses of the asymmetric inverters are reduced [12]. authors in [13-15] tried to reduce the number of switches to overcome the cost constraint, and improve the quality of output voltage waveform by increasing the number of levels in the output voltage. this paper presents a single-phase mli topology with symmetrical and asymmetrical voltages, which uses a reduced number of components compared to the existing topologies corresponding author: b. m. manjunatha engineering, technology & applied science research vol. 10, no. 3, 2020, 5719-5723 5720 www.etasr.com manjunatha et al.: an optimized multilevel inverter topology with symmetrical and asymmetrical dc … [16-18]. this configuration is the extension of the topology proposed in [10], which can be extended to three-phase [17]. ii. proposed topology similar to the recently introduced hybrid mlis, the proposed inverter also consists of two circuits. the first one is a level generating circuit, it works at the fundamental or at a high frequency and the second one is the h-bridge circuit operating at the fundamental frequency. the first circuit generates a positive stepped waveform across the h-bridge and the second generates positive and negative stepped waveforms in the output voltage. the generalized figure of the proposed optimized mli is presented in figure 1. the circuit can be powered with symmetrical or asymmetrical voltage. in the symmetrical topology, all input voltage magnitudes are maintained at equal values: v1: v2:v3:v4 : : : vk=1:1:1:1 : : : 1 and in the asymmetrical voltage topology, the voltages are maintained with the ratio of v1:v2: v3:v4: : : : vk = 1 : 2 : 3 : 4 : : : k, where: k represents the number of voltage sources. the level generating circuit is used for generating the positive stepped voltage levels across the h-bridge. it consists of voltage sources, level generating switches, and diodes to prevent the reverse of the current. the h-bridge circuit is used for polarity reversal, it is responsible of producing the positive and negative stepped voltage levels at the output and it consists of four switches. fig. 1. generalized structure of the proposed optimized mli the required number of output levels, control switches, and diodes with ns sources for the optimized mli with symmetrical voltages are: • levels generated in output with ns sources = (2ns + 1) • control switches required to generate n levels with ns sources = (3ns -1), for n ≥3 • diodes required for generating n levels = (ns 1) • peak output voltage = (2ns+1)×vdc the output levels, control switches, and diodes for the optimized mli with unsymmetrical voltages are: • levels generated in output with ns sources = ns (ns + 1) + 1 • control switches required to generate n levels with ns sources = (3ns -1), for n ≥3 • diodes required for generating n levels = (ns 1) • peak output voltage = (ns×(ns + 1) +1)×vdc iii. symmetrical and asymmetrical optimized mli to explain the operation of the mli shown in figure 1, two voltage sources with equal or unequal magnitude are considered (figure 2). a. operation of symmetrical optimized mli with two symmetrical sources (v1:v2 = 1:1), the proposed mli shown in figure 2 is capable of generating 5 levels at the output terminals, utilizing 2 dc sources, 6 control switches, and 1 diode. when compared with the conventional and recently proposed mlis, this topology requires a reduced number of power electronic switches, hence it is characterized by reduced size, controllability and switching losses. among the six switches, t1, t2, t3, and t4 are h-bridge switches, also called polarity reversing switches and the switches s1 and s1 1 are level generating switches. the various switching states for generating 5 levels at the output are shown in its switching table (table i). the first positive stepped (vdc1=v1) level is achieved by turning on the h-bridge switches t1 and t2 and the diode or level generating switch s1 1 . the second level (vdc2 = v1+v2) is obtained by turning on the h-bridge switches t1 and t2 and the level generating switch s1. during this instant, the diode d will not conduct, as a negative voltage is applied to the diode. fig. 2. the optimized mli with two symmetrical or asymmetrical voltage sources table i. switching sequence to generate five levels with two symmetrical sources output voltage h-bridge switches level generating switches t1 t2 t3 t4 s1 s1' v1+v2 1 1 0 0 1 0 v1 1 1 0 0 0 0 1 1 0 0 0 1 0 1/0 0/1 1/0 0/1 0 0 -v1 0 0 1 1 0 0 0 0 1 1 0 1 -( v1+v2) 0 0 1 1 1 0 the zero switching states can be obtained in two ways: one is using the h-bridge switches t1, t3, and the load and the other is using the h-bridge switches t2, t4, and the load. similarly, the negative stepped voltages are achieved by turning on the h-bridge switches t3 and t4 instead of t1 and t2 as in the case of positive voltage levels. all the gates are signaled by a simple pulse width modulation (pwm) technique, in which a sinusoidal reference signal is compared engineering, technology & applied science research vol. 10, no. 3, 2020, 5719-5723 5721 www.etasr.com manjunatha et al.: an optimized multilevel inverter topology with symmetrical and asymmetrical dc … with the carrier signal for generating the gate signal. these signals or pulses are anded and ored by a logical operator to obtain the required pulses. these final pulses are then given to the corresponding switches. b. operation of the asymmetrical optimized mli the 5-level topology shown in figure 2 is capable of generating 7 levels at the output terminals with two asymmetrical voltage sources. the two dc sources are considered with the ratio of 1:2. the various switching states for generating a 7-level output are given in table ii. the lower level positive stepped waveform is obtained by turning on the h-bridge switches t1 and t2 and the diode, the positive middle level can be obtained by turning on the level generating switch s1 1 along with h-bridge switches t1 and t2, and the highest level at the output is obtained by turning on the h-bridge switches t1, t2 and the level generating switch s1. similarly, the negative stepped voltages are achieved by turning on the hbridge switches t3 and t4 instead of t1 and t2. table ii. switching sequence to generate seven levels with two unsymmetrical sources output voltage h-bridge switches level generating switches t1 t2 t3 t4 s1 s1' v1+v2 1 1 0 0 1 0 v2 1 1 0 0 0 1 v1 1 1 0 0 0 0 0 1 /0 0/1 1/0 0/1 0 0 -v1 0 0 1 1 0 0 -v2 0 0 1 1 0 1 -(v1+v2) 0 0 1 1 1 0 iv. comparison with existing topologies to show the advantages and the originality of the proposed optimized mli, the data of conventional, recent, the proposed topologies are presented and compared in this section. the control difficulty and consistency directly depends on the number of required power electronic switches. the detailed comparison data are listed in table iii. table iii. symmetrical mli comparison [2] [3] [4] [10] [11] proposed main switches 2(n-1) 2(n-1) 2(n-1) 2(n-1)-2 (n+7) 2 (3n-5) 2 clamping diode (n-1)(n-2) 0 0 (n-3)(n-2) 0 (n-3) 2 flying capacitors 0 (n-1)(n-2) 2 0 (n+1) 2 (n-1) 2 0 dc bus capacitors (n-1) (n-1) 0 (n-1) 2 (n-3) 2 0 dc source 1 1 (n-1) 2 1 1 (n-1) 2 total components n 2 2 (n +3n-2) 2 (5n-5) 2 n 2 -2n+3 (3n+5) 2 (5n-9) 2 figure 3 represents the total devices required for generating the specific level. the proposed structure requires a comparatively very small number of switches with symmetrical or with asymmetrical voltage, and at any instant a maximum of 4 switches will conduct. fig. 3. total number of required components v. simulation and experimental results a. simulation results in order to verify the performance of a proposed mli, it was simulated in matlab/simulink platform with a linear load. the simulation results of the proposed mli with two symmetrical sources (v1:v2=100:100) and two asymmetrical sources (v1:v2 = 100:200) are discussed in this section. figure 4 shows the simulink model of the optimized mli (omli). fig. 4. simulink model of the proposed pli the output voltage, output current, and thd present in the voltage of the 5-level proposed omli with two symmetrical dc sources are shown in figure 5. engineering, technology & applied science research vol. 10, no. 3, 2020, 5719-5723 5722 www.etasr.com manjunatha et al.: an optimized multilevel inverter topology with symmetrical and asymmetrical dc … (a) (b) (c) fig. 5. (a) 5-level voltage, (b) 5-level current, (d) fft analysis with two symmetrical sources (a) (b) (c) fig. 6. (a) 7-level voltage, (b) 7-level current, (c) fft analysis with two asymmetrical sources to run the omli simulink model, ode 45 solver has been used with a run time of 0.04s for two cycles. form figure 5(a) and 5(b) it is observed that each level has a step change of 100v and 1a respectively. the %thd value of omli for the 5-level is 21.56% as shown in figure 5(c). output voltage, output current, and thd present in the voltage of the 7-level omli with two asymmetrical dc sources are shown in figure 6. form figure 6(a)-(b) it is observed that each level has a step change of 100v and 1a respectively. the %thd in output voltage is 12.14, having reduced by 44% when compared to the 21.56%. b. experimental results the proposed omli with two asymmetrical dc sources was tested experimentally in order to evaluate its performance. the prototype of the omli is shown in figure 7 and the experimental results in figure 8. fig. 7. photograph of hardware setup of the proposed mli the implementation of the proposed mli was carried-out by using an fpga spartan-6 controller, which is highly preferable to generate switching pulses in real-time implementations with an xilinx processor as ir2110 driver module and tlp250 opto-couplers. the power semiconducting switches used in the experimental prototype model are 6 nos of fga15n120 igbts with anti-parallel diodes and one uncontrolled switch. the outcome waveforms were measured and recorded with key-sight dsox2014a oscilloscope, with a 100mhz, 4 analog channels. from the simulation analysis, it was observed that the omli output voltage thd for the 7-level inverter was 12.14%. the thd of the prototype model was measured with a fluke 434 series-ii power-quality analyzer and the results are presented in figure 8(a) and (b). figure 8(a) shows the 7-level output voltage of the omli with asymmetrical sources and figure 8(b) shows the corresponding %thd which was 13.1% for the 7-level omli. from figure 8, it is clear that the experimental results are in close agreement with simulation and theoretic analysis with an acceptable error of ±2%. engineering, technology & applied science research vol. 10, no. 3, 2020, 5719-5723 5723 www.etasr.com manjunatha et al.: an optimized multilevel inverter topology with symmetrical and asymmetrical dc … (a) (b) fig. 8. (a) 7-level voltage (b) corresponding thd vi. conclusions in this work, an optimized multilevel inverter has been presented for sustainable energy applications. in comparison with the already existing and recently proposed topologies, this topology uses fewer components to produce the steps at the output side. thereby, the proposed inverter will be compact in size and its overall complexity will be reduced. the proposed inverter was simulated in matlab/simulink with the consideration of two symmetrical or asymmetrical voltage sources. it was seen that, with two symmetrical sources, the proposed inverter produces 5 levels at the output side, while with two asymmetrical sources it produces 7 levels. the simulated performance of the proposed 7-level inverter has been compared with the experimental results, which are in close agreement with the simulation results. references [1] h. akagi, “multilevel converters: fundamental circuits and systems”, proceedings of the ieee, vol. 105, no. 11, pp. 2048-2065, 2017 [2] z. zheng, k. wang, l. xu, y. li, “a hybrid cascaded multilevel converter for battery energy management applied in electric vehicles”, ieee transactions on power electronics, vol. 29, no. 7, pp. 3537-3546, 2014 [3] q. a. le, d. c. lee, “a novel six-level inverter topology for mediumvoltage applications”, ieee transactions on industrial electronics, vol. 63, no. 11, pp. 7195-7203, 2016 [4] x. yuan, “derivation of voltage source multilevel converter topologies,'' ieee transactions on industrial electronics, vol. 64, no. 2, pp. 966976, 2017 [5] a. boora, a. nami, f. zare, a. ghosh, f. blaabjerg, “ voltage sharing converter to supply single-phase asymmetric four-level diode clamped inverter with high power factor loads”, ieee transactions on power electronics, vol. 25, no. 10, pp. 2507–2520, 2010 [6] m. khazraei, h. sepahvand, k. a. corzine, m. ferdowsi, “active capacitor voltage balancing in single-phase flying-capacitor multilevel power converters”, ieee transactions on industrial electronics, vol. 59, no. 2, pp. 769-778, 2012 [7] n. prabaharan, k. palanisamy, “analysis of cascaded h-bridge multilevel inverter configuration with double level circuit,” iet power electronics, vol. 10, no. 9, pp. 1023-1033, 2017 [8] m. f. kangarlu, e. babaei, m. sabahi, “cascaded cross-switched multilevel inverter in symmetric and asymmetric conditions”, iet power electronics, vol. 6, no. 6, pp. 1041-1050, 2013 [9] j. venkataramanaiah, y. suresh, a. k. panda, “a review on symmetric, asymmetric, hybrid and single dc sources based multilevel inverter topologies”, renewable and sustainable energy reviews, vol. 76c, pp. 788-812, 2017 [10] j. zhao, y. han, x. he, c. tan, j. cheng, r. zhao, “multilevel circuit topologies based on the switched-capacitor converter and diode-clamped converter”, ieee transactions on power electronics, vol. 26, no. 8, pp. 2127-2136, 2011 [11] m. b. matam, a. k. d. venkata, v. k. mallapu, “analysis and implementation of impedance source based switched capacitor multilevel inverter”, engineering science and technology, an international journal, vol. 21, no. 5, pp. 869-885, 2018 [12] e. babaei, s. laali, z. bayat, “a single-phase cascaded multilevel inverter based on a new basic unit with reduced number of power switches”, ieee transactions on industrial electronics, vol. 62, no. 2, pp. 922-929, 2015 [13] k. k. gupta, a. ranjan, p. bhatnagar, l. k. sahu, s. jain, “multilevel inverter topologies with reduced device count: a review,” ieee transactions on power electronics, vol. 31, no. 1, pp. 135-151, 2016 [14] r. s. alishah, s. h. hosseini, e. babaei, m. sabahi, “optimal design of new cascaded switch-ladder multilevel inverter structure,” ieee transactions on industrial electronics, vol. 64, no. 3, pp. 2072-2080, 2017 [15] m. d. siddique, s. mekhilef, n. m. shah, a. sarwar, m. a. memon, m. seyedmahmoudian, b. horan, a. stojcevski, k. ogura, m. rawa, h. bassi, “asymmetrical multilevel inverter topology with reduced number of components”, 2018 ieee international conference on power electronics, drives and energy systems, chennai, india, december 1821, 2018 [16] u. b. tayab, m. a. al humayun, “modeling and analysis of a cascaded battery-boost multilevel inverter using different switching angle arrangement techniques”, engineering, technology & applied science research, vol. 7, no. 2, pp. 1450-1454, 2017 [17] a. nouaiti, a. saad, a. mesbahi, m. khafallah, m. reddak “design and rest of a new three-phase multilevel inverter for pv system applications”, engineering technology & applied science research, vol. 9, no. 1, pp. 3846-3851, 2019 [18] s. n. rao, d. v. ashok kumar, c. sai babu. “implementation of multilevel boost dc-link cascade based reversing voltage inverter for low thd operation”, journal of electrical engineering & technology, vol. 13, no. 4, pp. 1528-1538, 2018 microsoft word 376-1025-1-rv-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 522-525 522 www.etasr.com seifouri and faraji: simulation of optimized structure of laterally coupled distributed feedback … simulation of the optimized structure of a laterally coupled distributed feedback (lc-dfb) semiconductor laser above threshold mahmood seifouri shahid rajaee teacher training university, faculty of ece, lavizan, tehran, iran mahmood.seifouri@srttu.edu ata faraji ministry of education education organization of kurdistan bijar, iran faraji_elec@yahoo.com abstract— in this paper, the laterally coupled distributed feedback semiconductor laser is studied. in the simulations performed, variations of structural parameters such as the grating amplitude a, the ridge width w, the thickness of the active region d, and other structural properties are considered. it is concluded that for certain values of structural parameters, the laser maintains the highest output power, the lowest distortion bragg frequency δl and the smallest changes in the wavelength λ. above threshold, output power more than 40mw and smsr values greater than 50 db were achieved. keywords-laterally coupled distributed feedback laser; rate equation; coupled wave equation; transfer matrix method i. introduction the semiconductor dfb lasers, due to their low threshold current, narrow line width and single mode capability, are considered as the optical source in communications systems [1]. conventional dfb lasers with coupling refractive index with end facets coated with anti reflection (ar), are not singlemoded and have two symmetrical modes relative to bragg mode that appear simultaneously in the laser output. one way for having a single mode in ar dfb laser is by employing an equivalent phase shift at the center of the grating structure. these lasers are also named qws–dfb and have high efficiency but are sensitive to the reflection at the facets. lcdfb lasers use a lithographic fabrication step to define the distributed feedback grating, avoiding subsequent regrowth. this makes this type of lasers not only easier to fabricate but also less expensive [2-7]. for the first time, this article reports on the stability of lc-dfb lasers against spatial hole burning (shb), maximum output power and side mode suppression ratio (smsr) values above threshold conditions. the theoretical analysis is carried out by simultaneously solving both the coupled wave and rate equations using the transfer matrix method. in section 2, the theory and the physical model are explained. section 3 explains the results and the conclusion is summarized and discussed briefly in section 4. ii. theoretical and physical model figure 1 illustrates a simple design of a five-layered lcdfb laser and its features. in this figure, d, h and t are the active, buffer and wave guide layer thicknesses respectively. in figure 2, a clearer view of a lc-dfb laser is illustrated. it can be seen that there is a grating over the waveguide at both sides of the central area which in turn makes a distributed reflection in the laser. we consider the direction of the electric field along y-axis, (transverse electric (te) mode). electromagnetic waves propagate both in positive and negative directions along the zaxis in the cavity. the modified coupled-mode equations as formulated in [8] are:      =−− =− )()( )( )()( )( zajzaj dz zdb zbjzaj dz zda κδ κδ (1) where a and b are the forward and backward propagating complex amplitudes of the field respectively; κ is the coupling coefficient between forward and backward propagating modes; δ=β-β0 is the bragg wavelength detuning; β0=mπ/λ is the propagation constant, in which m is the grating order. carrier density in the active region follows the rate equation. this equation for the single-moded dfb laser is [9]: [ ] ),(),(),(),(),( 2 tzstzgtzc�tzb�a qd j t tz� −+++= ∂ ∂ (2) where ν(z,t) and s(z,t) are carrier and photon densities respectively, j is the input current density; q is the electronic charge; d is the active layer thickness; a, b and c are the nonradiative, spontaneous and auger rates respectively. photon density at every point is proportional to the sum of the square etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 522-525 523 www.etasr.com seifouri and faraji: simulation of optimized structure of laterally coupled distributed feedback … of forward and backward traveling wave amplitudes. in (2), g is the stimulated emission rate. fig. 1. simple design of a dfb laser structure with lateral coupling. fig. 2. the schematic of laterally-coupled distributed feedback laser [7]. analysis is based on solving both (1) and (2) simultaneously. the method employed is based upon the transfer matrix method (tmm) [10, 11]. table i. the values of the parameters parameters values cavity length (l) 500 mµ laser wavelength ( 0λ ) 1.5 mµ buffer layer thickness (h) 150 nm waveguide layer thickness (t) 150 nm internal dissipation of the active layer ( intα ) 20 1− cm improved line width coefficient ( 0α ) 6 spontaneous emission factor ( β ) 10-4 nonradiative combination rate (a) 10 8 s -1 spontaneous recombination rates (b) 8 × 10-11 13 −scm auger recombination rates (c) 7.5 × 10-29 16 −scm amplified spontaneous emission spectrum in dfb laser is computed using (3). both green's function and tmm are employed in the analysis [12]. ( ) ( ) ( ) ( ) 2 22 0 22 1 21 2 12 1 2 11 1 (3) l ase sp rhc p n z g z e z dz y r y r y rr yλ − = + − − ∫ where r1 and r2 are the facet reflection coefficients of the laser, nsp is the population inversion coefficient, yij are elements in the transfer matrix and e(z) is the solution of coupled wave equations. in this method, the cavity length is divided in to 200 equal parts and in every part different parameters of the laser including coupling coefficient, carrier density, refractive index and density of photons are assumed to be constant. but their values are different from one part to the next. ref. [7] has been used as the bench mark for our calculations for threshold conditions to the first order grating. the values of the parameters used in the calculations are presented in table 1. in lc-dfb laser structure by choosing a suitable ridge height and width and also an appropriate input current, a structure with minimum flatness parameter above the threshold conditions is obtained. for modeling purposes, first the effective refractive index method is employed and the changes both in the x and y directions are calculated. ultimately, the tmm only along the z direction is employed. the above procedure provides a simulation in all 3 directions. the effective refractive index under the ridge and the area around it has also been considered. then the effective index calculations were used to compute the lateral coupling coefficient on both sides of the ridge. iii. results and discussions figure 3 shows the amplified spontaneous emission (ase) spectrum with respect to δl, in laterally coupled distributed feedback laser structure for various ridge widths, at constant current. this figure shows various side modes and the bragg mode (the middle mode), which is amplified. in this figure it can be seen that with constant normalized current, b=3, with structure having w=2µm, maximum value of the smsr which is approximately 49 db, is achieved. fig. 3. amplified spontaneous emission spectrum of the δl for different ridge widths in lc-dfb structure above threshold. etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 522-525 524 www.etasr.com seifouri and faraji: simulation of optimized structure of laterally coupled distributed feedback … in figure 4, we see that for the maximum value of smsr for ridge width w=2 µm and grating amplitude a=0.1 µm with normalized current b=2, a value of 51 db is achieved. figure 5 shows changes of the output power with normalized current for different values of the active region thickness. as can be seen from figure 5, with increasing input current, output power pout increases and by increasing the thickness of the active region, the slope of the output power rises. with constant normalized current b=3, output power greater than 40 mw is achieved. the slope of pout with respect to normalized current is proportional to the external quantum efficiency. by increasing d, light intensity and external quantum efficiency of the laser are reduced. fig. 4. amplified spontaneous emission spectrum of the δl for active region with thickness d=1.5 µm in lc-dfb structure above threshold. fig. 5. output power vs. normalized current for lc-dfb laser structure for different values of active region thickness. figure 6 shows the variation of bragg deviation with different values of the active region thickness, (with respect to normalized current). changes in the mean normalized deviation from the bragg mode (δl) for d equal or greater than 0.2 µm is almost negligible. to better understand the effects of the electrical current on the performance of the device above the threshold, figure 7 illustrates the changes in λ for different values of the active region thickness. the wavelength variations and tenability of the device is estimated to be about 0.15 nm. fig. 6. changes in the mean normalized deviation from the bragg mode, δl vs. normalized current for lc-dfb laser for different values of the active region thickness. fig. 7. changes in the output wavelength vs. normalized current for lcdfb laser structure with different values of active region thickness. iv. conclusion in this paper, the lc-dfb laser above threshold condition has been analyzed and modeled for the first time. an output power more than 40 mw and smsr values greater than 50db were achieved. variations of structural parameters are considered in the simulations. the minimum changes in wavelength occurred with smaller values of the active layer thickness. the above advantages together with the device being single-moded, perhaps make this laser the most suitable choice for optical telecommunications systems. references [1] k. nosu, k. iwashita, “a consideration of factors affecting future coherent lightwave communication”, journal of lightwave technol. vol. 6, no. 5, pp.686-694, 1988 [2] r. millett, k. hinzer, t. hall, h. schriemer, “simulation analysis of higher order laterally-coupled distributed feedback lasers”, ieee journal of quantum electronics, vol. 44, no. 12, pp. 1145-1151, 2008 etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 522-525 525 www.etasr.com seifouri and faraji: simulation of optimized structure of laterally coupled distributed feedback … [3] r. millett, h. awad, m. poirier, v. tolstikhin, t. hall, k. hinzer, h. schriemer, “design and fabrication of a λ/4 phase shifted 1310 nm laterally-coupled distributed-feedback laser”, conference on lasers and electro-optics, 2008 and 2008 conference on quantum electronics and laser science, cleo/qels, san jose, 2008 [4] r millett, k hinzer, a benhsaien, t. j. hall, h schriemer “the impact of laterally coupled grating microstructure on effective coupling coefficients”, nanotechnology, vol. 21, no. 13, art. no. 134015, 2010 [5] r. d. martin, s. forouhar, s. keo, r. j. lang, r. g. hunsperger, r. tiberio, p. f. chapman, “ingaas-gaas-aigaas laterally-coupled distributed feedback (lc-dfb) ridge laser diode”, electronics letters, vol. 30 no. 13, pp. 1058-1060, 1994 [6] s. forouhar, r.m. briggs, c. frez, k.j. franz, a.ksendzov. highpower laterally coupled distributed-feedback gasb-based diode lasers at 2µm wavelength” applied physics letters, vol. 100, no. 3, 031107, 2012 [7] j. wang, j. tian, p. cai, b. xiong, ch. sun, y. luo, “1.55µm algainas–inp laterally coupled distributed feedback laser”, ieee photonics technology letters, vol. 17, no. 7, pp. 1372 1374, 2005 [8] w. streifer, d. r. scifres, r. d. burnham, “coupled wave analysis of dfb and dbr lasers”, ieee journal of quantum electronics, vol. 13, no. 4, pp. 134–141, 1977 [9] g. p. agrawal, a. k. dutta, semiconductor lasers, 2nd ed., new york, von nostrand reinhold, 1993 [10] f. shahshahani, v. ahmadi, “analysis of relative intensity noise in tapered grating qws-dfb laser diodes by using three rate equations model”, solid state electronics, vol. 52, no. 6, pp. 857-862, 2008 [11] t. makino, “transfer-matrix formulation of spontaneous emission noise of dfb semiconductor lasers”, journal of lightwave technology, vol. 9, no. 1, pp. 84-91, 1991 [12] t. makino, j. glinski, “transfer matrix analysis of the amplified spontaneous emission of dfb semiconductor laser amplifier”, ieee journal of quantum electronics, vol. 24, no. 8, pp. 1507-1518, 1988 microsoft word etasr_v13_n4_pp11166-11169 engineering, technology & applied science research vol. 13, no. 4, 2023, 11166-11169 11166 www.etasr.com venkateswarlu et al.: emotion recognition from speech and text using long short-term memory emotion recognition from speech and text using long short-term memory sonagiri china venkateswarlu dept. of electronics and communication engineering, institute of aeronautical engineering, india cvenkateswarlus@gmail.com siva ramakrishna jeevakala dept. of electronics and communication engineering, institute of aeronautical engineering, india jsrkrishna3@gmail.com (corresponding author) naluguru udaya kumar dept. of electronics and communication engineering, marri laxman reddy institute of technology and management, india joyudaya@gmail.com pidugu munaswamy dept. of electronics and communication engineering, institute of aeronautical engineering, india sidduvamsi@gmail.com dhanalaxmi pendyala dept. of electronics and communication engineering, institute of aeronautical engineering, india nanisp197@gmail.com received: 2 may 2023 | revised: 22 may 2023 | accepted: 23 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6004 abstract everyday interactions depend on more than just rational discourse; they also depend on emotional reactions. having this information is crucial to making any kind of practical or even rational decision, as it can help to better understand one another by sharing our responses and providing recommendations on how they may feel. several studies have recently begun to focus on emotion detection and labeling, proposing different methods for organizing feelings and detecting emotions in speech. determining how emotions are conveyed through speech has been given major emphasis in social interactions during the last decade. however, the real efficiency of identification needs to be improved because of the severe lack of data on the primary temporal link of the speech waveform. currently, a new approach to speech recognition is recommended, which couples structured audio information with long-term neural networks to fully take advantage of the shift in emotional content across phases. in addition to time series characteristics, structural speech features taken from the waveforms are now in charge of maintaining the underlying connection between layers of the actual speech. there are several long-short-term memory (lstm) based algorithms for identifying emotional focus over numerous blocks. the proposed method (i) reduced overhead by optimizing the standard forgetting gate, reducing the amount of required processing time, (ii) applied an attention mechanism to both the time and feature dimension in the lstm's final output to get task-related information, rather than using the output from the prior iteration of the standard technique, and (iii) employed a powerful strategy to locate the spatial characteristics in the final output of the lstm to gain information, as opposed to using the findings from the prior phase of the regular method. the proposed method achieved an overall classification accuracy of 96.81%. keywords-emotion recognition; speech recognition; mfcc; lstm; deep learning i. introduction applications that rely on human-machine connections have made emotional reactions a priority since they are such an integral part of human interactions. reactions can be analyzed and interpreted scientifically in a variety of ways, including facial characteristics, bodily indicators, and language. to engineering, technology & applied science research vol. 13, no. 4, 2023, 11166-11169 11167 www.etasr.com venkateswarlu et al.: emotion recognition from speech and text using long short-term memory achieve more natural and open interactions between humans and computers, it is necessary to regularly recognize and appropriately retain emotions represented by audio signals [1, 2]. in the last two decades, several studies have developed and refined several machine-learning (ml) approaches to the problem of emotion interpretation, such as speech emotion recognition (ser). there is a wide variety of uses for speech recognition technology. the effectiveness of audio interfaces and advisory services is measured by frustration identification. online businesses try to tailor their offerings to the unique needs of their customers on an emotional level [3]. monitoring the stress levels of flight crews has been shown to reduce the number of aircraft accidents. many studies used facialexpression recognition tools in their products to improve the user experience of people interacting with computers and increase user engagement [4]. web-based interfaces have improved the precision of emotion detection using real-time facial identification and emotion prediction, intending to attract as many customers as possible by making changes based on their preferences [5]. the primary emphasis is on evaluating input data, audio, and video evidence to determine the subject's state of mind and provide advice. there are two main factors to consider while designing an ser system: (i) locating and extracting relevant features from an effective emotional text database, and (ii) constructing a trustworthy lstm model using ml techniques. in actual use, the difficulty with which an ser program extracts emotional features is a major issue. several studies have defined basic speech characteristics that convey speech content, such as power, tone, amplitude intensity, time domain power spectrum values, mel-frequency cepstrum coefficients (mfcc), and amplification features. for this reason, the vast majority of specialists favor using mixed features, which are made up of various characteristics that together convey more information. in addition, using composite features increases the likelihood of mistakes, as it makes training more difficult for most deep learning algorithms due to the large size and repetition of voice signals. therefore, eliminating high-level speech duplication requires careful feature selection. feature extraction or feature selection may help improve the precision and efficiency with which an ml model is trained, decrease unnecessary effort, focus on a specific area, and minimize internal requirements. expressions of emotion in spoken language are ultimately classified. emotion recognition is achieved by applying energy spectrum features to real-world voice data. emotional nuances are reflected in the vocal signal in a multitude of ways. one of the trickiest parts of emotion analysis is deciding which features to use. several conversation recognition methods have been proposed, and a variety of deep neural networks have been introduced to facilitate automated discourse recognition with low power consumption [6]. the deep spectrum characteristic performs a comprehensive analysis of a novel acoustic classification produced by running data through a neural network audio classification and building a feature map from the activation of the final fully connected layer [7]. the features metrics for the identification of level 2 and level 5 speech-based emotions were compared with the traditional acoustic representation. it can be beneficial for people with autism who can use portable devices to understand their own feelings and emotions and possibly adjust their social behavior accordingly [8]. in [9], an mfcc was used to analyze spectral characteristics in audio data to classify the 7 emotions using the logistic model tree (lmt) algorithm, showing an accuracy of 70%. in [10-12], ml classifiers were used to improve the classification accuracy of fnirs signals, decoding cognitive states, and classification of power system stability. these approaches focus on some features and neglect others, while their accuracy cannot exceed 70%, which can influence performance in recognizing emotion in speech. this study used the lstm parameter to extract features from a speech and text dataset. ii. methodology this kind of technology is called voice emotion recognition, as talking is the way people communicate with computers and convey their feelings [13]. emotional content in spoken language may be extracted by combining several approaches to signal analysis. there are many models for analyzing speech signals to predict and determine the underlying mood. this study used a recurrent neural network model with lstm, for training and analysis of audio files with sequential data. this study aimed to design a system that can achieve good accuracy in detecting embedded emotions in speech. a. data collection data collection is fundamental to the development of datarelated activities. overfitting is a key issue that has to be mitigated when using a large dataset and deep learning methods. there is a plethora of speech recognition datasets accessible to download from a variety of websites online, and most studies use freely accessible resources. this study used a text-based dataset [14] that contained text-based emotion details for various emotions. fig. 1. the lstm model for speech recognition. engineering, technology & applied science research vol. 13, no. 4, 2023, 11166-11169 11168 www.etasr.com venkateswarlu et al.: emotion recognition from speech and text using long short-term memory participants were given the option to record audio that expressed a variety of feelings, including happiness, calmness, sadness, anger, surprise, fear, and disgust. using the python library keras, lstm models were constructed sequentially. making this model requires only a few simple procedures, as shown in figure 1. the layers of a neural network are the basic building blocks, and the sequential class provides the structure for this model. at first, a new sequential class instance was created. next, a stack of layers was constructed and set to communicate with each other. the memory cells in the recurrent neural layers were denoted by the symbol lstm(). the dense layer was a fully linked layer used to generate results before the lstm stack of layers. after a network has been constructed, it must be compiled. one of the benefits of compilation is the reduction in time it takes to complete. figure 2 shows a block diagram of a continuous speech recognition system based on the pattern recognition paradigm. the speech signal is analyzed as a resulting sequence of feature vectors grouped in speech unit (phonemes or triphones) patterns. each obtained pattern is compared with reference patterns, pre-trained, and stored with class identities. these pre-trained patterns, obtained in a learning process, are the acoustical models for speech units. the outcome of the speech recognition stage is the recognized word sequence. the series of primitive layers is transformed into a highly optimized collection of matrix transformation values. due to the way keras is configured, the syntax of this transformation must typically be one that can be executed by a cpu. additionally, the optimizer and error functions must be defined before the model is compiled. fig. 2. the lstm model for speech-to-text recognition. the datasets, consisting of a matrix of input patterns x and an array of output patterns y, must be specified before training the network. in addition, the constructed network was trained with a backpropagation method and optimized using a loss function and optimization strategy supplied by the model's construction. this approach requires training over a certain number of epochs, as shown in figure 3. once training was complete, the network was tested using non-overlapping training data. the accuracy of the prediction was used as a statistic because it helps in forecasting the performance of a constructed model. data predictions were made using the predict() command after the model's efficacy was assessed. b. model training the model was trained using the fit() function with the following parameters: train x, target x, validation data, and a number of epochs. the test set included in the dataset was partitioned into x_test and y_test for validation purposes. the model iterated the data a certain number of times, as defined by the epochs parameter. up to a point, the more the epochs, the better the model will become. from that point on, the model will no longer progress with each epoch. the model was trained for 31 epochs. fig. 3. model training for lstm. keras defines neural networks as a series of layers. the sequential class serves as a framework for these levels of layers. the first step is to build a sequential instance of a class, followed by building a stack of layers and arranging them in the sequence in which they should be interlinked. the lstm recurrent neural layers are made up of memory cells which are known as lstm () cells. the dense layer is a fully connected layer that frequently precedes the lstm stack of layers and is used to produce a result. \ iii. results the results of the proposed lstm ml model. were compared with those of [12], which used svm and autoencoder and acquired a 74.07% accuracy rate. the network was evaluated once it was trained with a separate set of training data. after evaluating the performance of the model, it was used to make predictions. this action was carried out using the predict() function, and the output format was the same as specified by the output layer. the results of the model show its effectiveness in achieving good results compared to other emotion recognition studies, as it achieved an accuracy of 96.82%. a web app was created for the real-time application of the proposed speech emotion recognition model. a user can enter the text in the prompt displayed to predict and display the output emotion. the user can select a speech input file from the required location and press transcribe. then, the speech will be converted to text and the emotion is displayed as output. the user can also select to use his microphone to record the voice input, convert it into text, and display the emotion as output. table i shows the possible texts and emotions considered in this study. engineering, technology & applied science research vol. 13, no. 4, 2023, 11166-11169 11169 www.etasr.com venkateswarlu et al.: emotion recognition from speech and text using long short-term memory there are three types of inputs; the first is by entering the text message and then displaying the predicted emotion for the given text. the second is by uploading a voice file and then displaying the predicted emotion output, and the third is by allowing the mic to record the voice, analyzing it as a text, and then displaying the predicted emotion output. every text, speech, and voice has an emotion. table ii shows the overall accuracy of the emotional classification model. table i. text and its considered emotions text emotion i didn’t feel humiliated sadness i am feeling grouchy anger i am grabbing a minute to post i feel greedy wrong anger i am ever feeling nostalgic about the fireplace love table ii. lstm overall accuracy testing speech text voice accuracy 96.81% 96.81% 96.81% iv. conclusion and future scope the primary goal of this study was to employ recurrent neural networks with lstm to determine a person's emotional state. this study used a dataset of text files that depict a wide range of emotions, such as happiness, sadness, fear, contempt, surprise, and apathy. as most ml models take numeric values as input, the data was transformed into arrays to use them for feature extraction. the libros package was used to extract the file and mfcc features were used in this model. the collected values were then fed into an lstm model, which used these characteristics to provide an overall anticipated emotion. the model achieved an overall accuracy of 96.81% for emotion recognition using speech, text, and voice data. this model was used to enhance a real-time speaker identification system using a digital signal processor. the volume of the system may be adjusted according to the environment. this system can be used for aid to disabled persons. applications and websites can use this approach to gauge user sentiment and decide how to best tailor their offerings to their audience. additionally, this approach can be used in voice-based virtual assistants, chatboxes, and call centers for handling customer complaints. references [1] mustaqeem and s. kwon, "a cnn-assisted enhanced audio signal processing for speech emotion recognition," sensors, vol. 20, no. 1, jan. 2020, art. no. 183, https://doi.org/10.3390/s20010183. 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[9] a. a. a. zamil, s. hasan, s. md. jannatul baki, j. md. adam, and i. zaman, "emotion detection from speech signals using voting mechanism on classified frames," in 2019 international conference on robotics,electrical and signal processing techniques (icrest), dhaka, bangladesh, jan. 2019, pp. 281–285, https://doi.org/ 10.1109/icrest.2019.8644168. [10] m. m. h. milu, m. a. rahman, m. a. rashid, a. kuwana, and h. kobayashi, "improvement of classification accuracy of four-class voluntary-imagery fnirs signals using convolutional neural networks," engineering, technology & applied science research, vol. 13, no. 2, pp. 10425–10431, apr. 2023, https://doi.org/10.48084/ etasr.5703. [11] s. r. jeevakala and h. ramasangu, "classification of cognitive states using task-specific connectivity features," engineering, technology & applied science research, vol. 13, no. 3, pp. 10675–10679, jun. 2023, https://doi.org/10.48084/etasr.5836. [12] n. a. nguyen, t. n. le, and h. m. v. nguyen, "multi-goal feature selection function in binary particle swarm optimization for power system stability classification," engineering, technology & applied science research, vol. 13, no. 2, pp. 10535–10540, apr. 2023, https://doi.org/10.48084/etasr.5799. [13] s. r. bandela and t. k. kumar, "emotion recognition of stressed speech using teager energy and linear prediction features," in 2018 ieee 18th international conference on advanced learning technologies (icalt), mumbai, india, jul. 2018, pp. 422–425, https://doi.org/10.1109/icalt.2018.00107. [14] "emotion detection from text." https://www.kaggle.com/datasets/ pashupatigupta/emotion-detection-from-text. microsoft word etasr_v11_n1_pp6650-6656 engineering, technology & applied science research vol. 11, no. 1, 2021, 6650-6655 6650 www.etasr.com alghamdi et al.: healthcare analytics: a comprehensive review healthcare analytics: a comprehensive review alshymaa alghamdi college of computer and information systems umm al-qura university mecca, saudi arabia s44180219@st.uqu.edu.sa tahani alsubait college of computer and information systems umm al-qura university mecca, saudi arabia tmsubait@uqu.edu.sa abdullah baz college of computer and information systems umm al-qura university mecca, saudi arabia aobaz01@uqu.edu.sa hosam alhakami college of computer and information systems umm al-qura university mecca, saudi arabia hhhakam@uqu.edu.sa abstract-big data have attracted significant attention in recent years, as their hidden potentials that can improve human life, especially when applied in healthcare. big data is a reasonable collection of useful information allowing new breakthroughs or understandings. this paper reviews the use and effectiveness of data analytics in healthcare, examining secondary data sources such as books, journals, and other reputable publications between 2000 and 2020, utilizing a very strict strategy in keywords. large scale data have been proven of great importance in healthcare, and therefore there is a need for advanced forms of data analytics, such as diagnostic data and descriptive analysis, for improving healthcare outcomes. the utilization of large-scale data can form the backbone of predictive analytics which is the baseline for future individual outcome prediction. keywords-healthcare; big data; healthcare analytics; descriptive analytics; diagnostic analytics i. introduction data have become a topic of particular interest because of their high but often hidden potential [1]. their importance has been proven in almost all aspects of life. data give the ability to study the past and predict the future while developing the present. although profit is not the primary motivator, healthcare organizations should consider acquiring knowledge for available techniques, tools, and infrastructure to leverage big data [2]. in most sectors data grow exponentially. healthcare large scale data describe the large data volume [3] that overburdens a healthcare institution on a daily basis. existing logical methods can be applied to the tremendous amount of existing patient-related well-being and clinical information, offering more profound comprehension and improving healthcare [4]. in real world scenarios, individual information could help each doctor in deciding the most appropriate treatment for a given patient. healthcare has taken too long to utilize big data compared to other sectors. healthcare big data activities include collecting, analyzing, holding of consumer, patient, physical, and clinical data that are too large and complex to be understood by the traditional data processing methods. an example of this big data processing is the use of complex and sophisticated sensors in healthcare. as a result, big data are analyzed and processed by machine learning algorithms and specialized data scientists [5]. healthcare facilities require new methods to work out their recurrent challenges, especially concerning patients' diagnosis and treatment information. as a solution to these challenges that are related to data volume, velocity, variety, and veracity, healthcare facilities and organizations have to incorporate new technologies capable of data collection, storage, and information analysis to produce actionable insights [3]. different situations call for the application of different data strategies. the idea is to use healthcare analytics to create actionable information that can be utilized for improving patient care and the efficiency of processes. the paper at hand examines previous studies and evaluates the utilization of descriptive, diagnostic, and predictive healthcare analytics. ii. healthcare analytics the utilization of data analytics is helpful to healthcare professionals, especially in terms of predicting, diagnosing, and treating diseases, improving the quality of services and minimizing healthcare costs [6]. it is estimated that the u.s. healthcare system saves more than $450 billion annually through data mining [7]. many in-depth studies have examined the application of big data in mental health and other areas such as the methodological challenges of data mining perspectives [8]. this large volume of data is generated from fast-growing industries attracting clinicians' and scientists' attention [9], emerging the need for advanced forms of data analytics. healthcare professionals could significantly benefit from these techniques, reducing considerable effort, resources, and time, smoothening the running. these methods could also satisfy professionals by offering them more valuable knowledge and information [10]. big data analytics includes analysis, observation, influence, and prediction. corresponding author: alshymaa alghamdi engineering, technology & applied science research vol. 11, no. 1, 2021, 6650-6655 6651 www.etasr.com alghamdi et al.: healthcare analytics: a comprehensive review a. observation noting and taking records is essential for generating critical values from large scale data, and a new scientific field called "data science" has evolved [11]. a critical factor is data visualization in a quite friendly way which is vital for the development of society. management of these big data becomes challenging due to the organization and reorganization of the same data [12]. therefore highly advanced techniques are often employed for efficient and costeffective data management. healthcare services can be offered with analytics tools through proper storage [13]. b. influence data collection is important for every company which depends in future predictions [14]. more information causes more deliveries. gigabytes or terabytes are usually collected structurally in health monitoring toolkits, including sensors, structure, and data acquisition. large data volumes are often caused by either the number of sensors or the monitoring data structure size [15]. the scope is given by structure, while sensors provide resolution. c. prediction prediction becomes more useful when knowledge can be transformed into action. prediction and intervention need to be integrated into the same system in order to increase system's efficiency. this is a process of making future predictions based on historical data [16]. this analysis improves healthcare by improving decisions and personalizing care for each individual. healthcare organizations use predictive analysis drawn from new data streams directly from patients [17]. d. analysis analyzing big data has a workflow similar to what is described in [8]. a data warehouse is the storage of massive amounts of data produced from various sources. it uses analytic pipelines for smarter and affordable healthcare options. modern techniques have evolved to aid in this, increasing the resolution in which biological events are observed and recorded. therefore such big data analytics from medical healthcare systems can help providing new strategies [18]. iii. descriptive health analytics healthcare analytics are very important in medicine, as they offer insights into data, including hospital patient records, costs, and diagnoses, among others. descriptive analytics is a sub-branch of healthcare analytics [19], aiming to analyze raw data and come up with viable solutions to help patients. big data are firstly turned into actionable insights, mostly relying on public health and pharmacy among other factors [9]. descriptive analytics include various methods, entailing stages or processes whose outcomes enable easy manipulation and utilization to figure out solutions in real life. descriptive analytics use control data to categorize, characterize, aggregate, and classify data into valuable information for the healthcare professionals, in understanding and analyzing decisions, performance, and outcomes [20]. besides, data from descriptive analytics are prepared using tables and graphs showing the average length of stay in hospitals [4], the rate of discharge, and the rates of hospital occupancy among other indicators [21]. descriptive analytics is usually the easiest level of data to understand. moreover, control data are utilized in categorization, characterization, aggregation, and classification of the data, transforming them into valuable information for healthcare professionals in the process of understanding and analyzing decisions, performance, and outcomes. data visualization can answer specific questions related to patient care patterns, which ultimately highlight a broad perspective of evidence-based clinical practice [22]. as a result, real-time or near real-time data management has to be enabled in the process. using this method, literature predicts that previously unnoticed observed patterns in terms of hospital readmission are enabled to enhance a balance between cost and capacity [14]. descriptive analytics help because they connect previous decisions and their implications. it answers the question: "what happened?" giving a good basis of decision making. iv. classification of descriptive analytics a. data classification classification falls under supervised machine learning methods. artificial neural networks consist one of the most common underlying structures exploited [23]. training and validation sets are used whereas adequate output for given inputs is generated. this is the process of organizing healthcare data into relevant groups and categories that are easier to understand and analyze. this step is important as it allows easy data retrieval when needed. in healthcare applications the lack of data classification could result on much duplication complicating the tracking down of certain events and occurrences related to patients and health facilities. data classification process in healthcare widely revolves around content, context, and users. context refers to the location where it is applicable. user refers to the person who is using the data being classified. people in charge of the classification process have to take good care of the classification criteria, as wrong criteria can lead to wrong classifications. the categories should include information about the type of data included. moreover, security and privacy considerations should be examined with rules for data retrieval, transmission, storage, and possible risks associated with security policy violations [24]. b. data mining algorithms algorithms heuristic-based data mining algorithms in hospitals can be helpful in the stipulation of the relationship between different symptoms and a particular disease. the same algorithms can be used to stipulate the relationships between cause and effects of human behaviors and diseases [24]. one of their main roles is to ensure the standardization of healthcare practices. medical algorithms are evidence-based and data-driven [8]. c. methods/tools the methods applied are regression, association, clustering, data warehousing, and sequential pattern mining. data can be analyzed electronically or manually using traditional methods such as pen and paper through graphical methods [25]. this information is used by healthcare providers to shed light on facts such as occupancy rates and financial state of hospitals, number of inand out-patients, discharge, and length of stay among other entities or variables of study. other data analysis engineering, technology & applied science research vol. 11, no. 1, 2021, 6650-6655 6652 www.etasr.com alghamdi et al.: healthcare analytics: a comprehensive review methods are utilized including statistical analysis, which features descriptive, inferential, and diagnostic analysis among others. in healthcare, analysis of data is performed via statistical analysis using appropriate tools [7]. data from hospital financial records, number of patients, and staff can be inferred through statistical analysis of collected data. current data analysis tools include spss, matlab, sql, java, weka, rapidminer, r analytics suite, and python scikit-learn [7, 20]. d. problem domain problem domain analytics involve the process of creating a model that describes the problem to be solved. in healthcare, this deals with modeling solutions and curative measures for different diseases [26]. once there is a healthcare problem domain analysis for a given facility, this can be applied to multiple implementations at different periods as technology advances. problem domain analysis is fully independent of the platform where the solution is implemented [4]. e. data visualization data visualization is the process of representing data graphically. the visual elements used in this stage are charts, graphs, and maps. these elements along with data visualization tools enable one to see and understand patterns, trends, and outliers of data. data visualization is important for users in order to understand the enormous amounts of daily generated data quickly and effectively. in healthcare, where data are vital and the volumes of circulating data are huge, data visualization tools and technologies are essential to analyze information in order to enable data driven decisions. efficient use of data visualization techniques in healthcare enhances usability, hence the provision of quality care [27]. this stage should be taken seriously into consideration, as the advantages or benefits of effective data visualization are many, and they lead to better decision-making, hence improvement of the health sector. data visualization is incorporated in healthcare in an effort to answer specific questions or patterns of care, providing a broad view of evidence-based clinical practice. the activity of data analysis gives sufficient space for proper data management, use and study of operational content, and helps in capturing visual data and information including patient records. henceforth, data previously not observed and patterns not studied before are brought into light via data visualization [28]. differences brought up in patient records, financial records, and healthcare provision are captured and recorded through visualization tools. it is hard to imagine a healthcare institution that does not visualize data for its decision making [29]. v. diagnostic health analytics diagnostic health analytics is the second major health analytics method. this method is used in the analysis of healthcare organizations in order to transform them to fully data-driven institutions, offering competitive advantages. diagnostic analysis answers the "why" in a phenomenon [30], aiming at finding the causes of events. diagnostic analytics explain "why it happened" [30-31], such as "why did a patient got worse even with the best care". these answers enable healthcare providers to figure out problems and solutions. diagnostic health analytics take a critical look on data, trying to understand why events and behaviors occur [31]. a. data discovery, exploration, and analysis exploration, discovery, and analysis of data are major processes involved in diagnostic health analytics. discovery is bringing to light concealed structures and patterns [27]. this process is the act of collecting and examining data from different sources to gain insight from hidden patterns, trends, and outliers. it is the first step to fully exploit a health organization’s data and inform on critical clinical decisions [14]. through data discovery, data are gathered, combined, and analyzed in a sequence of steps. exploration of data is the initial step in data analysis where healthcare providers explore an extensive data set in an unstructured manner to uncover original patterns and trends, characteristics, and points of interest [32]. during clinical research or undertaking, even during decision making by healthcare providers, patient or organizational records are analyzed to get an insight of previous patterns and behaviors. this process is not meant to reveal any patterns in detail, but rather to create a broad picture of important trends, as data exploration is extracting data without knowing what it is looking for [33]. data exploration uses manual methods and automated tools, such as visualization tools. this process is vital in healthcare as it enables healthcare providers to cut down large sets of data to manageable sizes and focus on the efforts to optimize their analysis. analysis of data follows just after the discovery and exploration of data to emerge viable solutions to a healthcare organization's problems [20]. vi. qualitative and quantitative diagnostic analytics these are the two major classifications of diagnostic analytics. qualitative refers to interpreting meanings or processes, while quantitative aspect deals with numerals and statistical calculations of analysis [41]. qualitative diagnostic analytics focuses on meanings rather than quantifiable phenomena. qualitative diagnostic analytics puts more emphasis on the impact of the analysis on patients and healthcare providers as opposed to presumptions of the possibility of value-free inquiry [20]. therefore, qualitative diagnostic analytics aims at gaining an understanding of underlying motivations and reasons, while uncovering dominant trends in thoughts and opinions. quantitative diagnostic analytics, on the other hand, aim at quantifying data and generalizing results from a sample to the population of the study group [42]. a. focus of qualitative and quantitative methods qualitative research is widely used in research. it does not use statistics and mathematical operations to process data. qualitative research focuses on using research methods to address phenomena by analyzing experiments [34-35]. qualitative research focuses on the use of words or notes [36]. however, quantitative research uses methods, statistical processes, mathematics, and numerical data processing in a systematic experimental research of phenomena [37-38]. b. data collection during the qualitative research, both primary and secondary data collection methods are used. data could be collected from secondary sources such as social media platforms. linkedin engineering, technology & applied science research vol. 11, no. 1, 2021, 6650-6655 6653 www.etasr.com alghamdi et al.: healthcare analytics: a comprehensive review was used in [39], where authors looked for healthcare professionals, in order to get relevant data from prominent practitioners in the medical field. the research focused on big data analysis on linkedin as well as the management and surveillance of the diseases, while primary data were collected from interviews. people with relevant sources of information were interviewed in order to extract first-hand information. some questions were developed before the study, while other questions emerged during the study in order to adequately cover all relevant areas. c. objective the primary objective of health analytics is to provide insights in predicting and detecting the outcome of a disease, such as the prediction of heart-related diseases, hiv, and cancer [39]. moreover, it provides opportunities to health professionals for improvement in their field of operation, through the appropriate patient management service and their diagnosis. patients are served in the right manner, following the most suitable procedures. d. analysis healthcare analytics provide the most reliable information for a given patient. it also provides a given healthcare unit the right track about how its resources are being used [40], boosting accountability. the system is also used in detecting people who are most vulnerable to be infected by a particular infection. as a result, healthcare professionals are able to specify the most appropriate procedures to prevent the spread of a specific contagious disease. moreover healthcare analytics play a vital role in communication process within a particular healthcare center. e. findings big data strategies under healthcare analytics have major contribution to the research for new drugs [39]. the future of the health sector relies on big data strategies, since they enhance effectiveness, improve relations among the various stakeholders in a given healthcare unit, and help in reducing operational costs. some studies utilizing both qualitative and quantitative methods are shown in table i. table i. comparison of qualitative and quantitative methods feature qualitative method quantitative method references focus examining the breadth and depth of the phenomena, words and observations quantity (how much, number) focus on qualitative method: [34-35-36] focus on quantitative method: [37-38] objective descriptive, exploration descriptive, prediction focus on objectives: [39] analysis inductive (by the researcher) deductive (statistical) focus on analysis: [40] data collection interviews, observation questionnaire, test focus on data collection: [39] findings comprehensive precise, numerical focus on findings: [39] vii. classificaton of diagnostic analytics a. data classification diagnostic data discovery aims at making noisy data clear for classification, free of inconsistencies, and easy to understand. data discovery in healthcare is beneficial as it enables healthcare providers to gather actionable insights for better decision making, saves time, and makes data reusable. data discovery consists of five steps: connecting and blending, cleansing and preparation, sharing, analysis and generation of insights, and visualization [24]. data classification in diagnostic analytics aims on understanding the causes of events and behaviors. b. algorithms algorithms aim at answering why an event happened. due to their changing nature, algorithms change very fast. typically, algorithms utilize machine learning methods. c. methods/tools statistical methods are used in diagnostic analytics, and data can be analyzed in the same manner as in descriptive analytics. data can be analyzed electronically or manually using traditional methods [25]. this information is used by healthcare providers to shed light on entities or variables of study. in healthcare, data analysis is performed via statistical analysis using appropriate techniques [32]. d. problem domain in diagnostic analytics, the problem domain analytics has to be elaborated more than in descriptive analytics. it also involves the process of creating a diagnosis model to describe the problems that are needed to be solved. in diagnosis, this deals with modeling solutions and curative measures for different diseases [32]. once there is a healthcare problem domain analysis for a given facility, this can be applied to multiple implementations at different periods and as the technology advances. problem domain analysis is wholly independent of the platform where the solution is implemented. apart from descriptive analytics and diagnostics, there are predictive analytics and prescriptive analytics. predictive analytics is used to predict the future values for identification of unknown events, while prescriptive analytics is used for providing the best solution [19]. viii. predictive health analytics predictive analytics involve mining information out of raw data in order to predict future trends [43]. data mining and predicting is increasing progressively in the medical field. support systems based on different prediction frameworks have become key tools in disease diagn osis in order to ensure prevention and the quality of prediction for a possible disease [44]. disease prediction involves the extraction of hidden information and forecasting of the course of a disease development from medical data. many studies have been conducted to develop frameworks for predicting diseases based on machine learning techniques [44]. predictive health analytics is therefore the process of getting this information in engineering, technology & applied science research vol. 11, no. 1, 2021, 6650-6655 6654 www.etasr.com alghamdi et al.: healthcare analytics: a comprehensive review the health sector and processing it for exploiting in future predictions. health is one of the key areas that predictive analytics has been utilized [43]. predictive analytics applies known parameters to produce a model that can predict results for a different set of data. modeling gives this product as a prediction representing a probability of the variable being predicted based on estimates from input variables. most of the predictive modeling techniques in use include: decision trees, regression and neural networks. it has been noted that predictive analytics has been very useful in forecasting the pandemic of covid-19 [43]. healthcare institutions apply predictive analytics in various ways, such as in allocating resources based on previous trends, scheduling staff, gauging patient-risk to manage readmission costs, and manage pharmaceutical requirements. more than half of healthcare managers used predictive analytics in their organizations, and 57% of them believed that they were beneficial for their institutions [45]. in fact, 26% of them predicted saving over 25% of their total budget, as a result of applying such methods. ix. discussion this section discusses and compares descriptive and diagnostic health analytics. diagnostic health analysis mostly answers the question "why something happened". therefore, directed analysis and extensive exploration are required with the help of other tools, such as the use of visualization techniques that help uncover the genesis of problems, in order to help users to determine the extent to which these problems affect them [9]. for instance, it is possible to track down an increase in waiting times to provide several healthcare services, showing several factors that relate to patient, provider, or related organizational factors [8]. descriptive analysis usually gives an overview of what happened. it often deals with the discovery and exploration of new information in a given dataset. it connects previous decisions and their implications providing the best basis for decision making. it is a branch of health analysis aiming to analyze data and come up with relevant solutions that can help in proper decision making about a given patient. descriptive analysis quantifies events and transforms them into readable forms. in the health sector, descriptive analysis relies on clinical health support, public health, and pharmacy mental health among others, during the decision making process. on the other hand, diagnostic analysis enables any given healthcare unit to rely on data during the process of decision making, gaining competitive advantages over competing organizations. the diagnostic analysis is very essential since it gives detailed information about why certain things happened, for instance why a given patient situation worsened. this shows that diagnostic analysis explains the cause of events and behaviors, involving the discovery and exploration of any new data available. both descriptive and diagnostic analyses are outstanding and very essential in the decision making process. descriptive analysis relies on new information while the diagnostic analysis relies on already existing data. consequently, the most reliable conclusion emerges from combining these two methods. x. conclusion in general, healthcare analytics gives a deeper inspection of data in medical institutions. generation and access of data has been made easier these days, since they are global and mobile. it is evident that big data offer the ability to capture and manage visual data and records. an effective 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is applied and proposed for ecg signal modeling and noise reduction. the hopfield !eural !etwork (h!!) is a recurrent neural network that stores the information in a dynamic stable pattern. this algorithm retrieves a pattern stored in memory in response to the presentation of an incomplete or noisy version of that pattern. computer simulation results show that this method can successfully model the ecg signal and remove high-frequency noise. keywordshopfield �eural �etworks; ecg signal modeling; noise reduction i. introduction the electrocardiogram (ecg) signal is one of the diagnosing approaches to detect heart disease. ecg signals provide significance information about heart functional conditions and circulation system. by placing the electrodes on body surface the electrical activity of the heart muscles can be measured [1]. a typical ecg cycle waveform is shown in figure 1. the ecg signal is very weak, ranging from 10 µv to 5 mv, with a frequency from 0.05 hz to 100 hz. in addition, the ecg signal is often corrupted with noise. therefore, a correct diagnosis can be very difficult. the noise is generally generated from the equipment used and also from the body’s bioelectric activity [2]. since ecg signal is vital for an accurate diagnosis, ecg modeling and noise reduction is rather essential for clinical applications [3-6]. several methods have been applied for modeling and denoising of ecg signals, such as band pass filters [7], adaptive filters [8], the ensemble averaging technique [9] and extended kalman filters [10]. the adlpso algorithm [11] and wavelet neural networks (wnn) [12], denoising methods based on the wavelet transform, have also been used for ecg denoising. although these methods demonstrated good performance, they can be sensitive to varying parameters. neural networks have been recently used in all kind of modeling and their success and wide application encourage the consideration of neural networks as a method to model ecg signals with low signal to noise ratio (snr). in this study we used the hopfield neural network (hnn) for ecg signal modeling and noise reduction. the hnn is a recurrent neural network that stores the information in a dynamic stable pattern. the applied algorithm retrieves a pattern stored in memory in response to the presentation of an incomplete or noisy version of that pattern. the hnn consists of a set of n interconnected neurons which update their activation values asynchronously and independently of other neurons. all neurons are both input and output neurons [13]. figure 2 portrays a typical hnn that consists of a set of 4 interconnected neurons. all neurons are connected to each other and act as both inputs and outputs. ii. theoretical background modeling using an hnn follows four basic stages [13]: a. storage (learning). if x1, x2,…, xp indicated a known set of m-dimensional memories, the synaptic weights of the network can be computed as: , , 1 1 m m j i j i x x e m θ θ θ = = = ∑ ∑ (1) , , , 1 1 i i i x e x e θ θ θ θ θ β + ≥ = − <    � � (2) , , 1 1 , 0, p j i ij i j h m i j θ θ θ β β = ≠ = =      ∑ � (3) where hij is the synaptic weight from neuron i to neuron j and xθ,i is ith element of vector xθ. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 345-348 346 www.etasr.com bagheri et al: electrocardiogram (ecg) signal modeling and �oise reduction using hopfield… fig. 1. a typical ecg signal fig. 2. a hopfield network with four nodes b. initialization if u indicates an unknown m-dimensional input vector presented to the network, we will have: ,)0( jj ut = ϕ=1,...,μ (4) where tj(0) is the state of neuron j at time n = 0, and uj is the jth element of the vector u. c. iteration until convergence update the elements of state vector t(n) randomly in accordance with the rule: 1 ( 1) sgn ( ) m j ji i i u n h u n = + =      ∑ (5) repeat the iteration until the state vector u stays unchanged. d. outputting if ustable indicates the stable point computed at the end of stage c, the resulting output vector y of the network will be: stable uy = (6) if o indicates the target output for the algorithm then the error signal is defined as: e o y= − (7) and the mean-squared error is defined as follows: 21 [ ] 2 j e e= (8) where e is the statistical expectation operator. iii. application of the hnn both training and testing data were taken from [14]. the steps described below were followed in order to obtain data suitable for the hnn input: • data consists of 2 ecg signals with 30000 samples each. • a low pass filter used to calculate the baseline wander. with a sampling frequency of f s =20000 we have: ( , 0.7 / )baseline lpfilter data fs= (9) • to remove baseline wander the following equation was used: data-ew data baseline= − (10) • noise was added to data with respect to the definition of snr. signalpower s-r -oisepower = (11) the original data were noisy to begin with (figure 3) but in order to test the algorithm, high magnitude noise was needed and so an snr equal to zero was applied. hnn training included these steps: • storage: output data of step2 (clean signal) were given to the network to compute (1), (2) and (3). • initialization: output data of step 3 (noisy signal) were given to the network as an initialization vector to compute (4). • iteration until convergence: the algorithm was updated by (5). etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 345-348 347 www.etasr.com bagheri et al: electrocardiogram (ecg) signal modeling and �oise reduction using hopfield… • outputting: the unchanged output of (5) is the output of algorithm. for the considered application m=30000, p=2, number of iterations=100 and number of neurons=30000. each neuron stands for storing of one sample of the signal. matlab was used for all calculations. the clean signal is shown in figure 3 and the noisy signal is shown in figure 4. iv. results the results of applying the hnn algorithm to the considered data are shown in figures 5 and 6. it can be seen that the method successfully modeled the ecg signal and removed high-frequency noise. figure 7 shows the meansquared error versus the number of iterations. as it can be seen, the algorithm converges and the mean-square value of the error signal decreased as the number of iterations increased. fig. 3. original signal fig. 4. noisy signal fig. 5. noisy data, original data and output of the hnn for signal 1 fig. 6. noisy data, original data and output of the hnn for signal 2 v. conclusion the ecg signal is one of the diagnosing approaches to detect heart diseases but it is usually corrupted with unwanted interference. to reduce noise, methods employing filters and wavelet transform have been applied. although they demonstrated good performance, they tend to be sensitive to varying parameters. neural networks have widely been used for modeling, showing significant success and being less sensitive to varying parameters. in this study a hopfield neural network is applied for ecg signal modeling and denoising. the algorithm was applied to two different ecg signals. results showed that the method can successfully model ecg signals with low snr. more tests will be conducted to further investigate the performance of hnn in the future. other kinds of ecg signals will also be used to examine the clinical application of the method. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 345-348 348 www.etasr.com bagheri et al: electrocardiogram (ecg) signal modeling and �oise reduction using hopfield… fig. 7. mean-squared error vs iterations references [1] o. sayadi, m. b. shamsollahi, “ecg denoising and compression using a modified extended kalman filter structure”, ieee trans. biomed. eng, vol. 55, no. 9, pp. 2240-2248, 2008 [2] w. zhang, t. ma, l. ge, “enhancement of ecg signals by multiresolution sub band filter”, 2nd international conference on bioinformatics and biomedical engineering, icbbe 2008, china, 2008 [3] j. wang, z. li, “an ecg segmentation model used for signal generator”, 2nd international conference on innovative computing, information and control, icicic '07, japan, 2007 [4] y. lu, j. yan, y. yam, “model-based ecg denoising using empirical mode decomposition”, ieee international conference on bioinformatics and biomedicine, usa, 2009 [5] w. zgallai, m. sabry-rizk, p. hardiman, j. o’riordan, “music-based bispectrum detector: a novel non-invasive detection method for overlapping fetal and mother ecg signals”, proceedings of the 19th international conference of the ieee engineering in medicine and biology society, vol. 1, pp. 72-75, 1997 [6] r. swarnalatha, d. v. prasad, “a novel technique for extraction of fecg using multi stage adaptive filtering”, journal of applied scienses, vol. 10, no. 4, pp. 319-324, 2010. [7] i. i. christov, i. k. daskalov, “filtering of electromyogram artefacts from the electrocardiogram”, med. eng. phys., vol. 21, pp. 731–736, 1999. [8] n. v. thakor, y. s. zhu, “applications of adaptive filtering to ecg analysis: noise cancellation and arrhythmia detection”, ieee trans. biomed. eng., vol. 38, no. 8, pp. 785–794, 1991. [9] p. laguna, r. jane, o. meste, p. w. poon, p. caminal, h. rix, n. v. thakor, “adaptive filter for event-related bioelectric signals using an impulse correlated reference input: comparison with signal averaging techniques”, ieee trans. biomed. eng., vol. 39, no. 10, pp. 1032– 1044, 1992. [10] r. sameni, m. b. shamsollahi, c. jutten, “filtering electrocardiogram signals using the extended kalman filter”, in proc. 27th annu. int. conf. ieee eng. medicine biol. soc. (embs), vol. 6, pp. 5639–5642, 2005. [11] y. chen, b. yang, j. dong, “time-series prediction using a local linear wavelet neural network”, neurocomputing, vol. 69, no. 4-6, pp. 449465, 2006. [12] l. liu, j. jiang, “using stationary wavelet transformation for signal denoising”, 8th international conference on fuzzy systems and knowledge discovery, fskd 2011, vol. 4, pp. 2203-2207, china, 2011 [13] s. haykin, neural networks a comprehensive foundation, macmaster university, hamilton, 1994 [14] physiobank, the mit-bih noise stress test database, http://www.physionet.org/physiobank/database/nstdb/. microsoft word 30-2304_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3463-3469 3463 www.etasr.com maddah: numerical analysis for the oxidation of phenol with tio2 in wastewater photocatalytic reactors numerical analysis for the oxidation of phenol with tio2 in wastewater photocatalytic reactors hisham a. maddah department of chemical engineering king abdulaziz university rabigh, saudi arabia hmaddah@kau.edu.sa abstract—phenolic compounds in wastewater (even at low levels) are found to be quite toxic to humans due to their carcinogenic effects. photocatalysis has been widely studied for the removal of phenol from industrial wastewater. in this study, photocatalytic oxidation of phenol, under uv irradiation in the presence of tio2, has been numerically investigated. phenol mass balance and forward finite difference method (explicit) along with various assumed/calculated parameters, from previous works, were used to numerically plot phenol concertation profiles in water with different initial phenol concentrations. phenol compounds were observed to be totally oxidized at the bottom of the reactor and the maximum conversion rates occur near the reactor walls. it was found that higher irradiation times increase phenol oxidation rates due to higher water hydrolysis. oxidation rate of phenol (consumption) increases with the increase in initial phenol concentration. keywords-numerical; water treatment; photochemical; phenol i. introduction photocatalytic reactor is a reactor in which a chemical reaction can take place when there is enough light and catalyst. photocatalysis term is composed of two words, photo and catalysis. catalysis refers to the developments in chemical reaction rates for the transformation of reactants into products by the addition of an inert substance that does not get consumed and does not alter the desired product. catalyst substances increase reaction rates by reducing the required activation energy for that reaction. particularly, photocatalysis gets the benefits of light and utilizes its energy, using light irradiation, to activate the added catalyst substances that modify the chemical reaction rate without being involved and/or consumed [1, 2]. chlorophyll of plants is a typical natural photocatalyst (vital for photosynthesis). the difference between chlorophyll and synthesized titanium dioxide (tio2) photocatalysts [4], is that chlorophyll molecules absorb energy from sunlight to turn water and carbon dioxide into oxygen and glucose, whereas tio2 creates strong oxidation agents and electronic holes to breakdown the organic matter to carbon dioxide and water when light is available [3, 4]. the worldwide demand on fresh/clean water has been increasing enormously [5-7] due to the fact that water has always been prioritized as a top necessity for human beings [8]. sources of freshwater including rivers, lakes, snow packs, wetlands and aquifers make up a very small fraction (only 2.5 percent) of all water on the planet [9]. thus, improving current water treatment technologies is necessary to meet the growing demand on drinking water. wastewater such as industrial wastewater contains heavy metals, toxic organics (e.g. phenol compounds) and other dissolved solids that may pose serious health risks on humans [10]. photocatalysis has been widely studied for the removal of organic contaminants (e.g. phenol) from industrial wastewater. numerous studies showed that tio2 has received considerable attention as a promising catalyst since it has been used for optical coatings, photocatalysis agents, electrodes, gas sensors, solar cells and hydrogen storage [1, 11, 12]. the objective of this study is to analyze and investigate the concentration decay of phenol in water during the photocatalytic oxidation process under uv irradiation and in the presence of tio2. the effect of both initial phenol concentration and irradiation time on phenol decomposition have been numerically determined. oxidation reaction was assumed to be at steady state and therefore phenol concertation profiles were numerically plotted as a function of reactor height and radius. several parameters such as initial phenol concentrations, tio2 catalyst weight, reactor height, internal radius, external radius, diffusivity, velocity and phenol oxidation rate have been either assumed, calculated from experiments and/or taken from previous works to carry out our numerical analysis. the novelty of this work is associated with the numerical determination of the decay in phenol concertation profiles in industrial wastewater when using advanced oxidation processes (aops) as uv/tio2 with different initial phenol concentrations. determined phenol profiles would help future studies to build upon the visualized concentration change inside photocatalytic reactors. fig. 1. framework engineering, technology & applied science research vol. 8, no. 5, 2018, 3463-3469 3464 www.etasr.com maddah: numerical analysis for the oxidation of phenol with tio2 in wastewater photocatalytic reactors ii. photocatalysis mechanism when tio2 absorbs uv radiation from sunlight or an illuminated light source (fluorescent lamps), it will produce pairs of electrons and holes. electron of the valence band of titanium dioxide becomes excited when illuminated by light. excess energy of this excited electron promotes the electron to a conduction band creating a negative-electron (�– ) and a positive-hole ( �� ) pair. this stage is referred to as the semiconductor’s photo-excitation state. the energy difference between the valence band and the conduction band is known as the band gap. wavelength of light necessary for photoexcitation is 388nm that is calculated from dividing 1240 by band gap energy (3.2ev) where e(ev)=120/λ (nm). in figure 2, the positive-hole of titanium dioxide breaks water molecules apart to form hydrogen gas and a hydroxyl radical [1]. the negative-electron reacts with an oxygen molecule to form a super oxide anion. this cycle continues when light is available [13]. fig. 2. photocatalysis mechanism photocatalytic destruction of organic compounds depends on understanding semiconductor photochemistry. photocatalytic oxidation often proceeds via adsorption of organic pollutants on the catalyst surface, followed by a direct subtraction of the pollutant’s electrons by positively charged holes. another possible way is oxidation with oh radicals generated from an aqueous environment that takes place at the catalyst surface and its vicinity. both reactions may proceed simultaneously and the dominance preference depends on both chemical and adsorption properties of the pollutant. normally, two simple reactions, as shown in (1) and (2), occur to generate hydroxyl radicals that will be reacted with the organic pollutant and convert it to carbon dioxide and clean water [14, 15]. h�o → oh � � h� (1) organic � oh� → co� � h�o � mineral acids (2) iii. titanium dioxide catalyst titanium dioxide in photocatalytic reactors is the most common efficient, feasible and inexpensive way to remove phenol. titanium dioxide is considered cheap, it is insoluble in water, harmless, resistant to most chemicals and highly active to light [1]. recent studies showed that photocatalytic reactors are promising for the removal of phenol from water by using tio2 as a catalyst where phenol and its dihydroxy derivatives undergo destruction in the presence of illuminated tio2 according to first order kinetics [1, 16-18]. titanium dioxide exits in different crystalline forms, anatase, rutile and brookite, with its bandgap around 3.2ev and is activated only under ultraviolet (uv) light (about 8% of solar energy) [19-23]. tio2 is a semiconductor material with large surface energy, interesting quantum effect and high specific surface area which ensure its applicability in photocatalytic applications including water splitting, organic decomposition and energy harvesting. also, tio2 is preferred over other semiconductors due to its high reactivity, long-term chemical stability, low cost, nontoxicity and corrosion resistivity. tio2/uv irradiation systems enable water splitting and the generation of hydroxyl radicals (oxygen and hydrogen) that will be reacted with undesired organics to produce clean water [12]. pure tio2 is commercially available and can be synthesized in the laboratory. the specific surface area (ssa) of the catalyst mixture depends on the purity of tio2. pure tio2 (aldrich, >99% anatase) ssa can reach up to 7.1m 2 g -1 . more details about the physicochemical characterization and quantitative values of the optical properties of tio2 catalysts suspensions can be found in [24-26]. iv. literature on modeling of reaction rates modeling of photocatalytic reaction rates can be expressed by a set of ordinary differential equations (3), where each equation is established for the key chemical species in the photocatalytic reactor. equation (3) can be reduced to (4) with the following assumptions: (a) batch mode operation, (b) the weight of irradiation catalyst ��� ! is known and (c) mixing is high enough so that reaction rate constant can be defined in the irradiation reactor section. our assumptions are valid for reactors with suspended or immobilized tio2 [14]. " #$% #& ' (∑ *�,,-,. �� (3) /0 ' 1 2%33 #$% #& ' ∑ *�,,-, (4) where " is the total reactor volume, �4!, 5� is the concentration of the і chemical species (g·l-1), 7 is the reaction time (s), *�,, is a dimensionless stoichiometric coefficient for і species involved in reaction step 8, -, is the photoconversion rate of step 8, �� is the unit weight of irradiation catalyst (mol·gcat -1 ). most of the previous contributions devoted to the photocatalytic oxidation of phenol are focused on how the reaction rate is influenced by different catalyst loading, phenol concentration, ph, presence of inorganic species and additional oxidants such as ozone or hydrogen peroxide [27-30]. developments have been reported at a pilot plant scale for the photocatalytic treatment of phenol in effluents derived from integrated gasification combined cycle (igcc) power plants [31] and electroplating factories [32], including their economic assessment, but without considering engineering models to verify the scaling-up predictions from laboratory data. a few kinetic studies concluded that dependence of the reaction rate of phenol follows the langmuir-hinshelwood kinetic equation [28-30]. however, langmuir-hinshelwood kinetic equations do not consider explicitly the local radiation absorption rate inside the photoreactor leading to equations that are only valid for the experimental setup with estimated parameters (assumptions), making those models invalid for the design of photoreactors. it is necessary to determine intrinsic kinetic models that will allow us to describe the influence of the local volumetric rate of photon absorption (lvrpa) on the reaction rate in any position of the photoreactor volume [33-36]. engineering, technology & applied science research vol. 8, no. 5, 2018, 3463-3469 3465 www.etasr.com maddah: numerical analysis for the oxidation of phenol with tio2 in wastewater photocatalytic reactors development of supported catalysts in form of fixed beds, fluidized beds or slurries is vital to avoid catalyst recovery costs and other concerns about a potential toxicity of titanium dioxide nanoparticles [37, 38]. v. photocatalytic reactors laboratory scale and bench scale photoreactors were previously designed and studied for the removal of numerous pollutants (e.g. phenol and/or cyanide) from wastewater by catalytic oxidation under uv irradiation. required components and design setup of a laboratory/bench scale photoreactor used for wastewater treatment can be seen in [31]. typically, lab scale photoreactors are designed in a cylindrical shape with a total volume of 120cm 3 operating in a closed recirculating circuit driven by a centrifugal pump and with a stirred reservoir tank equipped with a device for withdrawal of samples. illumination can be carried out by an osram ultramed 400w uv metal halide lamp that provides a high uva irradiation with a controlled radiation flux values using neutral filters. it is possible to validate the scaling-up methodology with the bench scale photoreactor setup that has a total irradiation volume of 1250cm 3 (ten times higher than the laboratory scale). more details regarding the discussed reactor design (which was studied for cyanide removal and not phenol) such as dimensions, lamp type/position, electrical input power, uv emission spectrum and radiation flux can be found in [24-26]. a scaling-up methodology for the photocatalytic oxidation of phenol was studied and proposed in [31, 39]. scaling-up methodology depends on the experimental determination of the intrinsic kinetic parameters at a laboratory scale, in order to predict the performance of larger scale reactors without any adjustable parameters. this method was found to be valid in a bench scale photoreactor with different geometries and irradiation sources, both with commercial tio2 and silicasupported tio2. designing of a large photocatalytic reactor requires the determination of species mass balances to predict the macroscopic conversion of reactants [31, 39]. the kinetic model expresses the evaluation of the reaction rate with parameters based on phenomenological basis. simple equations of the langmuir-hinshelwood kinetic model only take into account the concentration of reactants and products, whereas the effect of the catalyst concentration and the radiation flux are considered implicitly in the kinetic constants. thus, the derived kinetic expressions are only valid for the developed experimental setup and cannot be extrapolated to other reactor configurations. kinetic models must be independent of the experimental features of the reactor and must be determined based on the detailed reaction mechanism of the process, including the radiation steps and therefore the rate of photon absorption. prior to the resolution of the mass balances calculations, the radiation field in the irradiated volume of the photoreactor must be modeled and evaluated. the inevitable radiation profiles that present in photocatalytic reactors lead to non-uniform distributions of the local values of the radiation absorption rates and thus of the reaction rates [31, 39]. the validation of the proposed kinetic scheme and the parameters’ values are recognized by an optimization algorithm that minimizes the error between the experimental results and the predicted values. once the intrinsic kinetics of the process are obtained exclusively from laboratory data, the design of the large-scale photoreactor becomes easy to determine. obviously, the construction of the designed photoreactor as well as the comparison of its experimental conversions with the simulated values would validate the whole scaling-up procedure. vi. methodology and modeling equations intrinsic kinetics in the laboratory scale photoreactor (with similar reactor dimensions and data from previous studies) were utilized to numerically obtain photocatalytic phenol oxidation rate, phenol mass balance in the reservoir tank and phenol concentration profiles at a specific tio2 catalyst weight, assuming that: (a) the system is perfectly mixed, (b) there are no mass transport limitations, (c) the conversion per pass in the reactor is differential, and (d) there are no parallel dark reactions, the mass balance can be expressed as follows: #$9: & #& |<=>, ' − 1@abcd 1efd 〈-hi �j, 7!〉1@abcd (5) where 5hi is the phenol molar concentration, " is the volume, tank, react and tot subscripts refer to the tank, reactor and total, respectively, 7 denotes reaction time, j denotes reaction position in space and -hi �j, 7! is the phenol oxidation rate as a function of both space (reactor height) and time (reaction time). average reaction rate (phenol oxidation rate) was calculated from (6) which was derived from discussed kinetic models. kinetic developments normally depend on the perceived reaction mechanism which explicitly refers to the spatial variations of the lvrpa produced by the inevitable radiation profiles existing in the photoreactor [33]. rmn = −sp cqrs tu vwx0�ty vwx z−1 + [1 + ∝]^_ v`ab erc (6) where -hi is the phenol disappearance rate, de is the catalyst specific surface area, 5f=& is the catalyst mass concentration, 5hi is the phenol molar concentration, �= is the lvrpa, and g� ( i=1 to 3) are the kinetic parameters. selected phenol molar concentrations (initial) were 200, 300, 400 and 500mg/l. according to (6), the evaluation of the reaction rate requires the estimation of the radiation field inside the photoreactor in order to calculate the lvrpa. authors in [31] estimated the lvrpa (�=) value of 8.93 × 10�mnopq7�op rs�t q�0 in the laboratory scale photoreactor for cyanide oxidation with tio2 (which was assumed to be similar for phenol oxidation with tio2). tio2 specific surface area was selected from literature as: sg=240m 2 g -1 . kinetic parameters g0 , g� and gt for tio2 have been previously estimated from experimental and simulation analysis of cyanide oxidation using a marquardtlevenberg non-linear regression algorithm. for simplicity, the values of the obtained kinetic parameters for cyanide oxidation are assumed to be similar for phenol oxidation, which were: α0 = 6.43 × 10�w cm s�0 α� = 1.64 × 1000 cm� s einstein�0 αt = 0 cmt mol�0 engineering, technology & applied science research vol. 8, no. 5, 2018, 3463-3469 3466 www.etasr.com maddah: numerical analysis for the oxidation of phenol with tio2 in wastewater photocatalytic reactors and then phenol disappearance rates were calculated from (6) for the four phenol initial concentrations (200, 300, 400 and 500mg/l) with tio2 catalyst weight of 0.5g·cm -3 as shown in table i. oxidation rate of every phenol concertation was determined from taking the same tio2 catalyst weight of 0.5g·cm -3 [28, 29, 31, 33]. table i. data for disappearance rate calculations* initial phenol concentration cph (||}) [g cm-3] kinetic parameters 200 [2 × 10�~] g0 = 6.43 × 10�w cm s�0 300 [3 × 10�~] g� = 1.64 × 1000 cm� s einstein�0 400 [4 × 10�~] gt = 0 rst s���0 500 [5 × 10�~] *de = 240 s� ��0, �= = 8.93 × 10�m nopq7�op rs�t q�0 it is important to remark that the intrinsic kinetic model determined in the laboratory reactor from (5) is applicable when other reactor configurations have light sources with a similar spectral distribution of the emitted radiation. hence, we can assume that obtained kinetic parameters for (6) are reasonable approximations and they are valid for the bench scale system [25, 33]. modeling and simulation of phenol concentration profile (oxidation rate) inside the photocatalytic reactor can be computed from the phenol mass balance equation in (7). a differential form of the mass conservation equation was used under the following assumptions: (a) steady state, (b) negligible thermal effects, (c) unidirectional vertical flow with symmetry, (d) negligible diffusion when compared to the convective flux, (e) incompressible flow (constant ρ), and (f) constant diffusion coefficient (dph-water=9.1×10 -6 cm 2 ·s -1 ) [40]. phenol mass balance can be expressed in cylindrical coordinates as [25, 33]: v��r! � vwx �� ,�!�� = dmn��rs�� �0� � �� �r � vwx �� ,�!�� �� + rmn�z ,r! (7) where � and / refer to reactor height and radii difference between inlet/outlet cylinders, respectively. the boundary conditions for solving (7) are derived from the following assumptions: (a) the nominal reactor height, h, coincides with the effective height and (b) the reactor walls are non-permeable [25, 33]: 5hi��, /! = 5� (8) � $9: �� , %�d! � = � $9: �� , a�d!� = 0 (9) the resolution of (7) requires the estimation of the velocity profile in the annular space, ���/!, that was calculated from (10) and under the assumptions: (a) laminar flow regime, (b) newtonian fluid, and (c) negligible end effects. assuming internal and external radii are 5cm and 7cm respectively, � = /�>&//��& , 〈��〉 is 6ml/min-1 representing the average velocity, and the velocity is constant under incompressible flow conditions and must be a positive value [25, 33]. ���/! = 2〈��〉 �0�� a�d⁄ ! ]�� u  ¡]¢�� u ¡⁄ !£¤>� a�d⁄ ! u  ¡¥ u  ¡]� u  ¡ ] ¢�� u ¡⁄ ! ¦ (10) the solution of the phenol differential mass balance in the photoreactor in (7) requires the description of the reaction rate -hi ��, /! given by the intrinsic kinetic model determined at the laboratory scale from (6) assuming that -hi ��, /! = -hi =r�pq7§p7. we may simplify the mass balance equation (7) to (11) – (15) with the assumptions: ���/! = r�pq7§p7 =���/̅!; /̅ = �/�> + /��&!/2 and -hi�� , /! = r�pq7§p7 = -hi: � vwx �� ,�! �� = ªwx «ab¬­®¯ �0� � �� �r � vwx �� ,�! �� �� + °wx®¯ (11) � vwx �� ,�! �� = β �0� � �� �r � vwx �� ,�!�� �� + ² (12) β = ªwx «ab¬­®¯ (13) ² = °wx®¯ (14) let 5hi �� , /! = 5�� , /! = 5. equation (12) becomes (15): � $ �� = ³ �$ � �1 + /∗ �$ � � + ² (15) a forward finite difference method (explicit) with neglecting higher orders [41], or called finite divided difference [42], was used to obtain the phenol concentration profile inside the reactor from the simplified mass balance equation (15), while assuming (µ∗ = /!¶ to give the following: v·̧ ¹u�v·̧∆� = β v·¹u ¸ �v·̧∆� �1 + r̅ v·¹u ¸ �v·̧∆� � + ² (16) c»¼�0 = β∆z �v·¹u¸ �v·̧∆� ��1 + r̅ v·¹u ¸ �v·̧∆� � + ²∆z + c»¼ (17) 5�>�0 = ³∆� ½5��0 > − 5�>∆/ ¾ z1 + �/�> + /��&!�5��0> − 5�>!2∆/ c … … … … +²∆� + 5�> (18) phenol concentration profile was numerically identified from (18) by using matlab, where �o, p! = ��,/! is referring to change steps in concentration (in two {for} loops) of reactor height and radius, with the known and/or calculated data of the total reactor system including reactor geometry, reactant (phenol in water) and catalyst (tio2) concentration. table ii shows the reactor system parameters and their selected/calculated values that were plugged into matlab for further analysis. vii. results and discussion since modeling and simulation analysis was carried out for understanding and visualizing phenol degradation rate inside the reactor, phenol concentration profile and the effect of irradiation time and initial phenol concentration on the oxidation rate of phenol have been investigated. a. phenol concentration profile inside the photoreactor phenol concentration profiles of wastewater with various initial phenol concentrations of 200, 300, 400 and 500mg/l are plotted in figures 3-6. understanding the plotted concentration profiles will help us to achieve better phenol degradation rate. it was observed that phenol compounds get totally oxidized at the bottom of the reactor (when wastewater is fed from reactor top-side) and that the maximum conversion rates (i.e. phenol concentration is zero) occur near the reactor walls (r=5cm and/or r=7cm, since there should identical figures from the symmetry boundary conditions), while lower phenol engineering, technology & applied science research vol. 8, no. 5, 2018, 3463-3469 3467 www.etasr.com maddah: numerical analysis for the oxidation of phenol with tio2 in wastewater photocatalytic reactors conversion rates occur at the center of the reactor (r=6cm). lower velocities adjacent to the walls increases the contact time between the catalyst and phenol, hence, higher irradiation time is maintained, thus, higher conversion is observed. most of the phenol gets consumed at the top-side of the reactor (near the inlet) when initial phenol concentration is less than 200mg/l. however, increase in initial phenol concentration leads to higher phenol diffusion along reactor height which indicates that higher oxidation times are required for the complete oxidation of high initial concentrations of phenol in water. table ii. photo-catalytic reactor parameters parameter symbol (unit) value/comments initial phenol concentration 5� (ààs) 200, 300, 400, 500 catalyst weight (tio2) 5f=& (� rs�t) 0.5 reactor height � (rs) 35 reactor internal radius /�> (rs) 5 reactor external radius /��& (rs) 7 phenol-water diffusivity áhi�2=&� (rs� q�0) 9.10 × 10–6 velocity* �� (s4 q�0) 25 reactor volume** "â�=f& (rst) 2639 total volume** "&ã& (rst) 7917 reactor/total volume ratio "â�=f&/"&ã& (n/a) 0.33 phenol oxidation rate*** -hi (s�� rs�t q�0) (3.3, 5, 6.6 and 8.3) × (–10 –7 ) for 200, 300, 400 and 500 mg/l, respectively. defined constant, (13) ³ (rs� s4�0) 3.64 × 10–7 defined constant, (14) ² (s�� s4��) (1.23, 2, 2.64, 3.32) × (–10 –8 ) for 200, 300, 400 and 500 mg/l, respectively. *calculated at / = 6 rs; that is the averaged value between /�> and /��& **reactor and total system volumes were calculated from " = ä /� ℎ at /�> and /��& for inner and outer cylinders as ("�>) and �"ãå& = "&ã&! , respectively, where "â=f& = "ãå& − "�> and total volume was assumed to be "&ã& = 3"â=f& ***oxidation rate of every phenol concentration ( mg/l) was calculated directly from using the averaged catalyst weight 0.5 � rs�t in (6). b. effect of irradiation time on phenol oxidation rate higher irradiation times increase phenol oxidation rates within the reactor as shown in figure 4 due to the following reasons: (a) probability of occurrence of water hydrolysis increases with higher irradiation times, (b) number of produced free hydroxyl groups (oh) in water should be increased with more water hydrolysis, (c) phenolic compounds get reacted (consumed) with free hydroxyl groups, as explained previously in (2), to produce clean water with mineral acids and release carbon dioxide to the atmosphere. c. effect of initial concentration on phenol oxidationrrate production rates of phenol (-hi) were determined for the four studied initial phenol concentrations 200, 300, 400 and 500mg/l as shown in figure 5. rates were calculated from using the assumed catalyst weight of 0.5g·cm -3 at every selected initial concentration. obviously, production rates of phenol were found to be in negative values which indicate that phenol is oxidized and consumed from water during the photocatalytic reaction. oxidation rate of phenol increases with the increase in initial phenol concentration as concluded from obtained production rates of -3.3×10 -7 and -8.2×10 -7 mol·cm -3 s -1 for 200 and 500mg/l, respectively. (a) (b) (c) (d) fig. 3. phenol concentration profile as a function of reactor height and reactor half-radius. tio2 concentration: 0.5g·cm -3 and inlet phenol concentrations: (a) 200mg/l, (b) 300mg/l, (c) 400mg/l, (d) 500mg/l, calculated from (7) and (18). note that [ppm]=[mg/l]. fig. 4. effect of irradiation time on phenol oxidation rate at different inlet phenol concentrations. note that [ppm]=[mg/l]. 0 20 40 60 80 100 120 100 150 200 250 300 350 c p h ( p p m ) irradiation time (min) 200 ppm 300 ppm 400 ppm 500 ppm engineering, technology & applied science research vol. 8, no. 5, 2018, 3463-3469 3468 www.etasr.com maddah: numerical analysis for the oxidation of phenol with tio2 in wastewater photocatalytic reactors fig. 5. effect of initial phenol concentration on phenol oxidation rate at different inlet phenol concentrations. note that [ppm]=[mg/l]. for comparison purposes, we went through the literature to check our numerical estimated removal efficiency with previous experimental works as shown in table iii. authors in [43] found that phenol removal efficiency through aops (uv/tio2) ranges from 6% to 55% depending on many variables such as tio2 wt. %, light intensity, reaction time and ph. in contrast, our findings showed a 45% phenol removal efficiency which is comparable the removal efficiency of 50% found in. authors in [44] found out that the lower the water ph, the more the phenol removal efficiency we get and that approximately 85% of phenol was removed by using tio2 (anatase) at ph 3.5 whereas only 70% removal efficiency was observed at ph 6.5. in a more recent study, 58.8% phenol removal efficiency at ph 8 was observed [45]. it is worth mentioning that our study data were calculated and/or assumed from previous literature (except for the removal efficiency) to estimate the removal efficiency and carry out the numerical analysis. obtained results predicted that phenol compounds can be totally oxidized at the bottom of the reactor if there are enough radiation time and appropriate catalyst concentration. our findings also confirmed that photocatalytic reactors with higher irradiation times increase phenol oxidation rates due to higher water hydrolysis; oxidation rate of phenol (consumption) increases with the increase in initial phenol concentration. table iii. comparison between literature data and determined efficiency of uv/tio2 ci (mg/l) ccat (g cm -3 ) ph t (h) η (%) rph (mol cm -3 s -1 ) ref. 2000 0.0025 6.5 20 50 n/a [43] 94.11 0.0062 3.5 1 85 –11.9×10 –10 [44] 94.11 0.0062 6.5 1 70 –6.8×10 –10 [44] 100 0.1 (w/w%) 8 1 58.8 –2.65×10 –10 [45] 350 0.5 7 2 45 –5.8×10 –7 [*] *this study. averaged data of assumed phenol concertation, tio2 wt. %, ph, time and oxidation rate were assumed and/or calculated to estimate phenol removal efficiency. æ refers to phenol removal efficiency. all other symbols are defined in table ii. viii. conclusions the concentration decay of phenol in water during the photocatalytic oxidation process, under uv irradiation and in the presence of tio2, has been numerically investigated. phenol mass balance, oxidation rate and velocity equations along with forward finite difference method (explicit) and assumed/calculated parameters were used to numerically plot phenol concertation profiles, as a function of reactor height and radius, for different initial phenol concentrations mimicking organics in industrial wastewater. it was observed that phenol compounds get totally oxidized at the bottom of the reactor and that maximum conversion rates occur near the reactor walls. when initial phenol concentration is low, most of the phenol gets consumed once it enters the reactor because low phenol concentrations require lower radiation times and catalysts. however, in general, higher irradiation times increase phenol oxidation rates within the reactor due to higher water hydrolysis which produce numerous free hydroxyl groups (oh) to be reacted with phenolic compounds. also, it was found that 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… stability of the data-model fit over increasing levels of factorial invariance for different features of design in factor analysis deyab almaleki department of evaluation, measurement, and research umm al-qura university makkah, saudi arabia damaleki@uqu.edu.sa abstract-the aim of this study is to provide an empirical evaluation of the influence of different aspects of design in the context of factor analysis in terms of model stability. the overall model stability of factor solutions was evaluated by the examination of the order for testing three levels of measurement invariance (miv) starting with configural invariance (model 0). model testing was evaluated by the chi-square difference test (∆x 2 ) between two groups, and root mean square error of approximation (rmsea), comparative fit index (cfi), and tucker-lewis index (tli). factorial invariance results revealed that the stability of the models was varying over increasing levels of measurement as a function of variable-to-factor (vtf) ratio, subject-to-variable (stv) ratio, and their interactions. there were invariant factor loadings and invariant intercepts among the groups indicating that measurement invariance was achieved. for vtf ratios 4:1, 7:1, and 10:1, the models started to show stability over the levels of measurement when the stv ratio was 4:1. yet, the frequency of stability models over 1000 replications increased (from 77% to 91%) as the stv ratio increased. the models showed more stability at or above 32:1 stv. keywords-model stability; factorial invariance; level of measurement invariance; model design i. introduction confirmatory factor analysis (cfa) is a form of factor analysis (fa) that tests hypotheses regarding how well the measured indicator variables represent the number of constructs [1]. cfa is a confirmatory method a researcher can use to examine, evaluate, and/or test a number of hypothesized factors underlying the variance/covariances in a set of measured indicator variables. cfa allows the researcher to test hypothetical and plausible alternative latent variable structures for the observed indicator variance/covariances [2]. more recently, cfa has also been used in exploratory analysis too [3-9]. three major concerns have emerged repeatedly in the literature related to the use and interpretation of fa in social science research: (a) determining an adequate number of indicator variables to describe the latent trait, (b) factoring a sufficient sample size to have reasonable confidence in the stability of the model estimate, and (c) establishing minimum communality levels to determine which indicator variables can represent a latent trait, especially in simulation studies [8, 1013]. fa assumes that the indicator variables used should be linearly related to one another. otherwise, the number of extracted factors will be the same as the number of original variables [2, 15]. survey instrument length and the number of variables differ based on discipline, purpose, sample frame, and method of data collection. recently, the online survey has become an important method of data collection for a variety of reasons (e.g. online surveys are easy to design, conduct, and often they are the only option for data collection). according to surveymonkey the median length of its paid surveys was 10 questions [9]. industry-specific surveys and market-research surveys tend to have more questions while event surveys and just-for-fun surveys tend to be shorter (see figure 1) [9]. if the length of the survey is about 10 questions or fewer, it can lead to a higher completion rate and increase the likelihood that people will choose to take more of the researcher’s surveys in the future. more recent studies of factor analysis do not include the vtf ratio 10:1 in their investigations [5, 12, 14-17], nor the way this number is relative to the sample size or the communality magnitude when factor analysis is conducted. ii. literature review a. observed variables in fa, the observed indicator variables can be viewed as representing a sample of potential variables, all of which measure the same construct or factor [1, 14, 16, 17]. authors in [18] examined the magnitude of the correlation between the observed variables and the factor components by manipulating sample size, number of variables, number of components, and component saturation. they concluded that the vtf ratio was important for factor stability, with more variables per factor yielding a more stable result. authors in [19], partially confirmed this conclusion. they found that the necessary minimum indicator variables to attain factor solutions that are adequately stable relative to population factors are dependent on several aspects of any given study, including the level of communality and sample size. similarly, authors in [20] found that when the vtf ratio increased the factor analysis solution improved. corresponding author: deyab almaleki engineering, technology & applied science research vol. 11, no. 2, 2021, 6849-6856 6850 www.etasr.com almaleki: stability of the data-model fit over increasing levels of factorial invariance for different features of design in … fig. 1. median survey length in different fields of disciplines. the issue of variable sampling has been used extensively in conceptual development but has received almost no empirical evaluation of those that has sampled indicator variables at random from the universe of variables. the assumption of random sampling is useful to minimize sampling issues and for developing generalizability rather than a prescription for applied research procedures. authors in [21] examined the quality of factor analytic research published between 1999 and 2009 in five leading developmental disabilities journals. they found 35% of the studies used some form of fa. however, the guidelines for using fa were largely ignored and failed to account for levels of overdetermination and commonalities among measured variables. furthermore, the authors in [19] found that there was a lack of validity in some common practice rules used in fa. thus, anything that influences or changes variance may affect the conclusions related to fa. researchers should determine an adequate number of indicator variables that is required to produce a stable and precise model in order to describe the latent trait. authors in [21] investigated the effects of indicator variables on pattern recovery to determine the sufficient number of indicator variables that is likely to produce patterns that closely approximate the population pattern. they reported that the number of indicator variables can strongly affect the degree to which a sample pattern reproduces the population pattern, and that a minimum of three variables per factor is critical. the information about the adequate number of indicator variables that is required to produce a stable and precise model can be used in the design of a study and, retrospectively, in the evaluation of an existing study. b. adequate sample size determining sample size requirements for fa is complicated because it is dependent on other aspects of design, such as vtf and h2. previous studies in fa revealed several approaches that have been used to propose guidelines for the sample size. however, most of these approaches were concerned with identifying either the subject-to-variable (stv) ratio or the absolute sample size, regardless of the effect of these rules on wsv. the examples below describe some reported results about sample size in the context of fa. a larger sample size is better than a smaller sample size because it is minimizing misfit and the probability of errors. in many cases, increasing the sample size may not be possible. in medical research, it is very difficult to collect a large sample of patients suffering from a certain disease [19-21]. investigating the minimum stv ratio or small absolute sample size to obtain the stability of the model is necessary. only a very limited number of studies on the role of sample size in fa have investigated real or simulated small sample size. authors in [17] investigated the minimum sample size necessary to obtain reliable factor solutions under various conditions. they concluded that under the conditions of high communality, high number of observed variables, and small number of factors, fa yields a stable estimate model for sample sizes below 50. selecting the adequate sample size is an important decision in study design. a researcher must determine how large the sample should be and what is the most appropriate sampling frame. one problem is that the proposed recommendations vary dramatically. clearly, the wide range in these recommendations causes them to be of rather limited value to empirical researchers. yet, there is a need to conduct studies examining systematically the model estimate stability latent variable variance with different facets of study experimental design (ed) and sampling design (sd). previous research has investigated the stability of factor solutions by the examination of chi-square value (χ� ) and overall model fit (omf) indices such as goodness-of-fit index (gfi), adjusted gfi (agfi), tucker-lewis index (tli), comparative fit index (cfi), root mean square error of approximation (rmsea), and root mean square residual (rmsr) [8, 10, 22-25]. omf indices examined global measures of data-model fit. examinations of measurement invariance (miv) (configural, weak, and strong) were used to evaluate model stability. the effects of communality magnitude in fa have been mostly vague. studies have revealed a varied range of communality magnitude and common practice rules [1, 3, 4, 16, 26, 27]. the communality measures the percent of variance in a given variable explained by the factors. if communalities are high, model stability in the sample data is normally very good [18, 26, 28, 29]. authors in [20] investigated the quality of factor solutions. they found that when the communalities were high, sample size tended to have less influence on the quality of factor solutions than when communalities are low. authors in [30] confirmed that communality magnitudes play an important role in determining the adequate sample size. moreover, authors in [21] found that the communality magnitudes became most relevant in determining the sufficient sample size and the number of variables per component. iii. methods a. simulation data simulation data are used in social science to answer a particular research question, solve a statistical problem, or improve analysis procedure techniques. statistical program developers and research designers usually perform simulation data techniques for several reasons: gathering real data may be difficult, time-consuming, expensive, or real data sometimes violate distributional assumptions. simulation data often lead to greater understanding of an analysis and the results one can engineering, technology & applied science research vol. 11, no. 2, 2021, 6849-6856 6851 www.etasr.com almaleki: stability of the data-model fit over increasing levels of factorial invariance for different features of design in … expect from various oddities of real-life data [31]. simulation may approximate real-world results yet requires less time and effort and gives the researcher a chance to experiment with data under various conditions. data can be simulated by several methods. the monte carlo technique is one popular method that has been used in social science since the 1940s [28]. a monte carlo simulation is a numerical technique that can be used to conduct experiments and repeated random sampling to simulate data for a given mathematical model. the key point of the simulation model was the development of the matrices for a 5-factor domain as an example of the factor. the statistical software package sas was used, and the syntax code was written by the researcher. b. estimation methods maximum likelihood (ml) is the most common method of factor extraction that estimates population values for fa by calculating loading that maximizes the probability of sampling the observed correlation matrix from a population [12] and is often used in cfa. the current study used ml as a method of factor extraction. authors in [21] concluded that if the data are normally distributed, ml is the best estimation option because it allows the computation of a mixed range of indexes of the goodness of fit of the model. the ml estimation method assumes that the data are independently sampled from a multivariate normal distribution with mean µ and variancecovariance matrix that takes this form: σ = ll′+ψ, where l is the matrix of factor loadings and ψ is the diagonal matrix of specific variances. authors in [32] indicated that the ml estimation method is the most precise when the data are continuous and normally distributed, but it does not provide accurate results with ordinal data or when the data violate the assumption of multivariate normality. table i illustrates the procedure for testing model stability starting with a cfa model relative to a known factor structure for each condition involved in the study separately. table i. pro cedure for testing model stability test name symbols statistics guidelines chi-square value χ� tucker-lewis index tli ≥ 0.96 good fit comparative fit index cfi > 0.95 good fit root mean square error of approximation rmsea 0.00-0.05 very good fit 0.05-0.08 fair fit 0.08-0.10 mediocre fit c. procedure for testing stability across models the procedure for testing measurement invariance was performed in order to evaluate the variation over increasingly levels of measurement invariance among models. there are different approaches that could be used to evaluate the measurement invariance among groups. the present study used a multiple-group confirmatory factor analysis (mgcfa) model to test invariance among the levels of stv ratios. table ii illustrates the order for testing measurement invariance starting with configural invariance (model 0). model testing was evaluated by the chi-square difference test (∆χ�) between two groups [20, 30, 33], and rmsea, cfi, and tli were used to evaluate all the model fits. as referenced above, the criteria values suggested in [20, 34] were used in this study: rmsea: 0.00 0.05 very good fit, cfi > 0.95 good fit, and tli ≥ 0.96 good fit. three levels of miv were tested. table ii. proced ure for stability testing among models configural invariance (m0) indicates that across groups, the pattern of group1 and group2 is equivalent λ��� � = λ��� � = ⋯ = λ��� � where, λ represents the number of factor patterns across the g�� group. configural invariance at best indicates that the group factors are similar but gives no indication that they hold measurement equivalence. ∆χ� was used to judge configural invariance. for instance, if the χ� was not significant, the indicator variables loaded to the same factors across the groups. in other words, there were no differences in factor construct between the groups. weak measurement invariance (m1) indicates that across groups, the corresponding factor loadings are equivalent: λ � ��� � = λ � ��� � = ⋯ = λ � ��� � , where λ � ��� � represents the factor loading of the j�� indicator variable in the group. factor loadings represent the direct effect of the latent construct on each indicator variable, and factor loadings are represented by lambda (λ) [11]. at this level (weak measurement invariance), variables were loaded to the same factors across the group and the factor loadings across groups were equal. ∆χ� was used to judge weak invariance. for instance, if the χ� was not significant, the factor loadings across groups were equal. in other words, there were no differences in the factor loading of the indicator variables and their construct between the groups. strong measurement invariance (m2) means that across groups, corresponding indicators’ means are equivalent, τ � ��� � = τ � ��� � = ⋯ = τ � ��� � , where τ represents the intercept (means) of the j�� indicator variable in the group. at this level (strong measurement invariance), indicator variables were loaded to the same factors across the groups. factor loading, and indicators intercepts across groups were equal. ∆�� ����� was used to judge strong invariance. for instance, if the χ� wass not significant, the variables intercepts across groups were equal. m test name �� symbol ∆� � test test statistics guide m0 m e as u re m e n t in v ar ia n c e ( m iv ) configural invariance ��: λ��� � = λ��� � = ⋯ = λ��� � !: the number of factor patterns across g groups if ∆χ� ns, the model shows configural factorial invariance in place m1 weak measurement invariance ��: λ� ��� � = λ � ��� � = ⋯ = λ � ��� � λ� ��� � : the factor loading of the j��indicator variable in the group ∆� � ����� if ∆χ� ns, the model shows weak factorial invariance in place m2 strong measurement invariance ��: τ� ��� � = τ � ��� � = ⋯ = τ � ��� � τ: the indicator variables intercept (means) of the j�� indicator variable in the group ∆� � ����� if ∆χ� ns, the model shows strong factorial invariance in place engineering, technology & applied science research vol. 11, no. 2, 2021, 6849-6856 6852 www.etasr.com almaleki: stability of the data-model fit over increasing levels of factorial invariance for different features of design in … d. design the main research question was if the stability of the simulated models varies over increasing levels of measurement invariance as a function of the following conditions and their interactions: • variable-to-factor (vtf) ratio • subject-to-variables (stv) ratio • communalities magnitude (h2) mgcfa was used to test the measurement invariance among the levels of stv ratios in order to evaluate model stability. figure 2 illustrates the study design. measurement invariance of the stv levels, as shown in table iii, were examined in each cell of the h� *vtf study. h� 4:1 7:1 10:1 mixed vtf fig. 2. design of interaction conditions. iv. results table iii presents the complete findings of measurement invariance for mixed communality among levels of stv over 1000 replications where each significant p-value is marked with "*". table iii. test of facto rial invariance for mixed commun ality acro ss vtf and stv ratio s averaged over 1000 replications vtf between groups #� m ∆#� p-value rmsea cfi tli 4:1 stv=2:1 & stv=32:1 369.18 m0 --0.0301* 0.0201 0.9893 0.9874 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=2:1 & stv=16:1 371.33 m0 --0.0252* 0.0285 0.9791 0.9754 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=2:1 & stv=8:1 375.77 m0 --0.0172* 0.0399 0.9602 0.9530 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=2:1 & stv=4:1 386.26 m0 --0.0065* 0.0573 0.9245 0.9104 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=4:1 & stv=32:1 340.29 m0 --0.2084 0.0117 0.9952 0.9950 356.07 m1-m0 15.78 0.3968 0.0117 0.9950 0.9951 370.63 m2-m1 14.56 0.4835 0.0114 0.9950 0.9954 stv=4:1 & stv=16:1 342.43 m0 --0.1859 0.0164 0.9907 0.9902 358.02 m1-m0 15.59 0.4098 0.0163 0.9904 0.9904 372.60 m2-m1 14.58 0.4820 0.0159 0.9905 0.9910 stv=4:1 & stv=8:1 346.89 m0 --0.1444 0.0237 0.9825 0.9808 362.81 m1-m0 15.92 0.3873 0.0236 0.9819 0.9810 377.46 m2-m1 14.65 0.4769 0.0229 0.9820 0.9820 stv=8:1 & stv=32:1 329.85 m0 --0.3402 0.0082 0.9971 0.9978 345.07 m1-m0 15.22 0.4356 0.0081 0.9970 0.9979 360.13 m2-m1 15.06 0.4471 0.0080 0.9969 0.9979 stv=8:1 & stv=16:1 331.88 m0 --0.3120 0.0115 0.9946 0.9957 346.96 m1-m0 15.08 0.4456 0.0113 0.9945 0.9958 362.06 m2-m1 15.1 0.4442 0.0111 0.9945 0.9960 stv=16:1& stv=32:1 325.34 m0 --0.4066 0.0063 0.9980 0.9990 340.40 m1-m0 15.06 0.4471 0.0062 0.9980 0.9990 355.28 m2-m1 14.88 0.4600 0.0061 0.9980 0.9991 7:1 stv=2:1 & stv=32:1 1257.15 m0 --0.0006* 0.0152 0.9942 0.9938 --m1-m0 ---- -- -- -- engineering, technology & applied science research vol. 11, no. 2, 2021, 6849-6856 6853 www.etasr.com almaleki: stability of the data-model fit over increasing levels of factorial invariance for different features of design in … --m2-m1 ---- -- -- -- stv=2:1 & stv=16:1 1262.68 m0 --0.0004* 0.0213 0.9888 0.9879 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=2:1 & stv=8:1 1262.65 m0 --0.0004* 0.0213 0.9888 0.9879 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=2:1 & stv=4:1 1310.82 m0 --<0.0001* 0.0425 0.9579 0.9544 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=4:1 & stv=32:1 1170.54 m0 --0.0686 0.0093 0.9975 0.9973 1200.54 m1-m0 30 0.4656 0.0092 0.9975 0.9974 1230.60 m2-m1 30.06 0.4625 0.0090 0.9975 0.9975 stv=4:1 & stv=16:1 1176.06 m0 --0.0549 0.0130 0.9952 0.9949 1206.12 m1-m0 30.06 0.4625 0.0128 0.9951 0.9950 1236.47 m2-m1 30.35 0.4478 0.0127 0.9951 0.9951 stv=4:1 & stv=8:1 1191.49 m0 --0.0279* 0.018 0.9905 0.9898 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=8:1 & stv=32:1 1137.82 m0 --0.2086 0.0062 0.9986 0.9987 1167.98 m1-m0 30.16 0.4574 0.0061 0.9986 0.9987 1197.93 m2-m1 29.95 0.4682 0.0061 0.9986 0.9987 stv=8:1 & stv=16:1 1143.33 m0 --0.1773 0.0086 0.9975 0.9975 1173.42 m1-m0 30.09 0.4610 0.0085 0.9975 0.9976 1203.61 m2-m1 30.19 0.4559 0.0084 0.9974 0.9976 stv=16:1 & stv=32:1 1122.39 m0 --0.3133 0.0044 0.9991 0.9993 1152.28 m1-m0 29.89 0.4712 0.0044 0.9991 0.9993 1182.31 m2-m1 30.03 0.4641 0.0044 0.9991 0.9994 10:1 stv=2:1 & stv=32:1 2640.05 m0 --<0.0001* 0.01241 0.9948 0.9946 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=2:1 & stv=16:1 2654.33 m0 --<0.0001* 0.0174 0.9899 0.9894 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=2:1 & stv=8:1 2681.11 m0 --<0.0001* 0.0244 0.9806 0.9796 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=2:1 & stv=4:1 2748.81 m0 --<0.0001* 0.0345 0.9621 0.9601 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=4:1 & stv=32:1 2464.25 m0 --<0.0001* 0.0076 0.9978 0.9978 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=4:1& stv=16:1 2478.53 m0 --<0.0001* 0.0108 0.9958 0.9956 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- engineering, technology & applied science research vol. 11, no. 2, 2021, 6849-6856 6854 www.etasr.com almaleki: stability of the data-model fit over increasing levels of factorial invariance for different features of design in … stv=4:1 & stv=8:1 2505.31 m0 --0.0059* 0.0154 0.9918 0.9914 --m1-m0 ---- -- -- -- --m2-m1 ---- -- -- -- stv=8:1 & stv=32:1 2396.55 m0 --0.1648 0.0047 0.9989 0.9990 2441.69 m1-m0 45.14 0.4661 0.0047 0.9989 0.9990 2486.29 m2-m1 44.6 0.4470 0.0046 0.9989 0.9990 stv=8:1 & stv=16:1 2410.83 m0 --0.1190 0.0069 0.9980 0.9980 2455.99 m1-m0 45.16 0.4652 0.0068 0.9980 0.9980 2500.68 m2-m1 44.69 0.4432 0.0067 0.9980 0.9980 stv=16:1 & stv=32:1 2369.77 m0 --0.2782 0.0034 0.9993 0.9995 2413.98 m1-m0 44.21 0.5053 0.0033 0.9993 0.9995 2458.99 m2-m1 45.01 0.4715 0.0033 0.9993 0.9995 vtf (4:1). the examination of the measurement invariance, begins with configural (m0) to weak (m1) and strong (m2). the findings revealed that for vtf ratios (4:1), χ� �$ showed statistically significant results when testing configural invariance: (2:1 with 32:1); (2:1 with 16:1); (2:1 with 8:1); and (2:1 with 4:1). thus, non-invariance was established precluding further invariance testing, e.g., weak, strong, and structural. however, at higher stv ratios, e.g. groups (4:1 with 32:1); (4:1 with 16:1); (4:1 with 8:1); (8:1 with 32:1), (8:1 with 16:1); (8:1 with 32:1); and (16:1 with 32:1), χ� �$ was not statistically significant indicating configural invariance was established. given the presence of configural invariance, testing for weak invariance was conducted. again, chi-square difference between ∆�� ����� was not statistically significant supporting the hypothesis of weak factorial invariance between the two groups. after weak invariance was supported, the examination of the indicator intercepts was conducted. the results again supported the finding of strong invariance, e.g. the ∆�� ����� was not statistically significant. in conclusion, there were invariant factor loadings and invariant intercepts among the groups indicating that measurement invariance was achieved as described above. vtf (7:1). the model begins with configural (m0) to weak (m1) and strong (m2). the findings revealed that for vtf ratio (7:1), χ� �$ showed statistically significant results when testing configural invariance: (2:1 with 32:1); (2:1 with 16:1); (2:1 with 8:1); (2:1 with 4:1); and (4:1 with 8:1). thus, noninvariance was established precluding further invariance testing, e.g. weak, strong, and structural. however, at higher stv ratios, e.g. groups (4:1 with 32:1); (4:1 with 16:1); (8:1 with 32:1), (8:1 with 16:1); (8:1 with 32:1); and (16:1 with 32:1), χ� �$ was not statistically significant indicating configural invariance was established. given the presence of configural invariance, testing for weak invariance was conducted. again, the chi-square difference between ∆�� ����� was not statistically significant supporting the hypothesis of weak factorial invariance between the two groups. after weak invariance was supported, the examination of the indicator intercepts was conducted. the results supported again the finding of strong invariance, e.g. the ∆�� ����� was not statistically significant. in conclusion, there were invariant factor loadings and invariant intercepts among the groups indicating that measurement invariance was achieved as described above. vtf (10:1). the findings revealed that for vtf ratios (10:1), χ� �$ showed statistically significant results when testing configural invariance: (2:1 with 32:1); (2:1 with 16:1); (2:1 with 8:1); (2:1 with 4:1); (4:1 with 8:1); (4:1 with 16:1); and (4:1 with 32:1). thus, non-invariance was established precluding further invariance testing. however, at higher stv ratios, e.g. groups (8:1 with 16:1); (8:1 with 32:1); and (16:1 with 32:1), χ� �$ was not statistically significant indicating configural invariance was established. given the presence of configural invariance, testing for weak invariance was conducted. again, chi-square difference between ∆�� ����� was not statistically significant supporting the hypothesis of weak factorial invariance between the two groups. after weak invariance was supported, examination of the indicator intercepts was conducted. the results supported again the finding of strong invariance, e.g. the ∆�� ����� was not statistically significant. in conclusion, there were invariant factor loadings and invariant intercepts among the groups indicating that measurement invariance was achieved as described above. table iv presents a frequency analysis of a chi-square pvalues > 0.05 was tested against the null proportion p = 0.05 to determine if there was a statistically significant number of invariance failures. the factorial invariance result revealed that the stability of the models was varying over increasing levels of measurement as a function of vtf, stv, and their interactions. v. discussion the study findings refuted some of the guidelines found in the literature, e.g. authors in [18] reported that the sample size was not an important factor in determining model stability, and authors in [35] reported that the stv ratio should be no lower than 5. the results of the current study revealed that sample size did have a strong effect on stability of the simulated models. for instance, when vtf ratio was 4:1, the mean values related to data-model fit indices were adequate at stv ratio >= 4:1. however, looking at the frequency of rejections based on engineering, technology & applied science research vol. 11, no. 2, 2021, 6849-6856 6855 www.etasr.com almaleki: stability of the data-model fit over increasing levels of factorial invariance for different features of design in … conventional thresholds over the 1000 replications depicted a different conclusion. the percentage of stable (invariant) models ranged from 77% at 4:1 stv to 91% at 32:1 stv clearly indicating that larger stv ratios are related to higher stability levels with a model. these findings validated the results in [16] who reported that the percentage of invariance tests varied based on the sample size per group. table iv. χ� frequen cy against the n ull proportion of structural mean invarian ce in mixed commun ality vtf nested models invariance status frequency & percent p-value 4:1 stv=4:1 & stv=32:1 successful 799 79.90 <0.0001* failures 201 20.10 stv=4:1 & stv=16:1 successful 765 76.50 <0.0001* failures 235 23.50 stv=4:1 & stv=8:1 successful 712 71.20 <0.0001* failures 288 28.80 stv=8:1 & stv=32:1 successful 899 89.90 <0.0001* failures 101 10.01 stv=8:1 & stv=16:1 successful 878 87.80 <0.0001* failures 122 12.20 stv=16:1 & stv=32:1 successful 933 93.90 <0.0001* failures 67 6.70 7:1 stv=4:1 & stv=32:1 successful 569 56.90 <0.0001* failures 431 43.10 stv=4:1 & stv=16:1 successful 513 51.30 <0.0001* failures 487 48.70 stv=8:1 & stv=32:1 successful 790 79.00 <0.0001* failures 210 21.00 stv=8:1 & stv=16:1 successful 752 75.20 <0.0001* failures 248 24.80 stv=16:1 & stv=32:1 successful 868 86.80 <0.0001* failures 132 13.20 10:1 stv=8:1 & stv=32:1 successful 734 73.40 <0.0001* failures 266 26.60 stv=8:1 & stv=16:1 successful 670 67.00 <0.0001* failures 330 33.00 stv=16:1 & stv=32:1 successful 840 84.00 <0.0001* failures 160 16.00 the findings of the current study do agree with [36] where in some models an stv of 30:1 was needed to produce stable model and minimize the amount of misfit. the study findings also contradict some previous research that investigated the effect of vtf ratio on stability of factor solutions. the authors in [18] concluded that the vtf ratio was important for factor stability with more indicator variables per factor yielding more stable result. vi. conclusion in general, this study provided an empirical evaluation of the stability of the data-model fit over increasing levels of factorial invariance for different features of design in fa. the study concluded that the stability of the models was varying over increasing levels of measurement as a function of vtf, 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[36] i. p. cobham, "the effects of subject-to-variable ratio, measurement scale, and number of factors on the stability of the factor model," ph.d. dissertation, proquest information & learning, usa, 1999. microsoft word etasr_v11_n3_pp7283-7289 engineering, technology & applied science research vol. 11, no. 3, 2021, 7283-7289 7283 www.etasr.com alshammari et al.: a local search-based non-dominated sorting genetic algorithm for optimal design … local search-based non-dominated sorting genetic algorithm for optimal design of multimachine power system stabilizers fahad a. alshammari department of electrical engineering university of hail hail, saudi arabia fahad.a.s.alshammari@gmail.com ahmed a. alzamil department of electrical engineering university of hail hail, saudi arabia aa.alzamil@uoh.edu.sa gharbi a. alshammari department of electrical engineering university of hail hail, saudi arabia gharbi.a.alshammari@gmail.com badr m. alshammari department of electrical engineering university of hail hail, saudi arabia bms.alshammari@uoh.edu.sa tawfik guesmi department of electrical engineering university of hail hail, saudi arabia tawfik.guesmi@istmt.rnu.tn ahmed s. alshammari department of electrical engineering university of hail hail, saudi arabia ahm.alshammari@uoh.edu.sa abstract-this study presents a metaheuristic method for the optimum design of multimachine power system stabilizers (psss). in the proposed method, referred to as local searchbased non-dominated sorting genetic algorithm (lsnsga), a local search mechanism is incorporated at the end of the second version of the non-dominated sorting genetic algorithm in order to improve its convergence rate and avoid the convergence to local optima. the parameters of psss are tuned using lsnsga over a wide range of operating conditions, in order to provide the best damping of critical electromechanical oscillations. eigenvalue-based objective functions are employed in the pss design process. simulation results based on eigenvalue analysis and nonlinear time-domain simulation proved that the proposed controller provided competitive results compared to other metaheuristic techniques. keywords-power system stabilizer; non-dominated sorting genetic algorithm; local search; eigenvalue analysis; nonlinear time domain simulation i. introduction the complexity of electricity networks due to several economic, ecological, and technical exigencies has obliged electric companies to operate at full network capacity in order to achieve a balance between the increased consumption and the production, under severe conditions increasingly close to the stability limits. under these drastic conditions and operating limits, the occurrence of any contingencies or disturbances such as short-circuits, sudden variations in loads, and line outage, can lead to a critical situation often starting with poorly damped electromechanical oscillations (emos) followed by loss of synchronism and system instability [1]. for instance, these low frequency oscillations may limit the transfer capacity of the power system and continue to grow up resulting in the separation of the system if no adequate response is quickly taken. to overcome the problem of emos and improve the system damping, additional stabilizing signals are usually added to the excitation system via the voltage regulator [2]. the conventional power system stabilizer (cpss) has long been employed to damp out emos. generally, cpsss are based on lead-lag compensators with fixed parameters determined at the nominal operating condition. however, power systems are strongly nonlinear with configurations and load changing over time, which implies that these fixed parameters of the stabilizers are no longer adapted to the new operating conditions [3]. therefore, the fundamental problem is not only to determine the optimal parameters of these stabilizers, but also to make them adapt to the modification of the operating points and system configurations. within this context, diverse research works have been directed towards the design of power system stabilizers (psss) with optimal performance for a wide range of system parameters, configurations, and operating conditions [4-8]. from the literature review, it was found that several ideas and methods have been suggested for the optimal setting of pss parameters. the most used pss design methods are summarized in [9-10] and are divided into three main categories which are adaptive control [11-12], linear approximation [13], and nonlinear models [14]. in [12], model reference adaptive system-based pss (mras-pss) design has been addressed. the performance of the mras-pss has been assessed through nonlinear time domain simulation (ntds). despite the fact that the adaptive control-based pss may mitigate the shortcomings of cpss, it appears complex in nature and costly. several numerical techniques have been suggested for the enhancement of small signal stability of interconnected multimachine power systems, such as linear programming and corresponding author: tawfik guesmi engineering, technology & applied science research vol. 11, no. 3, 2021, 7283-7289 7284 www.etasr.com alshammari et al.: a local search-based non-dominated sorting genetic algorithm for optimal design … gradient methods [15]. unfortunately, these classical methods require initialization of the problem solutions and they are iterative. thus, they may fail to converge to the global optima. to avoid the limitations of classical techniques, nonconventional optimization techniques have been used for solving several complex problems. in particular, these techniques have demonstrated high performance when applied to power system problems, such as the problem of the enhancement of power system stability. for instance, a genetic algorithm (ga)-based method for the optimal setting of leadlag psss parameters was suggested in [16]. in [4], the same regulators have been optimally designed using simulated annealing (sa) where the objective function has been optimized in order to shift all electromechanical modes to the left side in the s-plane. an artificial bee colony-based method has been suggested in [6] for dynamic stability enhancement and its performance was compared with other techniques. in [17], a time domain response based function has been minimized using particle swarm optimization (pso) in order to tune the parameters of pss regulators. these regulators are employed for damping inter-area oscillations and local modes. in [18], the whale optimization algorithm was used for tuning the pss regulators in order to suppress power system oscillations and maintain system stability after the occurrence of faults. the authors have considered an eigenvalue-based objective function in the design process. other metaheuristic techniques have also been employed for the enhancement of power system stability, such as the bacteria foraging optimization algorithm (bfoa) [19] and fuzzy gravitational search algorithm (fgsa) [20]. unfortunately, these randombased methods have been criticized for their low convergence rate and the fact that they can be trapped in local minima when complex multimodal problems are considered [21]. within this context, a modified version of the non-dominated sorting genetic algorithm (nsgaii) for the optimal design of pss regulators is presented in this study. the main contributions of this work are: • two eigenvalue-based objective functions are optimized simultaneously in order to provide optimum pss design. the first one is related to the real part of the electromechanical modes whilst the second one corresponds to the damping ratios of the same modes. the optimization of these two objective functions aims to shift all electromechanical modes as much as possible in the left side of the s-plane. in order to make the proposed controller more robust, the pss parameters are optimized over a wide range of operating conditions. • the aforementioned objective functions are minimized simultaneously using an improved version of the nsgaii. to do this, a local search procedure is embedded at the end of all iterations of the nsgaii in order to increase its convergence rate and avoid the convergence to local optima. decision variables of the problem are the pss parameters and the problem constraints are the bounds of these parameters. • the simulation results based on eigenvalue analysis and nonlinear time domain simulation demonstrated that the proposed controller provided results competitive with the other metaheuristic techniques implemented recently for the resolution of the pss design problem, such as nsgaii, sa [4] and fuzzy gravitational search algorithm (fgsa) [20]. ii. problem formulation of pss design a. power network model for stability studies, power network is mostly modeled by a set of nonlinear differential-algebraic equations (dae) as given in (1)-(3): �� = ���,�,� (1) 0 = ���,� (2) � =ℎ��,�,� (3) the state variables vector and the algebraic variables vector are represented by � and � respectively. � and � express the input variables vector and the output variables set respectively. the equations of network power flow are represented by a nonlinear algebraic set defined with the symbol � . the dynamics of the system and controller are expressed by the first-order nonlinear differential equations described by the function �. the output variables are described by function h. in this study, the state vector is � = [� � ��� ���  ]� . where � is the rotor angle, and � is the rotor speed. ��� is the internal voltage and ��� is the field voltage. the bus voltage magnitudes and phase angles constitute the vector y. the pss output signals constitute the control vector �. the pss design is based on a linearized incremental model of the power system. at an equilibrium point of the power system, the state equations of the system can easily be written if y is removed and it is assumed that the power flow jacobian is non-singular, as follows. ��� = ��+�� (4) fig. 1. ieee type-st1 excitation system with pss. it is worth noting that if the power network is with n machines and m psss, the state matrix a is a 4�×4� matrix and the control matrix b is a 4�× matrix. b. excitation system with pss structure the pss gives a control effect, by acting via the exciter, to the power system under consideration. this study considers the ieee type-st1 excitation system with pss [6] as shown in figure 1. !" is the generator terminal voltage and !$%� is the 1 a a k st+         + +         + + + i i i i w w i st st st st st st k 4 3 2 1 1 1 1 1 1 iω∆ fde∆ refv∆ tv∆ iu∆ + − + max fd e min fd e max pss u min pss u engineering, technology & applied science research vol. 11, no. 3, 2021, 7283-7289 7285 www.etasr.com alshammari et al.: a local search-based non-dominated sorting genetic algorithm for optimal design … reference terminal voltage. &' is the amplifier time constant, (' is the amplifier gain constant, �) is the output that is the supplementary stabilizing signal, and ��) is the input signal of the *th pss that is the normalized speed deviation. the pss's transfer function is shown in the following expression: �)�+ = () ,�-./,�0�./,�1 �./,�2 .�/,�3 �./,�4 5 (5) in (5), the washout block with time constant &6) is utilized as a high-pass filter, allowing signals in the range of 0.2-2hz associated with rotor oscillation to pass unchanged, and is generally between 1 and 20s [4]. compensating for the phase lag between the pss output and the control operation, which is the electrical torque, is conducted by the two first-order leadlag transfer functions. thus, the representation of pss comprises of two lead-lag blocks, a gain (), and a washout bloc with time constant &6). c. damping controller design the system closed-loop eigenvalues are measured after linearizing the power system around the operating point. using only the unstable or lightly damped electromechanical forms that need to be moved, the objective functions can be formulated. the issue of the parameter tuning of the pss controllers that stabilize the system is transformed into a multiobjective minimization problem in this study. one of the considered two eigenvalue-based objective functions stated in [6] aims to transfer the closed-loop eigenvalues to the left side of the line expressed by 7)8 = 79, as shown in figure 2(a). :. in (12) represents this function and the second objective function is defined by :;. in fact, and as presented in figure 2(b), minimizing :; equals to raising the damping ratios of all electromechanical modes and place the closed-loop eigenvalues in a d-shape sector corresponding to <)8 = <9. >? ?@ ?? aif def7)8g h 79 and *�f<)8g = <9, :. � def7)8g :; � l *�f<)8g else :. � :.mno :; � :;mno (6) where the real part and damping ratio of the i th electromechanical modes corresponding to the j th operating point are expressed by 7)8 and <)8 respectively. the fitness functions :. and :; are equal to their upper limits :.mno and :;mno if one or more electromechanical modes are outside the d-shape sector shown in figure 2(c). it is worth noting that functions j1 and j2 have to be minimized subject to the following inequality constraints that describe the bounds of the adjustable parameters of the regulators: maxmink k kii i≤ ≤ (7) maxmin 11 1t t tii i≤ ≤ (8) maxmin 22 2t t tii i≤ ≤ (9) maxmin 33 3t t tii i≤ ≤ (10) maxmin 44 4t t tii i≤ ≤ (11) the washout time constant tw is fixed to 5s in this paper, and typical ranges of the decision variables are [0.01–1.5] for t1i to t4i and [0.1–50] for ki. fig. 2. electromechanical modes location for different objective functions. iii. description of the proposed optimization technique due to its high computational complexity and absence of elitism, the first version of nsga has been criticized frequently in the literature. to overcome these drawbacks, authors in [22] proposed a new version of nsga, called nsgaii. the nsgaii algorithm comprises mainly of two parts, which are the non-dominated sorting of solutions and the preservation of the population diversity. in nsgaii, offspring population qt is combined with its parent population pt at each iteration t. the combined population is sorted based on nondominated sorting mechanism into fronts. then, solutions of one front are sorted using their crowding distances. fig. 3. flowchart of the local search algorithm. jω jω σ σ σ 0iσ σ≤ 0i ξ ξ≥ 0 0 i i σ σ ξ ξ ≤  ≥ (a) (c) (b) jω 0 σ engineering, technology & applied science research vol. 11, no. 3, 2021, 7283-7289 7286 www.etasr.com alshammari et al.: a local search-based non-dominated sorting genetic algorithm for optimal design … despite the tmodifications applied in the nsgaii, it suffers from its low convergence rate due to its random parameters. in addition, nsgaii may fail to converge to the global optima. in order to overcome these limitations, in this study, a local search mechanism is included at the end of nsgaii iterations. this mechanism explores the less-crowded zone in the current archive in order to obtain more non-dominated solutions nearby. the flowchart of the local search algorithm applied for an iteration k is shown in figure 3. iv. simulation and discussion in this section, the robustness and effectiveness of the lsnsga technique, proposed for the determination of the optimal pss parameters, is evaluated on the 3-machine 9-bus wscc (western system coordinating council). as shown in figure 4, this system comprises of 9 buses and 3 generators. all system data are extracted from [6]. fig. 4. single line diagram of the wscc system. for economic reasons, only machines 2 and 3 are equipped with psss. in order to increase the robustness of the proposed lsnsga-based controller (lsnsga-pss), 4 different operating conditions were used. these conditions are shown in table i. all experiments are implemented on matlab environment using a machine with 8gb ram, intel core i7 1.8ghz, and windows 7. maximum number of iterations and population size are selected to be 100 and 200 respectively. the mutation and crossover probabilities are 0.2 and 0.9. table i. system operating conditions (in pu) base case case 1 case 2 case 3 p q p q p q p q gen g1 0.72 0.27 2.21 1.09 0.36 0.16 0.33 1.12 g2 1.63 0.07 1.92 0.56 0.8 -0.11 2.00 0.57 g3 0.85 -0.11 1.28 0.36 0.45 -0.20 1.50 0.38 load a 1.25 0.50 2.00 0.80 0.65 0.55 1.50 0.90 b 0.90 0.30 1.80 0.60 0.45 0.35 1.20 0.80 c 1.00 0.35 1.50 0.60 0.50 0.25 1.00 0.50 a. implementation of the lsnsga for optimum pss design to investigate the performance of the proposed method, the results obtained using lsnsga-pss are compared with those of other metaheuristic techniques such as nsgaii, sa [4], and fgsa [20]. the convergence characteristic of the proposed optimization technique for the optimum tuning of pss parameters is illustrated in figure 5. optimum psss parameters for the proposed method and for the sa and fsga techniques are given in table ii. system eigenvalues and damping ratios corresponding to the optimal pss parameters, obtained using these techniques are given in table iii. fig. 5. convergence characteristics of the lsnsga. table ii. optimal pss parameters method gen k t1 t2 t3 t4 lsnsgaii-pss based on j1 g2 2.4238 0.8075 0.1611 1.0973 0.7417 g3 9.9970 0.9867 1.2183 0.2652 0.4252 lsnsgaii-pss based on j2 g2 2.4529 0.8034 0.1642 1.1028 0.7448 g3 9.9996 0.9840 1.2069 0.2252 0.4313 nsgaii-pss g2 2.4530 0.8035 0.1642 1.1027 0.7447 g3 9.9995 0.9834 1.2069 0.2267 0.4327 sa-pss g2 11.008 0.216 0.05 0.104 0.05 g3 0.319 0.410 0.05 0.233 0.05 fgsa-pss g2 30.911 0.222 0.012 0.34 0.054 g3 30.931 0.229 0.015 0.24 0.034 from table iii, it is obvious that the system is poorly damped when no controller is used for the base case, case 1, and case 2 and it is unstable for case 3. in addition, it can be seen that the proposed controller provides better damping of all electromechanical modes than the other controllers. it is worth noting that all electromechanical controllers obtained using lnsga-pss are shifted in d-shape zone defined by 0 1σ = − and 0 20ξ = % . b. nonlinear time domain simulation to assess the effectiveness and robustness of the proposed controller, a 6-cycle fault disturbance in the line 5-7, close to bus 5 is applied. the fault is cleared by tripping the line 5–7 with successful reclosure after 1.0s. nonlinear simulation results obtained using lsnsga are compared with the results from sa-pss, fgsa-pss, and without controller. system responses at the operating conditions specified above are shown in figures 6 and 7. figure 6 depicts the speed deviations in per unit and figure 7 illustrates the internal voltages. from figures 6 and 7, it can be clearly seen that the suggested lsnsga-pss controller improved greatly the system stability and it provided better damping of the electromechanical oscillations than the other techniques, at all operating conditions. g2 load c load b 2 7 g3 g1 8 9 3 load a 5 6 4 1 j 2 j 1 engineering, technology & applied science research vol. 11, no. 3, 2021, 7283-7289 7287 www.etasr.com alshammari et al.: a local search-based non-dominated sorting genetic algorithm for optimal design … table iii. eigenvalues and damping ratios of the electromechanical modes method base case case 1 case 2 case 3 without pss -0.1124±j7.7400, 0.0145 -0.0374±j7.8347, 0.0048 -0.2142±j6.3226, 0.0339 +0.0181±j8.0903, -0.0022 -1.3346±j9.1096, 0.1450 -0.7023±j10.5832, 0.0662 -0.8227±j6.9390, 0.1177 -0.4515±j11.3794, 0.0396 lsnsgaii-pss based on j1 -2.6031± j6.2412, 0.3849 -1.7361±j6.3024, 0.2656 -1.6459±j5.2350, 0.2999 -1.9885±j6.4392, 0.2951 -2.9611±j6.8626, 0.3962 -4.3102±j8.9358, 0.4345 -2.0874±j6.3268, 0.3133 -4.5721±j9.4259, 0.4364 lsnsgaii-pss based on j2 -2.6448±j6.1179, 0.3968 -1.7774±j6.3792, 0.2684 -1.6318±j5.2411, 0.2973 -2.0258±j6.5302, 0.2963 -2.7138±j7.3837, 0.3450 -3.9494±j9.3519, 0.3890 -1.9142±j6.5763, 0.2795 -4.2547±j9.9153, 0.3943 lsnsgaii-pss (best compromise solution) -2.5491±j 5.9300, 0.3949 -1.7847±j6.2809, 0.2733 -1.6283±j5.1460, 0.3017 -2.0326±j6.4097, 0.3023 -2.7394±j7.5113, 0.3426 -3.8660±j9.3531, 0.3820 -1.8925±j6.6077, 0.2753 -4.1434±j9.9371, 0.3849 sa-pss -1.6530±j5.1835, 0.3038 -1.3442±j5.6104, 0.2330 -1.3510±j4.5402, 0.2852 -1.4203±j5.6820, 0.2425 -0.7082±j7.6085, 0.0927 -0.6774±j8.6128, 0.0784 -0.4869±j6.4701, 0.0750 -0.6073±j9.1726, 0.0661 fgsa-pss -1.0692±j 1.9971, 0.4719 -0.9256±j2.4987, 0.3473 -1.0438±j1.8555, 0.4903 -0.9196±j2.5427, 0.3401 -0.2328±j4.1174, 0.0564 -0.1382±j4.5924, 0.0301 -0.3301±j3.6252, 0.0907 -0.1696±j4.4911, 0.0377 (a) base case (b) case 1 (b) case 2 (b) case 3 fig. 6. system responses for speed deviations in pu. 3 1 ( d e g re e ) 3 1 ( d e g re e ) 3 1 ( d e g re e ) 3 1 ( p u ) engineering, technology & applied science research vol. 11, no. 3, 2021, 7283-7289 7288 www.etasr.com alshammari et al.: a local search-based non-dominated sorting genetic algorithm for optimal design … (a) base case (b) case 1 (b) case 2 (b) case 3 fig. 7. system responses for internal voltages in pu. v. conclusion psss represent an effective means for damping electromechanical modes. however, current power networks are becoming strongly nonlinear with configurations and load changing over time. thus, it is mandatory to adjust the pss parameters in order to guarantee the optimal damping of system oscillations at any operating condition, system configuration, or disturbance. in order to do this, this study presents an improved version of nsgaii, referred to as lsnsga, for robust pss design over a wide range of operating conditions. in the proposed technique, a local search procedure is added to the original nsgaii in order to improve its convergence characteristics. the lsnsga is used to tune the psss parameters in a way that the system stability is optimally improved after the occurrence of fault. in the design process, two eigenvalue-based objective functions are 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[22] k. deb, a. pratap, s. agarwal, and t. meyarivan, "a fast and elitist multiobjective genetic algorithm: nsga-ii," ieee transactions on evolutionary computation, vol. 6, no. 2, pp. 182–197, apr. 2002, https://doi.org/10.1109/4235.996017. engineering, technology & applied science research vol. 7, no. 2, 2017, 1552-1558 1552 www.etasr.com kashani and baharmast: effect of supply chain information systems on firm performance… effect of supply chain information systems on firm performance: an empirical case study farideh haghshenas kashani faculty of management, central tehran branch, islamic azad university, tehran, iran shahram baharmast faculty of management, central tehran branch, islamic azad university, tehran, iran abstract—this study evaluates the effect of supply chain information systems on firm performance in ikamco as a empirical case study. for this purpose, the 132 ikamco employees selected by simple random sampling responded to a questionnaire. content validity of the questionnaire has been confirmed by experts in this field; its reliability has been confirmed by using cronbach's alpha and fisher’s test. kolmogorov-smirnov test is used to ensure normality of the data obtained from questionnaire. the hypotheses are tested using smartpls software. results show that the model is well fitted to the data. findings show that a lean and agile supply chain is effective on supply chain performance and supply chain performance is effective on firm performance. efficiency of information systems moderates the effect of lean supply chain on supply chain performance and firm performance. however, flexibility of information systems does not moderate the effect of agile supply chain on supply chain performance and firm performance. keywords-supply chain; information systems; firm performance; pls; agile supply chain; lean supply chain. i. introduction information is one of the most important assets of any organization; because of its high and vital value for any organization, information should be well protected [1]. information is often used for directing processes of employees from top to operational levels. decision-making is a very important process based on information processing [2]. in recent decades, many scholars have highlighted the role of business information in different aspects of organization as information revolution [3]. in current volatile and competitive environment, the survival and success of organizations depend on the optimal utilization of technologies and information systems which are able to facilitate internal process management and contribute to adaptation to market changes and rapid responsiveness to customer needs by proper flexibility. lean supply chain focuses on creation of a value stream in organizational processes through elimination of all wastes in time and inventory and unnecessary costs [4]. lean supply chain involves inventory management, standard product delivery, waste reduction, quality improvement and management. agile supply chain refers to ability of a supply chain for rapid response to changes in the market and customer needs [5]. agile supply chain involves respond to needs, change management, customization and higher production capacity. efficiency of information systems refers to application of information systems for operational support of intraand inter-organizational supply chain processes [6]. efficiency of information systems involves management of materials and parts of suppliers, cost management, quality management for parts and product, production management and parts production line. flexibility of information systems is evaluated for changes in business practices, competitors, suppliers, customers and generally all people who have influence on the organization and rapid changes in information technology. flexibility of information systems involves introduction of new products, monitoring of market changes, responsiveness to market changes and change in products. supply chain refers to a set of methods used for effective and efficient integration of activities of suppliers, manufacturers, warehouses, distribution centers and retailers to minimize system costs and meet requirements by producing and distributing products and services in the right place at the right time. performance facilitates communication and understanding between employees and supervisors and leads to more favorable working conditions and higher commitment to quality of service. market share, return on investment, market share growth, return on investment growth, profit margins. in [7], author evaluated the effect of aligned marketing strategies on supply chain and performance of entekhab industrial group. they found a positive and significant relationship between aligned marketing strategies and supply chain and supply chain performance. they also found a positive and significant relationship between supply chain performance and performance. in [8], authors evaluated the effect of it on supply chain capabilities and firm performance in saipa. they concluded that it implementation had a significant effect on supply chain capabilities and performance. this significant effect suggests that it capability can promote performance and supply chain capabilities. moreover, it implementation has direct and indirect positive effect on performance. it is noteworthy that indirect effect of it implementation on performance is revealed through supply engineering, technology & applied science research vol. 7, no. 2, 2017, 1552-1558 1553 www.etasr.com kashani and baharmast: effect of supply chain information systems on firm performance… chain capabilities. although supply chain capabilities do not directly increase performance, they increase the positive effect of it implementation on performance. in [9], the role of information systems of strategic management in strategic decisions of organizations was examined. it was concluded that information systems integrate analytic methods of the organization. these techniques extract concepts from primary information and convert them to decidable forms. in [10], authors analyzed the effect of strategic planning of information systems in improving performance of supply chain management. they concluded that supply chain planning is influenced by strategic planning of information systems. activities done for development of strategic planning of information systems can be considered as a good guidance for this. by evaluating quality of information and supply chain performance, author in [11] concluded that quality of life is significantly effective on supply chain performance and information sharing facilitates this process. in [6], author evaluated the effect of information systems of supply chain on performance and concluded that information flexibilities have a significant effect on supply chain of companies. moreover, they showed that supply chain has a significant effect on firm performance. studying cross-organizational information systems and supply chain performance, authors in [12] concluded that cross-organizational information systems improve quality of environmental factors and significantly influence supply chain performance. in [13], authors examined the relationship between information systems and configuration of activities and success of organizations. they concluded that information systems play a deterministic role in making organizational decisions and they are effective on organizational success. in [14], authors examined the role of information systems on supply chain performance. they concluded that technical, strategic and cultural aspects of information systems improve supply chain performance. iran khodro mehvarsazan company (ikamco) as the largest producer of axles for gasoline-powered vehicles considers customer satisfaction, profitability, employee welfare, reduced costs, improved quality of products and ontime delivery as a result of proper information systems used in the supply chain. therefore, the problem of this study is whether the supply chain information system has a significant effect on ikamco firm performance. ii. conceptual model this study examines the effect of supply chain information systems on the performance of ikamco. figure 1 shows research conceptual model based on the model proposed in [6]. fig. 1. the research model a. research hypotheses  h1: lean supply chain is effective on supply chain performance.  h2: agile supply chain is effective on supply chain performance.  h3: supply chain performance is effective on firm performance.  h4: efficiency of information systems mediates the effect of lean supply chain on supply chain performance and firm performance.  h5: flexibility of information systems mediates the effect of agile supply chain on supply chain performance and firm performance. engineering, technology & applied science research vol. 7, no. 2, 2017, 1552-1558 1554 www.etasr.com kashani and baharmast: effect of supply chain information systems on firm performance… iii. research methodology this was an applied research using descriptive methods for data collection. the studied population included 200 ikamco employees who used information systems of supply chain. cochran formula for finite population was used to select the samples: 2 1 / 2 2 2 1 / 2 ( )( ) ( ) (1 ) ( 1) ( ) ) ( ) (1 ) n z p p n n d z p p          where, n denotes the sample size required; n denotes the size of statistical population; p denotes the ratio of having the considered characteristic; z denotes the area under the standard normal curve, which is 1.96 considering α=0.05; and d denotes maximum error (accuracy). 2 2 2 ( 2 0 0 )(1 .9 6 ) ( 0 .5 )(1 0 .5 ) 1 3 2 ( 2 0 0 1)( 0 .0 5 ) (1 .9 6 ) ( 0 .5 )(1 0 .5 ) n       thus, sample size was estimated at 132. to collect data, a questionnaire was designed from [6]. the main structure of questionnaire is shown in table i. table i. structure of questionnaire variable number of questions question number lean supply chain 6 1-6 agile supply chain 5 7-11 efficiency of information systems 5 12-16 flexibility of information systems 4 17-20 supply chain performance 10 21-30 firm performance 6 31-36 a. validity and reliability of questionnaire validity and reliability are essential properties of measurement instruments. validity determines the extent to which measurement instrument measures the considered trait. without knowing validity of a measurement instrument, accuracy of data cannot be ensured. in other words, validity determines whether instrument measures the considered concept, or the instrument can measure the trait to be measured. content validity is usually used to examine constructs of an instrument. content validity is usually determined by experts in the studied subject. hence, content validity depends on judgments of experts. accordingly, the questionnaire used in this study is valid, because it was derived from [6]. moreover, content validity of this questionnaire was confirmed by the professors and experts in the subject. to ensure reliability of the questionnaire, 60 questionnaires were first distributed among the studied population. reliability of the questionnaire was examined by cronbach’s alpha and fisher’s exact test, results of which are listed in table ii. cronbach’s alpha>0.7 and fisher’s values which are higher than error probability (α=0.05) indicate good reliability of the questionnaire. table ii. reliability of the questionnaire variable number of questions cronbach’s α fisher probability result lean supply chain 6 0.914 0.472765823 reliable agile supply chain 5 0.789 0.682441032 reliable efficiency of information systems 5 0.926 0.656109777 reliable flexibility of information systems 4 0.792 0.161646769 reliable supply chain performance 10 0.821 0.629178337 reliable firm performance 6 0.858 0.392513894 reliable total 36 0.952 reliable iv. results a. demographic variables as findings showed, 92.4% of subjects were male and 7.6% were female; 9.1% were single and 90.9% were married; 20.5% aged 25-30 years, 16.7% aged 31-35 years, 16.7% aged 36-40 years and 46.2% were older than 40 years; 5.3% had high school diploma and lower, 14.4% had associate’s degree, 67.4% had bachelor’s degree and 12.9% had master’s degree; 17.1% of samples had less than 5 years of experience, 12.1% had 6-10 years, 35.6% had 11-15 years, 16.7% had 16-20 years and 16.7% had more than 20 years of experience. b. hypothesis testing as shown in table iii, sig<0.05 rejects the hypothesis on normal distribution of data. partial least square (pls) analysis was used to test the hypotheses. table iii. distribution of data (k-s test) v a ri a b le l ea n s u p p ly ch a in a g il e su p p ly ch a in e ff ic ie n cy f le x ib il it y s u p p ly c h a in p er fo rm a n ce f ir m p er fo rm a n ce k-s test 1.765 1.883 2.197 1.936 1.815 1.805 sig. 0.004 0.002 0.000 0.001 0.003 0.003 result nonnormal nonnormal nonnormal nonnormal nonnormal non-normal c. confirmatory factor analysis to validate the questionnaire, the confirmatory factor analysis (cfa) is applied for all research variables. the results of cfa are shown in figures 2 and 3. table iv shows that the items are well fitted and the questionnaire is able to measure the variables. engineering, technology & applied science research vol. 7, no. 2, 2017, 1552-1558 1555 www.etasr.com kashani and baharmast: effect of supply chain information systems on firm performance… fig. 2. estimates of significance engineering, technology & applied science research vol. 7, no. 2, 2017, 1552-1558 1556 www.etasr.com kashani and baharmast: effect of supply chain information systems on firm performance… fig. 3. standardized estimates table iv. fit indexes of the model fit index optimal value obtained value result 2 / df 2 / df ≤3 2.92 good fit root mean squared error of approximation rmsea ≤0.1 0.052 good fit normed fit index nfi ≥0.09 0.93 good fit non-normed fit index nnfi ≥0.09 0.95 good fit comparative fit index cfi ≥0.09 0.94 good fit incremental fit index ifi ≥0.09 0.95 good fit goodness of fit index gfi ≥0.09 0.92 good fit adjusted goodness of fit index agfi ≥0.09 0.9 good fit root mean square residual rmr ≤0.08 0.04 good fit standardized root mean square residual srmr ≤0.08 0.02 good fit d. model with estimates of significance only significance level of flexibility is lower than 1.96, while statistics of other paths are higher than 1.96. in other words, the relationships between all variables are significant except the relationships between flexibility of information systems and supply chain performance (figure 4). pls results for the standardized estimates show that β-value=44.5% between lean supply chain and efficiency of information systems, β-value=16.2% between lean supply chain and supply chain performance, β-value=830.8% between agile supply chain and supply chain performance, β-value=54.7% between agile supply chain and flexibility of information systems, βvalue=45.6% between efficiency of information systems and supply chain performance, β-value=6.7% between flexibility of information systems and supply chain performance, βengineering, technology & applied science research vol. 7, no. 2, 2017, 1552-1558 1557 www.etasr.com kashani and baharmast: effect of supply chain information systems on firm performance… value=67.1% between supply chain performance and firm performance (figure 5). fig. 4. model with estimates of significance fig. 5. model with standardized estimates e. model with removed moderators figure 6 shows that significance level of all variables is higher than 1.96; thus, the relationships between all variables are significant. as shown in figure 7, β-value=31.3% between lean supply chain and supply chain performance, βvalue=49.2% between agile supply chain and supply chain performance and β-value=67.1% between supply chain performance and firm performance. results of hypothesis testing and comparison with previous studies are listed in table v. managerial implications are suggested in table vi. v. conclusion this study determined the moderating role of information systems (from perspectives of efficiency and flexibility) in the performance of ikamco. the results showed that efficiency of information system moderate the relationship between lean supply chain and supply chain performance and firm performance. moreover, the results showed that flexibility of information systems does not moderate the relationship between lean supply chain and supply chain performance and firm performance. to improve performance of the organization, ikamco needs to increase flexibility and faster responsiveness to customers in order to use proper market management information systems such as crm to acquire information feedbacks of market conditions and customers, as well as information systems of internal process management to establish or modify new product design process, increase quality of product, use intelligent tools in production, concentrate on team activities, increase delegation to employees, increase personnel skills, use new technologies, produce diverse products, use flexible line feeding system, and produce in different quantities. table v. results of hypothesis testing hypothesis test statistic βvalue result previous result 1 lean supply chain is effective on supply chain performance. 2.193 0.162 h0 rejected h1 accepted consistent with [7, 14] 2 agile supply chain is effective on supply chain performance. 4.220 0.308 h0 rejected h1 accepted consistent with [6, 9, 13, 15] 3 supply chain performance is effective on firm performance. 15.077 0.671 h0 rejected h1 accepted consistent with [6, 12, 16] 4 efficiency of information systems moderates effect of lean supply chain on supply chain performance and firm performance. 5.139 0.456 h0 rejected h1 accepted consistent with [8, 10, 17] 5 flexibility of information systems moderates effect of agile supply chain on supply chain performance and firm performance. 0.742 0.067 h0 accepted consistent with [11, 18] fig. 6. model with estimates of significance and removed moderators engineering, technology & applied science research vol. 7, no. 2, 2017, 1552-1558 1558 www.etasr.com kashani and baharmast: effect of supply chain information systems on firm performance… table vi. managerial implications h1: lean supply chain is effective on supply chain performance. 1. improve ability of the organization to manage inventory in different stages of supply chain 2. improve ability of supply chain to provide standard products by using modern strategies 3. improve ability of the organization to manage non-standard orders 4. increase ability of supply chain to reduce wastes 5. increase ability of supply chain to provide and produce high quality products 6. improve ability of supply chain to control quality of products h2: agile supply chain is effective on supply chain performance 7. customize products by adding certain models required by customers 8. respond effectively to variable needs of design 9. increase ability of supply chain to change existing product or design new products 10. increase ability of supply chain to manage inventory in order to meet customer needs h3: supply chain performance is effective on firm performance 11. improve responsiveness to certain customer needs 12. produce diverse products 13. respond quickly to change or improve products 14. introduce new products quickly to the market 15. change production capacity quickly based on customer demands 16. increase ability of supply chain to facilitate activities of the organization and business partners 17. use outputs of integrated information systems in top management decisions, better interactions with suppliers and customers and monitoring of market changes 18. facilitate delivery at short time periods h4: efficiency of information systems moderates effect of lean supply chain on supply chain performance and firm performance 19. improve efficiency of activities of suppliers and the organization 20. manage inventory of suppliers and the organization optimally 21. manage raw materials required by the organization and suppliers 22. manage control of parts in production line of the organization and suppliers 23. coordinate parts and information available in suppliers and production line 24. introduce new products and services to the market 25. monitor changes in the market 26. increase ability of information systems to help the organization change design of products fig. 7. model with standardized estimates and removed moderators references [1] n. f. doherty, h. fulford, “do information security policies reduce the incidence of security breaches: an exploratory analysis”, information resources management journal, vol. 18, no. 2, pp. 21-39, 2005 [2] m. gerber, r. von solms, “management of risk in the information age”, computers & security, vol. 24, no. 1, pp. 16-30, 2001 [3] m. e. porter, v. e. millar, “how information gives you competitive advantage”, harvard business review, july, 1985 [4] a. agrawal, r. shankar, m. k. tiwari, “modeling the metrics of lean, agile and leagile supply chai an anp-based approach”, european journal of operational research, vol. 173, no. 1, pp. 211-225, 2006 [5] a. jafarnejad, b. shahaei, organizational agility and agile production. 1st ed. tehran: nashr mehrban, 2007 [6] s. qrunfleh, m. tarafdar, “supply chain information systems strategy: impacts on supply chain performance and firm performance”, international journal of production economics, vol. 147, no. 1, pp. 340-350, 2014 [7] m. r. dalavi-esfahani, h. ghorbani, m. bagheri-ghalesalimi, “effect of aligned marketing strategies on supply chain and performance”, marketing management, vol. 9, no. 23, pp. 95-109, 2014 [8] s. varedi, m. rostami-norouzabad, s. rahmani-norouzabad, z. samadi, “effect of it on supply chain capabilities and firm performance; a case study: saipa”, industrial management, vol. 8, no. 24, pp. 159-169, 2013 [9] f. kianfar, “role of information systems of strategic management in strategic decisions”, tomorrow management, vol. 7, no. 19, pp. 65-75, 2008 [10] a. amid, a. rezaeian, m. bagheri, “analysis of effect of strategic planning in information systems for improving supply chain management performance”, business management vision, vol. 7, no. 25, pp. 5-32, 2007 [11] p. marinagi, p. trivellas, c. reklitis, “information quality and supply chain performance: the mediating role of information sharing”, procedia social and behavioral sciences, vol. 15, no. 12, pp. 473-479, 2015 [12] h. lee, m. sun kim, k. kim, “interorganizational information systems visibility and supply chain performance”, international journal of information management, vol. 34, no. 2, pp. 285-295, 2014 [13] a. j. gilbert silvius, j. stoop, “the relationship between strategic information systems planning situational factors”, journal of international technology and information management, vol. 22, no. 1, art. no. 1, 2013 [14] r. rajaguru, m. jekanyika matanda, “effects of inter-organizational compatibility on supply chain capabilities: exploring the mediating role of inter-organizational information systems (iois) integration”, industrial marketing management, vol. 42, no. 4, pp. 620-632, 2013 [15] h. daoud, m. triki, “accounting information systems in an erp environment and tunisian firm performance”, the international journal of digital accounting research, vol. 13, no. 1, pp. 1 – 35, 2013 [16] u. sadiq, a. fareed khan, k. ikhlaq, g. bahaudin, n. mujtaba, “the impact of information systems on the performance of human resources department”, journal of business studies quarterly, vol. 3, no. 4, pp. 77-91, 2012 [17] s. petter, w. delone, e. mc lean, “measuring information systems success: models, dimensions, measures, and interrelationships”, european journal of information systems,vol. 17, no. 4, pp. 236–263, 2008 [18] r. haji-jabari, s. yazdani, e. dadashi-khas, “effect of accounting information systems on organizational performance”, productivity management, vol. 6, no. 23, pp. 125-148, 2012 microsoft word 40-3889-erratum engineering, technology & applied science research vol. 10, no. 5, 2020, 6386-6388 6386 www.etasr.com s. hota et al.: erratum and addendum: “a standalone pv system with a hybrid p&o mppt …” erratum and addendum: “a standalone pv system with a hybrid p&o mppt optimization technique” shubhakam hota dpt of electrical engineering, centre for advanced post graduate studies, biju patnaik university of technology, rourkela, odisha, india shubhakam143@gmail.com manoj kumar sahu dpt of electrical engineering, centre for advanced post graduate studies, biju patnaik university of technology, rourkela, odisha, india manojsahu.bls@gmail.com jagan mohana rao malla dpt of electrical engineering, centre for advanced post graduate studies, biju patnaik university of technology, rourkela, odisha, india nitya5311@gmail.com since the publication of our original paper in vol. 7, no. 6 of this journal [1], we have detected several misprints and errors that are corrected here, in the order in which they appear in the original paper. the third sentence in the abstract can be rephrased as “a comparative analysis of power-voltage characteristics of a pv cell with and without the p&o mppt module under various irradiations have been performed in simulink in order to investigate the efficiency of the module.” the fourth sentence of the abstract should be omitted. the third sentence of the introduction section should be rephrased as: “the efficiency of the solar cell is small as it converts at most a 30% 40% of solar irradiance into electrical energy.” the fourth sentence of the introduction section should be rephrased as: “to overcome this problem, the maximum power point tracking (mppt) is used which increases the production about 20%-30%.” the fifth sentence of the introduction section can be rephrased as “a mppt system is defined as an electronics device which guides the pv cell in a manner that a greater percentage of the power produced by the pv cell will be delivered to the load.” the third sentence of the first sub-section of section ii should be replaced with: “when the sun light falls on the solar cell, the free electron in the n-type semiconductor gets energized and moves towards the p-side to fill up the holes.” the fifth sentence can be replaced with: “if there is no load i.e. rl=0, then a short circuit condition occurs that means the short circuit current isc is maximum.” the remaining sentences should be replaced with: “when the cell is operated at isc=0 (open circuit), the shunt resistance rsh is very high.” in the second subsection of section ii the unit of top and tref are represented as k instead of oc. equation (3) can be replaced with: ( )       −      + = 1 v exp tη se sd irv ii (3) equations (4) and (5) should be attributed to [11]. figure 3 should be omitted and the rest of the figures should be renumbered. the last line should be replaced with: “figure 3 shows the p-v curve of the pv cell with no mppt considering the temperature and irradiation variation.” in section v, all sentences after the first one should be replaced with: “this model is simulated by considering c=number of cells=36, ns=np=1 (number of series and parallel paths). the simulations are performed under a standard temperature of 25 oc and various irradiation levels. as shown in figure 9, 10, and 11, the maximum obtained power for g=600 w/m2, g=800 w/m2 and g=1000 w/m2 (no mppt) is 12.375 kw, 13.387 kw and 14.82 kw respectively whereas the tracking efficiency is 38.67%, 41.83% and 46.31% respectively. figures 12 to 14 represent the p-v curves with the use of p&o mppt. as shown, for g=600 w/m2, g=800 w/m2 and g=1000 w/m2, the maximum obtained power now increases to 29.5 kw, 30.36 kw and 31.5 kw respectively whereas the tracking efficiency increases to 92.18%, 94.87% and 98.43% respectively. hence with an open circuit voltage of 1000 v and short circuit current of 47 a, the maximum power that can be tracked is 31.5 kw. at both voc and isc instances, the power becomes 0. when the linear multiplication of vi is maximum, the condition for maximum power is obtained. the point at which the linear product of v and i is maximum is named as mpp.” table i should be omitted. the last sentence of the last section should be replaced with: “under normal environmental condition maximum achievable power is 31.5 kw.” the last two references in the original paper should be replaced with [2] and [3] and a new reference ([4]) should be added in the reference list of the original paper which should now read: [9] j. m. r. malla, m. k. sahu, and p. k. subudhi, “pv based water pumping system for agricultural sector,” journal of materials today: proceedings, 2017. [10] t. a. binshad, k. vijayakumar, and m. kaleeswari, “pv based water pumping system for agricultural irrigation,” frontiers in energy, vol. 10, no. 3, pp. 319-328, may 2016. [11] ş. yılmaz, h. rıza özçalık, m. güneş, and o. doğmuş, “mathematical model derivation of solar cell by using onediode equivalent circuit via simulink,” international journal of education research, vol. 1, no. 12, pp. 1-12, dec. 2013. apart from figure 3, figures 10 and 11 should also be removed and the new figures shown below should be added: corresponding author: manoj kumar sahu engineering, technology & applied science research vol. 10, no. 5, 2020, 6386-6388 6387 www.etasr.com s. hota et al.: erratum and addendum: “a standalone pv system with a hybrid p&o mppt …” fig. 9. pv curve (g=600w/m2, t=25°c) (without mppt). fig. 10. pv curve (g=800w/m2, t=25°c) (without mppt). fig. 11. pv curve (g=1000w/m2, t=25°c) (without mppt). fig. 12. pv curve (g=600w/m2, t=25°c) (with p&o mppt). fig. 13. pv curve (g=800w/m2, t=25°c) (with p&o mppt). fig. 14. pv curve (g=1000w/m2, t=25°c) (with p&o mppt). fig. 15. the simulink model. engineering, technology & applied science research vol. 10, no. 5, 2020, 6386-6388 6388 www.etasr.com s. hota et al.: erratum and addendum: “a standalone pv system with a hybrid p&o mppt …” references [1] s. hota, m. k. sahu, j. m. r. malla, “a standalone pv system with a hybrid p&o mppt optimization technique,” engineering, technology & applied science research, vol. 7, no. 6, pp. 2109-2112, 2017 [2] j. m. r. malla, m. k. sahu, and p. k. subudhi, “pv based water pumping system for agricultural sector,” journal of materials today: proceedings, 2017. [3] t. a. binshad, k. vijayakumar, and m. kaleeswari, “pv based water pumping system for agricultural irrigation,” frontiers in energy, vol. 10, no. 3, pp. 319-328, may 2016. [4] ş. yılmaz, h. rıza özçalık, m. güneş, and o. doğmuş, “mathematical model derivation of solar cell by using onediode equivalent circuit via simulink,” international journal of education research, vol. 1, no. 12, pp. 1-12, dec. 2013. microsoft word etasr_v11_n3_pp7217-7222 engineering, technology & applied science research vol. 11, no. 3, 2021, 7217-7222 7217 www.etasr.com wali et al.: an end-to-end machine learning based unified architecture for non-intrusive load … an end-to-end machine learning based unified architecture for non-intrusive load monitoring syed wali faculty of electrical and computer engineering ned university of engineering and technology karachi, pakistan syedwali110@hotmail.com muhammad hassan ul haq faculty of electrical and computer engineering ned university of engineering and technology karachi, pakistan hassanulhaq@neduet.edu.pk majida kazmi faculty of electrical and computer engineering ned university of engineering & technology karachi, pakistan majidakazmi@neduet.edu.pk saad ahmed qazi neurocomputation lab, national centre of artificial intelligence, ned university of engineering and technology, karachi, pakistan saadqazi@neduet.edu.pk abstract-non-intrusive load monitoring (nilm) or load disaggregation aims to analyze power consumption by decomposing the energy measured at the aggregate level into constituent appliances level. the conventional load disaggregation framework consists of signal processing and machine learning-based pipelined architectures, respectively for explicit feature extraction and decision making. manual feature selection in such load disaggregation frameworks leads to biased decisions that eventually reduce system performance. this paper presents an efficient end-to-end (e2e) approach-based unified architecture using gated recurrent units (gru) for nilm. the proposed approach eliminates explicit feature engineering and has a unified classification and prediction model for appliance power. this eventually reduces the computational cost and enhances response time. the performance of the proposed system is compared with conventional algorithms' with the use of recall, precision, accuracy, f1 score, the relative error in total energy and mean absolute error (mae). these evaluation metrics are calculated on the power consumption of top priority appliances of reference energy disaggregation dataset (redd). the proposed architecture with an overall accuracy of 91.2 and mae of 25.23 outperforms conventional methods for all electrical appliances. it has been showcased through a series of experiments that feature extraction and event-based approaches for nilm can readily be replaced with e2e deep learning techniques allowing simpler and cost-efficient implementation pathways. keywords-non-intrusive load monitoring; gated recurrent units; end-to-end machine learning; reference energy disaggregation dataset i. introduction energy demand is increasing drastically with the increase in industrial development. this raises the need of managing energy usage effectively at consumer end. efficient demand management is possible by analyzing the appliance level power consumption in buildings [1]. today, this financially feasible solution, provided in 1992 [2], is known as non-intrusive load monitoring (nilm). the basic idea of nilm revolves around the decomposition of total demand into appliance level power consumption. since this load disaggregation approach does not depend on several data recorder sensors, it is therefore a costeffective solution adopted for demand reduction and load forecasting. the interest of researchers in this domain is significantly increasing with the development of smart meters, capable of delivering aggregate power information to the customer. with the advancements in machine learning (ml) domain, it is expected that nilm with high accurate power consumption analysis capabilities will serve as the backbone in the development of innovative smart grid services [3]. generally, nilm can be categorized into two types: eventbased approaches and event-less or state dependent approaches. in the event-based approaches, any significant change in the signal that is considered during load disaggregation is regarded as an event. all event-based approaches depend on previous training, thus supervised ml approaches are mostly adopted in this category [4]. the second category, i.e. the event-less approach, does not rely on event detection. it primarily uses statistical and probability-models to match consumption signal of single or group appliances to the aggregate power signal [3]. thus, label transitions are not required in this category. eventbased nilm methods primarily depend on finding edges in order to observe change in power demand. initially, hart formulated different clusters based on similar power change and characteristics of appliances using combinatorial optimization (co) for disaggregating power demand [2]. conventional edge detection approaches were then replaced by probability-based methods. these methods were comparatively less complex than the conventional methods [5, 6]. standard deviation was calculated in [5] instead of using a single fixed parameter. also, authors in [6] utilized a statistical approach for detecting the edges and power change signature of different appliances. later, classifiers such as support vector machines (svms) [7], decision tree [8], and other hybrid approaches corresponding author: majida kazmi engineering, technology & applied science research vol. 11, no. 3, 2021, 7217-7222 7218 www.etasr.com wali et al.: an end-to-end machine learning based unified architecture for non-intrusive load … were investigated to serve the purpose. hidden markov models (hmms) and their several variants were also utilized to model multi-state appliances and different possibilities of their combination [9-11], since the complexity of modeling multistate appliances increases with increasing number of appliances installed in customer premises [12]. therefore, inherent complexity of this methodology was reduced via the introduction of viterbi algorithm in [13]. the latest development in ml shifts the paradigm to deep learning based nilm. multilayer perceptron (mlp), convolution neural networks (cnns), deep neural networks (dnns), recurrent neural networks (rnn) k-nearest neighbor (k-nn) and naïve bayes classifiers are a few of the most widely used supervised ml techniques for load disaggregation [3]. cnns and rnn-based long short-term memory (lstm) have been explored for nilm in [12]. authors in [14] implemented 3 different dnn architectures for short term load forecasting. 1d cnn was implemented in [15] for examining the effect of variables dependent on power demand. hybrid cnn was also proposed in [16] where impact of reactive power, current, and apparent power were assessed on the performance of nilm disaggregation. the window of aggregate power signal was utilized in [15] to predict the power of the targeted appliance. the input sequence utilized for generating the sequence of output power is termed as sequenceto-sequence approach. if the same sequence predicts power at specific time instant only then it is termed as sequence-to-point. both sequence-to-point and sequence-to-sequence nilm approaches [15] were based on cnn architecture. the load disaggregation problem was treated as noise reduction in [17] using denoising autoencoders. this approach showed improved performance under different types of loads. one of the major drawbacks in the above stated deep learning based nilm architectures is their dependency on explicit features extraction from signal. this manual feature(s) extraction leads to biased decisions that eventually reduce the overall performance of nilm. in order to improve performance, these methods deploy extremely dense neural architecture with large number of layers. these dense architectures are time consuming and computationally expensive. moreover, dependency on separate classification and regression networks [15, 18] further increases computational power, thus making these solutions extremely expensive. the manhours required in feature engineering and in the collection of contextual information for deep neural architectures comprise a time taking procedure and there lies a strong probability of losing important load signatures in manual feature extraction. in order to address all of the above limitations in previously proposed nilm approaches, this paper presents an efficient end-to-end (e2e) ml based unified architecture using gated recurrent units (gru). the main characteristics of the proposed architecture are: • the e2e ml approach is adopted which does not depend on explicit feature extraction. the feed input of this e2e architecture is complete aggregate power signal, ensuring reliable and better prediction even under different load categories. • a unified module is an inherent characteristic of the proposed e2e architecture. since the proposed architecture considers both classification of appliance and prediction of consumption as a single problem, there is no need to use separate modules. • low computational cost due to the unified architecture as compared to the conventional pipelined architecture. real time load disaggregation is also possible due to the fast response time of the proposed architecture. it allows easy integration in modern smart metering devices. • improved performance of the proposed e2e architecture as compared to previously proposed dnn architectures despite of using comparatively lesser number of layers and neurons. the performance edge of the proposed approach is showcased on redd, which is a renowned load disaggregation dataset. ii. the proposed e2e machine learning based unified architecture an e2e ml based unified architecture for nilm is proposed in this work to completely eliminate the reliance on feature extraction. the proposed framework is presented in figure 1. it consists of dataset and preprocessing, e2e ml model, and evaluation metrics. fig. 1. the proposed e2e ml-based unified architecture for nilm a. load disaggregation dataset and preprocessing training and development of e2e ml model depends on datasets prepared for load disaggregation. the residential energy disaggregation dataset (redd) [4] is utilized in this research work. redd was made publicly available in 2011 [4] with the aim of fast paced research and development in load disaggregation domain. it was developed with two major objectives. firstly, it helps the researchers to apply algorithms and techniques directly on the available data instead of investing extensive efforts on the data acquisition stage of the nilm. secondly, this dataset provides globally accepted reference data for comparing different algorithms and techniques implemented by different researchers. the redd dataset contains information of the aggregate power signals and the power of each individual appliance installed in 6 different homes in massachusetts, usa. these 6 different homes cover almost all types of appliances used in consumer premises like washing machine, microwave, fridge, lights, air conditioning, electric stove, smoke detectors, etc. this dataset includes two-state, finite state, and continuously varying type of electrical loads. low frequency power data from the first building of redd dataset are selected for evaluation of the proposed algorithm. six top priority appliances with respect to power consumption from house1 of redd were considered. the selected dataset is preprocessed for removing erroneous readings, detecting gaps and downtime engineering, technology & applied science research vol. 11, no. 3, 2021, 7217-7222 7219 www.etasr.com wali et al.: an end-to-end machine learning based unified architecture for non-intrusive load … using nilm tool kit (nilmtk). the data are separated as training and testing subsets with a ratio of 50:50 b. the e2e ml model the gated recurrent unit (gru), a variant of rnn, is selected as the basic ml model for the proposed e2e architecture. rnn is selected due to its efficient information handling with smaller context [19]. gru is computationally simpler as compared to other rnn variants. it controls the flow of contextual information using just two gates as illustrated in figure 2. fig. 2. the gru architecture. the first gate of gru is the update gate. this gate is responsible to decide the extent to which information content from previous history should be passed for the determination of the future state. the output vector of the update gate (zt) depends on previous cell output (ht-1), present input (xt), calculated weights (wz, uz), and biased vector (bz). mathematically, the output of the update gate depends on the sigmoid function and can be represented as: �� � � ��� ∗ � � �� ∗ ��� � ��� (1) the second gru gate is the forget gate. this gate is responsible to filter and remove the flow of information from cells. it depends on current input (xt), previous output (ht-1), corresponding weights (wr, ur) and biased vector (br): �� � � ��� ∗ � � �� ∗ ��� � ��� (2) the final output produced by the gru depends on intermediate memory state (ĥt). this intermediate memory depends on weights (wh, uh), current input (xt), previous output (ht-1), and biased vector (bh). the mathematical model of this hidden memory state is shown in (3). it depends on tanh which is used as the activation function. ĥ� � ���h ��� ∗ � � �� ∗ �� ∗ ��� � ��� (3) the gru output depends on the hidden memory state and update gate as shown in (4): h� � �1 � z�� ∗ h��� � z� ∗ ĥ� (4) the proposed deep neural architecture consists gru hidden layers, whereas the convolution layer and the dense layer with linear activation function are the input and output layers. the number of layers and neurons for gru is selected for optimal performance using constructive approach in multiple passes. it starts with a small or undersized network having a smaller number of neurons and layers, and gradually its size increases until it achieves optimal performance. during the first pass, the number of neurons is steadily increased from 64 to 2100 with a step size of 100. better performance in terms of accuracy and mae is observed in the range of 500 to 700 neurons as shown in figure 3. in the second pass, neurons are gradually increased from 500 to 700 with a reduced step size of 10. it was found that the load disaggregation model suffered from overfitting when the number of neurons increased above 650. the best point in this region in terms of reduced mae and improved accuracy was 630 neurons, so it was selected as the optimum number of neurons. fig. 3. gru accuracy and mae for different numbers of neurons. single hidden layered architecture is insufficient as a network with a smaller number of layers or neurons often fails to extract details from the training data [20]. thus, 6 different architectures were tested comprising of 2, 4, 6, 8, 10, and 12 hidden gru layers. increasing architecture after 4 layers leads to overfitting and loss of generalization. table i tabulates the accuracy on training data against the number of gru layers. optimal performance was achieved with the model with 4 gru hidden layers of 1, 630, 1, and 1 neurons respectively. table i. accuracy on training data against the number of gru layers no. of layers accuracy overall test data fridge microwave washer dryer dish washer light socket 2 0.86 0.82 0.92 0.88 0.83 0.72 1 4 0.95 0.97 0.95 0.98 0.89 0.91 1 6 0.87 0.92 0.91 0.91 0.78 0.67 1 8 0.85 0.88 0.91 0.81 0.79 0.73 1 10 0.82 0.79 0.88 0.77 0.75 0.73 1 12 0.80 0.77 0.86 0.75 0.71 0.72 1 the learned model was then applied to the testing data. table ii tabulates the accuracy on the test data. the training and testing phases of the proposed e2e ml model are elaborated using the pseudocode shown in figure 4. engineering, technology & applied science research vol. 11, no. 3, 2021, 7217-7222 7220 www.etasr.com wali et al.: an end-to-end machine learning based unified architecture for non-intrusive load … table ii. accuracy of the learned model on test data appliance accuracy fridge 0.88 microwave 0.93 washer dryer 0.98 dish washer 0.81 light 0.87 socket 1 overall 0.912 fig. 4. ttraining and testing pseudocode of the proposed e2e ml model. c. evaluation metrics the prediction of each load consumption at a certain time instant is not purely a regression problem. the load disaggregator first identifies the presence of certain appliances in the aggregate power signal and then predicts their individual power consumption. thus, performance evaluation should not be based on regression indices only, classification accuracy must also be evaluated. recall, precision, accuracy, and f1 score are used to account classification performance, whereas, mean absolute error (mae) and relative error (re) in total energy are used for the assessment of values predicted by the load disaggregator: recall � $%&' ()*+,+-' ./0*' 1'2/,+-'3$%&' ()*+,+-' (5) precision � $%&' ()*+,+-' ./0*' ()*+,+-'3$%&' ()*+,+-' (6) f1 score � 2 ∗ (%'<+*+)=∗%'</00 (%'<+*+)=3%'</00 (7) accuracy � $%&' ()*+,+-'3$%&' 1'2/,+-' a%)&=b ()*+,+-'3a%)&=b 1'2/,+-' (8) re � |$),/0 e%'b+<,'b '='%2f�$),/0 /<,&/0 '='%2f| g/h�(%'b+<,'b i='%2f,k<,&/0 i='%2f� (9) mae � ∑ |'*,+g/,'b e)n'% /, ,�/<,&/0 e)n'% /, ,|opqopr $+g'�$� (10) iii. results and comparison the proposed e2e ml model was evaluated and compared with conventional load disaggregation algorithms. nilmtk is equipped with benchmark algorithms. two of the most widely used benchmark algorithms, i.e. co and fhmm, are selected for evaluation on the redd dataset, whereas one state of the art algorithm based on rnn architecture proposed in [21] is reproduced using the details provided by the authors. for fair comparison, all baseline algorithms were trained and tested with similar train tests split on 6 top priority appliances of redd, i.e. fridge, microwave, dishwasher, washer dryer, sockets, and lights. these top 6 appliances, with respect to power consumption, were used to evaluate the performance of the conventional and the proposed algorithms as shown in figure 5. fig. 5. performance evaluation of the nilm algorithms. engineering, technology & applied science research vol. 11, no. 3, 2021, 7217-7222 7221 www.etasr.com wali et al.: an end-to-end machine learning based unified architecture for non-intrusive load … the proposed gru shows a consistent performance in all the appliances, in terms of mae. the overall mae of the proposed model is 25.23, whereas, the mae of co, fhmm, and rnn is 61.88, 56.14, and 33.92 respectively. thus, the proposed approach shows reduced mae without being dependent on feature engineering approach. similarly, the overall accuracy of co, fhmm, rnn, and the proposed model is calculated as 66, 74, 64, and 91 respectively. fhmm shows better accuracy in fridge and light only, whereas, co is better in the case of the dishwasher. this clearly indicates a better and consistent performance of the proposed model in terms of accuracy. beside baseline algorithms, the proposed model is also compared with few of the latest dnn approaches convolution sequence to point (seq2point) [15], convolution sequence to sequence (seq2seq) [15], and denoising autoencoder (dae) [17]. these dnn approaches are compared in terms of mae and computational cost for two major appliances (fridge and microwave) of redd's house1. the number of layers depicts the computational complexity and time required for power disaggregation. table iii indicates that the proposed e2e architecture shows better performance in comparison to the modern approaches in [15, 17], whereas this unified and less dense architecture is also computationally efficient and fast to be used in real time applications. table iii. comparison with latest dnn approaches ref. algorithm layers comp. cost fridge mae microwave mae [15] seq2point 8 medium 28.10 28.19 [15] seq2seq 8 medium 30.63 33.27 [17] dae 10 highest 29.11 23.26 proposed e2e 6 lowest 22.12 23.19 iv. conclusion nilm is dominated by pipeline approaches with explicit feature extraction for load identification. the developments made in the domain of ml can eliminate the dependency on inherently low performing and computationally complex architectures. the proposed e2e ml based unified architecture using grus was evaluated on top 6 appliances of redd. comparative analysis of the proposed and previously reported algorithms showed that the proposed architecture has the ability to replace the feature-based load disaggregation approach. since the proposed architecture performs better in all cases irrespective of the appliance type, it depicts that it can improve performance of the load disaggregator and due to its less computational demand and fast response time it can also be integrated in modern smart metering solutions. references [1] m. sun, f. m. 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[21] j. kelly and w. knottenbelt, "neural nilm: deep neural networks applied to energy disaggregation," in proceedings of the 2nd acm international conference on embedded systems for energy-efficient built environments, new york, ny, usa, nov. 2015, pp. 55–64, https://doi.org/10.1145/2821650.2821672. microsoft word etasr_v10_n6_pp6469-6475 engineering, technology & applied science research vol. 10, no. 6, 2020, 6469-6475 6469 www.etasr.com vu et al.: radiation shielding properties prediction of barite used as small aggregate in mortar radiation shielding properties prediction of barite used as small aggregate in mortar hoang quoc vu faculty of civil engineering ho chi minh city university of technology (hcmut) vietnam national university ho chi minh city ho chi minh city, vietnam vqhoang@hcmut.edu.vn phong thanh nguyen department of project management faculty of civil engineering ho chi minh city open university ho chi minh city, vietnam phong.nt@ou.edu.vn van hoang tran faculty of civil engineering ho chi minh city university of technology (hcmut) vietnam national university ho chi minh city ho chi minh city, vietnam 1614062@hcmut.edu.vn nhi thi uyen le faculty of civil engineering ho chi minh city university of technology (hcmut) vietnam national university ho chi minh city ho chi minh city, vietnam 1612416@hcmut.edu.vn mai thanh le faculty of civil engineering ho chi minh city university of technology (hcmut) vietnam national university ho chi minh city ho chi minh city, vietnam thanhmaia8@gmail.com abstract-construction materials used in the nuclear industry used to be mainly heavy materials, including lead plates, radiationresistant heavy concrete, etc. however, these materials are either toxic after a long time of use (lead) or difficult to construct (radiation-resistant heavy concrete) and their cost is rather high. therefore, there is a need for the manufacturing of a new kind of material with good radiation resistance, which is light, easy to use, and costs less. barium is less toxic and more cost-effective than lead. due to the importance of barium compounds in radiation shielding, the study of gamma radiation interactions within these compounds becomes essential, so the most important part of such a study is the experimental one, which shows the effect of the barite powder in the radiation resistance of the mortar. the research results show that the higher the thickness and percentage of barite powder, the higher is the radiation resistance. keywords-barite mortar; radiation protection material; compressive strength; volumetric mass; construction material; civil engineering i. introduction currently, nuclear technology is being widely applied in industry fields that divert from the narrow energy sector. the application of this technology in the manufacturing process provides a solution for coping with the challenges of global development (i.e. ensuring energy security, environment protection, food safety, etc.). modern tendencies require creating better and safer lead-free materials [1, 2]. authors in [3] studied the influence of barite content in polymer composites, while the gadolinium oxide is presented as effective filler in [4]. authors in [5] gave an example of using bismuth as filler for protection against gamma-rays. in nature, the following types of radiation occur as the majority: gamma (including x-rays), beta, and alpha radiation. among these radiation types, gamma radiation is the most dangerous because of its high appearance probability and running distance. the running distance of alpha and beta radiation is shorter and their penetration is weaker, so any material that can block gamma radiation will also block alpha and beta. there is also the neutron-ray radiation that should be considered. an effective way to improve the resistance to neutron radiation is to increase the proportion of elements with low atomic mass. theoretically, materials like serpentin that contain much bonding water (including wet materials) or use modified additives based on paraffin emulsions will resist neutron radiation more [6]. in fact, the source of neutron radiation is usually placed in a heavy concrete water tank, which will prevent neutron rays and is a cost-effective solution. the gamma radiation will interact primarily with the encapsulated electrons in the atomic shell. that interaction means being completely absorbed or losing energy, which will corresponding author: hoang quoc vu and phong thanh nguyen engineering, technology & applied science research vol. 10, no. 6, 2020, 6469-6475 6470 www.etasr.com vu et al.: radiation shielding properties prediction of barite used as small aggregate in mortar weaken or destroy the gamma radiation. therefore, when choosing a shielding material, attention must be paid to the factor of high electron density (electron/cm3), but for high electron density, the number of protons (the z number) of the atoms should be large, and the density of the shielding material also should be greater (atoms/cm3) [7]. therefore, the metal element barium (ba) (z = 56) in the barium sulfate compound baso4 is suitable for radiation shielding, because it is chemically stable, easy to preserve, pack, and transport, less affected by the surrounding environment, easy to produce, has low cost, it is safe, and easy to use [8, 9]. however, blocking gamma and x rays completely is very difficult, almost impossible, because they can penetrate materials in large depths. however, we can still control the amount of these radiations when released into the environment within the permissible limit of not affecting human health. globally, fabrication and mortar experience show that the adhesives that make the mortar resistant are portland cement and portland cement blends. after hydration and curing, the cement will withhold a quantity of bonding water. this has a significant effect on the grout's ability to resist neutrons. if we add a mineral powder with a high molecular weight, it will increase the mortar's ability to resist gamma and x rays. ii. research background materials for manufacturing barite mortar include [10]: • cement: pcb40 cement and construction sand are commonly used. yellow sand is carefully screened. • high content of barite powder: the main ingredient of barite powder is baso4, an inorganic compound with massive molecular weight, thus an effective anti-radiation material [11]. • clean water: well water or tap water can be used. barite mortar is a particular type of mortar used to prevent radiation. therefore, when conducting experiments to check the technical properties of barite mortar, it is unnecessary to apply all the provisions of tcvn 4314-2003 for ordinary mortar. we conducted experiments examining the physical properties of the 11 calculated gradients shown in table i. depending on each experiment, the properties of some gradients or the whole material will be tested. the experiments' focus is the graded design for barite mortar equivalent to standard mortar, investigating barite mortar's resistivity. iii. results and discussion a. determing the consistency of fresh mortar before testing, the surface of the glass, cone, and pestle was wiped with a damp cloth. a cone-shaped stitch was placed in the middle of the ballast table. eleven pre-mixed fresh mortar samples were poured in two layers, each layer with compaction of about ten pieces so that the mortar was full and homogeneous in the stitch. when compacting, the stitch was helped on the flow table by hand, as shown in figure 1. the excess mortar on the surface was flattened with a trowel, the water and mortar on the surrounding glass were wiped off, the stitch was slowly lift up vertically and the ballast was left 15 times for 15s. the diameter of the bottom of the mortar mass was measured in two perpendicular directions to the nearest mm. the test result was the average of the two measurements. the consistency of the mortar sample is the average result of the two tests. if one of the two measurement errors was greater than 10% of the average value, the experiment was repeated (figure 2). table i. the aggregates of 11 test samples a g g r e g a te t h e o r e ti c a l g r a d e (n /m m 2 ) b a r it e c o n te n t (i n s m a ll a g g r e g a te ) weight of ingredients cement (kg) barite (kg) sand (kg) water (l) 0 10 0% 359.15 0.00 1400.25 388.3 1 10 10% 359.15 142.95 1286.56 388.3 2 10 20% 359.15 292.00 1168.02 388.3 3 10 30% 359.15 447.56 1044.31 388.3 4 10 40% 359.15 610.05 915.08 388.3 5 10 50% 359.15 779.96 779.96 388.3 6 10 60% 359.15 957.79 638.53 388.3 7 10 70% 359.15 1144.12 490.34 388.3 8 10 80% 359.15 1339.58 334.89 388.3 9 10 90% 359.15 1544.84 171.65 388.3 10 10 100% 359.15 1760.67 0.00 388.3 fig. 1. the fresh mortar into the cone shape of the flow table. fig. 2. the consistency of the mortar. the main findings were: • when adding 10-30% barite powder, the small surface area leads to a decrease of the amount of water required to wet the surface and the amount of cement slurry required to engineering, technology & applied science research vol. 10, no. 6, 2020, 6469-6475 6471 www.etasr.com vu et al.: radiation shielding properties prediction of barite used as small aggregate in mortar lubricate the aggregate surface also decreases, but the amount of water and cement remained unchanged resulting in increased fluidity. • the total surface area of barite powder is greater than the total surface area of sand, but the amount of cement remains the same, so the quantity of cement paste is not enough to cover all fine aggregate particles (mainly barite powder). this makes the particles easier to contact, increasing the dry friction, resulting in reduced fluidity of the mortar mixture. for barite ratio of 30%, the mortar achieves the highest fluidity. b. determining the setting time of the fresh mortar the utilized tools were a clock, technical scales to an accuracy of 0.1g, and vikat tools. the results are shown in figure 3. it was shown that the setting time of the mortar sample decreases when the concentration of barite in the aggregate increases. according to the theoretical scientific basis, barite powder is an inert compound with normal chemical behavior, which means that barite is almost impossible to participate in a chemical reaction with cement, sand, and water during the closing process. thus, adding barite to the mortar will not significantly change its setting time. however, according to figure 3, as the barite content increases, the setting time of the mortar decreases. this can only be explained because the higher the barite content of the mortar mixture, the more pliability, adhesion, and high frictional force with the vikat needle increase, this hinders the vikat needle settlement and leads to incorrect setting time. in addition, because the barite grain is smaller than the sand, the contact between cement and water is not limited, so the setting time is shortened. fig. 3. setting time of the mortar vs the barite content. c. flexural and compressive strength of the hardened mortar for sample preparation, it took approximately 2l of a prepared mortar sample. the mortar was cast in molds with a metal base. the mold was covered with a thin layer of mineral oil. the mortar was poured into the mold in two layers, using pestle to compact each layer. the molded mortar sample was cured for 1 day in the mold (sealed at room temperature) and, after the mold removal, for 27 days in water (figures 4-5). experiments with flexural and compressive strength of the mortar were conducted according to [12] (figure 6). fig. 4. the samples were cured for one day in the mold. fig. 5. the samples were cured for 27 days in water. (a) (b) fig. 6. bending test. (a) compressing sample, (b) barite mortar. the experimental results are shown in tables ii and iii. the strength of barite mortar increases over time as the percentage content of barite in the aggregate increases, the bending and compressive strength of the mortar samples decreases and becomes lower than the theoretically calculated strength of the mortar because barite powder has a higher fineness and smaller engineering, technology & applied science research vol. 10, no. 6, 2020, 6469-6475 6472 www.etasr.com vu et al.: radiation shielding properties prediction of barite used as small aggregate in mortar magnitude module than sand, so the total surface area of barite powder will be larger than sand’s. table ii. bending test results # theoretical grade (n/mm 2 ) barite content (in small aggregates) flexural strength ru (n/mm 2 ) 3 days 7 days 28 days 0 10 0% 2.67 2.91 3.77 1 10 10% 2.54 2.86 3.68 2 10 20% 2.52 2.69 3.49 3 10 30% 2.34 2.55 3.45 4 10 40% 2.23 2.53 3.33 5 10 50% 2.22 2.52 3.30 6 10 60% 2.17 2.45 3.12 7 10 70% 2.15 2.42 2.95 8 10 80% 2.14 2.28 2.88 9 10 90% 1.88 2.01 2.64 10 10 100% 1.71 1.85 2.47 table iii. compression test results # theoretical grade (n/mm 2 ) barite content (in small aggregates) compressive strength rn (n/mm 2 ) 3 days 7 days 28 days 0 10 0% 6.73 8.29 11.63 1 10 10% 6.59 8.03 10.98 2 10 20% 6.37 7.79 10.79 3 10 30% 6.33 7.56 10.61 4 10 40% 6.22 7.23 10.24 5 10 50% 5.59 6.29 10.16 6 10 60% 5.48 6.20 9.84 7 10 70% 4.67 6.14 9.80 8 10 80% 4.66 6.05 9.62 9 10 90% 4.62 5.98 9.35 10 10 100% 4.43 5.71 9.16 it takes more cement than the theoretical calculated cement to cover all fine barite particles. insufficient cement will cause poor bonding in the mortar structure resulting in reduced strength. the mixture of barite mortar has low mobility, it is challenging to mix, leading to irregular mixing, so many pores appear, reducing the barite mortar strength. d. the volume of solid mortar samples solidified mortar tablets which have been cast in 40mm×40mm×160mm molds were used. the mortar was cured under specified conditions, for not less than 28 days. the samples were dried at 1050°c +50°c, were cooled to room temperature, and weighed. three measurements were taken, the result of each edge is the average of the three measurements at 3 different locations. 1mp= l.b.h (1) where p is the mass of test pieces (kg/m3), m1 is the mass of the sample in dry state (kg) and l, b, h are the length, width, and height of the test piece (m). the test result is the average of the results of the two test pieces shown in figure 7. the more the barite content, the more the volume of solid mortar sample increases. e. the resistivity of solid mortar samples the following equation shows the resistivity of the antiradioactive material: d 0i=i ×e −∑ (2) where i is the radiation intensity after passing through the material, i0 is the radiation intensity without material thickness, d is the thickness of the material layer (cm), σ is the material's linear absorbance coefficient (also known as the linear attenuation coefficient of the radiation) (cm-1). it is equal to the mass absorption coefficient times the density of the material [13]. fig. 7. the volume of solid mortar sample vs the barite content. the mass absorption coefficient depends on the energy level of the radioactive source. the smaller the i, the smaller the ratio i/io and the better radiation resistant is the material. on the other hand, as the thickness d increases, the ratio i/io also decreases, leading to smaller i which means better radiation resistant material. after 28 days of water curing, the mortar samples were cut into pieces with different thicknesses (2cm, 3cm, 4cm and 5cm). these thicknesses need to be checked in order to investigate the radioactive resistance of barite mortar. the pieces were shot by radiation rays in the laboratory. the change in resistance was investigated considering two factors: the thickness of the mortar and the barite content. a total of 88 samples were sent to the ho chi minh city nuclear center laboratory. a collimator with an internal diameter of 2.5cm was used to orient the radiation, to create an accurate correlation between the gamma-ray position and the direction of that gamma-ray when interacting with the mortar sample. the collimator also helped limit the unnecessary radiation outside the study area (background radiation) and can be seen in figure 8. fig. 8. collimator. the mortar samples were placed on a support, in such a way that the radiation could penetrate them (figure 9). the testing time for each mortar sample was 15min. at first, the engineering, technology & applied science research vol. 10, no. 6, 2020, 6469-6475 6473 www.etasr.com vu et al.: radiation shielding properties prediction of barite used as small aggregate in mortar dose rate results when there was no sample were measured, then the sample was placed in the measuring position and the dose rate was measured. the obtained results were recorded on a detector in µsv/h (figures10 and 11). each sample was measured 10 times and the results were averaged. fig. 9. the posotion of the test mortar sample. fig. 10. equipment layout position. fig. 11. detector. fig. 12. radiation attenuation for various mortar thickness and barite content percentage values. the ratio i/i0 of the experimental results and xcom is compared in figures 13-16. from the ratio i/i0, the linear attenuation coefficient is computed and the experimental results with xcom can be compared as shown in table iv and figure 17. fig. 13. radiation attenuation of 2cm barite mortar. fig. 14. radiation attenuation of 3cm barite mortar. fig. 15. radiation attenuation of 4cm barite mortar. fig. 16. radiation attenuation of 5cm barite mortar. engineering, technology & applied science research vol. 10, no. 6, 2020, 6469-6475 6474 www.etasr.com vu et al.: radiation shielding properties prediction of barite used as small aggregate in mortar table iv. xcom and experimental linear attenuation coefficient # sum of xcom (cm -1 ) sum of experiment (cm -1 ) ∆ (%) 0 0.1477 0.1514 2.52 1 0.1546 0.1585 2.50 2 0.1600 0.1671 4.44 3 0.1613 0.1711 6.12 4 0.1675 0.1752 4.60 5 0.1711 0.1816 6.16 6 0.1769 0.1860 5.10 7 0.1798 0.1916 6.55 8 0.1817 0.1960 7.85 9 0.1854 0.1997 7.68 10 0.1939 0.2045 5.47 fig. 17. linear attenuation coefficient: comparison of the experimental results with xcom. both experiment and xcom results showed that as the thickness increases, the radiation resistance of the mortar increases, and as the barite content increases, the linear attenuation coefficient increases along with the radiation resistance of the mortar. the difference between the xcom and the experimental results is within the acceptable limits. the results of this experiment are in accordance with the ones in [14, 15]. the current research calculated the corresponding energy levels and the obtained result is shown in figure 18. for the high energy level (662kev), the radiation resistance will be more effective when increasing the mortar sample thickness. corresponding to the low energy level (150kev), when increasing the concentration of barite in the aggregate, the radiation resistance will be more effective. fig. 18. radiation attenuation when passing through barite layers of varying thickness and barite content. iv. conclusion the vietnamese economy shows growth overcoming obstacles and challenges [16-18]. this is partially due to the research successes of the construction and engineering material segments [19-22]. this paper showed that barite mortar's consistency is higher than standard mortar’s when sand is replaced with barite powder in percentages up to 30%. for replacement ratio above 30% a decrease in fluidity is noticed. therefore, when making barite mortar, it is necessary to increase the amount of mixing water and the corresponding amount of cement. when increasing the barite content in the mortar sample, the setting time of the mortar is shortened, but not significantly. the barite mortar sample's flexural and compressive strength decrease gradually as the barite content increases. this can be entirely overcome by increasing the amount of cement while increasing the corresponding amount of water when mixing. in addition, mechanical mixing helps to mix evenly and achieve high uniformity, which also improves the mortar's strength. when designing, a 100-grade mortar mix was chosen, but in fact, the purpose of using barite mortar is only to improve its radiation resistance. therefore, although the mortar's compressive strength after 28 days is lower than 10n/mm2 (design), it is completely applicable. acknowledgment this research is fund by the vietnam national university, ho chi minh city (vnu-hcm) under the grant number b2018-20-05. we acknowledge the support and the facility provision of the ho chi minh city university of technology (hcmut) and vnu-hcm. references [1] s. nambiar and j. t. w. yeow, “polymer-composite materials for radiation protection,” acs applied materials & interfaces, vol. 4, no. 11, pp. 5717–5726, sep. 2012. 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(c) by the authors | doi: https://doi.org/10.48084/etasr.5907 abstract this research work aims to investigate and subsequently optimize the operating parameters that affect thermal comfort and indoor air quality in the school environment. the proposed design uses a coupling between solar ventilation and the absorption chiller-air conditioning. the heating tower of an adsorption chiller connected to an air conditioning system can be driven by the waste heat from a solar ventilation (exhausted hot air) system thank to this linkage. in order to simulate variables like the velocity magnitude distribution in the air-conditioned room, mathematical modeling is numerically executed. air temperature evolution along the height of the conditioned room in the mid-length and the air velocity evolution along the length of the conditioned room in the mid-height are studied. according to the numerical simulation results, the inlet air temperature soars as the inlet air velocity rises. inlet air velocities of 0.05m/s, 0.5m/s, and 1m/s are correlated with inlet air temperatures of 20.7°c, 21.2°c, and 21.3°c, respectively. we conclude that an inlet air velocity in the order of 1m/s (in relation to a maximized air change rate) is in agreement with the general ashrae standards for indoor air quality in the case of the school environment, coupled with the essential need to limit as much as possible the spread of viruses. keywords-solar air conditioning absorption; ventilation; human comfort i. introduction the indoor air quality and the thermal comfort in school environment are highly important factors that affect learning and teaching performance. the optimization of such factors within the appropriate standards, will ensure healthy indoor air quality and enhance the human thermal comfort. in this framework, the recent literature reveals some interesting works. authors in [1] carried out an integrated experimental and simulation approach in order to evaluate the indoor environmental quality (ieq), principally in terms of acceptable thermal level as well as indoor air quality, under the climate conditions of florina, western macedonia, greece. authors in [2] monitored the indoor air quality, in terms of air temperature, air relative humidity, co2 concentration, pm2.5 and pm10, in 10 school classrooms, over a period of one year and under the climate conditions of victoria, australia. results show that the ventilation rates should be increased. authors in [3] modeled and simulated the effect of wind tower ventilation on classroom thermal comfort during august under the climate conditions of trabzon, turkey. the results show that the wind tower ventilation often induces thermal discomfort under the considered climate conditions. authors in [4] compared different standards to assess the indoor air quality and the thermal comfort in school buildings, under the northern italy climate conditions. the results show principally that the operative temperature is the most appropriate way to establish and check thermal comfort in classrooms. the covid-19 pandemic renewed the interest in indoor air quality and ventilation, in order to limit viruses spreading especially in school environment. authors in [5] investigated the effects of measures, associated to the covid-19 pandemic control and prevention, on the ventilation and thermal conditions in 31 dutch secondary school classrooms. the results show principally that the ventilation rate is enhanced mainly thanks to the occupancy reduction after the covid-19 lockdown. also, it was shown that the doors and windows openings were not enough to reach the required ventilation rate. authors in [6] evaluated the sars-cov-2 airborne risk of infection based on natural ventilation rate calculation in an elementary school classroom, under the climate conditions of uruguay. the results show that periodic ventilation permits to significantly reduce the airborne transmission, even if it is carried out during short time spans. in the same context, sustainable and hybrid natural ventilation-air conditioning systems are more and more developed to create indoor air quality as well as thermal comfort. authors in [7] designed a new sustainable hybrid solar ventilation-air conditioning system and investigated its engineering, technology & applied science research vol. 13, no. 3, 2023, 11036-11041 11037 www.etasr.com alquraish & abuhasel: sustainable hybrid design to ensure efficiency and air quality of solar air … ventilation and thermal performances under the climate conditions of gafsa, tunisia. technologically speaking, the ventilation is ensured by a solar chimney system while the air conditioning is based on desiccation and adsorption chilling. the coupling between the solar ventilation and the solar air conditioning is based on the use of the wasted heat of the hot air, coming from the outlet of the chimney, to power the heating tower and regenerate the desiccation compartment of the air conditioning system. authors in [8] proposed a novel natural ventilation design called wind chimney. this design permits to create natural ventilation in buildings located in zones with dominant wind flow, based on aerodynamics law and air pressure difference caused by wind flow. authors in [9] investigated the impact of the meteorological conditions on the daily incident solar flux on the facades of a house at adrar region, algeria. authors in [10] demonstrated by numerical simulation that the temperature of the internal air varies with climate conditions, location, number of covers, and the solar greenhouse shape. roofs may be used to generate electricity by connecting pv systems. authors in [11] studied the solar energy potential and presented an economic study of a 5kw grid-connected rooftop photovoltaic (pv) system in botswana. many researchers have proposed hybrid systems for air conditioning, electricity production, and desalination. authors in [12] presented a solar hybrid system designed for water desalination, air-conditioning, and electricity production. in saudi arabia, individuals are investing more time inside buildings where the utilization of air conditioning is essential. in schools, the chance of disease spreading through bead and vaporized transmission is exceptionally high. fitting ventilation/air recharging might be a proficient arrangement to decrease infection transmission or other chemical of physical operators delivered by actions (e.g. cooking or smoking) or environment (e.g. sandstorms). it is critical to create advances and consider techniques to handle hyperthermia. ii. system description the proposed design, shown in figure 1, uses a coupling between the solar ventilation and the absorption chiller-air conditioning. this coupling permits to recover the waste heat of a solar ventilation (exhausted hot air) system and reuse it to drive the heating tower of an adsorption chiller associated to an air conditioning system. a solar chimney system oriented south is used to ventilate a conditioned space naturally, and an absorption chiller-air conditioning system is used to cool it. in particular, in terms of clothes insulation and air renewal, the suggested design should ensure a person's thermal comfort and a healthy indoor air quality. the air gap is heated by the solar chimney system using the greenhouse effect. this will create a pressure difference that will allow the expelled air from the conditioned room outlet (the solar chimney's inlet (3)) to be driven in the direction of the absorption chiller's heating tower (7-8). the heating tower should be heated and driven by an auxiliary heater ah (6-7) associated with an auxiliary blower av (5-6) if the heat from the considered ejected air is inadequate to run the heating tower correctly (insufficient solar energy). the absorption chiller can be powered by the cooling and heating towers. the result is the production of the storage of cold water in a cold-water tank, and its use in a water-air radiator (heat exchanger (9)). the blower v1 (1) draws in fresh air (i-air) from the outside, which is then cooled by the waterair radiator (2). the final step is to inject the obtained process air into the conditioned chamber after being dusted off through the filer f1 (3). fig. 1. the proposed solar ventilation-absorption air conditioning system design. iii. mathematical modeling special interest is given to the examination of the ventilation and thermal performance of the conditioned area. in this way, the suitable numerical modeling is based on the navier-stokes conditions in terms of progression condition, x and y-momentums conditions, vitality preservation condition as well as turbulent dynamic vitality and turbulent scattering [4]. the heat exchange model is considered in bi-dimensional steady state with the k-ε turbulence model. the boussinesq estimation is expected since the air temperature contrast between solar chimney inlet and outlet is considered low. a. continuity equation the continuity equation reflects the principle of mass conservation in terms of relation between the air velocity and the cross-sectional area through which the fluid flows. the decrease of this cross-sectional area induces an increase of air velocity. the continuity equation is written as: 0 u v x y       (1) b. momentum εquations the momentum equations reflect the principle of linear momentum conservation along a specific direction in space. the momentum of an object is the product of its mass and its linear velocity. it represents the quantity of motion of the considered object. the momentum equations along the xand y-directions of the space are written as: 1 ( ) 1 2 + ( ) 3 t t uu vu u x y x x u k y y x                                (2) engineering, technology & applied science research vol. 13, no. 3, 2023, 11036-11041 11038 www.etasr.com alquraish & abuhasel: sustainable hybrid design to ensure efficiency and air quality of solar air … 0 1 1 ( ) 1 2 + ( ) ( ) 3 t t uv vv p v x y y x x v k g t t y y x                                       (3) c. energy conservation equation as its name suggests, this equation reflects the principle of energy conservation. it expresses the first law of thermodynamics as a balance equation for the rate of change of kinetic energy and internal energy. the energy conservation equation is written as: 1 pr pr 1 + pr pr t t t t ut vt t x y x x t y y                                 (4) d. turbulent kinetic energy the turbulent kinetic energy k reflects the intensity of turbulence in a flow. the equation governing the transport of the turbulent kinetic energy k is written as: 1 pr 1 1 + ( ) pr k k k k b k uk vk k x y x x k g g y y                                        (5) e. turbulence dissipation the turbulent dissipation reflects the viscous conversion of mechanical energy to heat. the equation governing the turbulence dissipation ε is written as: 1 3 2 2 1 pr 1 1 + ( ) pr t t t k b t u v x y x x c g c g y y k c k                                                  (9) where the empirical constants 1c , 2c and 3c have the values of 1.44, 1.92, and 0.09, respectively, prk and prε, are the turbulent prandtl numbers for the variables k and ε having values of 1.0 and 1.3, respectively, and gk indicates the gradients in mean velocity: j i ij j i i j j i tk x u k x u x u x u g                     3 2 (7) gb represents the production of the turbulent kinetic energy due to the buoyancy: it t ib x t gg    pr   (8) it can be concluded that the mathematical modeling governing the ventilation and the thermal performance of the conditioned area was elaborated under the assumptions of boussinesq approximation as well as the bi-dimensional steady state heat transfer with the k-ε turbulence model. in the next section, this mathematical modeling is numerically implemented. the simulation results are presented and discussed. iv. results a. air flow within the conditioned room figure 2 shows the air velocity magnitude distribution within a conditioned room with length x=4m and height h=3m. the inlet of the air is located to the lower right wall, while the outlet air is connected to the inlet of the solar chimney and it is located in the top of left wall. the inlet air velocity is varied as 0.05m/s, 0.5m/s, and 1m/s. it is clear that the air breeze (forced air flow) carried out between the air inlet and the outlet keeps almost the same shape with a global air velocity enhancement as the inlet air velocity increases. the global air velocity distribution above the air breeze is slightly more pronounced than that below. this is expected since the space occupied by the air above the air breeze is significantly larger than that below. it should be also noted that the air velocity magnitude in the neighborhood of the air outlet is enhanced. this is expected since the air outlet is connected to the solar chimney inlet where a strong air suction effect is applied. fig. 2. air velocity magnitude distribution in the conditioned room. engineering, technology & applied science research vol. 13, no. 3, 2023, 11036-11041 11039 www.etasr.com alquraish & abuhasel: sustainable hybrid design to ensure efficiency and air quality of solar air … figure 3 depicts the vertical evolution of the air velocity along the height of the conditioned room in the mid-length level defined by x=2m. the inlet air velocity is 1m/s, 0.5m/s, and 0.05m/s. the room air velocity rapidly increases from 0.26m/s, 0.14m/s, and 0.02m/s to reach a maxima in the neighborhood of h=0.7m of 0.91m/s, 0.45m/s, and 0.05m/s for an inlet air velocity in the order of 1m/s, 0.5m/s, and 0.05m/s, respectively. this is expected since the air velocity in this room region (room bottom) is highly influenced by the air breeze carried out between the air inlet and outlet of the conditioned room. between h=0.7m and h=1.45m, the room air velocity rapidly decreases to 0.3m/s, 0.15m/s, and 0.05m/s for an inlet air velocity of 1m/s, 0.5m/s and 0.05m/s respectively. between h=1.45m and h=2.6m, the room air velocity moderately decreases to 0.04m/s, 0.02m/s, and 0.005m/s for an inlet air velocity in the order of 1m/s, 0.5m/s, and 0.05m/s, respectively. this is expected since this room region is relatively far from the influence of the air. between h=2.6m and h=3m, the room air velocity moderately increases to reach 0.12m/s, 0.06m/s, and 0.01m/s for an inlet air velocity of 1m/s, 0.5m/s, and 0.05m/s respectively. this is expected since this room region is close to the inlet of the solar chimney (located in the top region of the room) where the air velocity is more pronounced due to the strong suction effect induced by the solar chimney. it should be noted that the air velocity increase and decrease rates are more pronounced for higher inlet air velocity. fig. 3. air velocity evolution along the height of the conditioned room in the mid-length. b. air temperature in the conditioned room figure 4 depicts the horizontal evolution of the air temperature along the length of the conditioned room in the mid-height level defined by h=1.5m. the inlet air velocity is varied as 0.05m/s, 0.5m/s, and 1m/s. the room air temperature rapidly decreases from 21.8°c, 22.4°c, and 22.45°c to a minimum in the neighborhood of x=0.5m (left side of the room) of 17.2°c, 17.1°c, and 17.1°c, for an inlet air velocity of 0.05m/s, 0.5m/s, and 1m/s, respectively. between x=0.5m and x=1.1m, the room air temperature evolutions rapidly increase to 18.4°c, 18°c and 17.9°c for inlet air velocity of 0.05m/s, 0.5m/s, and 1m/s respectively. this important increase and decrease rates are expected since the convection in this room region (close to the inlet of the solar chimney) is enhanced by the pronounced air velocity caused by the strong suction effect induced by the solar chimney. between x=1.1m and x=3.5m, the room air temperature evolutions stagnate around 18.3°c, 17.9°c, and 17.8°c for an inlet air velocity in the order of 0.05m/s, 0.5m/s, and 1m/s, respectively. between x=3.5m and x=4m, the room air temperature drastically increases to 20.7°c, 21.2°c, and 21.3°c for inlet air velocity of 0.05m/s, 0.5m/s, and 1m/s, respectively. it should be noted that the air velocity increase and decrease rates are more pronounced for higher inlet air velocity. fig. 4. air temperature evolution along the length of the conditioned room at the mid-height. fig. 5. air temperature evolution along the height of the conditioned room in the mid-length. figure 5 depicts the vertical evolution of the air temperature along the height of the conditioned room in the mid-length level defined by x=2m. the inlet air velocity is varied as 0.05m/s, 0.5m/s, and 1m/s. the room air temperature rapidly decreases from 19.47°c, 19.89°c, and 19.93°c to reach a minimum in the neighborhood of h=0.6m (left side of the room) in the order of 17.0°c for all inlet air velocity values. between x=0.6m and x=1.35m, the room air temperature rapidly increases to 18.5°c, 18.1°c, and 17.95°c for inlet air engineering, technology & applied science research vol. 13, no. 3, 2023, 11036-11041 11040 www.etasr.com alquraish & abuhasel: sustainable hybrid design to ensure efficiency and air quality of solar air … velocity of 0.05m/s, 0.5m/s, and 1m/s, respectively. it is to note that the air velocity increase and decrease rates are slightly more pronounced for higher inlet air velocity values. these increase and decrease rates are expected since the convection in this room region (located in the bottom side of the room) is highly influenced by the air breeze carried out between the air inlet and outlet of the conditioned room. between h=1.35m and h=3m, the room air temperature stagnates around 18.35°c, 17.95°c, and 17.85°c for inlet air velocity of 0.05m/s, 0.5m/s, and 1m/s, respectively. c. thermal comfort and indoor air quality the proposed design ensures two tasks:  acceptable thermal comfort in a school environment.  acceptable indoor air quality in a school environment. the comfort zone is within the air temperature range from 18°c to 27°c while the air relative humidity range is from 20% to 80% with a slight air temperature limitation from 28°c to 25°c when the relative humidity passes from 50% to 80%. taking into account the morning air relative humidity in the region of bisha, saudi arabia in may and june (globally around 47% and 29%, respectively), it is easy to locate the (inlet air temperature, inlet air relative humidity) points on the psychrometric chart. figure 6 shows that the inlet air is within the thermal comfort zone for both may and june. fig. 6. inlet air within the comfort zone in may and june. v. discussion and optimization of air conditioning parameters in this paper, the two major air-conditioning parameters, inlet air temperature and inlet air velocity, are optimized with the goal of improving thermal comfort and indoor air quality in the school environment. the air-conditioning optimization should ensure a compromise between appropriate inlet air temperature and inlet air velocity, inducing the highest possible air change rate and the lowest possible air temperature, while remaining within the limits of human thermal comfort. according to the results of numerical simulations, the inlet air temperature rises as the inlet air velocity rises (this is directly related to the air change rate). inlet air temperatures in the order of 20.7°c, 21.2°c, and 21.3°c are associated to inlet air velocities in the order of 0.05m/s, 0.5m/s, and 1m/s, respectively. the inlet air velocity in the range of 0.05m/s is disallowed within the parameters of the optimization under consideration because it causes stagnation, which significantly worsens thermal comfort and raises the risk of virus transmission. thus, an inlet air velocity in the order of 0.5m/s that is associated to the lowest inlet air temperature (21.2°c), shall be selected as a primary choice. however, the inlet air temperature associated to an inlet air velocity of 1m/s is in the order of 21.3°c. so, it is clear that there is no perceptible air temperature difference when the inlet air velocity passes from 0.5m/s to 1m/s. it is appropriate to choose, as the final optimization step, an inlet air velocity in the order of 1m/s associated with an inlet air temperature in the order of 21.3°c because the air change rate should be maximized as much as possible. the general ashrae standards [13] for indoor air quality in the case of a school environment, along with the crucial need to limit the spread of viruses as much as possible, are in agreement with an inlet air velocity in the order of 1m/s (in relation with a maximized air change rate). vi. conclusion the ability to create thermal comfort in the conditioned area and its thermal performance are numerically investigated, presented, and discussed in this paper. it is appropriate to select an inlet air velocity of 1m/s and an inlet air temperature of 21.3°c because the air change rate should be increased as much as possible in the school environment to prevent virus spreading. future research on the hybrid solar ventilation-air conditioning design is conceivable, with the goal of enhancing its ventilation, hygrometric, and thermal performance along with its sustainability in relation to the use of solar energy. also, a desiccant compartment can be integrated and investigated in order to improve the hygrometric and thermal capacities of the considered air-conditioning system. it should be noted that an appropriate coupling between the solar ventilation system and the desiccant compartment can be studied in the future. acknowledgment the authors are thankful to the deanship of scientific research at university of bisha for the financial support. references [1] g. papadopoulos, "ieq assessment in free-running university classrooms," science and technology for the built environment:, vol. 28, no. 7, pp. 823–842, https://doi.org/10.1080/23744731.2022.2052519. 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[9] a. oudrane, b. aour, b. zeghmati, x. chesneau, and h. massaoud, "study and simulation of the density of the incident solar flux on the walls of a building in adrar, algeria," engineering, technology & applied science research, vol. 7, no. 5, pp. 1940–1945, oct. 2017, https://doi.org/10.48084/etasr.1337. [10] j. yau, j. j. wei, h. wang, o. eniola, and f. p. ibitoye, "modeling of the internal temperature for an energy saving chinese solar greenhouse," engineering, technology & applied science research, vol. 10, no. 5, pp. 6276–6281, oct. 2020, https://doi.org/10.48084/ etasr.3728. [11] y. kassem, h. gokcekus, and f. a. r. agila, "techno-economic feasibility assessment for the promotion of grid-connected rooftop pv systems in botswana: a case study," engineering, technology & applied science research, vol. 13, no. 2, pp. 10328–10337, apr. 2023, https://doi.org/10.48084/etasr.5668. 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[13] 2016 ashrae handbook—hvac systems and equipment. ashrae, 2008. engineering, technology & applied science research vol. 11, no. 3, 2021, 7111-7117 7111 www.etasr.com kamil et al.: investigating the quality of milk with spectroscopy and scattering theory investigating the quality of milk using spectrometry technique and scattering theory nur ain insyirah muhamad kamil advanced devices and system (ads) faculty of engineering and built environment universiti sains islam malaysia negeri sembilan, malaysia wan zakiah wan ismail advanced devices and system (ads) faculty of engineering and built environment universiti sains islam malaysia negeri sembilan, malaysia juliza jamaludin advanced devices and system (ads) faculty of engineering and built environment universiti sains islam malaysia negeri sembilan, malaysia zatunnur syakirah nor’aini advanced devices and system (ads) faculty of engineering and built environment universiti sains islam malaysia negeri sembilan, malaysia sharma rao balakrishnan advanced devices and system (ads) faculty of engineering and built environment universiti sains islam malaysia negeri sembilan, malaysia irneza ismail advanced devices and system (ads) faculty of engineering and built environment universiti sains islam malaysia negeri sembilan, malaysia musab sahrim advanced devices and system (ads) faculty of engineering and built environment universiti sains islam malaysia negeri sembilan, malaysia abstract-milk is a dairy product that contains dissolved proteins, carbohydrates, fat, and many minerals. milk enhances body growth and provides vital energy and fatty acids. milk can turn bad after being kept at room temperature for several days. the endurance of milk could depend on its fat and protein composition. our work aims to compare the quality of milk after being kept at room temperature for several days using spectroscopy methods. modeling based on scattering theory is also provided to compare the light propagation in milk, water, and air. a vis-nir spectrometer was used to observe the light absorption, transmission, and reflectance whereas a modeling approach was applied to study the scattering, absorption, and extinction efficiencies. the milk samples consist of full cream milk kept at room temperature for 8 days, 11 days, 14 days, and 17 days. the results show that milk without fermentation has higher light absorbance and lower transmission compared to milk with fermentation, due to changes in milk composition after the fermentation process. milk scatters more light compared to water and air due to its fat globule and protein ingredients. the output of this study can be used as a reference for studies involving bacteria or microorganisms in milk. it also can be used to compare the quality of milk with and without air exposure. keywords-light propagation; absorbance; transmittance; reflectance; scattering; milk; spectroscopy i. introduction it is crucial to monitor the quality of milk in order to ensure we gain sufficient nutrients and minerals and prevent the occurrence of diseases. cow milk consists of water (87%), fat (4%), proteins (3.4%), lactose (4.8%), and minerals (0.8%) [1]. fat composition is not similar in full cream milk and skimmed milk. a layer of cream forms on the milk’s surface if it is exposed for several days. this cream consists of spheres of various sizes floating in milk surrounded by a fat globule membrane. the membrane is responsible for fat protection against enzymes and prevents any globule coalescing into butter grains [1]. the spectroscopy technique can be used to observe the optical properties of milk based on light absorbance, transmission and scattering. mie scattering theory is used to compute the absorption coefficient (μ ), the scattering coefficient (μ ), and the phase function p(θ), where θ is the scattering angle [2]. mie theory is used to calculate the spectral dependence for the extinction cross section of nanoparticle suspensions [3]. the pump source energy passes corresponding author: wan zakiah wan ismail (drwanzakiah@usim.edu.my) engineering, technology & applied science research vol. 11, no. 3, 2021, 7111-7117 7112 www.etasr.com kamil et al.: investigating the quality of milk with spectroscopy and scattering theory through the turbid media depending on optical properties such as the refractive index, scattering, anisotropic factor, and laser light absorption [4]. the optical properties of milk based on backscattering intensity can be used to study fat and protein concentrations [5]. the complex fluid of milk is made up of many components such as water, lipids, lactose and protein [6, 8]. spectroscopy is widely used to measure the optical properties of samples based on light propagation and fluorescence. color spectroscopy is used to obtain information about the atoms and molecules [8-9]. the absorbance spectroscopy is a technique used to measure the amount of absorbed light [10, 11] with the determination of solution concentration based on beer’s law [12]. nir spectrometer and vis-nir spectrometer with different wavelength ranges are used to determine the accuracy of the intensity spectrum in the spectroscopy analysis [13]. many recent studies on light propagation in milk involve backscattering [5], external cavity-quantum cascade laser spectroscopy [6], and laser diffraction and centrifugation [7]. authors in [8] introduced the simplified nir spectroscopy in measuring the end of milk fermentation by transforming sugar to lactic acid. the key characteristic of the fermentation process is the ph end point value, in the range of 4.4-4.5 [8]. this technique is quite complicated and costly. to the best of our knowledge, no comparison has been conducted using milk after several days’ exposure and water. the previous studies also do not provide a modeling approach on light scattering in milk. our previous work [14] compared the optical properties of full cream and skimmed milk using different spectrometer types. we found that full cream milk has higher absorption due to its higher fat content. this research is continued in the current paper, which aims to study the light propagation in various milk samples for different exposure at room temperature durations based on spectroscopy techniques using visible (vis) and near infra-red (nir) spectrometers. the technique is simpler and cheaper than the ones used in previous studies as indicated in the experimental section. the output shows that the newly opened milk sample absorbs more light than the other samples. a modeling approach based on mie theory was also provided to compare light scattering in milk, water, and air. ii. theoretical framework for the computation of mie efficiencies, there are two input parameters which are the complex refractive index m and the parameter size x as shown in (1) and (2) [12]. = ’ + " (1) = = (2) where ’ is the real refractive index, " is the imaginary refractive index, is wave number in the ambient medium, and is the sphere radius. the key parameters of mie theory are the computed amplitudes of the scattered field. the coefficients and are required to obtain the mie efficiency using spherical bessel function n (n=1, 2, …) of higher order and work well in the wider range of size parameters [15]. the efficiency of extinction and scattering can be identified in forward-scattering theorem and in the integration of the power scatters in all directions. the absorption efficiency can be identified with the equation of energy conservation [16]. meanwhile, the backscattering efficiency is applicable to monostatic radar [15]. equations for absorption, scattering and backscattering efficiency are: = ∑ (2 + 1) ( + ) (3) = ∑ (2 + 1)(| | + | | ) (4) = + (5) = |∑ (2 + 1)(−1) ( − )| (6) where x is the parameter size and n is the spherical bessel function order n. the efficiency of radiation pressure can be proven by the two-stream model and correlates with the asymmetry parameter [17]. = + ( ) (7) where is the scattering angle. amplitude functions 1 and 2 indicate the scattering properties or the scattering of an electromagnetic wave from a spherical particle. the scattering function is required for the far field scatterer [16]: ( ) = ∑ ( ) ( + ) (8) ( ) = ∑ ( )( + ) (9) where = 2 −1−1 . −1 − −1 −2 = . − ( + 1) iii. methodolodgy the research is conducted using experimental and theoretical methods. the light absorption and scattering analysis in milk are based on mie scattering theory. the scattering, absorption, extinction, and backscattering efficiencies are analyzed in a homogeneous dielectric sphere and its angular scattering using matlab. the analysis is also repeated for water and air. a. modeling approach the modelling part is used to determine the characteristics of light in a disordered medium using matlab. the light propagation efficiency with the justification of mie coefficient matrix is computed. the angular functions are also computed to produce the mie angular efficiency. figure 1 shows the flowchart of the constructed modeling approach. b. spe pro to dif yo flo 14 of pla engineerin www.etasr fig. 1. experimenta the ocean o ectrometer we opagation in m ensure the acc fferent days o gurt after 14 owchart of the fig the milk sam , and 17 days. milk and wa aced in a cuve ng, technology r.com the flowchar al approach optic flame ere used to ob milk. every ex curacy of the o of exposure w days of air experimental g. 2. the flow mples were ke the samples ater respective ette of 10mm y & applied sci rt of the modeling nir spectrom bserve the cha xperiment was output. five sa were used (th exposure). f method. wchart of the expe ept at room tem were diluted w ely. the prep m and shaken l ience research kamil et g approach. meter and vis aracteristics of s repeated 10 amples of milk he sample tur figure 2 show eriment. mperature for with a ratio of pared samples lightly. the cu h v t al.: investigat s-nir f light times k with rns to ws the 8, 11, f 1:100 were uvette was halo coll spe oce the clou larg fig. 8, 1 abs in l obs sam spe pro then spe the con spe effi fres yog qua and vol. 11, no. 3, 2 ting the quality s placed into ogen lamp (th lected by th ectrum graph w eanview softw experiments. udy but milk s ge milk particl fig. 3. the 4. fermented 1, 14, and 17 day the set-up for sorbance and tr liquid sample serve the refle mples were p ectrum of a sa obe. the probe n it was pla ectrum can be light propagat iv previous wo ncentrations ectroscopy. a iciency to con sh milk and a gurt fermentat ality of milk w d nir spectro 2021, 7111-711 y of milk with s a cuvette ho he light source) he vis-nir was displayed ware. figure 4 milk sample samples after les observed. experimental setd full cream milk s (from right to le r reflectance s ransmission sp es and solids. ctance intensi laced on the ample in the c e transmits the aced on the observed by tes inside the m v. results orks [5, 6] h of milk authors in [7 ntrol the deve authors in [8] tion automatio which is kept scopy. we do 7 spectroscopy an older and was ). the light fro spectrometer d on a compute 4 shows the mi es of 8 and 14 days becam -up for the spectr k samples after d eft) of exposure. spectroscopy is pectroscopy se nir spectrom ity spectrum o stage rtl-t cuvette was o e light from the stage rtl-t using a nir medium. s and discuss have analyzed through ba 7] studied th elopment of th used nir spe on. in this pa at room temp o a simple mo 7113 nd scattering t s illuminated om the cuvette (figure 3). er screen usin ilk samples us 11 days were me transparent ometry technique dilution with wate s different from etup. it can be meter was us of the samples t. the reflec observed by a e halogen ligh t. the reflec spectrometer w sion d fat and pr ackscattering he homogeniz he cream laye ectroscopy to aper, we study perature using odeling to com theory by a e was the ng the sed in e still t with e. er after m the e used ed to . the ctance fiber ht and ctance when rotein and zation er on study y the g vis mpare engineering, technology & applied science research vol. 11, no. 3, 2021, 7111-7117 7114 www.etasr.com kamil et al.: investigating the quality of milk with spectroscopy and scattering theory the light propagation in milk, water and air. the modeling analysis uses mie theory to compute the efficiency of scattering, absorption, extinction, backscattering, asymmetry parameter, and radiation pressure whereas the experimental section shows the output in terms of absorbance, transmission, and reflectance. the output from the theoretical and experimental study are analyzed and discussed thoroughly in this section. a. modeling based on mie scattering theory the measurements of scattering, extinction and absorption efficiency based on mie theory were conducted in matlab. the input parameters were the complex refractive index and the parameter size x [18]. modeling was done for milk, water, and air. figures 5 and 6 summarize the modeling results. (a) (b) (c) fig. 5. mie theory based efficiencies for (a) milk, (b)water, and (c) air. equations (3) to (7) were used in figure 5. figure 6 is plotted based on (8)-(9). the extinction, forward scattering, absorption, and backscattering efficiencies are represented by qext, qsca, qabs and qb respectively. figure 5 shows clearly that milk has better scattering efficiency than water and air. at parameter size 2, the scattering efficiency in milk (figure 5(a)) reaches 0.6, while the scattering efficiency in water (figure 5(b)) and air (figure 5(c)) are 0.7 and 5×10-7 respectively, prooving that the least light scattering occurs in the air, whereas milk and water consist of particles which can scatter the light. we presume that the light scattering and absorption are affected by the size and concentration of the particles, the incident light wavelength, and sample size [19]. milk depicts the highest efficiency of light absorption due to its composition of fat globules and proteins. figure 5 also shows that the forward scattering is more efficient compared to the backscattering for all samples due to the larger particles size of the samples. figure 6 shows the scattering angle of milk, water and air respectively. (a) (b) (c) fig. 6. angular scattering for (a) milk, (b) water, and (c) air. we observe that milk has larger value of angular scattering than water and air. it is clearly shown that milk has higher scattering effect. we attribute that to the milk contents which mostly consist of fat and proteins which can scatter light [20]. b. the sam tem an wa res ref fig sam sam the hig 17 to engineerin www.etasr experimenta the spectra o e samples w mples of fre mperature for nir spectr avelength ran spectively. fig flectance spect (a) (b) (c) g. 7. (a) abso mples for various figure 7(a) mples for diffe e absorbance gher than the m days. the abs high attenuati ng, technology r.com al results of reflectance, were monitore esh full-crea 8, 11, 14, and rometer and nges of 950nm gure 7 depicts tra of the milk orbance, (b) trans days of fermentat shows the ab ferent days of spectra in fre milk that has b sorbance of m ion coefficient y & applied sci , transmission ed with the m milk we 17 days. the a vis-nir m-1650nm an the absorbanc k samples. smission, and (c) tion. bsorbance spe exposure. it is eshly opened been kept at ro milk reaches its t which quick ience research kamil et n, and absorban spectrometer. re kept at experiment ut spectrometer nd 350nm-10 ce, transmissio reflectance of th ectrum of the s clearly show full-cream m oom temperatu s peak at 700nm kly absorbs the h v t al.: investigat nce of . the room tilized with 000nm on and he milk e milk wn that milk is ure for m due e light arou tem agg [21 mil dec fig. open ope mil ligh than dur ferm ferm as t vol. 11, no. 3, 2 ting the quality und 700nm. mperature, they gregate and cr ] (see figure 4 lk is gradual creases due to (a) (b) (c) 8. (a) absor ned milk sample, figure 7(b) ened and ferm lk has lower li ht transmissio n in the rest of ring the coagul mentation pro mented milk e the lactic acid 2021, 7111-711 y of milk with s when milk y undergo phy reate lumpy w 4). hence, the lly decreasing milk coagulati rbance, (b) trans water, and milk s shows the t mented milks. ight transmissi on in fermente f the samples a lation [21, 22] ocess which p experiences de bacteria grow 7 spectroscopy an k samples ar ysical changes which affect th e quality from g as the pro ion [22]. smission, and (c) sample after 17 da transmission s . the newly ion than the fe ed milk after as the particle ]. the protein produces lact ecay and the p w to produce th 7115 nd scattering t re kept at where the par he light absor fresh to ferm otein concentr ) reflectance of ays. spectra of fr opened full-c ermented milk 17 days is h s in milk aggr thickens due t tic acid [23]. ph level decr he acid [24]. theory room rticles rption mented ration newly reshly cream k. the higher regate to the the reases engineering, technology & applied science research vol. 11, no. 3, 2021, 7111-7117 7116 www.etasr.com kamil et al.: investigating the quality of milk with spectroscopy and scattering theory figure 7(c) shows the reflectance spectra of the milk samples. the reflectance of newly opened milk is higher than the fermented milk's. the low reflectance values for fermented milk are recorded due to its high water absorption [25]. hence, we suppose that the presence of fat globules and protein micelles in milk affect the light reflectance. the reflectance intensity decreases over the fermentation process due to the changes of protein and fat globules [26]. figure 8 shows the spectra comparison of milk samples and water. figure 8(a) shows that water absorbs most of the light at 600nm whereas the absorption peak of milk is at 700nm. milk and water depict similar transmission peaks at ~ 650nm (figure 8(b)). water sample shows higher transmission spectrum as it is more transparent than milk. newly opened milk samples have higher reflectance than water due to their fat and protein composition. the size and shape of particles, the composition, and the concentration of the tested samples can affect the absorption, transmission, and reflectance of the samples respectively [26]. newly opened milk samples consist of various particle compositions whereas the fermented milk samples have experienced physical state changes. v. conclusion in conclusion, this research investigates the quality of milk for samples freshly opened and after being kept at room temperature for several days using spectroscopy and scattering theory. the optical properties of milk samples were investigated using vis and nir spectrometers. newly opened milk samples have higher light absorbance and lower light transmission compared to the fermented milk, due to the aggregation of the fat and protein particles in milk during the fermentation process. besides that, modeling based on scattering theory was done to compare the light propagation in milk, water, and air. the modeling shows that milk scatters more light compared to water and air due to the presence of fat globule, protein, and minerals. the outcome of the study shows that the quality of milk is reduced when it is kept at room temperature for several days. this is proved by both naked eye observation and spectroscopy. the outcome of this study can be useful in supporting future analysis studies on dairy products. acknowledgement we acknowledge the support of the ministry of education of malaysia under the frgs grant (frgs/1/2018/stg02/ usim/02/2) and universiti sains islam malaysia (usim) for the funding and support. references [1] g. h. schmidt, l. d. v. vleck, and m. f. hutjens, principles of dairy science, subsequent edition. englewood cliffs, nj, usa: prentice hall, 1988. 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[14] n. a. i. muhamad kamil et al., "investigating light propagation in full and skimmed milk based on spectroscopy and monte carlo analysis," journal of engineering and applied science, vol. 67, no. 8, pp. 2265– 2278, dec. 2020. [15] c. matzler, "matlab functions for mie scattering and absorption," institut für angewandte physik, bern, switzerland, research report 2002–08, jun. 2002. [16] k. l. van der molen, "experiments on scattering lasers: from mie to random," ph.d. dissertation, university of twente, enschede, netherlands, 2007. [17] w. e. meador and w. r. weaver, "two-stream approximations to radiative transfer in planetary atmospheres: a unified description of existing methods and a new improvement," journal of the atmospheric sciences, vol. 37, pp. 630–643, mar. 1980. [18] y. ren, h. qi, x. yu, and l. ruan, "a forward-angle-scattering method for the determination of optical constants and particle size distribution by collimated laser irradiation," optics communications, vol. 389, pp. 258–264, apr. 2017, https://doi.org/10.1016/j.optcom.2016.12.060. [19] d. j. dahm, "explaining some light scattering properties of milk using representative layer theory," journal of near infrared spectroscopy, vol. 21, no. 5, pp. 323–339, oct. 2013. engineering, technology & applied science research vol. 11, no. 3, 2021, 7111-7117 7117 www.etasr.com kamil et al.: investigating the quality of milk with spectroscopy and scattering theory [20] l. c. andrews, field guide to atmospheric optics, second edition, 2nd ed. washington, dc, usa: spie--the international society for optical engineering, 2019. [21] c. hahn, m. sramek, s. nöbel, and j. hinrichs, "post-processing of concentrated fermented milk: influence of temperature and holding time on the formation of particle clusters," dairy science & technology, vol. 92, no. 1, pp. 91–107, jan. 2012, https://doi.org/10.1007/s13594-0110046-1. [22] s. l. thomsen, s. l. jacques, and s. t. flock, “microscopic correlates of macroscopic optical property changes during thermal coagulation of myocardium,” in laser-tissue interaction, jun. 1990, vol. 1202, pp. 2– 11, https://doi.org/10.1117/12.17605. [23] m. lu et al., "milk spoilage: methods and practices of detecting milk quality," food and nutrition sciences, vol. 4, no. 7, pp. 113–123, jul. 2013, https://doi.org/10.4236/fns.2013.47a014. [24] r. fernandes, ed., microbiology handbook: dairy products, 3rd ed. cambridge, uk: royal society of chemistry, 2009. 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[26] j. a. raty and k.-e. peiponen, "reflectance study of milk in the uvvisible range," applied spectroscopy, vol. 53, no. 9, pp. 1123–1127, sep. 1999. microsoft word etasr_v11_n1_pp6708-6713 engineering, technology & applied science research vol. 11, no. 1, 2021, 6708-6713 6708 www.etasr.com benzeguir et al.: reliability of buried pipes in heterogeneous soil subjected to seismic loads reliability of buried pipes in heterogeneous soil subjected to seismic loads hichem benzeguir department of civil engineering university djillali liabes of sidi bel abbes sidi bel abbes, algeria h_benzeguir@yahoo.fr djamel nedjar department of civil engineering university of sciences and technology of oran oran, algeria djamel_nedjar@yahoo.fr sidi mohamed elachachi civil and environmental engineering department university of bordeaux talence, france sm_elachachi@yahoo.fr mohamed bensafi department of civil engineering university of sciences and technology of oran oran, algeria moha_bensafi@yahoo.fr abstractdysfunctions and failures of buried pipe networks, like sewer networks, are studied in this paper from the point of view of structural reliability and heterogeneity of geotechnical conditions in the longitudinal direction. combined soil spatial variability and peak ground acceleration (pga) induce stresses and displacements. a model has been developed within the frame of geostatistics and a mechanical description of the soil–structure interaction of a set of buried pipes with connections resting on the soil by a two-parameter model (pasternak model). structural reliability analysis is performed considering two limit states: serviceability limit state (sls), related to large "counter slope" in a given pipe, and ultimate limit state (uls), corresponding to bending moment. keywords-reliability index; soil-structure interaction; spatial variability; sls; uls; seismic action i. introduction pipes that carry various substances need to be designed in a way capable of reducing the damage caused by ground displacements induced by earthquakes. the geoenvironmental effect has attracted concern on the performance of the buried pipes because of the associated hazards [1]. most buried pipelines in seismic areas have sustained substantial damage in the past due to earthquake events [2]. dysfunctions and failures of buried pipe networks, like sewer networks, are mainly caused by the heterogeneity of geotechnical conditions in the longitudinal direction and of the applied (seismic) action. combined soil defects (differential settlements along the pipe, landslides, voids surrounding the pipe, etc.) and peak ground acceleration (pga) induce stresses (which lead to an ultimate limit state-uls) and displacements (which constitute a violation of the serviceability limit state-sls). it is worth noting that the influence of the variability of the soil is not reflected in current european standards [3]. authors in [4] presented a comprehensive literature review on the seismic behavior of buried pipelines and underground structures summarizing the recent research. structural response to ground motion during earthquake cannot be accurately predicted because of the complexity of the structural properties and ground motion parameters [5]. in this paper, the response of buried pipe is investigated considering the seismic excitation by selecting real earthquake data. ii. soil pipe system modeling a. pasternak model among the models that describe the behavior of a beam resting on a soil and their interaction, the pasternak model [6] attracts the most interest. in the soil-pipe interaction, the soil opposes on the components of a sewer network (pipes) a distributed force r(x) (in n/m) given by (1): ���� = ����.� � (1) where p(x) is the stress under the pipe (pa), and dext the external diameter of the pipe (m). according to the pasternak model the stress is expressed as: ���� = � .���� − �� � � � � (2) where kw is the coefficient of subgrade reaction (or winkler coefficient in n/m 3 or pa/m), ks is the shear coefficient (n/m) and w(x) the vertical pipe displacement (and thus the settlement of the soil). pasternak’s idealization considers the soil as being a system of identical but mutually independent, closely spaced, discrete, linearly elastic springs related by an incompressible "shear layer" which is defined as a layer of linear-elastic material of unit thickness that resists vertical shear forces only [6]. thus it is a refinement of the well known winkler model which suffers from not describing shear influence. the use of a two parameter model to characterize the soil's response under loading can appear a too simplified concept. however, such a corresponding author: hichem benzeguir engineering, technology & applied science research vol. 11, no. 1, 2021, 6708-6713 6709 www.etasr.com benzeguir et al.: reliability of buried pipes in heterogeneous soil subjected to seismic loads simplification seems coherent if one takes into account the variability and uncertainties related to the characterization of the soil. the spatial correlations which will be introduced further will ensure, in fact, a coherence of displacements, like it exists in a continuous medium. one should note that the two coefficients kw and ks are not soil-specific parameters. they are also affected by the rigidity of the pipe. in fact, these stiffness parameters depend on several factors, such as the length and/or the width (or diameter) of the pipe, the laying depth, the type of material used, and the type of the pipe bed. the value of these coefficients can only be approached by semi-empirical methods. for a same set of values, a parametric study, conducted in [7], illustrated the fact that kw varies from 1 to 3. to the best of our knowledge the literature has not given ways on how to identify ks in practice from physical and geometrical data [8]. in order to integer the damping of the system, the pasternak model is adapted and expanded to a kelvin-voigt model by adding dashpots. the stiffness matrix of the soil–pipe system has been derived in [9] by using the energy method. we will consider two relative soil-pipe stiffness ratios, rp and rks which are defined by (3) and (4) and can be considered as governing parameters: �� = �� � ��� �� 5 (3) ��� = ����� !"� (4) where ep, i, dext, and l and are respectively the pipe's young modulus, the pipe's moment of inertia, the exterior diameter, and the length of the pipe. b. joint-connection stifness sealing between pipes is ensured by joints made of cement mortar or more frequently of elastomer. the rigidity of these joints is as variable as the technologies and geometries employed: it can be very weak (flexible joints) or very high (welded joints). it is difficult to identify realistic numerical values of the joint stiffness even if some laboratory experiments have focused on this question [10]. in this work, we assume a continuity of vertical displacements at joint connection and contrary to a model of continuous beam, a model was developed which enables introducing discontinuities of rotation between the ends of the pipes. the joints between two adjacent pipes are assimilated to rotation springs with stiffness rj relating to the proportionality between the bending moment m applied to the joint and the variation of the angle of rotation ∆ϕ: # = �$.∆& (5) to take into account this joint stiffness, the pipe-joint stiffness ratio rjoint is introduced which is defined by: �$'()� = *+�,-. (6) to summarize, the soil-pipe interaction system, one can say that it is governed by a geometric parameter l (pipe's length) and three relative (dimensionless) stiffness ratio parameters: rks (compression to shear), rp (soil to pipe), and rjoint (connection to pipe). iii. modeling the spatial variability of soil and its effects:the correlation length in many common geotechnical problems, the variability of soil is only one among many sources of uncertainty (others are for example reduced sampling measurement or model errors). it can be accounted for by taking conservative values of the soil parameters, even if geotechnicians need long practice to be able to justify the choice of these values [11]. in fact, the variability of soils cannot be reduced to case-by-case variability – as a result of its natural or man-made fabric (deposit processes, compaction processes). the soil properties can be considered as spatially structured. thus, tools like autocorrelation functions or semi-variograms appear to be appropriate for modeling. one must then identify the standard deviation or coefficient of variation of the studied property as well as the correlation length lc (i.e. the distance above which the local properties at two points can be assumed to be independent). the first consequence of the spatial correlation is that the representative value of any soil property depends on the volume concerned by the problem to be solved. this question has been analyzed in detail during the drafting of eurocode-7 but the code writers have limited themselves to general considerations, without prescribing any formal method: the representative value is only said to be a characteristic value defined as a cautious estimate of the parameter governing the studied limit state [12]. nevertheless, accounting for spatial correlation has direct consequences on the safety of designs. a simple illustration of the effects of spatial variability is that of the rotation (tilting) of a foundation of length l resting on a heterogeneous elastic soil and supporting a uniform loading. it was shown [13] that the magnitude of the rotation depends on the correlation length in the horizontal direction: it tends towards zero when lc is very small (which corresponds to very quickly varying properties, thus homogeneous at l scale) or very large (which corresponds to very slowly varying properties, thus also homogeneous at l scale) and it is maximum for an intermediate range. this illustrates a consequence of the spatially correlated variation of soil properties: tilting occurs only when the soil is not homogeneous and its magnitude depends both on the scatter in the soil properties (linearly) and on the correlation length, with a "worst case" for a particular range of lc values. since the role of the longitudinal variability of the filling appears essential, we chose to model it by using the theory of the local average of a random field developed in [14]. the random field of the coefficients kw or ks is defined by three properties: its average value w k (resp. s k ), its variance 2 w k (resp. 2 s k ) and its scale (or length) of correlation lc (resp. lcs). these scales are related to a function of correlation ρ(τ) in (7) where τ points out the distance between two points, and which describes the spatial structure of correlation of the properties: ρ(τ) differs whether the properties vary more or less quickly while deviating from a given point. this correlation length (length from which the correlation between soil properties tend to disappear) depends on the characteristic (modulus, porosity, water content, etc.) and on the direction (horizontal or vertical). engineering, technology & applied science research vol. 11, no. 1, 2021, 6708-6713 6710 www.etasr.com benzeguir et al.: reliability of buried pipes in heterogeneous soil subjected to seismic loads /�0� = exp �−2 |6|78 ) for 0 9 :; (7) the soil is subdivided in several zones. the random field value in each zone is thus a random variable whose value is estimated by the average of the space field over the zone. the local average and the variance in zone i of length di fulfil (8): �<� ��(�= = � >>>> (8a) var<� ��(�= = � bbbbcd��(� (8b) equation (8b) shows that the local variance var [kw(di)] depends on the length di of zone i while following a variance reduction function γ(di). d��(� = 2e78�fg c e�f78 − 1 i exp �− �f 78�g (9) γ(di) is a measure of the variance reduction due to the averaging of the random process according to the length of the studied zone. in this work, kw and ks follow a lognormal distribution. in order to show the effect of both the mean values of the winkler and shear coefficients and their correlation length, six cases were considered (table i) and applied to an example of a sewer section (set defined between two manholes) and which will be presented in further detail. the section is made of 20 pipes of unit length l=3m. for each computation, the outputs which are linked to limit states are processed all along the section and their worst value is kept. finally the cumulative density function (cdf) of these parameters (stress, displacement, bending moment) is drawn and used for comparison. figure 1 shows the cdf of the maximum bending stress in a concrete sewer's section. table i. values of kw, ks, lc and lcs parameters kw (kn/m 3 ) lc (m) ks (kn/m) lcs (m) case a 10 3 1 30 case b 10 30 1 3 case c 10 3 1 3 case d 10 3 10 3 case e 10 30 10 3 case f 10 3 10 30 fig. 1. cdf bending stress for the 6 different cases presented in table i. two observations can be made: • not taking into account the shear effect is not conservative (case c compared to case f) being given that the mean stress varies more than 20%, • the correlation length of the winkler coefficient seems to have more importance than the correlation length of the shear coefficient (case b compared to a and c cases or case e compared to d and f cases). iv. equations of motion the soil resistance to the pipe motion is generated by the relative motion u between the pipe and the soil. the pipe resistance comes from the absolute displacement u (figure 2). the governing equation of the system is [15]: j#� i #�'7klmno i jp� i p�'7klmqo i rs� i s i s�tumv = <#�'7=uwxn v i <p�'7wxq = i rs� i s�tuwv (10) in which mp and msoil are respectively the mass matrix of the pipe and of the soil, kp, kw and ks the stiffness matrices of the pipe and the soil, and cp and csoil the damping matrices of the pipe and of the soil respectively. we note that the damping matrices are constructed from the rayleigh damping. , , u, u u& && are respectively the vectors of absolute displacement, velocity and acceleration, u, , , and u u u& && are the vectors of relative displacement, velocity and acceleration, and , , and s s s u u u& && us are the vectors of ground displacement, velocity, and acceleration of the soil. denoting the total stiffness as [k] = [kp] + [kw]+ [ks], the total mass as [m] = [mp]+[msoil], the total damping as [c] = [cp] + [csoil], and the absolute displacement as {u} = {us} + {u}, the equations of motion in terms of the relative displacement can be rewritten as: <#=uwn v i <p=uwqv i yszuwv = −j#�kuwxn v − jp�wxq k − rs�tuwxv (11) these equations of motion are solved for each time history of the ensemble of real earthquake records. the boundary conditions can be considered either as fixed ends or as free ends if we want to eliminate their effects. fig. 2. pipe and ground motion. v. performance functions and limit states two performance functions are defined. one relates to the counterslope and corresponds to the sls, by relating the sewer's hydraulic performance to the local counterslope. the presence of too high counterslopes harms the flow of the effluents and facilitates the clogging of the pipes by the sedimentation of the suspended particles. the corresponding limit state function is: [\x = p]*−p]x (12) engineering, technology & applied science research vol. 11, no. 1, 2021, 6708-6713 6711 www.etasr.com benzeguir et al.: reliability of buried pipes in heterogeneous soil subjected to seismic loads where csr is the maximum acceptable counterslope and css is the maximum simulated counterslope. the other performance function relates to the stresses and defines the equivalent of an uls, by relating the cracking state (for a concrete pipe) to the bending stresses: [^ = _*−_x (13) where _* is the yield tension stress of the concrete and _x is the maximum bending stress. we assume that css and _x also follow lognormal distributions, whose means and standard deviations are obtained from coupling monte-carlo simulations and finite element method, and that csr as _* also follow lognormal distributions of means and standard deviations of 4%± 0.8%, and 2± 0.3mpa respectively. it should be noted that there is not any regulation limiting the counterslope, that's why we have chosen a 4% arbitrary limit based on the design considerations: trespassing such a value leads to damages or dismantling of the joints and to defects of sealing. the ± 0.8% can be seen as a model uncertainty on this sls criterion. the target values of the reliability index to be reached are 3.8 for the uls and 1.5 for the sls with a service life of 50 years. in the following, we will consider two reliability indexes βuls and βsls. vi. case study a. caracteristics of the sewer’s section lets consider a reinforced concrete material for the pipe (ep = 25000mpa) with an exterior diameter dext = 1m, a thickness of 0.08m, made of a set of 20 pipes with l = 3m unit length. it rests on a soil whose winkler coefficient is 10kn/m 3 and shear coefficient is 10kn/m. this type of configuration corresponds to a pipe-soil ratio rp = 0.678. it must be noted that the pipe geometry intervenes in the expression of inertia i and in that of the winkler coefficients. the pipes are subjected to a deterministic uniform loading of 50kn/m and to the earthquake of el-asnam (algeria, 1980). the ratio between the length of correlation lc and the pipe length l is defined as λ. in the following sections are analyzed: • the effect of the length of correlation on the response of the system, • the effect of the relative soil-pipe stiffness, for an unfavorable length of correlation (λ # 1), • and the effect of the relative joint-pipe stiffness. the values of the obtained reliability β indexes (uls or sls) must be considered rather comparatively that in an absolute way because of: • the arbitrary character of the values retained for csr as _*, • the type of the probabilistic distribution, • model uncertainties on soil characteristics (kw, ks). b. effect of correlation length the analysis is carried out for lengths of correlation ranging from 0.03m to 1500m, (10 -3 < λ < 5×10 2 ). two types of joints are considered: rigid (rjoint=10 +5 ) and flexible (rjoint=10 -5 ). figures 3 and 4 show the uls and sls reliability indexes. it can be seen that there is a critical length of correlation and thus a critical value of λ which causes the most unfavorable effects in the structure. the evolution of reliability is not monotonous. the existence of such a limit value is one of the invariants of the problems of (heterogeneous) soil-structure interaction [13]. reliability indexes grow when λ tends to zero or infinity. in these two situations, the soil tends to be homogeneous at the scale of the analysis, either because its variations are very fast are filtered by the pipe, or because its variations are very slow, inducing almost uniform values between close elements. we had seen that the rigid joints, and for a high coefficient of variation of kw, do not satisfy the uls for λ between 0.01 and 7, while the flexible joints provide much better results. on the other hand, if we consider the sls, the flexible joints provide results a little worse than the rigid joints. one thus notes at this level a conflict in the choice of the "good pipe length" to answer the uls and the sls. fig. 3. effect of the correlation length on the ultimate state reliability index for two values of the variation of coefficient kw and two of joints. fig. 4. effect of the correlation length on the service limit state reliability index for two values of the variation of coefficient kw and two of joints. c. effect of the joint-pipe stiffness ratio the effect of joints on the behavior of the system was analyzed by varying the joint-pipe ratio rjoint from 10 -5 to 10 +5 . figures 5 and 6 show the evolution of the reliability indexes for different coefficients of variation of winkler coefficient. the strong influence of the joints' stiffness should be underlined since the rigid joints are penalizing with the uls, by the fact that they necessarily induce more significant stresses. on the other hand, the flexible joints are penalizing with the sls. an intermediate joint stiffness must be chosen in order to carry out engineering, technology & applied science research vol. 11, no. 1, 2021, 6708-6713 6712 www.etasr.com benzeguir et al.: reliability of buried pipes in heterogeneous soil subjected to seismic loads the best compromise, since reliability is completely assured for both uls and sls. finally, one can also note that for a given value of rjoint, the uls index reliability and the sls index reliability decrease with the increase of kw coefficients of variation. fig. 5. effect of joint-pipe stiffness ratio on ultimate limit state reliability index for four values of the variation of coefficient kw. fig. 6. effect of joint-pipe stiffness ratio on the service limit state reliability index for four values of the variation of coefficient kw. d. effect of the soil-pipe stiffness ratio by maintaining the same set of pipes and soil parameters (λ = 1, rks = 1), we vary the soil-pipe stiffness ratio rp in the range between 0.4 and 1.7 which corresponds to a winkler coefficient in the range from 100kpa to 100mpa for four values of the coefficients of variation (cvkw = 0.1, 0.2, 0.4, and 0.8). while taking a length of correlation lc close to the length of the pipe (λ # 1), we refer to the situation in the vicinity of the most unfavorable geotechnical conditions. figures 7 and 8 present the values of the reliability indexes. whatever the type of joint, reliability is lower for high soil-pipe stiffness ratio, situation corresponding to sections of very stiff pipes or low soil stiffness. in the presence of rigid joints (figure 7) and high coefficient of variation of the soil's parameter, the eurocode βuls is not respected (lower than 3.8). we can see that increasing the coefficient of variation induces reduction of the reliability of the pipe section. so, it is better to have flexible rather than rigid joints, it is better to privilege a lower rp to ensure the "good" reliability of the network. fig. 7. effect of soil-pipe stiffness ratio on the service ultimate state reliability index for four values of the variation of coefficient kw. in terms of counterslopes (figure 8), it is better to have rigid than flexible joints. to ensure the reliability of the sewer's section using rigid joints imposes that the ground is rather homogeneous. it can be also noted that it is more profitable to be in the presence of a relatively homogeneous soil whose mechanical characteristics are poor that in the presence of a better ground but whose heterogeneity is more pronounced. fig. 8. effect of soil-pipe stiffness ratio on the service limit state reliability index for four values of the variation of coefficient kw. vii. conclusion a model which includes a description of the soil's spatial variability, within the frame of geostatistics has been developed in this paper. it is based on a mechanical description of the soil–structure interaction between a set of segmented buried pipes and the soil support represented by the pasternak model. the need to take into account the soil spatial variability is clearly recognized. several conclusions are drawn: soil heterogeneity induces effects (differential settlements, bending moments, stresses, and possible cracking) that cannot be predicted if homogeneity is assumed. these effects can significantly affect the sls or uls reliabilities. in addition to the effects of the soil stiffness, the magnitude of the induced stresses depends mainly on four factors or governing parameters: engineering, technology & applied science research vol. 11, no. 1, 2021, 6708-6713 6713 www.etasr.com benzeguir et al.: reliability of buried pipes in heterogeneous soil subjected to seismic loads • the magnitude of the soil variability (i.e. its coefficient of variation). • the soil-structure length ratio, which combines the soil fluctuation scale and a structural characteristic length (buried pipe length). a worst value, corresponding to the value leading (from a statistical point of view) to the (statistically) largest effects in the structure, can be found. • the soil-structure stiffness ratio. • the structure-connection (pipe-joint) stiffness ratio (relative flexibility). the principal benefit of such an approach is that it provides some new approaches for better considering phenomena such as the geometrical irregularities in the longitudinal profile during the control of soil compaction of sewer trench filling. this kind of approach can also give the experts new tools for better calibration of safety in soil-structure interaction problems, when the soil variability is an influential parameter. references [1] l. r. khan and k. f. tee, "quantification and comparison of carbon emissions for flexible underground pipelines," canadian journal of civil engineering, vol. 42, no. 10, jul. 2015, https://doi.org/10.1139/ cjce-2015-0156. [2] m. j. o’rourke and x. jiu, seismic design of buried and offshore pipelines. buffalo, ny, usa: mceer, university at buffalo, state university of new york, 2012. [3] eurocode 7, geotechnical design, part 1: general rules. brussels, belgium: cen, 1997. [4] g. manolis and d. e. beskos, "underground and lifeline structures," in computer analysis and design of earthquake resistant structures: a handbook, vol. 3, d. e. beskos and s. a. anagnostopoulos, eds. southampton, uk: computational mechanics publications, 1997, pp. 775–837. [5] r. a. hakim, m. s. a. alama, and s. a. ashour, "seismic assessment of an rc building using pushover analysis," engineering, technology & applied science research, vol. 4, no. 3, pp. 631–635, jun. 2014, https://doi.org/10.48084/etasr.428. [6] p. l. pasternak, "on a new method of analysis of an elastic foundation by means of two foundation constants," in gosudarstvennoe izdatelstro liberaturi po stroitelstvui arkhitekture, moscow, russia, 1954. [7] s. m. elachachi, m. bensafi, m. hamane, d. nedjar, and d. breysse, “comportement longitudinal en flexion d’une conduite enterrée dans un remblai hétérogène,” revue française de géotechnique, no. 108, pp. 17–29, 2004, https://doi.org/10.1051/geotech/2004108017. [8] k. morfidis and i. e. avramidis, "formulation of a generalized beam element on a two-parameter elastic foundation with semi-rigid connections and rigid offsets," computers & structures, vol. 80, no. 25, pp. 1919–1934, sep. 2002, https://doi.org/10.1016/s0045-7949(02) 00226-2. [9] s. m. elachachi, d. breysse, and l. houy, "longitudinal variability of soils and structural response of sewer networks," computers and geotechnics, vol. 31, no. 8, pp. 625–641, dec. 2004, https://doi.org/ 10.1016/j.compgeo.2004.10.003. [10] j. buco, f. emeriault, p. le gauffre, and r. kastner, "statistical and 3d numerical identification of pipe and bedding characteristics responsible for longitudinal behavior of buried pipe," in pipeline division specialty conference 2006, chicago, il, usa, aug. 2006, https://doi.org/10.1061/40854(211)83. [11] j. m. duncan, "factors of safety and reliability in geotechnical engineering," journal of geotechnical and geoenvironmental engineering, vol. 126, no. 4, pp. 307–316, apr. 2000, https://doi.org/ 10.1061/(asce)1090-0241(2000)126:4(307). [12] j. b. kovarik, "a propos des valeurs caractéristiques des propriétés des sols," in journées enpc de présentation des eurocodes, 1996. [13] d. breysse, h. niandou, s. elachachi, and l. houy, "a generic approach to soil–structure interaction considering the effects of soil heterogeneity," géotechnique, vol. 55, no. 2, pp. 143–150, mar. 2005, https://doi.org/10.1680/geot.2005.55.2.143. [14] e. vanmarcke, random fields: analysis and synthesis. singapore, hackensack, nj, usa: wspc, 2010. [15] d. nedjar, m. hamane, m. bensafi, s. m. elachachi, and d. breysse, "seismic response analysis of pipes by a probabilistic approach," soil dynamics and earthquake engineering, vol. 27, no. 2, pp. 111–115, feb. 2007, https://doi.org/10.1016/j.soildyn.2006.06.001. microsoft word etasr_v13_n4_pp11139-11145 engineering, technology & applied science research vol. 13, no. 4, 2023, 11139-11145 11139 www.etasr.com nanavati & shah: implementation and comparative study of pyramid-based image fusion techniques … implementation and comparative study of pyramid-based image fusion techniques for lumbar spine images manan m. nanavati gujarat technological university, india | biomedical engineering department, government engineering college, india manan.2507@gmail.com (corresponding author) mehul k. shah instrumentation and control department, vishwakarma government engineering college, india mkshah2000@yahoo.com received: 14 april 2023 | revised: 2 may 2023 | accepted: 10 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5960 abstract image fusion is a method of combining the necessary and relevant information from the set of source images into a single (fused) image which can be deemed to be more informative than the source. this paper discusses the implementation of various pyramid-based image fusion algorithms, such as the laplacian pyramid, the ratio of the low-pass pyramid, the contrast pyramid, and the filter subtract decimate pyramid on multimodal ct and mr images of the lumbar spine. the fused images were evaluated using various objective evaluation quality metrics. the experimental results demonstrated that the ratio of the low pass pyramid achieved better performance compared to the other pyramids implemented, indicating that the fused image can also be used for further image fusion application or analysis purposes. keywords-lumbar spine; medical image fusion; objective evaluation criteria; pyramid transform i. introduction research in medical image processing is rapidly evolving and notable studies have been conducted in the last two decades. the main steps in medical image processing involve the acquisition of the biomedical signal, the formation of the image from the acquired biomedical signal, the processing of the image, and the display of the image for diagnosis. the devices for acquiring medical images consist of hardware and software elements. there are various sensors, such as radiography, magnetic resonance imaging (mri), computed tomography (ct), ultrasound (us), thermography, and nuclear medicine, that are widely used by clinicians and have attracted the interest of the researchers working in the area of medical imaging [1]. x-ray and ct are suitable and widely used for stationary images or images of hard tissues. mri images are suitable for the examination of soft tissues, whereas single photon emission ct (spect) and positron emission tomography (pet) are nuclear imaging methods that provide details about organ metabolism [2]. ct and mri are widely used for diagnostic or screening purposes, ct scans use an array of x-ray sensors to provide information about bony structures or hard tissues, and mri uses a magnetic field to provide information on soft tissues, organs, and blood vessels. none of these imaging modalities can provide all the required details in one image. hence, the fusion of data acquired from multiple sensors is necessary to get all the necessary information in one representative image. medical image fusion combines data from different imaging sensors and merges the complementary information into a single representative image that can be used for better diagnosis and treatment. the main goal of medical image fusion is to conserve the necessary structures and information for improving clinical diagnosis and treatment planning. image fusion methods are broadly classified into three different types: pixel-level, feature-level, and decision-level [3]. pixel-level fusion directly uses the values of pixel information from the source images to perform image fusion. the pixel-level method is more robust, fast, and easy to implement compared to the other two methods, as it can be implemented in both the spectral domain as well as in the transform domain, where the value and attributes of a given pixel are directly processed to attain the desired fusion result [4]. methods like simple average, maximum or minimum selection, principal component analysis (pca) [4], intensity hue saturation (ihs) [5], and brovey transform [6] fall under the category of spatial domain techniques. the majority of the spatial domain techniques suffer from the drawback that they create spatial distortions in the output fused image which eventually leads to reduced spectral details. in most cases, this drawback is addressed by transform domain methods [7]. engineering, technology & applied science research vol. 13, no. 4, 2023, 11139-11145 11140 www.etasr.com nanavati & shah: implementation and comparative study of pyramid-based image fusion techniques … feature-level fusion involves the fusion of features of the image, such as the intensity of pixels, edges, and textures, that are obtained by segmenting the source image as per the desired feature that needs to be fused. decision-level fusion is a highlevel fusion method that uses statistics, prediction, fuzzy logic heuristics, etc. the pixel level method is preferred in the majority of image fusion applications, as it can preserve the pixel values, is time efficient, and its implementation is easier compared to the other two methods. several different image fusion methods have been proposed [8-10]. in [11], an image fusion method based on discrete wavelet transform (dwt) was proposed for medical images. in [12], a novel algorithm based on the quaternion discrete fourier transform (dft) for the multi-modal color image fusion of pet and ct images using the weighted fusion rule was proposed. in this method, the source image was first converted into a block and then into its quaternion form, and the fusion coefficients were computed using transform blocks by comparing the contrast value of subsequent coefficients. in [13], multi-resolution image fusion of mr and ct images based on dwt and ripplet transform was proposed. in [14], image fusion of mr and pet images was performed using hilbert transform (ht) with fourier transform (ft) and his, but no evaluation method or criteria were mentioned for the output fused images. in [15], image fusion on pet and ct images was performed using eight different types of discrete wavelets, such as haar, daubechies (db), symlets (sym), coiets (coif), discrete approximation of meyer wavelet (dmey), biorthogonal (bior), reverse biorthogonal (bior), and fejer-korovkin filters (fk). in [16], an image fusion method on pet and mri images was proposed using dwt without loss of anatomical information on mri images and minimum color distortion on pet images, pre-processing them with gaussian filters. in [17], image fusion of ct and mri images using a guided filter was proposed. in [18], another transform domain method for fusion was proposed, based on hadamard transform and hvs. the computational complexity and blurring of the output fused images were overcome by stationary wavelet transform (swt) [19]. the source image was decomposed into hf and lf coefficients using swt, and the maximum select rule was used for fusing hf and lf coefficients. the averaging method is one of the simplest methods for image fusion, which uses the average of pixels from two or more source images. the main drawback of this method is that it is unable to produce clear objects or structures in the fused image. the simple maximum method selects the respective maximum value of the pixel from the input images. its advantage is that it produces a high-focused image, but at the same time, the fused image suffers from a blurring effect that disturbs the local contrast. the ft method integrates the information concerning time, which results in a loss of information that varies with time in the fused image. the limitation of the quaternion ft approach is that it applies to color images such as pet and spect. in the case of image fusion using the guided filter, the pixel method performs better near edges rather than the whole image [20]. ht is very complex to understand and interpret when the source image has a very wide band frequency range, which is decomposed into its respective hf and lf coefficients. the ripplet transform has more computational requirements than other basic transform domain methods. the main drawback of the gaussian filter is that it loses the edge information, as it is mainly used in image smoothening. the dct method produces real value coefficients, even in the case of input information being an integer, hence, a step of quantization to convert the real value number into an integer is required. the degradation of spectral data is the major drawback of the pca method. similarly to the quaternion approach, ihs is mainly applied to color images. there are also various advanced methods based on convolution neural networks for image fusion, but the only limitation is that they work only when the ground truth is available. various multiscale transform methods, such as the laplacian pyramid, the ratio of low-pass pyramid, gradient pyramid, contrast pyramid, and dwt, have been proposed for image fusion. the conventional wavelet transform (wt) considers the local features of two images and the maximum absolute value of wavelet coefficients. wavelets are found to be effective in representing objects with isolated point singularities but fail to represent objects with line singularities. therefore, the methods based on wt or dwt are not able to preserve the edge quality and information from the source image to the output fused image. considering all these constraints, this study implemented various pyramid transform methods, as they have the advantage of preserving global and local information in the spatial domain. ii. image fusion using pyramid transform an image pyramid [21] usually contains the band pass or low copies of an image and can also be described as the representation of source images by dividing them progressively into smaller and low-resolution sub-images. at every fusion level of the pyramid, the corresponding pyramid has half the size of the previous level pyramid. the basic concept of image fusion using pyramid transform is to obtain the pyramid transform of the fused image from the source image and eventually perform inverse pyramid transform. the pyramid transformation consists of the following major steps:  decomposition  initial image formation  recomposition decomposition is the process of generating the pyramid at each consecutive level of fusion. in general, the level of decomposition is predecided before performing the fusion and depends on various factors and the desired results. the decomposition process is performed l times, where l is the number of levels, and consists of the following steps:  low pass filtering: various pyramid methods have their pre-defined filter to be used on the source or input images.  forming the pyramid from the filtered or convolved images using burt's or li's method.  decimate the input images to their half size and consider them as input for the next level of decomposition. engineering, technology & applied science research vol. 13, no. 4, 2023, 11139-11145 11141 www.etasr.com nanavati & shah: implementation and comparative study of pyramid-based image fusion techniques … initial image formation is performed by merging the input images after the process of decomposition. the resultant matrix of the image is considered as the input data of the recomposition process. recomposition is a process in which the resultant image is formed from the pyramids at each level of decomposition. the recomposition process is performed l times, where l is the number of levels, and consists of the following steps:  the input image is undecimated to the level of recomposition.  the undecimated matrix of the image is further filtered or convolved with the transposition of the filter vector used in the decomposition.  the filtered matrix is then further merged by the respective image fusion rules.  the newly formed image matrix will be considered as the input to the next level of recomposition.  the merged image at the final level of recomposition will be the final resultant fused image. different pyramids have different approaches to the decomposition and recomposition processes. the pyramids implemented in this study are described below. it would be better to understand the gaussian pyramid method before implementing any other pyramid method. the gaussian pyramid consists of low-pass filtered and downsampled images of the preceding level of the pyramid, where the base or first level is the source image, and creates a set of images by weighing down using the gaussian average and further scaling down. implementing it multiple times creates a stack of successive smaller images, where each pixel contains the local level information that corresponds to the neighborhood information on the lower level of the pyramid. a. filter substract decimate (fsd) pyramid the fsd pyramid is a computationally more efficient version of the gaussian pyramid. as per the name of the pyramid, the image fusion using the fsd pyramid consists basically of the following steps: 1. selection source image pair for fusion. 2. selecting low-pass filtering using the filter mask � = [ ��� , ��� , ��� , ��� , ���]. 3. selecting the level of fusion, i.e. decomposition level or recomposition level l. 4. the source images are filtered horizontally and vertically with the filter mask w. 5. the difference matrix is computed by subtracting the low-pass filtered images. 6. a pyramid is formed for the corresponding decomposition level using the select maximum or burt's method or li's method. 7. the formed pyramid is retained for the corresponding level l. 8. the images are decimated into half the size and steps 4 to 6 are repeated l times. 9. the final decimated pair named x image is processed using any of the following mathematical functions: a) average b) selection of maximum c) selection of minimum 10. the matrix x obtained in the above step is undecimated with alternative zero padding of rows and columns. 11. the undecimated matrix is filtered or convolved with the doubly scaled filter mask w. 12. the filtered matrix is added to the retained level of the pyramid. 13. the matrix generated in step 12 acts as an input matrix x for the next level of recomposition. 14. the recomposition steps, i.e. steps 10-13, are repeated l times, which undecimates the matrices of each level and leads to the final fused image with the same size as the input source image. the decomposition process takes steps 4-6, and the recomposition process takes steps 10-13. b. laplacian pyramid the laplacian pyramid of a particular image is a set of bandpass images where each is a bandpass copy of its predecessor. the bandpass copy of the particular image can be computed by taking the difference between two low-pass images at successive levels of the gaussian pyramid. the laplacian pyramid is identical to the fsd pyramid, but in the decomposition phase, the additional filtering is performed with a 2×w filter mask. c. ratio of low pass pyramid in the ratio of low-pass pyramid, every level of the image is the ratio of two successive levels of the gaussian pyramid. it is also identical to the fsd pyramid, where in the decomposition step the pixel-wise ratio is taken rather than the subtraction as in the fsd pyramid method. d. gradient pyramid the gradient pyramid is almost similar to the fsd pyramid with only the change of the filter mask and the additional directional filter implemented in the decomposition step. the filter mask uses � = [ ��� , ��� , ��� , ��� , ���] and = [�� , � , ��]. the directional filter masks implemented are the horizontal filter mask (h), the vertical filter mask (v), and the diagonal filter masks (d1 and d2), respectively. the rest steps are similar to the fsd pyramid. � = �0 0 01 −2 10 0 0� engineering, technology & applied science research vol. 13, no. 4, 2023, 11139-11145 11142 www.etasr.com nanavati & shah: implementation and comparative study of pyramid-based image fusion techniques … = �0 1 00 −2 00 1 0� �1 = � 0 0 0.50 −1 00.5 0 0 � �2 = �0.5 0 00 −1 00 0 0.5� e. contrast pyramid the contrast pyramid is similar to the ratio of low-pass pyramid but takes the ratio of the difference between luminescence and local background luminescence. luminescence is a measure of brightness and the amount of visible light leaving a particular surface area. iii. methodology and experimental setup a. methodology as discussed above, the main goal of image fusion is to combine two or more images and their information to produce a resultant single image that contains information from all the source images. image fusion basically involves three major steps: image registration, image pre-processing, and applying an image fusion algorithm. image registration is a process that involves overlaying or aligning two or more images that are recorded from different angles, different points, different distances, or different time instances by considering one image as a reference or fixed image [22]. the main purpose of registering an image before image fusion is to geometrically align two images generated from different sensors. as the image is generated through different sensors of the same body part and from different viewpoints, the image fusion process is not possible unless the two images are geometrically aligned with each other. in this study, the intrinsic approach based on landmarks, also known as control point mapping, was used as a method to register the source ct and mr images, as the dataset used contained very few pairs of images. the registration method requires users to manually select the landmark/control points in the source images. once the positions of the landmark points are obtained, geometric transformations like affine, projective, or polynomial geometric transforms are applied to the source images. one of the main advantages of the landmark-based image registration method is that it focuses on the specific features/points selected by the user rather than automatically registering the image based on all the features. this study performed spine fusion using landmark or focus areas of disc alignment, disc degeneration, and vertebrae(s). the major steps involved in image registration using landmark points are: 1. selecting the moving and the fixed image from a pair of source images. 2. manually selecting the landmark points. 3. fine-tuning the selected landmark points. 4. select the appropriate transform to apply to the source image, considering the selected points to obtain the registered image. the pre-processing stage mainly involves brightness and contrast matching of source ct and mr images to lose the least level of information. the main purpose of pre-processing is to match the level of contrast for a better fusion outcome, and it was also performed due to the source image taken from different sensors at different angles or heights. the pyramids discussed in the previous section were implemented to evaluate their image fusion performance. the level of decomposition was kept at 4 in all experiments. the low-frequency components were fused with the average rule, which takes the average of the absolute pyramid coefficient at each location from the input images as the coefficient at that location in the fused image. the main steps for the image fusion using pyramid-based transform are as follows:  step 1: image registration of the source images, so that the corresponding pixel or region of the image is aligned geometrically with each other.  step 2: application of pyramid transforms on the input images to get the decomposed images. the transformed image contains various levels of selected pyramids.  step 3: the appropriate fusion rule is applied for merging the pyramid levels of the source image.  step 4: the recomposition of the merged pyramid level was performed by applying inverse pyramid transform to produce the resultant fused image. figure 1 shows a schematic flow chart of the implemented pyramid transform-based approach. the goal of image fusion is to preserve maximum information, such as edges and textures, from the source images. in any image, the necessary and important features are generally larger than a pixel, and the conventional pixel-by-pixel fusion may not preserve the necessary information from the source image. for the fusion of high-pass coefficients, the max select rule with consistency check proposed in [23] was used, which effectively checks that the dominant features are incorporated into the fused image. b. experimental setup the source images were registered ct and mri t1 images of the lumbar spine with dimensions of 512×512. spineweb dataset 1 was used, which contains 17 pairs of multimodal ct and mr images [24]. the landmark-based method for image registration and pyramid transforms for image fusion was used, with a decomposition level of 4. the experiments were carried out in a ryzen 7 3.3ghz, 16gb ddr4 ram, 6gb nvidia graphics memory pc, and matlab v. 2021a. engineering, technology & applied science research vol. 13, no. 4, 2023, 11139-11145 11143 www.etasr.com nanavati & shah: implementation and comparative study of pyramid-based image fusion techniques … fig. 1. block diagram of image fusion based on pyramid-based transform. iv. objective evaluation metrics it is tough to evaluate the quality of the fused image when the reference image or ground truth is not available for comparison. in the past decade, many metrics have been proposed to compute quality, but none of them is universally accepted as a gold standard evaluation metric. hence, it is necessary to evaluate various metrics to summarize any study. this study analyzed the objective assessment following several quality metrics: spatial frequency, entropy (e) [25], mutual information (mi) [26], q ab/f [27], q mi [28], and q te [29]. v. result analysis for experimental analysis, various pyramid-based fusion algorithms were implemented and applied to the spineweb dataset 1. due to space limitation, only 4 cases are demonstrated here in the form of tables, out of which 2 cases are demonstrated with images. the outcomes of all pyramidbased fusion algorithms were evaluated using the quality metrics described above. figure 2 represents the source image of ct and mr for the 2 cases, while figures 3 and 4 show the output of the implemented fusion algorithms. table i shows the values of the quality metrics of the fused images of the two cases presented in figure 3 and figure 4, while table ii shows the quality metrics values for images not presented in this paper, but whose quality parameters are discussed. the best value of each quality metric is highlighted for every case. it is observed that the ratio of the low pass pyramid and the laplacian pyramid has consistently shown the best results in all four cases discussed. (a) (b) (c) (d) fig. 2. (a), (b) registered source image of ct and mr for case–1, (c), (d) registered source image of ct and mr for case–2. engineering, technology & applied science research vol. 13, no. 4, 2023, 11139-11145 11144 www.etasr.com nanavati & shah: implementation and comparative study of pyramid-based image fusion techniques … (a) (b) (c) (d) (e) fig. 3. output fused image of case–1 using: (a) laplacian pyramid, (b) ratio of low pass pyramid, (c) contrast pyramid, (d) fsd pyramid, (e) gradient pyramid. (a) (b) (c) (d) (e) fig. 4. output fused image of case–2 using: (a) laplacian pyramid, (b) ratio of low pass pyramid, (c) contrast pyramid, (d) fsd pyramid, (e) gradient pyramid. table i. quality metrics for cases 1 and 2 case pyramid type sf e mi q ab/f q mi q te 1 laplacian 15.3038 7.0184 2.7677 0.7011 0.4314 0.4314 rlp 17.0576 6.9415 3.7702 0.4640 0.5807 0.5807 contrast 14.8091 4.2662 2.0214 0.2278 0.4352 0.4352 fsd 12.0528 6.9588 3.1003 0.6464 0.4852 0.4852 gradient 11.9134 6.9444 3.1252 0.6479 0.4892 0.4892 2 laplacian 18.7665 6.7103 2.4883 0.7071 0.4328 0.4096 rlp 19.2908 6.6277 3.2522 0.4332 0.5508 0.4795 contrast 16.4682 3.5317 1.7548 0.2050 0.4606 0.3925 fsd 14.7722 6.5286 2.9068 0.6288 0.5097 0.4712 gradient 14.6945 6.5283 2.9203 0.6322 0.5116 0.4723 table ii. quality metrics for cases 3 and 4 case pyramid type sf e mi q ab/f q mi q te 3 laplacian 15.7928 6.5974 2.6297 0.7226 0.4581 0.4329 rlp 16.7283 6.4760 3.8602 0.4429 0.6530 0.5168 contrast 15.3242 3.2962 1.7120 0.1930 0.4788 0.3916 fsd 13.0246 6.4243 3.1716 0.6510 0.5568 0.5061 gradient 12.9487 6.4253 3.1954 0.6543 0.5606 0.5072 4 laplacian 15.2186 6.6256 2.4380 0.6826 0.4212 0.3936 rlp 17.2562 6.5498 3.1009 0.3791 0.5271 0.4944 contrast 15.5048 4.2799 2.0556 0.1638 0.4661 0.4163 fsd 12.2355 6.4844 2.9927 0.6154 0.5228 0.4809 gradient 12.1843 6.4821 3.0121 0.6187 0.5262 0.4923 mutual information (mi) indicates the amount of information from the source image that is retained in the fused image. the ratio of the low-pass pyramid has shown the highest value for mi in all the cases presented in this study compared to the other pyramid algorithms. the highest value in metrics such as sf, q mi , and q te , where a higher sf value means that the output fused image is of good quality and q mi and q te are information theory-based metrics, indicates that in the fused image, more information can be extracted from the source image. the value of entropy (e) and q ab/f was consistently higher in all four cases for the laplacian pyramid. higher values of entropy indicate the presence of more information in the fused image and higher values of q ab/f indicate that the laplacian pyramid method was able to preserve more edge information from the source image compared to the other pyramid-based methods. the spatial frequency value obtained for the fsd and gradient pyramid is the lowest, indicating the overall poor quality of the output fused images compared to the other pyramids. the entropy value and mi of the contrast pyramid method were low compared to the others, which indicates less information is present in the output fused images. comparing the values of entropy of the fused image in tables i and ii for the laplacian pyramid and the ratio of the low-pass pyramid, it was observed that there is no significant difference between. considering all the metric values obtained, the ratio of the low-pass pyramid performed well in all cases compared to the other pyramid-based algorithms. vi. summary this study implemented various pyramid-based image fusion algorithms on mri and ct images of the lumbar spine. the performance of the implemented algorithms was analyzed by measuring various quality metrics of the fused image. the experiments demonstrated that the ratio of the low-pass pyramid achieved comparable performance in terms of quality metrics compared to its counterpart pyramids implemented. the main goal of image fusion is to increase the accuracy of diagnosis and assist clinicians in decision-making. several studies have developed automated decision support systems based image features [30-31]. in the future, this study can be engineering, technology & applied science research vol. 13, no. 4, 2023, 11139-11145 11145 www.etasr.com nanavati & shah: implementation and comparative study of pyramid-based image fusion techniques … extended to implement various image fusion algorithms on a large multimodal dataset of the spine to develop a decision support system. references [1] r. jha and t. singh, "multinomial logistic regression for breast thermogram classification," in 2017 international conference on communication and signal processing (iccsp), chennai, india, apr. 2017, pp. 1266–1271, https://doi.org/10.1109/iccsp.2017.8286584. 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belkacem_sebti@yahoo.fr abstract-in this paper, a high-performance indirect field-oriented controlled dual induction motor (im) drive fed by a single inverter using type-2 fuzzy logic control will be presented. at first, the mathematical model of the im is implemented in the d-q reference frame. then, the speed control of the dual induction motor (dim) operating in parallel configuration with indirect field oriented control (ifoc) using pi and type-2 fuzzy logic controller (t2-flc) will be presented. for the control of this system, a dc supply and a space vector pulse width modulation (svpwm) voltage source inverter are introduced with constant switching frequency. also, the performance of t2-flc, which is based on the ifoc, is tested and compared to those achieved using the pi controller. the simulation results demonstrate that the t2-flc is more robust, efficient, and has superior dynamic performance for traction system applications. keywords-indirect field oriented control (ifoc); type-2 fuzzy logic control (t2-flc); dual induction motor (dim); space vector pulse width modulation (svpwm); mean control strategy i. introduction nowadays, industrial efforts are focusing on reducing weight and volume and on minimizing costs while guaranteeing high operating performance of the systems. a multi-machine drive system powered by a single inverter presents a desirable solution. these systems are used in several applications such as paper and steel rolling mills [1-3], conveyor systems [4], and electric propulsion systems such as electric traction, ship propulsion and electric vehicles [5-7]. for multi-motor drives, the structure and the control strategy of the drive system depend on the requirements of the application for which they are used as well as the necessary performance, speed and precision of the drive system. different modeling techniques for two induction motors with a single inverter have already been released. a graphical and a global modeling of a multi-machine system connected in parallel is used in [6, 8]. several couplings by criteria merging for multi-machine, multiconverter systems are presented in [9]. several control solutions have been presented: a modified v/f control strategy for a multi-machine multi-inverter drive system is given in [10] and fuzzy sliding and dtc-svm control of multi induction motors connected in parallel are presented in [11, 12]. authors in [13] present an optimal predictive torque control of two parallel permanent magnet synchronous machines fed with a single inverter. a technique based on master slave direct control of two synchronous machines is used in [14]. dive systems comprising multi-phase and multi-motor induction machines powered by a single inverter are studied in [15-17]. unlike the three-phase multi-machine system, multi-phase multi-machine systems supplied by a single inverter can be connected in series [18, 19] and in parallel [13, 14, 17, 20], which allows independent control of each machine. in this paper, two induction machines connected in parallel powered by a single inverter as presented in figure 1 [21] were considered. here, current and speed feedback is taken from both machines which are fed by a single voltage source inverter for calculating the reference voltages to be applied to the machines. to obtain a good dynamic response of the drive torque, two performance control strategies can be used to control twomachine systems with a single inverter: field oriented control (foc) [5, 15, 16, 21-23] and direct torque control (dtc) [1, 4, 6, 12, 24]. the speed control of the dual identical induction motor drive connected in parallel to a svpwm inverter supply using t2-flc is investigated in this paper. this system is corresponing author: alaeddine bounab engineering, technology & applied science research vol. 10, no. 5, 2020, 6301-6308 6302 www.etasr.com bounab et al.: evaluation of the high performance indirect field oriented controlled dual induction … suitable for applications using dual induction motor (im) drives with the advantage of compactness, lightness and economy [25-27]. fig. 1. block diagram of t2-flc fuzzy speed control of thedims. ii. system configuration a schematic diagram of the indirect field oriented control (ifoc) of dual motors connected in parallel associated to a single svpwm inverter is shown in figure 1. this method has been adopted in order to avoid the excessive magnetization of these motors [28]. this method is characterized by the calculation of the angular sliding speed, the stator flux angle and the angular speed of the rotor. speeds of the two induction motors are measured with the help of sensors. t2-flc or pi controllers are used in the speed control loops for the dims. the robustness of the proposed method is checked in terms of motor speed and load variations. iii. model of the induction motor among the various types of models used to represent the induction machine, there is one that uses each of the stator currents, stator flux, and speed as state variables and voltages (���,���) as control variables. this model is presented in (d, q) reference, related to the rotating field. this model is expressed by the system described in (1)-(4): ��� � ������ �� ∗ �� � ������� � �� ∗ ��� �� �� ∗ � � ������� � �� ∗ ��� ��� 0 �� ∗ �� � ������� � ��� � �ω � ∗ ��� ��� 0 �� ∗ �� � ������� � ��� � �ω � ∗ ��� (1) the components of the stator and rotor flux are expressed by: �� � ����� � ∗ �� � ! ∗ �� ��� � ∗ �� � ! ∗ �� ��� � ∗ �� � ! ∗ �� ��� � ∗ �� � ! ∗ �� (2) the mechanical equation of the machine is given by: " ∗ �ω �� � # ∗ ω $% � $� (3) the electromagnetic torque equation can be expressed in terms of stator currents and stator flux as: $% &'()*(� �+��� ∗ �� � ��� ∗ �� , (4) where ( ��� , ��� );( �� , �� );( ��� , ��� ) are the voltage, currents, and stator flux in d-q axis, ( �� , ω ) are stator pulsation and mechanical rotor speed, . 1, 2 are the first and second induction motor, (��, ��) the stator and rotor resistance, ( �, �) the stator and rotor cyclic inductance, and ( !, p) are the mutual inductance and the number of pole pairs. due to the similarity of the two induction machines, only the model of one machine is presented. fig. 2. current flows for parallel connected dual motor. in the case of dims systems connected in parallel supplied by a single inverter, the current is directly controlled by the inverter, to ensure the proper functioning of the system. the difference between the speeds or the parameters of the two motors causes an imbalance in the currents flowing in each motor. the currents ( �0) and ( �*), flowing in each stator winding can be represented by ( �) which flows equally in both stator windings and (1 �) which circulates between each stator winding as shown in figure 2. equations (5) and (6) show the relation of these currents. � �0 � �* (5) 1 � 2�3 42�5* (6) iv. control strategy of dims mean control strategy considers the average of the different input variables of both ims to create a “virtual mean motor”. the measured variables of both motors are the currents ( �0, �*) and the speeds (ω1, ω2). the average variables are obtained using (7) and (8). � 2�562�3* (7) ω ω56ω3* (8) rotor field oriented control (rfoc) is one of the best methods to drive ims and presents satisfactory performances. it requires the rotor flux (φr) and electromagnetic torque tem to be decoupled. the im modeling is done in the (d, q) reference frame, with the d axis linked with the rotor flux vector. the rotor flux can be written as: ��� �∗ � (9) engineering, technology & applied science research vol. 10, no. 5, 2020, 6301-6308 6303 www.etasr.com bounab et al.: evaluation of the high performance indirect field oriented controlled dual induction … ��� 0 (10) the reference voltages ( ��� , ��� � are derived by substituting (9) and (10) in (1) 7��� �� ∗ �� � � �2����� � � ∗� 8 � ∗ �� � (�9� ∗ �∗� ∗ � ∗�: ;��� �� ∗ �� � � �2����� � � ∗� � � ∗ �� � �∗� � (11) the component references of stator current and slip speed �∗�: can be expressed as: 7 ∗�� 0() ∗ �∗� ∗�� ()6(�'∗()∗�∗�� ∗ $∗% (12) �∗�: 9�∗()�()6(��∗�∗�� ∗ ∗�� (13) the index (*) represents the command variable. mean rfoc control offers symmetric behaviors of both motors to obtain stable average performance. on undisturbed functioning, both motors are identical so they have the same behavior. however, when a disturbance affects one motor the second reacts to compensate it, so it is also disturbed. the mean control reacts to offer stable average signals. to generate the reference voltage vectors (���0 , ���0 , ���* and ���*), pi controllers are introduced as shown in figure 1. v. pi controllers the overall system shown in figure 1 contains two pi controllers. the first is an inner loop for current control, and the second is an outer loop for speed control. the design of the two controllers is detailed in figures 3 and 4. fig. 3. speed pi controller block diagram. fig. 4. current pi controller block diagram. the pi controller of the speed shown in figure 3 is designed as follows: the transfer function of the pi controller is: <=�>� ?@' � ab�@ ?@' c1 � 0+abd ab�⁄ ,.@g ?@' 806h�.@h�.@ ; (14) where, ?@' , ?@ and i represent, the proportional gain, the integral gains, and the integral time of the controller respectively. the transfer function of the system is defined as: <@�>� 0j6k.@ 0j 8 006�k j�.⁄ @; l 8 006m�.@; (15) where, n�and l are the time constant and the system gain. the open loop transfer function of the system <o(�>�is presented as follows: <o(�>� <=�>�.<@�>� ?@' 806h�.@h�.@ ; 8 p06m�.@; (16) fig. 5. t2-flc block diagram. let: �1 � i . q� �1 � n� . q� the closed loop transfer function of the system is: <=( �q� rst ���06rst��� +p.abd, �h� .@�u�h� .@6p.abd � �h� .@�⁄ 0�h� p.abd�⁄ .@60 0hv.@60 (17) where iw is the time constant of the closed loop of the system. according to (14), (15) and (17) the gains of the controller are calculated as: ?@ abdh� (18) ?@' h�p.hv (19) the value of the time constant of the closed loop of the system (iw), is the same as the time constant of the system (n�). in the same way the gains (?= ) and (?=') of the pi controller of the current in figure 4 are obtained from the transfer function of the system which is defined as: <=��>� 09�6(�� lx 8 006my�@; (20) ?= abdh� (21) ?=' h�p.hv (22) vi. type 2 fuzzy logic controller the fuzzy logic control based on type 2 fuzzy sets (t2fs) present a suitable solution for the control of non-linear systems [29]. t2-fs were first proposed in [33-35] as an extension to type 1 fuzzy sets (t1-fs), to increase the engineering, technology & applied science research vol. 10, no. 5, 2020, 6301-6308 6304 www.etasr.com bounab et al.: evaluation of the high performance indirect field oriented controlled dual induction … fuzziness of the relations. several studies have shown the high performance of t2-flc, which uses the t2-fs interval instead of type 1 flc (t1-flc) in terms of handling the uncertainties [17, 28, 34]. in figure 5, we can see that the t2-flc differs from the t1-flc by the output processing block. in addition to the defuzzifier, it includes a block type reducer which allows transforming t2-fs to t1-fs. the type 2 fuzzy controller used in this work has two inputs: the first is the speed error (z�) and the second is the variation of the speed error (1z�). the output variable (uf) generated from the output processing, corresponds to the component of torque ($%). fig. 6. t2-flc speed controller. the membership functions used for the inputs and the output are presented in figures 7 and 8. the t2-flc in figure 6 is characterized by if-then fuzzy rules-base, but its antecedents and consequents are now t2-fs [29, 31, 32]. • rule 1: if z� is nl, and 1z� is nl then [j is nl. • rule 2: if z� is nl, and 1z� is nm then [j is nl. • rule 3: if z� is nl, and 1z� is zr then [j is nl. . . • rule 25: if z� is pl, and 1z� is pl then [j is pl. fig. 7. inputs membership functions. fig. 8. output membership function. the use of a t2-flc proves to be more advantageous than the use of a pi/pid controller, thanks to its modifiable control surface which offers better performance, especially when the order of the system is greater than two, while it includes oscillatory modes [30]. vii. space vector pulse width modulation the voltage vectors, produced by the 3-phase pwm inverter, divide the space vector plane into six sectors as shown in figure 9. in every sector, the voltage vector is arbitrary synthesized by the basic space voltage vector of the two sides of one sector and zero vectors. for example, in the first sector, vs ref is a synthesized voltage space vector and its equation is given by [7, 32]: �\]>�%j ∗ i� �\]w ∗ iw � �\]0 ∗ i0 � �\]* ∗ i* (23) i� iw � i0 � i* (24) where iw, i0 and i* are the work times of basic space voltage vectors �\]w, �\]0, and �\]*respectively. the determination of times t1 and t2 given by mere projections is given in figure 10. fig. 9. the diagram of voltage space vectors. �� � ���>^�%j h5h� ∗ _�\]0_ � ` �>a�%j h3h� ∗ _�\]*_ ∗ sin 8e&;` f�g�hijkl8mn; (25) engineering, technology & applied science research vol. 10, no. 5, 2020, 6301-6308 6305 www.etasr.com bounab et al.: evaluation of the high performance indirect field oriented controlled dual induction … 7 i0 h�*opq �√6�>^�%j � √2�>a�%j�i* h�opq +√2�>a�%j, (26) the rest of the period is applying the null-vector. the switching duration is calculated for every sector. the times of the vector implementation can all be related to the following variables: ��� �� u h�opq �√2�>a�%j� v h�*opq +√6�>^�%j � √2�>a�%j,w h�*opq +�√6�>^�%j � √2�>a�%j, (27) the implementation of the duration sector boundary vectors can be seen in table i. table i. duration sector boundary vectors sector 1 2 3 4 5 6 xy �z { | z �{ �| xy6} | z �{ �| �z { the third step is to compute the duty cycles to have the three necessary times: 7i~�� h�4h� 4h� �5* i��� i~�� � i ix�� i��� � i 60 (28) fig. 10. projection of the reference voltage vector. the last step is to assign the duty cycle (i`��) to the motor phase according to the sector. table ii. assigned duty cycles of the pwm outputs sector 1 2 3 4 5 6 �� x��� x��� x��� x��� x��� x��� �� x��� x��� x��� x��� x��� x��� �� x��� x��� x��� x��� x��� x��� viii. simulation results and discussion the modeling and simulation of the system presented in figure 1 was carried out in matlab/simulink environment. the parameters of the two 4kw motors used in the simulation are shown in the appendix. in order to properly test and compare the two speed controllers proposed in terms of performance, firstly both motors are subjected to a trapezoidal speed profile which includes positive and negative values respectively, as shown in figure 11. then, each motor undergoes a different load torque, as shown in figure 12. fig. 11. speed profile. fig. 12. load profile. fig. 13. speed response of im1 without perturbation. fig. 14. speed response of im2 without perturbation. engineering, technology & applied science research vol. 10, no. 5, 2020, 6301-6308 6306 www.etasr.com bounab et al.: evaluation of the high performance indirect field oriented controlled dual induction … fig. 15. stator currents of im1 with injected load. fig. 16. stator currents of im2 with injected load. the speed response of the two motors with the speed profile introduced is shown in figures 13 and 14. we can see that the response of both motors is identical, and the amplitude of the transient speed oscillations is lower with t2-flc which has better rejection of perturbations and responds well to speed reversal as shown in figures 15 and 16. table iii. comparison of calculated performance indices. controller mp (rad/s) se iae itae pi 104.17 -104.36 5.489 1.347 2.094 t2 flc 100.02 -100.01 0.994 0.887 1.196 fig. 17. speed response of im1 with injected load. for a clear comparison between the conventional pi controller and t2-flc, several performance measures such as maximum peak overshoot (mp %), integral squared error (ise), integral absolute error (iae), and integral of time multiplied absolute error (itae), are computed as shown in table iii. when the operating conditions are not similar for each im (the introduction of the load torque disturbance profile) the two engines react in a complementary way, i.e. their speeds deviate in an opposite way from the reference, in order to keep the average value of the speed close to the command value. for this, the control by t2-flc showed better results compared to the pi controller. finally, the simulation results of the electromagnetic torque of the dims connected in parallel associated with ifoc using t2-flc and pi controllers are presented in figure 19 for first the im and figure 20 for the second im. these results confirm that the t2-flc controller offers better performance under changing operating conditions. fig. 18. speed response of im2 witht injected load. fig. 19. torque response of im1, load profiles injected. fig. 20. torque response of im1, load profiles injected. the mean control strategy used in this paper, allowed the identical control of the two-motor drive. the simulation results are supported by the results of [1]. also the use of t1-flc proves its high performance for speed control of induction machines compared to the conventional pi/pid controllers, especially in transient mode, which is confirmed by the results obtained by [18], but the t2-flc developed in this paper gave better results compared to those achieved by [18], which are confirmed by the performance criteria presented in table iii. engineering, technology & applied science research vol. 10, no. 5, 2020, 6301-6308 6307 www.etasr.com bounab et al.: evaluation of the high performance indirect field oriented controlled dual induction … fig. 21. rotor flux response of im1. fig. 22. rotor flux response of im2. ix. conclusion in this paper, a high performance indirect field oriented controlled dual induction motor drive fed by a single inverter using type-2 fuzzy logic control has been proposed. this study is based in general on speed control of two induction motors connected in parallel associated to a single svpwm inverter with constant switching frequency, which uses ifoc as control technique. a comparison of the performances of the two controllers, pi and t2-flc has been conducted. the proposed ifoc algorithm has been implemented in matlab/simulink. the simulation results have shown that the t2-flc offers better performances compared to the pi controller in terms of dim speed reference tracking. also, the transient and steady state response of the motors speed is improved as compared to the conventional pi controller. the presented results show that control based on t2-fuzzy logic offers a desirable solution for applications with several induction motors. appendix induction motors parameters designation symbol value rated power �� 4kw rated voltage �� 380v nominal frequency � 50hz rated speed �� 1440rpm number of pole pairs � 2 stator resistance �� 1.2ω rotor resistance �� 1.8ω stator cyclic inductance �� 0.1554h mutual cyclic inductance �� 0.15h rotor cyclic inductance �� 0.1568h rotor inertia � 0.07kg�� viscosity coefficient � 0.001n.m/s references [1] b. m. joshi and m. c. chandorkar, “two-motor single-inverter fieldoriented induction machine drive dynamic performance,” sadhana, vol. 39, no. 2, pp. 391–407, apr. 2014, doi: 10.1007/s12046-014-0237-6. 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[35] e. nechadi, “adaptive fuzzy type-2 synergetic control based on bat optimization for multi-machine power system stabilizers,” engineering, technology & applied science research, vol. 9, no. 5, pp. 4673–4678, oct. 2019. microsoft word 6-jordanova.doc engineering, technology & applied science research vol. 4, no. 1, 2014, 591-595 591 www.etasr.com jordanova et al.: influence of bch and ldpc code parameters on the ber characteristic ... influence of bch and ldpc code parameters on the ber characteristic of satellite dvb channels l. jordanova l. laskov d. dobrev department of telecommunications, department of telecommunications, department of telecommunications, technical university of sofia, bulgaria technical university of sofia, bulgaria technical university of sofia, bulgaria jordanova@tu-sofia.bg laskov@mail.com dobrev@tu-sofia.bg abstract—this article presents the results of a study on the noise immunity of dvb channels when higher-order m-ary apsk modulation schemes and concatenated bch-ldpc codes are used. dependencies to determine the probability at the decoder output are given taking into consideration the bch and ldpc code parameters and the error probability in the communication channel. the influence of the bch packets length, the bch code rate, the number of maximum iterations and the parameters of ldpc parity-check matrix on the code efficiency is analyzed. research of the influence of the concatenated ldpc-bch code parameters on the radio channel noise immunity is conducted and dependencies to determine the required cnr at the input of the satellite receiver are given. keywords-satellite dvb channel; m-ary apsk; concateneted bch-ldpc codes; ber; cnr; qef reception i. introduction the design of a digital communication system aims to maximize the transmission bit rate, to minimize the probability of bit error, to minimize the required power, or equivalently, to minimize the required carrier-to-noise ratio, to minimize the required system bandwidth and to minimize the system complexity and cost. satellite digital video broadcasting (dvb) systems are particularly affected by power limitations, therefore ruggedness against noise and interference should be the main design objective, rather than spectrum efficiency [1, 2]. in order to achieve high power efficiency without excessively penalizing the spectrum efficiency, such a system should use noise resistant types of modulation and effective channel codes. recent trends in satellite communications show an increasing demand of higher-order m-ary modulation schemes. higher-order m-ary modulation schemes can provide greater spectral efficiency and thus the high data rate required for either digital multimedia applications or other applications such as point-to-point high data rate backbone connectivity and future earth observation missions requiring downlink data rates exceeding 1 gbps. in this regard, amplitude phase shift keying (apsk) represents an attractive modulation scheme for digital transmission over nonlinear satellite channels due to its power and spectral efficiency combined with its inherent robustness against nonlinear distortion. the design optimization analysis and results obtained for 16, 32 and 64 apsk modulation schemes are presented in [3-5]. the 16 apsk and 32 apsk have been proposed in the framework of the dvb-s2 standard [6] and their performance has been widely investigated over the awgn channel, by considering typical satellite scenarios, also in the presence of hpas. although these higher-order m-ary apsk modulation schemes have been specifically designed for operating over nonlinear satellite channels, they still show signal envelope fluctuations and are particularly sensitive to the characteristics of the satellite transponders which introduce channel nonlinearities. as shown in [7, 8], the power efficiency of apsk modulation schemes can be improved by using nonlinear compensation techniques in the uplink station. in dvb-s2 a concatenated error protection of bosechaudhuri-hocquenghem (bch) outer code and low density parity check (ldpc) inner code was chosen [6, 9]. this fec scheme can be thought of as a replacement of the dvb-s convolutional coding with ldpc coding and reed-solomon encoding with a different bch encoding. in [10-12] some new design techniques for ldpc and bch codes are represented which allow approaching the shannon’s capacity to within hundredths of a decibel. in the contemporary dvb systems it is necessary to provide quasi-error-free (qef) reception while the values of the cnr parameter are relatively low and the encoding and decoding equipment is not very complex. quasi-error-free means that the bit error rate (ber) at the input of the mpeg-2/4 demultiplexer is less than 10−10 to 10−11. in the dvb-s2 standard the requirement for qef reception shall be satisfied when ber before bch decoder does not exceed 2.10−7. for the satellite dvb channel the typical values of the carrier-to-noise ratio (cnr) are within 10 to 18 db and providing the required ber imposes some limitations on the order of the modulation [2, 13]. higher-order modulations provide greater transmission bit rate, but they require higher cnr to get the same ber at the output of the demodulator. in [8] and [14] it was shown that, depending on the selected code rate and modulation constellation, the dvb-s2 systems can operate at carrier-to-noise ratios from – 2.4 db (using qpsk 1/4) to 16 db (using 32 apsk 9/10), assuming an awgn channel and ideal demodulator. at the same time these systems provide up to a 30% capacity gain over dvb-s systems. the aim of this paper is to study the influence of the parameters of bch and ldpc codes on the noise immunity of engineering, technology & applied science research vol. 4, no. 1, 2014, 591-595 592 www.etasr.com jordanova et al.: influence of bch and ldpc code parameters on the ber characteristic ... a satellite radio channel when using 16 apsk, 32 apsk and 64 apsk modulation. it is known that, the 16 apsk and 32 apsk modes are mainly targeted at professional applications (digital tv contribution and news gathering), due to the higher requirements in terms of available cnr, but they can also be used for broadcasting. for this purpose they need to adopt advanced predistortion methods in the uplink station [7, 15] to minimize the effect of transponder nonlinearity. ii. error probability after bch decoder depending on the code parameter bch codes fall into the group of block codes, where the digital information is transmitted in packets of a k symbols length. each symbol consists of n bits, and the greatest applicability belongs to the dual bch codes, where n = 1. the bch codes are generally represented as bch(n, k, t), where n is the total number of coded symbols in a packet, and t is the number of repairable symbol errors. for the most common codes n = 2h – 1, where h can be every number which is greater than or equals to 3, and ht = n − k is the number of error protection symbols, or checksum. the symbol error probability after bch decoding ps is related to the symbol error probability in the communication channel ps by the following dependency [16]:  1 1 (1 ) n i i t n i s s s n i p p in p            to obtain the symbol error probability in the communication channel when using м-ary apsk (м = 16, 32 or 64) the equations given in [17] can be used. for the quality assessment of the received digital information the bit error probability parameter (respectively ber) is usually employed. as the paper studies binary bch codes, the bit error probability after the bch decoder pb is equal to the symbol error probability ps . the relation between bit error probability (pb) and symbol error probability (ps) in the communication channel is given by:  1 2(log )b sp p m    in the graphic dependencies represented below, instead of the bit error probability we have used its statistical evaluation вer. the bch code efficiency becomes greater with the increasing of the packets length, which makes them appropriate for error correction in packets whose length is far greater than the length of the disturbance. this is illustrated by the dependencies in figure 1, where the code rate rbch = 0.988, and the packets length changes from 12000 bits to 20000 bits. the results of the study show that the maximum acceptable values of ber at the input of the bch decoder which are necessary for providing qef reception, are within the interval of 1.841·10−5 to 8.222·10−6. the influence of the checksum on the radio channel noise immunity can be assessed by using the dependencies presented in figure 2. they are relevant for the case when the packets length is constant (n = 16200) and the number of information bits changes from k = 15880 to k = 16136 (the checksum introduced increases from 64 bits to 320 bits). it is evident that with the increase of the checksum, the radio channel noise immunity becomes better, but this is accompanied by a decrease of its effective bandwidth, and therefore a decrease of the bit rate. the results obtained from this study show that in order to provide ber = 10−11 at the bch decoder output (qef reception) it is necessary that the ber values at the decoder input do not exceed the following values: 8.81·10−7, for bch(16200,16136), 1.62·10−5 for bch(16200,16008) and 4.47·10−5, for bch(16200,15880). fig. 1. output ber versus input ber and bch packets length fig. 2. influence of the bch code rate on the output ber iii. error probability after ldpc decoding ldpc codes are linear block codes which have a sparse parity-check matrix of the type h(n − k) x n , where k is the engineering, technology & applied science research vol. 4, no. 1, 2014, 591-595 593 www.etasr.com jordanova et al.: influence of bch and ldpc code parameters on the ber characteristic ... number of information symbols and n is the total number of coded symbols in the packet. the dual ldpc codes have the widest application. in them every symbol consists of one bit. unlike most block codes, where the method of maximum likelihood is used for decoding, the decoding algorithm of ldpc codes is based on parallel processing of the parity-check equations with much iteration. ldpc codes are subdivided into regular and irregular: the latter are more widely used. for them, the dependency between bit error probability after the (i + 1)-th iteration in the ldpc decoder pi+1 and the bit error probability in the communication channel pb is described by the following expression [18]:    1 1 11 1 1 x x 1 1 (1 ) 1 1 1 1 1 1 c j j j j ll b i i b l b j l j lj j i i l i j p q q p l j q q l m m p p                                                    where    1 2 1 1 1 1 r q i q i q m p m m q m                  the following symbols are used in these expressions: j and q are the number of the units in a column and a row of the parity-check matrix respectively, λj is the relative number of the columns containing j number of units, ωc is the maximum number of units in a column, ρq is the relative number of rows, containing q number of units and ωr is the maximum number of units in a row. the value of the parameter αj is chosen as the smallest whole number αj > (j − 1)/2, for which the following requirement is fulfilled:        2 2. 1 1 11 1 2 j j j j ib j j b i i q mp p q m q                the ldpc codes in which the number of units in the paritycheck matrix rows is the same, and the number of units in its columns is different, have had a wide application in telecommunications. for repeat-accumulate codes, the number of units in the first row is one less than those in the other rows. it is such codes in particular that are used in the dvb standard and that are the research object of this paper. iv. influence of the code parameters on the ber characteristic of the ldpc decoder the influence of the maximum number of iterations imax which take place in the ldpc decoder on the code efficiency can be assessed by using the dependencies in figure 3. for this study we have used the parameters of the original code for the dvb standard. the parity-check matrix of this code is h16200 x 64800 , the number of units in a row is ωr = 14, the distribution of the number of units in columns is given in table i and the code rate is rldpc = 3/4. table i. distribution of the number of units in columns for the ldpc codes studied. orig. code code 1 code 2 code 3 code 4 code 5 code 6 j number of columns containing j number of units (λj ·n) 1 1 1 1 1 1 1 1 2 4049 4049 4049 4049 4049 4049 4049 3 10800 10300 9800 9300 8100 9450 5400 4 0 0 750 750 0 0 4050 6 0 250 0 250 4050 675 2700 8 0 750 750 1500 0 2025 0 12 1350 850 850 350 0 0 0 as seen in figure 3, at higher values of the parameter imax the effect of code efficiency increase becomes weaker. simultaneously, increasing the number of iterations results in longer decoding time, which requires the application of highspeed decoding devices. therefore, the authors recommend that the maximum number of iterations in the ldpc decoder should not exceed 30. fig. 3. influence of the maximum number of iterations in the ldpc decoder on the code efficiency for original ldpc code with code rate = 3/4 figure 4 shows dependencies of ber after ldpc decoder on ber in the communication channel for a standard and six more irregular ldpc codes. the codes applied have the following parameters: ωr=14, distribution of the number of units in columns, given in table i and rldpc=3/4. for this simulation study it is assumed that the maximum number of iterations in the decoder is imax=20. from figure 4 it is evident that when the error probability in the communication channel is greater than 6·10−2, the ldpc code efficiency is very low. the reason for this is the fact that in this case, simultaneously with the errors correction, the decoder also inverts correctly received bits. when the values of the channel ber are lower, the code efficiency increases very rapidly. engineering, technology & applied science research vol. 4, no. 1, 2014, 591-595 594 www.etasr.com jordanova et al.: influence of bch and ldpc code parameters on the ber characteristic ... fig. 4. ber characteristics of the ldpc decoder when imax = 20 the results of this study allow obtaining the maximum acceptable values of the ber channel, where a given value of ber at the ldpc decoder output is provided. if, for example, the aim is to obtain an ber=10−7 output, then the values of the ber channel are within the interval of 2.31·10−2 to 3.85·10−2. it is evident that the highest efficiency is achieved when using code 4 and code 6. the efficiency of the ldpc code 6 become high at lower value of the ber channel compared to other researched codes but its characteristic is considerably steeper. this is due to the lower number of columns containing three ones. table ii. parameters of effective ldpc codes. number of columns containing j number of units (λj ·n) j 1 2 3 4 6 8 12 code 7 (wr =12) 1 4049 8100 4050 0 0 0 code 8 (wr =15) 1 4049 7650 0 3150 1350 0 analogous studies have also been conducted for clarifying the influence of the maximum number of units in row ωr on the ldpc code efficiency. the results show that for achieving maximum efficiency, it is necessary to carry out a careful selection of the ωr and λj parameters of the codes used. the parameters of two ldpc codes which have shown the best results are given in table ii. v. radio channel noise immunity depending on the concatenated bch-ldpc code parameters considering the selection of a method for channel encoding, it is necessary to take into account the real achievable values of cnr at the input of the satellite dvb receiver. they depend on the equivalent isotropic radiated power (eirp) of the satellite transponder, the signal attenuation along the line satellite-earth l, the gain of the receiving antenna ga , the noise figure of the low noise convertor nflnc and the equivalent noise bandwidth of the receiver bn (the bandwidth is approximately equal to the channel bandwidth bch). to derive cnr we use the following formula [13]: a lnc10 lg 144chcnr eirp l g b nf       taking into account the values of the abovementioned parameters, that is eirp=45-65 dbw, l=205-211 db, nflnc=0.1-0.7 db and ga=36–38 db, it is easy to determine that cnr at the satellite receiver input varies within the limits of 9 to 18 db. these values cannot be provided when using only one of the codes studied. fig. 5. influence of the modulation type and bch-ldpc code parameters on the radio channel noise immunity the dependencies shown in figure 5 make possible the derivation of the required carrier to noise ratio, which ensures ber=10−11 at the input of the mpeg-2/4 demultiplexer, when concatenated ldpc-bch codes and m-apsk modulations (м = 16, 32 and 64) are used. during this simulation study it is taken that the ldpc code rate is 3/4, the bch code is bch(11880,11712), the maximum number of iterations in the ldpc decoder are imax=20 and the values of ωr and λj n are given in table i and table ii. the relationship between parameters cnr and eb /n0 is described as    0 bch ldpc10 lg 10 lg 1 4 10 lgbcnr e n m r r      where m = log2m is the number of bits per symbol, α is the rolloff factor of the root cosine square matched filter (α = 0.35, 0.25 and 0.20), rbch and rldpc are the code rates of the bch and ldpc code respectively. the dependencies in figure 5 refer to the case where α = 0.35. the analysis of the derived results shows that when concatenated ldpc code 6 and original bch code are used the radio channel noise immunity becomes higher than that engineering, technology & applied science research vol. 4, no. 1, 2014, 591-595 595 www.etasr.com jordanova et al.: influence of bch and ldpc code parameters on the ber characteristic ... which is provided in the case of standard concatenated codes. the calculated values of cnr needed for qef reception and benefits from usage of a modified code, when m-apsk modulations (м = 16, 32 and 64) are used, are given in table iii. table iii. cnr values for standard and optimized bch-ldpc code obtained by means of computer simulation modulation standard bchldpc code optimized bch-ldpc code benefit 16 apsk 13.67 db 12.65 db 1.02 db 32 apsk 16.35 db 14.85 db 1.5 db 64 apsk 19.17 db 17.25 db 1.92 db by application of concatenated bch-ldpc encoding bch and ldpc code rates can be increased and thus widen the effective channel bandwidth bch,e . as a result, the digital information transmission rate rb increases. to calculate the value of rb the following equation can be used:  ldpc bch, 1 1 b ch e chr b b r r            where ε=log2m denotes the bandwidth efficiency of the selected modulation method. as known, increasing the manipulation order m and the code rate results in deterioration of the radio channel noise immunity. therefore, when satellite dvb systems are designed, a reasonable compromise between transmission rate and noise immunity should be done. the calculated values of rb for the considered concatenated bch-ldpc codes are within the interval of 20 mbps (for channel bandwidth bch = 27 mhz, 16 apsk modulation and rldpc=1/4) to 155 mbps (for bch=36 mhz, 64 apsk modulation and rldpc=9/10). vi. conclusion the analytic and graphic dependencies presented in this paper make it possible for the optimal parameters of bch and ldpc codes to be determined taking into account the modulation method, signal attenuation and noise in the radio channel, the receiver parameters, the required ber at the channel decoder output, the transmission rate etc. these dependencies can be used in any other communication system in which such types of encoding are applied. the analysis of the obtained ber characteristics of satellite dvb channels, for whose formation 16, 32 and 64 apsk and concatenated bch-ldpc codes with different parameters are used, allows the following conclusion to be drawn. the highest noise immunity of the radio channel is achieved when using a combination of original bch code and ldpc code 6. in comparison with the standard concatenated bch-ldpc code the proposed one provides the following benefits regarding the cnr parameter: 1.02 db (16 apsk), 1.5 db (32 apsk) and 1.92 db (64 apsk). acknowledgment the research described in this paper is supported by the bulgarian national science fund under the contract no ddvu 02/74/2010. references [1] etsi en 300 421 v1.1.2, digital video broadcasting (dvb): framing structure, channel coding and modulation for 11/12 ghz satellite services, european telecommunications standards institute, 1997 [2] w. fisher, digital video and audio broadcasting technology: a practical engineering guide, springer, 2010 [3] k. liolis, r. gaudenzi, n. alagha, a. martinez, a. fаbregas, “amplitude phase shift keying constellation design and its applications to satellite digital video broadcasting”, floriano de rango (ed.), intech, 2010 [4] p. liolis, n. alagha, “on 64-apsk constellation design optimization”, proceedings of 10th international workshop on signal processing for space communications, greece, pp. 1-7, 2008. [5] w. sung, s. kang, p. kim, d. chang, “performance analysis of apsk modulation for dvb-s2 transmission over nonlinear channels”, international journal of satellite communications and networking, vol. 27, no. 6, pp. 295-311, 2009 [6] etsi en 302 307 v121, digital video broadcasting (dvb): second generation framing structure, channel coding, and modulation systems for broadcasting, interactive services, news gathering and other broadband satellite applications, european telecommunications standards institute, 2009 [7] r. de gaudenzi, a. g. fаbregas, a. martinez, “performance analysis of turbo-coded apsk modulations over nonlinear satellite channels”, ieee transactions on wireless communications, vol. 5, no. 9, pp. 23962407, 2006 [8] a. morello, v. mignone, “dvb-s2: the second generation standard for satellite broad-band services”, proceedings of the ieee, vol. 94, no. 1, pp. 210-227, 2006 [9] etsi tr 102 376, user guidelines for the second generation system for broadcasting, interactive services, news gathering and other broadband satellite applications (dvb-s2), european telecommunications standards institute, 2005 [10] c. berrou, codes and turbo codes, springer, 2011 [11] s. johnson, iterative error correction: turbo, low-density parity-check and repeat-accumulate codes, cambridge university press, 2009 [12] m. eroz, f. sun, l. lee, “dvb-s2 low density parity check codes with near shannon limit performance”, international journal of satellite communications and networking, vol. 22, no. 3, pp. 269-279, 2004 [13] l. ippolito jr, satellite communications systems engineering: atmospheric effects, satellite link design and system performance, john wiley & sons ltd., 2008 [14] r. gaudenzi, a. fabregas, a. martinez, “turbo-coded apsk modulations design for satellite broadband communications”, international journal of satellite communications and networking, vol. 24, no. 4, pp. 261-281, 2006 [15] newtec el470, ip satellite modem, www.newtec.eu. [16] b. sklar, digital communication: fundamentals and applications, prentice hall, 2001. [17] o. afelumo, a. awoseyila, b. evans, “simplified evaluation of apsk error performance”, electronics letters, vol. 48, no. 14, pp. 886-888, 2012 [18] m. luby, m. mitzenmacher, m. shokrollahi, d. spielman, “analysis of low density codes and improved designs using irregular graphs”, proceedings of the 30th acm symposium on theory of computing, new york, pp. 249-258, 1998 engineering, technology & applied science research vol. 8, no. 2, 2018, 2864-2868 2864 www.etasr.com azhar and shabbir: 5g networks: challenges and techniques for energy efficiency 5g networks: challenges and techniques for energy efficiency madeha azhar electronics department ned university of engineering and technology karachi, pakistan madiha_azhar@hotmail.com amna shabbir electronics department ned university of engineering and technology karachi, pakistan amna06@gmail.com abstract—the growing importance of energy efficient networks with high data rate requirements is a major concern for network operators. services provided by the network operators are required to ensure the consumers’ satisfaction. for the providing of high data rates with good signal quality, small cells are deployed. but these cells can increase energy consumption if not equipped with some intelligent power saving or distribution mechanism. in this paper, a previously tested small cell sleeping mode scheme is compared with the new proposed scheme of reducing power in low or normal traffic hours. this scheme provided 13-15% increase in energy efficiency. the new scheme resulted to beneficial simulated outcomes and can be applied to overcome the energy consumption issue. keywords—green communication; energy efficiency; power distribution i. introduction there is a huge growth in the usage of cell phones and the number of their users. devices like cell phones and tablets have become very handy and are available to almost everyone. there has been a tremendous growth in the number of cell phone subscribers requiring high data rates as well as speedy internet for faster browsing. the social media era brought the need of higher data rates. mobile operators, while trying to fulfill the data traffic and to accommodate every subscriber with acceptable quality of service, left the energy consumption issue at backend. service providers came up with the solution to deploy base stations (bss) in large quantity to provide higher data rates to the subscribers. network energy consumption rapidly increases when large numbers of bss are deployed to provide the demanded services to every user. as the number of bss increased a large amount of power was required for the huge macro bss to operate which resulted in increased energy consumption and increased co2 emission. heterogeneous networks were deployed having different cell sizes like macro, micro, pico and femto cells which have limited coverage areas providing services in allocated areas with substantial data rates and signal quality [1]. recently, the concern went towards energy saving. in recent years many of the researchers provided expectable solutions and techniques helpful to achieve energy efficiency [2-5]. energy efficiency can be achieved with several ways: by enhancing the performance of different hardware components, by turning off selected bs components, by the deployment of efficient heterogeneous networks, br using natural energy resources. by turning off selectively bs components, some energy can be conserved. power amplifiers on the other hand, are the main source of energy consumption in a bs, so, by improving the power amplifier performance, power consumption can be decreased. other techniques can also be implemented in order to achieve energy efficient networks but the quality of the provided service must not be jeopardized. ii. related work a. network basics mobile telephone systems have been through a major upgrade in the last few years and this development has resulted not only in the increase of mobile subscribers but also of their demands according to the trend of mobile telephone systems, after the subscriber connection request, the device is connected to the bs with the strongest signal at the given time. to understand and implement any technique involving mobile networks there are several important parameters that must be clearly understood. turning towards the heterogeneous networks, the simulation for each tier becomes difficult as the network complexity increases with the number of subscribers [6]. for example the macro bss are systematically distributed and have large coverage areas with higher transmitting powers in the range of 40w with large antenna gains. on the contrary, there are femto cells that are deployed with extreme efficiency and smaller coverage zones, evenly the femto cells can be placed in homes and small offices with central planning, with power in the range of 250mw. between these two extremes pico cells are deployed, mainly in the peak or huge traffic areas with limited coverage areas and, as estimated, 10 picos per macro cell is a suitable configuration. the pico cells are not randomly placed neither in a regular pattern and their transmit power is in the range of 250mw-2w. there are two ways to obtain energy efficiency in a cellular network. one way is to reduce the power consumption of the main energy consumers that are the power amplifiers and other hardware components by improving the performance of different hardware engineering, technology & applied science research vol. 8, no. 2, 2018, 2864-2868 2865 www.etasr.com azhar and shabbir: 5g networks: challenges and techniques for energy efficiency components or by using advanced software. the second method is the intelligent placement of bss in addition with the low power nodes. fig. 1. heterogeneous cellular network topology incorporating different forms of small cell deployments as an overlay on the macrocell network. b. deployment of small cells the small cells can operate in two major modes: open access mode, in which every user trying to connect is allowed access with a security check while in the closed access mode the access is given only to the registered user or to the subscriber authenticated by a procedure. there is another operating mode, the hybrid access mode, in which very limited resources are available to the users. substantial energy savings can be achieved by controlling the access mechanism and the sleep mode procedures. during the sleep mode of a bs, the user must be verified by the small cell circuitry or by a specific procedure which decides whether to provide service or not. choosing to place an unutilized bs into sleep mode is an efficient and direct way to help the energy saving in a network, but to implement sleep mode, one must first ensure the good signal quality of the other subscribers that are handed over to other cells. sleep mode in a cell brings coverage problems that must be considered [2, 5, 7]. there are two types of techniques of using the sleep mode in order to decrease the energy consumption of a network.  sleep mode implementation in macro bss  switching off small bss when not in use for adopting small cell bs sleeping modes different techniques and algorithms can be implemented:  small cell controlled sleep mode  core network control sleep mode  user equipment (ue) control sleep mode there has been a tradeoff in discharging traffic to macrocell and energy utilization of small cell. for implementing sleep mode procedures in macro bss some of the studies showed that the energy consumption of a network can be significantly reduced while retaining the proper coverage and user power utilization criteria. macro bss are considered to provide extensive coverage and hence their power consumption is huge. adopting sleep mode in femto cell bs can help in maintaining coverage but cannot contribute in energy saving. applying sleep mode in the macro bss can significantly reduce the energy consumption but can affect the coverage adversely. so this is tradeoff [7] between maintaining the coverage and the energy consumption by applying sleep mode in macro and femto bss (fbss). authors in [6] proposed an efficient solution of power conservation for huge number of femto cells in sleeping span. it is proposed that if femto cell cluster deployment has extensive coverage then it results in lesser energy usage which allows different femto bss to adopt various sleeping modes while macrobss serve to activate the fbss. iii. network model the considered network is a long term evolution network cellular model that is a three tier heterogeneous network. it comprises of the macrocells with the smaller size in surroundings and pico cells deployed inside houses for limited coverage to the indoor users hence indoor users are provided with femtocell access points. in highly populated areas giant macrocells are placed which are enough to provide coverage to a large number of users and the small cells are present in the surroundings to provide a bs for the traffic that is offloaded from macro bss and to increase network capacity to maximize the throughput. in the rest of the paper, preference is given to the power consumption performance of the smaller cell deployments and the femto cells are deployed inside homes for restricted use. the macro and pico cells are considered for evaluating the network performance. the numbers of macrocell and picocell sites are denoted by nmacro and npico respectively. it is considered in the given scenario that there are 70,000 mobile subscribers present in the area under evaluation with a total of 20,000 users uniformly distributed outdoors and 50,000 indoors. the indoor user distribution is calculated on an average of 5 users located in every household, so that there will be a maximum of 10,000 picocells to be deployed in all households. the subscribers located outside and inside are allowed to have the same traffic requirements that are between 500mbps and 900mbps.  assumption 1. there is no interference within the cell in the downlink.  assumption 2. for fbss the closed access mode is selected, i.e. fbss behave as regular bss and are in reach to the registered user equipment (ue) only. this access mode is considered to be used widely for households and small coverage area.  assumption 3. each ue can be served by at most one bs. cell selection is based on a maximum downlink received power of pilot signal. a single picocell in the network is considered to draw ƥpico =15w from the main power socket, can transmit up to 0.25w and can serve five simultaneous users. each macrocell site is comprised of three sectors that require a total power of ƥmacro =3kw. dynamic power saving modes are not considered here. for macrocells an average spectral efficiency of 1.7b/s/hz per macrocell sector is considered [7] and a 20mhz carrier bandwidth. engineering, technology & applied science research vol. 8, no. 2, 2018, 2864-2868 2866 www.etasr.com azhar and shabbir: 5g networks: challenges and techniques for energy efficiency the total energy consumption per annum (=8760 hours) of the network can be calculated by (1): εnetwork= (nmacro·ƥmacro + npico·ƥpico)·8760 (1) enetwork is calculated in wh and it is assumed that the core network components can be neglected for both macro and pico cells as they contribute very less to the total energy consumption. the combined voice and data traffic modeling of each subscriber is considered to be have a duty cycle of 17.15%. table i. network parameters serial number symbols description 1. nmacro number of macrocell sites 2. npico number of picocell sites 3. ƥpico power of a picocell or small cell 4. ƥmacro power of macrocell 5. εnetwork average network energy consumption per annum 6. ee energy efficiency 7. r average date rate provided of a base station 8. pc consumed power 9. ps signal power 10. pn noise power 11. coveragesmallcell small cell coverage detection by hardware 12. sn sniffer detection of rise in uplink power 13. rps received power strength 14. th threshold power 15. sc_power small cell initial processing and pilot signal transmission 16. ue_id to check user is registered or not 17. tin traffic intensity fig. 2. macrocell and femtocell connections there are three sleep mode schemes: small cell controlled sleep mode, core network controlled sleep mode and user equipment controlled sleep mode [8]. while examining these schemes it is observed that they are proposed only with the idea to shut down some of the specific hardware components that are not essential to remain constantly on, while the traffic pattern of the subscribers in the observed areas is not considered. all the areas have different user density and traffic pattern to determine the voice and data bits usage and demand. in this paper, the traffic of the area under observation is considered diversive. the user traffic intensity is broken up in two parts that are the normal and peak traffic hours. the macrocells are deployed in every area having high transmitting powers that can be utilized when ue could not find any small cell to provide coverage. thus small cells have a low power sniffer capability that detects any active call from ue unit to the macrocell. when there is no active calls made by any ue, the small cell is inactive and incase of any active users in the coverage area the small cells are activated. as the ue unit is detected inside the sensing range of small cell sniffer, the received power is increased. as the ue transmits at high power to connect to the macrocell so this rise in power is easily detectable and when ue is very close to the small cell, its pilot transmission is activated. if the requested user is allowed to the small cell so a macro to small cell handover takes place and the small cell serves the user, otherwise if the user is not allowed by the small cell, the macrocell serves the user. this process is repeated: for every user the small cell hardware determines the small cell traffic condition. the density of users is checked out periodically and when there is regular traffic load in a small cell, the power of cell is reduced to 40% of the total power delivered from the socket. when there is peak traffic load the power is 60% of the total power. if there are more users than the serving capability of small cell then some of the users are switched to be served by the nearby macrocell. a. working algorithm definitions:  coveragesmallcell=1 means user is in small cell coverage  sn=1 means sniffer detects rise in uplink power  sc_power=1 means small cell is activated and its pilot transmission is activated  ue_id=1 means the requested user is registered  tin=1 means traffic intensity is at normal condition and tin=0 means there is peak traffic algorithm: update coveragesmallcell and sn if rps>th update sc_power=1 update sc_power to macrocell if ue_id=1 assign sc_power=1 update tin if tin=1 p/=0.40*ppico else p/=0.60*ppico end end end engineering, technology & applied science research vol. 8, no. 2, 2018, 2864-2868 2867 www.etasr.com azhar and shabbir: 5g networks: challenges and techniques for energy efficiency iv. results a. users the total number of users indoors and outdoors and the maximum number of users are considered to be 70,000. users require different amounts of data rates at different times comprising a varied pattern of traffic. some times the data rate demand increases resulting in peak traffic hours. when the demand for data rate is under a threshold it is considered normal traffic hours. the number of users is plotted against the number of deployed pico cells in figure 3. the scheme named user equipment and the small cell controlled sleep mode for the reduction of average network energy consumption are taken as a reference [8]. the proposed scheme suggests reducing the input power or the distributed power according to the traffic pattern. if the traffic pattern is normal then the power is reduced to 40% of the input power and if the users increase their demands the supplied becomes 60% of the input power. b. energy a new parameter is calculated in this paper, the energy efficiency of the network. the energy efficiency parameter is very popular in determining the performance of the network and the most commonly used metric for the energy efficiency of a communication link is bit per joule, ee which is defined as the ratio of the total network throughput over the energy consumption within a given period, the unit of which is bits/joule. average network energy consumption is plotted in figure 4 against the number of pico cells. proposed normal and peak traffic hours power distribution scheme is applied to achieve energy saving. the normal traffic hour scheme provides the most efficient result but even in peak traffic the energy consumption is lower than that of sleep mode scheme. the graph of energy efficiency of pico cells considering different data rates, which is usually required these days is shown in figure 5. the energy efficiency of the network with different number of cells declines as the pico cell density increases but at higher data rates the energy efficiency shows improvement. the energy efficiency is calculated using (2): c ee r p  (2) fig. 3. energy consumption with picocells for different numbers of users fig. 4. energy consumed with number of picocells for different schemes fig. 5. energy efficiency with number of picocells for different data rates energy efficiency is evaluated for four different schemes (no sleep mode, ue, normal and peak hour mode) using data rate of 900mbps in figure 6. the change in the consumed power in every scheme leads to the result that energy efficiency during normal traffic hours is higher and even in peak traffic hours the energy efficiency is still higher than that of the small cell controlled sleep mode. fig. 6. energy efficiency with number of picocells for different schemes at 900mbps c. signal to noise ratio the signal to noise ratio is considered as one of the most important parameters of the communication system which is engineering, technology & applied science research vol. 8, no. 2, 2018, 2864-2868 2868 www.etasr.com azhar and shabbir: 5g networks: challenges and techniques for energy efficiency used to measure the effectiveness of the considered communication system or network. moreover, the signal quality is also dependent on the value of snr. snr is the main factor of how the signal is received big snr means radio receiver sensitivity performance. signal power snr noise power  or s n p snr p  (3) the energy efficiency is an important factor that needs to be monitored while the network is operational as much as when in rest mode. the energy efficiency against snr is plotted in figure 7 in decibels using different schemes. we see that, normal traffic hour scheme has the highest energy efficiency and the scheme with peak traffic even has energy efficiency greater than that of small cell controlled sleep mode. d. comparison from figure 6 we observe that that there is 14.7% improvement in the energy efficiency evaluation when small cell controlled scheme is compared with energy efficiency graph calculated during normal traffic, moreover there is 6.2% improvement when small cell controlled scheme is compared with energy efficiency graph calculated during peak traffic. fig. 7. energy efficiency with snr fot different schemes v. conclusion the results discussed in this paper illustrate that there is considerable improvement in the energy efficiency for both scenarios of the proposed scheme, the normal traffic mode and the peak traffic mode. when the number of users increases there is an increase in the demand of data rate, so the macro and pico cells are operated at full loads. the proposed scheme provides finer and better results when plotted for the normal traffic mode in the reduction of the average energy consumption of all the base stations. hence, it is concluded that the new proposed scheme of considering traffic pattern to reduce power supply according to the traffic mode gives profitable simulated results that show improvements in energy efficiency. references [1] y. s. soh, t. q. s. quek, m. kountouris, h. shin, “energy efficient heterogeneous cellular networks”, ieee journal on selected areas in communications, vol. 31, no. 5, pp. 840-850, 2013 [2] j. wu, y. zhang, m. zukerman, e. k. n. yung, “energy-efficient base-stations sleep-mode techniques in green cellular networks: a survey”, ieee communications surveys & tutorials, vol. 17, no. 2, pp. 803-826, 2015 [3] y. wang, y. zhang, y. chen, r. wei, “energy-efficient design of two-tier femtocell networks”, eurasip journal on wireless communications and networking, vol. 2015, 2015 [4] m. wildemeersch, t. q. quek, a. rabbachin, c. h. slump, a. huang, “energy efficient design of cognitive small cells”, ieee international conference on communications, pp. 2701-2706, budapest, hungary, june9-13, 2013 [5] j. peng, p. hong, k. xue, “stochastic analysis of optimal base station energy saving in cellular networks with sleep mode”, ieee communications letters, vol. 18, no. 4, pp. 612-615, 2014 [6] f. han, s. zhao, s., l. zhang, j. wu, “survey of strategies for switching off base stations in heterogeneous networks for greener 5g systems”, ieee access, vol. 4, pp. 4959-4973, 2016 [7] g. he, s. zhang, y. chen, s. xu, “energy efficiency and deployment efficiency tradeoff for heterogeneous wireless networks”, ieee global communications conference, anaheim, ca, usa, pp. 3189-3194, december, 3-7, 2012 [8] i. ashraf, f. boccardi, l. ho, “power savings in small cell deployments via sleep mode techniques”, ieee 21st international symposium on personal, indoor and mobile radio communications workshops, instanbul, turkey, pp. 307-311, september 26-30, 2010 engineering, technology & applied science research vol. 8, no. 3, 2018, 3009-3012 3009 www.etasr.com abbasi et al.: an investigation of temperature and wind impact on acsr transmission line sag … an investigation of temperature and wind impact on acsr transmission line sag and tension muhammad zulqarnain abbasi electrical engineering department iqra national university peshawar, pakistan babar noor electrical engineering department iqra national university peshawar, pakistan muhammad aamir aman electrical engineering department iqra national university peshawar, pakistan sidra farooqi electrical engineering department iqra national university peshawar,pakistan fazal wahab karam electrical engineering department comsats university abbottabad pakistan abstract—power transmission is mainly based on overhead transmission lines with conductors being supported by transmission towers. transmission lines are subjected to environmental stress (temperature changes, winds, snow etc), have an impact on the surrounding areas (visual pollution, building restrictions) and experience heavy losses due to resistive, magnetic and capacitive effects. thus, proper modeling and installation of these conductors are necessary. the conductors are generally installed in a catenary shape to minimize the capacitive effects and to balance the tension. this paper presents an investigation on the sag and tension behavior under different temperature and wind of acsr (aluminum conductor-steel reinforced) lines. four different cases of temperature and wind are tested to calculate sag and tension. simulation setup is done in etap (electrical transient and analysis program). results are recorded and discussed. keywords-acsr; overhead; line; transmission; conductors; span; sag; temperature; variation i. introduction overhead transmission lines are used to carry electrical power over long distances [1]. the performance of these transmission lines depends on their well-engineered modeling which is one of the major issues issue during the design stage. [2]. if the support structures are at the same height (which is rarely the case, however it provides a simplified base to study other parameters), then the sag is the height difference between the conductor’s lowest point and the height of the supporting points [3]. during the design (and construction) phase many parameters are to be considered. among them, the calculated tension, the safety distances (clearances), the location of rural areas etc. thus, mechanical modeling as well as geospatial data are usually employed [4]. the design stage results to certain routing, placement of towers, tower types, conductor sag and tension throughout the route [5]. different types of conductors are used for the transmission of electrical energy e.g. aac (all aluminum conductor), aaac (all aluminum alloy conductor), htls (high temperature low sag), acss (aluminum conductor, steel-supported), acsr (aluminum conductor-steel reinforced) with acsr being probably the most usual choice for transmission lines. acsr has a galvanized steel core that carries the mechanical load and outer strands made of high purity aluminum that carry the current [6]. to meet changing necessities, acsr is accessible in an extensive variety of steel substance from 7% by weight for the 36/1 stranding to 40% for the 30/7 stranding. early acsr outlines, for example, 6/1, 30/7, 30/19, 54/19 and 54/7 stranding, included high steel content, 26% to 40%, with accentuation on quality because of the fear of vibration fatigue. today, for bigger sizes, the most utilized standings are 18/1, 45/7, 72/7, and 84/19, involving a scope of steel substance from 11% to 18%. for the modestly higher quality 54/19, 54/7, and 26/7 standings the steel substance is 26%, 26% and 31%, respectively. the high-quality acsr 8/1, 12/7 and 16/19 standings are commonly utilized in special cases (e.g. intersections) [6]. overhead transmission lines are subjected to a variety of environmental stresses during their lifetime. sag or dip is considered in order to keep tension as low as possible. sag is conversely corresponding to the transmission line tension [6]. as the ground level varies in hilly areas so, the sag also does not remain constant [7].wind is a main common factor to most transmission lines and thus wind impact is often investigated (e.g. [6]). the minimum distance of a conductor from the ground is set by each county (and usually it also depends on the installations found-or to be constructedunder the line) but some usual distances are shown in table i. table i. voltage with ground clearance level voltage level clearance to ground less than 66kv 20 feet 66kv to 110kv 21 feet 110kv to 165kv 22 feet greater than 165kv 23 feet ii. mechanical design of a transmission line the sag of a transmission line depends on the following factors: the conductor’s weight, the span (distance between the sup and a. bet wit con t0= th tra ma hor b. bet c. act con app cal wh wh dv engineerin www.etasr pports), the tra d the temperat the catenary when a perf tween two ho th l be the spa nductor, t0 the =wc, ∅ the an hen if we co ansmission line ay be termed rizontal tensio so: s s = s = y=point p(a y = y = y = sag calculat by using (6) y c sag is maxim dmax d = for the whol substituting tween the poin wind effect o on transmiss ting horizontal nductor with plied from a p lculated with i ww = p.d.1 ww = p. (d + here ww = we with the effe hich is termed vertical = d ng, technology r.com ansmission lin ture. ry curve fectly flexible orizontal supp an distance, w e tension at th ngle between th onsider a tra e up to the poi d as s. thre on t0=wc, the c sin c ( ! a + a,b) measured c cos c (1 + ! c + tions we get: c = = dx mum when a = x = le conductor l s = a a = l/2 to nt o and the su and l = l on line sag sion lines, the lly and is mea length 1 m a point p horizo ice and withou without ice ef + 2t) .1 with ic eight of the con ect of wind th as vertical sag y & applied sci abbasi ne tension, the wire of unifo ports [8] it wi w the weight p he dip of the c he tension and avelling point int o (sag poi ee forces are weight i.e. w ! ⋯ above the orig ! ⋯ = sag is a + get the length upport end a or for the le e wind is usu asured in (kg/m and diameter ntally [8], the ut ice effect as ffect ce effect nductor in kg/ e sag makes a g and is equal t ience research et al.: an inves weather cond orm weight is ill form a cat per unit length conductor in k d the horizonta t p(a, b) o int), then this l acting on s s and the tens (1) (2) (3) gin vertically. (4) (5) (6) (7) (8) (9) h of the cond r b. evel supports. ually assumed m2). if we cons d and wind en the wind eff : /m2 an angle θ vert to h v stigation of tem ditions s hung tenary of the kg i.e. al axis. n the length s: the sion t. ductor to be sider a being ffect is tically a. sag and too dist line tran grid [11 the hor the ana the fig. on a a. tem and (ta b. win con are c. con tem vol. 8, no. 3, 20 mperature and ii modeling and the etap 12 g and tension o d distribution l to perform sa tribution lines es [10]. for sim nsmission line d station (pak ] is shown in e selected co rizontal. load newton raph alyzed using th different para 1. the transm iv four different acsr conduc case 1 five differen mperature i.e. d the correspo able ii). case 2 in case 2, the nd speed is hi nductor tension shown in tab case 3 in case 3, th nsidered with a mperature resul 018, 3009-3012 wind impact o ii. system d load flow a 2.6 [9] softwa of acsr trans line sag and ag and tension to ensure ade mulation setup e between ta kistan). the m figure 1. th onductor is a flow analysis hson method 1 he sag and ten ameters used. mission line mode v. result t cases of temp ctors with leve nt span length 5 oc with win onding values e temperature igher (50 n/m n changes whi ble iii. e maximum o a wind speed o lts to larger sa 2 on acsr trans implementat analysis are is used fo mission line. e tension modu n calculation fo quate operatin p, the model se arbela and sh model and its e tower heigh acsr and th is performed 10 (figure 1). sion library [1 el and its load flo ts and discus perature and w el supports. hs are analyze nd speed 25 n s of tension a is the same w m2). due to th ile sag is hardl operating temp of 25 n/m2. as g (table iv). 3010 smission line s tion r the estimatio etap transmi ule is an impo or transmission ng condition fo elected is a 50 heikh moham load flow ana hts are set to 1 e configuratio in etap base the losses are 12]. figure 2 s w analysis. ssion wind are consid ed under mini n/m2 using a and sag are sh with case 1 bu he wind effect ly affected. re perature (50 o s shown, the h sag … on of ission ortant n and or the 00 kv mmadi alysis 16 m. on is ed on e then shows dered imum acsr hown ut the t, the esults oc) is higher engineerin www.etasr tab spa (m 100 150 200 250 300 tab spa (m 100 150 200 250 300 ng, technology r.com fig. 2. etap ble ii. oper an ) wind spe (n/m 2 ) 0 25 0 25 0 25 0 25 0 25 ble iii. oper an ) wind spe (n/m 2 ) 0 50 0 50 0 50 0 50 0 50 y & applied sci abbasi editors for differ rating temperat eed ) sag 1.03 2.31 4.1 6.41 9.23 rating temperat eed ) sag 1.03 2.31 4.1 6.41 9.23 ience research et al.: an inves ent temperature a ture 5 oc tension 1967 1951 1927 1889 1825 ture 5 oc tension 2023 2007 1982 1943 1877 h v stigation of tem and wind effects o vol. 8, no. 3, 20 mperature and on acsr conduct tabl span (m) 100 150 200 250 300 tabl span (m) 100 150 200 250 300 018, 3009-3012 wind impact o tor for finding sag le iv. opera n wind spee (n/m 2 ) 25 25 25 25 25 le v. opera n wind spee (n/m 2 ) 50 50 50 50 50 2 on acsr trans g of different span ating temperatu ed sag t 1.24 2.79 4.96 7.76 11.17 ating temperatu ed sag t 1.24 2.79 4.96 7.76 11.17 3011 smission line s ns ure 50 oc tension 1625 1541 1433 1294 1119 ure 50 oc tension 1672 1585 1474 1317 1152 sag … engineering, technology & applied science research vol. 8, no. 3, 2018, 3009-3012 3012 www.etasr.com abbasi et al.: an investigation of temperature and wind impact on acsr transmission line sag … d. case 4 in case 4, temperature is set to 50 oc but the wind speed is set to 50 n/m2. the conductor tension increases while sag is hardly affected (table v). v. conclusion a significant factor in overhead transmission line design is sag and tension calculation which is performed considering the potential environmental stresses that the transmission line is expected to suffer throughout its life time. the most common environmental stress factors are wind and temperature. their impact is investigated in this paper, considering a part of an actual transmission line in pakistan modeled in etap. four different cases are considered and results show that an increase in temperature has a direct impact on sag whereas an increase in wind has a direct impact on tension. references [1] j. quintana, v. garza, c. zamudio, “sag-tension calculation program for power substations”, 42nd annual conference of the ieee industrial electronics society, iecon 2016, florence, italy, pp. 3889–3893, ieee, 2016 [2] m. keshavarzian, c. h. priebe, “sag and tension calculations for overhead transmission lines at high temperatures-modified ruling span method”, ieee transactions on power delivery, vol. 15, no. 2, pp. 777–783, 2000 [3] v. k. mehta, r. mehta, principles of power systems, s. chand, new delhi, india, 2011 [4] d. pylarinos, i. pellas, “incorporating open/free gis and gps software in power transmission line routine work: the case of crete and rhodes”, engineering, technology & applied science research, vol. 7, no. 1, pp. 1316-1322, 2017 [5] m. t. bedialauneta, i. albizu, e. fernandez, a. j. mazon, s. de arriba, “monitoring the tension and the temperature in an overhead line”, 16th ieee mediterranean electrotechnical conference (melecon), yasmine hammamet, tunisia, pp. 245–248, ieee, 2012 [6] f. i. oluwajobi, o. s. ale, a. ariyanninuola, “effect of sag on transmission line”, journal of emerging trends in engineering and applied sciences, vol. 3, no. 4, pp. 627–630, 2012 [7] southwire company, overhead conductor manual, southwire company, carrollton, georgia, usa, 2007 [8] a. k. akhani, mechanical design of overhead transmission lines, available at: http://top10electrical.blogspot.gr/2014/12/mechanicaldesign-of-overhead.html, 2014 [9] etap, “line sag & tension analysis”, available at: etap.com/product/line-sag-tension [10] c. j. soni, p. r. gandhi, s. m. takalkar, “design and analysis of 11 kv distribution system using etap software”, 2015 international conference on computation of power, energy information and commuincation, chennai, india, pp. 0451–0456, ieee, 2015 [11] m. aien, r. ramezani, s. mohsen ghavami, “probabilistic load flow considering wind generation uncertainty”, engineering, technology & applied science research, vol. 1, no. 5, pp. 126-132, 2011 [12] m. a. aman, s. ahmad, a. asar, b. noor, “analyzing the diverse impacts of conventional distributed energy resources on distribution system”, international journal of advanced computer science and applications, vol. 8, no. 10, pp. 390-396, 2017 microsoft word 3-pylarinos.doc etasr engineering, technology & applied science research vol. 1, no.2, 2011, 36-42 36 www.etasr.com pylarinos : a custom-made matlab based software to manage lc waveforms a custom-made matlab based software to manage leakage current waveforms dionisios pylarinos high voltage lab university of patras dpylarinos@yahoo.com abstract— leakage current (lc) monitoring is a widely employed tool for monitoring the performance of high voltage insulators. lc waveform monitoring is required to acquire a view of the phenomena experienced since the type of lc waveform’s shape is correlated with different types of electrical activity. in case of field monitoring, specially designed measuring systems, capable of operating under field conditions, have to be installed. the greek public power corporation (ppc) has issued a large project for monitoring the performance of outdoor insulators. a commercially available lc measuring system, was purchased and installed by ppc. the system was able to monitor various outdoor insulators, record several statistical values and intermittently record a lc waveform. the provided software lacked some capabilities that were required for certain research areas and a custom made software had to be developed. in this paper, two stand-alone matlab based softwares, “leakage current waveform file converter” and “leakage current waveform viewer”, both equipped with a user friendly gui, are presented. the first software was developed in order to automatically convert multiple files from the csv format (as extracted from the measuring system) to the mat format in order to allow data compactness and further processing. the latter software was developed in order to offer a tool for collective viewing, printing and extraction to jpeg format, of lc waveforms in groups of user-defined numbers. the latter function gives the opportunity for easy and fast creation of waveform archives. keyword: leakage current; waveform; data; software; gui; matlab i. introduction leakage current (lc) is a widely applied tool for monitoring the electrical phenomena experienced on outdoor insulators. leakage current waveform monitoring provides an actual view of the experienced phenomena since the shape of lc waveforms has been well correlated with different types of electrical activity. in addition, surface activity is strongly linked to environmental conditions and the accumulation and distribution of pollutants on the insulators’ surface and, therefore, monitoring leakage current can be an indirect method for evaluating the pollution severity of an installation site. it should be noted that field measurements are most suitable since they offer an exact view of the experienced phenomena and of insulators’ performance under real conditions. however, monitoring leakage current waveforms in the field is a rather complex task. the monitored insulators and the measuring system have to be installed in the field and to be subjected to various environmental and electrical stresses. further, approaching the measuring system is also an issue since it requires entering an outdoor hv site. therefore, specially designed measuring apparatuses that can operate unattended for long periods of time, under field conditions, have to be employed. such systems inevitably face restrictions and limited capabilities compared to systems designed for laboratory use. the greek public power corporation (ppc) has issued a large project to cope with the pollution problem in the case of crete, a greek island in the mediterranean sea [1-5]. as a part of this project a commercially available leakage current measuring system, on-line leakage current analyzer (olca) by ctlab [6], was purchased and installed at an 150kv high voltage substation. the system extracts and records a large amount of values calculated from the monitored lc and uses the time-window technique to intermittently record lc waveforms. the time-window technique allows the recording of a single leakage current waveform during a user-defined time window (e.g. one waveform per day) [7]. the system and the provided software was not oriented towards waveform monitoring and although it gave a large variety of functions related to extracted statistical amounts, it only allowed intermittently recording of waveforms and only a one by one viewing of recorded waveforms (the user can choose the starting and ending date). it also provided the ability to extract the measured waveforms to various csv files. as the amount of recorded waveforms increased over the years of monitoring, the need of developing custom made software emerged. two different stand-alone softwares were finally developed equipped with their own graphical user interface (gui) in order to maintain a user-friendly environment that would allow their use even by not specialized ppc personnel. ii. goals set for the developed software the software’s goals were to perform these basic functions: 1) conversion of multiple csv files, that contained different measurements recorded on the same insulator through different time-windows, to a single mat file representative of each insulator, that would allow further etasr engineering, technology & applied science research vol. 1, no.2, 2011, 36-42 37 www.etasr.com pylarinos : a custom-made matlab based software to manage lc waveforms processing. to save time, all csv files corresponding to different insulators should be converted sequentially. 2) navigation through lc waveforms, contained in a mat file, in groups of waveforms of a user-defined number. the user should have the capability to choose a partial sum of the waveforms contained in the mat file, using numerical or chronological criteria 3) automate the extraction of the various groups of waveforms to different jpeg files with user-defined names and dpi analysis 4) offer a user-friendly graphical user interface (gui) which would allow ease of use even by non-specialized personnel. 5) stand-alone capability of files and ease of execution desirably by providing exe files iii. developing environment & developed software two different softwares were developed using matlab, a high-level language and interactive environment manufactured by mathworks [8]. to achieve the first goal, “leakage current waveform file converter” was developed. to achieve goals 2 and 3, “leakage current waveform viewer” was developed. both softwares are equipped with a user-friendly gui and are provided in stand-alone executable formats (exe) (goals 4 and 5) iv. leakage current waveform file converter a. name pattern of csv files the measuring system stored all measurements in a not disclosed format that was used internally by the provided software. the provided software however was able to extract the measured waveforms in csv files. it should be noted that multiple csv files were created with each conversion, with some of them being null. all csv files followed the same pattern regarding their name as shown in figure 1. all files were named “olcaχ1peakwaveformschanχ2cχ3.csv” with x1 being the device model number, x2 being the number of the monitored channel (one channel for each monitored insulator) and x3 being a numerical value. the value x3 corresponded to the actual number of files minus one, since the first file had a zero value of x3. the files shown in figure 1 with 1kb size are null. the provided software created several such files when exporting measured waveforms to csv files. further, it should be noted that the number of extracted files differ in each case and the manufacturer did not provide any information for x3 or for the creation of null files. fig. 1. a screenshot from a folder containing csv files as extracted by the measuring system b. software gui and user settings the leakage current waveform file converter took into account the format of the cvs files and provided a gui where the user could define each value, as shown in figure 2. in addition, the user could decide if he wanted to convert just one csv file or perform batch conversion. the user could also choose to sequentially convert files corresponding to more than one channel. in case of batch conversion the user should set the number of the olca model, the maximum value of x3, the directory where the csv files are located, the number of channels and finally the destination directory where the mat files should be stored. c. converting files after the user defined all factors, the conversion would start when hitting the “convert” button. this procedure could be extremely time consuming so a “process info” button was added in order to give a view of the procedure and offer a double-check opportunity before converting. the message displayed when pressing the “process info” button is shown in figure 3. fig. 2. leakage current waveform file converter fig. 3. an example of pressing the “process info” button etasr engineering, technology & applied science research vol. 1, no.2, 2011, 36-42 38 www.etasr.com pylarinos : a custom-made matlab based software to manage lc waveforms d. program info a “program info” button was added in order to provide users with some information about the software as shown in figure 4. it should also be noted that when performing the conversion, a message appears that informs the user about the file the number of waveforms contained in the csv file that is currently converted and finally for the path containing the mat file. fig. 4. the message displayed when pressing “program info” e. format of csv files τhe software takes under consideration the format of the csv files which contain waveforms of 960 data points [7] as shown in figure 5. the first 5 rows of each file were occupied by general data and an empty line is inserted between different waveforms as shown in figure 5. fig. 5. some of the data in a csv file f. format and variables of each mat file the “leakage current waveform file converter” creates a mat file for all measurements regarding the same channel (insulator) (e.g. olca313ch0) based on the information provided by the user in paragraph iv-b. each mat file contains the measurements in a much more organized format. in addition, it allows the application of various signal processing techniques as employed in [4, 7, 9]. figure 6 shows the variables in a mat file that contains 7497 waveforms, as portrayed by matlab when using the “whos” command. as shown, the variables include two vectors that contain date and time information about each measurement and two matrices (“current” and “voltage”) that contain all current and voltage waveforms, with each waveform placed in an individual column. in addition, an “id” variable characterizes the sum of the waveforms and an “idwavetag” vector contains an individual name tag for each waveforms. the new form of the organized data gives the user far better viewing, managing and processing abilities compared to the csv version. fig. 6. variables contained in a mat file g. economy of space and compactness of mat files it should be noted that a significant save of space and a much more compact data appearance was achieved file-wise. each olca device monitors nine channels (numbered 0 to 8). all measurements from each channel were contained in a single mat file instead of numerous csv files. results of using the leakage current waveform file converter on csv files that were exported from two different olca devices are shown in table 1. the data now was included in just 18 files (instead of 477) and a significant save of space was achieved (from 2.92 gb to 32.75 mb) table i. results of using leakage curren t wavefo rm file converter olca device 1 2 sum number of csv files 225 252 477 size of csv files 350.6 μβ 2.57 gb 2.92 gb number of ματ files 9 9 18 size of ματ files 3.85 μβ 28.9 μβ 32.75 μβ total number of waveforms 8487 67377 75864 etasr engineering, technology & applied science research vol. 1, no.2, 2011, 36-42 39 www.etasr.com pylarinos : a custom-made matlab based software to manage lc waveforms v. leakage current waveform viewer the mat files created by “leakage current waveform file converter” can then be loaded into the “leakage current waveform viewer”. the “leakage current waveform viewer” was developed to satisfy goals 2 and 3 mentioned in paragraph ii. the gui of the software if shown in figure 7. fig. 7. leakage current waveform viewer a. loading a mat file at first the user has to load the mat file created by “leakage current waveform file converter”. it is obvious that using matlab one can alter (e.g. delete data correlated with certain waveforms) or unite different mat files. when a mat file is loaded, “leakage current waveform viewer” shows the number of waveforms that are contained in the file, the “id” variable that characterizes the group of waveforms (set by the user, may represent the type of the monitored insulator, the channel number combined with the olca model etc) and the time period that these measurements cover. an example is given in figure 8, when loading the mat file already mentioned in paragraph iv-f. “leakage current waveform viewer” now shows to the user the number of waveforms contained in the file (7497), the “id” variable (in this example it is set by the user to be “compb” which characterizes a monitored composite insulator), and the time period (from 26/11/2002 to 06/08/2008). to define the time period, “leakage current waveform viewer” uses the first and last value of the “date” variable (see paragraph iv). b. grouping the user is now ready to view, extract or print the waveforms contained in the file. at first, he should decide upon the group of waveform that he wants to manipulate. in the area with the heading “view” he can choose whether he wants to view all waveforms or just a part of them, defining either their number (e.g. from waveform number 556 to waveform number 2147) or the time period that they cover (by defining the year and the starting and ending month). the waveforms will be displayed in groups and the next step for the user is to define the number of waveforms in the group. the default value is 10 but several other values can be selected (1, 4, 6, 8, 10, …, 18, 20). fig. 8. leakage current waveform viewer (mat loaded) c. viewing leakage current waveforms to view the waveforms the user presses the “view waveforms” button. then, “leakage current waveform viewer” opens a new window as shown in figure 9. in this figure, the measurements portrayed were provided by the manufacturer with the purchase of the system. fig. 9. the view waveforms window (groups of ten) etasr engineering, technology & applied science research vol. 1, no.2, 2011, 36-42 40 www.etasr.com pylarinos : a custom-made matlab based software to manage lc waveforms d. the navigation menu the navigation menu is located at the top left of the window. a zoom-in version of the navigation menu is shown in figure 10a. the user can move to the next or previous group or stop. when he reaches the last group (in this case the last ten waveforms) then the navigation menu changes to the one shown in figure 10b giving him the opportunity to move to the first waveforms. (a) (b) fig. 10. the navigation menu: a) normal b) at the last group e. the main view window the main view window (the window that contains the waveforms) includes various informations. the window title contains the kind of measurement, the axis units and the path of the filename that contains the waveforms. a zoom in of the window title is shown in figure 11. further, some of the usual image managing buttons (move, save as, zoom etc) are also available. in addition, to the left of each waveform appear its place in the group (s. 1 stands for signal 1), their unique id tag (contained in the variable “idwavetag”) which contains the olca model, the channel and the number of the waveform in the mat file, the time when the waveform was recorded and the date. the “idwavetag” may seem redundant in the case of figure 11 but one should consider the possibility of choosing to view e.g. waveforms 75 to 154. in this case the first waveform (waveform 75) will have the first place in the selected group (s.1) but its” idwavetag “will portray its actual place in the file (75). in addition, using matlab the user can easily unite two mat files that contain waveforms from different channels and load them into “leakage current waveform viewer”. the “idwavetag” will also prove valuable in this case. an example is shown in figure 12. fig. 11. view window. detail of the window title fig. 12. viewing measurements recorded in different channels (zoom in) f. exporting & printing leakage current waveforms the images in the view waveforms window can be automatically printed or exported to jpeg image files. in case of exporting, the user has to define the destination folder for the jpeg files by pressing the “define directory” button. each group of waveforms will be printed in one page and/or exported in one jpeg file. that means that if a set of 120 waveforms is chosen to be displayed in group of 10 waveforms, then 12 jpeg image files will be created. the first image will contain waveforms 1-10, the second will contain waveforms 11-20 and so on. the user has to provide a prefix for the name of the jpeg files. for example if the user enters the prefix “images” then the first jpeg image file will be named “images_0001”, the second will be named “images_0002” and so on. the user can also define the dotsper-inch (dpi) analysis of the images. finally the user can choose to print or export or do both by pressing the corresponding buttons (“print”, “save”, “save & print”). g. process info the exporting and/or printing procedure can be time consuming. for example, when a mat file containing more than 7000 waveforms is loaded in the software, as the one showed in figure 8, and a grouping of 10 is chosen, this will result to the creation of more than 700 jpeg files. needless to say that the user should be sure about his settings before the procedure starts. therefore a question message has been added etasr engineering, technology & applied science research vol. 1, no.2, 2011, 36-42 41 www.etasr.com pylarinos : a custom-made matlab based software to manage lc waveforms as shown in figure 13. the message is different for each case (“save”, “print” or “save & print” of waveforms). (a) (b) (c) fig. 13. the “proceed” message in case of a)exporting to jpeg b) printing to paper c) exporting & printing h. program info the “program info” offers some information about the software. the message displayed when pressing the “program info” button is shown in figure 14. fig. 14. the message displayed when pressing “program info” vi. conclusions leakage current monitoring is a well established tool for monitoring outdoor high voltage insulators in the field. however, specially measuring designed systems have to be installed capable of operating unattended under real field conditions. the greek public power corporation purchased such systems as a part of a large scale project, to investigate and battle with the pollution of high voltage insulators in the cretan transmission system. in this paper, two stand-alone matlab based softwares that were developed in order to offer some custom capabilities that the provided software lacked, are presented. “leakage current waveform file converter” was developed to convert csv files, containing measurements exported from the measuring system, to mat files that would allow further processing. further, the software provided data in a much more compact form and allowed a significant save of disk space. “leakage current waveform viewer” was designed to manage the mat files created by “leakage current waveform file converter”. the software is able to divide the data in userdefined groups and display each group sequentially, providing a navigation menu. the user can also decide to manipulate only a part of the data-set using numerical or chronological criteria. the software provides the capability of automatically exporting all waveform groups to different jpeg files named using a user-defined prefix and an automatically assigned numerical value. the user can set the desired dpi analysis. finally, the software can automatically print images without exporting them, or export them and print them to paper at the same time. both softwares are equipped with user friendly gui’s that allows their use by non-specialized personnel and are distributed in exe format. they are currently employed to extend and enhance the research and investigation of field leakage current waveforms. references [1] k. siderakis, d. pylarinos, e. thalassinakis, i. vitellas, e. pyrgioti, “pollution maintenance techniques in coastal high voltage installations”, eng. technol. appl. sci. res., vol. 1, no. 1, pp. 1-7, 2011 [2] k. siderakis, d. agoris, “performance of rtv silicone rubber coatings installed in coastal systems”, electr. power syst. res., vol. 78, no. 2, pp. 248-254, 2008. [3] d. pylarinos, s. lazarou, g. marmidis, e. pyrgioti, e. thalassinakis, j. stefanakis, “investigation of leakage current on high voltage polymer (rtv sir) coated insulators”, iasted int. conf. on power and energy systems, usa, 2008 [4] d. pylarinos, s. lazarou, g. marmidis, e. pyrgioti, “classification of surface condition of polymer coated insulators using wavelet transform and neural networks”, icwapr int. conf. on wavelet analysis and pattern recognition, pp. 658-663, china, 2007 [5] e. thalassinakis, j. stefanakis, k. siderakis, d. agoris, “measures and techniques against pollution in the cretan transmission system”, europes european power and energy systems, greece, 2002 [6] ctlab electronic development manufacturing, http://www.ctlab.com/ [7] d. pylarinos, k. siderakis, e. pyrgioti, e. thalassinakis, i. vitellas, “impact of noise related waveforms on long term field leakage current measurements”, ieee trans. dielectr. electr. insul., vol. 18, no. 1, pp. 122-129, 2011 [8] mathworks web page: http://www.mathworks.com/ etasr engineering, technology & applied science research vol. 1, no.2, 2011, 36-42 42 www.etasr.com pylarinos : a custom-made matlab based software to manage lc waveforms [9] d. pylarinos, k. siderakis, e. pyrgioti, e. thalassinakis, i. vitellas, “automating the classification of field leakage current waveforms”, eng. technol. appl. sci. res., vol. 1, no. 1, pp. 8-12, 2011 authors profile dionisios pylarinos was born in athens in 1981. he received a diploma degree in electrical and computer engineering from the university of patras in 2007. presently he is with the high voltage laboratory of the department of electrical and computer engineering at the university of patras. he has worked as a scientific consultant for the greek public power corporation (ppc). his research interests include outdoor insulation, electrical discharges, signal processing and pattern recognition. . microsoft word etasr_v11_n1_pp6724-6729 engineering, technology & applied science research vol. 11, no. 1, 2021, 6724-6729 6724 www.etasr.com sahel et al.: logo detection using deep learning with pretrained cnn models logo detection using deep learning with pretrained cnn models salma sahel college of computer and information systems umm al-qura university makkah, saudi arabia salma.a.sahel@gmail.com mashael alsahafi college of computer and information systems umm al-qura university makkah, saudi arabia m.e.alsahafi@hotmail.com manal alghamdi college of computer and information systems umm al-qura university makkah, saudi arabia maalghamdi@uqu.edu.sa tahani alsubait college of computer and information systems umm al-qura university makkah, saudi arabia tmsubait@uqu.edu.sa abstract—logo detection in images and videos is considered a key task for various applications, such as vehicle logo detection for traffic-monitoring systems, copyright infringement detection, and contextual content placement. the main contribution of this work is the application of emerging deep learning techniques to perform brand and logo recognition tasks through the use of multiple modern convolutional neural network models. in this work, pre-trained object detection models are utilized in order to enhance the performance of logo detection tasks when only a portion of labeled training images taken in truthful context is obtainable, evading wide manual classification costs. superior logo detection results were obtained. in this study, the flickrlogos-32 dataset was used, which is a common public dataset for logo detection and brand recognition from real-world product images. for model evaluation, the efficiency of creating the model and of its accuracy was considered. keywords—logo detection; deep learning; convolutional neural networks; flickrlogos-32 i. introduction logo detection (ld) is important for several real-world applications [1] by enhancing the ability of users/systems to recognize the identities of items by their brand logos. as a result, ld is an area that many companies aim to explore to captivate their clients and make informed decisions regarding brand development [2]. ld is a sub-field of object detection which is the task of identifying wherever there is a specific object in an image. we are not only interested in simply identifying the existence of an object, but also to locate it within the image. there are many classical approaches to object detection such as key point-based detectors and local feature-based recognition. more recently, there has been a growing interest in using convolutional neural networks (cnns) to perform object detection tasks. this approach usually starts by capturing images by camera devices, probably experimenting with different resolutions, and then processing the images in order to be able to classify the images of the objects contained within [3]. more specifically, three steps can be used in traditional object detection and classification approaches, and these are: informative region selection, feature extraction, and classification [4]. in region selection, it is probable to scan the whole image consuming a multi-scale sliding window, as numerous substances (objects) might appear in different positions with several sizes and feature ratios. there are differences between ld and logo recognition (lr). lr is used to detect a logo's identity in an image, whereas ld is considered to detect a logo's position [5]. both ld and lr are based on classification methods. for example, [6] proposed the use of cnns for a recognition pipeline comprising a recall-oriented logo region. a cnn, in general, is considered as a widely used method in both ld and lr. research in ld has been addressed in several directions where general object detection with deep learning methods has always been an excessive realization. construction of a deep object detection model classically needs many categorized training data collected using wide manual classification. in this paper, rcnn, frcnn and retinanet were used for logo detection. this paper presents the current ld methods and sheds light on common datasets used in previous research. ii. literature review one of the aims of this research is to investigate the area of ld and examine the state-of-the-art approaches. it should be noted that due to the desire to explore new trends in ld, which is a very fast-growing area, we focused on papers published during the last five years or papers that have shown a considerable impact in terms of number of citations. table i shows the summary of the studied and referenced articles. corresponding author: tahani alsubait engineering, technology & applied science research vol. 11, no. 1, 2021, 6724-6729 6725 www.etasr.com sahel et al.: logo detection using deep learning with pretrained cnn models table i. summary of the reviewed articles reference year approach dataset performance [7] 2019 yolov3 vld-3 76.6-98.8 [8] 2017 faster r-cnn flickerlogo 0.52-0.67 [1] 2019 osld sdml blac and flickr-32 84.5-90.9 [9] 2018 retinanet inbreast guro 86-1.00 [10] 2017 faster r-cnn flickrlogos map 51-66% [11] 2020 faster r-cnn and yolov2 weblogo-2m map 36.8-46.9 [12] 2017 densenet16 -, resnet101 -, vgg16 flickrlogos-32 sportslogos 0.37-0.46 [13] 2017 scalable logo self training (slst) weblogo-2m map 34.37% [14] 2007 ann and support vector machine (svm), fisher classifier tobacco-800 39.3-84.2% [5] 2015 rcnn – frcn – sppnet logos-18 test set logos-160 test set 81.3-95.2% [15] 2019 faster r-cnn, ssd, yolov3 flickrlogos-32, pl2k 0.565 map [6] 2017 cnn flickrlogos-32 logos-32plus 0.1-95.8% [2] 2016 fast region-based convolutional networks (frcn) ilsvrc, flickrlogos-32 map 54.5-73.74% [16] 2018 retina u-net, mask r-cnn, faster r-cnn +, u-faster rcnn, + detu-net lidc-idri map 29-50.5% [17] 2017 faster r-cnn flickrlogo-32 toplogo-10 map 20.5-81.1% [18] 2020 densenet-cnn flickrlogo-32 92.8% a. logo detection methods several frameworks have been proposed in the ld area, and experimental evaluations show different results. for example, in [2], cnns were shown to be a reliable technique for ld, containing several layers that are similar to simple and complex cells in the primary visual cortex. in particular, it adopts a hierarchical structure that enables the recognition of visual patterns arising from image pixels. the convolutional layers alternate with other subsampling layers that have varying sizes. as a result, they help enhancing image clarity and improve ld. other researchers [11, 13] indicated that the technique of scalable logo self-co-learning can self-discover informative training pictures from the blaring web information. in particular, this can be helpful to enhance model capacity in a cross-model co-learning approach [13]. the scalability of the logo is of concern because it determines the level of categorization possible and the efficiency of the ld approach. the process enables the collection of many unconstrained images for review. the images need not undergo any finegrained instance level of labeling for the necessary aspects to become clearer to the users. however, sometimes, the use of proxies for the scalable lr enables the classification and identification of the logos [15]. in particular, this is because there is no clear definition of a logo and logos vary like brands. the proxies, however, facilitate the re-training of images to integrate all variations. although it may seem impractical, the utilization of proxies in scalable lr involves the use of a universal logo detector and a few-shot logo recognizer. as a result, the use of proxies can become a reliable tool because it can enable the users to enhance clarity and assess the image better. additionally, companies can utilize the proxies in scalable lr to achieve high precision and make informed decisions. authors in [16] used retina u-net for semantic separation in classifying medical images. retina u-net is a useful tool for logo detection and classification, which can guarantee the desired results for image analysis. retina u-net can be a reliable ld and image markup technology. companies can rely on this technology to enhance the clarity of their brands. they can make brands more attractive and can be easily valued by customers. in this regard, retina u-net can become a suitable tool through which companies can attract customers. authors in [14] proposed an ld method which used a boosting approach through multiple image scales particularly for ld and image extraction. it uses a trained fisher classifier, a kind of deep learning approach, to perform initial classification that can identify features from document context and linked components. in particular, each logo area is classified by a cascade of simple classifiers to continuously improve scales. it is considered to be able to detect regions to be refined and ignores false alarms. early research produces weak performance of faster r-cnn [10]. therefore, the researchers in [8, 10] introduced a fast rcnn approach which is based on deep neural networks where the convolutional layers are used to extract gradually abstract feature representations by using previous learned convolutions, then apply a non-linear activation task to the image. more recently, authors in [18] proposed a transfer-learning-based method aided by the use of densely connected convolutional networks (densenet) for logo recognition. they applied their proposed method to the flickerlogos-32 dataset. in computer aided diagnosis (cad) systems [9], the system utilizes a mass detection model based on retinanet. retinanet is a kind of deep cnn, where an object detector is mainly expected as a one-stage object detector that is fast and effective while achieving improved performance. however, new research in this area [11] argues that the current ld approaches typically consider a small number of logo sessions, with limited images per session and presume fine-tuning associated to each object annotation. however, this produces the problem of limited ability to be scalable to dynamic applications in the real world. their proposed approach tries to overcome these challenges by ignoring manual labeling and directly exploring web data learning principles. in particular, it proposes an incremental learning approach, named scalable logo self-co-learning (sl 2). this method can automatically self-discover informative training images from noisy web data for increasingly improving model ability in a cross-model colearning means. engineering, technology & applied science research vol. 11, no. 1, 2021, 6724-6729 6726 www.etasr.com sahel et al.: logo detection using deep learning with pretrained cnn models b. datasets used the datasets that have been used in recent studies come from various sources. authors in [14] utilized the tobacco-800 dataset which consists of 42 million pages of documents, whereas authors in [8, 10] have used four publicly available datasets. authors in [11] introduced a very large logo dataset which contains: 2,190,757 images of 194 logo classes, named “weblogo-2m” by designing an automatic approach for data collection and processing by automatically sampling web logo images from social media sources (twitter). in other studies, such as [2, 6, 15], the public dataset flickrlogos-32 was used. this dataset is one of the most commonly used datasets in the field of logos, it contains 8,248 pictures, with 32 images per brand. authors in [15] introduced a new logo dataset containing 2000 logos and 295k images collected from amazon, called pl2k. the dataset used in the current paper is flickrlogos-32 [19]. this dataset has 32 logos each has many examples and it also has well-articulated annotations. this is the most prevalent logo detection dataset containing and it has been used for the purposes of this research for comparisons with existing approaches in the area. sample data from this dataset can be seen in [6, 19]. c. evaluation stage evaluation of the considered methods has been conducted in a variety of ways through several steps. the framework presented in [10] has been evaluated on the dataset in order to improve the detection performance on small object instances. the evaluation of the approach presented in [8] was conducted on the dataset improving the rpn performance from 0.52 to 0.71 (map) and the detection performance from 0.52 to 0.67 (map). a description of the evaluation metrics will be presented in the following sections. other researchers [2] used metrics of performance for measuring ld performance such as the average precision (ap) for every logo class and the mean ap (map) for all classes, where the detection is considered true when the intersection over union (iou) overtakes 50%. in addition, two evaluations per each detector type (single and five shot) were used in [15]. the faster r-cnn model worked best with a map of 0.56558, where the map was decided by region proposals with a class detection threshold of 0.5. for example, the proposed models were trained on pl2k and evaluated on flickrlogos32 to achieve new state-of-the-art performance of 56.55% map. in the evaluation stage in [15], the researchers used an evaluation metric based on labeled ground truth to measure the quality of ld. in [11], the evaluation has been conducted by using extensive comparative evaluations demonstrating the superiority of sl 2 over the state-of-the-art contemporary web data learning methods and strongly weakly supervised detection models. the experimental evaluation of [9], shows that the considered model extracts inconsistent mass features from the single dataset as well as the combined dataset whose mammograms are collected from different sources, which proposes the ability of the model to be applied to different groups. the evaluation of the proposed model in [9] has been addressed in setups consuming pretrained weights, which uses weights pre-trained on guro, training and testing on inbreast. this shows that consuming the pre-trained weights on datasets produces the same performance as directly consuming datasets in the training stage. iii. methodology the studied dataset has been examined with the use of some pre-trained deep learning models for object detection based on cnns. a. cnn models 1) retinanet retinanet [20] consists of a support network, and binary sub-nets that use various features of the maps of the provision network. one establishment subnet categorizes the instance of the image, and one regression subnet registers out the bounding box. the model workflow is: • loading and preparing training data. • training a deep neural network using retinanet. • evaluating the model. • using the model for inference. 2) faster r-cnn faster r-cnn [21] assimilates the area suggestion algorithm into the cnn model. faster r-cnn model is composed of an rpn (region proposal network) and a firm rcnn with communal convolutional feature layers. the model workflow is: • using the image classification pre-trained model. • fine-tuning the rpn for the area proposal task, which is prepared using the pre-trained image classification model where optimistic samples have iou>0.7, while undesirable samples have iou <0.3. o slips a small n×n three-dimensional gap over the convention of the feature map of the complete image. o at the middle of each gliding window, it forecasts numerous areas of numerous balances and ratios concurrently. a presenter is a grouping of gliding the window center, scale, and ratio. for instance, for 3 scales + 3 ratios, then k=9 anchors at each gliding position. • trains the fast r-cnn ld model by the usage of the proposals formed by the current rpn. • uses the fast r-cnn system to modify the rpn training. through the observance of the public convolutional layers, solitarily fine tunes the rpn-precise layers. at this level, the rpn and the finding network have public convolutional layers. 3) r-cnn r-cnn [22] is one of the most common deep learning frameworks used to detect objects on a large scale. it is a combination of cnns and region suggestion. the model workflow is as follows: engineering, technology & applied science research vol. 11, no. 1, 2021, 6724-6729 6727 www.etasr.com sahel et al.: logo detection using deep learning with pretrained cnn models • train the cnn network for image classification. • propose category-independent regions of interest by selective search. • the areas of the objects are warped to make sure that they are in place for the fixed size needed by the cnn. • move on with the fine-tuning of the cnn which is warped over the proposal areas for k + 1 classes. the extra class is associated with the background (does not have many objects of interest). • assure that every image in the area, with one or more of the forwarded flows of movement throughout the cnn makes a feature vector. • decrease the localization of the errors. b. evaluation measures 1) localization and intersection over union as can be seen in [22], the object detection of the dataset can be estimated accurately by the iou which is known to be used in the evaluation stage [23]. the predication of locating the object is determined on how strict the model is, by the evaluation of the function of object localization of the model. this is usually accomplished by drawing a bounding box around the desired object [22]. the function of localization is evaluated by the iou: iou � ���� ��� ��������� �� ��� ∩��� ���� ���� �� ���� ���� ��� ��������� �� ��� ∪ ��� ���� ���� �� ���� � 0.5 (1) each object is associated with one bounding box, but in some cases, the bounding boxes might be more than one. when there are more than one bounding boxes regarded to one object, one box will either be true positive (tp) or false positive (fp) and the other box is vice versa. yet, an object can be recognized as false negative (fn) when there is no predicted bounding box. 2) mean average precision map is one of the most popular metrics in measuring the accuracy of object detectors, e.g. r-cnn. it is also called precision-recall for detecting bounding boxes. precision-recall is considered to measure how the network understands importance and how it removes invalid information. map enhances the information produced by precision-recall. the prediction is more accurate when the map score is higher. map � ! ∑ api�$ ! (2) the ap is the average of class predictions (n) measured over various thresholds, i.e., it is the average of precision values for various recall levels [24]. the current study aligns with the approach in [24]. in particular, in the current study, the ap curves for each logo class are based on the pre-trained models (r-cnn, faster r-cnn, retinanet). iv. implementation initially, we started by cleaning the dataset and checking if the annotation files were correct. then the dataset needed to be fed into each of the training models. since it takes too much time to build the model, the model needs to be stored and then reused. after that, we chose samples of pictures from the dataset to train each model on them, in order to produce weights. the remaining images were used for testing the models in order to find each one's testing accuracy. for implementation, colab notebook was used to execute code on google’s cloud servers. hardware specifications were: cpu: amd ryzen 7, gpu: 2080ti, ram: 16gb, gpu capacity needed for the build: 2.3gb for r-cnn, 1.5gb for fr-cnn, and 3.1gb for retinanet. v. results and discussion it has been found that r-cnn takes more time and gpu space, but obtained higher accuracy. hence, the increased accuracy comes with a cost. this is because the fr-cnn first applies cnn and then the zones where compared to the rcnn which makes the regions first and then applies cnn. when comparing the r-cnn and the fr-cnn to the retinanet, it was revealed that the retinanet takes fewer test time when compared to r-cnn, it demands more training time when compared to the fr-cnn and it takes more space than both r-cnn and fr-cnn because it checks layers more, because the quality of the image matters less to retinanet. fig. 1. r-cnn performance. as shown in figure 1, there is a considerable increase in the testing accuracy whereas there is a decrease in the training loss for the first 1000 iterations. similarly, as shown in figure 2, when the iterations increase, the training loss decreases linearly and the test accuracy increases significantly. for the first 600 iterations the training loss is close to 0.3. as shown in figure 3, with an increase in the training iterations, the loss decreases linearly and the test accuracy increases significantly for the first 3000 iterations, whereas the training loss is close to 0 after that. table ii shows the comparison of the results of the current and previous research. we have outperformed the faster r-cnn model of previous research results by 12% in map. we achieved high accuracy by training the dataset on the rcnn model, reaching 99.8%, a difference of 8.8% from [6]. our model also achieved a high accuracy of 95.2% with retinanet engineering, technology & applied science research vol. 11, no. 1, 2021, 6724-6729 6728 www.etasr.com sahel et al.: logo detection using deep learning with pretrained cnn models model with threshold 0.5, a difference of 0.6% behind the model presented in [24], at the same threshold. fig. 2. faster-rcnn performance. fig. 3. retinanet performance. table ii. result comparison for methods that used the flickrlogos-32 dataset method precision recall accuracy map [25] 0.909 0.845 0.884 [26] 0.896 [2] 0.955 0.908 [6] 0.976 0.676 0.910 [18] 0.928 [12] 0.464 [15] 0.798 0.565 [22] retinanet: threshold 0.5 0.948 0.829 0.946 0.620 ours: retinanet: threshold 0.5 0.952 0.40 ours: rcnn 0.998 0.65 ours: faster r-cnn 0.936 0.74 vi. conclusion applying cnns in ld is a common process for such purposes. many network architectures have been applied, resulting in varying accuracy. the process involves many challenges as the logos may appear on any scale, position, and under different perspectives in an image. the traditional techniques for lr include key point-based sensors and local feature-based recognition. however, by using different cnn models such as r-cnn and fr-cnn, better results can be achieved as it has been discussed in this study. as newer cnn models get available, more experiments should be done, taking into account the trade-offs between accuracy, training and development cost. references [1] m m. bastan, h.-y. wu, t. cao, b. kota, and m. tek, “large scale open-set deep logo detection,” nov. 2019, accessed: jan. 08, 2021. 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[online]. available: http://arxiv.org/abs/1510. 02131. engineering, technology & applied science research vol. 9, no. 1, 2019, 3786-3789 3786 www.etasr.com tunio et al.: effect of coarse aggregate gradation and water-cement ratio on unit weight … effect of coarse aggregate gradation and watercement ratio on unit weight and compressive strength of no-fines concrete zaheer ahmed tunio department of civil engineering, quaide-awam university of engineering, science & technology, pakistan zaheerahmedtunnio@gmail.com bashir ahmed memon department of civil engineering, quaide-awam university of engineering, science & technology, pakistan basher_m@hotmail.com noor ahmed memon department of civil engineering, quaide-awam university of engineering, science & technology, pakistan nahmedmemon@gmail.com nawab ali lakho department of civil engineering, quaide-awam university of engineering, science & technology, pakistan nawablakho@gmail.com mehboob oad department of civil engineering, quaide-awam university of engineering, science & technology, pakistan engrmahboob04@gmail.com abdul hafeez buller department of civil engineering, quaide-awam university of engineering, science & technology, pakistan engrabdulhafeezbuller@gmail.com abstract—self-weight of a structure comprises a major portion of the overall structural load which causes conservative structure design. reduction of structures’ self-weight is an active area of research today. one of the options is to use lightweight concrete and no-fines concrete is one of its types. this type of concrete is made with coarse aggregates, cement, and water. from the density point of view, it is the lighter concrete compared to normal weight concrete but it exhibits less strength. normally nofines concrete is manufactured with uniform size aggregates. the performance of no-fines concrete depends on the cementaggregate ratio and water-cement (w/c) ratio. this study focuses on investigating experimentally the effect of gradation of coarse aggregates and the w/c ratio on unit weight and compressive strength of no-fines concrete. nfc with two cement-aggregate ratios (1:6 and 1:8) having seven combinations of coarse aggregate gradations (10-5 mm, 16-13mm, 20-16mm, 20-13mm, 20-10mm, 16-10mm and 20-5mm) were studied. two w/c ratios are considered 0.38 and 0.42. the effect of coarse aggregate gradation, cement-aggregate ratio and w/c ratio are studied in terms of unit weight and compressive strength of nfc. the results reveal the pronounced effect of aggregate gradation on the compressive strength and unit weight of the concrete. also, a substantial effect on the unit weight and compressive strength is observed with the variation in cement-aggregate ration and the w/c ratio. keywords-no-fines;aggregate graddation;cement to agggregate proportion;compressive strength;texture i. introduction no-fines concrete is a form of light weight concrete, which is made with only cement, water and coarse aggregates. the coarse aggregates are coated with cement paste and connected point-to-point with thin cement paste which holds the aggregates in a matrix. however, it is believed that it has less strength than the ordinary concrete [1, 2]. no-fines concrete has many advantages including its prime property of lightweight and no segregation due to its porous nature avoiding need of vibration during its manufacturing [3]. due to its high porous nature it has many applications like permeable pavements [4], water purification plants [5], and parking for light weight vehicles. the ordinary concrete is impermeable which not only hinders the percolation of water to recharge the underground water but also causes high risks of flooding [6-8]. thus, an increasing trend is observed to use porous concrete in environmental problems and sustainable construction. no-fines concrete is generally made with uniform and large size coarse aggregates which produce pours/voids in the concrete resulting in the lightweight capacity of the concrete but exhibiting low compressive strength and workability. however, it is reported that the gradation of coarse aggregates also affects the strength properties of concrete, therefore it is suggested that with controlling coarse aggregate gradation strength can be increased [9]. tthe size of aggregates also affects its properties [10]. many attempts have been made to study the durability and corrosion [11], porosity and permeability [12] of no-fines concrete. strength of no-fines concrete is affected with amount, quality and type of cement. the cement-aggregate ratio of nofines concrete may vary from 1:4 to 1:10. the porous state of nfc causes decrease in workability [2]. hence w/c ratio also plays significant role in manufacturing nfc and its strength properties. this study is focused on investigating strength and unit weight properties of no-fines concrete with various coarse aggregate grades, cement-aggregate ratio and w/c ratio. ii. experimental procedure the main aim of this study is to investigate the unit weight and compressive strength of no-fines concrete. two cementcorresponding author: z. a. tunio engineering, technology & applied science research vol. 9, no. 1, 2019, 3786-3789 3787 www.etasr.com tunio et al.: effect of coarse aggregate gradation and water-cement ratio on unit weight … aggregate (c-a) proportions 1:6 and 1:8 of nfc were adopted. seven different coarse aggregate gradations (10-5 mm, 1613mm, 20-16mm, 20-13mm, 20-10mm, 16-10mm and 205mm) were used. nfc is cast with 0.38 and 0.42 w/c ratio to check its effect on the nfc behaviour. ordinary portland cement (opc) as per standard of astm c150 was used to manufacture the nfc. crushed stones obtained from the local market were used as coarse aggregates. they were washed and air dried up to ssd followed by accordingly sieving to achieve specified aggregate gradation. water acceptable for drinking was used for specimen casting and curing. a total number of 140 cube specimens of 150mm×150mm×150mm were cast. table i gives the details of the cast and tested specimens. table i. specimen details s.no aggregate gradation (cement-aggregate) (mm) cementaggregate (c-a) proportion w/c ratio number of specimens 1 (10-5) 1:6 0.38 5 0.42 5 1:8 0.38 5 0.42 5 2 (16-13) 1:6 0.38 5 0.42 5 1:8 0.38 5 0.42 5 3 (20-16) 1:6 0.38 5 0.42 5 1:8 0.38 5 0.42 5 4 (20-13) 1:6 0.38 5 0.42 5 1:8 0.38 5 0.42 5 5 (20-10) 1:6 0.38 5 0.42 5 1:8 0.38 5 0.42 5 6 (16-10) 1:6 0.38 5 0.42 5 1:8 0.38 5 0.42 5 7 (20-5) 1:6 0.38 5 0.42 5 1:8 0.38 5 0.42 5 all the ingredients of the respective mixes were batched accordingly in an electric operated mixer and casting of specimens was done accordingly. the specimens were demoulded after 24 hours of casting and kept in curing tank up to the age of testing. wet curing was applied. all specimens were tested at 28 days of age. before testing the specimens for compressive strength, all the specimens were weighed to determine their unit weight. to determine compressive strength, the cubes were tested in a universal testing machine (utm). the cubes were placed with the cast faces in contact with platens of the testing. then, compressive load was applied gradually. the ultimate load at the crushing failure of cube specimens was recorded. the load divided by the cross sectional area of the cube determines the ultimate compressive strength. five cube specimens of each mix were cast from each batch. the ultimate compressive strength and unit weight of each of the five specimens was measured. the average of the five values represents the ultimate compressive strength and unit weight of the respective batch of no-fines concrete. iii. results and discussion a. compressive strength the results of average compressive strength tests are presented in table ii. table ii. average compressive strength and unit weight s.no. aggregate gradation (mm) cementaggregate (c-a) proportion w/c ratio comp (mpa) unit weight(kg/m3) 1 (10-5) 1:6 0.38 9.2 1889 0.42 12.4 1965 1:8 0.38 7.1 1944 0.42 6.1 1835 2 (16-13) 1:6 0.38 4.7 1759 0.42 7.1 1717 1:8 0.38 3.6 1734 0.42 5.9 1769 3 (20-16) 1:6 0.38 8.7 1878 0.42 10.7 1778 1:8 0.38 6.8 1789 0.42 6.5 1717 4 (20-13) 1:6 0.38 8.9 1839 0.42 12.1 1840 1:8 0.38 7.9 1860 0.42 10.5 1924 5 (20-10) 1:6 0.38 11.2 1906 0.42 15.7 1881 1:8 0.38 8.8 1807 0.42 12.4 1859 6 (16-10) 1:6 0.38 9.6 1929 0.42 10.7 1846 1:8 0.38 6.5 1807 0.42 8.4 1833 7 (20-5) 1:6 0.38 9.7 1902 0.42 12 1924 1:8 0.38 7.9 1818 0.42 7.5 1834 figures 1 and 2 compare the effects of aggregate gradation and cement-aggregate (c-a) proportion on the compressive strength of no fines concrete. fig. 1. compressive strength v/s aggregate gradation and cementaggregate proportion at 0.38 w/c ratio. the results reveal the pronounced effects of aggregate gradation and the c-a proportion on the compressive strength. engineering, technology & applied science research vol. 9, no. 1, 2019, 3786-3789 3788 www.etasr.com tunio et al.: effect of coarse aggregate gradation and water-cement ratio on unit weight … figures 3 and 4 depict the effect of w/c ratio on the compressive strength of nfc. the significant effect of aggregate gradation is self-evident from the table values and the figures. fig. 2. compressive strength v/s aggregate gradation and cementaggregate proportion at 0.38 w/c ratio. fig. 3. compressive strength v/s water-cement of nfc with 1:6 cementaggregate proportion fig. 4. compressive strength v/s water-cement of nfc with 1:8 cementaggregate proportion nfc manufactured with (20-10)mm gradation exhibited the highest and nfc with (16-13)mm gradation yielded the lowest compressive strength in the respective group of nfc having the same c-a proportion and w/c ratio. the compressive strength of nfc with 1:6 c-a proportion exhibited higher compressive strength than the nfc with 1:8 c-a proportion with the same aggregate gradation and w/c ratio. the nfc produced with 0.42 w/c ratio yielded higher compressive strength than that of nfc with 0.38 w/c ratio when compared to the respective batches of nfc with aggregate gradation and c-a proportion. minimum compressive strength of nfc is found to be 3.6mpa manufactured with (16-13) mm gradation, 1:8 c-a proportion and 0.38 w/c ratio while the maximum value of the same mix was 7.1mpa with 1:6 c-a proportion and 0.42 w/c ratio. the same trend is observed in case of nfc having (20-10) mm aggregate gradation being 8.8mpa with 1:8 c-a proportion and 0.38 w/c ratio, increased to 11.2mpa (1:6, 0.38), 12.4mpa (1:8, 0.42) and 15.7mpa (1:6, 0.42). difference in compressive strength of the order of 336% is observed when highest compressive strength 15.7mpa of nfc having (20-10) mm aggregate gradation, 1:6 c-a proportion and 0.42 w/c ratio is compared to the lowest value of 3.6mpa of nfc having (1613) mm aggregate gradation, 1:6 c-a proportion and 0.42 w/c ratio. this infers the significance of aggregate gradation, cement-aggregate proportion and w/c ratio on the compressive strength of nfc. b. unit weight table ii also shows the values of average unit weight of nfc produced with different aggregate gradation, cement aggregate proportion and w/c ratio. the maximum unit weight of nfc observed is 1965kg/m3 and the minimum was found to be 1717kg/m3. the difference between maximum and minimum values is only 14.4%. the unit weight of nfc is affected by variations in aggregate gradation, c-a proportion and w/c ratio but it is not only marginal but also without any trend in terms of the gradation range, value of c-a proportion and w/c ratio (figure 5). the effect of aggregate gradation, c-a proportion and w/c ratio may be considered as marginal if the unit weight is the major parameter of consideration while producing nfc otherwise their effect may be ignored. fig. 5. unit weight of nfc with different aggregate gradation, c-a proportion and w/c ratio c. texture of nfc in addition to compressive strength and unit weight, the apparent texture of the nfc is also observed in terms of variation in aggregate gradation. figure 6 depicts texture pictorial comparison. as expected, nfc produced with aggregate gradation owing wider range of gradation and small size aggregates (e.g. 10-5mm and 20-5 mm) results in apparently dense and good looking texture with small voids as compared to the nfc having close range gradation and larger engineering, technology & applied science research vol. 9, no. 1, 2019, 3786-3789 3789 www.etasr.com tunio et al.: effect of coarse aggregate gradation and water-cement ratio on unit weight … size aggregates (e.g. 16-13mm and 20-10mm). however, in case of no fines concrete, this factor may not be considered as important as it is compressive strength and unit weight. fig. 6. pictorial views of the texture of nfc iv. conclusions • aggregate gradation, cement-aggregate proportion and w/c ratio significantly affect the compressive strength of no fines concrete. • a difference as high as 336% is observed between maximum and minimum compressive strength of no-fines concrete due to variation in aggregate gradation, c-a proportion and w/c ratio. • no-fines concrete produced with (20-10) mm gradation, 1:6 c-a proportion and 0.42 w/c ratio exhibited the highest compressive strength of 15.7mpa. • minimum compressive strength was found to be 3.6mpa in the case of (16-17) mm aggregate gradation, 1:8 c-a proportion and 0.38 ratio. • the unit weight of no-fines concrete is found to be marginally affected by the variation in aggregate gradation, c-a proportion and w/c ratio. • the maximum difference between the minimum and maximum unit weight is found to be only about 14%. • apparent texture of the no fines concrete was also influenced by the aggregate gradation. no fines concrete with wide rage gradation and smaller size aggregates exhibited apparently good looking and dense texture. based on the results of the conducted experimental study and the discussion and conclusions made above it may be concluded that while producing no fines concrete, gradation of aggregates, c-a ratio and w/c ratio may be chosen appropriately, particularly when the compressive strength is the major parameter of consideration. however, to a limited extent, unit weight and apparent texture also depend upon these factors. acknowledgment authors are grateful to the quaid-e-awam university of engineering, science and technology, nawabshah for providing the research facilities. references [1] m. a. memon, m. a. bhutto, n. a. lakho, i. a. halepoto, a. n. memon, “effects of uncrushed aggregate on the mechanical properties of no-fines concrete”, engineering, technology & applied science research, vol. 8, no. 3, pp. 2882-2886, 2018 [2] k. b. thombre, a. b. more, s. r. bhagat, “investigation of strength and workability in no-fines concrete”, international journal of engineering research & technology, vol. 5, no. 9, pp. 390-393, 2016 [3] t. kuennen, “a new era for permeable pavements. better roads for the government/contractor project team”, better roads magazine, vol. 2003, no. 4, pp. 28-32, 2003 [4] v. r. schaefer, k. wang, m. t. suleiman, j. t. kevern, mix design development for pervious concrete in cold weather climates, final report, center for transportation research and education, iowa state university, 2006 [5] j. t. kevern, “advancement of pervious concrete technology”, phd thesis, iowa state university, usa, 2008 [6] a. v. novo, j. r. bayon, d. castro-fresno, j. rodriguez-hernandez, “temperature performance of different pervious pavements: rainwater harvesting for energy recovery purposes”, water resources management, vol. 7, no. 15, pp. 5003-5016, 2013 [7] m. j. lee, m. g. lee, y. huang, c. l. chiang, “purification study of pervious concrete pavement’’, international journal of engineering and technology, vol. 5, no. 5, pp. 532-535, 2013 [8] a. k. jain, j. s. chouhan, “effect of shape of aggregate on compressive strength and permeability properties of pervious concrete”, international journal of advanced engineering research and studies, vol. 1, no. 1, pp. 120-126, 2011 [9] y. zhifeng, w. ma, w. shen, m. zhou, “the aggregate gradation for the porous concrete perviousroad base material”, journal of wuhan university of technology-matererials science edition,vol. 23, no. 3, pp. 391-394, 2008 [10] l. k. crouch, p. e., j. pitt, r. hewitt, “aggregate effects on pervious portland cement concrete staticmodulus of elasticity”, asce journal of materials in civil engineering, vol. 19, no. 7, pp. 561-568, 2007 [11] m. carsana, f. tittarelli, l. bertolini, “use of no-fines concrete as a building materials: strength, durability properties and corrosion protection of embedded steel”, cement and concrete research, vol. 48, pp. 64-73, 2013 [12] a. b. kabir, k. s. islam, “performance study on no fines concrete”, 3rd international conference on civil engineering for sustainable development (iccesd), kuet, khulna, bangladesh, february 12-14, 2016 (16-13) mm (10-5) mm (16-10) mm (20-10) mm (20-13) mm (20-5) mm (20-16) mm microsoft word 24-16-3728_s_on_hold__etasr_v10_n5_pp6276-6281 engineering, technology & applied science research vol. 10, no. 5, 2020, 6276-6281 6276 www.etasr.com yau et al.: modeling of the internal temperature for an energy saving chinese solar greenhouse modeling of the internal temperature for an energy saving chinese solar greenhouse abstract-the global rise in food demand requires urgent attention in the aspect of crop production. the microclimate of a greenhouse is a critical issue in agricultural practice, due to the variations of the external climatic conditions and their negative effect on crop production. in this work, a dynamic model of the internal air temperature of a chinese solar greenhouse was designed in matlab/simulink environment. the dynamic model was designed with the use of energy balance equations. the weather data consisting of solar radiation, relative humidity, ambient temperature, and photosynthetically active radiation (par) were acquired from meteorological stations. the results of the simulations show that the temperature of the internal air varies with weather conditions, location, number of covers, and the structure of the solar greenhouse. keywords-chinese solar greenhouse; dynamic model; relative humidity; temperature; agricultural practices; external climatic conditions i. introduction a greenhouse is defined as a covered structure that provides plants with an optimally controlled environment for adjustment of climate growth conditions, in order toreduce production cost and increase crop yield. global food production systems depend on the proper utilization of greenhouses. many greenhouse types are successfully used for plant protection worldwide. some may be better than others for particular applications, but no greenhouse type is considered the best [1]. control of the micro-climate of the greenhouse is essential in order to encourage crop production considering the unstable nature of temperature, relative humidity, co2 concentration, and solar radiation [2-8]. the possibilities offered by greenhouse climate computers have solved the problems relating to the regulation and respect of climate instructions required by protected cultivation. the greenhouse climate computer will have to be integrated as a tool for the dynamic management of production, able to choose the most appropriate climate route, meet objectives and production orders while minimizing inputs. computers have become quite popular in greenhouse management, even in countries where environmental conditions do not inhibit the development of plants. in developed countries, computers find a lot of application in irrigation, boilers and climate control, where they are used to regulate humidity, co2, and artificial lighting. the computers are used to determine climate set points and to monitor alarm functions. the literature on control theory and application of classical dynamic systems in the entire field of greenhouse control and modeling is sufficient [9]. the microclimate parameters inside a greenhouse are air temperature, soil temperature in addition to the soil sub-layer, relative humidity, and co2 concentration. they can be predicted experimentally or by simulation [10]. the evolution of the greenhouse model is fast and conducted by the control of the energy phenomena involved inside. in the literature, the modeling of the thermal energy balance can be static [11] or dynamic. various dynamic models of greenhouses have been developed [12, 13]. to overcome the less optimal climate conditions and to fulfil the specific environmental needs of various crops, energy saving greenhouse designs vary in structural shape, size, glazing materials, and in the type of equipment required to achieve the desired environmental conditions. in the current research, the simplified dynamic model of the energy balance for a chinese solar greenhouse is developed under the matlab-simulink environment. ii. materials and methods a. description since the focus of the design method is to model the internal temperature of the greenhouse, the set of design jamilu yau college of information and electrical engineering, shenyang agricultural university, shenyang, china and dpt. of electrical engineering, bayero university kano, kano state, nigeria ji jianwei college of information and electrical engineering shenyang agricultural university shenyang, china hui wang college of information and electrical engineering shenyang agricultural university shenyang, china olubakinde eniola department of electrical and electronic engineering federal polytechnic ile-oluji ondo state, nigeria folahan peter ibitoye research and development dpt., prototype engineering development institute, national agency for science and engineering infrastructure, ilesa, nigeria corresponding author: ji jianwei (jianweiji2001@hotmail.com) engineering, technology & applied science research vol. 10, no. 5, 2029, 6276-6281 6277 www.etasr.com yau et al.: modeling of the internal temperature for an energy saving chinese solar greenhouse elements and the selected functions and techniques are incorporated in the greenhouse climate model. in this model, heating is provided by the solar radiation and the heat storage system which influence the internal temperature and the temperature of the heating pipes. cooling and co2 are provided by natural ventilation. a typical greenhouse consists of soil, cover, crop, and internal air. in this research, the crop is neglected. the actual experimental greenhouse is located in shenyang, liaoning, china. the new energy saving solar greenhouse assembled with rock wool color plate uses a double-layer semi-circular arc steel structure. the inner layer is covered with a transparent material of 0.1mm thick polyolefin (po) film and the insulation cover on the outer layer is made up of rock wool color plate. in the low temperature season, the insulation covers on the outer layer are slid down, thus retaining heat and reducing heat loss effectively [14]. b. the dynamic model of the chinese solar greenhouse simplified models of the chinese greenhouse have been developed in [15-17]. the main objective of a climate control system is to maintain the temperature inside the greenhouse within a suitable range [18]. the layout for the chinese greenhouse in figure 1 shows the external and the internal parameters, where all the modelled elements have been schematized. the grey boxes indicate the calculated temperatures (state variables) while the white boxes represent the independent variables linked to the model with an external file (csv format) or are directly calculated. fig. 1. layout of a typical chinese solar greenhouse. the model is based on the following assumptions: • the outdoor weather conditions (white boxes in figure 1) are not influenced by the greenhouse indoor climate. • each span in the multi span glasshouse has the same layout with respect to the configuration of the heating pipes, the artificial lighting system, and its size. • the greenhouse air is considered as a “perfectly stirred tank”, which means that there are no temperature gradients or water vapour concentration differences, therefore all the model fluxes can be described per square meter. • all modelled elements (state variables) are homogeneous: they have a uniform temperature and an average thermal capacity can be used. when the transport of physical quantities like energy and mass is considered, for these quantities the law of conservation is valid for any volume. to establish a general rule, energy is considered first [18]. if an amount of energy per unit of time (qh, energy flux, js -1 ) enters a volume, then the amount of energy in the volume qh (j) will increase. of course if an energy flux leaves a volume, qh will decrease. the relation in which we compare the entering and leaving fluxes is called balance. we can set up an energy balance or a mass balance and for any volume. not only the inflows and outflows of energy contribute to the increase or decrease of the energy in the volume, but also the energy production in the volume ph (js -1 ), if any. from these considerations the energy balance over any volume can be set up in general terms as: ��� �� = ���, − �� �, + � (1) the term on the left is the change of energy per unit of time in the considered volume. it is determined by the terms on the right hand side, which are respectively the influx, the outflows and the production of energy per unit of time in the considered volume. it is assumed that no work is done by or on the medium in the volume, which in general is true for the greenhouse situation [18]. the amount of energy in the volume qh (internal energy) is directly related to the temperature t (k) of the volume through its thermal capacity caph (jk -1 ): � = ��� � (2) in this way the time rate of change of the internal energy is translated to a time rate of change of temperature that can be implemented in the balance: ��� �� ��� = ���, − �� �, + � (3) ��� = ���� (4) � = 0 (5) ���, = �� ��� (6) �� �, = ������� + � ���, ��! + ����" (7) where qshort is the heat gained by solar radiation, qheater is the heat gained by the heater, qvent is the heat loss through ventilation, qcond,conv is the heat loss through conduction and convection, and qlong is the heat loss due to the longwave radiation. solar radiation is the main heat source for a greenhouse and can be calculated as: �� ��� = # $ %& (8) where # is the cover’s absorptivity, $ is the cover’s transmittance, s is the cover’s surface area, and & is the total solar radiation. qinflit is the heat loss by infiltration: ������� = �'�'( )*+,-*./01 2344 (9) where �' is the density of the air, �' is the specific heat of the air, ( is the number of air changes per hour, ��� is the indoor air temperature (°c) and �� � is the external temperature. the heating pipe energy exchange belongs to the convective heat transfer which follows the newton’s law of cooling [19]: � 5'�5� = 1.95:�;�� − ���< =/2 (10) engineering, technology & applied science research vol. 10, no. 5, 2029, 6276-6281 6278 www.etasr.com yau et al.: modeling of the internal temperature for an energy saving chinese solar greenhouse where �' is the density of the air, �' is the specific heat of the air, ( is the number of air changes per hour, ��� is the indoor air temperature (°c), and �� � is the external temperature (°c). �!5�� = ��'�)��� − �� �1 (11) � = )?-@1abc.de-fc)*+,-*./01 gh)*+,-*./01 (12) where i is the evaporation coefficient (-), $ is the average transmittance of the greenhouse cover of solar radiation (-), %� is the solar radiation flux outside the greenhouse (wm -2 ), :� is the surface area of the greenhouse floor (m 2 ), j is the overall heat loss coefficient of the cover (wm -2 °c -1 ), % is the surface area of the greenhouse cover (m 2 ), ��� is the internal temperature, �� � is the external temperature, and �' is the specific heat of the air at constant pressure (j.kg -1 °c). � ���, ��! � j%)��� � �� �1 (13) where j is the overall heat transfer coefficient through the greenhouse walls and computed by: j � k ? l � mb nb � ? +o -? (14) wherep4 is the convective heat transfer coefficient of the outside greenhouse cover, p� is the convective heat transfer of the inside greenhouse cover, q is the cover thickness, and r is the heat transfer coefficient of polyolefin cover. for p4 and p�, (15) and (16) apply: p4 � 2.8 � 1.2�u (15) p� � 1.52|��� � �� �| ? 2� � 5.2 w xcbmy ? z� (16) where �u is the wind velocity, q is the length of the greenhouse, and % is the vertical section of the greenhouse. the long-wave thermal radiation from the greenhouse covering to the sky follows the stefan boltzman’s law: ����" � r : )1 � $g1;��� � ��[\< (17) where r is the heat transfer coefficient of the cover, : is the area of the cover, $ is the transmittance of the cover, ��� is the internal temperature, and ��[\ is the sky temperature. ��[\ � 0.0552)�� �1?.] (18) ���� ���� ��� = �� ��� + � 5'�5�−�!5�� �� ��� , ��! � ����" (19) ���� ��� � �^�._0 `��ah0a_ -�ba,0-�b.,c,b.,b -�d.,e fg gh (20) ��� � i �^�._0`��ah0a_ -�ba,0-�b.,c,b.,b-�d.,e fg gh � �� ,4 (21) where � is the volume of the greenhouse (m3), � is the air density (kg/m 3 ) �� is the specific heat capacity of the air (j/kg°c) and ��,4 is the initial value of the greenhouse temperature (°c). iii. the developed model the dynamic knowledge model of the energy balance of the new energy saving greenhouse described above is shown in figure 2. the simulation was performed using a weather database that was acquired in the shenyang liaoning, china during the period from april, 2016 to april, 2017 with a sampling time equal to 10 minutes and was divided into 3-day and 5-day intervals to enable faster simulation. this database includes the measurements of solar radiation, outside temperature, relative humidity, vapor pressure deficit, wind velocity, dew point and photo synthetically active radiation (par). the signal generator in the simulink was used to import the external database into it, thus allowing the calculation of the air temperature inside the greenhouse model. the input parameters used are summarized in table i. the subsystems generated in simulink are shown in figures 3-6. these subsystems depict how the different blocks in the simulink environment were connected. the level of solar radiation reaches the maximum of 756w/m 2 at noon. fig. 2. dynamic model of the chinese greenhouse in simulink. engineering, technology & applied science research vol. 10, no. 5, 2020, 6276-6281 6279 www.etasr.com yau et al.: modeling of the internal temperature for an energy saving chinese solar greenhouse table i. simulation parameters symbol numerical value units description kc 0.028 wm -2 k -1 heat transfer coefficient of the cover ac 1123.1 m 2 area of the greenhouse cover t k or °c temperature ε 0.9 emissivity between the cover and the sky σ 0.0000000567 stefan-boltzmann constant ρ 1.2 kg/m 3 air density cp 1006 jkg -1 k -1 specific heat of the air q m 3 /s air flow due to ventilation v 3088.6 m 3 greenhouse volume af 715 m 2 surface area of the greenhouse floor jk 0.87 transmittance of the cover i wm -2 total solar energy falling on horizontal surface ap 73.9 m 2 surface area of hot water pipes aw 95.033 m 2 surface area of back and front walls u wm -2 k -1 overall heat transfer coefficient through the greenhouse walls s 5 m 2 surface area of the greenhouse cover hi wm -2 k -1 convective heat transfer coefficient of the inside greenhouse cover h0 wm -2 k -1 convective heat transfer coefficient of the inside greenhouse cover lc m cover thickness l m greenhouse length r 3 m 3 /s number of air changes per hour sc m 2 vertical section of the greenhouse lm 0.1 cover absorptivity of solar radiation fig. 3. sub-system for the heat gained by solar radiation (qshort). fig. 4. sub-system for qinfilt. fig. 5. sub-system for qcond,conv. parts of the simulation results of internal and external temperature are shown in figures 7-9. the points where a decrease in internal temperatures is noticed coincide with the regions of lower external temperatures, confirming the validity of the simulation results. fig. 6. heat loss due to longwave radiation (qlong). fig. 7. simulation results obtained during 28-30 april 2016. temperatures were recorded every 10 minutes. fig. 8. simulation results obtained during 1-3 may 2016. temperatures were recorded every 10 minutes. fig. 9. simulation results obtained during 4–6 may 2016. temperatures were recorded every 10 minutes. engineering, technology & applied science research vol. 10, no. 5, 2020, 6276-6281 6280 www.etasr.com yau et al.: modeling of the internal temperature for an energy saving chinese solar greenhouse the variation of the external solar radiation and the external temperature are displayed with the use of the signal generator block in the simulink environment, as shown in figures 10-12, which show the hourly variation of solar radiation in the greenhouse and the temperature profile of its different components. the greenhouse outside temperature varied from 6.8°c to 32.2°c, solar radiation contributed significantly to greenhouse outside temperature fluctuations. fig. 10. (a) external temperature profile, (b) solar radiation profile for 28– 30 april, 2016. fig. 11. (a) external temperature profile, (b) solar radiation profile for 1-3 may, 2016. fig. 12. (a) external temperature profile, (b) solar radiation profile for 4–6 may, 2016. figures 10-12 show the hourly variation of solar radiation in the greenhouse and the temperature profile of the different greenhouse components. the greenhouse inside temperature varied from 19 to 25°c, while the outdoor temperature fluctuated between 6.8 and 32.2°c. solar radiation contributed significantly to greenhouse indoor temperature fluctuations, whereas the average indoor daytime temperature was 22˚c. the nighttime greenhouse temperature was mostly stable because an electric heater was turned on for heating purposes. indoor temperature, wall temperature, and soil temperature during daytime mostly followed a similar trend of solar radiation in the greenhouse because the electric heater was turned off during daytime. sometimes, mostly at noon, the internal temperature fluctuated, which could be caused by the operation of the natural ventilation system in the greenhouse. iv. conclusion in this paper, a simplified dynamic model of an agricultural greenhouse was developed in simulink environment in order to predict the dynamic pattern of its internal temperature. the analysis results showed that the internal temperature varies with season (summer, winter, spring or autumn), the external climate parameters (solar radiation, photosynthetically active radiation, wind speed, outside temperature, outside humidity), the location of the greenhouse, the structure of the greenhouse, the number of covers (double or simple) and the cover type. therefore, the simulation of the internal temperature can be used in making decisions about the location, structure, number of covers, and type of cover materials needed for the construction of a particular greenhouse. this study developed a steady state thermal model using matlab/simulink for the simulation of the heating requirements of the chinese greenhouse. the model was developed by considering most of the heat sources and sinks in greenhouses including evapotranspiration, the heating contribution of environmental control systems including supplemental lighting, the co2 generator, and the air-circulation system, which were mostly not considered in previous studies [17, 19]. on this study, it was discovered that the chinese solar greenhouse has been proved as an energy-efficient horticultural facility for crop production. so, its use could be an alternative option in order to reduce the heating cost of greenhouse production. a simulation model of the internal temperature in a chinese greenhouse is essential for feasibility studies regarding cold regions. the innovative concept of this study is the introduction of the simulink block diagram in the modeling of the internal temperature by varying some external factors such as solar radiation and external temperature. the robustness of the simulink model allows the use of different solvers such as ode4 (runge-kutta), the step size and the simulation time can also be varied, thereby improving computations. in comparison with previous studies such as [20], only matlab/simulink was used to model the internal temperature using the respective equations. the results show the necessity of considering other parameters in the design of greenhouses, especially when the intensity of solar radiation is minimal. then an alternate source of energy such as geothermal energy will be needed. references [1] r. a. aldrich and j. w. bartok, greenhouse engineering (nraes 33). ithaca, n.y: northeast regional agricultural engineering service (nraes), 1994. [2] h. a. ahemd, a. a. al-faraj, and a. m. abdel-ghany, “shading greenhouses to improve the microclimate, energy and water saving in hot regions: a review,” scientia horticulturae, vol. 201, pp. 36–45, mar. 2016, doi: 10.1016/j.scienta.2016.01.030. [3] b. alain, “greenhouse microclimate and its management in mild winter climates,” presented at the international symposium on protected cultivation of ornamentals in mild winter climates, doi: 10.17660/ actahortic.1989.246.1. engineering, technology & applied science research vol. 10, no. 5, 2020, 6276-6281 6281 www.etasr.com yau et al.: modeling of the internal temperature for an energy saving chinese solar greenhouse [4] a. baille, “trends in greenhouse technology for improved climate control in mild winter climates,” acta horticulturae, no. 559, pp. 161– 168, oct. 2001, doi: 10.17660/actahortic.2001.559.23. [5] v. castro, s. a. isard, and m. e. irwin, “the microclimate of maize and bean crops in tropical america: a comparison between monocultures and polycultures planted at high and low density,” agricultural and forest meteorology, vol. 57, no. 1, pp. 49–67, dec. 1991, doi: 10.1016/01681923(91)90078-5. [6] o. körner, j. m. aaslyng, and n. holst, “microclimate prediction for dynamic greenhouse climate control,” hortscience, vol. 42, no. 2, pp. 272–279, apr. 2007, doi: 10.21273/hortsci.42.2.272. [7] m. jomaa, m. abbes, f. tadeo, and a. mami, “greenhouse modeling, validation and climate control based on fuzzy logic,” engineering, technology & applied science research, vol. 9, no. 4, pp. 4405–4410, aug. 2019. [8] m. elashmawy, a. a. a. a. al-rashed, l. kolsi, i. badawy, n. b. ali, and s. s. ali, “heat transfer and fluid flow in naturally ventilated greenhouses,” engineering, technology & applied science research, vol. 7, no. 4, pp. 1850–1854, aug. 2017. [9] o. jolliet and b. j. bailey, “the effect of climate on tomato transpiration in greenhouses: measurements and models comparison,” agricultural and forest meteorology, vol. 58, no. 1, pp. 43–62, mar. 1992, doi: 10.1016/0168-1923(92)90110-p. [10] k. a. joudi and a. a. farhan, “a dynamic model and an experimental study for the internal air and soil temperatures in an innovative greenhouse,” energy conversion and management, vol. 91, pp. 76–82, feb. 2015, doi: 10.1016/j.enconman.2014.11.052. [11] o. jolliet, l. danloy, j.-b. gay, g. l. munday, and a. reist, “horticern: an improved static model for predicting the energy consumption of a greenhouse,” agricultural and forest meteorology, vol. 55, no. 3, pp. 265–294, jun. 1991, doi: 10.1016/0168-1923 (91)90066-y. [12] a. m. abdel-ghany and t. kozai, “dynamic modeling of the environment in a naturally ventilated, fog-cooled greenhouse,” renewable energy, vol. 31, no. 10, pp. 1521–1539, aug. 2006, doi: 10. 1016/j.renene.2005.07.013. [13] m. azaza, k. echaieb, a. mami, and a. iqbal, “optimized microclimate controller of a greenhouse powered by photovoltaic generator,” in 2014 5th international renewable energy congress (irec), mar. 2014, pp. 1–5, doi: 10.1109/irec.2014.6826937. [14] q. li, d. zhang, j. ji, z. sun, and y. wang, “modeling of natural ventilation using a hierarchical fuzzy control system for a new energy-saving solar greenhouse,” applied engineering in agriculture, vol. 34, no. 6, pp. 953–962, 2018, doi: 10.13031/aea.12757. [15] g. jian-kun, w. shun-sheng, w. feng, y. hong-guang, and h. jing, “modelling greenhouse thermal environment in north china based on simulink,” nature environment and pollution technology, vol. 15, no. 1, pp. 217–220, 2016. [16] m. s. ahamed, h. guo, and k. k. tanino, “modeling of heating requirement in chinese solar greenhouse,” presented at the 2016 asabe annual international meeting, orlando, fl, 2016, doi: 10. 13031/aim.20162455669. [17] l. chen, b. zhang, f. yao, and l. cui, “modeling and simulation of a solar greenhouse with natural ventilation based on error optimization using fuzzy controller,” in 2016 35th chinese control conference (ccc), jul. 2016, pp. 2097–2102, doi: 10.1109/chicc.2016.7553676. [18] j. c. bakker, g. p. a. bot, h. challa, and n. j. van de braak, greenhouse climate control: an integrated approach. netherlands: wageningen academic publishers, 1995. [19] m. a. lamrani, t. boulard, j. c. roy, and a. jaffrin, “se—structures and environment: airflows and temperature patterns induced in a confined greenhouse,” journal of agricultural engineering research, vol. 78, no. 1, pp. 75–88, jan. 2001, doi: 10.1006/jaer.2000.0568. [20] m. s. ahamed, h. guo, and k. tanino, “development of a thermal model for simulation of supplemental heating requirements in chinesestyle solar greenhouses,” computers and electronics in agriculture, vol. 150, pp. 235–244, jul. 2018, doi: 10.1016/j.compag.2018.04.025. microsoft word 37-2818_s_etasr_v9_n3_pp4271-4275 engineering, technology & applied science research vol. 9, no. 3, 2019, 4271-4275 4271 www.etasr.com solangi et al.: spatial analysis of soil salinity in the indus river delta, pakistan spatial analysis of soil salinity in the indus river delta, pakistan ghulam shabir solangi u.s. pakistan centers for advanced studies in water, mehran university of engineering & technology, jamshoro, pakistan solangi_shabir@yahoo.com muhammad munir babar u.s. pakistan centers for advanced studies in water, mehran university of engineering & technology, jamshoro, pakistan mmunirbabar.uspcasw@faculty.muet.edu.pk altaf ali siyal u.s. pakistan centers for advanced studies in water, mehran university of engineering & technology, jamshoro, pakistan aasiyal.uspcasw@faculty.muet.edu.pk pirah siyal national centre of excellence in analytical chemistry, university of sindh, jamshoro, pakistan pirahaltaf@chemist.com abstract—soil salinization is one of the most damaging environmental problems in coastal areas, including indus river delta (ird). due to the reduction of flow in the indus basin, saline water from the arabian sea is intruding into the ird and has degraded the agricultural lands drastically. focusing on the gravity of the problem, the present study was designed to explore the spatial distribution of soil salinity in the ird. physicochemical analysis of 375 soil samples randomly collected from 125 different locations within the study area was used. analysis revealed that for the top 0-20cm of soil, about 66.4% of the samples had electrical conductivity (ec) values, and 72.8% sodium content (esp) values higher than the fao guidelines. similarly, for soil depth of 20-40cm, 60.8% of the ec values, and 72% of esp exceeded the safe limits. finally, for 40-60cm of soil depth, 56.8% of the ec values and 79.2% of the esp values were higher than the safe limits. spatial analysis revealed that more than 50% of the ird samples were affected by soil salinity. reduced freshwater flow and the entry of saline water into the delta may likely be the causes of soil salinity in the ird. keywords-physicochemical properties; soil salinity; electrical conductivity; exchangeable sodium percentage; coastal areas; pakistan i. introduction soil salinization is the process of accumulation of soluble salts on the soil surface and within soil root zone [1] which results in the formation of salt-affected soils [2]. in arid and semi-arid regions of the world, it is one of the most common land degradation processes [2] which impacts social, economic, and environmental growth [3-4]. authors in [5] reported that in arid and semi-arid areas, soil salinization is a major geo-hazard. globally, more than 950 million hectares of land are saltaffected [6], out of which about 43 million hectares are attributed to secondary salinization [7]. authors in [8] reported that about one-third of the irrigated land is severely affected by salinity or is exposed to conditions that encourage soil salinization. due to evaporation, salts transport to soil surface from saline water table through capillary rise [9]. also, irrigation with saline water can develop soil salinity [10]. it adversely affects soil fertility, crop growth and yield, as well as groundwater quality. it changes the normal functioning of the soil-water-plant system, which reduces nutrient uptake and ultimately causes a significant reduction in crop productivity [11]. remotely sensed data are widely used worldwide for analysis of soil salinity [12]. these data have great potential to detect soil salinity spatially and temporally [13], which can be used for input into arcgis to evaluate and delineate soil salinity. currently, various geospatial techniques are used for the estimation of the spatial distribution of soil salinity throughout the world [14-15]. authors in [16] determined the spatial variations of salinity in the soils of alberta. they found kriging and cokriging tools of spatial distribution as suitable for ec estimation and sodium absorption ratio (sar) in the soil. author in [17] determined soil salinity and found geostatistical methods better than the use of empirical formulae/equations. authors in [18] used three spatial techniques, cokriging, spilain, and idw (inverse distance weighted) for delineating the spatial variations of soil salinity in australia. they reported cokriging and spilain as the best techniques for determining soil salinity. author in [13] argued that for the restoration of environmental degradation, information about the nature and spatial distribution of soil salinity is essential. in coastal areas there is a constant passage of salts from seawater into the mudflats and marshy lands, which may influence salt movement to the inland soil [9]. the proximity of the salty groundwater to the surface of the soil and the intrusion of seawater are among the potential causes of soil salinity in these areas [19]. ird is the world’s seventh largest delta, located in the southern part of sindh province of pakistan. due to diminishing river indus flows and uncertain rainfall patterns, the supply of freshwater to delta is significantly reduced. thus, corresponding author: ghulam shabir solangi engineering, technology & applied science research vol. 9, no. 3, 2019, 4271-4275 4272 www.etasr.com solangi et al.: spatial analysis of soil salinity in the indus river delta, pakistan increasing salinity is a crucial issue of the ird. due to increasing soil salinity, most of the agricultural lands in the ird are not suitable any more for agricultural production. therefore, quantification and mapping of soil salinity dynamics is essential for better planning and soil reclamation processes and thus for the prevention of ecological degradation [2]. so far, spatial analysis of soil salinity in the ird, pakistan has not been conducted. the present study was thus conducted using ground truthing field data to assess the gravity of the problem. the spatial distribution of soil salinity in the ird will provide an insight to policymakers, farmers, and agriculturists for ecological degradation prevention and restoration of the delta. ii. materials and methods a. the study area the indus delta is located between longitude 67°40'01" and 68°14'04" and latitude 23°48'29" and 24°57'19" in southern sindh province, pakistan (figure 1). most of the deltaic area lies within two administrative districts, thatta, and sujawal. the active area of the delta is about 0.6 million hectares [20], having 17 major creeks and numerous subordinate small creeks. it extends from sir creek in the east to the phitti creek in the west. the climate of the delta is arid, the delta receives an average of about 220mm of rainfall annually. once, all the creeks of the delta were active, but now due to insufficient and erratic river flows, only two creeks, i.e. khobar and khar get the freshwater [21]. as a result, the dynamic delta area has declined to just 10% of its original area [22]. about 1.76 million people live in the delta, most of them are uneducated and depend on agriculture and fishing. the main crops cultivated in the area include sugarcane, rice, wheat, cotton, and vegetables. the area has the 13 th largest arid-climate mangrove forest in the world [23]. the topmost soil layer is composed of sand (about 15m), followed by clay and bedrock [24]. geomorphologically, a shallow aquifer system with variable thicknesses exists in the delta [25]. once, the area was known for its richness; now it is considered one of the poorest zones in pakistan. fig. 1. gis map of the study area and soil sampling locations b. soil sampling georeferenced soil samples down to a depth of 60cm (0-20, 20-40, and 40-60cm) were collected randomly from various locations of the delta. a soil auger was used for the extraction of soil samples. their locations were recorded using a portable handheld garmin gps [26]. sampling locations are shown in figure 1(c). a total of 375 soil samples was collected from 125 different locations which were analyzed for various physicochemical parameters, namely texture, dry density, ec, ph, and esp. c. physicochemical analysis of soil samples in the present study, a hydrometer method and usda textural triangle were used for the determination of textural classes of soil samples. the oven drying method was used to determine the dry density of the samples. the ec of soil saturation extract was determined at 25 o c using a portable hanna model-8733, german ec meter. the edta titration method was used for the determination of calcium (ca +2 ), and magnesium (mg +2 ) cations in the soil. the soil ph was determined using a ph meter, and the sodium (na + ) concentrations were extracted with ammonium acetate solution (1mol/l) and were quantified according to [27]. the results of these chemical parameters were used to determine the sar and calculate the esp using the respective empirical formulas [27]. d. spatial analysis soil salinity mapping based on the results of the analysis, the interpolated maps of soil texture and most of the soil salinity indicators i.e. ec, ph, and esp were prepared through arcgis 10.5 using the spatial analysis kriging and idw approach. based on soil salinity maps, the area of the ird under salt-affected soils was determined. iii. results and discussion a. physicochemical analysis of soil samples the statistical summary of the results of physicochemical parameters of soil samples in the form of minimum, maximum, mean, mode, standard deviation (std), standard error of the mean (se) and confidence error (ci) is depicted in table i. the dry density at 0-20cm of soil depth varied from 1.20 to 1.40g/cm 3 with an average value of 1.30±0.02g/cm 3 . similarly, at 20-40cm depth, dry density varied from 1.19 to 1.44g/cm 3 with an average value of 1.27±0.01g/cm 3 , while that at a depth of 40-60cm it varied from 1.17 to 1.40g/cm 3 with an average value of 1.26±0.01g/cm 3 . analysis for soil texture revealed that loam and clay loam soils are the dominant textural classes in the top soil layer. about 37.8% of soil samples had loam, and 22.2% of soil samples had clay loam, 14.1% soil samples had clay, 8.9% had silty clay, 7.4% had silty clay loam, 5.9% had silty loam, 2.2% had sandy clay loam, 0.74% had sandy loam, and 0.74% had a sandy texture. thus, most of soils of the delta have fine textural class. the coarse-textured sediment is deposited in the upper regions while the river brings sediment dominated with fine particles at the tail end. ffc [28] reported that the suspended sediment in river indus below kotri contains on average 5.0% sand, 49.6% clay and 45.4% silt, hence the alluvial soils of the delta are dominated by fine-textured soils. however, the lower soil layers, i.e. from 20 to 60cm had almost similar soil texture distribution patterns. ec in 0-20cm soil depth varied between 0.45 and 55.2ds/m with an average of 14.28±2.45ds/m. the ec values at 20-40cm were between engineering, technology & applied science research vol. 9, no. 3, 2019, 4271-4275 4273 www.etasr.com solangi et al.: spatial analysis of soil salinity in the indus river delta, pakistan 0.56 to 48.0ds/m with an average of 11.52±2.08ds/m. the soil is considered as saline, if its ec value exceeds 4ds/m [29]. in this regard, in about 60.8% of the analyzed soil samples the ec values exceeded 4ds/m indicating they were in the category of saline to highly saline soils. however, the ec in the soil samples collected at 40-60cm depth varied from 0.66 to 41.8ds/m with a mean of 9.57±1.75ds/m. about 56.8% of the soil samples at this depth had ec values greater than the fao [30] guidelines. the soils having ec values of 0.7ds/m or less are not stressful to most of the plants [31]. however, soil with an ec>0.7ds/m causes problems for plants and many crop types. generally, the soils having ec>4ds/m are considered as salt-affected soils witch were about the 61.0% of the collected soil samples. the spatial distribution of ec at various soil depths is portrayed in figure 2. it is evident that the areas of the ird which are nearer to the coast are more affected by soil salinity compared to those which are far from the coast, likely due to the impact of seawater intrusion in these areas. table i. samples physicochemical parameters fig. 2. ec spatial distribution in various soil depths hydrogen ion concentration (ph) in the top 0-20cm soil layer varied from 6.8 to 11.42 with a mean value of 7.93±0.10, whereas, the ph of the 20-40cm soil layer varied from 7.1 to 9.2 with a value of 9.99±0.07. finally, the ph of the 40-60cm soil layer ranged from 7.2 to 9.21 with an average of 8.01±0.07. generally, the soils having a ph>8.5 are considered salt-affected (the soils with a ph>7.0, to the most extreme of 14.0, reflect increasing alkalinity). in the study area, most of the sampled soils (about 83.0%) had ph values within the range of 8.5. the esp values in the top 0-20cm of soil depth in the study area ranged from 1.37 to 65.58 with an average of 25.21±2.6. about 79.2% had esp>15 and are classified as saltaffected soils. at 20-40cm, the esp values ranged from 5.23 to 66.55 with a mean of 26.64±2.61. about 72.8% of soil samples had esp>15. the esp values at the 40-60cm soil depth ranged from 3.66 to 65.78 with an average of 27.06±2.57 and about 74.6% of the samples had esp>15. figure 3 shows the spatial distribution of esp in the soil samples. the maps portrayed that the samples collected from the areas nearer to the coast possessed higher esp values. fig. 3. esp spatial distribution thematic maps for at various soil depths overall, the study revealed that the ec of 57-66% of the soil samples collected from 0-60cm were beyond the permissible level of 4ds/m. similarly, the ph of 14-18% of the soil samples was higher than 8.5, and about 73-79% of the analyzed soil samples possessed esp values higher than 15, which has been suggested by the fao [30] as the limit for agricultural purposes. b. soil salinity spatial distribution analysis in the ird based on ground field data, spatial distribution thematic maps for various soil classes, i.e., normal, saline, sodic, and saline-sodic soils for all the three soil depths were prepared (figure 4). it is obvious that the soil salinity in the upper layer was higher than that in the subsoil, suggesting that the salts in the underlying layers transported upward and accumulated in the topsoil [9]. the spatial distribution soil salinity maps showed that more than 50% of the ird soils were salt-affected. the strongest level of salinity was in those samples which were taken from the coastal regions of the arabian sea, which most likely occured due to seawater intrusion [32]. parameter min. max. mean mode std se ci soil depth (0-20cm) dry density (g/cm 3 ) 1.20 1.40 1.30 1.28 0.05 0.004 0.02 ec (ds/m) 0.45 55.2 14.28 11.76 13.98 1.25 2.45 ph 6.8 11.42 7.93 7.5 0.58 0.05 0.10 esp 1.38 64.57 25.21 52.54 14.86 1.33 2.61 soil depth (20-40cm) dry density 1.19 1.44 1.27 1.27 0.04 0.004 0.01 ec 0.56 48.0 11.52 13.78 11.86 1.06 2.08 ph 7.1 9.2 7.99 7.5 0.43 0.03 0.07 esp 5.23 66.55 26.64 34.6 14.91 1.33 2.61 soil depth (40-60cm) dry density 1.17 1.40 1.26 1.27 0.04 0.003 0.01 ec 0.66 41.8 9.57 2.36 9.98 0.89 1.75 ph 7.2 9.21 8.01 7.7 0.43 0.038 0.07 esp 3.66 65.78 27.06 38.33 14.67 1.31 2.57 engineering, technology & applied science research vol. 9, no. 3, 2019, 4271-4275 4274 www.etasr.com solangi et al.: spatial analysis of soil salinity in the indus river delta, pakistan fig. 4. spatial distribution of soil classes to various depths iv. conclusions physicochemical analysis of soil samples collected from different depths of various locations within the indus delta revealed that about 66.4% and 72.8% of the samples collected from top 0-20cm soil layer had ec and esp values beyond the safe limits. similarly, for soil samples collected from the 2040cm soil layer, 60.8%, and 72%, had ec and esp values that exceeded safe limits. for the 40-60cm soil layer, 56.8%, and 79.2% had ec and esp values higher than the safe limits. on an average, the dry density in the soil samples varied from 1.26 to 1.30g/cm 3 . overall, spatial analysis of soil samples revealed that more than 50% of the ird soils were affected by soil salinity. reduction of the volume of freshwater flow in the indus basin, low rainfall, seawater intrusion in the delta and various anthropogenic activities occurring along the coast are the most likely causes of degradation of soils in the ird. the findings of this study are helpful to policymakers, farmers, and agriculturists in order to mitigate the ecological degradation in the indus delta and revive its soils. acknowledgement authors are extremely grateful to the u.s.-pakistan center for advanced studies in water (u.s.-pcas-w), mehran uet, jamshoro, pakistan for funding the project entitled “assessing the impact of seawater intrusion on soil, water, and environment in the indus delta using gis and rs”. the project was funded by the u.s.-pcas-w, under the applied research grants policy of the center. we are also thankful to dr. rick bereit, professor, the university of utah, united states of america (usa) for his constructive comments and suggestions. references [1] a. a. siyal, a. g. siyal, z. a. abro, “salt affected soil their identification and reclamation”, pakistan journal of applied science, vol. 2, no. 5, pp. 537-540, 2002 [2] e. asfaw, k. v. suryabhagavan, m. argaw, “soil salinity modeling and mapping using remote sensing and gis: the case of wonji sugar cane irrigation farm, ethiopia”, journal of the saudi society of agricultural 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migration in compacted soil using digital image technique yamusa bello yamusa school of civil engineering, universiti teknologi malaysia, skudai, malaysia, and department of civil engineering, nuhu bamalli polytechnic, zaria, nigeria yamusabello@yahoo.com radzuan sa’ari school of civil engineering, universiti teknologi malaysia, skudai, malaysia radzuans@utm.my kamarudin ahmad school of civil engineering, universiti teknologi malaysia, skudai, malaysia kamarudin@utm.my noraliani alias school of civil engineering, universiti teknologi malaysia, skudai, malaysia noraliani@utm.my mushairry mustaffar school of civil engineering, universiti teknologi malaysia, skudai, malaysia mushairry@utm.my loke kok foong school of civil engineering, universiti teknologi malaysia, skudai, malaysia edwinloke84@yahoo.com abstract—as leachate has been a source of groundwater contamination worldwide, this paper examines the phenomenon of leachate migration on different gradations of compacted laterite soil used as sanitary landfill liners. three different soil gradations (30%, 40% and 50% with respect to fines content) used in this study were compacted in circular acrylic columns to provide a clear visualization of leachate migration into the soils. digital image technique was used in capturing photos at successive time intervals to monitor the leachate migration. the captured digital images were fed into matlab and converted into hue-saturation-intensity (hsi) format. surfer software then read the hsi and generated 2d contour plots. the results of the experiments showed that the leachate moves downward faster in the soil gradation with the least fines content. hydraulic conductivity values decrease with increase in time duration and equally with increase in fines content. the hydraulic conductivities of the leachate for 30%, 40% and 50% fines were 3.64×10 -9 m/s, 2.40×10 -9 m/s, and 1.24×10 -9 m/s respectively. this reveals that for tropical laterite soils, gradation containing 50% fines content provides better hydraulic conductivity. the use of noninvasive digital image technique can enable designers/engineers to monitor and visualize the leachate migration in compacted soils in waste containment application systems. keywords-digital image analysis; monitoring leachate migration; soil gradation; groundwater protection; sanitary landfill i. introduction groundwater is one of the major sources of water supply for domestic and industrial purposes. however, its purity and quality is compromised because of the way waste is disposed [1]. groundwater is more reliable and safer to use than surface water as it is less exposed to numerous pollutants [2], though groundwater reliability is subjected to risks due to pollution caused by various sources. one of them is contamination by leachate through landfills because landfills are the final destinations of the majority of waste generated in most urban areas. a liquid that permeated through waste, and contains heavy minerals and suspended materials is defined as landfill leachate [3]. leachate is generated either from external water or from within the waste mass. leachate generated from urban solid waste contains heavy metals. these heavy metals leach out from the soil and enter the underlying aquifer, which affects the livelihood of the surrounding community [4-5]. to prevent leachate contamination through landfill, hydraulic barriers known as liners and covers are constructed. leakage of leachate through hydraulic barriers can be one of the main pollution hazards to groundwater. therefore, soil materials used as hydraulic barriers must have the following attributes which make them suitable in sanitary landfills: • they must contain significant amounts of fines and clay minerals [6-8]. • they must have hydraulic conductivity of ≤1×10 -9 m/s [911] and unconfined compressive strength of ≥200kn/m 2 [12-14]. • maximum allowable value of volumetric shrinkage should be 4% [15-18]. the methods generally employed to study and monitor groundwater quality include the use of observation wells and surface/subsurface geophysical techniques [19]. the use of observation wells, suction lysimeters, and phyto-screening are referred as invasive methods, while the use of photography and remote sensing, and rapid noninvasive field survey and screening are referred as noninvasive methods [20]. some of these noninvasive techniques are briefly explained below. a deformation measurement technique known as digital image correlation (dic) is used to compare two digital images corresponding author: y. b. yamusa engineering, technology & applied science research vol. 9, no. 1, 2019, 3685-3691 3686 www.etasr.com yamusa et al.: monitoring leachate migration in compacted soil using digital image technique by calculating their field incremental displacement and locating several small regions in both images to high subpixel accuracy. it is commonly referred to as particle image velocimetry (piv) in fluid mechanics applications [21]. light transmission visualization (ltv) is a method which relies on the transitory of electromagnetic energy through the tested media where the distribution of liquid saturation is measured as a variation in light intensity field. [22, 23]. researches that applied noninvasive imaging techniques produced precise depiction and improved understanding of the multiphase system. recently, image analysis techniques or digital image techniques (dits) are used to investigate the migration of fluids within soils [23]. the application of dit is widely used for double-porosity soil [22-30]. in this research, a noninvasive technique is applied using a dit that captures the successive migration of leachate through compacted laterite soil in the laboratory to simulate the leachate transportation in actual landfill. moreover, the effects of soil gradation with respect to fines content are also investigated. ii. materials and methods the laterite soil used in this study was extracted from skudai campus of universiti teknologi malaysia located at 1º33'39”n and 103º38'44”e. the soil is classified as mv according to the british standard classification [31]. the physical properties as well as the particle size distribution of the laterite soil were determined from laboratory tests and are presented in table i and figure 1 respectively. three different grading sizes (i.e. gravel, sand and fines) were gathered from the sieved natural laterite soil samples and then reconstituted into different gradations. the following gradations were investigated: • natural laterite soil with 30% fines, 40% sand and 30% gravel by weight of dry soil denoted as l1. • reconstituted laterite soil with 40% fines, 40% sand and 20% gravel by weight of dry soil denoted as l2. • reconstituted laterite soil with 50% fines, 40% sand and 10% gravel by weight of dry soil denoted as l3. the flow chart of the experiment is presented in figure 2. table i. laterite soil physical properties property value natural moisture content, % 34 liquid limit, % 76 plastic limit, % 42 plasticity index, % 34 bs classification mv specific gravity 2.7 omc, % 30 mdd, mg/m3 1.35 % passing bs 63µm sieve 30 a. soil compaction british standard light (bsl) compaction equivalent to standard proctor compaction is adopted as outlined in bs 1377: 1990: part 4. in preparing the soil samples, optimum moisture content (omc) was added to the three different laterite soil gradations. dried soil sample weighing about 2kg of l1 was mixed at omc of 30%. to allow proper moisture distribution, the soil was put inside a plastic bag for 24 hours. a circular plastic plate having similar diameter with the acrylic soil column was put on top of the soil before blowing to provide a flat surface. the soil was then compacted in 3 equal layers placed in a circular acrylic column. each layer was given 27 blows of the 2.5kg rammer falling freely from a height of 300mm. the acrylic soil column has been chosen to monitor and detect the changes occurring inside the whole area of circular column. the same procedure was followed for the l2 and l3 at their optimum moisture contents. fig. 1. particle size distribution curve fig. 2. flow chart of the experiment b. leachate preparation in this experiment, black dye solution is used as the permeant to simulate leachate. it was chosen to enhance the water color, so that it can be visible when migrating down the soil specimen. the chemical composition of the dye comprises of typically sodium chloride and proprietary dyes [32]. about 3.4g of dye was mixed with 340ml of water following the procedure in [33, 34]. similarly, authors in [35] prepared their salt solutions (nacl, kcl, and cacl2) by dissolving powdered salts in de-ionized water as permeant. these elements were chosen because sodium, potassium and magnesium are usually present at high concentrations in leachates, while chloride has engineering, technology & applied science research vol. 9, no. 1, 2019, 3685-3691 3687 www.etasr.com yamusa et al.: monitoring leachate migration in compacted soil using digital image technique high mobility and prevalence in the environment [36]. the leachate was poured instantaneously on the top surface of each compacted sample gently through the side wall of the acrylic columns as shown in figure 3. fig. 3. leachate on compacted laterite soil sample c. laboratory experimental procedure basically, the dit used in this research adopts the concept explained in [27]. it covers the migration of leachate in a 100mm height of soil in acrylic column. the dimension of acrylic cylinder to form the soil column was 150mm high, with a diameter of 100mm and 6mm thickness. the acrylic column was placed in-between a two-faced mirror to provide complete 360° visualization. these mirrors were placed at 105° with offset distance of 0.2m behind the soil column and facing the digital camera. a hitachi 40-watt lamp was installed over the soil column so that the whole setup was illuminated. the acrylic column was chosen to provide a clear visualization of leachate migration into the soil, so the leachate migration through the soil was observed promptly at any point and time throughout the experiment. a nikon d90 digital camera was used for image acquisition of the leachate migration at designated time intervals. the camera has a sensor size of 15.8mm by 23.6mm and pixel array of 3216×2136 pixels (12mpixels) , and operated at minimum shutter speed and aperture. the camera was rigidly positioned with a tripod and a remote control was used to capture images without shaking the camera. the soil column was positioned in a fixed place to avoid any movement. since the soil columns were in circular shape, images that reflected from the camera and the two mirrors have been combined and corrected to produce a complete single flat area of interest (aoi). a paper with grid lines size of 20mm×20mm was used to cover the soil column to a height of 100mm as shown in figure 4. the grid lines were used as a reference mark on a reference image. the reference mark is required in the image registration procedure to transform any distorted image according to the actual scale image. then a reference image was captured, and the grid line paper was removed from the soil column. afterwards, leachate was poured on top of the compacted soil sample. successive images were captured daily to monitor and record the migration behaviour. the digital image technique laboratory experimental setup is presented in figure 5. images for all the experiments were taken for one month. the duration of leachate migration from the top surface to the bottom was monitored during this period. fig. 4. soil column with reference grid lines fig. 5. laboratory setup d. digital image processing the digital images captured during the experiments were saved in jpeg format. images were then processed in surfer software. this software converts the digital image grid coordinates into surfer grid coordinates. the grid line images were then digitized and saved as generic data files (dat files) in order to be opened or referenced by a specific application like matlab, excel and surfer. in the object manager of the surfer, a post layer is added and saved as surfer file (srf file). the dat files were then copied from the surfer and pasted in excel. this was necessary in order to sort and filter the values and then saved them as excel files. the digital image processing routine was carried out using reival (matlab software). grid intersections of the image coordinates where extracted using surfer by digitization. as a parameter requirement in reival routine, these coordinates represent reference or control points. the development of this routine is to achieve image registration procedures such as: • conversion of image format from jpeg to hsi. • extraction of the hsi value area of interest. • saving the intensity value in text files in ascii format. an affine transformation method was selected to execute the image registration process. when the image registration was accomplished, a selected aoi was then implemented by the reival routine. the selected aoi was based on the pre-determined aoi. the aoi refers to the part of area of each image that corresponds to the migration area that contains the leachate. the reival routine then converted that aoi into red-green-blue (rgb) and hsi image format. the rgb and hsi intensity values of each pixel from each image were extracted and saved as standard ascii format. for each image, the reival routine would loop three times to extract and export the intensity values of all three aois of the soil column (i.e., the front and the reflected engineering, technology & applied science research vol. 9, no. 1, 2019, 3685-3691 3688 www.etasr.com yamusa et al.: monitoring leachate migration in compacted soil using digital image technique sections). surfer was used to merge the intensity values from the three images and plot the progress of the leachate migration based on the image hsi values. surfer then read the ascii data of hsi to generate a 2d contour plot. the schematic diagram is presented in figure 6. fig. 6. schematic of digital image processing [27] iii. results and discussion the effect of laterite soil gradations on leachate migration and the subsequent determination of their hydraulic conductivities using dit provide an innovative means of visualizing contaminant transportation in compacted soil liners. a. effects of soil gradation on leachate migration contour plots (2d) of hsi intensity value provide details and useful information in order to understand the characteristic of leachate migration behavior. the effects of gradation on the leachate migration for l1, l2 and l3 are presented in figures 7, 8 and 9 respectively. the red color represents the leachate movement inside the soil. figure 10 shows the measured values of cumulative leachate migration depth as a function of time for l1, l2 and l3 samples from the 2d contour plots. the leachate migration in these experiments shows a rapid progressive penetration within the first day, as the curves of the graph lines are steep within that duration. after the first day, the curve of the graph lines began to incline horizontally at a gradual pace until the seventh day. it remained constant after the seventh day until the end of the experiments depicting a gradual slowing of the downward migration of leachate. this could be explained in terms of tortuosity due to air entrapped at the bottom of the soil column which resists an equal pressure due to the leachate. fig. 7. leachate migration in soil column for l1 fig. 8. leachate migration in soil column for l2 d e p th ( m m ) d e p th ( m m ) d e p th ( m m ) d e p th ( m m ) d e p th ( m m ) engineering, technology & applied science research vol. 9, no. 1, 2019, 3685-3691 3689 www.etasr.com yamusa et al.: monitoring leachate migration in compacted soil using digital image technique fig. 9. leachate migration in soil column for l3 fig. 10. measured values of cumulative leachate migration depth as a function of time for l1, l2 and l3 samples according to [37], tortuosity is used to describe the difference between the actual distance traveled by fluid particles and the macroscopic travel distance, owing to the interconnectivity of pore spaces. a random distribution of interconnected pores in a discrete granular material is considered a porous medium. any non-interconnected pores, dead-end pores and stagnant pockets are referred to as ineffective pores. l1 demonstrated the fastest migration, covering a depth of 8.8mm in a month, followed by l2 and l3 which covered depths of 5.8mm and 3.0mm respectively. l1 showed the fastest migration because of the less fines content in the soil resulting in a more porous medium. the leachate migrates through the voids easier than in l2 and l3 with higher fines content. higher fines content means fewer voids inside the soil and less corresponding migration. the effects of fines content on voids of compacted laterite soil for l1, l2, and l3 are illustrated in figure 11. the compacted soils in acrylic column show clearly that the pores are greater in l1, followed by l2 and then l3 with porosity values at optimum moisture contents of 50%, 47.4% and 47.1% respectively. figure 11 shows the voids in the different gradations of compacted laterite soils captured during the digital image technique. fig. 11. effects of fines content on the voids of compacted laterite soil: (a) l1, (b) l2 and (c) l3 b. hydraulic conductivity at different gradations generally, hydraulic conductivity decreases with increase in time duration and subsequently with increase in fines content. after one-month monitoring, the hydraulic conductivities of the leachate for l1, l2 and l3 were 3.64×10 9 m/s, 2.40×10 -9 m/s, and 1.24×10 -9 m/s respectively. figure 12 illustrates the hydraulic conductivity values against time for different laterite soil gradations. fig. 12. hydraulic conductivity values against time for the different laterite soil gradations. from the experimental observations, it can be seen that the inter-aggregate pores of soil samples for l1 are obviously larger compared to l2 and l3. as hydraulic conductivity varies with the square of the pore radius [38], this condition may cause the leachate to move downward faster when the fines content is decreased. moreover, capillary pressure influences leachate movement. the pressure induces on the soil particle a compressive stress equal to the weight of the water column [39]. pores with larger size reduce the capillary pressure that liquid has to overcome to enter those pores and thus move through the soil easier [28]. the samples used in this research for l3 can be considered as liner materials because they have a hydraulic conductivity within the minimum range value of 1×10 -9 m/s. iv. conclusions laboratory experimentation was conducted on compacted laterite soil at different gradations to investigate their usability as liners. a digital image processing technique using matlab engineering, technology & applied science research vol. 9, no. 1, 2019, 3685-3691 3690 www.etasr.com yamusa et al.: monitoring leachate migration in compacted soil using digital image technique and surfer software was applied to monitor the leachate migration behavior in acrylic soil columns. the experiment successfully differentiated the patterns of leachate migration for l1, l2 and l3. the experiment results were determined through the observation of leachate percolation in the test samples, which were compared and the permeability rate was calculated. it was observed that the rate of migration of leachate decreased when the fines content increased. l1 exhibited the fastest migration, followed by l2 and l3. among these three different gradations, l3 (50% fines) provided the recommended hydraulic conductivity which can be used as soil liner in waste containment applications. therefore, the use of noninvasive digital image technique allows designers/engineers to monitor and visualize the migration of leachate in compacted soil. acknowledgement authors want to thankfully acknowledge the financial support given 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department of electrical engineering quaid-e-awam university of engineering, science and technology, sindh, pakistan kamransamo2@gmail.com imran ahmed samo department of energy & environment engineering quaid-e-awam university of engineering, science and technology, nawabshah, pakistan imran.samo@yahoo.com waqas mughal department of mechanical engineering quaid-e-awam university of engineering, science and technology, nawabshah, pakistan engr.pirbux@outlook.com andrew ragai henry rigit mechanical engineering department universiti malaysia sarawak, sarawak, malaysia arigit@unimas.my arslan ahmed sohoo department of electronic engineering quaid-e-awam university of engineering, science and technology larkana sindh, pakistan arslanahmed@quest.edu.pk abstract—the tidal range is a renewable energy source. in malaysia, most of the produced renewable energy is generated from the exploitation of the tidal range. the main purpose of this research is to determine a suitable system to produce tidal range energy from a potential site. a turbine selection chart is used. the mean tidal range of kuching barrage is 4.2m and the maximum flow rate over a gate is 226.9m 3 /s. therefore, for the extraction of electrical power, a bulb-type turbine with a rated power of 5.2mw is identified as suitable to be deployed at the site. keywords-tidal turbine; power; energy output; flow rate i. introduction ocean renewable energy sources are globally established as mainstream sources of energy [1]. it is calculated that the theoretical ocean energy resources are over 30,000twh/year and the net potential power is larger than the sum of wind and solar power [2]. malaysia is one of the biggest producers of solar photovoltaic (pv) panels and is ranked as world’s thirdlargest producer of solar pv energy [3]. however, ocean energy resources like tidal range energy can be used at a big scale for sustainable electrical power generation [4]. tidal range power is produced due to the consistent rise and fall of seawater [5, 6]. tidal range power can be generated where tidal range flow is available [7]. energy from tidal range can be used for electrical power generation. a potential site to generate renewable energy from tidal range at the east coast of malaysia can be determined [8]. power could be generated from the existing or a new barrage, in the isolated regions of east malaysia. this research found that bulb type turbine can be selected as the applicant turbine for kuching barrage. the selected turbine is proposed for electricity production in the sarawak state of malaysia. the aim of this research is to determine a suitable turbine for a suitable location at sarawak. kuching barrage is identified as a potential site that could yield 10.23gwh energy per year. the hypothesis of the research is that turbine selection is based on calculated parameters of potential sites, including tidal range and flow rate. ii. literature review a. selection of the tidal range turbine turbine selection is mostly dependent on the accessible tidal range and flow rate. the flow rate is used to conclude the turbine capacity. tidal barrage turbines usually have a low tidal range turbine. the lowest water range required for the operation of the turbine is between 1 and 1.5m. however, the most of tidal range power plants use low tidal range [8]. turbine efficiency and price are side factors. there are various turbine types of calculated tidal range, flow rate, and appropriate power [10]. there are four different types of turbines: pelton, francis, kaplan, and bulb type turbines [9]. the calculated ranges are between 50kw and 1,000mw and the flow rate values vary from 1.0 to 1000m 3 /s. corresponding author: kamran ahmed samo engineering, technology & applied science research vol. 10, no. 6, 2020, 6399-6402 6400 www.etasr.com samo et al.: suitable turbine selection based on the parameters of a potential site at sarawak, malaysia b. tidal range calculation tidal range is defined as the difference between the water level in low and high tides. in the present study, one way power generation is assumed. therefore, the difference in water level has been taken as the difference of high and low tide: t th h l= − (1) where ℎ is the tidal range (m), ℎ� is the high tide (m), and �� is the low tide (m). �� is defined as the discharge of water through a turbine. the water discharge through sluice gates �� can be designed based on its association with the consistent mean tidal range. 2s dq c a gh= (2) where �� is the discharge through the sluice gate (m 3 /s), �� is the discharge coefficient of the sluice gate (generally larger than 1), � is the flow area through the hydraulic building (m 2 ); is the acceleration of gravity (9.81m/s 2 ), and ℎ is the mean tidal range (m) [11]. similarly, by using (2), the flow rate can be calculated for each gate of the barrage. c. turbine rated head and power for a single turbine equation (3) is used to calculate the turbine rated head for mean tidal range lesser than 9m. the constant value 0.66 can be used for a single high basin plant with one direction and for conventional bulb type turbine [12]. by using (3), the rated head of a turbine can be achieved. in (3), mean tidal range is the same with ℎ (2): � ≈ 0.66 ×mean tidal range (3) equation (4) is used to calculate the rated power for a single turbine in mw [12]. the power output can be achieved by using (4). the number 8.22 is a turbine constant value taken from [13], whereas the number 1000 in the denominator is used for conversion from gw to mw: �� = �.������ ���� (4) iii. methodology a. method of turbine selection the selection of a suitable turbine will be conducted using the calculated parameters (tidal range and flow rate) of a site. the turbine presentation plan will be used to choose the appropriate turbine agreeing to the parameters of the chosen site. the turbine should not conflict with the current size of the barrage gates. the turbine should be capable to work effectively at the lower tidal range of the selected site. in order to install a turbine at the selected site, the turbine parameters will be determined according to the parameters of the selected site. b. tidal range and flow rate calculation for the calculation of tidal range, the tidal data for the year 2015 of the kuching barrage site will be utilized. the tidal pattern can be semi diurnal, diurnal and mixed, e.g. sarawak is semi diurnal. considering that kuching barrage is located in pending, it is assumed that the tidal pattern observed at pending is similar to the tidal pattern at kuching barrage. statistical analysis will be performed with sigma software for the calculation of the tidal range. histograms of a tidal range of each month will be plotted with the annual tidal range information of the site. on the information of histogram plots the annual mean tidal range and the monthly mean tidal range will be determined. in sigma, all data must be stacked first before any graph is to be plotted. tidal range and flow rate calculations are essential for turbine selection. the energy extraction from a potential site requires the data of tidal range and flow rate. low and high tides of each day have been collected and the tidal range was determined by (1). gate flow rate was calculated from (2). for the duration of the flushing process, the barrage gates are opened by 1m from the upstream (basin side). the opening space of the barrage gates will be considered to discover the real discharge at the barrage gate. table i presents the data of pending site for the january of 2015. the second column shows the high tide water level and the third column shows the low tide water level. the tidal range in the third column is calculated from (1). the data show that the mean of the tidal range is 4.1m. table i. high and low tide water level and tidal range of pending site, january, 2015 day high tide water level (m) low tide water level calculation (m) tidal range (m) 1 5.2 1.6 3.6 2 5.3 1.4 3.9 3 5.5 1.2 4.3 4 5.7 1.0 4.7 5 5.8 0.9 4.9 6 5.8 0.9 4.9 7 5.8 0.9 4.9 8 5.7 1.0 4.7 9 5.6 1.2 4.4 10 5.5 1.4 4.1 11 5.3 1.7 3.6 12 5.2 2.0 3.2 13 5.0 2.3 2.7 14 4.9 2.3 2.6 15 4.9 2.2 2.7 16 4.6 2.0 2.6 17 4.9 1.7 3.2 18 5.3 1.4 3.9 19 5.7 1.0 4.7 20 6.0 0.7 5.3 21 6.2 0.4 5.8 22 6.3 0.3 6.0 23 6.3 0.3 6.0 24 6.2 0.6 5.6 25 6.0 1.0 5.0 26 5.7 1.5 4.2 27 5.4 1.6 3.8 28 5.1 1.7 3.4 29 4.8 1.8 3.0 30 4.9 1.7 3.2 31 5.1 1.9 3.5 c. turbine rated head and power of one turbine to calculate the turbine rated head, (3) will be used. for calculating therated power of a turbine, (4) will be used. engineering, technology & applied science research vol. 10, no. 6, 2020, 6399-6402 6401 www.etasr.com samo et al.: suitable turbine selection based on the parameters of a potential site at sarawak, malaysia iv. results and discussions a. parameters at kuching barrage to select a suitable turbine for kuching barrage, it is important to determine the parameters of kuching barrage. the tide tables are used to calculate the tidal range of the pending site. b. tidal range of kuching barrage to calculate the tidal range and to analyze the tidal pattern of pending, the information from the tide tables of 2015 is used. the mean tidal range is 4.2m and, as can be seen in figure 1, the maximum tidal range is 6.2m. it can be seen that low tidal ranges (from 1.7m to 2.0m) have low occurring frequency while higher ranges (2.4m-6.2m) are more frequent. fig. 1. graph of calculated tidal range in 2015 at pending. table ii depicts the maximum, minimum, and the mean values for the tidal range of each month of the pending region. the lowermost tidal range, observed in december, was 1.7m and the maximum value, observed in october, was 6.2m. the highest peak mean tidal range recorded was 4.2m. the results do not relate to the monsoon, however they may seem like as coming from a hydroelectric dam. as the power generated from the barrage is one way (power generation is only generated during the low tide) and as per actual measurements of the tides it is visible that low tides are almost similar, which may be the reason of small variations in calculations. table ii. pending site tidal range in 2015 month maximum minimum mean january 6.0 2.6 4.1 february 6.0 2.8 4.2 march 5.8 2.9 4.1 april 6.0 2.8 4.2 may 5.8 2.7 4.2 jun 5.4 2.6 4.1 july 5.6 2.7 4.1 august 5.8 2.7 4.2 september 6.0 2.6 4.1 october 6.2 2.6 4.3 november 6.0 2.0 4.2 december 5.6 1.7 4.1 c. water flow rate of kuching barrage the water flow through the barrage gate is calculated by (2). during the flushing process, the barrage gates are mechanically unlocked by 1m from the upstream [14]. the kuching barrage opening area of each gate is 25m 2 while the gate width is 25m. one more parameter in defining water flowing rate is the “discharge coefficient” which is supposed to be equal to 1 [11]. on 4.2m tidal range and supposing discharge coefficients equal to 1, the total flow of four gates of kuching barrage is calculated to be 907.7m 3 /s (gate 5 is reserved for emergencies). the water flow calculated for each gate is 226.9m 3 /s. d. turbine selection based on kuching barrage parameters a turbine should be capable to work powerfully at low tidal range values. the turbine should not disturb the barrage gates’ size and ship lock. the turbine selection is based on tidal range and flow rate. for the selection of a suitable turbine, a presentation chart is used to choose the appropriate one. as shown in figure 1, the mean tidal range is 4.2m and the mean flow rate is 226.9m 3 /s. for these conditions, the most appropriate turbine is the bulb-type turbine. therefore, it is recommended to be installed at the kuching barrage. e. parameters of the selected turbine 1) rated head � equation (3) is used to calculate the turbine rated head for mean tidal range lower than 9m and a single basin tidal power plant. 2) power of a single turbine equation (4) is used to calculate the rated power of a turbine for �� = 226.9m 3 /s and �= 2.772m. the rated power is measured in mw. table iii depicts the calculated (bulb type) turbine parameters and the kuching barrage parameters. the rated head is calculated by (3), the gate flow rate is designed by (2), and the throat area of the turbine is calculated with the help of the turbine diameter and the area of a circle. the rated power output for a single turbine is calculated by (4). the turbine diameter is logically measured based on the space between the lsd of kuching barrage gate and the lowest tide level. the mean tidal range is the average of all mean tidal range values. gate flow rate is calculated by (2). the basin area is calculated with the help of google maps. table iii. pending site tidal range of each month of 2015 parameter symbol value rated head hr 2.772m throat area of the turbine f 4.3m 2 rated power output pr 5.2mw turbine diameter �� 2.35m mean tidal range h 4.2m gate flow rate �� 226.9m 3 /s basin area �� 2.94km 2 f. mechanical components of the selected turbine and its functions the main mechanical components of the bulb-type turbine are a kaplan runner, guide vanes, a propeller shaft, bearings, and the generator. the draft tube is the runner opening passageway of the turbine, fronting to the sea region in the tidal range engineering, technology & applied science research vol. 10, no. 6, 2020, 6399-6402 6402 www.etasr.com samo et al.: suitable turbine selection based on the parameters of a potential site at sarawak, malaysia kuching barrage tidal energy plant system. the key purpose of the draft tube is to decrease the velocity out of the turbine throat space. the kuching barrage draft tube is 11.32m long. guide vanes are important to modify the water flow in the runner agreeing to the design angles of the runner blades. the bulb-type turbine has two radial bearings to the horizontal shaft and provides thrust in the process [15, 16]. g. power output calculations the study exhibited that kuching barrage has the potential for power generation by the installation of tidal range turbines suitable for a tidal energy plant. the potential energy and the annual power output are calculated. h. calculated basin area of kuching barrage the basin area of kuching barrage was measured as 2.94km 2 . the total basin area bounded by the kuching barrage is 1430km 2 . however, this may not be valid when used for power generation. hence, it is assumed that the total bounded area may not be the effective area contributing power generation. the effective basin area has been assumed as 2.94km 2 . v. conclusion pending’s mean tidal range is about 4.2m and the discharged flow rate of a single gate is 226.9m 3 /s. the bulbtype turbine is proposed as the most applicable turbine for kuching barrage. the calculated diameter of the bulb-type turbine is 2.35m. the bulb-type turbine is planned to be installed at four gates of kuching barrage. the rated power is about 5.2mw/turbine. references 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[16] h. amiri, r. shafaghat, r. alamian, s. taheri, and m. s. shadloo, “study of horizontal axis tidal turbine performance and investigation on the optimum fixed pitch angle using cfd: a case study of iran,” international journal of numerical methods for heat & fluid flow, aug. 2019, http://doi.org/10.1108/hff-05-2019-0447. microsoft word etasr_v11_n3_pp7088-7093 engineering, technology and applied science research vol. 11, no. 3, 2021, 7088-7093 7088 www.etasr.com vu et al.: recurrent neural network-based path planning for an excavator arm under varying … recurrent neural network-based path planning for an excavator arm under varying environment nga thi-thuy vu school of electrical engineering hanoi university of science and technology hanoi, vietnam nga.vuthithuy@hust.edu.vn nam phuong tran school of electrical engineering hanoi university of science and technology hanoi, vietnam tranphuongnam3098@gmail.com nam hoai nguyen school of electrical engineering hanoi university of science and technology hanoi, vietnam nam.nguyenhoai@hust.edu.vn abstract-this paper proposes an algorithm to generate the reference trajectory based on recurrent neural networks for an excavator arm working in a dynamic environment. firstly, the dynamic of the plant which includes the tracking controller, the arm, and the pile is appropriated by a recurrent neural network. next, the recurrent neural network combined with a model reference adaptive controller (mrac) is used to calculate the reference trajectory for the system. in this paper, the generated trajectory is changed depending on the variation of the pile to maximize the dug weight. this algorithm is simple but effective because it only needs information about the weight at each duty cycle of the excavator. the efficiency of the overall system is verified through simulations. the results show that the proposed scheme gives a good performance, i.e. the dug weight always remains at the desired value (nominal load) as the pile changes its shape during working time. keywords-adaptive controller; excavator arm;neural network; path planning; uncertainties i. introduction the automatic control of an excavator system is a major issue in the field of excavator research [1, 2]. by unmanned operation, the excavator systems not only keep the workers safe but also increase efficiency. however, in order to finish the task without an operator, the trajectory should be designed carefully. thus, many researches on creating the trajectory for the general manipulator and the excavator have been published. in [3, 4], the 3d trajectory is built by using the information from sensors, cameras, and scanners. the advantage of these types of feedback signals is that they can track the change of the working environment. however, if the working environment lacks light or is dusty, the reliability of the obtained imagines can be reduced. in [5], a laser scanner is used to get the shape of the pile. from this information, the model of the pile is built and divided into small layers. the local path is designed according to these layers before creating the global path. in [6], the integrated physics-based model is presented for a mobile excavator. in this work, the current position of the excavator arm is returned to the control system to predict the trajectory for the next cycle. in [7, 8], a neural network is used to calculate the optimal trajectory for the excavator arm. however, these trajectories only work well in static environments. in [9], excavation trajectories are generated using the velocity and the acceleration of each hydraulic cylinder. the generated trajectories are optimal and stable but the velocity and the acceleration are difficult to measure. in [10], with the purpose of optimizing the efficiency for a semi-automated or fully automated excavator system, the trajectory is classified into 4 categories based on the location and the angle of the bucket. from these 4 trajectory types, the operator or the automatic controller will make a suitable decision as the environment changes. the problem of optimal working time and torque motion of the excavator in consideration with the boundary of the actuator’s ability is the role of path planning [11]. in this scheme, the trajectory is planned based on b-spline technique using information about soil parameters and system dynamics. neural networks are known as a good way of dealing with path planning problems. in [12-14], neural networks are used to generate collision-free trajectories for robots. in [12], the robot works in a dynamic environment with u-shaped and varying obstacles. the reference trajectory of the robot is generated by using a topologically organized neural network. in this network, the dynamic of each neuron is characterized by a shunting equation. the same neural network topology is used in [13] for a multirobot system with moving obstacles. the trajectory planning for the manipulator robot based on a neural network model of the harmonic function is introduced in [14]. trajectories are built based on neural networks to optimize the jerk in [15] or the working time in [16]. neural networks are used in the field of path planning with many different purposes [17-19]. corresponding author: nga thi-thuy vu engineering, technology and applied science research vol. 11, no. 3, 2021, 7088-7093 7089 www.etasr.com vu et al.: recurrent neural network-based path planning for an excavator arm under varying … in this paper, an algorithm based on neural networks is proposed for an excavator arm working in a dynamic environment. the dynamic model of the inner loop which includes the tracking controller, the excavator arm, and the pile is approximated by a neural network. a second, recurrent neural network (rnn) combined with the model reference adaptive controller (mrac) algorithm is used to calculate the reference trajectory for the system. by this combination, the calculated trajectory can be adjusted after each duty cycle to adapt with the change of the pile and the dug weight remains around the nominal value despite the reduction of the pile. the effectiveness of the overall system is verified through simulations. the contributions of the proposed algorithm are concluded as: • it can work in a dynamic environment, something that is restricted in [8]. • the dug weight remains in an acceptable range during the digging process although the material is reducing. the proposed scheme uses only the feedback signal from the weight sensor to generate the path. this is more reliable than cameras or scanners [3-5] and it is easier to measure than velocity and acceleration [9]. ii. problem description in order to maximize the efficiency of the excavator, one of the requirements is that during the digging process, the dug mass at each time must be maintained in a given acceptable range. however, the shape of the pile is changing while the excavator is digging up the material. therefore, if the trajectory of the excavator remains the same and the dug stack declines over each period of the process, the requirement will not be guaranteed. hence, the excavator driver has to observe the excavated weight and trajectories in the previous digging to choose an appropriate trajectory next time with an expectation that the mass in the next period will be acceptable. a trajectory generator based on this structure is proposed to replace the excavator driver, which will completely automate the digging process. before going to solve the described problem, the following assumptions are made: • the pile lies above the ground and has a triangular shape as shown in figure 1. • after a digging cycle, the material on the top of the pile will lie down and fill in the space that was taken, so the pile will maintain the triangular shape with a different slope. • the dug weight in each period is limited by the volume of the bucket. • the trajectory in each period is represented by a set of parameters. the task of the trajectory generator is to observe the weight and the trajectory’s parameters in the previous period in order to adjust suitably the trajectory parameters in the next one. in order to execute the algorithm, the excavator’s trajectory has a parabolic shape, however, in fact, the excavator’s trajectory often has a more complex shape due to many practical conditions. the parabolic shape is described by: ( ) 2 4 x h y k p − − = (1) where k, h and p are scalars. in this work, we have just change the parameter h, which corresponds to the coordinate of the vertex on the horizontal axis. therefore, each trajectory will be represented by a single value h. fig. 1. the shape of the hypothetical pile model. the block diagram of the overall system is illustrated in figure 2. it can be seen that the desired trajectory which is generated by the module is denoted as q*. the desired trajectory is a reference for the excavator controller, and the output of the excavator is q, which affects the dug weight. if the tracking controller has a good performance, the equivalent model of the controller and the excavator can be viewed as a dynamic model which has a static gain of one. in this paper, the equivalent model is considered as a first order system as follows: 1 ( ) 5 1 g s s = + (2) this means that the trajectory error reduces exponentially over time. fig. 2. block diagram of the overall system. iii. algorithm for generating the reference trajectory in fact, one does not have complete information about the dynamics of the pile. therefore, a decision on the appropriate trajectory can only be done in practice by observing the pile’s response in accordance with the trajectories that the excavator made. hence, the pile can be considered as a black box, and designing a controller for a black box leads to the idea of the neural network-based mrac. the control structure of the neural-network based mrac can be seen in figure 3. in this figure, the trajectory generator block can be seen as a controller of the outer loop. this controller is responsible for keeping the dug weight within the specific range as the shape of the pile changes. engineering, technology and applied science research vol. 11, no. 3, 2021, 7088-7093 7090 www.etasr.com vu et al.: recurrent neural network-based path planning for an excavator arm under varying … fig. 3. control structure of neural network-based mrac. this is an offline process, the first step of the design is identifying the plant with the usage of neural network, and the next step is creating a neural network-based controller according to the identified plant in the previous step. note that, the plant now contains the pile, the excavator, and the tracking controller. the input of the plant is the desired trajectory q*, whereas the practical trajectory created by the excavator is q because of the control error which should affect the dug weight. then, the robot excavates the pile with the trajectory q and obtains a weight m. in the identification problem, because the user concerns only about the dug weight after each time the excavator finishes, the object can be viewed as a discrete-time system. a discrete-time system can be described as: * * 1 ( ,..., , ,..., ) u yk k k n k k n m f q q m m − − − = (3) discrete-time system identification can be carried out by using a nonlinear autoregressive network with exogenous inputs denoted as narx. the narx’s architecture is illustrated in figure 4, where the input and feedback output of the network pass through the tapped-delay-lines (tdls) which make up the dynamics of the network. fig. 4. parallel and series-parallel architectures of the narx network. a feature that makes the narx become regularly usable in identification problems is that it has only a feedback from the network’s output. therefore, in the training process, one can remove this feedback and consider the feedback output as a second input to the network. the opened architecture, referred as a series-parallel architecture (figure 4), is used in one-stepahead prediction. the training process of the opened network is much simpler than that of the closed network, because one can utilize the traditional back-propagation algorithm for the opened network training. after the opened-network training process is completed, the network can predict one-step ahead, however the objective is to identify the system, which means that the network can make a multi-step-ahead prediction. therefore, the performance of the closed network is often not good enough. hence, one should continue training the closed network based on the opened network. however, training a closed network can still confront the problem of gradient vanishing, which is a well-known problem in the training of rnns. thus, the original training set is divided into subsets which have a smaller size. the network is trained with these subsets. when the training process with these subsets is over, the size of each subset is increased by a small number, and the training restarts with the new bigger subset. these steps are repeated until the size of the subset becomes equal with the size of the original training set. the algorithm is shown in figure 5, which begins with the size of each subset equal to the maximum number of delays (md) in the tdl of the network plus one that is equivalent to the training opened network. in figure 5, md is the maximum number of delays of both input’s tdl and feedback output’s tdl. q, c, n are the length of the original batch, the length of the mini batch, and the number of subsets’ respectively, x is the network’s parameters, eik represents the error which corresponds with the k th element of the i th subset, li(x) is the squared error which corresponds to the i th subset, l(x) is the loss function which is the mean square error of the original batch. fig. 5. training algorithm of the closed network. note that each adjacent subset has some similar elements, with size equivalent to md in the tdl. these elements are used as the initial conditions for the network. to guarantee that the objective function includes all elements in the original training batch, a subset is created to overlap the adjacent one. once the closed network has finished training, we will create the controller network based on the object network. to train the engineering, technology and applied science research vol. 11, no. 3, 2021, 7088-7093 7091 www.etasr.com vu et al.: recurrent neural network-based path planning for an excavator arm under varying … controller network, the whole structure that contains the plant network and the controller network must be considered as a major network. then, this network is used to approximate the given reference model. however, during the training process, only the controller network’s parameters are adjusted in order to optimize the objective function, while the object network’s parameters are kept unchanged. the well-known backpropagation algorithm is used to train the major network, the error between reference model’s output and this network’s output back-propagates through layers of the network, and the controller network’s parameters are updated. iv. network training and simulation a. plant network neural networks are known as a powerful technique to model a system with a mathematical model unknown or difficult to build [20, 21]. in this section, a neural network is used to model the plant which consists of the pile, the excavator, and the tracking controller. the first step of training the plant network is collecting data from the object. the performance of the network depends significantly on the way the data cover and describe the operating range of the object. in system identification problems, the data are often obtained by generating the input signal in the form of a sequence of step functions that have random durations and amplitudes. in this case, the reference input signal is produced with a random amplitude within the intervals [0.3, 0.5] and [0.5, 0.8] in the first 100 and the next 100 steps respectively. the duration of each step function is d∈[1, 10]. the main reason is that the collected data need to cover the operation range of the object. in the first 100 steps, because the size of the pile is still large, one should use a trajectory with small h. in contrast, in the next 100 steps, because a large amount of the pile is already taken, one needs to shift the range of the trajectory deep inside the pile with the expectation that the excavated weight is still acceptable. this signal is applied to the plant, then the plant’s output is collected. the obtained data are shown in figure 6. fig. 6. a mini batch of the training data for the plant network. note that there are 40 mini batches whose length is 200 samples, however figure 6 only shows an instance of the mini batches. before training, the input data are normalized in the range [-1, 1]. note that h is the representation of the desired trajectory, the control error in the controlling robot affects the practical trajectory, so the dug weight could not be the same as expected. in this case, the collected data include this control error. when the training data are available, the plant network can be designed. this network is illustrated in figure 7. the input of the network passes through a 0:1 tdl. the tdl of the input has a current element (zero delay) due to the pile feature. when one adjusts the excavator’s trajectory, the dug weight immediately changes depending on the shift of the trajectory, therefore the current component is added to demonstrate this feature. the tdl of network’s feedback output is 1:5. the bayesian regularization algorithm is used for training. the training result is shown in figure 8. then, the network is tested with the testing data. the test result is illustrated in figure 9. fig. 7. plant network’s architecture. fig. 8. training result of the plant network. fig. 9. testing result of the plant network. b. controller network first of all, one must choose an appropriate reference model. note that the plant network is of the 5th order, thus, a fifth-order dead-beat system is utilized as a reference model. the transfer function of the chosen reference model is: 1 2 3 4 5 5 4 3 2 ( ) 15 z z z z z gm z − − − − − + + + + = (4) the next step is collecting data from the reference model for the controller training set. the training data for the controller is demonstrated in figure 10. the left side in figure 10 shows the input data of the training set. the right side shows the response of the reference model. note that the initial value of the reference model’s output is the limited dug weight, this means that the dug weight can reach the maximum value in the first period. it can be seen that although the controller only engineering, technology and applied science research vol. 11, no. 3, 2021, 7088-7093 7092 www.etasr.com vu et al.: recurrent neural network-based path planning for an excavator arm under varying … operates with unit set-point, the input has different values that range from 0.4 to 1. the reason is that the controller has to work with different states of the object, so this type of input helps training the controller with practical states of the object, e.g. the controller can be trained to give a suitable trajectory that will help the dug weight increase from 0.5, which is its current value, to the desired value of 1. the training data have 8 mini batches, each mini batch having a length of 90 samples. figure 10 illustrates an example of the total training set. the major neural network’s architecture, which includes the plant network and the controller network, is shown in figure 11. the transfer function of the output layer of the controller is the tansig function, which means that the output of the controller is within the range from -1 to 1 which is equal to the normalized input range of the plant network. fig. 10. training data of the controller network. fig. 11. major network’s architecture. fig. 12. training result of the major network. the used training algorithm is the bayesian regularization. figure 12 describes the training result of the major network. it can be seen that the training error is very small, therefore the controller can be tested on the practical object. c. stability analysis the system contains a plant neural network and a controller neural network. it is a five-layer discrete-time rnn. to analyze the stability of the rnn, there are several stability criteria [22-25]. in this case, the stability criteria from [22] were applied. to do so, the recurrent neural network will be put in the standard form as: x(k+1) = f(w^1x(k)+w^2x(k+1)+b) (5) where x(k) is defined as a vector of layers' output in the past (such as a^1(k-1), a^2(k-1), a^2(k-2), a^2(k-3) ..., where a^i is the output of layer i, i=1,2…5), w^1 and w^2 are the weight matrices of layer 1 and 2. the size of the state vector is 41 in this case. we did obtain the matrices w^1 and w^2, b and f, but the upper bound and lower bound matrices for the function vector f(41×1) must be found as the requirement of the stability criteria in [20]. this leads to the problem that the equilibrium point of the system in (5) must be determined. it is not easy to find the equilibrium point in this case because its size is 41 and the function vector includes nonlinear functions such as the tansig. thus, in this work the stability of the system is verified through simulations. d. simulation results in order to verify the effectiveness of the proposed scheme, simulations are done in matlab/simulink. in the simulations, the initial path of the arm is set so that the dug mass is 0.4. the trajectory generator should calculate the reference trajectory for the plant to meet the requirement. the dug weight desired value is tracked during working time despite the change of the pile. figure 13(a) shows the change of the pile during working time. initially, the slope of the pile is about 62 degrees. because of the digging, this slope will decrease gradually and reach the value of 46 degrees at the 42 th step. figure 13(b) shows the values of h for each step. the initial value of h is set at -0.9 and after 50 steps its value is 0.8. corresponding with these 50 values of h, 50 trajectories will be generated to adapt to the change of the pile. (a) (b) fig. 13. the change of system during working time. (a) θ, (b) h. fig. 14. the dug weight response during working time. engineering, technology and applied science research vol. 11, no. 3, 2021, 7088-7093 7093 www.etasr.com vu et al.: recurrent neural network-based path planning for an excavator arm under varying … figure 14 illustrates the dug weight response of the system during working time. in the first step, the excavator works with the given trajectory and the dug weight is 0.4. the information about the trajectory and the weight will be given to the controller to calculate the reference trajectory for the next step. after 5 steps, the dug weight accomplishes the desired value and remains at this state during the working time despite the change of the pile. v. conclusion a simple but efficient algorithm has been proposed to design the reference trajectory for an excavator arm in a dynamic environment. the model of the tracking controller, the arm, and the pile is approximated, at first by an rnn. a second rnn combined with the mrac algorithm is used to calculate the reference trajectory of the system. by this combination, the calculated trajectory can be adjusted after each duty cycle to adapt with the change of the pile so that the dug weight remains around the nominal value despite the reduction of the pile. the effectiveness of the overall system was verified through simulations. the results show that the proposed scheme gives a good performance, i.e. the dug weight always tracks the nominal value as the pile changes its shape during working time. references [1] h. feng et al., "robotic excavator trajectory control using an improved ga based pid controller," mechanical systems and signal processing, vol. 105, pp. 153–168, may 2018, https://doi.org/10.1016/j.ymssp. 2017.12.014. 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[25] m. liu, "delayed standard neural network models for control systems," ieee transactions on neural networks, vol. 18, no. 5, pp. 1376–1391, sep. 2007, https://doi.org/10.1109/tnn.2007.894084. microsoft word 13-2372_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3556-3560 3556 www.etasr.com xuan et al.: prediction of the frequency response function of a tool holder-tool assembly based on … prediction of the frequency response function of a tool holder-tool assembly based on receptance coupling method xiao-jian xuan department of mechanical engineering national chin-yi university of technology taichung, taiwan qstar2013@gmail.com zhe-hao haung department of mechanical engineering national chin-yi university of technology taichung, taiwan lsky05210831@gmail.com kung-da wu graduate institute of precision manufacturing national chin-yi university of technology taichung, taiwan ffi85236@hotmail.com jui-pin hung graduate institute of precision manufacturing national chin-yi university of technology taichung, taiwan hungjp@ncut.edu.tw abstract—regenerative chatter has a fatal influence on machine performance in high-speed milling process. basically, machining condition without chattering can be selected from the stability lobes diagram, which is estimated from the tool point frequency response function (frf). however, measurements of the tool point frf would be a complicated and time-consuming task with less efficiency. therefore prediction of the tool point frf is of importance for further calculation of the machining stability. this study employed the receptance coupling analysis method to predict the frf of a tool holder-tool module, which is normally composed of substructures, tool holder and cutter with different length. in this study, the angular components of frfs of the substructures required for coupling operation were predicted by finite element analysis, apart from the translational components measured by vibration experiments. using this method, the effects of the overhang length of the cutter on the dynamic characteristics have been proven and successfully verified by the experimental measurements. the proposed method can be an effective way to accurately predict the dynamic behavior of the spindle tool system with different tool holder-tool modules. keywords-frequency response function; receptance coupling analysis method; tool holder-tool module i. introduction according to cutting mechanics, the occurrence of chatter is considered to be caused by self-excited vibration phenomena from the interactions of dynamics of machine tool structure and machining process [1-3]. therefore, the cause of chatter can be related to the cutting force and the structure characteristics of the machine tool structure. since the spindle-tool holder-tool system is the most important core component of the machine tool, its dynamic performance directly affects the machining ability and precision. for a specific machine tool, to meet the required machining operation with sufficient production rate, the machining conditions of a particular cutter should be appropriately selected from the stability lobes diagram of the spindle tool system [4-6]. generally, the machining stability of a cutter can be determined from the measured frfs. however this would be a complicated and time-consuming task, with less efficiency. a number of studies based on the receptance coupling substructure analysis (rcsa) method have been performed to predict the tool point frequency response functions and hence machining stability [5-8]. in the rcsa approach for the machine spindle tool system, the spindle-holder tool module is considered as three separate components: spindle, tool and holder, and the frequency responses of these components are required parameters for the coupling operation to predict the tool point frf. however, in practice, only the frequency responses of the linear displacement to the force can be directly measured through vibration tests. the other frequency responses associated with the linear or rotational displacement to the force or moment were obtained from analytical solution by modeling the spindle tool assembly as the euler-bernoulli or timoshenko beam model [9-11]. another approach based on first-order backward finite difference analysis was applied to derive the frequency responses of the rotational displacement-to-force from the measured linear frfs [12-14]. in this approach, two linear displacement-to-force frfs were measured at a specific point, such as tool tip, and its neighboring point at certain distance. the accuracy depends greatly on the distance between the two measured points [13]. another key point for accurate coupling operation is the modeling of the coupling interface within the assembled structures, which have been verified to affect tool point frf [11, 15-17], while the contact characteristics of the tool-holder interface and tool holder-spindle nose cannot be engineering, technology & applied science research vol. 8, no. 6, 2018, 3556-3560 3557 www.etasr.com xuan et al.: prediction of the frequency response function of a tool holder-tool assembly based on … measured experimentally or calculated analytically. therefore, identification approaches in different ways were proposed to identify the contact properties of the elastic interface from the experimentally measured frfs and the analytically derived frfs [17], which was further introduced in the receptance coupling operation of the assembled structures. in this study, the assembled module of tool holder and tool was employed for predicting the frfs based on the receptance coupling operation of the individual compliance matrix of each substructure. the effect of the tool length on the tool point frf was investigated. to lessen the inaccuracy of the approximation estimation of the compliance components associated with the rotational displacement or applied moment, we employed the finite element method to calculate the frfs of the linear displacement-to-moment or the rotational displacement-toforce of the substructure component such as the holder and cutter. also, the interface characteristics between the cutter and tool holder were identified by inverse coupling from experimental measurements on the tool holder-tool assemble, which was then implemented into the developed algorithm to calculate the dynamic response of the tool-holder-tool system when a tool with different length was used. the predicted tool end frfs were compared with the experimental measurements conducted on the physical modules. ii. basic theory of receptance coupling method in this study, receptance coupling method was used to predict the frequency response functions of a tool holder-cutter (assembled structure ab) from those of the cutter (substructure a) and tool holder (substructure b) with coupled effects of the bonding interface between the substructures a and b. as shown in figure 1, the assembled structure ab is formed by inserting the cutter into the collet of the holder. for the cutter (substructure a), the relationship between the displacements of points 1, a2 and forces f1, fa2 can be expressed as � x�xa�� � � ha�� ha�� ha�� ha�� � f� fa�� (1) for the tool holder (substructure b), the relationship between the displacement of point b2 and force fb2 is: �xb�� � �hb����fb�� (2) when the cutter is combined with the tool holder, we have: f2= fa2+fb2 ， x2= xa2= xb2 (3) the displacement of point 1 caused by the force f1 can be obtained as follows: g�� � ���� � ha�� �ha���ha�� �hb��� ��ha�� (4) where h2=ha22+hb22, representing the coupled term of substructure a and substructure b and g11 is the frequency response function at the tool end due to the excitation f1. actually, the displacement components measured at each point on the structure include the linear translation displacement (x) and the angular displacement (θ), which are caused by the force (f1) and moment (m1), respectively. the generalized relationship between the displacement vector �x�� and force vector �f�� can be expressed as follows: �x�� � � x� θ� �;�f�� � � f�m�� (5) [ ]1 1 11 11 111 1 1 11 11 1 a a a a a a x f h l f h m n p mθ         = =               (6) 1 1 1 1 11 11 11 11 1 1 1 1 a a a a x x h ,l ; n ; p f m f m θ θ = = = = (7) where [ ]11ah represents the frequency responses matrix or component receptance matrix of the structure. considering the elastic interface between the cutter (a) and tool holder (b), the coupled effect should be included in (4) through the interface characteristics matrix [9]: �k"� � � k#$ �iwc#$ kθ$ �iwcθ$k#( �iwc#( kθ( �iwcθ( (8) where kxf, kθf, kxm and kθm are the stiffness of the contact interface under transverse force f and bending moment m, and cxf, cθf, cxm and cθm are damping coefficients of contact interface. when the contact characteristics are included in receptance coupling operation, the coupling equation for prediction of the compliance matrix of structure assembly becomes �gt��� � *�ha���� �ha���∗ �h���� ∗ �ha���, (9) in which �h�� � �ha���� �hb���� �k"��� fig. 1. schematic of the substructure coupling iii. experimental measurement of frfs the frfs associated with the linear displacement-to-force required for receptance coupling operation were measured by vibration tests, including tool holder (bbt40), cutter and tool holder-cutter module respectively. in order to exclude the influences of the cutter geometry, cylindrical rods with diameter of 20mm were used, which were made in length of 110, 120, 130, 140 and 150mm. in the assembled module, each rod was clamped in the holder collet at the same length of 50mm, which had a different overhang length of 60, 70, 80, 90 and 100mm. the experimental configurations for different components are illustrated in figure 2. as shown, the testing rod was suspended by two wire ropes and excited at one end (point 1) by the impact hammer. two accelerometers were mounted on both ends, point 1 and point 2 to measure the vibration signals. the frfs were then extracted from the measured vibration spectrum. the measured frfs of the rods are illustrated in figure 3, and were termed as ha11. the results engineering, technology & applied science research vol. 8, no. 6, 2018, 3556-3560 3558 www.etasr.com xuan et al.: prediction of the frequency response function of a tool holder-tool assembly based on … show that the dominant natural frequency of the cylindrical rod decreases with increasing length and the compliance increases with increasing length. the frfs of the tool holder, termed as hb22, were measured in similar way, as shown in figure 4. the tool holder shows a higher frequency, about 7750hz and lower compliance, about 0.011um/n. the frfs, termed as g11, of the assembled structure of the tool holder and rod of different lengths are illustrated in figure 5 for comparison. it is found that the assembled tool holder-rod module with short overhang length shows higher frequency and lower compliance when compared to the assembled module with longer overhang length. for example, in the case of the rod with length of 150mm, the assembled module shows a maximum compliance of 9.8um/n at frequency of 1500hz. in the case of rod with length of 120mm, the maximum compliance of the tool holderrod assembly is 3.35um/n, occurring at 2250hz. this result shows that the tool holder with a longer tool behaves more complaint than with a shorter tool. (a) cylindrical rod (a) (b) tool holder (b) (c) tool holder and rod assembly (ab) fig. 2. vibration tests of tool holder and tool components. fig. 3. measured frfs of cylindrical rod with different lengths fig. 4. measured frf of tool holder. fig. 5. measured frfs of tool holder with tool in different length iv. predictions of frfs of tool holder and tool assembly a. estimation of the receptance compliance matrix as demonstrated above, the direct or cross compliance components in receptance matrix such as the ha11 and ha12, can be obtained from vibration test. however, the other terms such as the la11 =(x1/m1), na11=(θ1/f1) and pa11=(θ1/m1) can only be obtained by numerical approaches [11, 12], but with less accuracy. in this study, the components laij are predicted by finite element analysis and then are used to derive naij and paij. to this, finite element models of the substructures and assembled structures were created for analysis, as shown in figure 6, including the holder, cutter (cylindrical rod) and holder-rod assembled model. the material properties of the structure components are ρ=7860kg/m3, young’s modulus e=200gpa and poisson’s ratio µ=0.3. the interface between the collet of the holder and rod was modeled with surface to surface spring elements in radial and rotational directions with appropriate contact stiffness. the models were validated by comparing the frequency response functions obtained from finite element prediction and experimental measurements. according to harmonic analysis, the predicted frequency response functions, termed ha11, hb22 and gl11, associated with tool holder, tool and holder-tool assembly, respectively, are illustrated in figure 7. it is apparent that the peak compliance and the resonant frequencies for the three components agree well with the measurements. taking tool holder-tool assembly as an example, the differences in modal frequency and maximum compliance between finite element prediction and measurements are 1.1% and 2.2%, respectively. from the comparisons, the linear and rotational stiffness of the interface between tool holder collet and rod were identified as 3.03×108n/m and 3.25×103n-m/rad, respectively. (a) solid model of tool holder and tool (b) finite element model fig. 6. finite element model of tool holder-tool model and modeling of the contact interface with these validated models, the frequency response functions, such as ha11 and la11, associated with the linear displacements to the applied force or moment can be obtained by performing the harmonic analysis. as shown in figure 8, for rod model (substructure a), the direct compliance component la11, can be computed from frfs of linear displacement x1 under excitation of the moment m1 and the cross component engineering, technology & applied science research vol. 8, no. 6, 2018, 3556-3560 3559 www.etasr.com xuan et al.: prediction of the frequency response function of a tool holder-tool assembly based on … la21 can be computed from frfs of linear displacement x2 under excitation of the moment m1. in similar ways, the compliance components lb22 of the tool holder (substructure b) and gl11 of the holder-rod module (assembled structure ab) can be obtained from the harmonic analysis. (a) (b) (c) fig. 7. comparisons of the predicted and measured frfs of the tool, tool holder and the assembled tool holder fig. 8. harmonic analysis for frfs hxij and lxij of the cylindrical rod and tool holder-tool assembly prediction. b. prediction results and discussion in receptance coupling operation, the compliance matrices of the individual substructures such as [ha11], [ha12] and [hb22] in (9) are required. the general form of the compliance matrix is composed of four components, as indicated in (6) and (7). for each substructure, the direct component of linear displacement-to-force (ha11) can be measured through the vibration tests, and the la11 can be obtained by finite element predictions, na11 and pa11 are obtained by numerical approach employed in [14]. besides, the dynamic characteristic matrix [ks] of the bonded interface between tool holder and cutter should be introduced in coupling operation. however, these parameters are unavailable in practice and can only be identified through parameter identification from experimental measurements. this can be done by inverse coupling operation from (8), that is: -1 -1 -1 -1 sh 12 11 11 21 22 22 [k ]=[[ha ] ×([gt ]-[ha ]) ×[ha ] -[ha ]-[hb ]] (10) in which the terms [ha11], [ha21], [ha12] and [ha22] are compliance matrices of the frfs associated with the cylindrical rod, [hb22] is the compliance matrix of frfs associated with the tool holder and [gt11] is compliance matrix associated with the tool holder-rod assembled module. in this study, an assembled module of a tool holder with rod length of 150mm was used as the reference for inverse operation of receptance coupling analysis to identify the dynamic interface characteristics. by substituting the receptance compliance matrices associated with this assembled structures into (10), the dynamic interface characteristics between tool holder and cylindrical rod at the dominant mode of 1520hz were quantified and listed in table i. the linear translational stiffness and damping coefficient of the interface corresponding to the dominant mode are 1.2587 × 107n/m and 3378.1n⋅s/m, respectively. the interface contact stiffness and damping coefficient corresponding to the angular components are 3.8978×105nm/rad and 11.828nm⋅s/rad respectively. based on the receptance coupling analysis incorporated with the interface characteristics, the tool end frequency response functions of the assembled tool holder-tool module with different rod length can be obtained. table i. holder-tool interface dynamic contact characteristics. linear displacement to force stiffness (n/m) 1.2587×107 linear displacement to force damping (n⋅s/m) 3378.1 linear displacement to moment stiffness (n/m) 1.5740×106 linear displacement to moment damping (nm⋅s/m) 117.50 angular displacement to force stiffness (n/rad) 1.4474×106 angular displacement to force damping (n⋅s/rad) 13.811 angular displacement to moment stiffness (nm/rad) 3.8978×105 angular displacement to moment damping (nm⋅s/rad) 11.828 figure 9 shows the tool point frfs (gh11) predicted for the tool holder with a rod in length of 110, 120, 130 and 140mm. it is found that the predictions are well consistent with the measurements in vibration test of a physical unit. for the four different assemblies, the dominant frequency of the tool holdertool assembly predicted by receptance coupling operation is very close to the measured frequency, with difference less than 1.0%, which clearly demonstrates that the tool holder and tool interface dominates the vibration behavior of the assembled structure, while the difference of the predicted and measured tool compliance is about 2.0 %. basically, the difference can be ascribed to the fact that the real contact characteristics including the contact stiffness and interface damping property could be slightly affected to change with tool length. however, as noted above, the contact characteristics of the holder-tool interface identified in this study are appropriate for modeling the physical tool holder system. overall, the receptance coupling method presented in this paper works very successfully. v. conclusions this paper presents predictions of the frfs of the tool holder-tool assembly by using the receptance coupling operation method. in this proposed method, the compliance components associated with the linear displacement to forces were directly measured by conducting the vibration test on the physical structures while other components in linear and engineering, technology & applied science research vol. 8, no. 6, 2018, 3556-3560 3560 www.etasr.com xuan et al.: prediction of the frequency response function of a tool holder-tool assembly based on … angular displacements were computed by finite element approach and numerical approximation. (a) (b) (c) (d) fig. 9. predicted tool end frfs of tool holder and tool assembly with different tool lengths: (a) 110mm, (b) 120mm, (c) 130mm and (d) 140mm. the interface characteristics identified by inverse receptance coupling from experimental measurements have been used to couple the frequency responses of the substructures of holder and tool. comparisons of the frfs obtained from predictions and measurements clearly demonstrate that the contact characteristics of the holder-tool interface identified in this study are appropriate for modeling the physical tool holder system, which can accurately predict vibration behavior of the tool holder-tool assemblies with different tool length. as a whole, the receptance coupling method presented in this study can be applied for the prediction of the tool point frf of a spindle tool system. acknowledgement authors acknowledge the support for this work provided by the intelligent machinery technology center, industrial technology research institute and national science council in taiwan through project number most105-2622-e-167-011cc3. references [1] j. tlusty, m. polacek, “the stability of machine tools against self excited vibrations in machining”, in: international research in production engineering, pp. 465-474, asme, 1963 [2] j. tlusty, “dynamics of high-speed milling”, journal of engineering for industry, vol. 108, no. 2, pp. 59-67, 1986 [3] f. koenisberger, j. tlusty, machine tool structures—vol. i: stability against chatter, pergamon, englewood cliffs, 1967 [4] i. minis, r. yanushevsky, a. tembo, r. hocken, “analysis of linear and nonlinear chatter in milling”, cirp annals-manufacturing technology, vol. 39, no. 1, pp. 459-462, 1990 [5] t. l. schmitz, r. r. donalson, “predicting high-speed machining dynamics by substructure analysis”, cirp annals-manufacturing technology, vol. 49, no.1, pp. 303-308, 2000 [6] t. schmitz, m. davies, m. kennedy, “tool point frequency response prediction for high-speed machining by rcsa”, journal of manufacturing science and engineering, vol. 123, no. 4, pp. 700-707, 2001 [7] t. l. schmitz, t. j. burns, “receptance coupling for high-speed machining dynamics prediction”, 21st conference & exposition on structural dynamics, kissimmee, fl, usa, february 3-6, 2003 [8] o. ozsahin, y. altintas, “prediction of frequency response function (frf) of asymmetric tools from the analytical coupling of spindle and beam models of holder and tool”, international journal of machine tools and manufacture, vol. 92, pp. 31-40, 2015 [9] a. erturk, h. n. ozguven, e. budak, “analytical modeling of spindle– tool dynamics on machine tools using timoshenko beam model and receptance coupling for the prediction of tool point frf”, international journal of machine tools and manufacture, vol. 46. no. 15, pp. 19011912, 2006 [10] o. ozsahin, a. erturk, h. n. ozguven, e. budak, “a closed-form approach for identification of dynamical contact parameters in spindle– holder–tool assemblies”, 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mills”, international journal of machine tools and manufacture, vol. 43, no.9. pp. 889-896, 2003 [16] a. erturk, h. n. ozguven, e. budak, “effect analysis of bearing and interface dynamics on tool point frf for chatter stability in machine tools by using a new analytical model for spindle–tool assemblies”, international journal of machine tools and manufacture, vol. 47, no. 1, pp. 23-32, 2007 [17] e. budak, a. erturk, h. n. ozguven, “a modeling approach for analysis and improvement of spindle-holder-tool assembly dynamics”, cirp annals-manufacturing technology, vol. 55, no. 1, pp. 369-372, 2006 microsoft word etasr_v11_n5_pp7558-7563 engineering, technology & applied science research vol. 11, no. 5, 2021, 7558-7563 7558 www.etasr.com shar et al.: health risk assessment of arsenic in the drinking water of upper sindh, pakistan health risk assessment of arsenic in the drinking water of upper sindh, pakistan noor ul hassan shar institute of chemistry shah abdul latif university khairpur, pakistan noorulhassan4228@gmail.com ghulam qadir shar institute of chemistry shah abdul latif university khairpur, pakistan gqadir.shar@salu.edu.pk abdul raheem shar institute of chemistry shah abdul latif university khairpur, pakistan saifiraheem3863920@gmail.com shafi muhammad wassan department of community medicine ghulam muhammad mahar medical college sukkur sindh, pakistan wassanshafi1975@gmail.com zubeda bhatti department of physics shah abdul latif university khairpur, pakistan bhatti.zubeda@yahoo.com abida ali department of computer science shah abdul latif university khairpur, pakistan abida.ali@mckru.edu.pk abstract-water is a valuable compound for plants, animals, and humans. various contaminating agents pollute it, with arsenic being one of them. measurements of arsenic in potable water in upper sindh were conducted during this study. the samples were prepared by microwave-assisted digestion and analyzed by an atomic absorption spectrophotometer. a total of 240 potable water samples were collected from 8 talukas of upper sindh. dms coordinates were also recorded with the help of the global positioning system (gps). the highest arsenic content of 50µg/l was observed in garhi khairo taluka. the average arsenic content in water samples of all of the talukas, except miro khan, was found higher than the who permissible limit. the 69.2% of samples were found to be contaminated by arsenic. therefore, the water of the studied area is concluded to be in poor condition for cooking and drinking. keywords-arsenic; upper sindh; atomic absorption spectrophotometer; water health risk assessment i. introduction arsenic is a metalloid with high toxicity, which can be found in the environment in geological substrata, whereas it can also be released by human activities [1]. in numerous areas, arsenic in freshwater atmosphere, due to direct release from anthropogenic and natural sources, is a severe concern [2]. the concentration of arsenic ranges from 0.5 to 5000µg/l in freshwater [3]. four oxidation states of arsenic are observed in nature: (-3), (0), (+3) and (+5) whereas it can be found in various forms such as arsenate, arsenite, monomethylarsonic acid, dimethyl arsenic acid, trimethylarsine, arsenocholine, arsenobetaine, arsenosugras, etc. organic arsenic is less poisonous than inorganic arsenic, while pentavalent arsenic is less toxic than its trivalent state [4]. arsenic is accumulated in soil through human activities like fuel utilization, mining, smelting of arsenic ores, manufacture of arsenic–based compounds, and use of arsenic–based pesticides [5, 6]. biomethylation mechanism of micro-organisms and use of organo-arsenical pesticides are responsible for organic arsenic in natural water systems [7]. higher concentrations of arsenic in groundwater of countries like italy, vietnam, bangladesh, west bengal, hungary, china, mexico, chile, and argentina have been observed [8]. water resources are exploited because of the continuous development of global population. arsenic and heavy metal contamination of water sources are often found to be in extremely critical state [9]. these pollutants find their ways in surface and groundwater sources due to their high mobility. there are various groundwater and surface water sources [10]. when compared to surface water, groundwater is more secure regarding heavy metals and microbes [11]. therefore, most people use groundwater for drinking purposes [12], although a lot of research has been conducted on groundwater containing heavy metals [13]. about 100 million people of southeast asia were found to be at high risk of arsenic toxicity [14]. there are two main ways of arsenic accumulation in the human body, taking arsenic polluted potable water and consuming arsenic contaminated food [15]. stomach toxicity, brain, kidney, and liver cancers, and skin lesions may be the results of chronic corresponding author: abdul raheem shar engineering, technology & applied science research vol. 11, no. 5, 2021, 7558-7563 7559 www.etasr.com shar et al.: health risk assessment of arsenic in the drinking water of upper sindh, pakistan effects of arsenic. due to its toxicity, who and usepa have reduced the threshold limit of arsenic from 50 to 10µg/l in 2001 [16]. to the best of our knowledge, in the 8 talukas of upper sindh that constitute the studied area, arsenic contamination and health risk assessment in potable water have not been conducted. the present work aimed to identify arsenic contamination and its potential health risk assessment in upper sindh keeping in view the public, anthropogenic inputs and geology. ii. materials and methods a. study area the weather of upper sindh is moderate in winter and extremely hot in summer. the area is commonly considered as a hot arid zone. the lowest and the highest temperatures recorded are -3.9ºc and 52.8 0 c respectively. in the season of monsoon from july to september the rainfall is not sufficient. the average recorded annual rainfall is 122.5mm and the air is generally dry. upper sindh lies from 27°56' to 28°27' n and from 68° to 69°44' e covering an area of about 6,790km 2 . in its surroundings, thar desert is located on the eastern side, bahurai range in west, kherthar range in south west and suleman range in the north. at the south eastern side of jacobabad, indus river flows from north to south and besides the bolan river there are various canals and streams at the western and northern sides. there are parts of baluchistan highlands at northern, western, and south western areas and as a result, non-perennial streams are found towards the province of sindh [17]. fig. 1. hand pumps in the study area. b. chemicals and reagents reagents bought from merck (darmstadt, germany) along with de-ionized water were used for arsenic solution preparation. c. sampling in order to get groundwater samples it is necessary to run hand pumps at least for 5 minutes to eliminate insoluble impurities and sand particles and to get depth water of required elemental amounts [18]. water used for drinking was obtained from hand pumps whose depth was varied from 30 to 70 feet. plastic 1500 ml bottles were used to collect the water samples. eight talukas of upper sindh were selected to be sampled. the coordinates were recorded with the help of a gps device. in total, 240 potable water samples were collected from 8 talukas of upper sindh. after collection, the water samples were transported immediately to the laboratory. practical investigation of arsenic was conducted in the laboratory and its quantity was measured with the help of a calibration graph. d. instrumentation to measure the arsenic contamination from potable water, the technique of atomic absorption spectrophotometer (perkin-a 700) was used along with mercury hydride system (mhs–15). it is a precise and simple method of analysis of metals found in various samples [19]. e. microwave digestion method ptfe flasks were taken and 500ml of water samples were kept in them. after closing tightly, the flasks were subjected to microwave radiation in stopped up vessel microwave digestion using milestone ethos d model (sorisole-bg, italy). the digestion plan of microwave oven was 100w for 2min, 250w for 6min, 400w for 5min, 550w for 8min, and ventilation for 8min. after the cooling, the content of the flask was diluted with 0.2m nitric acid to 10ml. the same procedure was followed to prepare the reagent blank. the advantage of microwave digestion method is that it takes less time to digest water samples and the possibility of evaporation of elements is less, therefore more precise extraction of elements from samples can be accomplished as compared to conventional digestion methods. less acid is used for digestion as well [20]. iii. results and discussion more than 40% of the population of pakistan suffers from arsenic contamination in potable water. more than 20% of the people of punjab suffer from arsenic contamination in surface or groundwater sources, with the problem becoming bigger in industrial zones [21-24]. according to our results, the highest concentration of 50µg/l of arsenic was obtained in garhi khairo taluka and the minimum of 3µg/l was found in samples from ubauro, tangwani, kambar, and miro khan talukas. the mean arsenic content in all talukas except miro khan was higher than the who permissible limit. in daharki and kambar talukas, 80% of groundwater samples were contaminated by arsenic, in kashmore and garhi khairo 86.7%, and in ubauro, tangwani, thul, and miro khan the contamination percentage was 70%, 73%, 56.7%, and 20% respectively (table i). water quality is worse in heavily populated regions of pakistan such as peshawar, lahore, karachi, shaheed benazirabad [49] and other cities and towns. the groundwater of upper sindh is also contaminated and not safe for drinking due to its high arsenic contamination. some reported cities of pakistan with high arsenic content in groundwater are shown in table ii. arsenic concentration in various countries is given in table iii. descriptive statistics such as, minimum, maximum, mean and standard deviation of arsenic in potable water of upper sindh are given in table iv. engineering, technology & applied science research vol. 11, no. 5, 2021, 7558-7563 7560 www.etasr.com shar et al.: health risk assessment of arsenic in the drinking water of upper sindh, pakistan table i. arsenic concentration (µg/l) in the studied eight talukas of upper sindh daharki ubauro kashmore tangwani garhi khario thul kambar miro khan 5 10 9 21 17 38 11 9 11 12 12 7 16 13 3 6 14 20 12 9 12 12 16 4 11 18 13 18 11 8 21 5 5 19 10 19 4 7 12 6 10 26 14 16 9 8 3 5 11 18 11 12 20 5 15 18 14 15 10 20 13 16 21 17 15 12 12 33 12 9 18 16 5 24 15 24 12 8 26 17 16 37 12 37 4 8 34 7 17 25 16 10 17 6 49 5 13 38 18 8 22 13 26 3 15 25 18 6 13 18 11 6 5 3 13 9 4 9 10 7 19 14 15 14 16 8 16 9 20 13 19 16 22 12 15 7 17 11 9 11 19 18 11 9 14 17 14 17 27 15 10 6 13 9 13 25 35 23 3 15 18 6 13 39 50 31 8 6 17 5 14 25 27 46 19 7 10 7 15 3 12 23 12 15 13 9 17 9 11 8 11 7 11 18 24 22 16 7 15 10 12 19 27 20 13 12 12 5 14 18 17 19 34 9 33 6 13 20 17 26 25 30 24 7 13 5 21 18 20 21 19 5 27 6 12 15 30 16 29 9 table ii. concentration of arsenic in different cities of pakistan province area as (µg/l) references sindh sajawal 15.3 [25] ghorabari 50 [26] mirpursakro 80 [26] ketibandar 5–25 [27] khairpur 0.24−315.6 [28] gambat 0.01–126 [29] shaheed benazirabad 10–200 [30] dadu 8–67 [31] thatta 10–200 [32] jamshoro 13−106 [33] punjab sheikhupura 5–76 [34] rahimyar khan 20–500 [35] muzffargarh 0.01−900 [36] dera gazi khan 1–29 [37] balochistan sibi 0.3–3.5 [38] table iii. arsenic concentration in various countries country concentration (µg/l) reference india 44 [39] china (shanxi) 1932 [40] afghanistan 100 [41] taiwan 1800 [42] greece > 20 [43] bangladesh 398 [44] veitnam 3100 [45] nepal 260 [46] cambodia 3500 [47] inner mongolia, china 4000 [48] table iv. descriptive statistics of arsenic in potable water of upper sindh taluka n min max mean std. deviation daharki 30 5 27 13.3 4.78 ubauro 30 3 38 16.0 8.74 kashmore 30 9 27 14.7 4.18 tangwani 30 3 39 17.6 8.85 garhi khario 30 4 50 18.1 10.11 thul 30 5 46 15.2 10.00 kambar 30 3 49 17.1 10.11 miro khan 30 3 18 8.5 4.32 engineering, technology & applied science research vol. 11, no. 5, 2021, 7558-7563 7561 www.etasr.com shar et al.: health risk assessment of arsenic in the drinking water of upper sindh, pakistan a. pearson correlation coefficient the pearson correlation of the potable water of the 8 talukas of upper sindh is shown in table v. positive correlation was observed among garhi khairo and daharki (0.483). arsenic in potable water of thul and garhi khairo also showed positive correlation of 0.491, whereas the water of the kambar and ubauro talukas also displayed positive correlation of 0.415. negative correlation of arsenic in drinking water was found among talukas thul and ubauro. all relations were observed significant at the level of 0.05, and 0.1 respectively. b. human health risk assessment equation (1) was used to estimate the total arsenic intake [33]: adi = �� � �� (1) body weight (bw) and daily water intake for common people were supposed to be 65kg and 3 to 3.5l respectively. the results of the average daily intake (adi) are given in table vi. adi values at alarming levels were found in the water of all talukas of upper sindh with the exception of miro khan. the values ranged from 0.46 to 0.97µg/day. comparatively, tangwani, garhi khairo, and kambar talukas showed higher adi values. various problems may be caused due to high adi values such as diabetes, cardiovascular problems, hypertension, black foot disease, keratosis, bladder and lung cancer, and skin lesions [31] (tables vi, vii). table v. correlation coefficient of arsenic in groundwater of different upper sindh talukas daharki ubauro kashmore tangwani garhi khario thul kambar miro khan daharki 1 ubauro -0.097 1 kashmore 0.057 0.150 1 tangwani 0.097 0.023 -0.063 1 garhi khario 0.483 ** -0.308 0.040 0.319 1 thul 0.095 -0.432 * -0.132 0.262 0.491 ** 1 kambar 0.306 0.415 * 0.092 0.116 -0.004 -0.197 1 miro khan -0.136 -0.217 -0.300 0.159 -0.030 -0.029 -0.074 1 table vi. average daily intake of arsenic from drinking water of different upper sindh talukas daharki ubauro kashmore tangwani garhi khario thul kambar miro khan 0.27 0.54 0.48 1.13 0.92 2.05 0.59 0.48 0.59 0.65 0.65 0.38 0.86 0.70 0.16 0.32 0.75 1.08 0.65 0.48 0.65 0.65 0.86 0.22 0.59 0.97 0.70 0.97 0.59 0.43 1.13 0.27 0.27 1.02 0.54 1.02 0.22 0.38 0.65 0.32 0.54 1.40 0.75 0.86 0.48 0.43 0.16 0.27 0.59 0.97 0.59 0.65 1.08 0.27 0.81 0.97 0.75 0.81 0.54 1.08 0.70 0.86 1.13 0.92 0.81 0.65 0.65 1.78 0.65 0.48 0.97 0.86 0.27 1.29 0.81 1.29 0.65 0.43 1.40 0.92 0.86 1.99 0.65 1.99 0.22 0.43 1.83 0.38 0.92 1.35 0.86 0.54 0.92 0.32 2.64 0.27 0.70 2.05 0.97 0.43 1.18 0.70 1.40 0.16 0.81 1.35 0.97 0.32 0.70 0.97 0.59 0.32 0.27 0.16 0.70 0.48 0.22 0.48 0.54 0.38 1.02 0.75 0.81 0.75 0.86 0.43 0.86 0.48 1.08 0.70 1.02 0.86 1.18 0.65 0.81 0.38 0.92 0.59 0.48 0.59 1.02 0.97 0.59 0.48 0.75 0.92 0.75 0.92 1.45 0.81 0.54 0.32 0.70 0.48 0.70 1.35 1.88 1.24 0.16 0.81 0.97 0.32 0.70 2.10 2.69 1.67 0.43 0.32 0.92 0.27 0.75 1.35 1.45 2.48 1.02 0.38 0.54 0.38 0.81 0.16 0.65 1.24 0.65 0.81 0.70 0.48 0.92 0.48 0.59 0.43 0.59 0.38 0.59 0.97 1.29 1.18 0.86 0.38 0.81 0.54 0.65 1.02 1.45 1.08 0.70 0.65 0.65 0.27 0.75 0.97 0.92 1.02 1.83 0.48 1.78 0.32 0.70 1.08 0.92 1.40 1.35 1.62 1.29 0.38 0.70 0.27 1.13 0.97 1.08 1.13 1.02 0.27 1.45 0.32 0.65 0.81 1.62 0.86 1.56 0.48 note: safe arsenic daily intake in water is 0.66µg/day engineering, technology & applied science research vol. 11, no. 5, 2021, 7558-7563 7562 www.etasr.com shar et al.: health risk assessment of arsenic in the drinking water of upper sindh, pakistan table vii. mean adi of arsenic in potable water of the upper sindh talukas taluka mean (µg/l) adi mean (µg/day) daharki 13.3 0.72 ubauro 16 0.86 kashmore 14.7 0.79 tangwani 17.6 0.95 garhi khairo 18.1 0.97 thul 15.2 0.82 kambar 17.1 0.92 miro khan 8.5 0.46 iv. conclusion from the results obtained from the present work, it can be concluded that the groundwater of upper sindh is unfit for drinking due to the presence of arsenic in high amounts. with the exception of miro khan where only 20% of water samples were found to be contaminated, the potable water of the talukas was found highly contaminated due to the existence of arsenic concentration at alarming levels. contaminated water may cause various health hazards. therefore, it is suggested to the government of sindh to pay special consideration to the matter. it is also recommended that awareness among farmers must be increased to use chemicals, particularly pesticides, carefully. also, the government should provide safe drinking water by installing reverse osmosis (ro) plants in areas where people are using unsafe water for drinking and cooking. references [1] 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[49] n.-k. bhatti, s. r. samo, a. saand, m. a. keerio, and a. a. bhuriro, "ground water quality assessment of daur taluka, shaheed benazir abad," engineering, technology and applied science research, vol. 8, no. 2, pp. 2785–2789, apr. 2018, https://doi.org/10.48084/etasr.1925. engineering, technology & applied science research vol. 8, no. 4, 2018, 3294-3299 3294 www.etasr.com bella et al.: industrial bearing fault detection using time-frequency analysis industrial bearing fault detection using time-frequency analysis yasmina bella electrical engineering department ferhat abbes setif 1 university setif, algeria b_yasmina2014@ univ-setif.dz abdelhak oulmane department of mechanical engineering polytechnic school of montreal montreal, canada abdelhak.oulmane@polymtl.ca mohammed mostefai electrical engineering department ferhat abbes setif 1 university setif, algeria mostefai@ univ-setif.dz abstract—time-frequency fault detection techniques were applied in this study, for monitoring real life industrial bearing. for this aim, an experimental test bench was developed to emulate the bearing rotating motion and to measure the induced vibration signals. dedicated software was used to analyze the acquired measurements in the time-frequency domain using several distributions with varying resolution. results showed that each fault type exhibits a specific behavior in the time-frequency domain, which is exploited in the localization of the faulty component. keywords-time-frequency domain; industrial bearing; nondestructive test; vibration analysis i. introduction enhancement of the production system dependability is a major issue faced by competitive industrial companies. in this context, the predictive maintenance can play a fundamental role in improving the production system reliability and economic efficiency. in fact, the predictive maintenance is a corrective action applied on the equipment, systems or installations based on the previous knowledge of the operation conditions or performances. hence, using fault monitoring algorithms can provide real time information about the system health and allows a reliable maintenance decision-making tool [1]. in rotating machinery, the fault monitoring of the rolling element bearings (rebs) is of great practical interest. actually, bearing damage causes 40% of the total amount of failures in an induction motor [2]. a comprehensive review of the recent advances of rebs monitoring techniques can be found in [3]. current signature analysis method for the diagnosis of bearing faults forms an area of increasing scientific interest. the main idea beyond this technique is detecting faults based on the change of the stator current spectrum of the induction motor. this change causes a variation of the load and irregularities in the magnetic field. the latter affects the mutual and selfinductance and leads to side bands across the line frequency. despite the advantages of the current signature method, mechanical vibration signal analysis remains more immediate, simple and rich source of information for understanding the defected bearings (dbs) behavior [4]. vibration signals acquired from bearings can be either stationary or nonstationary. the stationary signals are characterized by timeinvariant statistical properties (moments, densities etc.), however, the statistical properties of a non-stationary signal variy over time [5, 6]. in fact, bearing vibration signals are almost always non-stationary since they are inherently dynamic (e.g. speed and load condition change over time) [7]. joint time-frequency analysis is an effective approach for addressing this issue, using signals which are presented in a timefrequency amplitude/energy density 3d space. hence, both the constituent frequency components and their time variation properties can be detected [8-10]. several time-frequency analysis methods are developed, e.g. short time fourier transform [11], wavelet transform [12, 13], bilinear/quadratic time-frequency distributions including cohen and affine classes distributions based on wigner-ville distribution [14-16]. in the same context, adaptive optimal kernel methods allow adaptive kernel modification and make the time-frequency distribution suitable for signal structures identification [17]. to suppress the cross-terms and improve time-frequency resolution, the reassignment method has been proposed in [18]. in order to deal with the non-linearity and non-gaussianity of signals, time-varying higher order spectrum methods such as wigner higher order spectrum were developed [19]. it is worth mentioning that most of the above mentioned time-frequency analysis methods have been applied to machinery fault diagnosis [20, 21]. in this paper, time-frequency vibration analysis method is used for fault detection of real world industrial bearings motivated by the promising results in induction motor condition monitoring field [22, 23]. for this aim, a bearing experimental test bench has been developed and the acquired vibration signals were examined using t-f analysis toolbox. the used approach consists of comparing several time-frequency bearing performances under different operation conditions. ii. non-destructive bearing testing based on timefrequency analysis vibration analysis is one of the most usual non-destructive methods utilized to evaluate the bearing conditions in an operating machine. different bearing faults induce different patterns in the time-frequency plane. in this section we give the frequency values associated to each type of bearing element defect (cage, ball, inner and outer raceways). thereafter, in order to overcome the drawbacks of the traditional spectral ana app mo bea the a. the spe wh ind do mo and cag am vib fau usi wh fre inn mo fro can fre not but cau ph equ def b. a mo engineerin www.etasr alysis techniq proaches are i ore precise d aring. this se e experimental bearings fau the rolling s e presence o ecifically, vibr hen the surfac dustrial bearin main. in fact oving over the d cause vibrat ge or the balls mplified. by ex brational signa ult occurs. th ing the formulf 1 2ff d 2df n 2f n 2 here: f is th equency, f t ner raceway fa fig. 1. however, b otion, the char om their calcu n be perform equency with t t only increas t also generat used by the enomenon can ual to the sh fects frequenc vibration an a straightfor time-varying odulating it ng, technology r.com ques, quadrat introduced. th discrimination ection represen l study. ult frequencie surface damag of high force rations are pro ce of one com ngs exhibit sp , as the inner e running sur tions. when th s are defected, xamining the al, specific fr he bearing fau las given in [191 d . f 1 2 . f 1 . f 1 the cage faul the outer race ault frequency. representation because of th racteristic freq ulated values ed by compa the theoretica ses the amplit tes harmonics e amplitude n be recogniz haft rotation f cies [24]. nalysis tools rward way to signal x(t) with a win y & applied sci tic time-frequ hese techniqu n between d nts the theoret es ge is caused by es at the con oduced by the mponent strik pecial behavio r or outer rin rface excite th he outer or the the amplitude frequency spe requencies are ult frequencies 9] as follows ( lt frequency, eway fault fre . of ball bearing ch he bearing c quencies may b (1%-2%). he aring the mea l ones. the b tude of the vi s associated to modulation. zed by an am frequency f0 a obtain the freq is to locali ndow function ience research b uency distribu ues allow easie defect and n tical backgrou y fatigue becau ntact points. e impacts that kes another su or in the freq ngs rotate, the he bearing stru e inner racewa e of the vibrati ectrum of a be e amplified w s can be calcu (see figure 1): (1a (1b (1c (1df the ball equency and f haracteristics. components s be slightly dif ence, fault iso sured charact earing deterio ibration freque o these freque the deterio mplitude modu around the be quency spectru ize the signa n h [25], b h v bella et al.: ind utions er and normal und of use of more occur urface. quency e balls ucture ay, the ions is earing when a ulated : a) b) c) d) fault the sliding fferent olation eristic oration encies encies oration ulation earing rum of al by before per the as f whe rep h a sign be e as f tech dom rep freq met signp whe kˆ( freq       whe f(ξ, (for givw dist freq φ(t, wig g an osc for foll vol. 8, no. 4, 20 dustrial bearing rforming the s frequency con follows: f t, f = x ere ∗ denotes resentation aro and we perform nal as well. h estimated by c follows: s t, f |f on the other hniques that mains simult resentations. quency distrib thod for the nals in many pt, f k ere z(u), z(f (u,v,t,f) are th quency transfo 2iπξ(s τ)e f (ξ,τ        ere f(ξ,τ) ,τ)=f(−ξ,−τ). i r example f(ξ en by (6): t, f z z f to reduce th tribution, we quency using ,f)=g(t)h(f). t gner-ville distφ t nd h are even another distr cillatory 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wing time-fre tion, known iven by (7): t , f f dt ows with h(0)= allows the m s the choi-wi on f has the fo s distribution 3295 -frequency an m (stft) to o gion of the win (2) 3]. for the spe translation win n on the wind f the signal x(t nitude of the s (3) alysis include me and frequ us time-frequ of quadratic most approp of non-statio dv v (4) nal and k(u,v ecial class of given by: (5) window veri pendent of ξ a r-ville distrib du (6) f the wignerthing in time equency win by the smoo df (7) =g(0)=1. minimization o illiams distribu ollowing form: (8) n is given by nalysis obtain ndow ectral ndow owed t) can stft, es the uency uency timepriate onary v,t,f), timeifying and τ bution -ville e and ndow: othed of the ution. y the p( wh dis dif the the equ the ded dec vib off fre tim    aut pro net a. bea 2). cal dat bea ide engineerin www.etasr 2 (t, f ) π |        actually, if wf ψ,τ here a is a con stribution and , | | we emphasiz fferent resolut e signal under ii a general de en the theoret uations of the e developed t dicated expe cisions about bration measur fers a wide ra equency analy me-frequency d it provides dimensions ( it detects an generate a lo it supervises process produ t-f analy tomatic clas ocessing throu tworks. bearing des computation we used th aring is a sing . the technic lculate the the ta sheet provid tabl p & w bea inner diam outer dia pitch diam widt contact a operating s operating s pw100#5 be aring was coll entified as o ng, technology r.com 2 2 22σ (s t ) / τσ e z( τ |   we choose the nstant. this d has the follow ze that each tim tion quality w study as illust i. experime escription of th tical fault freq previous secti theory, we lau erimental test the faulty st rements using ange of metho ysis. the adva domain are: a represent (amplitude-tim nd follows th w vibration po s machines i uces high amp ysis toolbox, ssification of ugh usage of cription and t n he pratt & w gle row ball m al specificatio eoretical fault ded by the con le i. beari aring id meter meter meter h angle speed 1 speed 2 earing is used lected from bo one of the y & applied sci *τ τs )z (s )e 2 2   kernel functio distribution is wing form: ∗ s me-frequency which allows a trated below. ental study he bearing str quencies are c ion. in order t unched severa t bench. fin tate, we eval g t-f analy ods in time, fr antages of sig tation of the me-frequency) he developme ower. in which the plitude of perio also offers m f rotating m f fourier desc theorical fau whitney pw1 model with rad ons of bearin t frequencies nstructor (tabl ing technical s pw100#5 brg 2.8347” 3.9292” 3.04 0.625” 0 1000 2000 for the shaft o ombardier com most problem ience research b 2iπfτe dsdτ (9) on as: (10 called born-j (11 distribution g accurate analy y steps ructure is give calculated usin to take advanta al experiments nally, for m luated the acq ysis toolbox w frequency and gnal analysis e signal in ent of defects e normal ope odic shocks. more applicatio machinery, criptors and n lt frequencies 00#5 bearing dial contact (f ng that we ne are taken from le i). specifications g roller bearing ” 2.8350” ” 3.9272” 4165” ” 0.630” 0o 0rpm 0rpm of the gearbox mpany and has matic compo h v bella et al.: ind 0) jordan ) gives a ysis of en and ng the age of s in a making quired which timein the three s that erating ons in image neural s g, this figure eed to m the g x. this s been onents. fur bea sum freq 1 3 b. me de the foll sup is c enti 360 bea (ta rota and can exte bea b whi acc for on t was mo only bea use disa bea vol. 8, no. 4, 20 dustrial bearing rthermore, the aring defects mmarized in quency. table ii fr 16.66hz 7 33.33hz 15 experimental several tests echanics depar montreal. the applied mec lowing eleme pported at its e connected to a ire system is 00rpm and su ams each. the able iii). the t ating machine d gears. all be n be easily dis ernal clampin aring sizes. fig. 2. table components base motor couplings bearing house s three acceler ich were conn celerometer a3 monitoring th the side of the s positioned h tor and thus t y the data fro aring fault diag ed for equipm assembled in aring (figure 4 018, 3294-3299 g fault detectio e frequencies are calcula table ii wh i. bearing t fcf f .64hz 108 5.28hz 216 l tests and me s on the bea rtment labora e test bench w chanics sectio ents: a rotor ends by an ass a gearbox via s driven by a upported by a test bench is test bench is d ry such as dam earings are mo sassembled. w ng sleeve assem pratt & whitne iii. test ben specific 2 h-beams w 2hp, 3600rpm 7/8inch snl 510 – h310 rometers were nected to a co 3 was position he bearing fau e bearing for m horizontally on test equipmen om a1 were gnosis. the re ment monitor order to remo 4, left). then, on using times associated w ated using ( here f is the theoretical fau forf fir 8.32hz 91.7 6.64hz 183.4 easurement ac aring were c atory at the ec was designed a on. the latte system cons sembly of two a transmissio a 2hp electr a set of two 6 1750mm long designed to tes maged bearing ounted on a cl we have design mbly to fit al ey bearing conside nch technical cations w8x8 67lb/ft m, 575volts h-linch – 1210ektn9 used, a1, a2 mputer for da ned horizontal ults, a2 was po monitoring the n the spindle nt condition. w analyzed, as w est of sensors ring. the te ove the shaft as illustrated 3296 -frequency an with the diff (1a)-(1d) and e bearing rot ult frequencie rf fbf 71hz 99.54 42hz 199.0 cquisition carried out in cole polytechn at the laborato er consists of sisting of a o skf bearing n belt system ric motor rate 67lb/ft h-weig g and 210mm st typical defec gs, mass imba lamping sleeve ned an interna ll pratt & wh ered for test. specifications manufacturer prometo toshiba rex omega skf canada 2 and a3 (figu ata acquisition ly over the be ositioned verti shaft faults an for monitorin we emphasize we are condu ’ information est bench can along with th d in the lower nalysis ferent d are tating es f 4hz 8hz n the nique ory of f the shaft s that m. the ed at ghted wide cts in alance e and al and hitney rs a ure 3) n. the earing ically nd a1 ng the e that ucting were n be he old right fig ord the tes sp spe the 50 sig spe dis no exc ben f wit dec t1a are pro con engineerin www.etasr gure 4, the ne der to insure e stretch bench sts were carrie p2) of 1000rpm eed range was e fault frequen 0rpm to 2200 gnal is less ma eed, the amp stinguishable f acceleration i cessive noise, nch. fig. 4. assem ro sp1 sp2 experimenta thout taking in celeration i.e. a-t1b and t2a-t e acquired usi ocessed using f for fault dia nsidered: sam ng, technology r.com ew bearing is successful ins h is reassemb ed out at two m and 2000rp s decided afte ncy reacts wel 0rpm [26]. at arked, less amp plitude genera from the back is generated. f there is an im fig. 3. expe mbling and disasse table iv otating speed (rp 1000 2000 al results are p nto considerat we only deal t2b (figure 5) ing ni pma6 tf-analys fig. 5. speed agnosis purpo mpling freque y & applied sci expanded by sertion into th bled and carefu different rota pm respective er the fact that ll over the ran t low and hig plified by the d ated by the f kground noise for high rotati mminent risk o erimental test ben embling of the bea v. test spee pm) rotati presented in a tion the times with the follow ). the accelera 61115 portable sis software. diagram for pw1 oses, only thre ency, time w ience research b heating to 110 he shaft. there fully calibrated ational speeds ely (table iv) t the peak fac nge of rotation gh-speed rang defect, i.e. for fault is not c e and for lowional speeds, d of damaging th nch. arings from the be eds ing speed (hz) 16.66 33.33 chronological of acceleratio wing time inte ation measure e monitor and 00#5 ee parameters window length h v bella et al.: ind 0◦c in eafter, d. the (sp1, ). the ctor of n from ge, the r highclearly -speed due to he test ench. order on and ervals: ements d then s were h and freq betw is o dom pos was win pos c. dist ana dist bett 1) pre dist non def a fr fro alm firf vol. 8, no. 4, 20 dustrial bearing quency windo ween time and obtained in the main and vice ssible resolutio s applied unde ndow lengths n sitive integer [ discussion an for different tributions obt alyzed. by adj tributions of c ter resolution o measurement from figures sents a bette tribution. the n-stationary s fects in bearing frequency peak om the spectru most equal to f value, which fig. 6. fig. 7. c fig. 8. sp 018, 3294-3299 g fault detectio ow length. it w d frequency re e time domain e versa. henc on for a partic er the conditio need to satisfy 3]. nd validation rotational spee tained by th djusting the so choi-william of the signal. t results for t s 6 and 7, th er resolution e signal modu ignal. the la g. the signal s k, which corr um graph, we n the inner race has a value of born-jordan dist choi-williams dis pectrum frequenc on using timewas essential esolution becau n then it is los ce, in order cular case a m on that both t y the equation of results ed values, the he time-frequ oftware param s and born-jo time-period t1 he distribution compared to ulation indicat atter confirms spectrum grap responds to th notice that the eway calculat f 91.71hz (tab tribution for speed stribution for spee y analysis for spe 3297 -frequency an to find a trad use if the prec st in the frequ to obtain the manual trial me time and frequ 2n−1, where n graphs of diff uency method meters for diff ordan one see 1a-t1b (sp1) n of choi-wil o the born-jo es the presen s the presenc ph (figure 8) s he value of 9 e peak frequen ted fault frequ ble ii). d of 1000rpm. ed of 1000rpm. eed of 1000rpm. nalysis de-off cision uency best ethod uency n is a ferent d are ferent eks a liams ordan ce of ce of shows 91hz. ncy is uency 2) val ch tha mo pre fro the we fre fre the and is c spe the sm engineerin www.etasr measuremen for this time lue of 2000rp hoi-williams d at the modu odulations are esence of defe om the spectru e fault frequen e noticed th equency trans equency fault. e percentage o d the experim calculated by (% δf the experim eeds of 1000rp e theoretically fig. 9. fig. 10. fig. 11. s the validity mall difference ng, technology r.com nt results for t e-period, the pm (sp2). ac distribution gr lation numbe present at low ects. as in sp um (figure 1 ncy firf (table hat for differ sformations i to validate t of relative err mental value of (12): mental fault fre pm and 2000rp fault frequenc born-jordan dis choi-williams di spectrum frequenc of the measu e between the y & applied sci time-period t2 rotation speed ccording to th aphs (figures er has almos w frequency, p1, the peak f 1) correspond e ii), which e rent rotating indicate the the obtained r ror between th f fault frequen 1 equency firfex pm is 0.77% a cy respectively stribution for spee istribution for spe cy analysis for sp urements is d e theoretical a ience research b 2a-t2b (sp2) d is doubled he born-jorda 9 and 10), we st doubled. which confirm frequency of 1 ds approximat equals to 183. speeds, the apparition o results we cal he theoretical ncy (%δfirf) w 100 (12 xperimental for ro and 0.23% les y (table v). ed of 2000rpm. eed of 2000rpm. eed of 2000rpm. emonstrated b and measured h v bella et al.: ind to the an and e note these ms the 183hz tely to 42hz. timef firf lculate value which 2) otating ss than by the d fault freq rot 1 2 isol obt calc obt sho imp vibr incl mon spe tran dec mai hum [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] vol. 8, no. 4, 20 dustrial bearing quencies, whic table v. ating speed fr t 1000rpm 2000rpm in this paper, lation method tained results culated resul tained results a ows the effect portant inform ration measur lude the stud nitoring whic ectrum of cri nsportation. in cisions (syste intenance, and man and mater e. l. bonaldi, g de oliveira, l. signature an http://dx.doi.org s. patidar, p. techniques for international jo 5, pp. 1803-180 s. nandi, h. diagnosis of ele conversion, vo s. choi, b. aki fault-diagnosis digital-signal-pr electronics, vo f. e. h. mont diagnosis of mechanical sys 2008 s. guoji, s. m experimental a diagnosis of gea no. 1, pp. 76-89 c. li, v. san element bearing transform guid transactions, v l. cohen, time s. qian, d. che ] p. flandrin, t 1998 ] a. prudhom, j. frequency vibra by bearing curr 84, no. a, pp. 7 018, 3294-3299 g fault detectio ch is less than summary ta theoretical firf 91.71 hz 183.42 hz iv. co , a time-freque d was applie are valid in ts. the diff and the theore tiveness of th mation about rements. furth dy of fault s h provides im itical applica n fact, real ti em stop, cur d control law r rial disasters. refer g. lambert-torre . e. b. da silva, nalysis to in g/10.5772/48045, kumar soni, r the diagnosis ournal of engineer 09, 2013 a. toliyat, x. ectrical motors-a ol. 20, no. 4, pp. 7 in, m. m. rahimi algorithm for in rocessing techniq ol. 58, no. 3, pp. 9 tero, o. c. medi rolling element stems and signal mclaughlin, x. y analysis of bispe ars”, mechanical 9, 2014 chez, g. zurita, g defect detection ded by time–f vol. 60, pp. 274-1 e-frequency anal en, joint time-fre time-frequency/t antonino-daviu, ation analysis for rents”, mechanic 747-762, 2015 on using time1% (%δfirf< able for the me experimental firf 91 hz 183 hz onclusion ency domain ed for indust n relation to ference of th etical ones is he used techn the bearing her directions severity and mportant infor ations such a me detection rative mainte reconfiguration rences esm, j. g. b. da , “predictive ma nduction moto , intech open a “an overview of rolling ele ring trends and t li, “condition review”, ieee t 719-729, 2005 ian, h. a. toliya nduction machin ques”, ieee tran 937-948, 2011 ina, “the applica bearings: a processing, vol. yongcheng, p. w ectrum of vibra systems and sign m. c. lozada, n using the genera frequency ridge 84, 2015 lysis, prentice ha equency analysis time-scale anal , h. razik, v. cli r the detection of al systems and s 3298 -frequency an 1%). easurement err relative erro %δfirf 0.77% 0.23% fault detection trial bearing. o the theoreti he experimen less than 1%. nique in extra health from of this work real time be rmation for a as aeronautic facilitates ma enance, predi n) in order to a silva, l. e. de l aintenance by ele ors”, available access publisher, on vibration an ment bearing f technology, vol. monitoring and transactions on e at, “implementatio nes based on adv nsactions on ind ation of bispectru theoretical appr 22, no. 3, pp. 58 white, “theoretic ation signals for nal processing, v d. cabrera, “r alized synchrosqu enhancement”, all, 1995 s, prentice hall, 1 lysis, academic imente-alarcon, “ f motor damages c signal processing nalysis ror. or n and the ically ntally this acting m the k will earing wide and aking ictive avoid lacerda ectrical e at: , 2012 nalysis faults”, 4, no. d fault energy on of a vanced dustrial um on roach”, 88-596, al and r fault vol. 43, rolling ueezing , isa 996 press, “time caused g, vol. engineering, technology & applied science research vol. 8, no. 4, 2018, 3294-3299 3299 www.etasr.com bella et al.: industrial bearing fault detection using time-frequency analysis [12] j. chen, j. pan, z. li, y. zi, x. chen, “generator bearing fault diagnosis for wind turbine via empirical wavelet transform using measured vibration signals”, renewable energy, vol. 89, pp. 80-92, 2016 [13] n. hess-nielsen, m. v. wickerhauser, “wavelets and time-frequency analysis”, proceedings of the ieee, vol. 84, no. 4, pp.523-540, 1996 [14] l. cohen, “time-frequency distributions-a review”, proceedings of the ieee, vol. 77, no. 7, pp. 941-981, 1989 [15] o. rioul, p. flandrin, “time-scale energy distributions: a general class extending wavelet transforms”, ieee transactions on signal processing, vol. 40, no. 7, pp. 1746-1757, 1992 [16] p. flandrin, p. goncalves, “geometry of affine time–frequency distributions”, applied and computational harmonic analysis, 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rolling element bearings”, tribology international, vol. 96, pp. 289-306, 2016 [22] c. yang, t. j. kang, d. hyun, s. b. lee, j. a. antonino-daviu, j. ponsllinares, “reliable detection of induction motor rotor faults under the rotor axial air duct influence”, , ieee transactions on industry applications, vol. 50, no. 4, pp. 2493-2502, 2014 [23] j. a. antonino-daviu, v. climente-alarcon, j. pons-llinares, e. j. wiedenbrug, “advanced rotor assessment of motors operating under variable load conditions in mining facilities”, 2014 ieee energy conversion congress and exposition (ecce), pittsburgh, usa, pp. 617621, november 13, 2014 [24] m. thomas, fiabilite, maintenance predictive et vibration des machines, puq, 2012 (in french) [25] b. boashash, time-frequency signal analysis and processing: a comprehensive reference,academic press, 2015 [26] c. migeon, emission acoustique et analyse vibratoire pour l’ etude des defauts de roulements pour differents regimes moteurs, msc thesis, universite de reims champagne-ardenne, 2011 (in french) microsoft word 21-3511_s_etasr_v10_n3_pp5700-5705 engineering, technology & applied science research vol. 10, no. 3, 2020, 5700-5705 5700 www.etasr.com duong & nguyen: application of sunflower optimization algorithm for solving the security … application of sunflower optimization algorithm for solving the security constrained optimal power flow problem thanh long duong faculty of electrical engineering technology industrial university of ho chi minh city ho chi minh city, vietnam duongthanhlong@iuh.edu.vn thuan thanh nguyen faculty of electrical engineering technology industrial university of ho chi minh city ho chi minh city, vietnam nguyenthanhthuan@iuh.edu.vn abstract—finding the optimal power flow (opf) which minimizes total generator cost is the answer to one of the most important problems in the electricity market operation. independent system operators (iso) face many challenges while operating the system in order to obtain economic benefits and security. the solution to this problem is known as security constrained optimal power flow (scopf). scopf is a very large-scale and nonlinear optimization problem with many complex constraints. this paper proposes the sunflower optimization (sfo) algorithm for solving the scopf problem. the proposed method is tested on the ieee 30-bus and the ieee 118-bus systems for both normal and outage cases. the result comparison with other known methods showed that the proposed sfo algorithm is an effective method for solving the scopf problem in the electricity market. keywords-opf; scopf; sfo, electricity market i. introduction the restructuring of the electricity industry made the electrical energy a commodity. however the independent system operators (iso) are facing many challenges in terms of system operation to obtain economic benefits and security. various factors such as the expansion of the generation and transmission systems have not been in accordance with the increase in demand. besides, the number of unplanned power exchanges increases and direct contracts between producers and consumers sometimes cause insecure operation of the system. hence, power system security [1] has become one of the most important aspects in the electricity market operation [2]. this problem is known as the security constrained optimal power flow (scopf) [3-5] which is an extension of the opf problem [6] which is used to obtain an economical operation of the system while considering not only normal operating limits, but also violations that would occur during contingencies. the scopf changes the system’s precontingency operating point so that the total operating cost is minimized, and at the same time no security limit is violated if contingencies occur. although the scopf still faces challenges related to computations, it is expected that it eventually become a standard tool in the electricity market [7]. various mathematical programming solutions have been proposed to solve the scopf problem such as iterative approach [8], benders decomposition approach [9], linear programming [10], quadratic programming [11], and interior point method [12]. recently, many artificial intelligence algorithms have been proposed for solving optimization problems in power system [13-18]. among them several approaches were used to deal with the scopf problem such as particle swarm optimization (pso) [16], genetic algorithm (ga) [17], and evolutionary programming (ep) [18]. in [19], a pso approach was presented to solve an optimal power flow (opf) problem with embedded security constraints represented by a mixture of continuous and discrete control variables, where the major aim is to minimize the total operating cost, taking into account both operating security constraints and system capacity requirements. a new robust differential evolution algorithm for scopf, considering detailed generator model is presented in [20], in which a hybrid constraint handling method has been proposed to enhance the diversity of the search process and increases the chance of finding the optimum solution. in [21], the authors presented a selforganizing hierarchical pso with time-varying acceleration coefficients (sohpso-tvac) for dealing with the scopf problem, which was designed to avoid premature convergence. the scopf problem has been solved in [22] with the use of adaptive flower pollination algorithm (apfpa), where the control variables are optimized based on an adaptive and flexible structure which allows creating diversity and balance between exploration and exploitation during the search process. in this paper, the sunflower optimization (sfo) algorithm [23] is proposed for solving the scopf problem. sfo algorithm is inspired by nature and is classified as an iterative, population-based, meta-heuristic optimization technique for multidimensional problems. the sunflowers operate in a cycle. in the morning they stir and follow the sun throughout the day. at evening, they move in the opposite direction and wait until the next morning. a population of flowers is created in a direction and takes random steps towards the sun based on their position. the proposed sfo algorithm is able to find a global optimal solution, without stucking in local optimal solutions. the advantage of the sfo algorithm is that it does not need corresponding author: thanh long duong engineering, technology & applied science research vol. 10, no. 3, 2020, 5700-5705 5701 www.etasr.com duong & nguyen: application of sunflower optimization algorithm for solving the security … derivatives when evaluating the objective function [24]. the proposed method is tested on the ieee 30-bus and the ieee 118-bus systems, and the results are compared with the results of other known methods. ii. objective function the scopf problem is a very large-scale and nonlinear optimization problem with many complex constraints. the scopf problem consists of optimizing the total generator fuelcost function, subject to power-balance and inequality constraints of the base-case state and the contingency-case states [3]. mathematically, the scopf problem can be formulated as follows: min f(x, u) (1) subject to the equality and inequality constraints of the normal case (2)-(3) and the outage case (4)-(5): g(x, u) = 0 (2) h(x, u) ≤ 0 (3) g(x c , u c ) = 0 (4) h(x c , u c ) ≤ 0 (5) where f is the fuel cost function of the generator, x is the vector of control variables, u is the vector of state variables, g(.) is the set of equality constraints, h(.) is the set of the inequality constraints, and c is the set of outage lines. the detailed model of the problem is formulated as follows: 1 min ( ) gn i gi i f f p = = ∑ (6) where fi(pgi) is the fuel cost function of generator i : 2 ( ) i gi i i gi i gi f p a b p c p= + + (7) where pgi is the power output of generator i and ai, bi, ci, are cost coefficients. the equality and inequality constraints for the normal and outage cases are: • power balance constraints: 1 | | | || | cos( ) bn gi di i ij j i j ij j p p v y v δ δ θ = − = − −∑ (8) 1 | | | || | sin( ) bn gi di i ij j i j ij j q q v y v δ δ θ = − = − −∑ (9) where qgi is the reactive power output of generator i, pdi and qdi are the active and reactive power demands at bus i respectively, i=1, 2,…, nb, nb is the number of buses in the system, |vi|∠δi and |vj|∠δj are the voltage at buses i and j, respectively, and |yij|∠θij is an element in ybus matrix related to buses i and j. • power generation limits: max,gigimin,gi ppp ≤≤ (10) max,gigimin,gi qqq ≤≤ (11) where pgi,max is the maximum active power output of generator i, qgi,min and qgi,max are the minimum and maximum reactive power outputs of generator i, i=1, 2, …, ng, and ng is the number of generators. • bus voltage limits: max,gigimin,gi vvv ≤≤ , i = 1, 2, …, ng (12) max,lilimin,li vvv ≤≤ , i = 1, 2, …, nd (13) • transmission line limits: max,ll ss ≤ , l = 1, 2, …, nl (14) vgi is the voltage at generation bus i, vli is the voltage at load bus i, vgi,max and vgi,min are the maximum and minimum voltages at generation bus i respectively, vli,max and vli,min are the maximum and minimum voltages at load bus i respectively, and nd is the number of load buses. iii. application of the sfo algorithm the flowchart of the process of applying the sfo for solving the scopf problem is shown in figure 1. its steps are presented below. step 1: read the power system data and select control parameters such as mortality rate m, population size n, pollination rate p, and maximum iteration number maxi.tr step 2: initialize a population of n individuals: each individual contains a vector of control variables represented by: 2 3 1 2 1 2 [ , ,..., , , ,..., , , ,..., ] 1,..., g gi g g gn g g gn c c n x p p p v v v q q q i n = = (15) each individual in the population is initialized by: (0) min max min 1 *( ) i i i i x x rand x x= + − (16) where xi max and xi min are the upper and lower limits of each individual and rand1 is a random numbers in the range [0,1]. step 3: evaluation of the initialized population: the power flow problem is solved for the initialized population and the obtained result is used to evaluate the quality of the initialized population via calculating the fitness function including the outage case: lim 2 0 1 1 1 lim 2 lim 2 0 0 1 1 2 0 ,max 1 lim, lim, 2 1 1 1 lim, 2 2 ,max, 1 1 ( ) *( ) * ( ) * ( ) * ( ) *( ) * ( ) * ( ) * ( ) g g d l g d l n f i gi p g g i n n q gi gi v li li i i n s l l l n c c p g g q gi gi i n n c v li li s l l c i l f f p k p p k q q k v v k s s k p p k q q k v v k s s = = = = = = = = + − + − + − + −  − + − + + − + −  ∑ ∑ ∑ ∑ ∑ ∑ ∑ 1 cn c=           ∑ (17) engineering, technology & applied science research vol. 10, no. 3, 2020, 5700-5705 5702 www.etasr.com duong & nguyen: application of sunflower optimization algorithm for solving the security … step 4: individuals adjustment: each individual (sunflower) adjust its position towards the best solution (sun) as shown in (18): * * , 1,2....,i i i x x s i n x x − = = − � (18) where x* is the overall best solution with the corresponding best fitness function ff in the population, and xi is the current solution. the furthest individuals are eliminated. step 5: solve the power flow problem for each individual after adjusting its position and update the best fitness value. step 6: individuals movements and update: the step of each individual towards the best individual is calculated in (19) and the individuals update their positions as shown in (20). ( )1 1i i i i i id p x x x xλ − −= × + × + (19) 1i i i i x x d s+ = + × � � (20) step 7: evaluate the new individuals: the power flow problem is solved for the new population xi (n) and the obtained result is used to calculate the fitness function ff (n) in (17). step 8: accept the new individuals if their fitness function value is better than the current values. step 9: check the stopping criteria. if n < nmax, n = n + 1 then return to step 4, otherwise, stop. fig. 1. the flowchart of the proposed process iv. results the proposed sfo algorithm has been tested on the ieee 30-bus and the ieee 118-bus systems for both normal and outage cases. the ieee 30-bus test system is composed of 6 generators at buses 1, 2, 5, 8, 11, and 13, four transformers and 41 transmission lines as shown in figure 2. the total system demand was 283.4mw and 126.6mvar. the bus and branch data with the fuel cost coefficients are given in [4, 31]. for the outage cases, the 5-outage lines 1, 2, 3, 5, and 7 are considered. the ieee 118-bus system consists of 118 buses, 186 branches, 99 load sides, 54 thermal units, and 9 transformers. in the outage cases, outages of lines 21 and 50 were considered. the data of the system are derived from [25, 32]. for the implementation of the proposed method, the control parameters of the proposed sfo for the test system are selected experimentally as follows. the population number n is set to 15, the mortality rate m to 0.1, the pollination rate p to 0.05, and all penalty factors to 10 6 . the number of iterations is set to 300 for the normal case, and 400 for the case with 5 outage lines. the proposed sfo method was coded in matlab 2014a and matpower platform, and ran in a microsoft windows 7 pc with intel(r) core(tm)2 duo cpu @ 2.0 ghz with 2 gb random access memory (ram). fig. 2. the ieee 30-bus system a. simulation results of the ieee 30-bus test system 1) normal case the obtained results from the proposed sfo have been compared with the ones from other methods such as tabu search (ts) [26], evolutionary programming (ep) [27], de [28], psade_alm [29], pso, pso-tviw and sohpsotvac [21, 30], hybrid da-pso [31]. the solutions of all methods for the normal case are given in table i. it can be seen that the total cost obtained by the proposed method is engineering, technology & applied science research vol. 10, no. 3, 2020, 5700-5705 5703 www.etasr.com duong & nguyen: application of sunflower optimization algorithm for solving the security … 802.01$/h which is close to the other methods’. as observed from figure 3, the sfo method has the ability to converge quickly and can reach an optimum solution. from the results comparison it was shown that the proposed sfo is able to find the optimal solution for the opf problem in the normal case. table i. result comparison for the normal case algorithm cost ($/h) time (s) ts [26] 802.29 na ep [27] 802.62 51.4 de [28] 802.28 5.02 sade_alm [29] 802.40 15.934 psade_alm [29] 802.40 17.295 pso [30] 802.58 28.208 pso-tvac [30] 802.67 11.255 pg-pso [30] 802.25 11.416 bpso [21] 803.13 35.15 pso-tviw [21] 802.11 33.756 pso-tvac [21] 803.56 35.82 sohpso-tvac [21] 802.03 29.43 da-pso [31] 802.12 287.13 proposed sfo 802.01 77.64 fig. 3. convergence characteristics of the sfo algorithm for the ieee 30bus system in the normal case 2) outage case fig. 4. convergence characteristics of the sfo algorithm for the ieee 30bus system in the outage case in a power system, if a line is corrupted, its power flow will be shared among the other lines of the system. this will lead to possible overloading of some of the lines. among the 41 lines in the ieee 30 bus system, the scenario considers five outage lines that have larger effect on the remaining lines. the optimal solution obtained by the sfo method for the outage cases is given in table ii. the best cost from the sfo method has been compared to those of other known methods in table ii. it can be seen that the total cost obtained by the proposed method was 826.245 which is approximate to the costs obtained from sade_alm, psade_alm [29] methods and slightly better than the costs obtained from pso and pso-tvac [30] methods. from figure 3, it can be seen that the sfo method has the ability to converge quickly and can find the best solution. the result comparison has proved that the proposed sfo is also effective in solving the problem in the outage case. table ii. result comparison for the case of 5 outage lines algorithm cost ($) time (s) sade_alm [29] 826.979 46.896 psade_alm [29] 826.242 119.812 pso [30] 827.186 175.245 pso-tvac [30] 828.012 130.59 proposed sfo 826.245 95.332 b. simulation results of the ieee 118-bus test system table iii gives the fuel costs obtained by sfo and the other optimization techniques in the normal and outage cases under the same conditions. it can be seen that the obtained total fuel cost using sfo in the normal case is 133232.24$/h and for the outage case it is increased by 1238.33$/h. from table iii, it can also be observed that the results using sfo can reach a better solution when compared with many of the other known methods. table iii. result comparison for the ieee-118 bus system algorithm cost ($/h) normal case outage case icbo [32] 135121.57 136353.31 cbo [32] 135072.99 135297.22 ecbo [32] 135172.26 135582.15 de [32] 142751.11 158920.80 abc [32] 135145.18 135759.01 bbo [32] 135272.19 135640.64 proposed sfo 133232.24 134470.57 figures 5 and 6 show the convergence characteristics of the minimum fuel cost of the sfo. it can be observed that the sfo has the ability to converge quickly and can find an optimum solution. fig. 5. convergence characteristics of the sfo algorithm for the ieee 118-bus system in the normal case 50 100 150 200 250 300 800 805 810 815 820 825 830 835 840 845 850 number of iterations f it n e ss f u n c ti o n ( $ /h ) 0 50 100 150 200 250 300 350 400 0 0.5 1 1.5 2 2.5 3 3.5 x 10 8 number of iterations f it n e s s f u n c ti o n ( $ /h ) 10 20 30 40 50 0 1 2 3 4 x 10 7 10 0 10 1 10 2 1.32 1.34 1.36 1.38 1.4 1.42 1.44 1.46 x 10 5 number of iterations = 500 f it n e s s f u n c ti o n ( $ /h ) engineering, technology & applied science research vol. 10, no. 3, 2020, 5700-5705 5704 www.etasr.com duong & nguyen: application of sunflower optimization algorithm for solving the security … fig. 6. convergence characteristics of the sfo algorithm for the ieee 118-bus system in the outages case v. conclusion the competitiveness of the electricity market leads to an increased volume of traded electrical energy between generator and distribution companies which may cause unpredicted power flow through some transmission lines. this may lead to situations in which the transmission network is not able to accommodate all the desired transactions due to violations of some system security constraints. thus, the independent system operators are facing many challenges in terms of normal system operation while trying to obtain economic benefits and 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siyal et al.: assessment of air pollution by pm10 and pm2.5 in nawabshah city, sindh, pakistan assessment of air pollution by pm10 and pm2.5 in nawabshah city, sindh, pakistan asif ali siyal department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan asifsiyal2007@quest.edu.pk saleem raza samo department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan zafar ali siyal department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan zafarsiyal@quest.edu.pk kishan chand mukwana department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan shakeel ahmed jiskani department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan abdullah mengal department of mechanical engineering, balochistan university of engineering and technology, khuzdar, pakistan ahmengal@yahoo.com abstract—increased traffic density due to urbanization is a major cause of air quality deterioration. atmospheric particulate matter (pm) constitutes one of the most challenging issues in environmental research. this study was designed to assess pm10 and pm2.5 pollution at ten main locations in nawabshah. analysis of pm10 and pm2.5 pollution was carried randomly at different selected locations of the city. the highest concentration of pm10 was found at mohini bazar (mb) and the highest concentration for pm2.5 was found at new naka (nn). the mean concentration of pm10 was 78.3% higher than world health organization (who) standards and 35% than pakistan’s national environmental quality standards (neqs). the mean concentration of pm2.5 was 47.3% and 26.3% higher respectively. mean concentrations of pm2.5 on day-2 and day-10 were found lower than those set by neqs, while mean concentrations of pm10 on all days exceeded the who and neqs standards indicating that the city was heavily polluted more with pm10 than with pm2.5. re-suspension of dust particles due to traffic flow, open burning of unmanaged solid waste on the sides of the road and in the street, and improper handling of construction and demolition waste were identified as the main sources for pm pollution in the city. exposure to higher levels of pm10 and pm2.5 can cause health problems. high levels of pm10 and pm2.5 are a call for the implementation of strict measures to control pm pollution at nawabshah in order to protect public health and the environment. keywords-particulate matter; pollution; environmental deterioration; human health; strict measures i. introduction potential threats to human health and the environment mainly due to air pollution have now become an increasing concern, attracting attention [1]. air pollution is one of the most critical global issues. urban air pollution epitomizes a global problem with a substantial effect on public health, primarily in major cities where the daily mass concentration of airborne particulate matter (pm) exceeds the permissible levels set by the who and neqs [2]. airborne pm comprises a complex mixture of different solid and liquid particles suspended in the air either for a long or short time depending upon their size and chemical composition in space and time [3, 4]. according to [5], pm is a heterogeneous mixture of organic, inorganic and biological compounds (e.g., dust, soot, metals, salts, polycyclic aromatic hydrocarbons (pahs), aromatic amines, bacterial products (endotoxins) and fungi). pm pollution is mostly described in terms of particle size. aerodynamic diameter is one of the most important criteria to classify pm into different categories. transportability of pm in the atmosphere and inhaling ability can be described according to its aerodynamic diameter [6]. pm size fractions range from pm1, pm2.5, pm4, pm7, to pm10. pm with an aerodynamic diameter ≤10 microns is known as coarse particles (pm10) and pm with an aerodynamic diameter ≥2.5 microns is termed as fine particles (pm2.5) [5, 7-9]. pm (e.g., pm2.5 and pm10) are generated from a variety of sources including natural and human sources. natural sources include windblown surface soils, sea sprays and pollutants from forest fires [10, 11]. man-made sources for pm2.5 include motor vehicles and fossil fuel combustion. sources for pm10 include construction and demolition activities, traffic-related resuspension of particles, abrasion of brakes and tires and industrial process related emissions [4, 12]. in the current study, the major sources of pm emissions were associated with road traffic. authors in [13] reported that major sources for the release of pm were related to traffic. presently the world’s most considerable health risks are primarily associated with air pollution, corresponding author: zafar ali siyal engineering, technology & applied science research vol. 9, no. 1, 2019, 3757-3761 3758 www.etasr.com siyal et al.: assessment of air pollution by pm10 and pm2.5 in nawabshah city, sindh, pakistan particularly pm pollution [14, 15]. like other air pollutants, pm is also considered as one of major concern [2, 4]. the presence of pm poses more danger to human health than that of ground-level ozone and other common air pollutants (like carbon monoxide) [8]. particle size is one of the significant features which stimulus the accumulation rate of particles in the respiratory system. the severity of health problems depends upon the size of pm. the smaller the pm size, the more deeply it will enter the body and affect the respiratory tract [16-19]. the health effects can be acute or chronic respiratory disorder (e.g., cardiovascular and lung cancer), depending upon the particle size [20, 21]. exposure to pm pollution may also cause increase in hospital admission, respirational symptoms, exacerbation of prolonged respiratory, decrease lung function and premature death [2225]. authors in [9] reported that an estimated 4.2 million people died worldwide mainly due to exposure of pm2.5 in 2015. authors in [26] elucidated that pm≤10 increased the prevalence of respiratory and cardiovascular disorders. air pollution, particularly pm pollution, became a major issue in nawabshah as it is expanding rapidly due to population growth, vehicle number, urbanization, and industries like habib sugar mill (hsm) and bandhi sugar mill (bsm). this study was designed to assess air quality deterioration by pm10 and pm2.5 pollution and to identify pm10 and pm2.5 sources in nawabshah, which has not been done previously by any study. the objectives of the current study are: • to survey the city areas and determine the sensitive points where pm concentration is significant. • to assess the concentration of pm in the ambient air of nawabshah. • to visit the hospitals and assess the health impacts associated with pm pollution. findings of the current study will be helpful for the government and environmental protection agencies to take strict measures for monitoring and control of pm pollution and to bring the levels according to standards provided by the local and international environmental agencies. ii. materials and methods a. site description and selection nawabshah is located in shaheed benazirabad district and is the central city of sindh province. nawabshah has latitude 26.25 o n and longitude 68.4 o e. being located at the center of district sindh, pakistan, nawabshah is considered as one of the most important and rapidly expanding cities. hsm is also located in nawabshah and during operation time of hsm, many pollutants are released in the atmosphere, including pm which can travel over a long/short distance depending upon the seasonal variation. a research study was conducted to assess and identify the current situation of pollution associated with pm and sources from which these particles were originated. significant health impacts, which may be caused by pm pollution, were also assessed by visiting various hospitals. health impact information was based on consulting with doctors, and it was assumed that respiratory diseases could be caused by exposure to pm pollution. in addition, the locations selected for carrying out this research work were categorized as (a) highly dense commercial and (b) residential areas. selecting the locations for pm pollution assessment required comprehensive study and the selection of the sites was based upon the criteria of increasing urban population growth, rapidly increasing quantities of transportation and the development level of the city. in order to get information about pm2.5 and pm10 in nawabshah, 10 main locations with different characteristics were selected for assessment. assessment of pm2.5 and pm10 pollution was carried out at different times and days. data were collected at each location for later analysis. table i shows the locations and their labels in nawabshah city, selected for data collection. table i. city locations location names labels new naka nn hospital road hr masjid road mr mohini bazar mb sakrand road sr railway station rs bucheri road br habib sugar mills hsm society chowk sc quaid-e-awam university of engineering, science and technology quest b. equipment and data collection hourly concentrations of pm10 and pm2.5 were taken for a month. the selection of sites was based on traffic oriented areas and on the occurrence of highest concentrations to which the population is likely to be directly or indirectly exposed. aerocet 531 was used to assess the concentrations of pm10 and pm2.5. this equipment can be used for testing/measuring pm size fractions pm1, pm2.5, pm4, pm7, pm10 and total suspended particles (tsp). aerocet 531 is a portable battery-operated unit which counts small particulates, calculates their mass profile per cubic foot of air samples and provides real time information. the equipment tests particle size of pm2.5 and pm10. the real time count information is displayed on lcd in two channels. the stored particle count data is used for 8 particle sizes and an algorithm derives the mass concentration for the sample. iii. results and discussion a. assessment of pm10 and pm2.5 pollution in nawabshah urbanization and growth in energy use leads to significant impacts on air quality. polluted air is considered as a severe problem globally, affecting the quality of life and environment to a greater extent. the selected city for the survey is passing from this serious issue, particularly pm pollution which is affecting public health, the value of life and the environment. the assessment of pm10 and pm2.5 pollution was carried out at various locations of nawabshah. random sampling at each location was carried out. statistical analysis of pm data was carried out by daily average concentrations of pm10 and pm2.5 using origin pro 9.0 software. table ii shows the daily mean, maximum and engineering, technology & applied science research vol. 9, no. 1, 2019, 3757-3761 3759 www.etasr.com siyal et al.: assessment of air pollution by pm10 and pm2.5 in nawabshah city, sindh, pakistan minimum concentrations of pm2.5 and pm10. the obtained results were compared with other national researches regarding pm pollution in other cities of pakistan. pm pollution was assessed at these locations at different times and dates, and figure 1(a)-(j) represents the levels of pm10 and pm2.5 on various days in the selected locations of nawabshah city. the trend in the assessment of pm10 and pm2.5 pollution in the selected sites was different depending upon the traffic density, domestic and commercial activities, and industry presence like habib sugar mills limited. each location of the city was assessed 10 times. during different assessment, observations were made on the concentration of pm10 and pm2.5 and the sources due mainly to which the concentrations were elevated. from figure 1(a), it seemed that the highest concentration (277µg/m 3 ) of pm10 was found at mb, indicating a higher level of pm pollution at the particular site. some of the locations (e.g., sr, rs, sc, and quest) at day-1 were found with pm2.5 pollution below the neqs (figure 1(a)). hsm was found more polluted with pm10 on day-2 (figure 1(b)). the reason could be the storage and transport of bagasse, produced from the sugar mill resulted in the release of particles in the atmosphere and hence elevated concentration. for pm2.5, the highest concentration of 41µg/m 3 was found at nn on the same day. many of the locations excluding nn, br, hsm, and sc were found with pm2.5 levels below neqs pakistan (figure 1(b)). on day 3-5, it seemed from figure 1(c)-(e), the highest concentrations were observed at hsm. the lowest concentrations of the same particles were found at quest. in the case of pm2.5, elevated levels on the same days were noted at hsm, hr and nn respectively (figure 1(c)-(e)). from figures 1(f) and 1(g)), higher levels of pm pollution were found at nn. the lowest concentration for pm2.5 was found at quest on day-7 (figure 1(g)). concentrations of pm2.5 at some locations were below neqs, and some were very near to neqs (figure 1(a)-(j)). however, in the case of pm10, it was evaluated that most of the locations were heavily polluted and concentrations were very much higher than neqs. some locations such as quest on days 3-6 were found having less pm10 concentration than neqs, possibly due to low traffic density in the current area. there is a link road connecting nawabshah and hyderabad via sakrand. on these days the traffic density over there was lower. some other locations (e.g., hr on day-5, rs on day-6 and mb, br and hsm on day-7) were also found with less pm10 concentration than neqs. the highest and lowest concentrations were noted for both pm10 and pm2.5. it was noted that the overall highest mean concentration of pm (e.g. pm10) was found as 230.8µg/m 3 on day-1. simultaneously the highest mean concentration of pm2.5 was reported as 47.5µg/m 3 on day-6. the pm levels were exceeding who guidelines set for pm2.5 (see table iii [31]). the pm levels also exceeded the permissible levels set by neqs. the mean concentrations of pm10 were 69.96-79.06% and 9.9-37.18% higher than those of who and neqs. meanwhile, the mean concentrations of pm2.5 were 24.9-47.36% and 5.66-26.3% higher than the guidelines set by who and neqs. on day-2 and day-10 the mean concentration of pm2.5 was below the neqs, and on day-1, day-4 and day-9 were very near to the neqs, indicating lower pm2.5 pollution in the city. fig. 1. concentrations of pm10 and pm2.5 at different days in various locations of nawabshah city. the mean concentrations of pm10 were found higher than the neqs, indicating that the city was heavily polluted with pm10 (table iv). it is important to mention that the city was more polluted with pm10 than with pm2.5. it was observed that concentrations of pm2.5 and pm10 at most of the locations of nawabshah city exceeded the who and neq standards established by the government indicating that the city was heavily polluted with both pm10 and pm2.5. these exceeded levels of pm pollution urged the environmental protection agencies to take strict remedy measures for the control of pm pollution. b. sources of pm pollution in nawabshah the population is increasing rapidly and consequently demands and lifestyle are changing. the increasing number of vehicles led to exceeded pm levels. further, it was observed that the main sources for the release of pm were engineering, technology & applied science research vol. 9, no. 1, 2019, 3757-3761 3760 www.etasr.com siyal et al.: assessment of air pollution by pm10 and pm2.5 in nawabshah city, sindh, pakistan associated with burning activities e.g. hsm and automobiles. dust storms usually take place in the surroundings and in the city and significant movement of the particles via wind from one place to another contributed to the suspension of a large amount of dust and sand particles in the environment. movement of these particles from heavily polluted to less polluted areas caused the deterioration of air quality in the city. it was observed during the assessment that transportation was one of the main sources of re-suspension of pm in the city. re-suspension of dust particles due to traffic flow, burning of unmanaged solid waste, improper handling of construction, and demolition waste were the main identified sources of pm pollution in the city. table ii. pm minimum and maximum concentrations days particulate matter types pm10 (µg/m 3 ) pm2.5 (µg/m 3 ) min. max. min. max. day-1 155 277 31 55 day-2 183 255 27 41 day-3 137 227 39 50 day-4 140 235 30 44 day-5 140 218 31 51 day-6 121 205 40 62 day-7 131 199 22 57 day-8 165 220 36 49 day-9 150 249 31 41 day-10 183 255 27 41 table iii. mean values of pm10 and pm2.5 compared with who and neq standards days particulate matter pm10 (µg/m 3 ) pm2.5 (µg/m 3 ) obtained who neq obtained who neq day-1 230.8 50 150 37.8 25 35 day-2 224.7 50 150 33.3 25 35 day-3 174.9 50 150 43.4 25 35 day-4 199.5 50 150 38.7 25 35 day-5 177.1 50 150 42.4 25 35 day-6 172.4 50 150 47.5 25 35 day-7 166.5 50 150 45.4 25 35 day-8 192.4 50 150 43.4 25 35 day-9 210.5 50 150 37.1 25 35 day-10 224.7 50 150 33.3 25 35 c. health impact associated with pm pollution air pollutants, if not managed appropriately may have adverse health, and environmental impacts and pm is one of the air pollutants posing serious health impacts to humans. it is recognized that an increase in respiratory diseases is often associated with pm pollution, mainly due to pm10 and pm2.5 air pollution. according to the environmental protection agency (epa) short-term and long-term exposure of humans to high concentrations of pm10 and pm2.5 can cause numerous health impacts and even deaths [27-30]. people of the city were suffering from various health problems like asthma, chronic bronchitis respiratory symptoms, weakened lung function, and cardiovascular diseases. several hospitals were visited during the research. table iv shows the hospitals visited and some patients who were possibly affected by pm pollution. in the national medical center, zohaib medical centre, civil hospital, and jinnah medical center, respectively about 20-30, 15-20, 40-60 and 15-25, patients were hospitalized per day out of which 15-25, 10-12, 20-30 and 10-12 people were possibly suffering from the diseases mentioned above. this study was conducted in 2015, so the current situation might be worse. table iv. hospitals visited during the survey hospital name total patients visiting per day no of possibly affected patients national medical centre 20-30 15-25 zohib medical centre 15-20 10-12 civil hospital nawabshah 40–60 2030 jinnah medical centre 15-25 10-12 iv. conclusion in this paper, assessment of pm2.5 and pm10 concentrations in nawabshah was carried out, and the obtained results were analyzed and compared with air quality standards. mean concentration of pm10 was 78.3% higher than who standards and 35% than neqs. similarly, the mean concentration of pm2.5 was 47.3% and 26.3% higher than the respective standards. these concentrations indicated that the air quality was deteriorated with the rapid growth of urbanization and transportation, and the public health was significantly affected. poor air quality monitoring, open burning of trash in the environment, improper management and handling of all types of solid waste, devastation of the paving material by road traffic and the release of pm from hsm were the main causes of elevated concentrations of pm2.5 and pm10 in nawabshah. pm10 and pm2.5 levels in nawabshah exceeded national and international air quality standards and adversely affected the public health. the adverse health effects of pm have provoked the government to progressively set strict regulations and policies to 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wood combustion to pm10 levels in portugal”, atmospheric environment, vol. 44, pp. 642-651, 2010 [30] l. w. stanek, j. d. sacks, s. j. dutton, j. j. b. dubois, “attributing health effects to apportioned components and sources of particulate matter: an evaluation of collective results”, atmospheric environment, vol. 45, pp. 5655-5663, 2011 [31] who, who air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide. global update 2005. summary of risk assessment, world health organization 2006 microsoft word etasr_pyl.doc etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 544-548 544 www.etasr.com pylarinos et al.: discharges classification using genetic algorithms and feature selection algorithms… discharges classification using genetic algorithms and feature selection algorithms on time and frequency domain data extracted from leakage current measurements d. pylarinos dr-ing electrical & computer engineer, researcher/consultant, greece dpylarinos@yahoo.com k. theofilatos pattern recognition lab, computer engineering and informatics dpt, university of patras, greece theofilk@ceid.upatras.gr k. siderakis electrical engineering dept., school of applied technology, technological educational institute of crete, greece k.siderakis@gmail.com e. thalassinakis islands network operation department, hellenic electricity distribution network operator s.a., greece e.thalassinakis@deddie.gr abstract— a number of 387 discharge portraying waveforms recorded on 18 different 150 kv post insulators installed at two different substations in crete, greece are considered in this paper. twenty different features are extracted from each waveform and two feature selection algorithms (t-test and mrmr) are employed. genetic algorithms are used to classify waveforms in two different classes related to the portrayed discharges. five different data sets are employed (1. the original feature vector, 2. time domain features, 3. frequency domain features, 4. t-test selected features 5. mrmr selected features). results are discussed and compared with previous classification implementations on this particular data group. keywordsinsulators; leakage current; discharges; classification; frequency; genetic algorithms; mrmr; t-test i. introduction high voltage insulators are an important component of a power system, as its integrity and reliability depends on their performance. the selection of insulator design and material is performed based on local conditions with pollution being probably the most important factor [1-3]. pollution is a well known problem experienced by all power systems, in various degrees, and several techniques can be applied to deal with the phenomenon [4]. as power networks keeps involving and demands increase, research and automatic monitoring of insulators’ performance becomes an issue of increased importance. leakage current monitoring is a well established technique for monitoring and assessing the performance of insulators during the research/testing stage and also during normal operation [5]. although, lab tests are widely conducted, and have been standardized e.g. [6-8], field monitoring and testing is also important as the phenomenon is highly localized and environmental conditions can not be reproduced in the lab. therefore, measurements are also conducted on already installed insulators [5] but also in specially designed open air test stations [9]. field measurements require long term monitoring which means that a vast amount of data has to be recorded and/or interpreted. to bypass this problem, the usual approach is not to record the raw measurement (i.e. the waveform of the leakage current) but to extract, record and study values such as the peak value, the charge and the number of pulses exceeding pre-defined thresholds [5]. however, it is widely accepted that it is the actual shape of the leakage current waveform that is correlated to the experienced electrical activity and the basic stages of activity have been well correlated with certain waveform shapes during lab tests [5, 1012]. recent research has shown that although similar shapes should be expected in the field [13-14], field waveforms are far more complex and thus, values as the ones mentioned above may be misleading [13-15]. therefore, research has also focused in the application of signal processing and pattern recognition techniques in order to automate the classification of field leakage current waveforms [13-15]. in this paper, field waveforms portraying discharges are classified in two different classes using genetic algorithms (gas). the classification is performed using twenty features, commonly used in the literature [5], that equally represent the time and the frequency domain (ten features from each domain). fourier and wavelet analysis are used for the extraction of the frequency domain features. the time and frequency domain features are used separately and combined, and thus three different feature sets are defined. further, two different feature selection algorithms (t-test and mrmr) are applied on the twenty features set, producing two additional sets. finally, the ga classification is performed on these five different feature sets. assessment and monitoring of high voltage insulators is of great importance for the hellenic electricity distribution network operator s.a. especially regarding the network in islands such as crete and rhodes [4]. insulators installed in etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 544-548 545 www.etasr.com pylarinos et al.: discharges classification using genetic algorithms and feature selection algorithms… these islands experience intense marine pollution due to the proximity of the network to the sea and the experienced weather conditions, while subjected to relatively high levels of voltage [4, 16]. therefore, a large project to battle the phenomenon has been initiated. several different techniques have been applied over the years [4, 16-17] with the large application of rtv sir coatings being the most dominant one, with significant economic benefits [18]. the latest part of this project is the construction and operation of talos high voltage test station [19-21] which provides further potential that include the technical background for long term waveform monitoring, utilizing past research on waveform identification and classification [13-15, 22]. ii. set-up and measurement sites eighteen different 150 kv post insulators (porcelain, rtv sir coated and composite) have been monitored for more than six years. the insulators were part of the grid, installed at 150 kv substations [20]. a collection ring was installed at the bottom of each insulator and the current was driven through a hall current sensor to acquire the measurement. the data was then transmitted to a commercially available data acquisition system (daq). each waveform recorded has a time length of 480 ms with a sampling rate of 2 khz. detailed specifications for the daq can be found in [14]. regarding waveform recording, the daq used the time-window technique in order to cope with the data size problem, which means that a single waveform was recorded during a pre-specified time window (e.g. a day), and the waveform selected was the one portraying the largest peak value [15, 22]. a number of 387 discharge portraying waveforms are used as the data set in this paper. to isolate discharge waveforms from sinusoids and noise, the techniques described in [13, 15, 22] were applied. a schematic representation, pictures from the measuring system and also from the sites are shown in figure 1. iii. extracted features and waveform classes the waveforms in the considered data set have been preclassified in two different classes, depending on the duration of discharges. class a includes waveforms that portray discharges that last four halfcycles or less (170 waveforms) and class b includes waveforms that portray discharges that last five or more halfcycles (217 waveforms). the feature set used for the classification consists of 20 different features, shown in table i. features 1-10 derive from the time domain, and features 1120 from the frequency domain, and have been chosen in order to evenly represent both domains and also considering the literature [5]. regarding time domain features, frequently used values such as the amplitude and charge, along with commonly used statistical values are employed. regarding the feature domain features, it was considered that the content of odd harmonics is commonly correlated to the occurrence of discharges and to the distortion of the waveforms’ shape and therefore several commonly used odd harmonic ratios [5] are employed. it should be noted that the fundamental frequency is 50hz and that the hd ratio is similar to the thd ratio, with the numerator being the sum of the odd harmonics’ content. further, wavelet analysis and especially mra is employed in order to acquire the std_mra vector [23, 24]. the std_mra vector contains the standard deviation (std) of the details of each level of the wavelet multiresolution analysis (mra) of the original waveform, with d1 referring to the first decomposition level, d2 to the second level etc [13, 15]. the distortion ratio [5] given by: 1 2 3 4 5 r d d d d d d     , is also calculated. the frequency bands of the std_mra vector’s components are shown in table ii. a b fig. 1. a. a schematic representation of the measuring set up and b. pictures from the installation table i. feature set no. feature no. feature 1 amplitude 11 third to first harmonic ratio 2 mean 12 fifth to first harmonic ratio 3 median 13 fifth to third harmonic ratio 4 variance 14 total harmonic distortion ratio (thd) 5 standard deviation 15 harmonic distortion ratio (hd) 6 median absolute deviation 16 std_mra vector ratio: d1/d5 7 skewness 17 std_mra vector ratio: d2/d5 8 kurtosis 18 std_mra vector ratio: d3/d5 9 interquartile range 19 std_mra vector ratio: d4/d5 10 charge 20 distortion ratio: dr table ii. frequency bands of mra decomposition level (a) approximation (hz) (d) details (hz) 1 0~500 500~1000 2 0~250 250~500 3 0~125 125~250 4 0~62.5 62.5~125 5 0~31.25 31.25~62.5 6 0~15.625 15.625~31.25 etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 544-548 546 www.etasr.com pylarinos et al.: discharges classification using genetic algorithms and feature selection algorithms… iv. feature selection algorithms & employed feature sets two different feature selection algorithms are employed on the 387 feature vectors that contain 20 features each. one univariate, the student’s t-test [25-26] and one multivariate, the minimum redundancy maximum revelance (mrmr) algorithm [27]. the main principle in both techniques is the calculation of a feature relevance score and the removal of lowscoring features. t-test or student’s t-test [25-26] is one of the simplest, oldest and most famous feature selection algorithms. the basic idea is to calculate ti and the degrees of freedom and check whether the significance of the ti value is high enough for each feature according to a standard table. the ti value and the degrees of freedom are given by various equations depending on the form of the data, with the form regarding unequal sample sizes and unequal variance being used in this paper. the t-test algorithm selected the features {1, 3~11, 13~17, 19~20]. in contrast to univariate techniques, multivariate ones examine the features as groups and not as single unities. the minimum redundancy maximum relevance (mrmr) algorithm [27] is a recently developed feature selection algorithm. being a multivariate method, mrmr is capable of taking advantage of the complex dependencies between features. its goal is to select a feature subset that illustrates the minimum redundancy between the selected features and the maximum relevance to the classes. several values can be employed to calculate redundancy and relevance, with the mutual information being used in this paper. the mrmr algorithm selected the features {3, 5, 7, 8, 11, 13, 15, 16, 18, 19} the classification is finally performed on five different feature sets, (time-domain features, frequency domain features, all features, t-test features and mrmr features) as shown in table iii v. classification using genetic algorithms genetic algorithms (gas) are general search metaheuristic algorithms based on the initial creation of a population of candidate solutions, called chromosomes, and their iterative differentiation using the operators of evaluation, selection, crossover and mutation until some termination criteria are reached [28]. gas have been proved useful and efficient in optimization problems where the search space is big and complicated or there is not any available mathematical analysis of the problem. further, the ability to define a different fitness function for each problem, and the flexibility of gas to function deploying various representations of candidate solutions have enabled their extensive use in a variety of problems. in the present paper, we applied gas for the classification of the waveforms in the pre-defined two classes, using five different data sets as shown in table iii. in order to achieve this linear classification, the two centers of the two classes should be determined. after the estimation of these centers is achieved, each waveform is classified in the class for which it has the minimum euclidean distance from its center. a simple ga is employed to solve this optimization problem [29]. the examined data set were firstly normalized. the candidate solutions of a genetic algorithm consist of 2*n genes whose values range from [0-1] with n being the number of features which are used as inputs. the initial population of the applied genetic algorithm was created by randomly initializing a number of candidate solutions. the optimal number of these solutions was found through experimentation using the training set to be equal to 100. the evaluate the performance of the proposed solutions we used the following fitness function: fitness= accuracy + geometric mean (1) where accuracy is the classification accuracy and geometric mean= sensitivity*specificity . the geometric mean was included to the fitness function as our dataset is imbalanced towards one class. the selection mechanism which was deployed is the probabilistic roulette wheel selection combined with an elitism mechanism which reassures that the best solution found so far will not be lost through the evolutionary process. the variation operators which were used in the proposed approach are the two points crossover operator and the gaussian mutation operator. the two points crossover probability was applied with probability 90% while the gaussian mutation operator with probability 10%. the gaussian mutation probability simply adds to a selected for mutation gene a random value taken from a gaussian distribution with center equal to zero and distribution equal to 0.1. the steps of evaluation, selection, crossover and mutation are applied iteratively until 1000 iterations are reached or the convergence criterion is satisfied. the convergence criterion is satisfied if the performance of the best member of the population is less than 5% away than the average performance of the population. in this case, the population is deemed as converged and most of the times if the algorithm is not terminated no new good solutions will be found. vi. results & discussion results on the independent test set which consists of half our dataset are shown in table iii for all five feature sets. classification accuracy ranges from 54.97% to 68.41%. the worst results are achieved when using the time domain feature set (54.97%), and they are only slightly improved when using all features (56.12%). using only the frequency domain features provides further improvement (56.82%), which is more increased when using the mrmr (60.2%) and the student’s t-test (68.41%) feature sets. this shows that adding more features is not necessarily helping the classification, but that what is important is the selection of features, which can provide significant improvement to the classification process. it is also shown that the best results are achieved when using the student’s t-test feature set, even though the mrmr algorithm is etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 544-548 547 www.etasr.com pylarinos et al.: discharges classification using genetic algorithms and feature selection algorithms… more sophisticated and recent algorithm. this should be attributed to the fact that a linear classification algorithm is used, and therefore a univariate feature selection algorithm (i.e. one that examines each feature separately) is bound to provide better results than a multivariate one (i.e. one that examines group of features). in addition, it should be noted that recent research has shown that other classification algorithms perform better [12], however this should largely be attributed to the selection of the feature set. when gas are applied for both feature selection and classification, accuracy can be significantly increased (88.48%) [30], however still be slightly inferior compared to support vector machines (svms) (90.21%) [13]. an added problem that should be noted here is the absence of an insight to the classification process as both svms and gas operate similarly to a black-box classifier. therefore, the next step of the project is the implementation of a hybrid system that will use svms for the classification, gas for the optimization of the feature set and system’s parameters, and fuzzy logic in order to produce comprehensive rules describing the classification process [31].. table iii. feature sets and classification results feature set i ii iii iv v features td {1~10} fd {11~20} all {1~20} t-test {1, 3~11, 13~17, 19~20} mrmr {3, 5, 7, 8, 11, 13, 15, 16, 18, 19} ga’s accuracy 54.97% 56.82% 56.12% 68.41 60.20 vii. conclusion & future work investigation and monitoring of the performance of high voltage insulators is of crucial importance for the integrity and reliability of power systems. leakage current measurements are widely applied as a research, assess and monitoring tool, both in lab and field conditions. experienced electrical activity is correlated to the shape of the leakage current waveform. however, managing leakage current waveforms, especially in the field where long term monitoring is required, is a rather complex task. in this paper, a novel approach is performed for the classification of discharge portraying waveforms: twenty different features are extracted, feature selection is performed and genetic algorithms are employed for the classification. the features used equally represent the time and the frequency domain. one univariate (t-test) and one multivariate (mrmr) feature selection algorithm are employed. the classification is performed on five different feature sets (time domain features, frequency domain features, t-test selected features, mrmr selected features, all features,). overall results show the significance of feature selection for classification performance and achieved accuracy. further, it is shown that the feature set selected by the univariate algorithm provides the best results, which is attributed to the linearity of the classification algorithm. comparison with previous implementations hints that using gas for feature selection may provide significantly better results than the commonly used feature selection algorithms that were applied in this paper, although still slightly inferior to support vector machines classification. a significant issue in any case, is the absence of a description regarding the classification process. therefore, future work focuses on the implementation of a hybrid support vector fuzzy inference system for the classification of leakage current waveforms portraying discharges, in order to achieve higher accuracy and also acquire an insight to the classification process through the definition of fuzzy rules describing the classification. references [1] iec/ts 60815, selection and dimensioning of high-voltage insulators intended for use in polluted conditions, 2008 [2] cigre wg 33-04, “the measurement of site pollution severity and its application to insulator dimensioning for a.c. systems”, electra vol. 64, p. 101-116, cigre, 1979 [3] cigre wg 33-04, tf 01, a review of current knowledge: polluted insulators, cigre, 1998 [4] k. siderakis, d. pylarinos, e. thalassinakis, e. pyrgioti, i. vitellas, “pollution maintenance techniques in coastal high voltage installations”, engineering, technology & applied science research, vol. 1, no. 1, pp. 1-7, 2011 [5] d. pylarinos, k. siderakis, e. pyrgioti “measuring and analyzing leakage current for outdoor insulators and specimens”, reviews on advanced materials science, vol. 29, no. 1, pp. 31-53, 2011 [6] iec 60507, artificial pollution tests on high-voltage insulators to be used on a.c. systems, 1991 [7] iec 60587, electrical insulating materials used under severe ambient conditions-test methods for evaluating resistance to tracking and erosion, 2007) [8] iec 62217, polymeric insulators for indoor and outdoor use with a nominal vlotage > 1000 v – general definitions, test methods and acceptance criteria, 2005 [9] cigre wg b2.03, guide for the establishment of naturally polluted insulator testing stations, cigre, 2007 [10] m. a. r. m. fernando, s. m. gubanski, “leakage current patterns on contaminated polymeric surfaces”, ieee trans. dielectr. electr. insul., vol. 6, no. 5, pp. 688–694, 1999 [11] t. suda, “frequency characteristics of leakage current waveforms of an artificially polluted suspension insulator”, ieee trans. dielectr. electr. insul., vol. 8, pp. 705–709, 2001. [12] j. li, w. sima, c. sun, s. a. sebo, “use of leakage current of insulators to determine the stage characteristics of the flashover process and contamination level predicition”, ieee trans. dielectr. electr. insul., vol. 17, no. 2, 2010 [13] d. pylarinos, k. theofilatos, k. siderakis, e. thalassinakis, i. vitellas, a. t. alexandridis, e. pyrgioti, “investigation and classification of field leakage current waveforms”, ieee transactions on dielectrics and electrical insulation, vol. 19, no. 6, pp. 2111-2118, 2012 [14] d. pylarinos, k. siderakis, e. thalassinakis, e. pyrgioti, i. vitellas, “investigation of leakage current waveforms recorded in a coastal high voltage substation”, eng. technol. appl. sci. res., vol. 1, no. 3, pp. 6369, 2011 [15] d. pylarinos, k. siderakis, e. pyrgioti, e. thalassinakis, i. vitellas, “impact of noise related waveforms on long term field leakage current measurements”, ieee transactions on dielectrics and electrical insulation, vol. 18, no. 1, pp. 122-129, 2011 [16] s. gubanski, “greek power company evaluates alternatives to combat pollution in transmission system on crete”, insulator news & market report (inmr), issue 58, volume 10, number 4, p. 30, 2002 [17] inmr, “greek utility battles pollution affecting island transmission system”, insulator news & market report (inmr), issue 78, volume 15, number 4, p. 24, 2007 etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 544-548 548 www.etasr.com pylarinos et al.: discharges classification using genetic algorithms and feature selection algorithms… [18] e. thalassinakis, “greek utility assesses economics of rtv silicone coatings as measure to combat pollution”, insulator news & market report (inmr), issue 64, volume 12, number 2, p. 66, 2003 [19] inmr, “greek utility readies to energize new insulator test station”, insulator news & market report, issue 82, volume 16, number 4, p. 32, 2008 [20] d. pylarinos, k. siderakis, e. thalassinakis, i. vitellas, e. pyrgioti, “recording and managing field leakage current waveforms in crete. installation, measurement, software development and signal processing”, isap 16th international conference on intelligent system applications to power systems, hersonissos, crete, greece, september 25-28, 2011 [21] talos high voltage test station, www.talos-ts.com [22] d. pylarinos, k. siderakis, e. thalassinakis, e. pyrgioti, i. vitellas, s. l. david, “online applicable techniques to evaluate field leakage current waveforms”, electric power systems research, vol. 84, no. 1, pp. 6571, 2012 [23] s. g. mallat, a wavelet tour of signal processing, academic press, 1999. [24] s. g. mallat, “a theory for multiresolution signal decomposition: the wavelet representation”, ieee trans. pattern analysis and machine intelligence, vol. 11, pp. 674-693, 1989. [25] r. a. johnson, g. k. bhattacharyya, statistics: principles and methods, john wiley & sons inc, 6th edition, 2010 [26] s. welleck, testing statistical hypothesis of equivalence, chapman & hall, crc, 2003 [27] h. peng, f. long, c. ding, “feature selection based on mutual information: criteria of max-dependency, max-relevance, and minredundancy”, ieee trans. pattern anal. mach. intell., vol. 27, no. 8, pp. 1226-1238, 2005. [28] j. holland, adaptation in natural and artificial systems : an introductory analysis with applications to biology, control, and artificial intelligence, cambridge: mass ;mit press, 1995. [29] z. michalewicz, genetic algorithms + data structures = evolution programs, springer-verlag, 3rd edition, 1996. [30] d. pylarinos, k. theofilatos, k. siderakis, e. pyrgioti, t. papazoglou, i. vitellas, e. thalassinakis, "feature selection and classification of field leakage current waveforms using genetic algorithms", cigre symposium 2013 lisbon, portugal, april 22-24, 2013 [31] k. theofilatos, d. pylarinos, s. likothanassis, d. melidis, k. siderakis, e. thalassinakis, s. mavroudi, “a hybrid support vector fuzzy inference system for the classification of leakage current waveforms portraying discharges”, electric power components and systems (accepted for publication) microsoft word 11-3891_s_etasr_v10_n6_pp6439-6443 engineering, technology & applied science research vol. 10, no. 6, 2020, 6439-6443 6439 www.etasr.com koondhar et al.: water penetration of concrete made with coarse aggregates from demolishing waste water penetration of concrete made with coarse aggregates from demolishing waste muhammad fahad koondhar department of civil engineering quaid-e awam university of engineering, science & technology nawabshah, pakistan kingblackzero@gmail.com bashir ahmed memon department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan bashir_m@hotmail.com mahboob oad department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan engrmahboob04@gmail.com faraz ahmed chandio department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan farazahmedchandio04@gmail.com sheerz ahmed chandio department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan sheeraz.ahmed030@gmail.com abstract-the results of laboratory investigations on water penetration in concrete made with coarse aggregates from demolishing waste are presented in this paper. seven batches of standard size concrete cubes were cast with recycled aggregates from demolished concrete replacing coarse aggregates in percentages from 0% to 60%. the compressive strength of the samples was evaluated by non-destructive testing with the use of the schimidz hammer. it was found that the strength reduces with an increase in recycled aggregate percentage. the maximum loss of strength due to the induction of recycled aggregates was 32% in the batch with 60%recycled aggregates. all samples were subject to constant water pressure of 5 bars for 72 hours. from the obtained results it was shown that the water penetration depth increases with increase in recycled aggregates rate. with 10% and 20% replacement the samples allowed less water to penetrate than conventional concrete samples, but 76% more penetration depth was recorded in samples with 60% replacement. strength and water penetration results from dosages up to 20% show that the durability of the produced concrete allows it to be used in structural members with consideration of strength reduction in the design process. however, more water penetration with higher dosages of recycled aggregates needs proper care in design and usage of the concrete particularly for locations where concrete is exposed to water pressure. keywords-green concrete; recycled aggregates; demolishing waste; permeability; water penetration i. introduction green concrete utilizes alternative concrete ingredients often involving waste generated from primary processes. waste generated due to demolishing of old structures poses a serious problem. this waste to some extent is utilized as filling material and the remaining goes to landfills. in agriculture dependent countries like pakistan, the land near the cities is agricultural. thus, dumping the waste in landfills will lead to adverse effects to the land and the environment. one of the options to minimize waste is by using it in new concrete as coarse aggregates. the green concrete developed by using the demolishing waste will not only reduce the waste amount to some extent, but will also reduce the negative impacts of quarrying for coarse aggregate production. however, the developed concrete should be checked for its properties with respect to conventional concrete to develop confidence in its use. research on the use of demolishing concrete as coarse aggregates is active the last few decades. in this regard, authors in [1, 2] published review articles on the recent developments on the use of waste in fresh concrete with reference to recycling of aggregates, issues associated with the processes and its impact on the final strength of concrete. among various concrete properties, permeability is one of the most important. it controls the water infiltration in concrete, thus preventing the rusting of steel and strengthening the bond strength between steel and concrete. also, it is the property which allows the flow of water through the concrete body if that is required, as in the case of thirsty concrete. in a research investigation, while checking the permeability of pavement concrete made with recycled aggregates and dolomite and marble waste, author in [3] observed the good permeability of the proposed material but noticed the decreased strength of recycled aggregate concrete in comparison with conventional concrete and concrete made with dolomite and marble waste. in another experimental study of the properties of pervious concrete, authors in [4] suggested 0.35 as water-binder ratio with enough strength of concrete to be used in sidewalks and civic paving projects. permeability characteristics of fiber reinforced high performance concrete and fiber reinforced corresponding author: mahboob oad engineering, technology & applied science research vol. 10, no. 6, 2020, 6439-6443 6440 www.etasr.com koondhar et al.: water penetration of concrete made with coarse aggregates from demolishing waste concrete made with recycled aggregates as coarse and fine aggregates have been studied in [5, 6]. based on the permeability results of the proposed concrete, the authors concluded that recycled aggregates partially replacing fine and coarse aggregates give almost similar properties as conventional concrete. the test results of concrete made with various alternative materials [7-17] regarding suitability [18], strength and durability [19], root cause of waste generation [20], sustained loading for 9 and 12 months [21, 22], fire resistance at 1000c for 18 and 24 hours [23, 24] show the promising effects of recycled aggregates as replacement materials suitable to be used in new concrete. demolishing waste has also been tested as replacement of fine aggregates. to this end, authors in [25] replaced fine aggregates with demolishing waste by 10%, 30%, 50% and 100%. laboratory tests of various properties of concrete showed results comparable to the conventional concrete’s. recycled aggregates with supplementary cementitious materials have been used in [26] to check the permeability of concrete at laboratory scale. the results revealed good resistance to water penetration in the proposed concrete. authors in [27] performed laboratory investigations on six different concrete mixes with recycled aggregates in order to study the permeability characteristics under desiccation conditions. the study considered fresh concrete in ventilated tunnel and showed a reduction in the bleeding of the concrete with low water cement ratio. liquid penetration depth and strength of concretes modified with polymer admixtures under the effect of crude-oil products was studied in [28]. although a few attempts have been made to study the water penetration in concrete with demolishing waste in different conditions with and without other ingredients, the scattering of the results shows that more work is needed to develop the confidence in the use of this material. therefore, this experimental study aims to evaluate the permeability of concrete made with coarse aggregates from demolishing waste at different percentages. it is hoped that the outcome will set a landmark for scholars and guidelines for relevant industry research. ii. materials and testing a. concrete ingidients demolished concrete was obtained from a 60 year old demolished reinforced concrete structure. the transformation of the material in coarse aggregates of maximum 25mm size was done manually by hammering. the obtained material was then sorted for debris and other unlikely materials followed by washing and drying in the laboratory. same size conventional coarse aggregates were obtained from the local market. sorting and washing of these aggregates were also done in similar fashion. these materials are shown in figure 1. to prepare the proposed specimens, hill sand confirming the astm requirements was used as fine aggregates. ordinary portland cement under the brand name pakland along with hill sand, obtained from the local market was used. b. specimen preparation a total of seven concrete mixes were made. among these mixes, one batch was prepared with only conventional coarse aggregates, whereas in the rest six batches, conventional coarse aggregates were replaced with recycled aggregates from demolished concrete with percentages from 10% to 60%. in each batch, four cubical specimens of standard size were prepared using 1:2:4 mix and 0.5 water to cement ratio. both parameters were selected due to their frequent occurrence in the construction industry. water obtained from the city water supply line having ph value equal to 6.9 was used for the preparation of the mixes. table i shows the details of the materials used in each batch. all the ingredients were mixed in a concrete mixer. fig. 1. conventional and recycled aggregates. table i. materials no 1 2 3 4 5 6 7 batch b1 b2 b3 b4 b5 b6 b7 rca (%) 0 10 20 30 40 50 60 no. of cubes 4 4 4 4 4 4 4 cement (kg) 6 6 6 6 6 6 6 fine aggr. (kg) 12 12 12 12 12 12 12 coarse aggr. (kg) 24.0 21.6 19.2 16.8 14.4 12.0 9.6 rca (kg) 0.0 2.4 4.8 7.2 9.6 12.0 14.4 water (kg) 3 3 3 3 3 3 3 cube specimens were prepared by first oiling the inner surface of moulds, followed by filling with concrete in layers. a table vibrator was used to compact the concrete in the moulds. the specimens were de-moulded after 24h and left in the laboratory to air dry for next 24h. curing of the specimens was done by fully immersing them in potable water for 28 days. c. specimen testing after the curing period, the specimens were taken out of the water and were allowed to air dry for 24h. all the specimens were then tested for compressive strength with the nondestructive testing (ndt) of the schimidz hammer. the obtained results are listed in table ii. after the strength testing, the specimens were tested for water penetration in accordance with the procedure defined by astm c642 for the purpose [29] and were mounted on a water penetration test machine (figure 2). the available machine tests six specimens at a time, therefore, the specimens were tested in turn. the specimens were mounted on the machine followed by filling of the cylinders with water. the water pressure was raised and kept equal to 5bars (5kg/cm2) for 72h. after the completion of this period, the specimens were un-mounted, and the surface water engineering, technology & applied science research vol. 10, no. 6, 2020, 6439-6443 6441 www.etasr.com koondhar et al.: water penetration of concrete made with coarse aggregates from demolishing waste was wiped off. the specimens were then split in to two parts in a universal testing machine (figure 3). the internal structure of the specimens was found compacted without any visible voids. the saturated surface was marked and the depth of water at six different locations was recorded. the obtained results are listed in table iii. fig. 2. water penetration test. fig. 3. specimens after water penetration. table ii. ndt compressive strength results batch sample no rca (%) compressive strength (psi) b1 1 0 2892 2 2953 3 2881 4 2853 b2 1 10 2567 2 2681 3 2645 4 2581 b3 1 20 2281 2 2181 3 2367 4 2367 b4 1 30 2119 2 2260 3 2119 4 2253 b5 1 40 2053 2 2045 3 2053 4 2181 b6 1 50 1912 2 1918 3 1881 4 1912 b7 1 60 1753 2 1767 3 1667 4 1781 iii. results and discussion the compressive strength results of all specimens within a batch are averaged and plotted in figure 4. the decreasing trend with increase in percentage of recycled aggregates can be observed. maximum loss of strength is recorded with the highest replacement level. with 10% and 20% replacement levels, the loss of strength is about 10% and 23% respectively. the water penetration results for all samples of all batches are averaged in table iv. it may be observed that the maximum and minimum depth of water penetration in conventional concrete is 70mm and 35mm, whereas for concrete with recycled aggregates they are 148mm and 10mm respectively. the minimum value is recorded in batch b1 (with 10% rca) and the maximum value is observed in batch b4 (with 40% rca), showing that the increase in the dose of recycled aggregates gave rise to water penetration. table iii. water penetration test results batch sample no rca (%) water penetration depth (mm) 1 2 3 4 5 6 b1 1 0 60 65 60 60 50 50 2 40 55 52 56 35 50 3 50 52 38 48 50 40 4 42 48 49 70 52 60 b2 1 10 30 40 70 20 20 10 2 56 55 70 42 35 56 3 60 53 65 40 50 50 4 62 62 45 60 60 74 b3 1 20 60 48 55 78 48 45 2 44 54 52 45 52 70 3 33 40 55 50 45 50 4 45 45 55 35 50 52 b4 1 30 110 65 70 55 70 100 2 95 64 60 50 70 110 3 70 70 55 65 65 75 4 100 100 74 70 70 66 b5 1 40 145 80 70 75 90 148 2 60 40 75 55 62 60 3 65 140 70 75 70 68 4 45 70 57 54 50 65 b6 1 50 72 67 75 42 70 64 2 130 88 50 70 50 128 3 110 65 58 48 55 120 4 98 50 90 60 106 100 b7 1 60 135 110 78 72 110 90 2 60 80 80 80 82 65 3 130 100 80 120 80 140 4 85 90 92 80 70 60 table iv. average water penetration depth the average water penetration in conventional concrete is equal to 51mm. an increasing trend in the water penetration depth with increase in quantity of recycled aggregates is rca (%) average water depth (mm) average depth of batch (mm) 1 2 3 4 0 58 48 46 54 51 10 32 52 53 61 49 20 56 53 46 47 50 30 78 75 67 80 75 40 101 59 81 57 75 50 65 86 76 84 78 60 99 75 75 80 90 engineering, technology & applied science research vol. 10, no. 6, 2020, 6439-6443 6442 www.etasr.com koondhar et al.: water penetration of concrete made with coarse aggregates from demolishing waste observed. water penetration depth of concrete with recycled aggregates is also compared with conventional concrete’s in figure 5. it may be observed that 30% and 40% replacement show identical values of penetration depths and very minor differences for 10% and 20% replacement of conventional coarse aggregates. the difference percentage of water penetration depth of concrete with recycled aggregates with respect to conventional concrete is shown in figure 6. fig. 4. average compressive strength fig. 5. average water penetration depth. fig. 6. the percentage change in penetration depth. it may be observed that 60% dosage of recycled aggregates results in 76% higher values than conventional concrete. lower dosages, i.e. 10% and 20%, show better performance of the proposed concrete with 1% and 2% lesser water penetration than the conventional concrete. it may also be noted that the obtained results are better than the results published by authors in [30] for concrete made with brick aggregates. they reported water penetration depth in the range of 225%-550% in comparison with conventional concrete. the comparison of the acquired results with those published in [31] show that for 20% replacement, the water penetration level results of this work are 29% less whereas for 60% replacement are about 12% more. although the internal structure of the specimens was observed good and similar to that of conventional concrete, yet an increase in water penetration is observed, probably due to the old mortar attached to the recycled aggregates which absorbs more water. also, during the compaction of the specimens or even under the sustained pressure of water, this mortar disintegrates resulting in some voids witch get filled when the concrete comes in contact of water. iv. conclusion in this research work, the results of laboratory investigations on the evaluation of water penetration depth in concrete made with recycled aggregates are presented. conventional concrete allowed the water to penetrate up to an average depth of 51mm. recycled aggregate concrete exhibited a slight resistance up to 2% with 10% and 20% replacement of conventional aggregates, but an increase up to 76% with increase in dosage of the recycled aggregates. the increased water penetration is mainly attributed to the old mortar attached to the recycled aggregates. based on the findings of compressive strength and water penetration tests, it is concluded that 20% replacement of conventional coarse aggregates 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[31] s. h. adnan, lee, y. l. lee, i. abdul rahman, h. mohd, and m. wimala, “water permeability of recycled aggregate concrete,” presented at the technology and innovation for sustainable development conference, khon kaen, thailand, jan. 2008. microsoft word etasr_v11_n3_pp7140-7145 engineering, technology & applied science research vol. 11, no. 3, 2021, 7140-7145 7140 www.etasr.com khan et al.: a holistic approach to urdu language word recognition using deep neural networks a holistic approach to urdu language word recognition using deep neural networks hashim raza khan department of electronic engineering ned university of engineering and technology karachi, pakistan hashim@neduet.edu.pk majida kazmi dpt. of computer and information systems engineering ned university of engineering and technology karachi, pakistan majidakazmi@neduet.edu.pk hamza khalid dpt .of computer and information systems engineering ned university of engineering and technology karachi, pakistan hamza@neduet.edu.pk muhammad abul hasan department of bio-medical engineering ned university of engineering and technology karachi, pakistan abulhasan@neduet.edu.pk nabeel fayyaz department of electrical engineering ned university of engineering and technology karachi, pakistan nabeelfayyaz@neduet.edu.pk saad ahmed qazi dpt. of computer and information systems engineering ned university of engineering and technology karachi, pakistan saadqazi@neduet.edu.pk abstract-urdu is one of the most popular languages in the world. it is a persianized standard register of the hindi language with considerable and valuable literature. while digital libraries are constantly replacing conventional libraries, a vast amount of urdu literature is still handwritten. digitizing this handwritten literature is essential to preserve it and make it more accessible. nevertheless, the scarcity of urdu optical character recognition (ocr) research limits a digital library's scope to a manual document search. the limited research work in this area is mainly due to the complexity of urdu script. unlike the english language, the urdu writing style is cursive, bidirectional, and character shapes and sizes highly vary depending on their position. holistic word recognition is found to be a better solution among many other text segmentation techniques as it takes the complete word into account instead of segmenting it explicitly or implicitly. for this project, the data of five different urdu words were collected for training and testing a convolutional neural network and 96% recognition accuracy was achieved. keywords-word recognition; urdu; deep learning; cnn; cursive writting i. introduction the urdu language is an indo-european language derived from the farsi alphabet, which stems from the arabic alphabet [1]. having more than a hundred (100) million native speakers in the south asian region, urdu is one of the two official languages of pakistan. similar to arabic, the urdu language is bidirectional. however, urdu has more isolated letters (38) than persian (32) and arabic (28). a great deal of history, literature, and lore of the south asian region is present in the form of handwritten manuscripts in urdu. to make them accessible to larger audiences through electronic media, the only possible solution is the digitization of the literature in searchable form. an obvious solution is manually sorting/annotation, which is a tedious and time-consuming task [2]. usually, if we want to bring any hard copy document in eformat, scanning is performed, bringing the data in image format. searching keywords from that image is not directly possible in urdu, persian, and arabic. this problem can be addressed with the help of optical character recognition (ocr) systems. ocr is defined as a process of classification of optical patterns in a digital image or as the conversion of images of typed, handwritten, or printed text into machineencoded text [3]. unlike english ocrs that first hit the market in the early 90s [4, 5], the earliest research conducted in urdu ocrs was reported in 2003 [6]. the complications associated with urdu script are: • urdu is a bidirectional language. it is written from right to left, and in some cases, such as numbers, it follows the left to the right direction. • each urdu letter can take four distinct shapes due to four different places, i.e. initial, middle, final, and standalone, as shown in figure 1 [7]. • urdu is always written cursively. interand intraword spaces are present in the urdu script. corresponding author: hashim raza khan engineering, technology & applied science research vol. 11, no. 3, 2021, 7140-7145 7141 www.etasr.com khan et al.: a holistic approach to urdu language word recognition using deep neural networks • words sometimes overlap each other and make the recognition process difficult. • some urdu characters have dots associated with them which can vary in numbers and locations. • sometimes in handwritten documents, open loops may get closed [8]. fig. 1. character variation depending on the position. research has been done on similar problem types, as mentioned above, in numerous languages, and text recognition has been experimented on text images using ocr [9]. ocr technique is used for converting images into editable text. however, for cursive scripts like urdu, results are not satisfactory as isolated scripts. hence, cursive scripts’ pattern recognition is challenging [10]. moreover, since arabic and persian languages’ characters are subsets of urdu language, it is practically impossible to use arabic/persian ocrs for urdu language. on the other hand, the general problem with ocrs is that the text that occurs in natural scene images, historical documents, or images hugely varies in appearance and layout or images with background objects cause false-positive detections [11]. due to these complications, converting an image with cursive text into editable text is not flawless, and accuracy is not satisfactory. word (keyword) spotting is another technique that can be defined as a process of finding all instances of a query word that exist in a document image without wholly recognizing the document. in the past years, research in handwriting recognition with ocrs has developed to a level that generates commercial applications. however, the success rate is much higher in online than offline recognition [9]. hence, in cases where the ocr system cannot assure human reader satisfaction, word spotting is a viable solution for information retrieval [2]. over the last few decades, there has been rapid development in text spotting methods. the majority of methods split the complete process into two major stages [12]: segmentation/text detection and word recognition. segmentation/text detection generates candidate character or word bounding boxes/region proposals [3]. it can be defined as decomposing an image into many sub-images, each containing a character/word. text detection tackles the standard text spotting pipeline and contributes to the whole process's error rate [12]. several segmentation strategies can be broadly classified into three main categories: implicit segmentation, explicit segmentation, and holistic approach. implicit segmentation (recognition-based segmentation) is a technique in which the system searches the images for components that match classes in its alphabet. however, this technique is adopted to integrate the processes of segmentation and recognition. accordingly, hidden makrov models (hmms) based approaches have emerged, and authors in [13] proposed a method based on hmms using an implicit segmentation approach and claimed word recognition accuracy of 88.2% on a lexicon of size 3,771. in explicit segmentation (classical approach), an input image is first partitioned into sub-images containing characters and then it is classified. explicit segmentation needs to find all the interconnection between words, also known as ligatures, and dissect the word images through all detected ligatures. authors in [14] proposed a direct segmentation approach for offline handwriting recognition. the accuracy of the segmentation approach was reported at 83.6%. however, over-segmentation and wrong segmentation are considerably high [15]. a holistic method tries to identify words instead of characters and considers them as units. it is therefore termed as intelligible word recognition (iwr) instead of a character recognition technique. there are other significant reasons for its popularity as well: the holistic approach is parallel to human reading and can be applied to historical documents whose poor quality makes it challenging to analyze with the classical approach [4]. due to the cursive handwriting style, changing the shape of characters depending on the urdu script's position, the classification using a holistic approach is more efficient and optimal [1]. besides these advantages, its major drawback is that the holistic approach is always restricted to a predefined lexicon since it does not deal directly with letters, but with words, so a specific lexicon of the word is a necessary constraint. whenever we want to modify the lexicon, the training stage is mandatory. this property makes this approach suitable where the lexicon is statistically defined [15]. after applying machine learning techniques in the image recognition domain, the lexicon size can be made quite large, making this technique suitable for many applications. a lexicon of size of 90,000 words has been claimed in recent works of word recognition [7]. a typical optical character recognition pipeline starts with looking at the picture, locating text areas, identifying the lines of the text, and at the end, it tries to recognize each character or word present in that image. the text recognition step receives a single word or character's cropped image and identifies the depicted object. characterbased classifiers are used to classify individual characters, which are then integrated to generate an entire word. different techniques are used for this classification task. authors in [16, 17] use convolutional neural networks (cnn) as character classifiers. authors in [17] used a complicated combination of cnns and hmms for a fixed lexicon to generate the final recognition results. an alternate approach for this text detection task is whole word-based recognition or holistic word recognition, extracting features from the entire word before performing word classification [7]. since we cannot use arabic and persian language recognition systems, our primary focus is to develop a word recognition system using a deep neural network for the urdu language. to that end, we have used a holistic or whole wordbased recognition approach. we have collected around 5298 samples of five urdu words: tawhid, namaz, hajj, rehmat, and jannat for our project. engineering, technology & applied science research vol. 11, no. 3, 2021, 7140-7145 7142 www.etasr.com khan et al.: a holistic approach to urdu language word recognition using deep neural networks ii. data preparation a. training and testing data data were collected from different people, with a diversity of writing styles, containing 5298 samples of 5 different words (approximately every word is written around 1000 times). seventy five percent of the samples were selected for training, and 25% were set for testing purposes. b. data pre-processing recognition results rely on the preprocessing phase. unwanted noise can degrade the recognition accuracy. our work in the preprocessing stages involves binarization and converting of the cropped images into a uniform size while creating the dataset. for data collection, we have used a4-sized papers with 26 rows and 10 columns. these papers were scanned at 300 dpi, and then individual characters were cropped using an open-source ocr helper tool. these cropped images were saved in binarized format in a text file, as shown in figure 2. this text file has three channels (rgb), which carries redundant information, so information from only one channel was extracted, and then these arrays were concatenated to form a complete dataset. the ocr helper tool facilitates the dataset preparation process by providing an adjustable binarization threshold, height and width sensitivity, and the export size of the blob. fig. 2. ocr helper tool for cropping and binarization. iii. the deep learning model a. model architecture neural networks are typically organized in layers, consisting of many interconnected nodes known as neurons. generally, there are 3 types of layers: input, hidden, and output layers. the input layer receives the input pattern and communicates it to the next (hidden) layer. a hidden layer is an intermediate layer between the input and the output layers. the processing is performed here via weighted connections. the last output layer of the neural network usually consists of n nodes, where n is the total number of classes. a convolutional neural network (cnn) is one of the most common types of artificial neural networks and it is considered a state-of-the-art technique in pattern recognition, outperforming several classifiers [18]. the cnn's architecture contains convolutional layers, pooling layers, and a fully connected layer. a cnn finds its application in a wide range of areas, e.g. natural language processing, video analysis, speech recognition, and pattern recognition [19]. the convolutional layer is the first layer in a cnn. this layer uses a number of n different filters or kernels (edge or curve detectors). each of these can be intuitively modeled as a feature identifier. these filters then convolve with the original image's sub-images according to their dimension and extract features from that image. to understand the process of convolution, consider a 6×6 image and a 3×3 filter. to extract features, we must convolve them. this operation is shown in figure 3. fig. 3. a simple convolution operation. the values of the output can be easily calculated as follows: x1=3*1+4*1+1*1+0*0+0*8+0*2+1*-1+6*-1+3*-1=-2 output dimensions can be found as: n−f+1*n−f+1 where n is the input image dimension (6 in this case) and f is filter's dimension (3 in this case). the output dimensions will be 4×4. pooling or subsampling layer is used to decrease the features' resolution, making the feature more robust against noise and distortion and making the system computationally effective. a fully connected layer is often used as the last layer in a cnn. the working principle of a fully connected layer is the same as traditional multi-layer perceptons. every neuron present in this layer receives input from every neuron of the previous layer and finally classifies the output. b. model training and testing to develop an urdu handwritten word recognition system, we created a deep feed-forward neural network architecture using the tensorflow library. we started our experiment with 5 different word classes, each having approximately 1000 samples. we trained our network on a non-gpu machine with varying image sizes, i.e. (60×60, 50×50, and 30×30 pixels) and different numbers of neurons and got meaningful results comparable with [20]. c. results we trained our model for 5 different words and tested it for accuracy and loss by changing the number of neurons and input image sizes. increasing the number of neurons resulted in better accuracy but increased training time. the highest accuracy achieved was 95.81%, with 60×60 image size and 2000 neurons in each layer. the words used to train the model were tawhid, namaz, hajj, rehmat, and jannat which were labeled as 0,1,2,3, and 4 respectively. figure 4 shows the random inferences from the test set, where ‘tr’ shows the original word and ‘pred’ shows the predicted output. 1) 30×30 pixel images the accuracies of individual words and of the complete development set on 30×30 images with different number of neurons is shown in table i. figure 5 shows the loss decrease and the accuracy increase with the number of epochs. figure 6 shows the individual accuracy of each word with a cnn containing 500 neurons. engineering, technology & applied science research vol. 11, no. 3, 2021, 7140-7145 7143 www.etasr.com khan et al.: a holistic approach to urdu language word recognition using deep neural networks fig. 4. prediction on the test set with randomly selected words. table i. accuracy on 30×30 images neurons accuracy (%) test set tawhid namaz hajj rehmat jannat 450 88.36 91.63 79.15 94.59 99.97 76.53 500 90.22 88.44 84.55 93.82 99.90 84.23 600 89.68 88.84 89.57 91.50 99.68 78.46 300 86.03 80.87 87.64 94.59 99.61 67.30 350 89.21 86.05 86.48 94.20 98.46 80.76 fig. 5. accuracy and loss with 500 neurons. fig. 6. individual accuracies with 500 neurons. 2) 50×50 pixel images the accuracies of individual words and of the complete development set on images of size 50×50 with different number of neurons is shown in table ii. figure 7 shows the loss decrease and the accuracy increase with the number of epochs. figure 8 shows the individual accuracy of each word with a cnn containing 1250 neurons. table ii. accuracy on 50×50 images neurons accuracy (%) test set tawhid namaz hajj rehmat jannat 1250 94.33 94.82 93.05 97.29 97.66 86.53 1400 94.25 97.61 94.59 98.45 97.50 80.76 1000 94.24 94.02 93.05 92.66 97.46 81.53 800 91.93 92.82 92.27 96.91 97.21 77.69 fig. 7. accuracy and loss of a cnn with 1250 neurons. fig. 8. individual accuracies with 1250 neurons. 3) 60×60 pixel images the accuracies of individual words and of the complete development set on images of size 60×60 with different number of neurons is shown in table iii. figure 9 shows the loss decrease and the accuracy increase with the number of epochs. figure 10 shows the individual accuracy of each word with a cnn containing 2000 neurons. fig. 9. accuracy and loss with 2000 neurons. engineering, technology & applied science research vol. 11, no. 3, 2021, 7140-7145 7144 www.etasr.com khan et al.: a holistic approach to urdu language word recognition using deep neural networks table iii. accuracy on 60×60 images neurons accuracy (%) test set tawhid namaz hajj rehmat jannat 400 87.82 80.87 87.25 94.98 98.60 75.76 800 92.63 93.22 88.03 97.68 98.94 84.23 1600 94.33 90.04 95.75 96.13 99.32 89.61 2000 95.81 95.21 96.52 98.45 99.61 88.84 2400 94.49 95.61 93.82 93.82 99.59 89.23 fig. 10. individual accuracies with 2000 neurons. iv. conclusion this report describes a system for handwritten urdu holistic word recognition using a deep neural network. this work's motivation was the existence of extensive valuable literature in the urdu language in many south asian libraries and the ongoing effort to digitalize these scripts. research work has already been conducted in this area on different languages, but the digitization of urdu script is a scarcely developed area. some work has been done for urdu word/character recognition using 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[20] u. khan, k. khan, f. hassan, a. siddiqui, and m. afaq, "towards achieving machine comprehension using deep learning on non-gpu machines," engineering, technology & applied science research, vol. 9, no. 4, pp. 4423–4427, aug. 2019, https://doi.org/10.48084/etasr.2734. microsoft word 36-2308_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3496-3501 3496 www.etasr.com shastri et al.: nonuniform c-band loop antenna nonuniform c-band loop antenna a new approach for future uwb applications s. p. shastri faculty of engineering pacific university, rajasthan, india shailendra.shastri@thakureducation.org r. r. singh thakur educational trust, mumbai, india ravishrsingh@yahoo.com k. v. ajetrao electronics and telecommunication department, k. j. somaiya college of engineering, mumbai, india kiranjetrao@somaiya.edu abstract—antenna design becomes very difficult at very small wavelengths and a special lab is required to manufacture a small antenna which costs a lot. a new approach is proposed to enhance the bandwidth of the loop antenna which can be designed at very high frequency using conventional pcb design technique. the proposed antenna is a nonuniform loop and covers uwb frequency range. the nonuniform structure of the loop is designed using the concept of both thin and thick loop antenna together which leads to an improvement in the antenna bandwidth. the proposed nonuniform loop antenna covers a band of 91.4% which is higher than any existing printed loop antenna. the frequency ranges from 3.54ghz to 9.5ghz and the measured result is in agreement with the simulated result. this technique can be very helpful in designing uwb antennas in the range of ku band or higher than this. keywords-coplanar stripline; thin loop antenna; thick loop antenna; wire antenna; ultra wide band; nonuniform loop antenna i. introduction uwb is a need of present and future communication systems as demand for more data is increasing. high-speed data transfer requires the availability of a larger band. in order to fulfill the need of larger bandwidth, broadband antennas are used as transmitting and/or receiving elements. other uwb applications include location tracking and ground penetrating radars. so far monopole antennas appeared as strong candidates to fulfill the requirements of uwb applications. in order to improve gain and other electrical and radiation characteristics, metamaterials or ebg structures were added to monopole antennas. dipole printed antennas fed with coplanar stripline (cps) cover bandwidth from 3.1ghz to 11.4ghz. this structure has too many dimensional parameters in the antenna design [1]. a closed loop structure provides larger scope for the researchers to contribute. a square printed loop with l shape portion to its arm offers excellent performance at the lowerband of uwb system, ranging from 3.1ghz to 5.1ghz [2]. the antenna exhibits a -10db return loss bandwidth over the entire frequency band. it is found that the lower band depends on the l portion of the loop antenna however the upper frequency limit is decided by the taper transmission line. the percentage of the bandwidth of the antenna is 48.78%. a printed loop antenna fed with coplanar waveguide can produce bandwidth of 1ghz and 1.14ghz. this antenna is suitable for applications in pcs and imt 2000 systems. the antenna has high gain with omnidirectional radiation pattern [3]. a small size loop antenna fed with cpw line produces a 70% bandwidth. the small size of the antenna makes it useful for array applications [4]. a single loop antenna has a narrow circular polarized bandwidth. when this antenna is added with another loop antenna as a passive element, then a second band is created and the combination of the antennas produces a larger bandwidth with circular polarization [5]. the band enhancement technique [2] was extended to a circular loop and bandwidth of 88.6% was achieved. the proposed work failed to give any justification on the enhancement of bandwidth and the impact of proposed shape on the antenna radiation pattern was not considered. ii. proposed nonuniform loop antenna a circular loop antenna with a thickness factor larger than 9, is called a thin loop antenna, otherwise it is called a thick loop antenna. the thin loop has multiple resonating frequencies and larger resistance with fluctuating characteristic. on the contrary, a thick loop antenna is capacitive in nature with low and uniform resistance [6]. the thickness factor is defined in (1), where ω is the thickness factor, � is the radius of the loop in m and � is the wire radius in m: ω = 2 ln (2 � �� ) (1) a loop antenna is basically a narrow band antenna. the bandwidth of the antenna can be improved when both thin and thick loop antennas are added together to have a uniform standing wave ratio (swr) [7]. its loop is comprised of a thick loop with 8.8 thickness factor and a thin loop with 11.7 thickness factor and covers 88.6% bandwidth. a wire loop antenna can be modified into a printed loop antenna using (2) as given in [8]. the thickness factor can be calculated using (1) and (2), where w is the width of the printed loop and b is the wire radius: � = 4⁄ (2) in order to further improve the loop antenna bandwidth, a new geometry is proposed and is shown in figure 1. the proposed geometry has a gradual increase in the width of the loop to have thin and thick loop properties together, unlike the engineering, technology & applied science research vol. 8, no. 5, 2018, 3496-3501 3497 www.etasr.com shastri et al.: nonuniform c-band loop antenna geometry in [7], which also has a step change in the width of the loop. (a) (b) fig. 1. nonuniform loop with (a) feed at narrow width w1 (b) feed at wide width w2. a loop antenna falls under two categories: 1) a large loop whose circumference is equal to or larger than a wavelength at a chosen frequency, 2) a small loop with circumference smaller than λ/10. a large loop is a good radiator while a small loop is a good receiver [9]. in order to cover the least frequency of 2ghz, the approximate radius of the loop using (3) and (4) is 24mm and the width of the loop is 1mm. ω of the loop is 12.76 so it is thin in nature. the same antenna for 12mm width has ω of 7.26 and is, a thick loop. � � 2 � � � (3) � � � �⁄ (4) where � is the circumference of the loop, r is the radius of the loop in m, � is the wavelength in m, � is the frequency in hz and �is the speed of light in m/s in free space. the antenna is simulated using cst studio. the substrate used is fr-4 with a height of 0.8mm. iii. feed location and width impact on the performance of the proposed antenna the proposed geometry has minimum width w1 and maximum width w2 to give a nonuniform dimension. the outer radius of the loop is taken as 24mm. in order to analyze the characteristics of the nonuniform loop and the effect of this geometry on feed location, a feed is applied at one width and the same or other width of the loop varies. a. feed impact at narrow width w1 with varying width w2 the possible advantage of the proposed structure is that there can be infinite locations for antenna excitation. this is because at different locations the feed will experience different loop width. therefore the loop electrical properties will be different for different locations of the excitation due to its nonuniform structure. nonuniform loop with thin width w1 of 1mm and thick width w2 of different values ranging from 6mm to 12mm is simulated. the feed to the loop is placed at the thin end w1. the result of the proposed nonuniform loop is compared with 1) a thin loop of 23.5mm radius with 1mm width having ω=12.76 and 2) a thick loop of 18mm radius with 12mm width having a thickness factor of 7.26. in order to have the same loop size, i.e. thin loop, thick loop and nonuniform loop, the outer radius is kept 24mm. since the proposed nonuniform loop has w1=1mm and width w2 varying from 6mm to 12mm, it is a combination of thin and thick loop. a thin loop of thickness factor of 12.76 shows a huge variation in resistance value. it ranges from 80ω to more than 400ω as is observed in figure 2(a). the thin loop resonates at about 1.9ghz as shown in figure 2(b). the thick loop of 7.26 thickness factor, as observed in figure 2(b), has stable resistance and resonates at 6ghz. (a) (b) fig. 2. comparison of impedances of uniform and nonuniform loop when feed is applied at narrow width w1 and varying width w2. it can be observed in figure 2(a) that the resistance variation of the proposed loop antenna is reduced to a greater extent but it is larger than the resistance of the thick loop for all simulated cases. similarly, the reactance of the nonuniform loop shows less variation when compared to the reactance of the thin antenna but it is larger than the reactance of the thick loop antenna as shown in figure 2(b). b. feed impact at wide width w2 with varying width w2 in order to analyze the effect of feed locations on the characteristic of the nonuniform loop antenna, the feed is placed at wide end w2 as shown in figure 1(b). the width w2 varies from 6mm to 12mm, while w1 is kept constant to 1mm. the behavior of the impedance of the nonuniform loop is shown in figures 3(a) and 3(b). it is observed that the resistance of the nonuniform loop approaches the resistance of the thick loop antenna of uniform width of 12mm with ω=7.26. the resistance varies between 24ω to 75ω from 3ghz onwards. in figure 3(b), it can be observed that as w2 increases from 6mm to 12mm, the reactance of the nonuniform loop decreases and approaches the reactance of the thick loop (ω=7.26) of 12mm width. the reactance of the nonuniform loop ranges from -75ω to +50ω for frequencies from 3.4ghz and onwards. the impedance of the proposed nonuniform loop under this case is smaller than in the previous case. the overall engineering, technology & applied science research vol. 8, no. 5, 2018, 3496-3501 3498 www.etasr.com shastri et al.: nonuniform c-band loop antenna impedance of the proposed loop for all cases is much smaller than the impedance of the thin loop with thickness factor of 12.76. any increase in w2 of the nonuniform loop reduces thickness factor of the antenna and antenna impedance approaches the impedance of thick loop with thickness factor 7.26. (a) (b) fig. 3. comparison of the reactance of uniform and nonuniform loop when feed is applied at wide width w2. c. feed impact at narrow width w1 with varying width w1 now the feed is placed at w1 and width w2 is kept at 6mm. w1 varies from 1mm to 2mm. the result of this nonuniform loop is compared with the uniform loop of 24mm outer radius with 6mm width. the outer radius of the nonuniform loop is kept at 24mm in order to keep the same maximum dimension of uniform and nonuniform loop. the uniform antenna of 6mm width with an outer radius of 24mm has uniform resistance less than 50ω from 3.3ghz and onwards as shown in figure 4(a). the nonuniform loop with w2 of 6mm and varying width w1 from 1mm to 2mm shows that antenna resistance decreases with increase in w1. any increase in w1 leads to uniformity in the structure of the loop and also causes a drop in the thickness factor of the proposed antenna. therefore the resistance of the nonuniform loop antenna decreases as shown in figure 4(a). the antenna with uniform width of 6mm resonates at 11ghz. it is capacitive from 1ghz to 11ghz and then switches to inductive reactance. on the other hand, the reactance of the nonuniform loop is larger and capacitive from 1ghz to 12ghz and above. as w1 increases from 1mm to 2mm, the antenna reactance reduces for obvious reasons as shown in figure 4(b). (a) (b) fig. 4. (a) resistance and (b) reactance comparison of uniform and nonuniform loop when feed is applied at varying narrow width w1. d. feed impact at wide width w2 with varying width w1 now the feed is located at wide width w2 and the width w1 varies from 1mm to 2mm. w2 is kept constant to 6mm. when the feed is shifted to w2 end, there is a huge difference observed in the reactance of the nonuniform loop antenna. in the uniform antenna, the shift in feed location does not influence the characteristics of the antenna as the dimension seen by the two terminal sources triggering the antenna is uniform. this is not the case with the nonuniform loop for the same two terminal sources. the nonuniform loop with thin dimension w1 of 1mm shows larger resistance. there is a continuous decrease in the resistance with increase in w1 as this leads to uniformity of the proposed structure. the variation in resistance is shown in figure 5(a). larger resistance is observed from 2ghz to 2.6ghz for w1 variation from 1mm to 1.5mm. the variation in resistance for w1 of 2mm is very small and is well aligned with the resistance variation of the uniform loop of width 6mm from 2.7ghz onwards. it can be observed in figure 5(b) that the reactances of uniform and nonuniform loop are well aligned from 3ghz and above. the two antennas, uniform and nonuniform, differ in their reactance from 2.45ghz to 3ghz. table i summarizes the impedance behavior of the loop with different w2 of 8mm and 10mm along with the earlier case of width w2 of 6mm. width w1 ranges from 1mm to 2mm for all three cases. it can be concluded that for a feed at w1 antenna impedance decreases significantly as w2 increases. a huge fall in antenna impedance is observed when the loop is fed at w2. therefore antenna impedance is a strong function of the feed location. furthermore, the antenna impedance can be varied by changing w1 and w2. this property of the proposed loop is not available in any other loop antenna available in the literature. engineering, technology & applied science research vol. 8, no. 5, 2018, 3496-3501 3499 www.etasr.com shastri et al.: nonuniform c-band loop antenna (a) (b) fig. 5. (a) resistance and (b) reactance comparison of uniform and nonuniform loop when feed is applied at wide width w2. table i. behaviour of proposed nonuniform loop antenna w2 (mm) w1 (mm) r/x (ω) (4ghz to 5ghz) r/x (ω) (8ghz to 9ghz) r/x (ω) (11ghz to 12ghz) feed at w1 feed at w2 feed at w1 feed at w2 feed at w1 feed at w2 6 1 219/-134 49/-77 102/-87 23/-18 87/-77 21.3/4 1.5 170/-124 52/-75 77/-80 24/-19 64/-66 21.6/3 2 140/-113 52/-72 62/-69 23/-19 52/-54 21.7/3.4 8 1 183/-148 41/-51 97/-93 19/-105 87/-79 19/25 1.5 146/-134 41/-49 76/-82 19/-1.7 66/-65 18/25 2 122/-122 40.5/-47 63/-72 19/-1.5 53/-52 18/25 10 1 178/-144 31/-34 102/-100 17/13 88/-76 19/48 1.5 140/-132 31/-33 80/-88 17/13 63/-64 19/47 2 117/-120 30/-32 65/-74 16/13.8 51/-52 19/46 r-resistance, x-reactance iv. locating feed for optimum bandwidth from the analysis above, it is concluded that antenna impedance is a function of the feed location. this section is dedicated to finding a suitable location of the feed to have the maximum bandwidth. the feed is applied from w1 end at 0 0 and is shifted to w2 end at 180 0 as shown in figure 6(a). the reflection coefficient for all cases is compared in order to find the optimum feed location. since the loop is a balanced antenna, it cannot be excited directly with sma connector or coaxial cable. in order to excite the proposed loop with the help of sma connector or any other unbalanced line, a coplanar strip line (cps) is added to the loop as shown in figure 6(b). for the simulations the outer radius of the nonuniform loop is kept at 24mm, the inner radius is 17.75mm with w1 of 2mm and w2 of 12mm. the inclusion of the cps line converts the unbalanced field distribution from the sma feed connector to a balanced field distribution at the loop [10]. the cps feed line is placed at different locations and the results are compared in figure 7. the detailed dimension of the cps line is included in figure 6(b). (a) (b) fig. 6. the proposed nonuniform (a) showing various feed locations from w1 to w2 (b) loop with cps feed line. fig. 7. comparison of the reflection coefficient of the nonuniform loop for different feed locations. it can be observed that the shift in the location of the feed influences the bandwidth of the antenna since the antenna impedance changes due to the change in the location of the feed as observed above. table ii summarizes the performance of the proposed loop in terms of % bandwidth of the loop with respect to different feed locations. it can be observed that the antenna gives the highest bandwidth when the feed is applied at 135 0 . the available bandwidth is 91.4%. the band has lower cut off frequency of 3.54ghz and higher cut-off frequency of 9.5ghz. table iii compares the proposed nonuniform loop antenna with other existing loop antennas. it can be observed that the proposed loop has the highest electrical and radiation bandwidth. figure 8 shows the radiation patterns in the range of 3.54ghz to 9.5ghz. the loop antenna is placed in x-y plane as shown in figure 6(b). the radiation pattern is of end fire type and is available along -y axis, opposite to the feed of the loop antenna. it was observed that the pattern is always available opposite to the feed of the loop for all cases listed in table ii. it is important to note here that when the proposed loop is compared with the loop proposed in [7], there is very little improvement in the antenna bandwidth. the advantages of the proposed loop over the earlier are summarized in table iv. the earlier loop requires balun transformer but the loop presented in this paper does not require it, so it occupies a smaller area on pcb. in addition, the size of the presented loop engineering, technology & applied science research vol. 8, no. 5, 2018, 3496-3501 3500 www.etasr.com shastri et al.: nonuniform c-band loop antenna is almost half the size of the earlier loop whose outer dimension was 45mm. there are only three distinct locations for feed in the earlier loop: a) on the wide arm of the loop, b) on the thin arm of the loop, and c) between the interface of wide and thin arm of the loop. the loop in this paper has theoretically infinite locations to feed the antenna. table ii. loop performance comparison for different feed locations using cps. sr. no. feed locations f1-f2 % bandwidth 1 0 0 4.9-6.7 31 2 22.5 0 5.4-7.6 34 3 45 0 6.5-9.2 34 4 67.5 0 4.8-8 50 5 90 0 3.58-6.7 60.7 6 112.5 0 3.78.8 81.6 7 135 0 3.54-9.5 91.4 f1, f2lower and upper cut off frequency table iii. proposed and other loop antennas comparison sr. no. %bandwidth reference year 1 88.6 [7] 2016 2 67 [11] 2015 3 40.7 [12] 2012 4 70 [4] 2010 5 48.8 [2] 2005 6 91.4 proposed ------ table iv. proposed loop and earlier loop comparison property size % bandwidth feed locations radiation pattern proposed loop smaller 91.4 infinite stationary earlier loop larger 88.6 three not available v. measurements and discussion figure 9 shows a photograph of the proposed antenna. the proposed nonuniform loop is excited with a sma connector directly. figure 10 shows the measured and simulated reflection coefficient for the loop with cps line feed at 135 0 . the measured result is in good agreement with the simulated one and ensures 91.4% bandwidth. the outer dimension of the loop is 24mm i.e. the antenna diameter is 48mm. the significant observation is that the loop antenna with outer dimension of 24mm and thickness factor of 12.76 resonates at around 1.9ghz. it resonates at about 6ghz when thickness factor changes to 7.26 as discussed earlier. the proposed loop is a combination of thin and thick loop with resonant frequency falling between 1.9ghz and 6ghz. the lowest cutoff frequency of the proposed loop is nearly 3.54ghz for which the antenna dimension should be smaller than 48mm. therefore this technique can be useful for designing very high frequency antennas such as ka band and higher where the dimension of the antenna becomes too small and a special lab is required for the manufacturing of the antenna. vi. conclusions the proposed nonuniform loop antenna has the unique property of having infinite possibilities to feed the antenna. the antenna offers different electrical properties for different feed locations. this property is not available in the conventional structure of loop antenna. (a) (b) (c) (d) (e) fig. 8. radiation pattern of the nonuniform loop at different frequencies. engineering, technology & applied science research vol. 8, no. 5, 2018, 3496-3501 3501 www.etasr.com shastri et al.: nonuniform c-band loop antenna the proposed structure with the cps feed line can be excited with a coaxial sma connector. the combination of thin and thick loop offers a wide bandwidth of 91.4%. the proposed dimension of the loop is expected to cover the lowest frequency of 2ghz but the lowest frequency obtained is 3.54ghz. this leads to an increase in the antenna dimension. fig. 9. photograph of the proposed nonuniform loop antenna. fig. 10. the measured and the simulated reflection coefficient of the nonuniform loop antenna. this approach can be used to design an antenna for ka band applications or higher than ka band where the antenna size becomes so small that a special lab is required to manufacture it. if this technique is used to design antennas at such a high frequency, the dimension of the loop will be sufficiently larger and simple pcb design technique can be used to manufacture the antenna at low cost. the proposed antenna shows wider % bandwidth than any other printed wideband loop antenna. the simulated and measured bandwidth of the loop is 91.4% with unidirectional radiation pattern oriented opposite to the feed. since the pattern is available in the opposite side of the feed, the proposed antenna can have multiple feed points and pattern reconfigurability can be achieved. references [1] t. k. roshna, u. deepak, p. mohanan, “a coplanar stripline fed compact uwb antenna”, procedia computer sciences, vol. 46, pp. 1365-1370, 2015 [2] k. y. yazdandoost, r. kohno, “design and analysis of an antenna for ultra-wideband system”, 14th ist mobile and wireless communication summit, dresden, germany, june 19-23, 2005 [3] t. a. denidni, h. lee, y. lim, “wide-band high-efficiency printed loop antenna design for wireless communication systems”, ieee transactions on vehicular technology, vol. 54, no. 3, pp. 873-878, 2005 [4] f. m. tanyer-tigrek, i. e. lager, l. p. ligthart, “a cpw-fed printed loop antenna for ultra-wideband applications and its linear-array performance”, ieee antennas and propagation magazine, vol. 52, no. 4, pp. 31-40, 2010 [5] r. l. li, g. dejean, j. laskar, m. m. tentzeris, “investigation of circularly polarized loop antennas with a parasitic element for bandwidth enhancement”, ieee transactions on antennas and propagation, vol. 53, no. 12, pp. 3930-3939, 2005 [6] q. balzano, k. siwiak, “the near field of annular antennas”, ieee transactions on vehicular technology, vol. 36, no.4, pp. 173-183, 1987 [7] r. r. singh, s. p. diwakar, s. shastri, “design of circular loop antenna with step change in loop width”, 2016 international conference on signal processing, communication, power and embedded system, paralakhemundi, india, october 3-5, 2016 [8] r. l. li, v. f. fusco, h. nakano, “circular polarized open-loop antenna”, ieee transactions on antennas and propagation, vol. 51, no. 9, pp. 2475-2477, 2003 [9] c. a. balanis, “small circular loop: loop antennas”, in: antenna theory: analysis and design, john wiley & sons, 2010 [10] k. wei, z. zhang, z. feng, “design of a wideband horizontally polarized omnidirectional printed loop antenna”, ieee antennas and wireless propagation letters, vol. 11, pp. 49-52, 2012 [11] k. xu, f. liu, l. peng, w. s. zhao, l. ran, g. wang, “multimode and wideband printed loop antenna based on degraded split-ring resonators”, ieee access, vol. 5, pp. 15561-15570, 2017 [12] j. wu, z. zhao, z. nie, q. h. liu, “a broadband unidirectional antenna based on closely spaced loading method”, ieee transactions on antennas and propagation., vol. 61, no. 1, pp. 109-116, 2012 engineering, technology & applied science research vol. 9, no. 1, 2019, 3750-3756 3750 www.etasr.com danikas et al.: propagation of electrical trees under the influence of mechanical stresses … propagation of electrical trees under the influence of mechanical stresses: a short review m. g. danikas department of electrical & computer engineering, democritus university of thrace, power systems laboratory, xanthi, greece mdanikas@ee.duth.gr d. papadopoulos department of electrical & computer engineering, democritus university of thrace, power systems laboratory, xanthi, greece dimopapa3@ee.duth.gr sayidul morsalin university of new south wales, school of electrical engineering and telecommunications, sydney, australia sayidul.moralin@unsw.edu.au abstract—the present paper deals with the phenomenon of electrical treeing in solid insulation, under the influence of mechanical stresses. in this short review, it is indicated that mechanical stressing can affect the propagation of electrical trees and –depending on whether it is tensile or compressiveit can facilitate (or render more difficult) the breakdown. in aged insulating materials, electrical trees can appear very quickly and can lead to breakdown. keywords-electrical trees; mechanical stresses; solid insulation; internal mechanical stresses; external mechanical stresses; partial discharges i. introduction electrical trees can come about from diverging electrical fields, as suggested in [1]. they usually have a distinct dendritic form, but –depending on the experimental conditions– can also acquire a bushy form. they develop from points of electric stress concentration. the latter can be either a sharp electrode edge, a sharp foreign conducting inclusion or a point where discharges in a weaker medium impinge on the dielectric surface [1]. electrical trees may appear, among others, in extruded cables, since these are intimately related to partial discharges [2]. in most breakdowns the ultimate failure is preceded by treeing, the time interval between the beginning of a tree and the final failure may vary from microseconds to months [3]. gaseous decomposition products may be formed during electrical tree formation [4]. it has been reported that a critical electric field is vital for the formation of a tree from a void [5]. the role of space charges in the formation of trees was discussed in [6], where the existence of a possible link between the concentration of space charges in the crystallineamorphous interfacial regions and the subsequent formation and propagation of tree channels was suggested. however, apart from the purely electrical stresses, high voltage insulation has to also be confronted with mechanical stresses. as reported in [7], a repeated maxwell stress (εe2 /2, with ε the relative permittivity of the material and e the applied electric field) is induced around a needle point by the applied ac voltage. a compressive force is subsequently applied to the insulating material. a mechanical stress perpendicular to the electric field direction appears causing crazing when a critical value is reached. crazing may develop to a void crack and gas discharges will expand the tree channel even further. earlier work has also pointed out that repeated maxwell stresses result into the time to initiate trees decreases with increasing frequency [8]. it is in the context of applied mechanical stresses that the present paper will try to give a short review of the propagation of electrical trees. in the context of the present review no mention will be made of water trees, which are altogether another significant factor affecting the lifetime of electrical insulations. ii. electrical trees and their nature electrical trees are a sign of insulation degradation. they consist of narrow hollow channels which are branched and have the general appearance of a botanical tree. such a network of gas-filled channels emanates from already existing cavities or contaminants. partial discharges may be responsible for such phenomena. if the degradation is complete, electrical trees go through the insulation and short-circuit it [9]. ionization causes chemical reactions and allows for the breaking of chemical bonds of the polymers. electrical trees ensue [10]. electrical trees may acquire the form of either a specific dendritic type or a bushy form [11]. it was noted quite early that, in case of ac voltage rising at a constant rate, the maximum length of a tree channel is related quantitatively to the maximum charge pulses which accompany the development of the tree channel and that the total length of the tree channel is also related quantitatively to the power of discharges obtained with the distribution characteristics of current pulses [12]. it is evident that partial discharges and electrical treeing are intimately related. an electrical tree may develop in three stages: first there is the period of initiation, then the period of development and after that the period of the widening of the already existing tree channels. in general, a certain amount of time is required in order for all three phases to fully develop. electrical trees are caused because of the electrical and/or the electromechanical deterioration of an insulating material, which may exist in regions of high local electric field. partial discharges affect the propagation of electrical trees, on the other hand the structure corresponding author: m. g. danikas of dis ele oth the cha the par of cha ob dis of ho neg fro vo bec pre wi nee pro pro po fav cha sim ele de and see cha fig plan engineerin www.etasr an electrical scharges, whi ectrical trees an hers, on the fr e geometry aracteristics o e humidity [13 as was repor rtial discharge the needle e annel through served tree le stribution of th the electrica mocharge is d gative charge om the needle ltage to the p comes very h eviously may ll be the cons edle tip and, ocesses. the ocesses will lymer. low vorable condit annels to form milar to that p ectrical tree o emocritus uni d with a point en that beside annel of break g. 1. typical e ne arrangement. ng, technology r.com l tree may w ch will furth nd the partial requency and of the ele of the insulatin 3, 14]. rted earlier, tre es in the tree. electrode is tr h the conductiv ength can be t he space charg al tree, it has developed arou carriers tend e tip during th positive half-c high since the enhance the f equences: (1) (2) it enhan energy relea eventually br density chan tions for subse m trees [16]. proposed in [1 obtained in o iversity of thr t-plane electro s the various kdown is also n electrical tree cha y & applied sci well define t er develop. t discharge acti the level of t ectrodes, the ng material, th ee propagation in this case, th ransferred to ve plasma of taken as a me ge [15]. regard s been report und the needle to move away he negative h cycle, the fiel negative spac field towards t it causes hole nces the vari ased from th reak the chem nnels will b equent impact in many resp 17, 18]. figure our high-volt race with a sa ode arrangeme electrical tree noticed. annels in a plexigl ience research danikas et al.: the type of p the propagati vity depend, a the applied vo physico-che he temperatur n can be induc he electric pot the tip of th gas discharge easure of the s ding the mech ed that a ne e tip and the m y as far as po half-cycle. wit ld at the need ce charge pro the needle tip e injection fro ious recombin hese recombin mical bonds o be created an t ionization in pects this theo e 1 shows a ty tage installatio ample of plex ent. it can be c e channels, the lass sample with a h v propagation of partial ion of among oltage, emical re and ced by tential e tree e. the spatial hanism gative mobile ossible th the dle tip oduced . two om the nation nation of the nd so n these ory is ypical on of xiglass clearly e final a pointstre redu frac stre cur num are craz orig mat inte mec earl the due that wer to vol tree ind perp a hi hig of p craz acti elec ion from mic mic are poly beh dev inte redu poly pro may insu mic pro elec low sho that disc mic con stre eve tree acti of vol. 9, no. 1, 20 of electrical tre iii. elect a polymer m ess in imposed duced and the cture is also ength of the m rve s-n (where mber of applie observed in zing because ginate from in terials or may erest of scien chanical stres ly [20]. it has decrease of d e to electrome t both the dc re increased by correlate with tage [21]. on e growth obs dicates the fo rpendicular to t enclosed mic int of a locally h applied elec partial dischar zing in the m ivity. such a ctrical trees. ization of the m electromec crocavities an crocavities, cra in contact w ymer [23-26] havior of el velopment of ernal stresses duction of the t ymer has as opagation of e y be introdu ulation, resul crocavities or obable. in such ctrical trees m wer than the yi ort term ac br t in [28] it was charges can crocavities, thu nditions, even esses will pull entually grow eing as a mec ion of local st the propaga 019, 3750-3756 ees under the in trical trees may breakdown d for longer pe material suff accelerated f material to alte e s is the appli ed cycles) [19] insulating m of the mechan nternal defect y be the resu ntists and eng ses on dielect been reported dielectric streng echanical fail c and impulse y compression h the percent the other han erved with m ormation of the direction o crocavities in t y deformed reg ctric field such rges. alternati material may repeated part electrical tr e polymer mo chanical stress nd from loc acks or crazes with a metallic . internal mec lectrical tree electrical tre are of tensil tensile strength a result the re electrical treei uced during lting thus in r rendering th h cases, partial may ensue. it i ield stress of a reakdown stren s reported that be initiate us causing ele n with low a l water into cr to water trees chanical dama tresses of elec ation of wat 6 nfluence of me and mechan n under static eriods, its mec fers from britt from an alter ernating stress ied stress mag ]. around 15% materials in s nical stresses. ts during the ult of external gineers about tric breakdow d that there we gth in elevated lure. other re e dielectric stre n [21]. mechan tage reduction nd, the change mechanically s an electricall of the applied t the insulating gion of the pol h microcavities ively, some pr accelerate a tial discharge rees may res olecules, from ses causing th cal thermal d s are far more c surface rath chanical stress es. they ma ees, depending le or of comp h and in fractu eduction of it ing [27]. hig the manufact n either ope he creation o l discharges m is worth notin a cable insulat ngth [28]. it sh t in case of dry ed in mec ectrical trees, applied ac razing zones, s (an interpret aging of the p ctrical origin a ter trees in 3751 echanical stress nical stresse stresses. whe chanical streng tle fracture. b rnating stress. ses is given fr gnitude and n % of all failure service are du such stresses preparation o l factors [19]. t the influenc wn was arisen ere indications d temperatures esearchers rep ength of polyt nical stress ap n in tree initi in the directi strained speci ly weak dire tensile stress [ polymer may lymer. under s may be the so re-existing cra a partial disch activity resul sult from ele thermal elect he developme degradation. e dangerous if her than insid ses may affec ay influence g on whethe pressive natur ure toughness o ts resistance t gh internal str turing of a ening up exi of new ones may be initiated ng that even st tion will reduc hould also be n y conditions p hanically fo whereas unde voltages max which in turn tation of the w polymer due t and the explan terms of p ses … es en the gth is brittle the rom a is the s that ue to s may of the . the ce of quite s that s was ported thene ppears iation on of imens ection [22]. y give some ource ack or harge lts in ectron trons, ent of such f they de the ct the the r the re. a of the to the resses cable isting more d and trains ce the noted partial ormed er wet xwell n may water to the nation plastic engineering, technology & applied science research vol. 9, no. 1, 2019, 3750-3756 3752 www.etasr.com danikas et al.: propagation of electrical trees under the influence of mechanical stresses … deformations of the amorphous interand intra-spherulitic spaces is given in [29]. however, it is beyond the scope of the present paper to also tackle the subject of water trees). a good overall picture of the development of electrical trees under dry conditions, albeit not under mechanical stresses, is given in [30]. references [27, 28, 30] conform with the data presented in [31], where externally applied tensile stress has as a result the deformation of xlpe samples and the formation of more ionizable species than in undeformed samples. consequently, mechanical deformation results in more space charges. the reason behind this is that whereas under normal circumstances cross-linking byproducts are locked in molecular chains of xlpe, with the tensile stress applied, molecular chains start to move. such movement may release the locked byproducts. in other words, the released byproducts form part of the ionizable species. the distinction between external mechanical stresses and internal mechanical stresses is also pointed out in [32], where it was discussed that either of them can influence the time required for inception and the extent of the growth of treeing process. the higher the mechanical stresses, shorter inception time and longer growth of electrical trees within a specified time were measured. earlier publications remarked that a plausible mechanism of failure in electrical machine insulation can be the inception of a microcrack, in which partial discharges or electrical tree mechanisms may become operative during the final stages of breakdown [33]. it has to be noted that in [33] only external mechanical stresses were taken into account. internal mechanical stresses from manufacturing as a cause of easier creation of electrical trees and consequently of reduction of breakdown strength in cable insulation was discussed in [34]. the importance of internal mechanical stresses in locally causing electrical field intensifications and subsequently electrical degradation mechanisms in mv cables was also discussed in [34]. another approach was adopted by some researchers, considering that tree initiation arises from the generation of small cracks (by fatigue failure due to cyclical electrostatic forces induced by the applied voltage) and tree propagation as the result of shock waves generated by microscopic explosions within the insulating material due to localized intrinsic breakdown on the crack surfaces [35-37]. in yet another publication [38], the authors considered a system of a propagating electrical tree and the regions surrounding the tree tips. such regions were defined as ‘damage process zones’ and they were considered as zones of irreversible damage (caused by electromechanical, thermal and chemical processes). such ‘damage process zones’ can coalesce to larger zones, i.e. to larger microcavities. the latter in turn can form a new tree channel. such an approach is reminiscent of the approach put forward several years ago in [39], in which the authors proposed a cumulative model for breakdown. in that publication, low-energy charge carriers are able to extend the defects and increase their density so that clusters of interacting defects may form. these clusters may grow into macroscopic defects in the direction of the applied field, which in turn will form a single channel with high probability of continuous conduction between the electrodes. supporting theoretical evidence to [38] and [39] comes also from [40], where it was remarked that a major factor for crack development is the existence of mechanical stress together with electrically induced stress. tree growth can be hindered by compressive forces and encouraged by tensile forces. space charges may also influence the local electric field, as already pointed out in [31]. a developing crack generates a momentarily low pressure path along the fracture path and in the field direction. electrical discharges may ensue. an experimental validation of the above comes from a recent study on mica/epoxy machine insulation with the aid of micro computed tomography (μct), which allows for 3-d reconstruction of the test object [41]. it was clearly shown that defects may coalesce into larger ones. moreover, it showed that mechanical stresses may help the creation of breakdown paths. in another study, insulating materials such as crosslinked polyethylene (xlpe), polyvinyl chloride (pvc) and polyphenylene ether (ppe), were tested regarding their mechanical properties [42]. pvc and xlpe were ductile and exhibited more elongation prior to breaking, whereas ppe exhibited brittle behavior. the durability of xlpe under strain fatigue testing was the largest, followed by pvc and ppe. reference [42] did not present any data on electrical treeing but its data on mechanical experiments are useful in indicating which materials are deemed to be suitable for high voltage applications. detailed analysis of the residual internal stresses in cable insulation with the aid of the photoelastic method was offered in [43], where it was shown that the highest resistance to electrical trees was observed in regions of the insulation in which the material presented the best uniformity. however, [43] did not find any significant influence of the residual mechanical stresses induced by the extrusion process on the insulation properties such as breakdown strength, tree inception voltage and tree propagation time, a conclusion that is somehow difficult to reconcile with the previous statement. the importance of mechanical stresses –mainly for electrical machines– was discussed in [44], where it was pointed out that the mechanical stress can appear in the form of compression, tension, bending, vibration, and impact. such factors may lead to fissures in the bulk of the material or at interfaces with other materials in an insulation system, which in turn may encourage electrical trees and subsequently the breakdown. the importance of defects or of extended defects or crazes aligned on an injecting/extracting site on an electrode was stressed in [45]. aligned free volume defects may act as nucleation sites for bigger cracks under the appropriate conditions. electrical tree propagation rates are mainly influenced by mechanical factors, although experimental results are sometimes confusing [45]. electrical trees propagate preferentially in a plane perpendicular to the direction of the tensile stress. ideas expressed in [45] are reminiscent of [39] as well as of [17, 18], where both coalescing of microdefects and the mechanism of injection/extraction of charge carriers were mentioned. the question of mechanical stresses together with the thermal expansion coefficients of the materials was mentioned in [46]. mechanical stress, which may be influenced by the modulus and thermal expansion coefficients of different materials, may be further increased by electromechanically induced stresses. such events may in turn cause electrical trees and lead to the breakdown path. in [47], experimental work engineering, technology & applied science research vol. 9, no. 1, 2019, 3750-3756 3753 www.etasr.com danikas et al.: propagation of electrical trees under the influence of mechanical stresses … indicated that polyester resin samples suffer from electrical trees when they are mechanically stressed and that the tree growth resistance weakens. however, the authors of [47] are not very explicit about the sort of mechanical stress they applied. the significance of mechanical properties in translucent as well as in transparent types of silicone rubber is apparent in [48], bearing also in mind the different chemical curing reactions. although [48] was mainly orientated in studying the breakdown strength, it is also evident from some experimental data that electrical trees are affected by the mechanical properties. the complexities of electrical tree growth and the factors affecting it were analyzed in [49], where the authors, in examining mechanically pre-stressed fiber reinforced araldite 5052 epoxy resin samples, they explained the apparent retardation of the tree growth by the compressive residual stresses in the resin, which tend to increase tree branching and therefore retard tree growth. a comparison between syndiotactic polypropylene (s-pp) and xlpe indicated that both tree branching and partial discharge activity were less in the former than in the latter. this was contributed by the researchers also to the superior mechanical properties (yield stress, ultimate stress, elongation at break and elasticity modulus) of s-pp [50]. it was reported that, in case of a tree branch reaching the ground electrode, the channel surface may re-crystallize and rapidly regain the previous breakdown strength. the combined effect of discharge gas pressure and surface melting can possibly explain the development of several parallel tree branches to the ground electrode before breakdown. internal residual mechanical strain was studied in [51], where the way of manufacturing of transparent insulating materials –polymethyl methacrylate (pmma), polystyrene (ps) and polycarbonate (pc)– and its influence on electrical treeing propagation with divergent electric fields was investigated. it was reported that electrical treeing stems from micro-cracks in the vicinity of the needle electrode, and in fact from its lateral side and not from the needle tip. this implies that the residual mechanical strain –formed during the manufacturing process– plays an important role. the conclusions of [51] are in qualitative agreement with those of [43]. the conclusions of [51] were confirmed with polycarbonate samples in a later publication [52], where it was pointed out that the melt flow directions and the fringe patterns may influence the direction and propagation of electrical trees. an indirect evidence of the above is offered in [53], where an investigation of the electrical trees in outer and inner layers of different voltage rating xlpe cable insulation indicated that the growth rate of electrical trees in a 66 kv cable is much larger than that in the higher voltage rating cables. this was attributed to the size of spherulites, the extrusion process, the crystallization state, which in turn were depended on the production process, i.e. on the inner mechanical stresses that may come about. in line with the above is also [54], where it was indicated that when the limit of mechanical elastic breakdown is surpassed, electrical trees are initiated and propagate. in conjunction to [53, 54], the researchers of [55] investigated a double electrical tree structure in xlpe and they found that the residual mechanical stress, among other factors, influenced the growth of the electrical tree and caused the insulation material around the core of xlpe cable to degrade seriously. the authors of [55] attribute the initiation and propagation of electrical trees to the charge injection-extraction mechanism, first proposed in [17, 18]. in [56], authors investigating silicone rubber, a material suitable for cable joints and cable terminals, showed that under tensile stress, the electrical tree length, fractal dimension and accumulated damage become larger as the tensile rate increases, indicating thus the higher tensile rate accelerates the treeing process. with a higher compressive rate, the opposite is true, i.e. the compressive stress retards the electrical tree propagation. the authors attributed the aforementioned phenomena to the fact that under tensile stress, the attraction bond between the molecules is weakened, whereas with a compressive stress more attraction bonds are generated and the microcavities are suppressed and consequently the initiation of electrical trees is hindered. regarding the respective influences of the tensile and the compressive stresses on the initiation and propagation of electrical trees, the conclusions of [56] do not qualitatively differ from those of earlier publications [57]. the experimental data from [56, 57] confirmed earlier observations reported in [58]. electro-mechanical stresses may irreversibly deform insulation. such a deformation becomes partly irreversible when the electrostatic energy is equal to the cohesion energy of the polymer with the result of weak attraction bonds breaking and the possible formation of radicals. at such a point, removing the electric field will not bring back the stressed molecules in their original state [59]. mechanical stresses in machine insulation may lead to molecule fracture, new charge carriers and generation of polar species, which in turn may lead to a change of tanδ, creation of nanoand micro-cracks, partial discharges and eventual formation of electrical trees. needless to say that such stresses combined with electrical and thermal stresses cause the rapid breakdown of machine insulation [60]. iv. proposals for future research in this short review an effort was made to point out some of the aspects of electrical treeing and the influence of mechanical stresses upon it. most of the work done until now was performed with conventional insulating materials. given the great advances in the field of polymer nanocomposites [61-63], it would be interesting to see how the various mechanical stresses act upon these materials. some studies in a relevant direction have already been done [64]. moreover, it would be interesting to see how both conventional insulating materials and polymer nanocomposites react to mechanical stresses which are not static in nature. an even more exciting prospect can be the designing of experiments and proposal of models in which electrical, mechanical and thermal stresses act at once on insulating materials. regarding also what was mentioned in [28] about the possibility of lower strains than the yield stress to cause the short time ac breakdown strength, it would perhaps be worthwhile to investigate this in relation to research done years ago w.r.t. the possibility of having charging effects below inception, which in turn may shorten the lifetime of an insulation [65]. in [28], as well as in [26, 65-68], it is indicated that there may be some sort of damage even below either the yield stress or the so-called inception voltage. such ideas may have some repercussion in estimating the remaining lifetime of insulation, especially if this is subjected to both electrical and engineering, technology & applied science research vol. 9, no. 1, 2019, 3750-3756 3754 www.etasr.com danikas et al.: propagation of electrical trees under the influence of mechanical stresses … mechanical stresses. needless to note that such ideas may also have some effect on some of the known lifetime models in which a threshold level of voltage is assumed. in relation to that, it would be worthwhile to investigate the electrical trees under mechanical stresses with very low frequencies. since partial discharge activity is inexorably related to electrical treeing, it would be interesting to follow the detectability of partial discharge activity and electrical trees at low frequencies [69]. another possibility for further work may be the simulation of electrical trees under both the influence of electrical and mechanical stressing. until now there were numerous publications on the simulation of electrical trees in solid insulation [70-75] but not much work has been done on the simulation of trees under the influence of the above mentioned stresses. still another possibility for further research would be the investigation of the role of mica barriers in machine insulation under the influence of both electrical and mechanical stresses. until now a lot of work has been done regarding either the effect of mica barriers in delaying electrical trees [76] or the simulation of electrical trees within machine insulation [77]. the prospect of experimentally investigating electrical tree propagation in machine insulation under mechanical stresses seems to be equally challenging. v. conclusions in the present paper a short review on the propagation of electrical trees in connection of the mechanical stresses was given. mechanical stresses, either external or internal, may influence the growth of electrical trees. the technical literature tends to indicate that electrical tree development is very sensitive to mechanical stresses. the latter tend to affect in a crucial manner the inner workings of the insulating material, providing thus possible paths to breakdown. a clear distinction between tensile and compressive stresses is given in the technical literature, with the former rendering electrical tree propagation easier, whereas with the latter electrical trees propagate with more difficulty. references [1] r. cooper, “breakdown in solids”, in: electrical insulation, edited by a. bradwell, eds. peter 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4, pp. 662-668, 2014 microsoft word 05-3253_s_etasr_v10_n1_pp5117-5125 engineering, technology & applied science research vol. 10, no. 1, 2020, 5117-5125 5117 www.etasr.com said & touahmia: evaluation of allocated areas for parks and their attributes: hail city evaluation of allocated areas for parks and their attributes: hail city mohamed ahmed said architectural engineering department university of hail hail, saudi arabia mo.said@uoh.edu.sa mabrouk touahmia civil engineering department university of hail hail, saudi arabia m.touahmia@uoh.edu.sa abstract—accessibility to parks and open spaces plays an important role in the urban quality of life. public parks play a vital role that affects all members of society regardless of their social ranking. accessibility (visitation) to parks and recreational areas has increased significantly all over the world. this scenario to some extent is the same in hail city, where the area allocated for parks and open spaces is very small. parks in hail are still suffering from many planning and design aspects that discourage people from frequent visitations. this study, therefore, aims to address this phenomenon by examining the area allocated for parks and park attributes. the study’s data are collected from the relevant literature regarding parks and their attributes. an assessment tool is designed and utilized to evaluate parks in hail. google maps software was used to measure the areas of neighborhoods and parks in addition to park distribution. this study shows that the areas allocated for parks are far below who requirements, and park attributes do not fully meet all visitors’ requirements. keywordspark evaluation; park attributes; assessment tool i. introduction in line with the kingdom's vision 2030 lifestyle improvement program, the ministry of municipal and rural affairs launched the humanization of cities initiative, with the aims of improving the quality of life in cities, improving urban landscape, and applying universal access standards in municipal facilities and pedestrian walkways. considering this issue, parks and open spaces are considered very important to the daily life routine [1-3]. the benefits of being in parks and recreational activities have long been well known [4, 5]. providing suitable environment for people to interact with each other will be reflected in their behavior [6, 7]. in addition, providing places for people to sit, gather and talk may encourage them to visit parks more frequently and it can contribute to a sense of a strong bonding with the community [8-10]. it has been found that workers with workstation views that include green elements were more satisfied at work and had more patience, less frustration, increased enthusiasm for work, and fewer health problems [11, 12]. parks and green areas in hail city are contributing in improving many aspects of life such as socialization and leisure, health, economy, and education [1, 13, 14]. it has been noted that nearby parks are an important part of places with a high quality of life [15, 16]. gardens, parks, and trees in cities lead to satisfaction and a positive outlook [11]. on the other hand, outdoor activities can help alleviate symptoms of alzheimer, dementia, stress, and depression, and improve cognitive function in those recently diagnosed with breast cancer [17-20]. areas adjacent to naturalistic parks and open spaces are valued 8-20% higher. consumer ratings increase steadily in proportion to the presence of trees, as getting in contact with nature helps children to develop cognitive, emotional, and behavioral connections with their nearby social and biophysical environments. nature experiences are important for encouraging imagination and creativity, cognitive and intellectual development, and social relationships [21-24]. having quality landscaping and vegetation in and around the places where people work and study is a good investment. visual access and being within green space help restoring the mind’s ability to focus, which can improve job and school performance, and help alleviate mental stress and illness. a basic and important point is that a park should be designed and managed to meet user requirements [25, 26]. it should be accessible to all age groups and allow visitors to do their activities freely, without contradicting with others, allowing people to make interrelation between the place and the world as a whole. numerous reasons have been raised as constraints to people’s use of public parks, including unavailable mobility, isolation, lack of services, constrained emotions such as fear, responsibility such as a social norm [27]. authors in [15, 28] found that the pleasantness factor includes enough space for children to play, room for a young adult to socialize, and a variety of activities to engage in. the quality of trees, plants, and landscape, and the presence of facilities such as toilets and shelters in the park will encourage frequent visitations. greater attention should be given to the location of park spaces, providing that the location of these facilities supports environmental functions and serves a different age group of users rather than merely stem from uses of vacant land [29]. the location of these facilities should be formative rather than merely residual. the park has to be spatially distributed [30, 31]. the european environment agency (eea) recommends that people should have access to green space within 15min walking distance, which is roughly 900–1000m [32, 33]. people visit recreational areas if they are well equipped with facilities and amenities [34, 35]. authors in corresponding author: mohamed ahmed said engineering, technology & applied science research vol. 10, no. 1, 2020, 5117-5125 5118 www.etasr.com said & touahmia: evaluation of allocated areas for parks and their attributes: hail city [15] found that the attributes of neighborhood open spaces (nos) that were relevant to older people’s life’s satisfactions were pleasantness and distance. residential parks are places that are characterized by the following: (a) free and open regularly to everybody irrespective of their race or economic background, (b) contain landscape either natural or manmade and facilities meant to draw the attention of people, and (c) provide physical, mental, recreational, and social benefits. the residence park planning ratio generally depends on the local conditions of each city. each resident of the city must have a specific area of green space in his proximity. the ratios of the percentage of open areas to the residential areas of some countries are: england 26%, germany 37%, iraq 17.5%, and hungary 15%. the planning ratio for open areas in industrialized countries ranges between 2,100-4,200m 2 /1000 inhabitants. ii. methodology a. instrumentation of research study various instruments were used to run this study: • the formulation from the literature review of an assessment tool considering the social and environmental issues of hail city with the help of planning standards for recreational areas of cities in saudi arabia. nine main items with numerous sub-items were formulated. these are surrounding environment and accessibility, quietness, internal environment, water features, services and facilities, health issues, security and safety, and aesthetics as shown in table i. table i. park attributes park attributes weight evaluation surrounding & accessibility 13% quietness 2% internal environment 10% water features 8% services and facilities 40% health issues 8% security and safety 11% aesthetics 8% total 100% • a calculation of parks’ areas and their geographical distribution throughout hail city. • the evaluation through surveying observations: this instrument was used to collect park relevant data such as attributes and number of visitors. • the method of descriptive analytical analysis was used. after piloting and improving the assessment tool, the targeted parks were visited and assessed. the percentage of the study factors calculation is shown in the appendix. there is a table including all factors, for example in factor (a) surrounding environment and accessibility, the number of visitors is categorized into five groups: the highest number is given 5 points and the lowest number is given 1 point. all sub factors are added together and divided by 118 (the total points of all factors) and multiplied by 100. at the end, every park was evaluated separately and took a score out of 118 points. at first all open spaces areas were added up together to obtain the percentage of areas allocated as parks and open spaces to the total residential areas to detect the shortage of open spaces and parks. secondly only fee free parks with areas of about 15 hectares and above were considered. b. the case of hail the city area is estimated at about 64855.82 hectares with a density of 4.3 persons/hectare. hail city includes many land uses: residential areas 30%, recreational areas and parks 3.39%, service areas 23.5%, reserve suitable for development 27.35%, military 16.15%, terrain and graveyards 0.61% (source: consultant, regional plan for the hail project 1425h). in the city center, which is the most heavily populated area of hail, the amount of green land is limited compared to most of the other parts of the city which don’t follow the planning and standards for recreational areas in saudi arabia (table ii). this can be seen in an nugrah neighborhood which is a new residential area, lacking parks and open spaces. in addition, in the central, northern and westerns parts, which contain a considerable proportion of the population, the amount of green area is remarkably less per inhabitant, compared to the eastern parts of the city as shown in figure 1. hail city center is composed of the 43 neighborhoods mentioned in table iii. some neighborhoods were not considered because they are new and not yet fully occupied by houses. only 14 (32%) out of 43 neighborhoods have access to parks or playgrounds. most of these parks and playground don’t meet the minimum park requirements, while they constitute only 0.13% of the total residential area, which is far below who requirements. because of population increment in hail (table iv), there is a high need for studying and planning parks in hail city. fig. 1. parks distribution throughout hail city iii. hail parks considering the guidebook of planning standards for recreational areas of cities, it can be seen that the classification of parks and open spaces in hail city doesn’t follow the requirements. engineering, technology & applied science research vol. 10, no. 1, 2020, 5117-5125 5119 www.etasr.com said & touahmia: evaluation of allocated areas for parks and their attributes: hail city table ii. hail neighborhoods, parks and playgrounds no. name area x (m 2 ) no. of parks park area y (m 2 ) y/x ratio remarks 1 az zahra 26300000 2 21891+49,686 0.08% 2 al khuzama 6000000 1 123000 2.05% 3 an nafl 1110000000 0 0 0 4 alyasmeen 3090000 1 123000 3.98 common park with alkhuzama 5 as suwayfilah 13510000 0 0 0 6 as suwayfilah 542000 0 0 0 7 almumlakah 750000 0 0 0 8 aja 4200000 1 6,522 0.15 9 al masyaf 11060000 0 0 0 10 durat mishar 549000 0 0 0 11 al muntazah al gharbi 5420000 5 290000+200000+90000+33391+10,052 11.60% 12 al muntazah ashargi 5610000 3 19391+12048+14522 0.80% 13 al aziziyah 2010000 0 0 0 14 al-wurud 984438 1 160000 16.25% 15 salah al-din al gharbi 987236 0 0 0 16 salah al-din al-shargi 542462 0 0 0 17 sababah 2080000 1 45000 2.16% one garden at the edge 18 al wusayta 5060000 1 6000 11.8 a playing field, many vacant places 19 al mahattah 2010000 0 0 0 20 samah 568213 2 3721+8353 2.12% 21 labdah 1070000 0 0 0 22 barzan 405104 0 0 0 23 al muzaabar 1940000 0 0 0 24 azzubarah 2920000 2 61000+9577 2.41% off center 25 aljamaien 2250000 1 12335 054 26 almatar 2050000 2 20279+19280 1.90% 27 as samrah 4660000 3 45794+108000+5511 2.43% 28 attilivizion 863966 0 0 0 29 sharg almujamaa 1230000 0 0 0 30 industrial area 11740000 0 0 0 31 an nugrah 10370000 0 0 0 32 ashifa 6460000 0 0 0 33 ashifa sharg 2270000 0 0 0 34 ashibaily sharg 902644 0 0 0 35 ashibaily garib 1400000 0 0 0 36 alwadi 7670000 0 0 0 37 hr rasf 3940000 0 0 0 38 gifar 7680000 0 0 0 39 al magaydah 1100000 0 0 0 40 al-badiah 2180000 0 0 0 41 al khummashiah 1010000 0 0 0 42 al buhirah 2030000 2 165000+91000 12.60% 43 alwidai 0 0 0 0 total 1277415063 1,748,093 = 0.136% source: field survey table iii. planning and standards for recreational areas in saudi arabia land area (hectares) population (thousands) means of transportation high density low density high density low density walking by car minutes km community / cluster garden 0.08 0.3 1.2 0.9 yes 5 0.1-0.2 playground 0.09 0.6 0.9 0.2 yes 5 0.15-0.275 neighborhood garden 0.4 0.5 5 3 yes 5-7 0.2-0.35 neighborhood playground 0.3 0.6 5 3 yes 5-7 0.25-0.5 district garden 0.5 1 15 10 yes yes 5-7 0.4-0.8 district playground 1.5 3.5 15 10 yes yes 5-10 1 sector garden 2 6 45 30 yes 15-20 2.5-5 city garden variable 7 100 and above yes variable recreational centers variable 0.2 the city yes yes variable camping variable the city yes variable specialist gardens variable the city yes variable parks variable the city yes variable source: directory of planning standards for recreational areas of cities, ministry of municipal and rural affairs, riyadh saudi arabia engineering, technology & applied science research vol. 10, no. 1, 2020, 5117-5125 5120 www.etasr.com said & touahmia: evaluation of allocated areas for parks and their attributes: hail city table iv. hail city population year 1992 2004 2010 2013 2015 2016 2017 2018 2019 ann. g. r. hail 411,284 526,882 597,144 654,700 907,494 928791 954797 981531 1009013 2.8 projection using the 2016 demographic survey from the general authority of statistics, riyadh, saudi arabia iv. hail parks a. prince saud bin abdul mohsin park this park is one of hail's largest parks, with an area of 290,000m 2 . it is one of the most beautiful parks to be visited in the entire country (figure 2). it has a 2200m long walkway, and is suitable for sports, hiking, and walking. palm trees are spread along the park for a distance of 300m, in addition to a variety of small and large waterfalls. it also has a distinctive lake where tables, chairs, and umbrellas spread throughout the area. some cafes and restaurants provide comfort services to the park's visitors. the downsides of this park are that the percentage of the green surface is less than 60%, there is no playing field for adults, the green area is either overused or not well maintained, and there is a lack of fences to protect children from the highway located beside it. moreover, the shaded areas are very limited, and the toilets are dirty and lack clean running water. additionally, the only available seats are located on the walking track, with no seats at children playground to facilitate monitoring, and the same situation occurs at the sitting area under shade. most of the playgrounds floor finish is sand which may harm children. fig. 2. prince saud bin abdul mohsin park b. az zaitoon (olive) park az zaitoon (olive) park is located on the king abdul aziz road in the west park occupying an area of 200,000m 2 (figure 3). fig. 3. az zaitoon park it is one of the most beautiful parks in hail, filled with olive trees, hence its name. one of the most important features of this park is its location in the center of hail, right on the intersection of king abdul aziz and king fahad roads. it is located besides restaurants and malls, which gives it merits over other parks. one of the problems that this park faces as a result of its location is air and noise pollution. moreover, the percentage of green surface in the park is low (less than 60%) while it is unmaintained. the park does not include an adult playing field or benches, in addition to the low condition of the sitting areas. the playground is old and filled with sand finishes that expose children to danger. the toilets are limited, not maintained, and dirty. the walking track is in poor condition and the amount of light coming in is not enough nor well distributed. no workers are available to clean and take care of the park, or provide security. the garbage containers are neither enough nor distributed equally around the park. the park has a fence which doesn’t surround all its area leaving some places without a fence. c. as salam park this park has an excellent location and an outstanding landscape with an area of 90,000m 2 (figure 4). it overlooks the foot of a mountain, giving it an extraordinary view and good airflow. the desert area is filled with mountains that contain green spaces and trees to make the landscape look like an attractive painting. fig. 4. al salam park the park is located at king fahad road and is a favorite destination for families because it has large areas for jogging, playing, etc. the park is also used for many official and local celebrations and festivals because of its accessible location and large size. the problem with this park is that the percentage of the green surface is less than 50%, and its quality is low due to overuse and improper care. moreover, there is no fencing to protect children from the highway beside the park. the shaded areas are very limited and they don't block enough sunlight for an easy afternoon out, the toilets are not clean and lack water, and there are no benches to sit on either for gathering or to monitor children. this park also has no adults’ playing fields, although it has a nice waterfall which softens the air and encourages frequent visitation. d. azzubarah park this park is located in the northern center of az zibarah neighborhood bordered by al-imam faisal bin turki in south side, hassan ibn thabit in north side, and al-amir migren bin abdulaziz from east and west sides. its location makes it engineering, technology & applied science research vol. 10, no. 1, 2020, 5117-5125 5121 www.etasr.com said & touahmia: evaluation of allocated areas for parks and their attributes: hail city difficult to access. the park stretches over a total area of 9,577m 2 , and the lack of car parking discourages visitation. as a result of its location, the park is noisy and polluted. it is totally abandoned, lacking water bodies or fountains, there is no kiosk, or sitting areas, although there are many big trees forming shaded areas. it has no adults’ playing fields, the finishing of the walkway is acceptable with no signboards, while no workers or security guards have been seen by the authors. lighting is available but not enough. the park has no fence to hinder children from going out or to stop cars from entering. the playgrounds are old and have no protection for children. nothing related to aesthetics has been seen in the park. overall, the parks’ elements are good compared with other parks (figure 5). fig. 5. azzubarah park e. prince sultan’s park this park is located in the southeast of the city. it is bordered on the north by the al-khamachiah neighborhood and south by prince abdullah bin abdul aziz al-dari road and prince abdul aziz bin masjid airport road and west by prince muqrin bin abdul aziz street neighboring commercial center that makes it attractive to visitors. it is close to many famous landmarks of the city, and it is one of the most popular tourist attractions in hail. the park stretches over a total area of 165,00m 2 (figure 6). fig. 6. prince sultan’s park the park location besides the highway makes it unsafe, noisy and air polluted and its location adjacent to al khamachiah lake invites mosquitos to disturb the visitors, as well as scattered thorns. the park is easily accessible with enough parking for cars located inside and adjacent to the highway. regarding the services, the park has no water features or fountains, and limited toilets which lack water, and in most cases are very dirty with no maintenance. it also lacks shaded areas, green surfaces, and seats except those scattered alongside the walking tracks, while no adults’ playing field was observed. the walking track is good but with no signboard either for the park or the walking tracks. the lighting is very dim with many areas lacking light, there are no workers to maintain the services or even security to keep the park safe and protect it from vandalism. aesthetic values are available but neglected. f. al warood park al warood park is located in the western part of hail city, on the southern border of al warood neighborhood. the park stretches over a total area of 160,000m 2 and contains extensive green spaces and a recreational area for families and children (figure 7). its downsides are: the absence of shelters for visitors to stay under during day time except scattered trees with no benches to sit. also, there is no fencing to protect children from the road, and the outside parking is placed beside the main road which makes the situation worse. the lighting system is not distributed throughout the park leaving some places with without proper lighting. there are some places of aesthetic value in the park, like the lake inside or the castle which is working as a waterfall. fig. 7. al warood park g. alruwad park alruwad park is located on the southeast part of hail city alongside hatim attai street. it is one of the most popular and attracting parks in hail. the park stretches over a total area of 91,00m 2 (figure 8). it is bordered by al-khammiya neighborhood, prince abdullah bin abdul aziz al-dari road and prince abdul aziz bin masjid airport road. its location besides the highway makes it unsafe, noisy, air polluted and the al khamachiah lake brings out mosquitos and scattered thorns. the park is easily accessible with enough parking for cars. it is located outside the park and is adjacent to the highway. fig. 8. alruwad park regarding services, the park has no water features, fountains, while it has a limited number of toilets which lack water, are dirty and unmaintained. it also lacks shaded areas, the green surfaces are very limited and constitute less than the 25% of its area, while benches are not available except those engineering, technology & applied science research vol. 10, no. 1, 2020, 5117-5125 5122 www.etasr.com said & touahmia: evaluation of allocated areas for parks and their attributes: hail city scattered alongside the walking tracks. a fenced adults’ playing field is observed, along with a good walking track without signboards. the lighting is very dim with many areas lacking light, there is no workforce to maintain the park or even security. there is no sign of aesthetic values available. h. al yasmeen park al yasmeen park is located in the west part of al khuzama neighbourhood, adjacent to king abdulaziz road which makes the park unsafe for children. the park stretches over a total area of 123,000m 2 , while it has green spaces, with a recreational area for families and a playground for children. the best a visitor can do is relax and get some rest in this place. it also has a walking track, which encourages people to walk and jog. the playground is in good condition as it is new, and the clean environment of the park is one of its merits encouraging frequent visitations. its problems are air and noise pollution as a result of its location besides the main road. there are no adult playing fields or seats except some benches located alongside the walking track. the green surface is almost the two-thirds of the whole area and doesn't contain weeds. there are shaded areas available but they are limited and do not have seats. lighting is not sufficient and not distributed properly, while it is also limited alongside the track. the park is vulnerable to vandalism. the arrangements of park and shaded area increase its aesthetic value. fig. 9. al yasmeen park v. results and discussion the amount of nearby green areas suitable for recreational usage increases the number of close-to-home outings of residents. this supports the argument that a good provision of opportunities promotes an active lifestyle. thus, recreation areas and facilities should be located close to residential areas, and provide safe, comfortable and year-round access for daily outings. referring to table ii, only 14 (32%) out of 43 neighborhoods in hail city, have an access to parks or playgrounds. besides this, most of these parks and playgrounds don’t meet the minimum park characteristics while they constitute only 0.136% of the total residential area. this percentage is far below who requirements (10m/person). some residential areas such as as suwayfilah, almumlakah, labdah an nugrah, ashifa, ashifa sharg, etc. have no access to open spaces and parks. however, in line with the kingdom's vision 2030 lifestyle improvement program, the ministry of municipal and rural affairs launched the humanization of cities initiative, with the aim of improving the quality of life in cities, improving the urban landscape and applying universal access standards in municipal facilities and pedestrian walkways. the ministry confirmed that the per capita rate of squares and public places rose from 3.48m 2 in 2015 to 4.14 m 2 in 2017. concentrating only on the number of open spaces provided, it is not enough, hence it is equally important to consider the quality of public open spaces and how they will be used, in order to maximize community value and its contribution to creating green spaces in the urban environment. accordingly, this part is going to highlight the quality of these facilities. regarding parks’ attributes and facilities shown in table v, azzaytoon park located in al muntazah al gharbi has got the highest mark (601 out of 800). its best observed attributes are the park quietness (100 points), its location with accessibilities is ranked second (93 points), and its aesthetic value is third (88points). the second highest park is alruwad park (549 points). the third ranked park is assalalm park in al muntazah al gharbi which got 533 point in all attributes. the park with the worst rank is alruwad park in al buhairah area which got 345 points. in this park there are not any water feature elements (0 points), the park is located in a noisy area (0 points). the second park from the bottom of the list is al yasmeen park in al khuzama area, which got 390 total points. from our observations, it can be said that almost all parks in hail city lack water features, their location is besides busy and noisy roads, and they lack security services to monitor undesired behavior. table v. results and discussion park name surroundings & accessibility (13%) quietness (2%) internal environment (10%) water features (8%) services and facilities (40%) health issues (8%) security and safety (11%) aesthetics (8%) total prince saud bin abdulmohsen park 86 0 66 77 67 77 46 66 419 azzaytoon park 93 100 83 44 87 66 40 88 601 assalam park 53 0 66 100 87 88 51 88 533 az zibarah park 73 100 81 0 50 55 34 33 426 prince sultan park 100 0 66 22 62 77 38 88 453 alruwad park 60 0 41 0 31 77 59 77 345 alwurud park 86 100 83 27 90 50 47 66 549 al yasmeen park 80 0 66 0 73 88 28 55 390 vi. conclusion easily accessible and high-quality recreation opportunities, which equally serve all population groups and inhabitants of different locations in the urban environment, are indicators of good living conditions and of quality of life. it is not easy to define whether an area is “adequate”, yet recreation specialists have come up with certain rough rules, which are often used. engineering, technology & applied science research vol. 10, no. 1, 2020, 5117-5125 5123 www.etasr.com said & touahmia: evaluation of allocated areas for parks and their attributes: hail city the amount of recreational area and parks allocated in hail is 0.136% from the total residential area, which is not adequate in addition to other issues regarding location, management, and usage. the parks throughout the residential area are not evenly distributed. hail’s parks are not easily accessible, most of hail’s parks are adjacent to a main road or a highway road and are thus exposed to noise and air pollution. water features are one important element of a park. lack of water features and green areas are traits of hail parks. the municipality did its part in creating parks but maintenance is also important. most of the green spaces are accessible to all people without any conditions or restrictions, but there is a decline in services in green spaces as a result of the users’ behavior and lack of follow up. toilets are commonly available but have many problems: their number is small, they are not clean and their positions sometimes do not serve. this is very clear in al yasmeen park which has only one toilet unit to serve a park which extends for over two kilometers. regarding security and safety, it was found that the majority of hail’s parks dot not have fences to protect children from hazards of accidences. it was also found that other services and facilities are not available. almost no parks have security forces to protect them from vandalism. car parking areas are located far from the parks making accessibility harder and reducing frequent visitations. also, there is a severe lack of private spaces. additionally, hail’s parks don’t have a place for elderly people of both sexes. vii. recommendations there are a few points needed to be enhanced to improve parks in hail. • in order to increase the percentage of recreational areas with respect to residential areas the number of parks and open spaces must increase. • it is necessary to have security people to protect parks from vandalism. • most of the parks lack trees and shaded areas. considering the nature in terms of using local materials, plants and trees should be used in shaping the area to become a part of nature, also helping in creating private spaces. • in the future, it is necessary to consider car parking with regard to the places where people practice their activities inside the parks. • it is necessary for parks to have a place for elderly people. when planning urban green areas and recreational services, more attention should be paid to the outdoor recreational needs of families, small children, and elderly people. • open space elements and furniture should be used in a way to form more private spaces for visitors to practice their activities with high privacy. • the municipality needs to take care of all parks’ attributes such as toilets and their distribution, especially when the park is in rectangle shape and the length is very long compared to the width. • workshops and seminars should be held to assist people to safeguard their parks while using them. acknowledgement the deanship of scientific research of the university of hail, saudi arabia funded this research under the research number 0160981 references [1] h. woolley, 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“residential development patterns and neighborhood satisfaction: impacts of density and nearby nature”, environment and behavior, vol. 38, no. 1, pp. 112-139, 2006 [9] j. kim, r. kaplan, “physical and psychological factors in sense of community: new urbanist kentlands and nearby orchard village”, environment and behavior, vol. 36, no. 3, pp. 313-340, 2004 [10] d. sinnett, n. smith, s. burgess, handbook on green infrastructure: planning, design and implementation, edward elgar publishing, 2015 [11] r. kaplan, “the role of nature in the context of the workplace”, landscape and urban planning, vol. 26, no. 1-4, pp. 193-201, 1993 [12] e. l. wight, w. w. chen, v. dodd, r. weiler, “healthy workplaces: the effects of nature contact at work on employee stress and health”, public health reports, vol. 126, no. 1, pp. 124-130, 2011 [13] e. o. smith, a. j. mowen, l. l. payne, g. godbey, “the interaction of stress and park use on psycho-physiological health in older adults”, journal of leisure 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appendix: assessment tool park name address area (m 2 ) a surrounding environment and accessibility total evaluation 1 park location visitors number 1-5 5 main road branch road 0 2 2 2 location of the main entrance main road branch road 0 2 2 3 car parks available rating 2 1,2,3, 5 4 location: neighboring to malls or supermarkets yes no 1 0 1 15 (13%) b surrounding environment and quietness 1 quite area noisy area 2 -1 2 2 (1%) c internal environment ( green area and its condition) 1 available not available percentage rating 2 0 1-5 1-5 12 12 (10%) d water features 1 water bodies, waterfalls available not available rating 1 0 1-3 4 2 fountains or springs available not available rating 1 0 1-3 4 3 drinking fountains available not available 1 0 1 9 (8) e services and facilities 1 toilets kiosks seats sitting areas shaded areas prayer areas 0-5 1 0-5 0-5 0-5 0-3 24 2 playground equipment for children and adults for children not available rating for adults not available rating 1 0 1-5 1 0 1-5 12 3 protected and shaded areas available not available rating 1 0 1-3 4 4 pedestrians available not available rating 1 0 1-3 4 5 signboards available not available rating engineering, technology & applied science research vol. 10, no. 1, 2020, 5117-5125 5125 www.etasr.com said & touahmia: evaluation of allocated areas for parks and their attributes: hail city 1 0 1,2 3 6 worker availability available not available 1 0 1 48 (40%) f health issues 1 air not polluted polluted 1 0 1 2 disturbing insects not available available 1 0 1 3 weeds not available available 1 0 1 4 cleanness not clean clean 0-3 3 5 garbage containers available not available enough not enough well distributed not well distributed 1 0 1 0 1 0 3 9 (8%) g safety and security 1 lighting: a handful to keep the park light and safe for those who stay late. automatically turns on and off by detecting the lightness in the environment or according to the government regulations. available not available rating 1 0 1-5 6 2 security guard: someone patrols the park daily 3 available not available 1 0 1 4 fencing available rating 0-3 1-3 6 5 hinders available not available 0 1 1 14 (12%) i aesthetics 1 monuments available not available 1 0 1 2 heritage features available not available 1 0 1 3 landmarks available not available 1 0 1 4 view from inside weight from outside weight 1-3 1-3 6 9 (8%) total 118 (100%) microsoft word 4-kambouz-ed.doc engineering, technology & applied science research vol. 4, no. 1, 2014, 581-586 581 www.etasr.com kambouz et al.: numerical analysis of crack progress in different areas of a friction stir welded bead… numerical analysis of crack progress in different areas of a friction stir welded bead for an 5251 h14 aluminum alloy specimen youb kambouz university of sidi bel-abbes materials and reactive systems laboratory y.kambouz@yahoo.fr mohamed benguediab university of sidi bel-abbes materials and reactive systems laboratory benguediab_m@yahoo.fr benattou bouchouicha university of sidi bel-abbes materials and reactive systems laboratory benattou_b@yahoo.fr abstract— the assemblies welded by friction stir welding have a major advantage which is the absence of a metal filler. this process contributes to the welding of materials that are known to be difficult to weld using the conventional techniques often employed in the field of transport, for example in the automobile body by applying a spot welding. the numerical modeling of this type of process is complex, not only in terms of the variety of physical phenomena which must be considered, but also because of the experimental procedure that must be followed in order to verify and validate numerical predictions. in this work, a finite element model is proposed in order to simulate the crack propagation under monotonic loading in different areas of the weld seam of a strain hardening ct-50 aluminum alloy 5251h14 specimen. keywordsfsw; micro hardness; 5251 h14 aluminum alloy; crack; stress intensity factor i. introduction considered as the most significant development in metal joining in the last decade, the friction stir welding (fsw) is a joining process with good energy efficiency that is also environmentally friendly and versatile. significant research has been conducted in various fields since the invention of this technique in 1991 [1]. generally, fsw specimens have higher resistance than specimens welded using the metal inert gas (mig) and tungsten inert gas (tig) processes [2–6]. ericson and sandstrom [2] compared fatigue results of friction stir welds with data obtained for conventional arc-welding methods, namely, mig-pulse and tig processes in aluminum alloy (t6 and t4 conditions). moreira et al. [3, 4] also compared the fatigue behaviour of joints performed by the traditional mig welding process and by the fsw process, observing that fsw and mig welded specimens had lower yield and ultimate stresses than the base material. in general, a higher lifetime for the friction stir welds in comparison with other welds was also observed [5]. it has also been observed that fsw leads to a decline of the mechanical properties of weld bead in comparison to the base metal [6]. furthermore, an important hardness decrease in the thermomechanically affected zone (tmaz) and the nugget zone average hardness was found. due to severely thermal and mechanical deformation in the weld zone during fsw, the weld zone generally possesses various microstructural features and various mechanical properties [78]. the crack propagation in the weld bead (fsw and classic) is known to be concerned by residual stress and/or hardness around the welded zone [9, 10]. cecile genevois [11] conducted hardness tests on micro-specimen. the limit of elasticity, tensile strength and young's modulus (e) of the aluminum alloy were measured using tensile tests on welded and non-welded specimens. modeling the tensile behavior of welded fsw for an aluminum alloy joint showed that the weak area is the tmaz [12]. welding parameters also affect the mechanical properties of the weld and its resistance is related to the speed of rotation of the welding tool [13, 14]. it is therefore advisable to choose the best parameters (speed, welding speed and good fixation of the parts) [15]. the overall objective of this work is to study using finite element (fe) analysis the effects of loading on crack propagation in different areas of fsw in the case of a 5251 aluminum alloy subjected to h14 treatment. in the numerical approach the stress intensity factor is determined by the finite element method using the abaqus software. ii. presentation of the material the material used is an aluminum alloy 5000 series subjected to h14 treatment (deformed 25%), which will help the investigation of the various phenomena that occur during welding without involving the precipitation phenomenon. a. mechanical properties of the material. the chemical and mechanical properties are given in tables i and ii. table i. chemical composition of the aluminum alloy 5251 si fe cu mn mg cr zn ti al 0.4 0.5 0.15 0.10 1.72. 0.15 0.15 0.15 remains engineering, technology & applied science research vol. 4, no. 1, 2014, 581-586 582 www.etasr.com kambouz et al.: numerical analysis of crack progress in different areas of a friction stir welded bead… table ii. mechanical properties of 5251 nuance metallurgic state rm [mpa] rp [mpa] a % e [mpa] hv 5251 [al-mg 2 ] h14 210 170 3-5 70000 82-84 b. hardness profile. the optimization of the weld process requires the mechanical characterization of the weld bead. the most commonly used practice is the measurement of microhardness which gives a first evaluation of the mechanical properties in different areas of the weld, in order to obtain a profile across it and to establish the weld zones. the cross-section thus provides a profile of microhardness [11]. pictures of the microstructure of the different areas of the 5251 h14 alloy aluminum can be found in [8]. iii. model used a. modeling of the cracked part the modeled weld is divided into several zones, as shown in figure 1, and a different mechanical behavior is assigned for each. the mechanical properties described in [11] are used. (a) (b) fig. 1. geometrical representation by abaqus of notched specimen « ct-50 ». a) representation of welding areas b) loading and fixing of the specimen in the model considered in this paper, the areas are fully supportive of each other, movement is continuous and normal stress is transmitted. this model allows the obtainment of a mapping of local deformations through a welded joint subjected to a uniaxial load p = 40 mpa (figure 1b). the part is considered as a ct-50 specimen, the cracking plane is considered normal to the loading axis and the crack front is considered straight. b. mesh of the cracked part the numerical analysis of the mechanical fields of a cracked part is strongly linked to the meshing quality of this part, particularly the vicinity of the crack tip. it is therefore important to manage the mesh to the crack tip (figure 2). fig. 2. mesh of the specimen iv. numerical results and discussions a. determination of the stress intensity factor on the crack front. crack propagation is a complex problem, depending on various factors such as the nature of the applied load, the level of residual stress, the geometry of the part etc. the kinetics of cracking along the crack front can be very diverse, leading to highly variable shapes of the crack front. as a result, the observation of crack propagation on the surface of the part is not enough to predict the propagation route. therefore it is important to predict the evolution of the crack front during the propagation. many authors use the following procedure to model the evolution of the crack front under monotonic loading or fatigue. at any edge, the stress intensity factor k is determined along the crack front. advanced δa is then attributed to the crack “a” to evaluate new values of k. this is repeated for different values of k in order to draw k curves on the length of the crack front for different areas of the weld (figure 3). it may be noted from figure 3 that for a given crack length a=15 mm, the minimal stress intensity factor (in the tmaz) is ki1=14.08 mpa.m 1 / 2. in the middle of the crack front (figure 4), against the surface (face of the crack) a ki2=11.88 mpa.m 1 / 2 is recorded. in the haz, in the middle of the crack front, ki1=17.60 mpa m 1/2 and at the surface ki2=13.75 mpa m 1/2. in the nugget ki1=19.15 mpa m 1 / 2 and ki2=17 mpa m 1 / 2. in the base metal, ki1=21.50 mpa m 1 / 2 and ki2=18.75 mpa.m 1 / 2. these curves (in different zones of the weld), also show that the evolution of the stress intensity factor is not straight along the crack front, but it tends to take a parabolic shape and that the minimum value of k is found at the surface (on the face of the crack) whereas the maximum is found at the heart (middle of the crack front). based on the values of the stress intensity factor k recorded in table ii it can be said that for the same advanced crack (a=15 mm), minimum and maximum values are recorded in the base metal then nugget, the haz and finally tmaz. engineering, technology & applied science research vol. 4, no. 1, 2014, 581-586 583 www.etasr.com kambouz et al.: numerical analysis of crack progress in different areas of a friction stir welded bead… (a) (b) (c) (d) fig. 3. variation of stress intensity factor k in a) bm, b) tmaz, c) haz, d) nugget. fig. 4. representation of the front and crack length “a” table iii. minimum and maximum values in the areas of fsw tmaz haz nugget b. metal kmin mpa m1/2 11.88 13.75 17.00 18.75 kmax mpa m1/2 14.08 17.60 19.15 21.50 b. determination of stress intensity factor according on the progress of crack. from the previous results the k=f(a) curves for each area of the weld are plotted as shown in figure 5. these curves represent the change of the stress intensity factor depending on the evolution of the cracks. ki1 is the stress intensity factor in the middle of the crack front (figure 6). ki2 is the stress intensity factor of the plane of the crack face (surface). table iv shows the evolution of the crack in different areas of the weld seam for the 5251 h14 alloy. as shown, the crack starts in the affected tmaz area that is equal to 2 mm for ki=6.75 mpa.m 1/2, then it continues to move forward without a declaration of crack in other areas until the value of ki=10 mpa.m1/2 . recording is equal to a crack in the haz 1.85 mm and 5.12 mm in the core against the tmaz 8.25 mm. the tmaz is the weakest area, and gradually as one approaches the nugget, the restoration and recrystallization are more advanced. therefore, the yield decreases sharply while the elongation increases [8]. recrystallization which is thin in the core enables an increase of the mechanical strength and the yield strength in this area compared to the tmaz. c. consequences of friction stir welding resistance to rupture in tmaz is equal to the yield strength of the base metal [8]. therefore when there is a rupture in the tmaz, the base metal is just beginning to deform plastically. these results are the consequences of fsw. d. analysis of the state of stresses and strains near the crack tip. a stress field and a strain field in the material adjacent to the border are associated to each movements of the crack surfaces. the calculations were made in abaqus by varying the crack length as a=2, 3,..., 15 mm, and in each case the fields of stresses and strains near the crack tip for different areas of the weld were determined. engineering, technology & applied science research vol. 4, no. 1, 2014, 581-586 584 www.etasr.com kambouz et al.: numerical analysis of crack progress in different areas of a friction stir welded bead… (a) (b) (c) (d) fig. 5. variation of stress intensity factor (max and min) depending on the progress of the crack in the different zones of the weld. (a) b.m. (b) tmaz (c) haz (d) nugget fig. 6. stress intensity factors k means according to the progress of the crack to the different zones of the weld bead. table iv. variation of the stress intensity factor according to the evolution of the crack a a (base metal) mm a(nugget) mm a(haz) mm a (tmaz) mm ki= 30mpa m 1/2 20 21.3 23 specimen failure ki=25 mpa m 1/2 16 18.5 21.5 specimen failure ki= 20mpa m 1/2 14 16.5 18 specimen failure ki= 15mpa m 1/2 9.9 11.5 13.75 19.50 ki=10 mpa m 1/2 no crack initiation 1.85 5.12 8.25 ki=7.5mpa m 1/2 no crack initiation no crack initiation no crack initiation 2.65 ki=6.75mpam 1/2 no crack initiation no crack initiation no crack initiation 2 fig. 7. distribution of stresses σyy and deformations εyy on the crack front (in tmaz) for a =15 mm engineering, technology & applied science research vol. 4, no. 1, 2014, 581-586 585 www.etasr.com kambouz et al.: numerical analysis of crack progress in different areas of a friction stir welded bead… fig. 8. distribution of stresses σyy and deformations εyy on the crack front (in the haz) for a = 15mm fig. 9. distribution of stresses σyy and deformations εyy on the crack front (in the nugget) for a=15 mm table v. maximum stresses and deformations along the crack front in different areas of the fsw. tmaz haz nugget bm stresses σyy (mpa) 4800 5287 6200 8200 deformations e22 (mm) 0.086 0.076 0.0485 0.0465 fig. 10. distribution of stresses σyy and deformations εyy on the crack front (in the base metal) for a=15 mm. figures 7-10 allow us to ensure that the maximum deformations along the crack front are the most important in the tmaz, haz then the nugget and finally the base metal. in the base metal which is harder than the tmaz (about 1.7 times), the maximum stress recorded are shown in table v. it should also be noted that the highest deformation is recorded in the tmaz, compared with other regions, although the yy stresses are low (should be attributed to the softer material of the tmaz). v. conclusion this article focuses on the study of the evolution of cracks in different areas of a friction stir welding under monotonic loading and of the variation of the stress intensity factor and of the distribution of stress and strain on the crack tip in the different zones of the weld bead. a preliminary study was done to show that the crack does not evolve in the same way in the middle of the crack front and on her face. the second part of this paper is devoted to the determination of the stress intensity factor as a function of the evolution of the crack. the last part shows the distribution of stress and strain on the crack tip in the different zones of the weld bead. modeling and simulation were performed using the abaqus software and results are depicted through various figures, and further discussed. references [1] w. m. thomas, e. d. nicholas, j. c. needham, m. g. murch, p. temple-smith p, c. j. dawes, “friction-stir butt weldin”, g.b. patent no. 9125978.8, international patent 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[12] m. mazari, “caractérisation mécanique des assemblages soudés par friction malaxage”, workshop: mécanique et matériaux de la microstructure à la structure: approches expérimentales & simulations numériques, mascara, 2010 [13] j. souto grela, e. b. blanco viana, d. martinez, e. piñeiro, “numerical simulation in welding process: optimizing structures with sequence and inertial study”, matériaux & techniques, vol. 100, pp. 317–326, 2012 [14] e. feulvarch, modélisation numérique du soudage par frictionmalaxage, thèse de doctorat de l’université de saint etienne, 2005 [15] m. merzoug, etude paramétrique du soudage par friction malaxage, thèse de doctorat, djillali liabes university of sidi bel abbes, 2011 microsoft word etasr_v11_n3_pp7069-7074 engineering, technology & applied science research vol. 11, no. 3, 2021, 7069-7074 7069 www.etasr.com masmali: implementation of lean manufacturing in a cement industry implementation of lean manufacturing in a cement industry majed masmali industrial engineering department college of engineering northern border university arar, saudi arabia majed.masmali@nbu.edu.sa abstractthe lean manufacturing concept is a systematic minimization of waste and non-value activities in production processes introduced by the toyota production system. in this research, lean manufacturing is implemented in a cement production line. value stream mapping (vsm) is applied to give a clear picture of the value chain in cement production processes and to highlight the non-value-added in the shop floor. to begin, the existing vsm is constructed based on the information and data gathered during visiting and observing the manufacturing process in the firm. as a result, the excess inventory between workstations was identified as a major waste generation, hence, the proposed vsm conducts further improvement and makes action plans to alleviate the unwanted activities. then, the takt time to ensure smooth material flow and to avoid any occurring delay or bottleneck in the production line was figured out. the supermarket pull-based production control is suggested to be adopted in the future map. two pull production strategies are selected in this case. the first is applying the kanban system to control the level of inventory between workstations. the other is the conwip approach to control the amount of work in process to the entire production line. the outcome of the proposed models indicates a decrease of the none-value time from 23 days in the current state to about 4 and 2 days in kanban and conwip systems respectively, so the conwip was suggested as most efficient. some suggestions for further research are also mentioned. keywords-cement industry; conwip; kanban; pull systems; value stream mapping; lean manufacturing i. introduction the cement industry is the most prominent building material industry, contributing greatly to the global and national economy and growth. since cement is a primary construction material, cement economics are closely related to the construction sector. the history of the cement industry goes back to 1824, when the portland cement was invented [1-3]. thereafter, the cement industry has developed and the volume of production has increased steadily. the raw materials include clay limestone transform into clinker. the clinker is transformed into cement by adding gypsum and other materials. the cement production process passes through numerous workstations including crushers, milling, rotary kiln, and milling finishing cements. between these manufacturing processes there are stocks and silos between workstations. the cement is made by mixing lime, clay, and iron materials in certain proportions to give the coated materials calcium, silica, corundum, and iron oxide. these raw materials are then grinded well to facilitate the burning process, which takes place at a temperature of 1500°c. this material after burning is called clinker. the lime materials for clinker make up about 90% of the cement mass, as gypsum material is added to it in proportions ranging from 3 to 5% to control the hardening and cohesion of the cement, which varies in terms of the added amount according to the type produced [1-6]. this series of activities from the suppliers to the customers is known as the value chain. the customer order is considered as the input of flow information, while the output is the order fulfillment. the aim of the value chain is to make the enterprise competitive [7, 8]. in order to ensure the sustainability of production and competitiveness with a view to improve the cement production line, production management principles should be implemented in this industry. the purpose of these strategies is to make decisions to develop and improve the shop floor operations in cement factories. one of these aspects is reducing the work in process, since the excess inventory could contribute to the holding cost. in addition, no value is added to the clinker and cement which are stored in the factory. therefore, the lean manufacturing concept is chosen in this research to be implemented in the production processes. it is a systematic minimization of non-value activities in the manufacturing systems [9, 10]. the lean manufacturing philosophy has been introduced in the toyota production system. the principle of this technique is to eliminate the waste that occurs in the production process. the waste in lean manufacturing comes from over production, waiting, transportation, over processing, movement, inventory, and defects [9-11]. liker [12] extended the definition by considering the non-utilized talents as a waste. when the lean manufacturing is implemented a sort of tools must be used to reduce and eliminate the added non-value, tools such as pull system, value stream map, heijunka, smed, total productive maintenance (tpm), poka-yoke 5’s, and kaizen [9-11]. lean manufacturing has been implemented to different manufacturing aspects. this part will focus on the studies corresponding author: majed masmali engineering, technology & applied science research vol. 11, no. 3, 2021, 7069-7074 7070 www.etasr.com masmali: implementation of lean manufacturing in a cement industry related to the cement industry. authors in [13] implemented the lean philosophy to improve the cement production line performance. maximum efficiency and minimum lead time and production cost can be achieved if the right training is provided to the employees and a motivation system is introduced to the workplace environment. authors in [14] developed an approach for the application of lean manufacturing in the cement industry. a numerical model was built to compare the current and future state vsm. the output of the proposed model outlined that there was an improvement in throughput and reduction in lead time. in addition, the kanban was applied to study the effects of the inventory in cement manufacturing. authors in [15] implemented tpm in the cement production line. authors in [16] applied vsm in order to explore the various non-value added activities in the supply chain of a cement factory. authors in [17] determined the essential points for implementing the management of just in time philosophy on the cement industry in pakistan. inventory management, production design, production plan, supply chain integration, and total quality control have been selected as factors in order to eliminate the waste of resources. authors in [18] demonstrated a numerical approach to study the cement manufacturing lines taking into account the supply chain management and its effect on just in time production. authors in [19] proposed a simulation model to study the supply chain management in cement industry. authors in [20] introduced a matrix for the waste relationship, a questionnaire of waste assessment, and a value stream analysis approach to eliminate the waste in cement production. in the previous study, the approach consists of four stages which are identification of waste, value stream analysis, fishbone diagram, and failure mode and effect analysis. the literature review shows significant contributions that should be further researched in terms of the application of lean production in the cement industry. in the current article, the vsm tool is applied in a cement production line. the main contribution of this article is the implementation of lean manufacturing in a cement factory in order to control and minimize the level of work in process. there is an opportunity to compare the outcomes of the proposed pull production systems which are kanban and conwip strategies among the push production system. ii. research methdology in this study, vsm is applied to implement lean manufacturing towards a cement production line. it is a significant lean tool that identifies the potential waste and forms a clear picture of the production process in order to build a road map of improving the production process. the four main steps of implementing vsm [11] are given in figure 1. fig. 1. value stream mapping process. production control customers supplier milling rotary kiln cement processing dispatchingcrushing 9 sec 4 days 10 sec n/a 12 sec 5 days 14 sec 9 days va =45 sec nva= 23 days5 days i weekly weekly i i i weekly weekly c/t = 10 sec uptime = 85% c/t = 9 sec uptime = 85% c/t = 12 sec uptime = 85% c/t = 14 sec uptime = 85% weekly weekly daily daily fig. 2. current value stream mapping. the research study is conducted at a cement factory. the design capacity of this plant is 6,000 tons per day, whereas the annual production is 1.98 million tons, based on 330 working days per year and taking into account the shutdown for engineering, technology & applied science research vol. 11, no. 3, 2021, 7069-7074 7071 www.etasr.com masmali: implementation of lean manufacturing in a cement industry maintenance. the current vsm is constructed according to the guidelines in [11]. the relevant data and information associated with the production processes, i.e. information flow, physical flow, and time line are gathered. information flow is related to the customer requests (from the sales department or from orders from the factory’s website) where the productionplanning can be conducted. the second element is material flow. data were taken during visiting the factory and observing the progress of operations and workflow in the shop floor, in order to understand the cement manufacturing industry processes. the cycle times are taken as the average cycle time from production department records. when it comes to the inventories, there are four stores between each workstation. the average time of materials stored in silos has been reported. the down time for each process has been assumed to be 15%. the third element is trend line. it consists of two time components. the first timeline is the non-value added time. it is also called the lead time or waiting time. it is the summation of the amount of each inventory. another timeline is value added time. it can be computed by the summation of cycle times for each workstation process. the current vsm is illustrated in figure 2. it can be seen that from the trend line, the non-value time is about 23 days, whereas the value time is approximately 45 seconds. iii. the proposed future value stream mapping based on the existing vsm outcomes, it is necessary for the proposed vsm model to eliminate the non-value added in the cement production line. first of all, the maximum time required to meet the customer demands should be identified in order to avoid any waste or delay of delivery. the takt time is computed as [11]: takt time �� ����� ���� �� � �� �������� ������ (1) the maximum demand required by customers for the cement production line is about 6000 tons per day. as the plant runs 24 hours a day, the available working time is 86,400 seconds. therefore, the takt time can be obtained as: takt time ��� ��!���� � ���� "�� ��# 14.4 seconds per ton this means that 1 ton of cement needs to be produced in 14.4 seconds. subsequently, the overall takt time is compared against cycle time for each workstation as shown in figure 3. in addition, the current production strategy for the factory follows the push production control shown in figure 4. each workstation pushes completed work to the next workstation. as a result, the inventory level between workstations is increased. in the proposed future map, pull production is applied to produce the right quantity of products at the right time. a common approach of pull based production process is the kanban. one of its benefits is the control of the level of inventory between workstations [21]. however, authors in [22-25] introduced another pull system, constant work in process (conwip), to control the production line. both the above pull approaches were implemented in the future state maps. fig. 3. cement production line balancing. a. kanban kanban is a lean tool associated with the pull production system and just in time production [7-9]. to demonstrate the use of the kanban pull system to control the excess inventory, the following assumptions are made: the cement production line is divided into four stages, as shown in figure 5. each phase consists of a process workstation which consists of the input buffer, processes, and the output buffer. the number of kanbans is computed [26] as (2): . /012 3 (2) where d is the average demand, l is the lead time, s is the safety stock, and c is the container size. to illustrate, the withdrawal kanban (wk) is transferred from the succeeding workstation to the preceding workstation and placed in the output buffer of the workstation and the production for the rotary kiln workstation respectively. for further details, the wk3 and pk3 are assigned as the numbers of withdrawal and production for the rotary kiln workstation respectively. the clinker container with withdrawl kanban (wk3) is moved from the cement processing station into the rotary kiln station and placed in the output of this workstation. the future state maps for the kanban approach is shown in figure 6. fig. 4. push production system. engineering, technology & applied science research vol. 11, no. 3, 2021, 7069-7074 7072 www.etasr.com masmali: implementation of lean manufacturing in a cement industry wk1 crushing station raw materials wk1 pk1 input buffer output buffer wk2 milling station wk2 pk2 input buffer wk2 output buffer rotary kiln station pk3 wk3 output buffer input buffer w k 3 cement processing station pk4 wk4 output buffer input buffer wk4 customers fig. 5. proposed kanban in the cement production line. production control customers supplier milling rotary kiln cement processing dispatchingcrushing 9 sec 1 day 10 sec n/a 12 sec 1 day 14 sec 1 day va = 45 sec nva=4 days1 day daily fig. 6. proposed vsm future state (kanban). fig. 7. the proposed conwip in the cement production line. b. conwip figure 7 shows the proposed mechanism of conwip in cement production line. the assumptions are made by identifying the maximum wip level in the cement production line, to ensure the level of inventory remains constant to the entire shop floor. the material flow directly enters the backlog. the backlog-sequencing rule in this proposed model is first in, first out (fifo). the required quantity of finished cement is dispatched to the customer. then, the next customer orders can be initiated. the benefit gains of reducing the work cycle time according to the little’s law are [27]: wip ct x th (3) where th is the throughput time that is the average output of a production process per unit time. the future state map for the conwip approach is illustrated in figure 8. engineering, technology & applied science research vol. 11, no. 3, 2021, 7069-7074 7073 www.etasr.com masmali: implementation of lean manufacturing in a cement industry fig. 8. proposed vsm future state (conwip). iv. results and discussion the comparison between the current value stream map and the proposed future maps is presented in figure 9. fig. 9. comparison of the push system and the pull systems. it can be seen that the longest value of lead-time is about 23 days in the push production system, while in the proposed maps they are about 4 and 2 days for kanban and conwip approaches respectively. the comparative results of non-value times in the cement production line for the proposed future maps is decreased by 50% in the scenario of conwip approach. the reason behind that is that there is no stock left between workstations in conwip. to illustrate, the finished cements are pulled out from the cement processing station which makes the production flows smoothly in the production line. in the case of push production system, the lead time is fixed as the material requirements are scheduled. the relationship between the level of work in progress, flow time and throughput rate is given in [27]. due to the increase in the wip level, flow time increases. consequently, the increase in throughput hindrates and delays the production process and as a result, the production may get congested. therefore, the recommendation is to implement the conwip approach to control the level of inventory in the cement production line. a significant contribution of this paper is the study of the impact of the pull-based production system on the cement production line. it was shown that kanban and conwip are tools capable of improving the shop floor process. they are able to control the excess inventories of clinker and cement and to eliminate the non-value activities in the cementmanufacturing environment. the outcome of this research is consistent with the foregoing findings. authors in [21-25] reported that conwip is an appropriate approach to control the level of inventory. in addition, the findings could extend the methodology of [14] to implement lean production in cement industry. the future prospect is to extend this research further in order to implement a plan to construct the proposed vsm towards a cement production line. v. conclusion the major issue in cement production process is the large inventories of clinker and cement. to cater and eliminate this issue, manufacturing strategies are applied. the vsm is a significant tool to evaluate the current state of manufacturing processes. the pull production systems (kanban and conwip) produce the right quantities in the right time by engineering, technology & applied science research vol. 11, no. 3, 2021, 7069-7074 7074 www.etasr.com masmali: implementation of lean manufacturing in a cement industry controlling the inventory level. both the proposed models are capable of improving the environment of cement manufacturing processes. there are further possibilities for future research. the design of experiments to run simulation models should be considered. in addition, the possibility of applying the lean manufacturing model in cement industry 4.0 should be explored. it is important to understand the dynamic manufacturing environment of the cement industry. the scheduling for dispatching products to customers based on the demand or the identification of time waste and bottlenecks during the cement production processes could be arranged by the integrated lean production with value stream tools to represent the real time and dynamic value chain of information and materials flows. acknowledgment the author wishes to acknowledge the support of this research study by the grant no. eng-2017-1-7-f-7137 from the deanship of scientific research of northern border university, arar, kingdom of saudi arabia. references [1] g. a. rankin, "portland cement," journal of the franklin institute, vol. 181, no. 6, pp. 747–784, jun. 1916, https://doi.org/10.1016/s00160032(16)90148-0. 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[21] r. p. marek, d. a. elkins, and d. r. smith, "understanding the fundamentals of kanban and conwip pull systems using simulation," in proceeding of the 2001 winter simulation conference, arlington, va, usa, dec. 2001, vol. 2, pp. 921–929, https://doi.org/ 10.1109/wsc.2001.977394. [22] m. l. spearman, d. l. woodruff, and w. j. hopp, "conwip: a pull alternative to kanban," international journal of production research., vol. 28, no. 5, pp. 879–894, 1990, https://doi.org/10.1080/ 00207549008942761. [23] m. bertolini, m. braglia, g. romagnoli, and f. zammori, "extending value stream mapping: the synchro-mrp case," international journal of production research., vol. 51, no. 18, pp. 5499–5519, 2013, https://doi.org/10.1080/00207543.2013.784415. [24] m. l. spearman and m. a. zazanis, "push and pull production systems. issues and comparisons," operations research., vol. 40, no. 3, pp. 521– 532, 1992, https://doi.org/10.1287/opre.40.3.521. [25] w. j. hopp and m. l. spearman, factory physics, 3rd ed. new york, ny, usa: mcgraw-hill, 2008. [26] l. j. krajewski and l.p. ritzman, operations management: strategy and analysis, 6th ed. new jersey, nj, usa: prentice hall, 2001. [27] j. d. c. little, "a proof for the queuing formula: l = λw," operations research, vol. 9, no. 3, pp. 383–387, jun. 1961, https://doi.org/ 10.1287/opre.9.3.383. microsoft word etasr_v11_n1_pp6656-6661 engineering, technology & applied science research vol. 11, no. 1, 2021, 6656-6661 6656 www.etasr.com alqahtani et al.: a survey of text matching techniques a survey of text matching techniques awatif alqahtani college of computer and information systems umm al-qura university makkah, saudi arabia s43980248@st.uqu.edu.sa hosam alhakami college of computer and information systems umm al-qura university makkah, saudi arabia hhhakam@uqu.edu.sa tahani alsubait college of computer and information systems umm al-qura university makkah, saudi arabia tmsubait@uqu.edu.sa abdullah baz college of computer and information systems umm al-qura university makkah, saudi arabia aobaz01@uqu.edu.sa abstract—text matching is the process of identifying and locating particular text matches in raw data. text matching is a vital component in practical applications and an essential process in several fields. furthermore, several dynamic techniques have been introduced in this context in order to create ease in pattern generation from words. the process involves matching of text files, text mining, text clustering, association rule extraction, world cloud, natural language processing, and text similarity measures (knowledge-based, corpus-based, string-based, and hybrid similarities). the string-based approach forms the most conspicuous form of text mining applied in different cases. the survey attempted in the present study covers a new research premise that uses text-matching to solve problems. the study also summarizes different approaches that are being used in this domain. keywords-text mining; similarity measure; matching; clustering; natural language processing; word cloud i. introduction nowadays, computer scientists are enjoying the convenience of many advanced tools and technologies to accomplish various tasks and duties, and pattern matching is no exception. text matching techniques are essential components in practical applications in various fields. pattern matching refers to the process of checking a specific order or structure of a token for the existence of the elements of a pattern. the matching is usually exact: the result is either a match or not. even though there are various ways of memorizing data, the text remains the primary form of exchanging information. before text is searched for patterns, it has to be structured by using various strategies such as text matching. as a result, text matching is the process of identifying and locating particular text matches in raw data. though there are many methods of applying this process, addressing inherent problems in these methods is needed to boost the efficiency of the process. in this regard, this paper focuses on natural language processing (nlp) algorithms and unsupervised text mining techniques, their inherent challenges, and ways to overcome them. many approaches have been proposed for text matching. most are mainly based on text mining which involves keyword matching, sequence matching and clustering. moreover, in matching texts, the similarity measure is used by measuring the similarity between words, sentences, paragraphs and documents. measuring of similarity is considered to be an important component in various tasks such as text summarizing, text matching, information retrieval, automatic essay scoring, document clustering, and machine translation [1]. ii. matching text file methods a. text mining text mining refers to the process of analyzing and exploring large sets of unstructured data to identify and isolate topics, keywords, concepts, patterns and other elements evident in data sets. the process is becoming more practical due to the emergence of large data platforms and various deep learning algorithms with the ability to analyze big sets of unstructured data [2]. through text mining, it is possible to focus on text data instead of other more structured forms of data examined in data mining. however, both the processes involve organizing and structuring the data in a particular fashion before subjecting it to qualitative and quantitative analysis. text mining comprises of a wide set of algorithms and topics for analyzing texts and spanning different communities [3]. some of the common text mining tools include text clustering, text visualization, and association rule extraction. text clustering rests on the cluster hypothesis that argues that clustering is possible when the relevant documents possess more similarities with each other than with non-relevant documents. it is a trustworthy technique that is largely applied in analyzing and examining big sets of data akin to data mining [4]. moreover, it is proven that text clustering remains an effective tool for theme analysis of texts, while it also facilitates topic analysis technique where named parties with concurrent occurrences are categorized together and the frequent entity is placed in various sets by using the graph-based approach [5]. currently, the corresponding author: abdullah baz engineering, technology & applied science research vol. 11, no. 1, 2021, 6656-6661 6657 www.etasr.com alqahtani et al.: a survey of text matching techniques procedure of topic ranking in a dynamic set of data is gaining the attention of researchers using text clustering in the digital field [6, 7]. even though text clustering remains vital in browsing and navigation processes, various text clustering strategies fail to address challenges such as space complexity and high time, less robustness, privacy risks, inability to comprehend contextual elements of words, etc. authors in [8] propose an efficient text-based clustering framework. they determined the similarities between words by using the cosine similarity. the data vector was designed from the component similarities and was later used to compute the clustering particles. following mutation to maximize clustering, the framework is examined by using mean square error (mse), processing time (pt), and peak signal to noise ratio (psnr) [9]. the findings indicate that the proposed framework produces optimal psnr, mse and pt compared to the pair-wise random swap (prs) and fuzzy cc means (fcm) approaches. authors in [10] reported that another way of overcoming challenges to text mining such as data dimension reduction and extraction is by using a deep learning vocabulary network [10]. the vocabulary network’s design is based on closely related word sets that contain the concurrence relations of terms or words. here, the frequency in feature vectors is replaced with the significance of words in terms of page rank and vocabulary network to create exact feature vectors that depict the meanings of text clustering. when the deep-learning vocabulary network was compared to other approaches such as representative algorithms, the results demonstrate that feature vectors determined by using deep learning vocabulary network portray improved clustering performance. furthermore, in addressing the diversity and complexity of natural language, the semantically responsive text clustering approach has been proposed in [11]. the authors suggest an extension-oriented modeling approach along with a similarity aggregation method and a space construction method. this approach has the ability to improve semantic sensitivity during the text mining process by organizing the generated clusters into different granularities [12]. the effectiveness of this approach is confirmed through recognized examinations of clustering data-sets and algorithms. authors in [13] collected and textually analyzed various documents from six scientific databases. text clustering was shown to be effective in matching texts from natural language documents. in cases where similarity was not detected, they attested it to ambiguity or interrelations between analyzed text documents. cosine similarity is still the most common metric of similarity. the collection of sentences is carried out by selecting sentences from each cluster on of basis of term frequency and inverse term frequency rankings in this same cluster [14]. b. association rule extraction approaches associated with association rule extraction focus on identifying the relationships in a big set of variables in data-sets. association-rule mining (arm) strategies identify the variable-value arrangements that occur repeatedly. it is also called knowledge discovery because it is likened to correlations analysis that focuses on the associations between two variables [15]. the association procedures for text mining focus on exploring the relationships among various factual notions or topics used to describe a body of data. the primary objective is to discover the vital association rules comparative to a body of data in such a manner that the existence of particular topics in articles may resemble the existence of other topics. some researchers agree that association rule mining is a prominent research field that used to unearth frequent patterns and arrangements in repositories of synthetic or real-world data-sets [16]. association rule mining underscores that various associations are related or occur among a group of datasets in the database [17]. in many arm approaches, the rules are evaluated from two main measures, namely confidence and support. support is the aggregate number of text data that are associated with each other in the database, while confidence is the portion of data-sets that contains associated text data in the database. here, the researcher employs a prior algorithm to find frequently occurring items over transaction data sets, and the technique is effective in matching similar and dissimilar text data to offer insight for decision-making. some researchers argue that association rule extraction remains an effective approach of finding accurate and vital knowledge from an assortment of documents. today, information technology and the internet are platforms that provide huge amounts of data and information to users [18]. however, a major issue facing text matching is that searching and finding precise and crucial information may be time-consuming or lead to misunderstandings. creating a method to generate knowledge discovery through the association rule extraction proves to be effective in both saving time and avoiding misunderstandings. authors in [19] support the use of a temporal approach in extracting negative and positive association rules from texts. data extraction by using the temporal approach is not popular amongst the arm researchers, especially for negative associations. however, the researchers insist that the rule allows the researchers to answer essential questions when applying association rules, which boosts the trustworthiness of the resulting association rules for use in matching texts. traditionally, association analysis is an unsupervised strategy mostly evident in knowledge discovery assignments. therefore, the majority of the relevant studies focus on simplifying association rules and improving the performance of algorithms. however, other problems arise when association rules are created and applied in various domains. some of the main challenges the association rules algorithms face include obtaining non-interesting association rules, discovering a huge number of rules, and poor algorithm performance [20]. troubleshooting for these problems should focus on the objective of an association model and its origin. c. word cloud another text mining technique in common use is word cloud. as noted, a word cloud or tag cloud is the visual representation of a word for a particular written content arrangement according to its frequency [21]. it is amongst the most common methods for graphically presenting text data, which makes it vital for examining different kinds of texts such as written opinions or short answers to a questionnaire or survey [22]. it is a preliminary phase during the in-depth analysis of particular text material and the needed information. nevertheless, this technique faces various challenges. a major engineering, technology & applied science research vol. 11, no. 1, 2021, 6656-6661 6658 www.etasr.com alqahtani et al.: a survey of text matching techniques drawback is that word cloud fails to contemplate the linguistic knowhow about text words and corresponding associations with a specific subject when offering a numerical summary to the isolated words [23]. as a result, in the majority of the systems, the word clouds are usually used in a numerical manner to summarize texts and offer little or no chance to correlate the data. authors in [24] provide the findings of a set of controlled research experiments that demonstrate that layouts where text words are structured into visually and semantically distinctive categories are more efficient and effective for acknowledging underlying topics compared to ordinary world cloud designs. the white space separators and spatially grouped color coding lead to considerably powerful understanding of the fundamental topics as compared to an ordinary word design or layout. as a result, data mining experts are developing data-sets for visually and semantically distinct category identification tasks for use in replicating results for word cloud formats and designs in the future [25]. authors in [26] agree that word cloud remains an effective text matching tool in writing and reading classes, especially english classes for esl learners. during the decade, many word cloud applications were designed to provide additional visual appeal to slide shows, posters, and websites amongst others. for writing and reading classes, word clouds are vital for reducing reading time and helping with vocabulary and writing comprehension. moreover, word clouds are also used for addressing rhetoric elements in instructors’ assignment descriptions, syllabuses, and students’ essays. the process locates a collection of vocabulary in texts for use in creating word clouds that assist students in understanding and summarizing texts, learning collocations and spellings, finding synonyms, and avoiding repetition, and using word maps for creating tone. d. natural language processing nlp is a sub field of artificial intelligence and computer science preoccupied with interactions and associations between human and computer languages. it is also applicable to machine learning algorithms for deciphering texts and speech. it has gained considerable attention in the field of computer science and text matching in particular. unlike ordinary machine learning roles that deal with structured data, it deals with unstructured text data [27]. also, one of the types of nlp called sentiment analysis, is a new hybrid approach for the analysis of social problems. it extracts the views from each statement, builds opinion structures of communication, and then decides their social issue alignments [28]. string searching algorithms are the most common nlp tools for use in text matching. in string searching, an algorithm is used to identify and isolate a location where a single or several strings and patters are found in a large body of text data. some of the most common algorithms are brute force, boyer-moore horspool, rabin-karp, and knuth-morris-pratt. authors in [29] found that a major challenge the pattern matching algorithms face is memory consumption, with the majority of the algorithms focusing on achieving efficiency at the expense of memory use. they offer a new idea to address both by using an algorithm that splits the query configuration into two parts and uses the second part as a query string for use in searching the collection of large text data. the proposed algorithm outperforms the s1 algorithm on memory use and time efficiency by increasing the length of a query configuration. authors in [30] proposed bidirectional (bd) exact pattern matching (epm) that introduces the novel idea of comparing patterns by using the selected text window (stw) of a text string using a double pointer simultaneously during the searching phase. the researchers identified that during the pre-processing phase, the algorithm boosted the shift decisionmaking by comparing the mismatched and rightmost character of its partial text window (ptw) to its left at a similar shift length. as a result, it reduced the time complexity of the preprocessing phase and was proved to be more effective than the existing algorithms. the boyer-moore-horspool algorithm increases the efficiency of intrusion detection systems. many intrusion systems use various string-matching algorithms to carry out searches for mischievous activities, but a major challenge these algorithms face is longer processing time. authors in [31] found that improving the algorithm by adding a hashing function called hbmh which is vital in reducing the comparison time. as a result, the findings attest that an enhanced algorithm performs faster and lowers processing time. it was also discovered that a variation of the boyermoore algorithm led to other versions with comparative advantages, disadvantages, and performance standards in various conditions. the variants included bmh, bmhs, bmsh2, bmi, and cbm. a bmh algorithm only applies the bad character shift [31]. regardless of the location of a mismatch, the distance of a shift to the right it calculated by the characters in text strings that are aligned to the last text or string on the pattern strings. since it removes the concept of good-suffix, bmh is easy to apply [32]. moreover, more jumps are realized by using this algorithm. furthermore, in case of a mismatch, it is possible to determine the shift value by using the char value instead of the mismatched character. however, the bmhs algorithm focuses on calculating the bad char function by considering the status of the next character to determine a right off-set. as a result, a major advantage is that the maximum shift is more than the pattern length by one [33]. however, a major issue is that fewer shifts are realized during a mismatch [34-36]. iii. text similarity measures there are four major categories of text similarities measures. the string-based similarity measure is one of the oldest methods. the main forms of string-based similarity comprise both character-based similarity and token-based similarity functions [36]. the corpus-based similarity follows semantic approaches. the methodology aids in the determination of similarity between two concepts in terms of information from the respective corpora, which is a collection of electronic, spoken, or written text. these methods enshrine some predefined set of sentences coupled with their translation in other dialects, with the intention of matching the input text within the corpus and the final translations [36]. the knowledge-based similarity measures are defined as a series of semantic measures enlisted for information adopted from semantic networks. the aim of such information is geared towards the identification of the extent of similarity within words. knowledge-based similarity consists of semantic engineering, technology & applied science research vol. 11, no. 1, 2021, 6656-6661 6659 www.etasr.com alqahtani et al.: a survey of text matching techniques relatedness and semantic similarity. hybrid classification similarity measures do not form a distinct group. they are combinations of the previous approaches in an effort to attain their merits [36]. these approaches work on recursive approaches to tackle limitations of the other measures. iv. literature review summary the reviewed methods, their advantages and disadvantages are summarized in table i. some of the research studies that contributed to solving specific problems of text matching techniques are summarized in table ii. table i. text matching methods text matching techniques definition advantages disadvantages text mining the process of analyzing and exploring large sets of unstructured data to identify and isolate topics, keywords, concepts, patterns, and other elements evident in data sets it is possible to focus on text data instead of other more structured forms of data examined in data mining, but both processes involve first organizing and structuring the data in a particular fashion before subjecting them to qualitative and quantitative analysis depends on other methods. text clustering it rests on the hypothesis that clustering is possible when relevant documents possess more similarities with each other compared to non-relevant documents it is a trustworthy technique that is largely applied in analyzing and examining big sets of data akin to data mining less efficient approach word cloud word cloud or tag cloud is the visual representation of used words arranged according to their frequency it is simple and the most common method for graphically presenting text data fails to contemplate the linguistic knowhow about text words and corresponding associations with a specific subject brute force algorithm bd epm that introduces a novel idea of comparing patterns by using the stw of a text string using a double pointer simultaneously during the searching phase efficient on memory use and time efficiency by increasing the length of a query configuration complex to use boyermoore horspool algorithm it increases the efficiency of intrusion detection systems easy to apply as it removes the concept of good suffix less shift is realized during a mismatch because of the character next to the last character, but not aligned or associated with the last pattern table ii. examples of text matching techniques ref text matching type problem approach used processes results year [38] string used for paralogism detection string matching n-gram with dice’s similarity coefficient generates a percentage of the similarity of the document, but the efficiency of processing time needs improvement 2019 [39] semantic to detect intelligent plagiarism topic modeling semantic text alignment based on sentence-level topic modeling topic modeling is a potential solution for detecting intelligent plagiarism 2016 [40] semantic transformation to solve the semantic gap in text matching semantic transformation model enhanced text matching method based on the cycle gan combined with the transformer network the semantic matching is improved significantly 2020 [41] hybrid knowledge neural network (nn) long text brings a big challenge to nn-based text matching approaches due to their complicated structures knowledge enhanced hybrid nn (kehnn) the three channels are processed by a convolutional nn to generate high level features for matching shows that kehnn can significantly outperform the state-of-the-art matching models and particularly improve matching accuracy on pairs with long text 2018 [42] knowledge to automatically answer medical questions online knowledge abstraction matching (kam) method the method consists of frequent segment n-gram mining, medical knowledge abstraction, medical segment matching and answer reretrieval generates more quality answers for melody qa with a significant improvement of question coverage under acceptable accuracy 2019 v. discussion the similarity between words can be expressed in lexical similarity terms (similar sequence of characters) or semantic similarity (same meaning) [37]. lexical similarity is based on string-based tools or algorithms [37, 43]. string-based algorithms for lexical similarity matching fall into two categories [37]. the first category consists of character-based algorithms such as lcs, damerau levenshtein, jaro, and ngram [43, 44]. the second category consists of term-based algorithms, such as the cosine similarity, block distance, euclidean distance, jaccard similarity, and matching coefficient [45]. however, semantic similarity techniques are more rational in finding substantial relationships between texts engineering, technology & applied science research vol. 11, no. 1, 2021, 6656-6661 6660 www.etasr.com alqahtani et al.: a survey of text matching techniques [37]. some of the innovative string-based tools include simmetrics [45], simpack, flamingo, and alignment api [46]. these tools have one major drawback, which is that they do not provide semantic analysis of texts. semantic analysis is based on corpus-based and knowledge-based algorithms [43]. corpus-based similarity matching techniques have gained widespread application. the most popular corpus-based technique is the latent semantic analysis (lsa), which assumes that words with similar meaning occur in similar texts. although lsa is easy to implement and offers good performance, it has inherent limitations for non-linear situations due to its linear approach and the probabilistic model may fail to match the observed data [47]. an alternative method is to use latent semantic indexing, which overcomes synonymy [48]. another technique based on the corpus approach is the explicit semantic analysis (esa), such as the wikipedia-based technique, which represents texts in the form of high-dimensional vectors [49]. although esa has proven useful in handling different contexts, it was found that the algorithm exhibits unexpected behavior [49]. knowledge-based approaches rely on information from semantic networks to determine the degree of similarity. the most popular knowledge-based tool is the wordnet, which consists of a lexical database of english words interlinked with conceptual relations [50]. recently, there have been attempts to combine multiple approaches. the simall tool combines features of string, knowledge, and corpus similarity approaches [51]. the best tool for semantic analysis is simall because it combines lexical and semantic analysis at different levels of granularity [28]. vi. conclusion some of the common text mining tools include text clustering, text visualization, and association rule extraction. even though text clustering remains vital in browsing and navigation processes, various text clustering strategies have disadvantages such as space complexity and high computational time, reduced robustness, privacy risks, and inability to comprehend contextual elements of words. when the deep-learning vocabulary network is compared to other approaches such as the representative algorithms, the results demonstrate that feature vectors determined by using deep learning vocabulary network portray improved clustering performance. rule mining underscores that various associations are related or occur among a group of data-sets in the database. in string searching, an algorithm is used to identify and isolate a location where a single or several strings and patters are found in a large body of textual data. some of the most common algorithms include brute force, boyermoore horspool, 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[51] w. h. gomaa and a. a. fahmy, "simall: a flexible tool for text similarity," in the seventeenth conference on language engineering esolec, vol. 17, pp. 122–127, 2017. microsoft word 37-3830_s1_etasr_v10_n5_pp6368-6373 engineering, technology & applied science research vol. 10, no. 5, 2020, 6368-6373 6368 www.etasr.com latreche & benaggoune: robust wheel slip for vehicle anti-lock braking system with fuzzy sliding .... robust wheel slip for vehicle anti-lock braking system with fuzzy sliding mode controller (fsmc) sadjia latreche lsteb laboratory electrical engineering department batna 2 university setif, algeria sadjo83_lat@yahoo.fr said benaggoune lsteb laboratory electrical engineering department batna 2 university batna, algeria s_benaggoune@yahoo.fr abstract-anti-lock braking system (abs) is used in automobiles to prevent slipping and locking of wheels after the brakes are applied. its control is a rather complicated problem due to its strongly nonlinear and uncertain characteristics. the aim of this paper is to investigate the wheel slip control of the ground vehicle, comprising two new strategies. the first strategy is the sliding mode controller (smc) and the second one is the fuzzy sliding mode controller (fsmc), which is a combination of fuzzy logic and sliding mode, to ensure the stability of the closedloop system and remove the chattering phenomenon introduced by classical sliding mode control. the obtained simulation results reveal the efficiency of the proposed technique for various initial road conditions. keywords-anti-lock braking system (abs); sliding mode control; fuzzy logic control; fuzzy sliding mode control; wheel slip ratio i. introduction anti-lock brake system (abs) is generally utilized in road vehicles. to diminish product cost, standard abs utilizes wheel speed sensors to distinguish angular velocities, which isn't sufficient to directly obtain the wheel slip required by the control unit, yet can be utilized to compute the reference slip proportions with estimated wheel precise speeds and the evaluated vehicle speed. the friction coefficient of the road, which decides the vehicle deceleration amid extreme braking, is an essential parameter in assessing vehicle speed. abs comprises of a hydraulic modulator (control valve), control electronics (central unit) and sensors on the wheels. sensors continually get information on braking power, although there are no sensors which can precisely distinguish road surface, and make this information accessible to the abs controller. the primary aim of abs is to maintain the wheel slip in the required value and to ensure the steerability of the vehicle when the brakes are applied suddenly. abs control is influenced by the nonlinear behavior of the dynamics of the brake and other factors such as the type of road surface, tire pressure, vehicle mass, etc. because the required wheel slip is continuously changing [1]. the target is the control of the wheel slip of each tire in order to continue running at its relating desired slip value. however, the wheel slip dynamics control is a difficult problem due to the nonlinear and complex behavior of the tire. in addition, the system is also suffering from parametric uncertainties, and is subjected to external disturbances from the environment leading to the emergence of many difficulties in the design of controllers for abs. this leads to the requirement of a controller which will be capable of dealing with these uncertainties and nonlinearities. one of the controllers which can successfully deal with the parametric and modeling uncertainties of the abs system is sliding mode control (smc). smc systems are generally utilized for abs control, since they are insensitive to parameter variations. the best advantages of this control approach are its fast convergence and good performance [2-3] and its robustness with respect to structural uncertainties and external disturbances [4]. sliding mode controllers have been developed and studied in [5, 6]. however, the presence of the sign functions in the control law, also known as the variable structure controller (vsc) causes a phenomenon of chatter that can excite high frequency and can damage the system [7-9]. to overcome this drawback, several solutions have been proposed, such as the introduction of a transition band around the sliding surface [1011] or fuzzy-sliding mode control (fsmc) which is a combination of fuzzy control and sliding mode control. the main advantages of fsmc is that it requires fewer fuzzy rules than fuzzy control and it is more robust against parameter variations [12-13]. fuzzy logic (fl) control is one of the accepted strategies to deal with uncertain control systems. control systems on fl have been developed for abs [14]. fl is a knowledge-based system which is very useful in handling systems whose models are not fully or accurately developed or the information about the system is uncertain. in this paper, a new robust fsmc for the abs model is proposed. the performance of the proposed fsmc is assessed through digital simulations for varying road surface conditions. ii. dynamic model of the pneumatic wheel a quarter-car model is utilized to create the longitudinal braking dynamics. it comprises of a single wheel carrying a quarter of the mass of the vehicle. at any given time, the vehicle is moving with a longitudinal velocity vv(t). before the corresponding author: sadjia latreche engineering, technology & applied science research vol. 10, no. 5, 2020, 6368-6373 6369 www.etasr.com latreche & benaggoune: robust wheel slip for vehicle anti-lock braking system with fuzzy sliding .... brakes function, the wheel moves with an angular velocity ωω(t) motivated by the mass in the direction of the longitudinal motion. due to the friction between the tire and the road surface, a tractive force is generated ft(t). when the driver applies the braking torque, it will cause the wheel to decelerate until it comes to a stop. the two degree of freedom quarter-car model is shown in figure 1. fig. 1. the dynamics of the vehicle wheel single-corner model. the dynamic equation of the abs system is the consequence of newton's law exerted to the wheels and the vehicle which is determined by the total sum of the forces applied to the vehicle during braking. n f v mi i 1 ′= ×∑ = 1 ( ) ( )v t f tv t mv − ′ = (1) the wheel rotational dynamics equation is given by: 1 ( ) [( )]t t t ttbj ωω = +′ (2) where ωω is the wheel angular velocity (r/s), j is the wheel rotational inertia (kg.m 2 ),tb is the effective braking torque (n.m), and tt is the torque generated by the sliding between the wheel and the road surface (n.m). the expressions of various forces are given by: (t) sin( )f m gz v α= (3) ( ) ( ) cos( ) 4t gv f t m µ λ α= (4) ( ) ( )tt t r f ttω = (5) where ft and fz are the braking force of tire and the vertical force respectively, a is the tyre side slip angle (rad), and rω is the tire radius (m) iii. wheel slip control and friction curve the wheel slip is the conventional and main controlled variable, still utilized in certain abs systems. the slip measurement is critical, since it requires the estimation of the speed of the vehicle. wheel slip control is the most reasonable decision for the structure of braking controllers that are robust with respect to road surface variables. the control target of the abs is to regulate wheel slip to maximize the coefficient of friction between the wheel and the road for any given road surface. in general, the coefficient of friction µ during a braking operation can be described as a function of the wheel slip ratio λ, which is characterized as: ( ) ( ) ( ) ( ) 1 ( ) ( ) t t tv t t tv v ω ω ωω ωλ ω ω − = = − (6) or: ( ) vv t rv ω ω= × (7) with ωv(t) being the angular velocity of the vehicle (r/s). note that, whatever the value of λ (0 ≤ λ ≤ 1), this control guarantees the uniqueness of the equilibrium point. the friction coefficient which characterizes the road and tire µ(λ) is a nonlinear parameter, with properties: µ(λ=0)=0 and µ(λ>0)>0. the expression of µ(λ) may change, according to different road conditions. . . . 2 4( , ) c (1 ). . . 1 3 v v c c v v e c e λ λ µ λ λ − − = −     (8) where c1 is the maximum value of the curve of friction, c2 is the shape of the curve of friction, c3 is the difference of the curve of friction between the maximum value and the value at λ=1, and c4 is the characteristic value of moisture. one µ(λ) curve for various road surfaces is shown in figure 2. fig. 2. slip-friction µ(λ) curves for different road conditions. the qualifying feature depends on the longitudinal: (1 ) ( ) wv t v λ ω ω λ ω ′ ′− − ′ = (9) iv. sliding mode controller based abs control smc is an approach of robust control that is used to control nonlinear systems such as the abs. the design of the smc is simple and the system is robust against variations in process dynamics and external disturbances. engineering, technology & applied science research vol. 10, no. 5, 2020, 6368-6373 6370 www.etasr.com latreche & benaggoune: robust wheel slip for vehicle anti-lock braking system with fuzzy sliding .... let a nonlinear system be represented as: ( ) ( , ) ( )t f t g u t n n λ λ′ = + (10) where: � (t) ( , ) . 1 ( ) , and ( ) b v r fff tttt m rn v v r mv v v a b u t t n c f j g t j ωλ λ ω ω ω ωω ω = − − = = ����� ��������� where fn(λ, t) and gn represent the nominal values of the system parameters. if uncertainties occur, then the controlled system can be modified: ( ) ( , ) ( , ) ( ) ( , ) ( ) ( , ) ( , ) ( )n n t t f t u t n n n ng f t g u t dn n d f f g t g t u t λ λ λ λ λ λ ′ = + ∆ + + ∆ × = + + = ∆         + ∆ (11) where ∆fn(λ,t) and∆gn(λ,t) are the uncertainties of the system and d is constant and positive. the control aim in this paper is to drive the longitudinal slip ratio to the desired slip in finite time and find a control braking torque in order to have the system track the desired slip (λd) error defined by: ( ) ( ) ( )t t t e d λ λ λ= − (12) τthe conventional sliding controller defines a scalar function of the sliding surface given by the equation: 1 , n s( t) ( k ) . i et λ λ ∂ −= + ∂ (13) in a system of the second order, the sliding surface is defined as: 1( , ) ( ) ( )s t t k te eλ λ λ ′= + (14) where k1 represents the surface parameters. the values of k1 determine the slope of the sliding surface and one of the conditions for the existence of sliding surface is that k1 is strictly positive real constant. to ensure the stability of system, the function form of lyapunov is given by the following relation: 1 2 ( , ) 2 v s tλ= (15) the above control law guarantees the system trajectories move toward and stay on the sliding surface s=0 for any initial condition, if the following condition is satisfied: 1 2 ( ( , )) ( , ). ( , ) ( , ) 2 v s t s t s t s t t λ λ λ η λ ∂ ′ ′= = ≤ − ∂ (16) where η is a positive constant that makes the system trajectories meet the sliding surface in a finite time. in these sliding surface designs the derivative of the surface is determined by: ( ) ( ) 1 s ( ,t) k a b cu t de d λ λ λ λ′ ′= − − + + + + (17) after substituting (17) into (16) we obtain: sign( ( , ))[ ( ) (t) ] 1 s t k a b cu de d λ λ λ λ η′− − + + + + ≤ − (18) with: 1 0 sign( ( , )) 0 0 1 0 if s s t if s if s λ − < = = >      the command law or control of braking torque (tb) guarantees that the trajectory of the system is coming at the desired sliding surface. in this specified sliding surface the equivalent control is decided from the condition s ’ =0 separating the first sliding surface and the equivalent control brake torque tb is obtained: 1 1 [ ( ) sign( ( , ))] e d u u a b k d s t c λ λ λλ ′= − + + + − (19) where d u is a positive constant that represents the gain of discontinuous control. the sliding mode control law is given by: e ht u u u= + (20) where ue is the equivalent command and uht the discontinuous command: [ ]1 1 ( ) e d u a b ke c λ λλ ′= − + + + (21) 1 sign( ( , )) u u c d s t ht λ−= −   (22) v. fuzzy sliding mode control smc is a nonlinear control technique. intelligence can be added to this controller by combining fl to the conventional smc. the reactions comprising of input control (brake torque) and slip ratio tracking error, are undesirable and full of chattering. in other words, when the vehicle is stopped, elevated oscillation is observed in control signals that causes deterioration of elements in the braking system. fl is a comprehension based system which is very much useful in systems whose models are not developed fully or precisely or the information about the system is uncertain. figure 3 shows the principals of fsmc controller for abs. engineering, technology & applied science research vol. 10, no. 5, 2020, 6368-6373 6371 www.etasr.com latreche & benaggoune: robust wheel slip for vehicle anti-lock braking system with fuzzy sliding .... fig. 3. close loop of the fsmc controller for the abs system. a. description of the fuzzy adaptive system fuzzy control is the proposed approach to overcome the problem. it is developed with two inputs, sliding surface s and derivative sliding surface s’, and the output is the error ε. triangular and gaussian membership functions are used as input and output for de-fuzzification (figure 4). (a) (b) fig. 4. the membership functions of (a) input and (b) output the inputs and outputs are all divided into five fuzzy subsets:[nb, ns, ze, pb, ps] (meaning negative big, negative small, zero, positive small, and positive big respectively). the fuzzy rules are listed in table i. table i. rules of the fuzzy logic controller ε s s� nb ns ze ps pb nb nb nb nb nb ze ns nb ns ns ze pb ze nb ns ze ps pb ps nb ze ps ps pb pb ze ps pb pb pb b. implementation of the order chattering phenomena is an undesirable effect of discontinuous control commands during sliding mode control. in one of the solutions in order to reduce the chattering phenomena, the sign function d u sign(s) is replaced by the saturation function in the control input of the first sliding surface: sat( ) f f s u k φ = (23) where sat( ) s φ is a saturation function that is defined as: 1 sat( ) sign( ) 1 s s if s s s if φ φ φ φ φ  ≤  =   ≥  (24) where φ is a positive constant. in this case, we can only ensure convergence tracking error in a neighborhood around zero. it can be concluded that this particular fsmc works as a boundary-layer of the switching surface. sat( ) s u u keqfsmc f = − φ (25) vi. results and discussion the abs system parameters used in this study are: mv=370kg, j=1.13kgm 2 , rω=0.33m, g=9.8m/s 2 , λd=0.2, vv0=70km/h, for t∈ [0, 12]. simulations were conducted for various street conditions. matlab/simulink is used for the simulations to assess the performance of proposed controller. the simulink model of the abs system with the fsmc controller is shown in figure 5. a. results of the smc controller using (14) we get: 1 ( ) ( ) 0t k te eλ λ ′ + = the model selected reference is: ( ) 10 ( ) 10 ( )t t t d d λ λ λ′ = − + in the first case, a wet road (µ=0.25) was chosen and the control law for simple conventional smc had the sign function u=d u sign(s) with k1=125 and d u =60. figure 6 presents the vehicle speed and wheel when the brake force is applied. the change of road surface obviously influences the stopping distance and effects wheel slip but the smc has more robustness under the changes of various road conditions. figure 7 shows the longitudinal slip ratio. we can see the tracking ability with enough response time (0.3s). it can be seen from the zoomed part of figure 8, that there is a rapid changeover between the maximum and minimum values of braking torque to maintain the wheel slip at the set point. this is called the chattering. the simulation results illustrate that the smc can achieve satisfactory control performance for wet road, but the result using a conventional sliding mode controller shows chattering in all the response results. the oscillation in these time responses tends to increase when the vehicle tends to stop. this phenomenon is highly undesirable as it may damage the system. engineering, technology & applied science research vol. 10, no. 5, 2020, 6368-6373 6372 www.etasr.com latreche & benaggoune: robust wheel slip for vehicle anti-lock braking system with fuzzy sliding .... fig. 5. simulink fsmc controller for the abs system model. fig. 6. vehicle and wheel speeds for abs system with smc for µ=0.25 fig. 7. longitudinal slip ratio for abs system with smc for µ=0.25 fig. 8. braking torque (tb) for abs system with smc for µ=0.25 table ii summarizes the performance comparison between fsmc and pi controller in terms of step response of slip rate which is maintained at a desired value. it can be seen that the proposed fsmc presents the optimum performance. figure 9 shows the distended view of the step response of slip ratio with fsmc and pi. table ii. performance comparison pi fsmc rise time 0.7s 0.25s peak repose 0.3 0.2 overshoot 50% 0% fig. 9. step response of slip rate with fsmc and pi controllers. vii. conclusion in this study, a robust controller, based on the fuzzy sliding mode approach has been proposed to control the wheel slip ratio. the fsmc control strategy was able to eliminate the chattering problem with elevated tracking precision and to improve the performance of the wheel slip control. the presented simulation results show that the fsmc converges to the desired value for various road conditions. engineering, technology & applied science research vol. 10, no. 5, 2020, 6368-6373 6373 www.etasr.com latreche & benaggoune: robust wheel slip for vehicle anti-lock braking system with fuzzy sliding .... references [1] d. hong, i. hwang, p. yoon, and k. huh, “development of a vehicle stability control system using brake-by-wire actuators,” journal of dynamic systems, measurement, and control, vol. 130, no. 1, jan. 2008, doi: 10.1115/1.2807190. 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[11] e. nechadi, “adaptive fuzzy type-2 synergetic control based on bat optimization for multi-machine power system stabilizers,” engineering, technology & applied science research, vol. 9, no. 5, pp. 4673–4678, oct. 2019. [12] m. amodeo, a. ferrara, r. terzaghi, and c. vecchio, “wheel slip control via second-order sliding-mode generation,” ieee transactions on intelligent transportation systems, vol. 11, no. 1, pp. 122–131, mar. 2010, doi: 10.1109/tits.2009.2035438. [13] c.-m. lin and c.-f. hsu, “self-learning fuzzy sliding-mode control for antilock braking systems,” ieee transactions on control systems technology, vol. 11, no. 2, pp. 273–278, mar. 2003, doi: 10.1109/tcst.2003.809246. [14] z. b. duranay, h. guldemir, and s. tuncer, “fuzzy sliding mode control of dc-dc boost converter,” engineering, technology & applied science research, vol. 8, no. 3, pp. 3054–3059, jun. 2018. microsoft word 07-3734_s_etasr_v10_n5_pp6191-6194 engineering, technology & applied science research vol. 10, no. 5, 2020, 6191-6194 6191 www.etasr.com alsheikhy et al.: logo recognition with the use of deep convolutional neural networks logo recognition with the use of deep convolutional neural networks ahmed alsheikhy electrical engineering department college of engineering northern border university arar, saudi arabia aalsheikhy@nbu.edu.sa yahia said electrical engineering department, college of engineering, northern border university, arar, saudi arabia and laboratory of electronics and microelectronics, faculty of sciences of monastir, university of monastir, tunisia said.yahia1@gmail.com mohammad barr electrical engineering department college of engineering northern border university arar, saudi arabia m.abarr@nbu.edu.sa abstract—automatic logo recognition is gaining importance due to the increasing number of its applications. unlike other object recognition tasks, logo recognition is more challenging because of the limited amount of the available original data. in this paper, the transfer leaning technique was applied to a deep convolutional neural network model to guarantee logo recognition using a small computational overhead. the proposed method was based on the densely connected convolutional networks (densenet). the experimental results show that for the flickrlogos-32 logo recognition dataset, our proposed method performs comparably with state-of-the-art methods while using fewer parameters. keywords-logo recognition; deep learning; convolutional neural networks (cnns); densenet; artificial intelligence i. introduction logos are symbols that are generally used by firms to identify themselves and their products. they normally contain colors, shapes, textures, and/or text [1]. logo recognition is a key problem for many applications such as copyright infringement detection, online brand management, vehicle recognition, contextual advertisement placement, etc. [2, 3]. although companies do not change their logos often, and it is only the context in which the logo appears that changes for each product of the same company, logo recognition is still a challenging task. some of the challenges for accurate logo recognition are perspective deformations, varying background, occlusions, warping, varying size, varying colors, etc. [1]. moreover, the growing number of brands having personalized logos makes the logo recognition task even more challenging. the logo recognition systems require high computational powers to support multi-class classification efficiently. traditionally, artificial intelligence (ai) techniques have been used to solve object recognition problems. in particular, convolutional neural networks (cnns) with deep structure and many hidden layers is a very popular model that is commonly used for solving object recognition problems [18, 19]. the approach followed by these techniques is based on two important tasks: feature extraction and feature classification. these tasks are commonly achieved using the convolutional layers as feature extraction modules and the fully connected (fc) layers for classification [17]. many techniques derived from cnns have been used for solving the problem of logo recognition. for example, authors in [4, 5] used pre-trained cnns for logo recognition. however, such techniques have high computational overhead associated with them. this limits the context in which such computational intensive solutions can be used. hence, the problem of accurate logo recognition using low computational effort remains unresolved. in this paper, the transfer learning technique was applied to a deep convolutional neural network (dcnn) model to ensure logo recognition without using huge computation resources and the results of the accuracy comparison with the state-of-the-art methods show that the proposed method performs similarly. ii. related works many solutions have been proposed for the problem of accurate logo recognition. earlier works on logo recognition were mainly based on keypoint detectors and descriptors. a feature bundling was proposed by romberg and lienhard [6] for scalable logo recognition. their method combined both local features and those from the spatial neighbourhood into a bag of words (bow). similarly, romberg et al. [7] proposed another logo recognition system based on the relative spatial corresponding author: yahia said engineering, technology & applied science research vol. 10, no. 5, 2020, 6191-6194 6192 www.etasr.com alsheikhy et al.: logo recognition with the use of deep convolutional neural networks layout of local features encoding and indexing (e.g. edges and triangles). the local features and the spatial layout helped them to quantize the regions in the logos. francesconi [8] presented a recursive neural network-based technique for the classification of black and white logos. the method also used contour trees to hold the topological structural information. although francesconi’s method was efficient, its main limitation is that its performance for more complex colored logos is not known. moreover, this approach assumes that the maximum number of children for each node are known in advance. duffner and garcia [9] also proposed a cnn-based solution for recognizing logos in television programs. in this technique, pixel values were directly fed into a cnn with two convolution layers to detect watermarks on television. the main limitations of this technique are its low detection rates and its limited applicability (i.e. only television logos can be detected). zhu and doermann [10] used fisher classifiers for recognizing logos in documents. a problem with their technique is that it cannot handle large variations [11]. authors in [3-5, 12] proposed deep learning-based solutions for the problem of accurate logo recognition. authors in [4, 5] relied on pre-trained cnns and synthetically generated data for logo detection. similarly, authors in [3] proposed and evaluated several network architectures while authors in [12] used pretrained cnn models along with fast region-based convolutional networks. the main limitations of these techniques are that they rely on pre-trained cnns. a major limitation is that the training data available for logo recognition was limited. authors in [2] proposed a deep learning-based logo recognition. the proposed recognition pipeline includes a logo region proposal module followed by a cnn module that is trained for logo identification. this method can also handle logos that are not localized. however, its accuracy is still limited. iii. proposed architecture for logo recognition cnns are one of the most powerful deep learning models. a cnn is composed of multiple layers of convolution, pooling, relu correction and fully-connected (fc) stocked in a robust manner. cnn models have demonstrated an impressive ability to generalize large datasets with millions of images. the input image passes through multiple hidden layers to be filtered, corrected, and compressed many times, to finally form a vector. for the classification task, the output vector presents the probabilities of class membership. all cnns must start with a convolutional layer and end with a fully-connected layer. the intermediate layers can be stacked in different ways, provided that the output of one layer has the same structure as the input of the next. in general, a cnn stacks multiple convolution and relu correction layers then adds a pooling layer (optional), and repeats this pattern multiple times. then, it stacks the fc layers. the more layers there are, the more “deep” the neural network is. to get more accurate cnns and achieve better results, we must use a model that can learn more competitive representations without a dramatic increase in network parameters. as we tackle recognition with a limited amount of original data, we are interested in efficient representations that can be achieved with a small number of parameters. in effect, exploring the densely connected convolutional networks (densenet) [14] can lead to efficient results. in densenet, the original cnn layers are replaced by dense blocks and transition layers except for the first convolutional layer. it outperforms the state-of-the-art cnn models in the classification task on many datasets using a lower complexity network. a densenet architecture with three dense blocks and two transition layers is illustrated in figure 1. fig. 1. densenet architecture. densenet is a revolutionary deep cnn with a stack of dense blocks and transition layers. a dense block is a group of convolution layers in which the layers are densely connected. each layer receives as input all previous layers’ outputs. a single dense block packs convolution layers followed by a relu activations layer and a batch normalization layer. to reduce the size of the feature maps, densenet uses transition layers which are composed of a batch normalization layer, followed by a 1×1 convolution and a 2×2 average pooling. the transition layer reduces the height and the width dimensions but leaves feature dimensions the same. the densenet stacks hundreds of layers without any optimization complexity. thus, densenet is one of the best deep cnn models for image classification and object recognition tasks. in order to classify logos, our custom-made model consists of four dense blocks and three transition layers. figure 2 presents the proposed cnn model. before the first dense block, a 7×7 convolution layer and a 3×3 max pooling layer are performed on the input images to extract more important features in order to detect small variations in the image. between each consecutive dense blocks, a transition layer composed of a 1×1 convolution followed by 2×2 average pooling layers was used. a 7×7 global average pooling layer with stride of 2 is placed after the fourth dense block to fix the size of the feature maps to be connected to the fully connected layer. finally, the transfer learning technique was used to configure the output layer for the logos classes instead of the original imagenet dataset classes [15]. fig. 2. the architecture of the proposed cnn model. densenet was trained to classify natural images according to the imagenet with 1000 classes. the transfer learning technique was applied which allows the reuse of existing deep cnn models without the need of a long time computing. the main idea of the transfer learning technique is to reuse the existing cnn models designed for a special application for a new application. in addition to accelerating network training, transfer learning helps prevent overfitting. indeed, when the engineering, technology & applied science research vol. 10, no. 5, 2020, 6191-6194 6193 www.etasr.com alsheikhy et al.: logo recognition with the use of deep convolutional neural networks collection of input images is limited, it is hard to train the cnn from scratch with random weight initialization. in effect, the number of parameters to learn is much higher than the number of images and this may lead to the risk of overfitting. so, implementing this technique is very effective and it is widely used in practice. it requires having a cnn already trained, preferably on a problem close to the one we want to solve. iv. experiments and results in order to evaluate the proposed model, the flickrlogos32 logo recognition dataset [7] was used for training and testing. flickrlogos-32 is a publicly-available dataset with a collection of 8240 real-world images of 32 different brand logos from flickr and it was built for the evaluation of logo retrieval and multi-class logo detection and recognition systems. the dataset was divided into three separated subsets: p1, p2, and p3. each subset contains images of all the 32 classes. the training set p1 contains 320 images, 10 images per class, while both the validation set p2 and the test set p3 consist of 3960 images each containing both 30 positive examples per class and 3000 negative examples containing no logos. figure 3 shows sample images of 32 logo classes of the flickrlogos-32 dataset. all experiments were performed using the caffe (convolutional architecture for fast feature embedding) framework [16] on an nvidia tesla k40c gpu with 12 gb ram. caffe is a deep learning framework written in c++, with a python interface. it supports many different types of deep learning architectures geared towards image classification and image segmentation. fig. 3. the 32 classes of the flickrlogos-32 dataset. the weights of our custom-made network were initialized with a pre-trained densenet model on the imagenet dataset. then, the network was fine-tuned on the flickerlogo32 training set. in effect, the pre-trained weights were loaded to the first convolution layer, the dense blocks, and transition layers while the weights of the output layer were updated until optimizing the loss function. then, the entire network including the first convolution layer was fine-tuned using the validation set. after the training of our model, the test set p3 was used for testing. table i shows the achieved accuracy of the custommade network compared to existing models. the proposed model achieves state-of-the-art performance with high classification accuracy. we can see that 92.8 % of average accuracy was achieved compared to 91.7 % achieved in [2]. table i. classification accuracies on flick rlo gos-32 dataset method dropout pretrain finetune accuracy [3] 0.5 imagenet-2012 flickrlogos-32 70.1% [3] (fullinception) 0.7 imagenet-2012 flickrlogos-32 77.1% [3] (googlenet) 0.7 imagenet-2012 flickrlogos-32 87.6% 0.8 imagenet-2012 flickrlogos-32 88.7% [3] (googlenetgp) 0.8 imagenet-2012 flickrlogos-32 89.1% 0.9 imagenet-2012 flickrlogos-32 89.6% [2] flickrlogos-32 91.7% [4] flickrlogos-32 84.6% [1] flickrlogos-32 88.9% proposed 0.9 imagenet-2012 flickrlogos-32 92.8% v. conclusion logo recognition is considered an important task for many applications. in this paper, a deep cnn model was designed for logo recognition based on the densenet model. the proposed model was trained and tested on the flickerlogo32 dataset. the obtained results were very encouraging compared to the state-of-the-art works. the proposed logo recognition and classification model can be used in many applications like online brand management and contextual advertisement placement. as potential future works, the design of a real-time logo recognition system for a mobile application may be considered. acknowledgment the authors wish to acknowledge the approval and the support of this research study by the grant n°eng-2019-1-10f-8140 from the deanship of the scientific research in northern border university, arar, ksa. references [1] r. boia, a. bandrabur, and c. florea, “local description using multiscale complete rank transform for improved logo recognition,” in 2014 10th international conference on communications (comm), may 2014, pp. 1–4, doi: 10.1109/iccomm.2014.6866723. 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[13] t. williams and r. li, “an ensemble of convolutional neural networks using wavelets for image classification,” journal of software engineering and applications, vol. 11, no. 2, pp. 69–88, feb. 2018, doi: 10.4236/jsea.2018.112004. [14] g. huang, z. liu, l. van der maaten, and k. q. weinberger, “densely connected convolutional networks,” in 2017 ieee conference on computer vision and pattern recognition (cvpr), jul. 2017, pp. 2261– 2269, doi: 10.1109/cvpr.2017.243. [15] o. russakovsky et al., “imagenet large scale visual recognition challenge,” international journal of computer vision, vol. 115, no. 3, pp. 211–252, dec. 2015, doi: 10.1007/s11263-015-0816-y. [16] y. jia et al., “caffe: convolutional architecture for fast feature embedding,” in proceedings of the 22nd acm international conference on multimedia, nov. 2014, pp. 675–678, doi: 10.1145/2647868.2654889. [17] u. khan, k. khan, f. hassan, a. siddiqui, and m. afaq, “towards achieving machine comprehension using deep learning on non-gpu machines,” engineering, technology & applied science research, vol. 9, no. 4, pp. 4423–4427, aug. 2019. [18] y. said, m. barr, and h. e. ahmed, “design of a face recognition system based on convolutional neural network (cnn),” engineering, technology & applied science research, vol. 10, no. 3, pp. 5608–5612, jun. 2020. [19] y. f. said and m. barr, “pedestrian detection for advanced driver assistance systems using deep learning algorithms,” international journal of computer science and network security, vol. 19, no. 9, pp. 9–14, sep. 2019. engineering, technology & applied science research vol. 7, no. 2, 2017, 1559-1566 1559 www.etasr.com khoobiyan et al.: taxonomy of manufacturing flexibility at manufacturing companies using… taxonomy of manufacturing flexibility at manufacturing companies using imperialist competitive algorithms, support vector machines and hierarchical cluster analysis mehdi khoobiyan department of management, ferdowsi university of mashhad, mashhad, iran khoobiyanm@yahoo.com alireza pooya department of management, ferdowsi university of mashhad, mashhad, iran alirezapooya@um.ac.ir ahmad tavakkoli department of management, ferdowsi university of mashhad, mashhad, iran tavakoli-a@um.ac.ir fariborz rahimnia department of management, ferdowsi university of mashhad, mashhad, iran r-nia@um.ac.ir abstract—manufacturing flexibility is a multidimensional concept and manufacturing companies act differently in using these dimensions. the purpose of this study is to investigate taxonomy and identify dominant groups of manufacturing flexibility. dimensions of manufacturing flexibility are extracted by content analysis of literature and expert judgements. manufacturing flexibility was measured by using a questionnaire developed to survey managers of manufacturing companies. the sample size was set at 379. to identify dominant groups of flexibility based on dimensions of flexibility determined, hierarchical cluster analysis (hca), imperialist competitive algorithms (icas) and support vector machines (svms) were used by cluster validity indices. the best algorithm for clustering was svms with three clusters, designated as leading deliverybased flexibility, frugal flexibility and sufficient plan-based flexibility. keywords-manufacturing flexibility; taxonomy; dominant groups; hierarchical cluster analysis; support vector machines; imperialist competitive algorithm. i. introduction in a stable environment, the concept of traditional management helps organizations achieve success. however, this management approach is restricted in preparing organizations to deal with environmental uncertainty. for this reason, new management theories have focused on the development of flexibility as an alternative approach for traditional management [1]. adaptability of a company with environmental uncertainty is heavily influenced by manufacturing flexibility [2]. in [3], authors stated that customer satisfaction and supplier trust is a key success in turbulent environments in which frequent changes are made in product features and volume of demand; to achieve these goals, the company needs flexibility. meanwhile, it seems reasonable to employ a manufacturing strategy which is the effective utilization of manufacturing capabilities as a competitive tool in order to achieve organizational goals and improve performance. one of the most important manufacturing capabilities is manufacturing flexibility; according to [4], manufacturing flexibility refers to the ability to change or to meet or achieve minimum loss in time, cost and performance. recent economic developments indicate that manufacturing flexibility is more important than ever; flexibility is considered as the main goal of many manufacturing systems [5]. during the recent decade, manufacturing flexibility has been addressed by academy and industry; moreover, research has been done on definitions, classification and identification of different dimensions of flexible manufacturing [6-9]. investment in manufacturing flexibility enables organizations to reconfigure or reduce uncertainty and create competitive position, or hold their capabilities to understand future uncertainty in order to adapt to uncertainty better [10]. manufacturing flexibility can be a vital and definitive source of competitive advantage, although it is the most difficult goal to achieve [4, 11]. in [12], author distinguished the difficulty in achieving manufacturing flexibility; as he suggested, this should not be considered as a commodity which can be bought from shops and used directly, but rather, it should be carefully planned and managed [13-16]. it is assumed that the organization can be flexible in some ways and less flexible in some others. managers should focus on proper dimensions of adaptation to their company and develop a particular set of manufacturing flexibility [17]. manufacturing flexibility has diverse dimensions and nature. its dimensions were first introduced in [18] as flexibility of machine, process, product, production line, production volumes, development, operation and production. interestingly, two studies conducted to determine types of manufacturing flexibility in organizations provided similar results; however, they addressed the same industry and there are similar competitive features in a specific industry [6]. in [5], authors stated that a certain degree of manufacturing flexibility is a future priority. dimensions of flexibility applied engineering, technology & applied science research vol. 7, no. 2, 2017, 1559-1566 1560 www.etasr.com khoobiyan et al.: taxonomy of manufacturing flexibility at manufacturing companies using… to any organization do not necessarily improve performance and may even reduce it; therefore, additional time and expense spent to implement dimensions which do not fit manufacturing organizations should be avoided [19, 20]. as noted earlier, works such as [17-18, 21] presented different dimensions for manufacturing flexibility of industrial organizations and showed that organizations use different dimensions of manufacturing flexibility based on their conditions and characteristics. in [6, 17] it was proposed that different organizations need to focus on different dimensions of manufacturing flexibility. however, none of these works have determined a harmonious and congruent combination of dimensions which can be planned and implemented in a company. in other words, they have not determined the dominant groups of manufacturing flexibility and their dimensions which are more efficient and effective for a company. in addition to the identification of these dimensions, manufacturing companies with different characteristics need to know the above factors, an issue that is addressed in this study. moreover, this study compares different algorithms for taxonomy and selection of dominant groups of manufacturing flexibility to select the best clusters by choosing the most efficient algorithm by cluster validity indices. for this purpose, this study reviews the literature and determines dimensions of manufacturing flexibility to identify the dominant groups of manufacturing flexibility; finally, different dominant strategic groups of flexibility are designated and conclusions and suggestions are made for future studies. ii. literature review management literature shows that flexibility is considered a positive asset [22]. organizations require flexible manufacturing to manage uncertainties in their environment [23]. however, since term flexibility is used excessively, its detailed concept is not clear [24]. in general, flexibility can be considered as an indicator linking the system and its external environment to absorb uncertainty, dynamics of the system as well as the ability to change and adapt [25]. scholars have used different types of flexibility for manufacturing flexibility. for example, in [9] authors divided flexibility in three groups: flexibility in decision making theory, flexibility in economy theory and flexibility in manufacturing systems. in the past few decades, the concept of manufacturing flexibility has been a key competitive criterion for many manufacturing organizations. a series of studies has been performed by different scholars on different aspects of flexibility [26]. in [27], authors stated that the above concept refers to the ability of the manufacturing system to adapt to changing and dynamic environment; another appropriate definition can be the ability of the system to cope with changes related to devices, processes and products [28]. however, in [2] authors stated that flexible manufacturing is the ability to produce a great variety of key features of the product; in overall, manufacturing flexibility can only be seen in output. the most inclusive definition which has been raised so far is the ability to change or react with the least possible loss in time, cost and performance [24]. all definitions specify three points: first, they all determine the extent and diversity of the subject; second, they agree that flexibility is the ability to respond to change; third, that flexibility has been proposed against uncertainty. according to [29], evidence shows discrepancies in existing definitions of flexibility; it is thus proposed that the concept is not well understood yet. to understand flexibility, it is essential to consider various aspects such as definition of flexibility, types of flexibility, criteria of flexibility and its effect on investment decisions [30]. manufacturing flexibility is a multidimensional phenomenon. in [18], authors presented eight dimensions of flexibility including machine, process, product, production line, production volume, extension, operation and production; then, other dimensions such as handling, labor, plan, market, delivery, moderation and services were added to the above dimensions [31]. a number of scholars have addressed manufacturing flexibility with a special glance at several dimensions. for example, in [32] eight dimensions were identified and in [33] eleven dimensions were identified. there are different classification logics including horizontal classification, vertical classification, time-based classification, target-based classification and combined classification for interpretation of various aspects of manufacturing flexibility [25]. in [6], authors presented a new classification for types of manufacturing flexibility. in [26], it was showed that manufacturing flexibility and labor flexibility has a positive effect on product innovation. in [34], it was concluded that formal organizational structures along with manufacturing flexibility improve performance. in [29], authors presented a new classification of previously known flexibilities. essential flexibility includes machine, product, labor, transportation, track and volume; components of sufficient flexibility include processes, operations, plans and materials; components of competitive flexibility include production, development and market. in [2], authors developed a model which considered manufacturing flexibility as a dynamic capability. in [3], authors presented a new business model for flexible organizations. in [35] 6 widely used dimensions of flexibility were measured. in [36] drivers and factors of flexibility in an unpredictable, unstable and operational environment of manufacturers were discussed. in [37], a conceptual model by using only two dimensions, production volume and process, was developed to show the effect of manufacturing flexibility on performance. according to [18, 31-33] that identified dimensions of manufacturing flexibility, the present study comprehensively addresses these dimensions, taxonomy of manufacturing companies based on these dimensions by comparing different grouping techniques and determines dominant groups of flexibility. iii. materials and methods a. population and sample this study addressed manufacturing flexibility in 379 manufacturing companies from seven industries as listed in table i. the distributed questionnaires were filled by top managers. engineering, technology & applied science research vol. 7, no. 2, 2017, 1559-1566 1561 www.etasr.com khoobiyan et al.: taxonomy of manufacturing flexibility at manufacturing companies using… table i. the studied companies industry food & beverage metal electrical & electronics chemical textile cellulose non-metallic mineral total n 135 144 35 26 19 11 9 379 studied company % 36 38 9 7 5 3 2 100 b. data collection and validation content analysis was used to identify the dimensions of manufacturing flexibility. based on this analysis, 18 dimensions of manufacturing flexibility were identified and are listed in table ii. to enrich the analysis, ten academic and industrial experts were asked to review the dimensions and provide their feedbacks about their relationship with flexibility and their differentiation from other dimensions. then, three dimensions including quality of input materials, quality and automation were discarded because their score was less than mean. new design was also considered as a part of new product; thus, this dimension was also discarded. table ii. dimensions of manufacturing flexibility dimensions definition literature 1 new product ability to change current product or produce new product quickly at minimal cost [6, 11, 17, 21, 23, 25, 28-29, 31-36] 2 production volume ability to take orders and produce at different volumes ranging from low to high profitably [6, 11, 21, 23, 25, 28-29, 31-36] 3 machine (machines) ability to perform various operations by machine without the need for spending too much time and cost to shift from one operation to another [6, 11, 21, 23, 25, 28-29, 31-35] 4 material handling ability of material handling system to transfer materials effectively to different parts in proper situations and process them for the required production unit [6, 11, 21, 23, 25, 28-29, 31-35] 5 product mix (process) ability to produce a large variety of products without inclusion of fines or large changes in performance of the final product [21, 23, 26, 29, 32-37] 6 extension ease of development of system capacity at the right time [6, 11, 21, 25, 28-29, 31-33] 7 labor ability of personnel to perform various tasks and their multidisciplinary nature [21, 23, 26, 29, 32-36] 8 routing ability to produce alternative routes (by different machines and operations) [6, 11, 21, 23, 25, 28-29, 31, 33] 9 plan ability of the system to work continuously without supervision and inspection (as long as the system can work without supervision, inspection, repair and maintenance) [6, 11, 23, 25, 28-29, 31] 10 market ability to adapt the production system easily to changing market conditions [6, 11, 25, 28-29, 31-32] 11 production ability to produce diverse parts / products without adding capital equipment [6, 11, 25, 28-29, 31] 12 operations ability to produce by different methods with alternative processing schemes or through interaction with or replacement of some operations by other types of operations [6, 21, 25, 28-29, 31] 13 delivery ability to shorten and extend delivery time and ability to prepare changing demands in a short time [6, 23, 33, 36] 14 modification ability to correct products without inclusion of fines or large changes in performance of final product [21, 35] 15 quality of input materials ability to use different quality inputs [29, 33] 16 quality ability of the system to change quality of product or products to fit the market demand [36] 17 automation level of automation and computerization of manufacturing technologies [6] 18 new design ability to design and introduce the product rapidly to the manufacturing system [6] then, the manufacturing flexibility questionnaire was developed based on 14 dimensions remaining. this questionnaire was composed of two parts; the first part involved demographic variables and the second part consisted of 14 dimensions and 45 scales. the questions were scored on a 5-point scale from very low to very high. the questionnaires were distributed among top managers of manufacturing companies. to avoid ambiguity, problems of managers with the questionnaire were resolved in person. content validity was used to validate the questionnaire. first, dimensions were extracted and listed in tables with their definitions in farsi and english and references; the listed dimensions were modified and approved by academic experts. second, the scales related to each dimension were listed in tables with their definitions in farsi and english and references and presented to experts; the listed scales were modified and approved by academic experts. third, dimensions and scales were presented to industrial experts; once they approved the dimensions and scales, the questionnaire was designed and used. convergent validity was used to determine construct validity by using confirmatory factor analysis (cfa). varimax rotation was used to validate the manufacturing flexibility questionnaire. kmo of a construct represents sampling adequacy for factor analysis. significance level of bartlett's test also shows that factor analysis can be used to identify constructs. there are different methods which can be used to determine reliability of the questionnaire. one of these methods is internal consistency. c. data analysis hierarchical cluster analysis (hca), imperialist competitive algorithms (icas) and support vector machines (svms) were used to cluster and identify dominant groups of manufacturing flexibility. matlab and r were the software used. six cluster validity indices were used to compare results of three algorithms and select the best results. clustering refers to splitting a heterogeneous group into several homogeneous engineering, technology & applied science research vol. 7, no. 2, 2017, 1559-1566 1562 www.etasr.com khoobiyan et al.: taxonomy of manufacturing flexibility at manufacturing companies using… subgroups to maximize between-group difference and minimize within-group difference [38]. there are two types of cluster analysis, hierarchical and non-hierarchical; hierarchical clustering is known as the most widely used cluster analysis. since the number of flexible clusters was not clear initially, hca was used in this study. svms can be considered as one of the most effective statistical training methods for classifying data. svms acts by findings support vectors and finding linear machines at high-dimensional feature space but non-linearly associated with input data space. svms are widely used as a fast method for classifying data [39]. icas are one of the new meta-heuristic methods [40]. although icas has been invented for few years, they been used in many problems such as skeletal structure design [41], data clustering [42], linear induction motor [43]. in addition to their efficiency, rapid convergence and high ability to optimize compared to existing algorithms [44], icas are highly preferred for their innovation and attractiveness. there are different methods and indices used to validate the results of clustering by different algorithms. this study used six cluster validity indices noted by different works such as [45-47]. the most efficient algorithm was the one in which all six indices were in better position. these indices included davies and bouldin index, dunn index, gdi11 index, wemmertgancarski index, ratkowsky-lance index, and calinskiharabasz index. note that the best value is characterized by the least value for davies and bouldin index and the highest value for other indices. iv. results a. validity and reliability as shown in table iii, kmo>0.5, p-value<0.05 and α>0.6 indicate good validity and reliability of the questionnaire. b. taxonomic results since the number of clusters was not clear initially in hca, dendrograms of 379 observations were plotted. figure 1 shows the dendrogram of 379 companies. according to the dendrogram and placement of observations in clusters, judgements can be made about the number of clusters. as shown in the figure, there are at least 5 clusters in the dendrogram. to evaluate minimum and maximum clusters possible, the number of clusters was set at 3 to 8 and observations were examined by six indices. the results are presented in table iv. the best number of clusters for hca was six. to cluster by svms, it is required to use a primary clustering. for this purpose, a part of data (data related to 100 companies) was used as training data based on which the model was trained. then, all data was used for clustering. primary clustering was done initially; training data was clustered by using k-means in 100 iterations assuming five clusters. the result was used to train the svms. the second row of table iv shows the results of 3 to 8 clusters examined by six different indices in svms. as the results show, the best number of clusters was three. three to eight clusters were created and the output was used for examining the indices. the third row of table iv shows the results of icas for different indices. as the results show, the best number of clusters was three. c. comparison of different clustering algorithms to select the most efficient algorithm table v was developed by considering the best number of clusters identified in table iv. this table lists the value of evaluation criteria for the selected number of clusters. for example, 0.1771 is the value of wemmert-gancarski for six clusters, and so on. as noted earlier, the best value is the least for davies-bouldin and the highest for other indices. therefore, the best values of indices in different algorithms and consequently the best algorithm are listed in the fifth and sixth row of table v. the sixth row shows the selected number of clusters for the selected algorithm. as shown in the table, three clusters have the highest selection in different indices. d. cluster designation considering three clusters for svms, table vi lists the results of cluster analysis for mean of different dimensions, rank of each dimension in each cluster and among other clusters. 1) cluster 1: delivery-based leading flexibility cluster cluster 1 was the first between three clusters in terms of production volume, new product, process, extension, labor, market, production, delivery and modification; moreover, delivery was the first dimension within the cluster 1. thus, cluster 1 was designated as delivery-based leading flexibility cluster. therefore, it can be claimed that the companies located in this cluster are leading in a large number of dimensions of flexibility and particularly consider delivery. they are able to deliver goods at different times to meet customer demand. 2) cluster 2: frugal flexibility cluster 2 was designated as frugal flexibility cluster. similar to the essential flexibility cluster of [29] which was the top priority in terms of machinery and routing, machinery and routing were the first in the cluster 2 between clusters and other dimensions were the third. within the cluster 2, machinery was the first. this indicates flexibility of machinery and the ability to perform different operations by machinery in this group. 3) cluster 3: plan-based sufficient flexibility the third cluster was designated as plan-based sufficient flexibility. the cluster 3 was the first between other clusters in terms of material handling, operation and plan. sufficient flexibility cluster of [29] also involved operation and plan. the plan-based sufficient flexibility cluster was the second between clusters in terms of other dimensions. plan was the first within the cluster 3; this indicates particular attention to system planning in this cluster. the companies located in this cluster can operate without monitoring and inspection for a longer time. engineering, technology & applied science research vol. 7, no. 2, 2017, 1559-1566 1563 www.etasr.com khoobiyan et al.: taxonomy of manufacturing flexibility at manufacturing companies using… table iii. validity and reliability of manufacturing flexibility questionnaire construct scale factor loading kmo bartlett iteration adjusted variance mi1 0.76 0 1 mi2 0.65 0 1 mi3 0.5 0 1 mi4 0.75 0 1 mi5 0.5 0 1 mi6 0.59 0 1 product mix mi mi7 0.51 0.79 0 1 0.68 0.78 v1 0.73 0 1 production volume v v2 0.73 0.58 0 1 0.63 0.6 np1 0.76 0 1 np2 0.81 0 1 new product np np3 0.65 0.63 0 1 0.64 0.67 ma1 0.68 0 1 ma2 0.77 0 1 machine ma ma3 0.64 0.61 0 1 0.66 0.69 mh1 0.56 0 1 mh2 0.53 0 1 mh3 0.5 0 1 mh4 0.72 0 1 mh5 0.51 0 1 material handling mh mh6 0.49 0.72 0 1 0.69 0.71 e1 0.76 0 1 e2 0.73 0 1 extension e e3 0.73 0.64 0 1 0.65 0.68 l1 0.48 0 1 l2 0.78 0 1 labor l l3 0.78 0.66 0 1 0.63 0.67 ro1 0.68 0 1 routing ro ro2 0.68 0.59 0 1 0.62 0.65 p1 0.5 0 1 plan p p2 0.5 0.61 0 1 0.62 0.69 mar1 0.67 0 1 market mar mar2 0.67 0.54 0 1 0.57 0.6 pr1 0.62 0 1 production pr pr2 0.62 0.55 0 1 0.54 0.62 o1 0.61 0 1 operation o o2 0.61 0.57 0 1 0.53 0.69 d1 0.66 0 1 d2 0.6 0 1 delivery d d3 0.46 0.62 0 1 0.66 0.68 mo1 0.48 0 1 mo2 0.67 0 1 mo3 0.50 0 1 mo4 0.70 0 1 modification mo mo5 0.74 0.7 0 1 0.64 0.71 table iv. number of clusters in three algorithms by using six cluster validity indices evaluation indices algorithm wemmert-gancarski ratkowsky-lance gdi11 dunn calinski-harabasz davies-bouldin frequency hca 6 4 6,7,8 6,7,8 4 5 6(3) svm 3 3 3 3 3 5 3(5) ica 3 3 5 5 3 8 3(3) v. discussion and conclusion content analysis was used to identify dimensions of manufacturing flexibility. then, experts were asked to provide their judgments on these dimensions and their relevance to industries existing in iran. content analysis showed that frequency, new product, production volume and machinery, respectively, were the most iterated dimensions in previous research. considering different judgements of experts on relevance of these dimensions to the industries existing in iran, content analysis of dimensions of manufacturing flexibility showed that priority of these dimensions is completely different for industrial organizations which seek for manufacturing engineering, technology & applied science research vol. 7, no. 2, 2017, 1559-1566 1564 www.etasr.com khoobiyan et al.: taxonomy of manufacturing flexibility at manufacturing companies using… flexibility in different dynamic environments and in different industries. this has also been noted in previous works [5, 6, 12, 17]. hca, icas and svms were used for taxonomy, clustering and identifying dominant groups of manufacturing flexibility. the results of clustering were evaluated by using cluster validity indices. the results indicated three dominant groups of flexibility considering 14 dimensions of manufacturing flexibility; these groups were designated as delivery-based leading flexibility, frugal flexibility and plan-based sufficient flexibility. new product was the first to third priority in all groups, which indicates high importance of new product. considering the change in customer needs and high competition in the market, it is particularly important to consider this dimension in all companies. this was not unexpected, because many previous studies such as [6, 11, 17, 21, 23, 25, 28, 29, 31-36] have noted this previously. new product was the most iterated dimension (14 iterations) in content analysis. unlike new product, production was the last dimension in three clusters; this indicates that production could not influence flexibility of iranian industries or at least companies could not be flexible in this dimension. this can be attributed to mass production system used in majority of iranian companies. this system is not flexible to changing needs of customers in minimum cost and short time. routing was one of the last dimensions in all the clusters; this indicates weakness of manufacturing companies in implementing this dimension of flexibility in their production system. this can be attributed to lack of flexibility of mass production system and expensiveness of production through different routes for manufacturing companies. that is why companies are less likely to work on this dimension. priority of dimensions of flexibility is different in most companies which are located in different clusters. delivery is the first priority in the cluster 1, while it is the fourth priority in the cluster 2 and 3. moreover, machinery is the first priority in the cluster 2, while it is the eighth priority in the cluster table v. results of evaluation indices for the appropriate number of clusters in different algorithms evaluation indices algorithm wemmertgancarski ratkowskylance gdi11 dunn calinskiharabasz daviesbouldin hca 0.1771 0.2460 0.1442 0.1442 40.4149 1.6898 svm 0.2121 0.2716 0.1764 0.1764 55.8881 1.3823 ica 0.1572 0.2536 0.1442 0.1442 46.7893 1.0834 optimum 0.2121 0.2716 0.1764 0.1764 55.8881 1.0834 the best algorithm svm svm svm svm svm ica appropriate number of clusters 3 3 3 3 3 8 table vi. results of cluster analysis for classifying manufacturing companies based on dimensions of manufacturing flexibility cluster mi v n ma mh e l ro p mar pr o d mo industry mean 3.09 3.52 3.03 3.08 3.04 3.49 3.39 3.89 2.98 3.37 2.87 2.96 3.61 3.19 wc rank 7 2 10 8 9 3 4 13 11 5 14 12 1 6 1 bc rank 1 1 1 3 2 1 1 2 2 1 1 2 1 1 122 mean 2.72 3.06 2.78 3.34 2.83 2.98 2.97 2.91 2.47 2.93 2.7 2.75 2.97 2.87 wc rank 11 2 9 1 8 3 4 6 13 5 12 10 4 7 2 bc rank 3 3 3 1 3 3 3 1 3 3 3 3 3 3 116 mean 2.97 3.25 2.85 3.28 3.17 3.19 3 2.78 3.3 3.21 2.81 2.98 3.23 3.06 wc rank 11 3 12 2 7 6 9 14 1 5 13 10 4 8 3 bc rank 2 2 2 2 1 2 2 3 1 2 2 1 2 2 141 fig. 1. complete dendrogram for the 379 companies • plan is the first priority in the cluster 3, while it is the eleventh priority in the cluster 1. • these different priorities suggest that different industries do not use different dimensions of manufacturing flexibility similarly. this has been supported by [5, 6, 17]. as the results show, food and beverage industry is the most frequent industry in cluster 1; 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[47] k. p. agrawal, s. garg, p. patel, “performance measures for densed and arbitrary shaped clusters”, international journal of computer science & communication, vol. 6, no. 2, pp. 338-350, 2015 microsoft word etasr_v10_n6_pp6597-6602 engineering, technology & applied science research vol. 10, no. 6, 2020, 6597-6602 6597 www.etasr.com mahessar et al.: rainfall analysis for hyderabad and nawabshah, sindh, pakistan rainfall analysis for hyderabad and nawabshah, sindh, pakistan ali asghar mahessar sindh barrages improvement project sindh irrigation department karachi, sindh pakistan abdul latif qureshi u.s.-pakistan centers for advanced studies in water mehran university of engineering and technology jamshoro, sindh, pakistan bushra sadiqui institute of water resources engineering and management mehran university of engineering and technology jamshoro, sindh, pakistan shafi muhammad kori department of civil engineering mehran university of engineering and technology jamshoro, sindh, pakistan kishan chand mukwana environmental and energy department quest nawabshah, pakistan abdul sami qureshi mehran university of engineering and technology szab campus khairpur mirs, sindh pakistan khalifa qasim leghari department of civil engineering mehran university of engineering and technology jamshoro, sindh, pakistan abstract-the climatic change has a visible impact in recent abnormal weather events, such as pakistan’s intensification of the hydrological cycle with changing precipitation pattern, water availability periods, and weather-induced natural disasters. the rainfall flush flood of 2010 alone displaced millionσ of people and damaged properties in just one stroke. the next year, the shocking rainfall flood of 2011 in sindh, only underscored the enormity of the challenge posed by climate change. the current paper presents the analysis carried out for one-day annual maximum rainfall for hyderabad and nawabshah cities, sindh, pakistan for the period from 1961 to 2011 using statistica software for interpolating and forecasting the rainfall time series. the maximum values of observed rainfall were 250.70mm and 256.30mm, while the minimum values were 3.0mm and 0.0mm for hyderabad and nawabshah respectively, while the mean of fifty-one (51) years of rainfall data is 51.96mm and 45.3 mm and the computed standard deviations were 42.693mm and 43.896mm respectively. the difference between the mean and standard deviation of one-day maximum rainfall is small, which showed the consistency of the data. the polynomial trend curved lines exhibited fluctuations in the rainfall data, which indicates a continual change in rainfall behavior. hence, the rainfall data are subjected to a moving mean smoothing with a duration shorter than 3 years. through these trends, the future one-day annual maximum rainfall can be predicted. the correlation of one-day annual maximum rainfall between hyderabad and nawabshah cities had r2 of 0.973. the computed results of return periods of 3, 5, and 10 years for one-day annual maximum rainfall for both cities revealed that the rainfall values for hyderabad are higher. keywords-rainfall; hyderabad; nawabshah; statistica; gis i. introduction the equilibrium of heat absorption and reflection from the earth is of paramount importance. changes in global temperature delicate heat unbalance and are the crucial factor for climate change. the overexploitation of resources has modified the earth and its atmosphere in a way that alters the climate of the globe. climate variables such as precipitation, temperature, humidity, and wind reach extreme conditions, hence, rainfall occurs abnormally [1-2]. any change in global climate has massive impacts to humanity and the environment [3]. rainfall variability rests on the movement of the atmosphere and its characteristics which are described as weather. scientists have been trying to characterize the weather for several decades [4]. water is a basic substance, required for the survival of life. normal precipitation is a part of the continuous process of the hydrologic cycle. the summer rainfall concentrates monsoon breaths formed from the bay of bengal and arriving pakistan from india. another mechanism of monsoon precipitation is the flow of moisture from the arabian sea. these phenomena strengthen the rainfall process and produce erratic intensity rainfalls in a short time [5, 6]. the seasonal unusual rainfall of july to september, 2011 over corresponding author: a. a. mahessar (amahessar@yahoo.com)corresponding author: a. a. mahessar (amahessar@yahoo.com) engineering, technology & applied science research vol. 10, no. 6, 2020, 6597-6602 6598 www.etasr.com mahessar et al.: rainfall analysis for hyderabad and nawabshah, sindh, pakistan pakistan, was 72% above normal (1961 to 1990) and is ranked as the fifth monsoon rainfall during the last 51 years. this seasonal rainfall was about 248% above the normal in sindh province [7]. based on 30 years of meteorological data, pakistan can be climatically divided into eight zones [8]. nawabshah comes in a zone of hot long summers and warm short winters, whereas hyderabad comes in the zone of hot long summers and mild short winters [9]. extraordinary heavy rainfall and cloud burst alarm about the change in climate. it is quite clear that the cities under study (i.e. hyderabad and nawabshah) are under unreliable rainfall zones, which shows an alarming change in climate which needs to be studied [10]. ii. study area and climatic conditions the two studied cities (hyderabad and nawabshah) are located at 25°22′45″n latitude and 68°22′06″e longitude and at 26°15′00″n latitude and 68°25′25″e longitude respectively. they are heavily populated, with no rainwater disposal drainage system, and are located at the center of sindh, on the left side of river indus [11-13]. climatically, these cities are situated in tropical and semi-tropical condition with the maximum and minimum temperatures varying from 46°c, to 02°c, in hyderabad and from 52°c, to 0°c, in nawabshah. the mean monthly maximum temperature in the summer season is about 43 o c to 44 o c, while during the winter, the minimum temperature is about 7 o c. western disturbances, dust storms, south east monsoon, and continental air are the main factors influencing the weather. from the hydrological perspective, the study areas belong to the arid and semi-arid region type, with a low precipitation average of 100mm and brackish and saline groundwater quality. fig. 1. the map shows the heavy rainfalls in sindh, paksitan (© sindh irrigation and drainage authority, hyderabad, sindh). iii. data collection the research study is based on the annual daily maximum rainfall for hyderabad and nawabshah. in this regard, the required data from a period from 1961 to 2011 were collected from pakistan meteorological department (pmd) for statistical analysis [9]. time series analysis is a time-consuming process, so the statistical software statistica was utilized to do the task with minimum computing cost [14-16]. it is a spread sheet-based statistical analysis software package, which provides the user with a graphical interface, the tools to perform simple analyses such as mean, mode, median, range, trends, and moving mean, all types of distributions and tests like t, f, z, etc., deviation, regression, anova, etc. it also creates two and three dimensional graphical displays of data. statistica has more than 14,000 statistics functions. the chronological daily maximum rainfall (1961-2011) data for hyderabad and nawabshah are shown in figures 2 and 3, which do not show a definite trend. fig. 2. one-day annual maximum rainfall (1961-2011) for hyderabad. fig. 3. one-day annual maximum rainfall (1961-2011) for nawabshah. the research objective is to study the time series characteristics of one day annual maximum rainfall at hyderabad and nawabshah through statistica for smoothing, interpolating, modeling, and future forecasting. iv. results and discussion a. rainfall data collection figures 4 and 5 display the representation outputs using statistica in terms of deviation of one-day annual maximum rainfall of hyderabad and nawabshah respectively from their respective mean rainfall value. these figures exhibit that the maximum positive deviation is about 200 and more than 200mm for hyderabad and nawabshah respectively, whereas the maximum negative deviation is less than 50mm. b. basic statistical parameters the basic statistical parameters maximum, minimum, mean, mode, median standard deviation, and coefficient of variance (cv) for the collected data series are described in table i. 0 50 100 150 200 250 300 1955 1965 1975 1985 1995 2005 2015 year o n e -d a y a n n u a l m a x im u m r a in fa ll (m m ) 0 50 100 150 200 250 300 1955 1965 1975 1985 1995 2005 2015 year o n e -d a y a n n u a l m a x im u m r a in fa ll (m m ) engineering, technology & applied science research vol. 10, no. 6, 2020, 6597-6602 6599 www.etasr.com mahessar et al.: rainfall analysis for hyderabad and nawabshah, sindh, pakistan mean deviation of annual maximum rainfall at hyderabad year r a in fa ll ( m m ) -50 0 50 100 150 200 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 fig. 4. mean deviation analysis of one-day annual maximum rainfall at hyderabad. mean deviation of annual maximum rainfall at nawabshah year r a in fa ll ( m m ) -50 0 50 100 150 200 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 fig. 5. mean deviation analysis of one-day annual maximum rainfall at nawabshah. table i. basic statistical parameters for one day maxim um rainfall for the period from 1961 to 2011 parameter hyderabad nawabshah maximum 250.70 256.30 minimum 3.0 0.0 median 41.60 35.10 mode 12.70 22.0 mean 51.90 45.30 standard deviation 42.69 43.89 cv 0.823 0.969 for computing standard deviation, cv, or dispersion, it is necessary to conduct trend and general trend analysis. in order to analyze the trends, the data were divided into four groups: 1961-1975, 1976-1990, 1991-2005, and 2006-2011 [17]. the first three periods last 15 years, and the fourth lasts only 6 years. the mean for these grouped data was determined and the difference of the means between the neighboring groups is shown in table ii. the trend of mean is represented in bar charts in figure 6, whereas the difference of means between neighboring groups is shown in figure 7. figure 6 shows that for both study areas the mean is about the same for the 1961-75 and 1976-90 periods, whereas it is decreased for the third period (1991-2005). on the other hand, the mean increased in both cities during the last period. it is to be noted that during the third period (1991-2005) there were droughts in sindh. table ii. trend analysis in terms of mean for various periods of the study area study area description period-i period-ii period-iii period-iv 1961-1975 1976-1990 1991-2005 2006-2011 h y d e r a b a d mean 52.23 57.51 37.45 73.70 d if f o f m e a n period-i and ii 5.27 period-ii and iii -20.05 period-iii and iv 36.25 n a w a b s h a h mean 46.64 45.73 37.90 59.53 d if f o f m e a n period-i and ii -0.91 period-ii and iii -7.83 period-iii and iv 21.63 fig. 6. variation of mean for the various periods of the study areas. fig. 7. variation of mean for neighboring periods for the study areas. c. linear trend apart from the above trend, the data were rearranged in descending order and their trend in terms of one-day annual maximum rainfall (mm) was determined in terms of rank. their best fit trend-line equations along with r-squared values, developed with statistica for hyderabad and nawabshah cities are shown in figures 8 and 9 respectively. these figures show the outputs in terms of best fit trend-line equations of one-day annual maximum rainfall (mm) value versus the rank 0 20 40 60 80 1961-1975 1976-1990 1991-2005 2006-2011 various periods m e a n o f th e p e ri o d o f o n e -d a y a n n u a l m a x im u m r a in fa ll ( m m ) hyderabad nawabshah -30 -15 0 15 30 45 period-i and ii period-ii and iii period-iii and iv neighbouring periods (np) v a ri a ti o n o f m e a n b e tw e e n n p (% ) hyderabad nawabshah engineering, technology & applied science research vol. 10, no. 6, 2020, 6597-6602 6600 www.etasr.com mahessar et al.: rainfall analysis for hyderabad and nawabshah, sindh, pakistan along with the r 2 value. the r 2 values for hyderabad and nawabshah cities come out as 0.7631 and 0.6883, which shows the fair linear relationship within the rainfall data. fig. 8. linear trend analysis at hyderabad. fig. 9. linear trend analysis at nawabshah. d. polynomial trend and mean 1) polynomial trend polynomial trend lines have been used to graphically display trends in rainfall data, to analyze problems in relation to the last 51 years rainfall, and to predict future trends. the polynomial trend line is a curved line that shows that the data are fluctuating. figures 10 and 11 are outputs of the statistica model, which consist of bars with polynomial lines at hyderabad and nawabshah respectively. the x-axis represents the years and the y-axis the one day annual maximum rainfall in mm. 2) moving mean smoothing the data were also analyzed with regard to moving mean smoothing. a shorter smoothing interval of 3 years has been preferred with secular trend. the smoothed series has a length of 49 years because one value was lost at each end of the series. figures 12 and 13 show the moving means with secular trend for hyderabad and nawabshah. through these trends, we can predict the future one-day annual maximum rainfall for both study areas. fig. 10. bar graph with polynomial trend at hyderabad. fig. 11. bar graph with polynomial trend at nawabshah. fig. 12. moving mean analysis/smoothing for hyderabad. fig. 13. moving mean analysis/smoothing for nawabshah. engineering, technology & applied science research vol. 10, no. 6, 2020, 6597-6602 6601 www.etasr.com mahessar et al.: rainfall analysis for hyderabad and nawabshah, sindh, pakistan e. correlation between rainfall datat the data of day annual maximum rainfall of hyderabad city were correlated with what of nawabshah city. the obtained correlation coefficient value is 0.973, which represents a high degree of rainfall correlation between the two cities. apparently, the year to year assessment does not match in rainfall performance between these two cities, however, the rainfall data of each station reveal close trend for the rank in ascending order as shown in figure 14. fig. 14. rainfall correlation between hyderabad and nawabshah. f. relative frequency and return period relative frequency distribution is more suitable than frequency distribution for data set comparison. the reason is that relative frequencies always fall between 0 and 1, and hence they provide a standard for comparison. relative frequency distribution is the ratio of the frequency of a class to the total number of observations. in figures 15 and 16 the x-axis indicates the return periods and the y-axis the observed rainfall in mm for the computation of relative frequency. fig. 15. relative frequency for hyderabad. fig. 16. relative frequency for nawabshah. table iii. one day annual maxim um rainfall return period (years) one-day annual maximum rainfall (mm) hyderabad nawabshah 3 67.6 50.2 5 84.5 68.8 10 104.2 98.6 table iii shows the one-day annual maximum rainfalls for the selected return periods of 3, 5, and 10 years for hyderabad and nawabshah, computed from figures 15 and 16. table iii shows that for the selected return periods, the one-day annual maximum rainfall for hyderabad is more than nawabshah. v. conclusions it is concluded that the one-day annual maximum rainfall for hyderabad and nawabshah time series has a secular trend. this trend in a time series describes the tendency to grow or decline over a long period of time. hence, secular trend techniques were used through the statistical software statistica. the maximum values of observed rainfall are 250.70mm and 256.30mm, while the minimum values are 3.0mm and 0.0mm, for hyderabad and nawabshah respectively. sudden variation in 51 year’s data indicates the change in the rainfall scenario. the mean of 51-year rainfall data at hyderabad and nawabshah cities is 51.96mm and 45.32mm and the standard deviations is 42.693mm and 43.896mm respectively. the difference between the means and the standard deviations are small, which shows that the data have good consistency. the technique of polynomial trend curved line was used, because the obtained rainfall data are fluctuating which indicates continuous change in rainfall pattern and behavior. rainfall data were subjected to a moving mean for smoothing with a smoothing interval of 3 years. the smoothed series has a length of 49 years. the moving average smoothing does not provide a forecast equation. the trend has been identified as an almost linear secular trend, so it was necessary to fit a reprehensive equation to the data. the coefficient of correlation between the two datasets is 0.973. the maximum values at hyderabad and nawabshah were recorded in 1962 and 1972 and the minimum values in 1969 and 1987 respectively. the concluded results of rainfall time series revealed that the pattern of change over time and the pattern to forecast and predict future values can be done through the statistica software. acknowledgment the authors are thankful to the mehran university of engineering and technology and the irrigation department of sindh irrigation and drainage authority, for providing the research facilities. references [1] m. a. mellieres and c. marechal, climate change: past, present, and future. john wiley & sons, 2015. 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[5] s. das, s. v. singh, e. n. rajagopal, and r. gall, "mesoscale modeling for mountain weather forecasting over the himalayas," bulletin of the american meteorological society, vol. 84, no. 9, pp. 1237–1244, sep. 2003, https://doi.org/10.1175/bams-84-9-1237. [6] g. rasul, q.-z. chaudhry, z. sixiong, and z. qingcun, "a diagnostic study of record heavy rain in twin cities islāmābad-rāwalpindi," advances in atmospheric sciences, vol. 21, no. 6, pp. 976–988, dec. 2004, https://doi.org/10.1007/bf02915599. [7] m. muslehuddin, h. mir, and n. faisal, "sindh summer (juneseptember) monsoon rainfall prediction," pakistan journal of meteorology, vol. 2, no. 4, pp. 91–108, nov. 2005. [8] s. khan and m. ul-hasan, "climate classification of pakistan," international journal of environment and pollution, vol. 10, no. 2, pp. 60–71, jan. 2019. [9] "drought bulletin of pakistan july-september 2012," national drought monitoring centre , pakistan meteorological department, islamabad, pakistan, 2012. [10] "pakistan: monsoon 2011, situation report no. 2," ocha pakistan, 2011. accessed: dec. 12, 2020. [online]. available: https://m.reliefweb.int/report/446066. [11] "climate of hyderabad, sindh," wikipedia. jul. 24, 2020, accessed: dec. 12, 2020. [online]. available: https://en.wikipedia.org/w/ index.php?title=climate_of_hyderabad,_sindh&oldid=969249380. [12] "climate of nawabshah," wikipedia. https://en.wikipedia-onipfs.org/wiki/climate_of_nawabshah.html (accessed dec. 12, 2020). [13] a. a. mahessar, s. qureshi, a. l. qureshi, k. ansari, and g. h. dars, "impact of the effluents of hyderabad city, tando muhammad khan, and matli on phuleli canal water," engineering, technology & applied science research, vol. 10, no. 1, pp. 5281–5287, feb. 2020, https://doi.org/10.48084/etasr.3269. [14] i. h. ibrahim, "differences between statistical software packages, (sas, spss, and minitab), as applied to binary response variable." 1999. [15] statistica quick reference. statsoft, incorporated, 2007. [16] d. c. montgomery, c. l. jennings, and m. kulahci, introduction to time series analysis and forecasting, 2nd edition. hoboken, nj, usa: wiley-interscience, 2015. [17] s. salma, s. rehman, and m. a. shah, "rainfall trends in different climate zones of pakistan," pakistan journal of meteorology, vol. 9, no. 17, pp. 37–47, 2012. microsoft word 21-3771_s_etasr_v10_n5_pp6259-6263 engineering, technology & applied science research vol. 10, no. 5, 2020, 6259-6263 6259 www.etasr.com my et al.: design of a four-element array antenna for 5g cellular wireless networks design of a four-element array antenna for 5g cellular wireless networks dang thi tu my quy nhon university binh dinh, vietnam dangthitumy@qnu.edu.vn huynh nguyen bao phuong quy nhon university binh dinh, vietnam huynhnguyenbaophuong@qnu.edu.vn tran thi huong huong ban mai education company limited da nang, vietnam huonggnouh@gmail.com bui thi minh tu danang university of science and technology, the university of danang, da nang, vietnam btmtu@dut.udn.vn abstract—this paper proposes a four-element array planar antenna based on a single antenna that combines the double positive (dps) and epsilon negative (eng) materials. the single antenna consists of a microstrip segment (which is equivalent to a dps material) connected to a grounded via microstrip segment (which is equivalent to an eng material). t-junction power dividers with one-input and two-output ports are used for feeding the two-element and the four-element array antennas. the proposed array antenna is designed to operate optimally at 30ghz frequency with finite element method (fem)-based simulation. the obtained simulation results show that the proposed array antennas have good radiation performances, in which the four-element array antenna has a -10db bandwidth ranging from 28.7 to 33.4ghz and 12.9dbi gain. keywordsdouble positive (dps) material; epsilon negative (eng) material; array antennas; zeroth-order resonance; 5g systems i. introduction the rapid development of the millimeter wave communication systems poses many challenges in matching the requirements of these systems, especially the antenna designs for 5g communication systems [1-2]. these modern antennas are required to be lightweight, to have small size, and to be fabricated easily. the conventional antennas are usually large because the operating wavelength is always relative to their size. related to this issue, there have been many techniques proposed to reduce the size of the antennas. transmission line metamaterials (tl-mm) [3] are employed to construct small resonant antennas. it is well known that the composite right/left-handed (crlh) transmission line (tl) has the unique property of an infinite-wavelength wave at a specific non-zero frequency where permittivity and permeability are zero [4-5]. the infinite-wavelength wave property is applied to many microwave components (power dividers, zeroth-order resonators (zor), zor antennas [6-8], etc.). nevertheless, the radiation of these antennas is the same with the monopole radiation, whereas wireless imaging transmission systems and space communications require a compact antenna with patchlike radiation [3]. zor happens in the meta-structured transmission line (mtl) with eng [5, 8]. several models have been proposed to decrease the resonance size of the mushroom-shaped antenna that consists of a rectangular patch with a series gap, is grounded, and has negative permittivity in the specific frequency band [7, 9]. in order to improve the size and power of the zor antenna, dps material is added [3]. the antenna pattern is designed on two components with different electromagnetics. by optimizing the dps segment size, the antenna length can be shortened. with the presence of the dps, the antenna frequency reduces significantly in comparison with the one zcquired by using only eng material. to realize a patch-like radiation zor antenna, a rectangular patch antenna is loaded with a transversally inhomogeneous substrate [3]. in this paper, a modified crlh model is used to design a one-dimensional antenna (two-element and four-element) using composite materials. the four-element array antenna exhibits wide-bandwidth and high gain that can be used for the millimeter wave systems at the frequency of 30ghz. ii. four-element array antenna design the single antenna’s design is based on the eng antenna reported in [4]. t-junction microstrip power dividers with oneinput and two-input ports (1:2) are used for feeding the fourelement array. this divider requires the power at the input port to be equally divided into two output ports. a. single antenna the single antenna consists of a pair of dps and eng material mtl. it is designed to resonate at zeroth-order mode and uses the eng material which is designed on a mushroom model structure [4]. this mushroom structure is a combination of the rectangular patch with a series gap and a grounded metallic cylindrical pin. it is usually employed to realize the mtl. the mtl with eng is realized with only the grounded cylindrical pin and has negative permittivity in the specific corresponding author: bui thi minh tu engineering, technology & applied science research vol. 10, no. 5, 2020, 6259-6263 6260 www.etasr.com my et al.: design of a four-element array antenna for 5g cellular wireless networks frequency band. to achieve the impedance matching of zor antennas, a gap feed g is employed [3]. the antenna is printed on a teflon substrate with dielectric constant �� = 2.1 and h = 1.57mm thickness. they have three cylindrical pins, each with a radius of 0.15mm. the configuration of the single antenna is shown in figure 1. (a) (b) fig. 1. configuration of the single antenna: (a) perspective view, (b) side view. b. two-element antenna array a one-dimensional two-element antenna array is effectuated by integrating two single antennas of figure 1. the t-junction power divider 1:2 is printed on a teflon substrate with a relative dieletric constant of 2.1 and a thickness of 1.57mm. the impedances at the inlet and two-outlet ports of the power divider are 100ω. the operating frequency is 30ghz. it can be done when (1) is satisfied: �������� = ������� = ������ (1) where �������� and ������� are the impedances of the two outputs and ������ is the impedance of the input. this divider requires the power at the input to be equally divided into two outputs. in addition, the output signal at the two ports must be in-phase to ensure isolation due to mutual influence. all corners of the divider are cut with an angle of 45 0 to reduce reflection. for given characteristic impedance �� and dielectric constant ��, the �/ℎ ratio can be calculated as [10]: � � = ��� ���� ��� �� < 2 (2) � ℎ = 2 � � − 1 − #$%2 − 1& + �� − 1 2�� (#$% − 1&+ 0.39− 0.61 �� ./ ��� �� < 2 (3) 0 = 123� 4 567� + 56�� 567� 80.23+ �.�� 56 9 (4) based on (2)-(4), the width of the microstrip line � can be easily calculated with a given height of the substrate ℎ. figure 2 shows the parameters of a one-dimensional two-element array antenna. (a) 100ω 100ω 100ω 70ω (b) 1.5 7.45 5.1 9.53 4.65 4.761.13 2.35 fig. 2. two-element antenna array: (a) 1:2 t-junction power divider, (b) detailed parameters. c. four-element antenna array four identical single antennas were integrated with the feeding network to create a higher gain antenna. this feeding network was also built on a teflon sheet with a thickness of h = 1.57mm. it consists of three 1:2 t-junction power dividers that have input and output impedances similar with the one of the two-element array. each element of the four-element antenna array was excited by the same power and phase (inphase excitation) which are created by the equal power divider. the configuration of the feeding and the four-element array are shown in figure 3. (a) 100ω 100ω 100ω 100ω 100ω 70ω 70ω 70ω (b) 9.53 09.53 20.2 fig. 3. the configuration of the four-element array: (a) 1:4 t-junction power divider, (b) detail parameters. engineering, technology & applied science research vol. 10, no. 5, 2020, 6259-6263 6261 www.etasr.com my et al.: design of a four-element array antenna for 5g cellular wireless networks iii. simulated results and discussion the ansys academic research hf was used for all the simulation cases of the single antenna and the array antennas. a. single antenna in this part, the antenna is optimized by investigating the resonant frequency versus different values of the dimension of the antenna’s radiator. firstly, the resonant frequency of the single antenna is verified with various lengths of the dps segment while the width of the radiator is fixed at wp = 1.5mm. as can be observed from figure 4, the center frequency of the antenna decreases when the length a increases. next, the width wp of the radiator is changed to determine the desired center frequency of the single antenna since the length of dps a is set as 4mm. the return loss simulated results of the antenna at the input are shown in figure 5. it is observed that the center frequency of the single antenna is inversely proportional to the radiator’s width. the resonant frequency of the antenna decreases as the length of the radiator increases. fig. 4. reflection coefficient with different dps length a. fig. 5. reflection coefficient with different antenna width wp. figure 6 shows the simulated reflection coefficient along with the simulated radiation pattern of the single antenna. figure 6(a) shows the simulated s11 of the single antenna. it is optimized with the length of dps a = 3.45mm and the radiator width wp = 1.5mm. the resonant frequency is centered at 30ghz. this can be easily achieved by investigating the length of the dps segment along with the width of the radiator. the final single antenna has a broad -10db bandwidth spreading from 27.3 to 32.4ghz. figure 6(b) presents the simulated radiation pattern of the single antenna. it can be observed that the antenna has an omnidirectional pattern in the xy plane with a gain of 8.0dbi. the optimal dimensions of the single antenna are shown in table i. (a) (b) fig. 6. simulated s11 and radiation pattern of the single antenna. table i. optimal dimensions of the single antenna (mm) parameter value parameter value ws 10 wp 1.5 ls 20 lp 7.5 wf 1.13 g 0.2 lf 5.1 a 3.45 b. two-element antenna array the simulated s11 of the two-element array antenna is presented in figure 7(a). it can be seen that the two-element array has -10db reflection coefficient and bandwidth between 28.4ghz and 32.6ghz covering the desired frequency. figure 7(b) shows the simulated radiation pattern of the two-element array. the array yields a directional pattern in the yz plane (eplane) with a maximum gain of 11.0dbi at 30ghz. c. four-element antenna array figure 8(a) presents the simulated s11 of the four-element array antenna. the obtained simulation results indicate that the array yields a -10db bandwidth from 28.7ghz to 33.4ghz. this array antenna has been successfully designed when its resonant frequency is still centered at 30ghz as the one of the single antenna. the simulated results of the radiation pattern of the antenna array are shown in figure 8(b). the antenna exhibits a directional pattern in the e-plane (yz plane) with a peak gain of 12.9dbi. 20 22 24 26 28 30 32 34 36 38 40 -50 -40 -30 -20 -10 0 s 1 1 ( d b ) frequency (ghz) a = 3.5 mm a = 3.7 mm a = 3.9 mm a = 4.1 mm a = 4.3 mm a = 4.5 mm 20 22 24 26 28 30 32 34 36 38 40 -60 -50 -40 -30 -20 -10 0 s 1 1 ( d b ) frequency (ghz) wp = 1.0 mm wp = 1.2 mm wp = 1.4 mm wp = 1.6 mm wp = 1.8 mm wp = 2.0 mm 25 26 27 28 29 30 31 32 33 34 35 -50 -40 -30 -20 -10 0 s 1 1 ( d b ) frequency (ghz) -30 -20 -10 0 10 0 30 60 90 120 150 180 210 240 270 300 330 -30 -20 -10 0 10 yz plane xy plane engineering, technology & applied science research vol. 10, no. 5, 2020, 6259-6263 6262 www.etasr.com my et al.: design of a four-element array antenna for 5g cellular wireless networks (a) (b) fig. 7. simulated s11 and radiation pattern of the two-element antenna array. (a) (b) fig. 8. simulated s11 and radiation pattern of the four-element antenna array. table ii. comparison between the proposed and other dipole antennas ref. no. of array elements feeding method center frequency/ bandwidth (ghz) gain (dbi) [11] array 2×2 siw 28/0.8 9.2 [12] array 2×2 microtrip feed 28/nm 12.3 array 1×4 microtrip feed 28/nm 12.5 this work array 1×4 microtrip feed 30/4.7 12.9 nm: not mentioned a comparison between the proposed 4-element antenna array with related works is shown in table ii. it can be seen that the designed 1×4 antenna array shows good performance in terms of bandwidth and gain in comparison with the listed array antennas. iv. conclusion in this paper, one-dimensional antenna array has been designed and simulated by combining two material structures that have dps and eng properties. applying array antennas to the design has improved the directional radiation significantly and increased the gain. the simulated results show that the four-element array antenna yields a wide bandwidth spreading from 28.7 to 33.4ghz. in addition, the antenna array represents a maximum gain of 12.9dbi. with this radiation performance, the designed antenna array can be used for millimeter wave applications, especially in the 5g system. acknowledgement this work was conducted at the calculation and simulation laboratory of the faculty of engineering and technology, quy nhon university, vietnam. references [1] h. alsaif, “extreme wide band mimo antenna system for fifth generation wireless systems,” engineering, technology & applied science research, vol. 10, no. 2, pp. 5492–5495, apr. 2020. [2] m. azhar and a. shabbir, “5g networks: challenges and techniques for energy efficiency,” engineering, technology & applied science research, vol. 8, no. 2, pp. 2864–2868, apr. 2018. [3] s. zhao, z. qian, and m. xiao, “microwave zeroth-order resonance antenna loaded with a pair of dps and eng materials,” in 2009 international conference on wireless communications signal processing, nanjing, china, nov. 2009, doi: 10.1109/wcsp.2009.5371675. [4] j.-h. park, y.-h. ryu, j.-g. lee, and j.-h. lee, “epsilon negative zeroth-order resonator antenna,” ieee transactions on antennas and propagation, vol. 55, no. 12, pp. 3710–3712, dec. 2007, doi: 10.1109/tap.2007.910505. [5] j. h. park, y. h. ryu, j. g. lee, and j. h. lee, “a zeroth-order resonator antenna using epsilon negative meta-structured transmission line,” in 2007 ieee antennas and propagation society international symposium, honolulu, hi, usa, jun. 2007, pp. 3480–3483, doi: 10.1109/aps.2007.4396287. [6] m. a. antoniades and g. v. eleftheriades, “a broadband series power divider using zero-degree metamaterial phase-shifting lines,” ieee microwave and wireless components letters, vol. 15, no. 11, pp. 808– 810, nov. 2005, doi: 10.1109/lmwc.2005.859007. [7] a. sanada, c. caloz, and t. itoh, “novel zeroth-order resonance in composite right/lefthanded transmission line resonators,” in 2003 asiapacific microwave conference, seoul, korea, nov. 2003, vol. 3, pp. 1588–1591. 25 26 27 28 29 30 31 32 33 34 35 -25 -20 -15 -10 -5 0 s 1 1 ( d b ) frequency (ghz) -20 -10 0 10 20 0 30 60 90 120 150 180 210 240 270 300 330 -20 -10 0 10 20 yz plane xy plane 25 26 27 28 29 30 31 32 33 34 35 -25 -20 -15 -10 -5 0 s 1 1 ( d b ) frequency (ghz) -20 -10 0 10 20 0 30 60 90 120 150 180 210 240 270 300 330 -20 -10 0 10 20 yz plane xy plane engineering, technology & applied science research vol. 10, no. 5, 2020, 6259-6263 6263 www.etasr.com my et al.: design of a four-element array antenna for 5g cellular wireless networks [8] j.-g. lee and j.-h. lee, “zeroth order resonance loop antenna,” ieee transactions on antennas and propagation, vol. 55, no. 3, pp. 994–997, mar. 2007, doi: 10.1109/tap.2007.891875. [9] n. k. kiem, h. n. b. phuong, q. n. hieu, and d. n. chien, “a novel metamaterial mimo antenna with high isolation for wlan applications,” international journal of antennas and propagation, vol. 2015, jul. 2015, art. no. e851904, doi: 10.1155/2015/851904. [10] d. m. pozar, microwave engineering, 4th ed. wiley, 2011. [11] y. feng, b. yang, y. ji, and j. zhou, “a 28ghz millimeter-wave antenna array with siw feeding network,” in 2019 international conference on microwave and millimeter wave technology (icmmt), guangzhou, china, may 2019, doi: 10.1109/icmmt45702.2019.8992115. [12] j. khan, d. a. sehrai, and u. ali, “design of dual band 5g antenna array with sar analysis for future mobile handsets,” journal of electrical engineering & technology, vol. 14, no. 2, pp. 809–816, mar. 2019, doi: 10.1007/s42835-018-00059-9. authors profile dang thi tu my received the b.e. and m.e. degrees from hanoi university of science and technology in 2000 and 2004 respectively. from 2016 she is a ph.d. student at the department of electronic and telecommunication engineering, university of science and technology, the university of danang. from october 2000 to present, she is a lecturer of the faculty of engineering and technology, quy nhon university. research interests: electronics and telecommunications, ultra-high frequency and antenna technology, and artificial networks. huynh nguyen bao phuong received the b.e, m.sc. and d.e degrees from hanoi university of science and technology, vietnam in in 2003, 2007, and 2014 respectively. now he is a senior lecturer of the faculty of engineering and technology, quy nhon university, vietnam. his research interests are high impedance surfaces (his), microstrip and metamaterial antennas, and mimo antennas. tran thi huong received the b.s degree in electrical and electronics engineering from utsunomiya university, japan in 2004 and m.e. and d.e degrees in electrical and electronics engineering from tokyo institute of technology, japan in 2006 and 2010 respectively. from 2010 to 2019, she was a lecturer at the department of electronic and telecommunication engineering, the university of da nang, university of science and technology. research interests: dielectric resonator, material measurements in millimeter wave bands, and high frequency planar antennas. bui thi minh tu received her ph.d. degree from the universite de technologie de compiegne, france in 2010. she started teaching at the faculty of electronic and telecommunication engineering, the university of danang, university of science and technology in 2010 and since 01/2015, she is the vice-dean of the faculty. her research interests include communication systems, signal processing, renewable energy, and sustainable development. microsoft word etasr_v11_n3_pp7100-7106 engineering, technology & applied science research vol. 11, no. 3, 2021, 7100-7106 7100 www.etasr.com hamzaoui & bouzid: the proposition of an ei equation of square and l–shaped slender reinforced … the proposition of an ei equation of square and l– shaped slender reinforced concrete columns under combined loading leila hamzaoui lgc–roi, civil engineering laboratory, risks and structures interactions faculty of science university of batna 2 batna, algeria l.hamzaoui@univ-batna2.dz tayeb bouzid lgc–roi, civil engineering laboratory, risks and structures interactions faculty of science university of batna 2 batna, algeria tayeb.bouzid@univ-batna2.dz abstract-the stability and strength of slender reinforced concrete (rc) columns depend directly on the flexural stiffness ei, which is a major parameter in strain calculations including those with bending and axial load. due to the non-linearity of the stress-strain curve of concrete, the effective bending stiffness ei always remains variable. numerical simulations were performed for square and l-shaped reinforced concrete sections of slender columns subjected to an eccentric axial force to estimate the variation of el resulting from the actual behavior of the column, based on the moment-curvature relationship. seventy thousand (70000) hypothetical slender columns, each with a different combination of variables, were used to investigate the main variables that affect the ei of rc slender columns. using linear regression analysis, a new simple and linear expression of ei was developed. slenderness, axial load level, and concrete strength have been identified as the most important factors affecting effective stiffness. finally, the comparison between the results of the new equation and the methods proposed by aci-318 and euro code-2 was carried out in connection with the experimental results of the literature. a good agreement of the results was found. keywords-flexural stiffness; reduction factor; reinforced concrete; rigidity; slender columns i. introduction for a bi-articulated column supporting a load p applied with an eccentricity e, the corresponding moment which is equal to p.e is called the "first order moment". under the action of this moment the column deforms in simple curvature and the bending moment is at its maximum at half height and equal to m=p.e+p.∆ .the increase of the latter caused by the displacement ∆ is called the p∆ effect or second order moment. the longer the column is compared to its cross section, the greater the lateral displacements will be and the greater the second order moment will be. buckling failure will occur under a lower resistance than that which would have caused the short column to fail. in this case, the strength of slender reinforced concrete (rc) columns is remarkably reduced. several factors contribute to this reduction. in addition to the p∆ effect, shrinkage, creep, and cracking occur along the length of the column and are directly related to the supported part of the compressive stress block in the concrete. leonhard euler who based his work on hook’s law and the moment-curvature relationship studied the buckling problem. he developed (1) to predict the minimum buckling load of a perfect column: ��� = ���� � (1) this equation did not depend on the strength of the crosssection but rather on the bending stiffness ei. it was valid only if the moment of buckling obeys hook's law, where the retained stiffness is constant. this is the case of a homogeneous isotropic and elastic material but this is not the case for reinforced concrete columns whose behavior in practice becomes clearly non-linear at the level of the descending branch of the σ-ɛ curve, therefore the buckling takes place in the non-linear domain. euler's expression remains valid if the bending stiffness is replaced by a value representative of the effective stiffness at the moment of failure which is either with the crushing material (case of short columns) or with buckling (case of thin columns). during the loading and due to the inelastic behavior depicted by the stress/strain curve of concrete the value of the ei varies at each point along the section. the difficulty to choose a single value of ei appears because some methods consider that the column stiffness is constant along the section and the length of the column, when in addition it is necessary to consider shrinkage, creep, and lateral deflection. if we introduce the effects of concrete cracking, this can cause a large variation in bending stiffness. the objective of this work is to develop an analytical model for the study and analysis of the non-linear material and geometrical behavior of slender reinforced concrete columns of square and "l" cross-section under axial load and biaxial bending in order to find a simple relationship explicitly describing the real behavior of the effective bending stiffness ei as a function of parameters such as concrete strength ƒc, steel yield strength ƒy, cross-sectional dimensions, percentage of reinforced steel ρ, and column length l. in addition, this corresponding author: leila hamzaoui engineering, technology & applied science research vol. 11, no. 3, 2021, 7100-7106 7101 www.etasr.com hamzaoui & bouzid: the proposition of an ei equation of square and l–shaped slender reinforced … stiffness is compared with experimental test results from the literature and design codes aci-318 [1] and ec-2 [2]. the studied columns were bent into a single symmetrical curvature, in non-oscillating frames subjected to short-term loads. the behavior of rc slender columns under axial loads and bending moments in the two main planes of inertia is of great interest for structural analysis and design .the difficulty in this case is in the fact that it is not possible to give a general mathematical formulation as in the case of uniaxial bending because the position of the neutral axis is not known in advance. the difficulty increases if the cross-section of the column is not symmetrical, and increases even more if the behavior law (σ-ɛ) is not linear. some researchers have proposed an iterative method initiated in [3] which consists of establishing by successive trials the neutral axis for which the internal forces in the section are in equilibrium with the external loads. other methods, based on the determination of interaction curves, interaction surfaces or interaction contours for loading, were used for calculation and verification [4]. in most computer programs for reinforced concrete structures, there are indications of the limit state justification of square and rectangular columns while the l-shaped cross-section is not treated. it is therefore interesting to fill in the gaps in the equations presented in the literature because they are valid only for ordinary sections, and in practice, there are sections of different shapes such as tee (t), simple cross (+), hexagonal or thin-walled boxes, and finally l-shaped. in fact, the latter presents several difficulties like the absence of vertical and horizontal axes of symmetry. ii. literature review flexural rigidity is a necessary component in the estimation of the deflection of rc elements subjected to bending moment and axial loading, especially slender columns. it should be noted that the deflection is important because it has a direct and strong influence on the second order moments induced by the axial loads. recently, major progress has been made in the development of nonlinear methods for the analysis of slender rc columns. numerous methods are used to evaluate the bending stiffness ei taking into account all the factors that contribute to its decrease at the level of the concrete stress block in compression (non-linear material behavior) and at the level of the lateral displacement length of the column (nonlinear geometric behavior) to determine the critical buckling load nearest to the effective values. accordingly, the effective bending stiffness of columns under short-term loading can be expressed as: ei=α.ec.ic+es.is where α is the stiffness reduction factor, ec and es are the elasticity modulus of concrete and steel respectively, ic and is are the moments of inertia of the cross-section of concrete and steel about the central axis of the cross-section respectively. after determining the factor α, the ei can be easily calculated. the factor α is a function of the material properties, the steel ratio, the axial load, and other parameters. this reduction factor of bending stiffness has been evaluated and studied by a number of researchers and some current codes and according to [1], is always taken equal to 0.2 for columns. the eurocode ec-2 [2] is provided with a coefficient of flexibility ke which is a function of a set of parameters such as: the relative normal force ν, the mechanical slenderness λm, the geometric reinforcement ratio ρ, the creep rate φeff, and the characteristic strength of the concrete compression cylinder at 28 days fck. many formulations have been proposed in the literature. authors in [5-7] have presented statistical evaluations of the flexural rigidity of rc columns and of rectangular crosssections of composite rc columns. authors in [8] proposed a reduction coefficient as a function of various parameters such as slenderness ratio (l/h), eccentricity ratio (e/h), and axial load ratio (p/p0). authors in [6] proposed a general expression to obtain an effective flexural stiffness applicable to any crosssectional shape under short or long-term biaxial eccentric loading for normal and high concrete strength. authors in [9] proposed a study for the reduction factor of the rc column with equi-axial t section and in [10] dealt with the crossshaped cross-section. authors in [11] presented new expressions for a beam with rectangular and t-shaped crosssections, square, rectangular and circular cross-sections for columns in function of concrete strength ƒc, steel percentage ρ, and level of charge p/p0. authors in [12] presented their approach to find effective flexural stiffness for circular columns. in this research, the stiffness reduction factor was suggested to treat slender square and l-section columns with equal flanges. some researchers have conducted studies on eccentrically loaded l-sections. authors in [13] presented an experimental and analytical research on the load carrying capacity of l-shaped rc columns with equal and unequal flanges. authors in [14] carried out a theoretical study on the calculation of l and square sections by the interaction approach. authors in [15] based their study on the finite element method to analyze and draw the interaction surfaces of l and square sections. an interesting research concerning the behavior of l-section and square composite columns under biaxial eccentric loading according to different laws of concrete behavior is presented in [16]. authors in [9] studied the l section with equal flanges and suggested a formula for the bending stiffness reduction factor of slender rc columns under different axial load levels and different seismic action levels. the current work is a contribution in this field of study and, in addition, a proposition of a simple solution for the calculation and verification of thin columns is presented. iii. analysis method in order to study the effective bending stiffness values of the slender rc column under combined biaxial bending and axial loading, nonlinear computer analysis was developed. material and geometric nonlinearity were included in the research study for l and square sections. it should be noted that articulated end columns with equal load eccentricities at the ends acting in the same plane have been taken in account. the analysis can be divided into three parts: (a) the cross-sectional strength (analysis of cross section), (b) the effect of slenderness on the column strength (analysis of second order), (c) the third and main objective is the development of a new formula for estimating the ei bending stiffness of slender biaxially loaded rc columns in which these factors are included. a. material behavior and assumptions the studied columns are all made of rc. this composite material consists of two elements with different characteristics. engineering, technology & applied science research vol. 11, no. 3, 2021, 7100-7106 7102 www.etasr.com hamzaoui & bouzid: the proposition of an ei equation of square and l–shaped slender reinforced … in order to simulate the non-linear analysis of the complete response of rc columns of square and l-shaped cross-sections with equal flanges under biaxial bending and compression, a computer program compiled by an integral numerical method was used, based on the following assumptions: • plane sections before bending remain plane after bending. • the tensile strength of concrete is neglected, and the stressstrain curve of concrete in compression refers to the unconfined diagram in [17], as shown in figure 1(a), whose curve characteristics are calculated using (2) and (3): σ = �� � 2. ������ � ����� �� (2) for 0 � ε� � ε�� = 0.002 σ = ���1 � ��� � � �0!" (3) for �# � � � �$ = 0.004 with: zu = �.()(�*+)�,, ε(�* = ./�.�0(.1234�12+3���, ε(�* 5 ε�, ��� mpa! • the stress-strain curve of steel is taken as the usual bilinear relationship shown in figure 1(b). the section is divided into a number of small fiber elements. the concrete element stress distribution is also divided into a number of small fiber elements. concrete shrinkage and creep are ignored. (a) (b) fig. 1. concrete and steel σ-ε diagram 1) cross section analysis this work presents an indirect method for the analysis of the ultimate limit states of rc columns of l and square crosssections subjected to biaxial loading. we consider a square section of dimensions b×b, and another square section of dimensions b1×b1 with b1<b being away from the corner of the original square (b×b). removing the section b1×b1 results in an l-shaped section, as shown in figure 2(a). for different values of b1, we can obtain different dimensions of the lsection. if (b1=0) the l-section becomes a square section. the ratio (b1/b) varies from 0 to 0.6. it is assumed that the steel reinforcement is evenly distributed around the perimeter of the cross-section (see figure 2(b))[14]. 2) internal forces the cross section is divided into infinitely small slices (see figure 3). for each one of them, the internal forces (concrete, compression reinforcement and tensile reinforcement) are evaluated to give finally an axial load and an ultimate moment. the resulting axial load and the resulting moment must be equal respectively to the sum of the internal loads and the sum of elementary moments. (a) (b) fig. 2. l cross section and steel reinforcement distribution. fig. 3. l cross section subjected to biaxial load. the resulting axial load and the resulting moment are equal respectively to the sum of the loads and elementary moment shown in (4), and (5): 9 = ∑ ��. ;�<. ∑ =�> � ��?. @. abc3��d<e3d<e3 (4) f = ∑ ��. g�h. ;�<. ∑ =�> � ��?. @. gh. abc3��d<e3d<e3 (5) where n is the number of slices, aci is the concrete area of the slice i, ρ=(as/ac).100 presents the percentage of longitudinal reinforcement, as is the area of longitudinal reinforcement, and yi is the distance from the edge of steel to the center of the section. analysis is done by sweeping the section parallel to the neutral axis. for the l-shaped section, the computer program studies different positions of the neutral axis according to the angle of inclination θ, where θ=tang-1(ex/ey) with ex and ey being the eccentricities along the x and y axis respectively. the computer analysis has been prepared by considering the axis of bending. figure 4 explains these cases: • case 1: uniaxial bending, angle of inclination θ=00. • case 2: uniaxial bending, angle inclination θ=900. engineering, technology & applied science research vol. 11, no. 3, 2021, 7100-7106 7103 www.etasr.com hamzaoui & bouzid: the proposition of an ei equation of square and l–shaped slender reinforced … • case3: biaxial bending, angle of inclination 0<θ<450. • case4: biaxial bending, angle of inclination 450<θ<900. fig. 4. the four cases of uniaxial and biaxial load. the codes of the above mentioned cases were developed in fortran and were used to obtain the ultimate resistance pu and moments mu as results of the different positions of the neutral axis. the input data include the size of the square b1, the depth b of the section, the depth of embedding dc, the characteristic strengths of concrete fc and steel fy, the moduli of elasticity of steel es and concrete ec, the angle of inclination θ, and the percentage of reinforcement ρ. iv. second order analysis columns with a moderate slenderness may have their secondary moments determined with an approximate analysis such as the moment magnifier method which is used in this study. this procedure uses a moment magnification factor δ to amplify the applied moment ma sufficiently for the account of secondary moments and to ensure safe design. for columns subjected to axial loading and equal and opposite end moments, the maximum bending moment can be taken as: f� = i. fj (6) where: i = 11 � kk�l where mc is the design bending moment that includes secondorder effects, ma is the applied column bending moment, p is the factored axial load acting on the column, and pcr is euler’s buckling strength. the secondary moment due to the column slenderness is calculated as the difference between the internal resisting moment and the applied moment. for the purpose of analysis, mc is replaced by the cross section bending moment mcs, and ma is replaced by the overall column bending moment (mcol) as shown in (7): f�m = n 33+ oobpq. f�rs (7) v. calculation of the flexural stiffnes of the column the design of the flexural stiffness as a function of the moment-to-curvature ratio m/φ is the most reasonable relation of the ei representation. the analysis studies show various cross-sectional parameters as well as axial loading influencing the bending stiffness. the computer program is structured according to the well-known (p, m, φ) relation. a linear strain is assumed and the kent & park relation [17] relates stress to strain. the curvature is calculated directly from the geometry (φ) and it is known as the exact value in this computer program and the extreme fiber is assumed to be at crush strain. the depth of the neutral axis xu can be incremented throughout the program to provide the necessary strain variation. therefore, this depth starts at a small fraction of the total section depth and is increased in defined increments until the maximum of the column capacity in pure axial compression is reached (p0). the curvature is obtained by dividing the stress of the extreme fiber (usually 0.003) by the depth of the compression zone (φ=0.003/xu). using this curvature and assuming a linear strain distribution, it is possible to find the stress in each fiber. for each increment, the axial load p, the bending moment of the cross section mcs, and the curvature φ are calculated. equation (1) is used to find the critical load pcr which allows calculating the bending moment of the column mcol through (7) whose slenderness effects were taken into account. the program uses the formulation mcol/φ to calculate the effective bending stiffness of a slender column whose nonlinearities due to p∆ effects and nonlinear behavior of the material are taken into account at all times. vi. proposed formula of the reduction factor of flexural stiffness in practice, the engineer often has difficulties to give a reasonable interpretation of the bending stiffness that represents the real behavior of slender rc columns. this stiffness is easy to calculate with the m/φ method, which gives satisfactory results, but it is not easy to solve manually making the use of a computer recommended which in this case makes it mandatory but not preferable. in order to simplify the estimation of ei bending stiffness under short-term loads, the well-known equation ei=α.ecic+esis is obtained. research and expressions have proposed to evaluate the reduction factor or the factor of effective stiffness which is of origin can be expressed by: t = ��+�u�u���� (8) thus, to evaluate the ei flexural stiffness, a simple expression is proposed to avoid sophisticated and complicated calculations. multiple linear regression approaches, taking into account the simulated theoretical stiffness data, are conducted to evaluate the ei expression. linear regression is chosen as the method of analysis because the objective is to develop a simple and accurate equation for the reduction factor α. this method is very useful in order to determine the effective behavior of certain parameters. for example the work in [18] was based on the same principle to give the equation of effective ductility as a function of shear reinforcement ratio and compressive strength of concrete. in this work the used analysis method consists in finding an expression describing the reduction factor α for different values of concrete strength ƒc, steel yield ƒy, percentage of reinforced steel ρ, steel ultimate strength fy, l section dimensions, square or equal flanges presented by the ratio b1/b, slenderness ratio l/b, the neutral axis angle θ which engineering, technology & applied science research vol. 11, no. 3, 2021, 7100-7106 7104 www.etasr.com hamzaoui & bouzid: the proposition of an ei equation of square and l–shaped slender reinforced … presents the loading angle, and the axial loading ratio p/p0, where p0 is the strength of the axial compression column under pure axial loading. this regression concerns a column of a square and equal l section presents the proprieties illustrated in table i, based on the statistical analysis of the theoretical values of α for all simulated columns in which p/p0 ranged from 0.1 to 1. over 70000 isolated reinforced concrete columns were simulated to generate the effective stiffness factor. each simulated column had a different combination of cross section, geometric, and material proprieties. table i. specified properties of studied rc columns proprieties specified values number of specified values fc 15 ;60 incr 5mpa 10 fy 200;600 incr 100mpa 5 b1/b 0 ; 0.6 incr 0.1 7 l/b 10 ; 30 incr 5 5 ρ 0.5 ;4% incr 0.5% 8 θ 00; 900 incr 100 8 total number =10×5×7×5×8×8=70000 columns finally the following equation of reduction factor α is obtained: α = � 0.074 + 0.0003·ƒc+ 0.488· kk� � 0.002· lb (9) the effect of ƒc has an increasing influence on the flexural stiffness of the slender column .this was already predicted and proven in [19] which presented the effect and impact of this strength on the general behavior of corner columns. in addition to the axial load level, it has an increasing effect on the ei of the column. the expression also indicates that a decrease in the ei value occurs as slenderness ration (l/b) ratio is increased. vii. validation for the experimentation of the proposed model a test series has been realized to determine the variation of the reduction factor according to the influence of different parameters on the behavior of the rc slender columns. the proposed method has been realized according to the expression of the reduction factor for an ultimate compressive concrete strain equal to 0.003 because it gives the best results among all other values of strain levels which varied between 0.002 and 0.004. the square cross section has dimensions b1=0 and b=300mm and the l section b1=100nm and b=300mm. five methods are considered in this work to predict the nominal capacity of the rc columns. the curves in figure 5 show the comparison between the proposed method, the codes [1, 2], and the methods proposed in [3, 6, 8]. all respective equations are presented in table ii. a comparison between the proposed method, and that suggested by bonet et al. in [6] for the l-shaped cross-section is presented in figure 6(a) showing the variation of the reduction factor as a function of the relative eccentricity η. this coefficient presented by bonet has been calculated as η=e/4.ic, where ic is the radius of gyration of the concrete section with respect to the bending axis and e is the first order eccentricity. the effective stiffness factor shows a non-linear behavior as a function of η. a second comparison with bonet equation presented in figure 6(b) shows the effect of ρ on the α of the slender column with a different angle loading θ. (a) (b) (c) (d) fig. 5. comparison of α with different authors and design codes for a square sections: effect of (a) e/b, (b) ρ, (c) ƒc, and (d) of the axial loading ratio on the α of a slender column. engineering, technology & applied science research vol. 11, no. 3, 2021, 7100-7106 7105 www.etasr.com hamzaoui & bouzid: the proposition of an ei equation of square and l–shaped slender reinforced … (a) (b) fig. 6. comparison between the bonet equation and the proposed α for the l shaped section. (a) effect of on α of the slender column, (b) effect of ρ on α with a variation of angle loading θ. table ii. ei equation comparison author effective flexural stiffness ei proposed ei=αecic+esis α=-0.074+0.0003fc+0.488(p/p0)-0.002(l/h) [1] ei=0.2ecic+esis/1+βd ei=0.4 ecic/1+βd [2] ei = kc · ec · ic + ks · es · is if ρl ≥ 0.2%, ks = 1, kc=(k1k2)/(1+ϕeff), k1=√fck/20, k2=ν λm/170 if ρl ≥ 1%, ks = 0, kc=0.3/1+0.5ϕeff [17] ei=(αecic/1+ ϕeff)+(esis/1+η) α=(1.95-0.035.λm-0.25ϕeff)(η-0.2) +((fc/225)+0.11) ̸< 0.1; if η˂0.2 α = (fc/225+0.45)(η-0.2)+(fc/225+0.11) ̸< 0.1 ; if η≥0.2 [6] ei=αecic+0.8esis α=0.47-0.35(e/h)(1/1+β(e/h))+0.003(l/h) where β = 7.0 for ρrs ≤ 2% ; and β = 8.0 for ρrs> 2%. [8] ei=αecic+esis α=0.38-0.011(l/h)-1.3(e/h)+0.45(1-(p/p0) 2) 0.1≤α≤0.85 ei = flexural stiffness of compression member, ec= modulus of elasticity of concrete, es= modulus of elasticity of reinforcement, ic= moment of inertia of gross concrete section, is = moment of inertia of reinforcement, p = axial load, p0= maximum load capacity, e/h = eccentricity ratio, l/h = geometrical slenderness ratio, βd = ratio of the maximum factored axial sustained load to the maximum factored axial load associated with the same load combination, ν=relative normal force, λm =mechanical slenderness ratio,ϕeff=effective creep ratio, fc =concrete strength, ρl=geometrical reinforcement ratio, fck=characteristic compressive cylinder strength of concrete at 28 days. viii. results and discussion this paper presents a statistical evaluation of the parameters that affect the flexural stiffness of slender columns subjected to short term loads with biaxial bending. five methods [1-3, 6, 8] for this comparison were considered to predict effective rigidity. in order to verify (9), variations of the e/b, p/p0, ρ, and fc were used. these parameters are the most appeared in the expressions proposed in the literature. it can be noticed that both design codes propose an effective stiffness factor α independent of all the parameters (figure 5), however other authors include the dependence of α. in general an equation of α is proposed that decreases with e/b and ρ and increases with fc and p/p0. the proposed equation confirms this behavior of α. the majority of tests considered the square cross section, with the exception of bonet’s expression which considered a cross section shape. a very large correspondence can be noticed between the bonet’s equation and the proposed equation (figure 6) despite that bonet's is nonlinear and the proposed expression is perfectly linear. liu et al. [9] proposed a reduction stiffness factor αe taking all the rigidity ei of the material, not only the concrete material of rc slender columns. the calculation model of columns has an l section of 600×600×200mm. the cross section details and dimensions of the specimen are shown in the table iii. the stiffness reduction factors calculated with liu formulation and the flexural stiffness ei corresponding for each axial load level are shown in table iv. a comparison of the results of liu with the flexural stiffness calculated with the proposed equation shows a good degree of accuracy between the results of liu and the proposed equation (figure 7). an average ratio of 0.983 was achieved. table iii. geometry and dimensios of the specimens in [9] column characteristic values b1 (mm) 400 b (mm) 600 dc (mm) 30 ρ (%) 2.512 fc (mpa) 14.3 fy (mpa) 360 l (mm) 2900 θ (°) 45 ec (mpa) 30000 es (mpa) 200000 ei=ecic+esis (kn.m 2 ) 77686 fig. 7. comparison of the proposed ei and the one of [9]. table iv. verification of the proposed equation with [9] axial load level αe eiliu=αe.ei (kn.m 2 ) eiprop (kn.m 2 ) eiprop/eiliu 0.10 0.4915 38182 31587 0.83 0.15 0.4782 37149 32662 0.87 0.20 0.4630 35968 33787 0.94 0.25 0.4464 34679 34790 1.00 0.30 0.4281 33257 35914 1.07 0.35 0.3996 31043 36981 1.19 average 0.983 engineering, technology & applied science research vol. 11, no. 3, 2021, 7100-7106 7106 www.etasr.com hamzaoui & bouzid: the proposition of an ei equation of square and l–shaped slender reinforced … ix. conclusion an iterative numerical procedure for the stiffness analysis and design of slender rc columns with square and l-shaped cross-sections under biaxial bending and axial loading using the unconfined kent and park stress is presented in this paper. the computational procedure takes into account the nonlinear behavior of the materials and includes the second order effects due to the additional eccentricity of the axial loading as applied by the moment-amplification method. the new equation suggested in this work is among the simplest proposed equations and its implementation is very easy to solve by manual calculation in a relatively short time. the concrete strength, the level of axial load, and the column slender ratio have been identified as the most important factors affecting the reduction coefficients and the effective bending stiffness ei. the formulation of the proposed method has been tested by comparison with other reported formulations. the results show that a good degree of accuracy and agreement has been achieved. references [1] aci 318-08: building code requirements for structural concrete and commentary. aci, 2008. [2] en 1992-1-1:2004 eurocode 2: design of concrete structures part 11: general rules and rules for. brussels, belgium: cen, 2004. [3] c. s. whitney and e. cohen, "guide for ultimate strength design of reinforced concrete," journal proceedings, vol. 53, no. 11, pp. 455– 490, nov. 1956, https://doi.org/10.14359/11524. [4] b. bresler, "design criteria for reinforced concrete columns under axial load and biaxial bending," aci journal, proceedings, vol. 10, no. 6, pp. 481–490, jan. 2005. [5] m. khuntia and s. k. ghosh, "flexural stiffness of reinforced concrete columns and beams: experimental verification," aci structural journal, vol. 10, no. 3, may 2004. [6] j. l. bonet, m. l. romero, and p. f. miguel, "effective flexural stiffness of slender reinforced concrete columns under axial forces and biaxial bending," engineering structures, vol. 33, no. 3, pp. 881–893, mar. 2011, https://doi.org/10.1016/j.engstruct.2010.12.009. 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[16] c. dundar, s. tokgoz, a. k. tanrikulu, and t. baran, "behaviour of reinforced and concrete-encased composite columns subjected to biaxial bending and axial load," building and environment, vol. 43, no. 6, pp. 1109–1120, jun. 2008, https://doi.org/10.1016/j.buildenv.2007.02.010. [17] d. c. kent and r. park, "flexural members with confined concrete," journal of the structural division, vol. 97, no. 7, pp. 1969–1990, 1971. [18] h. wang, y. zhang, and s. qin, "a study on ductility of prestressed concrete pier based on response surface methodology," engineering, technology & applied science research, vol. 6, no. 6, pp. 1253–1257, dec. 2016, https://doi.org/10.48084/etasr.855. [19] a. ali, z. soomro, s. iqbal, n. bhatti, and a. f. abro, "prediction of corner columns’ load capacity using composite material analogy," engineering, technology & applied science research, vol. 8, no. 2, pp. 2745–2749, apr. 2018, https://doi.org/10.48084/etasr.1879. microsoft word 9-2376_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3536-3540 3536 www.etasr.com memon et al.: effect of improper curing on the properties of normal strength concrete effect of improper curing on the properties of normal strength concrete ruhal pervez memon school of civil engineering, universiti teknologi malaysia, skudai, malaysia, ruhal_memon@hotmail.com abdul rahman m. sam school of civil engineering, universiti teknologi malaysia, skudai, malaysia, abdrahman@utm.my abdullah zawawi awang school of civil engineering, universiti teknologi malaysia, skudai, malaysia, abdullahzawawi@utm.my uroosa iqbal memon department of civil engineering, isra university, hyderabad, pakistan, uroosamemon57@gmail.com abstract—in real applications, 28 days are regarded as proper curing time for concrete. there is a self-evident need to minimize the duration of curing days. for this purpose, this research investigates 1 to 7 days of curing and compares it with concrete cured for 28 days. three grades of normal concrete strength grade 30, grade 35 and grade 40 were made. after curing, two exposure conditions were applied to the concrete, inside laboratory-controlled environment and outside environment. results indicate that slump increases with cement content in doe method at constant water content. the concrete density in all grades reduces when the concrete is subject to inside exposure in comparison with outside exposure. water loss from concrete reduces with increase in curing days in all concrete grades. compression strength of all concrete grades increases with increase in curing days. for the uniformity of concrete, ultrasonic pulse velocity indicated that with an increase in curing days, concrete becomes denser and a bit void. results showed that an increase in curing days also improves the surface quality of concrete. the significance point noticed is that there was not much difference in the concrete properties between 7 days of curing and 28 days of curing in all grades. keywords-curing; water loss; strength; concrete; grades i. introduction concrete is one of the major constituents in the construction field. curing of concrete is an important factor in getting required properties such as strength and durability. curing is of major importance, especially in the early stages of concrete to enhance the process of hydration of cement, control its temperature and moisture movement in and from concrete. the main reason of curing in early ages is to prevent the loss of water from the concrete, so that it can gain strength in its early days [1, 2]. curing is also important to prevent plastic shrinkage, permeability loss and to improve resistance to abrasion [3]. concrete hydration starts when water contacts with cement causing chemical reactions and increasing the concrete’s temperature [4]. if the concrete is not cured and exposed to dry air it gets almost the 50% of the strength of cured concrete, if it is cured for 3 days it gets the 60-70%, but if it is cured for 7 days it gets 80-90% of fully cured concrete strength [5]. so the canon is that concrete should be covered for at least 7 days [6]. the water loss of concrete occurs mostly from the surfaces exposed to the environment, where environmental humidity is lower than the humidity inside the concrete, which also results to reduced initial water-cement ratio and occurs due to cement hydration [7, 8]. however, at construction sites, concrete structures are usually exposed to dry conditions from an early stage. drying of concrete starts at the first day until several days after placing [9, 10]. theoretically, normal concrete consists of water-cement ratio greater than 0.42 and has enough water in the mixture for completion of its hydration process [4, 11]. on the other hand, in real life practice, in countries where temperature is high and relative humidity is low, concrete is subject to major water loss from the exposed surfaces [12]. improper curing of concrete occurs almost everywhere but especially it occurs on vertical members, inclined members, areas where water is in low quantity or not accessible for continuous curing [13-15] and where curing cannot be properly supervised [10]. in high-performance concrete, curing is very necessary because of its low water-cement ratio. the cement may reach a final degree of hydration that is less than 50%. initially, internal relative humidity drops very quickly, if it is not cured and relative humidity is dropped then it stops the hydration process [16]. it can exhibit early age cracking due to volumetric changes through self-desiccation [17, 18]. it happens when water evaporates which results in tensile stress inside the concrete and sometimes tensile stress exceeds the tensile strength [7, 19, 20]. in addition, high-performance concrete mostly contains supplementary cementitious materials, which may require prolonged curing [21]. due to improper curing in high-performance concrete, cementitious materials hydrate under sealed conditions, empty porosities are created within the concrete because the hydration products occupy less volume than the reacting materials. the core purpose of this research is to investigate the effect of improper curing on water loss, strength, and uniformity. also, to find the minimum curing days that are enough for concrete to get its desired strength. ii. methodology the range of normal strength concrete is between 30mpa to 40mpa. in this research, three grades of normal concrete were engineering, technology & applied science research vol. 8, no. 6, 2018, 3536-3540 3537 www.etasr.com memon et al.: effect of improper curing on the properties of normal strength concrete made that are grade 30, grade 35 and grade 40. the design of concrete was made according to doe method and the content of mixtures is shown in table i. the slump was kept between 60mm and 180mm. portland cement was the basic ingredient and type i cement was used. the maximum size of fine and coarse aggregates was kept to 4.75mm and 10mm respectively. table i. concrete parameters grade mix design w/c ratio cement (kg/m 3 ) water (kg/m 3 ) fine aggregates (kg/m 3 ) coarse aggregates (kg/m 3 ) g30 0.55 445 250 875 815 g35 0.51 495 250 840 810 g40 0.47 535 250 805 805 for the evolution of improper curing, a cube of 100mm×100mm×100mm size was casted according to bs 1881-108:1983. then, samples from each grade mixture of normal strength concrete were cured. after curing, the samples were taken out from the curing tank and kept inside the laboratory (controlled environment) and outside the laboratory (not controlled environment). this process was done for 1 to 7 and 28 days of curing. the workability of concrete mixtures was measured by slump cone test according to bs 1881102:1983. the density of hardened concrete was measured according to bs 1881-114:1983. water loss measured by weighing the sample every day until water loss became constant [14, 22, 23]. the compression strength and modes of failure on cubes were tested according to bs 1881-116:1983. ultrasonic pulse velocity of cubes was carried out according to bs 1881-203:1986. rebound hammer was tested on cubes according to bs 1881-202:1986. iii. results and discussion a. workability workability was measured to check the ease of concrete mixture. in this research, the slump was designed between 60mm and 180mm. it was observed that the increase of cement content at constant water-cement ratio increases the workability of concrete because of the total aggregate content decrease in doe method. increasing the amount of cement in the mixes and decreasing aggregate content led to an excess of water in the medium and hence, to an increase of the workability as shown in figure 1. the results agree with the findings in [24]. fig. 1. slump values of variou concrete grades. b. density of hardened concrete concrete is composed of cement, fine aggregates, coarse aggregates and water. the density of concrete varies depending on the amount and density of aggregates, amount of entrained air, cement and water. proper curing has a significant effect on the density of concrete [25]. in this research, for grade 30, 35 and 40, the density of concrete behaves differently when samples are exposed to laboratory and outside the laboratory conditions. in all grades, the density of the inside laboratory samples reduced at 28 days compared to the 1st day as shown in figures 2-4, due to water evaporation from concrete. in the case of samples placed outside the laboratory, the density of concrete increased at 28 days compared to the 1st day as shown in figures 2-4, mainly due to rainfall. results agree with the findings in [1, 26]. another trend was also noticed: increase in days of curing, reduces the difference between the 1-day density and 28-day density of concrete. seven days of curing have the same density as one day of curing. the concrete density is inversely proportional to the porosity of pore structures in concrete [27]. it can be observed that 7 days of curing do not affect the density of concrete. fig. 2. density of concrete grade 30 at 1 and 28 days. fig. 3. density of concrete grade 35 at 1 and 28 days. fig. 4. density of concrete grade 40 at 1 and 28 days. engineering, technology & applied science research vol. 8, no. 6, 2018, 3536-3540 3538 www.etasr.com memon et al.: effect of improper curing on the properties of normal strength concrete c. water loss from normal strength concrete the water content and concrete curing are essential in the concrete early ages. this research is carried out to see the effect of improper curing on the trend of water loss of concrete. for this purpose, the cured samples were kept inside and outside the laboratory for 1 to 7 days. as shown in figure 5, with increase in the curing days of concrete, water loss becomes low in all grades of normal strength concrete. at 7th day the samples cured for 1 day have more water loss as compared with the samples cured for 6 days. the same trend of water loss for grade 40 and grade 60 resulted in [14, 22]. the samples kept outside the laboratory after each curing day did not show a uniform trend of water loss as shown in figure 6. it is also noticed that as the water-cement ratio of concrete reduces, it also reduces the water loss due to the relative increase in the cement content, as was also reported in [23, 26]. fig. 5. water loss from concrete grade 30, 35 and 40 (inside). fig. 6. water loss from concrete grade 30, 35 and 40 (outside). d. ultrasonic pulse velocity the ultrasonic pulse velocity (upv) test is a nondestructive test that measures quality and homogeneity of concrete specimens to determine the existence of pores and cracks [28]. experimental results indicate that, in all grades of concrete, increase in curing duration results in increased upv due to more concrete hydration, it reduces voids and makes concrete dense [29]. upv values are in the range of 3.5-4.5, as shown in figures 7-9, which comes in good concrete quality, as shown in table ii. table ii. concrete quality based on upv [29] upv (km/s) quality of concrete >4 excellent 3.5–4.5 good 3.0–3.5 doubtful 2.5–3.0 poor <2.5 very poor it is also noticed that 28 days curing have the highest upv and this concrete comes in the category of excellent quality. less upv indicates high porosity of concrete and vice versa. higher values of upv give higher concrete strength [30, 31]. fig. 7. grade 30 upv results at 28 days. fig. 8. grade 35 upv results at 28 days. fig. 9. grade 40 upv results at 28 days. e. rebound hammer rebound hammer test was carried out to investigate the hardness and surface quality of concrete in depth up to 30mm inside from the surface. in this research, the test was carried out because water loss mostly occurs from the surface of concrete. first rebound hammer test should not be carried out before 14 days and later after 3 months as prescribed in bs-1881:2021981. in this research, it is noticed that increase in days of curing of concrete also increases rebound hammer number in all grades of normal strength concrete as shown in figures 1012. increase in grade of normal strength concrete also increases rebound hammer number. rebound hammer number of 1 day curing at 28 days is less than the one after 7 days and 28 days of curing because hydration process got stopped due to less curing than required and surface did not become hard. it has also been observed that 7 days curing, and 28 days curing have not much difference in rebound hammer number at 28 days in all grades of normal strength concrete. the comparative engineering, technology & applied science research vol. 8, no. 6, 2018, 3536-3540 3539 www.etasr.com memon et al.: effect of improper curing on the properties of normal strength concrete rebound hammer values according to british standard are given in table iii. so, 1 day to 7 days curing at 28 days was lying in good concrete quality, but 28 days curing has an excellent concrete quality in all grades of normal strength concrete. the same trend of results is also shown in [32]. table iii. comparative rebound hardness values rebound number quality of concrete >40 very good 30-40 good 20-30 fair <20 poor 0 very poor fig. 10. rebound number of grade 30 at 28 days. fig. 11. rebound number of grade 35 at 28 days. fig. 12. rebound number of grade 40 at 28 days. f. compression strength curing is a very important factor for the concrete to gain compression strength and is essential when there is high chance of water loss. that is occurring at the early ages of concrete, when cement hydration takes place. in this research, all samples were compared with the 28-day curing samples of concrete. as shown in figure 13, with increase in curing days the strength of concrete in all grades of normal strength concrete also increases, when exposed inside and outside the laboratory. if the grade 30 concrete is cured for 1 day and then kept 27 days inside the laboratory, then its compression strength at 28 days is 38% less than 28 days curing strength and 25% less than 7 days curing strength. when the sample was kept outside, its 1 day curing strength at 28 days was 26.5% less than 28 days curing strength and 20.5% less than 7 days curing strength. the same trend is also seen in other grades of concrete. the results in [14, 22] also showed that 1 day curing at 28 days has less strength when compared with 28 days curing strength, almost the same percentage of loss is noticed. in figure 13, it is also noticed that the samples kept outside the laboratory have a little bit higher strength when compared with the samples kept inside the laboratory. this occured because of the additional water gained from rain. from figure 13, it is also noticed that there is not much difference in the strength of 7 days curing and 28 days curing, inside samples cured for 7 days have 10% less strength than 28 days curing strength at 28 days and outside samples had 5% less strength at 28 days. fig. 13. compression strength values of grade 30, 35 and 40 at 28 days. iv. conclusion this research concludes that slump of concrete increases in doe method, when cement increases at constant water content and total aggregate content reduces for all grades of normal strength concrete. the density of concrete at 28 days is reduced when subjected to exposure inside the laboratory after curing. the water loss from concrete decreases with increasing curing days and all kept inside grade samples behaved differently than the samples subjected to outside exposure because, due to rainfall water, water loss was not estimated properly. the compression strength increases with increase in curing days in all grades of normal strength concrete but outside exposure samples had slightly higher compression strength when compared to the samples subjected to inside exposure. the uniformity of concrete also improved with increase in curing days, which indicates that by increasing the days, concrete becomes dense and voids lessen. rebound hammer test results indicate the concrete surface quality. the rebound hammer value increases with increase in curing days. the core point to be noticed is that there was no significant difference in the properties of 7 days curing and 28 days curing of all grades of normal strength concrete at 28 days, so it can be concluded that 7 days curing is enough for normal strength concrete. references [1] a. a. raheem, a. a. soyingbe, a. j. emenike, “effect of curing methods on density and compressive strength of concrete”, international engineering, technology & applied science research vol. 8, no. 6, 2018, 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pp. 167-175, 2014 [27] t. r. naik, “concrete durability as influenced by density and/or porosity”, cement and concrete institute of mexico symposium “world of concrete-mexico”, guadalajara, mexico, june 4-7, 1997 [28] h. mohammadhosseini, n. h. a. s. lim, a. r. m. sam, m. samadi, “effects of elevated temperatures on residual properties of concrete reinforced with waste polypropylene carpet fibres”, arabian journal for science and engineering, vol. 43, no. 4, pp. 1673-1686, 2018 [29] g. karaiskos, a. deraemaeker, d. g. aggelis, d. v. hemelrijck, “monitoring of concrete structures using the ultrasonic pulse velocity method”, smart materials and structures, vol. 24, no. 11, p. 113001, 2015 [30] k. haddad, o. haddad, s. aggoun, s. kaci, “correlation between the porosity and ultrasonic pulse velocity of recycled aggregate concrete at different saturation levels”, canadian journal of civil engineering vol. 44, no. 11, pp. 911-917, 2017 [31] w. zhong, w. yao, “influence of damage degree on self-healing of concrete”, construction and building materials, vol. 22. no. 6, pp. 11371142, 2008 [32] c sreenivasulu, j. g. jawahar, c. sashidhar, “predicting compressive strength of geopolymer concrete using ndt techniques”, asian journal of civil engineering, vol. 19, no. 4, pp. 1-13, 2018 microsoft word etasr_v13_n3_pp10843-10848 engineering, technology & applied science research vol. 13, no. 3, 2023, 10843-10848 10843 www.etasr.com kumar & kumar: free vibration analysis of steel-concrete pervious beams free vibration analysis of steel-concrete pervious beams prashant kumar department of civil engineering, national institute of technology patna, india pk0895300@gmail.com (corresponding author) ajay kumar department of civil engineering, national institute of technology delhi, india sajaydce@gmail.com received: 4 april 2023 | revised: 22 april 2023 | accepted: 24 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5913 abstract this study investigated the free vibration analysis of steel-concrete porous beams with partial or complete shear interface using a finite-element model based on the cubic order beam theory. the present model assumes uniform porosity distribution along the beam thickness. it is assumed that the axial displacement will vary cubically along the thickness of the layer. the cubic order beam theory is implemented using a continuous c 0 finite element containing three nodes and each node has eight degrees of freedom. shear locking is eliminated in the present model by the numerical integration of the stiffness matrix. comparing the present model with the published literature, it is found that the present model is robust in predicting the free vibration of the steel-concrete porous beam. keywords-steel-concrete porous beams; finite element method; free vibration; porosity; partial shear interface i. introduction new construction materials are constantly developed for various innovative engineering structures which must withstand static and dynamic loads. more and more companies are adopting cost-effective materials, while enhancing the safety and efficiency of engineering projects. many engineering practices use composite beams, such as steelconcrete beams, in buildings and bridges, wood-concrete floors, linked shear walls, etc. [1, 2]. in structural design, it is necessary to focus on the materials and the strength of the connectors. the structure of composite beams is affected by the interlayer slip under loading. the impact of partial contact on the structural behavior was investigated in [3]. the euler– bernoulli beam theory was used in [4] to investigate the free vibration characteristics of steel-concrete composite continuous beams. various experimental and analytical studies have been conducted to analyze composite beams [5]. applying the eigenfunction expansion method along with the quasistatic decomposition method, an analytical solution is presented in [6]. authors in [7, 8] worked on the vibrational behavior of nanocomposite beams. under the effect of a moving load, the beam is reinforced by random straight single-walled carbon nanotubes (swcnts). the accurate results of higher-order beam theory (hbt) intrigued researchers, so tbt has been replaced with hbt in order to obtain more accurate solutions. authors in [9] built on reddy's approach to an hsdt for multi-layered anisotropic composite laminates having complete shear interaction. c 0 finite element models were presented for evaluating composite and sandwich beams and the penalty function approach was used to find a c 0 continuous finite element formulation [10, 11]. analysis of 3 different porosity variations in the thickness direction and their impact on the vibrational properties of the beam are presented in [12]. free and forced lateral vibration analysis of beams made from functionally graded materials (fgms) using the finite element method (fem) is presented in [13]. the state-space technique was used in [14] to expand the static analysis to dynamic analysis without the use of axial force. from the literature review, it can be seen that there are a few studies regarding the free and forced vibration of a porous steel-concrete beam with a partial shear interface. therefore, the present study uses the cubic order equation for axial displacement. a linear finite element model is developed for the dynamic analysis of a porous composite beam. the proposed composite beam has a partial or complete shear interaction. the homogeneous porosity distribution along the beam thickness is used to parametrically calculate the material properties. different interfacial stiffness values are used to calculate the fundamental frequency. the present model is effective for analyzing the free vibrations of porous beams made of steel and concrete under various boundary conditions and moving loads. several new findings are presented in this paper, making it useful for the subsequent analysis of the free vibration of porous composite beams in the future. engineering, technology & applied science research vol. 13, no. 3, 2023, 10843-10848 10844 www.etasr.com kumar & kumar: free vibration analysis of steel-concrete pervious beams ii. formulation a. porosity distribution this study evaluates how steel and concrete porosity influence the free vibration of composite beams. due to the uniform distribution of porosity, the variation in young’s modulus, shear modulus, and mass density of the concrete and the steel layer is calculated by:           max max max 1 1 1 i i i i i mi i e y e g y g y e               (1) where ei(y), gi(y), ρi(y) are the young’s modulus, shear modulus, and mass density of the concrete (upper) layer and steel (lower) layer of the beam along the transverse direction (where i = c-concrete, s-steel). m i n m i n m a x m a x 1 1i e g e e g     (2) 1 1mi ie e   (3) where the range of the porosity coefficient for mass density (em), porosity coefficient of concrete (e0), and porosity coefficient of steel (e1) are 0 < ��� < 1 , and 0 < �� < 1 . ei = emi = 0 means that porosity is zero at maximum elastic modulus and greater porosity gives lower elastic modulus. 2 2 2 1 1 1i ie             (4) b. mathematical formulation high-order beam theory is used to investigate the free vibration analysis of a composite beam having a shear interface as shown in figure 1. the displacement field that was selected is unique. transverse shear stresses must cease on the beam surfaces and remain nonzero elsewhere for the requirements to be satisfied, which determines the shape. the beam's axial displacement is considered as the thickness's cubic function. the axial displacement equation for the upper layer is expressed in (5). h c /2 h c /2 h s/ 2 h s/ 2 yc ys fig. 1. porous steel-concrete composite beam with shear flexible interface.    2 31 ti i i c io i i iu y y y u       (5) where ��� = ���, �� , �� is the axial displacement along the top layer's reference axis passing through its centroid, �� = ���� is the bending rotation, and �� = ���� and �� = ���� are highorder terms. the transverse displacement is assumed to be the same for both layers and can be represented as: ( , , ) ( , , ) ( ) c c s s w x y z w x y z w x w   (6) the partial shear interaction between two layers of the composite beam is modelled by taking distributed shear springs at their interface. the interfacial stiffness and the shear slip at the interface are used to figure out the shear stress at the interface. interfacial slip (s) is calculated in (7) with u’c and u’s being the axial displacement of the upper and lower layer at the interface. ' ' ( ) c s s u u  (7) axial displacement equations, such as (5), are higher-order equations that are concerned with the warping of transverse sections, but do not describe the commonly used displacement parameters adopted in beam theories. so, higher order terms are eliminated by using shear stress-free conditions at the extreme surfaces of the composite beam. the shear stress at any point in the upper layer is calculated by:      2 1 2 3 1 c c c c c c c c t c c c g u w y y y x w x                           (8) where γc is the shear strain and gc the shear modulus of porous concrete layer. 2 3 2 3 2 3 2 3 2 3 2 2 3 2 2 3 2 3 12 16 1 , 5 5 12 16 , 5 5 4 12 , 5 5 2 4 5 5 12 16 1 , 5 5 c c c c c c c c c c c c s s s s y y a h h y y b h h y y c y h h y y d h h y y a h h b                                                                                     2 3 2 3 2 3 2 2 3 2 12 16 , 5 5 4 12 , 5 5 2 4 , and 5 5 s s s s s s s s y y h h y y c y h h dwy y d h h dx                                                (9) shear stress-free conditions are applied at the top and bottom surface of the beam to find the displacement equation. engineering, technology & applied science research vol. 13, no. 3, 2023, 10843-10848 10845 www.etasr.com kumar & kumar: free vibration analysis of steel-concrete pervious beams     ' t i i i i i io ii u a b c d u u      (10) the normal stress and normal strain at any point of the beam are calculated by:     j jj d     (11)       j j j jj jj j u x h u w y x                             (12) where σj is the normal stress, τj the shear stress, ej the modulus of elasticity, gj the shear modulus, εj the normal strain, and γj the shear strain of the j th layer, j=c represents the upper layer and j= s represents the lower layer of two-material composite beams. �� � is a function of yj and ���� is the function of xj which is coordinated along the axial direction. the expressions of �� � and ���� are:   0 0 0 0 0 0 0 0 0 1 j j j j j j j jj j j j j a b c d da db dc ddh dy dy dy dy           (13)   ' 'jo j j jo jj t j ddu d d w u dx dx dx dx x u u               (14) the strain energy as a function of stress and strain can be found by (11)-(12).                     1 2 1 2 t t c s c s t t c sc s c s u dadx d d dx                       (15) where       t c cc cc hd d h da    ,       t ss sss d d h dah       numerical integration is used to evaluate the cross-section rigidity matrix �� � and �� �. stored strain energy is calculated by (7) and distributed shear springs stiffness (ks):   2 ' '' 21 1 2 2 s s c s u k s dx k dxu u    (16) c. finite element formulation first of all, the 3-nodded iso-parametric c o element is selected. this theory assumes 8 nodal degrees of freedom to solve the present problem using a one-dimensional finite element approximation written as:    ' ' t coj cj cj j j soj s sf u u w u u   (17) the unknown nodal displacement vector ��� on the middle surface of a typical element is given by:       3 1 , .i i i d x y d   (18) where ψi is the shape function. the generalized strain vector as a function of the nodal displacement vector {d} can be found by:      3 1 i ij i p d    (19) where [pi] is the interpolation function differential operator matrix. the strain vectors are calculated by (13), (16), and (18) as a function of the stiffness matrix lk   .     1 2 t l u d k d    (20) where:             ts tl c c s scp p k d p d p dx      (21) similarly, the interfacial stiffness and stiffness due to the penalty function approach are given below:  ' ' 't sk p k p dx           (22)  tp p ppk p k p dx           (23) now we can integrate (21), (22), and (23) and combine them to find out the element stiffness matrix [k].   'l pk k kk              (24) an element's mass matrix and its geometric stiffness matrix can be found in the same way as the element stiffness matrix is calculated above. equations (16)-(18) are used to find out the displacement component vector at a point in the beam layer:       j j j u f f f f x d w                (25) where jf   is a matrix of order 2×8 which contains the coefficient of displacement component expressed in (25) and [x] is a shape function matrix of order 8×24. now, the consistent mass matrix of 3-nodded elements is developed by using (25) and is expressed as:        .t tj j jx f f dzm x dx dy        (26) free vibration analysis is conducted to find out the fundamental natural frequency from the given equation:    2 0g gk m     (27) where ω is the vibration frequency and   the eigenvector. engineering, technology & applied science research vol. 13, no. 3, 2023, 10843-10848 10846 www.etasr.com kumar & kumar: free vibration analysis of steel-concrete pervious beams iii. results and discussion a finite element technique based on the cubic order beam theory was used to examine steel-concrete beam features to assess the effectiveness of the recommended model. the findings are produced by implementing the proposed model in fortran code. a. comparison study for the validation of the results, a two-layered simple support composite beam having a t-cross section is considered. the four different boundary conditions (bcs) ss, sc, cc, and cf (ss = simply supported, c = clamped, f = free) and the partial interaction of the composite beams were taken into consideration. the results used for validation are taken [14], in which the state-step approach is used to tackle this issue. in this example, the cross-sectional size and material characteristics of a two-layered composite beam are stated as: span length (l) of beam equal to 4m, the upper and lower elements are 0.05×0.30m 2 and 0.15×0.05m 2 , respectively, the modulus of elasticity of the upper (e1) and lower elements (e2) are 12gpa and 8gpa, respectively, the modulus of rigidity of the upper (g1) and lower element (g2) are 5gpa and 3gpa, respectively, and the mass densities of the upper and lower elements are taken as ρ1 = 2400kg/m 3 and ρ2 = 500kg/m 3 , respectively, using partial interfacial spring stiffness ks = 50mpa. the free vibration frequencies (rad/s) for various bcs are listed in table i. fifty elements throughout the length of the beam are used to determine the present findings. the natural frequency of a simply supported (ss) beam determined in [14] and using the state-space technique is contrasted with the present results. the error percentages are also listed in parentheses. in the present simulation, the results are quite accurate and in close agreement with those in [14] with an accuracy of 99.76%. table i. validation of the fundamental frequency of a composite beam (e0=e1=0). s.no. bc fundamental frequency (rad/s) present [14] 1. cf 25.06 25.12 (0.24) 2. ss 64.56 64.85 (0.45) 3. sc 88.78 89.56 (0.88) 4. cc 116.66 118.50 (1.58) note: parameters in parentheses represent percentage errors. b. steel-concrete porous beam in the present study, steel-concrete two-material composite beams with different porosity, bcs, and different interfacial shear stiffness values are taken for analysis. the beam's crosssection (figure 2) is made up of a rectangular slab with a thickness and width of 0.15m and 2.25m respectively, an ishaped steel joist with a flange dimension of 0.1780×013m, and a web dimension of 0.380×0078m. the material properties of the two layers are as follows: beam span l = 15m, the modulus of elasticity ec and the modulus of rigidity gc of the upper (concrete) element are 13.55gpa and 6.775gpa, respectively, and the modulus of elasticity es and the modulus of rigidity gs of the lower (steel joist) element are 200gpa and 100gpa, respectively. the maximum densities of the concrete element and the steel layer are taken as ρc = 2396.45kg/m 3 and ρs = 7948.89kg/m 3 , respectively, and the uniform porosity distribution of the concrete and steel element is taken as 0, 0.05, 0.10, 0.20, 0.30, and 0.4. in the case of partial interaction, it is assumed that the interfacial shear spring stiffness ks is 100mpa. a moving point load of magnitude 100kn is applied. the point load is traveling from the left support to the right support at a constant speed v0 of 16.67m/s. bc tc bf tw tf hw fig. 2. cross section of the steel-concrete porous flanged composite beam. c. effect of boundary conditions, porosity, and interlayer spring stiffness on fundamental frequency in both cases, the fundamental frequency of a ss steelconcrete porous beam with partial or complete shear interface varies with the porosity as shown in figure 3. (a) (b) fig. 3. variations of fundamental frequency as a function of (a) porosity of the steel element and (b) porosity of concrete and steel elements. engineering, technology & applied science research vol. 13, no. 3, 2023, 10843-10848 10847 www.etasr.com kumar & kumar: free vibration analysis of steel-concrete pervious beams it decreases with an increase in the porosity of the concrete slab and steel joist. the fundamental frequency of the steelconcrete porous beam is greater with a complete shear interface than with a partial shear interface. table ii describes the effect of the porosity of steel (e1=0, 0.05, 0.1, 0.2, 0.3, and 0.4) and bcs on the fundamental frequency of complete and partial interface steel-concrete porous beams without considering the damping effect. it is maximum for the cc (clamped, clamped) and minimum for the cf (clamped, free) bc. table iii shows the effect of steel and concrete layer porosity variations on the fundamental frequency (e0=e1=0, 0.05, 0.1, 0.2, 0.3, and 0.4). the different boundary conditions are considered. table iv analyzes the impact of the interfacial shear stiffness (ks) on the fundamental frequency. porosity variation is taken into account in this scenario. fundamental frequencies increase as interfacial shear stiffness increases, as can be easily seen. the fundamental frequency of a steel-concrete porous simply supported beam is expected to change with its porosity. table ii. fundamental frequency of porous beam for different porosity (e1) and boundary conditions porosity (e1) fundamental frequency(rad/s) partial composite full composite cf ss sc cc cf ss sc cc 0.00 5.9217 15.5493 22.0437 29.6486 6.2464 17.4810 27.0829 38.8882 0.05 5.8527 15.3843 21.8207 29.3481 6.1676 17.2605 26.7407 38.3962 0.10 5.7815 15.2140 21.5914 29.0400 6.0863 17.0332 26.3879 37.8891 0.20 5.6318 14.8553 21.1112 28.3985 5.9155 16.5555 25.6468 36.8240 0.30 5.4703 14.4680 20.5966 27.7164 5.7320 16.0420 24.8503 35.6798 0.40 5.2944 14.0451 20.0388 26.9833 5.5327 15.4845 23.9859 34.4384 table iii. fundamental frequency of porous beam for eo, e1, and boundary conditions porosity fundamental frequency(rad/s) partial composite full composite eo e1 cf ss sc cc cf ss sc cc 0.00 0.00 5.9217 15.5493 22.0437 29.6486 6.2464 17.4810 27.0829 38.8882 0.05 0.05 5.8354 15.3453 21.7723 29.2861 6.1470 17.2027 26.6518 38.2691 0.10 0.10 5.7489 15.1407 21.5010 28.9246 6.0473 16.9239 26.2198 37.6488 0.20 0.20 5.5744 14.7276 20.9562 28.2019 5.8467 16.3625 25.3501 36.4000 0.30 0.30 5.3964 14.3058 20.4039 27.4742 5.6429 15.7920 24.4661 35.1307 0.40 0.40 5.2130 13.8700 19.8374 26.7337 5.4335 15.2062 23.5586 33.8276 table iv. fundamental frequency of porous ss composite beam for different porosity eo, e1, and interfacial stiffness (ks) porosity fundamental frequency(rad/s) eo e1 ks=10 -2 ks=10 -1 ks=10 0 ks=10 ks=10 2 ks=500 ks=10 3 ks=10 4 0.00 0.00 10.6498 10.6660 10.8244 12.0652 15.5493 16.9769 17.2189 17.4538 0.05 0.05 10.4803 10.4968 10.6577 11.9090 15.3453 16.7213 16.9527 17.1768 0.10 0.10 10.3105 10.3273 10.4909 11.7535 15.1407 16.4649 16.6858 16.8993 0.20 0.20 09.9686 09.9861 10.1557 11.4437 14.7276 15.9478 16.1479 16.3404 0.30 0.30 09.6212 09.6395 09.8164 11.1336 14.3058 15.4207 15.6003 15.7722 0.40 0.40 09.2644 09.2837 09.4695 10.8208 14.8700 14.8777 15.0371 15.1888 iv. conclusions in this paper, one-dimensional finite element methods based on cubic order beam theory are used to analyze the free vibration of pervious steel-concrete beams. the distribution of linear shear springs is used to simulate partial shear interaction between layers. the cubic order beam theory is implemented using a continuous c 0 finite element containing 3 nodes. this work presents a novel analysis of the effect of porosity on the fundamental frequency of layered composite beams. the main findings of this study are:  as the porosity of the steel-concrete composite beam increases from 0 to 0.40, the fundamental frequency decreases by 10% in partial interaction and approximately 13.0% in the complete composite.  the presented finite element formulation shows the relationship between the fundamental frequency and various parameters such as the interfacial shear stiffness and end supports.  in cf support, the fundamental frequency is minimum, whereas it is maximum in cc support.  it is greater for a complete shear interface than for a partial shear interface. an increase in interfacial shear stiffness from 10 -2 to 10 4 leads to an increase in fundamental frequency by more than 63%.  the proposed model is more accurate in predicting the free vibration of composite steel-concrete porous beams than the existing models based on ebt and tbt. acknowledgment the authors would like to thank the national institute of technology patna (india) for its financial support. engineering, technology & applied science research vol. 13, no. 3, 2023, 10843-10848 10848 www.etasr.com kumar & kumar: free vibration analysis of steel-concrete pervious 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[14] x. shen, w. chen, y. wu, and r. xu, "dynamic analysis of partialinteraction composite beams," composites science and technology, vol. 71, no. 10, pp. 1286–1294, 2011, https://doi.org/10.1016/j.compscitech. 2011.04.013. engineering, technology & applied science research vol. 7, no. 6, 2017, 2277-2281 2277 www.etasr.com kurmasha et al.: enhancement of edge-based image quality measures using entropy for histogram … enhancement of edge-based image quality measures using entropy for histogram equalization-based contrast enhancement techniques hasan thabit rashid kurmasha computer department college of education for girls kufa university najaf, iraq hasant.kurmasha@uokufa.edu.iq chen soong der department of graphics and multimedia college of information technology university tenaga nasional selangor d.e., malaysia chensoong@uniten.edu.my abbas fadhil hamzah alharan computer department college of education for girls kufa university najaf, iraq abbasf.abood@uokufa.edu.iq nur hanani azami department of graphics and multimedia college of information technology university tenaga nasional selangor d.e., malaysia trulyhanani@gmail.com abstract—an edge-based image quality measure (iqm) technique for the assessment of histogram equalization (he)based contrast enhancement techniques has been proposed that outperforms the absolute mean brightness error (ambe) and entropy which are the most commonly used iqms to evaluate histogram equalization based techniques, and also the two prominent fidelity-based iqms which are multi-scale structural similarity (mssim) and information fidelity criterion-based (ifc) measures. the statistical evaluation results show that the edge-based iqm, which was designed for detecting noise artifacts distortion, has a person correlation coefficient (pcc) > 0.86 while the others have poor or fair correlation to human opinion, considering the human visual perception (hvp). based on hvp, this paper propose an enhancement to classic edgebased iqm by taking into account the brightness saturation distortion which is the most prominent distortion in he-based contrast enhancement techniques. it is tested and found to have significantly well correlation (pcc > 0.87, spearman rank order correlation coefficient (srocc) > 0.92, root mean squared error (rmse) < 0.1054, and outlier ratio (or) = 0%). keywords-histogram equalization; contrast enhancement; image quality measures; distortions; human visual perception i. introduction automatic assessment of image quality is the target of an image quality assessment (iqa) algorithm, therefore a great deal of effort has been made to develop iqa algorithms that correlate well with human visual perception (hvp) of distortions. absolute mean brightness error (ambe) and entropy are two popular iqa algorithms for assessment of histogram equalization (he) based contrast enhancement method. he technique is widely used in various fields however, he could cause annoying distortions such as excessive brightness change, noise artifacts and brightness saturation (see figure 1) and because of this it is not commonly used in consumer electronic devices. hence, many modifications of he-based techniques have been suggested over the years. they can be distinguished in two main classes. automatic (the processing does not need user interference [112]) and adjustable (the user needs to adjust the parameters to control the degree of enhancement). it is important for the iqm to have a good correlation with hvp. therefore, this subjective evaluation investigates the problem of noise artifacts distortion in he-based technique from perspective of the iqm’s correlation with human opinion on the perceived annoyance of distortions in relating with the luminance and texture masking of hvp [13]. this paper concentrates on the problem of the second type of distortions (brightness saturation) in automatic he-based techniques. the paper is organized as follows: in section ii a review of basic iqms is presented. the proposed iqm framework and the algorithm details are presented in section iii. the evaluation and discussion of the work and results related to hvp in section iv. the conclusion and recommended future work in section v. ii. review of iqms a. ambe ambe is the absolute difference between the mean of input and output image and basically defined by (ambe = | e(x) − e(y) |) where, x and y denote the input and output image engineering, technology & applied science research vol. 7, no. 6, 2017, 2277-2281 2278 www.etasr.com kurmasha et al.: enhancement of edge-based image quality measures using entropy for histogram … respectively, and e (·) denotes the expected value, i.e. the statistical mean. ambe is designed to detect the excessive brightness change distortion. noise artifacts and brightness saturation distortions are not taken into account by ambe, hence using it to detect other types of distortion could be misleading as explained in figure 2. fig. 1. he’s three distorstions types. fig. 2. caps image with two different ambe values, (b) caps with less ambe (14.02) obviously shows the noise distortion in the background and brightness saturation in the image which is not seen in (a) with high ambe (37.31). b. entropy measure entropy is a measure of the uncertainty associated with a random variable (shannon entropy). it counts, in the sense of an expected value, the information contained in an information source (the image). hypothetically, higher entropy means more information is available from the information source. therefore, an image having higher entropy is considered to have a better quality [14]. since the global gray levels have relatively low probability density, he tends to combine them and results in decrease of entropy although such action tends to increase the contrast of an image as we see in figure 3. c. edge-based iqm in general, the noise artifacts distortions appear in the form of edges found in distorted images generated by he-based techniques. they however are not found in the original one. thus, edge detection is the basic step to extract the features of the image annoying distortion in this metric. basically, image annoying distortion can be classified as noise artifacts when the edge points are noticed in distortion image and not noticed in the original image. hvp masking incorporates with the detection of noise artifacts [13]. this paper proposes to develop this iqm by taking into account the second most popular type of distortion which is the brightness saturation incorporating with hvp. fig. 3. parrots image with two different entropy values, (b) parrots with lower entropy (5.72) clearly shows better contrast than (a) with higher entropy (5.74). iii. proposed iqm the generic framework of the proposed entropy-based iqm is developed as shown in figure 4. fig. 4. generic framework of proposed iqm. a. proposed iqm framework 1. brightness saturation’s features collection: this work’s purpose is to develop the edge-based iqm (noise detection) by concentrating on the brightness saturation which is commonly found in the output images of he-based techniques. in he-based technique, the brightness saturation occurs when there are very obvious and annoying noise artifacts. this is due to the contrast stretching mechanism of he which performs more contrast stretching to dominant gray levels which in turn may lead to the extension of noise artifacts, while contrast shrinks those which may cause brightness saturation [13]. hence, brightness saturation happens when several gray levels are grouped into one. therefore, it can be detected as a decline in the entropy of gray level and to measure that, hvp features were taken into account. the proposed enhancement will be further elaborated into the next subsection 2. algorithms gathering: to get two types of annoying distortion, all detected pixels of noise artifacts from noise algorithm and pixels of brightness saturation from brightness saturation algorithm are gathered according to their respective weight in a single iqm. engineering, technology & applied science research vol. 7, no. 6, 2017, 2277-2281 2279 www.etasr.com kurmasha et al.: enhancement of edge-based image quality measures using entropy for histogram … b. generic proposed iqm algorithm the general flowchart of the proposed entropy-based iqm algorithm is shown in figure 5. fig. 5. flowchart of the proposed iqm algorithm. prior to edge detection, the colour image is converted to grayscale image using the conversion in (1): igray(r,c)=0.2989ired(r,c)+0.5870igreen(r,c)+0.1140iblue(r,c) (1) edges are detected by using the sobel operator which has two masks, the horizontal mask (row mask) mh, and the vertical mask (column mask) mv, defined as: 1 2 1 1 0 1 1 1 0 0 0 , 2 0 2 8 8 1 2 1 1 0 1 h vm m                        (2) the edge magnitude of a point at row r and column c of an image is defined as below. 2 2( , ) r cem r c s s  (3) 1 1 0 0 ( 1 , 1 ) ( , ) n m r h i j s i r i c j m i j          (4) 1 1 0 0 ( 1 , 1 ) ( , ) n m c v i j s i r i c j m i j          (5) in a distorted image, if a point’s edge magnitude is equal or exceeds its predetermined threshold value while the edge magnitude of the same point in the original image is less than the predetermined threshold value then the point is classified as edge point. the threshold value thr_image_edge (r, c) for both images is counted based on the effect of luminance masking by considering two thresholds (thr_low_lum, and thr_high_lum) to compare with the luminance level average lum_avg(r,c) of each subimage n × n (n =3). the suggested standard threshold value t is chosen to be the standard threshold which is used for normalization of both the original and distorted images i(r, c) as shown below.    2thr_image_edge(r,c)=t , ( _ ( , ) _ _ _ ) , _ _ if lum avg r c th um and lum avg r c thr h r l i o u w l gh l m       (6) or:    2thr_image_edge(r,c)=2t , ( _ ( , _ , _ _ ) _ _ ) if lum avg r c t um lum avg r c h thr high r low l luo mr       (7) 1 1 2 0 0 1 _ ( , ) ( 1 , 1 ) n n i j lum avg r c i r i c j n          (8) a point is classified as noise if there is edge detected in distorted image (emd(r,c)≥thr_image_edge(r,c)) but not detected in original image (emo(r,c)<thr_image_edge(r,c) where emd(r,c) and emo(r,c) denote the edge magnitudes of distorted and original image respectively. in order to acquire the effect of texture masking for the original image, the activity of sub-image is computed by the local entropy entropy(r, c) where low entropy indicates low level of activity. only noise in sub-image with activity level less than the suggested predetermined threshold thr_noise_entropy is considered to be visible noise artifacts. o d 1 , if (em (r,c)<thr_image_edge(r,c)) and (em (r,c) thr_image_edge(r,c)) ( , ) and (entropy (r,c)<thr_noise_entropy) 0 , else noise o i r c        (9) 1 0 ( , ) ( ) log 2 ( ) l l l g entropy r c p g p g     (10) pl(g), means the probability of gray level g which is the total number of pixels with gray level g where nl(g) divided by the total number of pixels within the sub-image of size n ×n (n = 9). 2 ( ) ( ) ll n g p g n  (11) engineering, technology & applied science research vol. 7, no. 6, 2017, 2277-2281 2280 www.etasr.com kurmasha et al.: enhancement of edge-based image quality measures using entropy for histogram … 1 1 0 0 ( ) ( 1 , 1 ) n n l g i j n g i r i c j          (12) 1, ( , ) ( , ) 0, ( , ) g i r c g i r c i r c g        (13) in order to detect brightness saturation, based on entropy measure as:  0 d 0 1 , if entropy (r,c)-entropy (r,c)>thr_satur1 ( , ) and (entropy (r,c)>thr_satur2) 0 , else saturi r c               (14) each pixel is considered as saturation pixel if its activity into distorted image is less than its activity in the original image, or if the original entropy minus distorted entropy for that pixel is more than the saturation threshold thr_satur1. it is also ensured that the pixel activity in the original image is more than the saturation threshold thr_satur2 so that there is enough activity or details to be seen in the original image. the combination of inoise(r,c) and isatur(r,c) are applied with the logical or as: 1 1 & 0 0 ( , ) ( , ) | ( , ) n m noise satur noise satur r c i r c i r c i r c       (15) finally, the rating r indicates the result which is the ratio of the total number of pixels with noise artifacts and brightness saturation detected to the total number of pixels. 1 1 & 0 0 ( , ) height width noise satur i j i i j r height width        (16) c. implementation of proposed iqm the implementation of iqm was done with matlab 2012a version. the suggested threshold values were determined empirically to maximize the iqm correlation with mos of all test images, measured using pearson correlation coefficient (pcc), root mean squared error (rmse), spearman rank order correlation coefficient (srocc), and outlier ratio (or). the implementation is done for the noise artifacts and brightness saturation detection as shown in table i. table i. thresholds values used into iqm implementation propose d iqm thr_satur1 1.4 thr_satur2 5.6 thr_noise_entr opy 1 standard thresholds original image t = 0.019 distorted image t = 0.012 edgebased iqm brightness intensity range from (0 to 255) thr_low_lu m =30 thr_high_lum = 250 iv. evaluation of iqm correlation to hvp a. experiment setup a set of 9 source images from diverse image content was selected from the “kodak lossless true color image suite” [15] and live image database [16]. the outcome of 1935 human viewer opinion scores forms a subjective quality assessment in which image quality data were used to assess the iqms. more details about this experiment can be obtained from [13] and [17]. b. performance metrics according to [18], the performance of an iqm can be quantitatively evaluated with respect to its ability to predict subjective quality rating in three aspects (prediction accuracy, prediction monotonicity, and predication consistency). the evaluation was done after nonlinear regression for mos using a five-parameter logistic function to get a better fit for all data. furthermore, to evaluate the performance of our proposed iqm, current metrics were used for comparison. along with ambe and entropy, peak signal to noise ratio (psnr), multiscale structural similarity (mssim) and block-based spectral phase error (bspe) [19], information fidelity criterion (ifc) based measure [20], and human visual system filtered l2 norms (hvsl2) [21] were also evaluated. both mssim and ifc are prominent iqms designed to measure image fidelity in image code. table ii shows the results obtained. c. discussion the interpretation of performance metrics [22] shown in table iii explains the discussion of results in table ii.  ambe: has poor correlation with mos. this is agreeing with our review in section ii that brightness change does not always cause annoying effect.  entropy: all metrics except srocc indicate that entropy has poor correlation with mos. this indicates that entropy agrees well with relative magnitude of mos but fails to accurately predict.  ifc, hvsl2, psnr (log), pspe, and mssim: the performance metrics show a fairly relatively correlations to mos exclude the srocc of mssim which is good over the others.  noise iqm: the performance metrics show an excellent correlation to mos by taking into account the noise artifacts only.  proposed iqm: the performance metrics show a higher correlation to mos by taking into account the brightness saturation with noise artifacts. it clearly outperforms all other iqms in study. also, the execution times were recorded for the proposed iqm, the original iqm and the processes applied (sobel edge magnitude (em) and entropy) where 43 distorted plus 9 source images included into each iqm execution. table iv shows the engineering, technology & applied science research vol. 7, no. 6, 2017, 2277-2281 2281 www.etasr.com kurmasha et al.: enhancement of edge-based image quality measures using entropy for histogram … execution times as measured with matlab’s tic and toc functions. table ii. results of performance metrics to iqms iqms performance metrics pearson cc rmse srocc or amba 0.1346 0.7809 0.0802 0.2791 entropy 0.3291 0.7510 0.7682 0.2093 ifc 0.4025 0.7247 0.3961 0.1860 hvsl2 0.5729 0.6459 0.6284 0.1395 psnr(log) 0.7009 0.5624 0.7274 0.0930 bspe 0.7116 0.5536 0.7330 0.0698 mssim 0.7174 0.5490 0.7628 0.1395 edge-based iqm 0.8687 0.3964 0.8990 0 proposed iqm 0.8724 0.1053 0.9225 0 table iii. performance metrics interpretation value of correlation interpretation 0.00-0.40 poor 0.41-0.75 fair 0.76-0.85 good 0.86-1.00 excellent table iv. computation complexity iqms and important processes execution time (sec) edge-based iqm 128.015 proposed enhanced edge-based iqm 233.525 sobel edge magnitude process (original / distorted image) 0.045 ~ 0.095 entropy process (original / distorted image) 2.50 ~ 3.40 v. conclusions it is significant for the iqm to correlate well with hvp in order to develop new automated he-based techniques able to avoid annoying distortions. ambe and entropy are found to have poor correlation with hvp. this paper has proposed a generic framework of a new iqm over the two most common distortions and takes into account the significant properties of hvp masking. evaluation results show that the proposed iqm outperforms significantly the other iqms in study. future work recommendation is the reduction of the algorithm’s complexity in order to obtain close to real time processing. references [1] y.-t. kim, “contrast enhancement using brightness preserving bihistogram equalization”, ieee transactions on consumer electronics, vol. 43, no.1, pp.1-8, 1997 [2] k. wongsritong, k. kittayaruasiriwat, f. cheevasuvit, k. dejhan, a. somboonkaew, “contrast enhancement using multipeak histogram equalization with brightness preserving”, ieee asia-pacific conference on circuits and systems, pp. 455-458, 1998 [3] y. wang, q. chen, b. zhang, “image enhancement based on equal area dualistic sub-image histogram equalization method”, ieee transactions on consumer electronics, vol. 45, no. 1, pp. 68-75, 1999 [4] s. d. chen, a. rahman ramli, “preserving brightness in histogram equalization based contrast enhancement techniques”, digital signal processing, vol. 14, no. 5, pp. 413-428, 2004 [5] c. wang, z. ye, “brightness preserving histogram equalization with maximum entropy: a variational perspective”, ieee transactions on consumer electronics, vol. 51, no. 4, pp. 1326-1334, 2005 [6] h. ibrahim, n. s. pik kong, “brightness preserving dynamic histogram equalization for image contrast enhancement”, ieee transactions on consumer electronics, vol. 53, no. 4, pp. 1752-1758, 2007 [7] d. menotti, l. najman, j. facon, a. de a. 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sengee, h. k. choi, “image contrast enhancement using bi-histogram equalization with neighborhood metrics”, ieee transactions on consumer electronics, vol. 56, no. 4, pp. 2727-2734, 2010 [13] s. d. chen, “a new image quality measure for assessment of histogram equalization-based contrast enhancement techniques”, digital signal processing, vol. 22, no. 4, pp. 640-647, 2012 [14] s. d. chen, y. al-najja,n. h. azami, k. s. beh, “measuring image quality for assessment of contrast enhancement techniques”, australian journal of basic and applied sciences, vol. 7, no. 11, pp. 178-188, 2013 [15] rich franzen, kodak lossless true color image suite, http://r0k.us/graphics/kodak/ [16] h. r. sheikh, z. wang, l. cormack, a. c. bovik, live image quality assessment database release 2, http://live.ece.utexas.edu/research/ quality [17] s. d. chen, m. singh, “re-evaluation of automatic global histogram equalization-based contrast enhancement methods”, electronic journal of computer science and information technology, vol. 1, no.1, 2011 [18] vqeg, vqeg final report of fr-tv phase ii validation test, 2003 [19] z. wang, a. c. bovik, h. r. sheikh, e. p. simoncelli, “image quality assessment:from error visibility to structural similarity”, ieee transactions on image processing, vol. 13, no. 4, pp. 600-612, 2004 [20] h. r. sheikh, a. c. bovik, g. de veciana, “an information fidelity criterion for image quality assessment using natural scene statistics”, ieee transactions on image processing, vol. 14, no. 12, pp. 21172128, 2005 [21] i. avcibas, b. sankur, k. sayood, “statistical evaluation of image quality measures”,journal of electronic imaging, vol. 11, no. 2, pp. 206-223, 2002 [22] h. arsham, statistical thinking for managerial decisions, available at: http://home.ubalt.edu/ntsbarsh/business-stat/opre504.htm, 2014 microsoft word etasr_v11_n2_pp6935-6942 engineering, technology & applied science research vol. 11, no. 2, 2021, 6935-6942 6935 www.etasr.com halima et al.: design and study of an adaptive fuzzy logic-based controller for wheeled mobile … design and study of an adaptive fuzzy logic-based controller for wheeled mobile robots implemented in the leader-follower formation approach halima medjoubi department of electronics university of batna batna, algeria halimaautomatique@hotmail.com abdessemad yassine department of electronics university of batna batna, algeria yabdes@yahoo.fr hassam abdelouahab department of electronics university of setif setif, algeria abdelhassam@univ-setif.dz abstract-this paper presents a new design of an adaptive fuzzy logic control by implementing the leader-follower approach. the principle is to modify the feedback control of non-holonomic wheeled mobile robot (wmr) to be adaptive according to a fuzzy controller in the control loop, in order to adjust the feedback control gains according to the distance error between the reference path and the real position. the trajectory tracking control for a single wmr is extended to the formation control for two wmrs in which the first one is the leader and the second is the follower. simulation results are presented to demonstrate the effectiveness of the proposed controller. keywords-adaptive fuzzy control; feedback control; wheeled mobile robot (wmr); leader-follower formation; trajectory tracking control; non-holonomic i. introduction wheeled mobile robots are very useful devices that perform a wide range of tasks [1-3]. for many years, single mobile robots have been used to execute simple tasks and to achieve desired goals, such as tracking a desired path or avoiding obstacles [4-6]. recently, robotics research has been focused its interest to multi-robot systems. certainly, this kind of systems could accomplish several complex tasks more economically and efficiently than a singlerobot system [7, 8]. a team of mobile robots that performs a complex mission in short time, is necessary to work coordinately and cooperatively with respect to a specific formation. various formation control approaches have been mentioned in the literature, such as the behavior– based approach [9], virtual structure approach [10], and leaderfollower approach [11-13]. in the behavior-based approach, different desired behaviors (e.g. formation keeping, target seeking, etc.) are specified for each robot, where its action is depended on its role in the team. since this approach is complicated, exact formation control is hard to ensure [14-16]. on the other hand, in the virtual structure approach [7, 9], the entire formation is considered as a single rigid body, which means that all robots work as a single complex robot. this method can control the motion of the whole robot formation, but cannot change the formation when the environment is changed, which limits the scope of its application. the leader – follower method is also called as master-slave mode [15]. in the group shaped by multi-mobile robots, one robot is designed as the leader while the others are the followers. in this approach, the leader moves along a predefined trajectory while the followers are controlled to maintain a desired distance and bearing angle [16]. in robotics field, this is the most used technic, which allows the formation control to be transformed into two simple problems, a trajectory tracking by the leader and a control to keep the formation by the followers. here, we must ensure permanent communication between the leader and all the followers in order to maintain the formation [4, 5, 7]. this paper deals with the leader-follower formations of non-holonomic mobile robots. a new, adaptive fuzzy controller is proposed to ensure tracking and formation control for two mobile robots. the modeling and control of two mobile robots where one is modeled as a leader and the second one as a follower are presented. the obtained simulation results for tracking and formation control are discussed and a comparison with conventional methods is made. ii. multi mobile robot modeling and control usually, a mobile robot is presented in a cartesian 2d frame with its coordinates, such as position coordinates (�,�) and its orientation � [17]. in this study, a kinematic model is considered, taking into account linear and angular velocities for corresponding author: halima medjoubi engineering, technology & applied science research vol. 11, no. 2, 2021, 6935-6942 6936 www.etasr.com halima et al.: design and study of an adaptive fuzzy logic-based controller for wheeled mobile … both leader and follower mobile robots, and a controller for each one is designed. a. leader-follower formation modeling in order to model the kinematics of the leader robot, we use the configuration �� ��, ��, ����as shown in figure 1. the control input for the leader robot is the linear velocity vl and the angular velocity wl. fig. 1. mobile robot in 2d frame. the equations of the leader robot can be written as: ���������� � cos ��sin ��0 � . �� � � 001� . �� (1) the mobile robot wheels exhibit purely rolling motion and that assumed without slip. the nonholonomic constraint is expressed as: ����. sin �� � ���. cos �� 0 (2) the leader robot model under matlab/simulink is shown in figure 2. fig. 2. leader robot model. the same constraint is observed for the follower robot. the follower robot is modeled relatively to the leader robot. it follows the leader while maintaining a desired relative distance and desired separation bearing angle with respect to the leader robot in a strategy known as separation bearing control (figure 1), where: ��� is the separation bearing angle between the leader and the follower robot. �� denotes the separation distance between the center of the rear wheels of the leader, and the front castor of the follower robot. (�, �) is the position coordinates of the front castor of the follower robot. ! is the distance between the front castor wheel and the mid point of the rear wheels for each robot. ���, ��� is the midpoint on the axis between the rear wheels. �� ��, ��, ���� is the leader robot position. #� ��, ���� : control inputs of leader robot. �� $��, ��, ��%� : follower robot position. #� $��, ��%� : control inputs of follower robot. the follower position is calculated as: �� � � !. cos ���� � � !. sin �� (3) the follower robot model is represented with the state vector ��� $ ��, ���, ��%� expressed as: �� &'�� � �� � !. cos ��() � '�� � �� � !. sin ��() ��� * � +,-.+/2'�� � !. sin �� � �� , �� � �� � !. cos ��( � �� (4) finally, after differentiating the ��� state vector we obtain the kinematic model for the follower mobile robot: ��� ��. -123 � ��. -12��� � !. ��. 24/3�� �� 56 .789 :6;<5; .789 =<>6.�6;?@.>;.ab7 =�6; ��� �� (5) with: 3 �� � �� � ��� (6) figure 3 illustrates the follower detailed model under matlab/simlink. the condition (7) is considered in order to avoid collision between the leader and the follower and must always be verified. �� c 2. ! (7) b. control strategy the leader is controlled to follow a predefined path such as a circle or an eight shape. the control loop is presented in figure 4. considering a desired path, we can calculate the desired linear and angular velocities, and the kinematic controller is derived. in addition, the proposed adaptive controller is compare with a well-known kinematic controller presented in [18]. the kinematic controller explained with (8) is presented in detailed form in matlab/simlink in figure 5. d#ef�g�ef�g h d cos � sin �� i@ sin � i@ cos �h �� @ � j. tanh�no�o �p���@ � q. tanh�nr�r �p�� (8) engineering, technology & applied science research vol. 11, no. 2, 2021, 6935-6942 6937 www.etasr.com halima et al.: design and study of an adaptive fuzzy logic-based controller for wheeled mobile … fig. 3. detailed model of the follower robot. fig. 4. leader control loop. fig. 5. detailed kinematic controller of the leader. in (8), xp �@ � �� and �p �@ � �� are the current position errors in the axes t and u, respectively, vj c 0 and vq c 0 are the gains of the controller, wj ∈ y and wq ∈ y are saturation constants, and ���, ��� and ��@, �@� are the current and the desired coordinates of the point of interest, respectively. the detailed model for the follower kinematic controller from [19] is given by (9) and is presented in figure 6. fig. 6. follower kinematic controller in matlab/simlink. engineering, technology & applied science research vol. 11, no. 2, 2021, 6935-6942 6938 www.etasr.com halima et al.: design and study of an adaptive fuzzy logic-based controller for wheeled mobile … �� z � !. ��. tan 3 �� ab7 =@ . [v\ ��'���@ � ���( � ��. sin ��� � ]^ (9) where: ] ���� � z. sin 3 z n_`�6;a <�6; b?56.ab7 :6;ab7 =3 ��� � �� � �� (10) fig. 7. follower control loop. it is noticed that the kinematic gain controllers vj, vq, v\, and vc are constant during the mobile robot motion. so if one of the operation conditions changes, the actual gain value may no be adequate and may need to be adjusted. the main idea is to adjust the gain controller values in real time during the mobile robot operation. iii. adaptive fuzzy control for a multi-robot system a. fuzzy systems and fuzzy control fuzzy logic provides human reasoning capabilities to capture uncertainties, which cannot be described by precise mathematical models. traditionally, fuzzy logic controllers have been applied to the development of a complete navigation problem of a mobile robot [3]. fuzzy logic is widely used to control various types of systems and also to develop adaptive controllers [20, 21]. the overall structure of a fuzzy controller is shown in figure 8. fig. 8. internal structure of a fuzzy controller. fig. 9. proposed adaptive controller. in this paper, the proposed fuzzy controller will be added to the main controller where it can adjust controller gains according to the distance error as presented in figure 9. the same structure is used for all controller gains (leader and follower). b. adaptive controller parameter calculation both leader and follower robots are controlled by a kinematic controller. the controller gains are unique in value in order to give best results in a specific system status. in practice, the system statuses are not the same, and we come to a point for what adaptive gain controllers are necessary to satisfy several statuses. the idea here is to make changes in gain controllers in real time when the distance error between the desired path and actual robot position is different from zero. the larger distance error, the higher adaptation value will be applied to the gain controller value. in figure 9, we notice that if the distance error is equal to zero then we don’t need the fuzzy logic adaptation, which means that if it’s output is zero we must keep the original gain controller, therefore we add a constant to the proposed controller loop to avoid zero multiplication when the output of fuzzy controller is equal to zero. the fuzzy logic controller was chosen to be mamdani inference and the membership functions for input and output are presented in figure 10. the input is the distance error and the output is the adaptation gain. (a) (b) fig. 10. fuzzy controller: (a) input, (b) output. iv. results and discussion to show the performance of the proposed controller, let's consider a group of two mobile robots in which one is the leader and one is the follower. the adaptation loop is inserted into the main control loop [19] for both. circular and eightshaped paths are used to test the proposed controller. the simulations were carried out in matlab/simulink. all robots and controller equations were modeled in matlab/simulink blocs. the proposed fuzzy adaptive controller was implemented with the fuzzy logic toolbox of simulink. the simulation parameters were: mobile robot parameter: d=0.2m radius of desired circular path: ,gdeg�f@fedef@=5m radius of desired circular path : ,fdfgh@fedef@=10m engineering, technology & applied science research vol. 11, no. 2, 2021, 6935-6942 6939 www.etasr.com halima et al.: design and study of an adaptive fuzzy logic-based controller for wheeled mobile … leader-follower formation parameters: w��@fedef@ 2 i, ���@fedef@ jk ,+!. the desired path generator modeled in matlab/simulink is shown in figure 11. (a) (b) (c) fig. 11. detailed desired path generation model. (a) general structure, (b) the eight generator model, and (c) circle generator model. a comparison study was carried out between the kinematic controller ([18] for the leader and [19] for the follower) and the proposed adaptive kinematic fuzzy controller, considering paths and distance error. the results of the leader with and without adaptive controller are displayed in figure 12 which shows the results of following a trajectory with circular path (figure 12(a)), the error distance (figure 12(b)), and the gain adaptation for x and y gain kinematic controller (figure 12(c) and 12(d) respectively). (a) (b) (c) (d) fig. 12. results of leader robot for circular path it is noticed that the adaptation makes results better with a fast time response. the gain controllers are adapted to the distance error. the same remarks are observed for the eightshaped path in figure 13(a)-(c). the adaptation ensures that the system will not go out of the desired path once it reaches it because the gain controller will be decreased to a lower value while approaching the desired path. from figure 13(b) and 13(c), we can see that at the beginning, the gain controllers are at high values because the robot is far from the desired path and decrease as the robot comes close to it. this technique will ensure that the system will not lose stability once it reaches its desired path. as the next step, we give the results of the formation control for leader and follower with kinematic controller and our adaptive fuzzy kinematic controller. similarly to the leader result, the two paths are tested. figure 14(a)-(c) represent respectively the circular path, the distance between the leader and the follower, and the bearing angle between the leader and the follower. gain controller adaptation (for �� and ��� ) is displayed in figure 15. engineering, technology & applied science research vol. 11, no. 2, 2021, 6935-6942 6940 www.etasr.com halima et al.: design and study of an adaptive fuzzy logic-based controller for wheeled mobile … (a) (b) (c) fig. 13. results of leader robot for the eight-shapef path. (a) (b) (c) fig. 14. results of leader-follower for the circlular path. (a) (b) fig. 15. gain adaptation of leader-follower for the circlular path. (a) (b) (c) (d) (e) fig. 16. results of leader-follower for the eight-shaped path. engineering, technology & applied science research vol. 11, no. 2, 2021, 6935-6942 6941 www.etasr.com halima et al.: design and study of an adaptive fuzzy logic-based controller for wheeled mobile … it is clear from the results shown in figure 15 that the adaptive controller performs better than the kinematic one. the follower reached quickly the desired distance and bearing angle with the leader. the same observations are seen in figure 16. the obtained results show an improvement with the proposed adaptive kinematic fuzzy-based controller compared to the ones in [18, 19]. comparing the results, we can see that the system remains stable in our tests due to gains adaptation which will avoid excess value in gain controllers especially when the robot reaches its desired path. the time response will be faster and no oscillation can be seen after reaching the desired path. v. conclusion an adaptive fuzzy kinematic controller has been proposed in order to solve the tracking control and leader-follower formation problems. an auxiliary fuzzy controller was inserted into the main kinematic control loop to make the adaptive controller gains according to distance and bearing angle errors. simulations were carried out using two paths (circular and eight shaped) to test the effectiveness of the proposed controller. the obtained results showed that the proposed controller was better when compared with the kinematic controller in terms of time response for both tracking and formation control. for future work and to enlarge the present work, dynamics and obstacles avoidance will be considered. appendix the follower position is calculated geometrically according to the leader position using the model presented in figure 17. fig. 17. follower posistion calculation model. references [1] s. sang, h. wu, j. zhao, and q. an, "fuzzy logic control for wheeled mobile robots," in 2009 sixth international conference on fuzzy systems and knowledge discovery, tianjin, china, aug. 2009, vol. 6, pp. 237–241, https://doi.org/10.1109/fskd.2009.241. 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[18] f. n. martins, w. c. celeste, r. carelli, m. sarcinelli-filho, and t. f. bastos-filho, "an adaptive dynamic controller for autonomous mobile robot trajectory tracking," control engineering practice, vol. 16, no. 11, pp. 1354–1363, nov. 2008, https://doi.org/10.1016/j.conengprac.2008. 03.004. [19] s. ahmed and m. n. k. and r. n. k. loh, "control analysis and feedback techniques for multi agent robots," multiagent systems, jan. 2009, https://doi.org/10.5772/6597. [20] v. h. nguyen, h. nguyen, m. t. cao, and k. h. le, "performance comparison between pso and ga in improving dynamic voltage stability in anfis controllers for statcom," engineering, technology & applied science research, vol. 9, no. 6, pp. 4863–4869, dec. 2019, https://doi.org/10.48084/etasr.3032. [21] m. fouzia, n. khenfer, and n. e. boukezzoula, "robust adaptive tracking control of manipulator arms with fuzzy neural networks," engineering, technology & applied science research, vol. 10, no. 4, pp. 6131–6141, aug. 2020, https://doi.org/10.48084/etasr.3648. microsoft word etasr_v11_n5_pp7605-7609 engineering, technology & applied science research vol. 11, no. 5, 2021, 7605-7609 7605 www.etasr.com waseemullah et al.: tv ad detection using the base 64 encoding technique tv ad detection using the base64 encoding technique waseemullah department of computer science and it ned university of engineering & technology karachi, pakistan waseemu@neduet.edu.pk muhammad faraz hyder department of software engineering ned university of engineering & technology karachi, pakistan farazh@neduet.edu.pk maria andleeb siddiqui department of software engineering ned university of engineering & technology karachi, pakistan mandleeb@cloud.neduet.edu.pk muhammad mukarram department of computer science and it ned university of engineering & technology karachi, pakistan mukki0303@gmail.com abstract-automatic tv ad detection is a challenging task in computer vision. manual ad detection is considered a tedious job. detecting advertisements automatically saves time and human effort. in this paper, a method is proposed for detecting repeated video segments automatically, since generally, ads appear in tv transmissions frequently. at first, the user is allowed to browse the advertisements needed to be detected, and the video in which they are to be detected. the videos are then converted into a text file using the base64 encodings. in the third step, the advertisements are detected using string comparison methods. in the end, a report, with the names of the advertisements is shown against the total time and the number of times these advertisements appeared in the stream. the implementation was carried out in python. keywords-tv ads; ad detection; base64 i. introduction advertisements displayed in tv broadcasts are a very important part of a transmission as most of the revenue of a broadcaster is generated by advertising. fast and accurate advertisement discovery is an important issue in the computer vision field. the main challenge of ad detection is the lack of information about the tv transmission structure and the unpredictable appearance of advertisements in the transmissions. in this paper, a novel approach is developed for tv ad detection. an algorithm has been developed for tv commercial (ad) detection. the proposed algorithm breaks the videos into frames. the sub-regions of frames take part in the comparison. the pixel values of the middle region of the frames of the tv transmited video and the ad segment are compared. this approach results in tv ad detection with a 60% precision. meanwhile, it suffers from the problem that the results rely heavily on the size of the video file. another factor that significantly influences ad detection is the quality of the video. the proposed algorithm does not provide good results on grainy and poor-quality videos. the developed system based on the novel approach for tv ad detection can be used by the pemra (pakistan electronic media regulatory authority) to identify particular ads and their statistics. the framework is also usable for advertisement’s agencies to compute and visualize the air time used for different ads. the experimental results confirm the importance of the proposed framework. this study may be helpful to (figure 1): • tv ad detection and identification: many companies in marketing research and advertisement are keen on identifying commercial segments from tv broadcasts to verify the number of times a particular ad has been aired. • tv advertiser concerns: a product owner has to keep a close eye on their competitors’ marketing tactics by knowing the number of advertisements being aired per day and the total amount spent for advertising the products of a particular vendor. • tv consumer woes: to give viewers an uninterrupted service is an expensive luxury nowadays as the bombardment of ads in every program is taking a toll on audience viewing. a viewer may find it easier to avoid any such occurrence in advance if the system is equipped with a consumer-friendly tool that reduces the ads' nuisance in the future. • market analysts inspection: in relation to the revenue aspect, a media monitoring agency such as pemra may need to know the broadcasted time ratio for ad and non-ad transmission of a tv channel. the resulting information may help the agency answer questions such as how much revenue a tv channel is generating through advertisements and which advertiser is paying higher for advertisements. • government regulatory body surveillance: government agencies have to ensure that there should be no breaching in regulationg of enforced laws during channel transmission. corresponding author: waseemullah engineering, technology & applied science research vol. 11, no. 5, 2021, 7605-7609 7606 www.etasr.com waseemullah et al.: tv ad detection using the base 64 encoding technique one such agency would find useful a video segment identification application. on the other hand, many media observatory and regulatory bodies, want to know the real revenue generated by the various media channels. fig. 1. the possible applications for tv commercials detection. many approaches based on different features have been discussed [1, 2] for video detection and classification tasks. authors in [3] investigated the problem of retrieving ads depending on their salient semantics. semiotic is the knowledge of signs, associating signs with their meaning by communal conventions and particular cultural context. identifying cuts, dissolve, and rhythm is used for video segmentation. hough transform is used for calculating significant line slopes for describing shot content cluster analysis. practical, playful, topic, and critical were recognized as semiotic categories of commercials. evaluation was conducted on 150 ads from different italian channels in compliance with the one conducted by human experts. the system showed best results on playful and worst results on practical ads. authors in [4] explored the problem of real-time commercial detection using mpeg features in mpeg compressed videos. black frame, unicolor frame, and change in aspect ratio were used for ad detection. it was shown that the least duration for any ad is one minute. also, it was found that the strongest ad detecting parameter is the presence of black frames in commercial breaks. authors in [5] proposed a new learning-based approach for ad detection. the approach uses several audio and visual features for classification based on support vector machine (svm). average of edge change ratio, the variance of edge change ratio, average of frame difference, and variance of frame difference were used as visual features. nbc, espn2, and cnn tv channel transmissions of 10.75 hours was recorded for the evaluation, including different genres, i.e. movies, sports, and news. recall values of 88.21% and 91.77% were observed without and with post-processing respectively. the respective precision values were 89.39% and 91.65%. authors in [6] investigated the problem of identification and categorization of ads from tv transmission. boundary detection was performed through a multi-modal approach. the ads were separated through black frame and silence features. classification was conducted through text detection. in addition, the absence of a channel logo was also used for ad segmentation from the normal transmission. hidden markov model based on audiovisual features was used for training. the results showed a precision value of 90% and a recall value of 80%. authors in [7] proposed a commercial detection that is depending on cookery/cooking programs. audio-visual features were used for ommercial boundary detection, including zero crossing rate, short time energy, edge detection, and corner detection. furthermore, the logo of the program name was matched with a commercial break. authors in [8] proposed a signal-based approach that uses an automatic unsupervised method for the segmentation of tv transmission. using the general likelihood ratio and the bayesian information criterion ,this approach can be applied to audio signals, visual signals, or their combination. the evaluation was performed on recordings from french tv and the trecvid dataset with recall values of 93% and 89% respectively. the respective precision was 93% and 91%. an approach based on optical character recognition (ocr) and automatic speech recognition (asr) techniques for the classification of tv commercials was proposed in [9]. the output transcripts generated by these technologies normally produce a small number of keywords. these keywords are used to perform searching which results in semantically relevant information from the web. after that, retrieved information from the web was used to develop a feature vector based on text, and the commercial classification was performed based on text. the experimental results show that combining external resources improved the classification accuracy and helped avoiding speech recognition issues in tv commercial videos. a methodology based on subtitle detection to detect tv commercials in videos was presented in [10]. many constraints were used to distinguish subtitles and other text that appeared in a frame. after detecting subtitles, a scheme was presented that decides whether a tv commercial exists or not, based on the appearance of subtitles. then, the genetic algorithm was used to point out the mark-in and mark-out points. the reported precision and recall values were more than 90%. authors in [11] evaluated an algorithm for the detection of text that normally cannot be detected easily in a video. this algorithm performs text detection in cases like a scene with high texture background. the reported results were 96% and 82% for precision and recall respectively. authors in [12] introduced a framework for the automatic semantic annotation of unconstrained videos. the framework helps to minimize the semantic gap, i.e. the difference between the low-level visual information and the corresponding human perception. it was also proposed that integrating visual similarity matching with common sense semantic relationships is a highly effective approach to automated video annotation. authors in [13] investigated the problem of automatic management of videos taking into account syntactic and semantic features for tv news programs. authors in [14] presented an innovative solution of a smart emotional system for impaired people. they aimed to accompany the cognitive information contained in a movie, with the affective content for emotion recognition. the author in [15] described the tv stream as a collection of programs (p) and breaks engineering, technology & applied science research vol. 11, no. 5, 2021, 7605-7609 7607 www.etasr.com waseemullah et al.: tv ad detection using the base 64 encoding technique (advertisements) (b) [15]. a tv stream is a collection of program segments and break segments where c.1, c.2, and c.3 represent the different type of program segments having an aim of information or entertainment (figure 2 in [15]). each category of program segments is separated by breaks represented through c. ii. methodology in this research work, base64 encoding and decoding technique has been used to detect tv advertisements. the following section defines the technique first and the steps carried out to perform the advertisement detection. a. base64 encoding and decoding it is an encoding style that uses 64 numbers of characters to represent the binary data. initially, data were sent over the network, i.e. via email through only a set of text characters but after the advancement in multimedia technology, it was expected to send other data types, i.e. images (binary data), attachments, and executables as well. thus the need emerged for some encoding techniques for binary data to transport over the network. the encoding of binary data is needed to avoid the problem caused by the existence of null characters in binary data. the encoding table of base64 is shown in figure 2. fig. 2. base64 encoding and decoding values. b. the followed approach for tv advertisement detection. the first technique that we tried was to compare and count the times the frames of an ad appear in the main broadcast video. drawbacks such as high storage utilization, due to the splitting of videos into frames and more time, occurrred. the second technique that we tried to use was to detect the advertisements during a live broadcast. the main problem that occurred was more time utilization although less storage was needed. the third technique was to encode all the pixels of all the frames, of all the videos, and then perform the comparison. this required more storage utilization as the size of the produced file was large, and more time in performing the comparison. the final approach chosen for this project was to encode only selected pixels belonging to sub-regions of the frames of the videos and then perform the comparison in order to reduce the computation cost. the time and the storage capacity required in this approach were comparatively lesser than the approaches mentioned above. the proposed methodology is shown in figure 3. in figure 3, the "main file" is the video file that contains both advertisements and other program segments whereas the "ad file" denotes the separate categories of advertisements that may exist in the input video file. both advertisement files and the main file are converted into encoded text files using the base64 encoding. the resulting text files are compared line by line to find the match of any advertisement file in the main file. each line of the text file corresponds to a set of pixel positions in a frame. these pixel positions are picked from the middle region of the frame only. fig. 3. the proposed approach for tv advertisement detection. the obtained results were further presented in both textual and graphical forms. when the user selects the advertisements to be detected and the video they are to be detected in, instead of encoding each pixel of every frame, only selected pixels are encoded and saved into a text file and the file size remains small even for long videos. when the user hits the detect button, each pixel in each advertisement file is compared to each pixel in the main video file until a match is found. when each pixel in the advertisement file is found in the main video file in sequence, the count of the comparison for that specific advertisement increases. once the comparison is done for all selected ads, a table consisting of the ads against the time (seconds) they have appeared in the main video is shown to the user, with a graphical donut chart representation of the obtained results. details are given in the result section of this paper. the steps of the algorithm are: step 01: break the input videos (main video and ad videos) into frames. step 02: select the set of pixel values from each frame belonging to the sub-region of the selected frames. step 03: convert the set of pixel values into base64 type. step 04: compare all pixel values of an advertisement frame with the frame of the main video if the pixel points match then take the frame as an ad frame and move to the next frame repeat the process until the ad frame matches with the frames of the main video return the total number of frames matched else select the next frame in the sequence engineering, technology & applied science research vol. 11, no. 5, 2021, 7605-7609 7608 www.etasr.com waseemullah et al.: tv ad detection using the base 64 encoding technique c. end-user system a system has been developed for the end-user to evaluate the performance of the devised algorithm. the developed system is mainly comprised of four steps. step 01: in this step, the end-user is provided with the ad detection screen. the select main file button allows the user to select the video file which contains advertisements and nonadvertisement content. the select ad files button allows the user to either select a single advertisement segment or set of advertisement videos to be searched in the main file (figure 4). step 02: in this step, after providing the main file and the ad file, the end-user is provided with the upload button. the button converts the videos into frames and then converts these frames into base64 encoded strings (figure 5). step 03: in this step each file is converted into a base64 encoded text string (figure 6). step 04: the screen in figure 7 appears when the binary images are successfully converted into text files using the base64 encoding. the end-user is provided with the detect button to start the advertisement detection process with the developed algorithm. the system will produce two different forms of detection results, one in text form and another in graphical form. fig. 4. main screen of the system. fig. 5. selecting the main video file and the advertisement file. fig. 6. converting the main video file and the advertisement file into text files. fig. 7. after the successful conversion, the detect button appears. d. dataset the video dataset was recorded from national tv channel transmissions, including ary digital 1, and hum tv. the test data composed of three segments of transmission that were recorded from ary digital and hum tv. the two segments from ary had 2.5 hours length and the hum tv segment had a length of 1 hour 40 minutes. all three segments were recorded from a local cable provider and were sampled at 25 frames per second. iii. results and discussion the detection results were obtained in two ways: single ad and multiple ad detection as shown in figures 8-11. figure 8 shows the text file output of the results and figure 9 the produced graphical representation. they shows the detection of a kfc advertisement which lasts for 10 seconds in a given 152 second video file. fig. 8. single ad detection text results. fig. 9. single ad detection graphical results. figure 10 shows the text file output of the results of multiple ad detection and figure 12 their graphical representation. they show the number of detected advertisements. moreover, the name of each detected advertisement is given in the adjacent column along with their duration in seconds in another adjacent column. to the best of our knowledge, this is the first time the base64 encoding technique is used for tv advertisements detection. the engineering, technology & applied science research vol. 11, no. 5, 2021, 7605-7609 7609 www.etasr.com waseemullah et al.: tv ad detection using the base 64 encoding technique technique results in tv advertisement detection with 60% precision. on the other hand, it suffers from the problem that the results rely heavily on the size of the video file. one more factor that influences advertisement detection is video quality. the proposed algorithm does not provide good ad detection results on grainy and poor-quality videos. fig. 10. multiple ad detection text results. fig. 11. multiple ad detection graphical results. iv. conclusion many attempts have been made to find suitable features for tv commercial detection. it had been observed that some features that have been used by other researchers, such as silence, blank frame, and absence of tv channel logo during advertisement breaks have no use in pakistani tv transmissions. it had been noticed that silence may appear not only at the beginning and the end of an advertisement but also at several intervals during the shot transitions in an advertisement. the blank frame that exists in tv transmission in australia and european countries has been used by some researchers to detect the advertisement breaks, but pakistani tv transmission does not contain such 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[15] z. a. a. ibrahim, "tv stream table of content: a new level in the hierarchical video representation," journal of computer sciences and applications, vol. 7, no. 1, pp. 1–9, dec. 2018, https://doi.org/10.12691/ jcsa-7-1-1. microsoft word etasr_v13_n3_pp10931-10935 engineering, technology & applied science research vol. 13, no. 3, 2023, 10931-10935 10931 www.etasr.com aldhahri: the use of recurrent nets for the prediction of e-commerce sales the use of recurrent nets for the prediction of e-commerce sales eman aldhahri department of computer science and artificial intelligence, college of computer science and engineering, university of jeddah, saudi arabia eaal-dhahery@uj.edu.sa (corresponding author) received: 16 april 2023 | revised: 27 april 2023 and 28 april 2023 | accepted: 28 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5964 abstract the increase in e-commerce sales and profits has been a source of much anxiety over the years. due to the advances in internet technology, more and more people choose to shop online. online retailers can improve customer satisfaction using sentiment analysis in comments and reviews to gain higher profits. this study used recurrent neural networks (rnns) to predict future sales from previous using the kaggle dataset. a bidirectional long short term memory (bltsm) rnn was employed by tuning various hyperparameters to improve accuracy. the results showed that this bltsm model of the rnn was quite accurate at predicting future sales performance. keywords-e-commerce; sales; deep learning; prediction; rnns i. introduction the term e-commerce refers to any commercial transaction that takes place over the internet. e-commerce is divided into "non-payment e-commerce", which does not involve the exchange of money or the delivery of products to customers, and "payment e-commerce", which enables customers to make purchases and arrange shipments of items online [1]. along with the rest, "non-payment e-commerce", includes actions performed by delivery services and activities performed by vendors related to the sale of items [2]. e-commerce can be broken down into four distinct sub-industries: business-tobusiness (b2b), business-to-consumer (b2c), business-togovernment (b2g), and consumer-to-government (c2g). the first two types of electronic business transactions that come to mind are business-to-business (b2b) and business-to-consumer (b2c) [3]. e-commerce is often used to describe a new style of business operations that is distinguished from traditional by the fact that customers buy products or services using a browser and a server-based application hosted on an internet platform [1]. since 2013, there is a substantial rise in the use of the internet to deliver high-quality services and the frequency of electronic commercial transactions continues to grow [4]. traditional methods of sales forecasting are based on time series analysis and usually accept only input sales data from the most recent quarters. using these tactics, it is possible to effectively manage commodities whose sales trends are either consistent or seasonal [5]. in contrast to this, the prices of commodities sold through e-commerce are much higher and the sales trends of these commodities are highly unpredictable. in addition, the accuracy of the forecasts obtained using traditional methods is often excessively poor [6]. it is feasible to boost the accuracy of forecasts using the huge amount of data available in the e-commerce industry. feature engineering is the first step in traditional machinelearning approaches. this process involves manually extracting valuable features from easily accessible data [7]. the accuracy of a forecast model can be strongly impacted, both positively and negatively, by the quality and number of attributes contained within the model. however, the process of generating useful features is both challenging and timeconsuming. in addition, these attributes are often acquired on an individual basis for one-of-a-kind business scenarios, which makes it difficult to reuse the models if the data or requirements change in the future. when gathering further data for online sales, feature engineering should be carried out to include the information contained in the new data in the prediction model. it is possible that feature learning could eliminate the requirement to manually engineer features [6]. numerous studies have been conducted to extract features from unstructured data, such as photos, audio, text, and others, using deep neural networks. [8]. many studies have investigated reliable and accurate sales prediction, and most of them agreed that it is a challenging issue in the field of e-commerce. in [2], a method was presented to use information based on cross-series using the unified model. a long short-term memory (lstm) network was trained using the relationships based on the non-linearity in e-commerce product variety. moreover, a framework was presented for systematic preprocessing to address e-commerce challenges. several product grouping strategies have also been introduced to improve lstm learning. in [3], an lstm-based model was presented for consumer comments sentiment analysis to predict the short-term demand for products. the lstm model was carried out based on a sequence of time engineering, technology & applied science research vol. 13, no. 3, 2023, 10931-10935 10932 www.etasr.com aldhahri: the use of recurrent nets for the prediction of e-commerce sales series and the rating of sentiment comments to predict future sales. due to minimal historic data, the decision maker is needed to take proper actions and react toward the market. it was also suggested that the sentiment rating weight adjustment can improve the prediction accuracy. the proposed lstm approach performed well in terms of accuracy. in [7], a model called sen-bert-cnn was presented to analyze customer reviews, based on cnn and pre-trained bidirectional encoder representations from transformers (bert) to extract the sentiment information of a sentence. in [8], a method was used that combined the patterns of two graphs to predict the community trends on an item attribute. in [9], the lstm and the seasonal autoregressive integrated moving average (sarima) were used to predict the demand for a product based on previous sales and satisfy future customer requirements. in [10], genetic algorithms were used in conjunction with a profit-maximizing logistic model to forecast client attrition. in a similar strategy in [11], data-driven agent-based analysis of customer behavior was used, while in [12] a study was carried out to estimate and infer heterogeneous treatment effects utilizing random forests to determine the extent to which sales are associated with ecommerce. in the same spirit, machine learning was used in [13] to interpret internet of things data. in [14], a feature selection method was presented based on an artificial bee colony and a gradient-boosting decision tree. in [15], the accurate prediction of protein contact maps was presented by integrating residual two-dimensional bltsm with convolutional neural networks (cnns). this method was supported by a large number of additional studies that followed a similar line of reasoning. in [16], a prediction model was presented using cnns and rnns. in [17], a learning framework was described that incorporated various levels of knowledge representation for the analysis of aspect-based sentiments. in [18], a semantic study of social networks in educational settings was presented along with recommendations. in [19], a context was established in photo albums by understanding and modeling user behavior in clustering and selection. authors in [20] focused on convolutional neural networks and their applications in data mining and sales forecasting for e-commerce. some studies used deep neural networks, lstm, and particle swam optimization (pso) to predict long-term sales in e-commerce companies, as earlier studies that estimated short-term product demands found it possible to predict long-term future sales. sales remain a crucial variable in e-commerce. furthermore, there are several studies analyzing the ways a community uses a product based on some characteristics. ii. methodology figure 2 shows a flow diagram of the proposed method to predict e-commerce sales with the use of cnns to select features from a dataset and employing a bltsm model of rnns for the prediction. this process began with the building of the model, the gathering and the pre-processing of the dataset, and the experimental training and testing for the prediction. fig. 1. the flow process of the prediction experimental analysis and result presentation. engineering, technology & applied science research vol. 13, no. 3, 2023, 10931-10935 10933 www.etasr.com aldhahri: the use of recurrent nets for the prediction of e-commerce sales a. the bidirectional long-short-term memory (bltsm) model of recurrent neural networks (rnns) this study adopted a bidirectional lstm rnn model to predict the growth of sales for all products based on multiple factors [21]. a typical neural network does not function well when the data sequence is essential. language translation, word recognition, and sentiment analysis are only a few examples of this situation. however, rnns solve this problem, and blstm rnns are sophisticated in such problems [22]. this model operates in a fashion where neurons are set as the basic building blocks of rnns, and their strength is conveyed by weights. the rnns typically consist of input, hidden, and output layers, with each layer's neuron coupled to aid in the retracement of past computations. rnns excel in processing sequential data, especially when ordering is critical. lstm solves the gradient problem either by vanishing or exploding in rnns. the vanishing gradient problem results in an error that prevents rnns from learning when there are more than 5-10 time steps between the events that are input and the signals that are being targeted [23]. to keep the sequence going, the rnn cell takes into account not just the input cells, but also the output of the current cell. figure 2 shows an rnn cell. given an input feature sequence x = (x1, ..., xt ), the model can be constructed as a standard lstm rnn for computing the hidden vector h=(h1, ..., ht ) and the output vector sequence y=(y1 , ..., yt ) [23]. this can be determined by solving the following equations repeatedly, starting with time t equal to 1 and going up to t: (ℎ�, ��) = �( �,ℎ� �, �� �) (1) �� = ��ℎ� + ℎ� (2) where whyht is the hidden-output weight matrix of the lstmrnn, and c is the cell activation vector that has the same size as the hidden vector h [23]. the w terms describe the weight matrices and the b terms denote the bias vectors, e.g., by is the output bias vector. fig. 2. the architectural frame of an rnn –cell. the deep lstm-rnn has properties that are indicative of dnns in general. it is feasible to generate it by stacking some lstm-rnn hidden layers one atop another, with the output sequence of one layer functioning as the input for the succeeding in the stack. this process can be repeated as many times as necessary to generate it. tanh is a function frequently used as an activation for rnns. these relatively low values constrain the ultimate gradient while backpropagation takes place, but they have no impact on the weights. because of the vanishing gradient problem, the process of training the model goes more slowly. memory cells are added to the buried layers of the rnn to find a solution to this problem, and the original design of the rnn is transformed into a longand short-term memory system [25]. the lstm architecture is made up of memory cells, an input gate, a forget gate, and an output gate. the input gate in the lstm is responsible for determining whether the existing activation of the cell should be altered by the addition of new information obtained from the input network in the existing cell. the output gate has the responsibility to choose and pass pertinent information from the currently active cell to the next. the forget gate receives information from previous states, resets the action values, and contributes to the process of determining what information from the previous state should be discarded and what should be maintained. these gates alleviate the problem of disappearing gradients that can occur in lstms [26]. this is a similar approach to [27] on the detection and recognition of danger signs, to [28] on prediction, and to [29] on the planning of routes using rnns. the lstm is guided and uses the historical context maintained by the forget gate. using this context in both directions allows for accurate transcription to be completed. as a direct consequence, this study developed bidirectional lstms by fusing two lstms (forward and backward). it is possible to combine many blstm layers to achieve a greater sense of depth and abstraction. this method used two lstm layers, with 256 hidden cells in each. following this step, this study also used a dropout layer and adam as an optimizer. b. dataset generation and preprocessing the dataset consisted of e-commerce sales data from the kaggle repository, containing 23486 rows and 10 different feature variables. customer age, title, rating, recommended flag, and reviews were some of the factors that were included in the dataset along with other variables such as clothing identification, which was a categorical variable that refers to the item in question. anaconda and google collab were used to carry out the analysis. in addition, the recommended binary ind variable was used as a flag to indicate whether the client recommends the product (1) or ont (0). as a result, ratings, reviews, and the recommended flag were taken into account when creating the training dataset for the products. following this step, the dataset was cleaned out using several distinct forms of data preprocessing methods, such as tokenization and stop word removal, among others. tokenization is the first stage in any natural language processing (nlp) pipeline, as the results of this step have a considerable influence on the subsequent steps. using a tool called a tokenizer, unstructured data and text written in natural language are both sliced up into chunks of information that can be considered independent elements. a tokenization method was used to generate a vector that accurately represents this data, and then a technique known as the removal of stop words was also applied. these preprocessing steps are the most frequently used in a variety of nlp applications. the basic idea is to filter out any words present in every review in the dataset. both these terms are meaningless in the context of the prediction and recommendation task. figures 3 and 4 show a subset of the dataset and the relevant statistics. engineering, technology & applied science research vol. 13, no. 3, 2023, 10931-10935 10934 www.etasr.com aldhahri: the use of recurrent nets for the prediction of e-commerce sales table i. a dataset snapshot count rating recommended ind positive feedback count 0 4 1 0 1 5 1 4 2 3 0 0 3 5 1 0 4 5 1 6 5 2 0 4 6 5 1 1 7 4 1 4 8 5 1 0 9 5 1 0 10 3 0 14 11 5 1 2 12 5 1 2 13 5 1 0 14 3 1 1 15 4 1 3 16 3 1 2 17 5 1 0 18 5 1 0 19 5 1 0 20 4 1 2 21 4 1 14 22 2 0 7 23 3 1 0 24 5 1 0 25 3 0 0 26 2 0 0 27 4 1 0 … .... … … 23480 5 1 0 23481 5 1 0 23482 3 1 0 23483 3 0 1 23484 3 1 2 23485 5 1 22 fig. 3. sample of the dataset. fig. 4. sample and statistical analysis of the dataset. iii. experimental analysis and results this study used python v.3.6 and the scikit learn and tensof flow machine and deep learning libraries as backends to keras [30-31]. training and prediction were both developed with the help of the nvidia cuda parallel computing platform and api. in addition, the root mean square prediction error was calculated to compare the various outcomes of the proposed blstm model, as it provides an all-encompassing perspective of the error distribution. the dataset was partitioned into two subsets, namely 70% for training and 30% for testing. the model was trained for a total of 32 iterations to prevent overfitting. the model run with various numbers of epochs that ultimately resulted in a 91% accuracy. this shows that the factors used to predict e-commerce sales have a strong prediction performance. figures 5 and 6 show the model's accuracy and loss, respectively. fig. 5. model accuracy as a 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[31] a. géron, hands-on machine learning with scikit-learn and tensorflow: concepts, tools, and techniques to build intelligent systems, first edition. springfield, mi, usa: o'reilly media, 2017. microsoft word 34-3201_s_etasr_v9_n6_pp5056-5061 engineering, technology & applied science research vol. 9, no. 6, 2019, 5056-5061 5056 www.etasr.com mubarak et al.: the impact of digital transformation on business performance the impact of digital transformation on business performance a study of pakistani smes muhammad faraz mubarak kaunas university of technology, lithuania and shaheed zulfiqar ali bhutto institute of science and technology, pakistan muhammad.faraz@szabist.edu.pk fazal ali shaikh department of economics university of sindh jamshoro, sindh, pakistan fazal_110_shaikh@hotmail.com mobashar mubarik faculty of technology management and business, universiti tun hussein onn malaysia, malaysia mobashar.com@gmail.com kamran ahmed samo faculty of engineering university malaysia sarawak kota samarahan, sarawak, malaysia 13010086@siswa.unimas.my sanya mastoi faculty of technical and vocational education universiti tun hussein onn malaysia johor, malaysia gb180061@siswa.uthm.edu.my abstract—business ecosystems are continuously evolving. in this hyper-competitive era, firms are increasingly transforming their business operations through advanced digital technologies. gone are the days of mere testing and debating the influence of digital transformation and industry 4.0, yet the time has come for actionable steps. therefore, this study has identified the role of industry 4.0 technologies including big data, cyber-physical systems, internet of things and interoperability, on the performance of small and medium-sized enterprises (smes) in pakistan. a relevant questionnaire was developed and distributed randomly in the cities of karachi, lahore, peshawar, islamabad, gujrat, and sialkot. after applying multiple regression techniques through spss, it was found that big data, cyberphysical systems, and interoperability have a significant positive impact to improve business performance, while the insignificant effect of internet of things was revealed. since the research in the area of digital transformation and industry 4.0 is scant, the current study has contributed novel directions, insights and a framework for future researchers. moreover, this study will help managers to justify the allocation of resources towards technological infrastructure development in the operations of their firms. finally, policymakers will find it helpful in order to devise suitable strategies for developing human capital and to enhance their absorptive capacity. keywords-digital transformation; business performance; pakistani smes; industry 4.0 i. introduction digital advancement is forcing companies to rethink their organizational models. some firms are showing a superior ability to exploit digital technologies to gain a competitive advantage over the market in many industries. traditional companies, with their hierarchical, centralized, closed, topdown organizational structures, are unable to change and evolve at the speed required by digital disruption [1]. in order to survive, traditional companies have to question their organizational models, learn from digital disruptors and shift their organizational models and mindset [2]. we are transitioning towards a digital economy and society. although already underway for nearly half-a-century, the pace of change has quickened with the further deployment of digital infrastructure, the proliferation of smartphones which allows ubiquitous computing, and the generation of huge volumes of all kinds of data. these developments have turned data into an important strategic asset [3]. many now compare the digital transformation with earlier industrial transformations propelled by general-purpose technologies like steam or electricity. whether it is the second machine age [4], the third wave [5], or industry 4.0 [6], significant shifts are underway in the economy and in society more generally. with this transformation come rare opportunities to improve welfare and address pressing social issues from health care to education to the environment [7-9]. yet such benefits come with new challenges as digital transformation changes the nature and structure of companies and markets, raises concerns around jobs and skills, privacy, security, social and economic interaction [10], the formation and composition of communities, and notions of equity and inclusion in the present era of industry 4.0. researchers have endorsed the significant positive effects of digital transformation of businesses on productivity and performance on a macro level [11, 12]. the objective of industry 4.0 is to attain an advanced level of operational effectiveness and productivity, as well as a higher level of automation [13, 14]. as industry 4.0 has a significant role in the production and service sectors, it has a direct relationship with performance. authors in [1, 15] have mentioned that various features of industry 4.0 are highly connected with internet technologies and progressive corresponding author: muhammad faraz mubarak engineering, technology & applied science research vol. 9, no. 6, 2019, 5056-5061 5057 www.etasr.com mubarak et al.: the impact of digital transformation on business performance algorithms. however, they also specify that industry 4.0 is one of the technical procedures of value addition and effective knowledge management practices. despite the research on industry 4.0, a comprehensive review of studies on industry 4.0, is required [16]. consequently, this study proposes a framework with the help of industry 4.0 and presents the significance of this revolution in small and medium-sized enterprises (smes). the current study aims to enlighten the role of industry with respect of business performance. ii. literature review and theoretical framework a. smes in pakistan in the industrial development of a country, the importance of the sme sector cannot be overlooked. the meaning of smes in pakistan lies in the number of representatives (up to 250 individuals), paid-up capital (up to 25 million rs.), and yearly deals (up to 250 million rs.) [17]. smes constitute nearly 90% of all the enterprises in pakistan. they employ 80% of the non-agricultural labor force and their share in the annual gdp is approximately 40%. however, unlike large enterprises in the formal sector, a small and medium enterprise is constrained by financial and other resources. this inherent characteristic of an sme makes imperative the existence of a mechanism through which it may get support in different functions of business including technical upgradation, marketing, financial, and human resource training and development [18]. despite having economic importance, the smes of pakistan are suffering many shortcomings, which seriously impede their performance. the major shortcomings include the ineffective business information structure, lack of strategic planning, and lack of human capital required in the modern era business [19]. such inefficiencies can be resolved and the current state of smes can be uplifted by infusing the advanced digital technologies of industry 4.0 in their business operations [20, 21]. b. business performance and industry 4.0 the industrial expansion has continued for many decades, and currently, it is in the age of industry 4.0 [22]. the concept of industry 4.0 was originally planned for an emerging german economic system in the year 2011 [23]. the first industrial revolution started in the last period of the 18th century [24]. this revolution was characterized by automatic production plants using water and steam power. the second industrial revolution began in the early 20th century, characterized by mass labor production grounded in electrical energy. the third industrial revolution started in the 70’s with the distinctive features of programmed production grounded in new technology. finally, the fourth industrial revolution, namely industry 4.0, is continuing including the features of cyberphysical system (cps) production, grounded in diverse data as well as knowledge combination [24]. industry 4.0 has been described from various viewpoints. for instance, industry 4.0 is “the integration of complex physical machinery and devices with networked sensors and software, used to predict, control and plan for better business and societal outcomes” [25]. author in [26] defines industry 4.0 as “a new level of value chain organization and management across the lifecycle of products”. author in [27] described industry 4.0 as “a collective term for technologies and concepts of value chain organization”. four elements of industry 4.0, namely big data (bd), iot, interoperability, and cyber-physical systems are undertaken in this study. this collection has followed the notion of [1] which reported a significant connection of these factors with improved performance. these branches of industry 4.0 can resolve technological challenges of smes, and may ultimately increase sustainable business performance. moreover, they promote performance and exert significant effects on production and services. it is proven that industry 4.0 has a positive influence on production and services, and it increases performance [1, 28, 29]. various studies proved that technology adoption has a significant relationship with business performance [30, 31], and the structure and processes of an organization show a strong relationship with it implementation [32]. there is an effect on strategy or technology implementation from industry 4.0 that positively affects business performance among smes [28]. organization structure and process should be supportive of accepting and implementing new technology related to big data, iot and smart factory which will lead to better sustainable business performance among smes. c. digital transformation and its factors in order to enable digital transformation and modernization of firms, advanced human capital is needed. every area and department of a business should be open to being influenced by such technological makeover. industry 4.0 can be defined as an umbrella term, denoting a variety of recent concepts, as well as numerous linked disciplines within the industry to transform the business operations [33]. the factors of digital transformation taken in this study include iot, big data, cyberphysical systems (cps) and interoperability [1] (figure 1). such technologies have the potential to enable a paradigm shift towards business settings [33, 34], and the very phenomenon can be further elucidated as a technology push. fig. 1. factors of digital transformation 1) big data big data is one of the umbrella terms for any method utilized to process a vast quantity of data, knowledge or engineering, technology & applied science research vol. 9, no. 6, 2019, 5056-5061 5058 www.etasr.com mubarak et al.: the impact of digital transformation on business performance information, including capture, safety, transmission, storing, analysis, search, confidentiality, and data which is both structured and unstructured [16]. big data is generally used to handle massive amounts of data [35]. the nature of big data encompasses extensive measures to identify and interpret the data into new ideas. author in [36] mentioned that big data is a systematic visualization where the amount of data are just beyond technology’s capability to store, manage, and process efficiently. authors in [37] have categorized big data by volume, variety, and velocity. the term has a significant relationship with technology adoption [38]. the implementation of big data can overcome various technologyrelated challenges. it provides better technology, which helps to find better ways to store data efficiently [35]. therefore, we hypothesize that big data positively affects business performance: hypothesis1: big data has a positive impact on business performance 2) cyber-physical systems(cps) cyber-physical systems (cps) refers to a new generation of systems with integrated computational and physical capabilities that can interact with humans through many new modalities [28]. the capability to interact with and enlarge the abilities of the physical world with the help of computation and communication, as well as control, is a significant enabler for future technological developments. hypothesis2: cps has a positive impact on business performance 3) interoperability interoperability is what happens when we bring the above elements together. it is the connection of cyber-physical systems, humans, and smart factories communicating with each other through iot. in this direction, manufacturing partners can efficiently share various types of information error-free. basically, interoperability enables error-free transmission as well as translation. it is one of the basic requirements of a modern technological system [20]. therefore, it is assumed that interoperability improves performance. hypothesis3: interoperability has a positive impact on business performance 4) internet of things (iot) in current years, iot has been developed as the most significant subject in numerous industries. iot is not only a major buzz word in businesses but also an emerging drift, an established plan, and a ground-breaking technology. initially, author in [39] projected the idea of iot and defined iot as exclusively recognizable consistent objects with radiofrequency identification (rfid) expertise, which has the ability to alter the world. authors in [40] specified iot as networkconnected tools. a few initial iot applications have been previously industrialized in health sectors, transport, home utilization, and various self-propelled industries [14]. industry 4.0 is based on these vital skills of iot: rfid, cloud computing, middleware, and various software applications [41]. iot technologies have been extensively used in numerous industries, for instance, iot can advance logistics and supply chain effectiveness by providing more comprehensive knowledge [38]. it is predicted that iot would reach 26 billion parts in 2020, from 0.9 billion in 2009 [3]. therefore, we can understand the strength of the persuading power that iot skills can bring. presently, various studies focused on iot emphasing on the expansion of iot technologies and its applications, but no research has been conducted regarding the influence of iot execution on the performance of pakistani smes, therefore, this study aims to fill this gap. hypothesis4: iot has a positive impact on business performance d. theoretical framework this study suffices the theoretical underpinnings of resource-based view (rbv). concurrently, the rbv of it recommends that the it resources in the firm can be the competitive capability of the firm [42, 43]. it is further pointed out that the firm’s human it skills, it infrastructure, and it reconfigurability are the firm’s unique resources [42]. every single it resource is unique and complex to acquire. the combination of the technological resources creates a firm’s strong organizational capability which leads to superior performance [7, 42]. the current study focuses on the influence of industry 4.0 technologies including big data, iot, interoperability, and cps on business performance of smes as shown in figure 2. fig. 2. theoretical framework iii. methodology to evaluate the influence of digitalization of firms in industry 4.0 towards enhanced business performance in pakistani smes, four major digitalization factors were considered, namely big data, iot, interoperability, and cps. the questionnaire was distributed physically, and through email to various smes in karachi, lahore, islamabad, peshawar, sialkot, and gujrat. following the sampling table of [44], 390 questionnaires were distributed. the respondents of this study were employees of managerial level and above who have knowledge of industry 4.0 and digital transformation. random sampling was used for respondents’ selection. the engineering, technology & applied science research vol. 9, no. 6, 2019, 5056-5061 5059 www.etasr.com mubarak et al.: the impact of digital transformation on business performance data were collected using the 5-point likert scale from strongly disagree to strongly agree. the questionnaire was divided into two major parts. the first part included demographic items such as age, gender, marital status, and income and the second part regarded the key variables of this research which are big data, interoperability, cps, and iot. the questionnaire was adapted from [1] and [28]. this study applied multiple regression methods through spss to analyze the data. iv. results and data analysis from the total 390 questionnaires distributed 237 were usable responses selected out of the received 278. forty one questionnaires were excluded because they did not respond more than 60% of the questions of the survey. the selected questionnaires include 45 respondents from pharmaceutical firms, 83 from textile firms, 27 from cutlery firms, 68 from beverage companies, 32 from fan manufacturers, and 23 from surgical instruments manufacturing firms. the demographics of respondents are given in table i. the demographic details of targeted smes are shown in figure 3. table i. respondents profile designation number of respondents (%) entrepreneurs 34 14 managers 129 55 administrators 74 31 total 237 100 experience (years) 1-5 75 32 6-10 46 19 11-15 82 36 16-20 18 7 21 and more 16 6 total 237 100 fig. 3. number of targeted smes data analysis was performed in two phases. in the first phase, responses with higher missing values and outliers were eliminated manually and 278 responses were retained. the reliability of the data was checked using cronbach’s alpha. table ii shows cronbach’s alpha, mean and standard deviation values. cronbach’s alpha values of all items are higher than 0.80 which are within the acceptable range [45, 46]. the mean values of the independent variables including big data, cps, iot, and interoperability are 3.37, 3.35, 2.97 and 3.28 respectively. table ii. cronbach’s alpha, mean, and standard deviation variable number of items cronbach’s alpha mean s.d. big data 4 0.816 3.37 0.673 cps 4 0.834 3.35 0.570 iot 5 0.851 3.39 0.569 interoperability 3 0.880 2.97 0.681 business performance 10 0.827 3.36 0.522 in the second phase, multiple regression was applied which determines the degree of strength and direction of the linear relationship among research variables [47]. the regression analysis results exhibited in table iii indicate the relationships between the independent and dependent variables. big data, cps, iot, and interoperability were regressed against the business performance and variance accounted for, r2=36.6, r2=34.6, r2=32.2 and r2=33.8 correspondingly, which means that infusion of 36.6% in big data, 34.6% in cps, 32.2% in iot and 33.8% in interoperability can enhance the performance of smes in pakistan. it can also be seen in table iii that the impact of big data at p<0.05, with significance level of 0.000 is positively affecting performance. similarly, cps and interoperability are also found as effectively significantly to performance of business at p<0.05. however, the effect of iot is found as insignificant towards business performance, at significance level of 0.634. the beta values for big data, cps, iot, and interoperability are 0.307, 0.314, 0.170, and 0.283 respectively. these values denote that when 1% increase in big data will be made, the business performance will be improved by 30.7%. furthermore, 1% increase in cps leads to 31.4% increase in performance. also when 1% increase will be devoted to iot and interoperability, the performance of smes will be upgraded by 17% and 28.3% respectively. thus, in the light of these results h1, h2 and h4 are accepted, and h3 is rejected. table iii. regression analysis coefficients model unstandardized coefficients standardized coefficients t sig. b std. error beta 1 (constant) 0.884 0.124 4.683 0.000 big data 0.307 0.513 0.309 5.406 0.000 cps 0.314 4.972 0.314 4.629 0.001 iot 0.170 0.806 0.190 -0.477 0.634 interoperability 0.283 4.904 0.280 4.722 0.000 dependent variable: business performance v. discussion advancement of businesses through industry 4.0 means is currently one of the foremost concerns of strategic leadership. as a matter of fact, the majority of policymakers of developed countries are anticipating a significant strategic contribution of engineering, technology & applied science research vol. 9, no. 6, 2019, 5056-5061 5060 www.etasr.com mubarak et al.: the impact of digital transformation on business performance advanced technologies of industry 4.0 in the whole business ecosystem [2, 7]. these findings are in alignment with the ones in [1, 28, 48], which they also reported positive effects of these factors on performance of smes in thailand and indonesia. however, the influence of iot on performance was revealed insignificant in the current study, which is in contradiction with the results of [1] on the smes of thailand. the potential reasons for these inconsistent results can be the varying technological and business environment of pakistan and thailand. reportedly, thailand is a tourist country and it has adopted advanced technology earlier than pakistan, which has reasonably enhanced the absorptive capacity of its smes. however, despite the emergence and development of smes, the pace of growth and development of smes in pakistan is sluggish. gone are the days of mere reading such innovation discourses to find the corroboration of such technologies, it is rather the time to embrace it in order to attain competitive advantage and to sustain in the increasingly challenging marketplace [49, 50]. therefore, the managers need to balance the exploration and exploitation of their companies to attain agility which is a pre-requisite to evolve the business settings in modern times [51]. consequently, industry 4.0 tools including big data, cps, and interoperability are needed to balance such a situation in order to enhance productivity and performance while achieving competing advantage. vi. conclusion this study investigated the impact of industry 4.0 technologies including big data, cps, iot, and interoperability on the performance of smes in pakistan. the positive significant role of big data, cps, and interoperability in enhancing smes performance was verified. assimilating and exploiting modern technologies is in the limelight of businesses and firms are vulnerable to the impact of innovation. advanced technologies are transforming and overturning entire business models. the government of pakistan should facilitate and encourage smes to adopt such technologies in their operations extensively, thus not only reducing cost and increasing productivity, but also adding extra value to their products, value that is currently missing in pakistani smes. furthermore, the appropriate type of human capital equipped with modernday skills is inevitably needed in order to comply with the advanced business settings of industry 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international journal of advanced and applied sciences, vol. 6, no. 9, pp. 1–12, 2019 [51] g. c. kane, d. palmer, a. n. phillips, d. kiron, n. buckley, “strategy, not technology, drives digital transformation”, mit sloan management review and deloitte university press, vol. 14, pp. 1–25, 2015 microsoft word etasr_v11_n4_pp7386-7392 engineering, technology & applied science research vol. 11, no. 4, 2021, 7386-7392 7386 www.etasr.com nagao & tsutaba: evaluation methods of vertical subgrade reaction modulus and rotational … evaluation methods of vertical subgrade reaction modulus and rotational resistance moment for seismic design of embedded foundations takashi nagao research center for urban safety and security kobe university kobe city, japan nagao@people.kobe-u.ac.jp ryota tsutaba ex-faculty of engineering kobe university kobe city, japan ryota.ttb.0511@gmail.com abstract-in a seismic design of embedded foundations, the vertical subgrade reaction (sr) acting on a foundation bottom surface and the rotational resistance moment (rrm) generated by the sr are calculated using an sr modulus (srm). the srm and rrm depend on both ground rigidity and foundation width (fw). however, the srm and rrm calculation methods adopted in design codes might not properly consider their fw dependency. in this study, srm and rrm evaluation methods for embedded foundations subjected to a seismic load were examined by conducting a two-dimensional finite element analysis under the condition where ground rigidity and fw were changed considering the nonlinearity of the ground. the results show that when the seismic load is large and the nonlinearity of the ground appears, the sr distribution is different from the assumption in the design code. the fw dependency of the srm was lower than the assumption of the design code. furthermore, methods to calculate the srm and rrm in accordance with the fw and ground rigidity are proposed. keywords-subgrade reaction modulus; rotational resistance moment; foundation width i. introduction a structure’s foundation must ensure stability by transmitting the applied load to the ground. when the structure is heavy or the ground is soft, a columnar foundation is embedded in a sufficiently strong soil layer. in addition to a vertical load, such as the deadweight of the structure, a seismic load acts horizontally during an earthquake, rotating the structure. the vertical subgrade reaction (sr) acting on the foundation bottom supports the vertical load and generates a rotational resistance moment (rrm) to contribute to the structure’s rotational resistance. the sr is calculated by multiplying the foundation’s displacement and a sr modulus (srm). the srm depends on the ground rigidity and foundation width (fw) and increases with the increase in ground rigidity and decreases with the increase in fw [1-3]. therefore, various design codes, such as the japanese specifications for highway bridges (jshb) [4], apply the srm calculation equation in accordance with the fw. when the seismic load is large or when a large lateral spreading pressure is considered to act during an earthquake [5], the fw should be widened to enhance seismic resistance. however, when using the srm calculation equation adopted in the design code, the srm significantly decreases as the fw increases, and an increase in the sr proportional to the increase in the fw cannot be expected. therefore, the fw should be extremely wide when the seismic load is large. however, the results of the horizontal loading test of pier models where the fw was changed revealed that the seismic resistance becomes extremely high by widening the fw because the vertical sr becomes large [6]. it has been also highlighted that the fw dependence of the vertical srm is lower than that of the horizontal srm [7]. therefore, the horizontal and vertical srms should be evaluated differently, and the appropriate evaluation of the vertical srm is critical to perform rational seismic design. in this study, a two‐dimensional finite element analysis was conducted considering the nonlinearity of the ground. from the analysis results, evaluation methods for the vertical srm and rrm for embedded foundations subjected to seismic loads are proposed. since only vertical sr and srm are considered in this paper, they are described as sr and srm for simplicity in the following. ii. method a. analytical model two-dimensional finite element analysis was used to evaluate the characteristics of the sr to embedded foundations under seismic loading. the analysis code used is flip [8], which is widely used for the evaluation of the seismic stability of structures [9]. a foundation of 20m height was assumed to be 10m embedded, and the ground was modeled to a depth of 30m. to evaluate the difference in the srm because of the difference in the fw, four cases with fws (b) of 4, 6, 8, and 10m were set. figure 1 shows an analytical model and a finite element mesh diagram, taking the case of b = 4m as an example. the mesh height and width for structural and surrounding ground elements were set at 0.5m, which are smaller than those for other elements. the foundation was modeled using linear planar elements, assuming a reinforced concrete structure, with young’s modulus of e = 2.5×10 7 kn/m 2 , poisson’s ratio of ν = 0.20, and density of corresponding author: takashi nagao engineering, technology & applied science research vol. 11, no. 4, 2021, 7386-7392 7387 www.etasr.com nagao & tsutaba: evaluation methods of vertical subgrade reaction modulus and rotational … ρ = 2.4t/m3. for the ground, density ρ = 1.8t/m3 and poisson’s ratio ν = 0.33 were used. three cases of soft ground (case a), intermediate ground (case b), and hard ground (case c) were set using the n-values obtained from the standard penetration test (table i). fig. 1. analysis model and finite element mesh diagram. table i. ground conditions (n-values) depth(m) case a case b case c 0.0 to -5.0 10 10 10 -5.0 to -10.0 10 10 30 -10.0 to -30.0 10 30 50 the ground shear rigidity in the middle of each stratum is called the reference shear rigidity and is calculated by [10]: 0 68 131 14100 . ma g n= (1) where gma is the reference shear rigidity (kn/m 2 ) and n131 is the equivalent n-value for the reference effective overburden pressure of 131kn/m 2 . the ground shear rigidity gm at each depth is calculated using [11]: 0 5. m m ma ma ' g g ' σ σ   =     (2) where gm is the shear rigidity, gma is the reference shear rigidity, σm' is the effective confining pressure, and σma' is the reference effective confining pressure corresponding to the reference shear rigidity. young’s modulus of the ground is calculated using: 2 1 m m e ( )gν= + (3) where em is young’s modulus, gm is the shear rigidity and ν is the poisson’s ratio. the ground shows remarkable nonlinearity when the shear strain exceeds 10 −6 . in this study, the nonlinearity of the ground is expressed as in (4) using a hyperbolic model [12]: 00 1 1 m g gg γ τ = + (4) where g is the shear rigidity, g0 is the initial shear rigidity, γ is the shear strain, and τm is the shear strength, which is calculated using [10]: τm = σm' sin φ (5) where σm' is the effective confining pressure and φ is the shear resistance angle. by calculating the relative density using (6), the shear resistance angle is calculated using (7) [10]. the ground shear resistance angles under the foundation bottoms of cases a, b, and c are 39.0°, 40.7°, and 42.5°, respectively. 0 5 131 100 21 70 . v n dr 'σ   =   +  (6) 2 0 0003 0 0426 36 682. dr . dr .ϕ = + + (7) where dr is the relative density (%) and σv' is the reference effective overburden pressure (131kn/m 2 ). slipping or separation can occur on the contact surface between the foundation and the ground. to express these phenomena, joint elements are installed between the structure and the ground. the joint element transmits a compressive force corresponding to the initial rigidity perpendicularly to the element, whereas the tensile force is not transmitted, reproducing the separation of the ground and the structure. for the sliding direction, shear force corresponding to the initial shear rigidity is transmitted until the shear stress reaches shear strength. b. analysis method the analysis was conducted in two stages. at first, the deadweight of the foundation was applied, and afterwards the horizontal load was applied. the loading position of the horizontal load was set to be the top of the foundation to increase the rotational moment. table ii shows the loads applied for each fw. table ii. loads fw (m) horizontal load (kn) dead weight (kn) 4 1000 1920 6 1500 2880 8 1500 3840 10 1800 4800 to stabilize the analysis, the load was made zero for the first second and was gradually increased. calculations were performed with 1000hz sampling for deadweight loading and 400hz for horizontal loading. the loading rates were 2000kn/s and 200kn/s for the deadweight and horizontal loading respectively and the calculation was continued for 1s after the maximum load was reached. figure 2 shows the time history of the horizontal load. the srm is calculated using: engineering, technology & applied science research vol. 11, no. 4, 2021, 7386-7392 7388 www.etasr.com nagao & tsutaba: evaluation methods of vertical subgrade reaction modulus and rotational … v k dy σ = (8) where kv is the srm (kpa/m), σ is the normal stress (kpa) of the joint element, and dy is the vertical displacement of the foundation (m). fig. 2. time history of horizontal loading. iii. results and discussion a. comparison of sr in this study and in jshb figure 3 shows the time history of the sr and foundation displacement during horizontal loading, referring to b = 4m and 10m for case b respectively. the values in the legend indicate distances from the foundation edge on the side where settlement occurs. downward displacement is defined as negative. (a) (b) fig. 3. time history of sr and displacement. (a) b = 4m , (b) b = 10m. the sr shows a larger value as it moves closer to the foundation edge. especially at the foundation edge, the initial sr value is larger than those at other positions, correlating with the results of [7]. focusing on the srs at 1m, after 5s, when b = 4m, and after 9s, when b = 10m, they show almost constant values. however, the sr at the foundation edge continues to increase for 9–10s, where the horizontal load continues to increase, especially for b = 10m. the displacement continues to increase after the sr reaches the maximum value at each position, indicating that the ground shows strong nonlinearity and yielding occurs. furthermore, at 2m from the foundation edge with b = 4m, the sr decreases after 4s, and the foundation displaces upward. foundation rotation occurs at a position shorter than half of the fw. the result for b = 10m is similar. the sr decreases after 8s at 3m from the foundation edge, and upward displacement occurs at 4m from the foundation edge. this result is compared with the assumption of the jshb [4]. the jshb assumes that the rotational center is at the foundation’s center, and the sr is increased to the allowable bearing capacity with increasing horizontal load, regardless of the position. figures 4(a)-(b) show the assumption of the jshb. figure 4(a) shows the sr distribution when the sr at the foundation edge has reached the allowable bearing capacity (qa). as the horizontal load increases, the sr in the range up to the center of the foundation increases until it reaches the allowable bearing capacity (figure 4(b)). the allowable bearing capacity is calculated using: ( ) ( ) ( ) ( ) 1 2 2 2 1 2 1 1 1 1 1 4 d r f q a d f f s q r q q bn d n q q d d f sin n exp tan sin n n tan . βγ γ γ γ ϕ π ϕ ϕ ϕ = + = − + + = − = − (9) where qd is the ultimate bearing capacity of the ground, β is the shape factor of the foundation bottom, e.g. 0.8 for square, γ1 and γ2 are the unit weights of the ground below and above the foundation bottom respectively, b is the fw, df is the foundation embedded depth, qa is the allowable bearing capacity of the ground, fs is the safety factor (2 in the event of an earthquake), and φ is the shear resistance angle of the ground. figure 4(c) shows the sr distribution of this study. maximum sr is smaller than the allowable bearing capacity of the jshb and the rotational center is not necessarily at the foundation's center. (a) (b) (c) fig. 4. sr distribution. figure 5 compares the allowable bearing capacity from the jshb and the maximum sr at the foundation edge obtained in this study. the horizontal axis is the shear resistance angle of engineering, technology & applied science research vol. 11, no. 4, 2021, 7386-7392 7389 www.etasr.com nagao & tsutaba: evaluation methods of vertical subgrade reaction modulus and rotational … the ground at the foundation bottom. the maximum srs obtained in this study are smaller than the allowable bearing capacities of the jshb. the jshb sets the allowable bearing capacity lower than the ultimate bearing capacity by introducing the safety factor, however, it still overestimates the maximum sr. furthermore, in the jshb, the allowable bearing capacity increases as the fw increases, but in this analytical result, the change in the maximum sr with the change in the fw is slight. the allowable bearing capacity calculation equation adopted in the jshb is conventional for the condition that only a vertical load is applied and is not applicable when an inclined load is applied. in addition to overestimating the sr distribution, the jshb overestimates the rrms by assuming that the rotational center is always at the foundation’s center. fig. 5. comparison of maximum sr. b. ground stress characteristics under inclined loading when the foundation is subjected to an inclined loading, both compressive and shear strains are generated in the ground under the foundation. figure 6 shows the time histories of the compressive strain and shear strain in the ground under the foundation for the condition b = 4m of case a. the legend is the distance from the foundation edge. the compressive strain value is the largest at the foundation edge and decreases toward the foundation’s center. in contrast, no noticeable difference occurs in the shear strain because of the difference in the position from the foundation edge. fig. 6. ground stress characteristics. the compressive strain differs from location to location because it depends on the amount of foundation settlement. however, the shear strain depends on the foundation’s rotational angle because the foundation is rigid and bending deformation does not occur. therefore, no significant difference occurs in the shear strain according to the distance from the foundation edge. the relationship between shear stress and shear strain is nonlinear with increasing strain, and when the shear stress reaches a value close to the shear strength, the shear strain increases abruptly without an increase in the shear stress. therefore, the nonlinear behavior appears simultaneously regardless of the distance from the foundation edge. thus, the sr at positions other than the foundation edge does not reach the maximum value at the foundation edge, and the relationship between the sr and settlement shows nonlinearity. c. evaluation method of srm figure 7 shows the time histories of the srm, referring to the conditions b = 4m and 10m of case b. the legend is the distance from the foundation edge. at the foundation edge, the sr is large because of the influence of boundary conditions and the srm is larger than those at other positions, correlating with the result in [7]. in the early stage of loading, the srm shows a constant value because the ground does not exhibit nonlinear behavior. the srm decreases because of the effect of the nonlinear properties of the ground after 4s at b = 4m, and after 6s at b = 10m. we excluded the data at the foundation edge and obtained the average srm value for the range in which it shows a constant value. from the results, the calculation equation (10) of the srm was obtained. the srm calculation equation in the jshb is shown in (11). the srm calculation equation in this study has a weaker fw dependency than that in the jshb, correlating with [7]. (a) (b) fig. 7. time history of srm. (a) b = 4m, (b) b = 10m 1 2 0 15 m v r r e b k . b b −   =     (10) 3 41 0 3 0 3 v m b k e . . α −   =     (11) where kv is the srm, em is young’s modulus of the ground under the foundation bottom, b is the fw, br is the reference width of the loading plate used for the plate loading test to determine the srm, and br = 0.3m in this study. α is a coefficient specified as 2 (for example) when em is evaluated using the n-values from the standard penetration tests to obtain the srm values during an earthquake. the variation of the n-value is large in relation to soil rigidity and no unified equation exists to express their engineering, technology & applied science research vol. 11, no. 4, 2021, 7386-7392 7390 www.etasr.com nagao & tsutaba: evaluation methods of vertical subgrade reaction modulus and rotational … relationship. for example, in the jshb, em is calculated as 2800n. this study discusses the fw dependency of the srm and not the method to calculate the young’s modulus of the ground using the n-value. therefore, in the following, the srm results obtained from the jshb equations are shown as their changes by changing the fw under conditions where they are the same as the results of this study when b = 4m. figure 8 compares the srms obtained in this study and the jshb's. the srm decreases by 50% from the jshb equation if the fw is widened from 4m to 10m, however in this study, the srm decreases by only 33%. underestimation of the srm in the case of foundation widening leads to overdesign. therefore, the jshb equation is not applicable for a wide foundation. (a) (b) (c) fig. 8. fw dependency of srm. (a) case a, (b) case b, (c) case c. d. evaluation method of rrm the rrm is calculated using: v m k iθ= (12) where m is the rrm, kv is the srm, i is the geometrical moment of inertia of the foundation bottom around the rotational center axis, and θ is the foundation’s rotational angle. figure 7 shows that the srm decreases as the load increases, so the change in the srm must be considered according to the change in the rotational angle. the change in the rotational center position when increasing the load will also be considered. figure 9 shows the change in the sr distribution when increasing the horizontal load for the condition b = 6m of case b. the legend in the figure is the value of the horizontal load. the sr is shown as an increment from that before horizontal loading. the position where the sr becomes zero should be regarded as the rotational center. the distance from the foundation edge to the rotational center is defined as the rotational radius, which decreases when the load increases. the value of the rotational radius was obtained by regression analysis when excluding the sr at the foundation edge. figure 10 shows the relationship between the rotational angle and radius for the condition b = 6m of case b. here, the rotational radius is shown as a ratio to the fw. figure 11 shows the relationship between the rotational angle and the srm. here, the srm is shown as a ratio to its initial value. in the range where the rotational angle is minute, the rotational radius is half the fw, and the foundation rotates around its center. the rotational radius decreases as the rotational angle increases because the rear end of the foundation bottom floats. the higher the ground rigidity is, the more the rotational radius decreases. the srm decreases with the increase in the rotational angle, as with the rotational radius. the decrease in the rotational radius and srm when increasing the rotational angle results in the nonlinearity of the relationship between the rrm and the rotational angle (m-θ relationship). fig. 9. distribution of sr. fig. 10. relationship between the rotational angle and the rotational radius. fig. 11. relationship between the rotational angle and the srm. figure 12 shows the m-θ relationship for the condition b = 6m. the m-θ relationship shows a strong nonlinear characteristic because both the rotational radius and the srm decrease with the increase in the rotational angle. the rotational angle where the rrm reaches the upper limit is 4 6 8 10 5 10 3 × 1 10 4 × 1.5 10 4 × 2 10 4 × 2.5 10 4 × fw (m) s r m ( k p a /m ) 4 6 8 10 2 10 4 × 3 10 4 × 4 10 4 × 5 10 4 × fw (m) s r m ( k p a /m ) 4 6 8 10 3 10 4 × 4 10 4 × 5 10 4 × 6 10 4 × 7 10 4 × fw (m) s r m ( k p a /m ) 1 10× 2 10× 3 10× r r m ( k n m ) engineering, technology & applied science research vol. 11, no. 4, 2021, 7386-7392 7391 www.etasr.com nagao & tsutaba: evaluation methods of vertical subgrade reaction modulus and rotational … defined as the critical rotational angle. the higher the ground rigidity is, the smaller the critical rotational angle becomes. the critical rotational angles are 0.010rad, 0.005rad, and 0.003rad respectively for cases a, b, and c. the critical rotational angles are similar for other fws and do not depend on the fw but are strongly affected by the ground rigidity. fig. 12. m-θ relationship. the reduction in shear rigidity of the ground significantly affects the nonlinearity of the sr. figure 13 shows the relationship between the shear rigidity and the strain of the ground at the foundation bottom depth in each case. here, the initial value (g0 in (4)) normalizes the shear rigidity. the rotational angle of the foundation and the shear strain of the ground are equivalent in the range where the rotational angle is small. the shear strain corresponding to the critical rotational angle is evaluated. it corresponds to the shear strain where the shear rigidity is decreased to 15% of the initial value. therefore, in this study, the shear strain when g/g0 becomes 0.15 is the critical rotational angle. furthermore, the reduction rates of the srm and rotational radius corresponding to the critical rotational angle are both 0.9 and are independent of ground rigidity. the rrm is calculated using (13). the m-θ relationship is proposed as a simple bilinear characteristic considering the applicability to design practice. ( ) ( ) v c v c c m ak i ak i θ θ θ θ θ θ = ≤ = > (13) where θc is the critical rotational angle and a is a coefficient that considers the reduction in the srm and rotational radius when the rotational angle reaches the critical value. because the reduction in the rotational radius has a cubic effect on i, a is set to 0.9 4 . fig. 13. relationship between shear rigidity and shear strain. figures 14 and 15 compare the analytical values of the rrm under foundation widths of 6m and 8m respectively, with those values obtained by (13). the red line shows the analytical value and the blue line denotes the value according to (13). the proposed equation slightly underestimates the rrm for case a. however, case a’s foundation is embedded in the soft soil layer of the n-value = 10, which is not frequently realized in design practice. for cases b and c, the proposed equation evaluates well the rrms. (a) (b) (c) fig. 14. m-θ relationship (b = 6m). (a) case a, (b) case b, (c) case c. (a) (b) (c) fig. 15. m-θ relationship (b = 8m). (a) case a, (b) case b, (c) case c. iv. conclusions this study used the results of two‐dimensional finite element analysis considering the nonlinearity of the ground and proposed the srm and rrm calculation methods to be used for the seismic design of the embedded foundation. the main obtained conclusions are: 0.01 0.02 0.03 0.04 0.05 0 1 10 3 × 2 10 3 × 3 10 3 × rotational angle (rad) r r m ( k n m ) 0.01 0.02 0.03 0.04 0.05 0 1 10 3 × 2 10 3 × 3 10 3 × rotational angle (rad) r r m ( k n m ) 0.01 0.02 0.03 0.04 0.05 0 1 10 3 × 2 10 3 × 3 10 3 × rotational angle (rad) r r m ( k n m ) 0.01 0.02 0.03 0.04 0.05 0 2 10 3 × 4 10 3 × 6 10 3 × rotational angle (rad) r r m ( k n m ) 0.01 0.02 0.03 0.04 0.05 0 2 10 3 × 4 10 3 × 6 10 3 × rotational angle (rad) r r m ( k n m ) 0.01 0.02 0.03 0.04 0.05 0 2 10 3 × 4 10 3 × 6 10 3 × rotational angle (rad) r r m ( k n m ) engineering, technology & applied science research vol. 11, no. 4, 2021, 7386-7392 7392 www.etasr.com nagao & tsutaba: evaluation methods of vertical subgrade reaction modulus and rotational … • both compressive and shear strains occur in the ground when an inclined load is applied to the foundation. the compressive strain differs from position to position, however the shear strain does not differ significantly according to the position because it depends on the foundation’s rotational angle. therefore, the shear stress of the ground reaches the shear strength almost simultaneously when the rotational angle of the foundation becomes large and the shear strain increases sharply. therefore, at positions other than the foundation edge, the sr does not reach the maximum value at the foundation edge, and the rotational angle of the foundation increases sharply. the design code overestimates the maximum sr value not only at the foundation edge, but also at other positions. • a srm calculation equation related to fw and ground rigidity was proposed. the srm dependency on the fw was smaller than the assumption in the design code. • when the horizontal load is large and the rotational angle increases, the srm decreases under the influence of the nonlinearity of the ground, and the rotational radius decreases to half of the fw because the rear end of the foundation floats. therefore, the m-θ relationship shows nonlinearity. this study proposed a calculation equation for evaluating the m-θ relationship using the reduction rate of the rotational radius and srm when the rotational angle reaches the critical rotational angle, referring to the shear strain when the shear rigidity of the ground lowers to 0.15 of the initial value. the proposed equation is simple and bilinear considering its applicability to design practice and can evaluate rrm with high accuracy. acknowledgements the analytical modeling for fea was developed in collaboration with daisuke shibata. this research was supported by jsps kakenhi, grant number jp18k04324. references [1] k. terzaghi, "evalution of conefficients of subgrade reaction," géotechnique, vol. 5, no. 4, pp. 297–326, dec. 1955, https://doi.org/ 10.1680/geot.1955.5.4.297. [2] r. ziaie-moayed and m. janbaz, "effective parameters on modulus of subgrade reaction in clayey soils," journal of applied sciences, vol. 9, no. 22, pp. 4006–4012, 2009, https://doi.org/10.3923/jas.2009.4006. 4012. [3] j. lee and s. jeong, "experimental study of estimating the subgrade reaction modulus on jointed rock foundations," rock mechanics and rock engineering, vol. 49, no. 6, pp. 2055–2064, jun. 2016, https://doi.org/10.1007/s00603-015-0905-9. [4] nihon dōro kyōkai, specifications for highway bridges. part 4. tokyo, japan: japan road association, 2002. [5] t. nagao and d. shibata, "experimental study of the lateral spreading pressure acting on a pile foundation during earthquakes," engineering, technology & applied science research, vol. 9, no. 6, pp. 5021–5028, dec. 2019, https://doi.org/10.48084/etasr.3217. [6] t. nagao, "an experimental study on the way bottom widening of pier foundations affects seismic resistance," engineering, technology & applied science research, vol. 10, no. 3, pp. 5713–5718, jun. 2020, https://doi.org/10.48084/etasr.3590. [7] t. nagao, "effect of foundation width on subgrade reaction modulus," engineering, technology & applied science research, vol. 10, no. 5, pp. 6253–6258, oct. 2020, https://doi.org/10.48084/etasr.3668. [8] s. iai, k. ichii, h. liu, and t. morita, "effective stress analysis of port structures," soils and foundations, no. special, pp. 97–114, sep. 1998. [9] t. nagao and p. lu, "a simplified reliability estimation method for pilesupported wharf on the residual displacement by earthquake," soil dynamics and earthquake engineering, vol. 129, p. 105904, feb. 2020, https://doi.org/10.1016/j.soildyn.2019.105904. [10] t. morita, s. iai, h. liu, k. ichii, and y. sato, "simplified method to determine parameter of flip," pari, technical note 0869, 1997. [11] i. suetomi and n. yoshida, "nonlinear behavior of surface deposit during the 1995 hyogoken-nambu earthquake," soils and foundations, vol. 38, pp. 11–22, sep. 1998, https://doi.org/10.3208/sandf.38. special_11. [12] b. o. hardin and v. p. drnevich, "shear modulus and damping in soils: design equations and curves," journal of the soil mechanics and foundations division, vol. 98, no. 7, pp. 667–692, jul. 1972, https://doi.org/10.1061/jsfeaq.0001760. microsoft word etasr_v11_n1_pp6810-6818 engineering, technology & applied science research vol. 11, no. 1, 2021, 6810-6818 6810 www.etasr.com rahmane & abbaoui: the architectural genotype approach in contemporary housing (1995 to 2010) the architectural genotype approach in contemporary housing (1995 to 2010) the case study of setif, algeria ali rahmane habitat and environment laboratory ferhat abbas university setif, algeria rahmaneali@univ-setif.dz messaoud abbaoui habitat and environment laboratory ferhat abbas university setif, algeria messaoud.abbaoui@univ-setif.dz abstract-the current paper aims to analyze the architectural genotype principle that considers the arrangement of spaces as an abstract relational model. the goal is to demonstrate that syntactic measurements show that spatial structures allow messages to be decoded in each dwelling's inner spaces' architecture. the research uses the justified graphic technique for spatial syntax. twelve detached houses have been randomly selected out of a total of sixty-two contemporary buildings that were built in a subdivision of setif between 1990 and 2010. the analysis findings showed that the spatial characteristics and properties that constitute the generic rule underlying the studied space can be detected. this research supports the notion that the implementation of the spatial syntax method can aid in the proposition of innovative solutions regarding the design of sustainable housing projects. keywords-space syntax; self-built individual houses; architectural genotype; spatial configuration i. introduction housing constitutes an imperative of our daily life [1, 2] and is a symbol of human life and society. social success and individual and family happiness depend heavily on the quality of dwelling. the right to housing [3] is considered inalienable. housing can be regarded as a product from a single housing unit to a neighborhood or town housing stock [4]. housing can be approached as a process. this interpretation of housing allows researchers and practitioners to consider the multiple interrelations between housing conditions and human processes in particular localities [5]. in algeria, the adaptation of an analytical and critical approach to contemporary housing is reflected in large urbanization operations qualified as real new cities in terms of urban sprawl. however, the vast housing programs operated within the socio-economic challenges and changes have been increasingly funded by public authorities to absorb the high housing demand. the state has adopted this policy in the light of the new legislative and institutional means implemented in this dynamic sector. after a transitional period, the economic downturn has triggered profound changes from a communist regime to a democratic state with a market economy after integrating new political orientations. profound changes have taken place as a result of both accelerated urbanization and socio-economic shifts. the built environment is evolving and becoming the breeding ground for new social adjustment and urban integration. the residential mobility arising from these improvements contributes to the construction of new residential models [6-9]. however, the detachment of the state, which eliminates the land monopoly and allows private initiative, has enabled local authorities to develop a land portfolio. these land reserves have been compensated almost exclusively for residential properties [6]. consequently, a modern architectural expression and space creation has emerged as a reflection of the inhabitants' social, cultural, and ideological status [6]. in this study 12 new dwellings were chosen randomly for study from 62 houses in the hebbache brothers subdivision. the houses were built over a chronological period from 1990 to 2010 (from the beginning of construction until its final realization). to understand every new house's spatial layout, the space syntax via the agraph software using the justified graph technique has been utilized. by referring to syntactic measures such as total depth, mean depth, relative asymmetry, integration value, and control value it can be concluded that spatial genetic constants could maintain, at the level of its spatiality, any coherence which could be identified as an architectural genotype. the findings of this research study could be used as a design output for further housing construction in algeria. ii. literature review the purpose of the current paper is to identify the genotypes which form the basis for genesis. the meaning of the genotype in the fields of genetics and architectural studies, is presented below. the genotype is the information carried by the genome of an organism found in each cell in the form of deoxyribonucleic acid (dna). dna contains all the genetic information, called the genome, which allows organisms to grow, function, and reproduce. in other words, the set of genes (the chromosomes are made up of dna containing the genes) of an individual shapes its genome. the gene is an inherited dna fragment which forms an inherited genetic information unit [10]. the genotype has been identified as the complete genetic code for corresponding author: ali rahmane engineering, technology & applied science research vol. 11, no. 1, 2021, 6810-6818 6811 www.etasr.com rahmane & abbaoui: the architectural genotype approach in contemporary housing (1995 to 2010) the organism [11]. the idea is that the gene can be activated or not. the degree of gene activation may have functional significance at the behavioral level. latest observations have demonstrated that certain genes remain passive while waiting for stimuli to be activated. experimental and environmental factors have been found to be among the stimuli. the authors state that the phenotype is considered as the physical expression of the genes that have been activated and their degree of activation. in a technical sense, the phenotype is the totality of an individual's traits and characteristics [11]. the phenotype is not limited to physical traits. it also includes physiological traits, such as intelligence, emotional profile, and the predisposition to react in a certain way to a given situation. for other researchers the phenotype is considered at the level of a single character, at the cellular or molecular level [12]. it should be noted that genotype and phenotype are two different concepts. the genotype is a genetic code that encompasses the cell, nucleus, chromosomes, genes, and dna. the phenotype is the set of traits and characteristics of an organism. when translated into architecture, the genotype becomes the concept of architectural genotype. researchers define the genotype as abstract rules underlying spatial shapes in the field of spatial syntax [13]. field experts point out that the house study suggests evidence of at least one spatial-functional genotype defined in terms of relational and configurationally consistency. the dominant genotype is sometimes strongly detected when all the spatial-functional themes are present. in other cases, these genotypes are less likely to be detected when some themes are present, and others are missing. also, these themes seem to be completely absent or even reversed in some cases [14]. researchers also argue that as soon as common patterns are identified in integrating different functions or names of dwellings, cultural genotypes that acquire a spatial dimension are treated objectively [14]. sustainable architecture has been employed in order to deliver practical realizations and aesthetical buildings [15]. new publications have been issued explaining the basics of spatial syntax theory, how it works, and how it can be implemented in contemporary housing [16]. to measure the strength of a spatial genotype, authors used the difference factor. referring to a sample of traditional turkish houses from the 17th to the 19th century, the difference factor was deployed to identify households' functions, which are differentiated by their integration or relative separation. it is worth mentioning that these houses have been strongly structured and articulated with other houses. two signature patterns of integration arc have been noticed. in the same vein, a study conducted in syria has offered a review on the influence of the islamic culture on the architecture of the houses and the social practices. the paper analyzed how the architectural pattern of the islamic community has contributed in the increased privacy, mutual respect, and social segregation [17]. the author in [18] uses basic syntactic data according to the phases of the representation of justified graphs and calculations. this classification brings out seven genotypes. in [19-21], the authors compare domestic spaces through a sample of houses on three berber regions of algeria. the authors in [21] also focused on the different factors and highlighted certain similarities between the cases with some fundamental differences. taken as a whole, the use of the difference factor suggests a characteristic mode for structuring the domestic interior of traditional berber houses. the genotypes highlight centralized nuclei such as ammas n'taddart (the space on the ground floor in the m'zab), the main room in kabylia, or the main room on the first floor of the aures. berber houses tend to be integrated into the spatial configuration with a shallow core in the aures and kabylia regions and with a deep core and relatively segregated in the m'zab region. in another work on the m'zab region [19], the presence of a strong spatial genotype was shown. the visual map conducted on this same dataset reveals that these spaces are coherently located where multidirectional views can be managed. in contrast, other spaces such as the tisifri (women's living room) are much more closed and have deliberately limited visibility and permeability. ammas n'taddart, ikoumar, and tigharghart control access and offer a wide scope of vision by highlighting the different facets of the architecture towards dead-end spaces. authors in [20] confirmed through justified graphics that the genotypes of the m'zab house, ammas n'taddart, and the male guests' space on the ground floor (the houdjrat or douira) are relatively shallow. however, the men's room (the aali) on the first floor and the basement are deep. the justified graphics demonstrate the importance of the entrance in regulating the interior layout of the m'zab house and its depth. furthermore, the justified graphics also demonstrate that the outdoor area is always separated from the domestic life. this demonstration reinforces the social code in such a society. regarding the spatial interface between guest and inhabitant, the study provides an understanding of the domestic environment at m'zab in terms of guest/inhabitant interface. in real conditions, the interface is between male guests and the families who live in the houses. similar studies have categorized the different genotype types in the conclusion of their work. the topological genotype types a are the bedrooms, the kitchen, the guest bedroom, the toilets, and the stable. the topological types b are the courtyard, the penthouse, the patio, the roof, and the corridor. the topological types c are the courtyard, the guest room, the middling room, and the sideling room. finally, the topological types d are very rare [22]. authors in [23] demonstrated that the genotype of traditional oasis dwellings from el kantara to biskra (algeria) displays a tree structure signifying a less elaborate configuration than an annular complex. however, it should be noted that the above mentioned studies confirm the assumption that spatial syntax theory encourages the search for genotypes. iii. relevance and research questions the scientific motivation behind this research resides in the use of space syntax and the agraph software. the measurements of total depth, mean depth, relative asymmetry, integration value, and control value were used to identify spatial genetic constants that are architectural genotypes. it is worth mentioning that there is an absence of architectural studies using the space syntax method, particularly in setif. hence, the current paper proposes the space syntax method as an innovative solution for sustainable housing projects in setif. space syntax theory offers useful tools to understand configuration logic through its engagement with social engineering, technology & applied science research vol. 11, no. 1, 2021, 6810-6818 6812 www.etasr.com rahmane & abbaoui: the architectural genotype approach in contemporary housing (1995 to 2010) structure. it also helps social influences consider the properties of the spaces concerning the forms of correlation. consequently, a clearer comprehension of spatial logic is highlighted as well as each space's functions and activities are routinely known. this connection, interpreted in a coherent sequence, contributes to a social logic interpretation [14]. the advantage of space syntax is that by dissecting spaces, it allows great precision in analysis. syntactic analysis using the justified graph helps one examine the plans of these 12 new dwellings to create spatial arrangements and discover patterns of space described as architectural genotypes. the project aims to define structures of socio-cultural expression and social logic manifested in the spatial distribution of domestic space. thus, it is believed that the new housing could retain consistency in terms of its spatial structure that could be defined as an architectural genotype. the focal point resides in the intrinsic and complex relationship between the built environment and the human factor. while it is evident that society's comprehension cannot be restricted to this relevant equation alone, the fact remains that such contemplation, focused on the theory of space syntax and its methods for calculating mathematical order, remains central to the discovery of architectural genotypes. spatial syntax theory is used not just for the study of housing, but also for studying urban spaces [23-25], neighborhoods [26], and the city [27]. space syntax offers resources to interpret architectural reality differently. famous architects and urban planners have used the theory of space syntax, particularly the dynamic computer modeling techniques of space syntax, to design the internal and external environments of their projects in order to plan scheduled and unscheduled activities. through using the space syntax system, they were able to model a range of types of activities and also to build simulation models before and after the work was completed, much like the movement models with an accuracy of about 85% [9, 28-30]. in setif, architects and space designers are still trapped in their old form-function assumptions and their projects tend to be monotonous as can be seen throughout the city. the findings of this research would enable project managers and space planners to realize that there is another way to understand space architecture and to enrich their ventures. they would also encourage students to review their architectural analyses, which are often imprecise and vague, to focus on basic spatial relationships. iv. presentation of the analysis method this analysis's theoretical methodology is focused on using the space syntax approach, which derives its methodological foundation from converting architectural plans into a conveniently comparable data collection. thus, it is described as selecting suitable mathematical tools apprehended via graphs that reflect a constructed spatial area. the abstraction of plans in graphs contributes to understanding the spatial configuration and space-generating mechanism, considered important in social organization and intrinsic components. space syntax forecasts socio-spatial structure or architectural genotype information by developing its computational methods. the special relation between function and social meaning in a building is created by the space [13]. the research method applies to both quantitative and qualitative approaches reflected in a set of metrics. fig. 1. agraph software interface. engineering, technology & applied science research vol. 11, no. 1, 2021, 6810-6818 6813 www.etasr.com rahmane & abbaoui: the architectural genotype approach in contemporary housing (1995 to 2010) v. geographical location of the case study the studied area is located in the state of setif. it is a town in the highlands region of eastern algeria. it is 300km away from the capital of algiers and rises to an altitude of 1100m. it is one of the major cities of the country, covering an area of 127.30km² with a population density of 2259 inhabitants/km². the 56.46% of the population is located in the state's chief town, with 88% urbanization rate. the sample is a private residential city that is located 1500m from the city center. a. the subdivision of hebbache brothers the hebbache brothers subdivision, the object of our study, is a residential area in the city of setif. it began to grow after a state land session in favor of a subdivision as stipulated in circular no. 5 of 11 august 1987 on the creation of individual housing sectors. the subdivision, with a trapezoidal geometric shape, occupies a total area of 37800m2. a corpus of 12 self-built, arbitrarily chosen houses in the subdivision was the study's subject. b. the specifity of the hebbache brothers subdivision the specificity of the hebbache brothers subdivision resides in its proximity to the city center. it is also closely juxtaposed with tandja, one of the city's largest famous communities with population over 50,000 inhabitants (figure 2). this position creates a direct dialogue between two models of individual architectural expressions with regard to the dimension of constructions, shape and diverse spatial configuration. its specificity is also proved by the importance of the subdivisions in the city of setif (table i, authors' research), which ranks first nationally regarding the number and the scale of subdivisions in the urban tissue. fig. 2. housing typology in setif city (original image © the national institute of cartography and remote sensing. processed by the authors). table i. subdivisions in setif city number of subdivisions during 1986-2019 number of parcels total surface (m 2 ) built environment (%) 415 12965 2,493,000.00 63.15 % vi. indicators twelve houses from the 62 investigated cases were chosen and evaluated with the space syntax process. a justified graph simplifies the architectural strategy. any space, whether it is a place, a hall, or even a yard, is a field cell at this graph level. each field cell is defined by circles located according to each field's depth. the cell's depth-dependent value is determined based on the number of cells that can be crossed from an original (outside) point to reach it. to justify, each cell has the same depth and must be on the same imaginary horizontal axis. a graph composed of circles parallel to the depth of the imagined horizontal lines is deduced. the circles are, therefore intertwined in terms of their permeable interactions. the diagram's lines express the building's outbound connections. in other words, whether two fields are linked by door or entry, the circles they refer to are linked by a line in the justified graph that helps interpret the following indicators: • control value (cv): the cv is calculated for each node giving a total of one for all the nodes. the cv of node n is the total value received by the node n during this operation. • the total depth of a node (tdn): it is the total of the shortest distances from a node n to other nodes in the system. • the mean depth of a node (mdn): the average depth of a node n is the average depth (or the average of the shortest distance) from a node n to the other nodes. • relative asymmetry (ra): ra describes the integration of a node by a value between (or equal to) 0 and 1, where a low value describes a high integration. • the integration value (i): the i is a parameter which (unlike ra) describes integration by a high number when a node is highly integrated. the i is the inverse of ra. the indicators and their mathematical formulas are summarized in table ii. the studied houses' information is given in table iii and the codification of house spaces is tabulated in table iv. table ii. codification of indicators symbol mathematical formula tdn tdn= (0*n �) + (1*n �)+ (2* n �) +… (x*n �� mdn mdn= tdn/(k-1) (k=number of nodes in a set) ra ra= 2(mdn-1)/(k-2) i i=1/ra cv potential spatial control. (cv<1: low potential, cv>1: high potentail) table iii. studied houses' information house no. construction date area (m²) storys 1 1990 168.95 03 2 1992 203.82 03 3 1994 223.11 02 4 1997 300.00 02 5 1999 297.86 04 6 2000 190.00 03 7 2002 140.00 02 8 2004 135.00 03 9 2006 187.50 04 10 2007 96.65 03 11 2009 180.00 04 12 2010 280.00 03 the owner names are not published for privacy reasons, but are known to the authors engineering, technology & applied science research vol. 11, no. 1, 2021, 6810-6818 6814 www.etasr.com rahmane & abbaoui: the architectural genotype approach in contemporary housing (1995 to 2010) table iv. codification of constituent house spaces code space ext exterior h hall sej living room ch bedrom cu kitchen co courtyard san bathroom + shower vii. syntactic analysis a. the justified graphs in figures 3-8 we can see the justified graphs of the houses 1-12. the results are summarized in tables v and vi. viii. findings and discussion the syntactic data from justified graphs reveal that the shallowest space in 100% of the studied houses is the hall, which is readily accessible from outside. furthermore, the hall holds the lowest ra value and the highest cv, showing that the hall is the most integrated space in all houses and has the highest connection to other related spaces. the most profound spaces of the justified diagrams are usually the courtyard with the maximum ra value and the lowest cv, showing that the courtyard is the most isolated area with the lowest connectivity. the functional spaces among floors are entry, cooking, eating, working, sleeping, and ventilation. the main feature in all the studied houses is that the designs are formed around the hall's transitional area. this space is a multi-functional space used as either a tv room or a study or even as a daily sitting room. space syntax theory allows one to discover the underlying spatial arrangements and to demonstrate in-depth the sociospatial systems and the widespread genotype of architecture. the recurrence of such structural features is considered as the genotyping index. thus, the translation of this term into architecture implies a qualitative constancy by constancy of justified plans and another qualitative interpretation of digital data relating to the mean depth of the degree of power, the relative asymmetry, and the importance of integration. fig. 3. the justified graphs for houses 1 and 2. fig. 4. the justified graphs for houses 3 and 4. engineering, technology & applied science research vol. 11, no. 1, 2021, 6810-6818 6815 www.etasr.com rahmane & abbaoui: the architectural genotype approach in contemporary housing (1995 to 2010) fig. 5. the justified graphs for houses 5 and 6. fig. 6. the justified graphs for houses 7 and 8. fig. 7. the justified graphs for houses 9 and 10. fig. 8. the justified graphs for houses 11 and 12. engineering, technology & applied science research vol. 11, no. 1, 2021, 6810-6818 6816 www.etasr.com rahmane & abbaoui: the architectural genotype approach in contemporary housing (1995 to 2010) table v. syntactic measures for the houses h o u s e 1 exterior h sej ch1 ch2 ch3 san cu co min mean max mdn 2.00 1.12 2.00 2.00 2.00 2.00 2.00 1.75 2.62 1.12 1.94 2.62 ra 0.28 0.03 0.28 0.28 0.28 0.28 0.28 0.21 0.46 0.03 0.26 0.46 cv 0.14 6.50 0.14 0.14 0.14 0.14 0.14 1.14 0.50 0.14 1.00 6.50 h o u s e 2 ext h sej ch1 ch2 ch3 san cu co min mean max mdn 3.00 2.12 1.75 2.25 2.25 2.25 2.25 1.75 1.37 1.37 2.11 3.00 ra 0.57 0.32 0.21 0.35 0.35 0.35 0.35 0.21 0.10 0.10 0.31 0.57 cv 0.33 2.00 0.50 0.16 0.16 0.16 0.16 0.50 5.00 0.16 1.00 5.00 h o u s e 3 ext h sej ch1 ch2 ch3 san cu co min mean max mdn 2.00 1.11 2.00 2.00 2.00 2.00 2.00 1.77 2.66 1.11 1.95 2.66 ra 0.25 0.02 0.25 0.25 0.25 0.25 0.25 0.19 0.41 0.02 0.23 0.41 cv 0.12 7.50 0.12 0.12 0.12 0.12 0.12 1.12 0.50 0.12 1.00 7.50 h o u s e 4 ext h sej ch1 ch2 ch3 san cu co min mean max mdn 2.00 1.11 1.77 2.00 2.00 2.00 2.00 1.77 2.44 1.11 1.91 2.44 ra 0.25 0.02 0.19 0.25 0.25 0.25 0.25 0.19 0.36 0.02 0.22 0.36 cv 0.12 7.00 0.62 0.12 0.12 0.12 0.12 0.62 1.00 0.12 1.00 7.00 h o u s e 5 ext h sej ch1 ch2 ch3 san cu co min mean max mdn 2.00 1.11 1.77 2.00 2.00 2.00 2.00 1.77 2.44 1.11 1.91 2.44 ra 0.25 0.02 0.19 0.25 0.25 0.25 0.25 0.19 0.36 0.02 0.22 0.36 cv 0.12 7.00 0.62 0.12 0.12 0.12 0.12 0.62 1.00 0.12 1.00 7.00 h o u s e 6 ext h sej ch1 ch2 / san cu co min mean max mdn 1.85 1.14 1.85 2.00 2.00 / 2.00 1.71 2.57 1.14 1.89 2.57 ra 0.28 0.04 0.28 0.33 0.33 / 0.33 0.23 0.52 0.04 0.29 0.52 cv 0.66 4.50 0.66 0.16 0.16 / 0.16 1.16 0.50 0.16 1.00 4.50 h o u s e 7 ext h sej ch1 ch2 / san cu co min mean max mdn 2.00 1.14 2.00 2.00 2.00 / 2.00 1.71 2.57 1.14 1.92 2.57 ra 0.33 0.04 0.33 0.33 0.33 / 0.33 0.23 0.52 0.04 0.30 0.52 cv 0.16 5.50 0.16 0.16 0.16 / 0.16 1.16 0.50 0.16 1.00 5.50 h o u s e 8 ext h sej ch1 ch2 ch3 san cu co min mean max mdn 1.87 1.12 1.87 1.75 2.00 2.00 2.00 1.75 2.37 1.12 1.86 2.37 ra 0.25 0.03 0.25 0.21 0.28 0.28 0.28 0.21 0.39 0.03 0.24 0.39 cv 0.64 5.00 0.64 0.64 0.14 0.14 0.14 0.64 1.00 0.14 1.00 5.00 h o u s e 9 ext h1 h2 sej ch1 ch2 ch3 san cu co min mean max mdn 2.60 1.70 1.30 1.90 2.60 2.00 2.20 2.20 2.00 2.70 1.30 2.12 2.70 ra 0.35 0.15 0.06 0.20 0.35 0.22 0.26 0.26 0.22 0.37 0.06 0.25 0.37 cv 0.25 2.64 4.75 0.39 0.25 0.64 0.14 0.14 0.64 1.00 0.14 1.00 4.75 h o u s e 1 0 ext h sej ch1 ch2 ch3 san cu co min mean max mdn 2.00 1.12 2.00 2.00 2.00 2.00 2.00 1.75 2.62 1.12 1.94 2.62 ra 0.28 0.03 0.28 0.28 0.28 0.28 0.28 0.21 0.46 0.03 0.26 0.46 cv 0.14 6.50 0.14 0.14 0.14 0.14 0.14 1.14 0.50 0.14 1.00 6.50 h o u s e 1 1 exte h1 h2 sej ch1 ch2 ch3 san cu / min mean max mdn 2.50 1.62 1.25 2.50 2.12 2.12 2.12 2.12 2.12 / 1.25 2.05 2.50 ra 0.42 0.17 0.07 0.42 0.32 0.32 0.32 0.32 0.32 / 0.07 0.30 0.42 cv 0.33 2.16 5.33 0.33 0.16 0.16 0.16 0.16 0.16 / 0.16 1.00 5.33 h o u s e 1 2 ext h1 h2 sej ch1 ch2 ch3 san cu / min mean max mdn 2.55 1.66 1.11 1.77 2.00 2.00 2.00 2.00 2.00 / 1.11 1.91 2.55 ra 0.38 0.16 0.02 0.19 0.25 0.25 0.25 0.25 0.25 / 0.02 0.22 0.38 cv 0.33 1.62 6.83 0.45 0.12 0.12 0.12 0.12 0.12 / 0.12 1.00 6.83 ix. limitations and further research using the agraph program, the study focused on space syntax theory via the justified graph technique. it referred to indicator measurements (td, mdn, ra, i, and cv) to find the spatial genetic constants that form architectural genotypes. this study did not tackle the concept of phenotype due to time constraints and limited research objectives. therefore, future researchers are advised to associate genotype and phenotype in their inquiries. also, the physical features of the dwelling (shape, length, envelope) and the inhabitant (its gestures, expressions, postures, and social practices) were not addressed or spatially defined. this limitation could be another inherent space syntax barrier that other research can undoubtedly overcome. x. conclusion studies have noted that a residential corpus embodies a diffuse genotype [31]. ordinary households are more diverse and idiosyncratic than the ideal form recognizes, since they are a dynamic reflection of the occupants' social and individual status. their social structure and conventions are inextricably connected to the idiosyncratic, whimsical, arbitrary, or sometimes disorderly conditions of the inhabitants' daily lives. consequently, they present difficulties in recognizing and interpreting hidden orders. in syntactic details, this novel approach to investigating configuration relationships could be elaborated. applying to each house a graphic and numerical treatment can allow the comprehension of its vocabulary, engineering, technology & applied science research vol. 11, no. 1, 2021, 6810-6818 6817 www.etasr.com rahmane & abbaoui: the architectural genotype approach in contemporary housing (1995 to 2010) decode the syntax of this environment and further push the analysis of how this space is structured. table vi. calculated values, integration order house no. calculated values, integration order of spaces for the house conclusion 1 h 0.03<cu -0.21<sej -0.28=ch1 0.28= ch2 -0.28= ch3 -0.28= san 0.28= ext -0.28 <co -0.46 the most integrated space is the hall with with ra 0.03 and a strong cv of 6.50. 2 co 0.10 <cu -0.21= sej -0.21 < ch1 -0.35= ch2 -0.35= ch3 -0.35= san -0.35 < ext -0.57 the most integrated space is the courtyard with ra 0.10 and a strong cv of 5.00. 3 h 0.02<cu -0.19<sej -0.25=ch1 0.25= ch2 -0.25= ch3 -0.25= san -0.25= ext -0.25 <co -0.41 the most integrated space is the hall with ra 0.02 and a strong cv of 7.50. 4 h 0.02<cu -0.19 = sej -0.19 < ch1 -0.25= ch2 -0.25= ch3 -0.25= san -0.25= ext -0.25 <co -0.41 the most integrated space is the hall with ra 0.02 and a strong cv of 7.00. 5 h 0.02<cu -0.19 = sej -0.19 < ch1 -0.25= ch2 -0.25= ch3 -0.25= san -0.25= ext -0.25 <co -0.36 the most integrated space is the hall with ra 0.02 and a strong cv of 7.00. 6 h 0.04<cu -0.23 <sej -0.28 = ext -0.28 <ch1 -0.33 = ch2 -0.33 = san -0.33 <co -0.52 the most integrated space is the hall with ra 0.04 and a strong cv of 4.50. 7 h 0.04<cu -0.23 <sej -0.33 = ext -0.33 =ch1 -0.33 = ch2 -0.33 = san -0.33 <co -0.52 the most integrated space is the hall with ra 0.04 and a strong cv of 5.50. 8 h 0.03<cu -0.21=ch1 -0.21<sej 0.25= ext -0.25 < ch2 -0.28= ch3 0.28= san -0.28<co -0.39 the most integrated space is the hall with ra 0.03 and a strong cv of 5.00. 9 h2 0.06 < h1 0.15 <sej -0.20 <cu -0.22=ch2 -0.22< ch3 -0.26= san -0.26< ch1 -0.35= ext -0.35 <co 0.37 the most integrated space is the hall 2 with ra 0.06 and a strong cv of 4.75. 10 h 0.03<cu -0.21<sej -0.28=ch1 0.28= ch2 -0.28= ch3 -0.28= san 0.28= ext -0.28 <co -0.46 the most integrated space is the hall with ra 0.03 and a strong cv of 6.50. 11 h2 0.07 < h10.17< cu 0.32=ch2 -0.32= ch3 -0.32 = san 0.32 = ch1 -0.32< sej -0.42= ext 0.42 the most integrated space is the hall 2 with ra 0.07 and a strong cv of 5.33. 12 h2 0.02< h1 -0.16< sej -0.19 < cu -0.25=ch2 -0.25= ch3 -0.25 = san -0.25 = ch1 -0.25< ext -0.38 the most integrated space is the hall 2 with ra 0.02 and a strong cv of 6.83. the findings revealed a clear spatial genotype that applies to the hall and suggests that this space seems to be regularly located where it can order and coordinate multifunctional activities. in reality, the findings of this research have shown that the spatial arrangement was planned for the conventional courtyard from a central distribution through the hall room. this is the product of the local lifestyle, social behaviors originating in traditional society. however, the findings from syntactic data enable one to examine every calculation of the justified graph as to its spatial context. justified diagrams indicate that the 12 houses have the same morphological characteristics. indeed, the house arrangement appears to be identical in all instances, with the same features. thus, it can be argued that the spatial sense of residential spaces can be reconstructed from these dimensions. beyond 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[31] a. hamouda, "syntaxe spatiale comme outil d’analyse de l’espace architectural," international journal of innovative technical and applied sciences, vol. 2, no. 1, pp. 22–30, 2018. microsoft word etasr_v13_n4_pp11112-11118 engineering, technology & applied science research vol. 13, no. 4, 2023, 11112-11118 11112 www.etasr.com nguyen et al.: a novel pso-based modified smc for designing robust load-frequency control … a novel pso-based modified smc for designing robust load-frequency control strategies ngoc-khoat nguyen faculty of control and automation, electric power university, vietnam khoatnn@epu.edu.vn (corresponding author) duy-trung nguyen faculty of control and automation, electric power university, vietnam trungnd@epu.edu.vn; thi-mai-phuong dao faculty of electrical engineering, hanoi university of industry, vietnam daophuong@haui.edu.vn received: 18 april 2023 | revised: 5 may 2023 | accepted: 17 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5972 abstract in an electric power grid, load-frequency control (lfc) plays a crucial role as it aims to maintain the system frequency at a nominal value, 50 or 60 hz, by minimizing the effects of load changes. however, a modern power system is currently characterized by a huge number of nonlinearities and uncertainties, making control methodologies much more challenging. among them, the nonlinear features of governor dead-band (gdb) and generation rate constraint (grc) strongly affect the accuracy and performance of lfc applied to a power network. this study focused on designing an applicable and efficient lfc by proposing a novel sliding-mode control (smc) scheme. the traditional smc can successfully solve several nonlinear control problems, and in case of having a reasonable adjustment, it is completely suitable to design the lfc strategy. the modified smc, integrated with an effective optimization technique, i.e., particle swarm optimization (pso), can dramatically improve the performance of lfc. this paper presents numerical simulation results implemented in matlab/simulink to demonstrate the feasibility and effectiveness of the proposed control strategy. keywords-lfc; msmc; pso; nonlinearities; robust control i. introduction electricity consumption in a power system changes continuously and randomly over time, causing imbalances between load and demand, and therefore affecting the network frequency, which is one of the most important parameters in an electric power grid, forcing it to oscillate and deviate from the nominal value. as a result, the power system cannot maintain stable and economical operation. the load-frequency control (lfc) control strategy aims to deal with this problem and bring the network back to stability and efficiency [1-10]. a practical power system is usually characterized by nonlinearities, such as governor dead-band (gdb) and generation rate constraint (grc), which strongly affect the stability of a power system and make the implementation of lfc highly challenging [3-5]. in this aspect, applying traditional regulators, such as pi or pid, or modern controllers, based on fuzzy logic or neural networks, to efficiently solve the lfc issue cannot obtain acceptable performance. therefore, it is essential to design a robust control method to tackle the nonlinearities of a practical power system for frequency regulation. sliding mode control (smc) is known as a robust and efficient control strategy, which is typically adopted to deal with not only nonlinearities but also with the uncertainties of a system [11-23]. therefore, it has also been successfully applied to solve the lfc of a power system considering nonlinearities [10]. the current paper proposes a novel robust smc-based lfc, which is modified from the fundamental smc strategy. this robust control strategy is capable of dealing with the nonlinearities of a power system, especially the gdb and grc characteristics. the proposed control scheme was simulated and numerically analyzed in matlab/simulink, was compared with the pid regulator and the fuzzy logic controller, and the results obtained verified its feasibility and superiority. engineering, technology & applied science research vol. 13, no. 4, 2023, 11112-11118 11113 www.etasr.com nguyen et al.: a novel pso-based modified smc for designing robust load-frequency control … ii. related works lfc has been studied and applied in practical power systems for decades and a huge number of controllers have been proposed. in [2], several traditional lfc regulators, such as integral (i), proportional-integral (pi), and proportionalintegral-derivative (pid) were proposed. in [10], an effective integration of a pi-type fuzzy logic controller with suitable optimization techniques was introduced to address the lfc problem of an interconnected power system. in [4], several intelligent lfc controllers were presented, which exhibited feasible control performance. among them, the smc-based schemes applied for lfc have attracted the interest of researchers due to their ability to solve the control issues of uncertain and nonlinear power grids [12-14]. in [11], a control strategy was proposed using bess based on an adaptive fuzzy super-twisting smc method for a power system using wind energy. in [17], a new discrete-time smc was proposed, using a state estimation method based on the fast sampling of measured output variables for the lfc in control areas of a power system consisting of thermal and hydropower plants. a new high-order adaptive smc with a minimizing chattering mechanism was presented in [23]. in these studies, the smc schemes had fixed internal parameters and might not be optimized. this characteristic may lead to a shortcoming that can be improved by an optimization technique. this study aimed to solve this issue by designing a modified smc (msmc) strategy based on particle swarm optimization (pso), which is one of the most well-known evolutionary optimization algorithms. iii. traditional sliding mode control an overview as mentioned above, smc is a robust control strategy that addresses the nonlinearities and uncertainties of a system. to make a quick review of the smc scheme, let's consider a simple case of a single input single output (siso) nonlinear control system below [16, 19]: ��� = �� + �� = (�) + �(�). �� = �� + �� = ℎ(�) (1) where � = [��, ��, … , ��]� ∈ ℜ�is a state vector of the control system, � ∈ ℜ is the input control signal, � ∈ ℜ is the output signal, a, b, c, and d are state matrices for input and output vectors, (�) ∈ ℜ� and �(�) ∈ ℜ� are two functions describing the dynamics of the system, and ℎ(�) ∈ ℜ is a function representing a relationship between the state vector x and the output y. it is required that the real output signal y(t) should track the desired output yd(t), meaning that the error e between them must satisfy ����→∞�( ) = ����→∞|�( ) − �#( )| = 0 (2) assuming that it is possible to differentiate the system (1) a number of n times, one can be obtained as: �(�) = %(�) + &(�). � (3) where: %(�) = '(�ℎ(�) &(�) = ')'(�*�ℎ(�) ≠ 0 '(ℎ(�) = ,ℎ(-), (�) = .,ℎ(-),-/ , . . . , ,ℎ(-) ,-0 1 [ �(�), . . . , �(�)]� '(2ℎ(�) = ,34 56/ ℎ(-) , (�) ')'(2ℎ(�) = ,34 5 ℎ(-) ,�(�) the error between the desired and real output signals can be calculated as: �( ) = �( ) − �#( ) (4) this error and its differentials are used to determine the following function: 7 = �(�*�) + 8��(�*�)+. . . +8�*��� + 8�*�� (5) where n coefficients ξi (i = 1, 2, …n) are positive real numbers and they must be chosen to satisfy the hurwitz polynomial: 9(:) = :�*� + 8�:�*�+. . . +8�*�: + 8�*� (6) it is clear that all roots of the equation δ(s)=0 decide the transient response of the process given in (2) with the following constraint: 7 = �(�*�) + 8��(�*�)+. . . +8�*��� + 8�*�� = 0 (7) equation (7) defines a sliding surface with the characteristic polynomial ∆(s) indicated in (6). the purpose of the control methodology is to force y(t) to track the reference signal yd(t) with an acceptable tolerance. this requirement is converted into a simple control problem: determination of a control signal u(t) to meet 7 → 0. to prove the above statement, let's select a lyapunov function as follows: ; = �� 7� (8) the first-order differential of (8) is: ;� = 77� (9) the control signal u(t) needs to be chosen to satisfy the following constraint: ;� = 77� < 0 (10) from (5), it is straightforward to deduce the following: 7� = �(�) + 8��(�*�)+. . . +8�*��= + 8�*��� = �(�)( ) −�#(�)( ) + ∑ 8�*2�(2)�*�2?� (11) which in combination with (3) can give: 7� = −�#(�)( ) + %(�) + &(�). � + ∑ 8�*2�(2)�*�2?� (12) the control signal vector u(t) is selected to satisfy: 7� = −@:��a(7) (13) where k is a positive real number. eventually, the control signal u(t) is: engineering, technology & applied science research vol. 13, no. 4, 2023, 11112-11118 11114 www.etasr.com nguyen et al.: a novel pso-based modified smc for designing robust load-frequency control … �( ) = �b(-) c�#(�)( ) − %(�) − ∑ 8�*2�(2) −�*�2?�@:��a(7)d (14) with the above control law, the first-order differential of the lyapulov function can be computed as: ;� = 77� = −@7:��a(7) = −@|7| < 0(∀7 ≠ 0) (15) the statement mentioned in (15) clarifies the asymptotical stability of the given control system according to lyapulov's theory. the following section presents a modified smc strategy applied to the lfc proposition. iv. modified smc strategy applied to the lfc problem a modified control scheme needs to be proposed to apply smc as a more effective strategy. a. the modified smc strategy several smc methods deal with the nonlinear control problem. the smc method presented in the previous section is one of the fundamental versions and has been widely applied to simple siso systems. a modified version of smc was considered to create a more efficient lfc scheme for practical power systems with nonlinearities and uncertainties (i.e., gdb and grc). recall the state-space model of a nonlinear system in the following form: f�(�) = %(�, ��, �= , . . . , �(�*�), ) + &(�, ). �( )�(�)( ) = �(�)( ) (16) in this aspect, the sliding surface can be defined as follows: 7(�, ) = g ##� + hi (�*�) . �( ) (17) where e(t) is the error for the time between the real and the desired output, as mentioned in (4). when compared with the traditional sliding surface indicated in (5), it is clear that all coefficients ξi have been replaced with only one factor λ (17). it is highly significant to seek the optimal factors because the number of variables to be optimized has been dramatically reduced. therefore, this is the first proposed modification of the smc strategy. as mentioned above, the crucial idea of smc is to design the switching control law in a suitable way to assure the stability of the nonlinear system. the system state needs to be landed on the sliding surface and reach zero even in case of occurring disturbances. to design an appropriate switching law, the sliding surface mentioned in (17) needs to be carefully taken into consideration. differentiating this function gives: 7(�, ) = g ##� + hi � �( ) = ∑ #065(#�)065 h2�( )�2?j (18) similar to (11), combining (17) and (15), can give: 7�(�, ) = ��( ) − �#(�)( ) + h�[�( ) − �#( )] + ∑ #065(#�)065�*�2?� h2�( ) = −�#(�)( ) + c%k�, ��, �= , … , �(�*�), l + &(�, )�( )d + h�[�( ) − �#( )] + ∑ #065(#�)065�*�2?� h2�( ) (19) where ∑ #065(#�)065 h2�( ) = m̱(2)�*�2?� describes the lower-order nonlinear systems. these systems have lower order than n, and they can be omitted in a particular perspective on taking care of the n-order nonlinear system. it is assumed that the nonlinear part %(�, ��, �= , . . . , �(�*�), ) can be estimated as %̄(�, ��, �=, . . . , �(�*�), ). when the derivative of the sliding surface reaches zero, an estimate control law can be calculated: �p( ) = �b(-,�) [−%pk�, ��, �= , … , �(�*�), l + �#(�)( ) +h�k�( ) − �#( )l + m(2)] (20) the switching control law here can be chosen as: �( ) = �̄( ) − qb :��a(7) (21) where �̄( ) is computed from (20). to testify to the stability of the control law given in (20), a lyapunov function candidate similar to (8) can be selected as follows: ;(7) = �� 7� (22) from (19) and (21), omitting the lower-order systems, the following can be achieved: 7� = c%(�, ��, . . . , �(�*�), ) − %̄(�, ��, . . . , �(�*�), )d − @:��a(7) (23) assuming that the tolerance of the estimate is small enough, it is straightforward to deduce the following equation: 7� ≈ −@. :��a(7) (24) in this perspective, the derivative of the lyapunov function candidate is expressed as ;� (7) = 7. 7� = −@. 7. :��a(7) = −@. |7| ≤ 0∀7 (25) it is obvious from (25) that the modified control law presented in (21) can be asymptotically stable according to lyapulov's theory. hence, it can be applied to solve the lfc problem of an electric power interconnection with nonlinearities and uncertainties. b. the robust smc-based lfc scheme a power system with nonlinearities, such as gdb and grc, may be of a control plant which is difficult to apply the lfc strategies. in this context, the modified smc method, as mentioned previously, is capable of being a robust and efficient control solution. to clarify the superiority of the proposed lfc strategy based on the modified smc, let's consider a singlearea power system using a non-reheat turbine as shown in figure 1. the gdb and grc are also considered for this electric power grid. four steps need to be executed to design a robust smc-based lfc strategy. 1) step 1: build an ordinary differential equation (ode) model for the given control plant as shown in figure 1, the ode model can be built as follows. first, let the deviation of system frequency ∆f be set as engineering, technology & applied science research vol. 13, no. 4, 2023, 11112-11118 11115 www.etasr.com nguyen et al.: a novel pso-based modified smc for designing robust load-frequency control … a state variable x. from figure 1, considering the load-machine model, it is straightforward to yield the following: �(:) = 9 (:) = (9t�(:) − 9t3(:)) qu�vw�u (26) 9t�(:) = 9t3(:) + �uqu �(:): + � qu �(:) (27) thereafter, considering the non-reheat turbine model: 9t�(:) = (9xy(:) − 9t�(:)) ��z . � w (28) and combined with (27), it is easy to get: 9xy(:) = 9t3(:) + �uqu �(:): + � qu �(:) + 9t3(:)[�: +�z�u qu �(:):� + �z qu �(:): (29) from (29), the corresponding ode model can be obtained as follows: ∆xy( ) = ∆t3( ) + �uqu ��( ) + � qu �( ) + [�∆t3� ( ) +�z�u qu �=( ) + �z qu ��( ) (30) from a governor model, a relationship between control signal u and valve/gate position change ∆xg can be described as: .�(:) − �] �(:)1 ��vw�^ = 9xy(:) (31) the corresponding ode model is: 9x�y( ) = ��^ .�( ) − � ] �( ) − 9xy( )1 (32) differentiating (30), and then substituting it for (32), the final ode model is yielded below: �⃛( ) = − ` ��^ + � �z + � �ua �=( ) − ` � �^�z + � �z�u + � �u�^a ��( ) − ` qu ]�^�z�u + � �^�z�ua �( ) − qu �u ∆t3= ( ) −qu �^�u ∆t3� ( ) − qu �^�z�u ∆t3( ) + qu �^�z�u �( ) (33) 2) step 2: designing the sliding surface the ode model in (33) has an order of three, thus a twoorder sliding surface should be selected below: 7(�, ) = g ##� + hi � = �=( ) + 2h��( ) + h��( ) (34) it is noted that the desired frequency deviation should be equal to zero, hence, one can be obtained below: �( ) = �( ) − �#( )|-c(�)?j = �( ) (35) from (34) and (35), the derivative of the sliding surface is: 7�(�, ) = �⃛( ) + 2h�=( ) + h���( ) (36) 3) step 3: designing the equivalent control law from (36), letting the derivative of the sliding surface be equal to zero gives: �⃛( ) = −2h�=( ) − h���( ) (37) combining the above equation with (33), it is clear to establish an estimate of the control signal as follows: �p( ) = �qu k[y[� + [�[d + [d[y − 2h[y[�[dl�=( ) + � qu k[d + [y + [� − h�[y[�[dl��( ) + `�] + � qu a �( ) + [y[�∆t3= ( ) + [�∆t3� ( ) + ∆t3( ) (38) 4) step 4: designing the sliding control law as mentioned in (20), the sliding control law can be: �( ) = �p( ) − @:��a(7) = �eu k[y[� + [�[d + [d[y − 2h[y[�[dl�=( ) + �qu k[d + [y + [� − h �[y[�[dl��( ) + `�] + � qu a �( ) + [y[�∆t3= ( ) + [�∆t3� ( ) + ∆t3( ) − @:��a(7) (39) v. the electric power system under study figure 2 shows the simulated model built, in matlab/simulink, to investigate the applicability of the proposed smc-based lfc strategy in dealing with the nonlinearities of a power system (i.e. gdb and grc). this model includes a power system with the nonlinearities of gdb and grc. the simulation parameters are presented in [2]. in addition, an smc controller was built to create the control signal to the governor, to automatically modulate the opening angle of the heat steam valve of the turbine through the governor response. this control manner can hereby maintain the system frequency at the nominal value within an acceptable tolerance. to clarify the superiority of the proposed smc controller over the conventional lfc regulators, a pid [2] and a fuzzy logic [24] counterpart were also considered. when performing numerical simulations, the nonlinearities including gdb and grc are chosen as in [2]. it should be noted that the pso algorithm was adopted to determine three parameters, as it is one of the most effective optimization techniques [25]. the optimization mechanism begins with a random solution which is defined as initialization. the aim is to find the optimal solution by iterations similar to generations in the genetic algorithm. each solution must be evaluated by an objective or a fitness function. the candidate fitness function selected in this study is: � a�:: = f�gh = i |9 ( )|. j �j (40) where t denotes a simulation time. this fitness candidate was similarly employed to an integration of time and absolute error (itae) control criterion. three parameters need to be optimized: k and λ indicated in (34) and (39), and tf, which is used with regard to a time constant of a filter. it should be necessary to use a filter with a suitable time constant tf to the disturbance ∆pl(t), which is considered to be an input of the control system, to ensure its possible derivative when calculating the sliding control signal. figure 3 shows the operating principle of the whole system. a step-load change of a 2% amplitude is embedded in the system. engineering, technology & applied science research vol. 13, no. 4, 2023, 11112-11118 11116 www.etasr.com nguyen et al.: a novel pso-based modified smc for designing robust load-frequency control … fig. 1. a single-area power system considering gdb and grc. fig. 2. simulated model for applying robust msmc-based lfc strategy fig. 3. convergence results for the pso algorithm applied to the msmc. fig. 4. the convergence of three parameters resulting from pso. 0 10 20 30 40 50 60 70 80 90 100 0 20 40 60 80 100 120 140 iterations c o s t v a lu e local values mean value global values 0 10 20 30 40 50 60 70 80 90 100 200 300 400 k 0 10 20 30 40 50 60 70 80 90 100 5500 6000 6500 7000  0 10 20 30 40 50 60 70 80 90 100 0.8 0.9 1 t f iterations engineering, technology & applied science research vol. 13, no. 4, 2023, 11112-11118 11117 www.etasr.com nguyen et al.: a novel pso-based modified smc for designing robust load-frequency control … fig. 5. frequency deviation and sliding surface resulting of msmc. fig. 6. results for the proposed smc-based lfc strategy figures 3-6 illustrate the obtained numerical results. figure 3 shows the convergence of the pso algorithm. after several iterations, it is clear that the global and local values are the same, hereby the three parameters converge, as shown in figure 4. figures 5 and 6 show the frequency deviation and load changes regarding their values, the first and second derivatives, the fluctuations in the system frequency, and the sliding mode surface. figure 7 shows the simulation results of frequency deviations in the case of using msmc, pid [2], and pi-like fuzzy logic controllers (pi~flc) [24]. figure 8 describes the undershoots of oscillations regarding frequency changes for all three flc controllers. these figures show that the proposed msmc-based lfc can damp the dynamic deviation of frequency quickly against the presence of nonlinearities and disturbance. the pid-based lfc controller and the fuzzy logic one can also force the system frequency to zero, but obtain poor control performances such as higher undershoots and much longer settling times. fig. 7. frequency deviations resulting from different lfc controllers fig. 8. comparison of different lfc controllers regarding undershoots demonstrating the better performance of msmc. in this context, the msmc strategy outperforms the other two counterparts. in conclusion, the robustness and effectiveness of the proposed msmc control strategy were clearly demonstrated when dealing with the lfc problem considering nonlinearities. vi. conclusions this paper presented a novel robust smc-based lfc strategy to deal with the nonlinearities of an electric power system. the effect of nonlinearities (i.e. gdb and grc) was 0 5 10 15 20 25 30 35 40 45 50 -0.03 -0.02 -0.01 0 0.01 time(s) (a) oscillation of the frequency deviation  f( p .u .) 0 5 10 15 20 25 30 35 40 45 50 -3000 -2000 -1000 0 1000 time(s) (b) illustration of the sliding surface  (t ) f( p .u .) f( p .u .) d o t f( p .u .) d o td o t p l (p .u .) p l (p .u .) d o t p l (p .u .) d o td o t 0 5 10 15 20 25 30 35 40 45 50 (a) time (s) -0.02 -0.015 -0.01 -0.005 0 f (p .u .) f msmc 0 5 10 15 20 25 30 35 40 45 50 (b) time (s) -0.04 -0.03 -0.02 -0.01 0 f (p .u .) f pid [2] f pi~flc [24] u n d e rs h o o t f m a x (p .u .) engineering, technology & applied science research vol. 13, no. 4, 2023, 11112-11118 11118 www.etasr.com nguyen et al.: a novel pso-based modified smc for designing robust load-frequency control … minimized successfully when the proposed control method was applied. the superiority of the proposed control strategy over the traditional pid regulator and the traditional fuzzy logic counterpart was also proved through several numerical simulations. the promising results show the feasibility of the proposed control strategy. future work should focus on extending the power system to be more complicated and practical, e.g. having more generators and controllers. furthermore, uncertain parameters should be considered to reach the real conditions of electric power grids. references [1] v. vittal, j. d. mccalley, p. m. anderson, and a. a. fouad, power system control and stability, 3rd ed. hoboken, nj, usa: wiley-ieee press, 2019. [2] p. s. kundur, power system stability and control. new york, ny, usa: mcgraw hill, 1994. [3] h. bevrani, m. watanabe, and y. mitani, power system monitoring and control. hoboken, nj, usa: wiley, 2014. [4] h. b. hiyama takashi, intelligent automatic generation control. boca raton, fl, usa: crc press, 2017. [5] h. bevrani, robust power system frequency control. boston, ma, usa: springer us, 2009. [6] w. fan, z. hu, and v. veerasamy, "pso-based model predictive control for load frequency regulation with wind turbines," energies, vol. 15, no. 21, jan. 2022, art. no. 8219, https://doi.org/10.3390/ en15218219. [7] d. v. doan, k. nguyen, and q. v. thai, "a novel fuzzy logic based load frequency control for multi-area interconnected power systems," engineering, technology & applied science research, vol. 11, no. 4, pp. 7522–7529, aug. 2021, https://doi.org/10.48084/etasr.4320. [8] h. k. alaei, a. yazdizadeh, and a. aliabadi, "nonlinear predictive controller design for load frequency control in power system using quasi newton optimization approach," in 2013 ieee international conference on control applications (cca), hyderabad, india, dec. 2013, pp. 679– 684, https://doi.org/10.1109/cca.2013.6662828. [9] a. huddar and p. s. kulkarni, "a robust method of tuning the feedback gains of a variable structure load frequency controller using genetic algorithm optimization," electric power components and systems, vol. 36, no. 12, pp. 1351–1368, nov. 2008, https://doi.org/10.1080/15325000802258380. [10] t. dao, y. wang, and n. nguyen, "applying metaheuristic optimization methods to design novel adaptive pi-type fuzzy logic controllers for load-frequency control in a large-scale power grid," turkish journal of electrical engineering and computer sciences, vol. 24, no. 6, pp. 4900– 4914, jan. 2016, https://doi.org/10.3906/elk-1503-184. [11] z. deng, c. xu, z. huo, x. han, and f. xue, "sliding mode based load frequency control and power smoothing of power systems with wind and bess penetration," machines, vol. 10, no. 12, dec. 2022, art. no. 1225, https://doi.org/10.3390/machines10121225. [12] m. s. shah, t. mahmood, m. f. ullah, m. q. manan, and a. u. rehman, "power quality improvement using dynamic voltage restorer with real twisting sliding mode control," engineering, technology & applied science research, vol. 12, no. 2, pp. 8300–8305, apr. 2022, https://doi.org/10.48084/etasr.4734. [13] s. younsi and n. hamrouni, "control of grid connected three-phase inverter for hybrid renewable systems using sliding mode controller," international journal of advanced computer science and applications, vol. 9, no. 11, pp. 336–342, 2018, https://doi.org/10.14569/ ijacsa.2018.091146. [14] a. maafa, h. mellah, k. ghedamsi, and d. aouzellag, "improvement of sliding mode control strategy founded on cascaded doubly fed induction generator powered by a matrix converter," engineering, technology & applied science research, vol. 12, no. 5, pp. 9217–9223, oct. 2022, https://doi.org/10.48084/etasr.5166. [15] x. yu and m. önder efe, eds., recent advances in sliding modes: from control to intelligent mechatronics, vol. 24. cham, switzerland: springer international publishing, 2015. [16] g. bartolini, l. fridman, a. pisano, and e. usai, eds., modern sliding mode control theory: new perspectives and applications, vol. 375. berlin, heidelberg: springer, 2008. [17] k. vrdoljak, n. perić, and i. petrović, "sliding mode based loadfrequency control in power systems," electric power systems research, vol. 80, no. 5, pp. 514–527, may 2010, https://doi.org/10.1016/ j.epsr.2009.10.026. [18] h. sira-ramírez, sliding mode control: the delta-sigma modulation approach, 2015th edition. new york, ny, usa: birkhäuser, 2015. [19] b. bandyopadhyay, s. janardhanan, and s. k. spurgeon, eds., advances in sliding mode control: concept, theory and implementation, vol. 440. berlin, germany: springer, 2013. [20] a. rauh and l. senkel, variable-structure approaches: analysis, simulation, robust control and estimation of uncertain dynamic processes. cham, switzerland: springer, 2016. [21] l. fridman, a. poznyak, and f. j. bejarano, robust output lq optimal control via integral sliding modes. new york, ny, usa: springer, 2014. [22] y. shtessel, c. edwards, l. fridman, and a. levant, sliding mode control and observation shtessel 2014. basel, switzerland: birkhäuser, 2014. [23] j. guo, "the load frequency control by adaptive high order sliding mode control strategy," ieee access, vol. 10, pp. 25392–25399, 2022, https://doi.org/10.1109/access.2022.3152259. [24] n.-k. n. nguyen duy-trung, "a comparative study on pi – and pd – type fuzzylogic control strategies," international journal of engineering trends and technology, vol. 69, no. 7, pp. 101–108, 2021, https://doi.org/10.14445/22315381/ijett-v69i7p215. [25] y. xiao, y. wang, and y. sun, "reactive power optimal control of a wind farm for minimizing collector system losses," energies, vol. 11, no. 11, nov. 2018, art. no. 3177, https://doi.org/10.3390/en11113177. engineering, technology & applied science research vol. 8, no. 3, 2018, 2931-2936 2931 www.etasr.com boujelbene: process capability and average roughness in abrasive water jet cutting process of … process capability and average roughness in abrasive water jet cutting process of stainless steel mohamed boujelbene college of engineering of hail university of hail hail, kingdom of saudi arabia mboujelbene@yahoo.fr abstract—process capability analysis is frequently employed to evaluate if a product or a process can meet the customer’s requirement. in general, process capability analysis can be represented by using the process capability index. until now, the process capability index was frequently used for manufacturing processes with quantitative characteristics. however, for a process with qualitative characteristic like cutting surface, the data’s type and single specification caused limitations of using the process capability index. taguchi developed a surface quality by abrasive water jet cutting or quadratic quality loss function to address such issues. in this study, we intend to construct a measurable index which incorporates the process capability index philosophy concept to analyze the process capability with the consideration of the qualitative surface roughness. the manufacturers can employ the proposed index to self-assess the process capability. the objective of this study was to examine the effects of abrasive water jet machining variables like cutting speed of the stainless steel material. the roughness of the varied surface through the cut depth was also measured and determined as a process capability index of 3 zones machined surface. keywords-abrasive water jet cutting; process capability; cutting speed; surface roughness; stainless steel i. introduction the abrasive water jet (awj) cutting technique is one of the most rapidly improving technological methods of cutting materials. in this cutting technique, a thin, high velocity water jet accelerates abrasive particles that are directed through an abrasive water jet nozzle at the material to be cut. awj is one of the most widely used technological methods. the advantages of awj cutting include the possibility of cutting almost all materials e.g. titanium, aluminum, the absence of thermal distortion, high flexibility, small cutting forces and being environmentally friendly. due to these capacities, this cutting technique is more cost-effective than traditional and non-traditional machining processes [1-9]. the mechanism and rate of material removal during the awj cut depends on both the type of abrasive and the range of process parameters. a considerable number of studies have investigated the effects of cutting velocity, spreading distance, water pressure, abrasive grain size and other factors on the surface roughness [6-12]. thus, it is necessary to have a deeper knowledge of the optimal conditions of operation, which will allow us to ensure a good surface roughness. a large amount of research effort has been made, in recent years, to understand the awj process and improve its cutting performance such as the depth of cut and surface finish for various materials [11-12]. researchers used granite samples for their experimental studies and investigated the effect of process parameters on rock cutting. it was found that entraining of abrasive particles increase the cutting capability of water jets and increases of water jet pressure allow obtaining deeper cut depths. process capability analysis (pca) [13-16] is frequently employed by the manufacturers to evaluate if the capability of process can meet the customer’s requirement. process capability indices (pcis) are a quantitative measurement of the process capability in most manufacturing industries. pcis, such as cp and cpk are commonly used for most manufactures [15–16], can frequently measure the process capability for the quantitative response for example surface roughness. authors in [15] evaluate the related scale of the process mean with the tolerance specification (i.e. the difference between the upper tolerance limit and the lower tolerance limit). cp evaluates the related scale of the specification’s tolerance with process’s tolerance. while cpk simultaneously, evaluates the centering degree and the dispersion degree. these pcis will make some adjustments if there are necessary particulars like the unilateral specification. for the quantitative type, the theories on pca and pcis are well developed in [15-17] but qualitative data type may exist during the manufacturing environment, e.g. the production parts, pistons, gears, the integrated circuit manufacturing, so, the process capability analysis for qualitative data will be an important issue to study. however, most studies only focus on the pca application for the quantitative response data, and the qualitative response data is seldom mentioned [16-17]. several difficulties can be mentioned as: (i) the target of the qualitative data may lead to unobvious centering evaluation, e.g. the target will be set as zero defect, (ii) the limitation of the unilateral specification, especially only the upper specification exists, e.g. the defect rate may be less than 1% and (iii) the quantitative data utilizes the process mean (µ) and process deviation (σ) to compute the pcis, however, the qualitative data cannot directly utilize them to compute the pcis. under the global market environment, to realize the process capability comparison with other competitors can provide helpful inf ma eng hop pla [18 int low qu of cus nu pur req val ref con pro qu ma sho tha a t pro pro pro bei tig the pro int the bet val cos ens cus reg qu wa spe rou thr pro ma to the th spe cut a. fro sta ta engineerin www.etasr formation for aking strategic gineering has pe to achiev anning, side by 8-22]. the go troducing the west producti ality. hence, w the produc stomer’s qual mber of produ rchase contra quirement [14] lue which ref ference for ntrollers to acq ocesses [14, 19 ality measur anagement, se ould be addres an at the produ the pci valu task or to ach ocess mean an ocess mean an ocess mean cl ing incurred. ghtening the pr e conventiona oduct and pr tend to raise th e target value, tter product q lue can easily sts that result suring toleran stomer deman gard, the off-li ality loss and as to examine eed of the stai ughness ra. t rough the dept ocess capabi anufacturers w seek. in this s e surface roug he aim of this eed on surfac tting of 316l a i materials the material om profile x6 ainless steel an able i. this s ng, technology r.com r enhancing c decisions. n s become wid ve simultaneou y side, at an ea oals are to sho new product on cost and what is neede cer’s process ity requiremen ducers include acts with cu ]. one such m flects real-time real-time mo quire a better g 9-21]. althoug rements emp everal authors ssed at the beg uction stage, w ue is typically hieve a goal. nd process vari nd design targe ose to the des the process rocess toleranc al on-line pc rocess design he pci value b and by reduci quality. howe y create additi t from extra e nce control. h nds for qualit ine pci value d production c the effects o inless steel m the average th of cut was a ility. especia will be a signif study, we inte ghness machin s study was t ce roughness austenitic stain ii. materi l used in this e 6crniti18-10 nd its nominal steel is used y & applied sci boujel organizationa now, as the con dely accepted us product d arly stage of pr orten the time to the marke manufacturin d is a way to capability, nt. more imp this measurem ustomers, as measurement is e quality statu onitoring that grasp of the qu gh pci is cons ployed during s have pointed ginning of the where pca is t defined as the the controlla iance [16]. the et can be redu sign target with s variance ca ce, with extra c ci is used fo ns, designer e by locating the ing the toleran ever, simply onal and unne efforts and exp hence, there is ty and produc is introduced, cost. the obje of awj variab material on a su roughness of also measured ally, the pc ficant factor f nd to construc ned by the aw to examine th across the cu nless steel. als and meth experimental st 0. it is strong chemical com in many indu ience research lbene: process al competenc ncept of conc d, design eng design and pr roduct develop e span require et and to attai ng parts with measure the d in satisfying ortantly, a gro ment value in a documen s the pci whic us. pci acts a t enables pr uality of their sidered as one g on-line q d out that the e design stage typically done. e ability to car able factors ar e deviation be uced by locatin hout additiona an be lowere cost incurred. or pca durin engineers nat e process mean nce value to en increasing the ecessary produ pensive devic s a need to ba ction costs. in , in considerat ective of this bles such as c urface with av the varied su d and expresse ca for dif for the collabo ct a pci to ev wj cutting pr he effect of c ut surface in hods tudy has been gly allied aust mposition is giv ustrial sectors h v capability and ce or current gineers rocess pment ed for in the good degree g the owing n their ntation ch is a as the rocess onsite of the quality e pci rather . rry out re the etween ng the al cost ed by when ng the turally n near nsure a e pci uction es for alance n this tion of study cutting verage urface ed as a fferent orators valuate rocess. cutting awj taken tenitic ven in s, like aero is a b. cutt ultr max exp the stai c. mea cap incl be p leng resp zon eva fig vol. 8, no. 3, 20 average rough onautic, chem also used in va experiments m the experime ting system w ra-high pressu ximum water perimental stud awj machin inless steel of fig. table i. c s 0.06 1 table ii. t surface roug the average asured by a pable of perf luding vertica performed eas gth and evalu pectively. the nes of the mac aluated. surfac gure 2. fig. 2. 018, 2931-2936 hness in abras mical, electrical arious mechani machine tool ents were carri with a kmt s ure pumps sl r pressure of dy, there are 6 ne (awjm) pr 8mm depth sh 1. experimen chemical comp si mn .00 2.00 0 constant t technical param cutting lengt water pressu type of abrasi density of the ab abrasive grain nozzle diame ghness measur surface rough mitutoyo po forming mea al and upside-d sily in various uation length e surface rou chined surface ce roughness m experimenta 6 ive water jet c l, navy, nuclea ical pieces man l ied out on an streamline tm l-v 50 capab f 600mpa (f 6 constant para rocess to cut a hown in table ntal awj cutting s position in % of p s 0.045 0.015 technological meters valu th 150 m ure 415 m ive miner rasive 0.5 g/ size 80 g ter 0,76 m rement hness (ra) of ortable surface asurements in down, allowin situations and were fixed at ughness was e. all measur measurements al surface roughne 2932 cutting process ar and petroleu nufacturing. nc 3015 eb m system [2] ble of providi figure 1). in ameters throug a sheet metal o ii. system. the x6crniti18cr ni 18 10 parameters ue mm mpa ral /l g mm the workpiece e roughness n any orienta ng measuremen d setups. the c t 0.8mm and measured in ement values s tester is show ess tester. s of … um. it awj with ing a n this ghout of the 10 e was tester ation, nts to cutoff 4mm three were wn in engineering, technology & applied science research vol. 8, no. 3, 2018, 2931-2936 2933 www.etasr.com boujelbene: process capability and average roughness in abrasive water jet cutting process of … iii. experimental results and discussion a. surface roughness of the cut surface after machining operations by awj cutting process, the cut surface was monitored by optic microscope and is presented in figure 3 which shows the very good surface cut of the upper edge beginning of the cut (zone 1) and the bad surface machined in the lower edge, ending of the cut (zone 3). in this zone there is a presence of the striation marks (figure 3(b)). (a) (b) fig. 3. photograph of machined surface after awj cutting (a) good surface at low cutting speed, (b) coarse surface at high cutting speed. obtained photographs were analyzed and edited with the use of image manipulation software. cut surfaces were divided in two zones; upper zone (beginning of the cut with no visible presence of machining marks), and lower zone, (ending of the cut with visible machining marks) as shown in figure 3(b). lines outlining machining marks and showing their approximate curve angle were added. for the surface cut with the highest cutting speed v equal to 250mm/min, numerous grooves and elevations in the lower zone are clearly visible marks (figure 3(b)). with decrease in the cutting speed an improvement of surface quality in its lower part can be observed. for the lowest used cutting speed, machining marks are fewer and faintly visible. it can be observed that the width of the zone with visible machining marks and their curve angle increases with the growth in cutting speed. the presence of machining marks in the lower part of cut surfaces is linked to the decrease in kinetic energy of abrasive particles in awj. after machining by awj cutting process, with different cutting speeds, we measured the surface average roughness ra in three zones (see figure 4). table iii presents ra of the all work pieces, in the three zones. it was observed that the sensitivity of measured parameters is directly related to both cutting speed and distance from upper cut edge. with the increase in cutting speed v, a degradation of surface quality defined by analyzed parameters for zone 2 and zone 1 planes was observed (figures 3 and 5). based on the analysis of table iii and figure 5, it can be stated that the cutting speed v, has a significant influence on the surface roughness of the cut surfaces. also, the distance from the upper cut surface edge directly affects surface quality and measurement results. in the area where awj enters the cut material, decrease in cutting speed by around 20% (from v=250mm/min to 200mm/min) results in drop of roughness parameter by approximately 14% in zone 3. further decrease of the cutting speed to 150mm/min (decrease by approximately 40%) results in surface roughness parameters dropping by 26% in zone 3. fig. 4. measurement zones of ra of the machined surface. a downward trend can also be seen when analyzing the measurement results taken in the center of cut surfaces. however, this time the drop is more significant by 20% for the medium cutting speed and 40% for the lowest used cutting speed. in the lower part of the studied cut surfaces the sharpest growth in values of measured parameters can be seen for the highest used cutting speed of 250mm/min. for the lower cutting speeds, 150mm/min, the increase in roughness is not as intense when compared to the values observed for the upper, parts of cut surfaces (zone 1). this can be caused by the drop in the kinetic energy of abrasive water jet being less intense for lower cutting speeds. in this part of the surface, biggest increases in surface quality can be achieved by using the lowest researched cutting speed of 150mm/min. figure 5 shows an excellent surface roughness of the machined surface in the zone 1, and a bad surface quality in the zone 3, for cutting speed of 250mm/min. iv. process capability a. process capability process capability cp and pci cpk are considered shortterm potential capability measures for a process. in six sigma, we want to describe processes quality in terms of sigma because this gives us an easy way to talk about how capable different processes are by using a common mathematical framework. in other words, it allows us to compare, for awj zone 1 zone 3 zone 2 measurement zones of ra exa ana clu hav lan ta con ma aw wh oth but tol in wi wit det wit sta pro sta cla is pra sta dev low cap pro me engineerin www.etasr ample, millin alogy is shoo uster or groupi ve a high cp nding on the bu able iii. su exp n° v 1 2 3 4 5 6 7 8 9 cpk measure nsistent you a ay be perform way from his t hich indicates her hand, a pe t the variation lerance band ( such case cpk ll be higher on th minimum v as a quanti termine wheth thin customer atistical measu ocess specifica andard of pro assical method usually assum actical cases, able univariate viation σ, if w wer specifica pability (cp) ocesses (cpk easures that ar cpk m= ng, technology r.com ng processes oting at a targ ing in the same value. when ullseye, you n urface roughne v (mm/min) de 150 150 150 200 200 200 250 250 250 s how close are around you ming with min target towards lower cpk, w erson may be n in performan (i.e., specificat k will also be nly when you’ variation [18]. itative measu her a process r specification ures is to estim ations. further oduct quality ds, while norm med in the esti some non-no e normal proc we define us ation limits, and the proce k), defined in e inappropriat cp = cp cp min cpu μ =  y & applied sci boujel to turning p get. if the ro e spot anywhe you have a t ow have a hig ess after machin epth (mm) 8 zo 8 zo 8 zo 8 zo 8 zo 8 zo 8 zo 8 zo 8 zo you are to yo ur average perf nimum variati s one of the s whereas cp w on average ex ce is high (but tion interval, f e lower, but cp ’re meeting the ure, pcis are s is capable o n limits. the mate process v rmore, a pci p to suppliers mality of the qu imation proce ormal distribu cess with me sl and lsl to respectively, ess capability n (1) to (4), te for non-norm 6 usl lsl σ − = 3 usl l μ σ − = 3 lsl u μ σ − = , 3 lsl cpl μ σ − = ience research lbene: process processes. a ounds form a ere on the targe tight group of gh cpk. ning by awj cut ra (µm) one 1 2.71 one 2 3.69 one 3 5.36 one 1 2.98 one 2 3.93 one 3 6.28 one 1 3.21 one 2 5.26 one 3 7.27 our target and formance. a p ion, but he c specification l will be high. o xactly at the t t still lower th for example ± p will be high e target consis e widely use of producing objective of ariability relat provides a com and custome uality characte ess of pci, in utions occur. ean μ and sta o be the uppe then the pr ratio for off, are the cla mal processes. 3 usl μ σ −    h v capability and good good et you f shots tting. d how person can be limits, on the target, han the ±0.15). h. cpk stently ed to items these tive to mmon ers. in eristics many for a andard er and rocess center assical . (1) (2) (3) (4) esti dev ava nor mo cha mu b. f ra, surf are the lim the mac and con very pro spe ra cap an rou con con exp pro pre imp (fig f zon num cap pro of us the vol. 8, no. 3, 20 average rough in which, on imates defined viation s, re ailable in the rmal processe re than one aracteristics a ltivariate techn fig. 5. surf results of the for analyzing , in three zon face by awj presented in t awjc proces mit lsl 2.8µm e process cap chined surfac d cpk=1.74> nsidered to be ry good proce ocess is contai ecifications. fu in zone 2 (ra pability cp=5.9 excellent pro ughness value nforming prod ntrol. the proc perience least oduct. the proc sented potent plying that we gure 8). so we figure 8 show ne 3, which in mber of non-c pability is ina ocess mean is n non-conformin l is 731642.4 observed perf 018, 2931-2936 hness in abras ne can replac d as the samp espectively. a literature to es, in many p e quality ch are generally niques should face roughness ra e process capa the process ca nes (zone 1cutting (aw table iv and ss of the stain m and upper pability report e presented th 1.33 (cpk v e industry ben ss in zone 1 ined within sta urthermore, th a-z2) of mach 94 and cpk=5 ocess in zone es, in zone ducts as long cess owner can difficulty an cess capability tial capability e have a bad o e have to choo ws that the pr ndicates the po conforming pa dequate. for not centered a ng parts out 49 and there i formance (figu 6 ive water jet c ce unknown ple mean x an although vari estimate pci production pr haracteristics correlated, be employed. a as funtion of the ability apability of the 3) (ra-z1-3), wjc). the resu figures 6-8. t nless steel has specification t for ra in z he potential c values of 1.3 nchmarks), im (figure 6). t andard deviati he process ca hined surface p 5.24>1.33, imp e 2 (figure 1 and zone g as they rem n claim that th nd greater re y report for ra cp=6.63 and or not adequate ose another pro rocess capabil otential risk of arts. it denote a cp differen at the process w of the upper s a non value ure 8). 2934 cutting process μ and σ by nd sample stan ious methods of univariate rocesses, there involved. t and hence, e cutting speed v e surface rough of the mach ults of the me the process da lower specific limit usl 7. zone 1, (ra-z capability cp= 33 or greater mplying we ha his means tha ions of the pr apability repor presented pote plying that we 7). these su 2, will pro main in stati he customer sh eliability with a in zone 3 (r d cpk=-0.20< e process in zo ocess for this c lity deteriorat f an increase i es that the pr nt to the cpk width. the nu specification out of the ls s of … their ndard s are e non e are these some v. hness hined easure ata of cation 2µm. 1) of =6.38 r are ave a at the rocess rt for ential have urface oduce istical hould h this ra-z3) <1.33, one 3 case. ed in in the rocess k, the umber limit sl in engineering, technology & applied science research vol. 8, no. 3, 2018, 2931-2936 2935 www.etasr.com boujelbene: process capability and average roughness in abrasive water jet cutting process of … table iv. surface roughness ra in the 3 zones exp n° v (mm/min) ra-z1 (µm) ra-z2 (µm) ra-z3 (µm) 1 150 2.58 4.02 5.3 2 150 2.79 3.3 5.7 3 150 2.81 3.78 5.0 4 150 2.66 3.9 5.6 5 150 2.77 3.42 5.11 6 150 2.63 3.74 5.46 1 200 2.93 3.8 6.32 2 200 2.98 3.78 6.23 3 200 3.13 3.99 6.14 4 200 3.02 4.01 6.41 5 200 2.87 4.11 6.17 6 200 2.94 3.89 6.39 1 250 3.44 5.24 7.31 2 250 3.48 5.18 7.22 3 250 3.33 5.46 7.14 4 250 3.22 5.25 7.41 5 250 3.52 5.31 7.17 6 250 3.41 5.12 7.34 fig. 6. process capability report for ra in zone 1 of the cut surface. fig. 7. process capability report for ra in zone 2 of the cut surface. fig. 8. process capability report for ra in zone 3 of the cut surface. v. conclusion in this study, we constructed a quantitative measurement pci for the qualitative response of the surface roughness. the quantitative measurements are based on the taguchi’s quality function philosophy and pci concept. it is a ratio deriving from the customer’s quality loss with respect to the actual process’s quality loss. by employing the proposed pci, the manufacturers can assess and meet the customer’s requirement. the analysis of the machined surface by awjc process extracted the following conclusions: • edge quality of the cut surface is a function of cutting speed. • with decrease in cutting speed, cut surface quality visibly improves, which is most clearly noticeable for the lower part of examined cut surfaces. the difference in the measured value of ra parameter is about 26% between the highest and lowest researched cutting speeds, in favor of the latter. • cut surfaces are characterized by the occurrence of two zones. in the first zone, there are no visible machining marks. in the second one, machining marks can be easily observed. the second zone width and the visibility of machining marks is closely related to the cutting speed. • results of this research can have a practical use in determining surface roughness parameters best suited to adequately evaluate cut surfaces of elements machined with the use of awj. • this process will produce conforming products, in zone 1 and zone 2, as long as it remains in statistical control. • the process capability report for ra in zone 3, gives a bad or not adequate process in this zone, so, a new process must be chosen. references [1] a. akkurt, “cut front geometry characterization in cutting applications of brass with abrasive water jet”, journal of materials engineering and performance, vol. 19, no. 4, pp. 599–606, 2010. 7,26,66,05,44,84,23,63,0 lsl 2,8 target * usl 7,2 sample mean 3,4 sample n 6 stdev(overall) 0,109362 stdev(within) 0,114932 process data pp 6,71 ppl 1,83 ppu 11,58 ppk 1,83 cpm * cp 6,38 cpl 1,74 cpu 11,02 cpk 1,74 potential (within) capability overall capability ppm < lsl 0,00 0,02 0,09 ppm > usl 0,00 0,00 0,00 ppm total 0,00 0,02 0,09 observed expected overall expected within performance lsl usl overall within process capability report for ra-z1 (µm) 7,26,66,05,44,84,23,63,0 lsl 2,8 target * usl 7,2 sample mean 5,26 sample n 6 stdev(overall) 0,117473 stdev(within) 0,123457 process data pp 6,24 ppl 6,98 ppu 5,50 ppk 5,50 cpm * cp 5,94 cpl 6,64 cpu 5,24 cpk 5,24 potential (within) capability overall capability ppm < lsl 0,00 0,00 0,00 ppm > usl 0,00 0,00 0,00 ppm total 0,00 0,00 0,00 observed expected overall expected within performance lsl usl overall within process capability report for ra-z2 (µm) 7,156,505,855,204,553,903,25 lsl 2,8 target * usl 7,2 sample mean 7,265 sample n 6 stdev(overall) 0,105214 stdev(within) 0,110573 process data pp 6,97 ppl 14,15 ppu -0,21 ppk -0,21 cpm * cp 6,63 cpl 13,46 cpu -0,20 cpk -0,20 potential (within) capability overall capability ppm < lsl 0,00 0,00 0,00 ppm > usl 666666,67 731642,49 721682,06 ppm total 666666,67 731642,49 721682,06 observed expected overall expected within performance lsl usl overall within process capability report for ra-z3 (µm) engineering, technology & applied science research vol. 8, no. 3, 2018, 2931-2936 2936 www.etasr.com boujelbene: process capability and average roughness in abrasive water jet cutting process of … [2] j. valicek, s. hloch, d. kozak, “surface geometric parameters proposal for the advanced control of abrasive waterjet technology”, the international journal of advanced manufacturing technology, vol. 41, pp. 323–328, 2009 [3] a. daymi, m. boujelbene, e. bayraktar, a. ben amara, d. katundi, “influence of feed rate on surface integrity of titanium alloy in high speed milling”, advanced materials research, vol. 264-265, pp. 12281233, 2011 [4] y. wu, s. zhang, s. wang, f. yang, h. tao, “method of obtaining accurate jet lag informationin abrasive water-jet machining process”, the international journal of advanced manufacturing technology, vol. 76, no. 9-12, pp. 1827–1835, 2015 [5] i. miraoui, m. boujelbene, e. bayraktar, “analysis of cut surface quality of sheet metals obtained by laser 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am20 magnesium alloy by taguchi grey relational analysis”, journal of magnesium and alloys, vol. 3, no. 1, pp. 36-46, 2015 [20] k. abhishek, s. datta, s. s. mahapatra, “multi-objective optimization in drilling of cfrp (polyester) composites: application of a fuzzy embedded harmony search (hs) algorithm”, measurement, vol. 77, pp. 222-239, 2016 [21] a. jeang, “optimal process capability analysis for process design”, international journal of production research, vol. 48, no. 4, pp. 957– 989, 2009 [22] b. el aoud, m. boujelbene, e. bayraktar, s. ben salem, i. miskioglu, “studying effect of co2 laser cutting parameters of titanium alloy on heat affected zone and kerf width using the taguchi method”, mechanics of composite and multi-functional materials, vol. 6, pp. 143-150, 2018 microsoft word 11-2829_s1_etasr_v9_n4_pp4371-4376 engineering, technology & applied science research vol. 9, no. 4, 2019, 4371-4376 4371 www.etasr.com labidi et al.: a model-based approach of dc-dc converters dedicated to controller design … a model-based approach of dc-dc converters dedicated to controller design applications for photovoltaic generators zeineb rania labidi laboratory of application of energy, efficiency and renewable energies, faculty of sciences of tunis, tunis el manar university, tunis, tunisia zeinebrania.labidi@fst.utm.tn horst schulte department of engineering, university of applied sciences for engineering and economics, berlin, germany horst.schulte@htw-berlin.de abdelkader mami laboratory of application of energy, efficiency and renewable energies, faculty of sciences of tunis, tunis el manar university, tunis, tunisia abdelkader.mami@fst.utm.tn abstract—in this paper, a model-based approach of dc-dc converters dedicated to controller design applications for photovoltaic generators is introduced. the paper provides a mathematic averaging model, based on the state space method for dc-dc converters that is used as an adaptation level in photovoltaic generators. this modeling allows the dynamics of the system to be described by presenting a reliable model to be used for oriented controller design. the two most needed topologies of dc-dc converters are proposed, buck and buckboost, and an overview of integral state feedback controller design using a model-based approach for a boost converter connected to a photovoltaic generator described in our previous published work is provided. the model-based conception of both converter types is analyzed for optimal use in control-oriented design. the validation of each model is demonstrated by comparative curves represented by a detailed plant model using simscape devices available and implemented in simulink/matlab keywords-model-based approach; buck converter; buck-boost converter; state–space modeling; photovoltaic generator i. introduction recently, worldwide focus has been directed to the research of water management systems for agricultural and food production [1]. in providing these systems, especially to rural near-desert areas, the most optimal solution is the use of offgrid renewable energy generators [2, 3]. voltage adjustment between these generators (as photovoltaic (pv) arrays) and load requires the adoption of direct current-direct current (dcdc) converters, which enable the maximum extraction of power available through appropriate control techniques. these converters also regulate the output dc voltage that is needed as a dc bus connection for hybrid systems of renewable energy. the use of dc-dc converters, in turn, necessitates the implementation of a model-based approach to controller design. in this regard, interest lies in the dc-dc converters employed in pv generator applications. in [4], the authors compared different topologies on the basis of varying applications and comprehensively discussed the advantages and disadvantages of each topology in terms of costs, components, efficiency, and limitations. they indicated that a buck converter is optimal for standalone solar pv pumping systems intended to supply water to rural areas, that a boost converter exhibits good dynamic performance in load balancing, and that a buck-boost converter is the most efficient tool for drawing maximum power from pv panels, regardless of load conditions. in our previous work [5], integral statefeedback control was designed using a model-based approach to ensure control in a boost converter connected to a pv array, which was modeled as a current source. the present study aims at modeling two topologies (buck and buck-boost converter), necessary in the design of different control mechanisms, such as integral feedback control, model predictive control, and observer-based control. to this end, we used an analytical model-based approach that is relevant to practical applications. ii. overview of model-based approach for boost converter this section summarizes the most important steps in building an oriented controller through the proposed modelbased approach of a boost converter [5]. it also recounts the analysis of the oriented model for application purposes. we note that a detailed explanation of the pv generator is presented in [5], hence it will be applied directly in this work. a. model-based approach the particularity of the model-based approach of the boost converter connected through a pv array is that the input of the converter is not a simple voltage constant [6], but the equivalent circuit of the pv array as a current source (figure 1). this way, the system matrix describes the exact dynamic interaction between source (pv panels) and load. in the system, solar radiation is defined as a non-controllable input, whereas the duty cycle represents controllable input. �� �� �������� ���� ��� � � = � ��������� + � ���� + (1) corresponding author: zeineb rania labidi engineering, technology & applied science research vol. 9, no. 4, 2019, 4371-4376 4372 www.etasr.com labidi et al.: a model-based approach of dc-dc converters dedicated to controller design … to extract the average matrix of the system (2) and use it for the oriented controller [5], we first defined the system’s state variables, namely, the voltage and current flowing through inductors and capacitances. we then converted the differential equations for on and off modes into the form presented in (1). fig. 1. equivalent electrical circuit of the system with a boost converter �� �� �������� ���� ��� � � = �� �� �! "�#�$%&'$%� ! " �# 0") ! * $ $+'$, $+' $ $,) �$+'$� ! $) �$+'$� 0 $� �$'$+� ! "� �$'$+� � � ��������� + . $%&�#�$%&'$%�00 / �0 +�� �� 0$+$1 $2$+1$2 $) �$+'$� i + $) �$+'$� �45 + ") �6 ! $� �$'$+� i � � �" + . 0! ")0 /�6 (2) with ���� = *78 ,8= *797: (3) and ;)� = ;) ! ;� (4) with ;� = ;< =exp* �8�a -–1d + �8$%& + �8$%& efgh �5� and ;) = mmn#o p;)fgh + q rs �tsguu,w !tfgh,w�x (6) �y = z y[ \] ŝguu r̂gf (7) �� = ��� + _r;�� (8) equations (4), (5), and (8) are extracted from the equivalent electric circuit of figure1 by using kirchhoff’s laws. b. oriented controller model-based approach was established to improve the performance of the oriented controller. the plant of the system is represented in a boost converter that functions as an interface between the pv array and load. the purpose behind controloriented techniques is to achieve impedance matching between the output of pv panels and load conditions. to achieve such matching, the differential equations extracted through the state space averaging method were linearized around an operating point. in the steady state, we calculated the equilibrium point using taylor series. we thus used the closed loop of the system matrix that we obtained through the model-based approach to derive poles, after which we employed the ackerman formula and the pole placement method to calculate the feedback gain matrix. improving the efficiency of a controller designed for pv systems necessitates an accurate modeling plant as this enhances the choice of control technique to be used. the model-based approach provides an actual estimation of the dynamic behavior of a system and presents a simple means of verifying the occurrence of a fault by matching the difference between the measured and calculated parameters to reference values [7]. finally, it can advance the fault detection and diagnosis of solar systems given that most methods require the plant of a system. iii. buck converter this section describes the buck converter concept, its operation and a definition of the model-based approach adopted in this work. a. concept and operation a buck converter is a switching device that enables the simultaneous decrease of the output voltage and increase of the output current, respectively, while maintaining the level of power received in the input. figure 2 shows the topology of a buck converter connected to a pv array. in [8], an exact description of the topology and basic operation of a buck converter is presented. the authors demonstrated the use of the following equations: ��� = q ��� (9) ;�� = "̀ ;�� (10) by using (9) and (10) we obtain: � �] � = q0 �ab]ab (11) we know that: _�� = �ab]ab and _�� � � �] � (12) putting (12) in (11) results in: _�� � α0 _�� (13) q � d$ �$ab (14) for a buck converter to work effectively, according to (14), _�� must be always inferior to _�� because q is always inferior to 1. fig. 2. equivalent electrical circuit of the system with a buck converter b. model-based approach for a buck converter the first step in building the model-based approach is to extract the differential equations for on and off operations in the continuous conduction mode of the buck converter. figure engineering, technology & applied science research vol. 9, no. 4, 2019, 4371-4376 4373 www.etasr.com labidi et al.: a model-based approach of dc-dc converters dedicated to controller design … 3 illustrates the on mode of the buck converter connected to a pv array. fig. 3. electrical circuit of the on mode of the buck converter ������ � ! "�# �$%&' $%� �e� ! "�# i� $%&�# �$%&' $%� �)� (15) � �� � ") �e� ! * $ $+'$, $+' $ $,) �$+'$� � ! $) �$+'$� ��� (16) �� ��� � $� �$'$+� � ! "��$'$+� ��� (17) equations (15)-(17) represent the dynamic state–space modeling of the on stage illustrated in figure 3. equations (21)-(23) exhibit the derivative states of the off mode shown in figure 4.we note that the derivative of the state variable ��� is equal in the on and off mode because the dynamics of the system doesn’t change. ������ � ! "�# �$%&' $%� �e� � $%&�# �$%&' $%� �)� (18) � �� � !* $ $+'$, $+' $ $,) �$+'$� � ! $) �$+'$� ��� ! ") �6 (19) �� ��� � $� �$'$+� � ! "��$'$+� ��� (20) fig. 4. electrical circuit of the off mode of the buck converter if we go back to figure 1 describing the electrical circuit of the boost converter, we can tell that ��� is equal to � regardless of the on or off condition of the switcher because the capacitance input fg is very small, so (8) can be written as: �� � ��� � _r ; (21) where � represents the state variable through the inductance. for the buck converter defined in figure 3 we notice that ��� is different from � depending on the switcher’s mode, where: ��� � _gh�_gh�ij� �)� ! 1�_gh�ij� ��� (22) in this case, (8) can be written as: vl � $%&�$%&'$%�vmn � $%&op�$%&'$%� �)� (23) �)� is expressed in (4), ;) is the light generated by the sun and ;� is the diode current. the differential equations of the on and off modes can be summarized according to (24). the state space averaging system, which combines both time switches, is presented in (27) by using (25): qr��� � � q��� � ��q� �"��� � �s �0�t� (24) qr��� � qruv �" � qruhh �1 ! �"� (25) where the input �l � �" is related to the switch mode, and �)� is the incontrollable input representing the sun light. s=w x^ ; mosfet onx��; mosfet off with e����� � �", e������ � 1 ! �", �" ∈ �0,1�, q= ��e������ � � q"q0q�� (26) the system matrix of the buck converter connected to the pv array: ��� ��������� ���� ��� � � � �� �� �! "�#�$%&'$%� 0 00 ! * $ $+'$, $+' $ $,) �$+'$� – $) �$+'$� 0 $� �$'$+� ! "� �$'$+� � � ��������� + . $%&�#�$%&'$%�00 / ��4 +� ! " �# i") ��� � ") �6 0 � �l � . 0! ")0 /�6 (27) the validation of the state space model is confirmed by figure 5, which shows the similarity between the mathematical implementation of the equivalent circuit of the system and the use of simscape devices on simulink/matlab. iv. buck-boost converter a. concept and operation there are different buck-boost converter topologies [8, 9], each appropriate for a particular application. the buck-boost gives a negative output voltage when used without isolation. the property of this converter is that, it can be a step up or step down of the input voltage, according to the following notation: 0 5 its a boost converter 0 5 its a buck converter 0 5 its unity gain . , . , . , α α α > < = equations (28)-(30), express the relation between the input and output of the converter depending on the duty cycle: ��� � ` �"1`� �e� (28) ;�� � �"1`� ` ;e� (29) engineering, technology & applied science research vol. 9, no. 4, 2019, 4371-4376 4374 www.etasr.com labidi et al.: a model-based approach of dc-dc converters dedicated to controller design … ������ � * `"1`-0 ���]�� (30) applying (12) and considering (30), the expression of the duty cycle can be written as: `�"1`� � d$ �$ab (31) according to (31) and contrary to the boost and buck converter, the system will function properly in all scenarios, either when _�� is inferior, superior or equal to _e� . that’s why the equivalent electrical circuit of the buck-boost converter presented in figure 6 is the optimal solution to extract the maximum power from renewable energy systems (e.g. sun systems). fig. 5. validation of the model simscape vs state space fig. 6. electrical circuit of the system with a buck-boost converter b. model-based approach for a buck-boost converter the state space equations when the switcher is in the on mode are written in (32)-(34), according to figure 7. fig. 7. electrical circuit of the on mode of the buck-boost converter ������ � ! "�# �$%&' $%� �e� ! "�# i � $%&�# �$%&' $%� �)� (32) � �� � ") �e� – �$2' $,�) � (33) �� ��� � ! "��$'$+� ��� (34) the input �)� is defined in (4), and the same logic is applied as the buck converter regarding �� defined in (23) for both switching times. the state equations for the off state are given by (35)-(37), according to figure 8. ������ � ! "�# �$%&' $%� �e� � $%&�# �$%&' $%� �)� (35) � �� � !* $ $+' o�:' $ $,) $ � ! $+1$) $ ��� ! ") �6 (36) �� ��� � ! $� �$'$+� � ! "��$'$+� ��� (37) fig. 8. electrical circuit of the off mode of the buck-boost converter the state space averaging model for the buck-boost converter results in (38). it’s a set of state equations equivalent to the on and off switching states. we note that the matrix of the pv generator connected to the buck-boost was written according to (25) defined in the section of the buck converter. ��� �� ������� ���� ��� � � � ��� ��� ! "���$%&'ij� 0 00 ! � _ _�� rc2� _ _�� r � ! _�!_� r 0 ! i� �i'i�� ! �� �i'i�� � � ��������� + . $%&�#�$%&'$%�00 / ��4 +�� �� � ! " �# i") ��� � _ _�� rc2! _ _�� r i � _�!_� r ��� � ") �6$� �$'$+� i � � �l � . 0! ")0 /�6 (38) 0 0.5 1 1.5time(s) 400 600 800 1000 sun radiation 0 0.5 1 1.5 time(s) -100 0 100 200 300 400 500 vpv and vdc in simscape vs state space vpv simscape vpv state space vdc simscape vdc state space 0 0.5 1 1.5time(s) 0 1 2 3 4 5 ipv and idc in simscape vs state space ipv simscape ipv state space idc simscape idc state space engineering, technology & applied science research vol. 9, no. 4, 2019, 4371-4376 4375 www.etasr.com labidi et al.: a model-based approach of dc-dc converters dedicated to controller design … c. simulation and discussion the simscape notation means that the circuit was designed by using devices available in the simscape library and the state space means that the circuit was designed by mathematic modeling using the state space method (which consists of equations implemented in simulink and they are not the predefined devices available in simscape). the comparison between the simulation of the circuit designed by simscape devices and the one designed by the analytical solution confirms that the mathematic solution is as accurate as the circuit built by detailed devices given by simscape. for simulation, the powergui used in the simulink model is set as continuous mode with variable step size of maximum 0.0001s, and ode23tb (stiff/tr-bdf2) as a solver. in figure 9, we can see that when α=0.5 the input voltage and current of the buckboost converter is equal to the inverse of the output with �e� defined in (22) and ��� is as follows: ��� � � �$ (39) the model is validated by the comparison between the simscape and state space model for the three possibilities of the controllable input q presented in figures 9-11. fig. 9. validation of the model for q � 0.5 figure 10 shows the boost converter mode (e.g. the output voltage is higher than the input) but the polarities are inversed and figure 11 the buck converter mode (e.g. the output current is higher than the input). observing the equivalent electrical circuit of the on and off mode of each converter presented, can lead us to understand the flux of the current which represents the state variable i. it’s important to analyze the dynamic behavior of the states, so an accurate model can be built and used in a proper way to design the oriented controller. we have noticed that for the boost converter the state variable � is equal to the pv current �e�, for the buck converter the state variable � is equal to the output dc current ��� , and for the buck-boost converter the state variable � is different from �e� and ��� as shown in figure 9. this can influence the result given by the controller if we use the mathematical modeling without differentiating between the state variables and the inputs/outputs of the system. fig. 10. validation of the model for q � 0.6 (boost mode) fig. 11. validation of the model for q � 0.4 (buck mode) v. conclusion and outlook based on the simulation results shown in this paper, the model-based approach is validated. it also demonstrates the accuracy of the system matrix extracted from the differential equations depending on the equivalent electrical circuit of each converter connected to the pv array. the model-based approach is a mathematical modeling of the system based on the state space method destined for photovoltaic generators. it allows defining and understanding the comportment of the state variables, as well as the input and output signals. it consists of predefined models of boost, buck and buck boost converter and can benefit from further work that involves power conversion sun systems. in this paper an analysis of the buck and buckengineering, technology & applied science research vol. 9, no. 4, 2019, 4371-4376 4376 www.etasr.com labidi et al.: a model-based approach of dc-dc converters dedicated to controller design … boost converter was conducted. the state space model of the buck-boost converter will be used in our future research: it will be adopted to build an oriented controller design. nomenclature ¢: boltzmann’s constant (1.3806×10-23j.k-1) £: electron charge (1.6022×10-19c) ��: diode voltage (v) ;�: diode current (a) ;): generated light produced by the sun ;)fgh: reference of the generated light (1.2653a) t: temperature (k) ��/q: duty cycle _r: series resistance (16.135ω) _r¦: shunt resistance (254.8279ω) ;<: diode saturation current (2.2521×10-12a) q rs: temperature coefficient (1.904×10-3) \]: diode ideality factor (0.98117) ŝguu: number of cells in series s: irradiation of the sun efgh: reference of the sun irradiation (0.001) r̂gf: number of modules connected in series �̂§f: number of modules connected in parallel tfgh1z: 298.15k references [1] http://prima-med.org/ [2] a. m. garcia, j. gallagher, a. mcnabola, e. c. poyato, p. m. barrios, j. a. r. diaz, “comparing the environmental and economic impacts of on or off-grid solar photovoltaics with traditional energy sources for rural irrigation systems”, renewable energy, vol. 140, pp. 895-904, 2019 [3] s. meunier, m. heinrich, l. queval, j. a. cherni, l. vido, a. darga, p. dessante, b. multon, p. k. kitanidis, c. marchand, “a validated model of a photovoltaic water pumping system for off-grid rural communities”, applied energy, vol. 241, pp. 580-591, 2019 [4] n. h. baharudin, t. m. n. t. mansur, f. a. hamid, r. ali, m. i. misrun, “topologies of dc-dc converter in solar pv applications”, indonesian journal of electrical engineering and computer science, vol. 8, no. 2, pp. 368-374, 2017 [5] z. r. labidi, h. schult, a. mami, “a systematic controller design for a photovoltaic generator with boost converter using integral state feedback control”, engineering, technology and applied science research, vol. 9, no. 2, pp. 4030-4036, 2019 [6] r. h. g. tan, l. y. h. hoo, “dc-dc converter modeling and simulation using state space approach”, ieee conference on energy conversion, johor bahru, malaysia, october 19-20, 2015 [7] j. a. tsanakas, l. ha, c. buerhop, “faults and infrared thermographic diagnosis in operating c-si photovoltaic modules: a review of research and future challenges”, renewable and sustainable energy reviews, vol. 62, pp. 695–709, 2016 [8] i. batarseh, a. harb, power electronics: circuit analysis and design, springer, 2018 [9] y. chen, b. zhang, equivalent-small-parameter analysis of dc/dc switched-mode converter, springer 2019 microsoft word etasr_v11_n3_pp7107-7110 engineering, technology & applied science research vol. 11, no. 3, 2021, 7107-7110 7107 www.etasr.com phan & nguyen: the influence of fly ash on the compressive strength of recycled concrete utilizing … the influence of fly ash on the compressive strength of recycled concrete utilizing coarse aggregates from demolition works van tien phan department of construction vinh university vinh city, vietnam tienkxd@vinhuni.edu.vn, vantien.phan1010@gmail.com tien hong nguyen department of construction vinh university vinh city, vietnam tienhongkxd@vinhuni.edu.vn abstractthe compressive strength of recycled concrete with coarse aggregates with and without fly ash was studied in this paper. the recycled concrete was designed to have a compressive strength of rn=15mpa. the ratio of conventional aggregates and recycled coarse aggregates was 50-50. fifteen samples for each recycled concrete aggregate had been cast and were tested 7, 14, and 28 days after curing. the experimental results indicate that the strength development of the two recycled concrete mixes is relatively uniform. fly ash increased the compressive strength of recycled concrete by 11% for 7-day aged samples. the recycled concrete with fly ash had 7% less compressive strength than the concrete consisting of natural aggregates. keywords-fly ash; recycled concrete; demolishing work i. introduction nowadays, reuse of solid waste from demolition works is a common issue, especially at developing cities. construction solid waste is hardly reused due to various reasons such as the lack of solid waste treatment plants and concentration areas, strict environmental regulations, etc. in fact, many investors dump solid waste from demolition works to save time and money, which has a negative impact on the environment and the locals. reusing construction solid waste will contribute to satisfy the growing demand for stone materials in construction industry. thermal power plants are generating a huge amount of fly ash and slag waste, which, if not treated and reused, cause serious environmental pollution. the burial of waste, such as fly ash, from thermal power plants causes long-term harm to the environment (polluting groundwater sources, damaging cultivated lands, etc.). the reuse of this type of waste is being widely supported and, in fact, fly ash has been used in many applications of construction material production such as the production of unburnt bricks. the problem of recycling concrete from demolition works has been studied extensively. often, the structure of recycled concrete is similar to conventional concrete and even better in some cases. there have been many scientific publications about recycled concrete and its uses [1-8]. the most recent research aspects can be seen in [9], in which the authors investigate the effect of the strength of recycled concrete waste on the mechanical properties of recycled concrete. the results show that the reused concrete waste has almost no significant effect on compressive, flexural, and tensile strength of the recycled concrete. authors in [10] assess the mechanical properties and environmental impacts of self-compacting concrete using recycled aggregates. authors in [11] evaluate the use of recycled materials from waste concrete to self-compacted concrete. although the use of recycled concrete is a much studied issue, according to our understanding, there are limited studies evaluating the use of fly ash to increase the efficiency of recycled concrete using construction solid waste [12-14]. therefore, in this paper the effect of fly ash on the compressive strength of concrete with recycled aggregates from demolition works is studied. fig. 1. construction waste dumped on the side of the road and into a drainage canal. ii. experimental setup a. fly ash the used fly ash came from the duyen hai thermal power plant (tra vinh province – viet nam). the fly ash belongs to type f because its total content of oxides sio2 + al2o3 + fe2o3 is bigger than 70%. the technical parameters of the fly ash are shown in table i. b. sand the sand used in the experiments has the following mechanical properties: density 2.65g/cm 3 , modulus of magnitude 2.50, and volumetric mass 1660 kg/m 3 . density is corresponding author: van tien phan engineering, technology & applied science research vol. 11, no. 3, 2021, 7107-7110 7108 www.etasr.com phan & nguyen: the influence of fly ash on the compressive strength of recycled concrete utilizing … the mass per unit volume of a material in a completely solid state and volumetric mass is the mass per unit volume of material in its natural state. table i. technical parameters of fly ash nam of indicator results (%) standard 10302:2014 (%) total content of sio2+al2o3+fe2o3 82.9 ≥ 45 the content of sulfur and sulfur compounds converted to so3 0.03 ≤ 6 free calcium oxide content cao 0.02 ≤ 4 the loss content when heated 8.3 ≤ 15 harmful alkali content (soluble alkali) < 0.01 ≤ 0.1 c. cement nghi son portland cement pcb40 was used with the following mechanical properties: actual strength 40mpa and density 3.1g/cm 3 . d. coarse aggregates 1) natural coarse aggregates natural coarse aggregates were mixed with the recycled materials. in this study, aggregates of the most common size used in construction (20mm) have been used. the aggregates have the following mechanical properties: 2.61g/cm 3 density and 1430kg/m 3 volumetric mass. 2) recycled aggregates the obtained concrete waste after the demolition of a project was crushed. the resulting coarse aggregates were washed, dried, and pre-screened to remove dust particles. raw aggregates were screened to classify the particle sizes, then mixed again to be graded as standard for concrete in accordance with the provisions of vietnamese standard no. 11969: 2018. the recycled coarse aggregate composition according to sieve analysis can be seen in table ii. to avoid strongly absorbing recycled aggregates, affecting the setting of recycled concrete, the coarse aggregates before being mixed were soaked in water in order to absorb it. these aggregates were then let to dry under normal conditions. fig. 2. recycled coarse aggregates. e. the recycled concrete it is difficult to design high-grade recycled concrete. therefore, in this study, the designed recycled concrete has design compressive strength of rn=15mpa, equivalent to grade 150 concrete. the design slump is 7cm. the composition of the mix of 1 batch of 1m 3 of concrete is shown in table iii. table ii. granular composition of the recycled coarse aggregates sieve size quantity of sample per sieve (g) separate amount of residue on the sieve (%) amount accumulated on the sieve (%) the amount accumulated on the sieve according to the standard 40mm 0 0 0 0 20mm 780 7.8 7.8 0-10 10mm 4930 49.3 57.1 40-70 5mm 3740 37.4 94.5 90-100 >5mm 550 table iii. concrete composition mixing compositions (1m 3 ) cement (kg) sand (kg) coarse aggregates (kg) water (kg) 243.8 674.9 1231.1 195.0 cement (kg) sand (m 3 ) coarse aggregates (m 3 ) water (lt) 243.8 0.407 0.861 195.0 in this study, fly ash was added to the concrete composition. to find out the effect of fly ash on the compressive strength of recycled concrete, the aggregate composition of concrete was fixed. the coarse aggregates consisted of natural and recycled aggregates in 50%-50% ratio. the amount of fly ash for each sample was: • sample 1 (cp1): fly ash was not used (0%). • sample 2 (cp2): fly ash with a 5% content was used. the laryee uh5130 (6~300kn) universal hydraulic compressor was used to measure the compressive strength of the concrete samples (figure 3). fig. 3. the laryee uh5130 universal hydraulic compressor. the compressive strength of concrete was tested according to the vietnamese standard no. 3118:1993. cylindrical samples with size of d150×h300 were cast and cured in water before being compressed to determine their compressive strength. the loading speed was set to 0.5kn/s. the compressive strength after curing of the concrete samples was investigated after periods of 7, 14, and 28 days. for obtaining accurate results, the minimum number of test samples was 3 for each type (table iii). engineering, technology & applied science research vol. 11, no. 3, 2021, 7107-7110 7109 www.etasr.com phan & nguyen: the influence of fly ash on the compressive strength of recycled concrete utilizing … table iv. samples used in the compression test no. description 7 days 14 days 28 days 1 cp1: 50% recycled aggregates, 0% fly ash 3 samples 3 samples 9 samples 2 cp1: 50% recycled aggregates, 5% fly ash 3 samples 3 samples 9 samples iii. results and discussion table v shows the critical load values recorded in the compressive test. the compressive strengths were then calculated and the results are shown in table vi. in order to evaluate the effect of fly ash on the compressive strength of recycled concrete, the average value, shown in table vii, will be used. table v. critical load recorded in the compression tests no. critical load (kn) 7 days 14 days 28 dasy (9 samples) cp1 174.77 195.80 212.23 227.96 231.67 177.07 204.46 222.13 220.54 250.05 173.18 211.70 230.61 213.47 259.77 cp2 191.74 229.55 248.28 251.11 259.24 195.27 230.61 249.70 271.08 270.02 195.80 227.25 245.99 239.45 244.22 table vi. calculated compressive strength no. compressive strength (mpa) 7 days 14 days 28 days (9 samples) cp1 9.89 11.08 12.01 12.9 13.11 10.02 11.57 12.57 12.48 14.15 9.80 11.98 13.05 12.08 14.7 cp2 10.85 12.99 14.05 14.21 14.67 11.05 13.05 14.13 15.34 15.28 11.08 12.86 13.92 13.55 13.82 table vii. average compressive strength no. description compressive strength (mpa) 7 days 14 days 28 days (9 samples) cp1 50% recycled aggregates, 0% fly ash 9.90 11.54 13.00 cp2 50% recycled aggregates, 5% fly ash 10.99 12.97 14.33 fig. 4. strength development of the recycled concrete. figure 4 shows the strength development of the experimental concrete samples of cp1 and cp2. the results show that in the first 7 days, the speed of development was very fast and gradually decreased for 7-28 days. at 7 days of age, concrete reaches 76% (cp1) and 77% r28 (cp2) respectively. thus, it can be seen that the intensity development of the two experimental types of aggregates is relatively uniform. fig. 5. comparison of the strength of the two experimental recycled concrete mixes. figure 5 shows the result of the comparison of the compressive strength of the two types of the tested graded concrete samples. it can be easily seen that the strength of recycled concrete using 5% fly ash (cp2) is always higher than the compressive strength of recycled concrete without fly ash (cp1). this increase was 11% at 7 days old, 12% at 14 days old and 10.2% at 28 days old. thus, it can be seen that the use of fly ash increases the strength of recycled concrete by at least 11%. to evaluate the compressive strength of recycled concrete, the compressive strength of recycled concrete using fly ash 5% (cp2) is compared with the compressive strength of conventional concrete by design (rn=15mpa). the result is shown in figure 6. fig. 6. comparison of the strength of recycled concrete using fly ash with the conventional concrete. it can be seen that when using recycled aggregates in a 50% ratio and 5% fly ash, the difference between the compressive strength between the two is not much. according to the experimental results, the compressive strength of recycled engineering, technology & applied science research vol. 11, no. 3, 2021, 7107-7110 7110 www.etasr.com phan & nguyen: the influence of fly ash on the compressive strength of recycled concrete utilizing … concrete using fly ash is decreased by about 7% when compared to conventional concrete, according to the m150 design. this result is quite consistent with the results of [15], in which the authors conclude with: • fly ash content of 5% is the most optimal, giving the best compressive strength results among the experimental recycled concrete mixes. • the difference in compressive strength between conventional and recycled concrete using 5% fly ash is 11%. authors in [12] investigated the use of 30% fly ash as a partial substitute of portland cement for fly ash concrete production. they found that while embedding high amounts of recycled coarse aggregates could lower the resistance to chloride penetration, the carbonation of the concrete was still comparable and design strength similar to that of the control mix could still be achieved. combined with the above analysis results, it can be concluded that it is possible to use fly ash at a higher concentration to ensure the compressive strength of recycled concrete. iv. conclusions in this study, the compressive strength of two recycled concrete aggregates, with and without the utilization of fly ash, was studied. recycled concrete was designed with compressive strength of rn=15mpa, equivalent to m150. the ratio between conventional and recycled coarse aggregates from waste concrete was 50-50. fifteen samples for each recycled concrete aggregate had been casted, 3 were tested at the age of 7 days, 3 at 14 days, and 9 at 28 days. the drawn conclusions from the experimental results are: • the strength development of these two recycled concrete mixes is relatively uniform. during the first 7 days, the speed of strength development was very fast. in the period of 7-28 days, the speed gradually decreases. at 7 days of age, concrete reaches 76% r28 (with recycled concrete using no fly ash) and 77% r28 (with recycled concrete using 5% fly ash). • the strength of recycled concrete using 5% fly ash (cp2) is always higher than that of recycled concrete without the use of fly ash (cp1). this recorded increase was 11% at 7 days, 12% at 14 days, and 10.2% at 28 days. • the compressive strength of recycled concrete using 5% fly ash is about 7% less than the compressive strength of conventional m150 concrete. thus, it is possible to use fly ash at higher concentrations to ensure the compressive strength of the recycled concrete. references [1] m. f. koondhar, b. a. memon, m. oad, f. a. chandio, and s. a. chandio, "water penetration of concrete made with coarse aggregates from demolishing waste," engineering, technology & applied science research, vol. 10, no. 6, pp. 6445–6449, dec. 2020, https://doi.org/ 10.48084/etasr.3891. [2] m. oad, a. h. buller, b. a. memon, n. a. memon, and s. sohu, "flexural stress-strain behavior of rc beams made with partial replacement of coarse aggregates with coarse aggregates from old concrete: part-2: rich mix," engineering, technology & applied science research, vol. 8, no. 5, pp. 3338–3343, oct. 2018, https://doi.org/10.48084/etasr.2129. [3] m. oad, a. h. buller, b. a. memon, and n. a. memon, "impact of long-term loading on reinforced concrete beams made with partial replacement of coarse aggregates with recycled aggregates from old concrete," engineering, technology & applied science research, vol. 9, no. 1, pp. 3818–3821, feb. 2019, https://doi.org/10.48084/etasr.2498. [4] c. s. poon, s. c. kou, and l. lam, "use of recycled aggregates in molded concrete bricks and blocks," construction and building materials, vol. 16, no. 5, pp. 281–289, jul. 2002, https://doi.org/10.1016/ s0950-0618(02)00019-3. [5] quality protocol: aggregates from inert waste. northern ireland environment agency, 2013. [6] m. soomro, "use of selective recycled materials in civil engineering construction," 2013, pp. 635–684, https://doi.org/10.1142/97898144 49175_0010. [7] k. obla, h. kim, and c. lobo, "crushed returned concrete as aggregates for new concrete," rmc research & education foundation, 01649378, sep. 2007. [8] erläuterungen zu den normen din en 206-1, din 1045-2, din 1045-3, din 1045-4 und din en 12620: dafstb-heft 526, 2nd ed. berlin, germany: beuth verlag, 2011. [9] j. ahmad bhat, "effect of strength of parent concrete on the mechanical properties of recycled aggregate concrete," materials today: proceedings, vol. 42, pp. 1462–1469, jan. 2021, https://doi.org/10.1016/ j.matpr.2021.01.310. [10] j. li, j. zhang, s. ni, l. liu, and l. f. walubita, "mechanical performance and environmental impacts of self-compacting concrete with recycled demolished concrete blocks," journal of cleaner production, vol. 293, apr. 2021, art. no. 126129, https://doi.org/ 10.1016/j.jclepro.2021.126129. [11] c. sun, q. chen, j. xiao, and w. liu, "utilization of waste concrete recycling materials in self-compacting concrete," resources, conservation and recycling, vol. 161, oct. 2020, art. no. 104930, https://doi.org/10.1016/j.resconrec.2020.104930. [12] m. limbachiya, m. s. meddah, and y. ouchagour, "use of recycled concrete aggregate in fly-ash concrete," construction and building materials, vol. 27, no. 1, pp. 439–449, feb. 2012, https://doi.org/ 10.1016/j.conbuildmat.2011.07.023. [13] t. c. hansen, "recycled concrete aggregate and fly ash produce concrete without portland cement," cement and concrete research, vol. 20, no. 3, pp. 355–356, may 1990, https://doi.org/10.1016/00088846(90)90024-r. [14] s. c. kou, c. s. poon, and d. chan, "influence of fly ash as cement replacement on the properties of recycled aggregate concrete," journal of materials in civil engineering, vol. 19, no. 9, pp. 709–717, sep. 2007, https://doi.org/10.1061/(asce)0899-1561(2007)19:9(709). [15] s. a. chandio, b. a. memon, m. oad, f. a. chandio, and m. u. memon, "effect of fly ash on the compressive strength of green concrete," engineering, technology & applied science research, vol. 10, no. 3, pp. 5728–5731, jun. 2020, https://doi.org/10.48084/etasr.3499. engineering, technology & applied science research vol. 9, no. 1, 2019, 3796-3802 3796 www.etasr.com xu & yamanari: performance of steel frame with linkage system under earthquake excitation performance of steel frame with linkage system under earthquake excitation guang xu department of advanced industrial science kumamoto university kumamoto, japan xuguang1991@hotmail.com minoru yamanari faculty of advanced science and technology kumamoto university kumamoto, japan yamanari@kumamoto-u.ac.jp abstract—authors have already proposed a linkage system with rotational friction dampers that can be expected to dissipate seismic energy rather than the main frame. in this paper, the relationship between the rotational angle of the linkage system and inter-story drift angle of a structure was investigated. consequently, a three-bay twelve-story steel frame with linkage system was analyzed by a numerical simulation program based on a theory of non-linear dynamic analysis. the distribution of slipping moment of friction damper along with the height of the main structure was discussed. meanwhile, optimal slipping moment range was suggested according to analysis results. keywords-steel frame; linkage system; friction damper i. introduction there could be a big increase in the number of tremendous earthquakes around the world in the following years [1]. so far, it is difficult to predict where and when these earthquakes will occur. therefore, in order to protect people and properties, a number of methods to decrease structure vibration under earthquake excitation have been proposed. these methods/control systems could be divided into four patterns: passive, active, semi-active and hybrid [2]. a passive control system works without requiring an external power source, which is necessary for active and semi-active control system. generally, passive control system consists of one or more equipment designed to modify the structural properties like ductility and stiffness, causing a reduction in the structure seismic behavior. friction damper is a typical representative of passive control systems, which is used to dissipate the seismic input energy via solid friction. this type of device was pioneered in 1982 [3]. it is similar to automobile brakes, which use the mechanism of solid friction to dissipate seismic energy reducing the motion of the structure. commonly, the friction damper is made of a series of special steel plates that are bolted by a high strength screw. suitable friction pads can be clamped between these steel plates, in order to create frictional performance. because the clamping force is controlled by a screw, it is very convenient to change the frictional force to satisfy diffident purposes. however, a lower limit value of frictional force is also necessary, as it is not expected for friction damper to slip during a severe wind or earthquake. when the force or moment developing in the friction damper reaches a predetermined value, it will start slipping and keeping a steady status. that is a remarkable feature differing from other dampers, liking viscous damper, oil damper and tmd. according to the connection with the main structure, friction dampers can be divided into four types: pall friction damper, sumitomo friction damper, gap-screw connection damper, and rotational friction damper [4]. pall friction damper has two friction joints on the upper and down arm-brace, respectively. four cross braces are used to connect it with the main structure, which are pin connected at both ends. it has been widely used to strengthen the seismic behavior of many structures around the world [2, 5-10]. it is easily found that the pall friction damper has only translational movement at the friction joints when it starts slipping [11]. differing from it, in 2000 the damptech company presented a rotational friction damper in which the movements are rotational [12]. a common point of all dumpers is that they will dissipate seismic energy to protect structures from damage or collapse. in order to extend the dissipation energy to a maximum value, some researches about optimal friction force or moment have been done [2, 1215]. however, the optimal value of the friction damper in each story is the same with the one of the first story, but, seismic shear force gradually decreases along with the height of the structure. it means that if a same optimal value was used for every damper of each story, it will not get the best seismic performance of the structure because the top dampers will not slip or slip just a little bit. for this reason, the distribution of the optimal value along the height of the structure will be discussed in this paper. on the other hand, the capacity of energy dissipation within a friction damper almost depends on slip displacement and slip force. for the same slip force, if the friction damper slipped on a maximum displacement at each step, the amount of dissipated energy will be increased. hence, the objectives of this paper are: 1) to propose a linkage system, which will enlarge the slip displacement of friction damper. 2) to discuss the distribution of slipping moment in dampers along the structure height. 3) to find the optimal value for which the best seismic performance of the structure occurs. ii. linkage system as mentioned above, the capacity of energy dissipation in the friction damper almost depends on the slip displacement corresponding author: g. xu engineering, technology & applied science research vol. 9, no. 1, 2019, 3796-3802 3797 www.etasr.com xu & yamanari: performance of steel frame with linkage system under earthquake excitation and slip force. the proposed mechanism of displacement amplification is shown in figure 1. it can be regarded as a combination of pall friction damper and rotational friction damper. the friction joints, which are placed in the center of the side of the quadrangle in pall friction damper, are removed to its corner. the movement in the linkage system is rotational not translational as in the pall friction damper. when a tension or compression acts on the corner of the quadrangle, it will be shaped as a parallelogram, and the relative rotational angle can be obtained from the four corner joints. that is the slip displacement of the rotational friction damper. the connections of the other elements to the main structure are the same as in the pall friction damper. in the linkage system, cross brace is pinned to the main structure and the other end of it is directly connected to the damper. because the arm braces rotate on the contrary direction, there will be no moment generated in the cross braces like in the ones in pall friction damper. therefore, comparing to pall friction damper, it has a simplified construction in which the number of connection bolts, slip bolts and curve slots has been reduced. furthermore, instead of translational displacement, rotational displacement is used for energy dissipation. rotational friction damper arm brace cross brace pin connection force tension force bending moment h l r a b fig. 1. the conception of linkage system a b c a bo φ1 φ2 a’ b’o’ c+δ δα αφ1-β φ2-α β fig. 2. geometrical relationshiop iii. geometrical relationship with main structure to identify the mechanism of displacement amplification of the linkage system, the relationship between the rotational angle in the linkage system and the drift angle in the main structure needs to be formulated. in this section, it is assumed that deformation in elements will not be considered. the computation schematic for the half of linkage system is shown in figure 2, where a and b are the span and height of the linkage system, c is the length of the diagonal line, φ1 and φ2 are the inner angles of triangle aob, α and β are the rotational angles, δ is the increment of diagonal line. using cosine law, the relationship of a and δ may be written as: 2 2 2 1 ( ) cos( ) 2 ( ) a c b a c           (1) using addition theorem ,(1) could be written as: 2 2 2 2 ( )cos sin ( )a c bd e a c        (2) where, d and e are expressed as: d = cosϕ 1 = a2 + c2 − b2 2ac (3) e = sinϕ 1 = 1− d2 (4) taylor series expansion is used to simplify the rotational angle α: 2 2 2 21 2 2 ( )( )a c bd e d a c         (5) according to (5), α expressed by δ could be earned as: 2 1             ( ) ( )( )ace ae acd ad xce ecd d acd ad (6) in which, x1 is expressed as: 2 2 2 2 1 2 2 2( )x a b c acd c ad         (7) using the same method, the other rotational angle β could be expressed as: 2 2 ( ) ( )( )bcg bg bcf bf xcg gcf f bcf bf        (8) where, x2 is: 2 2 2 2 2 2 2 2( )x a b c bcf c bf          (9) then, the relative rotational angle of damper could be written as:     (10) using (1)-(10), the relationship between the damper relative rotational angle and the increment of quadrangle diagonal line could be obtained. in addition, the relationship between the drift angle of main structure and the increment of diagonal line of quadrangle is necessary. it is assumed that main structure deforms as shown in figure 3, where h is the height of main structure, l is the length of the span, and r is the drift angle. therefore, the increment of diagonal line of quadrangle could be expressed as: 2 2 2 2( )l hr h l       (11) using (10)-(11), the relationship between the damper’s relative rotational angle and the main structure’s drift angle can be obtained. to examine the accuracy of equations, numerical analysis is necessary. program opensees based on the finite element method is used to simulate the numerical example. the model shown in figure 1 is used for the analysis, where the lengths of arm braces a and b are 1.4m and 0.7m respectively, and height and span of structure are 3.5m and 7m respectively. the beam is assumed infinitely rigid and the columns are fixed at their bases. the steel columns are wide-flange sections with the moment of inertia of 3.4×10-5m4. the sectional area of the brace is 4×10-3m2 and the slipping moment of damper is set as engineering, technology & applied science research vol. 9, no. 1, 2019, 3796-3802 3798 www.etasr.com xu & yamanari: performance of steel frame with linkage system under earthquake excitation 20nm. the dead load is assumed as 392×103n and the critical damper ratio is 5%. newmark-β (β=0.25) method is adopted for the numerical integration. the comparison between the approximate value obtained by the equations and the geometrical exact value obtained by opensees is shown in figure 4. the results indicated that the accuracy of equations is very high in normal range (i.e. r≤0.06). r h l hr fig. 3. structure deformation 0 0.06 0.12 0 0.4 0.8 1.2 1.6 exact approximated ri ft , r ( m m ) relative rotational angle, φ (rad) fig. 4. accuracy of equations iv. finite element analysis a. finite element modeling for discussing the distribution of friction force in the damper along the height of main structure, two models are created by sap2000, as shown in figure 5. their difference will be introduced below. both are the models of a 12-story two-dimensional structure with 7m span lengths and a height of 3.5m, with 3 openings. supports are assumed to be fixed and the soil structure interaction effects are neglected. dead and live loads are concentrated mass at the beam-to-column node. the sections of the main structure, shown in table i, are made from sn490 (based on jis standard). the plastic behavior of elements in main structure is considered by simple hinges based on tables 9-6 in asce 41-13 [16], which are assigned to both ends of the elements. the cross braces and arm members should be considered strong enough to remain elastic during earthquakes. these elements are selected from circular cross section cables and beam element, respectively. meanwhile, the ratio of initial stiffness of the linkage system to one of the main structures is set as 1.0. in order to modify friction damper in linkage system, plastic-wen element is used in sap2000. the friction behavior is considered in r3 direction and the other directions are fixed. a yielding exponent of 10 indicating a sharp transition from linear to plastic phase and a post yield stiffness ratio of 0.0001 indicating a rectangular hysteresis loop are used to simulate the friction behavior of dampers [14]. the details of the damper model are shown in figure 6. in addition, p-δ effects are included to account for the geometrical nonlinearity effects and out-of-plane distortion of all elements is not considered. 4 2 m 21m cross brace rotational friction damper pin connection arm brace l=7m h = 3 .5 ma=1.4m b = 0 .7 m :mass=20,000 (kg) fig. 5. finite element model table i. the section used in main structure story no. column beam 10-12 500✕500✕19 450✕250✕12✕28 7-9 500✕500✕22 500✕300✕16✕25 4-6 500✕500✕25 550✕300✕16✕28 1-3 500✕500✕28 600✕250✕16✕32 ms -ms 0 φ k 0.0001k bar element beam element b ea m e le m en t plastic-wen element fig. 6. damper model and hysteretic curve b. analysis conditions and methods in this analysis, the damping of the model is considered as a rayleigh damping. first-order and second-order damping coefficients are both 2%. newmark-β method with β=0.25, α=0.5 is used to analyze the model. the output time step size is set at 0.001s and seismic duration is 40s. four observed seismic waves, shown in table ii, are used in nonlinear time history analysis. in order to observe the seismic behavior of the structure equipped with a linkage system under a tremendous earthquake, the peak ground velocity (pgv) of each wave is scaled to 1.0m/s. the input direction of seismic waves is horizontal. for determining the slipping moment of friction damper, slipping moment ratio as is defined as: 1 2 1 si sis si si m ma m m  (12) where msi is the slipping moment of friction damper in the i-th story, msi1 is a moment, which is generated in friction damper of the i-th story when a group of forces (base shear force=0.2g) according to ai distribution [17] were imposed on the structure and friction damper did not slip. in the same way, when the forces equating to the held horizontal yield strength of structure engineering, technology & applied science research vol. 9, no. 1, 2019, 3796-3802 3799 www.etasr.com xu & yamanari: performance of steel frame with linkage system under earthquake excitation [17] were imposed on the structure, the generated moment in ith story is determined as msi2. in this analysis, msi1 is set as the lower limit value of slipping moment in friction dampers and msi2 is set as the upper limit value. hence, the friction dampers will not slip under a slight earthquake and start to slip before the ultimate limit state of main structure. by changing as from 0.0 to 1.0, msi basing on ai distribution could be obtained by (12). from [18] we can see that a 5000kn capacity of damper has been designed and experimented successfully. by comparison with msi in this paper, the slipping moment is much smaller than that and can be considered to be achieved by controlling the axial force of bolts. however, it is worth noting that the above-mentioned distribution of slipping moment is only for model-a. for model-b, the slipping moment of damper in each story is the same as that of the damper in the 12th story so that the damper of each story can easily slip under earthquake. c. model analysis main and damped frame periods are shown in table iii. the periods of the damped frame were obtained by rigid joints instead of damper connection (i.e., plastic-wen element). table ii. seismic waves earthquake pgv (m/s) pga (m/s2) time (s) elcentro ns 1.0 10.21 40 tohoku ew 7.34 hachinohe ew 5.10 kumamoto ew 8.02 table iii. structure periods periods damped structure (s) main structure (s) 1st 1.06 1.56 2nd 0.35 0.55 d. comparison of the two models in order to observe the seismic behavior of two models that used different distribution of slipping moment, drift, bending moment, shear force and energy dissipation of friction dampers are used as reference indexes for a fixed value of as (as=0.0). drifts of the two models under the four seismic waves are shown in figure 7. it can be observed that each story drifts in model-a are smaller than the ones of each story in model-b under any seismic wave. however, according to various seismic waves, the drift reduction ratio is different. in the case of el centro ns, the maximum and minimum drift reduction ratios are 37% (5th story) and 4% (12th story), respectively. in another case of kumamoto ew, maximum and minimum drift reduction ratios dwindle to 17% (1st story) and 2% (5th story), respectively. despite all this, it still can be considered that for drift reduction, the distribution of slipping moment in model-a is much more efficient than that in model-b. a comparison of the bending moment of the beam element in the two models is shown in figure 8. the beam bending moment of model-a is smaller than that of model-b. it means the importance of the distribution of slipping moment. in the four cases, the bending moment reduction of the sub-structure is relatively more obvious than that of the upper structure. (a) 0 0.005 0.01 0.015 drift (rad) 2 4 6 8 10 12 s to ry n o . model-a model-b (a) (b) 0 0.005 0.01 0.015 drift (rad) 2 4 6 8 10 12 s to ry n o . (b) (c) 0 0.005 0.01 0.015 drift (rad) 2 4 6 8 10 12 s to ry n o . (c) (d) 0 0.005 0.01 0.015 drift (rad) 2 4 6 8 10 12 s to ry n o . (d) fig. 7. drift of each story in the two models: (a) elcentrons, (b) hachinoheew, (c) kumamotoew, (d) tohokuew. because shear force of the sub-structure is larger than that of the upper structure, the bending moment of friction damper installed in the sub-structure is easy to reach the predetermined value, and then the dampers can dissipate more seismic energy. it also means that energy dissipation of friction damper installed in the sub-structure is more than that in the upper structure. although in the case of kumamoto ew, a part of bending moment in model-a is almost the same with that in model-b, as a whole, the distribution of slipping moment in model-a is more efficient. the shear force of each story in the two models is shown in figure 9. the reduction of shear force in model-a exhibits the superiority of model-a. the maximum reduction ratios in four cases are 37% (elcentro ns, 5th story), 22% (hachinohe ew, 2nd story), 18% (kumamoto ew, 10th story), 26% (tohoku ew, 9th story), respectively. to compare the capacity of energy dissipation of friction damper in the two models, the percentage of total input energy dissipated by the engineering, technology & applied science research vol. 9, no. 1, 2019, 3796-3802 3800 www.etasr.com xu & yamanari: performance of steel frame with linkage system under earthquake excitation dampers is shown in figure 10 as we see the dissipated energy by the dampers in both models has exceeded the 50% of the total input energy. this means that the friction dampers have a large potential in energy dissipation. the dissipated energy in model-a is more than that in model-b. in the model-a, the maximum value is about 67% in the case of hachinohe ew. from figures 7-10 can be concluded that the distribution of the slipping moment in dampers along the height of model-a is more efficient. (a) 0 500 1000 1500 2000 2500 bending moment (knm) 2 4 6 8 10 12 s to ry n o . model-a model-b (a) (b) 0 500 1000 1500 2000 2500 bending moment (kknm) 2 4 6 8 10 12 s to ry n o. (b) (c) 0 500 1000 1500 2000 2500 bending moment (knm) 2 4 6 8 10 12 s to ry n o. (c) (d) 0 500 1000 1500 2000 2500 bending moment (knm) 2 4 6 8 10 12 s to ry n o. (d) fig. 8. bending moment of beam in each story: (a) elcentrons, (b) hachinoheew, (c) kumamotoew, (d) tohokuew. e. optimal value of slipping moment the optimal value of the slipping moment in model-a will be discussed in this section. the normalized response values of the structure should be studied as a function of the slipping moment ratio (as). the normalized drift is described by (13) in which rias=j is the drift in i-th story when as=j and r i as=0 is the drift in i-th story when as=0. 0 0 0 1 step 0 1 1 12 step 1, , , . , ,s s iai jratio ja rr j ir          (13) (a) 0 1000 2000 3000 4000 shear force (kn) 2 4 6 8 10 12 s to ry n o. model-a model-b (a) (b) 0 1000 2000 3000 4000 shear force (kn) 2 4 6 8 10 12 s to ry n o. (b) (c) 0 1000 2000 3000 4000 shear force (kn) 2 4 6 8 10 12 s to ry n o. (c) (d) 0 1000 2000 3000 4000 shear force (kn) 2 4 6 8 10 12 s to ry n o. (d) fig. 9. shear force of each story: (a) elcentrons, (b) hachinoheew, (c) kumamotoew, (d) tohokuew. elce ntro ns hac hino hee w kum amo toew toh oku ew 50% 55% 60% 65% 70% p er ce n ta ge ( % ) model-a model-b fig. 10. percentage of total input energy dissipated by damper similarly, the normalized bending moment of beam is presented by: engineering, technology & applied science research vol. 9, no. 1, 2019, 3796-3802 3801 www.etasr.com xu & yamanari: performance of steel frame with linkage system under earthquake excitation 0 0 1 step 0 1 1 2 step 1, , , . , ,s s ia ji jratio ia bmbm j ibm          (14) from figure 11, the drift of each story expresses a different variation trend with the increasing of as. in the four cases, the drift of the sub-structure (white marking) increased with the increasing of as. however, in the cases of elcentro ns and kumamoto ew, the drift of the upper structure (black marking) nearly kept constant. in the case of hachinohe ew, it kept decreasing. in the case of tohoku ew, it firstly decreased and then increased for as within the range from 0.0 to 0.6. (a) 0 0.2 0.4 0.6 0.8 1 slipping moment ratio 0.8 0.9 1 1.1 1.2 n o rm al iz ed d ri ft (a) (b) 0 0.2 0.4 0.6 0.8 1 slipping moment ratio 0.8 0.9 1 1.1 1.2 n o rm al iz ed d ri ft (b) (c) 0 0.2 0.4 0.6 0.8 1 slipping moment ratio 0.8 0.9 1 1.1 1.2 n o rm al iz ed d ri ft (c) (d) 0 0.2 0.4 0.6 0.8 1 slipping moment ratio 0.8 0.9 1 1.1 1.2 n o rm al iz ed d ri ft (d) fig. 11. normalized drift of each story in model-a: (a) elcentrons, (b) hachinoheew, (c) kumamotoew, (d) tohokuew. the normalized beam bending moment shown in figure 12 has a similar trend with the drift. however, in the case of tohoku ew, the minimum bending moment of the upper structure can be obtained when as=0.4. comparing the two figures, it can be observed that for the dampers installed in the sub-structure, the smaller the as the better. for those in the upper structure, the range of as from 0.0 to 0.4 is suggested. generally, the percentage of the total input energy dissipated by the dampers is an important index to determine an optimal value of slipping moment (figure 13). as shown in figure 13, more than 60% of total input energy has been dissipated by friction dampers, which is a very large value and obviously not suitable. the peak of the dissipated energy (black marking) is obtained for as within the range from 0.0 to 0.4. sometimes, the dissipated energy does not necessarily indicate the best performance of the structure, as it is accompanied by increase in the total seismic energy [12]. (a) 0 0.2 0.4 0.6 0.8 1 slipping moment ratio 0.9 0.95 1 1.05 1.1 1.15 1.2 n o rm al iz ed b en d in g m o m en t (a) (b) 0 0.2 0.4 0.6 0.8 1 slipping moment ratio 0.9 0.95 1 1.05 1.1 1.15 1.2 n o rm al iz ed b en d in g m o m en t (b) (c) 0 0.2 0.4 0.6 0.8 1 slipping moment ratio 0.9 0.95 1 1.05 1.1 1.15 1.2 n o rm al iz ed b en d in g m o m en t (c) (d) 0 0.2 0.4 0.6 0.8 1 slipping moment ratio 0.9 0.95 1 1.05 1.1 1.15 1.2 n o rm al iz ed b en d in g m o m en t (d) fig. 12. normalized bending moment of each story in model-a: (a) elcentrons, (b) hachinoheew, (c) kumamotoew, (d) tohokuew. engineering, technology & applied science research vol. 9, no. 1, 2019, 3796-3802 3802 www.etasr.com xu & yamanari: performance of steel frame with linkage system under earthquake excitation fig. 13. the effect of slipping moment ratio on energy dissipation v. conclusions basing on the feature of friction damper, (i.e., displacement dependence) a concept of linkage system that could be considered as a combination of the pall friction damper and the rotational friction damper has been presented. it can improve the capacity of energy dissipation of friction damper by increasing the rotational angle. the relationship between rotational angle and the main structure drift has been derived as a formula by trigonometric functions and the high accuracy of the formula has been verified by numerical analysis. two models having different distribution of slipping moment along the structure height have been analyzed and compared. analysis results demonstrated that a properly distribution of the slipping moment is necessary and the model-a is more efficient than model-b. in addition, the optimal value of slipping moment, (i.e. as) in model-a has been discussed. time history analysis results showed that for the friction damper installed in the sub-structure, the smaller the value of as the better and for the upper ones, a range of as from 0.0 to 0.4 is suggested. further research is needed to verify the above conclusions. in future studies, stiffness of linkage system, intensity of seismic waves, distribution of linkage system, etc. should be factored in and the construction of linkage system should be discussed and tested by a series of experimental and numerical analyses. references [1] united states geological survey, usgs real-time earthquake , available at https://www.usgs.gov/products/data-and-tools/real-timedata/earthquakes [2] s. m. zahraei, a. moradi, m. moradi, “using pall friction dampers for seismic retrofit of a 4-story steel building in iran”, topics in dynamics of civil structures, vol. 4, pp. 101-107, 2013 [3] a. s. pall, c. marsh, “response of friction damped braced frames”, journal of structural engineering, vol. 108, no. 9, pp. 1313-1323, 1982 [4] v. ruiz, k. walsh, m. m. abdullah, investigating the energy dissipating properties of passive friction devices, florida state university, &tokyo institute of technology, tokyo, japan, 2005 [5] r. chandra, m. masand, s. k. nandi, c. p. tripathi, r. pall, a. pall, “friction-dampers for seismic control of la gardenia towers south city, gurgaon, india”, 12th world conference on earthquake engineering, new zealand, january 30-february 4, 2000 [6] t. h. hale, r. pall, “seismic upgrade of the freeport water reservoir, sacramento, california”, 12th world conference on earthquake engineering, new zealand, january 30-february 4, 2000 [7] a. s. pall, r. pall, “friction-damper used for seismic control of new and existing buildings in canada”, atc-17-1 seminar on seismic isolation, passive energy dissipation and active control, san francisco, usa, march 11-12, 1992 [8] b. wu, h. li, l. lin, m. shan, “seismic retrofit of a city hall in northeast china with frictional energy dissipators”, journal of building structures, vol. 19, no. 5, pp. 28-36, 1998 (in chinese) [9] a. pall, s. vezina, p. proulx, r. pall, “friction‐dampers for seismic control of canadian space agency headquarters”, earthquake spectra, vol. 9, no. 3, pp. 547-557, 1993 [10] t. h. hale, r. t. pall, “seismic upgrade of the freeport water reservoir, sacramento, california”, 12th world conference on earthquake engineering, new zealand, january 30-february 4, 2000 [11] d. shao, a. pall, b. soli, “friction dampers for seismic upgrade of a 14-story patient tower with a 36-foot tall soft-story”, 8th us national conference on earthquake engineering, san francisco, usa, april 18-22, 2006 [12] h. i. mualla, b. borislav, “performance of steel frames with a new friction damper device under earthquake excitation”, engineering structure, vol. 24, pp. 365-371, 2002 [13] k. jafarzadeh, m. l. yaghin, r sabetahd, “evaluation pf pall friction damper performance in near-fault earthquakes by using of nonlinear history analysis”, world applied sciences journal, vol. 20, no. 2, pp. 264-270, 2012 [14] g. s. adithya, h. narendra, “performance evaluation of friction dampers under seismic loads”, international journal of research in engineering and technology, vol. 5, no. 14, pp. 10-15, 2016 [15] p. hosseini sarjou, n. shabakhty, “effect of the improved pall friction damper on the seismic response of steel frames”, engineering technology & applied science research, vol. 7, no. 4, pp. 1833-1837, 2017 [16] american society of civil engineers, seismic evaluation and upgrade of existing buildings, 2014 [17] architectural steel structure theory and design, kajima institute publishing, 2007 (in japanese) [18] i. h. mualla, e. d. jakupsson, l. o. nielsen, “structure behavior of 5000kn damper”, 14th european conference on earthquake engineering, republic of macedonia, august 30-september 3, 2010 microsoft word 31-2309_s engineering, technology & applied science research vol. 8, no. 5, 2018, 3470-3474 3470 www.etasr.com rao et al.: study of four element microstrip antenna array using patch type electromagnetic band … study of four element microstrip antenna array using patch type electromagnetic band gap structure k. prahlada rao department of pg studies and research in applied electronics gulbarga university gulbarga, india p. v. hunagund department of pg studies and research in applied electronics gulbarga university gulbarga, india r. m. vani university science instrumentation centre gulbarga university gulbarga, india abstract—this paper describes an enhancement in the performance of four element microstrip antenna array. the conventional microstrip antenna array is producing gain equal to 6.81db. with the introduction of u shape patch type electromagnetic band gap structure, the proposed microstrip antenna array is producing an improved gain of 20.33db. it is producing reduced mutual coupling of -31.44, -36.41 and 31.62db respectively. the radiation characteristics of the proposed microstrip antenna array are improved with appreciable decrease in back lobe radiation and increase in forward power. it is resonating at single band at 5.53ghz, producing an overall bandwidth of 109.45%, against 4.89% of conventional microstrip antenna array. microstrip antenna arrays are designed using mentor graphics ie3d software and measured results are obtained using vector network analyzer. keywords-corporate feeding; gain; microstrip antenna array; mutual coupling; resonant frequency i. introduction antennas play an important role in proper working and development of various communication systems. immense research towards the development of novel, sophisticated and efficient types of antennas is on the rise. microstrip antennas are made of radiating patch or conductor and ground plane placed on either side of substrate. microstrip antennas can be basically seen as sudden discontinuities which represent changes in their geometry and shape. these discontinuities are responsible for changes in the current, electric and magnetic field distributions. the most important inherent characteristics and serious limitations of microstrip antennas and arrays are narrow bandwidth and high mutual coupling values. the thickness of the radiating patch plays a crucial part when conductor losses are being calculated [1-7]. applications involving microstrip antennas and arrays have driven research towards enhanced antenna bandwidth. bandwidth of microstrip antennas and arrays can be enhanced by various methods like stacking, metamaterials, decreasing relative permittivity of the dielectric and defective ground structures. nowadays, electromagnetic band gap (ebg) structures are being employed on a large scale to improve the efficiency of microstrip antennas. these structures consist of periodically placed unit cells. one of the notable features of ebg structures is that the dimensions of the unit cell are lesser than that of the radiating patch [8-16]. ii. conventional microstrip antenna array conventional microstrip antenna array (cmaa) designed at 6ghz consists of four identical rectangular radiating patches. the substrate employed to design the antenna arrays is fr-4 glass epoxy which has a dielectric constant of 4.2 and loss tangent of 0.0245. the height of the substrate is 1.6mm. each of the radiating patches has dimensions of 15.73mm×11.76mm. the quarter wave transformer has dimensions of 6.47mm×0.47mm. the feeding element has dimensions of 6.52mm×3.05mm. cmaa is fed by corporate feeding technique. the distance between the adjacent radiating elements of cmaa is λ/4, where λ is the wavelength calculated at the design frequency of 6ghz. the schematic of cmaa is shown in figure 1 and its dimensions are shown in table i. fig. 1. schematic of cmaa. the four radiating patches of cmaa are arranged in such a way that the distance between the adjacent radiating patches is the same with that of figure 1. this setup is arranged to measure mutual coupling between the radiating elements. moreover, the elements of cmaa are excited independently with the same amount of power. the s-parameters s21, s31 and s41 designate the mutual coupling coefficients. in the sparameters the first digit designates the output port and the second digit designates the input port. figure 2 depicts the schematic of arrangement of elements of cmaa to measure the mutual coupling. engineering, technology & applied science research vol. 8, no. 5, 2018, 3470-3474 3471 www.etasr.com rao et al.: study of four element microstrip antenna array using patch type electromagnetic band … table i. cmaa parameter values parameter value(mm) length of the patch (lp) 15.73 width of the patch (wp) 11.76 length of the quarter wave transformer (lt) 6.47 width of the quarter wave transformer (wt) 0.47 length of the 50ω line (l1) 6.52 width of the 50ω line (w1) 3.05 length of the coupler 3.05 width of the coupler 3.05 length of the 70ω line (l2) 6.54 width of the 70ω line (w2) 1.62 length of the 100ω line (l3) 6.56 width of the 100ω line (w3) 0.70 length of the feed line (lf) 6.52 width of the feed line (wf) 3.05 fig. 2. schematic of arrangement of elements of cmaa to measure mutual coupling. iii. design of proposed microstrip antenna array the unit cell of the ebg structure is depicted in figure 3. the unit cell of the ebg structure employed consists of a ushape patch type. the dimensions of the unit cell are p=5mm and q=4mm respectively. the ebg structure employed to enhance the performance of cmaa is depicted in figure 4. fig. 3. schematic of unit cell of ebg structure. fig. 4. schematic of ebg structure. it consists of a matrix of 2 columns and 3 rows of u-shape patch type unit cells. the unit cells of the ebg structure are repeated after every 1mm along the x-axis and y-axis. the periodicity is represented by x. the proposed microstrip antenna array (pmaa) is designed by loading the ebg structure shown in figure 4 on the surface and in between the radiating patches of cmaa. the schematic of pmaa is shown in figure 5. in order to measure the change in the values of mutual coupling coefficients after the introduction of u-shape patch type ebg structure, the ebg structure depicted in figure 4 is kept on the surface of the schematic shown in figure 2. the schematic employed to determine the mutual coupling in the presence of u-shape ebg structure is depicted in figure 6. fig. 5. schematic of pmaa. fig. 6. schematic of arrangement of elements of pmaa for the measurement of mutual coupling. iv. fabricated microstrip antenna arrays figures 7-10 show photographs of the fabricated antenna arrays. fig. 7. photograph of cmaa. fig. 8. photograph of cmaa elements arrangement for mutual coupling measurement. (a) (b) fig. 9. photograph of pmaa, (a) front view, (b) back view. (a) (b) fig. 10. photograph of pmaa elements arrangement for mutual coupling measurement. (a) front view, (b) back view. engineering, technology & applied science research vol. 8, no. 5, 2018, 3470-3474 3472 www.etasr.com rao et al.: study of four element microstrip antenna array using patch type electromagnetic band … v. measured results the performances of cmaa and pmaa are judged in terms of bandwidth, return loss, resonant frequency, mutual coupling, gain, forward power, back lobe radiation, front to back ratio (fbr) and virtual size reduction. figures 11, 12 and 13 depict the graphs of return loss and mutual coupling versus frequency of cmaa. fig. 11. graph of return loss and mutual coupling–s21 versus cmaa frequency. fig. 12. graph of return loss and mutual coupling–s31 versus cmaa frequency. fig. 13. graph of return loss and mutual coupling–s41 versus cmaa frequency. figures 11, 12 and 13 indicate that cmaa is resonating at 5.53ghz and producing a return loss of -21.06db. the mutual coupling values measured at the resonant frequency of 5.53ghz of cmaa are equal to s21=-16.95db, s31=-14.22db and s41=-17.30db respectively. these values of mutual coupling plots are considered to be very high and need to be decreased. another result that can be extracted from figures 11-13 is that the graphs of return loss and mutual coupling are overlapping. this implies there is an interference level between the transmitting antenna 1 and the receiving antennas 2-4. parameter bandwidth can be determined from the return loss graph in figures 11-13. bandwidth is calculated by subtracting the lower frequency from the upper frequency where the return loss is crossing the -10db value. hence the bandwidth of cmaa is equal to 273mhz. bandwidth can be expressed in terms of percentage as: bandwidth %� = ����������������� ��������� × 100 (1) hence substituting the relevant parameters in (1), the bandwidth (%) of cmaa is equal to 4.89%. figures 14, 15 and 16 depict the graphs of return loss and mutual coupling versus frequency of pmaa. figures 14-16 depict that pmaa is resonating at the same fundamental frequency with cmaa i.e. at 5.53ghz. additionally, pmaa is resonating at single frequency. the total bandwidth produced by pmaa is very high and equal to 6.05ghz. in terms of bandwidth (%), it is equal to 109.45%. therefore, in terms of bandwidth (%) pmaa is a better candidate than cmaa, because pmaa is producing enhanced bandwidth (%) compared to cmaa, which is producing narrow bandwidth of 4.89%. fig. 14. plot of return loss and mutual coupling–s21 versus pmaa frequency fig. 15. plot of return loss and mutual coupling–s31 versus pmaa frequency. information about the mutual coupling coefficients of pmaa are obtained from figures 14, 15 and 16. at resonant 1 2 3 4 5 6 7 -30 -25 -20 -15 -10 -5 0 5 r e tu rn l o s s s 1 1 ( d b ) m u tu a l c o u p li n g s 2 1 ( d b ) frequency (ghz) return loss mutual coupling 1 2 3 4 5 6 7 -30 -25 -20 -15 -10 -5 0 5 r e tu rn l o s s s 1 1 ( d b ) m u tu a l c o u p li n g s 3 1 ( d b ) frequency (ghz) return loss mutual coupling 1 2 3 4 5 6 7 -40 -35 -30 -25 -20 -15 -10 -5 0 5 r e tu rn l o s s s 1 1 ( d b ) m u tu a l c o u p li n g s 4 1 ( d b ) frequency (ghz) return loss mutual coupling 1 2 3 4 5 6 7 8 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 r e tu rn l o s s s 1 1 ( d b ) m u tu a l c o u p li n g s 2 1 ( d b ) frequency (ghz) return loss mutual coupling 1 2 3 4 5 6 7 8 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 r e tu rn l o s s s 1 1 ( d b ) m u tu a l c o u p li n g s 3 1 ( d b ) frequency (ghz) return loss mutual coupling engineering, technology & applied science research vol. 8, no. 5, 2018, 3470-3474 3473 www.etasr.com rao et al.: study of four element microstrip antenna array using patch type electromagnetic band … frequency of 5.53ghz, the mutual coupling values of pmaa are equal to s21=-31.44db, s31=-36.41db and s41=-31.62db respectively. thus in the presence of u-shape patch type ebg structure, the values of mutual coupling coefficients are decreased. moreover, the plots of mutual coupling and return loss are no more crossing each other at the resonant frequency of 5.53hz. this implies that the amount of interference between the antenna element 1 and the antenna elements 2, 3 and 4 is considerably reduced. reduction of mutual coupling confirms that pmaa is performing better than cmaa in terms of mutual coupling. fig. 16. plot of return loss and mutual coupling–s41 versus pmaa frequency. the parameter gain is calculated by (2): # = 20log() * +,. / + 10log() 12 13 − #5 (2) where pt is the transmitted power, pr is the received power, r is the distance between the transmitting and the receiving antennas, λ is the wavelength at the resonant frequency of 5.53ghz, and gt is the gain of the transmitting antenna, given by (3): #5 = 10log() #6 (3) #6 = 7,89.: (4) where α and b are the length and width of the standard pyramidal horn antenna used as the transmitting antenna. dimensions α and b are equal to 24cm and 14cm respectively. the distance between the transmitting antenna (standard horn antenna) and the receiving antenna is given by (5): ; ≥ 7= : . (5) where d is the larger dimension of the transmitting antenna equal to 24cm. the value of r=71.86m. the transmitted and received powers in the case of cmaa are equal to 8.7µw and 12.414nw respectively. substituting these values in (1), the gain of cmaa becomes equal to 6.81db. in the case of pmaa, the transmitted and received powers are equal to 8.7µw and 0.279µw. substituting into (1), the gain of pmaa is 20.33db. hence with the introduction of u-shape patch type ebg structure, the gain of pmaa is increased, hence pmaa is a better antenna compared to cmaa regarding gain. figure 17 shows the radiation plot of cmaa and pmaa. fig. 17. radiation plot of cmaa and pmaa. using the radiation pattern, the amount of forward and backward power radiated is determined. to sketch the radiation pattern, the standard pyramidal horn antenna is employed as transmitting antenna and cmaa and pmaa as receiving antennas. the radiation pattern is plotted for angle from 0 0 to 360 0 in a polar plot. the forward power radiated is measured at 90 0 and the backward power at 270 0 . initially considering cmaa, the forward and backward powers measured are equal to -2 and -4.5db respectively. the corresponding powers radiated by pmaa are -0.5 and -8db respectively. we see that pmaa is radiating increased power in the forward direction and lesser power in the backward direction compared to cmaa. hence pmaa is a better radiator than cmaa in terms of forward and backward powers. parameter fbr is calculated by subtracting the backward power from the forward power. the fbr values of the microstrip antenna arrays cmaa and pmaa are equal to 2.5 and 7.5db respectively. the fbr value of pmaa is greater than that of cmaa. this confirms that pmaa is a better antenna than cmaa in terms of fbr parameter. tables ii and iii depict the comparison of measured results of cmaa and pmaa. table ii. summarized measured results antenna type resonant frequency (ghz) return loss (db) band width (mhz) band width (%) gain (db) cmaa 5.53 -21.06 273 4.89 6.81 pmaa 5.53 -26.12 6050 109.45 20.33 table iii. summarized measured results antenna type fbr s21 (db) s31 (db) s41 (db) cmaa 2.5 -16.95 -14.22 -17.30 pmaa 7.5 -31.44 -36.41 -31.62 after comparing the performances of cmaa and pmaa, we can say that pmaa outperforms cmaa. it is producing enhanced bandwidth, higher gain, better reduction in mutual coupling and superior radiation characteristics compared to its counterpart. vi. conlusions in this paper, a four element microstrip antenna array loaded with u-shape patch type ebg structure was 1 2 3 4 5 6 7 8 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 r e tu rn l o s s s 1 1 ( d b ) m u tu a l c o u p li n g s 4 1 ( d b ) frequency (ghz) return loss mutual coupling -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 0 30 60 90 120 150 180 210 240 270 300 330 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 cmaa pmaa engineering, technology & applied science research vol. 8, no. 5, 2018, 3470-3474 3474 www.etasr.com rao et al.: study of four element microstrip antenna array using patch type electromagnetic band … investigated. conventional and proposed microstrip antenna arrays were designed and fabricated successfully. the two dimensional ebg structure plays a prominent role in reducing the mutual coupling between the radiating patches below -20db level. furthermore, increase in gain by 13.52db is also obtained. the overall bandwidth (%) of pmaa is increased to 109.45%. measured results of front and backward power confirm that the radiation properties of pmaa are enhanced compared to cmaa. references [1] a. c. balanis, antenna theory, analysis and design, john wiley & sons, 1997 [2] i. j. bahl, p. bhartia, microstrip antennas, artech house, 1980 [3] g. l. matthaei, l. young, e. m. t. jones, microwave filters, impedance-matching networks and coupling structures, artech house books, massachusetts, 1980 [4] f. yang, y. rahmat-samii, electromagnetic band gap structures in antenna engineering, cambridge university press, 2009 [5] g. c. christodoulou, f. p. wahid, fundamentals of antennas: concepts and applications, prentice hall of india, 2004 [6] g. kumar, k. p. ray, brodband microstrip antennas, artech house books, 1980 [7] d. n. elsheakh, m. f. iskander, e. a. abdallah, h. a. elsadek, h. elhenawy, “microstrip antenna array with new 2d-electromagnetic band gap structure shapes to reduce harmonics and mutual coupling”, progress in electromagnetic research c, vol. 12, pp. 203-213, 2010 [8] f. benikhelf, n. boukli-hacene, “mutual coupling reduction in patch antenna arrays using ebg structure”, international journal of computer science issues, vol. 9, no. 4, pp.265-269, 2012 [9] m. m. bait–suwailam, f. o. siddiqui, m. o. ramahi, “mutual coupling reduction between microstrip patch antennas using slottedcomplementary split-ring resonators”, ieee antennas and wireless propagation letters, vol. 9, pp. 876-878, 2010 [10] d. saxena, s. agarwal, s. srivastava, “low cost e-shaped microstrip patch antenna array for wlan”, international journal of advanced research in electrical, electronics and instrumentation engineering, vol. 3, no. 4, pp. 8831-8838, 2014 [11] s. shajahan, a. vasuki, “a broadbanding microstrip patch antenna using electromagnetic band gap structures”, international journal of pure and applied mathematics, vol. 116, no. 11, pp. 71-79, 2017 [12] v. d. katrodiya, n. j. peshavaria, vivek ramamoorthy, “design of microstrip patch antenna array for wireless appliations”, international journal of electronics and communication technology, vol. 6, no. 2, pp. 61-64, 2015 [13] z. illuz, r. shavit, r. bauer, “microstrip antenna phased array with electromagnetic band gap substrate”, ieee transactions on antennas and propogation, vol. 52, no. 6, pp. 1446-1453, 2004 [14] n. mittal, r. khanna, j. kaur, “performance improvement of u-slot microstrip patch antenna for rf portable devices using electromagnetic band gap and defected ground structure”, international journal of wireless and microwave technologies, vol. 3, pp. 20-28, 2016 [15] r. rana, n. vyas, r. verma, v. kaushik, a. k. arya, “dual stacked wideband microstrip antenna array for ku-band applications”, vol. 4, no. 6, pp. 132-135, 2014 [16] a. verma, “ebg structures and its recent advances in microwave antenna”, international journal of scientific research engineering & technology, vol. 1, no. 5, pp. 84-90, 2012 microsoft word etasr_v11_n3_pp7195-7200 engineering, technology & applied science research vol. 11, no. 3, 2021, 7195-7200 7195 www.etasr.com majeed et al.: cetane number improvement of distilled diesel from tawke wells cetane number improvement of distilled diesel from tawke wells shwan m. noori khalifa majeed zakho technical institute duhok polytechnic university zakho, kurdistan region, iraq shwan.khalifa@dpu.edu.krd shinwar a. idrees chemistry department, faculty of science university of zakho zakho, kurdistan region, iraq shinwar.idrees@uoz.edu.krd veyan a. musa mechanical department, college of engineering university of zakho zakho, kurdistan region, iraq veyan.musa@uoz.edu.krd sherwan m. simo petroleum engineering department, college of engineering university of zakho zakho, kurdistan region, iraq sherwan.simo@uoz.edu.krd abraheem a. mohammed chemistry department, faculty of science university of zakho zakho, kurdistan region, iraq ibraheem.mohammed@uoz.edu.krd lokman a. abdulkareem petroleum engineering department, college of engineering university of zakho zakho, kurdistan region, iraq lokman.abdulkareem@uoz.edu.krd abstract-the current research aims to improve the cetane number of diesel extracted from the crude oil of tawke region in iraqi kurdistan. a specific mixture of chemical compounds was prepared which included m-nitrophenol, 4-nitro toluene, and nitrobenzene. the components' effects were investigated with regard to the cetane number, flash point, viscosity, and refractive index of diesel. the quantity of each compound mixed with diesel was prepared based on the statistical analysis of the experiment device (box–behnken designs-bbds). the tested mixture showed a good agreement and improvement of cetane and flash point and a very low effect on viscosity and refractive index. according to the statistical analysis, the main influence on cetane number and the flashpoint was from m-nitrophenol. the investigation showed that the best results were acquired from the samples of 25ppm 4nitro toluene and 50ppm m-nitrophenol with a cetane number of 65.3. the correlation and the interaction of the regression equation were linear with all cases. it is worth mentioning that all additives positively influenced the cetane number in the regression equation. the sulfur content was measured as well, and the obtained weight percentage of sulfur was 0.8404%. keywords-diesel improvers; cetane number; flash point; viscosity i. introduction additives are mixed with fuel to improve its quality and to enhance its efficiency. this process is termed as mixing with fuel of the trace elements. fuel in various forms like diesel and benzine does not perform well or reach the required international standards without improvers [1]. therefore, the search for new improvers is in great demand. the utilizing of influential improvers is very essential in order to reach the requested mechanical and environmental standards [2]. in the past, attempts have been made to ignite fuel readily and thus upgrade ignition quality. nitro compounds are commonly used as cetane number additives and such chemicals make the delay time of fuel ignition shorter and as a result the rate of knocking decreases [2]. such additives can be utilized with bio-diesel, which commonly has low cetane number [3]. the cetane number is affected by physical and chemical properties of fuel such as density, viscosity, surface tension, and vaporization. the cetane number is also influenced by the molecular structure of fuel and additives [4]. the octane number is a parameter that determines the quality of a fuel. fuels with high octane numbers, close to 100, knock less. oxygenated compounds, aromatic hydrocarbons, aromatic amines, and organometallic compounds have been exploited for this purpose as octane number modificators [4-6]. flash point temperature is another important factor to improve the valid ability of fuel in car engines [8], where lower flash point temperature means lower ignition temperature (piloted temperature) for the fuel oil ranging from 60 to 930c. however, this research article mainly considers cetane number improvement. the influence on the cetane number of adding dicyclopentadiene to diesel has been examined in [9]. the authors proposed a novel additive of hydrocarbon-based, dicyclopentadiene (dcpd) for diesel fuel which leads to minimized particulate emissions and also enhances cetane corresponding author: veyan a. musa. engineering, technology & applied science research vol. 11, no. 3, 2021, 7195-7200 7196 www.etasr.com majeed et al.: cetane number improvement of distilled diesel from tawke wells number. the improvement of diesel properties like viscosity, flash point, density, cloud point, water content, and sulfur content were investigated in [10]. the design of experiment (doe) to study any oil sample represents a significant part of chemo measurements (effects of chemicals on the yield). the universal benefit of doe is to ensure that the conditions between any test parameters and their yield of the reactions can be evaluated dependably with low cost and exertion with an insignificant number of trials and less amount of chemicals. doe can be isolated into a few subtopics, for example, confirming factors from an enormous arrangement of factors which is called screening structures, finding the impact of a blend organization on the reaction factors tended to blend plans, and discovering wellsprings of error in estimation frameworks. this leads to concocting ideal conditions inconsistent procedures (evolutionary operation), batch process (response surface methodology), or planning tests for ideal parameter estimation in numerical models (optimal design or optimization) [11]. different statistical doe models have been utilized to smooth out factors in the exploratory plan. accordingly, this helps to select the impact of exploratory factors by conventional methodologies. tests have been conducted with conscious changes of the specific boundaries. these assessments should be repeated to each boundary effect achieving a reliable number of runs [12]. numerous studies have been carried out to study the extracted crude oil from the wells of tawke region in iraqi kurdistan [13], but the investigation in crude oil and its components from the specific wells requires more investigations to reach the desired characteristics and to improve its properties. the tests described in the current paper were performed using a sample consisting of diesel mixed with a measured amount of m-nitrophenol, 4-nitro toluene, and nitrobenzene to aggregate the effect of those components on the diesel. ii. experimental setup and methods the portable analyzer instrument shatox sx-100m was used as the main device to analyze the octane/cetane numbers and to determine cetane and octane number, while a device ncl 120 cleveland open cup flash point tester manual120 astm d 92, ip 36, iso 2592 was utilized for flash point temperature determination as shown in figure. 1. fig. 1. the experimental devices. table i. levels of the parameters studied in the ccd statistical experiment. chemical compound unit levels -1 (low) 0 (middle) +1 (high) m-nitrophenol ppm 0 25 50 4-nitro toluene ppm 0 25 50 nitro benzene ppm 0 25 50 table ii. physical and chemical properties chemical compound m-nitrophenol 4-nitro toluene nitro benzene iupac name 3-hydroxynitrobenzene 1-methyl-4 nitrobenzene nitro benzene chemical structure formula c6h5no3 c7h7no2 c6h5no2 appearance colorless to yellow crystals yellowish crystals yellowish, oily, aromatic nitrocompound molecular weight 139.11g/mol 137.14g/mol 123.11g/mol solubility soluble in hot and dilute acids and in caustic solutions. insoluble in petroleum ether. very soluble in ethanol, ether, and acetone. in water, 13.550mg/l at 25°c soluble in alcohol, benzene, ether, chloroform, acetone. in water, 442mg/l at 30°c slightly soluble in carbon tetrachloride. very soluble in ethanol, diethyl ether, acetone, benzene. in water, 2.09×10+3mg/l at 25°c boiling point 194°c/70mmhg 238.3°c 210.8°c melting point 96-98°c 51.6°c 5.7°c density 1.485g/cm³ at 20°c 1.29g/cm³ 1.2037g/cm³ vapour pressure 1.5×10-4 mm hg at 25°c 0.0157mm hg at 25°c 0.245mm hg at 25°c toxicity ld50=328mg/kg (rat) ld50=2250mg/ kg body weight ld50=640mg/kg (rat) m-nitro phenol, 4-nitro toluene, and nitrobenzene supplied from germany were used as received. solutions of mnitrophenol, 4-nitro toluene, and nitrobenzene 50ml/l (ppm) were prepared in diesel and then were diluted to solutions according to table i. the prepared solutions were covered by aluminum foil and kept in dark to avoid the photodegradation of the 13 samples. diesel was brought from tawke oil well distillery and was used as received. different concentrations of improvers were prepared according to the needs of the experiments as shown in table i. table ii shows the physicchemical properties of the additives. it is essential to fit a logical model in order to depict the response directly in the test field by choosing the doe. generally, this model is suitable for illustrating a plane surface, as indicated by: � � �� � ∑ ���� � (1) where r is the response, βo is the constant term, βi represents the coefficients of the linear parameters, xi represents the parameters, and ε is the irregular error or commotion to the response. on specific events, it is called the essential impacts model since it incorporates just the principle impacts of the engineering, technology & applied science research vol. 11, no. 3, 2021, 7195-7200 7197 www.etasr.com majeed et al.: cetane number improvement of distilled diesel from tawke wells factors as explained intensively in [14]. if the interaction between the parameters is contained, then the first-order model becomes: � � �� � ∑ ���� � ∑�� ��� � ∑ ������ � (2) where βii indicates the quadratic coefficients of the variables and i < j. response surface methodology (rsm) was applied to identify the positive and negative effects of each factor. the experimental box behnken design (bbd) was also utilized to select the number of required experiments for the present research as represented in [14, 15]. the effect of cetane number was studied. all tests were carried out based on the experimental design that is derived from the minitab16 program (version 2018) as in table iii, where the estimated exact cetane number and the quantities of the mixed additives are stated. flash point, viscosity, and the refractive index were measured. the solutions were taken for each run according to the run order and levels as illustrated in table iii and table i. the mixtures were then put aside for 24 hours in order to assure solubility. in each run, before testing, the mixtures were shaken well for total miscibility. the readings were taken from the octane meter and flash point temperature meter. all runs were performed at ambient temperature and on the same day to avoid any environmental effect on the outcome. table iii. central composite design matrix -bbd. no. of run order nitro benzene (ppm) 4-nitro toluene (ppm) m-nitro phenol (ppm) 1 25 0 0 2 25 0 50 3 25 50 0 4 25 50 50 5 0 25 0 6 0 25 50 7 50 25 0 8 50 25 50 9 0 0 25 10 0 50 25 11 50 0 25 12 50 50 25 13 0 0 0 iii. results and discussion statistical analysis was employed to determine the effect of each additive and their interactions in order to indicate the best model. all models were studied. during the present study, the linear model showed the best agreement among other models and regression equations as in (1) and (2) were opbtained. the regression equation shows that all parameters have a positive effect on the cetane number. however, the effect is rational on octane number and flash point which means there is a negative effect from some additives. the effect of each parameter is determined by a factor in regression equations. a. effect of the added chemicals on the cetane number figure 2 demonstrated the relationship between the contour plot of the determined additives and cetane number, while figure 3 showed the surface plot of the obtained additives and cetane number. the effect of the additives m-nitrophenol, 4nitro toluene, and nitrobenzene on cetane number was positive. the greatest estimated impact was recorded from nitro phenol followed by 4-nitro toluene, and nitrobenzene by 0.3545, 0.0054, and 0.0035 respectively as shown in regression equation (1). the correlation between the parameters is very strong and equal to 98.92%. table iv contains the coefficients and anova parameters obtained from the current experiment, and table v demonstrates the cetane numbers results from the tested samples. fig. 2. contour plot for the determination of additives effect on cetane number. table iv. coefficients and anova parameters term coeficient se coeficient t f p constant 46.6417 0.534102 87.3273 0.000 regression 336.62 0.000 m-nitro phenol 0.3545 0.011157 31.7737 1009.57 0.000 4-nitro toluene 0.0050 0.011157 0.4481 0.20 0.666 nitro benzene 0.0035 0.011157 0.3137 0.10 0.762 model summary s = 0.788921, r-sq = 99.21%, r-sq(adj) = 98.92%, press = 11.2031, r-sq(pred) = 98.23% fig. 3. surface plot for the determination of additives effect on cetane number. according to the test, the correlation equation between the cetane number and the additive becomes: engineering, technology & applied science research vol. 11, no. 3, 2021, 7195-7200 7198 www.etasr.com majeed et al.: cetane number improvement of distilled diesel from tawke wells � ��� ���� � � 46.6417 � 0.3545 � � ����� ! ��" � 0.005 4 ����� ��"� � � 0.0035 ����� � �# � (3) table v. cetane number results no. of run order nitro benzene (ppm) 4-nitro toluene (ppm) m-nitro phenol (ppm) cetane number 1 25 0 0 46.9 2 25 0 50 64.1 3 25 50 0 47.3 4 25 50 50 65.2 5 0 25 0 47.3 6 0 25 50 65.3 7 50 25 0 47.4 8 50 25 50 65.2 9 0 0 25 55.3 10 0 50 25 54.3 11 50 0 25 54.9 12 50 50 25 55.4 13 0 0 0 46.9 b. effect of the added chemicals on flash point figures 4 and 5 exhibit the contour and surface plots on the flash point obtained from the present work. the effect of the additives on flash point temperature has been investigated. the results show that the additives present a negative effect on flash point temperature. this means that when the concentration of additives is increasing, the flash point temperature decreases by factors of 0.135, 0.005, and 0.06 respectively as shown in regression equation (3). the resulted correlation was about 45.41%. table vi illustrates the coefficients and anova parameters estimated from the runs, whereas table vii consists of the results of all tests with their run order. it is worth mentioning that the mixture flash point reaches the requirement of the international standards which is about 51-60 [17]. the equation between the flashpoint and the additive becomes: $"�%! ���� � 90.25 � 0.135 � � ����� ! ��" � 0.005 4 ����� ��"� � � 0.06 ����� � �# � (4) fig. 4. contour plot for thedetermination of additives effect on cetane number. fig. 5. surface plot fo ther determination of additives effect on flash point temperature. table vi. coefficients and anova parameters term coeficient se coeficient t f p constant 90.250 1.41605 63.7335 0.000 regression 8.3238 0.007655 m-nitro phenol -0.135 0.02958 -4.5638 20.8286 0.002 4-nitro toluene -0.005 0.02958 -0.1690 0.0286 0.870 nitro benzene -0.060 0.02958 -2.0284 4.1143 0.077 model summary s = 2.09165 r-sq = 75.74% r-sq(adj) = 66.64% press = 78.75 r-sq(pred) = 45.41% table vii. flash point temperature results no. of run order flash point nitro benzene (ppm) 4-nitro toluene (ppm) m-nitro phenol (ppm) 1 89 25 0 0 2 83 25 0 50 3 88 25 50 0 4 81 25 50 50 5 88 0 25 0 6 86 0 25 50 7 89 50 25 0 8 77 50 25 50 9 85 0 0 25 10 88 0 50 25 11 85 50 0 25 12 84 50 50 25 13 91 0 0 0 c. effect of the added chemicals on viscosity the effect of the selected additives are exhibited in figure 6. all additives had a negative effect on viscosity. this means that when the concentration of additives increased, viscosity decreased by the factors of -0.000080, -0.00044, and -0.00008 as shown in (5). nevertheless, the effect is very weak. table viii shows the coefficients and anova parameters obtained from the tests, while table ix states the results of the viscosity values. the regression equation is: (�%)�%��* � 3.15 � 0.00008 � � ����� ! ��" � 0.00044 4 ����� ��"� � � 0.00008 ����� � �# � (5) engineering, technology & applied science research vol. 11, no. 3, 2021, 7195-7200 7199 www.etasr.com majeed et al.: cetane number improvement of distilled diesel from tawke wells fig. 6. surface plot for the determination of additives effect on kinematic viscosity. table viii. coefficients and anova parameters term coeficient se coeficient t f p constant 3.14867 0.04942 63.71 0.000 regression 0.06 0.977 m-nitro phenol -0.000080 0.001032 -0.08 20.8286 0.940 4-nitro toluene -0.000440 0.001032 -0.43 0.0286 0.681 nitro benzene -0.000080 0.001032 -0.08 4.1143 0.940 model summary s = 0.0729989 r-sq = 2.4% r-sq(adj) = 0.0% table ix. kinematic viscosity results no. of run order kinematic viscosity cts/s nitro benzene (ppm) 4-nitro toluene (ppm) m-nitro phenol (ppm) 1 3.256 25 0 0 2 3.172 25 0 50 3 3.148 25 50 0 4 3.132 25 50 50 5 3.08 0 25 0 6 3.22 0 25 50 7 3.104 50 25 0 8 3.048 50 25 50 9 3.08 0 0 25 10 3.076 0 50 25 11 3.112 50 0 25 12 3.176 50 50 25 13 3.182 0 0 0 d. effect of the added chemicals on refractive index the influence of the chosen additives is shown in figure 7. m-nitrophenol, 4-nitro toluene, and nitrobenzene were studied with regard on their effect on the refractive index. the additives presented a very low impact on the refractive index which means their effect is negligible as shown in regression equation (6). table x demonstrates the coefficients and anova values obtained from the runs, and table xi shows the summed values of the tests with their run order. the regression equation is: � ,��)�� ��. / � 1.46 � 0.000013 � � ����� ! ��" � 0.0000224 ����� ��"� � � 0.000007 ����� � �# � (6) fig. 7. surface plot for the determination of additives effect on refractive index. table x. coefficients and anova parameters term coeficient se coeficient t f p constant 3.14867 0.04942 63.71 ---0.000 regression 0.06 0.977 m-nitro phenol -0.000080 0.001032 -0.08 20.8286 0.940 4-nitro toluene -0.000440 0.001032 -0.43 0.0286 0.681 nitro benzene -0.000080 0.001032 -0.08 4.1143 0.940 model summary s = 0.0729989 r-sq = 2.4% r-sq(adj) = 0.0% table xi. refractive index results no. of run order refractive index nitro benzene (ppm) 4-nitro toluene (ppm) m-nitro phenol (ppm) 1 1.4623 25 0 0 2 1.4624 25 0 50 3 1.4621 25 50 0 4 1.4631 25 50 50 5 1.4632 0 25 0 6 1.463 0 25 50 7 1.462 50 25 0 8 1.4624 50 25 50 9 1.4618 0 0 25 10 1.4632 0 50 25 11 1.4653 50 0 25 12 1.4629 50 50 25 13 1.4653 0 0 0 iv. conclusion the current statistical and experimental analyses have been performed to study the effect of three aromatic compounds as diesel cetane number improvers and their impact on flash point, refractive index, and viscosity of tawke oil well diesel. sample 6 gave the best result. to the best of our knowledge, no similar study has been conducted with the certain components to contrast the present outcome, however, many investigations to improve the cetane number of fuel have been performed including the transesterification and higher alcohol-diesel blends [17], the oxygenated compound for cetane number improvement di-n-pentyl-ether (dnpe) [18], and the ethanol with 2-ethyl hexyl nitrate (ehn) component [3]. mixtures of additives were added to the diesel samples and were measured regarding the cetane number improvement and engineering, technology & applied science research vol. 11, no. 3, 2021, 7195-7200 7200 www.etasr.com majeed et al.: cetane number improvement of distilled diesel from tawke wells flash point. three different organic chemicals were selected for the current research, namely m-nitrophenol, 4-nitro toluene, and nitrobenzene. statistical analysis was performed to determine the effect of each component and to calculate the regression equation. besides, the experimental design was utilized to calculate the most active mixture composition that presents the best performance and attains the international standards. the best mixture composition turn out to be the addictive consisting of run number 6 that consisted of no nitrobenzene, 25ppm 4-nitro toluene, and 50ppm mnitrophenol. viscosity and refractive index were measured as well and their effect was significant. acknowledgment the authors would like to thank the ministry of higher education and scientific research in kurdistan, the chemistry department of the university of zakho, and the petroleum department, polytechnic university of duhok/zakho institute for their support. also, the authors declare that no competing interests exist regarding the current work. references [1] p. e. oguntunde, o. o. ojo, o. a. oguntunde, and h. i. okagbue, "crude oil importation and exportation in nigeria: an exploratory and comparative study," engineering, technology & applied science research, vol. 8, no. 5, pp. 3329–3331, oct. 2018, https://doi.org/10. 48084/etasr.2172. 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[15] v.-m. t. taavitsainen, "experimental optimization and response surfaces," in chemometrics in practical applications, london, uk: intechopen, 2012. [16] p. calza et al., "multivariate experimental design for the photocatalytic degradation of imipramine. determination of the reaction pathway and identification of intermediate products," applied catalysis b: environmental, vol. 84, no. 3–4, pp. 379–388, 2008, https://doi.org/ 10.1016/j.apcatb.2008.04.015. [17] f. lujaji, a. bereczky, l. janosi, c. novak, and m. mbarawa, "cetane number and thermal properties of vegetable oil, biodiesel, 1-butanol and diesel blends," journal of thermal analysis and calorimetry, vol. 102, no. 3, pp. 1175–1181, 2010, https://doi.org/10.1007/s10973-010-0733-9. [18] m. marchionna, r. patrini, d. sanfilippo, a. paggini, f. giavazzi, and l. pellegrini, "from natural gas to oxygenates for cleaner diesel fuels," in studies in surface science and catalysis, vol. 136, paris, france: elsevier, 2001, pp. 489–494. microsoft word etasr_v13_n4_pp11277-11289 engineering, technology & applied science research vol. 13, no. 4, 2023, 11277-11289 11277 www.etasr.com kassem et al.: feasibility analysis of the wind energy potential in libya using the retscreen expert feasibility analysis of the wind energy potential in libya using the retscreen expert youssef kassem department of mechanical engineering, engineering faculty, near east university, cyprus | energy, environment, and water research center, near east university, cyprus yousseuf.kassem@neu.edu.tr (corresponding author) huseyin camur department of mechanical engineering, engineering faculty, near east university, cyprus huseyin.camur@neu.edu.tr almonsef alhadi salem mosbah high and intermediate institute of agricultural technology, libya almonsef4400@gmail.com received: 3 may 2023 | revised: 28 may 2023 | accepted: 31 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6007 abstract this study focuses on the evaluation of the economic viability of various scale wind farms and the assessment for the first time of the wind power potential of 22 locations distributed over libya. the study utilizes monthly mean wind data collected from the nasa power dataset. the analysis includes determining and analyzing the mean wind speed, frequency distribution, and weibull distribution scale and shape factors. the results showed that darnah is the most promising location for insulation wind farms due to the high value of wind speed. moreover, retscreen software is used to estimate the energy output and conduct an economic feasibility analysis of the wind farm. additionally, this paper establishes a relationship between the wake effect, airfoil losses, and the potential for greenhouse gas (ghg) mitigation and the performance of wind farms. the results indicate that wind projects are economically viable when the ewt-dw 52 with a capacity of 500 kw is used. the study findings show that the wake effect is a crucial consideration in wind farm design, and it can be minimized through strategic spacing and turbine design. furthermore, the accumulation of dirt and debris on wind turbine blades can significantly reduce a wind farm's energy output, causing turbine inefficiency and decreasing the overall energy production. additionally, the energy production cost from a wind farm is less than that of the electricity tariff and can result in a profitable wind energy project. keywords-libya; wind energy potential; grid-connected; wind farm; farmretscreen; feasibility analysis; wake effect; airfoil losses i. introduction renewable energy sources have significant potential to provide clean and affordable energy to developing countries like libya. according to the international energy agency (iea), over 1.2 billion people worldwide lack access to electricity. renewable energy can provide clean and reliable electricity to these populations, especially in rural and remote areas where grid access is limited [1]. moreover, many developing countries rely heavily on imported fossil fuels for their energy needs, which can make their energy systems vulnerable to price fluctuations and supply disruptions. investing in renewable energy can help these countries reduce their dependence on imported fuels, and increase their energy security [2]. furthermore, these countries are often the most vulnerable to the impacts of climate change. by transitioning to renewable energy, these countries can reduce their ghg emissions and contribute to the global effort to mitigate climate change [3, 4]. besides, burning fossil fuels for energy production can have significant negative impacts on human health, especially in developing countries where air pollution is often a major problem [5]. wind and solar energy have gained increasing attention in recent years as a way to reduce emissions and fossil fuel consumption. recently, the use of wind and solar energy has been increasing rapidly in many countries such as germany, china, usa, denmark, brazil, and costa rica [6-8]. renewable energy sources generate electricity without emitting harmful ghgs, which contribute to climate change. according to the intergovernmental panel on climate change (ipcc), the world must reduce its carbon emissions by at least 50% by engineering, technology & applied science research vol. 13, no. 4, 2023, 11277-11289 11278 www.etasr.com kassem et al.: feasibility analysis of the wind energy potential in libya using the retscreen expert 2030 to avoid the worst impacts of climate change [9]. this means transitioning to renewable energy is no longer an option, but a necessity. renewable energy is becoming more costeffective and competitive with traditional energy sources, making it more accessible to consumers [10]. a. literature review related to the current electricity situation in libya libya's electricity sector is dominated by fossil fuels. according to the iea, in 2018 natural gas accounted for approximately 98% of libya's electricity generation, with the remaining 2% coming from oil-fired power plants. the country has significant natural gas reserves, which have historically been used to fuel power plants and provide domestic heating and cooking fuel. however, the ongoing conflict and instability in libya have disrupted natural gas production and distribution, leading to shortages and disruptions in electricity supply. in addition, the damage to the oil infrastructure and the resulting decline in oil production has limited the fuel availability. as a result, many of libya's power plants have been operating well below their capacity, leading to frequent power outages and load shedding. the electricity sector in libya is also characterized by an aging and poorly maintained infrastructure, which has contributed to the unreliability of the electricity supply. many of the country's power plants and transmission lines require repair and modernization, and there have been limited investments in new infrastructure due to the political and economic instability. the libyan government has attempted to address some of these challenges through a series of electricity sector reforms, including the establishment of the general electricity company of libya (gecol) in 1979, which is responsible for electricity generation, transmission, and distribution. the government has also pursued partnerships with foreign companies to develop new power plants and improve the efficiency of the existing ones. however, the ongoing conflict and instability have hindered the implementation of these reforms and investments. in addition, corruption and mismanagement have been significant challenges in the electricity sector, with allegations of embezzlement and fraud involving government officials and foreign companies. despite these challenges, there have been some efforts to develop renewable energy sources in libya, particularly solar power. the country has abundant solar resources, with high levels of solar radiation throughout most of the year. the government has expressed interest in developing solar power projects, and there have been some private sector investments in solar energy during the recent years. nevertheless, the development of renewable energy sources in libya has been limited by the challenges posed by the ongoing conflict and instability, as well as the lack of regulatory frameworks and incentives for renewable energy development. in addition, the high cost of renewable energy technologies and the limited access to financing have been significant barriers to the development of renewable energy in libya. moreover, the generation capacity and power plant infrastructure in libya have historically been dominated by oil and gas-fired power plants. according to the libyan electricity company (lec), the country's installed generation capacity as of 2020 was approximately 7.5 gw, with a peak demand of around 7 gw. the majority of this capacity is made up of thermal power plants, which account for approximately 97% of the country's total installed capacity. the remaining 3% of the capacity is provided by hydroelectric power plants. additionally, there are currently eight main thermal power plants in libya, located in different regions of the country. the largest of these is the al-khums power plant, located on the mediterranean coast east of the capital city of tripoli, with a capacity of 2,500 mw. other major thermal power plants include the zawiya power plant near the city of zawiya, with a capacity of 1,200 mw, and the tripoli west power plant, with a capacity of 1,000 mw. in addition, there are also several smaller power plants located in different regions of the country, including diesel-fired and gas-turbine power plants. furthermore, the hydroelectric power plants in libya are all located in the western region of the country and have a total capacity of approximately 240 mw. the largest of these is the wadi al-khijir power plant, with a capacity of 130 mw. the electricity consumption in libya varies depending on the region and level of economic development. the majority of electricity consumption is concentrated in the major cities, particularly tripoli and benghazi, where the population is highest and economic activity is concentrated. according to the world bank, in 2019, the electricity consumption per capita in libya was approximately 1,100 kwh, which is relatively low when compared to other countries in the region. this is partly due to the challenges faced by the electricity sector in libya, including frequent power outages and the unreliable electricity supply. besides, the cost of electricity for domestic use in libya also varies depending on the region and the level of consumption. the libyan government heavily subsidizes the cost of electricity, to provide affordable electricity to households and promote economic development. however, the subsidies have been a significant burden on the government budget, and there have been concerns about the sustainability of the subsidies in the face of ongoing economic challenges. the cost of electricity for domestic use in libya was approximately 0.09 libyan dinars per kwh, which is equivalent to approximately 0.06 us dollars. this is relatively low compared to other countries in the region, where the cost of electricity is often higher due to lower levels of government subsidies. however, the reliability of the electricity supply remains a significant challenge, and households may need to rely on alternative sources of energy, such as diesel generators, to meet their electricity needs during power outages. the use of diesel generators as an alternative source of energy can be expensive and may not be feasible for households with limited financial resources. in addition to the challenges of cost and reliability, there have also been concerns about the environmental impact of the electricity sector in libya. the heavy reliance on fossil fuels, particularly natural gas, for electricity generation, has contributed to ghg emissions and air pollution. the development of renewable energy sources, such as solar power, could address these environmental challenges, while reducing the reliance on fossil fuels and promoting energy independence. as mentioned above, libya is a major oil-producing country and has historically been a net exporter of energy. engineering, technology & applied science research vol. 13, no. 4, 2023, 11277-11289 11279 www.etasr.com kassem et al.: feasibility analysis of the wind energy potential in libya using the retscreen expert however, due to the ongoing political and security instability in the country and the damage to the oil infrastructure during the country's civil war, libya has at times needed to import energy to meet its own domestic needs. according to the us energy information administration (eia), libya imported an average of 2,000 barrels per day of petroleum products in 2020. this was a significant decrease from the previous year when the country imported an average of 13,000 barrels per day. it is worth noting that these import figures may not fully capture the extent of libya's energy needs or imports, as some imports may occur through informal channels or may not be reported to the official statistics agencies. additionally, the situation in libya remains volatile and subject to change, and future energy import needs could fluctuate depending on a variety of factors. b. literature review related to renewable energy in libya libya has a significant potential for renewable energy resources, particularly solar and wind power. the country receives abundant sunshine throughout the year, and its coastal areas experience consistent winds. however, the development of renewable energy in libya has been hindered by political instability, security concerns, and the reliance on fossil fuels. notwithstanding these challenges, there have been some efforts to develop renewable energy in libya. in 2012, the country's national renewable energy authority (nrea) was established to promote the development of renewable energy projects. the nrea has identified several potential sites for wind and solar power plants and has signed agreements with international companies to develop renewable energy projects. in 2019, libya's first commercial-scale solar power plant, the 10 mw ubari solar power station, was inaugurated. the plant is located in the southwestern part of the country, an area with high levels of solar radiation. the ubari plant was developed by a consortium of companies from italy, china, and libya. libya has significant potential for wind energy, particularly along its coastal regions. the country's location along the mediterranean sea and its extensive coastline provide abundant opportunities for wind power generation. however, despite this potential, the development of wind energy in libya has been limited, largely due to political instability and the lack of investment in renewable energy. the coastal areas of libya experience consistent winds, particularly in the eastern part of the country, where wind speeds can reach values up to 10 m/s. this makes the region an ideal location for wind energy development, as high wind speeds are necessary to generate electricity efficiently. wind energy has the potential to contribute significantly to libya's electricity mix, as the country continues to rely heavily on fossil fuels for power generation. in 2014, the european union's joint research centre (jrc) published a study on the wind energy potential in the mediterranean region, including libya. the study estimated that the total wind energy potential for the mediterranean region was 766 gw, with libya accounting for 35 gw of this potential. additionally, libya has an estimated wind energy potential of around 10 gw, which is equivalent to the country's current electricity demand according to the renewable energy and energy efficiency authority (reeea) in libya. recently, the libyan government has shown interest in developing its renewable energy sector, including wind power. the country's first wind farm, the al-fataiah wind farm with a capacity of 1.25 mw, was inaugurated in 2018. plans are also underway to build several other wind farms along the coast and in other regions of the country [11, 12]. furthermore, several studies have investigated the potential of wind energy potential in libya [13-28]. for instance, authors in [13] estimated the wind power potential tripoli, nault, and esspeea using the weibull distribution function. the results showed that nault has the highest mean actual wind power (50.3w/m2) at a height of 10m. authors in [17] evaluated the wind power potential wind energy potential in al-fattaih-darnah. the results showed that the annual wind power density of the selected locations is categorized into class 3. authors in [26] estimated the wind energy potential in espiaa, msallata, alqatrun, and adirsiyah, also using the weibull distribution function. the results indicated that msallata has the highest value of wind power potential (444.74 w/m² at a height of 60m) compared to other cities. libya has a high potential for solar energy due to the sahara desert region, which experiences long hours of sunshine throughout the year. in recent years, there have been several studies conducted on the solar energy potential in libya. according to nrea [29], the country had a total solar energy potential of 6.5 kwh/m2/day, which is among the highest in the world. additionally, the jrc published a study on the solar energy potential in the mediterranean region, including libya [30]. the study estimated that the total solar energy potential for the mediterranean region was 332 twh/year, with libya accounting for 20% of this potential. the international renewable energy agency (irena) concluded that north africa had a total solar energy potential of 2,600 twh/year, with libya accounting for 1,050 twh/year of this potential [31]. in addition, there have been some private-sector initiatives to develop solar energy in libya [32, 33]. these projects are expected to contribute significantly to the country's electricity mix and reduce its dependence on fossil fuels. recently, several studies have investigated the potential of solar energy in different locations in libya [34-39]. for example, authors in [34] found that the city had an average solar radiation of 5.38 kwh/m2/day, which can be supported by the installation of photovoltaic (pv) panels with a total capacity of 508 mw. besides, authors in [37] concluded that benghazi had an average solar radiation of 5.8 kwh/m2/day, which could support the installation of pv panels with a total capacity of 313 mw. additionally, authors in [39] found that the sabha in southern libya was found to have an average solar radiation of 6.93 kwh/m2/day. this indicates that there is a potential for the installation of pv panels with a total capacity of 270 mw. c. importance of the current study the present study is of great importance due to the current situation in libya. it is imperative to conduct a comprehensive study on the economic and environmental aspects. this study will serve as a roadmap for the investment of wind energy in libya. the figures presented in this study provide a summary of the economic and energetic analysis conducted, while the environmental impact of the electricity crisis in the country has already been assessed. engineering, technology & applied science research vol. 13, no. 4, 2023, 11277-11289 11280 www.etasr.com kassem et al.: feasibility analysis of the wind energy potential in libya using the retscreen expert ii. materials and methods a. dataset choosing locations with suitable wind speeds requires obtaining wind information for the region, thus, an atlas map was utilized. in general, wind speed and global solar radiation are essential criteria for installing wind and solar power plants at specific locations. in general, there is a lack of instruments used to measure wind speed due to the civil war in libya. anyhow, several studies have evaluated the potential of wind energy at specific locations using satellite data such as the nasa power dataset [13, 40-46]. the nasa prediction of worldwide energy resource (power) dataset is a comprehensive set of meteorological data used for research and analysis of renewable energy resources, particularly solar and wind energy. it is provided by the nasa langley research center's atmospheric science data center (asdc) and is freely available to the public [47]. the dataset contains hourly, daily, and monthly data on a range of meteorological variables such as solar radiation and wind speed. the data are derived from a combination of satellite observations, reanalysis models, and ground-based measurements [47]. therefore, the monthly data (collected from the nasa power dataset), including wind speed at a height of 50 m, are used to assess the economic feasibility of large-scale wind power projects to generate electricity in the country. table i. information regarding the selected areas location no. region latitude longitude altitude l#1 al butnan 29.742 24.515 11 l#2 al jabal al akhdar 32.487 21.709 683 l#3 al jabal al gharbi 30.705 13.223 579 l#4 al jifarah 23.986 45.185 872 l#5 al jufrah 27.983 16.912 515 l#6 al kufrah 24.198 23.294 396 l#7 al marj 32.485 20.833 336 l#8 al marqab 32.646 14.244 58 l#9 al wahat 29.157 21.75 47 l#10 an nuqat al khams 32.854 12.239 4 l#11 az zawiyah 32.884 13.185 17 l#12 benghazi 32.119 20.087 7 l#13 darnah 32.700 22.681 250 l#14 ghat 26.020 10.434 594 l#15 misratah 32.375 15.092 9 l#16 murzuq 24.535 15.259 614 l#17 nalut 30.613 10.671 545 l#18 sabha 26.996 15.107 467 l#19 surt 29.971 16.677 315 l#20 tripoli 32.773 13.332 71 l#21 wadi al hayat 26.423 12.718 683 l#22 wadi ash shati' 27.56 14.449 346 b. weibull distribution wind speed (� ) characteristics play a crucial role in the design and operation of wind energy systems. probability distribution models are commonly used to analyze wind speed data and estimate the probability of different wind speeds occurring at a particular location. generally, examining the wind speed characteristics (wsc) is considered the first step for the evaluation of the wind energy potential at a specific location. different distribution functions have been suggested to represent wind speed data in particular areas. the 2parameter weibull (2p-w) is commonly utilized for studying the distribution of wind speed at a specific region [48]. the weibull distribution function is frequently used to model wind speed frequency due to its ability to accurately, simply, and efficiently fit a wide range of data [49]. the weibull distribution function is defined below: ���� = ��� � � ��� �� � � � (1) ���� = 1 − �� �− � � � � (2) where ���� is the probability distribution function, ���� is the cumulative distribution function, � is the scale parameter in m/s, and � is the shape factor of the distribution. in general, several methods can be used to estimate the parameters of the 2p-w, such as maximum likelihood estimation (mls), the method of moments, etc. [50]. in this study, mls, a widely used method for estimating the parameters of the weibull distribution function, is used for estimating the parameters of the 2p-w. � = �∑ � ���� � �� ∑ ��� − ∑ ��� ��� � ! �� (3) � = ��� ∑ �" ��� � �⁄ (4) c. wind power density generally, the amount of air flowing across the area of interest determines how much electricity a wind turbine can generate [51]. wind power density (wpd) is a measure of the amount of power that can be harnessed from the wind in a specific location. it is defined as the ratio of the power present in the wind to the area swept by the wind turbine. wpd is also referred to as wind power potential or wind power per unit area, and it provides a numerical representation of the energy potential in a given region. it can be expressed as [68]: $% & = � ' (�γ �1 + + � (5) where ,% is the mean wpd in w, �̅ is the mean wind speed in m/s, / is the swept area in m2, and ( is the air density ((=1.225 kg/m3). d. extrapolation of wind speed data the power law model is commonly utilized in wind energy evaluations to extrapolate wind speed to various hub heights. the model is represented by (6): 0 = � 11 0 2 (6) where � is the wind speed at the wind turbine hub height 3, ��4 is the wind speed at the original height 3�4 , and 5 is the surface roughness coefficient, which depends on the characteristics of the region. the wind speed data in this analysis were gathered at a height of 10 m above the ground level. therefore, the value of α can be determined by [52]: 5 = 4.+7�4.488��� 0���4.488���1 0 �4⁄ � (7) engineering, technology & applied science research vol. 13, no. 4, 2023, 11277-11289 11281 www.etasr.com kassem et al.: feasibility analysis of the wind energy potential in libya using the retscreen expert e. design of wind farms a wind turbine is a device that converts the kinetic energy of the wind into mechanical energy, which can then be used to generate electricity. there are two main types of wind turbines: horizontal axis wind turbines (hawts) and vertical axis wind turbines (vawts). hawts are more traditional. they have a rotor mounted horizontally on a tower and the blades rotate around a horizontal axis perpendicular to the wind direction. they are commonly used in large-scale wind farms and are well-suited for locations with strong and consistent winds. in general, designing a wind farm involves several considerations, including selecting an appropriate site, choosing the right type and size of turbines, and determining the optimal layout and spacing of turbines. according to [53, 54], the first step in designing a wind farm is to select a suitable site with high wind speeds and low turbulence. additionally, authors in [55] report that the choice of turbine depends on the site conditions and the energy requirements of the project. furthermore, the layout and spacing of the turbines will affect the performance of the wind farm [56]. the turbines should be spaced far enough apart to avoid the effects of wake, which is the turbulence created by the rotor blades as they rotate [57, 58]. if the turbines are spaced too closely, the wake effect can reduce the efficiency of downstream turbines. the wake effect occurs when the rotor blades of a wind turbine disrupt the air flow behind them, creating turbulence that can reduce the efficiency of downstream turbines [57, 58]. regular cleaning and maintenance procedures are considered important factors [59, 60]. table ii. specifications of the selected wind turbines specification turbine#1 turbine#2 turbine#3 hub height [m] 80 75 80 rated power [w] 2000 500 1500 cut in speed [m/s] 4.0 3.0 4.0 rated speed [m/s] 13.0 10.0 11.6 cut out speed [m/s] 25.0 25.0 fig. 1. power-speed curve for the selected wind turbines. in this study, three wind turbines (turbine#1: aaer-a2000 – 80m, turbine#2: ewt-dw 52 500kw 75m, and turbine#3: aw-70/1500 class i 80m) are considered. the power-speed curve and the specification of the selected turbines are shown in figure 1 and table ii, respectively. the capital, operation, and maintenance costs are assumed based on [61-66]. moreover, various types of losses are taken into consideration for the evaluation of energy production. f. software tool for feasibility study during the recent years, numerous simulation tools have been available for assessing the performance of wind farms, including retscreen and homer. retscreen expert is a comprehensive clean energy management software tool developed by the canadian government that allows users to evaluate the energy production, savings, and costs of various types of renewable energy and energy efficiency technologies. it provides users with a suite of tools and databases that can be used to analyze renewable energy and energy efficiency projects. it includes a database of over 1,000 pre-built energy efficiency and renewable energy measures, as well as a variety of performance and financial analysis tools. it can be used to evaluate the performance of various renewable energy technologies. moreover, it includes a suite of financial analysis tools that can be used to estimate the costs and financial returns of energy projects, including cash flows, net present value, and internal rate of return. several researchers have utilized retscreen for the evaluation of the techno-economic feasibility of wind farms. for instance, authors in [13] utilized retscreen to evaluate the economic viability of a 50 mw grid-connected wind farm. authors in [41] evaluated the feasibility of a 100 mw grid-connected wind farm in saudi arabia using retscreen. authors in [49] estimated the economic viability of wind farms in ghana using retscreen. consequently, retscreen expert is used for evaluating the economic and environmental viability of wind farms in the current study. the mathematical equations for the calculation of the capacity factor, the annual power production, ghg reductions, and economic indicators are discussed in [53]. iii. results and discussion a. wind power potential at 50 m height to evaluate the wind power potential at a specific location, the wsc should be evaluated based on the value of daily, monthly, or annual wind speed. in the current study, the average monthly wind speeds values were gathered over a period of 30 years. the descriptive statistics of wind speed data of each location are listed in table iii. in addition, the monthly variation in wind speed for each of the chosen locations is shown in figure 2. the mean wind speed is ranged between 5.66 m/s and 6.56 m/s at a height of 50 m. the values for mean speed and standard deviation (sd) indicate that the wind behavior is quite consistent. the coefficients of variation (cvs), which are within the range of 5.97-14.72%, are relatively low. the minimum and maximum values of 4.51 m/s and 7.68 m/s are recorded in l#15 (misratah) and l#13 (darnah) during august and february, respectively, as shown in figure 3. for the majority of the chosen locations, the skewness (s) values are negative, indicating that all distributions are left skewed. additionally, the values of kurtosis (k) vary from -1.65 to -0.56, and they are also moderately low as shown in table iii. the parameters of the 2p-w distribution functions were estimated using monthly mean wind speed with the mls. table iv presents the annual weibull distribution parameters of engineering, technology & applied science research vol. 13, no. 4, 2023, 11277-11289 11282 www.etasr.com kassem et al.: feasibility analysis of the wind energy potential in libya using the retscreen expert the selected locations. for all 22 locations, the calculated annual weibull scale parameter varies from 5.84 to 6.88 m/s and the range of the annual shape parameter is 8.78 to 21.49. the lowest and highest shape parameter is found at l#8 (al marqab) and l#14 (ghat), respectively. the graphic representation of the weibull probability is presented in figure 3. furthermore, the wpd is calculated for a year using (5). it should be noted that the average air density yearly values were determined using the ideal gas law. throughout the investigation period, the air temperature and pressure values were gathered for this purpose. the average annual wpd at three hub heights is presented in table v. it can be seen that the wpd values are within the range of 111.30172.91 w/m2. the minimum and maximum wpd values are recorded at l#1(al butnan) and l#13 (darnah) as 111.30 w/m2 and 172.91 w/m2, respectively. it can be concluded that despite the unsuitability of the region's wind power potential for high-capacity wind turbines, it may still be feasible to harness wind power through the use of small-scale wind turbines in the area. table iii. descriptive wind speed dataset location no. mean sd cv min. max. s k l1 5.66 0.41 7.31 4.92 6.17 -0.68 -0.64 l2 6.49 0.49 7.54 5.63 7.20 -0.40 -1.01 l3 5.92 0.53 8.97 5.06 6.52 -0.37 -1.62 l4 6.04 0.37 6.13 5.52 6.66 0.31 -0.56 l5 6.42 0.41 6.45 5.76 6.96 -0.22 -1.21 l6 5.90 0.48 8.19 5.10 6.44 -0.61 -1.20 l7 6.52 0.58 8.82 5.75 7.41 0.12 -1.48 l8 6.19 0.91 14.72 4.64 7.25 -0.43 -1.18 l9 5.85 0.47 7.99 5.06 6.53 -0.35 -1.09 l10 5.84 0.52 8.93 5.03 6.46 -0.36 -1.51 l11 6.09 0.73 12.02 4.89 7.01 -0.37 -1.27 l12 6.40 0.69 10.74 5.55 7.43 0.22 -1.65 l13 6.56 0.74 11.30 5.40 7.68 -0.11 -1.26 l14 6.08 0.36 5.97 5.48 6.57 -0.38 -1.27 l15 6.02 0.87 14.41 4.51 7.02 -0.52 -1.13 l16 6.55 0.45 6.86 5.81 7.12 -0.43 -1.24 l17 6.41 0.41 6.45 5.81 7.02 0.01 -1.40 l18 6.08 0.50 8.23 5.27 6.69 -0.24 -1.43 l19 6.06 0.44 7.31 5.35 6.65 -0.10 -1.53 l20 6.09 0.73 12.02 4.89 7.01 -0.37 -1.27 l21 5.98 0.39 6.50 5.40 6.51 -0.17 -1.44 l22 6.08 0.49 8.12 5.35 6.73 -0.17 -1.00 b. feasibility of a 100 mw wind farm in this study, retscreen was utilized to analyze the impact of wake effects (array losses in %) and airfoil losses in the percentage on the output of wind farms, cf, ghg emissions, and financial viability. in the current study, 11 scenarios were based on a 100 mw wind power project. the inputs and calculations were conducted using the level 3 analysis (level 2 for financial) in retscreen expert, which provides the highest level of detail. fig. 2. monthly average wind speed for all selected locations over 30 years at 50 m height. additional information about the scenarios and assumptions can be found in table v. as mentioned above, the performance of the wind farms in terms of wind power output and cf depends on the geographic location and wsc. based on the results, the maximum and minimum average monthly wind speed was recorded in darnah and al butnan, respectively. thus, the electricity exported to the grid (eeg), the cf, and the economic viability and environment feasibility were estimated for all the selected regions. engineering, technology & applied science research vol. 13, no. 4, 2023, 11277-11289 11283 www.etasr.com kassem et al.: feasibility analysis of the wind energy potential in libya using the retscreen expert table iv. annual weibull parameters and wpd values at 50 m height location shape scale [m/s] wpd [w/m 2 ] locations shape scale [m/s] wpd [w/m 2 ] l1 18.46 5.84 111.30 l12 10.79 6.70 160.31 l2 16.86 6.71 167.63 l13 10.70 6.88 172.91 l3 14.58 6.15 126.97 l14 21.49 6.24 137.49 l4 17.74 6.21 134.68 l15 9.17 6.37 133.63 l5 19.11 6.60 161.76 l16 18.88 6.74 171.92 l6 16.65 6.11 125.90 l17 18.36 6.59 161.07 l7 13.25 6.77 169.64 l18 15.26 6.30 137.49 l8 8.78 6.56 144.98 l19 16.72 6.26 136.20 l9 15.78 6.05 122.62 l20 10.67 6.40 138.40 l10 14.46 6.06 121.79 l21 18.96 6.15 131.04 l11 10.67 6.40 138.40 l22 15.21 6.30 137.61 fig. 3. graphic representation of the weibull probability for all the selected locations. table v. assumed case, inputs to the tool wind farm capacity 100 mw 100 mw 100 mw turbine turbine#1: aaer-a-2000 turbine#2: ewt-dw 52 500kw project life 20 years capital cost 2000 usd/kw replacement cost 1600 usd/kw operational and maintenance 50 usd/kw array (wake effects) losses ranged from 2% to 16% in step 4 airfoil soiling losses ranged from 2% to 10% in step 4 miscellaneous losses 6.00 availability factor 98.00 inflation rate 2.77 discount rate 9.52 debt ratio 70.00 debt interest rate 3.28 debt payments 15.00 electricity export escalation rate 5.00 the mean monthly value of eeg for all the proposed scenarios (cases) is shown in figure 4 for darnah and figure 5 for al butnan. it is observed that the eeg is within the range of 198888-31616.853 mwh for turbine#1 and 27055.9041458.69 mwh for turbine#2. the lowest value of eeg is recorded for case#11 (array losses = 16% and airfoil soiling losses = 10%), while the highest value is recorded for case#1 (array losses = 2% and airfoil soiling losses = 2%). also, it is noticed that turbine#2 (cut-in speed = 3 m/s and rated wind speed = 10 m/s) produced higher eeg than turbine#1 (cut-in speed = 4m/s and rated wind speed = 13 m/s). the results indicate that an increase in wake effect percentage resulted in reduced energy production from the wind farm. these results are supported by the findings in 69-73]. the power production from wind farms depends on the distance between the turbines and the operating condition of the upstream turbine. also, they found that the wake effect can cause up to a 30% reduction in power output. also, it is found that airfoil soiling losses can significantly impact the energy production of wind farms as shown in figures 4 and 5. it has been shown [73-75] that even a small amount of soiling can cause a noticeable decrease in the power output. fig. 4. monthly variation of the eeg of all proposed cases for darnah. furthermore, the annual cf was calculated for all cases as shown in figure 6. the annual cf varied from 30.97% to 57.69%. the results are supported by previous scientific studies. according to [76], the cf of wind farms under consideration ranged from 9.79% to 51.93%. authors in [77] reported that the cf of the proposed farms fell within the range of 5-42%. authors in [78] found the cf of the proposed farm projects in pakistan to range from 19% to 34%. in [79], the cf values were estimated to be within the range of 22.9-50.6% using different wind turbines. assessing the economic viability and sustainability of a project is crucial, and one way to do so is through techno-economic feasibility analysis. in this regard, the feasibility of the proposed projects was evaluated using retscreen, taking into consideration various financial parameters. the input parameters used for the analysis were based on previous studies and included an inflation rate of 2.77%, a discount rate of 9.52%, a reinvestment rate of 9%, a project life of 20 years, a debt ratio of 70%, a debt interest rate of 3.28%, and debt payment spread over 15 years. based on these input parameters, npv, alcs, sp, ep, and lcoe were estimated using retscreen. the npv was determined for each case and is illustrated in figures 7 for darnah and figure 8 for al butnan. engineering, technology & applied science research vol. 13, no. 4, 2023, 11277-11289 11284 www.etasr.com kassem et al.: feasibility analysis of the wind energy potential in libya using the retscreen expert fig. 5. monthly variation of the eeg of all proposed cases for al butnan fig. 6. annual cf for the proposed cases suing different wind turbines. c. feasibility of a 10 mw installed capacity wind farm in this study, the technical viability of turbine#2 (dw 52 500kw 75m) is evaluated for all the selected locations and the results were compared with turbine#3 (aw-70/1500 class i 80m). as mentioned above, the wind power output and the cf of the wind farms depend on the geographic location and wind speed characteristics. therefore, in this study, eeg and cf as well as the financial viability were estimated for all the considered locations with retscreen. fig. 7. economic performance for the developed wind farms in darnah. figure 9 shows the mean monthly eeg values for the proposed wind turbine models. it can be observed that the eeg ranges from 2165.497 to 4046.684 mwh for turbine#3 and from 2279.643 to 4641.675 mwh for turbine#2. it is noticed that turbine#2 produced higher eeg than to turbine#3. figure 10 shows the calculated annual cf. the results indicate that the annual cf varies from 38.39% to 56.79%. the cf of turbine#2 was found to be the highest. previous studies [7679] can be supported by these results. engineering, technology & applied science research vol. 13, no. 4, 2023, 11277-11289 11285 www.etasr.com kassem et al.: feasibility analysis of the wind energy potential in libya using the retscreen expert fig. 8. economic performance for the developed wind farms in al butnan. figure 11 shows the npv calculated for each location and the electricity export rate (eer), which indicated a positive value for each location, suggesting a potentially feasible project. additionally, the irr was estimated to evaluate the economic viability of the project, and it was found that the value for all locations was higher than the required rate of return. the alcs was calculated using the npv, discount rate, and project lifetime, and it was found to be in the range of 1798379 to 5640383 usd/year for all the proposed projects. the payback period, which represents the time needed to recover the initial investments made for the project, was also evaluated for all selected locations, as shown in figure 11. the ep and sp were found to be within the range of 6.99 to 4.47 years and 3.36 to 1.66 years, respectively, with turbine#2 having the lowest values. additionally, the epc was calculated to be within the range of 0.0707 to 0.0437 usd/kwh. fig. 9. monthly variation of eeg for all the selected locations. fig. 10. cf value of the selected wind turbines. d. climate co-benefit assessment estimating the environmental benefits in terms of reduced ghg emissions of the proposed system is crucial. calculation of the climate co-benefits in terms of ghg emission reduction was performed using retscreen for each location and is presented in figures 12 and 13 for 100mw and 10mw wind farms, respectively. the annual electricity generation was used to determine the total co2 emission reduction for each location. the results indicate that a large amount of co2 emissions can be avoided by implementing the developed wind farms. iv. limitations and future work although the results of the present study were derived from retscreen utilizing the nasa dataset, it is important to acknowledge that this study possesses certain limitations that could be explored and addressed in future research. first, the accuracy of the data from nasa for assessing the wind potential in libya is not evaluated in this study, therefore, wind resource assessment in libya should be investigated using various gridded satellite data, and the results should be compared with the measured data to find the best-gridded satellite data. second, terrain analysis was not considered in this study. future research should focus on the site selection of wind energy power plants using gis-multi-criteria evaluation. third, the influence of weather parameters such as air temperature, and relative humidity were not considered. engineering, technology & applied science research vol. 13, no. 4, 2023, 11277-11289 11286 www.etasr.com kassem et al.: feasibility analysis of the wind energy potential in libya using the retscreen expert therefore, future research should examine the influence of temperature, relative humidity, and density on wind power generation. finally, the impact of economic data, which is required for the techno-economic model on the performance of wind turbines, was not been investigated. hence, it is recommended that future research concentrates on examining the impact of economic data on the performance of wind farms. fig. 11. economic performance of the developed wind projects at the selected locations. v. conclusions libya faces a rising demand for electricity production due to its expanding economy and growing population. renewable energy sources, particularly wind energy, emerge as a readily accessible energy solution to address this demand. according to the global wind atlas, libya is blessed with abundant wind energy resources at a hub height of 50 m. accordingly, the main aim of the present study was to evaluate the wind potential at 22 locations over libya. the results showed that darnah has the maximum wind speed with a value of 7.68 m/s, while the minimum speed of 4.51 m/s was recorded in misratah. moreover, it was found that small-scale wind turbines are suitable for generating electricity in the country based on the value of wpd. moreover, the techno-economic feasibility of 100 and 10 mw wind farms was investigated using retscreen expert. the impact of wake effect and airfoil losses on the performance of wind farms was assessed to provide valuable insight for policymakers in the country. fig. 12. ghg emission reduction potential from 100 mw wind farms. fig. 13. ghg emission reduction potential from 100 mw wind farms. the results demonstrated that the wake effect is an important factor in wind farm design and can be mitigated through careful spacing and turbine design. additionally, airfoil soiling on wind turbine blades can have a significant impact on the energy production of a wind farm, reducing the efficiency of the turbine and lowering the amount of energy it can produce. thus, wind farm operators typically implement regular cleaning and maintenance procedures to minimize the impact of airfoil soiling on energy production. moreover, the results indicate that turbine#2 (ewt-dw 52 500kw) can be engineering, technology & applied science research vol. 13, no. 4, 2023, 11277-11289 11287 www.etasr.com kassem et al.: feasibility analysis of the wind energy potential in libya using the retscreen expert a suitable turbine for a wind farm with various installation capacities in libya. vi. recommendations the wind energy potential in libya is significant and could contribute significantly to the country's energy mix. however, the wind energy sector in the country faces several challenges, including inadequate infrastructure, inadequate investment, and policy gaps. addressing these challenges would require a clear policy framework for the sector, increased investment, and a focus on developing local capacity.  inadequate infrastructure: one of the main challenges of wind energy production is inadequate infrastructure. the country's electricity infrastructure is inadequate, and this affects the wind energy sector, as there is a lack of suitable wind turbines and other equipment for wind energy generation. there is also a lack of suitable transmission and distribution networks for wind energy, which limits the ability to integrate wind farms into the national grid.  inadequate investment: the wind energy sector suffers from inadequate investment, with most of the investment going to the oil and gas sector. the lack of investment has limited the development of wind energy projects and has hindered the growth of the sector. the lack of investment has also resulted in a lack of research and development in, which limits innovation and the adoption of new technologies.  policy gaps: the wind energy sector also faces policy gaps, with no clear policy framework. the lack of a clear policy framework has resulted in a lack of incentives for wind energy development and a lack of regulations. this has limited the growth of the sector 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[80] e. lantz, m. m. hand, and r. wiser, "past and future cost of wind energy: preprint," national renewable energy laboratory, golden, co, united states, nrel/cp-6a20-54526, aug. 2012. microsoft word 17-3257_s_etasr_v10_n1_pp5191-5194 engineering, technology & applied science research vol. 10, no. 1, 2020, 5191-5194 5191 www.etasr.com zerroug & dzelzitis: a study of modeling techniques of building energy consumption a study of modeling techniques of building energy consumption abdellah zerroug electrical engineering department ferhat abbas setif-1 university setif, algeria abzerroug@gmail.com egils dzelzitis institute of heat, gas and water technology riga technical university riga, latvia egils@lafipa.lv abstract—residential energy consumption accounts for more than 40% of the total energy consumed in the world. the residential sector is the biggest consumer of energy in every country, and therefore focusing on the reduction of energy consumption in this sector is very important. the energy consumption characteristics of the residential sector are very complicated and the variables affecting the consumption are wide and interconnected, so more detailed models are needed to assess the impact of adopting efficient and renewable energy technologies suitable for residential applications. the aim of this paper is to review some of the techniques used to model residential energy consumption. they are gathered in two categories: top-down and bottom-up. the top-down approach considers the residential sector as an energy sink and does not take into account the individual end-uses. the bottom-up approach uses the estimated energy consumption of a representative set of individual houses and extrapolates it to regional and national levels. based on the strengths, shortcomings, and purposes, an analytical review of each technique, is provided along with a review of models reported in the literature. keywords-energy consumption; modeling techniques; residential sector; top-down; bottom-up; co2 emissions i. introduction residential building energy consumption (rbec) is defined as the energy consumed by households excluding transportation uses. in the residential sector, energy is used for equipment and to provide heating, cooling, and lighting. it is affected by income, energy prices, building location, household characteristics, weather, type and efficiency of equipment, energy access, availability, and energy related policies. as a result, the type and amount of energy can vary widely within and across regions and countries [1]. in recent years, although measurements and policies have been taken to reduce energy consumption and gas emissions, and the residential buildings have continuously improved in efficiency, substantial differences in the residential energy consumption are still being observed in similar dwellings [2-4]. globally, residential energy consumption represents the 16-50% of the total and averages approximately at 30% as shown in figure 1 [5]. only 10% of the population of the world exploits 90% of fossil fuel resources. today's energy systems rely heavily on fossil fuel resources making them diminish ever faster. the world must prepare for a future without fossil fuels. sustainable energy consumption has become an urgent matter for all countries. world residential delivered energy consumption will increase by 57% from 2010 to 2040 (table i) [1]. fig. 1. residential energy consumption shown as a percentage of national energy consumption and in relative international form [1] in europe the built environment consumes 40% of the produced energy. a large part of this energy is consumed in residential buildings. households account for about 30% of the total building-related energy consumption in oecd countries [6]. a 30-57% of the energy consumed by households is spent on space and domestic water heating, making conservation in this area a matter of vital importance [2]. this significant consumption level indicates the crucial role that the residential sector plays in total energy consumption, which means that it is necessary to understand the characteristics associated to energy consumption to better prepare for the increasing energy demand in the future. in response to climate change, high energy prices, and energy supply/demand, there is an interest in understanding the detailed consumption characteristics of the residential sector in an effort to promote conservation, efficiency, technology implementation, and energy source switching, such as to on-site renewable energy[1]. other sectors such as commercial, agriculture, transport and industry have a regular energy consumption because usually these sectors are private or under centralized ownership and they are well defined and regulated. the energy consumption in the residential sector is very complex because of the large variety of construction types, sizes, thermal envelope materials, and the very wide variety of occupant behavior. corresponding author: abdellah zerroug engineering, technology & applied science research vol. 10, no. 1, 2020, 5191-5194 5192 www.etasr.com zerroug & dzelzitis: a study of modeling techniques of building energy consumption table i. global residential delivered energy consumption region 2010 2015 2020 2025 2030 2035 2040 average annual percent change 2010-2040 oecd 28.2 28.1 29 29.9 30.8 31.3 32 0.4 americas 13.2 12.8 12.9 13.2 13.5 13.9 14.2 0.3 europe 11.7 11.9 12.5 13.1 13.5 13.7 13.9 0.6 asia 3.3 3.4 3.5 3.7 3.8 3.8 3.9 0.5 non oecd 23.9 27 30.8 35.1 40.0 45.0 49.8 2.5 europe and eurasia 6.3 6.3 6.7 7.1 7.7 8.1 8.6 1.0 asia 10.6 12.8 15.6 18.7 22.2 25.9 29.6 3.5 middle east 3.4 3.9 4.2 4.4 4.6 4.7 4.8 1.2 africa 1.6 1.7 1.9 2.2 2.5 2.8 3.2 2.4 central and s. america 2.0 2.3 2.4 2.7 3.0 3.4 3.7 2.1 world 52.0 55.1 59.8 65.0 70.8 76.3 81.8 1.5 space heating and cooling, domestic hot water, appliances, and lighting are the major utilities that consume most energy in residential buildings. total residential energy consumption (rec) is defined as the energy required by the aggregates, including the losses due to energy transmission or appliances efficiencies. the energy consumed for heating and cooling space has the biggest share of the total rec. this energy can be supplied by different sources including passive solar gain, occupants gain, lighting and appliances gain. the total rec for a given area or a country gives the regional or national residential sector consumption. the mean object of the building energy consumption modeling is to quantify the energy needs and requirements as a function of input parameters. the most common reason for using models is to determine the energy supply requirements at a large scale, and the change in energy consumption in a dwelling due to renovation, retrofit, or improvement of equipment at a local scale. modeling rec can be very useful for policy makers and householders. rec models depend on climate variations, thermal zone, building construction, neighborhoods, local population, life standards, region or nation. our objective is to provide an up-to-date review of different modeling techniques used for modeling rec. two main approaches are identified: top-down and bottom-up. each method depends on different levels of input data information, different calculation or simulation techniques, and shows results with different applicability. a detailed review of each technique, focusing on the strengths, shortcomings, and purposes, is provided along with a review of the reported models. ii. overview of modeling methodologies in this section, we intend to outline the methodologies and the available techniques for modeling residential sector, as this has already been given in detail elsewhere [5, 7–11]. residential energy models strongly depend on input data to calculate or simulate energy consumption. the level of detail of the available input data can vary dramatically [11], resulting in the use of different modeling techniques which seek to take advantage of the available information. modeling and control of the air temperature and humidity in greenhouses in order to reduce energy consumption and keep a suitable microclimate are discussed in [12]. measures to control photovoltaic energy use and shading effect on energy consumption are developed in [13]. the measurements taken to reduce energy consumption in residential building should not affect thermal comfort conditions. some authors have suggested and studied the effect of facade shading and green roofs in conserving thermal comfort with less consumed energy [14-16]. these different modeling techniques have different strengths, weaknesses, capabilities, and applicabilities. the input data necessary to build residential energy models include information on the physical characteristics, occupants and their appliances, historical data of energy consumption, climatic conditions, and macroeconomic indicators of the dwellings, depending on the modeling methodology to be used. the preliminary estimate of the total residential sector energy consumption is usually published by governments which compile gross energy values submitted by energy providers (canada [11], usa [17], uk [18], and china [19]). these energy estimations give a good indication for energy consumption but may not be accurate as they do not take in account the onsite energy gain or generation. a more detailed source of energy consumption data, typically on a monthly basis for each dwelling, is the billing records of energy suppliers. however, with no additional housing information these energy consumption values are difficult to correlate due to the wide variety of dwellings and occupants. housing surveys are conducted to provide more detailed information about equipment energy consumption values. the target of these surveys is a sample of residential dwellings to determine building properties and occupant characteristics and appliances penetration levels (canada [20], usa [21], and uk [22]). usually, surveys aim to define the physical properties of the house such as geometry and thermal properties of the envelope, ownership of appliances, occupants and their use of appliances and preferred settings, and demographic characteristics. in addition, surveys may attempt to obtain the energy suppliers’ billing data and alternative energy source information (e.g. unreported wood usage) to correlate the energy consumption of the house with its characteristics identified during the survey. this will permit the calibration through reconciliation of a model’s predicted energy consumption with actual energy billing data. this level of information is superior to the previously mentioned energy supplier values, however it is limited due to collection difficulties and cost, and therefore it is imperative that the selected sample be highly representative of the population. also, occupant descriptions of their appliance use are highly subjective and can be influenced by the season during which the survey takes place [20]. some examples of surveys which have been condensed for the purpose of energy simulation are engineering, technology & applied science research vol. 10, no. 1, 2020, 5191-5194 5193 www.etasr.com zerroug & dzelzitis: a study of modeling techniques of building energy consumption [21-23]. estimated total sector energy, individual billing data, surveys, and sub-metering have been used to varying degrees in the development of residential energy consumption models. deciding which information is used depends on availability and model’s purpose. the purpose of models ranges widely and may be directed towards determining supply requirements, price and income elasticity, the energy consumption impacts of upgrades, or changes to behavioral patterns. iii. residential energy use modeling methodologies the complexity of residential energy use patterns and the dependence on data input level make modeling residential energy use potentially challenging. however, based on different capabilities, strengths, weaknesses, and the applicability of each modeling technique, matching input data with models that can best use them can produce satisfactory models. generally speaking, techniques employed to model residential energy use can be classified into two categories, “top-down” and “bottom-up”, and this terminology is referred to the hierarchal position of data inputs [5]. top-down models are mostly uses at a macroscopic level, by governments building departments while bottom-up models are used at microscopic level by engineers (see [5] for details). a. top-down models the use and development of the top-down modeling approach proliferated with the energy crisis of the late 1970s. in an effort to understand consumer behavior with changing supply and pricing, broad econometric models were developed for national energy planning. these models require little detail of the actual consumption processes. the models treat the residential sector as an energy sink and regress or apply factors that affect consumption to determine trends. most top-down models rely on similar statistical data and economic theory. as the housing stock in most regions is continuously undergoing improvement and increase, simply modeling the energy consumption solely as a function of economic variables is short termed. authors in [24] initiated an annual housing energy model of the usa. their model relied on econometric variables and included a component for growth/contraction of the housing stock. their work was expanded and improved over the following years resulting in an econometric model which had both housing and technology components [25, 26]. the housing component evaluates the number of houses based on census data, housing attrition and new construction. the technology component increases or decreases the energy intensiveness of the appliances as a function of capital cost. the economic component evaluates changes in consumption based on expected behavioral changes and efficiency upgrades made to the technology component. finally, market penetration is considered a function of income and demand/supply. the simulation model combines the changes in outputs of the components and estimates the energy consumption given historic energy consumption values. the authors felt their model was sensitive to major demographic, economic and technological factors, but recognized the need to continually update all assumed information to improve quality. authors in [25] developed a similar model for new zealand although it had a technological focus. b. bottom-up models the bottom-up approach was developed to identify the contribution of each end-user towards the aggregate energy consumption value of the residential stock. this refines the understanding of the details associated with the energy consumption. there are two distinct categories used in the bottom-up approach to evaluate the energy consumption of particular end-uses. the statistical models (sms) utilize dwelling energy consumption values from a sample of houses and a variety of techniques to regress the relationships between the end-uses and the energy consumption. sm models can utilize macroeconomics, energy prices, income, and other regional or national indicators, thereby gaining the strengths of the top-down approach. the engineering models (ems) category relies on information of the dwelling characteristics and end-uses themselves to calculate the energy consumption based on power ratings and use characteristics and/or heat transfer and thermodynamic principles. consequently, the engineering technique has strengths such as the ability to model new technologies based solely on their traits. once developed, the bottom-up models may be used to estimate the energy consumption of houses representative of the residential stock and then these results can be extrapolated to be representative of the regional or national residential sector. iv. conclusion top-down models are used mostly for supplying analysis based on long-term projections of energy demand by taking in account the historical response. bottom-up statistical models are used to identify the energy demand contribution of end-uses by introducing the behavioral aspects based on the data obtained from energy authorities and surveys. bottom-up engineering techniques are used to explicitly calculate energy consumption of end-uses taking in account the detailed descriptions of a representative set of houses, and they have the capability of determining the impact of new technologies. given today’s energy considerations that include supply, efficient use, and effects of energy consumption to the promotion of conservation, efficiency, and technology implementation, all modeling approaches are useful. top-down models are more useful in supply considerations because they are strongly weighted by historical energy consumption which makes their estimates of supply more accurate. bottom-up statistical models can account for occupant behavior and use of major aggregates, leading to understand which of behaviors and end-uses cause more energy consumption. lastly, bottomup engineering models may identify the impact of new technologies based on their characteristics and account for the wide degree of variety within the housing stock. to determine the impacts of such new developments requires a bottom-up model with more focus on efficiency and surveys on energy consumption generation at individual houses. in this fast technological development and implementation environment, the bottom-up techniques will likely provide much utility as policy and strategy development tools. although bottom-up building physics stock models are used to explicitly determine and quantify the impact of different combinations of technological measures on delivered energy use and co2 emissions, and therefore represent an engineering, technology & applied science research vol. 10, no. 1, 2020, 5191-5194 5194 www.etasr.com zerroug & dzelzitis: a study of modeling techniques of building energy consumption important tool for policymakers, there are some limitations associated with modeling. the most important shortcoming of all these models is their lack of transparency and quantification of inherent uncertainties. the lack of publicly available detailed data on the models inputs and outputs, as well as underlying algorithms renders any attempt to reproduce their outcomes problematic. in addition, the relative importance of input parameter variations on the predicted demand outputs needs to be quantified. references [1] energy information administration, international energy outlook 2016 with projections to 2040, technical report series, vol. 484, eia, 2016 [2] o. g. santin, actual energy consumption in dwellings: the effect of energy performance regulations and occupant behavior, ios press, 2010 [3] l. lutzenhiser, “a question of control: alternative patterns of room airconditioner use”, energy and buildings, vol. 18, no. 3-4, pp. 193–200, 1992 [4] h. jeeninga, m. uyterlinde, j. uitzinger, energieverbruik van energiezuinige woningen, ecn-c-01-072, ecn, 2001 (in dutch) [5] l. g. swan, v. i. ugursal, “modeling of end-use energy consumption in the residential sector: a review of modeling techniques”, renewable and sustainable energy reviews, vol. 13, no. 8, pp. 1819-1835, 2009 [6] l. itard, f. meijer, towards sustainable northern european housing stock: figures, facts and future, ios press, 2008 [7] s. d. tuladhar, m. yuan, p. bernstein, w. d. montgomery, a. smith, “a top–down bottom–up modeling approach to climate change policy analysis”, energy economics, vol. 31, pp. s223-s234, 2009 [8] c. bohringer, t. f. rutherford, “combining bottom-up and top-down”, energy economics, vol. 30, no. 2, pp. 574-596, 2008 [9] c. bohringer, t. f. rutherford, “integrated assessment of energy policies: decomposing top-down and bottom-up”, journal of economic dynamics and control, vol. 33, no. 9, pp. 1648-1661, 2009 [10] n. strachan, r. kannan, “hybrid modelling of long-term carbon reduction scenarios for the uk”, energy economics, vol. 30, no. 6, pp. 2947-2963, 2008 [11] n. behidj, j. bernier, s. blais, d. demers, s. genest, c. ramsum, k. sassi, energy use data handbook: 1990 and 1998 to 2004, natural resources canada, 2006 [12] m. jomaa, m. abbes, f. tadeo, a. mami, “greenhouse modeling, validation and climate control based on fuzzy logic”, engineering, technology & applied science research, vol. 9, no. 4, pp. 4405-4410, 2019 [13] a. s. saidi, m. b. slimene, m. a. khlifi, “transient stability analysis of photovoltaic system with experimental shading effects”, engineering, technology & applied science research, vol. 8, no. 6, pp. 3592-3597, 2018 [14] s. m. wahba, b. a. kamel, k. m. nassar, a. s. abdelsalam, “effectiveness of green roofs and green walls on energy consumption and indoor comfort in arid climates”, civil engineering journal, vol. 4, no. 10, pp. 2284-2295, 2018 [15] u. m. burciaga, p. v. saez, f. j. h. ayon, “strategies to reduce co2 emissions in housing building by means of cdw”, emerging science journal, vol. 3, no. 5, pp. 274-284, 2019 [16] s. wahba, b. kamil, k. nassar, a. abdelsalam, “green envelop impact on reducing air temperature and enhancing outdoor thermal comfort in arid climates”, civil engineering journal, vol. 5, no. 5, pp. 1124-1135, 2019 [17] energy information administration, annual energy review 2006, doe/eia-0384(2006), eia, 2006 [18] department for business enterprise & regulatory reform, energy consumption in the united kingdom, 2007 [19] national bureau of statistics of china, china statistical yearbook 2005, china statistics press, 2005 [20] office of energy efficiency, 2003 survey of household energy use (sheu)–detailed statistical report, natural resources canada, 2006 [21] energy information administration, residential energy consumption survey, u.s. energy information administration, 2001 [22] department for communities and local government. english house condition survey: technical report (2005 edition). west yorkshire: communities and local government publication centre, 2007 [23] international energy agency, mapping the energy future: energy modelling and climate change policy, international energy agency, 1998 [24] e. hirst, w. lin, j. cope, “a residential energy use model sensitive to demographic, economic, and technological factors”, quarterly review of economics & business, vol. 17, no. 2, pp. 7-22, 1977 [25] e. hirst, “a model of residential energy use”, simulation, vol. 30, no. 3, pp. 69-74, 1978 [26] d. l. oneal, e. hirst, “an energy use model of the residential sector”, ieee transactions on systems, man, and cybernetics, vol. smc-10, pp. 749-755, 1980 microsoft word etasr_v11_n1_pp6687-6690 engineering, technology & applied science research vol. 11, no. 1, 2021, 6687-6690 6687 www.etasr.com ali et al.: analyzing the impact of loop parameter variations on the transient response of second … analyzing the impact of loop parameter variations on the transient response of second order voltageswitched cp-pll darshna narwani department of electronic engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan darshna.narwani@muetkhp.edu.pk ehsan ali department of electronic engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan ehsan.ali@quest.edu.pk ahsan murtaza bughio department of electronic engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan ahsan.murtaza@quest.edu.pk nasreen nizamani department of electronic engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan nasreen_nizamani@quest.edu.pk shahid hussain siyal department of energy and environment engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan shahidsiyal@quest.edu.pk abdul rafay khatri department of electronic engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan arkhatri@quest.edu.pk abstract-the analysis of the behavior of charge pump phaselocked loop (cp-pll) is a challenging task due to its mixedsignal architecture. out of its two types, i.e. current switched cp-pll (cscp-pll) and voltage switched cp-pll (vscppll), the prior produces symmetrical pump currents, resulting in an appropriate transient performance to be analyzed. the loop parameters are important to set the gain, target frequency, and assure the stability of the system. the more important is the bandwidth of the loop, which is dependent on the loop filter parameters to perform stable operation and locking time. in this paper, the impact of loop parameter variations on the overall transient behavior of the system is investigated. it has been shown that loop parameters play an important role to ease the design of mixed-signal plls. keywords-charge pump pll; voltage switched charge pump; transient analysis; loop parameter variation; behavioral model simulations i. introduction the cp-pll is a mixed-signal architecture (i.e. a combination of digital and continuous time components) [1]. it is an essential building block in a variety of applications ranging from radio frequency (rf) communication like fm modulation and demodulation, frequency synthesis and multiplication, frequency discrimination, tone decoding, data synchronization and conditioning, voltage-to-frequency conversion and clock and data recovery, doppler shift frequency, mobile and wireless communication, servo control systems, and smart system applications [2-6]. as detailed in [7], cp-pll is a widely used subsystem due to its theoretical zero static phase shift, and is also one of the simplest and most effective pll-design platforms. the basic components of a cp-pll are described in [1]. the cp-pll works as a negative feedback device, in which its servo mechanism synchronizes the phase and frequency of divided feedback signal υdiv(t) produced by an oscillator with the phase and frequency of the reference signal υref(t). the phase error between υref(t) and υdiv(t) signals is detected by the digital phase-frequency detector (pfd) which then commands the charge pump (cp) circuit to compensate the error signal by producing correction signal (in the form of current or voltage signal during this interval) [6]. as a result, a subsequent pulse width modulated current signal is produced by the combined pfd-cp operation, which is the supplied to the loop filter (lf) circuit to establish a fine-tuned quasi-dc signal, driving corresponding author: ehsan ali engineering, technology & applied science research vol. 11, no. 1, 2021, 6687-6690 6688 www.etasr.com ali et al.: analyzing the impact of loop parameter variations on the transient response of second … the voltage controlled oscillator (vco) to produce the output frequency [9]. a cp-pll basically operates in nonlinear acquisition and tracking regions. it is unlocked in the acquisition region and works in a strongly nonlinear pull-in process, while in the tracking region, it is locked and follows the phase error variations within the [−2π, 2π] range [6, 10, 13]. there are two types of cp-pll on the basis of its configuration, namely voltage switched charge pump (vscp) and current switched charge pump (cscp) [6, 8, 9, 12]. most research attention has been given to the current switched charge pump (cscp) pll, as it ideally provides a symmetrical pump current, resulting in suitable transient response which is simpler and easier to be analyzed, as compared to that of voltage switched charge pump (vscp) which delivers asymmetrical pump currents to the electrical load of the lf, resulting in varying gain of the control system and hence affecting its tracking ability. however, the cost-effective and simplified design of constant voltage source has made vscp-pll commercially popular among charge pump plls [9]. so far, various models and methods have been developed for the analysis of vscp-pll behavior but this field still requires qualitative research for more efficient modeling and result accuracy in order to facilitate modern communication and control systems with improved tracking performance and stability. in this paper, analysis has been conducted to determine the way the variation in loop parameters affects the transient response of the 2 nd order vscp-pll, using behavioral model simulations. the results are compared with those obtained from the linear transfer function model of vscp-pll in the locked state to further verify its validation for the analysis of vscp behavior. ii. the peculiar effect in the vscp-pll architecture the cp-pll is one of the most utilized circuits in frequency synthesis function. due to the design simplicity of charge-pump, vscp-pll architecture is preferred in most applications. the vscp introduces a peculiar effect in the form of non-constant current ip(t): dn null up rr tv rr tv ti → → →        + − + − = 10 c1ss 10 c1dd p )( 0 )( )( υ υ (1) since the gain of the phase detector is associated with the pump current, thus it affects the overall loop gain of the system [8]. moreover, the engineers prefer the parameters of the linear model. the prediction of the system behavior of the cp-pll is based on the following assumptions: first of the all, the cp-pll is under locked condition, thus the phase error is between [0, 2π] and pfd is in the linear range. second, the output transfer characteristics of the vco are considered linear over the tuning range. considering these conditions, the linear time invariant (lti) system is represented with the transfer function, which is enough to predict the average behavior of the system: ������ = ɸ ����ɸ ����� = ����������� ��������� �� �� ����� ������� ������ ����� (2) generally, two parameters (ζ, ωn) are important to predict the system behavior using the linear approach: vs v dd n 0 1 1 1 2 ( r ) 1 [ ] 2 2 vs vs n v dd k v n r c k v n ω ω ζ τ = + = + (3) the value of !"� is not the same as of ! for the current switched cp-pll as given in [10]. the linear model represented by (2) is only valid in the locked state. if the output frequency deviates from the center frequency due to frequency excursions or non-linear function of the vco characteristics, then the linear representation may not be efficient enough to predict non-linearities at even a small scale. therefore, the impact of such peculiar effect complicates the analysis of vscp-pll systems. thus, more rigorous approaches may be required for analyzing the weakness of such systems in following the ramping system behavior. one of the best approaches apart from the circuit level are the behavioral modeling of such system [10, 11], which can be sufficient to predict non-linear acquisition region of such complex system. iii. transient analysis of 2nd order vscp-pll the p-pll has a non-linear switching behavior and is initial condition dependent. generally, the cp-pll operates in two regions, non-linear acquisition region (during unlocking) and tracking region (during locking). stable pll operation may be predicted by the transfer function model if the following condition is true: # ����#$�� ≥ 10 (3) the sampling ratio in the pulse width modulated behavior of vscp-pll is set by (3) [14]. generally the information is hidden in two parameters: damping factor (ζ) and natural angular frequency (ωn) ,which can be sufficient and a starting point toward the stability condition [15]. a set of parameters was chosen to perform behavioral simulations in simulnik. the transient behavior (in symmetrical condition during locking) of a second order vscp-pll is shown in figure 1. the symmetrical condition is only obtained when υctr(t)=vdd/2. a. loop parameter variations (changing n) the vscp-pll loop is defined by parameters designed to achieve stability and suitable transient characteristics. a vscppll can be used as a frequency synthesizer; the divider circuit is implemented to perform this function. it can be difficult to design multiband vco, thus by changing the value of n, the output frequency response that targets voltage can be changed easily. it can be observed that the slope of the rising voltage over the input of the vco is not constant as a consequence of the weak dynamics of vscp-pll due to the non-constant pump current. engineering, technology & applied science research vol. 11, no. 1, 2021, 6687-6690 6689 www.etasr.com ali et al.: analyzing the impact of loop parameter variations on the transient response of second … fig. 1. symmetrical transient behavior of the vscp-pll. fig. 2. the transient simulations by changing n. b. loop parameter variations (changing kv) as discussed in the above subsection, it can be difficult to change the gain of the vco (kv), or implement multiband vcos. the occurrence of non-linearities may impact the transient or steady state of the vscp-pll and may cause the system to unlock at any stage. thus, in behavioral simulations it may be easy to change the kv, however this is quite challenging during the design process. by changing the gain, the target voltage is changed in a similar way as changing the n under the locked condition: v ref target )( k nf t × =υ (4) from (4), it is easy to predict that the transient behavior can be changed by changing the linear gain (kv) of the vco or n. similarly, it can be observed that the vscp-pll exposes its asymmetrical behavior during non-linear pull in process during locking, as it is evident from the voltage steps during the up and dn cycles (figure 3). the target frequency can be changed either by changing n or kv. since the divider can be programmable, therefore it is more easier to modulate n. obviously, when the cspl-pll system is locked at different target frequencies, the transient parameters like rise time (tr), peak time (tp), percent overshoot and settling time (tr) vary. the two dynamic time parameters given in table i show how the response is changing when the system is locked in symmetrical or asymmetrical condition. moreover, the linear and behavioral model parameters are constant when the system is locked under symmetrical conditions, however these parameters divert when considering the symmetrical situation. it can be concluded that, the linear model is only valid in the symmetrical condition for a second order vscp-pll unlike cscp-pll. fig. 3. the transient simulations for different values of kv. table i. transient parameter variation at different kv with symmetrical and asymmetrical behavior transient parameter linear model (theoretical) behavioral model at kv=48mhz/v (()*+ �,� = -��� ) ζ vs =0.3070, ./"�=4.3853x104 rad/s, �01234 ��34 = 143.2787 tp 75.2 us 74 us tr 45.1 us 45 us at kv=96mhz/v (()*+ �,� 5 -��� ) ζ vs =0.4186, ./"�= 6.2017x104rad/s, �01234 ��34 = 101.3133 tp 55.7 us 47 us tr 35.5u s 32 us at kv=31.68mhz/v (()*+�,� 6 -��� ) ζ vs = 0.2586, ./"�= 3.5626 x104 rad/s, �01234 ��34 = 176.3639 tp 91.286 us 126 us tr 53.24 us 52 us c. loop filter parameter variations the lf parameters are important in obtaining stable system operation, as the overall bandwidth and damping of the system is related to the lf parameters. moreover, there is residual damping due to the inclusion of the vscp architecture. 1) impact of changing r1 on transient response the transient response of the 2 nd order vscp-pll for various values of r1 at symmetrical condition of the chargepump voltage, is shown in figure 4. it can be observed that the speed of response is affected and the system behavior is more damped as the value of r1 is increasing (figure 5). it is worth noting that when the r1 is set to zero the system expanses its weakly damped response. it is evident from (3) that the system has residual damping due to the vscp structure. changing r1 has a slight impact on the natural frequency of the system. 2) impact of changing c1 on transient response the lf parameters are very important in establishing the quasi-dc voltage at the input of the vco in order to produce a signal proportional to the control voltage. the time constant of the lf cirucit sets the speed of the vscp-pll which highly impacts transient parameters like rise time and locking time. as engineering, technology & applied science research vol. 11, no. 1, 2021, 6687-6690 6690 www.etasr.com ali et al.: analyzing the impact of loop parameter variations on the transient response of second … shown in figures 5-6, the transient simulation varies due to the variation of c1. the time constant is increasing and the natural angular frequency of the system is decreasing. however, there is less impact on the damping of the system. fig. 4. transient behavior of vscp-pll at different values of r1 (vdd=4v, r0=2mω, fref=1mhz, n=96, kv=48mhz/v, r1=10kω, r1=0, 5kω ,10kω and 15kω). fig. 5. transient behavior of vscp-pll at different values of c1 (vdd=4v, r0=2mω, fref=1mhz, n=96, kv=48mhz/v, r1=10kω, c1=100pf, 130pf, and 160pf). fig. 6. impact of varying capacitor c1 of the lf on the locking time of vscp-pll. iv. conclusion in this paper, the impact of variations in loop parameters (kv, n, and τ) on the vscp-pll’s transient behavior was investigated using behavioral simulations. the results revealed that the change in the divider ratio n and vco gain kv has direct impact on the overall transient characteristics as the loop gain is associated to charge pump current. by changing n and kv, the locking time and the natural angular frequency ωn vs of the system vary. moreover, changing the values of c1 of the lf circuit under symmetrical pump current, also affects the ωn vs whereas varying the values of r1 of the lf circuit has little impact on the ωn vs and the locking time of vscp-pll, however, it has significant influence on system’s damping response. these parameters highly affect the system’s transient characteristics such as rise time and peak. it was also shown that a vsc-based system exhibits weakly damped behavior even when the 71 is set to zero, unlike the cscp based system [8], however, it leads to improved system stability [15]. references [1] b. a. a. antao, f. m. el-turky, and r. h. leonowich, "behavioral modeling phase-locked loops for mixed-mode simulation," analog integrated circuits and signal processing, vol. 10, no. 1, pp. 45–65, jan. 1996, https://doi.org/10.1007/bf00713978. [2] gardner, phaselock techniques, 3rd edition, 3rd ed. hoboken, nj, usa: wiley-interscience, 2005. [3] r. e. best, phase-locked loops : design, simulation, and applications, 5th ed. new york, ny, usa: mcgraw-hill professional, 2003. [4] d. m. perisic and m. bojovic, "application of time recursive processing for the development of a time/phase shifter," engineering, technology & applied science research, vol. 7, no. 3, pp. 1582–1587, jun. 2017, https://doi.org/10.48084/etasr.1179. [5] h. e. taheri, "a 4-4.8ghz adaptive bandwidth, adaptive jitter phase locked loop," engineering, technology & applied science research, vol. 7, no. 2, pp. 1473–1477, apr. 2017, https://doi.org/10.48084/ etasr.1099. [6] e. ali, g. bhutto, k. amur, n. nizamani, r. khatri, and t. memon, "non-linear model of the second order voltage and current switched cpplls," sindh university research journal, vol. 45, no. 4, pp. 737–742, 2013. [7] p. k. hanumolu, m. brownlee, k. mayaram, and un-ku moon, "analysis of charge-pump phase-locked loops," ieee transactions on circuits and systems i: regular papers, vol. 51, no. 9, pp. 1665–1674, sep. 2004, https://doi.org/10.1109/tcsi.2004.834516. [8] c. hangmann, c. hedayat, and u. hilleringmann, "designing mixedsignal plls regarding multiple requirements taking non-ideal effects into account," in 2019 17th ieee international new circuits and systems conference (newcas), munich, germany, jun. 2019, pp. 1–4, https://doi.org/10.1109/newcas44328.2019.8961261. [9] e. ali, c. hangmann, c. hedayat, f. haddad, w. rahajandraibe, and u. hilleringmann, "event driven modeling and characterization of the second order voltage switched charge pump pll," ieee transactions on circuits and systems i: regular papers, vol. 63, no. 3, pp. 347–358, mar. 2016, https://doi.org/10.1109/tcsi.2015.2512759. [10] f. gardner, "charge-pump phase-lock loops," ieee transactions on communications, vol. 28, no. 11, pp. 1849–1858, nov. 1980, https://doi.org/10.1109/tcom.1980.1094619. [11] c. d. hedayat, a. hachem, y. leduc, and g. benbassat, "modeling and characterization of the 3rd order charge-pump pll: a fully eventdriven approach," analog integrated circuits and signal processing, vol. 19, no. 1, pp. 25–45, apr. 1999, https://doi.org/ 10.1023/a:1008326315191. [12] e. ali, w. rahajandraibe, f. haddad, c. hedayat, and c. hangmann, "simulative characterization of the stability for second order voltage switched cp-pll," in 2013 ieee 56th international midwest symposium on circuits and systems (mwscas), columbus, oh, usa, aug. 2013, pp. 153–156, https://doi.org/10.1109/mwscas.2013. 6674608. [13] n. margaris and v. petridis, "voltage pump phase-locked loops," ieee transactions on industrial electronics, vol. ie-32, no. 1, pp. 41– 49, feb. 1985, https://doi.org/10.1109/tie.1985.350140. [14] d. dhar, p. t. m. van zeijl, d. milosevic, h. gao, and p. g. m. baltus, "analysis of the effect of pfd sampling on charge-pump pll stability," in 2018 ieee international symposium on circuits and systems (iscas), florence, italy, may 2018, pp. 1–5, https://doi.org/ 10.1109/iscas.2018.8351180. [15] a. mansukhani, "phase lock loop stability analysis," applied microwave and wireless, vol. 12, no. 2, pp. 30–41, 2000. microsoft word 1-daoud.doc engineering, technology & applied science research vol. 4, no. 1, 2014, 566-569 566 www.etasr.com daoud et al.: the “stick-slip” phenomenon during the active earth pressure failure … the “stick-slip” phenomenon during the active earth pressure failure of a granular soil of analogical material sidi mohammed daoud civil engineering dpt djillali liabes university sidi bel abbes, algeria daoudmed22@yahoo.fr mourad meghachou civil engineering dpt djillali liabes university sidi bel abbes, algeria mourad_meghachou@univ-sba.dz abbad hichem civil engineering dpt djillali liabes university sidi bel abbes, algeria hi_abbad@yahoo.fr pierre vacher symme laboratory university of savoie france pierre.vacher@univsavoie.fr abstract—the aim of this paper is to highlight the "stick-slip" phenomenon in the mechanisms of failure related to active earth pressure of an analogical material simulating a granular medium. for this, a two-dimensional small-scale model was used and a phenomenological analysis of these mechanisms was conducted employing measurements of the fields of deformations using the method of digital image correlation. it was noted that a fluctuation in the response of the material occurs during the equal increments of displacements imposed on the mobile wall. this incremental response of the medium during the failure process related to active earth pressure explains the "stick-slip" phenomenon. keywordsstick-slip phenomenon; image correlation; smallscale model; granular material; analogical material i. introduction it is commonly accepted that when a shear failure is caused by active earth pressure, a line of rupture extends inside the ground and behind the plate. in the case of granular materials, this line represents the zone where mainly the slips, and consequently frictions between the grains of material, will take place. the failure of granular materials in this phenomenon is characterized by the formation of a rigid block which constitutes the moving part. this rigid block slips compared to the rest of material. one of the important occurrences of this friction is the stick-slip phenomenon. the stick-slip characterizes a jerky movement when an object is drawn on a scraping surface via a spring. the movement of this object is generally not uniform. schematically, periods where the object resists and does not move (stick period), and shorter periods where the resistance limit is exceeded and the object slips along an important distance (slip period), are observed [1]. the purpose of the experiment described in this paper is to cinematically study the influence of the incremental displacements of a mobile plate on the response of a granular material constituted of metallic cylindrical particles (analogical material). this way, it would be possible to highlight the stickslip movement during the active earth pressure failure. ii. the “stick-slip” behaviour in granular materials the “stick-slip” behaviour is observed in some granular materials during the shear failure [2, 3]. during the “stick” phase, the particles at the shear interface are closely interlocked and have shear strength. the material starts then a period of dilatance, and a slip takes place between some particles. an analysis regarding the “stick-slip” phenomenon during triaxial tests made on a glass balls material with diameters from 630 to 840 μm and with various strain rates (0.083 mm/min, 0.18 mm/min, and 0.5 mm/min), and related figures can be found in [4]. in addition, an acoustic measurement method allows hearing diffuse screeching during the deformation of granular materials [4]. they correspond to intermittent slips, localized atthe contacts between the grains. another approach is to study the stick-slip phenomenon by a fluctuation in the behaviour of glass balls and sand samples [5]. iii. the experimental model in order to reproduce the shear failure by active earth pressure of a granular soil, a small-scale model was designed, integrating a mechanism which allowed moving horizontally a vertical plate. behind this vertical plate an analogical material made of small metallic cylinders is laid down simulating a purely granular soil. the medium had a surface of 550 mm width and 300 mm height, dimensions allowing a semi-infinite medium. indeed, the observed slip lines when propagating are not blocked by the boundary of the experimental model. figures 1 and 2 illustrate the experimental device. it has been shown that the study of mechanic problems of granular materials can be approached using a 2d device by replacing the soil by a cylindrical particles [6]. in this case, the engineering, technology & applied science research vol. 4, no. 1, 2014, 566-569 567 www.etasr.com daoud et al.: the “stick-slip” phenomenon during the active earth pressure failure … cylinders are made of steel and have a 4mm diameter and 70mm length. the material is known as mono-disperse since only one diameter of cylindrical particles and only one material has been used. a unit weight of steel around 68.9kn/m3 confers to the material a weighing nature. the nondeformability of the cylindrical particles simulates an incompressible material. fig. 1. scheme of the experimental device used. fig. 2. picture of the device used. the deformations of the medium is studied from a macroscopic point of view supposing a continuous displacement field although the imposed displacement increments are discontinuous. the laying procedure of the cylindrical particles has been set to put them always in orthorhombic contact (figure 3). this is supposed to put the medium in a dense state. measurements on the apparent unit weight and the absolute unit weight with respective values of 68.9kn/m3 and 78.7kn/m3, gives a real void ratio equal to 0.142. in order to obtain a visual contrast, the ends of cylindrical particles were painted with 5 different colors. after each test the material was removed then replaced. that will avoid any heterogeneity of the medium and thus any localization of deformation. fig. 3. zoom on the material constituting the analogical material. iv. deformations measurement and experimental procedure the deformation analysis of the material will be made by a digital image correlation method using the “7d” software. 7d is a software for the analysis of digital images whose principal function is to measure displacements and to calculate deformations on plane or not plane surfaces by digital images correlation method. images have a resolution of 2592*1944 pixels. the dimensions of the medium in pixels are 1465*800 (dimension of a pixel corresponds to 0.375 mm). a base of measurement of 20*20 pixels was employed, which corresponds to a 7.5 mm point of measurement. uncertainties of measurement in terms of displacement are difficult to identify in the shear zones because of the discontinuities of the displacement fields (rotation of the cylindrical particles, brutal change of relative position etc). the displacement values for a zone located far from the slip surface, are approximately 0.01 mm. the measure uncertainty in a less deformed zone is thus approximately the 1/30th of a pixel. this relatively poor uncertainty is strongly related to the quality of the camera used. fig. 4. displacement rate of the mobile plate of the device and time of photo catches during the tests in discontinuous mode the shear failure in the medium will be initiated by the vertical mobile plate (which moves horizontally). the procedure is to drive the plate at a constant speed of 0.25 mm/s by a step of 1.5 mm, which corresponds to a displacement of engineering, technology & applied science research vol. 4, no. 1, 2014, 566-569 568 www.etasr.com daoud et al.: the “stick-slip” phenomenon during the active earth pressure failure … approximately 4 pixels on the images. the plate moves, then stops, a photo is taken, then the plate moves again etc. this mode of displacement is called discontinuous mode (figure 4). once all photographs have been recorded, two options of treatment are possible. a global analysis can be done, which corresponds to comparing each deformed state with the initial state (state1 and 2; state1 and 3; …; state1 and state n), or an incremental analysis can be done, which corresponds to comparing each deformed state with the previous one (state1 and 2; state2 and 3; …; state n-1 and state n) v. tests analysis and interpretations the displacements vectors fields for the first displacement increments of the mobile plate in incremental analysis (i.e. by comparing the results of each deformed state to the preceding one), clearly show the formation of a rigid wedge slipping compared to the rest of the medium. in order to better represent these data, a factor of amplification of 1600% was used. the slip of this rigid wedge has a fluctuated movement although the displacement increment of the plate is identical at each stage. this is highlighted by the analysis of successive stages. in stages 2 and 3, the maximum displacement increments are approximately 4.1 pixels, the horizontal component is well found and a weak vertical component appears (figure 5). this stage corresponds to the stick phase where the slipping corner of material sticks to the rest of material. (a) (b) fig. 5. displacement increments analysis of the medium between two stages of the displacement of the mobile plate: (a) displacement of 8 pixels (3mm). (b) displacement of 12 pixels (4.5mm) the movement of the wedge is more accentuated during the following phases. beyond a displacement increment of 4.5 mm, displacement vectors show an important and a sudden slump of the wedge with displacement increment values reaching 8.29 pixels locally, which correspond to the slip phase (figure 6). the wedge takes again a less accentuated movement, and the displacement increments approach those of the first phase (stick phase) (figure 7). fig. 6. displacement increment at the fourth stage of displacement of the mobile plate corresponding to the slip phase (a) (b) (c) fig. 7. displacement increments analysis of the medium between two stages of the displacement of the mobile plate: (a) displacement of 20 pixels (7.5 mm). (b) displacement of 24 pixels (9 mm). (c) displacement of 28 pixels (10.5 mm). engineering, technology & applied science research vol. 4, no. 1, 2014, 566-569 569 www.etasr.com daoud et al.: the “stick-slip” phenomenon during the active earth pressure failure … and it is only with the eighth displacement increment of the plate (8 × 4 pixels) that the wedge shows again an important slip, with displacement vectors reaching an important value of 17.83 pixels (figure 8). on the graphics of figure 9, the average of the displacements vectors measured on the entire medium for each displacement increment of the plate for three tests is depicted. thus, fluctuations during the displacement of the rigid wedge can be noted. fig. 8. displacement increment at the eighth stage of displacement of the mobile plate corresponding to the slip phase. fig. 9. average values of displacement vectors measured for each test. vi. conclusion the fluctuation in the movement of the rigid wedge slipping during the failure shows the property of the granular material to adopt a stick-slip movement during the shear failure, although there are uniform displacement increments of the wall. it would be interesting for future investigations to see the influence of the rate of this increment on the material. the mode of displacement in this paper is discontinuous. it would also be interesting to see how the behavior of the material for a continuous mode of plate displacement. references [1] l. bocquet, “approche physique du frottement”, 597éme conférence de l’université de tous les savoirs, paris, 2005 [2] i. albert, p. tegzes, r. albert, j. g. sample, a. barabàsi, t. vicsek, b. kahng, p. schiffer, “stick-slip fluctuations in granular drag”, physical review e: statistical, nonlinear, and soft matter physics, vol. 64, no. 3, pp. 0313071-0313079, 2001 [3] g. ovarlez, statique et rhéologie d’un milieu granulaire confiné, thèse de doctorat, université paris xi orsay, 2002 [4] f. adjemian, p. evesque,“experimental study of stick-slip behaviour”, international journal for numerical and analytical methods in geomechanics, vol 28, no. 6, pp. 501-530, 2004 [5] l. e. roussel, experimental investigation of stick-slip behavior in granular materials, msc thesis, civil and environmental engineering department, louisiana state university, 2005 [6] n. dolzhenko, etude expérimentale et numérique de modèle réduit bidimensionnel du creusement d’un tunnel. développement d’une loi de comportement spécifique, thèse de doctorat, insa de lyon, 2005 microsoft word etasr_v11_n5_pp7610-7614 engineering, technology & applied science research vol. 11, no. 5, 2021, 7610-7614 7610 www.etasr.com sadasivam et al.: an enhanced electroporator design for pulse generation an enhanced electroporator design for pulse generation sadasivam pachamuthu electrical and electronics engineering b. s. abdur rahman crescent institute of science and technology vandalur, chennai, india psvijay92@gmail.com kavitha sankaranarayanan au kbc research centre mit campus of anna university chennai, india kavitham@yahoo.com d. najumnissa electronics and instrumentation engineering b. s. abdur rahman crescent institute of science and technology vandalur, chennai, india najumnissa.d@crescent.education raja prabu ramachandran gandhi institute of technology and management deemed to be university vishakapatnam, andhra pradesh, india director_ar@gitam.edu abstract-an electroporator is an instrument used for delivering electrical pulses to a tumor. in this work, an electroporator consisting of three main system blocks, namely high voltage (hv) source, nanosecond (ns) switching, and pulse generation, was designed, developed, and evaluated to generate high voltage ns pulses to treat tumors. the high-voltage source block was used to convert the 9.6v dc from the battery to a variable hv output and store this charge for later use. the ns switching block contained a mosfet-based low-side switch which applies short ns pulses to the load. the pulse generation block generates short ns pulses and supplies the adequate current to turn on the mosfet at a quicker rate aiding the application of these pulses to the load. this process was simulated using pspice software and the results are presented. keywords-electroporator; electrochemotherapy; boost converter microcontroller; i. introduction cancer is the second most lethal disease, as it is responsible for almost the 13% of all human deaths. the extra economic burden related to cancer complicates the administration of presently adopted remedy strategies [1]. reversible electroporation is the process where a short electric field on a cell retains the membrane's ability to recover at a quicker rate, while the cell remains viable. on the other hand, irreversible electroporation is the process where longer and high-intensity pulses are applied breaking down the cell membrane irreversibly [2]. reversible electroporation can be further improved or optimized [3]. it is also feasible to electroporate using very brief and very strong electric pulses [4]. in this study, a new electroporator to produce nanosecond (ns) high voltage pulses for treating abnormalities of skin cells is designed, developed, and evaluated. the electroporator instrument consists of a pulse generator and an electrode for delivering the pulse to the tumor's location. the pulse generator produces an electric pulse of predetermined magnitude, width, and frequency. the basic principles used in almost all pulse generators are the capacitor charging and discharging mechanisms. three system blocks make up the miniature high voltage ns pulse: the high-voltage (hv) source block converts the battery's 9.6v dc into a variable high voltage output, and this charge is stored to use when creating the pulse. the ns switching block is a low-side switch with a mosfet that sends brief ns pulses to the load. the pulse generation block generates the ns pulses and provides sufficient current to turn the mosfet on quickly enough to deliver them to the load. ii. materials and methods the following materials were used: • pulse generator: a logic-based pic controller was used for creating the ns pulses using a program written in mikroc, converted into hex code, and loaded to the microcontroller. • programmable integrated circuit (pic) controller: the pic controller featured program memory, sram, eeprom, analog comparators, and pulse with modulation (pwm). all these characteristics make it appropriate for more advanced analog to digital applications. using a pic as a master controller to generate the pwm and interface with the lcd and the keypad reduced the required components and made the electroporator more compact. • hv source block: 0-12v dc was converted to 0-1000v dc using the hv module. the 230v ac supply was connected to an adjustable voltage regulator, which fed the hv module. a potentiometer was used to set the regulator voltage around 9vdc and obtain a 1000v output. two diodes were utilized to safeguard the hv module's output from transient spikes and damage. as the hv module was corresponding author: sadasivam pachamuthu engineering, technology & applied science research vol. 11, no. 5, 2021, 7610-7614 7611 www.etasr.com sadasivam et al.: an enhanced electroporator design for pulse generation rated at 10w, a 150k resistor was used to limit the current to 6.6ma and not exceed the module's rated output power. when the module was pulsed, it charged a 1uf capacitor which gave energy to the load. • ns switch block: the source of the mosfet was connected to the ground, and the drain was connected to the load's negative side. a fast switching diode was placed across it to reduce ringing on the load. a 150ω resistor was connected in parallel with the load to aid in measurements using an oscilloscope. • lcd: an lcd 4×16 display was used (figure 1). fig. 1. 4×16 lcd. • keypad: the keypad interfaced with the pic for obtaining input from the user. a 4×4 keypad was used, having the 0-9 digits and four keys for other operations. the keypad was used to select the parameters and protocols according to the program in the pic microcontroller. iii. proposed electroporator design in this work, a programmable electroporator using the pic16f877a microcontroller was designed and developed [5]. figure 2 shows the schematic arrangement of the programmable electroporator. the designed electroporator consists of a microcontroller, a power circuit as an electroporator, and an lcd. the electric supply is given to the electroporator through a boost converter. a logic-based pic controller is used for programming the pulses using embedded c. the program was written in mikroc integrated development environment (ide), converted into hex code, and loaded to the microcontroller. the pulses were generated at the output portb pin. the microcontroller can store up to 16 programs for different applications, and the user can select which fits its needs. figure 3 shows the boost converter's control diagram used for generating the high voltage supply for electroporation. the ac input is converted to a high voltage ac supply using the hv transformer and rectifier [6-8]. there are many ways to achieve a 1000v potential. one could be to transform 120vac and then rectify it to 1000v. this was not chosen because of the large size and weight of the needed transformer and rectifier. this study's motive was to keep the pulser small and portable using a high voltage dc-dc converter module (0-12vdc to 0-1500vdc). the battery voltage was applied to the variable voltage regulator and the high voltage module. a potentiometer was used to adjust the regulator voltage up to 8vdc to obtain an output voltage of around 1000v. figure 4 shows the booster voltage display and table i presents a comparison between an existing and the designed electroporator. fig. 2. schematic diagram of the programmable electroporator. fig. 3. boost converter control diagram. fig. 4. boosted voltage displayed in voltmeter. table i. comparison between existing and developed models of electroporator design existing model ecm 830 [9] developed model has more components for pulse generation. uses a pic controller uses an rc network and flip flops before sending the pulses to the ic driver uses an isolator between the pulse and the driver costs about 800,000inr costs about 50,000inr cannot use display and input device without having a separate processor which further increases its cost. already uses a controller so lcd and keypad can be easily attached. must be changed manually. logically controlled so multiple programs can be executed in a single device. a. switch block description pulses having a duration as low as 20ns were required in the design specifications; therefore an extremely fast rf mosfet was used, as shown in figure 5. a 5ns rise time 1200v mosfet was chosen as a switch. a high current driver was used to switch the mosfet. the 1960pf capacitance of the mosfet was charged through an initial high current draw using this driver. the 4ns rise time mosfet driver was used engineering, technology & applied science research vol. 11, no. 5, 2021, 7610-7614 7612 www.etasr.com sadasivam et al.: an enhanced electroporator design for pulse generation to make the driver act very fast. the battery was used to charge the mosfet driver with no specific regulations. the complementary metal-oxide-semiconductor (cmos) and the transistor-transistor logic (ttl) were the inputs of the mosfet driver, which were connected to the pulse generation circuit output. fig. 5. ns switch design. two cmos digital integrated circuits (ics) were used to construct a ns pulse generator circuit. those two ics were retriggerable monostable multivibrator and d flip flop. the pulses were produced by the re-triggerable monostable multivibrator, determined by the value of one external capacitor and resistor. the multivibrator was a dual ic, so using one multivibrator two pulses can be generated, and the pulses can be shifted by increasing the external resistor of the multivibrator. a variable resistance was connected in series with the external resistor for allowing pulse duration adjustments. these pulses were then used to clock and preset the d flip flop. separating the pulses by 20ns allows the d flip flop to be clocked high and then preset low 20ns later. the retriggerable monostable multivibrator needs a clock signal to repeat the pulses. a 555 timer was used to create a cmos clock of 1.5khz. the 555 timer was also built with potentiometers to allow adjustment of frequency and duty cycle. all three ics were powered using a simple 5vdc regulator. fig. 6. interfacing pic with lcd. b. interfacing pic with lcd the pic was interfaced with the lcd, as shown in figure 6, for displaying the output after the pulse. simple code was used for the interface, as the interfacing of an lcd and a keypad to a pic is simple. the number of delivered pulses was displayed in the lcd through software. c. hardware circuit testing and modeling of electroporator all hardware components (pulse generator, pic controller, hv source block, ns switch block, lcd, and keypad) were connected and tested in the laboratory, as shown in figure 7, and the results were evaluated. fig. 7. testing and modeling of the electroporator. d. steps for the electroporator using various applications • display the parameters to control the output of the electroporator. • choose a parameter, give an in-range value, and press ok. • pulses are applied through the electrodes. • the number of pulses applied will be displayed. • similarly, repeat for all the parameters and press ok. iv. results and discussion a. output waveforms the results depicted in figures 8-12 show the effect of electric pulses of 50mv magnitude, in both positive and negative, in cancer cell hep using the patch-clamp technique and obtained a single ion channel output which proves the electroporation effect. this technique provides knowledge on the permeability and the changes that occur while electric pulses are delivered to the cell membrane [10]. the electroporator consists of electrodes delivering high voltage pulses to the affected site, and other electronic components such as power converters to convert the low voltage to high [11, 12]. engineering, technology & applied science research vol. 11, no. 5, 2021, 7610-7614 7613 www.etasr.com sadasivam et al.: an enhanced electroporator design for pulse generation fig. 8. transient voltage graph of the hv block. fig. 9. the obtained output without the capacitor to reduce noise. fig. 10. the output of btx ecm 830. fig. 11. single pulse output of rapkviss. fig. 12. the output of rapkviss for skin cancer. v. conclusion electrochemotherapy is an effective technique that uses high voltage electrical pulses to build up the drug transport across the plasma cell membranes. moreover, it controls the drug proliferation rate by cancer cell apoptosis, as their morphological properties are identical to that of a human stem cell. in this paper, an electroporator was designed and developed to enhance the drug delivery in electrochemotherapy, using a pic microcontroller and a high voltage boost converter. the proposed electroporator had an lcd to display the parameters of the pulses delivered to the cancer cells. the effect of electric pulses was analyzed and a single ion channel output that proves the electroporation effect was obtained. the main advantages of the proposed electroporator are its low cost and its controllability, as multiple programs can be executed in a single electroporator. thus, the proposed electroporator was proved to be more advantageous over existing models and had additional features, like displaying the applied pulses with their parameters and a 4×4 keypad for data input to control its output. furthermore, it produced a more squarely output than any other electroporator existing to date. thus, the proposed design can be a costeffective and efficient pulse generator for electroporation in many applications such as gene transplantation, immunotherapy, and food processing for protection against microbes. references [1] j. c. weaver, "electroporation of cells and tissues," ieee transactions on plasma science, vol. 28, no. 1, pp. 24–33, feb. 2000, https://doi.org/ 10.1109/27.842820. [2] l. m. mir, o. tounekti, and s. orlowski, "bleomycin: revival of an old drug," general pharmacology: the vascular system, vol. 27, no. 5, pp. 745–748, jul. 1996, https://doi.org/10.1016/0306-3623(95)02101-9. [3] l. m. mir, "therapeutic perspectives of in vivo cell electropermeabilization," bioelectrochemistry, vol. 53, no. 1, pp. 1–10, jan. 2001, https://doi.org/10.1016/s0302-4598(00)00112-4. [4] t. b. napotnik, m. reberšek, t. kotnik, e. lebrasseur, g. cabodevila, and d. miklavčič, "electropermeabilization of endocytotic vesicles in b16 f1 mouse melanoma cells," medical & biological engineering & computing, vol. 48, no. 5, pp. 407–413, may 2010, https://doi.org/ 10.1007/s11517-010-0599-9. [5] a. gothelf, l. m. mir, and j. gehl, "electrochemotherapy: results of cancer treatment using enhanced delivery of bleomycin by electroporation," cancer treatment reviews, vol. 29, no. 5, pp. 371– 387, oct. 2003, https://doi.org/10.1016/s0305-7372(03)00073-2. [6] c. t. s. ching, t. p. sun, w. t. huang, s. h. huang, c. s. hsiao, and k. m. chang, "a circuit design of a low-cost, portable and programmable electroporation device for biomedical applications," sensors and actuators b: chemical, vol. 166–167, pp. 292–300, may 2012, https://doi.org/10.1016/j.snb.2012.02.065. [7] a. al-ateeq and a. j. alateeq, "soft-charging effects on a high gain dc-to-dc step-up converter with psc voltage multipliers," engineering, technology & applied science research, vol. 10, no. 5, pp. 6323–6329, oct. 2020, https://doi.org/10.48084/etasr.3773. [8] m. taherian, m. allahbakhshi, e. farjah, and h. givi, "a modular topology of marx generator using buck–boost converter," ieee transactions on plasma science, vol. 47, no. 1, pp. 549–558, jan. 2019, https://doi.org/10.1109/tps.2018.2876474. [9] btx harvard apparatus, holliston ma, usa, ecm 830 electroporation system user's manual, accessed: aug. 29, 2021. [online]. available: https://www.btxonline.com/media/wysiwyg/ tab_content/ecm_830.pdf engineering, technology & applied science research vol. 11, no. 5, 2021, 7610-7614 7614 www.etasr.com sadasivam et al.: an enhanced electroporator design for pulse generation [10] j. cutrera, m. torrero, k. shiomitsu, n. mauldin, and s. li, "intratumoral bleomycin and il-12 electrochemogenetherapy for treating head and neck tumors in dogs," in electroporation protocols: preclinical and clinical gene medicine, s. li, ed. totowa, nj, usa: humana press, 2008, pp. 319–325. [11] p. vu, d. t. anh, and h. d. chinh, "a novel modeling and control design of the current-fed dual active bridge converter under dpdps modulation," engineering, technology & applied science research, vol. 11, no. 2, pp. 7054–7059, apr. 2021, https://doi.org/10.48084/ etasr.4067. [12] b. zhao, q. song, w. liu, and y. sun, "overview of dual-activebridge isolated bidirectional dc–dc converter for high-frequencylink power-conversion system," ieee transactions on power electronics, vol. 29, no. 8, pp. 4091–4106, aug. 2014, https://doi.org/ 10.1109/tpel.2013.2289913. microsoft word etasr_v11_n2_pp6907-6911 engineering, technology & applied science research vol. 11, no. 2, 2021, 6907-6911 6907 www.etasr.com nuanmeesri & sriurai: thai water buffalo disease analysis with the application of feature selection … thai water buffalo disease analysis with the application of feature selection technique and multi-layer perceptron neural network sumitra nuanmeesri faculty of science and technology suan sunandha rajabhat university bangkok, thailand sumitra.nu@ssru.ac.th wongkot sriurai faculty of science ubon ratchathani university ubon ratchathani, thailand wongkot.s@ubu.ac.th abstract-this research aims to develop an analysis model for diseases of the water buffalo with the application of the feature selection technique along with the multi-layer perceptron neural network (mlp-nn). the data used for analysis were collected from books and documents related to water buffalo diseases and the official website of the department of livestock development. the data consist of the characteristics of 6 water buffalo diseases, including anthrax, hemorrhagic septicemia, brucellosis, foot and mouth diseases, parasitic diseases, and mastitis. since the amount of the collected data was limited, the synthetic minority over-sampling technique was also employed to adjust the imbalance dataset. the adjusted dataset was used to select the disease characteristics towards the application of two feature selection techniques, correlation-based feature selection and information gain. subsequently, the selected features were then used for developing the analysis model for water buffalo diseases towards the use of the mlp-nn. the evaluation results given by 10-fold cross-validation, showed that the analysis model for water buffalo diseases developed by correlation-based feature selection and mlp-nn provided the highest level of effectiveness with an accuracy of 99.71%, precision of 99.70%, and recall of 99.72%, implying that the analysis model is effectively applicable. keywords-water buffalo diseases; feature selection; multi-layer perceptron; neural network; synthetic minority over-sampling i. introduction in thailand, water buffaloes play an important role in the livestock economy. thai water buffaloes are the most common farm animals in asia and farmers typically use them for agricultural labor and as a source of food. to domesticate water buffaloes productively, it is vital to pay attention to their nutrition, habitats, sanitation, signs, behavior, and disease symptoms [1]. at present, water buffalo farmers are confronting many kinds of water buffalo diseases due to the seasonal changes, disease carriers, the lack of expertise and knowledge among farmers themselves, and the lack of experts who can analyze and diagnose these diseases. moreover, the internet only offers basic information about the diseases gained from statistical surveys, resulting in the retrieval of incorrect or inadequate data for disease analysis and, ultimately, misunderstanding or incorrect analysis. water buffalo farmers who lack attention may overlook the signs and symptoms of serious infectious diseases, which could be spread to other animals and cause sickness or even casualties [2-3]. the multi-layer perceptron neural network (mlp-nn) is one of the most popular techniques used to classify complex data. this research aims to develop an analysis model for water buffalo diseases towards the application of the feature selection technique and mlp-nn. two feature selection techniques were employed, correlation-based feature selection (cfs) and information gain (ig). after selecting the features, the data were then used for developing the analysis model by using the mlp-nn. the developed model can be applied to the development of a water buffalo disease analysis system, which is expected to help farmers timely analyze the diseases. ii. background a. data imbalance resolution this research applies the synthetic minority over-sampling technique (smote) to resolve the data imbalance problem. smote helps to resynthesize data by increasing the dataset’s size with a small amount of class data [4] to be compatible with the biggest dataset. this is done by randomizing a value and calculating the distance between the selected value with other values to find the nearest value [5]. b. feature selection techniques the goal of feature selection is to select the most significant features of each dataset in order to synthesize the model rapidly and increase the effectiveness of data classification. in this study, two feature selection methods are employed: 1) correlation-based feature selection (cfs) cfs is a feature selection method based on the relationship between the collections of features gained from the evaluation of feature prediction capacity used for data classification and irrelevant data management. cfs can rank the data subsets based on the data dimensions and select the data subsets based on the data dimensions with regard to high and low relationships between classes. any irrelevant data or any data with a low level of relationship will be excluded. the same will corresponding author: sumitra nuanmeesri engineering, technology & applied science research vol. 11, no. 2, 2021, 6907-6911 6908 www.etasr.com nuanmeesri & sriurai: thai water buffalo disease analysis with the application of feature selection … occur with complex data dimensions which shall be excluded from the data dimensions with a high level of relationship. the formula for evaluating the subsets of cfs data dimensions is shown in (1) [6]: ( 1) cf s ff kr m k k k r = + − (1) where k refers to the data dimension or features, s m refers to the value of s data dimension subset which composes of k data dimensions, cf r refers to the average value of the relationship between the variables and classes ( f s∈ ), and ff r refers to the average value of the relationship of data dimension. 2) information gain (ig) ig is a feature selection method in which the gain value of each mode is evaluated. if a node has the highest gain value, it will be chosen as the root node, and the rest of the data will be reassessed in order to find the gain value of the next node. the formula for finding the ig value is [7]: ( ; ) ( ) ( | )gain y x h y h y x= − (2) where y refers to the feature value, which is a data class belonging to the {y1, y2, …, yn} set where n is the number of features, x refers to the value of other features that are not classes ranging between {x1, x2, …, xn}, ( ; )gain y x refers to the score value gained from sample randomization ranging between 0 and 1, ( )h y refers to the probability value gained from the randomization of y samples, and ( | )h y x refers to the probability value gained from the randomization of y samples when compared to x. ( )h y and ( | )h y x are calculated in (3) and (4), respectively: 2 1 ( ) ( )log ( ) i k i i i h y p y y p y y = = = − = =∑ (3) 1 ( | ) ( ) ( | ) i k i i i h y x p x x h y x x = = = − = =∑ (4) where ( ) i p y y= refers to the probability value from y1 to yk, ( ) i p x x= refers to the probability value from x1 to xk, and k refers to the number of features. c. multi-layer perceptron neural network the mlp-nn, illustrated in figure 1, consists of an input layer, hidden layers, and an output layer [8]. in each layer, there are a collection of nodes. possibly, there are more than one hidden layers [9]. the mlp-nn operates by inserting data into the input layer to estimate and deliver the results to the output layer. the estimation requires the sum total of input data multiplied by weight values, as shown in (5). after that, the output is used for the calculation with the sigmoid function, as shown in (6). 1 k i i i n pw = = ∑ (5) where n refers to the sum total of input pi multiplied by the weight wi and i refers to the number of inputs or weight value. in (6), x refers to the input value. 1 1 x x f e − = + (6) the output of the hidden layer is delivered to the output layer, where there is a comparison between the estimated and the target outputs. if there are different values that cannot be accepted, the outputs will get into the backpropagation process and go back to the hidden and input layer. simultaneously, there is the weight adjustment process, which will find the most acceptable value after testeing with the data. subsequently, the output is estimated with the sigmoid function once again [8]. fig. 1. mlp-nn. d. similar studies authors in [13] compared the effectiveness of data imbalance resolution techniques by using diabetes patients’ data. the research team compared four different methods, which include oversampling, undersampling, hybrid method, and smote. two data classification techniques were applied, multinomial logistic regression analysis and decision tree, to classify diabetes patients. the research findings showed that the combination of the data adjusted by smote and the data classification with the decision tree technique provided the best results for the classification of the diabetes patients. authors in [14] studied the classification of heart diseases using mlp-nn and ig as a feature selection method. the findings showed that the number of features could be reduced from 13 to 8, while the accuracy of the training dataset increased by 1.1% and the accuracy of the trial dataset increased by 0.82%. authors in [15] studied the classification of ovarian cancer towards the application of smote and mlp-nn. the findings indicated that the smote technique could adjust the data balance, and after using the adjusted data to construct the model with mlpnn, the model’s effectiveness increased. the experiment results showed that the application of smote+mlp provided a data classification accuracy of 96%, which was higher than the one gained from the application of smote+rbf. authors in [16] applied feature selection along with mlp to predict chronic diseases. the research findings showed that applying these two methods provided higher effectiveness in terms of chronic disease prediction than the application of support vector machine (svm) and decision tree. engineering, technology & applied science research vol. 11, no. 2, 2021, 6907-6911 6909 www.etasr.com nuanmeesri & sriurai: thai water buffalo disease analysis with the application of feature selection … the developed model of the current research can be applied to the development of a water buffalo disease analysis system. two feature selection techniques were employed, cfs and ig. e. effectiveness evaluation the effectiveness evaluated by the confusion matrix is an evaluation method of discriminants’ accuracy, which means the discriminants can be classified in accordance with their genuine value. the accuracy can be calculated by (7) [10], while precision and recall can be calculated in (8) and (9) [11-12], with the values represented in figure 2. 100 tp tn accuracy tp tn fp fn + = × + + + (7) 100 tp precision tp fp = × + (8) 100 tp recall tp fn = × + (9) where tp refers to when the target class is "yes," and the model predicts it as "yes" (true positive), fp refers to when the target class is "yes," but the model predicts it as "no" (false positive), tn refers to when the target class is "no," and the model predicts it as "no" (true negative), and fn refers to when the target class is "no," but the model predicts it as "yes" (false negative). fig. 2. confusion matrix. iii. research methodology the research methodology for the analysis of thai water buffalo diseases consists of 1) data collection and preparation, 2) data imbalance adjustment using smote, 3) feature selection by cfs and ig, 4) model development using mlpnn, and 5) model effectiveness evaluation (figure 3). a. data collection and preparation this research collected data from books and documents related to water buffalo diseases [3] and the department of livestock development’s official website. there are totally 480 records of data. the data involves information about six water buffalo disease classes, namely anthrax, hemorrhagic septicemia, brucellosis, foot and mouth diseases, parasitic diseases, and mastitis. these data were used for developing the disease analysis model. there are 33 attributes and six classes, as illustrated in table i. table i. data characteristics used for developing the analysis model of thai water buffalo diseases symptoms data symbol data value fever symptom 1 high: aa1 moderate: aa2 no fever: aa3 drooling symptom 2 normal: ab1 excessive: ab2 breathing characteristics symptom 3 fast and frequent breathing: ac1 difficulty in breathing: ac2 normal breathing: ac3 bad breath symptom 4 bad breath: ad1 normal: ad2 swollen breasts symptom 5 little swollen: ae1 red, hard, and swollen: ae2 normal: ae3 endometritis symptom 6 inflammatory: af1 not inflammatory: af2 drowsiness symptom 7 drowsy: ag1 not drowsy: ag2 eating habits symptom 8 appetite loss: ah1 normal: ah2 swelling characteristics symptom 9 body or neck swelling: ai1 joint swelling: ai2 not swollen: ai3 urine characteristics symptom 10 blood in urine: aj1 normal urine: aj2 testicle characteristics symptom 11 swollen: ak 1 normal: ak2 stool characteristics symptom 12 stools contained blood: al1 melena: al2 smelly stools: al3 normal: al4 walking symptom 13 stiff: am1 normal: am2 milk characteristics symptom 14 sticky or purulent: an1 normal: an2 retained placenta symptom 15 retained: ao1 not: ao2 emaciation symptom 16 emaciated: ap1 not: ap2 blisters inside the mouth and on the feet symptom 17 has: aq1 has not: aq2 vesicular state (within mouth, tongue, beneath tongue, cheeks, hoofs, ankles, nipples, and breast) symptom 18 has: ar1 has not: ar2 wounds around the hoofs and/or ankles symptom 19 has: as1 has not: as2 weight symptom 20 weight loss: at1 normal weight: at2 hard and rough hair symptom 21 hard and rough: au1 normal: au2 sleep habits symptom 22 excessive sleep: av1 normal: av2 muscle characteristics symptom 23 shaky or twitching: aw1 normal: aw1 bleeding from nose, mouth, ears, eyes symptom 24 has: ax1 has not: ax2 lip characteristics symptom 25 pale: ay1 normal: ay2 oral mucositis and red eye sockets symptom 26 has: az1 has not: az2 forward head posture symptom 27 has: ba1 has not: ba2 tongue-tie symptom 28 has: bb1 has not: bb2 cough symptom 29 has: bc 1 has not: bc2 vaginal discharge symptom 30 has: bd 1 has not: bd2 amount of milk symptom 31 stopped milk production: be1 lower amount of milk: be2 normal: be3 excretion characteristics symptom 32 frequent: bf1 normal: bf2 recurrent seizures symptom 33 has: bg 1 has not: bg2 water buffalo diseases class anthrax hemorrhagic septicemia brucellosis foot and mouth disease parasitic disease mastitis engineering, technology & applied science research vol. 11, no. 2, 2021, 6907-6911 6910 www.etasr.com nuanmeesri & sriurai: thai water buffalo disease analysis with the application of feature selection … fig. 3. the model framework. after collecting the data illustrated in table i, the research team rechecked their reliability and accuracy to ensure that no attribute was incorrect or missing. for example, there are no data out of range for each attribute. then, the data were converted into .csv file format in order to be operated with the weka version 3.9, as shown in figure 4. fig. 4. data used for model construction. b. data imbalance adjustment using smote since the prepared data were found to be imbalanced in class/label, the research team decided to adjust the data imbalance of the datasets by increasing the number of datasets with a small size of classes. the best result was provided after increasing the k-nearest neighbor value from 1 to 5. it was experimentally found that k = 5 and randomseed = 1 give the best result. the data size was then increased from 100% until the highest level of effectiveness could be gained (as evaluated by 10-fold cross-validation). the experiment results showed that the data could be balancing and upsizing to 300%. thus, the new dataset increased to 528, 688, and 768 records for data balancing using smote at 100%, 200%, and 300% of its original size respectively. c. feature selection by cfs and ig the data with 33 attributes and 6 classes were brought into the feature selection process using the cfs and the ig in weka. in this work, there are 8 groups of data applied in this process, namely 1) the original dataset through the cfs, 2) the original dataset through ig, 3) 100% of smote through cfs, 4) 200% of smote through cfs, 5) 300% of smote through cfs, 6) 100% of smote through ig, 7) 200% of smote through ig, and 8) 300% of smote through ig. these resulting datasets will be used at the next step. d. model development using mlp neural network after the data imbalance had been adjusted, the data were transferred to the learning process to construct the model by which the research team applied two feature selection techniques, cfs and ig, along with the mlp-nn. in this research, the input layer consisted of 33 neurons. the output layer consisted of 6 neurons. therefore, the optimum parameters for the mlp-nn model set in weka were: hidden layer = 4, training time = 500, learning rate = 0.3, momentum = 0.2, and 21 epochs= 500. these values provided the highest level of effectiveness after being evaluated by 10fold cross-validation. besides, the model was also generated from the original dataset that smote, or cfs, or ig had not processed in any way, for effectiveness comparison with the other models that have undergone balancing and or feature selection. thus, 9 models were built from the original dataset and 8 feature selection datasets. iv. results according to the experiment results, the most appropriate data size adjusted by smote was 200%. then, the features of the complete dataset were selected by cfs and ig. afterwards, the mlp-nn was developed and its effectiveness was evaluated by 10-fold cross-validation, as illustrated in table ii and figure 5. table ii. model’s effectiveness evaluation method data (rows) precision (%) recall (%) accuracy (%) mlp (original data) 480 98.77 98.78 98.79 cfs+mlp 480 98.80 98.82 98.81 ig+mlp 480 91.59 91.54 91.52 smote (100%) +cfs+mlp 528 98.85 98.87 98.86 smote (200%) +cfs+mlp 688 99.70 99.72 99.71 smote (300%) +cfs+mlp 768 99.60 99.61 99.62 smote (100%) +ig+mlp 528 92.48 92.52 92.53 smote (200%) +ig+mlp 688 93.62 93.59 92.61 smote (300%) +ig+mlp 768 93.05 93.08 93.06 fig. 5. the comparison of the model’s effectiveness evaluation. engineering, technology & applied science research vol. 11, no. 2, 2021, 6907-6911 6911 www.etasr.com nuanmeesri & sriurai: thai water buffalo disease analysis with the application of feature selection … according to table ii and figure 5, the 10-fold validation data classification method of the smote (200%)+cfs+mlp dataset provided an accuracy of 99.71%, a precision of 99.70%, and a recall of 99.72%. these were the highest values. the results of the effectiveness comparison between the outputs of cfs and ig given by the mlp-nn showed that after being adjusted by smote, the cfs method provided better feature selection than the ig method. v. conclusion this research aimed to analyze the water buffalo diseases towards the application of feature selection techniques along with the mlp-nn. the data imbalance was adjusted by the smote method. two feature selection methods were employed: cfs and ig. after that, the data were classified by mlp-nn, and the model’s effectiveness was evaluated by 10fold cross-validation. the research findings showed that the most suitable data size after the data imbalance adjustment was 200%. after using the obtained data to construct the model, it was found that the model whose data size was adjusted by smote and developed by cfs and mlp-nn provided the highest level of effectiveness in data classification with an accuracy of 99.71%. so, the developed model can be applied to the development of an analysis system for water buffalo diseases. the results of this study conform to the research conducted in [15], in which the smote+mlp method was applied for data classification and a high level of effectiveness was reached with an accuracy of 90%, and also are in accordance with [16], in applied feature selection techniques were which alongside the mlp for data classification and gained a higher level of effectiveness. acknowledgment the authors are grateful to the institute for research and development, suan sunandha rajabhat university and the faculty of science at ubon ratchathani university, for supporting this research. references [1] thailand’s livestock statistics. bangkok, thailand: information and communication technology center, department of livestock development, 2015. [2] n. hongboonmee and p. sornrung, "applying decision tree classification techniques for diagnose the disease in cow on mobile phone," journal of science and technology, vol. 20, pp. 44–58, 2018. [3] p. booranamanas, water buffaloes and treatments, bangkok, thailand: thaiwattanapanich, 1988. [4] m. g. tsipouras, "uterine emg signals spectral analysis for pre-term birth prediction," engineering, technology & applied science research, vol. 8, no. 5, pp. 3310–3315, oct. 2018, https://doi.org/ 10.48084/etasr.2146. [5] p. paranya, "improving decision tree technique in imbalanced data sets using smote for internet addiction disorder data," information technology journal, vol. 12, no. 1, pp. 54-62, jum. 2016. [6] a. h. mark, "correlation-based feature selection for machine learning," ph.d. dissertation, the university of waikato, hamilton, new zealand, 1999. [7] t. puripat, "ensemble algorithm for feature selection", m.s. thesis, thammasat university, bangkok, thailand, 2016. [8] s. boubaker, s. kamel, and m. kchaou, "prediction of daily global solar radiation using resilient-propagation artificial neural network and historical data: a case study of hail, saudi arabia," engineering, technology & applied science research, vol. 10, no. 1, pp. 5228–5232, feb. 2020, https://doi.org/10.48084/etasr.3278. [9] a. montaphan, "comparison of feature selection methods to improve breast cancer prediction," royal thai air force medical gazette, vol. 65, no. 2, pp. 49-56, 2019. [10] m. b. ayed, "balanced communication-avoiding support vector machine when detecting epilepsy based on eeg signals," engineering, technology & applied science research, vol. 10, no. 6, pp. 6462–6468, dec. 2020, https://doi.org/10.48084/etasr.3878. [11] s. nuanmeesri, "mobile application for the purpose of marketing, product distribution and location-based logistics for elderly farmers," applied computing and informatics, 2019, https://doi.org/10.1016/ j.aci.2019.11.001. [12] a. n. saeed, "a machine learning based approach for segmenting retinal nerve images using artificial neural networks," engineering, technology & applied science research, vol. 10, no. 4, pp. 5986–5991, aug. 2020, https://doi.org/10.48084/etasr.3666. [13] w. kesornsit, v. lorchirachoonkul, and j. jitthavech, "imbalanced data problem solving in classification of diabetes patients," khon kaen university research journal, vol. 18, no. 3, pp. 11-21, jul. 2018. [14] a. khemphila and v. boonjing, "heart disease classification using neural network and feature selection," presented at the proceedings icseng 2011: international conference on systems engineering, las vegas, nv, usa, sep. 2011, vol. 64, pp. 406–409, https://doi.org/ 10.1109/icseng.2011.80. [15] m. a. hambali and m. d. gbolagade, "ovarian cancer classification using hybrid synthetic minority over-sampling technique and neural network," journal of advances in computer research, vol. 7, no. 4, pp. 109-124, nov. 2016. [16] s. k. hegde and r. hedge, "symmetry based feature selection with multi layer perceptron for the prediction of chronic disease," international journal of recent technology and engineering, vol. 8, no. 2, pp. 3316–3322, jul. 2019, https://doi.org/10.35940/ijrte.b2658. 078219. author profiles sumitra nuanmeesri received her ph.d. in information technology at the king mongkut’s university of technology north bangkok, thailand. she is an assistant professor in the information technology department, faculty of science and technology at suan sunandha rajabhat university, thailand. her research interests include speech recognition, data mining, deep learning, image processing, mobile application, supply chain management system, internet of things, robotics, augmented reality, and virtual reality. wongkot sriurai received her ph.d. in information technology at the king mongkut’s university of technology north bangkok, thailand. she is an assistant professor in the mathematics, statistics and computer department, faculty of science, ubon ratchathani university, ubon ratchathani province, thailand. her research interests include data mining, text mining, web mining, recommender system, information filtering, information retrieval, decision support systems, expert systems, multimedia technology, and computer education. microsoft word etasr_v11_n3_pp7251-7256 engineering, technology & applied science research vol. 11, no. 3, 2021, 7251-7256 7251 www.etasr.com bildik & yaşar: manufacturing of wear resistant iron-steel: a theoretical and experimental research … manufacturing of wear resistant iron-steel: a theoretical and experimental research on wear behavior oğuzhan bildik industrial design engineering department institute of graduate studies karabuk university karabük, turkey oguzhanbildik@gmail.com mustafa yaşar industrial design engineering department technology faculty karabuk university karabük, turkey myasar@karabuk.edu.tr abstract-in this study, four different alloys of steel blocks with a thickness of 15mm were manufactured in order to develop an alternative to steel plates used in wear exposed areas of construction machines, trucks, and asphalt production plants. to further increase the wear resistance of the manufactured steel blocks, their thickness was reduced to 10mm by the hot-rolling method. wear specimens were obtained from rolled blocks. these specimens were abraded at 20n, 40n, and 60n loads in reciprocating linear motion module astm g-33 standards to determine their wear resistance. sem and edx analyses were also conducted to see modifications on the worn surfaces. in addition, a theoretical model of wear behaviors was created, calculations were made with archard wear equation and ansys software, and the theoretical and experimental results were compared. keywords-steel plates; wear; hot rolling; archard wear analysis i. introduction steel powerfully impacts the way seven billion of us on the planet go about our daily lives, wherever we are [1]. this effect of steel in our lives brings along some engineering problems. a scientific, engineering and economic problem is the wear of mechanical parts caused by decrease of working surfaces' properties. the wear mechanisms are very complex, due to the interlinked factors. the intensity of interaction depends on the conditions of the environment, in which the mechanical parts are used as well as the type and parameters of the work. tribological properties such as wear play a critical role in deciding the service life of components that form a moving system or in repetitive/regular contact with each other [2]. wear resistant plates are a modern solution in the regeneration of worn machine parts and for producing new parts which bring together high wear and abrasion resistance with costs reduction. authors in [3] examined wear resistant steel materials with different chemical ratios by different manufacturers used in construction machines and similar fields and found that wear behavior and wear amounts in materials vary significantly depending on the chemical content of the material. in the mineral processing industry, the high stress conditions create a challenging environment for the wear protection steels. great amounts of highly abrasive rocks are processed and transported in earth construction, excavation, mining, and mineral processing, inducing heavy abrasion, gouging and impact wear. authors in [4] conducted wear tests at 20n, 40n, 60n, and 80n loads on steel plates with different c, mn, and si ratios. the c ratio varied between 0.15% and 2% and they found that the wear volume decreased by increasing c rate [4]. wear is an important phenomenon that adversely affects the efficiency and lifespan of all machine components in contact under relative motion. in this regard, there is a need to develop new instruments to attain a better understanding of the wear phenomenon. authors in [5] constructed a tribotester and used the topography of worn surfaces, to provide wear process and wear volume images along with more detailed correlation. ii. model analysis prior to casting, anycasting software was used for casting analysis of the model for molding, filling of the mold and prevention of internal cavities. in the anycasting, casting shape, casting type, runner, and other parts were first defined with the anypre module and the mold area was created by selecting the casting area and runner axis [6, 7]. then, a theoretical analysis was carried out as shown in figure 1 to get results such as casting filling time, solidification time, shrinkage cavities, which are of vital importance. after casting, corrections were made on the model by checking whether shrinkage cavities occurred on the piece. by reverse engineering the resulting model, downsprue, runner, nozzle, vent-riser design and calculations were made for casting [8-10]. iii. mold manufacturing most of the pieces manufactured through casting were shaped with the sand casting process. sand mold casting was conducted by pouring molten metal into a sand mold cavity and after the solidification process, breaking away the sand mold to remove the cast piece [11]. in the model-mold design for sand corresponding author: oğuzhan bildik engineering, technology & applied science research vol. 11, no. 3, 2021, 7251-7256 7252 www.etasr.com bildik & yaşar: manufacturing of wear resistant iron-steel: a theoretical and experimental research … mold casting, the shrinkage allowance on the model and the values obtained from anycasting software were checked for relevance. the model-flask used in sand mold preparation is shown in figure 2. fig. 1. shrinkage volume display. fig. 2. flask and model display prior to sand casting. for the preparation of the flask, 2800g of sand, 80-85g of resin, and 20-25g of chemical hardener were weighed on a precision scale and then were mixed in a separate container manually or by using a machine with adding resin and chemical hardener for 1.5-2 minutes. the mixed sand was emptied on the model inside the flask with a foundry trowel. while emptying the mixture, special attention was paid to the sand squeezing process for proper mold formation. the molds prepared for the casting process were joined together with special adhesive-refractory material. the molds were put in a dryer furnace for dehumidification and made ready for casting before pouring. iv. pouring process and spectral analysis a single material cannot meet all the high performance needs of long-lasting spare parts, so the properties of the material are improved by alloying through casting [12]. in pouring process, samples were taken from the furnace after burden materials fully melted and reached the desired temperature. the chemical analysis of the samples was carried out in a spectrometer to determine their chemical composition. proper rates of ferroalloy were added to the first alloys in the furnace after composition values were calculated in the analysis. after reaching the desired rate with calculations and adding ferroalloy, pouring process was completed. the mold was left for cooling and then the pieces were removed from the mold for cooling and cleaning process. the shake out after casting is shown in figure 3. gnr atlantis optical emission spectrometer was used for spectral analysis. the rates of cast specimens with different chemical compositions are shown in table i. fig. 3. the pouring moment-mold display after cooling. table i. chemical composition of samples after casting cast specimen number 1 2 3 4 specimen name n1 n2 n3 n4 c 0.48 0.54 0.59 0.58 mn 0.95-1.00 1.49 1.55 1.19 p max-0.016 max-0.020 max-0.020 max-0.019 s max-0.009 max-0.011 max-0.010 max-0.010 si 0.58 0.60-0.70 0.49 0.60-0.70 cr 1.30-1.40 1.26 1.27 1.24 ni 1.26 1.245 1.25 1.24 mo 0.54 0.62 0.63 0.61 v. rolling prior to the rolling process, cast specimens were cut at 100×30×15mm dimensions with a cutter in order to match the laboratory draw bench. then the prepared specimens were heated up to 1200±10°c in a pid controlled furnace with digital temperature and program display for hot rolling process. the 100×30×15 steel cast specimens were rolled on a draw bench with 150mm press surface width and 150mm cylinder mill diameter as shown in figure 4. fig. 4. rolling process in laboratory conditions. engineering, technology & applied science research vol. 11, no. 3, 2021, 7251-7256 7253 www.etasr.com bildik & yaşar: manufacturing of wear resistant iron-steel: a theoretical and experimental research … the rolling process was done in 3 passes. in the 1st pass the thickness was reduced to 14mm, in the 2nd pass to 12mm, and in the 3rd pass to 10mm. at the end of the rolling process, the average dimensions of the specimens were 140×37×10mm. the average, measured after rolling, brinell hardness of the specimens is given in table ii. table iii. average brinell hardness values after rolling specimen name brinell hardness(hv) n1 457 n2 612 n3 605 n4 670 vi. wear test tribometer t10/20 test equipment, manufactured by the uts company, was used for wear experiments (figure 5). before the experiments, the specimens were cut and sandpapered and then mounted on the equipment. the tests were carried out in accordance with reciprocating linear motion module and astm g-133 (standard test method for linearlyreciprocating ball-on-flat sliding wear) [11, 13]. 20n, 40n, and 60n loads were used in tests. test parameters and load amounts are shown in table iii. fig. 5. test set-up for wear testing. table ii. wear test parameters load (f) 20n/40n/60n frequency 3hz distance (x) 7mm sliding distance 250 m sliding velocity 42mm/s fig. 6. images of wear testing and specimen after wear test. figure 7(a)-(d) shows the sem views of the wear surfaces of steel specimens under 60n load. it can be seen that there are significant, superficial, groove-like scratches, along with deformation scratches that accumulate on the part that broke after wear and plastic deformation materials dispersed on its surface. it is observed that wear is less in areas with high manganese on their surfaces. especially in the samples given in figure 7(b) and (c), it is seen that the amount of abrasion is less and the highest wear occurred in the sample in figure 7(a). it has been observed that in all the figures, the materials show a serious resistance mechanism against abrasion that can be called abrasion resistant steel [14]. fig. 7. sem and edx images of abrasion test with 60n load in 1.00kx (a) sample1, (b) sample2, (c), sample3, (d) sample4. vii. archard fem analysis and result comparison the archard wear equation [15-17] or holm/archard law, introduced by j.f. archard in 1953, states the relationship among sliding wear volume (v), normal load (w), total sliding distance (l) and hardness of the softer of two contacting surfaces (h). the classical archard’s wear model is widely used in abrasive wear literature. the archard’s wear equation shows that wear rate is proportional to sliding velocity and normal contact force. the archard wear model defines wear direction along with wear rate, contact pressure, sliding velocity, and material hardness: � � � � � � � � (1) values such as wear coefficient, pressure exponent and velocity exponent were taken as constant: c1 = wear coefficient, k = 1.05×10 -2 , c2 = material hardness, h = variable as per specimen hardness [19], c3 = pressure exponent, m = 1, and c4 =velocity exponent, n = 0 [20]. different hardness values were designated as variable for different specimens after casting [18]. material hardness obtained after rolling were proportioned and hardness values were taken as 2400 for n1, 3250 for n2, 3120 for n3, and 3480 for n4. engineering, technology & applied science research vol. 11, no. 3, 2021, 7251-7256 7254 www.etasr.com bildik & yaşar: manufacturing of wear resistant iron-steel: a theoretical and experimental research … ansys software was utilized for finite element analysis and the experiment set-up shown in figure 8 was used for each specimen. the wear behavior at 250m distance was simulated for 20n, 40n, and 60n loads [21, 22]. fig. 8. finite element analysis and wear image. fig. 9. wear test applied to specimens 1,2,3, and 4 in table i, and wear volume comparison of load amounts as a result of finite element analysis. the result of wear experiment of specimen 1 at 20n load was 0.665mm³ and the result from the fem model was 0.673mm³ (figure 9(a)). both results shown in figure 9(a) were quite close, suggesting that the simulation and experiment data were consistent with each other. when the load amount reached 40n, wear volume was observed to increase in accordance with the load both in the experiment and in the finite element analysis. at 60n load, the experimental wear volume was 2.80mm³, while in fem analysis the wear volume was a bit lower with 1.97mm³. the result of wear experiment of specimen 2 at 20n load was 0.347mm³ and the result from the fem model was 0.497mm³ (figure 9(b)). when the load reached 40n, the wear volume increased in both experimental and finite element analysis to 0.639mm³ and 0.971mm³ respectively. at 60n load, the experimental wear volume was 1.358mm³, while in fem analysis the wear volume was a bit higher with 1.452mm³. in figure 9(c) the result of wear experiment of specimen 3 at 20n load was 0.445mm³ and the result from the fem model was 0.518mm³. when the load reached 40n, the experimental wear volume of the load was 0.847mm³ and 1.011mm³ for fem. at 60n load, the experimental wear volume was 1.54mm³, while in fem analysis it was 1.513mm³. in figure 9(d), the result of wear experiment of specimen 4 at 20n load was 0.438mm³ and the result from the fem model was 0.464mm³. the results were quite close. when the load amount reached 40n, the wear volume was observed to increase in both experimental and finite element analysis with 1.15 mm³ and 0.907 mm³ respectively, in accordance with the load. at 60n load, the experimental wear volume was 2.04mm³, while in fem analysis it was 1.356mm³. as can be seen from the results of wear experiment at 20n load (figure 10), the lowest wear volume was at specimen 2 with 0.347mm³ and the highest wear was 0.665mm³ at specimen 1 which had the lowest c amount. experimental wear and finite element results were very close in all specimens. wear experiment results and finite element simulation results at 40n load are shown in figure 11. at 40n load, the lowest wear value was at specimen 2 with 0.639mm³ and the highest at specimen 1 with 1.178mm³. in all wear test results, except specimen 4, experimental wear volume values were lower than the fem wear values. at 60n load, the highest wear was 2.80mm³ at specimen 1 which had the lowest c and mn content. the wear volume was higher than the fem value of 1.97mm³. the lowest wear was at specimen 2 and 3. these results were very close to the fem values. the experimental wear volume for specimen 4 was higher than the fem result. fig. 10. wear volume of specimens at 20 n load wear experiment. fig. 11. wear volume of specimens at 40n load wear experiment. figure 13 compares the wear values of the manufactured specimens to en 10029 and en 10051 standard steel materials, known as wear resistant steel plates in the market. engineering, technology & applied science research vol. 11, no. 3, 2021, 7251-7256 7255 www.etasr.com bildik & yaşar: manufacturing of wear resistant iron-steel: a theoretical and experimental research … fig. 12. wear volume of specimens at 60n load wear experiment. fig. 13. comparison of manufactured steel plates and market wear plates. en 10051 wear plate number 1 had the lowest wear resistance at all the tests. the en 10051 wear plate number 2 had higher wear volume than specimens n2, n3, and n4. it had less wear volume than specimen n1 only at 20n and 60n tests. at 40n test, its wear volume with 1.318 mm 3 was higher than specimen n1's. viii. results and evaluation this study aimed to manufacture different steel which has not yet entered the standards, and to examine its wear behavior. in particular, the aim was to provide an alternative to the wear parts in motorway vehicles which are subject to constant wear and that goal was achieved. manufacturing conditions were simulated in virtual environment before specimens were cast. the runner and the full filling of the mold cavity with liquid metal were optimized. the mold manufacturing was done in compliance with the conditions and the plates were cast using an induction furnace. as a material standard, different alloy and rolling conditions were tried similar to en 10029 and en 10051 standards used in the market. in order to optimize wear conditions, finite element software and archard wear theory were utilized. the experimental and theoretical results matched by 85%. the compliance rate was low for the results obtained from 60n wear load. the reasons are estimated to result from overheating and consequently 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[22] m. a. ashraf, r. ahmed, o. ali, n. h. faisal, a. m. el-sherik, and m. f. a. goosen, "finite element modeling of sliding wear in a composite alloy using a free-mesh," journal of tribology, vol. 137, no. 3, jul. 2015, art. no. 031605, https://doi.org/10.1115/1.4029998. microsoft word etasr_v10_n6_pp6481-6487 engineering, technology & applied science research vol. 10, no. 6, 2020, 6481-6487 6481 www.etasr.com oliko et al.: rice straw and eggshell ash as partial replacements of cement in concrete rice straw and eggshell ash as partial replacements of cement in concrete cyprian oliko sustainable materials research and technology centre jomo kenyatta university of agriculture and technology nairobi, kenya cyprianoliko@yahoo.com charles k. kabubo sustainable materials research and technology centre jomo kenyatta university of agriculture and technology nairobi, kenya kabcha@jkuat.ac.ke john n. mwero department of civil engineering university of nairobi nairobi, kenya johnmwero1@gmail.com abstract—this paper presents the properties of concrete made with cement partially replaced with rice straw ash and eggshell ash. the rice straws and eggshells were incinerated, sieved, and ground, and the physical and chemical properties of the resultant ash and the other materials incorporated in the concrete mixes were determined. a class 35 concrete mix with no partial replacement of cement with rice straw ash designed with the british research establishment method with a water/cement ratio of 0.5 was considered as the control mix. the cement in concrete was partially replaced with rice straw ash by 5% to 30% and its compressive and splitting tensile strength was determined after 7, 14, 28, 56, and 90 days of curing. durability, resistance to acid attack, and other wet and hardened properties of concrete with cement partially replaced with rice straw ash were also determined. an increase in compressive strength above the control mix was observed for concrete with 5% and 10% partial replacement of cement with rice straw ash. when eggshell ash was added to concrete mixes made with cement partially replaced with rice straw ash at 15% and 20%, the 28, 56, and 90-day compressive strength was found to increase. it can be concluded that rice straw and eggshell ash can be used to partially replace cement in concrete and result in a concrete whose properties compare favorably with control. keywords-rice straw ash; eggshell ash; chemical composition; partial replacement; concrete compressive and splitting tensile strength; durability; water absorption i. introduction concrete is the most popular construction material. it may be used alone as mass concrete or with steel as reinforced or pre-stressed concrete [1, 2]. ordinary portland cement (opc), which is the main component of various concrete types, is one of the most common construction materials worldwide. however, there is a global effort to utilize industrial or agricultural waste as raw materials for the concrete industry which will replace, at least partially, cement [3]. this has been inspired by economic, environmental, and technical reasons and aims at mitigating the environmental impact of concrete production and improving specific properties of the resultant concrete [4]. pozzolans are materials which are not cementitious in nature but in processed forms react with water to form cementitious compounds in the presence of water lime [5]. cement is manufactured from a mixture of calcium carbonate in form of limestone, silica iron oxide and alumina [6]. four major compounds in cement are dicalcium silicate, tricalcium silicate, tricalcium aluminate and tetra-calcium aluminoferrite. dicalcium silicate and tricalcium silicate are the compounds responsible for the strength of hydrated cement paste [7]. upon wetting of cement the dicalcium silicate, tricalcium silicate and tricalcium aluminate react with water to form dicalcium silicate hydrate, tricalcium silicate hydrate (cs-h), calcium alumino silicate hydrate and tricalcium alumino ferrite hydrate. during the process, calcium hydroxide (ca(oh)2) is produced as a byproduct. the main strengthening compound is calcium silicate hydrate (c-s-h) [8]. ca(oh)2 is responsible for the deterioration of concrete through leaching. when a pozzolanic material is added to portland cement, the silica in it reacts with the ca(oh)2 produced by cement hydration to produce additional calcium silicate hydrates and thus improves the cementitious properties [8-9]. the rice plant absorbs silica from the ground and assimilates in into its structure, so it is a good source of silica when appropriately incinerated [10]. rice straw is available in large quantities from rice irrigation schemes at negligible cost. chicken eggshells are normally considered as waste and are thrown away. they are available in large quantities from hatcheries and confectioneries. their main component is calcium carbonate (caco3) with magnesium, potassium, sodium, phosphorus, aluminum, zinc and copper found in small proportions [11]. during the incineration of the eggshells, the ca(co)3 decomposes to form cao/lime and co2. the co2 will escape while the cao will remain in the ash [12]. therefore, corresponding author: cyprian oliko engineering, technology & applied science research vol. 10, no. 6, 2020, 6481-6487 6482 www.etasr.com oliko et al.: rice straw and eggshell ash as partial replacements of cement in concrete eggshells are a suitable, eco-friendly and sustainable alternative to quarry limestone. from the reviewed literature, it has been observed that at higher percentages of partial replacement of cement with pozzolans, there is a decrease in the compressive strength of concrete, due to the high silica and low cao content in the pozzolans. higher percentages of partial replacement of cement with pozzolanic ash result in a reduction in the quantity of available cao in the mix which is required to react with silica to form calcium silicate hydrates that are responsible for concrete’s strength. this deficit can be remedied by the addition of eggshell ash. this study aimed at establishing the effect of partial replacement of cement in concrete with rice straw ash and eggshell ash on concrete strength and the extent to which rice straw ash and eggshell ash can partially replace cement in concrete. ii. methodology a. materials 1) rice straw ash oryza sativa (basmati) rice straws were used in this study and were collected from bunyala rice irrigation scheme, busia county, kenya. the straws were dried and then incinerated at 650 o c for 1 1 /2 hours [13]. the ash was successively sieved through 600µm, 425µm bs, and finally 75µm bs sieves. the resultant ash was further ground in a ball mill for 4 minutes. only particles passing the above sieves were used for partial cement replacement [14]. chemical analysis of the ash was done with an x-ray diffractometer at the mines and geology laboratory in nairobi. particle size distribution was done on the ash by hydrometer analysis. 2) eggshell ash the eggshells used were obtained from small scale hatcheries and hotels. they were cleaned to remove impurities, dried in the sun until their surface became dry and incinerated at 900 o c for 2 hours. the resultant ash was ground in a ball mill for 4 minutes. chemical analysis of the ash was done by an x-ray diffractometer at the mines and geology laboratory in nairobi. 3) aggregates river sand obtained from malaba river in western kenya was used as fine aggregates and crushed stone obtained from sirikwa quarry in eldoret, uasin gishu county, kenya as coarse aggregates. 4) cement the cement used in this study was opc type cem 1class 42.5n to kenya standard (ks eas 18-1:2001). chemical analysis was also done on the cement. b. concrete mix proportions the concrete mix design used in this research was done according to building research establishment (bre) method with target strength of 35n/mm 2 at 28 days. rice straw ash was used to replace cement at 5, 10, 15, 20, 25, and 30% by weight of cement. a water/cement ratio of 0.5 was used for all the mixes. fifteen concrete cubes and 15 cylinders were made for each mix ratio. the wet properties of the resultant concretes were determined immediately after mixing. the concrete was cast in 150×150×150mm cubes and 150mm diameter and 300mm height cylinders that were demoulded after 24 hours and cured in water for 7, 14, 28, 56, and 90 days. the hardened concrete properties were determined from the cast cubes and cylinders. iii. concrete tests a. slump test slump tests were conducted on wet concrete to bs 1881 part 102(1983). b. compaction factor test compaction factor tests were conducted on cement pastes with various % partial replacement of cement to indian standard 1199:1959. c. compressive strength test the cast cubes were crushed in a compressive strength testing machine according to bs 1881part 116(1983). d. split tensile strength test split tensile strength tests were conducted on the concrete cylinders in a compressive strength testing machine according to the bs 1881part 117(1983). e. durability test concrete cube specimens cured for 56 days were immersed in 0.5% dilute sulphuric acid. they were tested for residual compressive strength in a compressive strength testing machine. iv. results and discussion a. material properties table i illustrates the chemical composition of rice straw ash and opc. in table i, we notice that the main chemical oxides in cement composition were within the tolerances specified by the kenyan standard for cement ks eas 181:2001. the results of rice straw ash indicate that the rice straw ash was found to be composed of 72.379% sio2 (silica) by weight. from table i it can be observed that the combined percentage of silica and alumina is 74.34% which satisfies the 70% minimum specified by astm c 618 [15] for a material to be used as a pozzolan. the chemical composition of eggshell ash is shown in table ii. it can be observed that eggshell ash consists of 96.755% cao. in comparison, portland cement consists of 72.04% cao. it can be observed in figure 1 that the particles of rice straw were to have smaller size than those of cement since they recorded higher passing percentage than cement for all sieve sizes. b. setting time the setting time test results on cement pastes are illustrated in figure 2. engineering, technology & applied science research vol. 10, no. 6, 2020, 6481-6487 6483 www.etasr.com oliko et al.: rice straw and eggshell ash as partial replacements of cement in concrete table i. chemical analysis of cement and rice straw ash opc rice straw ash component percentage tolerance (ks eas 18-1:2001) percentage mgo 0.000 0.000 al2o3 4.076 3% – 8% 1.094 sio2 14.18 17% – 25% 72.379 p205 0.857 1.513 s 4.303 0.919 cl 0.138 0% 5% 1.450 k2o 0.746 16.174 cao 72.041 60% – 67% 5.067 ti 0.222 0.100 v 0.003 0.006 cr 0.001 0.006 mn 0.057 0.256 fe 3.087 0.836 co 0.000 0.000 ni 0.000 0.002 cu 0.004 0.013 zn 0.005 0.080 as 0.000 0.000 so 0.000 0.000 rb 0.004 0.070 sr 0.204 0.021 y 0.003 0.000 zr 0.007 nb 0.003 total 99.973 99.996 table ii. chemical analysis of eggshell ash component percentage standard deviation cao 96.755% 0.173 k2o 2.523% 0.116 sro 0.606% 0.006 so3 0.116% 0.006 total 100% fig. 1. particle size distribution of cement and rice straw ash vs sieve size. the initial and final setting times of concrete with 5 – 30% partial replacement of cement with rice straw were found to range between 85 and 615 minutes compared to the control which recorded an initial setting time of 65 minutes and a final setting time of 495 minutes. two main factors affecting setting time in cement are chemical composition and fineness. it can be observed that as the partial replacement of cement with rice straw increased, the initial and final setting time also increased. both initial and final setting time of concrete depend on chemical reactions that take place in cement. al2o3 present in cement is responsible for the formation of tricalcium aluminate which aids the quick hardening of cement. from the chemical analysis of the cement in table i, it can be observed that cement was found to contain 4.076% al2o3, while the rice straw ash was found to contain 1.094% al2o3. thus the partial replacement of cement with rice straw ash led to a reduction in in al2o3, hence the setting times for cement pastes with rice straw ash was increased. fig. 2. setting time vs partial replacement of cement with rice straw ash. c. slump the slump values for concrete with various percentages of partial replacement of cement with rice straw ash are exhibited in table ii and figure 3. table iii. slump values for various percentages of partial replacement of cement in concrete % partial replacement of cement with rice straw ash% 0 5 10 15 20 25 30 slump, mm 62 51 47 39 10 0 0 fig. 3. slump vs percentage of partial replacement of cement in concrete. engineering, technology & applied science research vol. 10, no. 6, 2020, 6481-6487 6484 www.etasr.com oliko et al.: rice straw and eggshell ash as partial replacements of cement in concrete the results in table iii and figure 3 indicate a steady decline in the slump value with increase in partial percentage replacement of cement with rice straw ash. the control mix had the highest slump of 62.0mm while concrete mixes with 25% and 30% partial cement replacement were found to have zero slump. thus, with increase in rice straw ash, the concrete became less workable. these findings are consistent with those of [13]. this reduction in consistency can be attributed to the additional water requirement caused by the smaller particle sizes of rice straw ash which also have porous surfaces, hence increased surface area. d. compaction factor the results of the compaction factor tests are presented in table iv. table iv. compaction factor for cement/rice straw pastes % partial replacement of cement with rice straw ash% 0 5 10 15 20 25 30 compaction factor (%) 0.685 0.680 0.674 0.668 0.666 0.654 0.622 it can be observed that as the percentage of partial replacement of opc with rice straw ash increases, the workability and hence the compaction factor of concrete decreases. this occurs because when the cement is replaced with an equal mass of rice straw ash, this leads to an increase in both the volume of mass due to the lower relative density of rice straw ash. the increased mass leads to increased number of particles and hence specific surface area due to the fact that the rice straw ash is less dense than the cement. this increase in surface area leads to increased water demand by the rice straw ash in the mix. this additional water demand reduces the water available for the workability of concrete and hence the workability decreases since the water to cement ratio was unchanged for all the mixes. comparing the results in table iii and table iv, it can be observed that the compaction factor is more sensitive than slump test for stiffer concretes. e. compressive strength in figure 4 we can notice an increase in compressive strength above the control for concrete mixes with 5% and 10% partial cement replacement for all the ages of testing. the 7, 14, 28, 56, and 90 days compressive strength was found to be 27.90, 33.00, 35.95, 36.55, and 38.70 for the control mix while the compressive strength was found to be 32.70, 36.70, 38.80, 40.25, and 41.30 representing 17.2%, 11.2%, 7.9%, 10.1%, and 6.7% increase above the control respectively for 5% partial cement replacement. for 10% partial replacement of cement the strength was found to be 33.65, 37.10, 40.20, 41.80, and 42.65 for 7, 14, 28, 56, and 90 days representing 20.6%, 12.42%, 11.8%, 14.3%, and 10.2% increase above the control respectively. the increase in concrete strength can be attributed to two factors: first, the filler effect of pozzolanic material which has smaller particles than cement resulted in denser packing of particles within the concrete matrix and at the aggregate/concrete interface. the second is the pozzolanic reaction between the silica in and ca(oh)2 produced by cement hydration which occurs after the hydration reaction and is responsible for strength gain during the later days of concrete curing. for mixes with partial cement replacement of 15, 20, 25, and 30%, a drop in compressive strength below the control was observed. the 7, 14, 28, 56, and 90 day compressive strengths were found to be 28.70, 31.60, 32.30, 33.70, and 34.70 respectively for 15% partial cement replacement and 28.40, 29.55, 31.80, 32.60, and 33.45 respectively for 20% partial cement replacement. for 25% partial cement replacement the strengths were found to be 24.00, 26.20, 28.70, 31.85, and 32.80 while for 30% partial cement replacement the compressive strength was found to be 10.85, 15.25, 18.95, 20.05, and 23.10 for 7, 14, 28, 56, and 90 days curing age respectively. since the rice straw ash was found to have a cao: silica ratio of 1:14.3 instead of the recommended 3:13 and a cao content of 5.07% instead of the recommended 61-67% (table i), the partial replacement of cement with rice straw leads to a reduction in cao and an increase in silica. at low percentages of replacement, the silica reacts with the cao released by the hydration of cement to form cementitious materials. at higher replacement levels of cement, there is an increase in the amount of pozzolan in the concrete mix however the replacement of cement with pozzolan has an effect of reducing the cement content in the concrete which in turn reduces the quantity of released ca(oh)2 by hydration of opc. this reduction in ca(oh)2 production leads to the reduced production of the cementitious product (c-s-h) that is responsible for the strength development in concrete. the optimum percentage of partial replacement of cement with rice straw ash was found to be 10%, in which there is equilibrium and all the ca(oh)2 produced by the cement hydration reaction combines with silica to form calcium silicate hydrates(c-s-h). beyond the optimum 10% of partial replacement of cement there is less ca(oh)2 produced by the cement hydration reaction, hence there is a reduced opportunity for ca(oh)2 to react with silica to form additional c-s-h. to reduce this deficit in cao and facilitate continuation of the silica – ca(oh)2 pozzolanic reaction, eggshell ash was added to the concrete mix in order to react with silica to form additional cs-h and mitigate the strength loss of the concrete at higher partial replacement levels of cement with rice straw ash. fig. 4. compressive strength vs the percentage of partial replacement of cement with rice straw ash in concrete. engineering, technology & applied science research vol. 10, no. 6, 2020, 6481-6487 6485 www.etasr.com oliko et al.: rice straw and eggshell ash as partial replacements of cement in concrete figures 5, 6, and 7 illustrate the 28, 56, and 90 days compressive strength of concrete with various percentages of partial replacement of cement with rice straw ash and concrete with partial replacement of cement with both rice straw and eggshell ash. fig. 5. 28-day compressive strength for concrete with various percentages of partial replacement of cement with rice straw ash and eggshell ash. fig. 6. 56-day compressive strength for concrete with various percentages of partial replacement of cement with rice straw ash and eggshell ash. from the compressive strength results, concretes with 15% and above partial replacement of cement with rice straw ash exhibited decrease in their strength. the 28, 56, and 90 days compressive strength of concrete with 15% partial cement replacement with rice straw ash and 0% eggshell ash were found to be 32.3, 33.7, and 34.7n/mm 2 while the compressive strength for concrete with 15% partial cement replacement with rice straw ash and 10% eggshell ash was 41.3, 42.7, and 44.85 representing strength increase of 25.3%, 26.7% and 29.2% respectively. on the other hand the 28, 56, and 90 days compressive strength for concrete with 20% partial cement replacement with rice straw ash and 0% eggshell ash was found to be 31.8, 32.6 and 33.8n/mm 2 while the compressive strength for concrete with 20% partial cement replacement with rice straw ash and 10% eggshell ash was 33.5, 34.7 and 34.85n/mm 2 representing strength increase of 5.34%, 3.26%, and 3.88% respectively. fig. 7. 90-day compressive strength for concrete with various percentages of partial replacement of cement with rice straw ash and eggshell ash. previous researchers reported a decrease in compressive strength at higher levels of partial replacement of cement in concrete with pozzolans. there is limited information on what can be done to remedy the concrete strength loss at higher partial cement replacement levels and still take advantage of the silica present in the pozzolans. none of the reviewed researches proposed a remedy. in the current research, eggshell ash was added to concrete mixes with higher partial replacement levels of cement with rice straw ash. eggshell ash, rich in cao reduced the cao deficit occasioned by replacing cement with rice straw ash owing to their dissimilar chemical composition. this ensured that even at higher cement replacement levels with rice straw ash, cao was available to react with silica from the pozzolan and form additional calcium silicate hydrates that are responsible for strength. this increased the concrete strength that had been initially recorded before the addition of eggshell ash as illustrated by the above results. thus, the objective of reducing the content of cement and the cost of concrete was achieved. f. splitting tensile strength figure 8 illustrates the variation of splitting tensile strength with the percentage partial replacement of cement with rice straw ash for various ages of curing. it can be observed that the splitting tensile strength for 5% and 10% replacement was found to be above the control. for 15%, 20%, 25%, and 30% partial replacement, the splitting tensile strength was found to be lower than the control’s. thus, for both compressive and splitting tensile strength, it can be said that 10% partial cement replacement in concrete is the optimum. beyond 10% partial replacement, the compressive strength decreases with the increase in replacement percentage. engineering, technology & applied science research vol. 10, no. 6, 2020, 6481-6487 6486 www.etasr.com oliko et al.: rice straw and eggshell ash as partial replacements of cement in concrete fig. 8. splitting tensile strength vs percentage of partial replacement of cement with rice straw ash in concrete. g. accelerated durability test the test results on concrete cubes cured for 56 days in water and immersed in bath containing 0.5% dilute sulphuric acid for 30 days are exhibited in table v. table v. mass loss of various concrete mixes immersed in 0.5% sulphuric acid concrete mix mass before immersion (g) mass after immersion (g) change percentage 0% partial replacement 8,529 8,443 -1.01 10% partial replacement 8,353 8,329 -0.29 in table v it is noticed that the control recorded the highest mass loss of 1.01%, while the concrete cubes with 10% (optimum) partial cement replacement with rice straw ash recorded the least loss in mass (0.29%) which is very close. the mass loss in concrete cube specimens can be attributed to the formation of gypsum, part of which dissolved in the solution and part appeared as a precipitate in the acid solution bath. sulphuric acid (h2so4) reacts with ca(oh)2 in the concrete matrix to form gypsum which is soluble [16]. for the specimen with no partial replacement of cement with rice straw ash, the ca(oh)2 that was formed by the hydration reaction reacts with sulphuric acid to form gypsum. these specimens did not have a pozzolan in their mixes to consume the ca(oh)2 formed by hydration hence there was greater opportunity for the reaction between ca(oh)2 and h2so4 to occur and form gypsum. they also lacked the packing effect of pozzolan particles in their concrete matrix to prevent percolation of acid solution into the concrete cube matrix. these factors could explain why they recorded the highest mass loss on exposure to acid solution. on the other hand, in the specimens with 10% partial replacement of cement with rice straw ash, the ca(oh)2 formed during hydration was consumed by the pozzolanic reactions with silica in the rice straw ash to form additional calcium silicate hydrates, hence reduced the opportunity for the reaction that leads to the formation of gypsum and thus reducing mass loss. table vi. compressive strength of various concrete mixes immersed in 0.5% sulphuric acid concrete mix compressive strength before immersion (mpa) compressive strength after immersion (mpa) change percentage 0% partial replacement 38.7 36.47 -5.77 10% partial replacement 42.65 41.1 -3.56 we can see in table vi that the control mix without partial replacement of cement with rice straw ash had the highest reduction in compressive strength at 5.77% while the mix with 10% partial replacement was found to have a compressive strength reduction of 3.56%. rice straw particles were found to be smaller in particle size than those of cement, as illustrated by figure 1, thus the concrete with partial replacement of cement with rice straw ash achieved denser packing of particles making them less porous to capillary penetration of the acid solution. the impregnating effect of rice straw ash along with the formation of additional calcium silicate hydrates by the pozzolanic reaction filled voids in the concrete matrix and enhanced the chemical resistance and capillary penetration of the acid solution in the concrete matrix and hence slowed its corrosion effect leading to reduced mass loss. v. conclusions • the studied rice straw ash meets the requirements of astm c 618 specifications for pozzolans. • the rice straw ash can partially replace opc in concrete up to an optimum percentage of 10%. the concrete compressive strength was found to increase by 11.8%, 14.3%, and 10.2% above control for 28, 56, and 90 days of curing. • eggshell ash used in this study was found to be composed of 96.75% cao when incinerated. the eggshell ash can be used in combination with rice straw ash to increase the strength of concrete with higher percentage of partial replacement of cement with rice straw ash that otherwise recorded a decrease in strength . • the optimum combination of eggshell ash and rice straw ash to be used together to partially replace cement in concrete was found to be 10% for both. • the rice straw ash was found to increase the resistance of the concrete to the acid solution, hence it can be used for concretes exposed to acidic environment and sulphate attacks. • concrete with cement partially replaced with rice straw ash was found to have lower capillary water absorption and hence improved durability. engineering, technology & applied science research vol. 10, no. 6, 2020, 6481-6487 6487 www.etasr.com oliko et al.: rice straw and eggshell ash as partial replacements of cement in concrete vi. recommendations a. recommendations for use • rice straw ash can be used to partially replace cement in concrete up in percentages up to 10%. • rice straw ash can be used to make concrete in environments that are susceptible to acid attack • eggshell ash can be used in combination with rice straw ash to partially replace cement and enable higher partial replacement of cement with pozzolans with reduced loss of concrete strength. b. recommendations for further research • varying the water cement ratio above or below 0.5 and compare the properties of concrete with the ones found in the current study. • obtaining rice straw from other irrigation schemes and using the ash for partial replacement of cement in concrete and compare the properties of concrete with the ones found in the current study. • incinerating the ashes at different temperatures and 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[16] b. m. reddy, h. s. rao, and m. p. george, “effect of sulphuric acid (h2so4) on blended cement (fly ash based) and its concrete,” international journal of applied engineering and technology, vol. 2, no. 2, 2012. microsoft word 42-3517_s_etasr_v10_n3_pp5837-5844 engineering, technology & applied science research vol. 10, no. 3, 2020, 5837-5844 5837 www.etasr.com ponnam & swarnasri: multi-objective optimal allocation of electric vehicle charging stations … multi-objective optimal allocation of electric vehicle charging stations and distributed generators in radial distribution systems using metaheuristic optimization algorithms venkata k. babu ponnam department of eee acharya nagarjuna university guntur, india kishore.ponnam@gmail.com k. swarnasri department of eee rvr & jc college of engineering guntur, india swarnasrik@gmail.com abstract—the acceptance rate of electric vehicles (evs) in the transport industry has increased substantially due to the augmented interest towards sustainable transportation initiatives. however, their impact in terms of increased power demand on the electric power market can increase real power losses, decrease voltage profile, and consequently decrease voltage stability margins. it is necessary to install electric vehicle charging stations (evcss) and distributed generators (dgs) at optimal locations to decrease the ev load effect in the radial distribution system (rds). this paper addresses a multiobjective optimization technique to obtain simultaneous evcs & dg placement and sizing. the problem is formulated to optimize real power losses, average voltage deviation index (avdi), and voltage stability index (vsi) of the electrical distribution system. simulation studies were performed on the standard ieee 33-bus and 69-bus test systems. harries hawk optimization (hho) and teaching-learning based optimization (tlbo) algorithms were selected to minimize the system objectives. the simulation outcomes reveal that the proposed approach improved system performance in all aspects. among hho and tlbo, hho is reasonably successful in accomplishing the desired goals. keywords-electrical vehicles (evs); electric vehicle charging stations (evcss); renewable energy sources; distributed generators (dgs); average voltage deviation index (avdi); voltage stability index (vsi); harris hawks optimization (hho); teaching-learning based optimization (tlbo) i. introduction ever-increasing demands for energy, the limited availability of fossil fuels, and the global climate change are some major concerns of the 21 st century. the co2 emissions from the transportation sector are one of the major causes of global climate change. researchers highlighted the significant impact of shifting from conventional vehicles to evs to reduce the transport sector's greenhouse gas contribution. developing countries are also attracted to evs due to the low electricity costs as compared to fossil fuel. one of the disadvantages of evs is the driving range limitation. after running a certain distance, evs need to recharge the battery at charging stations (css). thus, focus must be put on the construction of charging infrastructure for large-scale installation of evs. coordinated evcs planning is of prevailing importance for the sustainable growth of the ev industry. in [1], a multi-objective function is built that takes into account the performance indexes of the traffic and electrical distribution network, including traffic conditions, charging wait time, power loss, and node voltage, to plan the charging behavior of evs and achieve optimum efficiency of the entire system. nevertheless, for optimum location, the effect on the voltage profile and branch power losses needs to be examined. the low sensitivity voltage bus [2] could be the best location for the charging station. nevertheless, this approach fails to provide the optimum evcs on the higher radial bus systems. heuristic algorithms have been developed to optimize the placement of evcs not only for servicing evs but also to minimize losses and thus to increase voltage profile. to examine the effect of charging evs on the electrical distribution network the fast charging station (fcs) load is designed in [3] by taking into account the relationship between the power consumption of evs and grid voltage. the suggested model is also compared to the constant zip model and constant power load model. in [4], the genetic algorithm is used mainly to optimally place the evcss without considering losses and conductor thermal limits. this method of positioning evcss often impacts the reliability of the grid-connected distribution system. by reconfiguring the given rds [5], the effect of the charging stations could be minimized. in [6], the location of the evcss is identified in two stages. the evcss’ operation spectrum is calculated in the 1 st stage using the trip success ratio with the account of the volatility of trip distance and variability in the remaining electrical charge of the evs. in the 2 nd stage, the cs spectrum of operation is calculated for optimal cs location. in [7], a tri-objective optimization function that minimizes the charging station’s levelized cost of energy, emissions, and losses on the electrical grid by proposing the use of photovoltaic cells and of a battery storage system. most studies concentrate on the optimum location and corresponding author: venkata k babu ponnam engineering, technology & applied science research vol. 10, no. 3, 2020, 5837-5844 5838 www.etasr.com ponnam & swarnasri: multi-objective optimal allocation of electric vehicle charging stations … size of evcss [8–12]. improper positioning and sizing of evcss hurt the distribution system by increasing the network power losses and cause more depreciation in voltage profile. a detailed review of ev technologies and the impact of electrical demand from plug-in electric vehicles (pevs) on load profiles have been provided in [13]. authors in [14, 15] addressed the problem of dynamic economic dispatch by incorporating pevs that charge patterns into a 24-hour load demand in economic and environmental dispatch. authors in [16] suggested a control mechanism to increase the efficiency of the energy shared between a photovoltaic generator and an unbalanced system. in [17], the detrimental impact on the distribution network of resulting evcs loads is analyzed for voltage stability, reliability indices, power losses, and economic loss of the ieee 33 bus system. in [18], the simultaneous placement of evcss and dgs in the distribution system is proposed in order to reduce ev user charge and network power losses (npl) cost for the same station development cost and dg investment. non-dominated sorting genetic algorithm ii was utilized for achieving the optimal placement of evcs and dgs. the accuracy of the proposed methodology is checked on the 118 bus system. authors in [19] proposed a multi-objective function by considering the daily real power losses and voltage deviations under a 24-hour load pattern, including residential, industrial, and commercial loads. particle swarm optimization (pso) and butterfly optimization (bo) algorithms were applied to minimize the desired objectives. a repeated forward-backward load flow was used to determine losses and voltages. compared to pso, bo does well in achieving the desired goals. in [20], a multi-objective hybrid shuffled frog leap teaching learning based optimization (sfl-tlbo) algorithm was proposed for better planning of evcss and dgs in the combined electrical distribution and transportation network, considering the objectives of voltage deviation, power loss, dg power cost, and energy consumption. the proposed model has been assessed on the ieee 118 bus system and was confirmed to be accurate and stable for different ev population levels. when considering a large number of pevs charging and discharging during peak and off-peak grid hours, the optimum positioning of evs on the ieee-33 radial distribution system using the pso-cfa optimization algorithm was suggested in [21] to reduce power losses and enhance voltage profile. in [22], the artificial bee colony (abc) algorithm was proposed for optimal placement of battery swapping stations (bss) and dg in the rds to mitigate the power loss increment due to the ev load. if both the dg and bss are configured concurrently, the system's power losses and reliability are significantly improved. accordingly, the authors concluded that the simultaneous placement of dg and bss systems is the best choice to get the maximum benefit from the deployment of dg and bss in the network. pso algorithm [23] was used to reduce real power losses and enhance the voltage profile of the system with optimal placement of charging stations. this paper's main contributions are: • identifying the optimal locations of evcss by considering the distribution system losses, avdi, and vsi of rds. • finding optimum dg size and location by considering optimum evcs load to boost system bus voltage profile and reducing rds power losses. • placing different categories of dgs and evcss simultaneously while taking into account system constraints for minimizing system power losses and better system bus voltage regulation. • an efficient multi-objective function formed using tlbo [24] and hho [25] algorithms is proposed for finding the optimal solution of the optimal number of evcss, dgs, and their simultaneous positioning and sizing for minimizing distribution system losses, avdi and enhance vsi of rds. ii. problem formulation a. objective function the size and placement of evcss and dgs should be designed to minimize the impact of the increased ev load on distribution system’s performance. radial distribution system (rds) has a large r/x ratio and because of this basic load flow tools such as newton raphson or fast decoupled approaches do not provide accurate results. an efficient load flow method is presented in [26] based on the forward-backward method for solving the power flows of rds. the objectives of this study are minimizing power losses, avdi, and enhancing vsi. the objective function for power losses of the system is given by: ����� = min ∑ �� ∗ �������� (1) where ri is the resistance of the i th branch, ii is the current flowing in the i th branch, i is the branch number and br is the total number of branches. avdi is defined in terms of all bus voltage magnitudes are deviation w.r.t. reference voltage magnitude 1.0p.u. and is given in: ����� = �� ∑ |1 − ��|����� (2) where vk is the voltage at the k th bus, k is the bus number, and b is the total number of buses. the vsi of a receiving end bus of a branch can be determined by [27]: ����� = �|��|� − 4���� � + "�# �$� − 4���# � + � �$|��|�% (3) where vk is the voltage at k th bus, pk is the total real power demand at the k th bus, qk is the total reactive power demand at the k th bus, rjk is the resistance of the branch ‘jk’, and xjk is the reactance of the branch ‘jk’. vsik should be greater than 0 for stable rds operation. the lowest value of vsi can be considered as the overall stability of the given system. the ultimate objective function is developed to minimize power losses, average voltage deviation, and optimize the index of voltage stability. mathematically: &��� = min '(������ + (������ + (� ) �*+���, (4) b. constraints equality constraints: the constraints for power balance requirements: engineering, technology & applied science research vol. 10, no. 3, 2020, 5837-5844 5839 www.etasr.com ponnam & swarnasri: multi-objective optimal allocation of electric vehicle charging stations … ∑ �.�/0��� − �1 = �2 (5) ∑ ".�/03�� − "1 = "2 (6) where pgk and qgk are the active and reactive powers injected by dg at the k th bus, pl and ql are the active and reactive power losses at the k th bus, pd and qd are the active and reactive power demands at the k th bus, and ng is the total number of buses. inequality constraints: the acceptable limitation of distribution systems should not extend the highest possible allowable power generated from dgs, voltage deviation should be within 5%, the number of charging points (ncp) and the number of charging stations (ncss) should be between minimum and maximum allowable charging points and charging stations respectively, i.e.: �.�4�5 ≤ �.� ≤ �.�478 (7) ".�4�5 ≤ ".� ≤ ".�478 (8) 0.95 ≤ �� ≤ 1.05, k = 1,2,3 … … ., b (9) bc�4�5 ≤ bc� ≤ bc�478 (10) bcd4�5 ≤ bcd ≤ bcd478 (11) iii. hho for evcs and dg simultaneous optimal planning harris hawks optimization (hho) was proposed in 2019. the harris hawk is a predator bird that lives at steady communities found in the southern side of arizona, united states. harris hawk’s main tactic to catch prey is “surprise pounce” and it can also be recognized as the strategy of “seven kills”. in this strategy, many hawks try to strike together from different directions and concentrate on one rabbit. the assault can be easily accomplished by catching the surprised victim in a couple of seconds, although sometimes, with regards to the prey's escape capability and habits, the “seven kills” can include several, short length, rapid dives near the victim for several minutes. harris hawks can display a diverse range of hunting styles depending on complex nature and prey's escape patterns. when the best hawk (leader) bows down a prey and departs, a switching tactic occurs, and one of the party members can continue the chase. in different circumstances, such switching activities could be examined as they are helpful for annoying the escaping rabbit. the main benefit of such collaborative tactics is that the harris hawks can pursue to exhaustion the detected rabbit which cannot restore its defensive capabilities by confusing the predators and usually one of the hawks, which is often the most effective and skilled, catches the exhausted rabbit quickly and shares it with the others. generally, hho is modeled into exploration and exploitation stages inspired by harris hawks exploration of a prey, surprise pounce, and various attacking strategies. a. exploration phase the position of the hawk is changed in the exploration phase by random location and the other hawks and is given by (12) [25]: 1 2 3 4 lim lim ( ) | ( ) 2 ( ) |, 0,5 ( 1) ( ( ) ( )) ( ( )), 0.5 k k r m l t d l t d l t r l t l t l t d lb d u l r − − ≥ + =  − − + − < (12) where l is the hawk's position, lk is the position of a randomly chosen hawk, lr is the location of prey, t is the present iteration, ulim and llim are the threshold limits of the search area, d1, d2, d3, d4, and r are five discrete random numbers in [0, 1], and lm is the average location of the present hawks’ community, which can be calculated by: e4�f� = �g ∑ eh�f�gh�� (13) where lp is the p th hawk in the community, and h is the number of hawks. b. transition from exploration to exploitation the hho algorithm can be transposed from exploration to exploitation. the behavior of exploration is modified depending on the prey's escaping strength. mathematically, prey's strength to escape can be measured as d = 2di�1 − jk� (14) di = 2l − 1 (15) where t is the max number of iterations, s0 is the initial strength produced arbitrary in [-1, 1], and d is a random number in [0, 1]. when the prey’s escaping strength s is greater than 1, hho grants the hawks the possibility to hunt on various regions globally. on the other hand, hho boosts the local search of the best alternatives around the neighborhood when the prey's escaping strength is less than 1. c. exploitation phase during this phase, the position of the hawk is changed according to the scenarios described below. its behavior is controlled based on the prey's escape strength (s) and the prey’s chance to escape successfully (q<0.5) or not (q>0.5) before a surprise bounce. 1) soft besiege this phase appears when q≥0.5 and |s|≥0.5, and by using (16), the hawk adjusts its position: e�f + 1� = ∆e�f� − d|neo�f� − e�f�| (16) where s is the prey's escaping strength, lq is the position of prey, ∆l is the difference between the prey’s position and present hawk position, and j is the dive strength. the j and ∆l are calculated by [25]: ∆e�f� = eo�f� − e�f� (17) n = 2�1 − lp� (18) where d5 is a random number in [0, 1] that is modified in each iteration. 2) hard besiege this phase appears when q≥0.5 and |s|<0.5. in this scenario, the hawk updates its position using [25]: e�f + 1� = eo�f� − d|∆e�f�| (19) engineering, technology & applied science research vol. 10, no. 3, 2020, 5837-5844 5840 www.etasr.com ponnam & swarnasri: multi-objective optimal allocation of electric vehicle charging stations … 3) soft besiege with progressive rapid dives this phase occurs when q<0.5 and |s|≥0.5. the hawk is slowly selecting the best possible dive for capturing the prey. in this situation the hawk's new position is created as [25]: q = eo�f� − d|neo�f� − e�f�| (20) " = q + r ∗ estu�v� (21) where y and q are two recently produced hawks, j is the leaping power, n is the number of dimensions, a is an n dimension random vector, and levy is the levy flight function that can be computed as: estu�w� = 0.01 ∗ x∗y |z|[/] (22) where µ, ϑ are two separate random numbers created from the normal distribution, and σ is described as: ^ = _ `��ab�∗cde)fgh , `)[ijh ,∗b∗�) gk[h , l [] (23) where γ is a constant set to 1.5, and the location of the hawk is modified in this phase by: e�f + 1� = my if &�q� < &�e�f��" if &�"� < &�l�f�� (24) where f is the fitness function and y and q are two solutions derived from (20) and (21). 4) hard besiege with progressive rapid dives this is the last scenario and appears when q<0.5 and |s|<0.5. in this condition, the following two new solutions are created [25]: q = eo�f� − d|neo�f� − e4�f�| (25) " = q + r ∗ estu�v� (26) where lm is the average location of the hawks in the current community. the position of the hawk is subsequently modified as: e�f + 1� = my if &�y� < &�e�f��q if &�"� < &�e�f�� (27) iv. hho application for solving the objective function in this section, the sequential steps involved in solving the problem of optimal allocation of evcss and dgs using the hho algorithm are given. step 1) define the objective function subjected to equality and inequality constraints of the design variables and read the line and load data. step 2) initialize the number of hawk searches within the upper and lower limits of dg sizes in kw, locations of evcss and dgs, hho parameters and maximum number of iterations t. step 3) set iteration count k=1. step 4) using forward-backward load flow, determine the objective function value using (4) for each search hawk. step 5) identify the best hawk (lr), which has given the best objective function value. step 6) for each hawk lp, update the values of s, s0, and j by using (14), (15), and (18), respectively. step 7) if s≥1, update the hawk’s position by using (12), otherwise go to step 8. step 8) if s≥0.5, go to step 9 otherwise go to step 10. step 9) if q≥0.5, update the hawk’s position by using (16) otherwise update by using (24) and go to step 11. step 10) if q≥0.5, update the hawk’s position by using (20) otherwise update by using (25) and go to step 11. step 11) increment the iteration count k by 1 and if (number of iterations<maximum number of iterations) then go to step 4 otherwise go to step 12. step 12) return the final best solution stored (dg sizes and evcss-dgs locations). step 13) run the load flow and determine the power losses, average voltage deviation index, and voltage stability index. v. results and observations this section summarizes the simulation results of the 33bus, 69-bus [28] ieee test systems using the prescribed methods for optimizing the location and capacity of dgs along with the best placement of evcs. in this paper, evcss and dgs locations are categorically studied with three evcss and type i, ii, iii, and iv dgs [29]. in addition to the ev models (chevrolet volt, chang an yidong, tesla model x and bmw i3) given in table i, ac/dc level-2 type charging ports (cps) are also considered in the cs design. according to sae j1772 standard, this type of cps can suit both battery electric vehicles (bevs) and plug-in hybrid electric vehicles (phevs), and has a maximum power rating of 7kw [30]. some design features of cps are the evs types which can charge at a time in a particular cs and their power ratings in kw, the minimum and maximum number of cps for different types of evs and correspondingly the minimum and maximum power rating of cs (table i). for instance, if all the css are designed for only minimum cps as given in table i, the power rating of 1 cs is 975kw. similarly, for maximum number cps, the demand may increase to 1675.5kw. table i. evcs features for simulation ev type ev power rating (kw) no. of cps cs rating (kw) min max min max chevrolet volt 2.2 25 35 55 77 chang an yidong 3.75 20 30 75 112.5 tesla model x 13 15 25 195 325 bmw i3 44 10 20 440 880 sae j1772 standard 7 30 40 210 280 total power rating of cs (kw) 100 150 975 1674.5 hho and tlbo algorithms are utilized to decide the optimal position of evcss and the optimal position and size of engineering, technology & applied science research vol. 10, no. 3, 2020, 5837-5844 5841 www.etasr.com ponnam & swarnasri: multi-objective optimal allocation of electric vehicle charging stations … the dgs for minimizing distribution system losses, avdi, and enhance vsi of rds. in this article, the following summaries are presented to address the effect of type-i, ii, iii & iv dgs on the system. • scenario 1: rds without integrating dgs and evcss. • scenario 2: rds with minimum and maximum evcs load, without integrating dgs. • scenario 3: rds with three optimal locations of evcss with minimum evcs load without integrating dgs. • scenario 4: rds with three optimal locations of evcss with minimum evcs load and type-i, ii, iii, and iv dg integration. • scenario 5: rds with three optimal locations of evcss with maximum evcs load without integrating dgs. • scenario 6: rds with three optimal locations of evcss with maximum evcs load and type-i, ii, iii, and iv dg integration. a. scenario 1 1) 33 bus system the cumulative real and reactive demand on the system is 3715kw and 2300kvar. the minimum voltage of 0.9038p.u is observed at bus number 18, which is outside of the prescribed limit of ±5% after executing the distribution power flow algorithm by using the forward-backward method [26]. moreover, the cumulative active power loss of the system is 210.9897kw, and the cumulative reactive loss of the system is 143.1284kvar. the avdi of the system is 0.0041 and vsimin is 0.6661. it is recognized that 5.68% of the power is absorbed in the form of active power loss in the system. the regulation of voltage in the system is 9.63%. 2) 69 bus system the cumulative real and reactive demand on the system is 3801.4kw & 2693.6kvar. the maximum voltage deviation occurred at bus 65, and it is the worst among all other busses. the voltage at the 65 th bus is 0.9092p.u., the cumulative active power loss of the system is 224.8807 kw, and the cumulative reactive loss of the system is 102.1647 kvar. the avdi of the system is 0.0014, and vsimin is 0.6823. it can be noticed that 5.92% of the power is absorbed in the form of active power loss in the system. the regulation of voltage in the system is 9.08%. b. scenario 2 1) 33 bus system incorporation of a total of 3 evcss load in the system is assumed. by imposing a total power demand of 2925kw (975kw×3) for 3 css with the minimum number of cps at all evcss as given in table i, the new loading condition of the test system is determined. according to this, the real power load is increased from 3715kw to 6640kw. the corresponding test system performance is given in table ii. due to the increased evcs load, the real losses are increased to 576.1705kw from 210.9897kw, the average voltage deviation index is increased to 0.0108 from 0.0041, the stability index is decreased to 0.4984 from 0.6661, and the minimum voltage is decreased to 0.8408p.u. from 0.9038p.u. similarly, for the maximum number of cps in each evcs, the load can increase on the network by 5023.5kw (1674.5×3) for the 3 evcss. the corresponding system performance is given in table ii. the losses are increased to 1024.3908kw, the voltage deviation index is raised to 0.0187, the stability index is decreased to 0.3854, and the minimum voltage reaches 0.7888p.u. 2) 69 bus system as in the case of the 33-bus test system, 3 evcss were considered with different cps. by imposing a total power demand of 2925kw for 3 css with minimum cps, the test loading condition increased from 3801.4kw to 6726.4kw. due to the increased ev load, the real losses increased to 613.4994kw from 224.8807kw, the average voltage deviation index increased to 0.004 from 0.0014, the stability index decreased to 0.5114 from 0.6823, and the minimum voltage was reduced to 0.8462p.u. from 0.9092p.u. similarly, for the maximum number of cps in each evcs, the load on the network increased by 5023.5kw (1674.5×3) for the 3 evcss. the corresponding system performance is given in table ii. the losses increased to 1108.6266kw, the voltage deviation index increased to 0.0072, the stability index decreased to 0.3949, and the minimum voltage reached 0.7935p.u. table ii. system performance with minimum and maximum evcs load without placing-integrating dgs. system loading condition ploss (kw) avdi (p.u.) vsimin (p.u.) vmin (p.u.) 33 without evcs load 210.9897 0.0041 0.6661 0.9038 with minimum evcs load (without optimal placement) 576.1705 0.0108 0.4984 0.8408 with maximum evcs load (without optimal placement) 1024.3908 0.0187 0.3854 0.7888 69 without evcs load 224.8807 0.0014 0.6823 0.9092 with minimum evcs load (without optimal placement) 613.4994 0.004 0.5114 0.8462 with maximum evcs load (without optimal placement) 1108.6266 0.0072 0.3949 0.7935 c. scenario 3 it is assumed that 3 evcss are integrated at optimal locations in the test systems with a minimum number of cps at best locations (bus-2, 19, and 25), see table iii. the real losses are decreased to 295.6474kw from 576.1705kw, the average voltage deviation index decreased to 0.0047 from 0.0108, the voltage stability index improved to 0.6499 from 0.4984, and the minimum voltage increased to 0.8982p.u from 0.8408p.u for the 33 bus system. for the 69 bus system, the best locations are bus-2, 28, and 47. the losses decreased to 225.2186kw from 613.4994kw, avdi decreased to 0.0014 from 0.004, and vsi increased to 0.6822 from 0.51114. also, the minimum voltage increased to 0.9092p.u from 0.8462p.u. engineering, technology & applied science research vol. 10, no. 3, 2020, 5837-5844 5842 www.etasr.com ponnam & swarnasri: multi-objective optimal allocation of electric vehicle charging stations … table iii. system performance with evcs at optimal locations without integrating dgs system algo rithm ev locations ploss (kw) avdi (p.u.) vsimin (p.u.) vmin (p.u) 33 hho 2,19,25 295.6474 0.0047 0.6499 0.8982 tlbo 2,19,25 295.6474 0.0047 0.6499 0.8982 69 hho 2,28,47 225.2186 0.0014 0.6822 0.9092 tlbo 2,28,47 225.2186 0.0014 0.6822 0.9092 d. scenario 4 the line diagrams of the 33 and 69 bus systems with integration of evcs and dgs are shown in figures 1-2. placing different types of dgs results to the reduction of power loss and to the improvement of the voltage profile as shown in tables iv-v. total power losses are reduced by 68.07%, 25.85%,89.05%, and 44.79% for type-i, ii, iii, and iv dgs placed respectively for hho and 68.07%, 25.85%,89.02%, and 45.16% for tlbo. besides, with multiple dgs placed, the voltage profile improved significantly. the minimum voltage was 0.9685, 0.9267, 0.9845, and 0.9412p.u. for hho and 0.9685, 0.9268, 0.9845, and 0.9409p.u. for tlbo for type-i, ii, iii, and iv dgs respectively. fig. 1. single line diagram of the 33 bus system with evcs and dg integration fig. 2. single line diagram of the 69 bus system with evcs and dg integration table iv. system performance of the 33 bus system with evcs and dg integration at optimal locations algorithm / parameter ev and dg locations dg size (kva) total dg size (kva) ploss (kw) % reduction in ploss avdi (p.u.) vsimin (p.u.) vmin (p.u.) type-i dg hho 2,19,25 and 13,24,30 837.01,1500 and 1137 3474.01 94.3844 68.07 0.0047 0.8799 0.9685 tlbo 2,19,25 and 13,24,30 834.61,1500 and 1139.39 3474 94.3847 68.07 0.0047 0.8799 0.9685 type-ii dg hho 2,19,25 and 13,24,30 382.84,598.3 and 1035 2016.14 219.2107 25.85 0.0047 0.7378 0.9267 tlbo 2,19,25 and 13,24,30 388.77,584.61 and 1039.01 2021.39 219.2106 25.85 0.0047 0.7378 0.9268 type-iii dg hho 2,19,25 and 13,24,30 787.76+j436.64, 1500+j427.41 and 1155.62+j989 3443.38+ j1853.05 32.3824 89.05 0.0047 0.9392 0.9845 tlbo 2,19,25 and 13,24,30 852.64+j362.65, 1500+j579.53 and 1090.52+j1013.99 3443.16+ j1956.17 32.4586 89.02 0.0047 0.9391 0.9845 type-iv dg hho 2,19,25 and 13,24,30 663.07-j217.94, 1400-j460.16 and 717.08-j235.69 2780.15 j913.79 163.2147 44.79 0.0047 0.7846 0.9412 tlbo 2/19/25 and 13/24/30 645.41-j212.13, 1500-j493.02 and 727.71-j239.18 2873.12 j944.33 162.1358 45.16 0.0047 0.7837 0.9409 table v. system performance of the 69 bus system with evcs and dg integration at optimal locations algorithm/ parameter ev and dg locations dg size (kva) total dg size (kva) ploss (kw) % reduction in ploss avdi (p.u.) vsimin (p.u.) vmin (p.u.) type-i dg hho 2,28,47 and 11,17,61 516.98, 387.08 and 1716.7 2620.76 69.6232 69.09 0.0014 0.9185 0.9789 tlbo 2,28,47 and 11,17,61 523.68,382.42 and 1715.97 2622.07 69.6231 69.09 0.0014 0.918 0.9788 type-ii dg hho 2,28,47 and 11,17,61 408.34,233.12 and 1231.97 1873.43 145.1159 35.57 0.0014 0.7526 0.9314 tlbo 2,28,47 and 11,17,61 413.19,230.61 and 1232.42 1876.22 145.1166 35.57 0.0014 0.7526 0.9314 type-iii dg hho 2,28,47 and 11,17,61 388.15+j438.23, 440.43+j179.53 and 1692.93+j1214.89 2521.51+ j1832.65 4.7502 97.89 0.0014 0.9773 0.9942 tlbo 2,28,47 and 11,17,61 622.64+j277.77, 300+j300.08 and 1629.48+j1275.96 2552.12+ j1853.81 4.7817 97.88 0.0014 0.9773 0.9943 type-iv dg hho 2,28,47 and 11,17,61 377.71-j124.12, 294.12-j98.58 and 1255.9-j412.68 1927.73 j633.4 133.0426 40.93 0.0014 0.8283 0.954 tlbo 2,28,47 and 11,17,61 400.03-j131.45, 276.05-j90.71 and 1255.55-j412.57 1931.63 j634.73 133.091 40.91 0.0014 0.8283 0.9539 engineering, technology & applied science research vol. 10, no. 3, 2020, 5837-5844 5843 www.etasr.com ponnam & swarnasri: multi-objective optimal allocation of electric vehicle charging stations … e. scenario 5 as in scenario 3, the integration of 3 evcss at optimal locations in the test systems with a maximum number of cps at best locations (buses 2, 19, and 25) is assumed (table vi). the real losses are decreased to 390.6266kw from 1024.3908kw, the average voltage deviation index is decreased to 0.0053 from 0.0187, the voltage stability index is increased to 0.6381 from 0.3854 and the minimum voltage at bus-18 is increased to 0.8941p.u from 0.7888p.u. for the 33 bus system. for the 69 bus system, the best locations are buses 2, 28, and 47. the losses are decreased to 225.5766kw from 1108.6266, avdi is decreased to 0.0014 from 0.0072 and vsi increases to 0.6821 from 0.3949. also, the minimum voltage at bus-65 increases to 0.9092p.u from 0.7935p.u. f. scenario 6 placing different types of dgs by hho and tlbo technique results in the reduction of power losses and better voltage profile, (tables vii-viii). the total power losses are reduced by 64.81%, 20.36%, 81.05%, and 45.93% for type-i, ii, iii, and iv dgs placed respectively for hho and 64.81%, 20.36%, 81.05%, and 45.93% for tlbo. besides, with multiple dgs placed, the voltage profile has improved significantly. the minimum identified voltage was 0.9633, 0.923, 0.9706, and 0.9395p.u. for hho and 0.9633, 0.923, 0.9706, and 0.9395p.u. for tlbo for type-i, ii, iii, and iv dgs respectively. table vi. system performance with evcs and dg integration at optimal locations system algorithm ev locations ploss (kw) avdi (p.u.) vsimin (p.u.) vmin (p.u.) 33 hho 2,19,25 390.6266 0.0053 0.6381 0.8941 tlbo 2,19,25 390.6266 0.0053 0.6381 0.8941 69 hho 2,28,47 225.5766 0.0014 0.6821 0.9092 tlbo 2,28,47 225.5766 0.0014 0.6821 0.9092 table vii. system performance of the 33 bus system with evcs and dg integration at optimal locations algorithm/ parameter ev and dg locations dg size (kva) total dg size (kva) ploss (kw) % reduction in ploss avdi (p.u.) vsimin (p.u.) vmin (p.u) type-i dg hho 2,19,25 and 13,24,30 880.91,1500 and 1227.81 3608.72 137.4507 64.81 0.0053 0.8606 0.9633 tlbo 2,19,25 and 13,24,30 881.1, 1500 and1229.58 3610.68 137.4506 64.81 0.0053 0.8606 0.9633 type-ii dg hho 2,19,25 and 13,24,30 389.72,638.12 and 1040.4 2068.24 311.0932 20.36 0.0053 0.7258 0.923 tlbo 2,19,25 and 13,24,30 389.82,638.11 and 1041.18 2069.11 311.0911 20.36 0.0053 0.7258 0.923 type-iii dg hho 2,19,25 and 13,24,30 878.82+j381.86, 1500+j520.82 and 1204.88+j1003.6 3583.7+ j1906.28 74.0126 81.05 0.0053 0.8872 0.9706 tlbo 2,19,25 and 13,24,30 856.93+j378.37, 1500+j525.62 and 1230.96+j1004.27 3587.89+ j1908.26 74.0212 81.05 0.0053 0.8872 0.9706 type-iv dg hho 2,19,25 and 13,24,30 682.16-j224.21, 1500-j493.03 and 804.86-j264.54 2987.02 j981.78 211.221 45.93 0.0053 0.7792 0.9395 tlbo 2,19,25 and 13,24,30 682.44-j224.31, 1500-j493.03 and 805.87-j264.88 2988.31 j982.22 211.2217 45.93 0.0053 0.7791 0.9395 table viii. system performance of the 69 bus system with evcs and dg integration at optimal locations algorithm/ parameter ev and dg locations dg size (kw) total dg size (kw) ploss (kw) % reduction in ploss avdi (p.u.) vsimin (p.u.) vmin (p.u.) type-i dg hho 2,28,47 and 11,17,61 490.3,396.56 and 1724.6 2611.46 69.876 69.02 0.0014 0.9186 0.979 tlbo 2,28,47 and 11,17,61 529.49, 380.46 and 1719.77 2629.72 69.8763 69.02 0.0014 0.9185 0.979 type-ii dg hho 2,28,47 and 11,17,61 412.84,230.23 and 1231.34 1874.41 145.7912 35.37 0.0014 0.7525 0.9314 tlbo 2,28,47 and 11,17,61 413.21,230.62 and 1232.41 1876.24 145.797 35.37 0.0014 0.7525 0.9314 type-iii dg hho 2,28,47 and 11,17,61 416.13+j336.94, 416.13+j249.35 and 1681.09+j1205.83 2513.35+ j1792.12 4.7654 97.89 0.0014 0.977 0.9942 tlbo 2,28,47 and 11,17,61 438.25+j336.86, 412.29+j262.19 and 1683.56+j1173.63 2534.1+ j1772.68 4.7698 97.89 0.0014 0.977 0.9942 type-iv dg hho 2,28,47 and 11,17,61 319.64-j105.03, 308.58-j101.4 and 1262.96-j415 1891.18 j621.43 133.6038 40.77 0.0014 0.8282 0.9539 tlbo 2,28,47 and 11,17,61 402.82-j132.37, 276.06-j90.71 and 1256.14-j412.77 1935.02 j635.85 133.6074 40.77 0.0014 0.8282 0.954 vi. conclusions massive ev deployment has adverse impacts on the power grid. a significant amount of evcss connected to the grid increases the system power losses and significant voltage variation at remote buses from sources. in this paper, a novel approach for the simultaneous allocation of dgs and evcss to engineering, technology & applied science research vol. 10, no. 3, 2020, 5837-5844 5844 www.etasr.com ponnam & swarnasri: multi-objective optimal allocation of electric vehicle charging stations … increase bus voltage profile and decrease power losses in the distribution network. in addition to the ac/dc level-2 evcss suitable for bevs and phevs, different ev models (chevrolet volt, chang an yidong, tesla model x and bmw i3) are taken into account while designing the evcs with multiple cps and all four types of dgs. the multi-objective function is formulated and optimized using hho and tlbo algorithms. the simulation results presented on standard ieee 33-bus and 69-bus test systems have highlighted the technical benefits which can be achieved through the optimal allocation of evcss and dgs even with increased ev loading conditions. the main findings of the simulation are summarized as follows: • hho algorithm has superior performance when compared to tlbo in assessing optimal 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control strategies in a z-source inverter byamakesh nayak school of electrical engineering kiit university, bhubaneswar orissa, india electricbkn11@gmail.com saswati swapna dash dpt of electrical engineering ymca university of science & tech. faridabad, haryana, india reachtoswapna@gmail.com abstract— this paper presents the analysis for different control techniques in z-source inverters. the voltage gain versus modulation index from simulation result is compared with the mathematical calculated voltage gain. further detailed analysis of %thd, %harmonics of output voltage at different modulation indexes for different boosting techniques of a z-source inverter are also performed with respect to the traditional vsi by matlab based simulation. keywordsz-source inverter; shoot through; boost factor; voltage gain; voltage stress; total harmonic distortion (thd) i. introduction conventionally two types of three phase inverters are used, the voltage source inverter (vsi) and the current source inverter (csi). in vsi, a capacitor is used in a dc link to obtain a constant voltage source and in csi a large inductor is used to obtain a constant current source. these inverters have certain limitations. commonly used pulse width modulated (pwm) vsi is used for buck (step down) dc to ac power conversion. an additional dc-dc boost converter is needed to boost the ac voltage output. the csi is used as a boost inverter in dc to ac conversion. for a change in voltage range, it also requires additional buck (or boost) dc-dc converters. hence, no traditional inverter can be employed solely for buck and boost simultaneously, without additional dc link converters. to overcome the drawbacks of traditional inverters, the newly proposed impedance source or z-source inverter [1] can be used, which is virtually the combination of vsi and csi. it employs an impedance network as a dc link consisting of l and c to couple the converter bridge and the power source as shown in figure 1. a traditional pwm 3-phase vsi operates in eight states, six active and two null states. in active states, power is transported from the dc link to the ac output, whereas in null states the dc link capacitor is charged from the dc source. the shootthrough state is introduced within the null state of z-source inverter. this cannot be applied in voltage source inverter. the shoot-through state in z-source inverter enhances the voltage at the load end. it should be inserted in such a way that, equal null intervals are again maintained at the start and end of the switching cycle, to achieve the same optimal harmonic performance. this paper represents the comparison of voltage gain, %thd and %harmonics at different modulation indexes using different boosting techniques, in z-source inverter. the boosting techniques for the z-source inverter used in this paper are the simple boost control, the maximum boost control, the 3 rd harmonic injected constant boost control and the 3 rd harmonic injected maximum boost control method. fig. 1. z-source inverter ii. control techniques a. simple boost control in the sinusoidal pwm inverter, the gate pulses are obtained by comparing the 3-phase balanced sinusoidal carrier signals with triangular carrier signals. the drawback of the method is that it cannot be used for boosting of the output voltage because of the two null states in addition to the six active states in one cycle of operations. the shoot-through should be introduced in null states by various techniques as discussed in [1-2] to boost the output voltage. the shootthrough techniques are objectionable in sinusoidal pwm voltage source inverter. the shoot-through can be inserted in null-state if z-source is incorporated between the input dc voltage and the vsi inverter power circuit as shown in figure 1. in the vsi switching cycle, the zero state is produced when all sinusoidal waveforms are less or greater than the carrier signal. therefore, to provide shoot–through in zero state the etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 391-395 392 www.etasr.com �ayak and dash: performance analysis of different control strategies in a z-source inverter other two steady signals (vp,vn) whose amplitudes are equal to the amplitude of the sinusoidal waveform and the one is the negative of the other, are compared with triangular signal as shown in figure 2. as discussed in [1-2] the shoot through states are obtained in all three legs at a time, maintaining shoot through time per switching cycle as constant. the gate pulses for the simple boost method are shown in figure 2. the voltage gain in simple constant boost zsi is expressed as: ˆ (1) 2 ac o v g mb v = = where ac v̂ is the output peak phase voltage, vo is the input dc voltage, m is the modulation index and b is the boost factor. the boost factor is determined by following expression: 0 1 (2) 2 1 b t t = − where to is the shoot-through time interval over a switching period t. the duty ratio (t0/t) decreases with the increase of m in shoot-through state. thus the voltage gain can be expressed as: ˆ (3) 2 1 2 ac o v m g mb v m = = = − voltage stress [2] is given by: ( )2 1 (4)s o ov bv g v= = − fig. 2. gate pulse of simple constant boost zsi voltage stress in switches increases as the voltage gain increases. so, this control method cannot be implemented to obtain higher gain because of the limitation of voltage ratings of switches. therefore, other suitable control techniques can be adopted to operate the z-source inverter at higher gains. b. maximum boost control voltage stress is minimized on switches by maximizing to and b for a given modulation index. considering the previous method, a simple modification is required. the shoot-through state is achieved when the triangular carrier wave is either greater than the maximum curve of three sinusoidal references or smaller than the minimum of the references [2]. figure 3 depicts the gate pulse for six switches. averaging of the varying shoot-through times, the boost factor, voltage gain and voltage stress are given by the following equations: 1 (5) 2 3 31 ˆ (6) 3 3 2 3 3 (7) o ac o s o o b t m t v m g mb v m g v bv v π π π π π π = = −− = = = − − = = the voltage stress is much lower in comparison to the simple boost control. hence, the inverter can be operated at a higher voltage gain. c. third harmonic injection control this method is opted to use the increased range of modulation indexes. similarly to previous methods, the overshoot period can be maintained constant and variable. in third harmonic injection constant boost technique the sinusoidal reference signal is merged with third harmonic sinusoidal waveforms with one third amplitude of the fundamental, to generate non-sinusoidal waveforms. constant shoot-through is introduced in zero states by comparing the triangular carrier wave with a positive, negative constant magnitude and generated non-sinusoidal sinusoidal reference waveforms as in simple boost control. the gate pulses are shown in figure 4. further, variable shoot-through times are provided considering the third harmonic injected sinusoidal reference waveforms and triangular carriers like maximum boost control. the gate pulses are shown in figure 5. etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 391-395 393 www.etasr.com �ayak and dash: performance analysis of different control strategies in a z-source inverter fig. 3. gate pulse of maximum boost zsi fig. 4. gate pulse for third harmonic injected constant boost zsi fig. 5. gate pulse of third harmonic injected maximum boost zsi the average boost factor and voltage gain in the above two cases [2] are given as follows: 1 (8) 2 3 31 ˆ (9) 3 3 2 3 3 (10) o ac o s o o b t m t v m g mb v m g v bv v π π π π π π = = −− = = = − − = = the voltage gain remains the same as in the maximum boost control, so voltage stresses also remain the same. the only advantage in harmonic injected methods is the use of large range modulation indexes (m). iii. performance analysis matlab simulations were performed to verify and compare different control methods. the simulink model used is shown in figure 6. the parameters used are: l1=l2=0.5 mh, c1=c2=2 mf, v0=100 v (dc), switching frequency=2 khz, load: r/phase = 50 ohm, l/phase = 2 mh. the purpose of the system is to compare the performance of the different control techniques under different modulation indexes with constant dc voltage input. a comparative analysis of voltage gain at different m is performed based on the mathematical calculation and simulation result for various control techniques. results are shown in figures 7-10. the simulation results for voltage gain mostly matches the theoretical analysis, which verifies the above analysis and control concepts. the comparative bar graph in figure 11 for per unit output voltage at different modulation index shows the boosting of voltage with respect to vsi. table i and the bar graph shown in figure 12, compares the %thd of output voltage at selected modulation indexes for various control methods of zsi with vsi. thd in different boosting methods is a little higher in comparison to vsi, but their ranges are within the permissible limit. the maximum boost control technique yields higher %thd in comparison to constant boost technique. table i. %thd comparison of output voltage. mod. index %thd in different inverters vsi simple boost 3 h const. boost max. boost 3h max. boost 0.65 0.32 1.38 0.62 2.2 1.95 0.7 0.29 1.44 1.74 4.58 4.03 0.9 0.23 0.92 0.78 4.37 4.48 1.1 2.52 2.57 1.36 5.65 4.44 etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 391-395 394 www.etasr.com �ayak and dash: performance analysis of different control strategies in a z-source inverter fig. 6. circuit diagram of zsi fig. 7. voltage gain vs modulation index comparison for simple boost control fig. 8. voltage gain vs modulation index comparison for maximum boost control fig. 9. comparison of voltage gain vs modulation index for 1/6th third harmonic injected constand boost zsi fig. 10. comparison of voltage gain vs modulation index for 1/6th third harmonic injected max. boost zsi fig. 11. pu voltage comparison of zsi with vsi v o lt a g e g a in ( m b ) v o lt a g e g a in ( m b ) v o lt a g e g a in ( m b ) v o lt a g e g a in ( m b ) modulation index (m) modulation index (m) modulation index (m) modulation index (m) etasr engineering, technology & applied science research vol. 3, �o. 2, 2013, 391-395 395 www.etasr.com �ayak and dash: performance analysis of different control strategies in a z-source inverter fig. 12. comparison of %thd for different zsi with vsi at different modulation index table ii represents the comparison of %age harmonics of output voltage for third, fifth and seventh order in different control methods at selected modulation index (m). the percentage harmonics of constant boost zsi are at par with vsi. but the seventh harmonic in maximum boost control technique is slightly higher. the simulated output voltage and current waveforms at m=0.7 with passive r-l load in third harmonics injected maximum boost zsi is shown in figure 13 for illustration. table ii. % harmonics comparison of output voltage. (a) 3 rd harmonics mod. index % harmonics vsi simple boost 3 h const. boost max. boost 3h max. boost 0.65 0.02 0.21 0.24 0.11 0.16 0.7 0.01 0.21 0.09 0.07 0.05 0.9 0.01 0.04 0.12 0.30 0.16 1.1 0.01 0.33 0.28 0.14 0.07 (b) 5 th harmonics mod. index % harmonics vsi simple boost 3 h const. boost max. boost 3h max. boost 0.65 0.02 0.92 0.39 1.41 1.10 0.7 0.02 0.83 1.59 4.14 3.40 0.9 0.03 0.42 0.47 2.68 3.07 1.1 2.12 1.24 1.12 1.42 2.14 (c) 7 th harmonics mod. index % harmonics vsi simple boost 3 h const. boost max. boost 3h max. boost 0.65 0.24 0.54 0.24 1.09 0.96 0.7 0.21 0.29 0.49 1.18 1.91 0.9 0.18 0.17 0.07 3.07 2.93 1.1 1.33 1.62 0.31 5.07 3.56 fig. 13. simulated results of load line voltage and load current iv. conclusion this paper compares the performances of the control methods of zsi to achieve the maximum voltage output within the prescribed limit of harmonics and thd percentages. the method can achieve the minimum passive component requirement and maintain low voltage stress at the same time. this method can be suitable for controlling voltage sags and swells in drives. references [1] f. z. peng, “z-source inverter”, ieee transactions on industry applications, vol. 39, no. 2, pp. 504-510, 2003 [2] f. z. peng, m. shen, z. qian, “maximum boost control of the z-source inverter”, ieee transactions on power electronics, vol. 20, no. 4, pp. 833-838, 2005 [3] p. c. loh, d. m. vilathgamuwa, y. s. lai, g. t. chua, y. li, “pulsewidth modulation of z-source inverters”, ieee transactions on power electronics, vol. 20, no. 6, pp. 1346-1355, 2005 % t h d m microsoft word 1-2380_s_ca engineering, technology & applied science research vol. 9, no. 1, 2019, 3681-3684 3681 www.etasr.com rasras et al: a methodology based on steganography and cryptography to protect highly secure … a methodology based on steganography and cryptography to protect highly secure messages rashad j. rasras department of computer engineering al-balqa' applied university amman, jordan rashad.rasras@bau.edu.jo ziad a. alqadi department of computer engineering al-balqa' applied university amman, jordan natalia_maw@yahoo.com mutaz rasmi abu sara department of computer science taibah university al-medina, saudi arabia mabusara@taibahu.edu.sa abstract—steganography and cryptography are very important techniques used in data security to hide and secure secret messages in transmitted data. this paper will introduce, implement and test a novel methodology which can be used as a secure and highly efficient method of data hiding and data extracting. some efficiency parameters will be experimentally obtained and compared with other existing methods parameters to prove the efficiency of the proposed methodology. keywords-steganography; decryption time; mse; cryptography; encryption time; speedup; psnr i. introduction steganography is the process of hiding secret messages in such a way that no one except the sender and the intended recipient can see them. the process of hiding data is used in many important applications in order to maintain confidentiality of important data, prevent unauthorized persons from identifying or understanding the confidential message, or add mark or a tag to the digital image to be used in order to identify the digital image ownership. cryptography is the process of changing data so that they are not readable. unauthorized parties might see there are data communicated but can’t understand them. digital color images can be used as a media to carry the secret massage, because of their size, and because they are commonly presented by 3 2d matrices (one for the red color, one for the green color and the last one for the blue color) [1, 2]. the process of hiding a secret message can be realized by applying the following phases [3]: a. steganography • select the original covering color image. • select the secret message. • use an available method of data hiding to insert the message into the image. b. cryptography here we have to perform the following tasks: • get the holding color image. • use one of the available methods to encrypt the image and get the encrypted image. c. message extraction the process of getting the secret message (extracting the message) can be done by applying the cryptography and then the steganography based on the methods used in the hiding phase. the selected methods for data hiding-extraction and data encryption-decryption must be secure and efficient by achieving the following: minimizing hiding-extraction time, minimizing encryption-decryption time, maximizing the process throughput by increasing the number of bytes to be treated per second, and excluding any loss of information during the entire process. ii. related work many steganography methods are based on the least significant bit (lsb) method of data hiding and extracting [46]. some improvements were added to enhance the security level of lsb method in [7-9]. lsb is an unsecure method of hiding secret messages, and the process of data hiding can be implemented by reserving 8 bytes of the holding image to store one character of the message. lsb requires the binary version of the character, and each bit of this version can be inserted in the least bit of the selected byte of the holding image. the advantages of the lsb based methods are the low values of mean square error (mse), and the high values of peak signal to noise ratio (psnr) [10], which make difficult for the human eye to notice the changes in the holding image. authors in [11] proposed a method of color image encryption-decryption based on matrix reordering and with a medium throughput. authors in [12] suggested a method of encryption-decryption in digital color images by applying matrix multiplication. this method gave good efficiency parameters and high security level but the size of the private secret key used for encryption-decryption was very big and complicated and required big memory size to be stored. authors in [13] suggested a method of image encryptiondecryption based on a chaotic algorithm using the power and tangent functions instead of linear functions. the process of encryption is one-time-one-password system and is more secure (but not enough) than the des algorithm. also, it has low efficient parameters with big encryption-decryption time and low throughput. in [14], an asymmetric color image encryption-decryption method was introduced based on matrix corresponding author: r. j. rasras engineering, technology & applied science research vol. 9, no. 1, 2019, 3681-3684 3682 www.etasr.com rasras et al: a methodology based on steganography and cryptography to protect highly secure … transformation but it had high encryption-decryption time and thus low throughput. in [15] a method of color image encryption-decryption was proposed based on rubik's cube principle, with good security level but with low throughput. in [16] a method of color image encryption-decryption was presented based on using chaos-controlled poker shuffle operation. both variants of this method had poor throughput. iii. the proposed methodology a. image hiding hiding a secret message in a covering color image can be implemented by applying the following phases: 1) inserting the message into the image here we have to perform the following steps: • select the covering color image. • get the secret message. • define the starting position in the image and the message length (row, column, length). this position can be used as a first secret private key (key1). • insert the characters of the secret message, by reserving one byte of the image to one character of the message. • save the holding image and key1. 2) holding image encryption here we have to perform the following steps: • get the holding color image. • reshape the 3d color matrix to 2d matrix. • divide the 2d matrix into equal sizes blocks (in our paper block size=4×4 matrix). • select a 4×4 matrix with values in the range 0 to 255 to be used as secret private key (key2). • apply xor operations (each block with key2) to get the encrypted 2d matrix. • reshape the 2d matrix to 3d color matrix to get the encrypted color image. • save the encrypted color image and key2. b. message extraction extracting the secret message from the holding encrypted image can be implemented by applying the following phases: 1) color image decryption. here we have to perform the following steps: • get the encrypted color image. • reshape the 3d color matrix to 2d matrix. • divide the 2d matrix into 4×4 blocks. • get key2. • xor each block with key2 to get the decrypted 2d matrix. • reshape the 2d matrix to 3d matrix to get the decrypted color image. 2) extracting the secret message here we have to perform the following steps: • get key1. • use key1 to extract the characters from the image. iv. implementation and experimental results the proposed methodology was implemented and various images of different sizes and types were used. to show the efficiency enhancement the proposed methodology was implemented in two phases, inserting and extracting the secret message in the image. the following message "ziad alqadi" with length=11 characters was inserted-extracted by using selected position at first, and then by using the lsb method. figure 1 shows the original color image, while figure 2 shows the holding image. fig. 1. original color image with histograms. fig. 2. holding image with histograms. message insertion was implemented several times. the results of implementation are shown in table i, while table ii shows the results obtained with the use of the lsb method. table iii shows a summary comparison between the results of the two methods. engineering, technology & applied science research vol. 9, no. 1, 2019, 3681-3684 3683 www.etasr.com rasras et al: a methodology based on steganography and cryptography to protect highly secure … table i. results of position method: message length=11 image no. size (byte) hiding time (s) extracting time(s) throughput (bytes per sec) psnr mse 1 270948 0.0028 0.0028 4.4850e+07 144.1719 0.0356 2 151875 0.0029 0.0029 5.1967e+07 118.1217 0.4821 3 49152 0.0027 0.0027 1.8039e+07 101.5034 2.5004 4 1125600 0.0028 0.0028 2.6035e+08 151.1818 0.0177 5 540000 0.0035 0.0035 1.5337e+08 129.3189 0.1573 6 3396069 0.0053 0.0053 6.3618e+08 143.2701 0.0390 7 2359296 0.0052 0.0052 4.5703e+08 140.0368 0.0539 8 928800 0.0040 0.0040 2.3078e+08 155.3087 0.0117 9 432000 0.0031 0.0031 1.3759e+08 138.6389 0.0620 10 151353 0.0027 0.0027 5.5868e+07 135.3198 0.0863 avg. 940510 0.0035 0.0035 204602400 135.6872 0.3446 table ii. results of lsb method:message length=11 image no. size (byte) hiding time (s) extracting time(s) throughput (bytes per sec) psnr mse 1 270948 0.2325 0.0033 1.1653e+06 202.9637 9.9650e-05 2 151875 0.1474 0.0548 1.0305e+06 197.1750 1.7778e-04 3 49152 0.0441 0.0027 1.1133e+06 185.7361 5.4932e-04 4 1125600 0.9244 0.0049 1.2177e+06 217.2052 2.3987e-05 5 540000 0.4473 0.0037 1.2072e+06 209.8601 5.0000e-05 6 3396069 2.7665 0.0096 1.2275e+06 228.2482 7.9504e-06 7 2359296 1.8971 0.0076 1.2436e+06 224.6056 1.1444e-05 8 928800 0.7984 0.0045 1.1634e+06 215.2834 2.9070e-05 9 432000 0.3542 0.0036 1.2195e+06 207.6287 6.2500e-05 10 151353 0.1309 0.0029 1.1565e+06 197.1406 1.7839e-04 avg. 940510 0.7743 0.0098 1174450 208.5847 1.1901e-04 table iii. results comparison method size (byte) hiding time(s) extracting time(s) throughput (bytes per sec) psnr mse selected position (1) 940510 0.0035 0.0035 204602400 135.6872 0.3446 lsb (2) 940510 0.7743 0.0098 1174450 208.5847 1.1901e-04 speed up of (1) 0.7743/0.0035=221.2286 0.0098/0.0035=2.8000 from table iii we can see that the performance of the proposed selected position method is better than the performance of the lsb method (including encryption and decryption times and throughput) and that the snr and mse values for lsb method are better than those of the proposed selected position method. these parameters are not considerable because the second stage is encryption of the holding image, so mse and psnr are to be ignored. fig. 3. holding color image and histograms the second phase of secret message hiding-extracting was encryption-decryption. the output of the first phase was taken and implemented several times using the same images and applying encryption-decryption by dividing the image matrix into equal blocks (sized 4×4) and the results show a high value of mse (low value of psnr) between the holding image and the decrypted one, which is a good indicator. figures 3-5 show some outputs of the implementation. fig. 4. encrypted color image and histograms table iv shows the values of the efficiency parameters obtained during the process of implementation. in table v we see a result comparison of the proposed and other existing methods. engineering, technology & applied science research vol. 9, no. 1, 2019, 3681-3684 3684 www.etasr.com rasras et al: a methodology based on steganography and cryptography to protect highly secure … fig. 5. decrypted color image and histograms table iv. efficiency parameters of the proposed method img. size (bytes) encryption time (s) decryption time (s) throughput (bps) 1 270948 0.0380 0.0380 7.1302e+006 2 151875 0.0230 0.0230 6.6033e+006 3 49152 0.0070 0.0070 7.0217e+006 4 1125600 0.1620 0.1620 6.9481e+006 5 540000 0.0780 0.0780 6.9231e+006 6 3396069 0.4950 0.4950 6.8607e+006 7 2359296 0.3470 0.3470 6.7991e+006 8 928800 0.1560 0.1560 5.9538e+006 9 432000 0.0610 0.0610 7.0820e+006 10 151353 0.0210 0.0210 7.2073e+006 avg. 940510 0.1388 0.1388 6852930 table v. comparison with other methods method encryption time(s) decryption time(s) total time speedup of the proposed method proposed 0.0245 0.0245 0.0490 1.0000 [11] 0.0682 0.0662 0.1344 2.7429 [12] 0.2335 0.2335 0.4670 9.5306 [13] 0.5035 0.5035 1.0070 20.5510 [14] 0.4035 0.4035 0.8070 16.4694 [15] 0.1235 0.1235 0.2470 5.0408 [16] a-i 0.5635 0.5635 1.1270 23.0000 [16] a-ii 1.01 1.01 2.0200 41.2245 from table v we can see that the proposed methodology gives a good improvement in the efficiency parameter values. v. conclusions a methodology of secret message steganography was proposed, tested and implemented. the proposed methodology was based on selecting a position in the color image to start hiding the secret message and matrix blocking to encryptdecrypt the holding color image. the proposed methodology increased the security level by using 2 private keys, and enhanced the efficiency comparing with other existing methods. references [1] a. a. moustafa, z. a. alqadi, “color image reconstruction using a new r'g'i model”, journal of computer science, vol. 5, no. 4, pp. 250254, 2009 [2] k matrouk, a al-hasanat, h alasha'ary, z. al-qadi, h al-shalabi, “speech fingerprint to identify isolated word person”, world applied sciences journal, vol. 31, no. 10, pp. 1767-1771, 2014 [3] j. al-azzeh, b. zahran, z. alqadi, b. ayyoub, m. abu-zaher, “a novel zero-error method to create a secret tag for an image”, journal of theoretical and applied information technology, vol. 96. no. 13, pp. 4081-4091, 2018 [4] m. jose, “hiding image in image using lsb insertion method with improvedsecurity and quality”, international journal of science and research, vol. 3, no. 9, pp. 2281-2284, 2014 [5] r. m. patel, d. j. shah, “conceal gram :digital image in image using lsb insertion method”, international journal of electronics and communication engineering & technology, vol. 4, no. 1, pp. 2302035, 2013 [6] n. akhtar, p. johri, s. khan, “enhancing the security and quality oflsb based image steganography”, 5th international conference on computational intelligence and communication networks, mathura, india, seprember 27-29, 2013 [7] m. juneja, p. s. sandhu, “an improved lsb based steganography with enhanced security and embedding/extraction”, 3rd international conference on intelligent computational systems, hong kong china, january 26-27, 2013 [8] j. nadir, z. alqadi, a. abu ein, “classification of matrix multiplication, methods used to encrypt-decrypt color image”, international journal of computer and information technology, vol. 5, no. 5, pp. 459-464, 2016 [9] r. c. gonzalez, r. elwood, digital image processing, addison-wesley, new york, 1992 [10] j. n. abdel-jalil, “performance analysis of color image encryption/decryption techniques”, international journal of advanced computer technology, vol. 5, no. 4, pp. 13-17, 2016 [11] t. sivakumar, r. venkatesan, “a novel image encryption approach using matrix reordering”, wseas transactions on computers, vol. 12, no. 11, pp. 407-418, 2013 [12] h. gao, y. zhang, s. liang, d. li, “a new chaotic algorithm for image encryption”, chaos, solitons & fractals, vol. 29, no. 2, pp. 393399, 2006 [13] g. chen, y. mao, c. k. chui, “a symmetric image encryption scheme based on 3d chaotic cat maps”, chaos, solitons and fractals, vol. 21, no. 3, pp.749-761, 2004 [14] k. loukhaoukha, j. y. chouinard, a. berdai, “a secure image encryption algorithm based on rubik's cube principle”, journal of electrical and computer engineering, vol. 2012, articleid 173931, 2011 [15] x. wang, j. zhang, “an image scrambling encryption using chaos controlled poker shuffle operation”, ieee international symposium on biometrics and security technologies, islamabad, pakistan, april 23-24, 2008 microsoft word etasr_v10_n6_pp6563-6569 engineering, technology & applied science research vol. 10, no. 6, 2020, 6563-6569 6563 www.etasr.com mahessar et al.: sediment transport dynamics in the upper nara canal off-taking from sukkur … sediment transport dynamics in the upper nara canal off-taking from sukkur barrage of indus river ali asghar mahessar sindh barrages improvement project sindh irrigation department, karachi, sindh, pakistan amahessar@yahoo.com abdul latif qureshi u.s.-pakistan centers for advanced studies in water, mehran university of engineering and technology jamshoro, pakistan shafi muhammad kori department of civil engineering mehran university of engineering and technology jamshoro, pakistan ghulam sarwar faoowui institute of water resources engineering and management mehran university of engineering and technology jamshoro, pakistan nisar ahmed memon faculty of agricultural engineering sindh agricultural university tandojam, sindh, pakistan ashfaque ahmed memon department of civil engineering mehran university of engineering and technology jamshoro, pakistan khalifa qasim leghari department of civil engineering mehran university of engineering and technology jamshoro, sindh, pakistan abstract—sediment material transported by the indus river has two origins, the catchment and its wetted perimeter, whereas the amount of materials transported from the river itself depends on variables such as the flow type and the sediment load. the annual sediment load transported in the indus river ranged from 270 to 600 million tons (mt) before the building of dams and barrages. the average sediment load is 0.715 mt/day or approximately 260 mt/ year after the construction of hydraulic structures. the average particle size, d50, of the bedload is approximately 0.125mm at the sukkur barrage [1]. in this study, research was conducted to evaluate sediment problems in the nara canal, take-off from the left pocket of the sukkur barrage on the indus river. the collected data from the left pocket, the bed, and suspended material in upper nara and its off-taking canals were analyzed to assess sediment transport dynamics of upper nara canal at various locations and its off-taking canals. the bed material at rd 553+600 shows a minimum size of 0.07 and a maximum of 0.7mm with 54% fine-sand mixed with 46% medium-sand in 2003. fine-sand increased to an average of 75% while medium sand diminished to 25% at rd 553+600 in nara canal and at rd 595+000 in jamrao complex in 2013. the suspended load with low and high flows during 2012 exhibits that in all the cases the sand proportion was increasing in the upper nara canal system flowing to the jamrao complex. the sediment concentration value indicates that there is the deposition of sand at the upper nara canal and the jamrao complex causing a discharge reduction in the nara canal system. keywords-indus river; nara canal; sediment transport dynamics; silt deposition; irrigation system i. introduction the canals intake sediments from the rivers and tend to deposit them. even a very small proportion of sediment if deposited in the irrigation system changes flow behavior [1]. the sediment material transported by the indus river has two origins: the catchment and its bank and bed. the sediment yield from watershed varies with the size of catchment, the runoff volume, the geology, and the land cover. the amount of sediment originating from the river itself rests on the type of sediment and flow capacity. indus is a dynamic river which changes behavior both temporally and spatially by varying channel pattern, channel dimension, different morphologies can be found along its length while it frequently floods. it is braided, it has high and low sinuosity, it has meanders etc. the reach of the river, where the sukkur barrage is located, has also great variability [1]. the sediment transport fluxes of himalayan rivers are substantially higher than those of other mountainous regions of the world. if dams and barrages had not been constructed, the three principal rivers of the indian sub-continent would have annually transported a combined total sediment of 1.2 giga tons/year to the coast [2]. the five himalayan rivers viz. brahmaputra, ganga, indus, irrawaddy, and mekong carry 89% (1.6 giga tons per year) of the total corresponding author: ali asghar mahessar engineering, technology & applied science research vol. 10, no. 6, 2020, 6563-6569 6564 www.etasr.com mahessar et al.: sediment transport dynamics in the upper nara canal off-taking from sukkur … annual global flux. prior to the construction of barrages and dams the annual sediment load ranges from 270 to 600mt in indus river [3]. the indus carries a heavy sediment load that is estimated about 200mt/year in tarbela and about 330mt/year at kotri, downstream of the sukkur barrage. the average annual sediment load in the indus river at sukkur was about 360mt during 1902-1960 [4]. irrigation canals of indus basin receive high amounts of silt because they off-take directly from indus river and its tributaries [5]. the types of sediment in the lower indus range from silt to fine sand, with a decrease estimated in the annual sediment transport at sukkur and kotri barrages. the analyzed characteristic d90 of sediment near sukkur barrage was found it to be 0.23mm [3]. the sediment samples collected in july have been analyzed in order to study the sediment concentration and the size of the materials at different areas of the barrage and the canals. the representative material of the indus river at sukkur is very fine sand with a characteristic diameter d50 of approximately 0.125mm. the concentrations of sand are between 200 and 400ppm during high flows presenting some larger peaks, and are almost negligible during low floods [6]. most of the canal systems on indus basin irrigation system (ibis) are directly fed from the indus river and its tributaries which carry heavy sediment particles which settle down in canal beds, hence, create serious operation and maintenance problems. sediment transport from rivers varies in the canals. albeit canals and rivers have a similar nature, at the same time there are many variations in the width ratio, the sediment loads, hydrodynamics, etc. [7]. moreover, the design of the canal system is such that most sediment particles remain suspended and are distributed into the off-taking canals to reach the irrigation fields. despite this, these particles tend to settle down. thus frequent canal maintenance and de-siltation is required to keep the canal operational which causes an additional burden on national economy [8]. sedimentation and erosion of canals cause serious maintenance and operation problems [9]. if the velocity of the flowing water is high, it picks up the particles from the bed of the canal. if the velocity of the flowing water is low, the heaviest sediment particles deposit on the bed consequently [10, 11]. the bed load generally consists of coarser particles that control the shape, stability, and hydraulic characteristics of the channel [12]. the bed load is accumulated when there is low velocity within stream and heavier grain size sediments get settled. suspended transport load which is due to lighter grain size material kept in suspension with moving water [13]. sediment transport is studied from a physical point of view for almost two hundred years but it is not yet fully understood [14]. the canals carry sediment particles for the developing regime and equilibrium condition of the channel. under this condition, there are not deposition and erosion problems [15]. nonequilibrium conditions and deposition occur when the sediment concentration is higher than the transport capacity. it also depends upon the morphological characteristics of the river [16, 17]. in non-uniform flow, the sediment transport capacity keeps changing due to flow parameter differences along the canals. the consequence is the need to modify the sediment concentration in the water flow by unceasing either the deposition or the entrainment on/off the bed of the canal. these adjustment processes occur more or less instantly for bed load and relatively slow for suspended load. the transport mode occurs next to the bed, while it takes time and space to settle down for the suspended load. the time lag needed to adjustment process makes the sediment transport in nonequilibrium condition [18]. this research work has been conducted in order to compute the sediment transport dynamics in the upper nara canal and its off-taking canal systems. ii. research methodoloy a. study area sukkur barrage is located on the indus river and was commissioned in 1932 to supply water through a network of canals: 4 on the left bank (east and west kharipur feeder, rohri, and nara) and 3 on the right bank (dadu, rice, and north western). sukkur barrage comprises of 66 bays (60ft span each) and is divided in sections: right under-sluices (bays 1-5) to flush the right pocket, weir portion (bays 6-59) and left under-sluice (60-66) to flush the left pocket. nara canal offtakes from the left bank of the barrage which is located at 27 0 40’44"n latitude and 68 0 50’42"e longitude. nara is the largest canal in sindh having a length of 364km and its designed capacity is 13,602 cusecs (cubic feet per second). it behaves like a river and irrigates about two million acres of agricultural land. nara canal at jamrao complex controls the flows into the lower nara canal, jamrao canal, jamrao twin canal, and ranto canal. recently, three fall structures were constructed along the nara canal to stabilize the flow regime and curb silt deposition. the current study has been carried out in order to find the impact of sediment characteristic dynamics at the upper nara canal and at the jamrao complex where the lower nara, jamrao, twin jamrao, and ranto canals off-take. b. data collection in order to compute the behavior of sediment transport in the upper nara canal, data of sediment transport (bed and suspended load) were collected at locations rd 17+800, 550+000, 553+600, 576+000, 584+000, and 591+000, ranto canal, 5+100 and its off-taking canals including lower nara canal, 8+200, jamrao canal, 12+000 and twin jamrao, 2+100 (figure 1(b)). the locations from rd 550+000 to 584+000 are in the downstream of fall structure in the upper nara canal. data regarding bed and suspended material have been received from the water and power development authority (wapda) and sindh irrigation and drainage authority (sida) [19]. the sediment data for the above two sources have already been reported by scarps monitoring organization (smo), in collaboration with the international sedimentation research institute of pakistan (isrip) of wapda. the discharge and sediment measurements were carried out at the selected locations during the low flow (april, 2012) and the high flow (july/august, 2012) seasons in the prevailing conditions as the baseline data by sida. subsequently, sediment measurements were repeated during the high flow season (july to september, 2014), at the mentioned locations. engineering, technology & applied science research vol. 10, no. 6, 2020, 6563-6569 6565 www.etasr.com mahessar et al.: sediment transport dynamics in the upper nara canal off-taking from sukkur … (a) (b) fig. 1. (a) upstream of sukkur barrage (© 2020 google, © maxar technologies), (b) upper and lower nara canal and the jamrao complex (© sida, sindh irrigation department). c. laboratory analysis the suspended and bed sediment samples were collected during the field measurements and were analyzed for sediment concentration and for particle size gradation while the bed material samples were analyzed for particle size distribution. sediments coarser than 62 microns were analyzed by visual accumulation (va) / bottom withdrawal tube method / sieve method, while the analysis of finer sediments was carried out with the pipet method. the concentration of suspended sediment samples was determined with the use of the gravimetric method. d. development of gradation curves and percentile size the gradation curves of the observed bed load samples were developed for assessing the sedimentation bed load in the canal. seven percentile sizes, d5, d16, d25, d50, d75, d84 and d95 were obtained from the gradation curves [20]. e. transportation dynamics in order to study the transportation dynamics in the study area, the suspended sediment concentration was calculated. suspended sediment samples along with discharge were taken from various stations of the nara canal system, viz. the upper nara canal at the head reach (rd 17+800), the upper nara canal at rd 553+600, the jamrao canal at rd 12+000, the twin jamrao canal at rd 2+100, the lower nara canal at rd 8+200, and the ranto canal at rd 5+100. iii. results and discussion a. grain size characteristics of intaking canals from the left and right pockets of the barrage the monsoon season lasts from the 1 st of july to the 15 th of september and causes heavy rain falls in the catchment area of the indus river. high temperature is maintained which causes snow melting in the glaciers. in the last week of september, the flow in rivers recedes which reduces sediment transport load. figure 2 shows the sediment samples from the left and right pockets of the intaking canals. fig. 2. grain size distribution. suspended and bed load material at irrigation canals. figure 2 also shows that the suspended load varies from silt and clay to fine sand while the bed load varies from fine sand to medium sand. the d50 of suspended load ranges from 0.008 to 0.01mm and that of bed load ranges from 0.125 to 0.15. the sediment size distribution at the irrigation canals also show that the representative average sizes are approximately the same. it is clear from the plot that the bed samples in the canals correspond to very fine sand. this is the size of material that is depositing in the canals and therefore, it would be desirable to remove as much as possible before entering the canal. figure2 shows that there is a slight reduction of the percentage of coarser materials (average) that flows into the canals in relation to the one at the entrance of the left and right pockets. when comparing the concentrations of sand at the entrance of the pocket and at the irrigation canals, it can be observed that in general, similar or lower concentrations of sand are measured in the canals although higher values can be observed at particular days. the general trend of sedimentation concentration (ppm) in the left pocket is shown in figure 3. concentrations of sand are approximately 200-300ppm during high flows, presenting some lag peaks, whereas they are almost negligible during low flows. sand is transported as bed load and also in suspension although sediment samples show that silt and clay are the predominant sizes in suspension. floods during july and august carry the 70% of the total annual sediment of the river and approximately 80% of the total amount of sand (material coarser than 0.063mm). engineering, technology & applied science research vol. 10, no. 6, 2020, 6563-6569 6566 www.etasr.com mahessar et al.: sediment transport dynamics in the upper nara canal off-taking from sukkur … fig. 3. concentration of sand at the entrance of the left pocket of the four irrigation canals. b. grain size characteristics of nara canals and its offtaking canal system units for determining the grain size characteristics, data regarding bed and suspended load material in the nara canal system were collected and analyzed. sieve analysis of the bed load material (sampled in 2003 and 2013) was carried out. the average sediment size (d) has been computed for each bed material. these percentile sizes along with the calculated average sediment size are exhibited in table i. table i. passing percentile sizes and average sediment size (d) at various locations (rd) of the upper nara canal date rd d 5 d 16 d 25 d 50 d 75 d 84 d 95 d mar 18, 2003 553+600 0.08 0.09 0.095 0.105 0.12 0.13 0.17 0.101 apr 30, 2003 553+600 0.13 0.16 0.16 0.20 0.25 0.28 0.35 0.216 may 18, 2003 553+600 0.13 0.17 0.19 0.22 0.27 0.30 0.35 0.234 jun 14, 2003 553+600 0.13 0.145 0.80 0.21 0.26 0.29 0.35 0.314 sep 12, 2013 576+000 0.115 0.13 0.14 0.16 0.21 0.22 0.28 0.163 sep 18, 2013 576+000 0.11 0.13 0.135 0.16 0.20 0.23 0.27 0.161 sep 24, 2013 591+000 0.09 0.11 0.12 0.15 0.18 0.20 0.23 0.154 sep 25, 2013 584+000 0.075 0.09 0.10 0.14 0.20 0.22 0.25 0.143 sep 28, 2013 576+000 0.12 0.13 0.14 0.17 0.22 0.24 0.3 0.171 the values of d50 for the september 2013 vary from 0.14 to 0.17mm. the analyzed results of the collected samples on 18 march and 14 june 2003 show canal flow variation of the delivered indus river water. the results on table i clearly indicate that all bed load materials have size above 0.163mm, i.e. there is no silt proportion, the sand deposited is only of fine or medium size. usually the percentage of medium sand is less than the one of fine sand. from table ii it is concluded that there is no silt proportion being deposited in the bed of the canal. it is either fine or median grained sand. the deposited material also indicates that the proportion of sediment size (fine or medium in %) is being transported in the canal depending on its discharge and velocity, e.g. in march the velocity is sluggish, thus 97% of fine material gives up, and during the last week of april, it is 39%, with an average of 40%. the fine grand material percentage increases again during the september of 2013 readings. their average comes to about 75%. table ii. sediment size and material type for the bed load material of the upper nara canal s. no rd date sediment size type of passing material fine sand (%) medium sand (%) 1 553+600 mar 18, 2003 0.08 0.35 97 3 2 553+600 apr 30, 2003 0.12 0.50 39 61 3 553+600 may 18, 2003 0.12 0.50 32 68 4 553+600 jun 14, 2003 0.12 0.7 49 51 5 576+000 sep 12, 2013 0.115 0.35 72 28 6 576+000 sep 18, 2013 0.11 0.35 73 27 7 591+000 sep 24, 2013 0.08 0.35 85 15 8 584+000 sep 25, 2013 0.07 0.35 78 22 9 576+000 sep 28, 2013 0.11 0.5 66 34 this also indicates that no silt particles were found at the bed, they remained in suspension. rivers originating from the himalaya origin belt region are characterized by the predominance of fine sand and very fine sand [21-24]. on the contrary, the rivers draining from the northern indian craton region bring much coarser sediments and are characterized by the high content of coarseand medium-grained sand. as the indus alluvial plain originates from the himalaya region it carries finer bed load sediments. figure 4 shows the distribution of sand, silt, and clay from the upper nara canal at rd 17+800 to the upper nara canal at rd 553+600 during the low flow session of 2012. the figure clearly indicates that during the high flow of 2012, the sediment concentration is high irrespective of the location/rd. it also indicates that during the high discharge monsoon period, silt particles are at the highest level. however, the sand proportion is more at rd 553+600 than at rd 17+800. fig. 4. sediment concentration (ppm) in the upper nara canal for low and high flow, 2012. (a) (b) fig. 5. sediment proportions in the upper nara canal during 2012: (a) low flow, (b) high flow. engineering, technology & applied science research vol. 10, no. 6, 2020, 6563-6569 6567 www.etasr.com mahessar et al.: sediment transport dynamics in the upper nara canal off-taking from sukkur … it can be seen in figure 5 that the sand proportion from the upper nara canal at rd 17+800 to the rd 553+600 increased whereas silt and clay proportions decreased. this indicates that deposition occurred during the low flow. in figure 5, it can be seen that a substantial amount of sand and silt eroded from the upper nara canal between rd 17+800 and rd 553+600 during the high flow of 2012. it is a fact that if the flow of the water is high, erosion from bed and scouring from the sides of an alluvial canal like nara will be more. it has also been observed that the severity of erosion also depends on the turbulence of flow in the canal. on the contrary, when there is low flow, the suspended sediment particles are being deposited on the canal bed. c. sediment transport from jamrao complex to lower nara and off-taking canals during the high flows of 2012, the suspended load was distributed from the upper nara canal at rd 17+800 and rd 553+800 and from jamrao complex to its off-taking canals, i.e. the jamrao canal at rd 12+000, the twin jamrao canal at rd 2+100, and the ranto canal at rd 5+100 including the lower nara canal at rd 8+200 (figures 6-7). fig. 6. sediment transport from the upper nara canal to its off-taking canals at the jamrao complex during the high flow, 2012. fig. 7. sediment transport percentage from the upper nara canal to its off-taking canals at the jamrao complex during the high flow, 2012. figure 7 shows that the increase in the weight of sand, silt, and clay from the upper nara canal at rd 553+600 is 29.4%, 51.7%, and 18.8% respectively. this means that there is sand erosion/scouring (i.e. from 77ppm to 251ppm), whereas silt particles from the upper nara canal at rd 17+800 to rd 553+600 are reduced (from 945ppm to 689ppm). figures 6 and 7 show that from the jamrao complex to the off-taking canals, the distribution of sand, silt, and clay is 15.5%, 65.6%, and 18.9% respectively. in twin jamrao there is a small amount of sand, i.e. 5.6%, silt is increased to 70.3%, and clay is about 24%. in ranto canal, at rd 5+100 the percentage of sand is only 3.6%, silt is 68%, and clay is 28.5%. in the lower nara canal at rd 8+200, the sand proportion is increased. the percentages of sand, silt, and clay are about 14.2%, 64.5%, and 21.3% respectively. sediment transport from the upper nara canal to lower nara and the off-taking canals at jamrao complex is shown in figure 8, which shows the distribution of sand, silt, and clay concentrations from the upper nara canal at rd 553+600 to its off-taking canals, i.e. the jamrao canal at rd 12+000 and the twin jamrao canal at rd 2+100 including the lower nara canal at rd 8+200 during the low flow season of 2012. during the low flow of 2012, sand particles of the upper nara canal are either deposited in the jamrao complex or are carried out to jamrao and lower nara canals, whereas only less than 30% is transported into the twin jamrao canal as shown in figure 8. sand, silt, and clay proportions are shown in figure 9. sand and silt are not equally distributed from the jamrao complex to their off-taking canals. in the jamrao canal at rd 12+000, the sand proportion is 27.3%, the silt proportion is 64.9% and the clay proportion is 8%, whereas in the twin jamrao canal at rd 2+100, the sand proportion is about 36.5%, silt is 53.5%, and clay is 10%. fig. 8. sediment transport percentage from the upper nara canal to its off-taking canals at jamrao complex during the low flow, 2012. fig. 9. sediment transport from the upper nara canal to its off-taking canals at the jamrao complex during the low flow, 2012. from figure 9, it observed that the amount of weight percent of sand, silt and clay particles at lower nara canal rd 8+200 is 32.5, 59.4 and 8.0 respectively. it is observed that clay proportion is almost equally distributed from the jamrao complex to its off-taking canals. this figure shows that at the upper nara canal rd 17+800 sand, silt and clay proportions are 14.13%, 68% and 17.7% respectively whereas at the upper nara canal at rd 553+600, the weight percent of sand, silt and engineering, technology & applied science research vol. 10, no. 6, 2020, 6563-6569 6568 www.etasr.com mahessar et al.: sediment transport dynamics in the upper nara canal off-taking from sukkur … clay is about to 45.3, 48 and 6.7 respectively, which means they are not equally distributed to rd 17+800 and 553+600. table iv demonstrates that the ratio of high to low flow is about 2 in nara (upper and lower) and about 1.5 for jamrao and jamrao twin canals. however, the concentration ratio during the high to low flow is more than 2, it even reaches 6 to 7 times in upper nara at rd 17+800 and in twin jamrao at rd 2+100. table iii. 2012 high to low flow comparison of discharge and concentration fatios canal location observed discharge ratio observed sediment concentration ratio low flow high flow low flow high flow upper nara 17+ 800 8210 15909 1.94 181 1154 6.38 upper nara 553+600 6841 14257 2.08 494 1332 2.70 ranto closed 934 n. a. ----752 n. a. lower nara 08+ 200 2882 6043 2.09 510 1184 2.32 jamrao 12+ 000 1395 2122 1.52 425 1262 2.97 twin jamrao 02+ 100 2680 4204 1.57 170 1177 6.92 during the high flood, more sediment concentration was moving at rd 17+800 of the nara canal and in twin jamrao at rd 2+100. at rd 17+800 of the nara canal, most of sandy particles were transported from the indus river and were deposited in the upper nara canal system up to the jamrao complex, keeping only silt particles in suspension. at rd 2+100 of the twin jamrao, the concentration ratio from high to low flow shows a higher value, because of less sediment inflow during the low flow season as its concentration is only 170ppm. the deposition and erosion process of natural canals like nara depend up on the interaction between channel flow and sediment transport (i.e. suspended load) and bed forms as has been described in [19]. in alluvial channels, the flow regime has significant effects on channel morphology and sediment load transportation. during the monsoon, high discharge flowing in the canal controls the sediment transport dynamics. iv. conclusions the general trend in the left pocket is that sands have approximately concentration of 200-300ppm during the high flows and almost negligible during the low flows. sand is transported as bed load and also in suspension although sediment samples show that silt and clay are the predominant particles in suspension. floods during july and august carry the 70% of the total annual sediment of the river and approximately the 80% of the total amount of sand. the observed bed load material, during the year 2003 at rd 553+600 shows sizes from 0.07mm to 0.7 mm. it is concluded from the analysis that the bed load material consists of 54% fine sand mixed with 46% medium sand. it is also concluded that the sediment proportion of fine sand in the bed load has been increased in 2013 to an average of 75% keeping the medium sand to 25% at various rds in nara canal and the jamrao complex. this concludes that a substantial amount of fine sand has been deposited in this reach. the suspended load observed during the low and high flows of 2012 indicates that in all cases the sand proportion was increased in the upper nara canal system. the sediment concentration value clearly indicates that there is a deposition of sand at the jamrao complex, which has also been observed from the geo-morphological cross-sections. the analysis of the suspended sediment concentration concludes that the amount of sand deposited in the upper nara canal is not shared by the old jamrao and jamrao twin canals. from the morphological observations/cross-sections, it is observed that the dredging of bed material and the construction of fall structures have reduced the erosion and the transport of sediment towards the off-taking canals. hence, it is concluded that there is a considerable impact of the development works conducted for the water sector improvement. acknowledgment the authors are thankful to the sindh irrigation and drainage authority (sida), the mehran university of engineering and technology, jamshoro, sindh, pakistan and the water and power development authority (wapda). references [1] h. r. wallingford, "sukkur barrage morphological studies," ex 6847 r2, sep. 2012. 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[23] a. a. mahessar, k. ansari, g. m. arain, s. m. kori, s. qureshi, and a. l. qureshi, "impact of right bank outfall drain-i (rbod-i) / main nara valley drain (mnvd) on manchar lake, sindh, pakistan," engineering, technology & applied science research, vol. 9, no. 6, pp. 5074–5079, dec. 2019, https://doi.org/10.48084/etasr.3219. microsoft word 34-3820_s_etasr_v10_n5_pp6349-6355 engineering, technology & applied science research vol. 10, no. 5, 2020, 6349-6355 6349 www.etasr.com sookramoon: 80 kw updraft gasifier performance test using biomass residue waste from thailand ... 80 kw updraft gasifier performance test using biomass residue waste from thailand rural areas krissadang sookramoon faculty of industrial technology vallaya alongkorn rajabhat university pathum tani, thailand krissadangs@gmail.com abstract−this research presents the combustion test of kanchanaburi’s residue waste used in an 80kw updraft gasifier as biomass fuel. three types of selected biomass were considered: corncob, bagasee, and straw. the 80kw updraft gasifier was designed, fabricated, and experimentally studied. in the gasifier, a variable speed centrifugal fan acted as a forced convection unit, which was installed near the combustion chamber and transferred air volume to the updraft gasifier stove. the experimental results show the temperature in each zone of the thermochemical processes. the gasifier was evaluated by comparing the performance of the 3 different biomass fuels. the average producer gas from the burning of corncob, bagasee, and straw was 2.31m 3 /kg, 2.15m 3 /kg, and 2.11m 3 /kg respectively in the updraft gasifier. the recorded stove running times (h) for were 1.24, 1.2 and 1.05, respectively. the producer gas can be used to run a local cooking stove kiln with at normal rated heat generation successfully. keywords-updraft gasifier; residue waste; heating value; thermal performance; corncorb; bagasee; straw i. introduction thailand is an agricultural country with agricultural residues of high potential [1], which can be used as renewable energy sources such as sugar cane, cassava, oil palm, rice, corn, bagasse, fiber and palm shell, rice husk, and corncobs. they can be used as fuel for generating electricity and heat. in the past, waste biomass was usually left to form organic fertilizers on the farmlands and sometimes it was burned. biomass can be used as fuel because it provides heat at a level high enough to be considered as a source of heat energy. biomass energy is therefore an interesting alternative energy source for substituting fossil fuels. thailand has an area of approximately 6 million rai (1rai=1600m 2 ) for sugarcane cultivation representing an annual output of 6.8 million tons, according to the office of agricultural economics in 2009. most of the sugar cane is cultivated in the central, northeast and north. the major sugar cane cultivators are in kanchanaburi, nakhon ratchasima, khon kaen, nakhon sawan, and kamphaeng phet. the cultivation of sugar cane takes only one year and the harvest takes 6-7 months. the harvesting period for old sugar cane takes 14 months. corncobs are obtained from corn cultivation, in which an annual crop takes 3-4 months to harvest. there are two types of corn grown in thailand: sweet corn for consumption and forage corn. corn planting areas are provinces in the north and central regions. corncobs can be used to make biomass fuel. rice straw is agricultural waste or arising from rice cultivation. in 2008, it was estimated that the amount of discarded rice straw was approximately 4.63 million tons per year. the rice straw can also be used to make biomass fuel [1]. gasification is the combustion of fuel, by limiting air or oxygen properly, into a flammable gas, called producer gas. this gasifier is a cylindrical combustion chamber shape. the fuel ignites from the top according to the upstream combustion process. the utilization of biomass from nearby agricultural waste material was investigated in this paper. a gasifier can be designed for utilizing a variety of fuels such as charcoal or scrapped wood. agricultural waste such as corncobs or rice husk fuel can be used, but each source has different qualities, which depend on many factors such as fuel type, calorific value, and humidity. the important factor that has a significant effect on fuel quality is the amount of carbon contained in that fuel. fuels with high carbon content will increase the calorific value. fuel quality can be improved by increasing the carbon content, e.g. by applying coke on the chosen fuel type. this work focuses on synthetic gas production, composting of hydrogen and methane gas. our focus is both on gas production and on possible pathways to gas end use from biomass fuel in kanchanaburi province. this approach provides an overview of the potential for green synthetic fuels and discusses the technical feasibility of renewable fuel production, as well as its application in utilizing facilities. particular attention is also paid to the design issues related to the quality of gas for energy conversion. therefore, an 80kw updraft gasifier was constructed and experimentally investigated to find the combustion temperature in burning corncob, straw, and bagasse. the producer biomass gas contains hydrogen and carbon monoxide, which consist a source of energy capable of replacing lpg. ii. literature review a. gasification system gasification process is a process for converting carbon solid fuel components, such as wood, charcoal, coal, rice husk, sawdust, and combustible agricultural waste materials into combustion gas. providing oxygen for reacting process will get corresponding author: krissadang sookramoon engineering, technology & applied science research vol. 10, no. 5, 2020, 6349-6355 6350 www.etasr.com sookramoon: 80 kw updraft gasifier performance test using biomass residue waste from thailand ... the producer gas, which has carbon monoxide (co), hydrogen (h2), methane (ch4) as main components along with various volatile substances. the efficiency of producer gas production depends on the production process and the quality of the fuels used. renewable energy from producer gas has been widely used for 100 years, especially in europe. a coal source can produce producer gas, which can be used in a wide range of industries. producer gases can be used for cooking and heat or lighting provision to households. the objective of this research is to present a feasibility study of producer gas production derived from corncob, straw, and bagasse as a means of adding value to the crop. the two specific objectives of the current study are to provide the detailed design of an updraft gasifier that can be used with a variety of feedstocks and to test the quality and quantity of producer gas produced from the designed gasifier using local residue waste. b. biomass technology today, biomass fuel is used as a commercial alternative to industrial fuel. biomass can be derived from waste byproducts of the production process. biomass fuel can be converted to energy in a number of ways. figure 1 indicates the energy production technology for solid biomass. fig. 1. biomass fuel energy production technology. gasification technology is the disintegration of hydrocarbons in a controlled state of oxygen at a fraction lower than the one which causes complete combustion (stoichiometric fuel air ratio). this will attain the main components of gas, specifically co, h2, and ch4, which are termed as synthesis gas. the producer gas has originally a low calorific value, which gets higher if the reaction adds more oxygen to its content. the producer gas can be used as fuel for energy production or for the production of other forms of fuel. a gasification reactor can be divided into two systems: fixed bed and fluidized bed system. the fixed bed system is divided in 3 types: • the updraft gasifier [2] is an air-flowing furnace. the air flows from the bottom and then upward. the fuel moves downward in a counter-direction to the current gasifier. this type of stove has a high thermal efficiency because the hot gas generated by the combustion zone flows through the fuel. • the downdraft gasifier [3] is a downward direction gasfired furnace. the air flows in the same direction with the fuel. it is also known as the co-current gasifier. in this type of furnace, the product of the pyrolysis zone flows through the combustion zone, where the temperature is high, it breaks down into gas before dropping from the stove. the obtained fuel gas has low tar, but has a high range of temperature, ranging from 300°c to 500°c. • the cross draft gasifier is a cross-flow gas-fired furnace with fuel movement. the nature of the reaction layers, especially the combustion zone and the reduction zone, are closely related. therefore, it can produce gas rapidly and simply. the combustion area is usually centered on the gasproducing furnace, but the combustion scope may be expanded if the air has a higher speed. biomass gasifiers are devices that convert gaseous biochemical fuels. their products can be used for various engineering, technology & applied science research vol. 10, no. 5, 2020, 6349-6355 6351 www.etasr.com sookramoon: 80 kw updraft gasifier performance test using biomass residue waste from thailand ... purposes. there are three categories of gasifiers which produce production electric energy, heating, and hydrogen [4]. c. fluidized-bed system a fluidized-bed reactor (fbr) could be a combination of the two most common setups, mixed tank and pressed bed nonstop stream reactors [5]. it has fabulous warm and mass transfer characteristics. in fbr, cells are joined to solids within the frame of biofilm or granules [5, 6]. authors in [7] conducted an experimental study of the updraft biomass gasifier using biofuels, which concentrated on testing and comparing the composition of syngas produced in a 0.221m 3 fixed bed updraft gasifier from the combustion of coconut shell and biofuel briquettes. the gasifier was fired for 8h and readings were taken at regular intervals. it was concluded that coconut shell can be considered as a most suitable fuel for an updraft gasifier when compared to biofuel briquettes. authors in [8] studied updraft gasification. in the updraft gasifier the downward-moving biomass was first dried by the up flowing hot product gas. after drying, the solid fuel settled, giving char particles which continued to move down to be gasified, and pyrolysis vapors which are carried upward by the up flowing hot product gas. the product gas from an updraft gasifier thus contains a significant proportion of tars and hydrocarbons, which contribute to its high heating value. there is interest in the cleaning of the updraft gas for electricity production, as low temperature tars are more reactive and thus easier to be removed, than the high-temperature tars produced in much lower amounts by downdraft and fluidized bed gasifiers. authors in [9] designed and fabricated an updraft gasifier to run 15 to 18.6kw diesel engines. the gasifier was evaluated in the use of different biomass fuels. completely randomized design (crd) was used to statistically analyze the collected data. the average gas produced by burning rice husk, rice husk and sawdust, and sawdust produced 2.13m 3 /kg, 2.30m 3 /kg, and 2.54m 3 /kg producer gas with 1.66, 1.78 and 1.90h engine running times, respectively. the produced gas was successfully used to run a 15kw single cylinder diesel engine with dual fuel (25% diesel and 75% producer gas) at rated rpm. producer gas consists of co, h2, co2, ch4, traces of higher hydrocarbons such as ethane and ethylene, water vapors, n2 (if air is the oxidizing agent) and various contaminants such as small char particles, ash, tar, and oil [10]. authors in [3] studied the development of an equilibrium-based model of gasification of biomass by agricultural and forestry residues. they proposed an equilibrium-based model, developed by the commercial software aspen plus, of a co-current gasifier fueled by agriculture residues, which allows estimating the chemical composition and the heating value of the produced syngas. the prediction of such a model includes the main gaseous species, the yields of char and tar, and describes the gasification process through the mass and energy balances, the water-gas shift, (wgs) and the methanation reaction. the model validation was carried out through the comparison with experimental data, concerning two kinds of biomass with different moisture content and different gasification conditions, for sixteen cases. the comparison between the results of the simulations and the experimental data exhibited a good agreement. authors in [11] summarized an overview of the overall supply chain including production, transportation, storage, and end uses. available fuel conversion technologies use renewable energy for catalytic conversion of non-fossil feedstocks to h2 and syngas. the article shows how relevant technologies include thermochemical, electrochemical and photochemical processes. the quality of synthesis gas can be improved by catalytic reactions of co and co2 methylation for the generation of synthetic fuel. various attempts have been made to control harmful emissions from engines. authors in [12] conducted analysis of co2, co, no, no2, and pm particulates of a diesel engine exhaust. authors in [13] carried out the analysis of a target gas system based on tdlas & labview. they introduced target gas concentration detection techniques based on simulations of the gas detection system using the infrared absorption spectrum method. the detection of harmonics was measured with the wavelength modulation technique with the corresponding frequency signal and the gas absorption coefficient which can give the gas concentration, was obtained. authors in [14] carried out mustard and cotton waste-based biomass gasifier simulation. they introduced a biomass gasifier model using aspen plus. the manufactured model was validated for four different types of feedstock. the developed model estimates a well-predicted composition of ch4 and co, h2, and co2. authors in [15] studied the techno-economic and greenhouse gas aspects of decentralized biomass gasification for electrifying the rural areas of indonesia to reduce its dependence on fossil fuel power generation and to facilitate the electrification of its rural areas. iii. proposed updraft gasifier a. design and implementation the scope of the design was to make a gasifier that can be utilized to test the possibility of producer gas production in kanchanaburi biomass feedstock and be valuable for testing elective feedstocks. corncobs, straw, and bagasse were chosen as fuels for the experiment. due to its straightforwardness and flexibility, a settled bed, updraft arrangement was utilized (figures 2-3). to permit longer unfaltering states when testing different feedstocks, a semi-continuous bolster framework was utilized. the sizes of components for this gasifier plan were chosen based on the change rate craved for the framework and the need to utilize off-the-shelf sizes of components. the transformation rate of biomass for the maker, the gas per square inch of cross sectional region within the gasification chamber was evaluated based on the change rate within the sarah rowland [16] updraft gasifier. the design aimed to make a gasifier that may be utilized to test the achievability of the assessed change rate of 10kg/h which was chosen since the volume was sensible and the gasification chamber had a 18cm breath pipe installed. the gasifier consists of five crucial components: container and feedstock wood screw, gasifier body, instigator and scrubber framework, back outline, and information collection framework. the gasifier unit was fabricated at the faculty of industrial technology, vallaya alongkorn rajabhat university and the control unit at milada part and service company limited, pratimtani thailand. a sketch of the prototype is shown in figure 2 and the complete engineering, technology & applied science research vol. 10, no. 5, 2020, 6349-6355 6352 www.etasr.com sookramoon: 80 kw updraft gasifier performance test using biomass residue waste from thailand ... fabricated stove can be seen in figure 3. the advantage of the updraft gasifier is that no complicated components are required. a lot of biomass fuel can be combusted in not too high temperatures to provide high heating value producer gas. its disadvantage is the low quality of producer gas because of tar and soot associated. fig. 2. drawing of the 80kw gasifier. fig. 3. updraft gasifier 80kw prototype and its fabrication. b. thermal efficiency the thermal efficiency of the updraft gasifier system is the ratio of the energy derived from the produced synthetic gas of biomass fuel fed to the gas production system. the thermal efficiency equation of the system is [17]: η gasifier = hvsyngas×msyngas� lhvbiomass×fcbiomass ×100 (1) where ηgasifier is the thermal efficiency of the gasifier system, hvsyngas is the calorific value of the gas producer (mj/nm 3 ), msyngas is the mass flow rate of the producer gas (m 3 /s), lhvbiomass is the calorific value of the biomass (mj/kg), and fcbiomass is the consumption rate of the biomass (kg/s). c. biomass consumption rate biomass fuel consumption of gasifier systems can be determined by measuring the amount of biomass fed to the system over time under the operating conditions. the fuel consumption rate can be obtained from: fcbiomass= 3600×vf×ρ t (2) where fcbiomass is the rate of biomass fuel consumption (kg/h), vf is the volume of biomass in the fuel storage tank, ρ is the density of the biomass (kg/m 3 ), and t is the time of use of biomass fuels (s). iv. experimental set-up the moisture content of the biomass was determined by using astm standard 1775-01. the biomass had 10.6±2.3% dampness substance (damp premise) amid three dampness substance tests conducted during the period when gasification tests were performed. vitality substance was 12.99±0.02kj/g employing an automatic bomb calorimeter, weight measuring, and compression to tablets by a pressing machine. the biomass was dehumidified by drying in the sun, and then its heating value was measured. second desiccation biomass’ heating value was determined by weighing 0.6-1.5g and compressing the oxygen gas into a vessel containing the biomass at a pressure of 400-440psi. each sample took approximately 14min to analyze (figures 4-5). fig. 4. biomass preparation for heating value measurement. fig. 5. bomb calorimeter for heating value measurements. a. gasifier startup and operation a huge portion of the method included in testing a new gasifier design is deciding the suitable working methods for the framework and a given feedstock. after preparatory testing, the standard framework startup and operation methods for testing biomass feedstock were performed. the equipment was set up as shown in figure 6. biomass was loaded to the container and feedstock wood screw, then to the combustion chamber. paper was fired in the chamber hole to start burning the biomass fuel. engineering, technology & applied science research vol. 10, no. 5, 2020, 6349-6355 6353 www.etasr.com sookramoon: 80 kw updraft gasifier performance test using biomass residue waste from thailand ... the axial flow fan was turned on to permit the air flowing through the combustion chamber. the fan increases air draught and thereby combustion rate. the generated producer gas was checked by igniting. the control and display system shown in figure 7 displays the temperature in each zone of the combustion (drying, pyrolysis gasification, and combustion zones). another function of the control and display system is its ability to adjust the speed of the axial flow fan. the three types of selected biomass were corncob, bagasse, and straw (figure 8). fig. 6. gasifier startup and operation. fig. 7. control and display system. fig. 8. kanchanaburi selected biomass: corncob, straw, and bagasse. b. methodology the updraft gasifier was set up on sunny days (septemberoctober 2018) in the open air area. the container was filled with biomass and sealed. the graphtec data logger was initialized and temperature recording was initiated. throughout the operation, the scraper/agitator worked in conjunction with the feedstock wood screw to guarantee that feedstock moved to the gasification chamber. both the steering wheel and the wood screw rotated counter clockwise. wind speed was set to 8.12scfm (0.23m 3 /min). the combustion process took place after 3-5min until the two thermocouples reached temperature of approximately 40˚c and smoke started to come out of the gas outlet. when the feedstock within the gasification chamber was clearly lit, the burn was expelled and the stove was fixed with the cap. feedstock was supplied until the scraper/agitator met intense resistance, meaning the gasification chamber was full. the flow was balanced with the flow attempted at the time. airflow rate varried from 8.12 to 20.13scfm (0.23 to 0.57m 3 /min). ignition vessels were used as needed to maintain the flow within the feedstock. gas tests were conducted when the formation temperature was stable and the flame was maximum and most stable. after the data of all the tests of the day were collected, the gasifier was cooled and cleaned. the amount of biomass that remained in the silo was measured. fig. 9. the 80 kw updraft gasifier. v. experimental results a. physical and chemical biomass properties before use the biomass was dried in the sun for a week for moisture reduction. corncobs were brought from farmers around the corncob factory. the samples’ size ranged between 14-15cm in length and 5-6cm diameter. the size of the bagasse was average with length of 13-15cm length and 5-6cm diameter. the length of straw was in the range of 17-20cm and the diameter in the range of 0.3–0.8cm. the mean density values for corncob, bagasse, and straw were 250kg/m 3 , 260kg/m 3 , and 240kg/m 3 respectively, and the mean heating values derived from the automatic bomb calorimeter measurement are shown in table i. table i. heating values no. biomass avg. heating value (kcal/kg) avg. heating value (kj/kg) 1. corncob 2,152.948 9,013.958 2. straw 1, 911.588 8, 003.433 3. bagasse 1, 593.97 6, 673.630 engineering, technology & applied science research vol. 10, no. 5, 2020, 6349-6355 6354 www.etasr.com sookramoon: 80 kw updraft gasifier performance test using biomass residue waste from thailand ... the output of ash content in the three feedstocks was 0.9% for corncob, 1.42% for bagasse, and 10.39% for straw. b. results of using corncobs as fuel the experiment was carried out during 21-23 september 2018. the airflow rate fed into the combustion zone was controlled at 0.57m 3 /min and 4.7kg of corncobs were added to the hopper. the test duration was 1h and 24min. during the test the temperature in the furnace body in each combustion zone was measured using a thermocouple. the k-type thermocouple t1, t2 and t3, (combustion, reduction, and pyrolysis temperature) are displayed on the control panel of the furnace. temperature thermocouples t4, t5 and t6 were used for measuring and collected data on a gl-820 data logger. the experiment results are shown in figure 10. it was found that the maximum combustion temperature was 716.1°c after 1h and 24min and the initiation temperature of the gas was 260.4°c after 20min. fig. 10. the temperatures of burning corncob during 2018, sept,. 21-23. c. results of using straw as fuel the experiment was conducted on 28-30 september 2018. in this experiment, the airflow rate into the combustion zone was equal to 0.57m 3 /min and 4.5kg straw was loaded. the experiment period was 1h and 20min. fig. 11. graph of the burning straw, 2018, sept., 28-30. as before t1, t2 and t3 were displayed on the control panel display for data acquisition of the furnace body and t4, t5 and t6 were measured and stored into a data logger. the maximum combustion temperature was 528.15°c after 1h and 20min and the gas initiation temperature was 159.6°c after 26min as can be seen in figure 11. d. results of using bagasse as fuel the experiment was conducted during october 5-7, 2018. in this experiment, the airflow rate was 0.57m 3 /min and 4.5kg of bagasse was applied. the experiment period was 1h and 5min. again, t1, t2 and t3 were displayed on the control panel display and t4, t5 and t6 were measured and stored into a data logger and the result can be seen in figure 12. the maximum combustion temperature was 520.8°c after 65min and the gas initiation temperature was 199.5°c after 19min. fig. 12. graph of the burning bagasse, 2018, oct., 5-7. vi. conclusion and future scope the results of the corncob incineration experiment found that at airflow rate of 0.57m 3 /min, the maximum temperature of the furnace during the combustion was 716.1°c. the gas initiation temperature was 260.4°c after 20min when adjusting 100% airflow rate into the furnace as the maximum value, resulting in the fastest possible amount of oxygen to help burn the fuel. regarding straw burning, the results of the experiment showed that for airflow rate of 0.57m 3 /min, the maximum temperature of the furnace during combustion was 528.15°c. the gas temperature was 159.6°c after 26min. the results of the bagasse incineration experiments showed that the maximum temperature of the furnace during combustion was 520.8°c and the gas initiation temperature was 199.5°c after 19min. there is high loss of heat from gas production. using lpg as fuel will produce higher heating values than corncobs. burning corncob produced less smoke than burning straw and bagasse. the heating value of corncob is higher than that of straw and bagasse, but it produces more tar. corncob and straw can be used in a ceramic kiln, but a gas filter should be added to clean the gas. the calorific value of bagasse is relatively low and it must be cut down in order to reduce its size, so it is not suitable to be used as a fuel. the bomb calorimeter experiment found that corncob’s heating value of 9,013.958kj/kg was the highest, followed by straw with a heating value of 8,003.433kj/kg, while bagasse engineering, technology & applied science research vol. 10, no. 5, 2020, 6349-6355 6355 www.etasr.com sookramoon: 80 kw updraft gasifier performance test using biomass residue waste from thailand ... had the lowest heating value of 6,673.630kj/kg. these biomass-heating values correspond to the combustion temperature in the gasifier’s combustion chamber mentioned above. for comparison, woodchips used as fuel in the development and performance evaluation of a biomass gasification system for ceramic firing process have heating value of about 12-15mj/kg [18]. it can be concluded that kanchanaburi province has the potential of producing biomass energy with sources like as corncobs and rice straws that can replace the consumption of lpg gas. some of the issues the gasifier faces could be dealt with in as a next step. an automatic conveyer for biomass loading system can be installed for operation convenience. the stack could be extended in order to eliminate smoke rapidly during the operation. new types of locally available biomass fuel could be studied. acknowledgment the author would like to thank the national research council of thailand for their financial support for this research. references [1] biomass energy. department of alternative energy development and efficiency, ministry of energy, thailand. [2] “updraft biomass gasifier,” indiamart.com. https://www.indiamart. com/proddetail/updraft-biomass-gasifier-14040553933.html (accessed sep. 30, 2020). [3] a. gagliano, f. nocera, m. bruno, and g. cardillo, “development of an equilibrium-based model of gasification of biomass by aspen plus,” energy procedia, vol. 111, pp. 1010–1019, mar. 2017, doi: 10.1016/j.egypro.2017.03.264. [4] r. k. dabkeya, d. k. dhaked, and m. lalwani, “an overview of gasifier and its application in indian context,” in emerging trends in electrical, communications, and information technologies, singapore, 2020, pp. 291–307, doi: 10.1007/978-981-13-8942-9_25. [5] a. pandey, s. v. mohan, j. s. chang, p. hallenbeck, and c. larroche, biomass, biofuels, biochemicals, 2nd ed., elsevier, 2019. [6] “bubbling fluidized bed reactor,” chemical engineering world, jun. 09, 2019. https://chemicalengineeringworld.com/bubbling-fluidizedbed-reactor/ (accessed sep. 30, 2020). 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[15] s. you, h. tong, j. armin-hoiland, y. w. tong, and c.-h. wang, “techno-economic and greenhouse gas savings assessment of decentralized biomass gasification for electrifying the rural areas of indonesia,” applied energy, vol. 208, pp. 495–510, dec. 2017, doi: 10.1016/j.apenergy.2017.10.001. [16] s. rowland, “design and testing of a small-scale updraft gasifier for gasification of eastern redcedar,” m.s. thesis, oklahoma state university, stillwater, ok, usa, 2010. [17] mechanical wood products branch, forest industries division, fao forestry department, wood gas as engine fuel. fao, 1986. [18] p. punnarapong, a. promwungkwa, and n. tippayawong, “development and performance evaluation of a biomass gasification system for ceramic firing process,” energy procedia, vol. 110, pp. 53–58, mar. 2017, doi: 10.1016/j.egypro.2017.03.105. engineering, technology & applied science research vol. 7, no. 2, 2017, 1528-1534 1528 www.etasr.com gupta et al.: leakage reduction in water distribution systems with efficient placement and control… leakage reduction in water distribution systems with efficient placement and control of pressure reducing valves using soft computing techniques aditya gupta neeraj bokde dushyant marathe kishore kulat electronics and communication dpt visvesvaraya national institute of technology nagpur, india adityagupta2590@ gmail.com electronics and communication dpt visvesvaraya national institute of technology nagpur, india neerajdhanraj@ gmail.com electronics and communication dpt visvesvaraya national institute of technology nagpur, india dushyant.marathe@ gmail.com electronics and communication dpt visvesvaraya national institute of technology nagpur, india kdkulat@ ece.vnit.ac.in abstract—reduction of leakages in a water distribution system (wds) is one of the major concerns of water industries. leakages depend on pressure, hence installing pressure reducing valves (prvs) in the water network is a successful techniques for reducing leakages. determining the number of valves, their locations, and optimal control setting are the challenges faced. this paper presents a new algorithm-based rule for determining the location of valves in a wds having a variable demand pattern, which results in more favorable optimization of prv localization than that caused by previous techniques. a multiobjective genetic algorithm (nsga-ii) was used to determine the optimized control value of prvs and to minimize the leakage rate in the wds. minimum required pressure was maintained at all nodes to avoid pressure deficiency at any node. proposed methodology is applied in a benchmark wds and after using prvs, the average leakage rate was reduced by 6.05 l/s (20.64%), which is more favorable than the rate obtained with the existing techniques used for leakage control in the wds. compared with earlier studies, a lower number of prvs was required for optimization, thus the proposed algorithm tends to provide a more cost-effective solution. in conclusion, the proposed algorithm leads to more favorable optimized localization and control of prv with improved leakage reduction rate. keywords-leakage; pressure management; multiobjective genetic algorithm; pressure reducing valves; water distribution system i. introduction water losses in pipeline networks can be categorized into (a) apparent losses (such as unauthorized consumption and unmetered bills) and (b) real losses (such as leakages in pipelines and joints). leakages in pipelines are the main reason for non-revenue water (nrw) losses [11, 13, 19]. leakages occur due to pipeline deterioration, which is mainly caused by ageing and high pressure. because of these leakages, extra water has to be pumped out, which increases energy consumption, and consequently, increases the carbon footprint [12]. nowadays, leakage management is gaining attention among researchers for reducing real losses [14]. leakage management includes active leakage control, pressure management, and accelerating repair operations. a water distribution system (wds) is designed according to the peak hour water demand. for the remaining periods when the water demand is less, the water supply system remains under high pressure. leakages are directly proportional to pressure [18]; therefore, a decrease in the pressure will reduce the leakage rate of wds. hence, pressure management has become a crucial part of leakage management, which can be achieved by performing sectorization of the wds by using isolating valves or by inserting flow and pressure reducing valves (prvs) in pipeline networks to reduce flow and pressure [2]. correct placement of these valves along with optimized control is desire so that the wds will work with a good efficiency. the conservation of mass makes the optimization a nonlinear problem. for optimization, objective functions are required that will satisfy the needful constraints also. during the last decade, many researchers have attempted to optimize the water network using prvs as a pressure managing tool [6, 16, 26-27, 29]. mixed integrated nonlinear programing (minlp) was introduced in [28] for controlling pressure in pipeline infrastructure. a method has been proposed for the localization of valves for controlling pressure in [30] which has low accuracy and low reliability. minlp was modified as mathematical programming with complimentary constraints (mpcc) in [31]. mpcc also failed to optimize the valve location efficiently [4]. further research on mpcc was conducted in [24, 25, 32]. in [4], authors proposed a nonlinear program (nlp) algorithm to solve minlp problems. binary variables have been proposed to accelerate system performance. the results obtained using this algorithm was more favorable than those obtained using previously used algorithms for leakage reduction; however, it included higher engineering, technology & applied science research vol. 7, no. 2, 2017, 1528-1534 1529 www.etasr.com gupta et al.: leakage reduction in water distribution systems with efficient placement and control… computational complexity. in [34], authors proposed an extended model for calibrating optimal operational pressure valve of prvs using nlp algorithm. the proposed algorithm was applied in exnet wds, causing leakage reduction of 5.72 l/s. meta-heuristic search was also useful in pressure reduction in pipeline infrastructure [3, 7-8, 33]. in [8], authors proposed a scatter-search meta-heuristic approach for valve location and optimization of the pressure value across the valve. a concept of reference pressure was introduced, which proved to be efficient in determining the locations of prvs. a scatter-search algorithm was used to determine the optimized pressure value for prv. improved results were observed. in [5], authors used a pseudo-valve insertion method (similar to the one in [2]). in this method, a prv is inserted in the pipeline and parameters are calculated using genetics algorithm (ga). the metaheuristic approach was used to determine the optimized value of prvs. simulations were performed on a small-scale wds. in a real-world scenario, using this approach is difficult in complex pipeline infrastructure because of the large number of variables and computational complexity. sometimes, the metaheuristic approach may only be able to determine sub-optimal solutions. in [10], authors suggested splitting of the pipeline for pressure management. splitting results in the optimization of 60% of nodes at a desired pressure. this method appears suitable for an area having a tank at low height; however, the method was not investigated for systems having reservoirs and areas with tank at higher heights. genetic algorithms (gas) is a population-based technique that does not require the simplification of the hydraulic model. hence, gas are preferred for operational (prvs location and control and pump optimization) and design optimization of a water distribution system (wds) compared to classical deterministic optimization techniques. in [23], authors proposed a hybrid objective algorithm (ga and linear programing (lp)) for valve installations and pipe replacements for optimizing a wds. gas are used for optimized placement of valves and lp is used to search for an optimal setting of the control valve. in addition, their study explored a trade-off between the number of prvs and leakage volume. in [21], authors presented a harmony search (hs) model to determine the optimum control setting across the valves. they demonstrated more favorable efficiency with the hs algorithm than the ga for pressure reduction. optimization of water systems requires multiobjective functions, that is, to determine the optimized value and location of prvs and to minimize the leakage rate. these objectives attracted researchers [15, 20, 22] to nsga-ii for water infrastructure management. in [17], authors used the multiobjective algorithm to design a realworld wds. in [1], authors used nsga-ii for reducing leakages in the wds by using pressure management. nsga-ii was used to determine optimized valve locations. this algorithm uses a population size of 100 with 1000 generations. a higher reduction in the average leakage rate was observed compared with that in [5]. in [4], authors used mpcc and obtained more favorable results than in [1]. our study delineates the problem of optimization of water pipeline infrastructure by managing pressure using a different and efficient approach. flow-controlled prvs were used to modulate pressure. the entire operation was divided into two parts: a) to define reference pressure (pref) for the calibration of the number of prvs required along with their location. a new rule was introduced for this calibration. introduction of this rule led to new prv location, which led to a higher reduced leakage rate than that with standard techniques used in previous literature; b) after prv localization, nsga-ii was used to determine the optimized pressure of the valve (first objective) and to minimize the leakage rate (second objective). to apply it in a real-world wds, different water demand patterns were considered. epanet [9] was used as a simulation tool along with matlab r2015a for calibration, which was performed on a desktop pc (intel i7 processor with 16 gb ram). ii. pressure reducing valves for pressure management a prv is installed to control the pressure at the downstream end of the valve. prv operates in three modes: active, closed, and open. the mode of operation depends on upstream and downstream pressures, which can be defined as follows: active; (pdwn= pset) if pup > pset (1) open; if pup< pset (2) closed; if pup< pdwn (3) where pup is upstream pressure; pset is operational control setting of prv; and pdwn is downstream pressure. in the open mode, the valve is fully open. in the closed mode, the valve is fully closed to avoid reverse flow. in the active mode, the valve is partially closed. we aimed to determine the optimized value pset for all prvs present in the system. prv can be used in three modes. in the fixed prv mode, prv is set to a fixed value of pressure (pset=constant). this is possibly the simplest mode; however, higher optimization cannot be obtained because water demand pattern changes from time to time. in the second mode, the control value (pset) of the valve changes with respect to time by using a timing device. it is also the simplest and effective method when the demand pattern remains constant and repeats. such a system fails when the demand pattern changes frequently [1]. the third mode is based on flow modulation. optimized control value across prv (pset) was adjusted depending on the flow rate of water. although flow-controlled prvs are more complex, higher optimization can be achieved because of more flexibility. flow-modulated prvs were used in this study. a. leakage calculation leakage rate was calculated for the network by using the pressure-based leakage model. leakage rate calculations have been adopted from [1]. epanet [9] was used as a simulating tool for the water network. optimization and calculation were performed using matlab r2015a. according to conservation of mass, continuity at node is expressed as σjqij,k – k* qreq,i li,k = 0 (4) engineering, technology & applied science research vol. 7, no. 2, 2017, 1528-1534 1530 www.etasr.com gupta et al.: leakage reduction in water distribution systems with efficient placement and control… where qi,j,k is flow through pipeline between nodes i and j for load condition k; qreq,i is the required flow though node i; and li,k is the leakage associated with node i. li,k = cl* li*p y i,k (5) where cl is the coefficient of leakage per unit length of the link to service pressure; li is the total length of pipeline associated with node i; pi,k is the pressure of node i for demand k; and γ is the leakage exponential used to define relation between flow from orifice and head difference. leakage exponential value of 1.18 [2] is observed for cracks in pipe or joints which occurs due to difference in pressure of internal and external pipe. therefore writers adopted same value i.e. 1.18 for leakage exponential. total length of pipeline associated with node i (li) can be calculated using li = 0.5*σjlij (6) where li,j is the total length of pipeline connected with node i. head loss can be calibrated as hij,k =hi,k-hj,k (7) where hij,k is the head loss between node i and j; hi,k and hj,k are the head measured at node i and j for load condition k. head loss for pipeline using flow values, can be calculated using hazen-william equations: hij,k= 10.668 c ij -1.85 d ij -1.85lijqij,k 1.852 (8) where c ij= hazen-william coefficient; d ij is the diameter of pipeline; lij is length of pipeline connected to node i and j; and qij,k is the flow across pipeline for load condition k. head loss across prv, expressed as hij,k= 10.668 c ij -1.85 (υij.kd ij) -1.85lijqij,k 1.852 (9) where υij.k is the diameter multiplier when valve is present, during active mode υij.k varies between 0 to 1 (0 <υij.k <1) and for open mode υij.k is 1; qij,k ≥0, it means reverse flow of water is not allowed. the limitations associated with (9) is that, it can’t be used during case of close mode when the value of υij becomes 0. to overcome from this drawback, authors in [34] have modified the existing model used for calculating head losses under the presence of prvs, introducing new mathematical equations for calculating head loss in all three operational mode of a prv. for this study we have also adopted the extended model propped in [34]. adopting this model hij,k can be calibrated as hij,k = max(0,hi,k-hj,k)=10.668cij -1.85(υij.kdij) 1.85lijqij,k 1.852 (10) this prv model can able to describe all three operation modes i.e. open, close and active, which is required during optimization the pressure reduction process. now using the value of head, pressure at node i is calibrated using: pi,k= hij,k elei (11) where elei represents elevation at node i; and pi,k is the value of pressure at node i for load condition k. b. pressure reducing valve localization in [8], authors introduced the concept of reference pressure to restrict candidate valve locations to a set of pipelines. our study also uses the reference pressure technique for valve localization. pressure was considered for an average load condition. consider g is set of the entire pipeline present in wds. a subset gv (gv îg) is derived, which belongs to pipeline for prv candidate. n is the set corresponding to node. n1 (n1 î n) is subset of n, which represent the node where pressure exceeds the reference pressure. n2 (n2 î n and n2=n-n1) is also subset of n, whose pressure is below reference pressure. if node i belongs to subset of n2 and node j belongs to n1, then gv is the subset of pipeline for prv candidate between node i and j, is expressed as. rule 1. if nj > pref and ni < pref (12) where ni and nj is the pressure at node i and j. the reference pressure was selected during valve localization operation (using (12)). the reference pressure varied over a range to determine different values of gv,n (gv,n represents the number of candidate valve locations for a current value of pref). pressure value corresponding to a minimum value of gv,n was selected as the reference pressure. the (12) rule proposed, in [8] suffered from the drawback that, sometimes pressure difference between nodes ni and nj was slightly high. however, this location was not considered for prvs localization because pressure was above pref for both the nodes. if we were able to cut this excess pressure difference between node ni and nj, this will lead to high reduction in the leakage rate of wds. to overcome this drawback, a new rule (rule 2) is introduced for prv localization, with idea behind is, to also consider the pipeline connecting to nodes ni and nj as prv candidate (gv), which have pressure difference (between ni and nj) more than predefined threshold value. rule 2. if nj -ni > 0.1 × pref (13) to make this threshold as wds dependable, the threshold (≥0.1 × pref) is decided in accordance with reference pressure of existing wds. if we lower down the threshold (5% of pref) value, then number of prv candidate will get increase, therefore threshold is decided as 10% of reference pressure, to minimize number of prv candidate. rule 2 is applied to the wds, after rule 1, for the localization of prvs candidates. iii. multi-objective genetic algorithm for valve optimization the optimal value of prv was calibrated using the multiobjective ga. we aimed to determine the optimized control value of the prv with minimum leakage rates in the wds. after optimization, every node present in the system should maintain minimum pressure (pmin) to avoid pressure deficiency at any node. the multiobjective ga was implemented using a function in matlab given by: engineering, technology & applied science research vol. 7, no. 2, 2017, 1528-1534 1531 www.etasr.com gupta et al.: leakage reduction in water distribution systems with efficient placement and control… [p,leak_val]=gamultiobj(ff,nv,[],[],[],[], pmi, pma) where nv is 1(number of variables); p is the pressure control value across prv (pset) and varies from pmi and pma; ff is fitness function; and leak_val stores the leakage value in l/s corresponding to pset. fitness function includes two objective functions named as ᵮ1 (first) and ᵮ2 (second). the first objective (ᵮ1) was to determine the optimized pressure value (pset) of prv. min ᵮ1 = n w k l i i,k i=1 w c lp s å (14) subject to: pi,k ≥ pmin (15) nv ≤ nv (16) hi,j,k = hi,k hj,k (17) pmi ≤ pset ≤ pma (18) where pi,k is pressure at node i for load condition k; pmin is the minimum pressure that is required at each node; nv represents number of prv currently being used in wds; nv represents maximum number of prv allowed to insert in wds; pmi & pma are the minimum and maximum value allowed across the prv; ns represents number of node present in the system; and wk is the value of load (demand multiplier). the algorithm uses population of 50 for individual evolving for 200 generations. optimized value of prv has been found out for individual load condition at a time. the leakage rate (second objective) was calculated for all the optimized values (pset) generated from the first objective (ᵮ1). pressure corresponding to lowest leakage rate was selected. min ᵮ2 = n w i i,k i=1 cp s å (19) where ci (ci=li *cl) is the flow intensity at node i. the head and pressure value at each node of the pipeline is required to calibrate the function ᵮ1 and ᵮ2. when the control setting across prv (pset) changes, the value of the head, pressure and head loss changes across all the nodes and pipeline also change. calculating the value of the head and pressure for every change in value of pset in epanet is not feasible; therefore within the fitness function, another function was used to calculate hydraulic parameters such as the pressure and head at the wds nodes for current value of pset. equations 7-11 where used to calibrate the value of pressure at each node, due to variations in value of operational control setting of prv. the value of pset varied from pmi to pma. iv. results and discussion a. case studybenchmark wd optimization operation using prvs was performed for the water network as shown in figure 1. this was used as a benchmark in previous studies (nicolini and zovatto in [1]; araujo, ramos and coelho in [5]) for pressure management in the wds by using prv. the network included 22 nodes, three reservoirs, and 37 links (pipelines). fig. 1. layout of water network adopted for the analysis the height, length, and diameter of the reservoir, node, and pipe were similar to those used in [2]. the elevation of reservoir was set at 56 m. the system had a base demand of 150 l/s. the demand pattern varied with time, which is shown in table i. the demand varied from 0.6 to 1.4, with an average demand multiplier (load condition) of 1. the network was simulated in epanet initially without prvs. engineering, technology & applied science research vol. 7, no. 2, 2017, 1528-1534 1532 www.etasr.com gupta et al.: leakage reduction in water distribution systems with efficient placement and control… table i shows the leakage rate in the wds under different load conditions. using 4–6, the leakage rate was calculated for all load conditions, which varied from 0.6 to 1.4 with an average of 0.98. for leakage calculations, a typical value of 10−5 is considered for cl. calculated average leakage rate were 29.53 l/s. on considering only three load conditions (0.6, 1, and 1.4) as referred by other authors, the average leakage rate were 29.363 l/s. the profile plot of pressure for different load conditions is shown in figure 2. in the profile plot, green color indicates pressure (30–37 m), which is a desired pressure range. yellow indicates the moderate high pressure zone (40 m). red indicates a high pressure zone (>40 m). during the high peak hour demand (9:00 a.m.), only two nodes indicated high pressure, whereas during the low peak hour demand (12:00 a.m. and 3:00 a.m.), maximum number of nodes were under high pressure. figure 3 shows the average leakage rate associated with individual nodes. nodes corresponding to the high leakage rate were 15, 2, 3, and 22. table i. leakage rate (l/s) for different load condition at different time instances. daily time demand pattern (load condition) leakage rate (l/s) 12:00 am 0.8 30.481 3:00 am 0.6 31.11 7:00 am 1.0 29.261 9:00 am 1.4 27.735 1:00 pm 1.1 29.07 average 0.98 29.53 (a) 12:00 am (0.8) (b) 3:00 am (0.6) (c) 7:00 am (1.0) (d) 9:00 am (1.4) (e) 1:00 pm (1.1) fig. 2. profile plot of pressure with time and the load coefficient using 12 and 13 (rule 1, rule 2), valve locations were calculated for the average value of the load condition (0.98). value of reference pressure was selected using (12). the value of references pressure varied from 32 to 40 m. figure 4 shows a graph between "number of prv" versus "pref". figure 4 shows that the number of prv is minimum i.e. 4, for the reference pressures of 36 and 37; therefore, 36 was selected as the reference pressure. after applying rule 1 the number of valve location comes out to be 4. after this, rule 2 (13) has been applied for finding out additional prv localization to remove the drawback of rule 1. 3.6 m is decided as threshold value for rule 2, which is 10% of reference pressure. one additional location is observed for prv candidate after applying the new rule (13). thus maximum number of prv candidate location was fixed to 5 (nv). the locations of valves were at pipe 1, 31, 37, 15 (from rule 1), and 40 (from rule 2). when comparing proposed algorithm with reference pressure algorithm proposed in [8], the maximum number of prv candidate location (nv) has been increased from 4 to 5. the introduction of new rules has revealed new locations i.e. pipe-40 for prv candidate engineering, technology & applied science research vol. 7, no. 2, 2017, 1528-1534 1533 www.etasr.com gupta et al.: leakage reduction in water distribution systems with efficient placement and control… location while other 4 prvs candidate location (p-1, 31, 37, 15) are the same as that suggested from the scheme presented in [8]. the optimized operational value of prv was obtained using matlab. the optimized control pressure of prv (pset) was between 30 (pmi) and 35 (pma). the value of the minimum desired pressure (pmin) at every node was 30 m. matlab was also used to calculate the head and pressure at each node (using 7-11) for the pressure value of prv at pset. on performing a random check, the values of pressure at node, calculated using 7-11, varied from actual simulated values (from epanet) with a maximum error of ±1.3% (i.e. ± 0.5m). ga uses random population for generation of optimal solution. every time this system generates different optimal solution. as window is already provided for population generation, this minimizes the variations in final optimal solution by ±0.15m. therefore nsga-ii has been run for three times and optimal solution is selected by calculating the average of these solutions. calibrated value of prvs under different load condition are illustrated in table ii. fig. 3. average leakage rate (l/s) of individual nodes fig. 4. numbers of prvs versus pref initially, two prvs were installed at pipe 1 and 37. the third prv was installed at pipe 31 and fourth at pipe 40. high optimization was observed after inserting four prvs. after pressure management, the average leakage rate was reduced to 23.38 l/s from 29.53 l/s. after adding fifth prv at pipe-15 the prv remains open during load condition of 1, 1.1 and 1.4. whereas during load condition value of 0.6 and 0.8, it leads to nominal additional average leakage reduction of 0.22 l/s, which is less than 1% of initial leakage rate. hence adding fifth prv can't be efficient as addition of prv will increase the infrastructure cost of wds. thus only four prvs were used. table ii. optimal pressure value of prv (pset) in meters, obtained after applying nsga-ii. here different demand patterns (load conditions) have been considered number of prvs 0.6 0.8 1 1.1 1.4 2 (p-1, 37) 30.86 31.56 32.62 32.39 34.17 3 (p-1, 37,31) 30.73 31.93 33.21 33.52 34.37 4(p-37,40,1,31) 31.57 32.35 33.29 33.74 34.59 table iii. comparison of average leakage reduction rate (l/s). the average leakage rate has calculated for demand coefficient of 0.6, 1.4 and 1 number of prvs average decrease in leakage in l/s (proposed) average decrease in leakage in l/s ([1]) 2 4.65 3.33 3 5.35 4.04 4 6.05 4.33 5 4.41 leakage reduction (%) 20.64% 16.07% table iii shows that the leakage reduction rate was higher at every stage than that in studies using the same number of prvs. the leakage reduction in terms of percentage obtained after using four prvs from proposed algorithm was more than that observed in [1]; after using 5 prv, considering load condition of 0.6, 1.0 and 1.4 only. the leakage rate was reduced by 20.64% (6.05 l/s), which is more favorable compared with the results obtained in [1]. this proves the robustness of the system. the time taken to calibrate the optimal operational value of prv for present load condition is 3-5 sec. hence, the proposed algorithm can be implemented in real time. considerable reduction in pressure was observed after placing prv at pipe 40. prv at this location was not placed in previous studies. this is due to the new rule (rule 2, 13) proposed for localization in this study, which has contributed to the reduction in the leakage rate more than that observed in the previous study. v. conclusion our study presents an approach to determine the optimal location and optimized pressure value of prvs (flowcontrolled) for pressure management. two rules were implemented for the localization of prvs using reference pressure. the newly proposed rule 2 revealed new localization of valves (p-40), which resulted in more favorable leakage reduction due to the reduction of surplus pressure present in the wds. nsga-ii was implemented with an aim to: a) determine the optimal value of prvs under different load conditions and b) minimize leakages. minimum required pressure (pmin) is maintained at every demanding node. this avoids pressure deficiency (lower engineering, technology & applied science research vol. 7, no. 2, 2017, 1528-1534 1534 www.etasr.com gupta et al.: leakage reduction in water distribution systems with efficient placement and control… pressure than desired) at any node, thus allows wds to provide services efficiently. the leakage rate was reduced by 6.15 l/s (20.82%) after using the proposed algorithm in a benchmark wds, considering all the load condition. as shown, the proposed scheme offers an improved performance that also reduces the implementation cost. the proposed system showed successful results for small and medium water networks. future research should focus on its application in complex networks. acknowledgements the authors would like to express their gratitude to sudhir kumar mishra for revising and correcting the manuscript during the writing period. references [1] m. nicolini, l. zovatto, “optimal location and control of pressure reducing valves in water networks” journal of water resources planning and management, vol. 135, no. 3, pp. 178-187, 2009 [2] p. w. jowitt, c. xu, “optimal valve control in water-distribution networks” journal of water resources planning and management, vol. 116, no. 4, pp. 455-472, 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systems by a tabu search metaheuristic”, in: computing tools for modeling optimization and simulation, vol 1, kluwer, boston, ma, pp 279–298, 2000 [34] p. d. dai, p. li, “optimal pressure regulation in water distribution systems based on an extended model for pressure reducing valves”, water resources management, vol. 30, no. 3, pp. 1239-1254, 2016 microsoft word rev-2-28-2442_s engineering, technology & applied science research vol. 8, no. 6, 2018, 3673-3680 3673 www.etasr.com kimani & njiraine: cognitive radio spectrum sensing mechanisms in tv white spaces: a survey cognitive radio spectrum sensing mechanisms in tv white spaces: a survey kenneth kimani department of telecommunications & information engineering, jomo kenyatta university of agriculture and technology, juja, kenya kuriakimani@yahoo.com morris njiraine department of telecommunications & information engineering, jomo kenyatta university of agriculture and technology, juja, kenya morrisnjiraine@gmail.com abstract—frequency spectrum is a limited resource and the increasing demand caused by emerging services, augmented number of wireless users along with the demand for high-quality multimedia applications have resulted in the overcrowding of the allocated spectrum bands. the overcrowding of spectrum bands has been exacerbated by the current spectrum licensing policy which has emerged as a bottleneck to efficient spectrum utilization, due to its inflexibility, resulting in most of the licensed spectrum being severely under-utilized. however, the problem of scarcity of spectrum bands and the inefficient utilization of the already allocated radio spectrum can be smartly addressed through spectrum sharing by enabling opportunistic usage of the underutilized frequency bands. one of the most exciting ways of spectrum sharing is cognitive radio technology which allows a wireless node to sense the environment, detect the network changes, and then make intelligent decisions by dynamically changing its reception or transmission parameters to communicate while ensuring that no interference is affected to the licensed users. it thus improves the spectrum utilization by reusing the unused or underutilized spectrum owned by the incumbent systems (primary systems). in this paper, a comprehensive survey and review of recent research about the advances in cognitive radio technology will be carried out. we will also evaluate the various spectrum sensing techniques in a cognitive radio network in the uhf/vhf bands allocated for tv broadcasting. keywords-cognitive radio; spectrum sensing techniques; opportunistic spectrum access; i. introduction the rapid growth of wireless communication has exacerbated the problem of scarcity of available spectrum. since the bulk of the spectrum has already been assigned, it is extremely arduous to find new spectrum for either deploying new services or expanding already existing ones. although nearly all of the spectrum bands have already been allocated, these bands are seriously underutilized most of the time. the traditional practice of clearing and then reassigning portions of the allocated spectrum is not a sustainable model as it is both time-consuming and expensive. however, spectrum sharing is possible in order to better utilize the spectrum and make current wireless systems more efficient. spectral underutilization can be enhanced by permitting a cognitive user to access a licensed band when it is idle. efficient spectrum utilization is the most challenging hurdle in the evolution of wireless communication systems and radio devices. cognitive radios (crs) have emerged as a solution through opportunistic spectrum sharing of spatially and temporally unused spectrum bands. this helps to improve spectral utilization by reusing the unused or underutilized spectrum owned by incumbent systems (primary systems). one of the most fundamental aspects of a cr radio is spectrum sensing as it enables a secondary user to detect the parts of a spectrum band that are currently underutilized and unutilized in real-time. spectrum sensing algorithms are used to obtain awareness about spectrum occupancy and the existence of primary users in a given spectrum band. this allows spectrum sharing and gives opportunistic access to unused spectrum and hence enhances spectrum utilization. use of spectrum sharing instead of exclusivity has created new opportunities for new technologies such as a smart grid communication network. ii. cognitive radio technology cr devices are intelligent and self-conscious devices that can observe and detect changing environmental conditions and adjust their operating parameters like power, frequency, coding and modulation techniques, according to the changing communication environment culminating in efficient utilization of available resources [1]. spectrum scarcity and inefficient spectrum utilization are some of the most challenging issues in wireless communications. cr provides an answer to the spectral dearth by enabling the opportunistic exploitation of frequency bands that are not densely occupied by licensed users. this allows secondary users to utilize them momentarily hence enhancing utilization. by enabling opportunistic spectrum access (osa), cr helps mitigate the spectrum scarcity issue by allowing secondary devices to establish the un-/underutilized sections of licensed spectrum and exploit them opportunistically as long as no harmful interference is caused to the legacy spectrum users’ communications. the provisionally unutilized parts of spectrum are referred to as spectrum white spaces (ws) or spectrum holes and they may exist in time, frequency, or space domains. in the context of osa, cr users are referred to as secondary users (sus) in contrast to the primary users (pus). crs enable vacant engineering, technology & applied science research vol. 8, no. 6, 2018, 3673-3680 3674 www.etasr.com kimani & njiraine: cognitive radio spectrum sensing mechanisms in tv white spaces: a survey spectrum detection and spectrum sharing for a more efficient spectrum utilization. iii. opportunistic spectrum access cr enables the interim exploitation of unused spectrum. this allows the coexistence of two different systems within the same frequency range: the primary system and the secondary system. the primary system refers to the licensed users that have exclusive rights to make use of the assigned spectrum. the secondary system is the unlicensed cr users that do not own any rights to the spectrum but can access the spectrum momentarily as long as it is not used by the primary system [2]. in case the licensed user requires to use the spectrum, the cr vacates to another spectrum hole or remains in the same band, but alters its parameters like the power level or modulation scheme to avoid interference [3, 4]. the main reasons for spectrum underutilization are: 1. the spectrum occupancy ratio is higher during the day than during the night. this leads to underutilization of spectrum especially at night. 2. the presence of guard bands in the spectrum intended to safeguard against adjacent channel interferences between neighboring channels especially in the analogue tv broadcasts. ieee 802.22, is a wireless standard designed to utilize cr for regional area networks in tv white spaces by enabling the sharing of geographically unused television spectrum while ensuring that no interference is occasioned to the licensed pus. pus in this case includes both analog and digital tv transmissions, and licensed low power devices such as wireless microphones [5]. iv. major functions of cognitive radio there are four main steps in the cognitive cycle: a. spectrum sensing this refers to the detection of the unused spectrum portions that can be exploited without causing harmful interference to other users [6]. it is a vital requirement for the sus to identify the spectrum holes and is usually the first step of the cognitive cycle. b. spectrum management it is the process of detecting the best available spectrum to meet the cognitive user communication requirements. keeping track of the next available frequency band allows the sus to hop between multiple frequency bands in response to time varying channel characteristics or in response to the reappearance of the pu while still maintaining acceptable quality of service (qos) requirements. the spectrum management functions are categorized as: • spectrum analysis: in spectrum analysis, spectrum sensing results are examined to evaluate the available spectrum. this involves measuring the quality of spectrum accessed by a su. this quality can be evaluated using the average correlation, signal to noise ratio (snr) and white spaces availability. • spectrum decision: before the opportunistic spectrum access occurs, a decision model should be adopted. the decision model provides guidance on the rules and priority mechanisms to be followed in spectrum accessing. the complexity of such a model is dependent on the parameters to be considered in the spectral analysis (transmission bandwidth, data rate, transmission mode, etc. [7]). when both sus and pus are present in the system, a preference mechanism is required in order to determine the priority of spectrum access. sus can be cooperative or noncooperative. in a cooperative environment, the secondary crs collaborate with each other, to make a collective decision regarding the vacancy of a given frequency band. in that case, a central controller coordinates the spectrum management process [7]. c. spectrum mobility: this refers to the changeover of operating frequency band of cr users from one spectrum hole to another. when a pu reappears in a radio channel which is currently in use by a su, the cognitive user has to change its frequency of operation. this switch in operating frequency band is referred to as spectrum handoff [8]. it ensures that the unlicensed su continues with uninterrupted data transmission even after switching to the new band [8] by occupying the best available spectrum hole in order to meet user communication requirements. d. spectrum sharing this refers to the provision of a fair spectrum scheduling algorithm among the different users. since there might be many different sus who want to exploit the available spectrum holes at any given time, cr has to enforce policy rules to maintain fair spectrum scheduling among the different cognitive and non-cognitive users in the radio environment with a view to creating a balance between the goals of efficient information exchange and of sharing the available spectrum [7]. although dynamic spectrum access is championed as a solution to the current static allocation of spectrum due to its flexibility and high spectrum utilization, spectrum sharing is still a major challenge in an open spectrum usage environment due to the existence of some greedy sus who might not want to cede spectrum to other cognitive users. it provides a balance and fair spectrum scheduling method between coexisting sus and pus [3]. v. spectrum sensing classification sensing algorithms can be classified into three major categories: transmitter detection, cooperative sensing and interference based sensing. transmitter detection techniques are further categorized into energy detection, matched filter detection and cyclostationary feature detection (figure 1). vi. spectrum sensing techniques a. transmitter detection spectrum sensing is the cornerstone of a successful cr based communication as it determines the occupancy status of a spectrum band by periodically sensing the target frequency band. once a cr has detected a spectrum hole in frequency, engineering, technology & applied science research vol. 8, no. 6, 2018, 3673-3680 3675 www.etasr.com kimani & njiraine: cognitive radio spectrum sensing mechanisms in tv white spaces: a survey space or time domain, it has to also determine the access method in terms of transmit power to employ and access duration in order to transmit without interfering with a licensed user’s transmission [6, 9]. fig. 1. classification of spectrum sensing techniques although there are various techniques for establishing the presence of a pu signal transmission, the most effective way is to sense spectrum holes by detecting active primary transceivers in the vicinity of the cognitive radios. this is referred to as transmitter detection and can broadly be categorized into three main groupings, depending on the type of information required for the sensing operation: • noise dependent detection: these detection algorithms only require information on noise properties and do not need to make any assumptions on the primary signal characteristics. they do not need any prior knowledge of the signal but they do need very accurate information on noise statistics in order to obtain reliable detection performance. 
 • feature detection: these detection algorithms require prior knowledge of both source signal and noise power characteristics. they then employ knowledge of the structural and statistical properties of pu signals to make a decision on the presence or absence of a source signal. • blind detection: these detection algorithms rely on statistical analysis to identify the properties of a signal. these detection mechanisms detect the primary signal by sensing the surrounding environment without requiring any preliminary information of the noise power or the source signal. 1) various transmitter detection techniques a) matched filter detection a matched filter (mf) is a linear filter that aims at maximizing the output snr for a given input signal. this is a detection method that relies on prior knowledge of the pu signal, e.g. the modulation scheme, the pulse shaping, and the packet format. using this information, a su can correlate the detected signal with a corresponding pu signal, and then sample the output to determine if the detected signal is the pu signal [10, 11]. mf operation can be equated to correlation whereby an undetermined signal is convolved with a filter whose impulse response is a mirror and time shifted version of a reference (pu) signal [10]. it is therefore a feature detection algorithm. mathematically, matched filter operation can be denoted as: ���� = ∑ ℎ�� − � �� �� ��� (1) where y(n) is the output of the matched filter, given that x(n) is the received signal and h(n) is the filter response. its block diagram is shown in figure 2. fig. 2. block diagram for mf detection b) energy detection this detection method requires no prior information of the pu signal. it is a non-coherent method that detects the primary signal solely based on the sensed energy. pu is detected based on the sensed energy where the received signal energy is computed and compared against a pre-defined threshold. if the measured value surpasses the threshold, then the received signal is deduced to be a pu signal, and the spectrum band is assumed to be occupied. else, the spectrum band is inferred to be idle [12]. energy detection (ed) is categorized as a noise dependent signal detector since it approximates the presence of a pu signal by comparing the sensed energy with a known threshold derived from the noise statistics [11, 13, 14]. mathematically, signal detection can be simplified to a simple identification problem, defined as a hypothesis test: ���� = ���� h0 (pu absent) (2) ���� = ℎ ∗ ���� + ���� h1 (pu present) (3) where s(n) is the signal transmitted by the pus, x(n) is the signal received by the su, w(n) is additive white gaussian noise (awgn), and h is the amplitude gain of the channel. the estimated energy of the received signal can be expressed mathematical as: ∑ |����|����� (4) the energy can now be compared to the threshold to check the true hypothesis by using: h1 if ∈ > � (5) h0 if ∈ < � (6) spectrum sensing transmitter detection interference temperature sensing transmitter interference sensing receiver interference sensing cooperative detection decentralized sensing centralized sensing coordinated sensing uncoordinated sensing blind detection covariance based detection eigen value based detection noise detection energy detection wavelets transforms feature detection waveform based detection cyclostationary detection matched filter detection band pass filter matched filter threshold comparator h0 = absence of user h1 = presence of user engineering, technology & applied science research vol. 8, no. 6, 2018, 3673-3680 3676 www.etasr.com kimani & njiraine: cognitive radio spectrum sensing mechanisms in tv white spaces: a survey the steps in an energy detector are illustrated in figure 3. fig. 3. energy detector block diagram c) cyclostationary feature detection cyclostationary feature detection capitalizes on the periodicity in the received primary signal to determine the presence of a pu. most of the transmitted signals from the pus usually have periodic patterns. these periodic patterns are known as cyclostationarity and are used to detect the presence of licensed users. the periodicity is usually found in sinusoidal carriers, pulse trains, spreading code, hopping sequences or cyclic prefixes of the primary signals which results in periodicity of their statistics like mean and auto correlation [11]. when the cyclic spectral density (csd) of such signals is computed, it helps in highlighting such periodicities. due to cyclostationarity, primary signals can easily be identified since the features of periodic statistics and spectral correlation, are normally absent in stationary noise and in interference. this helps in distinguishing pus from noise. thus, prior knowledge of the signal features is necessary in cyclostationary feature detection. this method detects even in very low snr as the cyclostationarity embedded in the pu signal is non-existent in noise [13]. cyclostationary detection can be illustrated as shown in figure 4. fig. 4. block diagram for cyclostationary feature detection a received signal x(t) is said to be cyclostationary if its mean and auto correlation shows periodicity as [15]: ���� + �� = ���!� (7) "��� + � ,$ + � � = "� ��,$� (8) where the period of mean and auto correlation is t0. if t and u are substituted in the autocorrelation equation with t+τ/2 and tτ/2, then: "��� + % 2,� − % 2⁄⁄ � = ∑"� ( �%�)*�+(! (9) where "� ( depicts the cyclic autocorrelation function (caf) and α symbolizes the cyclic frequency. cyclic frequency is assumed to be a known parameter to the receiver. caf is computed as: "� ∝�%� = lim0→� 2 0 3 "� 2 0⁄ �2 0⁄ �� + % 2⁄ , � − % 2⁄ �)�*�+(!4� (10) cyclic spectral density (csd) is obtained as: 5� ��6� = 3 "� (( �( �%�)�7�+3 84% (11) where "� ∝�%� is the cyclic autocorrelation function (caf). d) wavelet detection the wavelet based detection method uses wavelets to detect edges in the power spectral density (psd) of a wideband channel [16] as shown in figure 5. fig. 5. block diagram for wavelet based sensing this approach breaks down the wide spectrum into small non-overlapping sub-bands and tries to identify the variations in the power level in these sub bands. the breakdown is accomplished by using wavelet transform which identifies the edges in psd. these edges in psd mark the boundary between occupied bands and spectrum holes thus assist in identifying the vacant bands. when these edges of sub bands are detected, the powers between two edges can be estimated [17]. this helps in determining whether the band is occupied or not. using this information, cr users can ascertain spectrum holes and exploit them [18]. it is a flexible and low cost blind detection technique [19, 20]. e) covariance based sensing technique covariance based detection (cbd) utilizes covariance matrixes for detection since the statistical covariance matrixes of noise are quite different from the ones of a received signal. this property is therefore used to distinguish if a licensed pu is present or absent in a channel. this technique uses the correlative nature of a received signal, to compute the covariance matrix of the detected signal samples and then compares it with the covariance of noise to determine if a primary signal is present [19, 21]. autocorrelation can also be used to compute the thresholds in place of covariance [17]. this approach does not need any previous information of the primary signal and works well for highly correlated signals. it has a very high probability of differentiating between the signal and noise even at extremely low snr values. it also has very low power consumption. its main weaknesses are the increased complexity and the increased computational overhead. since it needs no prior information on the primary signal, it is referred to as a low power blind detection technique. its block diagram is shown in figure 6. fig. 6. block diagram for covariance based detection f) radio identification based sensing. in radio identification technique, several features such as modulation, transmission range, transmission frequency, etc., are extracted from the received signal and they are then used to decide the most appropriate technology for the cr transmission. this approach tries to detect the presence of some threshold comparison psd integrator band pass filter bpf correlation feature detection n point fft averaging over time t engineering, technology & applied science research vol. 8, no. 6, 2018, 3673-3680 3677 www.etasr.com kimani & njiraine: cognitive radio spectrum sensing mechanisms in tv white spaces: a survey known technology being used by the sensed primary signal such that if the technology used by the pu for transmission is known, then its spectrum characteristics can be inferred [17]. cr users can then use this information to alter their transmission parameters in order to achieve communication [18]. this detection method is highly accurate, is robust to snr and has average sensing time. however, it has high power consumption due to its high complexity. g) random hough transform based detection hough transform is a technique that is widely used for pattern detection in image processing [18]. random hough transform of the detected signal is used to search for the presence of radar pulses in the operating channels of wlan systems. if some patterns related to pus are identified, cr users can presume that a pu is using the spectrum while the spectrum will be assumed to be idle if patterns related to the primary signal are not identified. this technique is ideal for observing signals with periodic patterns [17]. h) eigenvalue based sensing technique in eigenvalue sensing, the pu signal is identified by calculating the eigenvalues of the covariance matrix of the received signal [19]. this method utilizes the received signal samples and requires no prior knowledge of the signal or the channel hence eliminating any need for synchronization. eigenvalue based sensing can be categorized into two main approaches: • maximum-minimum eigenvalue detection (mme): in this approach, the ratio of maximum to minimum eigenvalue is used to identify the primary signal by employing random matrix theories (rmt). this ratio is then quantized to find the threshold value. • energy with minimum eigenvalue (eme) based detection: in eme, detection is carried out using the ratio of the signal energy to the minimum eigenvalue. eme compares the received signal energy with the minimum eigenvalues of the sample covariance matrix of the received signal. i) waveform-based detection this method takes advantage of the fact that known patterns are usually employed in wireless networks for synchronization purposes. such patterns corresponding to the signal, such as preambles, mid-ambles, regularly transmitted pilot patterns and spreading sequences are utilized to detect the signal presence. preambles are sets of patterns that are transmitted just before the start of the data transmission sequence whereas mid-ambles are transmitted in the median of the data sequence. these patterns are mostly used for synchronization purposes. therefore, if a known pattern of the signal is present, this detection method can be applied by correlating the received signal with a known copy of itself [18, 22]. the longer the length of these known patterns, the more accurate the detection. this is therefore a feature detection algorithm. for a received signal y(n)=s(n)+w(n), the waveform based sensing can be expressed as: μ = :);∑ <����′������2 > (12) in absence of a pu, the waveform based detection can be represented as: μ = :);∑ �����′������2 > (13) in presence of a pu, (13) becomes: μ = ∑ |����|����2 + :);∑ �����′��� � ��2 > (14) the presence or absence of a pu is determined by comparison of the decision metric m against a threshold value λw as shown in figure 7. fig. 7. block diagram for waveform based sensing 2) comparison of spectrum sensing techniques ed based spectrum sensing is the most popular spectrum sensing algorithm due to its low computation and implementation complexity. it requires no prior information of the pu signal resulting in short sensing time. its main disadvantage however, is that it does not work very well in low snr conditions which at times results in high probability of false alarm and miss-detection[11, 23]. mf detection on the other hand, has a very small observation period since a high processing gain can be achieved by coherent detection. its major drawback however, is that each cr requires a dedicated receiver for every pu class and prior knowledge of the pus' signal [24]. cyclostationary feature detection is an effective spectrum sensing technique for the detection of very weak signals in the background of noise. its major drawback however is that it has high computational complexity and it requires a long sensing time due to the longer observation time needed in order to identify the periodic patterns [11]. wavelet transform detection method requires high sampling rate. this results in high complexity and power consumption. waveformbased detection is highly robust, due to coherent processing that arises from utilizing deterministic signal components. its main drawback, however, is that it requires prior information of the pu signals and is susceptible to synchronization errors. 3) challenges of spectrum sensing a) hidden node problem due to the effects of multipath fading and shadowing, a cr user can at times not be able to differentiate between a deeply faded and an idle band. this can lead to what is commonly known as the hidden primary user problem. this is experienced when a su scans for a transmitting pu but cannot correctly predict its presence. cr devices then transmit causing undesired interference to the pu as the primary transmitter’s signal could not be correctly detected. cooperative sensing has been proposed as a means to deal with the hidden primary user problem [25]. b) sensing period since pus have a right to claim their frequency bands at any time, even while being used by the cognitive users, it is paramount that sensing to be carried out as often as possible to engineering, technology & applied science research vol. 8, no. 6, 2018, 3673-3680 3678 www.etasr.com kimani & njiraine: cognitive radio spectrum sensing mechanisms in tv white spaces: a survey prevent any possible interference to the pus. cr users should therefore be able to identify the reappearance of pus as soon as they reappear and vacate the band immediately. in order to do this, sensing algorithms should have a short but frequent sensing time period in order to avoid co-channel interference. this condition presents a constraint on the quality of sensing (qos) performance of a sensing algorithm since cr users must frequently interrupt their data transmissions in order to perform spectrum sensing. consequently, the selection of sensing parameters is constrained as there must be a continuous tradeoff between the sensing period duration and the reliability of sensing. c) primary user emulation attacks in a cognitive radio network, a selfish or greedy su can mask its air interface to resemble that of a pu in order to gain advantage over other cognitive radio users in what is known as a pu emulation (pue) attack. this can lead to misleading spectrum sensing results at the expense of legitimate sus. a solution is to maintain a database of all pus together with a signature public key encryption value for validating pu transmissions. this will prevent malicious cognitive users from masquerading as pus. legitimate pus would then be required to transmit their transmission together with the encrypted signature value. d) spread spectrum sensing some pus employ spread spectrum signaling which is very hard to sense as the signal power is dispersed over a wide frequency range although the actual information bandwidth maybe much narrower. this can be eliminated if the hopping pattern is known so that precise synchronization to the signal is achieved. it can also be solved by using uwb sensing techniques. e) receiver uncertainty problem in transmitter detection mechanisms, cr users are only concerned with information about the primary transmitter but have zero information about the primary receiver. a cognitive radio may therefore be located outside the transmitting range of a pu transmitter but is within a radius of a primary receiver receiving information from the pu. since it does not sense the presence of any transmitter, it might cause interference to the primary receiver if it tries to transmit. this may lead to interference and is known as the receiver uncertainty problem. a solution to this would be to exploit the local oscillator (lo) leakage power emitted from the rf front-end of the primary receiver to sense it. however, the lo leakage signal is in most cases noted to be very weak [22, 26, 27]. b. cooperative sensing individual node sensing is in most cases not sufficiently accurate for sensing the pu signal, due to fading, shadowing, and receiver uncertainty [28]. however, using cooperative sensing, sus can take advantage of the spatial diversity of each user to co-operate and share the collected sensing information so that the chances of incorrect detection are minimized. cooperative sensing is employed to improve the detection accuracy of transmitter detection mechanisms through cooperation among sus on spectrum sensing thereby providing a solution to most issues that come about in spectrum sensing due to noise uncertainty, fading, and shadowing [29, 30]. it also lowers the probabilities of false alarm and misdetection considerably. additionally, cooperation can help eliminate the hidden pu problem, hence decreasing sensing time. results have indicated that collaborative sensing results in significantly higher spectrum capacity gains when compared to local sensing. this happens mainly because, in individual node sensing, the cr acts without any information about the pus position, hence degrading its sensing performance. however, in collaborative spectrum sensing, each of the collaborating crs observes its own independent fading or shadowing and then these results are combined to paint a better picture of the presence of the pus. in order to coordinate the collaboration in cooperative sensing architectures, a control channel is required. the control channel can either be implemented using a dedicated band, an unlicensed band e.g. ism, or an underlay system e.g. ultra-wide band (uwb). the control channel can either be used to share the results of spectrum sensing or for sharing information about the channel allocation amongst the cognitive users [31]. the biggest weakness of cooperative sensing is its augmented delay since data has to be collected from all the cooperating nodes before a decision is made. cooperation can be executed in two ways: centralized or distributed. 1) centralized sensing in this kind of cooperation, a central unit called fusion center collects sensing data from the sensing cognitive nodes, identifies an available spectrum hole, and broadcasts this information to the other crs or uses this information to directly control cr traffic. figure 8 shows how centralized sensing operates. fig. 8. centralized sensing there are two main approaches in centralized sensing. a) data fusion with this approach, all sus send their entire raw sensing data, to the fusion center. cr users only collect the information but do not make any decision. it is the fusion center that determines the band status based on the sensing data received. sensing data includes the received signal power and the gps. a drawback associated with this approach is that, in case of a huge number of cr devices, the bandwidth required for reporting is very large. data fusion is also referred to as soft combining. b) decision fusion. with this approach, each cr user processes its sensing data engineering, technology & applied science research vol. 8, no. 6, 2018, 3673-3680 3679 www.etasr.com kimani & njiraine: cognitive radio spectrum sensing mechanisms in tv white spaces: a survey locally and makes a decision on the absence or presence of a pu. this decision is then relayed to the fusion center in form of binary data indicating the band status. the fusion center makes a final decision based on the received decisions from the individual cr users. the decision is done through a voting scheme. this approach requires less overhead than the data fusion approach as it does not send the entire sensed data to the fusion center. 2) distributed sensing in distributed cooperative sensing, individual cognitive nodes share sensing data amongst themselves but make individual decisions regarding which spectrum band to use. distributed sensing scheme is considered superior to centralized sensing as it does not need the deployment of a large-scale infrastructure thus has reduced deployment cost. there are two main approaches in distributed sensing. a) distributed coordinated techniques in this type of coordination neighboring sus exchange local sensing results. after receiving the sensing results from the others, a su can make its own judgment regarding the status of a spectrum band, basing it on its own sensing results and the data received from the other sus using a local criterion and without having the need of a controller (figure 9). fig. 9. distributed coordinated sensing b) distributed uncoordinated technique in some cases, a cognitive user may be adequately able to sense vacant bands but has a very weak reporting channel to the fusion center while another cognitive user within the same user’s vicinity has a weak ability to sense vacant channels but a strong reporting channel. in such an instance, both nodes can cooperate: when one senses the vacant, it sends its decision to the neighboring cognitive user which then transmits the information to the fusion center. therefore, the su behaves like a relay and the approach becomes a multiple-hop scheme. this technique is thus usually referred to as relay assisted cooperative sensing [32, 33] as shown in figure 10. c. interference based detection interference based detection works like a spectrum underlay (uwb) technology, where sus coexist and transmit simultaneously in the same spectrum band with pus but only transmit at extremely low power as determined by the interference temperature level in order to curtail any harmful interference to the pus [32]. there are two main approaches to interference based detection. fig. 10. distributed uncoordinated sensing 1) primary receiver detection in communications, whenever a receiver is receiving data from a transmitter, it usually emits a leakage power from its rf front end. the leakage power is referred to as lo leakage power. it is this leakage power that is exploited to find a pu signal by installing a low cost sensor node close to a pu’s receiver. the sensor then reports the sensed lo leakage power emitted by a given rf front end of the pu’s receiver within the communication range of a cr [34]. 2) interference temperature management this approach aims at measuring the interference at the receiver. it does this by setting an upper interference limit for a particular frequency band in specific geographic locations such that cr users are prohibited from causing harmful interference while using the specific band in a given area. usually, cr transmitters regulate their interference by regulating their out of band emissions (transmission power) based on their positions with respect to pus [6, 34]. thus, cr users do not carry out spectrum sensing. they transmit concurrently with the pus as long as they are within the specified preset power mask. they can never at any time relay their data with higher power than the preset power even if any pu is absent as they are prohibited to do so. accordingly, cr users are required to at all times be aware of the location and corresponding upper level of allowed transmit power levels so as to never interfere with the pu transmissions [6]. vii. conclusion current spectrum licensing policy has led to most of the spectrum being assigned to various services. recent technological developments have led to the development of many new wireless services. these new services require spectrum but were never factored in when the spectrum was first allocated. the spectrum policy is therefore not in tandem with the current needs. since spectrum is a fixed resource, a solution must be found to accommodate the new and emerging services within the existing spectrum. studies showed that most of the allocated spectrum is actually underutilized. cr has emerged as an alternative to exploit the underutilized spectrum more efficiently by enabling opportunistic spectrum usage. it has recently received widespread research interest. the cr approach is based on the cardinal rule of being able to correctly sense the available spectrum opportunities. this paper focused on various spectrum sensing mechanisms used by crs. the dynamic spectrum nature of engineering, technology & applied science research vol. 8, no. 6, 2018, 3673-3680 3680 www.etasr.com kimani & njiraine: cognitive radio spectrum sensing mechanisms in tv white spaces: a survey crs, where they access different frequency bands, anytime and anywhere, requires particular attention as it helps in spectrum sharing amongst primary and secondary users, thus ensuring there is efficient utilization of all available spectrum. the dynamic spectrum access solves some problems like spectrum scarcity, allowing the exploitation of new opportunities, but on the other hand creates new challenges for spectrum sensing. analysis showed that there is no perfect sensing mechanism and selecting the best one to use is a delicate process involving tradeoffs between specific requirements. due to the large range of frequency bands that needs to be explored and sensed to find spectrum holes, cr signal processors need to be faster, more accurate and robust while consuming low power in order to improve the battery life of cognitive devices. references [1] s. s. somawanshi, g. a.varade, j. m. mhase, “cognitive radio: an intelligent wireless communication system”, international journal of innovative research in science, engineering and technology, vol. 5, no. 3, pp. 3820-3828, 2016 [2] p. yadav, 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civil engineering research group, faculty of civil engineering, ton duc thang university, vietnam phantoanhvu@tdtu.edu.vn (corresponding author) received: 5 april 2023 | revised: 17 april 2023 | accepted: 21 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5915 abstract this study performed an experimental investigation of asphalt concrete with and without fiberglass geogrid reinforcement, using specimens in the laboratory and in situ. a 100kn/m fiberglass geogrid was used. the results showed that with the fiberglass geogrid reinforcement, the flexural strength of the asphalt increased by 24.82%, deformation was significantly reduced, and the elastic modulus did not improve significantly. in addition, using the hamburg wheel tracker test, the fiberglass geogrid reinforced asphalt samples had a 7.41%reduced rutting depth. finally, two segments in situ were also tested showing that the flexural strength of asphalt concrete increased by 24.27% and the structural strength of the pavement increased by 25.24%. these results show that pavement structures are significantly improved when reinforced with fiberglass geogrid. keywords-asphalt pavement; fiberglass geogrid; flexural strength; elastic modulus; hamburg wheel tracker i. introduction asphalt pavement, or flexible pavement, is widely used worldwide due to its excellent characteristics, such as favorable construction conditions, comfortable exploitation, and convenient maintenance [1]. in summary, asphalt pavement is popularly used as hot mix asphalt (hma), containing a mixture of approximately 94-95% stone, sand, filler, and 5-6% bitumen. the asphalt mixture is heated, mixed properly, placed on the base and subbase layer, compacted using a heavy roller, ready to be used when it cools. there are one or more hma layers for the surface course to design flexible pavement. the asphalt pavement is significantly affected by heavy traffic loading and seasonal temperatures. many types of damage, such as rutting, cracking, and raveling [2-3], occur on asphalt pavements. due to its importance, researchers and material experts try to find the best way to improve pavement rehabilitation with low cost and low use of raw materials. in general, to renovate an old road pavement, an overlay layer is usually paved over the existing surface to cover the existing cracked layers. however, the disadvantage of this method is sustained by the crack propagation of the current layer, which is known to be complex. with the recent development of new technologies and materials, geogrids are applied to reinforce asphalt pavements to improve stiffness, stability, and service life and reduce the thickness of additional pavement layers resulting in material and cost savings [4-14]. the mechanical properties of asphalt pavements are significantly affected by the properties and positioning of geogrids, the stiffness of the asphalt layer, the characteristics of the subgrade, the aggregate base course, and the hma [4-6, 8, 15]. in [15], it was shown that a higher-strength geogrid is more effective in improving asphalt pavement. for rehabilitation, geogrid can be used as an effective method to counteract the reflective crack of the existing surface [16]. in addition, the geogrid improves the flexible pavement in two ways, by reducing the surface rutting potential and by decreasing the base course [4]. this study aims to investigate the properties of glass geogrid-reinforced asphalt pavement in the laboratory and in situ. specimens were prepared by a semi-automatic roller compactor. the geogrid used was commercial fiberglass with a tensile strength of more than 100kn/m provided by a local company. flexural strength, elastic modulus, and hamburg wheel tracking tests were conducted in the laboratory. in addition, geogrid reinforcement was applied in situ to investigate the current situation, construction technology, resilient modulus, compacted asphalt layer, and flexural strength from boreholes. the results obtained provide guidelines for researchers, engineers, and designers in improving the method of designing reinforced asphalt pavements with fiberglass geogrid. engineering, technology & applied science research vol. 13, no. 3, 2023, 10791-10796 10792 www.etasr.com nguyen & phan: experimental performance of fiberglass geogrid in asphalt pavements ii. materials and methods a. asphalt concrete figure 1 shows the grain size distribution of the aggregate mix, which followed the requirements of tcvn 8819 [17]. a bitumen 60/70 grade was applied, which satisfied the current vietnamese standard. the mineral filler had a grain size less than 0.071mm and 2.731g/cm 3 specific gravity. table i shows the basic properties of the asphalt concrete. fig. 1. grain size distribution of the aggregates. table i. basic properties of asphalt concrete no characteristics unit results requirement 1 bitumen content % 5.32 2 compressive strength kn/cm 2 t = 20 0 c 51.44 t = 50 0 c 21.54 3 marshall stability kn 11.96 8.0 4 flow measurement mm 3.62 2-4 5 voids in the total mix % 4.42 3-6 6 voids in mineral aggregates % 16.70 min 15 b. fiberglass geogrid the fiberglass geogrid used is shown in figure 2 and had 100kn/m tensile strength. table ii shows its mechanical properties provided by the manufacturer. table ii. properties of fiberglass geogrid n o properties method unit result 1 tensile strength (md) astm d6637 kn/m ≥ 100 2 tensile strength (cmd) astm d6637 kn/m ≥ 100 3 elongation (md) astm d6637 % ≤ 3 4 elongation (cmd) astm d6637 % ≤ 3 5 coating with asphalt visual 6 color black md is machine direction, cmd is the cross-machine direction fig. 2. fiberglass geogrid used. c. sample preparation figure 3 shows the asphalt samples with and without fiberglass geogrid reinforcement. (a) (b) (c) (d) fig. 3. sample with different dimensions: (a, b) 320×260×80mm for flexural strength and wheel tracking tests; (c, d) 320×260×101.6 mm for elastic modulus test. specimens with dimensions of 320×260×80mm, denoted by m1, were prepared for flexural strength and wheel tracking tests. similarly, specimens with dimensions of 320×260×101.6mm were prepared for the elastic modulus test, denoted by m2. the specimens were compacted by a semiautomatic roller compactor syd 0703 with a 500mm wheel radius and a width of 300mm. the highest compaction pressure was 30kn/cm 2 , the roller compaction cycle was at least 12 times/1 minute, using a fully heated roller compactor plate. 320 asphalt concrete, 30mm tack coat 0.5 kg/m2 5 0 2 8 asphalt concrete, 50mm steel plate, 28mm 3 0 320 3 0 5 0 2 8 asphalt concrete, 30mm fiberglass geogrid asphalt concrete, 50mm steel plate, 28mm 320 4 0 .6 4 8 asphalt concrete, 60.96mm tack coat 0.5 kg/m2 asphalt concrete, 40.64mm steel plate, 8mm 6 0 .9 6 fiberglass geogrid 320 6 0 .9 6 4 0 .6 4 8 asphalt concrete, 60.96mm asphalt concrete, 40.64mm steel plate, 8mm engineering, technology & applied science research vol. 13, no. 3, 2023, 10791-10796 10793 www.etasr.com nguyen & phan: experimental performance of fiberglass geogrid in asphalt pavements subsequently, each specimen was cut into 5 small specimens with dimensions of 50×50×200mm for flexural strength, and dh=101.6101.6mm for elastic modulus tests. the temperatures used were 15, 30, and 50c for flexural strength, elastic modulus, and wheel tracking tests, respectively. the repeated loading was performed with a frequency of 25±2.5 cycles per minute and a pressure of 0.7mpa. iii. results and discussion a. flexural strength table iii shows the test results for the flexural strength of asphalt concrete samples with (mgc) and without fiberglass geogrid reinforcement (mkgc). figure 4 shows that the flexural strength values of the asphalt concrete with and without fiberglass geogrid reinforcement were 2.48 and 3.08mpa, respectively, indicating an increase of 24.82%. this can be explained as follows: at a temperature of 15c, the asphalt concrete becomes hard under the influence of loading, which causes cracks and destruction. the fiberglass geogrid in asphalt concrete samples absorbs part of the load and distributes it over a larger area. on the other hand, the tensile strength of the fiberglass geogrid-reinforced asphalt is higher, slowing down the deformation and failure of the sample. therefore, asphalt concrete samples with fiberglass geogrid reinforcement have higher tensile strength when bending than the unreinforced ones. table iii. flexural strength of asphalt concrete with and without fiberglass geogrid n o s a m p le dimension (mm) d e fo r m a ti o n (m m ) f le x u r a l st r e n g th ( m p a ) a v e r a g e st r e n g th ( m p a ) a v e r a g e d e fo r m a ti o n (m m ) w id e l e n g th h e ig h t 1 mkgc 1 53.0 200 54.7 1.67 2.5 2.5 1.66 2 mkgc 2 54.0 200 54.0 1.6 2.2 3 mkgc 3 53.3 200 54.7 1.7 2.6 4 mkgc 4 51.7 200 54.3 1.58 2.5 5 mkgc 5 51.3 200 55.7 1.75 2.5 6 mgc 1 50.0 200 54.0 2.29 3.2 3.1 2.29 7 mgc 2 50.7 200 55.3 2.3 3.2 8 mgc 3 53.3 200 55.3 2.32 3.2 9 mgc 4 54.7 200 54.7 2.22 2.9 10 mgc 5 51.0 200 55.7 2.32 2.9 as shown in figure 5, asphalt concrete samples without fiberglass geogrid reinforcement had a lower deflection than the reinforced ones when subjected to maximum load. the average deflection of the unreinforced samples was 1.66mm, while the average of the reinforced samples was 2.29mm, an increase of 37.89%. this can be explained by the fact that the fiberglass geogrid participates in the bending along with the asphalt concrete, thereby increasing the deflection of the sample. this means that the failure of the reinforced samples will take place more slowly, reducing the cracks in the concrete. in [18], it was shown that the flexural behavior of various geogrids (e.g. fiberglass, polyester, and geomembrane geogrids) had a significantly improved resistance to cyclic loading from 66 to 100%. fig. 4. flexural strength of asphalt concrete. fig. 5. deformation of asphalt concrete. b. elastic modulus table iv shows the elastic modulus of asphalt concrete samples with and without fiberglass geogrid reinforcement. these results show that the average elastic modulus of the samples reinforced with fiberglass geogrid increased from 508 to 521mpa, an increase of 2.6%. overall, the elastic modulus of fiberglass geogrid-reinforced samples did not change significantly. the explained is that when the samples were compressed, the area of the presser was equal to the contact area of the sample and the glass geogrid, so the influence of the fiberglass geogrid in this experiment was not significant. however, the results of this experiment do not accurately reflect the ability to increase the elastic modulus of the asphalt sample because the sample was small, so there are only one or two grid cells in the sample. c. hamburg wheel tracker (hwt) test the hwt test was conducted to investigate the rutting potential of asphalt concrete. the specimens were conditioned at a temperature of less than 25c and the test conditions included water of 50c and 15.000 cycles. figures 6 and 7 show the results for both types of specimens at various positions (left, right, and average). the horizontal axis is the cross of the wheel passing the specimen, and the vertical axis is the depth of the specimen. for normal asphalt concrete, the rutting depth was 7.26mm, 5.50mm, and 6.38mm for left, right, and average, respectively. for fiberglass geogrid reinforced engineering, technology & applied science research vol. 13, no. 3, 2023, 10791-10796 10794 www.etasr.com nguyen & phan: experimental performance of fiberglass geogrid in asphalt pavements asphalt concrete, the rutting depth was 6.76mm, 5.12mm, and 5.94mm for left, right, and average, respectively. table iv. elastic modulus of asphalt concrete with and without glass geogrid n o s a m p le dimension (mm) p r e ss u r e ( m p a ) d e fo r m a ti o n (m m ) e la st ic m o d u lu s (m p a ) a v e r a g e ( m p a ) h e ig h t d ia m e te r 1 mkgc 1 104.0 101.6 0.5 0.100 520.0 508 2 mkgc 2 104.0 101.7 0.5 0.103 507.3 3 mkgc 3 104.0 101.7 0.5 0.105 495.2 4 mgc 1 104.2 101.7 0.5 0.098 534.4 521 5 mgc 2 104.1 101.6 0.5 0.100 520.5 6 mgc 3 104.2 101.5 0.5 0.103 508.3 for asphalt concrete samples reinforced with fiberglass geogrid, the depth of the wheel track was reduced by 7.41% compared to those without reinforcement. when the number of cycles increased to 8000, the average settlement of the two samples was almost the same (mgc: 4.25mm and mkgc: 4.47mm). at this point, the resistance against the wheel track was taken by the asphalt concrete. furthermore, increasing the number of load cycles from 8000 to 15000 times, the mgc settlement increased on average from 4.25 to 5.94mm and the mkgc increased from 4.47 to 6.93 on average, showing that the reinforced concrete samples had less settlement. when the asphalt concrete samples were loaded vertically and the application time was continuously increased, the wheel pressure would be transmitted from layer 2 (thickness 30mm) to layer 1 (thickness 50mm). for the unreinforced concrete samples, this settlement was to assess the resistance of concrete to wheel load. regarding the reinforced concrete samples, when the load transmitted through concrete layer 2 (thickness: 30cm) and meets the glass fiber mesh, the mesh would receive and redistribute the load evenly throughout the sample surface, leading to a reduction in the load. the pressure was transmitted to layer 1 of asphalt concrete, thereby reducing the depth of the wheel track. however, this decrease in rutting depth was not significant, approximately 7.41%. in the same way, in [12], it was concluded that geogrid reinforcement reduced the horizontal movement of the granular material, especially in the longitudinal direction. d. evaluation of applying fiberglass geogrid in situ this study selected two segments in the kien giang province, southern vietnam, to investigate the potential of using fiberglass geogrid reinforcement in road construction in situ. two damaged road sections, with reflection cracks and turtle shells, on tran khanh du street, including 100m from km 15+660 to km15+760 and 100m from km 15+760 to km 15+860 located in the territory of rach gia city, were selected. this route is densely populated. the road surface is degraded, damaged, and deformed, and the width of the road is not uniform, making it difficult for people and vehicles to travel. therefore, repairing the existing road surface by reinforcing the asphalt concrete pavement and unifying the width of the road surface was an important issue. after improvement, the road would be smooth and continuous, develop a complete transport network, create favorable conditions for people to travel, and promote commercial activities, tourism services, and industrial development. fig. 6. hwt tests without fiberglass geogrid reinforcement. fig. 7. hwt test with fiberglass geogrid reinforcement. some specific steps were followed to improve the current pavement surface, such as blowing dust to clean the existing road surface, applying the tack coat, placing the hot mix asphalt compensation layer, installing the fiberglass geogrid, placing the hot mix asphalt, and compacting the asphalt pavement. similarly, a reference segment was also investigated without installing a fiberglass geogrid. after finishing the pavement improvement, the engineering properties of the asphalt concrete were investigated. the elastic modulus was measured by the benkelman apparatus. the specimens were cut off from the site and prepared to test their flexural strength. after the construction was completed, the street was put into operation for some time. laboratory experiments were carried out to evaluate the quality and the technical efficiency of the fiberglass geogrid reinforcement on the asphalt pavement. engineering, technology & applied science research vol. 13, no. 3, 2023, 10791-10796 10795 www.etasr.com nguyen & phan: experimental performance of fiberglass geogrid in asphalt pavements table v. elastic modulus of fiberglass geogrid reinforced asphalt pavement s e g m e n t s ta ti o n d e fo r m a ti o n (0 .0 1 m m ) e la st ic m o d u lu s (m p a ) c h a r a c te r is ti c d e fl e c ti o n ( 0 .0 1 m m ) c h a r a c te r is ti c e la st ic m o d u lu s (m p a ) k m 1 5 + 7 6 0 k m 1 5 + 8 6 0 km15+760 63.9 200.1 75.8 168.7 km15+765 68.2 187.6 km15+770 63.9 200.1 km15+775 68.2 187.6 km15+780 72.5 176.6 km15+785 59.7 214.4 km15+790 68.2 187.6 km15+795 59.7 214.4 km15+800 68.2 187.6 km15+805 72.5 176.6 km15+810 72.5 176.6 km15+815 63.9 200.1 km15+820 68.2 187.6 km15+825 63.9 200.1 km15+830 68.2 187.6 km15+835 72.5 176.6 km15+840 68.2 187.6 km15+845 68.2 187.6 km15+850 63.9 200.1 km15+855 72.5 176.6 table vi. elastic modulus of normal asphalt pavement s e g m e n t s ta ti o n d e fo r m a ti o n (0 .0 1 m m ) e la st ic m o d u lu s (m p a ) c h a r a c te r is ti c d e fl e c ti o n ( 0 .0 1 m m ) c h a r a c te r is ti c e la st ic m o d u lu s (m p a ) k m 1 5 + 6 6 0 k m 1 5 + 7 6 0 km15+660 85.2 150.1 95.0 134.7 km15+665 89.5 142.9 km15+670 81.0 158.0 km15+675 85.2 150.1 km15+680 89.5 142.9 km15+685 89.5 142.9 km15+690 85.2 150.1 km15+695 76.7 166.8 km15+700 81.0 158.0 km15+705 85.2 150.1 km15+710 76.7 166.8 km15+715 85.2 150.1 km15+720 85.2 150.1 km15+725 81.0 158.0 km15+730 81.0 158.0 km15+735 89.5 142.9 km15+740 89.5 142.9 km15+745 85.2 150.1 km15+750 81.0 158.0 at first, the specimen without reinforcement was tested, and the results showed that the degree of compaction was equal to or greater than 0.98 which is compatible with the requirements of the vietnamese standards. the benkelman test in situ indicated that when using geogrid, the strength of the pavement structure increased from 134.7mpa to 168.7mpa, an increase of 25.24%, as shown in tables v and vi. this shows the technical efficiency of re-enforcing the asphalt concrete pavement with fiberglass geogrid. it is noted that the current elastic modulus of the surface pavement was about 120mpa. the obtained experimental results show that the average flexural strength of the asphalt concrete reinforced with fiberglass geogrid increased from 2.39 to 2.97mpa, an increase of 24.27%. figure 8 shows the detailed results and proves the technical efficiency of the reinforced asphalt concrete pavement with fiberglass geogrid. this increased flexural strength means that the crack resistance of asphalt pavement improved. fig. 8. flexural strength obtained in situ. iv. conclusion the following conclusions can be drawn based on the results obtained in the laboratory and in situ:  the flexural strength of asphalt concrete reinforced with fiberglass geogrid and without it was 2.48 and 3.08mpa, respectively, an increase of 24.82%. the deflection, when subjected to the maximum load of the fiberglass geogrid reinforced asphalt concrete increased by 37.89% compared to the unreinforced because the fiberglass geogrid participates in bending together with the concrete, thereby increasing deflection. this means that the failure process of the samples reinforced with fiberglass geogrid takes place more slowly and reduces the cracks in the asphalt concrete.  the elastic modulus of the samples reinforced with fiberglass geogrid did not change significantly, because when the sample was compressed, the area of the presser was equal to the contact area of the sample, as well as the fiberglass geogrid. therefore, the influence of the fiberglass geogrid was not significant. however, the results of this experiment do not reflect the ability to increase the elastic modulus of the asphalt sample because the sample was small.  the average rutting depth of asphalt concrete without and with a fiberglass geogrid was 6.38 and 5.94mm, respectively. the rutting depth of fiberglass geogrid reinforced asphalt concrete was reduced by 7.41%. the engineering, technology & applied science research vol. 13, no. 3, 2023, 10791-10796 10796 www.etasr.com nguyen & phan: experimental performance of fiberglass geogrid in asphalt pavements results also show that the resistance to rutting of the fiberglass geogrid reinforced asphalt concrete sample improved.  when reinforcing asphalt concrete pavement with fiberglass geogrid in the studied segment, the flexural strength of the asphalt concrete increased by 24.27%, and the structural strength of the pavement increased by 25.24%. these results show that the pavement structure was greatly improved when reinforced with a fiberglass geogrid. references [1] s. s. kar, m. n. nagabhushana, and p. k. jain, "performance of hot bituminous mixes admixed with blended synthetic fibers," international journal of pavement research and technology, vol. 12, no. 4, pp. 370– 379, jul. 2019, 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[18] a. virgili, f. canestrari, a. grilli, and f. a. santagata, "repeated load test on bituminous systems reinforced by geosynthetics," geotextiles and geomembranes, vol. 27, no. 3, pp. 187–195, jun. 2009, https://doi.org/ 10.1016/j.geotexmem.2008.11.004. microsoft word etasr_v11_n2_pp6965-6969 engineering, technology & applied science research vol. 11, no. 2, 2021, 6965-6969 6965 www.etasr.com fayssal et al.: performance improvement for medical image transmission systems using turbo-trellis … performance improvement for medical image transmission systems using turbo-trellis coded modulation (ttcm) menezla fayssal department of technology and science, nour bachir university center of el-bayadh, algeria and lepo laboratory, djillali liabès university, algeria menezla@yahoo.fr mahdjoub zoubir lepo laboratory djillali liabès university sidi bel-abbès. algeria z.mahdjoub@yahoo.fr bendelhoum mohammed sofiane department of technology and science nour bachir university center of el-bayadhel-bayadh el-bayadh, algeria bendelhoum_med@yahoo.fr mohamed reda lahcene department of technology and science nour bachir university center of el-bayadhel-bayadh el-bayadh, algeria lahcenereda1@gmail.com abdelhalim zerroug sonatrach oil and gas company algeria eloual@yahoo.fr abstract-digital images have become an essential working tool in several areas such as the medical field, the satellite and astronomical field, film production, etc. the efficiency of a transmission system to exchange digital images is crucial to allow better and accurate reception. generally, transmitted images are infected with noise. in the medical field, this noise makes the process of diagnosing difficult. to eliminate the transmission errors, an error correcting code (ecc) can be used with the aim to guarantee excellent reception of the images and allowing a good diagnosis. in this paper, source and channel encoding/ decoding functions are studied during medical image transmission (lung). at first, the turbo-code (tc) is used as ecc and subsequently the turbo-trellis coded modulation (ttcm). the simulation results represent the curves giving the bit error rate (ber) as a function of the signal to noise ratio (eb/n0). in order to compare these two systems properly, the mssim (mean structural similarity) parameter was used. the obtained results showed the effect and importance of ecc on the transmission of medical images using ttcm which gave better results compared to tc with regard to increasing the performance of the transmission system by eliminating transmission noise. keywords-channel coding; turbo-codes; ttcm; mssim; medical image i. introduction given their importance and their massive use, digital images have become an essential mean of communication. medical images are widely used as a diagnostic tool and in biomedical research [1]. sometimes it is necessary to transmit such images to distant doctors to have their opinions/diagnosis. the transmitted images are very sensitive to transmission errors, so it is very important to protect them against transmission noise in order to have on reception a sharp and clear image identical to the original one, allowing doctors to make a good diagnosis. as a solution to the noise problem, error correcting code (ecc) can be added to the medical image transmission chain in order to eliminate the effect of noise during transmission. such codes are: block codes, convolutional codes, ldpc codes [2], turbo-code (tc) and turbo-trellis coded modulation (ttcm). tc and ecc allow approaching the theoretical limit of correction predicted by shannon more than 60 years ago [3-5]. more recently, a new family of eccs, the ttcm [6, 7], was introduced. in this article, we first explain the basic principles of tc and ttcm, then we will propose the model of our digital image transmission chain, in which we will transmit a medical image of a lung, using tc and ttcm in order to make a comparison between the two systems and propose the best solution for noisy transmissions. to evaluate our simulation results, additively to ber and signal to noise ratio (eb/n0) parameters, we will use the mssim (mean structural similarity) parameter to see and analyze the results in a subjective and objective way. the image [8] used in this article shows infected lungs with the corona virus. corresponding author: menezla fayssal engineering, technology & applied science research vol. 11, no. 2, 2021, 6965-6969 6966 www.etasr.com fayssal et al.: performance improvement for medical image transmission systems using turbo-trellis … ii. turbo-code the tc corrects error produced by transmission noise. this code, invented and presented by claude-berrou [4], is obtained by concatenation of two or more eccs of low complexity [5], allowing to approach the theoretical limit of correction. their decoding uses an iterative (or turbo) process. in the principal plan of tc [9] the input binary message of length k is encoded in its natural order and in a permuted order, by two coders called c1 and c2. the two elementary coders are identical, but this is not necessary. in our example, the performance of the natural encoding, without punching is 1/3, for each source bit (dk) three bits (x, y1, y2) are sent on the channel [7]. turbodecoding is carried out according to the principle of iterative decoding [10], based on the use of siso (soft-input, softoutput) decoders which exchange information from each other's reliability zk [11]. these are called extrinsic information, through a feedback, to improve the correction over the iterations. the circuit of a turbo-decoder is constituted by cascading p modules, corresponding to the p identical decoding iterations and its structure is perfectly modular [9]. the input of the p th module consists of the properly received delayed sequences ' 1 { } k p x − , ' 1 { } k p y − and the sequence ' 1 { } k p z − of the feedback generated by the (p-1) th module. iii. turbo-trellis coded modulation ttcm is an ecc introduced by robertson and wörz in 1995 [12, 13]. this code is based on the concatenation of two trellis coded modulations (tcm). the tcm was introduced in the early '80s [14] and is based on the joint optimization of error correcting coding and modulation. coding is done directly in the signal space, so the ecc and the binary signal code of the modulation can be represented all along using a single trellis. the optimization criterion for a tcm consists in maximizing the minimum euclidean distance between two coded sequences. in the ttcm scheme each mct coder consists of a recursive systematic convolutional coder, or csr coder, of efficiency q/(q+1) and of a modulation without order memory q = 2 q+1 [15]. binary symbols from the source are grouped by q-bit symbols. these symbols are coded by the first mct in the order they are issued by the source and by the second after interleaving. iv. simulation results to eliminate the noise introduced by the channel and to improve the reception quality of a given communication system, an error correction coder must be used [9, 16-20]. the aim of the conducted simulation is to show the effect of the tc and ttcm on a medical image transmission chain in a gaussian canal and to make a comparison between the performance of these two codes. in all simulations we use code of 1/2 return and maq16 modulation to have the same spectral efficiency in the two transmission chains. the spectral efficiency of a transmission is given by [9, 16]: ŋ = r log2 m (bit/s/hz) (1) so in both cases of our transmission chain, spectral efficiency is given by: ŋ = 1/2 log2 16 = 2bit/s/hz (2) the results are obtained by evaluating the signal to noise ratio (eb/n0) for a number of iterations. in each case the (ber) and the structural similarity index (ssim) are calculated. two ways are generally used to measure the quality of degraded images, the subjective methods and the objective methods. in this paper, besides the evaluation criteria, we will use a new criterion, which is the ssim. this criterion presents the similarity and compares the luminosity, the contrast, and the structure between each pair of vectors of the two images (original and received). the ssim between two signals x and y is given by [9]: ssim(x,y) = l(x,y), c(x,y) and s(x,y) (3) where l(x,y) represents the comparison of the brightness between the original and the received image, c(x,y) represents the comparison of the contrast between the original and the received image, and s(x,y) represents the comparison of the structure between the original image and the received image. the proposed simulation algorithm for the image transmission chain coded with tc and ttcm is presented in figure 1. fig. 1. block diagram of the image transmission chain. figure 2 shows the effect of tc in the transmission chain of the image. the obtained simulation results represent the evaluation of the ber function of the signal-to-noise ratio in a image transmission in a gaussian channel using tc with rate r=1/2 and maq16 modulation. figure 3 shows the effect of ttcm in the transmission chain. the obtained simulation results represent the evaluation of the ber function of the signal-to-noise ratio in a medical image transmission in a gaussian channel using ttcm with rate r=1/2 and maq16 modulation. figure 4 shows the performance comparison between the tc whit ŋ= 2 and ttcm whit ŋ= 2 in the transmission chain. engineering, technology & applied science research vol. 11, no. 2, 2021, 6965-6969 6967 www.etasr.com fayssal et al.: performance improvement for medical image transmission systems using turbo-trellis … fig. 2. the influence of tc on the transmission of a medical image in a gaussian channel with ŋ= 2bit/s/hz. fig. 3. the influence of ttcm on the transmission of a medical image in a gaussian channel with ŋ= 2bit/s/hz. fig. 4. comparison between the tc and ttcm on the transmission of a medical image in a gaussian channel with ŋ= 2bit/s/hz. the ber measurement gives a numerical value on the damage, but it does not describe its type, it does not quite represent the quality perceived by human observers. for medical imaging applications, where the degraded images must eventually be examined by experts, traditional evaluation remains insufficient. for this reason, objective approaches are needed to assess the medical imaging quality [21]. a new paradigm is evaluated to estimate the quality of medical images. for this reason and to have more details on our system the ssim will be used as indicated above. figures 5 and 6 show the effect of tc and ttcm in the transmission chain of a medical image. the obtained simulation results represent the evaluation of the ssim function of the signal-to-noise ratio in a medical image transmission in a gaussian channel using tc and ttcm with r=1/2 rate and maq16 modulation. figure 7 shows the comparison between the performance of the tc and ttcm. the results are represented in detail in tables i and ii and the histograms in figures 8 and 9. fig. 5. the obtained ssim using tc on the transmission of a medical image in a gaussian channel with ŋ= 2bit/s/hz. fig. 6. the obtained ssim using ttcm on the transmission of a medical image in a gaussian channel with ŋ= 2bit/s/hz. fig. 7. comparison of the ssim between the tc and the ttcm on the transmission of a medical image in the gaussian channel with ŋ= 2bit/s/hz. engineering, technology & applied science research vol. 11, no. 2, 2021, 6965-6969 6968 www.etasr.com fayssal et al.: performance improvement for medical image transmission systems using turbo-trellis … table i. obtained results of ber as a function of the signal to noise ratio and the number of iterations eb/n0 (db) iteration no. ber tc ttcm 4 1 0.150801 0.0196 2 0.1494215 0.0046 3 0.14854397 0.0020 4 0.148309 0.0011 4.5 1 0.11651121 0.00797721609113564 2 0.10195265 0.000585083659665361 3 0.0946173 0.000145781416874333 4 0.08811321 6.62157351370595 e -05 5 1 0.07558384 0.002655927376290500 2 0.03763973 6.20327518689925 e -05 3 0.01492702 1.19971520113920 e -05 4 0.006852973 5.00177999288003 e -06 5.5 1 0.038408685 0.000749875400498398 2 0.002993948 6.63937344250623 e -06 3 0.000058739766 1.03239587041652 e -06 4 0. 4.22997508009968 e -07 6 1 0.013770025 0.000176913492346031 2 0.000014239943 2.13599145603418 e -07 3 0. 0. 4 0. 0. fig. 8. graphical representation of the data in table i. v. comments and interpretation of the obtained results from the simulation results, it can be noticed that the role of the eccs is very important in the transmission of images. the simulation results show that by using transmission systems with ttcm, there is a coding gain compared to transmission systems that use tc. with ttcm, the ber and ssim results as functions of snr are quite satisfactory. in the case of ttcm it is more adequate to remain at the 3rd iteration, allowing the receiver to have an easy structure to put in. the decoding will be simpler and the time shorter leading to optimal results. to see the importance of our work and in order to justify the reliability of our system, we have compared the obtained results with the ones obtained in [21, 22]. in these articles, the authors chose joint encoding with tcm with a spectral efficiency of ŋ= 2bit/s/hz. it can be said that the obtained results of the current study have a significant coding gain and also we arrived at ssim = 1 (100%) which is not the case in the cited articles. table ii. obtained results of ssim as a function of the signal to noise ratio and the number of iterations eb/n0 (db) iteration no. ssim tc ttcm 4 3 0.132 13.2% 0.947 94.7% 4 0.133 13.3% 0.973 97.3% 4.5 3 0.227 22.7% 0.989 98.9% 4 0.247 24.7% 0.999 99.9% 5 3 0.681 68.1% 0.996 99.6% 4 0.852 85.2% 1 100% 5.5 3 0.995 99.5% 1 100% 4 1 100% 1 100% 6 3 1 100% 1 100% 4 1 100% 1 100% fig. 9. graphical representation of the data in table ii. vi. conclusion the main objective of our work is to study the performance of tc and ttcm when transmitting medical images over a gauss channel. the simulation results obviously depict that our proposed transmission scheme performs better for the transmission of digital images and ber is significantly decreased (ber=0). this efficiency leads to the best reception quality of the digital images, 100% close to the transmitted ones (ssim=1). moreover, we demonstrated that the ttcm implementation outperforms the tc. by using ttcm, it is suggested to stop the process at the 3rd iteration. this allows having a simple architecture of the decoder and optimizes the decoding process in terms of time and complexity. the obtained results make the proposed transmission scheme a strong candidate when transmitting medical images, allowing medical staff to have best quality at the reception and facilitate the diagnosis process. the obtained results are better than the results found in [21]. acknowledgement we express our sincere thanks to the general directorate of scientific research and technological development (dgrsdt) for their support in the development of this work. engineering, technology & applied science research vol. 11, no. 2, 2021, 6965-6969 6969 www.etasr.com fayssal et al.: performance improvement for medical image transmission systems using turbo-trellis … references [1] b. gharnali and s. alipour, "mri image segmentation using conditional spatial fcm based on kernel-induced distance measure," engineering, technology & applied science research, vol. 8, no. 3, pp. 2985–2990, jun. 2018, https://doi.org/10.48084/etasr.1999. 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[online]. available: https://hal.archives-ouvertes.fr/hal-00348734. engineering, technology & applied science research vol. 7, no. 6, 2017, 2334-2339 2334 www.etasr.com khoso et al.: health and safety of hyderabad industries’ labor: causes and awareness health and safety of hyderabad industries’ labor causes and awareness ali raza khoso department of civil engineering mehran university of engineering & technology jamshoro, pakistan engr.aliraza23@gmail.com muhammad akram akhund department of civil engineering isra university, hyderabad sindh, pakistan akhund42@gmail.com aftab hameed memon department of civil engineering quaid-e-awam university of engineering, sciences & technology, nawabshah, pakistan aftabm78@gmail.com fida siddiqui department of civil engineering mehran university of engineering & technology jamshoro, pakistan fidasiddiqui2@gmail.com shabir hussain khahro department of engineering management prince sultan university riyadh, saudi arabia shkhahro@gmail.com abstract—labor’s health and safety (h&s) is a matter of concern for all industries. occurrence of accidents in industries is becoming a common issue. both white collar and blue-collar workers are not shielded from materials that damage their health. this study identifies the critical factors affecting labor’s h&s in hyderabad, pakistan industries. the awareness of labor regarding prevention and consequences that affect workers’ h&s is also a matter of interest of this research. the severity of factors was determined through questionnaire survey from experts, h&s supervisors and managerial staff of industries. for the descriptive analysis the software spps 24.0 was used. this research also includes interviews form industry laborers about awareness regarding h&s critical factors. the results show that, improper ppe use, operating machines that are poorly maintained, long term exposure to high intensity noise, working extended and irregular hours and lack of knowledge of working instruments are the critical causes of accidents. also 60.9%, 73.9%, 69.6%, 78.3% and 89% of workers are not aware about these causes and their consequences. thus, this research is a road map for industrial employers, law makers, local, provisional and federal government of pakistan in order to help minimizing the workplace accidents and the providing of safe and secure working environment for laborers. keywords-health & safety; accidents; hyderabad industries; labor i. introduction a labor force is a key stakeholder in every industry. their health and safety is a prime concern as industries’ entire output depends on their shoulders. industries in hyderabad, pakistan are small and medium sized enterprises (sme). according to [1, 2], health and safety issues are more common in sme’s as compared to larger industries. unfortunately, no separate legislation regarding health and safety in pakistan is available. the major law that governs all the issues of health and safety is covered under factory act 1934 but it is not fully implemented and eventually labor is suffering. the international labor organization (ilo) assessed that every year universally, around 2.2 million individuals die from work related mishaps and sicknesses, while 270 million experience non-fatal wounds and diseases. according to ilo, accidents at site take around 2 million lives per year and their estimated cost is around $1,250,000 m [3]. industries which disregard health and safety may lose staff, increase product costs and thus have less profit. as authors in [4] found, there is expanding and convincing proof that giving a solid and safe workplace can increase labor productivity and enhances business profits. the major problem in such industries is the lack of awareness of the laborers regarding the consequences of working in unsafe environment i.e. on-site accidents, injuries, long term health issues, and several diseases like cancer, asthma, hearing loss, eye damage, reproductive disorder, mental illness etc. this condition is more severe in pakistan. the labor force is less literate so they are less aware of the workplace health issues and have no idea about their legal rights of health & safety. a study conducted by authors in [5], showed that 69% of labor force from different industries of hyderabad are suffering from severe health issues. a survey by the centre for the improvement of working conditions and environment (ciwce) in 2001 in lahore found that the industries are lacking basic hygiene facilities. they have inadequate fire prevention, exhaust filters, emergency transport, hazard warning signs, medical facilities (even first aid) and waste disposal services. the survey also showed that most of the laborers are illiterate and don’t know about protective measures [6]. in globalization of the world's economics, overworking is an issue. it affects a worker in both positive and negative ways, for example by working irregular and extended hours, a worker gets more money than normal but this affects his social life engineering, technology & applied science research vol. 7, no. 6, 2017, 2334-2339 2335 www.etasr.com khoso et al.: health and safety of hyderabad industries’ labor: causes and awareness along with severe negative impacts on his health. many researches such as [7-9] claim that the demand of productivity influences the health issues of labor [7-9]. health and safety issues are vital parts of risk management, quality management and corporate social responsibility. labor is exposed in exceptionally hazardous situations in industries, like harmful radiations and pollution. the scope of health and safety has increased steadily and constantly considering monetary, technological, political, and social change. a welldeveloped health and safety framework is not just a duty of a couple of representatives. it is a mutual commitment of every single worker and, therefore, every one of them will be profited from a protected workplace. a major problem is the laborers’ lack of knowledge and awareness of work hazards. this research is an attempt to discover the different potential hazards, which adversely affect labor health in industry. at later stage, the awareness of laborers regarding those potential hazards becomes a major concern of the study. severity of factors on labor’s health was analyzed based on the knowledge of field experienced health and safety experts. ii. literature review a. factors affecting health & safety in industries the arrangement of health and safety has become a critical factor in industry, it affects socially and economically both employers and workers. health and safety conditions can be enhanced by recognizing potential hazards something that significantly reduces the safety and health risks. most of the potential industry hazards are due to large size of machines, heavy operated tools and complex operation [10]. authors in [11] identified fungi, bacteria and viruses as biological factors, dust, fumes, heavy metals and smoke as chemical factors and temperature, mechanical vibrations, radiations and noises as physical factors affecting workforce health and safety. encyclopedia of occupational health and safety (1998) has identified repetitive motion, force, and mechanical vibrations etc. as health affecting causes [12]. modernization in technology and economic development has also increased the occupational injury rate [13]. all deaths, injuries and diseases are caused due to poor health and safety framework which significantly damages national economy and industry reputation. according to authors in [4] a healthy and safe workplace with very low potential hazards improves significantly the labor efficiency, industry reputation and profits. authors in [14] also propose that company productivity increases when health, safety, precautionary measures and workforce working conditions are improved. it is evident that noise has a significantly negative impact on labor’s health. it has become an attention seeking issue due to its potential hazards on human health and environment [15]. noise in a manufacturing industry is generated from numerous sources [16]. long term exposure to noise leads to psychological and physical stress to human beings [17]. workforce is more exposed to perils as compared to other people. they may experience physiological problems. labor may experience severe respiratory problems due to dust and smoky workplace conditions. they are more exposed to harmful radiations and heavy metals which increase their vulnerability to cancer and reproductive problems [8]. it is found in a study conducted by (niosh 2007) that 82% hearing impairment cases were reported from workforce in manufacturing industries [18]. according to authors in [19], the worker who smokes cigarette at work, doubles the severity of different hazards affects, because some of the poisonous constituents found in cigarette tobacco (e.g. benzene) may interact with toxic elements found at workplace while doubling its severity than alone exposure (e.g., asbestos). the heat produced by burning tobacco may also enhance the reactivity and toxicity of other chemicals inhaled. it is found that white collar workers are more exposed to hazards and problems caused by burning tobacco then blue-collar workforce. according to the national institute for occupational safety and health (niosh), working in a place where ventilation is poor or at place where temperature is high, can also be a health hazard [20]. working in high heat zone can lead workers to suffer from serious illnesses, heat strokes, skin rashes, heat cramps, fatigue and dehydration in labors body which is fatal in most cases [21]. authors in [22], investigated work health and safety in cotton ginning industries of pakistan. the research presented that sustaining crush injuries, injuries due to working at heights, injuries due to collision with electrical objects and vehicles are very common. authors in [23], showed that exposure to chemicals, risks associated with working at heights, heavy lifting, dust, pressurized devices, excessive, objects falling from overhead, heat, noise, risk of fire and steam are the major causes of health issues [23]. the literature covers sufficient factors of health and safety for labor working in different industries. however, this research work includes more factors, depending upon the condition of h&s in industries of hyderabad, pakistan. b. labor’s awareness issues in industries the industries are attempting to remain profitable and usually have no moral respect for their labor, which is a key element for their business. in the world of globalization, the labor is still less or not educated hence is less aware of potential workplace hazards. the global occupational hygiene community has worked diligently to develop ways to protect laborers. also, numerous standards and guidelines have been developed to help them. laws and regulations may refer to certain standards and compliance with them is compulsory. according to author in [24], occupational injuries are caused when dangerous conditions are consolidated with hazardous activities that start from the deficiencies of people due to lack of knowledge regarding hazards. the lack of knowledge and awareness contributes to 80 – 90% of all industrial accidents. it was observed in a research survey conducted in a manufacturing industry by kimberly-clark professionals in 2008 that 89% of the laborers were not aware about the proper use of personal protection equipment (ppe) and 6 % were reluctant to use ppe which put their lives in danger [25]. authors in [23], did a comprehensive research on risk assessment in north cyprus’ small and medium sized enterprises. according to their research 75% of laborers were engineering, technology & applied science research vol. 7, no. 6, 2017, 2334-2339 2336 www.etasr.com khoso et al.: health and safety of hyderabad industries’ labor: causes and awareness unaware about existing occupational safety & health (osh) laws, 3.3 % were fully unaware and 21.7% knew about laws but were unaware about employer obligations as written in law. moreover, 23% of employees were fully unaware about the problems at workplace that cause serious harm to them. authors in [26] reported regarding h&s in food production factory biyagama that nearly 28 % of employees had very low awareness of the importance of h&s at workplace. laborers especially in pakistan are working at low wages most of the time and since they want to earn more, they do overtime duties hence their health is affected. also, sometimes due to increase in productivity demand and competitive environment, workers experience extra workload which leads them to suffer from stress and depression [7, 9]. according to a survey conducted by government of pakistan in 2013, pakistan has a workforce of 54.9 million and 41 laborers out of 1000 receive injuries every year in occupational accidents. a large portion of the pakistan workforce is not aware of the proper use of the protective equipment; they have limited awareness and information regarding health, safety, emergency and preventive measures [18]. a survey conducted in lahore by ciwce in 2001, found that most of the laborers were illiterate and unaware about protective measures [6]. another study conducted in pakistan concludes that on textile industries of lahore, the laborers are not aware about the significance on h&s. the research further investigated that the workers are not aware about their legal rights. moreover, the use of ppe was too low at those industries [10]. pakistan has very poor laws and legislation for h&s and also poor infrastructure to promote it. in industries, many uneducated laborers are being employed regularly. also, children and women work in the industry while having no basic know how of h&s protection. hence the toll of injuries and fatalities is increasing. this research investigates the awareness of hyderabad industries’ labor. the investigated figures would help to notify the employers, h&s practitioners, law makers, local, provisional and federal government regarding the miserable situation of h&s of hyderabad industries’ labor. iii. methodology this study aims to determine potential hazards that affect health and safety of labor in industries of hyderabad and the awareness of workforce in those industries regarding critical hazards. from literature and safety standards, various critical factors related to health and safety were identified. the factors then were discussed with various field experienced h&s experts of pakistan for their suitability in industries of hyderabad. a questionnaire was then designed in order to know the severity of these factors. the data was collected from rich experienced h&s experts and managerial staff in those industries. in order to determine the labor awareness, a second questionnaire was designed. the information was only collected from laborers working in industries and not less than 6 months in same industry. the laborers were asked about the awareness of critical factors obtained from the analysis of first questionnaire in the form of ‘yes/no’. hence the study investigated the awareness of laborers about the potential hazards that can affect their health adversely. iv. research objectives 1. to identify factors influencing labor’s h&s of hyderabad, pakistan industries. 2. to explore the causes for critical issues of h&s factors for labors. 3. to investigate the awareness of labor regarding critical causes of h&s factors. v. data collections and analysis for the first round of data collection, 90 questionnaires were distributed among health and safety experts, managerial staff and h&s supervisors of visited industries. around 65 questionnaires were received that were valid for analysis. a five-point likert scale was adopted for questionnaire as 1= not severe, 2 = slightly severe, 3 = moderately severe, 4 = severe, 5 = extremely severe [27]. the collected data was then analyzed in spss 24.0. for the ranking of factors in spps, average index technique is used [28]. figure 1 illustrates the factors with their respective ranking. for the second round of data collection, around 230 laborers from different industries were targeted. they were asked about their awareness of those potential hazards and the consequences on their health. vi. results and discussion a. critical factors of worker’s health & safety the study highlights the top ten factors as major hazards of h&s for hyderabad industries. the causes are illustrated in figure 1 with their respective mean. from the analysis of questionnaire data, “improper ppe use” is top ranked factor with 4.83 mean value. there are several causes. the industries are not focusing on worker’s h&s, and mainly ignore the importance of ppe. also, the safety supervisors are not ensuring that, the laborers have their proper ppe whether they are using it or not. another important reason in hyderabad is the lack of safety culture. the second top factor is “operating machines that are poorly maintained”. most of the machinery is very old in these industries. employers are not interested to properly maintain those machines. also, most of the labor is illiterate and have no technical knowledge to handle those machines properly. the third top factor is “long term exposure to high intensity noise”. sound is the most common issue in every type of industry, however the condition in hyderabad industries is more critical. the sound level is beyond the maximum allowable range most of the working hours. also, the noise of various operations is extremely more than the usual due to improper maintenance. here the proper use of ppe is the only solution, which is already low in such industries. this long-term exposure to sound creates adverse effects on laborers. “working extended & irregular hours” is ranked fourth. laborers are forced to work for longer time due to employers’ harsh attitude and eagerness to earn high profits. employers are only interested in their outcome. also, another major cause is irregular working. when the demand is more, the employers are forcing the laborers to work overtime. the fifth critical factor is “lack of knowledge of instrument working”. this is more common in pakistan industries, due to engineering, technology & applied science research vol. 7, no. 6, 2017, 2334-2339 2337 www.etasr.com khoso et al.: health and safety of hyderabad industries’ labor: causes and awareness poor laborer education. the laborers are very poor and sometimes agree to work in a tuff environment. the employers are not giving properly training, and in result many workplace injuries occur. fig. 1. h&s factors & their average index (a.i) values “working near naked electrical wires” is also ranked fifth. “smoking cigarette in poor ventilated or close room” is the sixth critical factor. these issues are found to be very common. due to poor planning and monitoring, electrical wires are often spread over the working platform in the industries and workers are not paying attention. proper ventilation is another issue. smoking is not prohibited in the industries, and its ill effects are very common to the laborers. “stress due to workload” is another major cause. due to large productivity demands from employers, laborers work in extremely stressed conditions. “exposure to heavy metals”, “exposure to carbon monoxide” are ranking next. the industries have no proper guidance to labor for working with heavy metals and exposure to smokes such as carbon monoxide. thus, they have no knowledge for its ill effects. b. worker’s awareness about critical causes it is found from the research that 60.9% of the laborers were not aware about the proper use of ppe. 73.9% said that there is no safety issue in operating poorly maintained machines. 69.6% were not aware about the potential health and safety hazards of high intensity noise. only 21.7% of the laborers agreed with the point that working extended and irregular hours can cause stress and health problems while 78.3% weren’t aware about the stress and its hazards. 89% of the laborers said lack of knowledge regarding instrument working can lead to accident but 11% said engineering, technology & applied science research vol. 7, no. 6, 2017, 2334-2339 2338 www.etasr.com khoso et al.: health and safety of hyderabad industries’ labor: causes and awareness lack of knowledge cannot cause any harm. 69.5% answered that there is no safety risk in working near naked wires. only 35% agreed that smoking in poorly ventilated zones can lead to accidents and ill health effects. around 60% agreed that, workload can lead to mental sickness. 95.7% of the laborers don’t have any knowledge regarding heavy metals & carbon monoxide and its hazards. table i illustrates the awareness of labors for above discussed factors. the study also extended to investigate the awareness of basic elements inside the industry and found that 69.6% of the laborers were not aware of the directions and importance of emergency exit gates. 78.3% were not aware of the meaning of different health and safety symbols posted in their industry. table i. labor’s awareness for critical h&s factors awareness factor yes (%) no (%) awareness for hazards of lack of use of ppe 39.10 60.90 awareness for hazards of poorly maintained machines 26.10 73.90 awareness for hazards of long term exposure to high intensity noise 30.40 69.60 awareness for hazards of extended & irregular working hours 21.70 78.30 awareness for hazards of lack of knowledge of instrument working 11.00 89.00 awareness for hazards of lack of knowledge of instrument working 30.50 69.50 awareness for hazards of smoking cigarette in poor ventilated or close room 35.00 65.00 awareness for hazards of stress due to workload 40.00 60.00 awareness for hazards of exposure to heavy metals 04.00 96.00 awareness for hazards of exposure to carbon monoxide 04.00 96.00 vii. conclusion, recommendation and future directions occupational health and safety is a matter of concern that all manufacturing industries are facing. accidents in industries are increasing day by day. there are several factors affecting labor h&s. this study incorporates initially the potential factors that affect labor’s health and safety issue in hyderabad’s industries and then the labor awareness about those factors. the results showed that, there is absence of ppe among most of the laborers. employers and their upper staff like managers and h&s supervisors do not ensure that the laborers are wearing their ppe before working. lack of proper machine maintenance and noise due to various operations are also among the important causes of h&s risk. laborers are not working proper hours and usually they are lacking the knowledge of different operations and equipment in the industry. the research concludes that, h&s principles are not well integrated in the industries of hyderabad. the laborers are mostly illiterate and have lack of awareness regarding potential hazards. also, they are unaware about the most common operations and their effects on h&s. most of the laborers have no knowledge about basic elements, symbols, arrow directions inside the industry. due to these causes, h&s issues are arising among the laborers. the issue of h&s of labor in hyderabad can be resolved by creating proper awareness among labor through guidance, training, seminars, small courses, motivation etc. the research can be prolonged to investigate further the h&s issues of hyderabad industrial area. various data can be collected regarding accidents, injuries, sicknesses and diseases in each industry separately. a comprehensive study can be conducted to resolve each issue exclusively. acknowledgement the authors are deeply thankful to mr. aziz mahar in helping data collection and conducting interviews from the industry’s labor. we also acknowledge the efforts of dr. ashfaque pathan in directing the research work. references [1] b. fabiano, f. curro, r. pastorino, “a study of the relationship between occupational injuries and firm size and type in the italian industry”, safety science, vol. 42, no. 7, pp. 587–600, 2004 [2] o. h. sorensen, p. hasle, e. bach, “working in small enterprises is there a special risk?”, safety science, vol. 45, no. 10, pp. 1044–1059, 2007 [3] international labour office, safety culture at work safety in numbers – pointers for a global safety culture at work. ilo, international labour office, 1999 [4] f. lamm, c. massey, m. perry, “is there a link between workplace health and safety and firm performance and productivity?”, new zealand journal of employment relations, vol. 32, no. 1, pp. 72-86, 2007 [5] a. a. noonari, r. b. mahar, a. r sahito, “assessment of air pollution and its effects on health of workers of steel re-rolling mills in hyderabad”, mehran university research journal of engineering & technology, vol. 35, no. 2, pp. 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jamil, “severity of variation order factors in affecting construction project performance”, journal of basic and applied scientific research, vol. 4, no. 6, pp. 19-27, 2014 microsoft word etasr_v11_n4_pp7411-7416 engineering, technology & applied science research vol. 11, no. 4, 2021, 7411-7416 7411 www.etasr.com minh et al.: finite element modeling of shunt reactors used in high voltage power systems finite element modeling of shunt reactors used in high voltage power systems tu p. minh school of electrical engineering hanoi university of science and technology hanoi, vietnam hung b. duc school of electrical engineering hanoi university of science and technology hanoi, vietnam nam p. hoai school of electrical engineering hanoi university of science and technology hanoi, vietnam trinh tr. cong school of electrical engineering hanoi university of science and technology hanoi, vietnam minh b. cong school of electrical engineering hanoi university of science and technology hanoi, vietnam bao d. thanh university of quy nhon qui nhon, binh dinh,vietnam vuong d. quoc school of electrical engineering hanoi university of science and technology hanoi, vietnam abstract—shunt reactors are important components for highvoltage and extra high voltage transmission systems with large line lengths. they are used to absorb excess reactive power generated by capacitive power on the lines when no-load or under-load occurs. in addition, they play an important role in balancing the reactive power on the system, avoiding overvoltage at the end of the lines, and maintaining voltage stability at the specified level. in this paper, an analytical method based on the theory of magnetic circuit model is used to compute the electromagnetic fields of shunt reactors and then a finite element method is applied to simulate magnetic field distributions, joule power losses, and copper losses in the magnetic circuit. in order to reduce magnetic flux and avoid magnetic circuit saturation, it is necessary to increase the reluctance of the magnetic circuit by adding air gaps in the iron core. the air gaps are arranged along the iron core to decrease the influence of flux fringing around the air gap on shunt reactors' total loss. non-magnetic materials are often used at the air gaps to separate the iron cores. the ansys electronics desktop v19.r1 is used as a computation and simulation tool in this paper. keywords-shunt reactors; air gaps; inductance; joule power losses; copper losses; finite element method i. introduction the shunt reactor is a widely used component that improves the stability and efficiency in power transmission systems. high-voltage and extra-high-voltage power transmission systems usually have relatively large line lengths. under no or small load, parasitic capacitance will appear in the line, its value is quite large especially in long lines, which will increase the voltage along the line, causing overvoltage at the end of the line. this phenomenon is known as the ferranti effect [1-3]. in order to maintain voltage stability at the specified level, it is necessary to use shunt reactors to absorb the excess reactive power generated by the line capacitance, balancing the reactive power in electrical systems [3-5]. the construction of shunt reactors is correlated with power transformers such as windings, magnetic circuits, insulation structures, or shields. the shunt reactor can be considered as a transformer working with no load. however, the main difference in the shunt reactor, is that each phase is a winding. in order to reduce the magnetic flux and avoid the saturation of the magnetic circuit, the reluctance is increased by creating horizontal gaps. this leads to increased energy stored in the gap areas. the volume of gaps depends on the reactive power and the selected magnetic inductance. however, the gaps are also reasons to flux fringing along the gaps [6-8] which increases the power losses in the shunt reactor. the gap needs to be divided into several smaller gaps to reduce the effect of the flux fringing, thereby reducing power losses in the shunt reactor. shunt reactors have been extensively used, e.g. for the compensation reactive power in a power system [3, 4], the interaction between shunt reactors and the power system in different transient conditions [8, 9], and the vibration analysis [9, 10]. in this research, an analytical method based on the theory of magnetic circuit model and finite element method (fem) were used to compute and simulate the electromagnetic parameters of shunt reactors. ii. analytic method a. shunt reactor modeling the model of the shunt reactor is presented in figure 1. thanks to this model, when ignoring the leakage flux, it is possible to divide the magnetic circuit into different parts and is given in the equivalent magnetic circuit in figure 2. corresponding author: vuong d. quoc (vuong.dangquoc@hust.edu.vn) engineering, technology & applied science research vol. 11, no. 4, 2021, 7411-7416 7412 www.etasr.com minh et al.: finite element modeling of shunt reactors used in high voltage power systems fig. 1. modeling of the shunt reactor. fig. 2. equivalent magnetic circuit. fig. 3. reduced equivalent magnetic circuits. the electromotive force (emf) generated by the current i in the n turns of windings is denoted by f = i.n (a.turn). due to the symmetry of the magnetic circuit, the reluctances of the upper and lower yokes are determined by (1): �� � �� � �� � �� � �� � �� �� �.� .� (1) the reluctances of two sides and of the middle core can be defined by (2) and (3): �� � �� � �� � �� � .� (2) �� � �� �.�� �� ������ � (3) where µ is the permeability of the ferromagnetic material and lg is the total gap length in the core. wy, dc, hy, and dy are the parameters given in figure 1. the diagram in figure 2, it can be transformed into figure 3. the equivalent reluctance of the reduced equivalent magnetic circuits is defined as: �� � �� � ��������� � �.�� �� �����.�.� � � � �� ��� �� ��.� .� (4) the reluctance of the gap in the iron core is calculated as: �� � �� �.���.� � (5) the reluctance rc in (4) is very small in comparison with the reluctance of the air gaps. thus, the rc can be neglected in the equivalent magnetic circuit. b. parameter computations in this part, the single phase shunt reactor of 30.33mvar (500/√3 and 50hz) is considered in figure 1. the idea of this step is to increase the reluctance by adding air gaps in the iron core. the volume of the air gaps is defined via equations based on the magnetic circuit model. it should be noted that the volume of the air gaps depends on the main parameters of the shunt reactor, i.e. reactive power, magnetic flux density, winding inductance, frequency, and energy storage in the winding space air gaps. the reactive power is expressed by the electric current and the voltage, i.e.: # � $. % (6) the winding resistance is normally very small in comparison with the inductance, thus it can be neglected when defining parameters of the magnetic circuits. the electromagnetic force and the electric current are defined as: & � '��√�(. ).*.+, � '��√�(.). *.-,..� (7) % � .��/ � ' �√�(01.��� ./ (8) where +,,-,,.�, 3�,�� and μ8 are respectively the maximum magnetic flux, maximum flux density, area of the air gap, length of the air gap, air gap reluctance, and air permeability. based on (7) and (8), the volume vg is determined by the air gap length lg: 9� � .�. 3� � :;< .=.01� (9) where the reactive power, magnetic flux, and frequence are considered as constants and so the volume of the air gaps is also a constant. hence, the .� and 3� will be defined based on this air gap, because they are two important parameters that can be affected directly to total power losses and the size of shunt reactors. if the air gap area is equal to the core area, the dimension of core is written as: >� � ?�.@�� (10) dc hw ww hy dy yoke core blocks hc wy engineering, technology & applied science research vol. 11, no. 4, 2021, 7411-7416 7413 www.etasr.com minh et al.: finite element modeling of shunt reactors used in high voltage power systems from (10), the yoke area can be defined as: >a � >�, ba � @��.� (11 a-b) and the winding inductance is computed by the reactive power and voltage as: c � d�e.: (12) or c � *�.f8.g@��� h � *�.i� (13) from (13), the turns of the winding and the magnetic window are calculated as: * � j k� .�l�m� �, .n � on.bn � /.p qr.s (14 a-b) where tu is the filled factor of the windings in the magnetic window and v is the electric current density. in addition, it is seen that in a region around the air gap appears flux fringing as presented in figure 4. fig. 4. modeling of fringing flux around the air gap. thus, the flux fringing is defined as [7]: += � w -. x. � w � .y����.z .[.>� \ ]m��8 x^ (15) the magnetic conducting can be defined via the mmf and fringing flux as: i= � f8.>�. ln g1 � ��� �����.�� h (16) the magnetic conducting taking the flux fringing into account is expressed as: i�= � i� � i= (17) the turn number is finally written as: * � ? ka �a�b (18) the copper and core losses are defined as: icu � %�. t=.�d� (19) for �d� � e. �fg@hr � e. �./.�� � i��.j i�@hr iyk � tl.mno.po � n�. p�q (20) where tl is the auxiliary loss factor, no and n� are the losses in the core and yoke, and po and p� are the weights of the core and yoke. the calculated results of the shunt reactor are given in table i. table i. obtained results of the shunt reactor by the analytic method parameters notation results reactive power q (mvar) 30.33 rated voltage u (kv) 500/√3 rated current i (a) 105 total inductance l (h) 8.7457 core dimension dc (mm) 673 core height hc (mm) 1758 total air gap lg (mm) 363 turn number n (vòng) 2166 winding width ww (mm) 248 winding height hw (mm) 1488 copper loss pcu (kw) 51.9038 iron loss pfe (kw) 20.4260 iii. finite element method a. canonical magnetodynamic problem in this problem, the characteristic size of the studied domain r with boundary sr = t = t h ∪ t e, is considered much less than the wave-length v � w/) in each medium. hence, the displacement current density is negligible. the problem is described by maxwell’s equations [11-16]: curl | � }so~, curl � � ��, div~ � 0 (21a-b-c) and the behavioral relations of materials: ~ � f�, � � �| (22a-b) where ~ is the magnetic flux density, � is the magnetic field, | is the electric field, f is the magnetic permeability, � is the electric conductivity, � is the eddy current density belonged to the conducting part r� �r� ⊂ r�, and �� is the imposed electric current density defined in the non-conducting ω�c , with r� = r� ∪ r�c. equations (21a) and (21b) are to be solved with the boundary conditions (bcs) that the tangential component of the magnetic field on bc is � � �|�� , for n being the unit normal exterior to r. b. magnetic vector potential formulations based on the maxell’s equations along with the constitutive relations in (22), the weak form of ampere’ law (22b) is written [5, 11, 13] as: w � ∙ curl� �� xω � w � � � ∙ ��γ� xγ� � w �� ∙���� xω�,∀ �� ∈ �k8�curl;ω� (23) engineering, technology & applied science research vol. 11, no. 4, 2021, 7411-7416 7414 www.etasr.com minh et al.: finite element modeling of shunt reactors used in high voltage power systems in order to satisfy strongly the lower part of the tonti’s diagram [14], the constitutive laws (23 a-b) have to be introduced in (12), i.e.: � � w ~ ∙ curl� �� xω } σw | ∙ � �� xω� � w � � � ∙γ��� xγ� � w �� ∙ ���� xω�,∀ �� ∈ �k8�curl;ω� (24) by substituting b = curl a and | � }�so� � grad �� into (24), we get: � � w curl � ∙ curl� �� xω} σw so� ∙ � �� xω� �σ w grad � ∙ � �� xω� � w � � � ∙ ��γ� xγ� � w �� ∙ ���� xω� ∀ �� ∈ �k8�curl;r� (25) where �k8�curl;r� is a curl-conform function space defined on r containing the basis functions for � as well as for the test function ��(at the discrete level, this space is defined by edge finite elements). the electric scalar potential � is only defined in ω�. the energy and inductance are now defined via the magnetic flux density and magnetic intensity. this can be done in post-processing, i.e.: o, � �� w ~ ∙ � xω� , c � �. 1p� (26) iv. numerical test the calculated parameters of the shunt reactor given in table i were checked with the fem developed in section iii, with the help of the ansys maxwell 3d. ansys maxwell is a part of the ansys electronics software package created by ansys inc. a 3d model of the single phase shunt reactor with 8 air gaps is depicted in figure 5. the distribution of the current density in the windings is pointed out in figure 6. fig. 5. 3d model of the single phase shunt reactor. fig. 6. distribution of the current in the winding. fig. 7. magnetic flux density and magnetic flux line distribution. the magnetic flux density and flux line distribution in the magnetic core are presented in figure 7. in figure 7, c1-c2 is the line at the middle of core blocks, g1-g2 is the line at the middle of air gap, h1-h2 is the line along the core height and h3-h4 is the line along the height of windings. the flux density variation along c1-c2 and h1-h2 are depicted in figure 8 and 9 respectively. the flux density obtains maximum values near the edges and the corners of the air gaps (figure 8) and it is distributed equally along the h3-h4 as shown in figure 10. fig. 8. flux density variation along the line at the middle of core blocks. fig. 9. flux density variation along the height of the core. fig. 10. flux density variation along the height of the windings. engineering, technology & applied science research vol. 11, no. 4, 2021, 7411-7416 7415 www.etasr.com minh et al.: finite element modeling of shunt reactors used in high voltage power systems copper and core losses are shown in figures 11 and 12 respectively. the copper losses in the windings determined by the fem are 52.2859kw whereas the analytical result in table i is 51.9038kw, with the error being lower than 1%. it is seen that in order to avoid the increase of losses due to the fringing flux acting on the windings near to the gap area, it is necessary to divide a bigger gap into several smaller gaps. this reduces the fringing flux around the air gaps. fig. 11. energy variation along the line g1-g2 at the middle of the air gap. fig. 12. copper losses in the windings. fig. 13. core losses of the shunt reactor. table ii. inductance values comparison between fem and the an alytic method parameters fem analytic method error (%) total inductance l (h) 8.6619 8.7457 0.96% gap inductance lg (h) 5.6953 5.7819 1.50% fringing inductance lf (h) 2.0017 1.2212 63.91% leakage inductane ll (h) 0.9578 0.8746 9.51% similarly, the core losses obtained by fem are 25.7556kw while the analytical result is 20.4260kw, with an error equal to 26%. it can be seen that the analytical method cannot determine exactly the distribution of the magnetic flux density in the core and yoke, because the magnetic flux density at different positions leads to different losses. in addition, the fringing flux component at the gap areas towards the steel foil in accordance with the direction of magnetization at different angles causes eddy currents that increase the losses in the cores. table ii presents the result comparison between the fem and the analytic method. the error on the gap inductance between the two methods is 1.5% and lower than 1% for total inductance. however, the inaccuracy on the fringing flux is very big (63.91%), because the fringing flux cannot be defined exactly by the analytic method. v. conclusion in this study, the parameters of the shunt reactor were succesfully computed by the analytic method. thanks to the calculated results from the analytic method, a finite element model has been proposed to survey and compare the distributions of the magnetic flux density, inductances (total, leakage, and fringing flux), and energy storage in the gaps, determining the power loss components in the shunt reactor. the error of the calculation results of the total inductance between the two methods is only 0.96%, showing a very good agreement. this test problem can help researchers and manufacturers to standardize the type of iron cores of the shunt reactors in practice. acknowledgement this work was supported by the hanoi university of science and technology (hust). the authors also gratefully acknowledge quy nhon university for providing the means and conditions needed to carry out this work. references [1] g. deb, "ferranti effect in transmission line," international journal of electrical and computer engineering, vol. 2, no. 4, pp. 447–451, aug. 2012. [2] a. divya swarna sri, k. tejaswini devi, k. dhana raju, and b. tanya, "depiction and compensation of ferranti effect in transmission line," international journal for research in applied science & engineering technology, vol. 6, no. 3, pp. 1522–1526, mar. 2018, http://doi.org/ 10.22214/ijraset.2018.3234. [3] y. g. zhang, k. x. chang, and y. c. su, "shunt reactors compensation research of uhv accessed to jiangxi power grid," advanced materials research, vol. 1070–1072, pp. 1029–1034, 2015, https://doi.org/ 10.4028/www.scientific.net/amr.1070-1072.1029. [4] h, s. park, b. h. lee, y. s. cho, and s. o. han, "calculation of shunt reactor capacity in 400 kv power system using emtp," presented at the international conference on electrical engineering 2006, korea, jul. 2006. [5] k. dawood, g. komurgoz, and f. isik, "modeling of distribution transformer for analysis of core losses of different core materials using fem," in 2019 8th international conference on modeling simulation and applied optimization (icmsao), manama, bahrain, apr. 2019, https://doi.org/10.1109/icmsao.2019.8880392. [6] r. jez, "influence of the distributed air gap on the parameters of an industrial inductor," ieee transactions on magnetics, vol. 53, no. 11, pp. 1–5, nov. 2017, https://doi.org/10.1109/tmag.2017.2699120. [7] s. pokharel and a. dimitrovski, "analytical modeling of a ferromagnetic core reactor," in 2019 north american power symposium (naps), wichita, ks, usa, oct. 2019, https://doi.org/ 10.1109/naps46351.2019.9000352. 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[13] v. d. quoc, "accurate magnetic shell approximations with magnetostatic finite element formulations by a subdomain approach," engineering, technology & applied science research, vol. 10, no. 4, pp. 5953–5957, aug. 2020, https://doi.org/10.48084/etasr.3678. [14] j. ning, h. baoxing, z. ruoyu, m. hongzhong, x. lei, and l. li, "application of empirical wavelet transform in vibration signal analysis of uhv shunt reactor," in 2019 ieee milan powertech, milan, italy, jun. 2019, https://doi.org/10.1109/ptc.2019.8810623. [15] y. gao, k. muramatsu, k. fujiwara, y. ishihara, s. fukuchi, and t. takahata, "vibration analysis of a reactor driven by an inverter power supply considering electromagnetism and magnetostriction," ieee transactions on magnetics, vol. 45, no. 10, pp. 4789–4792, oct. 2009, https://doi.org/10.1109/tmag.2009.2024638. [16] m. mu, f. zheng, q. li, and f. c. lee, "finite element analysis of inductor core loss under dc bias conditions," ieee transactions on power electronics, vol. 28, no. 9, pp. 4414–4421, sep. 2013, https://doi.org/10.1109/tpel.2012.2235465. engineering, technology & applied science research vol. 8, no. 5, 2018, 3300-3309 3300 www.etasr.com danikas: breakdown in nanofluids: a short review on experimental results and related mechanisms breakdown in nanofluids: a short review on experimental results and related mechanisms m. g. danikas democritus university of thrace department of electrical and computer engineering power systems laboratory, xanthi, greece mdanikas@ee.duth.gr abstract—nanofluids seem to gradually become an alternative to traditional insulating liquids, such as transformer oil. in this paper, a short review of experimental results as well as of possible breakdown mechanisms and of some of the factors affecting the breakdown strength of the said fluids is conducted. most of the reports suggest that the addition of nanoparticles in insulating liquids improves the breakdown strength. however, some reports that contradict the above are also to be found. in view of this, an outline of future research is discussed. this review does not encompass all possible effects, parameters and factors affecting nanofluids but it is solely concerned with breakdown strength. keywords-nanofluids; breakdown strength; transformer oil; ester oil; partial discharges i. introduction traditional insulating liquids, e.g. transformer oils, have served well for many decades the high voltage industry. alternative liquids such as, among others, silicone liquids are also used. liquids are easy to fill a space, they can easily be circulated and they can dissipate heat. they have a satisfactory dielectric strength but, on the other hand, they can easily be contaminated from foreign particles, air bubbles etc.,. contamination has as a result the decrease of their dielectric strength. besides contamination other factors also play a role in affecting their dielectric strength. factors such as area, gap spacing, liquid volume under stress, type of applied voltage, rate of applied voltage, play a vital role in determining the dielectric strength and, in general, the performance of an insulating liquid [1, 2]. nanofluids have recently attracted the interest of the scientific and industrial community since they present good insulating properties and numerous people think them as an alternative to traditional insulating liquids. the basic new idea is that if insulating liquids are mixed with a certain percentage of nanoparticles, the thermal conductivity of the mixture increases and also the electrical properties are improved. it is the aim of the present short review to indicate aspects of traditional insulating liquids and also how such liquids can be improved with the addition of nanoparticles. it must be emphasized that the present review is not an exhaustive review on the parameters affecting the electrical behavior of nanofluids but it only concentrates on one basic quantity, that of their breakdown strength. it must be noted that in the context of the present work the terms “breakdown strength” and “dielectric strength” are used interchangeably. ii. traditional insulating liquids: general remarks insulating liquids can fill any required space, they have a relatively low dielectric constant (about 2.2-2.3), relatively low dielectric losses, and – under certain conditions they can recover their previous dielectric strength. an ideal insulating liquid must have, among others, high dielectric strength, low or high dielectric constant depending on the application, good thermal conductivity, low toxicity, good chemical stability and the appropriate viscosity [1, 2]. insulating liquids, however, are sometimes difficult to continue to have a high dielectric strength (especially if they have a large liquid volume) and they are easily contaminated (from foreign particles and air bubbles) [3]. moreover, some of them presented high toxicity (e.g. pcb) and they have been removed from service. in industrial applications, such as in transformers, insulating liquids suffer from aging and all the consequences that entails [4]. numerous publications refer to the factors affecting the dielectric strength of traditional insulating liquids. they all tend to some basic points: the dielectric strength of the insulating fluid decreases with the increase of the electrode area, with the increase of the gap between the electrodes, with the increase of the stressed liquid volume [5]. other vital factors of a good performance of insulating liquids are the cleanliness of the electrodes, the cleanliness and the way of preparation of the liquid, i.e. the quality of the liquid, the conditioning process [6]. the most widely used insulating liquid is probably the transformer oil which is used in transformers, switching gear, capacitors etc. transformer oil can age with time and it must be regularly checked in order to see whether its quality is still acceptable for further use. a variety of tests is available to researchers and utilities for this purpose. transformer oil must be controlled regarding a whole series of tests w.r.t. its color, surface tension, dielectric strength, density, tan delta, diluted gaseous substances, resistivity etc. [7, 8]. temperature is one of the factors influencing the electrical performance of transformer oil. increase of temperature implies engineering, technology & applied science research vol. 8, no. 5, 2018, 3300-3309 3301 www.etasr.com danikas: breakdown in nanofluids: a short review on experimental results and related mechanisms a decrease of its resistivity. temperature affects the dielectric constant of transformer oil, especially if it has some traces of moisture. increase of temperature means an increase in dielectric constant. humidity has also a negative effect on the performance of the oil since it decreases its dielectric strength. under certain conditions, traces of humidity cause breakdown channels [2]. it is imperative that humidity should not be allowed in transformer oil of industrial cleanliness . foreign particles create the so-called particle bridges, which in turn facilitate the breakdown channels and consequently the breakdown. such particle bridges are more conducting than the surrounding oil [9]. air bubbles trapped in the oil are also a determining factor for the oil dielectric strength. air bubbles, as having a lower dielectric constant than the oil, tend to elongate with increasing applied voltage. the larger the difference between the dielectric constants of air and oil, the smaller the required voltage for bubble elongation [10]. iii. breakdown in conventional liquids according to weak link theory, the dielectric strength of transformer oil is as good as its weakest spot. this theory entails some statistical approach and there are numerous papers in this direction [11-14]. there has also been some discussions as to what sort of statistical distribution such a theory follows, extremal or normal [5, 15]. other theories were based on bubble elongation and subsequent breakdown [10]. streamer theory has been followed in a number of papers [16]. streamer theory is based on the notion that electrons are accelerated – because of the applied voltage – and collide with liquid molecules, resulting thus in tine air pockets. such tine regions are regions of low density. such a low density region has a dielectric constant different from that of the surrounding liquid and a steamer will result. such a streamer will expand towards the anode and will eventually cause breakdown in the liquid. needless to say that such an emerging picture depends on the experimental conditions, such as the shape of the electrodes, the type of the applied voltage, the chemical constitution of the liquid and the hydrostatic pressure. positive streamer having originated from the anode and going to the cathode seem to be more filamentary than the negative streamers. both the positive and negative streamers seem to have four distinct modes of propagation [16]. iv. nanofluids nanotechnology originally was proposed as an alternative to the solution of problems in [17]. nanofluids as such were proposed in [18], who defined them as liquids having two phases: the conventional (that of the liquid) and nanoparticles (with dimensions between 1-100 nanom). various types of nanoparticles were proposed as additives for the nanofluids. nanoparticles may be classified as conducting, insulating and semiconducting. biofluids, insulating oils, ethyl glycol etc. as were considered as base liquids. nanofluids are colloid systems of two phases. a nanofluid must be stable, i.e. the nanoparticles must be evenly dispersed throughout the liquid, they must have prior treatment and they must not form agglomerations. nanoparticles are expected to improve the electrical and thermal properties of the insulating liquids since – because of their small dimensions – have large interfacial area. obviously, the interfacial zone increases dramatically by decreasing the particle size. a nanofluid – being a colloidal system – must have thermodynamic stability and depending on the relation between the attractive and repulsive forces among the nanoparticles – must avoid particle agglomerations. the behavior of a nanofluid can be explained with tanaka’s model developed in [19]. originally, the model was proposed for polymer nanocomposites. however, as it is based on colloidal chemistry, it can also be applied to nanofluids. nanoparticles are supposed to be covered by interfaces. such interfaces are formed by chemical reactions of the surface of the nanoparticles with liquid molecules [20]. according to [19], nanoparticles consist of three layers, one tightly bonded with a thickness of about 1 nm, the second bound layer of thickness of about 2-9 nm, and a third layer which is a loose layer of thickness of some tens of nm. it is the third layer that comes into contact with the surrounding base material and it creates the interface between the nanoparticle and the base material. it is true that originally this model was proposed for polymer nanocomposites but it can also be applied to nanofluids (a detailed descriptions of several nanocomposite models are given in [21-24]). actually the principles are the same, in the case of the nanofluids since we have again nanoparticles surrounded by a base material. one should not forget, however, that in the case of the nanofluids there is a larger and freer nanoparticle movement than in the case of the polymer nanocomposites. in fact, that model model must have inspired another model based on edl (electric double layer). in [25], it was reported that “according to the electric double layer (edl) theory, when the nanoparticles surface is in contact with transformer oil, the free charge in the oil will be attracted to the nanoparticles surface. the static charge on the nanoparticles surface will attract the counter-ions and repel the co-ions in the transformer oil. the charges on the particles surface and the re-arranged ions in the oil form the edl. immediately next to the charged nanoparticles surface, there is a layer of counter-ions that are strongly attracted to the particles surface and are immobile. this layer is called the compact layer. from the compact layer to the electrically neutral transformer oil, the net charge density reduces to zero gradually. ions in this region are affected less strongly by the electrostatic interaction and are mobile. this region is called the diffuse layer of the edl”. there are three basic methods to produce nanofluids. the eastman method is a one-step method which produces and disperses nanoparticles in the base fluid simultaneously. a disadvantage of this method is that it has a high cost and there may be byproducts remaining in the nanofluid because of insufficiently completed chemical reactions [26]. another method is a two-step method, in which nanoparticles initially form a nano-powder and then a mixture with the base fluid follows with the aid of ultrasonic agitation, with high shear mixing, homogenization and ball milling. it is a lower cost method since it is used now also for industrial purposes. it requires, however, that the nanoparticles are treated so that they do not form agglomerations [27]. a third method is that of submerged arc nanoparticle synthesis system (sanss) [28]. engineering, technology & applied science research vol. 8, no. 5, 2018, 3300-3309 3302 www.etasr.com danikas: breakdown in nanofluids: a short review on experimental results and related mechanisms v. experimental data regarding the breakdown in nanofluids the alteration of the nanoparticles’ surface is a good and economic way to reinforce the stability of nanofluids. surfactants (or coupling agents) have a significant influence upon the interface region between the nanoparticle and the base liquid. surfactants must be chosen in such a way that they must be well dispersed in the insulating oil. their quantity must be appropriate. in any other case, the use of a large quantity of surfactants may cause weak links between the nanoparticles and the base liquid. vi. influence of shallow traps on the breakdown of nanofluids having as base liquid the transformer oil nanofluids which have as a base liquid the transformer oil and nanoparticles tio2 present higher dielectric strength than that of plain transformer oil. in the nanofluid there is a large density of shallow traps. electrons may change their velocity to lower values because of the shallow traps and consequently the dielectric strength may increase [29]. another explanation of the improvement of dielectric strength was given in [30], where it was remarked that if the relaxation time constant of the [conducting] nanoparticles is small in comparison with the time development of a streamer in the nanofluid, then this can have an influence on the breakdown strength. if, on the other hand, the relaxation time constant is far too large, then it will have small effect on the streamer development. the charge relaxation time constant for the nanoparticles can be given as: 1 2 1 2 2 2         where, ε1 and σ1 are the permittivity and conductivity of the liquid insulation, ε2 and σ2 are the permittivity and conductivity of the nanoparticles. initially, there was the thought that conducting magnetic nanoparticles may capture the free electrons required for the streamer development and they could transform them into slower negatively charged particles because their relaxation time constant was much smaller than the time development of the streamers [30]. however, there were also indications that a certain kind of conducting nanoparticles with small relaxation time constant did not substantially increase the dielectric strength of the nanofluid in comparison with that of the transformer oil [31]. it has been observed that the addition of magnetic nanoparticles into transformer oil increased the breakdown strength of the resulting nanofluid [32, 33]. it is possible that the increase in dielectric breakdown voltage with the added magnetic nanoparticles to transformer oil might be because the conductive nanoparticles affect as electron scavengers in electrically stressed transformer oil-based nanofluids and change fast electrons into slowly negative charged nanoparticles for the electrical breakdown. to express it in other words, the extension of a net space charge zone at the streamer tip is hindered due to the slowly mobility of negative charged nanoparticles, and it is suppressed to the generated streamer propagation in the transformer oil for electric field propagation wave. the above publications confirmed previous experimental data on magnetic colloidal fluids found in [34] (full theory given in [35]). even minute additions of magnetic nanoparticle volume concentrations may substantially increase the breakdown strength of a nanofluid in comparison with the pure transformer oil (about 30% higher). similar results with magnetic nanoparticles have been reported in [36]. the latter, however, warned about the dangers of nanoparticle agglomeration and its negative effects upon the breakdown strength of nanofluids. lower increases in breakdown strength have been recorded with somehow larger volume concentrations of magnetic nanoparticles with lightning impulse voltages [37]. the reason as to why lightning impulse breakdown voltage is higher in the nanofluids was again traced to the very nature of the added nanoparticles, namely that they act as electron scavengers. the question as to whether addition of nanoparticles causes an increase or decrease of the breakdown strength was treated in [38], where it was shown that an increase or decrease depends on the nature of the added nanoparticles. according to [38] the dielectric strength of the transformer oil decreases substantially with increasing the nanoparticle volumetric concentration for multiwalled carbon nanotubes and diamond nanoparticles. very recently [39], it was noted that transformer oil-based nanofluids (with tio2 nanoparticles) present a higher breakdown strength than pure transformer oil under moisture conditions, the improvement being even larger as the moisture content is higher. in fact, as was reported, the breakdown voltage of the nanofluid at 1% probability of failure is 15.8% higher than that of the pure oil when the moisture content is 12 ppm, whereas the improvement of breakdown strength raises to 305.8% as the moisture content reaches 42 ppm. the authors contributed this increase in breakdown strength to the hydrophilicity of the tio2 nanoparticles, which can bind more dissolved water and other impurities in oil, as their size gets smaller and smaller. the bound water cannot be moved by the electrical field hereby devoting little to the breakdown process. for this reason, the ac breakdown strength and dispersion of tio2 nanofluids are much better than pure transformer oil with high moisture contents. the same group of authors [40] investigated mineral oil based nanofluids with various types of nanoparticles (fe3o4, tio2 and al2o3) employing positive lightning impulse voltages. they contributed the obtained higher breakdown strength in nanofluids to the trappingdetrapping of electrons due to the presence of the nanoparticles. the aforementioned authors realized that some differences exist as to the ability of different types of nanoparticles to contribute to the rise of the breakdown strength and they attributed this not only to the type of the nanoparticles but also to the interfacial characteristics between nanoparticles and transformer oil. the same approaches as to the breakdown mechanisms in nanofluids were also expressed in an earlier publication by the same group of authors [41]. the importance of nanoparticles for the breakdown strength of nanofluids was emphasized in [42], where magnetic nanoparticles, such as fe3o4, were dispersed in transformer oil. the authors attributed the improvement of the breakdown strength to the trapping-detrapping processes which delay the breakdown mechanism, to reduced space charge densities which in turn lead to more uniform electric fields distribution. there was, however, in the same paper also a warning against nanoparticle agglomerations. on the mechanism of scavenging engineering, technology & applied science research vol. 8, no. 5, 2018, 3300-3309 3303 www.etasr.com danikas: breakdown in nanofluids: a short review on experimental results and related mechanisms charge, also reported in [43], the authors of which also pointed out that above a critical concentration of nanoparticles, the inter–particle distance is reduced to the point wherein the liberated charges can traverse through the particle, and ‘flight’ on the next particle due to the intimacy and/or direct contact and reach to the opposite streamer zone. the percolation chains thereby act as agents that induce ‘merger’ of the streamers, often leading to numerous intermittent arc discharge and eventually leading to reduced breakdown strength. commenting on the same lines, the author of [44] pointed out that there are clearly two contrasting phenomena which are at work: charge injection and trapping occurs up to a certain nanoparticle concentration, whereas at higher nanoparticle concentrations the distance between the nanoparticles becomes too small and secondary charge emission may “bypass” the trapping behavior of nanoparticles and increase the global conductivity. addition of plasma surface treated sio2 nanoparticles into transformer oil in minute quantities (0.05wt% and 0.1wt%) greatly improves the breakdown strength of transformer oil. the authors of [45] claimed that instead of using surfactants, atmospheric pressure plasma treatment is an effective, simple, inexpensive and environmentally friendly method to improve the stability of nanofluids and enhance the characteristics of the nanofluids as well. addition of sio2 nanoparticles into a soya based natural ester oil also raised the breakdown voltage significantly (the 0.01 wt% concentration virtually tripled the breakdown voltage of ester oil without nanoparticles) [46]. moreover, the same authors presented data which showed that the partial discharge inception voltage of such nanofluids was higher than that of pure soya based natural ester oil [47]. there was further elaboration of the above in yet another paper, again with the use of sio2 nanoparticles [48], with the authors emphasizing the negative effects of nanoparticle agglomeration. they noted that while they moved from 0.05wt% to 0.1wt% concentration the electrical performance of sunflower oil started to decline. however, there were also reports that indicated that breakdown strength does not improve with the addition of nanoparticles (in particular with nanoparticles sic). such nanoparticles, on the contrary, decreased the breakdown strength of transformer oil [49]. the same authors concluded that, in view of such data, more experiments should be done, since some of the experimental results seem to be contradictory. the fact that there is not always an improvement in nanofluids breakdown strength was also stressed in [50], the authors of which investigated virgin linseed and virgin castor oil with 5 wt% addition of silica aerogel powder nanoparticles. they found that nanomodification increased streamer activity in the vegetable oils. the increased streamer activity was more aggressive in nanomodified castor oil than in nanomodified linseed oil. they proposed as a possible explanation for this the possible presence of contaminants left by a filler compatibilisation process which can worsen the electrical properties of a nanostructured material. authors in [51], it was noted that nanoparticles such as fe3 o4, zno, tio2, sio2, improved the ac breakdown strength of transformer oil in volumetric concentrations ranging from 0.0005% up to 0.02%. they pointed out the vital role of an appropriate surfactant for the breakdown strength improvement. regarding dc breakdown as well as impulse breakdown, they noted that results were encouraging for both polarities. experimental work performed by the authors of [52] showed that nanoparticles of zno with 0.04% volumetric concentration may give up to 63.5% enhancement in breakdown voltage compared with pure transformer oil. the authors remarked that there is an optimum concentration of nanoparticles which may give high breakdown voltage as well as high fire and flash points. experimental data was also produced in [53], where zno nanoparticles of 0.2wt% up to 1wt% were added into transformer oil. the breakdown voltage increased by about 10% in comparison with the pure transformer oil. it must, however, be noted that the nanofluid with more than 0.4wt% concentration showed an increase in electrical conductivity. a very recent development proposes transformer oil-based graphene quantum dots nanofluids [54]. however, as far as the breakdown strength is concerned, there was not any significant difference between pure transformer oil and its transformer oilbased nanofluid. the difference was minimal, such as not to warranty any replacement of transformer oil with the nanofluid, at least regarding the breakdown strength. in [55], it was indicated that carbon nanotubes, when dispersed in transformer oil, can increase substantially the breakdown voltage. in fact, it was shown that a concentration of 0.01 g/l carbon nanotubes may increase the breakdown voltage as much as 88.95% compared with the pure transformer oil. the authors also emphasized that there is a saturation point, after which the addition of carbon nanotubes does not improve the breakdown voltage but on the contrary may diminish it. transformer oil with nanoparticles of tio2 was investigated in [56]. the author worked by adding tio2 nanoparticles at a concentration of 0.0005 g/ml. the increase in breakdown voltage w.r.t. that of pure transformer oil was attributed to either the fact that polarized tio2 nanoparticles can act as electron traps to catch free electrons released from oil molecules under high electric stresses or to the higher chance of electron scattering in nanofluids due to the high specific surface area of nanoparticles. deviating from the usual added nanoparticles, a research team proposed the admixture of nanocrystalline manganese nickel ferrite powder concerning substitution degree of 20% (mn0.2ni0.8 fe2o4) into transformer oil at different concentrations of 0.02, 0.04, and 0.06 g/l [57]. the experiments were carried out with impulse voltage and the authors found that the optimum concentration was that of 0.04 g/l, which gave a breakdown voltage improvement of 42.3% as opposed to improvements of 37.7% and 39.1% for the 0.02 g/l and 0.06 g/l concentrations respectively. the authors, however, did not mention anything as to the stability of such mixtures in the long run. in [58], transformer oil with mgmnni nanoparticles were investigated regarding its breakdown strength (in some cases it almost doubled the breakdown strength in comparison with pure transformer oil]. the authors attributed the increase to the enhanced electric field dissipation due to the presence of magnetite nanoparticles. in [59], mgmnnife2o4 nanoparticles were dispersed in transformer oil (<1% by volume) improving by about 40% the breakdown strength in comparison with pure transformer oil. engineering, technology & applied science research vol. 8, no. 5, 2018, 3300-3309 3304 www.etasr.com danikas: breakdown in nanofluids: a short review on experimental results and related mechanisms diamond nanoparticles dispersed in small concentration (0.15 wt%) into transformer oil may raise the breakdown voltage considerably. the reason given in [60] was not any different from that given in other publications, namely that nanoparticles act as surface traps and, consequently, they can entrap the surface electrons. the fast electrons change to the slow ones, and subsequently an increase in the breakdown voltage results. although the explanation may not be entirely novel, the authors commented on the importance of surfactants for the nanoparticles and their influence not only on the breakdown voltage but also on viscosity, dielectric loss and thermal conductivity. the role of surfactants was also emphasized in [61], where it was shown that the surfactant volumetric concentration may be 40% of the complete nanoparticle volume. the authors showed that there is a strong dependence of the breakdown strength of a vegetable oil-based nanofluid on the nanoparticle size as well as on the thickness ratio between the nanoparticle diameter and that of the surfactant. it seems that smaller surfactant thickness offers more shallow traps and consequently a greater chance of electron trapping-detrapping. in [62], the ac breakdown voltage as well as the positive lightning impulse breakdown voltage of mineral oil-based nanofluids with alumina were shown to be higher than the respective quantities of the pure transformer oil. the authors, however, did not further elaborate as to why this should be so. sio2 nanoparticles were added to transformer oil in concentrations of up to 0.06% volume fraction and the ac breakdown voltage increased considerably up to 35% compared with pure transformer oil [63]. a further increase, however, of the nanoparticle concentration leads to a decrease of the breakdown voltage of the nanofluids. higher concentration may lead to the overlap of nanoparticles making thus a highly conductive region. the free charge will travel along the high conductive path and this process may cause a lower breakdown voltage. palm fatty acid ester (pfae) oil with three types of nanoparticles at a concentration of 0.01 g/l (fe3o4 conductive nanoparticles, tio2 semi-conductive nanoparticles and al2o3 insulating nanoparticles) was been tested in [64]. the nanofluid with the fe3o4 conductive nanoparticles presented the highest ac breakdown strength (an increase of 45% compared to 29% for tio2 nanoparticles and 34% for the al2o3 nanoparticles). the explanation regarding the improvements of the breakdown strength was attributed for the conductive nanoparticles to their electron scavenging capability, and to the semi-conductive and insulating nanoparticles to their shallow trap production. fe3o4 nanoparticles were dispersed in transformer oil at volume concentrations of 0.1-0.6 %, with the impulse lightning voltage being the highest at about volume concentration of 0.3% [65]. other researchers [66] experimented with ac voltages as well as with positive and negative lightning impulses in nanofluids having fe3o4 nanoparticles. they found that the ac breakdown voltage was by 16% higher than that of the pure transformer oil, the positive lightning impulse breakdown voltage by 36% higher than that of the pure transformer oil and the negative lightning impulse breakdown voltage by about 20% higher. they attributed such large differences to the well known theory developed in [67], according to which if the relaxation time constant of free charges accumulated on the surface of nanoparticle is shorter than the time scale of streamer propagation, the presence of nanoparticles will effectively alter the electrodynamics in the oil. yet another group of researchers dispersed tio2 nanoparticles in transformer oil [68]. the concentrations of tio2 nanoparticles in transformer oil are in the range from 0.001 g/l to 0.01 g/l. the optimum concentration was about 0.003 g/l for both fresh and aged transformer oils (4 and 15 years aged oils). they attributed the improvement –as others before them – to the electron scavenging properties of the nanoparticles. dispersion of tio2 nanoparticles in transformer oil in quantities of 0.05 up to 0.30 g/l and their effects on the breakdown strength was reported in [69]. the largest breakdown voltage was observed for 0.30 g/l concentration of tio2 nanoparticles. in a later publication, the same authors [70] reached the same conclusions, emphasizing the important role the surfactants play in the dispersion of nanoparticles. no surfactant or low surfactant concentration leads to nanoparticle agglomeration but, on the other hand, excess of surfactant concentration leads to double chains around the nanoparticles reducing thus their effectiveness. more recently, authors in [71] experimented with natural-ester transformer oil by adding cuo, zno and tio2 nanoparticles. the breakdown voltage with the two latter types of nanoparticles was greatly improved (with concentration of less than 0.05 wt%), whereas the nanofluid with cuo nanoparticles showed at first an increase in the said quantity and then a decrease. with concentration of more than 0.1 wt% the breakdown voltage did not improve as far as the nanofluids with zno and tio2 nanoparticles were concerned. from this publication it is evident that different types of nanoparticles with different added percentages affect differently the breakdown voltage of an insulating oil. the explanation of the authors as to why such an improvement results does not differ from that of other researchers. added tio2 nanoparticles into natural ester fluid (nanoparticle content 0.4 g/l) improved its breakdown voltage, especially after 150 hours of ageing [72]. the authors of [72], however, posed questions as to the long-term stability of such nanofluids. some other researchers experimented with soybean ester oil and palm ester oil with tio2 and zno nanoparticles [73]. both oils showed a higher ac breakdown voltage with 0.2 g/l nanoparticles (of either type). the explanation they offered as to the higher breakdown voltages with the nanofluids was not different from those of other scientists. it is to be noted, however, that increasing amounts of nanoparticles seem to have negligible effect on the flash point, fire point and viscosity [73]. thus, nanofluids have to be considered in all their properties before a final decision has to be made about the replacement of the more classical insulating liquids. an interesting aspect of tanaka’s model (which was proposed for polymer nanocomposites) was tackled in [74]. the authors tried to explain the superior breakdown strength of natural ester oil with boron nitride nanoparticles (with content of 0.005 wt% and 0.1 wt%) in terms of tanaka’s model, namely that with the decrease in size of the nanoparticles the interfacial regions become very important and they alter the charge distribution causing thus change in trap density and depth. the homocharge due to trapping reduces the electric field intensity and causes an increase of the voltage for charge engineering, technology & applied science research vol. 8, no. 5, 2018, 3300-3309 3305 www.etasr.com danikas: breakdown in nanofluids: a short review on experimental results and related mechanisms injection from the electrodes. this in turn causes the increase of the short term breakdown voltage. a point of contention in this paper is certainly the claim that there is an increase of the short term breakdown voltage. this, however, will be discussed in the following section. an improvement of the ac breakdown strength as well as of the positive lightning impulse strength (but not of the negative lightning impulse strength) of vegetable oil with fe3o4 nanoparticles was reported by [75]. the remarkable about this paper is that the authors attribute the higher breakdown strength of nanofluids to the larger electrical potential wells of nanoparticles in comparison with the ones of the pure insulating liquid. they also mention that the electrical potential wells are larger as the nanoparticle size becomes larger. such electrical potential wells inhibit the free charge spread and enhance the capability of the breakdown performance of the nanofluids. work carried out with natural ester based nanofluids (with commercial mions powder (pnf) and oleic acid surface modification, as well as with oleate-coated colloidal mions (colnf)) showed that breakdown voltage was the highest with the colnf at a concentration of about 0.008wt%). the authors attributed the decrease of the breakdown voltage after the surpassing of the 0.008wt% concentration to the [76] to the decreasing of interparticle distance and the formation of conductive paths. the positive influence of nanoparticles (sio2, tio2, zno, al2o3, fe3o4 and sic) in transformer oil and in natural ester oil was reported in [77]. the authors emphasized the importance of moisture in diminishing the breakdown strength in both types of oil. similar conclusions regarding the positive effect of sio2 hydrophilic nanoparticles were reached in [78], where, however, it was also remarked that their positive influence depended on their size and their volume concentration. similar conclusions regarding the moisture absorption on the hydrophilic surface of silica nanoparticles have been reached in [79]. nanoparticles of fe3o4 added to transformer oil in volume concentration of 0.2% raise the dc breakdown voltage in comparison with pure transformer oil [80]. such nanoparticles affect negatively the formation of bubbles and because of their extremely short charging time, they are excellent electron traps. a criticism levelled against the use of conductive nanoparticles was reported in [81], where it was mentioned that conductive nanoparticles tend to agglomerate in the long-term and nanoparticles such as fe3o4 tend to oxidize and become fe2o3 particles. the author of [81] proposed that nanoparticles such as tio2 and bn offer better possibilities to both mineral oil and ester based oils. the aforementioned nanoparticles in minute quantities improved the ac breakdown voltage and also the lightning impulse voltage of the said oils. adding nanoparticles of tio2 and zno (in concentration of 0.01wt%) into natural ester oils improved the ac breakdown voltage as well as the lightning impulse (both positive and negative) [82]. the authors of the latter publication distinguished between adding nanoparticles in liquid form and in powder form and they observed that the nanoparticles in liquid form gave the highest breakdown voltage, probably because of the better dispersion in liquid form. an improvement in breakdown strength was noted for both ac voltages and lightning impulse voltages. other researchers [83] investigated nanofluids based on transformer oil and on synthetic ester oil with sio2 nanoparticles. the increased lightning impulse breakdown voltage – with volume concentrations from 0.1% up to 1% they found was attributed to the hydrophilic nature of the sio2 nanoparticles and their altered degree of polarization. (researchers exploring various nanoparticles in mineral oil found that al2o3 and tio2 nanofluids remain good insulating liquids as far as their dielectric constant and loss tangent are concerned but they expressed their reservations as to the long term insulating properties over a broad range of frequencies (20 hz-1 mhz) because of water absorption from hygroscopic nanoparticles [84]). an improvement of breakdown strength of aged transformer oil by adding nanoparticles of either zno or tio2 in volume concentrations w/v% of 0.001%, 0.0015%, and 0.002% was observed in [85]. 10and 20year old oils were treated with nanoparticles and showed a satisfactory recovery in breakdown strength. similar conclusions about the beneficial effect of tio2 nanoparticles on the breakdown voltage and the insulation resistance of mineral oil (in concentrations of 0.06 g/l) were recently reached also in [86]. recently [87], there were reports about the improvement of ester oil breakdown voltage with egg shell nanoparticles in 0.0.001wt%, 0.0025wt% and 0.005wt% concentrations. the highest breakdown voltage was noted for 0.005wt% and it was attributed to the fact that such nanoparticles can absorb moisture. the authors reported stability of the nanofluid up to 48 hours without the formation of any precipitate/particles sedimentation. however, there are cases where the breakdown strength of transformer oil does not increase. recent work [88] indicated that tungsten (iii) oxide (wo3)-silver nanoparticles in concentration of 1wt%, 2wt% and 3wt% decreased the breakdown strength compared with that of pure transformer oil. perhaps the electrical conductivity of silver particles contributed to that decrease. vii. proposals for future research from the limited survey presented in this paper, it is clear that most of the researchers agree on the reasons of the improvement of the breakdown strength of nanofluids, i.e. on the workings of the mechanism which renders nanofluids superior to their respective base liquids. from the literature survey, it is evident that the concentration of nanoparticles into base insulating liquids depends on the oil itself, on the type of nanoparticles, on the surfactants and on the treatment, i.e. the way of preparation of the nanofluids. experimental data seems to be very sensitive to all the previous parameters. consequently, more work has to be done in the materials direction in order to better understand the properties of nanofluids and their effect on breakdown strength, especially in the light of some contradictory results, as reported in [89] and in [90]. the authors of the latter publication make the distinction between conducting, semiconducting and nonconducting nanoparticles claiming that the latter are more benign than the two former types of nanoparticles. furthermore, more work has to be performed in the direction of high and low dielectric constant nanoparticles since, according to recent research, it seems that the former tend to better trap engineering, technology & applied science research vol. 8, no. 5, 2018, 3300-3309 3306 www.etasr.com danikas: breakdown in nanofluids: a short review on experimental results and related mechanisms and de-trap electrons, whereas the latter do not have the ability for electron attraction [91]. among the things that remain to be seen and investigated, is whether the tanaka model (proposed for solid nanocomposites) is also valid for nanofluids. this point can be further elaborated: since tanaka’s model seems to work for solid dielectrics – nanoparticles act as nano-barriers against the treeing etc. – and nanoparticles in nanofluids seem to attract free electrons and thus hinder streamer propagation, it would be of interest to see whether tanaka’s model can find an application also in nanofluids. other nanomaterial models, such as those mentioned in [22], can also be tested for their validity in the field of nanofluids. breakdown studies in solid dielectrics show that nanoparticles act as barriers which hinder treeing and breakdown. breakdown studies in liquids, however, emphasize more the scavenging effects of nanoparticles. based on this difference, we think that tanaka’s model has to be modified somehow in order to take into account the scavenging possibilities of the nanoparticles. whether this is a right idea must be further explored. moreover, what has been done for classical insulating liquids (i.e. experiments with area effect, gap effect, volume effect, conditioning phenomenon) must also be performed with nanofluids. in traditional insulating liquids there has been an intensive study of such factors upon the breakdown strength. similar studies must be carried out for the nanofluids. statistical studies (based either on weibull or on any other distribution) should be done in order to see whether nanofluids follow also the pattern of the classical liquids (although it seems that most of the researchers tend to work with weibull distribution). the effect of nano-agglomerations needs also a closer look. the role of surfactants has to be thoroughly researched [92]. a question in need of an urgent answer is that of the long-term stability of nanofluids [44]. the already reported improvement of nanofluids – regarding their breakdown strength – because of electron scavenging from the nanoparticles, needs to be investigated in the long run and see whether experimental results are repetitive. another aspect of the nanofluids that has to be further researched is the compatibility of such liquids with solid insulation. given that the nanofluids present a somehow different dielectric constant from the base liquids, the question that arises is whether such difference in dielectric constants (between nanofluids and air pockets or voids) renders the use of such liquids more difficult. important work already done in relevant areas has to continue [93]. furthermore, nanoparticle research has to be performed with vegetable derived fluids or synthetic esters, which are supposed to have a more “green” behavior (such research is being already done but it has to be intensified). another aspect of nanofluids that has to be researched is their behavior at elevated temperatures. last but not least, and this is valid for all nanomaterials, the insulation community has to see how laboratory experiments and data can be translated into larger samples of industrial sizes. concerns as to how this can be realized have already been expressed [94]. needless to say that all the above can be realized under the assumption that adequate funding is and will be available [95]. viii. conclusions this publication is a short review on the breakdown of nanofluids. a large number of researchers converges as to the mechanism of breakdown in a nanofluid. nanoparticles seem to have a scavenging role regarding the free electrons and as a consequence a higher breakdown strength results. however, in the context of this paper, only one aspect has been 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596-599 596 www.etasr.com aditya and newwel: implementation of close loop speed control with vvvf control … implementation of close loop speed control with vvvf control and slip regulation on lim kunwar aditya m.tech, department of electrical engineering it bhu varanasi, india kunwar.aditya.eee10@itbhu.ac.in albert newwel m.tech, department of electrical engineering it bhu varanasi, india albert.newwel.eee10@itbhu.ac.in abstract: open loop vvvf control has the disadvantage of low output torque when working at low frequency and poor speed precision at different load conditions. various performanceimproving schemes have been proposed for the basic vvvf control by compensating slips occurring in the low frequency range and slips caused by changing loads and several papers have been published on the close loop speed control of rotary induction motor. in this paper a close loop speed control with vvvf control and slip regulation has been implemented for lim based conveyor belt test rig which compensates the disadvantages of traditional volts/hz control. simulink results are presented to validate the effectiveness of the proposed scheme. keywords-linear induction motor; close loop speed control; slip regulation; vvvf control i. introduction the vvvf scalar control scheme has been used broadly in the industry due to the speed/torque control advantage in rotary induction motor based drives. however, in the traditional vvvf scalar control the percentage voltage drop across the stator resistance is more dominant compared to the voltage drop for the production of the main flux at low frequencies. in addition, the vvvf scalar control scheme provides open loop control, and therefore the system cannot maintain speed accuracy both at low frequency and high load operation. to overcome these drawbacks, vvvf scalar control with slip frequency regulation is being widely suggested [1, 2]. recently, linear induction motors (lim) are being adopted for certain applications due to their obvious advantages over rotary induction motors [3]. practical applications of these motors to various linear drives are now numerous [4]. in this paper, vvvf control with slip frequency regulation has been implemented on a linear induction motor to demonstrate the effective closed loop control of linear speed. simulation results have been obtained using matlab/simulink. ii. control strategy figure1 represents the block diagram of the control strategy [2, 5] which has three distinct parts: the v-f control, the stator resistance voltage compensation and the slip frequency compensation. a strategic block diagram of close loop speed control is shown in figure 1. the actual speed of the secondary member (vr) is compared with its commanded value (vr*) and the error is processed through a pi controller and a limiter to obtain the slip-speed command, vsl*. the limiter ensures that the slip speed command is within the maximum allowable slip speed of the lim. the slip speed command is added to the speed of the secondary member to obtain the synchronous speed, vs* for generating a frequency command. the frequency command then generates a voltage command through a volts/hz function generator. to compensate for the primary-member-resistance-voltage drop, a boost voltage is added to the generated voltage so that the desired rated flux and hence the corresponding thrust becomes available down to zero speed. effect of boost voltage, however, becomes negligible at higher frequencies. figure 2 portrays a typical simulink model of linear induction motor in d-q stationary reference frame. the parameters and specification of lim based conveyor belt test rig used in the simulink model are given in table i. table i. parameters & specifications of lim voltage(line-line) 440 v frequency 50hz number of poles (p) 8 primary resistance (r1) 64 ω primary leakage reactance (x1) 108.7 ω magnetizing reactance ( xm) 76.15 ω secondary resistance (r2) 1.7 ω secondary reactance (x2) 72 ω mass of copper belt (m) 1.99 kg coefficient of friction (b) 0.028n-sec/kg pole pitch .099mts iii. simulation results the simulation results for the following cases are presented and discussed:  case a: effect of step change in reference speed at no load  case b: effect of boost voltage at low frequency  case c: effect of slip regulation  case d: performance under load variation engineering, technology & applied science research vol. 4, no. 2, 2014, 596-599 597 www.etasr.com aditya and newwel: implementation of close loop speed control with vvvf control … fig. 1. strategic block diagram of close loop speed control fig. 2. simulink model of close loop speed control with volts/hz control and slip regulation a. case a: effect of step change in reference speed at no load to validate the control strategy, at no load condition the frequency has been set to change in the simulink model from 15 hz to 50 hz at a frequency-step of 5 hz every 7 sec. the no load however includes the weight of the moving conveyor belt and the friction offered during motion. figure 3 shows that the variation of actual linear speed closely follows the reference linear speed (with respect to simulation time) due to the change in frequency. the variation of the inverter output phase voltage with respect to the simulation time due to the change in frequency is shown in figure 4. the results of figures 3 and 4 have been arranged in tabular form in table ii to demonstrate the validation of the model. table ii. variation of inverter output phase voltage and linear speed w.r.t. reference speed ref. speed (m/s) actual speed (m/s) frequency (hz) inverter output phase voltage (volts) volts-tohz ratio 2.97 2.97 15 64.5 5.41 3.96 3.96 20 86 4.95 4.95 4.95 25 107 4.64 5.94 5.94 30 133.8 4.46 6.93 6.93 35 152.25 4.35 7.92 7.92 40 169.6 4.24 8.91 8.91 45 187.4 4.16 9.9 9.9 50 205 4.1 fig. 3. variation of reference speed and actual linear speed with respect to simulation time due to change in frequency fig. 4. variation of inverter output phase voltage with respect to simulation time due to change in frequency from figures 3, 4 and table ii one can observe that actual speed is changing according to the desired reference speed. the inverter output phase voltage is also changing according to the change in frequency such that the volts/hz ratio is almost constant with slight variation at low frequency due to the incorporation of boost voltage. hence volts/hz control is simulated successfully. b. case b: effect of boost voltage at low frequency to show the effect of boost voltage under low frequency of 5 hz the model was simulated at 20n load condition applied at 15 sec. speed and thrust performance is compared without and with boost voltage. value of boost voltage was set at 20 volts by trial and error. fig. 5. speed and thrust response at 5 hz frequency and 20 n applied at simulation time of 15 sec without boost voltage engineering, technology & applied science research vol. 4, no. 2, 2014, 596-599 598 www.etasr.com aditya and newwel: implementation of close loop speed control with vvvf control … fig. 6. speed, thrust and air gap flux response at 5 hz frequency and 20 n applied at 15 sec with boost voltage of 20 volts. based on the simulation results, when a 20 n load is applied at a low frequency to the lim based conveyor belt system the following are observed: without boost voltage control the air gap flux becomes zero and the system becomes unstable as shown in figure 5, whereas the air gap flux does not becomes zero and the system remains stable when a boost voltage is applied as shown in the figure 6 c. case c: effect of slip regulation to demonstrate the effect of slip regulation under various loads the model has been simulated for scheduled changes in load in the sequence [0 5 10 20] n at the reference speed of 2.97 m/sec (i.e.15 hz frequency). the simulation results for cases without and with slip regulation are shown in figures 7, 8 and table iii. fig. 7. speed response without slip regulation for 15 hz frequency when a 20 n load is applied at simulation time t=15 sec fig. 8. speed response with slip regulation for 15 hz frequency when a 20 n load is applied at simulation time t=15 sec table iii. slip-speed at 2.97 m/sec (15 hz frequency) at different loading conditions loading condition without slip regulation with slip regulation 0 n 0.001 m/s 0 m/s 5 n 0.020 m/s 0.01 m/s 10 n 0.043 m/s 0.021 m/s 20 n 0.11 m/s 0.05 m/s figures 7, 8 and table iii depict that the speed accuracy at no load (i.e at 0 n) is good, both for the traditional vvvf control and the proposed closed-loop speed control method. but as the load increases slip speed for the traditional vvvf control (without slip regulation) increases whereas for the slipregulation control increase in the slip-speed is reduced. figure 9 demonstrates the effect of slip regulation under load efficiently. hence, it is shown that the proposed closed loop speed control with slip-regulation gives better speed accuracy. fig. 9. speed response at load condition d. case d: performance under load variation in this case, the reference speed is fixed to its synchronous speed of 3.96 m/s at 20 hz frequency and the load is being changed in the sequence [0, 10, -10, and -20 n]. it is observed from table iv that when the load becomes negative, lim has entered the generating region, as the slip becomes negative. the line currents, the secondary speed, and the electromagnetic torque are shown in figure 10. table iv. slip speed at different loading condition at reference speed of 3.96 m/sec (i.e. 20 hz) loading condition slip speed 0 0 10 n 0.22 m/sec -10 n -0.212 m/sec -20 n -.0411 m/sec iv. conclusion the traditional volts/hz control scheme has the disadvantage of poor speed precision at different loads and small output thrust when working in the low frequency. to overcome these disadvantages an alternative control scheme is proposed. the incorporation of boost voltage makes the system suitable for working under low frequency conditions. slip engineering, technology & applied science research vol. 4, no. 2, 2014, 596-599 599 www.etasr.com aditya and newwel: implementation of close loop speed control with vvvf control … regulation maintains the speed constant at loading conditions. the results obtained through simulink simulations were fair enough to validate the effect of volts/hz control, slip regulation and boost voltage. it should be noted that the simulation coefficient of friction was taken to be constant but in practical implementations it will change according to the speed. also, that the mass of the belt and friction was considered under no load conditions. to validate the simulation results and incorporate the effect of mass and friction a test rig has been developed in it bhu machines and drives lab [7]. work is in progress and experimental results will be presented in following papers. fig. 10. line current, linear speed and thrust response for programmed change in load. acknowledgement the authors acknowledge the usage of developed facility in the department of electrical engineering, institute of technology, banaras hindu university. references [1] z. yu, d. figoli, “ac induction motor control using constant v/hz principle and space vector pwm technique with tms320c240”, digital signal processing solutions, texas instruments, 1998, [online]. available at: http://www.ti.com/lit/an/spra284a/spra284a.pdf [2] b. k. bose, modern power electronics and ac drives, pearson education asia, 2002 [3] e. r. laithwaite, s. a. nasar, “linear-motion electrical machines”, proceedings of the ieee, vol. 58, no. 4, pp. 531–542, 1970 [4] g. v. sadler, a. w. davey, “applications of linear induction motors in industry”, proceedings of the institution of electrical engineers, vol. 118, no. 6, pp. 765-776, 1969 [5] s. p. muley, m. v. aware, “modeling and simulation of a scalar controlled induction motor using combined inverter machine interaction in state space” , 2009 second international conference on information and computing science, pp. 3–6, united kingdom, may 21-21, 2009 [6] a.k. rathore, s. n. mahendra, “decoupled control of attraction force and propulsion force in linear induction motor drive”, 2003 ieee international conference on industrial technology, vol. 1, pp. 524– 529, 2003 [7] s. velisetti, “simulation and implementation of vvvf, cvvf and cfvv controls on lim using dspace”, m.tech. dissertation supervised by prof. s. n. mahendra, department of electrical engineering, banaras hindu university, varanasi, india, 2011 microsoft word 04-mirdrikvand-ed.doc etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 310-314 310 www.etasr.com mirdrikvand et al: velocity boundary analysis of a flat plate heat exchanger in laminar flow… velocity boundary layer analysis of a flat plate heat exchanger in laminar flow: a case study mojtaba mirdrikvand research center of petroleum university of technology mirdrikvand@ gmail.com behrooz roozbehani research center of petroleum university of technology roozbehani.behrooz @gmail.com saeedeh imani moqadam research center of petroleum university of technology saeedeh.imani@ gmail.com ali cheshmeh roshan research center of petroleum university of technology mojtaba_pop@ yahoo.com yasin ramezani petroleum university of technology yasin.ramezani@ put.ac.ir abstract— in this article, a behavioral analysis of velocity boundary layer in a flat plate heat exchanger in laminar flow condition through cfd simulation using fluent software is done. the main objective of this study is to determine the velocity vectors between the flat plates of the heat exchanger. in addition, wake occurrence, differences of velocity at different surfaces between plates, angles of velocity vectors and the effect of wake phenomenon on the shear stresses exerted on the plates are discussed in detail. the study graphically illustrates results based on fluid’s behavior by a 3d and 2d simulation with air and water as cold and hot streams that affect plate’s situation and its hydro dynamical operations. consequently, some important design features regarding wake point occurrence and pressure loss are investigated. in addition, eddy current and reverse flows in the wake area and the angles of the velocity vectors are described. keywordsflat plate heat exchanger; wake; boundary layer; velocity; fluent; cfd i. introduction plate heat exchangers (phes) are among the most applicable thermal facilities in diverse industries, particularly in oil and gas operations [1, 2]. due to their high thermal efficiencies, phes are widely used in industries. plate heat exchangers are mainly made of thin plates that are pressed into a whole frame and shaped in a package. they are designed in various types based on which the plates might be flat or curved with different angles according to their applications [3, 4]. phes are much more sensitive to temperature and pressure than other heat exchangers. their sensitivity is due to their structures that are mainly specified by plate perforations and gasket designs [3, 5]. an accurate modeling of the phe not only simplifies fluid flows study and velocity governing equations but is also significant for proper equipment evaluation and design [6-7]. computational fluid dynamics, briefly recognized as cfd, technically models fluid behavior using computer simulation. referring to growth and establishment of computer programing in engineering science, development of cfd software packages is implemented to simulate complex pragmatic flow simulation. in a computational characterizing of flow behavior, mathematical equations that approve the flow dynamics roles are used to attain a proper treatment of flow. therefore, computational fluid dynamic (cfd) methods are used to model phes. in a cfd modeling, computational algorithms are used to model heat, mass, and momentum transfer [8]. it brings a rapid solution for designing and optimizing heat exchangers [9]. small cells are used to estimate the geometrical shape [10]. considering grids and boundary condition restrictions and implementing numerical solving methods help finding velocity boundary layers and analyzing them [11]. a simulation of a flat phe on plate surfaces has been investigated in this study in order to analyze velocity boundary layer using fluent [16]. the occurrence of the wake phenomenon and its influence on shear stresses that are exerted on plates are discussed in detail and illustrated graphically [18, 19]. this study was conducted to simulate a flat phe in the research center of abadan institute of technology, with dimensional features shown in table i, constructed from may 2010. the results of this paper are going to estimate the process conditions, and also the velocity boundary layers of the heat exchanger. a. using cfd for boundary layer analysis the basis of computational fluid dynamics, is solving fluid problems by using numerical methods to convert the partial differential equation to numerical equation. two numerical methods can be used for solving: fvm (finite volume method) or fem (finite elements method) [12]. b. finite volume method the finite volume method is a method for representing and evaluating partial differential equations in the form of algebraic equations [13, 15]. fvm refers to small volume surrounding each node point of a mesh. in the finite volume method, volume integrals in a partial differential equation that contain a divergence term are converted to surface integral, using the divergence theorem [17]. these terms are then evaluated as fluxes at the surface of each finite volume; these methods are conservative. another etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 310-314 311 www.etasr.com mirdrikvand et al: velocity boundary analysis of a flat plate heat exchanger in laminar flow… advantage of the finite volume method is that it is easily formulated for unstructured meshes. it is much easier to capture (as well as numerically possible) the characteristic nature of hyperbolic equations in fvm using flux split schemes, upwinding etc. [14, 15]. table i. plate’s main dimensions dimension value plate height, (mm) 550 plate thickness (mm) 1.0 distance between plates (mm) 5.0 height of channel (mm) 63.5 heat transfer area (m2/plate) 0.0635 distance between channels 40 ii. simulation the first step of a cfd simulation must be completed by mesh generation, which is the geometrical restriction that satisfies the equations for heat transfer and momentum transfer [13, 15]. hot fluid enters from top left channel of figure 1 and cold fluid enters from right bottom channel. the number of meshes reported from the software is 37240, created with the software gambit. fig. 1. gambit a) unmeshed shape b) gambit meshed shape a. using air as a hot and cold flow 3-d shape plate’s dimension is x=220 mm, y=550 mm, z=20 mm and the area of one 0.24 m 2 area channel is 0.0036 m 2 , sectional area is 0.004 m 2 and flow air velocity is about 0.05 m/s. b. results and discussion the problem was numerically solved using the finite volume method [12] with fluent 6.3.26. the simulations were carried in a core 2 duo cpu with 2 gb ram. by using 2 ddp mode and implicit formulation and considering pressure based solver by momentum and energy discretization in 2 dimensional space, it implies a 5000 number of iterations and 1e-06 residual. when fluid passes through the plates, the pressure decreases, this is due to head loss, as shown in figures 3(a) and 3(b) [20]. the color of hot flow input is orange but the color of hot flow output is blue, this shows that the pressure has been decreased (the magnitude of the figure is in gage). steady flow enters the channel but at the exit eddy current is produced, due to shear stresses and wake. in figure 6 eddy current is shown. fig. 2. 3-d plates fig. 3. a) contour of pressure (pa) b) eddy current at the exit of hot & cold flow at flow entrances the channel area is 0.0635 m 2 , but between the plates the cross sectional area is 0.005 m 2 , so the cross sectional area has been decreased, which causes an increase in flow velocity, as shown in figure 5. the shear stresses are exerted to the fluid by the wall. the velocity of a layer in contact with the wall is zero, and increases with d (distance from the wall). in figures 5 and 6 the magnitude of velocity near the plate is low, whereas far from the plate is high. at x=0, velocity is zero because the layer of fluid is connected with the plate. between x=0.002 and x=0.003 the magnitude of velocity is maximum because it is placed as far as possible from adjacent plates. fig. 4. contour of velocity (m/s) etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 310-314 312 www.etasr.com mirdrikvand et al: velocity boundary analysis of a flat plate heat exchanger in laminar flow… fig. 5. velocity vectors between plates fig. 6. velocity vectors at cross section of the plates table ii. velocity magnitudes at different differences surface vertex value (m) velocity magnitude (m/s) surface vertex value (m) velocity magnitude (m/s) -0.001 11.4077 0.001 11.660 -0.002 14.1264 0.002 14.443 -0.003 13.7345 0.003 14.061 -0.004 10.1425 0.004 10.360 -0.005 5.5176 0.005 1.2882 0 0 when the magnitude of velocity along a streamline increases, the magnitude of pressure will decrease. this is due to bernoulli equations. in figures 7(a) and 7(b), the color of velocity vectors near the channel is red. the color tends to blue at the cross sectional area as the flow, and the magnitude of pressure, decreases. as illustrated in figure 7, ‘wake’ occurs near the right wall. the direction of some vectors near the right wall is downward and the angle of vectors varies from -180° to 180°. c. 2-d plates.... fluid: water: assumption in fluent assumptions used in this study are the same as in the previous section. wake occurred in cold output and near the wall is shown in figures 8 and 9. according to figures 10(a) and 10(b), the magnitude of pressure through the plates decreases. the magnitudes of the velocity between plates increases compared with internal channel velocity. fig. 7. a) velocity vector b) pressure vectors fig. 8. wake occurred in cold output fig. 9. wake occurred near the wall fig. 10. a) velocity contour (m/s) b) pressure contour (pa) etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 310-314 313 www.etasr.com mirdrikvand et al: velocity boundary analysis of a flat plate heat exchanger in laminar flow… now we want to compare the velocity magnitude near the plate and far from the plate. figure 11 shows velocity magnitude vs. y at x=0.0002 m, and figure 12 shows velocity magnitude at x=0.0025 (exactly at the middle of the plates). average velocity at x=0.0002 m is equal to 4.73 m/s while the average velocity at x=0.0025 m is equal to 12.7 m/s. due to wake, the angle of vectors varies from -180 to 180 near the wall, as shown in figure 12 and 13, the angle of vectors in range [y=0.0635, y=0.175] is so various. due to the wake phenomenon, wall shear stress in y ranges [0.0635, 0.175] has vibration values. in range y [0, 0.0635] and y [0.4865, 0.55] there is no wall so the shear stress is equal to zero. d. (3-d plates…. fluid: air) using fluent in 3ddp mode and implicit formulation for steady state laminar flow and also pressure based solver in a 3d space, first order upwind solution for momentum discretization gives number of iteration=350 and residual=1e07. walls are located at z=0 and z=0.02 m, near the walls velocity magnitudes are low due to viscous fluid flow or shear stresses, as shown in figure 14. from figure 14 we understand that the magnitude of velocity increased from z=0 to z=0.01 m and decreased from z=0.01 to z=0.02 m. figure 14 shows the average magnitude of velocity at different surfaces from z=0 to z=0.02 m. maximum velocity is reached at z=0.01. based on table iii, at surface z=0 fluid is in contact with the plate so the velocity of the fluid is zero and the color of the surface is blue. the velocity increases as z increases from 0 to 0.01 m, so the color of the surfaces tends to red, then velocity decreases as z increases from 0.01 m to 0.02 m so the color of surface tends to blue. table iii. contour of velocity at different surfaces from surface z=0 to surface z=0.02 m surface vertex value (m) velocity magnitude (m/s) surface vertex value (m) velocity magnitude (m/s) 0.001 0.01238 0.013 0.0513 0.003 0.003188 0.017 0.04359 0.005 0.04482 0.019 0.03171 0.007 0.05257 0 0 0.009 0.05591 net 0.03732 0.011 0.05591 fig. 11. velocity magnitude at x=0.0002m fig. 12. angles of vectors versus y fig. 13. wall shear stresses versus y fig. 14. contour of velocity at different surfaces from surface z=0 to surface z=0.02 m at z=0.02 m, steady flow enters from the top channel so the color of the inlet channel is uniform green but in the outlet channel the flow is not uniform and exits with different velocities so the color of the outlet channel varies from green to red. based on table iii, the average velocity of fluid at surfaces near the wall changed more rapid than at surfaces far from the wall. etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 310-314 314 www.etasr.com mirdrikvand et al: velocity boundary analysis of a flat plate heat exchanger in laminar flow… iii. conclusion 1. the pressure of fluid decreases through the flow due to energy losses. 2. wake phenomenon occurs when the flow reaches the edge of the plate that is not located in the same direction as the flow. 3. due to the existence of the wake phenomenon it is better to install instruments measuring pressure, temperature, and other measuring devices away from the wake area. 4. due to the existence of the wake phenomenon and forces exerted on the wake area, the probability of corrosion increases. therefore, the thickness of the walls should be inspected regularly. 5. eddy current and reverse flows occur in the wake area so the angles of velocity vectors have -180 to 180 degrees variation from the direction of the flow. 6. the magnitude of velocity near the walls is smaller compared to areas far from the walls due to shear stresses exerted from the wall to the fluid. 7. by using cfd method we can design a shape for the phe that has less pressure losses. 8. by using cfd method we can design a more efficient plate heat exchanger 9. fluent software is suitable to analyze the behavior of the flow in a process or apparatus. references [1] k. grijspeerdt, b. hazarika, d. vucinic, “application of computational fluid dynamics to model the hydrodynamics of plate heat exchangers for milk processing”, journal of food engineering, vol. 57, no. 3, pp. 237– 242, 2003. [2] i. m. afonso, l. hes, j. m. maia, l. f. melo, “heat transfer and rheology of stirred yoghurt during cooling in plate heat exchangers”, j. food eng., vol. 57, pp. 179–187, 2003. [3] w.w. focke, j. zachariades, i. olivier, “the effect of the corrugation inclination angle on the thermohydraulic performance of plate heat exchangers”, int. j. heat mass transfer, vol. 28, no. 8, pp. 1469-1475, 1985. [4] g. zhang, m. tian, s. zhou, “simulation and analysis of flow pattern in cross-corrugated plate heat exchangers”, journal of hydrodynamics ser.b, vol. 18. no. 5, pp. 547-551, 2006. [5] j. a. w. gut, j. m. pinto, “optimal configuration design for plate heat exchangers”, international journal of heat and mass transfer, vol. 47, no. 22, pp. 4833–4848, 2004. [6] b. p. rao, p. k. kumar, s. k. das, “effect of flow distribution to the channels on the thermal performance of a plate heat exchanger”, chemical engineering and processing, vol. 41, no. 1, pp. 49–58, 2002 [7] f. a. tereda, n. srihari, s. k. das, b. sunden. “experimental study on port to channel flow distribution of plate heat exchangers”, proceedings of the fifth international conference on enhanced, compact and ultracompact heat exchangers, pp. 208–214, usa, 2005. [8] m. v. de bonis, g. ruocco, “conjugate fluid flow and kinetics modeling for heat exchanger fouling simulation”, international journal of thermal sciences, vol. 48, no. 10, pp. 2006–2012, 2009 [9] x. h. han, l. q. cui, s. j. chen, g. m. chen, q. wang, “a numerical and experimental study of chevron, corrugated-plate heat exchangers”, international communications in heat and mass transfer, vol. 37. no. 8, pp. 1008–1014, 2010. [10] j. ding, r. m. manglik, “analytical solutions for laminar fully developed flows in double-sine shaped ducts”, heat mass trans., vol. 31, no. 4, pp. 269–277, 1996. [11] j. c. leuliet, j. f. maingonnat, m. lalande, “thermal behaviour of plate heat exchangers with newtonian and non-newtonian fluids”, in: proceedings congres eurotherm 5 et 1er colloque tifan, compiegne, pp. 1–15, 1988. [12] j.c. leuliet, j .f. maingonnat, m. lalande, “etude de la perte de charge dans des echangeurs de chaleur a plaques traitant des produits nonnewtoniens”, rev. g en. therm., vol. 308–309, pp. 445–450, 1987. [13] f. delplace, j. c. leuliet, “generalized reynolds number for the flow of power law fluids in cylindrical ducts of arbitrary cross-section”, the chemical engineering journal and the biochemical engineering journal, vol. 56, no. 2, pp. 33–37, 1995. [14] m. m. a. bhutta, n. hayat, m. h. bashir, a. r. khan, k. n. ahmad, s. khan, “cfd applications in various heat exchangers design: a review”, applied thermal engineering, vol. 32, pp. 1-12, 2012. [15] g. taylor, “dispersion of soluble matter in solvent flowing slowly through a tube”, proc. roy. soc. lond. a, vol. 219, no. 1137, pp. 186– 203, 1953. [16] b. xia, d. –w. sun, “applications of computational fluid dynamics (cfd) in the food industry: a review”, computers and eletronics in agriculture, vol. 34, pp. 5–24, 2002. [17] s. jain, a. joshi, p. k. bansal, “a new approach to numerical simulation of small sized plate heat exchangers with chevron plates”, journal of heat transfer, vol. 129, no. 3, pp. 291-297, 2007. [18] m. a. mehrabian, r. poulter, “hydrodynamics and thermal characteristics of corrugated channels: computational approach”, appl. math. modell., vol. 24, no. 5-6, pp. 343–364, 2000. [19] m. ciofalo, j. stasiek, m. w. collins, “investigation of flow and heat transfer in corrugated passages—ii. numerical simulation”, int. j. heat mass transfer, vol. 39, no. 1, pp. 165–192, 1996. [20] polyflow 3.9 user’s guide, fluent inc., lebanon, usa, 2001. microsoft word etasr_v13_n4_pp11191-11196 engineering, technology & applied science research vol. 13, no. 4, 2023, 11191-11196 11191 www.etasr.com ramakrishna et al.: exploration of the hbsm mmc five-level inverter for d-statcom application exploration of the hbsm mmc five-level inverter for d-statcom application elluru ramakrishna eee department, jawaharlal nehru technological university anantapur, india ellururamakrishna@gmail.com (corresponding author) gadhamappagari jayakrishna eee department, holy mary institute of technology and science, india g.jayakrishna25@gmail.com sujatha peddakotla eee department, jawaharlal nehru technological university anantapur, india psujatha1993@gmail.com received: 16 april 2023 | revised: 5 may 2023 | accepted: 19 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5965 abstract this paper presents the concert exploration of a modular multilevel converter (mmc) and its application for d-statcom. the half bridge (hb) sub-module is adopted in the mmc due to its simplicity and low conduction losses. an advanced modulation technique of the phase disposition (pd) scheme is applied for the control of the hb mmc switches. the converters are facing dc voltage balance problems under nonlinear load conditions. the proportional and integral (pi) controller is adopted for the balance of dc voltage. performance parameters such as apparent power, active power, reactive power, power factor, dc voltage balance, and total harmonics distortion (thd) are presented and compared with the ones of the traditional two-level converter. the proposed scheme is simulated in matlab/simulink. keywords-modular multilevel converter (mmc); half bridge (hb) sub module; phase disposition (pd); pi controller; dc voltage balance i. introduction a distribution static synchronous compensator (dstatcom), is a compensating device that is typically utilized in distribution networks in order to maintain balance in the flow of reactive power [1-2]. the circuit layout has a significant impact on the d-statcom compensation effect, particularly accuracy. the control technique of d-statcom has a significant impact not only on the compensation effect but also on the speed with which it is achieved. the conventional reactive power compensation devices all have straightforward constructions, which make them incredibly user-friendly in terms of installation, operation, and upkeep. on the other hand, they can only compensate for preset reactive power and their adjustments cannot be made continuously. in addition, the system suffers from the issue of increasing harmonics. because of this, it may be unable to satisfy the requirements for the reactive power compensation. the majority of contemporary reactive power compensation systems can be divided into two categories. the first one is referred to as a static var compensator (svc). it is able to monitor the changes in reactive power and compensate for that power in stages, all while suffering minimal losses and being easy to regulate. it can monitor reactive power variations and compensate reactive power in phases with minimal losses and straightforward regulation. constant reactive power compensation remains challenging, and when reactive power fluctuates rapidly, the system's reaction time suffers. the second one is known as the static synchronous compensator [3] (statcom). in certain groups, it is also referred to as the static var generator (svg) [1]. the term d-statcom refers to a statcom that is utilized on the load or distribution side. it consists of a controllable complete bridge circuit that can be connected to the system either directly in parallel or indirectly through reactors. d-statcom is able to accomplish the goal of dynamic reactive power compensation due to the way it controls the current on the ac side. d-statcom's abilities to continuously monitor reactive power changes; quickly responding to changing conditions, and compensating for harmonics are just some of its many benefits. the dstatcom also has a fast response time. for power quality applications, there is a growing interest in the use of multilevel inverters in moderate voltage (less than 36 kv) power converters. if a converter has at least three different voltage levels from its phase to its neutral terminal, then it can be categorized as a multilevel inverter. the lack of need for a coupling transformer in applications involving medium voltage and the relatively low harmonic current content are two of the most significant benefits that multilevel inverters offer. engineering, technology & applied science research vol. 13, no. 4, 2023, 11191-11196 11192 www.etasr.com ramakrishna et al.: exploration of the hbsm mmc five-level inverter for d-statcom application realization of re-locatable and cost-effective d-statcom devices is made possible in this manner. hence, the mmc is adopted for d-statcom application in this paper. ii. mmc d-statcom the dstatcom connection is shunt [5] with regard to the pcc connection. in order to provide reactive power compensation, power factor correction, and harmonic filtering, it provides filter current (if) at the point of common coupling (pcc) [6]. the block diagram of a compensated system using d-statcom is depicted in figure1. the filter current (if) flowing through interfacing inductor (lf) is regulated by using three-phase hb mmc. the operation of hb mmc is supported by a dc storage capacitor (cdc) which maintains a steady voltage across the dc-link [17]. the feeder resistance and inductance are denoted as (rs) and (ls) respectively. fig. 1. dstatcom configuration. figure 2 depicts a structure that is constructed on a threephase half-bridge sub-module [8]. this construction may be found in the mmc. the corresponding switching states are listed in table i. research has been carried out recently to investigate whether or not mmcs and d-statcoms based on mmcs are effective in resolving power quality issues such as harmonics, imbalanced dc voltages, and reactive power correction. fig. 2. half bridge sub-module configuration. table i. switching states for hb sm mode sa1 sa2 output voltage 1 1 0 v0 2 0 1 0 iii. control methodology the actual voltage is kept relatively consistent with the nominal number by the voltage controller. it generates current reference commands and performs proportional (p) or proportional integral (pi) control action in response to errors in voltage signals. the current controller is provided with these reference instructions in order to carry out further controller exploit [9]. the voltage regulator is established with the help of standard control methods in accordance with the system's requirements. by drawing active power from the system, the purpose of the d-statcom stratagem is to achieve the goal of delivering the necessary reactive power to the connected loads [10]. the dc link capacitor will show signs of having energy stored in it as a result of the active power being depleted. the coupling association between the dc link and the ac side power determines how the dc link voltage is controlled. equation (1) provides a mathematical representation of the energy balance: ��� = −��� (1) the capacitor will retain the energy taken from the terminals as direct current (dc) energy. it has something to do with the side power of ac in the d-q region. ��� = � � � � � � (2) � � � � � � = −�� � + ����� (3) � � � � = −�� � + ����� (4) � � = ������������ ������ (5) it is possible to interpret the erroneous input to the pi controller as. ∆ � = � ���� − �� (6) the method of trial and error is used in the process of tuning the pi controller for the dc error. the control structure is illustrated in figure 4 [11]. the control structure consists of the dc voltage link controller and the pd pwm controller for controlling of the igbts of mmc-dstatcom. the phase disposition (pd) pwm is illustrated in figure 3. fig. 3. pd pwm. non-linear load d-statcom pcc vs rs,ls rf,lf rl g a b + a b + c v0 2 2 1 1 g m c e sa2 gm ce sa1 c 0 0.01 0.02 0.03 0.04 -1 -0.5 0 0.5 1 time (s) m a g n it u d e engineering, technology & applied science research vol. 13, no. 4, 2023, 11191-11196 11193 www.etasr.com ramakrishna et al.: exploration of the hbsm mmc five-level inverter for d-statcom application iv. result analysis the proposed mmc-dstatcom configuration as illustrated in figure 4 [12] was simulated in matlab/simulink. the proposed system was first simulated in uncompensated mode. in this situation, no d-statcom is connected. the result is illustrated in figure 5. the resulting non-linear currents are shown in figure 5(b). apparent power [13], active power, reactive power, power factor, and thd are recorded as 6388v a, 5532 w, 3194 var, 0.866, and 24.43%, respectively and the outputs are illustrated in figure 5 [14]. fig. 4. control structure of d-statcom. in the second scenario, a d-statcom that is based on a two-level voltage source is connected. the outcome of this scenario is depicted in figure 6 [15]. the resulting non-linear current is shown in figure 6. apparent power, active power, reactive power, power factor, and thd are recorded as 6376 va, 6232 w, 1345 var, 0.9775, and 11.76% and their outputs are illustrated in figure 6 [16]. the active power is improved and the reactive power is reduced. the thd is reduced from 24.43% to 11.76% but this does not satisfy the standards of ieee. hence, the five-level hb mmc based d-statcom is proposed and simulated to overcome this disadvantage using hysteresis current controller (hcc), as it is simple and easy to implement. in the third case, the five-level hb mmc based dstatcom is connected and its results are illustrated in figure 7. the resulting non-linear currents are represented in figure 7. apparent power, active power, reactive power, power factor, and thd are recorded as 6333 va, 6233 w, 1117 var, 0.9843, and 8.94% and their outputs are illustrated in figure 7. the active power is improved and the reactive power is reduced. the thd is reduced from 24.43% to 8.94%, but does not satisfy the standards of ieee. hence, the five-level hb mmc based d-statcom is proposed and simulated to overcome the above disadvantage using the advanced pd pwm modulation scheme. (a) (b) (c) (d) (e) (f) (g) fig. 5. response waveforms without d-statcom connected. (a) source voltage, (b) source current, (c) apparent power, (d) active power, (e) reactive power, (f) power factor, (g) harmonic spectrum of the source current. 0.2 0.25 0.3 0.35 0.4 -415 0 415 time (s) v o lt a g e ( v ) vsa vsb vsc 0.2 0.25 0.3 0.35 0.4 -8.5 0 8.5 time (s) c u rr e n t (a ) isa isb isc 0 0.5 1 1.5 2 0 3000 6388 8000 time (s) p o w e r (v a ) 0 0.5 1 1.5 2 0 3000 5532 time (s) a c ti v e p o w e r (w ) 0 0.5 1 1.5 2 0 1500 3194 time (s) r e a c ti v e p o w e r (v a r ) 0 0.5 1 1.5 2 0 0.5 0.866 1.2 time (s) m a g n it u d e 0 1 5 7 11 13 17 19 25 0 5 10 15 20 25 harmonic order fundamental (50hz) = 8.496 , thd= 24.43% m a g (% o f f u n d a m e n ta l) engineering, technology & applied science research vol. 13, no. 4, 2023, 11191-11196 11194 www.etasr.com ramakrishna et al.: exploration of the hbsm mmc five-level inverter for d-statcom application (a) (b) (c) (d) (e) (f) (g) (h) fig. 6. response waveforms of two-level vsi-d-statcom. (a) source voltage, (b) source current, (c) apparent power, (d) active power, (e) reactive power, (f) power factor, (g) dc voltage, (h) harmonic spectrum of the source current. (a) (b) (c) (d) (e) (f) (g) (h) fig. 7. response waveforms of five-level hbmmc-d-statcom using hcc. (a) source voltage, (b) source current, (c) apparent power, (d) active power, (e) reactive power, (f) power factor, (g) dc voltage, (h) harmonic spectrum of the source current. 0.2 0.25 0.3 0.35 0.4 -415 0 415 time (s) v o lt a g e ( v ) vsa vsb vsc 0.2 0.25 0.3 0.35 0.4 -8.91 0 8.91 time (s) c u rr e n t (a ) isa isb isc 0 0.5 1 1.5 2 0 2000 4000 6376 8000 time (s) p o w e r (v a ) 0 0.5 1 1.5 2 0 2000 4000 6232 8000 time (s) a c ti v e p o w e r (w ) 0 0.5 1 1.5 2 -2000 0 1345 2000 time (s) r e a c ti v e p o w e r (v a r ) 0 0.5 1 1.5 2 0 0.5 0.9775 1.2 time (s) m a g n it u d e 0 0.5 1 1.5 2 0 200 400 600 700 time (s) v o lt a g e ( v ) 0 1 5 7 11 13 17 19 25 0 5 10 harmonic order fundamental (50hz) = 8.916 , thd= 11.76% m a g (% o f f u n d a m e n ta l) 0.2 0.25 0.3 0.35 0.4 -415 0 415 time (s) v o lt a g e ( v ) vsa vsb vsc 0.2 0.25 0.3 0.35 0.4 -8.9 0 8.9 time (s) c u rr e n t (a ) isa isb isc 0 0.5 1 1.5 2 0 2000 4000 6333 time (s) p o w e r (v a ) 0 0.5 1 1.5 2 0 2000 4000 6233 8000 time (s) a c ti v e p o w e r (w ) 0 0.5 1 1.5 2 0 500 1117 1500 2000 time (s) r e a c ti v e p o w e r (v a r ) 0 0.5 1 1.5 2 0 0.5 0.9843 1.2 time (s) m a g n it u d e 0 0.5 1 1.5 2 0 350 700 time (s) v o lt a g e ( v ) 0 1 5 7 11 13 17 19 23 25 0 5 10 15 20 harmonic order fundamental (50hz) = 8.956 , thd= 8.94% m a g (% o f f u n d a m e n ta l) engineering, technology & applied science research vol. 13, no. 4, 2023, 11191-11196 11195 www.etasr.com ramakrishna et al.: exploration of the hbsm mmc five-level inverter for d-statcom application (a) (b) (c) (d) (e) (f) (g) (h) fig. 8. response waveforms of five-level hbmmc-dstatcom using pd pwm. (a) source voltage, (b) source current, (c) apparent power, (d) active power, (e) reactive power, (f) power factor, (g) dc voltage, (h) harmonic spectrum of the source current. in the fourth case, the five-level hb mmc based dstatcom using pd pwm is simulated and the results are illustrated in figure 8 [17]. apparent power, active power, reactive power, power factor, and thd are recorded as 6340 va, 6233 w, 1160 var, 0.9831, and 4.91% and their outputs are illustrated in figure 8 along with the source current [18]. the active power is improved and the reactive power is reduced. the thd is reduced from 24.43% to 4.91%, satisfying the standards of ieee. the complete comparison of all cases is exhibited in table ii. table ii. performance comparison parameter before compensation 2-level vsi hb mmc 5-level inverter hcc hb mmc 5-level inverter cbpwm s (va) 6388 6376 6333 6340 p (w) 5532 6232 6233 6233 q (var) 3194 1345 1117 1160 pf 0.866 0.9775 0.9843 0.9831 isa (a) 8.496 8.91 8.956 8.903 source current harmonics (% values) ih5 19.45 9.50 2.33 1.09 ih7 11.81 0.85 2.43 2.10 ih11 6.49 5.09 2.83 1.63 ih13 4.71 0.13 2.01 1.52 ih17 2.59 2.52 0.61 1.10 thd 24.43 11.76 8.94 4.91 v. discussion mmcs are commonly used nowadays in power quality, hvdc, statcom, shunt active power filters, and renewable energy sources. it is observed from the literature that there is a research gap in the implementation of mmc for dstatcom. hence, in this work the mmc based dstatcom using pd pwm is considered. the contribution of this work includes the adoption of the mmc as d-statcom for the improvement of power quality (active power, reactive power, power factor, and tdh). the proposed work is compared with the standard two-level inverter and with hcc pwm. from the results, it is observed that the proposed fivelevel mmc based d-statcom using pdpwm over performed the standard inverters. vi. conclusion the pd pwm control method for reactive power, harmonics, and dc voltage balancing in mmc-based dstatcom performance has been analyzed in this paper. it has been determined that the effectiveness of mmc-d-statcom when utilizing pd pwm-based control is satisfactory. harmonics, reactive power, and dc voltage balance, among other power quality issues, have been corrected with the help of mmc-dstatcom. the thd in the supply current was decreased to 4.91% from 24.43%. following the application of the compensation, the total harmonic distortio of the supply current was brought down to an acceptable level according to the criteria outlined in the ieee-519 standard [19-25]. this improvement in power quality was made possible by the mmc-ds-tatcom. the self-supported dc-link voltage of mmc-dstatcom is also referenced. 0.2 0.25 0.3 0.35 0.4 -415 0 415 time (s) v o lt a g e ( v ) vsa vsb vsc 0.2 0.25 0.3 0.35 0.4 -8.9 0 8.9 time (s) c u rr e n t (a ) isa isb isc 0 0.5 1 1.5 2 0 2000 4000 6340 8000 time (s) p o w e r (v a ) 0 0.5 1 1.5 2 2000 4000 6233 8000 time (s) a c ti v e p o w e r (w ) 0 0.5 1 1.5 2 0 500 1160 1500 2000 time (s) r e a c ti v e p o w e r (v a r ) 0 0.5 1 1.5 2 0 0.5 0.9831 1.2 time (s) m a g n it u d e 0 0.5 1 1.5 2 0 200 400 700 800 time (s) v o lt a g e ( v ) 0 1 5 7 11 13 17 19 23 25 0 5 10 15 20 harmonic order fundamental (50hz) = 8.903 , thd= 4.91% m a g (% o f f u n d a m e n ta l) engineering, technology & applied science research vol. 13, no. 4, 2023, 11191-11196 11196 www.etasr.com ramakrishna et al.: exploration of the hbsm mmc five-level inverter for d-statcom application references [1] v. narasimhulu, d. v. ashok kumar, and c. babu, "simulation analysis of switch controlled power filters for harmonic reduction," international journal of applied engineering research, vol. 11, pp. 7597–7602, jun. 2016, https://doi.org/10.37622/ijaer/11.12.2016. 7597-7602. 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[25] p. vaidya and v. k. chandrakar, "exploring the enhanced performance of a static synchronous compensator with a super-capacitor in power networks," engineering, technology & applied science research, vol. 12, no. 6, pp. 9703–9708, dec. 2022, https://doi.org/10.48084/ etasr.5317. microsoft word etasr_v10_n6_pp6438-6444 engineering, technology & applied science research vol. 10, no. 6, 2020, 6438-6444 6438 www.etasr.com rechtman et al.: structural analysis of steel transmission towers for large river crossing of … structural analysis of steel transmission towers for large river crossing of overhead transmission lines a case study in brazil mariana s. rechtman civil engineering department fluminense federal university niterói, brazil mariana.rechtman@gmail.com amauri menezes batávia engenharia niterói, brazil batavia@batavia.eng.br juliana n. m. motta civil engineering department fluminense federal university niterói, brazil juliana.motta@marteengenharia.com.br josé guilherme s. da silva structures and foundations department rio de janeiro state university rio de janeiro, brazil jgss@uerj.br orlando longo civil engineering department fluminense federal university niterói, brazil orlandolongo@gmail.com abstract-this study aims to investigate the structural behavior of steel transmission towers used for large river crossings. design standards usually applied to analyze these structures don’t consider situations in which the transmission towers are used in river crossings. in brazil, due to the fact that it is necessary to cross large areas owing to the rivers’ size, these towers assume great heights. it should be noted that the towers can weigh up to 24,500kn and exceed 300m in height. the current study develops an analysis that surpasses the existing standard methodologies, aiming for a structural optimization compatible with vast crossings and new materials, aiming to resolve this design challenge regarding power transmission lines. to do this, a river crossing spanning 2,300m, situated in the northern region of brazil, was studied based on the use of three different conductor configurations, electrically equivalent, commonly used wind design standards, and structural solutions utilizing tubular and angle profiles. keywords-steel transmission towers; power transmission lines; large river crossing i. introduction overhead transmission lines are used to transport high voltages between distant substations [1]. the expansion of the national interconnected system (sin) made compulsory the implementation of challenging projects, such as large river crossings in the amazon region [3, 4]. the main challenges of this type of projects are related to the physical dimensions of the venture, the regions of implementation, and the applied voltages, which can reach 800kv [2]. this type of project is characterized as essential and very relevant to the expansion of the sin, enabling the interconnection of previously electrically isolated regions. such regions depended essentially on thermal generation sources, which concentrate large co2 emissions [3]. figure 1 illustrates the large river crossing of the tucuruímacapá-manaus interconnection in the northern region of brazil. specific care is needed in the construction of transmission lines that cross the amazon forest aiming to produce the least possible impact. examples are the use of selfsupporting structures instead of guyed structures, occupying a smaller range of easement, as well as the adoption of higher structures, keeping the conductors’ catenaries above the treetops, preserving the fauna and flora. additionally, the transport of the structural elements must be carried out using rafts to avoid the construction of roads, in the midst of forest areas [5]. regarding the execution of these projects, it is necessary to evaluate regional environmental parameters, local destructive wind activity, relative air density, atmospheric correction factors, and regional lightning activity intensity [6]. corresponding author: mariana s. rechtman engineering, technology & applied science research vol. 10, no. 6, 2020, 6438-6444 6439 www.etasr.com rechtman et al.: structural analysis of steel transmission towers for large river crossing of … in addition, a detailed analysis is needed for insulation coordination procedures for voltages at 60hz and power surges, in order to determine safety distances, particularly considering operational safety requirements during construction [7]. due to the size of the rivers, towers for river crossings need to overcome large areas, and as a consequence, they assume great heights. therefore, these structures can weigh up to 24,500kn, and can exceed 300m in height [8]. fig. 1. tower for large river crossing related to the tucuruí-macapámanaus interconnection. another relevant aspect is the current limitations in standards in relation to tower heights. for example, the commonly used iec 60826 standard [9] is not accurate when calculating wind forces on a structure exceeding 60m in height. therefore, it is necessary to seek these definitions in other standards, such as [10, 11]. therefore, in this investigation, an analysis methodology was developed aiming for structural optimization compatible with existing large areas and with new available materials, based on the study of a 2,300m river crossing, located at the northern region of brazil. this research work presents the structural solutions based on the use of three different conductor configurations: 2xaccc monte carlo, 1xaccc 25mm, and 1xcala 630 (aacsr), electrically equivalent, although with distinct mechanical characteristics. the three above-mentioned wind design standards were studied along with the structural solutions based on the use of tubular and angle profiles. ii. enviromental parameters this section presents the methodologies applied to define the climatological and environmental data of the study area. atmospheric correction factors, ceramic index, and wind speeds values were defined, having in mind studies of coordination and isolation of the investigated crossing. the interactions of the analyzed transmission line with the environment have received consistent attention. the values of the climatic parameters were quantified based on the data available from the national institute of meteorology (inmet): average temperatures, maximum and minimum temperatures, relative air density, atmospheric correction factors and lightning intensity levels were considered. regarding the atmospheric correction factors, its inference followed the methodology presented in [12], added upon by the developments in the approach presented in [18]. the wind velocity was calculated based on the experimental measurements from inmet and the former depv (department of electronics and flight protection, ministry of aeronautics). a. wind velocities the wind velocities were defined based on the inmet and depv experimental data, considering the gumbel statistical model and utilising the annual maximum speeds recorded over periods ranging from 4 to 17 years (figures 2-4). the gust factor adopted for the region was 1.7pu for an average time of 3s, and 1.35pu for 30s. the variation coefficients of the maxima series vary from 13% to 19%. such values come from a parametric regionalization carried out through a weighted average using the collection time of each station. the gumbel model is widely used in brazil for several decades and its formulation can be found in detail in [9]. traditionally, power surges are associated with wind velocity which has a return period of 2 years while an average time of 30s has been considered in establishing safety distances [13]. fig. 2. isotachs for a return period of 250 years and 10min averaging time (km/h). fig. 3. isotachs for a return period of 250 years and 3s averaging time (km/h). on this matter, there is a method where milder velocities are used, speeds which, on average, can occur at least once every 2 years simultaneously with power surges. this calls for the use of parameters associated with this rare phenomenon. engineering, technology & applied science research vol. 10, no. 6, 2020, 6438-6444 6440 www.etasr.com rechtman et al.: structural analysis of steel transmission towers for large river crossing of … on the other hand, a more realistic analysis methodology that considers the weibull statistical distribution was used and in order to determine prospective wind velocities aiming to obtain their varied average times and return periods, the mathematical model represented by (1) was utilized. �� � �� � � � �2 / �1 (1) where y = -ln [-ln (1 − 1/t)], vt is the wind velocity referring to a return period of t years, vm is the average sample velocity of annual maximums, and c1 and c2 are the coefficients of the gubel distribution, based on the number of elements. in the development of the methodology, the average values were corrected according to a study that takes into account the effects of the surplus of turbulence verified in anemometric data in brazil [14]. this certainly introduces a cautious attitude in the results of forecasted wind velocities, although it is perfectly consistent with the measured data. samples from just a few years (less than 5 years) result in inferences for 250 years, which rarely exceed a confidence interval of ±20km/h [15-16]. the results presented in figures 2 and 3 will be used in this study to compare results of unit pressures on the towers and the other components of the transmission lines, according to the guidelines in [9-11]. fig. 4. isotachs for a return period of 2 years and 30min averaging time (km/h). b. atmospheric correction factors and lightning activity index similar with wind velocities, other environmental variables influencing structural design were the object of statistical evaluation, as suggested by the most recent standard approaches. in this regard, the following can be mentioned: average and extreme temperatures, relative air densities, relative and absolute humidity, atmospheric correction factors (acf), regional lightning activity, etc. [17]. due to their uncontested importance, the acf variables for 60hz and power surges and the regional lightning levels are given appropriate emphasis. iec 60060-1 [12] describes in detail the methodology to be followed in the calculation of the acfs. a systematic calculation with data from several airport collection stations over a period of 10 years provided an accurate evaluation of the statistical moments (means and standard deviations) [18]. figures 5 and 6 were developed based on the above mentioned data. the 99% and 90% safe values for the acfs of figures 5 and 6 account for the spatial and temporal variations to which these variables are subject and point out the discrete influence of the gap length in the quantification of the acfs. the calculation of the national lightning activity was based on maps produced at the federal university of rio de janeiro (ufrj) and reproduced in the brazilian standard nbr5422 [19] (figure 7). recently ons published a specific and updated map showing the atmospheric discharges (discharges/km 2 /year) that relate to lightning levels through various formulations (see (2) and (3)). when determining the values of lightning activity levels (lal), the average of the previously indicated formulations was adopted considering the uncertainties inherent to the phenomenon. ���� � 0.10 nc,���� � 0.20 nc (2) ���� � 0.04 ���.�� (3) where dens stands for “discharge density”. fig. 5. acf for 60hz exceeded 99% of the time. fig. 6. acf for power surges exceeded 90% of the time. fig. 7. number of days with storms in the region. engineering, technology & applied science research vol. 10, no. 6, 2020, 6438-6444 6441 www.etasr.com rechtman et al.: structural analysis of steel transmission towers for large river crossing of … iii. structure and component characteristics in order to broaden the scope of research on current international transmission line design standards, three of the most well-known and most frequently used methods for determining wind pressure on structures and other elements of transmission lines were chosen: iec 60826 [9], en 50341-1 [10], and asce 74 [11]. the first two use wind velocities collected in 10min time spans and the last one is based on 3s readings. theoretically, the three results should have some convergence as they seek strong wind gust loads (storms, cold fronts, or associated systems). the standards iec [9, 10] multiply the values of wind velocities collected in 10min time spans by their gust factors around 1.4-1.6, while the [11] reduces pressure values which result from speeds collected in 3s time spans by about 70-80%. table i and figure 8 present the general characteristics of the studied crossing. three solutions were considered regarding the configuration of the conductors: 2xaccc (monte carlo), 1xaccc (25mm), and 1xcala 630 (aacsr), with two opgw shield wires type opgw dual (stainless steel tube in an aluminium tube, on each side of the structure). the cable specifications are shown in tables ii and iii. the presented data were adopted in the current work, based on the authors’ experience with this type of structural projects, related to challenging spans, when considering transmission line systems commonly observed in river crossings in the amazon region. it should be noted that the tensions of the opgw shield wire were defined considering that, for each type of conductor, the sag of the shield wire in the eds condition equals to 90% of the sag of the conductor cable in the same condition. this type of accc (aluminium conductor composite core) conductor is quite promising for use in large crossings. table iv presents the geometric characteristics of the structure, respecting the required electrical safety distances, table v shows the calculated wind pressures for the transmission line elements and figure 8 illustrates the investigated structural system (steel towers and cables). it can be seen in table iv that the tower heights increase the sag of the adopted conductor cables proportionally (table ii), but the cable-ground electric distance is respected in all the studied configurations. table i. characteristics of the studied crossing wind gap (m) weight gap (m) crossing gap (m) 1350 2200 2300 fig. 8. investigated structural system (dimensions in m). table ii. specifications of the studied conductors conductors diameter (mm) unit weight (kn/m) rupture load (kn) eds tension (% of rupture load) final eds sag (m) 2xaccc monte carlo 20.79 0.0078 225.70 17 170 1xaccc 25mm 25.00 0.0119 247.20 17 210 1xcala 630 (aacsr) 36.32 0.0332 557.91 22 230 table iii. opgw cable specification opgw dual: stainless steel tube in an aluminium tube diameter (mm) unit weight (kg/m) rupture load (kn) 24.3 0.0239 405.40 table iv. main dimensions of the tower (m) conductor types 2xaccc 1xaccc 1xcala horizontal spacing between phases/shield wires 7.60 7.20 6.80 vertical spacing between phases 11.50 11.50 11.50 vertical spacing between conductor and shield wires 5.50 5.50 5.50 spacing between tower legs 46.0 46.0 56.6 maximum tower height 233 273 293 table v. wind pressures on cables, isolators and structure (kn/m²) 2xaccc monte carlo 1xaccc 25mm 1xcala 630 (aacsr) component iec en asce iec en asce iec en asce conductors 0.88 0.96 0.96 0.90 1.00 0.99 0.92 1.05 1.03 shield-wires 0.90 0.99 0.98 0.91 1.02 1.00 0.93 1.07 1.04 isolators 1.35 1.53 1.26 1.38 1.56 1.27 1.42 1.61 1.29 structure 0.671.23 0.541.40 0.821.39 0.671.27 0.531.45 0.801.39 0.671.31 0.531.51 0.781.42 wind pressures are calculated at 10m height and at the top of the structure, considering wind actions perpendicular to the transmission line. the other wind pressures are related to the obstacles heights. iv. applied loadings on the investigated structural system the following data show the loading assumptions applied to the structure considering the three studied conductor configurations and the three wind analyzed standards [9-11]. it must be emphasized that the main hypotheses related to the applied loadings on the investigated structural system were calculated using the data presented in section iii. table vi shows the applied loading for each type of cable and wind design standard. the vertical and transversal loads are referred to the extreme transversal wind load case and the longitudinal loads are referred to the conductor and shield-wire break. the storm wind application on the conductors and shield-wires is defined as the ¼ of the tower's wind gap. the application to high spans becomes less critical than extreme winds considering they are applied across the entire wind gap. thus, the load related to the conductors and shield-wires for storm winds in high span towers is less relevant than extreme winds. table vi. applied loads on the transmission line suspension tower loads (kn) conductors item 2xaccc monte carlo 1xaccc uls 25mm 1xcala 630 (aacsr) standard iec en asce iec en asce iec en asce conductors 1 79.4 86.7 85.7 50.9 56.5 55.0 73.2 83.3 80.6 2 65.2 65.2 65.2 35.7 35.7 35.7 10.0 10.0 10.0 3 63.0 64.5 64.5 46.9 48.1 47.9 105.7 107.9 107.5 shieldwires 4 44.4 48.7 48.3 44.9 50.2 49.2 45.8 52.6 51.2 5 124.3 124.3 124.3 100.6 100.6 100.6 91.8 91.8 91.8 6 71.2 72.2 72.0 71.3 72.5 72.3 71.5 73.0 72.7 1 and 4: transversal (extreme wind), 2 and 5: longitudinal (phase and shield-wire ruptures), 3 and 6: vertical (extreme transversal wind). engineering, technology & applied science research vol. 10, no. 6, 2020, 6438-6444 6442 www.etasr.com rechtman et al.: structural analysis of steel transmission towers for large river crossing of … in this investigation, conductors, shield-wires, and insulators were represented through vertical, transversal, and longitudinal loads, applied at the points of the tower where they were fixed, having in mind the traditional structural analysis methodology currently utilized in design practice. this way, these loads represent the weights, tensions and forces due to the wind action on these elements. table vi presents the applied loadings on the transmission line system, according to each studied load hypothesis. v. structural system weight estimation the approximate weight of the suspension structures for the investigated crossing was estimated, based on the use of empirical formulas developed by the bonneville power administration and existing structures with similar parameters, in terms of application, geometry, and applied loads [21]. this analysis methodology allows the calculation, approximately, of the weight of the transmission line structures, based on their dimensions and acting transverse, vertical, and longitudinal loads, as presented in (4). the mathematical formulation has used a constant, which is defined by applying it to a structure with similar characteristics to the studied one and with a calculated weight. once the constant is defined, (4) is applied to the studied structure with its dimensions and acting loads, obtaining an approximate weight, based on the study of other similar structures [21]. 2/3 1/2 2/3 ( ) ( ) ( ) ( ) 4.482 0.3048 4.4482 0.4482 0.4482 e p h t v l w ck   = + +    (4) where we it the approximate weight of the structure (n), c is a constant calculated using the adopted reference tower, h is the ground height to the centre of gravity loads acting on conductors (m), t is the total transverse load (n), v is the total vertical load (n), l it the longitudinal load (n), and kp is a variable depending on the distance between phases and tower function. for suspension towers: kp = (1.44 + (b/0.3048) 2 ) 1/2 and for anchor towers: kp = (2.89 + (b/0.3048) 2 ) 1/2 , where b is the distance between phases (m). thus, a relationship can be established considering already existing crossings, making an interactive calculation between the formulation in [21] and the investigated towers. it must be emphasized that the reference towers have considered all the connection plates, bolts, and/or welds used in this type of structure. the load cases applied on the reference towers were including all the hypotheses usually considered on this type of towers, including extreme winds, thunderstorm winds, construction, and assembly. table vii presents the total weight of the analyzed suspension towers. table vii. suspension tower weight (kn) conductors 2xaccc monte carlo 1xaccc uls 25mm 1xcala 630 (aacsr) standards iec en asce iec en asce iec en asce tubular tower 3,454 3,821 3,924 4,289 4,823 4,962 5,268 5,883 6,032 angle tower 4,605 5,095 5,232 5,718 6,431 6,617 7,023 7,845 8,043 it can be seen from table vii that the tower formed by angle profiles presents a weight about 30% heavier than those composed by tubular profiles. this is due to the fact that tubular profiles present geometric characteristics with greater resistance to buckling, resulting in less need for bracing and although the drag coefficient of tubular profiles is higher than that of angle profiles, the tubular tower has smaller wind act areas. comparing the three cable solutions presented, the 1xcala 630 solution (aacsr) results in a 22% heavier structure than the 1xaccc uls 25mm solution, which in turn was 25% heavier than the tower which adopted 2xaccc monte carlo, although the loads increase respectively, what determined the weight increase in the structures was their height and not the applied loadings. vi. structural design comparison the typical structures of transmission lines in general are designed with angular profiles, however due to the higher resistance to buckling and less need for secondary bracing, the tubular profiles are usually applied to high towers, as shown in table viii. table viii. long span transmission lines in china [22] project name voltage level tower height (m) tower structure built time zhoushan 220/500kv 370.00 steel tube & concrete filled steel tube jun., 2010 jiangyin 500kv 346.50 welding cross steel plate nov. 2004 nanjing shanjiangkou 500kv 294.50 steel tube feb., 2007 nanjing dashengguan 500kv 257.00 reinforcement concrete jun., 2000 nanjing shangjiankou 500kv 249.50 steel tube jun., 2005 shanghao wusongkou 500kv 177.50 steel tube jul., 2003 hangzhou qianjiang 500kv 128.00 steel tube jun., 2004 wuhu 500kv 229.00 steel tube sep., 2002 fuzhou minjiang 500kv 107.64 steel tube jul., 2002 luohe long 500kv 161.38 reinforcement concrete apr., 1989 nanjing yanziji 220kv 195.50 steel tube sep., 1976 in accordance with the most commonly used power level configurations, the 1xcala 630 cable was adopted in the structural design of the investigated suspension tower. the applied wind design standard was en 50341-1 [10], because it is for general use, and it can be applied to this type of structure. asce-10 [23] was the adopted structural design standard for angle profiles, and nbr 8800 [24] for tubular profiles. the steel transmission tower was numerically modelled applying the finite element method (fem), using the pls tower and strap computational programs. figure 9 illustrates the investigated structural model and the modeling of the tower geometry. in this investigation, the conductors, shield-wires, and insulators were represented based on the use of vertical, transversal, and longitudinal loads, as mentioned above, in order to adopt the very traditional structural design analysis methodology, currently used in day-to-day practice. engineering, technology & applied science research vol. 10, no. 6, 2020, 6438-6444 6443 www.etasr.com rechtman et al.: structural analysis of steel transmission towers for large river crossing of … 50.6 2 9 3 4 .5 9 9 1313 11 11 (a) (b) (c) fig. 9. investigated structural model (dimensions in m) and finite element models: (a) geometry, (b) tower composed by angle profiles in pls tower, (c) tower composed by tubular profiles in strap the steel tower’s structural system was modeled with the use of angle profiles (pls tower) and with tubular profiles (strap). the structural system using tubular profiles requires fewer bracings, since the geometric properties of tubular components have a higher resistance to buckling. on the other hand, the secondary bracing has the function of reducing the buckling length in towers. by disposing some of these secondary elements and considering the design based on the use of tubular profiles, the final result is a lighter tower. table ix presents the results of the steel tower structural design (most loaded main legs of the tower), considering angle and tubular profiles respectively, emphasizing that in both analyses, type astm a572 gr60 steel was used. table ix. structural response of the steel tower design: angle profiles versus tubular profiles tower main legs composed of angle profiles: 4l 203×203×19.1mm weight (kn/m) al (cm 2 ) ag (cm 2 ) r (cm) l (cm) λe fy (mpa) ncres (kn) ntres (kn) nc (kn) nt (kn) 2.28 267.8 295.2 6.27 600 96 414 8,924 9,944 7,100 2,756 tower main legs composed of tubular sections: diameter 356 mm t (cm) weight (kn/m) ag (cm 2 ) i (cm 4 ) r (cm) l (cm) fy (mpa) ncres (kn) ntres (kn) nc (kn) nt (kn) 2.22 1.82 232.5 32,451 11.9 800 414 6,433 6,620 5,256 1,893 al: net area, ag: gross area, r: spin radius, l: buckling length, λe: effective slenderness, fy: steel flow tension, t: thickness, i: moment of inertia, d: diameter of the tubular profile, ncres/ntres: resistant compression load/resistant tension load, nc/nt: active compression/tension load. this way, considering the tower designed with tubular profiles as a reference, and comparing this structure with the tower formed by angle profiles, it was concluded that tower structure using tubular profiles presents a 30% material weight reduction, as presented in table viii. the tubular geometry also allows lower drag coefficients, resulting in lower wind loads, reducing the forces acting on the structures and the displacements values. based on the results presented in table ix, it is possible to see that the compression loads (nc) on the main legs of the tubular steel towers are smaller due to the lighter weight of the structure and the lower drag coefficient. keeping in mind that the weld joining the flange to the tubular profile is twice as long as the width of the plate, so there is no reduction in the effective section (ct = 1). thus, even with a smaller profile area, the tension resistance assumes a significant value. in addition to the tubular profile of the main legs presenting greater buckling length, its linear weight is lighter than the profile composed of angles. vii. conclusions this study aims to develop an analysis methodology in order to make structural optimizations compatible with large existing river crossings. this way, a crossing situated at the northern region of brazil, with a 2,300m span between its banks was investigated. initially, the environmental parameters were defined, such as the wind speed and acfs. then, the structural solutions were applied using three electrically equivalent different conductor configurations: 2xaccc monte carlo, 1xaccc 25mm, and 1xcala 630 (aacsr) and three different commonly used wind standards: iec 60826 [9], en 50341-1 [10], and asce 74 [11]. afterwards, the estimated structural weight was presented for all the above mentioned cases and for structures composed of tubular and angle profiles. the structural design of the tower was considered through the use of tubular and angle profiles for the most common conductor configuration of the studied power level: 1xaccc 630 cable (aacsr) and wind standard en 50341-1 [10]. firstly, with regard to the statistical calculations of the rads (relative air density) and acfs it should be noted that for the purpose of transmission line projects, the methodology used for analysis can be improved by adding more meteorological stations. considering future wind velocity assessments to be more realistic in swing angle calculations, migrating from gumbel to weibull distribution can be supported by practical data. decisions involving power surges associated with powerup and restarting must be refined so that current operational needs are met. extrapolating the limitations in design standards for maximum support heights (60m) should be so advanced that the vertical wind profile in the case of long crossings would be carried out with greater precision. this way, there are two immediate actions that can be taken: a) installing, in the short term, anemometers in the aforementioned installations at three distinct heights (e.g. at 10m, at the mid height of the conductors, and at the top of the structures). modern collection systems can carry out velocity and direction readings every second and store them locally or remotely. b) a national archive consisting of data previously collected from wind farms, where the heights of the generators reach hundreds of meters. as an extension of this procedure, transmission lines considered more strategically important could similarly be equipped with the same wind measurement systems that are suggested here. in this way, the national experience with extreme wind velocities could be improved and consolidated. the problems with the approach regarding the transmission capacity of the transmission lines (ampacity) could be benefited by the adoption of the suggested collection system, using models of low wind velocities and dominant directions. engineering, technology & applied science research vol. 10, no. 6, 2020, 6438-6444 6444 www.etasr.com rechtman et al.: structural analysis of steel transmission towers for large river crossing of … the structural pre-design and the interface between all areas of a basic project are relevant for a successful final outcome. thus, this research has studied several structures. the weights of these structures have been calculated using practical and widely accepted methods. after this study, the weights were verified for the chosen structure using numerical modeling compatible with the desired precision, taking the process to the expected definition of global geometry and behavior of the structure. when the structural design was investigated with the use of the developed analysis methodology, it was concluded that the optimum solution was obtained with the use of the tubular structural system, which presented better performance when compared to the angle structures, with a relevant material weight reduction equal to 30%. it is worth mentioning that accc-type cables, although still in their development phase, are quite promising for use in long crossings which is the object of this study. finally, it is important to emphasize on the intention to perform a more refined finite element modeling of the crossing, aiming to represent the cables. this way, nonlinear dynamic analysis should be performed in order to evaluate the dynamic structural behavior of the system. the problem is certainly much more complicated and influenced by the nonlinear dynamic response of the cables, and in sequence further research will be carried out in this area. acknowledgements the authors gratefully acknowledge the financial support provided by the brazilian science foundation’s capes, cnpq and faperj. references [1] d. pylarinos, “overhead transmission line easement and right-of-way cases in crete, greece: a statistical analysis of 1220 cases from 1974 to 2019,” engineering, technology & applied science research, vol. 10, no. 3, pp. 5581–5589, jun. 2020, https://doi.org/10.48084/etasr.3591. [2] w. m. frota, “melhorias estruturais de suprimento para os sistemas elétricos isolados de manaus e macapá,” t&c amazonia, vol. 3, no. 6, pp. 23–29, 2005. [3] g. n. d. boile and r. l. nascimento, “linhão tucuruí-1800 km de integração regional,” revista t&d amazonia, vol. 8, no. 18, pp. 58–62, 2010. [4] j. n. m. motta, “análise do comportamento estrutural de grandes travessias em linhas de transmissã,” ph.d. dissertation, fluminense federal university, niterói, brazil, 2015. [5] a. l. silva and a. l. sales neto, “desafio amazônico – a complexidade de manutenção na faixa de servidão das linhas de transmissão oriximiná – silves e silves – lechuga,” presented at the xxiii snptee, brazil, 2015. [6] m. s. rechtman, “análise dinâmica não determinística de torres de telecomunicações submetidas à ação do vento,” m.s. thesis, fluminense federal university, niterói, brazil, 2018. [7] a. j. g. pinto, e. c. m. costa, s. kurokawa, and j. pissolato, “analysis of the electrical characteristics of an alternative solution for the brazilian-amazon transmission system,” electric power components and systems, vol. 39, no. 13, pp. 1424–1436, aug. 2011, https://doi.org/10.1080/15325008.2011.584106. [8] a. j. g. pinto, e. c. m. costa, s. kurokawa, j. h. a. monteiro, j. l. de franco, and j. pissolato, “analysis of the electrical characteristics and surge protection of ehv transmission lines supported by tall towers,” international journal of electrical power & energy systems, vol. 57, pp. 358–365, may 2014, https://doi.org/10.1016/j.ijepes.2013.12.015. [9] design criteria of overhead transmission lines, iec 60826:2017, international electrotechnical commission, switzerland, 2017. [10] overhead electrical lines exceeding ac 1 kv part 1: general requirements common specifications, cenelec en 50341-1, cenelec, belgium, 2012. [11] c. j. wong and m. d. miller, guidelines for electrical transmission line structural loading, 3rd ed. reston, va: american society of civil engineers, 2009. [12] high-voltage test techniques part 1: general definitions and test requirements, en 60060-1:2010, international electrotechnical commission, switzerland , 2010. [13] c. r. gontijo, “contribuição à análise e projeto de torres autoportantes de linhas de transmissão,” m.s. thesis, federal university of minas gerais, belo horizonte, brazil, 1994. [14] j. i. silva filho, l. a. m. c. domimgues, a. a. menezes, and a. p. ruffier, “assessment of environmental statistics as an accessible breakthrough to improve ohtls design,” in proceedings cigre session 2006, paris, france, 2006. [15] g. r. kendall, “statistical analysis of extreme values,” presented at the first canadian hydrology conferenc, canada, 1959. [16] b. m. alshammari, “probabilistic evaluation of a power system’s reliability and quality measures,” engineering, technology & applied science research, vol. 10, no. 2, pp. 5570–5575, apr. 2020, https://doi.org/10.48084/etasr.3441. [17] s. kurokawa, e. c. m. costa, a. j. g. pinto, and j. p. filho, “analysis of electric characteristics of high-elevation stretches of the tucuruí– macapá–manaus connection,” journal of control, automation and electrical systems, vol. 24, no. 5, pp. 714–724, oct. 2013, https://doi.org/10.1007/s40313-013-0059-5. [18] r. m. azevedo, j. i. silva filho, and v. h. g. andrade, “fatores de correção atmosféricos aplicados ao dimensionamento de isolamentos em ar nova metodologia de cálculo,” presented at the xvii snptee, andrade, brazil, oct. 2003. [19] projeto de linhas aéreas de transmissão e sub-transmissão de energia elétrica, abnt nbr 5422:1972, abnt associação brasileira de normas técnicas, brazil, 1972. [20] o. a. c. amarantes, j. zack, m. brower, and a. l. de sá, atlas do potencial eólico brasileiro. brasilia, brasil: ministerio de minas e energia, 2001. [21] m. marjerrison, “electric transmission tower design,” journal of the power division, vol. 94, no. 1, pp. 1–23, 1968. [22] z. lin, d. zhang, g. dai, b. li, c. whang, and w. zhao, “design, fabrication and erecting of the long span transmission tower for crossing the amazon river of 500 kv tl tucuruí – xingu – jurupari – oriximiná,” presented at the 2014 cigrè canada conference, toronto, canada, sep. 2014. [23] design of latticed steel transmission structures, asce 10, asce, reston, va, usa, 2015. [24] projeto de estruturas de aço e de estruturas mistas de aço e concreto de edifícios, nbr 8800: 2008, abnt associação brasileira de normas técnicas, brazil, 2008. microsoft word 396-ed.doc etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 562-565 562 www.etasr.com abbad et al.: interaction of rupture zones of adjacent anchor plates in an analogical medium interaction of rupture zones of adjacent anchor plates in an analogical medium hichem abbad djillali liabes university dept. civil engineering, fac.technology labo. civil engineering & environment lgce sidi bel abbes, algeria hi_abbad@yahoo.fr mourad meghachou djillali liabes university dept. civil engineering, fac.technology labo. civil engineering & environment -lgce sidi bel abbes, algeria mourad_meghachou@univsba.dz chahinez dekar djillali liabes university dept. civil engineering, fac.technology labo. civil engineering & environment -lgce sidi bel abbes, algeria ch_gecicat@yahoo.fr sidi mohamed daoud djillali liabes university dept. civil engineering, fac.technology labo. civil engineering & environment -lgce sidi bel abbes, algeria daoudmed22@yahoo.fr abstract — in this paper, an experimental study which required the design and implementation of a model containing plastic granules powder to simulate a natural environment, is presented. the latter is subjected to the removal of anchor plates. for each test, several digital photographs are taken to materialize different deformed configurations during the pullout process. these photos processed in couples by the 7d software (image correlation) giving the evolution of the displacement field and plane strain analogical environment. particular attention is paid to the discussion of the interference of rupture zones of neighboring anchors by reducing the axis between plates. keywordscorrelation of images; small-scale model; anchor plates; granular medium; shear; plane problem. i. introduction the anchor plates are light structural elements employed to withstand uplift forces as experienced by transmission towers, masts and structures subject to buoyancy effects as offshore stations. theoretical studies and experimental models of reduced contiguous plates embedded in granular soil [1-5] showed the influence of soil anchor, of the geometry of the plates, of the depth of the anchor and of the distance between two adjacent plates in their behavior. what actually happens in the environment of two adjacent anchor plates however, is always instructive. kinematic analysis, through physical modeling, allows the investigation of actual behavior. for example, ask the following question: what happens in a medium surrounding two contiguous anchor plates positioned at different distances from each other? it would be interesting to analyze the interaction of the deformed plates around these areas. in this paper, we present an experimental study that describes the displacement field and the strain field in a medium subjected to the removal of two adjacent plates, answering the first question. the use of an analogical environment in this kind of modeling provides an approach to the understanding of the phenomenology of real soils, as both materials have certain properties in common such as incompressibility grain and rubbing character. ii. experimental model the model on which we have carried out the tests, is a rectangular device of 100x80x5 cm dimension, designed to contain plastic granules (analogical material) simulating a granular medium. the front wall of the model is made of a glass plate 6 mm thick, with a constant refractive index throughout its surface. the other walls are formed by plates rigid with wood. wooden smoothed parallelepipeds of 5x5x2 cm dimensions model the anchor plates. they are in contact with threaded rods of 50 cm in length. nuts are welded to an attachment to the chassis of the model, and the tearing of the two plates can be controlled by unscrewing the rods. a strictly vertical movement is imposed on the anchor plates as they are guided by 5 mm thick rails, mounted on the rear wall, preventing any rotation, as shown in figure 1. the plastic grains average diameter is 1 mm, different colors (red, blue, yellow, green and black) are mixed to materialize a visually contrasting environment (natural speckle). to obtain a compact and homogeneous medium, the material is deposited uniformly over the entire width of the tray by small 2 cm thick layers. each layer is compacted through a metallic rammer compaction equal to 2.5 kg mass by exercising 75 blows with a drop height of 30 cm. the medium has a void index of 0.321, corresponding to a relative density of dr=96% (emin=0.302, emax=0.855), the unit weight of the dry analogical material is γd=14,6 kn/m 3, its cohesion is null and its natural friction angle it φ=39°. in view of the very low stresses involved, plastic grains constituting the studied areas are considered indeformable. to describe the displacement field and strain over the anchor plates, several series of tests were conducted. for each test performed, a series of digital photos, with a resolution of 3200x2400 pixels, is taken from the front and with the axis of the shooting perpendicular to the plane of the model. these photos materialize different deformations in the granular medium, caused by the tearing of the anchor plates. the recorded images are further processed to determine the strain field using the 7d software. it is a method of correlation between two images [6]: they are compared using the correlation coefficient of the gray level. in other words, the etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 562-565 563 www.etasr.com abbad et al.: interaction of rupture zones of adjacent anchor plates in an analogical medium points of the original image are found on successive images with a measurement uncertainty of about 0.1 pixel, or 0.01 pixel in small deformation. the image for which the strain is analyzed is divided into a number of square grid elements of 20x20 pixels.     fig. 1. view of the model iii. displacements and deformations over the anchor plates highlighting the influence of the distance between the centers of adjacent anchor plates on the behavior of the surrounding granular medium is deliberately kinematics, ignoring any measurement of the stress state. the tests in question were conducted for anchored at a depth of h=5b, where b is the width of the plates. the spacing axes distance s varied as follows: s=3b, s=4b, s=5b and s=7b. during image processing, a field of study is defined by the operator. we will follow in the evolution of displacements and deformations in this area. the tearing or lifting imposed on the anchor plates, occurs at constant pitches in the order of 0.266 mm that correspond to 1 pixel. a. displacement field figure 2 reproduces graphically the trajectories of grains for a tearing of 20 pixels and for a distance between the axes of respective anchor plates of 3b, 4b, 5b and 7b. note that the grain movement is growing vertically along the axis of the plate, and horizontally to the edges of it. the displacement vectors are plotted with an amplification coefficient of 7 (700%). first, we find that the displacement vectors are generally vertical and oriented upwards, the trajectories of grains damp, almost, approaching a horizontal plane parallel to the free surface of the massif, following an upwardly curved arc. fig. 2. displacement vectors for a pullout of 20 pixels and for different distances between axes of plates. (a) s = 3b, 20 pixels (b) s = 4b, 20 pixels (c) s = 5b, 20 pixels (d) s = 7b, 20 pixels granular medium consisting of plastic granules guide rails glass plate threaded rod anchor plate wood chassis b=5cm s h = 5b 100 cm 80cm etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 562-565 564 www.etasr.com abbad et al.: interaction of rupture zones of adjacent anchor plates in an analogical medium figure 3 represents the vertical displacement fields of the material applied by two anchorage plates with a space between axes respectively of 3b, 4b, 5b and 7b. tear is 20 pixels. locally over each plate, the medium behaves in a manner similar to an isolated plate. note that the formation of a "rigid wedge" over each plate confirms the high compactness of the material. according to the tear's intensity of the plates, a large displacement gradient is set up on a slightly curved triangular outline confirming the existence of the rigid wedge above the plates. we note that beyond the distance of s=7b, plates act independently on the material. at the distance of s=3b, the interaction of rupture zones of each plate creates a bulb of vertical displacement which reaches the value of 2.76 pixels at the surface of the massif at midway between the axes of the plates. the bulge of the grains is limited by inclined lines passing by the edges of the plates. the inclination of these lines is about 41° relative to the vertical. this inclination is substantially equal to the internal angle of friction of an analogical soil (φ=39°). these lines materialized slip lines (rupture surfaces). this mode of rupture has been observed by several researchers who have studied the phenomenon of interaction of anchor plates in granular soils [8, 9]. b. deformation field (maximum shear) figure 4 reproduces the strain fields (maximum shear) in the granular medium for a plate uplift of 20 pixels and for a spacing between axes of 3b, 4b, 5b and 7b. it is noticed that the shear (bulb shear) at the surface of the massif, midway the plates axes is larger when the plates move towards each other. the shear intensity reaches the value of 1.02% for a spacing of 3b whereas it does not exceed 0.23% for a spacing of 5b and 0.12% for a spacing of 7b. note the edge effect at the corners of bases of the upper faces of the plates. iv. conclusion the experimental study we conducted was based mainly on the evolution of the granular medium subjected to the pullout of anchor plates. the pullout tests performed were used to quantify the vertical displacement field and the deformations of granular medium over "anchor plates" with the image correlation technique. the choice of a pullout of 20 pixels (imposed displacement) is justified by the need to present strain fields corresponding to a state of failure. a multitude of coupled photos were processed, up to a pullout of 35 pixels and more. beyond 18 pixels, the deformed configuration is virtually unchanged, which shows that at this stage of sollicitation, the medium has reached a state of rupture and plasticity state occurs. the interaction of rupture zones of neighboring plates anchored at a depth of 5b is studied kinetically by varying the distance between the axes of the plates. it appears that a minimum distance between axes of approximately seven times the width of the plate (7b) is needed for the two adjacent anchoring plates to act independently on the medium. the formation of a "rigid wedge" on the top of each plate was demonstrated. the failure mode observed during the pullout process is in agreement with the previous results. fig. 3. vertical displacement field for a pullout of 20 pixels and for different distances between axes of plates. (a) s = 3b, 20 pixels (b) s = 4b, 20 pixels (c) s = 5b, 20 pixels (d) s = 7b, 20 pixels etasr engineering, technology & applied science research vol. 3, no. 6, 2013, 562-565 565 www.etasr.com abbad et al.: interaction of rupture zones of adjacent anchor plates in an analogical medium fig. 4. deformation field (maximum shear) for a pullout of 20 pixels and different distances between axes of plates. references [1] g. g. meyerhof, j. i. adams, “ the ultimate uplift capacity of foundations“, canadian geotechnical journal, vol. 5, no. 4, pp. 225244, 1968 [2] e. j. murray, j. d. geddes, “uplift of anchor plates in sand“, journal of geotechnical engineering, vol. 113, no. 3, pp. 202–215, 1987 [3] t. h. hanna, r. sparks, m. yilmaz, “anchor behavior in sand“, journal of the soil mechanics and foundations division, vol. 98, no. 11, pp. 1187-1208, 1972 [4] j. d. geddes, e. j. murray, “plate anchor groups pulled vertically in sand“, journal of geotechnical engineering, vol. 122, no. 7, pp. 509524, 1996 [5] k. kouzer, j. kumar, “vertical uplift capacity of equally spaced horizontal strip anchors in sand“, international journal of geomechanics, vol.9, no. 5, pp. 230-236, 2009. [6] p. vacher, s. dumoulin, f. morestin, s. mguil-touchal, “bidimensional strain measurement using digital images“, proceedings of the institution of mechanical engineers, part c: journal of mechanical engineering science, vol. 213, no. 8, pp. 811-817, 1999 [7] h. abbad, m. meghachou, p. vacher, “interaction of subjacent zones due to contiguous shallow foundations in analogical medium”, european journal of environmental and civil engineering, vol.15,no. 3, pp. 391409, 2011. [8] k. m. kouzer, j. kumar, “vertical uplift capacity of two interfering horizontal anchors in sand using an upper bound limit analysis”, computers and geotechnics, vol. 36, no. 6, pp. 1084-1089, 2009 [9] j. kumar, k. m. kouzer, “vertical uplift capacity of a group of shallow horizontal anchors in sand “, géotechnique, vol. 58, no. 10, pp. 821823, 2008 (a) s = 3b, 20 pixels (c) s = 5b, 20 pixels (d) s = 7b, 20 pixels (b) s = 4b, 20 pixels microsoft word tiwari-ed2.doc etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 325-337 325 www.etasr.com tiwari et al: a reflectance model for relatively clear and turbid waters a reflectance model for relatively clear and turbid waters s. p. tiwari dept. of ocean engineering indian institute of technology madras chennai-600036, india sptiwariiitm@gmail.com p. shanmugam dept. of ocean engineering indian institute of technology madras chennai-600036, india pshanmugam@iitm.ac.in y. h. ahn korea ocean satellite center korea institute of ocean science & technology seoul-425600, korea yhahn@kiost.ac j. h. ryu korea ocean satellite center korea institute of ocean science & technology seoul-425600, korea jhryu@kiost.ac abstract— accurate modeling of spectral remote sensing reflectance (rrs) is of great interest for ocean colour studies in highly turbid and relatively clear waters. in this work a semianalytical model that simulates the spectral curves of remote sensing reflectance of these waters is developed based on the inherent optical properties (iops) and f and q factors. for accommodating differences in the optical properties of the water and accounting for their directional variations, iops and f and q factors are derived as a function of phytoplankton pigments, suspended sediments and solar zenith angle. results of this model are compared with in-situ bio-optical data collected at 83 stations encompassing highly turbid/relatively cleared waters of the south sea of korea. measured and modeled remote sensing reflectances agree favorably in both magnitude and spectral shape, with considerably low errors (mean relative error mre -0.0327; root mean square error rmse 0.205, bias -0.0727 and slope 1.15 and correlation coefficient r 2 0.74). these results suggest that the new model has the ability to reproduce measured reflectance values and has potentially profound implications for remote sensing of complex waters in this region. keywords-remote sensing reflectance; semianalytical model; optical properties; coastal oceanic waters. appendix ss suspended sediment matter cdom coloured dissolved organic matter iops inherent optical properties aops apparent optical properties chl concentration of chlorophyll (mg m -3 ) ( , 0 ) w l λ + water-leaving radiance in the viewing direction w m -2 sr -1 nm -1 ( ) rs r λ above-surface remote sensing reflectance (sr -1 ) (0 )r − sub-surface irradiance reflectance (sr -1 ) f anisotropy factor of the light filed in the water q bidirectionality factor (a ratio of upward irradiance to upward radiance under water) dimensionless sun θ zenith solar angle (degree) ϖ single scattering albedo bb ω backscattering albedo ( )a λ total absorption coefficient of water (m −1 ) ( ) w a λ absorption coefficient of pure water (m −1 ) ( ) ph a λ absorption coefficient of phytoplankton (mainly chlorophyll; m −1 ) ( ) ss a λ absorption coefficient of non-pigment suspended matter (m −1 ) ( ) g a λ absorption coefficient of cdom (m −1 ) * ( ) ph a λ specific absorption coefficient of phytoplankton (mainly chlorophyll; m 2 mg −1 ) a * d(λ0) specific absorption coefficient of non-pigment suspended matter(m 2 mg −1 ) * 0 ( ) g a λ specific absorption coefficient of cdom ( )b λ total scattering coefficient of water (m −1 ) ( ) w b λ scattering coefficient of pure water (m −1 ) ( ) p b λ scattering coefficient of particulate matter (m −1 ) * 0 ( ) p b λ specific scattering coefficient of particulate matter (m 2 g -1 ) ( ) b b λ total backscattering coefficient of water (m −1 ) i. introduction the intrinsic colour of the ocean can be quantified in terms of spectral remote sensing reflectance, ( ), rs r λ which provides measures of the ratio of upwelling to downwelling light at the water surface. to first-order approximation, the ocean reflectance varies as the ratio of the backscattering coefficient, ( ), b b λ to absorption coefficient, ( ),a λ of seawater [1-4]. thus, the spectral character of natural light leaving the ocean depends largely on ( ) / ( ), b b aλ λ both are inherent optical properties (iops) that depend on the types and concentrations of various constituents present in the water. properties that are directly derived from the light field (e.g., rs r or rs r both spectral-dependent terms) are called the apparent optical properties (aops), thus when there is a change in light field that enters the ocean, it does not affect the iops. in order to deduce from these ocean colour properties the substances present in water and their concentrations, it is imperative to understand how different constituents of water contribute to absorption ( α ) and backscattering ( b b ) of light. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 325-337 326 www.etasr.com tiwari et al: a reflectance model for relatively clear and turbid waters optical properties of water vary for two primary reasons: variations in the concentrations of water constituents and variations in the materials themselves, e.g., variations in the size and refractive index of particles. an ocean colour model parameterized for a set of optically active constituents should be able to describe optical variability due to varying concentrations of those constituents. such a model could then be inverted successfully to retrieve the constituents’ concentrations and iops [2]. presently, empirical algorithms often focus only on retrieving a single constituent concentration, whereas semi-analytical algorithms are capable of retrieving three or more constituents simultaneously [5]. for semi-analytical algorithms, an inversion technique is usually applied to a parameterized ocean colour model whose parameters are determined from in situ bio-optical measurements [6-13]. precise radiative transfer calculations [1, 14] have provided a solid physical and analytical basis for quantitatively interpreting a measured ocean colour spectrum as a function of the iops (i.e., absorption and backscattering coefficients). the forward technique for remote sensing is used to predict the spectral intensity of the light based on a quantitative description of all the absorption, scattering and reflection characteristics of the optical components in the ocean. the simulation of the surface ( ) rs r λ as a function of both absorption and backscattering usually represents the reflected ocean signals from various in-water constituents. thus, the prediction of the availability and propagation of underwater lights from knowledge of its particulate and dissolved concentrations of water constituents is referred to as the forward modeling [15]. it is generally estimated based on the particle size distribution, refractive index of seawater, and optical bidirectional quantities q and f that mainly depend on the geometric structure of the light field. of these, the values of f factor vary [14, 16] with the illumination conditions at the surface (essentially with the sun position for clear skies). given an incident radiant field, f also depends on the iops of the water body and thus on the chl concentration and wavelength [17]. for remote sensing applications, the /f q factor is described as a function of chl for case 1 waters [18, 19]. however, in case 2 waters, by definition, the iops are not determined by chl alone because of the presence of other particles that do not co-vary with chl and therefore a case 1 water model for bidirectional effects is clearly not applicable. the objective of this study is to develop a semi-analytical ocean colour model for coastal oceanic waters. the new model incorporates the empirical relationships for iops, analytical expressions for total backscattering coefficients and the values of bidirectional parameters. the empirical relationships are developed based on a large in-situ data of iops and describe the variability of the four major components, such as backscattering ( ( ) b b λ ) by all particles and the absorption by pure seawater ( ( ) w a λ ), phytoplankton ( ( ) ph a λ ), gelbstoff ( ( ) g a λ ) and sediment (detritus) particles ( ( ) d a λ ). this paper also includes the bidirectional reflectance parameter term ( /f q ), particularly in view of improving the present ocean colour model. ii. formulation of reflectance model the present semi-analytical model includes the radiative transfer expressions and empirical relationships derived from in-situ data sets. in the following sections, the theoretical basis of this model and procedures for deriving its input parameters are presented. the derivation of individual terms in the radiative transfer equations is described and usefulness of the model is discussed. ocean colour is essentially the spectrum of light leaving the ocean, normalized to the incident light on ocean surface, carrying with it information on iops (total backscattering ( ) b b λ and total absorption ( )a λ of the water. thus, spectral ( ) rs r λ is related to backscattering, which redirects downwelling photons to travel upward and eventually leave the water surface, and absorption, which converts photons to heat or chemical energy. as upward traveling photons exit the water, they interact with air-water interface by refraction and internal reflection [20]. radiative transfer studies have shown that spectral ( ) rs r λ at any wavelength λ can be modeled through the approximation [21-23; 18]: 2 2 2 2 ( )( ) ( ) ( , 0 ) ( ) ( ) ( ) b rs b bt f t r r n q n a b λλ λ λ λ λ λ −= × = +       ( )( ) 0.54 ( ) ( ) ( ) b b bf q a b λλ λ λ λ = +       (1) both ( ) rs r λ and ( , 0 )r λ − are apparent optical properties (aops) as they are dependent upon the directional structure of the radiance distribution as well as the optical characteristics of the medium [24]. in theory, the bidirectional parameter of remote sensing reflectance of optical field q ranges from 0.3 to 6.5, but is generally expected to be 3 [19], n is the refractive index of seawater; austin [25] proposed the factor 0.54 for correlating radiance just above the surface to radiance just beneath the surface (t 2 /n 2 =0.54 is transmissibility of air-water interface), f is a constant of proportionality [19] and a function of solar zenith angle. however, a wide range of values of f is commonly found in the literature, from 0.33 [1] to 0.089 [26]. as reported earlier, /f q ( /f q =0.095 for sun θ => 20 0 ) is independent of the solar zenith angle changes [21, 27]. especially, both f and q are the key parameters which connect the remote sensing reflectance above the water to the iop parameters (e.g., absorption and scattering). according to the recent studies, the values of bidirectional reflectance parameters q and f have to be predetermined or are etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 325-337 327 www.etasr.com tiwari et al: a reflectance model for relatively clear and turbid waters considered constant for simulation of ( ) rs r λ . however, these optical parameters can be affected by many factors, including the viewing geometry of the sensor, the roughness of water surface, the bidirectional reflectance of water and the atmospheric condition, and are often different at different water locations and times [26]. estimating the values of q and f by inappropriate optical models or ignoring their variations will therefore introduce large errors in retrieved water qualities. this problem could be solved by calculating and incorporating the effects of bidirectional quantities ( f and q ) on optical properties of marine waters. in many previous studies, the values of f and q are set to be constant, for instance f equals 0.33 [28] and the q parameter is universally equal to 3.14 [29, 30]. in other studies, the values of f and q are calculated from optical models, which take the mean cosine (µ0) or sunθ as inputs [2, 27]. it is more appropriate to calculate the values of f and q from optical models than to set them to be constants. thus, the sun angle is used for calculating the f value according to morel and gentili [27] in (2). their relationship for deriving f values can be expressed as a function of the ratio of the molecular backscattering to total backscattering ( ( ) ( )), b bw b b bη λ λ= single scattering albedo ϖ and solar zenith angle cos( )sunθ as follows: )cos()0795.0 0111.00401.01875.02796.0( 2189.00167.0 0231.01045.01067.05575.0)( 2 2 2 sunb b b bb f θϖη ϖϖη ϖηϖ ηϖηλ ×× +×−×−×+− +××−× +×−+×−= (2) where ( )b b a b cϖ = + = is the single scattering albedo in which a and c are the absorption and attenuation coefficients respectively. in the above equation, the backscattering albedo ( ( ) b b ω λ ) is used as an alternative of the single scattering albedo. sun θ is the sun zenith angle. equation (2) takes into consideration the fact that f depends not only on the geometric structure of the light field, expressed by the parameter sun θ , but also on the absorption and scattering properties of the water. the spectral behavior of the bidirectional factor q , which is the ratio of the upwelling irradiance to upwelling radiance, ( ) / ( ), u u e lλ λ is determined by the expression: ( ) / ( )rsq r rλ λ−= , where ( )r λ is the irradiance reflectance and ( )rsr λ− is the remote sensing reflectance below the surface. )(λ− rs r can be calculated using the following relationship [31]: ( ) ( )rs rs br fλ ω λ − = × (3) the factor ( ) / ( ( ) ( )) b b b a bλ λ λ+ is an angle-independent factor that determines the water reflectance, which represents the probability of backscattering per extinction event when the quasi-single-scattering approximation is valid; i.e., when the forward scattered photons are considered not to be removed from the incident beam [32]. thus, the backscattering albedo is described as follow: ( ) ( ) / ( ( ) ( )) b b b b a bω λ λ λ λ= + (4) further simplification of (3) for derivation of remote sensing reflectance below the surface as a function of the total absorption and backscattering leads to [33]: ( ) ( ) ( ) ( ) b rs rs b b r f a b λ λ λ λ − = × + (5) where, 2 3 ( ) 0.0512 (1 4.6659 7.8387 ... 0.4021 0.1098 ... 5.4571 ) 1 1 cos cos rs b b b v sun f λ ω ω ω θ θ = × + × − × +     + × × + × +        the determination of the remote sensing reflectance from the irradiance reflectance is possible using the q factor, ( ) ( ) / rs r r qλ λ− = . the q factor is determined by the angular distribution of the underwater light field. the angular distribution of light is in turn controlled significantly by the iops and their concentrations; therefore, a parameterization of ( ) / ( )rsq r rλ λ−= . moreover, the q factor is derived as a function of solar zenith angle in-water and viewing angle inwater. )()( )( )( λλ λ λ b b ba b fr + ×= (6) f factor, as given by (6), is used to derive the irradiance reflectance values. sun θ , and v θ in (5) are the sun zenith angle (generally it is considered 30°) and viewing angle (it is considered 0°) respectively. a. parameterization of the reflectance model 1) absorption terms the total absorption can be partitioned into the cumulative sum of individual contributions by optically significant constituents of seawater such as water molecules , w a phytoplankton ph a , coloured dissolved organic matter g a , and suspended sediment ss a : )()()()()( λλλλλ ssgphwt aaaaa +++= (7) etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 325-337 328 www.etasr.com tiwari et al: a reflectance model for relatively clear and turbid waters all water constituents are treated as variables and parameterized as a function of chl and ss concentrations. the above-four components can be further expanded to give ( ) t a λ : 0 1 ( ) ( ) [ ( ) ( ) ln( )] (440) (443) exp[ ( 443)] (443) exp[ ( 443)] t w ph g g ss ss a a a a chl a a s a s λ λ λ λ λ λ = + + × × + − − + − − (8) where g s and ss s are the spectral slopes of the absorption coefficients of cdom and ss respectively. 2) absorption coefficient of water ( w a ) the absorption coefficient of water varies weakly in the near-uv (e.g., 280 nm), blue (e.g., 443 nm), and green (e.g., 530 nm) regions of the spectrum, but increases gradually as the wavelength rises above 570 nm and becomes significant in the red region (figure 1). the w a is assumed constant and equal to the reported values for pure water [34]. for visible wavelengths, w a does not change much between the fresh and salt waters [35]. however, due to the dissolved ions in the sea waters w a can change markedly for wavelengths in the uv range [35]. 3) phytoplankton absorption the phytoplankton absorption ( ) ph a λ is usually represented as *( ) ( ) [ ] ph ph a a chlλ λ= × (9) where [ ]chl is the chlorophyll concentration and )( * λ ph a (m 2 mg chl -1 ) is the chl-specific absorption coefficient of phytoplankton [36, 37]. changes in cell size and in the composition and degree of packaging of pigments could influence * ( ) ph a λ values [36, 37]. thus, * ( ) ph a λ is not constant, but parameterized as a function of chl [38]: * ( ) ( ) ( ) [ ] b ph a a chl λλ λ −= × (10) where ( )a λ and ( )b λ values are wavelength-dependent and measured over the wavelengths from 400-700 nm. this model is mainly applicable in clear waters. alternatively, lee in [39] derived ( ) ph a λ empirically as follows: 0 1 ( ) [ ( ) ( ) ln( )] (440) ph ph a a a chl aλ λ λ= + × × (11) where 0 a and 1 a are the empirical coefficients from [40], which are then linearly interpolated from 700 to 720 nm at an equal interval of 2 nm. in the above equation, (440) ph a is estimated as a function of chl using (figure 2a): 8555.0;)(0541.0)440( 27491.0 =×= rchla ph (12) this model (11 and 12) reproduces the spectral shapes of the ( ) ph a λ curves with peaks around 440 nm and 675 nm. 4) cdom and ss absorption coefficients cdom and ss are the important components of the ocean optical signal for the satellite-based measurements of ocean colour and can interfere in global and regional estimates of primary production [4143]. it is therefore highly desirable to retrieve the absorption coefficients of cdom and ss in coastal waters. since the terms ss a and g a have similar spectral shapes decreasing exponentially with increasing wavelength, they can both be fit to a curve of the form )443( )()( −−= λλλ s rxx eaa (13) the absorption coefficients of cdom and ss are estimated at two wavelengths (i.e., )412( x a and )443(xa ) in order to derive slopes of their absorption curves. in this equation, the subscript x refers to either the cdom absorption or the ss absorption, s is the spectral slope coefficient (nm -1 ) of exponential that determines the shape of the absorption curve, ( ) x r a λ is the absorption coefficient at a reference wavelength. the slope is used as a proxy for /cdom ss composition, and is often empirically determined. earlier studies have reported the average value of the spectral slope ( ss s ) for detritus to vary from 0.0058 to 0.011 nm -1 and ( g s ) for dissolved materials to vary from 0.014 and 0.015 nm -1 in typical marine environments [44]. the mean spectral slope ( g s ) of the overall retrieval determined here is 0.015 nm -1 . a) empirical relationships for deriving (412) g a and (443) g a and g s coefficients to estimate the absorption coefficient of cdom in the visible domain, relationships between the log-transformed g a at 412 and 443 nm and log-transformed chl were established using in-situ bio-optical data sets (figure 3). a goodness of fit was found between g a at 412 and 443 nm and chl concentrations, with correlation coefficient ( 2 r ) 0.63 for chl versus (412) g a and 0.46 for chl versus (443) g a . statistical regression analyses demonstrated the best-fit power functions as described below: 3448.0 ][189.0)412( chla g ×= ; 63.0 2 =r (14) 3269.0 ][153.0)443( chla g ×= ; 46.0 2 =r (15) etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 325-337 329 www.etasr.com tiwari et al: a reflectance model for relatively clear and turbid waters where (412) g a and (443) g a represent the absorption coefficients of cdom at 412 and 443 nm, and the values 0.189, 0.3448, 0.1525, and 0.3969 are the regression coefficients. the value of g s was derived based on a power fit of the absorption spectra to an exponential function over the wavelength range from 400 to 720 nm:         − = )443( )412( log )( 1 10 g g r g a a s λλ (16) the derived slope values are consistent with those of the measured values in the study region fig. 1. absorption and backscattering coefficients of pure seawater (a and b) and variability of the total absorption and backscattering spectra of coastal oceanic waters (c and d). fig. 2. (a) the empirical relationships between the (440) ph a and chl concentrations from in-situ data sets (n = 83). panels (b and c) are the 0 a and 1 a coefficients. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 325-337 330 www.etasr.com tiwari et al: a reflectance model for relatively clear and turbid waters b) empirical relationships for deriving (412) ss a and (443) ss a and ss s coefficient the absorption by suspended sediment ( ss ) is treated separately as it has a significant influence on the remote sensing reflectance spectra. similar to the absorption coefficient of cdom ss a values were derived at two wavelengths (412 and 443 nm) at which high absorption occurs. to estimate the absorption coefficient of ss in the visible domain, relationships between the log-transformed ss a at 412 and 443 nm and log-transformed [ ]ss concentrations were established using in-situ bio-optical data sets (figure 4). the expressions of ss a at 412 and 443 nm are given by: 0.681 (412) 0.089 [ ] ss a ss= × ; 70.02 =r (17) 0.5551 (443) 0.067 [ ] ss a ss= × ; 67.0 2 =r (18) where (412) ss a and (443) ss a represent the absorption coefficients of ss at 412 and 443 nm, and the values 0.0885, 0.681, 0.067, and 0.551 are the regression coefficients. the value of the spectral slope parameter ( ss s ) was derived for the wavelengths 400-720 nm using:       − = )443( )412( log )( 1 10 ss ss r ss a a s λλ (19) the derived slope values are comparable with those of the measured values in the study region. fig. 3. the empirical relationships between the (412) g a , (443) g a and chl concentrations from in-situ data sets (n = 83). fig. 4. the empirical relationships between the (412) ss a , (443) ss a and ss concentrations from in-situ data sets (n = 83). b. backscattering term ( b b ) in bio-optical modeling for remote sensing of chlorophyll in case 1 waters, analytical approximations of the spectral reflectance from the pigment content of water require establishing the relationship between b b and chlorophyll [44, 45]. while the dependency of p b on chlorophyll has been etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 325-337 331 www.etasr.com tiwari et al: a reflectance model for relatively clear and turbid waters empirically determined in several studies (recently by [46]), b b is usually derived from bpb , where bpb is modeled semianalytically as a function of chlorophyll [44, 45]. the ( ) b b λ is partitioned into a constant equal to the reported values for backscatter by pure seawater, ( ) bw b λ [47] and contributions by the particle fraction, ( , ) bp b chl λ and ( , ) bss b ss λ . ( ) ( ) ( , ) ( , ) b bw bp bss b b b chl b ssλ λ λ λ= + + (20) since no ( , ) bp b chl λ and ( , ) bss b ss λ measurements were made for this study, ( , ) bp b chl λ and ( , ) bss b ss λ are derived by considering the typical variations of * (550) bp b , * ( ) bss b λ and backscattering slope (y) by particulate matter. further, the ( ) b b λ can be decomposed as follows: ( )1 2 10 0.62 * ( ) ( ) 0.002 ... 550 ... 0.02[0.5 0.25 log [ ] ] ... ... [0.3 (550)] [ ] ( ) b w w bss b b chl c b ss b λ λ λ λ = × + + + − × × × × × − + × (21) for case 1 water, the individual scattering and absorption can be modeled through empirical formula with only one input variable: concentration of .chl the derivation of the backscattering coefficient ( ) b b λ starts with the use of an empirical expression [48], which relates the particle scattering coefficient bp b at 550 nm to [ chl ], as follows: 0.6 2 (5 50 ) 0.3 [ ] p b c h l= × (22) this relationship was indeed established for the total scattering coefficient (550) p b so that (550) w b must be subtracted to obtain (550) p b . a more accurate form of (21) should read 0.62 (550) 0.3 [ ] (550) p w b chl b= × − (23) even in the clearest waters, for example, when [ chl ] ~ 0.02 mg m -3 , the molecular scattering represents about 7% (at 550 nm) of the total scattering coefficient; therefore this contribution is negligible considering the uncertainty attached to the above statistical relationship. the particle backscattering coefficient ( ) bp b λ is then obtained from [44] through the expression: 0.62 10 ( , ) [0.002 0.02(0.5 0.25 ... 550 ... log ( ) ] [0.3 (550)] bp w b chl chl c b λ λ = + − × × × × × − (24) note that the wavelength dependency λ -1 only applies to this part (within the brackets) of the backscattering efficiency (the embrace), which varies with [ chl ]. then ( , ) bp b chl λ is added to (1/2) ( ) w b λ to obtain the total backscattering coefficient as follows: ( ) ),(),()()( 21 λλλλ ssbchlbbb bssbpwb ++×= (25) conversely to what happens for the total scattering coefficient, the molecular contribution is often important in forming the backscattering coefficient ( ) b b λ ; in effect, it becomes the dominant term at low chlorophyll concentration. the ( , ) bp b chl λ is parameterized at a reference wavelength of 550 nm, and the ( ) bw b λ is estimated using a backscattering ratio of 0.5 and the ( ) w b λ of [44] as tabulated in [47]. backscattering by suspended sediments is derived from the following expression given as below: * ( , ) ( ) bss bss b ss ss bλ λ= × (26) where the values of specific backscattering by suspended sediments are taken from [48]. iii. data sets in-situ bio-optical data sets collected from a wide range of coastal waters (33.5°n ~ 35.5°n; 125.5°e ~130°e) around the south sea of korea from 2001-2005 have been used to test the performance of the present model. the data sets include the remote sensing reflectance ( ) rs r λ , chlorophyll ( chl ) and suspended sediment ( ss ) concentrations, and absorption by phytoplankton ( ph a ), coloured dissolved organic matter ( g a ) and suspended sediment matter ( ss a ) (more details in [49-51]). after a careful examination, 83 in-water profiles of chl ,ss , ss a ph a and g a and ( ) rs r λ were selected representing highly turbid, relatively cleared and relatively clear waters. iv. results and discussions a. comparison of the derived absorption spectra ( , ss a ph a and g a ) with in-situ data absorption coefficients of non-algal particles ( ss a ) phytoplankton ( ph a ) and coloured dissolved organic matter ( g a ) derived from the respective models are compared with in-situ data collected at all 83 stations (figure 5). etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 325-337 332 www.etasr.com tiwari et al: a reflectance model for relatively clear and turbid waters fig. 5. comparison of the absorption spectral of ss a , g a , and ph a derived from the respective models with those measured from the water samples collected in turbid/relatively clear waters of the south sea of korea. their mean absorption spectra are shown in the bottom panels. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 325-337 333 www.etasr.com tiwari et al: a reflectance model for relatively clear and turbid waters the fitted spectral values of these numerical coefficients, which are used as inputs to the reflectance model, indicate small differences in the general variability, magnitude and spectral shape of both dissolved and particulate absorptions in turbid and relatively clear waters. cdom and ss absorption coefficients are strong in the blue (e.g. 412 and 443 nm) domain and exponentially decrease towards the longer wavelengths. looking at their mean absorption curves from the models reveals slightly lower ss a values at 412-443 nm and lower g a values in the longer wavelengths. higher values of g a from the in-situ data may result from a contribution of small particles that pass through a pore size of the filter paper (<0.45 µm). this suggests that g a values derived from the model reduced contributions to absorption by smaller particles. in contrast, absorption coefficients of phytoplankton derived from the model are tightly consistent with measured spectra in the green and red domains, but becoming smaller toward shorter wavelengths. the differences could be related to variability in absorption per unit chlorophyll resulting from pigment packaging effects [52]. as already reported, this spectrum typically has two peaks, one around 443 nm and another around 670 nm; there is relatively lower absorption between 550 and 650 nm [50]. these peaks are due to the presence of chl and the width of the peaks around 440 and 675 nm varies from sample to sample, due to the change in accessory pigments present and the package effect [52]. b. comparison of the derived remote sensing reflectance spectra with in-situ spectra a set of 83 reflectance spectra were generated using the new model for varying concentrations of ,chl ss and cdom contents in coastal waters of the south sea of korea. to illustrate differences (in terms of spectral shape and magnitude), simulated spectra of ( ) rs r λ are compared with the in-situ ( ) rs r λ spectra for three water provinces (e.g., relatively clear, highly turbid, and moderately turbid waters) (figure 6). it should be noted that simulated ( ) rs r λ are found in good agreement with the measured ( ) rs r λ curves from relatively clear and turbid waters. the agreement of spectral shape and magnitude are encouraging and show noticeable variability in the visible-near-infra-red domains (400-720 nm) due to the highly variable in-water constituents of these waters. ss values over 5 g m -3 are sufficient to mask the ,chl signal, thereby causing large errors in deriving the ( ) rs r λ values with this model. it is evident that when ,chl concentrations decrease with increasing or decreasing ss concentrations, the ( ) rs r λ curves become closer to the measured ( ) rs r λ spectra (figure 6a and b). fig. 6. comparison of the simulated remote sensing reflectance ( r s r ) with in-situ data in coastal waters of the south sea of korea. by contrast, ( ) rs r λ values from highly turbid waters peak toward the red wavelengths because of the high turbidity caused by tidal activities and bottom circulations (figure 6a). consequently, elevated ssc increased the backscattering more than the absorption in the longer wavelengths. this drew the attention of the researchers and encouraged them to exploit the usefulness of single band radiance or reflectance at these wavelengths for remote estimation of ss from satellites [53]. in cases of moderately clear waters, ( ) rs r λ values tend to increase in the blue wavelength region and decrease in the longer wavelength region. this suggests profound absorption by water itself with ,chl 1.9 mg m −3 and ssc 1.59 g m −3 (figure 6b) c. validation of the model results with in-situ data to assess the performance of new model, the results are compared with in-situ ( ) rs r λ values. few statistical measures were used to assess the model performance, namely the root means square error (rmse), mean relative error (mre), bias, slope, and correlation coefficient ( 2 r ) [54]. figure 7 shows the comparison of simulated ( ) rs r λ values with the in-situ ( ) rs r λ values at 400, 412, 440, 490, 510, 550, 670, 685 nm. table i presents the statistical results for the present model. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 325-337 334 www.etasr.com tiwari et al: a reflectance model for relatively clear and turbid waters fig. 7. scatterplots of the simulated remote sensing reflectance ( rs r ) versus in-situ rs r data for relatively cleared, turbid and relatively clear waters in the south sea of korea (n=83). etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 325-337 335 www.etasr.com tiwari et al: a reflectance model for relatively clear and turbid waters table i. statistical comparison between the simulated and in situ data of remote sensing reflectance. rmse and mre and linearregression results of the measured data at 400, 412, 440, 490, 510, 550, 670, and 685 nm . aops mre rmse slope r 2 bias : rrs(400) -0.0103 0.1537 0.9447 0.724 -0.0236 83 rrs(412) -0.02 0.1715 1.0188 0.7308 -0.0459 83 rrs(440) -0.0336 0.2104 1.1597 0.7496 -0.0765 83 rrs(490) -0.0499 0.2457 1.3093 0.7682 -0.1096 83 rrs(510) -0.0542 0.2369 1.2973 0.7874 -0.1175 83 rrs(550) -0.0517 0.1995 1.1952 0.7872 -0.1075 83 rrs(670) -0.0315 0.2325 1.1912 0.6942 -0.0769 83 rrs(685) -0.0104 0.1973 1.1002 0.6924 -0.0248 83 it is apparent that comparison of the simulated ( ) rs r λ values with in-situ data indicates good agreement over the entire range of data at all wavelengths, which suggests that the new model works very well in all three water provinces. hence, errors associated with the new model decreased and slopes and 2 r values increased at all wavelengths (mre -0.054~-0.01; rmse 0.15~0.24, bias -0.11~-0.023, slope 0.94~1.3, r 2 0.69~0.787). a slight overestimation of ( ) rs r λ values with the new model is still noticed at the lower end of the scatter plots, which suggests that there is profound effect of suspended sediment particles in seawater iops and hence in the aops. d. implications for the optical remote sensing the remote sensing reflectance is an essential parameter among the aops, which is normally used as a proxy for the derivations of all the iops. usefulness of remote sensing reflectance in coastal/oceanic waters is highlighted by many researchers on regional and global scales. most of the recent reflectance modeling approaches are based on the three distinct methods: analytical, semi-analytical and empirical. in these approaches parameterizations mainly depend on radiance. however, a semi-analytical approach has been developed as a function of chl and ss , which is totally independent on the radiance (aops). the new model provides encouraging results in coastal waters. the values of remote sensing reflectance can be effective for modeling the iops and to solve inversion problems in ocean optics. this model also has the potential to describe the variability of reflectance spectra in turbid and relatively clear waters. further, this variability shows the considerable scenario to understand and inspect the fluorescence phenomenon towards the red and near-infrared wavelength regions. v. conclusion in this study, a new reflectance model has been developed to simulate rs r and validate with in-situ data. for modeling, the optical properties of pure water were taken from [34, 47]. the values of specific backscattering by suspended sediments were taken from [48]. the present model for predicting the values of ( ) rs r λ relies upon descriptions relating to the inherent optical properties of absorption and backscattering through the ratio of /f q . the model uses ,chl ss and cdom contents as inputs to estimate the required iops ( , ss a , g a and ph a ). further, the q and f factors that are variable and depend in a complicated manner upon the solar zenith angle, the geometric structure of the radiance field, and on the seawater iops are estimated by their respective equations and used in the present model. as a result, the new model produces ( ) rs r λ curves closely matching with the insitu measurements data. the shape and magnitude of the ( ) rs r λ curves are also closely comparable with measured ( ) rs r λ data. these results suggest that our reflectance model has several potential uses, including the examination of regional variability in the ( ) rs r λ versus chl and other inwater constituents relationships. the present model would be helpful to study and understand the relative contribution of each constituent to the bio-optics of coastal waters of korea and serve as a guide for the improvement of novel models for the estimation of iops in these waters. it is expected that further developments in oceanographic and ocean optics instrumentation would provide better understandings of marine environment in these waters. thus, the future work will be on the raman scattering, bottom reflectance and fluorescence, and to refine our model based on understanding of the influences of the iops an in-water properties on the remote sensing reflectance property. acknowledgements this work received support from the korea ocean research and development institute (kordi), seoul 425-600, korea (contract number oec/10-11/101/kord/ psha). this work was also supported by incois under the grant (oec/1011/102/inco/psha) of the satcore program. references [1] h. r. gordon, o. b. brown, m. m. jacobs, “computed relationships between the inherent and apparent optical properties of a flat homogeneous ocean”, applied optics, vol. 14, no. 2, pp. 417-427, 1975 [2] a. morel, l. prieur, “analysis of variations in ocean color”, limnology and oceanography, vol. 22, no. 4, pp. 709-722, 1977 [3] d. stramski, e. boss, d. bogucki, k. j. voss, “the role of seawater constituents in light backscattering in the ocean”, progress in oceanography, vol. 61, no. 1, pp. 27–56, 2004 [4] p. shanmugam, “a new bio-optical algorithm for the remote sensing of algal blooms in complex ocean waters”, journal of geophysical research, vol. 116, c04016, 2011, doi:10.1029/2010jc006796. 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sensing”, korean journal of remote sensing vol. 17, no. 4, pp. 285-295, 2001 [54] z. p. lee, international ocean-colour coordinating group (ioccg), remote sensing of inherent optical properties: fundamentals, tests of algorithms and applications, in reports of the international ocean-color coordinating group, edited by rep. 5, dartmouth, n.s., canada, 2006 authors profile surya prakash tiwari received the b. sc. degree in mathematics & physics, m. sc. in physics with electronics specialization degree from gorakhpur university, uttar pradesh, india, in 2005 and in 2007 respectively and m. tech. in remote sensing and gis from srm university, chennai, india in 2009. he is currently working toward the ph.d. degree in the department of ocean engineering, indian institute of technology (iit) madras, chennai, india. his research interests are focused on ocean colour remote sensing, optical properties of oceanic and coastal waters and bio-optical modeling. palanisamy shanmugam received the ph.d. degree in optical remote sensing from anna university, chennai, india, in 2002. he is currently an associate professor with the indian institute of technology (iit) madras, chennai, india. he has undertaken a broad range of research in ocean optics and ocean color remote sensing at the korea ocean research and development institute (kordi), seoul, korea during 2003–2008. his research is focused on the development of atmospheric and in-water algorithms for ocean color remote sensing and the characterization of underwater light field in the coastal ocean. he has been a principle investigator of several projects funded by the indian government and kordi. yu-hwan ahn received the ph.d. degree in optical oceanography from paris university, paris, france, in 1990. he was the head of the ocean color remote sensing laboratory at the national fisheries research and development institute (nfrdi) between 1993 and 1997. he was then the director of ocean satellite remote sensing and observation technology research department, korea ocean research and development institute (kordi), seoul, korea and he was also leader of korea ocean satellite center (kosc) in kordi. he has been responsible for the korean geostationary ocean color satellite (goci) program. he is currently research emeritus in kordi. his research interests are in the field of optical oceanography, including optical properties of oceanic particles, under water light field and development of ocean color remote sensing techniques. joo-hyung ryu received the ph.d. degree in geology and earth system sciences from yonsei university, seoul, korea, in 2001. he is currently the leader of korea ocean satellite center in kordi, korea. he is currently the pi of the goci scientific ocean application project. his research is focused on the development of ocean color remote sensing techniques and understanding the coastal zone processes. microsoft word 30-3773_s_etasr_v10_n5_pp6323-6329 engineering, technology & applied science research vol. 10, no. 5, 2020, 6323-6329 6323 www.etasr.com al-ateeq & alateeq: soft-charging effects on a high gain dc-to-dc step-up converter with psc voltage soft-charging effects on a high gain dc-to-dc step-up converter with psc voltage multipliers ayoob s. al-ateeq electrical engineering department univerity of hail ha’il, saudi arabia abdulaziz j. alateeq electrical engineering department univerity of hail ha’il, saudi arabia abstract−this paper proposes a split-phase control diagram for a new design of a dc-to-dc boost converter which is called pscboost and studies its performance. the psc-boost has two sides, the primary is a psc converter and the secondary is a dc-to-dc boost converter. the effect of applying the split-phase control diagram helps reduce the output impedance successfully and increases efficiency by 3%. the simulated and analytical results have been proven to validate the effect of the split-phase diagram. the simulated design contains five switches, five capacitors, seven diodes, and three inductors to step up 10v into 160v at 200khz and 100khz switching frequencies. the ltspice simulator was used to design and test the proposed model. keywords-psc-boost converter; split-phase diagram; sc converters; ltspice i. introduction renewable energy has been proven to be an essential sustenance of conventional energy resources. sustainability and eco-friendliness are two motivations that motivate hundreds of renewable energy research projects, but the low produced power limits its usage, for instance, pv cells produce a voltage that ranges between 12 to 48v. to overcome this limit and expand renewable energy applications, boosting the dc produced voltage to a higher voltage level by using dc-to-dc boost converters is recommended. furthermore, dc-to-dc converters help finding the appropriate integration between renewable energy sources and grid utilities. there are two types of dc-to-dc boost converters: isolated or non-isolated converters. their main difference is that the isolated design has a power transformer that divides the converter into primary and secondary sides. having a power transformer increases the voltage gain, however it can produce electromagnetic interference. lower power density is another side effect of using a power transformer. thus, a non-isolated conventional boost converter is preferable over the isolated dc-to-dc converter due to the absence of the power transformer. duty cycle dependency and voltage inductor second balance are two operational aspects of the non-isolated boost converter. the proportional relation between the duty cycle and high voltage gain makes the increase in the duty cycle the only way to provide a higher voltage gain. however, the increase of duty cycle is limited by switches’ voltage stress, which could harm the converter’s efficiency. there are several alternative ways to increase the voltage gain at a lower duty cycle, such as adding voltage multipliers to the dc-to-dc boost converter [1, 2]. besides that, using a resonant approach for dc-to-dc converters, shows great improvement of the converters efficiency [3, 4]. the new dc-to-dc converter is known as a multilevel boost converter (mbc). adding more output multipliers and keeping the main converter part (primary side) is the main aspect of the mbc converter [5-13]. the mbc increases the regulated output voltage by adding voltage cells, which are basically switched capacitors cells, but have drawbacks, such as the failure to produce the actual output voltage at higher duty cycles [14]. the proposed model in [14] uses a switched capacitor converter (psc) as a primary stage on a conventional boost converter. the switched capacitors cells work similarly with the mbc converter, however, they are connected to the primary side of the conventional boost converter. the psc-boost converter has shown superiority in the efficiency and actual rated voltage achievement in comparison with the mbc converter. in [15], the proposed control diagram helps achieving the complete soft-charging operation. the proposed split-phase diagram helps in increasing the efficiency by reducing the psc converter’s output impedance. this paper complements our work in [14] by using a splitphase control diagram [15] to operate the 8 switches of the psc-boost. the implemented control diagram increases effectively the psc-boost efficiency in reducing the output impedance. analytical and simulated results are presented. ii. the psc switched-capacitor converter a. topology and operation figure 1 shows the topology of the 1-to-4 psc converter and its control signals. the control diagram in figure 2(a) shows how four modes of operation are possible. in each mode, the capacitors are connected to each other differently for voltage regulation purposes. in mode-1, the flying capacitor cf1 is charging and the flying capacitor cf2 is discharging. in mode-2, both flying capacitors cf1 and cf2 are discharging and in mode-4 they are both charging. in mode-3 cf1 is discharging and cf2 is charging. to find the gain voltage of the proposed converter, each mode has a total charge that can be derived from the following equations [15-18]: corresponding author: ayoob s. al-ateeq (a.alateeq@uoh.edu.sa) engineering, technology & applied science research vol. 10, no. 5, 2020, 6323-6329 6324 www.etasr.com al-ateeq & alateeq: soft-charging effects on a high gain dc-to-dc step-up converter with psc voltage ��� � ���� ����� �� ��� ������ (1) where � is the number of modes (1, 2, 3, 4). from mode-1 (figure 2) we have: �� � � ��� (2) ��� � �� � (3) �� � � �� � ��� � �� � (4) b.y substituting (2), (3) and (4) in (1) we get the total charge of mode-1 (5): �� � ������� � � � ������ ��� � � � �� � ���� �� � (5) to find the total charge of the rest of the modes, the same steps can be repeated: ��� � ������ � � � ����� ��� � ��� ������ (6) ��� � ������� � � � ����� �� ��� � ��� ������ (7) ��� � ������ � � � ������ ��� ��� ����� (8) fig. 1. the 2-level of the proposed psc-boost converter. in the steady state operation, the total charge of any pair of modes is assumed to be equal. in this work, we assumed that: �� � ��� (9) ��� � ��� (10) by simplifying (9) and (10) we get: 2����� ����� � ������ � 0 (11) 2����� � ����� � 0 (12) by combining (11) and (12), the 1-to-4 psc converter’s voltage gain can be calculated (13): ���� � 4��� (13) the general form of the proposed converter is: ���� � 2���� (14) where � is the number of the stage. b. slow-switching limit impedance (rssl) the sc converters suffer from losses related to the switches’ switching and the capacitors’ charging or discharging process. this capacitors’ loss can be characterized as an output impedance that is called a slow switching limit impedance !!". the charge flow analysis of the four modes has been applied to find the charge multiplier of the four capacitors #$� %$� � #$� %��� (15) %$ � &%��%��%� �%� �'( (16) in [13, 14] a useful technique was used to find the charge flow’s vector of all the operation modes. for the ith mode, kcl can be derived by: )�%� � 0 (17) where )� represent the reduced incidence matrices of the four modes of 1-to-4 psc converter: 1 1 0 1 0 0 1 1 0 1 0 0 0 1 1 1 1 0 0 1 1 0 1 0 1 2, 0 0 1 0 1 1 0 0 1 0 0 1 1 0 0 0 0 1 1 0 0 1 1 1 1 1 0 1 0 0 1 1 0 1 0 0 0 1 1 1 1 0 0 1 1 0 1 0 3, 4, 0 0 1 0 0 1 0 0 1 0 1 1 1 0 0 0 1 1 1 0 0 1 0 1 b b a b ba a − − − − −       − − −   = =    − − − −            − − −       − − − − − −  = =   − −    −          (18) to find the charge flow’s vectors, (17) can be solved for %�: %*"�+ � , .�31 �1 �2 2 3 1 2 2 2 2 3 %*"�+� � , .�31 �3 2 �2 3 1 2 2 2 2 3 %*"�+� � , .�2�1 3 1 �1 3 1 2 2 2 2 3 %*"�+� � , .�2�3 2 1 1 3 1 2 2 2 2 3 (19) the total output charge with respect to the output charge can be found in (20): %��� � %��� %���� %���� %���� (20) the total output charge with respect to the input charge is: %��� � %�� %�� �456� + �456 � = 5%�� (21) by using (21), (19) can be rewritten with respect to the output charge (22): %$ � , . 489: ; <489: ; <�489: ; �489: ; 1 2 2 2 2 3 %$� � , . 489: ; <�489: ; �489: ; <489: ; 1 2 2 2 2 3 %$� � , . <489: ; �489: ; 489: ; <489: ; 1 2 2 2 2 3 %$� � , . <�489: ; �489: ; 489: ; 489: ; 1 2 2 2 2 3 (22) by applying (15), the charge multipliers are: engineering, technology & applied science research vol. 10, no. 5, 2020, 6323-6329 6325 www.etasr.com al-ateeq & alateeq: soft-charging effects on a high gain dc-to-dc step-up converter with psc voltage #$ � , . ; < ; <� ; � ; 1 2 2 2 2 3 #$� � , . ; <� ; � ; < ; 1 2 2 2 2 3 #$� � , . < ; � ; ; < ; 1 2 2 2 2 3 #$� � , . <� ; � ; ; ; 1 2 2 2 2 3 (23) then by using tellegen’s theorem, !!" can be found for the proposed design: =89: 489: ∑ �?@,5� � �5 ��bcde �� � �f � 0 (24) where =89: 489: � !!". !!" � ∑ �?@,5� � �5 ��bcde �� � �f (25) fig. 2. 1-to-8 psc topology (three-stage). fig. 3. the charge flow direction for each operation mode. c. fast-switching limit impedance another important parameter in the sc converters’ analysis is finding the fast switching limit ( *!"). in the sc converter two parameters are responsible for increasing efficiency, which are high switching frequency and large capacitor size. the *!" depends on the switches’ g!_�� as: *!" � ∑ �#e,�����bcde �� i�f (26) where �#e,�� is the charge multiplier of eight switches in the 1to-4 psc converter. iii. a comparison between the proposed psc converter with three sc converter topologies the comparison between the proposed psc and three known sc converter topologies (1-to-4 series to parallel, 1-to-4 ladder, and 1-to-4 dickson) considers the fundamental efficiency and the output impedance. the psc converter is found to be superior over the three other topologies in high efficiency achievement whereas the 1-to-4 ladder has the lowest efficiency (figure 4). in addition, the psc converter successfully achieves the ssl limit at a lower switching frequency faster than the other topologies (figure 5). in other words, the psc converter requires less switching frequency to achieve lower output impedance. the second lowest output impedance among the compared topologies is accomplished by the series to parallel topology, which means that an additional comparison must be calculated between the psc converter and 1-to-4 series to parallel considering the number of switches and the maximum voltage stress across the switches [19-24]. fig. 4. efficiency vs rated power. iv. the proposed model the psc switched-capacitor converter can be used as a voltage multiplier and as a primary stage of a non-isolated boost converter. the multiplier cells can be increased with regard to the desired output voltage without distorting the conventional boost converter side. capacitors’ charging and discharging processes are successfully demonstrated by fully controllable semiconductor devices, which are switches. the 8 switches are controlled by the proposed split-phase diagram that allows dead time for each switch. in addition to applying a split-phase control diagram, the proposed switched inductor cell in [25] is used as an input inductor in the boost converter side (second-stage). the proposed control diagram is based on the increase of the periods of the transitions modes which are between any two existing modes. this allows a dead time for all eight switches (figure 3). applying the split phase control diagram helps to reduce the output impedance, thus exhibiting the converter’s efficiency. adding more modes would reduce the charge multipliers of each capacitor and thus reduce the engineering, technology & applied science research vol. 10, no. 5, 2020, 6323-6329 6326 www.etasr.com al-ateeq & alateeq: soft-charging effects on a high gain dc-to-dc step-up converter with psc voltage output impedance. to reduce the output impedance by using the convectional control diagram requires a higher switching frequency. this requirement can be recovered by applying the split-phase control diagram where the output impedance can be maintained low at a lower switching frequency. table i exhibits the comparison between the psc output impedance for traditional and split-phase control diagrams. fig. 5. output impedance vs switching frequency. table i. comparison between the psc output impedance for traditional and split-phace contro charging operation jkkl �mn,o�p conventional control diagram 1 6 r �#$,��� �� stu ��bcde �� � �f 5 2 split-phase control diagram 3 20 r �#$,��� �� stu ��bcde �� � �f 5 18 v. analysis of the proposed model the proposed converter has two stages, psc converter and conventional boost converter (figure 7). the boost stage has an input which is basically the psc converter output voltage. when replacing the input inductor of the boost converter by the switched-inductor model which has three inductors w , w� and w�, these three inductors are assumed to be ideal and equal. during mode-1 to mode-4, each of the three inductors has a voltage drop equal to ��� (27) due to their parallel connection: ��� � �x � �x� � �x� (27) y$ � <=89:z[ (28) where ���� and x are the output voltage and the load respectively. when s-boost is off, a series connection of w , w� and w� is exhibiting through mode-5 to mode-8: ��� � �x �x� �x� ���� (29) since w , w� and w� are the same, they will have the same voltage drop. ��� � �x �x� �x� ���� (30) 3�x � �x �x� �x� (31) we can rewrite (30) into (31) to get (32): ��� � 3�x ���� (32) �x � =56<=89:� (33) by assuming the inductor voltage’s second balance to (27) and (33), the voltage gain of the proposed model can be obtained: \��� � ��1 � \��=56<=89:� � (34) the converter gain of the second stage can be found by: =89: =56 � �]^ <] (35) by substituting ��� in (35) by the output voltage of psc we get: =89: =89:__`a � �]^ <] (36) ����_bi� � 2c��� (37) where n is the number of the converter stages. (a) (b) fig. 6. (a) a proposed timing diagram for the split-phase operation for the 1-to-4 psc converter, (b) the 8 operation modes of the 1-to-4 psc converter after applying the split-phase. engineering, technology & applied science research vol. 10, no. 5, 2020, 6323-6329 6327 www.etasr.com al-ateeq & alateeq: soft-charging effects on a high gain dc-to-dc step-up converter with psc voltage fig. 7. the proposed converter and its two stages, psc converter and conventional boost converter. by rewriting (36), the voltage gain of the psc-boost converter can be represented as: =89: =56 � �d��]^ � <] (38) vi. results and discussion ltspice simulator was used to study the psc-boost converter and its performance in split-phase control. based on the simulation parameters in table ii, the two-level psc-boost converter successfully converts 10v to 160v as presented in figure 8. table ii. sim ulation parameters o f the psc-boost parameter value input voltage (v) 12v switching frequency boost (khz) 100 switching frequency s1 to s8 (khz) 200 diode type mbrs240lt3 switches type irfi540npbf c1 to c7 94µf cf1, cf2 and co 188µf duty cycle of sboost 50% fig. 8. the output voltage of the proposed psc-boost converter. furthermore, the single inductor in the boost side was replaced by a switched inductor model to increase the proposed converter’s gain and its rated output power. the switchedinductor cell operates in two operation modes regarding to the sboost states. the three inductors have a parallel connection when sboost is on and a series connection when sboost is off. having parallel and series connections allows inductors to charge and discharge instantaneously. the dependency between sboost states and inductors’ connections can be proven by the waveform similarity between the switched inductor input current and the sboost gate driver, as indicated in figure 9. fig. 9. yin with the duty cycle, shows w1, w 2 and w3 parallel and series connections. fig. 10. the output impedance at two different control diagrams. fig. 11. the efficiency of psc multiplier cells at two different control diagrams. since the psc-boost converter consists of two stages (sc cells and a conventional dc-to-dc boost converter), in this engineering, technology & applied science research vol. 10, no. 5, 2020, 6323-6329 6328 www.etasr.com al-ateeq & alateeq: soft-charging effects on a high gain dc-to-dc step-up converter with psc voltage article the primary stage of psc cells was designed to operate in the complete soft-charging operation [13, 15]. the complete soft-charging operation effectively reduces the switching frequency requirement that is essential to decrease the sc converter’s output impedance as presented in table i. however, in order to achieve the complete soft-charging operation, a split-phase control diagram is needed. the splitphase diagram presents a transition mode between any two existing modes in the conventional operation. for instance, a transition mode, called mode-1b, will appear between mode-1 and mode-2. the difference between mode-1 and mode-1b is that mode-1b has three capacitors instead of four. the isolation of the fourth capacitor reduces the total charge multipliers, and as a result, lower output impedance will be achieved. the work in [14] has been completed in this paper. the psc converter is controlled by the split-phase control diagram instead of its conventional operation. figure 10 shows a comparison of the psc converter’s output impedance before and after using the split-phase control diagram. it can be clearly seen that using a split-phase control diagram helps to reduce the output impedance and as a result a lower switching frequency is required to reduce the capacitors’ losses. in addition to the output impedance reduction and low switching frequency requirement, the spilt-phase operations increase the converter’s efficiency. the reduction of the output impedance which represents the sc converter loss is behind the high efficiency achievement. vii. conclusion the ltspice simulator has been used to design the proposed model and successfully produces a 160v from 10v input. the effect of using a split-phase control diagram to improve the efficiency of the psc-boost converter was proven in this article. the spilt-phase control diagram reduces the switching loss and the output impedance. the split-phase control diagram was compared with the conventional control diagram in [9] and the efficiency effectively increased from 92% to 95%. this superior efficiency achievement is caused by the lower output impedance and dead time periods. in addition, the split-phase reduces the switching frequency required to reduce the output impedance of the psc stage. this requirement can be achieved at a lower switching frequency limit when the split control diagram is used. furthermore, the split-phase reduces the effect of the higher switching frequency in order to reduce the output impedance. this requirement can be instead achieved at a lower 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[24] j. c. dias and t. b. lazzarin, “steady state analysis of voltage multiplier ladder switched-capacitor cell,” in 12th ieee international conference on industry applications, curitiba, brazil, nov. 2016, pp. 1– 6, doi: 10.1109/induscon.2016.7874485. [25] a. alateeq, y. almalaq, and m. matin, “a switched-inductor model for a non-isolated multilevel boost converter,” in north american power symposium, morgantown, wv, usa, sep. 2017, pp. 1–5, doi: 10.1109/naps.2017.8107406. microsoft word 34-2832_s_etasr_v9_n3_pp4255-4260 engineering, technology & applied science research vol. 9, no. 3, 2019, 4255-4260 4255 www.etasr.com tung & khoa: an arduino-based system for monitoring and protecting overvoltage and undervoltage an arduino-based system for monitoring and protecting overvoltage and undervoltage doan duc tung faculty of engineering and technology quy nhon university quy nhon city, binh dinh, vietnam doanductung@qnu.edu.vn ngo minh khoa faculty of engineering and technology quy nhon university quy nhon city, binh dinh, vietnam ngominhkhoa@qnu.edu.vn abstract—in this paper, an experimental system based on arduino uno microcontroller board was developed for measuring electrical quantities and protecting overvoltage and undervoltage conditions in a single-phase power supply. the main components are described in detail, including the hardware and software to build the system in which an arduino uno platform is implemented as a vital microcontroller to read voltage and current measurement from a voltage sensor (zmpt101b) and a current sensor (acs712) respectively. in addition, the arduino is also used to send all measurement to a pc through a serial port for monitoring the measured data graphically. the proposed method for designing the software uses the root mean square (rms) method for measuring electrical quantities and then the rms voltage measurement is compared with the minimum voltage and the maximum voltage to switch on or switch off the load. the monitoring gui is designed with the use of the free and open-source telemetry viewer v0.5 software to monitor rms voltage, rms current, active power, and trip signal of the experimental system. the experimental results in this paper demonstrate that the system operated correctly. keywords-experiment system; overvoltage; undervoltage; realtime measurement; voltage relay i. introduction in modern power systems, voltage quality is becoming increasingly important with their growth in power electronics and their high sensitivity of electronic equipment. voltage quality covers a wide range of voltage disturbances and deviations in voltage magnitude or waveform from the optimum values. disturbances related to voltage quality could occur as a consequence of the operation of the power grid and/or of units connected to the grid. on the other hand, voltage irregularities are the major issues the industry and home users are facing and are often responsible for damages in sensitive equipment [1-2]. overvoltage or undervoltage often result in damaging equipment. electronic loads increase day by day and they are very sensitive to voltage variations [3]. in [4], authors proposed a method for monitoring voltage disturbances based on discrete wavelet transform and adaptive linear network. the types of voltage disturbances studied included voltage sag, voltage swell and voltage interruption. after applying the method, the voltage disturbances were classified according to ieee std. 1159-2009. authors in [5] proposed an algorithm based on a deep belief network for online voltage sags recognition. the causes and waveform characters of voltage sags were analyzed. then according to the characters of different sag waveforms, ten voltage sag characteristic parameters were proposed and proven to be effective, and finally a deep belief network model was built using the parameters to complete automatic recognition of the sag event types. an adaptive approach for voltage sag automatic segmentation was presented in [6]. an adaptive threshold for different waveforms was addressed, in which sag depth, mean square error, and entropy of the sag waveform were considered. because of the effects of voltage sags on power system operation, the dynamic voltage restorer, one of the most effective solutions for mitigating voltage sag in power system, was proposed in [7-8]. authors in [7] presented a configuration and control strategy for dynamic voltage restorer which used a closed-loop pi control law in the d-q reference frame and a linear kalman filter was employed to estimate three-phase voltage sag. in [8], a new control method of multifunctional dynamic voltage restorer for voltage quality correction was presented. the control method was designed in the stationary frame by combining proportional resonant controllers and sequence-decouple resonant controllers. the method can mitigate many different conditions such as voltage swell, voltage sag due to symmetrical and unsymmetrical short circuit, starting of motors, and voltage distortion. the aim of this work was to design and implement an experimental system based on an arduino uno microcontroller board that can monitor electrical quantities and protect over/under voltage in a power supply. the voltage sensor (zmpt101b) and the current sensor (acs712) are embedded as the sensors which transmit continuously real-time data of a single-phase power supply to the arduino uno board, and then the data are processed to measure all necessary measurements. ii. hardware design the hardware of the experimental system is designed to measure electrical quantities and then to protect overvoltage and undervoltage conditions in single-phase power supply as shown in figure 1. it includes the following main components: the voltage sensor zmpt101b used in this work is a voltage transformer ideal to measure the single-phase ac voltage. it corresponding author: ngo minh khoa engineering, technology & applied science research vol. 9, no. 3, 2019, 4255-4260 4256 www.etasr.com tung & khoa: an arduino-based system for monitoring and protecting overvoltage and undervoltage has high accuracy, good consistency for voltage and power measurement and it can measure up to 250v ac. it is simple to use and comes with a multi turn trim potentiometer for adjusting the analog-digital converter output. its features consist of measurement within 250v ac, onboard microprecision voltage transformer, analog output corresponding quantity can be adjusted, good consistency, for voltage and power measurement and high efficiency and accuracy. the current sensor acs712 provides economical and precise solutions for ac or dc current sensing in industrial, automotive, commercial, and communications systems. the device package allows easy implementation by the customer. its typical applications include motor control, load detection and management, switched-mode power supplies, and overcurrent fault protection. in this paper it is used to measure the ac current of the single-phase power supply. the arduino uno is a microcontroller board based on the atmega328. it has 20 digital input/output pins (of which 6 can be used as pwm outputs and 6 can be used as analog inputs), a 16mhz resonator, a usb connection, a power jack, an in-circuit system programming (icsp) header, and a reset button. it contains everything needed to support the microcontroller, it just simply needs to be connected to a computer (or appropriate wall power adapter) with a usb cable or with a ac-to-dc adapter or battery to get started. in addition, other components are used to build the experimental system such as an lcd to display all data measurements, a relay to switch the circuit when overvoltage or undervoltage occurs, push buttons for automatic/manual mode, trip and close command of the system. the completed experimental system for protecting overvoltage and undervoltage in this work built from the aforementioned components is shown in figure 2. fig. 1. the single-phase overvoltage and undervoltage protection system based on arduino uno. iii. software design a. real-time measurement of electrical quantities in general, the output signals of the voltage sensor zmpt101b and the current sensor acs712 are sinusoidal voltage waveforms which have their amplitude between 0v and 5v in order to coincide with the analog input of the arduino uno. the signals are continuously sampled with a specific sampling time which depends on the processing speed of the microcontroller board. for the arduino uno microcontroller board, both voltage and current signals from the voltage and current sensors have sampling time ts=4ms. the ac voltage source used to supply the experimental system in this work has a fundamental frequency f=50hz so the cycle duration is 20ms. this means there are 5 samples per cycle of the fundamental frequency. (a) (b) 1. lcd, 2. trip button, 3. close button, 4. auto/manual switch, 5. switch of the bulb, 6. 220vac 60w bulb, 7. voltage sensor zmpt101b, 8. current sensor acs712, 9. relay, 10. arduino uno, 11. usb cable, 12. breadboard fig. 2. the overvoltage and undervoltage protection system: (a) front (b) back it is assumed that the equations representing the value of the k th sample of voltage and current from the analog pin a0 and a1 of the arduino are: the voltage value at the k th sample is below: ( ) ( )sin= ωm sv k v k t (1) where vm is the voltage amplitude, ω=2πf (f is the fundamental frequency), ts is the sampling time (s), and k is the k th sample. the rms voltage value can be measured as follows: 2 1 1 n rms k k v v n = = ∑ (2) where vk is the voltage at the k th sample and n is the total number of samples. the current value at the k th sample is: ( ) ( )sin= ω −ϕm si k i k t (3) where im is the current amplitude, and φ is the initial phase angle of the current. the rms current value can be measured as: 2 1 1 = = ∑ n rms k k i i n (4) where ik is the current at the k th sample. the instantaneous power at the k th sample is: ( ) ( ) ( )= ×p k v k i k (5) therefore, the active and apparent power are defined as: ac-to-dc supply voltage sensor current sensor pc monitoring arduino uno microprocessor board display block relay block auto/trip/close singlephase ac voltage source engineering, technology & applied science research vol. 9, no. 3, 2019, 4255-4260 4257 www.etasr.com tung & khoa: an arduino-based system for monitoring and protecting overvoltage and undervoltage ( ) ( ) ( ) 1 1 1 1 = = = =∑ ∑ n n k k p p k v k i k n n (6) = ×rms rmss v i (7) b. the proposed algorithm in this research work, the arduino software is applied to write code and the code is then uploaded to the arduino uno board. the code is written according to the algorithm shown in figure 3 to measure electrical quantities such as voltage, current, and active power and to protect overvoltage and undervoltage. the proposed algorithm includes three main stages. stage 1 is to initialize parameters which represent the selection of auto/manual operation mode (if auto=0 the manual mode is selected and if auto=1 the automatic mode is selected), the trip signal to the relay (if relay=0 the circuit is closed and if relay=1 the circuit is open), and the position of the trip button and close button (if trip=1 the trip button is pressed and if close=1 the close button is pressed). then, the electrical quantities including voltage, current, and power are measured in stage 2. in this stage, voltage and current samples from the voltage sensor and the current sensor are continuously read from pins a0 and a1 of the board. then the samples are used to calculate rms voltage, rms current, apparent power, and active power based on the method mentioned in the previous section. after the rms voltage is measured at stage 2, it is used as an input of stage 3 to detect and protect overvoltage and undervoltage. in figure 3, the protection can be accomplished by automatic or manual mode. for automatic mode, the rms voltage will be compared with the minimum voltage (vmin) and the maximum voltage (vmax) to detect and protect overvoltage and undervoltage automatically. the proposed algorithm’s steps are: step 1. start. step 2. initialize the parameters including the selection of auto/manual operation mode (auto), the trip signal to the relay (relay), and the position of the trip button and close button (trip and close): 0; 0; 0; 0auto relay trip close= = = = (8) step 3. set the variables including voltage square (vsquare), current square (isquare), instantaneous power (pinst), and sample (k): 0; 0; 0; 1square square instv i p k= = = = (9) step 4. read the voltage sample v(k) and the current sample i(k) from pins a0 and a1 of the arduino uno board where the voltage sensor zmpt101b and the current sensor acs712 are connected. step 5. update vsquare, isquare, and pinst using the values of voltage and current samples in step 3 as follows: ( ) ( ) ( ) ( ) ( ) ( ) = + ×  = + ×  = + × square square square square inst inst v v v k v k i i i k i k p p v k i k (10) step 6. if k=n, go to step 7. otherwise, set k=k+1 and go back to step 5. step 7. calculate rms voltage (vrms), rms current (irms), active power (p), and apparent power (s) using (11). ; ; square square inst rms rms v i p v i p n n n = = = (11) step 8. if auto=1, go to step 9. otherwise, go to step 12. step 9. if vrms<vmin the relay will be tripped (relay=1). otherwise, go to step 10. step 10. if vrms>vmax, the relay will be tripped (relay=1). otherwise, go to step 13. step 11. if trip=1, the relay will be tripped (relay=1). otherwise, go to step 12. step 12. if close=1, the relay will be closed (relay=0). otherwise, go to step 13. step 13. if we need to stop, go to step 14. otherwise, back to step 3. step 14. end. fig. 3. the proposed algorithm of the experimental system for measuring electrical quantities and protecting overvoltage and undervoltage. k = n ? auto = 0; trip = 0; relay = 0 close = 0 vsquare = 0; pinst = 0; isquare = 0 k = 1 read v(k) from pin a0 read i(k) from pin a1 vsquare = vsquare + v(k)×v(k) isquare = isquare + i(k)×i(k) pinst = pinst + v(k)×i(k) vrms = vsquare n irms = isquare n ; s = vrms×irms ; p = p inst n auto = 1 ? vrms < v min? vrms > vmax? relay = 1 relay = 1 trip = 1 ? close = 1 ? relay = 1 relay = 0 stop ? k = k + 1 no yes no yes yes no yes no yes no no no yes yes start end engineering, technology & applied science research vol. 9, no. 3, 2019, 4255-4260 4258 www.etasr.com tung & khoa: an arduino-based system for monitoring and protecting overvoltage and undervoltage iv. results and discussion to test the overvoltage and undervoltage protection function of the experimental system, an experimental setup was established as shown in figure 4. in figure 4, three additional parts, namely a variable transformer, a pc monitoring, and a voltmeter are added to the setup. the key task of the variable transformer is to generate a variable voltage source. therefore, various voltage conditions including normal voltage, overvoltage, and undervoltage can be created by tuning the knob on the front of the variable transformer. then, its output voltage is used to supply the experimental system. all electrical quantities are measured and displayed locally on the lcd on the front of the system. moreover, the status of the electrical circuit which is closed or open is also monitored and displayed on the lcd. in order to validate the voltage measurement of the experimental system, the voltmeter is added and connected to the output of the variable transformer. the measurement results from the experimental system and the voltmeter can be compared. moreover, the monitoring software on a pc connected to the experimental system through a usb cable is designed to monitor all electrical quantities remotely. all measurements are continuously transmitted from the arduino uno board to the pc and are displayed on the pc's monitor graphically. from the monitoring software, we can observe and save all measurement data to a csv file, therefore, we can use the data for any further analysis. fig. 4. the set of the experimental system for testing overvoltage and undervoltage protection. in order to measure rms voltage and current of a circuit, the voltage and current signals from the voltage sensor and current sensor are sampled in the arduino uno. with the processing speed of the arduino uno, the sampling time for both voltage and current signals equals to 4ms. this means there are 5 samples of voltage or current per cycle. the ac power supply generated by a variable transformer is nominally 230v ac 50hz. using the variable transformer to generate different voltage conditions, in this paper, one voltage condition is established by reducing the voltage magnitude in a period of about 10s. the voltage waveform is recorded in the csv format file by the monitoring software and then it is plotted in matlab as shown in figure 5(b). moreover, we can obviously see the voltage waveform using its magnification from 5.2s to 5.6s as shown in figure 5(a). to consider the current through the circuit, a bulb is assumed as a fixed load of the experimental system. in addition, other loads can be connected to the system through the outlet on the front of the system. when the load changes, the current waveform through the circuit recorded by the monitoring software also changes. figure 5(d) shows a current waveform plotted in matlab from the data of the csv file. similarly, we can obviously see the current waveform using its magnification from 5.2s to 5.6s as shown in figure 5(c). the time in figure 5(c) is 0.4s corresponding to 20 cycles, therefore, there are 100 samples in the figure. from these samples of voltage and current, the proposed algorithm is applied to measure the aforementioned electrical quantities rms voltage, rms current, active power, etc. and then the rms voltage is used for detecting and protecting overvoltage and undervoltage. fig. 5. voltage and current waveforms. (a-b) voltage waveform from the pin a0; (c-d) current waveform from the pin a1. the proposed algorithm is uploaded to the arduino uno microcontroller board and is used to measure electrical quantities. the measurement results of the rms voltage and current are recorded and are presented in figures 6(a) and 6(b), respectively. with 4ms sampling time of the experimental system, the rms voltage is calculated and is shown as the blue line in figure 6(a). however, to display the rms voltage value on the lcd on the front of the experimental system, the rms voltage value is updated every 1.0s. in this case, the source voltage is reduced from 5s to 14s as shown in figure 6(a), therefore, the rms voltage measured from the proposed method is also reduced. consequently, the experimental system can use the rms voltage value to detect and protect the load from an overvoltage or undervoltage condition in the power supply, if the voltage is over the maximum value (vmax) or under the minimum value (vmin). depending on the nominal voltage of the grid, vmax and vmin can be set at different values and in this study they are set at 220v and 180v respectively. moreover, the current through the circuit is also measured in engineering, technology & applied science research vol. 9, no. 3, 2019, 4255-4260 4259 www.etasr.com tung & khoa: an arduino-based system for monitoring and protecting overvoltage and undervoltage order to calculate the power consumed by the load of the system. the current waveform shown in figure 5(d) is applied to test the method for calculating the rms current and this result is shown in figure 6(b). similarly, the current is also updated to display on the lcd of the system per 1.0s shown by the black dots in figure 6(b). (a) (b) fig. 6. voltage and current measurements using the proposed algorithm on arduino uno. according to the design of the experimental system presented above, there are two operation modes, the automatic mode and the manual mode. in the manual mode, the two buttons, namely the trip and closed button in the front of the system are used to switch the relay manually. in this design, the trip signal generated by pressing the trip button will be processed in the arduino uno microcontroller board and then transmitted to the relay to switch off the circuit. on the other hand, the closed signal generated by pressing the closed button will be also processed in the arduino uno microcontroller and then transmitted to the relay to switch on the circuit. therefore, if there is an overvoltage or undervoltage condition in the power supply, the trip button can be used manually to protect the load. after that, if the voltage of the power supply is remained within vmin and vmax, the closed button can be also used manually to switch on to continue supplying power. to evaluate the manual mode of the experimental system, a sequence of the trip-closed-trip-closed order is established while the voltage of the power supply will remain within acceptable limits as shown in figure 7(a). because the trip and closed buttons are pressed according to the order shown in figure 7(d), the relay will switch off and switch on the circuit, therefore, the current and the active power of the circuit will be changed as shown in figures 7(b) and 7(c) respectively. in the automatic mode, the system will trip overvoltage and undervoltage conditions to isolate the load out of the power supply. then the load will be supplied again if the voltage of power supply is between vmin and vmax. fig. 7. the experimental results of the manual mode: (a) rms voltage, (b) rms current, (c) active power, and (d) trip signal. in order to evaluate the automatic mode, the overvoltage and undervoltage conditions generated by the variable transformer are recorded in a period of 20s and are displayed on the pc monitoring software. the experimental results are saved in a csv file and matlab is used to plot all the results as shown in figure 8 which exhibits the experimental results including rms voltage, rms current, active power, and the trip signal as shown in figures 8(a)-(d) respectively. in this normal condition, the load of the system is a 220v ac 60w bulb, therefore, the rms current and the active power shown in figures 8(b)-(c) are consumed by the bulb. however, the rms current and the active power are equal to zero when there is an undervoltage or overvoltage condition in the power supply. as shown in figure 8(a), an undervoltage occurs between 20s and 40s and an overvoltage occurs between 55s and 75s. the overvoltage and undervoltage protection of the experimental system is shown obviously in figure 8(d) which demonstrates the trip signal transmitted to the relay in the system to protect the bulb. in addition, when the voltage of the power supply remains within vmin and vmax, the closed signal is transmitted to the relay to continue supplying the bulb with power. this is also demonstrated as the period from 40s to 55s in figure 8(a). engineering, technology & applied science research vol. 9, no. 3, 2019, 4255-4260 4260 www.etasr.com tung & khoa: an arduino-based system for monitoring and protecting overvoltage and undervoltage fig. 8. experimental results of the automatic mode: (a) rms voltage, (b) rms current, (c) active power, and (d) trip signal. v. conclusions in this research work, an experimental system based on the arduino uno microcontroller board was developed for measuring electrical quantities and protecting onvervoltage and undervoltage of a single-phase power supply. the hardware and software of the system were designed and tested in a laboratory at our university. in order to evaluate the effectiveness of the system, we generated many different scenarios including automatic and manual mode to demonstrate and test the operation of the system. the real-time measurement results are locally monitored at an lcd on the front of the experimental system. moreover, they can be graphically monitored through the monitoring gui software on a pc and they can be also saved in a csv file for further analysis. the main contribution of this work is the propose of an experimental method to build a system based on an arduino uno microcontroller board for protecting overvoltage and undervoltage in single-phase power supplies and to implement a simple method which is uploaded to the board for measuring electrical quantities. references [1] c. sankaran, power quality, crc press, 2001 [2] a. g. siraki, p. pillay, “comparison of two methods for full-load in situ induction motor efficiency estimation from field testing in the presence of over/undervoltages and unbalanced supplies”, ieee transactions on industry applications, vol. 48, no. 6, pp. 1911-1921, 2012 [3] m. h. j. bollen, i. y. h. gu, signal processing of power quality disturbances, wiley-ieee press, 2006 [4] d. t. viet, n. h. hieu, n. m. khoa, “a method for monitoring voltage disturbances based on discrete wavelet transform and adaptive linear neural network”, international review of electrical engineering, vol. 11, no. 3, pp. 314-322, 2016 [5] f. mei, y. ren, q. wu, c. zhang, y. pan, h. sha, j. zheng, “online recognition method for voltage sags based on a deep belief network”, energies, vol. 12, no. 1, pp. 1-16, 2018 [6] x. xiao, w. hu, h. zhang, j. ai, z. zheng, “an adaptive approach for voltage sag automatic segmentation”, energies, vol. 11, no. 12, articleid 3519, 2018 [7] d. t. viet, n. h. hieu, n. l. hoa, n. m. khoa, “a control strategy for dynamic voltage restorer”, 11th ieee international conference on power electronics and drive systems, sydney, australia, june 9-12, 2015 [8] d. v. tien, r. gono, z. leonowicz, “a multifunctional dynamic voltage restorer for power quality improvement”, energies, vol. 11, no. 6, articleid 1351, 2018 [9] c. moron, d. ferrandez, p. saiz, g. vega, j. p. diaz, “new prototype of photovoltaic solar tracker based on arduino”, energies, vol. 10, no. 9, articleid 1298, 2017 [10] p. p. machado, t. p. abud, m. z. fortes, b. s. m. c. borba, “power factor metering system using arduino”, ieee workshop on power electronics and power quality applications, bogota, colombia, may 31-june 2, 2017 [11] e. viciana, a. alcayde, f. g. montoya, r. banos, f. m. arrabalcampos, f. manzano-agugliaro, “an open hardware design for internet of things power quality and energy saving solutions”, sensors, vol. 19, no. 3, articleid 627, 2019 [12] t. j. ho, c. h. chang, “robust speed tracking of induction motors: an arduino-implemented intelligent control approach”, applied sciences, vol. 8, no. 2, articleid 159, 2018 time (s) (a) 20 40 60 80 100 0 100 200 undervoltage overvoltage time (s) (b) 0 20 40 60 80 100 0 0.2 0.4 time (s) (c) 0 20 40 60 80 100 0 50 100 time (s) (d) 0 20 40 60 80 100 -0.5 0 0.5 1 1.5 auto trip 1 auto trip 2 auto close 1 auto close 2 microsoft word 25-3205_s_etasr_v9_n6_pp5006-5010 engineering, technology & applied science research vol. 9, no. 6, 2019, 5006-5010 5006 www.etasr.com gomha & langat: performance investigation of different topologies of 1-100 ghz on-chip … performance investigation of different topologies of 1-100 ghz on-chip transformers using 130 nm sige bicmos siddig gomha department of electrical engineering, pan african university institute for basic sciences technology and innovation, nairobi, kenya and faculty of engineering, university of medical sciences and technology, khartoum, sudan siddig.gomha@gmail.com kibet langat department of telecommunication and information engineering jomo kenyatta university of agriculture and technology nairobi, kenya kibetlp@jkuat.ac.ke abstract—in this study, modeling and designing different topologies of on-chip transformers are presented using 130nm sige bicmos technology. interleaved, stacked, and full symmetrical interleaved transformers are investigated. octagon and square shapes are used for designing transformers with flipped and non-flipped feed lines. a comparison between performances of various configurations is presented using a fullwave simulator. the octagon stacked transformer with flipped feed lines showed a good performance at around 60ghz. the simulated results demonstrated a coupling factor k of 0.94, minimum insertion loss of 1.01518db, and q-factor of 9 with a minimum occupied area of 0.0019mm 2 . keywords-on-chip transformer; 130nm sige bicmos technology; interleaved transformer; stacked transformer i. introduction the growing demand for high quality and high data rate in a wireless telecommunication system increases the challenge for designing high performance electronics components. particularly for a high frequency bands applications [1, 2], the substrate losses in passive devices have become dominant due to the proximity and skin effect [3, 4]. on-chip transformer (tf) is one of the passive components for designing system-onchip (soc) applications. on-chip tf has been commonly used as a power splitter/combiner, and inter-stage impedance matching in many components design such as power amplifiers [5-7], low noise amplifiers [8, 9], mixers [10], and voltage controlled oscillators [11-13]. the tf is better to be compact, low loss, with high quality factor, easy impedance matching, and with the ability of conversion from differential to single ended for power combining as well as conversion from single ended to differential for power splitting [14]. many researches have been conducted in modeling and designing of the on-chip tf. the elements of the device can be extracted from the geometrical shape and technological data of the transformer [15]. however, this model is compatible up to 10ghz. other broadband models for millimeter-wave tf working up to 100ghz, and 110ghz have been proposed in [16, 17]. moreover, an on-chip six ports tf model was reported in [18]. in this paper, a simple model based on lumped elements of tf is presented. in addition, direct parameters extraction based on em s-parameters simulation is used for design and simulation of different topologies of on-chip transformer. ihp 130nm sige bicmos technology is considered in this study in the frequency range between 1–100ghz. ii. approaches of modeling on-chip transformer a transformer consists of two inductors for the primary and secondary windings. there are two approaches for extracting the parameters of these windings. the first method is using equivalent lumped components, while the second is direct parameter extraction from s-parameters using the em sonnet simulator. figure 1 shows the equivalent circuit for the on-chip tf. the primary inductor has two ports, p1 and p2, the equivalent circuit model consists of six elements, three series elements represented by series capacitance cp, inductance lp, resistance rp, as well as three substrate elements represented by oxide capacitance cp-ox, substrate capacitance cp_sub, and substrate resistance rp_sub. the same elements have also been considered for the secondary inductor with two ports s1, and s2. moreover, cps represents the mutual capacitance between the two windings. the values for the six elements of the lumped equivalent circuit shown in figure 2 can be calculated based on the dimensions of the inductor. the series inductor �� (nh) as a function of width w (µm), length l (µm), and thickness t (µm) can be calculated as [16]: �� = �.��× � . �. ln� �×� �.����(���)� + �.����(���) � − 1� (1) figure 2 shows the relationship between inductance (ph) and length of inductor (��) with variable width (��) of inductor and constant thickness (3��). it can be observed that, a smaller inductor width provides higher inductance. however, the width is constrained by the minimum width provided by the foundry. corresponding author: siddig gomha engineering, technology & applied science research vol. 9, no. 6, 2019, 5006-5010 5007 www.etasr.com gomha & langat: performance investigation of different topologies of 1-100 ghz on-chip … rs cs ls cs_oxcs_ox cs_subcs_sub rs_sub rs_sub rp cp lp cp_ox cp_ox cp_sub cp_sub rp_sub rp_sub cpscps s2 p2p1 s1 fig. 1. equivalent circuit of the on-chip transformer fig. 2. inductance values versus corresponding length with variable width and constant thickness=3µm the rest of the parameters for the primary and secondary inductors can be calculated using the following formulas [19]: !"#$"! ≅ &�×'×((&)"*+ ,⁄ ) (2) . = / ���0 ' (3) 2!"#$"! = 3×� 4×567 �67 (4) 289 = �.������567�67 (5) 2!:; � 0.5 � > � � � 2!$ (6) !:; � �����?@a (7) where, ., b, c89, d89 are skin depth, conductivity, permittivity, and thickness of the oxide layer respectively, while e!$ and 2!$ represent conductance and capacitance respectively for the silicon substrate (2!$ ≅ 10)�fg/i��, e!$=10)jk/i��). another approach for extracting parameters of the on-chip tf is using the 3d electromagnetic simulator (sonnet) to generate the s-parameters. in that case, the following expressions are used for calculating primary inductance ��#$, secondary inductance �!"l, q-factor for primary m�#$, qfactor for secondary m!"l, and coupling coefficient k [20, 21]: ��#$�no� � pqrs�tuu�∗&� u4 ��0 (8) �!"l�no� � pqrs�t44�∗&� u4 ��0 (9) m�#$ � pqrs �tuu�w"r� �tuu� (10) m!"l � pqrs �t44�w"r� �t44� (11) x � /pqrs�tu4�� pqrs�t4u�pqrs�tuu�� pqrs�t44� (12) moreover, the parameters of differential configuration for the on-chip tf can be extracted using [22]: yz � y&& � y�� � y&� � y�& (13) �z � pqrs�t[���0 (14) mz � pqrs�t[�w"r��t[� (15) where, yz, �z, and mz are differential impedance, differential inductance, and differential q-factor respectively. iii. performance comparison of different topologies of on-chip tf design many topologies of the on-chip tf have been investigated. for stackup configuration top layers tm1 and tm2 were utilized to design primary and secondary windings. for the interleaved configuration tm2 layer was used for designing two windings, while tm1 layer was used for designing the secondary winding feed line. figure 3 shows the eight different topologies of the on-chip tf considered in this study which are octagon interleaved tf with non-flipped feed lines (oitf)nf, octagon interleaved tf with flipped feed lines (oitf)f, octagon stacked tf with flipped feed lines (ostf)f, octagon stacked tf with non-flipped feed lines (ostf)nf, square interleaved tf with non-flipped feed lines (sitf)nf, square interleaved tf with flipped feed lines (sitf)f, symmetric square interleaved tf (sstf), and symmetric octagon interleaved tf (sotf). single turn for both windings was utilized in all on-chip tf topologies because this approach provides low loss in high frequency operation. table i shows the dimensions of on-hp transformer for all topologies. (a) (oitf)nf (b) (oitf)f (c) (ostf)f (d) (ostf)nf (e) (sitf)nf (f) (sitf)f (g) (sstf) (h) (sotf) fig. 3. different topologies of the on-chip tf engineering, technology & applied science research vol. 9, no. 6, 2019, 5006-5010 5008 www.etasr.com gomha & langat: performance investigation of different topologies of 1-100 ghz on-chip … table i. dimensions of on-hp transformers transformer type wp µm ws µm dp µm ds µm s µm area \\] octagon interleaved tf 5.45 5.45 58.97 43.87 2.1 0.0035 octagon stacked tf 5.45 5.45 43.87 43.87 2.1 0.0019 square interleaved tf 5.45 5.45 57.82 42.72 2.1 0.0033 symmetric square interleaved tf 5.45 5.45 57.82 42.72 2.1 0.0038 symmetric octagon interleaved tf 5.45 5.45 57.82 43.04 2.1 0.0038 this work addresses the effect of windings position on the performance of on-chip tf. lateral and vertical magnetic couplings are available according to the position of windings on the stackup layers. lateral magnetic coupling takes place in interleaved configuration when utilizing only one thick layer tm2 for the primary and secondary windings. on the other hand, vertical magnetic coupling takes place between windings as in stacked topology when utilizing two thick layers, tm1 and tm2. in addition, feed lines’ direction has a significant effect on the performance of on-chip tf. to compare the performance of the proposed topologies shown in figure 3, design and simulation of on-chip tf by using the sonnet em simulation has been carried out. figure 4 shows the comparison of primary and secondary inductance for all proposed topologies of on-chip tf. it can be observed that all topologies provide high resonant frequency, greater than 100ghz. the flipped feed lines of all topologies have greater inductance than the non-flipped ones. however, the flipped feed lines have slightly reduced coupling between windings. therefore, for selection between the two options of feed lines position, the minimum space layout for specific circuit design should be considered. amongst all topologies of the on-chip tf the symmetric square interleaved tf shape has the greatest inductance for primary and secondary windings. both (sstf) and (sotf) have the same inductance for their primary and secondary windings because of their high symmetrical shapes. figure 5 shows a comparison of q-factor for all topologies. both flipped and non-flipped feed line positions have been considered for simulation of the q-factor of the primary and secondary windings. it can be seen that the transformers with flipped feed lines (represented by dash lines) have better values of q-factor than the other transformers. the variation in primary and secondary values of q-factor for the interleaved octagon and square shapes is due to the differences in their lengths of primary and secondary windings. however, the symmetric octagon and square transformers have almost the same values of q-factors in their primary and secondary windings because they have full symmetrical shapes. moreover, the octagon stacked transformers with flipped feed lines have better values of q-factors than the one with nonflipped feed lines, which is because feed lines position in the same direction leads to imperfect coupling thus reducing quality factor. (a) (b) (c) (d) fig. 4. comparison of primary and secondary inductance for the different topologies of the on-chip tf, for the case of flipped (dash line) and nonflipped (solid line) feed lines. (a) octagon interleaved tf (b) octagon stacked tf (c) square interleaved tf (d) symmetrical square and octagon interleaved tf engineering, technology & applied science research vol. 9, no. 6, 2019, 5006-5010 5009 www.etasr.com gomha & langat: performance investigation of different topologies of 1-100 ghz on-chip … (a) (b) (c) (d) fig. 5. comparison of primary and secondary q-factor for different topologies of the on-chip tf, for the case of flipped (dash line) and nonflipped (solid line) feed lines. (a) octagon interleaved tf (b) octagon stacked tf (c) square interleaved tf (d) symmetrical square and octagon interleaved tf there are two approaches commonly used to find the figure-of-merit of tf. the first one is used when a tf is utilized in an application that requires high efficiency in power transmission. in this case the figure-of-merit can be calculated using maximum available gain gmax.{23, 24]: eqr9 = ^_4u_u4^`a − √a� − 1c (16) a � &)|_uu|4)|_44|4�|∆|4�|_u4_4u| (17) ∆� k&&k�� � k&�k�& (18) however, instead of using s-parameters, we can use zparameters: eqr9 � 1 �2`g � √g� � 1c (19) g � w"�tuu�w"�t44�)hw"�tu4�i4hpq�tu4�i4�hw"�tu4�i4 (20) the second method of determining the figure-of-merit of tf depends on the total loss of the device, using minimum insertion loss (ilm) expression [25]: j�q = &&��(9)k94�9) (21) g = w" (tuu).w" �t44�)hw" �tu4�i4hpq �tu4�i4�hw" �tu4�i4 (22) on-chip tf has many sources of energy loss. radiation loss takes place when dimension of the device is larger than the free space l . substrate coupling loss takes place according to capacitive coupling between substrate and conductor, therefore displacement current will leak into the substrate through lossy dielectric. in addition, ohmic losses (skin effect) as well as imperfect coupling between primary and secondary windings can be considered as a source of losses. figure 6 shows the simulated minimum insertion loss (db), and coupling factor k for all on-chip tf topologies. at high frequencies insertion loss increases, while k decreases according to the effect of imperfect coupling between tf windings. as seen in figure 6(a) the octagon stacked transforms have the lowest insertion loss compared to the rest of tf topologies, while the symmetrical square transformer has the largest values of insertion loss due to their larger winding size. because of the largest value of insertion loss for the symmetrical square transformer, this topology of tf has a worst value of coupling factor k as shown in figure 6(b), while the octagon stacked tf provides the best values of k amongst all topologies. iv. conclusion a comprehensive study of on-chip transformer using 130nm sige technology has been presented. different topologies, shapes, and feed line positions of transformers have been investigated, using the top thick metals tm1 and tm2 of the stackup layer technology. two methods of calculating elements of primary and secondary windings were explored, which are use of the geometry of windings and direct element extraction from the s-parameters. 3d electromagnetic simulation was carried out and the performance of transformers was compared in terms of inductance, quality factor, coupling engineering, technology & applied science research vol. 9, no. 6, 2019, 5006-5010 5010 www.etasr.com gomha & langat: performance investigation of different topologies of 1-100 ghz on-chip … factor, and minimum insertion loss. this study can present a guideline for designing on-chip transformer for purposes of power splitting and combining in applications like power amplifiers, voltage control oscillators, and mixtures. (a) (b) fig. 6. figure 6: comparison values of (a) minimum insertion loss, and (b) coupling factor k for different topologies of the on-chip tf references [1] s. bertoldo, c. lucianaz, m. allegretti, “on the use of a 77 ghz automotive radar as a microwave rain gauge”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2356–2360, 2018 [2] z. a. shamsan, m. alammar, a. alharthy, a. aldahmash, k. a. a. snaie, a. m. a. hetar, “micrometer and millimeter wave p-to-p links under dust storm effects in arid climates”, engineering, technology & applied science research, vol. 9, no. 4, pp. 4520–4524, 2019 [3] b. curran, c. tschoban, i. ndip, k. d. lang, h. kroener, a. ippich, “dielectric material characterization of high frequency printed circuit board laminates and an analysis of their transmission line high frequency losses”, 46th european microwave conference, london, uk, october 46, 2016 [4] t. tanigawa, e. mizushima, m. shimada, k. morita, m. kakitani, s. takanezawa, “low 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10-12, 2017 [24] k. t. ng, b. rejaei, j. n. burghartz, “substrate effects in monolithic rf transformers on silicon”, ieee transactions on microwave theory and techniques, vol. 50, no. 1, pp. 377–383, 2002 [25] b. leite, design and modeling of mm-wave integrated transformers in cmos and bicmos technologies, phd thesis, universite sciences technologies-bordeaux i, 2011 microsoft word etasr_v10_n6_pp6410-6417 engineering, technology & applied science research vol. 10, no. 6, 2020, 6410-6417 6410 www.etasr.com alghamdi et al.: a review of optimization algorithms for university timetable scheduling a review of optimization algorithms for university timetable scheduling hayat alghamdi college of computer and information systems umm al qura university makkah, saudi arabia s43980248@uqu.edu.sa tahani alsubait college of computer and information systems umm al qura university makkah, saudi arabia tmsubait@uqu.edu.sa hosam alhakami college of computer and information systems umm al qura university makkah, saudi arabia hhhakam@uqu.edu.sa abdullah baz college of computer and information systems umm al qura university makkah, saudi arabia aobaz01@uqu.edu.sa abstract—the university course timetabling problem looks for the best schedule, to satisfy given criteria as a set of given resources, which may contain lecturers, groups of students, classrooms, or laboratories. developing a timetable is a fundamental requirement for the healthy functioning of all educational and administrative parts of an academic institution. however, factors such as the availability of hours, the number of subjects, and the allocation of teachers make the timetable problem very complex. this study intends to review several optimization algorithms that could be applied as possible solutions for the university student course timetable problem. the reviewed algorithms take into account the demands of institutional constraints for course timetable management. keywords-timetabling; genetic algorithms; particle swarm optimization (pso) i. introduction many higher education institutions have teaching staff from various fields, who work together to meet the educational goals set. however, creating a timetable with no conflicts, which these lecturers can use is one of the challenges most universities face. generally, a timetable is a table of various events and their schedule [1]. therefore, in a university timetable, the institution assigns the courses taken by students and delivered by tutors to a defined finite set of resources, which include time slots and classrooms. this process presents many challenges. for example, in a typical school, there are several student groups who may or may not be taking the same course at the same time [2]. thus, when scheduling lectures, one has to ensure that learners, lecturers, and lecture halls do not conflict. this need makes the timetabling of university courses to be a complex and time-consuming task to complete. university timetabling committees cannot perform this distribution randomly as they must consider several decisive factors. there are several constraints that guide the process of making an effective timetable. these constraints, which are rules, policies, and preferences of universities, lecturers, and students, can be categorized as hard, soft, or medium. hard constraints are those guidelines that should not be violated or overlapped at all, soft constraints are desires of the involved stakeholders that can be ignored without any serious consequences, and medium constraints are preferences that they are preferred to not be violated [3]. the committee handling the timetabling must consider all these requirements to create an optimal outcome. due to the complexity of this problem, timetable coordinators spend a considerable amount of time looking for the best solution. however, even if they have a lot of experience, the resolution found may not be optimal due to the large number of possible combinations. thus, the distribution of workload among the various lecturers in an academic institution constitutes a problem of combinatorial nature. in general, resolving such challenges and obtaining exact optimal solutions is computationally intractable. therefore, the university timetabling problem is an example of a non-polynomial (np)-hard problem [4]. these are problems with no particular efficient solutions. in the case of timetabling where there is no specific algorithm that can be utilized to schedule classes since each institution has its special constraints [5, 6]. at the same time, when done manually, the obtained result depends on both the initial approach and the experience of the timetabling committee. public universities typically take days to manually schedule all the classes that students should take depending on the availability of lecturers and classrooms [7]. thus, the proposal to automate this process intends to meet real needs, with the main aim to reduce the time taken to complete it efficiently. describing the real problem by mathematical functions, the study seeks the values of such models with the use of optimization techniques. this way, it will provide a solution that maximizes the use of available human resources and satisfies the needs of all involved parties. this approach becomes very complex as more restrictions arise, such as the corresponding author: hosam alhakami engineering, technology & applied science research vol. 10, no. 6, 2020, 6410-6417 6411 www.etasr.com alghamdi et al.: a review of optimization algorithms for university timetable scheduling number of courses in the school and the availability of essential resources like lecturers, students, and classrooms. the presented solutions behave inefficiently when there is an expansion of the institution and their accuracy suffers as the number of courses and classes grow [8]. thus, a personalized computational approach to address the issue becomes important and a priority. due to the importance of the problem, several formalizations and solution methods have been proposed. the approaches based on meta-heuristics are considered to be particularly relevant. however, these optimization algorithms are not mutually exclusive. instead, they combine ideas from different areas, with the main aim of providing different solutions to the timetabling issue [9]. one of the most popular approaches is acquiring solutions based on genetic algorithms (gas) due to their high degree of computational parallelization and enhanced computational performance. overall, university course timetabling can be treated as organizing a group of classes to meet the specifications of particular institutions. over the years, various researchers have created various algorithms to find an optimal solution to this issue. for instance, authors in [9] created graph coloring schemes for timetable scheduling in 1967. their work formed the foundation upon which more sophisticated techniques have been based. one of these models is linear programming, which was used to solve a labor scheduling problem in [10]. moreover, a ga presents one of the best possible methods to address np-complete problems. at its core, a ga is a parameter optimization strategy that iterates over a population, seeking the best fit for a problem until it obtains an optimal solution [11]. several works have been completed with this algorithm for the treatment of timesheets. the ga borrows heavily from the field of natural sciences on the way it works. in particular, it allows observing events from the lens of natural phenomena, such as mutations and natural selection [12]. hence, it helps developing computational mechanisms, which resemble these processes. therefore, gas use and specify biological terminologies, such as crossing-over and mutation, in a precise and specialized way [13]. in particular, through the process of cross-over, the fittest generations pass on their attributes to their offspring. in turn, mutation helps to prevent stagnation within a population and is essential for the proper functioning of the algorithm. along this line, this study will use surveys to understand the general foundations for the problem of university lesson planning. this activity will assist in formulating the optimization model and describing the manner in which the algorithm can be adapted to make it applicable to the problem under investigation. ii. related wordk because university course timetabling is an np-hard problem, there are several methods that have been explored in attempts to find optimal solutions. the manual approach requires several days of work and often results in inefficient outcomes [4, 14]. however, there are several other procedures that can be used to schedule academic activities and in which restrictions related to the type of problem considered must be respected. nonetheless, the objective often involves distributing teachers and students in a particular course depending on time and resource availability, while also respecting their desires. educational timetables are of three types: school, course, and exam timetables [1]. scheduling the course timetable presents the most difficulties among the three as it is utilized frequently through a typical university semester and it covers only particular days within a week. university timetabling is not simple due to various constraints that would be applied to produce effective course timetabling [15-17]. eventually, the timetabling constraints can be classified as hard and soft; the hard constraints are considered as mandatory while the soft constrains are optional [18-20]. table i summarizes the most important soft and hard constraints of course timetabling. table i. soft and hard constraints hard constraints soft constraints ref. courses having common students cannot be allotted at the same time slot on the same day. the total number of available periods of the daily timetable is 8 hours (maximum) honours and general courses need to be scheduled in nonoverlapping time-slots. [15] a room cannot be assigned to more than one lecture in a given period. courses belonging to a curriculum must be assigned to different periods. -courses taught by a lecturer must be assigned to different periods. the number of students taking a course must fit into the assigned room. each additional student over the capacity of the room counts as a violation. lectures for a given curriculum must be consecutive. [16] the timetable should be scheduled based on the university calendar to open the course, a minimum number of students should be registered [17] considers the workload of the lecturers. takes into account the free time (i.e. office hours and resets) of the lecturers. [18] every course should be assigned to a venue at a particular timeslot. the scheduled courses must not exceed the venue capacity. [19] lecture rooms must not be booked twice at the same time. all lecture venues and rooms must be scheduled once not twice. break periods must be allocated before other courses. faculty general courses must be allocated to slots before departmental courses. [20] no student group has two events at the same time. no lecturer has two events at the same time. no event is in a room with less capacity than the number of students at the event. [21] hard and soft constrains are related to many factors such as courses, lecturers, students, classrooms, and operational dates and hours [16, 18, 19, 21]. thus, it is important to apply optimization algorithms for effective scheduling of the course timetable. the use of optimization techniques in problemsolving dates back several decades. nonetheless, it has recently been boosted by the advent of computers and the increase in their processing capacity, which has led to a rise of the number of scheduling approaches. however, the application of these methods to solve practical problems has not been verified at the same proportion as the rate of their development. one of the reasons is the complexities of the real behavior and the model generated, which are described by non-linear behavior functions and whose solution space may be non-convex [14]. heuristic methods have played an important role in resolving engineering, technology & applied science research vol. 10, no. 6, 2020, 6410-6417 6412 www.etasr.com alghamdi et al.: a review of optimization algorithms for university timetable scheduling these types of problems. primarily, they involve values of the functions in the process, regardless of whether there is unimodality of the function or continuity in their derivatives. on the other hand, they demand a large number of calculations as stated by authors in [22], who argue that instead of performing many additional computations to determine a gradient with mathematical programming techniques, it may be more beneficial to use this time and resources to explore the search space more intensively. among the heuristic optimization techniques, there are metaheuristic methods, which promise accurate and optimal solutions to the timetable scheduling issue. notable approaches of this nature include greedy randomized adaptive search (grasp), simulated annealing, tabu search, gas, microchanonic annealing, and microchanonic optimization [23]. scheduling problems are usually addressed by heuristic techniques due to their structure and complexity [22]. for instance, authors in [23] state that the simulated annealing scheme provides an efficient solution when applied to scenarios that require some form of programming. several authors present comparisons and evaluations of the performance of different metaheuristics in solving scheduling problems [24]. some of the common metaheuristic strategies include evolutionary algorithms, ant colony, local search, simulated annealing, and tabu search, but none of them can be singled out as the best. table ii shows a summary of some of these algorithms, including their advantages, disadvantages, and tools that can be applied to develop them. using this table, it is possible to identify the methodologies that can be applied to develop a solution to the university timetabling problem effectively. the problem of scheduling can be found in many areas, e.g. in the assignment of drivers to vehicles in a public transport company or in the development of school timetables. however, conflicts are common due to competing interests among the stakeholders involved and the existence of constraints that should be satisfied. in order to find the best possible solution to such issues, a swarm-intelligent algorithm, named particle swarm optimization (pso), can be used. this meta-heuristic was developed to find and optimize solutions for continuous problems. nonetheless, it turned out to be a very suitable method for achieving quick and good solutions within these applications. at this point, however, the process must be adapted to the given circumstances for this discrete problem. table ii. comparison of different scheduling and optimization algorithms reference year technique tools advantages disadvantages [25] 2015 pso programming languages, such as python. supported by gaussian 09 program package. simple to implement. does not converge fast. [26] 2017 integer programming various solver packages for global optimization. few parameters that need to be adjusted. difficult to define the initial design parameters. [27] 2016 multi-objective optimization can be implemented using various programming languages. able to run parallel computation. can converge prematurely. [28] 2016 hyper-heuristics python or r programming languages. can be robust. complex to implement for inexperienced programmers. [29] 2017 integer programming solver packages, such as baron. have higher probability and efficiency in finding the highest optimization cannot work out problems of scattering. [20] 2015 metaheuristic techniques python or r programming languages. can converge fast dos not have short computational time. [32] 2018 fix-and-optimize metaheuristic python or r programming languages. does not overlap and mutate not efficient in working problems linked with scattering. [32] 2015 great deluge algorithm matlab has short computational time. complex to implement for inexperienced programmers. [33] 2016 linear integer model solver packages, such as gams library. efficient in solving problems that do not have accurate mathematical models. complex to implement for inexperienced programmers. [34] 2017 artificial bee colony algorithm matlab it is easy to use and can interface with other algorithms efficiently. converges prematurely, resulting in no solutions in some instances. [35] 2017 stochastic gradient descent stochastic simulation toolkit (stochkit) simple to implement and works fast when applied to small datasets. hyperparameters need to be tuned manually. hence, people not familiar with it find it challenging to use. [36] 2018 broyden-fletchergoldfarb-shanno (bfgs) algorithm the liblbfgs library written in the c++. has better convergence than most algorithms performs poorly in the context of nonsmooth optimization. [37] 2020 simulated annealing algorithm. software tools, such as kdsimstudio and simulated conversation development tool. gradually converges to a global optimal solution and, thereby, escapes from a local solution. requires enhancements to function effectively. [38] 2020 tabu search algorithm available frameworks, such as the tabu search framework written in c++. together with a memory concept, it can be utilized to explore iteration problems more precisely than other algorithms. it performs poorly in large dimension problems. [39] 2020 tabu search algorithm frameworks, such as the tabu search framework. ignores recently explored neighborhoods to avoid settling on a local optimum solution. as it does not have memory, it requires other algorithms or additional components to function effectively. [40] 2020 elite immune ant colony optimization algorithm matlab combines the strengths of both the ant colony and immune theory to ensure its efficiency. complex to implement. engineering, technology & applied science research vol. 10, no. 6, 2020, 6410-6417 6413 www.etasr.com alghamdi et al.: a review of optimization algorithms for university timetable scheduling a. genetic algorithms the main task of scheduling algorithms in solving the university course timetabling problem is to find a solution that satisfies a set of restrictions. these limitations are either essential or nonessential. essential restrictions are those that generate an unworkable timetable if they are not satisfied. on the other hand, the nonessential ones improve the quality of the framework. gas are a strategy class that can be employed to resolve these conditions efficiently. they are based on the principles of genetics and natural selection, with the central idea being the selection of the fittest individuals in a population, who then recombine with others or mutate into new forms to generate new groups [41]. gas are particularly applied to complex optimization problems, which are challenges that have different parameters or characteristics that need to be combined in search of the best solution and, at the same time, cannot be represented mathematically [42, 43]. figure 1 illustrates the flowchart of the ga algorithm, from the initial population to when a suitable result is obtained. fig. 1. ga flowchart [41]. over the years, several researchers have applied gas to solve such problems. for instance, authors in [44] dealt applied the ga to address the issue of scheduling class timetables. the differential feature in this work is the use of crossover operators only between rows and, later, columns. many authors also utilize several methods to treat infective solutions, which are those that do not meet the essential restrictions. in [45], the algorithm was applied to resolve the problem in two phases. first, a ga was applied to generate solutions that only meet the essential restrictions, and, in the second stage, based on the initial population generated in the initial step, gas were employed to satisfy the non-essential conditions. in [46], a greedy approach was proposed to generate a robust initial population. subsequently, the authors applied the ga to optimize this solution further. other works, such as [47], propose the application of a repair function, which is introduced after crossover and mutation operations, to deal with infactible solutions. in [48], it is proposed to use local search methods to improve the solution, which, consequently, reduces the number of violations of non-essential restrictions. these methods are usually applied after the generation of each population in the evolution process. often, gas are implemented in the delphi 5.0 programming environment and the problem input data are imported from the saber software database. the problem of timetabling consists of scheduling a sequence of classes between teachers and students in a limited period of time, while satisfying a set of restrictions. this problem exists in any educational institution, but it becomes increasingly complex as the size of the establishments grows. primarily, this phenomenon arises because the timetabling of courses belongs to the np-hard class, for which polynomialtime algorithms have been unable to obtain optimal solutions [49]. the timetabling problem has been studied for several years, with pioneering solutions forming the foundation for more effective techniques. the literature reveals several types of solutions, such as graph-based techniques and other approaches that find a maximal sequence of pairings in the bipartite graph composed of teachers and classes. authors in [50] used programming by applying a lagrangian relaxation technique, while authors in [23] formulated and solved the problem as an allocation challenge. authors in [51] used flow resolution techniques in networks. as mentioned above, many authors divided the restrictions between hard and soft, where the hard restrictions define the feasible solutions, and the soft restrictions are included in the objective function. while satisfying the hard conditions means that the solution addresses the problem successfully, its quality is dependent on the procedure to blocks of different durations. another popular approach is the employment of a multiobjective ga, which combines two points of view: student-oriented and teacheroriented. moreover, one can use a two-stage grasp algorithm. others formulated another model for the problem, also using soft constraints in the objective function. one can explore a hyperheuristics framework based on graphs, researching local search algorithms based on low-level coloring algorithms. other approaches can also apply a tabu search, using domain-independent neighborhood structures to penalize neighborhoods unable to generate better solutions. a combination of the bee colony meta-heuristic with an assimilation policy to guide the search process has also been proposed. therefore, there are several approaches that can be followed to solve the university course timetabling issue, although they all have their advantages and disadvantages. b. particle swarm optimization pso was originally developed in 1995 to solve continuous problems [52]. the idea of simulating a swarm of bees has evolved into a meta-heuristic and presented an optimization procedure with some basic extensions. based on this premise, the pso procedure can be further modified to solve combinatorial problems [53, 54]. the boids (bird-like objects) model has been introduced, whereby each boid represents an individual who obeys three implemented rules in order to simulate swarm behavior for computer graphics and films, since it was found that the choreography of flocks of birds was aesthetic. the alignment ensures that individuals move in the same direction as their neighbors. merging several boids enables cohesion, in which a single boid moves in the middle of a defined group, whereas separation causes boids to diverge in a small space. depending on a given rule, a marked boid is aligned with the other boids. later on, rest areas were added to engineering, technology & applied science research vol. 10, no. 6, 2020, 6410-6417 6414 www.etasr.com alghamdi et al.: a review of optimization algorithms for university timetable scheduling the boids model [55]. the individuals also have a need to remain within the swarm. the more a boid approaches a resting place, the greater the desire to move towards it, pulling more boids in this direction. later, kennedy and eberhart developed the swarm optimization [55]. theoretically, individuals can benefit from the discoveries and past experiences of their colleagues when searching for food [56]. this advantage can become critical and outweigh the disadvantages of food competition if the resource is unpredictably patched [57]. kennedy and eberhart followed this hypothesis that information exchange between group members offers an evolutionary advantage in the further development of the pso by implementing social behavior in the birds and, hence, making them massand collision-free particles. they also extended the model by not only having them look for a rest area but also using a “cornfield vector” on which the best feeding place exists. these particles now have a memory of their best position in relation to such a feeding place and a knowledge of the best position so far within the entire swarm [57]. based on these considerations, the classic pso for continuous problems was developed. figure 2 shows the flowchart of the pso algorithm. fig. 2. flowchart of the pso algorithm. to optimize the solution, the pso developed for continuous problems was modified in such a way that it was suitable for solving combinatorial problems. various compositions of parameters were examined for their performance and it was observed that the attempt to modify the pso in such a way that it was able to solve a combinatorial problem without the characteristics of swarm-intelligence [59]. the pso significantly improved the quality of the solution of the manually created timetable with reasonable computing effort. in particular, the influence of an individual event can be emphasized in combination with swapping a random time window of the current solution. this exercise suggests a good current solution [60]. this exercise suggests a good balance between exploration and exploration of the solution space. since the method presented primarily deals with continuous problems, further research is needed to determine its suitability in addressing the university timetable problem. while formulating a time table, it is important to consider the context of the problem within the educational institution in question. the problem may vary according to the institution and its business model, as, for example, in public and private educational establishments. public schools usually have an open timetable model, in which subjects are offered and courses are built around them [60]. thus, students are free to choose the subjects and they want to take and at what times. as the subjects are free, there is no requirement for rooms where it should be taught, and this allocation is also part of the process as a whole [59, 61]. thus, it is possible for a course to be taught in several different classrooms throughout the week. in contrast, most private institutions follow a closed model. in this case, a course coordinator allocates the subjects that a student will take. eventually, the learner has to approve the given set of units according to the level of study. in addition, the subjects are linked to courses they are being offered, and they are completely free as in the case of public institutions. as a result, subjects should not be allocated to classrooms, as they have a fixed location. that is, the classroom to which they are assigned. thus, lecturers can switch rooms but not the student since teachers in private institutions can teach several subjects, although there is no requirement that a subject should always be taught by the same instructor. however, in public institutions, it is common for a teacher to be hired for one or more specific subjects. iii. discussion lesson planning deals with the scheduling of classes at a specific time in a given location, with particular participants that have to attend. in the best case, the solution of the problem results in plans that enable all students to take part in the meetings of interest at a certain location and time. there are, however, restrictions to the allocation of resources, which include time, space, and the availability of both teaching staff and the students. no other class should happen at the same time and venue with an ongoing one, and neither should two lessons demand the presence of the same group of students concurrently. double occupancy of rooms has the same potential for conflict. as mentioned above, creating an efficient timetable is a typical np-hard problem, which does not have a specific methodology of finding an optimal solution [62, 63]. moreover, course timetables do not consider the preferences of students, as is generally the case in appointment requests. in the case of university lesson planning, this phenomenon means that lecturers play the role of active agents and students that of passive agents. at the same time, a lecture hall has to be of appropriate size, should possess the required equipment, and be available at an acceptable time for all participants without causing violations of both essential and nonessential constraints [63]. therefore, the dates of a resulting timetable correspond to engineering, technology & applied science research vol. 10, no. 6, 2020, 6410-6417 6415 www.etasr.com alghamdi et al.: a review of optimization algorithms for university timetable scheduling assignments of a previously defined matrix of possible time windows. the conditions, which a timetable should satisfy can be divided into hard and soft constraints. violations of hard constraints are not permitted because they could lead to the unavailability of lecturers, e.g. they might be scheduled to attend two concurrent classes. on the other hand, soft constraints can be left unsatisfied since such a case does not affect the admissibility of the timetable. the punishment for non-compliance with soft constraints is included in the assessment of the timetable [14]. soft constraints occur, for example, when deadline requests for events cannot be met. in this case, these incidents can be shifted from their original desired dates to another time window without affecting the effectiveness of the timetable. the lesson planning activity in schools is further made difficult by the options that students have while selecting the classes to attend. for instance, one does not have to stick to given subject combinations, but can largely plan study programs independently. the attendance of individual courses does not have to take place in a particular semester, but can usually be integrated into the study period at will. the aim of university timetable scheduling is to use the resulting multitude of subject combinations to create a program, which is as free of overlaps as possible for all [64, 65]. although the problems of school and course timetabling may appear similar at a first glance, they present significantly different problem sets, with the latter’s being more complex than those of the former. while formulating a timetable, it is important to consider the context of the problem faced by the educational institution in question. the issue may vary depending on the establishment and its business model. for example, while they are both institutions of higher learning, public and private universities have different funding models, which affect how they offer their classes and the types of services their students enjoy. public schools usually have an open structure, in which subjects are offered and courses are built around them, while students are free to choose which subjects they want to take and at what time. as the subjects are free, there is no requirement for rooms where they should be taught, and this allocation is also part of the process as a whole [66]. thus, it is possible for a course to be taught in several different classrooms throughout the week. on the other hand, most private institutions follow a closed model. in this case, a course coordinator allocates the subjects that a student will take. eventually, the student has to approve the given set of units according to the level of study. in addition, the subjects are linked to courses in which they are being offered, and they are not completely free as in the case of public institutions. as a result, subjects should not be allocated to classrooms, as they have a fixed location. that is, the classroom to which they are assigned. thus, lecturers can switch rooms but not the student since teachers in private institutions can teach several subjects, although there is no requirement that a subject should always be taught by the same instructor. however, in public institutions, it is common for a teacher to be hired for one or more specific subjects. university course timetabling solves the problem of creating assignments given specific time slots, classrooms, teachers, and subjects. the goal is to prevent a room from being occupied by two subjects simultaneously, or two teachers teaching the same class, or a teacher to have to teach two classes at the same time. the quality indicator of a solution varies, with some researchers using the sum of the preferences of a given discipline, such as a teacher allocation, to measure the effectiveness of a timetable [66, 67]. others adopt soft restrictions and utilize them to assess the quality of the solution, while there are instances where student preferences or the spacing between classes has been employed to achieve the same goal. authors in [4] consider a matrix of conflicts between learners taking two courses i and j simultaneously. the objective function considers the minimization of the number of cases where i and j are scheduled at the same time. therefore, just as there are several methods of creating an optimal solution to the course timetabling problem, the quality of the resulting solutions can be evaluated in various ways. iv. conclusion the problem of planning school hours is described as having to schedule a series of meetings between teachers and students over a set period of time and meet a number of different types of constraints. since the types of restrictions generally change from one institution to another, different solutions to this problem have been proposed. the problem of school hours, it is a problem of combinatorial 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[67] m. a. al-betar and a. t. khader, “a harmony search algorithm for university course timetabling,” annals of operations research, vol. 194, no. 1, pp. 3–31, apr. 2012, https://doi.org/10.1007/s10479-010-0769-z. microsoft word aid-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 446-451 446 www.etasr.com zengah et al.: comparative study of fatigue damage models using different �umber of … comparative study of fatigue damage models using different number of classes combined with the rainflow method sahnoun zengah mascara university algeria zengahsahnoun@yahoo.fr abdelkrim aid mascara university algeria aid_abdelkrim@yahoo.com mohamed benguediab djillali liabes university of sidi bel abbes, algeria benguediab_m@yahoo.fr abstract— fatigue damage increases with applied load cycles in a cumulative manner. fatigue damage models play a key role in life prediction of components and structures subjected to random loading. the aim of this paper is the examination of the performance of the “damaged stress model”, proposed and validated, against other fatigue models under random loading before and after reconstruction of the load histories. to achieve this objective, some linear and nonlinear models proposed for fatigue life estimation and a batch of specimens made of 6082t6 aluminum alloy is subjected to random loading. the damage was cumulated by miner’s rule, damaged stress model (dsm), henry model and unified theory (ut) and random cycles were counted with a rain-flow algorithm. experimental data on highcycle fatigue by complex loading histories with different mean and amplitude stress values are analyzed for life calculation and model predictions are compared. keywordsdamage models; damaged stress model; performance; random loading i. introduction methods for fatigue-life assessment can be divided into two groups. one of them includes algorithms based on numerical methods of cycle counting [16] and the other group uses spectral analysis of stochastic processes [3, 5]. in the first group, the material loading is represented by stress or strain histories, and in the second group it is represented by their frequency characteristics, i.e., power spectral density functions [6]. engineering structures are often subjected to complex loads that undergo cyclic changes in time. they can be regular, when amplitudes and cycle shapes remain constant or irregular with stepwise changes in amplitudes or cycle shapes (so-called block loading), as well as stochastic, when amplitudes or cycle shapes vary in a random manner. cumulative fatigue damage is an old, but not yet resolved problem. in general, cumulative fatigue damage theories can be classified into two categories: (1) linear damage cumulative theories and (2) nonlinear damage cumulative theories. more than eighty years ago, in order to predict residual life, palmgren suggested the concept which was later popularised by miner [7] and is known as linear miner rule expressed in a mathematical form as: ∑∑ == == n i i n i ri i � n d 11 β (1) where ni is the number of cycles at a given stress amplitude, �ri is the number of cycles failure at the same stress amplitude and d is the damage variable (it is equal to 1 in correspondence of exhausted life). many researchers have tried to modify miner's rule, but, due to its intrinsic deficiencies, no matter which version is used, life prediction based on this rule is often unsatisfactory [8]. richart and newmark [31] introduced the concept of the damage curve to overcome the deficiencies associated with the linear damage rule. upon this concept and the results of load sequence experiments, marco and starky [9] proposed the first nonlinear load dependent damage theory, represented by a power law: ∑ = = n i x i id 1 )(β (2) where xi is a variable quantity related to the loading level. this rule allows taking correctly into account the effects of different loading sequences. experience has shown that only in some case and for some materials this law, and the other theories derived from it, have shown good agreement with experimental results. moreover, the involved coefficients xi have to be calculated for each different load and load condition limiting their use in engineering applications [10]. damage theories based on endurance limit reduction have also been developed. kommers and bennett [32,11] further investigated the effect of fatigue pre-stressing on endurance properties using a two level step loading method. their experimental results suggested that the reduction in endurance strength could be used as a damage measure. henry [12] is the first who correlated the damage parameter to life fraction. this model does not take into account the load interaction effects. with some assumptions [38], henry showed that damage d stored by a test bar may be defined as the relative variation of the fatigue limit: etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 446-451 447 www.etasr.com zengah et al.: comparative study of fatigue damage models using different �umber of … ' d d d d σ σ σ − = (3) expression of damage proposed by henry is written as: (4) 1 1 d d n �d n � σ σ σ =   −   + − or, if we set d d σ σ γ σ − = = stress ration and n � β = , ( ) 1 1 1 d β β γ = + − (5) where n is the applied number of cycles and n the number of cycles to crack initiation in the wöhler curve. it is noted that for ' 0 d σ = , we have d = 1 and that, when , 0 d σ σ γ→ → and 0d → . early theories accounting for load interaction effects were developed by corten-dolon [13] and freudenthal [14, 15]. both theories are based on the modification of the s-n diagram. bui-quoc, [16, 17] developed a theory named unified theory that used the concept of henry [12] and gatts [18] combined with some parameters of shanley [19] and valluri [20] theories. unified theory is based on the representation of the damage by reducing the endurance limit of the material; it is formulated as a relation of the type: 0 0 m md d m r r σ σ =             (6) the endurance limit decrease, according to the number of cycles, following the form: 2 0 0 0 0 1 d b d d d d d d d dn a σ σ σ σ σ σ σ σ = − −                  (7) where a and b are constants of the material. the damage is suggested by bui-quoc [21] as ( ) 8 2 2 2 / (1 ) 1 s fs s d β λ λ λ β β λ = − + − − (8) u f d σ λ σ = ; 2 d σ λ σ = where s is a parameter which is determined by the loading condition. a new nonlinear approach, based on damage mechanics, has been proposed with the original concepts developed by kachanov [39] and rabotnov [40]. lemaitre [22, 23] applied these principles to formulate a nonlinear damage evolution equation in the form: ( )[ ] ( ) n dm dd c c a δ σ δ β αβ . 1 11 0 1       − −−= + (9) where βc, m0 and α are coefficients of the chaboche model. βc and m0 depend on material and σa= σmax σm (σmax and σm are respectively the maximum and the mean stress of cycle); the exponent α depends on the loading (σmax ; σm) which results in non-separability between damage and loading. recently, a model was suggested and validated by mesmacque [24] and aid [25, 26, 27, 33, 41] that does not require too many properties of the material and it takes into account the loading history. this model is connected cycle by cycle with wohler’s curve. the damage is calculated with the relation ( )i d i i u i d σ σ σ σ − = − (10) where ( )i d σ is the damaged stress; i σ is the applied stress, and u σ is the ultimate stress. the indicator of damage at level i is calculated from (9), then it is transposed to the level i+1 by the relation: 1 1 equiv i i u i d σ σ σ σ + + − = − (11) where equiv σ is the equivalent stress of damage at the level i+1 and 1i σ + is stress at the level i+1. for more details refer to [25-27]. the experimental observations highlighted that when a positive average stress, σm, is superposed on the cyclic loading of amplitude the life of the specimens decreases. the inverse effect is observed in the presence of average stress of compression [42]. in order to take into account this phenomenon, complementary tests can be carried out in order to establish haigh’s diagram, for lifetime fixed at �r, the alternate equivalent stress σaeq according to the characteristics (σa, σm) of the cycle. this returns in fact to modify the curve of wöhler for each cycle with σm≠0. the real loadings are often more complex. estimation of fatigue life of a material subjected to random loading needs suitable calculation algorithms. in such algorithms, cycle counting [28] according to a given method (for example, the etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 446-451 448 www.etasr.com zengah et al.: comparative study of fatigue damage models using different �umber of … rain flow method) and damage accumulation according to the assumed hypothesis are the main operations. in this investigation, miner’s rule, henry model, unified theory and damaged stress model are retained to damage accumulation and lifetime prediction of components subjected under random loading. ii. material and method a. material, shape of the specimens and loading conditions the experiments were conducted on the aluminum alloy 6082-t6, its chemical composition and principal mechanical properties are respectively presented in table i and table ii. the tests were carried out on planar specimens, which were cut from a plate with a 8 mm thick (see figure 1). the fatigue tests were carried out using a 100 kn capacity instron servo-hydraulic machine 8500 for tests of planar specimens made of aluminum alloy 6082t6 under uniaxial tension–compression. while testing, the level of sinusoidal loading amplitude was controlled at zero mean value and 30 hz frequency. the experiments were carried out under uniaxial constant amplitudes for determining the wohler’s curves modeled by (12) according to astm standards [29]: ( ) .log( ) 6.8 0.1024.log( ) r r log a m � �σ = − = − (12) where �r is the number of cycles to fracture, σ is the stress amplitude and m is the exponent of the wohler’s curve. the fatigue limit of our material at �r = 2.10 6 is found to be σf = 220 mpa. table i. nominal chemical composition of the 6082t6 aluminium alloy table ii. mechanical properties of the 6082t6 aluminum alloy fig. 1. fatigue specimens-dimensions in millimeters b. random loading the specimens were tested under random spectrum (original spectrum generated between -1 and +1), (see figure 2), with different mean value of stress and various standard deviations (std) values. densities and the stress distributions for spectra, whose characteristics defined, are represented in figures 3 and 4. cycles were counted using the rain-flow method for numbers of classes equal to 11, 20, 25, 32, 40, 50 and 64. fig. 2. original load history. fig. 3. load density with constant standard deviation (std) and different mean value. fig. 4. 4. load density with constant mean value and standard deviation (std). element si fe cu mn mg cr zn ti al mean % 0.7 0.24 0.06 0.9 0.6 0.02 0.06 0.02 rest sy (mpa) uts (mpa) e (gpa) a (%) 347 370 73 12 etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 446-451 449 www.etasr.com zengah et al.: comparative study of fatigue damage models using different �umber of … fig. 5. comparison between theoretical results and experimental results for different number of classes ((a) 11, (b) 20, (c) 25, (d) 32, (e) 40, (f) 50, (g) 64). etasr engineering, technology & applied science research vol. 3, �o. 3, 2013, 446-451 450 www.etasr.com zengah et al.: comparative study of fatigue damage models using different �umber of … iii. results and discussion reconstruction techniques that create the exact original history from some compact characterization have not been achieved due to complex algorithms and large storage requirements [30]. reconstructions from statistical methods produce good results for random histories and, therefore, reconstructions based on cycle counting must be employed [43]. hence, reproduction of histories that yield damage equivalent to the original history, without necessarily being identical to the original history, is desirable [34]. reconstructions from simple cycle counting methods may produce histories with damage characteristics different from the original history. this problem arises from shortcomings in the cycle counting techniques [2]. reconstructions from the rain-flow technique, however, always produce the same load cycles. only the ordering of the cycles is different. life prediction and cycle counting are independent of each other. any pairing of the two procedures will yield a life prediction because any life prediction model requires cycle information for input. hence, fatigue life may be predicted once the cycle counting is performed. since the rain-flow cycle counting procedure is used for load spectrum regeneration, it is also used as an input to the life prediction model, as a matter of convenience. this is desirable; however, the rain-flow method typically predicts life better than the simpler cycle counting methods [35]. the experimental results and different model's (miner, dsm, henry and unified theory) life prediction under random loading, in the above conditions and for cycles count by a rain-flow algorithm with different number of classes are compared. comparison for a number of classes equal to 11, 20, 25, 32, 40, 50 and 64, are shown in figure 5. the prediction results show the following: • both unified theory and henry models are not affected by the variation of the number of classes, i.e their predictions are stable and independent of the number of classes. • henry model predictions are far from the experimental results and its relative error of predictions is always negative, therefore this model is highly non-conservative. • if the number of classes is equal to 11, the dsm model is non conservative. • if the number of classes is equal to 64, the miner's model is conservative. • unified theory predictions are in good agreement with experimental results. • if the applied number of classes tends to a normalized number (64), models (miner dsm) improve their predictions. vi. conclusion this study is conducted to show that the proposed model (dsm) is nonlinear and takes into account the loading history. the proposed model correctly follows the experimental results and takes into account the effect of loading history. it is based only on the s–n (wohler) curve which has to be known just for a part of the loading conditions; the unknown part can be estimated by a wide range of models. the results show that the proposed model is affected by the change of the number of classes and the predictions are improved if the number of classes tends to standards. the result obtained from the model are in good agreement with experimental results. references [1] astm e 1049-85, “standard 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mesmacque, s. garcia, a. amrouche, c. rubio-gonzalez, “sequential law in multiaxial fatigue, a new damage indicator”, international journal of fatigue, vol. 27, no. 4, pp. 461-467, 2005 [25] a. aid, z. semari, a. amrouche, g. mesmacque, m. benguediab, “nonlinear damage cumulative model in bloks loading conditions. application for gs61 spheroïdal graphite cast-iron loaded by torsion and plane bending”, journal of theoretical znd applied mechanics, vol. 38, no. 4, pp. 101-112, 2008 [26] aid, a. amrouche, a. bachir, b.a. and benguediab, m, “fatigue life prediction under variable loading based on a new damage model”. materials & design., 32(1),183–191, 2011 [27] a. aid, m. bendouba, l. aminallah, a. amrouche, n. benseddiq, m. benguediab, “an equivalent stress process for fatigue life estimation under multiaxial loadings based a new non linear damage model”, materials science and engineering: a, vol. 538, no. 15, pp. 20-27, 2012 [28] c. amzallag, j. p. gerey, j. l. robert, j. bahuaud, “standardization of the rainflow counting method for fatigue analysis”, international journal of fatigue, vol. 16, no. 4, pp. 287–93, 1994 [29] astm e739-91, annual book of astm standards 03.01, philadelphia, pp. 614–620, 1998 [30] a. conle, t. topper, “fatigue service histories: techniques for data collection and history regeneration”, sae technical paper 820093, society of automotive engineers, 1983 [31] f. e. richart jr, n. m. newmark, “a hypothesis for the determination of cumulative damage in fatigue”, proc. american society for testing and materials, vol. 48, pp. 767-800, 1948 [32] j.b. commerce, “the effect of overstress in fatigue on the endurance life of steel”, proc. american society for testing and materials, vol. 45, pp. 532-541, 1945 [33] a. aid, j. chalet, a. amrouche, g. mesmacque, m. benguediab, “a new damage indicator: from blocks loading to random loading”, fatigue design conf., paris, france, november, 2005 [34] o. buxbaum, “random load analysis as a link between 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d’endommagement en fatigue multiaxiale sous sollicitations variables, phd thesis, universitè de sidi-bel abbes, algérie, 2006 [42] x. pitoiset, méthodes spectrales pour une analyse en fatigue des structures métalliques sous chargements aléatoires multiaxiaux. phd thesis, université libres de bruxelles, 2001 [43] j. d. clothiaux, n. e. dowling, “verification of rain-flow reconstructions of a variable amplitude load history”, nasa contractor report 189670, virginia polytechnic institute and state university blacksburg, va, 1992 microsoft word etasr_v11_n3_pp7247-7250 engineering, technology & applied science research vol. 11, no. 3, 2021, 7247-7250 7247 www.etasr.com bitra & miriyala: an ultra-wideband band pass filter using metal insulator metal waveguide … an ultra-wideband band pass filter using metal insulator metal waveguide for nanoscale applications surendra kumar bitra department of electronics and communication engineering koneru lakshamaiah education foundation vaddeswaram, guntur district, andhra pradesh, india bitrasurendrakumar@gmail.com sridhar miriyala department of electronics and communication engineering koneru lakshamaiah education foundation vaddeswaram, guntur district, andhra pradesh, india sridhar.m@kluniversity.in abstract-a t-stub square ring resonator (srr) based ultrawide band (uwb) band pass filter (bpf) is studied and investigated in this paper. the proposed filter is based on coupled feed line connected to the t-stub srr. ultra-wideband characteristics can be realized by adjusting the t-stub lengths and coupling the gaps between both sides of waveguides and srr. the characteristics of the t-stub srr show that the miniaturized uwb bpf can be operated at thz frequencies. the proposed uwb filter is simulated and analyzed using the finite differential time domain (fdtd) solver-based computer simulation technology (cst) studio suite. the resonance conditions are explained and the transmission performance of the filter agrees with the simulated and theoretical calculations. the proposed filter is best suitable for electronic-plasmonic integrated circuits (epics). keywords-metal-insulator-metal (mim); ring resonator; coupled lines; finite differential time domain (fdtd); ultrawide band (uwb); t-stub i. introduction the light incident on a metal-insulator region produces a high-speed electromagnetic (em) wave called surface plasmon polarity (spp) [1]. spps are known for overcoming the diffraction limit of the light at nanoscale wavelengths. due to the low loss and high confinement of light at nanoscale range the metal-insulator-metal (mim) waveguide has been proposed by several researchers [2-4]. the subwavelength optical components that have been proposed when using mim waveguide are reported in [5-9]. several researchers worked on theories and experimentations of stub resonators like disk resonators [10], teeth-shaped resonators [11], rectangular [12], triangular [13], square [14], and circular [15] ring resonators. a band pass filter (bpf) with symmetric side couple nano-disk resonators is analyzed for 1310nm and 1550nm in [16]. a concurrent dual band bpf is designed using slot waveguides and the performance is carried out at the resonant frequencies of 1300nm and 1600nm respectively in [17]. a tunable stepped impedance ring resonator for dual band bpf is designed and analysed at o and l bands in [18]. however, most of the investigations are carried out in single-, dualand triple-band of operation for bpf. a limited work is carried out in ultra-wide band (uwb) bpf where the bandwidth is limited, and the size of uwb filters is more. the optical bands used for transmission are o-band (1260-1360nm), e-band (13601460nm), s-band (1460-1530nm), c-band (1530-1565nm), and the l-band (1565-1625nm). the ring resonators are a fundamental component used in the electronic-photonic integrated circuits (epics). mim and insulator metal-insulator (imi) are important geometries used in plasmonic waveguides. imi waveguides carry light in longer propagation distances than mim waveguides due to their cladding layers, but the mim structures have higher confinement. due to the high confinement and moderate propagation lengths, the mim structures are efficiently used by epics. authors in [19] designed a two-dimensional structure consisting of a mim waveguide with a ring resonator, and two resonant peaks observed. this work is a further extension of the srr for uwb applications. most of the existing resonators have symmetrical shapes. in this work, a nanoplasmonic t-stub loaded square ring resonator (srr) at optical bands is proposed. most of the existing work was carried out on the design of single and dual operating bands. in our proposed work, more than one band of frequencies are considered simultaneously (ultra-wide banduwb). ii. t-stub srr filter design srr filter for dual band and srr with stubs for triple band applications have been designed and their performance was investigated in our previous work [20]. in this paper, a t-stub srr filter is designed which is suitable for uwb applications with compact dimensions. the methodology of the proposed filter design is illustrated with the flowchart shown in figure 1. firstly, the t-stub srr is designed using the computer simulation technology (cst) studio suite. simulations are carried out under perfect magnetic layer (pml) boundary conditions for getting suitable transmission and reflection parameters. figure 2 represents the proposed uwb filter designed using srr. four t-stubs are included at the four sides of the square ring representing the proposed t-stub srr. the blue color in figure 2 represents the metal and the gray color corresponding author: sridhar miriyala engineering, technology & applied science research vol. 11, no. 3, 2021, 7247-7250 7248 www.etasr.com bitra & miriyala: an ultra-wideband band pass filter using metal insulator metal waveguide … indicates the insulator. silver is used as metal and silica is used as an insulator. the silver metal permittivity is calculated using the drude model [21], i.e. ( ) ( )2 2ε m = 1 ω ω ω+iγp p , where ωp (=1.38×10 16 ) is the plasma frequency and γ p (=2.73×10 13 ) is the collision frequency. sio2 ( 2.5iε = ) is used as an insulator and its permittivity is considered constant [21]. design the t-stub ring resonator using cst studio suite start optimize the ring resonator parameters for appropriate transmission and reflection parameters end simulation for field distribution plots at the resonating wavelengths fig. 1. methodology of proposed t-stub ring resonator. fig. 2. srr based uwb filter. two waveguides are situated on both sides of the t-stub srr filter. the dimensions of the waveguide, t-stubs and srr are tabulated in table i. the basic properties of mim waveguide like refractive index (neff), propagation length (pl) of spp and calculated dispersion relation are defined in [17]. the proposed t-stub srr filter is designed and analyzed using a commercially available finite differential time domain (fdtd) solver-based cst studio suite. pml boundary conditions with mesh size of 5nm×5nm were used in simulations. two power monitors were included at the two ports of the filter (port 1 and port 2) to measure the incident power (pin) and transmitted power (pout). at port 1 (input port), part of the em waves is reflected at the interface of the mim waveguide and the remaining part of the em waves is coupled to the srr cavity with a small gap (g). the transmitting and reflecting em waves in the srr form standing waves and these are again coupled to the output port (port 2). the rectangular ring resonance condition is given by [12]: ( ) 0 1 2 0 m g l l m λ λ β β + = = (1) where m=0,1,2,3…, (βg/β0) is the normalized propagation constant, and λ0 is the fundamental wavelength. the overall length of the srr can be calculated from ( )( )0 reg effl n n nλ λ= = where n=1,2,3…., gλ is the guided wavelength and eff n is the effective refractive index of the mim waveguide. table i. dimensions of srr based uwb filter s. no parameter dimensions (nm) 1 l 100 2 w 60 3 l1 1100 4 d 60 5 l2 295 6 w2 50 7 l3 275 8 w3 55 9 g 3 simulations were carried out for rectangular ring resonator observed the dual band operation [11]. including the t-stubs on the four sides of the srr forms the proposed uwb structure and operated o, e, s, and c bands simultaneously. the proposed filter is very useful for epics. the fabrication of mim waveguide can be done by film deposition and photolithography techniques. iii. results and discussion the reflection and transmission characteristics of the t-stub srr are represented in figure 3. the simulations were carried in the fdtd solver-based cst microwave studio suite under pml boundary conditions and mesh settings of 5nm×5nm. the simulation results of figure 3(a)-(b) clearly show the filter operating in the o, e, s, and c bands simultaneously. the transmission characteristics of the proposed t-stub srr depends on the electromagnetic resonance of the srr. the transmission and reflection characteristics are represented in figure 3(a) for varying l3, from 290 to 300 with a step size of 5nm. for increasing l3 the covering uwb is moved right as shown in figure 3(a). the optimum length l3 is 295nm. the bandwidth observed is ~300nm by the t-stub srr. by varying the optimum width w3 of the t-slot from 50nm to 60nm with a step size of 5nm, the uwb spectrum covers higher wavelengths i.e from 1240nm to 1570nm. however, the engineering, technology & applied science research vol. 11, no. 3, 2021, 7247-7250 7249 www.etasr.com bitra & miriyala: an ultra-wideband band pass filter using metal insulator metal waveguide … reflection coefficient is near to the -10db range bound. the optimimum width for the t-stub is 55nm. the other parameters l, w, w2, d, and l2 have negligible effect on the uwb spectrum. the varied w3 reflection and transmission coefficient is represented in the figure 3(b). by varying the gap g between the coupled waveguide and srr, the operating uwb band shifts to the right (figure 3(c)). the value of g varies from 2 to 4nm with a step size of 1nm. for the 2nm gap, the reflection coefficient is above -10db for wavelengths from 1360nm to 1450nm, for 3nm the rc is less than -10db throughout the bands, and for 4nm gap the bands are decreasing. due to that, 3nm is considered the optimum gap of the proposed uwb filter. the bandwidth of the proposed uwb observed from the simulation results is ~300nm. the symmetrical mim waveguides are located on both sides of the t-stub srr, the electromagnetic wave in the t-stub srr will form the stable resonance observed at three wavelengths shown in figure 3. (a) (b) (c) fig. 3. reflection and transmission coefficients for: (a) varying l3,(b) varying w3, and (c) varying gap g between the coupled feed and the srr. the proposed uwb filter is compared with existing filter models in terms of parameters like operating wavelength, extinction ratio (er), bandwidth (bw), area (l×w) occupied by the filter, and application bands. the proposed filter provides an improved bandwidth of 310nm when compared with the bandwidth (150nm) of the filter presented in [23]. even though the bandwidth is low for the proposed filter in comparison with the filter of [4] (320nm), it operates in four operating bands (o, s, c, and e). (a) (b) (c) fig. 4. field distributions: (a) 1264.94nm (237thz), (b) 1362.69nm (220thz), and (c) 1495.9nm (200.4thz). the proposed uwb t-stub srr is giving better performance in terms of bw, filter size, and application bands as can be seen in table ii. table ii. comparison of the proposed filter with existing models filter models operating wavelength (nm) er bw (nm) l×w (nm 2 ) application bands bpf based on arr [4] 1190–1510 ~38 320 1100×1620 o, s, c and partial e bpf based on u-shaped rr [23] 1280–1440 ~26. 5 150 1120×3232 o, s proposed filter based on srr 1240–1550 ~28. 1 310 1200×1506 o, s, c, and e engineering, technology & applied science research vol. 11, no. 3, 2021, 7247-7250 7250 www.etasr.com bitra & miriyala: an ultra-wideband band pass filter using metal insulator metal waveguide … the energy of the spp wave at uwb wavelengths shows the stronger coupling of the t-stub srr filter at 1264.94nm (237thz), 1362.69nm (220thz), and 1495.9nm (200.4thz) wavelengths as shown in figure 3. according to the simulation, the odd mode analysis has given better results than the even mode analysis of the t-stub srr filter. iv. conclusion in this paper, the t-stub srr filter for ultra-wide band applications based on transmission characteristics was studied. the coupled line mim plasmonic structure is composed of two straight waveguides and the t-stub srr. simulations were carried out using the fdtd based cst studio suite. the simulation results show that the t-stub srr filter gives better performance in o, e, s, and c optical bands. the transmission is slightly smaller at bigger wavelengths when comparing with the transmission at smaller wavelengths. the proposed t-stub srr is optimized for the parameters of l3 (length of the stub) and gap g between the mim waveguide and srr. the er for the proposed t-stub uwb filter is ~28.1 at 1252nm and ~17.5 at 1492nm respectively. the bandwidth for the uwb band is 310nm. the optimized parameters also show that the proposed filter is best suitable for optical uwb applications. a strong em coupling was observed at the mim waveguides and srr throughout the uwb range. the proposed uwb is best suitable for epics for transmitting high speed data. these structures are fabricated using lithographic techniques. references [1] w. mu and j. b. ketterson, "long-range surface plasmon polaritons propagating on a dielectric waveguide support," optics letters, vol. 36, no. 23, pp. 4713–4715, dec. 2011, https://doi.org/10.1364/ol.36. 004713. 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[23] p. osman, p. v. sridevi, and k. v. s. n. raju, "design of metalinsulator-metal based plasmonic ultra-wide band u-shaped resonators based band-pass filter," international journal for research in applied science and engineering technology, vol. 7, no. 5, pp. 3737–3719, may 2019, https://doi.org/10.22214/ijraset.2019.5615. microsoft word etasr_v11_n2_pp6970-6973 engineering, technology & applied science research vol. 11, no. 2, 2021, 6970-6973 6970 www.etasr.com samo et al.: the energy output from the kuching barrage in east malaysia the energy output from the kuching barrage in east malaysia kamran ahmed samo electrical engineering department quaid-e-awam university of engineering, science and technology, larkana, sindh, pakistan kamransamo2@gmail.com shahid hussain shaikh electrical engineering department quaid-e-awam university of engineering, science and technology, larkana, sindh, pakistan shaikhshahid@quest.edu.pk muhammad usman keerio electrical engineering department quaid-e-awam university of engineering, science and technology, nawabshah, sindh, pakistan usmankeerio@quest.edu.pk andrew ragai henry rigit mechanical engineering department universiti malaysia sarawak kota samarahan sarawak, malaysia arigit@unimas.my kishan chand mukwana energy &environment engineering department quaid-e-awam university of engineering, science and technology, nawabshah, sindh, pakistan kcmukwana@quest.edu.pk abstract—electricity generation from the sea has many advantages in comparison with other renewable energy resources. power can be generated from new or existing barrages. based on previous location research, a suitable system to produce tidal range energy from a potential site was developed in this paper. the main objective of this research is to calculate the energy output of the kuching barrage of sarawak state of malaysia. the daily flushing process of kuching barrage is conducted during the low tide period and therefore to put up the ebb generation process is appropriate. the calculated period of power generation is determined to about 6 hours. the annual energy output is calculated based on a theoretical method, with the average daily potential energy calculated to be 5.8mw and approximately 10.23gwh/year could be harnessed. this research can be beneficial for energy generation with the use of a double basin scheme for the construction of new barrages in east malaysia. keywords-generation; kuching barrage; energy output; potential energy; malaysia i. introduction the oceans possess a huge potential of generating electrical power [1]. the generation of electricity from oceans offers many advantages when compared with other renewable energy sources [2]. oceans are now globally established as mainstream renewable sources of energy [3]. it is calculated that the theoretical ocean energy resources are over 30,000twh/year and the net potential power is larger than wind and solar power combined [4]. malaysia is a big producer of solar photovoltaic (pv) panels and is ranked as the world’s third-largest producer of solar pv energy [5]. although malaysia is located at the equatorial zone and surrounded by sea, the ocean potential power has not been given full attention by the malaysian government [6]. the country’s total coastline is 4,675km with west and east malaysia having 2,068km and 2,607 km of coastline respectively [7]. the vast area of malaysia’s coastline is a huge advantage making tidal range energy a reliable alternative energy source [8]. tidal range energy is convertible and can be used at a big scale for sustainable electrical power generation [9]. tidal range power is produced due to the consistent rise and fall of seawater [10, 11]. tidal range power can be generated where the tidal range flow is available which means that it cannot be generated inland [12]. in malaysia, the overall renewable energy creation is 32% of the yearly target. malaysia has to restore its responsibility regarding accomplishing the target of electricity generation from renewable sources. worldwide, there are a few barrage plants in operation. the sihwa dam in korea and la rance in france have mounting energy capability of 254mw and 240mw respectively [14, 15]. the described project supports the government’s endeavors of electricity production from renewable energy resources and promotes tidal range energy. unlike other known renewable energy resources, tidal range is an expectable phenomenon. energy productions from a tidal range power can be assessed appropriately [13]. corresponding author: kamran ahmed samo engineering, technology & applied science research vol. 11, no. 2, 2021, 6970-6973 6971 www.etasr.com samo et al.: the energy output from the kuching barrage in east malaysia ii. literature review and methodology a. methods of calculating potential energy and annual energy output the theoretical calculation method is based upon derived equations. for tidal barrage, basin size and mean tidal range have important influence on power generation. equation (1) shows the correlation of potential energy in mean tidal range enclosed in a basin [16]: 2 0.5 p b b e ga hρ= ∆ (1) where ep is the potential energy over a tide cycle (gj), ρ is the density of sea water (1025kg/m 3 ), g is the acceleration of gravity (9.81m/s 2 ), ab is the horizontal area of the basin (km 2 ), and ∆hb is the monthly or annually mean tidal range in the basin (m). the factor 0.5 is its average value. the total basin area bounded by kuching barrage is 1430km 2 . however, this may not be valid when used for power generation therefore google maps was used to calculate the area. for coastal areas where tidal range power generation is economically attractive, the tidal regime generally consists of two flood and two ebb tides, with a semi-diurnal period of 12.42h at the low tide when the potential energy is zero. therefore, the total potential energy per day from the barrage approximates to 24/12.42 ep, and the corresponding mean potential power can be written as: 24/12.42 /86400 p p e= (2) where p is the power in (gw), and ep is the potential energy over a tide cycle (gj) and time (s) [14]. authors in [14] worked on the calculation of annual energy output from a tidal barrage. at the severn barrage, uk, researchers used a method for approximating the annual tidal energy output from a barrage. the total annual energy output from a barrage was calculated from the theoretical energy of tidal dynamics in the map of the bristol channel and severn estuary with the site of the severn barrage [14]. it was suggested that the energy available from a barrage depends on the area of the water surface seized by the barrage and the mean tidal range h. thus, the potential annual tidal energy output from a barrage can be considered as [17]: 2 0.987 yr b b e a h η= ∆ (3) where eyr is the potential annual tidal power output (gwh/year), b a is the horizontal area of the basin (km2), bh∆ is the tidal range in the basin (m), and η is the efficiency. the constant value 0.987 as mentioned in (3) is the converted value of tidal cycles per year [17]. the per cycle value is 1397 and the world mean period for tides is 12 hours and 24 minutes, hence, there are 706 tidal cycles per year, and therefore the converted value is 0.987kwh [17]. to sum up, the power output over a tide cycle can be calculated by using (1). total potential energy per day can be calculated by (2). the relationship of (1) and (3) is that (1) can be used to calculate the daily potential energy and (3) can be used to calculate the annually power output. authors in [18] researched the potential energy generation on total 34 sites at sabah and sarawak, malaysia and identified 18 sites as suitable for the construction of a barrage to generate energy. moreover, these suitable sites were supposed as preliminary, as the final sites should be supposed after conducting a feasibility study. among the 18 sites, 2 sites were selected as having the maximum potential. the maximum potential power calculated sites were at the tanjung manis and at the pending. the maximum energy potential was calculated to come from tanjung manis and was measured between 50.7kw and 39.2kw, while the second highest power was calculated for pending, between 33.1kw and 25.1kw. in continuity of the above research, the calculation of potential energy and annual energy of a tidal range energy extraction barrage at the kuching is calculated in the current research. b. calculation of potential energy and annual energy output: to calculate the potential energy over a tide cycle, (1) will be used to calculate the mean potential energy in a day. the calculation is completed by using (2) whereas (3) is used to calculate the annual energy output. the annual calculation power output was calculated with the theoretical method. the annual output power is calculated with the lower power conversion efficiency. iii. results and discussion a. calculated basin area of kuching barrage the basin area of pending site at kuching barrage is calculated to get the potential energy and annual power output. the total basin area bounded by kuching barrage is 1430km 2 , however, this may not be valid when used for power generation. hence, it is assumed that the total bounded area may not be the effective area contributing to power generation. the effective basin area has been assumed as 2.94km 2 . b. daily power output calculation based on (1) and with a mean tidal range of 4.2m, kuching barrage potential energy value is 260gj over a tide cycle. the daily potential energy is about 520gj with nil potential energy during the low tide. in demand to get daily power output, the potential energy is distributed with the tidal period. the tidal period of semidiurnal tidal form is 12.42h or 44712s. the daily potential energy is 24/12.42. equation (2) is used to calculate the daily potential energy. thus, kuching barrage expected mean daily potential energy is 0.0058gw or 5.8mw. however, the energy output may not be continuous during the 12h cycle (ebb tides occur twice a day) operation due to the changing sea level. the kuching barrage energy plant is calculated to produce energy output power for 6h. however, generation duration could accept dependency on tide pattern. due to this reason the mean tidal range reduces as the downstream water increases. as the mean tidal range decreases in height the power generation also reduces. figure 1 shows a simple cycle of power generation during the operation of kuching barrage gate. phases i, ii, and iii are respectively for filling, holding and generating. there is a 12h engineering, technology & applied science research vol. 11, no. 2, 2021, 6970-6973 6972 www.etasr.com samo et al.: the energy output from the kuching barrage in east malaysia operation during the ebb tide, a 6h generation and a 6h filing of the basin. the schedule of opening the kuching barrage gates to flush out the water to the sea depends on the tide level. the average schedule of opening the gates is 4-5h and sometimes 67h, depending on the tide level. flush out water to downstream is possible when there is a low tide. the main aim of kuching barrage is to flush out river water before upstream got flooded during rainy season. the flush out of the upstream water to the downstream is possible twice a day as of low and high tides. fig. 1. a simple cycle of power generation. c. annual power output calculation annual energy output is calculated by (3). at a minimum, 10.23gwh/year ( p η = 20%) of power can be harnessed with the lowest efficiency. table i summarizes the power output value of kuching barrage tidal energy plant system. in table i, the actual and theoretical annual energy output from different tidal power plants [14] are listed. table i documents the technical conditions of the tidal power plants, with the actual output and theoretical calculation range of the annual energy output from each plant. table i also depicts the installed capacity, basin area, and mean tidal range of 5 main tidal power plants. tidal range energy schemes were measured by low standards of power conversion efficiency, frequently reaching from 20% to 40%, (with an average of 33%). however, minimum power conversation efficiency (20%) is used to calculate the power output for this project. the mean tidal range is the monthly or yearly average. in table i, the theoretical standards are tabulated and are related to a present tidal energy plant to confirm the calculation methods. summarizing, kuching barrage is an additional proposed tidal power plant. the calculated basin area of kuching barrage is 2.94km 2 with calculated mean tidal range is 4.2m. the annual power output is calculated based on the lowest power conversion efficiency of 20%. the expected power output for kuching barrage tidal energy plant malaysia is calculated as 10.23gwh/year. table ii shows the power output of the kuching barrage tidal energy plant. the mean daily potential energy is calculated by (2). the potential annual power output is calculated by (3) at the lower efficiency of 20%. table i. comparison of theoretical and actual power output of tidal power plants country site installed capacity (mw) ab (km 2 ) ∆hb (m) eyr range at η = 20% (gwh/yr) actual or expected output (gwh/yr) france la lance 240 22.5 8.5 320.90 533 canada annapoils 20 6.0 6.4 48.51 50 china jiangxia 3.9 1.37 5.1 8.88 6-7 korea shiwa 254 43 5.6 266.19 553 uk severn 8640 570 7.5 6329.14 15600 malaysia *kuching barrage 2.94 4.2 10.23 10.23 *kuching barrage at pending site is our proposal for a tidal power plant scheme table ii. calculated power output of kuching barrage tidal range energy plant scheme power estimation value mean daily potential energy, p 2.8mw potential annual power, eyr 5twh/year (η= 20%) iv. conclusion tthe potential energy and annual power output of the pending site at the kuching barrage basin area were calculated in this paper. 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[18] k. a. samo, i. a. samo, z. a. siyal, and a. r. h. rigit, "determination of potential tidal power sites at east malaysia," engineering, technology & applied science research, vol. 10, no. 4, pp. 6047–6051, aug. 2020, https://doi.org/10.48084/etasr.3674. microsoft word 10-3522_s_etasr_v10_n3_pp5637-5642 engineering, technology & applied science research vol. 10, no. 3, 2020, 5637-5642 5637 www.etasr.com elfghi & gunay: mechanical properties of powder metallugry (ti-6al-4v) with hot isostatic pressing mechanical properties of powder metallugry (ti-6al4v) with hot isostatic pressing mohamed abdulla elfghi mechanical engineering department karabuk university karabuk, turkey elfghi@yahoo.co.uk mustafa gunay mechanical engineering department karabuk university karabuk, turkey mgunay@karabuk.edu.tr abstract—titanium alloys are widely used due to their high performance and low density in comparison with iron-based alloys. their applications extend to aerospace and military in order to utilize their high resistance for corrosion. understanding the mechanical properties and microstructure of titanium alloys is critical for performance optimization, as well as their implications on strength, plasticity, and fatigue. ti-6al-4v is an α+β two-phase alloy and is considered one of the most commonly used titanium alloys for weight reduction and high-performance. to avoid manufacturing defects, such as porosity and composition segregation, hot isostatic pressing (hip) is used to consolidate alloy powder. the hip method is also used to facilitate the manufacturing of complex structures that cannot be made with forging and casting. in the current research, ti-6al4v alloys were manufactured with hip and the impact on heat treatment under different temperatures and sintering durations on the performance and microstructure of the alloy was studied. the results show changes in mechanical properties and microstructure with the increase of temperature and duration. keywords-titanium alloy; ti-6-4; hot isostatic pressing (hip) i. introduction the utilization of titanium for industrial purposes became popular during the last fifty years due to its competitive properties in comparison with traditionally used metals, such as iron, steel, etc. [1]. titanium alloys are commonly used in aerospace and military applications due to their low density and high resistance to corrosion, high performance, and strength. despite being expensive and hard to manufacture, these alloys became the engineering choice for experts due to their light weight and high performance under high temperatures [2]. the applications of titanium alloys are correlated to their mechanical properties. therefore, it is important to understand the factors that affect these properties in order to optimize their performance. the mechanical properties of titanium alloys, such as creep, fatigue, plasticity, and strength, are highly affected by their microstructure [3]. the small size of α grains are correlated to the increase in ultimate tensile strength [4]. one of the most common titanium alloys is grade 5 (ti-6al4v or ti-6-4), which is used extensively for engineering and industrial purposes. due to its high mechanical performance and facilitation of weight reduction, applications of this alloy include marine equipment, automotive, and aerospace. medical and pharmaceutical applications can also be found for ti-6al4v due to its exceptional biocompatibility [5]. however, the alloy has a difficult machinability because of its low thermal conductivity and high strength to density ratio [6]. ti-6-4 is classified as an α+β two phase alloy with wide usage range in mechanical applications. due to the structure complexity of the manufactured components and defects such as composition segregation and porosity, forging and casting is not the most preferred manufacturing method [7]. thus, hot isostatic pressing (hip) is used for the consolidation of alloy powder in order to facilitate manufacturing complex components and avoid those defects [8]. the hip method has also economic advantages as it maximizes the utilization of material and reduces cost [9]. in [10], further advantages were found for the hip on ti-6-4 on the microstructure level. several studies attempted to optimize the heat and pressure conditions of the alloy in order to reach optimum performance. some studies solely tested the heat or pressure change implications on titanium alloys, while a few investigated the change in both parameters [11]. authors in [12] investigated the heat and pressure conditions of the hip and the cooling rate of the ti-64 samples on their microstructure and mechanical properties. they found that temperatures ranging between 900 and 940ºc and a pressure of 100mpa yield the most optimized tensile strength, with sample holding for 3 hours in room temperature. authors in [13] used hip with high temperature and pressure conditions: 1200ºc and 120mpa, while samples cooled in the furnace for 3 hours. microstructure analysis showed an increase on the needle structures of ti-6-4 and an increase in the nano hardness and the wear resistance of the samples. in the current study, ti-6-4 alloys were manufactured under hip and the samples were put under very high temperatures with different exposure timings. the impacts on wear resistance, microstructure, and mechanical properties were investigated and compared to the results of previous research for verification and possible enhancements on the properties of the alloy. ii. research aim and methods a. research aim the aim of this research was to investigate the effect of very high heat exposure on ti-6al-4v alloys manufactured by hip by comparing samples with different exposure durations. corresponding author: mohamed abdulla elfghi engineering, technology & applied science research vol. 10, no. 3, 2020, 5637-5642 5638 www.etasr.com elfghi & gunay: mechanical properties of powder metallugry (ti-6al-4v) with hot isostatic pressing b. material and sample preparation the ti-6-4 alloy used in the experiment was prepared through the cost-effective blended elemental (pm) technique. the hydrogenated titanium powder (3.5% h wt, ti particle size 100µm) was mixed with 60al-40v master alloy powder with particle size ranging between 40 to 63µm in order to obtain the required alloy composition [15], as shown in table i. table i. chemical composition of the alloy by wt% ti al v fe o n h balance 6.21 4.12 0.0 0.18 0.04 0.004 the powder was blended for 1200s (20m) and die pressed under 300mpa at a temperature of 500ºc for 4h to form green compacts of 60×60×3mm, as shown in figure 1. the approximate density of the sintered alloy was determined through hydrostatic weighing as 4.42g/cm 3 , corresponding to 97.73% of its theoretical value. the compacted specimens are shown in figure 2. for each produced sample, 50g of alloy powder was used, while the final average weight of each of the nine produced sample was 47.844g. fig. 1. pressing and heating of the ti-6-4 powder fig. 2. specimens produced after pressing the sintering of the specimens was performed in a vacuum furnace at a vacuum pressure of 10 -3 pa. the nine specimens were divided into three groups as shown in table 2. three temperatures were applied: 1200ºc, 1300ºc and 1400ºc, at 2, 4 and 8h for each group. the described properties of powder metallurgy compacts are not comparable to the obtained wrought metal. it is expected that the sintered metal would have lower ductility, for both alloyed and unalloyed titanium, than the wrought metal [16]. table ii. specimens and sintering conditions group specimen furnace temperature (ºc) sintering duration (h) a a1 1200 2 a2 4 a3 8 b b1 1300 2 b2 4 b3 8 c c1 1400 2 c2 4 c3 8 five tests were performed on each sample: wear resistance test, microhardness test, xrf analysis, xrd analysis, and sem analysis. the results are presented and discussed along with the relevant literature below. iii. results and discussion a. wear resistance the specimens were subjected to a wear resistance test, where machine parameters were set as shown in table iii. table iii. wear resistance test parameters parameter unit value load n 20 stroke mm 7 test cycles 14285.71 sliding distance m 200 sliding speed mm/s 56 frequency hz 4 as shown in figure 3, the friction coefficient for specimens in group a differed with the sintering duration. while the maximum friction coefficient increased from 3.054 in a1 to 3.882 in a2, it decreased to 1.929 in a3, which corresponds to the longest sintering duration. fig. 3. wear resistance friction coefficient change for group a in a1, fluctuations with an increase in friction appear between zero to 40m. smooth sliding gaps started appearing afterwards with the maximum friction towards the end of the distance. specimen a2 showed high fluctuation rate with a steady overall increase in friction, while a3 showed a steady friction coefficient with a wave of higher friction between 5 to 35m. the results for group b specimens are presented in figure 4. a reduction in the overall friction coefficient was found in b2. specimen b1 showed an increase of friction between 0 to 30m and had a maximum coefficient of 3.07. specimens b2 engineering, technology & applied science research vol. 10, no. 3, 2020, 5637-5642 5639 www.etasr.com elfghi & gunay: mechanical properties of powder metallugry (ti-6al-4v) with hot isostatic pressing and b3 showed more steady fluctuations at periodical intervals, with maximum coefficients of 2.109 and 3.382 respectively. fig. 4. wear resistance friction coefficient change for group b b. microhardness test vickers microhardness test was conducted by applying a load of 1kg for 15s by a ball indicator. values were measured through a calibrated optical microscope for the stress in mpa, as shown in table iv. table iv. hardness test values temperature( 0 c) time (h) value (1) value (2) value (3) average 1200 2 331 333 319 327 1200 4 389 398 405 397 1200 8 375 332 364 357 1300 2 403 387 379 389 1300 4 433 454 481 456 1300 8 488 491 499 485 1400 2 599 533 599 577 1400 4 427 481 477 461 1400 8 494 424 461 459 the average hardness values are presented in figure 5. the hardness value of group a increased with the increase of sintering time between 2h and 4h, while it dropped at 8h. for group b, the hardness value increased at both 2 and 4h, while it decreased for both sintering times for group c. generally, microhardness values increased with the increase of heat treatment temperatures, while increased sintering times decreased hardness values. authors in [17, 18] showed the increase in microhardness values between heat treated and untreated ti-6-4 samples and authors in [19] reported a decrease in the hardness values with the increase of heat treatment temperatures without specifying changes in sintering durations. fig. 5. average hardness values for groups a, b and c c. xrf analysis x-ray fluorescence (xrf) is a microscopy method used to determine the concentration of metals in an alloy in a specified area. the method is based on the interaction between the x-ray arrays with the matter through dislodging electrons from atoms and measuring the energy resulting to correlate it with a specific element [20]. table v shows the results of the xrf analysis in the tested alloy. table v. xrf analysis of the alloy component result unit det. limit el line intensity w/o normal analyzing depth (mm) b 0.7751 mass% 0.11345 b-ka 0.1816 0.9545 c 3.1998 mass% 0.03225 c-ka 4.4768 3.9402 n 13.1932 mass% 0.15751 n-ka 3.9806 16.2459 o 30.8619 mass% 1.09191 o-ka 0.4586 38.0030 na 0.0814 mass% 0.01053 na-ka 0.1706 0.1002 0.0030 mg 0.0781 mass% 0.00738 mg-ka 0.5700 0.0962 0.0046 al 0.4155 mass% 0.00380 al-ka 9.1576 0.5116 0.0069 si 0.1610 mass% 0.00156 si-ka 3.7107 0.1982 0.0099 p 1.8753 mass% 0.00281 p-ka 121.6887 2.3092 0.0137 s 0.1542 mass% 0.00082 s-ka 8.6498 0.1899 0.0174 cl 0.0401 mass% 0.00255 cl-ka 0.6165 0.0493 0.0240 k 0.0041 mass% 0.00221 k-ka 0.1213 0.0051 0.0506 ca 0.0198 mass% 0.00266 ca-ka 0.6777 0.0244 0.0658 ti 47.7941 mass% 0.02561 ti-ka 432.8491 58.8530 0.1127 v 0.6622 mass% 0.05760 v-ka 0.6306 0.8154 0.0402 fe 0.6684 mass% 0.00446 fe-ka 13.8373 0.8230 0.0619 ni 0.0041 mass% 0.00247 ni-ka 0.1708 0.0050 0.0919 cu 0.0047 mass% 0.00249 cu-ka 0.2469 0.0057 0.1119 mo 0.0071 mass% 0.00126 mo-ka 2.8908 0.0088 0.8550 the analysis depth ranged between 0.0030 to 0.8550mm. the titanium percentage reduced from 58.85% to 47.79%, while the percentages of al and v reduced from 5.12% to 4.16% and from 8.15% to 6.62% respectively. the 90:6:4 ratio has been confirmed for the ti-6-4 in various studies. authors in [21] tested 4 samples of ti-6-4 and confirmed the ratio with engineering, technology & applied science research vol. 10, no. 3, 2020, 5637-5642 5640 www.etasr.com elfghi & gunay: mechanical properties of powder metallugry (ti-6al-4v) with hot isostatic pressing error margins ranging between 0.13% and 10%, while authors in [22] identified 5.5% aluminium, 3.87% vanadium, and 0.22% iron by weight. d. xrd analysis identification of crystalline material in the samples that were subject to heat treatment was carried out through an xray powder diffraction (xrd) analysis. figure 6 shows the peaks of 8 samples, which are identical in phase pattern and position, while differing in intensity. the higher the temperature and duration of the heat treatment, the higher is the intensity. fig. 6. diffractogram of xrd analysis the shift in the peaks with the increase of the heat treatment conditions is caused by the creation of equilibrium phases of the lamellar structure α+β. the decrease in the width accompanied with the increase in intensity of the peaks is caused by the non-equilibrium α phase of the non-treated samples and the transformation to the equilibrium phase with heat treatment [23]. e. scanning electron microscopy (sem) the specimens a1 to c2 were analyzed through scanning electron microscopy (figures 7-14). the behavior of aluminum and vanadium vary under heat treatment. while al tends to enter the α phase, the v tends to enter the β phase [24]. in the images taken for the 8 specimens at the same magnification, the dark regions show the α phase, while the light regions present the β phase [25]. the presence of delamination wear, abrasion and debris in the sem pictures of ti-6al-4v is in accordance with the test results of other titanium alloy testing [26]. fig. 7. sem image of heat-treated specimens at ×500 for a1 (layer thickness: a1=8.8µm) fig. 8. sem image of heat-treated specimens at ×500 for a2 (layer thickness: a2=8.9µm) fig. 9. sem image of heat-treated specimens at ×500 for a3 (layer thickness: a3=11.5µm) fig. 10. sem image of heat-treated specimens at ×500 for b1 (layer thickness: b1=11.0µm) a1 a2 a3 b1 b2 b3 c1 c2 engineering, technology & applied science research vol. 10, no. 3, 2020, 5637-5642 5641 www.etasr.com elfghi & gunay: mechanical properties of powder metallugry (ti-6al-4v) with hot isostatic pressing fig. 11. sem image of heat-treated specimens at ×500 for b2 (layer thickness: b2=10.4µm) fig. 12. sem image of heat-treated specimens at ×500 for b3 (layer thickness: b3=10.4µm) fig. 13. sem image of heat-treated specimens at ×500 for c1 (layer thickness: c1=10.5µm) fig. 14. sem image of heat-treated specimens at ×500 for c2 (layer thickness: c2=9.7µm) iv. conclusion in the current research, ti-6al-4v alloys were manufactured with the hip method and the impact of heat treatment, under different temperatures and sintering durations on the performance and microstructure of the alloy, was studied. three temperatures were tested (1200ºc, 1300ºc and 1400ºc) with exposure durations of 2, 4 and 8 hours. the results show that sintering temperatures and durations had significant effects on wear resistance and hardness, namely higher temperatures and longer durations reduced wear resistance and hardness. xrd 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properties improvement of ti-6al-4v alloy specimens produced by electron beam powder bed fusion additive manufacturing”, metals, vol. 9, no. 11, article id 1207, 2019 [26] a. w. e. morsy, “wear analysis of a ti-5al-3v-2.5fe alloy using a factorial design approach and fractal geometry”, engineering, technology & applied science research, vol. 8, no. 1, pp. 2379-2384, 2018 engineering, technology & applied science research vol. 8, no. 3, 2018, 2975-2980 2975 www.etasr.com le and vu: effect evaluation of fault resistance on the operating behavior of a distance relay effect evaluation of fault resistance on the operating behavior of a distance relay kim hung le university of science and technology the university of da nang, da nang, vietnam lekimhung@dut.udn.vn phan huan vu center electrical testing company limited da nang, vietnam vuphanhuan@gmail.com abstract—this paper presents an application of a certain distance protection relay with a quadrilateral characteristic approach for the protection of the 110kv duy xuyen thang binh transmission line in vietnam using measured data from one terminal line. we propose the building process of a matlab simulink model for this relay that combines fault detection and classification block, apparent impedance calculation block for all types of faults and a trip logic block of three zone protection coordination. the proposed relay model is further tested using various fault scenarios on the transmission line. it is important to assess what happened, the actual conditions, the causes of maloperation etc. detailed explanation and results indicate that the proposed model behavior will help users to perform tests which correctly simulate real-world conditions besides that it properly interprets test results and troubleshoot distance function problems when results are not as expected. keywords-transmission line; distance protection relay; quadrilateral characteristic; logic trip; matlab/simulink i. introduction transmission lines are one of the main components in high voltage and extra high voltage power system. the main protection used to protect vietnam's transmission lines is a numerical distance protection relay (f21) as shown in figure 1 because of its suitability, simplicity, economy, and reliability. there are now various distance relays that have been implemented by different vendors. these relays help to protect safeguard transmission line from exposure to any type of faults (internal or external) which could intentionally or inadvertently damage electrical equipment and avoid a great effect on the stability of the entire power system. however, the distance protection also faces a number of factors which influence negatively its operation, and thus affect its accurate determination of the measured impedance. this then results in inaccurate fault location determination [1]. a relay device manufacturer, or a power system operator, needs to conduct a simulated use of all test scenarios due to factors such as human factor, fault resistance and load current, coupling of parallel lines, multiple feeder sections, power swing or multi-end sources testing to evaluate the operating behavior of relay’s characteristics. many operators are uncertain about the advantages and disadvantages of mho or quadrilateral characteristic related to fault type, system conditions, and look up the backgrounds of the mal-operation to remove errors. in practice, the relay provides satisfactory results for the operation condition of low resistance faults. but, in the case of high resistance faults, particularly for single phase to earth faults, it measures an incorrect value of fault impedance. consequently, the relay may over-reach or under-reach depending upon the forward/backward flow direction and the magnitude of fault resistance [2]. in order to prove this issue, the current paper focuses on the algorithm of siemens 7sa522 relay that uses a quadrilateral characteristic. thereafter, the 110kv duy xuyen thang binh transmission line model is selected as an example of fault simulation and the algorithm relay is tested in simulink. the proposed model has been assessed under several scenarios. conclusions based on the results are discussed along with the resistance fault factor affecting the relay’s accuracy. fig. 1. distance protection relay on transmission line ii. relay protection zones in [3, 4], the disadvantage of the mho relay is that, when it is used on long lines and the reach does not cover the section sufficiently along the resistance axis, it is incapable of detecting faults with high arc or fault resistances. the problem is aggravated in the case of short lines since the setting is low and the amount of the r axis covered by the mho circle is small in relation to the expected values of arc resistance. so that, the quadrilateral characteristic is a good choice to overcome the disadvantages of mho element when it is properly designed. in the case of medium lines, earth faults can, for instance, be covered with the quadrilateral characteristic and phase faults with the mho characteristic. in vietnam, the 110kv duy xuyen–thang binh transmission line has length less than 30 km and, as shown in engineering, technology & applied science research vol. 8, no. 3, 2018, 2975-2980 2976 www.etasr.com le and vu: effect evaluation of fault resistance on the operating behavior of a distance relay figure 2, is protected by a siemens 7sa522 distance protection relay with three forward quadrilateral zones (z1, z2, z3) which provide fault impedance coverage for both phase to phase and phase to earth faults. setting calculation is important in protection zone setup, so human error can affect the accuracy of the relay protection besides the large amounts of faults to be collected and processed. the transmission line parameter (line length=29 km, line angle=68o, line reactance=0.3304 ω/km), zero sequence compensation factor (re/rl=0.29, xe/xl=0.67), and fault resistance must also be taken into account. the zone settings of this transmission line are calculated by the central region load dispatch center in vietnam ensuring that they are properly coordinated with the adjacent system and comply with the existing guidelines. the three zones of quadrilateral characteristic used to protect transmission line are explained in table i [5]. we used the digsi operating software to enter configuration settings in the relay, it can automatically draw a relay operating characteristic graph as shown in figure 3. the quadrilateral characteristic permits separate setting of the reactance x and the resistance r. the resistance section r can be set separately for faults with and without earth involvement, therefore, this characteristic has an optimal performance in case of faults with fault resistance [6]. the effect of fault resistance on the reach of distance relays is better discussed with the simulation results. fig. 2. the 110kv power system table i. parameter setting on siemens 7sa522 on a 110kv duy xuyen–thang binh overhead line zone relay setting setting value zone 1 covers 85%ab, forward direction (0.85zab) operating mode z1: forward x(z1), rectance: 8.14ω r(z1), resistance for ph-ph faults: 30ω re(z1), resistance for ph-e faults: 40ω tz1, delay for fault: 0s zone 2 covers 100%ab + 60%bc, forward direction (zab + 0.6zbc) operating mode z2: forward x(z2), rectance: 11.5ω r(z2), resistance for ph-ph faults: 35ω re(z2), resistance for ph-e faults: 50ω tz2, delay for fault: 0.3s zone 3 covers 100%ab + 100%bc + 60%cd, forward direction (zab + zbc + 0.6zcd) operating mode z3: forward x(z3), rectance: 19.53ω r(z3), resistance for ph-ph faults: 40ω re(z3), resistance for ph-e faults: 55ω tz3, delay for fault: 1.5s iii. power system under study we model the power system that is supplied from both ends as shown in figure 4. it uses simulink to evaluate the distance protection function. the overhead line is 89.65 km long, and the system nominal operating voltage is 110 kv, 50hz. fig. 3. quadrilateral characteristic of siemens 7sa522 at the 171 overhead line of duy xuyen substation fig. 4. power system model this model consists of: 1. the transmission line: three phase section line is used to represent the transmission line. line sequence impedance is: rl1=0.1335ω, rl0=0.2496ω. ll1=1.0517mh, ll0=3.1657mh. cl1=0.038μf, cl0=0.038μf. engineering, technology & applied science research vol. 8, no. 3, 2018, 2975-2980 2977 www.etasr.com le and vu: effect evaluation of fault resistance on the operating behavior of a distance relay 2. a load of 110 kv, 35 mw, and 50 kvar is connected to the bus duy xuyen, thang binh, thang binh 2, tam thang. 3. three phase fault block to deduce fault types and fault resistance varying from 1 to 40 ohms. 4. three-phase measuring blocks to measure the three phase line, load current and voltage values. 5. the scopes already support the display of five inputs (voltages, currents, zones 1-3) of a simulated system, which allows a better signal comparison. 6. a siemens 7sa522 relay is located at bus duy xuyen. it has been developed for fault detection, fault location, and distance protection which will be presented in section iv. iv. distance protection relay siemens 7sa522 model the simulation model of the relay has been designed with four functional flow block diagrams (figure 5) by using matlab’s simulink library. firstly, measurement block reads the values of voltage and current of each phase. next, fault detection and classification are done by fd block and fault_type block. thirdly, impedance calculation block computes the value of rcal and xcal. afterwards, trip_logic block checks operating logics. if all four conditions are satisfied then they issue a trip signal otherwise all steps are repeated from start to end. this helps us monitor and analyze data to avoid severe misunderstanding in assessing any use issues that arose during testing. fig. 5. distance protection model a. current and voltage measurement the measurement block receives two input signals corresponding to the three phase voltages and currents from ct, vt and then it provides to the multiplexer to split the voltage and current signals into three single phase voltages and currents. after that, these quantities are passed through the fourier transform block to avoid the higher order harmonics as shown in figure 6. b. fault detection and fault classification according to the outputs of the measurement block (ia, ib, ic, and in), the fault detection in the transmission line is defined by the fd block. for earth current measurement, the fundamental component of the sum of the numerically filtered phase currents is supervised to detect if it exceeds the set value (parameter 3i0>0.5in) then output “n” equals 1. for phase current measurement, a fault occurrence is detected if ia, ib, or ic is greater than the threshold 1.3inorm. then output “a”, or “b”, or “c” is equal to 1 [7]. based on the information above, fault_type block performs fault classifying on the transmission line which can be summarized as in table ii. fig. 6. measurement block table ii. fault type classification no type fault a b c n 1 ag 1 0 0 1 2 bg 0 1 0 1 3 cg 0 0 1 1 4 ab 1 1 0 0 5 bc 0 1 1 0 6 ca 1 0 1 0 7 abg 1 1 0 1 8 bcg 0 1 1 1 9 cag 1 0 1 1 10 abc 1 1 1 c. impedance calculation to calculate the rcal, xcal of relay protection, it uses one of the six loop measurements (ag, bg, cg, ab, bc, and ca) listed in table iii. the measured fault loop is necessary to know the fault type, local voltages and currents along with the zero sequence compensation factors. the following equations are employed to evaluate the measured values [7]. for the calculation of the phase-to-earth loop, for example during an ag short-circuit (figure 7) it must be noted that the impedance of the earth return path does not correspond to the impedance of the phase. in the faulted loop the voltage ag, the phase current ia and the earth current ιe are measured. the impedance to the fault location results from: 2 cos( ) cos( ) 1 ( ) cos( ) e e u a u e a a l a a e e e e e e e a l l a l l a i x u i x r i x r i r x i x r i r x i                      engineering, technology & applied science research vol. 8, no. 3, 2018, 2975-2980 2978 www.etasr.com le and vu: effect evaluation of fault resistance on the operating behavior of a distance relay 2 sin( ) sin( ) 1 ( ) cos( ) e e u a u e a a l a a e e e e e e e a l l a l l a i r u i r x i x r i r x i x r i r x i                       table iii. short circuit types and fault loops for the distance measurement no type fault phases involved fault loop for distance measurement 1 single phase to ground fault ag bg cg ag bg cg 2 two phase short circuit without ground ab bc ca ab bc ca 3 two phase short circuit with ground abg bcg cag ag, or bg, or ab bg, or cg, or bc ag, or cg, or ca 4 three phase short circuit abc ab, or bc, or ca fig. 7. single-phase earth fault, fault loop in (1) and (2), ua is the short-circuit voltage of phase a, ιa is the short-circuit current of phase a, ιe is the earth shortcircuit current, φu is phase angle of the short-circuit voltage, φa is phase angle of the phase short-circuit current, and φe is phase angle of the earth short-circuit current. to calculate the phaseto-phase loop for instance during a two-phase short circuit bc (figure 8), the loop equation is: 2 2 cos( ) cos( ) 2 cos( ) b b c c b c b b u i c c u i bc b b c i i c u i u i r i i i i                 2 2 cos( ) cos( ) 2 cos( ) b c c b b c b c u i c b u i b b c i i c u i u i i i i i               2 2 sin( ) sin( ) 2 cos( ) b b c c b c b b u i c c u i bc b b c i i c u i u i x i i i i                 2 2 sin( ) sin( ) 2 cos( ) b c c b b c b c u i c b u i b b c i i c u i u i i i i i               fig. 8. two-phase fault clear of earth, fault loop in (3) and (4), ib, and ic represents short circuit phase current of phase b, and c. ub, and uc represents short circuit voltage of phase b, and c. φub, φuc are considered as phase angle of ub, uc. φib, φic are considered as phase angle of ib, ic. d. logic decision as mentioned in the description of the calculation impedance, the calculated rcal and xcal coordinate values define a point on the complex impedance plane. the logic decision compares the point with the quadrilateral characteristics of the relay, shown in figure 3. for example, the distance characteristic has been programmed as seen in figure 9 [7]. the point r3 and x3 are the setting points for zone 3. the time settings tz3=1.5s. if a measured impedance point is inside the zone 3, then the delay time can be started and when the impedance stays longer than tz3, the logic decision generates the true value of the related output binary signal. it means that relay will trip with zone 3 if the following conditions are met:  condition 1:   3 30 0 03 3 3 30 0 0 0 3 22 68 – 68 22 68 6 < 8 6 < 8 cal cal cal cal r x cotan cotan r r r x tan cotan cotan tan r r x tan x r                  condition 2:   3 30 0 3 3 0 0 0 0 22 68 0 – 22 68 68 22 cal cal cal cal r x x cotan cotan r r r cotan cotan tan r x tan                    condition 3: 3 0 0 30 0 cal cal cal x x x tan r        fig. 9. zone 3 protection v. simulation results after the building of the proposed model has been completed, it is ready to analyze the secure operation of the quadrilateral characteristics of the three protection zones applied with variation in fault parameters like fault types, fault location from -5 km to 50 km, fault resistance from 1 ω to 40 ω. during a fault, the current in the faulted phases increases. the voltage in the faulted phases decreases beginning at 0.3 s. engineering, technology & applied science research vol. 8, no. 3, 2018, 2975-2980 2979 www.etasr.com le and vu: effect evaluation of fault resistance on the operating behavior of a distance relay distance protection zone outputs such as z1, z2, z3, operate when the corresponding pre-set times are reached. after 10 ms the line is tripped and the voltage begins to recover. in case of an ag fault with rf=30 ω is created on the line duy xuyenthang binh at a distance of 35 km from duy xuyen bus (forward direction). the distance represents 120.7% of the line length. figure 10 shows the current and voltage waveform and a trip signal of protection zones before, during and after a fault. the fault occurs at 0.3 s, the current of phase a is increased and voltage of phase a is decreased. as a result, impedance trajectory seen by the relay entered into the characteristic second zone. fault location displays 28.38 km. relay takes 0.31 s to send trip signal z2 to the circuit breaker. figure 11 shows the operation of relay in zone 1 with the presence of ab fault at distance 15 km with rf=10 ω. the distance represents 51.7% of the line length. according to the change in voltage and current waveforms during the fault, the impedance trajectory moves quickly into zone 1, fault location displays 14.29 km which results in a tripping at 0.322 s. in figure 12, the result is shown where bcg fault is applied on the transmission line at distance 45 km with rf=40 ω. according to the change in voltage and current waveforms during the fault, the apparent impedance seen at relay point is reduced but the trip signals are deactivated due to the movement of impedance trajectory out of zone 3 area. fault location displays 37.65 km. as shown in figure 13, at 0.3 s an abc fault occurs on the transmission line at 50 km, rf=1 ω, and the fault duration is 1.5 s. according to the change in voltage and current waveforms during fault, relay impedance trajectory into zone 3, fault location displays 49.47 km, thus trip signal z3 is activated at 1.81 s. some of the results for various fault cases (ag, bc, abg, and abc) are given in table iv. fig. 10. voltage, current waves, trip sinals and impedance trajectory for faults at ag fault with rf=30ω at 35km from relay point fig. 11. voltage, current waves, trip sinals and and impedance trajectory for ab fault with rf=10ω at 15km from relay point fig. 12. voltage, current waves, trip sinals and impedance trajectory for faults at bcg fault with rf=40ω at 45km from relay point. the power system is supplied from both ends, its setting for zone 1 is 85 percent of line length or 24.65 km. similarly, zone 2 is 35.18 km, and zone 3 is 57.9 km. in the tests, the fault resistance influence on the measured distance to fault location, the highest fault resistance that allowed for reliable distance protection relay is 20 ω. in the case of the high engineering, technology & applied science research vol. 8, no. 3, 2018, 2975-2980 2980 www.etasr.com le and vu: effect evaluation of fault resistance on the operating behavior of a distance relay resistance fault, this value changes from 20 to 25 ω, the final point of fault impedance locus falls under zone 1 characteristic or under-reaching tendency. if it is higher than 40 ω, fault impedance locus out of zone protection with corresponding error increases. table iv. test results phase actual fault location (km) fault resistance (ω) measured fault location (km) zone trip ag -5 10 -12.2 / 5 1 4.718 z1 10 5 9.244 z1 15 10 13.7 z1 20 15 18.21 z1 25 20 22.78 z1 30 25 24.75 z1 35 30 31.42 z2 40 35 35.25 z2 45 40 38.35 / 50 1 49.67 z3 ab -5 10 -9.475 / 5 1 4.923 z1 10 5 9.633 z1 15 10 14.29 z1 20 15 18.96 z1 25 20 23.63 z1 30 25 28.15 z1 35 30 31.92 z2 40 35 35.31 z2 45 40 37.65 / 50 1 49.47 z3 bcg -5 10 -9.455 / 5 1 4.919 z1 10 5 9.919 z1 15 10 14.92 z1 20 15 19.93 z1 25 20 23.62 z1 30 25 28.14 z1 35 30 31.91 z2 40 35 35.31 z2 45 40 37.65 / 50 1 49.47 z3 abc -5 10 -9.48 / 5 1 4.919 z1 10 5 9.633 z1 15 10 14.29 z1 20 15 18.95 z1 25 20 23.62 z1 30 25 28.15 z1 35 30 31.92 z2 40 35 35.31 z2 45 40 37.65 / 50 1 49.47 z3 vi. conclusions in this study, the distance protection function with three forward zones has been implemented in a siemens 7sa522 distance protection relay on the 110kv duy xuyen–thang binh transmission line that was simulated easily and reliably in matlab simulink. the proposed model allows us to include the detailed analysis of the impedance (rcal, xcal) measured by the distance relay on one single end, fault detection, fault classification, and tripping protection zones for fault, considering fault location, fault type existing on the transmission line, and fault resistance. according to the obtained results, it has been shown that the accuracy of the relay depends on a fault resistance value. the high fault resistance causes the distance relay to over-reach or underreach. therefore, a correctly set distance protection relay can correctly compute the fault location, mitigate the problem of mal-operation, thus ensuring effective and reliable protection to the transmission line. fig. 13. voltage, current waves, trip sinals and impedance trajectory for faults at abc fault with rf = 1ω at 50km from relay point acknowledgment authors would like to thank the "electrical testing company limited, viet nam" for allowing the use of the project of relay protection used in this study. references [1] o. muhayimana, distance protection for parallel and double-circuit hv lines, msc thesis, brno university of technology, 2016 [2] v. h. makwana, b. r. bhalja, transmission line protection using digital technology, springer, 2016 [3] t. saengsuwan, “modelling of distance relays in emtp”, ipst'99 international conference on power systems transients, budapest hungary, pp. 213-217, june 20-24, 1999 [4] l. k. hung, n. h. viet, v. p. huan, “the effect of fault resistance on the performance of distance relay protection”, the 2011 international symposium on electrical-electronics engineering, ho chi minh city, vietnam, pp. 238-244, november 8-9, 2011 [5] central region load dispatch center, setting calculation of distance protection relay siemens 7sa522 at 171 overhead line of duy xuyen substation, decision no a3-03-2015/dux110, siemens, 2015 [6] g. ziegler, numerical distance protection: principles and applications, john wiley & sons, 2011 microsoft word etasr_v13_n4_pp11318-11325 engineering, technology & applied science research vol. 13, no. 4, 2023, 11318-11325 11318 www.etasr.com alotaibi: interference mitigation strategy for d2d communication in 5g networks interference mitigation strategy for d2d communication in 5g networks sultan alotaibi college of computer and information systems, umm al-qura university, saudi arabia srotaibi@uqu.edu.sa (corresponding author) received: 2 may 2023 | revised: 26 may 2023, 4 june 2023, and 7 june 2023 | accepted: 10 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6008 abstract device-to-device (d2d) communication is one of the most promising developments in 5g networks. d2d communication can reduce communication latency and increase spectrum efficiency and system capacity. however, implementing d2d communication in reuse mode with a traditional cellular network can result in severe interference that can significantly reduce network performance, as both networks share the same resources. it is essential to mitigate interference to improve network capacity when d2d communication coexists with traditional cellular networks. an effective power control strategy can help mitigate the potential detrimental impact of interference and maximize the potential benefits of d2d communication. in this study, a dynamic transmission power control strategy was proposed for d2d transmitters to allow them to dynamically adjust transmission power, aiming to minimize interference and maximize network capacity. the distance between and the number of d2d pairs that experience interference were the primary parameters considered for the proposed strategy, while its complexity was in polynomial time. a simulation was carried out to evaluate the proposed strategy and compare it with fixed and ranged-based approaches, and the results validated its effectiveness. keywords-5g; d2d; interference; power control i. introduction all wireless communication systems have shown impressive improvements during the past few decades. however, the increasing demand for communication services is not being met by the current state of wireless network improvement. the demand for ubiquitous high-speed internet access and the increase in the average number of connections per user have led to meteoric development in all these metrics for today's wireless communication systems. additionally, current wireless systems are not equipped to handle the increasing demand for hyperrealistic multimedia services, such as those used in vehicle-to-vehicle, wireless health applications, virtual reality, and internet of things (iot) applications, and the use of wireless networks as essential broadband access service [1]. mobile traffic is expected to expand at an annual rate of about 55% in 2024-2030 [2], which is a huge demand in terms of network resources and link capacity. moreover, effective management of limited resources is required to keep up with this growing demand. existing wireless network systems might not be able to handle the explosive growth in demand that future wireless network applications will require. according to recent developments, a new 5g network design is required to address spectrum challenges and satisfy customers' demands for high-speed connectivity. increased mobile data volumes, lower latency, huge network connectivity, and stable experience quality are all necessary for the 5g wireless network to provide seamless user experiences. several essential technologies have been proposed to enable the 5g network to achieve these goals. technologies include massive multiple-input multiple-output (mimo), device-todevice (d2d), millimeter wave (mm-wave), and ultra-dense network (udn). d2d communication is considered a promising technology for 5g networks, as it allows nearby devices to be directly connected without going through the main base station. in addition, d2d communications can reuse cellular resources [3-6]. d2d communication can be used as an underlying layer in cellular networks to support communication between nodes that are adjacent to each other with minimal latency and energy consumption. in addition, d2d communications would be implemented to offload traffic from macrocell bs, which is the fundamental driver to implement them. d2d technology has great potential to facilitate proximity-based applications, as proximity between connected devices improves spectrum utilization and supports the power efficiency of cellular networks [7-9]. the d2d communication procedure consists of the discovery and communication stages. in the d2d discovery stage, d2d helps user equipment (ue) to find nearby devices that might be able to communicate directly with it. in the communication stage, newly discovered d2d users set up communication channels to share information. procedures for establishing a connection between two or more d2d users in proximity are what this stage is all about. managing the interference introduced by the d2d transmitter and maximizing the efficiency of the ue power consumption have become essential requirements for the implementation of d2d engineering, technology & applied science research vol. 13, no. 4, 2023, 11318-11325 11319 www.etasr.com alotaibi: interference mitigation strategy for d2d communication in 5g networks communication [10]. this is the case despite the many advantages that d2d communications offer, which function in the underlay mode. for example, cellular links have to deal with cross-tier interference from d2d transmissions. d2d links should deal with interference between d2d transmissions, but also with interference between cellular links and d2d transmissions. the interference problem could be solved by multiple approaches. the power control approach is an essential method that can be used by cellular networks to regulate interference, protect cellular user equipment (cue), and provide communications that minimize power usage [1113]. cellular networks that support d2d communications are susceptible to interference on both types: co-tier and cross-tier. co-tier refers to the interference between d2d pairs that share the same resources, while cross-tier refers to the interference between d2d and cellular users in the same channel. cross-tier interference occurs when the resource that is allocated to a user of the cellular network is reused by one or more users of the d2d network. two types of interference occur when d2d communication coexists with conventional cellular networks:  d2d-to-cellular interference: depending on the direction of transmission, interference from d2d communication can occur at either the base station or the cues. in the uplink direction, the interference is received by the base station while it receives data from its cue. in the downlink direction, cue experiences interference from the d2d transmitter while receiving data from the macrocell bs.  cellular-to-d2d interference: the direction of communication can also play a role in interference between cellular and d2d networks. the cue that transmits to the base station is the source of interference to the d2d receiver in terms of the uplink transmission mode. in the downlink direction, the macrocell bs would be the source of interference for the d2d receiver. furthermore, undesirable mutual interference would be experienced when multiple d2d pairs compete for the same resource. d2d users in different pairings will always experience interference from each other, regardless of the direction of the transmission mode. sharing the same spectrum introduces the problem of interference. there are two main strategies for allocating the spectrum for d2d communication: in-band and out-band [14]. in the in-band strategy, the same licensed spectrum is shared between d2d and cellular communication. in the out-band strategy, d2d communication uses an unlicensed spectrum. the coexistence of cellular networks and d2d communication imposes the networks' elements to use the same frequency band. as a result, the problem of interference arises. thus, a power control strategy is needed to solve this problem [15]. moreover, the power control strategy could improve the use of the ue battery, as this issue has become an active research topic in the industry and academic community [16-17]. this study focused on the power control issue of d2d communication, to autonomously control transmission power. the d2d transmitter should be able to dynamically adjust its power to mitigate the undesirable impact of interference and improve network capacity. ii. related works power control is recognized as a promising strategy that can be used to mitigate interference. the geometric water-filing method was used in [18] to control the transmission power of the d2d transmitter. the proposed mechanism also included a resource allocation algorithm to distribute subcarriers among ues, assuming that the transmission power is infinite, where in reality the batteries of ues need to be recharged, so the transmission power is finite. in [19], two stochastic geometrybased power control algorithms were developed for interference coordination in underlaid d2d cellular networks, aiming to provide effective power control and showing that it was possible to increase the total capacity of the network. however, interference could not be canceled but can have an acceptable impact while still accounting for uplink transmission channels in a hybrid random network. in [20], an innovative power control strategy was presented for dense cellular networks operating in a frequency reuse strategy. this technique relied on setting the transmission power of d2d devices to reduce the interference they could cause. this study was conducted using a single scenario, and the findings suggested that introducing d2d communication into cellular networks could improve system capacity. in [21], a resourcesharing mechanism was proposed for channel assignment and power distribution in a downlink scenario for d2d communication, without affecting the quality of service. each pair of d2d reused multiple channels from a variety of cues, and multiple pairs of d2d could share the same channels that were used by a single cue. the lagrangian dual optimization method was used to assign channels with appropriate power transmission for each assigned channel to increase the overall data rate of d2d pairs to its maximum potential. the effectiveness of d2d communication for an uplink transmission mode in an underlay mm-wave-based technology was discussed in [22]. the mm-wave spectrum was responsible for a significant amount of interference and led to an attenuation of the user's signal due to path loss. maintaining transmission power between predetermined higher and lower limits, the suggested power control method guaranteed the highest possible throughput, and the reduced outage probability of the proposed approach ensured greater performance, as it enabled d2d communication in the 5g mm-wave network. in [23], a dynamic power control strategy was proposed to reduce interference and improve network performance, improving overall system throughput with consistent and dynamic power regulations that considered channel conditions. in [24], a power control mechanism for smart grids was presented, which could incorporate contemporary communication technologies with issues related to power supply management. the results of the suggested scheme demonstrated superior performance compared to similar current schemes. in [25], graph theory was used to optimize resource allocation, aiming to increase ergodic sum rates. the bipartite graph was constructed according to the required outage probability constraints, and the hungarian algorithm was used to identify the best solution. the simulation results showed an improved constrained spectrum efficiency of d2d pairs. however, the complexity of the proposed algorithm was high. engineering, technology & applied science research vol. 13, no. 4, 2023, 11318-11325 11320 www.etasr.com alotaibi: interference mitigation strategy for d2d communication in 5g networks an overlapping coalition game scheme was proposed in [26], where each due could reuse several resource blocks (rbs), and numerous dues could share a single spectrum. in addition, the proposed method ensured the security of the entire system and increased performance by increasing the system sum rate to its maximum. in [27], power optimization systems were proposed to coordinate interference between communication channels, prioritize cellular communication, and set a maximum data rate for each link. performance evaluations showed a considerable increase in data rates after taking into account all factors. in [28], a technique was presented to optimize power management in 5g iot networks. the experimental results showed that the proposed strategy performed well in terms of accurately predicting battery life and maintaining a specific degree of network connectivity. in addition, an effective channel selection and power allocation strategy was proposed in [29] to reduce d2d-to-cellular interference. furthermore, it increased the spectral efficiency in scenarios where each d2d pair could reuse numerous cellular subcarriers. the optimal power of the d2d user was calculated using the lagrangian approach to optimize the d2d data rates, as well as to maintain the quality of service for the cellular user. furthermore, this study explored how the location and distance between d2d and cellular users could affect the throughput performance of d2d pairs. in [30], a resource allocation strategy based on soft frequency reuse (sfr) was proposed, taking into account both licensed and unlicensed bands for d2d communications and using power control to prevent interference. the simulation results showed that the suggested strategy outperformed the traditional allocation scheme, which used only the licensed band and did not support d2d in terms of system capacity and blockage rate. in [31], a strategy was proposed to control transmission power, considering only a single cue that was sharing resources with multiple d2d pairs. the assumptions of this study relied on predetermined values such as the constant distance between the d2d transmitter and receiver, constant transmission power, and constant sinr thresholds. the derivation of the analytical model was simplified by these deterministic assumptions, which may often be unrealistic. this study aimed to:  propose a dynamic transmission power strategy for d2d transmitters. the proposed strategy aimed to control the transmission power for d2d transmitters under interference and capacity improvement constraints, enable d2d communication to mitigate interference, and run in polynomial time.  evaluate the proposed transmission power control strategy based on a 5g environment model, simulating a real-time environment for 5g networks.  carry out a matlab simulation to evaluate the performance of the proposed transmission power control strategy, use different performance metrics to investigate its feasibility, consider the average and the gained average throughput of the system, and measure the range of the transmission power value of the d2d transmitters. iii. system model this study considered a single macrocell scenario, where the macrocell bs was located in the cell's center. set d represents all d2d pairs in the system where d = [ 1, 2, 3,..., n]. the d2d pairs were randomly distributed within macrocell coverage. in addition, the in-band spectrum strategy was assumed, considering an underlay mode, where d2d communication and cue used the same licensed spectrum. accordingly, d2d communication would reuse the resources of cue. thus, the problem of interference would increase. this study considered cross-tier interference. there are two scenarios of interference in this context. figure 1 shows the scenario of the downlink transmission mode, where the cue experiences interference from the d2d transmitters. figure 2 shows the scenario of the uplink transmission mode, where d2d transmitters produce interference on the macrocell bs. fig. 1. downlink scenario. fig. 2. uplink scenario. first, the downlink transmission mode is discussed. assuming ptx is the transmitted power of the macrocell bs, the received power prx by cue in terms of the downlink is modeled as follows: ���   +  ���   .   �   +   ∑ ��   .   �� � (1) where gm denotes the channel gain between the macrocell bs and its attached cue, given as follows: � = ��  .  � (2) gd denotes the channel gain between cue and its interfered d2d transmitter, given as follows: � = ���  .  �� (3) where plμ represents the path loss between the macrocell bs and its cue. pld represents the path loss between the d2d engineering, technology & applied science research vol. 13, no. 4, 2023, 11318-11325 11321 www.etasr.com alotaibi: interference mitigation strategy for d2d communication in 5g networks transmitter and cue, λm represents the small-scale fading of the macrocell bs channel and its cue, and λd represents the small-scale fading of the d2d pair channel to the cellular ue. the calculation of the distance between the transmitter and the receiver nodes influences the calculation of the path loss. the distance between the transmitter and receiver nodes causes a propagation loss. thus, the distance between the transmitter and receiver is given according to the following formula [32]: �� = �� � + �� � − 2 �  �� ����� (4) where r represents the radius, and θi is randomly distributed in [0, 2π]. in the downlink transmission mode, the received signal by the cue is given as follows [33]: � = � ��  � ��  ℎ + �� ���  �� �� ℎ� (5) where hm represents the signal transmitted from the macrocell bs, hd represents the signal transmitted from the d2d transmitter, �  � �� denotes the received power from the macrocell bs, ��  �� �� denotes the received interfering signal from the d2d transmitter, and a is the path loss coefficient. path loss is given as follows [34]: �� ! = 128.1 + 37.6 '�() *km (6) where d is the distance in km. equation 6 is used when cue is linked to the macrocell bs, cue is linked to the d2d, and d2d is linked to the macrocell bs. however, the path loss for d2d communication is given as follows: ��� ! = 148 + 40 '�() *01 (7) in terms of downlink, the sinr at cue can be modeled according to the following: 2�3 = 45  . 65,89: ∑ ;<=  4> . 6>,89:?@a (8) where ε has a value of 1 when the d2d pair and the cue use the same subcarrier and 0 when this condition is not met. system noise is represented by n0. in terms of uplink transmission mode, the sinr at macrocell bs can be formulated as follows: 2b3 = 489: . 689:,5 ∑ ;<=  4> . 6>,5?@a (9) where pcue represents the transmit power of cue, pd represents the interfering signal transmitted by the d2d transmitter, gcue,m represents the channel gain between the cue and macrocell bs, and gd,m represents the channel gain between the d2d and macrocell bs. iv. the proposed power control strategy an adequate transmission power control strategy could play an essential role in mitigating the impact of interference between network elements and improving the performance of the network. in this study, a transmission power control strategy was developed to alleviate interference between the macrocell bs and d2d pairs and increase the capacity of the whole network. the main idea behind the proposed transmission power control strategy was to assist the d2d transmitter in adjusting its transmission power autonomously. the proposed transmission power control strategy allows d2d pairs to communicate with each other, addressing the interference challenge. the d2d transmitter reduces its transmission power when it interferes with adjacent cues and d2d pairs. the macrocell bs transmission power is assumed to be an essential parameter for the proposed transmission power control strategy. in addition, the coverage of the macrocell where the d2d pairs are located is considered by the proposed transmission power control strategy. consequently, the proportion between the macrocell bs transmission power and its coverage is identified to derive a suitable transmission power level for the d2d transmitter. thus, a proportional degree between the macrocell bs transmission power and its radius should be recognized. the following formula was used to configure the proportional degree between macrocell bs transmission power and its radius: � = 4cd ef (10) where ptx is the macrocell bs transmission power, and χm is calculated as follows: gh = '�( ijkhl (11) where rm is the macrocell radius. accordingly, the d2d transmitter established its transmission power based on the following formula: ��m = 1nop1q1j� .  g� , ��5st l (12) ��5st was set to 20 dbm and χd was calculated as follows: g� = '�( ijk� l (13) where rd represents the distance between the d2d transmitter and the d2d receiver. the d2d transmitter should determine the number of victim elements that interfered with its transmitted signals. in this case, the coverage of the d2d transmitter is considered to have a number of victims that are affected. the coverage depends on the distance between the d2d transmitter and the d2d receiver. the following formula was used to specify the area where other network elements could be affected and interfered with: u = v j2 .  k� l (14) where a represents the threshold of the possible distance in which network elements could interfere with and be affected by the d2d transmitter signal. after the number of victims is recognized, the d2d transmitter can derive a cost function to reduce its transmission power based on the impact of the interference on adjacent victims. the cost function was calculated for each active d2d pair according to: 2� = wx y (15) where τ represents the total active elements of the system such as the d2d transmitter and cue, and ωi represents the number of elements that interfered with a d2d transmitter. table i is used to construct ωi for every active element in the system. engineering, technology & applied science research vol. 13, no. 4, 2023, 11318-11325 11322 www.etasr.com alotaibi: interference mitigation strategy for d2d communication in 5g networks table i. constructed cost function e1 e2 e3 … en e1 0 1 0 … 1 e2 1 0 1 … 1 e3 0 1 0 … 0 e4 1 1 0 … … … … … … … en 1 1 0 … 0 ωi ω1=3 ω2=4 ω3=1 … ωn=2 accordingly, the proper level of transmission power for every d2d transmitter can be derived based on the following: ��x jmz=l = ��x m − [��x m  .  2� \ (16) the pseudo-code of the proposed transmission power control strategy is presented below. inputs  ←  ���,  kh ,  ^ get:gh ,  � while ^ ≤ 1 do for p = 1 to ^ do compute: ��x m = � .  g� � end for for p = 1 to ^ do compute u� compute: 2� = wx y compute: ��x jmz=l = ��x m − [��x m  .  2� \ end for end while end v. results a simulation was carried out to evaluate the proposed transmission power control strategy in a single macrocell scenario, with the macrocell bs located in the cell's center. d2d pairs and cues were randomly located within the macrocell extent. as d2d pairs would increase network capacity and interference, the distance between the d2d transmitter and the receiver should not be long. in this context, the maximum distance between the d2d transmitter and receiver was set at 40 m. d2d communication was used to offload traffic from the macrocell bs, using the model mentioned above. channel conditions such as noise and path loss were simulated, and table ii summarizes the assumptions and simulation parameters. the antenna type was omnidirectional, the white noise spectral density was -174 dbm/hz, and the channel bandwidth was 15 mhz. interference occurs when the d2d pairs communicate because the spectrum resources are reused. therefore, a power control/management strategy was used to alleviate the impact of undesirable interference. according to 3gpp standards, ues are classified into four classes based on their frequency band, and there is a minimum and maximum level of transmit power for each class. this study considered class 3 for ues, which represent d2d transmitters. the minimum transmission power was set at 23 dbm for class 3 ues for all frequency bands, and this class is an obvious example of handheld ues [35]. the maximum distance between the d2d elements was set to 40 m, to ensure that the d2d transmitters are connected to the closest receivers to mitigate interference and avoid excessive power. table ii. simulation parameters parameters value maximum distance between d2d elements 40 m maximum d2d tx power ��5st 23 dbm fixed d2d tx power �� 23 dbm macrocell tx power ��� 46 dbm frequency band 1900 mhz channel bandwidth 15 mhz antenna mode omni-directional maximum number of d2d pairs 25 pairs n0 -174 dbm/hz three power control methods were used in the simulation; the proposed transmission power control strategy, the fixedbased approach with fixed transmission power at 20 dbm without changes, and the range-based approach using (12). the third approach adjusts the transmission power of the d2d transmitter based on its distance from the receiver. the fixedbased approach was considered because it is used in real implementations where the d2d transmitter uses the maximum predefined transmission power. the range-based approach adjusts the transmission power according to the distance acknowledged between the transmitter and the receiver to alleviate interference by decreasing the transmission power when the distance is short. figure 3 shows the network average throughput, presenting the total capacity of the network, including macrocell and the active d2d pairs. the number of d2d pairs increased in each run to analyze the simulated power control strategies. the network capacity increased with the number of d2d pairs because traffic was offloaded to d2d pairs. the fixed transmission power strategy provided the best average throughput when the number of d2d pairs was low. in this case, the capacity was high because the d2d transmitter operates with the highest possible transmission power. transmission power affects the quality of the transmitted signal, which in turn affects the data rate. however, the performance of the fixed transmission strategy decreased when the number of d2d pairs increased to more than 10. the average throughput of the fixed transmission power approach with 5 d2d pairs was better than with 10 or 15 d2d pairs since the interference in the first case was less. the figure shows that the average throughput of the fixed transmission power approach constantly increased when the number of d2d pairs became more than 15. the range-based strategy provided the worst average throughput, as its behavior did not change with the number of d2d pairs. the range-based power control strategy tended to control the transmission power of the d2d transmitter according to the calculated distance from the receiver. as a result, the short distance between them leads to low transmission power and low data rates. on the other hand, the proposed transmission power control strategy could control transmission power considering interference and network capacity, providing acceptable average throughput for less than 10 d2d pairs. in this case, the proposed strategy delivered lower average throughput than the fixed transmission power approach, but higher than the range-based approach. however, for more than 10 d2d pairs, the proposed transmission power control strategy provided the best average throughput, as it increased by nearly 11% and 35% compared to the fixed and engineering, technology & applied science research vol. 13, no. 4, 2023, 11318-11325 11323 www.etasr.com alotaibi: interference mitigation strategy for d2d communication in 5g networks range-based approaches, respectively. the proposed transmission power control strategy constantly increased the average network throughput four times when the number of d2d pairs increased from 1 to 25. fig. 3. the network average throughput. figure 5 shows the average throughput achieved by implementing d2d communication. average throughput decreased as the number of d2d pairs increased due to the undesirable interference caused by them. in this case, a power control strategy is needed to mitigate interference and preserve the average gained throughput after implementing d2d communication. the range-based strategy delivered the worst average throughput, as its average throughput constantly decreased when the number of d2d pairs increased. according to the figure, the average throughput delivered by the rangebased strategy decreased by nearly 73% when the number of d2d pairs increased from 1 to 25. the fixed transmission power approach delivered the best average throughput when the number of d2d pairs was less than 10. however, when the number of d2d pairs increased to more than 10, its average throughput decreased. the fixed transmission power approach performed well for less than 10 d2d pairs, but this does not support a real environment where the number of d2d pairs would exceed this number. the fixed transmission power approach performs better with fewer d2d pairs because the distance between different distributed d2d pairs is long. as a result, the impact of interference on distributed d2d pairs is not robust. however, when the number of d2d pairs increases, the impact of interference becomes robust. the average throughput of the fixed transmission power approach decreased by nearly 65% when the number of d2d pairs increased from 1 to 25. on the other hand, the proposed transmission power control strategy delivered the best average throughput for more than 10 d2d pairs. the proposed transmission power control strategy performed the best, preserving the gained capacity, as it managed the transmission power considering both the interference and throughput aspects. mitigating interference leads to increased capacity. thus, the average throughput degradation of the proposed strategy is the least compared to the others. the average throughput of the proposed transmission power control strategy decreased by nearly 58% when the number of d2d pairs increased from 1 to 25. according to figure 4, the proposed transmission power control strategy performed better when the number of d2d pairs increased, which simulates a real environment, while the fixed transmission power approach performed better for less than 10 d2d pairs. fig. 4. d2d pairs average throughput. figure 6 shows the average transmission power for the d2d transmitters. as the transmission power of the fixed transmission power approach was set to 20 dbm, there were no changes when the number of d2d pairs changed. however, the proposed transmission power control strategy enables d2d transmitters to change their transmission power to mitigate interference, especially when the number of d2d pairs increases. consequently, the average transmission power ranged between 12 and 16 dbm. in addition, the average transmission power level constantly decreased as the number of d2d pairs increased. the average transmission power of the proposed strategy did not reach maximum, while it provided the best throughput compared to the other strategies. the average transmission power level of the range-based strategy was the lowest, as it ranged between 3.5 and 7 dbm, but delivered the worst performance in terms of average throughput compared to the other approaches. the proposed transmission power control strategy had 15% and 30% better network capacity compared to the fixed-based and range-based approaches, respectively. the average throughput of the d2d pairs for the proposed transmission power control strategy was 16.6% and 35% better than the fixed-based and range-based approaches, respectively. fig. 5. average transmission power for d2d transmitters. engineering, technology & applied science research vol. 13, no. 4, 2023, 11318-11325 11324 www.etasr.com alotaibi: interference mitigation strategy for d2d communication in 5g networks when the number of d2d pairs increases beyond 25, two scenarios will happen according to the simulation results. at first, the throughput of the entire network would increase as traffic is offloaded from the main cell to d2d pairs. however, the level of additional capacity gained for the entire network would remain stable as d2d pairs are added due to interference. in the second scenario, the throughput of the d2d pairs communication would decrease when the number of d2d pairs increases due to interference and its undesirable impact on throughput. vi. conclusion d2d communication has been recognized as one of the most promising developments in 5g networks, as it allows nearby devices to be directly connected without going through the main base station, improving network capacity. however, managing the interference introduced by the d2d transmitter and maximizing the efficiency of the ue power consumption have become essential requirements for implementing d2d communications. this study proposed a dynamic transmission power control strategy for d2d transmitters to allow them to dynamically adjust their transmission power, alleviate interference, and improve network capacity. the main factors considered in the proposed strategy were the number and distance of the d2d pairs that are affected by interference. a simulation was carried out to validate the proposed transmission power control strategy, and the results demonstrated its effectiveness compared to the fixed and rangebased approaches. references [1] "wireless technology 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[35] "5g nr ue power classes," techplayon, jan. 05, 2021. http://www.techplayon.com/5g-nr-ue-power-classes/. microsoft word 9-2381_s1_ca engineering, technology & applied science research vol. 9, no. 1, 2019, 3721-3725 3721 www.etasr.com memon et al.: assessment of wind power potential based on raleigh distribution model… assessment of wind power potential based on raleigh distribution model: an experimental investigation for coastal zone bisharatullah memon department of electrical engineering, mehran university of engineering & technology, sindh, pakistan mazhar h. baloch department of electrical engineering, mehran university of engineering & technology, sindh, pakistan a. hakeem memon department of electrical engineering, mehran university of engineering & technology, sindh, pakistan sajid h. qazi department of electrical engineering, mehran university of engineering & technology, sindh, pakistan raza haider electrical engineering department, baluchistan university of engineering & technology, khuzdar, pakistan dahaman ishak school of electrical and electronics engineering, universiti sains malaysia, malaysia abstract—the wind energy share in the global energy production is increasing rapidly. currently, the government of pakistan (gop) is moving towards renewable energy resources (rer), specifically wind and solar energy. in this paper, the wind energy potential of tando ghulam ali, sindh, pakistan is explored. for this purpose, one-year wind speed data are considered at various heights through various probability distribution functions (pdfs). statistical comparison of rayleigh, gamma, generalized extreme value (gev) and lognormal pdfs have been done with two methods, namely root mean square error and (��) in order to select the best pdf. results showed that the rayleigh distribution function is the best at the above area for finding various factors like site selection and wind power cost per kwh. keywords-wind energy; wind probability distribution function; fitting tool i. introduction several countries are investing resources in the direction of rer. energy sources like biomass, wind energy, hydro energy, and thermal energy have gained interest because of their friendly environment features [1, 21-23]. the wind energy is a drifting rer for production of energy, and can have better results over the reliability and stability of the power system. wind power recorded a yearly development of 25% rate over the past few years [2, 20] and is based on the wind speed estimation, which is uncertain in considering wind energy and the performance of the wind energy conversion system. wind speed at a location diverges unsystematically and its deviation in a specific area over a time period and can be characterized by pdfs. several pdfs are taken to estimate the wind speed features including rayleigh, weibull, gev, lognormal and gamma [3]. to find the most accurate of pdfs, prediction performance tests are suggested. in this paper, root mean square error (rmse) and coefficient of determination (r 2 ) tests are considered. in [4], it was shown that the outcomes of the weibull distribution dignified the pdf and are more suitable as compared to the rayleigh distribution in the peak height region of nepal [4]. authors in [5] ranked 7 different methods considering the examined error of calculations regarding wind energy. authors in [6] found the wind power density in a specific location of pakistan at various heights and considered different distribution functions for wind speed calculation and from 5 numerical methods. authors in [7] examined the comparison between the lognormal and weibull techniques by fitting the curve of observed wind speeds and concluded that the weibull distribution is more reliable than lognormal distribution to pronounce the performance of wind speed data. authors in [8] explored the number of distribution techniques to find the exact wind speed data in hong kong. this study summarizes the results of wind speed data at tando ghulam ali. this study tries to find the best distribution techniques from various pdfs like: rayleigh, gamma, gev and lognormal. from the results, it was proved that the rayleigh distribution function was the best distribution technique for the studied site. ii. mathematical pdfs the estimation of wind energy at a particular site involves statistical methods of pdf, which require wind speed data at a meteorological station. similarly, frequency distribution functions are used to estimate wind power density. some types of pdfs are chi-squared distribution, rayleigh distribution, generalized normal, three parameter log-normal, log normaldistribution, gamma distribution, kappa, wake by inverse gaussian distribution, normal two variable distributions, hybrid distribution, as well as normal square root of wind speed distribution [9-11]. corresponding authors: m. h. baloch (mazhar.hussain08ele@gmail.com), d. ishak (dahaman@usm.my) engineering, technology & applied science research vol. 9, no. 1, 2019, 3721-3725 3722 www.etasr.com memon et al.: assessment of wind power potential based on raleigh distribution model… a. rayleigh distribution model rayleigh distribution function [12]: ���� � � � � ��� �� (1) the shape parameter (k) is assumed to be 2 and the scale parameter (c) is defined as: � � �������� (2) where (m) is the mean and can be obtained as: � � �� ∑ �� ���� (3) b. gamma distribution model the gamma distribution function can be defined as [13]: ���� � !�" ��#� � � $� "% (4) where, & � ��'� (5) ( � '�� (6) where (s) can be obtained as follows: ) � $ ��*�∑ ��� � ������+ % �� (7) c. lognormal distribution model lognormal distribution can be defined as [14]: ���� � � "√�.�����/0/0� �*#�" ��1 (8) parameters from (8) are estimated as: & �23 234 �5�� 6�7�8 (9) ( � 523 23�1 : '���� (10) d. generalized extreme value distribution (gev) model it is a combination of frechet, gumbel and weibull maximum extreme value distributions and can be defined as [15]: ���� � �# $1� ;# �� � <�% ��*� =�$1� ;# �� � <�% ��>if a b 0 (11) with the support of the maximum likelihood method, the parameters of gev can be obtained as: dd � 23∏ f����; h,j, 2�k0��� � ∑ f����;h, 2�k0��/ /0 (12) iii. probability distribution model evaluation in this paper, for the initial evaluation of the process the graphical display of the wind speed of measured data is being superimposed by the fitted pdfs and visual comparison is done. rmse and r 2 criteria are considered for choosing the appropriateness of the fit method for the selected three functions along with their ability to estimate the energy and to predict the wind potential. the performance of these functions is analyzed through the following ways [16]: a. root mean square error (rmse)test the value of rmse that is nearest to the zero indicates a better distribution function. the rmse is calculated as [17]: lmno � ��∑ ��� � �����p�+ (13) b. l� test the r-squared goodness of fit test is hypothesis and comparison testing that determines the correlation between the predicted and observed data. greater value of r 2 shows better fit of the pdf. it can be defined as [18]: l� � 1 � ∑ �q�r���stu�∑ �q�q���svu� (14) c. wind power density function it is defined as the power generated by wind turbine per m 2 . it is helpful in the estimation of wind resources at a site. there are many ways to determine wind power density [6], and it can be defined as follows: wxy � ∑ ��z��[��������� (15) where the probability of wind speed at the i-th speed value is f(vi). the standard value of air density is considered to be ρ=1.225kg/m 3 . iv. results and discussion the proposed site, tando ghulam ali located near hyderabad, sindh province, lies in the southern region of pakistan, at 24°52’02.025’’n and 66°51’41.983’’e. one year’s wind speed data (from jan 2017 to dec 2017), with 10 minute sample intervals were used. the typical hourly and monthly measurements are calculated at the different heights of 80, 60, 40 and 20m. the average wind speed at different heights is shown in figure 1(a-b). table i summarizes the average values of wind speed and wind power density for all heights. (a) (b) fig. 1. (a) hourly and (b) monthly average wind speed at different heights. v d iu rn a l (m /s ) engineering, technology & applied science research vol. 9, no. 1, 2019, 3721-3725 3723 www.etasr.com memon et al.: assessment of wind power potential based on raleigh distribution model… table i. monthly average of wind speed and wind power density heights 80m 60m 40m 20m months/factors vavg (m/s) wpd(watts/m 2 ) vavg (m/s) wpd (watts/m 2 ) vavg (m/s) wpd (watts/m 2 ) vavg (m/s) wpd (watts/m 2 ) jan 5.948 199.339 5.492 146.349 4.631 83.229 3.568 40.876 feb 6.201 241.862 5.743 178.793 4.753 93.854 3.513 39.094 mar 5.967 188.372 5.546 147.580 4.897 102.387 3.913 55.409 apr 7.999 394.927 7.491 326.331 6.824 254.450 5.745 160.253 may 8.623 449.674 8.238 396.278 7.712 330.572 6.662 216.206 june 8.568 485.264 8.206 431.087 7.714 365.560 6.708 245.574 jul 8.385 464.414 7.997 408.468 7.475 340.660 6.466 224.809 aug 7.723 362.365 7.309 312.404 6.764 254.442 5.831 168.981 sep 6.351 181.119 5.908 146.452 5.353 112.059 4.534 71.889 oct 5.705 166.097 5.171 114.592 4.418 67.361 3.358 30.346 nov 5.506 176.713 5.082 128.415 4.230 66.299 3.057 23.446 dec 6.859 271.994 6.141 181.989 5.056 97.521 3.765 42.218 year 6.990 3.010.112 6.531 243.228 5.824 184.041 4.767 103.934 (a) (b) (c) (d) fig. 2. fitting of different pdfs over the data using matlab distribution fitting tool. figure 2 shows the fitting of each pdf over the data. it can be observed that for 80m, 60m, and 40m, the rayleigh distribution fitted best, followed by gamma, generalized extreme value and lognormal. due to the lower wind speed at 20m, lognormal fitted best followed by rayleigh, gamma and generalized extreme value. table ii shows the value of the parameters for each pdf. table iii shows the statistical errors for the different distribution functions and the value of both rmse and r 2 goodness of fit tests. for economical evaluation the cost of each turbine is considered as $1.5/w, other initial costs like transportation, installation, grid integration etc. are taken as 40% of the turbine’s cost, the cost of the maintenance and operations is 1.5% of the turbine’s cost at interest rate of 10% and the turbine life span is taken as 20 years. table ii. parameters of different pdfs pdf 20m 40m 60m 80m rayleigh a 2 2 2 2 � 3.7314 4.4750 4.9820 5.3376 gamma α 4.402 4.9230 4.9692 4.72186 ( 1.082 1.1832 1.3144 1.4805 gev k 0.00223 -0.1254 -0.19450 -0.2173 α 1.7813 2.2135 2.5327 2.7809 l 3.7259 4.7945 5.49120 5.8888 lognormal α 1.443 1.6571 1.7727 1.8350 β 0.506 0.4932 0.5001 0.5172 table iii. statistical errors at each height height method rmse r 2 80m rayleigh 0.010418 0.954265 gamma 0.019615 0.840719 gen extreme value 0.019931 0.834948 lognormal 0.026673 0.713073 60m rayleigh 0.010568 0.960678 gamma 0.018961 0.875165 gen extreme value 0.02168 0.841316 lognormal 0.02644 0.761952 40m rayleigh 0.010357 0.969184 gamma 0.014716 0.937879 gen extreme value 0.021199 0.879976 lognormal 0.022046 0.862584 20m lognormal 0.00994 0.978188 rayleigh 0.010305 0.976476 gamma 0.010919 0.972912 gen extreme value 0.01923 0.921165 d e n si ty d e n si ty d e n si ty engineering, technology & applied science research vol. 9, no. 1, 2019, 3721-3725 3724 www.etasr.com memon et al.: assessment of wind power potential based on raleigh distribution model… v. performance and cost assessments the investment cost of a wind power plant is extremely high, it is therefore important to estimate the cost of the energy generated by a turbine in $/kwh, which can be calculated by (16) [19]: \ � p]^_+` a �bcdef$1 + �g�����h*�������h i% (16) where pr is the rated turbine power, cf is capacity factor, m is the cost of operation and maintenance, i is the rate of interest and i is the investment cost. to assess the performance and economical evaluation of wind turbines at the candidature site, five different turbines were considered whose specifications are given in table iv. each turbine comes with different hub heights. the performance of wind turbines is taken at the hub height of 80m. estimated capacity factor, annual energy output (kwh/year) and cost/kwh in dollars, for each wind turbine are shown in table v. the gamesa g128/4500 wind turbine minimum cost is $0.05453 per kwh of energy generated, with a capacity factor of 40.87%. nordex n90/2500 model also costs minimum at $0.05453 per kwh with a capacity factor of 32.88%. the highest cost of $0.08019 per kwh energy generated by vestas v112/3000 with a capacity factor of 27.78%. table iv. wind turbines specifications model enercon e82 gamesa g128 nordex n90 repower mm82 vestas v112 rated power (kw) 2300 4500 2500 2050 3000 rotor diameter (m) 82 128 90 82 112 hub height (m) 138, 78 140, 120, 81 120,100, 80, 75 100, 59 119, 84 cut-in wind speed (m/s) 2 1.05 3 3.5 3.5 rated wind speed (m/s) 14 12 13-14 15 15.5 cut-out wind speed (m/s) 25 25 25 22 25 table v. estimated cost per kwh turbine model power generated (kw) energy produced (mwh) capacity factor cost/k wh gamesa g128 183913.03 1611078.14 40.870 0.05453 nordex n90 82216.61 720217.50 32.887 0.05453 repower mm82 65076.14 570066.99 32.538 0.06849 enercon e82 73937.89 647695.92 32.147 0.06932 vestas v112 83367.15 730296.23 27.789 0.08019 vi. conclusion the study concludes that the proposed site can be utilized for commercial purpose. government of pakistan (gop) can exploit this site for wind energy power generation. four techniques, gamma distribution, rayleigh distribution, lognormal distribution, and generalized extreme value distribution were employed and their statistical evaluation was conducted by rmse and r 2 through matlab distribution fitting tool. the following points are concluded: • in comparison to other pdfs, the rayleigh distribution function fits more accurately to the wind probability distribution at higher altitudes. while at lower wind speeds, lognormal showed better fitting. • the gamesa g128 wind turbine model is recommended, having lower cost regarding generated energy, with highest capacity factor of 40.8 %. • more feasibility study of wind power project is required, to exploit wind potential at the proposed site. • results showed that the highest wind potential is available during the summer season, during may-july and can be used for power generation. calculations were made to obtain the parameter of each pdf, and then the best fitted distribution technique was used to determine the wind potential. this site is in the premises of the national grid which is another advantage of installing wind projects there. finally, this site can be employed for commercial purposes. abbreviations v=wind speed (m/s), ρ=air density (kg/m 3 ), µ=mean of wind speed (m/s), m=mean of wind speed (m/s) f(v)=probability density function s=standard deviation δ=scale parameter of gev distribution (m/s), β=scale parameter of gamma distribution (m/s), α=shape parameter of gamma distribution (dimensionless), k=shape parameter of rayleigh distribution (dimensionless), c=scale parameter of rayleigh distribution (m/s), ζ=shape parameter of gev distribution (dimensionless) φ=standard deviation of natural logarithm γ= gamma function; λ: mean of natural logarithm rmse= root mean square error, r 2 =coefficient of determination. references [1] m. h. baloch, g. s. kaloi, j. wang, “feasible wind power potential from costal line of sindh pakistan”, research journal of applied sciences, engineering and technology, vol. 10, no. 4, pp. 393-400, 2015 [2] v. sohoni, s. gupta, r. nema, “a comparative analysis of wind speed probability distributions for wind power assessment of four sites”, turkish journal of electrical engineering & computer sciences, vol. 24, no. 6, pp. 4724-4735, 2016 [3] k. w. g. d. h. rajapaksha, k. perera, “wind speed analysis and energy calculation based on mixture distributions in narak kalliya, sri lanka”, journal of the national science foundation of sri lanka vol. 44, no. 4, pp. 409-416, 2016 [4] a. parajuli, “a 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multi-parameter distributions for offshore wind speed modelling: the johnson s e distribution”, applied energy, vol. 111, pp. 982-1000, 2013 [19] a. mostafaeipour, a. sedaghat, a. a. dehgan-niri, v. kalantar, “wind energy feasibility study for city of shahr babak in iran”, renewable sustainable energy reviews, vol. 15, no. 6, pp. 2545-2556, 2011 [20] m. h. baloch, s. a. abro, g. s. kaloi, n. h. mirjat, s. tahir, m. h. nadeem, m. gul, z. a. memon, m. kumar, “a research on electricity generation from wind corridors of pakistan (two provinces): a technical proposal for remote zones”, sustainability, vol. 9, no. 9, 2017 [21] m. h. baloch, g. s. kaloi, z. a. memon, “current scenario of the wind energy in pakistan challenges and future perspectives: a case study”, energy reports, vol. 2, pp. 201-210, 2016 [22] g. s. kaloi, j. wang, m. h. baloch, s. tahir, “wind energy potential at badin and pasni costal line of pakistan”, international journal of renewable energy development, vol. 6, no. 2, pp. 103-110, 2017 [23] m. h. baloch, j. wang, g. s. kaloi, “a point of view: analysis and investigation of wind power from southern region of pakistan”, international journal of energy conversion, vol. 3, no. 3, pp. 103-110, 2015 engineering, technology & applied science research vol. 9, no. 1, 2019, 3803-3806 3803 www.etasr.com chakravorty & sharma: dvr with modified y source inverter and mcfc dvr with modified y source inverter and mcfc jaydeep chakravorty electrical engineering department indus university ahmedabad, india geena sharma electrical engineering department baddi university himachal pradesh, india abstract—power quality is a big challenge nowadays. various disturbances present in the power system are voltage sag, voltage swell, harmonics, transients, interruptions, voltage collapse etc. to solve the problem of power quality, various custom power devices are generally used in a power system, dynamic voltage restorer (dvr) being one of them. dvr is used for the compensation of voltage sag and swell. in this paper, a model of dvr with molten carbonate fuel cell (mcfc) and y source inverter is proposed. the proposed model is compared with the existing ones to check its performance characteristics. matlab/simulink was been used to check and compare the performance of the proposed with existing models. keywords-y source inverter; dvr; mcfc i. introduction most conventional inverters commonly used in power systems are voltage source inverters (vsi) and current source inverters (csi). these traditional voltage source inverters have two major drawbacks: ac output voltage is less than the dc input voltage, so it is operated only in buck mode, and two switches in the same phase leg cannot turn on simultaneously, since this will create a short-circuit in the system. to overcome these problems impedance network has proven to be more effective and efficient in power conversion between the source and the load over a wide range of electric power applications. various impedance networks have been proposed with zsource [1] impedance being the pioneer and prominent network. it has been used in dc-dc [2], dc-ac [3], and acac [4]. in the later stages some modified z-source inverters were proposed like quasi-z [5, 6], embedded-z [7, 8], series-z [9] etc. authors in [12] applied z source inverter in dvr along with molten carbonate fuel cell (mcfc). this improved the performance of the system to a great extent. in this paper, y source inverter has been used in the dvr with mcfc and its performance has been compared with existing models [10, 11]. the proposed y-source inverter consists of a dc source, yimpedance network and pulse width modulation (pwm). the complete model has been simulated in matlab/simulink. a comparison between different network topologies based on passive components count is shown in table i. ii. proposed y source inverter the proposed y-source network in this study has a diode d, two capacitors c1 and c2 and a three winding transformers (w1, w2 and w3), as shown in figure 1. table i. comparison table name of inverter number of capacitors number of inductors number of diodes z source 2 2 1 quasi z source 2 2 1 γ source 2 1 inductor, 2 windings 1 trans z source 2 1 integrated, 2 windings 1 y source 1 1 integrated winding 1 fig. 1. proposed y source inverter. the proposed y-source network has a shoot-through and non-shoot-through operation. for shoot-through-operation the circuit is shown in figure 2. fig. 2. circuit for shoot-through operation. let vw1 be the voltage drop across w1. then from the circuit of figure 2 we have: vd + vc1 = vc2 vd + vc1 = vw1 n1 n3 − vw1 n1 n2 = vw1(n3−n2) n1 or 𝑉𝑊1 = (𝑉𝑑+𝑉𝐶1)𝑁1 𝑁3−𝑁2 (1) the circuit for non-shoot-through operation is shown in figure 3. let, vi be the dc link voltage, dsh the shoot through zero state of the inverter and m the modulation index. corresponding author: j. chakravorty (jaydeepchak@yahoo.co.in) engineering, technology & applied science research vol. 9, no. 1, 2019, 3803-3806 3804 www.etasr.com chakravorty & sharma: dvr with modified y source inverter and mcfc fig. 3. circuit for non shoot through operation. from the circuit of figure 3 we have: 𝑉𝑊1 = − 𝑁1 𝑁2 1+ 𝑁1 𝑁2 𝑉𝐶1 , or 𝑉𝑊1 = − 𝑁1 𝑁1+𝑁2 𝑉𝐶1 (2) and 𝑉𝑑𝑐 = 𝑉𝑖 + 𝑉𝑊1 + 𝑉𝑊1 𝑁1 𝑁2 , or 𝑉𝑑𝑐 = 𝑉𝑖 + 𝑉𝑊1 ( 𝑁1+𝑁2 𝑁1 ) (3) again, 𝑉𝐶1 = ( 1+ 𝑁1 𝑁2 𝑁3 𝑁2 −1 )𝑑𝑠ℎ 1−( 1+ 𝑁1 𝑁3 1− 𝑁2 𝑁3 )𝑑𝑠ℎ , or 𝑉𝐶1 = ( 𝑁1+𝑁2 𝑁3−𝑁2 )𝑑𝑠ℎ 1−( 𝑁3+𝑁1 𝑁3−𝑁2 )𝑑𝑠ℎ (4) and 𝑉𝐶2 = 1−𝑑𝑠ℎ 1−( 𝑁3+𝑁1 𝑁3−𝑁2 ) 𝑉𝑊1 (5) the peak value of the dc link voltage of the inverter is: 𝑉𝑖 (𝑑𝑐𝑝) = 1 1−( 𝑁3+𝑁1 𝑁3−𝑁2 ) 𝑉𝑊1 (6) the peak value of ac voltage per phase: 𝑉𝑖 (𝑎𝑐𝑝) = 𝑀 1−( 𝑁3+𝑁1 𝑁3−𝑁2 )𝑑𝑠ℎ 𝑉𝑊1 2 (7) if the values of the capacitor c1 and c2 are selected properly then the network can give continuous current with very little ripple. iii. control technique for the proposed model, the same fuzzy controller as in [12] has been used. the simulink model of fuzzy controller is shown in figure 4. fig. 4. fuzzy control technique. iv. proposed model the proposed y source inverter has been applied to the dvr model with mcfc [12]. the complete simulink model of the dvr with mcfc, ultra-capacitor and y source inverter is shown in figure 5. fig. 5. proposed dvr model with y source inverter. the schematic model of a mcfc is shown in figure 6. a fuel cell converts chemical energy into electrical energy. in mcfc co2 gas moves from the cathode to the anode through a molten electrolyte. here molten carbonate salt acts as an electrolyte where two porous electrodes are present. the electrode layer is formed in sub layers. between the gas and the electrode a thin porous metal plate is inserted. this acts as a diffuser, it helps in helping the gas mixture to enter into the porous electrode. when the co2 combines with o2 in the cathode gives carbonate ions and when it combines with hydrogen in the anode side it gives co2 and h2o. so there will be a movement of electrolyte from the anode’s side to the cathode side. the gas reaction at the anode side is: co + h2o ↔ co2 + h2 the electrochemical half reaction is: h2 + co3 −− ↔ co2 + h2o + 2e similarly the equation of cathode side will be 1 2 o2 + co2 + 2e ↔ co3 −− fig. 6. mcfc the equivalent electrical circuit of a singular cell mcfc can be seen in [13]. authors in [12] provided the details of the operation of mcfc and the detailed matlab/simulink representation of mcfc and its application in dvr. in this paper the same mcfc model with dvr has been used. the new proposed y source inverter in this paper has been applied to this model. the proposed model in this paper is compared engineering, technology & applied science research vol. 9, no. 1, 2019, 3803-3806 3805 www.etasr.com chakravorty & sharma: dvr with modified y source inverter and mcfc with the model of dvr with mcfc, ultra-capacitor and z source inverter presented in [12]. the system parameters used for testing are given in table ii. table ii. system parameters parameters dvr with z source inverter [12] proposed dvr with y source inverter voltage 120v 120v frequency 50hz 50hz transformer 1kva 1kva load r l r l dc source mcfc mcfc type of inverter z sourced y sourced filter r=0.4ω, l=3mh, c=25μf r=1.3ω, l=38mh, c=195μf v. simulation results the profile of supply voltage, load injected voltage and load voltage of the new proposed dvr with y source inverter and mcfc is shown in figure 7. the profile of the new proposed dvr for single phase sag and swell is shown in figure 8. the profile of the new proposed dvr for three phase sag and swell is shown in figure 9. the comparison of the proposed dvr with y source inverter and the dvr model of [12] is given in table iii. the thd analysis of the model in [12] is shown in figure 10 and the thd analysis of the proposed model is shown in figure. 11. fig. 7. profile of proposed dvr with y source inverter. fig. 8. single phase sag and swell profile of proposed dvr. fig. 9. three phase sag and swell profile of proposed dvr. table iii. comparison table percentage of voltage sag dvr with z source inverter [12] proposed dvr with y source inverter percentage of thd in dvr injected voltage percentage of thd in dvr injected voltage 10 1.5 0.58 30 2.4 0.63 50 2.3 0.72 70 2.2 0.79 90 2.1 0.67 fig. 10. thd analysis of the model of [12] fig. 11. thd analysis of proposed model with y source inverter vi. conclusion the proposed model has been simulated in matlab/simulink and gave good convergence with ode23s. but the speed of simulation was observed to be very slow. the proposed inverter has more circuit elements which makes it more complicated. it has been observed that in y-source inverter voltage gain is very high when operated at higher modulation index. the proposed dvr is capable of injecting appropriate voltages even when the system is subjected to deep voltage sags, without the need to have an energy source of higher rating. the proposed dvr performs robustly with reduced thd in the load voltage while keeping the stored engineering, technology & applied science research vol. 9, no. 1, 2019, 3803-3806 3806 www.etasr.com chakravorty & sharma: dvr with modified y source inverter and mcfc energy requirement low. from the above analysis it is clear that mcfc based dvr with fuzzy control is the most efficient device for the improvement of power quality in the power system. the thd level of the proposed model was found to be low compared with the model proposed in [12]. the proposed model is thus much better in comparison with the model in [12]. references [1] f. z. peng, “z-source inverter”, ieee transactions on industry applications, vol. 2, no. 39, pp. 504-510, 2003 [2] h. cha, f. z. peng, d. w. yoo, “distributed impedance network (z network) dc-dc converter”, ieee transactions on power electronics, vol. 11, no. 25, pp. 2722-2733, 2010 [3] y. tang, s. xie, c. zhang, “z-source ac-ac converters solving commutation problem”, ieee transaction on power electronics, vol. 2, no. 22, pp. 2146-2154, 2007 [4] x. p. fang, z. m. qian, f. z. peng, “single-phase z-source pwm ac-ac converters”, ieee power electronics letters, vol. 4, no. 3, pp. 121-124, 2005 [5] j. anderson, f. z. peng, “four quasi-z-source inverters”, 2008 ieee power electronics specialists conference, rhodes, greece, august 8, 2008 [6] p. c. loh, f. gao, f. blaabjerg, a. l. goh, “buck-boost impedance networks”, 2007 european conference on power electronics and applications, aalborg, denmark, january 4, 2008 [7] j. anderson, f. z. peng, “a class of quasi-z-source inverters”, 2008 ieee industry applications society annual meeting, edmonton, canada, october 5-9,2008 [8] p. c. loh, f. gao, f. blaabjerg, “embedded ez-source inverters”, ieee transactions on industry applications, vol. 46, no. 1, pp. 256-267, 2010 [9] y. tang, s. xie, c. zhang, “an improved z-source inverter”, ieee transactions on power electronics, vol. 26, no. 12, pp. 3865-3868, 2011 [10] c. bharatiraja, s. jeevananthan, r. latha, “fpga based practical implementation of npc-mli with svpwm for an autonomous operation pv system with capacitor balancing”, international journal of electrical power and energy systems, vol. 61, no. 1, pp. 489-509, 2014 [11] g. prakash, c. subramani, c. bharatiraja, m. shabin, “a low cost single phase grid connected reduced switch pv inverter based on time frame switching scheme”, international journal of electrical power & energy systems, vol. 77, pp. 100-111, 2016 [12] j. chakravorty, g. sharma, v. bhatia, “analysis of a dvr with molten carbonate fuel cell and fuzzy logic control”, engineering, technology & applied science research, vol. 8, no. 2, pp. 2673-2679, 2018 [13] j. milewski, a. miller, “influences of the type and thickness of electrolyte on solid oxide fuel cell hybrid system performance”, journal of fuel cell science and technology, vol. 3, no. 4, pp. 396-402, 2006 microsoft word etasr_v13_n4_pp11070-11077 engineering, technology & applied science research vol. 13, no. 4, 2023, 11070-11077 11070 www.etasr.com otieno et al.: mechanical and structural correlation of lateritic soil road base stabilized with cement … mechanical and structural correlation of lateritic soil road base stabilized with cement and selected biochars meshack otieno department of civil, construction and environmental engineering, jomo kenyatta university of agriculture and technology, kenya otimeshacko@gmail.com (corresponding author) charles kabubo department of civil, construction and environmental engineering, jomo kenyatta university of agriculture and technology, kenya kabcha@jkuat.ac.ke zachary gariy department of civil, construction and environmental engineering, jomo kenyatta university of agriculture and technology, kenya zagariy@eng.jkuat.ac.ke. received: 18 april 2023 | revised: 8 may 2023 | accepted: 11 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5973 abstract the study considers the strength and structural characterization of lateritic soil road base in order to increase the strength of low-volume sealed road construction. sugar cane bagasse ash (scba) and saw dust ash (sda), mixed with soil and in combination with different percentages of ordinary portland cement (opc), were utilized in the current study. structural and mechanical characterization of the investigated samples was performed by x-ray fluorescence (xrf), x-ray diffraction (xrd), standard proctor test (spt), unconfined compression strength (ucs) test, and california bearing ratio (cbr) test. the observed increase in strength may be due to the reduction of mica, quartz, and calcite in the investigated samples. cao and sio2 contribute to the development of strength in cement, while scba, and sda-stabilized lateritic soils. the microstructural study revealed that the mica, quartz, and calcite phases play a very important role in maintaining the strength and stability of the investigated samples. keywords-strength and structural characterization; x-ray diffraction; x-ray fluorescence; sugar cane bagasse ash; saw dust ash i. introduction lateritic soils are very common in sub-saharan africa. they are easy to extract and have a relatively low operating cost, hence, they are commonly used in road construction. however, the application of these materials is subjected to meeting certain criteria defined by existing technical specifications [1-2]. soil stabilization is a technique almost as common as road construction itself. it refers to the mixing of a foreign element in the construction material for the enhancement of the engineering properties of the construction project. another important advantage is the conservation of natural construction material and controlling of waste materials from polluting the environment [3]. a common antecedent for pavement failure of most roads is the poor quality of the lateritic soil used in its construction. this soil type is mainly differentiated by its poor workability, low shear strength, high compressibility and poor bearing capacity. stabilization with an additive will help ameliorate this type of soil for use in pavement construction rather than replace them with good quality soil which is uneconomical [4]. cement and lime stabilization are the most commonly used techniques for stabilization of expansive soils. nowadays, the concentration is on the use of industrial and agricultural waste materials along with cement or lime to achieve improved strength and waste management [5-9]. bagasse is a fibrous material that remains upon crushing sugarcane to extract its juice. bagasse ash contains a high percentage of silica (sio2), and is regarded as a sensitive pozzolanic material with non-reactive actions that has the possibility to be used in road subgrade stabilization [10]. saw engineering, technology & applied science research vol. 13, no. 4, 2023, 11070-11077 11071 www.etasr.com otieno et al.: mechanical and structural correlation of lateritic soil road base stabilized with cement … dust ash consists of loose particles or burned wood chippings obtained by sawing hard wood into standard useable sizes. clean saw dust without a large amount of bark has proved to be satisfactory due to its low organic content [11]. researchers are focusing on ways of using either industrial or agricultural waste, along with other additives, as alternative materials for improving the engineering performance of the soil. the utilization of these waste materials from the industry is economical and protects the environment [12]. authors in [13] observed that the increase in strength is due to the reduction of mica in the soil and, therefore, increase of the silica in the soil increases strength and stability. a microstructural study revealed that mica phase may play very important role in maintaining the strength and stability of the soil. authors in [5] concluded that mineralogical investigation on optimum lime content stabilized soil amended with 0.5% bagasse ash indicated reduction in peaks of quartz and montmorillonite and development of new peaks corresponding to reaction products of the pozzolanic reactions. authors in [14] confirmed from xrd results that rice husk ash and pond ash both have pozzolanic behavior. therefore, both can be used as partial replacement materials for cement. authors in [15] studied the assessment of the geotechnical and microstructural characteristics of lime-stabilized expansive soil with bagasse ash and concluded that the formation of cementitious products as a result of the time-dependent pozzolanic reactions between clay and bagasse ash particles along with hydrated lime plays a key role in the improvement in the strength and stiffness of the treated soils. authors in [16] studied the role of industrial precursors in the stabilization of weak soils with geopolymers. they observed that since there were no new minerals formed after stabilization, the binding effect of the geopolymer gels likely improved the mechanical properties of the soil. ii. environmental impact most developing nations face problems from weak waste management regulation processes, therefore impacting negatively on the environment and the air quality in these countries. the lack of a framework in dealing with the waste originated from sugarcane harvest and saw mills, produces a huge volume of residues which are often burned. burning sugarcane bagasse and saw dust leads to the degradation of the air quality and the emission of harmful combustion products such as volatile organic carbons (vocs) and carbon monoxide (co). in addition, sugarcane and fertilizer waste turn into nitrate reducing water oxygen content thus negatively impacting marine life [16-24]. agricultural pollution is a main source of air and water pollution. the combustion of bagasse and saw dust produces many harmful emissions. moreover, chemicals from fertilizers and pesticides leaking into groundwater cause many health-related problems [17]. the application of these wastes in construction can reduce the negative environmental effects. iii. materials and methods the materials used in this investigation were lateritic soil (ls), ordinary portland cement (opc), sugar cane bagasse ash (scba), and saw dust ash (sda). the ls used was obtained from kamiti prisons ground in the county of kiambu, kenya. the sampling location was located at 1 ◦ 09’00.4"s, 36 ◦ 53’00.2"e. the sampled soil was dried for two days to become completely dry. the opc used was cem i 42.5n, which was produced by the bamburi cement company in kenya and obtained from thika cement yards in kiambu county. the sda was obtained from timber processing yards, kiambu town, kenya. after collection, the clean saw dust was air dried and burnt in a furnace at a temperature of 800 0 c. this burning, which is different from that done by sawmills, was done in a closed furnace so that the ash produced did not escape into the atmosphere and thereby yielded large quantities of ash with minimized environmental pollution [25]. the sda was then sieved through 600-micron sieves to remove lumps, gravels, unburnt particles, and other materials deleterious to the soil. the remaining sda was used for this study. the used sugar cane bagasse was collected from sony sugar, awendo, migori county, kenya. the air-dried bagasse was burnt in a locally constructed incinerator at a controlled temperature range between 600°c and 700°c to acquire the bagasse ash [26] and the obtained scba was passed through bs no. 200 sieve. the ls used in this study was a-2-7 according to aashto classification, with a specific gravity of 1.97 and a ph of 6.78. the engineering properties of the soil were investigated in the laboratory in accordance with bis specifications which included optimum moisture content (omc), maximum dry density (mdd), california bearing ratio (cbr), and unconfined compressive strength (ucs). the soil was initially stabilized with the addition of varying proportions of cement (0%, 3%, 5%, 7%, and 9% by weight). previous studies adopted comparably the same proportions for soil stabilization for possible use in road construction [27-31]. the specified dosages for use in road construction are 5-7% opc for clayey soils and 5-8% opc for plastic gravels [32]. against this background, this research adopted the proportions of 0-9% opc for stabilization of ls. various tests were performed on the soil-cement samples in order to obtain the optimum cement content (p%). the conducted tests included compaction characteristics and cbr in accordance to bs 1377: part 4: 1990 and ucs in accordance to bs 1924:part 2: 1990. the ucs tests were carried out on samples compacted at their omcs in the standard proctor mold with an internal diameter of 100mm and an internal height of 115mm. after establishing the optimum cement content, the other tests to determine the optimum content of cement, sda and scba were conducted as illustrated in table i and compaction characteristics and cbr in accordance to bs 1377: part 4: 1990, ucs in accordance to bs 1924:part 2: 1990 were carried out for b1, b2, b3, b4, and b5 samples. the ucs samples at 28 days for b1, b2, b3, b,4 and b5, after testing, were packed in sealable polythene bags for xrd test and the procedure adopted in [5] was used in the preparation for the samples. crystal phase evolution in the ls, cement, scba, sda, and the investigated ucs stabilized samples was done through a shimadzu xrd 6000 diffractometer at the kenya electricity generating company (kengen) in kenya. the elemental analysis of the ls, opc, sda, and scba of the investigated samples was conducted with x-ray fluorescence (xrf) through the shimadzu edx-800hs, energy dispersive x-ray engineering, technology & applied science research vol. 13, no. 4, 2023, 11070-11077 11072 www.etasr.com otieno et al.: mechanical and structural correlation of lateritic soil road base stabilized with cement … spectrometer at the materials testing and research centre of the kenyan ministry of roads and transport. table i. strength and microstructural experimental design experimental design 1st investigation 2nd investigation ls cem s/n ls cem sda scba 100 0 b1 100-p p 0 0 97 3 b2 100-p p-1-1 1 1 95 5 b3 100-p p-2-2 2 2 93 7 b4 100-p p-3-3 3 3 91 9 b5 100-p p-3.5-3.5 3.5 3.5 iv. results and discussion a. mechanical properties 1) omc, mdd, cbr and ucs for cement-stabilized ls table ii presents the omc, mdd, cbr, and ucs of the cement stabilized ls. the results show that the omc, mdd, and ucs increased with the increase in cement content. the cbr increased for cement content up to 7% to the maximum of 175.7% and then decreased to 102.6% at 9% cement content. the increase of omc may be due to the flocculation and agglomeration of clay-sized particles because the cat-ion exchange causes increase in volume. with increase in cement content, the omc increased as well, maybe due to the increase in fines content or to the increased amount of water required for the hydration of the cement [33, 34]. the increase in omc may be caused by the stabilizing binder requiring more moisture for the dissociation of the calcium ions and subsequent hydration process [4]. the increase in mdd may be due to the greater affinity of water for the hydration process. the increase in cbr can be attributed to the chemical reaction between the stabilizing binder and the soil particles which is complemented by the compaction process. the increase in the ucs values is probably caused by the cementitious properties of the stabilizing binder which aids in the solidification of the soil matrix, thereby increasing strength [4]. the reduction in cbr value at 9% may be due to the excess cement that was not mobilized in the reaction, therefore reducing the bond in the cement-soil matrix [35, 36]. the strength gain due to cement is attributed to decreased soil porosity [28, 29]. table ii. variation of omc, mdd, cbr, and ucs with cement content cement content % omc (%) mdd (g/cm 3 ) cbr (%) ucs at 28 days (mpa) 0 18.0 1.72 30.9 0.275 3 21.5 1.76 67.5 0.472 5 21.5 1.76 119.5 0.688 7 24.5 1.77 175.7 2.258 9 24.7 1.79 102.6 2.729 2) omc,mdd, cbr, ucs of cement, scba, and sdastabilized ls from table ii, it is observed that the omc of the ls is 18.0, but when cement is added at 7%, which is the optimum cement content in this research, it increased to 24.5%. with the reduction in cement content and increase in scba and sda content, there is a slight increase in the omc as shown in table iii. table ii shows that the mdd of the ls is 1.72. when 7% cement was added, the mdd increased to 1.77. with the decrease in cement content and the addition of scba and sda, the mdd depicts an increasing and decreasing trend as shown in table iii. this agrees with the results of [37]. the minimal changes may be attributed to the addition of small amounts of sda-scba in the soil-cement mixture [38]. from table ii, it is observed that the cbr of the lateritic soil is 30.9%. with the addition of 7% cement the cbr increased to 175.7% and thereafter decreased to 102.6% at 9%. the increase in values of cbr is consistent with the findings of [39-41]. the increase in the values of cbr upon the addition of cement may be attributed to the presence of adequate amounts of calcium required for the formation of calcium silicate hydrate (csh) and calcium aluminate hydrate (cah), which are the major compounds responsible for strength gain [42]. the reduction in cbr value at 9% may be due to the excess cement that was not mobilized in the reaction, therefore reducing the bond in the cement-soil matrix [35, 36]. the ucs at 28 days increased from 0.275 mpa to 2.729 mpa with the increase in cement content as shown in table ii. the increase in ucs is consistent with the findings in [43]. the strength gain due to cement is attributed to decreased soil porosity when adding cement [29] and to the compaction and hydration of cement [44]. from table iii, it is observed that with further reduction in the cement content and increase in the scba and sda content, the cbr value decreases. the gradual decrease in the cbr may be due to the excess sda-scba that was not mobilized in the reaction, which consequently occupies space within the samples and therefore reduces bond strength in the soil-cement-sda-scba mixtures [45]. the chemical reaction between the stabilizers and the soil, complimented by compaction, may be responsible for the increase of the cbr. table iii. variation of omc, mdd, ucs, and cbr with cement, scba, and sda content sample name omc (%) mdd (g/cm 3 ) ucs (mpa) cbr% (soaked) b1 24.5 1.77 2.258 175.7 b2 24.5 1.78 1.913 149.0 b3 25.2 1.76 1.139 66.1 b4 25.7 1.76 0.841 53.4 b5 26.4 1.74 0.287 32.3 b0 (soil) 18.0 1.72 0.275 30.9 in table iii, it is shown that the ucs of the ls is 0.275 mpa. with the addition of 7% cement, the ucs increased to 2.258 mpa. as the cement content decreased and the scba and sda increased, the ucs decreased as well. the decrease of the ucs is due to the soil-scba reactions and soilsda reactions which result in the formation of cementitious compounds that bind soil aggregates and the availability of sufficient water that enhances the hydration reaction of cement which reacts with silica and alumina in the ls to produce secondary cementation compounds [46-48] and calcium ions that combined with reactive silica and aluminum, or both, to form insoluble calcium silicates or aluminates and other pozzolanic products and the agglomeration of the heterogenous materials of the sda-stabilized ls and scba-stabilized ls [37, 38]. the value of ucs at b2 satisfied the kenya pavement engineering, technology & applied science research vol. 13, no. 4, 2023, 11070-11077 11073 www.etasr.com otieno et al.: mechanical and structural correlation of lateritic soil road base stabilized with cement … guideline requirement for low volume sealed roads of 1.5 mpa for road base. for stabilized materials that are rigid or semi rigid, the cbr is meaningless [32]. the most convenient strength criterion for such materials is the ucs. b. structural properties 1) semi-quantitative elemental analysis of the studied samples from xrf spectrums tables iv-v show the semi-quantitative elemental analysis of the investigated samples from xrf which included ls, cem (cement), scba, sda, b1, b2, b3, b4, and b5. cao/sio2 and cao/(sio2 + al2o3) ratios are important factors for pozzolanic reaction in the stabilization process especially at longer curing times [48]. higher strengths are achieved when the ratios are in the range of 2 to 2.5. it was further observed that stabilizer’s constituents, especially cao, play a critical role in the strength gain characteristics of stabilized soils' early strength. other oxides (sio2 and al2o3) play a significant role at longer curing times, suggesting that there could be a higher strength realized at curing periods beyond 28 days. cao and sio2 were noted to be the dominant composition of the investigated samples. this explains why there is significant decrease in ucs and cbr values with decreasing ratios as shown in table v. table iv. elemental analysis of ls, cem, scba, and sda component scba sda cem ls fe % 11.58 2.58 4.08 28.47 mgo % 4.03 0.49 al2o3 % 7.09 0.96 6.02 18.29 sio2 % 59.92 25.30 42.94 k2o % 5.13 15.71 1.28 cao % 10.39 66.07 59.50 0.46 tio2 % 1.93 0.41 2.36 p2o5 % 1.50 3.69 0.21 s % 1.11 3.75 2.63 0.14 cl % 0.21 1.15 0.001 0.004 insoluble residue % 4.41 loss on ignition at 750 o c 4.39 soil stabilization can be achieved by the pozzolanic reaction between the cao present in the stabilizers and the soil particles. when scba and sda are added to the ls and mixed with water, the ca(oh)2 dissociates into ca 2+ and oh ions. these ions cause the silica and alumina contained in the ls to dissolve and combine with ca 2+ ions to form csh and cah which are the main products of the hydration of opc and are responsible for the strength in cement-based materials. the amorphous gel (csh and cah) binds the soil matrix and it is principally responsible for the increase in strength [50-52]. but for this particular study, there was a decrease in ucs with the addition of scba and sda at 1:1 ratio. authors in [53] observed that the main constituents of scba are silicon oxide (sio2) and lower contents of calcium oxide (cao), potassium oxide (k2o), and magnesium oxide (mgo), which agrees with this investigation as shown in table iv. authors in [54] found that sda contains calcite and silica while this study shows no traces of silica in the used sda, as indicated in table iv. table v. semi-quantitative elemental analysis of the investigated samples from xrf spectrums component b1 b2 b3 b4 b5 fe % 20.6 20.7 24.8 25.1 22.1 mgo % al2o3 % 6.8 7.9 9.4 11.0 10.1 sio2 % 26.2 31.5 34.9 39.1 39.8 k2o % 1.0 1.6 2.8 2.6 4.1 cao % 39.5 31.9 20.1 14.6 16.5 tio2 % 1.5 1.9 2.1 2.3 2.1 p2o5 % 0.5 0.4 0.7 0.2 0.9 s % 1.5 1.3 1.6 0.6 0.9 cl % 0.09 0.03 0.15 0.29 0.09 insoluble residue, % loss on ignition at 750 o c [cao/sio2] 1.5 1.01 0.57 0.37 0.41 [cao/(sio2 + al2o3)] 1.19 0.81 0.45 0.29 0.33 2) structural properties of cement, scba, and sda stabilized ls from xrd analysis in figure 1 and table vi, the xrd patterns of scba show that, it contains crystalline quartz and gismondine, amorphous mica, clinochlore, chlorite, and calcite. figure 2 and table vi show that the sda contains crystalline mica, chlorite, muscovite, amorphous clinochlore, calcite, and quartz. figure 3 and table vi present the xrd pattern of cement. they show that cement contains crystalline calcite (caco3) and amorphous mica, clinochlore, cristabolite, quartz, and gismondine. fig. 1. xrd pattern of scba. figure 4 and table vi present the xrd pattern of ls. it is observed that it contains crystalline quartz, mica, clinochlore, and gismondine. authors in [17] report that ls is composed mainly of quartz, iron-magnesium-manganese, and kaolinite. this is comparable with the results obtained in this study. the xrd patterns indicated that quartz is the predominant mineral present in the ls sample. quartz is silicon dioxide (sio2) having a moh’s hardness of 7. it is a durable material and it is highly resistant to both chemical and mechanical weathering. the presence of quartz in ls adds to its durability and will aid the formation of cementitious material (csh) when mixed with scba and sda in the presence of water. other minerals present in the ls are kaolinite, moganite (sio2), gismondine, sanidine, muscovite, and dickite [52], which partly agrees with the results found in this investigation. bagasse ash in te n s it y ( in a rb t. u n it s ) 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 2-theta scale 10 20 30 40 50 60 70 80 90 q + g q + g qqq + c ln + g c cln cln m m ch ch (m=mica, cln=clinochlore, ch=chlorite, q=quartz, c=calcite, g=gismondine) engineering, technology & applied science research vol. 13, no. 4, 2023, 11070-11077 11074 www.etasr.com otieno et al.: mechanical and structural correlation of lateritic soil road base stabilized with cement … fig. 2. xrd pattern of sda. fig. 3. xrd pattern of cement. table vi. chemical composition of the investigated samples from xrd analysis sample marks phases identified from xrd cement mica, clinochlore, cristabolite, calcite, quartz, gismondine scba mica, clinochlore, chlorite, quartz, calcite, gismondine sda mica, muscovite, chlorite, clinochlore, calcite, quartz b0 (ls) mica, clinochlore, quartz, gismondine, calcite, cristobalite b1 mica, clinochlore, quartz, gismondine, calcite b2 mica, clinochlore, calcite, cristobalite, quartz, gismondine b3 mica, clinochlore, cristobalite, quartz calcite, gismondine b4 mica, clinochlore, cristobalite, calcite, quartz, gismondine b5 mica, clinochlore, cristobalite, calcite, quartz, gismondine 3) structural properties of the investigated samples b1-b5 figure 5 shows the xrd pattern of b1, which is composed of 93% ls and 7% cement, contains mica, clinochlore, quartz, gismondine, and calcite. it is observed that the ucs at b1 is at the optimum value of 2.258mpa with cbr of 175.7. it is also observed from table iv that both cao/sio2 and cao/(sio2 + al2o3) are the highest for this combination, with values of 1.5 and 1.19, respectively. authors in [49] observed that stabilizer’s constituents, especially cao, play the most vital role in the strength gain characteristics of stabilized soil's early strength. increases in the amount of (quartz) silica, lead to increase in strength and stability [13]. the xrd scatter pattern gives a clear indication of the presence of crystalline and amorphous phases in the investigation samples. crystalline phases induce sharper peaks, whereas amorphous phases result in the formation of a broad hump [5]. figure 5 shows the mineralogy of b1, i.e. 7% cement stabilized ls. it shows both crystalline and amorphous phases of quartz, mica, clinochlore, calcite, and gismondine. the stabilization process results in the complete disappearance of the cristobalite peak of the mineral phase and a reduction in the intensity of the peaks, especially gismondine [5, 56]. fig. 4. xrd pattern of ls. fig. 5. xrd pattern of b1. fig. 6. xrd pattern of b2. figure 6 and table vi present the mineralogy of b2, which consists of 5.0% cement, 1.0% scba, and 1.0% sda stabilized ls. the results show both crystalline and amorphous phases of quartz, mica, clinochlore, calcite, gismondine, and cristobalite. the stabilization process does not cause a complete disappearance of the existing peaks of mineral phases, but a reduction in the intensity of the peaks, especially sawdust ash in te n s it y ( in a rb t. u n it s ) 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 2-theta scale 10 20 30 40 50 60 70 80 90 qq + m q q c c c m m m + c ln ch ch mu mu mumu cln cln cln (m=mica, mu=muscovite, ch=chlorite, cln=clinochlore, c=calcite, q=quartz) mu cln cement in te n s it y ( in a rb t. u n it s ) 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 2-theta scale 10 20 30 40 50 60 70 80 90 q + g q + g c c + g c c c + c ln c c c c c + c ln c + c ln cr cr m + c ln m + c ln (m=mica, cln=clinochlore, cr=cristobalite, c=calcite, q=quartz, g=gismondine) bo (neat) in te n s it y ( in a rb t. u n it s ) 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 2-theta scale 10 20 30 40 50 60 70 80 90 q + g q + m + c ln + g q + c ln q + g q + g c + c r c c q + c r cr m m + c r m + c r (m=mica, cln=clinochlore, q=quartz, g=gismondine, c=calcite, cr=cristobalite) cln sample b1 in te n s it y ( in a rb t. u n it s ) 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 2-theta scale 10 20 30 40 50 60 70 80 90 q + m + c ln q + g q + c + c ln q + c ln + g q + c ln + g q c c m m c ln + g (m=mica, cln=clinochlore, c=calcite, q=quartz, g=gismondine) sample b2 in te n s it y ( in a rb t. u n it s ) 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 2-theta scale 10 20 30 40 50 60 70 80 90 q + m + g q + g q q + c ln q + gc + c r c q + c c c r+ g m m + c ln clnc ln + g g g (m=mica, cln=clinochlore, c=calcite, cr=cristobalite, q=quartz, g=gismondine) engineering, technology & applied science research vol. 13, no. 4, 2023, 11070-11077 11075 www.etasr.com otieno et al.: mechanical and structural correlation of lateritic soil road base stabilized with cement … clinochlore. this observation is similar with the results in b3 (figure 7) which consist of 3.0% cement, 2.0% scba, and 2.0% sda, b4 (figure 8) which contains 1.0% cement, 3.0% scba, and 3.0% sda, and b5 (figure 9), which contains 0% cement, 3.5% scba, and 3.5% sda. fig. 7. xrd pattern of b3. fig. 8. xrd pattern of b4. fig. 9. xrd pattern of b5. pozzolanic reactions result in the formation of new reaction products whose peaks are identified in the phase identification process. authors in [57] reported the formation of csh, calcite, and portlandite along with quartz in hydrated pastes of limescba binders. v. findings the current study involved the investigation of the effects of scba and sda to cement stabilization of ls road base. a series of cement doses were added to the ls to obtain the optimum cement content. this optimum cement content was partially replaced with scba and sda to study their effects on the strength and structure of the cement stabilized ls. the findings of the research shed light on the following critical issues:  the omc and mdd of ls increased with the increase in cement content from 18.0% to 24.7% and 1.72 g/cc to 1.79 g/cm 3 , respectively.  the cbr of ls increased with the increase in cement content up to 7%, from 30.9% to 175.7% and thereafter decreased to 102.6% at 9% cement content.  the ucs of ls increased from 0.275 mpa to 2.729 mpa with the increase in cement content.  the omc of ls stabilized with cement, scba, and sda increased from 24.5% to 26.4% with reduction in cement content and increase in scba and sda content, while the mdd reduced from 1.77 g/cm 3 to 1.74 g/cm 3 .  both ucs and cbr decreased with the reduction of cement content and increase of scba and sda content from 2.258 mpa to 0.287 mpa and 175.7% to 32.3%, respectively.  from the xrf investigation, the cao and sio2 contribute to the development of strength in cement, scba and sda stabilized lateritic soils;  from the xrd patterns, it was found that mica, calcite, and quartz phases play a very important role in the increase and decrease of the strength of the samples. vi. conclusions  scba and sda were found to successfully enhance the stabilization performance of ls.  ground improvement, subbase, and base course of flexible pavements could use scba and sda as auxiliary additives in cement to stabilize the ls. moreover, this soil stabilization technique is both cost-effective and environmentally friendly.  by using industrial and agricultural waste, it becomes possible to control the production of cement and the extraction of lime resources and also enhance the disposal and management of industrial and agricultural waste, which could be very beneficial.  the use of scba and sda in ls can provide promising stabilization effects, similar to the conventional method and can prove to be a good alternative to the existing methods of soil treatment.  the utilization of scba and sda promote waste reduction and recycling, being an environmentally friendly and sustainable green material. sample b3 in te n s it y ( in a rb t. u n it s ) 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 2-theta scale 10 20 30 40 50 60 70 80 90 q + m + g q + g q qq + g q c c c crm q + mcln cln (m=mica, cln=clinochlore, cr=cristobalite, q=quartz, c=calcite, g=gismondine) sample b4 in te n s it y ( in a rb t. u n it s ) 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 2-theta scale 10 20 30 40 50 60 70 80 90 q + g q + m + g q + c ln + g qq + m + c ln + g q qc c c crcr cln cln (m=mica, cln=clinochlore, cr=cristobalite, c=calcite, q=quartz, g=gismondine) sample b5 in te n s it y ( in a rb t. u n it s ) 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 2-theta scale 10 20 30 40 50 60 70 80 90 q + g q + c ln + g q + c ln + g q + c ln + g q + g q + m + g q cc c c + c r cr m m m + c ln cln (m=mica, cln=clinochlore, cr=cristobalite, c=calcite, q=quartz, g=gismondine) engineering, technology & applied science research vol. 13, no. 4, 2023, 11070-11077 11076 www.etasr.com otieno et al.: mechanical and structural correlation of lateritic soil road base stabilized with cement … vii. novelty/contribution to the best of our knowledge, no previous study has investigated the effects of scba-sda-cement on ls in terms of strength and microstructure. this study explored the effect of the partial replacement of cement with scba and sda in ls stabilization by considering omc, mdd, ucs, cbr, and microstructure properties. funding statement the research is funded by the 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[57] j. f. martirena hernandez, b. middendorf, m. gehrke, and h. budelmann, "use of wastes of the sugar industry as pozzolana in limepozzolana binders: study of the reaction," cement and concrete research, vol. 28, no. 11, pp. 1525–1536, nov. 1998, https://doi.org/ 10.1016/s0008-8846(98)00130-6. microsoft word etasr_v10_n6_pp6500-6503 engineering, technology & applied science research vol. 10, no. 6, 2020, 6500-6503 6500 www.etasr.com nguyen & nguyen: seismic responses of npp structures considering the effects of lead rubber bearing seismic responses of npp structures considering the effects of lead rubber bearing duy-duan nguyen department of civil engineering vinh university vinh, vietnam duyduankxd@vinhuni.edu.vn can-ngon nguyen department of civil engineering vinh university vinh, vietnam canngonkxd@vinhuni.edu.vn abstract-this study investigates the effects of lead rubber bearings (lrbs) on floor response spectra (frs) of nuclear power plant (npp) structures. three main structures in the advanced power reactor 1400 (apr1400) npp including the reactor containment building, an internal structure, and an auxiliary building were numerically developed in sap2000. the structures were modeled using beam stick elements, and lumped masses were assigned to beam element nodes. all equivalent section properties of beam elements were calculated based on the designed cross-sections of the structures. a series of 40 ground motions with response spectra scaled to match the nrc 1.60 spectrum were utilized in numerical time-history analyses. finally, a thorough comparison of frs was conducted at different elevations of the structures, considering both with and without lrb. numerical results showed that the frs of baseisolated structures at higher elevations was significantly reduced compared to non-isolated structures. however, at lower elevations, the frs was higher for the base-isolated structures compared to the non-isolated ones. additionally, at a lowfrequency range, roughly smaller than 3 hz, the frs of baseisolated structures was always greater than that of the nonisolated ones. keywords-nuclear power plant; lumped mass stick model; floor response spectrum; lead rubber bearing i. introduction recent earthquakes such as the 2011 tohoku earthquakes in japan and the 2011 mineral virginia earthquakes in usa harmed the nuclear power plants (npps) in these regions. the 2016 gyeongju and the 2017 pohang earthquakes in south korea struck close to the nearby npps showing that peak ground acceleration can be larger than the design level of npps. therefore, more studies on the seismic performance of npp structures are needed. base isolators such as lead rubber bearing (lrb) or friction pendulum systems can mitigate the possibility of damage to the civil structures and npps during an earthquake [1-4]. numerous studies have been conducted on the effects of base isolators and the seismic performance of base-isolated npp structures. the effects of the variability of properties of lrb were evaluated in [5], including the material variability in manufacturing, aging, and the operational temperature effects on the response of a base-isolated npp structure. authors in [6] analyzed the vertical seismic response of based-isolated npp structures using lrbs, comparing the maximum accelerations at the top of the structures and the specific positions between fixed and various lrb models. in [7], the effect of the second hardening of bouc-wen model was investigated for lrb on frs of a base-isolated npp. authors in [8] compared the seismic response of seismically isolated npp containment structures using equivalent linearand nonlinear-lead-rubber bearing models. moreover they quantified the seismic responses, including displacement and shear force, between non-isolated and base-isolated systems. the effect of the mechanical properties of lrb on frs of npp structures was investigated in [9], measuring frs only at the top of the structures. the frs of a seismically base-isolated npp and a comparison between frs at the top of the structure between nonand base-isolated models was analyzed in [10]. however, the aforementioned works did not sufficiently compare frs at various elevations of npp structures, where the equipment and devices are possibly located, considering with and without lrb. this study investigates the effect of lrb on frs of npp structures. three main structures in apr1400 npp including the reactor containment building, internal structure, and auxiliary building were modeled. a series of 40 ground motions with response spectra scaled to match the nrc 1.60 spectrum [12] were utilized in numerical analysis. a thorough comparison of frs at various elevations of the structures was conducted, considering both with and without base isolator. ii. ground motions this study selected 40 ground motion records from worldwide earthquakes provided by the peer center [11], and scaled to match the us nrc 1.60 design spectrum [12]. the compatible matching spectra were generated using the seismomatch tool. figure 1 shows the response spectra of input ground motions and the nrc 1.60 spectrum. iii. numerical modeling the arp1400 npp was employed as an example, focusing on the reactor containment building (rcb), the internal structure (is), and the auxiliary building (ab). the npp structures were modeled in terms of a lumped-mass stick model using elastic beam elements in sap2000 [13], as shown in figure 2. all equivalent section properties were calculated corresponding author: duy-duan nguyen engineering, technology & applied science research vol. 10, no. 6, 2020, 6500-6503 6501 www.etasr.com nguyen & nguyen: seismic responses of npp structures considering the effects of lead rubber bearing based on the structures’ design cross sections. the lumped masses were also assigned to associated element nodes. elastic shell elements were applied for the base-mat foundation. figure 3 shows the based-isolated model and the arrangement of lrbs. more details of the modeling can be found in [14-19]. fig. 1. response spectra of ground motions. (a) rcb (b) is (c) ab (d) complete finite element model of npp structure fig. 2. lumped-mass stick model of the npp structures. (a) base-isolated npp model (b) arrangement of 468 lrbs fig. 3. base-isolated npp model and arrangement of lrbs. the 1st and 2nd modes of the non-isolated npp model are the horizontal translation modes of the containment building, while the 3rd and 4th modes represent the translational modes of the auxiliary building, as shown in figure 5(a). for the baseisolated npp model, the 1st and 2nd modes are translational modes of the superstructure, the 3rd mode represents the rotational mode, and the 4th mode is the translational model of the containment building, as shown in figure 5(b). (a) mode 1, t1 = 3.858s (b) mode 2, t2 = 3.859s (c) mode 3, t3 = 5.077s (d) mode 4, t4 = 5.351s fig. 4. modal analysis results of non-isolated npp. (a) mode 1, t1 = 0.476s (b) mode 2, t2 = 0.477s (c) mode 3, t3 = 0.709s (d) mode 4, t4 = 3.786s fig. 5. modal analysis results of base-isolated npp. iv. floor response spectra a series of linear time-history analyses were performed since npp structures are expected to vibrate within an elastic 0 0.2 0.4 0.6 0.8 1 1.2 0.1 1 10 100 a c c e le ra ti o n ( g ) frequency (hz) mean scaled spectra nrc 1.60 engineering, technology & applied science research vol. 10, no. 6, 2020, 6500-6503 6502 www.etasr.com nguyen & nguyen: seismic responses of npp structures considering the effects of lead rubber bearing range during an earthquake. all ground motions were imposed on the npp models in horizontal direction. normally, the lateral acceleration or displacement responses of structures are monitored during earthquakes [20-22]. the seismic response of both nonand base-isolated npp structures was obtained in terms of the frs. frs was monitored at different elevations of rcb, is, and ab, as floor accelerations of the primary structures are input loadings to the attached secondary components, such as mechanical devices, electrical equipment or relays, piping systems, and other machines in npps [23]. figure 6 shows the frs of rcb at various elevations considering the cases with and without base isolators. the thin gray curves represent all ground motion results, while the red curve is the mean spectrum. the non-isolated model’s frs at lower elevations not only amplified at the fundamental frequency (i.e. 3.9hz), but also at a higher frequency, approximately 10.2hz. however, at higher elevations, frs of the rcb purely magnified at the fundamental frequency. the base-isolated model’s frs of rcb was amplified at a wide range of frequency approximately from 2.5 to 9.0hz at lower elevation. as the elevation increased, frs was only amplified at the fundamental frequency of rcb (i.e. 3.8hz). (a) non-isolated model (b) base-isolated model fig. 6. frs of rcb with and without lrb. figure 7 shows the comparison of mean frs of rcb at different elevations for both nonand base-isolated models. it is obvious that frs was increased from lower to higher elevations of rcb. frs of non-isolated rcb was double amplified at the top node compared to the base-isolated model, as lrb dissipates the input energy and therefore the inertial forces are reduced in the base-isolated structure. figure 8 shows the frs comparisons for each elevation with and without lrb. at lower elevations, the frs of the base-isolated rcb is higher than the non-isolated model. this is attributed to the fact that the induced acceleration is always zero at the base of the fix-based model, while the accelerations along the height are distributed in a triangular shape. meanwhile, the baseisolated model has non-zero acceleration at the base, and it is gradually increasing along the height of the structure. these observed behaviors are consistent with the findings of [10]. it should be noted that the frs of base-isolated rcb showed to be larger than those of the non-isolated structure in a lowfrequency range, smaller than 3.0hz, due to the smaller fundamental frequency of the isolated model, and therefore the frs of the base-isolated structure is amplified at the lower frequency region. these trends were also observed for is and ab. (a) non-isolated model (b) base-isolated model fig. 7. comparison of frs of rcb in various elevations. fig. 8. comparison of frs of rcb with and without lrb. v. conclusion this study conducted a series of time-history analyses to obtain the frs at different elevations of rcb, is, and ab in the apr1400 npp. the effect of lrb on frs was considered by comparing the frss between a non-isolated and a baseisolated model. a set of 40 ground motions with response spectra matching the us nrc 1.60 spectrum was used. the following conclusions were drawn based on numerical analysis results. • as elevation increases, the frs of non-isolated structures is dramatically amplified. the frs at the top of the nonisolated structures is about 2-3 times larger than in baseisolated structures. • in npp structures with lrb, the frs at higher elevation is significantly reduced compared to the non-isolated structures. however, at lower elevation, the frs is higher for base-isolated structures compared to non-isolated. 0 0.1 0.2 0.3 0.4 0.5 0.1 1 10 100 a c c e le ra ti o n ( g ) frequency (hz) frs at h = 66.5 ft (20 m) individual mean 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0.1 1 10 100 a c c e le ra ti o n ( g ) frequency (hz) frs at h = 66.5 ft (20 m) individual mean 0 1 2 3 4 5 0.1 1 10 100 a c c e le ra ti o n ( g ) frequency (hz) frs at h = 177 ft (54 m) individual mean 0 1 2 3 4 0.1 1 10 100 a c c e le ra ti o n ( g ) frequency (hz) frs at h = 177 ft (54 m) individual mean 0 2 4 6 8 10 12 0.1 1 10 100 a c c e le ra ti o n ( g ) frequency (hz) frs at h = 310.5 ft (94 m) individual mean 0 1 2 3 4 5 6 7 0.1 1 10 100 a c c e le ra ti o n ( g ) frequency (hz) frs at h = 310.5 ft (94 m) individual mean 0 1 2 3 4 5 6 7 8 0.1 1 10 100 a c c e le ra ti o n ( g ) frequency (hz) comparison of frs h = 94 m h = 70 m h = 54 m h = 31 m h = 20 m 0 1 2 3 4 5 6 7 8 0.1 1 10 a c c e le ra ti o n ( g ) frequency (hz) comparison of frs h = 94 m h = 70 m h = 54 m h = 31 m h = 20 m 0 0.2 0.4 0.6 0.8 1 1.2 0.1 1 10 100 a c c e le ra ti o n ( g ) frequency (hz) frs at h = 66.5 ft (20 m) base-isolated non-isolated 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0.1 1 10 100 a c c e le ra ti o n ( g ) frequency (hz) frs at h = 102 ft (31 m) base-isolated non-isolated 0 0.5 1 1.5 2 2.5 3 3.5 4 0.1 1 10 100 a c c e le ra ti o n ( g ) frequency (hz) frs at h = 177 ft (54 m) base-isolated non-isolated 0 1 2 3 4 5 6 7 8 0.1 1 10 100 a c c e le ra ti o n ( g ) frequency (hz) frs at 310.5 ft (h = 94 m) base-isolated non-isolated engineering, technology & applied science research vol. 10, no. 6, 2020, 6500-6503 6503 www.etasr.com nguyen & nguyen: seismic responses of npp structures considering the effects of lead rubber bearing • at low frequency range, roughly smaller than 3hz, the frs of base-isolated structures is always larger than in nonisolated. • at the frequency of 12.1hz, the spectral acceleration of the base-isolated ab at various elevations is smaller than in non-isolated ab. references [1] t. h. lee and d.-d. nguyen, "seismic vulnerability assessment of a continuous steel box girder bridge considering influence of lrb properties," sādhanā, vol. 43, no. 1, p. 14, feb. 2018, https://doi.org/ 10.1007/s12046-017-0774-x. 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[23] h. s. park, d.-d. nguyen, and t. h. lee, "effect of high-frequency ground motions on the response of npp components: a state-of-theart review," journal of the korean society of hazard mitigation, vol. 17, no. 6, pp. 285–294, dec. 2017, https://doi.org/10.9798/ kosham.2017.17.6.285. engineering, technology & applied science research vol. 8, no. 4, 2018, 3184-3188 3184 www.etasr.com siddiqui et al.: health and safety issues of industry workmen health and safety issues of industry workmen fida siddiqui department of civil engineering mehran university of engineering & technology, jamshoro, pakistan fidasiddiqui2@gmail.com muhammad akram akhund department of civil engineering isra university, hyderabad, pakistan akhund42@gmail.com aftab hameed memon department of civil engineering quaid-e-awam university of engineering science and technology, pakistan aftabm78@hotmail.com ali raza khoso department of civil engineering mehran university of engineering & technology jamshoro, pakistan aliraza.khoso@faculty.muet.edu.pk hafiz usama imad department of civil engineering isra university hyderabad, pakistan usama.imad@isra.edu.pk abstract—flour milling is considered the oldest trade industry, initiated at least 6000 years ago. like every other industry, numerous problems arise during functioning and maintenance operations. the production process involves the breakdown of grains to separate their outer covering and inner endosperm grinding to fine flour particles. workers serving in the industry have been in an environment exposed to flour dust. after conducting several interviews and a questionnaire survey to the workers and sales managers of flour mills within hyderabad in pakistan, the workforce was found to be suffering from sensitization, occupational asthma, allergic rhinitis, obstructive lung diseases and eye infection. the core reason was the inhaled and swallowed flour dust. the majority of the respondents highlighted the improper flour milling process including intake and final product collection systems as the main causes of these health problems. the other part of the research work revealed that the majority of safety issues emerged due to the unavailability, the failure to use and the unawareness of personal protective equipment. regarding the suggestions received during the survey from respective stakeholders, the health and safety issues can be controlled by improving feeding and collection systems and by wearing personal protective equipment. keywords-flour milling industry; health issues; personal protective equipment; safety concerns i. introduction flour dust has been of an imperative importance in flour milling process from the beginning. several food industries including flour mills are facing the issue of exposure to flour dust. in developing countries, due to quick industrialization and fruitless measures for pollution control, indoor air pollution has become a main problem and the lack of public awareness of the impacts of indoor air pollutants on human health has increased it. flour mill workers are expected to be exposed to such threats for 8-10 hours per day averagely [1]. a handful of studies showed that exposure to flour dust causes respiratory symptoms and is highly related to lung function damage [2-3]. in mills, grinding operation is the initial point of danger in processing grains, as grain is ground into fine particles of dustlike size and flammable concentrations are unavoidable [4]. studies also show that potential allergens implicated are the components of wheat flour contaminants, such as weevils, mite sand moulds, or flour additives, especially yeast and aspergillus derived amylase [5]. flour dust can cause sensitization, occupational asthma and allergic rhinitis [3]. in flour mills, there is potential exposure to grain dust [6]. individuals who work in dusty environments face the risk of inhaling particulate materials which may lead to adverse respiratory effects [7]. in the baking industry, exposure to wheat flour dust may cause respiratory illness of different nature and severity, ranging from simple irritant symptoms to allergic rhinitis or occupational asthma. sensitization to such allergens may result in increased prevalence of respiratory symptoms and airway hyper responsiveness [5]. authors in [8] investigated the effect of exposure to flour dust on respiratory symptoms and lung function of flour mill workers and estimated the additive effect of smoking on pulmonary function. two hundred male workers with current exposure to flour dust and two hundred non-exposed male workers as a control group were interviewed and answered a self-designed study questionnaire and the parameters of their pulmonary function were measured. results indicated that respiratory symptoms such as cough, expectoration, wheezing and shortness of breath, were significantly (p<0.0001) higher among exposed workers when compared to unexposed workers. occupational hazards are inherent for individuals working with machines, especially when the machines are rotating and are unprotected. mishaps associated with flour mills are infrequent most likely due to the small setup involving less manpower or due to partition that is usually made between the machine and the worker reducing the accidental involvement in the machine. nevertheless, workers in the setup may, at times, involve in accidents [9-10]. another leading problem in several industries, including flour milling, is the un-availability and unawareness of personal protective equipment (ppe). several accidents occur because workers engineering, technology & applied science research vol. 8, no. 4, 2018, 3184-3188 3185 www.etasr.com siddiqui et al.: health and safety issues of industry workmen ignore safety measures during working hours. in many of the industries of developing countries, the unavailability of ppe is very common. in some industries, ppe is available but there are no regarding rules and regulations and no training is provided to ensure the use of ppe. study of some companies in nigeria’s north-eastern states shows that the causes of accidents in companies are the carelessness of the workers and to some extent the lack of machinery maintenance [11]. chronic obstructive pulmonary disease (copd) is a global health concern. according to the world health organization (who), it is presently the sixth leading cause of death in the world. indoor and outdoor air pollution and tobacco exposure are the main reasons. the burden of copd in asia is at present greater than that in the developed western countries [12]. there are about 75,000 workers in the united kingdom baking industry [13] with some 24,000 in occupations where exposure to flour is likely [14]. a smaller but unidentified number of workers are involved in milling and wheat processing. results from the surveillance of work-related and occupational respiratory disease (sword) project suggest an annual incidence of occupational asthma among bakery workers of at least one per 1000 [15]. aerosols like fine particles, so2 and co gases can enter into the trachea-bronchial and create frustrating effects in the respiratory tract. if exposed to pollution, the usual response of an individual would be in the forms of bronchospasm, cough, excessive production of mucus etc. and can lead to emphysema, fibrosis of the lungs if exposure is chronic [16]. the current study on flour mills revealed that workers are at substantial risk with two main problems causing severe health issues and accidents. the first one is the improper flour milling process including intake and final products collection systems. the second problem is the unawareness and unavailability of ppe. the intake system of feeding the wheat and the final product collection methods were the main causes of exposure to dispersed flour dust. there was neither a controlled mechanical system for opening the gate of intake hopper nor proper underground pits to place the bulk amount of wheat. on the other side, the concrete tanks built to collect and store the final products were uncovered. packing was carried out simultaneously. workers were required to put wheat from the intake hopper simultaneously when the bucket elevator was lifting grains to drum sieve. during this entire feeding process intake, hopper’s gate remained open and ample amount of dust was found rushing out and was directly inhaled. allergic rhinitis, asthma, obstructive lung diseases, and sensitization were found common in workers of these flour mills, in different ratios, elaborated in the result section. this study has been carried out on the flour mills of hyderabad city, pakistan in early 2017. ii. materials and methods numerous studies were taken into consideration to finalize the issues of flour mills’ workmen to solidify our work. initially, various reasons which contribute to the raising of accident rate and health issues at flour mills were identified from previously conducted research works throughout the world. as a part of the preliminary survey, unstructured interviews of workers, technicians, and managers of flour mills were conducted to finalize factors. a questionnaire was then prepared. it contained the factors to analyze the severity level and the workers were asked to fill up. collected data was analyzed by average index (ai) technique utilizing the statistical package for the social sciences (spss). the collaboration of flour milling technical, administrative and working staff helped to map out possible remedial measures and recommendations. the pictorial view of the methodology is shown in figure 1. fig. 1. methodological flowchart iii. results and discussion the ai value, calculated with the equations adopted from [17-18] is used in this research for factor analysis. the respondents were asked to encircle the appropriate item according to their experience. data was collected by a survey conducted through questionnaires. quantitative data analysis was done based on the likert scale (1-5). various demographical variables were inquired from the respondents along with the main focused health and safety issues of the industry. the respondents were a variety of people: workers, technicians and sales managers and their respective percentages are mentioned in figure 2 whereas figure 3 reports the number of years of experience of the respondents. fig. 2. occupation level engineering, technology & applied science research vol. 8, no. 4, 2018, 3184-3188 3186 www.etasr.com siddiqui et al.: health and safety issues of industry workmen regarding the demographic portion, the bar-chart shown in figure 4 depicts that majority (16) of people were uneducated as they were at a ‘worker’ grade in the industry. twelve workers were educated up to a primary level only. collectively, technicians and sales managers only were found out to be educated up to the graduation level. fig. 3. experience level fig. 4. education level table i enlists all the factors that contribute to accidents and health issues at flour mills along with their corresponding ai values. data analysis showed that dispersion of flour dust is found common in all flour mills with the highest severity level (ai=4.3). 36 out of 40 stakeholders collectively identified this factor as severe and very severe for creating health concerns. this dust is inhaled, swallowed and absorbed by workers leading to various diseases. results reveal that the reasons behind dispersion of flour dust were the improper feeding system of grain and the improper final product collection system as shown in figure 6. the second, third and fourth most critical factors are failure, unavailability and unawareness to use ppe with average index values of 3.72, 3.65 and 3.25 respectively. these three factors lead to accidents. as the owners of these small-scale flour mills are just concerned with the monetary benefits, no use of ppe was observed. because of being less educated, almost all workers were unaware of the safety measures which could be taken on site during working. that’s why 24 respondents marked ‘failure to use ppe’ as ‘severe’. apart from these reasons, the other leading causes of accidents were found to be the improper and heavy lifting of flour bags by the workers. many workers were less experienced so, they weren’t good at proper and easy techniques for lifting objects. figure 5 highlights the three main processing systems that contribute in flour dust dispersion. respondents had the choice to mark multiple options if more than one system contributed to the indoor air pollution. the systems marked come under category of flour milling process and nearly all workers, technicians and sales managers marked flour milling process as a cause of flour dust dispersion. thus, the systems need to be assessed properly in order to avoid such problems. fig. 5. the systems contributing in flour dust dispersion the preliminary survey performed at different flour mills in the region of hyderabad consisted of questions regarding whether the workers were suffering from any health issues before joining their milling job. as the workers’ experience ranged from 3 to 6 years, the majority of people readily responded that they faced these issues during their current job. as shown in figure 7, workers were found suffering from different health issues such as allergic rhinitis, sensitization, occupational asthma and lung diseases mainly because of the flour dust inhaled during working hours. it is known that smoking also leads to various diseases, so a question was deliberately asked in the questionnaire regarding the smoking habits of workers. analysis showed that only 5% people were smokers which further strengthened the results of multiple health issues due to flour dust dispersion. fig. 6. critical factors those contribute to accidents and health issues at flourmills engineering, technology & applied science research vol. 8, no. 4, 2018, 3184-3188 3187 www.etasr.com siddiqui et al.: health and safety issues of industry workmen table i. factors contributing health and safety issues # factors ns ss ms s vs ai median rank fah1 dispersed flour dust 1 2 1 16 20 4.30 4.50 01 fah2 ppe unavailability 0 2 14 20 4 3.65 4.00 03 fah3 ppe unawareness 4 3 16 13 4 3.25 3.00 04 fah4 electrical shock incident 34 6 0 0 0 1.15 1.00 16 fah5 noise sparking 30 10 0 0 0 1.25 1.00 13 fah6 sparking 39 1 0 0 0 1.02 1.00 17 fah7 improper lifting 1 24 15 0 0 2.35 2.00 06 fah8 carrying heavy loads 2 18 16 4 0 2.55 2.50 05 fah9 improper gripping 26 14 0 0 0 1.35 1.00 12 fah10 failure to use ppe 1 1 10 24 4 3.72 4.00 02 fah11 lifting greasy objects 32 8 0 0 0 1.20 1.00 14 fah12 poor physique 9 18 13 0 0 2.10 2.00 07 fah13 objects having sharp edges 30 10 0 0 0 1.25 1.00 13 fah14 foot injuries due to dropped objects 9 30 1 0 0 1.8 2.00 10 fah15 slipped disc due to improper posture in object lifting 5 35 0 0 0 1.87 2.00 09 fah16 strains to wrist or fingers 5 35 0 0 0 1.92 2.00 08 fah17 sprains, wounds hernias, fractures 6 33 1 0 0 1.87 2.00 09 fah18 getting hit by falling objects from overhead 9 31 0 0 0 1.77 2.00 11 fah19 falling in open tank without cover in level floor 33 7 0 0 0 1.17 1.00 15 fah20 accidents due to poor lighting 32 6 2 0 0 1.25 1.00 13 iv. remedial measures to control health and safety issues the following measures are suggested: 1. the mill owners must ensure proper use of ppe. 2. the workers should demand the usa of ppe to minimize the risk of accidents. 3. health and safety seminars should be conducted at a local level in languages understood by the workers. 4. intake and collection system should be modified. 5. processing facilities should be designed in a way that there should be a proper mechanical system of opening the gate of intake hopper. 6. underground pits of reasonable height should be built or grain intake pits on the ground should be designed to feed the bulk amount of wheat at once to reduce continuous exposure to dust. 7. the tank, where final products are collected and packed should be covered in order to prevent flour dispersion in the surrounding environment. 8. simultaneous packing and production should be avoided by increasing the size of final product collection tanks without compromising demand and supply. v. conclusion and recomendations being the oldest one at the global level, flour milling industry is frequently prone to hazard issues especially at local and regional levels that are not being monitored properly. this cross-sectional study is based on unstructured interviews and questionnaires. it was carried out in order to identify the health and safety issues of flour milling industry workmen of hyderabad, sindh. out of numerous factors, dispersed flour dust and ignorance towards ppe are highly ranked. workers did suffer from severe health impacts like allergic rhinitis, occupational asthma and lung diseases mainly because of flour dust dispersion. the reasons behind the sources for dispersion of flour dust were feeding and final product collection systems. on the other hand, ppe were unavailable and hence no such awareness amongst workers was observed. by considering the literature review and data evaluated during this study all problems should be addressed with keen importance at each concerned level. a study can be performed at a regional level again by developing a monitoring system for the period after the implementation of remedial measures suggested in the current study, to analyze the results. fig. 7. common workmen diseases in flourmill industry references [1] n. d. wagh, b. g. pachpande, v. s. patel, s. b. attarde, s. t. ingle, “the influence of workplace environment on lung function of flour mill workers in jalgaon urban center”, journal of occupational health, vol. 48, no. 5, pp. 396-401, 2006 [2] n. a. h. ajeel, a. k. al-yassen, “work-related allergic disorders among flour mill workers”, the medical journal of basrah university, vol. 25, no. 1, pp. 29-32, 2007 engineering, technology & applied science research vol. 8, no. 4, 2018, 3184-3188 3188 www.etasr.com siddiqui et al.: health and safety issues of industry workmen [3] s. k. dhillon, r. bassi, r. g. thamman, “effect of flour dust on lung volumes and capacities in flour mill workers”, national journal of integrated research in medicine, vol. 3, no. 2, pp. 91-95, 2012 [4] m. mittal, “explosion hazard and safety in industries handling grain products”, journal of engineering research and studies, vol. 1, no. 3, pp. 1-11, 2013 [5] a. b. bohadana, n. massin, p. wild, m. n. kolopp, j. p. toamain, “respiratory symptoms and airway responsiveness in apparently healthy workers exposed to flour dust”, the european respiratory journal, vol. 7, no. 6, pp. 1070-1076, 1994 [6] t. a. smith, g. parker, t. hussain, “respiratory symptoms and wheat flour exposure: a study of flour millers”, occupational medicine, vol. 50. no. 1, pp. 25-29, 2000 [7] a. m. said, e. b. abdel fattah, a. a. m. almawardi, “effects on respiratory system due to exposure to wheat flour”, egyptian journal of chest diseases and tuberculosis, vol. 66, no. 3, pp. 537-548, 2017 [8] m. a. mohammadien, m. t. hussein, r. t. el-sokkary, “effects of exposure to flour dust on respiratory symptoms and pulmonary function of mill workers”, egyptian journal of chest diseases and tuberculosis, vol. 62, vol. 4, pp. 745-753, 2013 [9] r. c. oginyi, o. s. mbam, c. o. abojei, o. n. james, “assessment of occupational health hazard and the use of safety measures among rice mill workers in ebonyi state, nigeria”, world applied sciences journal, vol. 35, no. 7, pp. 1133-1141, 2017 [10] r. bardale, s. dhawane, “fatal avulsion of scalp: unusual occurrence at flourmill”, journal of indian academy of forensic medicine, vol. 30, no. 3, pp. 151-152, 2008 [11] a. o. inegbenebor, “the effect of accidents on the productivity of some companies in north-eastern states of nigeria”, j. soc. & mgt. sci, vol. 6, pp. 46-52, 1999 [12] b. iftikhar, m. h. khan, h. hussain, m. iqbal, g. s. jadoon, “relationship between silica dust exposure and chronic obstructive pulmonary disease in workers of dust generating industries of district peshawar”, gomal journal of medical sciences, vol. 7, no. 1, pp. 4650, 2004 [13] u.k. office for national statistics, labour force survey 2017, available at: http://www.ilo.org/surveydata/index.php/catalog/1807/ study-description, 2017 [14] hse, a baker's dozen: thirteen essentials for health and safety in bakeries, hse books, 2003 [15] p. cullinan, d. lowson, m. j. nieuwenhuijsen, c. sandiford, r. d. tee, k. m. venables, j. c. mcdonald, a. j. newman taylor, “work related symptoms, sensitisation, and estimated exposure in workers not previously exposed to flour”, occupational and environmental medicine, vol. 51, no. 9, pp. 579-583, 1994 [16] g. m. latha, k. sarala, s. gouroju, “effect of construction and flour mill air pollution in rural area”, international journal of integrative medical sciences, vol. 2, no. 2, pp. 70-77, 2015 [17] j. m. hussin, i. a. rahman, a. h. memon, “the way forward in sustainable construction: issues and challenges”, international journal of advances in applied sciences, vol. 2, no. 1, pp. 15-24, 2013 [18] a. r. khoso, m. a. akhund, a. h. memon, f. siddiqui, s. h. khahro, “health and safety of hyderabad industries’ labor. causes and awareness”, engineering, technology & applied science research, vol. 7, no. 6, pp. 2334-2339, 2017 microsoft word etasr_v11_n5_pp7591-7597 engineering, technology & applied science research vol. 11, no. 5, 2021, 7591-7597 7591 www.etasr.com bangar raju & subba rao: evaluation of passive islanding detection methods for line to ground … evaluation of passive islanding detection methods for line to ground unsymmetrical fault in three phase microgrid systems microgrid islanding detection method l. bangar raju electrical and electronics engineering department koneru lakshmaiah educational foundation guntur, india lsmlbr@yahoo.in k. subba rao electrical and electronics engineering department koneru lakshmaiah educational foundation guntur, india principal.coe@kluniversity.in abstract-distributed generators (dgs) are incorporated in the power distribution systems to develop green energies in microgrids. islanding is a challenging task in a microgrid. different types of islanding methods, e.g. local and remote methods, have been developed for handling this task, with local methods being easier to implement, while remote methods are communication-based and costly. the local methods are classified as passive, active, and hybrid, out of which the passive methods are more simple and economical. in this paper, a passive islanding detection method is proposed to detect single line to ground fault. this fault is considered to represent the 60 to 70% of the total un-intentional faults of this category. the available passive methods cannot detect islanding at lower power mismatches as the variations in voltage and frequency fall within thresholding values. in this method, the voltage signals are first retrieved at the targeted dg output and then the phase angle is estimated. finally, the phase angle is differentiated to get rate of change of voltage phase angle (rocovpa) to detect islanding, and then it is compared with the rate of change of frequency (rocof) at zero percent power mismatch. simulation results depict that the rocovpa is more effective than rocof. the proposed method not only reduces detection time and nondetection zone (ndz) but is also stable during non-islanding cases like load connection and disconnection to avoid nuisance tripping. keywords-distributed generation; non detection zone; point of common coupling; rocovpa; rocof; line to ground fault i. introduction during the normal mode, a microgrid is in synchronism with the main grid feeding the connected loads and importing the mismatch power of the load from the grid. based on load demand, the mismatched power is supplied by the grid. but during unintentional unsymmetrical faults on the system, the microgrid has to detect the fault condition and isolate itself from the main grid within 2s as per ieee-1547-2018 regulations. there are symmetrical and unsymmetrical faults, but in this paper only unsymmetrical single line to ground fault was tested as the majority of faults are of this nature. the different islanding detection methods have their own advantages and disadvantages. the active methods affect the power quality due to perturbations during testing. the passive methods fail to detect islanding at lower power mismatches due to the smaller variation in voltage and frequency above threshold. the hybrid methods are good to detect islanding but power quality problems arise due to injections of perturbations. communication methods are good with a smaller non detection zone (ndz) but are costly. the implementation of such methods depends on the size of the microgrid and the criticality of loads. to mitigate these problems, in this paper the rate of change of voltage phase angle (rocovpa) method is proposed which detects islanding at zero percent mismatch power and also avoids nuisance tripping during non-islanding operations like load connection and disconnection. a simple methodology is used. at first, the voltage phase angle is calculated at the output of dg and then differentiated to get the rocovpa to detect islanding. in normal conditions, when there is no fault, the variations are within the threshold values but during fault conditions the variations exceed the threshold values to island the microgrid safely from the main grid within 2s. the dg feeds the connected load in droop control in islanded mode, without any power interruption to load. the proposed rocovpa methodology can be extended to detect symmetrical and unsymmetrical faults. in this paper, the rocovpa is tested and compared with the rate of change of frequency (rocof) method in matlab/simulink, in which rocovpa is proved to perform better. as per the result analysis, the proposed rocovpa method detects islanding at even zero percent mismatch power (0% ndz). the testing is extended for non-islanding cases during load connection and disconnection for stability. the rocovpa method is proved to be stable during non-islanding cases and also avoids nuisance tripping. the comparison of the proposed rocovpa method with rocof proves that it is better in discriminating islanding and non-islanding operations with less ndz and detection time. corresponding author: l. bangar raju engineering, technology & applied science research vol. 11, no. 5, 2021, 7591-7597 7592 www.etasr.com bangar raju & subba rao: evaluation of passive islanding detection methods for line to ground … ii. network and mathematical model the network model is shown in figure.1. the rocovpa islanding detection method is tested on a dg with 2.5kw with an interfaced inverter. a parallel rlc load is connected to the dg with a quality factor of 1.8 at the point of common coupling (pcc). the dg inverter is connected to the main grid to the pcc through a 3-phase circuit breaker. the inverter is connected to the pcc with filter values: ��=2�� ,��=2� , and �=10�. fig. 1. network model of the islanding detection rocovpa method. the mathematical model of the islanded microgrid in the abc frame is given by the following equations: �,��� � �� � ��,��� �� � � ��,��� � ��� (1) ��,��� � � ��� /r � �!,��� � � ��� ��� (2) ��� �� � � �"# � �$,��� � $ �$,��� (3) where �,��� , vabc, it,abc, and il,abc are the terminal's phase voltages and currents respectively of the inverter at the pcc . these three-phase instantaneous voltages and currents are to be transformed to the synchronous rotating frame dq0 in order to have control of active power (d-axis) and reactive power (q-axis), to keep mutual inductance constant, to achieve the desired output, to have infinite gain control on pi, pid, by adjusting integrators, and to make steady state error to zero to make computations easy. )()()( tbutaxtx += (4) )()( tcxty = (5) tdvtu =)( (6) a, b, c, and d are constants given by: 1 0 0 02 00 0 1 20 0 0 1 1 1 0 rt l lt t rlcrt l la rrl c l l c c rc ω ω ωω ω ω ω                          − − − − = − − − − − (7)       = 000 1 t t l b (8) [ ]0000=c (9) [ ]0=d (10) %& � '��� ��( �$� �) (11) these equations give the transfer functions of td d v v , where dv and tdv are the input and output components of the d axis. iii. non detection zone the efficacy of islanding detection depends on minimizing the ndz [4, 5]. the method depends on the percentage of active power mismatch, which as per ieee-1547 has to be smaller than 15% and the detection time has to be less than 2s. the network for the study of ndz is shown in figure 2. the dg is connected to the grid through an interfacing inverter, the pcc, and a utility switch [6]. the 3-phase parallel rlc load is connected at the pcc [7]. xdg grid p+jq p+jq circuit breaker local load utility switch r p j q∆ + ∆ l l l p jq+ c fig. 2. dg network connected with the grid system. equations (12) and (13) give the voltage and frequency at the pcc: r v pp 2 =∆+ (12) fl v qq π2 2 =∆+ (13) ( )pprv ∆+= (14) ( )qql v f ∆+ = π2 2 (15) in islanding conditions, δ+ and δ, become zero, as there is no main grid. the under/over voltage protection (uvp/ovp) and under/over frequency protection (ufp/ofp) methods are very simple and incorporated in all grid connected inverters and relays connected with dg system protection. in these engineering, technology & applied science research vol. 11, no. 5, 2021, 7591-7597 7593 www.etasr.com bangar raju & subba rao: evaluation of passive islanding detection methods for line to ground … methods, the voltage and frequency are both constantly monitored at the pcc [1, 8], where: ∆p = +$-./ − +/0 (16) ∆q = ,$-./ − ,/0 (17) if ∆p 1 0, then the voltage at pcc will fluctuate from the normal level, which is an indication of islanding condition. if ∆q 1 0, then the frequency at pcc will fluctuate from the normal level, which is an indication of islanding condition. both these islanding detection methods leave behind a large ndz. the islanding detection may fail, when ∆p and ∆q are close to zero [8]. voltage 3 and frequency �3 under islanding mode are given by: 3 � 4 5+6 (18) � 3 � 7389:$5;6 � <= 9:$5;6 (19) with these, the voltage and frequency deviations due to power mismatches are given by: > � v’ – v � 4 5+6 c 5+ � >+6 (20) >� � �3 d � � 738$5;6 738 $5; ef;6� <g= $g; <g5=efh6 $g5;ef; 6 (21) equations (20) and (21) show the variations in voltage and frequency due to power mismatch [2]. if the power mismatch is substantial, the variations in voltage and frequency can be identifiable. if the mismatch is too small (less than 15%) the islanding cannot be detected and hence the formation of the ndz. figure 4 shows the ndz for different power mismatch percentages [8, 9]. when the reference value is 88% and 110% (as per table i), under / over voltage and grid rms voltage i = 415v, then vmax = 456v and vmin = 365v. the schematic diagram of the grid-connected microgrid is shown in figure 3. the inverter gate pulses take the feedback grid voltage and the set reference. the trigger pulses are given to the inverter accordingly and the output voltage is controlled. the pv is connected to the buck/boost converter to have control on dc reference voltage. the dc/dc converter is connected to the interfacing inverter. the inverter is connected to the pcc via a low pass filter lcl. the microgrid is connected to the grid via a circuit breaker, so that the microgrid can be islanded during faults. a local parallel rlc load is connected to the microgrid at the pcc and the microgrid feeds this local load from the dg, even in the absence of grid. fig. 3. schematic diagram of the grid-connected micorgrid. ndz is the operating region in which islanding detection methods cannot detect islanding as specified by ieee-1547. it is expressed in terms of % power mismatch or in terms of parameters of the load like r, l, and c. the ndz of ovp/uvp and ofp/uvp islanding schemes are shown in figure 4 [10, 11]. these techniques fail to detect islanding in mismatched power less than 15%. in a distribution network, voltage values, as per standards are between 0.88p.u. and 1.1p.u. for voltage relays. these voltage levels are equivalent to dv = 0.12p.u. and dv = 0.1p.u. respectively. the calculated power mismatch for our test network (the inverter rated output power is 2.5kw) are 0.3kw and 0.25kw respectively. fig. 4. mapping of the ndz in ∆p versus ∆q for ovp-ufp relays. in grid mode, the load consumes the reactive power [12]. but in islanding mode, dgs cannot inject reactive power to the load, as dgs operate at unity power factor, because the load behaves like a resistance [13], since the load resonance frequency is equal to the system frequency at the pcc. hence, to find more deviations in frequency, the load selected is parallel rlc with a high quality factor of 1.8 in islanding mode [14, 15]. the quality factor is given by: ,j � kl � � mno$ � c p $ (22) where kl � 2r�l � s√$p. equation (20) gives the energy stored in the rlc circuit. high quality factor loads have high capacitance and small inductance with or without a high parallel resistance [16, 17]. the islanding detection is complex with resonant frequency loads of higher quality factor [18, 19]. the percentage mismatch is not the criterion for load parameters [20, 21]. the load reactive power is given by: ,$u�� � v�w9 x sn$ d k� y � δ, (23) equation (21) depicts the variation in reactive power for different values of l and c. the % mismatch power for ovp/uvp and ofp/ufp relays is shown in figure 3 and is given by the equations for active power imbalance: ∆p = 3vgi–35 � ∆ 6g [ � d3 g∆vg[ (24) ∆q = 3 ]8 n^ $ 51 d k9��6=3 ]8 n^ $ `1 d n8̂ na8b (25) where kc and kd are system and resonance frequencies [22, 23]. the system frequency varies until it reaches the resonant frequency of the load in islanding mode and is given by: engineering, technology & applied science research vol. 11, no. 5, 2021, 7591-7597 7594 www.etasr.com bangar raju & subba rao: evaluation of passive islanding detection methods for line to ground … kde s√$p (26) and the reactive power imbalance is given by: ∆q = 3 ]8 n^ $ f1 d ĵ8 gj^h∆i8jk (27) where �c is the nominal frequency. the different islanding standards are shown in table i. the frequency range as per ieee-1547-2018 is between 49 and 51hz, the voltage is between 365 and 456v and the range of the parameter ∆v= v’ – v is not considered as the case of zero power mismatch is considered [24]. in this case, the voltage fluctuations will not cross the limits. but in other cases, when load active power pl > generated active power pg,(-15%) or pl < pg (+15%) the voltage suddenly goes down or up respectively. table i. islanding standards standard detection time (s) quality factor trip frequency range, nominal frequency lm (hz) trip voltage range (v) iec 62116 t < 2 1 �l d15n � n �l+1.5 0.88 n n1.15 korean t < 0.5 1 59.3 n �l n 60.5 0.88 n n 1.10 ieee-15472018 t < 2 1 58.8 n �l n 61.2 0.88 n n 1.10 ieee-9292000 t < 2 2.5 59.3 n �l n 60.5 0.88 n n 1.10 iv. the proposed method of islanding detection the proposed method can detect islanding at zero % power mismatch and the detection time is less than in rocof. in this method, at first the voltage phase angle is measured at the targeted dg and then the rate of change of voltage phase angle is calculated to detect the islanding phenomenon. in nonislanding condition, the rate of change of the phase angle is negligible after certain time but in islanding this becomes substantial and the islanding is detected. rocovpa also avoids nuisance tripping, thus protecting the stability of the microgrid. fig. 5. current controller block diagram. the rocovpa method is tested with the 2.5kw dg with a current control mode inverter connected to an rlc load with 1.8 quality factor. figure 5 shows the current control mode to control the active and the reactive power of the load. in the proposed method, the variation of voltage phase angle is monitored at the specified dg. if there is a change in the voltage phase angle, the rate with respect to time is calculated. during the islanding, the deviations of the rate of change of the phase angle exceed the threshold in order to detect the islanding condition. if the relay threshold is fixed, then the trip command to circuit breaker can be initiated. the algorithm of the proposed rocovpa method of islanding detection is shown in figure 6. the voltage phase angle at the dg is measured first. after the measurement of the phase angle of the voltage, the rate of change of voltage phase angle is calculated. in a normal situation this value is smaller than 1deg/sec (fixed threshold value) but during islanding, the value suddenly crosses the threshold, depending upon the fault severity, by means of which the islanding is detected. during the non-islanding mode this value is in limit, hence nuisance tripping is avoided. fig. 6. flow chart of the proposed rocovpa. v. design parameters of the inverter the proposed rocovpa method was tested on the network shown in figure 1 with the parameters given in table ii. the dg capacity with interfaced inverter is 2.5kw. the interfaced inverter is connected to the main grid through a breaker via the pcc. a 3-phase parallel rlc load is connected at the pcc. the input dc voltage to the inverter is 500v. the output line to line voltage of the inverter is 380v. the line resistance and inductance are 1.5mω and 2mh respectively. the nominal grid frequency is 50hz. the inverter carrier frequency is taken as 1khz. the load parameters with a quality factor of 1.8 are: $ = 1.76mω, ll =3.2mh, �$ = 3.2µf. the load resonant frequency is 50hz. current controller gains are op = 0.4 and o� = 500. engineering, technology & applied science research vol. 11, no. 5, 2021, 7591-7597 7595 www.etasr.com bangar raju & subba rao: evaluation of passive islanding detection methods for line to ground … table ii. simulation inverter parameters component value and units dg power 2.5kw switching frequency 10khz dc input voltage 500 line voltage 440v filter capacitance �j 2µf filter inductance �j 5mh damping resistance j 10hms nominal frequency 50hz load resistance rl 1.76mω load inductance ll 3.2 mh load capacitance cl 3.2µf load quality factor q 1.8 load resonant frequency fr 50hz current controller proportional gain, qp 0.4 current controller integral gain, q� 500 vi. results, analysis, and discussion the designed network was tested in matlab/simulink for the islanding case of unintentional unsymmetrical l-g fault and non-islanding cases of connection and disconnection of non-linear load. the matlab simulation results of rocovpa and rocof were compared. it was proved that rocovpa is better than rocof. the proposed method was tested and compared with rocof for the islanding case of unintentional unsymmetrical l-g fault at 0% power mismatch. in this section the simulations are discussed for both rocovpa and rocof. a. islanding case for unsymmetrical fault an l-g unsymmetrical fault was initiated on the system at the pcc at 0.4s at 0% power mismatch. +$ = +0 is the condition for 0% power mismatch and at that load, a single line to ground fault was initiated on the grid side at 0.4s. the simulation graph is shown in figure 7. fig. 7. islanding detection of rocovpa for a l-g fault on the system. the proposed rocovpa detected islanding in 10ms within a fixed threshold of 1deg/s and the relay exactly detected and sent command to trip the circuit breaker to bring the microgrid to islanding mode from the grid mode. the total time is the sum of relay time and breaker time. any type of fault is to be cleared within 4 cycles (2 cycles, i.e.0.5s of relay operation plus 2 cycles, 0.5s). hence the rocovpa can detect the fault condition within less than a cycle and island the microgrid in around 1s by tripping the circuit breaker, which is less than the 2s of the ieee-1547 and ul-1741 standards. the same fault conditions were applied and tested with rocof in matlab as shown in figure 8 and the islanding was detected in 30ms. if the threshold value is fixed at 0.02hz/sec, the tripping of the circuit breaker can be actuated in around 1s which is below the 2s of the standards. the detection time of rocof is more than that of rocovpa. as the rocof is dependent on frequency, at lower % power mismatches, the threshold value cannot be fixed exactly. hence, the detection time varies inversely with % power mismatch. to mitigate these issues, rocovpa was proposed and proved to be a better islanding detection method for unsymmetrical faults. fig. 8. islanding detection of rocof for a l-g fault on the system. b. non-islanding case for non-linear load connection and disconnection at the pcc on the system system stability has been studied for different transient conditions during load connection and disconnection at the pcc with non-linear load for both rocovpa and rocof in matlab/simulink. both methods proved their stability by avoiding nuisance tripping within the threshold values. the rocovpa threshold value is 1deg/s and that of rocof is 0.02hz/sec. fig. 9. non-islanding case of rocovpa for non-linear load connection and disconnection. a non-linear load was connected at the pcc at 0.4s and was disconnected at 0.8s. the results of non-islanding scenerios of rocovpa and rocof are shown in figures 9 and 10. the readings of rocovpa and rocof show that the thresholds are much higher. hence, the system is stable without any nuisance tripping of the circuit breaker. engineering, technology & applied science research vol. 11, no. 5, 2021, 7591-7597 7596 www.etasr.com bangar raju & subba rao: evaluation of passive islanding detection methods for line to ground … fig. 10. non-islanding case of rocof for non-linear load connection and disconnection. vii. conclusions islanding detection is a major challenge when considering microgrids. the most common unintentional faults on the system are supposed to the be unsymmetrical l-g faults, in which one phase snapping and making phase to ground is involved. the proposed rocovpa passive islanding detection method was tested for islanding detection at 0% power mismatch (0% ndz) along with the widely used rocof and proved to be a better alternative having less detection time. the rocovpa method was also tested for its stability to avoid nuisance tripping during load connection and disconnection and found to be quite effective. it is also simple and faster in discriminating between islanding and non-islanding operations of the microgrid. the detection is more accurate as the phase angle does not depend on mismatched power like voltage and frequency relays. in the future, the proposed rocovpa method can be extended for the detection of symmetrical faults with hybrid dgs. acknowledgment the authors wish to thank the faculty of electrical and electronics department of koneru lakshmaiah educational foundation (deemed to be university). financial disclosure the authors declare that this research work received no financial support from anywhere. authors conflict/competing interest the authors declare that there is no conflict/competing interest. references [1] d. milošević and ž. đurišić, "technique for stability enhancement of microgrids during unsymmetrical disturbances using battery connected by single-phase converters," iet renewable power generation, vol. 14, no. 9, pp. 1529–1540, 2020, https://doi.org/10.1049/iet-rpg.2019.0625. 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[24] k. jyothi, k. s. srikanth, and h. s. jain, "control of stand alone and grid connected distributed energy resource: a review," journal of advanced research in dynamical and control systems, vol. 10, no. 12, pp. 1603–1615, 2018. author profiles l. bangar raju is currently working as an associate professor in swarna bharati institute of technology, khammam, telangana state, india. he received his b.e. from the jawaharlal nehru technological university, kakinada, a.p. india and m.sc. (engineering) in power systems from the calicut university. he has got 30 years of industrial experience in power, oil and gas, petrochemical, transmission, distribution, and utilization plants. he has published 10 international scopus indexed papers. he is a life member of iste (india) and ie (india). he is currently pursuing his ph.d. from the koneru lakshmaiah educational foundation (deemed to be university), guntur, a.p., india. his areas of interest are power system protection, distributed generation, and microgrids. k. subba rao is presently the principal at the college of engineering and a professor of electrical and electronics engineering, department of koneru lakshmaiah educational foundation (deemed to be university), guntur, a.p., india. he received his ph.d. from koneru lakshmaiah educational foundation, m.tech. from cit, coimbatore and b.tech. from dayalbagh university, agra. he has earned the best teacher award10 times. he is a life member of iste and of the indian society for quality. he has published national and international papers and a book. his areas of interest are power electronics, power systems, microgrids, and security systems microsoft word etasr_v11_n3_pp7207-7216 engineering, technology & applied science research vol. 11, no. 3, 2021, 7207-7216 7207 www.etasr.com mohammedi et al.: preparation of polypropylene/bentonite composites of enhanced thermal and … preparation of polypropylene/bentonite composites of enhanced thermal and mechanical properties using l-leucine and stearic acid as coupling agents nadia mohammedi department of process engineering ferhat abbas setif university 1 sétif, algeria chimiebatna2016@gmail.com fouzia zoukrami emerging materials research unit ferhat abbas setif university 1 sétif, algeria fzoukrami@univ-setif.dz nacereddine haddaoui department of process engineering ferhat abbas setif university 1 sétif, algeria n_haddaoui@univ-setif.dz abstract-the compatibilization of raw bentonite (bent) with a polymer matrix of polypropylene (pp) can improve the performance of the material in terms of thermal and mechanical properties. in this study, two kinds of untreated bentonite, bentonite-maghnia (bent-m) and bentonite-mostaganem (bentm), that differ in the proportion of al2o3 and in the particle size distribution were coupled to typical maleic anhydride grafted polypropylene pp-ma. stearic acid (sa) and l-leucine amino acid (aa) were selected as new coupling modifiers at a 5/5 ratio of bentonite/coupling agent. all pp/bent composites were prepared by melt mixing at 190°c. morphological observation revealed a good dispersion of bentonite into the pp matrix in the presence of aa, sa, and pp-ma. mechanical properties showed an increase in stiffness as bent-m or bent-m were associated with aa. for instance, pp/bent-m/aa composite underwent an improvement of about 13% in young’s modulus as compared to neat pp. on the other hand, the addition of sa into bent-m maintained stiffness and tensile strength at an acceptable level. an increase of around 40°c and 37% in the decomposition temperature and elongation at break was respectively observed for the pp/bent-m/sa composite. all coupled composites showed high degradation temperatures. keywords-bentonite; surfactant; coupling agent; mechanical properties; layered composite i. introduction recently, the development and characterization of polymer/clay nanocomposites has been the subject of increasing interest because these systems habitually show significant improvement in thermal, mechanical, and barrier properties when compared with virgin polymers or conventional micro or macro composites for the same amount of filler. usually, the improvement is due to the high surface area of layered silicates which is more than700m2/g, its aspect ratio of about 50–200, in addition to the possible exfoliation or intercalation and good dispersion of clay intopolymer matrix [1, 2]. at the melt state, the dispersion of clay particles into polyolefin matrix depends on several factors such as processing time, cationic surfactant modified clay, processing method, and interface modifiers. recent studies have reported the effects of these factors on the properties and clay basal spacing of pp/eva/nanoclay composites [3], pvc/bentonite organoclay system [4] and pp/clay composites [5, 6]. polypropylene (pp) is selected in polymer composite or nanocomposite systems because it is widely used in engineering materials, electronic cases and interior decoration for its excellent insulation properties, low cost, ease of processing [7], and recyclability [8]. to enhance the thermal stability and other properties of pp, researchers have tried to use nanotechnology [9]. on the other hand, bentonite, which is a geological material, is often used as filler in polymer matrix. bentonite has a structure that generally consists of two tetrahedral sheets (silicon/oxygen) separated by an octahedral sheet (aluminum/oxygen/hydroxyl) [10, 11]. the ions with positive charges on the clay surface can be adsorbed onto the bentonite structure due to the interaction between the negative and positive charges. bentonite is used in diverse branches of industry for the fabrication of several ceramic products mainly due to its rheological properties. also, it is used as a component in dyes, pharmaceuticals, paper [12–15], and in polymer composites [16]. the industrial and environmental applications of bentonite have showed an increase of interest in recent years [13]. for example, in [17], two different bentonite/pp composites were synthesized, with and without pore-enlarging treatment. these granular composite adsorbents were effective in eliminating pb2+ in aqueous solutions. corresponding author: nadia mohammedi engineering, technology & applied science research vol. 11, no. 3, 2021, 7207-7216 7208 www.etasr.com mohammedi et al.: preparation of polypropylene/bentonite composites of enhanced thermal and … moreover, the preparation of pp/bentonite micro or nanocomposites is not straightforward due to the poor interaction between the non-polar polymers like pp and polar bentonite. therefore, by adding pp-ma to the system as a coupling agent, the improvement in the interfacial adhesion is possible [8]. pp-ma is often used with a large number of polyolefin materials [12, 15]. authors in [18] reported that for pp/modified montmorillonite (mmt) and pp/treated sodium bentonite, diethyl maleic grafted pp (pp-dem) compatibilizer has lower polarity compared to maleic anhydride grafted polypropylene (pp-ma). they concluded that clay and matrix modification are the key factors and must be carefully and properly used to get the appropriate properties in the non-polar polymer based nanocomposites [19]. the ion exchange treatment of layered silicate is often influenced by the length of the alkyl chain, and the quality of multiple interactions [20, 21]. authors in [22] indicated that the exfoliated nanocomposite based cloisite 15a compatibilized with acrylic acid grafted high density polyethylene (hdpe-aa) and maleic anhydride grafted high density polyethylene (hdpe-ma) displayed a higher level of clay dispersion. however, hdpe compatibilized with ethylene–acrylic acid copolymer (eaa) leads to poor dispersion due to its immiscibility with the hdpe matrix. recently, authors in [23] confirmed that the composites containing modified bentonite in presence of stearic acid used as interface modifier induce a better dispersion of the filler, a decrease in viscosity and an increase in elongation at break of the composites based on pp matrix. also, authors in [24] established that stearic acid favored the dispersion of pp/mmt nanocomposites when used as interface modifier and clay surface treatment. the samples exhibited crystallization temperatures comparable to pure pp, with a good dispersion. in [25], the authors synthesized l-leucine micro/nanocrystals and showed that these samples have a large potential in pharmaceutical applications as dispersibility improvers. this coating design concept can also be used for diverse active pharmaceutical ingredients. in our study, two bentonites, bentonite-maghnia (bent-m) and bentonite-mostaganem (bent-m) from two different regions of algeria were incorporated into a pp matrix. the traditional reactive maleic anhydride-grafted polypropylene pp-ma was used as a coupling agent to produce, via direct melt intercalation, pp/bent-m/pp-ma and pp/bent-m/pp-ma composites. also, pp/bent-m/sa, pp/bent-m/sa, pp/bentm/aa, and pp/bent-m/aa composites were obtained using stearic acid, sa, and l-leucine amino acid aa, respectively as coupling agents. large utilization of pp-based layered composites is possible if a more effective or a less expensive compatibilizer is available. it is important to point out that stearic acid has a low cost and only small amounts are required. on the other hand, its hydrocarbon end is compatible with pp [24]. the purpose of this study is the use of raw bentonites, which have not previously been subjected to chemical treatments to improve their compatibility, as these treatments usually involve the use of chemicals difficult to eliminate [26]. stearic acid and l-leucine have been incorporated directly in pp/bent composites at the melt state. the preparation, characterization, and mechanical properties of the prepared materials are reported here. some formulations exhibited significant improvements in the mechanical properties and degradation temperature when compared to pure pp. to the best of our knowledge, there are no previous reports of the use of this amino acid in improving the mechanical and thermal properties of pp /natural microbentonite composites obtained in molten state and the use of stearic acid as interface modifier for this system when it is introduced directly with polymer matrix and filler in internal mixer has not been reported. ii. experimental part a. materials the pp used in this study (homopolymeradstif ha740n) was supplied by lyon dellbasell industries with melt flow index (mfi) of 12g/10min and density of 0.9g/cm3. the clays used as reinforcement filler are natural bentonites from algeria, supplied by bental society: bentonite of maghnia (bent-m) with average diameter of 10.7µm, %al2o3 of 17.79, and cation-exchange capacity (cec) of 65 meq/100g [27], and bentonite of mostaganem (bent-m) with average diameter of 24.8µm, %al2o3 of 13.78, and cec of 48meq/100g [28]. on the other hand, the ratio of sio2/al2o3 in bent-m is 3.62 and in bent-m 4.49, which classifies it as si-bentonite. three different coupling agents were used, maleic anhydride-grafted polypropylene pp-ma, which was provided by cromptonuniroyal chemical (polybond3200), with mfi of 90120g/10min and a density of 0.91g/cm3, stearic acid (sa), supplied by henkel (germany), and l-leucine c6h13no2 interface amino acid (aa), purchased from merck. all the materials were used as received. b. elemental analysis of raw bentonite the elemental analysis of raw bentonite shows that the bent-m has higher alumina content (al2o3 =17.79) than bent-m (al2o3 =13.78), however the iron content of bent-m is more. the stoichiometric analysis results are: bent-m (%mass): sio2-64.44, al2o3-17.79, cao-3.16, fe2o3-2.84, mgo-5.48, na2o-1.12, k2o-1.27, so3-0.02. bent-m (%mass): sio2-61.89, al2o3-13.78, cao-7.06, fe2o3-3.66, mgo-3.12, na2o-0.92, k2o-1.69, so3-0.14. c. preparation of pp/bentonite composites pp-ma pellets were pre-mixed in a bag with bentonite (bent-m/pp-ma) at 5:5 weight ratio as well as bent-m/aa, bent-m/aa, bent-m/sa, and bent-m/sa and then, with pp at 5% wt. all the coumpounds were dried in a vaccum oven for 24h at 80°c, except sa and were melted in a brabender mixing chamber (plasti-corder ec), which was pre-heated at 190°c. the rotor speed was set at 40rpm, and the time of mixing was fixed at 20min. mixing times between 8 and 50min and rotating speeds between 40 and 150rpm have been used in different laboratory polymer mixers [29–33]. the material was withdrawn from the mixer chamber with a spatula, compressed between hot plates at 190°c in a collin press, under 100bar, followed by cold pressing at 20ºc. d. characterization 1) xrd engineering, technology & applied science research vol. 11, no. 3, 2021, 7207-7216 7209 www.etasr.com mohammedi et al.: preparation of polypropylene/bentonite composites of enhanced thermal and … x-ray diffraction (xrd) spectra were recorded using a brucker d8 advance a25 diffractometer with a copper laser and a ssd160 tm detector. ni-filtered cukα radiation (wavelength of 0.1542nm) was produced at 40kv and 25ma. scattered radiation was detected at the angular range of (2θ) 0– 45° with a step of 0.02°. 2) ftir the different composites studied were analyzed by fourier transform infrared spectroscopy (ftir) in the transmission mode using kbr pellets for the powdered sample and films prepared by compression-molded for pp/bentonite composites. the spectra were recorded on a perkin elmer spectrum 1000 spectrometer at a resolution of 4cm-1 in the range of 4000 to 400cm-1. 3) sem for scanning electron microscopy (sem) micrographs, several acquisitions of images were performed on the surface of the sample in several zones and with different magnifications from 500x to 5000x in sem-edxquanta 250 tungsten filament equipment. 4) dsc the melting points (tm) of the pp composites and the virgin pp were analyzed with a differential scanning calorimeter (dsc) q 2000 thermal analyser. the samples were heated from -50°c to 200°c at the rate of 20°c/min under an inert atmosphere of nitrogen (50ml/min), after decreasing the temperature from room temperature to −50°c. then, the samples were heated up to 200°c and were maintained at this temperature for 5min. consecutive to the heating process, samples were cooled down to 25°c, and after that, new successive heating and cooling runs were performed. the crystallinity percentage (xc) was calculated with: ��� �∆��� ∅�∆ �� ×100 (1) where ∆hm is the measured heat of melting per gram of polymer during the second heating scan, ∆h0 (207.1j/g) is the theoretical heat of crystallization of 100% crystalline isotactic polypropylene [34], and ∅ is the weight fraction of pp in the composite. thermal analysis was performed in a q2000 ta instrument. the samples (±10mg) were weighed to 0.002mg with an electronic balance (perkin-elmer ad4). the samples were heated from 25°c to 900°c at a heating rate of 20°c/min in air. all the samples were previously dried at 80°c for 24h. 5) mechanical properties tensile tests were carried out according to une-enn iso 527-1 and 527-2 with an instron model 5500r60025 apparatus. one mm thick specimens were cut from the sheets with a wallace die cutter. across-head speed of 10mm/min was used. iii. results and discussions a. processability (torque value) figures 1 and 2 show the processing torque during the mixing of pp/bent composites. it was observed that the addition of 5% of aa and pp-ma to the polymer matrix loaded with 5% bent-m increased the torque values of the systems (31n.m, 25n.m), suggesting that the composites required more severe processing conditions in its presence. in contrast, 5% of sa conducted pp/bent-m system to processing torque reduction (15n.m) and improved flow properties. fig. 1. torque behavior of pp/bent-m composites fig. 2. torque behavior of pp/bent-m composites these results give possible confirmation that the stearic acid is acting as a coupling modifier and lubricant. the enhancement of lubricity through the processing provided fine dispersion of the filler, and it was also in accord with the decrease in dimension and quantity of agglomerates showed by the sem. this was in agreement with the findings of the authors of [23], who reported that during the processing of the pp/modified bentonite composites, the stearic acid is acting as an interface modifier and lubricant and thus decreases the viscosity of the melt compound due to the free movement of the polymer chains. these effects enhanced the mechanical behavior by improving the elongation at break of the composite. on the other hand, bent-m showed a different behavior than the bent-m with the addition of 5% of aa coupling agent. the torque decreased to 14n.m in pp/bentm/sa and to 11n.m in pp/bent-m/aa composites. the reduction in the torque values observed in this case is important and can be attributed to a decrease in particle/particle interaction which showed that different sa and aa coupling engineering, technology & applied science research vol. 11, no. 3, 2021, 7207-7216 7210 www.etasr.com mohammedi et al.: preparation of polypropylene/bentonite composites of enhanced thermal and … agents act as external lubricants that are able to facilitate the processing of the pp/bent-m composites. authors in [35] studied the effect of palm oil fatty acid and polypropylene grafted-maleic anhydride compatibilizers on the peak torque of bentonite filled pp. they showed that the incorporation of these coupling agents decreases the torque generated during mixing and the agents serve as external lubricants. the torque values of pp/bent-m composites in the presence of aa and pp-ma are higher. this behavior can be attributed to the good adhesion between the pp matrix and bent-m in the presence of these coupling agents, which may inhibit the chain flexibility and increase the composite torque. authors in [36] showed that the viscosity of hexamethylenediamine modified pp/montmorillonite nanocomposites is higher than that of the pure pp in the presence of maleic anhydride grafted polypropylene. clearly, in pp/bent-m composites, the integration of aa reduces the quantity of the generated torque during mixing as compared to pp/bent-m composites. the possible reason for the differences between the behaviors of the two bentonites (bent-m and bentm) in the presence of aa is the dissimilarity in particle size distribution: bent-m presents large particles with average particle size of 24.8µm which can form agglomerates. the introduction of aa as a coupling agent reduces particle-particle interaction resulting in the decrease of particle agglomeration and an enhancement of dispersion and flow properties. b. xrd figure 3 presents the xrd patterns of coupled pp/bent-m samples, revealing reflections assigned to planes (110), (040), (130), and (041) as reported in [37, 38]. fig. 3. xrd spectra of pp/bent-m composites. the addition of aa in pp/bent-m/aa samples exhibited reflections with diffractions angles around 11.75° and 23.4°. this result suggests the occurrence of partial decomposition of the organic modifier of aa during the mixing process with bentonite [39] or implies that partially intercalated structure took place in composite containing the aa coupling modifier. pp/bent-m/pp-ma composite was not influenced after blending and forming. the peak that appears for the diffraction angle around 6° in pp/bent-m/sa composite is due to the amount of stearic acid introduced as a coupling modifier. these results are in good agreement with the findings of the authors in [24] who reported that the addition of stearic acid as interface modifier showed the same peak at around 6° and provided better intercalation of the silicate layers in its nanocomposites when compared to the rest of the pp/bentonite nanocomposites. similar diffraction patterns were also observed for the composites with bent-m and with different coupling agents (not shown for brevity). c. ftir spectra figure 4 shows the ft-ir spectra of bentonite (bent-m and bent-m). the bands obtained at 3600-3200cm-1 are attributed to the oh stretching mode of si-oh groups [40]. the band between 1640-1620cm-1 belongs to the deformation of the adsorbed h2o molecules. the intense broad-band with the maximum at 1041cm-1 ranged at 1040-1080cm-1 corresponds to the si-o-si valence vibration of the sio4. in addition, the narrow peak at 797cm-1 corresponds to the silanol group [41] and at around 600cm-1 corresponds to si-o-al [23]. the peak recorded at 1439cm-1 is associated with the presence of calcite in the sample [42]. bent-m shows a much larger peak than the bent-m as the cao content is greater in the case of bent-m (7.06% mass) than of the bent-m (3.16% mass). on the other hand, bent-m is more hygroscopic than bent-m, because the intensity of the absorption bands at 3432.8cm-1 and 1635cm-1 assigned to the stretching and bending vibrations of the oh groups for the water molecules adsorbed on bentonite surface [43] are superior in the case of bent-m than bent-m (1619cm-1, 3432.8 cm-1). fig. 4. ftir spectra of (1) bent-m and (2) bent-m. the ft-ir spectra of pp(figure 5(a)) display absorption peaks which coincide with the literature. methylene groups vibrations are registered in the range 1445-1485cm-1 and methyl group vibrations are registered in the range 14301470cm-1 or 1365-1395cm-1 [44]. these peaks in our spectrum appear at 1455 and 1355cm-1 respectively. at 2838-2982cm-1, the peaks are attributed to the asymmetric and symmetric ch bands [40]. the characteristic vibrations of terminal unsaturated ch2 group absorbs at 840, 1000, and 1170cm -1 [44]. these peaks are detected in our spectrum at 840, 980, and 1170cm-1 (figure 5(a)). the ft-ir spectra in figure 5(c) and figure 5(d) display the contribution of aa in pp/bent-m and pp/bent-m composites. again the bands at 950-1080cm-1 are engineering, technology & applied science research vol. 11, no. 3, 2021, 7207-7216 7211 www.etasr.com mohammedi et al.: preparation of polypropylene/bentonite composites of enhanced thermal and … characteristic of the asymmetric and symmetric vibrations of si-o-si. the bands ranged generally at 1540-1640cm-1 attest of the stretching vibrations of co2 [45]. in our spectrum, there were registered at 1512-1608cm-1. the bending vibrations due to the symmetric ch3 and due to hch band absorb at 1385.5cm-1 were generally detected at 1408cm-1 [45]. this one disappeared in our composites. on the other hand, a differentiated absorption at 1295.5cm-1 associated with the bending vibration of ch3, stretching of cc and rocking of ch also disappeared in our composites. the peak in the spectra of pure aa at 1239cm-1 (figure 5(b)) is attributed to the rocking of nh3 and bending of coh, the intensity of the corresponding peak in our composites was decreased at this range. the peak generally located at 1133cm-1 was attributed to the cc stretch [45], and was seen at 1146cm-1. there is a displacement toward the high frequency region 1150cm-1 in our composites (figure 5(c)-(d)). while 769cm-1 is the peak of the bending of co2, a weak signal in the corresponding band was observed in our composites and these remarks suggested the immobilization of aa on the surface of bentonite. fig. 5. ftir spectra of (a) neat pp, (b) aa, (c) pp/bent-m/aa, and (d) pp/bent-m/aa. the ftir spectra of the pure pp-ma film (figure 6(b)) are characterized by the presence of two bands typical of the pure pp-ma at 1783cm-1 and 1717cm-1 which are attributed to the symmetric and asymmetric stretching vibration of the c=o group. the ftir spectra of the composite in figure 6(c)-(d) shows very weak peaks at 1783cm-1 and 1717cm-1 which attest the small amount of the carbonyl in a polymer molecule. c-o group is registered in the range of 1190-960cm-1 in pure ppma [44]. in our case, c-o absorption was detected at 1165 cm-1. it was observed that this absorption intensity is less strong in pp/bent-m/pp-ma composite and diminished in pp/bentm/pp-ma composite. also, the peak characteristic of c-o group shifted to 1167cm-1 in pp/bent-m/pp-ma. this suggested the presence of new hydrogen bands between ppma and bent-m. in the case of neat sa (figure 7(b)), broad and intense bands observed at 2916cm-1 and 2858cm-1 are attributed to the stretching vibration of c-h bands located generally in range of 2800-2900cm-1. the absorption in this region showed very weak peaks in the spectrum of composite (figure 7(c)-(d)). also, the original c=o absorption at 1704 cm-1 of sa shifted by 4cm-1 toward the high frequency region in the composites with sa. apparently these changes are due to the adsorption of sa on bentonite as reported in [24]. fig. 6. ftir spectra of (a) neat pp, (b) pp-ma, (c) pp/bent-m/pp-ma, and (d) pp/bent-m/pp-ma (d). fig. 7. ftir spectra of (a) neat pp, (b) sa, (c) pp/bent-m/sa, and (d) pp/bent-m/sa. d. scanning electron microscopy of film surface the morphologies of the film surface of uncoupled and coupled pp/bent-m and pp/bent-m composites are presented in figures 8 and 9 respectively. sem micrographs show microsized particles of 5wt% clay in pp/bent-m composite (figure 10), which is larger as compared to particles in coupled composites. this indicates an inhomogeneous distribution of clay in pp in the absence of a coupling agent. with further inclusion of sa and aa coupling agents, the presence of agglomerates in bent-m is almost unnoticeable, which is attributed to the good dispersion of bentonite bent-m in the pp matrix in the presence of these coupling modifiers and clarified the enhancement in some mechanical properties. stearic acid as coupling agent introduces an improved wetting of bentonite particles through the matrix of pp, owing to interactions between clay and pp. in this case, bentonite layers were aggregated with a size of 195nm in the polypropylene matrix. engineering, technology & applied science research vol. 11, no. 3, 2021, 7207-7216 7212 www.etasr.com mohammedi et al.: preparation of polypropylene/bentonite composites of enhanced thermal and … fig. 8. sem micrographs of (a) pp/bent-m, (b) pp/bent-m/pp-ma, (c) pp/bent-m/aa, and (d) pp/bent-m/sa. fig. 9. sem micrographs of (a) pp/bent-m, (b) pp/bent-m/pp-ma, (c) pp/bent-m/aa, and (d) pp/bent-m/sa. the sem micrographs of pp/bent-m composites (figure 9) with a clay content of 5wt% showed that the uncoupled composite included a small quantity of agglomerates of clay of size less than 50µm. by adding aa and sa coupling agents in the composite, no detectable particle agglomerates were observed at 2µm scale. this behavior indicates a good dispersion of bent-m in pp matrix in the presence of amino acid and stearic acid coupling agents. however, the pp/bentm/pp-ma micrograph shows large aggregates. the structure (figure 9(b)) observed in pp/bent-m/sa can be attributed to the needles structure of stearic acid and to the good dispersion of bent-m in the pp matrix in the presence of this coupling agent. e. differential scanning calorimeter properties table i illustrates the values of the crystallinity content (xc) calculated from ∆hm which is the enthalpy of melting of polymer in the composite, compared with the enthalpy of melting of 100% crystalline pp, the melting temperature (tm) and the crystallization temperature (tc) of all prepared samples. each composite in the presence of coupling agent exhibits similar tm regardless of the kind of bentonite. it is noticeable that tm and tc remained unaffected with the incorporation of the clay in the presence of different coupling agents in all composites, indicating that the crystal size of pp did not change [46]. the degree of crystallinity increased slightly in pp-ma and sa coupled composites as compared to that in pure pp (51%) and in uncoupled composite. pp/bent-m/pp-ma and pp/bent-m/sa present the higher degree of crystallinity, around 57%, while pp/bent-m/aa provides the lowest crystallinity due to the lower enthalpy of melting of the compatibilizer. this result confirms how the crystallization of pp matrix varied with the further inclusion of pp-ma, aa, and sa coupling agents [39]. the percentage of crystallinity did not change with the addition of bentonite. this signifies that the bentonite did not act as a nucleating agent in this compound. according to [36], the presence of coupling agents appears to decrease the crystallization process in bentonite filled pp composite and bentonite did not serve as nucleating agent in this system. table i. characteristic thermal parameters of pp/bent composites with and without coupling agents samples tm (°c) ∆hm (j/g) tc (°c) ∆hc (j/g) x % neat pp 165 107 126 113 51 pp/bent-m 166 103 127 110 52 pp-bent-m 166 102 127 109 52 pp/bent-m/pp-ma 165 106 127 109 57 pp/bent-m/sa 164 101 127 104 54 pp/bent-m/aa 165 99 127 108 53 pp/bent-m/pp-ma 165 103 126 109 55 pp/bent-m/sa 164 107 127 107 57 pp/bent-m/aa 165 93 127 103 50 f. mechanical properties the results of mechanical properties of pp and uncoupled and coupled pp/bent composites are exhibited in table ii. we observe a decrease in young’s modulus caused by the bent-m filler which appears to be related to the amount of clay and the size filler. the young’s modulus of pp/bent-m/aa composite engineering, technology & applied science research vol. 11, no. 3, 2021, 7207-7216 7213 www.etasr.com mohammedi et al.: preparation of polypropylene/bentonite composites of enhanced thermal and … was still improved even when compared to the other composites of pp/bent-m coupled to pp-ma or sa. the changes in young’s modulus reflect the nature of the interface between polymer and filler. the introduction of bent-m in pp provides a slight decrease in young’s modulus and pp/bentm/sa had the same stiffness as the uncoupled composite. no changes of young’s modulus in pp/bent-m coupled to pp-ma were observed, while this property was more improved for pp/bent-m/aa composite due to the effective adhesion between pp and clay in the presence of aa coupling agent, conducted by the homogeneous dispersion as shown by the sem images, providing an easy transfer of load throughout the composite [47]. as expected at 5wt.% of clay content, there is a significant decrease in elongation at break. the elongation at break for neat pp is above 140% and decreases to 103% especially in pp/bent-m. this decrease could be caused by the fact that the inorganic particles of filler are rigid and cannot be deformed by external stress in the samples but acted only as stress concentrators during the deformation process [36]. a significant decrease in elongation at break was reported in [48] for ldpe/tps/snc nanocomposites by adding 5wt.% of starch nanocrystals (snc) without dcp compared to pure ldpe. by introducing pp-ma coupling agent, an enhancement in elongation at break of about 21% is observed compared to uncoupled pp/bent-m composite. however, the percentage of improvement in elongation at break by using sa in pp/bent-m compound is 37%. this increase in ductility (i.e. elongation at break) might be due to the existence of fatty acids in sa which act as interface modifiers for bentonite into the pp matrix. consequently, the ductility of bentonite filled pp composites can be improved [35]. these results prove the results of torque values. according to [24, 35], fatty acids promote an improvement in elongation at break and the dispersion state of nanoclay and bentonite in a polypropylene matrix. it has been noted [35] that the elongation at break of composites under the presence of palm oil fatty acid (pofa) additive shows the highest value compared to composites with the presence of ppma. a similar trend is observed for the elongation at break and the strain at break change for all samples. table ii shows a reduction of the maximum stress by the incorporation of the unmodified bent-m or bent-m filler. this behavior can be explained by the low adhesion between bentonite and the pp matrix. the unmodified bentonite particles in uncoupled composite can serve as sites to initiate and activate the deformation mechanism and as a result, the yield stress decreases. on the other hand, there are some bentonite layers with good matrix adhesion based on sem micrographs in pp/bent-m and pp/bent-m composites coupled with pp-ma coupling agent. these ones can withstand the movement of the polymer chains and therefore increase the yield stress. improvement in yield values by the introduction of pp-ma compatibilizer in pp/modified clay has been reported in [49]. for coupled composites in the presence of sa and aa coupling agents and because they act as external lubricants in pp/bent-m composites (as seen on the torque results), free movement of the polymer chains is possible. the latter makes the physical sliding between the molecular segments easier which results in the decrease of the maximum stress. the same remark was noted for the coupled pp/bent-m/sa composite. from the results of this study, it can be supposed that the aa and sa coupling modifiers show certain degrees of interactions in the pp/bentonite system as observed in some improvement on mechanical properties. these interactions are superior for bent-m because of its low average particle size compared to bent-m. table ii. values of stiffness, elongation at break, strain break, and maximum stress of pp/bentonite samples young’s modulus (mpa) elongation at break % strain break % maximum stress (mpa) neat pp 1538±20 145±4 7.3±0.2 37.9±0.2 pp/bent-m 1516±6 103±3 5.3 0.4 34.0±0.6 pp-bent-m 1467±7 136±8 6.8±0.4 35.5±0.1 pp/bent-m/ppma 1539±5 125±3 6.3±0.2 35.8±0.3 pp/bent-m/sa 1516±24 141±1 7±1 32.5±0.2 pp/bent-m/aa 1719±52 83±4 4.2±0.2 30.5±0.4 pp/bent-m/pp-ma 1435±23 123±0.1 6.1±0.3 37.0±0.4 pp/bent-m/sa 1481±31 79±2 3.9±0.5 31.5±0.8 pp/bent-m/aa 1532±13 94 ±0.1 4.7±0.5 29.6±0.2 g. thermogravimetric analysis (tga) tga was employed to evaluate the thermal stability of each sample. figure 10 shows the tga curves of neat pp, pp/bentm, and pp/bent-m composites in the presence of different coupling agents. we do not observe an improvement in t5% in all cases of coupled pp/bentonite systems (excepted pp/bentm/aa). the temperature at 20% weight loss of all composites enhanced (excepted pp/bent-m/sa). the coupling agent can improve the stability at high temperatures [50]. the temperature at 50% weight loss of pp/bent-m/sa displays the highest value. this composite is more stable than neat pp, while a slight decrease is shown in pp/bent-m/sa. adding aa to pp/bent-m and pp/bent-m results in a lower improvement of t50% compared to sa (there is about 13°c of t50% improvement as compared to neat pp). pp-ma displays a slight increase in t50% in both pp/bent-m and pp/bent-m. however, there is an improvement in overall coupled composites in tmax, the highest being recorded for pp/bent-m/sa composite. it is noted that these materials become more thermally stable due to an improvement in the miscibility between all the added coupling agents [51]. also, thermal stability enhancement is a consequence of the fine dispersion of bentonite within the pp matrix and the interface which resulted in slower escape of decomposed smaller molecules[39, 52-53]. fig. 10. tga curves of selected samples of pp with pp/bent-m composites engineering, technology & applied science research vol. 11, no. 3, 2021, 7207-7216 7214 www.etasr.com mohammedi et al.: preparation of polypropylene/bentonite composites of enhanced thermal and … fig. 11. tga curves of selected samples of pp with pp/bent-m composites table iii. thermogravimetric parameters of pp and pp/bentonite coposites in the air samples t5% (°c) t20% (°c) t50% (°c) tmax (°c) neat pp 254 278 303 306 pp/bent-m/pp-ma 252 279 305 336 pp/bent-m/sa 241 294 347 353 pp/bent-m/aa 256 291 319 324 pp/bent-m/pp-ma 251 280 305 316 this increase in the decomposition temperature of about 40°c, as compared with the neat polymer, might be taken as a sign of the incidence of clay intercalation, since the intercalated or exfoliated clay will act as a barrier to the diffusion of atmospheric oxygen in the compound, inhibiting the polymer decomposition [54]. recently, it was reported that the incorporation of fatty acids like stearic acid between the layers of mineral ceramic facilitates polymer-ceramic interaction [55]. the degradation temperatures of all samples are listed in table iii. iv. conclusions this study has investigated the effect of the addition of different coupling agents such as pp-ma, sa, and aa on the mechanical properties, thermal stability, crystallinity, and rheological properties of pp/raw bentonite composites. fillers such as bentonite without treatment can be used as good reinforcement. according to xrd results, polar molecules of aa exhibited reflections that shift to smaller angles. this is an indication that aa was introduced in bentonite. pp/bent-m/ppma and pp/bent-m/sa composites present the higher degree of crystallinity of around 57% as compared to neat pp and uncoupled composites. pp/bent-m/sa composite is more stable than neat matrix while the improvement in decomposition temperature is about 13°c in pp/bent-m/aa composite. the presence of the different coupling agents in natural bentonite increases tmax in all the composites. the pp/bent-m/sa system can be considered as an important material, which improves the thermal stability and kept the modulus and elongation at break at a value almost similar to that of pp. in addition, pp/bentm/aa composite can also be selected as a material with high young modulus and good thermal stability. these enhancements were important as this behavior has not been reported in the literature. in most cases the elongation at break properties are reduced in pp filled with nanoclay. also, the increase in thermal stability and modulus of elasticity were observed after the addition of nanobentonite in the presence of stearic acid as interface modifier and not for pp/raw microbentonite composite containing 5wt.% of filler and 5wt.% of stearic acid or amino acid as coupling agents.the behavior of processing composites showed a decrease in torque values above the uncoupled system by using sa and aa coupling agents in pp/bent-m composites. the decrease is more significant in presence of sa in pp/bent-m composites. acknowledgment the authors appreciate the financial 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[55] n. el h. belkham, d. benachour, and a. mehamha, "elaboration and physico-chemical characterization of the gibbsite li(oh)3 hybrid material," engineering, technology & applied science research, vol. 11, no. 1, pp. 6740–6744, feb. 2021, https://doi.org/10.48084/ etasr.3988. microsoft word etasr_v11_n4_pp7370-7374 engineering, technology & applied science research vol. 11, no. 4, 2021, 7370-7374 7370 www.etasr.com chughtai: a realization of stabilizing the output light power from a laser diode a realization of stabilizing the output light power from a laser diode a practical approach muhammad tajammal chughtai department of electrical engineering university of hail hail, saudi arabia mt.chughtai@uoh.edu.sa abstract-semiconductor laser diodes (lds) are known for their sensitivity to variation in ambient temperature. with the rise in case temperature the threshold current of the ld increases, causing the output light power to deteriorate drastically. therefore, it is necessary to stabilize the temperature of the diode. various approaches could be adopted in this regard. in this paper, an active cooling approach using the temperature compensation technique has been followed and presented in the form of a full design of the circuit according to the various datasheet parameters of the ld and other components. as a result of temperature stabilization, a significant improvement in the output light power stabilization was observed and the results are presented. keywords-electronics; laser power; temperature stability i. introduction laser diodes (lds) have been known for their sensitivity towards changes in the case temperature due to operation over long durations or to ambient temperature. with the change in temperature, their operating point keeps shifting, i.e. with the increase in the temperature it keeps shifting away from the original operating point which results in reduced levels of optical power output. a proposed remedy to these problems is a temperature compensating bias system, which is capable of keeping track of any changes in the ambient temperature and hence providing a higher safety to the ld. many approaches have been adopted for keeping the operation of lds stable to work in continuous wave mode. one traditional method of achieving the objective is attaching a heat sink to the ld. authors in [1] designed a stabilized pump laser system to achieve square wave modulation. they managed to attain a spot size radius of 7mm, hence obtaining a uniform laser beam cove. authors in [2] proposed an optical scanning system wherein they suggested changing the intensity distribution from the center and the edge of the beam using a prism. authors in [3] used a double fabry perot interferometer acoustic sensor to get rid of temperature drifting. authors in [4] tried a number of alterations using silicone converters which helped increase the top-limit excitation power ranging from 60 to 180wcm. authors in [5] developed a heat sink having micro channels, for sinusoidal type channel structures which increased the stability and life time of the ld. authors in [6] reported a diamagnetic spring to act as a radiation pressure meter. authors in [7] developed a model using pspice simulation software and a comparison between the model and the actual diode was studied. the same problem of temperature dependence and stabilization in case of high power laser was encountered and studied in [8] in the case of high power diode-pumped tm: ylf. the authors achieved optical-to-optical efficiency of 36.8%. authors in [9] reported a self-referenced stabilization of a diode laser. however, the work was related to a high power laser of 2.1w. similarly, authors in [10] reported the stabilization of optical power in high power laser which achieved lateral mode stability. this property has been used in improving the stability of beam quality. authors in [11] worked towards power stability of a ld output power by controlling low and high frequency noises. however the stability remained short-term. authors in [12] achieved enhanced stability using double q switching hence attaining mode locked output. the ld under test had a peak power up to 20w with a good repetition rate. authors in [13] reported an electronic circuit based upon the principle of feedback. the circuit was implemented using cmos technology and gave promising results for average output power of hetero-structure laser for stabilized continuous operation. in order to keep the output optical power constant for a constant level of input current it is necessary that the bias voltage fed to the ld must track any changes in the temperature. authors in [14] studied the structure of an ld in order to compare the ld and a conventional light emitting diode. authors in [15] discussed a technique using labview software to compensate the non-linearity in temperature measurement using traditional sensors. a comparison between various modes of laser operation has also been presented. authors in [16] presented a review and discussed ld chaos and suggested various methods and their advantages for harnessing and application of chaos in various applications. changes in the temperature of the ld may cause the operating point voltage of the ld to exceed the typical rating value and may cause permanent damage or may give a lower than desired amplitude of optical power. if the applied voltage exceeds the operating voltage (as a result of a decrease in the temperature), a permanent damage to the ld may occur. additionally, a rise in temperature will shift the operating point, leading to a drop in corresponding author: muhammad tajammal chughtai engineering, technology & applied science research vol. 11, no. 4, 2021, 7370-7374 7371 www.etasr.com chughtai: a realization of stabilizing the output light power from a laser diode optical power output. authors in [17] studied a semiconductor laser using simulations to determine various parameters in relation to laser structure hence observing maintenance of output parameters at certain structural measurements. authors in [18] discussed a co2 stabilized laser in cutting processes and they carried out a discussion validated by the analysis of variance (anova). however, nothing was discussed for the stabilization of power. in previous works the temperature compensation in a range of applications have been presented by using passive [19] as well as active methods which are mostly based upon peltier coolers [20]. the present work has been carried out by making use of temperature sensor and reference. therefore, this work is considered as an active method but without the use of a peltier cooler. the complete design and calculations are presented with the aim that the users would be at ease to carry out calculations on the same pattern. however, the researcher has to use parameters, such as the temperature coefficient, according to the devices which would be chosen for the new system under consideration. ii. suggested options to maintain optical power output the three most common solutions to this problem are: • constant current operation. • maintenance of the temperature of the ld at a constant level. • bias the ld using a temperature compensated power supply. fig. 1. block scheme for temperature stabilization. the constant current power supply circuit is the one suggested in [21]. in this circuit a current stabilizer has been used to bias the avalanche photodiode, whereas a capacitor cs was used in charge banking role. however, the same arrangement may be used for achieving temperature and hence output light power stability. this may require a careful redesign of the circuit according to the specifications of the ld under consideration. another method of temperature compensation can be achieved by ensuring that the voltage of the ld tracks any temperature change by using another diode to produce a reference voltage signal. the schematic arrangement for such a circuit though for photodiode has been presented in [22]. in this scheme, a zener diode was used as a reference diode mounted on the same heat sink. the configuration of a differential amplifier has been used in the circuit for the purpose of bias control. the second method mentioned above, may cause condensation on the ld window and hence a poorer delivery of optical power output and the need to clean the window frequently. the third method to stabilize an ld is to design a circuit using temperature sensing components, as shown in figure 1. usually, temperature sensing components produce a current signal which varies with any change in temperature. this output current may be converted to voltage with the use of an operational amplifier, configured as a current to voltage converter. the output of this op-amp can then be fed to a summing amplifier in a non-inverting configuration, thereby summing up the voltage with the negative value from a conventional high voltage power supply and a reference voltage. the resultant output is used to control the base current of the bias control transistor. iii. design considerations a toshiba ld was used in this study. the temperature coefficient for this particular ld as given by the data sheet is 1×10 -3 %/°c. in order to convert this temperature coefficient into a voltage variation (volts/°c), noting that: 3 1 10 100 β − × = (1) where β is the temperature coefficient of the ld in volts/°c and vb is the bias voltage of the ld. the value of vb for this case is 3v, so (1) leads to [23]: o 30µv c β = (2) the practical circuit for a temperature compensated bias supply for an ld is illustrated in figure 2. fig. 2. schematic of the temperature compensated bias supply for ld. in order to understand the functioning of this, a gradual design and analysis of the circuit is presented below. a. constant reference voltage a constant voltage reference of −6.8v was obtained using the precision reference diode package lm329. this constant engineering, technology & applied science research vol. 11, no. 4, 2021, 7370-7374 7372 www.etasr.com chughtai: a realization of stabilizing the output light power from a laser diode reference voltage was then supplied to the temperature sensor 1c ad590, which has a temperature coefficient of 1µa/°k. b. current to voltage converter let us consider the combination of the temperature sensor ic1 and the operational amplifier a1. the total current generated by 1c1 for a rise of t ( o k) in the temperature will be t×10 -6 a. hence, the current i supplied by the temperature sensor for a rise of t o k will be: 6 o 10 a k i t − = × (3) therefore, the voltage at the output of the op-amp a1 with feedback resister r1 can be expressed as: 6 1 1 10 v t r − × = thus, the voltage change vl, becomes: 6 1 1 10 vv r t − = × × (4) c. the summing amplifier the operational amplifier a2 was used in a summing amplifier configuration so that it added all three voltages applied at its inputs to produce the output vo. this output vo was supplied at the base of an npn transistor q1, through a resistor. transistor q1 was configured so that the smaller the voltage signal at its base, the lower was the conduction between the collector and the emitter. when conducting, the transistor produced a flow of current between its collector and emitter of q1. in turn, this caused the +bias voltage point to float, hence, a variation in the -bias voltage point at the output could be observed. mathematically, this section of the circuitry can be expressed as follows: kirchhoff's current law states that, at any point in an electrical circuit, the algebraic sum of the currents meeting at that point is zero (figure 3). therefore, the current equation according to kirchhoff’s law at the input of a2 can be written as: 1 2 4 3 0 ref b v v v r r r + + = (5) however, substituting the value of v, from (4), (5) yields: 6 1 2 4 3 10 0 ref b v v t r r r r − × × + + = (6) differentiating (6), with respect to t, yields: 6 1 4 3 10 b dv r r dt r − × × = − (7) putting up dvb/dt = β, (7) can then be written as: 6 1 4 3 10r r r β − × × = − (8) this gives the value for the temperature coefficient β of the ld. substituting this value into (5) gives: 4 2 ref b v r v t r β × = − + × (9) solving (5), (8), and (9) simultaneously, the values for resistors r2, r3 and r4 may be calculated. iv. practical implementation from the data provided with the ld, the bias voltage of the particular ld under consideration was found to be 3v and, according to this value, the temperature coefficient as calculated at the beginning was 30µv/ºk. in order to calculate the appropriate values of the various resistors to be used in the circuit, this voltage value must be substituted into (2) using r1=20kω. this produces: 6 6 4 3 20 10 30 10 k r r − − × × − × = thus: 34 3 1 5 1 5 10 1 r . . r k − = = × (10) leading to the value 666×r4=r3. since it was already required that the ld should operate at a temperature of 300ºk (i.e. approximating to a normal room temperature, this implied that the following values were already fixed): t = 300ºk β = −300µv/ºk r1 = 20kω inserting these values in (9) led to a value for the reversed breakdown voltage: 4 2 0 09 b ref r v v . r = − − furthermore, it was required to operate the ld at a biasing voltage value vb = 3 volts. therefore: 4 2 3 0 09 ref r . v r + = − but: vref=5v 4 2 0 618 r . r = assuming that r2=10kω, (10) therefore leads to: r4=10k(0.618)=6.18k ≈ 6kω and: engineering, technology & applied science research vol. 11, no. 4, 2021, 7370-7374 7373 www.etasr.com chughtai: a realization of stabilizing the output light power from a laser diode 2 3 6 18 4 1mω 1 5 10 . k r . . − = = × inserting these design values for r1, r2, r3, and r4 into the circuit design, satisfactory performance of the temperature compensated power supply for the ld was obtained. however, in order to set the value of the temperature coefficient precisely, it was decided to insert a variable resistor instead of a fixed value for r2. this could then be adjusted until the required output value of the bias voltage was obtained. the designed circuit was assembled on a double sided printed circuit board (pcb) and is shown in figure 3. fig. 3. assembled circuit as used for testing and confirmation. v. results and discussion the performance of the ld was recorded with and without applying the temperature compensated bias circuit. figure 4 shows the trend of the ld output power. fig. 4. ld output power without temperature stabilization. the graph shows a drastic reduction in output optical power during the first 50 minutes of switching on. after 50 minutes of biasing up the ld lost more than 50% of its rated value before the output optical power settled down but the level of output power was at such a low level, which is not good enough for the purposed application. figure 5 shows a power drop of over 1mw before it settles down around 10mw of optical power, which was a sufficient and constant supply of optical power for the system under consideration. the circuit for temperature compensation of the ld was implemented and assembled on a double sided pcb, according to the design values of the components calculated in the previous section. in order to measure the variation in the optical power output, the observations were recorded for power output against time, as shown in figure 6. these were then plotted in the form of a graph for comparison purposes. the output power level was also recorded without temperature compensation, so that an easy comparison of both the situations could be made. it can be observed that the output optical power is well stabilized after attaching the ld to temperature compensation arrangement. fig. 5. stabilized output optical power after applying modified bias circuit. fig. 6. comparative graph of stabilized and un-stabilized output optical power. vi. conclusions reliable and reproducible results have been achieved using the designed parameters. the circuit was 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[23] r. j. mcintyre and p. p. webb, "silicon avalanche photodiode with low keff," us4463368a, jul. 31, 1984. microsoft word etasr_v11_n1_pp6719-6723 engineering, technology & applied science research vol. 11, no. 1, 2021, 6719-6723 6719 www.etasr.com mestiri et al.: aes high-level systemc modeling using aspect oriented programming approach aes high-level systemc modeling using aspect oriented programming approach hassen mestiri prince sattam bin abdulaziz university, college of computer engineering and sciences, department of computer engineering, alkharj, saudi arabia and higher institute of applied sciences and technology of sousse, university of sousse, tunisia and electronics and micro-electronics laboratory, faculty of sciences of monastir, university of monastir, tunisia h.mestiri@psau.edu.sa imen barraj mets research group, electrical engineering department, national engineers school of sfax university of sfax, tunisia and higher institute of computer science and multimedia of gabes university of gabes, tunisia imen.barraj@gmail.com mohsen machhout electronics and micro-electronics laboratory faculty of sciences of monastir university of monastir monastir, tunisia mohsen.machhout@fsm.rnu.tn abstract-the increasing complexity of the cryptographic modeling and security simulation of the advanced encryption standard (aes) necessitate fast modeling and simulation security environment. the systemc language is used in electronic system level (esl) that allows cryptographic models to achieve high security and modeling simulation speed. yet, the use of systemc in the security simulation requires modifications of the original code which increases the modeling complexity. the aspectoriented programming (aop) can be used in the cryptographic modeling and security simulations without any code modification. in this paper, a new aes systemc model using the aop technique is presented. a functional verification environment is proposed to test the functionality of the aes systemc aop model, the impact of aop on simulation time, and the size of the executable files. the design of the aes model is developed with the weaving of all modules by aspectc++ which is an aop language. the simulation results show the efficiency of the proposed aes model and the uses of the aop technique do not have a significant impact on simulation time or on the size of the executable file. keywords-security; cryptographic; aes; systemc; aop; highlevel i. introduction cryptographic systems are implemented in embedded systems to protect secret information. those systems store the encryption key in conjunction with the cryptographic algorithm execution [1-3]. the modeling complexity of cryptographic systems is increasing more than the verification capability and the design of the developers [4]. systemc is used for the modeling and verification of complex systems. it has been considered as a suitable language for developing cryptographic models. yet, its uses need to modify the original systemc code in order to weave any cryptographic modules [5, 6]. to avoid modifying the cryptographic algorithms code under test, a new technique is used: aspect oriented programming (aop). it consists of weaving a module into the original code without any modification [7, 8]. until now, a few cryptographic models and verification security environments using systemc and aop have been presented. in [9], the authors presented a security systemc benchmark for high-level synthesis. they developed a security benchmark suite in a behavioral language supported by all major hls vendors with different types of trojan hardware which produce different effects. a security threat analysis using systemc to simulate the power attacks is presented in [10]. the authors developed a new approach to simulate power attacks in early stages. the authors also developed a power consumption graphical interface to analyze the security of the elliptic curve cryptography and rsa encryption against simple power attacks and differential power attacks respectively. the authors in [7] proposed a new fault injection system based on aspect-oriented programming (aspectc++). this system allows an automated injection of errors without modifying the original code. the authors showed that their system provides automatisms to generate the test environment of embedded systems. corresponding author: hassen mestiri engineering, technology & applied science research vol. 11, no. 1, 2021, 6719-6723 6720 www.etasr.com mestiri et al.: aes high-level systemc modeling using aspect oriented programming approach in this paper, we present a new aes systemc model using the aop technique. we summarize our contributions as: • aspectc++ has been used as an aop technique to avoid modifying the cryptographic algorithm code. • a new cryptographic aes systemc model using the aop technique is proposed. • a functional verification environment is proposed to test the functionality of the aes systemc aop model. • the proposed aes systemc-aop model has been simulated in order to estimate the impact of aop on simulation time and on the size of the executable files. through the simulations, it was shown that the efficiency of the proposed aes model and the uses of aop technique do not have a significant impact on simulation time and on the size of the executable file. ii. aspect oriented programming aop is a programming technique based on the principle of the separation of concerns [7, 8]. in the aop, an application is made up of classes and aspects. the transversal code linked to non-functional concerns is put into modules in the form of aspects. the aspects will then be weaved into the functional code in order to generate a complete application. aspects are used to implement technical functionalities that are found to be dispersed in the code of an application. an aspect consists of two parts: pointcut and advice code. • pointcut allows defining the place where the code of the transverse functionality of the associated aspect will be applied. this is defined by one or more join points. each join point represents a point in which the code of a transverse functionality will be inserted. there are two types of join points: call and execute. • an advice code is a part of the code that will be inserted in the places defined by the join points. it denotes the way in which cross functionality will be weaving. an aspect can include several advice codes at the same time where each advice is associated with a cut. there are three types of advice codes: • before: the code will be executed before the cut. • after: the code will be executed after the cut. • around: part of the code will be executed before the cut and another will be executed after. to weave a new feature like an aspect into the code of an application, junction points must be defined in the primary code to indicate where the aspect should act. figure 1 shows how the aspect code of the new functionality is weaving into the application code. the aop technique is widely used in the field of testing embedded programs written in c ++ and java. in our work, in order to avoid the modifications of the source code when inserting the codes relating to the aes model and the analysis of the cryptographic system, the use of the aop technique to design a new aes model is proposed. since the aop technique allows the separation of transversal concerns, we can obtain a new distribution of the cryptographic model. this distribution consists of class and aspects which present the codes relating to the modules to be inserted. fig. 1. weaving aspect code into source code. fig. 2. diagram of the aes systemc aop design. engineering, technology & applied science research vol. 11, no. 1, 2021, 6719-6723 6721 www.etasr.com mestiri et al.: aes high-level systemc modeling using aspect oriented programming approach fig. 3. flowchart of the aes cryptosystem aspect. iii. systemc aes modeling the goal of this section is to design an aes model in systemc using the aop approach. for this purpose, the cryptographic operations performed by the aes cryptosystem were divided into several modules. figure 2 presents a detailed description of the proposed aes model. the diagram of the aes systemc model presents the different cryptographic modules as well as their interconnections using aspectc++ which is an aop language. the aes systemc aop model is described in 7 modules: • aes • key_generator • controller_unit • input_interface • output_interface • fault_detection_scheme • database figure 3 presents the flowchart of the aspect used by the aes cryptosystem. the aspect code is woven by the aspectc++ weaver into original code. the systemc-aop flow has four main phases. the aspect phase consists to create a new aspect for each aes cryptosystem module using aspectc++. the point-cutting phase consists to define the weaving location for each module. the third phase is to insert all modules in the pointcuts and then execute all functions: • the input_interface module reorganizes the input flow according to a standard format defined by the communications protocol. it executes the input_data_buffer and intput_key_buffer functions. • the controller_unit module is a state controller that allows the synchronization of all modules of aes cryptographic model. • the database module stores all variables and constants used in the encryption and decryption process. it processes two functions: variables and constants. • the aes module is the main module, it performs the encryption and decryption processes via 7 operations: subbytes, shiftrows, shiftrows, addroundkey, inv_subbytes, inv_shiftrows and inv_mixcolumns. • the fault detection ssheme (fds) module is developed to protect the aes module against fault attacks. it executes fault_detection and fault_analysis functions. • the output_interface module reorganizes the encrypted stream according to a standard format defined by the communications protocol. it executes the output_data_buffer function. in the fourth phase, after the weaving process, the resulting source code can be compiled by systemc and aspectc++ compilers and the resulted executable file is therefore generated. iv. functional verification environment in this section, the proposed functional verification environment developed to validate the aes model is presented. this environment is inspired by the transaction-based verification environment in the systemc. the aes model verification environment includes a reference model that presents a high level design description. this model is executed in parallel with the proposed model in order to compare the output results during the simulation. the reference model often models the interaction between modules at the transactional level rather than at the signal level. in this case, this module is written in tlm. figure 4 shows the proposed environment architecture. as presented by figure 4, the testbench scv is a module that randomly generates the encryption keys and plaintext for the proposed and the reference models. the transactor receives the stimuli from the testbench scv and applies them to the inputs of the proposed model. at the end of each transaction, the outputs are compared and the results are generated by a comparator module. engineering, technology & applied science research vol. 11, no. 1, 2021, 6719-6723 6722 www.etasr.com mestiri et al.: aes high-level systemc modeling using aspect oriented programming approach fig. 4. functional verification environment. (1) + (2): the stimuli are generated randomly by the testbench scv towards the two cryptographic models: proposed and reference models. (3): the transactions are converted into signals by the transactor module to be adapted to the inputs of the non-tlm model (proposed model). (4) + (5): both models use the database. (6) + (8): the aes systemc based aop outputs and the transactor outputs are the inputs of the comparator module. (7): the tlm output of reference model (8): the transactions converted into signals by the transactor to be adapted to the outputs of the non-tlm model. (9): the comparison report results are generated. v. results and discussion this section is devoted to the evaluation of the proposed systemc-aop model as well as to the analysis of the impact of using systemc and aspectc++ at the esl level on the cryptographic design. first, we will perform a series of simulations to validate the proposed systemc-aop model. this validation is performed using the functional verification environment where the proposed model is compared with the reference model. secondly, we will analyze the impact of using the aop technique on the simulation time and on the size of the executable file of cryptographic model. the modeling was carried out with systemc 2.3.2 language and aspectc++ 2.2, and the validation of the aes systemc aop model was carried out on a pc equipped with the ubuntu 18.4 operating system, an intel core i3-4010u 1.7ghz microprocessor, a ram of 6gb, and the gcc 7.2.0 compiler. a. aes systemc aop model validation a series of simulations will be performed in order to validate the proposed systemc-aop model. the validation is performed using the functional verification environment. the keys and data randomly generated by the testbench module are distributed to the reference aes model and the proposed aes model through the transactor module. the two models are simulated with the same simulation model and using the same test conditions. the verification results show that the proposed aes systemc model works perfectly and it provides the same results as the reference model. figure 5 shows an extract of the report simulation results. fig. 5. aes systemc aop: report simulation results. b. impact of aop on simulation time to analyze the impact of aop on simulation time, a series of simulations were performed using the developed environment. this process consists of measuring kernel time (ktime) and user time (utime) using two fault detection schemes. note that ktime and utime depend on the number of join points as well as the number of modules to be inserted via the aop technique. table i shows the simulation results in terms of ktime and utime using two scenarios (systemc and systemc_aop). we can see that the margin of error of the measurement tool (linux commands) that was used is very low and does not affect the accuracy of the simulation results. these results show that the weaving of key_generator, controller_unit, database, input_interface, output_interface and fds modules into the systemc model, using the aop technique, does not affect simulation times. another very important parameter for analyzing the impact of aop is the size of the resulting executable file. table ii presents the size of the executable files generated by aspectc ++ and the systemc kernel for the two scenarios. the simulation results show that even when the proposed model is modeled using two languages (systemc and aspectc ++) and that the weaving of all modules is carried out via the engineering, technology & applied science research vol. 11, no. 1, 2021, 6719-6723 6723 www.etasr.com mestiri et al.: aes high-level systemc modeling using aspect oriented programming approach aop technique, the size of the executable files remains almost unchanged. this shows that the aop does not have a significant impact on the size of the executable file. table i. simulation time analysis with and without aop aes (systemc aop) ktime (s) utime (s) systemc systemc_aop systemc systemc_aop aes model protected by fds [1] 0.039 0.041 2.133 2.135 aes model protected by fds [11] 0.036 0.037 2.065 2.070 aes model protected by fds [12] 0.041 0.038 2.259 2.265 table ii. simulation of the executable file with and without aop aes (systemc aop) systemc systemc_aop aes model protected by fds [1] 1.226mo 1.219mo aes model protected by fds [11] 1.305mo 1.309mo aes model protected by fds [12] 1.346mo 1.350mo vi. conclusion in this paper a new aes systemc model using the aop technique at the electronic system level was presented. a functional verification environment was proposed to test the functionality of the aes systemc aop model, the impact of aop on simulation time and on size of the executable files. the simulation results show the efficiency of the proposed aes model and the weaving of aes modules using the aspectc++ does not have a significant impact on simulation time and on the size of the executable file. acknowledgment this publication was supported by the deanship of scientific research at prince sattam bin abdulaziz university, alkharj, saudi arabia. references [1] h. mestiri, n. benhadjyoussef, and m. machhout, “fault attacks resistant aes hardware implementation,” in 2019 ieee international conference on design test of integrated micro nano-systems (dts), gammarth-tunis, tunisia, apr. 2019, https://doi.org/10.1109/dtss. 2019.8914979. [2] j. zhang, n. wu, f. zhou, f. ge, and x. zhang, “securing the aes cryptographic circuit against both power and fault attacks,” journal of electrical engineering & technology, vol. 14, no. 5, pp. 2171–2180, sep. 2019, https://doi.org/10.1007/s42835-019-00226-6. [3] e. s. i. harba, “secure data encryption through a combination of aes, rsa and hmac,” engineering, technology & applied science research, vol. 7, no. 4, pp. 1781–1785, aug. 2017, https://doi.org/ 10.48084/etasr.1272. [4] a. alamer and b. soh, “design and implementation of a statistical testing framework for a lightweight stream cipher,” engineering, technology & applied science research, vol. 10, no. 1, pp. 5132–5141, feb. 2020, https://doi.org/10.48084/etasr.3250. [5] b. lin and f. xie, “scbench: a benchmark design suite for systemc verification and validation,” in 2018 23rd asia and south pacific design automation conference (asp-dac), jeju, south korea, jan. 2018, pp. 440–445, https://doi.org/10.1109/aspdac.2018.8297363. [6] s. aygün, l. kouhalvandi, b. örs, and e. o. güneş, “karatsuba ofman multiplication implementation on systemc for diffie-hellman key exchange algorithm,” in 2017 ieee 4th international conference on knowledge-based engineering and innovation (kbei), tehran, iran, dec. 2017, pp. 0641–0645, https://doi.org/10.1109/kbei.2017.8324878. [7] u. t. gabor, c. von egidy, and o. spinczyk, “interface injection with aspectc++ in embedded systems,” in 2019 ieee 19th international symposium on high assurance systems engineering (hase), hangzhou, china, jan. 2019, pp. 131–138, https://doi.org/10.1109/ hase.2019.00028. [8] c. borchert and o. spinczyk, “hardening an l4 microkernel against soft errors by aspect-oriented programming and whole-program analysis,” acm sigops operating systems review, vol. 49, no. 2, pp. 37–43, jan. 2016, https://doi.org/10.1145/2883591.2883600. [9] n. veeranna and b. c. schafer, “s3cbench: synthesizable security systemc benchmarks for high-level synthesis,” journal of hardware and systems security, vol. 1, no. 2, pp. 103–113, jun. 2017, https://doi.org/10.1007/s41635-017-0014-1. [10] j. treus and p. herber, “early analysis of security threats by modeling and simulating power attacks in systemc,” in 2020 ieee 91st vehicular technology conference (vtc2020-spring), antwerp, belgium, may 2020, pp. 1–5, https://doi.org/10.1109/vtc2020spring48590.2020.9129426. [11] m. bedoui, h. mestiri, b. bouallegue, and m. machhout, “a reliable fault detection scheme for the aes hardware implementation,” in 2016 international symposium on signal, image, video and communications (isivc), tunis, tunisia, nov. 2016, pp. 47–52, https://doi.org/10.1109/ isivc.2016.7893960. [12] m. bedoui, h. mestiri, b. bouallegue, m. marzougui, m. qayyum, and m. machhout, “an improved and efficient countermeasure against fault attacks for aes,” in 2017 2nd international conference on anti-cyber crimes (icacc), abha, saudi arabia, mar. 2017, pp. 209–212, https://doi.org/10.1109/anti-cybercrime.2017.7905292. microsoft word etasr_v11_n1_pp6696-6702 engineering, technology & applied science research vol. 11, no. 1, 2021, 6696-6702 6696 www.etasr.com raza et al.: performance analysis of selective mapping in underwater acoustic orthogonal frequency … performance analysis of selective mapping in underwater acoustic orthogonal frequency division multiplexing communication system waleed raza college of underwater acoustic engineering and key laboratory of marine information acquisition and security, ministry of industry and information technology, and acoustic science and technology laboratory, harbin engineering university, harbin china waleed@hrbeu.edu.cn xuefei ma college of underwater acoustic engineering and key laboratory of marine information acquisition and security, ministry of industry and information technology, and acoustic science and technology laboratory, harbin engineering university, harbin china maxuefei@hrbeu.edu.cn amir ali college of underwater acoustic engineering, harbin engineering university, harbin, china amir@hrbeu.edu.cn asif ali college of nuclear science and technology, harbin engineering university, harbin, china aliasif@hrbeu.edu.cn asif raza college of mechanical and electrical engineering, harbin engineering university, harbin, china asif.raza57@yahoo.com shahabuddin shaikh college of underwater acoustic engineering, harbin engineering university, harbin, china shahabshaikh@hrbeu.edu.cn abstract-under-water acoustic (uwa) communication networks are commonly formed by associating various independent uwa vehicles and transceivers connected to the bottom of the sea with battery-operated power modems. orthogonal frequency division multiplexing (ofdm) is one of the most vital innovations for uwa communications, having improved data rates and the ability to transform fading channels into flat fading. moreover, ofdm is more robust on intersymbol and inter-carrier interferences (isi and ici respectively). however, ofdm technology suffers from a high peak to average power ratio (papr), resulting in nonlinear distortions and higher bit error rates (bers). saving power of battery deployed modems is an important necessity for sustainable underwater communications. this paper studies papr in uwa ofdm communications, employing selective mapping (slm) as a tool to mitigate papr. the proposed slm with the oversampling factor method proves to be less complex and more efficient. simulation results indicate that slm is a promising papr reduction method for uwa ofdm communications reducing ber. keywords-underwater acoustic communication; orthogonal frequency divisional multiplexing; peak to average power ratio; selective mapping i. introduction under-water acoustic (uwa) wireless communications are utilized in military and civil applications. for military purposes, reliable communication is needed between submarines and autonomous underwater vehicles on the battlefield [1], as the overall operations depend on fast and flexible communications. in civil applications, uwa is essential in studying the underwater environment, and investigating further oil and gas explorations [2, 3]. uwabased networks are different from terrestrial radio-based networks due to propagation delays, transmit energy, bandwidth, and multipath effects that affect the channel drastically [4-6]. acoustic signals have a limited propagation speed around to five orders of magnitude lower than radio signals. therefore, the techniques used in radiofrequency cannot be directly implemented in uwa-based networks. in uwa wireless communication, ofdm is implemented over uwa channels keeping in mind channel propagation and the complexity of the medium, while multipath arrivals and doppler shifts make it more challenging [7]. however, ofdm has several advantages as it improves the flexibility of channel conditions and data rates, and results in better bandwidth with high spectral efficiency [8-10]. however, ofdm has several drawbacks, such as high papr and carrier frequency offset. when the peaks of a signal move towards the nonlinear region of the power amplifier (pa), distortion is created, overall system's efficiency is reduced, particularly for pa, while the complexity increases sharply for analog to digital (adc) and digital to analog converters (dac) [11, 12]. ofdm has become a significant standard in communication networks. its major drawback of high papr corresponding author: xuefei ma engineering, technology & applied science research vol. 11, no. 1, 2021, 6696-6702 6697 www.etasr.com raza et al.: performance analysis of selective mapping in underwater acoustic orthogonal frequency … results in low energy efficiency, hence it is very difficult to implement an ofdm system in battery-powered modems in a uwa environment. utilizing high-power amplifiers (hpa) and linear converters could overcome this drawback, but would increase cost and complexity. efficient papr reduction techniques could solve this problem without complex hardware, keeping in mind the linear range of the power amplifier before design to avoid the saturation of hpa [12-15]. inand out-band distortions are created by the saturation process, which increases ber and band distortion, while it also causes adjacent channel interference [16-19]. in long-term applications of uwa communication networks, such as ocean monitoring, the pa always works in full power mode and the system becomes vulnerable due to limited powered modems. many factors influence the performance of papr, including the subcarrier number, modulation types and order, constellation type, and pulse shaping. papr can be reduced by many methods having merits and limitations, as there is always a compromising balance between bandwidth, computational complexity, average power, etc. many researchers introduced such techniques and classified papr into several classes. in terrestrial communication, clipping is the easiest way to mitigate papr [20-23]. moreover, reconstruction of the lost clipped signal, iterative clipping, and filtering have been introduced [24-26]. peak windowing is an improved clipping method [27], while a further enhancement was introduced in [28]. the concept of the envelope scaling method was suggested in [29]. in probabilistic schemes, slm and partial transmit sequence (pts) were suggested in [30-33]. tone reservation (tr) following as a linear programming problem and regarded as a projection onto convex sets (pocs) was studied in [34-35]. moreover, several types of companding techniques have been introduced [36]. an improved companding technique for uwa ofdm communication was presented in [37]. the tone injection (ti) method had a severe drawback, as signal power increased due to the injected signal [38]. the interleaving and active constellation extensions are also papr reduction techniques. this paper proposes the utilization of selective mapping (slm) with an oversampling factor in ofdm uwa communications to reduce papr and improve ber with lesser complexity. ii. system model and ofdm modulation in uwa a. ofdm modulation the summation of subcarriers is modulated separately by using phase shift key (psk) or quadrature amplitude modulation (qam) to form an ofdm signal. they are transmitted through a transducer as a data stream from the ofdm modulator. the inverse fast fourier transform (ifft) is applied as: 1 2 ,0 ( ) ( ) k n j f t n k k dn n x t d t nt e πφ ∞ − =−∞ =  = −  ∑ ∑ (1) [ ]2 0 0 otherwise ,k j f t k k d te t πφ ϕ = = ε (2) and: 0k d k f f t = + , ( 0,...., 1)k n= − (3) where fk shows the kth frequency of subcarriers, f0 is the lowest, and td represents the duration of each symbol. the number of subcarriers is indicated by n when different symbols are transmitted from the ofdm signal. it can be represented by dn,k with n intervals of time by using kth subcarrier. the orthogonality of the subcarrier φk(τ) is described as: 0* 1 0 0 ( ) ( ) ( 1) { dt t k k l d otherwise t t dt t kφ φ δ == − =∫ (4) the demodulator can be represented digitally due to the orthogonality relationship of the subcarriers, after it undergoes several processes such as mathematic operations ifft to fft and modulation to demodulation. the ofdm signal can be implemented as: ( 1) * , 1 ( )* ( ) d d n t n k k nt d d x t t dt t φ + = ∫ (5) figure 1 shows the framework of the proposed uwa ofdm communication system with slm. successively, signals are converted from serial to parallel, mapped in quadrature phase-shift keying (qpsk), and ifft is applied with the proposed slm reduction method to select the minimum papr signal. afterward, the cyclic prefix (cp) amplified by hpa is added, which reduces the isi. at the receiver side, the cp is removed from the signal, followed by the fft and the process of demodulation. finally, each qpsk demodulated symbol is decoded. fig. 1. the framework of uwa ofdm communication system. b. peak to average power ratio peak power is always higher than the average power in an ofdm signal, as the number of subcarriers is added, resulting in high papr. papr is very important in a uwa ofdm communication system, as it affects power efficiency and pa's performance. when papr is high, the peak signals are shifted towards the nonlinear region of the pa, decreasing power efficiency. the papr of an ofdm signal is equivalent to about 12db. isi and ici are due to the nonlinearity among ofdm signals. papr in terms of a discrete-time signal is given by: engineering, technology & applied science research vol. 11, no. 1, 2021, 6696-6702 6698 www.etasr.com raza et al.: performance analysis of selective mapping in underwater acoustic orthogonal frequency … 2 max ( ) 2 ( ) x n n papr e x n n =      (6) applying ifft, discrete time-domain samples are given by: [ ] 2 1 0 1 [ ] , 0 1 in n n i x n x i e n n n π − = = ≤ ≤ −∑ (7) the value of x[n] is zero when the gaussian variables are generated by increasing the value of subcarriers n. we will get rayleigh distributed variance when the value of x[n] is complex gaussian and the phase of the ofdm signal becomes uniform. the rayleigh distribution with a high peak value of signal exceeds nonzero digit probability. hence, the papr of the digital signal exceeds the threshold value 2 0 0 2 p n σ σ = . the ofdm signal x[n] is idft or ifft of complex data symbols. we get this oversampled orthogonal frequency divisional multiplexing signal with help of qam or psk at n subcarriers. papr increases with the subcarrier number n, if n is assumed as a gaussian random variable distributed identically ,0 1x n n n ≤ ≤ − and assume 0 mean and unit power. as we know 2 ( [ ])e x n n = is the mean power. then: 2 2 2 0 1 1 ... 1 e x e x e x n n n n − + + = (8) by adding xi coherently the maximum value is given by: 2 1 max ... 0 1 1 x x x nn    + + +      (9) 2 [ ] n n n = (10) equation (10) shows that the highest value of papr becomes n with the subcarriers (n). iii. selective mapping in uwa ofdm communication slm can be considered as the most prominent method in uwa ofdm communication systems. this process minimizes papr, as it transmits the signal having the least papr. the generated ofdm symbols are termed as candidates. selective mapping was introduced in [39]. the signal having the minimum papr is transmitted from a various number of identical data blocks. the expression for the original data block , ,..., 0 1 1 t x x x x n    −  is extracted by multiplying this mathematical expression with phase sequence ( ) ( ) ( ) ( ) , ,..., 0 1 1 tu u u u p p p p n  =  −  where 0,1, 2,3..., 1u u= − is the phase sequence defined by u. ifft is applied to each sequence to get a time-domain signal from the frequency domain, resulting in different time domains in the ofdm data blocks. the value of each data block is: u ( ) ( ) ( ) ( ) ... 0 1 1 tu u u u x x x x n   + + + −  and will get a various number of paprs. finally, the signal with minimum papr is selected in the transmitting transducer from the input data blocks and the candidates. the block diagram of the slm with oversampling factor is shown in figure 2. x ) is the ofdm signal candidate for actual transmission, which defined as: ( ) arg min [ ( )] 0 u x papr x u u = ≤ ≤ ) (11) fig. 2. the framework of selective mapping. using nyquist sample rate, the complex envelope of ofdm signal having n subcarriers is regarded as: 2 1 1 ( ) ,0 10 t j n nx t x e t ni in π −∑= ≤ ≤ −= (12) the modulated symbols are represented with xi. gaussian variables can be regarded when the value of x(t) is zero, assuming the subcarrier number n is larger, as proved in the central theorem. with 0.5 variance in the ofdm signal which has rayleigh distribution and the signal x(t) being complex gaussian, the signal phase remains unchanged. the nonzero probability occurs when the signal peaks have rayleigh distribution and will surpass any value. here we have assumed x(t) average power equal to 1, and for . .i i d random variables of rayleigh, it is represented as zn. the probability density function zn is given as: ( ) 2 , 0,1,2,3..., 1 z f z ze n n z n − = = − (13) the papr value is approximated to the maximum value zn. when the value of max z follows max max 0,1,2,3..., 1 z z n n n = = − the probability of papr and the complementary cumulative distribution function (ccdf) of max z below threshold can be given as: ( ) (1 ) z n p papr z e − ≤ = − (14) the papr value can be determined by the data realization on ofdm subcarriers and is also dependent on pilot symbols. to analyze the papr in an ofdm signal, the ccdf is considered as a performance metric when the threshold value is large. the threshold z is exceeded then to search the probability of papr, assuming the ccdf as: engineering, technology & applied science research vol. 11, no. 1, 2021, 6696-6702 6699 www.etasr.com raza et al.: performance analysis of selective mapping in underwater acoustic orthogonal frequency … ( ) 1 (1 ) z n p papr z e − > = − − (15) u phase sequences are created in each data block if the mapping of each phase sequence is not statistically dependent, so the ccdf of papr in the slm becomes: ( ) (1 (1 ) ) z n u p papr z e − > = − − (16) where z shows the threshold, n is the number of the subcarriers, and u represents the phase sequences. from (16) and assuming the subcarrier number n of large and independent samples u by using the nyquist sampling rate, without mentioning band limited and oversampling factor we get (17). a sampled signal doesn't need to have the highest point up to the original signal. at the same time, for getting real values of papr, the signal must be oversampled by an oversampling factor l. authors in [34] first indicated the acceptable four oversampling. then peak power distribution becomes very difficult to derive, hence the approximation of papr with n subcarriers and oversampling distribution with oversampling factors a and n. it was proven that a=2.8 is the better value to reach a decent papr by taking subcarrier number larger than 64. . ( ) ( ) (1 ) n z n p papr z f z e α− ≤ = = − (17) if the papr value surpasses the threshold z, the oversampling is defined as: . ( ) (1 (1 ) ) z n u p papr z e α− > = − − (18) this equation was employed to check the performance of the uwa ofdm communication system, by adding an oversampling factor a. iv. results and discussion the results and numerical analysis of the proposed system were considered with a different number of subcarriers and phase sequences. the uwa channel was established based on the bellhop ray-tracing model. simulations were carried out to further evaluate the performance of the slm scheme for papr reduction. the simulation parameters are shown in table i. table i. uwa ofdm simulation data parameters s/n parameters data 1 sampling frequency 100k 2 bandwidth 6.25k 3 fft points 4096 4 ofdm symbols 23 5 number of subcarriers 128,256,512 6 cyclic prefix time 25ms 7 modulation qpsk 8 pa saturation level 6 9 sound speed 1500m/s the operating frequency of the transmitted signal was kept between 12 and 15k. the bellhop ray tracing channel was created by giving a sound profile in the env file. the transmitting transducer was fixed at 1.5m depth, while a hydrophone was fixed at 5m depth at the receiver's side. the distance between the transmitter and the receiver was 2km, as shown in figure 3. the signal was passed through the power amplifier, transmitted by the transducer, and underwent an underwater acoustic channel before received by the hydrophone. figure 4(a) shows the eigen ray of the multipath bellhop channel. as it can be observed, the underwater acoustic channel had several multipath delays. the signal was reflected and refracted at the bottom of the tank/sea and the surface, while some signals arrived directly at the receiver. figure 4(b) shows the sound speed profile measured while establishing the bellhop multipath channel. fig. 3. schematic layout of uwa communication with single transducer and a single hydrophone. fig. 4. (a) multipath channel eigen ray, (b) sound speed profile in the water. fig. 5. bellhop channel impulse response. engineering, technology & applied science research vol. 11, no. 1, 2021, 6696-6702 6700 www.etasr.com raza et al.: performance analysis of selective mapping in underwater acoustic orthogonal frequency … figure 5 shows the channel impulse response of the uwa channel. the delay between two successive points can be seen with normalized amplitude. this is due to the nature of the uwa channel: the signal meets severe multipath and delays before reaching the destination. figures 6-8 illustrate the reduction of papr using the slm scheme. as it can be noted, increasing phase sequences (u) reduces papr, while increasing the number of subcarriers (n) increases papr. the least papr was observed with 128 subcarriers and 16 phase sequences. fig. 6. papr of ofdm signal with slm, n=128, u=1,2,4,8,16. fig. 7. papr of ofdm signal with slm, n=256, u=1,2,4,8,16. fig. 8. papr of ofdm signal with slm, n=512, u=1,2,4,8,16. in figure 9, the ber probability is described using the bellhop channel in the qpsk modulation. the proposed method was compared with the original signal, clipping, and pts. as it can be observed, the slm outperforms the other papr mitigation methods at the range between 20db and 25db. hence, the proposed method can be utilized in a uwa modem to design a less complex ofdm system. as it can be noted from table ii, the papr reduction is observed at different numbers of subcarriers and phase sequences. all data were extracted from figures 6, 7, and 8 respectively, where the ccdf of papr was equal to 10-4. the best performance of papr was 6.3db with 128 subcarriers and 16 phase sequences. the best performance using 256 subcarriers was achieved with 16 phase sequences. similarly, the optimum performance using 512 subcarriers was achieved with 16 phase sequences. hence, increasing the number of phase sequences in the slm method reduces papr. however, the complexity of the communication system is slightly increased. fig. 9. ber vs signal to noise ratio for qpsk modulation in the bellhop channel. table ii. reduction of papr using slm at various phase sequences and numbers of subcarriers number of phase sequences (u) number of subcarriers (n) papr at 10-4 1 128 11.2db 2 9.4db 4 8db 8 7.1db 16 6.3db 1 256 11.7db 2 10.1db 4 8.8db 8 8.1db 16 7.5db 1 512 12.2db 2 10.6db 4 9.6db 8 8.9db 16 8.4b v. conclusion and future work ofdm is considered as an important modulation technique in uwa communication systems, as it can convert frequency engineering, technology & applied science research vol. 11, no. 1, 2021, 6696-6702 6701 www.etasr.com raza et al.: performance analysis of selective mapping in underwater acoustic orthogonal frequency … fading channels to flat fading channels. it also has robustness over isi and ici, but it is very difficult to implement due to the severe environment of uwa channels. this paper focused on the study of the papr of a uwa ofdm communication, utilizing the slm method to design a novel energy-efficient system. simulation results showed that the slm is the most promising technique to reduce papr. we also showed that increasing the phase sequences in slm resulted in significant gains of the ofdm system in terms of papr and ber reduction. a future study could examine the improvements in the power efficiency of a uwa ofdm communication system by detecting different monomial phase sequences in probabilistic techniques. moreover, the authors plan to continue this research by introducing some innovative, less complex, and intelligent methods for the reduction of papr in uwa communication networks. acknowledgment this work was supported by key technology research of underwater long-time signal collector (no. mb70569), heilongjiang natural science foundation joint guidance project (no. jj2019lh0977), equipment pre-study ship heavy industry joint fund (no. 6141b042865)), key laboratory of the ministry of education of xiamen university (no. uac201804), key research & development and transformation plan of science and technology program for tibet autonomous region (no. xz201901-gb-16), and special fund for local universities supported by the central finance of tibet university in 2018. references [1] s. zhou and z. wang, ofdm for underwater acoustic communications. chichester, uk: john wiley & sons, 2014. 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[39] r. w. bäuml, r. f. h. fischer, and j. b. huber, "reducing the peak-toaverage power ratio of multicarrier modulation by selected mapping," electronics letters, vol. 32, no. 22, pp. 2056–2057, oct. 1996, https://doi.org/10.1049/el:19961384. author profiles waleed raza received a b.e. degree in electronic engineering from the department of electronic engineering, dawood university of engineering and technology, karachi, pakistan, in 2017. he is currently pursuing an m.s. degree in underwater acoustic communication engineering in the college of underwater acoustic engineering, harbin engineering university, china. his research areas of interest include underwater acoustic ofdm communication, machine learning, and digital signal processing. xuefei ma received a b.s. degree in electronic information engineering from the harbin engineering university, china, in 2003, an m.s. degree in information and communication engineering from the harbin engineering university, china, in 2006, and a ph.d. degree in signal and information processing engineering from the school of college of underwater acoustic engineering, harbin engineering university, china, in 2011, where he is currently an associate professor. his research interests include underwater acoustic communication and underwater acoustic signal processing. amir ali received a b.e in electronic engineering from mehran university of engineering and technology jamshoro, pakistan in 2016. he was a junior expert engineer in national engineering services pakistan from 2016 to 2018. currently, he is pursuing an m.s. in underwater acoustic engineering, from harbin engineering university, china. his research interests are wireless communication, underwater image processing, 5g, and iot. asif ali received a b.s degree in physics from shah abdul latif university, khairpur, pakistan in 2017. currently, he is getting an m.s. degree in nuclear engineering from harbin engineering university, china. his current research interests include system engineering, nuclear physics, and nuclear power plant safety. asif raza received a b.e in mechanical engineering from the quaid-e-awam university of engineering, science, and technology nawabshah, pakistan in 2015. currently, he is getting an m.s. degree in mechanical engineering from harbin engineering university, china. his current research interests include thermodynamic engineering, tensegrity compression, and expansion with interdependent dynamics. shahabuddin shaikh received a b.e in mechanical engineering from quaide-awam university of engineering, science and technology nawabshah, pakistan in 2002. he acquired an m.s. in underwater acoustic engineering from harbin engineering university, china in 2014. since 2006 he belongs to nescom in pakistan, and works as a general manager (technical). presently, he is pursuing a ph.d. in underwater acoustic engineering from harbin engineering university, china. his research interests are underwater sound propagation and marine sediments. engineering, technology & applied science research vol. 7, no. 6, 2017, 2340-2344 2340 www.etasr.com purdon and erturk: perspectives of blockchain technology, its relation to the cloud and its potential … perspectives perspectives of blockchain technology, its relation to the cloud and its potential role in computer science education ian purdon school of computing eastern institute of technology napier, new zealand ipurdon@eit.ac.nz emre erturk school of computing eastern institute of technology napier, new zealand eerturk@eit.ac.nz abstract— blockchain ledgers and the cloud are a perfect match. on the one hand, there is an inherent requirement for multiple separate authentication nodes to validate every blockchain transaction with each node requiring substantial encryption calculation capability. on the other hand, massive economies of scale can bring down the cost per transaction, and provide service continuity. additionally, the cloud provides a perfect incubator for proof-of-concept projects. this paper considers the future implications of blockchain, as the concept of disintermediated trustless ledgers stimulates the imagination of computer scientists and innovators. the cloud’s role in implementing this new paradigm is also highlighted, as a new decentralized p2p-cloud model. finally, this paper discusses how blockchain may be integrated into the university level computer science and information technology curriculum. keywords-blockchain; cloud; baas; it education i. introduction blockchain technology is defined as “a tamper-proof, shared digital ledger that records transactions in a public or private peer-to-peer network. distributed to all member nodes in the network, the ledger permanently records, in blocks, the history of asset exchanges that take place …” [1]. blockchain is named after its two key concepts: a) that all related simultaneous transactions are individually hashed and grouped into a “block”, which is cryptographically and uniquely identified with a merkle root hash of all constituent hashes, and b) that each block is permanently “chained” to its immediate predecessor-block. integrity can be verified by using merkle proofs across the entire blockchain, however merkle branch, rather than the header’s merkle root [2]. the unique blockchain contribution was to embed trust into the mechanism through two techniques, a) a free market of independent nodes where consensus of the majority verified integrity at every transaction, and b) permanent public visibility of the complete transaction chain via any of the distributed nodes [3]. for bitcoin, the profit-motive ensures the multiplicity of independent nodes that is necessary for the integrity of a chain, but also that there is an inherent incentive and mechanism to fund the chain in-perpetuity. blockchain implementations vary from the permission-less and completely decentralized model of bitcoin, free of any restriction on participation other than compliance with its protocols, to hybrid permissioned architectures, where relationships and transactions are more formalized [4]. fig. 1. the chracteristics of blockchain technology, from [12] blockchain technology was developed initially for the bitcoin cryptocurrency, to assure all parties that the payer had the means to satisfy the debt before concluding any transaction. however, much of the excitement (and hype) surrounding bitcoin was really about recognizing the innovation of its ‘trustless’ decentralized and consensus-based architecture this new paradigm had the potential to transform or disrupt many engineering, technology & applied science research vol. 7, no. 6, 2017, 2340-2344 2341 www.etasr.com purdon and erturk: perspectives of blockchain technology, its relation to the cloud and its potential … industries, from keeping track of title-deeds for land-registries, to tracking diamonds, to resolving industry-wide legislative reporting requirements in the mineral extraction industry [5]. within its first six years, blockchain progressed from an idea, and simply being the bitcoin enabler, to a “censorship-proof ‘world computer’” [6]. in 2015, melanie swan noted the following categorizations of existing and potential uses [7]. blockchain 1.0 corresponds to the original cryptocurrency uses. blockchain 2.0 arrived with the launch of the ethereum platform in january 2014, as an open-source platform enabling ‘smart contracts’, and focusing on financial contracts, loans, futures, stocks, etc. blockchain 3.0 was defined to cover the gamut of all other non-financial usages, in government, health, science, art, and so on. as a result, blockchain technology has already spawned a significant range of viable use-cases. some authors see blockchain as a foundational technology akin to tcp/ip, and predict an uptake and ubiquity of similar proportions: “it took more than 30 years for tcp/ip to move through all the phases: single use, localized use, substitution, and transformation, and reshape the economy… tcp/ip unlocked new economic value by dramatically lowering the cost of connections.” similarly, blockchain also promises to dramatically reduce the cost of economic transactions. [8]. ii. roadblocks and euphoria vitalik buterin, internet prodigy and chief scientist at ethereum noted that “scalability is now at the forefront of the technical discussion in the cryptocurrency scene ...the bitcoin network cannot process more than 7 transactions per second. if the popularity of bitcoin jumps up tenfold yet again, then the limit will force the transaction fee up to nearly a dollar, making bitcoin less useful than paypal ... there is only really one optimization that can be made: figuring out some way to get past the obstacle that every full node must process every transaction” [2]. bitcoin’s need for transaction transparency as a means to establish trust is also a roadblock against greater penetration of the technology, as privacy and confidentiality are paramount for new users. instruments with so-called permissioned blockchains are an attempt to limit and ensure secure access by only mutually known participants. the tendency to centralization due to the huge processing power required to verify transactions and mine new blocks is another major roadblock for conventional cryptocurrency blockchain 1.0 implementation. gartner fellow and vice president david furlonger notes that bitcoin “proof-of-work activity has been mostly consolidated into four primary mining organizations, all based in china”. if collusion or a single organization can control 51% of the nodes, then the basis of distributed consensual trust is wholly negated. additionally, consolidation of the it sector, may mean that more and more cloud-based solutions are being provided by the large corporations such as amazon and google. according to kopstein, “a failure in one location potentially causes chaos for multiple companies and countless users” [9]. however, it is difficult not be engulfed in the wave of euphoria which underpins most blockchain discussions. melanie swan, in her book 2015 ‘blockchain: blueprint for a new economy’, suggests that with its inherent decentralization, and as a new world-wide computing paradigm, it has “the potential for reconfiguring all human activity as pervasively as did the web … for the discovery, valuation, and transfer of all quanta (discrete units) of anything … hard assets … and intangible assets (votes, ideas, reputation, intention, health data)” [7]. stephan tual, cco of swiss nonprofit startup ethereum, claimed at their 2015 launch and ‘smart contracts’ blockchain, that “the vision of a censorshipproof ‘world computer’ that anyone can program, paying exclusively for what they use and nothing more, is now a reality.” he claims ethereum as the “world’s first zero infrastructure platform” [6]. in late 2016 gartner had blockchain close to arriving at the very pinnacle of their “peak of inflated expectations”, such is the fervor of its supporters [10]. some of the reasons are elaborated on by tyler smith of bhp billiton, in a speech to the international blockchain week 2016 conference organized by consensys media and ens, where he espoused the virtues of a shared consortia model (group of like-minded but possibly economically competitive organizations) which would share and retain public information to meet the regulatory requirements of countries where they mine for resources, whilst saving both the host country and other industry participants billions of dollars which are currently wasted delivering an inferior library via inefficient systems [11]. fig. 2. natural resources and mining industry’s interest, fron [11] the consortium model as proposed by bhp demonstrates the excitement surrounding blockchain due to processing efficiencies, the imbued accuracy of original source transaction information sharing, and the increased integrity and provenance gained through the greater participation of sometimes competing member organisations. iii. blockchain and the cloud the advantages of the cloud were recognized very early in the commentary about blockchain, especially as the world’s major technology vendors exacerbate the hype by jostling for market-share, and attempting to leverage their existing investments in cloud infrastructure. ed featherston writes in his blog, “public cloud providers have three key benefits to address the testing challenges: you can obtain your own dedicated testing environment... you only pay for what you use. you can configure for dynamic resource usage, allowing for true performance testing for application scaling and engineering, technology & applied science research vol. 7, no. 6, 2017, 2340-2344 2342 www.etasr.com purdon and erturk: perspectives of blockchain technology, its relation to the cloud and its potential … identifying breakpoints” [13]. this essentially means a full blockchain ecosystem for users to start working with. from a user’s perspective, the cloud seems to be at the heart of the birth of blockchain, with the random democracy of bitcoin node and mining participation fulfilling parts of the nist definition of cloud computing, as “a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources” [14], or at least, helping define a new form of distributed cloud termed p2p cloud, best espoused by a company called storj, “the first decentralized, end-to-end encrypted cloud storage that uses blockchain technology and cryptography to secure your files.” the article entitled ‘down with the data center: can a peer-topeer swarm replace cloud computing?’ argues that “we could wind up using p2p for some of the same tasks the cloud performs, with a distributed cloud instead of one focused around data centers, something less like a cloud and more like a swarm” [9]. the article goes on to illustrate this with startup space monkey putting a nas into private homes, with a third of the capacity for personal use (with encrypted distribution protection), and the remainder for the p2p distributed datacenter. the article also uses bitcoin and torrent as an argument for a new p2p data-sharing cloud paradigm. the cloud can mitigate many of the roadblocks previously noted for blockchain, by providing baas, a ready-made ecosystem, with best-practice decentralization built into the service. in september 2016, a press release by ibm ceo states: “ibm fuses blockchain, ai and cloud computing into one unit” [15], which reinforces the intertwinement of blockchain and the cloud. as recently as january 2017, microsoft trumpeted their project bletchley as the “code name for extending blockchain by creating both new middleware as well as secure cryptlets”, offering blockchain as a service (baas) on their azure cloud. froystad further elaborates on the ethereum / microsoft liaison: “what ethereum has gained through this partnership, is not only legitimacy but also a world-wide network of data centers that makes it significantly easier to launch a blockchain application. azure is available in 24 regions around the world, so that anyone anywhere can spin up a private blockchain” [16]. this is a way to fail fast and cheap at blockchain projects, and then figure out better ways to use the technology. this is a worldwide distributed lab environment for banks and consortia. by partnering with a company called ripple, whose specialty is inter-ledger protocols, microsoft has further leveraged itself as platformneutral in the cloud delivery of blockchain services. fig. 3. microsoft’s blockchain project [17] ibm have partnered with the linux foundation’s hyperledger offering, leveraging their bluemix cloud and linuxone cloud-capable mainframes. a good example of practical success is everledger, a startup guaranteeing provenance of individual diamonds traded around the world, by recording unique aspects of each stone, like a fingerprint, which then uses hyperledger.org’s open-source blockchain in the cloud hosted by the linux foundation, to record every transaction, with so much success that insurance companies can now repatriate assets, and identify ‘blood diamonds’ [18]. the linux and blockchain connection is also an interesting aspect by itself, and attests a new area where open-source technology can be globally beneficial [19]. amazon are using aws for their foray into financial blockchain use, announcing a “baas sandbox for developers” in partnership with digital currency group, “to spur innovation and facilitate frictionless experimentation” [20], as reported by richard kastelein, which also quotes dcg’s director of community, meltem demirors as saying “the venture capital model has to evolve to enable disruption in financial services, and aws was a natural collaborator given most of our portfolio relies on the aws cloud.”. there are advantages to using the cloud to host blockchains. cloud service providers are offering template driven trials, with very low cost of entry via baas provisioning, and pay-as-you-go operation. this involves user selectable number of nodes, and the inherent advantages of scalability. vendor organizations, with existing cloud services, are actively seeking industry partnerships and proof-of-concept projects in order to position themselves as major blockchain innovators, often providing free starter plans. in permissioned blockchains, a consortium of like-minded participants each contribute their own node as part of a pan-industry blockchain initiative. nodes could be provisioned privately, or use hybrid cloud infrastructure. google’s subsidiary deepmind health’s project for managing and protecting the uk’s health data uses a blockchain-like strategy to assure the public of its purelyintentioned analytical access to otherwise confidential personal health records [21], however in this particular implementation “the ledger won’t be distributed among members of the public, but stored by a number of entities including data processors like deepmind health and health care providers.” according to the company, this will not impede the verification process. the objective of this choice is to make the ledger more efficient. iv. the future of blockchain in the cloud while permissioned private consortia will always make up a significant segment of blockchain implementations, the larger potential appears to be in non-partisan sector-wide implementations, leveraging the value of separate nodes and invoking economies of scale from cloud infrastructure, to yield efficiencies through the strength of the architecture and the value of the shared data. while outlining the implications of new european union rules governing the finance and investment sector, i.e. mifidii (markets in financial instruments directive) due to come into force in january 2018, noelle acheson writes that luxembourg’s fundchain consortium is attempting “a sector-wide system that can leverage transparency, reliability and connectivity. plus, a way to share pricing and identity data without the risk of engineering, technology & applied science research vol. 7, no. 6, 2017, 2340-2344 2343 www.etasr.com purdon and erturk: perspectives of blockchain technology, its relation to the cloud and its potential … interference or centralized control” [22]. she goes on to say that “if luxembourg’s fund managers, service providers and regulators manage to adapt and implement a new type of interaction, the sector could be poised to harness the financial trends that point to an even greater role for wealth management in the world economy.”. outside of major institutions who may form such a consortium, and who have the capacity to maintain their own nodes privately, the vast majority of lesser solutions are likely to be built on platforms provided by the industry’s heavy-hitters, and especially those that have claimed the altruistic high-ground, as ethereum has done as a non-profit organization. similarly, chronicled.com aims at providing a blockchain platform “to create the world’s most trusted iot and supply chain ecosystems”, using quorum, hyperledger, or ethereum’s cloud offerings.” . it is likely that the near future will see a plethora of infrastructure and vendor offerings, and a multitude of proof-of-concept and operational systems, which may converge, as blockchain matures along with growing confidence. microsoft noted in reference to project bletchley, that “creating this open ecosystem will take some time. but if done properly the combination of distributed ledgers and the cloud can usher in the new collaborative economy” [23]. bhp billiton’s geophysicist r tyler smith explains their p2p infrastructure as follows: “in addition working with ethereum, bhp is also running its own nodes on the interplanetary file system (ipfs), a peer-to-peer file sharing protocol that is increasingly being used in conjunction with blockchain systems” [5]. as kopstein noted, there could also be a divergence from the traditional datacenter cloud infrastructure, towards a truer distributed and unrelated peer to peer cloud infrastructure, which would add further integrity and stability to blockchain implementations, with true disintermediation from any single party [9]. v. summary and conclusion integrity in a blockchain is guaranteed because previous data cannot be modified, each block cryptographically references the immediately prior block, and all nodes maintain a complete transcript. the immutability and the continual need to re-assert the full chain at every transaction may become an issue in the future unless ways are developed to streamline it. while data scientists continue to grapple with the issue of scalability, and organizations feel their way through the hype, it is worth noting how far the idea has come in a few years, and the range of industries attempting to realize its potential, from the original cryptocurrencies and financial securities to property registries and diamond and art provenance. furthermore, many of the software processes related to blockchains can be executed by so-called intelligent agents that can work and develop flexibly and independently [24]. concomitant with bitcoin and blockchain, the cloud has been an incubator, both through major it vendors jostling for market-share, but also by provisioning blockchain as a service on their cloud infrastructure. this fortuitous circumstance facilitates proof-of-concept applications without requiring significant startup costs or long-term commitment. using an innovative technology particularly suits online education providers or providers that are designing a new information system [26]. in this context, the hosting of software in the cloud also enables end users to connect and perform searches and queries through their mobile devices. blockchain technology has started being used in the education sector. one example of this is the issuance, tracking, and verification of certificates through a blockchain database, which is used either by a single institution or a consortium of education institutions [27]. furthermore, coupling a blockchain application with cloud use cam also facilitate the demonstration, use, and learning of this new technology at universities and other technology training situations. on one hand, the topic of blockchain may not take off initially and be as popular as internet of things (iot); since the latter also appeals to primarily kinetic and active learners, for example, through the use of connected robots and kits. there are also more job openings that are related to iot, as opposed to jobs involving blockchains. another concern will be around where to place and teach this concept in the computer science and information technology curriculum. the general options for covering any advanced topic include: placement within existing courses (generally at higher or graduate levels), creating new courses for the topic or technology, and addressing the new technology through extracurricular activities such as a symposium, guest speaker, or campus club [25]. the first one of the options above, using blockchain as a novel example or sub-topic within existing courses, has appeal, because it can help make the course more fun and interesting, in addition to being very feasible. this may be in the form of a theoretical discussion as well as a hands-on application. possible computer science courses that may incorporate a blockchain application include database systems, cloud computing, computer networking, advanced business information systems, computer security, computer cryptography, web hosting, and web administration. the authors of this paper hold the position that more research and preparation will be worthwhile to incorporate this interesting topic into the curriculum. teaching a blockchain application will be easier in the cloud, without needing or dedicating additional local hardware. therefore, a good follow-up project is to demonstrate step-by-step in detail how to host, run, and maintain a blockchain application using one of the popular cloud platforms available to university and tertiary institutions such as the google compute engine, amazon aws, or microsoft azure. references [1] s. brakeville, b. perepa, “blockchain basics: introduction to distributed ledgers”, https://tinyurl.com/ya6g6v2w [2] e. buterin, “ethereum scalability and decentralization updates”, https://tinyurl.com/y83q53h9 [3] p. evans, “a strategic perspective on blockchain and digital tokens”, https:// tinyurl.com/hqldvyq [4] m. herlihy, m. moir, “enhancing accountability and trust in distributed ledgers”, https://arxiv.org/pdf/1606.07490.pdf [5] p. rizzo, “world's largest mining company to use blockchain for supply chain”, https://tinyurl.com/y85eh24t [6] s. tual, “annoncement: ethereum launches”, https://tinyurl.com/paqpppp [7] m. swan, blockchain: blueprint for a new economy, o’reilly media, 2015 engineering, technology & applied science research vol. 7, no. 6, 2017, 2340-2344 2344 www.etasr.com purdon and erturk: perspectives of blockchain technology, its relation to the cloud and its potential … [8] m. lansiti, k. r. lakhani, “the truth about blockchain”, harvard business review, pp. 118-127, january/february 2017. [9] j. kopstein, “down with the data center”, https://tinyurl.com/y7dme9dp [10] a. forni, r. meulen, “gartner's 2016 hype cycle for emerging technologies identifies three key trends that organizations must track to gain competitive advantage”, https://tinyurl.com/zh4n83z [11] g. samman, “consortiums and shared ledgers: supply chains as a use case”, https://tinyurl.com/ycr8hqlo [12] a. collomb, k. sok, “blockchain / distributed ledger technology (dlt): what impact on the financial sector?”, digiworld economic journal, issue 103, 2016 [13] e. featherston, “moving test environments to the cloud”, https://tinyurl.com/ycbuptfd [14] p. mell, t. grance, “the nist definition of cloud computing”, https://tinyurl.com/zjqy993 [15] r. kastelein, “ibm fuses blockchain, ai and cloud computing into one unit”, https://tinyurl.com/ybkp85w2 [16] p. froystad, “analysing the ethereum/microsoft baas solution”, https://tinyurl.com/ydhk3jal [17] w. spies, “blockchain basics and partner strategy”, https://tinyurl.com/y6ugr8gw [18] h. levy, “the cio’s guide to blockchain”, https://tinyurl.com/h6ewetb [19] e. erturk, “international technology transfer: the case of free computer software”, international academy of business and public administration disciplines (iabpad) conference, orlando, florida, 2009. [20] r. kastelein, “amazon announces blockchain-as-a-service (baas) sandbox for developers”, https://tinyurl.com/y8psk9yc [21] j. vincent, “google's ai subsidiary turns to blockchain technology to track uk health data”, https://tinyurl.com/y8adefet [22] n. acheson, “why a quiet blockchain consortium could soon make noise”, https://tinyurl.com/ld66hlr [23] m. gray, “introducing project bletchley”, https://tinyurl.com/j9lhee5 [24] m. odhiambo, p. umenne, “net-computer: internet computer architecture and its application in e-commerce”, engineering, technology & applied science research, vol. 2, no. 6, pp. 302-309, 2012 [25] s. kursh, n. gold, “adding fintech and blockchain to your curriculum”, business education innovation journal, vol. 8, no. 2, 2017 [26] e. erturk, “an intelligent and object-oriented blueprint for a mobile learning institute information system”, international journal for infonomics, vol. 6, no. 3/4, 2013 [27] d. clark, “10 ways blockchain could be used in education”, https://tinyurl.com/ycd3uxtg authors profile ian purdon is a lecturer and postgraduate student at the eastern insittute of technology in new zealand. he is enthusiastic about computers. ian is also the former it development manager of enzafoods nz limited. emre erturk received his ph.d. from the university of oklahoma in 2007. he has later taught as an adjunct associate professor with the university of maryland (usa). currently, he works at the eastern institute of technology, new zealand. he has been involved in many it conferences and publications around the world. microsoft word etasr_v11_n1_pp6637-6644 engineering, technology & applied science research vol. 11, no. 1, 2021, 6637-6644 6637 www.etasr.com el fazazi et al.: design of an adaptive e-learning system based on multi-agent approach and … design of an adaptive e-learning system based on multi-agent approach and reinforcement learning hanaa el fazazi laboratory of signals, distributed systems and artificial intelligence enset mohammedia university hassan ii casablanca, morocco mouhcine elgarej laboratory of signals, distributed systems and artificial intelligence enset mohammedia university hassan ii casablanca, morocco mohamed qbadou laboratory of signals, distributed systems and artificial intelligence enset mohammedia university hassan ii casablanca, morocco khalifa mansouri laboratory of signals, distributed systems and artificial intelligence enset mohammedia university hassan ii casablanca, morocco abstract-adaptive e-learning systems are created to facilitate the learning process. these systems are able to suggest the student the most suitable pedagogical strategy and to extract the information and characteristics of the learners. a multi-agent system is a collection of organized and independent agents that communicate with each other to resolve a problem or complete a well-defined objective. these agents are always in communication and they can be homogeneous or heterogeneous and may or may not have common objectives. the application of the multi-agent approach in adaptive e-learning systems can enhance the learning process quality by customizing the contents to students’ needs. the agents in these systems collaborate to provide a personalized learning experience. in this paper, a design of an adaptative e-learning system based on a multi-agent approach and reinforcement learning is presented. the main objective of this system is the recommendation to the students of a learning path that meets their characteristics and preferences using the qlearning algorithm. the proposed system is focused on three principal characteristics, the learning style according to the felder-silverman learning style model, the knowledge level, and the student's possible disabilities. three types of disabilities were taken into account, namely hearing impairments, visual impairments, and dyslexia. the system will be able to provide the students with a sequence of learning objects that matches their profiles for a personalized learning experience. keywords-adaptative e-learning system; knowledge level; learning path recommendation; learning styles; multi-agent; qlearning; reinforcement learning; students’ disabilities i. introduction intelligent tutoring systems offer enable students to get educational resources that satisfy their requirements or interests [1]. most of the methods applied for adaptation are based on the individual characteristics of the learner in order to produce personalized learning content. the most used characters and preferences in adaptive e-learning environments are knowledge level and learning style [2]. the best known and most used is the felder-silverman learning style model (fslsm) [3]. this model is based on eight dimensions, each one containing two categories [4]. authors in [5] conducted a comparative study and analyzed the existing e-learning systems that use the multiagent approach. the conclusion was that none of the studied systems is open source and they all lack in including all the desired characteristics (collaborativeness, flexibility, adaptability, interactivity, and security) in the same system. authors in [6] proposed a model and architecture for developing a personalized multi-agent e-learning system. authors in [7] developed a model of an intelligent learning system based on an agent approach. this model is inspired by intelligent tutoring to present adaptability to distributed virtual learning environments. in addition of using multi-agent, the application of machine learning techniques can also improve elearning systems and make them more and more intelligent [8]. reinforcement learning, as a field of machine learning, can help students to obtain appropriate teaching materials from the learning process. authors in [9] give a technique based on reinforcement learning, more specifically the q-learning algorithm, to produce an adaptive system that matches the needs of each student. authors in [10] suggest an online learning method based on reinforcement learning that can deal with complex environments. the used algorithm, chooses suitable learning objects to recommend to a given student. the literature review showed a lack in the development of e-learning solutions that respond to various characteristics of students. most systems take into account one or two characteristics of learners and students' disabilities are little considerate in these solutions. we have tried to propose a system that takes into consideration the learning styles, knowledge level, and disabilities of the students by applying the multi-agent approach and reinforcement learning to provide an intelligent and adaptive e-learning system. this system will corresponding author: hanaa el fazazi engineering, technology & applied science research vol. 11, no. 1, 2021, 6637-6644 6638 www.etasr.com el fazazi et al.: design of an adaptive e-learning system based on multi-agent approach and … be able to generate the learning path to each student based on individual needs and preferences. in this paper, a design of an adaptive e-learning system based on a multi-agent approach and reinforcement learning is presented. the system will be able to recommend a learning path to students based on their learning style, knowledge level, and disabilities. three types of disabilities were taken into consideration, namely hearing impairment, visual impairment, and dyslexia. the application of multi-agent approach and reinforcement learning will increase system performance and make the process of adaptation more flexible and provide the underlying power of the proposed model. ii. the proposed adaptive e-learning system the proposed adaptive e-learning system aims to recommend a personalized, useful, and interesting learning resource based on students' characteristics and preferences. the principal components used in this system are the learner model, the content model, and the adaptation model. these components interact with each other to provide a customized adaptation of the system according to the learner model, which gathers all the information about the student, and the content model, which describes the learning resources and their structure. this system will try to choose the most suitable content structure for each student, taking into consideration his/her learning style, knowledge level, and disabilities. a. content model the content model contains the learning resources structured in a way that facilitates the process of adaptation when using intelligent e-learning systems. the adopted model consists of four layers represented as a hierarchical network of four levels: course, chapter, learning unit, and learning object (lo) as shown in figure i 1. fig. 1. course organization. the "course" layer is located at the top of the network and represents the root of the content model structure. in this context, the course is composed of a series of chapters corresponding to the different teaching concepts on a particular topic. below the course root, there are some "chapters", each of which deals exclusively with a particular element of the course. the third layer, the "learning unit" layer, contains the different learning units that deal with a part of the course (chapter), this learning unit at a level that is classified primarily as beginner, intermediate or advanced, each category determines its importance to the learner according to the knowledge level. the fourth layer contains the los that are associated with the learning unit. the learning object represents the smallest element of the proposed decomposition. each element of the given structure should be well indexed for the next goal of searching and reusing the learning material. for that reason, all of the elements in the designed structure can also add metadata, which is information about the component itself. these metadata can include the title, author, education level, level of difficulties, interactivity level and type, etc. by applying metadata, learning material searching and recognizing becomes easier since it can contain various information that can be used as an identity for a certain lo. in the context of the defined ontology methods, table i reviews the metadata that can be used for each element described in figure 1. table i. course component metadata * component metadata* course name, dificulty level, course description, course language, course duration chapter name, chapter level, prerequisite, chapter description learning unit name, goal, prerequisite, unit level, los id-lo, name, author, creation date, prerequisite, last modified, difficulty level, keyword, level of interactivity, disabily type, format type, relation type b. learner model adaptive systems typically use different user data depending on the purpose of the adaptation. in our approach, the user is a student, so the system should be able to customize the learning experience according to the needs of the students. since there is a wide range of learner characteristics that can be used in the learner model, the selection of the appropriate characteristics is necessary. a learner model is considered complete if it includes learning history, learner progress in the current learning element, learning style, and other types of learner information [11]. the model we used in the proposed system is based on five dimensions: • general personal information like name, age, gender, etc. generally remains static throughout the use of the system. • personal preferences like the preferred domain, language and media type. • the disability dimension is represented by three types of disabilities, namely hearing impairment, visual impairment, and dyslexia. these disabilities are described with a degree which refers to the gravity of the disabilities and it takes as values: low, medium, and severe. • learning styles are defined according to the feldersilverman model [4]. • information on personal learning status, which brings together the knowledge level, history, and learning objectives to generate a customize adaptation. this type of information will be constantly updated during the learning process. figure 2 describes the ontology used to define these dimensions. the learner profile explains how the learner learns best. it is the standard representation of learners' data that can engineering, technology & applied science research vol. 11, no. 1, 2021, 6637-6644 6639 www.etasr.com el fazazi et al.: design of an adaptive e-learning system based on multi-agent approach and … be collected in two ways: directly from the student or by analyzing his performance through a learning management system [11]. in the first interaction of the learner with the system and after the provision of personal information and type of disability, the learner takes the ils questionnaire to identify the learning style according to fslsm [12]. then, and after he/she chooses the course to study, the learner is asked to take an initial test to define his/her knowledge level and then build the learner profile. all this information is managed by the learner agent who will be explained in detail below. fig. 2. learner ontology. c. adaptation model the adaptation model aims to generate a suitable learning path in order to enhance learning. it uses the information stored in the learner model and the content model to provide the appropriate recommendation. the adaptation model provides a sequence of los according to the learning style, knowledge level, and disabilities of the student. this approach is based on the q-learning algorithm to decide which learning path to take in order to increase the results of the learning process. as presented in the content model and by choosing a learning unit, the learner can browse through the different los of the chosen learning unit. the learning unit can contain theoretical files, examples, exercises, quizzes, diagrams, etc. the learner can browse through these elements (by reading a theoretical file, seeing an example, solving an exercise, taking a quiz). the objective of our system is to choose the los and actions to be done for a more enriching learning process according to the learner profile. for this, we chose to use the q-learning algorithm, which is based on states and actions. the states in our approach are the los and the actions are the relations that link them. each action has a well-defined reward and the algorithm will choose the path with the maximum rewards. the recommendation task is provided by the adaptation agent, who will be discussed below. iii. multi-agent system architecture in this paper, a distributed architecture based on the multiagent approach for modeling the communication and coordination process is proposed which allows the suggested elearning system to recommend los adapted to the learner's profile according to his/her characteristics and preferences. to design this distributed model, we used a set of autonomous agents that are provided with behaviors (tasks and actions to be performed) to search and design an adequate response for the learners. this architecture is interconnected with two systems (two platforms), namely a multi-agent platform designed with java and the moodle lms system which is designed with php. to keep the communication and coordination process between these two systems a set of web services was adopted along with a shared database between them to facilitate access to information and keep the system running easily [13]. figure 3 shows the adopted multi-agent architecture for the implementation of the proposed models to adapt los. this architecture is based on intelligent agents, each agent is characterized with a set of behaviors and roles, i.e. the way to search for data and the way to process and adapt the results according to the requests of other agents, without forgetting the aspect of each agent's autonomy. these agents interact with each other to provide customized content adapted to the characteristics of the students' profile. in our case, each agent is equipped with a knowledge base represented by scenarios to be followed when the system meets the same requests. fig. 3. the multi-agent architecture of the proposed system. each agent entity will be modeled by a sequence of roles and tasks (figure 4) to be executed according to the needs of our system. the coordination process is executed dynamically, each agent can request information or data from other agents. the meshed topology gives us the possibility to have a highly connected architecture. this structure allows the system to optimize the inter-agent communication process as well as to speed up the work rate of the agents to build the best results in a short time. the communication process between agents is characterized by a communication protocol defined by the development platform used. to open a communication sequence between two agents, it is necessary to start first with the authentication of agents to download the profile of each entity. then a communication channel will be reserved for the sharing of data and actions according to a set of commands (inform, request, response). all communication process will be saved in a database that will be linked with the lms database. this link intends to separate the structural architecture of the moodle system from our agent-oriented engineering, technology & applied science research vol. 11, no. 1, 2021, 6637-6644 6640 www.etasr.com el fazazi et al.: design of an adaptive e-learning system based on multi-agent approach and … architecture (figure 5), without forgetting that our ontological architecture is also adapted and transformed into the basic structure of the moodle system to facilitate the process of injecting and consulting data. for data synchronization between the two databases, a set of triggers was used that are provided by the database management system to modify the content of each table without going through the gui. fig. 4. role and task model of agents. fig. 5. agent-oriented conceptual model for the interactions between the multi-agent system platform and the lms. iv. role and task model description for e-learning system actors the modeled architecture is based on multiple agents. these agents are designed to communicate and exchange data in order to provide relevant information to students, such as adequate learning resources that match their characteristics and preferences. the agents in this system must collaborate to carry out the process of adapting los. in our architecture, there are two types of agents. the first type is instantiated once and is a single entity that will be available to perform all the computation and processing required meeting the agents' requests. this approach allows us to reduce the number of agents and to centralize the calculation process in entities that have the roles and calculation methods, to prepare in advance the input values that will be reused by the other agents. the other type of agent (e.g. the learner agent) will be linked to students who are searching for courses in our system. this approach will allow us to create for each student an instance of the learner agent to control his/her profile and give our system the chance to distribute the calculation process and share the information among the students. this mechanism will allow us to make a decomposition of the global system with sub-systems to better manage the life cycle of each learner. a. adaptation interface agent the adaptation interface agent manages all communications between the interface and the system (figure 6). this agent acts as an intermediary who communicates the student's requests to the appropriate agents and then presents the learning material in a suitable format for the student. for the implementation of this agent, we opted to modify the source code of the moodle lms in order to integrate our own hook manager. these elements are needed to interpret requests from students and users of the moodle system to adapt it to our multi-agent system. in a multi-agent architecture, we need to have triggers, the role of these triggers is to inform/send a request or query to an agent to perform a task according to the parameters injected into the query. to enable this communication, the system will need an interface between two different types of programming language, namely the object-oriented php with which the moodle system is developed, and the object-oriented java used for setting up standalone agents. interfacing between these agents is done with web services. the role of these web services is to send http requests between the two platforms in order to design a communication middleware or a communication bridge between the two systems. fig. 6. communication model between the used platforms. b. learner agent in our system, each student will have his own learning agent, the purpose of this multiplicity is to create a distributed system where each student has his own preferences, characteristics, and pedagogical orientations. as soon as a student is logged in the lms, an agent will be created to encapsulate that learner's personal data. it should be noted that engineering, technology & applied science research vol. 11, no. 1, 2021, 6637-6644 6641 www.etasr.com el fazazi et al.: design of an adaptive e-learning system based on multi-agent approach and … in order to have a communication channel with the other agents, we must go through this agent. the learner agent is responsible for collecting information and storing and managing the data in the student's profile. this agent is in periodic communication with a set of agents namely the adaptation interface agent and the control agent. this agent is characterized by two main roles: • knowledge level calculation: each student must take an initial test for a specific course. the results of this test will be processed to identify the student's knowledge level according to the category "beginner", "intermediate", or "advanced". • learning style calculation: the student has to take the ils questionnaire. this questionnaire contains 44 questions [11]. the learner agent will process the answers provided by the learner and calculate the learning style according to the fslsm model. the learning style will be used by our agents to prepare the learning content according to the characteristics and needs of the learner. c. control agent the role of the control agent is to manage the calculation process of the agents and facilitate the access to information to speed up the calculation time within the system. this agent keeps the synchronization process between the agent-oriented system and the moodle platform. this agent controls the agent life cycle. sometimes the system can have anomalies in the execution of the agents or an overload processing may occur in the system, something usual when using java. so, we thought of an automated solution that allows us to create a set of cron jobs (scheduled tasks) that will be executed in the background to empty the agent cache and to restart the agents in a blocking state or else destroy the agent and restart it again. d. evaluation agent each course and unit within our system is characterized by an evaluation that helps us to position the learner in his learning process. in our case we have three different types of evaluation, namely initial tests, post-tests, and exams. this agent can load the list of the assessments associated with each course/unit to evaluate the student's knowledge level at each stage of the learning process. this process is required in order to evaluate the student's learning level and see if the suggested los by the system have improved it. e. adaptation agent the adaptation agent is responsible for generating the learning path to the learner according to the data received from the control agent and the learner agent. the adaptation agent communicates with the content agent to request the los that correspond to the student's learning style, knowledge level, and disabilities. once these data are received, the adaptation agent applies the q-learning algorithm to choose the most beneficial learning path for the current learner. the learning path will then be stored in the database. the process can be repeated if the learning style or one of the adaptation elements is modified. the adaptation agent records the results of the adaptation so that it can be reused for students with similar characteristics. f. content agent the content agent is responsible for searching for los in the database according to the query sent by the adaptation agent. it looks for los that correspond to the learning styles, knowledge level, and disabilities of the learner for a given learning unit. for each unit we have identified a list of los, so the content agent will launch a query to select and retrieve the list of los with a filter optimized according to the learner's profile. the hierarchical structure of the course entity facilitates the process of searching and constituting adequate resources for the learner. the content selected by this agent will then be presented to the learner. this content will then be saved in the database. if this agent will receive the same profile, he will just consult this table to retrieve the content, thus we can reduce the time wasted in processing requests. g. tracking agent as mentioned before, our system is a hybrid platform consisting of two modules. a module for course management and construction, which will be controlled by the moodle lms, and another which is dedicated to the multi-agent architecture. to keep the two modules synchronized we have designed a synchronization mechanism to adapt the content and data already stored in moodle to the needs of our agents. to perform this task, we have designed triggers at the database level and a set of hooks to encapsulate student http requests. the role of the tracking agent is to detect all new events in our system. it will use these hooks to filter the requests from the students and to instantiate and trigger the appropriate agents. v. simulation of the content adaptation process as the learning process is initialized in the system, each agent goes through a series of steps that form its life cycle. agents must communicate with each other in order to be able to exchange and request actions. to describe this communication process, we have used sequence diagrams to represent the interactions between the different agents of the proposed system. during the first interaction with the system, the learner is required to log in and fill in a personal information form. the next step is to take the ils questionnaire to identify the learning style according to fslsm. once the learner's profile is finalized, the learner can start using the system and choose the courses and learning elements that he or she wants to learn. at the beginning of the learning experience, the learner must identify the course to be learned. at this stage, the system asks the learner to take the initial test to determine his/her knowledge level. the initial test includes various concepts that the learner must understand. these concepts are represented by questions from each learning unit of the selected course with different levels of difficulty. the obtained score in this initial test allows us to classify the student in one of the three categories, i.e. "beginner", "intermediate", or "advanced". after determining the knowledge level, the student can begin the learning process by choosing the units to be learned. the system then presents the los of this unit and adapts them to the learner's profile. figure 7 shows the first interaction between a learner and the system. after the authentication of the learner, the system engineering, technology & applied science research vol. 11, no. 1, 2021, 6637-6644 6642 www.etasr.com el fazazi et al.: design of an adaptive e-learning system based on multi-agent approach and … will instantiate a learner agent to manage the profile of this student. then the system will propose the ils questionnaire. after the student completes the questionnaire, the learner agent will be able to calculate the ils score and identify the learner's learning style according to the fslsm model. the identified learning style will be added to the student's profile in the database, and will be displayed for the student. to identify the student's knowledge level about a specific course, three agents are used: the interface adaptation agent, the learner agent and the assessment agent. the course chosen by the student is transmitted to the learning agent. this message will be communicated to the evaluation agent to prepare the initial test by choosing a set of relevant questions from the database with different degrees of difficulty. after passing the initial test, the learner agent calculates the obtained score. this computation is carried out according to the classic method because each question consists of an answer indexed by a key, so when the student ticks an answer, the system will retrieve the value of the selected answer. the final result of this test will be used to identify the student’s knowledge level which will be added to the learner profile to be used in learning scenarios. fig. 7. sequence diagram of the learner's first interaction with the system. figure 8 explains the adaptation process. after receiving the parameters from the learner and control agents, the adaptation agent charges the content agent to select the los according to the learning style, the knowledge level, and disabilities of the learner and regarding a well-defined learning unit. once all los have been retrieved, they will then be transformed to the adaptation agent to determine the order in which they are displayed. because according to the learner's learning style, the system will reorder the los in a logical order that corresponds to the learner. at the end of this step, the learner agent will record the content exposed for the learner in his profile and then this data can be applied and reused in other cases if the system meets a learner who has the same characteristics as the current student. fig. 8. sequence diagram of adaptation process. vi. implementation example for learning path recommendation in this example, we assume the case of a learner who has the following profile: intermediate knowledge level, verbal learning style, and a hearing impairment. the adaptation agent receives this information and then communicates it to the content agent to select the los and their relationships. as discussed above, the los represent states and the relationships between them represent actions. the content agent returns all the resources that match the learner's profile. the adaptation agent must choose the most beneficial path for the current learner. in this example, the content agent reviews 5 learning objects: two text files, an example, an exercise, and a final test with the following actions: readfile, readmore, solveexercise, seeexample, takefinaltest (figure 9). each action has a reward: • readfile: +50 • readmore: +50 • solveexercice: +40 • seeexample: +20 • takefinaltest: +30 • previous: +10 fig. 9. example of lo list for the given student. engineering, technology & applied science research vol. 11, no. 1, 2021, 6637-6644 6643 www.etasr.com el fazazi et al.: design of an adaptive e-learning system based on multi-agent approach and … table ii. reward table of assumed state-action combination 0 1 2 3 4 5 0 0 +50 0 0 +40 0 1 0 0 +50 +20 +40 +30 2 0 0 0 0 +40 +30 3 0 0 0 0 +40 0 4 0 0 0 0 0 +30 5 0 +10 0 0 +10 0 table iii. q-table for the assumed state-action combination 0 1 2 3 4 5 0 0 115.7229 998544553 0 0 60.9999999 99991 0 1 0 0 93.8899 999588963 62.699999 971061 60.9999999 55544 29.99999 99997890 2 0 0 0 62.6999999 999999 0 29.999999 9999999 3 0 0 0 0 60.999999 999999 0 4 0 0 0 0 0 29.99999 99999999 5 0 0 0 0 0 0 fig. 10. example of a learning path starting from the beginning. fig. 11. example of a learning path starting from an example. the rows of table ii represent the states and the columns represent the actions. the result of the q-learning algorithm application to the above example are shown in table iii. the algorithm proposes the best learning path for a given student. the learner can choose to start with any lo and the system will provide the best learning path. for example, if the learner chooses to start learning from the beginning, the best learning path in this case is 0-1-2-4-5 (figure 10). if the student chooses to start with an example, the best learning path is 3-4-5 (figure 11). vii. conclusion in this paper, a design for an adaptive e-learning system based on a multi-agent approach and reinforcement learning has been proposed. the architecture used in this system is based on many agents, each agent taking charge of a welldefined task. the agents are all connected and they communicate permanently to ensure the regular operation of the system. the main functionality proposed in this system is the recommendation of learning paths according to the learning styles, the knowledge level, and the disabilities of the learners using the q-learning algorithm. the proposed architecture provides personalization of the learning experience and provides los that match the profile and the needs of the students. it is a distributed architecture based on autonomous agents that constantly communicate to respond to learner requests. the proposed system can be integrated with any learning management system. the functionalities adopted in this system allow it to interact and communicate with other systems without any obstacle. this interoperability is ensured through the use of web services as well as the ontological representation of the data. in future work, we intend to consider more states and actions to find the optimal learning path. this feature can increase the complexity of the model. deep qlearning seems to be a good solution to this issue. references [1] m. laaziri, s. khoulji, k. benmoussa, and k. m. larbi, "outlining an intelligent tutoring system for a university cooperation information system," engineering, technology & applied science research, vol. 8, no. 5, pp. 3427–3431, oct. 2018, https://doi.org/10.48084/etasr.2158. [2] m. t. alshammari and a. qtaish, "effective adaptive e-learning systems according to learning style and knowledge level," journal of information technology education: research, vol. 18, pp. 529–547, nov. 2019. [3] m. abdullah, w. h. daffa, r. m. bashmail, m. alzahrani, and m. sadik, "the impact of learning styles on learner’s performance in elearning environment," international journal of advanced computer science and applications (ijacsa), vol. 6, no. 9, 45/01 2015, https://doi.org/10.14569/ijacsa.2015.060903. [4] r. felder, "learning and teaching styles in engineering education," journal of engineering education -washington-, vol. 78, no. 7, pp. 674– 681, jan. 1988. [5] m. u. bokhari and s. ahmad, "multi-agent based e-learning systems: a comparative study," in proceedings of the 2014 international conference on information and communication technology for competitive strategies, new york, ny, usa, oct. 2014, pp. 1–6, https://doi.org/10.1145/2677855.2677875. 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[11] k. r. premlatha and t. v. geetha, "learning content design and learner adaptation for adaptive e-learning environment: a survey," artificial intelligence review, vol. 44, no. 4, pp. 443–465, dec. 2015, https://doi.org/10.1007/s10462-015-9432-z. [12] "index of learning styles questionnaire," nc state university. https://www.webtools.ncsu.edu/learningstyles/ (accessed dec. 20, 2020). [13] n. e. a. amrani, o. e. k. abra, m. youssfi, and o. bouattane, "a novel deep learning approach for semantic interoperability between heteregeneous multi-agent systems," engineering, technology & applied science research, vol. 9, no. 4, pp. 4566–4573, aug. 2019, https://doi.org/10.48084/etasr.2841. engineering, technology & applied science research vol. 13, no. 3, 2023, 11051-11057 11051 www.etasr.com chachar et al.: workability and flexural strength of recycled aggregate concrete with steel fibers workability and flexural strength of recycled aggregate concrete with steel fibers kashif hassan chachar department of civil engineering, quaid-e awam university of engineering, science & technology, pakistan kashif19956@gmail.com mahboob oad department of civil engineering, quaid-e-awam university of engineering, science & technology, pakistan engrmahboob04@gmail.com (corresponding author) bashir ahmed memon department of civil engineering, quaid-e-awam university of engineering, science & technology, pakistan bashir_m@gmail.com zameer ahmed siyal department of civil engineering, quaid-e-awam university of engineering, science & technology, pakistan zmeerahmedsiyal@gmail.com kiran fatima siyal department of civil engineering, quaid-e-awam university of engineering, science & technology, pakistan kiranf893@gmail.com received: 16 april 2023 | revised: 20 april 2023 | accepted: 28 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5921 abstract this study examined how concrete workability and flexural strength are affected by steel fibers and recycled aggregates. steel fibers were used in doses between 1-5%, with an increment of 0.5%, and 50% of the natural coarse aggregates were replaced by recycled. two mixes of conventional and recycled aggregate concrete without steel fibers were used as control mixes. concrete mixes were prepared using 1:2:4 and 0.45 water-to-cement ratios. workability was determined using the slump cone. three prism specimens sized 500×100×100mm were prepared for each batch and cured for 28 days in potable water. after curing, the specimens were air-dried in the laboratory and tested to evaluate their flexural strength under two-point loading. the load and deflection were monitored at regular intervals until failure. a comparison of results with control mixes showed that as the percentage of steel fiber increased, flexural strength increased by 69% and deflection decreased by 66%. the use of steel fibers improved the flexural strength of the recycled aggregate concrete by 59%. keywords-demolished waste; recycled aggregates; green concrete; steel fibers; flexural strength; sustainable development; waste management i. introduction the construction industry has undergone drastic changes over time and has faced great challenges, particularly for highrise infrastructures from a strength, safety, and durability points of view. the present global boom of construction is due to the modern development and the increasing accommodation needs in city centers. this increased demand forced the construction industry to opt for vertical instead of horizontal expansion. this requires the demolition of old deteriorated short buildings to construct tall ones. this procedure not only demands excessive engineering, technology & applied science research vol. 13, no. 3, 2023, 11051-11057 11052 www.etasr.com chachar et al.: workability and flexural strength of recycled aggregate concrete with steel fibers use of natural aggregates but also generates a huge quantum of demolition waste. approximately 450 million tons of demolition waste are generated per year in the european union [15], of which 50-55% is concrete. some of this waste is used under floors and in plinth protections but generally goes to landfills for dumping. on the other hand, the shortage of space, particularly in city centers, increases the serious problem of dumping. on-site use of demolition waste still leaves a large amount of waste. another possible use of it is in new concrete, and several studies investigated its use as a substitute for fine and coarse aggregates. concrete waste is large in volume compared to the other demolition waste ingredients. as the major space-taking component of concrete is coarse aggregates, the use of concrete waste as coarse aggregates would consume more waste, facilitating waste management and reducing the use of natural coarse aggregates (nca). furthermore, the use of demolition waste as coarse aggregate provides an alternative indigenous material as a component for concrete. various studies attempted to investigate this problem. one way to increase the strength characteristics of concrete is by using various types of fibers. the use of fibers also aids in the disposal of that material's waste. fibers in concrete have many advantages. the studies in [1-2] made field investigations to highlight the issue, its impact, and its remedies, pointing out that proper implementation of rules and regulations by governments will help to streamline its use. in [3-5], the tensile strength of concrete with recycled coarse aggregates (rca) was investigated, showing that it was similar to conventional concrete regardless of its source, quality, or quantity. in [6], waste from laboratory-tested cylinders was used in the preparation of new concrete beams to check their flexural strength, reporting a minimum difference in peak load from their counterparts, regardless of the dosage of rca. in [7], it was reported that demolition waste can be used as coarse aggregates with minimum loss of flexural capacity if proper design and application limits are considered. in [8], demolition waste was used as coarse aggregates in dosages of 30%, 50%, and 100% to check the flexural capacity of the produced concrete, observing similar crack patterns but a lower flexural strength when varying the tensile reinforcement ratio to 0.5%, 0.79%, and 1.14%. in addition, this study noticed that the ductility of the beams was not influenced by the dosage of the rca. adding recycled materials to concrete reduces its flexural strength [9]. in [10], flexural strength was reduced by 8.8% and 5.5% for 7and 28-day cured normal mix rc beams, respectively, and an 11.68% loss of strength was reported for 28-day cured rich mix concrete beams [11]. fire not only affects the appearance of reinforced concrete beams but also deteriorates their resisting capacity. in [12-14], a 1000°c fire on reinforced rca beams reduced bearing capacity by 8%, 22%, and 32.41% for fire exposures of 6, 18, and 24 hours, respectively. in [16], rca concrete samples were prepared and cured for 1, 2, 7, 28, and 56 days with a compressive strength target between 20-50mpa, and the test results revealed a residual concrete strength of 90% with only a 3% reduction in the modulus of elasticity. in [17-18], fly ash was used in rca concrete to improve strength, showing that a dosage of 25-35% fly ash allows a larger proportion of nca to be replaced with rca made from demolition waste. the studies in [19-22] investigated the mechanical and durability properties of rca concrete with fly ash and customizable water-binder ratios, demonstrating that the use of large amounts of fly ash in recycled aggregate concrete enhanced its properties in terms of compressive strength, tensile strength, and resistance to chloride action. in [23-24], it was shown that rca concrete containing biomass bottom ash behaved worse, concluding that it should only be used in non-structural concrete. in [25], the strength characteristics of rca concrete were positively affected by the quality of the parent concrete, as when the strength of parent concrete was 80-100mpa, rca concrete exhibited properties almost similar to the nca. several studies have investigated the use of fibers to improve concrete properties. the use of steel fibers from waste steel has been also examined in both concrete types. in [26], the effect of the aspect ratio of steel fibers on the flexural strength of rca concrete was studied, using steel fibers between 0.5-2.5% and four aspect ratios. the results indicated that the optimum dosage of steel fibers was 1.5% and that an increased aspect ratio resulted in an increase in strength. in [27], the collective effect of fly ash and steel fibers on the tensile and flexural strength of concrete was investigated, using different doses of fly ash and steel fibers. the results showed that using 2% steel fibers and 30% fly ash increased flexural strength to a maximum of 8%. in [28], the effect of steel fibers was studied in reinforced rca concrete exposed to temperatures of 200, 400, and 600°c, showing that the presence of steel fibers reduced the strength of the concrete but helped in preventing its spalling. in [29], 1-5% steel fibers were used in concrete, showing that the optimal dose was 3% as it provided an 18% and 52% increase in compressive and flexural strength, respectively. in [30], the use of 2.5% steel fibers provided a 61% increase in flexural strength. in [31], it was concluded that using 1% steel fibers in concrete containing 100% rca increased its strength up to 37%. in [32-34], the effect of normal and equivalent mortar volume methods on rca concrete containing steel fibers was studied, showing up to 50% and 35% increase in flexural strength for beams failing in shear and flexure, respectively. in [35] the use of polypropylene and steel fibers in rca was reviewed, concluding that mineral fibers have a better synergistic effect and produce concrete with better properties. in [36], the use of steel fibers in rca concrete improved the strength characteristics of both reinforced and unreinforced concrete beams. not only steel fibers, but also ggbf slag and fly ash [37], biomedical waste [38], curing methods [39], and curing types [40] have been investigated to check their effect on the strength properties of rca concrete. steel fibers and rca were also studied in [41]. although several studies investigated the use of steel fibers in rca concrete, there is a scattering in the optimum dosage, aspect ratio, and type of steel. a similar scatter appears in the results of studies on the flexural strength of fibrous rca concrete. this study attempted to laboratory investigate the flexuralstrength of fibrous rca concrete under two-point loading. engineering, technology & applied science research vol. 13, no. 3, 2023, 11051-11057 11053 www.etasr.com chachar et al.: workability and flexural strength of recycled aggregate concrete with steel fibers ii. materials and methods a. concrete ingredients this study used ordinary portland cement under the brand name pak land. the fineness of the cement was checked with a #100 sieve and was found to be 94%. the initial and final setting times of cement were 68 and 231 minutes, respectively. the values obtained for cement followed astm c150/c150m-18 [42]. hill sand obtained from approved sources was used as fine aggregate. figure 1 shows the sieve analysis results of the fine aggregates, while its fineness modulus was 2.375. the percentage passing through various sieves and the fineness modulus of the fine aggregates were within the allowable ranges of astm c136/c136m-14 [43]. fig. 1. sieve analysis of fine aggregates. fig. 2. sieve analysis of nca and rca. coarse aggregates were also obtained from approved sources and their maximum size was 25mm. the aggregates were sorted for unwanted substances, washed, and dried, and sieve analysis was performed. figure 2 shows the results of the sieve analysis, which were within the allowable ranges of astm c136/c136m-14 [43]. the fineness modulus of the aggregates was 3.18. demolished waste was collected from a demolished ground-story reinforced concrete building. mixed debris, as shown in figure 3, was brought to the laboratory and hammered to a maximum of 25mm, equal to the maximum size of nca, as shown in figure 4. the obtained aggregates were sorted, washed, and dried, and a sieve analysis was performed, as shown in figure 2. the fineness modulus of the recycled aggregates was recorded at 3.18. like conventional aggregates, the parameters of the recycled aggregates were within the allowable ranges of astm c136/c136m-14 [43]. this study used water, obtained from a water supply, with 7.1 ph. fig. 3. demolished waste. fig. 4. nca and rca. figure 5 shows the steel fibers used, which were cut from steel wire of 1mm diameter. the length of each fiber was 25mm. the tensile strength of the fibers was 1140n/mm2. fig. 5. steel fibers. the concrete was prepared in a 1:2:4 ratio. the water-tocement ratio was 0.5. the steel fiber content used in the concrete was 1-5%, with an increment of 0.5%, resulting in 10 batches (b1 to b10). additionally, two control mixes were prepared without steel fibers, one with nca (cc) and another with rca. table i provides the details of the mixes. b. water absorption and specific gravity the water absorption and specific gravity of the aggregates were evaluated following the procedures specified in astm c127 [44], and table ii shows the results. engineering, technology & applied science research vol. 13, no. 3, 2023, 11051-11057 11054 www.etasr.com chachar et al.: workability and flexural strength of recycled aggregate concrete with steel fibers table i. details of concrete mixes b# nca (%) rca (%) steel fibers (%) cement (kg) fa (kg) nca (kg) rca (kg) steel fibers (kg) cc 100 0 0.0 10 20 20 0 0 rca 50 50 0.0 10 20 10 10 0 b1 50 50 0.5 10 20 10 10 0.3 b2 50 50 1.0 10 20 10 10 0.6 b3 50 50 1.5 10 20 10 10 0.9 b4 50 50 2.0 10 20 10 10 1.2 b5 50 50 2.5 10 20 10 10 1.5 b6 50 50 3.0 10 20 10 10 1.8 b7 50 50 3.5 10 20 10 10 2.1 b8 50 50 4.0 10 20 10 10 2.4 b9 50 50 4.5 10 20 10 10 2.7 b10 50 50 5.0 10 20 10 10 3 table ii. water absorption and specific gravity aggregate type specific gravity water absorption (%) natural coarse aggregates 2.57 1.64 recycled coarse aggregates 2.31 3.42 c. workability the workability of the designed mixes was evaluated using the slump cone test following astm c143 [44]. cone filling, rodding, lifting, and measurement of the slump were carried out in a standard fashion, as shown in figure 6. table iii shows the slump values recorded for all mixes. fig. 6. slump cone test. table iii. slump cone test batch no. steel fibers (%) slump (mm) batch no. steel fibers (%) slump (mm) 1 0.00 70.0 7 2.50 60.0 2 0.00 62.0 8 3.00 59.5 3 0.50 61.5 9 3.50 57.0 4 1.00 61.0 10 4.00 55.0 5 1.50 62.0 11 4.50 54.5 6 2.00 61.0 12 5.00 54.0 d. sample preparation and curing three prism specimens with dimensions of 500×100×100mm were prepared in all 12 batches to check the flexural strength of the concrete. in total, 36 prism specimens were prepared. the concrete ingredients in the required proportion were batched by weight, followed by thorough mixing. water was then added, and the mixer was run until a uniform paste was formed. the inner side of the molds was oiled, and each mold was filled in 3 layers and compacted with a needle vibrator. the specimens were demolded after 24 hours and left at room temperature to dry for a day. then all the specimens were cured for 28 days in potable water. figure 7 shows a few specimens. fig. 7. specimens and curing. e. specimen testing after curing, the specimens were taken out of the water and left to dry for 24 hours. all specimens were tested on a universal testing machine under a two-point load, at one-third of either support, following astm c150. during testing, load and deflection were monitored at regular intervals. the failure of the specimens was checked at the maximum sustained load. figure 8 shows a few specimens during the test, and table iv shows the average results of five samples in each mix for both flexural strength and deflection. fig. 8. specimen testing. table iv. average flexural strength batch no steel fiber % load (kn) mean flexural strength (n/mm2) mean deflection (mm) 1 0.00 8.57 6.43 3.40 2 0.00 7.50 5.62 5.34 3 0.50 8.74 6.56 4.40 4 1.00 9.23 6.92 4.18 5 1.50 10.02 7.52 3.82 6 2.00 10.17 7.63 3.64 7 2.50 10.40 7.80 3.18 8 3.00 10.69 8.02 2.34 9 3.50 10.84 8.13 2.12 10 4.00 11.07 8.30 1.88 11 4.50 11.32 8.49 1.56 12 5.00 11.94 8.95 1.14 engineering, technology & applied science research vol. 13, no. 3, 2023, 11051-11057 11055 www.etasr.com chachar et al.: workability and flexural strength of recycled aggregate concrete with steel fibers iii. results and discussion both aggregate types satisfied the standard requirements of well-graded aggregates, as shown in the sieve analysis results. rca absorbed water at a rate of 3.42%, while nca absorbed 1.64%. a comparison of the specific gravity findings of the two aggregates showed that rca had 10% lower specific gravity than nca. this can be attributed to the age of the old concrete and the old mortar connected within the rca. both variables contribute to the higher water absorption of rca. the slump of the traditional concrete was within the acceptable range for the specific mix. however, the slump of the other mixes remained lower than that of conventional concrete. figure 9 compares the traditional and the fiber concrete, whereas figure 10 shows the percentile decrease in the slump of the rca mixes. adding more steel fibers to the mixture caused a drop in the slump value. the maximum drop in the slump (22.9%) was noticed when using 5% of fibers. this demonstrates that the water requirement of the blend is higher when using steel fiber, and it should be taken into account when choosing the w/c ratio for the mix, or else more admixture or mechanical effort will be needed to keep the necessary workability. fig. 9. comparison of slump values. fig. 10. change in slump vs control concrete figure 11 compares the flexural strength results of the concrete mixes with the control mix. it can be seen that rca reduced the flexural strength (-12.5%), but the problem was counteracted with the addition of steel fibers. in all mixes, an increase in flexural strength was observed with the increase in steel fiber content. it is also anticipated that a further increase in steel fiber content will further increase flexural strength and reduce workability, and this should be carefully considered when deciding the dosage of steel fibers. the increase in flexural strength is attributed to the strength of the steel fibers plus their function to provide good interlocking between the ingredients of the concrete matrix, leading to a higher loadcarrying capacity of the hardened concrete. therefore, it can be used in new concrete, along with 50% rca from demolition debris. this will not only lessen the waste management burden but also help in conserving conventional aggregates and protecting the environment. this study used steel fibers made from the new steel wire, but fibers can also be produced from waste steel, further reducing waste issues. figure 12 shows the percentile deviation of the flexural strength of concrete mixes with steel fibers with the control mix. it can be seen that at the highest dose of steel fibers, the increase in flexural strength was 39% compared to the control mix while the same against the recycled aggregate concrete was 59%. fig. 11. mean flexural strength. fig. 12. deviation of flexural strength. figure 13 compares the average deflection for all specimens with the control mix. the pattern of deflection is engineering, technology & applied science research vol. 13, no. 3, 2023, 11051-11057 11056 www.etasr.com chachar et al.: workability and flexural strength of recycled aggregate concrete with steel fibers reversed to flexural strength when increasing steel fiber content. this happens because the addition of steel fibers improves strength and thus reduces deflection. it is also anticipated that further addition of fibers will further decrease deflection, showing that steel fiber content can be used to control strength and deflection. however, it might contribute to the brittleness of the concrete and may result in sudden failure of the member. therefore, this aspect should be studied and considered before deciding on the required displacement control using steel fibers. it may further be observed that rca increased deflection by 57%, but when using 3% steel fibers, it was controlled and reduced by 66.5%. fig. 13. mean deflection test. it was also observed that the specimens failed in flexure which confirms the theoretical failure mode of plain concrete. the analysis of the specimens showed that at failure they did not split into two pieces but the fibers provided an interlocking medium. the same event may have helped improve strength, reduce cracks, and provide the interlocking mechanism to reduce the crack width. iv. conclusion this study examined the workability and flexural strength of binary blended concrete with rca and steel fibers. based on the observations of laboratory investigations, the following can be concluded: • rca had a lower specific gravity and greater water absorption than nca. this greater water absorption increased the water requirement of the concrete mix, necessitating an adjustment to the design. • the mechanical properties of the resulting concrete were significantly affected by rca. compared to the control mix, the use of 50% rca resulted in decreased workability and flexural strength and increased deflection. this is because of old, dry, and porous aggregates that are weaker in strength and need more water. • using a higher proportion of steel fibers and a consistent dosage of 50% rca, flexural strength and deflection increased significantly. the maximum strength increase was recorded at the highest dosage of steel fibers. it is also anticipated that a further increase in fiber content will further increase flexural strength, but the brittleness and durability of concrete may be a problem and need to be carefully considered before 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[44] "standard test method for slump of hydraulic-cement concrete," american society for testing and materials, west conshohocken, pa, usa, standard astm c143/c143m-20, 2020. microsoft word etasr_v10_n6_pp6589-6596 engineering, technology & applied science research vol. 10, no. 6, 2020, 6589-6596 6589 www.etasr.com al-dossari et al.: careerrec: a machine learning approach to career path choice for information … careerrec: a machine learning approach to career path choice for information technology graduates hmood al-dossari information systems department king saud university saudi arabia ziyad al-qahtani information systems department king saud university saudi arabia fawaz abu nughaymish information systems department king saud university saudi arabia mohammed alkahlifah information systems department king saud university saudi arabia asma alqahtani information systems department king saud university saudi arabia abstract-enterprises rely more and more on well-qualified and highly specialized it professionals. although the increasing availability of it jobs is a good indicator for it graduates, they nonetheless may find themselves confused about the most appropriate career for their future. in this paper, a recommendation system called careerrec is proposed, which uses machine learning algorithms to help it graduates select a career path based on their skills. careerrec was trained and tested using a dataset of 2255 employees in the it sector in saudi arabia. we conducted a performance comparison between five machine learning algorithms to assess their accuracy for predicting the best-suited career path among 3 classes. our experiments demonstrate that the xgboost algorithm outperforms other models and gives the highest accuracy (70.47%). keywords-recommendation system; information technology graduates; machine learning; career selection i. introduction information technology (it) jobs continue to grow in several disciplines, such as cloud computing, cyber security, mobile applications and big data analytics [1]. companies rely more and more on well-qualified and highly specialized it professionals. although the increasing availability of it jobs is a good indicator for it graduates, they nonetheless may find themselves confused about the most appropriate future career. thus, there is a need to design and implement a system that can assist it graduates in profession selection based on their skills. recommendation systems have been a research topic for a long time [2]. they are simple algorithms that aim to provide the most relevant and accurate items to the user. a recommendation engine discovers data patterns in a data set by learning users’ choices and produces outcomes that correlate to their needs and interests. the recommendee can make a huge difference in some industries by generating a huge amount of income, as with amazon or netflix. in this paper, we propose careerrec, a recommendation system that relies on machine learning algorithms to help it graduates choose their future career. the proposed system will recommend a career path based on some basic details about the it graduate’s skills, like soft skills (e.g. communication skills, logical thinking) and technical skills (e.g. programming languages, databases, uml, spark, networks). careerrec can be used by senior students, job seekers, and employees. senior students would benefit from the recommender’s guidance about which course is most relevant to their preferences and interests. the recommender can also be utilized by job seekers to explore and identify the skills required by the it market. finally, employees can benchmark themselves against the market and recognize the skills they need to improve their positions. to build careerrec, data were collected from 2255 employees in the it sector in saudi arabia, including their job titles and the skills they possess. the collected data have been used to train and test supervised machine learning algorithms to identify the most appropriate career for the it graduate among 3 career paths (developer, analyst, and engineer). we compared the trained classifiers to assess their accuracy in predicting careers. our experiments demonstrate that the xgboost algorithm outperforms other models in the performance of career advice recommendation. the xgboost algorithm gives the highest accuracy (70.47%) with the lowest error rate. all experiments were conducted using the python programming language. corresponding author: hmood al-dossari engineering, technology & applied science research vol. 10, no. 6, 2020, 6589-6596 6590 www.etasr.com al-dossari et al.: careerrec: a machine learning approach to career path choice for information … ii. background it plays an essential role in creating jobs in all industries. in the united states, for instance, more than 565,000 new it jobs were created between 2001 and 2011, over 95 times more than the total employment in other occupations [3]. furthermore, even over the recession, it jobs grew much faster than non-it jobs between 2007 and 2011, increasing by 6.8% and contributing almost $37 billion to the economy of the united states [4]. according to the us bureau of labor statistics [5], software developers and programmers are expected to add 279,500 jobs by 2022, accounting for about 40% of new jobs in the computing and mathematics fields. although the projected growth for information security analysts is smaller than for software developers and programmers, the rate of growth for information security analysts is expected to be 36.5% making this the fastest growing it job. demand for it occupations stems from a number of factors, including the increased need for cybersecurity, the implementation of electronic medical records, and the increase in the use of mobile technology. according to [6], the 10 most in-demand it jobs for 2020 are ai architect, business intelligence analyst, cloud architect, data professional, developer, devops engineer, helpdesk and desktop support professional, network/cloud administrator, network security professional, and system administrator. saudi arabia has experienced rapid economic growth that has been reflected in the increased adoption of information and communications technologies (icts) in many aspects of business and government organizations [7]. the spending on ict products and services has increased and reached 138.48 billion saudi riyals in 2017, which reinforces the ict market in saudi arabia as the largest in the middle east [7]. many new jobs in it are being created through growing industries that require advanced technical skills, putting pressure on local labor markets and technical education systems. in saudi arabia, the gap between supply and demand will nonetheless continue to expand [7]. reducing the gap between the skills the it market needs and the skills of it graduates is essential in bridging the gap between supply and demand in the ict sector. iii. related work several methods use recommender systems to support decision making [2]. collaborative filtering methods are widely used in recommender systems [8, 9]. generally, there are two collaborative filtering approaches: user-based [10] and itembased [11]. the user-based collaborative filtering approach defines the similarity between two users based on the services or products they commonly used or bought. the item-based collaborative filtering approach, on the other hand, defines the similarity between services or products instead of users. authors in [12] propose a career recommender system to support the decisions of senior high school students about the career they will pursue. to do so, they collected data from 716 senior high school students in the philippines. the proposed recommender was built upon a fuzz-based engine to provide suitable recommendation. they presented 72 rules for the fuzzy model and their system produces reasonable results for making decisions. a recommender system was proposed in [13], in order to help perspective students select suitable it companies in nigeria. the data were collected through an online questionnaire, with 200 respondents. this employed a collaborative filtering recommendation approach, using the c4.5 algorithm to classify the data and generate a decision tree model from the training data set (with 78.84% accuracy). the developed model was used as a knowledge base for a very beneficial front-end web application where students can enter their preferences and view company recommendations. authors in [14] developed a model to provide recommendations for job seekers by matching their profiles with persons with similar profiles (e.g. educational background, professional skills). the data were collected through a google survey distributed on social media in pakistan. this study used the apriori algorithm to mine and extract association rules from the collected data. the algorithm was implemented in r studio and 62 association rules were generated to support the recommendations. recommender systems for educational guidance were developed in [15] to support course selection by students. the proposed feasible predictions for student course selection were based on their marks and choice of job interests. the targeted population for this study consisted of students eager to join fields like engineering, medical, commerce, arts, etc. the authors collected data from 1500 students in india. they used clustering techniques such as the k-means clustering algorithm to find structures and relationships within the data. then, they used an association rule to inspect the associations linking the subgroups. this process was then applied to determine the student characteristics that align with individual characteristics. finally, classification based on fuzzy set theory and rough sets was applied. this system suggested suitable information based on courses, jobs, and activities to support a student’s decision. finally, students were able to make a final decision related to their studies. they filled out a feedback form students and satisfaction was expressed in 95% of the cases. authors in [13] proposed the use of data mining techniques to predict students’ final gpa based on their grades in previous courses. the data were collected from 236 transcripts of female students who graduated from computer sciences college at king saud university, saudi arabia in 2012. a decision tree was implemented using weka tools and then was used to predict students' gpa based on their grades in mandatory courses. this identified the most important courses in the study plan, which had the larger impact on the students' final gpas. authors in [17] investigated the impact of assessment grades and online activity data in the learning management system (lms) on students’ academic performance. the dataset consisted of 241 records of undergraduate students from six different courses delivered from 2017 to 2019. the data were obtained from the deanship of e-learning and distance education at king abdulaziz university. students' data included assessment grades and blackboard activity data. the classification algorithms were implemented using weka tools. five algorithms were used in this study: decision tree, random forest, sequential minimal optimization, multilayer perceptron, and logistic regression. the results revealed that the random forest algorithm performs better for predicting student academic performance, followed by the decision tree. the purpose of the authors in [18] was to investigate the acceptance engineering, technology & applied science research vol. 10, no. 6, 2020, 6589-6596 6591 www.etasr.com al-dossari et al.: careerrec: a machine learning approach to career path choice for information … level of the lms among students in payamnoor and farhangian universities. the study designed a questionnaire that was answered by 200 students, and the results show that most students, regardless of gender, age, and department, were satisfied with the usage of the lms. however, student’s grades seem to play a significant role in the level of satisfaction from the lms. authors in [19] proposed a model for the development of employees' learning (career path) in industrial enterprises. they used a descriptive survey method and field research, the statistical population consisting of all 110 the employees of dana baspar's enterprises. the result shows that the influence of workshop and experimental skills gained by apprenticeship, the effect of training by holding meetings and seminars with experts, and the experience acquired during work are all significant and positive on organizational productivity. the mediation variable of professional skills exists, but the influence of classic and academic training is not positive and significant on organizational productivity, considering the existence of mediation variables. authors in [29] proposed a weighting method that can be used to combine two or more social context factors in a recommendation engine that leverages an exponential random graph model (ergm) based on historical network data. in this paper and in the same (educational) context, we propose a recommender to support an it graduate in selecting his/her future career. the main idea is to calculate skill similarities between the candidate and current employees. iv. research methodology to develop the proposed recommender, the methodology suggested in this research includes the following phases: data collection, data pre-processing, and classification. the flow diagram of our proposed methodology is illustrated in figure 1, and the implementation and experimental study will be described below. fig. 1. flow diagram of the research methodology. a. data collection in this phase, a survey to collect data from current it employees in the saudi market was designed. the survey consisted of several parts such as demographic data, academic professions, and soft and technical skills. the survey was a combination of open and closed questions (see appendix). the survey was then published online, targeting it employees in saudi arabia. focus was given on collecting data from members who wrote on their linkedin profile that they work in it jobs. several enterprises, whether public or private, were covered in the survey, either by direct communication or via email (e.g. universities, elm company, saudi telecom, mobily, sabic, aramco, citc, kacst, and other companies). the data collection stage ended with 2255 responses, and after data filtering, the dataset used in the experiments contained 2167 records. b. data pre-processing in this phase, pre-processing was applied to the collected data to make them suitable for the model-building phase. first, duplicated rows were removed and missing values were assigned. the authors communicated directly with employees via their emails for data imputations or data corrections. then, some inconsistencies with data have been fixed, for example, the number of years has been written as 2 instead of "two". also, the inconsistency between university names and departments has been addressed (e.g. information systems instead of is, king saud university rather than ksu). finally, we conducted several data transformations as follows: • in the designed survey, the participants were asked to fill in 20 skills (10 soft skills and 10 technical and programming skills). the participants were asked to evaluate their level in a given skill as none, low, moderate, or high. programming skills, on the other hand, were designed as a text-free field where the participants entered the list of programming languages they know. after a quick exploration, we noticed that the programming skill included 49 unique programming languages, so we decided to create 49 additional attributes, where each represented a given language (e.g. python) and is "1" if the participant knows the language and "0" if not. • the academic profession has a feature identifying the main major for the respondents (your major/specialization). it had almost 251 unique values and we followed the acm.org curricula recommendations [21] to transform the specialization into its root. according to [21], there are 5 categories for computing specialists: computer science, information systems, information technology, computer engineering, and software engineering. it has been observed that some majors are actually not relevant to computing, although the respondents are working in the saudi it market. thus, in addition to these 5 categorizations, we added one more category for noncomputing majors. at the end of this exercise, the values of the "your major/specialization" feature were transformed into one of the six identified categories, shown in figure 2. fig. 2. distribution of computing majors. engineering, technology & applied science research vol. 10, no. 6, 2020, 6589-6596 6592 www.etasr.com al-dossari et al.: careerrec: a machine learning approach to career path choice for information … • finally, the "job title" feature had 565 unique values. cleaning up this feature was not trivial because the participants wrote job titles using different names for the same job. also, sometimes there were spelling mistakes in the job titles. by following [22, 23], we transformed the values of "job title" into 37 distinct job titles (figure 3). for the purposes of this study, we classified these 37 jobs into 4 groups (or career paths) shown in table i. the last group (others) represents job titles not directly relevant to computing (i.e. managerial or support jobs). fig. 3. distribution of job titles. table i. it jobs classification career path job titles analyst (10 jobs) analyst, systems analyst, business analyst, data analyst, application analyst, solution architect, database administrator, it consultant, it director developer (8 jobs) developer, programmer, business developer, information systems specialist, security specialist, quality assurance specialist, it specialist, software engineer engineer (4 jobs) engineer, system engineer, network engineer, system administrator, technical support specialist others (14 jobs) chief executive officer, head of it, it advisor, it assistant, it officer, it supervisor, project coordinator, researcher, team leader, ux/ui designer, vp of information technology, trainer, it manager, computer operator c. feature engineering in this phase, some irrelevant features that did not contribute to predicting the best career path for the it graduate were removed. features such as nationality, gender, email, job location, work sector, and work domain were removed from the data. we used label encoding with categorical variables (e.g. soft skill, technical skill, degree, and major). encoding is one way of using categorical predictor variables in various kinds of estimation models. the target categorical variable is encoded with a value between 0 and n, and the code can be easily decoded by using the same value. d. building the model the aim of this study was to develop a recommendation system to help it graduates select the career best suited for their skills. the research problem has been defined as a multiclassification problem where the potential graduate enters his own skills and the system suggests him/her one of three career paths (developer, analyst, engineer). to do this, the scikitlearn library in python was used to implement several machine learning algorithms. specifically, five machine learning algorithms were used to build the model: • k-nearest neighbors (knn): it is a simple and easy-toimplement supervised machine learning algorithm that can be used to solve classification and regression problems. the knn algorithm stores all available cases and classifies new cases based on a similarity measure. the knn classifies a new case by a majority vote of its neighbors [24]. • decision tree (dt): it is a supervised machine learning technique. in dt, each internal node represents a "test," each leaf node represents a class label, and the path from the root to leaves represents the classification rules [25]. • bagging meta-estimator: this is an ensemble metaalgorithm combining predictions from multiple decision trees through a majority voting mechanism [26]. • gradient boosting: it is a machine learning technique for regression and classification problems that produces a prediction model in the form of an ensemble of weaker prediction models, typically dts. gradient boosting employs a gradient descent algorithm to minimize errors in sequential models [27]. • xgboost: this is a dt-based ensemble machine learning algorithm that uses a gradient boosting framework [28]. xgboost is an optimized gradient boosting algorithm that uses parallel processing, tree-pruning, missing value handling, and regularization to avoid overfitting or bias. v. experiments and results in this section, we evaluate and compare the five classifiers. a. dataset description the data used in this study were collected by a survey distributed among it employees in the saudi market. the participants in the survey included employees, leaders, and decision-makers in the field of it in many government and private sectors. the data were collected during the period from february 2018 to october 2018 and the number of respondents was 2225. the main characteristics of the respondents are shown in figure 4. fig. 4. characteristics of the respondents. engineering, technology & applied science research vol. 10, no. 6, 2020, 6589-6596 6593 www.etasr.com al-dossari et al.: careerrec: a machine learning approach to career path choice for information … b. descriptive analytics in this phase, descriptive analytics were conducted to explore and understand the it market in saudi arabia. more specifically, we wanted to identify the most important skills that employees have in this sector. at first, we explored the skills of it employees who have spent at most five years (entry level) in the labor market. the knowledge of these skills is important for senior students and job seekers. figures 5 and 6 illustrate the soft and the technical skills of the entry-level employees in the saudi market. we suppose an employee posseses a skill if he identified himself as "high" in the targeted skill. fig. 5. percentage of employees identifying themselves as "high" in each soft skill. fig. 6. percentage of employees identifying themselves as "high" in each technical skill. from figures 5 and 6, in general, it is noticeable that the percentage of employees possessing soft skills is much higher that the percentage that possess technical skills. it is obvious that the percentage with the highest ranking technical skill is less than the percentage with the lowest ranking soft skill (29.04% in general programming languages is the highest score in soft skills, and 35.54% in decision making skill is the lowest score in technical skills). one possible explanation is that it is easier for it employees to evaluate whether they have a given technical skill. for example, the percentage of employees who identified themselves as "high" in mobile programming language skills (10.66%) is close to the percentage of those with programming skill in the language swift (13.24%). in contrast, personal skills are difficult to measure, so we find that employees may exaggerate these skills in a way that does not reflect reality. in figure 5, it is obvious that the most important soft skills for entering the saudi it market are logical thinking, working in teams, self-motivation, and problem solving. the most important technical skills, are general programming, software development, web programming, and database designing and coding. these 8 skills can be considered the minimum required skills to enter the saudi it market. figure 7 illustrates the top 7 programming languages that employees in the saudi markets know. java is at the top of this list at almost 67%, which is expected since computing departments at saudi universities teach this language in their programming courses. similarly, some departments teach c++ and php in their academic curriculum. fig. 7. percentage of entry-level employees with each pl. c. predictive analytics five machine learning algorithms were trained and tested to predict the best suited career path for the computing graduates. knn, dt, bagging meta-estimator, gradient boosting, and xgboost were trained using a dataset of 1707 employees to predict the most suitable career among three classes: analyst, developer, and engineer. the "others" class was omitted because the jobs in this class require long experience and specific requirements that do not exist among fresh graduates. these algorithms were trained using 27 features: 10 soft skills (figure 5), 10 technical skills (figure 6), and 7 programming language skills (figure 7). during data preparation, we observed that respondents mentioned 49 programming languages. to build the model, we chose the programming languages mentioned by more than 5% of the respondents. the result is shown in figure 8. fig. 8. accuracy of the 5 ml algorithms in the prediction of the best career path. the result of this phase shows that the gradient boosting algorithm achieved the highest accuracy score at 58.78%, engineering, technology & applied science research vol. 10, no. 6, 2020, 6589-6596 6594 www.etasr.com al-dossari et al.: careerrec: a machine learning approach to career path choice for information … followed by xgboost at 51.52%. from the confusion matrix in figure 9(a), it can be observed that the engineer class had the lowest accuracy (58%), as a large number of participants were incorrectly classified to this class (19% were classified as developers and 23% were classified as analysts). this occurred because this class is the least represented class in this experiment. in the other words, the dataset in this experiment was imbalanced (analyst 38.49%, developer 42.59%, engineer 18.92%). (a) (b) fig. 9. confusion matrix of xgboost algorithm: (a) imbalanced dataset, (b) balanced dataset. to address imbalanced datasets, an oversampling technique was used to replicate the minority class (engineer class in our case) in order to increase its cardinality. the new distribution of our classes after replicating the engineer class was almost balanced (analyst 32.36%, developer 35.81%, engineer 31.81%). the five ml algorithms were trained and tested again on the new dataset, and the result is shown in figure 10. fig. 10. accuracy of the 5 ml algorithms with a balanced dataset. it is obvious that xgboost achieves the highest accuracy at 70.47%, followed by the bagging algorithm at 63.98%. from figure 9(b), it can be noticed that the classification accuracy for the engineer class has improved significantly (from 58% to 80%), and a slight negative impact can also be observed on the accuracy of the classifications of the developer and analyst classes. vi. discussion the scope of this study was the prediction of the best career path for computing graduates as an application of ml algorithms in the field of human resources. this application is not only useful for the computing graduate but can also be used by employers to determine the applicant's suitability for a specific job position. the low accuracy achieved in our experiments can be justified by the small dataset that was used. collecting more data about it employees in the saudi market may help boost classification accuracy. one reason for the low classification accuracy is the method of data collection, which was direct asking the employees about their level of skill acquisition. this method is affected by the credibility and accuracy of the employee's self-evaluation. it might be useful to investigate and use other approaches to define and recognize employees’ skills rather than collecting them directly from the employees. one potential approach to improve the performance and reliability of the proposed model is to acquire employees’ skills indirectly from their colleagues and supervisors. moreover, additional data can be collected from the employees themselves to make sure they fit with their current jobs (i.e. that they are capable at and satisfied with the current position). on the other hand, it might be better to obtain the technical skills of it graduates from their academic records rather than asking them directly. in general, such models offer significant challenges in collecting data and in credibility. it must be emphasized that the accuracy and reliability of the collected data will directly affect the validity of any proposed model. vii. conclusion in this paper, we have proposed careerrec, a recommendation system that helps it graduates select the career that best suits their skills. to do so, five machine learning algorithms were trained and tested using a dataset of employees in the saudi it sector. the experimental results showed that the xgboost algorithm outperforms the other models in supporting career path selection for it graduates. the performance of the proposed system can be improved by collecting more data. more algorithms, such as deep learning models, can be considered to improve the accuracy of the proposed system. also, an alternative approach to measure it employees’ skills might be considered, to provide more accurate and trustworthy training data. appendix the questionnaire: engineering, technology & applied science research vol. 10, no. 6, 2020, 6589-6596 6595 www.etasr.com al-dossari et al.: careerrec: a machine learning approach to career path choice for information … references [1] c. m. veneri, here today, jobs of tomorrow: opportunities in information technology. bureau of labor statistics, 1998. 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[28] t. chen and t. he, xgboost: extreme gradient boosting. 2020. microsoft word 24-3635_setasr_v10_n4_pp6021-6026 engineering, technology & applied science research vol. 10, no. 4, 2020, 6021-6026 6021 www.etasr.com ali et al.: predicting the session of a p2p iptv user through support vector regression (svr) predicting the session of a p2p iptv user through support vector regression (svr) muhammad ali department of computer science & it university of balochistan quetta, pakistan mali.mscs@uob.edu.pk ihsan ullah department of computer science & it university of balochistan quetta, pakistan ihsanullah@um.uob.edu.pk waheed noor department of computer science & it university of balochistan quetta, pakistan waheed.noor@um.uob.edu.pk ahthasham sajid department of computer science buitems quetta, pakistan ahthasham.sajid@buitms.edu.pk abdul basit department of computer science & it university of balochistan quetta, pakistan drabasit@uob.edu.pk junaid baber department of computer science & it university of balochistan quetta, pakistan junaidbaber@ieee.org abstract—scalability and ease of implementation make peer-topeer (p2p) infrastructure an attractive option for live video streaming. peer end-users or peers in these networks have extremely complex features and exhibit unpredictable behavior, i.e. any peer may join or exit the network without prior notice. peers' dynamics is considered one of the key problems impacting the quality of service (qos) of the p2p based iptv services. since, peer dynamics results in video disruption to consumer peers, for smooth video distribution, stable peer identification and selection is essential. many research works have been conducted on stable peer identification using classical statistical methods. in this paper, a model based on machine learning is proposed in order to predict the length of a user session on entering the network. this prediction can be utilized in topology management such as offloading the departing peer before its exit. consequently, this will help peers to select stable provider peers, which are the ones with longer session duration. furthermore, it will also enable service providers to identify stable peers in a live video streaming network. results indicate that the svr based model performance is superior to an existing bayesian network model. keywords-p2p iptv; user behavior; machine learning; svr; bayesian network; session prediction i. introduction the advances in internet speed and bandwidth over the past decade and the growing acceptance of peer-to-peer (p2p) applications have changed the culture of networking. the idea of p2p has opened a new era for the future development of human society, and particularly the digital video industry, by creating platforms for people to cooperate in exchanging data such as files, pictures, videos and music. video streaming over the internet is challenging since initially the internet was not designed for such services. video streaming can involve a very large number of users and it requires huge amounts of bandwidth as compared to other services. live video streaming adds to the challenges as it imposes stringent playback deadlines and uses small buffers. to respond to the need of enabling live streaming over the internet, a number of solutions have emerged. these are client/server, ip multicast, cdn and p2p based architectures. in contrast to other architectures, p2p solution, also called p2p iptv, is potentially self-scalable and can be easily deployed with low cost over the existing infrastructure due to its implementation at application layer. in p2p approach, end-hosts become peers and they are placed in an overlay, virtual, self-organized network. hosts in a p2p network receive stream and relay it to the other peers in the overlay, thus joining peers not only consume but also share resources. nonetheless, implementing real-time video sharing applications through p2p networks poses many challenges due to the heterogeneity of the end-points and access networks, peer dynamics, and other ip network-inherited issues. peer dynamics in a p2p network, when peers join or leave the overlay network without warning, is considered a major problem. when a user leaves the network the availability of the stream to all its dependents peers is disrupted. the dependent peers need some time to reconnect to other stream provider peers to receive the stream. similarly, when a user joins a p2p system, the selection of a stable peer is needed. the majority of the existing approaches to find that stable peer are based on classical statistical methods which generalize the problem to a greater extent making it inappropriate for such a scenario which involves users. as user behavior is a complex issue, changing from one user to another, such models are not very efficient to observe the stability of an individual peer controlled by a user [1, 2]. a few latter works such as [3], attempt to model user behavior through bayesian network, which also considers contextual information. we chose the same approach and aimed at reducing the prediction error. in this paper, an svr based machine learning model is proposed to predict the session duration of a newly joined peer based on his past data. such an outcome can be used in a corresponding author: ihsan ullah engineering, technology & applied science research vol. 10, no. 4, 2020, 6021-6026 6022 www.etasr.com ali et al.: predicting the session of a p2p iptv user through support vector regression (svr) number of ways in topology management of p2p iptv systems for improved quality of streaming. for example, identification of a stable peer can be helpful to design and maintain stable topology resulting in better delivery of video stream. we also compare this model on the same data set with an existing bayesian network model. ii. related work user behavior is playing a vital role in the performance of p2p systems. in order to improve the performance of p2p live video streaming systems, many researchers have modeled different aspects of user behavior. these works can be broadly divided into two types, namely the classical statistics-based methods and machine learning based methods. users have daily patterns in arrivals and session length in a music streaming service. therefore, the user’s first session can predict the following sessions and downtime in the service [4]. similarly, the selection of stable peers enhances the streaming quality of peers and reduces playback interruptions [5]. to study user dynamics in live video streaming services, authors in [6] analyze how user join and leave the streaming service. they divide the user behavior based on the elapsed time and analyze the impact of stream disruption on stability. for this they intentionally put a disruption into a streaming session for 200 seconds and observe the number of remaining users in the session during this period. they notice that some of the users wait until 80 seconds, while others quit the session after 30 seconds. this clearly shows the importance of streaming quality for peer stability. to identify stable peers in the network, authors in [1] use the statistical correlation-based method which reveals that the time spent in the current session is positively correlated to the remaining time in the same session. they also propose a network topology where these socalled stable peers are placed near the root node. another approach [2] that creates a stable backbone and then allows unstable peers to connect to the backbone uses the same principle for the identification of stable peers, which is a core component of the whole approach since the reliability of the system depends upon the stability estimation of the peer. however, stability of peers comes from user behavior and its estimation only from peer’s age needs improvement since user behavior involves several metrics such as time of the day and day of the week [22]. a major contribution in this area appears in [7], in which survival analysis techniques are used to find the impacting factors of stability. they conjecture that stability is impacted by popularity, daytime and streaming quality. this work paves the way to consider models that involve more variables instead of the sole consideration of elapsed time. towards this, authors in [8] first compare the observations of numerous measurements performed over the behavior in live video streaming systems. they extract user behavior metrics, which are studied commonly. they also extract the relationships of these behaviors with the external environment and network performance variables. all this information is collected in the form of a causal graph which can be used in user behavior models. concerning the application of machine learning to iptv systems, a deep neural network-based model is proposed in [9] to choose the appropriate bit-rate to enable adaptive bit-rate streaming. similarly, authors in [10] propose a collaborative filtering method based on transfer learning, which predicts the neighbor peer having best qos by using his past usage experiences of a small number of other peers who have evaluated this node. to restrict the cloud rental cost to a desired qos level, authors in [11] use reinforcement learning in a cloud assisted p2p streaming system. fuzzy logic is used in [12] to construct a p2p iptv overlay. the authors define priority to choose a parent peer which is a combination of peer’s age, upload bandwidth, and utilization. fuzzy logic is used to determine the overall priority of a peer for parent selection. prediction of the next channel in iptv is used to pre-stream the likely channels to users they may choose to watch next. for this purpose an agent-based model attempts to predict the next channel in [13]. the efficiency of different classifiers over the prediction of the next channel has been evaluated in [14]. for session duration prediction, authors in [15] first analyze session length in mobile based online services and then propose a gradient boosted tree based algorithm to predict the length of the users’ sessions. they use this prediction for video recommendation. video disruption has a large impact on video streaming performance by creating high peer dynamics. so minimizing video disruption can improve streaming performance in p2p systems. to minimize video disruption due to user dynamics, one solution is to identify stable peers in the network. for stable peer identification, authors in [3] employ a contextual approach which not only considers users’ past sessions but also includes the impacting variables of the session. they use a bayesian network model in global and local scenarios. in the global scenario, a bayesian network is trained and tested on mixed data of all users while in the local case they train and test the model on data of individual users. their results show that accuracy is far better in the local case. we consider this latter approach to improve its performance further by reducing the prediction error. iii. machine learning models for sessions as discussed above, very few existing works have attempted to include all important variables to model user behavior, so our work aims to consider all established variables for which data are available. these variables have been taken from [8] which has synthesized user behavior measurements for extraction of these variables. these are time-of-day, content type, arrival rate, departure rate, session duration, and popularity. furthermore, we target a local model which learns and predicts the behavior of an individual user. such a model needs to be trained on the data of user activities. to test the model, we will provide it with other available information except the current session duration which it needs to predict. since we need to predict the session duration, which is a regression type problem, we chose to use support vector regressor (svr) model for this problem. to the best of our knowledge, svr has not been used before for this particular problem but it is used for many other regression problems. authors in [23] used svr machine learning models to improve the accuracy of short-term forecasting algorithms based on past electrical load data. to observe the efficiency of svr over this problem, we also re-use a bayesian network model from [3] and compare the results of svr and bayesian network. engineering, technology & applied science research vol. 10, no. 4, 2020, 6021-6026 6023 www.etasr.com ali et al.: predicting the session of a p2p iptv user through support vector regression (svr) a. support vector regressor (svr) as mentioned above, our problem is one of regression type, which is a generalization of the classification problem. in regression, the output of a model is a continuous value in contrast to an output belonging to a finite set. svr is a generalization of support vector machine (svm) which is aimed at binary classification problems. svms formulate the binary classification problems as convex optimization problems which require finding the maximum margins that separate the hyperplane. the hyperplane is represented through support vectors. introduction of an insensitive region around the function generalizes svm to svr. this region is termed as tube. svr attempts to solve the optimization problem of approximating the continuous valued function and in the meanwhile balancing the complexity of the model and prediction error. it means that first a convex insensitive loss function is minimized and the flattest tube (containing most of the training instances) is found. in the next step, the convex optimization problem is solved, which has a unique solution, through appropriate numerical algorithms for optimization. the support vectors represent the hyperplane which consists of training samples lying outside the tube boundary. the most influential instances affecting the shape of the tube are contained in the support vectors [16]. to build and test the svr model for our problem, we use the python machine learning library’s built-in svr model. the svr model has a large number of parameters, which are configurable according to the data nature. to maximize support vector regression efficiency we need to pick the best values for these parameters for the model. below, these parameters are described in detail and the selected value for our model. • kernel: our selected python machine learning library provides several kernel functions for svr. the kernel functions, which are widely utilized are linear, polynomial, sigmoid, and radial basis. one needs to select the right kernel when applying the svr technique. kernel selection is not trivial as it involves optimization strategies to get the best combination. we applied each kernel one by one and analyzed the results. in the developed svr model, we select the radial basis function (rbf) kernel [17]. rbf kernel is the most commonly used kernel with a strong learning efficiency. rbf kernel functions are valid regardless of the conditions. • gamma: the gamma parameter intuitively describes the degree of which the influence of a particular sample of training extends, with low values meaning “far” and high values meaning “near.” the gamma parameters can be interpreted as the opposite of the sample influence radius selected by the model as support vectors. we set different values for gamma parameter during experiments and select 0.1 as the best value for our developed model. • epsilon (ε): it specifies the epsilon-tube within which there is no penalty associated with predicted points within a epsilon distance from the actual value in the training loss function. parameter ε controls the width of the epsilon-tube, used to fit the training data. the ε value can influence the number of support vectors used to construct the regression function. the greater the ε, the fewer support vectors are chosen. however, greater ε values lead to more flat estimates. we set different values for epsilon and analyzed the results. we chose number 0.1 for epsilon, which gives higher accuracy than other values. • c: c is a regularization parameter that manages the tradeoff between obtaining a low training error and a low test error, which is the opportunity to generalize a model to unseen data. we set different values for c during the experiments and selected 100 as the best value for our developed model. b. bayesian network model a bayesian network (bn) is a pair (�,�) , where � = (�,�) is a directed acyclic graph (dag) containing vertices � and edges � [18]. vertices/nodes represent random variables and directed edges show informational or causal dependencies among variables [20]. let us consider a set of random variables, = �,…, . then � is a set of conditional probability functions �( �| �. � ∈ �������( �) ). a directed link in � from � to � means � is the parent of � . parent node has a direct influence on a child node through which the dependency relationships between the two variables is modeled. variables having no parent are independent. bayesian networks are a direct representation of the real world, not of the reasoning process. although the directed edges in a network show direct dependency relationship between the variables, the reasoning process can propagate the information in any direction depending on the required result. conditional independence makes a bayesian network efficient to find the joint distribution. it states that a variable is conditionally independent from all its descendants given the states of its parents. for a given bayesian network, the joint probability distribution over u can be computed as shown in (1): �( ) = ∏ �� �� �, � ∈ �������( �)� ��� (1) the network structure can either be manually constructed by a domain expert or it can be developed from data through learning algorithms [19]. similarly, parameters of each node which are needed to characterize each variable can be assigned manually to each node or learned from data [20]. such a model naturally suits the user behavior model in p2p iptv systems since session duration has dependency relationships with other variables such as content type and popularity. as shown in [3] the bayesian network has been manually constructed and parameters are learned from data. this bayesian network is a mix of continuous and discrete variables. time-of-day and content type are independent variables while the other variables are dependent ones. bayesian network allows estimating any variable in the model, in our case this variable is the session duration which will be estimated in the presence of other variables. we further explain these variables in terms of the dataset in the next section. iv. experiments a. data description the dataset generated through the established model of [21] was used. this model generates a synthetic dataset and it was used because a real dataset for such an experiment was not available. all the datasets we have analyzed either lack major engineering, technology & applied science research vol. 10, no. 4, 2020, 6021-6026 6024 www.etasr.com ali et al.: predicting the session of a p2p iptv user through support vector regression (svr) variables or they do not allow tracing individual users over different sessions. our dataset consist of 462,825 instances. the dataset is divided into two subsets, the training set and the test set using python library [18]. the train_test_split function of the library was used to divide the data. the random_state parameter was set to 5, which will ensure the same random number sequence is produced every time the code is run. the test_size parameter was set to 0.3, which divides the dataset into 70% for training and 30% for testing. we build our model using the training subset and evaluated it with the testing subset. b. feature selection • join time ��: this field includes a number from 1 to 1440 which reflects the user’s joining day time in minutes. this field is available in the dataset. • departure time �� : like joining time, departure time shows the time at which a user leaves a channel. this field is also available in the dataset. • session duration: the length of time between joining time and departure time which is essentially the time a user spends online. it is calculated from �� and ��. • arrival rate: arrival rate is the number of joins in a specific minute of the day. it is deduced from the dataset. • departure rate: it is calculated like the arrival rate by counting the number of leaves/quits in a particular minute. • population: population is the online user count at a given minute of the day. it is also called popularity. • content type: this feature shows the type of the content broadcasted at each minute of the day. there are three types of content, which are fiction, sports, and reality. these types are labeled as 1, 2, and 3 respectively. all these variables were provided to our chosen machine learning models except departure time, since [8] does not mention any impact of departure time on session duration. c. efficiency measurement to measure the performance of our model, we used mean absolute error (mae), mean squared error (mse) and root mean squared error (rmse). mae is an average of absolute differences between the actual target values and the model predicted values. the mae is a linear score which means that all the individual differences are weighted equally in the average: !� = (� )∑ |#� −ŷ�| ��� (2) where, � denotes the number of records in the data set and #� and ŷ� are the predicted and target value respectively the for &'( record. mse calculates the square difference between the model predicted value (session duration) and the actual target value for each point, and then averages those values. for a perfect model this value would be zero and the distance of its value from zero denotes the error. mse can be computed as: )� = (� )∑ (#� −ŷ� ��� )* (3) rmse is a metric similar to mse. it is actually measured in two stages. first, normal mean error is taken. the square root is added to allow the error ratio to be the same as the targets number. rmse is computed by (4): + )� = ,(� )∑ (#� −ŷ� ��� )* (4) d. results to develop the svr model, radial basis function kernel in python was used. similarly, for the bn model the bayes net toolbox for matlab [24] was utilized. furthermore, conditional gaussian inference was used as this model involves continuous variables and to learn the parameters we used the maximum likelihood learning algorithm. we trained the svr model on the training data subset making the session duration the target variable. then we fed the testing subset to our model to predict the session duration. for a fair comparison, we trained the bn model on the same training subset and evaluated it on the same test subset. a scatter plot of actual versus predicted sessions can be seen in figure 1 for both svr and bn models. (a) (b) fig. 1. actual versus predicted sessions (in minutes). engineering, technology & applied science research vol. 10, no. 4, 2020, 6021-6026 6025 www.etasr.com ali et al.: predicting the session of a p2p iptv user through support vector regression (svr) in such a plot the model with higher accuracy exhibits more points near the slope while their spread is small. it is obvious from these two plots that for svr the points are aligned in such a way that it shows a slope and furthermore their distribution is uniform for shorter and longer sessions. by contrast, in the case of bn, the spread is larger which shows larger errors and furthermore for certain lengths the error is further larger. this shows an inconsistency by the bn model and larger error than svr. for a concrete comparison, mae, mse and rmse were calculated for the two models and were plotted in figure 2. considering the three parameters, svr performance is far superior than bn’s. since the unit of session duration is the minute in our experiment, it is evident that the mae of 1.26 is a small error produced by svr. fig. 2. mae, mse, and rmse of svr and bn. to conclude the discussion on results, the plots in figures 1-2 clearly indicate the superior accuracy of svr model over the bn model for this problem on the considered dataset. v. conclusion p2p networking is a suitable choice for broadcasting live videos, thanks to its scalability and ease of deployment. since the building blocks in these networks are the peers, they exhibit the behavior of their users and this network becomes very dynamic. the leaving of a peer may disrupt streaming to consumer peers, which is the key problem for qos of the p2p network. to handle this issue we proposed in advance prediction of the session duration of each peer. this will enable each consumer peer to know the provider peer’s quit time. therefore, p2p network can be managed in such a way that stable peers function as provider peers avoiding the stream disruption due to abrupt departures. towards this, an svr model was proposed, which was compared with an existing bn model. we trained both models on the same training data subset and then evaluated them on the same testing data subset. our results show that svr model performs better than bn and reduces the rmse from 6.85 to 3.07 which is a significant improvement. as a future perspective, other machine learning models will be studied and will be evaluated on real datasets. furthermore, we plan to propose a complete framework for topology design and management through the predictions of machine learning models. references [1] y. tang, l. sun, j.-g. luo, s.-q. yang, and y. zhong, “improving quality of live streaming service over p2p networks with user behavior model,” in advances in multimedia modeling, t.-j. cham, j. cai, c. dorai, d. rajan, t.-s. chua, and l.-t. chia, eds. berlin, heidelberg: springer, 2006, pp. 333–342, doi: 10.1007/978-3-54069429-8_34. 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[24] “google code archive long-term storage for google code project hosting.” https://code.google.com/archive/p/bnt/ (accessed jul. 01, 2020). microsoft word 08-3737_setasr_v10_n5_pp6195-6199 engineering, technology & applied science research vol. 10, no. 5, 2020, 6195-6199 6195 www.etasr.com gatitu et al.: approaches on mitigating variation orders in road construction industry in kenya… approaches on mitigating variation orders in road construction industry in kenya: the case of kenya national highways authority (kenha) james njuguna gatitu sustainable materials research & technology centre jomo kenyatta university of agriculture and technology nairobi, kenya njuguna.g@gmail.com charles karimi kabubo sustainable materials research & technology centre jomo kenyatta university of agriculture and technology nairobi, kenya kabcha2001@gmail.com patrick ajwang department of agricultural and biosystems engineering jomo kenyatta university of agriculture and technology nairobi, kenya ajwang@agr.jkuat.ac.ke abstract−variation orders have been globally identified as a significant reason for poor performance of construction projects. several variation orders have been identified in the kenyan construction industry, however, there is a paucity of information on the approaches to minimize their occurrence. the aim of this study is to identify the practices for variation order mitigation in the public road construction sector in kenya. this is a crosssectional study that was carried out among the stakeholders (clients, consultants, and contractors) involved in road construction projects. the study used the purposive sampling technique whereby the data were collected with the use of distributed questionnaires among clients, consultants, and contractors’ staff with a technical background in civil engineering. the relative importance index (rii) was used for data analysis. according to the findings of the study, the top five recommended approaches for minimizing variation orders include the provision of adequate planning before the initiation of road construction projects, understanding of the contract provisions by all the parties before project implementation, solving of land disputes before the project tender awards, provision of complete project designs, and provision of a brief project scope during the tendering process. this research, therefore, contributes to a pool of knowledge that will enable practitioners and researchers in the construction industry to develop effective models for minimizing variation orders. keywords-variation orders; relative importance index i. introduction road infrastructure in kenya plays an instrumental role in economic development. road network development has experienced a steadfast growth, in line with the government agenda [1]. high quality road network positively impacts the gross domestic product (gdp) of a country [2]. high quality of road connectivity results in reduction of transportation costs and increased profitability of investments [3-8]. despite the recognized benefits of road network development, the majority of road construction projects in kenya is neither completed on time nor is its construction cost within the stipulated budgetary allocation. it has been reported that delays in completion time and increased cost occur in over 70% of the road construction projects in kenya [8]. this has been highly attributed to variation orders occurring during the project lifecycle [8]. variation orders encompass modifications introduced to the original contractual agreement made among the parties involved in the construction project [9, 10]. variations in road construction production predominantly emanate from clients, consultants, and contractors [9, 10]. some of the causes of variation orders that have been reported in construction industry include communication gaps between the stakeholders, delays in the design process, errors and discrepancies in design documents, limited project details, complexity in the nature of the project, insufficient site survey, poor coordination among the involved parties, limited financial resources, lack of qualified personnel, weather conditions, change in economic conditions, change of government policies, technological changes, and lack of knowledge in the availability of construction materials and equipment [11-18]. these factors consequently lead to poor project performance, which unfavorably affects completion time, cost, and the quality of the project [19, 20]. it has been reported that most variation orders are likely to impact constriction works adversely [21-23]. variations in road construction works can result in a substantial alteration of the contract terms, quality of the construction projects, and duration and cost of the project implementation [13, 22]. therefore, identification of ways to resolve and minimize variation orders may enhance the ability of the project team to improve project performance [11, 24]. corresponding author: james njuguna gatitu engineering, technology & applied science research vol. 10, no. 5, 2020, 6195-6199 6196 www.etasr.com gatitu et al.: approaches on mitigating variation orders in road construction industry in kenya… acquiring knowledge on the approaches to reduce variation orders can help the stakeholders to plan effectively before commencement of construction works [25, 26]. a systematic approach to the handling of variation orders in construction projects can effectively minimize cost overruns and time delays [27]. variation management models can be incorporated into project management systems to facilitate the process of handling variations that have occurred or are due to occur [28]. various studies have suggested several recommendations to minimize and handle variation orders [29-31], however, road construction industry has been unable to effectively eliminate them [2]. the complexity of road construction works suggests that it is unlikely to deliver projects without making changes during their lifecycle [30, 32]. liability to variations is a feature that generally embodies nearly all construction projects, although the use of a change management system in construction works can reduce variation orders effectively, however, such systems are yet to be established for use in most construction works [11, 31]. effective change management systems can be developed by recognizing the ways to minimize variation orders [29]. such strategies have been identified, however, none is specific to the kenyan road construction perspective. several variation orders are similar in many construction industries globally, however, some are project and country-specific [33]. the local construction industry is overwhelmed by variation orders which are detrimental to project delivery resulting in unachieved schedules and cost performance. information on the ways that can be utilized to minimize variation orders in the kenyan road construction industry is scarce. this study therefore aims to identify the potential approaches to minimize variation orders in kenya. ii. methodology the study was a cross-sectional descriptive survey. the target population was clients, consultants and contractors’ staff with a technical background in civil engineering that were working in ongoing road construction projects under kenya national highways authority (kenha) during the period of this study. a sample population of 80 participants was selected by purposive sampling technique. questionnaires were used to gather information related to recommendations on the reduction of variation orders in the road construction industry. the considered variables included, among others, adequate planning, identification, and understanding of contract terms before commencement of projects, resolution of land ownership disputes before awarding of project tenders, and the availability of complete designs at the project tendering stage. the variables were rated on a likert scale having values ranging between very important, less important, and not important. relative importance index (rii) was used to rank the importance of each recommendation provided by the respondents. the likert scale was converted into a four-point ranking scale ranging from 1 (not important) to 4 (very important) which was then used to calculate rii as follows: rii � ∑� �∗� (1) where w is the converted weight of likert scale response of the participants (ranging from 1 to 4), a is the highest weight (4 in this case), and n is the number of respondents. a high rii value indicates the importance of the recommendation [30]. iii. results and discussion responses were received from 70 out of a total of 80 distributed questionnaires, thus achieving a response rate of 87.5%. the responses were distributed among the stakeholders as shown in figure 1. fig. 1. participant distribution. the findings of the study on the recommendations to reduce variation orders in road construction industry are shown in table i. the results indicated that 85.7% of the participants recommended that sufficient planning before beginning the road construction project is very important. further, 74.3% recommended that identification and understanding of contract terms before commencement of road construction project is very important. a 74.3% of the study participants indicated that resolving land ownership issues before the project tendering stage is very important in the resolution of variation orders. it was also recommended by the majority (55.7%) of the respondents that it is very important to provide complete designs of the project during the tendering stage of the construction works. the approach of having a consultant to closely coordinate the project design stage was considered very important by the 64.3% of the respondents. the majority of the respondents (61.4%) also indicated that it is very important for experienced supervisors to manage construction works in order to minimize variation orders in road construction works. further, 67.1% of the respondents recommended that provision of a brief description of the project at the tendering stage is very important. communication and cooperation among project team members were indicated to be very important by the 52.9% of the respondents. additionally, most of the respondents (71.4%), recommended that the provision of a detailed description of the construction project is very important. the 45.7% of the respondents recommended that placement of experienced and knowledgeable executives in project planning is very important whereas 5.7% of the participants considered it less important. the results also showed that 44.3% of the respondent reported that it is very important the costing of construction projects to remain within the stipulated budget whereas 45.7% and 10.0% of the participants indicated that it was important and less important respectively. the provision of accurate details on the procurement procedure and the availability of resources was recommended to be a very important approach to resolve variation orders by 31(44.3%) of the respondents. engineering, technology & applied science research vol. 10, no. 5, 2020, 6195-6199 6197 www.etasr.com gatitu et al.: approaches on mitigating variation orders in road construction industry in kenya… further analysis based on rii indicated that the respondents ranked adequate planning before commencement of projects (rii=0.771) as the leading approach in reduction of variation orders in road construction projects. identification and understanding of contractual terms before project implementation (rii=0.749) was ranked second, followed by the resolution of land ownership issues before the project tender awards (r=0.749). table i. recommendations of reducing variation orders recommended strategies to minimize variation orders not important less important important very important rii rank (r) adequate planning before starting construction 0 0 10(14.3) 60(85.7) 0.771 1 identification and understanding of contract terms before the project starts 0 0 18(25.7) 52(74.3) 0.749 2 settle land ownership issues before awarding the tender 0 0 18(25.7) 52(74.3) 0.749 3 complete design provision during tendering 0 9(12.9) 22(31.4) 39(55.7) 0.743 4 the client should provide a brief scope of works during tendering 0 3(4.3) 20(28.6) 47(67.1) 0.726 5 the consultant should closely coordinate the project designing stage 0 1(1.4) 24(34.3) 45(64.3) 0.726 6 an experienced supervisor should manage the construction works 0 3(4.3) 24(34.3) 43(61.4) 0.703 7 communication and cooperation among project team members 0 3(4.3) 30(42.9) 37(52.9) 0.697 8 provide detailed site description during tendering (e.g. soil profile) 0 0 20(28.6) 50(71.4) 0.686 9 experienced and knowledgeable executives in the project planning department 0 4(5.7) 34(48.6) 32(45.7) 0.680 10 sufficient time equired for pre-tender planning phase 0 8(11.4) 25(35.7) 37(52.9) 0.674 11 the costing of the project should be within the approved budget 0 7(10.0) 32(45.7) 31(44.3) 0.666 12 accurate information on the procurement procedure and availability of material during tendering process 0 11(15.7) 28(40.0) 31(44.3) 0.657 13 other authors have reported several recommendations to reduce variation orders in construction industry. according to [34, 35], provision of sufficient site conditions with complete design would help reducing variation orders in construction industry. authors in [36] indicate that incomplete project design is the most significant cause of variation orders in pakistan, hence the provision of complete designs would significantly minimize variation orders. a similar study reported that adequate allocation of funds to construction works, adequate planning for controlling floods during rainy seasons and the utilization of skilled labor are potential approaches that can mitigate variation orders [18]. additionally, provision of adequate funds, correction of errors at the project designs stage and elimination of delay in award of tender were reported as probable strategies for elimination of variation orders in construction industry in ghana [37]. the findings of this study concur with the observation (in vietnam construction industry) that adequate planning of the construction project and clear understanding of the responsibilities of the parties in detailed contract terms are major practices that can minimize variation orders [38]. in gaza strip, it was reported that adequate planning before implementation of construction works and understanding of contract terms by the parties involved are key factors in elimination of variation orders [39]. authors in [17] state that provision of an accurate brief document about the requirements of the project before the design stage by the client would significantly reduce variation orders in saudi arabia construction industry. additionally, as was also observed in the present study, authors in [10] suggested that communication among parties involved in the construction works is paramount to project delivery, hence its enhancement during the project cycle could potentially minimize the occurrences of variation orders. it has been previously reported that incompetent and inexperienced project teams (clients, consultants, and contractors) are responsible for variation orders in construction works [38, 39]. authors in [38] provide a recommendation for the necessity of competent technical staff and executive personnel for effective project management. they also reported that recruiting highly experienced consultants and contractors is necessary in the reduction of variation orders in pakistan construction industry. a study conducted in saudi arabia also reported that hiring of experienced technical staff members would significantly decrease variation orders [17]. clients, consultants, and contractors should, therefore, ensure that their personnel are qualified with pertinent experience to minimize variation orders in construction industries [40, 41]. whereas this study concurs with other studies on the remedies for variation orders, it adds land issues as yet another important factor in resolution of variation orders. it should be noted that none of the studies done elsewhere found land to be a major issue. this seems to be a kenyan specific issue underscoring the point raised earlier that context matter [33] when providing solutions to mitigate variation orders. although this might be context-specific to kenya it might also be a challenge in other countries and it has yet to be researched. in this regard, this study provides a novel contribution to the body of knowledge of the remedies of variation orders. iv. conclusions and recommendations variation orders occur in construction industries worldwide. this study investigated probable preventive measures to reduce variation orders that are prevalent in road construction industry. from this report findings, it has been established that adequate planning before commencement of the project, identification and understanding of contractual terms before project implementation, resolution of land ownership issues before awarding of construction tenders, engineering, technology & applied science research vol. 10, no. 5, 2020, 6195-6199 6198 www.etasr.com gatitu et al.: approaches on mitigating variation orders in road construction industry in kenya… availability of complete project design during tendering, and provision of brief project scope during tendering could effectively minimize variation orders in the construction industry. the local and global construction industry can consider the factors presented herein as insights in the development of effective models that can mitigate variation orders during construction projects. in line with its findings, this study recommends that project implementers should: • ensure adequate planning before commencement of construction works, • 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university technology malaysia kuala lumpur, malaysia faizir.kl@utm.my abstract—one of the major priorities for manufacturing companies in the globalized economy is the ability to offer highquality products to customers at the lowest production cost. globally, process improvement methods and techniques are used to reduce waste and improve product and service quality. this paper aims to propose a systematic model based on process improvement methodologies and tools to help the manufacturing companies decide on cutting tool life and other manufacturing issues. this research seeks to prove that some common industry practices, such as changing cutting tools in machining processes, can significantly affect the economics of production and the overall performance of the plant. the research is mainly based on analyzing real field data using the dmaic methodology to identify improvements in order to achieve a balance between economy and quality in a saudi manufacturing plant. although the study was concerned only with changing cutting tools in the machining process in an air conditioning plant, its findings and conclusions can be generalized to all manufacturing processes. keywords-manufacturing process improvement; dmaic methodology; cutting tool life; machining operations i. introduction in many industries such as the automotive, the military, and the heat, ventilation, and air conditioning (hvac) industries, metal cutting and machining are heavily utilized in the manufacturing processes. the us cutting tool institute (uscti) reported data showing that cutting tool market was worth $2.2 billion on january 2020 [1, 2]. the cutting-tool consumption is usually considered an indicator of manufacturing activity in a specific industry, as those cutting tools represent a primary consumable element in many manufacturing processes. the consumption of cutting tools can be used as a leading indicator of the manufacturing activity, as it measures actual production levels in the manufacturing plant [2]. cutting-tool wear and consumption are considered subjects of major concern [2, 3]. this is of major importance for air conditioning manufacturers and military industries in saudi arabia, which has invested heavily in such industries within its 2030 saudi vision [4, 5, 6, 18]. it is estimated that the size of saudi investments in the hvac manufacturing sector stood at $3.7 billion in 2018 and is projected to grow up to reach $7.1 billion by 2024 [7]. according to [1], cutting-tool life and tool wear is of practical importance in manufacturing companies. cutting tools are used to cut materials to parts as they pass throughout the machining processes. naturally, the quality of the cutting tools will be affected by the modifications on the metal to form appropriate pieces. according to the results of previous studies in this field, the operating conditions and the state of the cutting tools are critical for ensuring the balance between production cost and quality of the final product [2, 3, 8]. the common practice in manufacturing processes when replacing cutting tools is to be based on the experience of the machinist or the operator. it is obvious that this practice has several implications on the process itself from an economic point of view [8]. therefore, the need to develop a more scientific approach to determine the frequency of tool replacement and the optimum corresponding author: ahmed baha eddine aichouni engineering, technology & applied science research vol. 11, no. 1, 2021, 6799-6805 6800 www.etasr.com aichouni et al.: a scientific approach of using the dmaic methodology to investigate the effect of … replacement time is a major concern in the industry [1]. for this reason, many approaches from different perspectives have been reported [1, 2, 3, 8]. the study presented in [2] proposed a cutting tool resource management model based on cam programming and the principles of lean manufacturing. the proposed model was shown to be suitable for increased productivity and cost reduction in machining, through an increased material removal rate (mrr), and maximized cutting tool utilization. the presented algorithm was adequate for efficient selection of cutting variables for maximum mrr, maximum tool utilization, minimum machining cost, and reduced waste in the manufacturing process. furthermore, the model permitted the estimation of aspects related to manufacturing process sustainability in terms of energy use, co2-footprint, and water consumption. recently, a study conducted on the reliability of cutting tools developed a stochastic cutting tool life model that helps to determine the most economic tool replacement time [8]. also, it investigated high-pressure cooling and showed that this practice can help making the machining process more efficient and more robust. interestingly, the research demonstrated how statistical tools can be adequately used to perform a reliability analysis and spot improvement opportunities in the manufacturing process. it was suggested that this approach needs to be tested and validated under real manufacturing conditions. the importance of developing and adopting a scientific method for replacing worn-out cutting tools for cnc machines in a us automotive factory was studied in [3]. it was noted that the actual practice of replacing the worn-out cutting tools was based on the experience of the machining operators. this practice has several limitations since it leads to two extreme situations. the cutting tools were being either underutilized or over-utilized. in both cases, cost-effectiveness and product quality were heavily affected. the proposed method was based on the use of statistical process control (spc) techniques to monitor the cutting tool wear in the production system through measurements of the dimensions of the produced parts. the methodology used was based on the monitoring of the quality characteristic using variable control charts (x̅-r and x̅-s) and process capability analysis. the author suggested that the occurrence of out of statistical control situations in the control charts indicate that the cutting tool is worn out and needs to be replaced in the machining process. it was also shown that this spc-based approach can be used by manufacturing companies in other industrial sectors to cut costs and produce high-quality products according to design specifications. other studies developed methods based on spc charts to investigate the stability of manufacturing processes and their capability to meet the design specifications [9, 10]. the dmaic six sigma methodology associated with the use of the seven basic quality tools, was successfully implemented in different industrial settings to reduce defects and to achieve sustainable improvement in process performance [11-15]. the objective of the paper is to propose a systematic model based on process improvement methodologies and tools to help manufacturing companies in the decision making concerning the cutting-tool life and other manufacturing issues. this study aims to investigate the effect of the cutting tool life in machining processes on the quality of the manufactured products and the production economics. ii. methodology an extensive literature review was performed and indicated that a large number of process improvement methodologies are available for manufacturing [16]. the study showed that the pdca and the six sigma dmaic methodologies present superior performance in problem-solving and process improvement compared to other improvement models. the dmaic methodology uses statistics and process improvement tools to locate and solve existing problems and improve processes. the goal of the dmaic process is to implement long-term solutions to current problems in manufacturing. the use of the dmaic methodology helps to identify, eliminate, and control issues of product quality and production process that may arise [17]. the six sigma dmaic (define, measure, analyze, improve, and control) methodology is used in this research. the problem is defined in the first step. furthermore, it is important to recognize and define the critical stages in the process. the measure phase involves measuring the key process characteristics and quantifying the problem through data collection and analytics. the purpose of the analysis phase is to identify the root causes of the problem and propose solutions. the two remaining phases, i.e. implement and control, concern the implementation of the proposed improvements and the control and monitoring of the process. control ensures maintaining the solution and its results and sustaining the gains achieved. monitoring leads to sustainable improvements and guarantees long-term success. permanent monitoring is therefore required [11, 13]. iii. results and discussion this section presents the results of the data analysis of the process data, using the dmaic methodology. the data collected from the manufacturing process at the hvac plant are presented in table i. these variables are believed to measure the problem of the use of cutting tools and their effect on the quality of the final product (produced parts). the following sections provide a complete description of the implementation of the dmaic methodology in the study of the research problem and in order to make improvement proposals. table i. process data and research variables process variables definition x factor tool life measured in terms of number of produced parts per change during the period from june to october, 2018. y factor produced part characteristics and design specification (product quality). a. step one: define the first step of the dmaic methodology starts by defining the problem and identifying the objectives to be achieved. the current project was performed in a hvac manufacturing company, which produces a variety of products mainly for heat ventilation and air conditioning systems. their engineering, technology & applied science research vol. 11, no. 1, 2021, 6799-6805 6801 www.etasr.com aichouni et al.: a scientific approach of using the dmaic methodology to investigate the effect of … main products range from small ac units for domestic and office use, to big chillers for industrial and commercial plants. the company serves as a supplier of manufactured parts to other industries, especially in the military sector. it was noted that the plant suffered from the problem of high consumption of cutting tools during production. therefore, the need to develop a scientific approach to investigate this problem and determine the root causes of the problem emerged. b. step two: measure this step consists of measuring the extent of the problem in the manufacturing process. the analyzed process data are the number of manufactured parts by each cutting tool. operations are referred in this case to the use of specific cutting tools to produce a number of produced parts. figure 1 shows the variation of the numbers of produced parts for each cutting tool change. it can be seen that there is a big variability in the number of manufactured parts by each cutting tool. table ii shows the basic statistics of the manufacturing data, which show the number of units produced during the study period for all operations. fig. 1. variation of the number of produced parts by each cutting tool. table ii. basic statistics of the manufacturing data operation / cutting tool mean stdev min max change operation 1 95 44.07 30 189 630% operation 2 147 32.32 95 210 221% operation 3 155 49.0 86 234 272% operation 4 246 54.4 186 362 195% operation 5 127 75.2 55 279 507% operation 6 185 78.2 49 321 655% operation 7 370 70.5 238 460 193% operation 8 224 56.7 132 300 227% average 363% it can be seen that there are large discrepancies and differences in the number of units produced for each cutting tool. the variations range from a percentage of 193% to a maximum of 655%, with an average of 363% as a percentage of the difference between production operations for each cutting tool. the differences between production operations for each cutting tool are shown in figure 2. such an observation would be clear evidence of the validity of the problem statement, as it is clear that there is variability in the cuttingtool life as measured by the number of the manufactured parts. this may have a significant effect on product quality in terms of process stability and capability, and the economy of the manufacturing process. this early conclusion will be verified in the following sections. fig. 2. box plot of the distribution of the number of produced parts for all operations c. step three: analyze at this phase, the objective is to investigate the data to find the causes of the problem and propose solutions and improvements. the focus is to take advantage of the analyzed data in order to investigate the effect of the variability in the machined parts by each cutting tool on the quality of these machined parts as final products. for that purpose, the dimensional characteristics for the machined parts were obtained with their specifications. data samples were obtained for periods where at least two or three cutting tool changes were made. 1) process stability analysis to investigate the consistency of the manufacturing process concerning product characteristics, spc control charts (� ̅-s charts) were used. figure 3 shows that the process was statistically stable in some cases (1st, 2nd, 3rd, 5th, 7th, and 8th operation), and out of statistical control in other cases (4th and 6th operation). this indicates the existence of special causes affecting the manufacturing process. these special causes of variation should be investigated to improve the production process. 2) process capability analysis process capability analysis was performed to test the manufacturing process's capability to produce parts that meet the design specifications. the data collected from the process allowed conducting a study of the production operation's capability to meet the specification by comparing the dimensions of the produced units with the design specifications. figure 4 shows the results of the capability analysis for two operations. the results show that the production operations 2, 3, 4, 5, and 8 could achieve the design engineering, technology & applied science research vol. 11, no. 1, 2021, 6799-6805 6802 www.etasr.com aichouni et al.: a scientific approach of using the dmaic methodology to investigate the effect of … specifications. on the other hand, operations 1, 6, and 7) were not capable of achieving the specifications. this conclusion can be obtained from table iii, which shows the process capability indices (cp, cpk) for each operation in the production processes. capability indices cp, cpu, cpl, and cpk greater or equal than 1 indicate that the process was capable to meet the design specifications. fig. 3. control charts for two operations (cutting tool type). 3) cutting tool life and product quality relationship in this section, a summary of the previous analysis is presented to identify the nature of the effect of the cutting tool's life on the production process in terms of its stability and capability to meet the product design specifications. figures 5 and 6 show the nature of the relationship between the factors of capability (cp, cpk) and the statistical values (average, highest value, and lowest value) of the produced parts. the data show that using the cutting tool at a lower rate to produce small quantities and reduce the period of use does not necessarily lead to production according to the design specifications. the use of the cutting tool for long periods does not affect the process's capability to produce according to the specifications. this manufacturing process remains under the influence of special causes underlying the process elements (5ms and e: manpower, machine, measurement, material, methods, and environment). this can be investigated using cause and effect analysis. fig. 4. process capability analysis for two operations. fig. 5. summary of cutting tools life analysis and production quality. engineering, technology & applied science research vol. 11, no. 1, 2021, 6799-6805 6803 www.etasr.com aichouni et al.: a scientific approach of using the dmaic methodology to investigate the effect of … table iii. capability indices operation 1 2 3 4 5 6 7 8 cp 0.86 1.13 1.59 1.53 2.00 0.86 1.14 1.01 cpk 0.68 0.75 1.42 1.24 1.12 0.85 0.75 0.59 overall capability status no yes yes yes yes no no no fig. 6. correlation between capability indices and the statistical values for cutting tool life. 4) cause and effect analysis the previous analysis revealed that the manufacturing process is under the influence of special causes. in some cases, its capability to achieve design specifications in the final product is rather weak. the causes of the variability in the cutting tool life should be investigated further. for that purpose, root cause analysis was performed using the cause and effect diagram (ishikawa diagram). electronic brainstorming sessions were conducted with the company's quality department, including technicians working in the production line and employees from other departments. this was the most suitable method during the covid-19 pandemic situation. experts in machining processes from academia and industry were consulted during these sessions. fig. 7. ishikawa diagram for the variability of the cutting tool. figure 7 presents the results of the cause and effect analysis. the most important causes of the problem from the point of view of the company's employees and machine operators are summarized in the figure. d. step four: improve based on the root causes analysis, another brainstorming session was performed to identify the most important causes and suggest appropriate solutions. a researcher guided the discussion based on world-class manufacturers' good manufacturing practices [7]. a root cause analysis tree was used to manage each category's proposed solutions (5m and e). this analysis contributes to the organization of the selection of solutions and facilitates the process of prioritizing them. figure 8 shows the problems and the suggested solutions. fig. 8. root cause analysis tree. following the root cause analysis and in order to formulate an action plan to improve the process, the solution selection matrix was used. this stage was done through brainstorming sessions that included all stakeholders, managers, and decisionmakers to further participate in the implementation plan. the selection matrix (also known as a priority matrix) was used to evaluate problems and the proposed solutions for each problem or potential preparations based on specific criteria which can be based on time effect, cost effect, and other factors. table iv represents the analytical approach proposed to help the management implement solutions to solve the high consumption of cutting tools and thus reduce subsequent manufacturing costs. through the proposed solution matrix, certain weights have been determined for each of the evaluation criteria. thus, the result of the matrix in arranging solutions is: • the manufacturer standards had the highest weight in the solution matrix with a 19% importance. this was a proposed solution for the lack of a method for determining the change conditions. consequently, from this point, it can engineering, technology & applied science research vol. 11, no. 1, 2021, 6799-6805 6804 www.etasr.com aichouni et al.: a scientific approach of using the dmaic methodology to investigate the effect of … be concluded that the research problem was a major concern for the company. • training provision for the employees was an anticipated solution. this was the second selected solution with an 18% importance. • preventive maintenance can be used as an effective solution for the problem of cutting tool life in manufacturing since it helps manufacturing operators to avoid major failures that result in the replacement and change of tools [19]. • calibration of measurement instruments and machine startup procedures were among other suggested solutions. table iv. selection matrix (priority matrix) solution c1 c2 c3 c4 c5 total percentage solution a: provide training for employees and machinists 8 8 5 1 2 24 18% solution b: search and implement manufacturer standards 7 5 2 5 6 25 19% solution c: maintenance plans for cutting tool machines 4 5 6 5 2 22 17% solution d: calibration of measurement instruments 3 5 3 4 5 20 15% solution e: cleaning the new tools before change 8 7 2 2 4 23 18% solution f: establish sop for startup for machine tools 5 6 5 1 2 17 13% the evaluation criteria: (1 = bad, 10 = good): c1: easy to implement, c2: feasible, c3: cost effectiveness, c4: time, c5: easy to maintain. e. step five: control the control phase of the six sigma dmaic cycle is ideally performed after implementing the proposed solutions. the control phase aims to sustain the improvements achieved through the other stages of the dmaic cycle. the control phase in dmaic is about controlling the "vital few" variables, identified during the earlier phases. in the present research, since the proposed solutions were not yet implemented, this phase is not covered. iv. conclusion in the current paper, the dmaic methodology was implemented in a saudi manufacturing plant. the main goal was to investigate the high consumption of cutting tools in the machining process and to evaluate its impact in the quality of the machined products. the dmaic methodology was adopted to find an optimal set of factors that can help the manufacturing plant's leadership optimize the use of the cutting tools and achieve a balance between quality and production economy. along the five dmaic phases, different quality tools were implemented in order to identify the root causes of the problem, to develop an action plan to reduce the impact of the problem on the production, and to minimize the process variability. the present manufacturing case study proved that through the application of quality tools, basic tools, and management and planning tools, it was possible to improve company's production processes. the research suggested the implementation of the six sigma dmaic methodology in order to eliminate unproductive stages and operations, and to develop and use the technology to drive improvements in the manufacturing process. although the study was concerned only with cutting tools life in the machining process in the hvac plant, the findings and conclusions can be generalized to all manufacturing processes suffering from such problems. references [1] f. s. s. staff 1162, "cutting tool consumption up 10.8% year-todate," american machinist, aug. 13, 2018. https://www.americanmachinist.com/cutting-tools/article/21902825/ cutting-tool-consumption-up-108-yeartodate (accessed aug. 26, 2020). 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[19] l. s. tavassoli, n. sakhavand, and s. s. fazeli, "integrated preventive maintenance scheduling model with redundancy for cutting tools on a single machine," engineering, technology & applied science research, vol. 10, no. 6, pp. 6542–6548, dec. 2020, https://doi.org/10.48084/etasr. 3903. microsoft word etasr_v10_n6_pp6476-6480 engineering, technology & applied science research vol. 10, no. 5, 2020, 6476-6480 6476 www.etasr.com nguyen: global sensitivity analysis of in-plane elastic buckling of steel arches global sensitivity analysis of in-plane elastic buckling of steel arches trong-ha nguyen department of civil engineering vinh university vinh, vietnam trongha@vinhuni.edu.vn abstract—steel arches are widely used in civil engineering and industrial structures. their response depends on material properties, geometric dimensions, and boundary conditions. the objective of the current study is to perform global sensitivity analysis, and to assess the influence of random input parameters on the in-plane elastic buckling of steel arches. the in-plane elastic buckling load of steel arches under uniform compression proposed in previous studies is adopted. the influence of the random input variables of the structure is evaluated using sobol’s global sensitivity analysis. monte carlo simulation is also employed to rank the influence of input random variables. keywords-in-plane elastic buckling; steel arches; sensitivity; global sensitivity; sobol’ indices; monte carlo simulation i. introduction global sensitivity consists of the individual sensitivity of each variable and its interaction with other variables. sobol’s sensitivity index is widely applied in the structural engineering field [1-5]. steel structures often present high durability while including slender components. sensitivity and reliability analyses for steel structures have been conducted by many researchers [6-12]. steel arches are widely used in civil engineering and industrial structures. arches resist external loadings by a combination of predominant axial compression and bending actions. the geometry of circular steel arches is shown in figure 1, and the uniform compression on the steel arches is shown in figure 2. if the steel arches are adequately designed with lateral bracings so that their out-of-plane failure is fully prevented, in-plane buckling failure may occur [13, 14]. the in-plane elastic buckling is important in the stability design of metal arch structures [15]. the in-plane elastic buckling of shallow arches with an arbitrary cross-section was investigated and the in-plane elastic buckling load of shallow arches was found to be much lower than that given by the classical theory [16, 17]. moreover, the classical in-plane buckling load should not be used as the reference load in the development of design methods for the in-plane strength of shallow steel arches. this paper studies the sensitivity assessment of the input random variables on the in-plane elastic buckling load of the steel arches under uniform compression. an algorithm using the global sensitivity method is proposed for utilization in analyses and assessments. the in-plane elastic buckling load of steel arches under uniform compression has been proposed in [14]. in addition, the effects of input random variables on the in-plane elastic buckling load of the steel arches under uniform compression are also examined. fig. 1. geometry of the arches. fig. 2. uniform compression. ii. theoretical framework a. in-plane elastic buckling of steel arches in this section, the buckling load of arches proposed in [14] is presented. arches with an included angle φ < 90o are considered as shallow arches and the dimensionless parameter λ is defined as: 4 x s r λ φ = (1) where s is the length of the arch, / x r i a= is the radius of gyration of the cross-section, i is the second moment of the area of the cross-section about its major principal axis, and a is the area of the cross-section. φ s f l r q qq f φ l corresponding author: trong-ha nguyen engineering, technology & applied science research vol. 10, no. 5, 2020, 6476-6480 6477 www.etasr.com nguyen: global sensitivity analysis of in-plane elastic buckling of steel arches the buckling load of the pin-ended shallow arch can be defined as in (2) and the buckling load of the fixed shallow arch is expressed as in (3): ( ) ( ) 2 4 2 0.15 0.006 ; 3.88 9.38 0.26 0.74 1 0.63 / ; 9.38 cr acr cr n for n n for λ λ π λ λ  + < <  =  + − >  (2) ( ) ( ) 2 4 2 0.36 0.0011 ; 9.87 18.6 0.6 0.4 1 3.109 / ; 18.6 cr acr cr n for n n for λ λ π λ λ  + < <  =  + − >  (3) when an arch has an included angle φ > 90o, it is considered to be a deep arch, and its elastic buckling load is given by [14]: ( )21 / ; for pin-ended archesacr crn nπ = − φ  (4) ( )21 /1.4304 ; for fixed archesacr crn nπ = − φ  (5) where ncr is the second mode elastic flexural buckling load of a corresponding fixed or pin-ended column with the same length. ncr is determined as: ( ) 2 2 0.5; for pin-ended arches , with 0.35 for fixed arches cr ei n k ks π  = =   (6) where e is the young’s modulus and i is the second moment of the area of the cross-section about its major principal axis. b. global sensitivity analysis sensitivity presents the influence of input design parameters (i.e. variables) ( )1 2, ,..., mx x x=x on the output model ( )f=y x . here, ( )1 2, ,..., mx x x=x is the vector of design parameters in m r space and ( )1 2, ,..., ny y y=y is the vector of output value in n r space. let us consider an integral function ( )f=y x which can be decomposed into elementary functions, expressed as [5]: ( ) ( ) ( ) ( ) 0 1 1 , ,..., i i ij i j i i j m m f f f x f x x f x x < = + + + + ∑ ∑ � � � x (7) where ix represents the input random variables with independent probability while the variance of the output variable can be expressed as [4, 5, 18]: [ ] 1... 1 1 ... m m i ij m i i j m var y v v v = ≤ < ≤ = + + +∑ ∑ (8) where ; i i ij i j i j v var e y x v var e y x x v v   =   = − −     [ ] 1 1 1 1 1... ... 1 1 1 ... m n m m m n i ij i i i i j m i i m v var y v v v − −= ≤ < ≤ ≤ < < ≤ = − − −∑ ∑ ∑ the first-order sobol’s indices are determined by: [ ] i i v s var y = (9) the second-order sobol’s indices are determined by: [ ] ij i v s var y = (10) the total-order sobol’s indices are then determined by: ... ... ti i ij ikl i n s s s s s= + + + + (11) the sobol’s indices are commonly estimated with the monte carlo method [19, 20]. in this research, the sobol’s indices of global sensitivity with monte carlo simulation are established with the use of matlab, the flowchart of the procedure is shown in figure 3. fig. 3. flowchart of the sobol’s indices sensitivity analysis by monte carlo simulation. iii. methodology a. safe condition according to [14], the safe condition of the in-plane elastic buckling load of steel arches, determined by (3)-(5), can be rewritten as follows: saf acr n n≤ (12) where safn is the external load, which can fluctuate randomly. b. deterministic model and uncertainty model deterministic model is the above buckling analysis problem, in which the input parameters are those of geometry ( ), , , , , ,w fs b d t t l φ and the young's modulus of elasticity of engineering, technology & applied science research vol. 10, no. 5, 2020, 6476-6480 6478 www.etasr.com nguyen: global sensitivity analysis of in-plane elastic buckling of steel arches steel ( )e . this model can be written in the form of , , , , , , , w f s b d t t e l = φ x : ( ) acr n = ℑ x (13) the uncertainty model is constructed based on the deterministic model by taking into account the randomness of input parameters. the parameters assumed to be random are ( ), ( ), ( ), ( ), ( ), ( ), ( ), ( ) w f s b d t t e lω ω ω ω ω ω ω ω = φ x , where ω represents the randomness of the parameters. this model can be written as: ( )( ) ( )acrn ω ω= ℑ x (14) c. global analysis by monte carlo simulation sensitivity analysis for in-plane elastic buckling load of the steel arches has been performed using the global sensitivity, which is based on sobol’s sensitivity indices. monte carlo simulation is established with the use of matlab. the flowchart is shown in figure 4. fig. 4. flowchart of the sensitivity analysis for in-plane elastic buckling load of steel arches based on the sobol’s indices of global sensitivity by monte carlo simulation. iv. numerical results a. validation of the matlab code of sobol’s indices sensitivity analysis in order to validate the matlab code of the sobol’s indices of global sensitivity by monte carlo simulation, a test function, namely ishigami’s function was employed, defined as [21]: ( ) 2 41 2 3 1 1 sin 7sin sin 10 y x x x x x= + + (15) where x1, x2, x3 are uniform distributions between -π and π. the numerical results are shown in table i. a comparison with the results from [5] implies the reliability of the proposed program. table i. mean estimation with 10,000 monte carlo samples of first and total sobol’s indices xi proposed code result in [5] error (%) si sti si sti si sti 1 x1 0.315 0.577 0.313 0.576 0.63 0.17 2 x2 0.432 0.440 0.434 0.438 0.46 0.45 3 x3 0.001 0.258 0.001 0.254 0.00 1.55 b. sensitivity analysis of in-plane elastic buckling load of steel arches global sensitivity based on sobol’s sensitivity indices was applied to evaluate the influence of input random variables on the in-plane elastic buckling load of steel arches under uniform compression. the input parameters are divided in two cases: case study 1: the in-plane elastic buckling load of the fixed steel arches under uniform compression with input parameters , , , , , , , . w f s b d t t e l φ case study 2: the in-plane elastic buckling load of the pinended steel arches under uniform compression with input parameters , , , , , , , . w f s b d t t e l φ 1) case study 1 the fixed steel arch under uniform compression is shown in figure 5. the input variables are shown in table ii. global sensitivity based on sobol’s sensitivity indices is applied to evaluate the influence of input random variables on the inplane elastic buckling load of the fixed steel arches under uniform compression. after 100,000 simulations in 67.0 minutes, the results of sobol’s sensitivity indices are shown in table iii and figure 6. fig. 5. the fixed steel arches under uniform compression and the crosssection of the arch. table ii. statistical properties of random variables for sobol’s indices sensitivity analysis properties variables distribution range units geometry s uniform /6.283 – 7.679/ m l uniform /9.00 – 10.00/ m φ uniform /0.628 – 0.768/ rad material e uniform /18e5 – 22e5/ mpa crosssection d uniform /0.235 – 0.287/ m b uniform /0.136 – 0.166/ m tw uniform /0.007 – 0.008/ m tf uniform /0.011 – 0.014/ m d x x b tw t f a) b) q qq φ l engineering, technology & applied science research vol. 10, no. 5, 2020, 6476-6480 6479 www.etasr.com nguyen: global sensitivity analysis of in-plane elastic buckling of steel arches table iii. mean estimation with 100,000 monte carlo samples of first and total sobol’s indices 1st order effects total effects x1 (s) 0.2942 0.2819 x2 (e) 0.0795 0.0690 x3 (d) 0.6577 0.6510 x4 (b) 0.0425 x5 (tw) 0.0425 x6 (tf) 0.0425 x7 (φ) 0.0425 x8 (l) 0.0425 (a) (b) fig. 6. (a) first order and (b) total sobol’s sensitivity indices of the fixed steel arches under uniform compression. table iii and figure 6 show the influence of input random variables on the in-plane elastic buckling load of the fixed steel arches under uniform compression based on sobol’s sensitivity indices. it can be seen that s, e and d are the most influential input random variables with proportions of 24.0%, 6.0%, and 53.0% of the first-order sobol’s sensitivity indices, respectively and the total order sensitivity indices are 28.0%, 7.0%, and 65.0%, respectively. meanwhile, the least influential input random variables are b, tw, tf, l and φ with a proportion of 3.0%. this is consistent with the qualitative concept and that means the importance of sensitivity analysis of the in-plane elastic buckling load of the fixed steel arches under uniform compression. 2) case study 2 the input variables are shown in figure 7 and table ii. global sensitivity based on sobol’s sensitivity indices was applied to evaluate the influence of the input variables on the in-plane elastic buckling load of the pin-ended steel arches under uniform compression. the results after 100,000 simulations in 69.0 minutes are shown in table iv and figure 8. fig. 7. the pin-ended steel arches under uniform compression and the cross-section of the arch. (a) (b) fig. 8. (a) first order and (b) total sobol’s sensitivity indices of the pinended steel arches under uniform compression. table iv. mean estimation with 100,000 monte carlo samples of first and total sobol’s indices 1st order effects total effects x1 (s) 0.2337 0.2788 x2 (e) 0.0472 0.0738 x3 (d) 0.6611 0.6844 x4 (b) 0.2337 x5 (tw) x6 (tf) x7 (φ) x8 (l) table iv and figure 8 show the influence of the input variables on the in-plane elastic buckling load of the pin-ended steel arches under uniform compression based on sobol’s sensitivity indices. it can be seen from table iv and figure 9 that s, e and d are the most influential input random variables with proportions of 26.0%, 6.0% and 60.0% of the first order sobol’s sensitivity indices, respectively and the total order sensitivity indices are 28.0%, 7.0% and 64.0% respectively. φ l q d x x b tw t f a) b) 1st order effects 26% 6% 60% 2% 2%2% 2%2% s e d b tw tf phi l total effects 28% 7% 64% < 1% s e d b engineering, technology & applied science research vol. 10, no. 5, 2020, 6476-6480 6480 www.etasr.com nguyen: global sensitivity analysis of in-plane elastic buckling of steel arches meanwhile, the least influential input random variables are b, tw, tf, l and φ with a proportion of 2.0%. from the above case studies, it can be seen that sobol’s sensitivity indices of random input variables on the in-plane elastic buckling load of steel arches condition of the fixed and pin-ended steel arches under uniform compression are not significant. the input random variables have a high sensitivity including s, e, and d. the obtained results show the significance of this research. v. conclusions this paper proposed an algorithm to assess the structural sensitivity of the in-plane elastic buckling load of steel arches. the numerical process is developed based on sobol’s sensitivity indices and monte carlo simulation. the in-plane elastic buckling load of steel arches condition of the fixed and pin-ended steel arches under uniform compression is considered in the structural sensitivity assessment. from the numerical analysis, the flowing conclusions can be drawn: • the algorithm is based on sobol’s sensitivity indices and monte carlo simulation and is developed for the sensitivity analysis of steel arches. a verification of the proposed algorithm is conducted using the ishigami’s test function. • the developed procedure can be applied for the in-plane elastic buckling load of steel arches as an important recommendation for the selection of the input random variables based on numerical analysis. • an extended application for other types of structures is highly feasible, however additional numerical tests and verifications are required. acknowledgment this research was funded by the vinh university. the authors declare that they have no potential conflicts of interest in this paper. references [1] d. g. cacuci, “sensitivity theory for nonlinear systems. i. nonlinear functional analysis approach,” journal of mathematical physics, vol. 22, no. 12, pp. 2794–2802, dec. 1981, https://doi.org/10.1063/1.525186. 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[21] t. ishigami and t. homma, “an importance quantification technique in uncertainty analysis for computer models,” in [1990] proceedings. first international symposium on uncertainty modeling and analysis, college park, md, usa, dec. 1990, pp. 398–403, https://doi.org/ 10.1109/isuma.1990.151285. microsoft word 13-2833_setasr_v9_n4_pp4384-4388 engineering, technology & applied science research vol. 9, no. 4, 2019, 4384-4388 4384 www.etasr.com truong & bui: hybrid pso-optimized anfis-based model to improve dynamic voltage stability hybrid pso-optimized anfis-based model to improve dynamic voltage stability dinh-nhon truong faculty of electrical and electronics engineering, ho chi minh city university of technology and education, ho chi minh city, vietnam nhontd@hcmute.edu.vn van-tri bui faculty of electrical and electronics engineering, ho chi minh city vocational college of technology, ho chi minh city, vietnam vantrihcm@gmail.com abstract—the objective of this paper is to perform a hybrid design for an adaptive neuro-fuzzy inference system (anfis) optimized by particle swarm optimization (pso) to improve the dynamic voltage stability of a grid-connected wind power system. an onshore 99.2mw wind farm using doubly fed induction generator (dfig) is studied. to compensate the reactive power absorbed from the power grid of the wind farm, a static var compensator (svc) is proposed. to demonstrate the performance of the proposed hybrid pso–anfis controller, simulations of the voltage response in time-domain are performed in matlab to evaluate the effectiveness of the designed controller. from the results, it can be concluded that the proposed hybrid pso-optimized anfis-based model can be applied to enhance the dynamic voltage stability of the studied grid-connected wind power system. keywords-adaptive neuro-fuzzy inference system; particle swarm optimization; static var compensator; voltage stability i. introduction renewable energy is important nowadays and wind generators or solar panels are used in many countries, while wind generators are applied more widely than before. an offshore wind farm can include many wind turbines and wind driven generators. the output power of the wind generators can be connected to form a wind farm and they can feed a power grid using a step-up transformer. in relevance to a wind generator, dfig (doubly fed induction generator) is the most prevalent generator because of its high efficiency compared to other types of wind generators such as permanent magnet synchronous generator (pmsg) and induction generator (ig) [1]. moreover, dfig has the capability of controlling both active and reactive power for better grid integration to the transmission line [2]. however, connecting the stator windings directly to the power grid, makes it very sensitive to power grid faults. besides, the randomness of wind energy affects the power quality of the connected power systems. some power quality problems such as voltage fluctuations, flicker, harmonic and voltage deviation of the baolian wind farm have been studied in [3]. the measurements of a wind farm located in the south-east part of poland were analyzed and compared with the acceptable values in [4]. in [5], a power quality study of a large-scale wind farm with and without storage was studied. authors showed that with the proposed storage system, voltage drops, and harmonic voltage and current distortion at the wind farm output can be improved when a short circuit occurs in the connection with the power grid. flexible ac transmission systems (facts) devices have been proposed and applied in power transmission systems and in this situation, static var compensator (svc) is used to enhance the voltage stability [6, 7]. in large systems, the svc is located in the middle of the transmission line to reduce the oscillation of the system and thus improve grid stability [8, 9]. in today's control devices, the controller plays an important role in improving the operability and flexibility of the device. pid (proportional-integral-derivative) is a linear controller and is used in many control systems. the main disadvantage of this controller is that it does not respond well when the input is large. recently, many algorithms have been applied to improve the efficiency of the device, such as a fuzzy logic controller used in vibration reduction control when linking generator systems in two large areas [10]. in addition, the fuzzy controller is used to replace the pid controller using the voltage deviation as the feedback signal in the voltage control at the link bus [11]. however, the main disadvantage of fuzzy logic controllers is that they depend on the programmer's experience. to improve the accuracy of the algorithms, combining algorithms together to exploit the advantages of each algorithm is a good solution that is being widely researched. in [12], authors proposed an algorithm combining fuzzy logic and an artificial neural network called anfis (adaptive-network-based fuzzy inference system). anfis is also a good structure for designing a controller of facts devices [13] because of its simplification and its ease of designing. anfis is used for replacing controllers that are not obvious or cannot be calculated by definite equivalence. in this research paper, a particle swarm optimization (pso) algorithm is proposed to optimize the parameters of the anfis controller for improving voltage stability. the proposed approach is based on the combination of pso and anfis controller. the idea of combining pso and anfis was applied to examine the electricity market of mainland spain [14] as well as for short-term electricity prices prediction [15] with many advantages. corresponding author: dinh-nhon truong engineering, technology & applied science research vol. 9, no. 4, 2019, 4384-4388 4385 www.etasr.com truong & bui: hybrid pso-optimized anfis-based model to improve dynamic voltage stability ii. system configuration a. studied system configuration the structure of the studied system in this paper is a practical 99.2mw wind farm in bac lieu province, vietnam including 62×1.6mw wind turbines as shown in figure 1. this project, panning an area of 1,000ha, transmits power to the national grid through two parallel 63mva transformers and two 110kv transmission lines. the wind farm has an estimated electricity output of 300gwh per annum. the wind turbine model is ge 1.6 xle – 1.6mw supplied by general electric using a dfig-based wind turbine with a single-line diagram [16]. the stator windings of the dfig are directly connected to the low-voltage side of the 0.69/22kv step-up transformer while the rotor windings of the dfig are connected to the same 0.69kv side through a rotor-side converter (rsc), a dc link, a grid-side converter (gsc), and a connection line. for normal operation of a dfig, the input ac-side voltages of the rsc and the gsc can be effectively controlled to achieve simultaneous output active power and reactive power control [17]. fig. 1. single-line diagram of the studied system. for normal operation of a wind dfig, the input ac-side voltages of the rsc and the gsc can be effectively controlled to achieve the aims of simultaneous output active power and reactive power control. the control block diagram of the rsc of the studied dfig and the control block diagram of the gsc of the studied wind dfig can be seen in [18]. b. svc model for improving voltage stability, a 40 mvar svc is proposed for adjusting the voltage at the connected bus by compensating the reactive power to the power grid. the equivalent model of svc is shown in figure 2. it consists of a thyristor switched capacitor (tsc) and thyristor controlled reactors (tcrs). the control scheme of the studied svc is presented in [19]. in the svc model, if the bus voltage is lower than the reference value, the value of the equivalent susceptance (bsvc) of the svc is positive and on the contrary, if the bus voltage is higher than the reference value, the bsvc is negative. the relationship between the firing angle ( )α and the steady state value of btcr is given as: 2( ) sin(2 ) ( ) π α α α π − + =l l b x (1) where [ ] 2 π α π= ÷ . the equivalent susceptance of svc (bsvc) is: 1 ( ) ( )α α= −svc l c b b x (2) fig. 2. single-line diagram of svc iii. hybrid pso–anfis controller design an anfis is a class of adaptive multi-layer feedforward network. it incorporates the self-learning ability of neural networks with the linguistic expression function of fuzzy inference. the structure of the anfis controller is depicted in figure 3. the anfis network is composed of five layers. fig. 3. structure of the anfis each layer contains several nodes which described as the following node equations: in layer 1, the output function 1 io shows the membership grade of a fuzzy set a1, a2 , b1, or b2 and it specifies the degree to the given input e or δe. 1 ( ), 1 2 i i o a e iµ= = ÷ (3) engineering, technology & applied science research vol. 9, no. 4, 2019, 4384-4388 4386 www.etasr.com truong & bui: hybrid pso-optimized anfis-based model to improve dynamic voltage stability or 1 2 ( ), 3 4 i i o b e iµ −= ∆ = ÷ (4) the membership functions for a and b are usually described by a generalized bell functions as described bellow: 2 1 ( ) 1 i i q i i a e e r p µ = − + (5) where , ,i i ip q r are the values of the bell function. in layer 2, the product output value 2 io is formed by multipling the incoming signals. in this layer, each node output represents the firing strength of a rule. 2 ( ). ( ), 1 2 i i i i o w a e b e iµ= = ∆ = ÷ (6) in layer 3, the outputs of this layer, 3 io , are called normalized firing strengths: 3 1 2 , 1 2i i i w o w i w w = = = ÷ + (7) in layer 4, the output 4 io is the contribution of the i th rule to the overall output: 4 ( . . ), 1 2 i i i i i i i o w z w a e b e c i= = + ∆ + = ÷ (8) where , ,i i ia b c are consequent parameters. in layer 5, the output 5 io is the final output as the summation of all incoming signals 5 , 1 2 i i i o f w z i= = = ÷∑ (9) in an anfis system, neural networks extract automatically fuzzy rules from numerical data and, through the learning process, the membership functions are adaptively adjusted. for improving the training process, pso is applied to optimize the parameters of the membership functions of the anfis controller [20]. the objective of this method is to discover the particle location that outcomes the finest assessment of a specified fitness function to minimize the training errors of anfis. in pso, a swarm specifies the number of probable solutions to a complex problem, where each probable solution is known as a particle. every particle set has its opening parameters in random fashion and is flown throughout the multi-dimensional search space during the initialization phase of swarm optimization [21]. as sketched in figure 4, an updating mechanism of the pso technique is presented, where x(t) and v(t) denote a particle’s position and flight velocity over a solution space, respectively. the following equations present the search mechanism: velocity update rule: 1 2 ( ) ( 1) ( ) ( ) i i pbesti i gbesti i v t v t x x t x x t ω ρ ρ = − + −   + −   (10) where ω is an inertia weight, ρ1, ρ2 are random variables, gbest is the best particle among all particles in the swarm, and pbest is the personal best position of each particle. fig. 4. updating new position mechanism of pso position update rule: ( ) ( 1) ( ), 1 i i i x t x t v t t t= − + = + (11) the results after training of the proposed hybrid psoanfis are shown in figure 5. it can be seen that the training error between the target and the output of the training data is very close to zero (figure 5(a)) and the error mean and error std are also very small (figure 5(b)). it means the proposed pso can optimize the parameters of the anfis controller. (a) training error (b) error mean fig. 5. training results of the proposed hybrid pso-anfi iv. simulation results the simulation results of the studied bac lieu power system with a wind farm and a proposed svc with hybrid pso-anfis controller are presented in figure 6 in which a severe three-phase short circuit fault happened at the 220kv bus in 0.1s. in figure 6, the black lines are the responses of the system with svc and pi controller, the blue lines are the responses of the system with svc and anfis controller which is trained by applying the anfis toolbox in matlab while the red lines are the ones with svc and the proposed hybrid psoanfis controller. active power and voltage of the wind farm are represented in figures 6(a) and 6(b). 0 50 100 150 200 250 300 -0.02 0 0.02 0.04 mse = 5.5726e-05, rmse = 0.007465 error -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0 20 40 60 80 error mean = -3.7379e-06, error st.d. = 0.0074783 engineering, technology & applied science research vol. 9, no. 4, 2019, 4384-4388 4387 www.etasr.com truong & bui: hybrid pso-optimized anfis-based model to improve dynamic voltage stability (a) active power of the wind farm (b) voltage of the wind farm bus (c) voltage of tra noc bus (d) voltage of dong hai bus (e) voltage of bac lieu bus fig. 6. the response of the system when a three-phase short circuit fault happens at 220kv level. legend: (a) voltage of bac lieu bus (b) voltage of the wind farm bus (c) voltage of dong hai bus fig. 7. the response of the system when a three-phase short circuit fault happens at 110kv level. legend: 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 -4 -2 0 2 4 6 8 10 12 t (s) p w f ( p .u .) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0.2 0.4 0.6 0.8 1 1.2 t (s) v w f ( p .u .) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0.2 0.4 0.6 0.8 1 1.2 t (s) v w f ( p .u .) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 0.2 0.4 0.6 0.8 1 1.2 t (s) v d o n g h a (p .u .) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 0.2 0.4 0.6 0.8 1 1.2 t (s) v b a c l ie u ( p .u .) pi anfis pso-anfis 0 0.25 0.5 0.75 1 1.25 1.5 0 0.2 0.4 0.6 0.8 1 1.2 t (s) v b a c l ie u ( p .u .) 0 0.25 0.5 0.75 1 1.25 1.5 0 0.2 0.4 0.6 0.8 1 1.2 t (s) v w f ( p .u .) 0 0.25 0.5 0.75 1 1.25 1.5 0.2 0.4 0.6 0.8 1 1.2 t (s) v d o n g h a (p .u .) pi anfis pso-anfis engineering, technology & applied science research vol. 9, no. 4, 2019, 4384-4388 4388 www.etasr.com truong & bui: hybrid pso-optimized anfis-based model to improve dynamic voltage stability the voltage of the three buses i.e. tra noc, dong ha and bac lieu are shown in figures 6(c)-6(e) respectively. from these figures, it is easily to see that by applying the hybrid pso-anfis controller for the svc device, the output values of these parameters are more stable and more effective. the voltage of each node is improved and the number of oscillations and the overshoot after a three-phase short circuit fault occurred, are also reduced. for more details, figure 7 exhibits the simulation results of the studied system when a three-phase short circuit fault happened at the bac lieu bus working at 110kv level and lasting 5 cycles. by obseving the response of the voltage at bac lieu bus shown in figure 7(a) it can be seen that voltage drop to zero occurred during the fault. however, with the response plotted in figures 7(b) and 7(c) the voltage magnitude of the wind farm bus and the voltage at dong ha bus only dropped to 0.2p.u. thanks to the operation of the svc and its designed controller, a large amount of reactive power was supplied in order to improve the voltage level of these buses. v. conclusions in this paper, a hybrid pso-anfis controller for svc was designed and applied in a grid-connected wind power system. svc can support fast response to the system to balance reactive power in the grid which helps to improve dynamic voltage stability. the results showed that the proposed controller can be used to improve the voltage quality and reduce the number and amplitude of oscillations in hard operating conditions such as a three-phase short circuit fault occurrence. it can be concluded from the time-domain simulation results on matlab that the hybrid pso-anfis designed controller has more advantages compared to the anfis controller and can enhance power quality of the studied system under severe operating conditions. references [1] r. pena, j. c. clare, g. m. asher, “doubly fed induction generator using back-to-back pwm converters and its application to variable-speed wind-energy generation”, electric power applications, vol. 143, no. 3, pp. 231-241, 1996 [2] l. wang, l. y. chen, “reduction of power fluctuations of a large-scale grid-connected offshore wind farm using a variable frequency transformer”, transactions on sustainable energy, vol. 2, no. 3, pp. 226-234, 2011 [3] q. xia, z. wang, f. liu, y. li, y. peng, z. xu, “study on power quality issues of wind farm”, 36th chinese control conference, dalian, china, july 26-28, 2017 [4] m. latka, m. nowak, “analysis of electrical power quality parameters in the power grid with attached wind farm”, progress in applied electrical engineering, koscielisko, poland, june 25-30, 2017 [5] g. a. ramos, m. a. riosm, d. f. gomez, h. palacios, l. a. posada, “power quality study of a large-scale wind farm with battery energy storage system”, industry applications society annual meeting, cincinnati, usa, october 1-5, 2017 [6] a. jain, p. p. singh, s. n. singh, “control strategies for output power smoothening of dfig with svc in wind conversion system”, region 10 humanitarian technology conference, agra, india, december 21-23, 2016 [7] e. a. awad, e. a. badran, f. h. youssef, “mitigation of switching overvoltages in microgrids based on svc and supercapacitor”, iet generation, transmission & distribution, vol. 12, no. 2, pp. 355–362, 2018 [8] y. chang, z. xu, g. chen, j. xie, “a novel svc supplementary controller based on wide area signals”, power engineering society general meeting, montreal, canada, june 18–22, 2006 [9] a. jalilvand, m. d. keshavarzi, “adaptive svc damping controller design, using residue method in a multi-machine system”, 6th international conference on electrical engineering/electronics, computer, telecommunications and information technology, pattaya, thailand, may 6–9, 2009 [10] l. o. mak, y. x. ni, c. m. shen, “statcom with fuzzy controllers for interconnected power systems”, electric power systems research, vol. 55, no. 2, pp. 87–95, 2000 [11] i. mansour, d. o. abdeslam, p. wira, j. merckle, “fuzzy logic control of an svc to improve the transient stability of ac power systems”, 35th annual conference of ieee industrial electronics, porto, portugal, november 3–5, 2009 [12] j. s. r. jang, “anfis: adaptive-network-based fuzzy inference system”, transactions on systems, man, and cybernetics, vol. 23, no. 3, pp. 665–685, 1993 [13] a. albakkar, o. p. malik, “adaptive neuro-fuzzy facts controller for transient stability enhancement”, 16th national power system conference, hyderabad, india, december 15-17, 2010 [14] c. g. martos, j. rodriguez, m. j. sanchez, “mixed models for short-run forecasting of electricity prices: application for the spanish market”, transactions on power systems, vol. 22, no. 2, pp. 544–552, 2007 [15] h. m. i. pousinho, v. m. f. mendes, j. p. s. catalao, “a hybrid psoanfis approach for short-term wind power prediction in portugal”, energy conversion and management, vol. 52, no. 1, pp. 397-402, 2011 [16] the windpower, 1.6xle, available at: https://www.thewindpower.net/ turbine_en_670_ge-energy_1.6xle.php, 2019 [17] j. p. s. catalao, h. m. i. pousinho, v. m. f. mendes, “short-term electricity prices forecasting in a competitive market by a hybrid intelligent approach”, energy conversion and management, vol. 52, no. 2, pp. 1061–1065, 2011 [18] d. n. truong, “statcom based fuzzy logic damping controller for improving dynamic stability of a grid connected wind power system”, international conference on system science and engineering, puli, taiwan, july 7-9, 2016 [19] v. t. bui, d. n. truong, “voltage stability enhancement of bac lieu wind power by anfis controlled static var compensator”, 4th international conference on green technology and sustainable development, ho chi minh city, vietnam, november 23-24, 2018 [20] m. a. shoorehdeli, m. teshnehlab, a. k. sedigh, m. a. khanesar, “identification using anfis with intelligent hybrid stable learning algorithm approaches and stability analysis of training methods”, applied soft computing, vol. 9, no. 2, pp. 833–850, 2009 [21] s. p. singh, s. c. sharma, “a novel energy efficient clustering algorithm for wireless sensor networks”, engineering, technology & applied science research, vol. 7, no. 4, pp. 1775-1780, 2017 authors profile dinh-nhon truong, phd is a senior lecturer at ho chi minh city university of technology and education, vietnam. he received his phd from the department of electrical engineering, national cheng kung university, tainan, taiwan. his research interests are grid-connected wind power systems, dynamic stability, and facts devices. van-tri bui, me, is currently pursuing his phd at the ho chi minh city university of technology, vietnam. his main research interest is the application of facts devices to improve dynamic stability of a gridconnected wind power systems. engineering, technology & applied science research vol. 9, no. 1, 2019, 3744-3749 3744 www.etasr.com waheed & hussain: effect of polyvinyl pyrolidone on morphology and performance of cellulose … effect of polyvinyl pyrolidone on morphology and performance of cellulose acetate based dialysis membrane hizba waheed school of chemicals and materials engineering national university of sciences and technology (nust) islamabad, pakistan hizbawaheed@scme.nust.edu.pk arshad hussain school of chemical and materials engineering national university of sciences and technology (nust) islamabad, pakistan arshad.hussain@scme.nust.edu.pk abstract—polyvinyl pyrolidone (pvp) was added as filler in cellulose acetate (ca) to produce mixed matrix membrane (mmm) for hemodialysis operation. phase separation induced by diffusion (dips) was used for fabrication of mixed matrix ca/pvp flat sheet membranes. the effect of adding pvp was investigated on the morphology and permeation efficiencies of ca membranes. the surface arrangement of polymer and additives in pure and blended membrane was studied by ftir, contact angle and sem. results revealed homogenous and significant mixing of pvp content into pure ca matrix. performance efficiency of blended membranes was investigated by means of pure water flux (pwf), urea clearance and % rejection of bovine serum albumin (bsa). the observable decrease of contact angle from 83° to 69° in ca/pvp mmm membranes of varying composition effectively revealed enhancement in hydrophilicity of mmm membrane surface. for protein rejection, all ca/pvp membranes rejected>90% of bsa relative to 25% for pure ca membrane. furthermore, urea clearance behavior for ca/pvp membranes was 62.4% in comparison to 52% for pure ca membrane. the incorporation pvp i.e 1% by weight (mpvp1) significantly improved the hydrophilicity, pwf, bsa rejection and urea clearance percentages of modified ca membrane for dialysis application. keywords-cellulose acetate; dialysis; membrane; poly vinyl pyrolidone i. introduction kidney problems either acute or chronic are one the major mortality causes. diseases related to kidneys have increased tremendously, main reasons being diabetes and hypertension which are common nowadays [1-4]. the increase in the amount of uremic toxics beyond the normal range within blood, effect adversely and is called uremic syndrome. to prolong life, kidney patients undergo dialysis which is an expensive procedure and costs more than 1 billion us$ annually [5]. hemodialysis is an important medical procedure for patients suffering from renal ailments. this process includes purification of blood from patient’s body using hemodialysis equipment (artificial kidney) to remove uremic wastes and returning the filtered blood back to person’s body [6]. the important part of hemodialysis apparatus is a membrane, which function is to separate toxic wastes produced as a result of metabolic activities and excess water from the patient through transport via diffusive and convective phenomena. during the process, essential protein loss is controlled or prevented via pore size exclusion of the membrane [7]. keeping importance of hemodialysis in view, progress is made in research field of high-performance membrane which will lead to enhance quality of treatment and increase patient’s life. different polymers used for dialysis membrane preparation other than cellulose-based materials include polysulfone (ps), polyacrilonitrile (pan), polymethyl methacrylate (pmma), polyamide (pa), and polyvinylalcohol (pva) [8–12]. many additives have been used to enhance dialysis performance of prepared membranes. among them are polyethylene glycol (peg), monosodium glutamate, polyethylene imine (pei) etc. in the present study, ca was chosen as a basic polymer for the fabrication of flat sheet dialysis membranes. phase inversion technique is commonly used for the preparation of asymmetric flat sheet membranes. casting solutions were made from ca in acetic acid as solvent and pure water as non-solvent agent. choice of cellulose was made on the bases of its easy availability and low cost. the only drawback for ca is its nonbiocompatibility. in order to overcome this problem, a biocompatible additive with good hydrophilicity was added to ca so that the synthesized membranes can have enhanced dialysis efficiency. pvp is hydrophilic additive which enhances the hydrophilic behavior of ca membranes. it is a watersoluble polymer which increases the porosity of membranes [13], and has good blood compatibility [14]. keeping that in mind, the casting solution was later modified using polyvinyl pyrolidone (pvp) in various weight percentages. surface morphology, functional group identification, pure water flux, bovine serum albumin rejection percentage and urea clearance values of ca/pvp were inspected and were compared with pure ca flat sheet membranes. the purpose of this research was to synthesize a new kind of ca/pvp membranes with high bsa rejection and better urea clearance for dialysis application. corresponding author: h. waheed engineering, technology & applied science research vol. 9, no. 1, 2019, 3744-3749 3745 www.etasr.com waheed & hussain: effect of polyvinyl pyrolidone on morphology and performance of cellulose … ii. materials and methods a. materials asymmetric polymeric membranes were synthesized for dialysis application. ca polymer with average mol. wt of 30,000 daltons having 39.8% degree of acetylation, 99.7% pure acetic acid, 98% pure urea with mol. wt 60.06, bovine serum with mol. wt of 66,000 dalton and peg with mol.wt 10,000 and 35,000 were obtained from sigma aldrich. pvp with average mol. wt. 30,000 was purchased from fluka. b. membrane synthesis several casting solutions of ca/pvp/acetic acid blend were prepared having constant ca weight % of 18.5. table i shows the compositions of casting solutions prepared during this work. the casting solutions were agitated constantly to confirm complete mixing of added ingredients including polymer, solvent and additive. when the casting solution showed complete dissolution of polymer and pvp, it was degassed for 2 hours using ultrasonic bath to remove trapped air bubbles. complete mixing of components is indicated by formation of clear solution. to slow down the aging process the casting solutions were kept in dark after degassing. the casting solution was poured on a glass plate and was spread with a doctor blade having wet membrane thickness of 200µm. the glass plate was instantly submerged in distilled water trough where phase separation took place [15]. during phase separation, exchange on solvent (acetic acid) and non-solvent (water) occurred. the prepared flat sheet membrane was then shifted to another trough containing fresh water and was washed to get rid of any excess solvent if present. washing was carried out for 3-4 times. finally, the casted membrane was kept in distilled water for 24 hours before final testing. table i. composition of membranes membrane ca wt. % pvp wt. % acetic acid wt. % mpvp0 18.5 80.5 mpvp1 18.5 1.00 81.5 mpvp3 18.5 3.00 78.5 mpvp5 18.5 5.00 76.5 mpvp7 18.5 7.00 74.5 it was observed that when we increased the pvp concentration beyond 5% the membranes formed were having visible pores and the casting was not possible as it was for the rest of the membranes. the visible physical difference in membranes with concentration less than 5% and beyond 5% is shown in figure 1. iii. membrane testing (wet) a. pure water flux dead end filtration setup was used to calculate pure water permeation flux (pwp) for dialysis membrane. the filtration cell was having 250ml capacity for feed solution and an active area of 12.57cm2. permeation experiments were operated under 2.0–3.0bar pressure. all experiments were carried out at ambient temperature at 25±0.5°c as shown in figure 2. the fabricated membrane was positioned in test cell and was tested for water flux. experiments were repeated several times to avoid data ambiguity. the pwp flux was measured using (1): flux (𝐽) = 𝑄/∆𝑡 × 𝐴 (1) in (1), j represents the permeation flux (lm-2h-1) for pure water, q is the volume of permeated solution, a shows the active area of membrane and δt is the permeation time (h) [16]. a similar method was used to analyze molecular weight cutoff for the fabricated membranes. solutions of bsa (average mol wt 66000) and peg with different molecular weights (peg 10,000 and peg 35,000) were used. all solutions were made having concentration of 1g/l. the concentrations of peg and bsa solutions were found using dragondorff reagent [17, 18] by uv-spectrophotometer. fig. 1. difference in apearance of membranes. b. hydrophilicity measurement contact angle and water uptake values were used to measure the ca/pvp membrane hydrophilicity. sessile drop method was used to measure contact angle at a tantec contact angle meter [19, 20]. single drop of deionized water was released on a dried membrane flat surface using a microsyringe. the tests were made under saturated water vapor atmosphere and the contact angle was measured after 10s. minimum 8 contact angle readings were made to get an average value and all readings were taken at room temperature. to calculate water uptake/absorption, the membrane sample (2cm×2cm) was cut and desiccated in an oven at 60°c for 12h prior to testing. the dried piece was weighed (mdry). the preweighed membrane sample was then waterlogged at room temperature for the next 24h. the waterlogged membrane was taken out and dapped with tissue paper to remove water. the membrane piece was weighed again (mwet). all measurements were made at 25±0.5°c. the water uptake was determined using (2) where mwet and mdry represent the wet and dry membrane weights: water take up = 𝑀𝑤𝑒𝑡−𝑀𝑑𝑟𝑦 𝑀𝑑𝑟𝑦 × 100 (2) iv. membrane performance membrane performance tests were based on the extent of removing uremic toxins and rejecting bovine serum albumin from feed solution. urea clearance and bsa rejection was measured separately using dialysis setup and dead-end filtration method. for urea clearance, the experiments were performed in a dialyzer with one compartment (donor) containing 50ml feed solution and the other (receiver) filled with 2l distilled water as shown in figure 2. engineering, technology & applied science research vol. 9, no. 1, 2019, 3744-3749 3746 www.etasr.com waheed & hussain: effect of polyvinyl pyrolidone on morphology and performance of cellulose … fig. 2. schematic presentation of dialysis setup. two similar stirrers were fitted in the compartments. the membrane to be tested was clamped between the two chambers. the concentrations of urea and bsa were kept similar to their concentrations in human blood. for urea clearance, experiments were started by bringing the feed solution in contact with the testing membrane. the concentration gradients of solute (urea or bsa) in two sides of the dialysis membrane act as the driving forces for the transport of urea and bsa from the feed side to the distilled water side. the concentration of urea was measured every 30min from the start of the experiments and the experiment was performed continuously for 210min. urea concentrations were tested using total organic carbon analyzer methods and uvspectrophotometric method was applied for measuring bsa concentration. the membrane performance, i.e. urea clearance and bsa rejection was calculated from (3) where ci and cf represent initial and final concentrations respectively. 𝑈𝑟𝑒𝑎 𝑐𝑙𝑒𝑎𝑟𝑎𝑛𝑐𝑒 % = 𝐶𝑖−𝐶𝑓 𝐶𝑖 𝑋 100 (3) bsa rejection % was estimated using dead end filtration cell (figure 3). a feed solution having concentration 1mg/ml bsa was prepared. the active membrane area was 12.57cm2. the quantity of bsa in feed and permeate was measured by observing its absorbance with a spectrophotometer (shidmazu uv mini 1240) operated at a wavelength of 278nm. the experiments were carried out at room temperature at 2-3bar pressure by employing (4) where cp, cr stand for permeate and retentate concentrations respectively [21]. 𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝑅𝑒𝑗𝑒𝑐𝑡𝑖𝑜𝑛 = (1 − 𝐶𝑝 𝐶𝑟 ) × 100 (4) fig. 3. dead end filtration setup. v. membrane characterization the cross-section and surface morphologies of casted membranes were analyzed using a jsm 6409a scanning electron microscope. the membranes were first frozen in liquid nitrogen and later were broken and spluttered with gold before undergoing sem analysis. ftir spectrum 100 perkinelmer, mid ir was used to carry out ftir analysis of prepared membranes. the membrane pieces were cut and placed in a pallet holder one after the other. the holder was then fixed in an instrument. wave numbers from 450 to 4000cm-1 were used to record the spectra in transmission mode. this procedure was repeated for every sample separately. vi. results and discussion a. effect of pvp addition on morphology and performance of ca membranes sem investigation was made to study the effects of adding pvp to ca matrix. figure 4 shows the micrographic view of surface morphology and cross-sectional arrangements of polymer and additive in all prepared membranes. as revealed in the surface morphology, addition of pvp to ca matrix leads to the generation of asymmetric membranes with compact top layer and sub-layer with finger like porous structures all over. from these images, it is seen that keeping bath temperature constant at 25°c and rising pvp concentration from 0 to 3wt.% caused development of macro voids and porous structure with good water flux. however, further increment of pvp concentration beyond 4wt.% resulted in formation of large visible pores making membranes not functioning for filtration, purification and dialysis operations. it was observed that the existence of hydrophilic additive pvp resulted in immediate demixing in the coagulation bath and generates macro voids in membrane structure till the concentration was below 3wt.% [22, 23]. whereas due to low affinity between pvp and ca polymer, large pores were formed when wt.% was increased beyond 4wt.% as shown in figures 1 and 4. conclusively, it is said that addition of a hydrophilic additive pvp, to the ca polymeric solution induces a dual effect on the membrane morphology. the membrane structure attained is subjected to the dominance of instantaneous or late demixing. these both phenomena are occurring because of the presence of the pvp casting matrix. conferring to figure 4, adding pvp from 0 to 3wt.% causes development of pores and voids in the membranes. however, increasing pvp concentration beyond 3% in ca matrix, results in formation of larger finger like projections and highly porous structures. therefore, it is concluded that little addition of pvp, i.e up to 3 wt.%, promotes immediate demixing, whereas further increment of pvp, beyond 3 wt.%, results in formation of membranes with large and visible pores. b. ftir analysis of ca/pvp blended membranes addition of pvp to ca matrix resulted in the broadening and shifting of bands and peaks in ftir spectrum (figure 5). ftir spectrum of ca/pvp blended membranes presented prominent carbonyl group (−c=o) stretching vibration of at ~1734cm-1 and stretching vibration of −ch group at ~2960cm−1, which are defining peaks of ca [24, 25]. mpvp1, mpvp2 and mpvp3 also showed stretching vibration of ( c=o-n ) amide carbonyl group at ~1656cm-1, bending vibration of −ch2− group at ~1498cm-1. c−n group also exhibited stretching vibration of tertiary at ~1295cm-1 [26, 27]. engineering, technology & applied science research vol. 9, no. 1, 2019, 3744-3749 3747 www.etasr.com waheed & hussain: effect of polyvinyl pyrolidone on morphology and performance of cellulose … it is visible from the spectrum that as wt. % concentration increases, the peaks are becoming sharper. mpvp5 shows the same trend as mpvp1 and mpvp3 but the values were small so not as prominent as in the case of the other two membranes. so, the presence of pvp in ca matrix is confirmed by the bands and peaks shown by mpvp1, mpvp3 and mpvp5. fig. 4. sem images showing the surface. fig. 5. ftir spectrum of ca and ca/pvp blended membranes. c. effect of pvp concentration on hydrophilicity and water uptake water absorption or water uptake capacities and contact angle measurements are commonly used to estimate the extent of hydrophilic or hydrophobic nature of the membrane. if a membrane has low contact angle and possesses high-water absorption then it is high hydrophilic. contact angle values and water absorption measurements for ca and modified ca membranes are shown in figure 6. it is seen that water absorption of the pvp membrane increases and increasing pvp concentration up to 5% decreased the contact angle. these results indicated that the assimilation of pvp can increase the hydrophilicity for ca membrane obviously. d. bsa rejection % study of ca/pvp blended membranes loss of albumin (≈67kda) occurs while renal patient undergoes dialysis treatment. for good dialysis operation, albumin loss should be avoided during operation. figure 7 signifies the % rejection of all pure ca and ca/pvp blend membranes. all membranes except pure ca have bsa rejection above 90% while membranes mpvp1, mpvp3 and mpvp5 have rejection of 96.7%, 97.8% and 99.2% respectively which is relatively attractive for commercial dialysis membranes to avoid albumin loss [28]. membrane mpvp1 with 96.7% rejection gives optimum properties for example urea clearance, contact angle, water uptake and water flux concerning dialysis. fig. 6. (a) contact angle and (b) water uptake of ca/pvp blended membranes. fig. 7. bsa rejection of ca/pvp blended membranes. e. effect of pvp concentration and evaporation time on pure water flux the desired membranes were prepared with different evaporation times of 0, 10, 20 and 30sec. the prepared membranes were tested for pure water flux calculation using dead end filtration arrangement and it was found that evaporation time has a visible impact on ca/pvp blended membrane’s performance. increasing evaporation time affects inner structure and compaction of polymeric and additive particles within the membrane structure. the greater the evaporation time, the more suitable is the pore formation and uniform is the distribution of pores on membrane surface. from figure 8, it is visible that the best membranes were casted when given 30s evaporation time to the casted membrane. these membranes gave optimum values of flux. f. urea clearance study of ca/pvp blended membranes urea clearance study is one of the major studies made to investigate the efficiency of hemodialysis membranes. removal of waste including urea, excess water etc. is essential to maintain balance in patient’s blood. for this purpose, prepared membranes were examined using the experimental arrangement shown in figure 2. a fine dialysis membrane should have urea clearance value of at least 60%. figure 9 demonstrates the % urea reduction of different ca/pvp blended membranes. sample mpvp1 exhibited urea reduction of 62% in comparison to pure ca membrane with 52.1%, which is better than considerations made for a good commercial dialysis membrane [29]. the percentage of urea clearance of mpvp0, mpvp3 and mpvp5 is shown in figure 9. engineering, technology & applied science research vol. 9, no. 1, 2019, 3744-3749 3748 www.etasr.com waheed & hussain: effect of polyvinyl pyrolidone on morphology and performance of cellulose … fig. 8. graphical presentation of effect of evaporation time on pure water flux. fig. 9. urea clearance of ca/pvp blended membranes. vii. conclusion during this research, pvp was used as additive for the manufacture of ca flat sheet membranes using phase inversion method. ca/pvp membranes showed compact structure with porous layer having macro voids when viewed in cross section. sem and afm characterization confirmed the uniform distribution of pores resulting in roughness at surface. ftir studies revealed the effective bonding between pvp and ca. the hydrophilic nature was also studied by under taking contact angle and water uptake experiments. all these characterizations showed that hydrophilicity increased with addition of pvp to ca matrix. the performance testing showed that the efficiency of ca/pvp blended membranes was enhanced in terms of pwp flux, bsa rejection % and urea clearance values. this study revealed that pvp is an appropriate additive to enhance uremic waste clearance. conclusively, the ca/pvp blended membranes can be used as a capable solution for hemodialysis treatment after some appropriate conditional changes. acknowledgment this work was supported by the school of chemical and materials engineering, national university of science and technology, islamabad, pakistan and chemical engineering department of university of waterloo, ontario, canada. references [1] s. farrukh, a. hussain, n. iqbal, “fabrication and characterization of microfiltration blended membranes”, desalination and water treatment, vol. 52, no. 10-12, pp. 1833-1840, 2013 [2] s. farrukh, f. t. minhas, a. hussain, s. memon, m. i. bhanger, m. mujahid, “preparation, characterization and applicability of novel calix[4]arene based cellulose acetate membrane in gas permeation”, journal of applied polymer science, vol. 131, no. 6, 2014 [3] a. hussain, s. farrukh, f. t. minhas, “two-stage membrane system for post-combustion co2 capture application”, energy & fuels,vol. 29, no. 10, pp. 6664-6669, 2015 [4] s. s. hayek, s. sever, y. a. ko, h. trachtman, m. awad, s. 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3749 www.etasr.com waheed & hussain: effect of polyvinyl pyrolidone on morphology and performance of cellulose … fiber”, separation and purification technolog, vol. 42, no. 3, pp. 291295,2005 [22] i. c. kim, k. h. lee, “effect of poly(ethylene glycol) 200 on the formation of a polyetherimide asymmetric membrane and its performance in aqueous solvent mixture permeation”, journal of membrane science, vol. 230, no. 1-2, pp. 183-188, 2004 [23] m. m. castillo-ortega, a. najera-luna, d. e. rodriguez-felix, j. e. encinas, f. rodriguez-felix, j. romero, p. j. herrera-franco, “preparation, characterization and release of amoxicillin from cellulose acetate and poly(vinyl pyrrolidone) coaxial electrospun fibrous membrane”, materials science and engineering: c, vol. 31, no. 8, pp. 1772-1778, 2011 [24] z. cai , x. song, q. zhang, t. zhai, “electrospun polyindole nanofibers as a nano-adsorbent for heavy metal ions adsorption for wastewater treatment”, fibers and polymers, vol. 18, no. 3, pp. 502-513, 2017 [25] s. ramesh, r. shanti, e. morris, “characterization of conducting cellulose acetate based polymer electrolytes doped with “green” ionic mixture”, carbohydrate polymers,vol. 91, no. 1, pp. 14-21, 2013 [26] j. bai, y. li, c. zhang, x. liang, q. yang, “preparing agbr nanoparticles in poly(vinyl pyrrolidone) (pvp) nanofibers”, colloids and surfaces a: physicochemical and engineering aspects, vol. 329, no. 3, pp. 165-168, 2008 [27] m. gao, l. sun, z. wang, y. zhao, “controlled synthesis of ag nanoparticles with different morphologies and their antibacterial properties”, materials science and engineering: c, vol. 33, no. 1, pp. 397-404, 2013 [28] y. iwasaki, h. yamato, t. n. k. a. fujieda, u. uchida, a. h. m. motojima, m. fukagawa, “uremic toxin and bone metabolism”, journal of bone and mineral metabolism,vol. 24, no. 2, pp. 172-175, 2006 [29] g. eknoyan, g. j. beck, a. k. cheung, j. t. daugirdas, t. greene, j. w. kusek, m. allon, j. bailey, j. a. dalmez, t. a. depner, j. t. dwyer, a. s. levey, n. w. levin, e. milford, d. b. ornt, m. v. rocco, g. schulman, s. j. schwan, b. p. teehan, r. toto, “effect of dialysis dose and membrane flux in maintenance hemodialysis”, the new england journal of medicine, vol. 347, no. 25, pp. 2010-2018, 2002 microsoft word 40-3208_s_etasr_v9_n6_pp5093-5098 engineering, technology & applied science research vol. 9, no. 6, 2019, 5093-5098 5093 www.etasr.com aroussi et al.: comparative study of two passive metals in aggressive biological medium … a comparative study of 316l stainless steel and a titanium alloy in an aggressive biological medium djelloul aroussi laboratory of applied biomechanics and biomaterials (labab) enpo-ma, oran, algeria djelloul_aroussi@hotmail.com benaoumeur aour laboratory of applied biomechanics and biomaterials (labab) enpo-ma, oran, algeria benaoumeur.aour@enp-oran.dz abdelhadi sabik bouaziz laboratory of mechanical manufacturing and technology enpo-ma, oran, algeria bouaziz_sabik@hotmail.com abstract—the electrochemical behavior of stainless steel and titanium alloys is affected after prolonged contact with basic or acidic solutions, indicating a change in their surface properties. the human body often rejects invasive devices that aim to alter the biological or chemical composition of blood or other body fluids. stents, fixation plates and screws, spinal implant devices, aneurysm clips, intramedullary nails and stems, temporary fixation devices and surgical instruments, etc. have been made from stainless steel aisi 316l for several years. although the mechanical performance of implants and devices may be governed by their bulk properties, their interaction with the environment is managed by the characteristics of their superficial layer. in the case of biomedical devices, resistance to corrosion and biocompatibility has paramount importance. this study compares the corrosion behavior of 316l stainless steel and a titanium alloy in a hank solution. the obtained results show that the titanium alloy has a higher potential than 316l stainless steel and lower corrosion current. keywords-corrosion; 316l stainless steel; titanium; passivation; biocompatibility i. introduction implants are organs and devices in order to replace a missing or a damaged organ of the human body, ensuring its vital functions optimally. biomaterials, one of the great therapeutic advances in implantation, work under biological stress and play an increasingly crucial role in our health and quality of life [1]. in order to protect people against the possible dangers and inconveniences of implants and devices, it is necessary to test sufficiently their elements without putting in danger the patient’s life. this is why large-scale studies and clinical trials are required [2]. experiments carried out over the years have shown that cells’ response to the surface of the biomaterial varies according to their type and state of maturation. in vitro and in vivo tests have led several authors to conclude that the attachment of osteoblasts is reinforced by the roughness of the surface [3, 4]. the first tests, regarding the resistance to corrosion in physiological environment, in vitro and in vivo, seem conclusive and should continue in the coming years [5]. research was carried out for orthopedic applications, such as knee and hip prostheses [6, 7]. this type of prosthesis undergoes significant mechanical frictional stresses, causing the release of metal particles in large quantities. metallic biomaterials have been used in various biomedical applications for a century, due to their low cost, excellent mechanical properties and inertness [8, 9]. stainless steel and titanium alloys are frequently employed in many biomedical applications, including cardiovascular stents/valves, orthopedic prosthesis and other devices and implants used in biomedicine, because of their biocompatibility and mechanical properties, such as high strength and toughness [10, 11]. titanium alloys are extensively used due to their attractive combination of high strength, low density, and good corrosion resistance [12,13]. moreover, the 316l stainless steel is known for its good ductility, fatigue resistance, and high strength toughness [14, 15]. however, there is always a concern about their corrosion resistance in physiological medium and their biocompatibility [16, 17]. the effects of surface treatment and metallic coating on the corrosion behavior and biocompatibility of surgical 316l stainless steel implants were evaluated in [18]. the experimental results indicated that nb coating and surface treatment of the stainless steel improved its corrosion behavior. the structural and bio-corrosion barrier performance of mgsubstituted fluorapatite coating on a 316l stainless steel human body implant was investigated in [19], concluding in improved corrosion resistance and biocompatibility. in [20] the microstructural evolution, mechanical, sliding wear and corrosion behavior of 316l stainless steel multi axially forged at 600°c was studied, showing that severely deformed ultrafine-grained metals have the potential to deliver improved implant performance. the electrochemical tests conducted in [21] showed that the surface enriched by molybdenum improved the corrosion resistance of the 316l stainless steel. recently, a comparative assessment of the corrosion intensity of orthodontic arch wires made of alloy steel, nickeltitanium and titanium-molybdenum alloys, in laboratory conditions, was presented in [22]. the highest resistance to corrosion was observed in nickel-titanium alloy arch wires, while steel wires had the lowest. surface modification allows improvements on the materials’ characteristics without compromising their important bulk properties. a review on stainless steel surface modification methods provides guidance corresponding author: djelloul aroussi engineering, technology & applied science research vol. 9, no. 6, 2019, 5093-5098 5094 www.etasr.com aroussi et al.: comparative study of two passive metals in aggressive biological medium … for selecting the appropriate modification routes, tailored for specific biomedical applications [23]. the purpose of this study is to compare the corrosion behavior of 316l stainless steel and titanium alloy in a hank's solution, utilizing electrochemical measurements, such as potentiodynamic and cyclic polarization. ii. studied materials aisi 316l stainless steel and titanium alloys are commonly used in the manufacturing of prostheses. the chemical composition of these materials was determined by spectroscopic analysis (tables i and ii). samples were cut in the form of a 14mm in diameter disc from cylindrical bars delivered in a raw state. table i. composition of 316l stainless steel (in mass %) c p s si mn cr ni mo ti n cu co 0.024 0.029 0.025 0.407 1.519 16.64 10.355 2.037 0.006 0.047 0.296 0.188 table ii. composition of the titanium alloy (in mass %). ti fe v pd 98.44 0.22 1.33 0.01 iii. surface properties and polishing techniques optimizing the properties of surface corrosion resistance is a wide and important research topic, given its potential application in different biomedical fields. corrosion resistance is one of surfaces’ major characteristics that must be optimized in order to improve the integration of implants. in this section, focus is set on roughness and electrochemical properties. anodic dissolution of the sample can produce excellent polishing results without deforming its surface. the sample is polarized at the anode and connected to the cathode through an electrolyte bath concentrated in acid. applying voltage creates a current that travels through the bath and thus preferentially alters the surface to be polished. previously, the surface of the sample was mechanically pre-polished on abrasive papers of decreasing grain size (up to 1500 grains/cm 2 ). it should be noted that for each electro-polishing treatment, a new fresh electrolyte was used because changes in the ionic metal concentration could have an influence on the electro-polishing states [24]. consequently, the sample was cleaned by immersion in a mixture of hydrofluoric acid (2% v/v), nitric acid (10% v/v) and di water (88% v/v), for 30s at 50°c, in order to dissolve the salts without attacking the metal [25]. after each operation, the sample was ultrasonically cleaned in a solution of water and acetone for 10 minutes and dried with compressed air. the roughness was measured using a “surftest 201” portable rugosimeter. each measurement was repeated five times at different locations and the roughness values of the samples are recorded in table iii. table iii. surface roughness of the studied materials raavg [µm] 316l (electrolytically polished) 0.05±0.02 titanium alloy (mechanically polished) 0.07±0.02 iv. results and discussion a. microhardness the microhardness tests were carried out under a load of 20g, load from which the impression is visible under the microscope, using a vickers microdurometer equipped with a microscope. vickers hv hardness is related to the length of the diagonal of the impression (d) and the applied load (m) by: 2 1.854 /hv m d= (1) with m in [kgf] and d in [mm]. the microhardness results for both materials are shown in table iv and represent the average of 10 measurements. it can be noted that the titanium alloy is mechanically stronger than 316l stainless steel. table iv. microhardness of the tested surfaces of the studied materials materials microhardness 316l stainless steel 166.8 ±0.2hv titanium alloy 354.0 ±0.2hv b. electrochemical analysis 1) used solution the hank solution was used as an aggressive environment, assimilated to the physiological medium prepared from the compounds given in table v. table v. chemical composition of the hank solution compositions quantity (g/l) nacl 8 cacl2 0.15 kcl 0.40 nahco3 0.35 glucose 0.1 mgcl2.6h2o 0.1 na2hpo4.2h2o 0.6 kh2po4 0.06 mgso4.7h2o 0.06 2) experimental conditions the samples were characterized electrochemically under the following conditions: • a simulated physiological environment (hank's solution of ph = 7.1) • environment temperature: 37°c (human body temperature); • sweep rate of the potential: 0.5 mv/s 3) evolution of the free potential this technique makes possible to follow the evolution over time of the sample potential (working electrode) in an open circuit (ocp) relative to a reference electrode. the sample was kept immersed in the electrolyte and the free electrode potential was measured as a function of time. the abandonment potential (ea) is determined from the potential follow-up curves as a function of time. this potential is a characteristic of the modification of the interface between a metal and its engineering, technology & applied science research vol. 9, no. 6, 2019, 5093-5098 5095 www.etasr.com aroussi et al.: comparative study of two passive metals in aggressive biological medium … environment. this simple technique provides preliminary information on the nature of the processes developed on the metal/electrolyte interface: corrosion and passivation. the general shape of the curve indicates whether the material becomes passive if there is an increase in potential as a function of time. so, free corrosion tests were performed for all treatment conditions [28]. the results shown in figure 1 indicate that in a hank’s solution the native passive films of electrolytically polished 316l steel have greater stability. indeed, during 1 hour of immersion the potential of 316l polished by electrolysis remains stable at -63mv/ecs, in agreement with [26]. fig. 1. evolution of free potential as a function of time of 316l steel in hank's solution the curve shown in figure 2 displays an increase in potential over time. in this case, the value of the potential is rapidly stabilized, in less than 30 minutes, at about -10 mv/ecs. in addition, the anodic and cathodic reactions are rapidly balanced. fig. 2. evolution of the free potential as a function of time of the titanium alloy in hank's solution the variation of the potential value with immersion time can be explained by the electrochemical reaction which begins to take place between the medium (hank's solution) and the exposed surface of the metal substrate, more or less adherent, causing a relative stability of the potential for corrosion abandonment. table vi. free potential results for studied materials e(free) (mv/ecs) 316l stainless steel -63 titanium alloy -10 4) potentiodynamic curves log(i)=f(e) a metal immersed in any electrolytic medium tends to dissolve and electrically charge creating a double electrochemical layer, comparable to an electric battery. after a long enough time, a steady state is established and the metal electrode takes, relative to the solution, a potential called the potential corrosion (ecor). the latter cannot be determined absolutely and it is marked with respect to a reference electrode. using an external generator and a counter-electrode, a current passes through the metal electrode, its steady state is modified and its surface takes a new potential value (the curves e=f(i) or i=f(e) constitute the polarization curves). figures 3 and 4 show the evolution of the polarization curve log(i) in terms of the potential e for both materials. the potential scanning range was set at a speed of 0.5mv/s. calculation of the density icor and corrosion potential ecor is performed by extrapolating the anode and cathode tafel lines to the corrosion potential ecor. the point of intersection gives us directly icor and ecor. the corrosion rate vcor, expressed in (mm/year), is calculated by [27]: ( )10 . . . . cor cor i t m v n e d = (2) where cor i is the corrosion current density (a/cm 2 ), t is the time corresponding to years, m is the average atomic mass of the studied material, n is the valence, and d is the density of materials. in figure 3, it is observed that the titanium alloy in the solution becomes passive and has a passivation plateau of the order of 500mv. the corrosion current is very low and is of the order of 0.01µa/cm 2 (table vii). so, the titanium alloy has a low rate of degradation (60×10 -3 mm/year). in fact, the corrosion current can be likened to a residual current resulting from an ion diffusion phenomenon through the passive layer that has been formed. a break in the passivation layer was noticed beyond +500mv/ecs. it should be noted that this break was partial because the measured currents remained low. beyond +1.0v/ecs, where the overvoltage is greater, the currents increase drastically, meaning that the layer is completely broken. this state gives a good behavior against corrosion. the 316l steel exhibits the same behavior as the titanium alloy. the polarization curve (figure 4) shows a passivation level of +500mv/ecs and a film breaking potential of +480mv/ecs. the corrosion current remains low, which is of the order of 2µa/cm 2 and the resistance to polarization is weak (10.7mω) (table viii). according to the results obtained in the hank solution for both alloys, significant differences were noted in their electrochemical characteristics values. the corrosion potential of the titanium alloy is close to -190.8mv/ecs and its corrosion current density was 9.8×10 -3 µa/cm 2 . compared to the 316l stainless steel values, titanium’s alloy values are engineering, technology & applied science research vol. 9, no. 6, 2019, 5093-5098 5096 www.etasr.com aroussi et al.: comparative study of two passive metals in aggressive biological medium … clearly favorable. this alloy has greater potential than 316l stainless steel and lower corrosion current. the corrosion rate for the titanium alloy is 60×10 -3 mm/year. this value is very acceptable in the corrosion field, showing better corrosion behavior in the hank solution (similar to physiological environment) compared to 316l stainless steel. titanium-based alloys and stainless steels are passive materials sensitive to pitting corrosion in the presence of specific aggressive materials. these are most often chloride ions (cl ), which are the most aggressive and play an important role in the pitting mechanism. fig. 3. potentiodynamic curve of the titanium alloy in a hank solution table vii. potentiodynamic results for titanium alloy corrosion parameter ecorr (mv/ecs) icorr (µa/cm 2 ) vcorr (mm/yr) rp (mω) titanium alloy -190.8 0.0098 60×10 -3 2.21 fig. 4. potentiodynamic curve of 316l stainless steel in a hank solution table viii. potentiodynamic results for 316l steel corrosion parameter ecor (mv/ecs) icor (µa/cm 2 ) vcor (mm/yr) rp (mω) 316l stainless steel -267.5 2.155 16.86×10 -3 10.7 pitting corrosion is related to localized attacks of heterogeneities that contribute to the deterioration of the passive layer protecting the material. this process of material deterioration generally leads to a generalized corrosion phenomenon. observation by an optical microscope of the samples for both studied alloys shows the attacking shape they experienced after a corrosion test in hank's solution (figure 5). (a) (b) fig. 5. illustration of pitting corrosion in the case of (a) titanium alloy and (b) 316l stainless steel 5) cyclic potentiodynamic curves the behavior of the oxide layer formed on the samples’ surface was studied by drawing the cyclic potentiodynamic curves. figure 6 shows the titanium’s alloy cyclic polarization curves over a potential range for a half-hour immersion time in hank's solution with a sweep rate of 0.5mv/s. there is a passivation stage with a slight increase in the corrosion potential compared to the previous value of ec for the “go” scan. on the other hand, during the “return” scan the corrosion potential is less great with higher current densities. this means that the formed oxide layer has instabilities. this degradation may be at the source of localized corrosion. fig. 6. cyclic potentiodynamic polarization curve of titanium alloy cyclic curves in the case of 316l (figure 7) indicate a different behavior. beyond the formation of the passivation layer on this alloy, an ennoblement of the potential corrosion in engineering, technology & applied science research vol. 9, no. 6, 2019, 5093-5098 5097 www.etasr.com aroussi et al.: comparative study of two passive metals in aggressive biological medium … the anodic direction of the order of 300mv and very low corrosion currents were noted. stable protective character can be established here. tables ix and x summarize the cyclic potentiodynamic results for titanium alloy and 316l stainless steel. it is noted that the polarization resistance of the titanium alloy is higher than that of 316l. table ix. cyclic potentiodynamic results for the titanium alloy corrosion parameter for the titanium alloy ecor (mv/ecs) icor (µa/cm 2 ) vcor (mm/year) rp (kω) -419.0 0.347 53.62×10 -3 62.51 fig. 7. cyclic potentiodynamic polarization curve of 316l stainless steel. table x. cyclic potentiodynamic results for the 316l steel corrosion parameter for 316l stainless steel ecor (mv/ecs) icor (µa/cm 2 ) vcor (mm/year) rp (kω) -38.5 3.92 30.65×10 -3 5.54 v. conclusion this work compared the behavior of two passive metals in a biological medium, the 316l stainless steel and a titanium alloy. several experimental techniques were used, starting with microstructural characterization and microhardness measurements for both materials. electrochemical tests allowed the study of the biological medium’s effects on the electrochemical behavior of the materials. the systems were studied by polarization curves, and were distinguished by different responses, proving that the biological medium has a great influence on the electrochemical behavior of both materials. due to the importance of biomaterials applications, especially in the biomedical field, the samples were immersed in a hank’s solution and the evolution of the surface state was examined over time. the results obtained can be summarized as: • microhardness measurements show that the titanium alloy is mechanically stronger than 316l stainless steel • the steady-state potentiodynamic curves determine equilibrium potential for both alloys. • in the hank’s solution significant differences were found in the electrochemical characteristics. the titanium alloy had higher potential than 316l stainless steel and lower corrosion current • the use of cyclic intensity-potential curves, can help determining the quality of the passive film • finally, the study of the polarization resistance evolution as a function of the immersion time shows that the two alloys retain their resistance properties as a function of the immersion time in the hank’s solution. acknowledgment the authors thank the laboratory of the alfon complex (algerian foundry society of oran) for their support and assistance in the determination of chemical compositions by spectroscopic analysis. references [1] b. d. ratner, a. s. hoffman, f. j. schoen, j. e. lemons, biomaterials science, academic press, 2004 [2] l. l. hench, e. c. ethridge, “biomaterials: the interfacial problem”, 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49294939, 2003 [7] p. torricelli, m. fini, v. borsari, h. lenger, j. bernauer, m. tschon, v. bonazzi, r. giardino, “biomaterials in orthopedic surgery: effects of a nickel-reduced stainless steel on in vitro proliferation and activation of human osteoblasts”, the international journal of artificial organs, vol. 26, no. 10, pp. 952-957, 2003 [8] m. xiao, y. m. chen, m. n. biao, x. d. zhang, b. c. yang, “biofunctionalization of biomedical metals”, materials science and engineering: c, vol. 70, no. 2, pp. 1057–1070, 2017 [9] h. hermawan, d. ramdan, j. djuansjah, “metals for biomedical applications”, in: r. fazel-rezai (ed.), biomedical engineering – from theory to applications, intech publications, 2011 [10] m. niinomi, m. nakai, j. hieda, “development of new metallic alloys for biomedical applications”, acta biomaterialia, vol. 8, no. 11, pp. 3888–3903, 2012 [11] h. zhang, j. han, y. sun, y. huang, m. zhou, “mc3t3-e1 cell response to stainless steel 316l with different surface 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[16] g. manivasagam, d. dhinasekaran, a. rajamanickam, “biomedical implants: corrosion and its prevention: a review”, recent patents on corrosion science, vol. 2, pp. 40–54, 2010 [17] h. hornberger, s. virtanen, a. r. boccaccini, “biomedical coatings on magnesium alloys: a review”, acta biomateralia, vol. 8, no. 7, pp. 2442–2455, 2012 [18] a. parsapour, s. n. khorasani, m. h. fathi, “effect of surface treatment and metallic coating on corrosion behavior and biocompatibility of surgical 316l stainless steel implant”, journal of materials science & technology, vol. 28, no. 2, pp. 125–131, 2012 [19] a. sharifnabi, m. h. fathi, b. eftekhari yektaa, m. hossainalipour, “the structural and bio-corrosion barrier performance of mg-substituted fluorapatite coating on 316l stainless steel human body implant”, applied surface science, vol. 288, pp. 331-340, 2014 [20] s. v. muley, a. n. vidvans, g. p. chaudhari, s. udainiya, “an assessment of ultra-fine grained 316l stainless steel for implant 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surface finishersw society, 1993 [25] b. o. elfstrom, i. olefjord, “preparation of alloys for esca investigation”, physica scripta, vol. 16, no. 5-6, pp. 436-441, 1977 [26] o. lavigne, caracterisation des films passifs pour la definition de nouveaux materiaux : application aux plaques bipolaires metalliques des systemes pemfcs, phd thesis, insa lyon, 2009 (in french) [27] h. f. hildebrand, j. c. hornez, “biological response and biocompatibility”, in: metals as biomaterials, wiley and sons, 1998 microsoft word 1-419-ed.doc engineering, technology & applied science research vol. 4, no. 3, 2014, 625-630 625 www.etasr.com benouis et al.: the mechanical behavior of bone cement in thr in the presence of cavities the mechanical behavior of bone cement in thr in the presence of cavities a. benouis mechanical engineering department djillali liabes university of sidi bel-abbes, algeria alymoh1980@yahoo.fr b. serier mechanical engineering department djillali liabes university of sidi bel-abbes, algeria serielem@yahoo.fr b. bachir bouiadjra mechanical engineering department djillali liabes university of sidi bel-abbes, algeria bachirbou@yahoo.fr abstract— in this work we analyze three-dimensionally using the finite element method, the level and the von mises stress equivalent distribution induced around a cavity and between two cavities located in the proximal and distal bone cement polymethylmethacrylate (pmma). the effects of the position around two main axes (vertical and horizontal) of the cavity with respect to these axes, of the cavity cavity interdistance and of the type of loading (static) on the mechanical behavior of cement orthopedic are highlighted. we show that the breaking strain of the cement is largely taken when the cement in its proximallateral part contains cavities very close adjacent to each other. this work highlights not only the effect of the density of cavities, in our case simulated by cavity-cavity interdistance, but also the nature of the activity of the patient (patient standing corresponding to static efforts) on the mechanical behavior of cement. keywordsbone cement; constraint; cavity; implant; interaction; statics i. introduction cements based on acrylic resin bone currently used in orthopedic surgery are pmma (polymethylmethacrylate) selfhardening rapid polymerization type. they are used for sealing prostheses in living bone during partial or total hip replacement, knee and other joints. several studies on the analysis of the stress distribution in the orthopedic cement have been conducted. benbarek et al [1] have numerically analyzed, using the finite elements method, the effect of the orientation of the axis of the implant in relation to that of the cup, on the level and distribution of stresses in bone cement containing a microcavity and hence the stress intensity factor at the crack tip heads from said cavity. in another study, bachir bouiadjra et al [2] have studied the behavior of cement out of the acetabulum by analyzing the intensity factor. they show that the fracture mode depends on the position of the crack. benbarek et al [1] showed that the stress intensity factors in mode i and mode ii depend not only on the direction of the crack initiated in the cement but also on the axis of the implant in relation to the cup. serier et al [3] have analyzed the effect of the position of the initial crack according to the position of the axis of the implant in relation to that of the cup, on the stress intensity factor. bouziane et al [4] showed three-dimensionally, using the finite element method, that the presence of cavities or bone inclusion in the cement, is a source of stress concentration. this study is in this context and analyzes three-dimensionally, using the finite element method, the amplitude of the induced stresses in the bone cement around a cavity, and the effects of the interaction of the implant-cement interface with another cavity on the intensity and the distribution of stresses in the material. this study was conducted in order to understand and explain the interconnecting cavities via cracks phenomena observed experimentally [5]. to do this, the effect of two patient activities on the mechanical behavior of cement was analyzed: standing position simulated by static forces and normal walking simulated by dynamic forces. a number of studies have investigated the performance of cemented prosthesis in terms of prosthesis survival [6-10]. it should be noted that, in general, cemented thr is relatively less expensive than uncemented thr [11]. daan waanders et al [11] studied the micromechanical behavior of cement near the cement-bone interface on pth damage. zouambi et al [13] have studied the behavior of bone cement into the acétabulum, and the effect of the presence of defects and their interactions; they show that an increase in the defect density results in significant stress intensity. ii. presentation of model this analysis uses the modeling of femur thr (total hip replacement) in three dimensions. this modeling was done using the abaqus 6.11.1 finite element software [14]. the complex geometry of a femoral bone implant, related with a cortical bone and cancellous bone through the bone cement, and is shown in figure 1. the cavities are placed in the analyzed region more solicited of the cement. that is to say, on the part of the cement, that it is under heavy intensity stress. it is in this part where the risk of fracture of the cement, thereby loosening, is the most probable. the mechanical properties of the components of the prosthesis and its structure consists of the elements shown in table 1. iii. boundary conditions and loading there are currently several models sold in total hip replacement, among which are: cmk, bm, and fram.a for the choice of model used in the simulation, we chose the cmk.3 (third generation prosthesis carnley of kerbooll) due to its availability in the domestic market. the chosen engineering, technology & applied science research vol. 4, no. 3, 2014, 625-630 626 www.etasr.com benouis et al.: effect of cavity cavity interaction on the mechanical behavior of orthopedic cement … model is characterized by the specific dimensions and mechanical properties of its components which are listed in table i: the femoral implant, cement and bone. for static analysis, a dependent of a person of 80 kg applied to the femoral head [15] as shown in figure 1 [16]. a load abductor muscle is applied in the anterior proximal (fabductor), and a vastus lateralis load is applied to the proximal side, as represented in table ii, and at fitting in imposed on the distal femur. we analyzed the mechanical behavior of cement during the process of normal walking of the patient; the decomposition cycle is illustrated in figure 2. this patient activity is simulated by dynamic forces. the mesh of the cement around the cavity at the interface with cavity and cement and interdistance between two cavities are shown in figure 3. iv. results a. stress distribution in the cement sound (cavity free) for a better illustration of the effect of the presence of a cavity in the bone cement on the intensity and distribution of the von mises stress induced in objects subjected to mechanical stress, figure 4 illustrates the variation of this constraint in the proximal, median and distal parts of the heart cement sound (cavity free). constraints induced by static were analyzed around the cement noted in zones a, b and c (anterior, lateral and posterior) in the proximal, medial and distal parts. this figure clearly shows that the highest stresses are induced in the proximal-lateral cement. the intensity of these stresses is significantly higher than that induced in the medial side. this high level of stress is due to the load applied to the implant as well as to the abduction charges. in this area of high stress localized cavities will be considered in order to analyze their effect on the mechanical behavior. constraints caused in heel strike are more intense than those resulting from static loads. table i. material properties of femur thr [12] part of model material elastic modulus (gpa) poisson’s ratio stem cocr-alloy/stainless steel 210 0.3 cement poltymethylmethacrylate 2.4 0.3 cancellous bone polyurethane foam 0.4 0.3 cortical bone glass-fiber-reinforced epoxy ex,ey=7.0, ez=11.5 gxy=2.6, gyz, gzx=3.5 νxy, νzy, νzx=0.4 table ii. maximum loading configurations of the major muscles [17] normal walking force (n) x y z f joint contact force -433.8 -263.8 -1841.3 fstatic abductor muscle 465.9 34.5 695.0 f1 vastus lateralis muscle -7.2 148.6 -746.3 f2 fig. 1. model, mesh, boundary conditions and static loads applied to the structure analyzed. fig. 2. cracks in acrylic bone cement observed under transmitted light engineering, technology & applied science research vol. 4, no. 3, 2014, 625-630 627 www.etasr.com benouis et al.: effect of cavity cavity interaction on the mechanical behavior of orthopedic cement … fig. 3. mesh cement around the cavity b. effect of a cavity located in the heart of cement the cavity is placed in the heart of the bone cement in the proximal and distal parts away from the cement-stem interface. constraints have been analyzed in the cement around the cavity in a ϕ relative to the axes of the cavity angle. recall that angle ϕ =0° corresponds to the horizontal axis in the direction toward the bone implant, and ϕ =90° to the vertical axis and the angles of 45° and 135° are located at 45° to either of these other two axes. the effect of the cavity on the level and distribution constraints of equivalent von mises on the proximal lateral and medial parts are illustrated in figure 5. according to this latter approach, cement usage is lower as given in figure 5. figure 5b shows that on its lateral region, the cement is high solicited and that these constraints are lower than those induced by a cavity located near the interface level as seen in figure 4. the most intense stresses are generated around the vertical axis (ϕ = 90°). around the other directions constraints are relatively low. compared to the lateral region, the most important constraints induced on the medial region are related to the horizontal axis (ϕ = 0°), followed by 90°, 135° and 45°. as can be seen from figure 6, the distal part is subject to low intensity stress. this is along the vertical axis were the stresses are highly localized. our results show that the stresses induced in the lateral proximal part in the cement are comparable to the breaking yield stress of the cement. they may pose a risk of rupture to the cement, thus of loosing the total hip replacement. c. effect of cavity-cavity interaction the presence of cavities can weaken the cement notch effect and interaction, thus it determines the sustainability of total hip replacement. the objective of this part of the study was the in three dimension analysis using the finite element method. figure 7 represents the effect of cavity-cavity interaction on the level and the von mises stress distribution induced by static loading in the bone cement between the two defects. this figure shows that most important constraints are located in the cement between the cavities. fig. 4. von mises stresses equivalent distribution on the bone cement around the perimeter abc. fig. 5. von mises stress distribution in the proximal lateral and medial parts of the cement around the cavity (a), (b). engineering, technology & applied science research vol. 4, no. 3, 2014, 625-630 628 www.etasr.com benouis et al.: effect of cavity cavity interaction on the mechanical behavior of orthopedic cement … fig. 6. von mises stress distribution in the distal part of the cement around the cavity. fig. 7. level and the equivalent stress distribution in the cement between two cavities at a distance d = 0.02mm (a) the three-dimensional distribution of the von mises stress in the proximal lateral part cement around a cavity in another 0.20mm (b) procimal latera. figure 8 represents the change in the induced stress in the cement between the two cavities in relation to the distance between them. the level of stress increases significantly when these defects are located in vicinity to each other. in this case, the stresses generated exceed the breaking yield stress threshold of the cement, and tend to compress. compared to the proximal part and no matter what the nature of the load, the distal part is subjected to stresses of low level, as shown in figure 9a. a migration of a cavity leads to increased levels as shown in figure 9b. the results obtained show that the von mises stresses induced between cavities in the bone cement in the proximal lateral part exceeds the breaking yield stress. this can lead to the initiation and propagation of cracks emanating from cavities and thus the interconnection of these volume defects. this seems to explain the experimental observation of this phenomenon [18]. this work highlights not only the effect of the density of the cavities, in our case simulated by cavity – cavity interdistance, but also the effect of a patient’s activity. fig. 8. the von mises stress induced in the cement between the two cavities according to the distance. (a) (b) engineering, technology & applied science research vol. 4, no. 3, 2014, 625-630 629 www.etasr.com benouis et al.: effect of cavity cavity interaction on the mechanical behavior of orthopedic cement … distal static d=0.02mm fig. 9. the von mises stress induced in the cement between the two cavities according to the distance. v. discussion porosity in the orthopedic cement plays a determining role for the diffusion of antibiotics; it constitutes a way of matter transfer. the results obtained in this work show that its presence in orthopedic cement is a source of stress concentration per notch effect. this effect is all the more important as the cavity is localized in the vicinity close to the interface with the implant. this cavity-interface interaction weakens the cement in traction. the interaction of the stress fields between these two defects is equivalent to the breaking stress. such a position of the cavity presents a great risk of unsealing of the total prosthesis in the hip. this behavior is strongly accentuated by the localization of two cavity very close one to the other. indeed the level of the constraints induced in the cement between these two defects, reaches that of its breaking stress in compression. vi. conclusion the results obtained in this work show that:  the highest von mises stresses induced in empty cement of the cavities are located on the proximallateral part.  compared to the proximal part, the distal region of the cement is subjected to low amplitude constraints.  the presence of cavity in the bone cement is the source of an additional constraint due to the notch effect. its location at the heart of this binder creates an intense stress. this is according to the horizontal and vertical axes that the level of these constraints peaked (that is at the maximum level). this maximum exceeds the critical level of breaking stress of the cement.  compared to a cavity, the existence of a second adjacent cavity causes stronger von mises constraints in the bone cement. the intensity of these constraints depends of the position of the second cavity in relation to the first. references [1] s. benbarek, b. bachir bouiadjra, t. achour, m. belhouari, b. serier, “finite element analysis of the behaviour of crack emanating from microvoid in cement of reconstructed acetabulum”, materials science and engineering: a, vol. 457, no. 1-2, pp. 385-391, 2007 [2] b. bachir bouiadjra,, a. belarbi, s. benbarek, t. achour, b. serier, “fe analysis of the behaviour of microcracks in the cement mantle of reconstructed acetabulum in the total hip prosthesis, computational materials science, vol. 40, no. 4, pp. 485-491, 2007 [3] b. serier, b. bachir bouiadjra, s. benbarek, t. achour, “analysis of the effect of the forces during gait on the fracture behaviour in cement of reconstructed acetabulum”, computational materials science, vol. 46, no. 2, pp. 267–274, 2009 [4] m. m. bouziane, b. bachir bouiadjra, s. benbarek, m. s. h. tabeti, t. achour, “finite element analysis of the behaviour of microvoids in the cement mantle of cemented hip stem: static and dynamic analysis”, materials and design, vol. 31, no. 1, pp. 545-550, 2010 [5] p. pernod, p. hernigou, “aspect morphologique de la porosité du ciment”, actualités en biomatériaux, vol. 3, pp. 235-240, 1996 [6] r. m. kay, f. j. dorey, k. johnston-jones, a. cracchiolo iii, h. c. amstutz, g. a. m. finerman, “long-term durability of cemented primary total hip arthroplasty”, the journal of arthroplasty, vol. 10, no. 1, pp. s29–s38, 1995 [7] r. p. katz, j. j. callaghan, p. m. sullivan, r. c. johnston, “long-term results of revision total hip arthroplasty with improved cementing technique”, journal of bone and joint surgery (british volume), vol. 79, no. 2, pp. 322–3266, 1997 [8] r. b. bourne, c. h. rorabeck, m. e. ghazal, m. h. lee, “pain in the thigh following total hip replacement with a porous-coated anatomic prosthesis for osteoarthrosis. a five-year follow-up study”, journal of bone and joint surgery (american volume), vol. 76, no. 10, pp. 1464– 1470, 1994 [9] p. yates, s. serjeant, g. rushforth, r. middleton, “the relative cost of cemented and uncemented total hip arthroplasties”, the journal of arthroplasty, vol. 21, no. 1, pp. 102–105, 2006 [10] s. r. goldring, m. jasty, m. s. roelke, c. m. rourke, f. r. bringhurst, w. h. harris, “formation of a synovial-like membrane at the bonecement interface. its role in bone resorption and implant loosening after total hip replacement”, arthritis & rheumatism, vol. 29, no. 7, pp. 836842, 1986 [11] m. jasty, w. j. malony, c. r. bragdon, d. o. o'connor, t. haire, w. h. harris , “the initiation of failure in cemented femoral components of hip arthroplasties”, journal of bone and joint surgery (british volume), vol. 73-b, no. 4, pp. 551-558, 1991 [12] d. waanders, d. janssen, k. a. mann, n. verdonschot, “the behavior of the micro-mechanical cement-bone interface affects the cement failure in total hip replacement”, journal of biomechanics, vol. 44, no. 2, pp. 228-234, 2011 [13] l. zouambi, b. serier, h. fekirini, b. bachir bouiadjra, “effect of the cavity-cavity interaction on the stress amplitude in orthopedic cement”, journal of biomaterials and nanobiotechnology, vol. 4, no. 1, pp. 30-36, 2013 [14] abaqus ver 9-11, user guide; 2011. h.k. sorensen. abaqus user manual. [15] h. f. el-sheikh, j. b. macdonald, m. s. j. hashmi, “material selection in the design of the femoral component of cemented total hip replacement”, journal of materials processing technology, vol. 122, no. 2-3, pp.309-317, 2002 engineering, technology & applied science research vol. 4, no. 3, 2014, 625-630 630 www.etasr.com benouis et al.: effect of cavity cavity interaction on the mechanical behavior of orthopedic cement … [16] g. bergmann, f. graichen, a. rohlmann, “hip joint loading during walking and running, measured in two patients, journal of biomechanics, vol. 26, no. 8, pp. 969-990, 1993 [17] g. bergmann, g. deuretzbachir, m. heller, f. graichen, a. rohlmann, j. strauss, g. n. duda, “hip contact forces and gait patterns from routine activities”, journal of biomechanics, vol. 34, no. 7, pp. 859871, 2001 [18] b. a. mccormack, p. j. prendergast, “microdamage accumulation in the cement layer of hip replacements under flexural loading”, journal of biomechanics, vol. 32, no. 5, pp. 467-475, 1999 engineering, technology & applied science research vol. 7, no. 2, 2017, 1464-1472 1464 www.etasr.com tiwari et al.: design of an iot enabled local network based home monitoring system with a… design of an iot enabled local network based home monitoring system with a priority scheme varun tiwari department of electronics and communication engineering, visvesvaraya national institute of technology, nagpur, india varun.etrx@gmail.com avinash keskar department of electronics and communication engineering, visvesvaraya national institute of technology, nagpur, india agkeskar@ece.vnit.ac.in n. c. shivaprakash department of instrumentation and applied physics indian institute of science bengaluru, india shiv@iap.iisc.ernet.in abstract—internet of things (iot) is a concept where all devices get connected to the internet to exchange information. iot can be utilized in order to make a home environment interactive and smart. the required connectivity can be provided by either making all the devices wi-fi capable, which is costly, or by setting a local wireless sensor network (wsn) which later connects to internet. in this work various devices and sensors are designed and connected in a wireless sensor network within a home environment which generates a sensor dependent data packet. these data packets are then sent to the cloud through a master node. the master sends the data using a proposed priority scheme so that the critical information can be sent early. simulations were performed to show that under the proposed scheme the loss of critical sensors information is reduced by around 75%. keywords-internet of things; sensor network; wireless communication; home monitoring; priority scheme i. introduction in order to improve human machine interaction all the machines need to have some information. generally, these machines have sensors to provide some information but still a lot of information remains unknown. so in order to overcome this problem the concept of internet of things (iot) came into existence. iot is a concept under which every device is connected to internet. hence, a lot of information is available to the device and can be processed when required. a smart home monitoring system can be a very suitable application of this iot based interaction technology, as it involves a variety of devices and parameters to be connected. connecting these devices requires the design of a network, through which all the information related to monitoring and control can be accessed over the internet. a lot of work has been done in the field of smart homes to increase human-system interaction [1]. authors in [2] discussed an agent based middleware for smart home environment. a tv set top box with a special gateway to access home appliances was used in [3]. authors in [4] used power line communication with a local wireless sensor network. designing a smart home based on iot requires smart units (smart light, smart sensors) which can be connected to a wi-fi network [5]. enabling every device with wi-fi capability is a costly solution. instead a local network can be set up which can collect all the data and send it to cloud. such a local network based system was implemented in [6-8]. proper monitoring of a home environment using local network based system requires a lot of sensor and control nodes. these nodes can generate a lot of data that can flood the network. so in order to overcome this problem, a local network based system is designed with a priority scheme, so that the most relevant data is sent to the cloud. a sensor depended data packet scheme is also used to decrease the data traffic [9]. the complete system is designed using open source platforms. ii. architecture figure 1 shows a typical arrangement of sensor network in a home environment. figure 2 shows the general architecture of such a system. different sensor nodes are connected to the master of the network, which is connected to internet to send/ receive data to/from cloud. if the number of sensors is more and the area to be covered is large then these sensor nodes can be connected through repeaters using different network topologies. the block diagram shows six sensors connected to master node through repeaters. in general architecture the sensors can sense (temperature, humidity, intruder, etc.) and send the data to the master as well as can receive the data to perform any control operation (switching on/off fan, t.v, acs, alarm, etc.). now depending upon the number of sensor nodes and local network topology there can be multiple hops before the data is actually received at the cloud. as the sensor node has to perform both sensing and controlling operation the network delay can be large, so a modified architecture can be designed in which the sensor nodes and control nodes can be formed to perform the separate operation. also for nodes performing critical control/sense operation can be directly connected to cloud. figure 2(b) shows the modified architecture. in this architecture the control and the work was financially supported by the department of electronics & information technology under ministry of communications and it, government of india and center of excellence on combedded systems, visvesvaraya national institute of technology, nagpur, india. engineering, technology & applied science research vol. 7, no. 2, 2017, 1464-1472 1465 www.etasr.com tiwari et al.: design of an iot enabled local network based home monitoring system with a… sensor node performing normal operation is connected to cloud through a local network and nodes performing critical operation are provided with dedicated wi-fi capability to connect directly to the cloud. fig. 1. arrangement of sensors in a home environment. fig. 2. sensor network architecture: (a) general architecture with only master connected to cloud; (b) modified architecture with master and critical nodes connected to cloud. the addition of such nodes brings parallel data transfer capability to the system. it also minimizes the network delay. the separate control nodes minimize the sensor node’s computational requirement. all the design components of the system are discussed in the next section. iii. system design the implementation of this system requires design of various sensor nodes, repeaters, control nodes, master nodes along with development of networking algorithm, cloud network and mobile application development. all these designs are discussed below. a. sensor node the sensor nodes can be of two types, one that has a dedicated wi-fi module to directly connect to the cloud to send data and the other that forms a local network and then send the data through the master node. the local network based sensor nodes can be developed using arduino nano [10] as the controller and zigbee/nrf24l01 as the transceivers. the nodes can be configured in star as well tree topology. a sensor node can send as well as receive data wirelessly. arduino nano v3 contains atmega328 microcontroller and has a 8-channel 10bit analog to digital converter (adc), which can be used to interface eight different analog sensors. it has 23 general multiplexed input-outputs (ios) which can be used for relay/device control as per requirement [11]. figure 3 shows the basic block diagram of a sensor node. different sensor nodes can be designed using different sensors. the sensors can be interfaced as analog sensor or digital sensor. the analog sensor provides analog output in relation with the measuring parameter. analog sensors can be interfaced by using adc with proper conversion relation. the digital sensors can be interfaced to digital input of the controller. the general algorithm of an analog sensor node is as follow: algorithm 1: 1. initialize the transceiver module with the address of the repeater/master node to send or receive data. 2. get the analog value of the sensor and apply analog to digital conversion to get the 10-bit digital equivalent. 3. apply the standard conversion formula to the obtained digital value to convert it to actual sensor value in proper units. 4. send this converted value to the repeater/master node. 5. wait for some time for other nodes to send data. 6. repeat from step (2). fig. 3. sensor node block diagram. 1) sensor node with temperature sensor lm35 can be used for temperature sensing. it provides the temperature information in terms of analog output [12]. pin 2 of the lm35 provides the output it is connected to one of the adc channel of the microcontroller. the adc provides the 10-bit value of the analog data. this data needs to be converted to find the actual temperature using the conversion formula given in table i. by using the conversion formula the temperature can be measured from -50°c to 150°c (upper limit of lm35). this range of value can be represented using 8-bit. the sensor node will send this 8-bit temperature data to the master node. now if we consider a typical range of temperature in a home environment, we can limit the temperature range from -10°c to 53°c which can be represented using 6-bits only. this will reduce the data transmission load by 25%. figure 4(a) shows a sensor node with a temperature sensor. 2) sensor node with humidity sensor dht11 can be used for humidity sensing. it also calculates the temperature. it uses 1-wire protocol for data transfer. it gives the relative humidity in terms of percentage and the (a) (b) engineering, technology & applied science research vol. 7, no. 2, 2017, 1464-1472 1466 www.etasr.com tiwari et al.: design of an iot enabled local network based home monitoring system with a… temperature in celsius [13]. when the microcontroller sends a start pulse, dht11 moves from low-power-consumption mode to running-mode and waits for the microcontroller to complete the start pulse. once it is completed, dht11 sends a response signal of 40-bit data that includes the 8-bit integer relative humidity, the 8-bit decimal relative humidity, the 8-bit integer temperature, the 8-bit decimal temperature and the 8-bit checksum. once the data is received, dht11 will change to the low power consumption mode until it receives a start signal from the microcontroller again. dht11 has a measuring range of 20-90% relative humidity and 0-50°c temperature. the measuring range of temperature is in the typical range of temperature in home environments and can be send using 6-bits considering only the integer part after rounding. the measuring range of relative humidity is also in the typical range of home environments and can be sent using 8-bits only, again considering only the integer part after rounding. now both the data can be sent using 14-bits with an accuracy of around ±0.5°c for temperature and 0.5% for relative humidity. this will reduce the data transmission load by around 43.75%. figure 4(b) shows the image of one such sensor node. 3) sensor node with soil moisture sensor soil moisture sensors are designed to estimate the water content of the soil based on dielectric constant of the soil [14]. the dielectric constant of the soil increases as the water content increases. the dielectric constant of water is much larger than the soil or air, so the increase of water content is soil increases its dielectric constants value. the sensor is interfaced as an analog sensor. for calibration purpose first the adc value is measured when the sensor is in air and then again adc value is measured when the sensor is in water. the in between values represent the different level of water content in soil. table i shows the conversion. the adc provides 10-bit value which can be classified as four different states of soil’s water content. thus the sensor node will have to send only 2-bit of data to master node. figure 4(c) shows the image of the sensor node. (a) (b) (c) fig. 4. sensor nodes; (a) sensor node with temperature sensor; (b) sensor node with humidity sensor; (c) sensor node with soil moisture sensor table i. sensor interfacing and conversion table. sensor interface and conversion method temperature (lm35) analog interface [ ( (adc value) *3300 / 1024 ) 500 ] / 10 temperature in celsius humidity dht11 sensor sends actual values through 1-wire protocol relative humidity in percentage, temperature in celsius soil moisture adc value < 200 => dry soil adc value ∈ [200,500) => limited water adc value ∈ [500,800] => sufficient water adc value > 800 => excess water soil magnetic relay (no) digital value: high – door open, low – door closed pir (hcsr501) digital value: high – change detected, low – settled no change lpg gas (mq6) c = 1036.5*((1024/s 1))^-2.392*(-0.0120*(t-20) * 0.0076*(h-65) + 1) where, c=concentration in ppm s=sensor value in range of [0,1023] t=temperature in celsius h=relative humidity in percentage 4) sensor node with magnetic relay magnetic relays [15] can be used as a digital sensor to monitor opening and closing of a door. it can be of normally open or normally closed type. depending upon the type of relay it changes its state (open to close / close to open) with the effect of magnetic field. to use it for a door sensor a small magnet can be mounted to the door. the node will send only 1bit to the master. multiple sensors can be placed on critical doors. figure 5(a) shows the image of the sensor node. 5) sensor node with passive infra-red sensor the passive infra-red sensors can be used for motion detection or light intensity change. hc-sr501 can be used as the sensor for motion detection [16]. it provides digital output and can be interfaced easily with any digital pin of the microcontroller. the node will also send only 1-bit to the master. figure 5(b) shows the image of the sensor node. 6) sensor node with lpg sensor mq-6 can be used as a lpg gas sensor. it is highly sensitive to lpg, iso-butane and propane with small sensitivity to alcohol and smoke. it can detect propane in the range of 300 ~ 10000 ppm [17]. it can be interfaced with the microcontroller as analog sensor. the 10-bit adc value can be converted in ppm by using the conversion equation given in table i. now considering the lower explosive limit (lel) of the propane and butane as specified by the ‘centers for disease control and prevention’ [18], the ppm concentration can be further classified as no leakage (<650ppm), leakage (650-950ppm) and danger (>950ppm). leakage is triggered at about 35% of lel (1900ppm) and danger is triggered at about 50% of the lel. now the node needs to send any of the three states which requires only 2-bit. figure 5(c) shows the sensor node. b. control node a control node is designed to control any appliance over internet. a control node can be of two types, one that is connected to the cloud through master node and the other that has dedicated wi-fi module for cloud connectivity and a relay connected to one of the i/o of the controller. these control engineering, technology & applied science research vol. 7, no. 2, 2017, 1464-1472 1467 www.etasr.com tiwari et al.: design of an iot enabled local network based home monitoring system with a… nodes can be used at critical locations where immediate control operation is required when triggered (such as: theft alarm system). it continuously fetches the data from the cloud to maintain the state of the relay as required. figures 6(a) and 6(b) show the block diagram of control nodes. figures 6(c) and 6(d) show the general and dedicated control nodes. (a) (b) (c) fig. 5. sensor nodes; (a) sensor node with magnetic relay; (b) sensor node with pir sensor; (c) sensor node with lpg sensor. fig. 6. control node: (a) general control node block diagram with transceiver; (b) dedicated control node block diagram with wi-fi module for direct connectivity to the cloud; (c) a sample image of general control node with relay; (d) a sample image of dedicated control node with relay and wi-fi module. the dedicated control node algorithm is as below: algorithm 2 (dedicated control node): 1. initialize the wi-fi module to connect to a specified wi-fi network. 2. connect to the cloud using api key. 3. get the values of switches from the cloud. 4. assign the switch status to the i/o pins of the controller. 5. repeat from step (2). c. repeater in order to increase the range of the wireless network repeaters can be used. a repeater consists of arduino nano as the controller and zigbee/nrf24l01 as the transceivers. a repeater is configured to receive data from different child nodes and send it to the other repeater or master node. figure 7(a) shows the block diagram of the repeater and figure 7(c) shows a sample repeater. the interfacing algorithm is described below. algorithm 3 (repeater node): 1. initialize the transceiver module to receive data from child nodes. 2. initialize the transceiver module with the address of the repeater/master node to send data. 3. wait to receive data from any child node. 4. send the received data to other repeater/master node. 5. repeat from step (3). d. master node the master node also uses the arduino nano as the controller along with zigbee/nrf24l01 as transceiver. a master node has wi-fi module for internet connectivity with the help of which it can send all the collected data from the nodes to the cloud. a master node can send as well receive data. figure 7(b) and figure 7(d) shows the block diagram and an image of master node. fig. 7. repeater and master nodes: (a) repeater node block diagram with transceiver; (b) master node block diagram with wi-fi module and transceiver; (c) a sample image of repeater; (d) a sample image of master node. e. cloud all the data collected by the master is continuously send to the cloud. a user can have his own private account so that nobody else can view the data. the private account is provided with a security key which is required by any other application programming interface (api) that wants to get the information. the information is kept and stored on the cloud and can be viewed by the user when required. different channels can be created to store data. a single channel can have multiple fields which can store information from various sensors. a single sensor is linked to a particular field of a channel. the information can be accessed in different ways such as: http (a) (b) (c) (d) (a) (b) (c) (d) engineering, technology & applied science research vol. 7, no. 2, 2017, 1464-1472 1468 www.etasr.com tiwari et al.: design of an iot enabled local network based home monitoring system with a… request can be send to cloud along with api keys to get the data from any field of a channel; small programs can be created to react on any conditions raised by any sensor value; talkbacks or commands can be created to handle switches or other http requests. figure 8 shows the architecture of the cloud [19]. fig. 8. cloud architecture for iot based device support. f. mobile application a mobile application can be developed for the system using mit’s app inverter [20] which is an open source platform. it provides a block based technique for creating android applications. this application is also secured and specific to a particular user as it uses the secured key that the user has on the cloud account. the application has the capability to access the data and to send any control signal to home from anywhere around the world. figure 9 shows the different screens of the application. fig. 9. mobile application for cloud based monitoring and control: (a) applications home screen; (b) main screen; (c) garden sensor control/monitor screen; (d) living room sensor control/monitor screen. the complete system has been designed with 8 sensor nodes 2 repeaters 2 dedicated control nodes and 1 master node. four sensor nodes are configured to send information to one repeater and the other four to the other repeater. the configuration requires updating transceivers with the address to which it has to send or receive data. the repeaters are configured to then send the data to the master node. now the master node sends the data to the cloud with a priority scheme which is discussed in the next section. iv. proposed priority scheme a sensor node will always sense and generate data. these sensor nodes if continuously send the data then the network will get flooded. so in order to avoid that, a periodic scheme can be adopted, where the sensor node will generate data depending upon its period. this sensing and sending period depends upon the priority of the sensor at the sensor node. table ii shows one such scheme where the intruder detection sensor has got the highest priority and the soil moisture sensor has got the lowest. a more critical parameter is measured more frequently. this periodic sensing reduces the energy consumption and the data transmission load of the network. table ii. sensor priority scheme. priority list traffic rate no. of bits after conversion no. of bits for transmission intruder detection sensor node every 1secs 1 1 lpg gas sensor node every 5secs 10 2 temperature sensor node every 1 minute 10 6 humidity sensor node every 1 minute 8 8 soil moisture sensor every 15 minute 10 2 all the data received by the master needs to be sent to the cloud. but, many times it is possible that we end up sending same information all the time as no parameter is changing. so a priority scheme can be adopted to reduce this data transmission load. in this proposed scheme the sensor node sends the sensor data along with an additional priority bit. the priority bit is set to ‘1’ whenever there is a change in the sensor value from the previous recorded value. so the master gets the data along with the information that the data is new or repeated. now, according to the priority bit of the sensor data, master prepares a priority table to send the data. this priority table has the sensor data whose values have been changed from the previous recorded value. again as different type of sensors has different priority level as shown in table ii this priority table is again rearranged so that the most critical data can be send with highest priority. also to reduce loss of information, redundancy in data transmission is used. a high priority data is given more redundancy compared to low priority data. figure 10 shows the flow chart for the master node with the priority scheme. (c) (d) (b)(a) engineering, technology & applied science research vol. 7, no. 2, 2017, 1464-1472 1469 www.etasr.com tiwari et al.: design of an iot enabled local network based home monitoring system with a… fig. 10. master node’s flow chart with priority scheme. v. simulation to investigate the benefit of the proposed priority scheme simulations were performed. table iii shows the simulation parameters. table iii. simulation parameters. sensor interface and conversion method total number of sensors (s) 100 priorities p1>p2>p3>p4 transmission frequency p1-every 1 second p2-every 2 second p3-every 3 second p4-every 4 second no. of sensors with different priorities 25 each probability of change in sensor reading randomly distributed for 100 sensors probability of loss of data packet from master to cloud ploss simulation time 6000 seconds transfer schemes 1. without redundancy in data 2. with redundancy 3. with proposed priority based redundancy in this simulation comparison is done in between the data transfer schemes from the master to the cloud. we consider a system where we have 100 sensors with four equally distributed different priorities. sensors with priority p1 sends data every 1 second, sensors with priority p2 sends data every 2 seconds and similarly with p3 and p4 sends at 3 & 4 seconds. as discussed previously, the master sends the data of the sensor for which there is change in the value. every sensor can have different probability of change in the sensor value depending upon the measuring parameter and position. to model this condition we randomly provide these 100 sensors a probability of change in sensor value. this probability of change is considered a uniform distribution so that wide variety practical sensors can be modeled during simulation. at any given time the master will have to send the data that is generated due to change in sensor value from different sensors. the changed sensor value is considered as a single data packet that the master will send to the cloud. if at a given time ‘n’ sensors have observed changes in value then there will be ‘n’ number of data packets to be sent to the cloud. these ‘n’ sensors can be of different priorities. figure 11 shows the plot of total number of sensors with change in sensor value with respect to increase in time. the plot shows the count of different priority sensors as well as the total count. due to more frequency of the priority p1 sensors more data packets are generated by these sensors. fig. 11. plot of number of sensors with change in sensor reading value versus time. while transmitting the data to the cloud there can be some information loss. this loss can be because of network congestion or limited number of retransmission from the transmission control protocol under packet loss. to model this condition ploss is defined as the probability of loss of data packet while transmission. figure 12(a) shows the plot of loss of data packets with time. here ploss is taken as 0.1 to model the effect in short time. the loss of data packet is proportional to the generated data packets by the sensors. if we want to reduce this packet loss then a redundancy based data transmission can be applied where multiple copies of each data is transmitted. this method will reduce the packet loss but will increase the transmission load. figure 12(b) shows the plot of the redundancy based transmission scheme. the overall data packet loss reduces with this scheme but the packet loss is again proportional to the generated packets. as we are more interested in high priority sensors data the proposed priority based scheme can be applied to the system. under this priority engineering, technology & applied science research vol. 7, no. 2, 2017, 1464-1472 1470 www.etasr.com tiwari et al.: design of an iot enabled local network based home monitoring system with a… based scheme the master arranges the changed sensor values according to the priority of the sensors and then more amount of data redundancy is applied to the high priority sensor compared to lower one. figure 12(c) shows the plot of the loss of data packets with this priority based scheme. it can be observed that the proposed scheme reduces the packet loss for the high priority sensors and most of the packet loss is due to the low priority sensors only. here the amount of redundancy applied to the sensor is four for p1 sensors, three for p3 sensors and two for p2 sensors. the packet loss for p1 sensors is reduced by about 88% and for p2 about 75%. fig. 12. loss of data packets: (a) without redundancy in transmission; (b) with redundancy=3 in transmission; (c) with priority based redundancy of 4, 3 and 2 for sensors p1, p2 and p3. figure 13 shows the plot of amount of data packets generated by the different priority sensors for the three discussed schemes. for sensors with p1 priority four times the actual data is generated. for p2 the generated data is three times which is equal to the priority-less redundancy based scheme. for p3 sensors less data is generated as it is of low priority in the priority based scheme. for p1 no additional data is generated under the priority based scheme to keep the transmission load less. figure 14 shows the plot of average total number of data packets generated under the three schemes after 10 iterations. it can be observed that there is a small increase in the data packets for the proposed scheme but with huge reduction in loss of data packets for high priority sensors. a minimum of 75% reduction in loss of data packets was observed for high priority sensors p1 and p2. fig. 13. amount of data packets generated under different schemes for different priority sensors. fig. 14. total data packets generated under different schemes. vi. reliability and fault detection sending most critical data at a given time makes the system reliable. any critical event (fire, intruder, lpg leakage, etc.) can be notified with priority. along with this the system can be further enhanced by maintaining redundancy in the number of same sensors with critical operations. a fire detection node will have multiple such sensors to detect fire, so that if one node fails the other can send the information. the system can also have a fault node detection scheme where the master can detect the faulty node. the network configuration is known to the (a) (b) (c) engineering, technology & applied science research vol. 7, no. 2, 2017, 1464-1472 1471 www.etasr.com tiwari et al.: design of an iot enabled local network based home monitoring system with a… master node. the network is connected using star and tree topology. so the repeaters are important in keeping the network connected. the master first sends an acknowledgement request to the repeaters one by one. if the acknowledgement is received within time tw (tw is the time for which master waits to receive the acknowledgement signal from the receiver) then it means the repeater is working, if not then the repeater is marked as a fault node. if all the repeaters are working properly then the master sends the acknowledgement request to the sensor nodes one by one. again if the acknowledgement is received within time r*tw (the factor r depends on the number of hops required from the master to the sensor through repeater) then the node is working properly otherwise is a fault node. once a node is found to be a faulty node, the master sends the information to the cloud so that it can be reflected on all the connected devices (mobile phones, cloud accounts of the user). vii. result and comparison the system was designed using ultra low power ics such as nrf24l01/zigbee as transceiver modules and esp8266/ cc300 as wi-fi modules. the complete system was designed and tested using 8 sensor nodes, 2 repeaters 1 master and 2 dedicated control nodes. four sensor nodes were configured to send the data to master through one repeater and the other four through the other repeater. the dedicated control nodes were directly controlled through cloud. once the system is live the user can monitor and control the system from anywhere using cloud. figure 15 shows the temperature on one of the field of the cloud channel. figure 9(c) and figure 9(d) shows the mobile application screen with live data from the sensors. table iv shows the power consumption of the ics used [11-13, 16-17, 22, and 24]. table v shows the comparison between two network modules zigbee and nrf24l01 [21-22]. table vi shows the comparison between the wi-fi modules [23-24]. fig. 15. temperature plot on the field of cloud channel. the system was designed and tested using both nrf24l01 and zigbee modules. the nrf24l01 module provided all the necessary features at a very low cost. the system developed is secured and reliable because:  the user has a login credentials for his cloud account to access or control live data.  the account can be made private which provides a special security key for access over internet.  an api key is must for any access along with the information of channel id with private accounts.  all the api keys can be hard coded in the hardware. table iv. power consumption of network modules. modules standby power down active nrf24l01 26ua 900na <13.5ma esp8266 -10ua 0.3ma (average) atmega 328 0.5ma @ 1mhz, 3.3v 0.2ua @ 1mhz, 3.3v >1ma dht11 100ua 100ua 0.2ma (average) mq6 - - less than 750mw heating consumption hc-sr501 --<65ma lm35 - - less than 158ua @ 5v, 125°c table v. comparison table of network transceiver modules. parameter xbee nrf24l01+ range 30m 50m power ultra-low power device (1ua at standby) ultra-low power device (1ua at standby) max data rate upto-250kbps upto-2 mbps topology star, tree & mesh star & tree hardware interface ttl spi configuration at commands firmware update price (approx.) 15$ 3$ table vi. comparison table of network wi-fi modules. parameter cc3000 esp8266 packets tcp and udp tcp and udp modes client & server client & server interface spi ttl serial encryption up to wpa2-psk up to wpa2-psk digital pins 0 9 analog pins 0 1 programmable microcontroller no yes price (approx.) 35$ 10$ viii. conclusion the system is developed on complete open source platforms using low cost and ultra-low power ics. the periodic data sending scheme helps in keeping the data traffic rate of the system low with low consumption of energy. sending the typical range of sensors also reduces the data transmission load. the proposed priority scheme helps in sending the most engineering, technology & applied science research vol. 7, no. 2, 2017, 1464-1472 1472 www.etasr.com tiwari et al.: design of an iot enabled local network based home monitoring system with a… relevant data at any given time to cloud. sensor redundancy in the system along with the fault node detection scheme makes the system more reliable. the system provides the monitoring and control to the user over the internet which can be linked to many other applications as required. acknowledgment the authors would like to thank dr. farukh hasmi for his suggestions to improve the quality of the paper and saurabh chakole for his suggestions in improving the hardware design. references [1] c. l. wu, l. c. fu, “design and realization of a framework for human– system interaction in smart homes”, ieee transactions on systems, man and cybernetics, part a: systems and humans, vol. 42, no. 1, pp. 15-31, 2012 [2] h. takahashi, t. ito, k. sasai, g. kitagata, t. kinoshita, “design and implementation of an agent-based smart home system”, 4th ieee international conference on awareness science and technology, pp. 227-232, 2012 [3] j. kim, e. s. jung, y. t. lee, w. ryu, “home appliance control framework based on smart tv set-top box”, ieee transactions on consumer electronics, vol. 61, no. 3, pp. 279-285, 2015 [4] m. li, h. j. lin, “design and implementation of smart home control systems based on wireless sensor networks and power line communications”, ieee transactions on industrial electronics, 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http://appinventor.mit.edu/explore/ [21] digi international, “xbee®/xbee‐pro® rf modules -802.15.4 ‐ v1.xex”, datasheet, september 2009 [22] nordic semiconductor, “nrf24l01+ single chip2.4ghz transceiver”, datasheet, september 2008 [23] texas instrument, “ti simplelink™ cc3000 module – wi-fi 802.11b/g network processor”, datasheet, november 2012 [24] espressif systems, “espressif smart connectivity platform: esp8266”, datasheet, october 2013 microsoft word etasr_v11_n2_pp6889-6901 engineering, technology & applied science research vol. 11, no. 2, 2021, 6889-6901 6889 www.etasr.com almaleki: examinee characteristics and their impact on the psychometric properties of a multiple … examinee characteristics and their impact on the psychometric properties of a multiple choice test according to the item response theory (irt) deyab almaleki department of evaluation, measurement, and research umm al-qura university makkah, saudi arabia damaleki@uqu.edu.sa abstract-the aim of the current study is to provide improvement evaluation practices in the educational process. a multiple choice test was developed, which was based on content analysis and the test specification table covered some of the vocabulary of the applied statistics course. the test in its final form consisted of 18 items that were reviewed by specialists in the field of statistics to determine their validity. the results determine the relationship between individual responses and the student ability. most thresholds span the negative section of the ability. item information curves show that the items provide a good amount of information about a student with lower or moderate ability compared to a student with high ability. in terms of precision, most items were more convenient with lower ability students. the test characteristic curve was plotted according to the change in the characteristics of the examinees. the information obtained by female students appeared to be more than the information obtained by male students and the test provided more information about students who were not studying statistics in an earlier stage compared with students who did. this test clearly indicated that, based on the level of the statistics course, there should be a periodic review of the tests in line with the nature and level of the course materials in order to have a logical judgment about the level of the students’ progress at the level of their ability. keywords-item response theory; item characteristics; multiplechoice; psychometric properties i. introduction a test is an educational tool that is frequently used to evaluate students' academic achievement and progress. tests also provide an opportunity to verify students' skills in many educational situations when it is not possible to use other assessment methods. despite the known problems of indirect measurement, a lot of traits such as mathematical abilities, verbal skills, resistance to stress, intelligence, dissatisfaction, different opinions about a particular topic, etc. cannot be directly observed and measured [1-3]. these are known as the latent traits, and they can be measured only indirectly, often using specially prepared questionnaires where the responses are closely related to the specific traits being studied. tests are frequently used to assess students' cognitive progress and to build question banks. as a result, the so-called latent trait models have been developed and are used to estimate the parameter values associated with the human personality [4-5]. these models provide a different type of information that in turn helps to develop and improve tests accordingly. many researchers rely on the information from data that are analyzed as a result of the subjects' responses. but it is important to ask whether the formulation of stimuli (questions) may provide another type of data or information that serves the research process [1, 6-8]. many researchers and specialists in the field of measurement and evaluation, are interested in the basic concepts and organizational theoretical frameworks of measurement and evaluation and ways to apply them [9-11], due to the great role this science plays in various fields of scientific research in general and educational and psychological research in particular. research activity according to the needs of educational institutions will positively affect development and improvement in accordance with saudi arabia’s vision 2030. furthermore, the means of developing tests and measurement methods are extremely important because the data issued from the measurement processes have to be valid and accurate, as some crucial decisions such as admission or promotion may be based upon them [12-16]. in addition, it is the responsibility of specialists in the field of measurement and evaluation to enrich the literature, develop tests used in the educational field, and reduce the possibility of potential measurement errors during the evaluation process [17, 18]. postgraduate tests in saudi universities have not yet been subjected to much scrutiny by local and international evaluation institutions, because most of the quality assurance agencies, such as the national commission for evaluation and accreditation (ncaaa), has only recently included postgraduate programs in its plans, providing the opportunity for universities to apply for accreditation for these programs. midterm and final exams and the way they are administered are some of the indicators used by the ncaaa or other agencies to accurately judge the progress of an academic program. therefore, improving these tests has become a necessary requirement. corresponding author: deyab almaleki engineering, technology & applied science research vol. 11, no. 2, 2021, 6889-6901 6890 www.etasr.com almaleki: examinee characteristics and their impact on the psychometric properties of a multiple … ii. significance of the current study the significance of the current study stems from the importance of the evaluation processes in the educational process. the process of improving tests and identifying their psychometric characteristics is the task of those working in the field of measurement and evaluation in order to provide a comprehensive understanding and a deep descriptive analysis of the advantages and disadvantages observed in those tests [19-21]. furthermore, the scarcity of this type of scientific studies has widened the gap between the tools currently used to measure the level of achievement of students and what is hoped that these tools should be like. the quality of these tools has not been determined or reviewed, and therefore they have not been assessed or evaluated [22-25]. the practical significance of this type of research lies in the use of item response theory (irt) models in analyzing students' responses to the achievement test in a more objective way, showing whether there is an effect of the multiplicity of characteristics of the participants on the test items (multiple choice) in terms of the accuracy of the estimates of the items’ parameters and the individuals’ ability parameters. it can also guide the composers of the test questions to take into account some points that may affect the psychometric properties of the items and the test and the accuracy of its results [26-29]. iii. item response theory there are many ways (i.e. models) to determine the relationship between individual responses and student ability. within the framework of modern measurement theory, many models and applications have been formulated and applied to real test data. this includes the measurement assumptions about the characteristics of the test item, the performance of the subject, and how this performance is related to knowledge [2737-40]. tests and evaluation processes in general form the basis of the education system, and their importance lies in improving educational planning, developing a mechanism for enhancing curricular content, measuring learners' competence, and comparing student performance or achievement data. evaluations also have a role for schools and teachers [30-33]. tests are a tool of assessment, and their quality depends on a large extent on the nature and quality of the information collected during the preparation of the assessment. over the decades, the test building system has undergone a lot of development through the emergence of many test building theories focused in many types of tests, such as oral tests, standardized tests, and realistic evaluation. until today, theories have continued to develop in order to keep up with the changes in policies and new educational practices [2]. the modern theoretical methods were largely developed in the sixties to the late eighties. the irt is a general statistical theory considering the characteristics of the test item, the subject's performance on the item, and how the performance is related to the abilities that are measured by the test items [12, 34-36]. the irt provides a rich statistical tool for analyzing educational tests and psychometric measures. the irt assumes the following: • the test performance of the subjects can be predicted (or explained) by a set of factors called traits or latent traits and abilities. • the relationship between the subject's performance and the properties of the test item can be described through a monotonic increasing function called the item information function. • the response on the test item can be either isolated or continuous and it can be binary or bimodular. item score categories can be ordered or unordered, and there can be one or many abilities behind the test performance. iv. characteristics of the irt models • the irt model should be defined as the relationship between the observed response and the unobserved infrastructure (latent trait). • the model should provide a method for estimating the degrees of the latent trait. • the subjects' scores will be the basis for the assessment of the basic construction of the model. • the irt model assumes that the subject's performance can be predicted or explained by one latent trait or more. in irt is often assumed that the examinee has some unobservable latent trait (also called latent ability), which cannot be studied directly. the purpose of the irt is to propose models that allow linking these underlying traits to some of the characteristics that can be observed on the subject [41]. there are many models in the irt and they have been classified into two types: models that use the cumulative natural curve and logistic models. logistic models are currently more widespread, they are suitable for two-stage items, and differ according to the number of the estimated item parameters [6, 31, 42-45]. however, there are three commonly used models for binary data, which use (1) for the correct response and (0) for the wrong response, and these models are the one parameter and the two-parameter logistic models, which will be examined below. a. one-parameter logistic model the concept of information availability plays an important role in irt as it can be used to evaluate how the item included in the test accurately measures the level of the latent trait with (parameter value θi). this latent trait could include, for example, the level of the student's knowledge, intelligence, ability, satisfaction, stress, etc. for example, in educational tests, the item parameter represents the difficulty of the item while the subject parameter represents the ability level of the people being evaluated. the greater the subject's ability in relation to the difficulty of the item (the parameter αj describes the degree of difficulty of the item and the level of influence of the item on the subject), the greater the probability of a correct response to that item. whereas, when the subject's position on the latent trait is equal to the difficulty of the item, according to rasch’s model, there is a 0.5 probability that a subject’s response is correct. accurate information about the value of θi depends on a number of factors, the most important of which is the properties of the questions (items) used to evaluate the parameter (the latent trait) [2, 30, 33, 46]. engineering, technology & applied science research vol. 11, no. 2, 2021, 6889-6901 6891 www.etasr.com almaleki: examinee characteristics and their impact on the psychometric properties of a multiple … b. two-parameter logistic model in the two-parameter logistic (2pl) model, the situation is different from the one in the one-parameter model. the oneparameter model assumes that questions differ only with respect to item difficulty, whereas, in the two-parameter logistic model, two parameters are assumed to be connected to the test item: the parameter αj which describes the difficulty of the item (question) and the additional parameter βj, which describes the discrimination of the item. the parameter β (the slope of the curve) describes the degree to which the question helps to distinguish between the subjects with the highest level of a trait compared to those with a lower level of the same trait. this parameter also shows the extent of the relevance of the item to the overall score of the test. the higher the value of that parameter, the greater the discrimination of the items (and the easier it is to select subjects with a high level and those with a low concentration of the same trait). it should also be noted that the most difficult test item is not necessarily the test item with the highest potential to discriminate between the subjects [2, 19, 36, 47, 48]. c. three-parameter logistic model the three-parameter logistic (3pl) model is used in irt, and it determines the probability of a correct response for a dichotomously scored multiple-choice item as a logistic distribution. the 3pl model is an extension of the 2pl logistic model as it introduces the guessing parameter. items now differ in terms of discrimination, difficulty, and probability of guessing the correct response [47]. after adding the guessing parameter, denoted ci, in the 3pl model, this parameter is the lower asymptote of the item characteristic curve and represents the probability of subjects who have a low ability to answer the item correctly. the parameter is included in the model to account for item response data from low-ability subjects, where guessing is a factor in test performance [48-50]. the basic equation for the 3pl model is the probability that a randomly selected examinee with a certain proficiency level on scale k will respond correctly to item j, which is characterized by discrimination (αj), difficulty (βj), and guessing probability (ci) [27, 35, 37, 38, 51]. v. multiple choice test analysis understanding how to interpret and use the information based on students' test scores is just as important as knowing how to create a well-designed test. an essential part of building tests is using the feedback from a good test analysis. among the most important statistical information provided by a good analysis of a multiple-choice test are the following: a. item difficulty the test item difficulty factor βj represents the percentage of the respondents who answered the item correctly. the difficulty factor ranges from 0.0 to 1.00. the higher the value of the difficulty factor, the easier the test item is. for example, when the value of the difficulty factor βj is higher than 0.90, the test item is described as very easy and should not be used again in subsequent tests since almost all students are able to properly respond to it. whereas when the value of the βj is less than 0.20, the test item is described as extremely difficult and should be reviewed in subsequent tests. the optimal test item difficulty factor is 0.50, and it insures maximum discrimination between high and low ability [52-54]. to maximize item discrimination, the desired difficulty levels are slightly higher than halfway between the probability of answering correctly by chance (1.00 divided by the number of alternatives for the item) and the ideal score for the item (1.00) [55-58]. for example, if the test item contains four alternatives to the answer, the probability of answering it correctly by chance would be 0.25 (1.00/4=0.25), and the ideal degree of difficulty for the item can be calculated by substituting in the following rule: ((ideal score for item probability of a correct answer by chance) / 2) + probability of a correct answer by chance table i. the ideal degree of difficulty guideline design of the test item ideal degree of difficulty for the test item multiple choice (5 alternatives) 0.60 multiple choice (4 alternatives) 0.62 multiple choice (3 alternatives) 0.66 multiple choice (2 alternatives) 0.75 b. item discrimination the test item discrimination factor is referred to using the symbol αj, as it represents the point relationship between the respondent's performance on the item and the respondents' total scores. the discrimination factor value ranges from -1.00 to 1.00. when the value of the test item discrimination factor is high, it indicates that the test item is able to distinguish between respondents. it distinguishes between those who scored high in the tests and were able to answer the test item correctly and those who obtained low test scores and were not able to respond to the item correctly [54, 59]. test items that have point values close to or less than zero should be removed. moreover, further consideration should be given to the item which was responded to better by those who generally performed poorly on the test than those who performed better on the test as a whole. the test item may be confusing in some way to top-performing respondents [52, 53, 58, 59]. table ii. the ideal degree of discrimination guideline discrimination factor value description of the test item ≥ 0.4 a very good test item 0.3 0.39 a good test item. possible improvements may be considered 0.2 0.29 a fairly good test item. it is recommended to improve it ≤ 0.2 a weak test item, with the recommendation of deleting it ≤ 0 it is recommended to directly delete the item vi. psychometric properties of the test psychometric properties are a statistical mechanism to verify the fairness, objectivity, and relevance of the test for the phenomenon to be measured. the most important psychometric properties are the following: • the individual data series for all test components. • the characteristics of the data collected for all test components. the fairness of the test lies in its freedom from engineering, technology & applied science research vol. 11, no. 2, 2021, 6889-6901 6892 www.etasr.com almaleki: examinee characteristics and their impact on the psychometric properties of a multiple … any bias and its suitability for the target group, regardless of gender, race, and religion. the psychometric properties of the test are tested to verify that it is objectively constructed and free of any bias. studying the rules for formulating multiple-choice test items is important because it has an impact on the level of performance on the items or the test as a whole. this means that the good construction of the test and the verification of all its psychometric properties ensures that the test avoids any violations in the structure of the items, which in turn affects the individual's performance on the test items [36, 60-62]. vii. methods the descriptive survey method was used to obtain data from a real-life scenario of giving postgraduate-level midterm and final exams to assess master’s students’ achievement level in the subject of applied statistics. this analytical study aimed to determine the quality of the test, its efficiency, and the reliability of its results despite the varying circumstances in which it is given. a. measurements a criterion referenced test (crt) was used to evaluate students' achievement in the course of applied statistics in a master’s degree level in order to verify the quality of the test as a tool to evaluate the level of students’ achievement. the test was developed and based on content analysis. the test specification table covered some of the course vocabulary for the applied statistics course. the test in its first form consisted of 25 test items that were reviewed by specialists in the field of statistics to determine their face validity, and 7 items were omitted as a result. so, in its final form, the test had 18 items, and they were applied to the study sample to verify their quality (table iii). the results of the thorough analysis of the test items were handed over to the central question bank in order to compare the performance of the test items and verify their lifespan when re-performing statistical operations on them later. to verify the test reliability, the kuder richardson (kr20) method was used because the binary data are coded using 0 and 1 after correcting the items, and because the test items differ in their difficulty parameter. the results indicated that the test has a high reliability coefficient of kr-20 = 0.842. b. sample the current study population consisted of all students of the applied statistics course at the master’s level at umm al-qura university on the main campus in makkah and all branches of the university. the size of the population was rather large, estimated at about 400 male and female students registered during the second semester of the academic year 2020. it was difficult to reach all the sample members because of the financial cost, time, and effort required. moreover, the educational and population environment conditions for all students are very similar and the previous studies using samples from students in the saudi universities’ population did not show any clear bias. therefore, the current study used a random sample consisting of 338 students, equivalent to the 84.5% of the study population, studying different disciplines in the college of education. table iii. test items test items alternatives (answers) 1. which of the following is true for the interval scale level? classification of individuals ranking of individuals and identifying differences both 2. if the value of the correlation coefficient is equal to (-0.8) this is an indication that the relationship is weak nonexistent strong 3. estimates that are calculated by studying the sample members are called variables parameters statistics 4. when the population is homogeneous and its number is very large, we use the following type of sampling simple random sampling stratified random sampling cluster random sampling 5. when studying the relationship between job performance and job satisfaction, job satisfaction is called dependent variable independent variable intruder valuable 6. which of the following statements is true for the relationship between the sample and the population? population parameters are a good estimate of sample statistics population parameters are a good estimate of raw scores sample statistics are a good estimate of population parameters 7. if the relationship between chronological age and academic achievement is (r = 0.91) then this is evidence of the greater the age, the greater the achievement the younger the age, the lesser the achievement the one or the other 8. if the sum of the squares of the deviations from the mean = 80 and the number of students = 21 then the standard deviation equals 2 4 6 9. the range of the relationship that exists between two quantitative variables is called slope connection range 10. the mode for the values (1, 4, 9, 12) is zero 12 no mode 11. the median of the values (9, 15, 7, 10, 12) is 7 9 10 12. in one of the regions in ksa, a study was conducted on the pros and cons of the e-learning system at the undergraduate level. in this study the academic level is variable constant other 13. the measure of central tendency not affected by outliers is the median the mode the one or the other 14. the number of training courses during a whole semester is a continuous quantitative variable discrete quantitative variable descriptive variable 15. achievement tests depend on the following level of measurement scale ordinal interval ratio 17. when the sample size is increased it increases the probability of a normal distribution it makes the sample to not comply with the normal distribution there is no relation between them 18. setting the confidence level at 95% is a prerequisite for educational sciences. yes it may take different values according to the nature of the study other the sample distribution when responding to the test is represented in tables iv and v. the members of the study engineering, technology & applied science research vol. 11, no. 2, 2021, 6889-6901 6893 www.etasr.com almaleki: examinee characteristics and their impact on the psychometric properties of a multiple … sample were contacted by e-mail, and a test link was created and made available on the student’s electronic page. the link was made available for one hour, representing the testing period, and prior coordination with the study sample was made to select a time appropriate for everyone. cases which had any type of technological problems were not recorded. electronic reminders via the university's electronic system were used before the test to alert the study sample about the test time. table iv. distribution of the study sample according to gender and current major g e n d e r current major in the master's study p sy c h o lo g y i s la m ic e d u c a ti o n c u r r ic u lu m a n d i n s tr u c ti o n e d u c a ti o n a l a d m in is tr a ti o n s p e c ia l e d u c a ti o n t o ta l male 45 38 37 30 30 180 female 29 31 29 32 37 158 total 74 69 66 62 67 338 table v. distribution of the study sample according to studying statistics in earlier stages and current major s tu d ie d s ta ti s ti c s i n e a r li e r s ta g e current major in the master's study p sy c h o lo g y i s la m ic e d u c a ti o n c u r r ic u lu m a n d i n s tr u c ti o n e d u c a ti o n a l a d m in is tr a ti o n s p e c ia l e d u c a ti o n t o ta l yes 56 51 52 42 34 235 no 18 18 14 20 33 103 total 74 69 66 62 67 338 viii. results figure 1 show the eigenvalue scree plot. it is clear that the first eigenvalue is much greater than the others, suggesting that a unidimensional model is reasonable for this data. fig. 1. eigenvalue scree plot. this test has items with one correct alternative answer that worths a single point, the item difficulty was simply the percentage of students who answer an item correctly, which is equal to the item mean. in this case, the item difficulty index in tables vi to x shows the ranges, based on the examinees' characteristics. the item difficulty ranged from 0.647 to 0.928. for students who studied statistics in earlier stages, the items' difficulties ranged from 0.878 to 0.970, however for students who did not, the items' difficulties ranged from 0.310 to 0.893, while the items’ difficulties based on gender ranged from 0.650 to 0.966 for male and 0.645 to 0.924 for the female students. regarding the students' current major, the item difficulty varied over subjects: for special education, it ranged from 0.522 to 0.985, for educational administration it ranged from 0.50 to 0.870, for curriculum and instruction it ranged from 0.651 to 0.999, for islamic education it ranged from 0.521 to 0.927, and for psychology it ranged from 0.837 to 0.999. for higher gpa the items' difficulties ranged from 0.857 to 0.994, whereas for moderate gpa they ranged from 0.400 to 0.936, and for low gpa they ranged from 0.021 to 0.869. table vi. overall item difficulty items overall q1 0.837 q2 0.668 q3 0.843 q4 0.751 q5 0.647 q6 0.928 q7 0.798 q8 0.763 q9 0.917 q10 0.857 q11 0.757 q12 0.792 q13 0.784 q14 0.739 q15 0.695 q16 0.825 q17 0.786 q18 0.828 table vii. item difficulty accoring to studying statistics in an earlier stage items studying statistics in earlier stages yes no q1 0.927 0.631 q2 0.787 0.398 q3 0.970 0.553 q4 0.842 0.543 q5 0.795 0.310 q6 0.944 0.893 q7 0.897 0.572 q8 0.765 0.757 q9 0.974 0.786 q10 0.944 0.660 q11 0.834 0.580 q12 0.868 0.621 q13 0.880 0.563 q14 0.872 0.436 q15 0.825 0.398 q16 0.910 0.631 q17 0.842 0.660 q18 0.893 0.679 engineering, technology & applied science research vol. 11, no. 2, 2021, 6889-6901 6894 www.etasr.com almaleki: examinee characteristics and their impact on the psychometric properties of a multiple … figures 2 19 present the combined curve for the 18 items based on the overall data. each item has one threshold. most thresholds span the negative section of the ability. item information curves show that the items provide a good amount of information for students who had a lower or moderate ability compared to high ability students. in terms of precision, most of the items were more convenient to lower ability students (e.g. items 9, 10, 17), while items 2, 5, 14 gathered more information for students who had moderate ability. table viii. items difficulty accoring to gender items gender male female q1 0.844 0.829 q2 0.661 0.677 q3 0.872 0.810 q4 0.761 0.740 q5 0.650 0.645 q6 0.933 0.924 q7 0.827 0.765 q8 0.688 0.848 q9 0.966 0.860 q10 0.861 0.854 q11 0.772 0.740 q12 0.816 0.765 q13 0.850 0.708 q14 0.777 0.696 q15 0.755 0.626 q16 0.888 0.753 q17 0.850 0.715 q18 0.838 0.816 table ix. items difficultyaccoring to the current major i te m s current master's study major s p e c ia l e d u c a ti o n e d u c a ti o n a l a d m in is tr a ti o n c u r r ic u lu m a n d i n s tr u c ti o n i s la m ic e d u c a ti o n p s y c h o lo g y q1 0.761 0.822 0.939 0.768 0.891 q2 0.522 0.645 0.712 0.521 0.918 q3 0.567 0.838 0.999 0.840 0.959 q4 0.731 0.693 0.848 0.623 0.851 q5 0.507 0.500 0.651 0.623 0.918 q6 0.985 0.725 0.954 0.956 0.999 q7 0.776 0.741 0.772 0.753 0.932 q8 0.820 0.822 0.893 0.608 0.689 q9 0.865 0.838 0.969 0.927 0.972 q10 0.656 0.870 0.984 0.782 0.986 q11 0.656 0.661 0.939 0.521 0.986 q12 0.761 0.709 0.954 0.637 0.891 q13 0.776 0.741 0.787 0.652 0.945 q14 0.567 0.596 0.863 0.710 0.932 q15 0.582 0.516 0.742 0.739 0.864 q16 0.791 0.629 0.878 0.869 0.932 q17 0.776 0.677 0.772 0.855 0.837 q18 0.791 0.725 0.893 0.840 0.873 figure 20 represents the test characteristic curve that was the functional relation between the true score and the ability scale. as we can see the probability of the correct response was near to 1 at the lowest levels of ability and it increased until it came to the highest levels of ability. the probability of correct response in this test is about 18 for high ability students. figure 21 presents the total amount of the information that has been obtained from the test. it appears clearly that the test gives good indicators to assess lower levels of agreement. table x. item difficulty accoring to the gpa items gpa ≥ 3.75 3.30-3.75 2.5 – 3.30 q1 0.950 0.809 0.456 q2 0.950 0.427 0.130 q3 0.989 0.872 0.195 q4 0.928 0.581 0.456 q5 0.956 0.400 0.021 q6 0.994 0.845 0.869 q7 0.939 0.700 0.478 q8 0.857 0.645 0.673 q9 0.983 0.936 0.608 q10 0.939 0.854 0.304 q11 0.972 0.554 0.282 q12 0.956 0.627 0.543 q13 0.956 0.627 0.478 q14 0.972 0.627 0.086 q15 0.939 0.527 0.130 q16 0.950 0.745 0.521 q17 0.923 0.700 0.456 q18 0.934 0.781 0.521 fig. 2. characteristic curve of item 1. fig. 3. characteristic curve of item 2. engineering, technology & applied science research vol. 11, no. 2, 2021, 6889-6901 6895 www.etasr.com almaleki: examinee characteristics and their impact on the psychometric properties of a multiple … fig. 4. characteristic curve of item 3. fig. 5. characteristic curve of item 4. fig. 6. characteristic curve of item 5. fig. 7. characteristic curve of item 6. fig. 8. characteristic curve of item 7. fig. 9. characteristic curve of item 8. fig. 10. characteristic curve of item 9. fig. 11. characteristic curve of item 10. engineering, technology & applied science research vol. 11, no. 2, 2021, 6889-6901 6896 www.etasr.com almaleki: examinee characteristics and their impact on the psychometric properties of a multiple … fig. 12. characteristic curve of item 11. fig. 13. characteristic curve of item 12. fig. 14. characteristic curve of item 13. fig. 15. characteristic curve of item 14. fig. 16. characteristic curve of item 15. fig. 17. characteristic curve of item 16. fig. 18. characteristic curve of item 17. fig. 19. characteristic curve of item 18. engineering, technology & applied science research vol. 11, no. 2, 2021, 6889-6901 6897 www.etasr.com almaleki: examinee characteristics and their impact on the psychometric properties of a multiple … fig. 20. test characteristic curve between the true score and the ability scale. fig. 21. test characteristic curve. fig. 22. test information curve according to male examinees. figures 22 to 33 represent the test characteristic curve according to the change in the examinees’ characteristics. the amount of information that has been obtained by female students appeared to be more than the information extracted by male and the test provided more information about students who were not studying statistics in earlier levels compared to students who were. figures 27 and 28 also confirm that the test provides a good amount of information for students who had a lower or moderate ability compared to students who had high ability. fig. 23. test information curve according to female examinees. fig. 24. test information curve according to examinees who were studying statistics in earlier stage. fig. 25. test information curve according to examinees who were not studying statistics in an earlier stage. engineering, technology & applied science research vol. 11, no. 2, 2021, 6889-6901 6898 www.etasr.com almaleki: examinee characteristics and their impact on the psychometric properties of a multiple … fig. 26. test information curve according to examinees who had a gpa of 3.75 and above. fig. 27. test information curve according to examinees who had a gpa in the range from 3.30 to less than 3.75. fig. 28. test information curve according to examinees who had a gpa in the range from 2.50 to less than 3.30. fig. 29. test information curve according to current major (special education). fig. 30. test information curve according to current major (educational administration). fig. 31. test information curve according to current major (curriculum and instruction). engineering, technology & applied science research vol. 11, no. 2, 2021, 6889-6901 6899 www.etasr.com almaleki: examinee characteristics and their impact on the psychometric properties of a multiple … fig. 32. test information curve according to current major (islamic education). fig. 33. test information curve according to current major (psychology). ix. discussion the study findings support previous researches [5-7, 63] for the use of irt models in analyzing students' responses to an achievement test in a more objective way, showing whether there is an effect of the multiplicity of characteristics of the participants on the test items (multiple choice) in terms of the accuracy of the estimates of the items’ parameters and the individuals’ ability parameters. the results also help determine the relationship between individual responses and their basic ability. within the framework of modern measurement theory, many models and applications have been formulated and applied to real test data. this includes the measurement assumptions about the characteristics of the test items, the performance of the subjects, and how performance is related to knowledge. this test clearly indicated that based on the level of the statistics course, there should be a periodic review of the tests in line with the nature and level of the course materials in order to have a logical judgment about the level of students’ progress and the level of their ability. this conclusion is consistent with the findings of [50, 64]. x. conclusion in general, this study seeks to further improve the evaluation practices 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underwater acoustic engineering harbin engineering university harbin, china waleed@hrbeu.edu.cn muhammad nazim college of materials science and chemical engineering harbin engineering university harbin, china nazimlakhan@gmail.com amir ali college of underwater acoustic engineering harbin engineering university harbin, china amir@hrbeu.edu.cn sajid hussain college of nuclear science and technology harbin engineering university harbin, china sajidhussainmaitlo@gmail.com abstract-the molten salt reactor (msr) is the most important system suggested by generation iv for the future direction in the nuclear reactor field. for more development of the msr reactor, the core system inside the tube is proposed by naturally circulating molten fuel salt. the nonlinear kinetic equations form a linearized function and are obtained in state-space form. reactivity feedback and delayed neutrons are extremely important for reactor control. in this paper, a thermal-hydraulic system for the commercial computation dynamic model is proposed. currently, there is no commercial software to simulate the natural circulation flow. the proposed method can be easily employed to detect faults and can provide a feasible overall system performance. keywords-molten salt reactor; thermal-hydraulic; state-space equation; delayed neutron precursor i. introduction there are six reactors in generation-iv. among them, molten salt reactor (msr) has a unique concept that distinguishes it from the other reactor types such as light water reactors, pressure water reactors, boiling water reactors, etc. the generation-iv reactors do not have solid nature but utilize a homogenous liquid. the benefits of the msr and its excellent characteristics and sustainability eliminate the fuel element fabrication accurately. therefore, high-temperature and high power density are reached in the msr core. in the present msr method, the circulated fuel itself is mixed with the fuel salt. correspondingly, the reactor control mechanism or trip primary circuit may allow or produce fuel salt in the primary circuit, and circulation of the delayed-neutron precursor is generated in the core. hence, the decay core is less important than the outer of the core [1]. the msr is normally operated in the liquid phase because its composition tasks are affiliated with dynamic reactors. furthermore, in the msr operation in steady-state, resultantly the loss of delayed neutrons affects the reactor. in terms of modeling, msrs are associated with solid fuel which is used in traditional reactors. nuclear power plants (npps) are widely sophisticated systems regarding the transit and duration of modeling time. the fuel salt is always held on the outer side of the msr core. the multiplier term for the neutron kinetics equations is added with the delayed neutron precursor [2, 3]. the msrs are completely different from thermal-hydraulic reactor systems. in the processes of the liquid fuel failure stability of materials can be easily resolved [3]. however, a graphite zone and a thermal-hydraulic system are developed in the core [4]. in [5, 6], the fuel region is modeled as a double lasting region, which is very important in order to improve the state space equation for the outlet core temperature. in previous studies, one or two lumped parameters were applied for the thermal-hydraulic system with two lumped regions. resultantly, the outlet core temperature is measured more accurately. the core outlet temperature is the same as the average temperature of the upper lumped region [7]. the stateaction space equation is used for the reactor, thermal-hydraulic modeling, energy balance, and controls all the volume of the core and the heat exchanger (hx) unit [8]. in msrs, when the core temperature increases, the measurement of the core outlet temperature will be inaccurate [8]. in this paper, we explore and propose a novel thermalhydraulic method which give us more accurate and confident results without the ambiguity of the previous models. ii. the thermal-hydraulic method a novel thermal-hydraulic method is proposed in which a new approach has been taken to detect and resolve the problems and faults from the core outlet. in the baseline corresponding author: yong-kuo liu engineering, technology & applied science research vol. 11, no. 2, 2021, 7023-7028 7024 www.etasr.com ali et al.: the development of a thermal-hydraulic and nonlinear dynamic system for molten salt … system, an energy equilibrium equation is obtained from fuel temperature which is used without any problems in the assembled system. a maintenance equation must be described considering the core outlet temperature. in the thermalhydraulic method, a balance equation is formed by using the control volume of the pipeline at the core outlet. due to this distinct temperature and the insulation, the pipe section is very small (relatively to the core region). during this process, the present temperature of the core can be calculated more accurately. the motion of delayed neutron precursors is calculated and analysis of the fuel cycle along the state action space equation is conducted. the core neutronic as well as the extended neutronic solver 1-d thermal feedbacks are acquired by the thermal-hydraulic and neutronic calculations. the thermal neutronic features of the msrs are resolved. before the msr fuel studies, the thermal response was known to have high neutronic in thermal-hydraulic characteristics. hence, the obtained power distribution from the fission salt, as corresponding fuel density distribution, and the fuel salt temperature distribution throughout the core flow loop were described by the thermal-hydraulic measurement. the schematic view of the conceptual msr is presented in figure 1. fig. 1. schematic representation of the msr primary circuit. the structure of the fast-spectrum thermal core is made by the graphite moderator elements, each of them characterized by the fast-thermal spectrum model [5, 9, 10]. the thermal spectrum liquid fuel reactor core is associated with fluoride salt and the thermal system generated a one-reserved fuel region. one circulating pump indicates the top-bottom side of the hx unit. the heat transfer mechanism is simulated with the statement of a "cooler" which operates to stabilize temperature. the heat transfer between the hot and cold sides is calculated by using the average temperature. the heat transfer coefficient is assumed to be constant [11-13]. iii. mathematical derivation and reactor neutrons of the msr in this work, the flow effect on the liquid fuel salt and the traditional point of view of the kinetic model of the msr core are studied and the behavior of delayed neutrons is analyzed. the acute response mechanism has been changed by the fuel density and temperature. the aggregate method has been used for fuel salt in both the reactor core and the hx unit. when more fuel salt is circulating inside the core then fission power is generated inside and outside of the core, due to the very fast delayed neutrons. the space kinetic equations derived for these regions are: ����� �� � � � ���� �� ∧ ���� � �������� (1) ����� �� � �� ∧ ���� � �������� � � ���� ���� � � �� �� !��" ���� � # � � $%&&�' (2) where ( and � represent the precursor concentration of the reactor power and delayed neutron precursor respectively. the terms )*��, ,���, ���� , and λ depict net reactivity and the fraction delayed neutrons emitted energy from the core. however, the various prompt neutrons per fission and the numerous delayed neutrons of precursor per fission affect the velocity of the delayed neutron decay constants of the precursor, and generation of neutron time respectively. $ shows the transit time [12]. the fuel salt passes through the core, pipe section #1, heat exchanger, and pipe section #2, and then it enters the core again as shown in figure 1. $%&&� denotes the transit time outlet of the core region and it is expressed as: $%&&� � $�� � $�. � $/ , where subscripts �1,�2 , and 2 represent pipe section #1, pipe section #2, and hx respectively. a. neutronic calculation model development the thermodynamic characteristics of the core region are represented by the thermal power which is provided by the fuel lumped region. the average temperature of the lumped region is represented by the core fuel salt temperature. in this study, the energy balance equations are determined via an one dimension (1-d) model. the specific heat capacity is assumed to be constant and it is computed at the average temperature of the fuel. the balanced equation for the core region can be expressed as: 3�4�,� �5���� �� � ���� � 3�4�,�678,&��� � 78,9���: (3) where 3� and 3; � show the fuel mass in the core and the fuel mass flow rate respectively, 4�,� represents the average heat capacity of the fuel in the core, 7�, 78,9, and 78,& show the core lumped fuel temperature of the moderator surface, the core inlet temperature, and the core outlet temperature [11, 14, 16]. the balanced equation for the fuel side of the hx unit is: 3/4�,/ <7/��� <� � 3/4�,/67/,9��� � 7/,&���: � �=>�/?7/��� � 7@9*a���b (4) where 3/ and 3; / represent the fuel mass in the hx and the fuel mass flow rate (3; / � 3; �) respectively, 4�,/ illustrates the average heat capacity of the fuel in the hx, 7/, 7/,9, 7/,&, 7@9*a engineering, technology & applied science research vol. 11, no. 2, 2021, 7023-7028 7025 www.etasr.com ali et al.: the development of a thermal-hydraulic and nonlinear dynamic system for molten salt … represent the lumped fuel temperature in the hx, the inlet and the outlet temperature of the hx, and the average temperature of the heat sink. = and >/ show the overall heat transfer coefficient of the hx unit and the heat transfer area or the hx. the overall heat transfer coefficient is assumed to be constant [15, 16]. the balanced equation for pipe section #1 can be expressed as: 3��4�,�� �5"c(�) �� = 3��4�,��678,&(�) − 7/,9(�): − (=>)��67��(�) − 7d: (5) where subscript �1 represents the pipe section #1, 7�� and 7d represent the lumped fuel temperature in pipe section #1 and the ambient temperature. it is assumed that the overall heat transfer coefficient is also constant for pipe section #1. table i. msr parameters and range of values in the literature parameters symbol unit range reactor power p mwth 400 – 4000 prompt neutron generation time λ s 10-6 – 10-7 initial balancing reactivity )e pcm ,���[ 1 − f�g ���!��" ����$8&h� + 1 − f �g ���!��" ] steady-state external reactivity ρjkl pcm )�m� = −)e effectively delayed neutron fraction βjoo ~0.00033 effectively delayed neutron decay constant ���� s −1 ~0.006 core transit time $8&h� s ~3�/3;� loop transit time $%&&� s $/ + $�� + $�. pipe section #1 transit time $�� s ~3��/3;� pipe section #2 transit time $�. s ~3�./3;� heat exchanger transit time $/ s ~3//3;� fuel temperature coefficient of reactivity q� k -1 ~3.04x10-5 fuel mass flow rate 3;� kg.s -1 depends on the power fuel mass in the core 3� kg <�@5�s8&h� fuel mass in the hx 3/ kg <�@5ts/ fuel mass in the pipe section #1 3�� kg <�@5"cs�� fuel mass in the pipe section #2 3�. kg <�@5"us�. specific heat capacity of the fuel salt 4� j.kg −1k−1 −1111 + 2.7827� heat exchanger heat transfer coefficient (=>)/ w.k −1 ( = yz[(=>)/∆7%] (**) average fuel temperature (in the core) 7� k ~975 average fuel temperature (in the hx) 7/ k ~975 the average temperature of the heat sink 7@9*a k 750-900 ambient temperature 7d k ~3000 the density of the fuel salt <� kg.m -3 49983.56 − 0.89827� the volume of the core s8&h� m 3 depends on the power the volume of the hx s/ m 3 depends on the hx capacity the volume of pipelines #1, #2 s��,�. m 3 depends on the design b. thermal feedback mechanism and state-action space the net reactivity of the msr can be expressed as: )*����� � )& � )�m���� � q�67���� � 7�&: (6) where )e illustrates the initial balancing reactivity, )�m� represents the external reactivity which can be added with bubbles, and q� represents the core fuel salt temperature which is changed by the graphite moderator and the reactiviy coefficient. similary, the inlet and outlet flow rates are the same, and 7�e represents the steady-state fuel temperature in the core. there is only one way to write in linear form the nonlinear differential equations considering the small perturbation around the steady-state operating point. these equations can be transformed into state-space form [16]. around the steady-state power ((e and �e), (1) and (2) can be written as: d�.��� �� �� d)��� � e����e���� ∧ �� ∧ d�(�) + ����d�(�) (7) d�.(�) �� ∧ d)(�) − ( ���� + � ���� d�(�) + � �� ���!��" ���� d�(� − $%&&�) (8) where ((�) = (e + d((�) , �(�) = �e + d�(�) , and )(�) = d)(�) = q�67�(�) − 7�e: due to the nature of the reactivity. the reactor has to be critical at steady-state operation, so the reference reactivity ()e + )�m�) will be zero at this point. the nonlinear term, d)(�)d((�) still exists in (7). it can be inferred that the point kinetics equations are linear only for constant reactivity conditions. to perform linear analysis, this second-order term is neglected in this study. lumped fuel temperatures for the core and the hx regions are calculated as: 7�(�) = � . 678,&(�) + 78,9(�): (9) 7/(�) = � . 678,&(�) − 78,9(�): (10) by taking into consideration the transit times at pipe sections #1 and #2, the following substitutions: 7/,9(�) ≈ 78,&(� − $��) (11) engineering, technology & applied science research vol. 11, no. 2, 2021, 7023-7028 7026 www.etasr.com ali et al.: the development of a thermal-hydraulic and nonlinear dynamic system for molten salt … 78,9��� f 7/,&�� � $�.� (12) can be made to state the relations between the temperatures. the temperature decrease of the fuel salt in the pipeline is neglected due to the insulation. by using (9)-(12), equations (3)-(5) can be written in the form of (13)-(15): 3�4�,�7;���� � �& � d���� � 3; �4�,/678,&��� � #$�� � $�.' � 27/#� � $�.': (13) 3/4�,/7;/��� � 23; /4�,/678,&#$ � $��' � 7/���: � �=>�/?7/��� � 7@9*ab (14) 3��4�,��7;8,&��� � 3; ��4�,��678,&��� � 78,&#� � $��': � �=>���678,&��� � 78,&#� � $��' � 27d:/2 (15) where: 7����� � 1 2g 678,&��� � 78,&#� � $��':. it is assumed that 7;����� f 7;8,&��� and that 7@9*a is constant. finally, (7), (8), (13)-(15) take the state space form as follows: dh; � >�h � >.h ∗ d#� � $%&&�' � >jh ∗ d#� � $��' � >kh ∗ d#� � $�� � $�.' � lm (16) where: h � ? d���� d����7����7/���78,&���b5 (17) >� � n o o o o o o o o p � �� ∧ ���� ∝��� ∧ 0 0 �� ∧ � ���� � � ���� 0 0 0 � ]��",� 0 0 .]; � ]� � ]; � ]� 0 0 0 � .]; � ]� � �rs�t ]��",t 0 0 0 0 0 � ]; �]� �sr�"c .]�8","c t u u u u u u u u v (18) >.w n o o o o p 0 0 0 0 0 �fg ���!��"/$8&h� 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 t u u u u v (19) >j � n o o o o o p 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .]; � ]� 0 0 0 0 � ]; � ]� � �sr�"c .]�8","ct u u u u u v (20) >k = n o o o o p 0 0 0 0 0 0 0 0 0 0 0 0 0 0 � ]; � ]� 0 0 0 0 0 0 0 0 0 0 t u u u u v (21) ,= n o o o o o p� x�yz { 0 0 0 0 0 0 � ]�8",� 0 0 0 0 0 �sr�t ]�8",t 0 0 0 0 0 �sr�"c ]�8","ct u u u u u v 5 (22) | � ?7�e (e 7@9*a 7db5 (23) it is important to note that 3; � � 3; / � 3; �� � 3; �. due to the closed-loop operation (the variation of the expansion tank level is neglected). all physical properties were taken as constant and were calculated at the average temperature of the lumped regions. calculated transit time can be divided into to the length of system (or height) by the velocity of the fluid. iv. results and discussion in this section, the results of the numerical analysis for the proposed system are presented. the primary loop of msr is simulated under the steady state in matlab/simulink. when the fuel pump rotation decreases in the start of transient, the primary flow will reduce within a few seconds. furthmore, the reactor core fraction of the delayed neutron precursors will increase becuase they have the tendency to improve the reactivity and the reactivity loss due to the fuel lumped temperature. therefore, heat is produced by fuel lumped temperature in the reactor core, so that the temperature difference between core inlet and core outlet is increased in the dynamic model as shown in figure 2. fig. 2. simulink model. the core dynamic model is asscoaciated with the neutronic and thermal-hydraulic coupled system. coupling is obtained by the reactivity feedback mechanism. in this device, the input components are outer reactivity, ambient temperature, and heat sink temperature. the output values are the reactor power and the core outlet temperature. the simulation parameters are given in table ii. several different msr concepts have been presented. therefore, there is a wide variety of values for both input and output parameters. the module "1" presents the msr (fast or thermal) parameters and their range value can be used for the developed model and tool. engineering, technology & applied science research vol. 11, no. 2, 2021, 7023-7028 7027 www.etasr.com ali et al.: the development of a thermal-hydraulic and nonlinear dynamic system for molten salt … table ii. msr parameters used in the simulation parameter value reactor power 4000mwth average core temperature 700oc core transit time 2s loop transit time 2s transit time for each pipe 0.1s effectively delayed neutron fraction 0.0033 effectively delayed neutron decay constant 0.0611s-1 prompt neutron generation time 0.95e-6s fuel temperature coefficient of reactivity 3.4e-5k-1 coolant bulk temperature 570oc ambient temperature 40oc fig. 3. the sub model of neutronic and thermal hydraulic. three sub models of the simulink model are used to describe the simulink model shown in figure 2 representing three individual parts of the simulink model. figure 3 shows the neutronic and thermal-hydraulic sub model. it is used to diagnose faults from the core and give information about the fuel salt temperature distribution from the core. figure 4 shows the reactivity model and the piping system #1 of the msr. therefore it shows the lumped fuel temperatue and it repsents all constant transfer temperatures in the piping system, while fuel salt passes through piping system #1. figure 5 represents the piping system #2 and the hx of the msr. it shows the heat capacity inlet and outlet temperature of the hx. figure 6 shows the thermal reactor which reached the 3.02gw equilibrium by using the parameters illustrated in table i. the reactor reached the steady-state equation level at 100s. the fuel temperature changes between the hx region and the core region, because temperature is reduced due to the loss of the pipeline of the heat by 1ok. the fuel temperature increased by 100ok in the reactor transverse core. these features can be used in the perturbation system. fig. 4. the sub model of the reactivity model and piping system #1. fig. 5. the sub model of the piping system #2 and the hx. engineering, technology & applied science research vol. 11, no. 2, 2021, 7023-7028 7028 www.etasr.com ali et al.: the development of a thermal-hydraulic and nonlinear dynamic system for molten salt … the proposed model's derived state-space equations can be used for any specific fast msr. the equations are written for generic parameters. the fuel temperature variance between the core region and the hx region is very small, due to the 1ok temperature decrease because of the losses of heat at the pipelines. in this type of reactor, temperature of 100ok is developed transversely in the core. the msrs can be simulated with the proposed model. this feature can also be applied into perturbation cases. the components of the reactor system are adopted from the literature. fig. 6. reactor parameters at steady-state operation. v. conclusion many dynamic methods considering the thermal msr have been presented in previous works. in this paper, we used two or more lumped regions at the reactor core for the thermalhydraulic modeling. it was assumed that the outlet core temperature is the same as the average temperature of the higher lumped region. the outlet core temperature is measured inaccurately due to the high temperature at the core reactor. for all types of msr, measuring the fast spectrum or thermal fuel types is very important. there are no distinct dynamic methods for the fuel position in the core. the methods regarding other positions of the thermal reactor have significant differences that are caused by the moderator region. considering the feedback effects, the moderator temperature of the graphite region has been modeled in the thermal msrs, even though there is no concept of the moderator region in the fast msr. a new kinetic method has been proposed for fast msrs in this paper. there is only one lumped region that has been assumed for the reactor core, which has only fuel salt. therefore, energy has been balanced for the outlet core temperature that is described using pipeline temperature. the steady-state operation of msr, the nonlinear kinetic equation, the matlab/simulink system, and the state-space model have been presented. the new model was tested in simulations and the conclusion is that the conceptual reactor can be used in real applications. acknowledgment the authors would like to thank the natural science foundation of heilongjiang province, china (grant no. a2016002), the foundation of science and technology on reactor system design technology laboratory (ht-kfkt14-2017003), the technical support project for suzhou nuclear power research institute (snpi) (no.029-gn-b-2018c45p.0.99-000 03), and the research institute of nuclear power operation (no. rin180149-sccg) for funding this research project. references [1] c. yu et al., "th-u breeding performance in a channel-type molten salt fast reactor with different starting fuels," annals of nuclear energy, vol. 122, pp. 91–100, dec. 2018, https://doi.org/10.1016/j.anucene.2018. 08.003. [2] v. singh, "study of the dynamic behavior of molten-salt reactors," m. s. thesis, university of tennessee, knoxville, tn, usa, 2019. [3] d. suescún-díaz and g. espinosa-paredes, "on the numerical solution of the point reactor kinetics equations," nuclear engineering and technology, vol. 52, no. 6, pp. 1340–1346, jun. 2020, https://doi.org/ 10.1016/j.net.2019.11.034. [4] v. v. ignatiev et al., "molten-salt reactors: new possibilities, problems and solutions," atomic energy, vol. 112, no. 3, pp. 157–165, jul. 2012, https://doi.org/10.1007/s10512-012-9537-2. [5] v. singh, m. r. lish, a. m. wheeler, o. chvála, and b. r. upadhyaya, "dynamic modeling and performance analysis of a two-fluid moltensalt breeder reactor system," nuclear technology, vol. 202, no. 1, pp. 15–38, apr. 2018, https://doi.org/10.1080/00295450.2017.1416879. [6] a. asif et al., "advancement of integral fast reactor," journal of applied and emerging sciences, vol. 10, no. 2, pp 149-154, dec. 2020, https://doi.org/10.36785/jaes.v10i2.453. [7] j. stewart, "gen-foam multiphysics model development for molten salt reactors," ph.d. dissertation, university of nevada, las vegas, nv, usa, 2020. [8] a. m. leandro, f. heidet, r. hu, and n. r. brown, "thermal hydraulic model of the molten salt reactor experiment with the neams system analysis module," annals of nuclear energy, vol. 126, pp. 59–67, apr. 2019, https://doi.org/10.1016/j.anucene.2018.10.060. [9] b. mignacca and g. locatelli, "economics and finance of molten salt reactors," progress in nuclear energy, vol. 129, p. 103503, nov. 2020, https://doi.org/10.1016/j.pnucene.2020.103503. [10] y. kassem, h. camur, and o. a. m. abughinda, "solar energy potential and feasibility study of a 10mw grid-connected solar plant in libya," engineering, technology & applied science research, vol. 10, no. 4, pp. 5358–5366, aug. 2020, https://doi.org/10.48084/etasr.3607. [11] c. shi, m. cheng, and g. liu, "development and application of a system analysis code for liquid fueled molten salt reactors based on relap5 code," nuclear engineering and design, vol. 305, pp. 378–388, aug. 2016, https://doi.org/10.1016/j.nucengdes.2016.05.034. [12] z. zou, c. shen, x. zhang, s. wang, and h. chen, "3d thermal hydraulic characteristics analysis of pool-type upper plenum for leadcooled fast reactor with multi-scale coupling program," nuclear engineering and design, vol. 370, dec. 2020, art. no. 110892, https://doi.org/10.1016/j.nucengdes.2020.110892. [13] a. asif et al., "recent advances in nuclear power plant for fault detection and diagnosis a review," journal of critical reviews, vol. 7, dec. 2020, art. no. 10, https://doi.org/10.31838/jcr.07.18.535. [14] p. zhao, z. liu, t. yu, j. xie, z. chen, and c. shen, "code development on steady-state thermal-hydraulic for small modular natural circulation lead-based fast reactor," nuclear engineering and technology, vol. 52, no. 12, pp. 2789–2802, dec. 2020, https://doi.org/10.1016/ j.net.2020.05.023. [15] b. doğan and t. ölmez, "a novel state space representation for the solution of 2d-hp protein folding problem using reinforcement learning methods," applied soft computing, vol. 26, pp. 213–223, jan. 2015, https://doi.org/10.1016/j.asoc.2014.09.047. [16] r. yoshioka, y. shimazu, and k. mitachi, "guidelines for msr accident analysis," presented at the thorium energy conference, shanghai, china, 2013. engineering, technology & applied science research vol. 7, no. 6, 2017, 2324-2327 2324 www.etasr.com ponferrada et al.: laboratory safety awareness among general physics undergraduate students laboratory safety awareness among general physics undergraduate students celina o. ponferrada earl john l. cabigon jesryl g. daque department of physics college of science and mathematics university of science and technology of southern philippines cagayan de oro, 9000 philippines celinaponferrada25@gmail.com department of physics college of science and mathematics university of science and technology of southern philippines cagayan de oro, 9000 philippines earljohn_cabigon@yahoo.com department of physics college of science and mathematics university of science and technology of southern philippines cagayan de oro, 9000 philippines jesryldaque1@gmail.com geraldine d labial don christian l. buadlart van ryan kristopher r. galarpe department of physics college of science and mathematics university of science and technology of southern philippines cagayan de oro, 9000 philippines cagayan de oro, philippines department of physics college of science and mathematics university of science and technology of southern philippines cagayan de oro, 9000 philippines donbuadlart@gmail.com department of physics/department of environmental science & technology college of science and mathematics university of science and technology of southern philippines cagayan de oro, 9000 philippines vanryangalarpe@gmail.com abstract—safety awareness in the laboratory is essential to reduce occupational risks. this study was conducted to determine the students’ safety awareness in a physics laboratory. this study determined the student perception towards safety awareness by factors of gender and college from which students are enrolled. a sum of 324 students enrolled in physics10 (mechanics and heat) and physics11 (electricity and magnetism) in the mindanao university of science and technology (must) were randomly selected as survey respondents. a modified survey questionnaire was used as research instrument. the results show that the students had positive level of safety awareness and perceived positively on the preventive measures to reduce laboratory risk. further, regardless of gender students enrolled in physics 10 were more positively aware towards safety awareness than students enrolled in physics 11. similarly, a variation among the students perception towards safety awareness from the college of engineering and architecture (cea) and college of industrial and information technology (ciit) occurred. overall, present findings indicate a need to introduce laboratory safety awareness in physics classes. keywords-physics laboratory; safety awareness; preventive measures i. introduction safety awareness is a critical component in a workplace especially in a laboratory, a facility implementing scientific discipline owing to health hazards exposure [1]. it is therefore essential for safety awareness to be observed considering the occupational hazards are inevitable. good laboratory practice (glp) must similarly be implemented in a science laboratory or in any educational research entity [2-6]. laboratory malpractice may occur whenever a laboratory working staff or technician fails to oversee the safety, accuracy, and precision of a laboratory work. in return this requires compliance to glp protocols to ensure safety. the gaps on this area can be associated to less attention on (1) introduction to the laboratory safety rules, (2) presentation of an experiment’s specific safety concern, and (3) basic quizzes regarding to the safety rules [7]. in an undergraduate laboratory the students are centered towards handling equipment and activities [3] which may directly expose them to potential risk. to minimize the risk it is essential that students themselves learn some basics about specific risks. however, most studies on glp awareness are focused on chemical testing education facilities [4-6, 8-10] and no literature was found to be focused on assessing students’ awareness in physics laboratories. the use of electronics and electrical equipment in physics laboratory presents similar potential occupational risks as much as the use of chemicals. this study was conducted in order to assess the safety awareness of physics 10 (mechanics and heat) and physics 11 (electricity and magnetism) among enrolled students in the former mindanao university of science and technology (must). the objectives were to determine the status of preventive measures implemented to reduce laboratory risk, to determine the perception of students towards laboratory safety by gender and by the college the students belong. engineering, technology & applied science research vol. 7, no. 6, 2017, 2324-2327 2325 www.etasr.com ponferrada et al.: laboratory safety awareness among general physics undergraduate students ii. materials and methods a. framework this study was conducted based on a former study on laboratory safety [4]. further, this was conducted to assess the safety awareness of the former mindanao university of science and technology, now university of science and technology of southern philippines (ustp) students enrolled in physics10 and physics11 from different colleges and programs of the university (see figure 1). a descriptive method of research was employed. this was done through modified questionnaire. the considered factors were: (1) status of the risks they encounter in the physics laboratory; (2) the status of preventive measures the students have taken to avoid risk (3) gender of the respondents and (4) the college where the students belong. figure 1 presents the conceptual framework of the study. fig. 1. framework of the study b. respondents of the study the number of participants of the study was taken from the actual number of students on the first semester of 2016-2017. 324 students were randomly selected from a total of 1734 enrolled students in physics course. the slovin’s formula was used to randomly determine the number of respondents. c. questionnaire the questionnaire was anchored from [1] to fit with the objectives of this study. the first section of the questionnaire tried to identify the perceived risk in the physics laboratory. given choices were, strongly agree (sa), agree (a), neutral (n), disagree (d), strongly disagree (sd). the second section of the survey questionnaire was categorical on the safety measures taken in the physics laboratory. d. data analysis all results were presented descriptively using frequency, mean, and percentage. the independent t-test was used to statistically determine if there is a significant difference on the students’ level of safety awareness in physics laboratory by gender and by college they are enrolled. iii. results and discussions a. safety awareness of students the first parameter of this study determined the awareness of the students towards laboratory safety. all results were presented in the form of mean. tables i and ii present the perception of students towards physics laboratory safety. overall, students were aware of the laboratory risks. the positive perception of the students could be reinforced by their chemistry and other sciences laboratory classes. present findings suggest a good laboratory awareness and workenvironment sensitivity among tertiary students [11]. table i. undergraduate students in physics 10 perception on laboratory safety perception statement physics 10 (mechanics & heat) sa a n d sd know that all activities in the laboratory have health risk. 330 284 72 2 0 dust is dangerous to health. 420 216 63 4 1 smoke is dangerous to health. 680 80 9 0 3 chemical reactions can result in fire hazard and poisonous gases. 535 192 15 2 1 burning can result in hazard. 470 224 33 0 1 explosions can take place in laboratory. 475 200 45 2 1 sudden increase of temperature in the laboratory is dangerous. 370 244 69 8 1 loud noise while working with wood and metal in the laboratory is dangerous to health. 175 172 135 24 7 not washing hands with soap after activity in the laboratory is dangerous. 470 176 45 6 7 it is important to make sure that the current is turned off before making adjustments in the circuit. 560 132 42 4 0 before turning on an electrical circuit, the instructor must first be asked to inspect the circuit. 540 148 33 0 3 legend: strongly agree (sa), agree (a), neutral (n), disagree (d), strongly disagree (sd) table ii. undergraduate students in physics 11 perception on laboratory safety perception statement physics 11 (electricity & magnetism) sa a n d sd know that all activities in the laboratory have health risk. 335 268 69 8 1 dust is dangerous to health. 385 248 57 10 1 smoke is dangerous to health. 560 108 30 8 1 chemical reactions can result in fire hazard and poisonous gases. 505 180 36 8 0 burning can result in hazard. 490 192 36 6 1 explosions can take place in laboratory. 430 196 36 6 1 sudden increase of temperature in the laboratory is dangerous. 320 270 66 10 5 loud noise while working with wood and metal in the laboratory is dangerous to health. 225 216 90 58 8 not washing hands with soap after activity in the laboratory is dangerous. 420 180 63 24 3 it is important to make sure that the current is turned off before making adjustments in the circuit. 500 172 33 12 2 before turning on an electrical circuit, the instructor must first be asked to inspect the circuit. 460 192 42 10 3 legend: strongly agree (sa), agree (a), neutral (n), disagree (d), strongly disagree (sd) engineering, technology & applied science research vol. 7, no. 6, 2017, 2324-2327 2326 www.etasr.com ponferrada et al.: laboratory safety awareness among general physics undergraduate students b. students perceived preventive measures students’ perception on the preventive measures in the physics laboratory is shown in figures 2-5. perception statements were answered categorically. the use of ppe’s was positively responded by students enrolled in both physics 10 and 11 (see figure 2). these students were similarly enrolled in chemistry laboratory classes which reinforced glp and ppe use. however about 45% of students in physics 10 and 37% in physics 11 do not use ppe’s (see figure 3). this result can be associated to the lack of laboratory protocols in physics. figure 4 showed less perceived response towards noise protection owing to limited experiments involving sound. on the other hand, about 88.27% and 87.65% of students enrolled in physics 10 and 82.09% and 79.01% of students enrolled in physics 11 responded positively towards radiation avoidance or any potential source of heating relevant to physics laboratory (figure 5). fig. 2. students’ response on having personal protective equipment (ppe) in the physics laboratory fig. 3. students’ response on using ppe as ear protection against physics laboratory noise c. students perception by gender the third parameter was designed to determine if gender plays a factor towards the level of safety (see table iii). a null hypothesis was established and tested by an independent t-test (level of significance is 0.05). overall, there was a significant difference in the level of awareness between male and female students enrolled in physics10 (tcal=2.28 >tcrit = 1.65). the students of physics11 had similar level of safety awareness in the physics laboratory (tcal =1.31<1.65). fig. 4. students response on avoiding to potential source of experiments involving heating fig. 5. students response on avoiding radiation sources in physics laboratory table iii. t-table on students perception on physics laboratory safety by gender gender physics10 physics11 tcritical tcalculated tcritical tcalculated male 1.65 2.28 1.65 1.31 female 1.65 2.28 1.65 1.31 n= 162; not significant ; p>.05 d. student perception by college the fourth parameter was designed to determine if the college the students were enrolled can be a factor towards the level of safety awareness among students in physics courses. a null hypothesis was established and tested by an independent ttest (level of significance is 0.05). however, owing to limited students enrolled in physics only three colleges were considered in the former must, namely, (i) college of industrial and information technology (ciit); (ii) college of engineering and architecture (cea); and (iii) college of arts and sciences (cas). overall, students from ciit and cea in both physics 10 and physics 11 showed variation in their level of safety awareness (tcal>tcrit). the present findings can be attributed to minimal exposure of ciit and cea students to engineering, technology & applied science research vol. 7, no. 6, 2017, 2324-2327 2327 www.etasr.com ponferrada et al.: laboratory safety awareness among general physics undergraduate students natural sciences laboratories unlike cas students. these laboratories were perceived to reinforced glp and safety awareness common among cas students. nonetheless, the findings can be a basis to develop learning strategies on safety awareness among ciit and cea students (see table iv). table iv. t-table on students perception on physics laboratory safety by college college physics10 physics11 tcritical tcalculated tcritical tcalculated ciit 1.96 2.81 1.96 2.81 cea 1.96 8.02 1.96 8.02 cas 1.96 1.65 1.96 1.65 n= 162; not significant; p>.05 iv. conclusions this study investigates the level of students’ safety awareness in a physics laboratory. the study considers factors such as the gender and the college where students are enrolled. a modified survey questionnaire is used as research instrument. results suggest that students should be more informed towards physics laboratory safety. students and faculty evaluation should be incorporated to assess further the safety awareness in physics laboratory overall, present findings indicate a need to introduce laboratory safety awareness in physics classes. references [1] a. o. udoh, “status of safety awareness among senior secondary school science students in akwa ibom state of nigeria”, academic journal of interdisciplinary studies, vol. 2, no. 2, pp. 275-279, 2013 [2] b. d. backus, k. fivizzani, t. goodwin, d. finster, e. austin, w. doub, s. d. wiediger, s. kinsley, “laboratory safety culture: summary of the chemical education research and practice – safety in chemistry education panel discussion at the 46th midwest and 39th great lakes joint regional american chemical society meeting, st. louis, missouri, on october 21, 2011”, in journal of chemical health and safety, vol. 19, no. 4, pp. 20-24, 2012 [3] r. artdej, “investigating undergraduate students’ scientific understanding of laboratory safety”, procedia-social and behavioral sciences, vol. 46, pp. 5058-5062, 2012 [4] v. r. k. r galarpe, n. c. lamela, r. alcantara, “preliminary evaluation of laboratory practices in cebu doctors’ university, philippines”, journal of chemical health and safety, vol. 20, no. 4, pp. 25-30, 2013 [5] m. a. balkhiour, “evaluation of the safety status in some university laboratories”, journal of king abdulaziz university: meteorology, environment & arid land agriculture sciences, vol. 22, no.1, 2011 [6] m. m. uy, “the status of chemical safety and security in universities in mindanao, philippines”, journal of chemical health and safety, vol. 18, no. 6, pp. 8-14, 2011 [7] i. miliszewska, e. m. sztendur, “playing it safe: approaching science safety awareness through computer game-based training”, issues in informing science and information technology, vol. 8, pp. 37-47, 2011 [8] m abbas, a. m. zakaria, m. a. balkhyour, m. kashif, “chemical safety in academic laboratories: an exploratory factor analysis of safe work practices & facilities in a university”, journal of safety studies, vol. 2, no. 1, pp. 1-14, 2016 [9] m. richards-babb, j. bishoff, j. s. carver, k. fisher, j. robertsonhonecker, “keeping it safe: chemical safety in the high school laboratory”, journal of chemical health and safety, vol. 17, no. 1, pp. 6-14, 2010 [10] d. mogopodi, b. paphane, s. petros, “assessment of chemical management practices and safety in junior secondary school laboratories in gaborone”, journal of chemical health and safety, vol. 22, no. 5, pp. 17-27, 2015 [11] american chemical society, creating safety cultures in academic institutions, american chemical society, 2012 microsoft word 32-3777_s_etasr_v10_n5_pp6335-6343 engineering, technology & applied science research vol. 10, no. 5, 2020, 6335-6343 6335 www.etasr.com khalifa et al.: farm-based environmental and economic impacts of drip irrigation system farm-based environmental and economic impacts of the drip irrigation system walid m. a. khalifa civil engineering department hail university, saudi arabia and fayoum university, egypt khalifawalid@yahoo.com hatem gasmi civil engineering department hail university, saudi arabia and tunis el-manar university, tunisia gasmi_hatem@yahoo.fr tayyab a. butt civil engineering department hail university hail, saudi arabia tayyebishfaq@yahoo.com abstract-drip irrigation has received considerable attention from policy makers, researchers, and economists for its ability to contribute significantly improvements to water resource development, agricultural productivity, economic growth, and environmental sustainability. in this paper, the impact of drip irrigation has been studied on a farming system in terms of environmental and economic conditions using the developed trickle irrigation system design modeling (tisd). the environmental conditions included soil type, land topography, climate zones, water sources, their quality, and the farm dimensions. the economic conditions comprised of real and nominal interest rates, raw land price, and the energy and labor escalation rates. the study considered only the benefit-cost ratio (bcr) to indicate the impact of environmental and economic parameters on the use of the drip irrigation system. the study used tomato-sesame as a crop rotation (line-source) and citrus as a long-life tree (point-source). some parameters such as soil type, land topography, and water quality had a significant impact on the bcr. keywords-trickle irrigation; system configuration; economics; environmental changes; citrus; tomato-sesame rotation i. introduction developing infrastructure for water resources and their management is a common policy agenda in many developing economies, particularly in arid and semi-arid tropical countries like egypt. a study by the international water management institute (iwmi) has shown that around 50% of the increase in water demand by the year 2025 can be met by improving the efficacy of irrigation [1]. drip irrigation systems require a general understanding of the economic and environmental site conditions. lack of consideration of economic conditions could lead to the failure of a system that may environmentally appear to be well designed. some of the environmental conditions that must be considered are: crops and cultural practices, farm size and shape, topography, soil type, climate, water supply, and water quality [2-11]. economic efficiency is paramount to the system selection process. the data required for economic analysis fall into two general categories, site-dependent and system-dependent [3]. site-dependent economic parameters include: interest rate, labor cost, energy cost, energy inflation factor, general inflation factor, property taxes (on equipment), water cost, land value, and the return to irrigation for each crop. interest rates are categorized as real or nominal. nominal rate is the current rate of interest charged by the lending institution that will provide the credit and includes an inflationary component and a risk management and profit component. the real rate (inflation-free and ranges from 5 to 7%) is used to determine the annualized cost of capital expenditures that tend to appreciate, such as land values and permanent improvement to the land, like land-leveling. nominal rate is used to determine the annualized cost of capital expenditures that depreciate or reach technical obsolescence with little or no salvage value. the energy inflation factor is the expected inflation rate for energy over the system’s economic life and is important for balancing capital and operating costs. inflation factors should be included for other input costs, such as for labor and water. system-dependent parameters include: system component costs, system component lifetimes, and labor, energy and maintenance costs. the economic impacts of drip method of irrigation (dmi) had been studied in [12] for sugarcane cultivation. the cost of cultivation was reduced in operations like weeding, intercultural and irrigation cost (both labor and other costs). the benefit-cost ratio varied from 1.98 to 2.02 (without subsidy condition) and from 2.07 to 2.10 (30% subsidy at different discount rates). further, the net present worth indicated that the entire capital cost was recovered from the income of the very first year itself even without subsidy. the measures of zero sales tax were suggested to bring down the cost of drip set. the effect of planting distance on guava yield, quality and economic return under dmi was conducted experimentally in [13]. the guava had been planted at 6m×6m corresponding author: walid m. a. khalifa engineering, technology & applied science research vol. 10, no. 5, 2020, 6335-6343 6336 www.etasr.com khalifa et al.: farm-based environmental and economic impacts of drip irrigation system (i) and 5m×5m (ii). the results produced 8.31t/ha and 15.0t/ha (i) and 12.0t/ha and 21.60t/ha (ii) after the 3rd and 4th year of plantin, respectively. the highest benefit-cost ratio (bcr or b/c) (2.20) was at (ii). the effect of salt-affected land production under dmi was reclaimed using a 1-3yr. field experiment in [14] to investigate changes in soil’s physical, chemical, and biological properties with cropping maize. the results indicated that the soil physical environment and nutrients status were both improved. author in [15] used a subsurface drip irrigation (sdi) system to examine the convenient streams of irrigation water in uncovered domains and greenhouses. authors in [15] examined and analyzed pipeline materials, emitters spacing, and soil texture. the study investigated the impacts of soil sort and climate on consumption of water. soil moisture was measured by two enviroscan sensors. in addition, the climate parameters were measured by two weather stations. software, based on penman–monteith approach, was used to estimate the crop evapotranspiration and the amount of irrigation water according to the fao guidelines as a reference. the outcomes manifested a significant increase in crop productivity by 18% when the proposed sdi system was used over the normal dmi. authors in [16] studied the effect of dmi of cultivation in terms of cropping pattern, resource use and yield. the dmi has been found to get an important effect on saving resources, cultivation cost, crops yield and farm profitability. authors in [17] studied the adaptability of the dmi with the aid of solar power. although the recurring cost for energy was waived due to the use of freely available solar energy, the initial investment for the solar powered drip system is high. further, the bcr was 2.64 for using solar operated drip rather than the diesel operated system which had bcr equal to 1.30. the study in [18] aimed to assess the techno-economic feasibility of solar and wind based pumping irrigation systems. in the first stage of the study, the irrigation water requirements were determined by using the cropwat software to assess two different crop patterns that represent existing feasible alternatives for small farmers. for 1ha, the pumping systems powered by solar, wind and diesel energy were sized based on the crop water requirements. the costs of irrigation due to the three technologies, the two crop patterns and the three methods of irrigation (surface, sprinkler and drip) were estimated and compared. the economic analysis was complemented by a cost-benefit analysis spanning over 20 years. the economic analysis showed that windmills are the most cost effective solution, with solar pumping systems in second place. diesel pumping systems are the least cost effective. to study the climate effect on the tomato yield under dmi, authors in [19] investigated three different combination levels (100, 75 and 50% of crop water requirement) and two mulches (black polyethylene sheet and paddy straw). the highest yield for each mulch was obtained when the 50% of water requirement was applied. the yield results were 81.12t/ha for polyethylene and 79.49t/ha for straw. with 100% water application, the strawmulched treatment produced higher yield than polyethylenemulched treatment. the highest water use efficiency of 592kg/ha/mm was acquired with 50% water application under polyethylene mulch. the highest net return (us$ 7098/ha), incremental net return (us$ 1556/ha), and incremental benefitcost ratio (7.03) were found for 50% water application with straw mulch. authors in [20] studied the economic and resource impacts of drip irrigation including its benefit–cost pattern using survey data in okra cultivation. the study results revealed that the drip irrigation usage can reduce about 15% of cultivation cost, save about 47% of water resources and electrical energy, and increase okra productivity by 49% for the same cultivated area under traditional methods of irrigation. farmers cultivating okra under the usage of drip irrigation acquired an extra farm trade income of rs 72,711 per acre over the non-drip adopters. author in [21] conducted economic analysis on seven crops and nine vegetables using the trickle irrigation system design (tisd) developed in a hypothetical field in egypt based on local environmental and economic conditions [22]. economic b/c analysis and net returns amounts were calculated. the results of the study showed that high values of net return were attained for most crop rotations. further, most b/c for crop rotations ranged from 1.5 to up to more than 2.0. authors in [23] used the tisd [22] linked with the measures of the economic analysis in [21] to study the effects of system configuration and lateral directions for longlife fruit trees on the selected economic bases. the study was conducted on eleven long-life fruit trees based on environmental, crop, and economic conditions. the results revealed that the drip irrigation system with configurations and lateral directions has a very small effect on bcr, annual net return, total annual costs, and net cultivated area. the used system has significance on initial capital cost and annual energy cost. moreover, the drip irrigation system configurations and lateral directions have a considerable effect on annual maintenance cost. the objective of this study was to assess the impact of environmental and economic parameters in drip irrigation systems in farms using the tisd. the considered environmental conditions were: soil type, land topography, climate conditions, and water source conditions. the economic conditions were: real and nominal interest rates, raw land price, and energy and labor escalation rates. ii. materials and methods this study used the tisd [22] to design the trickle irrigation system with the economic analysis detailed in [21] to estimate the impacts of farm conditions under drip irrigation system on the bcr. figure 1 shows the flowchart of the tisd. the conditions considered are the environmental and economic data and suitable crop rotations. the environmental site data are soil type [24-29], land shape and topography [30-31], water source position and type, irrigation water quantity and quality [32-34], and climate zone [35-37]. the economic data include: land price [38], real and nominal interest rates [12, 39], energy source type and fuel cost [40-43], energy inflation factor, labor availability and cost, labor inflation factor, and system components’ availability and costs. crop rotations are either long-life trees or combination of winter and summer field crops or vegetables. the crop rotations should be compatible against soil type, irrigation methods, climate zone, water quality, and agricultural recommendations. after designing the concerned system, tdis calculates the different system costs and returns to determine the different selection bases. the system costs include: installation, operation, maintenance, land, water (if any), and crop production (land preparation, seeding and planting, fertilization, weeding, pest control, harvesting, and engineering, technology & applied science research vol. 10, no. 5, 2020, 6335-6343 6337 www.etasr.com khalifa et al.: farm-based environmental and economic impacts of drip irrigation system transportation). to analyze this methodology, a farm with certain environmental and economic parameters was proposed as the base farm (base run). this base run will be used in comparison with the following runs. in this study, one crop rotation (tomato-sesame) and one long-life tree (citrus) cultivation were selected. the tisd model runs by using the environmental and economic data of the base run for tomatosesame and citrus with the drip irrigation system configurations and lateral directions. this step was repeated for different parameter values, by changing one parameter while keeping the others to the value of the base run. then, the effect of each environmental and economic parameter on the bcr as the only selection basis could be discussed. fig. 1. flowchart of the tisd program. a. proposed data for base farm (run) figure 2 shows the proposed farm’s shape and topography. the proposed data to complete the analysis procedures for the base run include environmental and economic conditions (table i). further, crop rotations are considering the environmental site data (table i) and the agricultural statistics in egypt [44] based on the required information of the concerned crop rotations (tomato-sesame) and long-life fruit trees (citrus) in 2018 (table ii). the tisd model proposes the suitable crop rotations and their average production costs, expected average crop productions, and average crop prices as in [21] and [23]. fig. 2. farm dimension, slopes, and north direction of the base run. table i. case study’s site data environmental conditions soil type: coarse texture (coarse or fine or loamy sands), code number=2 climatic conditions: hot climate (middle egypt), clz (code no.) = 3 wind speed (ws)=3.0mph farm shape: figure 2 farm topography: figure 2 crop conditions: [24, 45-48] plant spacing, plant root depth, shaded area (%), average rate of water use, seasonal water requirements, leaching requirement ratio obstructions: no water source: surface water suction head, hs =6.0m water quantity = no restriction frequency = continuous water quality, electrical conductivity, ecw= 640.0ppm=1.0ds/m water price=0.0us$/m 3 economic conditions raw land value: raw=1000 us$/ha real interest rate: rir=6.0% nominal interest rate: nir=10.0% electric energy: [49] energy cost=0.10 us$/kwh (2018 prices) energy escalation rate=27.0% (2018) labor: [50] available and reliable labor cost=4.5 us$/man-hr (2018 prices) labor escalation rate=5.0%. (2018 prices) construction elements: available for drip irrigation system available maintenance supports pvc specification = din (germany) pvc price=15us$/kg of pvc (2018) aluminum and steel pipe [3], outlets’ prices [51] b. proposed changes in base run’s data the proposed changes of the base run environmental and economic data are listed in tables iii and iv. to study the read the environmental crop conditions, and calculate the preliminary irrigation design factors according to the crops chosen read the farm dimensions, land slopes and static head, desired rate of interest, equivalent annual rate of energy escalation, pump efficiency, pipe specification type design the main pipe network for (line-source and point source) according to the pipe material, the required pressure head, and the critical uphill/downhill reaches due to the pressure head difference generated by the pump design the critical uphill/downhill reaches, inlet reaches of uphill and downhill rows of configurations [1] & [2], the composed reaches according to the velocity and adjacent sizes draw the neat sketch for the system showing the area dimensions and slopes, total number of subunits, dimensions of different subunits, and pump station position choose the lateral shape (single or double) using the required system configuration, calculate the subunits number, emitter conditions, lateral length and diameter, lateral discharge, lateral pressure head variation, inlet-exit lateral pressure head, best lateral inlet position on the manifold, manifold length and diameter, manifold discharge, manifold pressure head variation, inlet-exit manifold pressure head, best manifold inlet position on the mainline, uniformity and application rate end start estimate the costs according to the configurations engineering, technology & applied science research vol. 10, no. 5, 2020, 6335-6343 6338 www.etasr.com khalifa et al.: farm-based environmental and economic impacts of drip irrigation system effect of farm area and dimensions on system costs and returns, the base farm was divided into two, four, six, and eight equal parts. this partition was made by dividing the farm length and/or width and introduces dimension ratios (l/b) of (1.179, 1.272, 1.696, 1.769, 2.358, 3.39, 4.716, 5.089, 6.785, 7.075, and 9.433). other farm dimension ratios with constant farm area were also studied. the considered farm dimension ratios with the same farm area are: 1.0, 1.5, 2.0, 2.5, and 3.0. figure 3 shows the methodology flowchart. table ii. economic information for the case study [44, 2018] crop rotations fruit production price (us$/ha) average fruit production ton/ha) average fruit price us$/ton) * tomato 4064.11 40.9689 99.2 sesame 1183.84 1.2941 914.8 citrus 3726.2 24.11 154.55 *[44, 2017] fig. 3. flowchart of the methodology analysis. table iii. proposed changes on base run environmental parameters crop rotation environmental conditions soil texture land topography climate conditions water source (1) dz% dz1% (2) ws mph. ecw hs tomatosesame 4,5 2,4,8,16 1.5,3,6,12 5 3,6,12 2,8 30 citrus 4,6 2,4,8,16 1.5,3,6,12 2,5 3,6,12 2,4 30 (1) text code: code 4: very fine sandy loams, loams, and silt loams, code 5: clay loams, silty clay loams, and sandy clay loams, code 6: sandy clays, silty clays, and clays,(2) clz code: code 2: moderate climate, code 5: high desert climate table iv. proposed changes on base run environmental parameters crop rotations economic conditions land value real and nominal interest rates energy escalation raw us$/ha real % nominal % escr % lascr % tomatosesame 2000, 4000, 8000 4,8,10 8,12,14 3,5,9 2,6,8 citrus 2000, 4000, 8000 4,8,10 8,12,14 3,5,9 2,6,8 iii. results and discussion the tisd model was run for the preselected crop rotation (tomato-sesame) and long-life trees (citrus) under the drip irrigation system and configuration by using the environmental and economic data of the base run according to tables iii and iv. for tomato-sesame rotation, the laterals must be perpendicular to the north direction. for citrus trees, the laterals may be arranged parallel or perpendicular to the north. as in [22], if the laterals are parallel to the north direction, the configuration is either #1 (with pump at the farm center [dp1], with pump on the big side [dp11], with pump on the small side [dp12]) or #2 [dp2]. if the laterals are perpendicular on the north direction, the configuration is either #1 (with pump at the farm center [dn1], with pump on the big side [dn11], with pump on the small side [dn12]) or #2 [dn2]. a. effect of different environmental conditions on the bcr 1) soil type the effects of different soil types on the bcr of tomatosesame crop rotation and citrus trees are shown in figure 4. the figure shows the bcr (stated as b/c) of the base run (coarse texture, text = 2) with different configurations. figure 4 shows the changes of the base run bcr due to changes to the soil texture from coarse to medium and moderately fine (text = 4 and 5, tomato-sesame) and from coarse to medium and fine texture (text = 4 and 6, citrus). fig. 4. effect of soil texture and climate condition on the bcr. it could be noted that the effect of soil type on the bcr of line-source is considerable (about 15.0%) and for point-source is negligible (within 2.0%). the best b/c is obtained with medium soil. for point-source and line-source drip systems, the soil type has a negligible effect on the selection of system configuration and laterals’ direction (less than 0.5%). for linesource drip system, the improvement in the bcr due to the change to the soil texture from coarse to medium is considerable and due to this change the soil texture from coarse engineering, technology & applied science research vol. 10, no. 5, 2020, 6335-6343 6339 www.etasr.com khalifa et al.: farm-based environmental and economic impacts of drip irrigation system to medium to moderately fine is negligible. for the pointsource drip system, the improvement in the bcr due to change of the soil texture from coarse to medium or fine is negligible. so, it is preferable to use the point source drip system on the coarser soil textures. 2) uniform land topography the effects of different uniform land slopes on the bcr of tomato-sesame crop rotation and long-life citrus plantation are shown in figure 5. this figure shows the b/c of the base run (dz=dz1=0.0%) under the drip irrigation system configurations. the figure shows the resulting changes in the bcr of the base run due to changes in the farm slopes. from figure 5, it could be noted that the effect of land slope on the bcr depends on the slope value and direction, and the pump position. the negative effect of the land slope on the bcr could be avoided by putting the pump unit on the upper farm side (if possible). also, for the point-source drip system, it is better to arrange the lateral lines on the small slope direction. land slopes have a considerable effect on the configuration selection, especially for high slopes. configuration #1 with the pump on the upper farm side may improve b/c. configuration #2 improves the b/c due to increase in the land slope up to 2.0%. therefore, configuration #1 with the pump station at the farm’s center is not always the optimum configuration for inclined lands. fig. 5. effect of land topography on the bcr. 3) climate and wind conditions the effects of different climate zones (clz) and wind speeds (ws) on the bcr of tomato-sesame crop rotation and long-life citrus trees are shown in figure 4. it should be noted that there is no effect of ws on the bcr of drip irrigation systems. in addition, the effect of climate on the b/c is negligible for line-source, and small (3.0%) for point-source. climate has a negligible effect on the configuration’s selection. therefore, it is preferable to use drip systems in hot climate and high wind speeds. 4) water source quality conditions the effects of water source quality and type on the bcr of tomato-sesame crop rotation and citrus trees long-life plantation are shown in figure 6. fig. 6. effect of water source quality on bcr. it can be noted that the effect of water quality on the bcr of line-source and point-source drip systems depends on the salt concentration in the irrigation water. this effect is negligible if the salt concentration approaches the lower limit of the crop salt tolerance range, ecemin, (2.5ds/m for tomato and 1.7ds/m for citrus, [52-55]). when the salt concentration increases to approach the upper limit of the crop salt tolerance range, ecemax, (12.5ds/m for tomato and 8.0ds/m for citrus, [5255]), the system costs increase and the crop yield decreases [56-59]. the reduction in the bcr may be more than 45% with ecw = 8.0ds/m for tomato-sesame and more than 30% with ecw = 4.0ds/m for citrus trees. the bcr reduces about 5% to 35% due to increase in the suction head from 6.0 (base run) to 30.0m. water source quality and type have a negligible effect on the selection of system configurations or laterals’ direction. 5) farm’s size and shape the effects of different farm areas and dimensions on the b/c of long-life citrus trees are shown in figure 7. it can be noted that the effects of farm area and dimension ratio on the bcr of point-source drip system are small. the resulting changes in the bcr due to the farm partition are not bigger than 4.0%. the best improvement in the bcr was obtained with l/b ratio within 1.18-1.27 (l/2×b/2 and l/3×b/2) and farm area within 8.82-13.23ha. further, farm partition has a small effect on the selection of system configurations and laterals’ direction. for the same farm dimension ratio, l/b, (l×b/2 and l/2×b/4) and different farm areas (26.46 and 6.615ha, respectively), b/c improves by less than 1.0%. therefore, the farm area has a negligible effect on the bcr of the point-source drip system. further, the base run farm area remained constant (52.92ha) and the l/b ratio changed. the used dimension ratios, l/b, are 1, 1.5, 2.0, 2.5, and 3.0. the effects of l/b ratio on the base run b/c of tomato-sesame and citrus are shown in figure 8. it can be noted that the effect of farm dimension on the bcr is negligible. the bcr changes by less than 2.0%. the best l/b ratio is less or equal to 1.5. also, the farm dimension ratio has a negligible effect on the selection of system configuration and laterals’ direction. engineering, technology & applied science research vol. 10, no. 5, 2020, 6335-6343 6340 www.etasr.com khalifa et al.: farm-based environmental and economic impacts of drip irrigation system fig. 7. effect of farm partitioning on the bcr of long-life citrus trees. fig. 8. effect of farm dimensions on the bcr. b. effect of different economic conditions on the bcr 1) real and nominal interest rates interest rates are often categorized as real or nominal. nominal rates are the current rates of interest charged by the lending institution that will provide credit [60-61]. the rate includes an inflationary component and a risk, management, and profit component. the real rate is inflation-free, therefore, it is less than the nominal by the long-term inflation rate. the real rate is used to determine the annualized cost of capital expenditures such as land value and permanent land improvements (land-leveling). nominal rate is used to determine the annualized cost of capital expenditures that depreciate or reach technical obsolescence with little or no salvage value. the effects of real and nominal rates on the b/c of tomato-sesame and citrus are shown in figure 9. fig. 9. effect of real and nominal interest rates on the bcr. it can be seen that the effects of real and nominal interest rates on the bcr of the drip irrigation system depend on their values. the effects of real and nominal interest rates on the selection of system configuration and laterals’ direction are negligible for the drip systems. the bcr increases as the real and nominal interest rates decrease. the nominal interest rate has a higher effect on the bcr than the real rate due to the high values of construction elements compared with the land price. 2) raw land price the effects of raw land price on the bcr of tomato-sesame crop rotation and long-life citrus trees plantation are shown in figure 10. it can be noted that the effect of raw land value on the b/c depends on the land price. the bcr increases as the raw land price decreases. there is no effect for raw land price on the selection of system configuration or lateral lines’ direction. the effect of raw land price on the bcr of linesource and point-source systems is approximately the same (about 2.6% for every 1000us$/ha increase). 3) energy and labor escalation rates the effects of energy and labor inflation factors on the bcr of tomato-sesame crop rotation and long-life citrus trees are shown in figure 11. it can be seen that the effect of energy and labor inflation rates on the bcr depends on their values. the bcr increases as the inflation rates decrease. there is no effect for the energy and labor inflation rates on the drip system configuration or laterals’ direction. there is no effect for labor inflation rate on the bcr of drip systems. the effect of energy inflation rate on the bcr of the line-source and point-source drip systems is small and approximately the same (1.0% for every 1.0% inflation rate). fig. 10. effect of raw land value on bcr. engineering, technology & applied science research vol. 10, no. 5, 2020, 6335-6343 6341 www.etasr.com khalifa et al.: farm-based environmental and economic impacts of drip irrigation system fig. 11. effect of energy and labor escalation rates on bcr. the conducted analyses through the present study for different environmental and economic parameters (tables iii and iv) are summarized in table v. environmental and economic analyses were conducted based on the bcr for tomato-sesame crop rotation and long-life citrus trees cultivation. iv. conclusion the outcome of this study is based on the environmental and economic parameters of cultivating farms using the tisd software to fulfill the needs of the irrigation agencies and engineers. the tisd model was used to select the drip system’s configuration type that could potentially meet the desired economic goal of bcr. the effect of the soil type on the bcr and the configuration selection and laterals’ direction are considerable for line-source and negligible for point-source. the soil type has a negligible effect on the selection of system configuration for all drip systems. the effect of land slopes on the bcr depends on the slope direction with laterals and pump position. for the same slopes, it is preferable to arrange the point-source’s laterals on the small slope and put the pump on the upper farm side. also, the land slope has a considerable effect on the configuration’s selection of drip systems, especially with high slopes. the effect of high wind speeds on the b/c is negligible for the drip systems. the effect of climate on the bcr and the selection of configuration and lateral’s direction is negligible for line-source and small for pointsource. the effect of irrigation water on the bcr and configuration’ selection of drip systems is negligible up to the lower limit of the crop salt tolerance. the effect of water source type on the bcr and selection of configuration and laterals’ direction is small for drip systems. so, it is preferable to use drip systems with groundwater sources. the effect of farm partition on the bcr and configuration selection of the drip systems is very small. the effects of real and nominal interest rates on the bcr and configuration’ selection depend on their values. the nominal rate has a higher effect than the real rate on the b/c due to the higher installation cost. also, the nominal rate has a higher effect on the bcr of drip systems due to their initial installation cost. the effect of raw land value on the bcr depends on the land price. the effect of land value on the b/c of drip is negligible on the selection of system configuration or laterals’ direction. the effect of energy and labor inflation rates on the bcr depends on their values. there is no effect for the energy and labor inflation rates on the selection of system configuration or laterals’ direction. there is no effect for the labor inflation rate on the bcr of drip systems. the effect of energy inflation rate on the bcr of the line-source and point-source drip systems is small and approximately the same (about 1.0% for every 1.0% inflation rate). table v. effect of different environmental and economic conditions on bcr no. parameters drip sys. type drip sys. effect configuration effect lateral direction effect 1 soil texture l-source high no p-source very small negligible 2 land topography l-source small small p-source high high high 3 climate zone l-source negligible negligible p-source small negligible small 4 wind speed l-source no no p-source no no 5 water quality l-source very small no p-source very small negligible negligible 6 water source type l-source small no no p-source small negligible negligible 7 farm area l-source very small negligible p-source small very small small 8 farm dimension l-source negligible negligible p-source very small negligible negligible 9 interest rates l-source small no p-source considerable negligible negligible 10 raw land cost l-source small no p-source considerable negligible negligible 11 energy escalation l-source small negligible p-source small negligible negligible 12 labor escalation l-source very small negligible p-source negligible negligible negligible negligible 0.0 < effect < 1.0 % considerable 5.0 < effect < 10.0 % very small 1.0 < effect < 2.0 % high 10.0 < effect < 20.0 % small 2.0 < effect < 5.0 % very high effect > 20.0 % acknowledgment the authors are thankful to the deanship of scientific research at the university of hail, saudi arabia for the financial support under the contract (rg-191313). 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[61] c. banton, “interest rate: what the lender gets paid for the use of assets,” investopedia. https://www.investopedia.com/terms/i/interest rate.asp (accessed oct. 03, 2020). authors profile walid m. a. khalifa is an assistant professor at hail university, saudi arabia, and fayoum university, egypt. he received his b.s. in civil engineering from cairo university, and his ph.d. in water resources and environmental hydrology from cairo university. his research interests include water quality and hydrodynamics modeling, pressurized irrigation modeling, and design of rc water structures. dr. hatem gasmi is an assistant professor at hail university, saudi arabia. he received his b.s. in civil engineering and his ph.d. in geotechnical and soil risks evaluation from the national engineering school of tunis. his research interests include ground improvement and soil reinforcement, evaluation of soil risks, and innovation system and strategies. dr. tayyab a. butt is an assistant professor at hail university, saudi arabia. he received his b.s. in civil engineering from university of the engineering & technology, lahore, pakistan and hid ph.d. in environmental engineering from kaist, south korea. his research interests include energy & environment, adsorption engineering, and wastewater treatment technologies. microsoft word etasr_v13_n4_pp11182-11190 engineering, technology & applied science research vol. 13, no. 4, 2023, 11182-11190 11182 www.etasr.com sekerci & alp: investigation of european union horizon 2020 information and communication … investigation of european union horizon 2020 information and communication technology projects with the social network analysis method deniz sekerci department of industrial engineering, yildiz technical university, türkiye deniz.bukcez@gmail.com selcuk alp department of industrial engineering, yildiz technical university, türkiye alp@yildiz.edu.tr (corresponding author) received: 17 april 2023 | revised: 22 may 2023 | accepted: 23 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5967 abstract this study aims to examine the partnerships of the projects accepted in the horizon 2020 grant support program, which supports innovative research and development (r&d) projects of the european union, using social network analysis according to criteria such as participant countries, the project subjects in which they participate, and the number of funds they receive. social network analysis can be used in many different areas, as well as in the analysis of collaborations and partnerships. turkey's partnership has not been examined in detail for such international multi-partner collaborations. while taking advantage of the opportunity to follow the trend of technology by conducting innovative r&d studies with leading organizations in many different strategic fields, the interest and participation rate of turkey is increasing day by day in such programs, offering opportunities to obtain grant incentives. examining the network of collaborations established so far in this field can provide various inferences and suggestions for strategic partnerships. keywords-social network analysis; international collaboration; horizon 2020 i. introduction all institutions that are aware of the impact of international cooperation in the field of science and technology give priority to strategic partnerships [1]. social network analysis (sna) is used in many fields. although there are studies that investigate the projects and partnerships accepted in the eu horizon 2020 program, which is the subject of this study, no studies on turkey's performance and cooperation have been found for this program. this study aimed to fill this gap in the literature and reveal what kind of cooperation should be prioritized for turkey to be more effective in such programs. to observe the areas where countries are active, 1276 ict projects are classified into 20 different topics. the success of the countries in coordinating calls was calculated using weighting analysis and examined whether the calculated country achievement scores related to the degree of centrality. finally, the types of institutions of central countries and turkey were examined, revealing the types of turkish institutions that should be more active in such programs. studies have been carried out in many different fields, such as education, health, software, international and interinstitutional relations, etc., using sna. authors in [2] aimed to understand how the accuracy of centralization behaves according to various amounts of error in the dataset, investigating a large number of sample networks by adding a controlled amount of error. the results showed that accuracy decreases as the amount of error increases. in [3], a study was conducted in the software industry using sna, focusing on topics such as monitoring architectural changes, examining the effects of elements, and developing automated tools for architectural analysis. in [4], sna was applied to obtain design principles to form a clinical team, based on the interactions that are important to increase information flow and achieve the intended results. in [5], sna was used to explore patterns of collaboration and seek advice between schools, showing that while school networks are interconnected, overall interschool collaboration and advice-seeking activities are at low levels. in [6], a study was conducted on clean development mechanism (cdm) projects, suggesting that the status of a country on the network is a sign of its strength in the entire network. the results showed that the participating organizations could decide which countries are more attractive to invest in the cdm market. in [8], successful projects and engineering, technology & applied science research vol. 13, no. 4, 2023, 11182-11190 11183 www.etasr.com sekerci & alp: investigation of european union horizon 2020 information and communication … their partnerships in eureka were investigated using sna, aiming to map successful projects of central and southeast european countries and identify the best-performing countries between 2002 and 2009, publishing a report on the results of participation in the 7th framework program (fp7). according to the findings, 86% of the collaborations in the 6th framework program (fp6) were not renewed in fp7, and universities and research organizations "provided an advantage because they were centrally located in the joint participation network of the framework programs" [9]. in [10], sna was used to examine the international collaborations of the countries participating in the horizon 2020 program, showing that countries with a high degree of centrality obtained large funding. this study also showed that high centrality (degree, closeness, and betweenness) is not an indicator of success rate. in [11], the capabilities of the italy/calabria region were mapped with sna, demonstrating that its capacity in issues such as climate action, food and agriculture, and information and communication technologies is strong. ii. social network analysis a social network is a social structure consisting of individuals or organizations connected by one or more specific types of dependency, such as friendship, kinship, mutual interest, financial exchange, etc. [12]. sna aims to explore social structures using networks and graph theory. connected structures are characterized by nodes, which are individual actors, people, or things within the network. in addition, the ties that bind them are characterized by edges or links (relationships or interactions). the ability of sna to be used in a wide variety of domains is due to the flexibility of the nodes and ties. although primarily involving relations between people, ties between groups or organizations and relations between nation-states or international alliances can also be examined with sna [7]. the purpose of sna is not only to map and measure the relationships between nodes, but also to understand the structure of a network, draw conclusions about the impact of the relationship on an actor, and understand the defining characteristics, structures, and consequences of the relationships between them [13]. examples of social structures commonly visualized with sna are social media networks, information circulation networks, friendship networks, business networks, working relationships, collaborations, kinship, and disease transmission. in these networks, nodes are usually visualized as points, and ties are visualized as lines [14]. a. social network analysis metrics using many different metrics in the sna, inferences can be made about the location and status of each individual in the network, the status of the most important actors, and the general characteristic structure of the network. in this context, the centrality criterion and its breakdown within itself are evaluated as node-based criteria in the graph structure. apart from this, criteria such as cluster coefficient, cliques, diameter, density, etc., provide information about the general characteristic features of the graph. the centrality metric seeks answers to the questions of which actor is the most important on the graph and is the most common and effective metric to determine its importance. the centrality metric is expressed in three dimensions: the ability of an actor to communicate with others, his ability to control others, and his closeness to others [15]. according to these approaches, the centrality metric is examined under different sub-metrics, each showing different information about the node. this section examines the degree centrality, the closeness centrality, the betweenness centrality, and the eigenvector centrality. the number of links a node has with other actors in the network means the number of lines related to what is called degree centrality [8]. actors with a high degree centrality are the most visible actors and have more direct contact with other actors on the network [16]. although degree centrality is expressed as the number of edges connected to the node in undirected networks, it is handled as internal and external degrees in directed networks. the number of incoming connections to the relevant node represents the internal degree, the number of outgoing connections represents the external degree, and the node degree is the sum of these two values. in social networks, this metric is based on the principle that the actor with the most connections in real life is the most important. in other words, if the node has a higher degree centrality, it has more importance in the network. in directional networks, internal degree centrality represents the popularity of an individual in the social network, and external degree centrality represents the individual's sociability [17]. closeness centrality refers to how close an actor is to the other actors in the network. the main idea is that an actor's ability to interact quickly with others depends on its central location [16]. this metric can be used to identify the actors in the best position that can affect the entire network most quickly. when calculating the closeness centrality of a node, the average of the shortest path lengths of that node to all other nodes in the network is calculated, and the inverse of the obtained value is taken. betweenness centrality indicates which nodes are more likely to be in communication paths between other nodes. in other words, betweenness centrality is not concerned with the proximity of a node to other nodes, but with its location on the shortest path between other nodes [17]. when calculating betweenness centrality, first it should be found how many shortest paths exist between a pair of nodes (x, y), then count how many of the shortest paths between these two nodes contain the v node, and a ratio is obtained by dividing these two numbers. after this process is calculated for all pairs of nodes, the sum of the calculated ratios is found as the betweenness centrality of node v. eigenvector centrality is related to a node's connections with other nodes of high importance. a node with many connections does not need to have high eigenvector centrality, and a node with high eigenvector centrality does not necessarily need to have many connections. this approach is related to the ability to make many friends in high places in real-life networks [17]. a node's eigenvector centrality is affected by the importance and weight of other nodes to which it is connected. eigenvector centrality depends on both the quality and the number of connections. if a node has few but high-quality connections, its eigenvector centrality may be greater than a node with many but average-quality connections [18]. to define the diameter of a graph, it is necessary to first define the shortest path, which is the minimum number of links required to connect two nodes in the network. the diameter of a graph is defined as the longest of the shortest paths between engineering, technology & applied science research vol. 13, no. 4, 2023, 11182-11190 11184 www.etasr.com sekerci & alp: investigation of european union horizon 2020 information and communication … nodes in the network and is one of the key sna metrics that gives information on the size of the network in general [17]. density is obtained by dividing the total number of connections an actor has by the total number of possible connections that he can have. a high result indicates that the network is dense. dense networks are likely to be found in small and stable communities with few outside contacts and a high degree of social interaction. on the contrary, loose social networks tend to thrive in larger, unstable communities that have many external contacts and exhibit a relative lack of social cohesion [19]. density values can take values between [0, 1]. density will approach 1 if there is a strong relationship between the nodes of the graph and 0 if there is a weak relationship. it is a useful metric used to make comparisons and inferences. the clustering coefficient is a measure of the probability that two partners of a node will be partners. the basis of this metric is the concept of transitivity. it is considered that there is a high probability of a relationship between the x and z nodes in a graph if there is a relationship between the x and y and a relationship between the y and z nodes. a complete graph is formed when all nodes are related to each other [18]. iii. horizon 2020 horizon 2020, is the european union's research and innovation grant support program that operated between 2014 and 2020. the main purpose of the program, with a total budget of 80 billion euros, was to strengthen europe in all areas by encouraging technology development and multiinternational cooperation. this program aimed to enable europe to produce world-class science, eliminate barriers to innovation, and facilitate the public and private sectors to work together to deliver innovation [22]. different types of legal entities participated in horizon 2020, such as universities, small and medium enterprises (smes), large companies, research institutions, and non-governmental organizations (ngos). the biannual work programs at horizon 2020 included funding opportunities and calls. the minimum number of participants and the requirements for the projects varied according to the type of project. the main condition sought in all applications to the framework programs, except for individual projects, is cooperation. in general, at least three independent organizations from at least three different eu member states or associated countries should take part as partners in horizon 2020 projects. turkey participated in this program since the eu 6th framework program. the eu 6th framework program took place between 2002 and 2006, was replaced by the eu 7th framework program covering the years 2007-2013, continued from 2014 to 2020 as the horizon 2020 program, and was followed by the horizon europe program that covers the years 2021-2027. turkey's representative tübi̇tak transferred 451 million euros to this program, as each country participates by giving a contribution. therefore, organizations in turkey were allowed to apply for this fund program. each country aims to receive at least the amount of contribution it gives as a result of the international cooperation it establishes [24]. today, technology development has proven to be very important in the analysis and processing of the volume of scientific information produced [25]. horizon 2020 aimed to drive europe's economic growth by combining research with innovation, focusing on three key pillars of scientific excellence, industrial leadership and competitiveness, and societal challenges. this study focused on the field of ict, located in the facilitator and industrial technologies section, under industrial leadership [23]. european commission appoints independent experts who evaluate project proposals and project operations and monitor program and policy processes [24]. projects with evaluation scores above a threshold are ranked. projects with higher scores are entitled to be funded if they do not exceed the budget allocated for the applied call. the community research and development information service (cordis) [27] is the main source of results for projects funded by the european commission's framework programs for research and innovation. cordis has a rich and structured public repository containing all project information from the european commission, such as project fact sheets, participants, reports, outputs, and links to open-access publications. cordis has published a dataset on the european union open data portal, including information on projects and participants funded by the eu under the horizon 2020 framework. iv. methods and application a. data and visualization this study used data from cordis. datasets are updated monthly on the cordis portal, and all projects accepted in the horizon 2020 program are publicly published. this study analyzed data from 1276 projects with a total of 11384 partnerships. the dataset for each participant is listed with its cordis registration number (rcn), project id, project abbreviation, the role of the organization in the project (participant or coordinator), the name of the organization, the type of organization, the grant amount given by the european commission (in eur), and the country in which the organization is located. figure 1 shows a network where the countries with the highest degree-centricity (with the most diverse partnerships in all ict projects) are positioned to be the most centrally located and have the largest symbols. fig. 1. network image of horizon 2020 ict projects created by 92 countries. this study selected a total of 31 countries, including eu countries, england, switzerland, norway, and turkey, which are the main participants of the horizon 2020 program, to make a more specific analysis. in this context, when the network analysis graph was drawn again, a clearer visual was obtained, engineering, technology & applied science research vol. 13, no. 4, 2023, 11182-11190 11185 www.etasr.com sekerci & alp: investigation of european union horizon 2020 information and communication … as shown in figure 2. the countries in the most central positions are italy, germany, england, spain, greece, and france. this image also highlights the strength of the bonds, showing the countries that have the strongest ties to the central actors, which are belgium, switzerland, the netherlands, and austria. fig. 2. network image created with 31 countries in horizon2020 ict projects. b. general features of the network table i shows the number of nodes, the number of links, the density degree, the average distance, and the diameter values of the undirected network consisting of 31 countries. table i. network features feature value nodes 31 ties 908 density 0.976 average distance 1.024 diameter 2 there are 31 actors and 908 ties in the network. the density of the mesh was found to be 0.976. since this value is very close to 1, it can be said that this network has a high density and the actors are connected by strong ties. diameter, another basic metric that gives information about the size of the mesh, took the value 2. so, the longest of the shortest paths in the node is at a distance of 2. furthermore, the average distance between two actors was 1.024. as a result, it can be thought that the network is not very large, but it can be said that the density of the network is very high and therefore the actors are positioned very close to each other. c. analysis of social network analysis the positions of the countries were examined by performing sna centrality metrics and clustering coefficient. centrality values were calculated to examine the positions of the actors in the network. table ii shows the values of the countries in degree, betweenness, closeness, and eigenvector centrality, and their rankings according to these values. in figure 3, the trend lines increase linearly according to degree centrality. since the ranking of degree centrality and closeness centrality are the same, the two lines appear as a single line of green color. around this linear line, the line highlighted in red indicates the betweenness centrality, and the line highlighted in dark blue indicates the eigenvector centrality ranking. table ii. ranking of countries by degree of centrality degrees betweeness closeness eigenvector it 72 ie 366.295 it 0.0091 it 0.181 de 70 it 284.502 de 0.0089 uk 0.181 uk 69 de 271.051 uk 0.0088 es 0.179 es 67 uk 223.356 es 0.0087 el 0.179 fr 66 fr 193.535 fr 0.0086 de 0.175 el 66 es 187.545 el 0.0086 fr 0.175 pt 62 at 175.547 pt 0.0083 pt 0.171 ie 60 el 160.905 ie 0.0082 be 0.167 be 56 pt 157.637 be 0.0079 no 0.163 ch 55 ch 94.77 ch 0.0079 pl 0.163 nl 55 nl 78.423 nl 0.0079 ch 0.162 no 53 be 77.43 no 0.0078 nl 0.159 at 51 no 67.887 at 0.0076 at 0.158 pl 51 lu 61.306 pl 0.0076 fi 0.157 fi 49 fi 36.588 lu 0.0075 ie 0.156 lu 49 pl 30.391 fi 0.0075 hu 0.155 bg 46 bg 28.532 bg 0.0074 ro 0.154 cz 42 cy 12.027 cz 0.0071 cz 0.147 se 41 ro 11.719 dk 0.0071 si 0.144 dk 41 se 11.126 se 0.0071 hr 0.142 si 40 sk 10.411 sk 0.0070 se 0.14 sk 40 cz 9.471 si 0.0070 sk 0.138 hr 39 si 4.273 hr 0.0070 dk 0.136 tr 35 hr 3.82 tr 0.0068 tr 0.122 lt 30 lt 0 lt 0.0066 lt 0.117 mt 23 mt 0 mt 0.0063 mt 0.092 fig. 3. representation of country rank change by centrality metrics. as can be seen in table iv and figure 3, when looking at the country rankings according to their degree centrality, italy developed the most cooperation by establishing connections with 72 out of 92 partners in ict projects, while germany, england, spain, and greece followed. on the other hand, turkey established partnerships with 35 different countries and ranked 29th. ireland, italy, germany, england, and france are the countries with the highest values of betweeness centrality. ireland ranked 8th in degree centrality and 1st in betweenness centrality. this shows that ireland is an effective actor with the ability to control the flow of information in the network. in addition, other countries that stand out in the chart and jumped into betweenness centrality are austria, sweden, and turkey. turkey has risen to the 20th place in betweenness centrality. this shows that turkey's ability to cooperate with a wide range of actors is less than its capacity to influence the flow of engineering, technology & applied science research vol. 13, no. 4, 2023, 11182-11190 11186 www.etasr.com sekerci & alp: investigation of european union horizon 2020 information and communication … information in the network by taking the shortest paths. as stated earlier, closeness centrality is related to the sum of the shortest path lengths of an actor to other actors in the network. turkey was ranked 29th. when the eigenvector centrality is examined, italy, england, spain, greece, and germany are seen as the actors with the higher values. this metric, since the importance of the actors with whom the actors are connected is included, shows that these countries have a high degree of relationship with the important actors. although norway and poland have lower rankings in other metrics, they are among the top 10 countries in the eigenvector centrality ranking. this shows that norway and poland are partnering with strong partners, even if they do not establish more partnership relations than the more centralized countries in the network. in addition to that, ireland and finland showed a dramatic decrease in this ranking, which was one of the most striking changes in the chart. turkey is seen to be in the 29th place in this ranking. to examine the positions of the actors in the network, the centrality values were calculated first. table iii shows the values of the countries in degree centrality and their ranking. table iii. ranking of countries by degree centrality country clustering coefficient npairs number of neighborhoods de 40.28 435 30 es 42.06 435 30 it 42.86 435 30 fr 43.00 435 30 uk 43.24 435 30 el 44.89 435 30 nl 46.19 435 30 be 46.29 435 30 ch 47.42 435 30 pl 47.89 435 30 ie 48.26 435 30 fi 48.27 435 30 pt 48.41 435 30 at 49.19 435 30 dk 49.66 435 30 ee 50.03 435 30 cy 50.08 435 30 lu 50.15 435 30 bg 50.36 435 30 ro 50.70 435 30 hu 50.71 435 30 se 51.96 406 29 no 53.29 406 29 si 53.33 406 29 cz 53.47 406 29 sk 54.39 406 29 lv 54.41 406 29 lt 57.85 378 28 hr 57.87 378 28 tr 61.70 351 27 mt 85.77 210 21 the second column, "npairs", represents the number of all possible pairs of actors in the neighborhood formed by the neighbors with whom the actor is in contact or, in other words, all possible connections. neighbor numbers are given in the fourth column. when the clustering coefficient of each actor is ranked from the smallest to the largest, it is seen that germany's neighbors are connected with the least intensity, followed by spain, italy, france, england, and greece. in addition, malta, turkey, croatia, and lithuania were last on the list, and their neighbors also bonded highly. the fact that the actors with low clustering density are those with a high degree of centrality indicates that these actors are the most active in the network and their clustering densities are low because their neighbors are not as active as themselves. on average, actors with higher rankings have been reported to have lower clustering coefficients on average [26]. d. partnerships of turkey table iv shows the countries with which turkey cooperates the most. turkey has realized the higher cooperation with countries with the highest degree centrality. this may be a natural consequence of those countries' maximum number of partnerships in this program. table iv. turkey’s top ten partnerships country number of partners country number of partners es 99 el 38 de 67 pt 27 it 54 nl 24 fr 47 be 23 uk 43 at 21 increasing the number of collaborations with ireland, which has the highest degree of betweenness centrality and, as a result, the ability to affect the information flow at the highest level, can enable turkey to achieve greater success in this field. in addition, increasing cooperation with countries with high eigenvector degrees can enable turkey to meet successful partners in important positions. norway and poland, which are not included in table iv but have achieved a slight jump in eigenvector centrality, are actors that can be considered in this regard. furthermore, as a result of the examination made using clique analysis, switzerland was found to be the ninth country participating in the clustering and showed closeness to the most central partners. considering the current situation of turkey, increasing its ties with switzerland may allow it to be more included and positively affect its performance. e. partnerships of turkey the acceptance rates of all ict calls were calculated by dividing the number of projects accepted within its scope by the total number of applications, and then inversely, the importance of that call was obtained. the coordinator partner is responsible for establishing and coordinating the project consortium. additionally, the coordinator has the largest role in writing a good project proposal. for this reason, during the calculation of the success rates of countries by weight analysis, the number of times the countries participated as coordinators was considered. ict calls are classified under 20 different headings according to subject areas and the calculated country success scores were distributed according to the classification made under these headings. in the weighting analysis management, engineering, technology & applied science research vol. 13, no. 4, 2023, 11182-11190 11187 www.etasr.com sekerci & alp: investigation of european union horizon 2020 information and communication … the acceptance rate of ict-x call (car) was calculated first by: ��� = ���� ���� (1) where nnax is the number of applications accepted in the opened ict-x call, tnax is the total number of applications in the opened ict-x call. the k-th country's coordinator achievement score is given by: � � = ∑ ��� � ��� �� ��� � = 1,2, … ,31 (2) where ncckx is the number of coordinator ships from the k-th country on the x-th call. as can be seen in table v, the top 5 most successful countries according to the total success score are spain, england, germany, italy, and france, while turkey ranks 24th in this list. this situation shows that turkey does not take an active role as a coordinator in the program. although germany and spain seem to be the partners with the highest scores on an equal number of topics, spain's high success, especially in the "horizontal ict innovation action", made it the first in the ranking of the most successful countries in total scoring. when examining the countries with which turkey has cooperated the most, it is seen that there is a strong amount of cooperation with the first six most successful countries according to the weight analysis. however, finland, the seventh most successful country, is not among the top ten countries with which turkey has developed a great deal of cooperation. for this reason, further cooperation between finland and turkey may be an important step in obtaining successful project applications. table v. achievement scores according to the weighting analysis of countries 5 g a n e w g e n e r a ti o n o f c o m p o n e n ts a n d s y st e m s a d v a n c e d c o m p u ti n g a n d c lo u d c o m p u ti n g a i a n d d ig it is in g e u r o p e a n in d u st r y a n d e c o n o m y c o n te n t te c h n o lo g ie s a n d in fo r m a ti o n m a n a g e m e n t c r o ss -c u tt in g a c ti v it ie s c y b e r se c u r it y e u r o p e a n d a ta i n fr a st r u c tu r e : h p c , b ig d a ta a n d c lo u d te c h n o lo g ie s h o r iz o n ta l ic t i n n o v a ti o n a c ti o n ic t c r o ss -c u tt in g a c ti v it ie s ic t k e y e n a b li n g t e c h n o lo g ie s in n o v a ti o n a n d e n tr e p r e n e u r sh ip s u p p o r t in te r n a ti o n a l c o o p e r a ti o n a c ti o n s m ic r o a n d n a n o e le c tr o n ic te c h n o lo g ie s, p h o to n ic s n e x t g e n e r a ti o n i n te r n e t (n g i) p la tf o r m s a n d p il o ts r e sp o n si b il it y a n d c r e a ti v it y r o b o ti c s a n d a u to n o m o u s sy st e m s s u p p o r t a c ti o n s s u p p o r t to h u b s t o ta l su c c e ss es 33 14 36 87 335 0 23 65 1193 36 18 15 6 43 264 28 2 87 0 10 2295 uk 0 21 18 20 261 8 0 9 805 6 11 0 9 12 190 0 5 80 14 0 1469 de 40 124 37 n 202 8 21 51 305 44 16 10 9 63 170 12 0 82 0 8 1202 it 22 42 27 63 136 20 31 37 404 42 22 7 30 18 184 12 0 148 0 5 1250 fr 8 100 31 108 49 8 12 5 540 6 25 12 3 39 79 6 7 65 0 9 1112 el 23 23 22 79 189 13 13 93 128 21 14 7 11 22 188 0 0 23 0 2 871 fi 8 4 0 29 45 4 0 0 306 15 12 3 0 7 35 5 0 19 0 6 498 at 0 36 0 31 60 13 3 25 169 12 20 0 3 11 71 0 7 31 0 0 492 nl 3 10 0 40 102 0 6 9 141 6 24 0 11 30 41 0 0 40 0 10 473 be 3 32 22 34 74 8 4 0 23 12 14 0 0 32 88 0 7 20 0 2 375 ie 0 21 5 9 73 0 0 19 99 0 4 0 21 0 86 7 2 0 9 0 355 pt 3 4 0 14 8 13 15 13 152 0 0 0 9 0 74 8 0 0 0 2 315 se 3 10 0 35 26 0 0 0 148 0 0 0 9 3 25 0 0 48 0 0 307 dk 0 10 0 5 8 0 8 0 163 0 0 0 0 6 25 0 5 27 9 2 268 no 5 10 9 13 26 0 0 13 130 24 7 0 9 0 11 0 5 0 0 3 265 pl 0 0 5 0 20 8 0 0 178 0 0 0 0 0 8 0 0 6 0 3 228 hu 0 0 0 0 0 0 8 0 153 0 0 7 0 0 15 0 0 0 0 0 183 ee 3 10 0 0 0 0 0 0 143 0 0 7 0 0 3 0 0 0 0 0 166 ch 0 15 0 8 14 12 0 35 5 0 0 0 7 0 38 0 0 9 0 3 146 si 0 0 0 9 0 0 0 9 99 0 0 0 0 0 12 0 0 11 0 0 140 cz 0 0 0 0 8 0 0 5 41 0 0 0 0 0 5 0 0 0 0 0 59 lu 0 0 0 0 0 0 0 0 41 0 0 0 0 2 8 0 0 0 0 0 51 tr 0 0 0 0 0 0 0 0 41 0 0 0 0 0 0 0 0 0 0 0 41 cy 0 0 0 0 0 0 0 0 23 0 4 0 0 0 0 0 0 9 0 0 36 lt 0 0 0 7 0 0 0 0 18 0 0 7 0 0 0 0 0 0 0 2 34 sk 0 0 0 0 0 0 0 0 23 0 0 0 0 0 8 0 0 0 0 0 31 rs 0 0 0 0 0 0 0 0 0 15 0 0 0 0 0 0 0 0 0 0 15 ro 0 0 0 0 5 0 0 9 0 0 0 0 0 0 0 0 0 0 0 0 14 bg 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0 0 0 5 f. comparison of country achievement scores with sna metrics and country success percentage the relationship between country achievement scores, degree centrality, and country success percentages was examined. the success percentage of the countries, which is the ratio obtained from the total number of project applications made in the horizon 2020 ict field and the number of accepted project applications, was taken from the eu horizon 2020 indicator panel [26]. table vi shows the degree centrality, success percentages, and success scores of the countries. engineering, technology & applied science research vol. 13, no. 4, 2023, 11182-11190 11188 www.etasr.com sekerci & alp: investigation of european union horizon 2020 information and communication … table vi. degree centralities, success rates, and success scores per country country degree centrality success rates success scores ch 55 17.90% 144 cz 42 17.42% 59 be 56 16.17% 374 at 51 15.65% 492 fr 66 15.38% 1114 no 53 15.25% 264 fi 49 15.21% 51 nl 55 15.21% 474 dk 41 14.81% 308 de 70 14.68% 1280 ie 60 14.65% 354 lt 30 14.07% 35 lu 49 13.61% 498 el 66 13.43% 873 se 41 13.16% 268 uk 69 12.86% 1469 pl 51 12.73% 226 si 40 12.32% 31 cy 44 12.06% 36 es 67 12.02% 2293 pt 62 11.92% 316 sk 40 11.68% 140 it 72 11.51% 1251 hu 46 10.93% 183 ee 45 10.66% 167 ro 45 10.40% 14 tr 35 7.85% 41 bg 46 6.61% 5 ch 55 17.90% 144 cz 42 17.42% 59 be 56 16.17% 374 correlation analysis provides information on the direction and power of the relationship between two variables. a correlation analysis was conducted to examine the relationship between degree centrality, success percentages, and achievement scores of the countries. to understand whether there is a relationship between the variables, the following hypotheses were established: h0: there is no relationship between the two variables h1: there is a relationship between two variables to determine the result of the hypothesis test, the correlation table and the p-value were examined, and figure 4 shows the results. fig. 4. country’s degree centrality, success rates, and success scores in the correlation analysis, if the p-value is less than 0.05, the h0 hypothesis is rejected and the h1 hypothesis is accepted. as can be seen in the figure above, there is a relationship between degree centrality and country success scores. however, the country's success percentage is not related to its achievement score and degree centrality. italy, germany, england, spain, and france were the top five countries in terms of degree centrality and country success scores, while switzerland, czech republic, belgium, austria, and france are the most successful countries in country success percentages. the reason the country's success percentages have such a different ranking is that these countries have a good acceptance rate even if they are not as active as the most centralized countries in the ict program. france, which is among the top five countries in both comparisons, has achieved both high cooperation and a good coordinator experience, although it has made far fewer applications than other central countries. g. comparison of the types of institutions receiving the funds by country table viii compares the types of the most successful organizations in germany, england, france, spain, and italy, which are the most central countries, and turkey. table vii. comparison of the most successful organization percentage country university private sector research institute public institution turkey 10% 80% 10% 0% italy 40% 30% 40% 0% germany 30% 50% 20% 0% england 50% 30% 10% 10% spain 40% 20% 40% 0% france 20% 50% 30% 0% as can be seen in table vii, research institutes and universities, as well as the private sector, are actively involved among the institutions that receive the highest funding in the most central countries. this situation can offer important clues about the issues turkey needs to improve itself. although only 10% universities and 10% research institutions are on the list of the most successful in turkey, most of them are private sector institutions. in the most centralized countries, the sum of universities and research institutions makes up half and even more than half of the list. universities and research institutes, which mostly carry out studies at the stage of basic research and the creation of new knowledge in a technology field, take an important role in the first steps of new knowledge and discovery and become an actor that directs the course of technology. v. conclusion and recommendations sna can be used in many different sectors and fields and is considered one of the powerful methods in examining collaboration and partnership relations. conducting a network analysis provides a holistic view of the position of the partners in the network and information about the relations between them. this study used sna to examine the projects that were accepted in the field of ict in the horizon 2020 program. the results showed that italy, germany, england, spain, and france were the countries with the highest degree and closeness centralities. ireland ranked first in betweenness centrality. the fact that ireland achieved a high value in betweenness centrality shows that the country is an important factor that can control the flow of information. however, ireland is not on turkey's top partnership country list. therefore, increasing engineering, technology & applied science research vol. 13, no. 4, 2023, 11182-11190 11189 www.etasr.com sekerci & alp: investigation of european union horizon 2020 information and communication … cooperation with ireland may improve turkey's position. in addition, new collaborations can be developed with other potential partners in important places by establishing cooperation with norway and poland, which have rising rankings in eigenvector centrality. in addition, clustering coefficient and clique analysis were performed, and the percentages of actors' neighbors being neighbors to each other and which actors were closer to each other were examined. as a result, it was seen that the clustering coefficients of the countries could be low if they have high degree centrality. this situation is related to the fact that the neighbors of the central countries are not as active as themselves and do not establish much connection. the clique analysis showed that the central countries, with spain and germany in the first place, achieved the first merger by showing closeness. switzerland, which is not on turkey's top ten partnership countries list, was seen to establish close relations with the central countries by being included in the grouping in the 9th place. turkey was found in the 25th place and was characterized as an isolated actor. turkey can consider switzerland as another country that should increase its cooperation. another country that stands out is sweden. although sweden has a low rank in degree centrality, its rise of ten places in the clique analysis shows that it also has strong relations with central european countries. these results show, with exceptions, that geographical closeness also affects collaboration. in horizon 2020 projects, it is an undeniable fact that the coordinator actor plays an essential role in the success of the project. the coordinator success of the countries was calculated under 20 different headings by weighting analysis. spain, england, germany, italy, and france are the most successful countries, respectively. whereas turkey is seen to have developed high partnerships with the first six countries in the coordination success ranking, more cooperation with finland, the seventh most successful country, can lead to successful projects. degree centrality, country success scores, and country success percentages were compared, showing that there is only a relationship between degree centrality and country achievement scores. france is the only country in first place in all three rankings, has established partnerships with a high number of different countries, has developed coordinator skills, and is almost as successful as the other central countries, even though it makes much fewer applications. finally, the most centralized countries and turkey's mostfunded institution types were compared, showing that universities and research institutions in other countries have much more active participation than universities and research institutions in turkey in horizon 2020 ict projects and have an important role in the success of the country. participants in turkey are mostly private sector organizations. more active participation of universities and research institutions, which carry out basic research and play an important role in introducing new knowledge and technology, will increase turkey's success in the program and will be an 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[27] "european commission webgate," r&i organisation profiles qlik sense. https://webgate.ec.europa.eu/dashboard/sense/app/a22d669565d1-4f7a-a06f-b5bf3f3cc59c/overview. microsoft word etasr_v10_n6_pp6510-6514 engineering, technology & applied science research vol. 10, no. 6, 2020, 6510-6514 6510 www.etasr.com blasi & alsuwaiket: analysis of students' misconducts in higher education institutions using decision … analysis of students' misconducts in higher education institutions using decision tree and anns anas h. blasi department of computer information systems mutah university karak, jordan ablasi1@mutah.edu.jo mohammed a. alsuwaiket department of computer science and engineering technology hafar batin university hafar batin, saudi arabia malsuwaiket@uhb.edu.sa abstract—a major problem that the higher education institutions (heis) face is the misconduct of students’ behavior. the objective of this study is to decrease these misconducts by identifying the factors which cause them on college campuses. crisp-dm methodology has been applied to manage the process of data mining and two data mining techniques: j48 decision tree (dt) and artificial neural networks (anns) have been used to build classification models and to generate rules to classify and predict students' behavior and the location of misconduct in college campuses. they take into consideration seven factors: student major, student level, gender, gpa cumulative, local address, ethnicity, and time of misconduct by month. both techniques were evaluated and compared. the accuracy results were high for both classification models, whereas the j48 decision tree gave higher accuracy. keywords-j48 decision tree; artificial neural networks; machine learning; student misconduct; student behavior i. introduction higher education institutions (heis) constitute an environment in which students, families, educators and community members have opportunities to learn, teach, and grow. educators do their best to provide students with a stable and positive learning environment. often, heis face problems which impede the educational process, problems related with students' prohibited behavior which results in dangerous misconducts in the short and the long term. in fact, the challenges associated with students with severe behavior problems are increasing [1]. in addition, these behaviors are reflecting on other students, either in or out of the class. effective heis are safe institutions. therefore, heis appreciate the need to prevent misconducts that threaten safety, and they need highly effective ways to respond effectively to such misconducts. to achieve heis' mission to educate students and maintain campus safety, they must be able to recognize and prevent these misconducts before they occur. recently, many heis' departments and local school districts have taken steps to decrease these behaviors and support all the developed ways and enhance the educational process to keep the educational environment secure and safe for all students. the subject of student behavior misconducts is one of the most significant and major subjects in heis. however, many researches concentrate on student’s behaviors and their inter-relations to decrease the misconducts that occur in college campuses. unfortunately, the literature is very limited in propositions of models to predict these behaviors to reduce the number of college student’s misconducts. there many studies describing the danger of problematic behaviors and different solutions have been suggested to decrease the number of misconducts that affect negatively the environment of heis' and its safety, but very limited studies have used data mining (dm) methodologies and techniques in this area. applying dm in higher education is a recent research field which is also known as educational data mining (edm). edm is concerned with developing different ways for exploring the unique types of data that come from the education environment. the process of applying dm to educational systems can be interpreted from different points of view [2]. from an educational viewpoint, it can be shown as an iterative cycle of hypothesis formation. in this process, the objective is not only turning data into useful information, but also to filter the mined knowledge for decision-making about how to enhance the environment of education to improve students’ behavior and learning. from a dm viewpoint, it can be very similar to the general knowledge discovery and data mining (kdd) process. there is increasing interest in using dm in higher education. authors in [3, 4] focused on attendance rates and they found that a lower attendance rate negatively affects a student’s gpa. the study in [5] focused especially on students’ alcohol consumption. it was found that there is a negative affect increment on student gpas and alcohol usage. authors in [6] used the dm prediction technique to find the effective factors that determine a student’s test grade, and then these factors were adjusted to improve the students’ performance. authors in [7-9] applied different dm techniques to improve the education process in the higher education system by improving different assessments methods. authors in [10] used dm techniques to develop new curricula and help engineering students choose an appropriate major. regarding alcohol issues, the research on the spread of alcohol-related problems at traditional four-year institutions is vast, even though little is known about alcohol consumption and related issues among college students.[11-13]. data mining and criminology analysis can be divided into two main areas: misconduct control which tends to use corresponding author: anas h. blasi engineering, technology & applied science research vol. 10, no. 6, 2020, 6510-6514 6511 www.etasr.com blasi & alsuwaiket: analysis of students' misconducts in higher education institutions using decision … knowledge from the analyzed data to control and prevent the occurrence of misconduct, and criminal suppression which endeavors to catch a perpetrator in the act by using the person’s history recorded in dm [14]. studies of dm in terms of misconducts and intelligence analysis for national security are in their ongoing growth stage. the following techniques have been discussed in misconduct dm: entity extraction, clustering, and classification. the current study focuses on nine problematic behaviors or behavior issues: alcohol use, drug issues, theft of property or services, endangering, threatening or causing physical harm, stalking or communicating in a manner likely to cause injury, distress, or emotional or physical discomfort and which serves no legitimate purpose, harassment, including sexual harassment, sexual assault, rape, hazing, unauthorized entry into or use of university premises, and violations of published university regulations or policies. ii. research methodolgy crisp-dm (cross-industry standard process for data mining) is a dm model that deals with dm from different perspectives. the purpose of this model is to increase knowledge of the data [15]. crisp-dm life cycle consists of six stages, which are described below. a. business understating phase the first phase determines the objectives and requirements of the study and the used techniques. decision tree (dt) and artificial neural networks (anns) will be used in this study. different tools (weka tool, orange canvas, minitab, and matlab) will be used for the implementation. b. data understanding phase the data of this study were collected from the office of student conduct at binghamton university. the dataset consists of the data of 1374 students (1017 male, 357 female). the considered attributes of the data set are shown in table i. all students in this sample have been charged with one of the referred attributes/behaviors, whereas the whole student population of the university is 13000 students. c. data preparation phase the data preparation phase consists of five tasks: data selection, data cleaning, data construction, data integration, and data formatting [16]. data were cleaned and prepared to be suitable for the modeling and implementation phase. d. modeling phase this section describes in detail the classification techniques which will be used in this study. 1) j48 decision tree the dt technique is one of the most widely used methods in dm [17, 18]. dt is used to split data into a set of branches. the construction of the tree is conducted from top to bottom in a recursive divide-and-conquer manner. the main objective of dt learning is to select the attribute that is most useful for classifying samples [19]. a suitable measure of the significance of an attribute is the information gain that it measures. this measure is used to pick an attribute from the candidate attributes at each step while building the dt [20]. dts are used to represent decision making (visually and explicitly). the result of the classification can be an input for the decision making step and the tree can be a descriptive means for calculating conditional probabilities [1]. table i. attribute descriptions attribute description possible values attribute type academic_major student academic major art, undeclared, languages, science, management nominal std_level student level freshman, junior, sophomore, senior nominal student_gender student gender male, female nominal gpa_cume student accumulative gpa between 2 and 4 numeric local_city student's address on-campus, off-campus nominal misconduct_location the misconduct location on-campus, off-campus nominal misconduct_date misconduct date between january and december date charge charge "student behavior" alcohol, drug, theft, published university policy, endangering, harassment, disobedience, unauthorized entry nominal ethnicity student's ethnicity american, black_non_hispani, white_non_hispanic, hispanic, asian, white-not specific nominal j48 is a version of an earlier algorithm developed by j. ross quinlan. the very popular c4.5 offers powerful ways to express structures in data. c4.5 implementation in weka toolkit is known as the j48. j48 employs two pruning methods [21]: • sub-tree replacement: nodes in a dt are replaced with a leaf reducing the number of tests along a certain path. • sub-tree raising: a node moved upwards towards the root of the tree, replacing other nodes along the way. sub-tree raising often has a negligible effect on decision tree models. j48 dt technique will be applied to the data when the output is the "charge (behavior)", while the second application will take place when the output is the "misconduct location". each time the data will be trained and validated. figure 1 shows the results of the training set using j48 dt when the output is "charge", which has an accuracy of is 97.8894% and a mean square error of 0.0688. figure 2 shows the results of a 50 fold cross validation run. the correctly classified instances (accuracy) in this case are 98.1077% and the root mean squared error is 0.0697. if we compare the results of the 50 fold cross validation with the training set, we conclude that the accuracies of the two tests are close. the test was repeated many times in different folds and the results were close in every run. engineering, technology & applied science research vol. 10, no. 6, 2020, 6510-6514 6512 www.etasr.com blasi & alsuwaiket: analysis of students' misconducts in higher education institutions using decision … fig. 1. training test evaluation when the output is "charge". fig. 2. cross-validation test evaluation when the output is "charge". table 2 demonstrates the generated rules of the training set when the output is "charge". table ii. generated rules of the training set when the output is "charge" no generated rules 1 if gpa_cume <= 2.84 and gpa_cume <= 2.79: alcohol (498.0) 2 if gpa_cume <= 2.84 and gpa_cume > 2.79: disobedience (40.0/1.0) 3 if gpa_cume > 2.84 and gpa_cume <= 3.45 and gpa_cume <= 3.3: drugs (311.0/7.0) 4 if gpa_cume > 2.84 and gpa_cume <= 3.45 and gpa_cume > 3.3 and gpa_cume <= 3.42: endangering (79.0) 5 if gpa_cume > 2.84 and gpa_cume > 3.42: harassment (22.0/1.0) 6 if gpa_cume > 3.45and gpa_cume <= 3.6: publish_university_policy (118.0/19.0) 7 if gpa_cume > 3.45 and gpa_cume > 3.6 and gpa_cume <= 3.93: theft (266.0) 8 if gpa_cume > 3.45 and gpa_cume > 3.6 and gpa_cume > 3.93: unauthorized_entry (40.0/1.0) the results of applying j48 decision tree on all the inputs individually with the output "charge" show that the student gpa has the better rank, then misconduct date, student level, gender, ethnicity, academic major, and finally student local address. the input with higher accuracy can help to predict the charge better than the lower accuracy. figure 3 shows the results of the training test using j48 dt when the output is "misconduct location". the correctly classified instances (accuracy) are 99.7817% and the root mean squared error is 0.0465. figure 4 shows the results of a 50-fold cross validation run. the accuracy in this case is 99.7817% and the root mean squared error is 0.0467. if we compare the results of the 50fold cross-validation and the training set, we can see that the accuracies of the two tests are close to each other. the test was repeated many times in different folds and the results were always very close. table iii shows a sample of the generated rules (37 rules totally) of the training set when the output is "misconduct location". fig. 3. training test evaluation when the output is "misconduct location". fig. 4. cross-validation test evaluation when the output is "misconduct location". table iii. generated rules of the training set when the output is "misconduct location" no generated rules 1 if local_city = on_campus and gender = male and misconduct_date = january: on_campus (15.0) 2 if local_city = on_campus and gender = male and misconduct_date = february: on_campus (32.0) 3 if local_city = on_campus and gender = male and misconduct_date = march: on_campus (209.0) 4 if local_city = on_campus and gender = male and misconduct_date = april and academic_major = art: on_campus (21.0)academic_major = management: off_campus (5.0) 5 if local_city = on_campus and gender = male and misconduct_date = april and academic_major = undeclared: on_campus (18.0) 2) artificial neural network an ann will be used to classify inputs into a set of target categories. the neural network pattern recognition tool by matlab will assist data selection, network creating and training, and performance evaluation using mean square error and confusion matrices. a two-layer feed-forward network, with a sigmoid hidden layer and output neurons can classify vectors arbitrarily well, given enough neurons in its hidden layer. the network will be trained with scaled conjugate backpropagation gradient (trainscg). the ann classifier will be applied to the data twice, at first when the output is the "charge (behavior)" and the second time when the output is the "misconduct location". each time the data will be trained and validated. the data in the ann have been divided into three groups: the first group is the training set which is presented to the network during training, and the network is adjusted according to its error, the second group is the validation which is used to measure network generalization, and to halt training when the generalization stops improving, and the third is the testing which has no effect on training and provides an independent measure of network performance during and after training. in this study, the training sample consisted of 962 samples (70%), the validation sample of 206 samples (15%), engineering, technology & applied science research vol. 10, no. 6, 2020, 6510-6514 6513 www.etasr.com blasi & alsuwaiket: analysis of students' misconducts in higher education institutions using decision … and the testing sample consisted of 206 (15%). the number of the hidden neurons is 50. figure 5 shows the ann diagram when the output (target) is the "charge" (the number of charges is 8). the inputs are 7 (student major, student level, student ethnicity, student local address, student’s gpa, and misconduct time). fig. 5. ann diagram when the output (target) is "charge". figure 6 shows the training, validation, and testing results. however, these results are represented by the mse (mean squared error), which is the average squared difference between outputs and targets. for mse, lower values are better, since zero means no error) and %e (percent error: indicates the fraction of samples which are misclassified). a value of %e=0 means no misclassifications whereas 100 indicates maximum misclassifications. fig. 6. training, validation, and testing results when the target is "charge". figure 7 shows the neural network diagram when the output (target) is the "misconduct location. the inputs are the same as before. figure 8 shows the results of the training, validation, and testing. these results are again represented by mse. fig. 7. ann diagram when the output (target) is "misconduct location". fig. 8. training, validation, and testing results when the target is "misconduct location". iii. results and discussion from the summarized results in table iv, it can be concluded that the dt can be considered a better classifier than the ann in terms of accuracy and rmse when the target is "charge". however, when the target is "misconduct location", both classifiers have the same accuracy and little difference in rmse. table iv. dm results dm technique target "charge" "misconduct location" dt j48 accuracy rmse accuracy rmse 98.1 0.0697 99.8 0.0467 ann accuracy rmse accuracy rmse 91 0.115 99.8 0.014 according to the results of this study, the predictor that resulted from the j48 decision tree, can be used to predict and thus decrease the students’ behavior misconducts by considering the generated rules shown in tables ii and iii. also, and by knowing the factors that affect students’ behavior that cause misconducts, we can decrease the future number of misconducts in college campuses. for instance, the misconduct time is highly correlated (high accuracy) with both outputs (charge, misconduct location). this factor can be used to predict the charge and the misconduct location, so from this point of view, some plans can be suggested in accordance to the predicted charge and location in order to decrease the students’ misconducts in college campuses. iv. conclusion and future work two different dm techniques, anns and j48 dt have been applied in data referring to the misconducts of students in heis. crisp dm methodology has been applied in this study to mine student's data and identify the factors which cause misconducts in college campus. the phases of crisp dm methodology have been used to manage all the processes in this study. the implementation part of the study has been presented and discussed. the weka tool and matlab have been used to build the classification models and the results were compared. as a result, the j48 dt can be considered a more accurate classifier and predictor. regarding future work, the use of different methods such as fuzzy logic [22], optimization algorithms [23], and other dm techniques such as k-nn and decision tree [24] will be considered. references [1] v. berikov and a. litvinenko, "methods for statistical data analysis with decision trees," novosibirsk, sobolev institute of mathematics, 2003. 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[15] p. chapman et al., crisp-dm 1.0: step-by-step data mining guide. spss, 2000. [16] j. han, m. kamber, and j. pei, data mining: concepts and techniques, 3rd ed. haryana, india; burlington, ma, usa: morgan kaufmann, 2011. [17] m. kantardzic, data mining: concepts, models, methods, and algorithms, 2nd ed. hoboken, nj, usa: wiley-ieee press, 2011. [18] t. mitchell, "decision tree learning," in machine learning, the mcgraw-hill companies, inc., 1997, pp. 52–78. [19] a. el-halees, "mining students data to analyze learning behavior: a case study," in the 2008 international arab conference of information technology (acit2008), sfax, tunisia, dec. 2008. [20] c. h. yu, s. a. digangi, a. jannasch-pennell, w. lo, and c. kaprolet, "a data-mining approach to differentiate predictors of retention," presented at the educause southwest conference, austin, tx, usa, feb. 2007. [21] i. witten, e. frank, m. hall, and c. pal., data mining: practical machine learning tools and techniques, 4th ed. morgan kaufmann, 2016. [22] a. blasi, "scheduling food industry system using fuzzy logic," journal of theoretical and applied information technology, vol. 96, no. 19, pp. 6463–6473, oct. 2018. [23] a. blasi, "performance increment of high school students using ann model and sa algorithm," journal of theoretical and applied information technology, vol. 95, no. 11, pp. 2417–2425, jun. 2020. [24] m. a. a. lababede, a. h. blasi, and m. a. alsuwaiket, "mosques smart domes system using machine learning algorithms," international journal of advanced computer science and applications (ijacsa), vol. 11, no. 3, 40/30 2020, https://doi.org/10.14569/ijacsa.2020.0110347. engineering, technology & applied science research vol. 7, no. 6, 2017, 2266-2267 2266 www.etasr.com bangwar et al.: replacement of coarse aggregate with locally available brick aggregate replacement of coarse aggregate with locally available brick aggregate daddan khan bangwar department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, sindh, pakistan daddan@quest.edu.pk abdullah saand quaid-e-awam university of engineering, science & technology nawabshah, sindh, pakistan abdullah@quest.edu.pk manthar ali keerio quaid-e-awam university of engineering, science & technology nawabshah, sindh, pakistan mantharali99@quest.edu.pk mukhtiar ali soomro department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan eng.soomro@gmail.com abdul nasir laghari department of energy and environment engineering, quaid-e-awam university of engineering, science and technology nawabshah, pakistan mashaalnasirlaghari@gmail.com abstract-due to the abundant usage of concrete as a construction material, there is a fast dwindling source of aggregates. there are regions where there is scarcity of coarse aggregate, so to resolve this problem, bricks aggregates (bas) can be used as coarse aggregate. a concrete mix ratio of 1:2:4 having characteristics strength of 3000 psi has been used in this experimental work. compressive and tensile strength of concrete mix where 50% coarse aggregate is replaced with brick aggregate and concrete mix where 100% coarse aggregate is replaced with brick aggregate and addition of silica fume as a supplementary cementing material have been evaluated at 7, 14 and 21 days of age. the experimental test results revealed the compressive and tensile strength of concrete where coarse aggregate is replaced at 50% is almost the same as that normal concrete at the 7, 14, 21 and 28 days. keywords-concrete; brick; aggregate; coarse; compressive; strength; tensile; silica fume i. introduction the rigorous use of aggregates in constructions is a very vital environmental apprehension. in a county like pakistan, the ease of use of aggregates becomes a severe problem. in order to decrease the exploit of natural aggregates from natural resources and for energy preservation, the use of recycled aggregates may be employed. plentiful studies illustrate the possibility of recycling aggregates such as ceramics [1], rubber [2, 3], glass [4], and demolition wastes, i.e. bricks and concrete. because of the high quantity of concrete from demolition wastes, this material was studied as substitution of natural aggregates by several researchers [5–8]. nevertheless, these aggregates are highly porous, and contain a high amount of impurities [8, 9]. limited studies were conducted on the possibility of fresh concrete waste. these aggregates are mainly composed of over ordered fresh concrete. the benefit of this waste is that it contains limited quantity of impurities in contrast with other recycled aggregates. a concrete batching plant receives from numerous construction sites a huge amount of over ordered fresh concrete. currently, the practice of managing over ordered fresh concrete is to use it in road or to dump it into landfill, which is deemed as a non-advantageous solution. moreover, it will be of high cost in the close future because of the saturation of landfill areas [10]. recycling this material is of particular consideration due to its use it can significantly trim down the problem of waste storage, and simultaneously it helps the conservation of natural aggregate resources. recent successful studies on the use of fresh concrete waste as aggregates in concrete have been reported [11, 12]. in this experimental study, concrete mixes with fine and coarse aggregates recycled from brick bates as a substitution of natural aggregate and addition of silica fume as a supplementary cementing material have been studied. ii. experiential procedure opc was used throughout in this experimental work. the concrete ratio of 1:2:4 having designed strength of 3000 psi and along with silica fume, coarse aggregate having maximum size of 25 mm, brick aggregate having 25 mm and fine aggregate having maximum size of 4.75 mm were used. the compressive and tensile strength of concrete replacing coarse aggregate 50% by brick aggregate and concrete mix where coarse aggregate is replaced by 100% brick aggregate and with the addition of silica fume (sf) as a supplementary cementing material at the ages of 7, 14, 21 and 28 days. a total of 120 specimens were prepared with mixes designed as shown in table i. engineering, technology & applied science research vol. 7, no. 6, 2017, 2266-2267 2267 www.etasr.com bangwar et al.: replacement of coarse aggregate with locally available brick aggregate iii. results and discussion figure 1 shows the mean compressive strength of the normal concrete, concrete replacing 50% coarse aggregate with brick aggregate (ba) and concrete replacing 100% coarse aggregate with (ba) with the addition of 10% sf. as shown in the figure, the concrete having 50% ba is achieving almost the same strength as the specified strength of 1:2:4 concrete mix. however the strength of the concrete mix where coarse aggregate is replaced by 100% and with the addition of 10% silica fume reaches somewhat below the 28-characteristic strength of the concrete mix. this decrease in strength clearly points out the importance of aggregate in concrete in terms of strength irrespective of the addition of silica flume as a supplementary cementing material. furthermore, the decrease in the strength may be due to the reason of more absorption capacity of brick aggregate and silica fume. the 28-days tensile strength of the concrete depicts same behavior as that of the compressive strength of the concrete mixes at the different ages. table i. mix proportion of concrete s. no concrete mix cement (kg/m3) s.f (kg/m3) water (kg/m3) f.a (kg/m3) b.a (kg/m3) c.a (kg/m3) slump (mm) 1 normal concrete 346 0 173 692 0 1384 2550 2 50% replacement of ca with ba 346 0 173 692 692 692 25-50 3 100% replacement of ca with ba +10% sf 346 34.6 173 692 1384 0 25-50 fig. 1. elemental composition of rhas sample iv. conclusion in this study, the characteristics of concrete mixes with fine and coarse aggregates recycled from brick bates with the addition of silica fume as a supplementary cementing material have been studied. results show that coarse aggregate could be replaced by brick aggregate up to 50% by weight in the production of normal use of concrete without any loss of strength and other basic properties of the concrete. acknowledgement the authors express their thanks to civil engineering department quest nawabshah for the necessary support. references [1] a. r. khaloo, “properties of concrete using crushed clinker brick as coarse aggregate”, aci materials journal, vol. 91, no. 2, pp. 401–407, 1994 [2] n. segre, i. joekes, “use of tire rubber particles as addition to cement paste”, cement and concrete research, vol. 30, no. 9, pp. 1421–1425, 2000 [3] a. turatsinze, s. bonnet, j.-l. granju, “mechanical characterisation of cement-based mortar incorporating rubber aggregates from recycled worn tyres”, building and environment, vol. 40, no. 2, pp. 221–226, 2005 [4] i. b. topcu, m. canbaz, “properties of concrete containing waste glass”, cement and concrete research, vol. 34, no. 2, pp. 267–274, 2004 [5] j. m. v. gomez-soberon, “porosity of recycled concrete with substitution of recycled concrete aggregate: an experimental study”, cement and concrete research, vol. 32, no. 8, pp. 1301–1311, 2002 [6] t.-y. tu, y.-y. chen, c.-l. hwang, “properties of hpc with recycled aggregates”, cement and concrete research, vol. 36, no. 5, pp. 943– 950, 2006 [7] s.-c. kou, c.-s. poon, m. etxeberria, “influence of recycled aggregates on long term mechanical properties and pore size distribution of concrete”, cement and concrete composites, vol. 33, no. 2, pp. 286– 291, 2011 [8] r. zaharieva, f. buyle-bodin, f. skoczylas, e. wirquin, “assessment of the surface permeation properties of recycled aggregate concrete”, cement and concrete composites, vol. 25, no. 2, pp. 223–232, 2003 [9] r. boder, substitution des granulats alluvionnaires dans l’industrie du béton par les granulats marins, concassés ou recyclés, cerib, epernon, france, 2003 [10] v. w. y. tam, c. m. tam, “economic comparison of recycling overordered fresh concrete: a case study approach”, resources, conservation and recycling, vol. 52, no. 2, pp. 208–218, 2007 [11] s. l. correia, f. l. souza, g. dienstmann, a. m. segadaes, “assessment of the recycling potential of fresh concrete waste using a factorial design of experiments”, waste management, vol. 29, no. 11, pp. 2886–2891, 2009 [12] s.-c. kou, b.-j. zhan, c.-s. poon, “feasibility study of using recycled fresh concrete waste as coarse aggregates in concrete”, construction and building materials, vol. 28, no. 1, pp. 549–556, 2012 microsoft word 21-3260_s_etasr_v10_n1_pp5211-5216 engineering, technology & applied science research vol. 10, no. 1, 2020, 5211-5216 5211 www.etasr.com chung: evaluation of reactive power support capability of wind turbines evaluation of reactive power support capability of wind turbines phan dinh chung electrical engineering department the university of danang-university of science and technology danang city, vietnam pdchung@dut.udn.vn abstract—reactive power plays an important role in the operation of power systems, especially in the case of wind energy integration. this paper aims to evaluate the reactive power support capability of wind turbines in both normal and voltage sag conditions. the three 2mw wind turbines studied are a fixed speed wind turbine and two variable speed wind turbines with full-scale and power-scale power converters. comparison results indicate that at normal operation, the fixed speed wind turbine with a static synchronous compensator is able to consume the highest reactive power, while the variable speed wind turbine with full-scale power converter can supply the highest reactive power. in case of low voltage, the fixed speed wind turbine with the static synchronous compensator can support the highest reactive power if the static synchronous compensator’s capacity is similar to the wind turbine’s capacity, while if its capacity is equal to 25% of the generator’s capacity, the variable speed wind turbine with full-scale power converter has the best performance. keywords-capacitor bank; statcom; reactive power capability; voltage sag; wind turbines i. introduction renewable energy resources have attracted great interest and are exploited in many countries. many wind farms have been connected to power grids contributing significant electric energy yields to their demands. integrating a wind farm into the power system has a negative impact on its voltage profile [1]. active power generated from wind farms is not smooth, while the voltage drop on the connected lines depends proportionally on it and hence, voltage at nodes of the power system varies, no matter of the constant voltage control at the terminal of the wind farm. in order to reduce this impact, the reactive power on the grid should also vary inversely and compensate the active power’s variation, adjusting the wind farm’s reactive power. additionally, the power system requires from the wind farm to generate or receive a reactive power quantity to support the voltage control at nodes of the power system, or to reduce power loss on the grid [2-6]. however, the reactive power exchange capability of a wind farm depends on the type of the installed wind turbines and the power system operator should know this characteristic in order to request reasonable reactive power quantities. in general, there are three kinds of wind turbines: fixed speed wind turbines (fswt), variable speed wind turbine with partial-scale power converter (pc-vswt) and variable speed wind turbine with full-scale power converter (fcvswt) [7]. many researches have been conducted solely on the reactive power capabilities of these wind turbines [8-10]. it can be noted that the vswt can adjust reactive power exchange with the grid by the power converter, while fswt always receives reactive power from the grid, as it is not equipped with a power converter. to overcome this disadvantage, a capacitor bank or a static synchronous compensator (statcom) is suggested for fswt [11], in order to supply reactive power to the grid. however, the reactive power support capability of an fswt equipped with reactive power compensation equipment has not yet been compared to other wind turbines’ capabilities, especially in the case of low voltage. this paper evaluates the reactive power capability of wind turbines during operation in two modes: normal operation and voltage sag. the wind turbines considered in this research are pc-vswt, fc-vswt, fswt with capacitor bank and fswt with statcom. this study points out which kinds of wind turbines should be utilized from the perspective of reactive power support capability and can help power system operators to determine the reactive power quantities, which wind farms can support. ii. wind turbine system in general, a wind turbine system consists of a wind turbine, a generator and a shaft-gearbox system, which connects the wind turbine and the generator transferring mechanical power. depending on the kind of generators used, no, full, or partial-scale power converter is required. a. fswt this wind turbine uses a squirrel cage induction generator (scig) and can be connected to the grid without using a power converter [12]. it has poor controllability in both active and reactive power and during operation it always receives reactive power from the connected grid. hence, fswt is often equipped with compensating equipment, such as a capacitor bank [11] or a statcom [11, 13]. the configuration of fswt with capacitor bank or statcom is shown in figure 1. corresponding author: phan dinh chung engineering, technology & applied science research vol. 10, no. 1, 2020, 5211-5216 5212 www.etasr.com chung: evaluation of reactive power support capability of wind turbines b. fc-vswt this turbine is equipped with a permanent synchronous generator (pmsg) and its stator is connected to the grid via a full-scale power converter, as shown in figure 1(c) [12, 14, 15]. during operation, the generated power is transferred through this converter and the converter’s capacity is at least equal to the generator’s, providing good performance control. (a) (b) (c) (d) fig. 1. wind turbine configuration: (a) fswt with capacitor bank, (b) fswt with statcom, (c) fc-vswt, (d) pc-vswt c. pc-vswt this wind turbine is equipped with a doubly-fed induction generator (dfig) and it is well-known as the dfig-wind turbine [12]. a partial-scale power converter is installed at the rotor side, while its stator winding can be directly connected to the grid, as shown in figure 1d [16-18]. the slip range of dfig is between 25% and -25%, so the capacity of converter is about 25% of the generator’s rating. via this converter, pcvswt has a good controllability. hence, pc-vswt can adjust the reactive power flow so that it can supply or absorb reactive power from the grid. iii. reactive power ability a. fswt the equivalent circuit of an scig can be seen in [12]. � is reactance, � is resistance, � is current, � is voltage, � is the slip of scig and subscriptions �, �, � and � � stand for the rotor side, stator side, magnetizing core, and generator. active power generated by scig, � ���, is given by [12]: � ��� � ��������� ��� (1) where � � �� � � . reactive power generated by scig, � ���, is given by: � ��� � ��������� ��� � ��� �� (2) from (1) and (2), we have: � ��� � ��� ����������� ��!�"�#$%��� � &��� ' ��� �� (3) hence, (� ��� � � & ) *&� � *��+, & � � ���& � )���&�+ & (4) for any given value of � ��� , � ��� is always negative. fswt always receives reactive power from the connected grid. in order to reduce the reactive power quantity flowing from the grid, compensating equipment must be installed at scig’s terminal. two types of compensating equipment are considered: capacitor bank and statcom. 1) fswt with a capacitor bank installing a capacitor bank at the terminal of fswt, generates reactive power as: ��� ./� & (5) where, . is the capacitance of the capacitor bank and / is angular frequency. the real and reactive power quantities exchanged with the connected grid, are computed by: � � � � ��� (6) � � � � ��� � ��� ��� �����0�!1"�#�2� &� ' �� � �� � ./� & (7) equation (7) indicates that at a constant active power � �, the reactive power, � �, exchanged with the grid is constant. reactive power depends on the capacitance of the capacitor bank . and if capacitance is high enough, reactive power � � can be positive. 2) fswt with statcom when a statcom is installed at the terminal of an fswt, the reactive power flowing to the connected grid is the sum of the reactive power from scig and statcom. the statcom configuration is shown in figure 2 and its reactive power is limited by: � 34& � � 34& 5 1� 34,���2& � 1�4 �6#& � 34,�2& (8) where, � 34 and � 34 are active and reactive power from statcom, �� is the voltage at the statcom terminal, � 34,� and �4are the rated current of statcom and the modulation index of its controller, respectively. engineering, technology & applied science research vol. 10, no. 1, 2020, 5211-5216 5213 www.etasr.com chung: evaluation of reactive power support capability of wind turbines fig. 2. statcom configuration remaining at a constant dc voltage �7�, the capacity of statcom will limit its reactive power capability as: � 34& � � 34& 5 1�4 �6#& � 34,�2& � 18 34,�2& (9) where 8 34,� is the rated capacity of statcom. moreover, the limitation of power transmission from statcom’s terminal to the connection point is described as: � 34& � 1� 34 � ����9 2& 5 1 �$�� �9 2& � 1�4 �6#�� &�9 2& (10) where �: � /;: is the reactance of the filter at statcom and � is the voltage at the connected point. here, �7� depends on the active power, � 34, supplied from the connected grid. normally, the active power � 34 is almost insignificant. if � < 0, the active power from fswt or the connected grid is able to keep �7� at a constant value. here, it is supposed that � 34 > 0. in this case, (9) and (10) become: '8 34,� 5 � 34 5 8 34,� (11) ' ����9 ' �4 �6#�� &�9 5 � 34 5 ' ��� �9 � �4 �6#�� &�9 (12) and reactive power generated by statcom is limited as: ? 34 5 � 34 5 @ 34 (13) where: ? 34 � �abc' ����9 ' �4 �6#�� &�9 , '8 34,�d (14) @ 34 � ��ec' ����9 � �4 �6#�� &�9 , 8 34,�d (15) hence, from (3) and (13), the power transmitted from fswt with statcom to the connected line, � , is: � � � ��� (17) � � � ��� � � 34 (18) and the reactive power is limited by � f�g 5 � 5 � f4h (19) where, � f4h � @ 34 � ��� �����0�!1"���2� &� ' �� � �� (20) � f�g � ? 34 � ��� �����0�!1"���2� &� ' �� � �� 1212 b. fc-vswt reactive power supplied to the grid by fc-vswt must be limited by the rated capacity of the converter: �k& � �k& 5 8�,�& (22) where, 8�,� is the rated current capacity of the grid side converter (gsc). moreover, reactive power depends on the transmitting capability of the filter installed at the terminal of gsc [10]: �k& � 1�k � �% � �9 2 & 5 1�$�%�9 2 & � 1�4 �6# �%&�9 2 & (23) where �: is the reactance of the filter at gsc terminal, �4 is the modulation index of its controller, and �7�, �� and �� are voltages at dc–link, gsc terminal and the connected grid respectively. from (22) and (23), the reactive power capability of fc-vswt is limited by: �k,f�g 5 �k 5 �k,f4h (24) where, �k,f4h � ��e18�,�, �1�4 �6# �%&�9 2& ' �k& – �%� �92 (25) �k,f�g � �ab1'8�,�, '�1�4 �6# �%&�9 2& ' �k& – �%� �9) (26) c. pc-vswt in pc-vswt, the power exchange with the connected grid is the sum of power on the stator side and the gsc. the power output on the stator side is limited by both the stator winding’s rated current � ,� and the rotor winding’s rated current ��,� , whereas the power in the grid side depends on the capacity of gsc, 8�,� and the transmitting capability of the filter installed on gsc [9]: � & � � & 5 1� ,�� 2& (27) � & � 1� � ����� 2& 5 1� ����,� �� 2& (28) ��& � ��& 5 8�,�& (29) ��& � 1�� � �� � �9 2 & 5 1�4 �6# ��&�9 2 & (30) where, � and � are the active and reactive power in the stator side, �� and �� are the active and reactive power in gsc, � and �7� are the voltages on the stator side and the dc-link, �4 is the modulation index of the controller applied to gsc, and � , �f and �: are the reactance of stator winding, magnetizing of dfig and the gsc filter respectively. these can be summarized as: � ,f�g 5 � 5 � ,f4h (31) ��,f�g 5 �� 5 ��,f4h (32) where: � ,f�g � �ab1'? , '@ ) , � ,f4h � ��e1? , @ 2 (33) ? � p1� ,�� 2& ' � &, @ � �1������,��� 2& ' � & ' ��� �� (34) ��,f�g � �ab1'?�, '@�2, ��,f4h � ��e1?�, @�2 (35) ?� � p8�,�& ' ��&, @� � �1�4 �6#��&�9 2& ' ��& – ��� �9 (36) engineering, technology & applied science research vol. 10, no. 1, 2020, 5211-5216 5214 www.etasr.com chung: evaluation of reactive power support capability of wind turbines reactive power �7 and active power �7 exchanged with the connected grid are: �7 � � � �� (37) �7 � � � �� (38) hence, from (27) to (38), the reactive power exchanged with the grid is limited by: �7,f�g 5 �7 5 �7,f4h (39) where: �k,f4h � � ,f�g � ��,f�g (40) �k,f�g � � ,f4h � ��,f4h (41) iv. comparison of reactive power capability in order to obtain this objective, 2mw wind turbines are examined with output voltage at 690v/60hz (table i). it is supposed that the capacitor bank of fswt can generate 2mvar, so that in normal operation: . � 6.4�t or ��� √3./� & � 2yz?� so that it can generate a unity power factor at the rated active power. in statcom installation, its capacity is 2mvar and the reactance of its filter, �:, is 41.2mω. table i. wind turbines’ parameters [19-21] parameter’s name pc-vswt fswt fc-vswt generator’s stator reactance � 78,3mω 54,9mω generator’s rotor reactance �� 32.7mω 78.2mω generator’s magnetizing reactance �f 1.8935ω 1.74ω filter’s reactance xf 12mω 41.2mω dc-link voltage 1380v 1380v gsc’s capacity 0.5mva 2.2mva in order to obtain the reactive power capability of each wind turbine, the limitation curves of the reactive power for each wind turbine were plotted in matlab, using data from (6)(41) and table i. a. normal operation in normal operation, the voltage on the connected grid’s terminal is rated at 690v. the reactive power capability of each wind turbine is shown in figure 3. in general, the reactive power depends on the active power output of the generator. figure 3(a) indicates that in normal operation, fswt (scig) always receives the reactive power from the grid and its quantity depends on the active power. the higher the active power output is, the higher reactive power is consumed. in the case of a 2mvar capacitor bank installation, fswt supplies reactive power to the connected grid. however, at a given active power, it only generates constant reactive power, indicating the lack of adjusting ability. the use of statcom increases fswt’s performance in reactive power adjustment, as it can supply or absorb reactive power. the quantity of the exchanged reactive power is limited by the curves ab and cd in figure 3(b). fswt with statcom is able to receive more reactive power than it can supply to the grid and its consumption range is always larger than its generation range. moreover, the lower the active power output is, the lower reactive power can be consumed, but the higher reactive power can be generated. in comparison with the capacitor bank case, the adjustable area of fswt with statcom is larger. both the gsc and the filter’s capacity limit the reactive power exchanged between fc-vswt and the connected grid. its adjustable area is abcde in figure 3(c). if its active power output is over 1mw, its reactive power consumption ability is the same as its generation ability and it can supply maximum 2mvar, while it can consume more. (a) (b) (c) (d) fig. 3. reactive power support capability in normal operation: (a) fswtcapacitor bank, (b) fswt-statcom, (c) fc-vswt, (d) pc-vswt unlike fc-vswt, pc-vswt can supply or receive reactive power from both the stator and the converter’s grid side. as a result, the adjustable area of pc-vswt is abcd, which is the sum of the stator side’s adjustable area efgh and the gsc’s area ijkl in figure 3(d). the connected grid can require pc-vswt either to support or to absorb reactive power within a wide range. however, at constant active power generation, the reactive power consumption range is always larger than the generation range. fswt with a capacitor bank engineering, technology & applied science research vol. 10, no. 1, 2020, 5211-5216 5215 www.etasr.com chung: evaluation of reactive power support capability of wind turbines cannot adjust reactive power but fswt with a statcom can provide reactive power control ability, similar to pc-vswt or fc-vswt. comparing to variable speed wind turbines, the reactive power consumption capability of fswt with a statcom is the best but its reactive power generation capability is the poorest. in variable speed wind turbines, fcvswt’s reactive power generation is better but its consumption ability is worse than pc-vswt. in other words, during normal operation, in order to ensure the utilization of electrical energy from wind turbines, power system operators should request fswt with statcom to consume reactive power, while they should request fc-vswt to supply reactive power, especially in the case of low wind power. b. voltage sag in this section, it is supposed that the voltage at the connection point is reduced by 20%, 40%, 60%, and 80% of the rated value. in the case of pc-vswt, it is supposed that its crowbar will be activated as the stator voltage is below 70% of the rated value. in this case, the crowbar’s resistance of 11�� is added to the rotor winding, whereas gsc plays the role of statcom. this means that pc-vswt becomes an fswt with a statcom. the reactive power versus active power curves are shown in figure 4. as it can be noted, the lower the voltage, the smaller the maximum active power output is. the active power cannot be transmitted to the connected grid in case of low voltage. the reactive power exchange capability is also reduced during voltage reduction. for fswt, the voltage reduction makes the p versus q curve move to the zero point, as it is shown in figure 4(a). hence, in the case of an fswt with a capacitor bank installed, the reactive power supply to the grid is reduced, as shown in figure 4(b), as the reactive power generated by the capacitor bank is proportional to its terminal voltage square. however, in an fswt with a statcom installed, the lower the voltage, the higher the reactive power supply capability is, as shown in figure 4(c). at 20% of the rated voltage, fswt with statcom can supply approximately 2mvar. the reactive power support capability of fc-vswt depends heavily on the gsc. as voltage is reduced, its supply capability is reduced and its minimum support capacity is 0.44mvar for voltage reduced to 20% of the rated value, as shown in figure 4(d). when voltage is over 70% of the rated value, the reactive power capability of pc-vswt is reduced sharply, because of the rated rotor current limitation, as shown in (28). at maximum active power generation, the reactive power range is reduced from -1.48 to 0.91mvar to -0.66 to 0.13mvar, as the voltage is reduced to 80% of the rated value. when the voltage is below 70% of the rated value, pc-vswt operates as an fswt with a 0.5mvar statcom. hence, if we continue the utilization of active power generation, at 60% of the rated value, the grid must supply reactive power. to support reactive power, pc-vswt’s output should be below 0.8mw and the maximum reactive power at this voltage is 0.35mvar at 0mw. the lower the voltage, the higher the reactive power support capability is. the highest value of the reactive power is 0.48mvar, as the voltage is 20% of the rated value. (a) (b) (c) (d) (e) fig. 4. reactive power at voltage sag: (a) fswt, (b) fswt-capacitor bank, (c) fswt-statcom, (d) fc-vswt, (e) pc-vswt from the above analysis of the considered wind turbines, fswt with the capacitor bank owns the worst reactive power ability, whereas fswt with statcom can support the highest reactive power to the grid as voltage is lower than 80% of the rated value. comparing to pc-vswt, fc-vswt has better reactive power support capacity if voltage is over 20% of the rated voltage. however, the reactive power support capability of fswt with statcom depends heavily on the statcom’s capacity. if its capacity is equal to the capacity of the gsc used in pc-vswt, its support capability cannot be better than pc-vswt. in general, if statcom’s capacity in fswt is similar to the capacity of the converter used in fcengineering, technology & applied science research vol. 10, no. 1, 2020, 5211-5216 5216 www.etasr.com chung: evaluation of reactive power support capability of wind turbines vswt, fswt has the best reactive power support. however, if its capacity is similar to the capacity of the converter used in pc-vswt, fc-vswt has the best performance. v. conclusion this research studied and compared the reactive power capability of wind turbines in both normal and voltage sag conditions. the results showed that during normal operation, in order to ensure the utilization of the electrical energy from wind turbines, fswt with statcom can absorb the highest reactive power, while fc-vswt has better capability to supply the reactive power, especially in the case of low wind power. in the case of low voltage, fswt with a statcom installed can support the highest reactive power to the grid if statcom’s capacity is similar to the wind turbine’s capacity, while if its capacity is equal to the capacity of the converter of a pcvswt, fc-vswt has the best reactive power capability. references [1] r. m. mathe, k. a. folly, “impact of large scale grid-connected wind 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sri lanka, vol. 43, no. 4, pp. 347355, 2015 [20] h. s. ko, g. g. yoon, n. h. kyung, w. p. hong, “modeling and control of dfig-based variable-speed wind-turbine”, electric power systems research, vol. 78, no. 11, pp. 1841-1849, 2008 [21] m. s. ali, “evaluation of damping controls of a permanent magnet synchronous generator wind system with statcom”, msc thesis, king fadh university of petroleum and minerals, 2012 microsoft word etasr_v11_n1_pp6691-6695 engineering, technology & applied science research vol. 11, no. 1, 2021, 6691-6695 6691 www.etasr.com karoui et al.: bandwidth enhancement of a bell-shaped uwb antenna for indoor localization systems bandwidth enhancement of a bell-shaped uwb antenna for indoor localization systems mohamed salah karoui national engineering school of sfax university of sfax enis, leti laboratory sfax, tunisia mohamedsalah.karoui@issatm.rnu.tn mongi lahiani national engineering school of sfax university of sfax enis, leti laboratory sfax, tunisia mongi.lahiani@enis.rnu.tn nadia ghariani national engineering school of sfax university of sfax enis, leti laboratory sfax, tunisia ghariani.nadia @gmail.com hamadi ghariani national engineering school of sfax university of sfax enis, leti laboratory sfax, tunisia hamadi.ghariani@ enis.rnu.tn abstract-in this paper, a simple method of enhancing the bandwidth of the bell-shaped uwb antenna for indoor localization systems is proposed. therefore, a modified version of the bell-shaped ultra-wide band (uwb) antenna for indoor localization systems is presented. the proposed antenna is printed on a low-cost fr-4 substrate of 21×27×1.6mm 3 size. it is composed of a bell-shaped radiating patch and a multi-slotted ground plane. the measured results show that the proposed antenna has an impedance bandwidth of about 11.2ghz ranging from 3.16ghz to 14.36ghz at s11<−10db. compared to the original version, an enhancement of about 5.56ghz in the measured impedance bandwidth was observed. keywords-localization systems; printed monopole antennas; slotted ground plane; ultra wideband systems. i. introduction during the last years, a large variety of antennas have been implemented for indoor localization systems. the selection of the appropriate antenna depends on many parameters and has considerable effects on the performance of the system. the study presented in [1] sums up the antenna requirements for indoor localization systems and more particularly for reference nodes. these requirements are more or less stringent, depending on the localization technique, the localization model, the metric being used during localization process and the nature of the signal being processed. as impulse radio ultra wide band (ir-uwb) -based localization systems are commonly characterized by the transmission of ultra-short pulses over a large bandwidth, the smallest distortions introduced by the antennas lead to large localization errors. to reduce the effect of the antenna on localization accuracy, the designed antenna should respect these characteristics [1, 2]: • large bandwidth; ideally from 3.1ghz to 10.6ghz • linear phase and constant group delay over the entire bandwidth • high radiation efficiency, typically > 70 % • omni-directional and stable radiation pattern • flat gain over the entire bandwidth • small size and low cost the implementation of antennas with circular polarization over the entire bandwidth is another important characteristic for uwb antennas used for reference unit. this parameter enables the detection of targets with unknown polarization [3]. to achieve all these requirements, several antenna structures have been proposed, including 3d and planar forms. the microstrip patch antennas have gained more attention, due to their low profile, low cost, ease of fabrication, and good radiation properties. unfortunately, they suffer from limited bandwidth. to improve their bandwidth, antenna designers have used several techniques including [2, 4-7]: • various feeding techniques • slot antenna geometry • addition of a slot on the radiating patch • insertion of an additional stub on the patch • addition of steps to the lower edge of the patch • insertion of multiple slots in the ground plane in this study, a compact microstrip line-fed uwb antenna with partial ground plane is presented. three slots with the same dimensions were inserted in the top edge of the ground corresponding author: mohamed salah karoui engineering, technology & applied science research vol. 11, no. 1, 2021, 6691-6695 6692 www.etasr.com karoui et al.: bandwidth enhancement of a bell-shaped uwb antenna for indoor localization systems plane. with this technique, an enhancement of 5.56ghz in the measured impedance bandwidth of the antenna was achieved. ii. antenna configuration the proposed antenna is realized on an fr-4 substrate of size (wsub = 21mm × lsub = 27mm) with height h = 1.6mm, relative permittivity εr = 4.4, and loss tangent tan δ = 0.02. (a) (b) fig. 1. geometry of the proposed antenna: (a) front view, (b) back view. as shown in figure 1, the front view is composed of a bellshaped radiating patch fed by a 50ω microstrip feed line with width wf = 3mm and length lf = 10mm. the radiating patch has the same shape and dimensions as the antenna presented in [8]. it is formed by the association of a trapezoid with dimensions wb = 17mm, wsub = 21mm, le =8.5mm and a semicircle of radius rc = 8.5 mm. the back view of the structure consists of a partial ground plane with length lg = 7mm. three rectangular slots with size of ws = 3mm × ls = 2mm are added in the upper edge of the ground plane to enhance the impedance bandwidth of the antenna. iii. parametric study to meet the uwb antenna requirements, a parametric study was carried out using the high frequency simulation software (hfss) v.13. to achieve the largest impedance bandwidth and to find the optimal antenna parameters, the effects of varying slot number, slot dimension, and slot positions were analyzed. during the simulations, an sma coaxial connector was connected to the feed line to obtain more realistic results. the ground plane shape and dimensions are sensitive parameters in uwb antenna design [9-12]. actually, the distance between the ground plane and the feed line changes the input impedance and hence the operating bandwidth of the antenna giving a better or a worst return loss. by inserting first a slot in the upper edge of the ground plane, the gap between the feed line and the ground plane is enlarged resulting in a change on the impedance bandwidth. the tuning results of slot size and position are presented in figures 2 and 3 respectively. it can be seen from the figures, that a slot of dimensions ws = 3mm × ls = 2mm placed in the middle of the ground plane gives the largest impedance bandwidth. according to the simulated results, the -10db return loss bandwidth of the antenna is about 7.89ghz ranging from 3.16ghz to 11.05ghz. to further enhance the impedance bandwidth of the antenna and to cover the entire uwb frequency band, more slots were inserted in the upper edge of the ground plane. the simulation results of s11 as a function of the number of slots are shown in figure 4. fig. 2. variation of the s11 for different slot dimensions. fig. 3. variation of the s11 for different slot positions. fig. 4. variation of the s11 as a function of the number of slots. it can be observed from figure 4 that the impedance bandwidth of the proposed antenna is getting larger as the number of slots increases. actually, with the insertion of three slots in the ground plane, an enhancement of 4.47ghz in the simulated impedance bandwidth is noticed. the proposed antenna covers the frequency band from 3.16ghz to 14.11ghz, thus ensuring the coverage of almost the entire uwb frequency band. these results confirm the effect of ground plane on impedance bandwidth and prove the effectiveness of slot insertion on impedance bandwidth enhancement. engineering, technology & applied science research vol. 11, no. 1, 2021, 6691-6695 6693 www.etasr.com karoui et al.: bandwidth enhancement of a bell-shaped uwb antenna for indoor localization systems iv. results and discussion the prototype of the proposed antenna was fabricated on a low cost fr-4 substrate of compact size (figure 5). all the antenna parameters were measured in the imep-lahc research laboratory (grenoble, france). the impedance characteristics were measured using the anritsu 37369a (40mhz – 40ghz) vector network analyzer while the gain and the radiation pattern were measured using an satimo anechoic chamber. fig. 5. picture of the realized antenna. a. impedance bandwidth the simulated and measured return losses of the proposed antenna are presented in figure 6. as shown in the figure, the measured impedance bandwidth of the proposed antenna is about 11.2ghz ranging from 3.16ghz to 14.36ghz while the simulated impedance bandwidth is about 10.95ghz ranging from 3.16ghz to 14.11ghz. there is a good agreement between the simulation and the measurement results with a slight offset at the resonant frequencies and the high frequency. these discrepancies are mainly caused by the connector soldering, the fabrication process, and the nature of the substrate. fig. 6. simulated and measured return loss. b. group delay the simulated group delay of the proposed antenna over the frequency band from 2ghz to 16ghz is presented in figure 7. the simulation results show that the antenna has a group delay less than 0.5ns over the uwb frequency band and greater than 1ns outside this band. these results prove that the antenna introduces a low distortion on the transmitted uwb signal. fig. 7. simulated group delay. c. peak gain the simulated and measured peak gains of the proposed antenna in the frequency band from 2ghz to 16ghz are presented in figure 8. we see that the gains are larger than 1.8dbi for frequencies above 3ghz. the measured gain varies from 1.82dbi to 4dbi in the uwb band with a peak of 4.1dbi at 6.9ghz while the simulated gain varies from 0dbi to 4.38dbi with a peak of 4.38dbi at 10.3ghz. actually, there is a slight difference between simulation and measurement results. this offset is due to the difference in the number of frequency points and the number of cuts taken during measurements. fig. 8. simulated and measured peak gain. d. radiation pattern figure 9 illustrates the simulated and measured radiation patterns of the antenna in the e-plane and the h-plane at different frequencies (4.1ghz, 7ghz, 10ghz and 13ghz). the radiation pattern results show a good match between simulation and measurements with a visible offset especially at 4.1ghz and 10ghz frequencies. as shown in figure 9, the radiation patterns of the proposed antenna are nearly omnidirectional and stable in both planes. e. radiation efficiency the simulated radiation efficiency of the proposed antenna is depicted in figure 10. it can be seen that the proposed antenna has a maximum radiation efficiency of 98.44% at 8.6ghz with an average of 95.78%. engineering, technology & applied science research vol. 11, no. 1, 2021, 6691-6695 6694 www.etasr.com karoui et al.: bandwidth enhancement of a bell-shaped uwb antenna for indoor localization systems (a) -40 -30 -20 -10 0 10 0 30 60 90 120 210 240 270 300 330 f = 4.1 ghz d b -60 -40 -20 0 20 0 30 60 90 120 210 240 270 300 330 f = 4.1 ghz d b (b) -40 -30 -20 -10 0 10 0 30 60 90 120 210 240 270 300 330 f = 7 ghz d b -60 -40 -20 0 20 0 30 60 90 120 210 240 270 300 330 f = 7 ghz d b (c) -40 -30 -20 -10 0 10 0 30 60 90 120 210 240 270 300 330 f = 10 ghz d b -60 -40 -20 0 20 0 30 60 90 120 210 240 270 300 330 f = 10 ghz d b (d) -40 -30 -20 -10 0 10 0 30 60 90 120 210 240 270 300 330 f = 13 ghz d b -40 -30 -20 -10 0 10 0 30 60 90 120 210 240 270 300 330 f = 13 ghz d b fig. 9. simulated and measured radiation patterns (left: e-plane, right: hplane) at: (a) 4.1ghz, (b) 7ghz, (c) 10ghz, and (d) 13ghz. fig. 10. simulated radiation efficiency. v. comparative study a comparative study between antennas with slotted ground plane referenced in the literature and the proposed antenna is shown in table i. the comparative parameters are impedance bandwidth, antenna dimensions, fractional bandwidth and maximum gain. the proposed antenna has the most compact size, a large impedance bandwidth, a high fractional bandwidth but a low gain. it is a good compromise between bandwidth and size. fortunately, it covers the entire uwb frequency band, but in comparison with other structures, the antenna presented in [2] has larger bandwidth and gain. table i. bandwidth, dimensions, fractional bandwidth and gain comparison antenna -10db bandwidth (ghz) dimensions (mm 2 ) fbw (%) max gain (dbi) [2] 2.57–16.72 30×22 146.7 6.27 [4] 2.6–12.3 39×40 130.2 5.52 [13] 3.66–14 24×36 117.1 [14] 3.8–12 28×29 103.79 4.5 [15] 3.09–10.85 30×30 111.33 [16] 3.1–10.6 32×40.57 109.49 proposed 3.16–14.36 27×21 127.85 4.1 vi. conclusion in this study, a compact and low cost microstrip bell-shaped patch antenna with three slots in the ground plane has been designed and fabricated. the return loss results prove that the insertion of rectangular slots on the upper edge of the ground plane improves the impedance bandwidth of the antenna. indeed, compared to the original version, the measurement results show a bandwidth enhancement of about 5.56ghz, thus reaching 11.2ghz. the proposed antenna has a large impedance bandwidth ranging from 3.16ghz to 14.36ghz, which covers the entire uwb frequency band. consequently, it remains suitable for being used in uwb localization systems with its stable gain, its low group delay and its nearly omnidirectional radiation patterns in both planes. acknowledgment the authors would like to thank dr. than phu vuong, head of the imep-lahc laboratory in grenoble, france. references [1] l. brás, n. b. carvalho, p. pinho, l. kulas, and k. nyka, "a review of antennas for indoor 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[11] y. lu, y. huang, h. t. chattha, and p. cao, "reducing ground-plane effects on uwb monopole antennas," ieee antennas and wireless propagation letters, vol. 10, pp. 147–150, 2011, https://doi.org/ 10.1109/lawp.2011.2119459. [12] p. c. ooi and k. t. selvan, "the effect of ground plane on the performance of a square loop cpw-fed printed antenna," progress in electromagnetics research, vol. 19, pp. 103–111, 2010, https://doi.org/ 10.2528/pierl10102907. [13] q. ain and n. chattoraj, "a compact novel tapered u slot ultra wideband antenna," international journal of applied science and engineering, vol. 11, no. 3, pp. 301–315, 2013, https://doi.org/10.6703/ ijase.2013.11(3).301. [14] n. george and b. lethakumary, "a compact microstrip antenna for uwb applications," microwave and optical technology letters, vol. 57, no. 3, pp. 621–624, 2015, https://doi.org/10.1002/mop.28910. [15] c.-y. sim, w.-t. chung, and c.-h. lee, "novel band-notch uwb antenna design with slit ground plane," microwave and optical technology letters, vol. 50, no. 8, pp. 2229–2233, 2008, https://doi.org/ 10.1002/mop.23621. [16] b. saidaiah, a. sudhakar, and k. p. raju, "a new olympic ring shaped antenna for uwb applications," engineering, technology & applied science research, vol. 6, no. 3, pp. 1010–1012, jun. 2016, https://doi.org/10.48084/etasr.682. authors profile mohamed salah karoui was born in bizerte, tunisia in 1979. he received the electrical engineering degree from the national engineering school of sfax in 2003, the msc degree on electronics in 2004, and the doctorate on electrical engineering in 2010. he is currently working toward a hdr on electrical engineering. he joined the higher institute of applied sciences and technology of mateur in 2006. currently, he is an assistant professor at the same institute. also he is a member of the leti laboratory enis sfax. his researches are focused on wideband antennas, bandwidth enhancement, rfid. nadia ghariani was born in sfax, tunisia in 1984. she received the advanced technician diploma in electronics and communication from the higher institute of electronics and communication of sfax – tunisia in 2006 and the electrical engineering degree from the national engineering school of sfax –tunisia in 2009, the research msc degree in electronics in 2010 and the doctorate on electrical engineering at the same eengineering school in 2016. she is a member of the leti laboratory enis sfax tunisia. her current research interests are uwb localization systems in indoor environments and uwb antennas. mongi lahiani was born in sfax, tunisia, in 1957. he received the electrical engineering degree from the university of sciences and techniques of sfax-tunisia in 1984 and the doctorate of engineer in measurement and instrumentation from university of bordeaux, france, in 1986. since 1988, he is a professor at sfax university. he joined the national engineering school of sfax in 1990 and he is a professor in the fields of analog electronics and microelectronics. his research interests are design of circuits in medical electronic and integration of microwave circuits of micro-strips with screen-printed thick films technology. hamadi ghariani was born in sfax, tunisia, on july 1956. he received the electrical engineering degree from the university of sciences and techniques of sfax-tunisia in1981, the dea degree in 1981and his doctorate of engineer in 1983 in measurement and instrumentation from the university of bordeaux france. he joined the national engineering school of sfax in 1984. currently, he is a professor in the same school. his research activities have been devoted to topics such as medical electronics, communication systems for medical telemetry, measure and instrumentation. microsoft word 12-2274-dion_ok engineering, technology & applied science research vol. 8, no. 6, 2018, 3550-3555 3550 www.etasr.com arjmand and giannakeas: fat quantitation in liver biopsies using a pretrained classification … fat quantitation in liver biopsies using a pretrained classification based system alexandros arjmand department of computer engineering technological educational institute of epirus, kostakioi, gr47150 arta, greece alexarjmnd@gmail.com nikolaos giannakeas department of computer engineering technological educational institute of epirus, kostakioi, gr47150 arta, greece giannakeas@teiep.gr abstract—non-alcoholic fatty liver disease (nafld) is a common syndrome that mainly leads to fat accumulation in liver and steatohepatitis. it is targeted as a severe medical condition ranging from 20% to 40% in adult populations of the western world. its effect is identified through insulin resistance, which places patients at high mortality rates. an increased fat aggregation rate, can dramatically increase the development of liver steatosis, which in later stages may advance into fibrosis and cirrhosis. during recent years, new studies have focused on building new methodologies capable of detecting fat cells, based on the histology method with digital image processing techniques. the current study, expands previous work on the detection of fatty liver, by identifying once more a number of diverse histological findings. it is a combined study of both image analysis and supervised learning of fat droplet features, with a specific goal to exclude other findings from fat ratio calculation. the method is evaluated in a total set of 40 liver biopsy images with different magnification capabilities, performing satisfyingly (1.95% absolute error). keywords-liver biopsy; steatohepatitis; fatty liver; machine learning; image analysis i. introduction fatty liver develops in 90% of the population, with an alcohol consumption of over 60g on a daily basis. however, a fatty liver may be further classified as non-alcoholic (nafl) [1], by the presence of hepatic steatosis without indicating any hepatocellular damage, but by swollen hepatocytes and circular fat cells. nafld has been targeted as a massive disease, particularly in western country’s adults, due to the expanding predominance of obesity and insulin resistance. the latter has the effect on patients with nafld developing hepatitis c at high risk, which may lead to cirrhosis, a reduced hepatocyte activity due to a large number of histological scar tissues. hvc (hepatic virus c) has been documented to be the leading cause of deaths from 2003 to 2012 in usa [2]. in particular, hepatitis c is capable of extending the incidence of liver cancer by 50%, indicating an irreversible pathological condition, as opposed to hepatitis b (15%). diagnosis of nafld requires a liver biopsy, which is obtained by needle insertion. each biopsy specimen is followed by histology for precise steatosis evaluation. in most cases, a single or even a two-part tissue sample is divided into formalin-fixed and hematoxylin-eosin (h&e) stained sections (figure 1). a biopsy slide is then scanned through microscopy and a digitized image is extracted by the software. through this technique, each digitized sample can reveal several liver structures, including a) fat cells, b) ballooned cells, as swollen fat wrapped hepatocytes c) central veins, and d) sinusoids, being responsible for mixing nutrientrich blood from the portal vein and with corresponding oxygenrich blood from the hepatic artery. traditional nafld examination by a pathologist, involves in most cases a lengthy and highly subjective visual interpretation of the biopsy slides through a microscope. as a result, “intra-observer” and “inter-observer” variability, can cause a critical degree of inaccuracy during the quantification of steatosis, among several clinicians. due to these limitations, researchers have undertaken the task of developing reliable automated software for the accurate assessment of steatosis prevalence, with widespread and also cutting-edge methods, based on the digital biopsy image processing. in earliest years, simple stereological and morphometric techniques, for steatosis microvesicular and macrovesicular quantification have been introduced [3]. consequently, some studies that identified significant quantitative deviations in the fat ratio, between a computerized method and a pathologist’s manual scaling have been presented [4]. earliest image analysis methods composed a 2-class detection problem, to isolated tissue and fat pixels according to their intensity values [5]. a combination of fat cell separation with body mass index (bmi) and its insulin resistance prevalence degree has also been presented [6]. some studies used diverse color spaces either by replacing h&e dye with toluidine-blue (tb-pas) tissue coloring [7], or by utilizing different color spaces of the processed image [8]. in recent years, the conversion of an rgb image to grayscale, in order to indicate the bright white objects of interest, has been attempted [9]. another work focuses on the detection of large droplet macrovesicular steatosis (ld-mas), using the radial hepatic nucleus displacement calculation [10]. one of the most extensive works, identifies various histological findings using machine learning techniques [11], where a series of annotated histological features is included for non-fat shapes exclusion. finally, two recent studies are based on the parameters of engineering, technology & applied science research vol. 8, no. 6, 2018, 3550-3555 3551 www.etasr.com arjmand and giannakeas: fat quantitation in liver biopsies using a pretrained classification … solidity, roughness, elongation [12] and the circular shape of fat cell [13], in order to separate them from other regions of interest. fig. 1. h&e stained image including 4-class liver structures. the current work introduces a complete methodology for image analysis of liver biopsies, aiming to steatosis assessment. the proposed method is based on image processing techniques, which are combined with clustering and classification algorithms. apart from classic segmentation of the image to provide histological findings detection, the method proposes a pre-trained classification step for their identification. the identification of four different findings and the accurate isolation of fat droplets, leads to the elimination of many false positive outcomes. specifically, the method defines a 4-class classification problem, focusing on the separation between four categories of findings (classes), which are: a) fat cells, b) ballooning degeneration, c) sinusoids and d) veins. the proposed method improves the concept of histological finding classification and characterization, including ballooning degeneration as an alternative finding class, in contrast with the method proposed in [11]. ballooned cells, which in various cases appear as circular formed structures comparable to fat droplets, are now an interesting field of research according to pathologists. the classification stage could be incorporated into already developed fat detection methodologies, as the last identification stage before fat ratio extraction. ii. methods the classification method consists of four essential steps: • the implementation of a clustering-based algorithm to separate tissue from the background, • an iterative morphological opening for circular structure detection and irregular object elimination, • feature extraction of an annotated set of objects, • training of a classifier, employing the extracted histological features driven by the annotated ones. the trained system will have the ability to separate each region of interest into fat droplets, ballooned cells, sinusoids, or veins and lead to the calculation of fat ratio with respect to the isolation of identified fat cells. figure 2 presents a flowchart of the proposed method, enclosed into a general fat identification methodology and fat ratio quantification. fig. 2. flowchart of the classification procedure. a. histological image segmentation after a biopsy slide scanning, usually a large part of the digital image represents a white background, therefore it contains high intensity values on the rgb color channels. in contrast, the histological h&e staining sample consists of low intensity pixel values. thus, by applying clustering techniques, such as the k-means algorithm, hepatic tissue pixels could be separated from other background pixels, using only their color values as features. more specifically, during this step, kmeans divides the image elements into two clusters (k=2), providing a segmented binary image: 1) white pixels will be the background and 2) black pixels will be the tissue. at the algorithm convergence, the outer tissue boundaries are determined by the most remote cluster data points, whereas at each iteration the pixel segmentation is achieved according to the lowest square error criterion and expressed as: ���� � � ����� � � � �� �� �� ��� � ��� (1) where �� and �� denote the number of image rows and columns, respectively. at the same time, �� indicates the feature vector of each pixel with the following relation: �� � ��� ���, �� �����, �� �� �! (2) where via the following formula: � � " 1 �� ⋅ ��%���� �� �� �� ��� (3) the two clusters (k=1, 2) centroid calculation is updated in every current iteration until the convergence of k-means. this action is performed according to the already stored pixel intensities at each segmentation step. as a result, the centroid with the highest intensities sum characterizes the background pixel cluster, while the other the tissue cluster, respectively. by default, euclidean metric is applied to the cluster data point distance calculation. engineering, technology & applied science research vol. 8, no. 6, 2018, 3550-3555 3552 www.etasr.com arjmand and giannakeas: fat quantitation in liver biopsies using a pretrained classification … b. object of interest detection the next stage attempts an object of interest detection to the previous segmented color image. the algorithm aims to include circular white regions of interest with various sizes. a recurrent morphological opening method is applied to detect circular structures, which are probably fat droplets. although morphological operators have the ability to locate objects of a particular structure, the size of fat droplets in the biopsy tends to vary (figure 3). as a starting point, a circular mask with a minimum radius of 5 pixels is defined as the initial structural element. then, morphological opening procedure increases the mask radius (2 pixels) after each subsequent loop. as a result of the morphological opening between the binary image and the circular mask, the binary image imorph is produced as: �&'�() � �*�+ ∘ -�� � .�*�+ ⊝ -��0 ⊕-��, (4) where ⊖ and ⊕ are the morphological operators of erosion and deletion, respectively [14]. ibin denotes the original binary image and mci the circular mask of the i th iteration. the mci radius tends to increase by 2 pixels in each iteration, to allow larger circular structures to be detected. next, the current imorph image produced by the i th iteration, is placed as an input to a logical or. through this control step, the loop process terminates, if no further changes are detected between the last two consecutive imorph images. fig. 3. binary tissue conversion and circular objects detection. based on the above methodology, each region is filtered according to the size, so that very small circular structures along with the correspondingly large ones, are eventually discarded from upcoming calculations. specifically, small regions (<5 pixels) are considered as noise, due to resulting errors in the image capture process. whereas, large regions (>1000 pixels) are associated with other large histological structures, such as central veins, portal veins and arteries, sinusoids and bile ducts. c. features selection to develop the pretrained system, a set of 13 biopsy samples, with the standard h&e histological staining derived from nafld patients, has been annotated. the concept is to make use of knowledge extracted by the annotation in order to train a classification based system. thus, several features have been extracted from the annotated regions. one part of this subset presents a high steatosis prevalence, while in several cases a high rate of hepatocyte ballooning degeneration is observed. the entire number of findings in all 13 liver images is 7305. this dataset is collected from patient cases within st. mary hospital imperial college healthcare nhs trust of london, uk. they were digitized with a hamamatsu microscope, providing a magnification of ×40. each one of these contains hundred regions of interest, most of which are fat droplets and ballooned cells. taking under consideration this particular advantage of clinical specimens, an adequate set of training instances becomes available for annotation, which at a later stage can be fed into supervised machine learning classifiers. as shown in figure 4, fat areas, as well as ballooning degeneration, sinusoids and veins, have been manually labeled by specialist pathologists, through hamamatsu’s ndp.view 2 annotation tool. for each of the annotated structures, an xml structured file is exported directly. each record includes a unique id and title as a description. in addition, x and y points which correspond to the exact location of the freehand tool area, in the original ×40 liver color image. to deal with the above information, a parsing function for retrieving different annotated findings from xml files has been developed, by recognizing ids, coordinates and color of the freehand contour (ex. ff0000red, ffff00-yellow, etc.) of all regions. according to the calculation of the histological features in table i, an identification label is given in each region of the 4-class objects: a) fat → 1, b) ballooning → 2, c) sinusoid → 3 and d) vein → 4. a visualization of the manual region selection is achieved, using a grayscale image with the same size as the initial rgb color tissue sample. the four varied findings are remarked with different gray levels, along with colorful sign dots. figure 5 presents the demonstration of the annotated regions as described above. as a final step of the annotation extraction, a list of features for each distinct liver image is computed, while at the same time, a corresponding set of class objects from the entire subset of 13 biopsy images, is gathered as the main training set of data. thus, a large number of regions from all 13 annotation images has been extracted. it is noted that a total count of a) 4023 fat droplets, b) 3064 cases of ballooning, c) 165 sinusoids and d) 53 hepatic veins, was initially obtained providing a sufficient training set. the created dataset is unbalanced, due to the various existing anatomical features. hence, the clinical classification problem becomes harder to solve. thereby, only a few hundred fat and balloon cells are included, randomly selected from all the 13 annotated images. aiming the training of a supervised algorithm, an informative feature set is extracted for each annotated region of interest. details for the annotation and the dataset, which have been employed to provide knowledge, are presented in the next subsection. each feature is selected in accordance with the characteristics of histopathological findings. the features are grouped into five feature categories, to highlight the differences between the four classes (table i). the shape is characterized as a key calculation feature, providing valuable information about biopsy structures. histological objects also tend to carry various peculiarities resulting in one of the four detection classes (fat droplets, balloon cells, sinusoids, veins), including the size, texture and set of pixel intensity. for instance, lipid droplets of fat have a circular shape, with an increased brightness intensity, and smoothed texture. in the case of ballooning degeneration, there is a significant distinction in the region texture, due to the interference of fat-swollen engineering, technology & applied science research vol. 8, no. 6, 2018, 3550-3555 3553 www.etasr.com arjmand and giannakeas: fat quantitation in liver biopsies using a pretrained classification … hepatocytes. on the other hand, sinusoids are described as noncircular and irregular shaped objects. finally, veins are distinguished by their large size with a slight deviation of the mean pixel intensity, due to the occurrence of a number of red blood cells. fig. 4. ndp.view 2 freehand annotation tool. fig. 5. visualization of annotated regions table i. extracted features feature category description 1 shape-based eccentricity, major/minor axis length, extent 2 intensity-based mean intensity 3 texture-based intensity standard deviation, solidity 4 position-based x, y coordinates 5 magnitude diameter, perimeter, area d. classification training the training set is employed in algorithm learning, where the computed features set provide the input of several supervised classifiers, including: naive bayes classifier, k nearest neighbors, decision tree using (c4.5 algorithm) and support vector machines. naive bayes (nb) algorithm [15], is part of a probabilistic classifiers’ family based on the bayes theorem. its assignment is to associate an unknown liver sample, to a class that carries the greater posterior probability. here, each one of the above extracted histological features is considered as independent [16]. in k nearest neighbors (k-nn) algorithm [17], the classification model decides about the class of a new sample taking into account the majority of its k nearest neighbors. thus, its euclidean distance is estimated in order to find out the members of its neighborhood. employing the c4.5 decision tree induction algorithm, a histological object is identified through a repetitive branching process [15]. given an unknown input sample, the process starts from the tree root and runs repeatedly on the internal nodes, until a terminal leaf yields a decision value. as a conclusion, when a branching presents high homogeneity, a leaf node is added to the corresponding class. in support vector machines (svm) [18] the overall process involves the optimal determination of hyperplanes, whereby a histological sample is classified with a maximum margin value, in case it carries the same predictive value with an annotation label. iii. results and discussion for the evaluation of the proposed method, a second subset of 27 h&e images is employed, this time carrying a smaller magnification of ×20 for testing-diagnostic purposes. pathologists have provided the fat ratio for these biopsies. for all magnification settings in this study, the captured biopsy images originally consisted of sizes exceeding 10,000×10,000 pixels. at first, the visualization results for the efficiency of the method are examined. in figure 6 the detected circular structures are marked with a green contour after the biopsy image processing. fig. 6. visualization results of the proposed method as found in the histological sample ms12-23945, all cases of hepatocyte ballooning along with other structures, such as the long-length liver vein (pointing arrow), have been successfully excluded during the initial segmentation stage. however, a weakness of the method is observed, in the ms149711 sample, in which the high steatosis prevalence (29.8%) in combination with the lower magnification ×20, results in an agglomeration of some adjacent circular regions (red area). this type of regions exhibit a feature set that does not match the size, circularity and eccentricity of a typical fat droplet, so they are excluded from the classification stage, resulting in an underestimation of the total fat ratio. however, it should be noted that as the magnification of an image increases, this phenomenon is eliminated, as the computer vision algorithm tends to present a greater discrimination capability among the engineering, technology & applied science research vol. 8, no. 6, 2018, 3550-3555 3554 www.etasr.com arjmand and giannakeas: fat quantitation in liver biopsies using a pretrained classification … densely occurring droplets of fat. that means that the outer steatosis structure boundaries become more evident, causing in that way fewer agglomeration regions to be formed. after the exclusion of non-fat objects, for each of the 27 testing images, the fat ratio is computed dividing the cumulative area of fat structures and the whole tissue area. this value is derived both from the segmentation method and a semi-quantitative annotation procedure by st. mary’s pathologists. therefore, the difference between these percentages presents the absolute error for each biopsy image and each classification algorithm, as follows: 34��'�.�0 � |67++'8 � 6�97::|100%, (5) where sannot indicates the estimated fat ratio from the st. mary’s pathologists’ annotations, while sclass is equivalent to the percentage of liver fat, based on the automated detection including the classification stage. in addition, it is feasible to compare the absolute error with and without expanding our methodology with the classification stage, and measure the improvement in fat quantitation by providing a second value of absolute error: 34��'�.�0 � |67++'8 � 6=>?|100%, (6) where 6=>? is the fat ratio after the 2 stages of image segmentation, without performing the classification. in table ii, it is perceived that in all 27 histological samples, the classification stage computes lower values of fat ratio than that of the segmentation. it is emphasized that the four classifiers have reduced the mean fat ratio up to 1.5%, in comparison with the 17.3%. this is because the false positive ballooning, sinusoid and vein findings were excluded from all steatosis calculations. the results of the third main column, show all fat percentage values, according to semi-quantitative estimates of specialist pathologists. table ii. accuracy results testing image classification results fat ratio after regions classification (%) fat ratio w/o classification (%) fat ratio from annotation (%) 34��'�.�0 (%) 34��'�.�0 (%) nb k-nn c4.5 svm nb k-nn c4.5 svm ms12-23945 9.3 9.1 9.4 9.3 9.9 7.6 1.7 1.4 1.8 1.7 2.2 ms13-11663 5.0 5.0 5.1 5.0 5.4 3.5 1.5 1.5 1.7 1.5 2.0 ms13-12414 15.4 14.0 15.6 15.3 16.3 14.1 1.3 0.0 1.6 1.3 2.3 ms13-18536 11.3 11.0 11.4 11.3 11.8 10.6 0.6 0.4 0.8 0.7 1.1 ms13-9453 25.8 25.7 25.7 26.0 27.4 24.1 1.6 1.5 1.5 1.8 3.3 ms13-9925 25.0 24.5 25.5 25.1 25.9 24.0 1.0 0.6 1.6 1.1 1.9 ms14-10783 14.8 14.6 15.1 14.9 15.8 16.1 1.4 1.5 1.0 1.2 0.3 ms14-10801 9.0 9.3 9.7 9.0 10.0 9.8 0.8 0.5 0.1 0.8 0.2 ms14-11933 6.7 6.8 6.9 6.7 7.2 3.8 3.0 3.0 3.1 2.9 3.5 ms14-13040 12.3 12.1 12.4 12.3 12.8 12.6 0.4 0.5 0.2 0.3 0.2 ms14-1559 23.3 22.6 23.4 23.4 24.3 26.9 3.5 4.2 3.5 3.4 2.5 ms14-2449 12.0 11.3 12.4 12.2 13.0 14.7 2.7 3.4 0.2 2.5 1.7 ms14-2451 14.9 14.3 15.0 14.9 15.2 14.0 0.9 0.3 3.5 0.9 1.2 ms14-3215 12.6 11.5 13.5 12.4 14.3 10.8 1.7 0.7 0.2 1.6 3.5 ms14-3686 4.4 4.4 4.4 4.4 4.6 2.3 2.1 2.1 3.5 2.2 2.3 ms14-3854 23.6 22.6 25.1 24.0 27.2 24.3 0.7 1.7 0.2 0.3 2.9 ms14-5561 5.9 5.8 6.3 6.0 6.8 4.5 1.4 1.3 3.5 1.5 2.3 ms14-6402 14.6 14.2 14.8 14.7 15.2 13.4 1.2 3.4 1.4 1.3 1.8 ms14-786 28.0 27.6 28.5 28.3 29.3 32.5 4.5 0.3 4.0 4.2 3.2 ms14-8355 41.1 39.5 40.7 40.9 42.3 44.5 3.4 0.8 3.8 3.6 2.2 ms14-9198 11.8 11.8 12.0 11.8 12.2 7.1 4.7 4.9 4.9 4.7 5.1 ms14-9711 29.1 28.3 30.1 29.4 32.2 29.8 0.7 5.0 0.3 0.4 2.4 ms15-1128 15.6 15.7 16.1 15.8 16.5 19.3 3.7 4.7 3.2 3.5 2.8 ms15-2103 4.8 4.4 4.9 4.7 5.1 2.8 2.0 1.5 2.1 2.0 2.3 ms15-2670 29.5 28.7 29.7 29.6 31.0 29.6 0.1 3.6 0.1 0.0 1.4 ms15-805 11.8 11.6 11.9 11.6 12.3 9.1 2.7 1.6 2.8 2.5 3.2 ms15-991 18.7 18.8 20.4 19.3 22.7 15.6 3.1 0.9 4.8 3.7 7.1 mean value: 16.2 15.8 16.5 16.2 17.3 15.8 1.9 2.0 2.0 1.9 2.4 std: 9.17 8.91 9.22 9.22 9.69 10.57 1.25 1.51 1.37 1.29 1.45 it is important to emphasize the improvement of diagnostic accuracy of the method, initially with the mean absolute error between the doctors and the diagnosis coming from each trained classifier (aerror(1)), and then to compare it with the mean absolute error originating from the doctors’ estimation and the segmentation method without the classification stage (aerror(2)). according to the results, it is noted that the trained classifiers present a diagnostic reliability in the majority of ×20 testing samples reducing the absolute error rate up to 0.5%, as opposed to the one of segmentation and equal to 2.4%. specifically, a total mean value of the absolute error of 1.95% is performed, using the pre-trained classification step algorithms. the percentage error results are also presented in figure 7, using bars, emphasizing to the reliability of the engineering, technology & applied science research vol. 8, no. 6, 2018, 3550-3555 3555 www.etasr.com arjmand and giannakeas: fat quantitation in liver biopsies using a pretrained classification … proposed for the methodology classifiers, compared to the segmentation stage prior to the hepatic structures identification. due to the above agglomeration phenomenon and based on table ii, the method shows a reduction in performance in 6 images (ms14-10783, ms14-1559, ms14-2449, ms14-786, ms14-8355 and ms15-1128). however, in most of the cases (21 biopsies) it achieves an optimal performance. through this observation, current outcomes are sufficient for pathologists, in comparison to semi-quantitative methods and tend to keep up with similar fat region classification performances in a previous study [19]. fig. 7. graphical represenation of methodology’s classification error iv. conclussions in this study, a pretrained method for various annotated liver tissue findings is presented, employing image processing and machine learning techniques. according to the overall performance, it is concluded that the classification stage improves the reliability of the results, for a number of biopsies. the main advantage of the method lies in the fact that the biopsy structures are discerned by a series of histological features including shape, magnitude, pixel intensity and texture. based on this inclusion, it is shown that the trained classifiers can detect main differences between circular balloon cells and fat droplets in nafld patients. at the present time, ballooning degeneration is at the heart of the clinical interest among research pathologists, as its assessment emerges as a critical factor in chronic liver diseases. thus, the proposed work could be also considered as a follow-up of a previous study [20] for ballooned cell identification and ballooning degeneration quantification. references [1] r. s. o’shea, s. dasarathy, a. j. mccullough, “alcoholic liver disease”, the american journal of gastroenterology, vol. 105, no.1, pp. 14-32, 2010 [2] j. w. ward, “viral hepatitis and liver cancer”, u.s. department of health and human services, services centers for disease control and prevention, 2016 [3] a. m. zaitoun, h. a. mardini, s. awad, s. ukabam, s. makadisi, c. record, “quantitative assessment of fibrosis and steatosis in liver biopsies from patients with chronic hepatitis c”, journal of clinical pathology, vol. 54, no. 6, pp. 461-465, 2001 [4] h. marsman, t. matsushita, r. dierkhising, w. kremers, c. rosen, l. burgart, s. l. nyberg, “assessment of donor liver steatosis: pathologist or automated software”, human pathology, vol. 35, no. 4, pp. 430-435, 2004 [5] v. roullier, c. cavaro-menard, c. guillaume, c. aube, “fuzzy algorithms to extract vacuoles of steatosis on liver histological color images”, 29th annual international conference of the ieee engineering in medicine and biology society, france, august 22-26, 2007 [6] b. turlin, g. a. ramn, d. m. purdie, f. laine, m. perrin, y. deugnier, g. a. macdonald, “assessment of hepatic steatosis: comparison of quantitative and semiquantitative methods in 108 liver biopsies”, liver international, vol. 29, no. 4, pp. 530-535, 2009 [7] g. e. liquori, g. calamita, d. cascella, m. mastrodonato, p. portincasa, d. ferri, “an innovative methodology for the automated morphometric and quantitative estimation of liver steatosis”, histology and histopathology, vol. 24, no. 1, pp. 49-60, 2009 [8] a. m. el-badry, s. breitenstein, w. jochum, k. washington, v. paradis, l. rubbia-brandt, m. a. puhan, k. slankamenac, r. graf, p. a. clavien, “assessment of hepatic steatosis by expert pathologists: the end of a gold standard”, annals of surgery, vol. 250, no. 5, pp. 691-697, 2009 [9] j. kong, m. j. lee, p. bagci, p. sharma, d. martin, n. v. adsay, j. h. saltz, a. b. farris, “computer-based image analysis of liver steatosis with large scale microscopy imagery and correlation with magnetic resonance imaging lipid analysis”, ieee international conference on bioinformatics and biomedicine, usa, november 12-15, 2011 [10] n. i. nativ, a. i. chen, g. yarmush, s. d. henry, j. h. lefkowitch, k. m. klein, t. j. maguire, r. schloss, j. v. guarrera, f. berthiaume, m. l. yarmush, “automated image analysis method for detecting and quantifying macrovesicular steatosis in hematoxylin and eosin-stained histology images of human livers”, liver transplantation, vol. 20, no. 2, pp. 228-236, 2014 [11] s. vanderbeck, j. bockhorst, r. komorowski, d. e. kleiner, s. gawrieh, “automatic classification of white regions in liver biopsies by supervised machine learning”, human pathology, vol. 45, no. 4, pp. 785-792, 2014 [12] m. sciarabba, m. vertemati, c. moscheni, m. cossa, l. vizzotto, “automated lipid droplets recognition in human steatotic liver: some preliminary results”, in proceedings of the medical image understanding and analysis conference, london, uk, pp. 20-24, 2015 [13] n. batool, “detection and spatial analysis of hepatic steatosis in histopathology images using sparse linear models”, sixth international conference on image processing theory, tools and applications, oulu, finland, december 12-15, 2016 [14] b. jahne, digital image processing, 5th revised and extended edition, springer science & business media, 2002 [15] t. dietterich, c. bishop, d. heckerman, m. jordan, m. kearns, introduction to machine learning, second edition, ethem alpaydin, the mit press, 2010 [16] k. p. murphy, machine learning: a probabilistic perspective, adaptive computation and machine learning, the mit press, 2012 [17] p. cunningham, s. j. delany, “k-nearest neighbour classifiers”, technical report ucd-csi-2007-4, 2007 [18] m. mohri, a. rostamizadeh, a. talwalkar, foundations of machine learning, the mit press, 2012 [19] n. giannakeas, m. g. tsipouras, a. t. tzallas, m. g. vavva, m. tsiplakidou, e. c. karvounis, r. forlano, p. manousou, “measuring steatosis in liver biopsies using machine learning and morphological imaging”, 30th ieee international symposium on computer-based medical systems, thessaloniki, greece, june 22-24, 2017 [20] a. arjmand, at. tzallas, m. g. tsipouras, r. forlano, p. manousou, n. ketertsidis, n. giannakeas, “fat droplet identification in liver biopsies using supervised learning techniques”, proceedings of pervasive technologies related to assistive environments, corfu, greece, june 26-29, 2018 engineering, technology & applied science research vol. 8, no. 1, 2018, 2520-2525 2520 www.etasr.com soomro et al.: 3d numerical analysis of the effects of an advancing tunnel on an existing loaded … 3d numerical analysis of the effects of an advancing tunnel on an existing loaded pile group mukhtiar ali soomro department of civil engineering, quaid-e-awam university of engineering, science & technology nawabshah, pakistan eng.soomro@gmail.com daddan khan bangwar department of civil engineering, quaid-e-awam university of engineering, science & technology nawabshah, pakistan skb_khan2000@yahoo.com mohsin ali soomro department of civil engineering, quaid-e-awam university of engineering, science & technology nawabshah, pakistan drmohsin@quest.edu.pk manthar ali keerio department of civil engineering, quaid-e-awam university of engineering, science & technology larkana, pakistan mantharali99@quest.edu.pk abstract—tunnels are often preferred for underground transportation in densely populated areas. in these areas, it is almost inevitable for tunnels to run close to some existing pile foundations. since tunnelling activities induce stress relief and soil movement in the ground, existing piles may suffer from additional axial and lateral forces, bending moments, settlements and lateral deflections. most of the previous researches on the responses of pile foundations due to tunnel construction were carried out under the plane strain condition. in this paper, a three-dimensional, elasto-plastic and coupled-consolidation finite element parametric study has been carried out to investigate the effects of a 6 m open-face advancing tunnel on a two by two pile group in saturated stiff clay. the influence of different cover-todiameter (c/d) tunnel ratios (namely 2.0, 2.5 & 3.0) was studied. the objectives of this study are to determine the changes in axial load distribution, changes in shaft resistance along the shaft of pile group and settlement of pile cap due to an advancing openface tunnel. keywords-finite element analysis; open face tunnelling; settlement of pile cap i. introduction a piled foundation transfers the load of the structure into the ground, generating stresses in the surrounding soil. in contrast, tunnel excavation induces stress relief to the surrounding soil and results in ground movements around the tunnel, which propagate through the soil to the ground surface. nowadays, tunnelling is a very popular technique to facilitate congested urban traffic systems in big cities like london, hong kong and singapore. since tunnel construction inevitably induces soil movement and stress changes in the ground, it may cause additional settlement and tilting to nearby existing piled foundations. tunnelling remains a big challenge for geotechnical engineers, particularly when a tunnel is to be excavated in soft ground. to understand the pile–soil–tunnel interaction mechanism, many researchers have conducted field monitoring studies and centrifuge model tests [1-9]. moreover, this problem has also been studied by the proposing of analytical solutions and numerical modelling [10-19]. all authors in [10-19] concluded that tunneling adjacent to existing pile foundations caused pile settlement, additional axial load on piles and induced bending moments along piles, which is unfavourable for piled foundations. the magnitudes of which likely depended on the relative locations of tunnels and piles. authors in [20] described the effects of a 7.5 m tunnel excavated in stiff london clay on a bored piled foundation. the clear spacing between the springline of the tunnel and the nearest 1.2 m diameter pile was only 1 m. the measured horizontal pile and ground movements were similar. maximum horizontal displacement of 10 mm of the nearest pile to the tunnel was reported. authors in [21] reported the measured settlement of a building due to the excavation of a 7.9 m diameter tunnel in hong kong. the building was supported by 2 m diameter bored piles varying in length from 41 m to 64 m. the tunnel depth was above the level of the pile toe. maximum building settlement due to tunnel construction was recorded to be 12 mm. authors in [22] reported measured results of the effects of 6.5 m diameter shield tunneling on the adjacent piled foundations of bridge piers in singapore. the piers were supported by 2×2 pile group of 1.2 m diameter and 62 m long piles. the piles were embedded in completely weathered material (residual soil) with spt values varying from 15 to 100. the nearest tunnel-pile foundation distance was 1.6 m. tunnel depth was located at about the mid pile depth (i.e. 21 m).the maximum volume loss due to the tunnel excavation was reported as high as 1.5 %. the monitoring results showed that the piles were subjected to large dragload, and the maximum induced bending moment in the piles was at the tunnel springline due to the tunnel advancement. authors in [23] carried out a 3d elasto-palstic analysis to study the effects of a tunnel on a single pile and a 2×2 pile group pile group at different cover-to-tunnel-diameter (c/d) ratios. computed results showed that there was significant reduction of the induced axial force and bending moment on the pile furthest away from the tunnel (i.e., the rear pile) due to the group effect. engineering, technology & applied science research vol. 8, no. 1, 2018, 2520-2525 2521 www.etasr.com soomro et al.: 3d numerical analysis of the effects of an advancing tunnel on an existing loaded … however, the settlement, tilting of the pile group and the load transfer mechanism between piles was not reported [23]. in previous studies, researchers were mostly interested in the tunnelling-induced axial forces and bending moments in piles due to tunnel excavation. the load transfer within the piles of a group and the induced tilting due to the tunnel advancement has not been reported. besides this, the location of a tunnel relative to a pile foundation has not been studied systematically. with the prime objective of investigating the tunnel location effects relative to the piled foundation, 3d parametric coupled-consolidation finite element analyses were carried out at different cover-to-tunnel-diameter ratios (c/d = 1.5, 2.5 and 3.5). the effects of an advancing, open face, 6m diameter tunnel on a 2×2 pile group in stiff saturated clay were investigated. settlement, pile group tilting and load transfer among piles at various tunneling stages were studied and discussed. ii. 3d coupled-consolidation analyses a hypothetical tunnel excavation in a stiff, nonhomogeneous and over consolidated saturated clay is modeled. figure 1 shows tunnel geometry and pile group size and location relative to the tunnel. tunnel diameter (d) is taken as 6 m with different cover depths (c) of 12 m, 15 m and 18 m. a (2×2) pile group with 2.5 m center to center distance, 19 m length (1 m above ground surface) and each pile, with 0.8 m diameter, is located at a distance of 5.5 m from tunnel center line. for the ease of descriptions and discussion, p1 and p2 are referred as front and rear piles, respectively (see figure 1b). the purpose of this numerical study is to investigate the effect of tunneling on the nearby pile group at different c/d ratios, while keeping the pile group length unchanged. the finite element program, abaqus, was used to carry out these numerical analyses. a. finite element mesh and boundary conditions figure 2 shows a three-dimensional finite element mesh (soil, pile group and pile cap), adopted for all the numerical runs. taking advantage of symmetry, only the half of the domain is simulated at x=0. the finite element mesh is 60 m long, 60 m wide and 36 m high. this mesh consists of 12,276 elements and 15,331 nodes. the eight-noded brick elements, four-noded shell elements and two-noded beam elements are used to model the soil, lining and pile cap and pile group, respectively. a monitoring section is selected at pile group center line for reference. roller supports and pin supports are applied on vertical sides and mesh base respectively. therefore, the movement to normal direction of vertical sides of mesh and movement in all directions of mesh base are restrained. the water table is assumed to be located at ground surface. at the first step pore water pressure distribution profile is assumed to be hydrostatic. free drainage is allowed at the top of the mesh. tunnel lining is assumed to be impervious. b. constitutive models and model parameters an elasto-plastic soil model using drucker-prager failure criterion with non-associated flow rule is used to model the behaviour of stiff clay for these numerical analyses. the strength parameters effective cohesion (c’), effective angle of friction (’) and angle of dilation () for stiff clay are assumed as 5kpa, 200 and 110 respectively [12]. stiffness parameters for stiff clay are assumed as anisotropic and increase linearly with depth [1]. all the soil parameters used for the numerical analyses are summarized in table 1. the concrete piles, cap and tunnel lining are assumed to be linear elastic with young’s modulus of 35 gpa and poisson’s ratio as 0.25. lining thickness and pile cap are taken as 0.25m and 1m respectively. the unit weight of concrete is assumed 24 kn/m3. piles are assumed to be rigidly connected with cap. (a) sectional view d ire ct io n of tu nn el e xc av at io n p3p4 p2 p1 monitoring section (b) plan view fig. 1. geometry of problem studied fig. 2. three-dimensional finite element mesh engineering, technology & applied science research vol. 8, no. 1, 2018, 2520-2525 2522 www.etasr.com soomro et al.: 3d numerical analysis of the effects of an advancing tunnel on an existing loaded … table i. soil parameters used in finite element analyses. soil parameter dry density (d) 1500 kg/m3 void ratio (i) 1.0 vertical effective young’s modulus (e'v) 7500+3900z kpa horizontal effective young’s modulus (e'h) 12000+6240z kpa shear modulus in vertical plane (gvh) 0.44e'v kpa n= e'h/e'v 1.6 poisson’s ratio () 0.125 coefficient of permeability (k) 110-9 m/s effective cohesion (c') 5 kpa effective angle of friction (') 220 angle of dilation () 110 coefficient of lateral earth pressure at rest (k0) 1.0 c. numerical modeling procedure two separate numerical runs were carried out on two different finite element meshes. the first numerical run was conducted to determine the ultimate axial load carrying capacity of pile group and the second numerical run was conducted to determine the effects on pile group. the numerical modeling procedure steps are summarized as follows: 1. establish the initial stress condition using k0=1.0. 2. determine the axial load carrying capacity of wished-inplace pile group from numerical load test by conducting first numerical run. 3. then create another mesh with same initial stress condition as in step 1. carry out second numerical run after applying working load, computed from first numerical run, on pile group with fos=3 at initial stress condition. 4. allow the excess pore pressure to dissipate, developed in response of working load on pile group. 5. then start to excavate tunnel with 3m (d/2) unsupported length. 6. apply the 250 mm thick lining to exposed surface of tunnel. 7. advance the tunnel excavation, repeating the same procedure until the tunnel is completed. an open face tunnel sequential excavation was modeled in this study. tunnel excavation was simulated by deactivating the elements located in tunnel zone and tunnel lining was simulated by activating elements of lining. d. determination of pile group axial load capacity prior to tunnel excavation, it is desirable to determine pile group axial load carrying capacity. for this purpose, a numerical pile load test was carried out. in pile test, load was increased from 0 to 24,000 kn on the pile cap middle for over a period of 24 hours. figure 3 shows the load settlement curve obtained from the pile load test. the ultimate axial load capacity was determined based on new displacement-based failure criterion proposed in [10]. the failure criterion is expressed as follows: ,max 1 0.045 2 h p ph p p p p l d a e    (1) where ph = pile head load, lp= pile length, ep= pile shaft elastic modulus, ap= cross sectional area of pile and dp = pile diameter. as shown in figure 3, the ultimate load capacity of the simulated pile group was determined to be 21,210 kn. with a factor of safety 3.0, a working load of 7,070 kn was applied on the mid of pile cap. an initial pile cap settlement of 6.5 mm (0.8% dp) was calculated due to applied working load. the excess pore pressure, generated due to working load prior to tunnel excavation, was allowed to fully dissipate. 0 5000 10000 15000 20000 25000 30000 0 10 20 30 40 50 60 70 settlement (mm) l oa d (k n ) failure criterion by ng et al. 2001 working load (7070 kn) equivalent pile load due to tunneling (13400 kn) fig. 3. load settlement curve of simulated pile group load test iii. computed results in this section, computed results are presented. from the computed data, it was observed that the most critical moment is when tunnel face aligns with the pile group center line (monitoring section). however, there are not any significant changes in surface settlement as tunnel face passes beyond the y/d3 from the monitoring section. therefore, it can be assumed that monitoring section attains the plane strain condition. a. transverse surface settlement trough figure 4 shows the normalized immediate surface settlements (s), when tunnel face reached monitoring section (y/d=0) and at the plane strain condition, when tunnel face passed beyond monitoring section at a distance of y/d3, for all three cases. although the surface settlements were initially induced due to load applied on the pile group, only tunnellinginduced settlements are considered here. it can be seen that immediate settlement is less than settlement at plane strain condition. this occurs because of the dissipation of excessive pore water pressure, after the tunnel face has passed through monitoring section. the gaussian distribution curves [11] are fitted on the basis of smax and i (distance from tunnel center line to the curve inflexion point) at plane strain condition, computed from each numerical analysis. the calculated values of i, at engineering, technology & applied science research vol. 8, no. 1, 2018, 2520-2525 2523 www.etasr.com soomro et al.: 3d numerical analysis of the effects of an advancing tunnel on an existing loaded … plane strain condition are 9.9 m, 10.8 m and 11.7 m from tunnel center line for c/d = 2.0, 2.5 and 3.0, respectively. the computed maximum surface settlements at tunnel center line are 10.3 mm, 10 mm and 9 mm for c/d=2.0, 2.5 and 3.0 respectively. based on smax and i, it can be observed that with the increase of c/d ratio, maximum settlement decrease and settlement trough become wider. the volume loss associated due to tunnel excavation calculated on the basis of area of settlement trough is about 0.9% for each case. 0.00 0.05 0.10 0.15 0.20 0 2 4 6 8 10 x/d s/ d (% ) immediate settlement c/d=2.0 c/d=2.5 c/d=3.0 settlement at plane strain c/d=2.0 c/d=2.5 c/d=3.0 gaussian distribution c/d=2.0 c/d=2.5 c/d=3.0 fig. 4. transverse settlement at monitoring section due to tunnelling b. pile group settlement due to tunnel advancement figure 5 shows the incremental settlement of pile group due to tunnelling for c/d=2.0, 2.5 and 3.0. it can be observed that as tunnel advances to monitoring section, excessive settlement occurs in the pile group. in the case of c/d=2.0, the pile group settlement due to tunneling is less than in the other cases. settlement profiles for the cases c/d=2.5 and c/d=3.0 are similar because the pile group base is subjected to stress release due to tunneling in both cases. the pile group settlements due to tunneling advancement are 5.6 mm for c/d=2.0 and 7.5 mm for both c/d=2.5 and c/d=3.0 at plane strain conditions (i.e. y/d3). this implies that total pile group settlement due to tunneling is 12 mm (1.5%dp) for c/d =2.0 and 14 mm (1.75%dp) for c/d=2.5 and c/d=3.0. since there is not much difference in total pile group settlement for all three cases, therefore from load settlement curve (figure 3), the load corresponding to 14 mm settlement is 13,400 kn. it can be considered that the pile group is subjected to an equivalent load of 13,400 kn after tunnel passes beyond monitoring section, which reduces the factor of safety from 3.0 to 1.6 in each case. c. changes in unit shaft friction along the length of pile p1 and pile p2 due to tunnelling. figure 6 shows the changes in the unit shaft friction along the shafts of both p1 and p2, when tunnel face is at monitoring section (i.e. y/d=0). the unit shaft friction reduces significantly in p1 at the upper part of the shaft (i.e.0z/d2.5), when tunnel is located at c/d=2.0. it indicates the reduction in shaft resistance because of the stress release around p1 due to tunneling. the maximum reduction of 35 kpa in unit shaft friction of p1 is observed at the tunnel crown (i.e. z/d=2.0). however, the unit shaft friction increases along the lower part of p1 below tunnel horizontal axis (z/d2.5). as a result, base load of p1 is increased. unit shaft friction also reduces along the upper part of shaft of p2 (i.e. z/d2.25). the increment in unit shaft friction at the lower part of shaft of p2 shows that base load is mobilized. it is clear that most of the load has transferred to the pile group base in case of c/d=2.0. when the tunnel is located at c/d=2.5, unit shaft friction increases along the upper part of the shaft (i.e. z/d 1.4) of p1. however, the unit shaft friction near the base of p1 is reduced. it implies that no significant base load is mobilized which is discussed below. however, the negligible reduction in unit shaft friction is observed along the shaft of p2 except for the lower part of the shaft. it suggests that both shaft friction and base load of p2, support the additional load transferred from p1. it can be observed that unit shaft friction increases along the upper part of the shaft (z/d2.25) of p1 in the case of c/d=3.0. however, unit shaft friction reduces significantly at the lower part of p1 (i.e. z/d>2.25). this shows that the base load of p1 reduces significantly. the maximum reduction of 44 kpa in unit shaft friction occurs at tunnel crown (z/d=3.0). however, unit shaft friction along the upper part of the shaft of p2 (0z/d2.5) almost remained unchanged. the shaft resistance increases at the lower part (z/d2.5) of p2. it suggests that the load is shared by both shaft resistances and the pile base. most of the load in p1 is supported by shaft resistance after tunnel face passes through monitoring section in the case of c/d=3.0. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 -5 -4 -3 -2 -1 0 1 2 3 4 5 y/d  /d p (% ) c/d=2.0 c/d=2.5 c/d=3.0 0.0 1.0 fig. 5. pile cap settlement due to tunnel advancement unit shaft friction is decreased significantly in p1 and p2 above the tunnel crown, when tunnel is located at c/d=2.0. as a result, base load of p1 is increased and pile head load is significantly decreased. pile head load and base load of p2 increased substantially. it is clear that some part of the load is transferred to the base of p1 and some part of the load is transferred to p2. the head load of p1 reduced by 8%, whereas the head load of p2 increased by 7%. the base load of both piles p1 and p2 increases by 60% and 32%, respectively. in the case of c/d=2.5, tunnel horizontal axis is at the pile group base (i.e. z/d=3.0). therefore, almost negligible change is observed engineering, technology & applied science research vol. 8, no. 1, 2018, 2520-2525 2524 www.etasr.com soomro et al.: 3d numerical analysis of the effects of an advancing tunnel on an existing loaded … in the base of both piles. due to load transfer mechanism in pile group, the load transfers from p1 to p2. the reduction in pile head load is 10% and pile head load of p2 increased 10% of total load on each pile. the base load of p2 is mobilized to take additional vertical load, transferred from p1, to maintain vertical equilibrium. the base load of p1 and p2 increased 13% and 30%, respectively. when the tunnel is located at c/d=3.0, almost no change of shaft friction is observed along the shaft of p1. however, base load of p1 reduces significantly. it is because the tunnel crown is located at the pile base (i.e. z/d=2.5). to establish vertical equilibrium, the load transfers from p1 to p2. as a result of this, base load of p2 is mobilized to carry the additional load transferred from p1. the head and base load of p1 reduce 7% and 35% respectively. the head and base load of pile p2 increase 7% and 11%, respectively. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 -50 -40 -30 -20 -10 0 10 20 30 40 50 changes in unit shaft friction (kpa) z/ d pile p1 pile p2 c/d=2.0 c/d=2.0 c/d=2.5 c/d=2.5 c/d=3.0 c/d=3.0 tunnel crown (c/d=2.0) tunnel crown (c/d=2.5) tunnel crown (c/d=3.0) fig. 6. changes in unit shaft friction due to tunnelling 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 axial load (kn) z/ d at working load pile p1 c/d=2.0 c/d=2.5 c/d=3.0 pile p2 c/d=2.0 c/d=2.5 c/d=3.0 fig. 7. axial load changes in p1 and p2 due to tunnelling iv. conclusions computed results make clear that surface settlement troughs at monitoring sections follow gaussian distribution curve very well for all three cases. when the tunnel is excavated at c/d=2.0, it causes the reduction of shaft resistance in both the front (p1) and rear (p2) piles and load transfers from front pile to rear pile. this leads to an increase in base load by 60% and 32% in the front and rear piles, respectively. when tunnel is constructed at c/d=2.5, the shaft resistance and base load of front pile reduces significantly. consequently, the load transfers from the front (p1) to the rear (p2) pile. the base load as well as shaft resistance of the rear pile is mobilized to support additional vertical load, transferred from the front pile to maintain equilibrium. each base load of front and rear piles increases by 13% and 30%, respectively. when tunnel is excavated at c/d=3.0 (i.e. the tunnel crown is located at pile base), the excavation causes the reduction of 35% in the base load of front pile (p1) and leads to load transfer from the front to the rear piles. this results in an increase of base load of rear pile (p2) by 11%. the maximum reduction of 35 kpa, 40 kpa and 44 kpa in unit shaft friction is observed near tunnel crown in case of c/d=2.0, 2.5 and 3.0, respectively. due to the additional settlement of pile group resulting from tunnelling, it can be deduced that the pile group is subjected to an additional equivalent load of 13,400kn. this means that the factor of safety for pile group is reduced from 3.0 to 1.6 in each case. references [1] a. bezuijen, j. s. van der schrier, “the influence of a bored tunnel on pile foundations”, centrifuge’94, pp. 681-686, 1994 [2] t. boonyarak, k. phisitkul, c. w. w. ng, w. teparaksa, z. z. aye, “observed ground and pile group responses due to tunneling in bangkok stiff clay”, canadian geotechnical journal, vol. 51, no.5, pp. 479-495, 2014 [3] s. w. jacobsz, j. r. standing, r. j. mair, t. hahiwara, t. suiyama, “centrifuge modeling of tunneling near driven piles”, soil and foundations, vol. 44, no. 1, pp. 49-56, 2004 [4] c. j. lee, k. h. chiang, “responses of single piles to tunneling-induced soil movements in sandy ground”, canadian geotechnical journal, vol. 44, no.10, pp. 1224-1241, 2007 [5] a. m. marshall, r. j. mair, “tunneling beneath driven or jacked endbearing piles in sand”, canadian geotechnical journal, vol. 48, no.12, pp.1757-1771, 2011 [6] c. w. w. ng, h. lu, “effects of construction sequence of twin tunneling at different depth on a single pile”, canadian geotechnical journal, vol. 51, pp. 173-183, 2013 [7] c. w. w. ng, h. lu, s. y. peng, “three-dimensional centrifuge modeling of effects of twin tunneling on as existing pile”, tunneling and underground space technology, vol. 35, pp. 189-199, 2013 [8] c. w. w. ng, m. a. soomro, y. hong, “three-dimensional centrifuge modelling of pile group responses to side-by-side twin tunnelling”, tunnelling and underground space technology , vol. 43, pp.350-361, 2014 [9] c. w. w. ng, y. hong, m. a. soomro, “effects of piggyback twin tunnelling on a pile group: 3d centrifuge tests and numerical modelling”, geotechnique , vol. 65, no. 1, pp. 38-51, 2015 [10] l. t. chen, h. g. poulos, n. loganathan, “pile responses caused by tunneling”, journal of geotechnical and geoenvironmental engineering, vol. 125, no. 3, pp. 207-215, 1999 [11] c. y. cheng, g. r. dasari, y. k. chow, c. f. leung, “finite element analysis of tunnel-soil-pile interaction using displacement controlled model”, tunneling and underground space technology, vol. 22, pp. 450–466, 2007 [12] m. huang, c. zhang, z. li, “a simplified analysis method for the influence of tunneling on grouped piles”, tunneling and underground space technology, vol. 24, pp. 410–422, 2009 engineering, technology & applied science research vol. 8, no. 1, 2018, 2520-2525 2525 www.etasr.com soomro et al.: 3d numerical analysis of the effects of an advancing tunnel on an existing loaded … [13] y. hong, m. a. soomro, c. w. w. ng, “settlement and load transfer mechanism of pile group due to side-by-side twin tunnelling”, computers and geotechnics, vol. 64, pp.105-119, 2015 [14] c. j. lee, “numerical analysis of the interface shear transfer mechanism of a single pile to tunnelling in weathered residual soil”, computers and geotechnics, vol. 42, pp.193-203, 2012 [15] c. j. lee, “three-dimensional numerical analyses of the response of a single pile and pile groups to tunnelling in weak weathered rock”, tunnelling and underground space technology, vol. 32, pp.132–142, 2012 [16] c. j. lee, “numerical analysis of pile response to open face tunnelling in stiff clay”, computers and geotechnics, vol. 42, pp. 116-127, 2013 [17] a. m. marshall, “tunnel-pile interaction analysis using cavity expansion methods”, journal of geotechnical and geoenvironmental engineering, vol. 138, no. 10, pp.1237-1246, 2012 [18] h. mroueh, i. shahrour, “three-dimensional finite element analysis of the interaction between tunnelling and pile foundations”, international journal for numerical and analytical methods in geomechanics, vol. 26, no. 3, pp. 217-230, 2002 [19] g. t. k. lee, c. w. w. ng, “the effects of advancing open face tunneling on an existing loaded pile”, journal of geotechnical and geoenvironmental engineering, vol. 131, no. 2, pp.193–201, 2005 [20] r. j. mair, r. n. taylor, “bored tunneling in the urban environment”, 14th international conference on soil mechanics and foundation engineering, balkema, vol.4, pp.2353-2385, 1997 [21] r. a, forth, c. b. b, thorley, “hong kong island line predictions and performance”, international symposium on geotechnical aspects of underground construction in ground, balkema, pp. 677–682, 1996 [22] d. r. coutts, j. wang, “monitoring of reinforced concrete piles under horizontal and vertical loads”, international conference on tunnels and underground structures, pp. 541–546, 2000 [23] k. w. d. tang, “numerical studies of multiple natm tunnel interaction in soft ground”, msc thsis, the hong kong university. of science and technology, hong kong, 2001 [24] j. b. burland, j. c. kalra, “queen elizabeth ii conference center: geotechnical aspects”, proceedings of the institution of civil engineers, vol. 80, no. 6, pp. 1479–1503, 1986 [25] c. w. w. ng, t. l. y. yau, j. h. m. li, w. h. tang, “new failure load criterion for large diameter bored piles in weathered geomaterials”, journal of geotechnical and geoenvironmental engineering, vol. 127, no. 6, pp. 488-498, 2001 [26] r. b. peck, “deep excavations and tunnelling in soft ground”, 7th international conferenve smfe, state of the art, vol. 3, pp. 225-290, 1969 soil mechanics, mexico, pp. 225–290, 1969 microsoft word etasr_v11_n2_pp6864-6868 engineering, technology & applied science research vol. 11, no. 2, 2021, 6864-6868 6864 www.etasr.com hussain et al.: complexity and limitations of gnss signal reception in highly obstructed enviroments complexity and limitations of gnss signal reception in highly obstructed enviroments arif hussain department of electrical engineering sukkur iba university sukkur, pakistan arif.hussain@iba-suk.edu.pk faheem akhtar department of computer science sukkur iba university sukkur, pakistan fahim.akhtar@iba-suk.edu.pk zahid hussain khand department of computer science sukkur iba university sukkur, pakistan zahid@iba-suk.edu.pk asif rajput department of computer science sukkur iba university sukkur, pakistan asif.ali@iba-suk.edu.pk zeeshan shaukat faculty of information technology beijing university of technology beijing, china wakeupzee@yahoo.com abstract-multipath (mp) and/or non line-of-sight (nlos) reception remains a potential vulnerability to satellite-based positioning and navigation systems in high multipath environments, such as an urban canyon. in such an environment, satellite signals are reflected, scattered or faded, and sometimes completely blocked by roofs and walls of high-rise buildings, flyover bridges, complex road structures, etc. making positioning and navigation information inaccurate, unreliable, and largely unavailable. the magnitude of the positioning error depends on the satellite visibility, geometric distribution of satellites in the sky, and received signal quality and characteristics. the quality of the received signal (i.e. its statistical characteristics) can significantly vary in different environments and these variations can reflect in signal strength or power, range measurements (i.e. path delay and phase difference), and frequency, all of which distort the correlation curve between the received signal and receiver-generated replicas, resulting in range errors of tens of meters. therefore, in order to meet stringent requirements defined for the standard positioning service (sps), the characterization of distortions that could significantly affect a global navigation satellite system (gnss) signal is essentially important. the scope of this paper is to detect possible imperfections/deviations in the gnss signal characteristics that can occur due to mp or nlos reception and analyze its effects. for this purpose, analysis of fading patterns in received signal strength (i.e. carrier-to-noise ratio and strength fluctuations) is carried out in both clear los and high mp environment and then its impact on satellite lock state (i.e. tracking) is assessed. furthermore, phase fluctuations and range residuals are computed to analyze the effects of path delays. the results show that significant variations can occur in gnss signal characteristics in the mp environment that may result in loss of lock event and inaccurate/faulty range measurements. keywords-blockage; availability; continuity; nlos; accuracy i. introduction satellite-based navigation systems (i.e. gnss/gps) are providing accurate and reliable positioning, navigation, and timing (pnt) services to hundreds of civilian and military applications across the globe. some of these include road, rail, and aerial transport, precision agriculture, electric power grids, stock exchange systems, autonomous navigation, intelligent transportation systems (its), etc. [1, 2]. although gnss is now widely used and providing pnt services with an acceptable level of accuracy in clear open-sky views, the precise positioning and navigation is quite a challenging task in urban canyons. in such an environment, the satellite signals are reflected, scattered, fluctuated (i.e. amplitude and phase) and sometimes completely blocked by roofs and walls of high-rise buildings, fly-over bridges and complex road scenarios, making positioning information inaccurate, unreliable and largely unavailable [3]. specifically, obstructions in urban canyons can affect the availability and accuracy of gnss based positioning and navigation services in two ways. at first, they can completely block signals from line-of-sight (los) satellites resulting in a reduced number of visible satellites. secondly, they can give rise to a phenomenon commonly known as multipath (mp) that results in biased range measurements. mp refers to the combination of los and a number of nlos signal corresponding author: faheem akhtar engineering, technology & applied science research vol. 11, no. 2, 2021, 6864-6868 6865 www.etasr.com hussain et al.: complexity and limitations of gnss signal reception in highly obstructed enviroments components reflected off nearby obstacles one or more times before reaching the receiver [2]. the mp effects when severe, can significantly affect the quality of the received signal (i.e. statistical characteristics) and thus result in poor positioning performance of the gnss receiver. in order to ensure that a receiver in a field has achieved the required navigation performance (rnp) threshold, precise analysis of signal characteristics and noise residuals is essentially important [4] and mp/nlos detection and error analysis under realistic conditions is often a necessary part of the receiver's performance assessment. the main contribution of this paper is the analysis of the performance of commercial grade gnss receivers in urban canyons by detecting the possible anomalies in the gnss signal reception and analyzing its impact. for this purpose, carefully planned field experiments were conducted on presurveyed candidates to acquire the actual gnss data. for a comprehensive analysis of multipath/nlos effects, five fundamental gnss signal parameters were investigated and compared. these parameters include carrier-to-noise ratio (cnr) and its variations, satellite lock time, phase fluctuations, and range residuals. furthermore, the fading patterns in cnr are analyzed in mp/nlos conditions and their impact on satellite lock state (i.e. tracking) is assessed. ii. gnss fundamentals and observation model the positioning and navigation problem considered in gnss is based on estimating the position of a receiver from signals sent by several satellites containing positioning and timing information. more precisely, by measuring the signal propagation time between a specific satellite and the ground receiver, the receiver is able to compute the distance or geometric range. gnss signals have very low power, and hence they are prone to several errors and biases. the geometric range measured by the receiver is contaminated by these errors or biases, which is why it is called the pseudorange [5, 6]. the general pseudorange observation [7] equation is given as: � � ��� � ���� �� � � � �� � �� ��� � (1) where, � represents the pseuodrange between the ��� satellite and the receiver (u), �� � ��� , �� , ���� is the satellite position available in navigation messages,�� � ��� , �� ,��� � represents the receiver position to be estimated, ‖�� � ��‖� � ���� � ���� ��� � ���� ��� � ���� is the true distance or actual geometric range between the satellite and the receiver, � and �� are the troposheric delay and ionospheric delay respectively, �� � � � �� is the error due to clock biases whereas � is the receiver's clock bias, � is the satellite's clock bias, represents the speed of light, ��� is the error factor due to mp/nlos reception, and � represents the receiver or measurement noise. iii. methodology in an urban area, gnss signals may arrive at the receiver not only through the direct (los) path, but also through several indirect paths due to the presence of different obstructions (high rise buildings, trees, bridges, etc.) in the way of the signal. the superposition of direct los and one or more indirect signals yields a compound signal (i.e. mp signal) [7]. the mp/nlos can affect the quality of the navigation signal in a number of ways, e.g. it can introduce random fluctuations in amplitude and phase of the received signal or it can result in biased range measurements. in this research, the detailed analysis of mp/nlos effects is carried out by investigating and comparing the five fundamental parameters of the gnss signal. these parameters include cnr, variations in cnr, satellite lock time, phase fluctuations, and range residuals as shown in figure 1. generally, the mp signal [8, 9] can be modeled as: �� � !" # cos�∅� !( # cos �∅ ∆∅� (2) where !" and !( indicate the amplitudes of direct (los) and reflected (nlos) signals respectively, ∅ denotes the phase and ∆∅ denotes the phase shift in the nlos signal [10, 11]. the amplitude composite signal ( �� ) and phase shift can be estimated as: !� � �!"� !(� 2!"�!(� +,∆∅ (3) ∆∅� � -. /-0 1 23456∆∅ 278239:4∆∅ ; (4) where ∆∅� and !� denote the phase shift and amplitude influence by the multipath (i.e. the composite signal). fig. 1. navigation signal analysis methodology. a. carrier-to-noise ratio cnr is the fundamental quality indication factor of any rf (i.e. gnss) signal and it represents the strength/power of the received signal. in gnss, the quality of the signal is directly linked with positioning and navigation accuracy. strong cnr values with minimal fluctuations result in better positioning performance [12, 13]. however in urban canyons, the cnr tends to be lower and fluctuates around the nominal asynchronously due to superposition of direct los and one or more nlos signals. the cnr can be estimated as: engineering, technology & applied science research vol. 11, no. 2, 2021, 6864-6868 6866 www.etasr.com hussain et al.: complexity and limitations of gnss signal reception in highly obstructed enviroments <=> � !"� !(� !?� 2!"�!(�!?� +,∆∅ (5) it is obvious that cnr can be significantly influenced by mp effects. the multipath can either be destructive or constructive depending upon the phase shifts. b. variations patterns in cnr as discussed above, in mp environment, the cnr may fluctuate asynchronously around the nominal. these fluctuations and their impact depend upon the severity of the mp effect. the variations in cnr can be estimated as: ∆<=> � @a#�bcdefg�h@a#�bcdeij� @a#�bcdefg�8@a#�bcdeij� (6) where <=>�kl and <=>�56 are the maximum and minimum cnr values of the received signal respectively. c. satellite lock state in a gnss receiver, the signals are initially acquired, tracked and then a navigation message is decoded to estimate the positioning solution. during the tracking stage, the receiver keeps track of the acquired satellite and maintains it in lock state. the mp/nlos reception can interrupt the signal tracking due to the degraded signal quality and may result in the loss of lock events. the loss of lock interrupts the connection between the satellite and the receiver leading to non-visibility of the satellite even if the satellite is present at the particular time and place. the duration and occurrence of loss of lock events depends upon the strength of the signals. lower cnr values and/or significant cnr variations may result in frequent loss of locks. d. phase deviations according to (4), mp signal can introduce phase shifts in the received signal which ultimately contaminates the range measurements. these shifts/variations in phase can be quantified by computing the standard deviation of phase over a certain interval (60s). in mp free environment, these variations are observed to be negligible. e. range residuals pseudorange represents the distance between the satellite and the ground receiver, measured by the estimation of the propagation time of the satellite signal. the propagation time can be affected by several factors like the ionospheric delay, the tropospheric delay, clock biases, and longer travel time due to mp/nlos resulting in extended pseudorange and thus inaccurate and unreliable positioning solution. mp/nlos remains an unmodeled and major source of error due to its nondeterministic nature, while other effects can be compensated or modeled. the mp error in the pseudorange can be quantified by range residuals. the range residuals are simply the change in pseudorange from one epoch to the next. in case of a static receiver, the range residuals remain almost zero for direct los signals, however this may not be the case in mp environment [14]. iv. field experiments and data collection in order to precisely investigate the complexity and limitation of gnss signal reception in real time, a carefully planned field experiment is conducted on a pre-surveyed candidate site to acquire and record (log) the gnss signals. the field experiment was performed in the sukkur iba university, pakistan. the site, as shown in figure 2, has a high degree of realism, being surrounded by buildings and dense tress. in such an environment, there are significant chances of mp and nlos receptions that can degrade the positioning and navigation accuracy. fig. 2. experimental site for gnss raw data/signal acquisition (google maps, © cnes / airbus, maxar technologies).. during the field experiment, real time gnss signals/data were logged by a septentrio polarx5s receiver connected to a polant choke ring b3/e6 antenna and the post processing was done in matlab. the setup is shown in figure 3. the septentrio polarx5s gnss receiver is multi–frequency, multi– constellation, capable of receiving 544 hardware channels to engineering, technology & applied science research vol. 11, no. 2, 2021, 6864-6868 6867 www.etasr.com hussain et al.: complexity and limitations of gnss signal reception in highly obstructed enviroments instantaneous track all satellites signals and can log data at 50hz. the septentrio receiver locked the gps (l1c/a, l1p, l2p, l2c, l5), glonass (l1, l2, l3) galileo (e1, e5ab, altboc, e6), beidou (b1, b2, b3), sbas (l1, l5), qzss (l1, l2, l5) signals [15]. the letters show the frequency bands related to each particular gnss system. it has the capability of logging real time gnss data for all frequencies. the polant choke ring antenna is a high precision wideband antenna that is compatible with the polarx group and has the capability of receiving all gnss signals [16]. fig. 3. experimental setup for capturing gnss data. v. results and discussion the precise positioning and navigation is highly dependent on the quality/characteristics of the gnss signal. the comprehensive analysis of gnss signal characteristics in nlos or multipath environment is presented in figures 4 and 5. this study is performed on actual gnss data acquired in mp environment in static mode and it is focused on identifying/showing the signal parameters affected by mp/nlos reception. figure 4 shows the fundamental signal characteristics (cnr, cnr variations in relationship with elevation angle and lock time) of one satellite prn 12 for an observation period of 5 hours (from 05:30 to 10:30 utc). based on the signal characteristics, the observation period is categorized into two segments: mp/nlos and los. figure 4(a) shows the cnr of the l1 and l2 signals. it is obvious that cnr is significantly influenced by the mp effect. under mp conditions, the acquired cnr is much lower (it drops to 30db) and significantly fluctuates between 30 and 40db even at good elevation angles (θ≥20). furthermore, the receiver is not able to acquire/track when the cnr drops below 30db. for better analysis of the severity of the nlos/mp effects on cnr of the received signal, the variations in the cnr are analyzed and quantified with respect to the elevation angle. figure 4(b) shows the cnr variations (∆cnr) in relationship with the elevation angle. due to the mp/nlos, significant variations in cnr even at higher elevation angles (20≤θ≤40) are observed. the results show that when the ∆cnr is greater than 0.3, there are significant chances of the loss of lock event. this can be seen in figure 4(c). in gnss, when a connection between the satellite and the receiver is established (i.e. the satellite is in tracking) then the satellite is in lock state. figure 4(c) shows that mp/nlos can interrupt the lock state of the satellite. it can be clearly seen that the lock state of the satellite is frequently interrupted when cnr variations are higher. frequent loss of locks may affect the continuity of gnss service and overburden the processing load because the receiver has to reinitiate the acquisition process. fig. 4. satellite signal characteristics in urban canyon. multipath (mp) signals are reflected by obstacles one or more times before reaching the gnss antenna. since we are estimating distances to the satellites, and that is the foundation of the positions in gnss, a signal that bounces from an obstruction before it reaches the gnss antenna causes a problem. if there is a bend in the signal, it will affect the range measurement. these effects can be analyzed by observing phase fluctuations/deviations and computing range residuals. figure 5 shows the range characteristics (phase deviations and range residuals) of the same satellite, and for the same observation period. it can be observed that mp/nlos obviously affects both parameters which are highly correlated with the signal characteristics presented in figure 4. when the mp effect is significant, it may cause rapid fluctuations in phase and/or results in large range residuals. the results show that during the window from 09:00 to 10:00, phase deviations up to 0.3 were observed along with range residual jumps to 20m. this may result in large positioning error. engineering, technology & applied science research vol. 11, no. 2, 2021, 6864-6868 6868 www.etasr.com hussain et al.: complexity and limitations of gnss signal reception in highly obstructed enviroments fig. 5. satellite range characteristics in urban canyon. vi. conclusion in this paper, the characteristics of gnss signal in both los and nlos conditions were investigated and compared. this study is focused in detecting possible imperfections/ deviations in the gnss signal characteristics that can occur due to mp or nlos reception only and analyze their effects. based on the comprehensive analysis of the fundamental characteristics of the signal, it is established that mp/nlos reception can significantly affect the quality of the received signal. the severe mp effects can result in frequent loss of locks and range errors of more than 10m. furthermore, the statistical characteristics of direct los signal significantly differ from the indirect nlos signal's. references [1] "gnss market report," eu gnss, jul. 03, 2012. https://www.gsa.europa.eu/market/market-report (accessed feb. 03, 2021). 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[12] p. xie and m. g. petovello, "measuring gnss multipath distributions in urban canyon environments," ieee transactions on instrumentation and measurement, vol. 64, no. 2, pp. 366–377, feb. 2015, https://doi.org/10.1109/tim.2014.2342452. [13] l. jordanova, l. laskov, and d. dobrev, "influence of bch and ldpc code parameters on the ber characteristic of satellite dvb channels," engineering, technology & applied science research, vol. 4, no. 1, pp. 591–595, feb. 2014, https://doi.org/10.48084/etasr.394. [14] t. suzuki, "mobile robot localization with gnss multipath detection using pseudorange residuals," advanced robotics, vol. 33, no. 12, pp. 602–613, jun. 2019, https://doi.org/10.1080/01691864.2019.1619622. [15] "polarx5s," septentrio. https://www.septentrio.com/en/products/gnssreceivers/reference-receivers/polarx5s (accessed feb. 03, 2021). [16] "polant choke ring b3/e6," septentrio. https://www.septentrio.com/en/ products/antennas/chokering-b3-e6 (accessed feb. 03, 2021). microsoft word etasr_v11_n3_pp7262-7272 engineering, technology & applied science research vol. 11, no. 3, 2021, 7262-7272 7262 www.etasr.com koklonis et al.: utilization of machine learning in supporting occupational safety and health … utilization of machine learning in supporting occupational safety and health decisions in hospital workplace kyriakos koklonis biomedical engineering laboratory national technical university of athens athens, greece kkoklonis@biomed.ntua.gr michail sarafidis biomedical engineering laboratory national technical university of athens athens, greece msarafidis@biomed.ntua.gr maria vastardi metaxa cancer hospital of piraeus piraeus, greece mariavastardi@yahoo.gr dimitrios koutsouris biomedical engineering laboratory national technical university of athens athens, greece dkoutsou@biomed.ntua.gr abstract-the prediction of possible future incidents or accidents and the efficiency assessment of the occupational safety and health (osh) interventions are essential for the effective protection of healthcare workers, as the occupational risks in their workplace are multiple and diverse. machine learning algorithms have been utilized for classifying post-incident and post-accident data into the following 5 classes of events: needlestick/cut, falling, incident, accident, and safety. 476 event reports from metaxa cancer hospital (greece), during 2014-2019, were used to train the machine learning models. the developed models showed high predictive performance, with area under the curve range 0.950-0.990 and average accuracy of 93% on the 10-fold cross set, compared to the safety engineer’s study reports. the proposed dss model can contribute to the prediction of incidents or accidents and efficiency evaluation of osh interventions. keywords-occupational health and safety; osh; machine learning; hospital workplace i. introduction occupational accidents and diseases result in an additional economic burden on public social security agencies. these losses are estimated at 3.9% of the global gross domestic product (gdp) and 3.3% of the european gdp, as it has been reported from the european agency for safety and health at work (eu-osha) (with variance according to working fields, legislative context and prevention incentives) [1]. according to the eu-osha, proper management of occupational safety and health (osh) leads to numerous benefits, such as reduced absenteeism, lessened costs and improved efficiency of working methods and technologies [2]. this necessity becomes even more imperative during periods of economic recession, since poor osh outlays valuable resources. particularly, regarding the healthcare sector, the hospital workplace is characterized by increased level and diversity of occupational risks. in addition, the coronavirus disease 2019 (covid-19) pandemic and its immediate aftermath pose a significant burden of workload and a major strain on mental health of healthcare workers [3]. health professionals constitute a significant part of the total european and greek workforce. according to a relevant study of the greek labor inspectorate body in 2015, 10% of workers in the european union (eu) belong to the healthcare sector [4]. more specifically, according to the hellenic statistical authority, the number of greek hospitals amounted up to 283 during the 2015-2018 period. moreover, their staff, during 2017, consisted of 38,952 nursing, 23,354 medical, 6,044 auxiliary nursing ,, and 7,752 paramedical staff [5]. in greek healthcare sector, a high percentage of work accidents (34% higher than the corresponding average in eu, according to the eu-osha) and an increased incidence of musculoskeletal disorders (second largest after construction sector) are recorded. according to the data from the hellenic statistical authority, in 2018, 3.2% of all work accidents that have been officially recorded are related to the health and social care sector [6]. concurrently, there is a dramatic public health funding reduction of up to 60% for the last three years [4]. computational intelligence and machine learning (ml) approaches can be utilized towards an improved management of osh. their potential in occupational accident analysis has been highlighted from several studies, as they have been reviewed in [7]. indicatively, statistical methods have been used for analyzing health and safety issues of women in industry [8], the osh risk in fuel stations has been assessed through failure mode and effects analysis (fmea) method corresponding author: kyriakos koklonis engineering, technology & applied science research vol. 11, no. 3, 2021, 7262-7272 7263 www.etasr.com koklonis et al.: utilization of machine learning in supporting occupational safety and health … [9], naive bayesian (nb) model has been used for coding causation of workers’ compensation claims [10], bayesian networks (bns) have been used for analyzing data on occupational accidents [11–13], and decision trees have been used in the industrial mining sector for predicting the type of accident [14]. artificial neural networks (anns) have been used to correlate causes and osh conditions [15–19] and they have been combined with support vector machines (svms) for the prediction of occupational accidents [20]. in addition, analytical hierarchical process (ahp) has been used in order to analyze, control, and provide the occupational risk in the industrial mining sector [21], and fuzzy logic has been used for occupational risk assessment [22]. the self-organizing map and k-means clustering (som k-means) methods have been used for identifying the dynamics of critical accidents [23]. in [24], body-mounted sensors were combined with ml techniques to evaluate the ergonomic risk levels caused by overexertion. the performance of ml algorithms in classifying post-incident outcomes of occupational injuries in agro-manufacturing operations has been evaluated in [25]. the minimization of the undesirable adverse effects in the development and implementation of ml-based decision support systems (dsss) was the objective in [26]. particularly in the healthcare sector, ml has been utilized for targeting specific hazards. for instance, anns have been used to approach the burnout process [27] and statistical analysis has been employed to identify factors of musculoskeletal disorders in nursing staff [28] and to improve the management of indoor air quality in the hospital workplace [29]. correlation methods have been used to assess the quality of work-life (qwl) for the nursing profession in china [30]. in a more generalized approach, a tool for estimating osh conditions through factor analysis has been evaluated in [31]. factor analysis has also been used for the assessment of workplace violence towards healthcare staff in public hospitals in turkey [32]. in addition, a fuzzy logic model for osh risk assessment has been proposed in [33] and a fuzzy cognitive map approach for the impact assessment of processes on the osh management system’s effectiveness has been used in [34]. ambulatory monitoring devices, such as wearable and environmental sensors, have been combined with ml algorithms for a better understanding of stress evolution in healthcare workers [35]. based on the previous concise literature review, there is a promising research activity in capitalizing ml methods for better implementing effective preventive measures and policies in the osh framework. most of the published studies are based on questionnaires to osh experts [12, 13, 36], instead of supporting immediate incident or accident investigations and following up the efficiency of the proposed interventions. to the best of our knowledge, a dss which utilizes the legally established safety engineer investigations and their audit reports has not been reported in the literature. the present study proposes a dss model which integrates all incident or accident data along with the safety engineer investigations and audit reports in the hospital workplace. through the input data utilization, our dss aims at supporting osh decisions by predicting future possible incidents or accidents and by assessing the efficiency of osh interventions. ii. materials and methods a. data in order to train and test the ml models, 476 event reports from metaxa cancer hospital (reference period from january 1, 2014 to december 31, 2019) were collected and utilized. the reports were categorized into 5 classes depending on the occurred events: 136 reports of "needlestick /cut" injuries, 59 reports of various "incidents", 20 reports of "falling" injuries, 23 reports of "accidents" and 238 reports of "safety" conditions. one event report consists of multiple variables derived from various reports, as detailed below. reports including undone corrective actions or incomplete data, during the reference period, were not included in the dataset. the worker population of the 476 records included nursing staff (52.52%), medical staff (13.45%), cleaning staff (10.50%), laboratory staff (9.24%), administrative staff (5.46%), technical staff and workers (4.62%), and auxiliary staff (4.20%). the mean age of the worker population of the records was 46.61 years and the mean experience was 16.98 years. our study has been approved by the scientific and administrative council of the metaxa hospital. under the regulation (eu) 2016/679 of the european parliament (general data protection regulation – gdpr) on the protection of natural persons [37], pseudonymization was used during the coding and data entry process. b. software waikato environment for knowledge analysis version 3.8.3 has been used for the data analysis and predictive modeling of the system [38]. this software has been chosen because of its wide applications in data mining and ml. moreover, it is freeware and publicly available under the general public license, it includes several data mining and ml methods, libraries, and relative supporting tools–procedures, it is compatible with other hardware or software platforms, and it includes a graphical user interface, making its usage easier even without programming knowledge. c. risk assessment method a very common risk assessment method is the one which is consistent with the memorandum on occupational risk assessment by directorate-general for employment in labor relations and social affairs (dg v) of the eu (1997) [39]. this methodology has also been recommended by the technical chamber of greece in a relevant conference [40]. in addition, it is widely used by safety engineers and osh auditors. this risk assessment method was used in the proposed model. its approach is based on defining a risk value as a product of three factors: the seriousness of the consequences of the potential hazard (values 1, 4, 8, 16), the frequency of exposure to the hazard (values 1, 2, 3, 4), and the probability of occurrence of this hazard (values 1, 2, 3, 4), according to the principle of reasonable ambiguity. therefore, the risk value (r) lies within the range of 1 to 256. the usage of these three factors is in accordance with relevant legal requirements according to greek law (law 3850/2010, article 43). these factors are presented in table i. the risk values and their correlation with the necessity of taking actions are presented in table ii. engineering, technology & applied science research vol. 11, no. 3, 2021, 7262-7272 7264 www.etasr.com koklonis et al.: utilization of machine learning in supporting occupational safety and health … table i. risk – rating factors factor rating interpretation seriousness 1 negligible minor injury without work absence 4 middle injury or disease with work absence 8 critical major injury or disease with the possibility of permanent health damage 16 disastrous death frequency 1 zero an employee is exposed to the hazard once a year or more rarely 2 limited an employee is exposed to the hazard up to once a week 3 often an employee is exposed to the hazard daily 4 continuous an employee is exposed to the hazard during his/her whole work time probability 1 zero impossible to happen 2 low it can happen 3 middle possible to happen 4 high about to happen table ii. risk rating risk value r risk description measures actions r<16 negligible: risk is very low and may not increase during the near future without changing working conditions measures – corrective actions are not necessary 16<r<32 low: risk is under control, but the incident is possible need for monitoring and actions for risk reduction. measures – corrective actions are not an urgent need 32<r<64 middle: risk is not effectively controlled. an incident cannot be excluded need for programming measures – corrective actions for risk reduction 64<r<128 high: risk is not effectively controlled. a serious incident is possible need for programming measures – corrective actions for risk elimination and urgent measures – corrective actions for risk reduction r>128 critical: possibility of human loss. a serious incident is about to happen need for urgent measures – corrective actions for risk elimination d. dss model information flow the osh related events are categorized into two main categories: incidents and accidents. the accidents, according to greek law, are all the events that result in damage, injury or harm and require, at least a two-day, medical leave and relevant notification to the labor inspectorate body. the incidents (near-misses) are less serious events that have unintentionally happened and are linked to absence from work only on the specific day of their occurrence. the procedure that is followed after an occupational incident or accident in the hospital workplace is described below: the supervisor of the relevant division and the responsible desk officer are alerted. the update of the associated data files follows, according to the internal process of the hospital and the relevant legal requirements (law 3850/2010, article 2, paragraph 2). the issue is registered in the book of incidents, the book of accidents, the incident – accident report, the record of exposure to biological agents at work, the report to the social insurance institute, the police and the electronic notification to the labor inspectorate body. then, the safety engineer in charge investigates the incident or accident in order to identify its causes and propose interventions, by completing risk assessment tables manually in printed versions (law 3850/2010, articles 14, 15). the safety engineer’s actions aim at ensuring that repetition of the incident or the accident could be avoided in the future. the manually filled tables are in accordance with the methodological guide for the assessment and prevention of occupational risks of the hellenic institute for occupational health and safety [41] regarding the coding of hazards, and with the method described in the previous section [39] regarding the risk values. the safety engineer cooperates with the occupational doctor, when necessary. the above-mentioned data for every incident and accident are used as an input to the proposed dss. for the efficient management of this information, the basic idea was to organize and incorporate the data into a database, which makes the information more usable and manageable in comparison with the printed forms. the information flow diagram of the proposed dss is depicted in figure 1. there are three major blocks in this diagram. firstly, the block of recording and notifying incidents – accidents (upper left) which describes the process that the responsible personnel follow to record every incident and accident in the corresponding books, to fill in the incident – accident report and notify the authorities. secondly, the block of risk assessment and investigation (lower left) which describes the process that the safety engineer and occupational doctor follow to identify osh hazards, to express the corresponding risk values and to associate these hazards with every incident and accident through investigation and estimation of osh interventions. these two blocks are the inputs to the proposed dss model. the output is the third block which describes the results of the classification process, according to the trained models. the decision is based on the risk values of the different variables. the input of the model includes two sets of variables. the first set consists of 6 variables (f1 – f6) from the first block which are related to the employees. their values come up from the incident or accident relative paper report. the second set consists of 77 variables (f7 – f83) from the second block. all 83 variables are summarized in table iii. the selection of these variables was based on [41]. the main categories of this set are workplace related variables relevant to the infrastructural building, machinery equipment, electrical installation, hazardous substances, fire, chemical physical biological factors, and transversal organizational risks. each occupational event corresponds to one instance and was categorized into one of the following 4 classes: "needlestick/cut", "falling", "incident" and "accident" according to their type. the class of "incident" was divided into three different subclasses because of the frequency distribution of incidents in the hospital workplace. needlesticks/cuts and falling events present the highest frequency, which is in accordance with [4]. for this reason, two separate classes were used for this kind of incidents, "needlestick/cut" and "falling", respectively. the class named "incident" was used to include all other kinds of incidents in the hospital workplace. the class "accident" was used to include all kinds of accidents. the values for these variables express the osh conditions and hazards that are related to the incident or accident, as they have been identified by the safety engineer. these values were engineering, technology & applied science research vol. 11, no. 3, 2021, 7262-7272 7265 www.etasr.com koklonis et al.: utilization of machine learning in supporting occupational safety and health … recorded according to the safety engineer’s reports and risk assessment tables after investigation of the corresponding incident or accident. finally, after the completion of the corrective actions, all the above instances were assigned with updated risk values and were categorized into the class "safety". each new instance of "safety" originated from one instance of "needlestick/cut" or "falling" or "incident" or "accident". in this way, our dataset consists of 238 incident/accident instances and 238 safety instances (as described in section "data"). more specifically, the values for the instances of "safety" express the proposed measures or interventions to reduce risk at acceptable levels (r≤32 for accidents and r≤24 for incidents, according to the relative methodology). these values were recorded according to the post-investigation safety engineer's updated reports and risk assessment tables after up to two months for every incident or accident. during this period, the corrective actions had been completed and confirmed according to the safety engineer’s proposed measures. the output of the system is one of the above-mentioned 5 classes (y1 – y5) and expresses the type of the event that certain occupational conditions could lead to (table iii). as the predicted classes were a priori known, our model appertains to supervising learning algorithms. table iii. variables of the proposed model variables code type values employee variables age f1 numeric years experience f2 numeric years training f3 nominal yes, no repetitive training every six months at least f4 nominal yes, no relative ppe during the incident/accident f5 nominal yes, no satisfaction for osh climate f6 numeric 1-5 workplace variables relatively to infrastructural building floors/stairs f7 numeric 1-256 workplace space f8 numeric 1-256 workplace height f9 numeric 1-256 workplace volume f10 numeric 1-256 doors/windows f11 numeric 1-256 space illumination f12 numeric 1-256 storage/lofts f13 numeric 1-256 uncovered gaps f14 numeric 1-256 obstacles f15 numeric 1-256 exits/escape routes f16 numeric 1-256 walls f17 numeric 1-256 shelves/dexions f18 numeric 1-256 ceilings f19 numeric 1-256 basements f20 numeric 1-256 walkways f21 numeric 1-256 roof f22 numeric 1-256 cleanliness f23 numeric 1-256 lack of access to exits or fire-extinguishing system f24 numeric 1-256 safety/escape signing f25 numeric 1-256 workplace variables relatively to machinery – equipment maintenance protocol f26 numeric 1-256 lack of safety during usage f27 numeric 1-256 guards for avoiding the accidental start f28 numeric 1-256 guards from moving parts f29 numeric 1-256 ejectable particles f30 numeric 1-256 ce signing f31 numeric 1-256 cutting works f32 numeric 1-256 lifting machinery f33 numeric 1-256 transport vehicles f34 numeric 1-256 ladders f35 numeric 1-256 pneumatic tools f36 numeric 1-256 elevators f37 numeric 1-256 other machinery f38 numeric 1-256 non-usage of ppe f39 numeric 1-256 pressure devices f40 numeric 1-256 access to facilities or equipment f41 numeric 1-256 workplace variables relatively to electrical installation electrical installation f42 numeric 1-256 inappropriate usage of electrical installation f43 numeric 1-256 inappropriateness in explosive atmospheres f44 numeric 1-256 lack of safety during usage of electrical installation f45 numeric 1-256 lack of safety during maintenance of the electrical installation f46 numeric 1-256 hazardous substances related to equipment (generators, batteries, etc.) f47 numeric 1-256 workplace variables relatively to hazardous substances toxic substances f48 numeric 1-256 caustic substances f49 numeric 1-256 corrosive substances f50 numeric 1-256 irritant substances f51 numeric 1-256 oxidizing substances f52 numeric 1-256 explosive substances f53 numeric 1-256 flammable material f54 numeric 1-256 appropriate cabinets f55 numeric 1-256 workplace variables relatively to fire fire signing f56 numeric 1-256 banning smoking f57 numeric 1-256 banning flame f58 numeric 1-256 storage of flammable material f59 numeric 1-256 lack of fire protection systems f60 numeric 1-256 training in fire emergency plan f61 numeric 1-256 fire rxtinguishers f62 numeric 1-256 lack of training in fire security f63 numeric 1-256 workplace variables relatively to chemical factors dust f64 numeric 1-256 fibres asbestos f65 numeric 1-256 smoke/steam f66 numeric 1-256 particles f67 numeric 1-256 other substances f68 numeric 1-256 dipping/splashing f69 numeric 1-256 workplace variables relatively to physical factors noise f70 numeric 1-256 vibrations f71 numeric 1-256 radiation f72 numeric 1-256 illumination f73 numeric 1-256 microclimate f74 numeric 1-256 workplace variables relatively to biological factors bacteria f75 numeric 1-256 fungi f76 numeric 1-256 viruses f77 numeric 1-256 other factors f78 numeric 1-256 workplace variables relatively to transversal risks settlement manual handling f79 numeric 1-256 psychological factors f80 numeric 1-256 provision intervention programs f81 numeric 1-256 ergonomy f82 numeric 1-256 hardship conditions f83 numeric 1-256 output falling y1 nominal yes, no needlestick/cut y2 nominal yes, no incident y3 nominal yes, no accident y4 nominal yes, no safety y5 nominal yes, no engineering, technology & applied science research vol. 11, no. 3, 2021, 7262-7272 7266 www.etasr.com koklonis et al.: utilization of machine learning in supporting occupational safety and health … fig. 1. the information flow diagram of the proposed model. e. prediction models and classification ml is concerned with the development of intelligent systems that can learn from data. these systems can be used to classify an object into a correct class based on features characterizing the object. actually, the algorithms are searching for patterns in data. the ml algorithms that implement pattern classification are known as classifiers. there are several classifiers, each one of them having certain limitations and advantages [42]. in this study, in order to develop the proposed dss model, we employed and tested 4 classifiers: the naive bayesian (nb) classifier [43], the bayesian network (βν), the k-nearest neighbors (k-nn) classifier, and the multilayer perceptron (mlp) network. the choice was based on the fact that the use of conditional probabilities offers a practical metric as it can model occupational health in a class conditional way. this formulation helps us elucidate class conditional variables of interest. nb classification is one of the most popular data mining algorithms. its efficiency comes from the assumption of attribute independence [40, 41]. it is a simple probabilistic classifier based on bayes’ theorem and it uses the method of maximum similarity. it can work in complex real-world situations and it requires a small amount of training data [42, 43]. bn is an effective tool to demonstrate complicated relationships and a powerful tool for knowledge representation and reasoning. it is also suitable for small and incomplete datasets. it is particularly convenient for modeling causal relationships among variables (with a combination of different sources of information) and handling of uncertainty for decision analysis [13]. it is a model of probabilistic inference defined by a triplet (x, g, p), where x = (x1, x2, ⋯, xn) is the set of factors, g is a directed acyclic graph, and p is a joint probability distribution. the nodes for g are labeled with the elements of x and the arcs of g represent the probabilistically conditional dependence relationship between nodes. each factor is associated with a conditional probabilistic table that defines the probability of each state for that factor [10, 44]. the k-nn is a simple and intuitive classifier. it classifies a sample based on the k-closest training samples in the feature space, by computing the distances between the new sample and the samples of the training set. according to these distances it classifies the sample to the class of the closest training samples (neighbors) [39, 45]. an mlp is a class of feedforward ann and one of the most widely used. it consists of the input layer, which receives external inputs, one or more hidden layers, and an output layer. each layer includes one or more neurons linked between successive layers. the back-propagation (bp) algorithm was used for the training of the model. in this technique, information about the errors of the network on known data is propagated backwards, the connections are adjusted, and the error is minimized [49]. all weka parameters for each of the above models are summarized in the appendix. the classifiers were designed to classify the cases into one of the afore-mentioned 5 classes. each classifier takes as inputs the data from the reports of each event and outputs its classification group, providing in this way a prediction regarding the actual occupational risk of hazards of each hospital worker in their certain hospital workplace, and under certain osh conditions. f. training, validation, and performance evaluation the train/test split method [50] was used as a validation technique for training. the available dataset was divided into 2 subsets: the training set (80% of cases 379 cases) which was used to train the classifiers, and the test set (20% of cases 97 cases) which was used to evaluate their predictive performance (previously unseen data). the 2 sets were properly stratified so that the distribution of classes in each subset is approximately engineering, technology & applied science research vol. 11, no. 3, 2021, 7262-7272 7267 www.etasr.com koklonis et al.: utilization of machine learning in supporting occupational safety and health … the same as that in the initial dataset. thus, each subset contains representative samples of the same larger population. to minimize sampling bias, k-fold cross-validation was also used for the whole dataset for training and test (k=10). in this technique, k dataset divisions are used for equivalent separation of the dataset into folds, k-1 folds are used for training and onefold is used for test. the process is repeated k times. through this process, each one of the available data is used one time as a member of the test set and k-1 times as a member of the training set [48, 49]. data entry was done in a spreadsheet file, since this format can be easily used in daily osh practice by the safety engineer and hospital staff. files were saved in .csv type. inserting and processing files to weka needed their conversion to the .arff type. considering that incidents and accidents are stochastic events, that are very differentiated in detail, a certain methodology has been used for risk assessment (including a certain set of risk variables that should be investigated in every case). feature selection method was not applied. in order to evaluate the performance of the proposed dss model compared to the safety engineer’s reports involved in this study, we calculated the recall (sensitivity), and the area under the receiver operating characteristic (roc) curve of the models on the basis of detecting the 5 output classes. the roc curve is a standard validation approach for probabilistic classifiers [50, 51]. a roc curve is a two-dimensional graph in which the true positive rate (tpr) (sensitivity or recall) is plotted on the y-axis and the false positive rate (fpr or 1 specificity) is plotted on the x-axis, as a function of the threshold u, ranging from 0 to 1 [55]. the area under the curve (auc) can be interpreted as a measure of overall accuracy, varying from 0.5 (random guess) to 1 (perfect performance) [56]. the recall metric answers the question of what proportion of actual positives is correctly classified. its choice was based on the fact that recall measure penalizes false negatives but not false positives [57]. in an osh approach, we want to capture as many positives as possible (we want to capture any contingent incident or accident even if we are not totally sure). these metrics can be expressed according to the number of true positives (tp), true negatives (tn), false positives (fp), and false negatives (fn) classifications through the following equations [58]: recall = sensitivity = tpr = tp/(tp+fn) (1) 1 – specificity = fpr = fp/(tn+fp) (2) the confusion matrices obtained through testing the classifiers on the training and the test sets were also used for the predictive performance of the models. each column in a confusion matrix represents the instances that are classified in one class and each row represents the instances in their real class. the error rate of the classified instances was calculated for each class. iii. results a. performance comparison of the algorithms figure 2 presents the performance of the different models compared to the safety engineer’s reports involved in this study, in terms of mean recall, auc, error rate, and the overall accuracy of each model (percentage of the correctly classified instances). the detailed table with the predictive performance of the models for each of the 5 classes is included in the appendix. fig. 2. the predictive performance of the models. the overall classification accuracies of the developed models on the training set, test set, and 10-fold cross set were 97%, 77%, and 93% respectively. the mlp showed the highest accuracy for the test set and the 10-fold cross set (94.85% and 96.01%, respectively). the mlp and the bn showed the lower average error rate (er) on the test set (10.71% and 14.35%, respectively) and on the 10-fold cross set (6.99% and 8.82%, respectively). the mlp showed the highest sensitivity (recall) for the test set and the 10-fold cross set (89% and 93%, respectively). in addition, this model showed the most highly balanced combination of sensitivity results on the 10-fold cross set (see figure 2). the average auc was high for both the test and the 10-fold cross sets (0.91 and 0.98, respectively). the mlp showed the highest auc value for the test set and the 10-fold cross set (1.00 and 0.99, respectively). it must be noted that all of the developed models showed high auc (range: 0.83-1.00 on the test set and range: 0.95-0.99 on the 10-fold cross set). b. practical implications safety engineers carry out inspections of workplaces, equipment, and osh conditions, during their visits. the safety engineers complete risk assessment tables manually in printed versions to record the results of their inspections. this process is repeated after every incident or accident. in this case, the assessment focuses on causes that are related to the specific incident or accident. the developed dss model aims to engineering, technology & applied science research vol. 11, no. 3, 2021, 7262-7272 7268 www.etasr.com koklonis et al.: utilization of machine learning in supporting occupational safety and health … support the safety engineer with evidence for the risk values of hazards and recommended actions. the mlp and the bn models (10-fold cross set) were used in the dss, as they were the models with the best predictive performance. a further elaboration of the solution methodology including the proposed model is depicted in figure 3. the utilization of the dss model can start in every case of incident, accident or audit. the associated data files should be then updated by the responsible personnel and the safety engineer. coding these event reports to instances in risk assessment tables should follow in order to update the database. afterwards, the re-trained or the existing models can be used to support with evidence any osh decision (efficiency of osh intervention, employee’s movement, appropriateness of workplace or equipment etc.). fig. 3. a solution methodology including the proposed model. in order to evaluate the proposed dss model, a case study was carried out. the new case study test set resulted from a regular process. a typical instance of this process is the following: the safety engineers of the hospital, during the audit in specific departments and workplaces (01/2020), proceeded in identifying hazards of possible incidents. in parallel, they proposed specific corrective actions for the limitation or the elimination of these hazards by inserting the desired risk values for the model’s variables (assuming that corrective actions have been taken). the basic safety engineers' observations, during the one-month period, and the corresponding incidents were: • in the archive room, an employee used a chair instead of an appropriate ladder for catching files from shelves. moreover, there was a lack of tidiness in the workplace and several obstacles prevented the free movement (possible incident: "falling"). • when the safety engineer came out of the archive room, he observed that even though the floor had just been wiped out, the sign "caution: slippery floor" had not been placed (possible incident: "falling"). • during their visit to the pathologist laboratory, the safety engineer found out that there was no preventive nor corrective maintenance file for one microtome according to its operation manual. in a conversation with an employee in this laboratory, the latter expressed complains about osh conditions (possible incident: "needlestick/cut"). • during the visit in the surgery room, a surgical nurse complained about excessive workload and lack of training (possible incident: "needlestick/cut"). • in the laundry room, and specifically in the bedsheet folder machine, the proper guard of the moving part was missing (possible incident: "incident"). • a member of the waiting staff used an unfunctional trolley and lifted many food trays simultaneously to carry them to each patient room (possible incident: "incident"). for each one of these instances, a "safety" class was also recorded, relatively to the corresponding measures – corrective actions. the dataset that came up from this scenario was used as a new case study test set for the proposed dss model. the total 12 instances were correctly classified by the dss model. only one instance was incorrectly classified by bn model. even in this case, the result was not classified as a "safety" instance but one "falling" was classified as "incident". this result was expected since this kind of incident (falling from chair) was not included in the training set of the used model. to evaluate further the usability of the proposed system, the dss model was used to support human resource management for an internal employee movement decision approached from an osh perspective. in january 2020, 10 hospital workers were moved in different departments to cover the respective demands. the safety engineer inspected the destination workplaces and completed the relevant risk assessment tables manually in printed versions. these tables were classified to 9 instances of "safety" and 1 instance of "incident". the proposed interventions for the case of "incident" included training on the work practice (waiting staff duties) and corrective actions in equipment (lighter trays and functional trolleys). the movement was done after the completion of these measures. the "safety" state was confirmed by the safety engineer one week after the movement. iv. discussion and conclusions the aim of this study was to create a dss model for the prediction of incidents and accidents in the hospital workplace. this model is based on the incident and accident data from reports of personnel and safety engineer investigations and audits in the hospital workplace. the preliminary results suggest that the proposed system may support osh decisions by predicting incidents and accidents, and also by assessing the effectiveness of the osh interventions. through the evaluation of the different classification models, we concluded that mlp on the 10-fold cross set had the most balanced predictive performance in terms of overall accuracy (96.01%), er (6.99%), auc (0.990), and recall (93%), rendering this model reliable as a tool in osh analysis in accordance with [13–17, 25]. furthermore, the high predictive performance of all the developed models is notable (auc range: 0.95-0.99 and average accuracy: 93% on the 10-fold cross set). a major benefit of the proposed dss model is that it utilizes processes and resources that already exist and are engineering, technology & applied science research vol. 11, no. 3, 2021, 7262-7272 7269 www.etasr.com koklonis et al.: utilization of machine learning in supporting occupational safety and health … applied in the daily hospital working life. the exploitation of these printed data records for incidents and accidents, and safety engineer audits and investigation reports are essential for osh management. the utilization is related with identifying hazards that can lead to incident or accident, reducing the occupational risk, evaluating the efficacy of osh measures – interventions, supporting management decisions (employee’s recruitment or movement to a different department, etc.) from the osh perspective, improving osh conditions and reducing the overall cost of injuries [23, 34]. the proposed change is related to the transfer of coded paper records into a dss which is promising for osh decisions. this process could result in faster and more accurate predictions according to osh injuries and interventions, in accordance with [9, 34, 62], emphasizing the significance of quantitative analysis of empirical injury data in the safety science [25]. another advantage of the proposed model is the fact that it can be adjusted to various working sectors, depending on the training sets and the existing records of incidents and accidents in each of them. for its application in other hospitals, the system can be easily updated with new datasets, according to the status of each hospital (incidents and accidents that take place and osh conditions). the frequency of updating or retraining the classification models depends on the type and the frequency of incidents and accidents. to maximize the usability and the practicality of the dss model, a certain approach for the risk values of various factors should be followed. for instance, the classes "incident" and "accident" may be confused during initial workplace risk assessment of a random scenario, because of the lack of knowledge about the necessity of the required medical leave and its length. the dataset for accidents needs to be improved, however, any kind of incident should be interpreted as an alert which can anytime lead to an accident. incidents are very important for osh, in the sense of "near miss", as a situation that could lead to an accident, particularly in the case of repeated incidents of the same kind [59, 60]. in addition, certain incidents can evolve in occupational diseases (like blood-borne diseases because of needlestick/cuts and chronic musculoskeletal disorders) [61]. an occupational disease according to the domestic legislative framework is equivalent to an occupational accident [62]. the experience of the safety engineer and the accordance with the corresponding methodology are very important key factors for this assessment. according to the proposed dss model, an alert for taking corrective actions is related to all the classes that are different from the "safety" one. the proposed measures and corrective actions target the elimination of hazards. the elimination is not always possible in all cases. instead of elimination, limitation of hazards to acceptable levels should be the next step forward. the relation between cost and optimal level of risk is formed according to the alarp (as low as reasonably practicable) theory [60, 61]. in other words, entering the minimum values of risk for "safety" class has no practical meaning since total lack of risk cannot happen in real conditions, both in terms of cost and inherent risk (a risk that is related to the nature of work). on the contrary, "armor logic" should not be applied during risk assessment by inserting maximum values during identifying and highlighting a hazard. in any case, the interesting point related to the values of risk variables is the threshold where the value of a specific risk factor leads to the transition from one class to another. a field for further research is the extensibility of the proposed dss model and its development as a user-friendly web application platform. the development of the proposed dss as a web app could make it more usable and accessible. furthermore, the directions of this extensibility can include the facilitation of data entry to the system through natural language process (nlp) (because there are several handwritten records) and the interconnection between the proposed dss model and other tools/applications that will improve the efficiency of the proposed measures and corrective actions or/and the validity of risk assessment (scales for musculoskeletal disorders like key item method [66], working stress questionnaires, optimal allocation of osh capital investment, etc.). acknowledgment we would like to thank the administration, the scientific council, and the personnel of metaxa cancer hospital of piraeus, greece for their approval and participation in the implementation of the proposed model. appendix weka parameters for classification algorithms model weka parameters nb batch size = 100 debug = false kernel estimator = false donotcheckcapabilities = false usesuperviseddiscretization = false bn batch size = 100 debug = false donotcheckcapabilities = false estimator = sample estimator – a 0.5 searchalgorithm = k2-p1-s bayes useadtree = false k-nn k = 9 batch size = 100 crossvalidate = false debug = false distanceweighting = no donotcheckcapabilities = false meansquared = false nearestneighboursearchalgorithm = linearnnsearch euclidean distance first-last mlp autobuild = true batch size = 100 debug = false decay = false donotcheckcapabilities = false hiddenlayers = a, where a = (number of attributes + number of classes) /2 = 44 learning rate = 0.3 momentum = 0.2 nominaltobinaryfilter = true normalizeattributes = true normalizenumericclass = true reset = true seed = 0 trainingtime (number of epochs) = 500 validationsetsize = 0 validation threshold = 20 engineering, technology & applied science research vol. 11, no. 3, 2021, 7262-7272 7270 www.etasr.com koklonis et al.: utilization of machine learning in supporting occupational safety and health … predictive performance of the different models vm a ma a (%) performance evaluation metrics mv a accident falling incident cutting safety nb train set (80%) (379) 93.40 er (%) 0.00 0.00 23.40 3.70 5.26 6.47 recall 1.000 1.000 0.766 0.963 0.947 0.94 auc 1.000 0.995 0.968 0.982 0.986 0.99 test set (20%) (97) 71.13 er (%) 60.00 0.00 16.67 3.57 47.92 25.63 recall 0.600 1.000 0.833 0.964 0.521 0.78 auc 0.753 0.992 0.862 0.964 0.991 0.91 10-fold cross (476) 92.23 er (%) 8.69 15.00 28.81 3.67 4.20 12.07 recall 0.913 0.850 0.712 0.963 0.958 0.88 auc 0.995 0.944 0.890 0.969 0.966 0.95 k-nn train set (80%) (379) 95.78 er (%) 0.00 37.5 21.28 0.00 0.00 11.76 recall 1.000 0.625 0.787 1.000 1.000 0.88 auc 1.000 0.986 0.990 0.997 1.000 0.99 test set (20%) (97) 70.10 er (%) 0.00 50.00 25.00 3.57 47.92 25.30 recall 1.000 0.500 0.750 0.964 0.521 0.75 auc 0.875 0.985 0.983 0.997 0.751 0.92 10-fold cross (476) 92.86 er (%) 0.00 50.00 37.29 1.47 0.00 17.75 recall 1.000 0.500 0.627 0.985 1.000 0.82 auc 1.000 0.981 0.966 0.994 1.000 0.99 bn train set (80%) (379) 97.10 er (%) 0.00 18.75 10.64 2.78 0.00 6.43 recall 1.000 0.813 0.894 0.972 1.000 0.94 auc 1.000 0.993 0.987 0.996 1.000 1.00 test set (20%) (97) 72.16 er (%) 0.00 0.00 16.67 7.14 47.92 14.35 recall 1.000 1.000 0.833 0.929 0.521 0.86 auc 0.875 1.000 0.810 0.900 0.570 0.83 10-fold cross (476) 91.18 er (%) 0.00 15.00 13.56 5.88 9.66 8.82 recall 1.000 0.850 0.864 0.941 0.903 0.91 auc 0.975 0.985 0.979 0.994 0.913 0.97 mlp train set (80%) (379) 99.74 er (%) 0.00 0.00 2.12 0.00 0.00 0.42 recall 1.000 1.000 0.979 1.000 1.000 1.00 auc 1.000 1.000 0.984 0.998 1.000 1.00 test set (20%) (97) 94.85 er (%) 0.00 25.00 25.00 3.57 0.00 10.71 recall 1.000 0.750 0.750 0.964 1.000 0.89 auc 1.000 1.000 0.992 0.996 1.000 1.00 10-fold cross (476) 96.01 er (%) 0.00 10.00 22.03 2.94 0.00 6.99 recall 1.000 0.900 0.780 0.971 1.000 0.93 auc 0.999 0.996 0.971 0.991 1.000 0.99 a. vm: validation model, ma: model accuracy, mv: mean value. references [1] d. elsler, j. takala, and j. remes, "an international comparison of the cost of work-related accidents and illnesses," european agency for safety and health at work, 2017. 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[66] k. koklonis, a. anastasiou, o. petropoulou, s. pitoglou, d. iliopoulou, and d. koutsouris, "utilizing key item method to manage musculoskeletal disorders in a hospital workplace," in 41st annual international conference of the ieee engineering in medicine and biology society, berlin, germany, jul. 2019, pp. 3420–3423, https://doi.org/10.1109/embc.2019.8857649. microsoft word etasr_v13_n4_pp11332-11337 engineering, technology & applied science research vol. 13, no. 4, 2023, 11332-11337 11332 www.etasr.com ghaly et al.: diagnosis of two-phase oil/gas flow in a closed pipe using an 8-electrode ect system diagnosis of two-phase oil/gas flow in a closed pipe using an 8-electrode ect system sidi mohamed ahmed ghaly electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia | ecole normale supérieure, mauritania smghaly@imamu.edu.sa mohammed shalaby electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia myshalaby@imamu.edu.sa mohammad obaidullah khan electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia okkhan@imamu.edu.sa khaled alsnaie electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia kalsnaie@imamu.edu.sa asad ali mohammed electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia asad207@imamu.edu.sa faisal baloshi electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia fbaloshi@imamu.edu.sa abdalmajid imad electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia aimad@imamu.edu.sa majdi taha oraiqat electrical engineering department, imam mohammad ibn saud islamic university, saudi arabia mtoraiqat@imamu.edu.sa received: 4 may 2023 | revised: 24 may 2023 and 26 may 2023 | accepted: 29 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6011 abstract electrical tomography techniques have been developed to monitor the internal behavior of industrial processes. electrical capacitance gives the best benefits over other tomography modalities, as it has no radiation, is non-intrusive, and has a low cost. this study investigated the diagnosis of two-phase oil/gas flow in a closed pipe, using an image data capture system for an 8 external electrode electrical capacitance tomography (ect) sensor. the system had a high-resolution ratio, a small measurement error, and was able to remove the effects of stray capacitance. experimental measurements were carried out on two different materials that filled the space inside the pipe in different proportions to determine the sensitivity and accuracy of the measurement. the results showed that the system had fast image data capture time, high accuracy, a very small resolution ratio, and a good signal-to-noise ratio and quality factor. engineering, technology & applied science research vol. 13, no. 4, 2023, 11332-11337 11333 www.etasr.com ghaly et al.: diagnosis of two-phase oil/gas flow in a closed pipe using an 8-electrode ect system keywords-ect sensor; imaging; electrode; permittivity; fluid dynamics; sensitivity; accuracy i. introduction electrical capacitance tomography (ect) is a widely used imaging technique in monitoring and diagnosing the internal dynamics of the flow mechanism of gaseous or liquid materials in the process industry [1-5]. ect is an economic, noninterrupting or non-invasive, and fast-responding imaging scheme, as it can produce real-time images with an approximate speed of 100 fps. different experimental studies showed that the water-in-liquid ratio (wlr) and gas volume fraction (gvf) in an oil-gas-water flow can be roughly calculated or measured by ect with suitable algorithms [6-7]. obtaining a high-speed image along with quantitative measurements of a multiphase flow system is a challenging demand in the petroleum industry and hydraulic applications. ect can also be used to detect corrosion and leakage or monitor liquid dynamics in a petroleum/gas pipeline network [8-10]. it can also be used to investigate the distribution of spatial permittivity in a defined region in the interior of a closed pipe. ect works on the principle of measuring capacitances between electrodes located outside the sample portion in the region of investigation. in general, the specimen region can be a hollow pipe carrying a liquid or gas. the data obtained from these electrodes are processed to reconstruct the internal image of the pipe. the necessary elements of a typical ect system are a set of multi-electrode sensors mounted equidistant around the pipe, a data retrieval or acquisition system, and an image reconstruction block, as shown in figure 1 [11-12]. using n electrodes in the sensor for capacitance measurements, there will be m independent capacitance measurements as expressed in: � = � (���) (1) in the present case, as shown in figure 2, an 8-electrode sensor needs 28 independent measurements of electrode pairs as:1-2, 1-3, ..., 1-8; 2-3, 2-4, ..., 2-8; ..., up to 7-8. fig. 1. a typical ect system with 8 electrodes. fig. 2. cross section of a typical 8-electrode ect system. in general, ect systems directly employ the "raw" capacitance data obtained from the sensor to develop images using linear back-projection (lbp) and recursive or neural network algorithms [10]. the lbp algorithm is one of the most popular methods due to its simplicity and high rates of image reconstruction. an lbp image is obtained by overlaying the sensor sensitivity maps for all electrode pairs after weighting by the corresponding measured changes in normalized capacitance. this can be represented mathematically as: (�) = ∑ ∑ � � � �(�)��� �� ��� �� ∑ ∑ ���(�)��� �� ��� �� (2) ��� = � � ��� � � � � � �� � � (3) where n represents the number of electrodes in the ect sensor, x(p) is the fraction of a high permittivity material in the p-th pixel, s is the sensitivity of electrode pair i-j at the p-th pixel, cij represents the capacitance of the electrode pair i-j when the sensor is filled with low and high permittivity materials, respectively, c m is the raw measured capacitance of the electrode pair i-j, and λij is the change in normalized capacitance of the respective electrode pair. ii. electrical modeling of the ect sensor without radial screen consider an ect sensor with eight external electrodes without radial screens, as shown in figure 2. these electrodes can be made with a flexible printed circuit board with greater precision in size and position. without radial screens, the external capacitances must be considered, as they have considerable capacitance. a model of capacitance measured cm with radial screens for one pair of electrodes, that is the capacitance between two measurement electrodes through the space outside them, can be given as the combination of an internal capacitance cx, two pipe wall capacitances cw1, cw2, and two stray capacitances cs1, cs2, as demonstrated in figure 3(a). this can be further simplified as shown in figure 3(b) [13]. the equivalent capacitance cm can be calculated mathematically as: �� = ��� ��!�" (4) (a) (b) fig. 3. electrical model of 8-electrode sensing system without radial screen: (a) model with all capacitances, (b) simplified model. the unknown capacitances cw and cx can be found by filling a material of known relative permittivity r1 into the sensor. this process is repeated with another material of known engineering, technology & applied science research vol. 13, no. 4, 2023, 11332-11337 11334 www.etasr.com ghaly et al.: diagnosis of two-phase oil/gas flow in a closed pipe using an 8-electrode ect system relative permittivity of r2 and the air. thereafter, by finding cx and cw, the internal capacitance with any fluid existing inside the region of interest in the pvc pipe can be calculated from the raw capacitance measured using (4). this can be rearranged as follows: � = �# �$ /��# & �$ � (5) iii. calculation of the sensitivity map of the 8-electrode ect consider the circular sensor filled with one-phase with air dielectric constant and fitted with eight electrodes. the wall permittivity is constant. thus, the domain of the model is the unit square ω on the x-y plane, representing the cross-section of the scaled sensor area. the electrodes are placed on the unit square x 2 =1, where x is the length of the side and the boundary of ω. suppose that the relative radial thickness of the wall is t0 (0<t0<1), and denotes the interior cavity by [14-15]: '( = )(*, ,): * . (1 & 0() 1 (6) the electric potential u(x, y) on ω is governed by poisson’s equation derived for the static electric field, which is given by: ∇(3∇4) = 0' (7) where ε = ε(x, y) > 0 is the relative permittivity distribution in ω. a finite difference method was employed to discretize the differential equation for the numerical solution using rectangular coordinates. the simulation was assumed for a cross-sectional circular shape, which can be a cylindrical non-metal container. ect is difficult to perform on metallic cylinders, as the metals leak the charge all over their surface and make the theoretic assumptions wrong for calculations. on a non-metallic surface, the electrodes are attached and a voltage is applied, which passes through the non-metallic cylinder from the inside and through the fluid or gas. this creates a small charge that accumulates in the fluid or gas and creates a small capacitance since when a potential is applied to one electrode, the other 7 electrodes act as ground. the technique of 8-electrode ect is like 7 capacitors along the surface of the cylinder. however, as the permittivity and voltage between the plates are very small and the distance between the electrodes is greater, a very low capacitance is measured. if the permittivity of the fluid or gas and their potential breakdown are known, an increase in voltage below the breakdown voltage can lead to better performance of the ect technique. the breakdown voltage is the voltage at which an arc occurs between the electrodes. figure 4 shows the electric potential between the energized electrode 1 and the grounded electrodes 2-8. the sensitivity map sij is obtained on a cylinder object fixed with 8 electrodes. figure 5 shows s12 between the first and second electrodes. electrode 1 is energized at a low voltage of 0.02 v and electrode 2 is grounded, which has some stray charge on it, as the metal electrodes cannot be charged after applying an electric field. similarly, electrode 1 is energized at a low voltage of 0.02 v, and electrode 3 is grounded having some stray charge. the potentials for electrodes 1 and 3 are illustrated below. this can be demonstrated for all combinations of 1-8 electrodes in the ect sensor, as shown in figure 6. figure 7 shows s13 between the first and third electrodes. fig. 4. electric potential between electrodes 1 and 2. fig. 5. sensitivity map between electrodes 1 and 2. fig. 6. electric potential between electrodes 1 and 3 at low intensity. fig. 7. sensitivity map between electrodes 1 and 3. engineering, technology & applied science research vol. 13, no. 4, 2023, 11332-11337 11335 www.etasr.com ghaly et al.: diagnosis of two-phase oil/gas flow in a closed pipe using an 8-electrode ect system figure 8 illustrates the potential distribution from electrode 1 to electrode 3 when a high voltage of 1000 v is applied. if carefully analyzed, there is a continuous decrease in voltage until the second electrode is approached. it seems as an exponential decrease in voltage, but when applying a higher voltage at electrode 1, a more positive expectation of capacitance is measured. the application of higher voltage is due to the limitation of the medium which is transmitted through the cylindrical pipes, and its effect needs to be studied. fig. 8. electric potential between electrodes 1 and 3 at high voltage. iv. implementation for sensitivity measurement the ac-ect system includes hardware and software, in particular software drivers and ectgui. as shown in figure 9, the hardware has a front-end unit in a 19'' eurocase, with an internal power supply and an ni daq board/card operated by a host pc. two ni daq units are supported: the ni pci-6024e daq board that works with a desktop pc and the ni pcmcia 6062e daq card that works with a laptop. both ni daq units use a 68-way ribbon cable with the same female connectors connected to the 19'' eurocase, but a different female connector at the other end to connect to the pc [16]. fig. 9. hardware blueprint. this section presents the results of the experiments carried out using the 8-electrode ect sensor, with dimensions specified in table i, to quantify its sensitivity. the accuracy of the sensor may also depend on physical specifications and assumptions. if the tube wall is made up of a dielectric material, electrodes can be installed inside or outside [17-18], but if the wall is conductive there is only one choice to design the electrode location (external electrode). however, as the proposed design used dielectric material, the electrodes were put outside the pipe because it is easier to design. the number of electrodes depends on capacitance, circuit complexity, and data acquisition speed. using more electrodes provides a better image, but they are difficult to measure. in most cases, the number of electrodes used is 8 or 12, whereas this study used 8. a guard electrode is required to improve measurement sensitivity and prevent the electric field from reaching the ground and the end of the measuring electrode [19]. they must be used if the length of measuring electrodes is less than approximately twice the sensor diameter. finally, it is important to add a discharge resistor. the resistor must be connected between each electrode and the driven guard and earth to avoid a static charge and damage to the measuring sensor. typically, the resistance value is 1 mω. if the capacitance of the inter-electrodes is around 1 pf, an earthed screen is required around the electrodes to avoid unwanted or external signals. figure 10 shows a photo of the typically developed prototype. fig. 10. a typical 8-electrode ect sensor. table i. dimensions of the sensor parts component dimensions electrode dimensions= length×width 15×1.7 cm gap between electrodes 0.275 cm external circumference of pipe 15.8 cm outer radius of pipe 2.51 cm inner pipe cross section area 19.86 cm2 total volume of the ect section (electrode region): vtotal= 19.86×15 297.9 cm3 v. result and discussion a. sensitivity of measurements two dielectric materials were used to calibrate the developed sensor: oil and air. then, different amounts of oil were introduced into the pipe, where the air surrounded the oil. figure 11 shows that the smallest amount to be detected had a cross-sectional area of 0.97 cm 2 (volume = 14.56 cm 3 and quantity = 0.67 l). a minimum detectable value was defined as the product of the dielectric constant to describe the pos sensitivity of the ect sensor. the difference between the two dielectric materials (air and oil) was multiplied by the minimum detectable volume of the object and divided by the volume of the sensor section as in (6): engineering, technology & applied science research vol. 13, no. 4, 2023, 11332-11337 11336 www.etasr.com ghaly et al.: diagnosis of two-phase oil/gas flow in a closed pipe using an 8-electrode ect system 678 = ∆3: ;�< ;=>=?� × 100 (6) where pos is the percentage of sensitivity [20], δεr is the difference between the dielectric constants of the full and empty states, vmd is the minimum detectable volume of the object, and vtotal is the total volume of the ect sensor. in the present case of oil δεr = 6. from figure 10, the calculated sensitivity of the pos measurements was 67.4%. figure 11 shows the decrease in the amount of oil gradually searching for the minimum detectable volume of the object vmd. (a) (b) fig. 11. sensitivity patterns with variable amounts of different materials. b. accuracy of the obtained image the accuracy of the measurements [21] was calculated from the images obtained. two different dielectric materials were considered, where the empty state was air and the full state was lubricating oil (density = 823 kg/m 3 ). an amount of lubricating oil was introduced so that when the pipe was placed horizontally, it was half filled with lubricating oil. referring to figure 11, it was discovered that the separation line between the lubricating oil and the air deviated from being a sharp line. the gradual change from blue (air) to red color (lubricating oil) indicates that the accuracy of the sensor was not high enough. to quantify the accuracy of the ect sensor, the percentage of accuracy (poa) was defined as follows: poa = d1 & efgh ijfklghmmnopqh rfpohihst × 100 (7) the poa term was introduced to represent the percentage of accuracy. in the case of figure 12, poa was achieved to be as high as 82%. fig. 12. illustration of sensitivity pattern with two different materials when it is placed horizontally. figure 12 shows the line separation between the two different dielectric materials (lubricating oil and air) when the pipe is placed horizontally. the results obtained with the developed sensor with eight external electrodes show that the larger the width of the electrodes, the more accurate the measurements. moreover, the shorter the electrode length, the more sensitive the measurements. these observations were made while keeping the same gap between the electrodes and for the same cross-sectional area. vi. conclusion this paper presented the modeling, simulation, and experimental measurements of an ect sensor having eight external electrodes. in terms of modeling, the potential distribution, the electric field, and the sensitivity map were obtained to extract the dependence of the sensor characteristics in terms of sensitivity and accuracy on the sensor parameters. to verify the modeling results, an 8-electrode ect sensor was developed and implemented, and experimental measurements were carried out on two different materials filling the pipe with different proportions to determine the sensitivity of the measurements and the accuracy of the probe. furthermore, definitions of accuracy and sensitivity were developed and calculated for the developed sensor to validate the simulation results. acknowledgement this project was funded by the national plan for sciences, technology, and innovation (maarifah), king abdulaziz city for science and technology, kingdom of saudi arabia award number (14-ele741-08). references [1] k. j. alme and s. mylvaganam, "comparison of different measurement protocols in electrical capacitance tomography using simulations," ieee transactions on instrumentation and measurement, vol. 56, no. 6, pp. 2119–2130, sep. 2007, https://doi.org/10.1109/tim.2007.908315. 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[21] t. a. york, "status of electrical tomography in industrial applications," journal of electronic imaging, vol. 10, no. 3, pp. 608–619, jul. 2001, https://doi.org/10.1117/1.1377308. microsoft word etasr_v13_n3_pp10973-10977 engineering, technology & applied science research vol. 13, no. 3, 2023, 10973-10977 10973 www.etasr.com abuhasel: sustainable green city development project analysis using the critical path method (cpm) … sustainable green city development project analysis using the critical path method (cpm) and the crashing project method on time and cost optimization khaled abuhasel mechanical engineering department, university of bisha, kingdom of saudi arabia kabuhasel@ub.edu.sa (corresponding author) received: 20 april 2023 | revised: 3 may 2023 | accepted: 6 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5980 abstract due to the increase in population all over the world, the term city development has emerged using the method of sustainable green cities, which are cities designed taking into account the environmental impact to reduce the required input from energy, water, and food production. this study discusses this topic with three main objectives; the first is to analyze the project work network of the sustainable green city development project, the second is to investigate the impact of speeding up the project on network planning, and the third is to determine the cost differences before and after acceleration. the critical path method (cpm) is valuable for managing complex projects if the activity durations are known. however, in reality, the projected durations may vary in the course of a project due to multiple factors, such as equipment breakdowns, human errors, and material shortages. this study used the cpm and crashing methods to determine the optimal project turnaround time using critical path optimization techniques. analysis using cpm showed that the initial project duration was 1205 weeks but can be reduced to 1197 weeks. however, with acceleration, there is a slight difference, corresponding to a 0.67% decrease in the duration and approximately 8 weeks. the study showed that the total cost of the project work is us $55m at the normal duration and became us $59m after acceleration, which is a slight increase. keywords-critical path method (cpm); crashing method; network planning; optimal duration; optimal cost i. introduction project scheduling involves determining the timeline, resources, labor, and materials required for each project activity [1]. it is important to ensure that the implementation of a project follows the schedule plan, which is achieved by selecting the most appropriate planning game. the game practice provides certainty in the completion of the project, minimizing delays and negative impacts on quality, cost, and time [2]. the optimal scheduling of a home energy system has a significant effect on its operating cost [3]. in the current competitive business landscape, completing projects quickly and cost-effectively is crucial for successful project management. effective planning and timely completion of projects provide a significant advantage in terms of cost, time, and customer satisfaction. consequently, there is an increasing interest in project management methods to ensure timely delivery success. project planning is a crucial step in project management and employs various methods. critical path method (cpm) is one of the most preferred methods due to its effectiveness. cpm identifies the critical path, which is the path from the beginning to the end of the project, where all slack times are zero [4]. this method also helps to identify critical activities on the critical path, allowing for resource concentration to reduce project length. furthermore, cpm can also identify bottlenecks in the project [5]. when it comes to real-life applications, it can be difficult to determine the exact duration of the activities of projects. expert opinions and estimates are used to determine activity durations, but different experts may provide different estimations for the same project [6]. cpm is a valuable approach for determining the project completion time by considering the priority relationships among activities. in real-life scenarios, cpm is an effective tool for planning and managing intricate projects [7]. the project network diagram always starts with an event marking the project's beginning and concludes with an event indicating its completion [8]. a project can contain multiple paths or routes from the initial event to the final [9]. "crashing project" refers to the process of accelerating the period of a project [10-11], reducing its overall duration by shortening the activities while minimizing the associated costs. the goal of crashing is to expedite the project schedule without causing a significant increase in cost. this can be achieved by identifying engineering, technology & applied science research vol. 13, no. 3, 2023, 10973-10977 10974 www.etasr.com abuhasel: sustainable green city development project analysis using the critical path method (cpm) … critical activities that are hindering the project's progress and allocating additional resources. crashing ensures that the project is completed on time or ahead of schedule while maintaining quality standards and meeting all requirements. this study aimed to address the issue of delayed completion time in the sustainable green city development project by effectively planning and scheduling project activities and subactivities. to achieve this goal, cpm was used to design network planning that takes into account the priority relations between project activities. the implementation of effective network planning can provide a more organized work schedule, resulting in optimized time and cost management. the crashing method was also used to expedite the project timeline without cost increases, further ensuring that project completion occurs within the stipulated time. ii. methods a. critical path method (cpm) cpm is a scheduling technique that is used to manage a series of activities that depend on each other in terms of their start and end times. these times converge eventually to arrive at the expected outcome of the project. the goal of this method is to identify the critical path that must be followed to reach the project endpoint within the given time and explore different options that may arise in case the durations of activities change [12]. to understand cpm, it is important to understand some basic concepts. a project network refers to a graphical representation of activities and their prioritized relationships within the project. activity is any work that contributes to the completion of the project. a predecessor refers to an activity that must be completed before another, known as a successor, can begin. the earliest start (es) of an activity is the earliest time it can begin once all preceding activities have been finished. the earliest finish (ef) is the time obtained by adding the duration of the activity to the es of the activity. the latest start (ls) is calculated by subtracting the activity completion time from the latest finish (lf). lf is determined by adding the activity duration to ls. slack (s) is the time available between the es and ls or lf and ef times for an activity. the critical path refers to the sequence of activities that have no slack time [13-14]. any delay in these critical activities will delay the overall project. therefore, it is essential to manage the project efficiently to avoid delays in these activities [15-17]. critical chain project management (ccpm) is a toc tool used for planning and project management. it can be used in oneand multi-project structures, where resources are used in several projects simultaneously [18-19]. table i provides definitions of the activities and sub-activities for the sustainable green city development project, which will be planned and scheduled using cpm to optimize time and cost and minimize delays. table i also shows the activities and subactivities of the project. the sub-activities are given an alphabetical code, and figure 1 shows a gantt chart of the subactivities. figure 1 shows that the critical path of the project passes by the sub-activities a, d, i, j, k, and l. it can also be noted that the total project duration is 25 years, based on the approximate timing of each of the critical sub-activities described in figure 1. table i. activities and sub-activities of the sustainable green city development project no activity sub-activity code 1 reduce carbon emissions investing in renewable energy sources a 2 supporting the tourism sector creating new tourism products and experiences that showcase the local culture and environment b 3 increase green areas promote local tourist attractions c planting trees in public parks d preserving natural areas e 4 improving public facilities and services developing programs to support small businesses and entrepreneurs f attracting investors from outside the region g 5 improving healthcare and physical fitness develop programs to promote healthy eating and lifestyle h providing mental health support services i 6 improve transportation services implementation of bicycle and pedestrian paths j encouraging the use of alternative means of transportation to reduce carbon emissions k 7 improving cultural and entertainment services hosting international sports events l fig. 1. gantt chart of the sustainable green city development project. table ii shows a comparison of the normal schedule cost and duration compared to the crash, mentioning the subactivity precedence. this table shows that shortening the duration of an activity will cause its cost to increase. for example, shortening the duration of activity a by 2 weeks will increase the cost by $1m. this observation applies to all the activities mentioned in table ii. table ii. analysis results according to possible values activity es ef ls lf slack ls-es on critical path a 0 332 0 332 0 yes b 0 128 523 651 523 no c 0 300 351 651 351 no d 332 624 332 624 0 yes e 332 404 552 624 220 no f 0 150 591 741 591 no g 300 390 65 741 351 no h 390 573 741 924 351 no i 624 824 624 824 0 yes j 824 924 824 924 0 yes k 924 1117 924 1117 0 yes l 1117 1205 1117 1205 0 yes table iii shows the results of optimizing project time and cost. the total cost of the project based on the normal schedule engineering, technology & applied science research vol. 13, no. 3, 2023, 10973-10977 10975 www.etasr.com abuhasel: sustainable green city development project analysis using the critical path method (cpm) … was $55m and will last 1205 weeks. shortening an activity by one week will increase its cost by $0.5m. this indicates that shortening the overall project duration from 1205 to 1197 weeks will increase the overall cost of the project from $55m to $59m. figure 3 shows the variation of the project cost with its duration. it can be noted that the relationship between duration and cost is a linear relationship with a negative slope. at 1205 weeks duration, the cost is $55m. as the duration shortens, the cost increases by $0.5m/week. table iv shows the same results differently. table iii. results of time and cost optimization using crashing methods cycle activity time cost total cost duration 0 55,000,000 1205 1 a 2 500,000 56,000,000 1203 2 d 2 500,000 57,000,000 1201 3 k 1 500,000 57,500,000 1200 4 l 3 500,000 59,000,000 1197 fig. 2. the activity-on-mode network diagram of optimizing time using crashing methods. fig. 3. reduction of the project's duration from 1205 to 1197 weeks with cost increasing to $59m. b. optimization using the crashing method this is a structured and logical approach to reduce the time required for a project [20]. the goal of this method is to optimize the duration of the project activities in a cost-efficient manner. the method involves a trade-off between time and cost, which means that a reduction in the duration of the project activities is achieved at an additional cost. this cost incurs due to the increase in work efficiency to reduce the project's overall duration. the use of the crashing method can significantly impact project delays by decreasing the time allocated to activities on the critical path. this method applies a cost slope, which refers to the additional cost when the time required for project completion is reduced. c. experimental analysis cpm involves several steps, such as the identification of individual activities, the determination of their sequence, the organization of the network diagram, the estimation of the completion time for each activity, and the definition of the critical path [6]. table iv provides a list of activities, their predecessors, and their expected normal and crash durations and costs, which are essential to estimate the overall duration of a project. additionally, the table illustrates the project's network diagram, which highlights the relationships between the project activities and their dependencies. table iv. data of the sustainable green city development project activity precedence normal crash time (weeks) cost ($) time (weeks) cost ($) a 332 5,000,000 330 6,000,000 b 128 1,000,000 127 1,500,000 c 300 2,500,000 299 3,000,000 d a 292 3,000,000 290 4,000,000 e a 72 500,000 71 1,000,000 f 150 9,000,000 148 10,000,000 g b, c 90 13,000,000 90 13,000,000 h g, f 183 4,000,000 180 5,500,000 i d, e 200 3,500,000 200 3,500,000 j h, i 100 7,000,000 100 7,000,000 k h, j 193 2,000,000 192 2,500,000 l k, j 88 4,500,000 85 6,000,000 figure 4 shows the activity-on-mode (aon) network diagram for the normal schedule. the figure also shows the critical path, which is a, d, i, j, k, and l. it can also be observed that the total project duration is 1205 working weeks. table iii also shows the earliest start, latest finish, earliest finish, latest start, slack, and the presence of the activities on the critical path. it can be seen that all critical activities that lie on the critical path have zero slack. figure 4 also shows the aon network diagram for the crash schedule. the crash schedule can be shortened to 1197 weeks, but this shortening will increase the overall cost of the project. fig. 4. the aon network diagram of the project. engineering, technology & applied science research vol. 13, no. 3, 2023, 10973-10977 10976 www.etasr.com abuhasel: sustainable green city development project analysis using the critical path method (cpm) … iii. observations and discussion the process of determining the time needed to complete a project and identifying the critical path involves using the expected durations of the activities and establishing sequential relationships among them. based on these observations, the results were presented in table ii, indicating that the duration of this particular project was estimated to be 1205 weeks, while the critical path was a, d, i, j, k, and l. so, any delay in completing any of the activities in the critical path will directly impact the overall project duration. therefore, the project manager should focus on these critical activities to ensure the project's timely completion. accelerating activities in the critical path increases the total cost by us $4m. a time shortening of 8 weeks can be obtained by adopting cpm to optimize resources and manage the critical path. this means that the project can be completed 8 weeks earlier than the expected time of 1205 weeks. the time efficiency gained by using the cpm methodology was (12051197)/1197×100%=0.67%. this shows that the cpm method can help project managers significantly reduce the time required to complete a project, optimize project resources, and deliver the project within the expected timeline. a. using crashing methods to optimize time and cost the crashing method was used to optimize project completion time while minimizing costs. the method involved adding extra labor, such as us $500 per person per week, in critical activities to speed up project completion. by deploying additional labor, activities on the critical path can be completed quicker, resulting in the overall project's time and cost optimization. b. trade-off analysis (time and cost) reduction stage with maximum crashing duration:  cost slope = us $0.5m/week  time normal = 1205 weeks  crashing time = 1197 weeks  total crashing = 8 weeks  total project duration = 1197 weeks  direct costs = normal direct costs + cost slope = $55m + (0.5m *8)= $59m. iv. conclusion effective project management is crucial for the success and future of any enterprise in modern days. due to the high competitiveness in the business environment, the ability to complete projects within stipulated time and cost is becoming increasingly important. this study focused on the sustainable green city development project, and the results showed that cpm is an effective tool for project management. using cpm, the critical path for the project was determined as a, d, i, j, k, and l, with a duration of 1205 weeks. the study also demonstrated the use of the crashing method to optimize the project completion time while minimizing costs. by accelerating the duration of critical activities, the project completion time was reduced to 1197 weeks, with a total cost of us $59m. the time efficiency gained by using cpm was 0.67%. these findings show the importance of using project management tools, such as cpm and the crashing method, to optimize project completion time, reduce costs, and ensure project success. acknowledgments the author would like to express his gratitude to his students, miss ghada khushail & miss reema almotawa, for their help during the research, as well as to the deanship of scientific research at the university of bisha for supporting this work through the fast-track research support program. references [1] p. ahmadi, m. h. nazari, and s. h. hosseinian, "optimal resources planning of residential complex energy system in a day-ahead market based on invasive weed optimization algorithm," engineering, technology & applied science research, vol. 7, no. 5, pp. 1934–1939, oct. 2017, https://doi.org/10.48084/etasr.1324. 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[20] o. m. elsahly, s. ahmed, and a. abdelfatah, "systematic review of the time-cost optimization models in construction management," sustainability, vol. 15, no. 6, jan. 2023, art. no. 5578, https://doi.org/ 10.3390/su15065578. authors profile khaled ali abuhasel received his b.sc. and m.sc. degrees from the university of central florida, orlando, fl, usa, in 2009 and 2010, respectively, and his ph.d. degree from new mexico state university, las cruces, nm, usa, in 2012, all in industrial engineering. he is currently a professor in the mechanical engineering department, university of bisha, saudi arabia. he holds three u.s. patents, and more than 60 publications in journals and proceedings of very reputable conferences. his research interests include optimization, systems engineering, project management, healthcare systems, intelligent systems, artificial neural network methodologies, and statistical analysis. microsoft word etasr_v11_n4_pp7458-7463 engineering, technology & applied science research vol. 11, no. 4, 2021, 7458-7463 7458 www.etasr.com zisopol et al.: a theoretical and experimental research on the influence of fdm parameters on … a theoretical and experimental research on the influence of fdm parameters on tensile strength and hardness of parts made of polylactic acid dragoș gabriel zisopol mechanical engineering department petroleum – gas university ploiesti, romania zisopol@zisopol.ro ion nae mechanical engineering department petroleum – gas university ploiesti, romania inae@upg-ploiesti.ro alexandra-ileana portoaca mechanical engineering department petroleum – gas university ploiesti, romania alexandra.portoaca@upg-ploiesti.ro ibrahim ramadan mechanical engineering department petroleum – gas university ploiesti, romania ing_ramadan@yahoo.com abstract-fused deposition modeling (fdm) is a rapid prototyping method, widely used in the manufacture of plastic parts with complex geometric shapes. the quality of the parts manufactured by this process depends on the plastic material used and the fdm parameters. in this context, this paper will present the results of a theoretical and experimental research on how fdm parameters influence the tensile strength and hardness of samples made of pla (polylactic acid). keywords-3d printing; experimental tests i. introduction with the increasing complexity of industrial products and the requirements related to environmental protection and resource conservation, new manufacturing technologies are needed. fdm is the most significant technique in additive manufacturing (am) that refers to the process in which successive layers of material are stored in a computercontrolled environment to create a three-dimensional (3d) object [1]. since 2009 the demand for fdm has grown steadily and many experts believe that this technology has the potential to revolutionize production in many sectors [2]. the main advantages of fdm are [2]: the manufacturing process is simple, allowing the making of parts with complex geometries and cavities, the dimensional accuracy is good, and it is a more cost-effective method compared to other 3d printing techniques. additive technologies represent a field that is suitable for the needs of today's society through specific interdisciplinary and application possibilities in various areas such as: medicine, engineering, aeronautics, automotive, architecture, etc. however, there are still some limitations and disadvantages, especially in terms of the lower mechanical properties of fdm parts compared to products by conventional methods, such as injection and compression techniques [2, 3]. since mechanical characteristics are extremely important for functional parts, it is necessary to investigate the influence of process parameters on the mechanical performance and geometrical qualification [3, 4]. further research is also needed to determine the printing parameters, such as: deposition orientation, layer thickness, and deposition speed, mainly because the relevant information in the literature is diverse in terms of the values obtained by the mechanical characteristics of parts made with 3d printers. this applies to pla material, which unlike abs has not been extensively analyzed [5-10]. the novelty of this paper consists in the comparison of different printing parameters (layer thickness and infill percentage), which can be used in order to optimize the mechanical characteristics obtained for different applications. ii. a comparison of the materials used for 3d printing in fdm technology fdm has the advantage of using a wide range of materials. table i shows a comparison between the physical and mechanical characteristics of various such materials used. the data were collected from the manufacturers' data sheets specifications. these values are indicative and depend heavily on the printing conditions. the mechanical properties considered refer to the orientation of the horizontal test specimen (xy orientation). under these conditions, this paper analyzes the influence of technological conditions of deposition on the mechanical characteristics of the deposited material. economic, environmental, and safety challenges have caused scientists and economic agents to partially replace petrochemical with biodegradable polymers [11] such as the pla. corresponding author: ion nae engineering, technology & applied science research vol. 11, no. 4, 2021, 7458-7463 7459 www.etasr.com zisopol et al.: a theoretical and experimental research on the influence of fdm parameters on … table i. physical-mechanical characteristics of the most used filaments in fdm technology [8-10] material physical-mechanical characteristics extrusion temperature (°c) bed temperature (°c) density (g/cm 3 ) tensile strength (mpa) specific deformation (%) charpy impact strength (kj/m 2 ) details pla 210 ± 10 25-60 1.31±0.02 15.5-72 34.5 ± 8.1 5.7 ± 0.4 colored filament pp 240 ± 10 80 0.89 14 >200 10 translucent bvoh 210 ± 10 60 1.14 45 9 21 soluble in water petg 240 80 1.25 31.9 ± 1.1 6.8 ± 0.9 5.1 ± 0.3 flexible 316 l 240 ± 10 105 ± 15 5.6 ±0.2 561 53 1110 stainless steel ultem 350 ± 10 150 ± 10 1.27 81 3.3 6 thermoplastic abs 210 ± 10 80 1.10 33.9 4.8 10.5 very rough iii. experimental methodology a. setting up parameters the mechanical properties of 3d printed parts are important indicators for evaluating print quality. the experimental research program includes tests performed to determine how the technological parameters of the printing influence the mechanical characteristics of the deposited material. in these conditions, the working parameters of the printer used must be taken into account. the initial data targeted in the experimental determinations were grouped into two categories (table ii). the first category refers to process parameters considered as constant quantities: deposition direction, printing speed, filling pattern, and deposition temperature. the second category is the process parameters considered as variable parameters: layer thickness (g), infill percentage (gu), flow rate (fr). test specimens were made and were grouped on sets of samples, each set of samples consisting of 5 specimens, belonging to a group of process parameters, highlighted in table iii. table ii. constant and variable printing parameters parameters process parameters used (constant quantities) variable parameters of the technological process build orientation x-y layer thickness (g) print speed (ps) 80mm/s infill procentage (gu) deposition temperature (dt) 200°c flow rate (fr) infill model lines, 45° orientated table iii. program of experimental determinations layer thickness (mm) and infill percentage printing parameters flow rate (mm 3 /s) temperature (°c) print speed (mm/s) 0.2 (100%) 6.4 200 80 0.2 (75%) 6.4 200 80 0.2 (50%) 6.4 200 80 0.2 (25%) 6.4 200 80 0.15 (100%) 4.8 200 80 0.15 (75%) 4.8 200 80 0.15 (50%) 4.8 200 80 0.15 (25%) 4.8 200 80 0.1 (100%) 3.2 200 80 0.1 (75%) 3.2 200 80 0.1 (50%) 3.2 200 80 0.1 (25%) 3.2 200 80 b. experimental set-up the adopted material for making the test specimens was pla. the recommended melting temperature for this material is between 200-220°c, while the temperature of the heated plate has been set to 60°c. the filament used to obtain the test specimens was creality pla, with a diameter of 1.75mm [12]. the specimens were made on the creality cr-x printer, equipped with 2 extruders, with an extrusion nozzle diameter of 0.4mm. work methodology was applied as in figure 1. the shape and main dimensions of the specimen are shown in figure 2. the specimens used in this study to assess dimensional accuracy (figure 3), repeatability and mechanical properties are modeled on american society for testing and materials astm d638, type iv standards for tensile testing of plastic [13]. fig. 1. work methodology. fig. 2. tensile test specimen's dimesional details [13]. the specimen model was designed using autodesk inventor software [14], transformed into stl format, and the g-code was made using the 3d printer software creality slicer [15]. in this software the change of parameters was possible. engineering, technology & applied science research vol. 11, no. 4, 2021, 7458-7463 7460 www.etasr.com zisopol et al.: a theoretical and experimental research on the influence of fdm parameters on … fig. 3. representation of the test piece from the creality slicer software and the infill method (linear). fig. 4. electro-mechanical testing machine with a 2.5kn load cell and a high performance extensometer. fig. 5. shore d type durometer. each set of samples consisted of 5 specimens, each belonging to a group of process parameters, highlighted in table iii. a total of 60 specimens were manufactured by 3d printing. the specimens were subjected to mechanical tests to determine the strength characteristics of the material: ultimate tensile strength (rm), elongation at break (ε), tensile young’s modulus (el), and hardness (hs). tensile tests were performed on an electro-mechanical machine with a force cell of 2.5kn, at a speed of 5mm/min (figure 4). elongation at break was measured using an axial extensometer (figure 4). hardness was measured at the points specified in figure 3. the values of hardness were determined on 15 specimens, with infill percentage of 50%, 75%, and 100%, in 6 points per specimen (figure 4), with a shore d durometer (figure 5). iv. results and discussion the experimental tests were designed to investigate the behavior of plastic parts (pla), under the action of traction forces, made by 3d printing, taking into account the manufacturing conditions as input factors of the testing process. a. tensile properties obtained from the experimental tests the initial information for the tensile tests consisted of the shape and dimensions of the test specimen (figure 2), the type of plastic used (pla), 3d printing equipment (electromechanical machine lloyd lrx force tester figure 4), as well as the process parameters considered as constant quantities: deposition direction (x-y), printing speed (80mm/s), filling pattern (lines), and deposition temperature (200°c). the process parameters considered as variables were: the thickness of the deposited layer (g = 0.1; 0.15; 0.20mm) and the infill percentage (gu = 25%; 50%; 75%; 100%). the experimentally determined quantities were: ultimate tensile strength (rm), elongation at break (ε), tensile young’s modulus (el), and hardness (hs). the test methodology was performed in the conditions in which the variation parameters were the thickness of the deposited material layer g and the infill percentage gu. graphs were drawn that express the dependence of the mechanical characteristics (cm) of the tested specimens according to the infill procentage cm = f(gu) for different thicknesses of the deposited layer. under these conditions, the following dependencies were drawn: • figure 6 shows the dependence rm = f(gu) for g = 0.1mm and gu = 25%; 50%; 75%; 100%. • figure 7 shows the dependence ε = f(gu) for g = 0.1mm and gu = 25%; 50%; 75%; 100%. • figure 8 shows the dependence el = f(gu) for g = 0.1mm and gu = 25%; 50%; 75%; 100%. • figure 9 shows the dependence rm = f(gu) for g = 0.15mm and gu = 25%; 50%; 75%; 100%. • figure 10 shows the dependence ε = f(gu) for g = 0.15mm and gu = 25%; 50%; 75%; 100%. • figure 11 shows the dependence el = f(gu) for g = 0.15mm and gu = 25%; 50%; 75%; 100%. • figure 12 shows the dependence rm = f(gu) for g = 0.20mm and gu = 25%; 50%; 75%; 100%. • figure 13 shows the dependence ε = f (gu) for g = 0.20mm and gu = 25%; 50%; 75%; 100%. • figure 14 shows the dependence el = f (gu) for g = 0.20mm and gu = 25%; 50%; 75%; 100%. engineering, technology & applied science research vol. 11, no. 4, 2021, 7458-7463 7461 www.etasr.com zisopol et al.: a theoretical and experimental research on the influence of fdm parameters on … fig. 6. dependence rm = f(gu) for g = 0.1mm. fig. 7. dependence ε = f(gu) for g = 0.1mm. fig. 8. dependence el = f(gu) for g = 0.1mm. fig. 9. dependence rm = f(gu) for g = 0.15mm. fig. 10. dependence ε = f(gu) for g = 0.1mm. fig. 11. dependence el = f(gu) for g = 0.15mm. fig. 12. dependence rm = f(gu) for g = 0.20mm. fig. 13. dependence ε = f(gu) for g = 0.20mm. engineering, technology & applied science research vol. 11, no. 4, 2021, 7458-7463 7462 www.etasr.com zisopol et al.: a theoretical and experimental research on the influence of fdm parameters on … fig. 14. dependence el = f(gu) for g = 0.20mm. b. shore d hardness the shore d hardness for 50, 75, and 100% gu can be seen in figure 15. v. conclusions the objective of the paper was to establish the variation of the mechanical characteristics of the pla material, deposited by 3d printing, depending on the parameters of the technological process. we have started from the characteristics of the raw material (table i) which show a wide range of characteristic values: rm varying from 15.5 to 2mpa, and ε = 34.5 ± 8.1%. from the analysis of the obtained results it was found that the values of ultimate tensile strength (rm), are within the limits of rm, specimen varying from 21.0 to 40.07mpa, and for εspecimen from 6.92 to 16.1%. by comparison with the values from manufacturers' data sheets it is found that rm, specimen represents only 55.6% of the maximum value of rm and for ε the values obtained on specimens are below the recommended lower limit for the raw material εbrut, min = 26.4%. graphs were drawn that express the dependence of the cm of the tested specimens according to the infill percentage cm = f(gu), in which gu = 25%; 50%; 75%; 100%, for different thicknesses of the deposited layer (g = 0.1, 0.15, 0.20mm). the analysis of the experimental data showed that the maximum value of rm, test piece = 40.07mpa resulted in the conditions g = 0.15mm and gu = 100%. given that the thickness of the layer of the deposited material changed to g = 0.20mm and the infill percentage remained the same gu = 100%, a decrease in ultimate tensile strength was observed, which reached the value rm, specimen = 35.8mpa. this phenomenon can be explained by the low cohesion of the deposited layers, which involves establishing the influence of the deposition temperature. the flow rate of the raw material is directly proportional to the thickness of the layer as can be seen in table i. various studies [5, 16-19] have shown that the ultimate tensile strength increases with the thickness of the deposited layer. in this study, although the maximum value was highlighted for the layer thickness of 0.15mm, a higher elongation at break is observed in the specimens with a layer thickness of 0.1mm. all graphs reveal better performance with the increase of infill percentage and less influence of the layer thickness (similar results). it is well known that despite the fact that results can be less satisfying, surely other criteria can be accomplished by using 3d printing. in this context, further experiments could be developed to evaluate the effect of other input factors of the manufacturing process on the behavior of the parts in the tensile stresses of the material. regarding hardness, there is no correlation between the infill percentage and the shore d hardness, because of the shell layers (thickness of 0.8mm) and bottom and top thickness of the layers applied on all infill types of specimens. further research and possible modification of the shell structure might reveal different results in this direction. references [1] n. mohan, p. senthil, s. vinodh, and n. jayanth, "a review on composite materials and process parameters optimisation for the fused deposition modelling process," virtual and physical prototyping, vol. 12, no. 1, pp. 47–59, jan. 2017, https://doi.org/10.1080/17452759. 2016.1274490. 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[15] a. garcía-domínguez, j. claver, a. m. camacho, and m. a. sebastián, "analysis of general and specific standardization developments in additive manufacturing from a materials and technological approach," ieee access, vol. 8, pp. 125056–125075, 2020, https://doi.org/10.1109/access.2020.3005021. [16] a. garcía-domínguez, j. claver, a. m. camacho, and m. a. sebastián, "analysis of general and specific standardization developments in additive manufacturing from a materials and technological approach," ieee access, vol. 8, pp. 125056–125075, 2020, https://doi.org/10.1109/access.2020.3005021. [17] n. li, y. li, and s. liu, "rapid prototyping of continuous carbon fiber reinforced polylactic acid composites by 3d printing," journal of materials processing technology, vol. 238, pp. 218–225, dec. 2016, https://doi.org/10.1016/j.jmatprotec.2016.07.025. 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[19] f. ning, w. cong, j. qiu, j. wei, and s. wang, "additive manufacturing of carbon fiber reinforced thermoplastic composites using fused deposition modeling," composites part b: engineering, vol. 80, pp. 369–378, oct. 2015, https://doi.org/10.1016/j.compositesb.2015.06.013. microsoft word danikas-rev-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 511-515 511 www.etasr.com bairaktari et al.: behaviour of water droplets under the influence of a uniform electric field … behaviour of water droplets under the influence of a uniform electric field in nanocomposite samples of epoxy resin/tio2 α. bairaktari democritus university of thrace, dpt of electrical and computer engineering, power systems lab, greece agbairaktari@ gmail.com m. g. danikas democritus university of thrace, dpt of electrical and computer engineering, power systems lab, greece mdanikas@ ee.duth.gr x. zhao xi’an jiaotong university, state key laboratory of electrical insulation and power equipment, xi’an, p. r. china tuan.zx@ stu.xjtu.edu.cn y. cheng xi’an jiaotong university, state key laboratory of electrical insulation and power equipment, xi’an, p. r. china cyh@ mail.xjtu.edu.cn y. zhang xi’an jiaotong university, state key laboratory of electrical insulation and power equipment, xi’an, p. r. china zy0026@ stu.xjtu.edu.cn abstract— in this paper nanocomposite samples of epoxy resin and tio2 nanoparticles were investigated with water droplets on their surface. a uniform electric field was applied and the behaviour of the water droplets was observed. parameters that were studied were the water conductivity, the droplet volume, the number of droplets and the droplet positioning with respect to (w.r.t.) the electrodes. all above mentioned parameters influence the flashover voltage of the samples. it is to be noted that – at least in some cases – the water droplet positioning w.r.t. the electrodes was more important in determining the flashover voltage than the droplet volume. keywordsflashover voltage; surface discharges; nanocomposites; uniform electric field; water droplet; water conductivity i. introduction epoxy resin is an insulating material widely used in high voltage various applications [1, 2]. traditional base polymeric materials improve their electrical properties when they are mixed with small percentages of nanoparticles [3]. addition of small quantities of nanoparticles in percentages weight smaller than 10% also improve the thermal and mechanical properties of the nanocomposites. for such materials, the interfaces play a most important role [4]. nanocomposite polymers may be classified in intercalated nanocomposites (formed when there is limited inclusion of polymer chain between the clay layers with a correspondingly small increase in the interlayer spacing of a few nanometers) and exfoliated nanocomposites (which are structures formed when the clay layers are well separated from one another and individually dispersed in the continuous polymer matrix) [5]. nanocomposite polymers present higher breakdown strength than their base counterparts [6]. space charges have a much more even distribution in nanocomposite polymers than in base polymers [7]. the thermal conductivity of nanocomposite polymers is also improved compared with their base polymer counterparts [8]. electrical treeing behaviour is also improved in nanocomposites [9, 10]. the addition of nanoparticles in conventional polymers helps also in increasing their resistance against partial discharges (pd) [11]. in this paper, epoxy resin with tio2 nanoparticles was investigated. samples with 1% and 3% weight percent (wt) were tested. the purpose of this work was to see how water droplets arrangements on the surface of such samples under the effect of uniform electric field affect the flashover voltage. parameters, such as water droplet conductivity, number of droplets, droplet volume and droplet positioning w.r.t. the electrodes were examined. ii. water droplets on polymer surfaces and the factor of hydrophobicity the forces acting on a droplet on a solid insulating surface, in case no electric field is applied, are the surface tension of the liquid, the surface tension of the solid and the interfacial tension between the droplet and the solid. an applied electric field results in a deformation/elongation of the droplet. this deformation will eventually influence the distribution of the electric field. local field intensifications may ensue and microdischarges may occur between droplets. such a mechanism may cause the formation of dry zones and the root of the electrochemical deterioration of the insulator surface [12]. most polymeric materials used for outdoor applications have some sort of hydrophobicity, i.e. the capability of retaining discrete droplets on the insulator surface. loss of hydrophobicity may result from surface discharges, pollution of the insulator surface and/or from ultraviolet radiation. etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 511-515 512 www.etasr.com bairaktari et al.: behaviour of water droplets under the influence of a uniform electric field … the contact angle is given as 1 2 90 tan 2 r b rb b θ −  − = −   −  where b, θ and r as in figure 1. fig. 1. model for the calculation of contact angle generally speaking, when a water droplet is positioned on a nanocomposite surface under a high electric field parallel to the surface, discharges may appear and surface tension may be reduced with the increase of temperature at the edge of the droplet. in this way, the droplet starts deforming and continuous discharges may ensue between the edges of the droplet and the electrodes [14]. iii. experimental arrangement the voltage was supplied from a 20 kv transformer. the dimensions of the electrodes are shown in figure 2. the electrodes were made of copper and they are half cylindrical with rounded edges. no asperities were allowed on the electrode surfaces. they were positioned on the epoxy resin sample at a distance of 2.5 cm from each other. the aim of the experiments was to measure the flashover voltage with different droplet arrangements at different conductivities. fig. 2. top view of one of the electrodes and cross section the water droplets were positioned on the sample surface with the aid of a special arrangement consisting of a metallic frame and three rules, one of which had two laser indicators. the water droplets were poured into the sample surface with the aid of a syringe. the droplet arrangements are shown in figure 3, with all dimensions given in cm. fig. 3. droplet arrangements for the experiments (all dimensions in cm) etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 511-515 513 www.etasr.com bairaktari et al.: behaviour of water droplets under the influence of a uniform electric field … the conductivities investigated were 1.4 µs/cm, 100 µs/cm, 200 µs/cm, 500 µs/cm, 1000 µs/cm, 2000 µs/cm, 5000 µs/cm and 10000 µs/cm. the conductivity measurements were performed with the aid of an electronic measuring device of conductivity of type wtw inolab cond level 1 with a probe wtw tetracon 325 (figure 4). the following droplet arrangements were used: 1) one droplet of 0.05 ml volume each, 2) two droplets of 0.05 ml volume with a distance of 0.8 cm between their centres, 3) three droplets of 0.05 ml volume each, forming a triangle, 4) four droplets of 0.05 ml each, 5) one droplet of 0.1 ml volume at a distance of 1.25 cm from the electrodes and 6) two droplets of 0.1 ml each at a distance of 1 cm from each other and 1.25 cm from the electrodes. in figure 5, various droplet arrangements on the nanocomposite samples are shown the surface roughness of the samples was measured with the aid of a perthen type perthometer m4p device. surface roughness for the epoxy nanocomposite samples of 1% wt was 0.19 and 0.20 µm and for the 3% wt nanocomposite samples was 0.15 µm and 0.20 µm. after positioning the droplets on the epoxy resin surface, the voltage was slowly raised until flashover occurred. after that and after cleaning the surface and positioning new droplets on it, the voltage was raised up to the previous flashover value minus 1.2 kv, so that no new flashover would occur. at this voltage value, the arrangements would stay for 5 min. if no flashover occurred, the voltage was raised by 0.4 kv and the procedure was repeated until flashover occurred. the new flashover value was recorded. the reason for allowing the voltage for 5 min at each voltage level was because a certain time was required for the droplets to deform and for the pd to start. fig. 4. device for conductivity measurements iv. experimental results and discussion in figures 6 and 7 the experimental results with the various droplet arrangements, the different water conductivities and droplet volumes are given. it is evident that water conductivity and droplet volume have an inportant effect on flashover voltage, i.e. a larger droplet volume may imply a shorter distance of the droplets from the respective electrodes. if we compare, for example, the results between the droplet of 0.1 ml and that of 0.05 ml, we see that the latter gives higher flashover voltage for both investigated nanocomposites. the number of droplets is also a factor not to be neglected. increasing water conductivity implies a reduced flashover voltage for both nanocomposites, irrspective of their content in tio2 nanoparticles. another significant parameter affecting the flashover voltage of the nanocomposite is the positioning of the droplets w.r.t. the electrodes. having in mind the water droplet arrangements used, if we compare, for example, the results between the arrangement with two droplets of 0.05 ml each and the arrangement of two droplets of 0.1 ml each, we realize that the latter offers a higher flashover voltage than the former. this is valid for both nanoparticle contents. it is indicated from the above figures that the distance of the droplets from the electrodes plays an important role and – sometimes – a more critical than the droplet volume. if the results of figure 6 and figure 7 are compared with those of pure epoxy resin (i.e. without any nanoparticles, figure 8 [15]), it is evident that the addition of nanoparticles improves the flashover voltage of epoxy resin. the nanocomposite epoxy resin is proven to give higher flashover voltages than the epoxy resin without nanoparticles. of the two nanocomposite polymers investigated here, the one with 1 %wt has the superior flashover voltage for most droplet arrangements. evidently, the optimum percentage of nanoparticles depends on the base material as well as on the nature of the nanoparticles. the addition of nanoparticles can improve the flashover voltage of a polymeric material up to a certain point. if a larger percentage of nanoparticles is added, the electrical properties of the nanomaterial may deteriorate. fig. 5. various droplet arrangements it was proposed that in the event of a surface flashover in nanocomposite polymers, the regions that are destroyed are those of epoxy resin, with the consequence of the nanoparticles coming to the surface and forming agglomerations. such nanoparticle agglomerations contribute to reducing the degradation of the surface [16]. moreover, sem photographs etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 511-515 514 www.etasr.com bairaktari et al.: behaviour of water droplets under the influence of a uniform electric field … of degraded polymer surfaces showed that the channels caused by surface degradation are much deeper and wider in the case of the base polymers than in the case of nanocomposites [17]. this may be due to the beneficial effect of the nanoparticles coming up to the surface and thus hindering discharge channels to be created [17, 18]. regarding the flashover event in nanocomposite epoxy as well as in simple epoxy resin, one may say that under a.c. voltages more carbonization of the material was observed when simple epoxy resin was tested than when nanocomposite epoxy was tested. this is in agreement with previous research [17, 18]. under ac voltages, the water droplet was first oscillating and then approaching one of the electrodes. the flashover voltage was recorded either as a flashover through the air or through the water droplets. in most experiments the water droplet(s) started oscillating at the voltage at which flashover was observed. in other experiments there was a deviation of 0.6 kv on average. fig. 6. results with epoxy resin nanocomposite with 1% wt of tio2 nanoparticles fig. 7. results with epoxy resin nanocomposite with 3% wt of tio2 nanoparticles fig. 8. results with epoxy resin (without nanoparticles) a criticism that may be leveled at this work is whether, given the small size of the electrodes, the applied electric field was uniform. having in mind the small volumes of the droplets used, we consider – with the size of the electrodes employed in this work – the electric field was uniform. we plan, however, in the future more research with the same droplet volumes but with bigger electrodes. fig. 9. droplet deformation under the influence of electric field v. conclusions in this paper, several factors affecting the flashover voltage on nanocomposite polymeric surfaces were investigated, such as water droplet volume, droplet number, water conductivity and positioning of droplets w.r.t. the electrodes. the flashover voltage is influenced by all these parameters. it is to be noted that in some cases, the positioning of water droplets w.r.t. the electrodes is more important than the droplet volume. references [1] d. kind, h. kaerner, “high-voltage insulation technology”, eds. vieweg & sohn, braunschweig, germany, 1985 [2] m. g. danikas, a. d. karlis, “some observations on the dielectric breakdown and the importance of cavities in insulating materials used etasr engineering, technology & applied science research vol. 3, �o. 5, 2013, 511-515 515 www.etasr.com bairaktari et al.: behaviour of water droplets under the influence of a uniform electric field … for cables and electrical machines”, advances in electrical and computer engineering, vol. 11, no. 2, pp. 123-126, 2011 [3] j. k. nelson, “dielectric polymer nanocomposites”, eds. springer, heidelberg, germany, 2010 [4] k. y. lau, m. a. m. piah, “polymer nanocomposites in high voltage electrical insulation perspective: a review”, malaysian polymer journal, vol. 6, no. 1, pp. 58-69, 2011 [5] r. sarathi, r. k. sahu, p. rajeshkumar, “understanding the thermal, mechanical and electrical properties of epoxy nanocomposites”, materials science and engineering: a, vol. 445-446, pp. 567-578, 2007 [6] y. okazaki, m. kozako, m. hikita, t. tanaka, “effects of addition of nano-scale alumina and silica fillers on thermal conductivity and dielectric strength of epoxy/alumina microcomposites”, 10th ieee international conference on solid dielectrics (icsd), potsdam, germany, pp. 1-4, 2010 [7] j. k. nelson, “the promise of dielectric nanocomposites”, ieee international symposium on electrical insulation, toronto, pp. 452-457, 2006 [8] z. han, j. w. wood, h. herman, c. zhang, g. c. stevens, “thermal properties of composites filled with different fillers”, isei 2008, ieee international symposium on electrical insulation, vancouver, pp. 497501, 2008 [9] s. alapati, m. joy thomas, “electrical treeing in polymer nanocomposites”, 15 th national power systems conference (npsc), iit bomaby, pp. 351-355, 2008 [10] m. g. danikas, t. tanaka, “nanocomposites-a review of electrical treeing and breakdown”, ieee electrical insulation magazine, vol. 25, no. 4, pp. 19-25, 2009 [11] t. tanaka, s. kuge, m. kozako, t. imai, t. ozaki, t. shimizu, “nano effects on pd endurance of epoxy nanocomposites”, international conference on electrical engineering, korea, art. no. me1-01, pp. 1-4, 2006 [12] m. g. danikas, “surface pphenomena on resin-type insulators under different electrical and non-electrical stresses in the early stage of ageing”, facta universitatis, vol. 13, no. 3, pp. 335-352, 2000 [13] y. khan, “degradation of hydrophobic properties of composite insulators in simulated arid desert environment”, international journal of engineering & technology, vol. 10, no. 1, pp. 86-90, 2010 [14] r. sarathi, m. g. danikas, “understanding discharge activity due to water droplet in epoxy nanocomposites using acoustic emission technique”, journal of electrical engineering, vol. 59, no. 6, pp. 294301, 2008 [15] y. cheng, x. zhao, m. g. danikas, d. d. christantoni, p. zairis, “a study of the behaviour of water droplets under the influence of uniform electric field in epoxy resin samples”, journal of electrical engineering, vol. 63, no. 3, pp. 196-200, 2012 [16] m. kozako, r. kido, t. imai, t. ozaki, t. shimizu, t. tanaka, “surface roughness change of epoxy/tio2 nanocomposites due to partial discharges”, proceedings of 2005 international symposium on electrical insulating materials, kitakyushu, japan, vol. 3, pp. 661-664, 2005 [17] p. maity, s. basu, v. parameswaran, n. gupta, “degradation of polymer dielectrics with nanometric metal-oxide fillers due to surface discharges”, ieee transactions on dielectrics and electrical insulation, vol. 15, no. 1, pp. 52-62, 2008 [18] m. kozako, s. kuge, t. imai, t. ozaki, t. shimizu, t. tanaka, “surface erosion due to partial discharges on several kinds of epoxy nanocomposites”, annual report conference on electrical insulation and dielectric phenomena (ceidp), nashville, usa, pp. 162-165, 2005 microsoft word 46-2836_s1_etasr_v9_n4_pp4561-4565 engineering, technology & applied science research vol. 9, no. 4, 2019, 4561-4565 4561 www.etasr.com babesse: design of two optimized controllers of a hydraulic actuator semi-active suspension design of two optimized controllers of a hydraulic actuator semi-active suspension a comparison study saad babesse department of electrical engineering, ferhat abbas university setif i, setif, algeria saad.babesse@univ-setif.dz abstract—a parallel optimization of proportional, integral and derivative (pid) controller and a sixth order phase lead-lag compensator of a high order naturally oscillatory hydraulic actuator are proposed in this paper. the pid controller parameters (proportional, integral and derivative) and the compensator parameters (gain, poles and zeros) are obtained by minimizing the integral of time absolute error (itae) criterion. the proposed methods are demonstrated through a realistic numerical synthesis example of a hydraulic actuator dedicated to a semi-active suspension modeled by an eighth order transfer function. a simulation comparison is investigated for both controllers to compare their performances. keywords-parallel pid; phase lead lag compensator; hydraulic actuator; itae i. introduction the pid controller has been widely used since its invention [1]. it is a simple and easy way to tune control structures. since many control systems using pid control are proven to be satisfactory, it still has a wide range of applications in industrial control. in 1989, more than 90% of the control loops were of the pid type [2, 3]. however, most of the classical methods for pid control design suffer from usability restrictions. this may be caused by many reasons such as character of the plant (regarding zeros and poles character and position) or its order [4]. in this paper, we achieve the optimization of the pid parameters with the effective application of integral criterion (itae) as an objective function. on the other hand, with the powerful tools provided by matlab, many optimal control problems can be converted into conventional optimization problems. with the above-mentioned function, some optimal controller problems can be easily solved. although not allowing elegant analytical solutions, numerical methods are extremely powerful practical techniques for controller design. in this context, a sixth order phase lead-lag compensator based on itae criterion minimization was designed and a comparison study between the two previous controllers through a realistic numerical example was conducted, based on time performances such as settling time, response time, and overshoot. ii. background there are many pid control configurations, but the most common implementation of this controller is the feedback‐loop with a single input and a single output [5] (figure 1). the typical structure of the pid controller is shown in figure 2. the signal error ���� enters the pid control block and the resulting excitation signal is the sum of the error signal affected by the proportional, integral and derivative actions. fig. 1. block diagram of the simplest pid controller. fig. 2. block diagram of the typical strucure of pid controller. a simulink model for the pid control, with itae descriptions, is established as shown in figure 3, where the variable names to be optimized are kp, ki, kd and the objective function is the itae criterion. in figure 4, an optimal controller design is explored to calculate the gain, poles and zeros of the desired phase lead lag compensator by reducing the objective function (itae criterion) [5]. for both controllers, matlab function fmincon can be used to solve the constrained optimization problems. corresponding author: saad babesse engineering, technology & applied science research vol. 9, no. 4, 2019, 4561-4565 4562 www.etasr.com babesse: design of two optimized controllers of a hydraulic actuator semi-active suspension fig. 3. simulink model of optimized pid based on itae criterion. fig. 4. simulink model of optimized compensator based on itae criterion. iii. numerical example considering the studied single input single output (siso) high order system as a hydraulic actuator dedicated to a heavy vehicle anti-roll bar mechanism which has a seven order transfer function, and by adding a first order lead-lag pre-filter, the overall system becomes with an eight order transfer function. a cad model [7] of one axle fitted with active components can be seen in [6]. the roll plane model of the truck is described in [8, 9]. the truck body (referred to as the ‘sprung mass’) is connected to the suspension trailing arms and axles (referred to as ‘unsprung masses’) by dampers and springs representing the suspension stiffness and damping. the damping has been assumed to be linear and tyre compliance (and therefore roll angle contribution) has been neglected. the suspension consists of two trailing arms free to rotate about their axis independently of each other. each end of the anti-roll bar is attached to one trailing arm whose position is determined by the wheels and actuator positions. the actuators are mounted between the anti-roll bar and the frame of the trailer. by extending one actuator and retracting the other, the anti-roll bar is twisted and torque is provided to counteract the moment generated by the lateral acceleration and tilt the vehicle into the turn. the different transfer functions are given below [6, 7]. the transfer function between the displacement transducer extension � and the actuator extension �� is given by: �̅ �� � ��� ��� �� ����� ����������������������� ���� ! ��""" #$%!� ����� ����������������������� ���� ! (1) the transfer function between the actuator extension �� and the servo-valve spool displacement �& is given by: �� �' (�) �**�+��*�����*+���*, .�& (2) with: .// 0121345(�� ,./� 8��521(�� 9 01:�345(��;, ./< 81 9 ��5:�(�� 9 01�>345(��;,./3 ��5�>(�� the servo-valve is modeled as a second order butterworth filter. it is a low-pass filter with a cut-off frequency of 15hz, which is given by: ?@�a� b%��c��4������cb%��b%��c��4�� (3) where: ωc=30π.rad/sec, a=0.5949, and β=0.2830. to keep the entire system stable with the range of given references, we add a lead-lag pre-filter, given by: de�a� f*��/f���/ (4) g/,g�were chosen to enable a reasonable choice of the regulator parameters: g/ 0.001 s,g� 2 a. the open loop transfer function of the overall system is given by the following transfer function: k�a� l+�+�l����l*��lm�n��o�o��p�p��q�q��,�,��+�+�������*���m (5) where: r< 1.135.103, r� 1.135.10u,r/ 1.897.10y rz 1.897.10/�,.u 122.1,.[ 2.175.10\ .\ 2.421.10u,.3 8.836.10_,.< 4.288.10y a� 1.046.10//,a/ 1.167.10//,az 3.271.10/z this plant has uncontrollable modes, since: a.bc�d� 8,a.bc�e� 3 �d,?� are extracted from the state space representation of the plant k and e f�ar�d,?� is the controllability matrix. this property can make control difficulties, presented as oscillations in the response. to design the two controllers, we adopt the following time specifications: settling time: less than 4s, rise time: less than 2.5s, and overshoot%: less than 5%. a. optimized pid based on itae criterion using the matlab function fmincon with pid parameters initialization: x0=[0.001;0.001;0.001], minimization of the objective function itae, and after 80 iterations, the solution is [10, 11]: cg 0.0288,ch 0.0090 ,c� 0.0112 engineering, technology & applied science research vol. 9, no. 4, 2019, 4561-4565 4563 www.etasr.com babesse: design of two optimized controllers of a hydraulic actuator semi-active suspension b. optimized compensator based on itae criterion the previous matlab function is used with gain, poles and zeros initialization, and the optimal compensator is obtained by minimising the itae criterion. the order of the compensator is choosen after several trial-and-error designs. the best obtained is a sixth order phase lead lag compensator. after 51 iterations, the compensator parameters are obtained as follows: the gain is: k=0.003667. the zeros are: z1=-0.5887, z2=-0.5347, z3,4=2.9765±11.8634j, z5,6=6.9850×10 -3 ±4.2237×10 2 j. the poles are: p1=-2.34, p2=-5.768×10 -7 , p3,4=-1.2615±2.5105j, p5,6=-1.2280×10 -9 ±4.0890×10 2 j. c. simulations first, we compare the performance of the designed controllers with [7]. the pid controller gains found are: ig 0.05;ih 0.03 ;i� 2.10�< and then, we apply the different controllers to track the setpoint (roll angle) as the input of the hydraulic actuator. we choose as simulation time: ts=20s, and the step function as a set-point. fig. 5. time characteristics of optimized controllers closed loop step response. fig. 6. response of the hydraulic actuator. fig. 7. tracking errors. fig. 8. generated anti-roll bar moment. figure 5 shows that all time characteristics (overshoot%, rise time and settling time) of the optimized compensator are better than those of the optimized pid. in figure 6, the response of the hydraulic actuator to 5° roll angle setpoint gives good tracking and less overshoot in the optimized compensator case comparing it with optimized pid and that of [7]. this can also be expressed by the errors shown in figure 7. the response of the pid controller of [7] gave oscillations and an overshoot of 40%. the required roll moment generated by the antiroll bar is shown in figure 8. one can see that the maximum moment is towards -11.8×10 4 n.m in the case of the optimized compensator and -11.2×10 4 n.m for the optimized pid and -16.4×10 4 n.m for the pid case of [7] (these values must be less than the maximum tolerated moment of the actuator). sign (-) indicates that the roll moment and the roll angle are in opposite directions. now, we apply a variable setpoint to the three controllers, and then we compare their behaviors. figures 9-10 show that the controllers track the variable setpoint plant with fast response of the optimized compensator comparing it with optimized pid. but the oscillations always persist for the pid case of [7]. engineering, technology & applied science research vol. 9, no. 4, 2019, 4561-4565 4564 www.etasr.com babesse: design of two optimized controllers of a hydraulic actuator semi-active suspension fig. 9. response of the hydraulic actuator. fig. 10. tracking errors. fig. 11. generated anti-roll bar moment. the optimized compensator requires an antiroll moment greater than that of the optimized pid, but less than the maximum tolerated roll moment of the antiroll bar mechanism, as shown in figure 11. the comparison between the different time characteristics of the proposed controllers is summarized in table i. table i. comparison of the controllers performances controller time characteristics overshoot (%) rise time (s) settling time (s) optimized pid 4.69 3.3 4.34 optimized compensator 1.54 1.72 3.1 [7] 40.9 1.47 10.92 table ii. antiroll bar parameters parameter description value kl mn o�p q effective bulk modulus of hydraulic oil 6.89×106 dg�o�� area of piston of hydraulic actuator 0.0123 e mna o�p q damping force coefficient 10000 r��o� distance to the actuator from the centreline of suspension 0.215 r��o� distance to damper from centreline of suspension 0.23 r��o� distance to air spring from centreline of suspension 0.535 rs�o� half track width 0.93 t�ul�iv.o�� moment of inertia of anti-roll bar about roll centre of suspension 6.10 tg�iv. o�� moment of inertia of sprung mass about roll center of suspension 9500 c��n/o� air spring stiffness 2.37×105 c�ul�no/a.r� roll stiffness of anti-roll bar 1.02×106 c! 8 no. a.r; spring stiffness in merritt’s valvepiston model 1.1033×10 7 cgl x o< apn o�p y servo-valve total flow pressure coefficient 4.2×10 -11 cz x o< apo y servo-valve flow gain coefficient 2.5 {�o� distance to displacement transducer from centreline of suspension 0.552 |}�cv� mass of load in merritt’s valve-piston model 65.9816 ?g ~8 cv.no.a.r; z.\� damping coefficient in merritt’s valve-piston model 539.6201 d��r.a� supply pressure of hydraulic system 210 �}�o<� volume of ‘trapped’ oil at high pressure in the hydraulic system 0.0014 iv. conclusion two optimized controllers based on integral time absolute error minimization criterion and utilizing matlab/simulink are proposed. it was shown that the optimized compensator gives better time characteristics performances than the optimized pid and pid based on root locus method. a simulation comparison, using step set-point and variable set-point, was investigated. the optimized compensator presented in this work can enhance considerably the control of this type of antiroll bar mechanisms mounted on experimental and real trucks references [1] a. firoozshahi, “innovative tank management system based on dcs” , ieee, elmar 2010, zadar, croatia, september 15-17, 2010 [2] c. c. yu, autotuning of pid controllers: relay feedback approach, springer-verlag, 1999 [3] k. j. astrom, t. hagglund, automatic tuning of pid controllers, instrument society of america, 1988 engineering, technology & applied science research vol. 9, no. 4, 2019, 4561-4565 4565 www.etasr.com babesse: design of two optimized controllers of a hydraulic actuator semi-active suspension [4] s. ozana, t. docekal, “pid controller design based on global optimization technique with additional constraints”, journal of electrical engineering, vol. 67, no. 3, pp. 160-168, 2016 [5] m. milosawlewitsch-aliaga, r. a. osornio‐rios, r. j. romerotroncoso, “model‐based iterative feedback tuning for industrial pid controllers”, journal of scientific and industrial research, vol. 69, no. 12, pp. 930‐936, 2010 [6] d. j. m. sampson, p. g. mckevitt, d.cebon, “the development of an active roll control system for heavy vehicles”, 16 th iavsd symposium on the dynamics of vehicles on roads and tracks, pretoria, south africa, 1999 [7] a. j. p. miege, development of active anti-roll control for heavy vehicles, first year report submitted to the university of cambridge, university of cambridge, 2000 [8] s. babesse, d. ameddah, f. inel, “comparison between rst and pid controllers performance of a reduced order model and the original model of a hydraulic actuator dedicated to a semi-active suspension”, world journal of engineering, vol. 13, no. 1, pp. 66-71, 2016 [9] s. babesse, d. ameddah, “neuronal active anti-roll control of a single unit heavy vhicle associated with rst control of the hydraulic actuator”, international journal of heavy vehicle systems, vol. 22, no. 3, pp. 236254, 2015 [10] r. a ,waltz, j. l. morales, j. nocedal, d. orban, “an interior algorithm for nonlinear optimization that combines line search and trust region steps”, mathematical programming, vol. 107, no. 3, pp. 391–408, 2006 [11] t. k. kiong, w. qing-guo, h. c. chieh, t. j. hagglund, advances in pid control, springer verlag, 2000 engineering, technology & applied science research vol. 7, no. 5, 2017, 2098-2103 2098 www.etasr.com ahmed and malik: a review of works on shaped charges a review of works on shaped charges mukhtar ahmed school of chemical & materials engineering (scme) national university of sciences & technology (nust) islamabad, pakistan mukhtar@scme.nust.edu.pk abdul qadeer malik school of chemical & materials engineering (scme) national university of sciences & technology (nust) islamabad, pakistan aqmalik@scme.nust.edu.pk abstract—shaped charges are used to pierce hard targets in all three versions of warfare land, air and naval. high explosives compositions fillings produce a thin high velocity metal jet which is used for target damage. shaped charges can efficiently damage tanks possessing thick armour protection, bunkers and aircraft and are also useful for attacking ships and submarines. shaped charges have a very long history since the second world war theoretical modeling started with the steady state theory of birkhoff in 1948, which was modified by the non-steady state theory known as per theory of shaped charges. to review the development in the shaped charges three stages are defined. in the first stage development until 1990 is presented when shaped charge theory was fully developed and penetration predictions with fairly good accuracy were possible. in the second stage, review of the work carried out in the last decade of the 20th century is discussed. during this period experimental verification of different parameters was established. the third stage deals with all the work carried out in the 21st century (2000-2010), including tools for advanced diagnostics, new fabrication and inspection, as well as new liner materials were included. the anomalies occurred were resolved by further refinements in the theoretical models. keywords-high explosives; liners; jet formation; shaped charges; target penetration i. introduction the weapon industry has concentrated on the growth of the lined cavity shaped explosive charges, often known as cone bombs, shaped charges or munroe bombs during the last few decades [1]. during the world war ii, various explosives developers and mining companies have focused their attentions on the use of lined cavity shaped charges in military and mining applications. in view of remarkable military achievements, the general lack of success in the civil uses suggests that perhaps the commercial investigator overlooked some factors in the design of shaped utilization. from what can be determined concerning most of the projects that failed, this was indeed the case. two main factors are generally considered as the cause of disappointment. the first of these was the field of application. most of the work was carried out with the aim of the lined cavity charge by secondary blasting tool but the lined cavity charge is most suitable for punching a hole in the target, not for breaking it. the second and most serious problem was the type of explosive used. generally low velocity, low brisance explosive will not yield a workable lined cavity shaped charge. on the other side high velocity, high brisance explosive are difficult to manufacture. the lack of high explosive coupled with the fact that relatively little was known about the lined cavity shaped charge outside the ordnance circles meant that many of the early efforts failed to achieve workable shaped charges. the purpose of this paper is to provide a basic review of the history the shaped charge, main theories involved and to provide a detailed history. ii. history of the lined cavity charge phenomena the unlined cavity effect is primarily known as the munroe effect in united states and u. k. and as the neumann effect in most european countries, in honor of groundbreaking contributors. both of them only reported the experimental results on the unlined cavity effect. the origin of the lined cavity explosive charges is dubious. it is proclaimed that germany used the lined cavity shaped charges during world war i. also some shaped researcher attributed the discovery of lined cavity charges to neumann during world war ii. presently most of the investigators accredit the discovery of lined cavity shaped charge to r. w. wood of the johns hopkins university, as he found that the dimpled blasting cap produced a high velocity jet of metallic particles from copper sheath comprising the dimple. korolev and pokrovskii in 1944 published an article in russia about the jets emitted by no. 8 blasting cap covered with copper. many nations started research on the basis of dr. wood’s discovery to utilize the lined cavity weapons. most of these projects were successful. the most well known lined cavity weapon of that time was the bazooka, which consists of a lined cavity shaped mounted on a small rocket. many other lined cavity weapons have been used for demolition purposes but most of the research publications have been classified due to military interests. the research on fundamentals of lined cavity shaped charges was not available since 1940. the mining and allied industries were highly disappointed from results regarding the lined cavity phenomena. failures were occurring due to lack of data available at that time. this started to change after 1946 with published research mainly focusing on non-military applications (mining, drilling, tunnel construction etc). shaped charges started to become commercially available in late 40s and related brief articles surfaced. to summarize the historical aspects, a considerable fundamental literature is now available engineering, technology & applied science research vol. 7, no. 5, 2017, 2098-2103 2099 www.etasr.com ahmed and malik: a review of works on shaped charges concerning the hydrodynamic mechanism of jet formation. only limited data is available for other mechanism and a very little data is available on penetration on targets, especially non ductile targets such as rock and other earth materials. shaped charges are cylindrical explosive filled charges with hollow cavity at one end and a detonator on the opposite side of the cavity. they are known as hollow charges or sometimes as explosively formed penetrators (efp). the hollow cavity is usually lined with a metallic material made of copper, steel or aluminum. on detonation of the explosive charge, huge pressure up to around 300 kbr is generated and the metallic liner collapses to form a high velocity jet, whose tip may attain a velocity in excess of 10 km/sec and rearward tail called "slug" can attain a velocity up to 2 km/sec. the velocity gradients along the length of the jet leads to jet stretching. the jet continues to stretch and after a certain limit it fractures under the effect of severe elongation, if uninterrupted. the most common terms used in shaped charge phenomena are explosive, liner, casing, booster and target. generally copper liner is preferred due to ease of fabrication and easy analysis. the most common shape of liner used is conical. the main parameters of the shaped charges including performance and dimensional parameters are expressed in terms of charge diameter (d). the charge length, stand-off distance, target penetration have been described in terms of multiples of the shaped charge diameter (d). the explosives used are described by velocity of detonation and chapman-jouguet (c-j) pressure. the liner material in theoretical modeling is described its density, dynamic strength and thickness.. the geometry of the lined cavity is described by the apex angle, which is an important factor for the performance assessment of the shaped charge.. the shaped charges can be fabricated as unconfined charges or confined charges with aluminum and steel casing. the hydrodynamic theory basically known as per theory [2] was verified by experiments and the effect of target strength in penetration depth assessment was highlighted in [3]. aluminum, steel and lead were used as the target materials and it was observed that the static strength was not sufficient for depth of penetration measurements. dynamic strength was determined and it was established that the ratio of the dynamic strength to the static strength varies for various materials. the hydrodynamic theory started gaining in importance with little modification based on experimental results and the sequence of events occurring during the shaped charge detonation. several research articles have been cited in [4]. in the us army military command pamphlet (amcp), the steps related to the design of the shaped charge were enumerated in detail in [5]. the copper cone diameter (d) is empirically related to the thickness of the armour (t) plate by the relation d=(t+2)/5. for short stand-off distances, copper, aluminum, steel, zinc, lead or glass liners are preferred depending upon their penetration capability. the materials having high ductility always give better penetration. the copper liner gives a better penetration at a stand-off distance 1-3 charge diameter (cd) in case of fixed steel target, while aluminum gives maximum penetration at a stand-off distance of 5-7cd. hence for maximum penetration at a short stand-off distance, copper liner should be preferred. for longer stand-off distances like aircraft as a target, the low density liner should like aluminum should be preferred, because low density target receives highest penetration with a low density liner. it is also mentioned in the literature that cone apex angle for a shaped charge should be between 40° and 60°. since a liner with a smaller cone apex angle gives penetration at smaller stand-off distances. however machining the liner with a small cone apex angle is a challenge. the maximum wall thickness is also in the range of 2-4% of the cd. the generalized analytical approach to shaped charge design is presented in [6]. this report describes the practical aspects of the shaped-charge warhead design and discussion on the utilization of the non-steady state theory for jet formation and 1-dimensional finite difference continuum mechanics formulation to calculate the whole process of jet formation for any generalized asymmetric shaped charge has been made. this report also includes experimental findings. the liner velocity is not constant and acceleration is discontinuous. the velocity gradients at the time of collapse decreases with increase of liner radius. in [7], experimental observations were presented and an attempt was made to describe shaped charge effects using a computer code, known as hocc. it was concluded that the complete shaped charge effect has many intermediate phenomena, like charge diameter, lengthening if metallic liner, velocity of detonation of the explosive used, booster location etc. it was very cumbersome to isolate these effects. the pieses code handled these aspects, but with more complexities. in [8], the per theory was modified slightly to match the experimental results, making it more versatile for different formulations. the advantages of these developments are: the input of geometrical parameters and coefficients to the program in a functional form makes it easy to use. the computer runtime is short and the parametric study can be facilitated in the software. in [9], the jet formation is studied using radiographic technique and some preliminary calculations are made regarding jet stability. in [10], the jet breakup and penetration of the broken jet is studied. the jet breakup is studied using stability approach based on 1-dimensional stability theory for stretching of plastic jets. it is observed that if the stretching rate is decreased, the rate of disturbance growth increases. however if the ratio of flow stress to the density is increased, the rate of disturbance growth also increases. the theory and design of shaped charges were so refined during the 80s that a manual was published [11]. this manual included both the principals of birkhoff and per. this report highlights the parameters governing the shaped charge design by real experiments. in another report from us army ballistic research laboratory [12], an assumption based on the fact, that jet curvature is the major factor for non-ideal jet penetration is established. the concept of tandem shaped charge which consists of two shaped charges, a precursor and the main charge emerged in the 70s. both are placed in tandem and ignited one after another for longer penetration. the increase in penetration from a shaped charge was described by providing a follow-through charge in the jet-hole created by the initial shaped charge. the tandem warhead used two shaped charges, one behind the other, with the rear charge also called the initial charge initiated first. the front charge had a central opening called aperture, through which the jet from rear charge is engineering, technology & applied science research vol. 7, no. 5, 2017, 2098-2103 2100 www.etasr.com ahmed and malik: a review of works on shaped charges passed. the slug from the rear charge is restricted by the aperture diameter, and this ignites the front shaped charge. the front has the explosive of higher velocity of detonation than the rear charge [13]. a tandem shaped charge warhead is described in [14], with the main aim of the improvement in performance, reduction in weight of the warhead and neutralization of the active armour on the tanks. overall the theory about the shaped charges, their designs, their modeling, experimental testing, development of 1-d software, validation through 2-d software and several other empirical equation related were perfected in the 90s. the shaped charge modeling entered a new phase in this decade, with concepts based on development and simulation. iii. developments during 1990-2000 during this period the interest on shaped charges studies was renewed. many important conclusions were made from experimental results and utilization of these results into the theory of the shaped charge became prime concern. various articles of the diagnostic tools for shaped charge studies were explored. 450 kv flash x-ray radiographic technique was used to investigate the shaped charges of different calibers (30, 60 and 90 mm) in [15]. the compendium of work done until 1993 is available in a very precise form in [16], which includes separate chapters on shaped charge mechanism, the jet formation, the experimental evidence and penetration of targets. in [17], 3-d computer codes were proposed for penetration performance of the shaped charge jets. the use of copper-tungsten alloys for shaped charge liners lead to an improvement in jet penetration against homogeneous steel targets [18]. in [19], a density deficit of at least 6.5% was proposed as one of the unexplained effects of the shaped charge jet. density deficit is present in stretching, unarticulated shaped charge jet, after all known sources of errors are evaluated and all contributing factors are considered. it is proposed that a “vacancy avalanche" mechanism, which is operating only during the highest strain-rate interval, preceding particulation, can generate high transient vacancy concentrations required to explain the observed density deficit. in [20], the largest shaped charge ever built was presented. shaped charge was successfully tested in penetrating 3.4 meters in high-strength armour steel. the largest shaped charge ever built produced a jet of molybdenum, which travelled several meters in air before interaction with several block of steel. the simulations were performed using cale (c-language-based arbitrary lagrangian-eulerian), a 2-dimensional hydrodynamic code. authors used x-radiography, the rotating mirror, a kind of motion picture camera, which can shoot millions of frames in a second. the newest tool was the image-converter (ic) camera was developed in the mid-1980s, which provided the higher solution images of jet formation and early flight of the shaped charge jet. in [21], the shape of the liner was changed to enhance the penetration of a well-perforator. the main objective was to increase jet energy and performance as much as possible. the strategy was to replace the conical liner with a bell-shaped with variable thickness. the outcome was an improved design which produced a jet with 10% more kinetic energy than before. the penetration into concrete targets was increased by 28% from that of a reference range. in [22], the shaped charge jet effect on glass armor was examined. the shaped charges with a caliber of 115 mm were fired at a constant stand-off distance of 3cd (charge diameter) from 0-60 degree nato angles. the jet tip velocities and the length of the disturbed jets were analyzed using double flash-ray pictures. under small angles the tip regions and under large angles the residual jet velocity regions, have been more disturbed. this results because under small angles the closure effect of the glass is more efficient. research on modeling of shaped charge jets carried out in japan is presented in [23]. the shaped charge jet formation and its penetration against targets was simulated using autodyn-2d hydrocode with a conical liner of aluminum. in this paper the mass decrease of the jet during the flight towards the target is investigated. the density and jet shape effects on the crater formation in the target were simulated. these findings are useful for the calibration of jet mass and the jet velocity. in the area of tandem shaped charge warheads, efforts were made to improve the performance against the advancements in tank protection domain. the development of active armour necessitated on board adjustments of initiation delay and angle of attack on active targets [24]. the calculation based on different combinations of measured mean distances from different sensors were presented in the patent. the method for stand-off distance approximation used for warhead activation is also discussed. in [25], the precursor of kinetic energy and chemical energy warheads were made attachable without affecting the overall length of the warhead. during the last decades of the 20th century, many new ideas were proposed based on modeling. x-ray has been used in experimental observations for understanding the particle velocity and jet breakup time. different hydrocodes have been used to carry out the simulation regarding shaped charge phenomena. investigations were made in which copper liner was replaced with copper-tungsten, molybdenum, aluminum, magnesium, graphite and other composite materials. steel, glass and lead were investigated as target materials. iv. developments during 2000-2010 during this period, the theory became more refined and most of the research work was focused on matching the simulated results with the experimental results. the diagnostic tools and the experiments planned were matured with great precision and variable parameters. the cut-off velocity for a shaped charge was investigated and a model was developed for limiting velocity in [26]. in [27] limiting velocity below a certain target’s strength was investigated. the limiting velocity depends upon target hardness and density. the aluminum and titanium alloys having high hardness have been used in this paper having limiting velocity of about 3.0km/sec. a preliminary experimental study was carried out to understand the penetration effectiveness of titanium against shaped charge jets [28]. shaped charge jets emerged from 100-mm charge diameters with 42°, apex cone angles fabricated from tantalum were directed towards titanium targets. this work indicates the first study of hypervelocity, high density jet penetration into titanium alloys. in [29], various penetration degradation mechanisms were investigated. the mechanisms included were: particle shape effects, particle separation, the extent of engineering, technology & applied science research vol. 7, no. 5, 2017, 2098-2103 2101 www.etasr.com ahmed and malik: a review of works on shaped charges necking, the deposition of jet material and the effects of collisions of the particles with the crater wall. in each case the effects of one or more copper particles impacting upon a semiinfinite rolled homogeneous armour target were modeled. it was concluded that the particle shape and impact speed are the significant factors that contribute to the penetration degradation. in [30], authors investigated shaped charge jet particulation, which was modeled as asymmetrical, dynamic necking instability of a viscoplastic metallic material. liner perturbation analysis was used to model the jet breakup time, velocities and their aspect ratio. comparisons were made with the experimental results obtained from flash radiographs for copper jets. a good agreement was obtained between theoretical and experimental data using typical values of the strength and strain rate sensitivity of copper at high strain rates. in [31], authors described a novel investigation of the impact of hollow shaped charge impact on steel target. the impact speeds considered were between 2 to 8 km/sec. it was observed that a reverse jet, travelling back through the hollow section, was formed, which was similar to that observed by earlier workers. it was concluded that the presence of hollowness is likely to cause significant disruption to the penetration process in real jets. the selection criteria for liner material was discussed in [32]. the high ductility of the liner materials during their jet elongation was strongly correlated with the microscopic structure, which depended on the original material properties and the mechanism used to produce the liners. it was amazing that the jet was influenced by the original crystal structure during the particulation process, even after undergoing sever deformation, collapse and flow. in [33], a closed form analytical solution derived for an unsteady inviscid jet caused by the asymmetric collapse of a 2-d ring using linearized small disturbance, velocity potential theory and classical analytical methods. the associated governing equation was solved by the laplace transformation and elementary eigen-function expansion methods. the shape of the jet was computed using analytical model and the results were compared with cth (hydrocode) simulations and the limited experimental data. the results showed reasonable agreement. the issue of rotational symmetry, the effect of boundary loading disturbance to the jet and the effect of finite arrival time of detonation wave conditions were also simulated. in [34], authors analyzed a copper liner and compared the numerical and experimental results for shaped charge jets. shaped charge jet breakup was analyzed by a combination of numerical /analytical analysis. the dependence of fragmentation characteristics on the grain size in the liner was also well predicted. shaped charge effects were investigated in [35]. shaped charges with higher jet tip velocities resulted in more residual penetration behind special targets. shaped charges having larger diameters gave more residual penetration behind special targets compared with smaller base diameters. in [36], authors investigated the penetration reduction at larger stand-off and presented an explanation which differed from already existing conventional explanations. the common reason for penetration retardation is lateral dispersion of the jets, but this cannot be accomplished using flash radiographic investigations. the elasto-plastic model for shaped charge jet penetration was investigated in [37]. this paper included the detailed mathematical modeling of high-rate penetration of a metal target by high velocity shaped charge jet. the main idea was to investigate the penetration velocity, be it subsonic, transonic or supersonic. this was achieved by considering the residual stresses produced by the moving plasticized region of the target. in [38], experimental evidence was proposed to correlate the parameters responsible for the estimation of shaped charge jet breakup time. it was proposed that the vpl parameter depends on the ratio of the liner thickness (tl) to the explosive charge diameter (cd) via relation 1/vpl=13.9101×(tl/cd). an attempt to explain this formula was made. in [39], authors presented warhead simulation studies. the effects of performance parameters like confinement, length of warhead, length to charge diameter ratio, etc in rolled homogeneous armour (rha) were discussed. the shift of the initiation system towards the shaped charge liner resulted in no improved performance. in [40], the advantages of field filled shaped charges with liquid explosives were listed as minimized toxic and explosive hazards, consistent performance, rapid filling, safe transportation, easy decommissioning and a cheap alternative. the superiority of diethylenetriamine (deta) and ethylenediamine (eda) over other amines was stated. however the disadvantages of increased toxicity and transient time dependant variation in sensitivity had to be accepted by the user. in an extension of the above work, a thick plastic tube having 4 mm thickness was filled with gelled nitromethane (nm) and was fitted with 1.25 mm thick copper cone having apex angle of 60°. the shaped charge was tested against mild steel (ms) target at a stand-off distance of 5 cd [41]. in the explosive filling, gelling, the addition of micro-balloons and ployox reduced the velocity of detonation and penetration of the charge. it was also reported that with 10% concentration of both additives, the copper liner spattered onto the plate and a penetration of the order of only 15 mm was achieved, because of the vod reduction to 4292 m/s. the design constraint for smaller shaped charge warheads was elaborated in [42]. the experimental results for small caliber tandem warhead concluded that the stand-off distance would be smaller than 6.5 times the diameter of the charge. the shielding should be in the middle of two charges. the detonation device for the first shaped charge should be smaller than the second with a short delay. the performance of ke penetrator including a precursor shaped charge was increased. in [43], the penetration of the shaped charge against sand targets using hydro-codes was investigated. the tandem shaped charge was examined experimentally using the design of detonation interrupter and detonation propagation parameters in [44]. a proper design of detonation interrupter and detonation propagation parameters could lead to the best coupling of the two-stage shaped charge during formation and relay penetration. the penetration depth was increased about 10-15% and radial crater by a shaped charge jet penetration was enlarged. the influence of asymmetry in trumpeted shaped charge liners on their performance was also investigated in [45]. four defects of the shaped charge had been analyzed within the scope of the work, as off-centre ignition of the explosive charge, detachment of the high explosive filling from the casing, air bubbles inside the high explosive filling and shaped charge liners dimensional inaccuracies. the effect of engineering, technology & applied science research vol. 7, no. 5, 2017, 2098-2103 2102 www.etasr.com ahmed and malik: a review of works on shaped charges each defect on the jet performance was determined in terms of radial drift velocities. in [46], a patent was presented in the area of tandem shaped charge for a long ignition delay between the front and rare charges. the patent suggested the explosive reduction and heavy confinement for the front charge to offset the ill-effects of poor penetration by the rear charge. a 50-60% explosive reduction, 20-40% reduction in overall warhead length and 10-20% weight reduction is claimed in the embodiment. additionally, movement of confinement from the central axis resulted in a clear passage for the jet of the secondary rear charge. in [47], a shaped charge assembly consisting of a first shaped charge, a wave shaping relay charge and a second charge was placed in housing. the assembly was configured in such a way that a first active element formed by initiation of the first shaped charge detonated the wave shaping relay charge, which in turn initiated the second shaped to form a second active element. the first active element moved out of the housing to cause damage of the first kind to an external target, and the second element caused damage to the second kind of the target. to summarize, during the 00s, consolidation of theory and simulation of experimental observations were the main emphasis in the area of shaped charges. in addition, several new concepts were proposed and experimentally tested. tantalum liner was used in shaped charges against titanium targets. among the new areas of research, the jet cut-off velocity, the study in penetration degradation, the effect of liner thickness, the reduction in penetration at increased standoff distance, the use of nm as an explosive filling in shaped charges, and the parameters for performance of tandem shaped charges etc. were investigated during this period. v. conclusion shaped charge modeling is a dynamic field, which is continuously growing. the present review is focused on works related to the theoretical modeling of the shaped charges. three distinct periods are considered in this paper: the period before 1990 as the era of theory development, the 1990s as the decade that brought the experimentation and validation of several 1d codes and the 2000s as the decade where various new aspects such as the use and theoretical investigation of the filled shaped charges having liquid explosives along with perturbation parametric studies surfaced. vi. references [1] w. walters, introduction to shaped charges, u. s. army research laboratory, 2007 [2] e. pugh, r. eichelberger, n. rostoker, “theory of jet formation with lined conical cavities”, j. appl. phys, vol. 23, no. 5, pp. 532-536, 1952 [3] r. eichelberger, “experimental test of the theory of penetration by metallic jets”, j. appl. phys., vol. 27, no. 1, pp. 63-68, 1956 [4] w. walters, j. zukas, fundamental of shaped charges, john wiley & sons, 1989 [5] research and development of material, engineering design handbook, warhead-general (u), amcp 706-290, july 1964 [6] l. behrmann, calculation of shaped-charge jets using engineering approximation and finite difference computer codes, vol. 1: generalized analytical approach to shaped-charge warhead design, air force armament laboratory, usaf, technical report aftal-tr73-160, aug. 1973. [7] e. perez, shaped charge physics, experimental results and recent theory, national technical services, usa, report39/74, n77-13228, 1974 [8] j. carleone, p. chou, c. tanizo, user' s manual for desc-1, dyna east corporation technical report de-tr-75-4 rev. 2, 1975 [9] p. chou, c. tanzio, j. carleone, r. cicarelli, shaped charge jet breakup studies using radiograph measurements and surface instability calculations, brl contract report no. 337, 1977 [10] j. carleone, p. chou, r. cicarelli, shaped charge jet stability and penetration calculations, brl contract report no. 351, 1977 [11] manual for shaped-charge design, navord report, 1248, ad no. adb954297, 1982 [12] s. b. seglets, drift velocity computations for shaped-charge jets, memorandum report arbrl-mr-03306, us army armament research and development command, ballistic research laboratory, aberdeen proving ground, maryland, 1983 [13] c. godfrey, r. jandrisevits, status of the lll tandem-shaped charge designs, preprint ucrl-82395, february 22, 1979 [14] a. chaumeau, e. crotet, a. kerdraon, j. ragonnet, warhead with tandem shaped charges, united states patent no. 4714022, 22dec., 1987 [15] s. tatake, d. kharat, “flash x-ray: a diagnostic tool for shaped charge studies”, defence science journal, vol. 42, no. 4, pp. 259-264, 1992 [16] j. carleone, “tactical missile warheads”, progress in astronautics and aeronautics, american institute of aeronautics and astronautics, usa, vol. 155, 1993 [17] l. zemow, e. chapyak, s. mosso, “a new 3d computational model for shaped charge jet breakup”, 16th international symposium on ballistics, san francisco, ca, pp. 23-28, september, 1996 [18] t. wang, z. rong, “copper-tungsten shaped charge liner and its jets”, propellants explos. pyrotech., vol. 21, pp. 193-196, 1996 [19] l. zemow, “the density deficit in stretching shaped charge jets”, int. j. impact eng., vol. 20, pp. 849-859, 1997 [20] k. walter, “shaped charge pierce the toughest targets”, science and technology review, pp. 17-19, 1998 [21] d. davidson, d. pratt, “a hydrocode-designed well perforator with exceptional performance”, 17th international symposium on ballistics, midrand, south africa, march 1998 [22] m. held, “glass armour and shaped charge jets”, propellants explos. pyrotech., vol. 23, pp. 105-110, 1998 [23] m. katayama, a. takeba, s. today, s. kibes, “analysis of jet formation and penetration by conical shaped charge with the inhibitor”, int. j. impact. eng., vol. 23, pp. 443-454, 1999 [24] p. tripptrap, j. peter, t. niemeyer, h. scholles, tandem warheads for combating active targets, united states patent no. 5744746, 28 april, 1998 [25] a. mikhail, anti-armor projectile with autonomous attachable precursor warhead, united states patent no. 6109185, 29 aug. 2000 [26] s. hancock, “an extension of the umin model for cutoff of high precision jets”, int. j. impact. eng., vol. 26, pp. 289-298, 2001 [27] w. gooch, m. burkins, w. walters, a. kozhushko, a. sinani, “target strength effect on penetration by shaped charge jets”, int. j. impact. eng., vol. 26, pp. 243-248, 2001 [28] w. walters, w. gooch, m. burkins, “the penetration resistance of a titanium alloy against jets from tantalum shaped charge liners”, int. j. impact eng., vol. 26, 823-830, 2001 [29] f. mostert, p. konig, k. werneyer, “predicted and experimental results of shaped charge penetration with liners of measured wall thickness variation”, 19th international symposium of ballistics, interlaken, switzerland, pp. 741-747, 7-11 may, 2001 [30] m. rodriguez, v. jeanclaude, j. petit, c. fressengeas, “breakup of shaped-charge jets: comparison between experimental and numerical engineering, technology & applied science research vol. 7, no. 5, 2017, 2098-2103 2103 www.etasr.com ahmed and malik: a review of works on shaped charges data”, 19th international symposium of ballistics,interlaken, switzerland, 711 may, 2001. [31] j. mills, j. curtis, “a theoretical investigation of the penetration properties of hollow particles”, int. j. impact. eng., vol. 26, pp. 523531, 2001 [32] m. held, “liners of shaped charges”, journal of battlefield technology, vol. 4, no. 3, pp. 1-7, 2001 [33] l. j. de chant, “an analytical solution for unsteady, inviscid jet formation due to asymmetric during collapse”, int. j. impact. eng., vol. 30, pp. 685-698, 2004 [34] j. petit, v. jeanclaude, c. fressengeasa, “breakup of copper shapedcharge jets: experiments, numerical simulations, and analytical modeling”, j. appl. phys., vol. 98, pp. 123521-123521-10, 2005 [35] m. held, “predominance of shaped charge diameter to performance quality against special targets”, propellants explos. pyrotech., vol. 30, no. 6, pp. 435-437, 2005 [36] g. wijk, a. tgemberg, shaped charge penetration reduction with increased standoff, report no. foi-r-1750-se, 2005 [37] r. novokshanov, j. ockendon, “elastic-plastic modeling of shaped charge jet penetration”, proc. r. soc. a., vol. 462, pp. 3663-3681, 2006 [38] e. hirsch, “scaling of the shaped charge jet breakup time”, propellants explos. pyrotech, vol. 31, no. 3, pp. 230-233, 2006 [39] w. arnold, e. rottenkolber, “penetrator/ shaped charge system part ii: influence of design parameters”, 23rd international symposium on ballistics, tarragona, spain, pp. 271-278, april 16-20, 2007 [40] m. cartwright, “liquid explosives for shaped charges and their use in explosive ordnance disposal (eod)”, explosive engineering, pp. 7-11, 2009 [41] m. cartwright, d. roach, p. simpson, “non-solid explosives for shaped charge target penetration with metal liner devices using sensitized nitromathane liquid explosive”, j. energ. mater., vol. 27, no. 3, pp. 145-165, 2009 [42] c. ling, y. dong, s. jun, “the design of small-caliber tandem warhead against tank with reactive armour”, 19th international symposium of ballistics, interlaken, switzerland, pp. 691-695, may 711, 2001 [43] c. wang, t. ma, j. ning, “experimental investigation of the penetration performance of shaped charge into concrete targets”, acta mech sen, vol. 24, pp. 345-349, 2008 [44] h. zhengxiang, z. xianfeng, “study on tandem shaped charges technique”, 23rd international symposium on ballistics, tarragona, spain, pp. 1205-1210, april 16-20, 2007 [45] o. ayisit, “the influence of asymmetries in shaped charge performance”, int. j. impact. eng., vol. 35, pp. 1399-1404, 2008 [46] w. walters, tandem shaped charge warheads having confined forward charge and a light weight blast shield, united states patent no. 7493861 b1, 24 feb, 2009 [47] p. konig, shaped charge assembly and method of damaging target, united states patent no. 7779760 b2, 24 aug., 2010 microsoft word etasr_v13_n4_pp11100-11105 engineering, technology & applied science research vol. 13, no. 4, 2023, 11100-11105 11100 www.etasr.com le & nguyen: the effect of cracks on the free vibration of a plate with parabolic thickness the effect of cracks on the free vibration of a plate with parabolic thickness vinh an le faculty of civil engineering, university of transport and communications, vietnam levinhan@utc.edu.vn xuan tung nguyen faculty of civil engineering, university of transport and communications, vietnam ngxuantung@utc.edu.vn (corresponding author) received: 7 april 2023 | revised: 29 april 2023 and 13 may 2023 | accepted: 17 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5923 abstract this paper uses first-order shear deformation theory and the finite element method to analyze the vibrations of rectangular plates with one or more cracks. the study investigated the influence of cracks (length, angle of inclination), the number of cracks, and the ratio of plate thickness to the natural vibration frequency of the plate, using phase field simulation. plate thickness varies nonlinearly with the parabolic function. the results of the proposed method were compared with reputable studies to verify its reliability. in addition, some pictures of the characteristic vibration patterns of the plate with varying thickness are presented when cracks appear. keywords-cracked plate; free vibration; phase field; variable thickness i. introduction plates with variable thicknesses are often used when aesthetic elements are needed to ensure the bearing capacity of a structure. in [1], the vibration frequency of orthogonal nanoplates with variable thickness was explored using eringen's theory combined with the nonlocal classical plate theory. in [2], the vibration frequency and bending load of a rectangular multilevel plate were calculated based on the classical plate theory (kirchhoff). in [3], the free oscillation of a variable thickness plate was analyzed using first-order shear deformation and the higher-order shear deformation plate theories. in [4], the frobenius method was used to determine the buckling load for an elastic rectangular plate with variations in thickness, elastic modulus, and density. in [5], the twovariable refined plate theory and the hamilton principle were used to calculate the free vibration frequencies of orthogonal plates. in [6], a general integral transformation technique was used to study the flexural resistance of rectangular plates with linearly variable thickness lying on a pasternak elastic foundation. structural plates are used quite frequently in fields such as mechanical engineering, construction, etc. during itsw lifetime, the plate may develop cracks due to local damage. to determine the degree of damage, it is necessary to re-evaluate the working capacity of the structure at that time. scientists have proposed several theories and research methods on this issue, such as isogeometric analysis (iga), finite element method (fem), extended finite element method (xfem), etc. in [7-8], fem and stochastic high-order fem were applied to analyze a continuous beam. in [9], an analytical solution was used to dynamically analyze a functionally graded plate. more recently, in [10-16], the phase-field theory and fem were used to analyze the stability and free vibration of a cracked rectangular plate. to the best of our knowledge, no study has investigated the free oscillation of cracked plates with varying parabolic thickness. this study focused on calculating the vibration frequency parameter of a plate depending on the ratio of the plate edges, the length and angle of crack inclination, and the number of cracks. ii. establishment of equations using reissner-mindlin first-order shear deformation plate theory, the displacement in the mid-plate section is given by: ��(�, �, �, �) = ��(�, �, �) + � �(�, �, �) ��(�, �, �, �) = ��(�, �, �) + � �(�, �, �) (1) ��(�, �,�, �) = ��(�, �, �) where ��, ��, �� are displacements at any point along the x, y, and z axes, respectively, θx and θy are rotation angles in the xz and yz faces, and u0, v0, and w0 are the displacements at the center of the plate. the deformation components of are given by: �εγ� = �ε�0 � + ��ε�γ� � (2) where: engineering, technology & applied science research vol. 13, no. 4, 2023, 11100-11105 11101 www.etasr.com le & nguyen: the effect of cracks on the free vibration of a plate with parabolic thickness �� = � ��,���,���,� + ��,�� �� = � �,� �,� �,� + �,�� (3) � = ! � + ��,� � + ��,�" the relationship between stress and strain is: �#$� = %&' 00 &�( �)*� (4) and the strain energy in the plate is expressed by: +(,) = -. / 0��12�� + ��13�� + ��13��+��1&��� + �1&� � 45 67 (5) where: &' = 8-9:; <1 > 0> 1 00 0 (1 − >)/2b (6) &� = keh.(1+:) c1 00 1d (7) and: (2, 3, &�) = / (1, �, �.)&'6�e/.9e/. (8) with k being the shear correction factor. in phase field theory, the variable s represents the deterioration of the material when the plate cracks [7-13]. it takes the value 0 when fully cracked and 1 when the material is in its normal state. values of s from 0 to 1 represent the fracture zone of the material, where the object changes continuously from normal (s = 1) to complete cracking (s = 0). the deformation energy when the plate has cracks is given by: +(,, f) = ⎩⎨ ⎧-. / f. 0��12�� + ��13�� + ��13�� ++��1&�� + �1&� � 45 67+ / jk5 ℎc(-9�);lmn + op|rf|.d 67 ⎭⎬ ⎫ = �/ f.v(,)67 + / jk5 ℎc(-9�);lmn + op|rf|.d 675 � (9) where s simulates the state of the material, lc is the crack width, gc is the energy release rate, and δ is the displacement vector. the kinetic energy of the plate is determined by: wx = -. / f.�y 1z5[ �y67 = -. ,y1\x,y (10) the lagrange function is calculated according to: ](,, f) = w(,, f) − +(,, f) (11) ](,, f) = / �f.ψ(,) − jpℎ c(-9�);lmn + op|∇f|.d�a 6ω (12) after taking the variation of l(δ, s) in terms of δ and s, a system of equations is used to determine the frequency of free vibrations of the cracked plate: c(∑ e x + f. ∑ \x ), = 0 / �2fg(,),f − 2jkℎ <− (-9�)h�lmn+oprfr(,f)b� 67 = 05 (13) after solving the system of (13) the free vibration frequency of the cracked plate will be found. in this part, the finite element used is a triangular element with a function of the form: ij = k1��l �mjnjoj � with: mj = p�q�r9�r�qs(.5[) nj = p�q9�rs(.5[) oj = p�t − �us/(27x) the element stiffness matrix is: vx = / ℎ3w1&3w67 =5[ ℎ7x3w1&3w with the deformation matrix-node displacement of the element: 3w = �m-0m.0mx00n-0n.0nxn-m-n.m.nxmx� the element mass matrix is: \x = / ℎi1zi675[ i = !i-0i.0ix00i-0i.0ix" figure 1 shows the triangular element with area ωe and vertices 1(x1 , y1), 2(x2 , y2), and 3(x3 , y3). fig. 1. the triangular element of plate. iii. numerical results a. comparison of the free oscillations of the parabolic thickness plate the free oscillation of the parabolic thickness plate was calculated and compared with [3]. the plate is made of steel (sus304), whose elastic modulus, mass density, and poisson coefficient are e = 201.04 gpa, ρ = 8166 kg/m 3 , and υ = 0.3, respectively. figure 2 shows the thickness of the plate, which varies along the x direction with a quadratic rule: ℎ(�) = ℎ�(yz. − 2yz + 1),y = 1 − ℎ{/ℎ� engineering, technology & applied science research vol. 13, no. 4, 2023, 11100-11105 11102 www.etasr.com le & nguyen: the effect of cracks on the free vibration of a plate with parabolic thickness fig. 2. rectangular plate with parabolic variable thickness. the square plate has side dimensions a = b = 0.5 m. the natural vibration frequency of the plate is calculated by [14]: f� = fn.|zℎ�/&�/}. (14) where: &� = ~ℎ�x/(12(1 − >.)) table i shows the frequency of the plate with different thickness ratios and boundary conditions of the four-sided mount. it can be seen that the difference between this study and [3] is very small, demonstrating the reliability of the method. table i. free oscillation frequency of plate with varying parabolic thickness μ h0/a [3] this study diff. (%) 0.25 0.1 2.8316 2.83135 -0.01% 0.2 2.4311 2.42521 -0.24% 0.3 2.0533 2.03532 -0.88% 0.4 1.7503 1.71872 -1.80% 0.5 0.1 2.2850 2.2846 -0.02% 0.2 2.0573 2.05506 -0.11% 0.3 1.8090 1.80115 -0.43% 0.4 1.5870 1.57104 -1.01% b. comparison of the free oscillations of a constantthickness plate with a central crack the vibration of a cracked plate with constant thickness was found and compared with [17]. figure 3 shows the crack in the center of the plate with length c and angle of inclination α. the plate was made of ceramic al2o3, with elastic modulus, density, and poisson coefficient of ec = 380 gpa, ρc = 3800 kg/m 3 , and υ = 0.3, respectively. the square plate has a single support boundary condition on the four sides (ssss), side dimensions a = b = 0.5 m, and sheet thickness h = a/50. the free oscillation frequency is calculated according to [15]: f� = f(n./ℎ)|zp/~p (15) table ii shows that the difference between the proposed method and [17] (three-dimensional elasticity theory and ritz method) or [12] (high-order shear deformation theory) is very small. table ii. frequency of constant thickness plate with a crack c/a [17] [12] this study max diff (%) 0 5.965 5.96947 5.96961 0.08% 0.1 5.939 5.92339 5.92562 -0.23% 0.3 5.665 5.71588 5.71592 0.90% 0.5 5.318 5.34453 5.34569 0.52% c. free oscillation of a single-crack plate with parabolic thickness variation the properties of the material and the dimensions of the plate are the same as in a. the plate had a crack with length c in the middle, and an angle a between the crack and the x-axis, as shown in figure 3. the frequency of the plate was calculated with (14). this plate had a single support boundary condition on four sides (ssss) and a thickness of h0 = 0.005 m. table iii shows the frequency for the square plate with a = b = 0.5 m and a thickness ratio of ha/h0 = 0.5. table iii shows that as the length of the crack increases, the stiffness of the plate decreases, leading to a decrease in the free vibration frequency. this is also shown in tables iv, v, and vi. as the crack inclination angle a increases, the frequency increases (a relatively small amount) until an angle of 75° and then decreases at 90°. figure 4 shows that the natural frequency decreases with increasing thickness index and plate edge ratio (a/b). as the thickness ratio decreases, the plate becomes thinner at the side parallel to the y-axis, causing the plate stiffness to decrease, leading to a corresponding decrease in frequency. table iii. frequency of the plate depending on crack length and angle. crack angle c/a 0 0.1 0.3 0.5 0.7 0 0 1.31854 1.31116 1.29279 1.2672 1.23825 15 0 1.31854 1.31119 1.29276 1.26679 1.23688 30 0 1.31854 1.31127 1.29278 1.26604 1.23426 45 0 1.31854 1.31141 1.29302 1.26604 1.23412 60 0 1.31854 1.31158 1.29372 1.26726 1.2358 75 0 1.31854 1.31854 1.29519 1.2716 1.24469 90 0 1.31854 1.31173 1.29425 1.26893 1.23899 fig. 3. the cracked plate with parabolic thickness. fig. 4. the relationship between frequency and plate thickness index. engineering, technology & applied science research vol. 13, no. 4, 2023, 11100-11105 11103 www.etasr.com le & nguyen: the effect of cracks on the free vibration of a plate with parabolic thickness table iv shows the frequency of the plate depending on the edge ratio, thickness ratio, and crack length. the crack inclination angle is α = 0, i.e., the crack is parallel to the x-axis. with b = 0.5 m, as the aspect ratio a/b increases, the mass of the plate increases, and as the frequency of vibration is inversely proportional to the mass, leads to a decrease in the frequency of vibrations. figure 5 shows the first four vibration patterns of the cracked plate with parabolic thickness, with parameters values h0 = 0.005 m, a = b = 0.5 m, ha/h0 = 0.6, c/b = 0.5, and a = 0°. table iv. effect of edge ratio and thickness ratio on frequency of cracked plate c/a a/b ha/h0 0.9 0.8 0.7 0.6 0.5 0 0.5 4.65504 4.30576 3.95052 3.58864 3.21947 1 1.86601 1.73149 1.59556 1.45801 1.31854 1.5 1.34604 1.24703 1.14624 1.04326 0.93746 2 1.16278 1.07465 0.98408 0.89053 0.79326 0.2 0.5 4.62233 4.27621 3.92457 3.56684 3.20244 1 1.81979 1.68984 1.5588 1.42652 1.29279 1.5 1.2765 1.18422 1.09059 0.99529 0.89778 2 1.06977 0.9906 0.9097 0.82666 0.74079 0.4 0.5 4.56125 4.22142 3.87646 3.52585 3.16907 1 1.72443 1.60394 1.4828 1.36095 1.23825 1.5 1.14271 1.06326 0.98308 0.90196 0.81948 2 0.90419 0.84051 0.77593 0.71018 0.64277 0.6 0.5 4.4955 4.16295 3.82544 3.48241 3.13333 1 1.62882 1.51802 1.40684 1.29527 1.18319 1.5 1.02176 0.954 0.88588 0.81721 0.74767 2 0.76769 0.7168 0.6654 0.61326 0.55999 fig. 5. the first four vibrations of the cracked plate. d. free oscillation of a multi-cracked plate with a parabolic variation of plate thickness figure 6 shows a plate with parabolic thickness and 3 cracks parallel to the y-axis. table v shows the frequency versus the number of cracks, crack length, and the distance between cracks. the ratios of the plate thickness and the two plate sides remain ha/h0 = 0.6 and a/b = 0.6. for two cracks, when the crack length is small, i.e. c/b = 0.2 or c/b = 0.4, increasing the distance between them (d) will increase the frequency; conversely, with a crack length greater than 0.6b, the frequency decreases. this is explained by the different energy released by the parabolic plate thickness. figure 7 shows the first four vibration patterns of a plate with two cracks parallel to the y-axis and h0 = 0.005 m, a = b = 0.5 m, ha/h0 = 0.4, c/b = 0.6, and d = 0.25a. fig. 6. the parabolic thickness plate with three cracks. table v. frequency of a plate with many cracks number of cracks c/b d/a 0.1 0.2 0.3 0.4 1 0.2 1.03342 1.03342 1.03342 1.03342 0.4 1.01087 1.01087 1.01087 1.01087 0.6 0.984192 0.984192 0.984192 0.984192 0.8 0.962094 0.962094 0.962094 0.962094 2 0.2 1.02582 1.02822 1.03341 1.03917 0.4 0.990864 0.992979 1.00401 1.01917 0.6 0.952778 0.948374 0.957069 0.974258 0.8 0.918942 0.905287 0.905997 0.914716 3 0.2 1.02128 1.02058 1.0246 1.02968 0.4 0.985226 0.976855 0.98136 0.991659 0.6 0.948196 0.928833 0.926322 0.93481 0.8 0.913994 0.883802 0.872667 0.874046 fig. 7. first four oscillations of parabolic thickness plate with 2 cracks. engineering, technology & applied science research vol. 13, no. 4, 2023, 11100-11105 11104 www.etasr.com le & nguyen: the effect of cracks on the free vibration of a plate with parabolic thickness table vi shows the frequency of a plate with three cracks depending on the thickness index and constant ratio of the two sides and distance between the cracks a/b = 1.25, d/a = 0.25). table vi. frequency of a plate with three cracks c/b ha/h0 0.9 0.8 0.7 0.6 0.5 0.1 1.51561 1.40593 1.29479 1.18186 1.06664 0.3 1.443 1.33958 1.23474 1.12807 1.01897 0.5 1.35095 1.25477 1.15702 1.05716 0.95445 0.7 1.26551 1.17647 1.08552 0.992 0.89496 figure 8 shows the data in table vi. when the thickness index (μ = 1 ha/h0) increases, the impregnation becomes thinner, leading to a decrease in frequency. in particular, when c/b and μ increase together, the stiffness of the plate decreases faster, so the frequency decreases very quickly. figure 9 shows the first four vibration modes of a plate with 3 cracks and a = b = 0.5 m, ha/h0 = 0.5, c/b = 0.7, and d = 0.25a. fig. 8. relationship between frequency and thickness ratio of the plate with three cracks. fig. 9. first four oscillations of parabolic thickness plate with 3 cracks parallel to the y-axis. the cracks have a significant effect on the frequency and vibration patterns of the plate, as was clearly shown in figures 5, 7, and 9. iv. conclusion this study used the phase-field theory in destructive mechanics and the first-order shear strain theory to study the free vibrations of a plate, whose thickness varies with a parabolic function and has cracks. numerical results showed that for the case considered: (i) when the crack length is increased, the stiffness of the plate decreases, so the free vibration frequency of the plate will be reduced; (ii) as the number of cracks increases, the free oscillation frequency of the plate decreases; (iii) when the sheet thickness ratio is increased (h0/ha), the free oscillation frequency of the plate decreases; (iv) when increasing the plate length ratio (a/b), the plate is thinner and the vibration frequency decreases. these results would be very helpful when analyzing plate vibrations as cracks propagate over time. acknowledgment this research was funded by the vietnam ministry of education and training under grant number b2022-gha-02. references [1] k. akiyama and m. kuroda, "fundamental frequencies of rectangular plates with linearly varying thickness," journal of sound and vibration, vol. 205, no. 3, pp. 380–384, aug. 1997, https://doi.org/ 10.1006/jsvi.1997.1058. [2] y. xiang and c. m. wang, "exact buckling and vibration solutions for stepped rectangular plates," journal of sound and vibration, vol. 250, no. 3, pp. 503–517, feb. 2002, https://doi.org/10.1006/jsvi.2001.3922. [3] i. shufrin and m. eisenberger, "vibration of shear deformable plates with variable thickness — first-order and higher-order analyses," journal of sound and vibration, vol. 290, no. 1, pp. 465–489, feb. 2006, https://doi.org/10.1016/j.jsv.2005.04.003. [4] m. saeidifar, s. n. sadeghi, and m. r. saviz, "analytical solution for the buckling of rectangular plates under uni-axial compression with variable thickness and elasticity modulus in the y-direction," proceedings of the institution of mechanical engineers, part c: journal of mechanical engineering science, vol. 224, no. 1, pp. 33–41, jan. 2010, https://doi.org/10.1243/09544062jmes1562. [5] h. t. thai and s.-e. kim, "levy-type solution for free vibration analysis of orthotropic plates based on two variable refined plate theory," applied mathematical modelling, vol. 36, no. 8, pp. 3870–3882, aug. 2012, https://doi.org/10.1016/j.apm.2011.11.003. [6] g. fu, y. tuo, b. sun, c. shi, and j. su, "bending of variable thickness rectangular thin plates resting on a double-parameter foundation: integral transform solution," engineering computations, vol. 39, no. 7, pp. 2689–2704, jan. 2022, https://doi.org/10.1108/ec-11-2021-0692. [7] t. d. hien, n. d. hung, n. t. hiep, g. v. tan, and n. v. thuan, "finite element analysis of a continuous sandwich beam resting on elastic support and subjected to two degree of freedom sprung vehicles," engineering, technology & applied science research, vol. 13, no. 2, pp. 10310–10315, apr. 2023, https://doi.org/10.48084/etasr.5464. [8] h. t. duy, n. d. diem, g. v. tan, v. v. hiep, and n. v. thuan, "stochastic higher-order finite element model for the free vibration of a continuous beam resting on elastic support with uncertain elastic modulus," engineering, technology & applied science research, vol. 13, no. 1, pp. 9985–9990, feb. 2023, https://doi.org/10.48084/etasr. 5456. [9] d. t. thuy, l. n. ngoc, d. n. tien, and h. v. thanh, "an analytical solution for the dynamics of a functionally graded plate resting on viscoelastic foundation," engineering, technology & applied science engineering, technology & applied science research vol. 13, no. 4, 2023, 11100-11105 11105 www.etasr.com le & nguyen: the effect of cracks on the free vibration of a plate with parabolic thickness research, vol. 13, no. 1, pp. 9926–9931, feb. 2023, https://doi.org/10. 48084/etasr.5420. [10] p. p. minh and n. d. duc, "the effect of cracks on the stability of the functionally graded plates with variable-thickness using hsdt and phase-field theory," composites part b: engineering, vol. 175, art. no. 107086, oct. 2019, https://doi.org/10.1016/j.compositesb.2019.107086. [11] p. p. minh and n. d. duc, "the effect of cracks and thermal environment on free vibration of fgm plates," thin-walled structures, vol. 159, feb. 2021, art. no. 107291, https://doi.org/10.1016/j.tws. 2020.107291. [12] p. p. minh, d. t. manh, and n. d. duc, "free vibration of cracked fgm plates with variable thickness resting on elastic foundations," thinwalled structures, vol. 161, apr. 2021, art. no. 107425, https://doi.org/ 10.1016/j.tws.2020.107425. [13] n. d. duc and p. p. minh, "free vibration analysis of cracked fg cntrc plates using phase field theory," aerospace science and technology, vol. 112, may 2021, art. no. 106654, https://doi.org/ 10.1016/j.ast.2021.106654. [14] p. p. minh, "analysis free vibration of the functionally grade material cracked plates with varying thickness using the phase-field theory," transport and communications science journal, vol. 70, no. 2, pp. 122– 131, 2019, https://doi.org/10.25073/tcsj.70.2.35. [15] minh p. p., "using phase field and third-order shear deformation theory to study the effect of cracks on free vibration of rectangular plates with varying thickness," transport and communications science journal, vol. 71, no. 7, pp. 853–867, 2020, https://doi.org/10.47869/tcsj.71.7.10. [16] v. a. le, m. p. pham, and t. a. bui, "stability of cracked plates with nonlinearly variable thickness resting on elastic foundations," journal of materials and engineering structures, vol. 9, no. 4, pp. 641– 651, dec. 2022. [17] c. s. huang, p. j. yang, and m. j. chang, "three-dimensional vibration analyses of functionally graded material rectangular plates with through internal cracks," composite structures, vol. 94, no. 9, pp. 2764–2776, sep. 2012, https://doi.org/10.1016/j.compstruct.2012.04.003. microsoft word etasr_v11_n2_pp6974-6978 engineering, technology & applied science research vol. 11, no. 2, 2021, 6974-6978 6974 www.etasr.com boukendakdji et al.: the effects of steam-curing on the properties of concrete the effects of steam-curing on the properties of concrete mustapha boukendakdji college of engineering university of hail hail, saudi arabia m.boukendakdji@uoh.edu.sa mabrouk touahmia college of engineering university of hail hail, saudi arabia m.touahmia@uoh.edu.sa belkacem achour college of engineering university of hail hail, saudi arabia b.achour@uoh.edu.sa ghazi albaqawy college of engineering university of hail hail, saudi arabia g.albaqawy@uoh.edu.sa mohamed abdelhafez college of engineering university of hail hail, saudi arabia mo.abdelhafez@uoh.edu.sa khaled elkhayat college of engineering university of hail hail, saudi arabia m.elkhayat@uoh.edu.sa emad noaime college of engineering university of hail hail, saudi arabia e.noaime@uoh.edu.sa abstract-worldwide, concrete is the most preferred construction material. the steam curing method is favored when there is a need for accelerating strength. this paper presents the study of the compressive and flexural tensile strength of concrete subjected to eight different steam cures. in addition, the stressstrain curve and the modulus of elasticity were determined at the age of 28 days. the compressive strength test results show that after treatment, strength increases with concrete maturity. a cycle with a pre-heating period gives better results than a cycle without a pre-heating period. the longer the duration of the maximum temperature period, the lower the strength drop compared to the control concrete. the best results were obtained for concrete treated according to the following cycle: a 3-hour pre-heating period at 20 o c, a 2-hour increase of temperature from 20 to 70 o c, and a 3 hour of maximum temperature of 70 o c. keywords-steam curing; compressive strength; flexural tensile strength; modulus of elasticity; maturity i. introduction concrete is extensively used as a construction material and, globally, it is the second highest consumed material [1]. ordinary portland cement (opc) is usually used as the primary binder to make concrete and is one of the most energyintensive construction materials. the primary reason for using steam in the curing of concrete is to produce high early strength, which is very desirable to the manufacturers of precast and pre-stressed concrete units [2]. there are many advantages in steam curing such as the production of concrete with high early strength, short production cycle, and superior economic benefits [3, 4]. the steam curing process includes the following four phases: the delay period, the isothermal period, the heating period, and the cooling period [5]. heat treatment has been used to accelerate the development of the strength of concrete products, such as bricks and small concrete elements. by increasing temperature and duration, the strength of concrete is increased [6]. authors in [7] showed that 85°c is the optimum temperature in order to obtain high early strength. authors in [8] demonstrated the improved early-age strength of high performance concrete through steam curing. authors in [9] showed that as the temperature increases, the compressive and flexural strength of concrete at early age increase. authors in [5] reported that 65% of the strength of the control concrete at 28 days was obtained by thermal treatment within 24h after mixing. similar results have also been reported in [6,10, 11]. the same results have been obtained for concrete with superplasticizers [12] and slag [5]. in order to obtain good final strength, it is not advisable to immediately heat the concrete. the faster the speed of temperature rising, the more the final strength of the treated concrete is weakened. authors in [9] showed that the increase in temperature has significant impact on the compressive and flexural tensile strength of concrete. however, there is no effect on strength when hard concrete is exposed to 6-hour fire at 1000°c [13]. authors in [5, 14] reported that the effect of heat treatment on the modulus of elasticity is the same as that on strength. authors in [14] reported that the optimum rate of heating and preset period should be selected based on the maximum chamber temperature in use in order to secure the desired results. there was enhancement in the early compressive strength due to the effect of steam curing, however the delay period before steam curing is very essential for the early strength gain [2, 15]. authors in [5] showed that the reduction in shrinkage of steamcured concrete when compared to normal cured concrete is about 10%. finally, steaming leads to a reduction of 20 to 30% of the creep compared to the same concrete, cured at room temperature and loaded with equal stress/strength ratio [16]. this reduction in creep has been confirmed by [5, 12]. ii. materials and experimental details nine concrete mixtures were tested in this program. the concrete had an opc content of 350kg/m 3 . the total aggregate/ cement ratio was 5.41, the gravel/sand ratio was 1.61, and the corresponding author: mustapha boukendakdji engineering, technology & applied science research vol. 11, no. 2, 2021, 6974-6978 6975 www.etasr.com boukendakdji et al.: the effects of steam-curing on the properties of concrete water/cement ratio was 0.57. for all the mixtures, the coarse and fine aggregates were weighed in dry room conditions. the control opc concrete was designed to develop a 28-day cube compressive strength of 35mpa. all the concrete mixtures were mixed for 2min in a laboratory mixer. all molded specimens were cured for 24h under wet hessian, then were demolded and cured in water at 20±2 o c for 28 days. for each mixture, twelve 100mm cubes were made to determine the compressive strength and two 300×150mm diameter cylindrical specimens were used to determine the static modulus of elasticity. the flexure tensile strength was measured on 100×100×500mm prisms (figure 1). the compressive strength was measured after 1, 3, 7, and 28 days (figure 2). the flexural tensile strength, the stress-strain curve and the modulus of elasticity were determined at the age of 28 days. fig. 1. the concrete specimens. fig. 2. the cube compessive strength test. the studied types of concrete were: a control concrete stored in water at an ambient temperature (20 o c) and concretes subjected to 8 different steam curing cycles (table i). the curing cycles necessarily include four distinct phases: • preheating period • heating period • maximum temperature period • cooling period the molds were placed into the steam chamber, the latter being at the processing temperature. this steam chamber is equipped with a fan allowing the circulation of ambient air. a thermocouple was placed in the concrete in the middle of the central specimen of the cubic mold. after demolding, the concrete specimens were stored in water at 20 o c table i. different types of curing cycles cycle preheating period (h) heating period (h) max. tem. period (h) initial tem. ( o c) max. tem. ( o c) maturity ( o c.h) a 0 2 3 20 70 350 b 1.5 2 3 20 70 395 c 3 2 3 20 70 440 d 3 2 1.5 20 70 320 e 3 2 0 20 70 200 f 1.5 2 3 20 50 315 g 1.5 2 3 24 70 405 h 1.5 2.5 3 24 70 433 iii. results and discussion a. influence of the duration of the pre-heating period on compressive strength figure 3 shows that the strength at the end of the treatment (0 days) and after 28 days of curing is minimal for zero preheating period. the decrease in final strength (28 days) compared to control concrete kept at 20 o c is around 33%. for the cycles b and c, the fall is 26% and 15% respectively. so it is not advisable to heat the concrete immediately after pouring, which is in agreement with the results in [10]. the heating of fresh concrete causes the appearance of physical and chemical phenomena [17]. the physical order phenomena are essentially linked to the expansion of the various constituents of concrete under the effect of the rise in temperature. however, these various constituents have very different linear expansion coefficients. the rise in temperature causes the material to expand, which ultimately results in the appearance of pores. these pores indeed remain after the consolidation of the concrete structure. it is well known that the strength of concrete is inversely proportional to the number of pores in it. chemical phenomena are linked to the appearance of insoluble, compact hydrate films, which oppose the subsequent penetration of water and somehow isolate the grains of cement [17]. fig. 3. the effect of the delay period on concrete strength. engineering, technology & applied science research vol. 11, no. 2, 2021, 6974-6978 6976 www.etasr.com boukendakdji et al.: the effects of steam-curing on the properties of concrete b. influence of the speed of temperature rise on compressive strength in order to study the influence of the speed of temperature rising, the evolution of the compressive strength for heating at 70 o c with rise speeds of 18 o c/h and 24.8 o c/h are compared in figure 4. it is observed that the best strength at 28 days is obtained for slowly heated concrete (18 o c/h). however, the quality of treated concrete remains lower than that of control concrete. the drop in strength compared to control concrete is 13% and 15% for concrete heated to 18 o c/h and 24 o c/h respectively. this confirms the results of [5]. the physical cause of this alteration is known: it is the very significant expansion of the constituents of fresh concrete, water and air. a high rate of temperature rise causes disorders in the structure of concrete which can go as far as the appearance of micro-cracks. fig. 4. the effect of heating period on concrete strength. c. influence of maximum temperature when the temperature rises the compressive strength increases more rapidly at 0 days, whereas at 28 days, the strength of concrete treated at 50 o c is greater than that of the concrete treated at 70 o c (figure 5). authors in [7] found that the optimum maximum temperature of steam curing was near 60ºc. however, higher temperatures of 70ºc and 80ºc show a distinct reduction in strength after 28 days [7]. a significant increase of compressive strength for fly ash mortars has been found at the early age of 3 days when curing temperature was raised [18]. d. influence of the maximum temperature period time in order to study this phenomenon, three cycles of heat treatments (c, d and e) were considered, so the maximum temperature period varied from 0 to 3h. the three cycles had the same preheating period (3h), heating period (2h), and maximum temperature (70 o c), however the maximum temperature period was 3, 1.5, and 0h respectively. it should be noted that the longer the maximum temperature period time, the higher the compressive strength in the short and long term is (figure 6). concrete maintained at a 3hour level presents, at 28 days, a reduction in strength around 15% compared to control. for 1.5h and 0h concrete, the strength drop is around 24% and 28%, respectively. therefore, the greater the duration of the maximum temperature period, the smaller the drop in strength compared to control concrete at 28 days, which is in agreement with the results in [19]. fig. 5. the effect of maximum temperature on concrete strength. fig. 6. effect of maximum temperature holding time on concrete strength. e. maturity factor we can see that the compressive strength after treatment increases with maturity (figure 7). the latter is the sum of the product of temperature and time: ( )10omaturity t c t= + ×∆∑ (1) where t is the temperature in o c and ∆t is the time interval (h). fig. 7. relationship between maturity and cube compressive strength. engineering, technology & applied science research vol. 11, no. 2, 2021, 6974-6978 6977 www.etasr.com boukendakdji et al.: the effects of steam-curing on the properties of concrete f. tensile strength the values of tensile strength are given in table ii. it can be seen that the maximum tensile strength (4.27mpa) is obtained by the control concrete. the tensile strength of all concrete mixtures was determined by the flexure test and is presented as a function of cube compressive strength in figure 8. the european concrete committee (ceb) suggests that the axial tensile strength (ft) can be related to the characteristic compressive strength (fc) by: 2/3 0.3 t c f f= (2) the flexural tensile strength of all the concrete mixtures ranged between 2.9 and 4.27mpa. for a given compressive strength, the values for flexural tensile strength for all concretes are slightly higher than to the curve proposed by the ceb in (2). the ratio of the flexural tensile strength to the compressive strength was about 0.13. the results of [21] showed that the steam-curing provides better performance at 3 days for flexural strength and the ratio of the flexural tensile strength to the compressive strength was about 0.10. fig. 8. relationship between tensile and cube compressive strength. table ii. flexural tensile strength cycle control a b c d e f g h tensile strength (mpa) 4.27 3.45 3.75 3.64 3.72 3.86 4.01 2.90 4.14 g. stress-strain curve the stress-strain curves in compression of the control and both b and c concretes are shown in figure 9. it is clear that the shape of the curves is similar for all concretes. moreover, it is worth mentioning that before failure, it is difficult to assess any value for limiting axial strain. however, comparison can be made on the basis of 95% of failure stress. the limiting axial strain for control concrete is about 1880 microstrains. however, for concretes b and c, these values are 1420 and 1596 microstrains respectively. these values are 24% and 15% lower than the control concrete's. the secant modulus of elasticity, as measured at a stress-strength ratio of 0.3 is shown in table iii. compared with normal concrete, the values of concrete b and c are less by approximately 14% and 8% respectively. on the other hand, the value proposed by aci [14] is 24.3gpa. this result is in agreement with the results in [20] for steam-cured slag concrete. fig. 9. stress-strain curves for concretes in compression. table iii. secant modulus of elasticity (gpa) age (days) control b c 28 26.5 22.8 24.4 iv. conclusion for the materials and test conditions reported in this study, it was found that: • a decrease in the final strength of about 33% compared to that of the control concrete was observed for the cycle without pre-heating (cycle a). however, for the cycles b and c (with pre-heating 1.5 and 3 hours), the decrease was 26% and 15% respectively. • the greater the maximum temperature period time, the smaller the drop in compressive strength at 28 days compared to the control. • the best result for the treated concrete is obtained according to the following cycle: o a 3-hour of pre-heating period at 20 o c, o a 2-hour increase of temperature from 20 o c to 70 o c, and o a 3-hour heating at the maximum temperature of 70 o c. acknowledgment the current research was funded by the deanship of scientific research at the university of hail, saudi arabia, under the contract no. rg-191241. the authors would like to extend their gratitude to the deanship of scientific research and to the college of engineering at the university of hail for providing all the required facilities. references [1] a. a. jhatial, s. sohu, n. ul k. bhatti, m. t. lakhiar, and r. oad, "effect of steel fibres on the compressive and flexural strength of concrete," international journal of advanced and applied sciences, vol. 5, no. 10, pp. 16–21, oct. 2018, https://doi.org/10.21833/ijaas.2018. 10.003. engineering, technology & applied science research vol. 11, no. 2, 2021, 6974-6978 6978 www.etasr.com boukendakdji et al.: the effects of steam-curing on the properties of concrete [2] r. nayaka, g. s. diwakar, and v. gudur, "effect of steam curing on the properties of high early strength silica fume concrete," iop conference series: materials science and 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[17] a. m. neville, properties of concrete, 5th ed. harlow, england, uk ; new york, ny, usa: trans-atlantic publications, 2012. [18] j. payá, j. monzó, m. v. borrachero, e. peris-mora, and f. amahjour, "mechanical treatment of fly ashes: part iv. strength development of ground fly ash-cement mortars cured at different temperatures," cement and concrete research, vol. 30, no. 4, pp. 543–551, apr. 2000, https://doi.org/10.1016/s0008-8846(00)00218-0. [19] m. ba, c. qian, x. guo, and x. han, "effects of steam curing on strength and porous structure of concrete with low water/binder ratio," construction and building materials, vol. 25, no. 1, pp. 123–128, jan. 2011, https://doi.org/10.1016/j.conbuildmat.2010.06.049. [20] m. boukendakdji, "mechanical properties and long-term deformation of slag cement concrete," ph.d. dissertation, university of leeds, leeds, uk, 1989. [21] y. h. ahmed and r. azhari, "effect of atmospheric steam curing parameters on concrete strength and durability," in second conference of civil engineering in sudan, khartoum, sudan, dec. 2018, pp. 48–54. engineering, technology & applied science research vol. 8, no. 4, 2018, 3218-3222 3218 www.etasr.com yerrawar & arakerimath: parametric analysis of magnetorheological strut for semiactive suspension … parametric analysis of magnetorheological strut for semiactive suspension system using taguchi method r. n. yerrawar department of mechanical engineering d y patil institute of engineering & technology pune, maharashtra, india rahul.yerrawar@gmail.com r. r. arakerimath department of mechanical engineering g h raisoni college of engineering & management pune, maharashtra, india rrarakerimath@gmail.com abstract—magnetorheological (mr) strut is among the leading advanced applications of semi-active suspension systems. the damping force of mr damper is controlled by varying the viscosity of mr fluid. in this work, the viscosity of mr damper varies by changing the current from 0.5a to 0.7a. the design of experiments is taken into account in concert with the product/process development as one completely advanced tool. the parameters used for ride comfort optimization are sprung mass, spring stiffness, tire pressure, current, and cylinder material with two levels of each. taguchi orthogonal array method is used to select the best results by parameter optimization with a minimum number of test runs. in this paper, from taguchi l16 array and s/n ratio analysis, it is observed that the cylinder material with al and cs for damper cylinder is a key parameter for performance measure of semi-active suspension system. from regression analysis, a linear mathematical model is developed for al and cs as cylinder materials. the interaction of cylinder materials with all four parameters is plotted. the methodology implemented for measurement of acceleration as a ride comfort is as per is 26311997. the more economical model of magnetorheological damper will motivate indian auto industry to broader applications. keywords-magnetorheological damper; parametric analysis; semiactive i. introduction an effective automotive mechanical system has to give comfort and good road holding ability, once the vehicle is moving on any road disturbance. the vehicle body is supposed to have considerable damping or resistance to avoid massive oscillations. comfort optimization is predicated on spring stiffness, damping and sprung mass. normally, such system types are developed by experimental approach. the procedure for designing and modeling of a novel large-stroke mr damper is tested in [1] under impact load and it is observed that the inertia damping force could not be ignored like in the common mr damper due to large acceleration. 2d axisymmetric model was built up in [2] to investigate and analyze the mr damper qualities predicting the damping force characteristics. the bingham model of mr damper was proposed and compared with experimental results for magnetic saturation. this work inferred that the obtained magnetic saturation model can show effect on current, amplitude and excitation frequency. the phenomenon of magnetic saturation is simulated in [3] and obtained results are compared with the experimental results. optimization technique is used to maximize magnetic flux density which affects the force developed by damper [4]. the mr fluid structure and properties, damper description and parametric damper models which are connected in various ways with the actual behavior of the mr fluid were presented in [5]. recommendations for the design of main-spring and shock absorber of motor vehicle suspensions were given in [6]. indications acquired for the shock absorber allow us to obtain the damping coefficients in the compression and rebound strokes and to calculate the power dissipated during the vehicle oscillatory movement. an extensive work has been done on the transmissibility of vibration isolator in [7], where authors proposed the concept of output frequency response function in order to examine the force transmissibility of mdof structures with a cubic non-linear viscous damping device. control strategies can be divided into two main categories: active and semiactive. in the case of active systems the performance is superior and optimum transmissibility has no resonance. semiactive systems provide reliability comparable to passive suspension systems [8]. in [9], it is observed that the vertical acceleration of body mass is substantially reduced by using a controlled mr damper. sensitivity analysis for leaf springs with different stiffness was done in [10] on roll bar of front suspension system by using adams simulation software. static test results were compared with the dynamic test ones. from the simulation results, it is observed that the parametric effect on suspension system is not satisfactory by using static analysis. the experimental results carried out in [11] regarded optimization of suspension system used for vehicle occupant seat for a quarter car model. the taguchi method was implemented in order to reduce vibrations. from the simulation results it is observed that stiffness and damping preliminary values are the control variables of the suspension system. authors in [12] studied the dynamic loads enforced on suspension components through bushings and joints. in order to predict the vehicle com mi pro me exp ach tha opt pro sus stif dam th for des ma and dam vis a. fʈ wh cyl engineerin www.etasr mponent life e inimizing the oposed in [13 ethod and use periment was hieve suspensi at both suspe timization. t ocesses and a spension para ffness, sprung mper are cons his standard re r vehicle which table i. accelera less th 0.315 0.5 0.8 t 1.25 greate the mr dam signed accordi athematical m d magnetic ci mping force scous compone fig. 1 damping fo the damping and viscous co fd=fʈ+fƞ = (2.07 (1 here, q= ap × the calculati linder gap as ng, technology r.com estimation, ta stress value 3] robust opt es adams sof s designed ba ion pareto solu ension and ro the design of lot of time. in ameters such g mass and mo sidered to achi ecommended h is represente comfort reac tion (m/s2) han 0.315 to 0.63 5 to 1 to 1.6 to 2.5 er than 2 ii. damp mper damping ingly. for calc model suggeste ircuit shown i is divided in ents . . magnetic ci orce calculatio g force fd is d omponent fƞ a ƞƞ . 2ʈ 12ƞqltap wh3 v , ap= (d 2 ions are obtain s 1.2mm and y & applied sci yerrawar & aguchi method of the lower timization is ftware to mod ased on the t ution set and t obustness imp f car robustn n the current w as tire pressu st important, c ieve good ride the accelerati ed in table i. ctions to vibrat l not unc a little un fairly un uncom very unc extremely u per fabricati force is calcu culation of the ed by the bing in figure 1 is nto an induced ircuit design of m ons divided into a y as in (1) and (2 ʈ p 2 do 2) , w = π ned by conside velocity as ience research arakerimath: p d is implement r control arm based on ta del suspension taguchi meth the result illus proved a lot ness needs v work, the semi ure, current, s cylinder mater e comfort (rc) ion as rc me tion environmen level comfortable ncomfortable ncomfortable mfortable comfortable uncomfortable ion ulated for 250k e damping forc gham plastic m s used in whic d yield stress, f mr damper yield stress in 2). (1) (2) π ( ) ering the pisto 10 kmph. ta h v parametric an ted by m. the aguchi n. an hod to strated after arious active spring rial for ) [14]. easure nt kg and ce, the model ch the fʈ and nduced on and able ii sho can roa use test mas min (co test setu acc mo acc pc acc acc fig. cycl vol. 8, no. 4, 20 alysis of magn ows the dimen n see the fabric table ii. param piston rod and c dista cylinder t length o piston and cylin piston r distance amo radius of p iii. exp in order to st ad holding, th ed. test set up t the suspens ss is connecte nimize frictio mpatible for ting. figure 3 up is provide cording to con tor. it contain celerometer, a and connectin celerometer. t celeration of w 3. experimen linder 018, 3218-3222 etorheological nsions of the m cated damper. fig. 2. fabr . dimension meter oil width radial ance thickness of pole nder clearance radius ong the poles piston rod perimental p tudy the suspe he quarter ca p has arrangem ion on differ ed to the verti on. double mcpherson ty 3 demonstrate ed with a ca nstant wave f ns instruments loaded pc, m ng cables for the model i wishbone and o ntal setup of quar 2 strut for semia mr damper a icated mr dampe ns of fabricated notations h t l h r l r program for ension effects ar model exp ments for varyi rent loading c ical column b wishbone su ype of suspen es the experim am exciter w form and pow s like data acq mr damper, po r the dc curr is tested for on sprung mass rter car model wi 3219 active suspensi and in figure er d mr damper dimensions(m 5 3 9 1.5 18.03 42 9 r mr damper and study rc perimental setu ing sprung ma conditions. sp y linear bearin uspension sy nsion) is use mental setup. which is desi wered by a pm quisition hardw ower supply fo rent controller r measuremen s. ith mr damper w ion … 2 we mm) c and up is ass to prung ng to ystem d for the igned mdc ware, or the r and nt of with cs engineering, technology & applied science research vol. 8, no. 4, 2018, 3218-3222 3220 www.etasr.com yerrawar & arakerimath: parametric analysis of magnetorheological strut for semiactive suspension … iv. experiment design the experiment design is taken into account in concert with the product/process development as one completely advanced tool. the experiment design takes into consideration wideranging applications in the development of product/process. there are the two approaches of doe. a. full factorial design in full factorial experimental approach, two (at least) or more factors are used in a feasible level and the required units take all probable combinations of all levels of these factors. for 9 factors with 2 levels for each, 512 runs are required for a full factorial design. in this method, each parametric effect on response variables and the interaction between factors is studied. b. taguchi method the major shortcoming of full factorial design is that the number of experiments to be carried out is large which means more laborious work on a large number of parameters. to avoid this troublesome work, taguchi recommended a specially intended method called orthogonal array to learn the whole parameter effect with lesser quantity of experiments. c. selection of control factors it is observed that spring stiffness and electric current need to be appropriately considered under positive range of sprung mass and road conditions. for exceedingly rigid suspension the vehicle system will be vastly stable but acceleration of occupant body will be high and comfort will be low. for a smaller amount of hard suspension, passenger comfort will increase but vehicle stability decreases. the selected parameters for suspension are described in table iii. table iii. taguchi parameter table parameter unit levels level 1 level 2 tire pressure kgf/cm2 (psi) 2 34 40 spring stiffness n/mm 2 14000 8000 damper cyclider material --2 al (+1) structural carbon steel (-1) sprung mass kg 2 72 97 current (a) 2 0.5 0.7 d. orthogonal arrays taguchi developed the orthogonal array method to study systems whose performance is affected by different factors, in a more convenient and rapid way. this method can be used to select the best results by optimization of parameters with a minimum number of test runs. application of taguchi method can achieve the best results out of various tests by selecting the optimum combination of different factors. final product quality can be improved in terms of process optimization, product design and system analysis. to study a sufficient number of experiments with a large number of variables, taguchi recommended the orthogonal array method for experimental design. the conclusions made after a sufficient number of experiments are usable over the whole experimental area covered by control factors and their ranges. orthogonal array method was discovered before taguchi implemented it for doe. in this method, the columns of tabulated sets are orthogonal and consequently linear graphs are plotted to fit the specific project applications. in the current study, five parameters, tire pressure, spring stiffness, damper cylinder material, sprung mass and electric current, each one with two levels are used. table iv defines the l16 array. the number following the “l” indicates the number of runs in the design, and 16 means the array requires 16 runs (25), which indicates that the design estimates up to 5 main parameters at 2 levels each. table iv. taguchi l16 orthogonal array run air pressure spring stiffness cylinder material sprung mass current 1 34 14000 1 72 0.5 2 34 14000 1 97 0.7 3 34 14000 -1 72 0.7 4 34 14000 -1 97 0.5 5 34 8000 1 72 0.7 6 34 8000 1 97 0.5 7 34 8000 -1 72 0.5 8 34 8000 -1 97 0.7 9 40 14000 1 72 0.7 10 40 14000 1 97 0.5 11 40 14000 -1 72 0.5 12 40 14000 -1 97 0.7 13 40 8000 1 72 0.5 14 40 8000 1 97 0.7 15 40 8000 -1 72 0.7 16 40 8000 -1 97 0.5 e. analysis of s/n ratio to measure the performance characteristics, taguchi recommends the use of the loss function that is deviating from the desired target value. the value of this loss function is further transformed into signal-to-noise (s/n) ratio or snr. the preferred parameter settings are determined through snr analysis where the optimized parameters are considered those that maximize the appropriate snr [15-17]. to analyze snr three types of performance characteristics are considered. 1) the smaller the better (for making the system response as small as possible) =-10log( ∑ ) (3) 2) the nominal the best (for reducing variability around a target) =10 log( ) (4) 3) the larger the better (for making the system response as large as possible): =-10 log( ∑ ) (5) lower values of passenger seat displacement and displacement settling time are the prime requirements to achieve passenger rc and safety, thus in present work, snr with lower-is-better characteristic is selected. table v represents the l16 orthogonal array with acceleration as output. engineering, technology & applied science research vol. 8, no. 4, 2018, 3218-3222 3221 www.etasr.com yerrawar & arakerimath: parametric analysis of magnetorheological strut for semiactive suspension … table v. taguchi l16 array with acceleration and sn ratio r u n a ir p re ss u re s p ri n g s ti ff n es s c y li n d er m a te ri a l s p ru n g m a ss c u rr en t a cc el er a ti o n (r c ) s n r 1 34 14000 1 72 0.5 0.7250 2.79324 2 34 14000 1 97 0.7 0.6820 3.32431 3 34 14000 -1 72 0.7 1.1150 -0.94550 4 34 14000 -1 97 0.5 0.8852 1.05917 5 34 8000 1 72 0.7 0.9980 0.01739 6 34 8000 1 97 0.5 0.9250 0.67717 7 34 8000 -1 72 0.5 1.2500 -1.93820 8 34 8000 -1 97 0.7 0.9960 0.03481 9 40 14000 1 72 0.7 0.6520 3.71505 10 40 14000 1 97 0.5 0.8250 1.67092 11 40 14000 -1 72 0.5 0.8524 1.38713 12 40 14000 -1 97 0.7 0.7920 2.02550 13 40 8000 1 72 0.5 0.5240 5.61337 14 40 8000 1 97 0.7 0.9152 0.76968 15 40 8000 -1 72 0.7 1.2100 -1.65571 16 40 8000 -1 97 0.5 1.1600 -1.28916 f. optimum level prediction the results obtained are depicted in table vi. it is observed that cylinder material ranks first and figure 4 shows the optimum parameter level. from table vi it is observed that cylinder material performs ranks first and from the main effect plot of sn ratios (figure 4), p34k8000cm-1m97i0.7 shows optimum level of parameter. table vi. snr response tables level air pressure spring stiffness cylinder material sprung mass current 1 0.6278 0.2787 -0.1652 1.1233 1.2467 2 1.5296 1.8787 2.3226 1.0341 0.9107 delta 0.9018 1.6001 2.4879 0.0893 0.3360 rank 3 2 1 5 4 fig. 4. main effect plot for snr v. snr interaction plot taguchi designs conventionally focus on the main effects, but it is important to test the supposed interactions. in order to determine the effect of one on another parameter with respect to its response, taguchi uses a method known as interaction plot. to study the interaction plot, the interpretation of table vii is considered. according to snr response table, ranks are established. from table vi, cylinder material takes first rank. in order to check the cylinder material’s effect on the other four parameters, its interaction plot with tire pressure, spring stiffness, sprung mass and current is plotted. table vii represents the interpretation of interaction lines. the regression equation (6) is generated from regression analysis. _ 1 1.718 0.0134 0.000030 0.1259 0.00073 0.134 rc p k cm m i       (6) table vii. interpretation of interaction lines position of interaction lines interpretation parallel no interaction between two factors not parallel interaction between two factors vi. conclusion taguchi l16 array and snr analysis show the cylinder material with al and cs for damper cylinder is a key parameter for performance measure of semi active suspension with mr damper. it is observed that damper cylinder material is a key parameter to design the mr damper. from the interaction plot, it is concluded that cylinder material interacts more with spring stiffness and tire pressure compared to sprung mass and current. the low price model developed will have wide range of applications to indian auto industry. fig. 5. interaction plot for sn ratios acknowledgment this work is supported by bcud, board of college & university development, savitribai phule pune university, pune, india under university research grant scheme and we would like to thank mes college of engineering, pune for providing the research facilities. references [1] x. jiang, j. wang, h. hu, “designing and modeling of a novel magneto-rheological fluid damper under impact load”, 3rd international conference on mechanical engineering and mechanics, beijing, china, pp. 203-207, october 21−23, 2009 [2] s. k. mangal, a. kumar, “experimental and numerical studies of magnetorheological (mr) damper”, chinese journal of engineering, vol. 2014, article id 915694, 2014 [3] z. d. xu, d. h. jia, x. c. zhang, “performance tests and mathematical model considering magnetic saturation for magnetorheological damper”, 4034 2.5 2.0 1.5 1.0 0.5 0.0 140008000 1-1 9772 0.70.5 p m ea n of s n r at io s k cm m i main effects plot for sn ratios data means signal-to-noise: smaller is better 3.0 1.5 0.0 140008000 9772 3.0 1.5 0.0 3.0 1.5 0.0 4034 3.0 1.5 0.0 0.70.5 3.0 1.5 0.0 1-1 p k cm m i 34 40 p 8000 14000 k -1 1 cm 72 97 m 0.5 0.7 i interaction plot for sn ratios data means signal-to-noise: smaller is better engineering, technology & applied science research vol. 8, no. 4, 2018, 3218-3222 3222 www.etasr.com yerrawar & arakerimath: parametric analysis of magnetorheological strut for semiactive suspension … journal of intelligent material systems and structures, vol. 23, no. 12, pp. 1331–1349, 2012 [4] h. krishna, h. kumar, k. gangadharan, journal of the institution of engineers (india): series c, vol. 98, no. 4, pp. 533-539, 2017 [5] b. sapinski, “analysis of parametric models of mr linear damper”, journal of theoretical and applied mechanics, vol. 41, no. 2, pp. 215240, 2003 [6] i. preda, “about the preliminary design of the suspension spring and shock absorber”, in: iop conf. series: materials science and engineering, vol. 147, iop publishing, 2016 [7] z. k. peng, z. q. lang, l. zhao, s. a. billings, g. r. tomlinson, p. f. guo, “the force transmissibility of mdof structures with a non-linear viscous damping device”, international journal of non-linear mechanics, vol. 46, no. 10, pp. 1305-1314, 2011 [8] s. segla, j. kajaste, p. keski-honkola, “optimization of semi-active seat suspension with magnetorheological damper”, in: vibration problems icovp 2011, springer proceedings in physics, vol. 139, pp. 393-398, springer, 2011 [9] h. f. lam, c. y. lai, w. h. liao, automobile suspension systems with mr fluid dampers, technical report, smart materials and structures laboratory, department of mechanical and automation engineering, the chinese university of hong kong, 2002 [10] e. sert, “improvement of the vehicle stability using suspension optimization methods”, international journal of automotive engineering and technologies, vol. 6, no. 2, pp. 70–84, 2017 [11] m. b. s. sreekar reddy, p. vigneshwar, d. raja sekhar, k. akhil, p. l. reddy, “optimization study on quarter car suspension system by rsm and taguchi”, in: proceedings of the international conference on signal, networks, computing, and systems, lecture notes in electrical engineering, vol. 396, pp. 261-271, springer, 2016 [12] j. h. kim, h. c. sin, b. j. kang, n. w. kim, “characteristic study of bushing compliance in consideration of stresses in a vehicle suspension system by the taguchi method”, in: proceedings of the institution of mechanical engineers, part d: journal of automobile engineering, vol. 220, no. 10, pp. 1383-1399, 2006 [13] s. liao, k. cao, h. wei, j. liu, c. xie, “robust optimization of multilink suspension compliance characteristics based on taguchi method”, advances in computer science research, vol. 74, pp. 726-132, atlantis press, 2017 [14] iso2631-1, mechanical vibration and shock – evaluation of human exposure to whole-body vibration – part 1: general requirements, international organization for standardization. geneva, pp. 1-31, 1997 [15] g. m. reddy, v. d. reddy, b. s. kumar, j. shyamsunder, “experimental investigation on radial ball bearing parameters using taguchi method”, journal of applied and computational mechanics, vol. 4, no. 1, pp. 69-74, 2018 [16] m. b. silva, l. m. carneiro, j. p. a. silva, i. s. oliveira, h. j. i. filho, c. r. de oliveira almeida, “an application of the taguchi method (robust design) to environmental engineering: evaluating advanced oxidative processes in polyester-resin wastewater treatment”, american journal of analytical chemistry,vol. 5, pp. 828-837, 2014 [17] c. f. j. kuo, m. y. dong, “application of the taguchi method in analyzing the impact of modified gemini surfactants on tio2 nanosuspension”, journal of surfactants and detergents, vol. 15, no. 4, pp. 471–476, 2012 engineering, technology & applied science research vol. 8, no. 3, 2018, 2981-2984 2981 www.etasr.com laghari et al.: analysis of hydrological response considering climatic variability a hydrological response analysis considering climatic variability case study of hunza catchment a. n. laghari energy & environment engineering department, quaid-e-awam university of engineering, science & technology nawabshah, pakistan w. rauch unit of environmental engineering university of innsbruck austria m. a. soomro civil engineering department, quaid-e-awam university of engineering, science & technology nawabshah, pakistan abstract—the hydrological response of mountainous catchments particularly dependent on melting runoff is very vulnerable to climatic variability. this study is an attempt to assess hydrological response towards climatic variability of the hunza catchment located in the mountainous chain of greater hindu kush-himalaya (hkh) region. the hydrological response is analyzed through changes in snowmelt, ice melt and total runoff simulated through the application of the hydrological modeling system prevah under hypothetically developed climate change scenarios. the developed scenarios are based on changes in precipitation (prp) and temperature (tmp) and their combination. under all the warmer scenarios, the increase in temperature systematically decreases the mean annual snow melt and increases significantly glacier melt volume. temperature changes from 1°c to 4°c produce a large increase in spring and summer runoff, while no major variation was observed in the winter and autumn runoff. the maximum seasonal changes recorded under the tmp+4°c, prp+10% scenario. keywords-mountain region; hunza catchment; melting contribution; water resources i. introduction pakistan is an agrarian country and its agriculture is mainly dependent on one of the world’s largest irrigation systems, the network of the indus basin (ibis). the irrigation system is largely fed through the indus river system (irs) comprised of indus river and its tributaries. indus river and most of its tributaries originates from the greater hindu kush-himalaya (hkh) region. the region is famously known as “the water tower of asia”. this mountain region works as a large reservoir, seizing precipitation and retaining it till released into various tributaries of the irs. this system connects to the other most important reservoir, groundwater, but also constitutes a source of recharge of aquifers in the plain areas of indus basin. the river system discharges an annual average volume of 175 billion m3 which supports directly about 60% of total irrigation requirements, while the rest is provided through groundwater exploitation-which is already close to its maximum potential. therefore, indus basin is considered as a closed basin-due to the exploitation of the full potential of ground and surface water resources [1, 2]. further burgeoning population, industrialization and urbanization will require a 30% more increase in water demand in the next 2 decades. moreover, it is projected that climate change will further exacerbate the problem through changes in river seasonality, time of occurrence and peak flow volume in the mountain regions [3]. earlier studies conducted over the himalayan part of indus basin projected that alteration in climatic parameters would result in modification of the hydrological cycle and consequently affect the quantity and quality of river flows [4]. likewise, numerous other authors also supported the same conclusion in the european alps [2, 5, 6]. they concluded that any change in climatic parameters may alter the snow and ice storage. this may result in change of both the time of occurrence and the flow volume of mountain tributaries, which may have severe repercussions on adjoining plain areas. this would eventually affect seasonal water availability. the change in seasonality may hamper development in the agricultural sector, including future planning and operation of hydrological installations. due to heavily dependent on melting runoff, the upper region of indus basin (part of hkh) is extremely sensitive to climate change [7]. therefore, it is worth to scrutinize the hydrological response against climatic variability of the hunza catchment which is not thorough studied. this study investigates the hydrological response of the hunza catchment to a warmer climate through the application of the hydrological modeling system prevah. the developed scenarios are based on changes in (tmp) ranging from 1°c to 4°c and in (prp) ranging from -10% to +10%. ii. description of the study region the hunza catchment encompasses an area of some 14746 km2 within greater hkh region. its altitude ranges from 968m to over 7500m a.s.l (figure 1). hundreds of peaks exceed 6000m elevation. one-third of the catchment area remains under permanent glacial ice fields with about 808.79km3 ice reserves. there are hundreds of glaciers, but the 15 largest ones, like the hispar (521km2), batura (336km2) and khurdopin (205km2), dominate the hydrological flow regime. figure 2 indicates the climatic conditions of the basin. the summer monsoon of the subcontinent has very little influence ov blo is v fee acc hig win the gla wa fig run hy cha me in aut mo rep app engineerin www.etasr er the precipi ock monsoon very low and eding mostly cumulation. t gh in summer nter is very lo e total stream acier melting. arm and dry m fig. g. 2. the 30 y noff computed at g iii. m the preva ydrotope) mo aracteristics eteorological p soil types, l thors have s ountainous cat present mount plied to sim ng, technology r.com itation regime rains. therefo predominantly y the snow the temperatu and very low ow. overall the flow regime. accordingly months and less 1. map of stu year average (19 gauge station (da model develo ah (precipita odel has been of mountain parameters and and use, cov successfully tchments [2, 5 tain region ch mulate the hy y & applied sci e, as its south ore, the precip y restricted to cover and ure regime v w in winter, th e ice melt con temperature glaciers prov s water in wet udy area-hunza ca 960-1990) of mo ainyor bridge) for opment and a ation-runoff-e n developed n regions, e d consider phy ver and topog applied the 5, 6, 9, 10]. d haracteristics, p ydrological re ience research lag hern borders m pitation of the o winter season the glacier varies signific herefore the fl ntribution dom controls the r vide more wa and cool mont atchment onthly (tmp), (pr r the hunza catchm application evapotranspi to truly rep .g., variabilit ysical heterog graphy [8]. s model to v due to its abil prevah has esponse of h h v ghari et al.: ana mostly basin n thus r ice cantly: low in minates rate of ater in ths. rp) and ment iration present ty in eneity everal arious lity to s been hunza catc data line the effi than resu very hyd clim clim 4°c cha tab m ana par gen sen mo scen dec is o whi und sno to und scen pea con volu run -10 sno hum vol. 8, no. 3, 20 alysis of hydrol chment. the m a for the years ear nash-sutc calibration iciency is abov n 5.5%. the ults prove tha ry well. the d drological resp mate. the fut mate scenarios c temperature anges. ble i. mod ti sp overall results 19 19 annual results 19 19 19 monthly results 1 1 1 iv the hydrolo alyzed by asse rameters again nerated clima nsitivity of sno thy basis. it narios, snow creases in june observed in a ile maximum der warmer a ow melt durati april/june. t der higher pre narios, while ak snow mel nditions, incre ume but incre noff. this effec 0% to +10% owmelt runoff mid and dry s 018, 2981-2984 logical respons model was dev s 1986-1988 an cliffe efficienc and validatio ve 85% and d e monthly an at model repro developed mo ponse of catc ture warmer s based on po e increase an del efficiency (c calibration res ime pan dev (mm) 986988 -35 986 -31 987 -23 988 19 1 -09 2 -01 3 -12 4 -03 5 08 6 -02 7 -21 8 -17 9 -11 10 15 11 11 12 07 v. results ogical sensiti essing snow m nst climatic va ate change sc ow melt agains is clearly in w melt runoff e/july. the ma april/may und decrease of a and humid co on from may/ the volume o ecipitation scen no significant t occurrence. ease in prec ease in tempe ct can be seen changes in f varies betwe scenarios. the 4 se considering veloped and a nd 1990-1992 cy and volum on periods. t difference in f nd annual ca oduced catchm odel was then chment under climate is re ossible combin d -10% to + calibration and ults v r2 tim spa 0.90 1990 199 0.92 199 0.90 199 0.85 199 0.99 1 0.99 2 0.99 3 1.00 4 0.87 5 0.82 6 0.89 7 0.88 8 0.83 9 0.87 10 0.99 11 1.00 12 s and discuss vity of hun melt, ice mel ariability thro cenarios. fig st various deve ndicated that f increases i aximum increa der warmer an about 45mm i ondition scena /july is shifted of peak snow narios and vic t effect observ in case of cipitation will erature will tri n over a tmp + precipitation een 5 mm to e monthly sno 2982 g climatic varia applied to avai . table i show metric deviatio the mean an flow volume is alibration/valid ment character n applied to a r a future wa epresented thr nations of a 1° +10% precipit d validation) validation results me n dev (mm) 092 -41 0 90 -36 0 91 34 0 92 -39 0 -11 0 -08 0 -13 0 -06 0 -10 0 20 0 06 0 -11 0 13 0 0 -11 0 -01 0 2 -09 0 sion nza catchmen lt, and total ru ough hypotheti ure 3 shows eloped scenari under all ado in april/may ase of about 2 and dry condit s observed in arios. the cu d one month e melt is incre ce versa unde ved over timin humid and l grow snow igger a faster +4°c scenario n, where mo o 10 mm bet ow melt varia ability ilable ws the n for nnual s less dation ristics assess armer rough °c to tation s r2 0.87 0.90 0.85 0.85 0.98 0.99 0.99 0.99 0.86 0.69 0.92 0.90 0.74 0.85 0.99 0.99 nt is unoff ically s the os on opted and 25mm tions, june urrent earlier eased er dry ng of drier wpack melt o with onthly tween ations bet sno con con ref and cur eff sho gla inc fig bas ta mo inc ho inc are com sce engineerin www.etasr tween the two ow melt contri table ii indi ndition (tmp ntribution in ference contrib d humid con rrent snowme fect of differen own in figur acier melt run creases linearly g. 3. influence sis from (april to able ii. infl snowmelt ru 1992) climatic sc prp. sc. + tmp. sc. + + + c o m b in ed s ce n a ri o s tm prp tm prp tm prp tm prp tm prp tm prp under all th onths earlier creased flows owever, under creased, thus s ea, resulting mparatively pr enarios. figur ng, technology r.com o scenarios ha ibution in tota icates that un p+4°c, prptotal stream bution of 40.4 ndition (tmp elt contributio nt combined s e 4 which cl noff starts earli y with increas e of climatic scen july) for 1990-19 luence of clim unoff, glacier m enario % co r ref. mean annu snowm t (40.4% 10% 36.2% +10% 44.3% +2°c 38.3% +3°c 36.9% +4°c 35.4% mp+2°c p-10% 34.4% mp+2°c p+10% 42.1% mp+3°c p-10% 33.0% mp+3°c p+10% 40.5% mp+4°c p-10% 31.7% mp+4°c p+10% 38.9% he adopted sc than existing s each month r humid cond snow cover re in late sta roduces lower re 4 supports y & applied sci ave drastic effe l stream flow. der the adopt 10%) scenar flow reduced % to 31.7%, w p+4°c, prp+1 on just reduc cenarios on gl early demons ier under all w ing temperatu narios on snow m 992 matic scenario melt runoff, an ontribution to reference* . n al mel %) ref. mean annual ice melt (73.3%) % 74.9% % 71.8% % 89.9% % 98.9% % 108.0% % 91.4% % 88.5% % 100.2% % 97.5% % 109.4% % 106.7% *mean a cenarios, glaci conditions ( h under all ditions, the sn emains a bit lo art of glacie r glacier runof s this fact, w ience research lag fect on mean a ed warmer an rio, the snow d from the c while under w 0%) scenario ced to 38.9% lacier melt run trates that mo warm scenario ure. melt runoff on m os on mean a nd stream flow % change to reference* ref. mean annual stream flow (--) -0.7% 0.8% 18.5% 28.2% 37.7% 16.6% 20.4% 26.1% 30.2% 35.6% 40.0% annual value: 639.5mm ier melting st (june) and pr adopted scen nowpack volu onger over gla er melting, w ff than dry con where the mo h v ghari et al.: ana annual nd dry wmelt current warmer o, the %. the noff is onthly os and monthly annual w (1990tarts 2 roduce narios. ume is aciated which ndition onthly glac prp 10% tem mon glac ado scen whe cur res mel wou bee ran pre ann tab tab cha con for 6.9% +0. war tem sub flow infl volu reco amo mon thei infl p tm vol. 8, no. 3, 20 alysis of hydrol ciers melt run p) are compar % decrease in mperature linea nths. monthly cier melt contr opted scenario nario produce ere mean ann rrent reference sults show tha lt runoff. in uld result in gl the result of en shown in f nges between cipitation have nual stream fl ble iii. ble iii. infl on mean seaso τhe change ange mean sea ntribution (1.7% spring, 67.7% % for autumn 8%. however rmer climate mperature sign bsequently incr w. this can b luence of tem umes. the h orded in ma ount backed nthly flows. t ir significant luence over s climatic scenar rp . sc. -1 +1 mp. sc. +2 +3 +4 c o m b in ed s ce n a ri o s tmp prp tmp prp tmp prp tmp prp tmp prp tmp prp 018, 2981-2984 logical respons noff under hum ratively lower n prp). it is arly increases y glacier melt r ribution to tota os, warmer a es highest in nual glacier m e contribution at the rate of the long run lacier depletio f variation in p figure 5. as 200mm to 25 e very little im low volume. luence of hypot onal stream flo in precipitati asonal flow con %) to 1.5-1.8% % to 66.9-68.6 n, while annua r, the major im change scen nificantly incr reased glacier be seen in fig mperature cha highest increas ay-june period with earlier the early star contribution i stream season rio seas winter ref. (1.7%) 10% 1.5% 10% 1.8% 2°c 1.9% 3°c 2.2% 4°c 2.5% p +2°c -10% 1.6% p +2°c +10% 2.1% p +3°c p-10% 1.9% p +3°c +10% 2.4% p +4°c p-10% 2.2% p +4°c +10% 2.8% 4 se considering mid conditions than dry con also projecte s glacier melt runoff increas al stream flow and drier (tm ncrease in gla melt contributi n 73.3% to temperature c n, warmer and on and retreat. prp on month the average 50mm annual mpact over mo the effect ca thetical climat ow (1990-1992) ion from +10 ntribution from % for winter, 2 6% for summe al change will mpact has be narios, in w rease glacier melt contribu gure 6, which ange on mon ses in total m d, where inc glacier melt rt of snow an in total stream nality (tables sonal % contribu r ) spring ref. (24%) 24.5% 23.5% 34.4% 40.0% 45.6% 35.1% 33.8% 40.4% 39.6% 45.9% 45.4% 2983 g climatic varia (+10% increa ndition scenari ed that increa t runoff in va ses significantl w volume. und mp+4°c, prpacier melt ru ion increased 106% (table controls the gl d dryer condi ly stream flow basin precipit lly, the chang nthly, seasona an be observe te change scen 0% to -10% m current refer 24% to 23.5-2 er and 6.6% to l be around -0 en observed u which increase melt runoffution in total st h demonstrate nthly stream monthly flow reased snow causes a surg nd glacier mel m flow has a m ii-iii). chang ution to referenc summer ref. (67.7%) au r (6. 66.9% 6 68.6% 6 74.8% 7 78.2% 7 81.5% 8 73.2% 6 76.5% 8 76.6% 7 79.8% 8 80.0% 7 83.1% 8 *mean annual value: 6 ability ase in ios (ase in arious ly the der all 10%) unoff, from iii). lacier itions w has tation ges in al and ed in narios will rence 24.5% o 6.30.7 to under es in and tream es the flow s are melt ge in lt and major ge in ce* tumn ref. .6%) .3% .9% .4% .8% .1% .7% .0% .1% .4% .4% .8% 39.5mm (tm con 46 cha tem sum (tm no flo fig july fig to j fig to j tem wh enh th wa nut run dem wi con engineerin www.etasr mp) from 2°c ntribution from % for spring, ange was ob mperature sens mmer months mp) from 2°c significant im ows. g. 4. influence y) glacier melt ru g. 5. influence july) stream flow g. 6. influence july) stream flow the change i mperature) ha here change hanced averag he maximum i armer and hu tshell, the ma noff as comp monstrates tha ll be deplete nclusions can ng, technology r.com c to 4°c wi m current refer , 68% to 75-8 bserved in a sitivity is obse s. in this pa c to 4°c still s mpact was ob e of climate chan unoff (1990-1992) e of precipitation (1990-1992) e of temperature c (1990-1992) in spring and ave drastically in (tmp) fro ge annual strea increase of ab umid scenario aximum effec pared to snow at if temperatu ed and retrea be drawn for y & applied sci ill increase m rence contribu 81% for summ autumn and w erved to be lim articular catch seems below m bserved over nge scenarios on ) changes on magn changes on magn summer flows y increased m om 2°c to am flow from bout +40% is o (tmp+4°c ct is observed w and total ru ure continues t ated in the r the dry seaso ience research lag mean seasonal ution (24%) to mer. no signi winter flows. mited to sprin hment, variati melting point, autumn and w n the monthly (a nitude of monthly nitude of monthly s (due to incre mean annual f 4°c have lin +18.5% to +3 observed und , prp+10%). d over glacier unoff. this c to grow, the gl long run. s on. however, t h v ghari et al.: ana l flow 34%ificant . the ng and ion in hence winter april to y (april y (april ease in flows, nearly 37.7%. der the in a r melt clearly laciers imilar this is rev tem catc scen cha run in g leav par to a sign the and pro stre the fact this incr [1] [2] [3] [4] [5] [6] [7] [8] [9] vol. 8, no. 3, 20 alysis of hydrol ersed in the c mperature. this study an chment again narios. it is co ange in temper noff and subse glacier runoff ve a catalyst e rticular catchm a large increa nificant chang e maximum se d humid con oduce about 4 eam flow volu long run, th tors in glacier s could be the rease in tempe j. briscoe, u. q university pres a. n. laghari, change result in alps”, hydrolo ipcc, climate of working g intergovernmen press, 2007 p. singh, s. k contribution in development, v d. vanham, e. hot summer on and technology d. vanham, e. alpine water re conditions”, w 1801, 2009 p. singh, l. be basin to climat 2385, 2004 d. viviroli, m. hydrological m processing-tool 10, pp. 1209–12 m. verbunt, m coupled hydro in the rhine ba 238, 2006 018, 2981-2984 logical respons case of humid v. co analyzed the h nst hypothetic oncluded that rature would s equently increa f and ultimate effect over sea ment, the obser ase in spring ge was observ easonal change ndition scenar 40% accumul ume. in a nuts he warm and rs retreating a vice versa in c erature. refer qamar, pakistan’s ss, 2009 d. vanham,l w n a shift in alpin gical sciences jo change 2007: th group i to the ntal panel on c k. jain, n. ku n the chenab ri vol. 17, pp. 49–56 fleischhacker, w water supply secu y, vol. 59, no. 3, . fleischhacker, esources managem water science and engtsson, “hydro te change”, hydr zappa, j. gurtz, modelling system s”, environmenta 222, 2009 m. zappa, j. gu meteorological m asin”, journal of h 4 se considering d conditions w onclusion hydrological r cally develope under all deve ignificantly in ase total stream e effect over asonality of st rved seasonal and summer ved in winter e was recorded rio. overall s lative increase shell, it can be dry condition and depletion case of humid rences s water economy w. rauch, “to wh ne hydrology? a urnal, vol. 57, no he physical scien e fourth asses climate change, umar, “snow an iver at akhnoor 6, 1997 w. rauch, “impac urity in an alpine pp. 469-477, 200 w. rauch, “imp ment under prese technology, vo ological sensitivity rological process r. weingartner, m prevah an al modelling & s urtz, p. kaufman modelling approac hydrology, vol. 2984 g climatic varia with no chan response of h ed climate ch eloped scenar ncrease glacier m runoff. the total runoff w tream flow. in change is con runoffs, whil and autumn f d under the wa seasonal incr e in mean an e concluded th ns will be cr process. how conditions wi y: running dry, o hat extend does c case study of au o. 1, pp. 103-117 nce basis. contri sment report o cambridge univ nd glacier melt r”, mountain re ct of an extreme d region”, water s 09 pact of snowmaki ent and climate c ol. 59, no. 9, pp. y of a large him es, vol. 18, pp. “an introduction nd its preand software, vol. 2 nn, “verification ch for alpine tribu 324, no. 1-4, pp ability ge in hunza hange ios, a r melt e gain would n this nfined le no flows. armer reases nnual hat in ritical wever ith no oxford climate ustrian , 2012 ibution of the versity runoff esearch dry and science ing on change 1793malayan 2363– n to the post4, no. n of a utaries p. 224– microsoft word 16-3226_s_etasr_v10_n2_pp5428-5433 engineering, technology & applied science research vol. 10, no. 2, 2020, 5428-5433 5428 www.etasr.com hazim et al.: impact of roadside fixed objects in traffic conditions impact of roadside fixed objects in traffic conditions nabil hazim department of civil engineering al-ahliyya amman university amman, jordan n.hazim@ammanu.edu.jo lina shbeeb department of civil engineering al-hussain technical university amman, jordan lina.shbeeb@htu.edu.jo zaydoun abu salem department of civil engineering applied sience private university amman, jordan z_abusalem@asu.edu.jo abstract—highway capacity manual (hcm) assumes that traffic flow rates are equally distributed between lanes, which is not always the case. lane distribution and speed are influenced by lateral clearance on the roadsides. in jordan, the absence of wellmarked lanes and poor lane discipline results in under-utilizing of the freeway capacity. the objective of this study is to look into the impact of the presence of roadside objects on lane distribution and speed. test sections were selected on six-lane freeway segments located in sub-urban areas on tangent highway segments. speed measurements and distribution counts made for each lane on a directional three-lane segment of the freeway. the results showed that lane distribution significantly varies depending on lateral clearance and traffic. as lateral displacement increases, right-lane-use and left-lane-use increases while the middle-lane use remains almost at the same level. average speed increases as the lateral clearance increases. the results also showed that average speed and lane distribution for 1.5m lateral clearances are very similar to no obstacle conditions. the impact of an obstacle is more significant on the right lane while the use of the left lane fluctuates with a significant increase if traffic flow rates reach high levels. keywords-lane distribution; obstacle; speed i. introduction traffic lane distribution in freeways consist an important parameter regarding traffic, which receives considerable attention. hcm assumes that traffic flow rates are equally distributed between lanes, which is not always the case, particularly at low traffic flow rates. other factors may influence lane distribution and average speed, including lateral clearance. lateral clearance is defined as an obstacle free area beginning at the edge of travel lane and extending to a minimum distance such that it does not interfere with the operation of the roadway. in jordan, the absence of wellmarked lanes and the poor lane discipline result in underutilizing of the freeway capacity. there is a need to understand traffic behavior by a detailed simulation model, by giving important inputs (headway time and vehicular speed). the lane flow-distribution can directly influence the capacity of the freeway section under investigation, and in the presence of high volumes, more vehicles travel on the median lane rather than on the shoulder lane [3, 5-7, 10-15]. in [7], the distribution of the total traffic flow in individual lanes was derived mathematically. two-lane and three-lane carriageways were studied. the frequency of lane changing was also considered. unfortunately, the mathematical derivation in his work contains a minor error, although this does not significantly affect the numerical results. the flowdistribution in individual lanes is re-derived and extended to carriageways with more than three-lanes. the model is then calibrated with field data obtained from germany. authors in [14] investigated the impact of a median barrier on mean traffic speeds on selected sites with passed speed zones of 70km/h and 80km/h. the findings suggested that mean speed on section with barriers was actually higher than the base free flow speed along road section without barriers. authors in [17] stated that aggressive driving and infringement of traffic laws and regulations were noticed to be the main factors of road traffic accidents in saudi arabia and that road conditions or objects on roads had minor effects. authors in [1] reported that on-street parking can create stop-start traffic flow behavior for the lanes adjacent to the parking lane affecting the capacity of the road section and any obstacle vision on the road located closer than 1.8m from the edge of traffic lane means that lateral clearance is not ideal and therefore the road capacity will be reduced. also they reported that the road capacity value drops due to various “non-ideal conditions” including changes in speed or travel time, traffic interruptions or restrictions. authors in [4] show that a solid barrier induces an updraft motion and lofts the vehicle emission plume. author in [8] discussed the capacity and quality of service of two-lane highways and defined some of the factors that affect the capacity such as heavy vehicle presence, lane width, and lateral clearance and reported about the weather and road capacity and discussed how the weather affects the capacity and the extent of the proportion of influence in different situations. authors in [12] investigated lane utilization by vehicle type. a study on four lane−two way and six lane−two way highways showed that light vehicles and heavy vehicles were using the middle lane, whereas most motorcycles were using the curb lane or the middle lane. authors in [13] investigated both lane density and lane flow distribution on freeways with its systems. two concepts were introduced: lane flow distribution ratio and the land density distribution ratio to resemble factors for congestion estimation. corresponding author: zaydoun abu salem engineering, technology & applied science research vol. 10, no. 2, 2020, 5428-5433 5429 www.etasr.com hazim et al.: impact of roadside fixed objects in traffic conditions authors in [17] indicated that traffic volume on a major road is a significant predictor of crashes at un-signalized intersections and the geometric characteristics and features of un-signalized intersections have also been found to be potential explanatory variables in crash prediction models. authors in [11] investigated speed distribution profile by considering vehicle types and analyzed time headway distribution profiles for different vehicle types at five different traffic densities ranging from 0 to 80 pcu/km with an increment of 20pcu/km. lane flow-distribution is different from country to country. the difference can be attributed to the prevailing laws and regulations and the associated level of enforcement and road user behavior. for example, the typical shape of lane flowdistribution on german motorways is a consequence of the strict regulations of “commandment of driving on the right” and “prohibition of overtaking on the right”. in general, the country-related lane flow distribution should be investigated further. ii. study objective this study investigates the impact of the presence of roadside objects on traffic parameters such as lane distribution and speed. the study attempts to define obstacle’s clearance that would minimize its impact on traffic parameters. iii. collection of field data observations lane distribution counts and speed measurements were made at four-lane and six-lane test sites in the spring of 2019. the counts begun at 11 am on march 9, 2019 and continued in an hourly basis for the duration of one week (to 1 am, march 16, 2019). the choice of the starting date was considered unimportant as long as no major changes in the traffic flow were anticipated. for this reason, the counts and speed measurements were not made during holidays. the procedure for collecting lane distribution data and speed measurements consisted basically of observing the lane of choice for each vehicle passing the test sites. lane distribution counts were made at the test sites in quarter hourly intervals beginning at the start of each hour. lane distribution data and speed measurements were recorded for a particular test site, direction of travel on a data sheet prepared for the purpose. because of the large number of vehicles anticipated at the test sites, counters were used for recording vehicle repetitions by lane. at the end of each hour, the counter readings were transferred on the data sheets, the counters were zeroed, and a new set of sheets were initiated for the next time period. this procedure was repeated throughout the testing period. four locations for placing obstacles were selected varying in half meter intervals starting from the edge of the travel lane (zero distance). the test sections were 30m long and the lateral clearances were formed by placing a series of traffic cones spaced in 0.3m intervals. data were also collected for the same sections but without obstacles. test sections were selected on six-lane freeway segments with fully controlled access located in sub-urban areas along queen alia international airport highway in amman district (figure 1). these sites were chosen so that there would be no influence from lateral restrictions as access ramps, grade separation structures, traffic signs, and (or) rest areas. the test sites were located on long-tangent highway segments. the tangent distances from the horizontal curves are of sufficient length so that the lane distributions at the test site were not affected by these curves. lane distribution counts made for each lane of the directional three-lane segment. the grade and rate of vertical curvature are minimal throughout the tangent length (geometric design criteria stipulate a minimum slope for drainage purposes). the three-lane test sections were located reasonably near each other so that the traffic streams observed at all test sites were nearly identical. there is a suitable observation point at each test site for the data collectors with good visibility of the traffic while providing maximum concealment of the data collection operation. fig. 1. test section on queen alia international airport highway the cross sections of the highway at the test sites are typical of that constructed along the entire highway length. the pavement surface characteristics are consistent, with respect to appearance and roughness for all lanes and along the entire highway length. striping is distinct and properly positioned on the roadway. finally, the physical conditions of the shoulders and medians were sufficient. iv. analysis methodology the fifteen-minute-counts were converted to hourly traffic flow (qsum). given the total flow rate of a freeway, qsum, the relationship between the proportion of traffic flow rates, p1, p2, and p3 on the right, middle and left traffic lane respectively, can be calculated as a function of the total flow rate qsum. hence, the following relationships always hold: p1=q1/qsum, p2=q2/qsum, p3=q3/qsum, and p1+p2+p3=1, where q1, q2, and q3 are traffic flow rates for right, middle, and left lane respectively [2, 9, 16]. the generalized procedure selected as most applicable for analyzing the lane distribution data taken in this study consisted of descriptive analysis including graphical presentation describing lane distribution versus traffic volume for each tested site, each obstacle location and comparison with the no obstacle case. inferential tests were conducted to detect what would be the impact of lateral clearance on some traffic parameters (lane distribution and speed). f-test and paired sample t-tests were used for the analysis. v. analysis results table i represents a summary of the results of this study. it shows that lane distribution differs by obstacle distance (lateral clearance) from the carriageway edge and traffic flow rates. engineering, technology & applied science research vol. 10, no. 2, 2020, 5428-5433 5430 www.etasr.com hazim et al.: impact of roadside fixed objects in traffic conditions however, the overall average suggests small difference in lane use proportion as a function of directional traffic flow that can be explained by lateral clearance. it seems that in jordan, drivers tend to be more aggressive while approaching obstacles. they normally would force their way in and thus a variation in the findings of this research and those of other studies can be explained. the variation of the lane distribution is related to lateral clearance (the distance of the obstacle measured from the travel-lane edge) as indicated in figure 2. the average lane distribution changes with the lateral clearance (0m, 0.5m, 1.0m, and 1.5m). table i. lane distribution by traffic flow and lateral clearance hourly traffic flow (veh/h) 0.0m 0.5m 1.0m 1.5m no obstacles right middle left right middle left right middle left right middle left right middle left 400-799 0.13 0.51 0.36 0.19 0.44 0.38 0.32 0.32 0.36 0.18 0.46 0.35 800-1199 0.20 0.40 0.39 0.19 0.43 0.37 0.21 0.42 0.38 0.23 0.41 0.36 0.26 0.37 0.37 1200-1599 0.22 0.40 0.38 0.27 0.37 0.35 0.22 0.41 0.37 0.23 0.42 0.36 0.23 0.44 0.33 1600-1999 0.22 0.39 0.39 0.28 0.37 0.35 0.26 0.40 0.34 0.26 0.40 0.33 0.27 0.41 0.32 2000-2399 0.23 0.34 0.43 0.29 0.34 0.37 0.27 0.35 0.38 0.27 0.37 0.36 0.25 0.34 0.41 average 0.21 0.39 0.39 0.25 0.39 0.36 0.23 0.41 0.37 0.25 0.39 0.35 0.25 0.40 0.35 fig. 2. average lane distribution change with lateral clearance (0m, 0.5m, 1.0m, 1.5m and the no obstacle) at high traffic flow rates, the use of the middle lane decreases while the use of the right lane increases. the uses of left-lane marginally differ by traffic flow rate magnitude except when traffic flow rate reaches 2000 vehicles per hour (veh/h). figure 2 suggests that the same pattern of traffic lane distribution is noted for lateral clearance less than or equal to 1, engineering, technology & applied science research vol. 10, no. 2, 2020, 5428-5433 5431 www.etasr.com hazim et al.: impact of roadside fixed objects in traffic conditions but not the magnitude. for instance, right lane use starts to increase as traffic volume increases, but the difference between its use when the traffic flow rate is low and when it is high is more profound when the distance to travel lane edge is 0.5m. right lane use tends to stabilize when flow rate exceeds or is equal to 1,600vel/h when the obstacles are placed 0.5m from the travel lane edge and increases to 2,000veh/h for 1m distance. figure 2 also suggests that generally a similar trend of lane distribution is observed between a distance of 1.5m and the no obstacle case with some exceptions related to traffic flow rate less than or equal to 1,200veh/h. if the obstacles are placed at 1.5m from the travel-lane’s edge, the distribution of traffic flow rate over the three lanes is, to some extent, similar to the distribution related to the no-obstacle case. the similarity is more obvious for left-lane use. it decreases with the increase of low traffic flow rate, but for high traffic, it increases. rightlane use is high at low flow rate and then it decreases until it reaches a level of 1600veh/h where it starts to increase. the trend of middle-lane-use is opposite of the right-lane use. it starts low and increases up to 1600veh/h where its starts to decrease. for the no-obstacle case, the lane-use distribution fluctuates with no clear pattern, except the left lane use as explained above. the statistical analysis shown in figure 3 indicates that inlarge and with few exceptions, there is no significance difference in lane distribution that could be explained by lateral clearance. significant difference is mainly associated with the right-lane-use for traffic flow rate over 800veh/h. as indicated above, left-lane-use follows a similar trend for different traffic flow rates but not when it reaches high level (2000-2399veh/h). the statistical analysis proves that there is a significant difference that could be explained by obstacle location. rightlane-use differs significantly by obstacle location. the difference is higher at low traffic flow rates and tends to decline at higher traffic flow rates (figure 4). middle-lane uses also differ according to obstacle locations for all traffic flow categories but not for the highest level (2400veh/h). the difference is either statistically significant or marginally significant. no significant difference of left-lane-use distribution has been reported for all traffic categories, except at high traffic flow rate (2400veh/h). a further look into lane distribution as a function of flow rate, shows that there is significant difference in right lane use (f=6.626, p=0.000). figure 5 shows that as traffic flow rates increase the right-laneuse increases. on the other hand, as traffic flow rates increase, the use of middle-lane-use decreases with significant difference (f=7.283, p=0.000). the left-lane-use marginally fluctuates with significant difference (f=3.792, p=0.006). data was aggregated by averaging lane distribution for all traffic flow rates for each obstacle location as given in figure 5. it suggests that right lane use increases with increase of the lateral clearance. there is significant difference in right-lane use due to obstacle location (f=4.339, p=0.002). traffic group <800 800-1199 1200-1599 1600-1999 2000-2399 direction right lane middle lane left lane right lane middle lane left lane right lane middle lane left lane right lane middle lane left lane right lane middle lane left lane f 1.698 3.044 .147 4.711 2.131 .605 4.067 7.191 2.206 4.791 2.921 2.796 9.604 1.821 9.420 sig. 0.254 0.095 0.958 0.003 0.090 0.661 0.007 0.000 0.084 0.004 0.036 0.042 0.000 0.169 0.000 fig. 3. lane-use distribution function of lateral clearance and traffic flow rates the use of the middle lane remains constant and the difference due to obstacle location is not statistically significant (f=0.691, p=0.559). on the other hand, the left lane use decreases as the lateral clearance increases. the difference due to lateral clearance is statistically significant (f=5.259, p=0.001). figure 6 suggests that there is no difference in lane engineering, technology & applied science research vol. 10, no. 2, 2020, 5428-5433 5432 www.etasr.com hazim et al.: impact of roadside fixed objects in traffic conditions distribution between the case of lateral clearance of 1.5m and the no obstacle case. fig. 4. effect of lateral clearance on traffic flow rates fig. 5. relationship of lane distribution vs traffic flow rates fig. 6. lane distribution function of lateral clearance “obstacle location” speed data clearly show that as the obstacle moved further from the carriageway edge, the speed begun to increase (figure 7). the speed related to the no obstacle location is almost identical to that related to 1.5m lateral clearance. table ii presents the paired-sample t-test used to investigate the speed differences between the no obstacle location and the lateral clearance under assessment. it shows that there is significant difference for all tested pairs that can be attributed to lateral clearance. there are significant speed differences between all tested pairs due to obstacle locations. fig. 7. relationship between vehicle speed vs lateral clearance table ii. pair-sample t-test: speed differences obstacle location vs no obstacle case paired differences t-value dfa sigb mean std. dev. std. error mean 95% confidence interval lower upper vs zero distance 13.28 5.78 0.52 12.26 14.30 25.67 124 0.00 vs 0.5m distance 6.79 3.13 0.29 6.22 7.36 23.56 117 0.00 vs 1.0m distance 6.37 4.57 0.41 5.56 7.18 15.58 124 0.00 vs 1.5m distance 6.13 4.01 0.36 .5.42 6.84 17.1 124 0.00 df: degrees of freedom vi. conclusions this paper investigated the impact of placing obstacles on the right edge of the road’s travel-lane (lateral clearance) on lane distribution and speed. test sections were defined and obstacles were formed by placing a series of traffic cones on four different distances (0.0, 0.5, 1.0 and 1.5m). as a reference case, traffic parameters were also collected for a section with no obstacles. the analysis covers the change in lane distribution for different traffic flow rate for each obstacle location. the average traffic speed for each obstacle location was compared. factors used in the analysis include obstacle location and traffic flow rate category (<800, 800-1199, 12001599, 1600-1999 and 2000-2004 vehicles per hour). the results showed that lane distribution significantly depends on lateral clearance and traffic category. as obstacle distance measured from the carriageway edge increases, right-lane-use and leftlane-use increases while the middle-lane remains almost at the same level. average speed increases as lateral clearance increase. the results also showed that average speed and lane distribution for the 1.5m obstacle distances are very similar to engineering, technology & applied science research vol. 10, no. 2, 2020, 5428-5433 5433 www.etasr.com hazim et al.: impact of roadside fixed objects in traffic conditions the prevailing traffic parameters describing the no obstacle condition. regarding the impact of traffic flow rate on lane distribution, the results showed that, there is no significant difference in lane distribution due to obstacle location for each flow rate category with exceptions related to right-lane-use and left-lane use for high traffic flow rates (2000-2399veh/h hour). the main conclusions that can be drawn are that drivers tend to use the middle lane more than others. a small percentage of the drivers would select the right lane particularly with the presence of obstacles. this implies that the impact of lateral clearance is more profound and significant on the right lane. the use of the left-lane marginally fluctuates with significant increase if traffic flow rates reach high levels. references [1] m. m. m. abdel-aal, a. e. a. el-maaty, h. a. a. samra, “factors affecting road capacity under non-ideal conditions in egypt”, nova journal of engineering and applied sciences, vol. 7, no. 1, pp. 1-13, 2018 [2] m. r. amin, j. h. banks, “variation in freeway lane flow patterns with volume, time of day, and location”, transportation research record, vol. 1934, no. 1, pp. 132–139, 2005 [3] f. j. breuer, b. beckmann, “geschwindigkeit und spurenbelegung auf autobahnen. schriftenreihe stadt – region”, land des institutes für stadtbauwesen, vol. 6, no 1969. rwth aachen, 1969 (in german) [4] m. ghasemian, s. amini, m. princevac, “the influence of roadside solid and vegetation barriers on near-road air quality”, atmospheric environment, vol. 170, pp. 108-117, 2017 [5] f. 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gatiba, “predicting injury severity of angle crashes involving two vehicles at unsignalized intersections using artificial neural networks”, engineering, technology & applied science research, vol. 9, no. 2, pp. 3871-3880, 2019 [18] m. touahmia, “identification of risk factors influencing road traffic accidents”, engineering, technology & applied science research, vol. 8, no.1, pp. 2417-2421, 2018 microsoft word etasr_v11_n3_pp7130-7134 engineering, technology & applied science research vol. 11, no. 3, 2021, 7130-7134 7130 www.etasr.com singh & shrivastava: evolutionary algorithm-based feature selection for an intrusion detection system evolutionary algorithm-based feature selection for an intrusion detection system devendra kumar singh department of computer science & engineering guru ghasidas university bilaspur, india devendra.singh1700@gmail.com manish shrivastava department of computer science & engineering guru ghasidas university bilaspur, india mannbsp@gmail.com abstract—keeping computer reliability to confirm reliable, secure, and truthful correspondence of data between different enterprises is a major security issue. ensuring information correspondence over the web or computer grids is always under threat of hackers or intruders. many techniques have been utilized in intrusion detections, but all have flaws. in this paper, a new hybrid technique is proposed, which combines the ensemble of feature selection (efs) algorithm and teaching learningbased optimization (tlbo) techniques. in the proposed, efstlbo method, the efs strategy is applied to rank the features for choosing the ideal best subset of applicable information, and the tlbo is utilized to identify the most important features from the produced datasets. the tlbo algorithm uses the extreme learning machine (elm) to choose the most effective attributes and to enhance classification accuracy. the performance of the recommended technique is evaluated in a benchmark dataset. the experimental outcomes depict that the proposed model has high predictive accuracy, detection rate, false-positive rate, and requires less significant attributes than other techniques known from the literature. keywords-classification; feature selection; teaching learningbased optimization; intrusion detection i. introduction despite the increasing alertness in cyber-security problems, the present ongoing solutions are not suitable for shielding computer applications or undertaking security frameworks against the risk from consistently ever-propelling organized assaults [1]. adaptable security methods were developed to solve this issue, but they turned out to have further issues. typical cyber-security methods are insufficient to entirely defend web computer security, since they face problems from intruder attempts at the initiation of the security procedure, e.g. user authentication and firewalling [2, 3]. thus, a different line of threat protection is acutely mentioned in the intrusion detection systems (idss). an ids is a program that observes the internet for venomous actions and policy contraventions [4]. at present, ids along with safe-guard applications have resolved into an indispensable element of computer security of most companies. the union of the above-mentioned security machines provides increased opposition in network-attacks and improves network security. ii. related work gradually, inexhaustible applications, e.g. choice and order models have been put in to intrusion datasets (i.e. kdd cup 1999) for detecting network problems and attacks. attribute selection with learning algorithms couldn’t control or scale to very large volumes of datasets [5]. to beat this impediment, authors in [6, 7] proposed another hybrid feature selection technique that diminishes the non-applicable features and selects the best ideal component subsets. the recurring pattern study in [8] indicated that individual hunt calculation locates the most suitable subsets that amplify information over-fitting, while a probing interest is less prone to information over-fitting in the part assurance, developing a modest number of tests [9]. authors in [10] proposed the use of elm and alpha profiling to diminish the required time while superfluous highlights were disposed of utilizing a group of separated, relationship and consistency-based feature selection procedures. a. filter-based methods optimum and appropriate feature subset selection is a task accomplished by choosing the qualities dependent on the high connections of concerning classes and uncorrelated features. from the conditional mutual information maximization (cmim) method, feature/attributes subset selection (fss) is conducted depending on maximizing conditional mutual information [11] regarding the class. in addition, it is extremely close with class attributes and uncorrelated to attributes. it makes a compromise between the predictive power of the nominated competitor (significance for the class carrier) and its freedom from all recently chosen attributes. mutual information (mi) estimation between the class label y and attributes x is calculated in: ���; �� = ���� − �� �� � (1) where ���� and �� �� � show the entropy and conditional entropy of the class change respectively. some writers have mentioned issues using the mutual information-based feature selection (mifs) technique [7, 12]. therefore, we used this strategy to decrease the readability between class y and data attributes as shown in (2). the primary objective of cmim is to choose the final feature subset that conveys as much information as possible from the sample s: corresponding author: devendra kumar singh engineering, technology & applied science research vol. 11, no. 3, 2021, 7130-7134 7131 www.etasr.com singh & shrivastava: evolutionary algorithm-based feature selection for an intrusion detection system ������� = ��� ∈� ��� ��; �� ��� � (2) where ���� estimates the mutual information between the full features set �� and certain features �� regarding class label y, whereas s shows the subsets of the selected features. � ��; �� ��� � measures the quantity of the classification information that �� affords when �� has been selected [13]. selected feature subset s cannot provide this information. as comparison to � ��; ��� , � ��; �� ��� � does not contain the superfluous data of pair wise attributes for categorization. the importance of the input attributes defined by the jmi is shown in (3): ������ = ∑ ���∈� ��; ��; �! ∝ ∑ ��� ∈� ��; �� ��� � (3) where � ��;��; �! signifies the mutual information between the novel attribute subset �� and the selected attributes �� regarding class y. in linguistics of mutual information, the determination of attribute choice is to reduce attribute subsets s with n attributes with a maximum holding on the target class c. this structure, called max-dependency, has the form of: #$� %��, �� = ���; �',�(, … , �*� = ����� � � �+,�,,…,� � (4) in (3), the holding among attribute � is resultant and can have a high value [14]. the correspondence between readability between attributes is expressed in (5) and (6): min z �x, c � = 1 ∣ 6( ∣⁄ ∑ ���∈8 ��; ��! (5) max ∅�%, =� = w – z (6) the incorporation (i.e. integration) of (5) and (6) is known as the minimal-redundancy-maximal-relevance (mrmr) [15]: @�a�a�∅� = ��b;�� − 1 ∣ 6( ∣⁄ ∑ ���∈8 ��;��! (7) where �� is a selected subset of attributes s and �� is a native feature set. b. the proposed ensemble feature selection the pre-owned feature selection strategies are mrmr, jmi, and cmim which can relegate the position of the ids datasets and the output is aggregated utilizing a combination strategy [7]. c. frequency vote frequency vote (fv) is a cooperative decision making framework that has been proposed as more useful than other increasingly complex plans [16]. thus, we can follow the most voted prediction as to the last prediction or expectation as per (8): ∑ c�,�£�e' = $fg#$��∈{',(,⋯,j} ∑ c�,�£�e' (8) where £ shows the number of attribute choice methods, and l is a selection of some attributes. for attribute j, the sum ∑ c�,�£�e' tabulates the number of votes for j. d. using teaching learning-based optimization (tlbo) tlbo [17-19] is the best and most powerful metaheuristic method to apply high convegence rate with less adjusting parameters. it is an easy and simple computation of tuning the control parameters with less memory requirments. the working methodology of the tlbo algorithm can create better evaluation outcome [20]. the position of the ith learner is : ��,� = l��,', ��,(, … , ��,mn (9) where op shows the lower limit and qp shows the upper limit of the r dimension in the search area ��,m ∈ [ op , qp] [21]. the learner � is unplanned, initialized in the search area [22]. the development (i.e. evolution) of ��,� is generated by: ��,� = op,� + f' ∗ qp,� − op,� ! (10) where i=1, 2, 3, ..., nwop, x = 1,2,3, … , r , f' signifies the unplanned variable, op,� shows the lower limit and qp,� shows the upper limit value, and npop denotes the population count [23]. the simulation of an old-style initiation procedure is arranged into two critical stages of the tlbo calculation: the teacher stage and the learner stage. in tlbo algorithm, the teacher is a quantification of obtaining an ideal output gained from optimization problems. therefore, the teacher can grow the mean result of a classroom to a specific result which relies on the ability of the complete classroom. let �,�= (1/nwop) (σ��,�) be the mean value of the particular subject where k=1, 2,…,r. equation (11) shows the updating equation process: ��,��[\ = ��,�]^_ + f( ∗ �`[abc[d − ef ∗ �,�! & ef= round[1+rand(0,1)] (11) where �`[abc[d is the greatest begineer of the embrance group (i.e. population) at the current duplication of the algorithm, f( represents random numbers, ef behaves as a teaching element that chooses the merit of the mean to be changed. in each iteration, ��,��[\ is updated from the old merit ��,�]^_. ��,��[\ and ��,�]^_ denote the k-th beginer choice after or before it is modernized by the teacher. e. the fitness function the fitness function must maximize the categorization accuracy of the calculations accomplished by the best attributes during the progresive (i.e. evolutionary) process, which is defined as: accuracy = ghig*ghig*ijhij* tp, tn, fp, and fn stand for true positive, true negative, false positive, and false negative respectively. iii. experimental results and discussion during the experiments, every record had features such as feature name, records, and feature portrayal. most ids numerical studies have been performed on nsl-kdd [24]. this data set have varying data importance and feature integrity. authors in [25] analyzed the deliberate intrusion dataset called kdd cup 1999 [36]. every record is tagged as engineering, technology & applied science research vol. 11, no. 3, 2021, 7130-7134 7132 www.etasr.com singh & shrivastava: evolutionary algorithm-based feature selection for an intrusion detection system normal or as an attack type in the dataset. the flowchart of the proposed method can be seen in figure 1. instance transformation hybrid feature selection method reduced ids dataset reduced ids dataset training data data pre-processing testing data building learning algorithm using elm detection model decision making result attack recognition tra ining phase testing phase ids dataset data normalization fig. 1. general structure of the proposed model for intrusion detection. a. results and discussion different exploratory tools and techniques were used on the nsl-kdd dataset (see table i) [14, 25, 26]. the classification performance is estimated with the assistance of the support vector machine categorization with four execution variables. these exhibition measures, along with accuracy, are [27-29]: detection rate: dr tp tp fn = + precision: pr tp tp fp = + f-measure = 2* pr* re pr re+ false alarm rate: far tp tn fp = + b. result comparison tenfold cross-validation was applied to elm [7] and other classifiers, namely svm [30, 31] and nb in the ids dataset. table i shows the comparison of the performance of the proposed algorithm with existing known algorithms. the result shows that the proposed algorithm performs better on the basis of parameters like feature, dr, fpr and accuracy in the same data set. only five of the attributes have been selected by the proposed method which can identify intrusion attacks in the network with maximum accuracy. table i. performance comparison of the proposed and existing algorithms in the same database algorithm feature dr fpr accuracy lssvm-ids + fmifs [32] 18 98.93 0.28 99.94 tuids [33] all 98.88 1.12 96.55 http based ids [34] 13 99.03 1.0 99.38 hybrid ids [35] all 99.10 1.2 * proposed 5 99.31 0.19 99.95 iv. conclusion in this study, a novel hybrid model called efs-tlbo with elm is proposed, to easily identify threats by using the attribute choice algorithm [7] which increases the perceptive power for better class distinction. for exhibiting the superiority of the proposed technique, the nsl-kdd database of intruders was employed. the results show that the proposed technique provides an important depletion to the required features and outperforms the advanced attribute selection techniques from the literature. the practical results show that the suggested technique achieved an accuracy of 99.95% in the nsl-kdd data set of intruders [36, 37], surpassing the other techniques. future work is going to be focused on multi-objective algorithms that combine ensemble filter and classification methods for pattern analysis and intrusion attack detection. also, some different optimization algorithms for elm parameter optimization are going to be researched. references [1] a. praseed and p. s. thilagam, "ddos attacks at the application layer: 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[35] g. kim, s. lee, and s. kim, "a novel hybrid intrusion detection method integrating anomaly detection with misuse detection," expert systems with applications, vol. 41, no. 4, part 2, pp. 1690–1700, mar. 2014, https://doi.org/10.1016/j.eswa.2013.08.066. [36] "nsl-kdd datasets," canadian institute for cybersecurity | unb. https://www.unb.ca/cic/datasets/nsl.html (accessed apr. 23, 2021). [37] a. s. a. aziz, s. e.-o. hanafi, and a. e. hassanien, "comparison of classification techniques applied for network intrusion detection and classification," journal of applied logic, vol. 24, pp. 109–118, nov. 2017, https://doi.org/10.1016/j.jal.2016.11.018. authors profile devendra kumar singh got his b.e. from the b.u. university of bhopal (mp) in 2000 and his m.e from aaidu allahabad (up) in 2006. he is currently pursuing his ph.d. and works as an assistant professor in the department of computer science & engineering, sos, e&t, ggv bilaspur (cg) since 2005. he is a member of aieng. he has published more than 10 research papers in reputed international journals. his main research work focuses on intrusion detection systems. he has 15 years of teaching experience and 6 years of research experience. engineering, technology & applied science research vol. 11, no. 3, 2021, 7130-7134 7134 www.etasr.com singh & shrivastava: evolutionary algorithm-based feature selection for an intrusion detection system manish shrivastava, is an assistant professor at the department of computer science & engineering, institute of technology, guru ghasidas university, bilaspur. he obtained his m.tech. degree from davv, indore, and ph.d. from guru ghasidas university, bilaspur. he has about 15 years of teaching and research experience, and a number of papers in various national and international journals to his credit. his field of interest is network security. he has served as a chairman of the board of studies, computer science & engineering, guru ghasidas, bilaspur. he is a life member of the indian society for technical education and a senior member of iacsit . microsoft word 07-3835_s_etasr_v10_n6_pp6422-6426 engineering, technology & applied science research vol. 10, no. 6, 2020, 6422-6426 6422 www.etasr.com mangra: design and numerical analysis of a micro gas turbine combustion chamber design and numerical analysis of a micro gas turbine combustion chamber a. c. mangra combustion chambers and unconventional energies laboratory comoti national research & development institute for gas turbines bucharest, romania andreea.petcu@comoti.ro abstract-the interest in micro gas turbines has been steadily increasing. as a result, attention has been focused on obtaining optimal configurations for micro gas turbines depending on the applications in which they are used. this paper presents the cfd modeling results regarding an annular type combustion chamber, part of an 800n micro gas turbine, predestined to equip a small scale multifunctional airplane. two configurations have been taken into consideration and 3d rans numerical simulations have been conducted with the use of the commercial software ansys cfx. the liquid fuel droplets were modeled by the particle transport model, which tracks the particles in a lagrangian way. an initial fuel droplet diameter of 500µm has been imposed. the numerical results obtained are encouraging. the flame was developed in the central area of the fire tube, its walls thus not being subjected to high temperatures. also, the maximum temperatures were obtained in the primary zone of the fire tube. the temperature then decreased in the fire tube's secondary zone and dilution zone. the numerical results will be validated by conducting combustion tests on a testing rig which will be developed inside the institute's combustion chamber laboratory. keywords-cfd; combustion chamber; jet a; vaporizers i. introduction micro gas turbines are smaller-scale versions of gas turbines used in aviation or various cogenerative applications, with power output ranging from 30kw to 200kw. micro gas turbines are used to generate power in auxiliary power units (apus), backup generators, and other standby electricalgeneration needs. they are also commonly used in propulsion systems for unmanned aerial vehicles (uavs) [1, 2]. micro gas turbines usually consist of a single-stage compressor connected through a shaft to a single-stage turbine. the combustion chamber is of annular type, in order to reduce the overall dimensions [1, 2]. the scaling down of gas turbine technology impacts negatively the heat and combustion processes which reduce the turbine power output and efficiency. hence, micro gas turbines often operate at very high shaft speeds (up to 100000rpm). micro gas turbines offer the advantages of compact size, low weight per unit power and multi-fuel capability [1, 2]. the first micro gas turbine for aviation applications has been developed by the french manufacturer jpx. soon two other companies, amt and schreckling, have produced their own micro gas turbines [3]. in this paper, the results of cfd modeling regarding an annular type combustion chamber, part of a 800n micro gas turbine destined to equip a small scale multifunctional airplane are presented. in the first stage, an annular type combustion chamber equipped with 8 pressure-swirl injectors has been proposed. the numerical investigation results are presented in [3]. although the numerical results were encouraging, the manufacturing of injectors small enough to fit in the available space is problematic. thus, in the second stage the use of vaporizers instead of injectors was proposed. in this paper, two combustion chamber configurations are presented which have been taken into consideration. both configurations are equipped with 16 vaporizers. the fuel is sprayed from the fuel supply ramp into the vaporizing tubes which are positioned inside the fire tube. these tubes are heated by combustion and thus the fuel droplets inside them vaporize before passing into the fire tube. inside the fire tube, the fuel vapors are mixed with pressurized air received from the compressor. the reacting mixture thus obtained is burned, transforming the fuel's chemical energy into heat. the resulted hot exhaust gases expand in the turbine producing mechanical work. the fire tube is divided into three zones: the primary zone, the secondary zone and the dilution zone [4, 5]. the main function of the primary zone is to anchor the flame and provide sufficient time, temperature, and turbulence to achieve complete combustion of the fuel-air mixture. in the primary zone, a recirculation zone is created to ensure flame stability and to entrain a portion of the hot combustion gases in order to provide continuous ignition to the incoming fuel-air mixture. in the secondary zone, the temperature is dropped to an intermediate level by the addition of air. this allows further combustion of co and other unburned hydrocarbons (uhc) resulting from the primary zone. the role of the dilution zone is to admit the remaining air and to provide an exhaust gases stream with a temperature distribution that is acceptable to the turbine [4, 5]. over the years cfd techniques have proven useful in designing different component parts of a gas turbine [6, 7], including the combustion chamber [8-16]. however, the numerical simulation of the complex phenomena which take corresponding author: a.c. mangra engineering, technology & applied science research vol. 10, no. 6, 2020, 6422-6426 6423 www.etasr.com mangra: design and numerical analysis of a micro gas turbine combustion chamber place inside the combustion chamber is still problematic. the interaction turbulence combustion process has to be modeled. in the given case, in comparison with other research works in which the fuel was considered in gaseous state [8, 9, 13, 15, 16], a liquid fuel, jet a, was used. this is a further complication of the processes which take place inside the combustion chamber. the atomization and vaporization of the liquid fuel have also been simulated. the use of vaporizers instead of pressure-swirl injectors [14] is another complication. in this case, the heat transfer between the hot gases inside the fire tube and the vaporizers' walls has been taken into consideration and modeled. given all the above, the article brings a contribution to the field of designing combustion chambers using cfd techniques. ii. numerical simulation setting in order to develop the new combustion chamber, a 3d steady rans numerical integration of the navier-stokes equations has been carried out using the commercial software ansys cfx. the computational domain is composed of the combustion chamber, starting from the compressor's stator exit and ending at the turbine stator entrance. the data presented in table i was the starting point for developing the new combustion chamber. table i. initial data parameter value unit air mass flow 1.4 kg/s p2 476201 pa t2 481.452 k compressor exit flow angle -18 ° t3calc. 1173 k fuel mass flow 0.0274 kg/s a. geometry and mesh in figure 1 the two proposed combustion chamber configurations are presented. starting from these geometries, unstructured type computation grids (figure 2) have been generated using icem cfd. the mesh has been refined in the zone of the vaporizers and in the fire tube's primary zone. (a) (b) fig. 1. the proposed combustion chamber configurations: (a) configuration 1, (b) configuration 2. (a) (b) fig. 2. the proposed combustion chamber configurations: (a) configuration 1, (b) configuration 2. in both configurations, the computational domain is composed of a fluid body and 16 solid bodies representing the 16 vaporizers. thus, the thickness of the vaporizer walls has been taken into consideration. this was necessary in order to be able to simulate the conductive heat transfer taking place inside the vaporizers walls. the grid area-averaged y+ value for wall regions of importance, like the vaporizer walls, is 80 and for less important walls is 150. at this point, the interest has been more on the gases mixing inside the fire tube, than on the forces acting on the fire tube walls. b. boundary conditions the reference pressure has been set to 1bar. at the air inlet a relative total pressure of 3.76201bars and a total temperature of 481.452k have been imposed. also, a flow angle of -18° has been taken into consideration. total mass flow of 1.4274kg/s, representing the air mass flow (1.4kg/s) plus the fuel mass flow (0.0274kg/s), has been imposed at the outlet. the fuel is introduced in the computational domain through 16 surfaces of 0.6mm, representing the outlet of the fuel supply ramp, one for each vaporizer, as seen in figure 3. the morphology option selected for the fuel is particle transport fluid. the liquid fuel droplets are modeled by the particle transport model, which tracks the particles in a lagrangian way. an initial fuel droplet diameter of 500µm has been imposed. fuel mass flows corresponding to each vaporizer of 0.0017125kg/s and fuel temperature of 288k have been set. the fuel droplets atomization process has been modelled using the cab (cascade atomization break-up) model, available in the ansys library. the fuel droplets vaporization process has been modeled using the liquid evaporation model available in ansys library. (a) (b) fig. 3. fuel inlet: (a) configuration 1, (b) configuration 2. a rans type turbulence model has been chosen, namely, the k-ε model, which is a numerically stable and robust model and very popular in the realization of technical applications and numerical simulations. along with this turbulence model, the scalable wall function formulation developed by ansys cfx has been used. the chosen combustion model has been the eddy dissipation model (edm), based on a two-step keroseneair reaction mechanism, imported from the ansys library, which also takes into consideration the formation of no. a simple reaction mechanism has been chosen because the pollutant emission level has not been of interest at this point. the popular edm model has been chosen because of its simplicity and robust performance in predicting turbulent reacting flows. in the numerical simulations the heat transfer through conduction inside the vaporizers’ walls and the heat engineering, technology & applied science research vol. 10, no. 6, 2020, 6422-6426 6424 www.etasr.com mangra: design and numerical analysis of a micro gas turbine combustion chamber transfer by convection have been taken into consideration. the fire tube walls have been considered adiabatic. iii. results the total relative pressure field on a longitudinal plane through the fire tube is presented in figure 4. the average total pressure along the fire tube has been monitored in order to better understand the phenomena that take place inside the fire tube during the combustion process (figure 5). in figure 5, a normal behavior of the total pressure can be observed inside the fire tube. the points represent the mean values of the total pressure on traverse planes at different values of the z coordinate along the fire tube. the total pressure decreases from a maximum value in the primary zone of the fire tube, to a minimum at the fire tube exit. (a) (b) fig. 4. total relative pressure field on a fire tube longitudinal plane: (a) configuration 1, (b) configuration 2. (a) (b) fig. 5. average total relative pressure along the fire tube: (a) configuration 1, (b) configuration 2. in figures 6-7 the flame developed inside the fire tube can be observed to not exceed its length. the flame was developed in the central area of the fire tube, its walls not being subjected to high temperatures. in configuration 1, the maximum temperatures have been obtained in the primary zone of the fire tube. in configuration 2, temperatures above 2000k have also been obtained in the fire tube intermediary zone. (a) (b) fig. 6. total temperature field on the fire tube longitudinal plane: (a) configuration 1, (b) configuration 2. from figure 8 the normal behavior of the total temperature inside the fire tube can be observed. the points represent the mean values of the total temperature on traverse planes at different values of the z coordinate along the fire tube. the temperature rises in the primary zone of the fire tube, as the combustion reaction takes place, reaching a maximum. the temperature then decreases in the secondary zone and the dilution zone of the fire tube. this is achieved by introducing a larger quantity of air through holes placed on the fire tube walls. however, it is observed that the average temperature in the intermediary zone of the fire tube is higher in the case of configuration 2 compared to configuration 1. this is consistent with the results shown in figures 6-7 1800k isosurface 2000k isosurface 2200k isosurface 2400k isosurface configuration 1 configuration 2 fig. 7. total temperature isosurfaces (a) (b) fig. 8. the average total temperature along the fire tube: (a) configuration 1, (b) configuration 2. the fuel droplets trajectories and mean diameter distribution are shown in figure 9. a better swirling of the kerosene droplets in the case of configuration 1 is observed, due to the vaporizers shape and positioning. this favors a more frequent collision of the droplets with the vaporizers’ walls, engineering, technology & applied science research vol. 10, no. 6, 2020, 6422-6426 6425 www.etasr.com mangra: design and numerical analysis of a micro gas turbine combustion chamber which leads to a more efficient vaporization process. as the vaporization process takes place, the fuel droplets’ diameter decreases from the initial value of 500µm to 0. in figure 10, the vaporizers’ wall temperature is presented. a better heating of the vaporizers' walls is observed in the case of configuration 1. this favors a better vaporization of the fuel droplets. due to their shape and positioning, the vaporizers in configuration 1 are better immersed in the hot central zone of the fire tube. in configuration 2, the flame is developed mainly between the vaporizer and the fire tube inner wall, as can be seen in figure 6(b). thus, only a small portion of the vaporizers is immersed in the hot central zone of the fire tube. this led to less efficient vaporizer walls heating, as can be seen from figure10(b). (a) (b) fig. 9. jet a droplets trajetories and droplets mean diameter distribution: (a) configuration 1, (b) configuration 2. (a) (b) fig. 10. vaporizer wall temperature: (a) configuration 1, (b) configuration 2. in figures 11-13 the total pressure outlet field, the total temperature outlet field, and the velocity outlet field are presented. ideally, a uniform pressure/temperature/velocity field at the combustion chamber exit is desired, which is impossible to obtain. from figure 11 it can be observed that a more uniform pressure field has been obtained for configuration 1. also, in the case of the temperature field, the obtained results in the case of configuration 1 are better, as can be seen from figure 12. the maximum temperature at the combustion chamber outlet in configuration 1 (1464k) is lower than in configuration 2 (1680k). this is important in order to not subject the turbine to high temperatures during the micro gas turbine operation. regarding the velocity field, the differences between the two configurations are not significant, as can be seen from figure 13. (a) (b) fig. 11. total relative pressure outlet field: (a) configuration 1, (b) configuration 2. (a) (b) fig. 12. total temperature outlet field: (a) configuration 1, (b) configuration 2. (a) (b) fig. 13. velocity outlet field: (a) configuration 1, (b) configuration 2. in table ii the average values of the operating parameters at the combustion chamber exit are presented. table ii. operating parameters’ average values at the combustion chamber exit parameter configuration 1 configuration 2 unit p3 455938 455293 pa pres. loss = ����� �� ∙ 100 4.2 4.4 % t3 1187 1189 k � � �� � �� ∙ 100 1.2 1.3 % v3 104.5 104 m/s exit flow angle -16.6 -12.8 ° iv. conclusions the cfd modeling results regarding an annular type combustion chamber, part of a 800n micro gas turbine designed to equip a small scale multifunctional airplane have been presented in this paper. the manufacturing of pressure swirl injectors small enough to fit in the available space is problematic. thus replacing the pressure swirl injectors with vaporizers has been taken into consideration. two combustion chamber configurations, both with 16 vaporizers, have been analyzed using cfd modeling. the operating parameters average values at the combustion chamber exit, presented in table ii, are very similar for the two proposed combustion chamber configurations. however, in configuration 1 the maximum temperatures have been obtained in the fire tube's primary zone, while in configuration 2, temperatures over 2000k have been also obtained in the fire tube’s secondary zone. the combustion chamber outlet total temperature is more uniform in configuration 1 than in configuration 2. higher temperature at the combustion chamber outlet was reported for configuration 1 than for configuration 2. thus it was decided to go along with configuration 1. the next step is the manufacturing of the combustion chamber assembly. then the experimental procedure will begin and the numerical results will be compared with the experimental ones. engineering, technology & applied science research vol. 10, no. 6, 2020, 6422-6426 6426 www.etasr.com mangra: design and numerical analysis of a micro gas turbine combustion chamber acknowledgment this work was carried out within “nucleu” program, supported by the romanian minister of research and innovation, project number pn 19 05 01 05 references [1] p. breeze, “chapter 8 microturbines,” in gas-turbine power generation, p. breeze, ed. academic press, 2016, pp. 77–82. 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[16] h. a. bhimgade, c. a. mahatme, p. s. barve, and n. d. gedam, “cfd approach as design optimization for gas turbine tubular combustor,” journal of research in engineering and applied sciences, vol. 01, no. 02, pp. 92–102, apr. 2016. authors profile andreea cristina mangra was born in 1986. sha tooke her phd in aerospace engineering, in 2016 at politehnica university of bucharest and is a scientific researcher since 2010, carrying out experimental activities and numerical investigations of the combustion process in the combustion chamber laboratory of the comoti national research & development institute for gas turbines, bucharest, romania. she is experienced in 3d design using catia and in cfd numerical simulations using ansys cfx. she is the author of 20 scientific papers published in peer reviewed journals (wos and bdi) and conference proceedings and a co-author of 3 chapters of scientific books and of 2 patents in the field of combustion. microsoft word etasr_v11_n4_pp7436-7441 engineering, technology & applied science research vol. 11, no. 4, 2021, 7436-7441 7436 www.etasr.com al-shammari et al.: cardiac stroke prediction framework using hybrid optimization algorithm … cardiac stroke prediction framework using hybrid optimization algorithm under dnn naif k. al-shammari mechanical engineering department college of engineering university of ha’il ha’il, saudi arabia naif.alshammarif@uoh.edu.sa ahmed a. alzamil electrical engineering department college of engineering university of ha’il ha’il, saudi arabia aa.alzamil@uoh.edu.sa mohammd albadarn electrical engineering department college of engineering university of ha’il h’ail, saudi arabia s.abadran@uoh.edu.sa syed thouheed ahmed school of computing and information technology reva university bangaluru, karnataka, india syedthouheed.ahmed@reva.edu.in syed muzamil basha school of computer science and engineering reva university bangaluru, karnataka, india muzamilbasha.s@reva.edu.in ahmed saud alshammari electrical engineering department college of engineering university of ha’il ha’il, saudi arabia ahm.alshammari@uoh.edu.sa ahmed maher gabr physical therapy department faculty of applied medical sciences university of ha’il ha’il, saudi arabia am.mohammed@uoh.edu.sa abstract-heart weakness and restricted blood flow into the cavities can cause a range of strokes from mild to severe heart strokes are primary caused due to the fat deposited on artery walls. the process reduces the intake of blood and internally causes a pseudo vacuum of air bubbles leading to a stroke which can be identified with high-end instrumentations. in this article, a detailed evaluation is processed with a hybrid optimization algorithm (hoa). in the proposed technique, data are preprocessed using a label encoder and the missing values of the dataset are filled. whale optimization algorithm (woa) and crow search algorithm(csa) extract inter-connected patterns and learning features using a dedicated deep neural networking (dnn) support. the proposed hybrid optimization algorithm extracts features and the resultant values demonstrate a high accuracy range of 97.34%. keywords-cardiac stroke prediction; cardiovascular disease; whale optimization algorithm; crow search algorithm; hybrid optimization algorithm i. introduction a cardiac stroke occurs when the blood flow to the heart is blocked. a buildup of fat, saturated fat, and other substances in the blood vessel that stream the heart, known as plaque, is the most prevalent cause of obstruction. plaque can break and generate clot, blocking blood flow. some portions of the heart muscle can get injured or damaged if the blood flow is disrupted. some of the common symptoms of a cardiac stroke are pressure, nausea, heartburn, fatigue, and shortness of breath. not all patients have the same symptoms or symptom intensity. some people experience modest pain, while others severe agony [1]. some persons have no signs or symptoms. for others, abrupt cardiac arrest may be the first symptom. the larger the number of symptoms one experiences, the more likely the patient suffers a heart attack. although some heart attacks occur unexpectedly, many patients have warning signs and symptoms such as recurrent chest pain that is provoked by exercise and eased by rest. according to the world heart federation, by 2030 there would be more than 23 million heart disease-related deaths annually [2]. heart related diseases are the most common cause of death in the us according to the american heart association. in the us, over 605,000 new congestive heart failures and 200,000 frequent congestive heart failures take place each year [3]. the process of predicting a stroke is commonly a cardiologist's task. these experts rely on medical information and practical demographic images such as computerized tomography (ct), magnetic resonance imaging (mri), and positron emission tomography (pet), invalidating the blockages. still, due to the more significant extent of the population and the lack of sufficient number of experts, the validation process is challenging and with a high corresponding author: naif khalaf al-shammari engineering, technology & applied science research vol. 11, no. 4, 2021, 7436-7441 7437 www.etasr.com al-shammari et al.: cardiac stroke prediction framework using hybrid optimization algorithm … order of false-positive predictions. the cardiac stroke is validated under higher-computational techniques to resolve an exact process of prediction by experts. the computational approach improves a prediction to validation ratio as it deals with sensitive medical information processing [4, 25]. the association of deep neural networks (dnns) provides a reliable process for data mapping and digitalization-based learning. the learned datasets are pre-processed and synchronized timely to form reliable training datasets. these datasets can be used for primary filtering and for providing accurate decision support. the inclusion of deep learning datasets improves the prediction rate and the dependability ratio. ii. literature review cardiac stokes are also known as heart attacks, heart jamming, vascular blockages, etc. predicting a heart stroke is a challenging endeavor. fuzzy clustering means (fcm), an unsupervised classification technique, was used to envisage early heart attacks on utilizing the patient medical information. data mining techniques were used to preprocess the information in the patient record, and a fuzzy c means classifier was used to classify the attributes in [5]. the effectiveness of the classifier was evaluated using data from 270 patients and had an accuracy of 92%. medical professionals can use a cardiac stroke prediction system to forecast patients' heart disease status based on their clinical data [6]. heart disease was classified using an artificial neural network algorithm, with 80% accuracy [6]. to assess the chance of increase in heart disease, the algorithm considers 13 factors. heart disease database tests classification algorithms such as decision trees, naive bayes, and neural networks were utilized in [7] with 100%, 99.62%, and 90.74% accuracy for neural networks, decision trees, and naive bayes respectively. a neural network was merged in a coactive neuro-fuzzy inference system in [8]. the presence of the disease was diagnosed with a fuzzy logic qualitative technique combined with a genetic algorithm. the coactive neuro-fuzzy inference system (canfis) performance was assessed in terms of training results with 0.000842 mean square error. the system for predicting heart disease in [9] used ensemble deep learning and feature fusion methods. the information gain methodology reduced the computational burden and improved system performance by removing inappropriate and unnecessary components with 98.5% accuracy. the enhanced deep learning aided convolutional neural network in [10] increased cardiac stroke prediction. it combines multi-layer perceptron’s model with learning techniques and was executed on an internet of medical things platform. it achieved a precision as high as 99.1%. the hybrid random forest with a linear model (hrflm) tried to uncover relevant features using machine learning approaches, enhancing the accuracy of cardiac stroke estimation with various combinations of data [11] with an accuracy of 88.7%. to distinguish between heart disease patients and healthy people, researchers in [12] employed a deep learning system based on multiple kernel learning (mlk) with adaptive neuro-fuzzy inference system (anfis). the anfis classifier uses the mlk approach to categorize heart disease and healthy subjects. the system offers 98% sensitivity, 99% specificity, and 0.01% mean square error. for the initialization of neural network weights, the hybrid system in [13] employs a global optimization genetic method. the learning is faster, more consistent, and accurate, with an accuracy of 89% in predicting the risk of heart disease. iii. methodology the dataset for the proposed system is taken from the open cleveland data base repository of 270 patients [14]. this multimodal dataset needed to be pre-processed before it could be used in the deep learning model. the misplaced values in the dataset were filled in the pre-processing step. using the label encoder approach, the data were converted to a numerical representation. resampling technique was used to reduce data imbalances, and the standard scalar methodology was used to normalize the data to a value ranging from 0 to 1. in the proposed system, we used 13 attributes for feature extraction: age, gender, chest pain type, blood pressure, cholesterol, blood sugar during fasting, rest ecg, thal (3 = normal; 6 = fixed defect; 7 = reversible defect), exercise-induced angina, old peak (st depression induced by exercise relative to rest), slope of the peak exercise st segment, maximum heart rate, and number of major vessels colored by flourosopy. there are significant and insignificant features in this normalized dataset. the dataset was subjected to the whale optimization algorithm (woa) for feature selection. the structural threshold extraction is done using the crow search algorithm (csa). this bio-inspired meta-heuristic algorithm assisted in selecting the most important attributes from the dataset to guarantee that the resulting predictions were as accurate as possible. the choice of optimum hyper parameters affects the prediction results given by a deep neural network (dnn) model. the grid search approach is used to optimize the hyper parameters. the proposed methodology aims to provide a reliable and self-significant system for predicting strokes in early stages. the proposed method is termed as hybrid optimization algorithm (hoa) with reference to pattern segmentation based on attributes and woa. the hoa tends to apply the schematics of multiple information systems validating and reconfiguring the incoming datasets. the architecture of hoa is presented in figure 1. a. whale optimization algorithm woa has better performance than recent meta-heuristic methods [15]. in woa, a population of baleen whales searches for food in a multi-dimensional search space. the individuals' locations are denoted as diverse decision variables. the space among the baleen individual whale and the sustenance relates to the objective cost value. three operational processes measure the time-dependent position of an individual whale: (1) reduction in encircling prey, (2) bubble-net attacking, and (3) the exploration for prey. 1) encircling of the prey a baleen whale identifies the place of the prey and encompasses it. the optimum design position in the search space is not possible to be known upfront. hence, the woa adopts the paramount solution as the target prey closest to the optimum position. once the best agent is identified, the engineering, technology & applied science research vol. 11, no. 4, 2021, 7436-7441 7438 www.etasr.com al-shammari et al.: cardiac stroke prediction framework using hybrid optimization algorithm … remaining agents update their place relatively to the best agent [16]. this behavior is depicted by: ��� � ����� ⋅ ��� �� ��� ��� (1) ��� � � 1� � ��� �� �� ⋅ ��� (2) where a indicates the current iteration, �� and ���� are coefficient vectors, ��� is the prey position vector, and �� represents the position vector of a whale. the vectors �� and ���� are computed as per the following equation: �� � 2�� ⋅ ������ � ��� (3a) ���� � 2 ⋅ ������� (3b) the value of �� is linearly reduced from 2 to 0 for the repetitions and ������ and ������� are random vectors in [0, 1]. fig. 1. block diagram of the proposed hoa. 2) bubble-net attacking method two types of approaches are used to represent the bubbleneck behavior of the baleen whales mathematically [17]. these approaches are: a) shrinking encircling mechanism the value of �� is decreased where the variation of �� is decreased by ��. a is allocated with an arbitrary value within the interim [-x, x], whereas the value of s is declined from 2 to 0 during repetitions. the new point of the search agent is assigned amongst the original position and the existing agent position by providing arbitrary values for s in [-1, 1]. b) spiral updating position finds the space between the whale (a,b) and the prey (a*, b*). the helix-shaped movement is represented using the spiral equation (4): �� � � 1� � ���������cos 2 !� � �∗����� �� (4) where ������ � ��∗����� �� �� ��� indicates the best solution, y is a constant describing the logarithmic spiral shape, and a is a random value ranging between [-1, 1]. 3) the search process for the prey the vector �� is varied to search the prey where random whales search randomly based on each other’s positions [18]. the mathematical model is: �� � ������#$%& → ��� (5) �� ! � 1� � �#$%& → ���� (6) where �#$%& → is the random position vector of the whale. b. crow search algorithm the csa is based on crow behavior and social interaction. it is a population-based method. crows are smart birds that live in clusters and have a large brain compared to their body size. they can hide food and memorize locations. even after several months, they can retrieve the stashed food [19]. the csa imitates the crow behavior of hiding and recovering food. a population-based algorithm is used. n individuals (crows) make up the flock's size, which is m-dimensional with m being the problem's dimension. the point xx,y of the crow a in a specific iteration y is described as: �(,� � *�(,� � ,�(,� � ……�(,� , (7) where x=1,2,….n, y=1,2,….n, and n is the number of maximum iterations. every crow can recall the location nx,y to hide food untill the present iteration. .(,� � */(,� � ,/(,� � …./(,1 2 (8) c. deep neural network a dnn is a complex neural network with more than two layers. to process data, these networks employ sophisticated mathematical models. a neural network mimics the human brain activity [20]. the network is designed to simulate pattern recognition techniques, with multiple layers of network connections simulating input processing. an input layer, an output layer, and hidden layers in between make up the basic framework of a dnn. each layer performs its own sorting and ranking, resulting in a feature hierarchy [21]. this advanced neural network aids in processing unstructured and unlabeled data, where artificial intelligence is utilized to classify and organize data outside of standard input-output protocols. the use of dnn in designing health care applications based on internet of things technology is studied in [27]. the system is aided with supported, trained datasets for mapping and operation management. these datasets are termed as reliable sources of information prediction and validation. according to regional information scheduling, the processing paradigm is dependent on repeated updating and synchronization of trained datasets. the dnn framework supports the process of validation under hoa. the primary layer of dnn is proposed under the action of input alignment and missing parameter gapping. the dnn middle layer is supported to build a series of interconnected information systems to support reliable engineering, technology & applied science research vol. 11, no. 4, 2021, 7436-7441 7439 www.etasr.com al-shammari et al.: cardiac stroke prediction framework using hybrid optimization algorithm … decision support. the overall system is supported under hoa for improvized performance estimation and processing. iv. experimental setup and results this section discusses the proposed work's experimental findings. google colab, was used to implement the proposed task. on the cardiac stroke dataset, python 3.7 was used to train and evaluate the proposed model. missing values were replaced with attribute mean in the pre-processed balanced dataset. the histogram of the dataset is shown in figure 2 shows the frequency of occurrence of attributes in a certain range of values in continuous and predetermined intervals. the x axis represents the range of values with different scale and the y axis represents the frequency of the value in each attribute. (a) age (b) gender (c) chest pain type (d) blood pressure (e) cholesterol (f) fasting blood sugar (g) rest ecg (h) thal (i) exercise-induced angina (j) oldpeak (k) slope (l) maximum heart rate fig. 2. histogram of the cardiac stroke dataset. the heat map is a two-dimensional data visualization where colors represent values, and it is used to understand data easily. complex datasets can be understood with more sophisticated heat maps. when we want to see which intersections of two lines overlap, a heat map can be informative. the data are more concentrated in categorical values in comparison to others. figure 3 uses a heat map to depict the correlation between the dataset attributes. both axes represent the attributes of the dataset and the value in each cell represents the co-relation strength. woa and csa are used to extract interconnected patterns and features. deep learning algorithms are only capable of working with numerical data. the label encoder scheme is used in this study to turn non-numerical into numerical data. the next stage is to extract features using a hybrid optimization technique. in order to train a deep learning model, it is critical to extract the essential features. by selecting the best attributes that positively impact categorization, feature selection minimizes training time and improves performance. in this study, a hybrid optimization strategy was employed because it has rapid convergence rate and avoids getting stuck in local minima, which aids in selecting the best features. 70% of the dataset was used to train the model. the proposed model was tested and validated with the remaining 30% of the dataset. the accuracy computation of hoa is significantly higher when compared to previous approaches and techniques in the area of predicting heart strokes and failures. the proposed hoa generated an accuracy of 97.34% surpassing techniques such as engineering, technology & applied science research vol. 11, no. 4, 2021, 7436-7441 7440 www.etasr.com al-shammari et al.: cardiac stroke prediction framework using hybrid optimization algorithm … woa, ant-colony optimization (aco) algorithm, and dnns, as presented in figure 4. the method has also computed stoke prediction rate and validation rate regarding secure computing. fig. 3. heat map of the cardiac stroke dataset. fig. 4. comparative analysis on performance efficiency. table i. comparative results ref. feature extraction/selection classification accuracy [22] wavelet transformation genetic fuzzy logic system 78.7% [23] laplace smoothing naïve bayes 86% [11] -na hybrid random forest 88.7% [24] principal component analysis deep learning 89% [25] fast conditional mutual information support vector machine 92.37% proposed woa+csa dnn 97.34% v. conclusions and future work a deep learning-based framework helps to classify the heart stroke dataset providing valuable insights. the dataset used is the publicly available stroke dataset in [14]. the data were preprocessed by filling in the missing values and were transformed with the label encoder technique for conversion to numerical format. the transformed data were resampled, for treating the imbalances, and normalized using the standard scalar technique. the proposed hoa is based on the schematics of woa, csa, and dnn combined in an observed ecosystem of information validation. the proposed hoa exhibited higher prediction rate in comparison with previous techniques and approaches. the trained dataset of hoa is iteratively updated to assure the data threshold is a self-learning framework towards supporting the neural networking model. acknowledgment this research has been funded by the scientific research deanship at university of ha’il saudi arabia through project number rg-191344. references [1] k. dracup, d. k. moser, m. eisenberg, h. meischke, a. a. alonzo, and a. braslow, “causes of delay in seeking treatment for heart attack symptoms,” social science & medicine, vol. 40, no. 3, pp. 379–392, feb. 1995, https://doi.org/10.1016/0277-9536(94)00278-2. 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[25] j. p. li, a. u. haq, s. u. din, j. khan, a. khan, and a. saboor, “heart disease identification method using machine learning classification in e-healthcare,” ieee access, vol. 8, pp. 107562–107582, 2020, https://doi.org/10.1109/access.2020.3001149. [26] n. k. al-shammari, h. b. almansour, and m. b. syed, “development of an automatic contactless thermometer alert system based on gps and population density,” engineering, technology & applied science research, vol. 11, no. 2, pp. 7006–7010, apr. 2021, https://doi.org/ 10.48084/etasr.4103. [27] n. k. al-shammari, t. h. syed, and m. b. syed, “an edge – iot framework and prototype based on blockchain for smart healthcare applications,” engineering, technology & applied science research, vol. 11, no. 4, pp. 7326–7331, aug. 2021, https://doi.org/10.48084/ etasr.4245. microsoft word 28-3211_s1__etasr_v10_n2_pp5496-5500 engineering, technology & applied science research vol. 10, no. 2, 2020, 5496-5500 5496 www.etasr.com bhutto et al.: numerical analysis of rapid drawdown of an embankment dam numerical analysis of rapid drawdown of an embankment dam amjad hussain bhutto department of civil engineering quaid-e-awam university of engineering science and technology nawabshah, pakistan amjadbhutto62@gmail.com ghulam shabir bhurgri department of civil engineering quaid-e-awam university of engineering science and technology nawabshah, pakistan ghulamshabirbhurgri14@gmail.com shahnawaz zardari department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan shahnawazzardari@gmail.com muhammad auchar zardari department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan muhammad.auchar@quest.edu.pk riaz bhanbhro department of civil engineering quaid-e-awam university of engineering science and technology nawabshah, pakistan riaz@quest.edu.pk bashir ahmed memon department of civil engineering quaid-e-awam university of engineering science and technology nawabshah, pakistan bashir_m@hotmail.com abstract—numerical analysis for the safe rate determination of lowering of an embankment dam was performed in this study with the use of the finite element method. coupled deformation and consolidation analysis were carried out for staged construction and drawdown of a 59m embankment dam for varying undrained shear strength of the clay core. the lowering of the reservoir was performed at different depths between two extreme scenarios, i.e. rapid lowering rate (1m/day) and slow lowering rate (0.1m/day). the reservoir of the dam was lowered to a depth from 10m to 55m in gradual increments. the results indicated that the safety of the dam was satisfactory when the reservoir was lowered at the quick rate for a depth of 10m, 20m, 30m respectively when the undrained shear strength of the clay core was taken as 20, 25 and 30kn/m 2 . regarding the case of slow drawdown rate of the reservoir, it was found that the reservoir could be lowered up to a depth of 55m at a rate of 0.1m/day when the undrained strength of clay core was 25kn/m 2 . the stability of the dam was also found satisfactory even though the reservoir was lowered at a rate of 0.25m/day for a depth of 55m when the undrained shear strength of clay core was 30kn/m 2 . keywords-rapid drawdown; stability; safety factor; consolidation; undrained shear strength i. introduction in this paper, slow and rapid drawdown of a rainfed embankment dam is presented. the reservoir of the dam lies in an area where the rainfall is erratic. this study focuses on the way the dam would behave if there was a rainfall shortage in the reservoir area and water would continue to be used. it is possible high rain intensity periods to give way to long drought periods. in this situation, it is very imperative to examine the safe rate of drawdown that could be allowed to discharge water. in addition, quick lowering of the reservoir could be necessary in a case of an emergency. the main parameters on which the safety of a dam depends are soil properties, pressure of water, and geometry [1-3]. in case of drawdown, pore pressures in the upstream side of the dam reduce which ultimately disturbs the equilibrium conditions of the dam. as a result, the upstream side of the dam is likely to slide due to imbalance of the water pressure that is present before lowering of the reservoir. when the reservoir level is increased, two types of pore pressure develop in the dam: seepage pore pressure and excess pore pressure. in an emergency, if it is required to lower the reservoir level, then the upstream face of the dam is likely to slide due to the presence of pore pressures, which have not dissipated as quickly as the lowering of the reservoir. this occurs because with the decrease of the water level there is a loss of stabilizing effect of water without decrease in pore pressure. if the permeability of the soil is low, it will take a long time to drain. consequently, there might be a chance of sliding of the upstream slope of the dam. it has been found that the likelihood of failure of a dam depends on lowering speed, permeability, and the compressibility of the soil of the dam [4]. rapid drawdown may occur, if the reservoir is lowered so rapidly that the soil does not have enough time to drain sufficiently. the stability of embankment dams is very important for public safety and the economic development of a country. stability of an embankment dam under rapid drawdown situation is complicated because of the time dependent generation of pore pressures in embankment and foundations. such analysis may require advanced numerical tools based on finite element method [5]. several embankment dam failures due to continuous lowering of the reservoir are reported in [510]. it is reported that the common rates of lowering of the reservoir range from 0.1m/day to 1m/day [11]. if the upstream face of the dam is of high permeability or the side slopes are corresponding author: amjad hussain bhutto engineering, technology & applied science research vol. 10, no. 2, 2020, 5496-5500 5497 www.etasr.com bhutto et al.: numerical analysis of rapid drawdown of an embankment dam flat, the embankment dams can sustain more drawdown as compared to the soils with low permeability. since every embankment dam has specific geometry and foundation soils, the safe rate of lowering of the reservoir is site specific and varies, depending on the case. ii. materials and methods a rainfed dam located in sindh province is analyzed with consideration of rapid drawdown conditions that might arise due to uneven distribution of rainfall and continuous discharge of water. the cross section of the dam is presented in figure 1. the main material zones are sandy gravel, random fill, clay core, and sandy siltstone. in addition, grouting was provided to control seepage in the foundation. the numerical analysis was carried out with the finite element program plaxis 2d [12]. the various soil material properties were obtained from field and laboratory tests [13] (table i). for the development of the finite element model of the dam, the layers were gradually placed at a rate of three meters in thirty days. the ground water level is 15m below the surface. after gradual raising of the dam at the specified rate, the reservoir was slowly filled in 120 days up to a level of 56.6m (figure 2). the stress strain behavior of all materials was modeled with mohr-coulomb model. the gradual raising process of the dam was carried out with consolidation analysis. for computation of safety at various stages during the service life of the dam, safety analysis was performed. fig. 1. cross section of a rainfed embankment dam table i. material properties used material saturated unit weight (kn/m 3 ) cohesion (kn/m 2 ) friction angle (deg) modulus of elasticity (kn/m 2 ) permeability (m/day) clay 18.85 [13] 9.57 [13] 30 [13] 50000 [13] 0.000263 [13] sandy gravel 21.5 [14] 0 37 [15-17] 50000 [18] 86.4 [19] random fill 18.85 [13] 0 34 [13] 50000 [13] 0.263 [13] washed gravel 21.5 [14] 0 37 [15-17] 45000 [20] 864 [21] d/s slope protection 19.5 [22] 0 34 [15-17] 40000 [23-24] 8640 [21] riprap 19.5 [13] 0 34 [13] 40000 [23-24] 8640 [21] sand filter 18.85 [13] 0 36 [13] 40220 [13] 26.33 [13] drainage blanket 21.5 [17] 0 37 [15-17] 45000 [21] 864 [24] sandy siltstone 20.4 [13] 12 [13] 29 [13] 70000 to 125000 [25] 0.00063 [13] fig. 2. high reservoir level location of the embankment dam rapid drawdown was carried out using coupled deformation and consolidation analysis. before performing rapid drawdown calculations, the effective strength and stiffness parameters (see table i) of the clay core were changed with undrained shear strength values of the clay core ranging between 20 to 30kn/m 2 . the values of undrained shear strength were evaluated based on the consistency index [26]. the values were computed as: ���������� ���� � 1 � �� (1) �� � ���� ����� (2) where li is the liquidity index, w is the natural moisture content, pl is the plastic limit, and ll is the liquid limit of clay: �� � ��.�����.�� ��.����.�� � 0.273 (3) ���������� ���� � 1 � �� � 1 � 0.273 � 0.726 (4) based on the consistency index value of 0.726, the undrained shear strength (su) of soil lies in the range of 20 to 40kn/m 2 . in this paper, the drawdown calculations were performed for undrained strength of clay of 20, 25 and 30kn/m 2 . in addition, since the clay became saturated, its modulus of elasticity was taken as 30000kn/m 2 instead of the initial value of 50000kn/m 2 . drawdown of the dam was performed for different rates ranging from 1m/day to 0.1m/day. the lowest value of the drawdown was 10m and highest was 55m as shown in figures 3 and 4 respectively. fig. 3. 10m lowering of the reservoir at the rate of 1m/day fig. 4. a view of lowering of reservoir up to a depth of 55 m at 0.1 m/day engineering, technology & applied science research vol. 10, no. 2, 2020, 5496-5500 5498 www.etasr.com bhutto et al.: numerical analysis of rapid drawdown of an embankment dam iii. results and discussion a. dam stability at the end of construction and after filling of the reservoir the stability of the dam was evaluated by computing the safety factor of the dam. the computed values of safety factor were 1.6 and 1.5 for the end of construction and after the filling of the reservoir respectively. the corresponding failure zones for the end of construction and after the filling of the reservoir conditions are shown in figures 5 and 6. it can be observed that failure zone was developed on the upstream face at the end of construction, when regarding after the filling of the reservoir, failure zone was developed on the downstream side. this occurred because the reservoir water produced a stabilizing effect on the upstream side by creating a likelihood of failure on the downstream side. three cases are discussed in this paper regarding the undrained shear strength of the clay core. the values of undrained shear strength were utilized as 20, 25 and 30kn/m 2 . in every case, the drawdown is shown at different increasing rates of 0.1, 0.125, 0.25, 0.5 and finally 1m/day. the drawdown rates of 0.1m/day and 1m/day are respectively called as slow drawdown and rapid drawdown of the embankment dam. fig. 5. failure zone of the dam after the end of construction fig. 6. failure zone of the dam after the filling of the reservoir b. dam stability during drawdown when the undrained strength of clay is 20kn/m 2 figure 7 shows the safety factor of the embankment dam versus time at different rates of drawdown varying from 0.1m/day to 1m/day. it can be observed that for rapid drawdown of 1m/day, the dam has shown enough stability for up to 15 days (15m lowering of the reservoir depth) at which the factor of safety was 1.2. when the rapid drawdown of the dam was allowed beyond the 15 days, the dam showed instability in terms of safety factor, which reduced to 0.92 at 35 days (35m lowering of the reservoir). when the reservoir lowered beyond 35m depth, the computed results showed complete collapse of the soil, because of the quick lowering of the reservoir, which resulted in imbalance of the support provided by the water to the upstream face. when the rate of drawdown was 0.5m/day, the dam showed stability for 30 days (15m lowering of the reservoir), with a factor of safety of 1.2. the dam became instable when the reservoir was lowered continuously beyond 30 days. figure 7 shows the limiting value of factor of safety of 1.2 as a straight line. the curves of safety factor are plotted for different rates of lowering of the reservoir. above the limiting value of 1.2, they are considered satisfactory. if the dam is lowered up to 20m at a rate of 0.1m/day for 200 days, the dam would be safe with a factor of safety of 1.2. fig. 7. safety factor vs time at different rates of lowering of the reservoir, when the undrained shear strength of clay is 20kn/m 2 the failure zones for rapid drawdown at a rate of 1m/day (10m depth of lowering of the reservoir) and slow drawdown at a rate of 0.1m/day (20m depth of lowering of the reservoir) are shown in figures 8 and 9. for the rapid drawdown situation, the failure was initiated in clay core and then was extended to the downstream side which is less permeable than the upstream side. for slow drawdown, the failure zone was initiated in the clay core and then was extended to the upstream side of the dam. fig. 8. failure zone of the dam when the reservoir was lowered at a rate of 1m/day for a depth of 10m (su=20) fig. 9. failure zone of the dam when the reservoir was lowered at a rate of 0.1m/day for a depth of 20m (su=20) engineering, technology & applied science research vol. 10, no. 2, 2020, 5496-5500 5499 www.etasr.com bhutto et al.: numerical analysis of rapid drawdown of an embankment dam c. dam stability during drawdown when the undrained strength of clay is 25kn/m 2 the safety factor values versus time for different rates of lowering of the reservoir of the dam are shown in figure 10. it can be observed that when the dam is lowered at the quick drawdown rate, the dam showed stability for up to 20 days (20m lowering of the reservoir) having a factor of safety of 1.2. when the rate of drawdown was 0.5m/day, the dam showed stability for up to 40 days with a factor of safety of 1.2. for the slow rate of lowering of the reservoir, the dam showed stability for 550 days (55m lowering of the reservoir). fig. 10. safety factor vs time at different rates of lowering of the reservoir, when the undrained shear strength of clay is 25kn/m 2 the failure zones for rapid and slow drawdown are respectively shown in figures 11 and 12. for both situations, the failure was initiated in the clay core and was then extended to upstream side of the dam. fig. 11. failure zone of the dam when the reservoir was lowered at a rate of 1m/day for a depth of 20m (su=25) fig. 12. failure zone of the dam when the reservoir was lowered at a rate of 0.1m/day for a depth of 55m (su=25) d. dam stability during drawdown when the undrained strength of clay is 30kn/m 2 figure 13 illustrates that the dam is safe if its reservoir is lowered up to a depth of 55m even at a rate of 0.25m/day in 220 days. if the lowering of the reservoir is performed quickly at a rate of 1m/day, the dam is stable up to a depth of 23m only. it is also interesting to note that for all rates of lowering of the reservoir, the factor of safety initially decreased and then gradually increased even when the lowering was continued beyond the depth of 35m, because the clay core and upstream material (sandy gravel) are wider at the base than at the top surface. due to the bigger width of the clay core and upstream sandy gravel at the deeper layers of the dam, the soil became more hardened, therefore the safety factor was increased. in general, a decrease in drawdown rate showed an increase in the safety factor of the dam. this indicates that the stability of the dam improved when the drawdown rate was relatively reduced. fig. 13. safety factor vs time at different rates of lowering of the reservoir, when the undrained shear strength of clay is 30kn/m 2 the failure zones for rapid and slow drawdown are shown respectively in figures 14 and 15. for both cases the failure was initiated in the clay core and was then extended to the upstream side of the dam. fig. 14. failure zone of the dam when the reservoir was lowered at a rate of 1m/day for a depth of 20m (su=30) fig. 15. failure zone of the dam when the reservoir was lowered at a rate of 0.1m/day for a depth of 55m (su=30) e. pore pressure during rapid drawdown in addition to stability during rapid drawdown and slow drawdown of the dam, it is also necessary to observe how the engineering, technology & applied science research vol. 10, no. 2, 2020, 5496-5500 5500 www.etasr.com bhutto et al.: numerical analysis of rapid drawdown of an embankment dam excess pore pressure and total pore pressure have developed and dissipated with respect to time. a detailed summary of the development and dissipation of pore pressure is presented in table ii. it can be observed that the total pore pressure has been reduced as the reservoir level lowered from 0 to 55m. excess pore pressure has been developed more quickly during rapid drawdown and at a relatively slower rate during slow drawdown. table ii. development and dissipation of excessive and total pore pressure during drawdown undrained shear strength su (kn/m 2 ) drawdown rate (m/day) drawdown depth (m) compressive pore pressure compressive excess pore pressure after reservoir filling 0 1700 120 20 1 10 1600 360 20 0.1 20 1600 280 25 1 20 1600 335 25 0.1 55 1400 320 30 1 20 1600 300 30 0.1 55 1400 280 iv. conclusion in this paper, the results of numerical modeling of safe lowering rate of the reservoir are presented. it was observed that the safe lowering rate of the reservoir depends mainly on the magnitude of the undrained shear strength of the clay core. adoption of a value of 25kn/m 2 is suggested for the undrained shear strength of the clay. the computed results indicate that the reservoir of the dam could be lowered safely up to 20m and 55m, if the rates of drawdown are respectively 1m/day (rapid drawdown) and 0.1m/day (slow drawdown). references [1] a. h. bhutto, s. zardari, g. s. bhurgri, m. a. zardari, r. bhanbhro, b. a. memon, m. m. babar, “mohr-coulomb and hardening soil model comparison of the settlement of an embankment dam” , engineering, technology & applied science research vol. 9, no. 5, pp. 4654-4658, 2019 [2] a. h. bhutto, s. zardari, g. s. bhurgri, m. a. zardari, r. bhanbhro, b. a. memon, m. m. babar, “post construction and long term settlement of an embankment dam computed with two constitutive models”, engineering, technology & applied science research vol. 9, no. 5, pp. 4750-4754, 2019 [3] a. h. bhutto, s. zardari, g. s. bhurgri, m. a. zardari, r. bhanbhro, b. a. memon, m. m. babar, “parametric analysis of stability of an embankment dam”, engineering, technology & applied science research, vol. 9, no. 6, pp. 5016-5020, 2019 [4] s. s. athani, c. h. solanki, g. r. dodagoudar, “seepage and stability analyses of earth dam using finite element method”, aquatic procedia,vol. 4, pp. 876-883, 2015 [5] d. r. vandenberge, “total stress rapid drawdown analysis of the pilarcitos dam failure using the finite element method”, frontiers of structural and civil engineering, vol. 8, no. 2, pp. 115-123, 2014 [6] m. m. berilgen, “investigation of stability of slopes under drawdown conditions”, computers and geotechnics, vol. 34, no. 2, pp. 81-91, 2007 [7] h. hasani, j. mamizadeh, h. karimi, “stability of slope and seepage analysis in earth fills dams using numerical models. (case study: ilam dam-iran)”, world applied sciences journal, vol. 21, no. 9, pp. 13981402, 2013 [8] m. y. fattah, h. a. omran, m. a. hassan, “behavior of an earth dam during rapid drawdown of water in reservoir: case study”, international journal of advanced research, vol. 3, no. 10, pp. 110-122, 2015 [9] s. a. khattab, “stability analysis of mosul dam under saturated and unsaturated soil conditions”, al rafdain engineering journal, vol. 18, no. 1, pp. 13-27, 2010 [10] y. gao, d. zhu, f. zhang, g. h. lei, h. qin, “stability analysis of three-dimensional slopes under water drawdown conditions”, canadian geotechnical journal, vol. 51, no. 11, pp. 1355-1364, 2014 [11] n. m. pinyol, e. e. alonso, s. olivella, “rapid drawdown in slopes and embankments”, water resources research, vol. 44, no. 5, 2008 [12] r. b. j. brinkgreve, s. kumarswamy, w. m. swolfs, plaxis reference manual, plaxis bv, 2017 [13] wapda, project planning report of nai gaj dam, water and power development authority of pakistan, 2006 [14] j. schleiss, r. m boes, dams and reservoirs under changing challenges, crc press, 2011 [15] m. carter, s. p. bentley, soil properties and their correlations, john wiley & sons, 2016 [16] f. cobb, structural engineer's pocket book: british standards edition, elsevier, 2008 [17] r. f. craig, soil mechanics, springer, 2013 [18] r. a. rajapakse, geotechnical engineering calculations and rules of thumb, butterworth-heinemann, 2015 [19] g. e. barnes, soil mechanics: principles and practice, palgrave macmillan, 2011 [20] j. l. justo, j. saura, “three‐dimensional analysis of infiernillo dam during construction and filling of the reservoir”, international journal for numerical and analytical methods in geomechanics, vol. 7, no. 2, pp. 225-243, 1983 [21] b. g. look, handbook of geotechnical investigation and design tables, crc press, 2014 [22] m. n. sara, site assessment and remediation handbook, crc press, 2003 [23] p. j. burgess, d. sarabia, j. small, h. g. poulos, j. sinha, “settlement behaviour of a major dam”, ancold 2006 conference: dams: the challenges of the 21st century, manly, australia, november 19-22, 2006 [24] l. ormann, m. a. zardari, h. mattsson, a. bjelkevik, s. knutsson, “numerical analysis of strengthening by rock fill embankments on an upstream tailings dam”, canadian geotechnical journal, vol. 50, no. 4, pp. 391-399, 2013 [25] d. u. deere, r. p. miller, engineering classification and index properties for intact rock, air force systems command, 1966 [26] n. a trenter, earthworks: a guide, thomas telford limited, 2001 engineering, technology & applied science research vol. 8, no. 2, 2018, 2704-2708 2704 www.etasr.com laghari et al.: water availability in snow dominated regions under projected climatic variability water availability in snow dominated regions under projected climatic variability a case study of alpine catchment, austria abdul nasir laghari department of chemical engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan mashaalnasirlaghari@gmail.com mohsin ali soomro department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan zafar ali siyal department of energy and environment quaid-e-awam university of engineering, science & technology nawabshah, pakistan sajad h. sandilo department of mathematics quaid-e-awam university of engineering, science & technology nawabshah, pakistan tania ali soomro department of architecture and planning dawood university of engineering & technology karachi, pakistan abstract—this study analyzes the response of various hydrological parameters and future water availability against anticipated climate variations in snow dominated alpine catchment in austria. the parameters assessed are base flow, environmental flow, total flow, evapotranspiration, and snow cover duration. the distributed hydrological modeling system prevah is developed to assess the impacts through the combination of various climate change scenarios produced under the framework of the european project prudence. the model results clearly indicate an apparent shift from observed trends in monthly, seasonal and annual values. the mean annual changes observed by all model scenarios range between 45% to 60% decrease in snow cover duration, 15% to 20% increase in evapotranspiration, 5% to 15% decrease in base flow, and 15% to 25% decrease in total runoff values. however, mean annual changes observed in available water are marginal, just ranging from -3% to +2%. all regional model projections show more or less the same identical pattern of changes in analyzed parameters. keywords-climate change; alpine catchment; hydrological response; water availability i. introduction the mid-20th century, considered as an era of industrialization, has led to unprecedented use of fossil fuels which are a major cause for releases of anthropogenic greenhouse gases [1]. the clear-cut outcome is ever increasing temperature. the increasing temperature trend is a main catalyst behind change in climatic parameters. these changes have exhibited far-reaching effects on man and its eco-system. in [1], authors concluded that warming of the earth’s atmosphere is unambiguous and since the mid of the 19th century, the last three decades are the warmest ones at the earth’s surface than any preceding ones. the 30 year period from 1983-2012 is probably the hottest one in the last 14 centuries. they also reported a 0.85°c global temperature rise since 1880s [1]. however, the change in mountain regions is almost three times higher than the 20th century global average. similar trend is observed in european alps, a major supply source of 4 alpine rivers: danube, rhine, rhone and po. therefore, the region is considered highly prone to climatic variations [2]. these variations may affect region’s hydrological cycle. several researchers already concluded that climatic variability alters the snow storage which subsequently affects timing and flow volumes in alpine catchments. anticipated seasonality change may also bring severe complications for adjacent lowland areas [3-7]. furthermore, it may affect constant water availability, hydropower generation, water tourism etc. numerous other studies are also not only raising concerns over reliability of water supply sources but also acknowledge severe complications for water management systems [4, 8]. in such context, the present study analyzes catchment flow component’s sensitivity towards future climate change scenarios and subsequent impact on water availability. the hydrological modeling system prevah is developed to analyze mean flow, low flow (q95) and base flow changes. most of the studies generally investigate the climate variation effect on average flow conditions. however, there is a possibility that variation may not affect average flow conditions but may affect low flow conditions. hence, may affect reliability of water supply sources. similarly the temporal and spatial patterns (in raster format) of base flow analysis would indicate total water available for infiltration to, or abstraction from the ground water system. the findings will benefit the protection of ground water resources, land use engineering, technology & applied science research vol. 8, no. 2, 2018, 2704-2708 2705 www.etasr.com laghari et al.: water availability in snow dominated regions under projected climatic variability allocation and development, and future water resource planning and management. ii. study area the study is conducted over kitzbüheler ache catchment located in region of north-eastern alps, austria. the catchment is non-glacierized and its elevation ranges from 600m to 2400m, with mean level of 1291m. it encompasses an area of about 323km2. the average annual precipitation varies from 1474mm to 1784mm, with peaks receiving much higher precipitation than valleys. similarly, high altitude areas remain more (5-7 months) under snow cover than valley areas (2-4 months) [2]. flow characteristics of the catchment can be distinguished as high flows in spring and early summer due to melting contribution and low flows in winter due to snow accumulation. the average winter runoff is just one-third of summer runoff (392mm). one-third of total precipitation evapo-transpirates, the rest emerges as total runoff. almost half of the studied area (catchment) is covered by forest. high altitudinal areas are covered with alpine meadows, while low altitudes are covered with pastures. urban area occupies very small percentage and is confined to the valleys. mountain tops are covered with bare rocks. fig. 1. average catchment (1961-90), monthly water balance components iii. climate change scenario development generally hydro-climatic studies are based on atmosphere ocean general circulation model (ao-gcm) projections. these models simulate realistic climate projections. however, at regional scale, its course resolution and limited physical representation produce higher uncertainty and lack the detailed spatial structure of climatic parameters. these issues drastically limit its application in qualitative, detailed assessment of climate change studies at regional level [9]. to satisfy the need to have such detailed information and certainty in future climatic parameters, prudence project was initiated. in this project, many state of the art high resolution regional climate models (rcm) with different boundary conditions (gcms), varying resolutions and sres emission scenarios are used. the climate scenarios used in this study are the outputs of regional climate models (i.e. rcao, hirham, racmo, clm) downscaled from the gcm hadam3h (hadley centre) experiment run, based on sres a2 emission scenario produced under the frame work of eu project prudence. the climate scenarios are based on catchment average monthly precipitation and temperature output grid cells extracted in gis-raster format from the prudence project homepage. the retrieved data sets are basically two time slices, one for recent conditions (1961-1990), and the other for future climate (2071–2100). the relative changes in both parameters, known as “climate scenarios” are presented as seasonal averages in table i. all scenarios suggest winter temperature increase by 4.5°c and precipitation increase by 17% whereas, summer temperatures increase by 5.2 °c and the total amount of precipitation may decrease by 38%. the observed climate model projections are generally similar with the trends of the greater alpine area projections except little variation in magnitude [10]. earlier findings in [11, 12] also concluded that the alps will be much wetter and warmer in winter, and drier and hotter in summer in the latter part of the 21st century. after model development (calibration and validation), the observed data base precipitation and temperature series (1961-1990) is perturbed with climate scenarios by means of the so called “delta change” approach. similar methodology is also adopted in earlier studies [2, 13]. the delta-perturbed series are then utilized as input for the prevah model. table i. catchment relative changes in average daily temperature and precipitation extracted from the prudence project database season parameter rcao racmo hirham clm winter precipitation (%) 16.85 11.93 16.49 10.42 temperature (°c) 3.93 3.57 4.45 4.10 spring precipitation (%) 5.27 9.37 2.95 12.92 temperature (°c) 3.47 3.37 3.46 3.55 summer precipitation (%) -37.84 -32.48 -21.59 -29.5 temperature (°c) 5.20 4.33 4.34 4.37 autumn precipitation (%) -13.89 -9.09 -19.9 -7.78 temperature (°c) 4.00 3.94 5.40 3.95 iv. model development the distributed model system prevah has been developed to represent hydrological characteristics of mountainous catchments. it has been successfully applied in a number of mountain catchments [2, 6, 7, 14-16] and is also applied to this study. the details about various data sets i.e. meteorological data, soil types, land use, land cover, elevation model, various modules and schemes used for model development for this specific catchment are given in [2]. for details about prevah model, see [17]. the first model was calibrated over the 1983-1988 period and the latter validated over the 30 year baseline period of 1961-1990. the results of calibration and validation periods are compared to the observed hydrographs both graphically and statistically, and are shown in figures 2 and 3. the linear (elin) and logarithmic (elog) engineering, technology & applied science research vol. 8, no. 2, 2018, 2704-2708 2706 www.etasr.com laghari et al.: water availability in snow dominated regions under projected climatic variability nash–sutcliffe efficiencies are about 0.84 for calibration and above 0.80 for validation period and are shown in table ii. fig. 2. graphical comparison of observed and simulated daily hydrograph at the gauge station (st johann i.t) of the kitzbüheler ache catchment for calibration period (1983-88). fig. 3. graphical comparison of observed and simulated daily hydrograph at the gauge station (st johann i.t) of the kitzbüheler ache catchment for validation period (1961-90). v. results and discussion to analyze the effect of projected climate scenarios on base flow conditions, the base flow simulations for the period (20712100) are compared to present condition (1961-90) simulations. the mean monthly, present and future, base flow patterns along with percent deviation in volume are shown in figure 4. mean annual changes are illustrated in figure 10. it is clearly highlighted that under the current situation, most of the base flow is produced in spring and early summer months. snow melt is assumed to be the most important factor. however, the generation volume associates with the amount of winter snowfall, and corresponding degree and extent of snow melt season. the catchment average is approximately 753 to 794mm/year, approximately half the precipitation amount. in future context, this decreases by around 5-9%. at seasonal scale, winter volume is increased about 90% to 95%, whereas, in other seasons decreased about 9% to 15% for spring, 25% to 40% for summer, and 15% to 23% for autumn. in winter season, warm temperatures cause higher rain to snow ratio, thereby resulting in massive increase in baseflow volume. however, at spatial scale, the distinct hydraulic properties of underlying soil result in variation of base flow volume across the watershed (figure 5). similar understanding is also reported in [18], that soil and other subsurface properties directly influence spatial variation in base flow volume. snowfall trend is recognized to be the main cause behind variation in base flow volume. snow cover maps given in figure 6 endorse this assumption. relative to present condition mean annual snow cover days (160 days), all models predicted reduced snow cover days: 74 days for clm, 65 days for hirham, 83 days for racmo, and 76 days for rcao model. an earlier onset of melt season due to increase in temperature results in shortened total snow cover days. these may have totally disappeared, but partially have been compensated by the increased winter precipitation trends. another cause of variation in base flow volume can also be attributed to seasonal variation in precipitation trends and increased evaporative losses. the increase in evaporative losses is recorded in all seasons, with 10-15% relative loss at mean annual scale (figure 6). the seasonal contributions to mean annual losses are changed from 6% to 10% for winter, 21% to 28% for spring, 50% to 52% for summer and 23% to 27% for autumn for all model scenarios. similar trends of evaporative losses are also reported for swiss catchments. the rising trend of temperature has significantly increased evaporative losses in winter and spring. however losses in remaining two seasons stayed at moderate side (figure 7). the projected increased summer temperatures may have increased evaporative losses, but that is compensated due to reduced projected precipitation amount. in quantitative terms, summer losses are still at higher side. table ii. mean monthly elin and elog values for calibration and validation period month calibration period (1983-88) validation period (1961-90) lin (e) log (e) lin (e) log (e) jan 0.89 0.91 0.92 0.90 feb 0.96 0.92 0.89 0.86 mar 0.81 0.77 0.77 0.76 apr 0.84 0.83 0.79 0.78 may 0.88 0.93 0.82 0.87 jun 0.85 0.87 0.78 0.81 jul 0.76 0.79 0.83 0.80 aug 0.82 0.77 0.76 0.79 sep 0.79 0.78 0.77 0.75 oct 0.84 0.79 0.79 0.85 nov 0.90 0.87 0.80 0.89 dec 0.80 0.91 0.83 0.87 fig. 4. the mean monthly baseflow values (2071-2100) with their corresponding present day (19961-1990) baseflow values along with monthly percentage change in volume under a2-emission scenario. projected climatic scenarios have also influenced seasonal patterns of environmental and total flow volume (figure 8). a significant increase is observed in winter flow volume while engineering, technology & applied science research vol. 8, no. 2, 2018, 2704-2708 2707 www.etasr.com laghari et al.: water availability in snow dominated regions under projected climatic variability decreasing trend is observed in the other three seasons. relative to recent climate (1961-90), the average seasonal flow to mean annual flow is changed from 12% to 25% for winter, 34% to 27% for spring, 35% to 20% for summer, and 20% to 16% for autumn at the end of the 21st century. peak flow pattern is switched from may to march-april along with reduced volume. an anticipated increase in spring flow volume due to projected increase in precipitation amount is compensated by early snow melting to winter months and greater evapotranspiration (figure 7). a similar conclusion is also drawn in [5, 6, 11] for alpine catchment. the increased evapotranspiration along with decreased precipitation amount in summer and fall may also reduce flow volume in these seasons. similarly, the projected environmental flows (q95) follow the same identical patterns of projected total mean seasonal flow patterns. low precipitation amount along with increasing evapotranspiration losses results in decreasing volume from april to september. therefore, environmental flow trend may have serious consequences over quality and supply in summer months. fig. 5. the relative seasonal change in baseflow volume under a2emission scenario. fig. 6. the comparison of projected mean annual snow duration maps with their corresponding base period (19961-1990) snow duration map. the changes in flow variables i.e. environmental flow and total mean flow may have altered water availability in various months. figure 9 demonstrates this effect, where water availability is calculated by means of difference between total flow and environmental flow volumes. all model projections clearly show increasing patterns from december to march and decreasing patterns from may to august. however, marginal change is observed at mean annual scale (figure 10). projected total flows appear extremely critical from may to september, where they are just narrowed down to current environmental flow volumes. fig. 7. the relative seasonal shift in actual under a2-emission scenario. fig. 8. the projected mean monthly environmental flow (q95) and total stream flow regime under a2-emission scenario fig. 9. the projected mean monthly available water (2071-2100) with their corresponding present day (19961-1990) values along with monthly percent of change in volume under a2-emission scenario. engineering, technology & applied science research vol. 8, no. 2, 2018, 2704-2708 2708 www.etasr.com laghari et al.: water availability in snow dominated regions under projected climatic variability fig. 10. the relative mean annual changes in snow cover duration (scd), actual evapotranspiration (aet), baseflow (bf), total flow and total available water under a2-emission scenario. vi. conclusions this study clearly demonstrates that catchment flow regime i.e. baseflow, environmental flow, and total flow is highly vulnerable to climatic variations. the projected increasing temperatures, seasonal shift in precipitation patterns, subsequent effect over high rain to snow ratio in winter, anticipated early onset of snowmelt season, and increasing evaporative losses are attributed to be the major driving factors behind a clear-cut shift in observed seasonality of flow variables. relative to present condition scenario, the base flow volume in winter is increased about 90% to 95%, whereas is decreased, about 9% to 15% in spring, 25% to 40% in summer, and 15% to 23% in autumn. further variation observed in base flow volume is non-uniform across the catchment at spatial scale. this could mainly be attributed to distinct hydrogeologic properties of underlying soil across the catchment. moreover, projected model simulations also indicate the same identical pattern of changes in total mean flow, environmental flow as in base flow regime and subsequent effect over seasonal water availability patterns. reference [1] ipcc, synthesis report of the ipcc fifth assessment report (ar5), ipcc, 2014 [2] a. n. laghari, d. vanham, w. rauch, “to what extend does climate change result in alpine hydrology? an example of kitzbüheler ache catchment in the austrian alps”, hydrological sciences journal, vol. 57, no. 1, pp. 103-117, 2012 [3] p. etchevers, c. golaz, f. habets, j. noilhan, “impact of a climate change on the rhone river catchment hydrology”, geophysical research atmospheres, vol. 107, no. d16, pp. acl 6-1-acl6-18, 2002 [4] b. schaefli, quantification of modeling uncertainties in climate change impact studies on water resources: application to a glacier-fed hydropower production system in the swiss alps, phd thesis, ecole polytechnique fédérale de lausanne, 2005 [5] b. zierl, h. bugmann, “global change impacts on hydrological processes in alpine catchments”, water resources research, vol. 41, no. 2, 2005 [6] d. vanham, e. fleischhacker, w. rauch, “technical note: seasonality in alpine water resources management – a regional assessment”, hydrology and earth system sciences, vol. 12, no. 1, pp. 91-100, 2008 [7] d. vanham, e. fleischhacker, w. rauch, “impact of snowmaking on alpine water resources management under present and climate change conditions”, water science and technology, vol. 59, no. 9, pp. 17931801, 2009 [8] k. jasper, p. calanca, d. gyalistras, j. fuhrer, “differential impacts of climate change on the hydrology of two alpine river basins”, climate research, vol. 26, no. 2, pp. 113–129, 2004 [9] a. bronstert, “rainfall–runoff modeling for assessing impacts of climate and land-use change”, hydrological processes, vol. 18, pp. 567–570, 2004 [10] j. h. christensen, o. b. christensen, “a summary of the prudence model projections of changes in european climate by the end of this century”, climate change, vol. 81 (suppl 1), pp. 7–30, 2007 [11] m. r. marinucci, f. giorgi, m. beniston, m. wild, p. tschuck, a. ohmura, a. bernasconi,”high resolution simulations of january and july climate over the western alpine region with a nested regional modeling system”, theoretical and applied climatology, vol. 51, no. 3, pp. 119–138, 1995 [12] m. w. rotach, m. r. marinucci, w. wild, p. tschuck, a. ohmura, m. beniston, “nested regional simulation of climate change over the alps for the scenario of a doubled greenhouse forcing”, theoretical and applied climatology, vol. 57, no. 3–4, pp. 209–227, 1997 [13] a. m. akhtar, a. n. ahmad, m. j. booij, “the impact of climate change on the water resources of hindukush-karakorum-himalaya region under different glacier coverage scenarios”, journal of hydrology, vol. 355, pp. 148-163, 2008 [14] j. gurtz, m. zappa, k. jasper, h. lang, m. verbunt, a. badoux, t. vitvar, “a comparative study of modelling runoff and its components in two mountainous catchments”, hydrological processes, vol. 17, pp. 297-311, 2003 [15] m. zappa, f. pos, u. strasser, j. gurtz, “seasonal water balance of an alpine catchment as evaluated by different methods for spatially distributed snow melt modeling”, nordic hydrology, vol. 34, pp. 179202, 2003 [16] m. verbunt, m. zappa, j. gurtz, p. kaufmann, “verification of a coupled hydro meteorological modeling approach for alpine tributaries in the rhine basin”, journal of hydrology, vol. 324, pp. 224–238, 2006 [17] d. viviroli, m. zappa, j. gurtz, r. weingartner, “an introduction to the hydrological modeling system prevah and its preand postprocessing-tools”, environmental modeling & software, vol. 24, pp. 1209–1222, 2009 [18] d. vanham, integrated water resources management in alpine regions—development and application of methodologies for the analysis of current and future conditions, phd thesis, university of innsbruck, 2011 microsoft word 03-bhowmik.doc etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 90-97 90 www.etasr.com bhowmik and �ag chowdhury: prograph based analysis of ssspps with few distinct positive lengths prograph based analysis of single source shortest path problems with few distinct positive lengths biswajit bhowmik assistant professor dpt of computer science & engineering bengal college of engineering and technology durgapur – 713 212 india biswajitbhowmik@gmail.com sreyasi nag chowdhury dpt of computer science & engineering bengal college of engineering and technology durgapur – 713 212 india sreyasi_nc@yahoo.com abstract — in this paper we propose an experimental study model 23 ps of a fast fully dynamic programming algorithm design technique in finite directed graphs with few distinct nonnegative real edge weights. the bellman-ford’s approach for shortest path problems has come out in various implementations. in this paper the approach once again is re-investigated with adjacency matrix selection in associate least running time. the model tests proposed algorithm against arbitrarily but positive valued weighted digraphs introducing notion of ographpr that speeds up finding the shortest path over previous implementations. our experiments have established abstract results with the intention that the proposed algorithm can consistently dominate other existing algorithms for single source shortest path problems. a comparison study is also shown among dijkstra’s algorithm, bellman-ford algorithm, and our algorithm. keywords — shortest path; negative weight cycle; weight matrix; variants; program-graph; spl; dense network; scanned vertices; relaxation. i. introduction computation of shortest path )(sp is one of the most fundamental problems in graph theory. both in operations research over and above theoretical computer science areas, the single source shortest path problem )(ssspp is an extremely well-studied problem because of its broad applicability in a wide range of domains [1, 2]. the wide spectrum of its applications ranges from the routing problem in communication networks to robot motion planning, highway and power line engineering etc. many optimization problems solved by dynamic programming or more complicated matrix searching techniques, such as the 0/1 knapsack problem, construction of optimal inscribed polygons, sequence alignment in molecular biology, length-limited huffman coding etc, are expressed as shortest path problems. these also include scheduling problems such as critical path computation in pert [3] charts. moreover, the shortest-path problem as well has numerous variations such as the minimum weight problem, the quickest path problem etc. our motivation for focusing on the algorithmic processes of these shortest path problems with few distinct edge lengths initiates from a problem that arises in social networks [1-7]. the shortest path problems )(spps have been, and still is, investigated by many researchers and mathematicians. with the rapid advancements and developments in communication, computer science and transportation systems, more variants of the spps have appeared. some of these are the traveling salesman problem, k-shortest paths, constrained shortest-path problem, multi-objective shortest path problem, network flow problems, and so forth including our key ssspp [2, 4, 8]. in this paper, we propose a model 23 ps that provides an algorithm similar to classical bellman-ford procedure that solves ssspp . the model is represented with a digraph with few positive real edge weights introducing graphogrampr or simply ographpr [9, 10] where each computation is performed at every node. the paper has been organized in the following sections. • problem definition. • negative weight cycle. • representation of weight matrix. • mathematical background. • shortest path variations. • proposed work. • experimental results. • comparison study. • conclusion. the bellman-ford’s approach for shortest path problems has come into practice with different tools. the approach in this paper is re-investigated with adjacency matrix selection in associate least running time. the proposed model 23 ps on experiments has established abstract results with the intention that the proposed algorithm can consistently dominate other existing algorithms for the underlying problem. a comparison etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 90-97 91 www.etasr.com bhowmik and �ag chowdhury: prograph based analysis of ssspps with few distinct positive lengths study is shown among dijkstra’s algorithm, bellman-ford algorithm and our algorithm. ii. statement of problem let us consider a weighted directed graph ),,( wevg = with vertex set v of size n , edge (or simply arc) set e of size m , and weight function rew →: assigning a real valued weight (cost) to each edge in g . then, a directed shortest path length )(spl from a given source (starting) vertex s to each other vertex v in g can be defined in (1) as:     ∞ ∃→ = otherwise vtosfrompathaifvspw vsspl p , ,):)(min( ),( (1) here, >=< k vvvp ,....., 21 is a shortest path )(sp from vertex 1 v to vertex nkv k ≤≤1, . therefore, spl (also termed weight) of p is the sum of the weight of its constituent edges. thus, ),()( 1 1 1∑ − = + = k i ii vvwpw (2) as a consequence, spl from vertex s to v in g means any path p with weight, ),()( vssplpw = [4, 11, 12]. iii. negative weight cycle we assume that all vertices are reachable from s otherwise unreachable vertices can be deleted from g in a linear-time at preprocessing steps. in some instances of ssspp , there may be edges whose weights are negative. if the graph g has either no negative-weight edges, or no reachable negative-weight cycles from s then vv ∈∀ , the ),( vsspl remains well defined during computation even if it has a negative value; otherwise spls are not well defined. no path from s to a vertex on the cycle in this case can be a shortest path and a lesser-weight path can always be found that follows the proposed shortest path and then traverses the negativeweight cycle. if there is a negative-weight cycle on some path from vertex s to v , we define −∞=),( vsspl . illustration in figure 1 exemplifies the effect of negative weights and negative-weight cycles on shortest path weights. (a) (b) fig. 1. directed weighted graph with negative weight cycle. within each vertex its shortest-path weight from source s is shown. vertices e and f appear in a negative-weight cycle reachable from s , so they have shortest-path weights of ∞− . because vertex g is reachable from a vertex whose shortestpath weight is ∞− , it, too, has a shortest-path weight of ∞− . vertices h , i , and j are not reachable from s , and so their shortest-path weights are ∞ , even though they lie on a negative-weight cycle [1, 8, 11, 13, 14]. iv. weight matrix representation edge weights ),( jiw for the edges ),( ji can be interpreted as metrics (adjacency matrix, adjacency list etc) [8, 11, 15] other than distances. they are often used to represent time, cost, penalties, loss, or any other quantity that accumulates linearly along a path and that one wishes to minimize. in a weighted digraph g , w has been defined in (3) using adjacency matrix description of g as:      ∞ ∈ = = otherwise ejiedgetheoftc ji jiw , ),(cos, ,0 ),( (3) consider a digraph shown in figure 2. etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 90-97 92 www.etasr.com bhowmik and �ag chowdhury: prograph based analysis of ssspps with few distinct positive lengths fig. 2. digraph without any self loop and negative weight by definition in (3), weight matrix (also called cost matrix) would be constructed in table i below. table i. adjacency matrix of the graph shown in figure 2 v. mathematical interpretation shortest-paths algorithms typically rely on the property that a shortest path between two vertices contains other shortest paths within it. consider any i and j such that vjis ≤≤≤ , let >=< jij vvvp ,....., 21 is the sub-path of ),( jispl . then, ij p is a shortest path from vertex i v to j v . let, ][vspl k be spl of vertex k from s under the constraint that spl contains at most k edges. obviously, nvvswvspl ≤≤= 1],][[][1 . our goal is to compute vvvspl k ∈∀− ,][1 assuming this spl contains at most 1−k edges and there are no cycles of negative length possible. taking strength (advantages) of dynamic programming [4], the following observations [8, 11, 16] can be made. • ][][ 1 vsplvspl kk −= , if spl has at most k edges has no more than 1−k edges. • }}]][[][{min,][min{][ 11 viwvsplvsplvspl k i kk += −− , if some intermediate vertex i enters in spl . both figure 3 and figure 4 [17, 18] in sections vi and vii respectively give an idea about the above discussion. fig. 3. how an edge enters the solution thus, the above observations could be a symbol of the following recurrence relation for spl . 1k2,}}]][[{min,][min{][ 11 −≤≤+= −− nviwsplvsplvspl k i kk (4) vi. variants a number of variations are possible depending on the type of network and costs involved, and source/destination pairs of vertices (nodes) for which we need solution [4, 8, 11, 19]. • cyclic or acyclic problems – graph with at least one cycle. otherwise, acyclic. • %on-negative or %egative distance problems – if the distances (edge weights) are non-negative or if there is at least one negative distance. • %on-negative cyclic or %egative cyclic problems – cyclic problems with non-negative length of all cycles or with at least one cycle has negative length. • sparse or dense network problem – a network with m , number of edges, closer to 2 n ( n is the number of nodes) is a dense network. • single-source shortest path problem – shortest paths from a source vertex s to all other vertices in the graph. • all-pairs shortest path problem – shortest paths between every pair of vertices v , 'v in the graph. • single destination shortest path problem – shortest paths from all vertices in the graph to a single destination vertex d . thus, a problem of finding a shortest path in many network as well as transportation related problems may arise as a main decision question or as a step in some situation. vii. proposed work the literature on the ssspp is large, since computing shortest paths in a given graph (both directed and undirected) can be done in various ways. for example, consider figure 4 [18]. it shows how an intermediate vertex vk ∈ enters into a tentative solution of shortest path from a source vertex s to target vertex v . as one of the fundamental problems, vi \ vj v1 v2 v3 v4 v1 0 26 14 ∞ w[i][j] = v2 21 0 9 22 v3 11 8 0 ∞ v4 ∞ 12 ∞ 0 etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 90-97 93 www.etasr.com bhowmik and �ag chowdhury: prograph based analysis of ssspps with few distinct positive lengths competent way for finding spl is still an important field of research in computer science. fig. 4. various ways to compute shortest path from source the proposed algorithm for 23 ps model is based on computation of cost of each vertex independently. the algorithm maintains a cost ][vspl for each vertex v tentatively, such that some path from s to v has total cost ][vspl . as the algorithm proceeds, these costs will decrease in succession until for each vertex v , ][vspl is the cost of a minimum-cost path from s to v . instead of normal termination, the proposed algorithm finishes execution at the moment when two successive stages of the algorithm, i.e. two consequent instances of the ographpr of the given g, have the same shortest path cost ][vspl for each vertex v . initially, it is assigned that 0][ =sspl and ∞=][vspl for every vsv ∈≠ [13]. the algorithm maintains n partitions at most of the n vertices. each partition consists of each vertex v and its corresponding adjacent vertices. each partition acts as respective node of our ographpr with node s as its root. still, these n partitions can be sub-grouped into three states: • unlabeled vertices: those with infinite provisional costs. • labeled vertices: those with finite provisional cost whose minimum cost is so far unknown. • scanned vertices: those whose minimum cost is known. we start with s as labeled root node and all other vertices are as unlabeled. the prograph based shortest path algorithm named as ()__pr pathshortestograph described below executes comparable to bellman-ford approach to some extent. a variety of methods and algorithms are available for the solution of ssspps depending on the nature of specific problem [19]. because of the nature of our problem, the algorithm suggested in this paper consists of the following steps and repeats till all vertices are scanned: algorithm: prograph_shortest_path (g, e, v, w) where g = weighted connected graph e = set edges in g. v = set of vertices in g. w = weight matrix (in adjacency matrix form). assumptions: negative weighted edge (s) and self loop(s) are removed. (1) initialize: p = q = 1 (2) set i = source_vertex = 1 (3) repeat for i = 1 to |e| (4) source[p++] = source_vertex (ei) // keep source // vertices (5) end[q++] = terminal_vertex (ei) // keep terminal // vertices (6) m=1 // determines number of nodes in prograph (7) repeat for j = 1 to |e| (8) if i = source(j) (9) continue (10) else (11) i= source(j) (12) m++ (13) set i = 1 // source vertex (14) spl[i] = 0 // source distance is 0 (15) k = 1 (16) x[k++] = y[k++] = 0 // lists to check // termination condition (17) repeat for i = 2 to |v| (18) spl[i] = ∞ // initialize shortest path to // all vertices from source // with unknown value. (19) x[k++] = y[k++] = 0 (20) z = 1 (21) t = 0 // termination condition (22) n = 1 // node 1 of prograph (23) k = j = i = 1 (24) repeat while source[j] = i through line 32 // compute spl from n to its adjacents (25) if end[j] = source_vertex (26) j++ (27) continue // skip edge (source(j), end(j)) (28) spl[end(j)] = min{spl[end(j)], spl[source(j)] + w(source(j), end(j)} (29) y[k++] =1 (30) j++ (31) i = source[j] (32) n = n + 1 (33) if n ≤ m (34) go to line 24. (35) repeat for i = 1 to |y| (36) if x[i] ≠ y[i] (37) t = 1 (38) break (39) repeat for i = 1 to |y| (40) x[i] = y[i] (41) if t = 1 (42) z++ // determines number of iterations (43) go to line 21. (44) exit etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 90-97 94 www.etasr.com bhowmik and �ag chowdhury: prograph based analysis of ssspps with few distinct positive lengths complexity analysis: the running time complexity of the ()__pr pathshortestograph algorithm could be analyzed in the following ways: (1) the number of edges e with non-negative weight can be found in ω(|e|) time. (2) lines 3 – 5 enqueue source and terminal vertices in two lists needed for relaxation [8] and needs ω(|e|) time. (3) lines 6 – 12 compute number of nodes m which are to be in our ographpr . this can also be computed in ω(|e|) time. (4) now, m ≤ |v|, before relaxation of edges, all the vertices are assumed to have unknown cost (shortest path reachable from source) with reachable path length of source vertex s is 0]1[ =source . these initializations necessitate ω(|v|) time. (5) whenever two consecutive instances of the ographpr of the underlying problem are identical, relaxation is stopped. this checking is done z (a constant) times. this z naturally is reasonably a very small non-negative integer number. generally z is 2. (6) reachable tentative path lengths from source vertex s to other vertices v are computed through lines 21 – 43. these relaxations will be continued till yx = . thus, overall running time complexity of the algorithm executes in θ(z|v||e|) time. since z is a constant and has numerical value 2 in general, thus the proposed algorithm runs in θ(|v||e|) time. viii. experimental results in this section we will now look at an example of how our suggested algorithm works on a weighted digraph shown in figure 5 to solve ssspp in optimal way with ographpr . fig. 5. weighted digraph for spl computation now, the edge set e = {(v1,v2), (v1,v4), (v1,v5), (v2,v1), (v2,v3), (v2,v4), (v3,v1), (v3,v4), (v3,v5), (v4,v2), (v4,v3), (v4,v5), (v5,v3), (v5,v4)}. when there are no cycles of negative length, we know that there is a shortest path between two vertices. the digraph in figure 5 contains 5== vn vertices. so, a spl between any vertices has at most 1−n edges on it. the proposed algorithm during execution examines updating spl on the cost matrix w constructed in table ii along with its reflection on the nodes of the ographpr worked out in sequence from figure 7 through figure 12. table ii. adjacency matrix of the graph shown in figure 5 suppose, 1vs = , the first vertex (source of journey) is appeared in spl . we follow the convention vertex iv simply as vertex i . so, path length for s is 0]1[]1[ == splvspl . for simplicity, we need to have spl from this s to remaining vertices. typical initial configuration of the ographpr would look like as figure 6. fig. 6. initial arrangement of prograph for spl from vertex 1 node 1 consists of source vertex s and its adjacent vertices. similarly, it is applicable to other nodes. however, each node each is related in top-down manner. tentative path length value of a vertex in a node of the ographpr will be treated with its present value in next node if the vertex appears. but source vertex s would not be appeared as adjacent of the current vi \ vj v1 v2 v3 v4 v5 v1 0 4 ∞ 5 14 w[i][j] = v2 2 0 8 7 ∞ v3 8 ∞ 0 1 3 v4 ∞ 9 5 0 2 v5 ∞ ∞ 7 3 0 etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 90-97 95 www.etasr.com bhowmik and �ag chowdhury: prograph based analysis of ssspps with few distinct positive lengths vertex in current node. following iterations give details how to compute spl from s through relaxation [8] of edges in e . iteration i: x[1… n] = y[1… n] = {0} compute node 1 (n1) relaxing edges with starting vertex 1 i.e. 1v spl [2] = min {spl [2], spl [1] + w [1][2]} = min {∞, 0 + 4} = 4 y[2] = 1 spl [4] = min {spl [4], spl [1] + w [1][4]} = min {∞, 0 + 5} = 5 y[3] = 1 spl [5] = min {spl [5], spl [1] + w [1][5]} = min {∞, 0 + 14} = 14 y[4] = 1 fig. 7. computation at node 1 relaxing edges with starting vertex 2 i.e. 2v spl [3] = min {spl [3], spl [2] + w [2][3]} = min {∞, 4 + 8} = 12 y[5] = 1 spl [4] = min {spl [4], spl [2] + w [2][4]} = min {5, 4 + 7} = 5 y[6] = 1 fig. 8. computation at node 2 relaxing edges with starting vertex 3 i.e. 3v spl [4] = min {spl [4], spl [3] + w [3][4]} = min {5, 12 + 1} = 5 y[7] = 1 spl [5] = min {spl [5], spl [3] + w [3][5]} = min {14, 12 + 3} = 14 y[8] = 1 fig. 9. computation at node 3 relaxing edges with starting vertex 4 i.e. 4v spl [2] = min {spl [2], spl [4] + w [4][2]} = min {4, 5 + 9} = 4 y[9] = 1 spl [3] = min {spl [3], spl [4] + w [4][3]} = min {12, 5 + 5} = 10 y[10] = 1 spl [5] = min {spl [5], spl [4] + w [4][5]} = min {14, 5 + 2} = 7 y[11] = 1 fig. 10. computation at node 4 relaxing edges with starting vertex 5 i.e. 5v spl [3] = min {spl [3], spl [5] + w [5][3]} = min {10, 7 + 7} = 10 y[12] = 1 spl [4] = min {spl [4], spl [5] + w [5][4]} = min {5, 7 + 3} = 5 etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 90-97 96 www.etasr.com bhowmik and �ag chowdhury: prograph based analysis of ssspps with few distinct positive lengths y[13] = 1 fig. 11. computation at node 5 now y is compared with x . if both are same, no further visit of nodes in the ographpr takes place. otherwise content of y is transferred to x follow by start computing spl from s again as the above procedure. in iteration i it is just observed that yx ≠ . computation needs again relaxation beginning with first edge (source [1], end [1]). after iteration i the ographpr would look like as illustrated in figure 12. fig. 12. shortest path length from vertex v1 to others in iteration i minimum path length in terms of edge cost from source vertex 1v to all remaining vertices is shown in association with starting vertex of every node vi%i ≤≤1, . proceeding in the same way ( z times) we would have our preferred solution. as 2=z , the ographpr of the final solution would be same as portrayed in figure 12 at the end of iteration ii, since no change does takes place. thus, spl from source vertex s to rest of the vertices can be viewed at a glance like as figure 13. fig. 13. shortest path length from vertex v1 to others fig. 5 every node ):( c%i in figure 13 represents a node vi%i ≤≤1, and its associated cost say c )..( splei from s . ix. comparison study the 23 ps model could be solved easily with bfs [8, 16] graph traversal algorithm under a special case when all weights are 1 or shortest paths with unweighted graphs [12]. theoretically, most efficient known algorithm for the problem was devised by dijkstra in the year 1959 and since then it is known as the dijkstra’s algorithm [8, 16]. it is believed that first polynomial run time algorithm for shortest path problem which is based on greedy approach is this dijkstra’s algorithm. dijkstra's original algorithm runs in o(n 2 ) time. later the algorithm has been implemented more efficiently in o((m + n)logn) ≈ o(mlogn) time. however, this algorithm does not work on the digraphs with negative edge weights. richard bellman, samuel end and lester ford jr. solved the underlined problem with more powerful approach called dynamic programming [8, 11, 16]. and the algorithm they devised is popular as bellman-ford algorithm. it runs in θ(n 3 ) time and θ(mn) time whenever adjacency matrix and adjacency list are used correspondingly [16]. although few non-negative edge weights have been considered in the proposed 23 ps model, it allows negative edge weights without any “loss of generality” [8, 11] of the dynamic programming approach. therefore, this algorithm which also runs in θ(mn) time using adjacency matrix, should be considered preferable due to its open acceptability and powerfulness of dynamic programming [4] and superb easy understandable way to represent solution using ographpr . the illustration computes a shortest-path tree similar to bfs tree. x. concluding remarks our optimization technique is to detect vertices with exact distance labels from source vertex s . it should be noted that the proposed algorithm is competitive to algorithms used commonly in practice for shortest path computations. we implemented our approach without adjacency list representation of cost matrix and are able to estimate overall complexity in θ(|v||e|) time. two lists x and y in this paper etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 90-97 97 www.etasr.com bhowmik and �ag chowdhury: prograph based analysis of ssspps with few distinct positive lengths have replaced the significance of the adjacency list. we showed that our algorithm has better time complexity over classical bellman-ford algorithm. still no algorithm is known that is asymptotically faster for this ssspp . before we draw a concluding remark it should have to be brought up to date that our algorithm suggests and in addition yields exact result whenever negative weighted edges are allowed. acknowledgment the first author would like to express heartily gratitude to his beloved madhurima mondal and her friends, b.tech 3 rd year students, department of computer science & engineering, bengal college of engineering and technology, durgapur, india for their useful notes with solved assignments without which the draft of this paper would not be completed in time. the author would also like to convey his thankfulness to dr. s. ranbir singh, assistant professor, department of computer science & engineering, indian institute of technology guwahati for his valuable suggestions, and remarks. references [1] james b. orlin, kamesh madduri, k. subramani, m. williamson , “a faster algorithm for the single source shortest path problem with few distinct positive lengths”, journal of discrete algorithms, elsevier, vol. 3, no. 1, pp. 1-10, 2009 [2] ammar w. mohemmed, nirod chandra sahoo, “efficient computation of shortest paths in networks using particle swarm optimization and noising metaheuristics”, discrete dynamics in nature and society, vol. 2007, no. 4, pp. 1-25, 2007 [3] rogger s. pressman, software engineering – a practioner’s approach, mc-graw hill, 2001 [4] biswajit bhowmik, “dynamic programming – its principles, applications, strengths, and limitations”, international journal of engineering science and technology, vol. 2, no. 9, pp. 4822 – 4826, 2010 [5] f. b. zahn, c. e. noon, “shortest path algorithms: an evaluation using real road networks”, transportation science, vol. 32, no. 1, pp. 65–73, 1998 [6] g. desaulniers, f. soumis, “an efficient algorithm to find a shortest path for a car-like robot”, ieee transactions on robotics and automation, vol. 11, no. 6, pp. 819–828, 1995 [7] david eppstein, “finding the k shortest paths”, 1997, available at http://www.ics.uci.edu/»eppstein/. [8] thomas h. coremen, charles e. leiserson, ronald l. rivest, clifford stein, introduction to algorithms, phi, 2008 [9] biswajit bhowmik, “studies on dimultigraph and prograph based applications of graph theory in computer science”, international journal of computer and communication technology, vol. 1, no. 2, 3, 4, pp. 57-61, 2010 [10] n. deo, graph theory with applications to engineering and computer science, phi, 2002 [11] biswajit bhowmik, design and analysis of algorithms, s. k. kataria and sons, 2011 [12] http://gabrielistrate.weebly.com [13] ravindra k. ahuja, kurt mehlhorn, james b. orlin, robert e. tarjan, “faster algorithms for the shortest path problem”, journal of the association for computing machinery, vol. 37, no. 2, pp. 213-223, 1990 [14] m.h. alsuwaiyel , algorithms design techniques and analysis, phei, 2003 [15] d. samanta, classic data structures, phi, 2010 [16] ellis horowitz, sartaj sahani, sanguthevar rajasekaran, fundamentals of computer algorithms, golgotia, 1998 [17] surender baswana, tobias friedrich, somenath biswas, piyush p. kurur, benjamin doerr, frank neumann, “computing single source shortest paths using single-objective fitness functions”, foga’09, january 9–11, 2009 [18] http://theory.cs.uiuc.edu/~jeffe/teaching/algorithms/notes/13-sssp.pdf [19] farrukh shehzad, muhammad akbar ali shah, “evaluation of shortest paths in road network”, pakistan journal of commerce and social sciences vol. 3, pp. 67 – 79, 2009 authors profile biswajit bhowmik is a very renowned faculty member currently with bengal college of engineering and technology, durgapur, india as assistant professor in the department of computer science & engineering. he is a member of different professional bodies such as ieee, iacsit, iaeng, pass, iaoe, and uacee. he is also member of some leading professional societies such as ieee computer society, ieee communications society, iaeng society of computer science, iaeng society of software engineering, iaeng society of wireless networks, and iaeng society of artificial intelligence. he is reviewer of several international journals such as ijcsic, ijcsis, jacsm, ijoat, jwmc etc in the area of computer science. he has authored a book titled design and analysis of algorithms. he has many publications in international journals including international conference proceedings on the subjects ranging from algorithms analysis, graph theory, compiler design, and mobile computing. in addition his area of interests includes data structures & algorithms, software engineering, computational geometry, and green computing. he has guided several projects at under graduate level. sreyasi 3ag chowdhury is a 3 rd year ug (b.tech) student in the department of computer science & engineering at bengal college of engineering and technology, durgapur, india. microsoft word etasr_v11_n2_pp6902-6906 engineering, technology & applied science research vol. 11, no. 2, 2021, 6902-6906 6902 www.etasr.com maddah: predicting flux rates against pressure via solution-diffusion in reverse osmosis membranes predicting flux rates against pressure via solutiondiffusion in reverse osmosis membranes hisham a. maddah department of chemical engineering king abdulaziz university rabigh, saudi arabia hmaddah@kau.edu.sa abstract-this paper suggests a new method of predicting flux values at reverse osmosis (ro) desalination plants. the solutiondiffusion model is utilized to determine the osmotic pressure drops for seawater sources. the same technique was applied to the groundwater source at the abqaiq plant (500 ro plant) to calculate the osmotic pressure. the calculated osmotic pressures were utilized to determine the appropriate flux rates and membrane resistances of different bwro toray membranes and a performance comparison between various membranes has been established. the model results confirm an inverse relationship between membrane thickness and water flux rate. also, a proportional linear relation between the overall water flux and the applied pressure is identified. higher flux rates and lower salinity indicate lower membrane resistance yielding higher production. the modeled data predict that bwro toray tm720d-440 with an 8" membrane is the optimal choice for treating waters from the three water sources at the abqaiq plant. keywords-reverse osmosis; treatment; desalination; modeling i. introduction the solution-diffusion model is a popular expression used to explain the transport in dialysis, reverse osmosis, gas permeation, and pervaporation. previous experimental data and modeling results verified that the flux rate is proportional to the gradient in the chemical potential [1]. there are two different models that describe and control the permeation in membranes for better separation. the first model is the solution-diffusion model where permeants dissolve (sorption) in the membrane material at the upstream interface in the presence of a concentration gradient that allows permeants to diffuse through the membrane and desorbed on the downstream interface side. the separation between different permeants occurs because each material has a different diffusion rate in the membrane. the solution-diffusion model has been used since 1940 to explain the transport of gases across polymeric membranes. a second model, called the pore-flow model, depends on the presence of a pressure gradient for a convection flow of permeants through the membrane's tiny pores, and is more limited compared to the first model. exclusion or filtration of larger permeant's pores is the separation technique explained via the pore-flow model [1, 2]. there is a major difference between the solution-diffusion model and the pore-flow model in expressing the chemical potential. in the solution-diffusion model, the pressure within a membrane is uniform and the chemical potential gradient is expressed only as a concentration gradient. solution-diffusion membranes transmit pressure in the same way as liquids, which is the reason for expressing the pressure difference across the membrane as a concentration gradient only. on the other hand, the chemical potential gradient in the pore-flow model is expressed only as a pressure gradient since the concentrations of both solvent and solute within a membrane are uniform. comparisons between the two models for a one-component solution in a pressure-driven permeation system were conducted in [1, 2]. the objective of this work is to estimate the osmotic pressure drop value of the high rejection brackish water ro membrane (toray tm720d-400 with 8") by using the solutiondiffusion model that is applied to the abqaiq plant (500 ro plant) for shedgum/abqaiq groundwater at saudi aramco, dhahran, saudi arabia. osmotic pressure drops have been calculated for the groundwater, the arabian gulf water, and the red sea water at the same plant configuration and operating conditions of the abqaiq plant in aramco. the calculated osmotic pressures are utilized to determine the applied pressure drop across the membrane and the applicability of using different bwro toray membrane types for the treatment of seawater. the maximum achievable water flux values are determined for the various suggested bwro membranes for the three water sources. also, the membrane resistance values have been investigated for comparison purposes. the ideal membrane for the treatment of various water sources at a ro plant with the same configuration of the abqaiq plant has been selected. the feasibility of using bwro membranes in the desalination of red sea water in jeddah, saudi arabia is studied at the same flux rate of the arabian gulf water source and the same plant conditions. osmotic pressure drop, applied pressure drop, flux rates, and membrane resistance values for the red sea water source were compared with those of shedgum/abqaiq groundwater and arabian gulf water. ii. reverse osmosis in reverse osmosis, water flows from the salt solution to the pure waterside by applying pressure (∆�) that is greater than the osmotic pressure (∆�) [1]. generally, in reverse osmosis, the condition ∆� > ∆� must be satisfied all the time to allow water to pass through the membrane and reach the permeate corresponding author: hisham a. maddah engineering, technology & applied science research vol. 11, no. 2, 2021, 6902-6906 6903 www.etasr.com maddah: predicting flux rates against pressure via solution-diffusion in reverse osmosis membranes side [1, 2]. reverse osmosis membranes are preferred over ultrafiltration and nanofiltration since they are capable of removing 90 to 99% of tds in water [3]. the osmotic pressure ∆π is defined as the pressure difference �� − �ℓ across the membrane. if a pressure higher than the osmotic pressure is applied to the feed side of the membrane [1]. this process is called the reverse osmosis. the driving forces in a reverse osmosis membrane according to the solution-diffusion and the pore-flow models are visualized in [1]. �� and � are the chemical potential and activity coefficient, respectively, of component i [1]. iii. method and equations collected abqaiq 500 ro plant data (table i) have been used to determine osmotic pressure drop values for the ro membrane (toray tm720d-400 with 8") from (1) and (2). however, in order to calculate the osmotic pressure for seawater sources, the same information of shedgum/abqaiq groundwater at abqaiq 500 ro plant was applied, except for the flux and salinity values, for the treatment of either the arabian gulf or the red sea waters as listed in table i [1, 4]. water permeability is approximately determined to be 9.5×10 -7 cm 2 /s [8]. for water-salt solution, reverse osmosis permeation expression can be simplified as [1, 5]: �� = �(�� − ��) (1) � = ���������ℓ (2) where �� is the membrane flux of component �, water (gfd), δ� is the applied pressure drop across the membrane (psi), δ� is the osmotic pressure drop across the membrane (psi), a is the water permeability constant (cm/atm×s), �� is the permeability of component � , water (cm2/s), ��� is the initial mole concentration of water (ppm), �� is the water molar volume (cm 3 /mol), t is the w ater temperature (k), r is the gas constant, and ℓ is the membrane thickness which is assumed to be similar to spacer thickness (mil). membrane resistance [8] constants for each bwro toray membrane have been calculated by using (3). �� = ∆%& ℛ( (3) where �� is the membrane flux of component �, water (gfd), δ� is the applied pressure across the membrane (psi), ) is the dynamic viscosity of water (lb s/ft 2 ), and ℛ* is the membrane resistance (1/ft). π = ℳ-. (4) in (4), ℳ is the molar concentration of dissolved species (mol/l), r is the ideal gas constant (0.08206l.atm/mol.k), and t is the water temperature (k). equation (5) defines the ability of a membrane to separate salt from the feed solution which is known as membrane removal percentage (/) and it increases with the applied pressure. the feed tds concentration is taken from the three studied sources, as shown in table i, while the outlet tds concentration is determined by using (5) at a similar removal percentage of toray tm720d-400 with 8’’ membrane that is 99.8% (table iv). the water molecular weight (18g/mol) should be used to convert the ppm values to molar concentrations of tds. / = 0�1�2�1ℓ�1� 3 × 100 (5) where / is the membrane removal percentage, �7� is the initial concentration of component 8, salt (ppm), and �7ℓ is the final concentration of component 8 (ppm). table ii shows the applied pressure drop must be at 20psi or below per element (ro module) and 60psi or below per vessel [4, 6]. the assumption of having equal pressure on membranes per vessel would simplify our calculations. altaee’s study showed that permeate flow, pressure and recovery rate are distributed almost equally to membranes per ro vessel [10]. a field study confirmed an improved performance by rearranging the elements in pressure vessels in order to reduce the pressure drop and permeate conductivity across the vessel [11]. typical flux rates and maximum recovery values for the groundwater and the two studied water source scenarios (the arabian gulf and the red sea waters) at abqaiq 500 ro plant are given in table iii. table i. data of ro membrane process at abqaiq 500 ro plant and the two seawater studied scenarios [1, 4, 6, 7] parameter shedgum/abqaiq groundwater arabian gulf water red sea water membrane type toray tm720d-400 with 8" ro module 72 parallel membranes × 8 units membrane thickness (ℓ) [3] assumed to be similar to spacer thickness of 34 ;�< membrane area (�=>?) [3] 400ft2 max pressure drop per vessel (∆�) ~60psi max pressure drop per membrane (∆�) ~20psi water salinity (���)* ~2800 [4] ~41070 [6] ~42070 [7] membrane water flux (�� )* ~18gfd ~12 gfd ~12 gfd water temperature (.) 25c water permeability constant (��)** 9.5×10-7cm2/s water molar volume (��) 18cm3/mol gas constant (-) 8.2057×10-5m3.atm/mol.k *averaged values ** taken from [2], regardless of the temperature effect on permeability. can be calculated at different temperatures [16] engineering, technology & applied science research vol. 11, no. 2, 2021, 6902-6906 6904 www.etasr.com maddah: predicting flux rates against pressure via solution-diffusion in reverse osmosis membranes table ii. operating design limits of the overall ro module at abqaiq 500 ro plant [4, 12, 13] operating limits maximum operating pressure 600psi (4.1mpa) maximum feed water temperature 113°f (45°c) maximum feed water sdi15 5 feed water chlorine concentration not detectable feed water ph range, continuous operation 2-11 feed water ph range, chemical cleaning 1-12 maximum pressure drop per element 20psi (0.14mpa) maximum pressure drop per vessel 60psi (0.4mpa) table iii. characteristics of groundwater source and studied water sources at the abqaiq 500 ro plant [4] water source shedgum/abqaiq groundwater arabian gulf red sea feed silt density index @ab < 3 @ab < 4 @ab < 4 typical target flux (gfd) 18 12 12 max. element recovery (%) 19 14 14 the determined osmotic pressure values for the ro membrane (toray tm720d-400 with 8") of the groundwater and the two studied water sources are used again in (1) to calculate the applied pressure drop and suggested flux values. the same osmotic pressure drop for each case is utilized to determine the results of different toray bwro membrane types at high, low, and standard operating pressure as shown in table iv. tm-720-370 and tm720-440 are standard bwro membranes and tm720c-440, tm720l-400, and tm720l440 are low-pressure bwro membranes whereas tm720da400, tm720d-400, and tm720d-440 are highpressure bwro membranes. it is worth mentioning that our applied pressure drop must be higher than the calculated osmotic pressure in order to have a positive flux. ts-diagrams [7] are used to determine the exact value of water densities at different feed sources from the average water temperature and water salinity (table v). the exact water densities allow us to convert gas constant values from m 3 .atm/mol.k to kg.atm/mol.k to progress calculations. table iv. toray brackish water ro 8’’ diameter membranes [13, 14] category type rejection (%) thickness (mil)* standard bwro tm720-370 99.7 31 tm720-440 99.7 28 highpressure bwro tm720da400 99.8 31 tm720d-400 99.8 34 tm720d-440 99.8 28 low-pressure bwro tm720c-440 99.2 28 tm720l-400 99.5 31 tm720l-440 99.5 28 * the membrane thickness is assumed to be the same as spacer thickness table v. water densities from ts-diagrams [4, 6, 7, 15] water source temperature (°c) salinity (ppm) density (kg/m 3 ) shedgum/abqaiq groundwater 25 2800 [2] 999.19 arabian gulf 25 41070 [4] 1027.97 red sea 25 42070 [6] 1028.67 iv. results and discussion equations (1) and (2) allow us to calculate the osmotic pressure drop for each water source (table vi). the osmotic pressure of the groundwater source is less than the arabian gulf and the red sea water sources which is related to the flux rates and water salinity. flux rates for the arabian gulf and the red sea waters are approximately the half of the groundwater source. however, the water salinity of the groundwater source is much lower than the other sources. therefore, the required applied pressure drop must be larger in the case of seawater sources due to their higher determined osmotic pressure values. since the plant configuration has 8 elements per vessel, we should have a maximum osmotic pressure of 60psi or less per vessel which is equivalent to a max pressure of 7.5psi per membrane, assuming that the pressure is distributed equally on membranes per vessel. the selected applied pressure range for our study is 6.5 to 7.5psi. maximum pressure values are assigned to the different membranes based on their category as illustrated in table vii. table vi. calculated osmotic pressure drop (∆�) for each water source water source a (cm/atm.s) ji (cm/s) ji/a (atm) ∆π (atm) ∆π (psi) ∆π per vessel < 60 (psi) shedgum/ abqaiq groundwater 0.00808 0.00083 0.1028 0.44 6.48 51.84 arabian gulf 0.00755 0.00056 0.0742 0.47 6.90 55.21 red sea 0.00754 0.00056 0.0743 0.47 6.90 55.20 table vii. assigned pressure values for toray bwro membranes category type ∆d eange (dfg)* standard bwro tm720-370 6.50 7.25 tm720-440 6.50 7.25 high-pressure bwro tm720da400 6.50 7.50 tm720d-400 6.50 7.50 tm720d-440 6.50 7.50 low-pressure bwro tm720c-440 6.50 7.00 tm720l-400 6.50 7.00 tm720l-440 6.50 7.00 * high and low-pressure values are taken relative to the standard pressure the relationship between the applied pressure drops and the overall water flux rates for the groundwater source are obtained in figure 1(a)-(c) for standard, high-pressure, and low-pressure toray bwro membranes. figure 1 shows that the maximum possible flux for the groundwater in the standard membranes is around 11gfd for tm720-440 membrane. in figures 3(b) and 3(c) the highest observed groundwater flux in the high-pressure and low-pressure membranes are 14.7gfd for tm720d-440 and 7.5gfd for tm720c-440 and tm720l-440 respectively (blue and green lines overlap). this observation is associated with the membrane thickness in which the least membrane thickness (28mils) has been capable to achieve the highest flux. this confirms an inverse relationship between the membrane thickness and the water flux rate. further, there is a linear relationship between the applied pressure drop and the overall water flux. engineering, technology & applied science research vol. 11, no. 2, 2021, 6902-6906 6905 www.etasr.com maddah: predicting flux rates against pressure via solution-diffusion in reverse osmosis membranes fig. 1. effect of different applied pressures on the groundwater flux for (a) toray standard bwro membranes, (b) toray high-pressure bwro membranes, and (c) toray low-pressure bwro membranes. figure 2 identifies a proportional relationship between the water flux and the applied pressure across the membrane. the highest recorded flux is accounted for tm720d-440 for shedgum/abqaiq groundwater because water tds is low for groundwater and tm720d-440 has the lowest thickness and the highest pressure range. the arabian gulf and the red sea water sources almost have similar flux rates at the same applied pressures due to the similarities in their water salinity levels. tm720c-440, tm720l-400, and tm720l-440 membranes reserved the lowest flux values since they are categorized as low-pressure bwro membranes. fig. 2. observed water flux for various water sources at different applied pressures using toray bwro membranes. figure 3 demonstrates the membrane resistance for the three studied water sources. seawater sources have higher membrane resistances than the groundwater source because of their lower flux and higher tds. tm720l-400 has the highest membrane resistance since it is in the low-pressure category and has the highest membrane thickness of 31mils. equation (4) calculations are shown in table viii. the study predictions estimated that the overall osmotic pressure drops required for seawater and groundwater treatment plants are approximately 55psi and 830psi respectively. the higher the salinity difference between the fed and the produced water, the more the osmotic pressure drop we need to overcome in order to produce treated water (positive flux). fig. 3. observed membrane resistance of various water sources in toray bwro membranes. table viii. van't hoff calculations for the required osmotic pressures water source concentration (mol/l) membrane removal (%) osmotic pressure (atm) |∆i| (psi) tdsin tdsout πin πout |∆i| shedgum/ abqaiq groundwater 0.156 0.00031 99.8 3.81 0.01 3.80 55.80 arabian gulf 2.282 0.005 99.8 55.82 0.11 55.71 818.41 red sea 2.337 0.005 99.8 57.18 0.11 57.07 838.34 v. conclusion the application of the solution-diffusion model to the abqaiq plant (500 ro plant) is initiated by using various parameters to calculate the osmotic pressure of toray tm720d-400 with 8" membrane for shedgum/abqaiq groundwater treatment. for the same membrane, the osmotic pressure values are determined for the arabian gulf and the red sea waters to predict flux rates in other membranes for seawater situations. low, standard, and high pressure bwro toray membranes performances have been compared to identify the optimal membrane for treating saline water from the three studied water sources at the abqaiq 500 ro plant. engineering, technology & applied science research vol. 11, no. 2, 2021, 6902-6906 6906 www.etasr.com maddah: predicting flux rates against pressure via solution-diffusion in reverse osmosis membranes the assumption of having a membrane thickness that is similar to its spacer thickness may not seem very accurate. however, it is true that we should have a proportional relation between both thicknesses which suggests that our results are still valid. a linear relationship has been observed between the water flux and the applied pressure drops. it is proved that membrane flux decreases with the increase in membrane thickness at constant pressure drop. modeling results endorse that bwro toray tm720d-440 with 8"membrane is the optimum membrane choice for the water treatment from the three water sources at abqaiq 500 ro plant since it has the lowest membrane resistance and the highest overall water flux. references [1] j. g. wijmans and r. w. baker, "the solution-diffusion model: a review," journal of membrane science, vol. 107, no. 1, pp. 1–21, nov. 1995, https://doi.org/10.1016/0376-7388(95)00102-i. [2] d. r. paul, "reformulation of the solution-diffusion theory of reverse osmosis," journal of membrane science, vol. 241, no. 2, pp. 371–386, oct. 2004, https://doi.org/10.1016/j.memsci.2004.05.026. [3] h. a. maddah and a. m. chogle, "applicability of low pressure membranes for wastewater treatment with cost study analyses," membrane water treatment, vol. 6, no. 6, pp. 477–488, nov. 2015, http://dx.doi.org/10.12989/mwt.2015.6.6.477. [4] abqaiq plants: 500 ro plant, operator handbook. dhahran, saudi arabia: saudi aramco company: training & career development center, 2008. [5] a. sagle and b. freeman, "fundamentals of membranes for water treatment," the future of desalination in texas, vol. 2, no. 363, 2004, art. no. 137. [6] r. smith, a. purnama, and h. h. al-barwani, "sensitivity of hypersaline arabian gulf to seawater desalination plants," applied mathematical modelling, vol. 31, no. 10, pp. 2347–2354, oct. 2007, https://doi.org/10.1016/j.apm.2006.09.010. [7] e. a. abdel-aal, m. e. farid, f. s. m. hassan, and a. e. mohamed, "desalination of red sea water using both electrodialysis and reverse osmosis as complementary methods," egyptian journal of petroleum, vol. 24, no. 1, pp. 71–75, mar. 2015, https://doi.org/10.1016/j.ejpe. 2015.02.007. [8] j. c. crittenden, r. r. trussell, d. w. hand, k. j. howe, and g. tchobanoglous, mwh’s water treatment: principles and design, 3rd ed. hoboken, nj, usa: john wiley & sons, 2012. [9] j. prausnitz, r. lichtenthaler, and e. g. de azevedo, molecular thermodynamics of fluid-phase equilibria, 3rd edition. upper saddle river, nj, usa: pearson, 1998. [10] a. altaee, "a computational model to estimate the performance of 8 inches ro membranes in pressure vessel," journal of membrane and separation technology, vol. 1, no. 1, pp. 60–71, oct. 2012. [11] s. s. madaeni, m. afshar, n. jaafarzadeh, f. tarkian, and k. ghasemipanah, "rearrangement of membrane elements in the pressure vessels for optimum utilization of reverse osmosis process," chemical engineering research and design, vol. 89, no. 1, pp. 48–54, jan. 2011, https://doi.org/10.1016/j.cherd.2010.04.021. [12] "toraytm720d-400 with 8"," in romembra® toray ro membrane, tokyo, japan: toray corporation, 2011. [13] "brackish water & sea water membranes, tm (inner connecter type) datasheets," in romembra® toray ro membrane, tokyo, japan: toray corporation, 2016. [14] maintenance and handling manual for membrane elements (rev. 105, 106). poway, ca, usa: toray membrane usa, 2016. [15] t. beer, environmental oceanography, 2nd ed. boca raton, fl, usa: crc press, 1996. [16] h. a. maddah, "application of finite fourier transform and similarity approach in a binary system of the diffusion of water in a polymer," journal of materials science and chemical engineering, vol. 4, no. 4, pp. 20–30, apr. 2016, https://doi.org/10.4236/msce.2016.44003. authors profile hisham maddah is an independent researcher and a faculty member working with the chemical engineering department at king abdulaziz university in rabigh (kau-rabigh). he has been awarded a full scholarship and received his phd in "naturally-sensitized photoanodes for molecular photovoltaics" from the university of illinois at chicago (uic) by summer 2020. he has completed his ms and bs in chemical engineering in the university of southern california (usc) in 2017 and kau in 2012 respectively. he is an expert in organic-inorganic dye-sensitized solar cells for solar energy harvesting. his research interests include mini-passive solar stills, machine learning for solar-desalination systems, membrane separation, capacitive deionization, and activated carbons for water treatment, separation technologies, and higher education administration. he has published more than 50 articles and 3 book chapters in reputed international peer-reviewed journals and conferences and co-arranged 5 outreach activities on thirdgeneration solar cells. microsoft word faraji-ed.doc etasr engineering, technology & applied science research vol. 2, no. 5 2012, 273-277 273 www.etasr.com seifouri et al: numerical analysis of shb effects in laterally-coupled distributed feedback… numerical analysis of shb effects in laterallycoupled distributed feedback (lc-dfb) lasers mahmood seifouri shahid rajaee teacher training university, faculty of ece, lavizan, tehran, iran mahmood.seifouri@srttu.edu fatemeh shahshahani alzahra university, faculty of science vanak, tehran, iran f.shahshahani@alzahra.ac.ir ata faraji shahid rajaee teacher training university, faculty of ece, lavizan, tehran, iran airin_208@yahoo.com abstract—in this paper the stability of laterally-coupled distributed feedback (lc-dfb) lasers against the spatial hole burning (shb) effect is analyzed theoretically. the stability of the laser structure is evaluated using the flatness parameter f. it is shown that the lc-dfb lasers are stable in a wide range of different values of ridge width and amplitude grating. the stability is sustained with increasing injection current. the results show that the flatness parameter is minimal for certain values of the amplitude grating. the numerical calculations have been done by coupled wave and carrier rate equations on the basis of the transfer matrix method (tmm). keywords-component; laterally coupled distributed feedback laser; spatial hole burning; rate equation; coupled wave equation; transfer matrix method i. introduction the semiconductor dfb lasers, due to their low threshold current, narrow line width and single mode capability, are considered as an important optical source in communications systems [1]. conventional dfb lasers with coupling refractive index with end facets coated with anti reflection, ar, are not single-moded and have two symmetrical modes relative to bragg mode that appear simultaneously in the laser output [2]. one way for having a single mode in ar-dfb laser is by employing an equivalent phase shift at the center of the grating in the structure [3, 4]. this laser, which is also named qws – dfb, has high efficiency but is sensitive to the reflection at the facets [5]. another major problem of this structure is its high non-uniformity in the distribution of photons in the direction along the length of the cavity which in turn results in undesirable spatial hole burning (shb). this is because of the effect of phase shift which causes instability in the laser [6]. on the other hand, lc-dfb lasers use a lithographic fabrication step to define the distributed feedback grating, avoiding subsequent regrowth. by avoiding regrowth steps, these lasers may be monolithically integrated with other optoelectronic devices [7, 8].this makes this type of lasers not only easier to fabricate but also less expensive. this article reports, for the first time, on the stability of lc-dfb lasers against shb, considering both the structural parameters and alterations of the density of carriers and photons along the length of the cavity structure and its dependence to the current above threshold conditions. the theoretical analysis is carried out by simultaneous solving both the coupled wave and rate equations using the transfer matrix method. in section 2, theory and the physical model are explained. section 3 explains the results and section 4 summarizes the conclusions. i. theoretical and physical model figure 1 illustrates a simple design of a five-layered lcdfb laser and its features. in this figure, d, h and t are the active, buffer and wave guide layer thicknesses respectively. a clearer view of a lc-dfb laser is depicted in figure 2. as shown, there is a grating over the waveguide at both sides of the central area which in turn makes distributed reflection in the laser. fig. 1. simple design of a dfb laser structure with lateral coupling fig. 2. the schematic of laterally-coupled distributed feedback laser [10]. etasr engineering, technology & applied science research vol. 2, no. 5 2012, 273-277 274 www.etasr.com seifouri et al: numerical analysis of shb effects in laterally-coupled distributed feedback… we consider the direction of the electric field along y-axis, te mode. electromagnetic waves propagate both in positive and negative directions along the z-axis in the cavity. the modified coupled-mode equations, first described by streifer, are given by [9]:      =−− =− )()( )( )()( )( zajzaj dz zdb zbjzaj dz zda κδ κδ (1) where a and b are the forward and backward propagating complex amplitudes of the field respectively; κ is the coupling coefficient between forward and backward propagating modes; 0ββδ −= is the bragg wavelength detuning; λ= πβ m0 is the propagation constant, in which m is the grating order. carrier density in the active region follows the rate equation. this equation for single-moded dfb laser is as follows [11]: [ ] ),(),(),(),( ),( 2 tzstzgtzcntzbna qd j t tzn −+++ = ∂ ∂ (2) where ),( tzn and ),( tzs are carrier and photon densities respectively, j is input current density; q is the electronic charge; d is the active layer thickness; a, b and c are the nonradiative, spontaneous and auger rates respectively. photon density at every point is proportional to the sum of the square of forward and backward traveling wave amplitudes. in (2), stimulated emission rate g is equal to: ),(),( tzgvtzg matg = (3) in which g v is the group velocity and ),( tzgmat has linear relationship with carrier density, as shown in (4) below [12]: ]),([),( tnmat ntznatzg −= (4) where t n is the carrier density in transparency conditions and n a is the differential gain coefficient. the refractive index changes in the active region in the following equation depend on carrier density [13]: π λα 4 ),( ),( 0 tzna tzn nh ∆ −=∆ (5) in which h α is the line width coefficient and n∆ is the carrier density fluctuation with relation to the threshold conditions. also δ above threshold conditions considering the changes in the refractive index is as follows: λ −γ∆+= π λ π δ n nntz eff )( 2 ),( 0 (6) where λ is the grating period and eff n is the effective refractive index. equation (7) shows the relationship between mat g and the modal gain, almod α [14]: ac alm mat g γ + = mod 2 αα (7) in this equation ac γ is the optical confinement factor in the active layer and almod α is the average internal loss. the values of m α and δ are obtained by using the boundary conditions )0()0( 1 srr = and )()( 2 lrrls = . 1 r and 2 r are the reflection coefficients of the mirrors that are assumed to be zero here. the stability of the laser against shb effect is measured using the flatness parameter f, which is defined as follows: ∫        −= l avg dz i zi l f 0 2 1 )(1 (8) in (8), i(z) is the optical field intensity along the cavity length and avg i is the average value of i(z). 22 )()()( zezezi sr += (9) the smaller the value of f, the more uniform is the distribution of light field along the cavity and less is the possibility of the existence of shb. experimentally it has been shown that for sustainable performance of single mode dfb laser f should be less than 0.05 [6]. analysis is based on solving both the coupled wave equations (1) and rate equation (4) simultaneously. the method employed based upon tmm [15, 16]. etasr engineering, technology & applied science research vol. 2, no. 5 2012, 273-277 275 www.etasr.com seifouri et al: numerical analysis of shb effects in laterally-coupled distributed feedback… in this method, the cavity length is divided in to 200 equal parts and in every part, different parameters of the laser including coupling coefficient, carrier density, refractive index and density of photons are assumed to be constant. but their values are different from one part to the next. ref. [10] has been used as the bench mark for our calculations for threshold conditions to the first order grating. the values of the parameters used in our calculations are presented in table 1. in lc-dfb laser structure by choosing a suitable ridge height and width and also an appropriate input current, we will obtain a structure with minimum flatness parameter above the threshold conditions. table i. the values of the parameters parameters values cavity length (l) 500 mµ laser wavelength ( 0λ ) 1.5 mµ buffer layer thickness (h) 150 nm waveguide layer thickness (t) 150 nm internal dissipation of the active layer ( intα ) 20 1−cm improved line width coefficient ( 0α ) 6 nonradiative combination rate (a) 10 8 s -1 spontaneous recombination rates (b) 8× 10-11 13 −scm auger recombination rates (c) 7.5× 10-29 16 −scm for our modeling purposes, first we have employed the effective refractive index method [17], and have calculated the changes both in the x-and y-directions. ultimately, we then used the tmm only along the z-direction. the above procedure makes our simulation in all 3 directions. we have considered the effective refractive index under the ridge and the area around it. we then used our effective index calculations to compute the lateral coupling coefficient on both sides of the ridge. ii. evaluation of results in figure 3, the flatness parameter in terms of the grating amplitude, a, for three different values of the ridge width, w, (1.5, 2, 2.5 mµ ) is depicted and as shown, the flatness parameter for certain values of the grating amplitude is minimum. the corresponding grating amplitudes are known as the critical amplitudes, ac. this critical value depends on the width of the ridge. for example, when w=1.5 mµ , the critical amplitude is approximately 0.04 mµ . also the critical amplitude for ridge widths of 2 mµ and 2.5 mµ are 0.04 mµ and 0.07 mµ respectively. figures 5 and 6 show the same trend for different values of w and ac. it is important to note that the behavior of the photon and carrier densities for grating amplitudes, smaller and/or greater values than that of the corresponding critical amplitude are different. figure 4 is for w=1.5 mµ and ma c µ04.0= . fig. 3. flatness changes vs grating amplitude fig. 4. shows np and nc changes along the cavity length for mac µ04.0= and w=1.5 mµ . fig. 5. shows np and nc changes along the cavity length for w=2 mµ and mac µ07.0= . fig. 6. shows np and nc changes along the cavity length for w=2.5 mµ , mac µ14.0= etasr engineering, technology & applied science research vol. 2, no. 5 2012, 273-277 276 www.etasr.com seifouri et al: numerical analysis of shb effects in laterally-coupled distributed feedback… as shown, when c aa〈 , photons density np at the two ends of the laser is increased and when c aa〉 photons density at the center of structure has its maximum value. when c aa = , the photon density has its least changes as compared to other values of a . this is also true for the carrier density, nc in the structure. this behavior of lc-dfb laser shows that in critical amplitude regime, shb has the least effect on the laser. figures 7-9 illustrate the flatness parameters in terms of the input current for mw µ5.1= , mw µ2= , mw µ5.2= respectively. it can be seen from the figures that the minimum flatness parameter is achieved at the critical amplitude, ac even though the input current is on the rise. fig. 7. flatness parameter vs. input current for different value of grating amplitudes with w=1.5 mµ . fig. 8. flatness parameter vs. input current for different value of grating amplitudes with w=2 mµ . figure 10 shows the changes of flatness parameter in terms of varying input current for different grating amplitudes. it is shown that the structure relating to the critical amplitude, has the minimum flatness parameter f. also it is important to note that the structure with critical parameter ac has the minimum changes of f with changing current. this fact indicates that the best stability against shb is achieved with those structures with critical amplitudes. fig. 9. flatness parameter vs. input current for different value of grating amplitudes with and w=2.5 mµ . fig. 10. changes of flatness parameter in terms of varying input current for different grating amplitudes ii. conclusion flatness parameters in lc-dfb lasers in and above threshold conditions are analyzed theoretically. calculations show that the f parameter has the least value for different structures at critical amplitude and at points close to the corresponding critical amplitude is less than 0.05. considering the changes of both carrier and photon densities along the cavity and also above the threshold, shows that the minimum density changes occur for structures with critical amplitudes. also changes in f for different structures at critical amplitudes, above threshold conditions with increasing input current, are negligible. these results show the high stability of lc-dfb lasers against shb effect with increasing input current. references [1] k. nosu, k. iwashita, “a consideration of factors affecting future coherent lightwave communication”, j. lightwave technol. vol. 6, no. 5, pp. 686-694, 1988 [2] h. kogelnik, c. v. shank, “coupled-wave theory of distributed feedback lasers”, j. appl. phys., vol. 43, no. 5, pp. 2327-2335, 1972 [3] k. utaka, s. akiba, k. saki, y. matsushima, “ 4λ -shifted ingaasp dfb laser,” iee j. quantum electron., vol. 22, no. 7, pp. 1042-1051, 1986 [4] h. ghafouri-shiraz, b. s. k. lo, distributed feedback laser diodes: principles and physical modelling, john-wiley & son, 1996 [5] j. kinoshita, k. matsumoto, “yield analysis of sml dfb lasers with an axially-flattened internal field”, iee j. quanrum electron., vol. 25, pp. 1324-1332, 1989 etasr engineering, technology & applied science research vol. 2, no. 5 2012, 273-277 277 www.etasr.com seifouri et al: numerical analysis of shb effects in laterally-coupled distributed feedback… [6] h. soda, y. kotaki, h. sudo, h ishikwa, s. yamakoshi, h. imai, “stability in single longitudinal mode operation in single longitudinal mode operation in gainasp/inp phase-adjusted dfb lasers”, ieee j . quantum electron., vol. 23, no. 6, pp. 804-814, 1987 [7] r. millett, k. hinzer, t. hall, h. schriemer “simulation analysis of higher order laterally-coupled distributed feedback lasers”, ieee j. quantum electron. vol. 44, no. 12, pp. 1145-1151, 2008. [8] r. millett, h. schriemer, t. hall, k. hinzer, “properties of laterallycoupled distributed feedback lasers with higher order gratings,” nusod '08, international conference on numerical simulation of optoelectronic devices, pp. 13-14, united kingdom, 2008 [9] w. streifer, d. r. scifres, r. d. burnham, “coupled wave analysis of dfb and dbr lasers”, ieee j. quantum electron., vol. 13, no. 4, pp. 134–141, 1977. [10] j. wang, j. tian, p. cai, b. xiong c. sun, y. luo, “1.55µ m algainas–inp laterally coupled distributed feedback laser”, ieee photonics technology letters, vol. 17, no. 7, pp. 1372-1374, 2005. [11] g. p. agrawal, a. k. dutta, semiconductor lasers, van nostrand reinhold, 1966 [12] m. osinsky, m. j. adams, “gain spectra of quaternary semiconductor”, iee proc. in solid-state and electron devices, vol. 129, no. 6, pp. 229236, 1982 [13] s. f. yu, “double-tapered-waveguide distributed feedback lassers for high-power single mode operation”, iee j. quantum electron., vol. 33, no. 1, pp. 71-80, 1997 [14] k. david, j. buus, g. morthier, r. baest, “coupling coefficients in gain coupled dfb lasers: inherent compromise between coupling strength and loss”, ieee photonics technology letters, vol. 3, no. 5, pp. 439441, 1991 [15] f. shahshahani, v. ahmadi, “analysis of relative intensity noise in tapered grating qws-dfb laser diodes by using three rate equations model”, solid-state electronics, vol. 52, no. 6, pp. 857-862, 2008 [16] t. makino, “transfer-matrix formulation of spontaneous emission noise of dfb semiconductor lasers”, j. lightwave technol., vol. 9, no. 1, pp. 84-91, 1991 [17] g. agrawal, fiber-optic communication system. john wiley & sons, 1992 microsoft word etasr_v11_n2_pp7054-7059 engineering, technology & applied science research vol. 11, no. 2, 2021, 7054-7059 7054 www.etasr.com vu et al.: a novel modeling and control design of the current-fed dual active bridge converter … a novel modeling and control design of the current-fed dual active bridge converter under dpdps modulation phuong vu school of electrical engineering hanoi university of science and technology hanoi, vietnam phuong.vuhoang@hust.edu.vn do tuan anh school of electrical engineering hanoi university of science and technology hanoi, vietnam tuananhdo.hust@gmail.com hoang duc chinh school of electrical engineering hanoi university of science and technology hanoi, vietnam chinh.hoangduc@hust.edu.vn abstract-this paper proposes a novel control design for a current-fed dual active bridge (cfdab) converter in boost mode. the double pwm plus double phase shifted (dpdps) modulation is applied to the converter due to its considerable merits. a small-signal model is developed to control the output voltage stably in boost mode. simulations of the control design for the cfdab converter were conducted to verify the proposed model. the results show that the system can achieve high performance, not only in the dynamic response but also in the steady-state. keywords-current-fed dual active brigde (cfdab) converter; small-signal model; double pwm plus double phase shifted (dpdps) modulation i. introduction nowadays, the growth in renewable power systems urges researchers and engineers to solve the problems of managing integrated storages and exchange powers to enhance overall system efficiency. in order to connect the battery at low voltage to the dc link at high voltage in a storage system, the utilized dc/dc converter needs to have a high gain voltage factor and an ability of bidirectional transferring power. the dc/dc converters can be classified as isolated and non-isolated. between these two, the isolated dc/dc converter is highly recommended for its high reliability. it is able to eliminate current leakage in the system. this undesired current is the cause of emi, additional loss, and unsafe installation and operation [1]. another advantage of the isolated dc/dc converter is that the flexible gain ratio can be obtained by using a high frequency transformer [2, 3]. the dual active bridge (dab) converter belongs to the isolated dc/dc type and is well-known for its advantages of high frequency operating ability, inherit zero voltage switching, and bidirectional power flow [4-6]. the structure of the dab can have modified flexibly with different power sources [7-8]. the dab converter is divided into two categories: voltage-fed (vfdab) and current-fed (cfdab). when using the vfdab structure in a variety of applications [9-11], the voltage source is directly supplied to the converter, which produces high current ripple and becomes large and costly. besides, the vfdab needs a bulky capacitor in series-connection with the primary coil to avoid the flux saturation of the transformer [11]. therefore, the cfdab structure is used to deal with these problems, the input interleave boost inductors in cfdab help to decrease the current ripple significantly, and zvs can be achieved for all switches over a wide range of load [9-12]. on the other hand, a small-signal model needs to be built for the accurately controlling problem. naturally clamped cfdab modeling structure has been introduced in [13, 14]. besides, a state-space model under spspwm modulation for interleaved boost cfdab structure is mentioned in [15]. in the current research, dpdps modulation technique in comparison with spspwm modulation [9] is applied, and a small-signal model to regulate the output voltage is built up in boost mode. the simulation results show the effectiveness of the proposed method. ii. research method a. operation principles and control structure 1) operation principles the applied structure of cfdab converter in this research is presented in figure 1, which consists of 2 main parts: the interleaved boost part and the dual active full-bridge part. in the interleaved boost part, two dc inductors are considered as two current sources. the inductor ldc1 is combined with the left leg containing the switch pair q1, q1a to create the first boost converter, while the right leg containing the q2, q2a switch pair is combined with the inductor ldc2 to create the second boost converter. these boost converters are 180˚ phase-shifted in order to compose an interleaved boost part, in which the boost voltage is kept by the clamp capacitor cc. on the other hand, the dual active full-bridge part consists of two h-bridge modules in two sides of an isolated high frequency transformer with the turn ratio of n: 1. corresponding author: phuong vu engineering, technology & applied science research vol. 11, no. 2, 2021, 7054-7059 7055 www.etasr.com vu et al.: a novel modeling and control design of the current-fed dual active bridge converter … r fig. 1. structure of the cfdab converter. the voltages of the clamp capacitor and the output capacitor are assumed as the low-voltage side (lvs) and high-voltage side (hvs). the bidirectional transfer power between the lvs, the hvs, and the power flow are determined by the phase shifted angle. the ac inductor lr, which is the sum of the primary-referred transformer leakage inductor, which can be considered as a power link between the two sides of the converter. 2) modulation strategy due to the high amount of switch devices and inductors, the modulation strategy for the converter needs to be considered before designing the control loop. to handle the voltage ratio variation problems and to minimize the conduction loss in power transfer stages, the pwm plus phase shifted (pps) is introduced while the duty cycle for hvs switches is equal to 50% and the duty ratio for the main lvs switches q1, q2 is a variable d. however, in the non-power transfer stage of pps, the circulation loss is significant with high leak current spike. an additional phase shifted in double pwm plus double phase shifted (dpdps) method [9], which equals to (2d 1) / 2 s t− × , is applied to eliminate the leak current spike. figure 2 illustrates the modulation rule of the cfdab converter, where the phase shifted between q1 – q2, q2 – s1 and s1 – s4 are 180˚, ϕ and s ϕ respectively. the value of e ϕ determines the power flow and direction, where 0 e ϕ > represents the operation boost mode with power flow from lvs to hvs and vice versa. by utilizing dpdps modulation, 8 operation modes in one switching period along with leakage current, the switching lvs voltage and the transformer voltage waveform vcd are displayed in figure 3 [9]. phase shifted sawtooth phase shifted d 0.5 phase shifted fig. 2. dpdps modulation technique for the cfdab converter. ab v cd v lr i 1 q 1a q 1 q 2 q 2a q 2a q 3 s 3 s 1 s 2 s 2 s 4 s 0 π 2π mode i mode ii mode iii mode iv mode v mode vi mode vii mode viii tω tω tω ϕ 2 dπ (1 )2d π− cv fig. 3. pulse patterns, transformer voltage, and leakage current waveforms. 3) control structure for cfdab converter structure, the transfer power is related to the clamp voltage vc and the phase shifted eϕ between the two h-bridges. therefore, the control structure in boost mode has to control the voltage of the clamp capacitor and the output capacitor simultaneously. there are two pairs of control variables: vc−d and vo−ϕ , as presented in figure 4. lead-lag duty ratio primary phase shift pri and sec q1 q2a s1 s4 battery discharge d pi vc-control fig. 4. control structure in boost mode. b. small signal modeling it is required to determine the transfer functions of the two pairs of control variables mentioned above so that the control scheme in figure 4 can be implemented. the transfer function perturbations between clamp voltage ˆ c v and duty ratio d̂ is depicted in (1) [9]: engineering, technology & applied science research vol. 11, no. 2, 2021, 7054-7059 7056 www.etasr.com vu et al.: a novel modeling and control design of the current-fed dual active bridge converter … ( )1 2 _ 2 2ˆ ˆ 2 (1 ) 2 c c r l lc v d r d v l i iv g d l c s d ϕ ω ϕ ω ϕ π − + = = + − − (1) in this paper, the small signal model along with the closed loop controller is proposed to regulate the output voltage of the converter under dpdps modulation. in the secondary side, the output capacitor is charged and discharged in power transfer and non-power transfer stage respectively. from the switching sequence in figure 3, the time interval of each switching mode is given by: 1 3 5 7 4 8 2 6 2 1 , 2 1 2 2 d d d d d d d d d d ϕ π ϕ π  = = = =  = = −  −  = = −  (2) the relationship between small signals of variables is presented in table i for 8 modes in one dpdps switching period. the inductors and capacitors are considered as ideal, i.e. the internal resistors are neglected. the continuous-time equation of output voltage is defined as: ( ) ( ) ( ) ( ) 4 8 1 2 3 4 5 6 7 8 5 5 1 1 o o o vdv c c n d d dt lr v d d d d d d d d r v vc c nd nd l lr r ϕ ω π θ ϕ θ ϕ ω ω = − + − + + − − + + − + − + − − (3) using the average model: 7 2 , 2 c c d v v ϕ θ π= + = , 3 (2 1) 2 d ϕ θ π= − + we can obtain: ( ) ( ) ( ) 0 0 4 8 1 5 0 1 2 3 4 5 6 7 8 2 c c r r v vdv c n d d n d d dt l l v d d d d d d d d r ϕ ϕ ω ω = + + + + − + + − − + + − (4) replacing (2) to (4) we get: ( ) 2 0 0 0 4 3 2 (1 ) 2 c r dv v v c d n d dt r l ϕ ϕ π ω  − = − + + −    (5) using the perturbations of duty ratio, phase-shifted angle output voltage, and clamp voltage we have: ( ) 00 2 ˆ ˆ( ) ( )ˆ4( ) 3 ˆˆ( ) ˆˆ2( )(1 ( ) 2 o o o c c r d v v v v c d d dt r v v n d d l ϕ ϕ π ω + + = + − +   +− φ+ + + φ+ − +    discarding the steady-state value and the second order perturbations and assuming that ˆ ˆ 0 cc d v= = we get: ( ) 2 0 0 0 4 3 2 (1 ) 2 c r dv v v c d n d dt r l ϕ ϕ π ω  − = − + + −    (7) by laplace transformation, the transfer function from ô v to ϕ̂ in the frequency domain can be expressed as: ( )_ 0 (2 2 ) 4 3o c v r r nrv d a g rl c s l d bs c ϕ π ω ω φ − − = = − − + (8) table i. small signal model in each switching mode mode continuoustime equations mode i [0, φ] ( )0 00 , c ts lr lr r vdv v c ni i dt r l θ ϕ ω = − − = − mode ii [ ,(2 1) ]dϕ π− 0 0 0 , 0 lr dv v c i dt r = = mode iii ( ) ( )2 1 , 2 1d dπ π ϕ− − +   ( )0 00 , 2 1 c ts lr r vdv v c i d dt r l θ π ω = = − −   mode iv ( )2 1 ,d π ϕ π− +   0 0 0 , c ts lr lr r vdv v c ni i dt r l ϕ ω = − + = mode v [ ],π π ϕ+ ( ) 0 0 0 , c ts lr lr r vdv v c ni i dt r l π θ ϕ ω = − + = − + mode vi [ ],2dπ ϕ π+ 0 0 0 , 0 lr dv v c i dt r = = mode vii [ ]2 ,2d dπ π ϕ+ [ ] 0 0 0 , 2 c ts lr r vdv v c i d dt r l θ π ω = = − − mode viii [ ]2 ,2dπ ϕ π+ 0 0 0 , c ts lr lr r vdv v c ni i dt r l ϕ ω = − − = − c. simulation verification the control design with the proposed method is firstly verified by simulation in matlab/simulink (figure 5). the specifications of the converter are given in table ii and the transfer function in frequency domain between ô v and ϕ̂ is turned into: 4 _ ˆ 1.643 10 ˆ 0.3213 4.7 o vo v a g bs c s ϕ ϕ × = = = + + (9) a pi controller is applied to regulate the output voltage: 1 (1 ) c p g k tis = + (10) where ti is equal to the pole of _ovg ϕ : 0.068 i b t c = = . the output voltage close loop transfer can be written as: 1 1 k k g t s = + (11) engineering, technology & applied science research vol. 11, no. 2, 2021, 7054-7059 7057 www.etasr.com vu et al.: a novel modeling and control design of the current-fed dual active bridge converter … with * k p b t a k = . by choosing 45* 10 k s t t −= = , kp = 0.276. the simulation scenario consists of 4 steps: the clamp capacitor is charged from 0 to 0.2s, at 0.2s the vc controller starts and the lvs switches are enabled, at 0.25s the vo controller starts and in the final step, the load changes suddenly to the nominal value. figures 6, 7 show the simulation results of clamp and output voltage respectively. as can be observed, in the start-up period, the voltages of the two capacitors are charged and controlled to increase gradually as well as track the reference values with negligible error and no over-shoot. fig. 5. simulink model for the control of the cfdab converter in boost mode. table ii. simulation parameters specification symbol value nominal power pn 2500w input voltage vin 144v output voltage vout 400v duty ratio d 0.64 clamp voltage vc 391v switching frequency fs 50khz nominal duty cycle d 0.64 nominal phase-shifted φ 0.241 fig. 6. voltage response on the clamp capacitor. fig. 7. voltage response on the output capacitor. furthermore, the currents through the boost inductor and the leakage inductor with little spike in the start interval which ensure the feasibility of the control design in the experiment, are shown in figures 8 and 9. the clamp voltage and the out voltage decrease slightly, about 3v, at 0.45s when the nominal load is changed. after that, they quickly return to the reference value within 0.01s and 0.03s. in steady-state operation, the voltages on both the lvs and hvs side of the transformer along with leakage current are shown in figure 9. due to the engineering, technology & applied science research vol. 11, no. 2, 2021, 7054-7059 7058 www.etasr.com vu et al.: a novel modeling and control design of the current-fed dual active bridge converter … small difference between the reference of clamp voltage and the output voltage, the bias current in the leakage current helps hvs switches achieve the zvs easier [16]. in addition, the switches voltage and current are presented for s1 and q2 in figures 10 and 11. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 -10 0 10 20 30 ildc1 ildc2 fig. 8. interleaved-boost current in simulation. 0.63262 0.63263 0.63264 0.63265 -400 -200 0 200 400 vab 0.63262 0.63263 0.63264 0.63265 -400 -200 0 200 400 vcd 0.63262 0.63263 0.63264 0.63265 -10 0 10 ilr fig. 9. voltage on the two sides of the transformer and leakage current. 0.63152 0.63153 0.63154 0 200 400 <s1 voltage> 0.63152 0.63153 0.63154 -10 0 10 <s1 current> fig. 10. voltage and curent on switch device s1. iii. conclusion the current paper presents the control structure along with the modeling of the cfdab converter in boost mode. a small signal model is built up with the chosen modulation technique to control the output voltage of the converter. simulations were carried out to verify both the proposed model and the control design. the simulation results prove the good performance of the control design not only in the steady-state but also in the dynamic responses. 0.637955 0.63796 0.637965 0.63797 0.637975 0 100 200 300 400 <q2 voltage> 0.637955 0.63796 0.637965 0.63797 0.637975 -20 0 20 40 <q2 current> fig. 11. voltage and curent on switch device q2. acknowledgment this research is funded by the vietnamese ministry of education and training under the project number ct2020.02.bka.004. references [1] w. chen, x. yang, w. zhang, and x. song, "leakage current calculation for pv inverter system based on a parasitic capacitor model," ieee transactions on power electronics, vol. 31, no. 12, pp. 8205–8217, dec. 2016, https://doi.org/10.1109/tpel.2016.2517740. [2] y. almalaq and m. matin, "two-switch high gain non-isolated cuk converter," engineering, technology & applied science research, vol. 10, no. 5, pp. 6362–6367, oct. 2020, https://doi.org/10.48084/etasr.3826. [3] k. jayaswal and d. k. palwalia, "performance analysis of non-isolated dc-dc buck converter using resonant approach," engineering, technology & applied science research, vol. 8, no. 5, pp. 3350–3354, oct. 2018, https://doi.org/10.48084/etasr.2242. [4] b. zhao, q. song, w. liu, and y. sun, "overview of dual-activebridge isolated bidirectional dc–dc converter for high-frequencylink power-conversion system," ieee transactions on power electronics, vol. 29, no. 8, pp. 4091–4106, aug. 2014, https://doi.org/ 10.1109/tpel.2013.2289913. [5] b. j. byen, b.-h. jeong, and g.-h. choe, "single pulse-widthmodulation strategy for dual-active bridge converters," journal of power electronics, vol. 18, no. 1, pp. 137–146, jan. 2018, https://doi.org/ 10.6113/jpe.2018.18.1.137. [6] b. j. byen, c.-h. ban, y.-b. lim, and g.-h. choe, "an efficiencyoptimized modulation strategy for dual-active-bridge dc-dc converters using dual-pulse-width-modulation in the low power region," journal of power electronics, vol. 17, no. 6, pp. 1413–1421, nov. 2017, https://doi.org/10.6113/jpe.2017.17.6.1413. [7] m. l. mendola, m. di benedetto, a. lidozzi, l. solero, and s. bifaretti, "four-port bidirectional dual active bridge converter for evs fast charging," in 2019 ieee energy conversion congress and exposition (ecce), baltimore, md, usa, sep. 2019, pp. 1341–1347, https://doi.org/10.1109/ecce.2019.8912252. [8] n. hou and y. w. li, "a tunable power sharing control scheme for the output-series dab dc–dc system with independent or common input terminals," ieee transactions on power electronics, vol. 34, no. 10, pp. 9386–9391, oct. 2019, https://doi.org/10.1109/tpel.2019. 2911059. [9] d. sha and g. xu, high-frequency isolated bidirectional dual active bridge dc–dc converters with wide voltage gain, 1st ed. berlin heidelberg, germany: springer, 2018. engineering, technology & applied science research vol. 11, no. 2, 2021, 7054-7059 7059 www.etasr.com vu et al.: a novel modeling and control design of the current-fed dual active bridge converter … [10] a. k. rathore and u. prasanna, "comparison of soft-switching voltagefed and current-fed bi-directional isolated dc/dc converters for fuel cell vehicles," in 2012 ieee international symposium on industrial electronics, hangzhou, china, may 2012, pp. 252–257, https://doi.org/ 10.1109/isie.2012.6237093. [11] a. pressman, k. billings, and t. morey, switching power supply design, 3rd ed. new york, ny, usa: mcgraw-hill education, 2009. [12] y. shi, r. li, y. xue, and h. li, "optimized operation of current-fed dual active bridge dc–dc converter for pv applications," ieee transactions on industrial electronics, vol. 62, no. 11, pp. 6986–6995, nov. 2015, https://doi.org/10.1109/tie.2015.2432093. [13] p. xuewei and a. k. rathore, "small signal modeling of naturally clamped soft-switching current-fed dual active bridge dc/dc converter and control design using cypress psoc," in 2014 ieee international conference on power electronics, drives and energy systems (pedes), mumbai, india, dec. 2014, https://doi.org/10.1109/pedes.2014. 7041961. [14] a. pal and s. kapat, "discrete-time modeling of a naturally commutated current-fed dual active bridge dc-dc converter," in 2019 ieee applied power electronics conference and exposition (apec), anaheim, ca, usa, mar. 2019, pp. 2877–2881, https://doi.org/10.1109/apec.2019.8722235. [15] a. pal and s. kapat, "accurate discrete-time modeling of an interleaved current-fed dual active bridge dc-dc converter," in 2019 ieee applied power electronics conference and exposition (apec), anaheim, ca, usa, mar. 2019, pp. 1616–1621, https://doi.org/10.1109/ apec.2019.8721870. [16] d. sha, x. wang, k. liu, and c. chen, "a current-fed dual-activebridge dc–dc converter using extended duty cycle control and magnetic-integrated inductors with optimized voltage mismatching control," ieee transactions on power electronics, vol. 34, no. 1, pp. 462–473, jan. 2019, https://doi.org/10.1109/tpel.2018.2825991. microsoft word etasr_v11_n1_pp6730-6733 engineering, technology & applied science research vol. 1, no. 1, 2021, 6730-6733 6730 www.etasr.com samo et al.: the development of a preliminary design for a tidal energy plant the development of a preliminary design for a tidal energy plant kamran ahmed samo electrical engineering department quaid-e-awam university of engineering, science and technology larkana, sindh, pakistan kamransamo2@gmail.com azhaili baharun mechanical engineering department universiti malaysia sarawak kota samarahan, sarawak, malaysia bazhaili@unimas.my andrew ragai henry rigit mechanical engineering department universiti malaysia sarawak kota samarahan, sarawak, malaysia arigit@unimas.my abstract—renewable energy sources are considered a part of the future of energy production in malaysia. the main objectives of this research are to append a new energy extraction technique that harvests energy from tides and to develop a preliminary design for a tidal energy plant at kuching barrage. knowing the diameter of the turbine, the dimensions of the powerhouse are achieved in conjunction with site conditions. the centerline should be at least below the low water tide so that the tide is at all times guaranteed to be submerged. based on this, the powerhouse has a 24.61m length, is about 100m in distance across, and its elevation is 36.39m. the construction is located downstream and the centerline habitation at -1.15 and below lsd. the calculated tidal energy plant is comprised of four bulb-type turbines installed at each barrage gate. the bulb-type turbine blades would face the sea site with 11.32m length of the draft tube. this study detailed feasibility study can be implemented. keywords-tidal range; powerhouse; renewable energy; malaysia; kuching barrage i. introduction renewable energy in malaysia is considered a great source of energy and a factor of the green energy revolution in malaysia. the malaysian government is working on various renewable power plants across the country. the most significant renewable energy sources in malaysia are solar energy from photovoltaic (pv) panels, biogas, biomass, and small hydro. in the upcoming four years, the malaysian government proposes to generate 2080mw of electricity from renewable energy. on the other hand, the sustainable energy development authority [1] in malaysia is skeptical about achieving this target by the year 2020, since from 30th september 2015, the verified renewable energy creation was only about 319.5mw. malaysia ought to restore its responsibility regarding accomplishing the target of electricity generation from renewable resources. the current research project is expected to raise awareness regarding renewable energy in malaysia, particularly tidal range technologies, as at present there is no tidal energy plant in malaysia. unlike other known renewable energy resources, tidal range energy harvesting is an expectable phenomenon. energy production from a tidal range power can be assessed appropriately [2]. more than 80% of energy production comes from nonrenewable energy resources such as fossil and coal and they are slowly depleting [3]. about 40 sites have been recognized in the world as ideal sites for the harvesting of tidal range technology [4]. however, this site number is relatively low and no malaysian site is included among these suggested sites. the reason may be the lack of research on this area and the lack of interest of the malaysian authorities. this lack of research in malaysian tidal range energy can be overcome with further studies on the malaysian ocean and with expected technological improvements. the states sabah and sarawak have isolated regions near the coastline which have a shortage in the supply of electric power. there are various modes of electricity used to disband electricity to far-flung locales, such as grid-based and diesel-based generators which are well-known modes of electricity disband. one of the common modes of electricity is grid extension, however, it is costly, takes time, is not economically viable in certain remote areas that are not easily accessible, and often requires sophisticated technologies. it is considered that as a not very feasible mode. hence, renewable energy sources are being patronized as a green, trustworthy, and economical solution, for the far-flung areas. among various available green energy options, tidal range energy and tidal stream energy have the best potential due to the reason that they are in sheer abundance, have high density, and they are powerful and predictable and void of any weather conditions, in contrast to solar and wind that are highly subject to metrological conditions. also, their impact on environmental and human activity is less [5, 6]. corresponding author: kamran ahmed samo engineering, technology & applied science research vol. 1, no. 1, 2021, 6730-6733 6731 www.etasr.com samo et al.: the development of a preliminary design for a tidal energy plant in previous studies conducted at the coast of sarawak malaysia, researchers argued that no site in the coast of sarawak state is meeting the standards of peak speed (more than 1.5m/s) [7, 8], except pulau triso at batang lupar where maximum speed of 2.06m/s was recorded. therefore, this is a potential area to generate renewable energy from the tidal range at the east coast of peninsular malaysia that covers kelantan and terengganu [9]. according to [9], power could be generated from the existing or new barrage. worldwide, there are many barrage plants in the operation process. the sihwa dam in korea and la rance in france have mounting energy capability of 254mw and 240mw respectively [10, 11]. resource mapping is the initial stage in the development of tidal range and tidal stream schemes [11]. tidal range power generation requires power calculations using real data (tidal range and area of barrage) from the region. the real data can be displayed with the help of resource mapping by indicating the potential sites for the development of tidal energy plants. the aim of this research is to investigate the potential of coastal areas around the east malaysian states for generating tidal range power plants and also to develop a preliminary design for a tidal energy plant at the chosen areas. ii. literature review a. designing the tidal range energy plant the design of a tidal power plant at the saemangeum project in south korea was developed in [13]. in the first step, the final measurements of the turbines were calculated. the final measurements of the turbine are the diameter and centerline of the turbine. with the measurement information of the turbines, the powerhouse’s dimensions can be calculated with the combination of specification site realities [13]. dimensions of the powerhouse are the draft tube and turbine bay. the powerhouse is to be constructed at the space required of barrage gates. b. dimensions of the tidal range energy plant the calculation of the powerhouse at saemangeum was done through empirical formulas and the design process was proposed in [14, 15]. the height of the powerhouse is mainly determined by water levels. other factors may also influence the structural design, such as a projected road on the barrage and spaces for operation and maintenance. the applied experimental procedure measurements of the future site of this study are concluded. the total length, width, and elevation of the power plant for the future site can be calculated [16]. iii. development of the preliminary design of the tidal range energy plant the development of a preliminary design of a tidal energy plant at the potential site might be established on the basis of the saemangeum tidal power plant in korea [13]. knowing the diameter of the turbine, the dimensions of the powerhouse are achieved in conjunction with the specific site conditions. the centerline should be at least below the low water tide so that the turbine is at all times guaranteed to be submerged. the design of the tidal energy plant is based on the selected turbine of the chosen site. future power generation sites will be developed accordingly. cad software such as autocad is an important tool to be imparted in this ongoing project. the development of preliminary designs of tidal energy plants is also proposed. in order to achieve the novelty of this research project, a structured research flow chart with distinct phases and sets of objectives is to be established. it will comprise the development of the tidal energy plant and the generation of electricity by means of constructed barrage or new processes. experimental procedures were applied to conclude the measurements of the saemangeum powerhouse in korea [14]. it is important to know that the turbine should not disturb the lsd level and not cross the lowest tide level and the kuching barrage gate. the lsd at kuching barrage gate is –8.0m, the lowest tide level is –3.3m, so the space between lsd and the lowest tide is 4.7m. logically, the kuching barrage turbine diameter should be 2.35m. for the turbine to be under water at all times, the centerline should be at least at the depth of –1.15m. the calculated parameters and plan drawing are shown in figure 1. the measurement information of the turbine and powerhouse dimensions are calculated with the combination of specification site data and the selected bulb type turbine to be installed at kuching barrage are shown in figure 1. the total length of the kuching barrage power plant is 18.37m. since kuching barrage's low tide is at –3.30m and if the turbine diameter is 2.35m, the centerline should be at least at the depth of –1.15m. fig. 1. kuching barrage tidal energy plant powerhouse dimensions. the proposal of the kuching barrage powerhouse is exhibited in figure 2. the powerhouse is to be constructed at the downstream of the kuching barrage opening. this would faceplate the flushing process of the present barrage. the proposal in figures 1 and 2 is drawn according to the reported design. the further construction length is 24.61m, its width is 100m, and its elevation is 36.39m, as presented in figures 2 and 3. in figure 2, the powerhouse is comprised of two stop logs at the bay and the exit of the turbine. the main purpose of the stop logs is to support short-term block of water flow during maintenance works. at kuching barrage, the structure of the powerhouse and the fixing of fish screens at each gate of engineering, technology & applied science research vol. 1, no. 1, 2021, 6730-6733 6732 www.etasr.com samo et al.: the development of a preliminary design for a tidal energy plant the barrage is important. furthermore, the centerline of the powerhouse is positioned at lsd (–1.15m) to ensure that the turbine is plunged all the time. fish screens are needed to be fixed at the upstream (basin) to avoid fish incoming to the turbine area. figure 3 shows that the total width of the barrage is 125m and its length is 37m. however, the width of the barrage is taken as 100m. the four bulb-type turbines are installed at each gate of kuching barrage except gate five, which is reserved for emergencies. fig. 2. powerhouse layout of kuching barrage tidal energy plant. fig. 3. plan view of kuching barrage tidal range energy plant scheme at four gates. figure 4 illustrates the proposal of a selected bulb-type turbine at one gate of kuching barrage. it is required that the turbine must be installed below low tide level. when the hydrodynamic pressure is below the vapor pressure of the liquid, there is a formation of the vapor phase (bubbles). the formation of bubbles and their subsequent collapse is called the cavitation problem. the right hand is a basin and the left-hand shows the seaside (upstream-downstream). iv. proposed operation kuching barrage is located in sarawak and was built to mitigate the floods in kuching city. it also has the potential for the development of a tidal energy station. if the kuching barrage is being used for tidal energy harnessing, then the tidal energy plant would function during the daily flushing operation. the kuching barrage is a one-way process in which the turbine will only work at flushing times. fig. 4. schematic diagram of one gate of bulb turbine for kuching barrage. a. power generation by ebb generation the kuching barrage tidal energy plant will produce energy by ebb generation. figure 2 reports the cross-section of the suggested tidal energy plant arrangement at kuching barrage. the barrage gates are locked at all times in order to maintain the river water level and also to avoid saltwater pass into the river. the gates are unlocked for the period of daily flushing process at the ebb tide. in order to accommodate the barrage process, it is suitable to produce energy in the flushing process. furthermore, out of the three mentioned processes of power generation, ebb generation is the most suitable. the water would flow into the turbine bay, moving the turbine blades and it would flow out of the draft tube. at that time, the shaft would transfer the kinetic energy to the generator and the movement of the coil in the moving magnetic field inside the generator would produce energy. b. one-way operation with single basin system the calculated tidal energy plant consists of four bulb-type turbines installed at each barrage gate. the bulb-type turbine blades would face the seaside with the 11.32m length of the draft tube for a turbine diameter of 2.35m as shown in figures 1 and 2. the nominated bulb-type turbine is a one-way process, in which the turbine will only work during flushing. the oneway operation is better since reversible turbines are challenging and costly [2]. the kuching barrage gate will be closed, so the turbine will not be able to run. during the implementation of turbines at kuching barrage gates, flushing operation with pumping would also be supported. v. conclusion kuching barrage already exists in the pending site. therefore, it is identified as a potential site that could yield 10.23gwh/year of energy. the design of a powerhouse tidal energy plant at kuching barrage is proposed. the plant will produce power by ebb generation. the data collected from engineering, technology & applied science research vol. 1, no. 1, 2021, 6730-6733 6733 www.etasr.com samo et al.: the development of a preliminary design for a tidal energy plant kuching barrage will be also helpful in future studies. the development of the preliminary design of the tidal energy plant scheme can serve as a benchmark or reference for project proposals of similar nature. this project plays a catalyst role in the promotion and introduction of energy harnessing from tides. the proposed powerhouse length is about 24.61m, across in 100m distance, and the elevation is 36.39m. the construction is located downstream and the centerline habitation at −1.15m below lsd. the calculated tidal energy plant consists of four bulb-type turbines installed at each barrage gate. the bulb-type turbine blades would face the seaside with the 11.32m length of the draft tube. the proposed bulb-type turbine is a one-way process, in which the turbine will only work during the flushing process. the one-way operation is better since reversible turbines are challenging and costly. references [1] sustainable energy development authority malaysia, "renewable energy: current status and further development," mar. 2016. [2] s. waters and g. aggidis, "tidal range technologies and state of the art in review," renewable and sustainable energy reviews, vol. 59, pp. 514–529, jun. 2016, https://doi.org/10.1016/j.rser.2015.12.347. [3] o. yaakob, y. ahmed, m. mazlan, k. jaafar, and r. muda, "model testing of an ocean wave energy system for malaysian sea," world applied sciences journal, vol. 22, no. 5, pp. 667–671, apr. 2013. [4] a. etemadi, y. emami, o. asefafshar, and a. emdadi, "electricity generation by the tidal barrages," energy procedia, vol. 12, pp. 928– 935, jan. 2011, https://doi.org/10.1016/j.egypro.2011.10.122. [5] f. behrouzi, m. nakisa, a. maimun, and y. m. ahmed, "global renewable energy and its potential in malaysia: a review of hydrokinetic turbine technology," renewable and sustainable energy reviews, vol. 62, pp. 1270–1281, sep. 2016, https://doi.org/10.1016/ j.rser.2016.05.020. [6] k. a. samo, i. a. samo, z. a. siyal, and a. r. h. rigit, "determination of potential tidal power sites at east malaysia," engineering, technology & applied science research, vol. 10, no. 4, pp. 6047–6051, aug. 2020, https://doi.org/10.48084/etasr.3674. [7] l. chai, c. shiun, j. abdullah, g. w. chiun, j. w. k. sing, and a. r. h. rigit, "sarawak’s potential in small renewable energy," presented at the third international conference on water resources and renewable energy development in asia, sarawak, malaysia, 2010. [8] a. q. jakhrani, a. r. h. rigit, and s. r. samo, "estimation of tidal stream energy resources at sarawak coastline and their potential impact on environment.," australian journal of basic and applied sciences, vol. 7, no. 6, pp. 503–514, 2013. [9] k. n. a. maulud, o. a. karim, k. sopian, s. nur, and f. a. aziz, "determination of tidal energy resource location in east coast of peninsular malaysia using geographical information system," in proceedings of the 3rd wseas int. conf. on on energy planning, energy saving, environmental education, 2009, pp. 25–31. [10] j. xia, r. a. falconer, b. lin, and g. tan, "estimation of annual energy output from a tidal barrage using two different methods," applied energy, vol. 93, pp. 327–336, may 2012, https://doi.org/10.1016/ j.apenergy.2011.12.049. [11] tidal energy technology brief. irena, 2014. [12] z. defne, k. a. haas, and h. m. fritz, "numerical modeling of tidal currents and the effects of power extraction on estuarine hydrodynamics along the georgia coast, usa," renewable energy, vol. 36, no. 12, pp. 3461–3471, dec. 2011, https://doi.org/10.1016/j.renene.2011.05.027. [13] h. a. j. swane, "tidal power plant in saemangeum," m.s. thesis, tudelft, utrecht, neatherlands, 2007. [14] h. miller, "choice of hydro-electric equipment for tidal energy," in proceedings of the korea tidal power symposium, korea, oct. 1978. [15] j. raabe, hydro power: the design, use, and function of hydromechanical, hydraulic, and electrical equipment. düsseldorf, germany: vdi-verlag, 1985. [16] m. l. tuballa and m. l. s. abundo, "operational impact of res penetration on a remote diesel-powered system in west papua, indonesia," engineering, technology & applied science research, vol. 8, no. 3, pp. 2963–2968, jun. 2018, https://doi.org/10.48084/etasr.1984. microsoft word 25-3637_s_etasr_v10_n4_pp6027-6033 engineering, technology & applied science research vol. 10, no. 4, 2020, 6027-6033 6027 www.etasr.com marar et al.: mandible bone osteoporosis detection using cone-beam computed tomography mandible bone osteoporosis detection using conebeam computed tomography rasha f. abu marar department of computer science faculty of information technology middle east university amman, jordan ramarar82@gmail.com diaa m. uliyan department of information computer science college of computer science and engineering university of hai’l hai’l, saudi arabia d.uliyan@uoh.edu.sa hamza a. al-sewadi department of computer science faculty of information technology middle east university amman, jordan hsewadi@meu.edu.jo abstract-osteoporosis is a common health problem that affects one-third of women over the age of 50 and it may not be detected until bone fractures occur. osteoporosis is low bone mass and microarchitectural deterioration of bone tissue, which affects bone fragility and raises fracture risks. early mandible bone osteoporosis detection could help reduce the risk of jaw fracture and dental implant failure. to solve this problem, a diagnostic algorithm for automatic detection of osteoporosis in cone-beam computed tomography (cbct) images is presented and 120 mandible cbct images of 50-85 year-old women have been utilized. these images are classified into two classes: normal and osteoporotic. their classification is based on the t-score which derives from the dual-energy x-ray absorptiometry (dexa). the proposed algorithm consists of image processing, feature extraction, and artificial neural network (ann) classification. images are segmented and edges are detected. then, texture features are extracted from the segmented regions. finally, a feed-forward back-propagation ann classifier is employed. seven parameters were involved in the experiment data preparation as input: coarseness, contrast, direction, number of edges, length of edges, mean length of edges, and the number of edge pixels. the results demonstrate the effectiveness of the proposed method. with the help of the proposed method, dentists will be able to predict osteoporosis accurately and efficiently without the need for further examination since cbct has been widely accepted in dentistry and the dentist is the most common health care professional that elderly visit regularly. keywords-artificial intelligence; neural network classifiers; osteoporosis; cone-beam ct; image processing i. introduction osteoporosis is the decreased bone mass and microarchitectural deterioration of the bone scaffold, leading to bone fragility and enhanced susceptibility to fractures [1, 2]. the golden standard measurement of bone mass density (bmd), or aspects related to bone structure is dexa [3]. osteoporosis is common in the elderly whereas the dentist is often the only healthcare professional that they visit regularly. in dentistry, early detection is important as patients with osteoporosis may suffer from high risk of jaw fracture. conebeam computed tomography (cbct) has been widely accepted in dentistry since its introduction in 1998 [4]. current cbct devices do not produce grey-scale values not a calibrated housefield unit (hu) values. however, the values differ for different devices as well as on the object placement in the imaged field of view (fov) [5]. despite the ability to detect bone density and the quality of structures, some studies have been conducted on the use of hu values in detecting osteoporosis [6, 7]. authors in [8] used the evaluation of alveolar bone changes as a valuable predictor for osteoporosis. mandibular cortical index (mci), mandibular computed tomography (mct), mental index (mi), and bone loss were assessed from the radiographs. no significant relationship was found in the mi between the right and the left side at the mental foramen region, and a statistical significance between mi and mci was reported. authors in [9] found a strong correlation coefficient accuracy in predicting osteoporosis in the lumbar vertebrae and the femoral neck. there finding should be confirmed on other cbct devices, and the cervical vertebrae which rarely appears in cbct for dental matters. authors in [10] evaluated the validity of cbct for assessing mandibular bone quality using the klemetti classification which was not adequate means of assessing bone quality with cbct. authors in [11] determined the region of interest (roi) of the condyle mandibular as a biomarker for feature extraction and classification of bone conditions. bone mineral density (bmd) was classified in two classes, normal corresponding author: diaa m. uliyan engineering, technology & applied science research vol. 10, no. 4, 2020, 6027-6033 6028 www.etasr.com marar et al.: mandible bone osteoporosis detection using cone-beam computed tomography and abnormal with results with 88.0% accuracy and 88.0% sensitivity. authors in [12] found that there is no relationship between the right and the left side at the mental foramen region. also, there was a statistical significance between mi and mci. authors in [13] observed a positive correlation of spine bmd in the right and left mandibular ct values and hu measurements. the study didn’t conclude an accurate unique value for detecting osteoporosis. authors in [3] found that it is possible to predict the osteoporosis through the radiographic density (rd) related to the body of c2 and the left lateral mass of c1 more accurately than from other areas. the techniques are strict and hard to implement and the study didn’t conclude to an accurate unique value for osteoporosis detection. authors in [14] found that the risk of osteoporosis is significantly affected by the bone density of mandibular condyle, age, and gender. each of the discussed above studies achieved a certain goal, but did not conclude to an accurate value to surely detect osteoporosis from mandible cbct without the need of a dexa scan. this approach intends to design and implement image analysis and ai algorithms in order to specify feature values in cbct with the main purpose of detecting osteoporosis, by selecting mandibular rois from cbct images. the images are enhanced by processing on all rois followed by segmentation and feature extraction. these features are the potential features of the osteoporosis predictor. finally, the selected features will be used as input for classifying the patients into two classes (healthy or osteoporotic) using back propagation artificial neural networks (anns). ii. proposed method the algorithm proposed in this paper is designed for automatic detection of osteoporosis in cbct images. the system consists of six steps: (a) input the dicom image, (b) image preprocessing, (c) extraction of image features, (d) recognition using ann classifier, (e) detection of osteoporosis. figure 1 shows the overall system architecture. fig. 1. architecture of the proposed algorithm. a. input image image acquisition is the process of obtaining a mandible slice were both foramina appear simultaneously on the coronal views (the green line in figure 2). this is checked by navigating through all the cbct image slices. b. image preprocessing image preprocessing is a required preparatory step to ensure the high accuracy of the subsequent steps. preprocessing becomes necessary because most of real life data are noisy, inconsistent, and incomplete [15]. preprocessing in a bone image is a crucial initial step before texture analysis is performed. dicom images pass through the preprocessing steps which include noise removal and the elimination of redundant information as much as possible. images were taken from a cs8100 3d machine, 75kvp and 4mas. figure 3 shows the block diagram of image preprocessing. this sub section describes the steps of image preprocessing. fig. 2. mandible slice with both foramina appearing simultaneously. fig. 3. block diagram of image pre-processing steps. 1) gray scale image conversion in image recognition applications such as medical image analysis, it is common to convert the input images to grayscale since grayscale features have a good impact on recognition performance. the considered images in the proposed method are grayscale images. the method starts by reading an indexed mandible image i with rgb color map and converts it to a grayscale color map image by removing the hue and saturation features while retaining the luminance. the conversion function ᶃ takes a ������color image and converts it to a ���� representation. r values are assumed to be [0-1]. r, g, and b channels represent linear without gamma corrected features. the function is defined as follows: ᶃ� �� ��� � 0.3 �� � 0.95 �� � 0.11 �� (1) here, luminance is the standard algorithm where it is implemented by matlab's rgb2gray() function. to enhance the gamma from the image due to light inconsistency in the image, the equation can be rewritten as follows: ᶃ��������� � 1 100 !116 ∗ $!%& ' (& (2) the function ᶃ��������� is a nonlinear transformation [16] which increases the lightness to be more closely related to human perception. in our experiments c=16. f(y) is defined as: % � 0.2126 �� � 0.7152 �� � 0.0722 �� (3) and engineering, technology & applied science research vol. 10, no. 4, 2020, 6027-6033 6029 www.etasr.com marar et al.: mandible bone osteoporosis detection using cone-beam computed tomography $!%& � + % ,-, % / ! 012&�3� ∗ 4120 51 ∗ % � 612 , 789:;<=>: (4) as a result, the image f(y) is a normalized lightness image in the range [0-1]. 2) filtering acquired medical images’ visibility is often affected by light scattering. in order to detect and remove poor visibility in cone beam images, filtering process has an effective method for visibility enhancement from a single gray cone beam image. visibility enhancement techniques of degraded images are classified into three main classes: histogram equalization [17], discrete wavelet transform [18] and retinex method [19, 20]. the retinex method was developed in [20] and relies on the fact that color saturation has little or no correspondence with luminance variation. retinex is a well-known method used in image enhancement. it analyzes the illumination reflectance model of image via the following equation: �!?,%& � @!?,%& a!?, %& (5) where i is the gray scale image, l is the illumination and r is the reflectance of point lines in (x, y) position. the goal of the retinex method is to eliminate the l while retaining the reflectance component r. it improves the low-contrast images of typical poor visibility conditions via the mathematical equation: a!?,%& � @7b �!?, %& ' @7b c!?,%& ∗ �!?,%& (6) where r(x, y) represents the retinex, i(x, y) is the image distribution and ‘ ∗ ’ is the convolution operator. c!?,%& � f:g!�h i jh&/�h is the gaussian function with c being a constant equal to 16. a small value of c results in a narrower surround. k is selected such that ∬ c!?,%& m? m% � 1. the result of filtering would be like the example shown in figure 4. fig. 4. image after filtering. 3) canny edge detection canny edge detection is a standard edge detection technique. since its creation by john canny at mit in 1983, it still outperforms many newer algorithms [21]. the algorithmic steps for canny edge detection technique are: • smooth image f(r, c) with a 5×5 gaussian filter as given by: n′!?,%& � �!?,%& ∗ n!?,%& (7) where n!?,%& � 31 pq h : g r h hsh is the gaussian function with t � u1 ' 6v. • get the first derivatives in horizontal (gx) and vertical direction (gy). from these two images, we can find edge gradient and direction for each pixel as follows: n �w�� �x w���� � yn�1 � nj1 (8) and n w�x����z� � 8[\ g3!�]�r& (9) gradient direction is always perpendicular to the edges. it is rounded to one of four angles representing vertical, horizontal and two diagonal directions. • apply non-maximal or critical suppression to the gradient magnitude. • apply threshold to the non-maximal suppression image [22]. figure 5 shows the image of figure 1 after applying canny edge detection. fig. 5. image after canny edge detection. 4) segmentation image segmentation is the process of partitioning a digital image into multiple regions or sets of pixels. fig. 6. the segmented mandible image. we employed a segmentation method based on image histogram projection and otsu threshold [23] to produce a set of regions that cover the entire mandible bone image and a set of contours extracted from the image. after digitally segmenting the image to extract the inner trabecular bone, it will look like the one illustrated in figure 6, where only the engineering, technology & applied science research vol. 10, no. 4, 2020, 6027-6033 6030 www.etasr.com marar et al.: mandible bone osteoporosis detection using cone-beam computed tomography roi for the test is left, while all outer region pixels are removed. the basic idea of otsu thresholding is examining the optimal or several optimal grayscale values for splitting the inner trabecular bone as roi in a mandible bone image from the background based on their grayscale histograms. the histogram of the image i with size n×m is calculated using two main features: the gray level of a pixel $!?,%& and its local average gray level: b!?,%& = 3 �� ∑ ∑ $!? + =,% + _&�`ab � �ab . the histogram of the image is defined using probability measure as follows: c�` = xde ��� (10) where rij is the total number of occurrence of image points (i,j) in image i, and =, _ = 0, 1, . . , l-1. here, l represents the number of divergent gray scales and ∑ ∑ !c �`& � 1�g3`ab�g3�ab . the pixels in the image are classified into two main classes c0 and c1 to represent background and objects respectively via probabilities of class occurrence f and class means g as follows: (h[>> 1 → fb!>,8& = ∑ ∑ c �`�g3`ab�g3�ab (11) (h[>> 2 → f3!>,8& = ∑ ∑ c �`�g3`ab�g3�ab (12) where s and t are threshold values determined from image histogram, i.e. s=maximum (gray scale values), t=maximum (local average gray scale values). the intensity mean value vectors of the two classes and the total mean vector can be expressed as follows: gb!gbb,gb3& j = [ ∑ k!�,j&∗ldem n ,∑ �!�,j&∗ldem n�g3`ab�g3�ab ] j (13) g3!g3b,g33& j = [ ∑ k!�,j&∗ldem , ,∑ �!�,j&∗ldem ,�g3`ab�g3�ab ] j (14) and saved into the vector: gjaugbb,gb3,g3b,g33] j (15) finally, the desired threshold vector [s, t] is selected by maximizing the trace of inter class matrix as follows: o p � ∑ 3qab mr∗!srgst& h mn∗!3g mn& (16) c. feature extraction feature extraction is one of the most crucial steps for osteoporosis recognition from the mandible cbct image. hence, an extra care was taken to look for the most important trabecular bone texture features that can assist the investigation of the under study classification. to describe the mandible cbct image’s texture properties, tamura [24] suggested six different texture properties: coarseness, contrast, directionality, line-likeness, regularity, and roughness. in most cases, the first three features are used because these features capture the high-level attributes of a texture and are also useful for the browsing of images [25]. 1) trabecular bone texture features the important structure parameters to be measured in this part include seven parameters namely trabecular nodes, trabecular termini, and trabecular separation, trabecular spacing, trabecular number, trabecular thickness, and bone volume ratio [26]. some of these features are illustrated in figure 7. fig. 7. bone structure parameters. (a) trabecular nodes, (b) trabecular termini, (c) trabecular separation, (d) trabecular spacing, and (e) trabecular thickness. the seven criteria shown in the qualitative comparison for the trabecular bone structure between normal and osteoporotic bone are shown in table i. table i. normal and osteoporotic bone comparison features normal osteoporotic p1 trabecular nodes (tb.nd) high low p2 trabecular termini (tb.tm) low high p3 trabecular separation (tb.sp) low high p4 trabecular spacing (tb.sc) low high p5 trabecular number (tb.n) high low p6 trabecular thickness (tb.th) high low p7 bone volume over total volume (bv/tv) high low 2) hybrid feature of tamura texture based extraction method coarseness, contrast, direction, number of non-zero pixels, length of edges, number of edges, and mean edge length, are good indicators of the bone parameters mentioned above. if the bone has a low tb.nd, tb.n, tb.th, and bv/tv and high tb.tm, tb.sp and tb.sc then coarseness, contrast, direction, length of edges, and mean edge length will be high and the number of non-zero pixels and the number of edges will be low, which is an evidence of osteoporosis presence. if the bone has high tb.nd, tb.n, tb.th, and bv/tv and high tb.tm, tb.sp and tb.sc then coarseness, contrast, direction, length of edges and mean edge length will be low, the non-zero pixels and the number of edges will be high which means a normal bone case. coarseness, contrast and direction are evaluated by applying the extension of tamura texture features for 3d images [27]. the 3d tamura includes coarseness, contrast, and direction. a) 3d tamura coarseness its computation follows the same steps as in the 2d case, but another dimension is added to the first step, for each point (x, y, z), as in (17): uh!?,%,v& = 3 1-w ∑ x∑ $!?,%,v&ji g3`ajg y �i g3 �a�g (17) engineering, technology & applied science research vol. 10, no. 4, 2020, 6027-6033 6031 www.etasr.com marar et al.: mandible bone osteoporosis detection using cone-beam computed tomography where m=2 e−1 and e determines the size of the neighborhood, that is 2 l × 2 l × 2 l . this part of the algorithm depends on the size of particular images. in the second step of computing 3d tamura coarseness, take the differences by the same way as in 2d case but for three directions instead of two, calculated by the equations 18, 19, and 20 for the x-axis, y-axis, and z-axis, respectively. z�,� � |u�!? � 2�g3, %,v& ' u�!? ' 2�g3,%,v&| (18) z�,| � |u�!?,% � 2�g3, v& ' u�!?,% ' 2�g3,v&| (19) z�,} � |u�!?,%,v � 2�g3& ' u�!?,%, v ' 2�g3&| (20) b) 3d tamura contrast the algorithm for contrast is applicable on images of any dimensionality, and the feature from tamura's set can be derived in the 2d case by simply adding another dimension. tamura contrast in 3d is used in the same way as it was presented for the 2d case. c) 3d tamura directionality 3d tamura directionality cannot be derived straight forwardly in the 2d case. first, it is needed to form convolution kernels to compute the derivation in three directions along the three axes as shown in figure 8. (a) (b) (c) fig. 8. convolution kernels (a) kernel x, (b) kernel y, and (c) kernel z. these kernels are used to create derivatives in the x-axis (∆x), y-axis (∆y), and z-axis (∆z) by convolution with the input image. then following are calculated: ~3 � tang3 ∆�∆� � p1 (21) ~1 � tang3 ∆�∆� � p1 (22) ~� � 8[\g3 ∆�∆� � p1 (23) then the 16 bin histogram is created with each of n values, where n ϵ<1, 2, 3>. then the final result is acquired in the same way as in the 2d case. four more parameters were suggested and calculated by the authors, namely the number of non-zero pixels, the length of the edges, the number of the edges, and the mean edge length. these features will be used as the input parameters for the ann classifier, whose output would classify the patient as having osteoporosis or not. the ann will be trained according to the steps described below. d. the bp-nn classifier many methods such as k-nearest neighbor (knn), support vector machine (svm), or anns can be used for classification. in this work, an ann will be implemented as the classifier with back propagation training algorithm based on the deepest-descent technique. the applied ann is able to minimize the error of nonlinear functions of high complexity, and is provided with a suitable number of hidden units [28]. 1) the proposed diagnosis model a feed-forward back propagation ann (bpann) is proposed to perform the classification for the diagnosis of osteoporosis. the bpann consists of three layers: an input layer, one hidden layer, and an output layer. fifteen hidden layer neurons are created and trained. the input and target samples are randomly chosen and automatically divided into 60% for training, 40% for validation and test sets. sigmoid signal is selected as the activation function. the sigmoid function is a non-linear s-shaped curve function which is suitable for classification problems. it is a strictly increasing function. the input layer neuron number is determined by the number of features selected. the input neurons correspond to the seven input features (p1 to p7 of table i). the number of neurons of the output layer is determined by the number of expected targets, which can take only two values in the proposed work, namely either 1 or 0 corresponding to the osteoporosis test which can be either positive or negative. the number of hidden neurons is determined by the hecht-nielsen theorem [29] which states that any continuous function can be represented by a neural network that has only one hidden layer with exactly 2n+1 nodes, where n is the number of input nodes. the proposed ann is shown in figure 9. fig. 9. architecture of the bpann (7:15:1) 2) learning methods of the bpann supervised learning is implemented during the learning process. in this process, the expected output is already presented to the network. the collected data, in which the patient is already known as either an osteoporosis case or not are divided into two groups, one is used for training the ann and the other is used for testing the trained network [30]. matlab is used as the computation tool for the training and implementation of the classification phase. the summary of the network components and parameters for the ann classifier are listed in table ii. table ii. architecture and parameters of the ann architecture (bpann classifier) number of input neurons, n 7 number of hidden layers 1 number of neurons in hidden layer, m 15 number of output layer neurons 1 activation function sigmoid learning method (rule) back-propagation learning rate, α 0.1 number of iterations (epochs) 32 measurements cross-entropy engineering, technology & applied science research vol. 10, no. 4, 2020, 6027-6033 6032 www.etasr.com marar et al.: mandible bone osteoporosis detection using cone-beam computed tomography iii. experimental results the extracted feature names and meanings for the involved data in the experiment for the mandible cbct images that are practically used in the experimentation on the proposed scheme are shown in table iii. table iii. definitions of the used input variables input parameter feature p1 coarseness p2 contrast p3 direction p4 number of edge pixels p5 length of edges p6 number of edges p7 mean edge length the proposed method has been implemented using matlab 2018b. the database contains 120 cbct images, organized in two classes, each consisting of 60 images, normal and osteoporotic. seventy two images were used for training and 48 were used for testing. table iv is the confusion matrix for the proposed bpann classifier. table iv. confusion matrix for classification n=48 prediction: healthy prediction: osteoporotic total actual: healthy tn=23 fp=1 24 actual: osteoporotic fn=0 tp=24 24 total no. of images 23 25 48 tn: true negative, fn: false negative, tp: true positive, and fp: false positive to evaluate the performance of the classifier, basically three metrics can be used, namely precision, recall, and accuracy. these measures are defined below. accuracy � ������ �� ��������� ���������� �.����� ��� ��� ����� ������ �� ������� ��� ��� (24) precision � �����  �����¦�� �����  �����¦��i§����  �����¦�� 0 ¨ p ¨ 1 (25) recall � �����  �����¦�� �����  �����¦��i §���� ������¦�� 0 ¨ r ¨ 1 (26) evaluating accuracy, precision, recall, and f1-score for the bpann classifier using the above equations resulted in the values summarized in table v. the classifier converged in 35 epochs. table v. bpann classifier performance testing sample percentage accuracy (a) precision (p) recall (r) f1-score 40% from the dataset. 97.917% 0.96 1 0.97959 applying the ann to distinguish between healthy and osteoporotic persons resulted to almost 98% successful classification rate of the testing set. table vi lists the training state values (the cross entropy) as a function of the number of iterations. these state values are clearly shown in figure 10, which shows that the best validation performance occurs at 2.8548e-007 at epoch 35, which is the lowest possible value in our calculations using matlab. table vi. cross-entropy values for number of epochs number of epochs training validation testing 5 0.03862 0.02563 0.03862 10 0.005012 0.001818 0.003238 15 0.0007033 0.0002521 0.0004626 20 9554e-05 2.27e-05 6.118e-05 25 1.294e-05 3.229e-06 7.279e-05 30 1.853e-06 3.601e-07 1.169e-06 35 9e-09 5.576e-08 9e-09 fig. 10. cross-entropy calculation as a function of the number of epochs. iv. conclusion as cbct images are inevitably used by dentists to evaluate the bone adequacy for dental implants, the proposed algorithm is designed to utilize the mandible trabecular bone properties found in these images for the early detection of osteoporosis. the experimental data set consists of 120 cbct image slices obtained anonymously from local cbct radiology centers. the performance of the suggested feed forward bpann classifier was measured by precision, recall, and accuracy which were 0.96, 1, and 97.917%, respectively. it is worth mentioning 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[30] c. peterson, t. rognvaldsson, and l. lonnblad, “jetnet 3.0—a versatile artificial neural network package,” computer physics communications, vol. 81, no. 1–2, pp. 185–220, jun. 1994, doi: 10.1016/0010-4655(94)90120-1. microsoft word etasr_v10_n6_pp6570-6577 engineering, technology & applied science research vol. 10, no. 6, 2020, 6570-6577 6570 www.etasr.com danikas & sarathi: alternative fluids – with a particular emphasis on vegetable oils – as … alternative fluids – with a particular emphasis on vegetable oils – as replacements of transformer oil a concise review m. g. danikas department of electrical & computer engineering, democritus university of thrace, greece mdanikas@ee.duth.gr ramanujam sarathi indian institute of technology madras, department of electrical engineering, high voltage laboratory, india rsarathi@iitm.ac.in abstract-for many decades transformer oil has served as a wellknown insulating medium. its electrical properties, among others, have been studied in length. in recent years, with the increasing concern for the environment, alternative insulating liquids have been proposed. in the context of this concise review, such alternative fluids are investigated. some conflicting evidence regarding experimental results that still persist are discussed and aspects of vegetable oils in need of further work are pointed out. keywords-alternative fluids; vegetable oils; transformer oil; mineral oil; dielectric strength; breakdown voltage; oxidation; fluid viscosity; cooling function; flash point; fire point i. introduction during the last decades, transformer oils, consisting of a mixture of hydrocarbons including paraffins, isoparaffins, naphthenes and aromatics, have enjoyed extensive use [1]. such a liquid undergoes aging depending on its exposure to prolonged heating and electrical stresses. aging of transformer oil results to gradual change in its electrical and thermal properties, i.e. a change in color and a formation of solid byproducts. transformer oil, although an excellent insulating medium, has also its weak aspects, such as its sensitivity to humidity (it has been reported, for example, that oil at 20 o c with water contents of 44ppm will have only 25% of its normal dielectric strength [2]). various studies have been carried out regarding the properties and aging of transformer oil, such as the dielectric strength, the humidity content, the role of air bubbles on its electrical behavior, the variation of dielectric constant and density w.r.t temperature etc. [3-7]. in [8], a comprehensive review was given regarding the properties and applications of a variety of insulating liquids. in that review, except the transformer oil, there were comments on silicone oil, fluorinated liquids, chlorinated and phosphate fluids, and ester and synthetic hydrocarbons. polybutene liquids were also mentioned as possible substitutes to transformer oil, especially regarding the dielectric strength [1, 9] (in fact the dc dielectric strength of some polybutene oils was found to increase with increasing liquid density up to 65mv/m at a density of 880kg/m 3 as compared to untreated transformer oil under the same conditions). the mechanisms of breakdown in transformer oil have been thoroughly studied [10-12]. moreover, efforts have been made to improve the general electrical performance of transformer oil by adding minute quantities of certain substances, as has been reported in [1316]. furthermore, the state of transformer oil has been investigated with classical diagnostic techniques [17], as well as with more modern diagnostic techniques [18]. although transformer oil has served satisfactorily the high voltage industry for many years, it became evident that there were some less positive aspects about it, such as its inflammability and the fact that it is not biodegradable. the aim of the present paper is to give a concise review of some alternatives to transformer oil and comment on their various aspects. it is evident that in the context of the present review there will be no mention of nanofluids [19, 20]. it must be emphasized that the present short review does not by any means include all possible alternative fluids to transformer oil since only vegetable oils are particularly mentioned and discussed. ii. earlier proposals for alternatives to transformer oil earlier attempts to replace transformer oil with other liquids are reported in [8]. ester hydrocarbons can be chemically tailored so as to produce high thermal stability or fire resistance if used in transformers [8]. polybutene oils were reported as having certain advantages regarding their dielectric strength in comparison to transformer oil [1, 9, 21]. moreover, polybutene oils present, among others, high fire resistance and heat dissipation as well as arc discharge quenching [22]. silicone fluids further enhance the thermal stability properties [21]. they are fire resistant but at least at the initial stages of their development – they suffered from poor heat transfer [23]. as noted in a later publication [24], silicone fluids w.r.t. their cooling and insulating properties, compare reasonably well with mineral oils. silicone oils are environment friendly with a strong resistance to oxidation and sludge formation, but they are rather expensive and they have high viscosities at 200ºc [25]. fluorinated oils may be excellent insulating liquids but were expensive with a questionable effect on the environment [8]. polychlorinated biphenyl (pcb)-based insulating liquids, although they have high fire security standards, they proved to be a liability because of their toxicity and their bioaccumulation [8, 21, 24, 26-28]. phosphate esters were engineering, technology & applied science research vol. 10, no. 6, 2020, 6570-6577 6571 www.etasr.com danikas & sarathi: alternative fluids – with a particular emphasis on vegetable oils – as … another alternative because they were relatively cheap. they were, however, more destined as lubricants and rather poor insulants [29]. questions also have been raised regarding their environmental hazards [8]. other approaches for alternative liquids, such as electronegative fluids or liquefied elemental gases will not be mentioned here, since the former played more the role of refrigerants, and the latter were destined for use in superconducting magnets in high energy particle machines [8]. moreover, the subject of liquefied gases was partially dealt with in a recent review publication [30]. iii. factors that may influence the behavior of insulating liquids as was noted in [8], transformers require a fluid which has both good insulating properties and which can also be an efficient coolant. low loss tangent and high resistivity are also required. the fluid must be non-flammable, non-toxic and biodegradable. low gas absorption and low expansion coefficient must also characterize a transformer fluid. the fluid must be – as far as it is possible free of impurities (dust, fibers, and metallic particles) and its gas content should be as small as possible. gas bubbles may enhance electron emission and cause premature failure and thus should be avoided [31]. since in a liquid filled system such as a transformer, heat is transferred mainly by convection, the thermal conductivity of the fluid is of primary importance [8]. the temperature effect is a complex phenomenon because of the possible changes in cathode emission, gas content and fluid viscosity [31]. let us not also forget the interplay between moisture and temperature, since it has been reported that oil having small amounts of moisture showed an increase in dielectric strength, whereas the opposite effect was observed with dry oil [31]. viscosity is another significant parameter in determining the heat flow in a transformer. as temperature increases, the fluid viscosity rapidly falls and consequently the cooling effect is greatly enhanced [8]. needless to say that big differences may exist between new and aging oil, as has been reported previously, especially regarding the dissipation factor and the dielectric strength, and this is the reason of periodic control of the oil quality and – if need be – its replacement [32-34]. yet another vital parameter is the resistance of the fluid to discharges. this, however, depends on the nature of the fluid. other insulating liquids release gas bubbles, whereas others absorb gas bubbles, as was noted in [8, 35]. besides the factors, it would be fitting to add that for some of the liquids mentioned above, there are serious objections. fluorinated oils, for example, have a high cost, so that their use is rather prohibitive [36, 37]. polybutene oils, although non-toxic and environmentally friendly with rather satisfactory flash points, are rather expensive for use in large volumes [24]. iv. possible alternatives to transformer oi: modern approaches silicone oil, synthetic ester and natural ester oils are possible alternatives to transformer oil. silicone oils, however, besides some problematic aspects as mentioned above, are still highly viscous at higher temperatures and present limited biodegradability [38]. as noted in [24], in order to avoid large temperature rises during operation, silicone-filled transformers must be de-rated (up to 10%) or provided with additional cooling capacity. on the other hand, synthetic esters are usually derived from the combination of more than one alcohol functional group (polyol) with carboxylic acids leading to a central polyol structure. most preferably the synthetic ester is defined as a family of polyol esters and in particular these fluids are pentaerythritol tetra ester as shown in figure 1. fig. 1. structure of synthetic ester. where r represents an alkyl group ranging from c5h11 to c9h19. synthetic esters present high oxidation stability, have a very good cold temperature performance and are easily biodegradable [38]. synthetic ester liquids can absorb significantly more moisture than transformer oil before their insulating properties deteriorate [24]. tetraesters (or pentaerythritol esters) are environmentally friendly but they are expensive. tetraesters can absorb moisture produced by thermal degradation of cellulose (paper) present in the windings, their viscosity, however, is higher than that of transformer oil [24, 39]. in [39], it is noted that the high saturation limit of such liquids (many times higher than that of mineral oil) reduces the moisture content in the solid insulation due to water diffusion into the liquid, having better insulating performance as a consequence. it should also be pointed out that the higher moisture content implies the formation of free fatty acids [24]. the higher absorption of moisture of tetraester fluids is due to their carbonyl structure, as reported in [40]. phosphoric esters have high fire point and permittivity. in certain aspects, such as breakdown voltage, dissipation factor and resistivity, they are supposed to be comparable or even better than mineral oil, but they tend to also have some negative aspects because they pose some environmental risks [24, 41]. because of the latter, their use is rather limited. natural ester consists of a glycerol backbone with different fatty acid groups and it can be saturated, mono unsaturated, and poly unsaturated. vegetable oils can easily be obtained from natural products and are considered reasonable replacements of transformer oil. as was noted in [24], they consist essentially of triglycerides (figure 2), which are naturally synthesized by the esterification of the tri-alcohol glycerol with three fatty acids. one of the aforementioned oils is castor oil, which is a vegetable oil from the castor bean. it is colorless to very yellow pale with mild or no odor or taste. its boiling point is 313°c (595°f) and its density is 961kg/m3. it is a triglyceride in which approximately between 87% and 90% of fatty acid chains are ricinoleic acid [42]. it was found in the same engineering, technology & applied science research vol. 10, no. 6, 2020, 6570-6577 6572 www.etasr.com danikas & sarathi: alternative fluids – with a particular emphasis on vegetable oils – as … publication, however, that the dielectric strength of castor oil is not as good as that of transformer oil. the results of [42], were somehow contradicted in [43], where it was shown that castor seed oil gave breakdown values that were comparable (but not superior) to those of transformer oil. on the contrary, castor seed oil’s flash point, pour point, and viscosity were found to be better than those of the transformer oil. in yet another publication, castor oil was blended with madhucaindica oil and the mixture showed to have satisfactory heat transfer, pour point, flash point, and viscosity compared to transformer oil but its dielectric strength was found to be lower than that of transformer oil. the authors concluded that such a blend can work for low but not for high voltage transformers [44]. they remarked, however, that with more refinement this blend can also be used for high voltage transformers. fig. 2. structure of natural ester. in figure 2, the structure of natural ester is depicted, where r, r’, and r’’ refer to the different alkyl groups with a major variation in the number of c=c double bonds. the chemical composition of different fatty acid groups (table i) determines the physical properties of the oil, i.e. with higher amount of saturated acids in the ester group, the fluid is more stable towards oxidation and less viscous compared to unsaturated acids which makes them unstable [45]. table i. fatty acid composition of vegetable oils oil fatty acid saturated fatty acid monounsaturated poly unsaturated palmitic acid (c16:0) stearic acid (c18:0) oleic acid (c18:1) linoleic acid (c18:2) palm 45 4 40 10 olive 11 3 71 10 rapeseed 4 2 62 22 sunflower 7 5 19 68 soyabean 11 4 24 54 vegetable oils were investigated in [46], where their advantages and disadvantages were treated accordingly. it was remarked that vegetable oils are susceptible to oxidation, and thus hermetic sealing is required in order to ensure optimum performance. the use of vegetable oils in transformers – because of their higher viscosity results in increased temperatures of between 10 and 30°c. the higher viscosity, however, has also its positive aspect since it implies reduced spread in case of spillage conditions. on the other hand, their pour point is satisfactory, they are classified as low flammability liquids, their breakdown voltages tend to be much higher than those of mineral and silicone oils even with substantial amounts of moisture, and, last but not least, the operating temperatures of vegetable oils are clearly higher than those of mineral oils. the latter point of [46] is contested in [47], where it was claimed that in the case of power transformers (e.g. 160mva) temperature increase in transformers filled with esters can be even greater as compared to the temperature of the transformer filled with mineral oil. therefore, according to [47], in order to use synthetic or natural ester, the changing of the geometry of the transformer (increasing its size), the reduction of the load, or the modification of the cooling system should be considered. another perspective on vegetable oils was given in [48], where soya bean oil and palm kernel oil were investigated. the authors concluded that both aforementioned oils can be used as replacements for mineral oil on the condition of refinement since they possess a lower dielectric strength and they hold more moisture than mineral oil. the viscosity of both oils is higher than that of mineral oil and their flash point is much higher than that of mineral oil. the authors seemed to reluctantly propose both vegetable oils as replacements of the transformer oil on the condition of further purification. authors in [48] seem to agree with the results published before, where mineral oil was compared with vegetable oil and synthetic ester oil in the presence of pressboard [49]. in [49], partial discharge (pd) levels were found to be higher in both alternative oils than in mineral oil. although no specific reason was given for such differences in the pd level, [49] was an effort to investigate solid/liquid insulation as is used in transformer windings. although there was some skepticism, as reported above, there were other publications that suggested the use of vegetable oils, since these presented a dielectric strength comparable to that of mineral oil and the saturated fatty acid content in such oils retarded the deterioration of the insulating fluid in hightemperature environments or long-term storage conditions. moreover, vegetable oils showed more cooling ability and high insulation capacity than mineral oil [50]. authors in [51] agree with [50], reporting that while oxidation of mineral oil produces sludge precipitates, vegetable oils are much more resistant to oxidation. vegetable oils have been researched in [52], where the authors carried out a detailed study of rice bran oil (rbo), corn oil (co) and transformer oil. their investigations indicated that when the viscosity of transformer oil is lower than those of rbo and co, the flash point and the fire point of the vegetable oils were much higher than those of the transformer oil, with the dielectric strength of rbo being higher than that of transformer oil. all in all, the authors of [52] concluded that, because of the rich content of fatty acids, vegetable oils – and particularly rbo – give enhanced performances compared to the transformer oil. rbo was also investigated in [53] along with with sesame oil, sunflower oil, and mineral oil in a comparative study. rbo was superior to the other examined oils regarding the flash point (but not the fire point, where sesame oil was found to be superior), the breakdown voltage and the viscosity. the oxidation stability of the aforementioned vegetable oils, however, was not as good as that of the mineral oil. the latter statement on oxidation stability is in agreement with [54, 55], where it was reported that olive oil offered excellent resistance to aging, rapeseed oil engineering, technology & applied science research vol. 10, no. 6, 2020, 6570-6577 6573 www.etasr.com danikas & sarathi: alternative fluids – with a particular emphasis on vegetable oils – as … offered intermediate properties whereas corn and sunflower oil oxidized appreciably after aging. authors in [55] reported that partial discharge magnitudes of palm fatty acid ester (pfae) are slightly lower than those of petroleum-based mineral oil during the aging time, which somehow contradicts the findings in [49]. in [56], the authors investigated the problem of dielectric strength of mineral oil, corn oil, sunflower oil, and rapeseed oil from another viewpoint, namely that of statistical analysis. they found that for the above mentioned oils and with plane-plane electrodes, the vegetable oils had a higher mean dielectric strength than mineral oil. a later work [57], pointed out that the ac dielectric strength of the synthetic ester oil and the natural ester oil were higher than the dielectric strength of mineral oil as moisture was increasing. in the same work, the impulse dielectric strength of the vegetable liquids seemed to be less affected than that of mineral oil. it should be noted, however, regarding pd activity, both palm oil and corn oil showed a lower activity than mineral oil with a rod-plane electrode arrangement at 25 kv, especially after thermal aging of 30 and 45 days [57]. the pd results of [57] are in disagreement with the results of [49]. coconut oil was the exclusive subject of [58], where it was claimed that its dielectric strength with both mushroom and spherical electrodes was satisfactory. the authors studied the variation of its dielectric strength w.r.t. moisture content but they did not compare coconut oil with mineral oil. their claim, however, that coconut oil can be an alternative to transformer oil was supported from an earlier publication [59], where coconut oil was shown to have higher dielectric strength than transformer oil, having also a much higher flash point. the experimental results of [58] are in accordance with those of [60], where coconut oil was found to be even superior to refined, bleached, deodorized palm oil (rbdpo). further detailed studies with soybean oil, coconut oil, palm oil and rice husk oil revealed that all of them have higher flash and fire points than mineral oil, with coconut oil, palm oil and rice husk oil having also higher breakdown values than mineral oil [61]. soybean oil was found to be no better than mineral oil regarding breakdown voltage. in that, reference [61] was at variance with the data presented in [48]. the experimental results of [61] deviate significantly from those of [62], where a surprisingly very low dielectric strength for coconut oil was observed in comparison with mineral oil. no specific explanation was given by the authors of [62] for such low dielectric strength values of the coconut oil. coconut oil has indeed lower dielectric strength than virgin coconut oil and palm oil [63], but not as low as that reported in [62]. on the other hand, there have been earlier reports mentioning the rather low dielectric strength values of coconut oil in comparison to transformer oil [64], but not as low as those of [62]. yet again, such data are contradicted from recent experimental results suggesting that the dielectric strength of coconut oil is very similar to that of mineral oil [65]. recent studies showed that vegetable oils are possible replacements for mineral oil [66]. the authors in [66] investigated a variety of vegetable oils, such as corn oil, castor oil, olive oil, and ester oil. especially the dielectric strength of corn, castor, and olive oils was higher than the dielectric strength of mineral oil. the authors concluded that such vegetable oils can replace mineral oil in power transformers. in [67], both the positive and negative aspects of vegetable oils have been discussed. the author remarked that, besides the positive aspects – which have been referred to also above -, there are also some negative aspects of vegetable oils, namely that their cooling function is not as good as that of the mineral oil and the dielectric strength under lightning voltages is inferior to that of the mineral oil. furthermore, and in relation to kraft paper, the positive and negative aspects have been discussed in [68]. others reported that higher rates of water migration from paper to the oil was observed during heating of natural ester oil in comparison with mineral oil [69]. in a further publication it was reported that the kraft paper/mineral oil combination lowered the degree of polymerization (dp) index, defined as the average number of repeating units that are contained in the molecular chain of a polymer, even more than the kraft paper/vegetable oil combination [70]. the authors of [70] used two vegetable ester-based oils without, however, giving full details about them. agreeing with [70], another work reported that testing with jatropha curcas oil, the latter’s combination with kraft paper gave a rather satisfactory dp. moreover, the refining process of jatropha curcas oil, although it did not influence the physical properties of density, viscosity, and fire point, it improved somehow its flash and pour points giving also a very satisfactory dielectric strength [71]. it has to be noted, however, that without antioxidants, jatropha curcas oil tends to be considerably oxidized during accelerated aging [72]. the better cooling function of mineral oil in comparison to vegetable oils has also been reported in [73]. in the latter publication, however, emphasis was given on other aspects of vegetable oils, such as their rather satisfactory ac dielectric strength, high biodegradability, and fire safety. of the vegetable oils tested, rbdpo was found to have a high breakdown voltage and low dissipation factor among the other candidates (soybean oil, sunflower oil, rapeseed oil, coconut oil), and thus it was suggested as the best alternative fluid to mineral oil. other researchers, however, reported that extra virgin olive oil and castor oil have very high dielectric strengths [74]. extensive work on soybean-based oil revealed that it releases more ethane than mineral oil, whereas the dielectric dissipation factor (ddf) is normally higher for a vegetable oil than for a mineral oil [75]. experimental work on rapeseed oil revealed that its dielectric strength is comparable to that of mineral oil [76], and that it can be used for power transformers, especially if improved through the use of an antioxidant [77]. v. challenges involved with alternate fluids for transport applications the higher thermal class of ester fluids makes them viable in densely populated areas or commercial buildings such as shopping malls and airports. further, the transformers filled with such liquids can be placed closer to the buildings which benefit from its reduced equipment spacing requirements as specified in the national electrical code (nfpa 70). when comparing the installation of transformers containing ester fluids with existing mineral oil, it also provides additional benefit of shorter low voltage (lv) cable runs and hence engineering, technology & applied science research vol. 10, no. 6, 2020, 6570-6577 6574 www.etasr.com danikas & sarathi: alternative fluids – with a particular emphasis on vegetable oils – as … lower losses. the ester fluids are hygroscopic in nature, so precautionary measures on storage and handling such liquids must be taken care of in order to prevent their reaction with atmospheric moisture and hence these liquids are recommended in non-breathing transformers. the relative permittivity of any dielectrics affects the electric field distribution in the winding structures and must be considered before the use of new alternate liquids inside the transformers, where the stress exerted at the oil/pressboard interface is very low on the usage of ester fluids due to its minimal variation in permittivity. also, the fluid flow characteristics along with thermal modeling of windings must be considered before designing in order to evaluate the difference in temperature rise for an ester filled transformer, compared to standard mineral oil. vi. some thoughts on future research interest in vegetable oils was noted a long time ago [78, 79]. excellent reviews have been published on alternative fluids to transformer oil [80]. without doubt, vegetable oils can be a hope for the future replacement of mineral oil in power transformers. there are, however, efforts to be undertaken in order to clarify certain pending issues. some conflicting data reported above must be further looked upon and further experiments should be carried out. there is still some uncertainty regarding the dielectric strength of some vegetable oils as well as their pd behavior [81, 82]. further research should be directed towards this goal. the weakness of vegetable oils w.r.t. lightning impulses should also be further researched. moreover, studies on the long-term performance of paper insulation with vegetable oils must be carried out. considerable efforts regarding the study of paper/vegetable oil insulation have already been undertaken [83, 84]. detailed reports on pre-breakdown and breakdown phenomena regarding the vegetable oils must also be produced, as was the case in more conventional fluids [12, 85-88]. in conjunction to pre-breakdown and breakdown phenomena and related mechanisms, vegetable oil-based nanofluids must be investigated regarding their dielectric strength, volume resistivity, and dissipation factor [89]. furthermore, techniques that proved to be useful in studying pd in transformer oil, should be tried 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casablanca mohammedia, morocco ssdia laboratory enset mohammedia hassan ii university of casablanca mohammedia, morocco abstract—information system is a guarantee of the universities' ability to anticipate the essential functions to their development and durability. the alignment of information system, one of the pillars of it governance, has become a necessity. in this paper, we consider the problem of strategic alignment model implementation in moroccan universities. literature revealed that few studies have examined strategic alignment in the public sector, particularly in higher education institutions. hence we opted for an exploratory approach that aims to better understanding the strategic alignment and to evaluate the degree of its use within moroccan universities. the data gained primarily through interviews with top managers and it managers reveal that the alignment is not formalized and that it would be appropriate to implement an alignment model. it is found that the implementation of our proposed model can help managers to maximize returns of it investment and to increase their efficiency. keywords-university; business strategy; it strategy; information system; is alignment; strategic alignment model i. introduction higher education institutions offer an increasingly broad range of services. their information systems are complex because of the variety and volume of information to be processed, the security of information to ensure and of the diversity of users: managers, students, teachers, administrative and external stakeholders. they represent the service production tool and the appropriate support solution in the face of speed, responsiveness, agility and flexibility. the merging of universities, the internationalization and virtualization, the massive number of students, push the information systems to the needs of constant growing. their governance must be an integral part of the governance of the institution. in effect, a bad governance of the information system would negatively affect the performance of the university, the quality of education and research and the management of internal processes and costs [1, 2]. the strategic alignment has emerged as a major concern for it professionals and business leaders [3]. it is an important topic for researchers and practitioners both. studies have attracted the attention on its importance, [47]. other research has shown that it provides organizations with the maximum of benefits and a competitive advantage and contributes to the improvement of their organizational performance [8] and to the creation of business value [9]. the majority of these studies concern the industrial and financial fields. author in [10] found that it alignment has been limited by the lack of knowledge on the banking sector. in a study on the alignment in the insurance sector, authors in [11] shown that the know-how shared between businesses and it executives was the strongest predictor of the alignment social dimension. nevertheless, in the context of education, there is need for more research [12]. our study proposes to contribute to the understanding of the concept of the alignment through the definitions reported in the literature, to examine the alignment of the strategy of the information system to the business strategy in moroccan universities and to propose an approach to align these two strategies. ii. strategic alignment despite the amount of produced research on the strategic alignment, this subject remains as one of the top concerns identified by it executives and managers. this section provides a portrait of the state of alignment knowledge and presents some alignment models. engineering, technology & applied science research vol. 8, no. 1, 2018, 2471-2476 2472 www.etasr.com ahriz et al.: an elaboration of a strategic alignment model of university information systems … a. concept of the strategic alignment strategic alignment appears in the literature under different terminologies. among which we find: “fit”, “integration” [13], “liaison” [14] “adjustment” [15], “bridge” [16], “harmony” [17], “fusion” [3]. despite their subtle differences, these terms relate to all the approximations of the strategy of the organization to its information system [18]. the alignment is the dominant term in the literature but other terms are also used such as congruence and covariation. strategic alignment aims to put in coherence the strategy of an organization and its internal and external functioning, which includes its information system. a number of authors have worked on the strategic alignment, either in a global perspective [19] or focused on more specific aspects of the strategy, such as the information system [18, 20]. several other definitions of the alignment are proposed in the literature [7, 14, 17, 21]. by browsing through these definitions, we find that there is no consensual definition about the concept of alignment or a detailed description of the elements of the organization involved. but they all agree that there are at least two areas to align, integration of the organizational strategy with the it strategy and proposed approach support. b. alignment models several models have been proposed to help organizations to achieve it alignment. some of them explained the alignment theoretically, others sought to evaluate it. the model of the organizational balance of scott morton advocates an alignment between the organizational domains that are the strategy and technology, the roles of individuals and the culture of the organization, the management processes and the structure. author in [22] stressed four main areas: the business strategy, the it policy, the organizational strategy and culture, and the financial strategy. authors in [23] have examined the alignment of it with the company, while authors in [24] focused on the strategic direction of the business and information systems. authors in [25] analyzed the relationship between aspects of organizational culture and the it policy in the units of the public sector. the model in [26] advocates the detailed description of an organizational entity, the application of the architecture principles and the choice of the good level of analysis to make an alignment between the components of this entity with its environment. the model in [17] identifies the enablers and inhibitors of the alignment as well as the criteria for its assessment. the strategic alignment model (sam) proposed in [13] remains one of the most widely known and used among is researchers [27]. it is focused on four areas, namely the business strategy, the it strategy, infrastructure and organizational processes, it infrastructure and process. the common point between the most of these models is that they incorporate the fact that the strategy often changes and that alignment of it with the rest of the organization must integrate these strategic changes continuously. although the models developed in literature are numerous, sam remains one of the most utilized models in literature and in corporations [18]. c. the strategic alignment model (sam) the structure of the sam model contains three classes composed of different elements.  domains: business and information technology.  levels: subdivision of areas in strategy for the external level and structure for internal level  the components: structuring and characterization of each level in scope, skills and governance for the external level and infrastructure, skills and processes for the internal level. the concept of the strategic alignment between it and business is based on two building blocks:  strategic fit: it is a link between internal and external domains. it refers to the use of strategy to determine the infrastructure of the business.  functional integration between business and it domain. it takes two distinct forms: o the strategic integration is the integration between it strategy and business strategy and establishes the potential of it at a strategic level. o the operational integration is the link between organizational infrastructure/ processes and it infrastructure/processes. in the external level, the business strategy concerns the decision-making in relation with products and the positioning of the company on the market. the it strategy concerns the technological scope, the technological skills and it governance. in the internal level, the organizational structure relates to the process of activities. the technological infrastructure and the processes of is design concern the technical architecture of is, the design process, evolution and maintenance of is as well as the management of technological knowledge and skills. on the basis of these two levels, the model offers four distinct perspectives of alignment that can guide the strategy of an organization in terms of its technological choices: execution of the strategy, technological transformation, competitive advantage, level of service [27]. iii. research model the moroccan university currently knows important organizational changes generated by the legislation in force and by management constraints imposed by its environment (the process of fusion, huge number of students, technological evolution, and infrastructure change). all these variables require universities to restructure their information systems. an is consists of several heterogeneous applications dedicated to its specific areas in which the mapping is presented in figure 2. universities are a special type of organizations where it alignment has not attracted the researcher attention it deserves [21, 28]. according to [12] there is a lack of research related to it aligment in universities. the main concern of their managers is to have an integrated, efficient is and especially aligned to their overall strategy and to the user expectations. in order to fill this gap and to contribute to the achievement of this strategic objective, our study proposes the adaptation of the mechanisms of sam and to address a generic approach for modeling the strategic alignment in universities. it consists in characterizing the notion of alignment at the strategic and engineering, technology & applied science research vol. 8, no. 1, 2018, 2471-2476 2473 www.etasr.com ahriz et al.: an elaboration of a strategic alignment model of university information systems … operational level and in maintaining the consistency between all information systems. fig. 1. sam structure fig. 2. mapping of areas of moroccan universities the objective of this a model is to show the strategic role that it plays in enabling organizations to maximize the return on investment in information technology, to provide them a competitive advantage and to increase their efficiency and profitability. the method used in this research is based on an exploratory approach which aims to make an inventory of the apprehension of the concept of alignment by internal information system’s users. we have analyzed official documentation relating to moroccan universities and information gathered through direct interviews with business and it managers to finally propose the following steps to build our proposed model: a. step 1: selection of the business process to align we have chosen to adapt the sam model to the alignment of the integrated system of accounting and financial management is fam, taking into account the strategic role it plays in the university management. this solution allows the management of the whole of the accounting processes and university budget, the preparation and the rapid execution of the annual budget and constitutes a reporting tool and aid to decision-making promoting better strategic thinking. it is used by more than 120 higher education institutions. nevertheless, some of its modules have been little exploited so far, in spite of their importance due to several reasons among which we quote the resistance to change of certain users, which justifies the proposal for this alignment approach. understanding the process to align is an essential condition for the achievement of the alignment. as the accounting and budgetary management process was not formalized and in order to facilitate its understanding, we propose hereafter a schematization in terms of operations and management rules which will serve as a basis for harmonizing the methods of identifying needs and possibly standardizing them for all academic institutions. b. step 2: identification and interpretation of entities to align the concept of alignment implies the existence of relations between several entities that need to be considered at once. by analogy to the original model, our model baptized samu (strategic alignment model for universities) distinguishes an external level (strategies of the university in terms of finance and accounting, and the strategy of the is) and an internal level (business processes and management, infrastructure and technological processes) and presents the alignment according to these four dimensions. the different entities of the university can be organized for work harmoniously toward a common goal. we are trying to put in coherence the fam and it strategy as well that the fam process and the it process to achieve this goal. the implementation of an alignment model requires a well known business strategy to all stakeholders to which the it strategy can be aligned by bringing its expertise to support business choices. it is for this reason that the communication of the strategy and the information of all the participants in the process of alignment are essential conditions for its success. the following is a description of these entities: university strategy: the implementation of the is fam aims at a flexible and efficient budget management and thus the improvement of the general framework for steering and strengthening the internal governance system through traceability of various financial transactions and movements, involvement of all departments in the monitoring and sharing of budgetary and financial information. this strategy facilitates audits and management control to ensure transparent accountability and assessment. it strategy: it strategy makes available a simple, adapted, scalable, secure and modular fam system. information systems must therefore be harmonized in order to ensure simple, rapid and coherent interfacing. the is fam must be linked to the university reporting platform to provide real-time access to the necessary information. also, procedures must be put in place to avoid redundancy while ensuring the continuity of the activity, the confidentiality and the automatic data backup as well as the audit and the security of the is fam. organizational processes: the formalisation of the budgeting process and communication is crucial. to do this, necessary skills must be developed. also the sharing of the platform of the fam system between the institutions and the presidency is mandatory. in addition, it is necessary to ensure the involvement of the staff responsible for economic and financial business in each academic institution for a better use of the system. engineering, technology & applied science research vol. 8, no. 1, 2018, 2471-2476 2474 www.etasr.com ahriz et al.: an elaboration of a strategic alignment model of university information systems … fig. 3. needs idendification fig. 4. structure of the samu is process and infrastructure: for efficiency reasons, a process identity card must be clearly defined. thus, the choice of systems, applications, databases will be facilitated. the development of a scalable it infrastructure undoubtedly requires the development of technical and computer skills capable of adapting, analysing business needs, accompanying users in operation and upgrading systems. c. step 3: identification of possible interaction constraints between these entities an efficient strategic alignment provides a competitive advantage to the organization. to achieve this objective, the overall strategy must be clear and communicated to all stakeholders. the potential of information and communication technologies must be taken into account in the strategy formulation. in addition, a dialogue between business department, top management and it department must be established to facilitate interactions between entities. d. step 4: choice of the alignment perspective of the samu achieving is fam alignment with the university's strategy is a first step towards aligning the is of the university both internally and externally. the alignment approach is to identify the role played by each field in the alignment perspective, establishing relations between different areas and recognize how tasking decisions regarding one of them affects the others. by analogy to the original sam, each of these perspectives involves three of the four areas to align and involves a strategic fit and a functional integration. to understand the perspectives, we will define three domains:  the anchor domain is the strongest one in which changes are made. it corresponds to the dimension that the organization controls best. it is the enabler of change that directly impacts the pivot domain.  the pivot domain is the weakest one where solutions are sought. it implements the anchor which in turn affects the impacted domain.  the impacted domain corresponds to the domain which will feel the greatest impact from the change in the anchor domain and where the main changes will take place. four alignment perspectives emerge from this domain characterization (figure 5). we have kept the original model outlook because it corresponds well to the case studied. the anchor domain is the strongest domain at the strategic level. the impact domain is located at the internal level at which changes are made. the university strategy (arrow 1 in figure 5) is based on business and organizational processes, which in turn must be engineering, technology & applied science research vol. 8, no. 1, 2018, 2471-2476 2475 www.etasr.com ahriz et al.: an elaboration of a strategic alignment model of university information systems … aligned with the it layer. this first perspective is the most dominant in our case. it is of the type "execution of the business strategy" and is anchored by the choices of the university’s strategy (anchor domain). it triggers change needs in the entity "infrastructure and organizational processes" (pivot domain), like developing new skills and justifying the implementation of new processes and technologies (impacted domain). the second sequence (arrow 2) that we propose puts in scene three areas of our samu model: business strategy, it strategy and the it process. the functional integration between business strategy and it strategy initiates the sequence of alignment. it is followed by a strategic fit between the it strategy and it process. this perspective is to decline the is fam strategy through an it strategy appropriately so that it must be operationalized by identifying the technical infrastructure and the most appropriate it processes. fig. 5. alignment perspectives in the third sequence (arrow 3), the technology exploitation is ensured via the it strategy area of anchor that impacts the organizational process. it is the driver of change. the business processes are transformed by the adoption of is fam. once the technology is chosen and implemented, the first transformation affects the skills and roles of individuals. these are gradually formed in the use of the new technology. in the fourth perspective (arrow 4), change is initiated by the it strategy dimension that impacts the entity "organizational processes" thus targeting the it process in order to provide an excellent level of service to the business process. in general, the choice of the perspective depends on area which requires an evolution and with which there is need to develop the communication and increase understanding. finally, it is to be noted that the same organization can be brought to follow different modes of alignment depending on the activity and the desired positioning. iv. results and discussion from this study, we can deduct that there is a weak apprehension of the concept of alignment as well as the absence of alignment models use in the moroccan universities. literature review revealed that the sam model is the most adapted or extended in different domains, with the exception of that of higher education, which is the subject of our study. the work presented in this article aimed to introduce a presentation of the strategic alignment and to formalize the alignment approach based on the sam model in universities. we have therefore formalized the results of the interviews in a model expressing the two strategies (business and it) and the two processes (business and it), the main objective is to provide appropriate rules and methods in order to construct the alignment process and to present an approach to facilitate and successfully implement sam within these institutions. v. conclusion and future work in this study, we have used the strategic alignment model (sam) to compose the structure of samu. this model analyzed the relationship between the four areas involved in the alignment process. it will allow university managers to optimally manage it investments, to optimize resources, to have an integrated and coherent is able to support the strategy to be implemented and finally to improve the performance of university’s processes. in addition to the internal actors of the system, the fam process also involves external partners such as ministries, suppliers and customers. we plan to work on the full alignment of the system with external partners, the environment and technological developments. we will work on the relationship with the users taking into account the dynamic nature of the alignment due to the increased instability of the environment and its uncertain evolutions. references [1] s. ali, p. green, “effective information technology (it) governance mechanisms: an it outsourcing perspective”, information systems frontiers, vol. 14, no. 2, pp. 179-193, 2012 [2] m.-s. pang, g. lee, w. h. delone, “it resources, organizational capabilities, and value creation in public-sector oragnizations : a publicvalue management perspective”, journal of information technology, vol. 29, no. 3, pp. 187-205, 2014 [3] j. n. luftman, e. mclean, “key issues for it executives”, mis quarterly executive, vol. 3, no. 2, pp. 89-104, 2004 [4] e. mclean, j. v. soden, strategic planning for mis, 1977 [5] j. c. henderson, j. g. sifonis, “the value of strategic is planning: understanding consistency, validity, and is markets”, mis quaterly, vol. 12, no. 2, pp. 187-200, 1988 [6] r. almeida, r. pereira, m. m. da silva, “it governance mechanisms: a literature review”, international conference in exploring services science, 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topfel, “business-it alignment in municipalities—the swiss case”, 22nd americas conference on information systems, pp. 1-10, 2016 engineering, technology & applied science research vol. 8, no. 1, 2018, 2471-2476 2476 www.etasr.com ahriz et al.: an elaboration of a strategic alignment model of university information systems … [13] j. c. henderson, h. venkatraman, “strategic alignment: leveraging information technology for transforming organizations”, ibm systems journal, vol. 38, no. 2, pp. 472-484, 1993 [14] b. h. reich, i. benbasat, “measuring the linkage between business and information technology objectives”, mis quarterly, vol. 20, no 1, pp. 5581, 1996 [15] m. e. porter, “what is strategy ?”, harvard business review, nov.-dec. ,pp. 61-78, 1996 [16] c. u. ciborra, “de profundis? deconstructing the concept of strategic alignment”, scandinavian journal of information systems, vol. 9, no. 1, pp. 67–82, 1997 [17] j. n. luftman, t. brier, “achieving and sustaining business-it alignment”, california management review, vol. 42, no 1, pp. 109122, 1999 [18] d. avison, j. jones, p. powell, d. wilson, “using and validating the strategic alignment model” journal of strategic information systems, vol. 13, no. 3, pp. 223-246, 2004 [19] r. s. kaplan, d. p. norton, l'alignement stratégique, créer des synergies par le tableau de bord prospectif, editions d'organisation 1ère édition, 2007 [20] m. kalika, y. rival, “measuring internet performance within the organization”, 16th information resources management association international conference, usa, 2005 [21] t. j. winkler, “it governance mechanisms and administration/it alignment in the public sector: a conceptual model and case validation”, proceedings of international conference on wirtschaftsinformatik, pp. 831-845, 2013 [22] h. pankratz, “strategic alignment: managing for synergy”, business quarterly, vol. 55, no. 3, pp. 66-67, 1991 [23] c. v. brown, s. l. magill, “alignment of the is function with the enterprise: towards a model of antecedents” mis quarterly, vol. 14, no. 8, pp 371-403, 1994 [24] y. e. chan, b. h. reich, “it alignment: what have we learned?”, journal of information technology, vol. 22, no 4, pp. 297-315, 2007 [25] s. kanungo, s. sadavarti, y. srinivas, “relating it strategy and organizational culture: an empirical study of public sector units in india”, journal of strategic information systems, vol. 10, no. 1, pp. 2957, 2001 [26] j. a. zachman, “a framework for information systems architecture”, ibm systems journal, vol. 26, no. 3, pp. 276–292, 1987 [27] a. renaud, i. walsh, m. kalika, “is sam still alive? a bibliometric and interpretive mapping of the strategic alignment research field”, the journal of strategic information systems, vol. 25, no. 2, pp. 75-103, 2016 [28] s. vander elst, f. de rynck, “alignment processes in public organizations: an interpretive approach”, information polity, vol. 19, no 3,4, pp. 195-206, 2014 engineering, technology & applied science research vol. 7, no. 6, 2017, 2303-2307 2303 www.etasr.com hajinezhad et al.: biodiesel production potential from native tehran oil crops using gis biodiesel production potential from native tehran oil crops using gis ahmad hajinezhad faculty of science and technology modern university of tehran iran hajinezhad@ut.ac.ir saeed rahebi faculty of science and technology modern university of tehran iran shafabakhsh@semnan.ac.ir sepide abedi faculty of science and technology modern university of tehran iran ahadad@semnan.ac.ir abstract—one of the main factors in the field of alternative fuel economy is the primary raw materials. importing raw materials and preparation conditions for cultivation of non-native species require high expenditures. using native species can reduce the production cost. therefore in this paper, for the first time a comprehensive study of indigenous tehran oil plants is presented. three indigenous non-edible species, rapeseed, cotton and barley were selected due to their feasibility of producing biodiesel. the purpose of this study is to propel relevant policies in the country towards greater use of domestic raw materials and known potentials. the potential for biodiesel production from plant sources, in this region was studied using gis software. the present paper describes the zoning map and identifies the potential map of producing biodiesel from indigenous plant sources in tehran province. according to the map, concentration of biodiesel production is in the central and western cities of province. this map shows that 116806.8665 hectares with the greatest potential to produce biodiesel. also we calculated the potential of biodiesel production from introduced species, considering the yield per hectare and their oil content. the results show that the potential of biodiesel production for the three species of rapeseed, cotton and barley are respectively 98117.77, 58403.43, 83516.91 tons in tehran province. non-edible rapeseed having the highest production potential has been introduced as a superior indigenous species for the future investments in biodiesel production in tehran province. keywords-biodiesel; indigenous oil plants; gis; biodiesel production potential i. introduction endemic plant species, as a factor strategy to ensure environmental sustainability in agricultural programs, provide genes which are resistant to unfavorable environmental factors, disease and pest, are one of the most important national and natural assets. biodiesel (biodiesel technically is termed as fatty acid methyl ester) is a clean diesel fuel from renewable natural resources such as vegetable oils and animal fats. oil plants are one of the biodiesel production sources. this study is based on the evaluation of producing biodiesel as an alternative fuel from endemic oil plants. because the performance of biodiesel in compression ignition engines is the same as diesel fuel, therefore, its use doesn’t need engine modifications. using biodiesel in a conventional diesel engine can reduce unburned hydrocarbons, carbon monoxide and particulate matter. also, due to its oxygen and complete combustion to co2, the proportions of carbon are reduced in the suspended particles. sulfate present in the oil sector are absent due to the absence of sulfur in biodiesel. thus, despite similar physical and chemical properties of biodiesel with conventional diesel, the exhaust output of the bio fuel has an advantage over conventional gasoline fuel. when the production of biodiesel started the process of transesterfication (what we do to make biodiesel) was used to separate glycerine from oil. glycerine was widely used in the cosmetic, food and explosive industries [1]. as petroleum fuels were plentiful and cheap, the main interest was on designing increasingly more sophisticated fuel injection systems [2]. over the years, this meant that vehicles evolved to run thinner fossil diesels rather than thicker vegetable oils. once the price of crude oil increased though, there was an incentive for research on alternative fuels. it was already pretty much accepted that unmodified vegetable oil was not suitable for modern injection systems. the transesterfication process was pretty much old science and was used to reduce the viscosity of the oil; producing biodiesel [3, 4], so commercial process to turn waste cooking oil into biodiesel was developed [5]. in the 2000’s when crude prices started rising, government subsidy of biofuel industries became common. this has given the industry the economic security needed to invest in biofuels. in iran, researches around producing biofuels are performed since 1996, especially in case of biodiesel from different resources [6] as using native species can greatly reduce production cost. in iran potential assessment of biodiesel production hasn't been studied yet. however, in the field of geothermal and wind power, production potential has been using gis systems [7-9]. in this study, a gis based approach is employed to investigate the biodiesel production potential based on native tehran oil plants ii. research methodology the sources of iranian native plants have been investigated and native oil plants of tehran province have been extracted to provide tehran native oil plant statistics. information related to the oil content of plants, vegetation and habitat conditions was engineering, technology & applied science research vol. 7, no. 6, 2017, 2303-2307 2304 www.etasr.com hajinezhad et al.: biodiesel production potential from native tehran oil crops using gis obtained. using climate and land use maps of iran, the cultivation potential of these plants in all types of province surfaces is studied and finally, a map based on potential of producing biodiesel from native tehran oil plants is presented. tehran is located on the southern slopes of alborz mountains, and in approximately equal distance from eastern (afghanistan) and western (turkey, iraq) borders, sitting on the ancient and famous city of rey. tehran is not far from khazar (caspian sea) with an aerial distance of 100 kilometers. on one hand it is situated on the route from anatolia to india and china along alborz mountains and on the other hand, at the intersection of roads that extend from southern parts of the country along zagros mountains. today, tehran metropolis is the most urbanized area between istanbul and karachi. these distinct elements have formed the region’s landscape as well as its natural, social and cultural environment. tehran is a mountainside city with an altitude of 900 to 1700 meters above sea level. its urban area spreads entirely over the iranian plateau, on the slopes of a very high and dense mountain barrier, with a peak of 3933 m which is 2200 m higher than the residential areas with rivers that are full in spring time and dry in summer time. in higher parts of the slope, it becomes cooler while major water resources in the area provide for the development of big and arborous villages. lower parts, between 900 to 1200 m, have a fertile soil and a gentle slope that permits a productive agricultural activity. in these plains, there are many sources of surface or underground water tables, supplied by aqueducts, flood ways and branched out rivers [10, 11]. in the southern part of tehran and its suburbs, the desert begins. from geographic, natural and human points of view the same desert is the negative of the mountain side and has no significant role in tehran’s landscape and activities. the geographical situation of tehran province and its cities are shown in figures 1 and 2. fig. 1. tehran province in iran the more factors involved in a feasibility study of biodiesel production, the more accurate the conclusion will be. based on the available information and scientific resources of this area, some factors were selected as most important for determining appropriate zones in tehran province to produce biodiesel. these factors included the type of climate, annual precipitation (mm), temperature (°c), soil texture and salinity. in this study, the digital maps have been prepared from jamab company research department and have been studied by geographic information systems (gis). at the beginning, maps of tehran province were extracted regarding rain, temperature and soil maps of iran. then, according to the model presented in figure 3, suitable areas for cultivation of the raw plant sources of biodiesel production in tehran province were presented. fig. 2. the cities of tehran province iii. results and discussion annual rainfall and temperature, soil texture and soil salinity maps of tehran province were prepared from iran resource maps. then, according to table i these maps were classified separately in gis. in tehran province, average annual rainfall was classified from 150 to 800 mm per year by gis. as can be seen in figure 4, the highest average precipitation of 300 mm occurred in the central regions of the province. rainfall levels in the northern part of tehran located in the foothills of alborz mountain are above 500 mm. average annual temperature classified from minimum 5 °c to maximum 17.5 °c. southern and south-western parts of the province with average temperatures of 12.5 degrees and above are more favorable for cultivating crops (figure 5). soil texture levels are classified to heavy, medium, light, rough and for non-agricultural land use. medium level has the best soil texture for calculation which is concentrated in the western parts of the province (figure 6). soil salinity is categorized from low to extra salinity. obviously, areas with less salinity are more suitable for production. as can be seen most of these areas are located in northern, eastern and some of them in western parts of the province (figure 7). fig. 3. gis conceptual model used in this study. engineering, technology & applied science research vol. 7, no. 6, 2017, 2303-2307 2305 www.etasr.com hajinezhad et al.: biodiesel production potential from native tehran oil crops using gis table i. classification of measures to produce raw materials for biodiesel production. classes name classes range classes measures inappropriate 0-150 1 annual rainfall (mm) relatively poor 150-350 2 medium 350-550 3 modest 550-750 4 appropriate 750< 5 inappropriate <10 1 annual temperature (oc) relatively poor 10-12 2 medium 12-14 3 modest 14-16 4 appropriate 16-18 5 heavy 1 soil texture medium 2 light 3 macro 4 land without soil 5 low 1 soil salinity medium 2 high 3 quite a lot 4 land without soil 5 fig. 4. average annual precipitation levels fig. 5. average annual temperature levels. fig. 6. soil texture levels. fig. 7. soil salinity levels some non-proliferation and dispersion endemic species have remained in the same small origin area. tehran province has a diverse cover based on climate and other geographical conditions. oil plants of tehran are introduced in table ii. after identification of indigenous oil resource plants, levels of the products cultivation and their growth area were examined. plants with low oil content (below 20%oil content in seed or 10% in residue germ) or plants directly used as food and edible oil have been abandoned. in order to produce biodiesel, only three non-edible plants were looked upon: rapeseed, cotton and barley bran due to their compatible growing conditions with tehran climate, high oil content, yield per hectare and not applicant as nuts or major edible. non-edible rapeseed (brassica carinata) is an oilseed crop with 30 to 50 percent oil content [12]. in this study, its industry variety was considered which isn’t edible. cotton (gossypium sp.) with 25 to 30 percent of oil content is among the oilseed crops [13]. the fiber of this plant is used for industrial production. cotton oil seeds can be used to produce biodiesel. barley (avena sativa) is a kind of cereal that its shell and bran contains significant amounts of oil (11% oil in residue germ) [14]. more cultivation of this plant in addition to increasing domestic production can provide large amounts of raw materials to produce biodiesel. suitable areas for cultivation of these plants in province were looked for. since the above mentioned plants need low water requirements, therefore, the average of annual rainfall of above 300 mm was selected as appropriate rain class (figure 8). base temperature for canola, cotton and bully is respectively 5 °c, 1215 °c and 11 °c. since the lowest temperature that all the three plants have the ability to grow is 12 °c therefore classes with (12-14 °c), (14-16 °c) and (16-18 °c) were selected as the suitable temperature class (figure 9). as mentioned earlier, the most suitable areas for cultivation are the ones with medium texture soil and low salinity. thus, as shown in table i, only class 2 of soil texture and class 1 of the soil salinity were selected as the suitable layers (figures 10 and 11). after provision of the favorable region maps to produce biodiesel raw material in tehran province, four maps were obtained and overlaid and finally the feasibility map of producing biodiesel from oil plants in this province was presented (figure 12). considering the map, concentration of biodiesel production is in the central and western cities of province. also this map shows that 116806.86 hectares of land have the greatest potential to produce biodiesel. engineering, technology & applied science research vol. 7, no. 6, 2017, 2303-2307 2306 www.etasr.com hajinezhad et al.: biodiesel production potential from native tehran oil crops using gis table ii. oil plants of tehran province. common name scientific name family oil content oil organ walnut juglans regia juglandaceae 60 seed hazelnut corylus colurna l. cupuliferae 55 seed pistachio pistacia vera l. anacardiaceae 54 seed sunflower heliantus annus compositae 45 seed rapeseed brassica.napus.oleifera cruciferae 30-54 seed almond prunus communis rosaceae 50 seed soybean glycin max fabaceae 57 seed apricot prunus armeniaca rosaceae 40-50 seed prune prunus domestica rosaceae 35 seed tomato solanum lycopersicum solanaceae 35 seed cotton gossypium sp. malvaceae 20 seed chickpea cicer arietinum leguminoseae 5 seed wheat triticum poaceae 2 germ sea buckthorn hippophae rhamnoides elaeagnaceae 3-5 fruit 8-18 seed apple calocarpum mamossum rosaceae 27.5-28 seed grape vitis vinifera vitaceae 12 seed oat avena sativa poaceae 11 bran fig. 8. suitable class of precipitation. fig. 9. suitable class of temperature fig. 10. suitable class of soil texture fig. 11. suitable class of soil salinity. fig. 12. feasibility map of biodiesel production in tehran table iii. suitable oil producing plants for tehran province plant canola cotton barley yield (tn/ha) 2.1 2.5 6.5 oil contant (%) 40 20 11 biodiesel production (tn/he) 0.84 0.5 0.715 biodiesel production in tehran (ton) 98117.77 58403.43 83516.91 engineering, technology & applied science research vol. 7, no. 6, 2017, 2303-2307 2307 www.etasr.com hajinezhad et al.: biodiesel production potential from native tehran oil crops using gis iv. conclusion one of the main factors in the alternative fuel economy is feedstock. the importing of raw materials and the preparation conditions for the cultivation of non-native species require high expenditure. therefore, using native species can greatly reduce biodiesel production cost. the purpose of this study is to propel relevant policies in iran towards greater use of domestic raw materials and known potentials. the results of this study are as follows:  this study was the first time that native oil plants of tehran province and their oil content with suitable growth conditions was presented.  three non-edible species namely rapeseed, cotton and barley were selected due to their feasibility of producing biodiesel.  after a survey of indigenous oil plant species of tehran province, the potential for biodiesel production from plant sources, in this region has been studied using gis software.  the present paper describes the country zoning map and identifies the potential feasibility map of producing biodiesel from indigenous plant sources in tehran province.  considering the selected map, concentrating of biodiesel potential production is in the central and western cities of province.  the selected map shows 116806.86 hectares of land with the greatest potential to produce biodiesel.  potential of biodiesel production from introduced species, considering to the yield per hectare and their oil content, was calculated. the results show the potential of biodiesel production for the three species canola, cotton and barley are respectively 98117.77, 58403.43, 83516.91 tons in tehran province.  canola, with the highest production potential of 0.84 ton per hectare is introduced as a superior species for future investments in biodiesel production in tehran province. this map can also affect policy of the agricultural sector. investing in the cultivation of biodiesel plants in these 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ghobadian, tmu research and development strategic plan on biomass and bioenergy. internal report prepared for bioenergy research laboratory, tarbiat modares university, 2001 [7] η. yousefi, υ. noorollahi, s. ehara, r. itoi, a. yousefi, y. fujimitsu, j. nishijima, k. sasaki, “developing the geothermal resources map of iran”, geothermics, vol. 39, no. 2, pp. 140-151, 2010 [8] h. yousefi, s. ehara, y. nurollahi, “geothermal potential site selection using gis in iran”, 32nd workshop on geothermal reservoir engineering, pp. 174-182, 2007 [9] y. nurollahi, m. a. ashraf, m zamani, “wind power potential evaluation of bakhtar regionl using geographical information system (gis)”, iran energy journal, vol.14, no. 1, pp. 121, 2011 [10] l. khodapanah, w. n. a. sulaiman, n. khodapanah, n. “groundwater quality assessment for different purposes in eshtehard district, tehran, iran”, european journal of scientific research, no.4, pp. 543-553, 2009 [11] l. khodapanah, h. jahanbin, m. sabzevari, annual report of groundwater resources exploitation, deputy for water resources study and research, tehran regional water authority, 2005 [12] h. myghany mashhadi, research on the use of rapeseed oil methyl ester as a fuel in a compression ignition engine with low round, phd thesis, university of medical sciences, tehran, iran, 2006 [13] d. k. agarwal, p. singh, m. chakrabarty, a. j. shaikh, s. g. gayal, cotton seed oil quality, utilization and processing, central institute for cotton research, technical bulletin no. 25, 2003 [14] n. t. dunford, “germ oils from different sources”, in: bailey’s industrial oil and fat products, wiley, vol. 6, 2005 microsoft word 22-3227_s_etasr_v10_n1_pp5217-5220 engineering, technology & applied science research vol. 10, no. 1, 2020, 5217-5220 5217 www.etasr.com pamplona & alves: civil aircraft emissions study and pollutant forecasting at a brazilian airport civil aircraft emissions study and pollutant forecasting at a brazilian airport daniel alberto pamplona air transportation department aeronautics institute of technology sao jose dos campos, brazil pamplonadefesa@gmail.com claudio jorge pinto alves air transportation department aeronautics institute of technology sao jose dos campos, brazil claudioj@ita.br abstract—in recent decades, the emissions of air transport industry pollutants and their impact on human health attract increased focus. the continued growth of air traffic and public awareness has transformed this field into one of the most important topics of commercial aviation. in the next 20 years, the estimated global demand for air transport will grow by an average of 5%. one of the direct consequences would be the increase in emissions, affecting significantly the communities around airports. the aim of this paper is to present an econometric model forecast of pollutant emissions generated by domestic flights in salvador airport. this model includes a derivative study of demand until the year 2020, considering the number of flights and emissions generated in the takeoff and landing cycles. results present a predictive model for the number of pollutant emissions. keywords-pollution; air transportation; forecast i. introduction in recent years, the environmental effects of aviation, the impact of aircraft engines on the emission of pollutants and the consequences on health and quality of life of the residents, have become major discussion points. the energy consumption of the primary world increased by 2.2% in 2017 [1]. moreover, fossil fuels are the most dominant energy source by a rate of 85% [2]. the burning of fossil fuels emits pollutants such as nitrogen oxide (nox), carbon monoxide (co), carbon dioxide (co2), sulphur dioxide (so2), and other harmful gases [3]. emissions from diesel fuels contribute to the occurrence of many respiratory, cardiovascular and cancer diseases. besides air, water and soil pollution, these emissions cause visibility reduction and contribute to the global climate change [4]. one liter of combusted diesel fuel produces 2.9kg of greenhouse gases, while one liter of combusted petrol produces 2.7kg [5]. according to [6], mobile sources, such as various fuel type engines, directly emit co2, methane (ch4), nitrogen oxide (n2o), co, non-methane volatile organic compounds (nmvocs), so2, particulate matter (pm), and nox that cause or contribute to air pollution. the aim of this paper is to conduct a prediction study about the emission of pollutants at salvador airport. this airport has the largest passenger and takeoff traffic in the northeast region of brazil. at first, the projected demand for the airport was used [7]. consequently, a derived study for the emission of pollutants until 2020 was conducted, using data from the intergovernmental panel’s on climate change (ipcc). the academic gain is achieved through the prediction of passenger’s demand and the estimation of the emission of pollutants by regular flights. unlike other studies, this emission forecast is not limited to a single model of aircraft, but studies various aircraft types. ii. literature review civil aviation as a cause of air pollution has attracted an increasing importance over the years, since the overall air traffic, conforming to former evaluations, is predicted to expand in the present and the upcoming decades [8]. field and data investigations have showed an interrelationship between pollutant concentration and aircraft traffic at airports in the us and europe [9]. in [10], the environmental impact of civil aviation was analyzed, given the high fuel consumption and the increase of the co2 emissions. in [11], the importance of studying the impact on airport neighborhoods in a wide range of areas was pointed out, including the case of air pollution. the local impact of zurich’s airport traffic was studied in [12], examining additionally the variation of pollutant emissions. the ultrafine particle number concentrations (pcns) emitted at high rates by jet aircrafts at logan international airport (boston, ma, usa) were examined in [13]. results showed that pncs were positively correlated with flight activity after considering weather conditions, time of day, week and traffic volume. the global impact of aircraft emissions near the los angeles international airport (lax) was assessed in [14], comparing the airport’s with the vehicular emissions on roads. particle accumulation was, on average, 4.1 ± 1.2 times higher at lax’s neighborhood than the considered freeways. results revealed that lax airport was a main source of pollution within its area of impact, compared to freeway emissions. health damage functions varied across airports for each precursor-pollutant relationship modeled in [15]. the variable patterns among health damage functions led to variable contributions of emitted pollutants to total health impacts across individual airports. two measurement campaigns of total pnc, near a medium-size airport in central italy (ciampino airport), were implemented in [16], implementing statistical regression models relating pnc data to the presence of aircraft activities. in [17], the air quality and climate benefits of holding aircrafts at their gates for up to 25 minutes to reduce corresponding author: daniel alberto pamplona engineering, technology & applied science research vol. 10, no. 1, 2020, 5217-5220 5218 www.etasr.com pamplona & alves: civil aircraft emissions study and pollutant forecasting at a brazilian airport congestion minimizing fuel burn and emissions from taxi operations by 35-38%, relative to no gate holds, was estimated. the future growth of aviation, the resulting fuel demand and the deployment of biofuels in the aviation sector in europe was studied in [18], projecting data for aviation growth and fuel demand on a year-by-year basis up to 2030. outdoor and indoor pncs from 16 residences located in two study areas in the greater boston metropolitan area were investigated in [19]. results indicated that aviation-related outdoor pnc infiltrate indoors and resulted in significantly higher indoor pnc, providing evidence for the impact of aviation-related emissions on residential exposures. emissions from the engines are approximately 70% co2, slightly less than 30% h2o and slightly less than 1% for nox, co, sox and nmvoc. modern engines emit low levels of n2o. ch4 emissions can occur when the aircraft is idle, while modern aircrafts emit low levels of this gas. aircraft operations are divided into landing/take-off (lto) cycle and cruise flight for the calculation of pollutants emissions [20]. air pollutants, may have detrimental effects and environmental impacts and pm is one of the air pollutants affecting, by severe ways, public health. an increment in respiratory diseases is usually linked to pm pollution, mainly due to pm10 and pm2.5 air pollution [21]. co2, a non-combusted gas released when fuels with carbon composition are combusted, is a substantial criterion of an engine’s exhaust emissions. co emissions are colorless, odor free and toxic. pm air pollution is an air-suspended combination of solid and liquid particles depending upon size, shape, surface area, number, chemical arrangement, solubility, and origin [22]. co is responsible for cardiovascular diseases, especially in persons with heart problems. nox cause lung irritation and lower resistance to respiratory infections. nmvocs are responsible for eye and respiratory irritations, headaches, dizziness, visual disorders, and memory impairment [6]. ipcc data were used to determine co2, ch4, n2o, nox, co, nmvocs and so2 emissions. when on ground and during the lto cycle, an aircraft produces approximately 10% of its emissions, except hydrocarbons and co. the lto cycle includes emissions during takeoff and landing below 3000 feet height [23]. this study uses a prediction of passenger demand model to estimate future environmental impacts, in relation to the emission of pollutants by regular flights in an airport, taking into account the variety of aircraft types. iii. estimation model and results the projected demand for the salvador airport, as studied in [7], was used to assess the impact of the economic growth in the number of domestic passengers. it was estimated that an annual economic growth of 1% would increase the number of domestic passengers by 0.744%. initially, the impact of 1, 2, 3, and 4% of annual economic growth and the direct increase in the number of passengers was simulated. the results are shown in figure 1. the expansion of passengers would lead the airlines to increase the number of flights, increasing the emissions of pollutants. a conservative annual economic growth of 1% was chosen and the flight schedule of july 2015 was used for the prediction of the total number of commercial aircrafts operating annually. table i shows the percentage of aircraft types operating per week. an average aircraft passenger occupancy rate of 80% was used for total passenger estimation. figure 2 shows the passengers’ forecast from 2014 to 2020. figure 3 shows the total number of aircrafts, per model, in the period from 2014 up to 2020. fig. 1. time series of the predicted number of passengers table i. percentage of aircraft type per week aircraft model participation (%) a318 4 a319 3 a320 31 at72 6 e190 12 b737-700 4 b737-800 36 total 100 fig. 2. passenger’s forecast by aircraft type from 2014 to 2020 fig. 3. time series of the predicted number of aircrafts by type engineering, technology & applied science research vol. 10, no. 1, 2020, 5217-5220 5219 www.etasr.com pamplona & alves: civil aircraft emissions study and pollutant forecasting at a brazilian airport figure 4 shows the total emission of pollutants estimated per year, where rows have their values represented on the left axis and columns on the right axis. fig. 4. total emissions of pollutants estimated in kg per year results show that the increase in air transportation demand will lead to an increase in the emission of pollutants. in the present study, a constant growth of demand of 0.744% per year would lead to a 65% increase in the emission of pollutants on 2020. the increase of gas emissions could lead to an increase to heart and respiratory diseases, among others, in the airport’s surroundings. this notes the concern that should be taken with aviation and its effects on health. iv. conclusion in recent years, researchers have become more interested in the environmental effects of aviation. the aim of this article was to study and predict the emission of pollutants at brazil’s salvador airport. the study showed that increasing demand would increase the emission of pollutants, affecting the areas and the population living around the airport. the main problem of this method is that lto data are only available for scheduled flights. general aviation flights, helicopters, instructional or leisure flights are not included in this methodology. in most countries, the emission levels of these flights would be insignificant, but may be significant, depending on country and region. in this study, these flights were considered insignificant. civil aviation is predicted to expand in the present and the upcoming decades. academic studies have showed an interrelationship between pollutant concentration and aircraft traffic at airports, highlighting the importance of studying the impacts in airport neighborhoods in a wide range of areas, including air pollution. studies should focus on airport base, since there is variability on aircraft fleet and traffic. companies that have market dominance are those that emit more pollutants, bringing consequences to people living close to airports. moreover, ways to compensate the community should be thought out. future studies should focus on this aspect, seeking to investigate in the increase of flight frequency and hospital admissions. these findings point out the need for more environmental studies examining aircraft 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emissions”, environmental research letters, vol. 10, no. 3, article id 034001, 2015 [10] m. grote, i. williams, j. preston, “direct carbon dioxide emissions from civil aircraft”, atmospheric environment, no. 95, pp. 214-224, 2014 [11] m. masiol, r. m. harris, “aircraft engine exhaust emissions and other airport-related contributions to ambient air pollution: a review”, atmospheric environment, vol. 95, pp. 409-455, 2014 [12] g. schurmann, k. schafer, c. jahn, h. hoffmann, m. bauerfeind, e. fleuti, b. rappengluck, “the impact of nox, co and voc emissions on the air quality of zurich airport”, atmospheric environment, vol. 41, no. 1, pp. 103-118, 2007 [13] n. hudda, m. c. simon, w. zamore, d. brugge, j. l. durant, “aviation emissions impact ambient ultrafine particle concentrations in the greater boston area”, environmental science & technology, vol. 50, no. 16, 2016 [14] f. shirmohammadi, m. h. sowlat, s. hasheminassab, a. saffari, g. ban-weiss, c. sioutas, “emission rates of particle 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m. t. bhatti, q. a. qazi, b. h. kaurejo, i. a. qazi, s. h. solangi, a. s. jamali. “analysis of co2, co, no, no2, and pm particulates of a diesel engine exhaust”, engineering, technology & applied science research, vol. 9, no. 6, pp. 4912-4916, 2019 [23] international civil aviation organization, “local air quality”, available at: https://www.icao.int/environmental-protection/pages/local-air-quality .aspx, 2015 microsoft word 18-3263_s1_etasr_v10_n1_pp5195-5200 engineering, technology & applied science research vol. 10, no. 1, 2020, 5195-5200 5195 www.etasr.com abbassi: sogi-based flexible grid connection of pv power three phase converters under non-ideal … sogi-based flexible grid connection of pv power three phase converters under non-ideal grid conditions rabeh abbassi college of engineering, university of hail, hail, kingdom of saudi arabia university of tunis, ensit, latice laboratory, tunisia higher institute of applied sciences and technology of kasserine, university of kairouan, tunisia r_abbassi@yahoo.fr abstract—this paper proposes a control strategy of improving the power quality of the energy exchanged between a photovoltaic generator (pvg) and an unbalanced grid. a voltage source inverter (vsi) allowing the control of the zero-sequence during unbalanced regimes is proposed. a second-order generalized integrators-based approach (sogi-ba), which suitably fits with the network's imbalances while ensuring the perfect isolation of the pvg from the adverse effects of the imbalance, is investigated. the investigation will focus mainly on three control objectives: the generation of a balanced current system, the active and reactive power's dependent control, and the elimination of the second frequency dc bus voltage fluctuations. the performance of this new approach is approved by various tests via matlab environment simulations. keywords-power quality; photovoltaic generator; voltage source inverter; active and reactive power dynamic control; voltage ridethrough; ancillary services; symmetrical components; sogi integrators i. introduction electronic power converters are a technology that allows efficient and flexible interconnection of different types of generators to the utility grid [1-3]. with the growing trend to increase the integration rate of distributed generation based on renewable energy systems (res), it is required to pay a particular attention to converters interfacing with the grid [4-5]. this requirement is a result of their important role as “synchronous converters” in future power systems. this is analogous to the critical role that the synchronous machines play in centralized power systems [6]. in addition, the role of the filter, usually dominated by inductors, remains crucial especially during the transitional operation phases. moreover, a further complication that derives from the management of the fluctuating power produced by the distributed generation systems, leads to the use of multiple voltage levels and thus more complex structures of converters [7]. also, challenges and opportunities for the design and control of the grid side converter (gsc) are strongly related to the availability of new powerful and intelligent computing devices [8-10]. these devices must be controlled to obey the need to operate with the lowest possible switching frequency in order to control the highest power level. various control schemes for balancing the output voltages of the grid-side converter (gsc) have been published [11-17]. the majority of them relies on vector (dq) control. a current and voltage dual-loop control method relying on instantaneous active and reactive power theory is suggested for the gsc in [3]. although this method shows excellent performance under balanced grid states, it is unable to convert ac quantities to dc quantities allowing pi controllers to process them quickly while ensuring zero error in steady-state [4]. however, under faulty grid conditions, the apperance of the negative sequence decreases the control accuracy. to resolve these drowbaks, an improved approach using a 4-leg inverter is suggested in [5] to allow a relatively low degree of imbalance. five reference current generation techniques have been developped in [18-19] to generate sinusoidal currents of the symmetrical sequences. in the same context, a simplified repetitive predictor-based grid-voltage feed forward approach has been designed for gridtied high-power vsi [16]. a phase locked loop-free slidingmode-based power control for grid-tied vsis under unbalanced grid conditions has been proposed in [21]. in addition to the emphasis on design and control of converters connected to the network, other basic and advanced topics related to synchronization with the network and control of pv systems under grid defects have been analyzed in [22-24]. to address the above issues, the present paper proposes an oriented control contribution to implement new concepts to remedy the interaction of the symmetrical components and thus manage the oscillations of the active and reactive powers. this contribution will aim achieving the safety of the operation and the continuity of service of the photovoltaic generator (pvg) connected to the distribution network. in order to ensure a coordinated control of the active and reactive powers for a better integration of a pvg into an unbalanced electrical grid, new control algorithms for the gsc during grid imbalances are proposed below. after presenting the pv generator modeling and control, the main objectives of this work are: corresponding author: rabeh abbassi engineering, technology & applied science research vol. 10, no. 1, 2020, 5195-5200 5196 www.etasr.com abbassi: sogi-based flexible grid connection of pv power three phase converters under non-ideal … • to introduce symmetrical sequence generation using fortescue theory and its drawbaks. • to develop and implement in matlab the proposed sogi-ba control algorithms for the gsc with lcl filter. • to present and discuss the results of time domain simulations under various symmetrical and asymmetrical conditions. • to outline the conclusions and suggest future work. ii. pv generator modeling and control accuracy is the most important factor to take into consideration when selecting an appropriate simulation model. the system configuration adopted in this work is the intermediate dc bus one depicted in figure 1. pvscpvs gsc lpv rpviii pv iopv vi v pv c r irc vdc electricalgrid 2 2gf gfr l 1 1gf gfr l f f r c g gl r i pv vpv vmpp * ii * vi viii v pv ipv 1 vi vdc − proposedcontrol system for gsc * pg * qg fig. 1. on-grid pv system used in simulations this decision is dictated by the importance of both the dcdc converter responsible for the maximum power point tracking and the dc-ac inverter to prevent the total and immediate stoppage of the energy production in case a problem occurs upstream of this converter [3]. a detailed modeling of the chosen model has been presented in [5]. iii. introduction to symmetrical sequences generation a. using fortescue theory traditionally, the analysis of three-phase systems has been carried out thanks to the symmetrical components making it possible to easily extract the characteristic information of such systems. the transformation of the space vector is derived from that of the symmetric components. the fortescue transformation, applicable to sinusoidal function phasors, allows the analysis of asymmetrical three-phase systems under sinusoidal conditions. the application of this transform to temporal quantities is given by (1), (2) and (3) leading to positive, negative and zero sequences, respectively [5]: [ ] ( ω φ ) 2 π ( ω φ ) 3 2 π ( ω φ ) 3 1 ² 1 ² 1 3 ² 1 g p g p g p j t pp a a a j t p p pb b b p j tc c c p v e v v va a v v e f v a a v a av v v v e ⋅ ⋅ + ⋅ ⋅ ⋅ − + ⋅ ⋅ ⋅ + +  ⋅                       = ⋅ = ⋅ = ⋅ ⋅                       ⋅   (1) [ ] ( ω φ ) 2 π ( ω φ ) 3 2π ( ω φ ) 3 1 ² 1 1 ² 3 ² 1 g n g n g n j t nn a a a j t n n nb b b n j tc c c n v e v v va a v v e f v a a v a av v v v e ⋅ ⋅ + ⋅ ⋅ ⋅ + + ⋅ ⋅ ⋅ − +  ⋅                       = ⋅ = ⋅ = ⋅ ⋅                       ⋅   (2) [ ] ( ω φ ) ( ω φ ) ( ω φ ) 1 1 1 1 1 1 1 3 1 1 1 g z g z g z j tz za a a j tz z zb b b z j t c c cz v ev v v v v e f v v v v vv e ⋅ ⋅ + ⋅ ⋅ + ⋅ ⋅ +       ⋅                = ⋅ = ⋅ = ⋅ ⋅                ⋅        (3) where : 2. 3 . π = j a e . b. positive sequence calculation on αβ reference frame the clarke transformation can be applied to calculate the components of the abc voltage vector in the αβ reference frame: 1 1 1 2 2 2 3 3 3 0 2 2 a a b b c c v v v t v v v v v α αβ β     − −         = ⋅ = ⋅ ⋅             −      (4) in the same reference frame, the instantaneous positive sequence voltage can be expressed by (5): [ ] [ ] 1 2 2 1 11 1 = 12 2 1 p p a a p b p bp p c c p j j v v v t v t f v v v v v t f t v v ve q qv v e α αβ αβ β α αβ αβ β π α α π β β − − −              = ⋅ = ⋅ ⋅                         = ⋅ ⋅ ⋅              − −   ⋅  ⋅=      −       −  (5) in time-domain, q is defined as a phase-shift operator [25]. it allows the generation of the quadrature-phase signal (90 degrees lag) of the original in-phase signal of αβ voltage vector. a disadvantage of fortescue components is that the transformation matrix is complex, which poses serious difficulties. for these reasons and others, new techniques such as sogi have been proposed for the synthesis of symmetric sequences. iv. system configuration of sogi-based control for gsc with lcl filter a. sogi for quadrature signal generation (qsg) to generate 90 degrees phase shifted signals of the components vα and vβ, various techniques are conceivable. engineering, technology & applied science research vol. 10, no. 1, 2020, 5195-5200 5197 www.etasr.com abbassi: sogi-based flexible grid connection of pv power three phase converters under non-ideal … given the inadequacy of these techniques, in this work we have resorted to the use of a generalized second-order integratorbased pll (sogi-pll) [12-13] whose base is illustrated in figure 2. the transfer function is as follows: 2 2 2 2 2 ' ( ) ( ) ' ( ) ( ) ' ' ' ' ' ' v d s s qv q s s k s v s k s k v s k s ω ω ω ω ω ω = = = = + + + + (6) k and ω’ are the damping factor and set resonance frequency of the sogi-qsg, respectively. for the sinusoidal grid voltage with frequency ω, the dq sogi-qsg outputs of the phasor v are expressed by (7) and (8), respectively: ( ) ( ) d d 22 2 2 2 2 1 d v' d.v d . .v ' d ' ' ' d tan ' j e k m k k ωω ωω ω ω ω ω θ ωω − = =  = = + −    − = =     (7) q q d q q q.v' q.v q . .v ' q . d 2 j e m m ω ω π θ θ = =  = =   = = −  (8) based on the previous mathematical foundations, the shematic of double sogi-qsg-based symmetrical sequences generation (dsogi-qsg) is depicted in figure 3 [25]. 1 s k v v′ q v′ ω′ ω′ 1 s fig. 2. equivalent schematic of the sogi-qsg vα vβ αβv vα′ qvα′ vβ′ qvβ′ p vα ′ p vβ ′ n vα ′ n vβ ′ 1 2 1 2 p αβ ′v n αβ ′v fig. 3. dsogi-qsg based symmetrical sequences generation after having generated the symmetrical sequences’ components referring to the stationary reference frame αβ, the following section focuses on the implementation of the proposed control approach in case of the connection of the gpv to an unbalanced grid via the gsc and an lcl filter. b. lcl filtering model as shown in figure 1, the passive damping at the lcl filter is ensured by the resistors in series with the capacitor [19]. if no damping resistors are integrated, the transfer function is: , 3 1 2 1 2 1 ( ) ( ) f d gf f gf gf gf v s l c l s l l s = + + (9) otherwise, in the presence of filter damping resistors, such a function is rewritten: , 3 2 1 2 1 2 1 2 1 ( ) ( ) ( ) f f f d gf f gf f gf gf f gf gf c r s v s l c l s c l l r s l l s + = + + + (10) the main contribution of the resistors rf is to attenuate the peak of the filter transfer function when only the inductive and capacitive elements are present. c. proportional resonant current controller for the inner loop control of gsc for the gsc inverter, one of the key objectives is the accuracy of the inner loop control of the converter. knowing that various types of controllers can be introduced to ensure this task, the proportional resonant (pr) current controller is used in this paper thanks to the simplicity of its implementation and its solid performance. however, it should be noted that for reasons of stability, which require the implementation of a damped or bandpass structure, the transfer function is expressed by: 2 2 0 ( ) 2 pr p r c s g s k k s sω ω = + + + (11) d. current reference generation under unbalanced conditions, the simplest strategy for power control is to keep the injected currents into the grid sinusoidal and balanced. this is the subject of the balanced positive sequence control (bpsc) [25]. the main scheme of the proposed control approach is depicted by the schematic in figure 4. if the quality of such currents is crucial, only the components of the positive sequence of the grid voltages is used to calculate the grid currents references as follows: * * 2 gp p p p p p i v g v v = ⋅ = ⋅ (12) the reference current vector *pi is perfectly sinusoidal and balanced. under unbalanced conditions, the instantaneous active power delivered at the point of common coupling (pcc) is different from its reference * g p due to the interaction between the positive sequence of the injected current *pi and the negative sequence of the grid voltage *nv . indeed: engineering, technology & applied science research vol. 10, no. 1, 2020, 5195-5200 5198 www.etasr.com abbassi: sogi-based flexible grid connection of pv power three phase converters under non-ideal … � � * 2 * * * * . . . gp p p p p n p g p v i v i v i ω = = + � (13) i p k s k s + +2 2ω dc v dc v ∗ * g p * g q i g v g p g q iαααα ∗∗∗∗ iββββ ∗∗∗∗ i ϕϕϕϕ q controller p controller dc v controller pq calculation i iαααα iββββ iαααα ∗∗∗∗ iββββ ∗∗∗∗ current controller current controller vαααα ∗∗∗∗ vββββ ∗∗∗∗ i p k s k s + +2 2ω i p k k s + i p k k s + i p k k s + (((( )))) g g 1 3 a a b b c c ab a bc b ca c p v i v i v i q v i v i v i = + += + += + += + + = + += + += + += + + abc αβ * v αβ abc ωωωω fig. 4. schematic of the proposed sogi-ba here, ω2 ~p is the power fluctuating at the second harmonic frequency. if the reference of the reactive power * g q is set to zero, its instantaneous value can be calculated as: � �20 * * * . . . q p p p n p g q v i v i v i ω = = + � (14) where 2 q ω � is the amount of reactive power oscillating at twice the fundamental grid frequency. in order to provide a smooth tracking capability and achieve zero error during the steady state condition, pr current controllers are applied for the inner current control loop of the gsc inverter. v. simulation results and discussions this section focuses on the matlab simulation results of the proposed algorithms. a detailed comparative study was carried out to highlight the performance of the dsogi-ba. the structure of the implemented simulation model consists of a grid-tied pv system, as presented in figure 1, where two power electronics converters ensure the interfacing with the grid. the first one is the mppt-controlled boost dc-dc converter. the second is the grid-side converter delivering 15kw to the grid. the simulated fault consists of a three-phase voltage drop affecting the three phases of the network with respective decreases of 75%, 50% and 25% of amplitude on phases a, b and c at t=0.1s (figure 5(a)). it is worth noting that the technique of filtering and generating the quadrature signal on the α axis does not have a large static error and the reconstructed signal ' rv α joins the real signal rvα after a reasonable time as depicted in figure 5(b). the error between ' rv α and rvα is canceled after a short time and the same observation is valid for the β axis. from the perspective of proving the robustness of the sequence separation technique, figure 6(a) shows the simulation results of the αβ components of the positive and of the negative sequence. in addition, the positive and negative sequences of the three-phase voltages, which were reconstructed from the detected amplitudes and phase angle are depicted in figure 6(b). (a) (b) fig. 5. (a) unbalanced grid voltages, (b) dsogi-qsg-based αβ components generation (a) (b) fig. 6. (a) αβ components, (b) fundamental component of the three phase postive and negative sequences extracted from grid voltages using sogi method the results previously analyzed clearly show the satisfactory performance of the technique used for the separation of symmetrical sequences and the grid synchronization of the command. in the following, special attention is paid to the quality of currents and active and reactive powers exchanged with the utility grid. indeed, faced with the same fault conditions, the results of simulations of the bpsc approach application show that, although the currents injected into the grid remain sinusoidal balanced and in phase with the corresponding voltages, the amplitude of such currents is increased to maintain the average injected active power when the fault occurs (figure 7(a)). unfortunately, we note the presence of oscillations of the second harmonic of the active and reactive powers exchanged with the grid pg and qg. it is important to note that the appearance of these oscillations is expected due to the interaction between the current of the positive sequence and the voltage of the negative sequence in engineering, technology & applied science research vol. 10, no. 1, 2020, 5195-5200 5199 www.etasr.com abbassi: sogi-based flexible grid connection of pv power three phase converters under non-ideal … (16)-(17). this is detrimental to the stability of the power system as shown in figure 7(b). the examination of figure 7 and its enlargement of its encircled portions shown in figure 8 verifies that the currents generated by the sogi-ba control system are perfectly sinusoidal and balanced even in the presence of the grid fault. (a) (b) fig. 7. (a) grid currents at pcc, (b) exchanged active and reactive powers at pcc the amplitude of these currents is constant despite the fact that a few minor oscillations are recorded during the appearance and disappearance of the asymmetric three-phase fault (figure 8(a)). with regard to the active (psogi-ba) and reactive (qsogi-ba) powers exchanged at the pcc, it is clear that the sogi-ba approach has succeeded in generating active and reactive powers that are almost insensitive to the occurrence of the asymmetric fault. (a) (b) fig. 8. zoom version of (a) grid currents at pcc, (b) exchanged active and reactive powers at pcc only a few rapidly amortized and canceled fluctuations can be seen at the moments of appearance and disappearance of the studied fault as depicted in figure 8(b). figure 8 depicts the expanded portions of figure 7. again, we can see that the sogi-ba control system achieves the best performance regarding power quality standards in terms of delivered currents and exchanged active and reactive power, because it garantees the fictive isolation of the gsc from the fault in the grid. vi. conclusion in this paper, a control approach based on second-order generalized integrators (sogis) and symmetrical sequences theory was proposed to provide effective support of gridconnected voltage source inverters’ operation under non-ideal grid conditions. the proposed control method involves the extraction of the symmetrical sequences of the unbalanced grid voltages using sogis, the coordinated control of active and reactive powers and the voltage and current control loops. simulations developed and programmed in matlab environment have proven the performance of the proposed approach in ensuring the service continuity even during asymmetrical grid voltage faults. acknowledgment the author acknowledges the financial support of the deanship of scientific research, university of hail, saudi arabia of this work through the project no. 160978, 2018. references [1] a. abbassi, m. a. dami, m. jemli, “a statistical approach for hybrid energy storage system sizing based on capacity distributions in an autonomous pv/wind power generation system”, renewable energy, vol. 103, pp. 81-93, 2017 [2] m. a. destek, a. aslan, “renewable and non-renewable energy consumption and economic growth in emerging economies: evidence from bootstrap panel causality”, renewable energy, vol. 111, pp. 757763, 2017 [3] r. abbassi, s. chebbi, “energy management strategy for a gridconnected wind-solar hybrid 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numerical-analytical hybrid approach for the identification of sdm solar cell unknown parameters”, engineering technology & applied science research, vol. 8, no. 3, pp. 2907-2913, 2018 [24] s. latreche, a. e. badoud, m. khemliche, “implementation of mppt algorithm and supervision of shading on photovoltaic module”, engineering, technology & applied science research, vol. 8, no. 6, pp. 3541-3544, 2018 [25] p. rodriguez, a. v. timbus, r. teodorescu, m. liserre, f. blaabjerg, “flexible active power control of distributed power generation systems during grid faults”, ieee transactions on industrial electronics, vol. 54, no. 5, pp. 2583-2592, 2007 engineering, technology & applied science research vol. 8, no. 5, 2018, 3369-3372 3369 www.etasr.com akhund et al.: contributing factors of time overrun in public sector construction projects contributing factors of time overrun in public sector construction projects muhammad akram akhund department of civil engineering, isra university, hyderabad, pakistan akhund42@gmail.com hafiz usama imad department of civil engineering, isra university, hyderabad, pakistan usama.imad@isra.edu.pk nafees ahmed memon department of civil engineering, mehran university of engineering & technology, jamshoro, pakistan nafees.memon@faculty.muet.edu.pk fida hussain siddiqui department of civil engineering, mehran university of engineering & technology, jamshoro, pakistan fida.siddiqui@faculty.muet.edu.pk ali raza khoso department of civil engineering, mehran university of engineering & technology, jamshoro, pakistan aliraza.khoso@faculty.muet.edu.pk abbas ali panhwar sindh irrigation department, sindh, pakistan abbasalipanhwar@gmail.com abstract—time overrun is a major issue in construction projects. its causes vary, depending upon the nature and size of the project. developing countries are more susceptible to this problem due to limited resources and lack of managerial skills. this paper focuses on the identification and classification of time overrun factors in public sector projects in pakistan. data was collected by the use of a questionnaire given to different professionals in the construction field. average index (ai) was used to determine each factor’s relative importance. results indicate that financial difficulties faced by constructor, inadequate planning and scheduling, financial difficulties faced by client, delays in payment by the client, delays in decision making by the client, design mistakes, frequent design changes, material shortage, incompetent sub-constructor assigned by the constructor, poor site management and supervision and inadequate constructor’s experience are the most significant factors of time overrun in public sector construction projects in pakistan. this study aims to be useful in addressing the issue of time overrun in the construction industry. keywords-time overrun; construction industry; public sector i. introduction in pakistan, the construction industry is growing and contributing significantly to the economic growth of the country. although pakistan is spending a significant amount of money on the construction industry, still it faces several issues and serious challenges [1], with frequent project time overrun being one of the major ones. project time overrun can be defined as the exceeding of project completion time from the anticipated and estimated duration of the project [2]. time overrun in public sector construction projects is a global issue. this tendency is augmented in developing countries. in an estimate, time and cost overruns are about more than 100% of the estimated time and cost. [3-5]. it has been identified that due to poor risk management applications, time overrun is a common issue in construction projects [6-7]. it has an adverse effect on the owner, consultant and constructor in terms of relationships development, issue of cash flow, distrust, legal actions and a general feeling of unease toward one other. ii. reasons of time overrun author in [1] presents the significances of schedule delay in construction. authors in [8] determined 83 factors of time overrun in construction projects of hong kong. in nigeria, 61 building construction projects were considered as a case study in [9], in which delay and budget overrun were found as the most responsible factors of time overrun. authors in [10], conducted a research in malaysian construction industry, and identified the effects and causes of delays: poor planning, contractor’s poor site management, poor constructor experience, insufficient funds provided from client on the completed work, issues with sub-constructors, shortage of materials at site, equipment availability and failure, labor supply, mistakes during execution. author in [11], studied the most common cases of time overrun in road construction projects in palestine. results revealed that the most significant common possible risks occur due to overrun factors such as constructor’s financial status, delays in payment by the client, breakdown in the marketing shares of west bank and political conditions, poor communication among construction stakeholders, poor equipment efficiency and high competition in bids. after the egyptian revolution, a case study [12], highlighted 99 causative factors of time overrun. from determined causes, the top most ranked factors were poor funding, material bribes and tactics policies, equipment shortage at the construction site, poor project scheduling, poor financial control on site, poor site management and supervision, rework due to mistakes and errors, poor planning and inadequate constructors. engineering, technology & applied science research vol. 8, no. 5, 2018, 3369-3372 3370 www.etasr.com akhund et al.: contributing factors of time overrun in public sector construction projects authors in [13] studied the schedule delay in construction projects of gwalior, india. the most important factors causing time overrun was poor planning and scheduling, poor documentation work, delay in material delivery and poor work progress. similarly, authors in [14] studied the causes and schedule delays in indian construction projects. the findings of their research were: poor constructor’s work and experience, poor risk management system, poor coordination and communication among client, constructor sub-constructor, consultant, designer, worker and supplier, delay in material delivery, poor planning and scheduling, poor supervision and site management, poor managerial skills, unqualified labor, delay in progressive payment, delay in sub-constructors work, change in orders from client and poor client’s experience and involvement. authors in [15] identified 12 major causes of delays in nigerian construction industry. the construction sector in bahrain is also facing the problem of time overrun which is caused by the shortage of manpower, poor communication between the stakeholder’s, poor planning and scheduling, inexperienced personnel, poor supervision and site management, difficulties in project financing [4]. authors in [16] investigated bridge construction projects of pune and found insufficient crane capacity, unavailability of skilled labor, design issues, labor issues, conventional method of bar cutting and bending, delay in procurement of bearing plate, poor site layout resulting in poor labor productivity and shortage of concrete as major issues affecting project time. authors in [17] conducted a questionnaire survey to determine the causes of time delay of road over bridge (rob) in india. from the list of 29 different causes the study identified, the top 5 factors identified as responsible for causing time delay and cost overrun of rob construction projects were land acquisition, many stakeholders, network displacement, legal requirements, and claims and disputes. authors in [18] also conducted a questionnaire survey and personal interviews to analyze factors affecting scheduling performance in ethiopian construction projects through the engineers’ perspective. from the list of 35 time overrun attributes, they identified 4, namely: conflict among project participants, poor human resource management and project manager’s ignorance and lack of knowledge which cause significant delay. similarly, authors in [19], based on questionnaire survey identified the top 10 delay factors in norwegian construction industry. most of the existing research has been carried out for private sector projects in different countries. no such research work has been reported regarding the public sector construction projects in pakistan and this research fills this gap. this study will help the stakeholders of the industry to deal with project time overrun in upcoming projects. hence, the purpose of this research is to identify the most significant factors of time overrun in public section construction projects in pakistan. this research study identifies the common factors of time overrun which can be thought of and so anti measures can be planned in order to minimize cost overrun in public projects of pakistan. iii. data collection and analysis various reasons which contribute to time overrun in construction projects were identified from the literature review in the previous section. among the list of identified factors responsible for time overrun, the related factors to pakistan’s construction industry were separated via a preliminary survey. as a part of the preliminary survey, unstructured interviews of constructors, consultants, clients, and experts were conducted to finalize factors. a questionnaire was then prepared for data collection. the finalized questionnaire was distributed among the experienced personnel involved in public sector construction projects of pakistan. the respondents were asked to rank the significance of these factors on a likert scale ranging from 1 (extremely significant) to 5 (not significant). the level of significance has been calculated with the statistical software package spss 20.0 through average index (ai) method [20, 21]. the ai obtained for each factor represents the importance or significance of the said factor as per given criteria: 4.50 <ai<5.00: extremely significant (es), 3.50 <ai<4.50: very significant (vs), 2.50 <ai<3.50: moderately significant (ms), 1.50 <ai<2.50: slightly significant (ss), 1.00 <ai<1.50: not significant (ns). iv. results and discussion one hundred and fifty questionnaires were distributed amongst practitioners who were selected randomly from clients, consultants, and constructors. of these 150 questionnaires, 111 were returned completed. data cleaning and data validation required a rejection of 6 questionnaires. hence, a total number of 105 completed questionnaires were considered for data analysis. figure 1 shows the summary of the data collection of the questionnaire survey. fig. 1. data collection summary the demographic feature summary of respondents participated in data collection for this research is shown in table i. the statistics regarding the correspondents’ experience indicate that most of the respondents have good experience in handling public sector projects in pakistan. engineering, technology & applied science research vol. 8, no. 5, 2018, 3369-3372 3371 www.etasr.com akhund et al.: contributing factors of time overrun in public sector construction projects table i. demographic features of respondents frequency percentage cumulative type of organization client 35 33.33 33.33 consultant 35 33.33 66.66 constructor 35 33.33 100.00 type of projects commercial 12 11.40 11.40 roads 17 16.20 27.60 residential 28 26.70 57.30 social amenities 10 9.50 63.80 bridges 9 8.60 72.40 others 29 27.60 100.00 total working experience 0-5 years 40 38.10 38.10 5-10 years 25 23.80 61.90 11-15 years 13 12.40 74.30 more than 15 years 27 25.70 100.00 level of position superintendent engineer 4 03.80 03.80 project manager 9 08.57 12.37 executive engineer 15 14.28 26.65 resident engineer 9 08.57 35.22 director 3 02.86 38.08 others 65 61.90 100.00 a. reliability test analysis before data analysis, a reliability test was performed to check the degree of consistency of the collected data. inner consistency was measured with the help of the cronbach’s α coefficient. for assessment of the reliability, the value of cronbach’s α in the range of 0.5 – 0.6 is desirable, while if α is less than 0.3, then the reliability is in low level and would not be accepted [7]. if cronbach’s α is more than 0.7, then the consistency index shows high reliability and it would be acceptable. cronbach’s α value for the collected data was found as 0.91 which is desirable and acceptable. the result of the reliability test confirmed the reliability of the collected questionnaire survey data which can be used for further analysis. b. ranking of time overrun reasons in construction projects ranking of factors leading time overrun has been evaluated with the ai method. table ii depicts the results and highlights the significant ranking of each time overrun factor, their respective ai and standard deviations. the first four factors are described below. 1) financial difficulties faced by the constructor public sector construction project personnel ranked financial difficulties faced by the constructor as extremely significant factor of time overrun. the respondents consider this issue as the main cause in the delay of work execution as hindrances in finance even at the constructor side might delay or stop the work. 2) inadequate planning and scheduling the stakeholders ranked inadequate planning and scheduling as the second highest ranked factor of time overrun. due to inadequate planning and scheduling, many other issues may be initiated. it might even lead to financial loss for the contractor and ultimately client too. the resolution of this problem can be in the form of hiring a good planner so that proper scheduling may become possible. table ii. ranking of time overrun factors factors es vs ms ss ns ai s.d rank financial difficulties faced by constructor 74 17 10 3 1 4.52 0.86 1 inadequate planning and scheduling 78 14 5 5 3 4.51 0.99 2 financial difficulties faced by client 39 31 24 7 4 3.90 1.10 3 delays in payment by client 42 27 23 9 4 3.90 1.14 4 delays in decision making by client 27 41 20 11 6 3.69 1.14 5 design mistakes 36 23 24 16 6 3.64 1.26 6 frequent design changes 28 31 25 16 5 3.58 1.17 7 material shortage at site 26 30 27 20 2 3.55 1.12 8 incompetent subcontractor 20 43 21 14 7 3.52 1.14 9 poor site management and supervision 26 26 35 12 6 3.51 1.15 10 inadequate constructor’s experience 23 33 29 14 6 3.50 1.14 11 delays in contractor's payment to subcontractor 23 28 26 23 5 3.39 1.19 12 incomplete drawings provided by consultant 21 36 21 16 11 3.38 1.26 13 excessive change in orders 23 24 33 18 7 3.36 1.19 14 lack of coordination among client, consultant and constructor 19 23 39 18 6 3.30 1.13 15 inadequate consultant’s experience 19 28 31 19 8 3.30 1.18 15 delay in material delivery 18 31 26 22 8 3.28 1.20 16 shortage of skilled labour 15 33 28 24 5 3.28 1.11 16 shortage of equipment 15 28 31 28 3 3.23 1.09 17 poor labour productivity 14 28 37 19 7 3.22 0.88 18 mistakes during construction 16 25 33 24 7 3.18 0.87 19 change in the project scope 18 29 24 21 13 3.17 0.87 20 lack of communication among client, consultant and constructor 16 19 44 18 8 3.16 0.87 21 fluctuation in material prices 17 22 34 23 9 3.14 0.87 22 improper construction methods 11 28 38 20 8 3.13 0.87 23 insufficient equipment 15 23 33 29 5 3.13 0.87 23 contractual claims 8 33 32 24 8 3.09 0.86 24 inspection delays of site by consultant 11 30 28 25 11 3.05 0.86 25 complex design of project 10 25 41 16 13 3.03 0.85 26 rework due to poor quality 11 26 28 26 14 2.94 0.86 27 excessive bureaucracy 10 29 28 19 19 2.92 0.86 28 changes in material specifications 11 22 28 32 12 2.89 0.86 29 changes in rules and regulations 14 21 25 27 18 2.87 0.87 30 unforeseen ground conditions 9 19 29 36 12 2.78 0.88 31 bad weather 14 10 21 36 24 2.56 0.91 32 accidents on site 14 9 21 37 24 2.54 0.91 33 3) financial difficulties faced by the client the third highest cause affecting the estimated time of construction project completion, was financial difficulties faced by the client. if the owner party wants to complete the projects on time with the specific requirements then a system must be generated by the owner’s party to resolve this issue. engineering, technology & applied science research vol. 8, no. 5, 2018, 3369-3372 3372 www.etasr.com akhund et al.: contributing factors of time overrun in public sector construction projects 4) delay in decision making by the client like other significant factors of time overrun, delay in decision making by the client is the fourth highest ranked factor by public sector construction personnel, which means it is quite a significant factor affecting construction projects completion time. this issue seems to be highly related to the financial difficulties faced by the constructor, inadequate planning, and scheduling, financial difficulties faced by the client and delays in payment by the client. v. conclusion this paper focused on uncovering factors of time overrun in public sector construction projects in pakistan. extensive literature review was carried out which helped in structuring the questionnaire for data collection. statistical analysis results of the questionnaire survey shown in table ii ranked financial difficulties faced by the constructor, inadequate planning and scheduling, financial difficulties faced by the client and delays in payment by the client, as the most significant factors of time overrun. identified factors will help stakeholders to plan accordingly in order to avoid the issue of time overrun. references [1] d. m. leishman, “protecting engineer against construction delay claims ndc”, journal of management in engineering, vol. 7, no. 3, pp. 314-333, 1991 [2] a. u. elinwa, m. joshua, “time-overrun factors in the nigerian construction industry”, journal of construction engineering and management, vol. 127, no. 5, pp. 419-425, 2001 [3] m. abd el-razek, h. bassioni, a. mobarak, “causes of delay in building construction: projects in egypt”, journal of construction engineering and management, vol. 134, no. 11, pp. 831-841, 2008 [4] r. hassan, a. m. s. suliman, a. y. malki, “an investigation into the delays in road projects in bahrain”, international journal of research in engineering and science, vol. 2, no. 2, pp. 38-47, 2014 [5] e. g. sinesilassie, s. z. s. tabish, k. n. jha, “critical factors affecting schedule performance: a case of ethiopian public construction projects–engineers’ perspective”, engineering, construction and architectural management, vol. 24, no. 5, pp. 757773, 2017 [6] n. ejaz, i. ali, m. f. tahir, “assessment of delays and cost overruns during construction projects in pakistan”, available at: http://dl.lib.mrt.ac.lk/handle/123/9431, 2013 [7] s. meepol, s. o. ogunlana, “factors affecting cost and time performance on highway construction projects: evidence from thailand”, journal of financial management of property and construction, vol. 11, no. 1, pp. 3-20, 2006 [8] d. w. chan, m. m. kumaraswamy, “a comparative study of causes of time overruns in hong kong construction projects”, international journal of project management, vol. 15, pp. 55-63, 1997 [9] a. a. aibinu, g. o. jagboro, “the effects of construction delays on project delivery in the nigerian construction industry”, international journal of project management, vol. 20, pp. 593-599, 2002 [10] m. sambasivan, y. w. soon, “causes and effects of delays in malaysian construction industry”, international journal of project management, vol. 25, pp. 517-526, 2007 [11] i. mohammid “common risks affecting time overrun in road construction projects in palestine: contractors’ perspective”, australasian journal of construction economics and building, vol. 13, no. 2, pp. 45-53, 2013 [12] r. f. aziz, “ranking of delay factors in construction projects after the egyptian revolution”, alexandria engineering journal, vol. 52, pp. 387-406, 2013 [13] a. upadhyay, v. gupta, m. pandey, “a case study on schedule delay analysis in construction projects in gwalior”, international research journal of engineering and technology, vol. 3, no. 5, pp. 13121315, 2016 [14] d. kumar, “causes and effects of delays in indian construction projects”, international research journal of engineering and technology, vol. 3, no. 4, pp. 1831-1837, 2016 [15] m. murray, m. seif, “causes of project delays in the nigerian construction industry”, european journal of civil engineering and architecture, vol. 10, pp. 1-7, 2013 [16] j. k. shah, r. m. apte, “causes of delay in construction of bridge girders”, journal of mechanical and civil engineering, vol. 12, no. 1, pp. 8-12, 2015 [17] c. b. venkateswaran, r. murugasan, “time delay and cost overrun of road over bridge (rob) construction projects in india”, journal of construction in developing countries, vol. 22, pp. 79-96, 2017 [18] e. g. sinesilassie, s. z. s., tabish, k. n. jha, “critical factors affecting schedule performance: a case of ethiopian public construction projects–engineers’ perspective”, engineering, construction and architectural management, vol. 24, no. 5, pp. 757773, 2017 [19] y. j. t. zidane, b. andersen, “the top 10 universal delay factors in construction projects”, international journal of managing projects in business, vol. 11, no. 3, pp. 650-672, 2018 [20] m. a. akhund, a. r. khoso, u. memon, s. h. khahro, “time overrun in construction projects of developing countries”, imperial journal of interdisciplinary research, vol. 3, no. 5, pp. 124-129, 2017 [21] m. akram, t. h. ali, n. a. memon, s. h. khahro, “causal attributes of cost overrun in construction projects of pakistan”, international journal of civil engineering and technology, vol. 8, no. 6, pp. 477483, 2017 microsoft word etasr_v13_n4_pp11271-11276 engineering, technology & applied science research vol. 13, no. 4, 2023, 11271-11276 11271 www.etasr.com karasahin & karali: performance comparison of different fuzzy logic controllers on vehicle… performance comparison of different fuzzy logic controllers on vehicle-caravan systems ali tahir karasahin department of mechatronics engineering, faculty of engineering, karabuk university, türkiye tahirkarasahin@karabuk.edu.tr (corresponding author) mehmet karali department of mechatronics engineering, faculty of engineering, necmettin erbakan university, türkiye mkarali@erbakan.edu.tr received: 20 april 2023 | revised: 3 june 2023 | accepted: 10 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5982 abstract active control techniques in vehicle-caravan (vc) systems are designed to prevent instability modes. this study used fuzzy logic controllers (flcs), developed using the differential braking method, to prevent instability modes in a vc system and increase yaw stability. four different flc-based controllers were designed for the vc system: type-1 mamdani, type-1 sugeno, simplified type-2, and interval type-2 (it2). flc-based controllers are used in vc systems due to nonlinear characteristics. this study showed that unstable situations can be prevented with flcs according to the inputs obtained from a single imu sensor placed in the caravan. the performance of the controllers developed in matlab/simulink was assessed using carsim. experimental studies showed that the skidding that occurs after the double lane change (dlc) maneuver is prevented by flc-based controllers and the yaw stability is increased. keywords-fuzzy logic controller; type-2 fuzzy sets; vehicle-caravan; differential braking i. introduction vehicle and trailer applications that are towed over a connection point are frequently preferred to increase vehicle carrying capacity and create different usage options. among these options, caravans are among the most common. despite the advantages of such uses, caravans complicate the dynamics of the vc system [1-4], and instability modes such as swing, folding, snaking, and jackknifing can occur in vc systems. active control techniques are used in vc systems against instability modes [5-24]. active control techniques can be used in both the towing vehicle and the caravan system. active steering control (asc) and active differential braking (adb) are active control techniques used in vehicle-caravan systems. in asc, a moment is created in the center of gravity to prevent skidding by giving a steering angle to the front or rear wheels [9], while the mechanism of the front or rear wheel must be arranged accordingly to use asc. in the case of understeer in the adb braking system, braking is applied to the right or left wheels, and a torque is applied in the opposite direction to the yaw moment that occurs around the center of gravity to damp the swing [7, 9, 16-21]. the adb system is often preferred, as it does not require much extra hardware compared to the asc. various studies have been carried out using the adb control method, and different control techniques have been used to determine the braking rate to be applied in the adb. model-based and model-independent methods are used in active control techniques developed using adb in vc systems. the model predictive control (mpc) controller was developed to increase the lateral stability of the trailer system and prevent the occurrence of unstable situations [7, 21-22]. examining the performance of the braking controller using the linear quadratic regulator (lqr) technique showed that stable responses were produced [4, 6, 22]. model-based controllers have the disadvantage that the system model can be used after modeling with different degrees of freedom according to the application area. the vc system has been modeled with different degrees of freedom, demonstrating the accuracy of different tests [1, 4, 23-24]. another requirement of the modelbased controller is that the state variables must be measured directly or obtained by estimation methods. it is not always desirable to perform these operations. at this point, for the reasons stated, model-independent control techniques are used instead of model-based controllers. this study used the fuzzy logic method as a modelindependent control technique, as there is no need for a system model if it is used as an active control technique in the vc system. several studies used the flc technique in vc systems, showing that unstable states were prevented [9, 21-24]. such studies usually compare the proposed controller with other control techniques or when the controller is turned off. this study investigated the performance of different flc controllers for vc systems. at first, the vc system was modeled with 3 engineering, technology & applied science research vol. 13, no. 4, 2023, 11271-11276 11272 www.etasr.com karasahin & karali: performance comparison of different fuzzy logic controllers on vehicle… degrees of freedom to obtain the system model required for the model-based controller and better understand the system dynamics. then, the flc design used in the adb method was carried out. flc controllers were designed using type-1 mamdani, type-1 sugeno, simplified type-2, and interval type-2 (it2) methods, and their performance was investigated using the double lane change (dlc) test. ii. vehicle-caravan modeling to better understand the forces and moments on the vc system, the system model needs to be derived. in the case of using model-independent controller methods, the system dynamics should be understood to form the rule base. therefore, the vc system is modeled with three degrees of freedom: vehicle lateral velocity (m/s), vehicle yaw rate (rad/s), and hitch angle (rad). figure 1 shows the free-body diagram of the vc system. wheels on the same axle in the vehicle and caravan were assumed to have the same slip angle, and the visualization was carried out on a single wheel. the symbols used in the equations are the vehicle lateral speed (v), yaw rate (r), longitudinal speed (u), hitch angle (ψ), steering angle (δ), caravan lateral speed (v'), yaw rate (r'), longitudinal speed (u') and wheel lateral forces (fiai). fig. 1. the free-body diagram of a 3 dof vehicle-caravan model. the equations of motion on the vehicle are given by: ����� � �. � �� �. ���� � � � � � (1) ����� � �. � ������ � ������� � � �. ���� � �� (2) �� � � �. ������ � �. ������ � �. � �. ���� � �. �� (3) similarly, the equations of motion on the caravan are given by: ����′� � �′. ′ � �� � � � . ��� � �� . ��� (4) ����′� � �′. ′ � ������ � � . ���� � �� . ��� (5) �� ′� � �ℎ. ������ � ". � . ��� � ". �� . ��� (6) the vc is a system that is connected via the hitch point. in this case, their velocities and accelerations at the connection point are considered equal. therefore, if the hitch angle, longitudinal and lateral velocity, and yaw rate are known, the longitudinal and lateral velocity of the caravan can be determined by: �# � �. ��� � �� � � ���� (7) � # � �. ��� � �� � � ���� � ". ′ (8) the equations of motion specified in (1)-(6) are nonlinear expressions. if a model-based controller is developed for the vc system, the equations of motion should be linearized. for this, the longitudinal velocity u is assumed constant, and (1) is ignored. using the small angle approximation, it was assumed that cosy=1 and sinψ=ψ. in addition, for the initial condition, it is necessary to act according to the case � � � #. to complete the equations of motion of the vc system, the lateral tire forces generated by the tires must also be modeled. using the linear tire model, it can be expressed as follows: �$ ��$ � � %$ �$ (9) the slip angles on the tires can be calculated by: �� � &'() * � �+ (10) �� � &,(* (11) �� � .&,(�/'0'1�'�0'1�2� 3 * � (12) after linearizing the motion equations of the vc system under the above-mentioned assumptions, they can be expressed in state-space form for the controller. in this case, the expression for the vc system is: 456� 7 � 8567 � �� � 0 (13) the state variable used in the vc system can be determined by: 567 � 5� � 7 (14) the m, d, and f matrices mentioned in (13) are shown in [6]. a. active trailer differential braking system the equations of motion must be updated to use the active control differential braking method in the vc system. in this case, the moments around the center of gravity of the caravan are the following: �� ′� � �ℎ. ������ � ". � . ��� � ". �� . ��� � δm= (15) in this case, (13) needs to be updated, as: 456� 7 � 8567 � %> � �� � 0 (16) > � δ4? (17) no changes were made in the m, d, and f matrices used in (16), which was formed because of the equations updated with the atdb method. the cb matrix added to this set of equations is shown in [6]. iii. fuzzy logic controller design the controller design was developed based on fuzzy logic to prevent instability modes in the vc system. fuzzy logic systems are often used for systems that contain nonlinear or time-varying expressions. these nonlinear dynamics and uncertainties can be modeled with the fuzzy set approach. fuzzy logic systems expressed as type-2 have emerged as a solution to problems experienced in correctly determining the membership function. type-2 fuzzy logic systems are preferred in the modeling of the system or in cases where there are engineering, technology & applied science research vol. 13, no. 4, 2023, 11271-11276 11273 www.etasr.com karasahin & karali: performance comparison of different fuzzy logic controllers on vehicle… uncertainties and nonlinear characteristics arising from the variability of use cases [22-23]. figure 2 shows the flc designed for the vc system. fig. 2. block diagram of the fuzzy logic controller scheme. flc determines the braking rate only based on data from the inertial measurement unit (imu) on the caravan. the type-2 fuzzy logic system includes the type-reducer operator, unlike type-1. figure 3 shows the schematic design of the type-2 flc designed to prevent unstable situations that may occur in the caravan system. fig. 3. scheme of type-2 the fuzzy logic controller. apart from this, the methods used in the type-1 fuzzy logic system were used similarly. flc design was carried out in matlab/simulink [23]. in it-2 flc, input values of yaw rate and lateral acceleration are created when determining the braking rate to prevent skidding. figure 4 shows the membership functions used in the fuzzification of the it-2 flc input values. fig. 4. input membership function of yaw rate. figure 5 shows the membership function of the lateral acceleration, which is another input value used in the flc. the input yaw rate membership function used in the it-2 flc was set to fuzzification yaw rates between -15 deg/s and 15 deg/s. the lateral acceleration input was adjusted to fuzzification values between -3 m/s 2 and 3m/s 2 . figure 6 shows the crisp membership function output of the it2-flc. fig. 5. input membership function of lateral acceleration. fig. 6. output membership function of differential brake. as a result of the type-reducer mechanism, five different crisp outputs were produced by the defuzzification. these were: negative big (nb), negative small (ns), zero (ze), positive small (ps), and positive big (pb). table i shows the rule-based relationship between inputs and outputs in it-2 flc. table i. fuzzy logic controller rule base yaw rate lateral acceleration nb ns ze ps pb nb nb nb nb nb nb ns nb nb ns nb nb ze nb nb ze ps pb ps pb pb ps pb pb pb pb pb pb pb pb figure 7 shows the control surface for the relationship between the input and the output membership functions used in the it-2 flc. the response surface, which is used to visualize the relationship between input and output membership functions outside of the rule table, increases the expert's command of the rule base. engineering, technology & applied science research vol. 13, no. 4, 2023, 11271-11276 11274 www.etasr.com karasahin & karali: performance comparison of different fuzzy logic controllers on vehicle… fig. 7. response surface of interval type 2 fuzzy logic controller. iv. tests the flc-based yaw controller of the vc system was developed in matlab/simulink in four variants: type-1 mamdani, type-1 sugeno, simplified type-2 [24], and it-2. the performance of the flc controllers was evaluated with the dlc test and compared with the results of a separate test with the controller turned off. figure 8 shows the steering angle applied for the dlc scenario performed at 80 km/h. fig. 8. steering angle applied in the dlc test. the results obtained for the closed and open conditions of the controller were compared. the it-2 flc results were used in the controller test, and figure 9 shows changes in caravan yaw rate, lateral acceleration, and hitch angle in the dlc test. figure 9(a) shows the caravan yaw rate in the cv system, where a maximum of 37 deg/s was obtained when the controller was off and 24 deg/s when it-2 flc was active, showing a 35% improvement. figure 9(b) shows the lateral acceleration value on the caravan, showing a maximum value of 0.63 g when the controller was off and 0.57 g when it was active. it-2 flc exhibited 10% more stable behavior when comparing lateral accelerations. figure 9(c) shows the angle change that occurred at the hitch point between the vehicle and the caravan, showing a maximum change of 14.7 deg when the controller was off and a maximum change of 6.46 deg when it-2 flc was active. fig. 9. performance of active control technique based on the it-2 flc for dlc: (a) yaw rate, (b) lateral acceleration; and (c) hitch angle. a comparison of the performance of different flc-based controllers designed to prevent instability modes that may occur in the vc system was performed with the dlc maneuver. figure 8 shows the steering angle applied for the dlc maneuver. the controllers determined the braking rate to prevent the instability modes after this input. the yaw was prevented due to the applied braking force. figure 10 shows the results of the controller performance comparison. fig. 10. performance of active control technique based on different flc for dlc: (a) yaw rate, (b) lateral acceleration; and (c) hitch angle. engineering, technology & applied science research vol. 13, no. 4, 2023, 11271-11276 11275 www.etasr.com karasahin & karali: performance comparison of different fuzzy logic controllers on vehicle… the change in yaw rate was 65 deg/s when the controller was off and 31.5 deg/s when the flc-based controller was active. according to the hitch angle data, flc-based controllers were 51.5% more successful. in terms of lateral acceleration, peak-to-peak was 0.893 g when the controller was off and 0.686 g when the flc-based controller was active. in terms of lateral acceleration, the flc-based controller was 23% better. in terms of hitch angle, a 23.85 deg change was observed when the controller was off and a 10.6 deg swing occurred when it was active. according to the data obtained, the flc-based controllers were successful at a rate of 55.5%. these results show that flc-based controllers successfully prevent instability modes in the vc system. in addition to examining these variations, the forces occurring at the hitch point were observed, as they are included in the system dynamics that affect the lateral stability of the vc system. the longitudinal and lateral forces acting on the connection point affect the moments formed around the center of gravity. additionally, the force acting on the connection point on the z-axis affects the dynamics that occur on the roll axis of the caravan. figure 11 shows the longitudinal, lateral, and vertical forces at the connection point. fig. 11. force values at the hitch point after the dlc maneuver: (a) x-axis hitch force, (b) y-axis hitch force, and (c) z-axis hitch force figure 11(a) shows the results obtained for the longitudinal force change at the hitch point. the lower longitudinal force when the controller was off was because no braking force was applied to the caravan tires. this value was 1600 n when the controller was off and increased to 3600 n when active. figure 11(b) shows the variation in lateral force that occurred on the hitch. the reason for obtaining higher values with an active controller is the braking force applied by the tires. a force of 780 n was observed on the y-axis when the controller was off, while it was 1370 n when the flc-based controller was active. when examining the braking forces applied by the flc-based controller, it was observed that reactions were produced that prevented the formation of instability modes. figure 11(c) shows the vertical forces that occurred at the hitch point. like other axes, a value of 570 n was observed in the z-axis when the controller was off, and a 910 n was determined in the case of active flc-based controllers. to detect instability modes that may occur on the roll axis, it is necessary to follow the vertical forces that occur at the hitch point. when examining the vertical forces at the hitch point after the dlc maneuver, it was observed that less force acted when the t1-sugeno controller was active. v. conclusion this paper presented an flc-based yaw controller to prevent instability modes in a vc system, as these controllers are preferred due to the non-linear characteristics of vc systems. the performance of these controllers, developed in matlab/simulink, was evaluated with the dlc maneuver applied in carsim. simulations were carried out when the controllers were active and offline, and the results were compared. the designed flc-based controllers were: t1mamdani, t1-sugeno, simplified t2, and it-2. according to the results obtained, it was shown that different types of fuzzy logic-based systems prevent instability modes. the t1-sugeno and it-2 flc controllers were more successful than the others, according to the yaw rate, lateral acceleration, changes in the hitch angle, and the force values formed at the hitch point. various optimizations can be applied to the interval values of the membership functions to further improve the results of the it-2 flc. it was observed that different types of fuzzy controller systems performed close to each other. therefore, the use of type-1 and it2 flc is preferred, which were developed according to the constraints on the hardware to be used in the field test. references [1] y. he and j. ren, "a comparative study of car-trailer dynamics models," sae international journal of passenger cars mechanical systems, vol. 6, 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pakistan aj_balouch@ yahoo.com chemical engineering dpt, mehran university of engineering & technology, pakistan zeenat.ali@ faculty.muet.edu.pk abstract—rice husk has the potential to be used as a source of alternative energy e.g. as biofuel. its high lignin content, however, poses difficulty to this use. this study investigates the use of microwave assisted acidic and alkaline pretreatment methods to improve the characteristics of rice husk for energy production. the use of microwave assisted 3.5% naoh provided optimum pretreatment of rice husk; the lignin content was reduced from 17.8 to 10.2%, the cellulose content increased from 38.6 to 59.3% and the c/n ratio was within the optimum range of 25-35. the results showed enhanced potential of biofuel production from rice husk by this pretreatment. keywords-chemical pretreatment; microwave; rice husk; lignocellulose biomass i. introduction fossil fuels have been a main energy source in modern world. their continuously diminishing reserves, however, have raised concerns about their sustainability. pollutants from the derivation and usage of these fuels are also detrimental to the environment. these concerns stipulate an energy source, that is economical, abundantly available, sustainable, and environment friendly [1,2]. agricultural wastes (biomass) are viewed as good candidates for alternative energy sources. with an estimated worldwide annual production of 140 billion metric tonnes, agricultural wastes have the potential to produce energy approximately equivalent to 50 billion tonnes of oil. biomass derived energy contributes to energy security and clean climate change mitigations, and is environment friendly and carbon neutral [3]. producing biogas by anaerobic digestion of different solid wastes and residues, like municipal solid wastes and agricultural solid wastes, has been experimentally investigated and due to its economic feasibility, it is considered one of the best future options available [4, 5]. agricultural biomass waste along with holocelluloses also contains lignin. the holocelluloses are tightly packed by the lignin layers, these lignin layers limit digestion by acting as a protective wall in plant materials. thus the lignocellulose biomass pretreatment is necessary for an effective and rapid biodegradation or anaerobic digestion. pretreatment causes delignification and results in increased surface area and porosity of biomass, while decreasing the holocelluloses crystallinity and reducing the degree of polymerization. pretreatments are classified as:  mechanical or physical pretreatment: in this pretreatment the lignocellulose biomass waste is pretreated by different physical techniques like milling, grinding, irradiation, thermal, and hydrothermal.  chemical and physico-chemical pretreatment: in this pretreatment the lignocellulose biomass waste is mixed with chemicals, or soaked in chemical solutions, like acid, alkali, or oxidizing agents. this pretreatment also includes gas treatment, steam explosion, and solvent extraction techniques.  biological pretreatment: in this pretreatment the fungi and/or actinomycetes are used to pretreat the lignocellulose biomass waste biologically [4,6]. all the pretreatment techniques are useful in treating lignocellulose biomass, but the effectiveness of any pretreatment varies widely and is determined by the method selected. researchers have reported that chemical or physicochemical pretreatment provides better results in treating lignocellulose feed stocks as compared to other treatments [6]. there are several treatment techniques classified as chemical or physico-chemical pretreatment, but acidic and alkaline pretreatments are considered most effective and useful for lignocellulose disruption. different acidic or the alkaline concentration solutions are used for pretreatment, but mostly dilute acid and alkaline concentrations are preferred so that the chemical concentration must only be sufficient to disrupt the lignin content, as high concentrations may result in the loss of holocelluloses, which is to be degraded into biofuels. authors in [7] reported increase in cellulose content to more than 50 % using 0.5 to 1% sulphuric acid pretreatment on rice straw. authors in [8] compared various alkaline pretreatments to evaluate their effects on lignin disruption and enzymatic digestibility of various lignocellulose biomass (eucalyptus residue, larixleptolepis, pinups rigida, rice straw and barley engineering, technology & applied science research vol. 8, no. 3, 2018, 3084-3087 3085 www.etasr.com laghari et al.: delignification of rice husk by microwave assisted chemical pretreatment straw); they found that alkaline pretreatments were effective in lignin degradation. authors in [9] studied the time reaction of alkaline pretreatment on rice husk and found that alkaline pretreatment caused lignin degradation. microwave irradiation is also a useful physical pretreatment and has been shown to be very effective over conventional thermal treatment for waste sludge [10]. in [11] microwave assisted alkali pretreatment was used for rice straw and reported increase in cellulose content from 38.9% to 69.3% with lignin reduction from 13.6 to 5%. in [12] sugarcane baggase lignocellulose disruption was studied by using microwave assisted sulphuric acid, and reported increase in cellulose content from 52.25% to 67.31%. rice husk is one of the most abundant agricultural wastes. the worldwide annual husk output is about 140 million tonnes [13]. it has good potential for bioethanol production [14], however like other lignocellulosic biomass it also contains high lignin content. rice husk has been successfully pretreated for enhancing energy generation as a result of delignification and sachrification. authors in [15] studied the pretreatment of rice husk with various acidic and alkaline solutions, and found that hydrochloric acid produced best results by increasing cellulose content to 65.1%. authors in [16], investigated wet air oxidation pretreatment, and found that under optimized conditions it is possible to decrease lignin from 19.4% to 4.46% and increase cellulose content from 42.2% to 65.33%. authors in [17] studied the ultrasonic pretreatment for increasing bio-oil yield, and reported that yield of bio-oil increased from 37.1% to 42.8%, as a result of delignification and increased exposure of cellulose. in [18], the comparative effects of pretreatment using dilute sulphuric acid and sodium hydroxide on rice husk for bioethanol production and enzymatic hydrolysis were studied, and it was reported that 3% sodium hydroxide was successful in reducing lignin content from 19.2% to 9.6% and increasing cellulose content from 37.6% to 54.2%. ii. materials and methods a. materials rice husk was obtained locally at tronoh, and was milled and ground to the size of 1 mm or less by using a rocklabs mortar grinder type btrm model 1a. the ground rice husk was then subjected to the soxhlet extraction overnight by nrel extractives removal procedure [19, 20] to remove extractives in order to get accurate lignin values, after extractives removal the rice husk sample was placed in the air tight containers for use later. b. chemical solutions a total of 12 solutions using four chemicals viz., sulphuric acid, sodium hydroxide, hydrogen peroxide, and sodium carbonate, each at 3 different concentrations i.e. 2%, 3.5%, and 5% were prepared. strong solutions of sodium hydroxide and sodium carbonate were prepared using solid pellets, and then they were diluted to the desired strength. 1 g of rice husk was mixed with 10 ml of each solution for 48 hours, the sample was then heated by microwave irradiation for 5 min. each experiment and analysis was at least repeated three times. c. microwave faber microwave oven model fmo 7020 with input power 1050 w and output power of 700 watt was used. this microwave oven has 5 settings as low, medium low, medium, medium high, and high, with the output of 17%, 33%, 55%, 77%, and 100% microwave energy respectively [21]. in this pretreatment medium low setting with 33% output microwave energy was used. d. analytical methods the elemental analysis was performed using leco chn900/chns-932/vtf-900 elemental analyzer before and after pretreatment. rice husk samples were analyzed for composition, to determine the quantity of cellulose, hemicellulose, and lignin content before and after pretreatment by standard procedure according to [22]. in this process lignin was analyzed by two stage acid hydrolysis and the carbohydrates were examined by hplc. the hplc system consisted of agilent hiplexpb column and refractive index (ri) detection system. the isocratic mobile phase selected was deionized water at a flow rate of 0.6ml/min and 80°c. and the moisture content was obtained by drying overnight in oven at 105°c by the procedure specified in [23], while the ash content was analyzed by using a benchtop muffle furnace in accordance with [24]. iii. results and discussion a. elemental composition table i shows elemental composition with c/n ratios obtained by different microwave assisted chemical pretreatment methods. c/n ratio of 22.7 was observed for untreated rice husk, while the pretreated rice husks gave a range of c/n ratios varying from 10.4 to 40.7. table i. elemental composition of rice husk before and after pretreatment serial no. sample carbon % hydrogen % nitrogen % 01. untreated rice husk 40.60 5.06 1.79 naoh mw treated rice husk 2% 32.94 3.84 0.81 3.5% 36.72 3.33 1.20 5% 38.81 4.51 1.39 na2co3 mw treated rice husk 2% 29.02 2.53 1.17 3.5% 25.07 4.38 1.38 5% 22.12 2.43 1.69 h2o2 treated rice husk 2% 24.32 2.99 1.07 3.5% 23.77 3.50 1.38 5% 22.37 1.97 1.64 h2so4 mw treated rice husk 2% 21.30 1.97 0.95 3.5% 18.13 1.85 1.27 5% 14.69 1.59 1.41 the minimum and maximum c/n ratios were obtained for pretreatments with 5% sulphuric acid and 2% sodium hydroxide respectively. c/n ratio range of 25 to 35 is considered suitable for optimum biogas production by ana pre hy lev b. cel lig pre ric con so eff mi sod ric ta in s engineerin www.etasr aerobic dige etreatments by droxide, incre vel as shown in chemical co table ii sho llulose, hemic gnin data sho etreatments ap ce husk. figu ntent of micr odium hydrox fective among icrowave assis dium hydroxid ce husk was ob able ii shows all microwav s. no. 1 u fig. 3. per ng, technology r.com estion [25]. y 3.5% sodiu eased the c/n n figure 1. fig. 1. c/n omposition ows the comp cellulose, ligni ows that all pplied were ab ure 2 shows th rowave assiste ide pretreatm gst the pretr sted alkali pre de, the percent btained as 36. that cellulose ve assisted che sample untreated rice hu 2% 3.5% 5% 2% 3.5% 5% 2% 3.5% 5% 2% 3.5% 5% rcentage of cellulo y & applied sci it was o um hydroxide ratio of rice h n ratio of sample mposition of ri in, ash and mo microwave ble to reduce th he percentage ed pretreated ment was foun reatment met etreatment usi tage decrease i .5, 42.7 and 3 content incre emical pretrea table ii. cell usk ose increased in p ience research laghari et a observed that e, and 5% so husk to the opt es ice husk base oisture conten assisted che he lignin cont e decrease of rice husk sam nd to be the thods studied ing 2, 3.5, an in lignin level 30.3 % respect ement was obs atment of rice chemical comp lulose % 38.6 51.6 59.3 57.4 n 40.3 42.6 44.5 44.3 47.2 48.3 44.7 54.2 49.3 pretreated rice hus h v al.: delignificat t the odium timum ed on nt. the emical tent of lignin mples. most d. for nd 5% in the tively. served husk. fig mic per sod 5% and c. has etha cell gra 710 wit per reco fig. verti position of rice hemicellulos 19.7 naoh mw trea 13.7 10.5 9.3 na2co3 mw trea 18.9 18.4 17.6 h2o2 mw treat 17.8 16.1 13.6 h2so4 mw trea 15.9 11.4 13.8 sk lim acid wer hus wer beh ach vol. 8, no. 3, 20 tion of rice hu gure 3 shows t crowave assist rcentage increa dium hydroxid % sodium hydr d 2% sodium h energy poten cellulose has s been successf anol or bioga lulose can pro ams of co2 [2 0 ml of biogas th 51 to 56 rformed in th overy from ric 2. percentag ical lines shows t husk before an se % li ated ated ted ated the use of ri mited by its h dic and alkalin re able to enha sk. the study re effective i havior of the hieved with m 018, 3084-3087 usk by microwa the percentage ted pretreated ase in cellulos de pretreated roxide (48.7% hydroxide (33. ntial s a very high p fully used for as. it has bee oduce up to 5 26]. it has also can be recove 6% methane his study is ce husk by incr ge decrease of lig the standard error nd after pretrea ignin % a 17.8 11.3 10.2 12.4 16.4 15.7 14.5 15.2 14.6 14.1 16.5 14.8 14.2 iv. co ice husk as a high lignin co ne pretreatmen ance the poten has shown th in changing rice husk sa microwave assi ave assisted ch e increase of c rice husk sam se content was rice husk (53 %), 3.5% sulph 7%). potential of en biofuel genera en reported t 51.4 grams of o been reporte ered from each [27]. thus, capable of reasing the cel gnin content in pr s atment ash content % 12.5 13.6 9.4 11.2 14.9 13.3 13.7 12.8 11.2 13.3 12.9 10.3 12.8 onclusion a source of alt ontent. the m nt methods ap ntial of energy hat the pretre the chemical amples. optim isted alkaline 3086 hemical pretrea cellulose conte mples, a signif s observed in .6%), followe huric acid (40 nergy recovery ation in the for that 100 gram f ethanol and ed that theoreti h gram of cellu the pretreat enhancing en llulose content retreated rice hus moisture % 7.9 6.3 6.9 6.4 6.1 6.7 6.2 7.2 7.4 7.2 6.5 6.4 6.2 ternative ener microwave ass pplied in this recovery from atments perfo l composition mum results pretreatment u atment ent of ficant 3.5% ed by 0.4%) y, and rm of ms of 48.6 ically ulose, tment nergy t. k. the % rgy is sisted study m rice ormed n and were using engineering, technology & applied science research vol. 8, no. 3, 2018, 3084-3087 3087 www.etasr.com laghari et al.: delignification of rice husk by microwave assisted chemical pretreatment 3.5% naoh solution. the lignin content was reduced from 17.8 to 10.2%, whereas the cellulose content increased from 38.6 to 59.3%; the c/n ratio was within the optimum range of 25-35. the increase in cellulose content will be effective in enhancing production of biofuels like bioethanol, biomethane or biohydrogen by fermentation or anaerobic digestion. acknowledgement financial assistance in the form of graduate assistantship to the first author by the universiti teknologi petrona, seri iskandar, perak, malaysia is acknowledged. the authors are thankful to the institute of advanced research studies in chemical sciences (iarscs), university of sindh, and jamshoro, pakistan for the assistance in sample analyses. references [1] m. fatih demirbas, m. balat, h. balat, “biowastes-to-biofuels”, energy conversion and management, vol. 52, no. 4, pp. 1815-1828, 2011 [2] c. escamilla-alvarado, e. ríos-leal, m. t. ponce-noyola, h. m. 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[21] faber, faber microwave oven instruction manual, model: fmo 7020 [22] a. sluiter, b. hames, r. ruiz, c. scarlata, j. sluiter, d. templeton, d. crocker, determination of structural carbohydrates and lignin in biomass, national renewable energy laboratory, u. s. department of energy, 2012 [23] a. sluiter, b. hames, d. hyman, c. payne, r. ruiz, c. scarlata, j. sluiter, d. templeton, j. wolfe, determination of total solids in biomass and total dissolved solids in liquid process samples, national renewable energy laboratory, u. s. department of energy, 2008 [24] a. sluiter, b. hames, r. ruiz, c. scarlata, j. sluiter, d. templeton, determination of ash in biomass laboratory analytical procedure (lap), national renewable energy laboratory, u. s. department of energy, 2008 [25] w. mussoline, g. esposito, a. giordano, p. lens, “the anaerobic digestion of rice straw: a review”, critical reviews in environmental science and technology, vol. 43, no. 9, pp. 895-915, 2013 [26] p. c. badger, “ethanol from cellulose: a general review” in: trends in new crops and new uses, ashs press, alexandria, 2002 [27] a. w. khan, t. m. trottier, g. b. patel, s. m. martin, “nutrient requirement for the degradation of cellulose to methane by a mixed population of anaerobes”, journal of general microbiology, vol. 112, pp. 365-372, 1979 engineering, technology & applied science research vol. 7, no. 2, 2017, 1482-1485 1482 www.etasr.com malalla and shareef: a novel approach for arabic text steganography based on the “bloodgroup”… a novel approach for arabic text steganography based on the “bloodgroup” text hiding method suhad malalla department of computer science university of technology baghdad, iraq suhad_malalla@yahoo.com farah r. shareef department of computer science university of technology baghdad, iraq sabahaliraq2014@gmail.com abstract—steganography is the science of hiding certain messages (data) in groups of irrelevant data possibly of other form. the purpose of steganography is covert communication to hide the existence of a message from an intermediary. text steganography is the process of embedding secret message (text) in another text (cover text) so that the existence of secret message cannot be detected by a third party. this paper presents a novel approach for text steganography using the blood group (bg) method based on the behavior of blood group. experimentally it is found that the proposed method got good results in capacity, hiding capacity, time complexity, robustness, visibility, and similarity which shows its superiority as compared to most several existing methods. keywords-information security; steganography; hiding message; text steganography; arabic stego i. introduction exchanging hidden information is an important domain of information security which includes different methods such as cryptography, steganography, etc. [1]. steganography is a newfangled approach of securing messages from outside interference/attacks in an exceptional way. this technique provides a way that anticipated recipient recognizes the subsistence of the message(s). this is just obscuring a file, message, image, or video within another. steganography is a way of covering a message surrounded by an extra message, so that nobody can have a notion of its presence. messages can be perceived by the pre-determined addressee only. in steganography the information is concealed in the cover media so no person observes the presence of the secret information. the working of steganography has been implemented on different medias like text, video, images, and sounds [2]. fundamentally, stenographic techniques need to find insignificant bits of medium or cover files. thus, any kind of modifications to those insignificant bits shouldn't damage the integrity of the cover medium. nevertheless, undetectability might be generally implemented by adding invisible modifications to the cover file. for text steganography method, the stego text fidelity is generally utilized to evaluate and calculate the undetectability of the steganography method used. nonetheless, fidelity describes the possibility of persons to discover variations between the stego and cover text. nonetheless, the cover text integrity is not conserved with steganography because some parts of the cover file needs to be modified or changed to be able to hide the secret message and obtain the stego file [3]. text stenography is not usually utilized since the files of text a have tiny amount of unnecessary data. the aim of this paper is to describe a new method for text steganography through text and proposed a novel steganography technique for arabic language called “blood group” stenographic method. ii. previous works the first proposal in the arabic text steganography was done in [4]. their schema is dependent on concealing binary values within persian or arabic scripts by using a characteristic of coding strategy. this approach is dependent upon the points inherited within the persian, urdu and arabic letters. the points' location on the letters conceal certain data. the hidden data length (i.e. the secret object) is considered as a binary using the first several bits. the middle text, (i.e. the cover object) is scanned in such a way when a pointed letter is detected. the position of the point is shifted up slightly when the hidden value is 1otherwise, the location remains unchanged. the advantage of this method is the large amount information will be concealed in text due to the large number of points in letters for both persian and arabic. authors in [5] proposed a new steganography approach to conceal hidden secret data within arabic text cover media. the suggested method employs arabic language diacritics that are utilized for vowel sounds and it’s located in several religious documents. about 8 of these symbols are found in arabic. they discovered that the “fatha” symbol has been used in arabic text more than the other 7 symbols. thus, they used the “fatha” symbol to present 1 and the other symbols to present 0. the benefit of this method is the big capacity due to each arabic character is relevant for a diacritic. the downside is that concealing some diacritics can get the reader’s attention. in [6] the reverse “fatha” was used to conceal data in the cover text rather than the regular “fatha”. this was not as easily noticed by third parties which is a benefit for this method. the downside of this method is the requirement for a new font to apply the "inverse fatha” as it isn't a standard diacritic. engineering, technology & applied science research vol. 7, no. 2, 2017, 1482-1485 1483 www.etasr.com malalla and shareef: a novel approach for arabic text steganography based on the “bloodgroup”… in [7], authors proposed a new method by using “kashida”. several algorithms were developed and performed in a stego method named mscukat (maximizing steganography capacity using “kashida” in arabic text). the enhancements with this attempt involve maximizing the capacity of cover media to conceal more secret information, minimizing the file size that rise after hidden the secret and improving the security of the encoded cover media. it was shown that this method was superior over similar previous. in [8], eight different techniques that deal with using arabic natural language to hide secret message were considered. the authors of this paper have also published a previous similar study in [9]. iii. the proposed technique a. architecture the architecture of system is same as in [9], which is organized with two portions: the sender side that encrypt the secret message, compress it and then embed it and the receiver side that decodes the stego message and by using the same encrypted key. b. stego module the hiding process is used by the sender to hide the secret message into the cover text. this process involves select the input file, which represents the encrypted compressed secret message, and a group of sub processes as represented in (1). the proposed method is based on employing two stego options of “kashida” and change the unicode of the letter based on the behaviour of the blood group (abo). covertext+secretinformation = stegotext (1) let group a connect dotted arabic characters like ( ـثـ,ـتـ,ـبـ( except characters of the ab group, group b connect not-dotted arabic characters like ( ـسـ,ـر,ـح( except characters of ab group, and group ab separate arabic characters like ( د, س,ر,أ( . the steps of blood group apply algorithm is as following. 1. assume that p is previous character and c is current character. 2. if p is (a group) and c is (a group) or p is (b group) and c is (b group) then insert kashida and return, for example: o example 1: case (p is (a group) and c is (a group)): if the word is ( رةشج ), where (p=ش, c=ج), the result after applying kashida on p, will be (شـجرة). o example 2: case (p is (b group) and c is (b group)): if the word is (سماح), where (p=س, c=م), the result after applying kashida on p, will be (سـماح). 3. if c is ab group:  if p is (a group or b group), replace c from iso-88596(arabic) code to medium type, for example: o example 3: case (p is (a group) and c is (ab group)): if the word is (غرفة), where (p=غ , c=ر),the result after applying medium type on c letter, will be (0xfeae). o example 4: case (p is (b group) and c is (ab group)): if the word is (سد), where (p=س , c=د),the result after applying medium type on c letter, will be (0xfeaa).  if p is ab group or ab` group, replace c from iso-88596 (arabic) code to isolated type, for example: o example 5: case (p is (ab group) and c is (ab group)): if the word is (در), where (p=د , c=ر), the result after applying isolated type on c letter, will be (0xfeae). figure 1 shows the blood group behavior and table i the mapping from ab to ab` for isolated characters. fig. 1. behavior of blood group stego method. table i. mapping from ab to ab` for isolated characters № unicode character isolated type medium type 1 0x0621 0 ءxfe80 0xfe80 2 0x0622 0 آxfe81 0xfe82 3 0x0623 0 أxfe83 0xfe84 4 0x0624 0 ؤxfe85 0xfe86 5 0x0625 0 إxfe87 0xfe88 6 0x0627 0 اxfe8d 0xfe8e 7 0x0629 0 ةxfe93 0xfe93 8 0x062f 0 دxfea9 0xfeaa 9 0x0630 0 ذxfeab 0xfeac 10 0x0631 0 رxfead 0xfeae 11 0x0632 0 زxfeaf 0xfeb0 12 0x0648 0 وxfeed 0xfeee the stego algorithm of this method is described in follows: 1) embedding algorithm input: encrypt compressed secret message (ecsm) , arabic cover. output: arabic stego text. step 1: start. step 2: read two characters (p-previous, c-current). step 3: call for blood group a (dotted letters), blood group b (nondotted letters) and blood group ab (isolated letters). step 4: check:  if (esm/ecsm-bit=1) and (previous letter is from a or b) and (current letter is from a or b) then: engineering, technology & applied science research vol. 7, no. 2, 2017, 1482-1485 1484 www.etasr.com malalla and shareef: a novel approach for arabic text steganography based on the “bloodgroup”… i. remove kashida from arabic cover text (if exist). ii. check arabic letters conditions:  arabic code zone.  not start or end of a word.  not between ل and ا .  kashida table. iii. put “kashida” after the previous letter.  if (esm/ecsm-bit=1) and (previous letter is from a) and (current letter is from ab) then change the unicode to medium type for the current letter.  if (esm/ecsm-bit=1) and (previous letter is from b) and (current letter is from ab) then change the unicode to medium type for the current letter.  if (esm/ecsm-bit=1) and (previous letter is from ab) and (current letter is from ab) then change the unicode to isolated type for the current letter. step 5: combine the results and return. step 6: output arabic stego text. step 7: end. 2) extracting algorithm input: arabic stego text output: encrypted compressed secret message (ecsm) step 1: start. step 2: convert stego-cover to utf-8. step 3: check:  if (previous letter is from a) and (code of kashida is exist) and (current letter is from a) then return 1.  if (previous letter is from b) and (code of kashida is exist) and (current letter is from b) then return 1.  if (previous letter is from a) and (code of unicode for current letter is exist) and (current letter is from ab) then return 1.  if (previous letter is from b) and (code of unicode for current letter is exist) and (current letter is from ab) then return 1.  if (previous letter is from ab) and (code of unicode for current letter is exist) and (current letter is from ab) then return 1.  otherwise, return 0. step 4: gather each 8-bits to get byte and then convert it to string. step 5: end iv. results this part shows the experiments results used to evaluate the performance of the proposed system. the system has been utilized in c#. the tests were run in a workstation laptop (dell) with the following specifications: cpu 1.8 ghz core i3, ram , 4gb ddr3, os windows 8 64bit, visual studio 2013 a. capacity at first we calculated the secret messages sizes before and after encryption and compression ratio to determine the changes and the gain from using compression to reduce the message sizes that will be improving the hiding process by reducing cover capacity needed. as shown in table ii, the results show that compression with (gzip) is very useful with large secret message that is be practically efficient. b. hiding capacity the hiding capacity (in bits/bytes) need to hide two secret messages with fixed cover. the cover capacity needs for blood group stego method is shown in table iii. c. time complexity in order to calculate the actual time needed to embed with the blood group method a timer function was used. table iv shows the embedding time needed for this stego method for 2 secret messages with a fixed cover message. d. robustness, visibility, & similarity robustness is the resistance of the steganography technique against modifying or destroying the secret message. results are shown in table v. v. conclusion a hybrid method that combines both cryptography and steganography is considered in this paper. a novel algorithm called “bloodgroup” is proposed. the new scheme demonstrated rather good results in terms of capacity, speed, robustness, printing, copying and pasting, font changing, similarity, visibility and security but poor results in ocr which should be attributed to the poor level of the available arabic ocr software. further improvement is achieved when the gzip compression technique is also employed. table ii. secret message capacity with or without encryption and compression before encrypt+ compression after encryption(ae) after encrypt+ compression (aec) secret message language secret message (length) no. of 1’s no. of char. no. of 1’s no. of char. no. of 1’s no. of char. comp. ratio* arabic 1340 8871 19152 9659 19736 4261 8472 57.0% english 3212 11395 25720 13114 26264 6713 13592 48.2% *comp. ratio=(size before comp. (ae)-size after comp. (aec))/size before comp. (ae) table iii. hiding capacity for 2 secret messages with fixed cover (length=258107). length of cover (real used) with (encrypt + compression) real used of cover secret (s1) hiding capacity (bits / bytes) real used of cover secret (s2) hiding capacity (bits / bytes) 37572 8472 bits 22.5 60330 13592 bits 22.5 *(hiding capacity= secret (bits) / real used of cover (bytes) engineering, technology & applied science research vol. 7, no. 2, 2017, 1482-1485 1485 www.etasr.com malalla and shareef: a novel approach for arabic text steganography based on the “bloodgroup”… table iv. embedding time needed for three different secret message with fixed cover embedding time (seconds) secret message (s1) secret message (s2) encryption encryption + compression encryption encryption + compression 0.486 0.509 0.535 0.547 table v. robustness, similarity and visibility robustness printing ocr copying & pasting font changing retyping similarity visibility √ x √ √ x 0.926 hard to notes references [1] m. shirali-shahreza, m. h. shirali-shahreza,an improved version of persian/arabic text steganography using "la" word, 2nd malaysia conference on photonics. nctt-mcp 2008 and 6th national conference on telecommunication technologies 2008 and 2008, august 26-28, 2008 [2] c. cachin, “an information-theoretic model for steganography”, 2nd information hiding workshop, vol. 1525, pp. 306-318, 1998 [3] r. j. anderson, f. a. p. petitcolas, “on the limits of steganography”, ieee journal on selected areas in communications, vol. 16, pp. 474481, 1998 [4] h. shirali-shahreza, m. shirali-shahreza, “a new approach to persian/arabic text steganography”, 5th ieee/acis international conference on computer and information science (icis-comsar 06), pp. 310315, 2006 [5] a. mohammed, a. sameh, e. abdul rahman, g. adnan, “arabic diacritics based steganography”, ieee international conference on signal processing and communications (icspc’07), pp. 756–759, dubai, uae, 2007 [6] a. m. jibran, k. kamran, k. hameedullah, “evaluation of steganography for urdu/arabic text”, journal of theoretical and applied information technology, vol. 4, no. 3, pp. 232–237, 2008 [7] g. adnan, a. n. ahmed, “high capacity steganography tool for arabic text using ‘kashida”, the isc international journal of information security, vol. 2, no. 2, pp. 107–118, 2010 [8] a. a. maisa, a framework to design and implementation of linguistic steganography system, phd thesis, department of computer science, university of technology, 2016 [9] s. malalla, f. r. shareef, “improving hiding security of arabic text steganography by hybrid aes cryptography and text steganography”, journal of engineering research and application, vol. 6, no. 6, pp. 6069, 2016 microsoft word 4-596-ed.doc engineering, technology & applied science research vol. 5, no. 5, 2015, 864-870 864 www.etasr.com dossis: high-level synthesis integrated verification high-level synthesis integrated verification michael f. dossis dept. of informatics engineering tei of western macedonia kastoria, greece mdossis@yahoo.gr abstract—it is widely known in the engineering community that more than 60% of the ic design project time is spent on verification. for the very complex contemporary chips, this may prove prohibitive for the ic to arrive at the correct time in the market and therefore, valuable sales share may be lost by the developing industry. this problem is deteriorated by the fact that most of conventional verification flows are highly repetitive and a great proportion of the project time is spent on last-moment simulations. in this paper we present an integrated approach to rapid, high-level verification, exploiting the advantages of a formal high-level synthesis tool, developed by the author. verification in this work is supported at 3 levels: high-level program code, rtl simulation and rapid, generated c testbench execution. this paper is supported by strong experimental work with 3-4 popular design synthesis and verification that proves the principles of our methodology. keywords-high-level synthesis; formal verification; e-da i. introduction embedded, high-performance and portable computing systems digital circuits have highly complex design control & module hierarchy as well as interconnection schemes. this complexity cannot be dealt anymore with conventional methods such as register transfer level (rtl) coding, since they involve highly iterative design flows, detailed and prolonged simulations and thus, prohibitive development times. these development problems often cause products to miss the market windows and thus, a lot of engineering effort is thrown in the rubbish bin. as a consequence, commercial and academic organizations have invested in high-level synthesis (hls) and electronic system level (esl) methodologies to achieve design automation, quality of implementations and short specification-to-product times [1-6]. nevertheless existing hls tools produce lower quality of implementations than manual methods, and the generated hardware models are difficult to handle. also, during synthesis a great number of assumptions about the targeted computing platform and transformation heuristics are taken, in order to deal with the np-complete synthesis problems, which makes synthesis results suboptimal [3, 5]. the most explored and formulated problems of hls include high-level optimizations, scheduling, allocation and binding and they can be found in [1-6]. high-level optimizations are based on software compiler optimizations, allocation is selection of functional units and storing resources for the data and operations objects found in high-level program code, binding is the actual mapping of the above units to real hardware elements such as flip-flops, latches and combinatorial blocks such as functional operator hardware units, and scheduling is the arrangement of elementary operations to finite state machine (fsm) states in system’s clock cycles. although these problems have been studied in research labs, the optimization of real-world complex applications, as well as their mapping onto custom hardware fails to produce competitive to manual implementations. this is because they are not able to handle complex, nested control flow constructs and large data objects, as well as sophisticated interfaces through complex hierarchy and module configuration and tofrom external shared memory interfaces. logic programming [7] and compiler generators found in other areas, such as artificial intelligence and software compilers can benefit synthesis tools. the cubed-c framework [4] combines techniques from compiler generators and artificial intelligence logic programming so as to deliver formal synthesis of high-level programs (in ada or c) into fully synthesizable and simulatable rtl (vhdl or verilog) and executable testbenches (c). in this way specification to product development times are compressed significantly, since lengthy rtl or gate-level simulations are avoided. ii. related work and background a. high-level synthesis tools the first high-level synthesis research results emerged in the 80s and the first linear design (data-flow oriented) processing hls tools appeared in the early 90s. the most complex of the synthesis tasks is the building of a reliable scheduler [3]. from relevant research it is evident that when the system complexity increases linearly, the complexity of the scheduler algorithm increases exponentially and for some very complex applications, scheduling is np-complete [3, 6]. the difficulty to handle complex code control becomes critically difficult and it can prevent synthesis whatsoever in practice when source code models with complex module and control flow hierarchy (e.g. nested while, if-then and for loops) are encountered [4, 6]. academic or commercial hls tools are still not accepted by the engineering community because of the poor synthesis engineering, technology & applied science research vol. 5, no. 5, 2015, 864-870 865 www.etasr.com dossis: high-level synthesis integrated verification results. this is true, particularly for large applications with complex module and control-flow hierarchy as stated above [35]. however, real-world applications can be benefited the most from automated techniques such as hls. often hls tools produce suboptimal solutions when synthesis heuristics are used to shorten the long optimization and processing times. most of the existing hls tools are suited for linear, and dataflow dominated (e.g. stream-based) applications, such as pipelined digital signal processing (dsp), image processing and video/sound streaming. nevertheless even such straightforward applications are not possible to process when the specification model contains any of the excluded programming constructs (such as while loops and loop breaks). most of the tools impose proprietary extensions or restrictions (e.g. exclusion of while loops) on the programming model of the specifications that they accept as input, and various heuristics on the hls transformations that they utilize (e.g. guards, speculation, loop shifting, trailblazing) [2]. however, when design complexity is over than a dozen states, manual rtl coding becomes prohibitive for delivering products in realistic times. some of the existing commercial hls tools are the catapult-c from calypto (previously developed by mentor graphics), and cynthesizer from forte design systems. they both accept as input a small subset of the system-c and c++ languages. however, both of these tools have too complicated user interfaces, and package libraries, for the average system modeler and developer and they are the most expensive of their class since they are licensed for something less than 300,000 dollars per year. in this way, commercial synthesizers are inaccessible for most of small and medium sized asic/fpga (application-specific integrated circuit/field programmable gate arrays) design smes. other hls tools are symfony c compiler from synopsys, impulse-c from impulse accelerated technologies, cyberworkbench from nec, c-to-silicon from cadence, and the free web-based tool c-to-verilog from an israel-based group, all accepting small c subsets as input and mainly linear dataflow-oriented applications. popular academic hls tools are the spark tool [2] which accepts as input a small subset of the ansi-c language (e.g. while loops are not accepted), and a conditional guard based optimizer [6] forming the basis for optimizing conditional source code methods at the beginning of the previous decade. a multi-speculative technique that composes complex adders during datapath synthesis, contributes only towards linear data flow oriented designs can be found in [8]. in [9] a fixed-point accuracy analysis and optimization of polynomial data-flow graphs is analyzed, with respect to a reference model that is found in many digital signal processing applications. a technique to improve nested loop pipelining for high-level synthesis, called polyhedral bubble insertion is discussed in [10]. an equivalence checking method of fsms with datapaths based on value propagation over model paths, for validation of code motion transformations usually applied during the hls scheduling phase can be found in [11]. a formal hls method for accurate high-level casting of optimal adders and subtractors is analyzed in [12]. an exploration approach, called spectral-aware pareto iterative refinement, that uses response surface models (rsms) and spectral analysis for predicting the quality of the design points without resorting to costly architectural synthesis procedures is presented in [13]. however, most of these approaches concern only either linear, dataflow oriented applications or attempt to solve only minor sub-problems of hls, and therefore they don’t impact the complete synthesis flow as a whole system. b. integrated verification, the cubed-c approach in our approach, the high-level c or ada model is first executed to confirm the correctness of the specification model in a rapid, compile-and-run way. when the specification executable model is fully debugged, it is passed to the cubed-c hls synthesizer to generate correct-by-construction, register transfer level (rtl), vhdl/verilog implementations. computation-intensive algorithms and other real-world application can in this way be rapidly prototyped. rtl simulations are executed to verify the functionality and prove the correctness of the automatically generated rtl vhdl implementations, which is expected due to the formal nature of the synthesis transformations. the cubed-c synthesis includes the frontend and the backend compilers, which communicate with each other via the itf database. itf is a formal prologlike format for capturing all of the semantic categories of a programmed algorithm. the frontend compiler is built using compiler-compiler techniques and the backend compiler using logic programming techniques [4]. moreover the itf syntax and semantics are formally defined in [14]. all of these methods are protected with international patents [15]. the parcs scheduler is used in the backend runs to optimize the generated operations schedule. parcs is a formal optimizer which parallelizes as many operations in the same clock cycle as possible, as long as control/data dependencies and resource constraints are obeyed, unless specific block/operator constraints are provided by the user. the cubed-c tools now automatically and formally generate ansi-c testbenches that capture the functionality of the hardware fsm that is synthesized with the hls tool. these testbenches are cycle-accurate simulators that can be compiled and executed with any of the available c development environments such as the gnu-c compiler and linker. thus, the user can see through the fsm state transactions the changes in the values of registers. moreover, the following options are possible: resetting the registers, providing input to all the inputs of the design and examining the values of the output registers of the design at any time in the cycle-accurate simulation. this method is formal but different than formal verification, since the cubed-c method integrates both synthesis and verification methods in the same run. therefore, functional and fsm bugs can be caught and corrected in an easy and a rapid manner. this integrated synthesis and verification flow in the cubed-c framework is shown in figure 1, where red frames show verification tasks and blue frames show synthesis tasks. the high-level verification can be compared manually or automatically with a suitable testbench with cycle-accurate simulation (which was done in our experimental tests at the end of this paper) to confirm the matching of the two functionalities. engineering, technology & applied science research vol. 5, no. 5, 2015, 864-870 866 www.etasr.com dossis: high-level synthesis integrated verification during recent years, model checking is a formal means of confirming the system functionality with mathematical assertions. however it is not practical for large applications where the state space is increasing to prohibiting levels. an attempt to deal with this is reported in [17]. a method based on a formal attribute grammar, used to translate human language into correct computation tree logic from specific comments in the hdl code, is described in [18]. transformations of the behavioral rtl fsmd model are proposed in [19] in order to deal with false negative results of the equivalence checking of state sequences from conditional paths in equivalent checking. static and dynamic analysis of the rtl source code is exercised in [20] to define and compute code coverage of assertions in the rtl code. simulation-based verification is executed in [21] with generated scenario-based stimuli which are triggered in various ways. the effort aims to compact the stimuli while satisfying the coverage requirements. fig. 1. integrated, formal verification in the cubed-c synthesis flow iii. integrated hls verification the integrated with high-level synthesis verification flow is depicted in figure 1. the relevant tasks start with writing and debugging the c or ada code which is the executable specification model at the highest possible abstraction level. this is done in a rapid manner since well understood compile and execute is performed on the improved versions of the high level model’s code. along with the specification code modules, special testbench modules are coded in c or ada which help the functional debugging process to complete sooner. it must be noted that although the specification module should follow the cubed-c coding guidelines, the testbench and any other modules built for debugging are free to code in any style of the ansi-c or gnu-ada programming languages. after removing all the functional bugs quickly and rapidly at the highest functional level, then the debugged ada/ c model code is passed to the cubed-c synthesizer which automatically, rapidly and formally generates functionallyequivalent and provably-correct vhdl or verilog rtl synthesizable models. these models are synthesizable with any commercial or academic rtl synthesizers into technology ic implementations. the cubed-c compiler backend optimizes the state schedule into optimal fsms and datapaths and generates from the same optimized fsm model a cycleaccurate ansi-c compatible simulator for each of the ada/c subprograms (design modules). the generated simulators can be rapidly compiled and executed to fully debug the generated modules in a much faster way than rtl, and without involving the designers with the hardware details of the rtl code. each of the generated cycle-accurate simulator steps includes options for resetting all registers, setting the inputs, advancing to the next fsm step (state) cycle, and reading the registers and the outputs of the circuit. all these are done with just pressing a keyboard key and quickly re-verify the provably-correct behavior of the generated circuit in a rapid manner. the user can write in any style the rtl testbench and the automated testbench to automatically or semi-manually compare the test vectors and outputs of the generated circuit against the vectors that were used in the abstract functional level, as clearly shown in figure 1. iv. verification experiments and results there have been run many integrated synthesis and verification experiments through the design flow of figure 1. three of them will be discussed analytically here: a computer graphics algorithm, a dsp fir (finite impulse response) filter and the classical high-level synthesis benchmark, the second order differential equation approximation solver. fig. 2. the high-level ada model verification a. the computer graphics algorithm the computer graphics application is a line drawing algorithm with the digital differential analyzer (dda) approximation method. due to its iterative and conditional nature is a good representative for testing the cubed-c‘s performance to the loop and if-then type of behaviors. ada or c input design model ada or c testbench verified and debugged ada or c input designs rapid, high-level verification based on compile and execute cubed-c high-level synthesis rtl models and ansi-c cycle accurate simulators rapid backend verification functional equivalence checking engineering, technology & applied science research vol. 5, no. 5, 2015, 864-870 867 www.etasr.com dossis: high-level synthesis integrated verification first the line drawing algorithm is coded in ada (a similar experiment is done using the c language entry). also, an adabased testbench is coded and the whole set of programs is compiled, executed to verify the correct behavior at this high level. figure 2 shows the high-level testbench run, where the input start and end points as well as the intermediate line points are clearly formulated and shown in this experiment run. fig. 3. beginning of he cycle-accurate simulation of the line draw app after the high-level model is debugged and verified it is synthesized into a rtl fsm and the cycle-accurate simulator is extracted from the machine. figure 3 shows the beginning of the cycle-accurate simulation where the start and end points of the line are entered into the simulator. then the simulator is executed cycle by cycle and this is shown in figure 4. fig. 4. running the line draw cycle-accurate sim. cycle by cycle after the last state is reached (which is indicated with a message to the user) the outputs of the simulator can be read as shown in figure 5. because we used the option to position of the line’s points into an external shared memory we notice in figure 5 the last transactions on the signals that interface with the memory modules. alternatively we could follow the synthesis option to position the line’s points in embedded memory in the line draw processor, but this exceeds the purpose of this paper. fig. 5. reading the simulator’s outputs b. simulating the rtl for reassurance in order to reassure in practice the formal nature of the synthesis process the generated rtl for the line draw app. is simulated as shown in figure 6 and figure 7. figure 6 shows the whole duration of the generated rtl execution and figure 7 the time duration of the transactions with the external memory of the fsm results. figure 7 clearly shows the transfer of the 8 line points to the external memory. fig. 6. rtl simulation of the generated line draw hardware fig. 7. zoomed rtl simulation at the last 8 pixel transactions with the memory engineering, technology & applied science research vol. 5, no. 5, 2015, 864-870 868 www.etasr.com dossis: high-level synthesis integrated verification c. assertion-based testbench for line draw figure 8 shows the execution of an automatic, assertion based testbench that automatically compares the results (pixel by pixel) of the high-level and the rtl simulations. as expected there were no differences between the two. this testbench asserts suitable success/fail messages to the user, as it is shown in figure 8. in this way, all 3 levels of integrated verifications can be co-verified and compared seamlessly. fig. 8. assertion-based, automatic testbench for the line draw d. dsp fir filter the next benchmark to present here is a 5-tap dsp fir filter model in ada and subsequently in vhdl and cycleaccurate simulator runs. in this paragraph, the high-level and the cycle-accurate models execution is discussed, although rtl simulations were run as well. figure 9 shows the execution of the algorithmic, high-level ada model and testbench of the 5-tap filter. the setting of the history, the 5 coefficients and the outputs after 5 shift-outs are clearly shown in this picture. figure 10 shows the cubed-c backend cycleaccurate testbench execution during the beginning of the run, where the inputs, the history (taps) and the coefficients are set. figure 11 shows the end of the cycle-accurate execution where the outputs are read and they are clearly the same as the highlevel testbench of figure 9. fig. 9. execution of the high-level ada code model testbench fig. 10. beginning of the fir cycle-accurate simulation fig. 11. results of the completion of the cycle-accurate fir simulator e. the hls differential equation solver benchmark in this subsection the synthesis integrated verification experiment with the typical hls benchmark is described, namely the second order differential equation solver. figure 12 shows the execution of the functional, high-level ada model and testbench execution in order to rapidly verify at this level the differential equation solver benchmark synthesis model. the same input values are used in the run of figure 13 where the rtl simulation (giving the same result) of the synthesized circuit is shown. figure 14 shows the cycle-accurate simulation near the beginning (setting the inputs) and figure 15 shows the cycle-accurate simulation results from the same model that is produced by the same synthesis step as the rtl code. as expected in all cases, the results of all types of verification match. fig. 12. functional high-level testbench of diff. eq. solver engineering, technology & applied science research vol. 5, no. 5, 2015, 864-870 869 www.etasr.com dossis: high-level synthesis integrated verification fig. 13. rtl simulation of the synthesizeed diff. eq. solver circuit fig. 14. setting the inputs of the diff. eq. solver cycle-accurate model fig. 15. results of the cycle-accurate simulation v. conclussions and future work a formal, rapid and integrated with synthesis, verification approach based on the cubed-c high-level synthesis system was discussed in this paper. the major contribution of this work is that the presented approach cuts down by orders of magnitude the verification effort required for digital design projects. all the presented simulations were completed in matters of seconds and the formal nature of the synthesis and testbench generation mechanism guarantees the correctness of the generated implementations. in this way the synthesized circuit features the same behavior as the input specification. moreover, by having as specification executable code models makes the whole flow into a rapid, formal and seamless as well. also, no modifications on the model and testbench code were required and raw programming language constructs were used. future work includes generating cycle-accurate models in more verification languages such as c++ and system-c, and better use of the backend hdl writer for system verilog flows. references [1] b. l. gal, e. casseau, s. huet, “dynamic memory access management for high-performance dsp applications using high-level synthesis”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 16, no. 11, pp.1454-1464, 2008 [2] s. gupta, r. k. gupta, n. d. dutt, a. nikolau, “coordinated parallelizing compiler optimizations and high-level synthesis”, acm transactions on design automation of electronic systems, vol. 9, no. 4, pp. 441–470, 2004 [3] r. a. walker, s. chaudhuri, “introduction to the scheduling problem”, ieee design & test of computers, vol. 12, no. 2, pp. 60–69, 1995 [4] m. f. dossis, “a formal design framework to generate coprocessors with implementation options”, international journal of research and reviews in computer science, vol. 2, no. 4, pp. 929-936, 2011 [5] p. g. paulin, j. p. knight, “force-directed scheduling for the behavioral synthesis of asics”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 8, no. 6, pp. 661–679, 1989 [6] a. a. kountouris, c. wolinski, “efficient scheduling of conditional behaviors for high-level synthesis”, acm transactions on design automation of electronic systems, vol. 7, no. 3, pp. 380–412, 2002 [7] u. nilsson, j. maluszynski, logic programming and prolog, john wiley & sons ltd., 2nd edition, 1995 [8] a. a. del barrio, r. hermida, s. o. memik, j. m. mendias, m. c. molina, “multispeculative addition applied to datapath synthesis”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 31, no. 12, pp. 1817-1830, 2012 [9] o. sarbishei, k. radecka, “on the fixed-point accuracy analysis and optimization of polynomial specifications”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 32, no. 6, pp. 831-844, 2013 [10] a. morvan, s. derrien, p. quinton, “polyhedral bubble insertion: a method to improve nested loop pipelining for high-level synthesis”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 32, no. 3, pp. 339-352, 2013 [11] k. banerjee, c. karfa, d. sarkar, c. mandal, “verification of code motion techniques using value propagation”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 33, no. 8, pp. 1180-1193, 2014 [12] r. sierra, c. carreras, g, caffarena, c. a. lópez barrio, “a formal method for optimal high-level casting of heterogeneous fixed-point adders and subtractors”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 34, no. 1, pp. 52-62, 2015. [13] s. xydis, g. palermo, v. zaccaria, c. silvano, “spirit: spectral-aware pareto iterative refinement optimization for supervised high-level synthesis”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 34, no. 1, pp. 155-159, 2015 [14] m. dossis, "intermediate predicate format for design automation tools", journal of next generation information technology, vol. 1, no. 1, pp. 100-117, 2010 [15] m. dossis, patent number 1005308, 5/10/2006 by the greek industrial property organisation, 2006 [16] d. amanatidis, m. dossis, “high level synthesis of geometric active contours”, 2nd global virtual conference, slovakia, april 7-11, 2014 [17] l. wu, h. huang, k. su, s. cai, x. zhang, “an i/o efficient model checking algorithm for large-scale systems”, ieee transactions on very large scale integration (vlsi) systems, vol. 23, no. 5, pp. 905915, 2015 [18] c. b. harris, i. g. harris, “generating formal hardware verification properties from natural language documentation”, 2015 ieee international conference on semantic computing (icsc), anaheim, ca, pp. 49-56, february 7-9, 2015 [19] r. a. hernandez, m. strum, w. j. chau, “transformations on the fsmd of the rtl code with combinational logic statements for equivalence checking of hls”, 16th latin-american test symposium (lats), puerto vallarta, mexico, pp. 1-6, march 25-27, 2015 [20] v. athavale, m. sai, s. hertz, s. vasudevan, “code coverage of assertions using rtl source code analysis”, 51st acm/edac/ieee engineering, technology & applied science research vol. 5, no. 5, 2015, 864-870 870 www.etasr.com dossis: high-level synthesis integrated verification design automation conference (dac), moscone center, san francisco, ca, usa, pp. 1-6, june 1-5, 2014 [21] yang shuo, r. wille, r. drechsler, “improving coverage of simulationbased verification by dedicated stimuli generation”, 17th euromicro conference on digital system design (dsd), verona, italy, pp. 599606, august 27-29, 2014 authors profile dr michael dossis holds an advanced engineering diploma from ntua, greece, and a phd in electronic engineering from university of bradford, uk. he is the main author of a high number of international patents and quality publications in reputable international journals and conferences. michael dossis has a great experience as an asic project engineer and telecoms applications in companies such as lsi logic europe, arm ltd, virata ltd and intracom telecom s.a. he has experience in numerous programming and hardware description languages, and many design and cad tools. his main interests include amongst others e-da, high-level synthesis and esl, formal methods, ai applications and embedded vlsi systems. microsoft word etasr_v11_n4_pp7446-7451 engineering, technology & applied science research vol. 11, no. 4, 2021, 7446-7451 7446 www.etasr.com duc et al.: a study on the response of the rehabilitation lower device using sliding mode controller a study on the response of the rehabilitation lower device using sliding mode controller dao minh duc faculty of engineering and technology pham van dong university quang ngai, vietnam dmduc@pdu.edu.vn tran xuan tuy faculty of mechanical engineering da nang university of science and technology da nang, vietnam tranxuantuy@yahoo.fr pham dang phuoc faculty of engineering and technology pham van dong university quang ngai, vietnam pdphuoc@pdu.edu.vn abstract-this paper presents the application of the sliding mode controller to simulate the control of a 3 degree of freedom (dof) robot model that supports lower extremity rehabilitation exercises for stroke patients. the 3 dof robot model has an established dynamic differential equation for each joint. this paper studied the response of links of the research model with a sliding mode controller proposed as the control solution. matlab software was used in simulations of ankle, knee, and hip joints' drive for 2 cases, without and with load. compared with other studies, the research results show that the sliding controller results in slight angular errors when applied to the research model, while the torque of the joints remains low. this result is the basis for calculating and selecting parameters for the actuator when manufacturing the actual equipment. keywords-sliding mode controller; ankle; knee; hip; rehabilitation i. introduction according to the world health organization (who), worldwide, each year 15 million people suffer a stroke, of which 5 million die and 5 million become permanently disabled [1]. vietnam has a population of more than 90 million people and the respective number of newly infected people is 225,000 with 540,720 surviving and 117,900 people dying annually [2]. a cerebrovascular accident will leave severe consequences to some patients. the survivors of strokes commonly are not able to perform daily activities such as dressing, eating, and bathing. in recent years, different researches have been done to develop robotic devices for rehabilitation, especially for the neurorehabilitation of poststroke patients [3]. rehabilitation after stroke exercise for patients has become an urgent major social issue. currently, in hospitals and rehabilitation centers, the demand for automatic rehabilitation equipment has increased significantly. robotic rehabilitation has some benefits over conventional manual rehabilitation, such as: • robots can efficiently perform repetitive therapeutic exercises. • employing different sensors in robotic systems enables either accurate exertion of torques/forces or precise quantitative evaluation of the patient's recovery during the rehabilitation program. • rehabilitation strategies using robotic systems provide simultaneous and coordinated actuation of the patient's joints. in this study a controller is designed for an exoskeleton rehabilitation robot, performing different passive, assistive, and resistive therapeutic exercises [4]. research and manufacturing of equipment to support rehabilitation exercises for stroke patients have achieved certain achievements [5-6]. to successfully research and manufacture assistive devices for stroke patients, calculating and simulating the device's response is the first thing before manufacturing. thanks to the development of computers over the years, simulation has become an indispensable tool for synthesizing control laws in mechanical systems, allowing the verification of the behavior of control laws on a virtual model of an automatic system called simulation model. currently, the pid controller is widely applied [7], especially in robot control, to support rehabilitation for stroke patients with the advantages of simple and easy to control structure [8]. the disadvantage is that it is difficult to find the kp, ki, kd coefficients when the load changes. in addition, modern control theory is increasingly widely applied [9]. the use of a fuzzy controller to control the device has resulted [10]. authors in [11] used a combination of fuzzy and pid controllers to control their research equipment. the advantage of this controller is that it optimizes the search for control parameters and can automatically adjust the control parameters of other controllers when combined with a pid controller. corresponding author: dao minh duc engineering, technology & applied science research vol. 11, no. 4, 2021, 7446-7451 7447 www.etasr.com duc et al.: a study on the response of the rehabilitation lower device using sliding mode controller however, for more accuracy, it needs more fuzzy grades, which increases the rules, the lower speed, and the long run time of the system exponentially. in this paper, we introduce the sliding mode controller for the research model. this controller has the advantage of being less affected by load changes. however, it is necessary to overcome the chattering phenomenon of the controller. ii. dynamic equations of the research model in this study, a drive model of lower extremity joints was established with 3 degrees of freedom (dofs) for hip, knee, and ankle joints flexion/extension exercises. the range of motion for hip, knee, and ankle joint was 0-90 0 , -135 0 -0 0 , 40 0 120 0 respectively [12]. the mechanism that drives the joints is a linear actuator with the advantage of large load capacity and self-braking to protect the patient during the exercise. this paper introduces a research model to contribute to the creation of lower limb rehabilitation equipment. the hip, knee, and ankle joints are reduced to a system with only 3 dofs, and the dynamic computational model for the research model is presented in figure 1. in the model, link 1 is for the hip joint, link 2 is for the knee joint, and link 3 is for the ankle joint. setting up the dynamic equation for each link is an essential factor to calculate and simulate the motion of the joints, from which it is possible to calculate the design of the mechanical structure and the controller so that it is suitable for research models. y 1 y 2 y 3 x 1 x 2 x 3 z 1 z 2 z 3 θ 1 θ 2 θ 3 linear actuator drive hip joint linear actuator drive knee joint linear actuator drive ankle joint fig. 1. the research model. y x θ 1 θ 2 θ 3 c 1 c 2 c 3 o fig. 2. dynamic mathematical model. to establish the dynamic equation of the device [13-14], we conduct a dynamic analysis of the joints. the diagram of the dynamic analysis of the research model is shown in figure 2. the rotation angles of the joints are shown with the rotation angles of the hip joint is θ1, the knee joint is θ2, and the ankle joint is θ3. to simplify the establishment of kinematic equations of joints, we reduce the mass of each link to the centroid of each link. the dynamic equation of the model is described as follows: ( ) ( ) ( )n n n n n n n n 1 n 2 3 d q h , gθ θ θ θ τ θ θ θ θ + + =    =      &&& (1) equations (2)-(4) are the dynamic equations of each joint. the dynamic equation of link 1: ( ) ( ) ( ) ( ) ( ) 2 1 1 1 2 2 2 1 2 1 2 2 2 2 2 1 1 1 2 3 1 2 2 3 1 3 2 3 2 3 3 2 3 2 2 2 1 2 2 2 2 2 2 3 1 2 2 3 1 3 2 3 2 3 3 2 cos 2 cos 2 cos 2 cos cos cos cos 2 cos c c c c c c c c c c m l i m l r l r l l r l l m l r l r i i m r l r i l r l l m l r l r θ τ θθ θ θ θ θ θ θ θ θ  +    + + +   =   + + + +  +   + +     + +  + + + +  + + +  + + +  && ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 3 2 1 2 3 1 2 2 2 2 2 1 3 2 3 2 3 1 3 2 3 3 2 3 3 3 2 1 2 3 1 2 2 1 2 3 1 3 2 3 2 1 3 3 1 3 2 3 3 2 3 3 sin sin sin sin 2 2 sin 2 sin sin sin c c c c c c c c c i m l r m l l m l r m l r m l r m l r m l l m l r m l r m l r m l r θ θ θ θ θ θ θ θ θ θ θ θ θ θ θ θ θ             + −  + +   − + +    + −  + +    + +  −  +  && & & & & & ( ) ( ) ( ) ( ) 2 3 3 1 3 2 3 3 2 3 3 1 3 1 1 1 2 1 1 2 1 2 1 1 2 1 2 3 3 1 2 3 2 sin 2 sin cos cos cos cos cos . cos c c c c c m l r m l r m gr m g l r l l m g r θ θ θ θ θ θ θ θ θ θ θ θ θ θ θ θ θ − + +   + +  + +    + + +   + + +   & & & (2) the dynamic equation of link 2: ( ) ( ) 2 2 2 1 2 2 2 2 2 2 3 1 2 2 2 3 1 3 2 3 1 2 3 3 3 cos cos cos cos c c c c c m r l r i l r l l m l r l r i θ θ τ θ θ θ θ  + +     + +    = + + +     +    +    && (3) engineering, technology & applied science research vol. 11, no. 4, 2021, 7446-7451 7448 www.etasr.com duc et al.: a study on the response of the rehabilitation lower device using sliding mode controller ( ) [ ] ( ) ( ) [ ] ( ) 2 2 2 2 3 2 2 2 3 22 3 3 3 2 3 3 2 3 3 3 3 2 3 1 3 3 3 2 1 2 3 1 2 2 1 2 3 1 3 2 3 3 2 3 3 2 3 3 1 3 2 3 3 2 3 2 cos cos sin sin sin 2 sin sin 2 sin c c c c c c c c c c c l r m r i m l r i m r l r i m l r m l r m l l m l r m l r m l r m l r θθ θ θ θ θ θ θ θ θ θ θ θ θ θ θ   + + +   + +    +   + + +  −  + −  + +   − + − + && && & & & & & ( ) ( ) ( ) 1 3 3 2 2 1 2 2 1 2 3 3 1 2 3 cos cos . cos c c m gr l m g r θ θ θ θ θ θ θ θ θ θ        +     +  + +  +    + +     & & the dynamic equation of link 3: ( ) ( ) [ ] ( ) [ ] ( ) 2 3 1 3 2 3 3 3 12 3 3 3 2 3 3 2 3 3 3 2 2 3 3 3 3 2 3 1 3 3 3 3 1 3 2 3 1 2 3 2 3 3 2 3 3 1 3 2 3 3 2 3 3 cos cos cos sin sin sin sin sin c c c c c c c c c c c r l r m l r i m r l r i m r i m l r m l r m l r m l r m l r θ θ τ θθ θ θ θ θ θ θ θ θ θ θ θ θ θ θ θ   + + +    =     +   + + +   + +  − − +   − − + +  && && && & & & & & ( ){ } 1 3 3 3 3 2 1 . . .cos c m g r θ θ θ θ θ  + + + & & (4) the general form as (1) is rewritten as follows: ( ) ( ) ( )n n n nd c , gθ θ θ θ θ τ+ + =&& & (5) where l1, l2, l3 are the lengths, c1, c2, c3 the centers, r1, r2, r3 the lengths of the centers, dn the inertial matrix, hn the matrix of centrifugal and coriolis forces, and gn the gravitational force matrix of the links 1, 2, and 3 respectively. [ ] [ ] t n 1 2 3 t n 1 2 3 t n 1 2 3 t n 1 2 3 θ θ θ θ θ θ θ θ θ θ θ θ τ τ τ τ =  =    =   = & & & & && && && && [ ] 11 12 13 n 21 22 23 31 32 33 11 12 13 n 21 22 23 31 32 33 t n 1 2 3 d d d d d d d d d d c c c c c c c c c c g g g g    =         =      = iii. sliding mode controller for the researched model the sliding mode controller is generally utilized in industry and biomedical robots [15-16]. the controller can be planned regardless of the boundaries of the exploration model. consequently, the sliding mode controller priorities include robustness, responsiveness, insensitiveness to parameter changes and noise, a simple physical model, and easy programming for the software driver. the block diagram that controls the lower extremity rehabilitation device based on the sliding mode controller is shown in figure 3. + setpoint sliding surface function sliding mode controller actuator rehabilitation lower feedback error fig. 3. sliding mode controller block diagram. tracking error: ( ) ( ) ( )de t t tθ θ= − (6) where θd is the setpoint and θ is a reference. velocity and acceleration tracking error: ( ) ( ) ( ) ( ) ( ) ( ) d d e t t t e t t t θ θ θ θ = − = − & && && &&&& (7) the dynamic equation (5) can be written as: ( ) ( ) ( ){ }1d q c , gθ τ θ θ θ−= − −&& & (8) sliding surface choice function: ( ) ( ) ( )s t e t e tλ= + & (9) where λ is a positive constant. derivative sliding surface: ( ) ( ) ( )s t e t e tλ= +& & && (10) the control signal is the torque at the joints, according to [14] the control signal consists of two components which are: ( ) ( ) eq n u when s ,t 0 u u when s ,t 0 θ θ  = =  ≠ engineering, technology & applied science research vol. 11, no. 4, 2021, 7446-7451 7449 www.etasr.com duc et al.: a study on the response of the rehabilitation lower device using sliding mode controller we can calculate the control signal from the differential condition s(t)=0 and from (10) and (8). ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ){ } ( ) ( ) ( ) ( ) ( ) ( ){ } d 1 d 1 d eq s t e t e t 0 s t e t t t s t e t t d c , g s t e t t d u c , g λ λ θ θ λ θ θ τ θ θ θ λ θ θ θ θ θ − − = + = = + − = + − − − = + − − − & & && && &&& & && && & && && & ( ) ( ) ( ) ( ) ( ) ( ){ } ( ) ( ) ( ) ( ) ( ) ( ) 1 d eq 1 1 eq d s t e t t d u c , g 0 u e t t d c , d g λ θ θ θ θ θ λ θ θ θ θ θ θ − − − = + − − − = = + + + && && & && && with n u k sgn( s ).= the sliding mode control for each joint is shown as: ( ) ( ) ( ) ( ) ( ) ( ) 1 n eq d 1 u u u e t t d c , d g ksgn( s ) λ θ θ θ θ θ θ − − = + = + + + + && && (11) we use the lyapunov method to check the stability of the sliding mode controller. the lyapunov function associated with the research model is: 21 v ( s ) s 2 v ( s ) ss v ( s ) -k sgn( s ) = = = & & & for the controller to be stable we must choose a positive k to satisfy the stability condition: v ( s ) k sgn( s ) 0= − <& iv. simulation in matlab we utilized matlab to simulate the response of the research model when using the sliding mode controller. the parameters of the research model are shown in table i. simulations for the research model were conducted for 2 cases, namely without and with a torque of load acting on the joints of the research model. the position of the initial joints of the research model is: 0 1 0 2 0 3 0 90 90 θ θ θ  =  = −  = the setpoint angle for the joint simulates the range of motion of the human lower limb joints. 0 0 1 _ setpo int 0 0 2 _ setpo int 0 0 3 _ setpo int 45 sin( 2 * * 0 ,1* t ) 45 135 135 s in( 2 * * 0 ,1* t ) 2 2 40 s in( 2 * * 0,1* t ) 80 θ π θ π θ π  = +   = − −   = +  the simulation results of the case without load are shown in figures 4-6 and with load in figures 7-9. table i. simulation parameters of the research model simulator parameters description value parameter 1 mass of link 1 5 m1 (kg) 2 mass of link 2 5 m2 (kg) 3 mass of link 3 1 m3 (kg) 4 length of link 1 0.4 l1 (m) 5 length of link 2 0.45 l2 (m) 6 length of link 3 0.2 l3 (m) 7 length center of link 1 0.2 rc1 (m) 8 length center of link 2 0.225 rc2 (m) 9 length center of link 3 0.1 rc3 (m) 10 moment of inertia of link 1 0.2667 i1 (kg.m 2 ) 11 moment of inertia of link 2 0.3375 i2 (kg.m 2 ) 12 moment of inertia of link 3 0.0133 i3 (kg.m 2 ) 13 cofficient k 40 14 cofficient λ 20 15 load torque on link 1 50 (n.m) 16 load torque on link 2 50 (n.m) 17 load torque on link 3 10 (n.m) fig. 4. response of link 1without load. fig. 5. response of link 2 without load. figures 4-6 present the response of the research model's hip, knee, and ankle joints when using the sliding mode controller without load. the hip joint results are: settling time = 1s, maximum torque = 150nm, and overshoot = 0. the knee joint results are: settling time = 0.5s, maximum torque = 30nm, and overshoot = 0. the ankle joint results are: settling time = 0.5s, maximum torque = 6nm, and overshoot = 0. engineering, technology & applied science research vol. 11, no. 4, 2021, 7446-7451 7450 www.etasr.com duc et al.: a study on the response of the rehabilitation lower device using sliding mode controller fig. 6. response of link 3 without load. the sliding mode controller results for the case with load are shown in figures 7-9. the hip joint results are: settling time = 1s, maximum torque = 80nm, and overshoot = 0. the knee joint results are: settling time = 0.5s, maximum torque = 31nm, and overshoot = 0. the results of the ankle joint are: the settling time = 0.5s, maximum torque = 6nm, and overshoot = 0. fig. 7. response of link 1 with load. fig. 8. response of link 2 with load. fig. 9. response of link 3 with load. v. discussion in this study, a sliding controller for a lower extremity rehabilitation exercise aid was designed and its response was simulated in matlab. the simulation results of the device in the flexion/extension movements of the hip, knee, and ankle joints are shown in figures 4-9. the hip joint results are shown in figures 4 and 7, which show that this is the joint that bears the most significant internal load due to the influence of the weight of the structure and the external force, thus creating the most torque. for the knee joint, the results are shown in figures 5 and 8. the joint can only bear the internal load of the mechanism and the external force, so the maximum torque is 31n.m. finally, the results of the ankle joint are shown in figures 6 and 9. this is the joint that only bears the internal load of the mechanism and the minor external force, so the torque is minimal. in addition, in order to assess the adequacy of the proposed controller, the comparison of the trajectory tracking of the proposed controller with several controllers studied in [17-19] was conducted. the trajectory error tracking of the study compared with the works in [17-19] is similar, however, the response time in this study was better (1s instead of 2s). in addition, the above studies have not considered the influence of external [17] or small [18-19] loads on the research model and have not analyzed the action moments of each joint. therefore, this study demonstrates that the sliding controller can control the lower extremity rehabilitation device for patients with fast response time and slight error. the advantage of this study is that we have created a controller that is not affected by external forces, which makes the device response stable, which is essential in the rehabilitation setting for patients. the main limitation of the current study is that it only simulates the response, so it is not possible to conclude that this is the actual response when the controller is applied to real devices. the development direction of this research is to check the correctness of the controller when applied on real devices. vi. conclusion a sliding controller that controls a 3 dof robot model that supports lower extremity rehabilitation was presented in this paper. the dynamic model of the research model was studied. it is proposed to apply the sliding mode controller to study the engineering, technology & applied science research vol. 11, no. 4, 2021, 7446-7451 7451 www.etasr.com duc et al.: a study on the response of the rehabilitation lower device using sliding mode controller dynamic response of the links of the research model. the study results have been verified in matlab simulations of the response of the links of the research model. the proposed sliding mode controller for the research model has shown a good response with small error tracking and torque compared to other studies. this result is the basis for manufacturing an actual device to support lower extremity rehabilitation for stroke patients using a linear actuator. acknowledgment this work is funded by the pham van dong university, vietnam, project 13/2017/khcn. the authors are grateful for the financial support. references [1] e. berge and p. sandercock, "specific treatment of acute ischemic stroke," in warlow’s stroke, john wiley & sons, ltd, 2019, pp. 587– 656, https://doi.org/10.1002/9781118492390.ch13. [2] l. v. thanh, "network of care for stroke, the past and the future", journal of clinical medicine, vol. 10, pp. 11-14, 2015. [3] d. shi, w. zhang, w. zhang, and x. ding, "a review on lower limb rehabilitation exoskeleton robots," chinese journal of mechanical engineering, vol. 32, no. 1, aug. 2019, art. no. 74, https://doi.org/ 10.1186/s10033-019-0389-8. [4] m. rahmani and m. h. rahman, "novel robust control of a 7-dof exoskeleton robot," plos one, vol. 13, no. 9, 2018, art. no. e0203440, https://doi.org/10.1371/journal.pone.0203440. [5] m. torabi, m. sharifi, and g. vossoughi, "robust adaptive sliding mode admittance control of exoskeleton rehabilitation robots," scientia iranica, vol. 25, no. 5, pp. 2628–2642, oct. 2018, https://doi.org/ 10.24200/sci.2017.4512. [6] s. zhu, x. jin, b. yao, q. chen, x. pei, and z. pan, "non-linear sliding mode control of the lower extremity exoskeleton based on human–robot cooperation," international journal of advanced robotic systems, vol. 13, no. 5, sep. 2016, art. no. 1729881416662788, https://doi.org/ 10.1177/1729881416662788. [7] y. tu et al., "an adaptive sliding mode variable admittance control method for lower limb rehabilitation exoskeleton robot," applied sciences, vol. 10, no. 7, jan. 2020, art. no. 2536, https://doi.org/ 10.3390/app10072536. [8] s. babesse, "design of two optimized controllers of a hydraulic actuator semi-active suspension: a comparison study," engineering, technology & applied science research, vol. 9, no. 4, pp. 4561–4565, aug. 2019, https://doi.org/10.48084/etasr.2836. [9] m. k. joyo et al., "optimized proportional-integral-derivative controller for upper limb rehabilitation robot," electronics, vol. 8, no. 8, aug. 2019, art. no. 826, https://doi.org/10.3390/electronics 8080826. [10] h. medjoubi, a. yassine, and h. abdelouahab, "design and study of an adaptive fuzzy logic-based controller for wheeled mobile robots implemented in the leader-follower formation approach," engineering, technology & applied science research, vol. 11, no. 2, pp. 6935–6942, apr. 2021, https://doi.org/10.48084/etasr.3950. [11] w. huang, h. xu, x. fan, and y. lin, "control of lower limb rehabilitation robot based on fuzzy pid," in 2018 3rd international conference on control, automation and artificial intelligence (caai 2018), aug. 2018, pp. 6–8, https://doi.org/10.2991/caai-18.2018.2. [12] g. al rezage and m. o. tokhi, "fuzzy pid control of lower limb exoskeleton for elderly mobility," in 2016 ieee international conference on automation, quality and testing, robotics (aqtr), clujnapoca, romania, may 2016, https://doi.org/10.1109/aqtr.2016. 7501310. [13] d. jiang, g. shi, z. pang, s. li, and y. tian, "control of a new cycling rehabilitation robot based on fuzzy pid," journal of physics: conference series, vol. 1622, sep. 2020, art. no. 012119, https://doi.org/10.1088/1742-6596/1622/1/012119. [14] z. chen, q. guo, y. yan, and d. jiang, "robust sliding mode control for a 2-dof lower limb exoskeleton base on linear extended state observer," mechanical engineering science, vol. 2, no. 2, dec. 2020, https://doi.org/10.33142/mes.v2i2.3160. [15] j. liu, y. zhang, j. wang, and w. chen, "adaptive sliding mode control for a lower-limb exoskeleton rehabilitation robot," in 2018 13th ieee conference on industrial electronics and applications (iciea), wuhan, china, may 2018, pp. 1481–1486, https://doi.org/10.1109/iciea. 2018.8397943. [16] b. maalej, h. medhaffar, a. chemori, and n. derbel, "a fuzzy sliding mode controller for reducing torques applied to a rehabilitation robot," in 2020 17th international multi-conference on systems, signals devices (ssd), monastir, tunisia, jul. 2020, pp. 740–746, https://doi.org/10.1109/ssd49366.2020.9364130. [17] t. b. trung, g. l. t. hong, q. d. hai, and n. p. v. bach, "advanced method for motion control of a 3 dofs lower limb rehabilitation robot," international journal of innovative technology and interdisciplinary sciences, vol. 2, no. 4, pp. 316–325, nov. 2019, https://doi.org/10.15157/ijitis.2019.2.4.316-325. [18] z. shen, j. zhou, j. gao, and r. song, "fuzzy logic based pid control of a 3 dof lower limb rehabilitation robot," in 2018 ieee 8th annual international conference on cyber technology in automation, control, and intelligent systems (cyber), tianjin, china, jul. 2018, pp. 818–821, https://doi.org/10.1109/cyber.2018.8688089. [19] d. t. hai and d. t. vu, "an intelligent control for lower limb exoskeleton for rehabilitation," international journal of electrical and electronics engineering, vol. 4, no. 8, pp. 13–19, 2017, https://doi.org/ 10.14445/23488379/ijeee-v4i8p103. engineering, technology & applied science research vol. 7, no. 6, 2017, 2184-2188 2184 www.etasr.com bangwar et al.: development of an amorphous silica from rice husk waste development of an amorphous silica from rice husk waste daddan khan bangwar department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, sindh, pakistan daddan@quest.edu.pk abdullah saand quaid-e-awam university of engineering, science & technology nawabshah, sindh, pakistan abdullah@quest.edu.pk manthar ali keerio quaid-e-awam university of engineering, science & technology nawabshah, sindh, pakistan mantharali99@quest.edu.pk mukhtiar ali soomro department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan eng.soomro@gmail.com nadeem-ul-karim bhatti department of civil engineering quaid-e-awam university college of engineering, science and technology larkano, pakistan knadeem_b@yahoo.com abstract—this article presents a study on the development of amorphous silica from rice husk (rh) waste. for ascertaining the optimum proportion of temperature and burning duration required for the development of an amorphous silica from rh waste, different rice husk ash (rha) samples, i.e. rha (500oc1.5hr), rha (500oc-2hr), rha (600oc-1.5hr), rha (600oc-2hr), rha (700oc-1.5hr), rha (700oc-2hr), rha (800oc-1.5hr), rha (800oc-2) and rha (900oc-1hr) were extracted by burning the husk at different temperatures and durations. energy dispersive spectrometry (eds) analysis was carried out for ascertaining the existence of main and insignificant elements in the rhas samples and it was noticed that the extracting of silicon dioxide (sio2) was exclusively dependent on the temperature and burning duration. after eds, x-ray diffraction (xrd) analysis was used to find out the crystalline and non-crystalline nature of obtained silica at different temperatures and burning durations. through eds and xrd, it has been found that that the extracted rice husk ash at the temperature of 800oc for 2hr is rich in amorphous sio2 content, i.e. 91.74% which meets the requirements of astm 61803 for a pozzolanic material. keywords-amorphous silica; strength activity index; xrd; rha; cement replacement i. introduction rice husk is an agrarian by-product substance that constitutes at around 20% weight of rice. it is composed of 80% organic volatile material and 20% silica [1]. rice husk ash is a wide-ranging term describing all kinds of ash formed from burning rice husk. silica ash is produced upon burning and subsequently cellulose and lignin are removed. every ton of rice generates 40 kg of ash [2]. rha is a very fine pozzolanic material and is an extremely reactive pozzolanic material to be obtained upon the calcination of rice husk under the crystallization temperature at 7800c [3, 4]. in practice, the sort of ash differs significantly according to the burning method. the ash manufactured by controlled burning of the rice husk between 550oc and 700oc burning temperature for 1 hour converts the silica content of the ash into amorphous phase [5, 6]. the silica in the ash undergoes structural changes depending on the temperature, at 550–800oc amorphous silica is formed and at greater temperatures, crystalline silica is formed. rice husk ash modified concrete is exceptional in terms of strength and durability performance [7-9]. usually after the extraction, the produced rha is ground by using abrasion machines, however, the researchers in [2] stated that non-ground rice husk ash could be used to substitute 15% of portland cement with similar mechanical and durability properties. the researchers in [10, 11] showed that by blending rha as cement replacement material in concrete, the wideranging enhancements in durability properties that can be achieved are otherwise difficult to attain by use of ordinary cement only. the main focus of this research is to develop supplementary cementing material from locally available waste material rice husk, and to mitigate the ecological contamination initiated by the rice husk as well as cement production. ii. experimential procedure a. rice husk ash sample preparation rice husk was collected from nawabshah district, sind, pakistan. the husk was cleaned thoroughly by picking unwanted substances like stone, debris etc. nine samples of rice husk ash were extracted with the help of a muffle furnace having temperature ranged up to 1000oc and these samples were categorized as rha(500oc-1.5hr), rha(500oc-2hr), rha(600oc-1.5hr), rha(600oc-2hr), rha(700oc-1.5hr), rha(700oc-2hr), rha(800oc-1.5hr), rha(800oc-2hr) and engineering, technology & applied science research vol. 7, no. 6, 2017, 2184-2188 2185 www.etasr.com bangwar et al.: development of an amorphous silica from rice husk waste rha(900oc-1hr). all samples were burnt under the temperature scheme for one and a half or two hours, respectively except the sample rha (900oc-1hr) which was extracted under the duration of one hour only. b. chemical analysis of rice husk ash elemental composition of all extracted rice husk ash samples, i.e. rha(500oc-1.5hr), rha(500oc-2hr), rha(600oc-1.5hr), rha(600oc-2hr), rha(700oc-1.5hr), rha(700oc-2hr), rha(800oc-1.5hr), rha(800oc-2hr) and rha(900oc-1hr) was determined through (x-ray energy dispersive spectrometry) eds test by applying energy of 15 kev accelerating voltages to ensure the peaks record. c. loss on ignition to determine the amount of carbon in produced rice husk ash (rha), the loss on ignition was determined by keeping the samples in muffle furnace at a temperature of 950oc for 45 minutes. d. crystalline and non-crystalline nature of rice hush ash the amount of amorphous silica present in the material is an important factor in determining how effective it will be as a pozzolan. studies have shown that the greater the amount of amorphous, the better pozzolanic reactivity a material will have when combined with water. the “degree of amorphous” can be measured using x-ray diffraction (xrd) which was used in this study. the crystalline and non-crystalline characteristics of the samples were determined qualitatively by x-ray diffraction (xrd). the diffractograms were obtained using cu monochromator for ground sample over a 10–73oc at 2θ range. e. fineness fineness is the ratio of surface area to weight which is deemed to be a significant quality index of a pozzolanic material that gives the average size of grain of a material. fineness controls the rate and completeness of hydration. the blaine specific area of the rha (800oc-2hr) is determined as per astm c204. f. specific gravity the specific gravity of rha (800oc-2hr) was calculated with the help of density bottle method. each sample of rha (800oc-2hr) was dried in oven at 110oc to remove any moisture. g. density the average density of the extracted rha (800oc-2hr) has been determined as per astm standards. h. strength activity index mortar specimens were cast by 20% replacement of cement with extracted rice husk ash rha (800oc-2hr) by weight. the mortar mixes were designed by using a sand-to-binder ratio (s/b) of 2.75 and w/b of 0.49, as per astm c 311. the mix details are given in table i. mixing, compaction and molding have been carried out in accordance with astm c305 [12] and astm c109 [13] respectively. the specimens were cast and taken out of the molds after 24 hours and kept in a totally wet environment for 7 and 28 days for curing and strength activity index (sai) was calculated. table i. mix proportion of mortar mix(id) cement (gm) rha (800oc-2hr) w/b (ratio) sand (gm) a 1000 --0.49 2750 b 800 200 0.49 2750 iii. results and discussion a. chemical analysis rice husk ash the energy dispersive spectrometry (eds) analysis was carried out to categorize and figure out the primary and secondary elements existing in the samples of produced rice hush ash. elemental composition of all samples is shown in figure 1. figure 1 shows that rha contains a high proportion of pure silica ranging from 37.7% to 43.04%, with each of other minor elements having lower percentage. elemental compositions in percentage by weight in oxidation form are tabulated and are shown in table ii. the results in the table verify that the material is largely composed of sio2 ranging from 80.68% to 92.11% which is solely dependent of temperature and burning duration. such trend of the material is also validated by [14]. additionally, a comparison is made between the eds results of the samples. it can be seen that there is an increasing trend in the quantity of silicon dioxide content with the increase of temperature and burning duration. the results in table ii also validate that the extracting of silica purely depends upon the temperature and burning duration. furthermore, the sum of major elements like sio2+al2o3+fe2o3 in all samples is above 70%. all the extracted samples conform to the requirement of astm c61803. fig. 1. elemental composition of rhas sample b. loss on ignition of rice husk ash the loss on ignition for rice husk ash is usually due to the presence of unburned carbon (indicating the burning efficiency of the furnace). burning the husk at high temperature causes instability of the mineral phases [15]. figure 2 shows the engineering, technology & applied science research vol. 7, no. 6, 2017, 2184-2188 2186 www.etasr.com bangwar et al.: development of an amorphous silica from rice husk waste relationship between loss on ignition (loi) and extraction of sio2 of all samples. loi went on decreasing as the temperature and its duration kept on increasing resulting in more extraction of silica content. the increased loi suggests that an increased quantity of less burnt carbon content in rhas has adverse effects when blended with cement. in order to achieve better results rice husk ash blended concrete or mortar in terms of strength and durability, the ash must have less loi as per requirement of astm. table ii. chemical analysis of rha at different temperature and duration samples chemical analysis (%) sio2 al2o3 cao mgo k2o loi rha(500oc-1.5hr) 80.68 1.04 1.51 0.78 4.60 6.00 rha(500oc-2hr) 83.37 1.06 1.22 0.75 4.02 5.00 rha(600oc-1.5hr) 83.33 1.08 1.34 0.78 4.02 4.00 rha(600oc-2hr) 86.80 0.91 1.61 1.06 4.08 3.67 rha(700oc-1.5hr) 86.58 0.91 1.27 0.73 3.11 3.00 rha(700oc-2hr) 90.52 1.02 1.39 0.98 2.79 2.45 rha(800oc-1.5hr) 91.72 0.98 1.15 1.06 2.43 2.00 rha(800oc-2hr) 91.74 0.98 1.12 0.81 2.18 1.50 rha(900oc-1hr) 92.11 2.00 1.15 0.76 2.23 1.00 c. crystalline and non-crystalline nature of rice hush ash after combustion, xrd analysis was carried out to assess presence of crystalline and amorphous substances in all samples. the xrd patterns of the rhas at different temperatures and durations are presented in figures 3 to 11. the results in figures 3 10 show that the xrds patterns of rha(500oc-1.5hr), rha(500oc-2hr), rha(600oc-1.5hr), rha(600oc-2hr), rha(700oc-1.5hr), rha(700oc-2hr), rha(800oc-1.5hr) and rha(800oc-2hr) having broad peak at 2θ angle of 19° confirming the material contain an amorphous silica structure. conversely, the xrd of rha (900oc-1hr) shows sharp peaks at around 2θ angle of 19° and 33° which clearly indicates converting of the nature of the silica from amorphous to crystalline nature because of increased temperature (figure 11). it means that reactivity of rice husk ash is generally decreased by the increasing of burning temperature and the heating duration. furthermore, a comparison is made between the xrd patterns of rhas as shown in figure 12 which is clearly indicating the conversion of silicon dioxide from an amorphous state to crystalline state, i.e. the development of sharp peaks at around 19o and 33o due to the increased temperature. the extracted silica must be kept at a non-crystalline state in order to produce an ash with high pozzolanic activity. the optimum temperature range for rha has not been in common agreement, since it has reported to be 600 to 800oc [16], 500 to 700oc [17] and 700 to 800oc [18]. from the current research study it is clear that the combination of 800oc temperature for 2 hour burning time seems to present the optimized solution resulting in non-crystallized rha. such type of noncrystallized rha is a suitable supplementary cementing material, since high pozzolanic activity is necessary for it is to substitute cement or be admixtured in concrete. fig. 2. extraction of silica di-oxide under various temperatures and durations fig. 3. xrd pattern of rha (500oc-1.5hr) d. blaine fineness specific surface area of the optimized rha (800oc-2hr) is shown in table iii. the results suggest that it is slightly coarser than ordinary portland cement. from fineness test, the fineness of the rha (800oc-2hr) as retained on 45 µm was found 20% and 80% passing, which is within the limits defined by astm c618-03 and the ash conformed to grade a of dry pulverized– fuel ash based on astm c430 [19]. e. specific gravity specific gravity of the optimized rha (800oc-2hr) is shown in table iii. the results show that the material is lighter in nature than the cement. the found specific gravity falls within the range of the values seen in the work carried out by other researchers [20, 21]. f. strength activity index strength activity index (sai) demonstrates a greater pozzolanic activity index of the optimized rha (800oc-2hr). sai at 7-days and 28-days was 88% and 92%, respectively. the sai results clearly indicate that rha (800oc-2hr) is in amorphous state and reactive in nature. furthermore, the strength gaining percentage is above the standards demarcated by the astm c 618-03 as shown in table iii. such strength gaining pattern is validated by [22, 23]. engineering, technology & applied science research vol. 7, no. 6, 2017, 2184-2188 2187 www.etasr.com bangwar et al.: development of an amorphous silica from rice husk waste fig. 4. xrd pattern of rha (500oc-2hr) fig. 5. xrd pattern of rha (600oc-1.5hr) fig. 6. xrd pattern of rha (600oc-2hr) fig. 7. xrd pattern of rha (700oc-1.5hr) fig. 8. xrd pattern of rha (700oc-2hr) fig. 9. xrd pattern of rha (800oc-1.5hr) fig. 10. xrd pattern of rha (800oc-2hr) fig. 11. xrd pattern of rha (900oc-1hr) fig. 12. comparison of rxds of produced rha at different temperatures and duration table iii. physical properties the optimized rha physical properties astm c-618 rha (800oc-2hr) blaine fineness (cm2/g) 2251 fineness 34 20 strength activity index (%) 75 88 & 92 specific gravity 2.05 engineering, technology & applied science research vol. 7, no. 6, 2017, 2184-2188 2188 www.etasr.com bangwar et al.: development of an amorphous silica from rice husk waste iv. conclusion in-depth analysis of the extracted rice hush ash (rha) samples at different temperatures and durations from locally available rice husk has been investigated and found that the extracted ash at the temperature of 800oc for 2 hour duration is the optimum one in terms of amorphous silicon dioxide, with a percentage of sio2 at 91.74%. thus chemical and physical properties of the extracted ash at the temperature 800oc for 2 hour duration fulfill the requirements of astm c618-03 standard as a pozzolanic material. consequently, the developed ash can be used as a supplementary cementing material. acknowledgement the authors express their thanks to civil engineering department quest nawabshah for the support. references [1] s. r. kamath, a. proctor, “silica gel from rice hull ash: preparation and characterization”, cereal chemistry, vol. 75, pp. 484-487, 1998 [2] r. zerbino, g. giaccio, g. c. isaia, “concrete incorporating rice-husk ash without processing”, construction and building materials, vol. 25, no. 1, pp. 371-378, 1, 2011 [3] v. m. malhotra, p. kumar mehta, pozzolanic and cementitious materials vol. 1, taylor & francis, 1996 [4] q. yu, k. sawayama, s. sugita, m. shoya, y. isojima, “the reaction between rice husk ash and ca(oh)2 solution and the nature of its product”, cement and concrete research, vol. 29, no. 1, pp. 37-43, 1999 [5] j. james, m. s. rao, “silica from rice husk through thermal decomposition”, thermochimica acta, vol. 97, pp. 329-336, 1986 [6] a. a. boateng, d. a. skeete, “incineration of rice hull for use as a cementitious material: the guyana experience”, cement and concrete research, vol. 20, no. 5, pp. 795-802, 1990 [7] m. anwar, t. miyagawa, m. gaweesh, “using rice husk ash as a cement replacement material in concrete”, waste management series, vol. 1, pp. 671-684, 2000 [8] j. sousa coutinho, “the combined benefits of cpf and rha in improving the durability of concrete structures”, cement and concrete composites, vol. 25, no. 1, pp. 51-59, 2003 [9] m. f. m. zain, m. n. islam, f. mahmud, m. jamil, “production of rice husk ash for use in concrete as a supplementary cementitious material”, construction and building materials, vol. 25, no. 2, pp. 798-805, 2011 [10] c. l. hwang, s. chandra, “the use of rice husk ash in concrete”, in waste materials used in concrete manufacturing, william andrew publishing/noyes, norwich, ny, pp. 184-234, 1997 [11] m. l. gambhir, concrete technology, tata mcgraw-hill education, 2004 [12] astm, c305, standard practice for mechanical mixing of hydraulic cement pastes and mortars of plastic consistency, annual book of astm standards, astm international, pa, 2006 [13] astm, c109/c109m-16a. standard test method for compressive strength of hydraulic cement mortars (using 2-in. or [50-mm] cube specimens), astm international, pa, 2002 [14] v. vaibhav, u. vijayalakshmi, s. mohana roopan, “agricultural waste as a source for the production of silica nanoparticles”, spectrochimica acta part a: molecular and biomolecular spectroscopy, vol. 139, pp. 515-520, 2015 [15] j. de c. izidoro, d. a. fungaro, f. s. dos santos, s. wang, “characteristics of brazilian coal fly ashes and their synthesized zeolites”, fuel processing technology, vol. 97, pp. 38-44, 2012 [16] m. rozainee, s. p. ngo, a. a. salema, k. g. tan, m. ariffin, z. n. zainura, “effect of fluidising velocity on the combustion of rice husk in a bench-scale fluidised bed combustor for the production of amorphous rice husk ash”, bioresource technology, vol. 99, no. 4, pp. 703-713, 2008 [17] d. g. nair, a. fraaij, a. a. k. klaassen, a. p. m. kentgens, “a structural investigation relating to the pozzolanic activity of rice husk ashes”, cement and concrete research, vol. 38, no. 4, pp. 861-869, 2008 [18] s. huang, s. jing, j. wang, z. wang, y. jin, “silica white obtained from rice husk in a fluidized bed”, powder technology, vol. 117, no. 3, pp. 232-238, 2001 [19] astm, c430. standard test method for fineness of hydraulic cement by the 45-μm (no. 325) sieve, astm international, pa, 2003 [20] l. a. bui, c. chen, c. hwang, w. wu, “effect of silica forms in rice husk ash on the properties of concrete”, international journal of minerals, metallurgy, and materials, vol. 19, no. 3, pp. 252-258, 2012 [21] p. k. mehta,“rice husk ash-a unique supplementary cementing material”, in advances in concrete technology, canmet, 1992 [22] c. y. kawabata, h. savastano jr, j. sousa-coutinho, “rice husk derived waste materials as partial cement replacement in lightweight concrete”, ciencia e agrotecnologia, vol. 36, no. 5, pp. 567-578, 2012 [23] r. madandoust, r. ghavidel, “mechanical properties of concrete containing waste glass powder and rice husk ash”, biosystems engineering, vol. 116, no. 2, pp. 113-119, 2013 microsoft word 28-3782_setasr_v10_n5_pp6309-6315 engineering, technology & applied science research vol. 10, no. 5, 2020, 6309-6315 6309 www.etasr.com khan et al.: state of quality engineering practices: the pakistan perspective state of quality engineering practices: the pakistan perspective muhammad naeem ahmed khan independent researcher islamabad, pakistan mnak2010@gmail.com aamir mehmood mirza baluchistan university of information technology, engineering and management sciences quetta, pakistan mirza.aamir@buitms.edu.pk mahwish shahid university of management and technology (umt) lahore, pakistan mahwish.shahid@umt.edu.pk raja asif wagan baluchistan university of information technology, engineering and management sciences quetta, pakistan raja.asif@buitms.edu.pk imran saleem university of management and technology (umt) lahore, pakistan imran.saleem@umt.edu.pk abstract−this study analyzes the state of quality engineering practices being exercised in the software industry of pakistan. statistics have been collected and analyzed to access important aspects of quality engineering including quality policy, review mechanism, quality assurance activities and practices, quality standards and models, and quality management systems. for this purpose, an elaborated questionnaire was prepared to pertain to various aspects of quality management and more than 30 software houses and software development organizations were surveyed in islamabad and rawalpindi. the survey results and a description of the concluding remarks are reported in this paper. keywords-quality assurance; software testing; software quality models; software quality engineering; quality management system i. introduction software is used in almost every sphere of human activity and its usage is growing constantly. software quality is an important issue, not only for software designers and developers, but also for customers, users, and communities. software quality has a major role to play in assessing a software product's success or failure [1]. the quality of software systems is a complex and multi-faceted concept which is difficult to define and measure [2]. it cannot be expressed by a single metric [3], because it includes various aspects such as flexibility, reliability, usability, performance, maintenance, and portability. it pertains to the intrinsic features and characteristics along with customer satisfaction which make hard to precisely define quality. intrinsic quality refers to the quality of the software itself and customer satisfaction refers to the user perception of quality [4]. value may be implicitly provided by other methods, or specifically given in the forms of international standards, general guidelines, or detailed checklists. a common approach to deal with this problem is designing and implementing quality models in an organized manner. implicitly quality can be provided by certain methods or explicitly can be provided in the forms of universal standards, guidelines, or comprehensive checklists. as a result, quality models have been subjected to extensive study for, a variety of heterogeneous quality models have emerged, e.g. different domain models or test models. the advancement made with these models and standards tends to fit for certain approaches that may be optimum for some projects, but is often ill-suited for others [5]. since the software industry is experiencing rapid changes due to the advancements in technology, ever-growing user requirements, modernization of business processes, revolutions in network infrastructure and hardware, sophistication in development and execution environment, etc., most of the software quality improvement activities concentrate on the technological aspects of the software development process. during the last four decades, several quality methods and standards have been developed to steer software developing companies by defining their processes in an effective manner. these quality models are continually evolving, which has eventually become a complicated matter for software industries. in addition, many companies develop indigenous standards and subsequently improve the quality of their systems, when their own software development processes mature. the current state of the affairs of software systems and software development is categorized by the growing sophistication of the end product and the growing demand to produce cost effective software on time [6]. during the last few years, the software industry in pakistan has seen steady growth. according to the statistics from the pakistan software export board (pseb) [7] 144 out of 1500 companies in pakistan achieved international process or product quality certifications. out of these 144 businesses, 110 have iso 9001 certification, 23 have cmmi certification and 11 have iso 27001 certification. these figures are quite alarming and indicate a corresponding author: mahwish shahid engineering, technology & applied science research vol. 10, no. 5, 2020, 6309-6315 6310 www.etasr.com khan et al.: state of quality engineering practices: the pakistan perspective strong need to improve the quality of services, products, and it-infrastructure in the software industry of pakistan. in this study, the different methodologies and practices of software quality models currently followed by it organizations in pakistan were investigated. the study also focuses on the analysis and evaluation of software quality models being practiced for manufacturing high-quality software products. furthermore, problems and challenges regarding the implementation of these quality models and standards for possible enhancements are discussed. the main aspects of the current study are: • a discussion of the importance of quality attributes and techniques with respect to their industrial usage. • the employment of specific quality models by the practitioners. • the potential for further improvement of the quality models. the center of focus of the research is to find answers of the following questions to achieve the above-mentioned objectives: • rq1: what is the role of quality objectives in a software organization’s quality policy? • rq2: what quality assurance procedures and practices do the software organizations adopt to ensure the software product quality? • rq3: do software organizations have a tendency towards quality attributes and their prioritization? • rq4: do process improvement models play a role to achieve the customer’s level of confidence in quality? • rq5: what is the significance of review process of quality management systems? a. pakistan software industry: an overview pakistan's tech industry has risen steadily from its initial start in the late 1980s, and is now ready for a take-off based on its initial success. pakistan provides various competitive advantages over other outsourcing destinations, including the ease of doing business and state-of-the-art it infrastructure. the government of pakistan has been developing the it sector over the last few years, having established it parks with low rents, foreign ownership of equity invested in it and having offered an exemption on income tax from exports of computer software and related services. table i highlights the key facts of software industry in pakistan. table i. facts and figures of pakistan software industry key facts figures skilled workforce 110000 software companies 1500 software technology parks (stps) 9 stp area 700,000 sq. ft. standards and certifications iso 9001 110 cmmi 23 iso 27001 11 us$2.8 billion is the estimated share of pakistan's it industry in the global market whereas it is offering numerous business opportunities both in public and private sectors [8]. ii. related work quality in general, is critical for the success of a product. quality of a product is significantly dependent on the quality of the development process. authors in [9] published the findings of a survey on software quality practices. most of the survey questions were related to methodical topics rather than the use of models for product quality. the results of the study showed that 41% of the respondents reported that have no structured quality assurance plan, while the rest used their own technique/process rather than an external one [9]. t. hall examined the activities related to quality, particularly the attitudes of developers and managers towards quality. the study results showed that 99% of developers used programming standards, 74% employed code reviews or inspections, and 62% collected software metrics data [10]. authors in [11] conducted a survey on iso 9126 aiming to investigate whether the categorization of quality attributes was correct and accurate. this resulted in an improved categorization to provide guidance for revising the standard. this new categorization includes separating security from functionality, which is the latest recommendation of the new standard iso 25010. a survey in australia was conducted in [12] in order to identify which testing methodologies, techniques, and tools were used in the software industry of the country. the major barriers found for testing were time and cost. the results showed that only 55.3% of the surveyed companies believed that metrics helped them boost the quality of software. in addition, the study found that the use of manual static analysis, i.e. formal and informal evaluations, was more widespread than the automated and tool-based analysis. authors in [13] interviewed product managers from swedish companies to determine their quality criteria, establishing that making the criteria well defined and testable was an arduous task [13]. a survey in canada [14] showed that inadequate testing and training and the lack of standardization for testing increase the likelihood of defects in the production and release versions of software products. the ability to identify patterns that lead to reduced quality and to determine the root causes of decline in product quality suffer from the lack of rigorous testing of the product. organizations that train their developers on quality assurance and testing procedures, increase the likelihood that process and product defects are detected and resolved accordingly. cost and lack of expertise are two major obstacles in the adaptation of testing methodology and tools. a study conducted in brazil with the goal of defining the understanding of respondents about the relationship between it governance models and the adoption of quality instruments. the obtained findings provided a description of the impact of it-related issues in companies and the degree of expertise, significance, and adoption of different quality instruments [15]. a survey of the quality models practiced in germany focused on areas of software development, such as standard software being used, custom development methodologies, embedded systems and company size [16]. an exploratory survey of software practices by tech companies in five asean countries engineering, technology & applied science research vol. 10, no. 5, 2020, 6309-6315 6311 www.etasr.com khan et al.: state of quality engineering practices: the pakistan perspective found that software industry fell short in the following four areas: use of automated estimation tools, use of requirements traceability matrices, use of quantitative quality metrics, and the use of change control boards. the best practices of quality orientation, autonomous research teams and software engineering process group (sepg), peer reviews, and quality management systems were discussed [17]. agility supports quality objectives and increases the efficiency of the software development process, thus improving overall product quality. the agile approach should be used when dealing with unpredictable requirements. agile is a quick process with fast iterations and earlier releases. different tasks carried out in each increment, reduce the production cost and improve product quality. one of the key benefits of the agile approach is that the customer is involved in the development process and gives feedback. in the agile development, client at site, pair programming, and frequent integration activities enhance the production process in particular, thus enhancing the overall product quality. extreme programming (xp) is a development methodology within the agile paradigm and it works on many areas to improve quality [18]. xp not only reduces the time of production but also increases the overall quality of software because it is focused on standards that need to be implemented throughout the software development lifecycle [19]. there is a prevalent misguided assumption that quality means goodness or shininess. the word “quality” is often used to denote the relative value of something which means different things to different people. therefore, quality must be defined as “compliance to requirements”. consequently, non-compliance found in the software pertains to the absence of quality, and in such situations quality problems become non-compliance problems, and then quality becomes undefined [20]. software quality is the entirety of features and characteristics of a product or service that underpin its ability to satisfy given needs [21]. quality has six attributes: functionality, reliability, usability, efficiency, portability, and maintainability. software quality appears to be particularly problematic when compared to other areas. the main reason for this is that software has no physical existence. clients do not know of what they need, they periodically need changes, the advancements in hardware and software are rapid, and customers have high expectation levels [22]. iii. research methodology this study aims to explore the state of affairs of quality models, standards, and optimum practices used in the software industry of pakistan. the literature review formed the basis for formulating the questionnaire that was addressed to software companies. a mixed approach method was used, i.e. open/close interviews were conducted for qualitative data and the survey was conducted to get an understanding of the problem on a larger scale. a. sample data quantitative data were collected through a survey with a total of 100 respondents. the sample size consisted of 50 software houses of various sizes situated in the cities of islamabad and rawalpindi. b. framework of the study a comprehensive analysis was performed to identify the problem areas and challenges faced while implementing the best quality engineering practices. research questions were addressed using the quantitative research method. the solutions were discussed along with the challenges in the discussion section. figure 1 gives an overview of the research process. fig. 1. research methodology. iv. results in this section, detailed analysis of the results derived from the surveys is presented. every survey question (sq) presented in table ii is discussed, and the results are shown in figure 2 and table iii. table ii. survey questions sq # survey question sq 1 do you have any defined quality objectives in your quality policy? sq 2 do you have any framework to review/update quality objectives in your quality policy? sq 3 do you have any defined organizational structure for validation and verification to assure quality? sq 4 do you analyze the customer requirements about the quality of the product? sq 4 (a) do you formally record the requirements mentioned in sq 4? sq 5 do you have any documentation to formally record customer’s quality requirements? sq 6 do you have any formal procedures to record non-functional requirements? sq 7 do you have any quality control plans for design and development phases? sq 8 do you have a mechanism to ensure that the product meets the requirements (functional and non-functional) of the customer? sq 9 do you follow any standards/models for development processes’ improvement? sq 10 if yes in sq 9, then are you satisfied with the performance of the quality models? sq 11 which process improvement model is adopted by your company? sq 12 do you have any review or audit mechanism for processes in your company? sq 13 is there any quality management system in your company? sq 14 do you have a review process for a quality management system? a. organizations quality policy sq 1: do you have any defined quality objectives in your quality policy? software quality is about conforming to functional and nonfunctional requirements. achieving structural quality which refers to incorporating non-functional requirements is far more difficult than meeting functional quality. to develop high quality software, companies need to define quality objectives engineering, technology & applied science research vol. 10, no. 5, 2020, 6309-6315 6312 www.etasr.com khan et al.: state of quality engineering practices: the pakistan perspective [23]. for this purpose, companies are required to develop software quality metrics, define defect target levels, and identify quality attributes and factors that affect software quality. it is quite alarming that only 67% of the organizations surveyed in this study define quality objectives. sq 2: do you have any framework to review/update quality objectives in your quality policy? the field of computing is much dynamic as new tools and techniques are developed every day. on the other hand, the new tools and techniques bring about new challenges due to the constantly emerging computing paradigms. quality policy and objectives cannot remain stagnant. they must be reviewed and updated frequently. in this study, it has been observed with concern that only 53% of the respondent companies have a framework for reviewing, 30% do not have any framework and the rest (17%) did not answer this question. fig. 2. survey results (%). table iii. survey results sq # sq 1 sq 2 sq 3 sq 4 sq 5 sq 6 yes 67 53 67 87 70 77 no 17 30 20 10 23 13 no response 17 17 13 3 7 10 sq # sq 7 sq 8 sq 10 sq 12 sq 13 sq 14 yes 67 63 70 70 63 47 no 20 10 10 17 7 20 no response 13 27 20 13 30 33 b. software quality assurance activities and practices sq3: do you have any defined organizational structure for validation and verification to assure quality? it is of utmost importance to have a well-defined organizational structure and dedicated teams for validation and verification to ensure the high quality of software products. as depicted in figure 2 and table iii, only 67% of participating organizations have a defined quality organizational structure. those who do not have their own quality assurance teams are 20% while 13% did not answered this question. sq 4: do you analyze the customer requirements about the quality of the product? software quality could simply be defined as meeting the customer requirements. quality is always required, but it is never stated explicitly and remains a non-functional requirement. thus, it is crucial to understand the customer’s perspective about quality when analyzing quality requirements. this study revealed that 87% of the participants perform quality related analysis. sq 4 (a): do you formally record the requirements mentioned in sq 4? it is important to record quality requirements from customer perspective. only 77% of the participating companies formally record these requirements, while 20% do not record and 3% did not respond. sq 5: do you have any documentation to formally record customer’s quality requirements? non-functional requirements are not explicitly stated by users, but are described informally and are often conflicting. this makes them hard to model, measure and evaluate. to make them measurable, it is important to discuss and if required, negotiate with the customers. it is observed that 70% of the participating companies have developed procedures to deal with non-functional requirements and 23% organizations do not have any formal procedures. sq 6: do you have any formal procedures to record nonfunctional requirements? studies have shown that defects identified at an early stage can be fixed at a lower cost. therefore, quality control activities should be initiated at the very early phases of software development lifecycle and product quality should be maintained throughout the sdlc. this requires meticulous planning and mechanism to ensure the execution of the developed plan. every phase of sdlc should have a detailed quality control plan, which includes all the required methods, processes, and procedures. among the participating companies 77% have quality control plans for design and development phases, 13% of them do not, and 10% did not answer this question. sq 7: do you have any quality control plans for design and development phases? validation and verification activities finish with the delivery of products to customers. validation and verification teams act as client's representative and ensure that the end product meets all functional and non-functional requirements. validation and verification (v&v) teams develop methods to control and prevent the delivery of products that do not conform to the requirements. only 67% of the participating companies ensure that no such product is released, 20% do not have any mechanism for controlling the delivery of nonconforming products while the 13% of participating organizations did not answer this question. sq 8: do you have a mechanism to ensure that the product meets the requirements (functional and non-functional) of the customer? engineering, technology & applied science research vol. 10, no. 5, 2020, 6309-6315 6313 www.etasr.com khan et al.: state of quality engineering practices: the pakistan perspective software quality metrics are used to assess the development process, project, and product. companies use these metrics to assess the performance and quality, and if necessary, take corrective action to fix those areas that cause defects or violate the targeted defect level/threshold. a 63% of the participating companies ensure software quality metrics, whereas 10% answered that they have no such mechanism. c. quality standards and models quality cannot be improved if we cannot measure it. for this purpose, attributes should be identified and quantified. prioritizing these attributes is also important in order to ensure that neither the most desired attributes are compromised nor the least priority attributes get more than desired consideration. table iv and figure 3 depict quality attributes and their importance for different responding organizations. the study results indicate that functionality, usability, and reliability are high priority attributes while portability is the least important attribute. table iv. quality attributes and their priority attribute priority 1 2 3 4 5 6 7 functionality 16 04 0 01 00 02 00 reliability 09 05 02 04 01 01 01 usability 03 09 02 03 02 02 01 efficiency 02 07 07 03 01 00 02 maintainability 03 03 02 05 04 01 03 portability 04 03 02 01 03 03 04 did not reply 02 fig. 3. quality standards. sq 9: do you follow any standards/models for development processes’ improvement? quality can only be accessed if minimum threshold and baseline are defined and proper quality standards have been developed or followed. quality standards could be procedurespecific or resource-specific. it is observed that most of the organizations have defined quality standards either for all resources or all the procedures (figure 3). developing high quality software is a challenging task, hence the main focus of the entire software industry remains on developing sophisticated processes to produce better quality products. the development processes need continuous assessment and improvement due to the nature of the product which keeps changing. in this survey, 66% companies have implemented models, standards, and optimum practices for quality products. sq 10: if yes in sq 9, then are you satisfied with the performance of the quality models? among those who have developed quality standards and models, only 70% are satisfied with the performance of the quality models, 10% think it is under-performing and 20% did not answered this question. sq 11: which process improvement model is adopted by your company? the participants were given a list with possible answers. the results are shown in figure 4. we can see that the majority used either an iso model or a company specific solution. fig. 4. process improvement model statistics (%). sq 12: do you have any review or audit mechanism for processes in your company? reviews and audit activities ensure that the defined processes are actively being practiced for all the undertaken projects. any anomaly is identified as minor or major nonconformance and project managers take appropriate corrective actions. it is observed that 70% of the participating companies have developed review and audit mechanisms, 17% organizations do not and 13% did not answer the question. d. quality management system sq 13: is there any quality management system in your company? in complex and large software development, defect identification is a difficult task. therefore, it is very important to identify defects as early as possible. failure to do so results in significant increase in risk of time or cost overrun. to prevent this, software companies deploy quality management systems which can prevent defects from occurring. it is observed that 63% of the participating companies have implemented a quality management system. sq 14: do you have a review process for a quality management system? reviewing the effectiveness of the quality management system at planned intervals enables companies to take preventive and corrective actions, but only 47% of the engineering, technology & applied science research vol. 10, no. 5, 2020, 6309-6315 6314 www.etasr.com khan et al.: state of quality engineering practices: the pakistan perspective participating companies do so, while 20% do not whereas 33% did not answer this question. v. discussion the nature of software quality is dynamic, with changing face of technology, it should be revisited and upgraded according to new challenges. to produce high quality software, it is important to develop a quality policy in accordance with the organizational priorities and measures of success. additionally, a mechanism to timely review and update this quality policy should also be established. quality policy and objectives cannot remain stagnant, they should be reviewed and updated frequently. this study identified that only 67% of the surveyed companies met the defined quality objectives and only 53% have a framework for reviewing and updating quality objectives and policy. quality policy cannot be implemented without a well-defined organizational quality structure. it includes dedicated and independent v&v teams which ensure that the developed product meets the goals and objectives defined in the quality policy. the study data shows that only 66% of the participating organizations have a defined quality organizational structure. their v&v teams develop methods to control and prevent the delivery of the products that do not conform to the requirements. apparently, only 60% of the organizations ensure that no product that does not adhere to the required quality standards is released. there are several quality models like iso 9126 or iso/iec 25010:2011 which can be adopted for quality attainment. as the most of the revenue of pakistan’s software industry comes from outsourced projects, an internationally recognized quality model can improve the confidence level of the customers of it companies. nevertheless, companies may also develop their own quality models to achieve a certain level of confidence about the quality of the developed products. defect identification and resolution is a costly task. quality management systems can prevent defects from occurring, which allows overcoming the risk of schedule and cost overrun [24, 25]. it has been observed that 63% of the participant companies have adopted and implemented a quality management system. reviewing the effectiveness of a quality management system at planned intervals enables companies to take timely preventive and corrective measures. data should be collected to assess and improve the effectiveness of quality management systems, but the survey results show that only 47% of the surveyed companies have a review process. vi. conclusion the main objective of this study was to analyze the state of quality engineering practices in pakistan with focus on four aspects: organization’s quality policy, software quality assurance activities and practices, quality standards and models, and quality management system. this research contributes towards the understanding of the software quality assurance best practices in pakistan and analyzes product quality models and differentiates them with respect to their usage as well as possible improvement potentials from the viewpoint of quality managers and quality model users. this study can help software development companies to identify whether these quality models and standards assert considerable impact to achieve, enhance, and sustain the quality 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[22] a. gillies, software quality: theory and management. london, uk: chapman & hall, 1992. [23] p. jain, a. sharma, and l. ahuja, “a customized quality model for software quality assurance in agile environment,” international journal of information technology and web engineering (ijitwe), vol. 14, no. 3, pp. 64–77, jul. 2019, doi: 10.4018/ijitwe.2019070104. [24] m. n. a. khan, a. m. mirza, and i. saleem, “software risk analysis with the use of classification techniques: a review,” engineering, technology & applied science research, vol. 10, no. 3, pp. 5678–5682, jun. 2020. [25] a. chenarani and e. a. druzhinin, “a quantitative measure for evaluating project uncertainty under variation and risk effects,” engineering, technology & applied science research, vol. 7, no. 5, pp. 2083–2088, oct. 2017. authors profile muhammad naeem ahmed khan is an independent researcher from islamabad, pakistan aamir mehmood mirza is an assistant professor at the department of computer science, baluchistan university of information technology, engineering and management sciences, pakistan. he received his m.s. degree in embedded systems in 2008 from halmstad university, sweden. his areas of interest are software quality engineering practices, embedded systems and measures, and metrics. mahwish shahid is a research associate at the office of research innovation and commercialization (oric), university of management and technology, lahore, pakistan. she received her m.s. degree from uet, lahore in 2016. her areas of interest include blockchain technology, gamification, software engineering, machine learning, and data mining. raja asif wagan is an assistant professor of information technology, balochistan university of information technology, engineering and management sciences quetta, pakistan. his areas of interest are wireless sensors, networks communication, algorithms, and routing protocols. imran saleem is an assistant professor at the school of professional advancement, university of management and technology, lahore, pakistan. he received his m.s. degree in software engineering management from southampton solent university, uk in 2010. his areas of interest are blockchain technology, software engineering measurement and metrics, and quality engineering. engineering, technology & applied science research vol. 8, no. 3, 2018, 2943-2948 2943 www.etasr.com oghonyon et al.: block milne’s implementation for solving fourth order ordinary differential equations block milne’s implementation for solving fourth order ordinary differential equations j. g. oghonyon department of mathematics covenant university ota, nigeria godwin.oghonyon@covenantuniversity.edu.ng s. a. okunuga department of mathematics university of lagos akoka-lagos, nigeria nugabola@yahoo.com k. s. eke department of mathematics, covenant university ota, nigeria kanayo.eke@covenantuniversity.edu.ng o. a. odetunmibi department of mathematics covenant university ota, nigeria wole.odetunmibi@covenantuniversity.edu.ng abstract—block predictor-corrector method for solving non-stiff ordinary differential equations (odes) started with milne’s device. milne’s device is an extension of the block predictorcorrector method providing further benefits and better results. this study considers milne’s devise for solving fourth order odes. a combination of newton’s backward difference interpolation polynomial and numerical integration method are applied and integrated at some selected grid points to formulate the block predictor-corrector method. moreover, milne’s devise advances the computational efficiency by applying the chief local truncation error] (clte) of the block predictor-corrector method after establishing the order. the numerical results were exhibited to attest the functioning of milne’s devise in solving fourth order odes. the complete results were obtained with the aid of mathematica 9 kernel for microsoft windows. numerical results showcase that milne’s device is more effective than existent methods in terms of design new step size, determining the convergence criteria and maximizing errors at all examined convergence levels. keywords-milne’s device; predictor-corrector method; suitable step size; convergence criteria; maximum errors; chief local truncation error] i. introduction the extension of predictor-corrector method is important for providing some computational benefits to numerical integration of ordinary differential equations. these computational vantages are enlisted in [1, 2]. this composition is primarily concerned with presenting approximate solution of fourth order odes of the form [1-3]: 0 1 2 3 '''' ( , , ', '', '''), ( ) , '( ) , ''( ) , '''( ) y f x y y y y y a y a y a y a          for ≤ ≤ and : × → (1) the numerical solution to (1) is broadly defined as ∑ = ℎ ∑ (2) where the step size is h, = 1, , = 0,1,…, , are unknown quantities which are unequivocally fixed in a way that the expression is of order m as seen in [3, 4]. it is accepted that rf  is sufficiently differentiable to a certain degree on interval ],[ bax  and meets applicable lipchitz condition, i.e., thither is a unvarying ≥ 0 such that | ( , ) − ( , | ≤ | − |, ∀ , ∈ . beneath the given assumption, (1) ascertained existence and quality of singularity outlined on bxa  , likewise looked at to satisfy the weierstrass theorem [5, 6]. [ , ,…, ] , = [ , , . . . , ] and = [ , , . . . , ], spring up in real world practical applications for state of difficulty in scientific research and applied science such as fluid dynamics and rocket motion [7]. it has been proposed that the established method of solving (1) is by reduction to first-order odes. this technique of simplification possesses real severe hindrance which includes waste of human exertion, complication in the use of mathematica package/computer software for coding and squandering implementation time [2-3, 8-15]. scholars have developed straight methods for approximating (1) with better results and efficiency. these methods include block method, block predictor-corrector method, block implicit method, block hybrid method, bdf etc.. however, there are advantages and disadvantages for implementing them. block predictorcorrector method was hinted in [2-3, 10, 12-15]. the backward differentiation formula (bdf) is gear’s method recognized for engineering, technology & applied science research vol. 8, no. 3, 2018, 2943-2948 2944 www.etasr.com oghonyon et al.: block milne’s implementation for solving fourth order ordinary differential equations stiff odes as seen in [7, 16-19]. the target is to employ milne’s device to develop a variable step-size block predictorcorrector method [1, 6, 20, 21]. milne’s device is seen as the numerical estimation of initial value problems (ivps) and this technic is based on numerous ingredients [2, 17]. these include convergence criteria, predictor-corrector pattern braces of like order, designing suitable step-size and chief local truncation error. in addition, this subject field possesses a great deal of superior qualities as discoursed in [1-3, 6, 20, 21] definition: − , − ℎ . if r denotes the block size and h is the stepsize, then block size in time is ℎ. let = 0,1,2,… represent the block number and = , then the − , − method can be written in the following general form: = ∑ + ℎ∑ (3) where = [ ,…, ,…, ] = [ ,…, ,…, ] and are × coefficient matrices [16]. therefore, from the above definition, a block method has the computational reward that in each practical application, the output is valuated to a greater extent or at more than one point concurrently. the number of points depends on the construction of the block method. hence, utilizing this method can provide speedier solutions to the problem which can be processed to bring forth the sought-after accuracy [2, 3, 7, 18, 19]. thus, the motivation of this paper is to suggest milne’s device of variable step-size block predictor-corrector method for solving non-stiff and mildly stiff odes implemented in p(ec)m or p(ec)me mode. this technique possesses the advantages like designing a suitable step size/changing the step size, specifying the convergence criteria (tolerance level) and error control/minimization likewise addressing the gaps posited above. ii. materials and methods to showcase this process, a variable step-size block predictor-corrector method enforcing the explicit adamsbashforth b-step method as a predictor and the implicit adamsmoulton b-1-step method as a corrector of the same order is prepared [1-3, 21]. this discussion section expends the newton’s backward difference formula to prepare the block predictor-corrector method. presuppose f(x) has a continuous ℎ derivative, xn=x0+nh, fn=f(xn), and backward differences are interpreted as ∇ = ∇ − ∇ where ∇ = , then ( ) = + ∇ + ( − )( − − 1) ∇! ++( − )( − − 2)∇! …+ ( − )… −∇( )! + ( − )… − ( )( )! (4) where ( )( ) is the ℎ derivative of measured at some approximate time interval owning , , and . setting = ( ) and = − 1, (4) turns over as 1 1 1 1 ( ) 1 ( ) ... 0 1 ( 1) ( 1) ( ) 1 m m q q q q q m r r f x f f r r f h f q q                                       where = ( )…( )! and 0 = 0 interchanging the above in ( ) = ( ) + ( ) , to acquire ( ) = ( ) + ∑ (−1) − ∇ +(−1) ℎ − ( )( ) 1 1 1 0 1 1 ( 1) 0 ( ) ( ) ( 1) ( ) q i m i m i q q y x y x h f r y ds q                      (5) if the terminal figure in (5) is dropped, the unexpended will be addressed with − adams-bashforth formula = + ℎ∑ ∇ (6) establishing the backward differences in terms of the valuates at upholding points as ∇ = (−1) equation (6) can be written as = + ℎ∑ (7) where = (−1) ∑ − 1 equation (7) shows in terms of info at , ,…, . proceeding with (7) produces the block b-step adams-bashforth formula [22]. likewise, the implicit multistep method-the adams-moulton method can be derived by putting = in (4) and subbing into ( ) = ( ) + ( ) , to arrive at ( ) = ( ) + ∑ (−1) − + 1 ∇ +(−1) ℎ − + 1 ( )( ) engineering, technology & applied science research vol. 8, no. 3, 2018, 2943-2948 2945 www.etasr.com oghonyon et al.: block milne’s implementation for solving fourth order ordinary differential equations dropping the error term, succumbs the method as = + ℎ∑ ∗∇ (8) interchanging for ∇ in terms of , , ,…, sets up the form = + ℎ∑ ∗ (9) where ∗ = (−1) ℎ∑ ∗. in good continuation with (9), the block b-1-step adamsmoulton method will be brought forth [22]. a. examining some selected theoretical properties of block method embracing [5, 6, 9, 10, 20], the consociated block methods (2) and the difference operator can be set as 0 4 0 ( ( ); ] ( ) ''''( ) k i i k i l y x h a y x ih h y x ih         (10) accepting that y(x) is sufficiently and continuously differentiable on an time interval [a, b] and that y(x) possesses many higher derivatives as needed, then, penning the terms in (10) as a taylor series formulation of ( ) and ( ) ≡( ) as ( ) = ∑ ( )! ( )( ) and ( ) = ∑ ( )! ( )( ) (11) replacing (10) and (11) into (2), the next formulation is incurred as [ ( );ℎ] = ( ) + ( ) + ⋯+ ℎ ( )( ) +…+ ℎ ( )( ) + ⋯ (12) holding onto [5, 6], the block method of (2) maintains order p, if , = 0,1,2,…, = 1,2,… , are presented as: , = 0,1,2,…, = 1,2,… , are given as follows: = + + + ⋯+ , = + 2 + + ⋯+ , = ! ( + + + ⋯+ ) − ( + + + ⋯+), = ! ( + 2 + ⋯+ ) − ( )! ( + 2 +⋯+ ), = 5,4,… so, the block method (2) is stated to sustain order p≥1 and error constants quantity established by the vector, ≠ 0. agreeing with [6, 20], the block method (2) possesses order p if [ ( );ℎ] = 0ℎ , = = = ⋯ = == = 0, ≠ 0. (13) consequently, is the error constant quantity and ℎ ( )( ) is the chief local truncation error at the point . b. stability analysis for properly analyzing the block method for stability, the block predictor-corrector method is renormalized and scripted as a block method displayed by the matrix finite difference equations as seen in [5, 23]. ( ) = ( ) + ℎ ( ( ) + ( ) ), (14) where = ... , = ... = ... , = ... . the matrices ( ), ( ), ( ( ), ( ) are r by r matrices while , , , are r-vectors outlined above. in accordance with [6, 23], the boundary locus method is employed to ascertain the region of absolute stability of the block method in preparation to find the roots of absolute stability. thus, subbing the test equation = − and ℎ=ℎ into the block method (14) to arrive at (0) ( 0) 4 4 (1) (1) 4 4 ( ) det[ ( ) ( )] 0 r r a b h a b h         (15) replacing h=0 in (15), the roots of the inferred equation will either be less than or equal to 1. therefore, definition [6] of absolutely stability is gratified. in addition, by [16], the boundary of the region of absolute stability can be gotten by stepping in (2) into )( )( )( r r rh    (16) and where cos sinir e i     then after simplification together with valuating (16) within [0o, 180o] the boundary of the region of absolute stability rests on the real axis. adamsmoulton method will be brought forth [22]. c. milne’s implementation on block predictor-corrector method consorting with [1, 6, 20-21], the milne’s implementation in the p(ec)m or p(ec)mε mode turns indispensable for the explicit (predictor) and implicit (corrector) methods if both are discrete and of the same order, and this touchstones make important for the step number of the explicit method to be one step higher than that of the implicit method. accordingly, the mode p(ec)m or p(ec)mε can be formally analyzed as succeeds for μ=1,2,..... p(ec)m: engineering, technology & applied science research vol. 8, no. 3, 2018, 2943-2948 2946 www.etasr.com oghonyon et al.: block milne’s implementation for solving fourth order ordinary differential equations fhyy in k i iin k i ikn ]1-[ 10 4][ 10 ]0[ ∑∑           , [ ] [ ] 1 1 [ 1] [ ] 4 [ ] 4 [ 1] 0 0 ( , ) , 0,1,.... 1 u u n k n k n k k k u u n k i n i j n k i n i i i f f x y y a y h f h f u                          (17) p(ec)mε: fhyy in k i iin k i ikn ][ 10 4][ 10 ]0[ ∑∑           , [ ] [ ] 1 1 [ 1] [ ] 4 [ ] 4 [ 1] 0 0 ( , ) , 0,1,.... 1 u u n k n k n k k k u u n k i n i j n k i n i i i f f x y y a y h f h f u                          [ ] [ ]( , )n j n k n kf f x y      mentioning that as m   , the result of approximating with either modality will pitch to those applied by the mode of correcting to convergence. moreover, predictor and corrector pair based on (2) can be implemented. p(ec)m or p(ec)mε modes are specified by (16), where h is the step size. since the predictor and corrector both have the same order p. *4 4,p pc c  are the error constant quantities of predictor and corrector respectively. the following effects are true: d. proposition let us assume that the predictor method gives order p* and the corrector method gives order p engaged in p(ec)m or p(ec)mε mode, where p *, p, μ are integers and p*≥1, p≥1, μ≥1. then, when p*≥p (or p*<p with μ>p-p*), then the predictorcorrector method gives the same order and the same plte as the corrector. if p*<p with μ=p-p*, then the predictor-corrector method gives the same order as the corrector, but not the same plte. if p*<p with μ≤p-p, then the predictor-corrector method gives the same order equal to p*+μ (less than p). in distinction from others, when the predictor gives order p* and the corrector gives order p, pec responds to bring forth a method of order p. nevertheless, the p(ec)m or p(ec)mε scheme gives always the same order and the same plte as discoursed in [5, 6]. milne’s device put forward that it is practicable to approximate the chief local truncation error of the explicit and implicit (predictor-corrector) method without approximating higher derivatives of y(x) [1, 6, 20, 21]. accepting that p=p*, where p*and p set the order of the explicit (predictor) and implicit (corrector) methods with the same order. right away, for a method of order p, the chief local truncation errors can be scripted as       4* 4 54 pp p p n n k n k y oyc h x x w h        (18) also,       44 54 pp p p n n k n k y oyc h x x c h        (19) where wn+k and cn+k are the predicted and corrected approximations which are presented by the method of order p while * 4pc  and 4pc  are autonomous of h. dropping terms of degree p+5 and above, it is well-fixed to make approximates of the chief local truncation error of the method as  ( 4)44 4 * 4 4 pp p n p n k n k p p yc h x c w c c c           (20) mentioning the realness that cp+4≠c * p+4, wn+k≠cn+k , and ε is the bound of convergence criteria. moreover, the approximate of the chief local truncation error (20) is applied to check whether to consent the effects of the current step or to reconstruct the step with a smaller step size. the step is consented based on a test as ordained by (20) [24]. equation (20) is the convergence criteria differently anticipated as milne’s estimate for adjusting to convergence. even more, (20) examines the convergence criterion of the method throughout the try out valuation [24]. iii. numerical examples two problems were examined and worked out enforcing mi employing several distinguishable convergence criteria: 10 ,10 , 10 ,10 , 10 and 10 [8, 10-14]. a. examined problem 1: ( ) + ( ) = 0, (0) = 0, (0) = . , (0) = . , ′′(0) = . solution: ( ) = . . b. examined problem 2: ( ) − 4 ( ) = 0, (0) = 0, (0) = 3, (0) = 0, ′′(0) = 16 , 0 ≤ ≤ 1. solution: ( ) = 1 − + − . iv. discussion of results the final results present the functioning of the milne’s implementation for solving fourth order odes. the accomplished final results were obtained with the assistance of mathematica 9 kernel on microsoft windows (64-bit). table i presents the mathematical final results of utilizing mi compared to existent methods. the steps for computing the maximum errors and ascertaining the convergence criteria (tolerance level) are set as follows:     4444 * 4 ppp p n n j n j p c c h p y x p c c         engineering, technology & applied science research vol. 8, no. 3, 2018, 2943-2948 2947 www.etasr.com oghonyon et al.: block milne’s implementation for solving fourth order ordinary differential equations remark that c*p+4≠cp+4 and pn+j≠ cn+j. c * p+4 and cp+4 are autonomous of h and are the calculated chief local truncation errors of predictor and corrector method. pn+j and cn+j are the predicted and corrected estimations granted by the method of order p. table i exhibits the mathematical resolutions for working out examined problems in the former section enforcing mi. table i. milne’s implementation method max error cover as-scmm 1.63736e-08 10-8 mi 1.6798e-09 10-8 mi 1.21782e-09 aosz-sm 2.93232452209e-12 10-12 mi 2.15055e-13 10-12 aafo-spibm 3.5121472e-14 10-14 mi 0.47906e-15 10-14 mi 2.23218e-15 fsbm 8.0491e-16 10-16 mi 8.13829e-18 10-16 mi 4.71357e-17 aez-snm 1.5897083e-07 10-7 mi 1.37682e-08 10-7 mi 1.80613e-08 aosz-sm 5.14028819509e-10 10-10 mi 3.06153e-11 10-10 dsoivp 7.218014e-11 10-11 mi 4.90652e-12 10-11 table ii. nomenclature mi milne’s implementation for solving 4rth order odes. cover convergence criteria method method used maxerror magnitude of the maximum errors aafo-spibm an accurate five off-step points implicit block method for direct solution of 4rth order differential equations [11] aez-snm an efficient zero-stable numerical method for 4rth-order differential equations [12] aosz-sm an order six zero-stable method for direct solution of 4rth order odes [13]. as-scmm a six-step continuous multistep method for the solution of general 4rth order initial value problems of odes [10]. dsoivp direct solution of initial value problems of 4rth order odes [14] fsbm five step block method for the solution of 4rth order odes [8] a. algorithm a composed algorithmic program that will blueprint a new step size and assess the maximum errors of the predictorcorrector method in the word form of p(ec)m or p(ec)mε mode, if the mode is run m times. step 1: choose a step size for h. step 2: the order of the predictor-corrector method must be the same. step 3: the stepnumber of the predictor method must be one step more eminent than that of the corrector method. step 4: posit the chief local truncation errors of both predictor-corrector methods. step 5: set the convergence criteria (tolerance level). step 6: input the predictor-corrector method in any mathematical language. step 7: use any one step method to bring forth starting economic values if needed, if not disregard step 7 and advance to step 8. step 8: implement the p(ec)m or p(ec)mε mode at m step. step 9: if step 8 fails to converge, reiterate the procedure once more and divide the step size (h) by 2 from step 0 or if not, continue to step 10. step 10: valuate the maximum errors after convergency is attained. step 11: print maximum errors. step 12: utilize this formula expressed below to formulate a new step size since converge is reached.  cc pp wh 1 * 1-2 4 1    v. conclusion mathematical final results have certified the mi is achieved with the assistance of the convergence criteria. this convergence criteria (tolerance level) adjudicates whether the result is admitted or reiterated. the final results establish that mi’s performance is observed to yield a better maximum errors than the as-scmm, aosz-sm, aafo-spibm, fsbm, aezsnm and dsoivp as sited in [1, 8-10, 12-14]. therefore, it can be resolved that the devised method is suitable for solving non-stiff and stiff odes. acknowledgment authors would like to express their gratitude to covenant university for their financial backing through grants during the study period. references [1] j. r. dormand, numerical methods for differential equations, approach. crc press, 1996 [2] j. g. oghonyon, s. a. okunuga, s. a. iyase, “milne’s implementation on block predictor-corrector methods”, journal of applied sciences, vol. 16, no. 5, pp. 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prentice-hall, inc., 1971 [23] l. i. ken, i. f. ismail, m. suleiman, block methods for special second order ordinary differential equations, academic publishing, 2011 [24] u. m. ascher, l. r. petzold, computer methods for ordinary differential equations and differential algebraic equations. siam, philadelphia, 1998 microsoft word vorozhtsov-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 259-264 259 www.etasr.com vorozhtsov: on some unsolved problems of mathematica on some unsolved problems of mathematica evgenii v. vorozhtsov khristianovich institute of theoretical and applied mechanics, siberian branch of the russian academy of sciences, 4/1 institutskaya street, 630090, novosibirsk, russia vorozh@itam.nsc.ru abstract— in this paper, some unsolved problems of the mathematica software package are documented. at first, it is shown, using a number of examples, that the processing (simplification) of rational-fractional expressions involving powers in the general form, has been implemented in maple more carefully than in mathematica. then, an error in mathematica is demonstrated, leading to incorrect results at a change of a function’s body. for each example of symbolic or symbolicnumeric computations, alternate routes for solving the emerged problem are proposed (where possible). an added problem, related to mathematica’s computing speed is documented, employing examples related to two-dimensional gas dynamics problems. it is shown that mathematica computes rather slowly (about one thousand times slower) compared to a fortran code. keywords-mathematica; analytic; numerical; computations; simplification; expressions; fortran i. introduction modern theoretical mathematics and the development of information technologies are strongly connected to powerful software packages, widely applied in the areas of science and engineering, such as mathematica [1], which is one of the most powerful tools supporting scientific research, applied design, and teaching of specialists, postgraduates and students. mathematica was designed as software mainly aiming to automate the work of scientists and mathematicians. the software contains a wide spectrum of mathematical methods and numerical algorithms for conducting theoretical and applied research as well as a powerful system for the visualization of obtained results. starting from version 2, the subsequent versions of mathematica are the world leaders in the area of symbolic mathematics for pcs, providing the execution of numerical computations, employing elegant graphical output forms, and also the execution of especially laborious analytic computations and transformations. mathematica has been adapted to the most recent operating systems and hardware, making it available to most platforms including microsoft windows, apple mac and linux. mathematica enables the performance of laborious analytic computations. however, the possibility of errors in the produced results due to internal software design is a rather important issue, considering that the source of such problems is rarely detected by the user. even after the error has been localized, the end-user will need further time in order to replace the piece of his code where some built-in operators or mathematica functions work incorrectly. even though, it is usually possible to implement such alternate approaches, due to the large number of available functions, such internal errors and/or imperfections of mathematica reduce its efficiency. most importantly, in some cases, the erroneous results produced may be externally believable and thus not identified as such. therefore, when there are no verifying mathematical relations, it is necessary to duplicate the analytic computations by using a different software system, for example, maple, reduce, etc. in the examples of analytic, symbolic-numeric and numeric computations presented in the following, the licensed copies of the following program packages were used: mathematica 3.0.0 (license l2718-0816), mathematica 4.1.0 (license l29892426), mathematica 8.0.4.0 (license l3427-3055), and maple 7 (license p/n: 01-0701-00-b-sn-a-e-0, serial number 693366959). further, the licensed copy of the operating system windows xp professional (license e85-05798) was used. the capabilities of seven general-purpose systems for analytic computations, namely axiom, derive, macsyma, maple, mathematica, mupad, and reduce were analyzed previously [2] on 542 short problems. mathematica produced completely wrong results in 13 of the 542 examples. some added examples, not included in the above set, are documented in the present paper. in these cases, mathematica either outputs an incorrect result or outputs a correct result having a bulky form, and one fails in its simplification with the aid of the builtin functions of the system. for each such example, alternate solving routes are proposed where possible. ii. insufficnet efficiency of simplification functions consider the basic problem of mathematical analysis of the calculation of the sum: s = 2 + 2·3x + 3·4x 2 + … + n(n – 1)x n–2 . etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 259-264 260 www.etasr.com vorozhtsov: on some unsolved problems of mathematica the mathematica command: s=sum[j*(j-1)*x^(j-2),{j,2,n}], where sum[…] is the built-in function of the system, gives the following solution: 2 1 2 1 2 2 2 3 2 2 2 = ( 1 ) n n n n n n x nx n x x n x nx n x s x x + + + + − + + + − − + − + (1) it is clear that this expression can be simplified by dividing its numerator and denominator by x. instead of doing this by hand using the pen and paper one can try to use the built-in function simplify[…], which is intended for the simplification of expressions. however, instead of the expected simplification of (1), the function produces the same result (1). another built-in function, powerexpand[…], enables the simplification of expressions involving power functions. but the application of this function to (1) also leaves this expression without change. the mathematica function expand[s] expands a complex fraction s into the sum of elementary fractions: . )1()1()1( 2 )1( 2 )1()1()1( 2 = 3 12 3 1 3 2 33 12 3 1 3 x xn x nx x xn x x x xn x nx x s nnn nnn +− + +− − +− − +− + +− + +− + +− − ++ +−+− (2) it can be seen from (2) that mathematica has performed in each elementary fraction the divisions of both the numerators and denominators by the factor x. therefore, one can now hope that the subsequent application of the function simplify[…] to the sum of fractions (2) would yield the desired result. however, at the simplification of (2), mathematica has multiplied both the numerator and denominator of the final expression by x, with the output being again the original expression (1). mathematica also contains the function together[…] which reverts the sum of fractions to a single fraction. since there is no factor x in the denominators of (2), one may hope that this function will produce the result in the desired simplified form. however, the application of this function to (2) leads again to expression (1). it should be noted that the maple software produces the desired result for this task, using its simplify command, as shown below: s:=simplify(sum(j*(j-1)*x^(j-2),j=2..n)); . )1( 222 = 3 )1(2)1(2)1(2)1( − −+++−− −−++ x nxnxxnxnxnx s nnnnnn the problem of the ideal incompressible fluid flow around a motionless sphere is a relatively simple example of a threedimensional fluid dynamics problem. the fluid flow is assumed to be directed at infinity along the z axis of a cartesian coordinate system zyxo . the solution of this depends on three dimensional coordinates zyx ,, . let wvu ,, be the dimensional components of the fluid velocity vector along the axes zyx ,, , respectively, and let p be the dimensional pressure of the fluid. the nondimensionalization of independent and dependent variables in the problem under study is given by: ,,,,,,, 2 ∞∞∞∞ ======= u p p u w w u v v u u u r z z r y y r x x ρ where r is the dimensional sphere radius, u∞ is the freestream velocity and ρ is the fluid density. it is assumed for definiteness that the sphere center lies in the coordinate origin (0,0,0) of the coordinate system oxyz. the exact solution of the problem under consideration is then obtained with the aid of the velocity potential theory so that, for example, the velocity component u has the form: 5 3 r xz u −= , (3) where r = (x 2 + y 2 + z 2 ) 1/2 . one can try to obtain expression (3) with the aid of mathematica by performing: r = sqrt[x^2+y^2+z^2];fi=v0*r* (1+1/2*(r/r)^3)*z/r; u = d[fi, x]; u1 = u/.{x-> r*x1,y-> r*y1,z-> r*z1} u1a=powerexpand[u1/v0]; print["u1a = ",u1a]; the following notations are used here: fi is the velocity potential, v0 = u∞, x1, y1 and z1 are the dimensionless spatial coordinates and u1a is the dimensionless velocity component along the x-axis. the following expression is obtained for u1a as a result: . )111(2 113 1 2/5222222 5 zryrxr zxr au ++ −= (4) it is shown from (4) that the function powerexpand[u1/v0] has “missed” the presence of the common factor r 2·5/2 = r 5 in the denominator. etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 259-264 261 www.etasr.com vorozhtsov: on some unsolved problems of mathematica u1b= simplify[u1/v0]; print["u1b = ",u1b]; . ))111((2 113 1 2/52222 5 zyxr zxr bu ++ −= the function simplify[u1/v0] was able to detect the common factor r 2 only in the base of the power function. and, finally, u1c=powerexpand[u1b]; print["u1c = ",u1c]; . )111(2 113 1 2/5222 zyx zx cu ++ −= (5) it is seen from (5) that the combination of the functions simplify[…] and powerexpand[…] has led to the correct result. it is interesting to solve the same task with maple and to see how many steps are needed to obtain (5): u:=-3*r^3*v0*x*z/(2*(x^2+y^2+z^2)^(5/2)); u1c:=simplify(subs(x=x1*r,y=y1*r,z=z1*r, u/v0),assume=positive); iii. some peculiarities of the processing of complex quantities in mathematica beside the capability of executing the basic arithmetic operations on complex numbers, in mathematica the built-in functions re[z], im[z], conjugate[z], abs[z], and arg[z]are also included. the purpose of each of these functions is clear from its name. the letter i is reserved in the system to denote the imaginary unit i = 1− . example: z = 5 – 4i; print[“re(z) = “, re[z], ”; im(z) = “, im[z]]; answer: re(z) = 5; im(z) = –4. let now z = cos 2 x + i tg(x)/x, where x is a real variable. the application of function re[z] in this case gives the answer re(z) = re(cos 2 (x)) – im(tg(x)/x) because it is assumed in mathematica that each of the functions cos 2 (x) and tg(x)/x may be complex. the function complexexpand[z] performs the simplification of the complex number z = a + ib under the assumption that both expressions a and b are real. example: z = cos[x]^2 + i*tan[x]/x; complexexpand[re[z]] the answer is obtained in the form re(z) = cos 2 x. however, the operation zim1 = complexexpand[im[z]] leads to: sin(2 ) im( ) (1 cos(2 )) x z x x = + (6) instead of the expected: tg( ) im( ) . x z x = (7) using the well-known trigonometric relations it is easy to transform (6) to (7). the right-hand side of (6), however, requires 20 symbols, and the right-hand side of (7) requires 7 symbols, if one counts the horizontal bar separating the numerator from the denominator as a single symbol. the builtin function bytecount[expr] available in mathematica counts the number of bytes used internally by the system to store the expression expr. the call bytecount[zim1] gives for the right-hand side of (6) the answer 488 bytes. let us now try to simplify expression (6) with the aid of the function simplify[…]: the command zim2 = simplify[zim1] gives (7). bytecount[zim2] gives 160 bytes. this means that the internal representation of (6) in mathematica is three times longer compared to (7). the danger of the appearance of bulky expressions like (6) in the process of symbolic manipulations consists of the fact that if (6) is used at the next stages of the analytic procedure then this may lead to a multiple “swell” of the final expressions. further, bulky expressions deteriorate the visibility and understanding of final results. it is, therefore, desirable to execute the multi-stage analytic procedures in the interactive regime. as soon as a bulky expression of type (6) suddenly appears at a stage, one can try to simplify it with the aid of the following functions: simplify[…],expandall[…], fullsimplify[…],expand[…], powerexpand[…]. let us now see how the maple system solves the task of finding the imaginary part of the complex number z = cos 2 x + i tg(x)/x. the function evalc(…)in the maple system is an analog of the function complexexpand[…] of mathematica. thus, we have in maple: z:= cos(x)^2 + tan(x)/x*i; evalc(im(z)); the answer is (7). thus, the function evalc(…) immediately outputs the answer, which is optimal from the viewpoint of its length. let us return to mathematica. in a search for a simple alternative way of obtaining im(z) in the optimal form (7) one can use the following definition of the imaginary part of the number z: im(z) is the coefficient affecting i. etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 259-264 262 www.etasr.com vorozhtsov: on some unsolved problems of mathematica to find the coefficients affecting some variable, the function coefficient[…] is provided. let us use it: z = cos[x]^2 + i*tan[x]/x; zim = coefficient[z, i] (8) in this case, mathematica prints the following diagnostic message: “coefficient:: ivar : i is not a valid variable. >>” and does not output any result. one can circumvent this situation by replacing i in (8) with a different letter, say j: coefficient[z/.i -> j, j]. the answer is then obtained in the optimal form (7). summarizing the contents of this and foregoing sections one can draw the following conclusion: the simplification of analytic expressions has been implemented more carefully in maple than in mathematica. iv. an example of incorrect work of mathematica at a change of a function’s body as a preliminary discussion, we assume that there is a variable parameter m in the user’s mathematica code, which must be specified at the beginning of the code. to conserve the information about already computed variants it is important to store in the program the information about already considered values of the parameter m. this is also convenient from the viewpoint that it will be easy to return again to one of the computed runs, which proved to be the best among all other variants. it is very simple to store the information about already used values of m in the following way: m = 5; m = 10; m = 15; m = 20. here the last assignment operator cancels any of the foregoing assignment operators of the form m = …, so that one can be sure that the mathematica program of the user will execute the next run with the value m = 20. this is always the case in practice. let us now consider the following mathematica program: f[x_]:=x*x/;x>1; expr1=y^2-f[x]*z/.x-> 2 here the first command defines the function in the case when x>1. the system yields a correct result of the symbolic computation in the second command: expr1 =y 2 – 4z. let us now assume that it is necessary to replace the body of the function f[x_] at some stage of the analytic computation with a different body, for example, with the body f[x_]:=-x/;x ≠ 1; it is obvious that this new definition of the function should cancel the foregoing definition of this function. let us now assume that it is necessary to calculate the expression: expr2=expr1^2-f[x]*z/.x-> 2; in the next line of the mathematica code. mathematica outputs the following answer: expr2 = (y 2 – 4z) 2 – 4z. this answer is obviously incorrect because f[2]=-2 in accordance with the new definition of function f[x_]. that is, mathematica has ignored the new definition of the function f[x_]:=-x/;x ≠ 1 and continues using the old definition f[x_]:=x*x/;x>1. below we present the solution of the given problem within the mathematica framework: f1[x_]:=-x/;x ≠ 1; expr2a=expr1^2-f[x]*z/.f[x]-> f1[x] expr2=expr2a/.x-> 2 this time, mathematica has produced the correct result: expr2 = (y 2 – 4z) 2 + 2z. v. slow numerical computations many engineering problems are described by systems of partial differential equations. common examples include problems of fluid dynamics, magnetohydrodynamics, elasticity theory etc. problems whose solutions depend on two or three spatial variables and the time variable t are considered the most laborious computationally. such problems are commonly computed with the use of advanced supercomputers and parallel computations. the ability to perform an on-line analysis of the results obtained through the simulation of multidimensional problems increases significantly with the use of graphical representations. ansys fluent (www.ansys.com) is a well known software that integrates not only the programs for the numerical solution of gas dynamics problems, structural mechanics, and electromagnetics but also a number of computer graphics procedures for the visualization of the results of multidimensional computations. since the mathematica software had already integrated initially the means for symbolic manipulations, numerical computations and graphical visualization of the results with the aid of numerous built-in functions, it appeared to be attractive for the specialists concerned with numerical modeling of various applied problems. examples of the numerical solutions of some relatively simple one-, two-, and three-dimensional problems of continuum mechanics were presented in [3], which may be computed with acceptable cpu time expenses within the framework of mathematica at a fairly moderate total number of spatial computing mesh nodes. an attempt to apply mathematica for the numerical solution of two-dimensional problems of gas dynamics on curvilinear spatial computing meshes was implemented successfully in [4]. but it turned out that the developed mathematica code had a computational speed, which was many times smaller than the speed of the corresponding fortran code. the developers of the considered system recommended the use of the built-in function compile[…] to accelerate the numerical computations in mathematica. however, its application reduced the cpu time needed for solving the two-dimensional etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 259-264 263 www.etasr.com vorozhtsov: on some unsolved problems of mathematica problems of gas dynamics only by the factor of 5/3 = 1.67 [4] rather than by the factor of 20, as it was declared in [1]. the euler equations, which represent one of the basic mathematical models for gas dynamics problems, have the following form for the two-dimensional flow of an inviscid, non-heat-conducting compressible gas: ∂w/∂t + ∂f(w)/∂x + ∂g(w)/∂y = 0, (9) where x and y are the cartesian spatial coordinates, t is the time, and w = (ρ, ρu, ρv, ρe) t , f(w) = (ρu, ρu 2 + p, ρuv, ρuh) t , g(w) = (ρv, ρvu, ρv 2 + p, ρvh) t . (10) here p,ρ,u, and v denote the pressure, density, and velocity components; e = ε + (1/2)(u 2 + v 2 ), ε is the specific internal energy, h = e + (p/ρ). the superscript t denotes the transposition operation. the ideal gas equation of state p = (γ – 1)ρε, γ = const > 1 is used. an explicit tvd method as applied to equations (9) and (10) was described in detail in [5], and therefore, the computational formulas of this method are not presented here. the method has either the second or third order of accuracy in spatial variables and in the subregions of smooth flow depending on the numerical value of the available weight parameter φ. the method uses the flux limiters as well as the roe averaging. as in other tvd methods, a switching from the higher approximation order to the first approximation order is carried out in the regions of shock waves and contact discontinuities for the purpose of obtaining monotonous profiles of numerical solution [5]. the problem of the oblique shock reflection from a wall is frequently used for verification of new numerical methods for solving (9) and (10). the exact solution of this test problem represents a piecewise constant function and is found numerically with machine accuracy with the aid of the theory of the oblique shock waves [3]. the value φ = π/6 for the angle between the incident shock and the x axis was used in the computational examples presented below, as shown in figure 1. numerical solution was found by the pseudo-unsteady method. at the initial moment of time, the entire flow field was specified equal to the values of the undisturbed supersonic free stream, which were specified for subregion 1, as shown in figure 1, that is the initial gas flow was parallel with the xaxis. the criterion for the difference solution w n convergence to the limiting stationary solution was taken in the form res(n) < ε, where ε is the user-specified small positive number; ( ){ },|||,||,||,|maxmax=)( ,4,,3,,2,,1, , n kj n kj n kj n kj kj rrrrnres (11) where { } , ˆˆˆˆ =,,, 2 1/2,1/2, 1 1/2,1/2, ,4,,3,,2,,1, h gg h ff rrrr n kj n kj n kj n kjtn kj n kj n kj n kj −+−+ − + − n is the time layer number (n = 0,1,2,…), n kj n kj gf 2/1,,2/1 ˆ,ˆ ±± are the difference approximations of fluxes f(w) and g(w) in (9) by the method of [5], h1 and h2 are the steps of the uniform rectangular computational grid in the (x,y) plane. for the numerical solution of the given problem, two codes were developed: one in mathematica and the other in fortran 90. both results have coincided. all the computations were carried out on a pc with an 3ghz intel processor. the mathematica code was run both in mathematica 4.1.0 and in mathematica 8.0.4.0. to execute 2600 time steps the mathematica 4.1.0 and mathematica 8.0.4.0 needed 22457 and 27312 seconds, respectively. fortran needed only 21.45 seconds for the same computation. thus, mathematica 4.1.0 computes this two-dimensional task 1047 times slower than the fortran code. in the case of mathematica 8.0.4.0, the corresponding slow-down factor is equal to 27312/21.45 = 1273.29. the computations of the same problem were also done in mathematica 4.1.0 and in fortran 90 on a coarser grid of 80x20 cells, and 1600 time steps were done. in this case, mathematica 4.1.0 needed 3455 sec. of cpu time, and the fortran code needed only 3.36 sec. of cpu time. the corresponding slow-down ratio is 3455/3.36 = 1028.28. the discrepancy in the slow-down factors of 1047 and 1028 is explained by the well-known fact that a larger number of the intermediate printouts leads to larger cpu time expenses in mathematica. in both runs — on the 160x40 grid and on the 80x20 grid — the information about the solution residual was printed every 50 time steps. on the 160x40 grid, 2600 time steps were executed, and on the 80x20 grid, a much smaller number of 1600 time steps were done. one can assume with an insignificant error that the twodimensional gas dynamics problems are solved in mathematica 4.1.0 one thousand times slower compared to fortran. in the case of mathematica 8.0.4.0, the corresponding slow-down factor is higher and is equal to about 1270. such unfavorable slow-down factors make the considered versions of mathematica inapplicable for numerical solution of complex multidimensional problems of fluid dynamics. it should be noted that mathematica has been written using the c language. this language was developed at later times compared to the fortran language. therefore, the c compilers have absorbed the later developments in the area of the programming theory. in this connection, it is reasonable to expect that c compilers should generate exe files which should fig. 1. spatial region in the problem of the oblique shock wave reflection. etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 259-264 264 www.etasr.com vorozhtsov: on some unsolved problems of mathematica be no less efficient compared to the exe files created by fortran compilers. on this background, an extremely slow speed of numerical computations in the arithmetic of floating-point machine numbers in mathematica looks rather strange. (a) (b) (c) (d) fig. 2. the problem of the oblique shock wave reflection from a solid wall: (a) mach number contours; (b) gas pressure in section y = 0.5; (c) residual (11) as a function of the number of time steps n; (d) the surface m = m(x,y). mathematica has a large number of the built-in functions of computer graphics, which enable the obtaining of highquality graphs of curves, pictures of surfaces, contour plots, etc. in order to use these possibilities for the purpose of a rapid on-line visualization of the results of numerical solution of complex multidimensional problems of fluid dynamics and mathematical physics the present author has implemented a simple interface between fortran and mathematica. the realization of this interface reduces to the following: upon termination of the basic computation by fortran, an output of the computed results to the external file or several external files in mathematica format was implemented. and a small program is then written in mathematica which ensures the graphical visualization of computed results in a form suitable for the user. the exit from the fortran shell and entry into the mathematica program needs about 3 seconds of the user’s time, and then the mathematica program is started by pressing the keys shift/enter. it reads the arrays of numerical results from the external files created by the fortran code, and the user can see in a few seconds the computed results in a graphical form on the monitor screen. figure 2 shows the results of numerical computation, by fortran, of the problem of the oblique shock wave reflection from a solid wall, which were obtained by the steadying computation using the method of [5] on a uniform grid of 160x40 cells; the parameter of the method φ = 1/3, which ensures the third-order accuracy of the method in spatial variables in smooth flow subregions. all these graphical results were obtained with the aid of the above-described small mathematica 8 program, which reads the arrays of numerical results from external files created by fortran. figure 2(a) shows the lines of the constant mach number m= cvu / 22 + , where = /c pγ ρ is the sound velocity. the solid line in figure 2(b) is the exact solution, and the dashed line is the result of the computation by the method of [5]. figure 2(c) shows the residual (11) in the case of the method of [5]. it can be seen that 2400 time steps are needed to ensure a drop of the solution residual norm to the level of machine round-off errors 10 –10 – 10 –12 . vi. conclusions 1. as the above-presented examples show, the processing (simplification) of the rational-fractional expressions involving power functions is implemented in maple more thoroughly than in mathematica. 2. an error in mathematica is demonstrated, which leads to an incorrect result of the user’s program at a change of a function’s body. 3. it is shown by the example of numerical solution of a well-known model of a two-dimensional gas dynamics problem that the two-dimensional problems of gas dynamics are computed slower in different versions of mathematica, by factors ranging from 1000 to 1273 compared to fortran. such an unfavorable ratio of the cpu time expenses makes the considered mathematica versions unacceptable for numerical solution of complex multidimensional fluid dynamics problems. references [1] s. wolfram, the mathematica book, 3 rd edition, cambridge university press, cambridge, uk, 1996 [2] m. wester, “a critique of the mathematical abilities of ca systems” in: computer algebra systems: a practical guide, john wiley & sons, chichester, united kingdom, pp. 25–60, 1999 [3] s. p. kiselev, e. v. vorozhtsov, v. m. fomin, foundations of fluid mechanics with applications: problem solving using mathematica. birkhäuser, boston, 1999 [4] v. g. ganzha, e. v. vorozhtsov, “implementation of aerodynamic computations with mathematica”, 2 nd workshop on computer algebra in scientific computing, pp. 101–114, munich, 1999 [5] s. r. chakravarthy, s. osher, “a new class of high accuracy tvd schemes for hyperbolic conservation laws”, aiaa paper, no. 85-0363, 1985 microsoft word etasr_v11_n3_pp7118-7124 engineering, technology & applied science research vol. 11, no. 3, 2021, 7118-7124 7118 www.etasr.com tuan & chieu: the effect of moisture and fine grain content on the resilient modulus of sandy … the effect of moisture and fine grain content on the resilient modulus of sandy clay embankment roadbed nguyen anh tuan faculty of transportation engineering ho chi minh city university of transport ho chi minh city, vietnam tuanna@ut.edu.vn phan quang chieu faculty of civil engineering tien giang university tien giang, vietnam phanquangchieu5@yahoo.com abstract-this paper studies the effect of moisture and fine grain content on the resilient modulus of sandy clay embankment roadbed in the mekong delta, vietnam. the study analyzed the grain content of 30 soil samples on the annually flooded routes of the mekong delta according to the aashto t88-97 standard. the triaxial compression test at room temperature was used to estimate the resilient modulus of the samples belonging to 6 moisture levels. the experiments were conducted using 3 levels of lateral pressure, 0, 21, and 41kpa. five deflection stress tests of 14, 28, 41, 55, and 69kpa, were conducted for each lateral pressure. the results showed that as the percentage of grains finer than 0.075mm increased, the variation ratio of the resilient modulus also increased. the content of grains finer than 0.075mm was between 54.1%-93%, while the variation ratio of the resilient modulus ranged between 53.7% and 89.1%. moreover, as the percentage of grains finer than 0.075mm increased, water absorption capacity increased and resilient modulus decreased. as moisture and fine grain content influence the resilient modulus of the roadbed, this study’s results will help to limit and prevent the erosion of sandy clay embanked roadbeds, especially on frequently flooded areas such as the mekong delta. keywords-resilient modulus; moisture content; fine grain content; roadbed; in situ plate loading test i. introduction the resilient modulus of the roadbed is one of the most important parameters for designing a new or restoring a soft road surface in case of deformation. the thickness of the road surface layer is determined based on the resilient modulus of the roadbed. moisture content affects the resilient modulus of the roadbed significantly, as it increases the road surface's deformation causing cracks and subsidence, especially in sandy clay embanked roadbeds which are flooded for long periods. the resilient behavior of cohesive soils (fine-grained soils) related to moisture has been studied for over 40 years. the influence of density and water content on the resilient behavior of florida subgrade soils was studied in [1], while the subgrade resilient modulus was estimated by using standard tests in [2]. the degree of saturation affecting the resilient modulus of tennessee soils was studied in [3]. an improved evaluation procedure of roadbed soil’s resilient modulus was introduced in [4]. the effect of moisture on the resilient modulus of the ohio roadbed was investigated in [5]. in [6], a correlation between the relative moisture and the resilient modulus of the roadbed was proposed. the elastic and deformation characteristics of bottom ash in road construction, in particular young’s modulus and poisson’s ratio, were studied in [7]. according to [8], the settlement response of the embankment dam was similar for the mohr-coulomb and the hardening soil models for three material zones (clay core, sandy gravel, and random fill), having a modulus of elasticity in the range 25000-50000kpa. these studies showed that the resilient modulus of soil embanked roadbed depends heavily on soil type, moisture content, and soil condition [9]. the current study carried out laboratory experiments to observe the effects of moisture and fine grain content on the resilient modulus of a sandy clay embankment roadbed in the mekong delta of vietnam. ii. materials and methods a. determination of the resilient modulus the resilient modulus is determined based on elastic strain. in road constructions, it is used to calculate the roadbed and road surface subsidence. due to the transient workload, the loading and unloading time is extremely fast and repeated, while after several loads the accumulated plastic strain is reduced or eliminated. the subsidence of road works depends heavily on the elastic strain of the roadbed and road surface structure. resilient modulus is defined, according to [10], as: �� = (�� − � ) ��⁄ = � ��⁄ (1) where σ1 and σ3 are the major and minor principal stresses, σd is the deviator stress, and εr is the accumulated plastic strain. b. factors affecting resilient modulus it has been shown that the resilient modulus of cohesive soil depends on soil type, moisture content, saturation, the content of the grains that can go through the no.200 sieve, deflection stress, suction force, plasticity index, pore water corresponding author: nguyen anh tuan engineering, technology & applied science research vol. 11, no. 3, 2021, 7118-7124 7119 www.etasr.com tuan & chieu: the effect of moisture and fine grain content on the resilient modulus of sandy … pressure, lateral pressure, and lateral compression strength [1130]. c. effect of moisture content on the resilient modulus moisture content is the main parameter affecting the resilient modulus of sandy clay, as in low moisture the water binds soil grains and increases the effective stress between them through its suction and surface tension, leading to high resilient modulus values. moreover, at low moisture content, the sandy clay produces strong suction in water enough to reproduce a significant temporary colloidal effect between soil grains. increased moisture damages this phenomenon. the state of sandy clay depends heavily on water capacity, namely the physical bonding layers of water surrounding the coarse soil grains. when the soil is completely dry, the corresponding state is extremely hard or solid, the deformation is negligible, and the resilient modulus of the sandy clay increases due to the attraction between the opposite ions. moisture content increases gradually with a strong water suction layer, increasing effective stress between soil grains through the suction and the surface tension of water. however, the soil sample volume remains unchanged until the grains are fully deposited in the water suction layer, the soil volume begins to increase due to the thickness of the water shells, the water takes up the voids that push the soil grains apart, the surface suction force decreases, the soil's resilient modulus value decreases, the soil becomes semi-hard and flexible, and when free water appears, the resilient modulus gradually decreases as the soil turns into the liquid state. too much water causes the soil to enter a suspension state [31]. the resilient modulus value of the sample with the optimum moisture content is much greater than the resilient modulus value of the saturated sample. d. effect of fine-grained content on resilient modulus the resilient modulus of a cohesive embankment roadbed depends on the type of cohesive soil. the grain content is also an important factor affecting the resilient modulus of cohesive soils, especially the percentage of the grains that can go through the no. 200 sieve. when moisture is low, water binds soil grains (especially of fine-grained soil) and increases the effective stress between soil grains through the suction and the surface tension of water. in this case, the deformation of the soil is negligible. the clay may crack and become extremely hard when it is dry. moisture gradually increases until the grains are fully deposited into the water suction layer, the soil volume begins to increase due to the thickness of water shells, the water takes up the hollow holes pushing the soil grains apart, and the soil becomes semi-hard and flexible [31, 32]. e. laboratory experiments 1) purpose the main purpose of the experiments was to identify the physical characteristics of moisture content, saturation, unconfined compressive strength, plasticity index, liquid limit, optimum moisture, and the content of grains finer than 0.075mm. the rapid compression test utilized a 3-axis compression chamber to determine the resilience of the soil samples and calculate the resilient modulus. a total of 124 rapid compression tests were conducted to determine the resilient modulus, while 30 experiments were conducted to determine the physical characteristics and the grain content of the soil. 2) standards and methods the soil samples were sandy clay samples with different moisture values. soil samples were collected from the trunks of roads in annually flooded areas and classified according to aashto m 145-91 [33] based on grain composition and atterberg limit. the resilient modulus was determined according to aashto t294-03 [34]. the simulation of vehicle load was performed on soil samples at 6 moisture values (2% and 3% dryer than the optimum, the optimum, 2% and 3% over the optimum, completely saturated). liquid limit and plasticity index were determined according to aashto t89-07 [35] and t90-10 [36], while the grain content was analyzed according to aashto t88-04 [37]. the maximum dry density and the optimum moisture were determined according to aashto t180-01 [38], while the moisture was determined according to aashto t265-04 [39]. 3) sample collection and experimentation thirty soil samples were collected at 30cm depth in the road body of the annually flooded roads in dong thap, long an, and tien giang provinces. the natural moisture content of the samples was 9.9-32.7%. the basic physical characteristics of the samples were determined, including liquid limit, plasticity limit, grain content, standard compaction, and unconfined compressive strength. table i shows the results of liquid limit, plastic limit, and grain content analysis. table i. grain content and atterberg limit of samples no. sample liquid limit plasticity index sand (%) dust (%) clay (%) 1 la842.1 33.0 14.8 15.2 48.9 33.9 2 la842.2 34.3 12.1 12.4 48.9 35.9 3 la842.3 39.7 14.6 14.0 49.8 35.4 4 dt942.1 39.6 12.0 16.6 45.4 35.1 5 dt942.2 36.0 11.3 17.7 43.0 32.1 6 dt942.3 38.3 11.6 15.3 43.5 39.8 7 dt942.4 39.0 11.9 21.5 38.4 34.8 8 dt942.5 38.8 11.6 10.8 53.4 34.6 9 dt942.6 35.3 11.4 10.7 50.9 31.6 10 dt942.7 39.7 11.5 5.2 54.4 38.6 11 dt942.8 38.2 11.8 15.7 51.9 31.9 12 dt942.9 39.6 11.6 11.3 44.2 39.2 13 dt942.10 39.9 11.7 7.3 55.1 36.2 14 dt847.1 38.3 12.4 14.0 49.4 36.2 15 dt847.2 38.9 11.5 10.6 53.8 35.2 16 dt847.3 38.8 11.3 12.6 43.4 41.4 17 dt847.4 39.9 11.5 16.9 42.4 38.1 18 dt847.5 39.5 16.4 24.8 38.7 33.6 19 dt847.6 39.4 15.3 34.5 30.1 31.6 20 dt847.7 39.4 15.3 16.6 45.2 33.7 21 dt847.8 38.0 13.8 27.1 36.5 33.7 22 dt847.9 38.4 13.2 13.8 50.1 35.1 23 dt847.10 37.3 12.3 19.7 38.2 37.3 24 dt847.11 38.3 12.0 20.5 46.6 32.6 25 dt847.12 39.1 11.6 20.0 47.6 31.6 26 dt847.13 38.0 14.8 33.9 31.2 31.2 27 dt867.1 38.2 13.3 33.9 29.1 33.1 28 dt867.2 39.0 11.6 23.5 33.7 37.3 29 dt867.3 38.8 13.3 42.2 22.9 31.2 30 dt867.4 39.0 12.1 36.8 29.5 32.5 engineering, technology & applied science research vol. 11, no. 3, 2021, 7118-7124 7120 www.etasr.com tuan & chieu: the effect of moisture and fine grain content on the resilient modulus of sandy … an unconfined compressive strength test, according to aashto t208-05 [40], was carried out with a speed of 1mm/min right after compressing the sample to determine the value of the resilient modulus. the unconfined compressive strength was determined from the stress-strain curve. it is the maximum compressive stress value that the sample has to withstand or the value corresponding to 20% strain if this case happens first. axial compressive stress σ1 (kpa) was determined by: �� = � �(���) �� � � 100 (2) f. determining the resilient modulus of the soil the purpose of this test was to measure the resilient strain of the soil samples under the effect of fast compressive loading and determine the influence level of moisture and grains with a finer than 0.075mm size on the resilient modulus. for each soil sample collected, 15kg were selected through a 5mm sieve, they were divided into 6 equal weight parts, placed into 6 trays, and 6 different water quantities were sprayed on them to obtain the required moisture levels: 2% and 3% drier than the optimum, the optimum, 2% and 3% wetter than the optimum, and one saturated. wet soil was mixed, covered with a damp cloth, and incubated for 12h. the preparation of a test sample m (g) with the desired moisture value w (%) requires the determination of the moisture content of the sample w1(%) and the calculation of the amount of water q (g) to be sprayed according to: � = �0.01� (1 � 0.01��)⁄ � � (� − ��) (3) a compacting mortar with 125mm diameter and 127mm height was placed on a hard and leveled ground. the prepared soil was taken into the mortar with 3 layers, each one occupying about 1/3 of the mortar’s volume. a 2.5kg hammer was used on free fall from a height of 300mm, evenly distributed over the surface of the soil layer. each layer was compacted with 40 hammer drops. the compacted soil was removed from the mortar by pressing a cutting ring, having 36mm diameter and 76mm height, vertically into the core of the soil. the cutting ring was removed from the soil by whittling. the removed sample was weighted to determine its natural volume and placed in a rubber wrap. a 3-axis compression device model 28-t0401, shown in figure 1, was used to perform the tests. fig. 1. the triaxial compression device system. the prepared samples were placed in the laboratory chamber to eliminate the residual strain by applying lateral and vertical pressure. by loading and unloading many times with a strain rate of 1mm/min, the sample accumulated the residual strain until there was only resilient strain left. the water inlet valve was opened until the chamber was full. three levels of lateral pressure were applied (41, 21, and 0kpa) with 5 deviator stress levels (14, 28, 41, 55, and 69kpa). during the experiment, the bottom drain valve was unlocked. the results of loading for an unsaturated sample (dt.942.7-2) are shown in figure 2. table ii. loads on unsaturated sample no. lateral pressure σ3 (kpa) σd (kpa) times of loading (times) note 0 0 69 many times residual strain elimination 1 41 14 3 get the average value 2 41 28 3 3 41 41 3 4 41 55 3 5 41 69 3 6 21 14 3 7 21 28 3 8 21 41 3 9 21 55 3 10 21 69 3 11 0 14 3 12 0 28 3 13 0 41 3 14 0 55 3 15 0 69 3 16 0 destroy the sample determine qu fig. 2. results of loading with unsaturated soil samples (dt.942.7-2). in each deviator stress level test, it was necessary to load and unload 3 times to get the average of the deviator stresses corresponding to the average of the resilient strain. figure 3 shows the deviator stress-resilient strain relationship of the sample. the average values of the deviator stress and resilient strain can be used to calculate the resilient modulus value according to (4). the resilient strain generated after each load level consists of two resilient strain parts: an instant resilient strain part generated when the load is applied to the soil and another due to the rheological behavior in load time. slower speeds of loading (on the road when the car is running slower) cause greater resilient strains, as shown in figure 4. similar resilient values cause different p loads, resulting in different soil resilient modulus. engineering, technology & applied science research vol. 11, no. 3, 2021, 7118-7124 7121 www.etasr.com tuan & chieu: the effect of moisture and fine grain content on the resilient modulus of sandy … fig. 3. the relationship of σd with the resilient strain σ3 is unchanged (dt.942.7-2). fig. 4. the resilient strain curve of the compressing test when the load increases with each level at a uniform speed. fig. 5. determining the unconfined compressive strength (dt.942.7-2). the unconfined compressive strength test was carried out immediately after the completion of five deviator stress levels, with zero lateral pressure and vertical load at 1mm/min until the sample was damaged to determine the compressive strength qu. figure 5 shows a strain graph for determining qu of 637.2kpa for sample dt942.7-2 having 15.7% moisture content. the unconfined compressive strength of the test samples was between 60.6 and 774.3kpa. the correlation coefficient between the resilient modulus and the unconfined compressive strength (qu) was 0.6788 (r 2 ). for saturated samples, the test was only performed with zero lateral pressure level and five levels of deviator stress: 14, 28, 41, 55, 69kpa. during the experiment, the bottom drain valve was locked. the loading method for saturated samples is shown in table iii, and the results of loading for the saturated samples (dt.942.7-5) are shown in figure 5. table iii. load on saturated samples no. lateral pressure σ3 (kpa) σd (kpa) times of loading (times) note 1 0 14 3 2 0 28 3 3 0 41 3 4 0 55 3 5 0 69 3 6 0 destroy the sample determine qu the resilient modulus determined from a 3-axis compression test is the ratio of the deviator stress and the relative resilient strain of the sample: �� = � /� (4) � = �� − � (5) � = !/! (6) the resilient strain of soil samples was recorded by the data collection system according to each load level. it was necessary to choose the average resilient strain value of the three load times for each load level to calculate the resilient modulus. fig. 6. load result of unsaturated soil samples (dt.942.7-5). iii. results and discussion figures 7-9 show the experimental results for the resilient modulus of the 30 soil samples. in figure 7, a lateral pressure of 41kpa was applied during the experiment, with 5 samples having moisture content of 14.5%, 15.7%, 17.4%, 19.6%, and 20.3%. five deviator stress levels were performed to determine the resilient modulus, at 14, 28, 41, 55, and 69 kpa. figures 8 and 9 show similar experiments by applying lateral pressures of 21 and 0kpa respectively. the results illustrate the effect of moisture content, deviator stress, and lateral pressure on the resilient modulus. the resilient modulus is significantly affected by moisture content, as it decreased as the moisture engineering, technology & applied science research vol. 11, no. 3, 2021, 7118-7124 7122 www.etasr.com tuan & chieu: the effect of moisture and fine grain content on the resilient modulus of sandy … content increased at constant lateral pressure level. the resilient modulus decreased as the deviator stress increased, tending to change nonlinearly with the deviator stress at the same lateral pressure level. the resilient modulus increased as the lateral pressure increased at the optimum moisture value and the same level of deviator stress. the resilient modulus of the saturated samples decreased by 24.8-56.6% from the optimum moisture content. the correlation coefficient (r 2 ) between the resilient modulus and moisture was 0.8849. the r 2 between the resilient modulus and saturation was 0.6741. fig. 7. mr according to moisture and deviator stress, lateral pressure 41kpa (model dt942.7). fig. 8. mr according to moisture and deviator stress, lateral pressure 21kpa (model dt942.7). fig. 9. mr according to moisture and deviator stress, lateral pressure 0kpa (model dt942.7). figure 10 shows the effect of the grain content with a size finer than 0.075mm on the variation rate of resilient modulus due to the change of moisture content. the content of grains with size finer than 0.075mm varied from 54.1% (sample dt.867.4) to 93.0% (sample dt.942.7), while the value of the resilient modulus varied from 53.7% (60,548 28,043kpa) to 89.1% (95,533 10,426kpa). the more the content of grains having size finer than 0.075mm was, the more it affected the variation ratio of the resilient modulus. the content of grains having size finer than 0.075mm accounts for 54.1% (sample dt.867.4) to 70.1% (sample dt.847.10) corresponding to the rate of value variation of the resilient modulus from 53.7% (60,548 28,043 kpa) to 65.6% (45,531 15,681 kpa). the content of grains having size finer than 0.075mm accounts from 72.3% (sample dt.867.6) to 93.0% (sample dt.942.7) corresponding to the variation rate value of the resilient modulus from 65.8% (48,903 16,709kpa) to 89.1% (95,533 10,426kpa). the r 2 between the resilient modulus and the content of grains having a size finer than 0.075mm was 0.7358. the correlation coefficient between the resilient modulus and plasticity index was 0.5412. fig. 10. effect the content of grains having size finer than 0.075mm on mr. the obtained results demonstrate that the resilient modulus is significantly influenced by moisture and the content of grains having size finer than 0.075mm. the increased moisture content of the sample caused a drop in the resilient modulus. in many cases, the resilient modulus value of the saturated samples was reduced by more than 56.6% (35,698 15,489kpa) compared to the samples at optimum moisture content. the resilient modulus decreased nonlinearly when the deflection stress increased. increasing lateral pressure led to an increase in the resilient modulus of the soil sample. the higher the percentage of clay grains, the larger the area they cover, and the greater the resilient modulus of the soil is due to the attraction between opposite ions. the increased moisture corresponds to the thickness of the water shells. the greater the volume of water that occupies the voids, the farther apart the soil grains are, and the lower the surface suction of soil grains decreases. thus, the resilient modulus of the soil decreases significantly. iv. conclusions the resilient modulus was significantly affected by the moisture content, as it decreased rapidly as the moisture content increased by 1-2%. the resilient modulus for saturated samples was reduced by 56.6% in comparison to the optimum moisture content (sample dt942.7). the resilient modulus reached the smallest value of 8.153kpa when the sample had a moisture content of 23.3% and the content of grains having size finer than 0.075mm accounted for 88.1% (sample dt942.5). the percentage of grains having size finer than 0.075mm 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[40] standard method of test for unconfined compressive strength of cohesive soil, aashto t208-05, american association of state highway and transportation officials, 2005. microsoft word etasr_v11_n4_pp7393-7398 engineering, technology & applied science research vol. 11, no. 4, 2021, 7393-7398 7393 www.etasr.com ho & anand: the influence of bath temperature on the properties of silar deposited cobalt … the influence of bath temperature on the properties of silar deposited cobalt selenide thin films soon min ho centre for american education inti international university putra nilai, negeri sembilan, malaysia soonmin.ho@newinti.edu.my t. joseph sahaya anand faculty of mechanical and manufacturing engineering technology, universiti teknikal malaysia melaka durian tunggal, malacca, malaysia anand@utem.edu.my abstract-in this paper, cobalt selenide thin films have been deposited onto glass slides with the silar method under various bath temperatures. the structure, optical properties, and morphology of thin films were investigated. the x-ray diffraction patterns confirmed that the number of peak intensities increased with increasing bath temperature. from the afm images, bigger sizes and thicker films were observed for the films prepared at 80°c. the average grain size was estimated to be 0.2µm, 0.15µm, and 0.25µm when the bath temperature was 40°c, 50°c, and 80°c respectively. the highest absorbance value was observed for films prepared at 80°c. the band gap values range from 2ev to 2.4ev. keywords-thin films; cobalt selenide; semiconductor; band gap; solar cells; silar technique i. introduction growing fuel prices and the fast depleting of conventional energy sources lead to the necessity of the investigation on sustainable and efficient energy sources. renewable energy has been suggested as a viable approach. presently, many research groups have focused on solar energy as the most promising renewable energy to cater the future energy demand due to its abundance and inexhaustibility [1, 2]. due to the effort of finding new materials, transition metal chalcogenides (tmcs) are proposed as the most satisfactory semiconductor materials for photo electro chemical (pec) application. tmcs are a combination of transition metals and chalcogenides (group 16), mx2 (m: cd, mo, co, zn, cu, ni, fe, sn, etc., x: s, se, and te). tmcs possess excellent optical, electrical, and semiconductor properties, especially in the thin film form [3]. this advancement has motivated many researchers to investigate tmc materials namely, cds [4], cdse [5], zns [6], sns [7], znse [8], cuinte2 [9], cuinse2 [10], znte [11], ni3pb2s2 [12], cute [13], and cu4sns4 [14]. chalcogenide thin films can be fabricated by electrodeposition, spray pyrolysis, electrochemical deposition [15], and sputtering [16]. one attractive method for producing cobalt chalcogenide thin films, due to the possibility of large area deposition at low cost, is the successive ionic layer adsorption and reaction (silar) deposition method. it is a cost-effective method that can be controlled easily [17, 18]. it is the process of enlarging the thin film by separating the weakly bound elements in the pure water from the surface after immersing the substrate material at certain times and immersing it in cationic and anionic solutions [19, 20]. the silar method consists of four steps [21]: dipping into cationic solution, rinsing in de-ionized water, dipping in an ionic solution and rinsing again in de-ionized water. it is shown that cobalt chalcogenides have higher electronegativity, so it is proposed to study the synthesis, growth mechanism, optical and semiconducting properties of these thin films in a more systematic way. selenium and sulphur (x= s, se), are non-metal while tellurium (te) is a metalloid. hence, the chemical behavior and reaction of sulphur and selenium are similar to telluride. in the present research work, focus is given only to cobalt selenide. the aim of this work is to investigate the influence of bath temperature on the formation of cobalt selenide thin films. the silar deposition technique was used to synthesize films for the first time. characterization of films was carried out by using xrd (x-ray diffraction), afm (atomic force microscopy), and an uv-visible spectrophotometer. thin films can be used in various fields including solar cells, optical devices, energy storage devices, environmental applications, laser devices, and telecommunications devices. these materials have a great impact on the modern era of technology. thin films (binary, ternary, quaternary, and penternary compounds) can be produced by physical and chemical deposition techniques [22-24]. the selection of deposition method depends on the production cost, the specific application, the properties of films and available resources. cobalt sulphide [25-30], cobalt telluride [31-34], and cobalt selenide [35-40] thin films have been synthesized via various deposition techniques. in this work, the silar method was selected to produce cobalt selenide films. staring materials such as cobalt (ii) chloride hexahydrate and sodium selenite were used to deposit thin films onto glass substrate for the first time. ii. experimental part cobalt (ii) chloride hexahydrate (cocl2.6h2o) and sodium selenite (na2o3se) were used without further purification. microscope glass slide was used as substrate during the deposition process. this substrate was cleaned by acetone and de-ionized water before use. during the deposition process, the glass substrate was immersed in a 0.25m cationic solution (co2+ ion) with ph=3 for 30s. after rinsing with de-ionized corresponding author: soon min ho engineering, technology & applied science research vol. 11, no. 4, 2021, 7393-7398 7394 www.etasr.com ho & anand: the influence of bath temperature on the properties of silar deposited cobalt … water for 10s, it was immersed in 0.25m anionic solution (se2 ions) with ph=3 for 30s. then, it was rinsed with de-ionized water for 10s again in order to remove the loose material. the reaction solutions were put in a beaker into the water bath under various temperatures (40, 50, and 80°c). after the deposition process (after 10 cycles), the films were collected, rinsed by de-ionized water, and finally, put in the oven for 24h. the structure of the film was investigated by xrd with a malvern panalytical diffractometer (empyrean) equipped with a cu kα (λ=0.15418nm) radiation source. data were collected by step scanning from 10° to 80° with a step size of 0.02° (2θ). surface morphology, thickness, and roughness were examined by recording the afm images with bruker. the mode was scanasyst peak force tapping. the cantilever was scanasyst-air (material: silicon tip on nitride lever) with spring constants of 0.4n/m and resonance frequencies of 70khz. the optical properties of the films were studied with the perkin elmer uv/vis lambda 35 spectrophotometer. the band gap energy values were calculated based on the absorption data. iii. results and discussion afm measurements were carried out in order to investigate surface roughness and surface topology. the surface roughness was studied on the rq value which is defined as the root mean square average of height deviation taken from the mean image data plane. figure 1 shows the afm images of silar deposited cobalt selenide thin films under different bath temperatures. these images were measured over 1µm×1µm scanning range. the films deposited at lower temperatures (40°c and 50°c) indicated uneven morphology in comparison with the ones deposited at higher temperature. uniformly grained and compact morphological surface was observed at 80°c. these results are consistent with several other studies, indicating that grain grows more compactness and regularity in morphology with increase in temperature [41, 42]. the average grain size (0.2, 0.15, and 0.25µm) and surface roughness (0.0191, 0.0102, 0.0192µm) were reduced from 40 to 50°c and increased at 80°c. on the other hand, we found that film thickness (1.4 to 1.7µm) increased with increasing temperature. the temperature effect on the film thickness has been reported by many researchers [43, 44]. figure 2 indicates the xrd patterns for the cobalt selenide thin films prepared under various bath temperatures. it can be seen that the xrd patterns exhibited diffraction peaks at 2θ=13°, which can be indexed as reflection from the (111) plane of the cubic structure co9se8 compound (films prepared at 40°c and 50°c). other researchers have reported similar findings (cubic cobalt selenide structure) [45, 46]. an additional peak attributed to the (113) plane became more visible for the films synthesized at 80°c. a sharp diffraction peak can be observed in figure 2(c) reflecting the better crystallinity of the sample. the obtained xrd patterns were well matched with the standard joint committee on powder diffraction standards (jcpds) (reference code: 98-004-4857) as indicated in table i. based on the jcpds data, the lattice parameter values are a=b=c=10.431å. the crystal system, space group and space group number were cubic, fm-3m and 225 respectively. table i. comparison of observed d-spacing values with standard d-spacing values of cobalt selenide thin films. temperature (°°°°) reflection plane (hkl) observed dspacing values (å) standard dspacing values (å) 40 111 6.8 6.0 50 111 6.8 6.0 80 111 113 6.8 3.2 6.0 3.1 (a) (b) (c) fig. 1. afm images for films prepared at (a) 40°c, (b) 50°c, (c) 80°c. engineering, technology & applied science research vol. 11, no. 4, 2021, 7393-7398 7395 www.etasr.com ho & anand: the influence of bath temperature on the properties of silar deposited cobalt … (a) (b) (c) fig. 2. xrd patterns for the films prepared at (a) 40°c, (b) 50°c, (c) 80°c. figure 3 exhibits the absorbance spectra (at wavelengths from 300 to 1000nm) of cobalt selenide thin films prepared under different bath temperatures. generally, we observe that all the samples showed high absorption in the visible range, which allows the use of these materials in photo electrochemical and solar cells. the absorbance decreases with increasing wavelength. a similar tendency was also observed in [47, 48]. from figure 3, we note that the highest absorbance value can be observed for films prepared at 80°c due to increased grain size with thickness. larger size reduces the reflectivity of incident photon on the film surface [49, 50]. the band gap was calculated by the stern equation which is a very useful and commonly used method [51-57]. fig. 3. optical absorbance spectra of thin films prepared at (a) 40°c, (b) 50°c, (c) 80°c. � � ������ � �/� �� (1) in (1) v is the frequency, h is the planck’s constant, k is a constant, while n carries the value of either 1 or 4. the n value is 1 for a direct gap material and 4 for indirect gap material. the plot of (ahν)2 against hν is shown in figure 4. extrapolation of the linear portion of the curve to (ahν)2=0 produces the band gap energy. the band gap increased from 2.1ev (40°c) to 2.4ev (50°c), and dropped to 2ev (80°c) as shown in figure 4. other research groups have highlighted similar band gap values (table ii). these cobalt selenide films have been prepared by using different methods including chemical bath deposition, electro deposition, magnetron sputtering method and mechano chemical method. the obtained thin films could be used in solar cell applications because of direct band gap between 1 to 2ev [58, 59]. table ii. band gap energy of cobalt selenide thin films prepared under different deposition techniques remarks band gap value (ev) reference thin films were produced onto glass substrate by using chemical bath deposition method in the presence of ammonia, cobalt (ii) acetate and sodium selenosulphite. 1.8 to 3.6 [35] thin films were synthesized onto tin oxide glass substrate via electro deposition technique in the presence of h2seo3 and co(ch3coo)2 solutions. 1.53 [36] thin films were prepared onto nonconducting micro glass slide through chemical bath deposition method, in the presence of cobalt nitrate, ammonia and sodium selenosulphate. 1.7 [37] thin films were produced using magnetron sputtering method 1.53 [38] thin films were synthesized onto tin oxide coated glass by using electrodeposition method. 1.53 [39] thin films were grown using the mechanochemical method. 1.7 [40] engineering, technology & applied science research vol. 11, no. 4, 2021, 7393-7398 7396 www.etasr.com ho & anand: the influence of bath temperature on the properties of silar deposited cobalt … (a) (b) (c) fig. 4. (ahv)2 curve against (hv) for thin films prepared at (a) 40°c, (b) 50°c, (c) 80°c. iv. conclusions the influence of bath temperature on the formation of silar deposited cobalt selenide thin films was studied in this paper. the xrd data supported the existence of cubic phase cobalt selenide films. the xrd patterns confirmed that the number of peaks increased with increasing bath temperature. the films prepared at 80°c have higher absorption, crystallinity, and the most homogeneity. band gap values were observed in the range of 2ev to 2.4ev. acknowledgment this research work was supported by the inti international university under inti internal research grant inti–cae-0101-2018. references [1] t. j. s. anand, s. sharir, and s. i. abd. razak, "electrosynthesized transition metal chalcogenide thin films for photoelectrochemical cell applications," current topics in electrochemistry, vol. 21, pp. 131–150, 2020. 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[59] t. sinha, l. verma, and a. khare, "variations in photovoltaic parameters of cdte/cds thin film solar cells by changing the substrate for the deposition of cds window layer," applied physics a, vol. 126, no. 11, oct. 2020, art. no. 867, https://doi.org/10.1007/s00339-02004058-4. authors profile soon min ho is a professor in inti international university in malaysia. he received his ph.d. in materials chemistry at putra university, malaysia. he has taught a variety of chemistry courses such as physical chemistry, organic chemistry, general chemistry, chemistry & society over the last ten years. his research areas include chalcogenide metals, activated carbon, wastewater treatment, green chemistry, semiconductors, nano materials, and thin film solar cells. he has authored or co-authored more than 155 articles in scopus/isi/international referred journals and successfully produced more than 45 book chapters. he has been appointed as a journal reviewer, editorial board member, and thesis external examiner. t. joseph sahaya anand is an expatriate staff who was born in india on july 30, 1975. as a physics graduate he completed his pg and m.phil from st. joseph’s college, affiliated to bharathidasan university. he received his ph.d. in materials science from the university of hong kong in 2004. he has been awarded with post-doctoral fellowship by the tohoku university, sendai japan during 2004–2005. he is currently a professor of materials science in the faculty of mechanical and manufacturing engineering technology. his research interests are materials synthesis and characterization of transition metal chalcogenides and intermetallic aluminides for electronic / semiconductor applications. microsoft word etasr_v10_n6_pp6584-6588 engineering, technology & applied science research vol. 10, no. 6, 2020, 6584-6588 6584 www.etasr.com rajput et al.: a versatile decentralized 3d volumetric fusion for on-line reconstruction a versatile decentralized 3d volumetric fusion for on-line reconstruction asif rajput department of computer science sukkur iba university sukkur, pakistan asifali@iba-suk.edu.pk faheem akhtar department of computer science sukkur iba university sukkur, pakistan fahim.akhtar@iba-suk.edu.pk arif hussain department of electrical engineering sukkur iba university sukkur, pakistan arif.hussain@iba-suk.edu.pk zahid hussain khand department of computer science sukkur iba university sukkur, pakistan zahid@iba-suk.edu.pk hina magsi department of electrical engineering sukkur iba university sukkur, pakistan hina.magsi.iba-suk.edu.pk abstract-advancement in depth-sensing technology has allowed mobile robots to visualize the surrounding environment in 3d models. regardless of the sensing technology (i.e. active, passive, or laser-based), a complete system that integrates recent depth data in previous 3d models in real-time is done by employing simultaneous localization and mapping (slam) algorithms followed by a 3d reconstruction engine. unfortunately, both the slam algorithm and the 3d reconstruction engine are usually executed on a single computing device, making the whole system exceptionally costly and heavy and restricting the robot's mobility. this paper proposes a decentralized, modular reconstruction system capable of employing various sensors to facilitate online 3d reconstruction from a resource-limited mobile robot. keywords-3d reconstruction; visual slam; depth fusion i. introduction the recent development of active depth-sensing technology in which a known pattern is projected onto a suspected surface to measure depth has attracted impressive research and development momentum. for instance, google initiated the project tango [1] where active depth perception capabilities have been integrated within a standard mobile device to facilitate depth perception, area learning, motion tracking, and augmented reality (ar). similarly, plug and play devices such as structure [2] allow consumers to develop a 3dimensional map of surroundings to facilitate relatively accurate 3d measurements and 3d scanning. applications of active depth sensors are more common in mobile robots due to their higher sensing rate (a.k.a. frame-rate), lightweight design, and publicly available development resources [3, 4]. therefore, various applications exist in which semi-autonomous or autonomous mobile robots equipped with such sensors are deployed to perform mundane to specialized tasks. for instance, a mobile robot equipped with a depth sensor can scan the 3d geometry of a medium size room and store the output meshes in relatively good quality. unfortunately, scaling the overall design to accommodate larger environments requires a complete 3d fusion-based reconstruction (such as infinitam [5], fastfusion [6], and rfusion [7]) executed with higher computational and memory resource computing devices. furthermore, their working principle limits active depth sensors to be bounded in an indoor environment, hence, scanning mechanisms should exhibit generic qualities to facilitate outdoor reconstruction. therefore, a decentralized 3d reconstruction system in which both computing and scanning devices are connected through a well-known data sharing architecture to reconstruct large-scale environments is expected to efficiently handle such scenarios, as shown in figure 1. this paper proposes a novel decentralized approach to the 3d reconstruction framework, shown in figure 2. the overall workload is divided, so that process of depth sensing and localization is performed in a scanning node, and every potential keyframe is integrated with a remote computing node. simultaneously, both computers are connected with a wellknown robot operating system (ros) [8] publisher/subscriber architecture over tcp/ip. this allows flexible, scalable, and corresponding author: faheem akhtar engineering, technology & applied science research vol. 10, no. 6, 2020, 6584-6588 6585 www.etasr.com rajput et al.: a versatile decentralized 3d volumetric fusion for on-line reconstruction independent architecture, which can be adapted in potentially countless applications. fig. 1. a typical 3d fusion framework. fig. 2. a decentralized 3d fusion framework. ii. literature review many visualslam algorithms exist that are explicitly designed to target particular sensor systems. for instance, large scale dense (lsd) monocular slam [9] is a computationally lightweight algorithm that can directly be implemented in mobile devices such as cellphones and tablets. in principle, lsd-slam takes the live camera image stream and localizes camera position by tracking features within frames while estimating sensor ego-motion. unfortunately, monocular slam algorithms are prone to accumulate estimation drift caused by lower potential features and depth ambiguity. to solve the estimation drift, algorithms such as rgbd-slam [10] and stereo-lsd slam [11] counter the problem by introducing additional features such as the 3d geometry of the environment. in principle, 3d information acquired from a depth camera from either active depth camera or passive stereo estimation can be used to generate vital features with an improved overall tracking efficiency. unfortunately, these algorithms are explicitly designed, which restricts the generic nature of overall framework design. in other cases, various implementations of visualslam algorithms use predictive filtering (such as kalman filters) to fuse tracking information with sensor ego-motion from the inertial measurement unit (imu). these fusion-based slam algorithms [12] provide further sensor localization accuracy at the expense of extended hardware and computational resources. fortunately, orb-slam2 [13] 's generic nature provides state-of-the-art tracking information without affecting the overall computational profile. it is therefore expected that employing orb-slam2 in scanning systems will provide unrestricted sensor selection to accommodate both smalland large-scale 3d reconstruction. authors in [14] proposed the core concept of volumetric 3d integration in 1996. they proposed that range images may be represented and integrated by a voxel grid containing signed distance function (sdf) from the expected surface. in principle, each incremental update of range image is represented in implicit form, and weighted addition is applied to update globally consistent 3d models. unfortunately, the integration approach did not receive research interest due to its extensive memory and computational resources. in 2011, microsoft released a software development kit (sdk) with support for their kinect depth sensor, which revived the 3d fusion and reconstruction concept. kinectfusion [15] was the first standalone reconstruction framework that performed localization and integration with gpu computational resources using an active depth camera. initially, the scale of reconstruction supported by kinectfusion was bounded due to limited gpu resources. authors in [17] extended the working of kinectfusion to accommodate large scale reconstruction. at present, various implementations of volumetric fusion [5, 6, 16, 17] utilize modern cpu and gpu architecture to facilitate virtually boundless reconstruction with the help of hashed voxel grids. therefore, in the presented system, we have extended a regularized implementation of [7] that provides controlled regularization to facilitate the implicit representation smoothing. in this paper, a novel 3d reconstruction framework is proposed to facilitate a decentralized, remote 3d reconstruction scenario. the proposed framework is targeted to utilize multiple computationally inexpensive computing nodes that efficiently distribute the visual slam algorithm and 3d reconstruction framework workload. unfortunately, authors could not find an appropriate baseline framework for extensive comparison to view the presented work's novelty and the problem domain. however, our work will serve as the baseline for upcoming research in this application domain. iii. proposed methodology a. scanning node in order to maintain generality, it is presumed that a depth sensor of either active or passive depth sensing nature is attached to mobile computing devices such as laptops and streams of color and depth images are easily available. for further simplicity, it is presumed that both color and depth cameras are calibrated, and their respective intrinsic parameters such as focal lengths and central points are known. in general, all sensors can produce a steady image stream of 30 frames per second, a single registered time-stamped depth and color image that can be respectively denoted. in our implementation of the proposed system, the latest version of orbslam2 is employed as a localization algorithm to track camera movements within the environment. furthermore, the generic nature of orbslam2 allows flexibility in sensor selection to accommodate both smalland large-scale 3d reconstruction. after the successful estimation of camera poses within the localization module, an instance is created containing respective depth and color image and camera pose information in standard notation, which contains rotation and translation information respectively. therefore, each depth sample can be converted easily to a world coordinate system by using (1): engineering, technology & applied science research vol. 10, no. 6, 2020, 6584-6588 6586 www.etasr.com rajput et al.: a versatile decentralized 3d volumetric fusion for on-line reconstruction �� = ��. � � � � �� − ��� �� ���,���� �� ���� − ��� �� ���,���� � !� �� ,���� " # # # $ + '� (1) at this moment, (� is broadcasted through ros tcp/ip as a packet (referred to as topic in ros terminology) which is received by a computing node to perform 3d integration and rendering to provide real-time 3d reconstruction. b. computing node the computing node accepts each keyframe and performs 3d fusion by employing recursive total variation based implicit regularization to reduce noise effects. the system first converts each valid depth sample to a list of the 3d point cloud (denoted compactly as in upcoming text) in the world coordinates using rotation and translation. the system then employs a least square-based regularized integration that inherently reduces noise effects and produces smoother iso-surfaces. the process of regularizing the implicit surface involves representing the obtained in the axis-aligned volumetric grid in which each cell (referred to as voxel) contains a projective signed distance from the surface. for each valid 3d point ) ∈ +� , the system extracts a set of voxels (referred to as sdf-signal in [7]) that lie along the ray from camera position and ). in least squares terminology, the extracted sdf-signal (denoted as , ) is presumed to be the current measurement of the system which is prone to accumulate estimation noise. assuming a linear relation between , and the unknown true state of system with a system matrix a exists (see [18] for more details), an estimated state of the system .can be calculated by minimizing the following least squares system: -. = /�0min�4‖6−,‖778 (2) however, in order to introduce a smoothing aspect in (2), an additional regularization term is added which acts as counter weight and influences the . to accommodate neighboring elements. such minimization system can be written as: -. = /�0min�4‖−,‖77 + 9‖0 -�‖778 (3) where λ is a regularization parameter that controls the influence of neighboring elements and 0 -� is a function which approximates the second order finite difference of . in principle, the number of elements in -,, and . (referred to as support in [5]) directly affects the noise handling properties of the overall system. therefore, longer streams are suitable to handle high degrees of depth noise, such as those acquired from passive depth sensors. simultaneously, shorter support can easily accommodate relatively accurate depth information captured from an active depth camera. after solving the minimization task, the values of . are updated to particular voxel locations. the complete process of regularized integration ensures that the underlying implicit representation is smooth, and the resulting volumetric grid can be easily rendered using a standard marching cube algorithm [19]. iv. evaluation two distinct datasets were selected to evaluate the proposed decentralized system's generic nature containing a series of stereo image pairs and traditional rgb-d images from kitti [20] and corbs [21] datasets respectively. the kitti vision benchmark suite (written compactly as kitti) contains a comprehensive set of visual and numerical data such as stereo image pairs, lidar point cloud, and vehicle gps information. the versatile nature of the data present in the kitti dataset allows researchers to quantitatively evaluate their research in the fields of stereo matching, scene flow, optical flow, depth estimation, visualslam, and object tracking (as explained in [20]). similarly, the corbs dataset contains a set of rgb and depth images captured from the kinect v2 camera. simultaneously, the ground truth pose of the camera and 3d models are also provided to evaluate slam and 3d reconstruction algorithms' efficiency. it is worth mentioning that the system's goal is to perform well in an online scenario where the localization algorithm (e.g. orbslam2, etc.) estimates sensor position in real-time. the baseline for performance benchmark is calculated by employing localization and fusion modules on the same computing device (referred to as the traditional approach). such baseline implementation highlights the strain of processing as well as throughput delays caused by severe data processing. to isolate and quantify throughput delays, a precise timing mechanism is applied. the localization module issues and attaches a timestamp to the processing instance (i.e. either rgb-d or stereo image pair). the fusion module is designed to execute in an independent processing thread, another timestamp is generated, and the difference is recorded as a processing delay. in the optimal scenario, the difference between timestamps is expected to contain a smaller value, while non-optimal systems are expected to produce higher values. such high processing delays further degrade the system's performance as previous time differences can accumulate to hinder the reconstruction framework's real-time profile. figure 3 illustrates the problems caused by throughput delays in a traditional 3d fusion framework. the system’s performance is decreased with every successive input keyframe, and the system crashes after processing approximately 60 and 25 keyframes due to memory overflow in both 06_kitti and 07_kitti trajectories, respectively. contrarily, the proposed system continues to work with an average throughput delay of 500ms for all input instances. similar observations have been observed during the experimentation process of the desk1 trajectory from the corbs dataset (referred to as corbs_d1) and are shown in figure 4. absolute trajectory error (ate) is an important measure that compares the estimated camera poses with ground truth trajectory. it calculates statistical error measures such as min, max, mean, median, standard deviation, and rmse quantities to establish a fair comparison between the estimated trajectories between the traditional system and the proposed decentralized system. all camera poses estimated from the proposed system were truncated and then compared by a publicly available analysis tool [21]. although no modifications were performed in the visualslam engine of the proposed method and the traditional system, it was observed that throughput delays indirectly affect engineering, technology & applied science research vol. 10, no. 6, 2020, 6584-6588 6587 www.etasr.com rajput et al.: a versatile decentralized 3d volumetric fusion for on-line reconstruction the estimation process of slam. this counter-intuitive finding is caused by the fact that traditional on-line visualslam modules are usually memory dependent. once the memory buffer is filled with incoming successive keyframe images, the system either compensates with increasing the memory buffer area or drops incoming frames. we suspect that due to the dropping of keyframes, the visualslam module fails to register the camera movement successfully, and the final result is increased in overall absolute trajectory error. figure 5 shows the reconstructed 3d models from 06_kitti and 07_kitti trajectories. it is worth mentioning that these models are the result of fusing 428 and 242 keyframes respectively. since traditional on-line 3d fusion frameworks crashed at much smaller keyframe numbers, their partially reconstructed results are deliberately withheld. (a) (b) fig. 3. processing delays in traditional and proposed method for: (a) 06_kitti and (b) 07_kitti trajectory. fig. 4. processing delays in traditional and proposed method for the desk1 trajectory. (a) (b) fig. 5. reconstructed 3d models from (a) 06_kitti and (b) 07_kitti trajectories. v. conclusion this paper proposed a decentralized online 3d reconstruction framework capable of working with various available depth sensors. the experimental results show that a decentralized online 3d reconstruction framework is robust enough to handle traditional visualslam limitations, such as integrating fast incoming keyframes on its own. furthermore, it was observed and shown with quantitative results that the proposed system also facilitates a modular approach, which, in result, can offer extendibility without changing the complete system. the communication between decentralized computing nodes is done with the state-of-the-art robot operating system, which is open source and performs with exceptional reliability. finally, it is shown that a lightweight decentralized system outperforms a traditional 3d reconstruction system. references [1] j. kastrenakes, "google’s project tango is shutting down because arcore is already here," the verge, dec. 15, 2017. https://www.theverge.com/2017/12/15/16782556/project-tango-googleshutting-down-arcore-augmented-reality (accessed dec. 11, 2020). 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[21] o. wasenmüller, m. meyer, and d. stricker, "corbs: comprehensive rgb-d benchmark for slam using kinect v2," in 2016 ieee winter conference on applications of computer vision (wacv), lake placid, ny, usa, mar. 2016, pp. 1–7, https://doi.org/10.1109/ wacv.2016.7477636. microsoft word etasr_v11_n5_pp7585-7590 engineering, technology & applied science research vol. 11, no. 5, 2021, 7585-7590 7585 www.etasr.com alshammari et al.: a new particle swarm optimization based strategy for the economic emission … a new particle swarm optimization based strategy for the economic emission dispatch problem including wind energy sources gharbi a. alshammari department of electrical engineering university of hail hail, saudi arabia gharbi.a.alshammari@gmail.com badr m. alshammari department of electrical engineering university of hail hail, saudi arabia bms.alshammari@uoh.edu.sa fahd a. alshammari department of electrical engineering university of hail hail, saudi arabia fahad.a.s.alshammari@gmail.com ahmed s. alshammari department of electrical engineering university of hail hail, saudi arabia ahm.alshammari@uoh.edu.sa tawfik guesmi department of electrical engineering university of hail hail, saudi arabia tawfik.guesmi@istmt.rnu.tn naif a. alshammari department of electrical engineering university of hail hail, saudi arabia naif.a.s.alshammari@gmail.com abstract-power dispatch has become an important issue due to the high integration of wind power (wp) in power grids. within this context, this paper presents a new particle swarm optimization (pso) based strategy for solving the stochastic economic emission dispatch problem (eedp). this problem was solved considering several constraints such as power balance, generation limits, and valve point loading effects (vples). the power balance constraint is described by a chance constraint to consider the impact of wp intermittency on the eedp solution. in this study, the chance constraint represents the tolerance that the power balance constraint cannot meet. the suggested framework was successfully evaluated on a ten-unit system. the problem was solved for various threshold tolerances to study further the impact of wp penetration. keywords-economic emission dispatch; wind energy; stochastic optimization; particle swarm optimization i. introduction wind energy has expanded rapidly the recent years at a global level. wind power is becoming more and more economically competitive compared to conventional energy production methods due to improvements in turbine efficiency and rising fuel prices [1]. in addition, wind energy sources are growing at a rapid pace reaching a technical maturity that allows them to become important components of the energy industry. on the other hand, the inclusion of wind energy in power grids introduced new challenges. the high penetration of wind energy has a significant impact on system security due to its intermittent characteristics [2]. one of these challenges is the power dispatch problem. in general, the dispatch problem aims to find the optimal generation of all generators and sources minimizing energy production cost and system losses. in addition, global warming and increased initiatives to protect the environment are forcing producers to reduce the gas emissions produced by fossil fuel combustion in power stations. the fuels used in thermal power stations (coal, fuel oil, natural gas, etc.) produce harmful gases like carbon dioxide (co2), sulfur dioxide (so2), and nitrogen oxides (nox) which are toxic and cause the greenhouse effect. thus, the reduction of the emission of these gases during electricity production has become a primordial task [3]. several studies combined the economic and environmental aspects in one problem called economic emission dispatch problem (eedp) [4-5], considering several constraints such as generation capacity, power balance, and valve point loading effects (vple) [4-5]. various methods have been suggested in the past two decades to solve this nonlinear and nonconvex problem. for instance, classical techniques such as dynamic programming [6], linear programming [7], lambda iteration [8], and interior-point [9] have been widely used for solving the dispatch problem. however, in these techniques, the fuel cost was approximated by a quadratic, and vple constraints were neglected. in addition, these conventional methods were iterative and required an initial solution which may affect the convergence of the employed method and produce only local solutions. various intelligent optimization methods were presented to overcome the limitations of classical methods, like the genetic algorithm (ga) [10], artificial bee colony (abc) [11], bacterial foraging algorithm (bfa) [12], particle swarm optimization (pso) [13], differential evolution (de) [14], and simulated annealing (sa) [15]. in general, these metaheuristic techniques have achieve good results in solving corresponding author: tawfik guesmi engineering, technology & applied science research vol. 11, no. 5, 2021, 7585-7590 7586 www.etasr.com alshammari et al.: a new particle swarm optimization based strategy for the economic emission … various engineering problems. however, the aforementioned techniques minimized fuel cost and emissions by seeking the optimal production of the existing thermal units. at the moment, wind energy has attracted much attention in the power sector due to its zero fuel cost and emissions. hence, the inclusion of wind power in the eedp formulation has gained wide attention. in [16], a new mathematical formulation was developed based on the here-and-now approach for the stochastic eedp integrating wp sources. the intermittency of wind power was described by the weibull distribution function. the same approach was extended for the dynamic eedp in [17]. various fuzzy membership functions were suggested in [18], taking into account that system security may be affected by the randomness of wind power, to describe the dispatcher’s attitude regarding wp penetration. two objective functions, based on operational cost and risk level, were considered and minimized using a pso-based method, but emissions were not included in the problem formulation. the risk level of wp uncertainty was considered in [19], incorporating vple in the cost function. fuzzy quadratic functions that described dispatcher’s attitudes were investigated in [20] to determine the quantity of additional wp to minimize generation cost without affecting system security. the effect of fluctuations of wp on the eedp was modeled in [21] by overand under-estimation costs of available wp, where a hybrid algorithm combining pso and gravitational search was used to minimize the objective functions. in [22], the underand over-estimation costs of uncertain wp were also included in the total production cost, using an improved fireworks algorithm to find the optimal generation. the randomness of wp was modeled by a chance constraint in the dispatch problem formulation to avoid the overand under-estimation costs in [23], where wp was represented by a weibull distribution function, and the impact of wp penetration on the total fuel cost and emissions was studied and analyzed. in recent years, pso-based techniques have been favored by researchers due to their low parameter number, convergence rate, and easy implementation. pso was introduced in [24] as an efficient optimization tool for complex optimization problems. this study presents a new pso-based strategy for solving the stochastic eedp incorporating a wind farm. at first, the problem is formulated as a stochastic optimization problem. then, the stochastic constraint, which describes power balance, was converted to a deterministic constraint. the weibull distribution function was used to describe the randomness of wp. the pso algorithm was used to solve the obtained deterministic problem. the effectiveness of the proposed method was tested on a 10-unit system, investigating the cases with and without wp sources. moreover, the impact of wp penetration rate was studied. ii. problem formulation the eedp is treated as a multi-objective mathematical programming problem that attempts to minimize both cost and emissions simultaneously while satisfying equality and inequality constraints. the following objectives and constraints were taken into account in the eedp problem formulation: a. objective functions the thermal units with multi-steam admission valves that work sequentially to cover the ever-increasing generation increase the nonlinearity order of the total fuel cost due to the vple, as illustrated in figure 1. fig. 1. fuel cost function with five valves (a, b, c, d, e). the fuel cost function of a thermal generator, considering the vple, is expressed as the sum of a quadratic and a sinusoidal function. thus, the total fuel cost in terms of real power output can be expressed as [23]: �� = ∑ �� + �� � + � ���� � + ��� ������� ���� − ���� (1) where ai, bi, ci, di, and ei are the cost coefficients of the i-th unit, pi is the output power in mw, and the total cost ct is in $/h. the second objective function considered is the atmospheric pollutants such as sulfur (sox) and nitrogen oxides (nox) caused by fossil-fueled generator units. this can be modeled as the summation of a quadratic polynomial and an exponential function [23]: �� = ∑ �� + �� � + �� �!� + "� �#$ %� �!�� � (2) where ai, βι, γi, ηι , and ξi are the emission coefficients, and the total emission is in ton/h. in several works, the bi-objective eedps were converted into a mono-objective optimization problem [3], and the price penalty factor (ppf) based method was adopted. thus, the combined economic-emission objective function can be described by: &� = '�� + 1 − '!)�� (3) where, ' = rand 0,1! , ft will be minimized for each generated value of µ to obtain the optimal solution that can be a nominee solution in the pareto front, and λ is the average of the ppf thermal units. as shown in (4), the ppf of the i-th unit is the rate between its fuel cost and its emission for maximum generation capacity, and (5) gives the expression of λ. )� = 0123451234 (4) ) = �� ∑ )��� � (5) b. problem constraints the eedp can be solved by minimizing the ft defined in (3) for the following constraints [23]: generation (mw) f u e l c o s t ($ /h ) without vple with vple e c a b d engineering, technology & applied science research vol. 11, no. 5, 2021, 7585-7590 7587 www.etasr.com alshammari et al.: a new particle swarm optimization based strategy for the economic emission … • generation capacity: because of the unit design, the real power output of each unit i should be within its minimum ���� and maximum limit ��78: ���� ≤ � ≤ ��78 � = 1, … , ; (6) • real power balance constraints: the total of real power generation must balance the predicted power demand pd plus the real power losses pl in the transmission lines, at each time interval over the scheduling horizon: ∑ �< − =< − ><�� � = 0 ? = 1, . . . , a (7) pl can be calculated using a constant loss formula [4]: >< = ∑ ∑ �b�c c + ∑ bd� � + bdd�� ��c ��� � (8) where bij, boi, and boo are the loss parameters also called bcoefficients. • prohibited operating zones (poz) constraints: the poz constraints are described as: �< ∈ f � ��� ≤ � ≤ �,�gdh� �,ij�kl ≤ � ≤ �,igdh�  , n = 2, . . . , p� �,q1kl ≤ � ≤ ��78 (9) where �,igdh� and �,ikl are the down and up bounds of poz number k, and iz is the number of poz for the i-th unit due to the vibrations in the shaft or other mechanical faults. therefore, the machine has discontinuous input-output characteristics [4]. c. description of wp randomness a major challenge in integrating wind power output into a power network is its uncertainty, fluctuation, and intermittent nature. hence, wp output should be expressed as a stochastic variable utilizing a transformation from wind speed to power output. a simplified linear piecewise function can describe the actual relationship between them when ignoring some minor nonlinear factors. this study adopts the two-factor weibull distribution [16]. the main advantage of this distribution type is that if its parameters are specified at a given altitude, they can be found for another one. the probability density function (pdf) and the cumulative distribution function (cdf) of wind speed are described by (10) and (11), respectively: rs t! = iu vwuxij� �#$ y− vwuxiz (10) &s t! = [ rs \!w] �\ = 1 − �#$ ^− vwuxi_ ,   t ≥ 0 (11) where, k and c are positive parameters called shape and scale factors for a given location, respectively. the speed-power characteristic of the wind turbine can be described by: a = b c! = 0,  if  c < t��  or  c > tdk< (12) ( ) ( ) ifφ − = = ≤ < − in r in r r in v v w w v v v v v v (13) ( ) , ifφ= = ≤ <r r outw v w v v v (14) based on probability theories, the cdf corresponding to the wp can be described by: &f g! = h a ≤ g! = 1 − �#$ f− iv1 + jhhk x t�� l i m + �#$ ^− vtdk< xi_ ,   0 ≤ g < gn (15) where, ℎ = wk jw1pw1p . taking into account the intermittency characteristic of wp, the power balance constraint given by (7) can be modified as: hq∑ ��� � + a ≤ = + > } ≤ s} (16) where pr(x) is the probability of event x, w is the wp output of the wind farm, and σ is the tolerance that power balance between total generation, load, and total system losses cannot meet. iii. the pso algorithm pso is considered an efficient and robust method that can be applied to nonlinear optimization problems and more particularly on electrical systems [25-26]. this algorithm ignores several conditions, such as differentiability and continuity regardless of the objective functions and the constraints to be optimized or respected. for an optimization problem with n decision variables, the i-th particle at iteration k is presented by its position t�i = �t��i , … , t��i � that is considered as a candidate solution and velocity c�i =�c��i, … , c��i �. at the next generation k+1, the velocity and the position of this particle will be updated according to: c�iu� = gc�i + �h� �$���?�i − t�i � + �h� �v���?i − t�i � (17) t�iu� = t�i + c�iu� (18) where, w, c1, and c2 are the pso parameters, r1 and r2 are random numbers in the range [0,1], and $���?�i and v���?i are the best solution of the i-th particle and the overall population at the k-th iteration respectively. at each iteration k, the inertia weight w used for balancing between local and global searches can be calculated as: g = g�78 − h 234 jh 21p i234 ∗ n (19) where n�78 is the maximum number of iterations, and g�78 and g��� are the upper and lower bounds of w. from (19), it is clear that g�78 is the initial value of the inertia weight while g��� is its final value. iv. simulation and results two cases were studied to verify the effectiveness of the suggested strategy for solving the eedp including a wind farm. simulations were carried out on matlab r2009a installed on a pc with an i7-4510u@2.60ghz cpu. the studied cases were: a ten-unit system without a wind farm engineering, technology & applied science research vol. 11, no. 5, 2021, 7585-7590 7588 www.etasr.com alshammari et al.: a new particle swarm optimization based strategy for the economic emission … (case 1) and a ten-unit system with a wind farm (case 2). all data of both systems were taken from [3, 23]. the wind parameters are shown in table i. table i. wind parameters k c vin vout vr 1.7 15 5 45 15 a. case 1 since the eedp is a multi-objective optimization problem, a set of non-dominated solutions is required. table ii shows a list of non-dominated solutions obtained for various values of µ ranging from 0 to 1. from table ii, it can be noted that as µ increases, the total production cost decreases and the total emissions increase. the convergence characteristics of the proposed pso-based technique for the economic (µ=1) and the emission (µ=0) dispatch problems are shown in figure 2. the pareto-front resulted from the pso-based strategy is depicted in figure 3. the best economic dispatch solution correspond to 111498.49$/h fuel cost and 4567.27ton/h total emissions, while the best emission dispatch solution corresponds to 3932.24ton/h total emissions and 116412.49 $/h total fuel cost. το further test the effectiveness of the proposed method, the simulation results obtained using the proposed pso-based method were compared with various algorithms. from table iii, it is clear that the proposed pso method outperforms the others in solving power dispatch problems. (a) for µ=1 (b) for µ=0 fig. 2. convergence characteristics of the proposed method (case 1). table ii. pareto solutions for various values of µ (case 1). λλλλ 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 p1 55.0000 55.0000 55.0000 55.0000 55.0000 55.0000 55.0000 55.0000 55.0000 55.0000 54.9736 p2 80.0000 80.0000 79.9999 80.0000 80.0000 80.0000 80.0000 80.0000 80.0000 79.9980 80.0000 p3 81.1292 81.1079 81.0693 81.8332 83.0377 84.7423 86.7683 88.4989 90.57678 98.1322 106.2337 p4 81.3701 81.1322 80.8085 81.2860 82.1286 83.4244 84.9239 85.9500 87.2575 93.1849 100.3274 p5 160.0000 160.0000 160.0000 160.0000 160.0000 143.7728 126.1284 109.9550 96.7236 88.4957 82.5885 p6 240.0000 240.0000 240.0000 219.5599 189.0966 164.2697 142.7271 121.8599 103.5178 92.2169 82.98739 p7 294.4776 292.2409 289.7346 291.3277 294.5846 299.5123 300.0000 300.0000 300.0000 299.9786 299.9923 p8 297.2982 296.9563 296.5578 300.8168 307.3015 315.4370 321.2987 327.2378 333.8038 340.0000 340.0000 p9 396.7566 398.0034 399.4279 406.0273 415.3302 427.8233 442.3925 456.2269 469.9842 470.0000 469.9574 p10 395.5627 397.2015 399.1011 406.2881 416.3488 429.8128 445.6171 461.2196 469.9878 469.9907 469.9736 ct 116412.49 116399.01 116384.25 115599.76 114608.47 113504.92 112644.77 112023.28 111650.66 111530.31 111498.49 et 3932.2432 3932.3162 3932.5799 3961.3722 4014.4321 4105.6762 4210.6645 4325.7406 4434.2593 4501.6670 4567.2691 pl 81.5947 81.6424 81.6993 82.1394 82.8283 83.7950 84.8563 85.9483 86.8517 86.9972 87.0343 fig. 3. pareto-front (case 1). table iii. simulation results obtained for case 1. best cost best emission cost ($/h) emission (ton/h) cost ($/h) emission (ton/h) pso 111498.49 4567.27 116412.49 3932.24 de 111565.71 4572.68 116418.34 3946.24 fa 111500.79 4581.00 116443.05 3932.62 b. case 2 in this case, a wind farm with a rated power of wr=1.0pu on a 100mva base was incorporated in the ten-unit system. the problem was solved for various values of the tolerance σ to investigate the impact of the penetration level of wp on the eedp solutions. figure 4 shows the convergence characteristics of production cost (µ=1) and emissions (µ=0) for σ=0.3. b e st c o st ( $ /h ) engineering, technology & applied science research vol. 11, no. 5, 2021, 7585-7590 7589 www.etasr.com alshammari et al.: a new particle swarm optimization based strategy for the economic emission … table iv. pareto solutions for various values of µ (case 2 – σ = 0.3). λλλλ 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 p1 55.0000 55.0000 55.0000 54.9927 54.9975 55.0000 55.0000 55.0000 55.0000 55.0000 55.0000 p2 79.3793 79.0572 79.2443 80.0000 79.9935 80.0000 80.0000 80.0000 80.0000 80.0000 79.9671 p3 79.2368 79.1410 79.1944 95.6866 89.4404 87.6390 86.3276 84.6486 83.0527 81.3265 80.1881 p4 79.4393 78.8639 79.1835 87.6092 85.3617 84.0826 83.7210 82.7481 81.6908 80.3916 79.6187 p5 160.0000 160.0000 160.0000 71.2762 80.4537 91.7389 105.7879 120.9868 138.6410 158.8935 160.0000 p6 240.0000 240.0000 240.0000 70.2414 82.0695 97.1504 116.1033 135.7649 157.5176 180.8750 210.0817 p7 283.2762 278.7705 281.1587 299.6879 296.3502 294.8372 296.4263 2.9430731 290.9290 285.5700 282.3278 p8 285.6298 285.0466 285.3679 337.1601 327.7143 319.2092 316.2059 314.8193 306.9338 297.6583 291.2683 p9 384.6910 387.3684 385.9387 470.0000 469.9934 459.1521 444.9970 431.0097 418.3983 405.4202 396.0864 p10 383.5466 387.0554 385.1589 469.9973 469.9908 466.8807 450.0184 434.2659 420.3902 406.4300 396.3520 ct 113553.68 113527.38 113541.18 108361.08 108398.65 108566.61 108947.91 109504.42 110317.96 111457.33 112401.88 et 3752.5080 3752.8219 3752.5756 4411.1741 4341.4299 4251.0979 4136.8332 4033.7302 3934.7089 3841.9554 3791.0480 pl 77.4441 77.5478 77.4915 83.8963 83.6103 82.9351 81.8324 80.7956 79.7983 78.8100 78.1351 (a) µ=1 (b) µ=0 fig. 4. convergence characteristics for case 2 (σ=0.3). the pareto solutions for various values of the weight factor, ranging from 0 to 1, are presented in table iv. meanwhile, the pareto-front for this case is shown in figure 5. figure 6 illustrates the impact of the variation of the tolerance on the minimum fuel cost and the total emission functions. from this figure, it is obvious that the more the tolerance that power balance constraint cannot meet is, the less the cost and emissions are because the more the tolerance is, the more the wp penetration is. v. conclusion this study presented a pso-based strategy for solving the multi-objective eedp incorporating wind energy sources. the power balance constraint was converted into a chance constraint and the intermittency of wp was described by the weibull distribution to consider the stochastic characteristic of wp. this chance constraint represents the probability that the power balance constraint cannot meet. fig. 5. pareto-front for case 2 (σ=0.3). fig. 6. impact of the tolerance on the eedp solutions (case 2). engineering, technology & applied science research vol. 11, no. 5, 2021, 7585-7590 7590 www.etasr.com alshammari et al.: a 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[26] a. mahor, v. prasad, and s. rangnekar, "economic dispatch using particle swarm optimization: a review," renewable and sustainable energy reviews, vol. 13, no. 8, pp. 2134–2141, oct. 2009, https://doi.org/10.1016/j.rser.2009.03.007. microsoft word etasr_v11_n1_pp6668-6673 engineering, technology & applied science research vol. 10, no. 1, 2021, 6668-6673 6668 www.etasr.com mbugua et al.: identification and ranking of key performance indicators in building construction … identification and ranking of key performance indicators in building construction projects in kenya magdaline mbugua department of sustainable materials research and technology centre jomo kenyatta university of agriculture and technology nairobi, kenya mbuguamagdaline@gmail.com p. ajwang' department of sustainable materials research and technology centre jomo kenyatta university of agriculture and technology nairobi, kenya ajwang@agr.jkuat.ac.ke matthew m. o. winja department of civil construction and environmental engineering jomo kenyatta university of agriculture and technology nairobi, kenya matthewwinja@yahoo.com abstract-building construction projects suffer from many dangers such as cost and time overruns. a major reason for the failure of such projects is the lack of measurements of the construction performance. there is usually a disparity of judgment among the stakeholders when it comes to the perception of failure and success of a building construction project because it is based on personal indices. the aim of this study is to identify and rank the key performance indicators in their relative importance as a way to assist in building construction performance. a thorough literature review was conducted and 10 key performance indicators were identified. a questionnaire survey and interviews were used to collect data and the results were analyzed using the analytical hierarchical process, pair-wise comparison. as a result, the highest prioritized key performance indicator was safety, followed by time effectiveness and client satisfaction. the least prioritized key performance indicator was the environmental performance. the results of this paper may serve as a guideline in improving building construction projects. keywords-key performance indicators; constrruction performance measurements; building; construction performance management i. introduction performance measurement is a continuous and systematic process of obtaining valid information about the performance of a project and of identifying the factors that affect performance while project performance management uses the generated information [1]. performance measurement is the heart of a ceaseless improvement and it is utilized for many reasons including decision making, strategic reasons, and benchmarking [2, 3]. traditionally, the main aspects of construction project performance measurements are cost, schedule, and quality [4]. this is not efficient and inevitably it led to a shift to a modern way of measuring performance. this has been the focus of research since the 1980’s, where increased globalized competition forced companies to consider non-traditional measures [5]. the main reason for the fails of traditional performance is that it lags indicators, because it reports on decisions and results that cannot be improved. the performance should be identified with the ongoing basis also known as ‘leading’ [5]. authors in [6] emphasize on the need of balancing both financial and non-financial measures in the construction industry and the need to shift from productoriented performance to process-oriented performance. globally, the construction industry is generally considered to underperform when compared to other industries [6]. the lack of general agreement on measuring construction performance makes it hard for the construction top management to make the best decisions on the project [7]. this affects projects in kenya as well, as kenyan construction projects seldom go according to the implementation plan [8]. a project faces enormous challenges in quality assurance, cost, schedule, environmental performance, and safety [9]. despite the high quality of training of consultants in the building industry and regulation of the industry in major urban areas in kenya, construction projects do not always meet key performance goals. this is unfortunate and failure to try to resolve this key issue, may lead to more poorly performed construction building projects [10]. authors in [6] recommend the implementation of a performance management framework which will motivate and assist the management team to achieve project success. the aim of this research is to identify and rank the key performance indicators (kpis) according to their priority weight. it can assist in bringing a standard performance measurement framework for building construction projects in kenya. ii. key performance indicators performance assessment remains a major problem of the construction sector [11]. over the years, many industries have come up with effective ways to measure performance [12]. thus, these methods have been tried to the construction industry. construction is a complex organization that involves many people, hence it is assured that the degree of coordination is high when compared to other industries [13]. performance indicators consist one of the ways to measure the performance in an industry. according to [6], most companies assume the financial measure as indicator which is a mistake because it only indicates the results of the past, it indicates when but not how. indicators should also include non-financial measures such as employees’ motivation, leadership, and many others. corresponding author: magdaline mbugua engineering, technology & applied science research vol. 10, no. 1, 2021, 6668-6673 6669 www.etasr.com mbugua et al.: identification and ranking of key performance indicators in building construction … according to [14], the performance indicators are defined as factors that have a major influence on the success or failure of a construction project and should be identified in order to improve the project performance. they are also referred as critical success or failure factors. the criteria in which project success/failure has often been assessed have also been called key performance indicators or dimensions [15]. models developed to measure construction project performance are the integrated performance index, and the kpi. good examples of kpi are: a. balance scorecard balance scorecard measures the performance with the main indicators which might affect the financial status of the company: customer service, internal and business processes, etc. [16]. b. european foundation for quality management (efqm) excellence model this excellence model assists in understanding and managing the complexity in business. it gives a cause-andeffect relationship between what the companies do and what results they will achieve [17]. efqm is based on 8 concepts which are meant to improve the business performance: result orientation, customer focus, leadership and constancy of purpose, management by processes and facts, people development and involvement, continuous innovation, learning and improvement, partnership development, and corporate social responsibility [18]. c. analytical hierachial process (ahp) ahp is a multi-criteria decision-making method that was originally developed by thomas saaty. it is a tool with numerous applications in areas of planning and management [38]. ahp uses a pairwise comparison to generate weightings for criteria instead of listing and ranking their level of importance. ahp prioritizes the kpis of a framework [38]. d. literature summary kpis are meant to be objective and can be easily measured. identification of the suitable quantitative interpretations and requirements on all kpis could reduce the degree of subjectivity and biasness [7]. it should also involve different stakeholders as different stakeholders value different indicators depending on their interests in the project [6]. authors in [6] describe the construction industry as project-based and construction project managers need to devise mechanisms to measure performance. the identified kpis could be combined to come up with a comprehensive model. this includes examining various indicators and evaluating their impact on performance. the proposed index could be customized depending on different building projects [7]. several studies have been conducted to come up with kpis in construction performance. most common used indicators have been compiled into a list in the current study. these indicators were discussed among construction professional experts with more than 15 years of experience to check the relevance of each kpi in the kenyan building construction. some of the kpis became performance metrics to the main kpi. the concluded list of the 10 kpis is shown in table i. table i. literature summary of 10 kpis affecting building construction projects in kenya. kpis performance metrics sources cost change in cost planning. effectiveness of predictability of cost planning. [19-24] time construction time. construction speed. on time completion. [7, 19-24] quality defects. quality control. quality assurance. rework factor. [7, 19-24] safety annual accident rate. lost time accidents [19-23, 26] client satisfaction client’s responsiveness. proper communication. [19-23, 25] environment environmental protection measures. energy saving. extended building life cycle. increased user comfort. waste management. environment friendly equipment. [19, 20, 23, 27, 28] team satisfaction clear goals. knowledgeable leadership. appropriate management of internal conflicts. effective communication. matching employees to areas of expertise. [20, 22, 23, 29-32] project leadership leader’s professional qualification. leadership style. technical skills. managerial skills. high employee relationship. management of stakeholders communication and collaboration. [6, 19-23, 33, 34] productivity labor productivity. machine productivity. materials consumption. utilization of advanced technology. regular equipment maintenance. [20, 22, 23, 28, 35] proper training and recruitment availability of skilled manpower. knowledge and experience. [11, 19, 22, 23, 36] iii. research objectives the main objective of this research was to develop a performance index for construction building projects in kenya. the specific objectives were: • identify and rank the kpis in kenya building construction industry. • integrate and quantify the kpis in kenya building construction industry. iv. research methodology the distributed questionnaire was based on three sections: • the respondent’s profile, i.e. type of organization they work for and the respondent’s position in the firm. • the respondents' construction experience and their performing measurement tools. • measuring and prioritizing the kpis in building construction project. engineering, technology & applied science research vol. 10, no. 1, 2021, 6668-6673 6670 www.etasr.com mbugua et al.: identification and ranking of key performance indicators in building construction … a pilot study was done with 5 experienced professionals with 5-10 years of experience in construction industry and then the questionnaire was revised to reduce the required respond time. afterwards, it was distributed to the respondents via email, whatsapp and messages. the target population of this study was professionals in the building construction industry with at least 5 years of experience on kenya building construction firms. the sample size of this research was based on the number of the registered professionals in kenya. according to [36], a construction project involves developers, contractors, consultants, and sub-contractors. the sampling method used was random stratified sampling, focused on contractors, consultants, and developers. the sample size was determined by the equation in [37] that provided 95% confidence level. the sample size was found to be 172 and the random stratum sampling was 40%, 20%, and 40% of the sample size, for consultants, developers, and contractors respectively. a developer is considered as a professional company who develops a land through building construction and sells the outcome for a profit. consultants include construction managers, architects, structural engineers, quantity surveyors, and landscape architects. the pair-wise comparison and the linear saaty scale on the kpis [38] were used. the printed questionnaire was filled by 13 respondents while 49 completed the online questionnaire making a total of 62 respondents, representing a response rate of 36% which is accepted and sufficient for research [39]. the data collected were 58.26%, 29.57%, and 12.17% for consultants, contractors, and developers respectively. incomplete pair-wise comparison occurred as some of the respondents missed a comparison or stopped filling the questionnaire when they were almost done. this did not affect the study as [40] proved that one can delete 50% of comparisons with no significantly affecting the results. v. results and discussion a. construction completion within the proposed time and cost the data collected show that 43% of the construction stakeholders indicated that all their building projects were completed within the proposed time and cost while 54% of them indicated the opposite, as shown in table ii. b. construction performance tools as can be seen in table iii, 59% of the respondents indicated that they use performance measurement tools and 41% did not. the performance measurement tools include earned value-based management, project management software, proposed cost vis-à-vis the actual cost of the project, proposed time the vis-à-vis actual time of the project, contractor experience, and client satisfaction. table ii. construction completions within proposed time and cost results were the construction completed within the proposed time and cost? frequency percentage yes 46 42.99% no 58 54.21% can't remember 3 2.80% table iii. construciton performance tools results response frequency percentage yes 61 59.22% no 42 40.78% c. an evaluation of priorities of key performance indicators the priority of kpis was informed by the aggregation of individual judgments. authors in [41] define the aggregation of individual judgment as aggregation on the individual pair-wise comparisons to obtain a new judgment matrix. the aggregation of individual judgement was achieved through the geometric mean method of what each individual respondent selected as suggested in [42]. this assists group systematic decision making with a holistic vision of reality and subjacent ideas of literal thinking [41]. table iv is the pairwise comparison matrix and total column summation was conducted for the normalization of the indices. d. matrix normalization matrix normalization was done by total summation of each column with judgment values. then, each judgment value was divided by the summation. this yields the normalized score of table iv. the average is also known as the eigen vector and it gives the priority weight of each kpi. when all the averages are added up, the summation is 1. using the eigen value, the ranking of the kpi is achieved with the highest value being the most prioritized kpi as shown in table v. the consistency index for this study was 0.04 which is acceptable as the acceptable consistency index should be less than 0.1 [38]. the ranking of the kpis is shown in table vi. table iv. comparison matrix of key permormance indices q ce te saf pl ep prod ts cs pt quality 1 1.3445 1.5188 0.6936 1.0998 1.3542 1.268 1.3514 0.8593 0.9766 cost effective 0.7438 1 0.9209 0.8996 0.5223 1.9982 1.1443 0.484 0.8191 1.2153 time effective 1.9275 1.0859 1 1.0805 1.6763 1.8709 1.1068 1.7076 0.7883 0.6357 safety 1.4418 1.1116 0.9255 1 1.82 2.1419 2.364 2.8962 1.696 1.6144 project leadership 0.9093 1.9146 0.5966 0.5495 1 0.8717 0.5293 0.646 1.1795 1.1236 environmental performance 0.7384 0.5005 0.5345 0.4668 1.1472 1 0.7497 0.938 0.5861 1.0508 productivity 0.7886 0.8739 0.9035 0.423 1.8893 1.3339 1 1.7797 0.8599 1.9461 team satisfaction 0.74 2.0661 0.5856 0.3453 1.548 1.0661 0.5619 1 0.6791 1.0993 client satisfaction 1.1637 1.2209 1.2686 0.5896 0.8478 1.7062 1.1629 1.4725 1 1.6303 proper training 1.024 0.8228 1.5731 0.6194 0.89 0.9517 0.5138 0.9097 0.6134 1 total 10.4771 11.9408 9.8271 6.6673 12.4407 14.2948 10.4007 13.1851 9.0807 12.2921 q:quality, ce: cost effective, te: time effective, saf: safety, pl: project leadership, ep: environmental performance, prod: productivity, ts: team satisfaction, cs: client satisfaction, pt: proper training and recruitment engineering, technology & applied science research vol. 10, no. 1, 2021, 6668-6673 6671 www.etasr.com mbugua et al.: identification and ranking of key performance indicators in building construction … table v. normalization matrix of key performance indices q ce te saf pl ep prod ts cs pt total avg quality 0.095 0.113 0.155 0.104 0.088 0.095 0.122 0.102 0.095 0.079 1.048 0.105 cost effective 0.071 0.084 0.094 0.135 0.042 0.140 0.110 0.037 0.090 0.099 0.901 0.090 time effective 0.184 0.091 0.102 0.162 0.135 0.131 0.106 0.130 0.087 0.052 1.179 0.118 safety 0.138 0.093 0.094 0.150 0.146 0.150 0.227 0.220 0.187 0.131 1.536 0.154 project leadership 0.087 0.160 0.061 0.082 0.080 0.061 0.051 0.049 0.130 0.091 0.853 0.085 environmental performance 0.070 0.042 0.054 0.070 0.092 0.070 0.072 0.071 0.065 0.085 0.692 0.069 productivity 0.075 0.073 0.092 0.063 0.152 0.093 0.096 0.135 0.095 0.158 1.033 0.103 team satisfaction 0.071 0.173 0.060 0.052 0.124 0.075 0.054 0.076 0.075 0.089 0.848 0.085 client satisfaction 0.111 0.102 0.129 0.088 0.068 0.119 0.112 0.112 0.110 0.133 1.085 0.108 proper training 0.098 0.069 0.160 0.093 0.072 0.067 0.049 0.069 0.068 0.081 0.825 0.083 total 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 10.000 1.000 q:quality, ce: cost effective, te: time effective, saf: safety, pl: project leadership, ep: environmental performance, prod: productivity, ts: team satisfaction, cs: client satisfaction, pt: proper training and recruitment table vi. key performance indices ranking kpi ranking priority weight safety 1 0.154 time effective 2 0.118 client satisfaction 3 0.108 quality 4 0.105 productivity 5 0.103 cost effective 6 0.090 team satisfaction 7 0.085 project leadership 8 0.085 proper training and recruitment 9 0.083 environmental performance 10 0.069 total 1.000 safety is the most and environmental performance is the least prioritized kpi. notably, this research result is not consistent with the traditional iron triangle (cost, time, and quality) as the primary indicators for building construction performance. the top three indicators include only one factor from the iron triangle, time effectiveness. this is in contrast with the findings in [7] and is an indication that the building construction industry in kenya has already incorporated nonfinancial measures in performance measurement and this needs to be reflected in the current methodologies. the least three prioritized indicators are project leadership, proper training and recruitment, and environmental performance which are nonfinancial measures. this results supports most research studies that have identified non-financial measures as the least prioritized [7]. productivity was ranked as the 5th important indicator, contradicting the findings in [6], which show that productivity has insignificant impact on project performance. the kpis are similar to the uk kpi report that has been globally used to measure construction performance as it includes cost, time, safety, productivity, client satisfaction, and quality [43]. the current study added more kpis such as environmental performance, proper training and recruitment, and project leadership, because over the past 10 years, kenya has been promoting clean and sustainable environment and this has led to authorities such as the nema (national environment management authority) to be involved in building construction project approvals. the boards that regulate construction professionals in kenya have also increased in the last 20 years while currently there is a draft bill that regulates construction professionals. the prioritized kpis can be integrated to come up with a proposed index that could be used as a guideline in assessing the final outcome of kpis and the general performance of a building construction project [7]. vi. conclusion and recommendations the current study confirmed that most construction professionals based the performance of building projects on their opinion which is subjective, biased, and varying across all stakeholders in the same project. this was evidence of the need of this research and the knowledge gap it fills. safety, time effectiveness, and client satisfaction were most important to most professionals, differentiation the results from traditional performance measurements which focus on the financial measure as the most important kpi. the results support the need to explore modern performance measures, including the reported leading indicators. quality, which belongs to the iron triangle, was ranked only fourth, below client satisfaction and safety, while proper training and environmental performance were among the kpis ranked least. these kpis are social factors, they affect the community and society at large. most construction professionals (57%) have ways of measuring their performance, however most tools are personal indices or just focus on one indicator in the project. and though this is a big percentage, 41% is also a big number of construction professionals who need to be able to measure their performance. a performance that cannot be measured, cannot be improved. national construction authority (nca) is the regulatory board for contractors in kenya, and has categorized contractors based on the cost of the projects they have done, with the lowest cost being nca grade 8 and the highest cost being nca grade 1. it could be an opportunity for the nca to increase transparency within the construction industry by grading them according to their performance within the building construction industry. this could enhance the fair competition among the contractors and build confidence of the clients on what the contractors can achieve within their projects. the limitation of this research was that although the number of respondents was acceptable to carry out the analysis, it was rather low. further research should be conducted on the way kpis relate to each other and the impact each can cause to the others. engineering, technology & applied science research vol. 10, no. 1, 2021, 6668-6673 6672 www.etasr.com mbugua et al.: identification and ranking of key performance indicators in building construction … appendix questionnaire this questionnaire aims to collect information related to indicators that have an important impact on perceptions of building project success. this will help in developing a performance index framework for building construction projects in kenya. kindly answer the following questions according to the instructions. section a: respondent profile respondents’ position in the firm consultant [ ] contractor [ ] developer [ ] what type of organization do you work for? government [ ] nongovernment organization [ ] private firms [ ] other (specify)……………………………….…. how long have you been involved in building construction projects? less than 5 years [ ] between 5 to 20 years [ ] above 20 years [ ] don’t remember [ ] section b: respondent’s construction experience how many construction projects have you or your firm been involved in? less than 2 [ ] between 2 and 5 [ ] between 5 and 10 [ ] more than 10 [ ] can’t remember [ ] were all these construction projects completed within the initial contract period and sum? yes [ ] no [ ] can’t remember [ ] do you have any method in measuring the construction performance of your project? yes[ ] no[ ] if yes, which method is it? section c: ranking of key performance indicator to what extent do the following factors affect performance management in comparison to each other in building construction in kenya? table i explains the intensity of importance against the scale used. explanation of the scale used in the questionnaire intensity of importance definition illustration/ example 1 equal importance (equal) element a and b are equally favored 3 moderate importance of one over the other (slightly favors) slightly favor element a over b 5 essential importance (strongly favors) strongly favor element a over b 7 demonstrated importance (very strong favors) element a is favored very strongly over b 9 absolute importance (extreme favor) the evidence favoring element a over b is of the highest possible order of importance example: quality (9) (7) (5) (3) (1) (3) (5) (7) (9) cost effective quality is very strongly favored compared to cost effective time effective (9) (7) (5) (3) (1) (3) (5) (7) (9) quality quality is slightly favored compared to time effective. this is the scale that was used to compare the kpis below. quality vs cost effective, quality vs productivity, quality vs time effective, quality vs safety, quality vs team satisfaction, quality vs client satisfaction, quality vs environmental performance, quality vs project leadership, quality vs proper training, cost effective vs time effective, cost effective vs environmental performance, cost effective vs client satisfaction, cost effective vs team satisfaction, cost effective vs project leadership, cost effective vs safety, cost effective vs productivity, cost effective vs proper training, time effective vs safety, time effective vs project leadership, time effective vs productivity, time effective vs proper training, time effective vs environmental performance, time effective vs client satisfaction, time effective vs team satisfaction, safety vs team satisfaction, safety vs client satisfaction, safety vs proper training, safety vs environmental performance, safety vs project leadership, safety vs productivity, project leadership vs productivity, project leadership vs client 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[43] "the kpi report for the minister for construction," kpi, department of the environment, transport and the regions, uk, 2000. microsoft word etasr_v11_n1_pp6680-6686 engineering, technology & applied science research vol. 11, no. 1, 2021, 6680-6686 6680 www.etasr.com phung & le: load shedding in a microgrid with consideration of voltage quality improvement load shedding in microgrids with consideration of voltage quality improvement bao long nguyen phung electrical and electronics department hcmc university of technology and education ho chi minh city, vietnam 16142018@student.hcmute.edu.vn trong nghia le electrical and electronics department hcmc university of technology and education ho chi minh city, vietnam trongnghia@hcmute.edu.vn abstract-microgrids have become more and more popular their usefulness as a renewable energy resource has been recognized. the core ability and promise of microgrids is addressing the environmental concerns due to climate change that have been growing during recent years. the innovation of microgrids is that they are designed to operate either in island mode or interconnected with the main grid system. however, when the microgrid operates in islanded mode, faults may occur which can cause system collapse or even blackout. load curtailment schemes can be utilized to decrease the quantity of associated load to a level that can be securely supported by accessible generation in isolated mode. the main goal of this research is to evaluate the optimal amount of shedding power considering sustainable power sources, with the help of primary and secondary adjustments of the generator to restore the frequency to the allowed range. particle swarm optimization algorithm is applied in this paper to determine the distributed shedding power on each demand load bus which can improve the voltage quality of the isolated microgrid system. the effectiveness of the proposed method is demonstrated through the simulation of ieee 16bus microgrid. keywords-load shedding; islanded microgrid; primary and secondary adjustment; particle swarm optimization i. introduction the imbalance between the power supply and demand loads, when a microgrid (mg) is separated from the main grid by fault or by automatically switching to islanded mode may lead to frequency and voltage droop. in this case, the mg may be overloaded or even collapse and bring the whole system to blackout [1, 2]. load shedding schemes can operate to decrease the quantity of associated load to a level that can be securely supported by accessible generation during an emergency. the calculation of the amount of load shedding power is generally based on frequency droop [3]. if the calculation is deficient, it will not be able to restore the frequency to a permissible value and will cause over shedding. researches on load shedding mainly calculate the amount of load shedding power based on the rotation motion of the rotor [4]. however, these strategies do not consider the actual operating conditions such as the primary and secondary control of the generating sets. the techniques of load shedding are divided into three main areas of study [5]: conventional load shedding, adaptive load shedding, and intelligent load shedding. the conventional load shedding is a method of load shedding by using under frequency load shedding (ufls) [6], or under voltage load shedding (uvls) relays. the ufls method is known as one of the most used strategies. ufls technique has a few disadvantages: the load is arbitrarily chosen on the grid when the frequency arrives at the load shedding limit. this technique is not effective when the load shedding areas are spread over the grid and in some cases over shedding or under shedding occurs [7]. besides the researches on conventional techniques and their development, many intelligent algorithms are used in studying and making new load shedding schemes, for example fuzzy logic, genetic algorithm (ga), artificial neutral networks (anns), analytic hierarchy priority (ahp), particle swarm optimization (pso), etc. the fuzzy logic based load shedding scenario is efficient in restoring the frequency of an islanded mg system quickly [6, 8-12]. in some researches, fuzzy – ahp logic algorithm was used in load shedding strategies to measure the weight of load nodes in the system in various load levels [13]. the ann-based load curtailment method can optimize the amount of load shedding in order to stabilize the power system [16]. a load curtailment based on a combination between ann and neuro-fuzzy was proposed in [15]. the results show that the ann can compute the total amount of active power that needs to be shed but it does not determine the number of loads or the distributed load shedding power that need to be shed in each demand load. authors in [16, 17] proposed a load shedding method based on ga gain that can be used in the calculation of the optimal amount of shedding power. in fact, the ga can help in making the calculation speed for load shedding scenario robust, however the limitation of this algorithm is that it cannot help in optimal distributed load shedding for each demand load bus. the efficiency of pso has been applied in load shedding techniques in [15, 18]. the studies show that pso can forecast the frequency droop and optimize the amount of the required load demand. however, in this strategy, there’s still no limitation in the optimal shedding power. in [19], an ufls technique based on pso was studied, and the main objective was to calculate the optimal shedding power in order to stabilize the system frequency. however, the proposed method did not consider the voltage quality criteria in the system. despite the fact that there are many studies that corresponding author: trong nghia le engineering, technology & applied science research vol. 11, no. 1, 2021, 6680-6686 6681 www.etasr.com phung & le: load shedding in a microgrid with consideration of voltage quality improvement show the effectiveness of pso in optimal load curtailment scheme, most of the methods are used in general or islanded grid systems, not on islanded mgs with renewable sources. the main objective of this paper is to plan an optimal load shedding strategy for islanded mgs with renewable energy sources during the islanded operation. the minimum shedding power will be computed based on the ability of primary control of the generators' governor and the reserve power of the generators for the secondary adjustment of the generators. the application of pso algorithm will determine the optimal distributed shedding power of each load bus. and from that, it can optimize the voltage droop and improve the voltage quality. the effectiveness of this method is tested by the simulations of the ieee 16-bus system, and the results are compared with a conventional under-frequency load-shedding scheme. calculated and simulated results showed that the proposed method has less amount of shedding power than the ufls relay method. furthermore, the recovery of frequency was still held within the allowable values and maintained the stability of the power system. the current research can be used as a reference for mg system operators and electrical engineering graduate students when considering the issue of optimizing load shedding in the mg system when there is a disconnection from the main grid. ii. theoretical background a. primary and secondary frequency adjustment under ordinary conditions and in the case of power losses in the framework, the power balance of the mg is introduced by: _ _ p p p p p main grid gi g storage res lj + + + =∑ (1) where pmain_grid is the power from the bulk grid, pgi is the power of the i th generator that has a speeder or a distributed generator with auto frequency controller (afc), ∑plj is the real power of the j th load in normal operation, and pg_storage and pres are the capacity of energy storage system and power of renewable energy sources (res). when the mg disconnects from the main grid, the first reaction of the system will be the primary frequency adjustment. it’s a reaction of a power source that has a speeder or an afc. these frequency controllers will increase the power of generators in relation to the frequency [20, 21]. in figure 1, we see the characteristics of the generators under normal operation before and after the connection loss of the mg from the main grid. characteristic lines (f), (g) illustrate the characteristic of the load power in the normal operating conditions and during load shedding respectively. characteristic lines (b), (d) show the output power of a generator without a governor corresponding to the normal condition, after disconnection from the main grid. the (a), (c) and (e) characteristics are the power. pgn and pgn-1 are the total value of the output power in the normal operating conditions and during the outage generator respectively, f0 is the rated frequency in the normal operating conditions, f1 is the frequency of the mg during the islanded operation (in the case that the generators have a governor and the distributed generators have a droop controller), f1’ is the frequency of the outage generator (in case of the generator without a governor), f2 is the frequency of the system after the primary and secondary control, and fallowed is the restored frequency (59.7hz for power grids with a rated frequency of 60hz). fig. 1. the relationship between frequency and output power deviation. when the primary adjustment process for the power source is initiated, the response of the load to the frequency change is also performed. in addition, the ress that respond slowly to frequency changes are considered not capable of adjusting the primary and secondary process, so they can be considered as negative loads. equation (1) can be rewritten as: ( ) _ _ ( ) p p gi primary p p p p p lj main grid g storage res l freq +∆ = − − + −∆∑ (2) where: 1 1 n f p primary ri i − −∆ ∑∆ = = is the amount of primary control power of the system when fault occurs. in this case it will be the islanded operation mode of the mg. ∆f is the frequency droop when the mg turns to islanded operation. ri is the ratio between the frequency and generator’s power. it also represents the adjustment of the speed of slip. ∆pl(freq) is the load whose power changes with the frequency. if the frequency will not go back to the allowed range after the primary adjustment process, the secondary adjustment will proceed. the secondary adjustment process is the process of the primary adjustment made through the effect of the automatic generating center (agc) system on a number of specified units, or a dispatch command [20, 21]. the balance power equation will be rewritten as: sec ( ) _ _ ( ) p p p gi primary ondary p p p p p lj main grid g storage res l freq +∆ +∆ = − − + −∆∑ (3) where sec , p p p ondary gn i primary ∆ = −∆ is the maximum secondary power adjustment of the generator. b. particle swarm optimization pso was first studied in 1995 [22]. in pso, the expression "population" alludes to the particles which are dependent upon the best method of conduct. these particles can run in two engineering, technology & applied science research vol. 11, no. 1, 2021, 6680-6686 6682 www.etasr.com phung & le: load shedding in a microgrid with consideration of voltage quality improvement modes: stochastic mode and deterministic mode. mathematically, the searching process can be presented by simple equations using the position vector [ , ,...., ]1 2x x x xi i i in= and the velocity vector [ , ,...., ]1 2v v v vi i i in= according to the specific dimension of the searching space. in addition, the optimum of the solution in the pso algorithm depends on the particle position and velocity update by the following equations: 1 . [ ] [ ] 1.1 2 2 k k k k k k v wv c r x x c r x x i i pbest i gbest i + = + − + − (4) 1 1k k k x x v i i i + + = + (5) where vi k , xi k represent the velocity and position of each particle i at iteration k, w is the inertia constant, ranging usually between 0 and 1, c1 and c2 are cognitive coefficients, ranging from 0 to 2, r1 and r2 are random values generated for each velocity update, and k x pbest , k x gbest are the global best positions earned in the swarm’s experience and the best position of each particle respectively. each part of (4) is defined as: . k w v i is the inertia component, which is responsible for keeping the particle search in the same direction, [ ] 1.1 k k c r x x pbest i − is the cognitive component representing the particle’s memory. the cognitive coefficient c1 affects the step size of the particle to move toward its local best position xpbest. [ ]2 2 k k c r x x gbest i − is the social component. it represents the movement of the particle towards the best region found by the swarm so far. the c2 factor is known as the social coefficient, and it also controls the step size of the particle to find the global best positon xgbest. equation (5) presents the situation of every individual particle by utilizing the new speed and its past position. in other words, a looking through cycle is re-initiated in order to locate the global ideal arrangement. the cycle rehashes itself until it meets one completion criterion, e.g. maximum number of repetitions. iii. the proposed load shedding method c. construction of the formula of optimal amount of shedding power when the primary and the secondary adjustment do not recover the frequency back to nominal stage, then load shedding is required. in that case, the power balance equation will be: r sec ( ) _ _ ( ) _ min p p p gi p imary ondary p p p p lj main grid g storage res p p l freq shed +∆ +∆ = − − +∑ −∆ −∆ (6) 1 sec 1 ( ) _ _ .( ) _min fn allowedp p gi ondaryri i p p p p lj main grid g storage res d p shed ω ⇔ −∆− + +∆∑ = = − − +∑ − −∆ −∆ (7) where f f f allowed n droop ∆ = − is the allowed drop of the frequency, ∆pshed_min is the minimum amount of load shed that has the ability to bring the frequency close to the nominal value, d is the characteristic factor change of load in percentage frequency change, ranging between 1% and 2%. the factor d is experimentally determined, e.g. if d= 2%, then if the frequency changes by 1%, it will lead to the change of loads by 2%. from the above equation, the minimum amount of load shedding can be determined as: _min [ ( ) .( )] _ _ 1 ( ) sec 1 p shed p p p p d lj main grid g storage res fn allowedp p gi ondaryr i i ω ∆ = − − + − −∆∑ −∆− − + +∆∑ = (8) fig. 2. proposed load shedding method. the load shedding method is illustrated in figure 2. the first step will be to determine all the necessary parameters of the system, including the parameters of loads and generators. then the operation mode of the system will be considered as well. the next step to calculate the frequency droop, then primary and secondary power adjustment if necessary. after that, the minimum amount of load shedding and the amount of load shed at each bus will be determined by the pso algorithm. after the amount of load shed is calculated, the load shedding process will be operated. and finally, the overall check must be processed to ensure the system is safe and secure. d. construction of the objective function for pso the objective function in the pso algorithm is based on the voltage quality on each load bus. the main purpose of this function is to find the optimal amount of load shedding on each load bus if the mg turns into islanded mode in order to get the best result of voltage droop. this optimized load shedding scheme not only prevents the system from blacking out when the disconnection occurs, it also provides an improved way to shed load that avoids unnecessary loss. to obtain the objective function or voltage droop control function, the jacobian matrix will be applied because of its resolution which is finding the amplitude of voltage and phase angle based on the real and engineering, technology & applied science research vol. 11, no. 1, 2021, 6680-6686 6683 www.etasr.com phung & le: load shedding in a microgrid with consideration of voltage quality improvement reactive power in an electrical system. the basic formula of the jacobian matrix is shown below: 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 p p p p v v n n m p p p p p n n n n p v v n mn n q q q q q v v n n m q n q q q q n n n n v v n mn δ δ δ δ δ δ δ δ  ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ − −  ∆     ∂ ∂ ∂ ∂  − − − −   ∆ ∂ ∂ ∂ ∂ −− −  =  ∆ ∂ ∂ ∂ ∂      ∂ ∂ ∂ ∂  − −   ∆ −  ∂ ∂ ∂ ∂ − − − − ∂ ∂ ∂ ∂ −− … … � � � � � � � � � … … � � � � � � � � � 1 1 1 n v v n m δ δ           ∆                ∆   −  ×                       −             � � (9) where n is the number of nodes in the grid, m is the number of generators in the system, and n-m represents the loads in the electrical network. by converting (9) and ignoring the 1st generator from the bulk grid in the system because it will be removed after the islanded operation occurs, (10) can be claimed. besides, in order to achieve the voltage droop equation, the j2 and j4 elements of the jacobian matrix will be measured: 2 2 2 2 2 2 2 2 2 22 2 2 2 2 2 2 2 2 2 22 p p p p v v n n p p p p n n n n v v nnn v q q q q v v n n v n q q q q n n n n v v nn δ δ δ δ δδ δ δ δ δ  ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∆     ∂ ∂ ∂ ∂   − −   ∂ ∂ ∂ ∂ ∆   =   ∂ ∂  ∂ ∂     ∂ ∂ ∂ ∂         ∂ ∂ ∂ ∂ − − ∂ ∂ ∂ ∂  … … � � � � � � � � � … … � � � � � � � � � 1 2 2 p p n q q n −  ∆          ∆   ×   ∆           ∆                � � (10) the final function will be the voltage droop control on each bus: 1 1 2 4 v p j q j i i i − −∆ =∆ × +∆ × (11) according to the power electrical triangle, tanq p i i ϕ∆ =∆ × , so (12) can be written : 1 1 tan 2 4 v p j p j i i i ϕ − −∆ =∆ × +∆ × × (12) where |vi| is the voltage droop on each bus, ∆pi is the real power on the bus, 1 2 j − and 1 4 j − are the inverse j2, j4 elements of the jacobian matrix, and tanφ the phase angle (tanφ=0.8). from (12), the detailed voltage droop equation can be obtained: 1 1 ....+ 2( ,2) 2 2( , ) 1 1 ......+ 2( , 1) 1 2( , ) 1 tan ...... 4( , 1) 2 1 + tan 4( ,2 2) v j p j p i i i m m j p j p i m m i n n j p i n j p i n n ϕ ϕ − −∆ = ×∆ + ×∆ − −+ ×∆ + ×∆ + + − + ×∆ × + + − ×∆ × − (13) in load shedding, the voltage droop will be enormous, and that is one of the most critical dangers of such schemes. this will make the system unstable and cause the whole system to collapse. there are still limitations in the control of that droop, therefore, the first thing that the objective function must do is to find the maximum value that can occur when the voltage falls, then from all the maximum values it must call out the least in the aforesaid index by using the pso algorithm to make sure that the system is safe and secure after the disconnection. so, the objective function for pso will be expressed as: 1 1 min(max( )) min(max( tan ) 2 4 v p j p j i i i ϕ − − ∆ = ∆ × +∆ × × (14) this algorithm has two main constrictions: • the amount of shedding power in each load must not be larger than its base power: 0<∆p<pbase. the base power of each load is the power that must not be shed, for example, pbase=30%pload. this constraint helps in optimizing the amount of load shed in each load in order to avoid unnecessary loss and prevent overshedding. • the sum of all the shedding powers of each load is equal or larger than the minimum load shedding power: σ∆ρ≥∆ρshed_min the constraint makes sure the frequency droop is in control and the amount of shedding power is not under-shed. fig. 3. flowchart of the pso algorithm for load shedding. the steps of the pso algorithm are shown in figure 3. the first step in the pso process is to modify the value of shedding power in each load, in other words, setting the value of pbase. in this case, the value of pbase will be 30% of each load power. in the index of the voltage droop that has been calculated, the maximum value will be taken. the process will do over the initialization step and find the maximum value again and again, until the maximum value is unchanged after 2 or 3 iterations. the value of the formula min(max(∆|vi|)), which is calculated by the pso algorithm, is the optimal value of shedding power in each load. iv. experiments and results the mg system chosen to simulate the effectiveness of the proposed method consisted of 16 buses and 6 sources [23], including a transformer at bus 16 which is considered as the engineering, technology & applied science research vol. 11, no. 1, 2021, 6680-6686 6684 www.etasr.com phung & le: load shedding in a microgrid with consideration of voltage quality improvement main, connected to the mg at bus-1, 2 diesel generator sources, 1 pv panel source, 1 source of wind energy (wind turbine), and a storing energy system which in this case is batteries. when the system goes into islanded mode, the diesel generator at bus-2 is considered as the balancing node. the linear diagram of the system is shown in figure 4 and the parameters of the sources and the loads are shown in tables i and ii respectively. the system was simulated in powerworld simulation 2019. the bus connected to the main grid is bus-1, which had a fault that caused the mg system to lose connection with the main grid and was forced to operate in islanded mode. table i. parameters of power sources in the mg system sources pg (mw) pgn,i (mw) r main grid 3.87 diesel generator (bus2) 5.00 6.00 0.05 diesel generator (bus8) 0.90 1.0 0.05 battery (bus 11) 0.3 0.5 0.00 pv panels (bus 14) 0.5 1.00 0.00 wind turbine (bus 15) 2.00 3.00 0.00 table ii. parameter of loads in the mg system loads power (mw) load 3 1.06 load 4 1.53 load 5 1.95 load 7 1.17 load 9 1.81 load 10 2.09 load 12 1.2 load 13 1.17 total load power 11.98 e. calculating the minimum shedding power in this experiment, two diesel generators will participate in the frequency adjustment. applying (2) and the parameters of generators and loads of table i and ii, the frequency droop after the mg disconnection from the grid will be: 6 ( ) 5 0.9 0.05 60 0.05 60 11.98 0.02 ( ) 11.98 0.3 2 60 1.4033 60 1.4033 58.596 hz f f f f hz f f f droop n × −∆ −∆ + + + = × × × × −∆ − − − ⇒ ∆ =− ⇒ = +∆ = − = (15) figure 5 shows that the frequency has fell below the safety range after the disconnection. that incident would make the system instable and lead to black out. so, the primary and secondary frequency adjustments need to be processed in order to restore the frequency back to its nominal stage. in this experiment, the primary frequency adjustment will be automatically operated by the speeder due to the reaction of the turbine. the amount of primary control power of the system will be: 6 0.3 1 0.3 0.7mw 0.05 60 0.05 601 n p primary i − − − − ∆ = × + × =∑ = the amount of maximum secondary power adjustment of the diesel generator at bus-2 is: 6 5 0.6 0.4mw sec p ondary ∆ = − − = fig. 4. linear diagram of the mg model. fig. 5. system frequency after the primary and secondary adjustments. the frequency has been recovered thanks to the adjustment process, however, it is still under the allowed range, and that could still harm the system. therefore, load shedding must be applied in order to restore the frequency to normal. equation (8) is applied to compute the minimum shedding power: 11.98 0.3 2 0.5 _min 11.98 0.02 ( 0.3) 6 ( 0.3) 5 0.9 60 0.05 60 1 ( 0.3) 0.4 2.1788mw 0.05 60 p shed ∆ = − − − × × − − × − + − − − × − × − − − = × to prove the effectiveness of the proposed method, the load shedding method using ufls relay is used for comparison. the process of ufls is implemented when the frequency drops below the frequency setting threshold [24]. the load is usually shed step-by-step based on the load shedding table that is pre-designed based on overall principles and administrator experience. the table manages the amount of load that should engineering, technology & applied science research vol. 11, no. 1, 2021, 6680-6686 6685 www.etasr.com phung & le: load shedding in a microgrid with consideration of voltage quality improvement be shed at each step depending on the decrease of frequency. these values are shown in table iii. table iii. 4 stages of the ufls scheme stage frequency (hz) cumulative amount of load pshed (%) i 59 35 ii 58.8 30 iii 58.4 20 iv 58 15 the frequency droop is 58.596hz, so the amount of load shedding will be the 30% of total load: 0.3 11.98 3.594mw _ p shed ufls ∆ = × = the result shows that the proposed load shedding method has better optimal amount of shedding power than the ufls method. the frequency comparison between the proposed method and ufls is illustrated in figure 6. fig. 6. comparison of the frequency between the proposed method and ufls. the recovery frequency of the proposed method is 59.7hz in comparison with the 59.96hz of the ufls method. the comparison result shows that although the recovery frequency of the proposed recovery method is not as good as the ufls method, it is still in the permissible range while it reduces the amount of shedding power. the shedding power is 1.4152mw lower than that of the traditional ufls method. f. applying pso to compute the optimal distributed load shedding on each bus load the restriction of the amount of shedding power that can be shed in each load bus will be considered as the pbase. the upper bound and the lower bound of the pso calculation in this experiment will be: pbase=30%pload. table iv. parameters of base power of loads loads load power (mw) pbase (mw) load 3 1.06 0.318 load 4 1.53 0.462 load 5 1.95 0.585 load 7 1.17 0.351 load 9 1.81 0.543 load 10 2.09 0.627 load 12 1.2 0.36 load 13 1.17 0.351 using (14) to calculate the index of minimum voltage droop and optimal shedding power on each load bus and by using the comparison by percent, the best result is chosen for the distributed load shedding for each load bus, as shown in table v. table v. optimal shedding power on each load loads shedding power (mw) load 3 0.185 load 4 0.24623 load 5 0.22319 load 7 0.2125 load 9 0.48086 load 10 0.33978 load 12 0.26464 load 13 0.22673 total shedding power 2.1788 fig. 7. voltage droop of the mg before and after load shedding. figure 7 shows that the voltage quality has been improved after applying the proposed load shedding strategy. in addition, the result of pso algorithm (table v) confirms the proposed method of determining the optimum amount of shedding power on each load bus in order to limit the damage when load shedding is processed while still meeting the technical requirements of the operating specifications of the mg system. v. conclusion in this paper, an optimal shedding method for mgs in islanded operation with consideration of sustainable power sources has been proposed. the proposed method has recovered the frequency back to the normal stage to maintain the stability of the islanded mg system, based on its ability of adjusting the primary and secondary generators in order to calculate the minimum shedding power and restore the frequency of the system. the effectiveness of the proposed method has been demonstrated on the ieee 16-bus system. its performance is better than that of the conventional ufls method. the result shows that the proposed method can reduce the amount of shedding power while satisfying the technical operating conditions of the network. the current research also applies the pso algorithm to optimize the amount of distributed shedding power of each load bus in order to improve voltage quality and to prevent damage during the islanded operation. in the future, this project can be developed in several ways, for instance: engineering, technology & applied science research vol. 11, no. 1, 2021, 6680-6686 6686 www.etasr.com phung & le: load shedding in a microgrid with consideration of voltage quality improvement • multi-objective load shedding can be considered, i.e. combining other algorithms like ahp, fuzzy logic, anns or the variants of pso in order to determine the way in optimizing several issues including load shedding, economic dispatch, etc. • more research can be conducted in real time cases in order to get better results and solutions that can be used in real systems. • applying ai in solving the problem. references [1] z. zhao, p. yang, j. m. guerrero, z. xu, and t. c. green, "multipletime-scales hierarchical frequency stability control strategy of medium-voltage isolated microgrid," ieee 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[24] q. zhou, z. li, q. wu, and m. shahidehpour, "two-stage load shedding for secondary control in hierarchical operation of islanded microgrids," ieee transactions on smart grid, vol. 10, no. 3, pp. 3103–3111, may 2019, https://doi.org/10.1109/tsg.2018.2817738. microsoft word etasr_v13_n3_pp11020-11025 engineering, technology & applied science research vol. 13, no. 3, 2023, 11020-11025 11020 www.etasr.com soomro et al.: assessment of the flexural strength of binary blended concrete with recycled coarse … assessment of the flexural strength of binary blended concrete with recycled coarse aggregates and fly ash rizwan ali soomro department of civil engineering, quest, pakistan rizwansoomro40@gmail.com (corresponding author) mahboob oad department of civil engineering, quest, pakistan engrmahboob04@gmail.com sadam hussain aamur department of civil engineering, quest, pakistan amursadamhussain@gmail.com imran ali channa department of civil engineering, quest, pakistan imranalichanna@quest.edu.pk samreen shabbir department of civil engineering, dawood university of engineering and technology, pakistan samreen.shabbir@duet.edu.pk tariq ali department of civil engineering, islamia university of bahwalpur, pakistan tariqdehraj@gmail.com received: 7 april 2023 | revised: 20 april 2023 | accepted: 22 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5924 abstract this study investigated the effect of blending fly ash and recycled aggregates as replacements for cement and conventional coarse aggregates, respectively. recycled concrete helps to reduce waste management issues and protect the environment. fly ash was used in percentages from 0% to 10% with an increment of 2.5%, whereas demolition debris was used in a proportion of 50% with conventional aggregates. the 1:2:4 mix with a 0.5 w/c ratio was used to make six concrete mixtures, one of them made entirely of congenital aggregates. slump tests were performed for all mixtures. a total of 30 prisms of size 500×100×100mm were made and cured for 7 and 28 days. the flexural strength of the specimens was assessed under a two-point bending test till failure. the 5% fly ash and 50% recycled coarse aggregates (rca) mixture produced better results than the other mixes, showing a decrease in flexural strength of 10.74% and 15.75% after 7 and 28 days of curing, respectively. the small reduction in flexural strength compared to preserving conventional deposits and reducing the hazardous environmental impact of cement production and debris waste makes this mix suitable for use in structural members. keywords-green concrete; recycled aggregates; demolishing waste; fly ash, workability; flexural strength; twopoint loading engineering, technology & applied science research vol. 13, no. 3, 2023, 11020-11025 11021 www.etasr.com soomro et al.: assessment of the flexural strength of binary blended concrete with recycled coarse … i. introduction many researchers are actively investigating partial or alternative replacements for concrete materials to increase the strength of the final concrete and protect the environment from the emissions caused by the primary manufacturing processes of concrete ingredients. many different materials have been investigated for this reason, among them demolition rubbles from concrete constructions as coarse aggregates in fresh concrete. as garbage management is an important concern, using filler material as coarse aggregates in fresh concrete on the work site has many advantages. yet, the quality of aggregates and the concrete created in this way are impacted by the age of the concrete and the old mortar adhering to it. in particular, green concrete's strength is lower than that of conventional since it uses recycled aggregates from demolition waste. for a few decades, research has actively sought strategies to address this shortcoming. the effects of green concrete on the environment and its contributions to a sustainable environment were studied in [1-2]. the inconsistent nature of the waste's reported results demonstrates the need for additional research in the field to increase confidence in its application [3-4]. in [5-6], the basic properties of materials, the workability of wet concrete, and the mechanical behavior of concrete incorporating different replacement levels were determined, suggesting the use of recycled coarse aggregates (rca) at suitable replacement levels. in [7-10] the effects of curing methods, water-cement ratio, and temperature on hardened concrete with recycled aggregates were investigated. fly ash is a very fine powder created during the primary combustion process. every year, large amounts of this waste are produced all over the world, seriously harming the ecosystem. fly ash has been used in concrete as a pozzolanic cement replacement (siliceous and aluminous) to reduce waste and its associated issues. when water is added, calcium hydroxide interacts with it and creates cementitious compounds. in [11], fly ash was reviewed as a supplementary material for concrete and mortar, focusing on its chemical properties and concluding on its use as a sustainable material for green concrete production. to create m15, m20, and m25 concrete, fly ash substituted cement in amounts of 20%, 40%, and 60% in [12], presenting a numerical model for the strength vs water-cement ratio based on the obtained fundamental and strength characteristics of the concrete. the curves developed from the model can be used to calculate the amount of fly ash needed to provide the required strength on concrete. in [13], fly ash was used to produce high-strength concrete, showing an increase in strength and a decrease in sorptivity after 28 days of curing. fly ash was also used to create concrete without increasing carbon dioxide emissions [14], suggesting the use of stainless steel as a reinforcement and cladding for greater longevity. in [15], fly ash was used in large volumes as a cementitious compound to study micromechanics characteristics, showing that its use increased the tensile strain capacity of the concrete, but the compressive strength determines its dosage. in [16], fly ash and alkaline solutions were used to determine the mix design criteria and produce cement-free concrete. the comparison to standard concrete revealed strong connections. in [17], laboratory research was conducted on the use of fly ash from 10% to 30% by volume of cement, showing that although fly ash had a detrimental effect on compressive strength, a dosage of up to 20% resulted in increased density and tensile strength. in [18], fly ash was used in dosages of 0-20% to produce m20-grade concrete, exhibiting increased strength and durability after 7 and 28 days of curing. in [19], quarry dust and fly ash were used in dosages of 0-30%, concluding that using both materials together improved strength and contributed to environmental preservation. fly ash has a significant impact on the strength of concrete, but this impact varies greatly depending on the water-to-cement ratio. early strength is often lower when fly ash is used as a substitute compared to ordinary portland cement [20]. when using large amounts of fly ash, the final strength may not exceed 70% of the control mixture. hydration products (csh jell) are formed when fly ash combines with calcium ions in the pore solution of concrete and water [21-23]. authors in [24-26] concluded that the replacement of cement with suitable doses of fly ash in conventional or recycled concrete has positive effects that can lead to indigenous material and environmental preservation to some extent. many studies have been conducted on fly ash as a cement replacement, but very few investigated the use of both fly ash and demolished concrete as partial or total replacements for cement and coarse aggregates, respectively. it is evident that more studies are required to fully understand the collective effects of materials on the strength properties of concrete. as a consequence, this study examined the impact of using fly ash as a partial replacement for cement on the flexural strength of concrete made with a partial replacement of conventional coarse aggregates with recycled concrete. furthermore, this study evaluated strength under two-point loading, which is believed to be better than the one-point loading generally used. ii. materials and testing this study used ordinary portland cement from pakistan and hill sand from a nearby market which was sieved to eliminate lumps and larger particles. the aggregates came from debris from the demolition of a two-story reinforced concrete building in nawabshah, pakistan, and the huge blocks were pounded to generate coarse aggregates with a maximum size of 25mm. the aggregates were cleaned, washed, and then left to dry after removing unwanted materials. the same-sized traditional coarse aggregates acquired from the local market were washed and dried. fly ash class c from a coal power plant was used as cement replacement in weight-for-weight doses of 0, 2.5, 5, 7.5, and 10%. figure 1 shows the aggregate produced from demolished waste and figure 2 shows the cement, sand, and fly ash. a. sieve analysis hill sand from approved sources from the local market was used as fine aggregates. figure 3 shows the aggregate sieve analysis. the fineness modulus of the fine aggregates was 2.4. the percentage passing through various sieves and the fineness modulus of the aggregates was within the allowable range of astm c136/c136m-14 [28]. figure 4 shows the sieve analysis results of both the conventional and the recycled engineering, technology & applied science research vol. 13, no. 3, 2023, 11020-11025 11022 www.etasr.com soomro et al.: assessment of the flexural strength of binary blended concrete with recycled coarse … aggregates, following the normal practice to verify properly graded aggregates in the concrete mix. the fineness modulus of the aggregates was 5.33 for normal concrete aggregates (nca) and 5.35 for rca. the results of the sieve analysis were within the allowable ranges of astm c136/c136m-14 [28]. fig. 1. coarse aggregates. fig. 2. fine materials. fig. 3. sieve analysis of fine aggregates. fig. 4. sieve analysis of nca and rca. b. mechanical properties of aggregates the mechanical properties of aggregates play an important role in the preparation of the desired concrete, particularly water absorption and specific gravity. table i shows the determined water absorption, specific gravity, abrasion, soundness, and impact and crushing values of both nca and rca, following the relevant astm standards [30]. table i. water absorption and specific gravity test nca rca water absorption 1.64 3.42 specific gravity 2.57 2.31 abrasion 18.5 43.1 soundness 3.9 5.62 impact value 19.8 28.4 crushing value 26.2 34.1 equal halves of traditional coarse aggregates and debris from demolition building waste were used. the dosage of recycled aggregates was chosen according to [27]. concrete ingredients were combined in a 1:2:4 ratio with a 0.5 water:cement ratio. six different concrete mixes were prepared, namely cm, b1, b2, b3, b4, and b5. fly ash doses of 0%, 2.5%, 5%, 7.5%, and 10%, each with 50% recycled aggregates were used for 5 concrete mixes, while only traditional elements were used to produce the control concrete mix (cm). the water used had a ph level of 6.7 (see table ii). table ii. material details batch # cement (kg) fly ash (%) fa (kg) nca (kg) rca (kg) water (kg) cm 10 0 20 40 0 5 b1 10 0 20 20 20 5 b2 9.75 0.25 20 20 20 5 b3 9.5 0.5 20 20 20 5 b4 9.25 0.75 20 20 20 5 b5 9 1 20 20 20 5 c. workability of concrete each concrete mix was tested separately using the slump cone method to check its workability, according to astm c143 [29], and table iii shows the results. table iii. slump cone results of all mixes batch no. fly ash (%) slump (mm) 1 0.0 50.0 2 0.0 42.0 3 2.5 41.5 4 5.0 41.0 5 7.5 39.5 6 10.0 38.0 d. preparing and curing of specimens five prisms of 500"×100"×100" were prepared for each of the 6 batches. the concrete was prepared for the molds, poured, and compacted according to the astm c31/31m-19 [30]. the specimens were demolded on the next day and allowed to dry in the air for 24 hours in the laboratory. all specimens were then totally immersed in potable water for 7 and 28 days. thus, a total of 60 specimens were used in this study. figure 5 shows the specimens and the curing process. e. flexural strength after the respective curing time, the specimens were moved out of the water and their surface was wiped off with a dry clean cloth. the specimens were then dried in the air for 24 hours. a universal testing machine was used to determine engineering, technology & applied science research vol. 13, no. 3, 2023, 11020-11025 11023 www.etasr.com soomro et al.: assessment of the flexural strength of binary blended concrete with recycled coarse … flexural strength under two-point loading, following astm c78 [31]. the load application rate on the testing device was set to 0.5kn/sec, and it increased until failure. figure 6 shows some specimens and table iv shows the specimens' flexural strength, as calculated from their failure load and dimensions using the standard formula. fig. 5. casting and curing of specimens. table iv. average flexural strength # batch fly ash (%) 7-day curing 28-day curing mean load (kn) mean strength (n/mm 2 ) mean load (kn) mean strength (n/mm 2 ) 1 cm 0.0 7.02 5.29 8.77 6.61 2 b1 0.0 5.82 4.37 7.28 5.46 3 b2 2.5 5.91 4.42 7.39 5.53 4 b3 5.0 6.34 4.72 7.646 5.572 5 b4 7.5 5.76 4.32 6.80 5.10 6 b5 10.0 5.42 4.01 6.41 4.80 fig. 6. beam testing. iii. results and discussion the results of the fine aggregate sieve analysis were used to evaluate the fineness modulus, which was found to be in the range of fine sand. the percentage of the aggregates passing on various sieves met the required ranges. both used coarse aggregates confirmed the standard requirements of well-graded aggregates. with only a small variation in range values over a sieve, both curves' trends were quite comparable and the percentage passing on various sieves met the requirement of coarse aggregates. the water absorption of recycled aggregates was 108% more than that of conventional, while the specific gravity was 11.25% less. similarly, the abrasion values, the soundness, and the impact and crushing values were 132%, 44%, 43.4%, and 30% higher. the deviation of the properties of the recycled aggregates confirms the findings of previous studies and shows that the strength of the concrete using the aggregates may also be affected. indeed, the deviation was due to the age and exposure of concrete during previous use and mortar attached to the recycled aggregates. thus, the higher demand of the recycled aggregates for water was adjusted in the water-cement ratio, and 0.5 was adopted. the slump test results indicate that the slump of traditional concrete was within the acceptable range. however, the results of other mixtures were lower than those of ordinary concrete. figure 7 compares the slump values of the mixes with the control mix. it can be noted that adding more fly ash caused the slump value to decrease more. the maximum slump decrease, which was approximately 30%, was seen for 10% fly ash cement replacement. this shows that there is more water needed for mixes with fly ash. furthermore, while choosing the w/c ratio for the mix, more admixture or mechanical effort will be needed to maintain the requisite workability. fig. 7. comparison of slump values. fig. 8. flexural strength (7-day curing). engineering, technology & applied science research vol. 13, no. 3, 2023, 11020-11025 11024 www.etasr.com soomro et al.: assessment of the flexural strength of binary blended concrete with recycled coarse … fig. 9. flexural strength (28-day curing). fig. 10. average flexural strength comparison of 7and 28-day cured specimens. figures 8 and 9 compare the average flexural strength of all specimens. it was observed that the included rca affected flexural strength by 17.40% and 17.51% for 7and 28-day curing, respectively. on the other hand, the addition of fly ash up to 5% countered the problem and gave a better result. the increase of fly ash beyond 5% decreased flexural strength. increasing fly ash percentage reduced both workability and flexural strength. the results show the comparison of average flexural strength between the control mix and the one using just 50% recycled aggregates. among all the mixtures, the mix with 5% fly ash and 50% recycled aggregates provided the highest flexural strength. the average flexural strength decreased by 10.74% and 15.75% for 7and 28-day cured specimens, respectively, when compared to the control mix. figure 10 compares the flexural strength results for the 7 and 28-day cured specimens, showing the same trend of increase in strength. for the standard curing period of 28 days, it may be observed that the loss of strength due to the use of recycled aggregates was counteracted by the addition of 2.5% of fly ash. a similar trend in strength was observed with 5% fly ash in addition to the small increase in strength, but further addition of fly ash resulted in a decrease in strength. this was attributed to the lesser bonding capability of fly ash than cement. based on these results, the recommended dosage of fly ash was 5% along with 50% rca from demolished waste. iv. conclusion this study used fly ash and recycled aggregates from demolition debris in concrete to investigate their impact on the workability and flexural strength of concrete. the mechanical properties of aggregates were found to maintain the workability of the desired concrete, particularly water absorption and specific gravity. the findings showed that the specific gravity of rca was lower and that their water absorption was higher than that of 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[31] "standard test method for flexural strength of concrete (using simple beam with third-point loading)," american society for testing and materials, west conshohocken, pa, usa, standard astm c78/c78m22, 2022. engineering, technology & applied science research vol. 7, no. 3, 2017, 1638-1646 1638 www.etasr.com sareban: evaluation of three common algorithms for structure active control evaluation of three common algorithms for structure active control mohammad sareban department of civil engineering shahrood branch, islamic azad university shahrood, iran abstract—recently active structure controllers were considered to deal with the impact of earthquake forces and the result of the investigations provided multiple algorithms to calculate force control and many different ways to apply these forces on the structure. in this study, the efficiency and effectiveness of three methods (linear quadratic regulator, fuzzy logic and pole assigning) are investigated. in addition, three buildings with different height classes with an active tuned mass damper (atmd) on the top floor are considered to compare the active control methods. examples with known mass and stiffness and with variable mass are considered. the results show that all three control methods used for the atmd device reduce the structural response. the fuzzy control method, caused a sharp decline in relative displacement of building floors up to 80%. but in lqr and pole allocation procedures the applied force is limited. the best performance of fuzzy control is for high-rise buildings. the three different methods of control are stable in different masses and even under a random change of floor masses, their effectiveness can be trusted. keywords-active control; configurable active mass damper; linear quadratic optimal control; fuzzy control; pole allocation control; uncertainty. i. introduction controlling wind or seismic induced vibrations can be performed by passive, active, semi-active or combined control systems. each of these control systems uses various instruments to reduce seismic responses. as semi-active systems are reliable as passive systems and adaptive as active systems, they have attracted the attention of many researchers in the structural control field. active control systems, in contrast to passive systems, require an external energy for their operation. active control systems can be mainly divided into force applying mechanisms and algorithms to calculate the control force. although reducing damage caused by large loads is the main target in structural engineering, little attention has been given to directly control damage parameters. this is because valid damage parameters involve various variables while modern control theories, such as lqr, lqg, sliding mode control based on state space models, have the ability to involve state variables in the performance index. many researchers have studied the use of different control algorithms and tools in order to reduce response and improve the behavior of structures and achieved good results. in [1], authors provided an overview of modeling and controlling structures. they raised advancements in the field of modeling and seismic structural control and considered a variety of control methods including linear control, nonlinear control and intelligent control. in [2], authors investigated the application of an active system in vibration control of three and two-floor non-linear structures. due to the nonlinear behavior of the structure, researchers used fuzzy control to determine the control force. in [3], authors used a fuzzy control system and an active mass damper (atmd) to shield buildings against earthquakes. ii. materials and methods a. active control of structures an active control system is made from an external power source or hydraulic or electromechanical actuator force that applies a predetermined force to the structure. such forces can be used to attract or waste energy. the function of this system is based on measures by sensitive receptors that have been installed in floors and are sent to the cpu for processing. then, based on a predetermined control algorithm, the optimal controlling force is decided. the control process starts when the measured amplitude of oscillations is equal to or greater than a preset limit. such an approach is considered to bear increased efficiency compared to passive control strategies [4]. 1) damper with variable mass this system is a modified form of a damper with coordinated mass in which, an additional object with a driver is connected to the primary system. thus, there is a renewed impetus in system that complements the generated force by the coordinated mass and increase the damping force of the system. 2) linear quadratic method regulator (lqr) 2 lqr equations are one of the most widely used optimization algorithms for active control. the equation of multi-floor building’s motion as a shear frame model with controller is as follows: ¨ ¨ * * *m x(t) c x(t) k x(t) η x (t) γu(t)g     (1) after obtaining the solution to (1), the equation of motion is transferred to state-space. engineering, technology & applied science research vol. 7, no. 3, 2017, 1638-1646 1639 www.etasr.com sareban: evaluation of three common algorithms for structure active control       ¨ u rz t az t b u t b x (t)g   (2) in lqr procedure the below energy integral should be minimal: 1t t t 0 j ( z q z u r u )dt  (3) if the matrix q is large, structural response will be less and control force increases. if r is large, the response of the structure is high and control force decrease. the control force can be obtained from (4). as can be seen, the control force is linked to the structural response. if the structure response is large, more control force is applied respectively. the ontrol force u(t) can be obtained from the following equation:      1 tuu t gz t r b pz t    (4) in which, g is the gain matrix and p is a matrix obtained from nonlinear rikati equation. by combining (2) and (4) we have:      1 tu u rz t az t b ( r b pz t ) b f (t)    (5) considering * ( 1 ) t u ua a b r b p   we have:    * rz t a z t b f (t)  (6) to solve in state space we need the following equation:  y ez t lf (t)  (7) 3) fuzzy control the fuzzy control algorithm is based on fuzzy logic and uses intuition and knowledge of experts instead of differential equations to explain the behavior of a system [5] and in this case to determine the control force. there are many ways to generate fuzzy rules that include logical reasoning, and learning tests and simulations of the sample. so the control using this method is naturally robust and yet simple. to get answers to the equation (1), the equation of motion is transmitted to state-space.       ¨ u rz t az t b u t b x (t)g   (8) to conduct a fuzzy control, (8) is written as follows:      u rz t az t b (b u t b f(t))s   (9)    u rf t b u t b f(t)fu   (10) to solve in state space we also need the following equation:    *y ez t l f tfu  (11) fuzzy control can be incorporated in a closed loop control system similar to conventional controllers. fuzzy rule defines the relationship between fuzzy input and output based on a mamdani model. the law contains two parts: introduction and results made of if-then statements. each rule is as follows: 1 2r i i i iifx a and x b then y c    (12) where i is number of control laws, x1 and x2 are introduction variables and y is result variable. also ai, bi and ci are linguistic values of fuzzy variables. in this study, the fuzzy controller design directly from the numerical and clear structure data model. controller acts based on two input variables (velocity and displacement of the top floor), each having five triangular membership function (figure 1a) and an output variable (the active control) with seven triangular membership function (figure 1b). the abbreviations of input and output membership functions for fuzzy variables to define the phase space are: lp=big and positive; p=positive; z=null; n=negative; ln=large negative (for input variables), and pl=positive and large, pm=moderate positive; ps=positive and small; zr=null; nl=large negative; nm=high negative; ns=negative and small (variable output). details of inference rules used in this study are shown in table i. table i. fuzzy system rule base σφάλμα! τα αντικείμενα δεν μπορούν να δημιουργηθούν από την επεξεργασία κωδικών πεδίων.(displacement) σφάλμα! τα αντικείμενα δεν μπορούν να δημιουργηθούν από την επεξεργασία κωδικών πεδίων.(velocity) ln n z p lp lp ns ns nm nl nl p ns nm nm nm nl z ps zr zr zr ns n pl pm pm pm ps ln pl pl pm ps ps fuzzy controller uses the mamdani method for making non-fuzzy to change the linguistic values to numerical and clear values. linguistic output values between -1 and 1 must be multiplied by a factor to produce active control force. fig. 1. (a) membership functions of input variables (displacement and velocity), (b) membership functions of the output variable (active control force) 4) pole allocation method unlike lqr algorithms, this algorithm solves structures inversely to encourage them to the desired response. this means that the structure's primary poles are determined from the beginning of the algorithm and then the system with respect to dampers increase the damping ratio of structures and by solving the main determinant of algorithm determines the new poles of structure so that systems moves toward increasing stability. therefore new active structure poles define the (a) (b) engineering, technology & applied science research vol. 7, no. 3, 2017, 1638-1646 1640 www.etasr.com sareban: evaluation of three common algorithms for structure active control system. however, changeable points in the algorithm should be considered from first variations advance through usable results for passive structural damper design. as a result, damping and stiffness values in the system are introduced only where there is permission to change them. to get answers to the (1), the equation of motion is transmitted to state-space.       ¨ u rz t az t b u t b x (t)g   (13) eigenvalues of matrix a are as follows: 2ρ 1 ; 1i i i i i j j         (14) in (13), u(t) is as follows:    u t gz t  (15) by combining (13) and (15), we have:      u rz t az t b ( gz t ) b f (t)    (16) considering * u a a b g  (13) is expressed as follows:    * rz t a z t b f (t)  (17) eigenvalues of matrix a* are as follows: * *2ρ 1 ; 1i i i i i j j         (18) by increasing the amount ξ to ξ* and considering g unknown, g is acquired using place command in matlab software and thus the amount of control force is obtained. to solve the problem in state space we also need following equation:  y ez t lf (t)  (19) b. uncontrolled structure equation of motion for multi-floor buildings with shear frame model without a controller is as follows: ¨ ¨ m x(t) cx(t) kx(t) mr x (t)g    (20) after obtaining the response of motion equation (20), we transmit the equation of motion to state-space.     ¨ rz t az t b x (t)g  (21) in addition to solve in the state space equation (21) is needed in addition to equation (22).   ¨ y ez t l x (t)g  (22) iii. numerical example three buildings with different heights (low height of 5 floors, the average height of 10 floors and high height of 20 floors) are taken into account. for the 5 and 10 floor buildings, the mass of each floor is 1*105 kg and the stiffness of each floor is 5*107 n/m and a structural damping ratio of ξ=0.05 is considered. fig. 2. n floor building with shear frame and an atmd in roof in these two cases, an atmd is installed on the top floor (roof) to reduce the structural response (figure 2). its mass is equal to mt=5*104 kg. since the first structure frequency is crucial for the specification of atmd, stiffness of atmd is calculated from the following equation: 2 t t lk m .w (23) where wl is the first frequency structures. atmd damping ratio equal to that taken into account, since the damping ξt=0.05 atmd to be achieved as follows: t t t lc 2ξ .m .w (24) the only difference in the 20 floor building is the stiffness of floors which is considered equal to 8*108 n/m. for each building, three control methods have been used. the first control method employed is the linear quadratic regulator method (lqr). in all cases r=1*10-4 and q=αi, α=1*109 are considered in relation. the higher α increases control force. the results showed that for amounts larger than α=1*109 the controlling force does not increase and this is a disadvantage to this approach. the second control method employed is fuzzy control. in this method the response of the structure as displacement and velocity of top floor are used as fuzzy logic inputs. control force output is between -1 and 1. it should be multiplied by a factor to result to a larger control force. this factor is considered equal to 1*106 in all cases. the final method employed is pole assignment, with a structural damping of ξ=0.05, increased to ξ=0.15 for the first two buildings and to ξ=0.07 for the 20 floor building. the ultimately gain matrix g and control force each time step is calculated with the relationship u (t)=gz (t). new damping ratios were calculated in a way that greatest reduction occurs in floor displacements. two earthquake records corresponding to loma prieta and northridge earthquakes were used for all states. these accelerograms can be seen in figures 3 and 4.. engineering, technology & applied science research vol. 7, no. 3, 2017, 1638-1646 1641 www.etasr.com sareban: evaluation of three common algorithms for structure active control the structural response results of northridge earthquake is further explained in detail with tables and graphs. the impact of the northridge earthquake is considered in table ii for three 5-floor buildings where the three methods were compared. maximum atmd controlling force in these three methods shows that with the fuzzy control method a large control force can be produced. a weaker control force is created with the other two methods. also, the displacement of the controlled mode to uncontrolled in all floors and for all three control methods is under one, which shows a decrease in displacement for all control methods. because of the large control force in fuzzy method, the controlled to uncontrolled mode displacement ratio is very low and there is 50% to 70% reduction in movement. this reduction is greater on the upper floors. the reduction in other two methods is about 20%. fig. 3. northridge earthquake accelerograms fig. 4. loma prieta earthquake accelerograms table ii. displacement ratio (uncontrolled to controlled state) and maximum control force in the 5 floor building 3 2 1 state pole allocation fuzzy lqr control algorithm 5370 47210 10240 maximum control force (kn) 0.77 0.44 0.82 floor 1 0.79 0.43 0.83 floor 2 0.81 0.40 0.84 floor 3 0.82 0.36 0.83 floor 4 0.84 0.32 0.83 floor 5 in figure 5, controlled and non-controlled displacement time-history chart of first and fifth floors of a 5-floor building with the lqr procedure can be observed. in both floors variation range of controlled state is less than that of the uncontrolled state. lqr control method reduced the initial peaks of graph up to 20% and this reduction increased in further time steps. this is a good result, although the initial peaks of graph reduced slightly, high displacement reduction in next time steps, causes less cyclic structure fatigue. fig. 5. time-history graph of controlled and non-controlled states of mode 1 in figure 6, the force control generated by the fuzzy logic can be observed at different time steps. history shows that the force is very logical control force and corresponding actions earthquake is generated. the maximum control force is found to be 5*104 kn. time-history graph for the controlling force in lqr method can be observed in figure 6. maximum experienced control force is 1*104 kn. in figure 7, the maximum absolute displacement of various floors for controlled and non-controlled states of a 5-floor building with lqr method is presented. in this figure reduced displacements for each floor are presented, the reduction is larger for upper floors. according to figure 8, the variation range of controlled state is less than that of the uncontrolled state on both floors which reflects the decreasing displacement in fuzzy method for five floor building. the fuzzy control method reduces the displacement of steps in same size and approximately the same decrease can be observed. in figure 9, the control force generated by the fuzzy logic control at different time steps can be observed. the history of control force shows that the force is very logical and control force is generated corresponding to applied earthquake. the maximum experienced control force is 5*104 kn. stronger quake produces greater control force. fig. 6. timehistory graph for control force in lqr method of mode 1 in figure 10, the maximum absolute displacement of different floors in controlled and uncontrolled states of mode 2 floor 1 floor 5 engineering, technology & applied science research vol. 7, no. 3, 2017, 1638-1646 1642 www.etasr.com sareban: evaluation of three common algorithms for structure active control can be observed. reduced displacement for each floor is visible, while the reduction in upper floors is more for the fuzzy control method. the variation range of controlled state is less than that of the uncontrolled state which shows a reduction in displacement for pole allocation method of the 5-floor building. displacement reduction in pole allocation control method in all steps is approximately the same as lqr method. in figure 12, the control force produced by the pole allocation method in different time steps can be observed. the maximum experienced control force is 5*103 kn. in figure 13, the maximum absolute displacement of different floors in controlled and uncontrolled state of mode 3 is shown. reduction of displacement in all floors is observed in this figure. reduced displacement for pole allocation method in all floors is observed, while the reduction in the upper floors is larger. fig. 7. the maximum absolute displacement in different floors for controlled and uncontrolled states of mode 1 fig. 8. time-history graph of controlled and uncontrolled state for mode 2 as shown in table iii, in the case of 4 to 6 with 10 floors the displacement of controlled state to uncontrolled state in all floors and for all three control methods is the same that shows a decrease in displacement for all control methods and also the maximum control force is about the same in all three control methods. but control force generated by the lqr method is a bit lower which cause reduction in displacement about 10 to 30%. floor displacement reduction in fuzzy method is 25 to 40%. in pole allocation method this reduction is 20 to 35%. weak performance of fuzzy method compared to previous state is because stiff floors in a 10 floor building, in comparison to mass and stiffness of a 5-floor building remained unchanged and the frequency and period of structure has changed. fig. 9. time-history graph for control force in fuzzy method of mode 2 fig. 10. maximum absolute displacement in different floors in controlled and uncontrolled state of mode 2 fig. 11. time-history graph of controlled and uncontrolled state for mode 3 floor 5 floor 1 floor 1 floor 5 engineering, technology & applied science research vol. 7, no. 3, 2017, 1638-1646 1643 www.etasr.com sareban: evaluation of three common algorithms for structure active control fig. 12. time-history graph for control force in pole allocation method of mode 3 fig. 13. maximum absolute displacement in different floors in controlled and uncontrolled state of mode 3 table iii. displacement ratio (uncontrolled to controlled state) and maximum control force in 10 floor building. 6 5 4 state pole allocation fuzzy lqr control algorithm 7750 7970 5440 maximum control force (kn) 0.65 0.70 0.71 floor 1 0.66 0.65 0.73 floor 2 0.67 0.61 0.76 floor 3 0.69 0.61 0.81 floor 4 0.70 0.69 0.87 floor 5 0.70 0.73 0.91 floor 6 0.73 0.75 0.91 floor 7 0.76 0.74 0.90 floor 8 0.79 0.72 0.90 floor 9 0.81 0.70 0.90 floor 10 in figures 14-16, the reduction of maximum floor displacements in uncontrolled and controlled state of a 10-floor buildings can be seen. in all three control methods for 10-floor building, displacement reduction for all floors is seen that the reduction in the upper floors is more. the fuzzy method shows weak performance, because of the increasing stiffness of floors in comparison to the 5-floor building. in table iv, states 7 to 9 with 20 floors, maximum atmd control force in three considered methods is shown that a large control force is created by the fuzzy method and a weaker control force is created by the other two methods. the control force generated by the lqr is slightly larger than that of pole allocation. displacement reduction is about 13% for lqr, 35 to 50%. for the fuzzy method and 11% for the pole allocation method. fig. 14. maximum absolute displacement of different floors in controlled and uncontrolled state of mode 4 fig. 15. maximum absolute displacement of different floors in controlled and uncontrolled state of mode 5 fig. 16. maximum absolute displacement of different floors in controlled and uncontrolled state of mode 6 engineering, technology & applied science research vol. 7, no. 3, 2017, 1638-1646 1644 www.etasr.com sareban: evaluation of three common algorithms for structure active control table iv. displacement ratio (uncontrolled to controlled state) and maximum control force in 20 floor building. 8 9 7 state fuzzy pole allocation lqr control algorithm 62440 6010 12760 maximum control force 0.66 0.89 0.87 floor 1 0.66 0.89 0.87 floor 2 0.66 0.89 0.88 floor 3 0.66 0.89 0.88 floor 4 0.65 0.89 0.88 floor 5 0.65 0.89 0.88 floor 6 0.65 0.89 0.87 floor 7 0.64 0.88 0.87 floor 8 0.63 0.88 0.87 floor 9 0.62 0.88 0.87 floor 10 0.61 0.87 0.86 floor 11 0.60 0.87 0.86 floor 12 0.59 0.87 0.86 floor 13 0.58 0.87 0.86 floor 14 0.57 0.87 0.86 floor 15 0.56 0.87 0.86 floor 16 0.55 0.87 0.86 floor 17 0.54 0.87 0.86 floor 18 0.53 0.87 0.86 floor 19 0.53 0.87 0.86 floor 20 figures 17-19 show the reduction of the maximum displacement of floors in uncontrolled and controlled state of a 20-floor building. in all three control methods for 20-floor building reduced displacement for all floors can be seen that the reduction in the upper floors is more. meanwhile, the fuzzy method shows the best performance. tables v-vii 7 show the displacement of controlled state to uncontrolled state and the maximum control force in 5, 10 and 20 floor buildings under loma prieta earthquake. same results of northridge earthquake can be seen for loma prieta. fig. 17. maximum absolute displacement of different floors in controlled and uncontrolled state of mode 7 fig. 18. maximum absolute displacement of different floors in controlled and uncontrolled state of mode 8 fig. 19. maximum absolute displacement of different floors in controlled and uncontrolled state of mode 9 in figures 20-22 with changing mass of floors from 20% less than the original mass to 20% more than the original mass, its impact on reduction of floor displacements in uncontrolled and controlled states with three methods is shown. the results show that all three methods of control are stable in different masses and random change of floor masses we can safely reduce structural displacement. in 5-floor buildings, as shown in figure 20, it can be seen the displacement of structures for various masses decreased in all three control methods, and also increasing floor masses, the reduction of structural displacement is reduced. graphs of displacement variation in three control methods are nearly parallel to displacement variation graph of uncontrolled displacement. as can be seen fuzzy control method has high performance in 5-floor building. according to figure 21, in 10-floor buildings, the displacement of structures for various masses decreased in all three control methods and displacement variation with mass changes is very small. in lqr method, same results are observed, and despite the reduced displacement, the displacement variation graph is unchanged. in pole allocation method with mass increase, displacement is slightly reduced. engineering, technology & applied science research vol. 7, no. 3, 2017, 1638-1646 1645 www.etasr.com sareban: evaluation of three common algorithms for structure active control the greatest effect of floor mass change in 10 floor buildings is in fuzzy control method that the mass increase causes a strong increase in displacement. the increase from 80% of mass to 120% of the mass is about 25%. so it is possible that with excess increase in floor masses, fuzzy logic method in 10-floor building lose its efficiency. table v. displacement ratio (uncontrolled to controlled state) and maximum control force in 5 floor building. 3 2 1 state pole allocation fuzzy lqr control algorithm 2820 20800 5160 maximum control force (kn) 0.58 0.24 0.66 floor 1 0.59 0.23 0.66 floor 2 0.61 0.21 0.68 floor 3 0.63 0.18 0.69 floor 4 0.65 0.16 0.71 floor 5 table vi. displacement ratio (uncontrolled to controlled state) and maximum control force in 10 floor building. 6 5 4 state pole allocation fuzzy lqr control algorithm 4050 6280 2500 maximum control force (kn) 0.89 0.72 0.91 floor 1 0.86 0.71 0.89 floor 2 0.82 0.70 0.85 floor 3 0.77 0.68 0.80 floor 4 0.74 0.66 0.78 floor 5 0.71 0.65 0.78 floor 6 0.69 0.64 0.77 floor 7 0.67 0.63 0.77 floor 8 0.67 0.61 0.77 floor 9 0.68 0.59 0.76 floor 10 table vii. displacement ratio (uncontrolled to controlled state) and maximum control force in 20 floor building. 9 8 7 state pole allocation fuzzy lqr control algorithm 3000 30990 6270 maximum control force (kn) 0.82 0.31 0.84 floor 1 0.82 0.30 0.84 floor 2 0.82 0.30 0.84 floor 3 0.82 0.29 0.84 floor 4 0.82 0.29 0.83 floor 5 0.82 0.28 0.83 floor 6 0.82 0.28 0.83 floor 7 0.82 0.27 0.83 floor 8 0.83 0.27 0.83 floor 9 0.83 0.26 0.83 floor 10 0.83 0.26 0.84 floor 11 0.83 0.25 0.84 floor 12 0.83 0.25 0.84 floor 13 0.83 0.26 0.84 floor 14 0.83 0.27 0.84 floor 15 0.84 0.28 0.84 floor 16 0.84 0.29 0.84 floor 17 0.84 0.30 0.84 floor 18 0.84 0.31 0.84 floor 19 0.85 0.32 0.84 floor 20 according to figure 22 in 20-floor buildings, displacement of structures for various masses decreased in all three control methods, in controlled and uncontrolled case and increasing mass increases displacement. this change is less in fuzzy control method. this shows that the fuzzy method has very high performance in high-rise buildings. also fuzzy method drastically reduces the structural response of high rise building. fig. 20. maximum displacement change of the top floor of 5-floor buildings to change floor masses. fig. 21. maximum displacement change of the top floor for 10-floor buildings to change of floor masses. fig. 22. maximum displacement change of the top floor for 20-floor buildings to change of floor masses. iv. conclusion all three control methods used in this study (lqr, fuzzy and allocation pole) for atmd reduces the structural response. but fuzzy control method drastically reduced floor displacement up to 80%. further, in lqr and pole allocation methods limited control force was conducted. therefore, the engineering, technology & applied science research vol. 7, no. 3, 2017, 1638-1646 1646 www.etasr.com sareban: evaluation of three common algorithms for structure active control fuzzy control method provides the best results. however, if the controlling force is greater than a specific amount, rather than reducing floor displacement, increases them. it should be noted that the fuzzy control method performed best in the case of high-rise buildings. references [1] s. thenozhi, w. yu, “advances in modeling and vibration control of building structures”, annual reviews in control, vol. 37, no. 2, pp. 346-364, 2013 [2] m. al-dawod, b. samali, k. kwok, f. naghdy, “fuzzy controller for seismically excited nonlinear buildings”, journal of engineering mechanics, vol. 130, no. 4, pp. 407-415, 2004 [3] r. guclu, h. yazici, “vibration control of a structure with atmd against earthquake using fuzzy logic controllers”, journal of sound and vibration, vol. 318, no. 1, pp. 36-49, 2008 [4] s. m. nigdeli, m. h. boduroglu, “active tendon control of torsionally irregular structures under near ‐ fault ground motion excitation”, computer‐aided civil and infrastructure engineering, vol. 28, no. 9, pp. 718-736, 2013 [5] t. kobori, r. minai, “analytical study on active seismic response control”, transactions, architectural institute of japan, vol. 66, no. 2, pp. 256-257, 1960 engineering, technology and applied science research vol. 8, no. 1, 2018, 2542-2545 2542 www.etasr.com satheesh et al.: electric field simulation around contaminated sir insulators using matlab electric field simulation around contaminated sir insulators using matlab g. satheesh department of electrical and electronics engineering sr engineering college warangal, telangana, india satheeshtrrec@gmail.com b. basavaraja department of electrical and electronics engineering university b.d.t. college of engineering, karnataka, india banakara36@gmail.com p. m. nirgude uhv research laboratory central power research institute telangana, india nirgudepm@yahoo.co.in abstract—high voltage insulators are mainly used to support transmission lines. this paper focuses on simulating the electric field along the surface of contaminated silicone rubber (sir) insulators. the electric field (ef) distribution is important to determine the ef stress occurring on the insulator surface. so, the ef distribution is analyzed using a fem tool in matlab under various conditions. two types of insulators, straight and alternate sheds, were considered. results showed that higher ef stresses occurs on the trunk portions of both straight shed and alternate shed types. also, the results showed higher ef magnitude on the straight shed compared to the alternate shed, under both clean and contamination conditions. keywords-electric field distribution; electric potential; finite element method; silicone rubber insulator; water droplet i. introduction electrical insulators are electrically insulating components used in various electrical installations. the main aim of this paper is to focus on simulating the electric field (ef) distribution around a silicon rubber (sir) insulator under various conditions using matlab. insulators may fail when pollutants accumulate on their surface and certain environmental stresses occur [1-8]. these conditions are commonly seen in the field with in-service insulators located near polluting sources like coastal areas and agricultural fields [1-8] . the ef distribution is important to find the electric field stress occurring on the sir insulator surface under various conditions. two types of insulators, having straight and alternate sheds were used for analysis of ef along insulators. up until 1963, the insulator manufacturing industry produced mainly ceramic (glass and porcelain) insulators. but in the recent years, composite (sir) insulators have gained a large share of the market. compare to conventional insulators, silicon rubber insulators offer certain obvious advantages such as low weight, but the most significant advantage is related to their hydrophobic surface that allows them to operate fault and maintenance free in polluted areas [1-8]. to analyze the characteristics of sir insulators, modeling and simulations were done under different contaminated conditions. sir insulator consists of the frp core, housing, sheds and metal end fittings. the core of a non-ceramic insulator has the dual burden of being the main insulating part and also of being the main load-bearing member be it in suspension, cantilever or compression modes. sheds made from various non-ceramic materials are shaped and spaced over the rod in various ways to protect the rod and to provide maximum electrical insulation between the attachment ends (also considering weather patterns). end fitting transmits the mechanical load to the core. they are usually made of metal. the most commonly used housing material for composite insulators is sir due to its properties related to surface hydrophobicity [1-8]. the effect of contamination on sir insulator is usually analyzed by placing dust along with droplets on the surface while a voltage source is applied to one end (usually the lower electrode). ii. fem four classical methods for solving the partial differential equations (pde) are the charge simulation method (csm), the finite difference method (fdm), the boundary element method (bem) [9] and the finite element method (fem) [10-12]. out of these four, fem has a dominant position because of its strong interchangeability [13-15]. the finite element approach is based on the suggestion of building an elaborate object with easy blocks or dividing an elaborate object into small and manageable pieces. in fem the area is split right into a finite number of elements. these elements are related at nodes. a suite of linear algebraic equations are to be solved in case of linear issues. higher precision may also be accomplished by increasing the number of elements and for a discretized problem approximation results in a set of sparse equations. this leads to resolve issues with a number of unknown nodal values. finite element methods are enormously versatile and powerful and can permit designers to obtain know-how concerning the electrical stresses taking place on the outside of insulators [14-15]. regardless of the big advances which were made in establishing finite element applications, the received outcome ought to be cautiously examined before applied in real conditions. essentially the biggest challenge of finite element methods is that the resolution accuracy is traditionally a function of the mesh decision. any regions of enormously centered electrical stress have to be carefully analyzed with the usage of a sufficiently sophisticated mesh. today's finite engineering, technology and applied science research vol. 8, no. 1, 2018, 2542-2545 2543 www.etasr.com satheesh et al.: electric field simulation around contaminated sir insulators using matlab element applications are powerful tools which have come to be more and more indispensible to insulator design and evaluation. however, additionally they make it effortless for users to make errors. iii. simulation results in this study, clean and contaminated conditions have been simulated with the use of pde tool in matlab. the two dimensions of sir insulator under contaminated and clean conditions for fem analysis are shown in figures 1 and 5. the finite element discretization results are shown in figures 2 and 6. the simulation result under clean condition is illustrated in figure 3. also, the simulation result under contamination conditions are illustrated in figures 7 and 8. as illustrated in figures 7 and 8 the dusts along with droplets have the most effect on ef along insulator. in case of straight sir insulator, situation of contamination is simulated by means of putting dust and 42 drops as shown in figure 5a. the simulation outcomes are illustrated in figures 7a and 7b with dust and drops. in step with obtained results, existence of various dusts together with drops would create ef enhancement on insulator. it is also observed that the stresses occuring on the trunk portions of insulator are high compare to other portions of insulator. in case of an insulator with alternate sheds, condition of contamination is simulated via placing dust and 56 drops as in figure 5b. the simulation outcomes are illustrated figures 8a and 8b with dust and drops. according to obtained results, the existence of dust and water drops would create ef enhancement on insulator surface. it is observed that the field stresses occuring on insulator trunks are high compare to other portions of insulator. the results illustrated in figures 4 and 9 show that the highest ef occur on the trunk portion than shed portion for both straight and alternate shed sir insulators. the ef stress on insulator of straight shed sir is higher than the insulator of alternate shed sir from table i under clean condition and from table ii under contamination condition. also ef stress occurring on straight shed sir insulator is 7% to 31% higher than stress occurring on the alternate shed insulator under various conditions. table i. electric field comparison clean insulators s. no. type of insulator max. electric field e (kv/c.m) on insulator under clean condition near hv end near ground between sheds 1 straight shed 2.75 2.75 1.4 2 alternate shed 2.4 2.4 1.25 table ii. electric field comparison – polluted insulators s. no. type of insulator max. electric field e (kv/c.m) on insulator with cement dust and water drops with plywood dust and water drops near hv end near ground between sheds near hv end near ground between sheds 1 straight shed 2.5 2.5 1.5 2.9 2.9 1.65 2 alternate shed 2.35 2.35 1.2 2.2 2.0 1.35 a. straight shed insulator b. alternate shed insulator fig. 1. 2d view of sir insulator under clean condition for fem analysis. a. straight shed insulator b. alternate shed insulator fig. 2. discretization results under clean condition for fem analysis. engineering, technology and applied science research vol. 8, no. 1, 2018, 2542-2545 2544 www.etasr.com satheesh et al.: electric field simulation around contaminated sir insulators using matlab a. straight shed insulator b. alternate shed insulator fig. 3. ef distribution under clean conditions. a. straight shed insulator b. alternate shed insulator fig. 4. ef along insulator under clean conditions. a. straight shed insulator b. alternate shed insulator fig. 5. 2d view of sir insulator under contamination condition for fem analysis. a. straight shed insulator b. alternate shed insulator fig. 6. discretization results under contamination condition for fem analysis. a. cement dust and drops b. plywood dust and drops fig. 7. electric field along straight shed sir insulator considering contamination. engineering, technology and applied science research vol. 8, no. 1, 2018, 2542-2545 2545 www.etasr.com satheesh et al.: electric field simulation around contaminated sir insulators using matlab a. cement dust and drops b. plywood dust and drops fig. 8. electric field along alternate shed sir insulator considering contamination. a. straight shed insulator b. alternate shed insulator fig. 9. electric field along insulator under contamination. iv. conclusion in this paper, ef distributions were investigated by using a pde tool in matlab to simulate clean and polluted sir insulators of two types: straight and alternate shed. according to the obtained results, higher ef stresses occur on the trunks of both straight and alternate shed sir insulators and ef stress also depends on the pollutants. higher ef is computed in the case of straight shed insulators (7% to 31% higher). references [1] k. o. papailiou, f. schmuck, silicone composite insulators. materials, design, applications, springer, 2013 [2] cigre tf 33.04.01, polluted insulators: a review of current knowledge, cigre, 2000 [3] k. chrzan, z. pohl, t. kowalak, “hygroscopic properties of pollutants on hv insulators”, ieee transactions on electrical insulation, vol. 24, no. 1, pp. 107-112, 1989 [4] n. mavrikakis, e. koudoumas, k. siderakis, d. pylarinos, e. thalassinakis, o. kokkinaki, a. klini, c. kalpouzos, m. polychronaki, d. anglos, "insulators’ pollution problem: experience from the coastal transmission system of crete", 52nd international universities' power engineering conference (upec 2017), heraklion, crete, august 29september 1, 2017 [5] k. siderakis, d. pylarinos, e. thalassinakis, i. vitellas, e. pyrgioti, “pollution maintenance techniques in coastal high voltage installations”, engineering technology and applied science research, vol. 1, no. 1, pp. 1-7, 2011 [6] d. pylarinos, k. siderakis, e. thalassinakis, "comparative investigation of silicone rubber composite and rtv coated glass insulators installed in coastal overhead transmission lines", ieee electrical insulation magazine, vol. 31, no. 2, pp. 23-29, 2015 [7] m. dimitropoulou, d. pylarinos, k. siderakis, e. thalassinakis, m. danikas, "comparative pollution field measurements on outdoor insulators of different material and design", engineering, technology & applied science research, vol. 5, no. 2, pp. 764-774, 2015 [8] d. pylarinos, k. siderakis, e. koudoumas, e. thalassinakis, "polymer insulators and coatings in the cretan power system. the transmission line case", 9th mediterranean conference on power generation, transmission distribution and energy conversion, athens, greece, 2-5 november, 2014 [9] k. eldridge, j. xu, w. yin, a. m. jeffery, j. ronzello, s. a. boggs, “degradation of a silicone based coating in a substation application”, ieee transactions on power delivery, vol. 14, no. 1, pp. 188-193, 1999 [10] h. singer, f. gutfleisch, k. forger, j. a. gomollon, “calculation of high-voltage fields by means of boundary element method”, ieee transactions on power delivery, vol. 9, no. 2, pp. 743-749, 1994 [11] m. v. k. chari, g. bedrosian, j. d. angelo, “finite element applications in electrical engineering”, ieee transactions on magnetics, vol. 29, no. 2, pp. 1306-1314, 1993 [12] c. r. i. emson, j. simkin, c. w. trowbridge, “a status report on electromagnetic field computation”, ieee transactions on magnetics, vol. 30, no. 4, pp. 1533-1540, 1994 [13] v. t. kontargyri, i. f. gonos, i. a. stathopulos, “measurement and simulation of electric field of high voltage suspension insulators”, european transactions on electrical power, vol. 19, pp. 509-517, 2008 [14] w. sima, q. yang, c. sun, f. guo, “potential and electric-field calculation along an ice-covered composite insulator with finite-element method”, iee proceedings-generation transmission and distribution, vol. 153, no. 3, pp. 343–349, 2006 [15] u. van rienen, m. clemens, t. wieland, “simulation of low-frequency fields on high-voltage insulators with light contaminations”, ieee transactions on magnetics, vol. 32, no. 3, pp. 816-819, 1996 microsoft word etasr_v13_n4_pp11130-11138 engineering, technology & applied science research vol. 13, no. 4, 2023, 11130-11138 11130 www.etasr.com bin lashram et al.: hclpars: α new hierarchical clustering log parsing method hclpars: α new hierarchical clustering log parsing method arwa bin lashram university of jeddah, saudi arabia arwa.alashram@yahoo.com (corresponding author) lobna hsairi university of jeddah, saudi arabia lalhabib@uj.edu.sa haneen al ahmadi university of jeddah, saudi arabia hhalahamade@uj.edu.sa received: 5 may 2023 | revised: 17 may 2023 | accepted: 18 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6013 abstract event logs are essential in many software systems’ maintenance and development, as detailed runtime information is recorded in them, allowing support engineers and developers to monitor systems, understand behaviors, and identify errors. with the increasing size and complexity of modern software systems, parsing their logs by the traditional (manual) method is cumbersome and useless. for this reason, recent studies have focused on automatically parsing log files. this paper presents the hierarchical clustering log parsing method, called hclpars, for automatically parsing log files, consisting of 3 steps: parameter removal according to acquired knowledge in order to avoid errors, grouping similar raw log messages, and getting the set of keys that make up the log. experiments were run on 16 real system log data, and the performance of the proposed algorithm was compared with the one of other 14 algorithms. it was shown that the hclpars outperformed the other log parsers in terms of accuracy, efficiency, and robustness. keywords-event log mining; system logs; log parsing; log analysis; log management; execution trace; hclpars; agent i. introduction each system or application has its own log files containing detailed information about the operating time (execution traces). these execution traces play an important role in developing, maintaining, and sustaining software systems. they help developers and support engineers to understand the system behavior [1, 2] and track and diagnose errors and malfunctions that may arise [3, 4]. but despite the enormous information buried in the logs, finding ways to effectively analyze it remains a huge challenge [5], for two reasons: first, modern software systems routinely generate tons of records in seconds. this huge volume of logs makes it difficult to inspect log messages manually. second, these log messages are unstructured in nature. to be able to analyze such files, the first and most important step is logging parsing, which is converting the raw log messages into a sequence of structured events [69]. as the example illustrated in figure 1, each raw log message records a specific system event with a set of fields: timestamp, verbosity level (e.g. error/info/debug), component, and event. a raw log message has constant and variable parts. the constant part reveals the log key or event template for the log message, which remains the same for every event occurrence, and varies from event to event, while the variable part records runtime information (i.e. parameters and states), which may vary among various event occurrences. the goal of log parsing is to automatically separate the constant part and the variable part of a raw log message, or otherwise match each raw log message with a specified log key (constant part) [10]. so, we need to extract the log keys first, and then use it in the parsing process. the traditional method of extracting log keys relies on handcrafted regular expressions [11]. simple as it may seem, writing custom rules manually for a large volume of records is a time-consuming and error-prone method, and the logging code is frequently updated in modern software systems, leading to regular reviewing of these rules. to reduce the manual efforts in extracting log keys, some studies [12, 13], have suggested techniques for extracting log keys directly from the source code. these technologies are applicable in some cases, but in practice, the source code is not always accessible, and engineering, technology & applied science research vol. 13, no. 4, 2023, 11130-11138 11131 www.etasr.com bin lashram et al.: hclpars: α new hierarchical clustering log parsing method often these technologies are limited to specific software or applications. meanwhile, a static and generic analysis tool is needed for all programs across different programming languages, and to achieve this, several data-driven approaches have been proposed, including iterative mining (slct [14]), iterative segmentation (iplom [15]), and hierarchical clustering (lke [16]). in contrast to handcrafted rules and source-based parsing, these methods can learn patterns from log data and automatically generate common log keys, but are unable to handle huge datasets, so a parallel log parsing method, called pop was proposed [17]. pop is able to handle large datasets with high accuracy, as it was implemented on top of spark, and it used resilient distributed datasets (rdd) abstraction, which is ineffective with data of small size because it consumes more time, while using it is expensive when the size of the data increases [18]. to address these issues, we propose the hierarchical clustering log parsing method (hclpars), that works on top of spark like pop [17], but with a different abstraction type, which is data frame (df). hclpars was evaluated on large-scale real-world data sets, and the results demonstrate its ability to achieve speed, accuracy, and efficiency. for example, hclpars can parse an hdfs dataset in less than one minute, while pop requires 7 minutes and iplom 30 minutes and lenma and logsig fail to finish in a reasonable time. fig. 1. example of raw log message and log key. ii. related work log key extraction has been studied extensively and has been categorized into three approaches: rule-based, sourcecode-based, and data-driven. many researchers use rule-based methods [19, 20], which despite their accuracy, require domain expertise and are also limited to specific rather than general application scenarios. for example, authors in [19] a rule-based system for software failure analysis, taking advantage of artifacts that were produced at the time the system was designed and establishing a set of rules to formalize the placement of registration instructions within the source code. authors in [21] proposed the novel beehive system, which identifies potential security threats for a large volume of logs by unsupervised collecting of specific data features, then manually categorizing outliers. source-code-based analysis has been used to extract a log key. but it is ineffective because the source code is often unavailable or incomplete to access. meanwhile, most modern systems incorporate open-source software components written by hundreds of developers. for example, authors in [13] proposed a general methodology for log analysis based on source code analysis to discover largescale system issues by extracting log events from console logs. authors in [1] proposed an automated approach for log analysis to extract log keys directly from the source code and then produce an ordered list of all possible event occurrences. also, several data-driven approaches have been proposed, which have the advantage that they do not require domain expertise and can learn patterns from log data and automatically generate shared registry key templates. for example, in [22] a new clustering algorithm (slct) that analyzes the log file using frequent pattern mining was presented, which helps discover frequent patterns and identify anomalous lines in log files. authors in [16] presented a novel algorithm called iplom (duplicate partition log mining) to extract the log keys from event logs. it performs a 3-step hierarchical partitioning process of the log using unique log message properties. authors in [17] proposed a technique for log analysis to detect anomalies. it first preprocesses the data using empirical rules and then performs hierarchical clustering of log messages using weighted edit distance, and finally, log keys are created from the resulting clusters. but although the overall accuracy of these log parsing approaches is high, they are not effective in datasets whose logs are growing at a large scale (for example, 100 million record messages), as these approaches fail to complete in a reasonable time (e.g. 1 hour), and most of them can’t handle such data on a single computer. more recently, authors in [3] proposed a log parsing method through the parallelization on spark called pop. pop handles logs with simple domain knowledge. then, it uses iterative partitioning rules to divide the logs hierarchically into different groups. then, the static parts are extracted to create the event log. finally, similar groups are combined using hierarchical clustering to create the log keys. it is a basic system for processing large-scale data using the parallelization power of computer clusters. pop was implemented on top of spark and used rdd abstraction. rdd cannot modify the system to work more efficiently and uses sequencing and garbage collection techniques, increasing the load on the system’s memory and thus slowing the execution of operations. looking at the issues of the existing research, we suggest a new method to extract the log key. this method is based on a data-driven approach to analyze the execution log, which was built on top of spark and used the df abstraction. df abstraction is characterized by its efficiency in analyzing files with high accuracy without the knowledge of the program, as well as its high speed in analyzing files of any size. we used hashcode and equals method to find similarities between messages to ensure accuracy and speed instead of using the iterative partitioning used in [3], which consists of more than one steps, increasing execution time while it is not accurate enough. we used an intelligent agent that does this process and we called it the prepossessing agent. a comparison between the reviewed papers is illustrated in table i. iii. methodology a log message usually records a run-time behavior of the program, including events, state change, and interactions between components. it often contains two types of information: a free-form text string that is used to describe the semantic meaning of a recorded program behavior and a parameter that is used to express some important characteristics of the current task. engineering, technology & applied science research vol. 13, no. 4, 2023, 11130-11138 11132 www.etasr.com bin lashram et al.: hclpars: α new hierarchical clustering log parsing method table i. summary of the existing researches for log key extraction ref. approach data-driven approach use of spark abstraction [19] rule-based no [21] rule-based no [13] sourcecode-based no [1] sourcecode-based no [21] data-driven frequent pattern mining no [16] data-driven iterative partitioning no [17] data-driven hierarchical clusterin no [3] data-driven iterative partitioning + hierarchical clustering yes rdd hclpars data-driven hierarchical clustering yes df in general, due to the various parameter values, the number of different types of log messages is massive or even infinite. thus, the dimension problem of the direct consideration of log messages as a whole during log data mining may be troublesome. to resolve this problem, we replace every log message with its corresponding log key to perform analysis. a log key is defined as the common content of all log messages which are printed in the source code by the same log-print statement. the parameters are defined as a variable value printed by the log-print statement. in other terms, without any parameters, a log key equals the free-form text string of the log-print statement. for example, the key log message 1 and 3 is "info dfs.datanode$packetresponder: packetresponder x for block x terminating" (shown in figure 2). we analyze logs based on log keys for the following reasons:  different log-print statements often output different log text messages. each specific log-print statement in the source code corresponds to a specific type of log key. so, a sequence of log keys will reveal the system’s execution path and this will help us predict failures during implementation by identifying the normal execution path of the system.  the number of key log message types is limited and much less than the number of raw log message types. it can help us avoid the dimension issue while extracting and analyzing data. it also provides a simplified view of all the events that occurred while the system was running for administrators. fig. 2. example 1 of raw log message and key log message. the difficulty here is in identifying the log keys because we do not know which log messages are printed by the same statement print or the location of the parameters in the log messages. generally, the log messages printed by the different log-print statements are often completely different, while the messages printed by the same statements are completely similar to each other. according to this observation, we can use clustering techniques to group the log messages printed by the same statement together and then find their common part as the log key. parameters can cause some clustering mistakes because some of the different log messages contain a lot of matching parameter values, for example, raw log messages 1 and 2 have many similar parameters (shown in figure 3). so, the prepossessing agent will remove the parameter values first, according to acquired knowledge, to avoid errors. then, it groups the similar raw log messages and finds the common parts in each group to get the log keys. a. erasing parameters via acquired knowledge the parameters are mostly in the form of numbers, ip addresses, uris, or follow special symbols like the colon or the equal sign. they are often included in parentheses or square brackets. it is easy to classify such content. therefore, simple regular expression rules are often used to recognize and remove these parameters [23], for example, removing block id in figure 3 by "blk [-?[0-9]]+". for parameter removal (ip addresses, numbers, etc.) we used gained knowledge from previous research to define the types of parameters for each dataset (shown in the second block in figure 5). fig. 3. example 2 of raw log message and key log message. b. removing the duplicate raw log key in this step, the prepossessing agent is partitioning the raw log keys into groups, so we need to find a proper metric to find the similarity between the raw log keys. we found that the hashcode and equals method is the best metric for finding the similarity between raw log keys, because most programmers tend to write log keys firstly, and add the parameters afterward. fig. 4. four log messages from the hdf dataset. so, the log keys printed in the source code by the same logprint statement have the same hashcode. based on this observation, the prepossessing agent is generating a hash code for all raw log messages. then it puts the raw log messages that have the same hash code in the same group by using the equals method to find matches between them. after selecting all the matching raw log messages, the agent removes the duplicate results in each group, and it gets the log keys, while their number is limited. examples of log keys are shown in the third block in figure 5. engineering, technology & applied science research vol. 13, no. 4, 2023, 11130-11138 11133 www.etasr.com bin lashram et al.: hclpars: α new hierarchical clustering log parsing method fig. 5. step of extracting log keys. c. merge groups by log key each log key contains the component (server), log event, and message and most groups contain log keys that share the same component and log event but differ in the message. for example, figure 4 contains 4 log messages from the hdfs dataset. the four log keys that contain the same component are dfs.datanode$dataxceiver, and the same log event is writeblock, but differ in the message. to improve parsing accuracy, the prepossessing agent clusters similar groups based on the component and their log events, through several steps. 1. the first step is to generate a regular expression that will be used to separate the log by using the whitespaces (ws) shared between all log keys in all groups as separators. algorithm 1 provides the pseudo-code of generating regular expressions. the prepossessing agent considers every log key from the previous step as a sentence and stores them as a list of sentences (line 1). the number of ws in each log key (sentence) is calculated, and the results are added into the lengthlogkeys list (lines 6-13). then it finds the smallest common number of ws from lengthlogkeys list (line 14). for example, the third block in figure 5 contains 5 log messages from the hdfs dataset. these 5 log keys contain a different number of ws (6, 3, 4), whereas the smallest common number of ws is 3. the last step is generating a regular expression, where it replaces the number of ws from the previous step with the symbol ("\s"), for example, if the smallest common number of ws is 3, then the regular expression will be: ([ˆ\s] +\s) ([ˆ\s] +\s) ([ˆ\s] +. *). finally, the regular expression is returned (line 16). 2. the second step is to use a regular expression from step 1 to separate all the log keys in groups. in this step, every log key is transformed from sentence to columns, to find the common parts between the log keys in all groups. the fourth block of figure 5 provides some examples of separated log keys. algorithm 1: pseudo code for generating a regular expression input: a list of log keys from step b (logkeysl) output: regular expression for common space between all log keys 1: listlogkeys  logkeysl 2: lengthlogkeys  => list() (initialize with empty list) 3: regex  null => (initialize with empty string) 4: smallestl  null => (initialize with empty integer) 5: llog  null => (initialize with empty integer) 6: curlog  first log in listlogkeys 7: while (curlog has white-space) = true do 8: llog  compute a white-space in curlog 9: add llog to lengthlogkeys 10: remove curlog from listlogkeys 11: curlog  next log in listlogkeys 12: until listlogkeys is empty 13: end while 14: smallestl  find smallest length in lengthlogkeys 15: regex generation of regular expression 16: return regex 3. in the final step, the prepossessing agent uses hierarchical clustering [22-25] to cluster similar groups based on components and their log events. the groups in the same cluster will be merged. this step assumes that if logs from different groups have the same component and log event type, then the texts of the component and the log events engineering, technology & applied science research vol. 13, no. 4, 2023, 11130-11138 11134 www.etasr.com bin lashram et al.: hclpars: α new hierarchical clustering log parsing method that generated from these groups will be similar, so the the hamming distance [25] is calculated between the texts (component and log event) of two logs to assess the similarity between them. ����� ��, � �� � 0 � � � 1 ��ℎ������ (1) where a is the value of the component in the first log and b is the value of the component in the other log. if a and b are equal, it returns 0, otherwise 1. for example, we have 3 components, the first is "dfs.datanode$dataxceiver:", the second is "dfs.fsdataset:", and the third is "dfs.datanode$dataxceiver:". we calculated the hamming distance between these and found that the first and the third are classified in the same group because they are exactly equal in value. we used the hamming distance because it is a very practical metric for measuring the similarity and difference between data strings. besides, the hamming distance is intuitive, which makes parameter adjusting easier. after the above steps, we obtained the log key set (shown in the fifth block in figure 5) from the training log messages in the training log files. the first part refers to the event (e1) and the second part refers to the message (1). with this step, we were able to know each component of the system, what events are issued by it, and what message types are issued for each event. so, this step provides the administrators with an overview of the system and what messages are issued from it. iv. implementation the prepossessing agent uses spark to make a large-scale analysis of records efficient [22, 26]. spark is a platform for quickly processing data on a large scale and can also distribute data processing tasks across multiple computers, either alone or in conjunction with other distributed computing tools. apache spark offers three data abstractions: rdd, df, and ds. in hclpars, we use the df api for several reasons: first, the df resolves performance and measurement limitations that occur while using the rdd. second, it uses input optimization engines, for exemplify, catalyst optimizer, to process data efficiently. we can use the same engine for all java, python, r, and scala dataframe api. third, it provides a schematic view of the data, meaning that the data has some meaning when it is stored, and this serves to provide a simplified view of the data for the administrators. fourthly, df optimally manages memory, it stores data outside the heap but still inside ram (outside the main java heap), which in turn reduces garbage collection overload, while rdd stores data in memory (inside the main java heap). lastly, it is characterized by flexibility and scalability. it supports various formats of data and can be combined with many other big data tools. in our case, a df can represent execution traces, where each message in execution traces is a row. each step of the hclpars requires specific tasks that are executed on every message. to speed up these tasks and execute them with high accuracy, we invoke spark df specially designed operations to work in parallel. figure 6 illustrates the implementation of the prepossessing agent on spark. the numbered arrows represent the interactions between the spark cluster and the main program, where the main program works at spark driver, which is responsible for allocating spark tasks to workers in the spark cluster [27]. for the spark application, in step 1, the prepossessing agent uses sqlcontext.read.text() to read the text file (e.g. hdfs execution traces), converts every message or line into a single row at a single string column called value (df), and loads the df to the spark cluster (arrow 1). then, it uses withcolumn() to preprocess all log messages (erasing parameters) (arrow 2). after preprocessing, it caches the preprocessed log messages as schema in off-heap memory and returns a df as the reference (arrow 3). in step 2, it uses distinct() to drop duplicate rows (in the column) from the df (arrow 4) and return them (arrow 5). in step 3, it generates regular expressions for all log messages (arrows 6, 7) as described above. then, the driver program separates the column (value) into many columns based on the regular expression from the previous step and adds them into new df (arrows 8, 9). when all the columns are separated, it runs hierarchical clustering on them, and then it uses groupby() to merge log message (row) based on the clustering result (arrow 10). finally, the merged df (log keys) are outputted as a csv file by use coalesce(1).write() (arrow 11). fig. 6. extracting log key steps. v. data collection and evaluation in this section, we present the data sets that were used in the evaluation process and the evaluation methodology. the performance of hclpars is evaluated in terms of its accuracy, efficiency, and effectiveness and the results are compared with those of existing log parsers. a. data collection the loghub dataset [6] were used during the training and test phases. loghub is a large collection of logs from 16 realworld systems, including operating systems, mobile phone systems, distributed systems, supercomputers, standalone software, and server applications. all these logs are over 77 gb in size and contain 440 million log messages. table ii provides a summary of the dataset. the columns are marked with the symbol (#), as in [29]. b. evaluation the parameters of the log parsers are fine-tuned through over 8 runs and the best results are reported to avoid the randomization bias. engineering, technology & applied science research vol. 13, no. 4, 2023, 11130-11138 11135 www.etasr.com bin lashram et al.: hclpars: α new hierarchical clustering log parsing method 1) evaluation measures accuracy, robustness, and efficiency were considered for the evaluation of the results [29].  accuracy is a measure of the ability of a log parser to distinguish between fixed and variable parts. therefore, we define the accuracy metric of parsing as the ratio of properly parsed log messages to the total number of log messages. a log message is parsed correctly if its event template matches one of the previously extracted log message templates.  robustness of a log parser is measured by the extent of its ability to work continuously within different datasets or different sizes with the same efficiency.  efficiency is measured by the amount of time it takes the parser to parse the data. τhe less time spent, the higher the efficiency. table ii. summary of the loghub dataset dataset # description # log size # templates (total) # hdfs hadoop distributed file system log 11,175,629 30 spark spark job log 33,236,604 456 hadoop hadoop mapreduce job log 394,308 298 zookeeper zookeeper service log 74,380 95 openstack openstack software log 207,820 51 linux linux system log 25,567 488 mac mac os log 117,283 2,214 thunderbird thunderbird supercomputer log 211,212,192 4,040 bgl blue gene/l supercomputer log 4,747,963 619 hpc high performance cluster log 433,489 104 apache apache server error log 56,481 44 openssh openssh server log 655,146 62 proxifier proxifier software log 21,329 9 android android framework log 30,348,042 76,923 health app health app log 253,395 220 2) evaluation procedure to evaluate hclpars, we compared it with 14 log parsers by using 16 standard datasets. the log parser parameters were finely tuned through more than 8 runs, and the best results were recorded. vi. results a. accuracy in this part, we evaluate the accuracy of hclpars, and compare it with the accuracy of 14 existing log parsers. to make the comparison fair, we performed accuracy experiments on subsets of the original log datasets, each containing 2,000 log messages. table iii presents the accuracy results of the log parsers evaluated in 16 log datasets. each column indicates the accuracy for 1 log parser across the datasets, helping define its robustness across different log types. each row represents the accuracy of the parsing for different log parsers in a single dataset. for ease of observation, we marked the accuracy values greater than 0.9 in boldface, and highlighted the best accuracy with an asterisk (*). we can observe that most of the datasets were parsed accurately (more than 90%) by at least 2 log parsers. totally, 12 out of the 15 log parsers provide the best accuracy on at least 3 log datasets. to measure the overall effectiveness of the log parsers, we calculated the average accuracy of each log parser across different datasets, as shown in the last row of table iii. we can observe that hclpars is the most accurate on average with a score of 0.9605, achieving high accuracy (over 0.9) in 12 out of 16 datasets. it was followed by pop, which achieved high accuracy in 10 datasets. fig. 7. accuracy distribution of the log parsers in different types of logs. b. robustness robustness is an important measure of the practical use of a log parser. in this part, we evaluate the robustness of hclpars and compare it with the existing log parsers from 2 aspects: across different types and sizes of logs. figure 7 (boxplot diagram) indicates the accuracy distribution of each log parser across the 16 log datasets. for each box, the highest point of the vertical line corresponds to the maximum accuracy values, while the lowest point corresponds to the minimum accuracy values. in figure 7, from left to right, the log parsers are arranged in ascending order of average accuracy. it can be noted that hclpars has the highest average accuracy. this means that it can efficiently parse different types of log data, as its minimum accuracy is 0.889. additionally, we evaluated the robustness of hclpars on different log sizes. we sampled 40 original real-world datasets, such as hdfs, bgl, spark, hadoop, zookeeper, open-stack, hpc, and proxifier (table iii). hdfs, spark, hadoop, zookeeper, openstack are log files from distributed systems, while hdfs, bgl, hpc, zookeeper, and proxifier were used in [17, 20]. for log dataset, we changed the size based on its total size. for example, hdfs has a total size of 1.47 gb. we changed its size to 300 kb, 1 mb, 10 mb, 100 mb, and 1 gb, successively. table iv shows the number of raw log messages in the datasets. each row presents 5 sample datasets created from a real dataset. we chose the log parsers that achieved high accuracy in more than 4 log datasets, i.e. ael, iplom, lenma, molfi, spell, drain, and pop and compared them with hclpars. engineering, technology & applied science research vol. 13, no. 4, 2023, 11130-11138 11136 www.etasr.com bin lashram et al.: hclpars: α new hierarchical clustering log parsing method fig. 8. log parser accuracy on dataset log size. figure 8 shows the results of the parsing accuracy on different log dataset volumes. note that some lines are incomplete in the figure because some parsers, such as molfi and lenma, cannot finish the parsing in a reasonable period (4 hours). the results show that pop works continuously in most cases except for the 0.24 drop in openstack, while the rest of the log parsers have clear drops in accuracy or clear fluctuations with increasing data volume in most datasets (except for hdfs, zookeeper, and spark). the experimental results of hclpars are shown in table iv and figure 8. note that the accuracy of hclpars is very consistent for all datasets. the accuracy on hdfs and spark is 1 for all 5 samples. for bgl and hadoop, the fluctuation of the accuracy is 0.001 at most. for proxifier and zookeeper, the fluctuation of the accuracy is 0.02 at most. when compared to the other parsers, hclpars is the only to obtain consistently high accuracy in all datasets. c. efficiency efficiency is an important aspect to consider when parsing log data. to evaluate the efficiency of the log parser, we record the runtime it takes to complete the entire parsing process. like previous experiment settings, we evaluate the runtime of log parsers on 40 sampled datasets from original real-world datasets. the results can be seen in figure 9. it is obvious that the size of the log is directly proportional to runtime, i.e. parsing time increases with log size. it is also obvious that the efficiency of the log parser depends on the number of event templates. the simpler the log data, containing a limited number of templates, the easier the parsing process. the efficiency of the log parser is shown when there are many log templates. drain and iplom have better efficiency, which scales linearly with log size. pop has better efficiency with large data. ael and spell do not scale well with many event templates. lenma and molfi do not scale well with large data. fig. 9. running time of log parsers on dataset log size. for instance, bgl contains 619 event tem plates. pop can finish parsing within 5 min, while drain and iplom take 10 min. ael and spell take a long time to complete parsing (1 hour), while lenma and molfi cannot finish parsing 1 gb of bgl in 2, 4, or 6 hours, respectively. the experimental results of hclpars are also shown in table vi and figure 9. engineering, technology & applied science research vol. 13, no. 4, 2023, 11130-11138 11137 www.etasr.com bin lashram et al.: hclpars: α new hierarchical clustering log parsing method table iii. accuracy of log parsers across different log types dataset slct ael iplom lke lfa logsig shiso log cluster lenma log mine spell drain molfi pop hclpars best hdfs 0.455 0.978 1 * 0.998 0.875 0.800 0.978 0.546 0.998 0.851 1 * 0.997 0.998 1 * 1 * 1 hadoop 0.432 0.567 0.956 0.700 0.900 0.654 0.865 0.566 0.885 0.867 0.778 0.938 0.957 0.998 0.955 * 0.999 spark 0.685 0.905 0.920 0.634 0.994 0.544 0.920 0.795 0.887 0.576 0.905 0.920 0.418 0.999 1 * 1 zookeeper 0.726 0.921 0.992 * 0.578 0.839 0.700 0.660 0.789 0.841 0.688 0.964 0.967 0.839 0.990 0.987 0.992 openstack 0.867 0.758 0.871 0.787 0.200 0.200 0.722 0.696 0.743 0.743 0.764 0.733 0.213 0.880 0.900 * 0.900 bgl 0.573 0.758 0.939 0.128 0.854 0.227 0.711 0.835 0.69 0.723 0.787 0.963 0.960 0.990 0.996 * 0.996 hpc 0.839 0.900 0.800 0.574 0.817 0.354 0.325 0.788 0.830 0.784 0.654 0.887 0.824 0.950 1 * 1 thunderb 0.882 0.941 0.663 0.813 0.649 0.694 0.576 0.599 0.943 0.919 0.844 0.955 * 0.646 0.955 * 0.955 * 0.955 mac 0.558 0.764 0.673 0.366 0.555 0.478 0.595 0.604 0.698 0.872 0.757 0.787 0.636 0.889 * 0.889 * 0.889 windows 0.697 0.690 0.567 0.990 0.588 0.689 0.701 0.713 0.566 0.993 0.989 0.997 0.406 0.876 1 * 1 linux 0.297 0.673 0.672 0.519 0.279 0.169 0.701 0.629 0.701 0.612 0.605 0.690 0.284 0.701 0.894 * 0.894 android 0.882 0.682 0.712 0.909 0.616 0.548 0.585 0.798 0.880 0.504 0.919 * 0.911 0.788 0.876 0.919 * 0.919 healthapp 0.331 0.568 0.872 0.592 0.549 0.235 0.397 0.531 0.174 0.684 0.639 0.780 0.440 0.772 0.900 * 0.900 apache 0.731 1 * 1 * 1 * 1 * 0.582 1 * 0.709 0.999 1 * 1 * 0.998 1 * 1 * 1 * 1 openssh 0.521 0.538 0.802 0.426 0.501 0.373 0.619 0.426 0.925 0.431 0.554 0.788 0.500 0.998 0.999 * 0.999 proxifier 0.518 0.518 0.519 0.455 0.145 0.969 * 0.517 0.951 0.508 0.517 0.527 0.527 0.013 0.900 0.930 * 0.969 average 0.624 0.760 0.809 0.614 0.647 0.513 0.679 0.702 0.835 0.735 0.782 0.864 0.640 0.923 0.960 table iv. log size of sample datasets dataset sample 1 sample 2 sample 3 sample 4 sample 5 hdfs 300 kb 1 mb 10 mb 100 mb 1 gb bgl 400 kb 1 mb 10 mb 100 mb 500 mb spark 300 kb 1 mb 10 mb 100 mb 1 gb hadoop 600 kb 1 mb 10 mb 15 mb 20 mb zookeeper 4 kb 8 kb 16 kb 32 mb 64 kb openstack 600 kb 1 mb 10 mb 15 mb 20 mb hpc 600 kb 1 mb 10 mb 15 mb 20 mb proxifier 300 kb 600 kb 1200 kb 1800 kb 2400 kb table v. accuracy of hclpars on the sample datasets of table iii. dataset sample 1 sample 2 sample 3 sample 4 sample 5 hdfs 1 1 1 1 1 bgl 0.996 0.996 0.996 0.996 0.995 spark 1 1 1 1 1 hadoop 0.999 0.999 0.999 0.998 0.999 zookeeper 0.987 0.987 0.987 0.980 0.987 openstack 0.900 0.900 0.900 0.900 0.900 hpc 1 1 0.996 1 1 proxifier 0.93 0.93 0.91 0.91 0.93 table vi. running time of hclpars (sec) on sample datasets in table iii. dataset sample 1 sample 2 sample 3 sample 4 sample 5 hdfs 4.67 4 5 10 30 bgl 15.98 20.98 34.76 40.15 60 spark 8.403 18.7 20 44.67 50.89 hadoop 7 7.98 15 30.38 50 zookeeper 2.120 4.203 18.23 23.78 31.67 openstack 5.21 6 17.95 30 45 hpc 4.98 5.45 34 50 52 proxifier 3.09 7.56 10.45 12.33 10.94 obviously, the runtime that hclpars consumes is directly proportional to the log size, and the run time of hclpars does not exceed 1 minute for the largest dataset size (1 gb). compared to the other log parsers, hclpars conducts the fastest parsing, as it can parse large logs in a record time that does not exceed 1 minute. vii. conclusion this paper studied the automated parsing for large system event logs. initially, a comprehensive study was conducted on the existing log parsing methods and the way they work. based on the result, the automatic log parsing (hclpars) method using spark was proposed, which consists of three steps: removing parameter values according to acquired knowledge, grouping of raw log messages based on similarity, and finding the common parts in each group to get the log keys. many experiments were conducted on 16 sets of real-world data logs. the results from these experiments indicate that hclpars is very effective, as it works accurately and efficiently on all types of data logs, regardless of their size. in the future, we hope to test this method on more data logs. acknowledgement this work was funded by the university of jeddah, jeddah, saudi arabia, under grant no. 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[30] w. xu, "system problem detection by mining console logs," ph.d. dissertation, university of california, berkeley, ca, usa, 2010. engineering, technology & applied science research vol. 8, no. 4, 2018, 3149-3152 3149 www.etasr.com nelaturi & sarma: compact wideband microstrip patch antenna based on high impedance surface compact wideband microstrip patch antenna based on high impedance surface suman nelaturi department of electronics and communication engineering national institute of technology warangal warangal, india nelaturi.suman4@gmail.com n. v. s. n. sarma department of electronics and communication engineering national institute of technology warangal warangal, india sarma@nitw.ac.in abstract—a compact single probe feed asymmetrical semicircular fractal boundary patch antenna based on his (high impedance surface) is proposed for wide bandwidth at wi-fi band. circular polarization operation can be obtained by embedding semi-circle fractal curves along the edges of the square patch antenna. the 10-db return loss bandwidth is 15.13% (2.32ghz-2.70ghz). the 3-db axial ratio bandwidth is 4.11% (2.38ghz-2.48ghz). the close relationship between simulation results and measured results establishes the antenna usefulness. keywords-high impedance surface; circular polarization; semi circular fractal i. introduction a microstrip patch antenna (being compact, low profile, easy to manufacture and multifunctioning) is the most coveted candidate for modern day wireless communication applications. wideband antennas with circular polarization operation are mostly used in handheld device applications. orientation mismatch between receiver and transmitter can be avoided by using circularly polarized (cp) antennas. cp antennas are widely used in wlan, wi-fi and wimax applications. metamaterials are a good choice in designing novel antennas like compact wide band antennas because of their artificial electromagnetic properties [1-10, 12]. metamaterials are classified into single negative materials (sng) [1, 2, 9, 11], double negative materials (dng) [5-8], electromagnetic band gap materials (ebg) [13, 14] and chiral materials. ebgs are divided into mushroom ebg structures and via less ebg structures. fractals are the self-repetitive curves used to design compact antennas [15]. a compact microstrip antenna with dual-band operation having both unidirectional linear polarization and omni directional circular polarization properties based on epsilon negative materials is designed in [11]. dual band patch antenna with unidirectional circular polarization (cp) and omni directional cp based on ebg is designed in [14]. in this paper, a compact microstrip patch antenna on his with semi-circle fractal curves is designed and simulated in single frequency with good 10-db return loss bandwidth and 3-db axial ratio bandwidth. the impedance bandwidth of the proposed antenna is 15.13% (2.32ghz-2.70ghz). the 3-db axial ratio bandwidth is 4.11% (2.38ghz-2.48ghz). ansoft hfss (high frequency structure simulator) software tool was used to simulate the antenna. ii. antenna geometry the semi-circle fractal boundary patch antenna geometry is shown in figure 1 which is also printed on rogers rt/duroid with dielectric constant 2.2. the presented antenna has two substrates (bottom and top), on the top substrate the recommended antenna is designed and on the bottom substrate the his with a planar array of 3x3 fractal mushroom unit cells is printed. the circular polarization (cp) operation can be obtained by inserting semi-circle curves with if's rx and ry along x and y axes respectively. the 10-db return loss bandwidth and axial ratio bandwidth can be improved by optimizing if along each edge of the antenna. the optimized dimensions of the proposed antenna are given in table i. table i. parameter values parameter value in mm l1 38 l2 30 a1 8 a2 13 h1 1.6 h2 1.6 rx1=rx2=rx 2 ry1=ry2=ry 5 iii. semi-circle fractal curves and simulation results equal indentation radii (rx1=rx2=ry1=ry2) along the four sides of the square patch antenna result in linear polarization. circular polarization radiation can be obtained by loading different indentation radii along each side of the patch (rx1≠rx2≠ry1≠ry2) or (rx1=rx2=rx≠ry1=ry2=ry) or (rx1≠rx2≠ry1≠ry2). high bandwidth can be obtained when the indentation radii along the same axis are equal and at the same time are not equal along the perpendicular axis (rx1=rx2=rx≠ry1=ry2=ry). operation of the proposed antenna can be understood by considering an evolution of patch antenna design shown in figure 2. square patch ant1 on single substrate is chosen as reference which is resonating at 3.05ghz engineering, technology & applied science research vol. 8, no. 4, 2018, 3149-3152 3150 www.etasr.com nelaturi & sarma: compact wideband microstrip patch antenna based on high impedance surface with linear polarization. the semi-circle fractal curves with different indentation radii are inserted into ant1 to get antennas ant2 to ant11, which results in single band of operation with less 10-db return loss bandwidth and axial ratio bandwidth. the 10-db return loss characteristics of all simulated antennas on single substrate are shown in figure 3. the impedance bandwidth of each antenna is listed in table ii. l1 l2 patch mushroom co ax feedground h1 h2 (a) (b) ry2 ry1 rx1 rx2 (x,y) (c) fig. 1. (a) geometry of the proposed antenna (b) top view of the his (c) top view of the patch fig. 2. evaluation of the proposed antenna on single substrate fig. 3. simulated return loss characteristics of antennas ant1 -ant11 table ii. impedance bandwith of each antenna antenna irs (in mm) impedance bandwidth rx ry ant1 --(3.13-3.25) 3.76% ant2 1 2 (3.11-3.23) 3.78% ant3 1 3 (3.03-3.27) 7.61% ant4 2 3 (3.05-3.19) 4.56% ant5 1 4 (2.98-3.27) 9.29% ant6 2 4 (3.01-3.19) 5.80% ant7 3 4 (2.94-3.13) 6.27% ant8 1 5 (2.80-2.86) 2.12% ant9 2 5 (2.82-2.88) 2.10% ant10 3 5 (2.92-3.23) 10.26% ant11 4 5 (2.94-3.13) 6.27% to get widened impedance bandwidth with circular polarization at wi-fi band the same antenna is implemented on his (figure 4). his is made of planar array of 3x3 fractal mushroom unit cells. each unit cell has 8x8mm2 square patch and 0.5mm radius via where all unit cells connected to ground through vias. the semi-circle fractal curves are inserted into each square mushroom unit cell to make required his. finally ant20 is the proposed antenna with good wide bandwidth. the 10-db return loss characteristics of all simulated antennas on fractal mushroom his are shown in figure 5 and the impedance bandwidth of each antenna is listed in table iii. the simulated current distribution of the proposed antenna at 2.4ghz is shown in figure 6. the simulated radiation efficiency of the proposed antenna is shown in figure 7. the efficiency is good at 2.4ghz (98%). table iii. impedance bandwith of each antenna antenna irs (in mm) impedance bandwidth rx ry ant12 --(2.40-2.56) 6.45% ant13 1 2 (2.42-2.56) 5.60% ant14 1 3 (2.40-2.58) 7.22% ant15 2 3 (2.42-2.58) 6.45% ant16 1 4 (2.30-2.58) 11.47% ant17 2 4 (2.34-2.56) 8.90% ant18 3 4 (2.40-2.56) 6.45% ant19 1 5 (2.28-2.70) 16.86% ant20 2 5 (2.32-2.70) 15.13% ant21 3 5 (2.30-2.60) 12.24% ant22 4 5 (2.36-2.54) 7.34% engineering, technology & applied science research vol. 8, no. 4, 2018, 3149-3152 3151 www.etasr.com nelaturi & sarma: compact wideband microstrip patch antenna based on high impedance surface fig. 4. evaluation of the proposed antenna on his fig. 5. return loss characteristics of his antennas fig. 6. simulated current distribution of proposed antenna at 2.4ghz fig. 7. radiation efficiency of the proposed antenna iv. measured results and discussion the proposed antenna (ant20) is fabricated on rogers rt/duroid substrate (figure 8). fractal mushroom his and fractal patch antenna are individually fabricated. his is printed on bottom substrate and the patch antenna is placed on top substrate without ground. the vias are fabricated with the help of through hole copper plating technique. both substrates are attached with the help of paper tape. the dimensions of both substrates are 38x38x1.6mm3. the return loss characteristics are measured using agilent 8719a microwave network analyzer. radiation pattern measurements are taken in an anechoic chamber having physical dimensions 22.5x12.5x11.5m3. the operating frequency range of the anechoic chamber is 400mhz to 18ghz. the input power given to transmitter is -40dbm. (a) (b) fig. 8. photos of fabricated ant20: (a) top view (b) bottom view the measured return loss characteristics along with simulated data are given in figure 9. measured results are in close agreement with simulated results. the discontinuity at patch mode band indicates possibility of circular polarization radiation. the axial ratio characteristics are given in figure 10. while the impedance bandwidth is 15.13% (2.32ghz2.70ghz), 3-db axial ratio bandwidth is 4.11% (2.38ghz2.48ghz). the minimum axial ratio value of 0.5 db occurred at the center frequency. the radiation patterns of the proposed antenna are depicted in figure 11. the measured and simulated gains are given in figure 12. v. conclusion a compact single probe feed semi-circle fractal boundary microstrip patch antenna based on fractal mushroom his is proposed and studied experimentally for wide impedance and axial ratio bandwidths. the 10-db return loss bandwidth is engineering, technology & applied science research vol. 8, no. 4, 2018, 3149-3152 3152 www.etasr.com nelaturi & sarma: compact wideband microstrip patch antenna based on high impedance surface 15.13%. the 3-db axial ratio bandwidth is 4.11%. the proposed antenna covers wlan (2.4ghz) band. fig. 9. simulated and measured return loss characteristics of ant20 fig. 10. simulated and measured axial ratio characteristics of ant20 (a) (b) fig. 11. simulated and measured radiation patterns at 2.4 ghz (a) e plane (b) h plane fig. 12. simulated and measured gain of the proposed antenna references [1] g. v. eleftheriades, k. g. balmain, negative-refraction metamaterials: fundamental principles and applications, john wiley & sons, 2005 [2] c. caloz, t. itoh, electromagnetic metamaterials: transmission line theory and microwave applications, john wiley & sons, 2005 [3] a. sanada, m. kimura, i. awai, c. caloz, t. itoh, “a planar zerothorder resonator antenna using a left-handed transmission line”, 34th european microwave conference, amsterdam, netherlands, october 12-14, 2004 [4] d. sievenpiper, l. zhang, r .f. j. broas, n. g. alexopolous, e. yablonovitch, “high-impedance electromagnetic surfaces with a forbidden frequency band”, ieee transactions on microwave theory and techniques, vol. 47, no. 11, pp. 2059-2074, 1999 [5] a. lai, t. itoh, c. caloz, “composite right/left-handed transmission line metamaterials”, ieee microwave magazine, vol. 5, no. 3, pp. 34-50, 2004 [6] c. j. lee, k. m. k. h. leong, t. itoh, “composite right/left-handed transmission line based compact resonant antennas for rf module integration”, ieee transactions on antennas and propagation, vol. 54, no. 8, pp. 2283-2291, 2006 [7] y. dong, h. toyao, t. itoh, “compact circularly-polarized patch antenna loaded with metamaterial structures”, ieee transactions on antennas and propagation, vol. 59, no. 11, pp. 4329-4333, 2011 [8] k. saurav, d. sarkar, k. v. srivastava, “dual-polarized dual-band patch antenna loaded with modified mushroom unit cell”, ieee antennas and wireless propagation letters, vol. 13, pp.1357-1360, 2014 [9] j. h. park, y. h. ryu, j. g. lee, j. h. lee, “epsilon negative zerothorder resonator antenna”, ieee transactions on antennas and propagation, vol. 55, no. 12, pp. 3710-3712, 2007 [10] h. tang, x. zhao, “center‐fed circular epsilon‐negative zeroth‐order resonator antenna”, microwave and optical technology letters, vol. 51, no.10, pp. 2423-2428, 2009 [11] w. q. cao, “compact dual-band dual-mode circular patch antenna with broadband unidirectional linearly polarised and omnidirectional circularly polarised characteristics”, iet microwaves, antennas & propagation, vol. 10, no. 2, pp. 223-229, 2016 [12] w. q. cao, a. j. liu, b. n. zhang, t. b. yu, d. s. guo, y. wei, z. p. qian, “multi-band multi-mode microstrip circular patch antenna loaded with metamaterial structures”, journal of electromagnetic waves and applications, vol. 26, no. 7, pp. 923-931, 2012 [13] w. q. cao, a. liu, b. zhang, t. yu, z. qian, “dual-band spiral patchslot antenna with omnidirectional cp and unidirectional cp properties”, ieee transactions on antennas and propagation, vol. 61, no. 4, pp. 2286-2289, 2013 [14] j. kamiya, k. shirota, t. yagi, t.nakazawa, “study of ebg structures using metamaterial technology”, oki technical review, no. 219, pp. 1-4, 2012 [15] v. v. reddy, n. v. s. n. sarma, “compact circularly polarized asymmetrical fractal boundary microstrip antenna for wireless applications”, ieee antennas and wireless propagation letters, vol. 13, pp. 118-121, 2014 microsoft word 15-3742-ok_etasr_v10_n5_pp6231-6236 engineering, technology & applied science research vol. 10, no. 5, 2020, 6231-6236 6231 www.etasr.com danikas et al.: dealing with the size effect in insulating liquids. a volume effect, an area effect or … dealing with the size effect in insulating liquids. a volume effect, an area effect or even a particle effect? a concise review michael g. danikas democritus university of thrace, school of engineering, department of electrical and computer engineering, power systems laboratory, xanthi, greece george e. vardakis democritus university of thrace, school of engineering, department of electrical and computer engineering, power systems laboratory, xanthi, greece ramanujam sarathi indian institute of technology madras, department of electrical engineering, high voltage laboratory, chennai, india sayidul morsalin university of new south wales, school of electrical engineering and telecommunications, high voltage laboratory, sydney, australia abstract-insulating liquids play an important role as insulating media in various high voltage applications and infrastructure installations. the dielectric strength of an insulating liquid depends on the experimental conditions (in case of laboratory testing) and/or the service conditions (in case of apparatuses in service). one of the main factors affecting the dielectric strength of insulating liquids is the so-called size effect, i.e. the effect of the size of the electrodes, of the size of the liquid volume under stress and of the gap spacing between the electrodes. all the aforementioned parameters are investigated in the context of the present short review. keywords-insulating liquids; liquid dielectrics; transformer oil; dielectric strength; volume effect; gap effect; area effect i. introduction for several decades the mechanism of electric breakdown in insulating liquids has been a subject of great interest [1-3]. although a considerable amount of data has been obtained and promising hypotheses on the mechanism of breakdown have been published, results often indicate serious inconsistencies and this fact has prevented the adoption of a universally accepted theory capable of explaining the workings of electric breakdown in these liquids [1-2]. comprehensive reviews on breakdown of insulating liquids were published some years ago [4, 5]. it is generally agreed that electrical breakdown in liquids is statistical in nature and the dielectric strength depends on pressure, temperature, field geometry, electrode area, liquid volume, gap spacing, voltage waveform, electrode material and finish, additives and impurities, past history, time and magnitude of pre-stress. it is the purpose of this short review to investigate the dielectric strength of insulating liquids with reference to the socalled size effects, i.e. the effects the gap spacing, the electrode area and the oil volume under stress. it is understandable that the terms “dielectric strength” and “breakdown strength” in the context of the present paper are used interchangeably. it is also understandable that since transformer oil played a predominant role in high voltage engineering applications in the past several decades, a particular emphasis is given on this specific liquid. ii. size effects the existence of a size effect for insulating liquids is accepted by the researchers although there is no agreement whether this should be a volume effect or an area effect. either can occur depending on the test conditions. the weak links presumably have a statistical distribution of magnitude and number, as noted in [6]. according to the weak link theory, an increase in the size of the specimen results in increased probability of a large weak link being present in the test gap and a corresponding reduction in dielectric strength. the weak links are in the liquid bulk or on the surface of the electrodes; which particular link causes breakdown will depend on its magnitude and the experimental conditions. if a weak link present in the liquid bulk initiates breakdown a volume effect should result. if a weak link present on the electrode surface initiates breakdown, an area effect should result. as was pointed out in [6], whether the size effect is area or volume dependent is determined by the relative quality of the insulating liquid compared with that of the electrode surfaces and the time of application of stress. iii. gap effect many researchers reported a decrease in breakdown strength as the electrode separation increases [1]. a definite tendency for the dielectric strength to increase for smaller gap corresponding author: michael g. danikas engineering, technology & applied science research vol. 10, no. 5, 2020, 6231-6236 6232 www.etasr.com danikas et al.: dealing with the size effect in insulating liquids. a volume effect, an area effect or … spacings using spherical electrodes was reported in [7]. the authors of [7], however, did not find a similar phenomenon for larger gaps. they suggested that electrons are supplied to the liquid by emission from the cathode but breakdown will occur only if the number of electrons is adequately multiplied by an ionization process in the bulk of the liquid. spherical electrodes were also used in [8], where it was suggested that a surprisingly large increase in dielectric strength was noted as the gap was reduced. the author of [8] suggested that the small gaps restrict cumulative ionization. a dependence of the dielectric strength on gap spacing was reported in [9]. furthermore, it was reported a dependence of the breakdown strength on gap for various electrode configurations using n-hexane [10]. in yet another research paper, the dependence of dielectric strength and breakdown voltage on gap was investigated [11]. similar to [9], a relationship was found to exist between the dielectric strength and the gap spacing in [11]. it was suggested that the dependence of dielectric strength on gap length arises from a collision ionization process [11]. another approach was proposed in [12], where the authors, investigating the electrical breakdown for long gaps and nonuniform geometries, concluded that electrical breakdown initiation using ac and dc voltages is governed to a large extent by impurities in the oil or on the electrode surfaces. in [13], a strong dependence of the breakdown voltage on gap spacing was indicated and it was remarked that for small gap lengths the electrode surface pretreatment is of additional importance [13]. in [14], an effort was made to explain the relationship between the breakdown conduction current and the gap length suggesting that longer gaps would be capable of providing more positive ions. these ions would drift to the cathode thereby forming a positive space charge thus enhancing electron emission and they would also increase the probability of liquid dissociation by energetic electrons and the subsequent bubbler formation. authors of [15] and of [6], working independently, proposed that the breakdown voltages versus oil gaps between electrodes, line up on a straight line in a log scale paper and they postulated that the relation between breakdown voltage and gap can be expressed by a simple equation, v=k·d n (1) where v is the breakdown voltage, k a constant, d the gap length and n takes values between 0 and 1. moreover, it was reported that for ac ramp voltages, the gap effect is stronger than the area effect suggesting that a simple volume effect should not be expected. iv. area effect an older study indicated a considerable increase in dielectric strength when used electrodes of smaller diameter were used [16]. before that, the importance and influence of the electrode area effect was recognized in [17]. in [18], the idea that the area effect is due to the inherent variability in dielectric strength was proposed. a formula was established in [19-20], in which the modal dielectric strength was related to the electrode area, based on extreme value statistics, v1–v2=[s·loge(a2/a1)]/σν (2) where v is the modal dielectric strength, a the area, s the standard deviation of n measured breakdowns and σn the function of the number of n breakdowns only (it is true that, conventionally, voltages are symbolized by v and dielectric strengths by e. in (2), however, we strictly followed the symbols of [19, 20]). equation (2) was verified by the authors for impulse and 60 hz voltages under carefully controlled conditions. in [19, 20] it was indicated that any difference, which may exist in the breakdown mechanism between impulse and 60 hz tests, does not change the predicted area effect. the above proposed model was influenced by the “weak link” theory developed in [21], where it was pointed out that the “weakest link” concept, when applicable, may be the key to the occurrence of certain observed relationships between the strength of specimens and their size. in yet another publication [22], it was shown that from a statistical point of view, the effect of selecting the lowest breakdown from two tests on a given specimen is equivalent to a hypothetical test on twice the specimen, providing that enough measurements are taken for the full statistical meaning of the test. in [6], it was shown that a certain decrease in breakdown strength was observed when the electrode area was increased for both impulse and ac testing. however, the data of [6] show a reduction in standard deviation with increasing area, which is in disagreement with what is predicted by the extreme value theory (the latter requires that the standard deviation remains constant). in [23], 12 pairs of spheres in parallel under oil were used, in order to investigate the statistical nature of the area effect. the authors of [23] showed that the distribution of the breakdown voltages of a random sample arbitrarily chosen from the parent population, is a gaussian distribution, which is in contrast to the findings of [19, 20]. both research groups established, however, the existence of the “minima of groups area effect,” which states that if from a total of n breakdowns (the stressed area of the test object being q), only the p lowest breakdown voltages from p groups, each of q breakdown values, are considered, where n=p·q, the effect is the same as that of p readings taken on another test object with a stressed area of q·q. in general agreement with the above, publication [4] remarked that if there is a distribution in the sizes of the asperities on the electrode surface and the most prominent of these initiates breakdown, then an increase in the area of the electrodes will lead to a greater probability of breakdown. the consequence of the area effect is that the modal values of breakdown strength as observed with flat electrodes having different areas, but at a constant gap, would decrease approximately with the logarithm of the area. as was remarked in the same publication, the electrode pretreatment affects the breakdown strength of a given oil sample. roughening of either the cathode or the anode or both affects the strength and also the area effect, because it increases the number of preferential sites from which breakdown can be initiated by electron emission. v. volume effect a volume effect results if the weak links exist in the liquid itself. it was reported that the primary factor determining the unit dielectric strength of commercial oil of controlled quality engineering, technology & applied science research vol. 10, no. 5, 2020, 6231-6236 6233 www.etasr.com danikas et al.: dealing with the size effect in insulating liquids. a volume effect, an area effect or … for electrodes of different geometries is the volume of that oil under stress [8]. in the same publication, the stressed volume was defined as the volume enclosed by the 90% equigradient surface. another researcher [24], testing a range of electrode areas and gaps in pure oil found that the 50 hz ac strength was a function of the stressed volume. for a gap range of 1 to 4 mm and electrode areas 10 -1 to 10 3 cm 2 , the mean breakdown strength associated with ‘v’ ccs of oil could be expressed as e(v)=e1–k·log10 (v) (3) where e(v) is the mean breakdown strength, e1 is the value for 1 cc and k = 25 kv/cm (rms). it was reported [25], that a volume effect for both ac and impulse voltages is possible. it the aforementioned publication, the stressed volume was defined as in [8]. the distribution function was shown to be gaussian although the data could be plotted equally well on extreme value probability paper. the ac breakdown strength of the oil was also found to be affected by the level of particle contamination. in [15], it was reported that the oil breakdown could be described by its stressed oil volume in a wide range from 10 -2 to 10 5 cm 3 . it was also pointed out that oil breakdown probability, gaussian or extreme value distribution, might be affected by the test conditions. according to [15], larger volumes of oil give larger standard deviation and their distribution function approaches more closely the extreme value distribution. in [26], it was shown that the experimental results were more consistent with a volume theory rather than with a simple area effect for both impulse and ac voltages. in the same publication, however, it was pointed out that the adoption of the stressed volume as the dominant factor affecting the breakdown does not imply that breakdown is uninfluenced by the nature of the electrode surface. in [6], although it was indicated that for impulse voltages a simple volume effect exists since the area and gap effects were approximately equal, for ac voltages the dielectric strength dependence on gap spacing was much greater than on area. therefore, a simple volume effect was not observed. vi. some further remarks on the size effects researching further the question of size effects on transformer oil, it was reported that for rather small areas (up to 20 cm 2 ), the breakdown strength decrease with increasing electrode area was at first 70 kv/cm/decade, while it falls at about 35 kv/cm/decade for areas in the range of 30 to 1000 cm 2 and it almost disappears for electrode areas larger than 1000 cm 2 [27]. a non-linear relationship exists between the breakdown strength and the logarithm of the electrode area. this is due to the fact that transformer oil breakdown strength has a minimum value and a leveling off the line relating the strength with the area should be expected. a similar downward trend was observed in [15]. the average change of approximately 35 kv/cm/decade noted in [27] was also in agreement with data reported earlier in [6]. in [27] it was also pointed out that the breakdown strength reduces with increasing the gap spacing. it was further remarked that, up to an electrode area of 1240 cm 2 , the gap effect was approximately 80 kv/cm/decade. the gap spacing effect is a complex phenomenon. the breakdown voltage increase is somewhat less proportional to the gap length for uniform electrode arrangements [27]. this is in agreement with earlier research data [13]. an increase of the gap can also increase the population of impurities entering the gap, which might act as nucleation sites and subsequently reduce the breakdown strength, as was suggested in [14, 28]. in [29], it was reported that the charge of a particle in contact with an electrode is proportional to gap voltage and not to the local electric field, a conclusion not unjustified in the light of the work done in [27]. the effect of gap spacing on breakdown strength is complicated since there are many influencing factors, such as physical size factors (for example, flushing action is better for larger gaps but the higher voltage level produces more decomposition products at breakdown) and weak links existing in the oil volume and/or on the electrode surfaces. if a simple volume effect exists (i.e. a volume effect which can be fully traced to the gap effect and the area effect), area and gap effects should be equal. however, it is realized that the gap effect seems to be stronger than the area effect, suggesting thus that a simple volume effect should not be expected [27]. an increase of specimen size leads inevitably to the introduction of imperfections which may vary from those of molecular dimensions up to gross defects arising from inclusions [30]. the question, however, as to whether a size effect can be attributed to a volume effect or to an area effect seems to be open since in [31] it was reported that dielectric degradation can be attributed to either the electrode area or the stressed oil volume. vii. later research on size effects the cleanliness of electrodes is of paramount importance since clean electrodes restrict the sites from which streamers can emanate [32]. besides the cleanliness of the electrodes, other factors such as the rate of voltage rise play a role in determining the variance in the time to breakdown, when impulse voltages are applied [32]. initiation sites from the electrodes, in quasi-uniform arrangements, play a dominant role in determining discharge initiation in mineral oil of technical purity [33]. however, as the electrode radius becomes larger, the volume effect gains in importance [33]. this is somehow contradicted in [34], where particular attention was paid to the electrode surface since the probability density function of streamer inception on a small element of electrode area depends on local electric field. such a function, described as µ(ε), depends on the electrode radius for hemispherical electrodes. it is to be noted, however, that in the same publication [34], it is also remarked that in the case of narrow gaps, the effective area of hemispherical electrodes is proportional to the product of the radius of electrode to the gap length, leaving thus some room for further discussion as to the possibility of a volume effect. in [35], it is implied tacitly that a volume effect is at work since the effect of the shape of the electrodes is not considered stronger than the effect of gap length. it must be pointed out that in [35] different electrode geometries were used, such as sphere-sphere, plane-plane, mushroom-mushroom and sphereplane. the conclusions of [35] are not fundamentally at engineering, technology & applied science research vol. 10, no. 5, 2020, 6231-6236 6234 www.etasr.com danikas et al.: dealing with the size effect in insulating liquids. a volume effect, an area effect or … variance with those of [29]. in [36], an emphasis was put on the electrode configuration, remarking that when the flux lines are more uniformly distributed higher breakdown voltages are expected. it was reported that electrode arrangements such as rogowski-plane or sphere-plane should be preferred to arrangements such as rod-plane [36]. no indication was given however, as to a clear area or volume effect with the tested arrangements. although [37] did not tackle the problems of either area or volume effect, it pointed out that the type of the statistical distribution of breakdown voltage values in transformer oil testing depends on whether the oil is of poor quality (in this case a positively skewed distribution results), of relatively good quality (when we are likely to have a negatively skewed distribution) or of moderate quality (when it is expected a more or less normal distribution). it is tacitly implied that such quality variations may also have an effect on whether an area effect or a volume effect will appear. reference [37] is in agreement with an earlier publication [38], where it was remarked that larger volumes and larger areas increase the probability to find larger elongated particles in the vicinity of the electrodes and thus to facilitate streamer initiation. reference [38] tends to support the view that a particle effect seems to be more probable than a pure area or volume effect. the views expressed in [38] were already expressed in earlier publications [39], where the possibility that the observed decrease in breakdown voltage with an increase in particle count may be related more to the presence of large particles at the higher particle concentrations than to the higher concentration itself. it must, however, be remarked that the approach of [38] was more elaborate than the one in [39]. emphasis on the role of foreign particles was also given in [40] and it was remarked that the measured ac breakdown voltage of an insulating liquid mostly represents its quality rather than its characteristics. relatively recently, there was a report on size effects [41], where the authors used an old idea proposed in [8], by using the notion of the 90% equigradient surface (which in [41] is named effective electrode area aeff). the conclusions of [41] were that the breakdown strength e can be expressed both as a function of the effective electrode area aeff as well as a function of the gap length. although no clear proposal as to a pure area effect or a volume effect was formulated, one of the points made was that the effective electrode area is equivalent to the pit area, i.e. the electrode area affected by the activity of discharges. viii. some further comments it is true that most of the research on area effect and volume effect was carried out not in the most recent decades. testing larger and smaller electrode areas as well as larger and smaller oil volumes was of interest more in earlier times than it is nowadays. the advent of modern techniques, such as the schlieren technique, shifted the interest of the researchers from the macroscopic investigations to the microscopic level and more to the mechanism and the dynamics of breakdown in insulating liquids [5, 42-46]. the size effects were investigated thereafter in conjunction with these or similar techniques [34]. as the years passed by, there were also other ways to approach the questions concerning the transformer oil insulation [47]. there was, so to speak, a shift in research interests to the more fundamentals of insulating liquid breakdown. it is also true that, from the experience of past decades with various insulating liquids and, in particular, with transformer oil, evidently the electrode surface quality as well as the liquid quality determine to a significant extent whether there may be an area or a volume effect. this is not, however, to imply that the questions regarding the size effects in insulting liquids have all been answered. new insulating liquids require further work w.r.t. the size effects, such as liquids in very low temperatures [48-50] as well as the nanofluids [51-53], not to forget challenging alternatives to transformer oil, such as silicone fluids [54] and vegetable oils [55]. publications [56, 57] refer to a variety of possibilities regarding new promising insulating liquids and one can easily draw the conclusion that there is a lot more research to be done w.r.t. the size effects. furthermore, such size effects must also be investigated in conjunction with the new proposed insulating liquids with solid insulation [30, 58]. furthermore, since transformer oil is subjected to repetitive pulse stresses in some applications, it would be interesting to investigate the size effects also in relation to such pulse stresses [59]. in the aforementioned case, it is of interest to see whether foreign particles may play a role as suggested before [38] with 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[59] a. pokryvailo and c. carp, “comparison of the dielectric strength of transformer oil under dc and repetitive multimillisecond pulses,” ieee electrical insulation magazine, vol. 28, no. 3. pp. 40-49, 2012. microsoft word etasr_v11_n3_pp7273-7278 engineering, technology & applied science research vol. 11, no. 3, 2021, 7273-7278 7273 www.etasr.com anwer et al.: attack detection in iot using machine learning attack detection in iot using machine learning maryam anwer department of computer science & it ned university of engineer and technology karachi, pakistan maryam.anwer2@gmail.com muhammad umer farooq department of computer science & it ned university of engineer and technology karachi, pakistan umer@neduet.edu.pk shariq mahmood khan department of computer science & it ned university of engineer and technology karachi, pakistan shariq@neduet.edu.pk waseemullah department of computer science & it ned university of engineer and technology karachi, pakistan waseemu@neduet.edu.pk abstract-many researchers have examined the risks imposed by the internet of things (iot) devices on big companies and smart towns. due to the high adoption of iot, their character, inherent mobility, and standardization limitations, smart mechanisms, capable of automatically detecting suspicious movement on iot devices connected to the local networks are needed. with the increase of iot devices connected through internet, the capacity of web traffic increased. due to this change, attack detection through common methods and old data processing techniques is now obsolete. detection of attacks in iot and detecting malicious traffic in the early stages is a very challenging problem due to the increase in the size of network traffic. in this paper, a framework is recommended for the detection of malicious network traffic. the framework uses three popular classification-based malicious network traffic detection methods, namely support vector machine (svm), gradient boosted decision trees (gbdt), and random forest (rf), with rf supervised machine learning algorithm achieving far better accuracy (85.34%). the dataset nsl kdd was used in the recommended framework and the performances in terms of training, predicting time, specificity, and accuracy were compared. keywords-cyber security; artificial intelligence; iot; machine learning i. introduction the internet of things (iot) is probably the greatest modern advancement, considering its effect on our daily life, while the zones of its utilization are quickly expanding. in 2018, the quantity of iot devices was roughly 28 billion. this amount is expected to touch 49.1 billion by 2022 and the showcase size of iot is estimated to reach around $10 trillion by 2022. iot is recognized as a method regarding suitable mechanisms that interconnect by servers, sensors, and various software. a city structure, is shown in figure 1 which comprises of three main layers: fog, cloud, and terminal layer. the data obtained from the iot are saved on the cloud computing (cc) ecosystem which has progressively high-level processors and sufficient memory. the cloud layer has grown fast by the modern developments in iot. fog-to-things is created with a feasible clarification of those difficulties. in the fog layer, devices can experience some larger values of data basically given to the cloud layer, which decreases power damage, bandwidth, network traffic, and eliminates the data storage and communication challenges. in addition, it tries to accelerate the estimated method near the endpoint, facilitating some fast reply to the iot-based urban use. there are two advantages of attack detection in the fog-to-things layer. either the internet service provider or the network administrator can practice certain measures which can stop extensive destruction if these network attacks are recognized in the fog layer. besides, this strategy does not prevent the regular daily experience for the people. fig. 1. framework of a smart iot-based city. the model traces the web traffic which passes by every fog-to-things node. as fog-to-things connections resemble iot devices, it will be more efficient to recognize these network attacks at the fog-to-things connections rather than at the cloud corresponding author: shariq mahmood khan engineering, technology & applied science research vol. 11, no. 3, 2021, 7273-7278 7274 www.etasr.com anwer et al.: attack detection in iot using machine learning layer. immediate attack detection can inform the network controllers of the iot devices of those attacks, which will then support them to evaluate and improve their systems. artificial intelligence technology like machine learning (ml) will do the whole evaluation and send video pictures to people who can react speedily to solve troubles and maintain residents’ safety. there are two types of attack detection: primarily signature-based or primarily anomaly-based. in the former, a primarily based solution fits the in-coming traffic closer to acknowledge attack/crime kinds in database whilst the latter checks the behavior of everyday traffic. ii. related work many research studies in the application of ml have presently been presented in the domain, like object identification/recognition, pattern recognition, text processing, and image processing. in addition, much security research had been done using the deep learning (dl) approach [1]. authors in [2] describe the expansion of big data and the evolution of iot in a smart city. the author in [3] explains the evolution of cc and how big data have been engaged in the advancement of smart cities. he proposed a framework for managing big data for smart city purposes. the framework concentrates on difficulties related to smart cities for real-time decision planning. many aspects and components of a smart city for upgrading the standard of the people are described in [4]. authors in [5] suggest a platform design to secure a smart city facing cyber attackers. the structure is giving a warning dl model to identify attackers based on the user's data performance. in [6], resource administration methods of fogcomputing are analyzed, well-systematic research in taxonomy is presented, and various features of resource administration, i.e. mass balancing, resource/device scheduling and allocation, job/task allocation, device/resource provisioning, and task offloading, are highlighted. the given resource management procedures are analyzed by estimating factors such as: qos metrics, different researches, and applied methods. the benefits and hindrances of these approaches are compared. authors in [7] used the idea of an unknown and secure total plan (asas) in mist-based open distributed computing. in asas, the cloud gives advanced information about open cloud servers. when the asas is used, the fog gives devices to exchange information with pcs. authors in [8] reported the advancements of remote sensor organization (wsn), correspondence innovation, and iot innovation. authors in [9] used ml techniques such as knn, svm, dt, naïve bayes, neural networks, and rf which can be applied in ids. the authors compared ml models for multi and binary class combinations on the data set of bot-iot. depending on these models they calculated the f1 score, recall, precision, and accuracy. the detection of attacks in fog design was examined in [10], in which ml is compared with deep-learning neural networks working on an internet-available dataset. authors in [11] examined tcp syn network attacks and authors in [12] introduced deep neural networks for attack detection in iot systems. the self-adaptive identification method of the security index of the network was studied, performed risk assessment was conducted, and the system was mapped. authors in [13] developed network nids based on the conception of dl. for attack detection, they implemented network intrusion detection system on fog node. authors in [14] used a novel method that combines isolation forest and one class support vector machine (ocsvm) with an active learning method to detect attacks with no prior information. authors in [15] used a two-stage approach combining a fast preprocessing or filtering method with a variation auto encoder using reconstruction probability. authors in [16] performed a distributed denial of service (ddos) attack using the ping of death technique and detected it using rf algorithm by using the weka tool with classification accuracy of 99.76%. authors in [17] proposed the detection of network dictionary attacks using a data set collected as flows based on a clustered graph. the results of the mentioned methods on the caida 2007 data set give high accuracy for the model. iii. gap analysis these are some prefaced problems taken from earlier research. • worst performance of the detection of attacks on the fog layer. • feature selection decreasing the accuracy. • low accuracy of dos, r2l, and u2r attack types. • execution of multiple classifier algorithms on reduced data sets • false positive rate and false negatives rate is still in doubt. iv. a framework to solve attack detection in iot using machine learning the proposed model for this research work is an ordinary huge organization or a smart city going through an increasing variety of iot-associated cyber threats, such as heavyobligation ddos attacks, achieved with an enormous botnet, e.g. mirai, which exploit default or weak passwords. the current research specializes in advanced attacks which can be primarily based on violations of organizational protection guidelines. once completed, an attacker is permitted to take advantage of individuals who connect unauthorized styles of iot devices to the smart town. the previous approaches have been used broadly because of their excessive detection accuracy and low fake alarms. however, they lack the capability of seizing novel attacks. on the other hand, anomaly detection detects new attacks, although it lacks accuracy. in both procedures, classical ml analysis has been used prominently. popular devices gaining knowledge of algorithms are incapable to detect complex data breaches [18]. in this research, we examined different algorithms for the different sub-processes of the framework shown in figure 2 [19]. a. approaches to solve attack detection using ml there are six main approaches in ml: • supervised learning: in this, the data should be labeled like feeding a model with multiple examples of files and decide whether they are malware or not. based on this data labeling [20], the model could decide on extra data. it is also called the task driven approach. engineering, technology & applied science research vol. 11, no. 3, 2021, 7273-7278 7275 www.etasr.com anwer et al.: attack detection in iot using machine learning • ensemble learning: it is an addition of label data like supervised learning while combining multiple models to solve the task. • unsupervised learning: in this learning, unlabeled data are used and the model marks them by itself based on the data properties. it is considered to be the more powerful and it usually finds anomalies in the data set [21]. this is also called the data-driven approach. • semi-super user learning: it tries to combine both supervised and unsupervised approaches when there is a data set with some labeled data [22]. • reinforcement learning: this behavior should be used in a changing environment. it is also called the environment driven approach [23]. • active learning: it works like a teacher who can help in correcting error and behavior in environmental changes [24]. it is a subclass of reinforcement learning. fig. 2. a framework to solve attack detection in iot using ml. b. attack detection using ml methods in this part, the attack detection problems are studied by statistical classification of measurements using the implementation of ml. the spam filter in cyber security separates spam from different communications services. spam is apparently the leading ml method applied in information security. the supervised learning labeled data method is usually used for classification. in our research, we used the gradient boosted dt, svm, and rf classifications and the results were compared. 1) support vector machine it is the most popular and widely recognized technique. it can be used for regression, but mostly it is used in classification algorithms. in svm, we sketch data items by the point in an ndimensional area where n represents the considered features [25]. it creates a hyper plane and separates the data into classes [26]. 2) gradient boosted decision tree gbdt is an ensemble of dts. gbdt is an ml algorithm which constructs vulnerable dts through the boosting technique. for building the tree ensemble, we need to train over the algorithms on different samples. unfortunately, we cannot train them on a single set. gbdt uses the present-day ensemble to predict the label of every instance, after which the results are compared with the accurate labeled data. it works on large datasets and has high predicting power [27]. 3) random forest rf [28] is based on random subspace, bagging, and uses cart dts as base algorithm. it works on both regression and classification. the education is achieved in parallel. it injects randomness within the learning (testing and training), a process in which each tree isn't the same with the others. in predictions, each tree is combined, which reduces the variance of prediction and hence improves performance [29]. v. experiments and results in this section, the dataset, which is applied for the experiment and for testing results, is described along with the performance metrics used for result comparison and the recommended model is reviewed by applying various selections and classifications. three ml algorithms were applied for the evaluation of the given proposed model [30]. a. dataset the nsl kdd dataset was used in this research. this dataset is available in csv and json files. we can use this for the model and the evaluation phase. the dataset is modifiable, extensible, and reproducible [31]. b. proposed method our research is a novel combination of several independent ml algorithms. in our framework, the first step is the dataset collection and analysis. in this process, the data were collected and observed deeply to analyze the types of data. in the data preprocessing step, the data were cleaned, visualized, and feature engineering was applied along with implemented vectorizations. hence, the data were converted into feature vectors [32]. after the analysis of the nsl-kdd dataset, the attacks can be categorized into four principal classes: • unauthorized to remote (r2l) • denial-of-service (dos) • unauthorized to root super user privileges (u2r attack) engineering, technology & applied science research vol. 11, no. 3, 2021, 7273-7278 7276 www.etasr.com anwer et al.: attack detection in iot using machine learning • port scanning attack (probe) the details of each attack are shown in figure 3. table i. train set of nsl-kdd type original records distinct records reduction rate attacks 3,925,640 262,178 93.3 normal 972,782 812,814 16.44 total 4,798,431 1,074,992 78.05 table ii. test set of nsl-kdd type original records distinct records reduction rate attacks 250,436 29,378 88.26 normal 60,591 47,911 20.92 total 311,027 77,289 75.15 fig. 3. attack categories of the iot ecosystem. our data is converted into feature vectors. the dataset is then split into 80% for training and 20% for testing sets (tables i-ii). for the learning algorithm, the training data set was utilized and our final model was deployed using a boosting technique. figure 4 shows the data distribution in testing and training subsets. fig. 4. nsl-kdd dataset distribution. c. algorithm the algorithmic steps are mentioned below. • load the nsl-kdd data set. • apply the pre-processing technique. • divide into 80-20 ratios of testing and training datasets. • select feature selection vectors. • the training dataset is given to the classifiers. • the test data set is fed to the three selected classifiers for classification. • calculate accuracy, specificity, fpr, and tpr. d. classifiers and training for the model training, rf supervised ml algorithm was selected. the algorithms which combine dt with ensemble learning have several advantages, such as their need of only a few input parameters and their resistance to overfitting. the number of tree parameters is set to be 500. when the number of branches increases, the variance would be decreased without ensuing in bias. rf has changed into applied to traffic data sets, which include in-network traffics misuse detection and command and control (c&c) iot attack detection from traffic flow-base [33]. e. performance metrics in the suggested framework, four performance metrics were considered: accuracy (a), training time (tt), which is the total time to train a classifier, specificity (s), and prediction time (pt), which is the total time which an algorithm takes to predict all the data. tp (true positive) represents the correct identification of an attack, fp (false positive) represents the incorrect identified attacks, tn (true negative) represents the correctly identified normal connections, and fn (false negative) represents the number of attacks that were not correctly identified [34]: accuracy = a true positive = θ false positive = ξ true negative = ω false negative = π accuracy shows how accurately the algorithm can detect the normal and attack connections: a θ ω θ ξ ω π + = + + + (1) specificity is used for measuring the negatives which are correctly identified: s ω ξ ω = + (2) roc gives a graphical representation that compiles the review of a classifier's overall thresholds on a diagnostic criterion. that is created on mapping the true positive rate (tpr) against the false positive rate (fpr) as the use of the engineering, technology & applied science research vol. 11, no. 3, 2021, 7273-7278 7277 www.etasr.com anwer et al.: attack detection in iot using machine learning threshold is different for selecting algorithms for a provided class: fpr ξ ξ ω = + (3) tpr θ ξ θ = + (4) a threshold is the expected value for all the predicted classes. the roc curve can be drawn using binary classes. the values of the tpr and fpr range from 0 to 1. f. experimental setup the experiments were conducted on a lenovo thinkpad system with ubuntu 20.04 operating system, 4500u processor, 8gb memory, integrated amd (attached nvidia) graphic card which was used for training the dataset. during data preprocessing, cleaning, and feature selection, numpy and pandas libraries were used. g. result analysis as mentioned above, three ml algorithms were applied to the nsl-kdd dataset, namely rf, gdbt, and svm. from the cross-validation, rf has performed best in terms of testing and training accuracy. the results show that the rf obtained the highest accuracy on fog layer which is 85.34%. the obtained accuracy of svm and gdbt was 32.38% and 78.01% respectively, as shown in table iii. in terms of specificity, gdbt algorithm performed best with 97.02%. the specificity achieved by svm and rf was 2.02% and 95.09% respectively. table iii shows the result of the performance evaluation of the mentioned algorithms including a, tt, pt, and s. table iii. result analysis table method a s tt pt svm, rf 32.38 2.02 10.87 1.056 gdbt 78.01 97.02 7.78 1.6 rf 85.34 95.09 6.10 1.345 vi. conclusion through the obtained results, it can be confirmed that supervised ml can be used to analyze traffic data and accurately expose the data that are maliciously traveling over iot devices. to identify that traffic accurately, nsl kdd dataset is critically evaluated by making use of ml techniques. this dataset is used for the comparison of the given framework by employing functions such as selection and classification. overall, the rf algorithm provided the best accuracy of 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(fbsa)for the purpose of managing corruption risks threatening the iraqi construction sector. corruption in iraq is a widespread phenomenon that threatens to degrade society and halt the wheel of economic development, so it must be reduced through appropriate strategies. a total of eleven corruption risks have been identified by the involved parties in corruption and were analyzed by using probability and impact matrix and their priority has been ranked. bowtie analysis was conducted on four factors with high score risk in causing corruption in the planning stage. the number and effectiveness of the existing proactive measures to prevent threats from resulting in corruption and were examined for each threat. keywords-corruption risk; bowtie; prevention; risk analysis i. introduction corruption is an old phenomenon that threatens the administrative apparatus in iraq. as it was stated in the reports of transparency international [1], iraq is third among 180 countries in corruption and the phenomenon is increasing. the phenomenon of corruption largely stands in the way of the process of construction and progress at all economic levels. it costs money, time, energy, and impedes the performance of responsibilities and the fulfillment of jobs and services. corruption can be defined as a social habit which is deeprooted in mankind's history. it is considered to be comparable to other crime types, which occur likely in the procurement of works through local authorities along with the complexity to monitor the expenditures of a project [2]. authors in [3] provided a thorough overview of the corruption causes from certain studies in identified construction management journals for addressing the already-indicated issues. forty-four corruption causes were indicated from a total of 37 publications and were examined with regard to current corruption factors, thematic categorizations of observed variables, and yearly trends of publications. the major causes were bad professionalism, ethical standards, close relationships, bad working and industrial conditions, insufficient sanctions, and bad role models. authors in [4] identified factors which lead to fraudulent practices in every stage of the construction life cycle. those extracted fraudulent aspects have been mapped into a matrix form for checking the factor's similarities. a total of 42 contributing factors were verified and divided into 5 phases of the construction project life-cycle. with regard to the frequency, the main factors with regard to each stage were project approvals in the stage of planning, collusions between public officers and tenderers in the stage of design and tendering, insufficient compliances with the design for audit and report in the stage of construction, avoiding difficulties in the contract inspections in the stage of finishing, and utilizing sub-standard materials and services in the stage of maintenance. ii. literature review corruption is one of the biggest problems the governments face and it stands as an obstacle to sustainable development. most projects in iraq have suffered high deviations in cost, time, and quality which lead to wasting public money through exploiting public officers or authorities to achieve personal benefits that destroy the country's economy. authors in [5] proposed a model for the performance and application control of rational decision-making with the best use of available resources and ongoing performance monitoring at all stages of the implementation of projects in order to eliminate aspects of financial and administrative corruption and reduce wastage in one of the most important formations carried out by the government in iraq. authors in [6] developed an artificial neural network (ann) model for assessing the collusion risks in the construction projects in china. the ann has been utilized in a real life metro project, while the evaluated results established a complete framework regarding the collusive practices in the construction projects in china, that includes a total of 20 collusive practices associated with all the contracting entities. authors in [7] presented the critical risk factors for design-build projects in the construction industry in vietnam, factors affecting the on schedule implementation completion. the top 3 critical risk factors were: delays in project approval and licensing, interest rate fluctuations, and design or technical specifications deficiency and changes. authors in [8] stated time overrun in construction projects is a very dangerous issue in developed countries. a quantitative corresponding author: semaa hazim najim alani engineering, technology & applied science research vol. 11, no. 3, 2021, 7223-7227 7224 www.etasr.com alani & mahjoob: corruption risk analysis at the project planning stage in the iraqi construction … approach was adopted to present the main causes of time overrun in the construction projects in pakistan and the riw (relative importance weight) approach was used for collecting data. the precise beginnings of the bowtie method are unclear [9], but it probably was originated in the 1970s via the imperial chemical industries (ici). the first company integrating bowties totally in business practices is the royal dutch/shell group. now, the use of bowties has been spread between nations, industries, and companies. authors in [10] indicated that the bowtie analysis is a qualitative risk-assessment methodology providing an approach of efficient communication in complicated risk situations in simple graphical formats that shows the relations between damage escalation potential and the unwanted events' causes. iii. methodology the methodology that will be used in this paper is as follows: • identification of the corruption risks during the conception (planning) stage, which actually occurred in some completed construction projects by reviewing the quarterly reports of the fbsa of projects from 2004-2013 and after some interviews with construction industry experts. • distribution of a prepared questionnaire on the fbsa staff in order to determine the probability and the effect of such risks. • implementing qualitative risk analysis on the corruption risks by using a probability impact matrix to identify the priority of these risks. • application of bowtie methodology on these risks (threats). iv. risk rating a. risk probability for each of the risk occurrences, the probability must be set at a single value which is representing the best team judgment from the provided available data. in addition, the team must not be considering the effect while assessing the probability. the probability values and terms utilized in a 5-point scale to suit the likelihood of getting the risk can be seen in table i [11]. other classifications can be used according to what suits a project. table i. risk probability term value risk probability (%) (1) very high 0.9 > 70 (2) high 0.7 50-70 (3) moderate 0.5 30-50 (4) low 0.3 10-30 (5) very low 0.1 0-10 b. risk impact the risk impact is measuring the consequences on the project when a risk occurs. a scale that is comparable to the one of risk probabilities should be set up with regard to risk impact (table ii [12]). table ii. risk impact term value (1) very high 0.8 (2) high 0.4 (3) moderate 0.2 (4) low 0.1 (5) very low 0.05 c. probability and impact matrix a probability and impact matrix has been utilized for looking up a combined risk rating, also referred to as the risk score, with regard to specific combinations related to probability and impact values. in addition, the score was utilized for prioritizing the risks for later activities of risk management. a graphical probability and impact matrix is efficiently communicating the relative severity regarding risk scores. the module is addressing the details regarding evaluating the risks and impacts, along with the way for applying such measures. furthermore, a measure regarding the risk effect might be evaluated via multiplying risk probability (p) by risk impact (i) for producing risk score (rs) with regard to each one of the risks. rs=p×i (1) in the heat map of figure 1, the resulting high risks are colored red, the moderate risks yellow, and the low risks green [12]. fig. 1. probability and impact matrix (heat map). d. the questionnaire a questionnaire survey has been carried out for obtaining perception-based data related to corruption measurement items from 2 viewpoints, which are (1) probability (the occurrence possibility regarding each one of the measurement items), and (2) severity (the consequence's impact regarding each one of the measurement items), with the use of a 5-point likert scale from 1 for very high to 5 for very low. about 60 questionnaire forms about corruption risk were distributed by hand to resident engineer's offices of fbsa projects in iraq. twenty two answered forms were not considered because they were partially answered and 8 were not received. a total of 30 answered questionnaires were considered. the responders belong to senior management staff, having 8 to 40 years of engineering, technology & applied science research vol. 11, no. 3, 2021, 7223-7227 7225 www.etasr.com alani & mahjoob: corruption risk analysis at the project planning stage in the iraqi construction … experience. table iii shows some details about the questionnaire responders whose responses were considered in this study. e. responders characteristics summary table iii shows the experience of the respondents, table iv their level of education, and table v the scientific areas of their education. table iii. respondents' experience no. experience (years) frequency % 1 8-14 8 27 2 15-18 15 50 3 20-22 3 10 4 36-40 4 13 total 30 100% table iv. respondents' level of education no. level of education frequency % 1 b.sc. 18 60 2 diploma 1 3 3 m.sc. 7 23 4 ph.d. 2 7 5 cpa 2 7 total 30 100% table v. respondents' scientific areas no. area frequency % 1 civil engineering 15 50 2 mechanical engineering 4 13.33 3 electrical engineering 2 6.67 4 architecture engineering 1 3.33 5 law 5 16.67 6 control and auditing 2 6.67 7 accounting 1 3.33 total 30 100 v. results the areas of risk concern at the stage of planning came from project documents and are provided in table vi and figure 2. we can see that the cr3 (the estimated cost of the project compared to the building area was exaggerated) is ranked at the first place with a risk score of 0.4196, which makes it a high risk rating. this result is in contrast with the findings in [15]. the second ranked risk is cr2 (there is a lack of a careful study of the estimated cost of the project within the feasibility study report), scoring 0.3067, which also makes it a high risk which leads to inaccurate cost estimations of the project. this result is in line with the findings of [14]. the third risk cr6 (there is no ownership of the land on which the project is located, and some lands were transgressed) scored 0.1956, which is also a high risk rating, in line with the findings in [2]. the fourth risk is cr1 (there is no technical and economic feasibility study to the project) that scored 0.182, which is a high risk rating, and is one of the requirements for approving the financial allocations for the implementation of any project. this result is in contradiction to article (a-3) of the instructions for implementation of governmental contracts no. 1 in 2008 [13] and is line with the findings of [15]. table vi. corruption risks rating in the planning stage id involved parties corruption risk risk score risk rating rank cr1 client no technical and economic feasibility study to the project. 0.182 high 4 cr2 client there is a lack of a careful study of the estimated cost of the project within the feasibility study report. 0.3067 high 2 cr3 client the estimated cost of the project compared to the building area is exaggerated. 0.4196 high 1 cr4 client the technical and economic feasibility study has not been sent out to the ministry of planning for the purpose of obtaining approval to include the project in the investment budget table. 0.0472 low 9 cr5 client there is no holistic vision in the department about the project requirements to be translated and escalated according to a careful planning process into engineering plans. 0.1469 moderate 7 cr6 client there is no ownership of the land on which the project is located, and some lands were transgressed 0.1956 high 3 cr7 client the work is divided into several contracts and a feasibility study is prepared with an estimated cost for each contract, even though the project was included in the ministry’s plan according to one feasibility study and one holistic cost. 0.176 moderate 5 cr8 client a technical study has not been prepared about the contracting party’s ability to provide the necessary staff. 0.0261 low 11 cr9 client, consultant soil was investigated for the project long before the work was carried out. this leads to geological changes to the site's soil, and this causes these investigations mismatch the reality of the project. 0.1493 moderate 6 cr10 client project planning that requires a true contemplation and practical forecasting is poor. 0.0496 low 8 cr11 client the project in the investment budget is included before specifying estimated and total costs of the project that was later completed. 0.0271 low 10 the fifth risk is cr7 (the work is divided into several contracts and a feasibility study is prepared with an estimated cost for each contract, even though the project was included in engineering, technology & applied science research vol. 11, no. 3, 2021, 7223-7227 7226 www.etasr.com alani & mahjoob: corruption risk analysis at the project planning stage in the iraqi construction … the ministry’s plan according to one feasibility study and one holistic cost) that scored 0.176 which is a moderate risk rating. this result is in line with the findings in [2]. the sixth risk is cr9 (soil was investigated for the project long before the work was carried out), scoring 0.1493 which is a moderate risk rating. this result is in line with the findings in [2]. the seventh risk is cr5 (there is no holistic vision in the department about the project requirements to be translated and escalated according to a careful planning process into engineering plans) that scored 0.1469 which is a moderate risk rating. this result is in line with the findings in [15]. fig. 2. the risk score for the corruption risk in planning stage. the other risks have low risks ratings. cr10 (project planning that requires a true contemplation and practical forecasting is poor) scored 0.0496, cr4 (the technical and economic feasibility study has not been sent out to the ministry of planning for the purpose of obtaining approval to include the project in the investment budget table) scored 0.0472 in line with the findings in [2], cr11 (the project in the investment budget is included before specifying estimated and total costs of the project that was later completed-in contradiction to the instructions for implementation of governmental contracts (no. 1) in 2008 that stated that an updated study on the estimated cost or the required contract to be executed within the feasibility study for the purpose is to be used as a standard when analyzing bids and awarding contracts) scored 0.0271, and cr8 (a technical study has not been prepared about contracting party's ability to provide the necessary staff) scored 0.0261. vi. application of bowtie xp on the corruption risk after identifying the probability and impact (consequence) for each risk, the corruption risks in the planning stage of construction project were ranked. it was adopted that the risks with low and moderate rating can usually be managed using routine procedures, and the bowtie xp software [16] was applied on the risks with high rating. in a bowtie, the representation is that a threat (on diagram's left hand side) causes the top event (hazard release), which results in a consequence (harm to someone of something). we than have the opportunity to put in preventive barriers on diagram's left hand side to prevent the hazards, and barriers on diagram's right hand side to mitigate the harm from occurring. practical recommendations for combating or eliminating the identified hazards were led via applying bowtie methodology, which leads to excellent understanding regarding the hazard protection and prevention needed for corruption risks in the sector construction. the causal factors that were used in bowtie xp to manage corruption risks threatening the construction sector in the planning stage were identified by a multidisciplinary team in the fbsa as the prevention barrier, effectiveness, and barrier type for each causal factor (threat), and corrective barrier, effectiveness, and barrier type for each consequence as shown in figure 3. to the best of our knowledge, the current research is the first one that uses the application of bowtie methodology with corruption risk in the construction sector. fig. 3. bowtie diagram of corruption risks in the planning stage . engineering, technology & applied science research vol. 11, no. 3, 2021, 7223-7227 7227 www.etasr.com alani & mahjoob: corruption risk analysis at the project planning stage in the iraqi construction … vii. conclusion the bowtie methodology is considered to have high flexibility regarding corruption risk management. at the same time, its adaptability might be improved by the use of some adequate tools. on the basis of the system approach, bowtie methodology helps auditors and managers responsible for creating the project plan with the necessary requirements from the estimation cost of the project, offering a technical and economic feasibility study. the conception of threats, consequences, and barriers in the bowtie diagrams facilitate the comprehension regarding the protection and prevention actions needed for corruption risks. typically, the bowtie has the ability to be vital in managing the corruption risks that we can process before they appear by taking proactive actions for these threats. the bowtie methodology was used to demonstrate the effectiveness of corruption risk management in construction projects in iraq. the use of bowtie software assists in the analysis and management of hazard and risks in any sector. it provides reports and documents all information that will be used in risk management and supports the audits in the government institutions. viii. risk management recommendations a set of recommendations regarding risk management for corruption-related risks follows: • a study combining bowtie methodology and simulation model should be conducted. • there is a need to identify the corruption risks in other stages of the construction sector and appropriate quantitative risk analysis should be conducted. • the application of the bowtie methodology should be expanded in other sectors such as the 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[6] m. shan, y. le, k. t. w. yiu, a. p. c. chan, y. hu, and y. zhou, "assessing collusion risks in managing construction projects using artificial neural network," technological and economic development of economy, vol. 24, no. 5, pp. 2003–2025, oct. 2018, https://doi.org/ 10.3846/20294913.2017.1303648. [7] p. t. nguyen and p. c. nguyen, "risk management in engineering and construction: a case study in design-build projects in vietnam," engineering, technology & applied science research, vol. 10, no. 1, pp. 5237–5241, feb. 2020, https://doi.org/10.48084/etasr.3286. [8] f. a. soomro, m. j. memon, a. f. chandio, s. sohu, and r. soomro, "causes of time overrun in construction of building projects in pakistan," engineering, technology & applied science research, vol. 9, no. 1, pp. 3762–3764, feb. 2019, https://doi.org/10.48084/etasr.2449. [9] a. lidstone, "the use of bowties to aid the management of risk," 2017. [10] i. voicu, f. v. panaitescu, m. panaitescu, l. g. dumitrescu, and m. turof, "risk management with bowtie diagrams," iop conference series: materials science and engineering, vol. 400, p. 082021, sep. 2018, https://doi.org/10.1088/1757-899x/400/8/082021. [11] d. allen, risk management in business. cambridge, uk: cambridge university press, 1995. [12] pmbok® guide a guide to the project management body of knowledge, 6th ed. pmi (project management institute, 2107. [13] "ministry of planning government implementation instructions no. (1) for the year 2008." ministry of planning, 2008, [online]. available: https://mop.gov.iq/static/uploads/7/pdf/151012302174946107c03fdf610 a3ea1241cbc53a2--file1.pdf. [14] m. sohail and s. cavill, "accountability to prevent corruption in construction projects," journal of construction engineering and management, vol. 134, no. 9, pp. 729–738, sep. 2008, https://doi.org/ 10.1061/(asce)0733-9364(2008)134:9(729). 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[16] "bowtiexp virtual risk assessment," cge risk. https://www.cgerisk. com/products/bowtiexp/ (accessed may 08, 2021). engineering, technology & applied science research vol. 8, no. 2, 2018, 2724-2730 2724 www.etasr.com khairi et al.: a review of anomaly detection techniques and distributed denial of service (ddos) … a review of anomaly detection techniques and distributed denial of service (ddos) on software defined network (sdn) mutaz h. h. khairi university technology malaysia johor, malaysia taza1040@gmail.com sharifah h. s. ariffin university technology malaysia johor, malaysia sharifah@fke.utm.my n. m. abdul latiff university technology malaysia johor, malaysia muazzah@fke.utm.my a. s. abdullah university technology malaysia johor, malaysia shahidan@fke.utm.my m. k. hassan university technology malaysia johor, malaysia memo1023@gmail.com abstract—software defined network (sdn) is a network architecture in which the network traffic may be operated and managed dynamically according to user requirements and demands. issue of security is one of the big challenges of sdn because different attacks may affect performance and these attacks can be classified into different types. one of the famous attacks is distributed denial of service (ddos). sdn is a new networking approach that is introduced with the goal to simplify the network management by separating the data and control planes. however, the separation leads to the emergence of new types of distributed denial-of-service (ddos) attacks on sdn networks. the centralized role of the controller in sdn makes it a perfect target for the attackers. such attacks can easily bring down the entire network by bringing down the controller. this research explains ddos attacks and the anomaly detection as one of the famous detection techniques for intelligent networks. keywords-software defined networking; distributed denial of service; anomaly detection i. introduction the goal of software defined networking (sdn) is to enable cloud and network engineers and administrators to respond quickly to changing business requirements via a centralized control console. sdn encompasses multiple kinds of network technologies designed to make the network more flexible and agile to support the virtualized server and storage infrastructure of the modern data center. software defined networking was originally defined as an approach to designing, building, and managing networks that separate the network control (brains) and forwarding (muscle) planes enabling the network control to become directly programmable and the underlying infrastructure to be abstracted for applications and network services. sdn is an emerging architecture that is dynamic, manageable, cost-effective, and adaptable, making it ideal for the high-bandwidth, dynamic nature of today's applications. this architecture decouples the network control and forwarding functions enabling the network control to become directly programmable and the underlying infrastructure to be abstracted for applications and network services. sdn offers a virtualized execution platform that decouples the network control functions from the underlying traffic forwarding network [1] consisting of various network devices, e.g. switches, routers, access points, etc. it allows the execution of different network control functions as a logical centralized software based controller. the controller facilitates easy and on-demand dynamic configuration of the network and its resources. one of the objectives of sdn paradigm is to provide better flexibility and configuration control to the users which adapts with the network performance requirements [2]. anomaly detection (also outlier detection) is the identification of items, events or observations which do not conform to an expected pattern or other items in a dataset. typically the anomalous items will translate to some kind of problem such as bank fraud, a structural defect, medical problems or errors in a text. anomalies are also referred to as outliers, novelties, noise, deviations and exceptions.[3, 4]. a denial of service (dos) attack is defined as one attempt made by a malicious user to compromise the regular functioning of a network. ii. proposed problem definition a virtual network is a computer network which does not contain any physical link between two computational nodes. instead, they connect through virtual links. in recent years, the virtual network is managed by sdn. sdn is one of the most promising emerging network technologies. most of the companies configure their networks in sdn. it has been found important to understand the security issues that are being raised in any large scale development from any new technologies that engineering, technology & applied science research vol. 8, no. 2, 2018, 2724-2730 2725 www.etasr.com khairi et al.: a review of anomaly detection techniques and distributed denial of service (ddos) … have been raised in recent years. though the system acquires many benefits from sdn, the system has to do some work in security phase. this work confers four kinds of dos attacks that are specific to networks in the openflow (of) sdn in different layers[5]. iii. objectives of this paper  study and analysis of developments in the field of the networking and its application especially in sdn security area.  study and analysis of anomaly detection techniques and prediction of ddos attacks in sdn. iv. sdn evolution  sdn has evolved from several different research tracks, starting with research into active networks. although some of these tracks were unsuccessful, they were all motivated by the challenges faced by managing a growing internet and the desire to have more flexible and programmable networks.[6] a. active networks research into sdn was first motivated by the field of active networks. active networking provided an ability to embed computation into packets and network devices, allowing for the computation to occur inside the network as a packet traveled through it [6]. this system provided a sdn-like interface to programmers and allowed for interesting classes of applications, such as the ability to modify packet headers at different points in a packet's flow or implement common network functions, including firewalls or proxies, inside the network without the need for extra hardware. however, active networking introduced some fundamental challenges that proved to be difficult to solve [4]. the largest of these issues was a lack of a single clear motivation for deployment. although many applications for the technology could be described, none of them provided a compelling reason for system deployment [5]. without this reason, network operators had no incentive to deploy the extensive hardware upgrades that would have been required to support the system [6]. b. early sdn active networks, despite their limitations, represent a design that attempts to provide the flexibility that current sdn strategies strive for. learning from the motivational issues that prevented the adoption of active networks, researchers focused on narrower and more clearly defined problems, which led to a focus on a separation between the control plane and the data plane. this focus was prompted by the increase in traffic volumes as the internet grew in size, leading administrators to search for a new control interface for their networks. early technologies attempted different methods of creating a separation between control and data planes [4, 5]. however, many of these technologies proposed the use of standard apis for control of the data-plane, while leaving the operation of the data-plane essentially unchanged. these designs left little incentive for adoption by hardware vendors [5], as they would have allowed new competitors access to their products. new technologies were soon proposed that created clean-slate designs for centralized network control [7, 8]. such technologies allowed entirely new methods for control while still using existing protocols in the data-plane, such as ip, arp, tcp and others. in addition, these designs allowed easier deployment as they could be deployed alongside existing traditional networks. this included a full-scale deployment of an sdn system that supported end hosts and existing network devices unmodified, which provided clear example of a functioning system. these works proved to be the first attempts at sdn designs, and led to the design of the of protocol [7]. v. sdn architectural components sdn applications are programs that explicitly, directly, and programmatically communicate their network requirements and desired network behavior to the sdn controller via a northbound interface (nbi). in addition, they may consume an abstracted view of the network for their internal decision making purposes. an sdn application consists of one sdn application logic and one or more nbi drivers. sdn applications may themselves expose another layer of abstracted network control, thus offering one or more higher-level nbis through respective nbi agents. the sdn controller in sdn is the “brains” of the sdn network, relaying information to switches/routers ‘below’ (via southbound apis) and the applications and business logic ‘above’ (via northbound apis). recently, as organizations deploy more sdn networks, sdn controllers have been tasked with combining sdn controller domains, using common application interfaces like of and open virtual switch database (ovsdb). of is considered one of the first software defined networking (sdn) standards. it originally defined the communication protocol in sdn environments that enables the sdn controller to directly interact with the forwarding plane of network devices such as switches and routers, both physical and virtual (hypervisorbased), so it can better adapt to changing business requirements. the sdn datapath is a logical network device that exposes visibility and uncontested control over its advertised forwarding and data processing capabilities. the logical representation may encompass all or a subset of the physical substrate resources. an sdn datapath comprises a cdpi agent and a set of one or more traffic forwarding engines and zero or more traffic processing functions. these engines and functions may include simple forwarding between the datapath's external interfaces or internal traffic processing or termination functions. one or more sdn datapaths may be contained in a single (physical) network element—an integrated physical combination of communications resources, managed as a unit. an sdn datapath may also be defined across multiple physical network elements [2]. vi. concerns and issues related to sdn a. concerns related to open flow many of the recent works in sdn security research utilize or are concerned with the of protocol. in this section are presented three categories related to of security. the first of these is the research that attempts to solve the scalability and fault-tolerance issues that exist in of controller design. these engineering, technology & applied science research vol. 8, no. 2, 2018, 2724-2730 2726 www.etasr.com khairi et al.: a review of anomaly detection techniques and distributed denial of service (ddos) … issues are not directly motivated by security concerns, but are directly applicable as they improve the durability of the network under load, as may be seen during a dos attack. the second category is the research that directly addresses security vulnerabilities that exist in the of specification. the chief of these issues is the communication bottleneck between the data and control planes that can be easily be inundated with control traffic in many situations. the third category is the research that uses of to solve existing security vulnerabilities. due to the visibility of the network that is proved to the controller, applications are able to utilize the protocol to create networkwide policies that are more effective than what is available in traditional networks [8]. b. concerns related to controller controller is one of the most important elements in sdn architecture. the number of applications and the network size affect the number of controllers used, thus some sdn architecture have more than one controller, and in order to manage these controllers, one of them must be defined as main controller. the first generation controllers such as nox, beacon and floodlight provide low-level interfaces. as a result, multiple tasks may not be executed simultaneously as only a single set of rules is installed in the switches [9]. even in nox, each flow request is processed individually, thereby making it difficult to process multiple tasks concurrently. controllers such as maestro, having multitasking capabilities, should be used: for accomplishing multiple tasks independent modules are used in a network. but the separation of these modules is not possible as packet-handling rules installed/uninstalled by one module mostly overlap rules with the rules in other module.[10] vii. security related threats in sdn the ability to control the sdn network by means of software as well as centralized controller(s), are the two main reasons that may easily attract malicious users [9]. the most threatening attack in sdn is the attack on vulnerabilities in controllers as this attack may influence the entire network. replication as well as periodic refreshing of the system may help to check or to overcome this attack [11]. an example of one attack top controller is packet-in, where the attacker may send a large number of packet-in messages to the controller. in such a situation, the controller may not be able to make decisions about the rest of the network [12]. viii. anomaly detection techniques in the context of abuse and network intrusion detection, the interesting objects are often not rare ones, but unexpected bursts in activity. this pattern does not adhere to the common statistical definition of an outlier as a rare object, and many outlier detection methods (in particular unsupervised methods) will fail on such data, unless it has been aggregated appropriately. instead, a cluster analysis algorithm may be able to detect the micro clusters formed by these patterns [13]. as advances in networking technology help to connect the distant corners of the globe and as the internet continues to expand its influence as a medium for communications and commerce, the threat from spammers, attackers and criminal enterprises has also grown accordingly. it is the prevalence of such threats that has made intrusion detection systems the cyberspace’s equivalent to the burglar alarm, joining ranks with firewalls as one of the fundamental technologies of network security. however, today’s commercially available intrusion detection systems are predominantly signature-based. they are designed to detect known attacks by utilizing the signatures of those attacks. such systems require frequent rule-base updates and signature updates, and are not capable of detecting unknown attacks. in contrast, anomaly detection systems, which are a subset of intrusion detection systems, model the normal system/network behavior which enables them to be extremely effective in finding and foiling both known and unknown or “zero day” attacks. while anomaly detection systems are attractive conceptually, a host of technological problems need to be overcome before they can be widely adopted. these problems include: high false alarm rate, failure to scale to gigabit speeds, etc. fig. 1. networking anomaly detection techniques a. anomaly applications anomaly detection is applicable in a variety of domains, such as intrusion detection, fraud detection, fault detection, system health monitoring, event detection in sensor networks, and detecting eco-system disturbances. it is often used in preprocessing to remove anomalous data from the dataset. in supervised learning, removing the anomalous data from the dataset often results in a statistically significant increase in accuracy [15]. b. anomaly application to data security anomaly detection was proposed for intrusion detection systems (ids) [16]. anomaly detection for ids is normally accomplished with thresholds and statistics, but can also be done with soft computing and inductive learning. types of statistics proposed included user profiles, workstations, networks, remote hosts, user groups and programs based on frequencies, means, variances, covariance and standard deviations. the counterpart of anomaly detection in intrusion detection is misuse detection[15, 16]. an intrusion detection system is a machine with software application that evaluates and monitors a network or system for virulent activity or policy violations. any detected activity or violation is typically reported to an administrator using a security information and event management system. engineering, technology & applied science research vol. 8, no. 2, 2018, 2724-2730 2727 www.etasr.com khairi et al.: a review of anomaly detection techniques and distributed denial of service (ddos) … c. network intrusion detection systems network intrusion detection systems (nids) are placed at a strategic point or points within the network to monitor traffic to and from all devices on the network. they analyze passing traffic on the entire subnet, and match the traffic that is passed on the subnets to the library of known attacks. once an attack is identified, or abnormal behavior is sensed, the alert can be sent to the administrator. an example of an nids would be installing it on the subnet where firewalls are located in order to see if someone is trying to break into the firewall. ideally one would scan all inbound and outbound traffic, however doing so might create a bottleneck that would impair the overall network speed. opnet and netsim are commonly used tools for simulating network intrusion detection systems. nids are also capable of comparing signatures of similar packets to link and drop harmful detected packets which have a signature matching their records. when we classify the design of the nids according to the system interactivity property, there are two types: on-line and off-line nids, often referred to as inline and tap mode, respectively. on-line nids deal with the network in real time. they analyze the ethernet packets and apply some rules to decide if there is an attack or not. off-line nids deal with stored data and pass it through some processes to decide if there is an attack or not.[17] d. techniques used in anomaly detection  statistical anomaly detection.  machine learning based anomaly detection.  data mining based anomaly detection.  artificial intelligent.  physical models. ix. denial of service (dos) attack a dos attack can be defined as an attempt made by a malicious user to compromise the regular functioning of a network. if this attempt comes from a group of hosts, instead of only one host, we are talking about distributed denial of service (ddos) as shown in figure 2. this group of hosts is coordinated by certain malicious user. a ddos attack consists of four elements: the main attacker that is behind the attack planning and intelligence, the handlers or masters which are compromised hosts that have special programs running on them that control multiple agents, the compromised hosts that run the attacking program and generate the packet streams designed for the targeted victims (also known as zombie hosts when the owner of the agent system is unaware of the malicious program that is running on his/her computer) and the targeted destination. a. highest ddos attacks examples: udp flood attack, icmp flood attack and tcp flood attack have been reported as the three highest ddos attack incidents, and will explained in this section: in a udp flood attack, a large volume of udp packets are sent to a random or specified port forcing the system to look for the application attached to these ports. since no waiting application is usually found, an icmp destination unreachable message is sent back to the spoofed source address. the processing of the attack on the udp packets and generation of icmp responses may cause the targeted host to run out of resources and crash [18]. in icmp flood attack, the zombie hosts send a large number of icmp_echo_request packets, also known as ping packets, to the target address. the target shall reply back to all the requests simultaneously which causes it to crash [19]. tcp syn flood attack takes advantage of the nature of tcp threeway connection setup handshakes. upon receiving an initial syn, the server replies back with a syn/ack and waits for the final ack that is never replied to by the attacking host. exhausting the network resources using heavy traffic loads is the mutual aspect of all the aforementioned attacks.[20] fig. 2. ddos attack structure b. ddos attacks in sdn: sdn is defined as one of the intelligent and useful networks with many different applications so it can be a target of ddos attacks just like a normal network. since sdn consists of three main functional layers, infrastructure layer, control layer, and application layer, potential malicious ddos attacks can be launched on these three layers of sdn’s architecture. table i presents a few ddos possible attacks on various sdn layers. based on the possible targets, the ddos attacks can be classified into three categories regarding sdn [21]: 1) application layer ddos attacks there are two methods to launch application ddos attacks. one is to attack some applications and the other is to attack northbound api. since isolation of applications or resources of sdn is not well solved [11], ddos attacks on one application can affect other applications. 2) control layer ddos attacks the controllers could potentially be seen as a single point of failure risk for the network, so they are particularly attractive target for ddos attack in the sdn architecture. the following methods can launch control plane ddos attacks: attacking controller, northbound api, southbound api, westbound api or eastbound api. for example, many conflicting flow rules from different applications may cause the ddos attacks on the control layer. within the operation of sdn, data plane will typically ask the control plane to obtain flow rules when the engineering, technology & applied science research vol. 8, no. 2, 2018, 2724-2730 2728 www.etasr.com khairi et al.: a review of anomaly detection techniques and distributed denial of service (ddos) … data plane sees new network packets that it does not know how to handle. there are two options for the handling of a new flow when no flow match exists in the flow table: either the complete packet or a portion of the packet header is transmitted to the controller to resolve the query [22]. 3) infrastructure layer ddos attacks infrastructure layer ddos attacks consist of two types. one is to attack some switches and the other is to attack southbound api. for example, if only header information is transmitted to the controller, the packet itself must be stored in node memory until the flow table entry is returned. in this case, it would be easy for an attacker to execute a ddos attack on the node by setting up a number of new and unknown flows. as the memory element of the node can be a bottleneck due to high cost, an attacker could potentially overload the switch memory (e.g., targeting to exhaust ternary content addressable memory (tcam). the generated fake flow requests can produce many useless flow rules that need to be held by the data plane, thus making the data plane hard to store flow rules for normal network flows [22]. table i. ddos attacks on sdn layers plane possible attacks data plane tcam exhaustion, switch ddos, another traditional ddos (icmp flood, tcp flood, tcp_syn flood, etc.) control plane resource depletion, open flow bandwidth exhaustion, amplification attacks. application plane exhausting northbound api, application layer ddos (http flooding, slowloris, etc.) c. effects of ddos attacks on control plane this research focuses on control layers of ddos attacks in sdn network, where the attacker's aims are to exhaust the control plane bandwidth by flooding the network with carefully crafted packets that the switch had to send to the controller. for example, if the switch receives a large number of new packets in a short time, its buffer is filled and the complete packet must be forwarded to the controller. this result leads to heavy consumption of control plane bandwidth. this attack may increase the delay of installing new flow table entries, and in the worst case, the switch may not be able to forward traffic from new flows [23, 24]. d. ddos attack detection in sdn various methodologies and techniques for detecting ddos attacks in sdn have been proposed and evaluated. a possibility of using machine learning for mitigating ddos was proposed in [25]. it suggests that techniques like neural network, support vector machine, genetic algorithms, fuzzy logic, bayesian networks, and decision trees could be utilized to distinguish normal network flow from malicious one. these techniques have a self-learning capability allowing them to adapt according to the traffic flow and identify the malicious flow. machine learning-based techniques are widely applied in traditional intrusion detection systems (ids) [26, 27]. a support vector machine-based dds detection was proposed in [27]. they suggested that the use of support vector machine for detection of ddos with a previously trained dataset will give the least false positive results compared with other machine learning techniques. this was only an offline comparison, hence, we cannot say that its results would be similar during online implementation. a scheme for using traffic statistics was proposed in [28]. it has two modules, namely, packet migration and data plane cache. packet migration module monitors the packet in message with the help of the controller. anomaly threshold is set to determine a potential attack. as the threshold is crossed, all table-miss flows are redirected to data plane cache using a wild-card rule written by a packet migration module. data plane cache distinguishes fake packets from normal packets by implementing symbolic execution of tablemiss flows. all incoming flows are fed in a packet handler that generates a proactive rule for these packets in messages. packet handler identifies whether the flow is genuine or not. of-guard is an attack-driven approach that is triggered only by an attack without requiring any changes in controller applications and sdn hosts [30]. in addition to of devices, a monitoring plane is also added to this proposal. a flow statistic collector module of monitoring plane collects flow information from of switches and forwards it to detection engine. detection engine takes these flow statistics from the collector as input and generates security alerts when anomalous flows are identified. alert in turn triggers policy engine which on reception of attack alert, generates some rules to address the anomalous flow that has been identified. these rules are stored in a lookup table for later enforcement. a path lookup function is with policy engine, which is used to define the path to be given to certain flow. a malicious flow is directed through a path leading to sinkhole. the framework also allows incorporating further security functions. further, middleboxes are also used in this framework to enforce security policies to switches in order to mitigate attack. this framework monitors and is capable of mitigating ddos attack from data plane. middleboxes need to be implemented as a part of the network itself. in [30] authors have proposed such a model that is able to trace the attack source. each device’s information with its location is recorded with a controller that is used to identify the correct source of packet. at regular time interval, port statistics from each switch are retrieved, if there is any suspicious flow, it is removed from that switch’s table. this approach is good for tracking the source, but detection of exact attack traffic is not clearly specified in this proposal. authors in [31] used maximum entropy estimation to estimate the benign traffic distribution in order to detect network security problems in home and office networks using sdn. traffic is divided into packet classes and maximum entropy estimation is then used to develop a baseline benign distribution for each class. packet classes are based on protocols and destination port numbers. experiments were conducted using of switches and a nox controller. however, the authors only used the low rate network traffic to do the experiments as they were focused on a home environment. authors in [32] proposed an algorithm to realize information security management. this algorithm is based on soft computing, which was implemented for intrusion detection in sdn. its prototype implementation consists of statistic collection, processing module and decision-making module. these modules are based on the beacon controller in java. the algorithm first collects and aggregates network statistical data. engineering, technology & applied science research vol. 8, no. 2, 2018, 2724-2730 2729 www.etasr.com khairi et al.: a review of anomaly detection techniques and distributed denial of service (ddos) … then, it processes these statistical data and makes operation decisions. finally, they train the decision-making module by applying machine learning techniques to adapt to a constantly changing environment. the intrusion detection was implemented based on algorithms called trw-cb and rate limit. performance evaluation was performed with a mininet of emulator. as a result, the proposed system was able to identify 95 % of the tested attacks at 1.2 % false positives. authors in [33] combined an of and s flow for anomaly detection to reduce processing overhead in native of statistics collection. as the implementation was based on flow sampling using s flow, false-positive was quite high in attack detection. authors in [34] proposed a ddos blocking application (dba) using sdn to efficiently block legitimate looking ddos attacks. the system works in collaboration with the targeted servers for attack detection. the prototype was demonstrated to detect http flooding attack. authors in [35] proposed a system to detect ddos attacks in the controller using entropy calculation. their implementation depends on a threshold value for entropy to detect attacks which they selected after performing several experiments. the approach may not be reliable since threshold value would vary in different scenarios. in [36], authors proposed an entropy based light-weight ddos detection system by exporting the flow statistics process to switches. although the approach reduces the overhead of flow statistics collection in the controller, it attempts to bring back the intelligence in network devices. authors in [37] proposed a deep learning based multi-vector ddos detection system in (sdn) environment. the study implemented system as a network application on top of an sdn controller and used pox controller, used deep learning for feature reduction of a large set of features derived from network traffic headers, and evaluated the system based on different performance metrics by applying traffic traces collected from different scenarios. the system identifies individual ddos attack class with an accuracy of 95.65%. it classifies the traffic in normal and attack classes with an accuracy of 99.82% with very low falsepositive. however, the approaches have limitations in processing capabilities. x. results and conclusion there is no doubt that sdn has a lot of benefits because of it decouples control from the data plane. however, there is still a vulnerable relation between sdn and ddos attacks. sdn itself may be a target of ddos attacks. network capabilities, such as global network view, dynamic updating of forwarding rules and so on can facilitate ddos attack detection. in [38] for instance, an attacker can use the characteristics of sdn to launch ddos attacks against the control, infrastructure and application layers of sdn. ddos attacks are designed to exhaust the victim's resources, such as network bandwidth, computing power, and operating system data structures. many well-known sites, like cnn, amazon, and yahoo, are targets of these attacks. since the emergence of ddos attacks, many solutions have been proposed to mitigate these attacks [28]. most previous works as in [21, 23, 25, 33, 34, 36, 39-42] have shown various techniques for ddos attack detection in sdn layers. but there is still work in order to improve the existing ddos detection techniques. the current proposal focuses on ddos attack detection on the control plane in sdn by using anomaly 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challenges for software-defined networks”, ieee communications magazine, vol. 51, no. 7, pp. 36-43, 2013 [23] r. kandoi, m. antikainen, “denial-of-service attacks in openflow sdn networks”, ifip/ieee international symposium on integrated network management, ottawa, canada, may 11-15, 2015 [24] a. ramanathan, j. mitchell, a. scedrov, v. teague, “probabilistic bisimulation and equivalence for security analysis of network protocols”, international conference on foundations of software science and computation structures, fossacs 2004. lecture notes in computer science, vol, 2987, springer, berlin, heidelberg, pp. 468483, 2004 [25] j. ashraf, s. latif, “handling intrusion and ddos attacks in software defined networks using machine learning techniques”, national software engineering conference, rawalpindi, pakistan, november 1112, 2014 [26] c.-f. tsai, y.-f. hsu, c.-y. lin, w.-y. lin, “intrusion detection by machine learning: a review”, expert systems with applications, vol. 36, no. 10, pp. 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december 17-19, 2014 [41] n. z. bawany, j. a. shamsi, k. salah, “ddos attack detection and mitigation using sdn: methods, practices, and solutions”, arabian journal for science and engineering, vol. 42, no. 2, pp. 425-441, 2017 [42] l. barki, a. shidling; n. meti; d. g. narayan; m. moin mulla “detection of distributed denial of service attacks in software defined networks”, international conference on advances in computing, communications and informatics, jaipur, india, september 21-24, 2016 engineering, technology & applied science research vol. 8, no. 1, 2018, 2447-2451 2447 www.etasr.com alghamdi: relationship between grain size distribution and radon content in surficial sediments … relationship between grain size distribution and radon content in surficial sediments of wadi arar, saudi arabia mohammed a. m. alghamdi engineering geology, earth science faculty king abdulaziz university jeddah, saudi arabia mmushrif@gmail.com abstract—surficial sediments with low radon content are desirable materials in construction applications. in this study, the relationship between grain size and radon content was investigated in sediments collected from seven sites in wadi arar, saudi arabia, with the intent of determining whether grain size analysis could be used for rapidly assessing the suitability of potential construction materials. thirty-five samples were collected (five per site) and the grain size distribution was determined using sieves. radon contents were measured on composite samples with a rad7 radon detector. among the sediment types (gravel, coarse sand, medium sand, fine sand, and silt and clay), the best linear correlations between grain size and radon contents were found for the coarse sand (negative slope, r=0.82) and fine sand (positive slope, r=0.78). polynomial relationships were also tested. a fourth-degree polynomial equation effectively described the correlation between grain size and radon content (r2 = 0.933). as shown by this model, the highest correlations with radon contents were detected at grain sizes smaller than 2.0 mm. thus, grain size may be useful for preliminary site assessment work. keywords-grain size distribution; rad7; radon; construction material; polynomial i. introduction radon in construction materials can pose health hazards to building occupants. thus, knowledge of radon contents in potential source materials would be valuable before natural resources are extracted from particular sites. the health hazard of radon gas is due to its radioactivity. the link between radon and lung cancer has been already established through epidemiological studies in many countries [1-3]. moreover, authors in [4] correlated radon concentrations with geodynamic, volcanic, and tectonic events. authors in [5] observed that the radon exhalation rate increases with grain size. their estimated values of radon exhalation rates for all studied samples were found to be lower than the internationally accepted value of 57–60 bq m-2 h-1. authors in [6] presented an improvement on previous models of radon emanation from the soil by incorporating soil grain size in addition to moisture. authors in [7] found that the correlations between raw values of radon concentrations, soil particle size fractions, and elevation were weak. furthermore, as a result of differences in geological structure, lithology, and climate parameters, an anomaly of 222rn around uro in western sudan was reported in [8]. regarding construction material selection, authors in [9] found that dune sands located east of jeddah city should be mixed with crushed fine aggregates prior to use as a construction material, and authors in [10] found that the addition of both lime and cement has a pronounced effect on soil stability by changing its mineralogy. this research therefore makes an important contribution to the literature by highlighting radon as another important factor affecting the selection of construction materials. wadis in saudi arabia are a common source of sediments for construction applications. this study investigates the relationship between sediment grain size and radon contents in wadi arar in saudi arabia. the objective is to determine if grain size can be used as a rapid assessment technique for predicting radon contents and assessing the suitability of sediments for construction applications. ii. methodology a. site and sampling description in this work, the relationship between radon content and the grain size of deposits along a 20 km stretch of wadi arar (figure 1) was investigated. the radon content was measured using the rad 7 technique. the soil is composed of cretaceous sedimentary rocks such as sandstone, shale, and limestone. the quaternary sediments within wadi arar have previously been investigated [11, 12] and classified as silty sand sm according to the unified soil classification system [11]. the cr-39 technique was previously used to determine the radon contents of wadi arar in northern saudi arabia [13, 14]. this study expands the results of [14], in which author developed a polynomial equation to determine radon content by incorporating grain size. developed a polynomial equation to determine radon content by incorporating grain size. engineering, technology & applied science research vol. 8, no. 1, 2018, 2447-2451 2448 www.etasr.com alghamdi: relationship between grain size distribution and radon content in surficial sediments … b. samples thirty-five fresh surface disturbed samples were collected from seven locations labeled a, b, c, d, e, f, and g. each location profile included five samples. profile a was located at the ne point of wadi arar adjacent to arar city, profile g was located in the sw direction facing aljouf city. the remaining five profiles b, c, d, e, and f were located between a and g (figure 1). a shovel was used to collect approximately 1 kg of sediment at each sampling point, and the samples were stored in 20 l plastic buckets and transported at room temperature to the laboratory of northern border university. the samples were analyzed within one week of collection. fig. 1. the seven sampled locations in the study area c. radon contents radon content was measured with a rad7 electronic radon detector according to the methods described in [13]. a single radon concentration value was measured in a composite sample created from portions of the five sediment samples taken at each site. to ensure environmental safety with regard to the radon hazards, the maximum readings for the radon contents (bq/m3) were used. d. grain size distribution the grain size distribution was determined using a mechanical shaker and a standard set of sieves, as in [14]. percentages of the retained grains in nine sieves were calculated. the diameters of the used sieves were 4.75, 3.35, 2.0, 1.0, 0.85, 0.425, 0.25, 0.15, and 0.075 mm. according to the unified soil classification system (uscs), the geometric means of each profile were grouped into five groups: gravel (g), coarse sand (cs), medium sand (ms), fine sand (fs), and silt & clay (sc), based on the following sizes in mm: g ≥ 4.75 4.75 > cs ≥ 2 2 > ms ≥ 0.425 0.425 > fs ≥ 0.075 0.075 > sc e. data analysis microsoft excel was used for the linear regressions and polynomial analysis. iii. results a. mean and variability the harmonic mean of the maximum radon content was calculated and then the standard deviations (σ) and coefficients of variation (cv%) were determined. for the grain size distribution, the geometric means, σ, and cv% were constructed from [14] (table i). according to statistical analysis of the geometric mean, σ and cv%, the relative quantitative distribution of different grain size fractions in wadi arar changes with location. sites a and d show homogeneous grain size distributions, yet sites b, c, e, f, and g are characterized by significantly larger relative quantities of mediumsand, coarse sand, silt & clay, gravel and fine sand, respectively. sites c, e, and f are also characterized by significant smaller relative quantities of fine sand, medium sand, and coarse sand, respectively. according to the coefficient of variation, the fine sand fraction is relatively more homogenous throughout the study area, whereas gravel is less homogeneous. according to harmonic mean, σ, and cv% values, high radon content was observed in location g. b. correlation between radon content and grain size correlation coefficients (r) were calculated to detect and compare the strength and direction of the linear relationship between radon content and various grain size fractions. figure 2 shows the correlation between radon content and grain size fractions. according to hypothesis testing, coarse sand and fine sand show a highly significant correlation with radon content (p-values less than 0.05) with correlation coefficient values equal to -0.82 and 0.78, respectively. all other fractions show a weak correlation. according to the negative and weak correlation results, all grain sizes except fine sand are suitable for use as a construction material. at a coefficient of determination (r2) equal to 0.93, and based on measurements obtained, the relationship between grain size and its correlation is a function of a fourth degree polynomial (figure 3). c. polynomial relationship the main goal of this work is to find the best model for the maximum radon content in terms of various grain size class percentages because it is much simpler and cheaper to measure grain size percentage than radon content. the term ‘best model’ refers to the statistical polynomial fit between rad7-max and grain size with the highest r2 value. to achieve that target, the following two parameters must be calculated: 1. the degree of the polynomial 2. the grain size fraction or fractions with the highest r2 value as there are only seven profiles, the highest possible polynomial degree is six. the polynomial fit used is a statistical polynomial fit with a 95% confidence interval. the relationship between radon content and different grain size fractions was plotted, and the best fit line of the data was deduced for different functions that could represent the relationship, such as linear, logarithmic, power, or polynomial functions. according to the highest values of the coefficient of determination (r2), engineering, technology & applied science research vol. 8, no. 1, 2018, 2447-2451 2449 www.etasr.com alghamdi: relationship between grain size distribution and radon content in surficial sediments … the polynomial function was selected as the best function to represent the relationship between radon content and grain size contents. figure 4 shows the plots and equations for all grain size contents using the fourth degree polynomial function. table i. max radon content and percentages of grain size fractions for gravel (g), coarse sand (cs), medium sand (ms), fine sand (fs), and silt and clay (sc). site rn g cs ms fs sc a 35 19.23 13.82 22.55 19.63 24.77 b 35 10.57 14.63 27.91 18.98 27.91 c 38 16.2 15.49 22.56 18.01 27.74 d 40 13.13 13.1 20.71 19.88 33.18 e 42 9.77 10.98 17.29 20.56 41.4 f 43 31.62 7.57 20.56 20.45 19.8 g 45 11.2 9.91 24.68 23.2 30.99 mean 39.38 16.29 12.17 22.49 20.32 28.73 σ 3.9 7.68 2.84 3.37 1.62 6.82 cv% 9.91 47.14 23.33 14.97 8 23.74 fig. 2. correlation between radon content and various grain size fraction (*correlation is statistically significant at 0.05) fig. 3. grain size vs. its correlation with radon content according to cumulative % passing fig. 4. polynomial relationship between radon content and grain size contents d. r2 versus polynomial degree the polynomial is more representative when the value of r2 is high. according to the best fit line of r2 of each grain size fraction at different polynomial degrees (figure 5), the relationship between r2 and the degree of the polynomial can be classified into two clusters. the first cluster indicates a straight line relationship, which includes coarse sand, fine sand, and silt and clay, while the second cluster describes a curved model that includes medium sand and gravel. for the straight line models, coarse and fine sand reflects strong r2 values for all polynomial degrees (>0.67 and 0.61, respectively), while the silt and clay fraction reflects strong r2 values for the 3rd degree polynomial (0.61). for the curved models, strong r2 values are observed for medium sand at the 4th degree polynomial (0.93) and for gravel at the 6th degree polynomial (1.00). e. relationship strength according to the value of r2, the strength of the polynomial relationship between radon content and grain size can be classified into three categories: good, medium, and weak. good relationships are observed for coarse and fine sand, which have the highest values of r2 at different polynomial degrees. medium relationships are found for medium sand and silt and clay, which have high r2 values at the 4th or higher degree of the polynomial. a weak relationship is observed for the gravel fraction, which contains almost all the lowest r2 values (figure 5). fig. 5. r2 values for different degrees of the polynomial function and different grain sizes iv. study comparison a comparison with [14] indicates that coarse sand and fine sand display highly significant correlations with both techniques used in these studies. the correlation between grain size and radon content measured using the rad7 technique is generally higher than that measured using cr-39 (figure 6). the relationship between the two correlations is linear, with an r2 of 0.97 (figure 7). the relationship between the r2 values of both techniques is linear for fine sand and polynomial for all other fractions (figure 8). engineering, technology & applied science research vol. 8, no. 1, 2018, 2447-2451 2450 www.etasr.com alghamdi: relationship between grain size distribution and radon content in surficial sediments … fig. 6. correlation between radon content and various grain size fractions for both cr-39 and rad 7 techniques fig. 7. relationship between radon content and grain size correlations determined using cr-39 and rad 7 techniques fig. 8. relationship between r2 values for the correlations determined using cr-39 and rad7 techniques v. conclusions the relationship between grain size and radon content was investigated in sediments collected from seven sites in wadi arar, saudi arabia, with the intent of determining whether grain size analysis could be used for rapidly assessing the suitability of potential construction materials. the main conclusions are as follows:  the polynomial function is the best model to represent the relationship between radon content and grain size.  coarse sand has a correlation coefficient of -0.82 with radon content, which is a strong negative relationship.  fine sand has a highly positive correlation with radon content, with a correlation coefficient of 0.78.  according to r2 values, the strength of the polynomial relationship between radon content and grain size is good for coarse and fine sand, which have the highest r2 values at all polynomial degrees, medium for sand and silt and clay, and weak for gravel.  the relationship between the coefficient of determination r2, and the polynomial degree shows two different behaviors: a straight line relationship for coarse sand, fine sand, and silt and clay, and a curved relationship for medium sand and gravel.  according to the fraction type, both linear and polynomial relationships were representative.  the rad7 technique reflects higher correlations between grain size and radon content than the cr-39 technique.  this research shows that fine sand grain size would make bad construction material. references [1] s. darby, d. hill, a. auvinen, j. barros, h. baysson, f. bochicchio, h. deo, r. falk, f. forastiere, m. hakama, i. heid, l. kreienbrock, m. kreuzer, f. lagarde, i. makelainen, c. muirhead, w. oberaigner, g. pershagen, a. ruano-ravina, e. ruosteenoja, a. s. rosario, m. tirmarche, l. tomasek, e. whitley, h. e. wichmann, r. doll, “radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 european case-control studies”, bmj, vol. 330, vol. 7485, p. 223, 2005 [2] j. h. lubin, z. y. wang, j. d. jr boice, z. y. xu, w. j. blot, l. de wang, r. a. kleinemen, “risk of lung cancer and residential radon in china: pooled results of two studies”, international journal of cancer, vol. 109, no. 1, pp. 132–137, 2004 [3] d. krewski, j. h. lubin, j. m. zielinski, m. alavanja, v. s. catalan, r. w. field, j. b. klotz, e. g. letourneau, c. f. lynch, j. l. lyon, d. p. sandler, j. b. schoenberg, d. j. steck, j. a. stolwijk, c. weinberg, h. b. wilcox, “a combined analysis of north american case-control studies of residential radon and lung cancer”, journal of toxicology and enviromental health, part a, vol. 69, no. 7, pp. 533–597, 2006 [4] g. imme, r. catalano, g. mangano, d. morelli, “radon exhalation measurements for environmental and geophysics study”, radiation physics and chemistry, vol. 95, pp. 349–351, 2013 [5] n. ahmad, m. s. jaafar, s. a. khan, “correlation of radon exhalation rate with grain size of soil collected from kedah, malaysia”, science international, vol. 26, no. 2, pp. 691–696, 2014 [6] a. sakoda, k. hanamoto, y. ishimori, t. kataoka, a. kawabe, k. yamaoka, “first model of the effect of grain size on radon emanation”, applied radiation and isotopes, vol. 68, no. 6, pp. 1169–1172, 2010 [7] a. h. khayrat, m. a. oliver, s. a. durrani, “the effect of soil particle size on soil radon concentration”, radiation measurements, vol. 34, no. 1-6, pp. 365–371, 2001 [8] h. idriss, i. salih, a. s. alaamer, m. y. abdelgalil, s. a. salih, a. m. hasan, m. a. eltahir, m. m. o. ahamed, “study of radon in soil gas, trace elements and climatic parameters around south kordofan state, sudan”, environmental earth sciences, vol. 72, no. 2, pp. 335–339, 2013 [9] e.-s. s. abu seif, a. r. sonbul, b. a. h. hakami, e. k. el-sawy, “experimental study on the utilization of dune sands as a construction material in the area between jeddah and mecca, western saudi arabia”, bulletin of engineering geology and the environment, vol. 75, no. 3, pp. 1007–1022, 2016 engineering, technology & applied science research vol. 8, no. 1, 2018, 2447-2451 2451 www.etasr.com alghamdi: relationship between grain size distribution and radon content in surficial sediments … [10] e. mutaz, m. a. dafalla, “chemical analysis and x-ray diffraction assessment of stabilized expansive soils”, bulletin of engineering geology and the environment, vol. 73, no. 4, pp. 1063–1072, 2014 [11] m. a. m. alghamdi, a. a. e. hegazy, “physical properties of soil sediment in wadi arar, kingdom of saudi arabia”, international journal of civil engineering, vol. 2, no. 5, pp. 1–8, 2013 [12] a. al-khattabi, s. dini, c. wallace, a. banakhar, m. al-kaff, a. alzahrani, geological map of the arar quadrangle, sheet 30, saudi geological survey, saudi arabia, 2010 [13] m. a. m. alghamdi, h. diab, “measurement of radon content in silty sand soil using rad7 and cr-39 techniques at wadi arar, saudi arabia: comparison study”, international journal of management and applied science, vol. 2, no. 5, pp. 126-132, 2016 [14] m. a. m. alghamdi, “math model of grain size distribution versus radon content of wadi arar, kingdom of saudi arabia”, iastem international conference, pp. 14-17, 2017 microsoft word articlesilvanobertoldoafterminorrevision.doc etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 246-250 246 www.etasr.com bertoldo et al: an operative x-band mini-radar �etwork to monitor rainfall events … an operative x-band mini-radar network to monitor rainfall events with high time and space resolution s. bertoldo c. lucianaz o. rorato m. allegretti cinfai (consorzio interuniversitario per la fisica delle atmosfere e delle idrosfere), presso det (dipartimento di elettronica e telecomunicazioni), politecnico di torino corso duca degli abruzzi, 10129, torino, italy. silvano.bertoldo@polito.it, claudio.lucianaz@polito.it a. prato g. perona envisens technologies s.r.l. spinoff del politecnico di torino località baraggino presso campus tecnologico 10034, chivasso (to), italy. andrea.prato@polito.it abstract— the increasing frequency of extreme and very localized precipitation events have been causing landslides, floods and casualties, especially in sicily, due to its complex orography, and to the presence of densely inhabited areas just at the mouth of small basins. in order to monitor such phenomena with the needed high resolution in time and space, an experimental network of x-band mini-radars, exclusively devoted to monitor rain, has been installed in some parts of sicily since 'ovember 2010. the network is made up by 4 mini weather radars able to acquire a rain map every minute (or even at shorter intervals) with a radial space resolution better than 100 m within a range of up to 30 km. their low cost and the easiness of installation make such radars ideal for monitoring small areas or even just limited angular sectors, since it is more convenient to install more than one instrument instead of choosing special site locations or spending for installation support. the raw data are immediately processed in real time by the software installed on each radar unit, cartesian maps are locally produced, compressed and transmitted via gprs to a server where ad hoc products for the users are prepared and made available on a web site. a few examples of final products and some comparisons with rain gauges are presented. keywords x band radar; radar meteorology; high time resolution; high space resolution; rainfall events i. introduction the frequency of high intensity rainfall events is steadily increasing in the mediterranean area and especially in the hilly and mountainous parts of italy. just in two months, october and november 2011, three serious floods occurred. on the 25th october 2011, in the la spezia province and in lunigiana, 520 mm of rain fell in less than 6 hours causing floods and the death of eight people. on 4th november 2011 a dramatic flood occurred over the city of genoa with 400 mm rainfall falling in just a few hours. six people died during this flood [1]. on 22nd november 2011, more than 200 mm of rain fell over the province of messina (sicily) where four people died [2]. in these situations, in order to efficiently monitor river flow, floods and landslides an unrealistic extremely dense rain gauge network is needed, considering the nature of the localized rain events of limited extension and the size of the river basins of interest. alternatively, c-band or s-band meteorological radars are able to monitor rain fields over wide areas, but with not enough space and time resolution, and with high purchase and maintenance costs. indeed, in these last years, x-band meteorological radars are beginning to appear [3, 4]. the radars described in [4] are certainly simpler (non-coherent, pulsed, one polarization only, non-doppler, with a fixed elevation), but exclusively devoted to rain measurements (able to produce one rain map in a few seconds). furthermore, their extremely low cost, the lack of any special installation needs, practically maintenance-free and the possibility to be remotely controlled with software adjournments, make them able to conveniently cover limited areas or even just limited angular sectors, since it is less expensive and time consuming to install more than one near-by instrument instead of choosing special site locations and spending for installation . the studies and researches about the x-band mini weather radar started during the foralps (“meteo-hydrological forecast and observations for improved water resource management in the alps”) project in 2004 [5, 6] and the network described in this paper is the first fully operational one. the experimental network installed in sicily consists of 4 x-band mini radars designed and installed by the local operative unit of cinfai at polytechnic of turin (consorzio interuniversitario nazionale per la fisica delle atmosfere e delle idrosfere), in collaboration with envisens technologies s.r.l. spinoff of polytechnic of turin, through a cooperative project with the civil protection of the regional province of palermo and the regional civil protection of sicily. the first radar is located in palermo, the second and the third one are installed in bisacquino (pa) and gangi (pa) and the last one in roccafiorita (me). all the sites have been chosen in agreement with the civil protection of the regional province of palermo and the regional civil protection of sicily. the radar units, installed from november 2010 to march 2011, after a first calibration period are now completely operative and transmit the cartesian rain maps to a server maintained by the cinfai. in order to further reduce the overall operational costs only free and open source software solutions have been used and tailored to the specific needs. etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 246-250 247 www.etasr.com bertoldo et al: an operative x-band mini-radar �etwork to monitor rainfall events … ii. network technical description table i reports the main technical specifications of the radars and two radars are shown in figure 1. considering their compactness, it should be noted that all the electronic equipments (antenna, radiofrequency unit, the data processing unit, the communication unit for data transmission and remote control, the power unit) are placed inside the radome. the radome itself may be secured to any flat surface and it needs to be connected with a power supply (less than 200 w at 220 v). table i. micro weather radar unit technical specifications radome height 150 cm diameter 90 cm material polyester transmitter peak power 10 kw pulse length 600 ns transmitted frequency (9410 ± 30) mhz pulse repetition frequency (prf) 800 hz modulator solid state receiver receiver type logarithmic, solid state dynamic range from 0 to –100 dbm intermediate frequency (if) 60 mhz receiver filter bandwidth (20 ± 2) mhz other technical specifications front end microwave integrated circuit noise figure < 3.5 db duplexer ferrite circulator with state solid diode limiter antenna rotation speed (22 ± 2) r. p. m. power 24 vdc fig. 1. the x band mini radar with and without the radome the radar controller operating system is gnu linux, debian distribution. this choice allows great reliability and flexibility in the configuration and full control of active processes and packages. in addition it allows easy future increase of the number of radar units of the network simply by replicating the pre-configured software package without the need for subscription for new licenses. the server in the central unit stores the radar maps in a database. the same server has two more functions: • it acts as a web server, in order to provide web services that can be browsed by users • it also acts as a ftp server, allowing selected access from expert operators wishing to do their own data analysis. the radar maps produced by each radar unit are transmitted to the server via a gprs communication network: a ftp connection to the server is open and each map is transferred. scheduled software running at specific time intervals manages data stored in the database in order to compute precipitation maps. all software has been developed partly in c and partly by using bash scripting and process scheduling. web services have been developed with php and javascript functions. iii. signal processing the next two paragraphs describe the main processing steps, performed in each radar unit and in the server. a. data acquisition and processing in the radar unit every 3 sec a georeferenced radar map of 4096 × 2048 data (respectively in range and azimuth) is acquired. if the antenna lobe is blocked by buildings or mountains, it is possible to inhibit the pulse generation and transmission in the corresponding angular regions (the so-called “blanked regions”). raw data are expressed in 8 bit dn (digital numbers), covering the signal range from -100 to 0 dbm, and are generated from the analog to digital converter operating at 120 mhz. only 1 out of 3 data are taken to form the above georeferenced map. these data are immediately processed with an “anti-bang” filter to remove signal spikes due to interference with other pulsed radars, located near-by, and operating at the same frequency, and then transformed from logarithmic to linear scale. all the maps collected in one minute are averaged into a new matrix with the same size of 4096 × 2048. a series of anti-clutter filters is then applied to the data to recover, as far as possible, rain signature even in presence of clutter. a first anti-clutter filter is based on a matrix where different threshold values are defined for each matrix cell (“pixel”). each threshold value is represented by the median value of such cell with the addition of a constant term. the matrix is automatically and dynamically modified in time. the choice of the median as a threshold is to be preferred to the average since it is more statistically sensitive in the presence of extreme values. the adaptive threshold matrix is formed when the radar unit is turned on for the first time. each day the computed threshold matrix is stored on the control pc of the radar unit to avoid the threshold adaptive computation process to start from the beginning in case of system power failure. a second anti-clutter filter is then applied in order to exploit the high range resolution available. sequences of pixels along each ray with values greater than zero are considered: sequences with a length shorter than a fixed constant are removed since it is assumed that rain events have a bigger spatial correlation etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 246-250 248 www.etasr.com bertoldo et al: an operative x-band mini-radar �etwork to monitor rainfall events … from this still polar matrix is derived a cartesian 1024 × 1024 matrix, where each value is the average of the polar pixels whose center of mass is falling within the considered cartesian pixel. it is to be noted that each cartesian pixel has a “virtual” dimension of 60 × 60 square meters: of course only the original physical range resolution is of the same order (approximately 90 m) while the average range resolution is much larger (at 30 km range it is approximately 1500 m), however in this way at least some of the detailed information present in the original range resolution data may still be preserved in the final data. finally, the data are transformed back in logarithmic units, compressed, and sent via ftp to the server for the next processing steps. b. radar map processing at the server at the server, the maps are stored as dn in the data base with all the needed ancillary data added, and a last anti-clutter filter is adopted: a square matrix of 21 × 21 pixels centered on each pixel of the matrix is examined; if the number of non zero pixels in the matrix is less than a given constant (fixed, after a calibration period, at 150), the central pixel is put to zero. before passing to the web presentation, dn values are converted into reflectivity z and into rainfall rate r through a z-r equation [7]. finally, images are processed in order to be plotted on the web services, as shown in figure 2, where the rainfall pixels are colored, the zero rain pixels are left transparent and the blanked areas are painted gray. it should be noted that web services present rain rate maps constructed with a chosen radar equation assumed appropriate for the rain typology examined, however the database still contains dn values, that can be retrieved and processed using different relations. iv. web services processed real time radar maps can be browsed on the official network web site where they are projected over a common cartographic system as shown in figure 2. fig. 2. data processing scheme at the server fig. 3. map example (no rain) projected over a cartographic system provided by google©. the image refers to the radar installed in bisacquino (pa). the gray area is the graphical representation of a blanked region. following the requirements suggested by institutions responsible for natural hazards preventions some specific web services have been implemented, e. g. : accumulated precipitation over the entire observed area by each radar at different time intervals (every hour, six hours, twelve hours and every day), as shown in figure 4, production of a specific weekly report, accumulated precipitations in a given userdefined area with an automatic alert output signal if a given threshold is passed (it is possible to implement a simple hydrology balance equation for the same area), time laps representation at different velocities of the last 15 maps in order to visualize the time evolution of the phenomena. each service can be accessed by a simple and intuitive web interface. fig. 4. rain accumulation maps from the radar installed in palermo. the left one is evaluated within a time interval of 6 hours and the right one refers to a time interval of 1 hour, in the same day. v. network calibration a. hardware and software calibration and adjustment a continuous and automatic monitoring of the microwave transmission/reception line is performed through a systematic analysis in time and space of ground clutter in clear sky in order to put in evidence significant calibration problems. if necessary, the receiver filter may be adjusted remotely to avoid losses due to the mismatch between the transmitted frequency and the central frequency of the receiver filter. etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 246-250 249 www.etasr.com bertoldo et al: an operative x-band mini-radar �etwork to monitor rainfall events … similarly, the operators may modify remotely , through gprs, not only the constants used in the data processing at the installed radars, but even change the algorithm used in constructing the data maps transmitted to the server. b. occultation mask the fixed occultation masks have been computed during the first operating period of the radar network. for each radar, a set of rain events has been acquired and at the same time a visibility study has been done using a free dem [8]. it has been possible to evaluate a visibility-occultation mask for each radar, combining the results of the 360° radar visibility analysis together with the total cumulative rain map obtained from the set of rain events occurred during the calibration period. c. preliminary radar – rain gauge comparison to validate radar network rainfall measurements some comparisons with existing rain gauge networks data have been analyzed. in particular, sias (servizio informativo agrometereologico siciliano) rain gauges have been used. rain data for comparisons have been obtained computing a temporal integration over a time interval of 1 hour, while radar data have been obtained adopting evidently the same temporal integration and a spatial integration over 1 square km area centered around the rain gauge. radar maps values are converted into reflectivity z and into rainfall rate r through the z-r common equation. the fixed z-r relation used here is the one proposed by rosenfeld in [9], with a=250 and b=1.2, initially proposed for tropical rain but usable also for intense and persistent rain not only in tropical regions. figure 5 shows an example of the comparison between the radar installed in bisacquino (pa) and the gauge at giuliana (pa) considering an event on 26 th april 2011. figure 6 and 7 show other examples of comparisons between the radar installed in palermo and the gauges of partinico (pa) and uditore (pa) considering the rainfall events of 18th february 2011. all comparisons show a good agreement between radar rainfall amount estimation and rain gauge measurements. vi. conclusions and outlooks the x-band radar network gives accurate rain field monitoring and good rain measurements with high space and time resolution. it provides a set of web services finalized to territory monitoring in order to give alarms with the time advance compatible with the real dimensions of the monitored basins, helping to lower the problems caused by extremely high rainfall events. other network services (e.g. in [10]) may be implemented, always according to the institutions responsible for natural hazard prevention. the network is still under developments. future studies will concern the analysis of some of the extreme rainfall events occurred over sicily, aiming specifically at analyzing the spatial and intensity distribution of extreme events. massive and systematic radarrain gauge comparisons will be performed together with cband radar data in order to put in evidence the improvement in rain fields analysis that can be reached by using these three different observing systems at the same time. acknowledgments the present work has been produced as result of a wide research and experimental activity promoted by the local operative unit of cinfai (consorzio interuniversitario nazionale per la fisica delle atmosfere e delle idrosfere, www.cinfai.it) at polytechnic of turin. the activities have been developed in collaboration with envisens technologies s.r.l. (www.envisens.com), spinoff of polytechnic of turin, and have been promoted by the civil protection of regional province of palermo and the regional civil protection of sicily. a special thank is due to sias (servizio informativo agrometereologico siciliano) for providing us its rain gauge network data. 0 5 10 15 20 0 5 10 15 20 25 time [h] r a in [ m m ] rain gauge radar comparison rain gauge: giuliana(pa) radar: bisacquino (pa) fig. 5. example of rain gauge – radar comparison. day: 26 th april 2011. radar: bisacquino (pa). rain gauge: giuliana (pa) 0 5 10 15 20 0 5 10 15 20 25 30 time [h] r a in [ m m ] rain gauge radar comparison rain gauge: partinico (pa) radar: palermo fig. 6. example of rain gauge – radar comparison. day: 18 th february 2011. radar: palermo. rain gauge: partinico (pa) etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 246-250 250 www.etasr.com bertoldo et al: an operative x-band mini-radar �etwork to monitor rainfall events … 0 5 10 15 20 0 0.5 1 1.5 2 2.5 3 time [h] r a in [ m m ] rain gauge radar comparison rain gauge: uditore (pa) radar: palermo fig. 7. example of rain gauge – radar comparison. day: 18th february 2011. radar: palermo. rain gauge: uditore (pa) references [1] m. gigliotti, http://www.scienze-naturali.it/ambiente-natura/maltempoe-cattiva-edilizia-cosa-sta-accadendo-alle-nostre-localita-italiane. [2] a. fuccello, r. bove, http://www.meteoam.it/?q=alluvione_messina_ calabria_22novembre2011 [3] d. mclaughlin, d. pepyne, b. philips, j. kurose, m. zink, d. westbrook, e. lyons, e. knapp, a. hopf, a. defonzo, r. contreras, t. djaferis, e. insanic, s. frasier, v. chandrasekar, f. junyent, n. bharadwaj, y. wang, y. liu, b. dolan, k. droegemeier, j. brotzge, m. xue, k. kloesel, k. brewster, f. carr, s. cruz-pol, k. hondl, p. kollias, “short-wavelength technology and the potential for distributed networks of small radar systems”, bull. am. meteorol. soc., vol. 90, no. 12, pp. 1797-1817, 2009 [4] f. s. marzano, e. picciotti, g. cinque, m. montopoli, l. 1a bernardini, g. giuliani, e. anagnostou, m. anagnostou, y. fessas, a. volpi, a. telleschi, j. kalogiros, v. cazac, r. pace, f. sanna, “hydrorad project: integrating x-band mini-radar networks and hydro-meteorological forecast models in moldova territory”, erad 2010-the sixth european conference on radar in meteorology and hydrology, sibiu, romania, september 6 th 10 th , 2010. [5] r. notarpietro, m. zambotto, m. gabella, s. turso, g. perona, “the radar ombrometer: a portable, low-cost,short-range, x band radar for rain estimation within valleys”, 3rd voltaire workshop joint with the 7th european conference on application of meteorology (ecam7) and the european meteorological society meeting (ems05), utrecht, the netherlands, september 12th – 16th, 2005. [6] m. gabella, f. orione, m. zambotto, s. turso, r. fabbo, a. pillon, “a portable low cost x-band radar for precipitation monitoring in alpine valleys: analysis of radar reflectivities and comparison bewteen remotely sensed and in situ measurements; test of a prototype in friuli venezia giulia”, foralps technical report 3, università degli studi di trento, dipartimento di ingegneria civile e ambientale, trento, italy, pp. 52 , 2008. [7] j. s. marshall, w. m. palmer, “the distribution of raindrops with size”, j. meteorol., vol. 5, no. 4, pp. 165-166, 1948 [8] h. sauvageot, radar meteorology, artech house publisher, norwood, ma., 1992. [9] d. rosenfeld, d. b. wolff, d. atlas, “general probability matched relations between radar reflectivity and rain rate”, journal of applied meteorology, vol. 32, no. 1, pp. 50 – 72, 1993 [10] m. montopoli, e. picciotti, s. di fabio, a. telleschi, a. volpi, f. s. marzano, “x-band weather radar monitoring products at urban scale: spatial calibration hail detection and tracking accuracy evaluation”, erad 2010 the sixth european conference on radar in meteorology and hydrology, sibiu, romania, september 6 th 10 th , 2010. engineering, technology & applied science research vol. 8, no. 5, 2018, 3484-3487 3484 www.etasr.com mohamed: studies of the properties and microstructure of heat treated 0.27% c and 0.84% mn steel studies of the properties and microstructure of heat treated 0.27% c and 0.84% mn steel masoud ibrahim mohamed chemical and materials engineering department northern border university, arar, saudi arabia on leave from mechanical engineering department, faculty of engineering, fayoum university, egypt ibrahim_64@yahoo.com abstract—in the present work, different heat treatments like hardening with different cooling rates followed by tempering at different temperatures have been performed. the material used in this study is carbon steel of 0.27% c and 0.84% mn. samples of as-rolled steel were subjected to different heat treatment processes. the steel was heated to the austenitizing temperature of 870°c for 2hrs followed by water quenching, oil quenching, air and furnace cooling. water and oil quenched samples were subjected to tempering for one hour at temperatures of 250°c, 350°c, 450°c and 550°c. tensile and impact tests were carried out for as rolled and heat-treated steel. results show that the heat treated steel revealed an excellent combination of tensile strength and impact strength, which is suitable for structural applications. optical metallographic investigation was carried out for all samples compared with the as rolled steel. the heat treatment revealed remarkable changes in steel morphology and mechanical properties. keywords-medium carbon steel; heat treatment; mechanical properties; optical micrograph; tempering i. introduction steel with low carbon content has nearly the same properties as iron, it is soft and easy to deform, and it has low tensile strength and hardness. as the carbon content increases, the steel becomes harder and stronger but less ductile and more difficult to weld [1-3]. carbon steel with 0.27% c and 0.84% mn is broadly used in the production of machinery parts like shafts and gears, and as structure steel in many industrial applications [4-7]. the need to produce higher strength steels, stronger than those obtained in conventional controlled rolled high strength micro-alloyed grade has led to the improvement of microstructural strengthened steels through different heat treatment. heat treatment involves the application of heat to a material in order to bring changes in the microstructure and modify the material properties. during the heat treatment process, the material usually shows phase microstructural and crystallographic changes [8-11]. the purpose of heat treating carbon steel is to change the mechanical properties of steel, usually ductility, hardness, yield strength tensile strength and impact resistance. the impact strength of the heat-treated specimens are higher than that of the as rolled, because of the martensite formed during the heat treatment processes [9-11]. ii. experimental method the chemical composition of medium carbon steel (astm a-36) used for this investigation is given in table i. table i. steel chemical composition, wt.%. c mn si cu p s zn 0.27 0.84 0.24 0.095 0.02 0.02 0.05 samples for mechanical tests and microscopic scanning were cut out from the as rolled (ar) steel. the samples for tensile test were prepared according to astm e8. the impact test sample was cut with dimensions of 55mmx10mmx10mm that follow standard dimensions for charpy impact test astm e23. the samples for the mechanical tests and microstructure investigations would be heat-treated (ht) to 870oc followed by, furnace cooling (fc), air-cooling (ac), water quenching (wq) and oil quenching (oq). water quenched samples were tempered at temperatures of 250oc (wqt1), 350oc (wqt2), 450oc (wqt3) and 550oc (wqt4). oil quenched samples were tempered at the same temperatures (oqt1-oqt4). tensile and impact tests were be carried out for ar and ht samples. all samples (ar and ht) would undergo microstructure analysis using metallurgical microscope. the results of the mechanical tests and optical micrograph were analyzed. iii. results and discussion a. tensile test tensile tests were carried out for ar and ht steels. figure 1 shows the effect of quenching media of the stress strain curve for steel astm a-36. maximum stress increased by the effect of hardening (wq, oq) with a decrease of elongation. figures 2 and 3 show the effect of tempering temperatures on wq and oq steels respectively. wq steels show a slight decrease in uts with higher increase in elongation tempering at t1 and t2 while all tempering temperatures remarkably decrease uts of th oq steels, with t1 and t3 revealing higher ductility. figure engineering, technology & applied science research vol. 8, no. 5, 2018, 3484-3487 3485 www.etasr.com mohamed: studies of the properties and microstructure of heat treated 0.27% c and 0.84% mn steel 4 is a summary for the effect of tempering temperature on the ultimate tensile stress (uts) and yield stress (σy) of the wq and oq steel. it is clear that, the uts increased after wq and oq compared with ar steel. after tempering, uts decreased while maximum elongation increased. fig. 1. effect of quenching media from 870°c into water and oil quenching fig. 2. effect of water quenching at 870°c followed by tempering at t1, t2, t3 and t4 fig. 3. effect of oil quenching at 870°c followed by tempering at t1, t2, t3 and t4 fig. 4. effect of tempering temperature after different quenching on uts and yield stress. b. optical micrograph the effect of quenching media on the microstructure of astm a -36 steel is shown in figure 5. the ar steel reveals ferrite and perlite phases while, fine needle like martensite were obtained from wq steel. oil quenched steel shows retained austenite with some martensite. this change in the microstructure due to hardening can explain the increase in maximum strength obtained in figure 1. the effect of tempering temperature on wq and oq steels is shown in figures 6 and 7 respectively. figure 6 shows the effect of tempering temperature on the wq steel. water quenched steel revealed the formation of lath martensite. tempered martensite is shown for the tempered wq and oq steel. (a) (b) (c) fig. 5. optical micrograph of (a) ar, (b) wq and (c) oq steel. c. impact tests the effects of heat treatment on the absorbed energy of medium carbon steel are shown in figure 8. the absorbed engineering, technology & applied science research vol. 8, no. 5, 2018, 3484-3487 3486 www.etasr.com mohamed: studies of the properties and microstructure of heat treated 0.27% c and 0.84% mn steel energy increased by tempering of wq steel at temperature of 450°c. (a) (b) (c) (d) fig. 6. optical micrograph of wq and tempered steel at (a) 250°c, (b) 350°c, (c) 450°c and (d) 550°c. iv. conclusions microscopic investigations, tensile and impact tests were carried out for astm a-36 steel of 0.27% c. the results of the experimental work can be summarized as: • wq and oq steels revealed higher tensile strength due to the effect of martensite formation. • uts, yield strength and % elongation of wq steel seems to be higher than that of oq steel after tempering at 350°c. • tempering after quenching revealed remarkable improvement especially at temperature of 350°c. • impact energy for wq steel is higher than for oq steel, impact energy increased to maximum at tempering temperature of 450°c for wq steel. (a) (b) (c) (d) fig. 7. optical micrograph of oq and tempered steel at (a) 250°c, (b) 350°c, (c) 450°c and (d) 550°c. engineering, technology & applied science research vol. 8, no. 5, 2018, 3484-3487 3487 www.etasr.com mohamed: studies of the properties and microstructure of heat treated 0.27% c and 0.84% mn steel fig. 8. effect of tempering temperatures on the absorbed energy of wq and oq steel nomenclature ar as rolled wq water quenched oq oil quenched wqt1 water quenched + tempering at 250°c wqt2 water quenched+ tempering at 350°c wqt3 water quenched+ tempering at 450°c wqt4 water quenched+ tempering at 550°c oqt1 oil quenched+ tempering at 250°c oqt2 oil quenched+ tempering at 350°c oqt3 oil quenched+ tempering at 450°c oqt4 oil quenched+ tempering at 550°c om optical micrograph hv hardness vickers uts ultimate tensile strength σy yield stress acknowledgement author wishes to acknowledge the approval and the support of this research study by the grant no. (7390-eng-2017-1-8-f) from the deanship of scientific research in northern border university, arar, ksa. references [1] d. o. oluyemi, o. i. oluwole, b. o. adewuyib, “studies of the properties of heat treated rolled medium carbon steel”, materials research, vol. 14, no. 2, pp. 135-141, 2011 [2] o. o. daramola, b. o. adewuyi, i. o. oladele, “effects of heat treatment on the mechanical properties of rolled medium carbon steel”, journal of minerals & materials characterization & engineering, vol. 9, no. 8, pp.693-708, 2010 [3] b. s. motagi, r. bhosle, “effect of heat treatment on microstructure and mechanical properties of medium carbon steel”, international journal of engineering research and development, vol. 2, no. 1, pp. 713, 2012 [4] n. m. ismail, n. a. a. khatif, m. a. kamil, a. kecik, m. a. h. shaharudi, “the effect of heat treatment on the hardness and impact properties of medium carbon steel”, iop conf. series: materials science and engineering, vol. 114, no. 1, pp. 012108-012106, iop publishing, 2016 [5] d. a. fadare, t. g. fadara, o. y. akanbi, “effect of heat treatment on mechanical properties and microstructure of nst 37-2 steel”, journal of minerals & materials characterization & engineering, vol. 10, no. 3, pp. 299-308, 2011 [6] o. o. joseph, o. o. joseph, r. o. leramo1, o. s. ojudun, “effect of heat treatment on microstructure and mechanical properties of sae 1025 steel: analysis by one-way anova”, journal of materials and environmental science, vol. 6, no. 1, pp. 101-106, 2015 [7] j. k. odusote, t. k. ajiboye, a. b. rabiu, “evaluation of mechanical properties of medium carbon steel quenched in water and oil”, au journal of technology, vol. 15, no. 4, pp. 218-224, 2012 [8] v. k. murugan, p. k. mathews, “effect of tempering behavior on heat treated medium carbon (c 35 mn 75) steel”, international journal of innovative research in science, engineering and technology, vol. 2, no. 4, pp. 945-9540, 2013 [9] s. a tukur, m. m usman, i. muhammad, n. a sulaiman, “effect of tempering temperature on mechanical properties of medium carbon steel”, international journal of engineering trends and technology, vol. 9 no. 15, pp. 798-800, 2014 [10] a. k. tanwer, “effect of various heat treatment processes on mechanical properties of mild steel and stainless steel”, american international journal of research in science, technology, engineering & mathematics, vol. 8, no. 1, pp. 57-61, 2014 [11] a. calik, “effect of cooling rate on hardness and microstructure of aisi 1020, aisi 1040 and aisi 1060 steels”, international journal of physical sciences, vol. 4, no. 9, pp. 514-518, 2009 engineering, technology & applied science research vol. 7, no. 4, 2017, 1811-1819 1811 www.etasr.com phanendra babu et al.: a new power system restoration technique based on wams partitioning a new power system restoration technique based on wams partitioning n. v. phanendra babu electrical engineering department, national institute of technology warangal, telangana, india p. suresh babu electrical engineering department, national institute of technology warangal, telangana, india d. v. s. s. siva sarma, electrical engineering department, national institute of technology warangal, telangana, india abstract—an important feature of a wide-area measurement system (wams) is the ability to recover data during a communication failure. this paper presents a novel scheme of partitioning a pmu installed power network into a number of wams regions in order to make the power system restoration process simpler. this algorithm also proposes the optimal placement of phasor data concentrators (pdcs) in each region to record the data from pmus. this paper considers the restoration constraints like transformer equivalent bus, generation-load balance and the observability of region for the partitioning of power system. the proposed scheme is demonstrated with an ieee-30 bus system. it is then applied on ieee-39, ieee-118 bus systems and on a northern regional grid of the indian power grid. keywords: wide-area monitoring system; wams; power system observability; power system restoration; phasor data concentrators; pdcs i. introduction blackouts are obviously the most dangerous outages that may happen in a power system, that call for immediate restoration [1]. this can be achieved by a restoration strategy called build-up strategy [2]. a delay in restoration causes damages to consumers and subjects the system to many economic and political costs. the build-up strategy recommended here follows a mutual interconnection of islands after restoring them separately. the build-up strategy and its importance are clearly explained in [2-5]. but sectionalizing a network into separate islands was not considered. a scheme was suggested in [6] to sectionalize a network into separate islands, but it failed to produce stable islands as it didn’t considers the generation-load constraints during initial partitioning. generally, during restoration, a circuit breaker between two buses should not be closed with a larger phase angle because it may damage the system by causing unwanted outages. moreover, if the phasor measurement unit (pmu) installed power system is partitioned, it may lose its observability because of the line openings between islands. the present paper proposes a restoration based sectionalizing method for a pmu installed network. it is a model based algorithm that can handle even large-scale networks. unlike [6], it considers power generation-load balance constraints during system initial partitioning. it also considers observability constraints at the final stage of the sectionalizing process. these two constraints have really increased the stability and observability of feasible islands. this would probably help power companies in protecting power systems from large catastrophes like blackouts just by isolating the islands that are being faulted. at the end it also suggests an optimal location strategy for phasor data concentrators (pdcs) to provide phase angle data across the lines between any two islands. the proposed algorithm is demonstrated using the ieee-30 bus system and then applied to the ieee-39 and ieee-118 bus systems and to a northern region of the indian power grid. ii. optimal pmu placement a pmu gives synchronized measurements of electrical parameters like voltage, current and frequency of the bus on which it is installed. this section will optimize the number of pmus required for observing the system completely. actually, this optimization problem was introduced in [7]. many heuristic methods like genetic algorithms [8], particle swarm optimization [9], hybrid genetic particle swarm optimization [10] and many others have been applied since. meta-heuristic methods such as binary imperialistic competition algorithm (bica) [11], artificial bee colony (abc) algorithm [12] and firefly algorithm [13] have also been employed. an integer linear programming (ilp) is developed in [14] for system complete observability. this was extended with and without conventional measurements in [15] and [16] respectively to include the zero-injection bus (zib) effect. recently, researchers presented an integer quadratic based pmu placement policy [17]. an accurate solution for complete observability was presented in [18] using a participation factorbased method. in this paper it is assumed that the pmu placement has been conducted before partitioning the network. the optimal pmu placement problem is carried out using the binary cuckoo search (bcs) technique. the pmu locations obtained are tabulated in table i. the problem is formulated as below. minimize  nq qx (1) subjected to engineering, technology & applied science research vol. 7, no. 4, 2017, 1811-1819 1812 www.etasr.com phanendra babu et al.: a new power system restoration technique based on wams partitioning sp(x)≥1, np  (2) where xcs q nq pqp    , np  (3) here, (1) is the objective function for the optimal pmu placement; sp represents observability function at bus p. the parameter cpq from (3) gives the binary connectivity of all buses in the network. for the bus to be observable, it must be connected to at least on bus which is installed with pmu. the value of sp will be equal to or greater than 1. it can be defined as,        else connectedareqandpif qpif c pq ,0 ,1 ,1 (4) table i. pmu llocations test system locations of pmus ieee-30 2,3,6,9,10,12,15,19,25,27 ieee-39 2,6,9,10,12,14,17,20,22,23,26,29,33 ieee-118 2,5,9,12,15,17,21,34,29,25,27,32,45,37,42,49,56,64, 62,53,68,70,71,76,77,80,94,101,105,85,90,86,110 nrip 74,85,104,92,69,58,79,46,50,54,45,80,71,65,72,11,5, 76,97,96,15,238,234,40,235,215,218,209,187,48,191,206, 194,24,190,205,182,199,200,27,28,130,162,157,19,168, 173,167,181,20,158,116,229,121,112,120,146,141,132, 153,34,109,106,244,129,243,130,105,140,142 iii. constraints for wams power system restoration after sectionalizing the network, each island should be independently observable. for this, the process of network partition should be undergone three constraints like transformer equivalent bus, generation-load balance and observability of each island. the constraints will be explained as follows. a. generation-load balance this constraint ensures that there should be enough amount of active power to all the loads in each island. it can be represented as,   nn rr i li i gi pp 11 > , i = 1, 2, 3.....r. (5) where, r represents the number of regions, nr represents the number of buses in each island, pgi gives maximum generation at ith bus and pli gives the load at ith bus. this constraint must be satisfied in each-iteration of network partitioning. b. joining the islands on either sides of transformer for the individual regions to run independently, it is required that the transformer and its buses should be allocated to the same region. this can be achieved by joining the islands present on either sides of transformers. it is a constraint that will be applied only after partitioning the complete system initially. c. observability of islands this constraint will be checked by kk pp xa                   1 . . 1 1 (6) where, the matrix ap gives the system connectivity of the pth region. it can be calculated from (7). the vector xp of the pth region is the binary variable vector which can be calculated from (4), k is the number of buses in the pth island. this is the last constraint that will be applied only after checking the second constraint. this constraint needs to be satisfied by each island, otherwise the island is said to be unobservable. iv. proposed network sectionalizing here, the partition method is illustrated by considering an ieee-30 bus system as shown in figure 1. after considering the system, the first step is to identify the number of islands. for this, let us consider the network connectivity matrix 'a' whose elements can be defined as,      otherwise connectedarejandibusesorjiif aij ,0 ,1 (7) during the restoration, after the blackout, all the regions which are stable must be connected together to restore the system completely. moreover, the number of islands decides the restoration time. so, while partitioning the system it should be assured that each region should have at least one generator and an allowable load connected to it. the number of regions can be selected as follows, fig. 1. ieee-30 bus system          n i n i i n i i mlgr 111 ,,min (8) where,       otherwise loadaffordableanwith connectedibusatgeneratoraisthereif gi ,0 ,1 (9) engineering, technology & applied science research vol. 7, no. 4, 2017, 1811-1819 1813 www.etasr.com phanendra babu et al.: a new power system restoration technique based on wams partitioning     otherwise ibusatbusloadaisthereif li ,0 ,1 (10)     otherwise pmuhasibusif m ,0 ,1 (11) after selecting the number of regions (r), a matrix r called regional matrix will be formulated. r is a r×n matrix in which each row corresponds to one region. initially all elements in every-row of the matrix r set to 0 except for the buses with generator with affordable load and the corresponding load buses. then, the next order regional matrix can be calculated using (12) given below. 1,' 1   karr kk (12) where a is system connectivity matrix, r'k-1 is rk-1 after corrections. this equation will be calculated iteratively until all the nodes (or buses) of the system were assigned. the corrections needed for higher order regional matrix will be defined as below: 1. the node once assigned, it should not be reassigned to any other region in the next iteration. 2. if any entry in the regional matrix is greater than unity, it should be corrected to 1 before the matrix is considered for next order regional matrix. 3. if a node appears in one region then it can be assigned to that particular region provided this correction should satisfy (5), otherwise the entry should be reset before it is being considered for next iteration. 4. if a node appears for more than one region, based on the nature of the bus it can be assigned to a region as follows: load bus:  if a load bus appears in more than two regions, then it should be assigned to the one with the smaller power rating that could afford the load. the goal is to increase the number of regions (islands) and hence to reduce the restoration time.  if there is no single region that could supply the load alone, the regions that are incident to load bus should be combined in order to supply the load. zero-injection bus (zib);  if a zib appears in more than one regions then it should be assigned to the region with the smaller power rating. the goal is to increase the number of regions. generator bus:  if a generator bus appears in more than one regions, then it is suggested to assign it to the region with the smaller power rating. the goal is to improve the stability of an island. v. final partition of the network for the islands to be observable, (6) needs to be verified. if it is not satisfied, it means some of the buses whose entries represent '0' need to be made observable by moving them into their adjacent islands provided the restoration constraints would not be disturbed. while making the unobservable buses observable, few situations that may arise will be handled as follows:  unobservable bus is a load/generator bus: yhe bus is then moved to an island via boundary line where it would be made observable provided this movement should not disturb the restoration constraints one and two. if this change causes violation of any constraint then the home island and the target island need to be joined.  unobservable bus is zib: if the unobservable bus is zib then it should be moved to a region where it would be observable. the flowchart of the proposed methodology is shown in figure 2. fig. 2. flow-chart of the proposed algorithm vi. phasor data concentrator placement pdc archives the data from multiple pmus installed over a wide area and aligns it for analytics /visualization. so, this must be placed in every island to provide certain functions like wide-area monitoring and protection. this section presents a new methodology to place pdcs in each island optimally with respect to the pmus of that particular island. the problem of pdc placement can be defined as follows: engineering, technology & applied science research vol. 7, no. 4, 2017, 1811-1819 1814 www.etasr.com phanendra babu et al.: a new power system restoration technique based on wams partitioning minimize    r j pxs 1 (13) subjected to 1s p (14) where xcs p i ijp nr    1 (15)     itherwise busobservedpmuisjorpmuhasibusif cij ,0 ,,1 (16) where, xp is a binary pdc placement variable, sp is a pmu placed constraint function at bus p, cij is a network path connectivity matrix. once the network is partitioned, this method will be applied for all the islands. vii. results and discussions the partition method is illustrated by considering an ieee30 bus system as shown in figure 1. after identifying the number of islands as 6, the initial regional matrix becomes r1 as shown in (17). and, the second order uncorrected regional matrix will be obtained as (18). on applying the corrections suggested in section 4, the second order regional matrix of ieee-30 bus system is obtained as (19). the final regional matrix is obtained as (20). from this equation it is quite clear that the regions r3 and r5 were combined so as to supply the load at bus 19. so, the system is portioned into 5 stable regions as shown in figure 3. the system presented in figure 3 inherently exhibits generation-load balance as the first constraint is satisfied. next, the regions that present on the either side of transformer need to be joined in order to satisfy the second restoration constraint. so, regions r2, r3 (or r5) will be joined.                      100100 000000 000000 000000 000000 000000 000000000000000000000000 010000000100000000000000 001100000000000000000000 000000000001100000000000 000000000000000000001010 000000000000000000000101 1r (17)                      221201 000000 000000 000000 000000 000000 000000000000000000000000 120000100210100000000000 102200000000002000000000 000000001112200000001000 000000000000000000112112 000000000000000000000111 ' 2r (18)                      111101 000000 000000 000000 000000 000000 000000000000000000000000 010000100110000000000000 101100000000001000000000 000000001001100000000000 000000000000000000111010 000000000000000000000111 2r (19)                      111111 000000 000000 000000 000000 000000 000000000000000010000000 010011111111100000000000 101100000000011100000000 010011111111100000000000 000000000000000001111010 000000000000000000000101 4r (20) engineering, technology & applied science research vol. 7, no. 4, 2017, 1811-1819 1815 www.etasr.com phanendra babu et al.: a new power system restoration technique based on wams partitioning on applying the final portioning step for the system obtained above, the set of regions (r3, r6), (r2, r6) are combined via boundary lines because the target island (r6) individually cannot afford the loads at buses 24 and 8. figure 4 represents the final network after all these modifications. and, it infers that the island r3 covers larger. this is because of the fact that the generation in this region is accumulated where as the load is distributed. fig. 3. initial partition of the ieee-30 bus system the locations of pdcs obtained on applying the pdc placement algorithm are shown in table ii. on applying the proposed scheme to a ieee-39 system initially, it is clear that bus 18 is not observable and also it is found that it can be made observable by the pmu on bus 17. moreover, as the island r2 is able to afford the load at bus 18, it has been moved to region r2. figures 5 and 6 show the initial and final partitioning of ieee-39 test system respectively. table iii gives the regions, pmu locations and pdcs locations after final partition. fig. 4. final partition of the ieee-30 bus system table ii. regional information and pdcs locations after final partitioning ieee-30 bus system region buses pmu locations pdc locations r1 1,3 3 3 r4 14,15,18,23 15 15 r2 2,4,5,6,7,8,9,1,0, 11,12,13,16,17,19, 20,21,22,24,25,26, 27,28,29,30 2,6,9,10,12, 19,25,27 4,9,19,27 fig. 5. initial partition of ieee-39 bus system table iii. regional information and pdcs locations after final partitioning ieee-39 bus system fig. 6. final partition of ieee-39 bus system region buses pmu locations pdc locations r1 1,2,3,8,9,25,30,37,39 2,9 2,9 r2 4,5,6,7,10,11,12,13,14,15,16,17, 18,19,20,21,22,31,32,33,34,35 6,10,12,14, 17,33,20 11,14, 17, 19,22 r3 26,27,28,29,38 26,29 29 r4 23,24,36 23 23 engineering, technology & applied science research vol. 7, no. 4, 2017, 1811-1819 1816 www.etasr.com phanendra babu et al.: a new power system restoration technique based on wams partitioning similarly for the ieee-118 system, buses 48, 55, 59, 65, 78, 95, 106 and 107 are found to be unobserved. bus 48 is moved to the island containing bus 49 which could observe bus 48. similarly, buses 78 and 95 have been moved to the regions containing buses 77 and 94 respectively. even though the island with the pmu-installed bus 56 could observe buses 55, 59 and 65, it cannot supply the required load at the respective buses. so, these two islands are combined. similarly the island containing buses 106 and 107 is joined with an island that contains bus 105 which could make buses 105 and 107 observable. figures 7 and 8 depict the initial and final partition of the ieee-118 test system. table iv contains the pmus and pdcs location for different islands. an actual northern region of the indian power grid (nrip) has also been considered. its final partition is shown in the figure 9. the details of pmus and pdcs are given in table v. from the results, it is shown that this method has successfully produced more stable and observable islands which will really help countries which are yet to establish wams. fig. 7. initial partition of the ieee-118 bus system table iv. regional information and pdcs locations after final partitioning ieee-118 bus system region buses pmu locations pdc locations r1 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,33,34,35,36,43,113,117 2,5,9,12,15,17,21,34 8,12,21,34 r3 23,25,26,27,32,114,115 25,27,32 27 r6 24,47,68,69,70,71,72,73,74,75,76,77,78,116,118,82 72,75,77,116 25,69,71,115 r2 28,29,31 29 29 r5 37,38,39,40,41,42,47,48,49,50,51,55,56,57,58,59,60,61,62,63,64,65,66,67,68 37,42,49,56,62,64 40,66,56,64 r4 44,45,46 45 45 r7 52,53,54 53 53 r8 79,80,81,96,97,98,99 80 80 r9 92,93,94,95,100,101,102,103,104,105,106,107,108 94,101,105 100,105 r10 83,84,85,88,89,90,91 85,90 89 r11 86,87 86 86 r12 109,110,111,112 110 110 engineering, technology & applied science research vol. 7, no. 4, 2017, 1811-1819 1817 www.etasr.com phanendra babu et al.: a new power system restoration technique based on wams partitioning fig. 8. final partition of the ieee-118 bus system table v. regional information and pdcs locations after final partitioning nrip region buses pmu locations pdc locations r1 84,246,94,69,131,10,8,88,74,103,85,102,83,104,95,78,92,12,82,86,91,75,70, 89,80,44,57,25,46,64,55,63,39,7,67,56,58,51,54,52,49,62,4,43,71,3,72,73,179, 235,60,9,11,13,5,90,96,87,100,110,66,98,17,93,15,99,101,76 74,85,104,92,80,71,45,46,5 0,54,58,69,79,65,5,11,72,7 6,97,115,96 5,11,49,56,58,70, 76,78,79,90,95, 103 r2 40,41,32,33,218,215,211,59,214,212,217,216,213,196,77,31,30,209,2,189,187, 204,47,219,197,185,184,208,210,186,207,206,48,210,220,124,190,29,188,221, 191,192,195,220,183,194,24,226,222,223,225,205,227,133,228,26,203,224,39, 1,152,200,231,27,202,28,198,159,30,231,200,201,28,199 40,215,218,187,48,206,219 ,191,194,24,190,205,182,1 99,200,27,28 29,47,48,152,191, 194,196,199,202, 211,218 r3 23,180,22,157,162,176,177,161,175,21,19,166,178,169,173,167,163,167,181, 172,230,164,160,168,174,165,158,171,170,37,20,156 180,187,162,19,168,20, 173,167,158,181 21,157,166,170, 181 r4 240,235,38,233,24,239,238,234,237,230,36,118,232,130,105,242,42,129,126, 127,114,105,107,243,108,120,113,123,244,245,131,135,109,112,122,16,125, 124,106,34,150,153,132,139,143,152,240,144,121,229,136,138,141,150,153, 149,147,140,18,142,145,142,154,61,119,117,35,17,134,146,148,53,155,111, 116,151,137, 128 235,234,238,130,105,129,1 20,112,121,229,106,244,24 3,109,34,141,146,153,132, 140,142,116 35,106,108,118, 122,126,128,137, 140,147,235,240 viii. conclusion this paper assures a faster restoration process by partitioning the network into many regions which are easier to be restored during a build-up strategy. initially this partition starts with sectionalizing the network subjecting to the generation-load balance constraint, and next these sections are reorganized to ensure the remaining two restoration engineering, technology & applied science research vol. 7, no. 4, 2017, 1811-1819 1818 www.etasr.com phanendra babu et al.: a new power system restoration technique based on wams partitioning constraints. this approach provides synchronized phase angle data between any two adjacent islands thus ensuring the complete observability of all regions. this partition algorithm was applied on three different 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[14] b. xu, a. abur, “observability analysis and measurement placement for system with pmus”, ieee power systems conf. exposition, , vol. 2, pp. 943–946, october 2004 [15] b. gou, “optimal placement of pmus by integer linear programming”, ieee trans. power syst., vol. 23, no. 3, pp. 1525–1526, 2008 [16] b. gou, “generalized integer linear programming formulation for optimal pmu placement”, ieee trans. power syst., vol. 23, no. 3, pp. 1099–1104, 2008 [17] s. chakrabarti, e. kyriakides, d. g. eliades, “placement of synchronized measurements for power system observability,” ieee trans. power del., vol. 24, no. 1, pp. 12–19, 2009 [18] e. caro, r. singh, b. c. pal, a. j. conejo, r. a. jabr, “participation factor approach for phasor measurement unit placement in power system state estimation”, iet gener. transm. distrib., vol. 6, no. 9, pp. 922– 929, 2012 engineering, technology & applied science research vol. 7, no. 5, 2017, 1962-1966 1962 www.etasr.com desouky et al.: a new contribution in reducing electric field distribution … a new contribution in reducing electric field distribution within/around medium voltage underground cable terminations s. s. desouky electrical engineering department port said university port said, egypt sobhyserry@yahoo.com a. z. el-dein electrical engineering department aswan university aswan, egypt azeinm2001@hotmail.com r. a. abd el-aal electrical engineering department port said university port said, egypt ramadanhv@gmail.com n. a. a. el-rahman electrical engineering department workers university ismalia, egypt eng_nagwa77@yahoo.com abstract—ιn medium voltage cables, the stress control layers play an important part in controlling the electric field distribution around the medium voltage underground cable terminations. underground cable accessories, used in medium voltage cable systems, need a stress control tube in order to maintain and control the insulation level which is designed for long life times. the term “electrical stress control” refers to the cable termination analysis of optimizing the electrical stress in the area of insulation shield cutback to reduce the electrical field concentration at this point in order to reduce breakdown in the cable insulation. this paper presents the effect of some materials of different relative permittivities and geometrical regulation with the curved shape stress relief cones on the electric field distribution of cable termination. the optimization was done by comparing the results of eight materials used. also, the effect of the change in the thickness of the stress control tube is presented. the modeling design is very important for engineers to find the optimal solution of terminator design of medium voltage cables. this paper also describes the evolution of stress control systems and their benefits. a developed program using finite element method (fem) has calculated a numerical study to the stress control layering electric field distribution. keywords-stress control analysis; cable terminations; comsol analysis; stress control tube (sct) i. introduction distribution of power is generally implemented using overhead lines or underground cables [1]. underground cables are commonly used in low voltage and medium voltage solutions. the development of medium voltage underground cable accessories requires basic understanding of the stress caused by the electric field in different parts of the insulating structures. material properties and product design play a key role in the durability of terminations and joints [2]. terminations and joints are needed to make connections between lines or to an electrical device [3]. the main accessories of the underground power cables are terminations. different sides are considered when designing the cable terminations because it must have the same quality as its associated cables if one wants to make connections between lines [3]. in cable composition, medium power cables need electrical stress control when terminated. when the insulation shield is removed from a cable, high potential values are concentrated at this point, presenting high electrical stress. electric field increase at those points can cause local discharges that produce either flashover along the insulation surface or insulation failure causing cable breakdown. the design of underground cable terminations must eliminate the electric field concentration to reduce the breakdown of the cable. or, the electrical field has to be controlled in a cable termination [3]. underground cable accessories used in medium voltage cable systems need a highly reliable stress control system in order to maintain and control the insulation level which is designed for estimated life times longer than 30 years [4]. at the shield cut-back of a termination, an increase of the electric field strength happened, which makes discharges in the first time and later on to breakdown or flashover. stress control materials are used to obtain a better field distribution in the cable termination [5]. a screening is the weakest area in a termination. terminations without stress control suffered from the high electric field peak and at the end have failed with high voltage [6]. in electrical engineering, an insulated electrical conductor fitting into a grounded screen, is a common configuration that causes problems in the electric field distribution. near the screen there is a critical area where an increase of the electric field happens [7]. ii. requirements of stress control on cable terminations the cable setting up is needed for all types of underground cable terminations to present a better electrical and mechanical quality. the installation of the cable termination is presented in [3]. the removal of the shield of the insulation area changes the radially symmetric capacitor build of the cable. there becomes a high stress point at the shield terminus after the insulation area is terminated. and, high potential gradients are present between the insulation and the surrounding medium [8]. medium voltage cable terminations should be controlled to engineering, technology & applied science research vol. 7, no. 5, 2017, 1962-1966 1963 www.etasr.com desouky et al.: a new contribution in reducing electric field distribution … reduce the stress that exists at a point where the screen or shield is terminated [9]. a precise determination of the electrical stress in insulated conductors will lead to an optimum design and a better selection of both wire size and the type of insulation for full utilization of the insulating conductors [10]. a graphical model of the cable termination can be found in [3]. there are five different areas in the model. these areas are: conductor (r1), insulation (r2), screen (r3), stress control tube (r4) and air (r0). iii. finite element analysis the finite element analysis software needs to get suitable numerical formulation of the given nonlinear partial differential equation for the electric potential calculation. hence, the original problem is replaced with its variation form of differential equation for the finite element model. the finite dimensional set is represented by a complete basis set and iterative solution is done to get accurate solution [11]. in highly non-homogeneous fields this assumption can lead to inaccurate results. calculation accuracy can easily be improved by making the element net denser. this increases the amount of calculations and cannot be done unlimitedly [12]. comsol multiphysics is a simulation software package that uses finite element method. the basic idea of fem is to divide the examined area to small elements where each field's magnitude is described by a function. the potential v is used as field magnitude when static electric fields are examined minimizes interfaces from fluid flow and heat transfer to structural mechanics and electromagnetic analyses [13]. iv. finite element compution finite element computations were taken in 2-d dimensions with the ground screen modeled as floating with a dielectric of 1000. in the computation, the conductor screen was not modeled. the cable was typical of 10 kv class cable with conductor of 13.6 mm diameter, insulation thickness 5.5 mm with dielectric constant 2.3, the grounded screen was 0.7mm thick with a dielectric constant 1000. the dimensions of single core cable termination are provided in [14] and presented in table ii. the algorithm for the finite element analysis techniques starts with the maxwell equations used in potential formulations. then, the laplace equations for the nonconducting regions and diffusion-like nonlinear equation for the stress control region are defined. boundary conditions combine these equations. these differential equations are solved by an iterative method to obtain the field distribution of the model [15]: 0[ ( ) ] 0c v v fρ ρ = 0 0 0 2 0 4 ( ) ε ( ) i sct k r c v k r k r t                          0 2 2 0 4 4 0 0 ( ) k r f k r v t t k r t                          where, k is a regular point in the defined region. the original problem is replaced with its variation form of differential equation for the finite element model. the finite dimensional set is represented by a complete basis set and iterative solution is done to get accurate solution. the solution method obtains nodal values of the variation form on each element. these potentials in vector form are then used in the system solution. finally, the system of equations results in the form of: k·u=f where k is a n×n matrix, u is the nodal potential column vector, f is a n vector obtained by finite element method. [16] v. validation of the simulation method in this section the validation of the simulation results is done by comparing some simulation results with the experimental results obtained by others [1]. the effect of permittivity and conductivity were studied separately in[1]. the conductivities of the masses are generally between 10-8 and 1012. the properties of tubes also vary greatly as relative permittivities from about 20 to 40 and conductivity from 10-7 to 10-13 [1]. all simulations were done using the same boundary with 12 kv and simulation setting by using comsol program. the results give that the use of a higher permittivity for the tube is better. it is seen that the permittivity affects the result more than conductivity does. the permittivity of the mass has a higher impact on the resulting peak. the highest permittivity for the mass and the tube results in about 25% lower electric field peak at the cutting point of the screening than the one that would be with the lowest permittivity values. the conductivity of materials does not affect the electric field peak greatly. the difference between the best and the worst setup is significant. the use of the highest permittivities and conductivities leads to about 55% lower electric field peak than without any grading. the lowest permittivities and conductivities lead to about 39% lower electric field peak than without any grading [1]. measuring the electric field can be so hard since the probe used for measurement can upset the field. the implementation of simulation results was carried out by studying the behavior of terminations in high voltage tests. the tests were done using a baur pgk 110 / 5 hb high voltage test set. the broken terminations were cut open to study the reason of the failure [1]. failures occurred at the cutting point of the screening which makes the insulation to melt and allowed current to flux between the conductor and the grounded cable screening. the hole in the insulation was not exactly at the cutting point but instead a bit away from it. this was considered the weakest point in the insulation. the cause of the failure is unknown since no clear installation error could be seen. the breakthrough could be a result of quality issues in the stress control mass or even in the cable insulation. wrong engineering, technology & applied science research vol. 7, no. 5, 2017, 1962-1966 1964 www.etasr.com desouky et al.: a new contribution in reducing electric field distribution … electric properties in the mass could lead to a much higher electric field concentration at the cutting point of the screening. improper structure of the mass could also give a breakthrough if air bubbles were left inside the termination [1]. partial discharges generated inside the air bubbles would start to slowly burn the insulation and could lead to failure. the electric field peaks are comparatively lower than the 12 kv voltages that were used in the simulations. it is however necessary to note that all simulations give perfect insulators without any air bubbles or uncleanness between layers. no insulator is ideal though and air bubbles exist in all areas. therefore the resulting electric field distribution is always higher than that represented in simulations [1]. table i. electric field peak results for terminations [1]. simulation setup permittivity[ε r] field peak [kv/mm] 1 20 5.45 2 40 5.45 3 20 5.45 4 40 5.45 5 30 4.5 6 30 4.5 7 30 4.5 8 30 4.5 table ii. dimension of cable termination [14]. volt (kv) indoor termination outdoor termination up to 12/20 170 230 18/30 230 290 ( z ) dimension ( mm ) vi. stress control tube (sct) model the application of stress control tube on the cable termination models is used considering the material properties. thus, the thickness and the relative permittivity effects of the stress control area are presented using finite element method. the favorable model design is done by using comsol program. in the cable termination model; the relative permittivity of the stress control tube is the variable properties. the effect of changes in the properties of the stress control tube is done by comparing the results of different simulations. the simulations solve the electric field distribution over the given model. the result analysis includes the electric field distribution at every point of the finite element model. so, the results are estimated as execution properties to optimize the design. vii. relative permittivity impact on the stress control tube model in our study, the effect of the relative permittivity of the stress control tube used on the underground cable termination is obtained. stress control is also achieved by employing materials having relative permittivity significance higher than the cable dielectric. the relative permittivity of the stress control tube is a variable and is changed in each simulation. the optimization was done by comparing the results obtained by 8 different materials. stress control tube materials with relative permittivity changing from 5 to 1000 were used. the results of the analysis are obtained using comsol multiphysics shown in following figures with 2d and 3d models of electric field distribution. figure 1 shows the maximum electric field distribution without sct across the medium voltage cable termination. when, sct is applied with ɛr=5 (figure 2) the electric field is decreased. figure 6 presents the 3d model of electric field distribution with sct ɛr=5. figure 4 shows that the peak value of electric field at cutting point is higher than when no stress control tube is used. the use of the highest permittivities leads to roughly 59% lower electric field peak than without using sct. the maximum electric field distribution with changing stress control tube relative permittivity and the values of maximum electric field at cutting point at the screen are shown in table iii. figure 5 shows the maximum values of the electric field distribution with different relative permittivity. in figure 6, the change of the relative permittivity is effective from 5 to 40 and the electric field does not change as the relative permittivity becomes greater than 40, so the best effect of the stress control tube is with relative permittivity ɛr =40. figure 6 presents the percentage of maximum values of the electric field reduction with different relative permittivity. viii. thickness effect on stress control tube model the thickness of the stress control tube is changed from 1mm to 5mm and the relative permittivity is supposed to be constant with ɛr =40. the results of the analysis are obtained by using comsol program. figure 7 shows the electric field distribution with 2mm thickness. this value is compared with different thickness of the stress control tube in table iv. from the obtained results presented with constant relative permittivity equal 40, it is seen that the change of the stress control tube thickness has no effective role. for cost consideration, the best value of the cable termination model is considered with stress control tube of 1mm thickness. table iii. maximum values of the electric field distribution with different relative permittivity ɛr emax (kv/mm) 5 3.39 10 2.731 20 2.463 40 2.463 60 2.463 100 2.463 500 2.463 1000 2.463 table iv. the maximum values of the electric field distribution for different thickness of the stress control tube d (mm) 1 2 3 4 5 emax (kv/mm) 2.473 2.463 2.474 2.458 2.459 engineering, technology & applied science research vol. 7, no. 5, 2017, 1962-1966 1965 www.etasr.com desouky et al.: a new contribution in reducing electric field distribution … fig. 1. electric field distribution without sct fig. 2. electric field distribution with sct ɛr = 5 fig. 3. the 3d model of electric field distribution with sct ɛr = 5 fig. 4. the maximum electric field distribution with and without sct in the cable termination fig. 5. maximum values of the electric field distribution with different relative permittivity fig. 6. the percentage of maximum values of the electric field reduction with different relative permittivity fig. 7. electric field distribution with 2 mm thick ix. cable termination model with deflector the second method for terminating stress control is using the stress cones (geometric system). the stress cones use the geometrical structure for controlling. geometric stress control involves an extension of the shielding extending the diameter at which the terminating cutout occurs and thereby reduces the stress at the cutout. the curved shape of the stress cones uniformly scatter the equipotential lines which outcomes reduced the electric field distribution the stress cone is extended beyond the screen termination, so that the potential gradient at the dielectric surface is reduced to a level where discharges will not occur. the numerical model of the deflector engineering, technology & applied science research vol. 7, no. 5, 2017, 1962-1966 1966 www.etasr.com desouky et al.: a new contribution in reducing electric field distribution … is presented with the comsol program. the results of the analysis are obtained as the electric field distribution using comsol multiphysics with 2d and 3d models are shown in figures 8 and 9. the deflector model reduced the concentrating of the electric field at the termination area with its geometrical structure. figure 8 shows that the electric field is decreased with the curved geometry of the deflector model to 3.1 kv/mm compared with 5.9 kv/mm without stress control. figure 9 shows the 3d model of electric field distribution with deflector. the deflector model should be achieved more neatly because it is determined as its ideal geometrical structure ecological factors affect the effective implementation of the deflector. the implementation needs high versed working. so the total cost of the application is considered substantial disadvantage to implement the deflector. fig. 8. electric field distribution with deflector fig. 9. the 3d model of electric field distribution with deflector x. conclusions in this work, cable termination models with sct and geometrical regulation with the stress relief cones are presented. the electric field distributions are simulated, and the results are evaluated. the stress control tube is consisting of a layer with different relative permittivity. the stress control tube applied on the cable screen reduces electric field at the termination area successfully. increasing relative permittivity of sct between 5 and 40 has effect. the stress effect is not seen in the screen cut point when the relative permittivity is increased greater than 40. hence, the effect of the electric field distribution is best achieved by a material with ɛr =40. also, from the obtained results it is clear that for relative permittivity 40, the change of the stress control layer thickness has no effect. for cost consideration, the best cable termination model is considered with stress control tube of 1 mm thickness. the deflector model decreases the concentrating electric field distribution at the termination area. the results show that the electric field is decreasing with the curved geometry of the deflector. the stress control tube reduces the electric field stress at the termination significantly compared with stress control cone. references [1] k. vakevainen, the effect of material properties to electric field distribution in medium voltage underground cable accessories, degree thesis, arcada university, finland, 2010 [2] m. aro, j. elovaara, m. karttunen, k. nousiainen, v. palva, suurjännitetekniikka, otatieto, 2003 [3] g. bas, electric field analysis in stress controlled high voltage cables, msc.thesis, middle east technical university, 2005 [4] r. strobl; w. haverkamp; g. malin; f. fitzgerald, “evolution of stress control systems medium voltage cable accessories”, ieee/pes transmission and distribution conference and exposition, vol.2, pp. 843-848, 2001 [5] l. bayon; f. buret; c. koelblin; t.toledo, “field distribution measurement and simulation of stress control materials for cable accessories”, proc. ieee international conference on solid dielectrics, vol.2, pp. 534-537, 2004 [6] n. raicevic; s. ilic, s. aleksic, r. dimitrijevic, “improving safety of cable networks by modeling deflectors of cable accessories," 4th international conference on power engineering, energy and electrical drives, istanbul, pp. 70-75, 2013 [7] d. carstea, i. carstea, “numerical simulation of electric field distribution in cable terminations”, 6th international conference on telecommunications in modern satellite, cable and broadcasting service, vol. 2, pp. 479-482, 2003 [8] j. w. hoffman, “insulation enhancement with heat-shrinkable components”, ieee electrical insulation magazine, vol. 7, no. 2, pp. 33-38, 1991 [9] s. s. el-dessouky, a. a. rasmi, f. m. h. youssef, “experimental investigation of the flashover problem at the xlpe cable terminations under coastal environments," ieee international symposium on electrical insulation, toronto, pp. 208-212, 1990 [10] a. a. hossam-eldin, s. s. dessouky, s. m. el-mekkawy, r. a. abd elaal, “study and analysis of field enhancement and h.v rating of power cables containing micro cavities," annual report conference on electrical insulation and dielectric phenomena, vancouver, pp. 797801, 2007 [11] j. jin, the finite element method in electromagnetics, ieee press [12] comsol multiphysics, ac/dc module, available at: http://www. comsol.fi/products/acdc/ [13] a. aarnio, characterization of non-metallic materials for medium voltage cable accessories, msc thesis, tampere: university of technology, 2010 [14] elastimold egypt, instalation instruction single core termination [15] d. k. cheng, field and wave electromagnetics, addison-wesley publishing company [16] c. petrarca, d. cerbasi, v. tucci, m. vitelli, “numerical analysis of performances of stress grading cable accessories made of different anisotropic composite materials”, annual report conference on electrical insulation and dielectric phenomena, victoria, vol. 2, pp. 494-497, 2000 engineering, technology & applied science research vol. 7, no. 5, 2017, 2062-2067 2062 www.etasr.com el yamami et al.: representing it projects risk management best practices as a metamodel representing it projects risk management best practices as a metamodel abir el yamami souad ahriz khalifa mansouri signals, distributed systems and artificial intelligence laboratory enset mohammedia university of hassan ii mohammedia, morocco abir.elyamami@gmail.com signals, distributed systems and artificial intelligence laboratory enset mohammedia university of hassan ii mohammedia, morocco ahrizsouad@gmail.com signals, distributed systems and artificial intelligence laboratory enset mohammedia university of hassan ii mohammedia, morocco khmansouri@hotmail.com mohammed qbadou el hossein illousamen signals, distributed systems and artificial intelligence laboratory enset mohammedia university of hassan ii mohammedia, morocco qbmedn7@gmail.com signals, distributed systems and artificial intelligence laboratory enset mohammedia university of hassan ii mohammedia, morocco illous@hotmail.com abstract—although still relatively new, the field of it governance has its own bodies of knowledge that include various methodologies, frameworks and techniques supported by an increasing growing base of research. it project risk management has since emerged as its own field. many frameworks and methodologies were proposed by both practitioners and researchers. a review of the literature about the subject shows that there is a divergence between the two. the practitioners propose a set of good practices from professional environment but the heaviness of the proposed guides does not allow its application and adoption by managers or it’s improvement by researchers. thus it calls for specific focus on it governance frameworks best practices modelling in order to reach fusion between practitioners and researchers contributions. in this paper, special attention is dedicated to project management institute’s guides. the main objective is representing it project risk management best practices as a metamodel in order to complement different areas of knowledge. keywords-project management; risk management; pmbok; prince2 i. introduction projects management frameworks are becoming an obligation in order to face the environment requirements and to meet the strategic objectives designed by the organization. authors in [1] precised that project management serves as primary capabilitiy of an organization to respond to change and gain a competitive edge. authors in [2] define project management as a critical competency for organization strategy. despite the proliferation of project management frameworks/ methodologies/ software, many projects fail. according to international standish group study, project failure rate is high in technology sector, most of projects are over budget/ deadline with a lower quality than expected, project success rate has declined from 34% in 2004 to 32% in 2009 [3]. author in [4] defines a project management success as a subset of project success, an internal measure of efficiency. a survey study was realized in [4] in order to investigate any linkages among organization project management maturity factors, project success factor and project management performance factors. the result of this study suggests that organizations encouraging project manager to obtain project management professional certification (pmp) are likely to have procedures and policies in place. conventional project risk management is reactive. risk managers are involved only when the project is already over budget, over deadline or underperforming. software allowing project management has been designed but less attention has been devoted to the assessment of projects risks. in the other hand, risk management principles are described by international standards which don’t prescribe how the process can be implemented. it managers must have a global and a complete idea about methodologies and frameworks existing in order to choose the best framework for each specific project. yet, managers prefer specific project methodologies and find difficulties to manage other projects that use other methodologies. in the other hand, it projects management software are designed to meet the requirements of only one framework. furthermore, the heavy nature of framework guides doesn’t allow it governance interested researchers to improve these frameworks. hence the need for representing it governance framework knowledge areas as consistent basic models. engineering, technology & applied science research vol. 7, no. 5, 2017, 2062-2067 2063 www.etasr.com el yamami et al.: representing it projects risk management best practices as a metamodel this paper is focused on exploring any linkages among project management and project risk management knowledge areas. for that aim, we will analyze two of the most used frameworks for project management: pmbok and prince2, and respectively we will compare pmi’s risk management framework and m_o_r guide established by ogc. this comparison will provide a better understanding of it management framework. then we use this comparison to suggest a global model of the management of it projects in organizations by combining different knowledge areas derived from these it projects frameworks, which allows a better alignment of projects with the company crafted strategy. the rest of this paper is organized as follows: firstly, we present an overview of related works and we explain the motivation for our contribution in section ii. secondly, we present a description and analysis of project management frameworks, and project risk management guides respectively in section iii and iv. then we provide our proposed it project risk management metamodel in section v. finally we discuss the main outcomes and we highlight a number of limitations and perspectives of our works in conclusion. ii. related works and motivation several risk management approaches have been presented by researchers. authors in [5] have integrated a few of the most effective risk management recommendations of different researchers with the elementary risk management process in the form of a database. authors in [6] established an evaluation model for software project risk based on bp neural network and the algorithm process [6]. authors in [7] use importance measure technique in order to model the complex risk management field. they provide an application to assess both risks and risk interactions in order to establish priorities for further decision making. authors in [8] proposed a two phase method focusing on the characteristics of dynamic risk and multi attributes, based on markov to evaluate risk in the first phase and then topsis for selecting risk management strategy. authors in [9] established a project risk management method based on bayesian network model for predicting of job completion time and preventing delay of delivery. authors in [10] used ahp model to construct a risk model to find knowledge relating to risks. despite of many risk management approaches presented by researchers and the widely use of it project management frameworks by it managers, the success rate of project is very low [3, 11, 12]. the paper points out the enhanced need for analyzing, comparing and integrating it management best practices. the objective of our contribution is to integrate effective techniques for risk management identified form professional literature with the elementary project management conceptual model in order to make it more effective. thus, five growing and established project methodologies were compared, and a generic project management metamodel has been suggested. in our case, we use uml language to model the concepts of it project risk management and to show the relations maintained between each other. uml is a standard maintained by the omg [13]. it is originally a software design language that allows specifying objects manipulated in applications (class diagram). in the field of research, uml language has been used in different areas: it allows to structure meta-models within the framework of an mda approach [14], to model ontologies [15], to specify domain models for the trades within architecture framework [16] or to specify multi-agent systems [17], which makes uml a stable and a reference language for modeling concepts and their relationships. iii. review of project management framework according to [18], project management is an iterative process that is considered as a lock-step sequence of activities with the application of skills, tools, knowledge and techniques in order to meet the project stakeholder needs and expectation. a. pmbok (porject management body of knowledge) pmi’s pmbok guide is a set of standard terminology and knowledge for project management. it is a combination of 9 knowledge areas and 5 processes group with 44 kpa (key process areas), it handles the project life cycle and phases, the project stakeholders, the organizational and the socioeconomic influences and the general management skills needed by the project manager. pmbok processes are described as a standard for project management because the pmi is approved by the american national standards institute to be a standard developer. pmbok does not prescribe any specific life cycle for small projects, it only specifies that the project life cycle should be divided into phases, which is a difficult process for the small project managers [18]. b. prince2 prince2 is the successor of promptii, it was released by the uk government in 1996, its most recent edition was released in 2009. prince2 is a methodology for managing effectively all types of projects. it is combined of 5 phases and 8 high level processes (6 main processes and 2 supporting processes). prince2 is mostly used in uk organizations. prince2 requires a high degree of support from the top management to get the desired results, and it doesn’t provide any support for people and contract management. c. pmbok and prince2 comparison and analysis the two methodologies discussed have commonalities in their features and ultimate goal. they perform tasks with common goal but with different approaches. we provide a basic comparison of pmbok and prince2 structure trough in table i. the pmbok guide is described as descriptive while prince2 is often described as perspective, because the pmbok guide contains lots of descriptions of tools, techniques and processes. pmbok describes the output of each process but does not explain what information must be recorded in such outputs. unlike pmbok, prince2 provides description about what information must be recorded in the outputs of its processes and who is responsible for the recording. the main strength of the pmbok guide is that is provides a range of useful tools and techniques. (119 tools compared with only 40 tools referred in prince2 guide). the greatest strength of prince2 is that the majority of decisions must be based on business case. prince2 allows a better engineering, technology & applied science research vol. 7, no. 5, 2017, 2062-2067 2064 www.etasr.com el yamami et al.: representing it projects risk management best practices as a metamodel understanding of the benefits versus costs. moreover, prince2 provides a detailed description of multiple project management team roles, describing the responsibilities for a total of 9 different project management team roles. the biggest weakness of prince2 is its lack of tools and techniques, since it only describes 2 techniques. prince2 and pmbok both are not intended to tell managers how to use any of techniques or tools described, they only lay out the process. table i. pmbok and prince2 comparison prince2 pmbok guide 7 principles no principles 7 thems 10 knowledge areas 7 processes 5 process groups 41 activities 47 processes 2 techniques described in detail and 40 techniques referenced 119 tools and techniques described table ii. comparison of pmbok knowledge area and prince2 theme prince2 theme pmbok guide knowledge area change, progress integration plan, process scope, time, cost quality quality organization communications, stakeholder risk risk plans human resource not covered procurement business case not covered iv. review of project risk management models several risk maturity models exist in literature. among them: pmi’s risk management model, m_o_r guideline and iso31000. a. pmi’s risk management model according to the project management institute pmbok, risk management is one of the ten knowledge areas in which a project manager must be competent. risk management is defined as an organizational policy for optimizing investments and risk to minimize the probability of failure. pmi provides a practice standard for project risk management based on pmbok guide. it explains the purpose of risk management and provides a list of critical success factors for implementing risk management. these factors are applicable to most organizations and projects regardless of their size. pmi’s risk management standard distincts between individual project risks and overall project risks, and discusses the role of the project manager in risk management. it also identifies six risk management processes: • plan risk management • identify risks • perform qualitative risk analysis • perform quantitative risk analysis • plan risk responses • monitor and control risks b. m_o_r guideline the uk commerce government office published a risk management guide called m_o_r. the m_o_r guide provides a maturity model for risk management so-called “health check” and offers a framework that consist of four main steps: • identify • assess • plan • implement c. is0 31000 the iso technical management board working group had developed an international standard that focuses on risk principles and guidelines which is the iso 31000:2009. it provides a guideline for risk definition and risk management process. it focuses on risk assessment. • communication and consultation • establishing the context • risk assessment • risk identification • risk analysis • risk evaluation • risk treatment • monitoring and review d. project risk management standards comparison while iso is a stand-alone risk management standard, pmi’s framework is highly integrated within the pmbok framework. the main advantage of pmi’s risk management standard is that it provides much more specific information on how the process can be implemented and that it differentiates between qualitative and quantitative risk analysis. the principle disadvantages of pmi’s standard are that it does not include the articulation of organizational objectives and the risk evaluation process. much like pmi’s framework, iso 31000 underscores the importance of accounting for the context which risk management is implemented. moreover, risk management processes are similar to those proposed in the pmi’s management framework and do not contradict each other. iso 31000 addresses risk in general while pmi’s framework addresses project management risk. it differentiates between three types of risks: qualitative, semi-quantitative and quantitative risks. m_o_r is based on the iso 31000, but it focuses on practical application and provides more details about risk management. for our contribution, we have selected the pmi’s frameworks for many reasons: • the standards of pmi have achieved extensive exposure and worldwide acceptance [19]. engineering, technology & applied science research vol. 7, no. 5, 2017, 2062-2067 2065 www.etasr.com el yamami et al.: representing it projects risk management best practices as a metamodel • pmi’s frameworks provide more details, tools and techniques about project management. • pmi’s practices standard for project risk management is generic and can be applied to any organization. • finally, pmi is involved in the iso/pc236 project committee and iso/tc258 committee, so iso and pmi’s risk management standard will be more closely aligned [19]. yet, we will propose a project management metamodel based on the pmbok guide and pmi’s risk management standard. v. proposed metamodel the objective of this section is to present the concepts manipulated in our proposed model for it project risk management. the proposed integrated model (figure 1) is composed of two packages, one for the pmbok derived model and the second for pmi’s risk management standard derived model. to explain our model, we will start by describing pmbok and pmi’s risk management standard architectures, then we will present the relation between the two original packages. a. pmbok model the main classes for project management model are derived from [20, 21]. pmbok covers human and physical resources, activities, deliverable, the organizational concepts and their associated classes. an organization has a collection of programs, each program is combined of a set of projects directed by one given stakeholder [20]. a stakeholder may assume one or many roles in a project. each project is composed of a set of phases which are related to activities that can be divided in tasks. for each activity, the associated stakeholders, and their respective roles must been defined. activities are related to deliverables as an input or output and each deliverable has a type and a responsible. the pmbok guide defines five process groups (such as: initiating, planning, executing, monitoring and controlling, and closing), each activity is related to a management process that is associated to one ore many knowledge areas (such as scope, time, cost, quality) [20]. the knowledge areas can be classified as core or facilitating knowledge areas. b. pmi’s risk management standard our model must ensure the requirements defined in pmi’s risk management domains: d1. risk strategy and planning: this domain allows quantifying risk tolerances in order to assess risk thresholds for the project, developing a project risk strategy in order to establish the outline for the risk management plan, and establishing evaluation criteria for risk management processes based on project objectives in order to measure effectiveness of the project risk process. d2. stakeholder engagement: this domain allows assessing stakeholder risk tolerance, prioritizing project risk and promoting risk ownership and engaging stakeholders on risk prioritization process based on stakeholder risk tolerance in order to optimize consensus regarding priorities. d3. risk process facilitation: this domain aims to facilitate risk identification, evaluation, prioritization and response among project team members. to apply risk assessment processes and tools in order to quantify stakeholder risk tolerances and determine risk levels, and to provide risk data to cost and schedule analyst/estimators to ensure that project risk is properly reflected in cost and schedule estimates for the project. d4. risk monitoring and reporting: this domain allows creating custom reports using risk-related metrics in order to communicate risk management activities and status. d5. perform specialized risk analyses: this domain aims to evaluate identified risk attributes using advanced quantitative tools and qualitative techniques in order to estimate overall risk exposure of the project, and to support stakeholder decision making for the project. thereby, the pmi defines risk as a probability of threat or damage which any occurrence can impact resources and activities. for each risk, the pmi specifies a set of risk policies, risk evaluation criteria and one or more risk tools that can be qualitative techniques or quantitative tools. it defines risk type that can be operational, tactical or strategic and risk strategy that can be corrective or preventive strategy. a risk occurrence is under the responsibility of a risk manager, for each risk occurrence the risk level is designed, the stakeholders are engaged on risk prioritization process based on stakeholders risk tolerance. the pmi defines a risk assessment plan that enables decision makers to manage risks. the assessment place risk occurrence in one of four risk response categories: mitigate risk if risk impact is small, avoid risk in case of activities with a high likelihood of loss and large financial impact, transfer risk in case of activities with a large financial impact to a third party and accept risk if cost benefit analysis determines the cost to mitigate risks is higher than cost to bear the risk. integrating it project management model with risk management best practices allows early identification and a better understanding of the faced risks nature and proactively risks identification which makes easy the making of plan for mitigating effects of potential risks. the metamodel introduced in figure 1 is able to represent the fundamental structure from which it project risk management enhanced models can be derived with respect to pmi’s guides’ processes. this metamodel can be adapted to a new application domain so that the logic of it project risk management can be reused with a reasonable tailoring effort. vi. conclusion and future works the main objective of this paper was to understand risk assessment concepts in order to develop a model for it project risk management. most project management models proposed by researchers do not allow managing risks in compliance with risk management standards. this research paper is an attempt to overcome these challenges and provide a conceptual model for the development of project management and risk assessment solutions. for that aim, we have compared the most engineering, technology & applied science research vol. 7, no. 5, 2017, 2062-2067 2066 www.etasr.com el yamami et al.: representing it projects risk management best practices as a metamodel utilized methodologies within organizations, and we have chosen the pmi’s standards. therefore, our conceptual model is based on a combination of pmbok guide and pmi’s risk management standard by combining different knowledge areas derived from these guides. the integration of these standards allows the starting of risk management process early in the project lifecycle by including key stakeholders in the process, evaluating project risks periodically during the project lifecycle and to develop risk mitigation plans, which provides a better alignment of projects with the strategy crafted by the company. fig. 1. it projects risk management best practices metamodel the paper points out the enhanced need for analysing, comparing and integrating it management best practices in order to have a more efficient project management. our contribution presents some limitations: the model is primarily focused on pmbok best practices. this framework does not take into consideration the business case management, which does not allow managing it investment processes. in addition our model does not present it investment management knowledge areas. this process can be considered and explored in the future for developing an it strategic project alignment model in order to improve return on investment. besides that, our model does not define the organizational change management processes, next research should explore the integration of pmbok and prince2 best practices for engineering, technology & applied science research vol. 7, no. 5, 2017, 2062-2067 2067 www.etasr.com el yamami et al.: representing it projects risk management best practices as a metamodel supporting organization’s maturity plan. future efforts can also be focused on integrating project management maturity models in order to benchmark and improve project management performance. references [1] a. amaral, m. araujo, “project portfolio management phases: a technique for strategy alignment”, world academy of science, engeneering and technology, vol. 3, no. 10, pp. 1919-1927, 2009 [2] m. hurt, j. l. thomas. “building value through sustainable project management offices,” project management journal, vol. 40, no. 1, pp. 55-72, 2009 [3] the standish group international inc., chaos summary 2009: the 10 laws of chaos, 2009 [4] v. anantatmula, p. rad, “linkages among project management maturity, pmo, and project sucess”, engineering, technology and innovation (ice) & ieee international technology management conference, pp. 1-12, 2013 [5] u. iqbal janjua, j. jaafar, i. b. a. aziz, “integration of supportive processes with elementary processes for making current practices of software project risk management more effective”, international symposium on mathematical sciences and computing research, pp. 292-297, 2015 [6] l. bai, f. li, “the model of project risk assessment based on bp neural network algorithm”, 3rd international conference on computer science and network technology, pp. 326-329, 2013 [7] c. fang, f. marle, m. xie, “applying importance measures to risk analysis in engineering project using a risk network model”, ieee systems journal,vol. 11, no. 3, pp. 1548-1556, 2016 [8] g. jiang, y. fu, “a two-phase method based on markov and topsis for evaluating project risk management strategies”, 27th chinese conference on control and decision, pp. 1994-1998, 2015 [9] y. s. kim, t. murata, “global, project risk management in manufacturing environment”, 15th iiai international congress on advanced applied informatics, pp. 1016-1021, 2016 [10] g. h. zhang, w. j. tang, m. j. liao, “project risk management analysis model based on ahp: a case of hangqian freeway project”, 8th international conference on intelligent computation tecnology and automation, pp. 663-666, 2015 [11] j. dhlamini, i. nhamu, a. kachepa, “intelligent risk management tools for software development”, annual conference of the southern african computer lecturers' association, pp. 33-40, 2009 [12] c. lopez, j. l. salmeron, “risks response strategies for supporting practitionners decision-making in software projects”, procedia technology, vol. 12, pp. 437-444, 2012 [13] object management group, omg unified modeling language infrastructure, 2010 [14] s. j. mellor, k. scott, a. uhl, d. weise,“model-driven architecture”, advances in object-oriented information systems, lecture notes in computer science, pp. 290-297, 2002 [15] s. cranefield, “networked knowledge representation and exchange using uml and rdf”, journal of digital information, vol. 1, no. 8, 2001 [16] m. lankhorst, enterprise architecture at work: modelling, communication and analysis, springer–verlag berlin heidelberg, 2009 [17] f. bergenti, a. poggi, “ exploiting uml in the design of multi-agent systems”, engineering societies in the agents world, springer–verlag berlin heidelberg, pp. 106-113, 2000 [18] a. u. rehman, r. hussain, “software project management methodologies/frameworks dynamics 'acomparative approach'”, international conference on information and emerging technologies, karachi, pp. 1-5, 2007 [19] e. s. dunne, project risk management: devloping a risk framework for translation projects, phd thesis, kent state university, 2013 [20] w. duncan, a guide to the project management body of knowledge, project management institute, usa, 1996 [21] k. schwalbe, information technology project management, course technology, 2002 microsoft word etasr_v11_n1_pp6609-6613 engineering, technology & applied science research vol. 11, no. 1, 2021, 6609-6613 6609 www.etasr.com blasi et al.: machine learning approach for an automatic irrigation system in southern jordan valley machine learning approach for an automatic irrigation system in southern jordan valley anas h. blasi computer information systems department mutah university al karak, jordan mohammad a. abbadi computer science department mutah university al karak, jordan rufaydah al-huweimel computer science department mutah university al karak, jordan abstract—the agriculture sector is the most water-consuming sector. due to the critical situation of available water resources in jordan, attention should be paid to the issues of water demand and appropriate irrigation in order to spread the right management ways of modern irrigation to the farmers. the objectives of this paper are to improve the irrigation process and provide irrigation water to the highest possible extent through the use of artificial intelligence to construct a smart irrigation system that controls the irrigation mechanism using the necessary tools for sensing soil moisture and temperature, giving alerts of any change in the parameters entered as the baseline values for comparison, and installing system sensors buried at a depth of 35 inches below the roots to measure the moisture content in the soil. the sensors measure the humidity and temperature in the soil every ten minutes. they prevent the automatic irrigation process if the humidity is high, and permit it if the humidity is low. the smart automatic irrigation system model was built using the decision tree (dt) algorithm, which is a machine learning algorithm that trains the system on a part of the collected data to build the model that will be used to examine and predict the remaining data. the system had a prediction accuracy of 97.86%, which means that it may be successfully used in providing irrigation water for the agricultural sector. keywords-irrigation; agriculture; artificial intelligence; sensor; machine learning; decision tree algorithm i. introduction jordan has a mediterranean climate. rainfall varies from 50mm in the desert to about 580mm (per year) in the northern highlands. snow falls at short intervals on most mountain highlands in the north, central, and south of the kingdom and is sometimes accumulated [1]. agricultural lands are widely spread, mainly in the jordan valley (northern, central, and southern). the total agricultural area in jordan in 2017 was amounted to 1894324 dunums (1 dunum=1000m 2 ), whereas 864549.3 dunums are irrigated against 102,977,7.7 which depend on rainwater [2]. these lands contain field crops, while irrigated agriculture lands cover all the needs of productive trees, vegetables, and field crops also. irrigated agriculture relies on water sources (from dams, groundwater, etc.). the available quantities of water in jordan are somewhat low [3], especially as agricultural land is scattered in places with higher temperatures, which increases the demand. there is a need to look for an irrigation method that suits the water supply and the plants' needs. traditionally, the first thing that comes to mind is drip irrigation. drip irrigation is a water-saving system that provides water by slowly spraying water into the soil or plant root which contributes in reducing the spread of herbs, plant diseases, and is suitable for all soil types, but it relies on pipes which need regular maintenance. another element that plays a major role is the soil. the soil is a surface layer that covers the surface of the ground and consists of fragmented rock materials that have been changed because of the exposure to environmental, biological, and chemical factors [4]. the soil has several physical properties which mainly affect the growth of plants, the most important of these properties are [4]: • soil strength: represents the aggregation or arrangement of granules in the soil. the soil strength is classified to four types [4]. • organic matter: contributes to the binding of granules in the soil texture and increases the ability to retain water. good soil contains 1-6% organic matter. • soil texture: is the percentage of mineral grains in the soil from sand, silt, and clay and is considered as the most important property of the soil. these characteristics are closely linked in the agricultural process because of their direct effect on the plants. the soil properties in gour alsafi and al karak are described in [3]. we can see in table i that the soil type in gour alsafi is loamy sand soil, which means that the soft, coarse, and medium grain proportions are almost equal. a result of these homogeneous proportions is that the soil has medium water permeability, characterized by moderate ventilation and good fertility rate and is easier to deal with in terms of ease of cultivation and productivity. the weather conditions in jordan range from extreme heat to extreme cold and from extreme dryness to excessive rainfalls, in addition to the irregularity in the rainfall distribution throughout the year. the idea behind this work is the application of machine learning in irrigation with less cost and effort, by designing an irrigation system model based on weather and soil type. the aim of this paper is to create an intelligent irrigation system that combines the advantages of traditional drip irrigation with a pipe control mechanism, which contributes to the reduction of diseases and the use of chemical pesticides. an automatic irrigation system is responsible to water the plants efficiently while providing a system that can reduce the needed manpower while saving water. corresponding author: anas h. blasi engineering, technology & applied science research vol. 11, no. 1, 2021, 6609-6613 6610 www.etasr.com blasi et al.: machine learning approach for an automatic irrigation system in southern jordan valley table i. gour alsafi soil properties soil layers layer depth (cm) soil texture sand % silt % clay % sat % wp % field capacity % ksat (mm/hr) salinity (ms/cm) layer 1 0-20 loamy sand 76.2 20.2 3.6 27.8 2.7 6.5 27.6 9.3 layer 2 20-46 loamy sand 84.4 12.9 2.7 29.0 2.1 4.3 42.7 2.7 layer 3 46-87 loamy sand 88.9 8.9 2.1 30.0 1.9 2.8 65.6 1.8 ii. related work many studies have been published in relation with the use of artificial intelligence applications in agriculture and irrigation. through the review of these papers, the absence of arab countries on the research in this field has been noticed, since there is only one arab country that has recently started working on this, which is the united arab emirates, so the current paper may be considered as one of the first that look at the field of artificial intelligence in agriculture in arab countries. authors in [5] presented a fully automated drip irrigation system in india. this system takes an image of the plant to check its height. if the plant is short, it spreads a fertilizer on it, if there is no need of fertilization, it checks the temperature and soil moisture, if they are less than the set point, the system opens the water motor. all irrigation orders are controlled by the farmer since the sensor reads the moisture and temperature in the soil, assesses the plants need for water, and then sends a short message to the farmer. the system uses a fuzzy logic algorithm to water the plants based on a set of rules. the idea in [6] was to design an automated irrigation system based on scheduling irrigation and fertilization. the irrigation depends on the soil moisture using special sensors. the system will start automatically when the level of moisture is low and it will automatically stop when it reaches a suitable level. additionally, the system handled the fertigation process by injecting fertilizers through the pipes of the system thrice a week by using a water pump which supplies fertilizer mixed with water to the plants. the authors applied the bernoulli’s theorem in order to find the pressure of the water supply, the flow rate of water supply, and the water losses. the system utilizes a microcontroller to convert and manipulate the data obtained from the soil moisture sensors to get the actual humidity values. the control unit will instruct the pump to start working based on the obtained data and the pump will stop working also based on the obtained data. authors in [7], considered the role of artificial intelligence in improving the agriculture sector and dealing with the huge amount of data obtained daily (soil reports, plant needs for fertilizer), and the use of robots in improving crop harvesting. the authors focused on the use of image-based insight generation to conduct a complete field analysis of agricultural land by combining computer vision technology, internet of things (iot), and drone data to monitor crops and fields, and used all these in combinations in disease detection, field management, crop readiness identification, identification of the optimal mix for agronomic products, crop health monitoring, and automation techniques in irrigation. india was taken as an example of the ai agricultural state, because at present in india, in the state of andhra pradesh, microsoft corporation is working with farmers rendering farm advisory services using the cortana intelligence suite which includes machine learning and power bi, which transform data into intelligent actions. the soil's water needs vary from one area to another, so the irrigation decisions must be based on local needs and rules. authors in [8] tackled this problem by categorizing all what we consider as ambiguous in the agriculture sector in general, and the rate of irrigation in particular, considering the type of soil, the type of crops, place and time, irrigation method, and fuzzy logic. all these factors were integrated with gis for decision-making in the irrigation process thus obtaining an intelligent irrigation system called the fuzzy inference system, an intelligent deduction system based on accurate irrigation knowledge, capable of creating guidance maps to control the speed of rotation of the irrigation central axis whose inputs are processed images based on soil characteristics and precise quantities of irrigation using mathematical equations to process the ambiguous data. authors in [9] discussed the groundwater, its characteristics, and its suitability for irrigating crops through an experiment in the nanded, maharashtra, india, indicating the area characteristics in terms of climate, rainfall, and soil quality. an artificial neural network/back propagation algorithm was used to study the soil concentration in salts and minerals, the physical and chemical analysis, and the design of the optimal model to predict the validity of groundwater for irrigation. fifty representative groundwater samples were collected from different locations in rural and agricultural areas. the model consisted of 13 input neurons (salts and minerals), 7 hidden neurons, and 5 output variables to calculate the suitability of groundwater for irrigation in the study area. the result is a high accurate spatial distribution map of the measured and the predicted values. the proposed ann model can be applied in measuring the ground water suitability for irrigation. this model can be considered by local development authorities for better management of groundwater resources. authors in [10] presented a proposal for a photoelectric irrigation system based on a sensor buried in the root zone that transmits soil readings to an arduino board which controls the water pump. the irrigation is done automatically according to the level of soil moisture, and saves electrical energy as the pumps are powered by solar energy through the use of solar cells and thus is compatible with remote areas where there is no electricity grid. authors in [11] aimed to build an automatic irrigation system in indonesia that depends on a programmed chip that controls the launch of water sprinklers to irrigate crops based on the soil moisture. the system works using many sensors and boards and is an extraction from previous research studies in the same field. authors in [12] also used photovoltaic panels to produce the needed electrical energy. in their system, a humidity sensor detects the moisture level in the soil and sends the information to an arduino controller which in turn detects the water level in the tank with an ultrasonic sensor. depending on the water level, the arduino controls the water flow through valves, an lcd monitor displays the information engineering, technology & applied science research vol. 11, no. 1, 2021, 6609-6613 6611 www.etasr.com blasi et al.: machine learning approach for an automatic irrigation system in southern jordan valley about soil moisture content and water level, and that information can be conveyed to the end user in the form of short messages through a gss module. through the previous review of the published papers related to the use of artificial intelligence in the field of agriculture, it was noted that the potential of machine learning techniques in this field is big and its application can contribute in the agriculture development. this field is very active and promising new solutions are being developed continuously to meet the challenges. nevertheless, the respective efforts in arab countries are quite limited, and this work comes to cover that gap. iii. research methodology there are many data mining methods that can be applied to projects related to modern science data. one of the most common of these is the knowledge discovery in database (kdd) method, which has been adopted in this paper. kdd is the process of discovering useful knowledge from a set of data [13], through a set of steps described below. a. data collection the data used in this paper are real data obtained from the directorate of agriculture of the southern jordan valley / department of agricultural extension [3] and the national center for agricultural research and extension / soil survey project [4]. in addition, weather data were acquired from taqs al-arab website and the department of meteorology [1]. the data were compiled as a table in a csv file containing 1498 records and 15 attributes such as: plant name, type of plant (fruits, leaves, roots, etc.), protected/exposed which is indicating the nature of the environment in which the plant is grown, land area (dunums), soil type which describes the nature of the soil with regard to its ability to retain water and moisture, month which is the planting season, temperature, morning weather humidity, midnight humidity, noon weather humidity, soil moisture, soil salinity which is the percentage of salts, evaporation transpiration (m 3 /donum/month) which is the amount of water that one dunum of agricultural land loses in a month as a result of its evaporation, and average daily water consumption (mm) which is the amount of water a plant needs to reach the desired degree of hydration. b. data selection and preparation from the collected data, a target data set was created, by selecting a subset of variables (soil humidity, soil type, soil salinity, and temperature) which directly affect the irrigation process. the selected data were processed, analyzed and correlated using python programming language. the data preprocessing was done for the collected dataset from numerical to categorical data, since this model was built using the decision tree (dt) algorithm which is a very simple, understandable, easy to implement, and also gives high accurate results. it is widely known and used in many businesses to support decision making and risk analysis [14, 15]. this algorithm works only on categorical data types. c. decsion tree algorithm data mining (dm) is the extraction of useful information from a large data set. in that sense, dm is also known as knowledge discovery (kd) or knowledge extraction (ke). one of the main purposes of dm is that the information gathered from it helps to predict hidden patterns, future trends and behaviors, and boosts decision making. it can be applied to any type of data, e.g. data warehouses, transactional databases, relational databases, multimedia databases, spatial databases, time-series databases, and the world wide web. in the process of dm, the large data sets are first sorted, then patterns are identified, and relationships are established to perform data analysis and solve problems. this process is called data classification which is the process of finding a model that describes and distinguishes data classes and concepts. classification is the problem of identifying to which of a set of categories (subpopulations), a new observation belongs to, on the basis of a training set of data containing observations and whose categories membership is known. the data set was split into two groups. at first, the training dataset consisting of 67% of the data, was used to train the machine classifier and then create a general classification model using the dt algorithm with the available training set. the second is the testing dataset which consisted of the 33% of the data, which entered the model for testing based on the training result. the constructed model was used to predict class labels and hence estimate the accuracy of the classification rules. after dividing the data into the previous groups, the training process begun by measuring the temperature and degree of soil moisture through sensors buried at a depth of 3-5 inches below the roots. the sensors measure the humidity and temperature in the soil every 10 minutes, preventing the automatic irrigation process if the humidity is high, and permitting it if the humidity is low. during the testing phase, the testing data were the input for the designed model, and the comparison results between the prediction and the result were recorded. python programming language is considered the most suitable and has been used in this study. however, the prediction model will be built using sklearn with some important libraries and methods such as accuracy_score, train_test_split, decisiontreeclassifier and panads. iv. results and evaluation it is useful to control water consumption, especially in agriculture sector, since it is the most water consuming. also this may affect the production quality, as controlling the amount of water reduces fungi and plant diseases and thus increases yield and profit. in this paper, an automatic irrigation system has been designed that measures soil moisture and temperature, in addition to some characteristics affecting the irrigation process such as soil quality and salinity. using this system the farmer can monitor the crops without the need of extra manpower, saving the time and cost required for the irrigation process. although somewhat inexpensive, the smart irrigation system is economically feasible and highly accurate. the confusion matrix is often used to describe the performance of a classification model on a set of test data for which the true values are known. the confusion matrix itself is relatively simple to understand. table i shows the system's confusion matrix which is an evaluation method for the dt model results. we note that the sum of true positive (tp) and true negative (tn) predictions reaches a percentage as high as the 98% of total predictions. engineering, technology & applied science research vol. 11, no. 1, 2021, 6609-6613 6612 www.etasr.com blasi et al.: machine learning approach for an automatic irrigation system in southern jordan valley table i. confusion matrix n=1497 predicted "no" predicted "yes" actual "no" 240 6 actual "yes" 26 1225 table ii. cross-validation results accuracy precision recall f1 score mse 0.0 0.98 0.9 0.98 0.94 0.0213 1.0 0.98 1.0 0.98 0.99 the classification report of table ii displays the accuracy, precision, recall, f1 score, and mean square error (mse), of the model. in order to support easier interpretation and problem detection, the metrics are defined in terms of tp, false positive (fp), tn, and false negative (fn) predictions. using this terminology, the metrics are defined as [16-18]: • precision is the ability of a classifier to not label an instance as positive when it is actually negative. for each class it is defined as the ratio of tp to the sum of tp and fp. the irrigation system model has a high precision equal to 0.90. • recall is the ability of a classifier to find all positive instances. it is defined as the ratio of tp to the sum of tp and fn. the proposed model has a recall value of 0.98. • the f1 score is a weighted harmonic mean of precision and recall such that the best score is 1.0 and the worst is 0.0. generally speaking, f1 scores are lower than accuracy measures as they embed precision and recall into their computation. as a rule of thumb, the weighted average of f1 should be used to compare classifier models, not global accuracy. • mse measures the average squared difference between the estimated and true values. it is a risk function, corresponding to the expected value of the squared error loss, always nonnegative, and the values closer to zero are better. the mse for the irrigation system model is equal to 0.0213. • accuracy is the most commonly used metric to judge a model which is the sum of tp with tn divided on the sum of all predictions (tp, tn, fp, fn). the proposed model has a high accuracy, equal to 0.98. v. conclusion and future work the provision of water in the agriculture sector is an important research area because agriculture is the most water consuming sector and the available water resources are scarce. attention should be paid to the water needs of plants and to the appropriate irrigation scheduling in order to effectively transfer to the farmers, modern and optimum ways of irrigation management. in this paper, the most prominent agricultural area of jordan was covered, i.e. the southern jordan valley and the needed data to design a model for the irrigation process based on soil properties and temperatures were collected. this system helps in providing the quantities of water needed for irrigation while improving productivity. there are other agricultural regions in jordan that have different characteristics from the southern jordan valley, especially in temperature, so we may not be able to generalize the results of this model to all regions. this model can be improved in the future in order to be able to be applied to other regions in jordan. this model can be further developed to include scheduling of the fertilization process, or to be able to heat the pipes to solve the problem of frost in the winter, and to use irrigation pipes to improve soil aeration and inject organic materials needed to improve agricultural production combining the automatic irrigation system with image processing through a set of cameras to monitor plant growth in terms of size and disease detection. in the future, different data sets will be applied from different regions of jordan. in addition, other machine learning algorithms can be utilized, such as artificial neural networks (anns) [19, 20], fuzzy logic [21], k-nn [22], and other data mining techniques [23, 24], and the results will be compared with the dt results. references [1] "arabiaweather," arabiaweather. https://www.arabiaweather.com/ (accessed dec. 16, 2020). [2] "annual report 2015," ministry of water & irrigation, water authority jordan valley authority, 2015. [3] "soil survey project -gour al-safi/al-karak," the national center for agricultural research and extension. [4] r. r. weil and n. c. brady, the nature and properties of soils, 15th edition. columbus, oh, usa: pearson, 2016. [5] s. jadhav and s. hambarde, "android based automated irrigation system using raspberry pi," international journal of science and research, vol. 5, no. 6, pp. 2345–2351, jun. 2016, https://doi.org/ 10.21275/v5i6.nov164836. [6] a. norazizan, m. muzni, m. ramsaid, m. ismail, and m. mazalan, "design and development of the irrigation system for planting (part 1)," mechanical system design, may 2016, https://doi.org/ 10.13140/rg.2.1.4088.1529. 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[17] m. hasnain, m. f. pasha, i. ghani, m. imran, m. y. alzahrani, and r. budiarto, "evaluating trust prediction and confusion matrix measures for web services ranking," ieee access, vol. 8, pp. 90847–90861, 2020, https://doi.org/10.1109/access.2020.2994222. [18] m. hossin and m. n. sulaiman, "a review on evaluation metrics for data classification evaluations," international journal of data mining & knowledge management process, vol. 5, no. 2, pp. 1–11, nov. 2019, https://doi.org/10.5281/zenodo.3557376. [19] a. blasi, "performance increment of high school students using ann model and sa algorithm," journal of theoretical and applied information technology, vol. 95, no. 11, pp. 2417–2425, jan. 2017. [20] r. a. aroud, a. h. blasi, and m. a. alsuwaiket, "intelligent risk alarm for asthma patients using artificial neural networks," international journal of advanced computer science and applications, vol. 11, no. 6, 58/30 2020, https://doi.org/10.14569/ijacsa.2020.0110612. [21] a. blasi, "scheduling food industry system using fuzzy logic," journal of theoretical and applied information technology, vol. 96, no. 19, pp. 6463–6473, oct. 2018. [22] m. a. a. lababede, a. h. blasi, and m. a. alsuwaiket, "mosques smart domes system using machine learning algorithms," international journal of advanced computer science and applications, vol. 11, no. 3, 40/30 2020, https://doi.org/10.14569/ijacsa.2020.0110347. [23] m. alsuwaiket, a. h. blasi, and k. altarawneh, "refining student marks based on enrolled modules’ assessment methods using data mining techniques," engineering, technology & applied science research, vol. 10, no. 1, pp. 5205–5210, feb. 2020, https://doi.org/ 10.48084/etasr.3284. [24] m. alsuwaiket, a. h. blasi, and r. a. al-msie’deen, "formulating module assessment for improved academic performance predictability in higher education," engineering, technology & applied science research, vol. 9, no. 3, pp. 4287–4291, jun. 2019, https://doi.org/ 10.48084/etasr.2794. engineering, technology & applied science research vol. 7, no. 2, 2017, 1450-1454 1450 www.etasr.com tayab and al humayun: modeling and analysis of a cascaded battery-boost multilevel inverter using… modeling and analysis of a cascaded battery-boost multilevel inverter using different switching angle arrangement techniques usman bashir tayab school of electrical system engineering university malaysia perlis perlis, malaysia usman.tayab@yahoo.com md. abdullah al humayun school of electrical system engineering university malaysia perlis perlis, malaysia humayun0403063@gmail.com abstract—multilevel inverters have the capability to produce an ac staircase output waveform without using a bulky passive filter. therefore, the multilevel inverters are gaining more and more popularity, among the different types of inverters, for photovoltaic applications in the modern era of technology. however, if the switching angle arrangement technique is not selected appropriately then the total harmonic distortion of the voltage output waveform may become undesirable. in this paper, half-equal-phase, feed-forward and selective harmonics elimination pulse width modulation switching angle arrangement techniques at different power factors (i.e., 1.0, 0.75 and 0.50) are applied to a cascaded battery-boost inverter. psim software is used to evaluate and compare the performance of a 9level cascaded battery-boost inverter with three switching angle arrangement techniques at power factors of 1.0, 0.75, and 0.50, respectively. simulation results show that the selective harmonics elimination pulse width modulation technique can produce an output voltage and current waveform with the lowest total harmonic distortion. on the other hand, the output current waveform produced by power factor 0.50 had the lowest total harmonic distortion. keywords-half-equal-phase method; multilevel inverter; switching angle; selective harmonics elimination pulse width modulation; total harmonic distortion. i. introduction solar energy is probably the dominant renewable energy source available nowadays. the electric power generated by photovoltaic (pv) panels is obtained in dc form. therefore, it needs to be converted into ac form using a power inverter [1, 2]. several inverter topologies have been proposed in the past and each inverter topology has different characteristics. the conventional inverter requires a bulky filter to produce a sinusoidal ac voltage waveform [3]. recently, multilevel inverters gained popularity. unlike the conventional inverters, the multilevel inverter does not require bulky filters to generate a near sinusoidal ac output waveform [4, 5]. the concept of multilevel inverters has been introduced in 1975. with the development of the new technologies, the first multilevel inverter was proposed in 1981 which was actually a 3-level inverter [6]. the basic multilevel inverter can be divided into three types such as: diode-clamped, flyingcapacitor and cascaded battery-boost multilevel inverter. among these three types of multilevel inverters, the cascaded battery-boost multilevel inverter is gaining popularity for stand-alone pv systems [7]. however, if the proper switching angle arrangement technique is not applied then the resulted total harmonic distortion (thd) of cascaded battery-boost multilevel inverter may become unacceptable. therefore, in this paper three different types of switching techniques are presented. the main switching angle drives using half-equalphase (hep), feed-forward (ff) and selective harmonics elimination pulse width modulation (shepwm) techniques are applied to a 9-level cascaded battery-boost inverter. ii. methodology a. cascaded battery-boost multilevel inverter the cascaded battery-boost multilevel inverter was proposed in [8] and it has become the most popular inverter topology in standalone pv systems. figure 1 shows the block diagram of a cascaded battery-boost multilevel inverter. fig. 1. cascaded battery-boost multilevel inverter. the full-bridge inverters are connected in series with their output voltages summed up and hence, the final voltage boosting capability. it is highly reliable with low voltage engineering, technology & applied science research vol. 7, no. 2, 2017, 1450-1454 1451 www.etasr.com tayab and al humayun: modeling and analysis of a cascaded battery-boost multilevel inverter using… unbalance problems. with n number of full-bridge inverters, the output staircase ac voltage produced consists of 2n+1 levels [9]. this inverter topology requires a separate dc source for each full-bridge as seen in figure 1. b. power factor the power factor (pf) can be expresses as the ratio between the resistance and the impedance or the cosine of the phase angle between current and voltage. table i shows the value of resistor (r), frequency (f) and inductor (l) at different power factors. table i. parameters value at different power factor. parameter pf = 0.50 pf = 0.75 pf = 1.0 r 10ω 10ω 10ω l 55.13mh 28.075mh 0 f 50hz 50hz 50hz c. switching angle arrangement techniques the multilevel inverters have various topologies and a wide range of advantages. however, the exiting topologies are unable to produce a pure sinusoidal output waveform as long as the switching angles are not appropriately arranged [10]. in order to obtain good power quality and low thd, three different switching angle arrangements techniques are carefully investigated. figure 2 shows the output voltage waveform for an m-level multilevel inverter. for an m-level waveform in the period (02π), there are 2(m-1) switching angles to be determined. the switching angles are defined as shown in (1) by the time sequence. the sine wave is dividing into four quadrants. the switching angles in 1st quadrant period (0-π/2) are defined as main switching angles. 1 2 2 1, ,...... ,m m     (1) for an m-level (m is an odd number) waveform, the main switching angles are (m-1)/2. the main switching angles in 1st quadrant (i.e., 0-π/2) are: 1 2 ( 1)/2, ,...... m    (2) the switching angles in the 2nd quadrant (i.e., π/2-π)) are: ( 1)/2 1m     (3) the switching angles in the 3rd quadrant (i.e., π-3π/2) are: ( 1)/2m m     (4) the switching angles in the 4th quadrant (i.e., 3π/2-2π) are: (3 1)/2 12m     (5) for the analysis, only main switching angles need to determine. the other switching angles can be derived from the main switching angles in the 1st quadrant (0-π/2). fig. 2. output voltage waveform for multilevel inverter. 1) half-equal-phase (hep) method to obtain a good quality output voltage waveform from multilevel inverter, the hep method has been introduced for determining the switching angles [10]. the main switching angles are calculated by the following formula: 1 8 0 ( ) 1 i i m     (6) 2) feed-forward (ff) method there is wider gap between the positive half-cycle and the negative half-cycle by using the hep method [10]. in order to reduce the gaps, another method is derived to determine the main switching angle which is knows as feed-forward method. the main switching angles are in the range (0-π/2), which is determined by the following formula: 11 2 1s in ( ) 2 1 i i m      (7) 3) selective harmonic elimination pulse width modulation (shepwm) method the shepwm method is widely used to control multilevel inverter and produced output voltage with low thd [11-13]. the output ac voltage (0-2π) shown in figure 2 can be represented mathematically in a fourier series as given by the following equation:  1 1,3,5,... 4 ( ) cos(i ) cos(i ) sin(i )dcout n i v v t t i            (8) the peak voltage of each ith harmonic component is given by the following formula:  (i) 1 2 4 c o s (i ) c o s (i ) c o s (i )d cp n v v i         (9) the shepwm equations can be written with the desired fundamental peak voltage of v1 and peak voltage of higher order harmonics are zero. engineering, technology & applied science research vol. 7, no. 2, 2017, 1450-1454 1452 www.etasr.com tayab and al humayun: modeling and analysis of a cascaded battery-boost multilevel inverter using…  1 1 2 1 2 1 2 4 cos( ) cos( ) cos( ) 0 cos(3 ) cos(3 ) cos(3 ) 0 cos((2 1) ) cos((2 1) ) cos((2 1) ) dc n n n v v n n n                              (10) by solving the shepwm equation sets given by (10), switching angles at fundamental frequency can be obtained, with the elimination of higher order harmonics. iii. results and discussion in this section, simulation results are presented for 9-level cascaded battery-boost inverter using three switching angle arrangement techniques at different power factor load (i.e., 1.0, 0.75 and 0.50). psim software is accurate simulator for this task. the cascaded battery-boost multilevel inverter is simulated for 9-level with a dc voltage supply of 120v. the data of simulation is analyzed based on the comparison of thd resulting from the hep, ff, and shepwm switching techniques. the switching angles for the 9-level cascaded battery-boost inverter are generated by using switching angle arrangement techniques such as: hep, ff, and shepwm as shown in table ii. table ii. switching angles for 9-level cascaded batteryboost inverter. angle hep method ff method shepwm method θ1 18 3.59 10.02 θ2 36 11.02 22.14 θ3 57 19.34 40.75 θ4 72 30.53 61.77 θ5 108 149.47 118.23 θ6 126 160.66 139.25 θ7 144 168.98 157.86 θ8 162 176.41 169.99 θ9 198 183.59 190.02 θ10 216 191.02 202.14 θ11 234 199.34 220.75 θ12 252 210.53 241.77 θ13 288 329.47 298.23 θ14 306 340.66 319.25 θ15 324 348.98 337.86 θ16 342 356.41 349.99 figure 3 shows the output voltage waveforms for the 9level cascaded battery-boost inverter. the output voltage waveforms were obtained using three different switching angle arrangement techniques mentioned before at different power factors of 1.0, 0.75, and 0.50. from figure 3, it is ascertained that the value of the output voltage was ±120v for the hep, ff, and shepwm methods at three different power factors. the current waveforms for 9-level cascaded battery-boost inverter at identical power factors are shown in figures 4-6. the output voltage and current waveforms were obtained using the hep, ff, and shepwm methods at power factors of 1.0, 0.75, and 0.50. figure 4-6 shows that the output current was ±12a for hep, ff, and shepwm method at power factor 1.0. when the power factor was decreased to 0.75, the output currents were decreased to ±8.2a, ±10.8a and ±9a for hep, ff, and shepwm method, respectively. when the power factor was decreased to 0.50, the output currents were decreased to ±5.2a, ±6.08a and ±6a for hep, ff, and shepwm method, respectively. from these results, it was concluded that the output current decreases when the power factor decreases. 0.00 0.01 0.02 0.03 0.04 0.05 0.06 -120 -90 -60 -30 0 30 60 90 120 v o lta g e ( v ) time (s) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 -120 -90 -60 -30 0 30 60 90 120 v o lta g e ( v ) time (s) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 -120 -90 -60 -30 0 30 60 90 120 v o lt a g e ( v ) time (s) fig. 3. voltage output waveform with power factor 1.0, 0.75, 0.50: (a) hep method (b) ff method (c) shepwm method. figure 7 shows the results of thd of the 9-level cascaded battery-boost inverter and figure 8 shows the results of current thd with power factors of 1.0, 0.75 and 0.50, respectively. the results of voltage thd at power factors of 1.0, 0.75, and 0.50 are demonstrated in figure 7, which shows that the voltage thd are the same for each power factor as the function of the inductor is to filter the current distortion. thus, the inductive load only affects the thd of the current; it does not affect the thd of the voltage at all. from figure 8, it is revealed that the current thd decreased slightly for each switching angle arrangement technique as the power factor decreased from 1.00 to 0.50. with a power factor of 1.0, where the load is purely resistive, the level of resultant current thd for hep, ff and shepwm methods are 22.05%, 21.44% and 10.15%, respectively. with a power factor of 0.75 the level of (a) (c) (b) engineering, technology & applied science research vol. 7, no. 2, 2017, 1450-1454 1453 www.etasr.com tayab and al humayun: modeling and analysis of a cascaded battery-boost multilevel inverter using… resulting current thd for hep, ff and shepwm methods are 8.84%, 9.68% and 1.56%, respectively. similarly, with power factor 0.50 the level of resultant current thd for hep, ff and shepwm methods are 7.08%, 7.75% and 1.23%, respectively. 0.00 0.01 0.02 0.03 0.04 0.05 0.06 -12 -9 -6 -3 0 3 6 9 12 c u rr e n t (a ) time (s) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 -12 -9 -6 -3 0 3 6 9 12 c u rr e n t (a ) time (s) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 -12 -9 -6 -3 0 3 6 9 12 c u rr e n t (a ) time (s) fig. 4. current output waveform with power factor 1.0: (a) hep method (b) ff method (c) shepwm method. the simulation results of the 9-level cascaded battery-boost inverter indicated that when the power factor decreases from 1.0 to 0.75, for the hep and the ff method, the current thd declined sharply to 60% approximately. conversely using the shepwm method, the thd decreased to 85%. furthermore, when the power factor was decreased from 0.75 to 0.50 using hep, ff and shepwm switching angle arrangement techniques, the current thd decreased sharply to 20%. finally from the overall discussion of the outcome of the research it can be concluded that when the value of power factor decreases, the current thd will decrease and the output waveform will become smoother. 0.00 0.01 0.02 0.03 0.04 0.05 0.06 -12 -9 -6 -3 0 3 6 9 12 c u rr e n t (a ) time (s) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 -12 -9 -6 -3 0 3 6 9 12 c u rr e n t (a ) time (s) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 -12 -9 -6 -3 0 3 6 9 12 c u rr e n t (a ) time (s) fig. 5. current output waveform with power factor 0.75: (a) hep method (b) ff method (c) shepwm method iv. conclusion it is clearly shown that the selection of the switching techniques is an important factor for such a multilevel inverter. without the proper switching angle arrangement techniques implemented, the output voltage distortion of the inverter can become worse. consequently, the comparison of three switching angle arrangement techniques has been performed to identify the method, which yields the lowest thd for the 9level cascaded battery-boost inverter. based on simulation results, it can be concluded that the voltage thd for hep, ff, and shepwm switching angle arrangement techniques was the same at every power factor used in this research. however, the current thd was different for hep, ff, and shepwm at different load power factors (1.0, 0.75 and 0.50) due to the inductive load. furthermore, among three switching angle arrangement techniques, the shepwm switching angle arrangement technique has the lowest voltage and current thd compared to the other two. due to the lowest thd the shape of voltage and current output waveform is more (a) (a) (c) (b) (b) (c) engineering, technology & applied science research vol. 7, no. 2, 2017, 1450-1454 1454 www.etasr.com tayab and al humayun: modeling and analysis of a cascaded battery-boost multilevel inverter using… sinusoidal. on the other hand, the 0.50 power factor provides the lowest current thd compared to 1.0 and 0.75. 0.00 0.01 0.02 0.03 0.04 0.05 0.06 -12 -9 -6 -3 0 3 6 9 12 c u rr e n t (a ) time (s) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 -12 -9 -6 -3 0 3 6 9 12 c u rr e n t (a ) time (s) 0.00 0.01 0.02 0.03 0.04 0.05 0.06 -12 -9 -6 -3 0 3 6 9 12 c u rr e n t (a ) time (s) fig. 6. current output waveform with power factor 0.50 (a) hep method (b) ff method (c) shepwm method fig. 7. voltage thd of the 9-level cascaded battery-boost inverter. fig. 8. current thd of the 9-level cascaded battery-boost inverter. references [1] t. demirdelen, r. i. kayaalp, m. tumay, “a modular cascaded multilevel inverter based shunt hybrid active power filter for selective harmonic and reactive power compensation under distorted/unbalanced grid voltage conditions”, eng. technol. & appl. sci. res., vol. 6, no. 5, pp. 1133-1138, 2016 [2] s. daher, j. schmid, f. l. m. antunes, “multilevel inverter topologies for stand-alone pv systems”, ieee trans. power. electron., vol. 55, pp. 2703-2712, 2008 [3] a. k. panda, s. s. patnaik, “analysis of cascaded multilevel inverters for active harmonic filtering in distribution networks”, int. j. of electric. power & energy syst., vol. 66, pp. 216-226, 2015 [4] h. rashid, power electronics: circuits, devices, and applications, prentice hall, 2004. [5] b. nayak, s. s. dash, “performance analysis of different control strategies in a z-source inverter”, eng. technol. & appl. sci. res., vol. 3, no. 2, pp. 391-395, 2013 [6] g. n. rao, p. s. raju, k. c. sekhar, “harmonic elimination of cascaded h-bridge multilevel inverter based active power filter controlled by intelligent techniques”, int. j. of electric. power & energy syst., vol. 61, pp. 56-63, 2014 [7] e. babaei, m. f. kangarlu, m. sabahi, m. r. a. pahlavani, “cascaded multilevel inverter using sub-multilevel cells”, electric power systems research, vol. 96, pp. 101-110, 2013 [8] l. jih-sheng, p. fang zheng, “multilevel converters-a new breed of power converters”, ieee trans. industry appl., vol. 32, pp. 509-517, 1996 [9] m. sadikin, t. senjyu, a. yona, “high-frequency link dc for power quality improvement of stand-alone pv system in cascaded multilevel inverter”, power electronics and drive systems, pp. 597-601, 2013 [10] f. l. luo, “investigation on best switching angles to obtain lowest thd for multilevel dc/ac inverters”, 8th ieee conference on industrial electronics and applications (iciea), june 19-21, 2013 [11] k. corzine, y. familiant, “a new cascaded multilevel h-bridge drive”, ieee trans. power. electron., vol. 17, no. 1, pp. 125-131, 2002 [12] k. ganesan, k. barathi, p. chandrasekar, d. balaji, “selective harmonic elimination of cascaded multilevel inverter using bat algorithm”, procedia tech., vol. 21, pp. 651-657, 2015 [13] v. k. gupta, r. mahanty, “optimized switching scheme of cascaded hbridge multilevel inverter using pso”, int. j. of electric. power & energy syst., vol. 64, pp. 699-707, 2015 (a) (b) (c) microsoft word etasr_v11_n1_pp6760-6765 engineering, technology & applied science research vol. 11, no. 1, 2021, 6760-6765 6760 www.etasr.com zuhaib et al.: collision avoidance of a kinodynamically constrained system from passive agents collision avoidance of a kinodynamically constrained system from passive agents khalil muhammad zuhaib department of electronics engineering quaid-e-awam university of engineering, science & technology, larkana campus, pakistan kmzuhaib@quest.edu.pk junaid iqbal department of mechanical engineering quaid-e-awam university of engineering, science & technology, larkana campus, pakistan ji.bhatti@quest.edu.pk ahsin murtaza bughio department of electronics engineering quaid-e-awam university of engineering, science & technology, nawabshah, pakistan ahsan.murtaza@quest.edu.pk syed abid ali shah bukhari department of electrical engineering quaid-e-awam university of engineering, science & technology, larkana campus, pakistan abidshah@quest.edu.pk kelash kanwar department of electronics engineering quaid-e-awam university of engineering, science & technology, nawabshah, pakistan kelashkanwar@quest.edu.pk abstract-robot motion planning in dynamic environments is significantly difficult, especially when the future trajectories of dynamic obstacles are only predictable over a short time interval and can change frequently. moreover, a robot’s kinodynamic constraints make the task more challenging. this paper proposes a novel collision avoidance scheme for navigating a kinodynamically constrained robot among multiple passive agents with partially predictable behavior. for this purpose, this paper presents a new approach that maps collision avoidance and kinodynamic constraints on robot motion as geometrical bounds of its control space. this was achieved by extending the concept of nonlinear velocity obstacles to incorporate the robot’s kinodynamic constraints. the proposed concept of bounded control space was used to design a collision avoidance strategy for a car-like robot by employing a predict-plan-act framework. the results of simulated experiments demonstrate the effectiveness of the proposed algorithm when compared to existing velocity obstacle based approaches. keywords-collision avoidance; dynamic environment; motion planning; navigation; mobile robot; kinodynamic constraint; velocity obstacle; pedestrian environment i. introduction most modern applications of mobile robots require them to navigate in a dynamic environment among moving obstacles such as people, pets, cars, etc. robots working in such environments must be able to successfully navigate while multiple agents are moving around them. to achieve this objective, mobile robots need to generate a short collision-free path in real-time concerning an obstacle's future position. furthermore, the generated path should be system compatible, as most of the mobile robots have kinodynamic constraints, such as car-like robots [1, 2]. many motion planning approaches, such as in [3-5], were proposed to navigate a robot with kinodynamic constraints in a static environment, and extended their application in dynamic environments [6-8]. some important works in the direction of robot navigation in a dynamic environment were introduced in [9-11], focusing on a complete trajectory plan to the goal. these approaches don’t perform well in a dynamic environment, especially when it is possible to predict only partially the future motion of other agents, e.g. pedestrian environment, for many reasons. the first reason is that these approaches don’t consider predicting the future motion of other agents, thus the robot becomes blinded to a possible future collision. secondly, a limited time is available for computing a solution in a dynamic environment. therefore, it is very likely that the planner will be unable to compute the complete collision-free trajectory during the available time slot. other works, such as [12, 13], proposed approaches that search in state time-space to compute a system compliant collision-free trajectory to the goal, based on the other agent's future path. these methods assumed that the complete path of the agents is known in advance, limiting their application on pedestrian or multiple passive agents environments. the moving agents have free will in such environments. their future behavior can only be partially predictable, if at all. agents' future behavior is predicted through various on-line prediction approaches, such as the ones proposed in [14-17]. in such prediction approaches, the model of the future motion is obtained at an instant and it is valid for a short period. therefore, a navigation approach should be designed to take into account the duration of the environment model's validity and the limited available time for computing a collision-free solution. an alternative approach to achieve motion planning is to plan a motion locally. in such approaches, the robot employs a continuous predict-act-plan cycle. in each cycle, the robot must compute its action based on predictions to avoid static and moving obstacles as it moves towards the goal. some of the dominant works in this direction were based on the concept of velocity obstacle (vo) [18], corresponding author: khalil muhammad zuhaib engineering, technology & applied science research vol. 11, no. 1, 2021, 6760-6765 6761 www.etasr.com zuhaib et al.: collision avoidance of a kinodynamically constrained system from passive agents which considers the future behaviors for collision avoidance. the vo-based navigation approach consists of planning a local motion toward the next (sub) goal, which is extracted from a global waypoint plan. vo was formulated for a simple robot model, where the obstacle path was assumed to be along a straight line. in [19], the nonlinear velocity obstacle (nlvo) concept was proposed for collision avoidance of a robotic system with a linear equation of motion, where the passive agent was assumed to be moving along an arbitrary possibly nonlinear path. to expand the concept of vo, authors in [20] considered the kinematic car-like robot avoiding collision with multiple passive agents, proposing the concept of generalized velocity obstacle (gvo). this approach principally acts as the opposite of nlvo, where a car-like system with a nonlinear motion equation should avoid collision with obstacles having linear motion equations (straight paths). vo was expanded in [21] proposing the acceleration velocity obstacle (avo) method for a system with acceleration constraints. this approach was proposed for reciprocal collision avoidance among active agents, where each one shares the responsibility. this approach assumed that every active agent involved in a collision should run a similar collision avoidance algorithm for avoiding it. in [22], the concept of safe control space for collision avoidance was proposed to deal with various sources of un-modeled uncertainties. some other studies which examined collision avoidance were presented in [23-24]. this study addressed the problem of navigating a car-like robot system under kinodynamic constraints among multiple passive agents with partially predictable behaviors. at first, the idea of nlvo [19] was extended to define a generalized approach for handling collisions of a car-like robot with obstacles moving along arbitrary paths. a formulation was given to represent geometrically the bounds of robot motion as bounds of the robot's control space. the bounded control space was named valid control space. moreover, this paper provides a framework for finding the optimal control within the bounded control space, which can be used to locally navigate a robot to a goal. the proposed method's performance was evaluated for a dynamic environment similar to [20], where the entire responsibility of collision avoidance belongs to the robot. as shown in figure 1, passive agents' predicted trajectories can change frequently. simulations showed that the proposed approach performs better than existing vo based approaches. ii. valid control space this section presents the idea of valid control space, which addresses the difficulty of overcoming the kinodynamic constraints of a car-like robot. this was achieved by introducing a control obstacle concept, which was a generalization of the nlvo. a. notations and assumptions �� ⊂ �� denotes the robot’s state space, and ���� denotes the state of the robot � at time �. the robot workspace is ��, where typically � � 2. the robot position at time t in robot configuration space, denoted by ���� , is obtained from the state of the system through a nonlinear projection function: ���� � ������ (1) where � ∈ �� → �� . furthermore, it is assumed that the dimension of workspace is equal to the robot’s input control space � ⊂ ��. the robot's state transition equation is probably a nonlinear function �:�� � � → ��: ����� � ������ ,��� (2) where ���� ∈ �� is the robot state at time �, and ��� ∈ � is the control input. the state at any given time greater than zero for a given current state �� � ���0 and a constant input control � � ��0 is given by: �� � ����,�, � (3) where �:�� �� � � → �� is the solution of (2). fig. 1. multiple simulation snapshots at different time instances. the robot in green starts from its initial position at (5,10) and moves towards the goal marked in yellow while avoiding collision with the multiple passive agents marked in red. b. dynamic obstacle representation this study assumed that there will be a system in addition to the mobile robot, as introduced in [16-17], tracking passive agent states and estimating their future trajectories. each agent has a disc-like shape with a radius and a trajectory. the list of passive agents and their future behaviors is given as the set of points representing time and their estimated future positions. c. control obstacle the geometry of the robot was considered to be its bounding circle, as in [18]. the mobile robot shares its workspace with several passive agents. � and �� are sets of points representing the robot and the i-th agent geometry respectively, while � is the minkowski sum of � and �� geometries � � �⨁��. at � � 0, the position robot's center and the i-th passive agent are represented by ���0 and ���0 respectively. the predicted position of the i-th passive agent at � " 0 is given as ���� . the robot will avoid collision with the engineering, technology & applied science research vol. 11, no. 1, 2021, 6760-6765 6762 www.etasr.com zuhaib et al.: collision avoidance of a kinodynamically constrained system from passive agents i-th passive agent within a time interval [0,#] if the relative position vector for input � remains outside �. �$����,�,� % & ���� ∉ �,∀� ∈ )0,#* (4) the temporary component of control obstacle ����� induced for the robot due to i-th agent at time � ∈ )0;#*, can be defined as: ����� � ,�|�$����,�, � % & ���� ∈ �. (5) where ����� is the set of all � ∈ � for which the relative position vector �$����,�,� % & ���� will be inside � at time � ∈ )0,#*. thus, the control obstacle induced for robot over time horizon )0,#* due to the i-th agent can be defined as: ��� 0 � ⋃ ����� 23450 (6) where ��� 0 is the set of all � ∈ � that will maneuver the robot towards a collision with an i-th agent at time � ∈ )0,#*. the robot will remain collision-free from the i-th agent within the time horizon )0,#* if the selected robot's control input does not belong in the control obstacle (� ∉ ��� 0). this collision avoidance approach can be extended for multiple dynamic agents. 6 � ,1,2,…n. is the index of the dynamic agents to avoid. the control obstacle induced for the robot by the dynamic agents can be given as: ��0 � ⋃ ��� 0 �∈: (7) a robot selecting � ∉ ��0 will navigate without collision with n dynamic agents for at-least # seconds. d. valid control space the constraints of robot motion are defined by constraint functions �;��,� bounded in )<=;<>*, where �<=;<> ∈ � . these constraints restrict the admissible controls for the robot in a control space over a time horizon )0,# *. the admissible space of the controls is denoted by �?�. the valid control space at time � ∈ )0,#*, denoted by �@?a�� 0 �� , is: �@?a�� 0 � �?�\��0 (8) �@?a�� 0 models all possible sub-trajectories satisfying all constraints. every point chosen in �@?a�� 0 will satisfy the kinodynamic constraints and collision avoidance over � ∈ )0,#*. this approach is based on the geometrical construction of �@?a�� 0 as it is described in forthcoming sections. e. example – single integrator the concept of �@?a�� 0 is explained considering a mobile robot with simple dynamics as of a single integrator. system's position at any time � for constant input � can be given as ���� � ���0 c ��, where ���0 is the current position of the robot. the motion of the system is constrained by d����� e fg?h, where fg?h is the system's maximum speed limit. as the state transition equation of a single integrator is ����� � �, �?� will be a set of input where ‖�‖ e fg?h. �?� has the shape of a disc with a center at the origin and a radius of fg?h in robot's input control space. ����� will be equivalent to 6jk��� for the single integrator. it also has the shape of a disc, with its center at (���� & ���0 /� and radius equal to �m� c m� /� in robot input control space �, where m� and m� are the radius of the robot and the n & �� passive agent. figure 2 shows �@?a�� 0 where ����� is considered at equally spaced time instances by o� � 0.1� and up to # � 5� time horizon. the other parameters were set as: ���0 =(0,0), m� � m� � 0.4, fg?h � 1 �rn�/�, and ���� � �2,0 . fig. 2. the constraints on control space. the green region shows: (a) �?�, (b) �\��� 0, (c) �@?a�� 0 , for a considered robotic system as a single integrator. iii. collision avoidance approach this section presents the proposed collision avoidance approach based on the concept of �@?a�� 0 , formulating the problem of robot navigation in a dynamic environment as an optimization problem. given a random starting point, the proposed procedure will navigate the robot towards the goal without collision with any moving passive agent present. the goal position is assumed to be extracted from some waypoint plans for global navigation. the proposed algorithm allows the robot to quickly re-plan its course as new passive agents are discovered or new information regarding their future predicted states are received. �s�tu is a control input to the kinodynamic model that leads the robot towards its goal. the exact value of � � �s�tu, which is required to reach the goal, can be found by solving the equation ������,�,# � �v . if this point belongs to �@?a�� then all motion constraints are satisfied and the shape of the trajectory can be defined. otherwise, control �∗ that is given to the robot is the solution that minimizes the following cost: �∗ � arg min]∈ _̂`abcd e�s�tu & �e (9) this navigation problem is formalized as the problem of finding the � ∈ �@?a�� 0 that is nearest to �s�tu, in terms of the euclidean distance between them in control space � . the solution lies in the boundaries of �@?a�� 0 and is denoted by f�@?a�� 0 . the procedure used to find a roughly optimal solution is as follows: �?� 0 represents a square grid of size � denoted by �?� 0 (�), and the grid elements belonging to ��0 are discarded. the algorithm in figure 3 summarizes the procedure for finding and selecting an optimal control input by the robot for collision avoidance. a quadtree [25] was used to obtain precise tiling with rectangles over the boundaries of �@?a�� 0 . the best point is selected from all the remarkable points (center and/or corners) of rectangles. a rough optimization is performed by obtaining an optimal point from all rectangles, i.e. the controls that are closest to the preferred control. predict-plan-act cycle: after each time step, the robot receives the predicted states of passive agents over a future time horizon of # seconds, and �@?a�� 0 is built. the best control �∗ ∈ �@?a�� 0 is computed with (9). the trajectory corresponding (a) (b) (c) engineering, technology & applied science research vol. 11, no. 1, 2021, 6760-6765 6763 www.etasr.com zuhaib et al.: collision avoidance of a kinodynamically constrained system from passive agents to �∗ will be collision-free for the next # seconds. the computed trajectory is executed for one scan cycle of δ� ≪ #, until a new scan cycle begins. this results in a continuous predict-plan-act navigation framework. fig. 3. algorithm: find best control input u*. iv. implementation and results the proposed approach was applied to a car-like robot model for evaluating its performance. a. considered robot model a robot with car-like kinodynamic was considered with the following parameters: its real-wheel axle center is �� � )i�,j�*k, its orientation is l, and its steering wheel angle is m. the state transition equations of the robot are given by: i���� � fno�l; j���� � f�nrl; l���� � fp (10) where f is the input speed control. as in [20], the curvature was taken directly as input, while the steering angle m can be computed for p as m � tan=r pj, where jis the wheelbase of the car. the motion of a car-like robot is considered to be constrained as: di���� s c j���� s ∈ )0,fg* (11) t�u�4 @�4 ∈ )&pg,pg* (12) where fg is the maximum speed constraint and pg is the robot's maximum curvature constraint. �?� for this system was defined by pg and fg , and its geometry was a rectangular region of the input control space. robot's position at time � can be obtained by integrating (10) assuming that controls will remain constant over the time horizon )0,�*, as: • if p v 0: ���� � �w c p=r �lw )sin�fp� 1 & no��fp� * k (13) • if p � 0: ���� � �w�� c �lw )�f 0*k (14) where �w is the current position and lw is the current orientation of the robot, and the rotation matrix �l2 is: �l2 � )no�lw & �nrlw ;�nrlw no�lw* (15) b. implementation details simulations setup the maximum speed and curvature were set to 1.5�rn�/� and 1.5�rn�=r respectively. the radius of the robot was set to 1. an open environment was constructed for the simulations, bounded by (0,0) and (22,22). this environment was set to be crowded by multiple passive agents of circular shape and radius equal to one. the scan cycle was set to δ�=0.05s. each passive agent was set to move along a specific trajectory, i.e. straight lines or arcs, with speed less than or equal to 1. the probability of an agent changing its path and speed within one second was set to 0.2. the interaction time horizon # was set to 3.5s. figure 1 shows the snapshots of simulations at multiple time instances, where the green marked robot successively avoids multiple red marked passive agents and reaches the yellow marked goal. experiments are carried out on an intel core i5-3550/4gb ram computer and the proposed algorithm was implemented using c++. c. performance results each result value was a mean of 20 trials. figure 4 shows the performance comparison with grid size � as 16 and 32. comparisons were drawn for a varying number of passive agents using three parameters. the time needed for computing optimal control �∗ in a scan cycle is shown in figure 4(a). the time needed by the robot to reach the goal is shown in figure 4(b). the success rate, which indicates the percentage of the trail in which the robot successfully reaches the goal from the starting position, is shown in figure 4(c). for d=16 the computation time is much less on average, whereas its success rate is nearly the same when comparing it with d=32. however, when d=32 the robot takes a more direct path to the goal, and the time to reach a goal is less on average, as shown in figure 4(b). fig. 4. (a) computation time, (b) time to goal, and (c) success rate on various numbers of passive agents with grid size d={16,32}. engineering, technology & applied science research vol. 11, no. 1, 2021, 6760-6765 6764 www.etasr.com zuhaib et al.: collision avoidance of a kinodynamically constrained system from passive agents d. comparative analysis the proposed approach was compared with gvo and avo for a grid size of d=16. figure 5 shows the comparison of the proposed approach with a gvo having 256 controls sampled. results showed that the proposed algorithm performed better than gvo on all three parameters. the proposed approach's computation time and the time to goal was much less, while the success rate was averagely higher compared to gvo. an additional advantage emerges as gvo is restricted to a linear equation of motion of passive agents, while the proposed approach has no such restriction. fig. 5. (a) computation time, (b) time to goal, and (c) success rate on various numbers of passive agents for the proposed approach vs gvo. figure 6 shows a comparison of the proposed approach with avo. the reciprocal collision avoidance aspect of avo was removed to make a relative comparison, while the linear programming based optimization aspect was kept. the results showed better performance for the proposed approach �@?a�� 0 on all three parameters, pointing out its effectiveness on the considered problem. v. conclusion this paper presented a new approach that maps different constraints on a robotic system as geometrical bounds on the robot's input control space, allowing the computation of the optimal control input for collision-free local navigation using quadtree. as it was shown, this computation can be executed in real-time. furthermore, the proposed collision avoidance approach had superior performance compared to other velocitybased approaches for a considered environment. moreover, an implementation of the proposed approach on a car-like robot was presented. this implementation can be easily adapted to other types of robotic systems, which is an additional advantage which can be studied in the future. fig. 6. 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[25] r. a. finkel and j. l. bentley, "quad trees a data structure for retrieval on composite keys," acta informatica, vol. 4, no. 1, pp. 1–9, mar. 1974, https://doi.org/10.1007/bf00288933. microsoft word etasr_v12_n1_pp8096-8100 engineering, technology & applied science research vol. 12, no. 1, 2022, 8096-8100 8096 www.etasr.com mahamid: critical factors influencing the bid / no bid decision in the palestinian construction industry critical factors influencing the bid / no-bid decision in the palestinian construction industry ibrahim mahamid civil engineering department arab american university jenin, palestine imahamid@ymail.com abstract-the purpose of this study is to identify and rank the factors influencing the bid/no-bid decision according to their relative importance from the perspective of the contractors in the west bank in palestine. to achieve the study objectives, a questionnaire survey was conducted. the survey covered a randomly selected sample of 64 contractors involved in the construction industry in the west bank. the questionnaire’s structure is based on the related literature, the pilot study, and the feedback from local experts in the construction industry. a total of 32 factors that might influence the bid/no-bid decision were identified and considered. then, the targeted population was asked to rank these factors according to their relative importance. the results indicate that the top five factors affecting a contractor’s decision to bid or not include the financial stability of the client, the identity and reputation of the client in the industry, the promptness of the client in the payment process, the expected profitability, and the project’s source of funding. on the other hand, the least affecting factors are the type of the project, client’s requirements, taxes, laws and government regulations, and weather conditions. the paper provides a comprehensive understanding of the factors affecting the bidding decision. construction parties and researchers could benefit from the results of this study. keywords-bids; bid/no-bid; construction; contractors i. introduction the construction industry is a major business sector that provides necessary ingredients for the development of an economy [1, 2]. for instance, as an industry sector, construction contributes about 10% of global gdp and absorbs more than 7% of labor [3]. however, it is becoming more and more complex due to the huge number of parties involved in the construction process and of the sophistication of the process itself. according to [4], the construction industry is the business sector that faces most failures in comparison to other industries. this happens because it is too risky and full with uncertainties [5]. in palestine, the construction industry plays a critical role in providing homes, infrastructure, and public facilities. it also plays a major role in absorbing the national workforce and in improving the palestinian national economy as a whole. according to [6], the construction activities in palestine absorb about 17.9% of national workforce. in 2011 and 2012, the construction industry accounted for 11.2% and 10.3% of the value added to the gross domestic product (gdp) [6]. however, many local construction projects report poor performance due to reasons such as 214538_s_etasr_v12_n1_pp8096-8100 shortage in skilled labor or materials, bad relations between the construction parties, shortcomings in bidding strategy, and lack of managerial skills [7]. construction projects, public and private, are usually awarded to contractors via tenders. the bidding process involves the bid/no-bid decision which is crucial and associated with risks and uncertainties due to various factors that influence it [8]. the influencing factors might relate to the contractor himself, to the client, or to the project conditions and the general environment. bidding decision problems are highly unstructured. typically, contractors make their decisions based on their common sense or the rule of thumb which may lead to suboptimal decisions. this is why many researchers have been involved in the development of bidding strategy models. the objective of this study is to identify and rank the factors that might influence the bid/no-bid decision according to their relative importance from the perspective of the contractors in west bank, palestine. the next sections provide a summary of the previous studies conducted to identify the related factors, the research methods and the study results. ii. previous studies the literature abounds with studies that have investigated the topic of bidding decisions and the relative strategy. many of these studies focused on identifying the main factors influencing the bid/no-bid decision in construction projects. authors in [9] concluded that the critical factors affecting the bidding decision in saudi arabia to be client financial capacity, prompt payments, project payment system, clarity of the work and specifications, and project cash flow. authors in [10] conducted a study to identify the factors affecting the bidding decision in construction projects in qatar, and found 10 critical factors. authors in [11] revealed that bidding policy has a high impact on variation orders during the construction phase. authors in [8] identified and ranked the factors that affect the bid/no-bid decision from the contractors’ perspective. the factors are classified into 4 groups: (a) external environmental factors, (b) factors related to the contractor, (c) factors related to the clients, (d) factors related to contract and project characteristics. they found that the top affecting factors include the stability of the construction industry, the contractor's financial capability, the reputation of the client, and corresponding author: ibrahim mahamid engineering, technology & applied science research vol. 12, no. 1, 2022, 8096-8100 8097 www.etasr.com mahamid: critical factors influencing the bid / no bid decision in the palestinian construction industry the financial value of the project. the author in [12] considered the bid/no-bid decision factors in auckland with the utilization of face-to-face structured interviews incorporating a questionnaire. he concluded that bid/ no-bid decision making is very dependent on the location. he also indicated that the macro environment has a great influence on bidding decision. authors in [13] reported a significant negative relationship between risk perception and bidding decision and a significant positive relationship between risk propensity and bidding decision. authors in [14] conducted a study to investigate and rank the critical factors influencing the bid/no-bid decision criteria and their importance in the australian construction industry. they identified the 26 most common decision-making criteria and they accordingly grouped them into 5 categories, namely project, market, contractor, client, and contract. using a questionnaire survey, they revealed that the most highly ranked factors are: client financial capability, project risk, project future benefits, profitability, and number of competitors. authors in [15] stated that one of the critical decisions taken by contractors is whether or not to bid for a project, due to the complexity and uncertainty surrounding this decision, which is influenced by many factors. they conducted a study in saudi arabia to find out the key factors affecting the contractors’ bidding decisions in construction projects. they concluded that the top 6 (out of 31) critical factors were: project size, project type, company strength, design quality, expected profit, and cash flow. authors in [16] conducted a study to identify the main factors influencing contractors’ bidding decisions in construction projects in nigeria. they concluded that the most significant factors affecting the bid/no-bid decision are: financial capability of clients, availability of capital, and availability of material. author in [17] conducted a study to identify the factors affecting the bidding and markup decisions of contractors, considering a total of 55 factors. the top 3 factors were the need for work, the number of competitors, and the amount of experience on such projects. authors in [18] indicated that the decision to bid is a complex activity that requires the consideration of several factors. these factors can be related to capability, time requirement, and cost implication. they performed a study to evaluate the factors related to time and cost performance to test their effect on the bidding decision. structured questionnaires were used to gather data from construction professionals in both consulting and contracting firms. the study reported the reputation of the client as the most critical factor related to time performance that influences bidding decisions, while location and condition of the site were identified as the key factors related to cost performance. thus, the reputation of the client, the location, and the condition of the site should be given the most priority by a contractor at the time of bidding. authors in [19] investigated the factors affecting bid/no-bid decisions of international projects in chinese construction projects. a total of 41 factors were identified through a literature review as having an impact on the bid decision. ultimately, 9 main factors were identified as influencing the bidding decision, with contractor’s capability and country risk of the host country, being the most important. authors in [20] investigated and ranked the critical factors influencing the bid or no-bid decision and their importance for the indigenous small building contractors within the tanzanian construction industry. the 7 most highly ranked factors (among the 30 considered) are: availability of capital, financial condition of the client, project size, expected profit, project type, need of work, and current workload. authors in [21] examined the effects of different factors on the success or failure of bids for infrastructure projects in australia. they found that the most significant factors that increase the success chances of bid are: having a competitive advantage and a local partner and also not competing against a local company. they also concluded that the essential factors to be able to compete include: relevant expertise, resource availability, previous relationship with the client, and previous relationship with consortium members. authors in [22] and [23] linked the delays in construction projects and bid award policy. iii. research method thirty two (32) factors that might affect the bid/no-bid decision were identified from the literature review and the feedback from local construction experts. the factors were tabulated in a questionnaire. the questionnaire was developed to evaluate the importance of the identified factors from the target population (contractors). the information was collected from the palestinian contractors union (pcu). the survey was used as a tool to collect the data, and then the data were analyzed with the relative importance index (rii). a. questionnaire design the questionnaire is divided into two parts. part 1 includes general questions related to the respondent and company such as the respondent’s role in the company, experience in the line of work, decision makers in the company, etc. part 2 included the list of factors affecting the bid/no-bid decision in construction projects. these factors were categorized into 4 groups according to their sources, namely: (1) factors related to client characteristics, (2) factors related to contractor characteristics, (3) factors related to contract and project characteristics, (4) factors related to the general environment. the respondents were asked to identify the impact level of each factor on the bidding decision. impact level is classified on a 4point scale as follows: very important, important, somewhat important, and not important (a 4 to 1 point scale). b. study population the target population in this study is the total number of contractors with valid registration in the palestinian contractors union (pcu) with grade 1, grade 2 and grade 3 (120 registered contractors). equation (1) was used to calculate the representative sample size [24]: n = n'/(1 + n'/n) (1) where n is the sample size of the population, n' is the sample size, which can be calculated from: [n' = s²/v²], n is the total population (120 contractors), v is the standard error of sample population, equal to 0.05 for 95% confidence level, t =1.96, s² is the standard error variance of population elements, s² = p (1-p), maximum at p = 0.5. engineering, technology & applied science research vol. 12, no. 1, 2022, 8096-8100 8098 www.etasr.com mahamid: critical factors influencing the bid / no bid decision in the palestinian construction industry the sample size for the contractors' population can be calculated from (1) as follows: n' = s² / v² = (0.5)² / (0.05)² = 100 n contractors = 100/(1 + 100/120) = 54 which means that the minimum sample size needed for this study is 54 respondents. the questionnaire was distributed to 80 contractors. the contractors were selected randomly from an available list obtained from the pcu. sixty-four questionnaires were received (response rate = 80%). the respondents indicate that the bidding decision is mostly taken by the general manager of the company (92% of the cases) and sometimes by the project manager (8% of cases). figure 1 shows the respondents’ positions in their organizations. the distribution of the respondents’ years of experience in the line of work indicates that 13.2% had less than 5 years of experience, 18.8% had between 5 and 10 years of experience, 45.9% had between 10 and 20 years of experience, and 32.1% had more than 20 years of experience. the distribution of project types that the respondents are involved in shows that 52% are involved in building construction projects, 18% are involved in infrastructure projects, and 30% are involved in both building and infrastructure projects. fig. 1. respondents’ position. c. data analysis the statistical tools of microsoft excel were used to analyze the collected data. the considered factors were ranked by the measurement of rii, which is calculated based on the importance level identified by the respondents. rii can be calculated according to (2): rii% = � � �� � � � �� � � � �� � � � �� � � � ×100% (2) where n4, n3, n2, n1 represent the number of respondents for very important, important, little important, not important and n it the total number of respondents. for example, the rii% of the "financial stability of client", which got these values: n4 = 33, n3 = 30, n2 = 1, n1 = 0 from the survey, is: rii% = � � �� � � � � � � � � � � � � � � � 100% = 87.50% the group index is calculated by using the average of factors under each group as shown in (3): group importance index (%) = ∑ xi/n�� (3) where xi is the relative importance index of factor i under the group and n is the number of factors under the group. iv. results and discussion the factors under each group are ranked by the measurement of rii according to (2). a. general environment factors table i shows the rii and the ranking of each factor under the general environment group from contractors’ view. seven factors are considered under this group. the results show that the top 3 factors are: economic environment (rii = 80.64%), political situation (rii = 77.27%) and probable number and identity of competitors (rii = 76.59%). table i. ranking of general environment factors factors related to the general environment group rii% rank economic environment 80.64 1 political situation 77.27 2 probable number and identity of competitors 76.59 3 inflation rate 69.21 4 taxes 62.50 5 laws and government regulations 58.47 6 weather conditions 54.45 7 b. factors related to the contract and project characteristics nine factors are identified under this group. table ii shows the rii and ranking of each factor under the contract and project characteristics group from the contractors’ point of view. the results show that the top 3 factors are: size or project (rii = 82.19%), location of project and accessibility (rii = 80.88%) and adequacy of tender information (rii = 78.25%). table i. ranking of contract and project characteritics factors factors related to the contract and project characteristics rii % rank size of project 82.19 1 location of project and accessibility 80.88 2 adequacy of tender information 78.25 3 identity of consultant & designer 75.62 4 contract duration 71.01 5 complexity of the project 69.69 6 time available for tendering preparation 69.69 6 contract conditions 67.72 8 type of roject 67.06 9 c. factors related to the client characteristics table iii shows the rii and ranking of each of the 7 considered factors under the client group. the results indicate that the top 3 factors under this group are: financial stability of the client (rii = 87.21%), identity and reputation of client in the industry (rii = 86.15%), and promptness of the client in payment process (rii = 84.91%). d. factors related to contractor characteristics table iv shows the rii and ranking of each of the 9 factors under the contractor group. the results indicate that the top 3 factors under this group are: expected profitability (rii = 83.80%), current workload (rii = 82.46%), and need for work (rii = 81.79%). engineering, technology & applied science research vol. 12, no. 1, 2022, 8096-8100 8099 www.etasr.com mahamid: critical factors influencing the bid / no bid decision in the palestinian construction industry table ii. ranking of client characteritics factors factors related to client characteristics rii% rank financial stability of the client 87.21 1 identity and reputation of the client in the industry 86.15 2 promptness of client in payments process 84.91 3 project source of funding 83.24 4 previous experience of contractor with the employer 73.05 5 type of client 72.4 6 client’s requirements 66.48 7 table iii. ranking of contractor characteritics factors factors related to contractor characteristics rii% rank expected profitability 83.80 1 current workload 82.46 2 need for work 81.79 3 classification criteria for the contractors 81.12 4 strategy of the company 78.43 5 availability of required cash 76.13 6 availability of required resources (raw materials, labors, equipment) 74.41 7 previous experience in similar projects 71.72 8 pre-qualification requirement 71.05 9 e. overall ranking the rii and ranking of the investigated 32 factors affecting the bidding decision in construction projects in the west bank from the contractors’ view are listed in table v. the results show that the top 5 factors are: financial stability of the client, identity and reputation of client in the industry, promptness of the client in payment process, expected profitability, and project source of funding, whereas the least affecting factors are: type of project, client’s requirements, taxes, laws and government regulations, and weather conditions. it can be noted that among the top 5 factors, 4 factors are related to the client characteristics group, while the 5th factor is related to contractor characteristics group. 1) financial stability of the client in general, financial stability of the client indicates his ability to meet debts as they fall due. financial stability in construction leads to good cash flow for contractors during the project which implies that the contractor will be able to pay for labor, materials, equipment, and other expenditures. in contrast, instability of the clients’ economic condition leads to payment delay which affects the contractor’s financial abilities and might lead to poor project performance. this result is in line with the findings in [1, 8-10]. 2) identity and reputation of the client a contractor seeks smooth performance for his project. his performance will affect his reputation in the industry. therefore, clients with good reputation will encourage the contractors to take the bidding decision more comfortably. on the other hand, bad reputation of the client will make the bidding decision to be more difficult, since bad expectations, such as financial problems and delays, will come to mind along with the fact that this may affect the reputation of the contractor himself. this result is in line with the findings in [10]. 3) promptness of client in payment process contractors take into considerations in their deals, the client’s payment process during the project. it is very important for the contractor to have good cash flow conditions in order to continue the work smoothly. therefore, promptness in payment of the client is considered as a very important factor that the contractors care about during their bidding decision. clients that make payments on time will encourage contractors to deal with them and will facilitate their decision to bid. conversely, delays in payments might lead to conflicts between construction parties which might affect the process of bidding decision making. this result agrees with [9]. 4) project source of funding the source of funding of the project is one of the main factors that the contractors have to know before making their decision to bid. the source of funding may be a person, private institutions, governmental institutions, or donors. each source has its advantages and disadvantages. fund sources may differ in their financial stability, payment methods, and promptness. moreover, contractors may prefer a specific source of funding over the others as they may have previous experience with it and this will significantly affect their bidding decision. 5) expected profitability expected profitability is a significant factor that affects the bidding decision. if the contractor feels that he will not achieve the expected profit, he probably will not enter the tender. the profit made in projects that the contractor experienced in the past could possibly forecast the possible profit that can be made from the proposed project. usually, contracting companies submit for bids and opportunities that are expected to exceed the minimum acceptable rate of return (marr). normally, there is no need for contractors to submit bids when the expected profit is less that the targeted one. however, in some cases the contractors are forced to bid for projects that do not exceed the marr due to reasons such as the need for work and to cover overhead costs. this result is in line with [14, 15]. table iv. top five factors affecting bid/no bid decision factor rii% overall rank financial stability of the client 87.5 1 identity and reputation of the client in the industry 86.15 2 promptness of client in payments process 84.91 3 expected profitability 83.80 4 project source of funding 83.24 5 v. conclusion in this paper, a total of 32 factors affecting the bidding decision in construction projects were identified and categorized in 4 groups. the identified factors were ranked according to the rii of the contractors’ point of view in the west bank in palestine. overall, the results indicate that the top 5 factors affecting a contractor’s decision to bid or not are the financial stability of the client, the identity and reputation of the client in the industry, the promptness of client in payment process, the expected profitability, and the project's source of funding. economic environment, political situation, and the probable number and identity of competitors are ranked in the top 3 engineering, technology & applied science research vol. 12, no. 1, 2022, 8096-8100 8100 www.etasr.com mahamid: critical factors influencing the bid / no bid decision in the palestinian construction industry positions under the environment group. laws and government regulations in construction and weather conditions are ranked in the bottom 2 positions as factors having a weak influence on the bidder’s decision. size, location, and accessibility of the project along with the adequacy of tender information are considered key factors affecting a contractor’s decision to participate in tenders. therefore, full and clear tender information should be provided by the owner and consultants to help contractors in taking the bidding decision. contract conditions and type of project are ranked in the lowest 2 positions and have a weak influence on a bidder’s behavior. the current workload and the need of work are identified as the top factors affecting contractor’s strategy in bidding. current and projected workload should be known to the contractor in order to be able to know whether to bid or not. the contractor doesn’t want to exceed his capabilities because this might affect his performance and lead to negative effects in terms of delay and disputations with the owners. on the other hand, contractors with low current workload will bid for projects 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[24] l. kish, survey sampling. new york, ny, usa: wiley-interscience, 1995. authors profile ibrahim mahamid received his bsc in civil engineering from birzeit university of palestine in 2001, and his phd in construction engineering and project management from norwegian university of science and technology (ntnu), norway in 2011. he is currently the head and an associate professor at the civil engineering department, arab american university, palestine. his research interests include construction engineering and surveying. engineering, technology & applied science research vol. 7, no. 5, 2017, 2041-2046 2041 www.etasr.com mahmoud and zabihi: numerical simulation of a single-phase flow through fractures … numerical simulation of a single-phase flow through fractures with permeable, porous and non-ductile walls nader pour mahmoud mechanical engineering department urmia university urmia, iran n.pormahmod@urmia.ac.ir aidin zabihi mechanical engineering department urmia university urmia, iran st_a.zabihi@urmia.ac.ir abstract—this paper attempts to study flows within fractures through a set of numerical simulations. in addition, a special care is given to hydraulic features and characteristics of fractures. the research is performed through the application of calculative fluid dynamics and a finite volume discrete schema. the investigated flows are laminar, single-phase and stable flows of water and air through fractures with penetrable walls. the selected fracture geometry is inspired from the tomographic scan of a stone fracture. water and air are modeled in fractures with permeable walls and different permeability levels. it has been observed that in case of permeable matrixes, the friction coefficient is lower compared to impermeable matrixes. in fact permeability reduced friction. in addition, highest pressure drops were observed in areas with smaller fracture diaphragms. nonetheless, the surrounding area of the fracture is analyzed with the consideration of darcy's rule. keywords-fracture; pressure gradient; porous media; singlephase flow numerical simulation; darcy's rule; laminar flow; matrix i. introduction fractures of earth crust are in different scales. these fractures are significant for certain fields of study including geology, oil engineering and mechanical engineering as well. fractures provide an easy route for the flow of fluid and facilitate the flow through barriers throughout the whole fracture and act as a hydraulic conductor. the amount of carbon dioxide present in atmosphere has significantly increased during the past few years. this high level of carbon dioxide results in ground warming. underground brines have the highest capacity for storage of carbon dioxide. underground brine aquifers are made of porous stones with low permeability. there are also fractures on these stones that can act as natural fluid pipelines. therefore, carbon dioxide can be stored in these underground structures. it is assumed that fractured areas in reservoirs are of a lower permeability. considering the low surface tension underground or undersurface fluids, it can be concluded that carbon dioxide is stored in these reservoirs with a low viscosity. several experimental studies have been performed regarding the contexts of a single-fracture [1], flows within intersecting fractures [2], and flows through fractured porous environments [3]. the present study analyzes the flow through a fracture and evaluates the flow rate for different types of pressure drops and various permeability levels for matrixes of fracture surroundings. it is worth mentioning that navier-stokes nonlinear equations have been used for expression of behavior of flows through fractures [4]. several models have been proposed for the investigation of flows through porous environments and fractures [5]. more recently, the behavior of flow through rough fractures was studied. in addition, other researchers have investigated the behavior of flow of fluids through real fractures through the application of the finite differences formula [6]. the aforementioned researchers have shown that in fractures, flow behavior depends on twists and roughness of fractures. authors in [7] used the 2tough code for analysis of non-saturated flows within fractured stones. they concluded that the method of continuity is suitable. in addition, their simulations revealed that matrix permeability can have a significant effect on behavior of flow traffic behavior. authors in [8] investigated the flow and transfer of salts around an injection well with a growing crack. authors in [9] measured the surfaces of stone fracture through the application of 3d laser scan method. this study investigates the reliability of fractal models for fracture geometry. in this regard, a theoretical fracture model was developed and the results were compared with those obtained from experimental observations. authors in [10], used the brazilian test method for a fractured layered brea sand stone with a length of 10.15 centimeters and width of 2.64 centimeters. it is worth mentioning that the overall dimensions of experimental sample were 10.2 by 2.7 by 0.77 centimeters. in addition a high quality ct-scan and 240 cubic micrometers voxel were used. the present study elaborates on simulation of a single-phase flow through a fracture with permeable surrounding. the geometry under investigation is obtained from a ct-scan slice of brea sand stone prepared by [10]. authors in [11] calculated the friction coefficient for fractures with impermeable walls. engineering, technology & applied science research vol. 7, no. 5, 2017, 2041-2046 2042 www.etasr.com mahmoud and zabihi: numerical simulation of a single-phase flow through fractures … numerical simulations of the present study have been performed through solvation of navier-stokes equations through the application of cfd ansys fluent. in addition it must be stated that similar flow rates have been calculated for various pressure gradients. a fracture surrounding permeability rate of 2-2000 md has also been selected for both flows of water and air. results obtained regarding the fluid flow of water have been compared with those obtained by other researchers. results of this simulation have several applications in reservoirs with constant pressure and several fractures. the following explains the manners of modeling of flow, and simulation of marginal condition of the flow [12]. afterwards, results of simulations are expressed and ultimately, the mentioned results are compared with results obtained from earlier research works. ii. equations governing the flow simulation of a flow using the stokes equation is a relatively easy task and requires significantly fewer calculations compared with the full navier-stokes formula. however, the stokes equation is only applicable to laminar flows. we have modeled the equations of flow of fluids through fractures through numerical solutions. the physical principles of flow through fracture can be defined using the mass and momentum related equations. however, the movement equations of a single-phase newtonian and incompressible fluid flow can be written as follows: / / / 0u x v dy w x        (1) 2 2 2 2 2 2 ( ) ( ) u u u u p u u u u v w t x y z x x y z                           (2) 2 2 2 2 2 2 ( ) ( ) v v v v p v v v u v w t x y z y x y z                           (3) 2 2 2 2 2 2 ( ) ( ) w w w w p w w w u v w t x y z z x y z                           (4) in the upper equations, expressions of u, v and w are respectively the components of velocity in respective order of x, y and z directions. equation (1), is the continuity equation and equations (2), (3) and (4) are the navier-stokes equations that express the movement of an incompressible fluid in a three dimensional figure. the hypothesis of incompressibility of fluids (for example water, oil, gas and air) under the surface of crust is already accepted. by the use of steady state form of navier-stokes equation, the flow of fluid can be rewritten in the following vector form: 2( . )u u u p     (5) the upper equation is a differential equation with partial derivatives and no general solution in a way that, several hypothesis need to be considered in order to be able to analytically solve it. hypothesizing a steady state with no compressibility will not give us a general solution because the equation is still non-linear. the main problem in solvation of the upper equation is presence of the ( . )u u  term. in certain cases, this term is minimal while modeling for undersurface flows. in these cases, this term can be neglected. when this term is removed from the navier-stokes equation, the equation gains a high level of simplicity. therefore it becomes easily solvable. laminar and dense flows are examples of models of fluid movement that can be expressed by mathematical linear equation of stokes. 2u p   (6) the upper equation can be used for simulation of flows through fractures; however in case of fractures with parallel walls. it is also a very suitable approximation for extremely laminar flows even when the fracture walls are not perfectly parallel. in terms of low velocities, the importance of the upper term is signified when the geometry of fracture has bended or there are sharp corners or when the goal is analysis of a suitably scaled flow near the wall of fracture with high coarseness frequency. the method of calculative fluid dynamic (cfd) namely as ansys fluent, is made use of in order to numerically solve the steady state navier-stokes equation. these equations are solved through the finite volume method based on transformation of governing mathematical equations into algebraic equations which are solved numerically. the fractured stone sample under investigation is prepared. the former sample is made of brea sand stone and has the dimensions of 2.54 by 10.15 centimeters. nazirdoust et al. have transformed the two dimensional data of the former sample into three dimensional data through the scanning method. statistical characteristics of the fracture including average diaphragm and standard deviation have been already calculated in [12]. fracture diaphragm ranges between 240 microns to 1.2 millimeters. there are no complete barriers in this fracture and therefore, simulation of the two dimensional flow can be performed with least difficulty. in order to put the results of simulation into real applications, certain minimum statistical characteristics of the fracture are required. average and variance values of fracture opening can be these characteristics. however, investigation of curvatures is harder and is accompanied with more complexities. authors in [12] have calculated the data regarding average fracture opening (height of plates) (h avg), standard deviation, fracture area and curve area. curve or bending is defined as percentile increase in traveled distance by the fluid through a fracture resulting from coarseness or hardness of fracture walls. according to the definition provided in [12] curve or bending is calculated as follows: 1flow l l    (7) in the upper equation, l flow is the route that fluid passes through and l is the length of fracture. in physical conditions, it is difficult to measure the amount of bending. therefore, the lines of flow route along the fracture lines for laminar flows can be measured through the cfd method. in order to measure the bending, a water fluid flow with velocity of 0.1m/s and with at least 4 particles of 10nanometer drops was simulated through the discrete phase modeling method. it is worth mentioning that brownian effects have been neglected. engineering, technology & applied science research vol. 7, no. 5, 2017, 2041-2046 2043 www.etasr.com mahmoud and zabihi: numerical simulation of a single-phase flow through fractures … a 155000 cell calculative network has been performed in ansys and afterwards, fluent method has been used for this simulation. a single-phase water and air flow has been passed through a fracture. a density of 998.2 kg/m3 and viscosity of 0.001 kg/m·s have been supposed for water. in addition, in case of air, the former values have been respectively supposed as 1.225 kg/m3 and 1.8x10-5. in addition in terms of pressure, a gradient of 1000 to 5 pa has been considered for water and a range of 20 to 0.1 pa has also been considered for air. furthermore, permeability of the porous matrix with porosity of 20% ranges between 0.2 md and 2000 md. nonetheless, a 155000 cell calculative network has been used for this model. densities and viscosities of water and air are as they're mentioned above. a total 40 simulations have been run for 40 different pressure gradients under single-phase water and air flows. iii. network independence in order to guarantee the validity of our solvation, first of all, a network independence test must be performed. the following graph shows the results of investigation of network independence. determination of a suitable network size consumes the highest amount of time among components of a three dimensional simulation. this is because the quality of network mesh has significant effects on the process of convergence. numerical solvation of a problem related to fluid dynamics should be network independent. in other words, as the network gets smaller, responses to changes must become more negligible. with respect to the fact that only numerical data are comparable with friction coefficient and in order to find such networks, we are required to draw the graph of changes of friction coefficient according to the number of elements. in this regard, a network with 155000 nodes was established. calculations have been performed by making use of two parallel computer devices equipped with intel core i7 processors and a total memory of 16 gigabytes. iv. marginal conditions marginal conditions of input pressure have been made use of for the input that can be seen on the right side of the aforementioned figure. input pressures have been considered for both the fracture and surrounding matrix. in addition, output pressure has also been considered for both the fracture and its surrounding. furthermore, a symmetric state has been considered for the upper and lower bounds of the fracture. remaining surfaces have been considered as solid walls with no flows. the input and out pressures for both the fracture and its surrounding matrix have been considered equally. nonetheless, a 20% porous environment has been considered for the matrix. table i. network independence calculation time friction (water): 10 pa; perm.: 2000 md friction (air): 0.2 pa; perm.: 2000 md number of elements number of nodes mesh 8 hours 496.234444 8120.498634 662329 337679 small 3 hours 496.345423 8132.873460 301995 155462 medium 0.5 hours 507.98568 8796.976339 11384 11887 large v. simulation results throughout the entire calculations, a constant pressure gradient has been taken into account for surroundings of fractures. as shown, the pressure drop is linear along the flow route (following the darcy rule). significant pressure changes are observed near the fracture profile which is due to changes in opening of fracture. following figures 1-2 show the changes in pressure for both pressure gradients of 5 pa under permeability of 2000 md, and 1000 pa under permeability of 2000 md. as it was expected, fluid flow is more concentrated in the fracture. this has been shown in upper images. the following figures 3-4 show the flow of air with pressure range of 5 pa to 1000 pa under a permeability rate of 2000 md and a porosity of 20%. vectors of velocity show that lower flow rates are associated with surroundings of fractures. this figure reveals the complex relations of fluid flow between fractures and their surrounding matrixes. as it can be seen, the rate of flow in matrixes surrounding fractures is low and in these cases, the fluid moves through the interface between fracture and impermeable matrix. in terms of laminar flow rates, the calculated pressure drop is linear and is comparable with flow rate. results of simulations have shown that a significant portion of pressure drop in fractures takes place in areas with smallest openings or diaphragms. figures 5-6 show the friction coefficient according to flow rate for the steady pressure gradient model for both the water and air flows under different permeability in surrounding matrices. in addition, our simulations have shown that matrix permeability can have significant effects of flow's transfer behavior. as shown in the following diagrams, the low amount of permeability has been diagnosed with the highest friction coefficient in terms of constant flow rates. the relation between coefficient of friction and rate of flow linearly increases along the logarithm diagram and as the flow rate increases, the value of friction coefficient decreases. table iii shows the results of comparison of value of friction coefficient under permeability values of 20 md and 2 md. it can be seen that under constant pressures, the friction coefficient of permeability of 2 md is higher than the permeability of 20 md. therefore, it may be concluded that as the permeability is increased, the value of friction coefficient decreases. engineering, technology & applied science research vol. 7, no. 5, 2017, 2041-2046 2044 www.etasr.com mahmoud and zabihi: numerical simulation of a single-phase flow through fractures … fig. 1. factors of pressure gradient under equal permeability for flow of water fig. 2. factors of pressure gradient under equal permeability for flow of air fig. 3. velocity vector lines under permeability of 2000 md for 5 pa air flow fig. 4. velocity vector lines under permeability of 2000 md for 1000 pa air flow engineering, technology & applied science research vol. 7, no. 5, 2017, 2041-2046 2045 www.etasr.com mahmoud and zabihi: numerical simulation of a single-phase flow through fractures … fig. 5. diagram of friction coefficient according to flow rate under pressure gradients of 5, 10, 100 and 1000 pa and permeability of 0.2, 200 and 2000 md for water flow fig. 6. diagram of friction coefficient according to flow rate under pressure gradients of 5, 10, 100 and 1000 pa table ii. investigation of effect of permeability on friction coefficient material pressure flow rate reynolds permeability fric. coeff. permeability fric. coeff. air 20 42.348 2.882 20 81.305 2 81.667 air 2 4.26 0.289 20 816.233 2 819.846 air 0.2 0.426 0.029 20 8163.404 2 8199.635 air 0.1 0.213 0.0145 20 16313.524 2 16385.922 water 1000 33.003 31.945 20 4.382 2 4.404 water 100 3.872 3.865 20 49.785 2 50.008 water 10 0.383 0.382 20 500.908 2 503.132 water 5 0.19174 0.191 20 1003.92 2 1008.375 vi. conclusions & suggestions in this paper authors have numerically simulated a singlephase laminar flow with constant pressure gradient through a fractured profile with various permeability rates. considering the results of the simulations performed in this paper, a relationship has been developed for the evaluation of friction coefficient in fractures surrounded by impermeable matrixes. in addition, this article has proven that the existence of permeable matrices reduces the value of friction coefficient. considering the permeability factor throughout the fracture has resulted in the creation of a suitable understanding of features or characteristics of flow through fractured areas. some of the most important conclusions made by this model are:  the presence of permeable matrices results in reduction of friction coefficient compared to impermeable matrixes  highest rates of pressure drop are observed in areas with smaller diaphragms engineering, technology & applied science research vol. 7, no. 5, 2017, 2041-2046 2046 www.etasr.com mahmoud and zabihi: numerical simulation of a single-phase flow through fractures …  application of marginal conditions in terms of the relation between fracture and porous matrixes results in an approximate 10% reduction in simulated flow rate. regarding the issues related to the present article, the following could be suggested as future work:  investigation of marginal friction, loss of viscosity and other effects including those resulting from orientation, magnetic fields or the effects of radiation in heat transfer in porous matrixes  development of methods of flow modeling in porous environments and interfaces of fluids. references [1] j. s. konzuk, b. h. kueper, “evaluation of cubic law based models describing single-phase flow through a rough-walled fracture”, water resources research, vol. 40, no. 2, 2004 [2] j. johnson, s. brown, “experimental mixing variablity in intersecting natural fractures”, geophysical research letters vol. 28, no. 22, pp. 4303-4306, 2001 [3] m. billstein, u. svensson, n. johansson, “application and validation of a numerical model of flow through embankment dams with fractures, comparisons with experimental data”, canadian geotechnical journal, vol. 36, no. 4, pp. 651-659, 1999 [4] r. w. zimmerman, g. s. bodvarsson, “hydraulic conductivity of rock fractures”, transport in porous media, vol. 23, no. 1, pp. 1-30, 1996 [5] a. e. scheidegger, physics of flow through porous media, university of toronto press, toronto, 1974 [6] v. muralidharan, d. chakravarthy, e. putra, d. s. schechter, “simulation of fluid flow through rough fractures”, spe annual technical conference and exhibition, pp. 26-29, 2004 [7] m. lespinasse, j. sausse, “quantification of fluid flow: hydromechanical behaviour of different natural rough fractures”, journal of geochemical exploration, vol. 69-70, pp. 483–486, 2000 [8] h. h. liu, c. b. haukwa, c. f., ahlers, g. s. bodvarsson, a. l. flint, w. b. guertal, ”model flow and transport in unsaturated fractured rock: an evaluation of the continuum approach”, journal of contaminant hydrology, vol. 62–63, pp. 173–188, 2003 [9] s. l. bryant, r. k. paruchuri, k. p. saripalli, “flow and solute transport around injection wells through a single growing fracture”, advances in water resources, vol. 26, no. 8, pp. 803–813, 2003 [10] t. hirono, m. takahashi, s. nakashima, “in situ visualization of fluid flow image within deformed rock by x-ray ct”, engineering geology vol. 70, no. 1-2, pp. 37–46, 2000 [11] z. t. karpyn, g. li, p. m. halleck, a. s. grader, “factors favoring the formation of fluid banks during counter-current flow in porous media”, egs-agu-eug joint assembly, 2003 [12] k. nazridoust, g. ahmadi, d. h. smith, “new friction factor correlation for laminar, single phase flows through rock fractures”, journal of hydrology, vol. 329, no. 1-2, pp. 315–328, 2006 microsoft word etasr_v11_n5_pp7702-7708 engineering, technology & applied science research vol. 11, no. 5, 2021, 7702-7708 7702 www.etasr.com abbas & ismael: automated pavement distress detection using image processing techniques automated pavement distress detection using image processing techniques iman hashim abbas department of civil engineering college of engineering university of baghdad baghdad, iraq i.altaie1901m@coeng.uobaghdad.edu.iq mohammed qadir ismael department of civil engineering college of engineering university of baghdad baghdad, iraq drmohammedismael@coeng.uobaghdad.edu.iq abstract-pavement crack and pothole identification are important tasks in transportation maintenance and road safety. this study offers a novel technique for automatic asphalt pavement crack and pothole detection which is based on image processing. different types of cracks (transverse, longitudinal, alligator-type, and potholes) can be identified with such techniques. the goal of this research is to evaluate road surface damage by extracting cracks and potholes, categorizing them from images and videos, and comparing the manual and the automated methods. the proposed method was tested on 50 images. the results obtained from image processing showed that the proposed method can detect cracks and potholes and identify their severity levels with a medium validity of 76%. there are two kinds of methods, manual and automated, for distress evaluation that are used to assess pavement condition. a committee of three expert engineers in the maintenance department of the mayoralty of baghdad did the manual assessment of a highway in baghdad city by using a pavement condition index (pci). the automated method was assessed by processing the videos of the road. by comparing the automated with the manual method, the accuracy percentage for this case study was 88.44%. the suggested method proved to be an encouraging solution for identifying cracks and potholes in asphalt pavements and sorting their severity. this technique can replace manual road damage assessment. keywords-pavement distress; aeop; python code; image processing i. introduction road traffic accidents are globally becoming a big issue [1]. according to recent world health organization reports, more than 1.25 million people are killed, and 50 million are injured in road traffic accidents annually [2]. road defects play a significant role in the occurrence of accidents [3]. road networks are an essential part of our daily life. pavements deteriorate over time for a variety of causes. the load of the travelling vehicles may cause a pavement to deteriorate. transverse cracks, longitudinal cracks, block cracks, and alligator cracks are the four types of cracks found in early pavement deterioration. if these early deteriorations are not addressed, potholes emerge, making the road more unsafe. rehabilitation procedures, such as fixing potholes, will cost 10 to 20 times as much as resealing cracks. pavement detection and rating are important to maintain the cost of repairing road deterioration low [4]. traditionally, the cracks in the pavement are manually inspected. manual inspection is not only timeconsuming, inefficient, and prone to errors, but it can also lead to security incidents. most researches aim to locate and fix pavement cracks as fast as possible [5]. several studies have been carried out to create a system for automated detection of pavement cracks that solves the restrictions of the manual technique [6]. according to threshold values obtained from histograms of an image, the authors in [7] did an entropy and image dynamic thresholding to automatically divide pavement crack pixels into crack and non-crack pixels. every binary image achieved by using the threshold value was classified into non-overlapping blocks in which the occurrence of cracks was confirmed using the entropy function and the thresholding operation although the findings are not consistent with every examined image, because of the various lighting circumstances while utilizing a single threshold. authors in [8] presented another use of image processing on crack identification, focusing and getting an extra specific crack image free of noise. the given approach appears hopeful, but it is time-consuming because it analyzes a one-lane 10m road for a few minutes. authors in [9] suggested a mixed method for automatic crack identification based on 3d ultra laser-imaging pavement data. matched filtering was applied to show the cracks, while tensor voting was used to find the main directions of the cracks, and the minimal spanning tree was utilized to identify the crack path. meanwhile, authors in [10] developed an approach for detecting and segmenting cracks in pavement images by utilizing a steerable filter with two shifted and rotatable tails to achieve satisfactory crack segmentation accuracy. authors in [11] recently made an automated algorithm-based image processing approach for segmenting and improving pavement crack identification utilizing 3d pavement images. although image processing techniques have been used effectively in crack finding, there are yet certain concerns regarding the accuracy and efficiency that must be addressed. authors in [12] gave an image processing algorithm, special for the rapid evaluation of cracking in the pavement surface. authors in [13] invented a photogrammetric method to corresponding author: iman hashim abbas engineering, technology & applied science research vol. 11, no. 5, 2021, 7702-7708 7703 www.etasr.com abbas & ismael: automated pavement distress detection using image processing techniques categorize and enumerate the number of pavement cracks automatically. authors in [14] proposed a novel automatic crack discovery approach depending on a segment extending for sophisticated pavement movie frames. interrelated segments are connected to produce a crack by analyzing the relationship between connected domains, and the character of crack trend could be best employed in crack differentiation. real pavement surface images were utilized to investigate the method's execution, and the results demonstrated that the surface pavement crack could be accurately and automatically classified. authors in [15] proposed a way to detect and categorize the defects on road pavement surfaces automatically by using an anisotropy measure. authors in [16] designed a 3stage method for crack investigation through high-contrast images. the method is based on the detection of cracks in the pavement through the evaluation of curves and the mathematical formation in the presence of a percentage of noise in the processed image. it was depended on the mathematical morphology and evaluation of curvature that detects the crack-like patterns in a noisy environment. authors in [17] evaluated the achievement of 6 frequently applied segmentation methods. according to their findings, the dynamic optimization-based method surpasses the other algorithms. authors in [18] state that the goal of incorporating the shuffled frog-leaping algorithm (sfla) into the electromagnetism-like mechanism (em) is to improve pavement crack properties in lighting invariant images. authors in [19] created a pavement distress detection method that helps reduce noise and sharpen the linear characteristics of raw images. authors in [20] utilized wavelet transform on image processing in order to automatically locate and highlight cracks. the suggested method has restrictions because it is hard to detect cracks due to sharp surface consistencies that create noise in the last image. because crack pixels have more darkness than the surrounding pavement pixels, some thresholding approach has been used by many studies to locate cracks on the pavement. ii. study objectives the essential goals of this study are: • to develop new algorithms for automatic detection and classifications of pavement cracks and potholes in images and videos. • to compare the manual method (visual survey) and the automated method. iii. methodology with the high-performance optical sensor technology and the increasing number of algorithms that rely on computer vision, the development of civil engineering-related applications increased. most of these applications are dependent on image and video processing techniques by emphasizing the specific properties of the image and increasing the probability of correct detection [21]. two python codes were used in this study. the first one, which dealt with images, attempted to categorize the types of 2d pavement distress and assess their severity. the second, which dealt with videos, attempted to evaluate sections of road pavement. fig. 1. work flowchart. a. image possessing code (ipc) 1) image capturing and reading images obtained from the road were used to detect cracks (horizontal, vertical, and alligator) and potholes and to assess their severity. the images were captured from a gopro 8 hero camera that was positioned with an angle of 90 o and a height of 1.10m from the pavement surface as shown in figures 2 and 3. a captured image must be in jpg format for the code to understand it. the reading of the image is an essential phase of the computer vision flow chart. it enables the framework to get the information. fig. 2. the angle between the camera and the surface of the pavement. 2) apply blur step 2 is used to reduce noise by gaussian blur, which is the most commonly used smoothing technique to eliminate noises in images. in this technique, an image should be convolved with a gaussian kernel to produce the smoothed image. it can be considered as a nonuniform low-pass filter that preserves low spatial frequency [22]. engineering, technology & applied science research vol. 11, no. 5, 2021, 7702-7708 7704 www.etasr.com abbas & ismael: automated pavement distress detection using image processing techniques fig. 3. the height of the camera from the surface of the pavement. 3) covert to grayscale and resize for many image processing applications, color information doesn't help in identifying important edges or other features. so, the image will be converted from rgb to grayscale to neutralize colors. also the image is resized to 200×200 pixels. 4) apply thresholding it is a sort of image segmentation in which the pixels of an image are changed to make the image easier to analyze. thresholding is a famous technique used in image processing algorithms to extract features. thresholding is most commonly used to identify regions of interest in an image while disregarding areas of no concern [23]. for a given image, this work involves creating a histogram of grayscale values to find the vertices in the image. a threshold is then chosen according to the restricted area confined between two peaks. the failure areas of the pavement within the captured image are often marked by abrupt changes in the grayscale level of adjacent regions. 5) apply canny (edge detection) canny edge detection sets the edges of each pixel in the image to determine the color value after converting the image from grayscale to binary, ensuring that there are only two colors (black and white) in the image. the canny edge detection algorithm process consists of 4 steps: • apply a gaussian filter to smooth the image and remove the noise because edge detection is prone to noise. a a 5×5 gaussian filter is used to remove the noise from the image. • find the intensity gradients in the image: the image is then smoothed and filtered in both horizontal and vertical dimensions with a sobel kernel to have the initial derivative in horizontal and vertical direction, gx and gy. the edge gradient and direction for each pixel are calculated from: ����_���� � ��� � ���� � ��� (1) � ����� � tan��� �� �� (2) the direction of the gradient is always perpendicular to the edges. it is rounded to one of these different angles: vertical, horizontal, and the two diagonal directions [24]. • non-maximum suppression: after the identification of the extent and the direction of the gradient, the image is completely inspected to discard any unwanted pixels. every pixel is assessed to look if it is a regional maximum in its neighbourhood in the gradient's direction [24, 25]. • hysteresis thresholding: this step decides if the edges are real or not. this requires two thresholding values, minval and maxval. pixels with intensity gradient of the edges greater than maxval are guaranteed to be edges, while those with an intensity gradient less than minval are guaranteed to be non-edges and are therefore eliminated. the ones located between the two criteria are sorted as edges or nonedges according to their connection. if they are linked to "sure-edge" pixels, they are regarded to be edges. if not, they will be removed as well [24]. 6) dilate filter application a dilate filter is applied to fill the empty holes. a 5×5 kernel size is used. dilation is applied to the binary images. the primary action of dilation on a binary image is that the boundaries of regions of foreground pixels are continuously increased (for example, white pixels). as a result, foreground pixel areas grow in size, while gaps within those regions shrink. image dilation is used over erosion because erosion contracts the object. since the noise is gone, it won’t return, but the object area increases. it is useful in connecting the broken parts of an object back together. 7) image processing the processing on the images consists of the following steps: • detect all contours in the image (finding all objects): contours can be defined as a curve linking all continuous points (along the border) of matching color or intensity. the contours are important tools for object recognition and shape evaluation [26]. a find-contours function retrieves all the contours in the image that it can detect. contours can appear in an image in a variety of ways. some might be grouped in other contours etc. this technique is used to simplify locating the contours of interest and to understand the hierarchy in which the contours are nested [26]. • calculate contour area: image moments assist in calculating some properties usually selected to have attractive features. it is used to define objects and to detect uncomplicated features of the image like area, intensity, centroid, orientation [26], etc. image moment can be defined as a weighted average (moment) of the image pixels' intensities • filter areas larger than the selected minimum crack area: minimum crack size can be variant using the software ui, and changes will be seen in real-time for crack detection. • calculate arc length: arc length is used to calculate the perimeter of the contour. this is used to know more about the crack length and later to decide its type. • get the arc borders edges that approach a curve or a polygon with another curve such that the distance between them is less or equal to the particular accuracy, then calculate the number of curves/polygon endpoints to know how many endpoints are in the crack. for example, longitudinal and transverse have two endpoints and the alligator type has a minimum of 5 endpoints. engineering, technology & applied science research vol. 11, no. 5, 2021, 7702-7708 7705 www.etasr.com abbas & ismael: automated pavement distress detection using image processing techniques • get the arc type, based on these conditions: if width < 100 and h > w × 2, it is a longitudinal. if w > h × 2 and h < 100, it is a transverse. if the endpoints of the edge are larger than 5 and the shape is adequate, it is an alligator crack. else, it is a pothole. • draw contours on the screen. • draw the arc path to detect crack areas and their width. • get the severity based on user-entered values for low, medium, and high severity. • draw result texts and border around the crack. 8) show the results an example can be seen in figure 4. fig. 4. the obtained result. b. movie processing code (mpc) 1) import video the video is imported from the computer as an mp4 type. video reader instructions are used by the code to read the movie. 2) calculate the total number of frames the total number of frames in the movie is calculated by using a high-speed (240 fps) camera. 3) select the frames that will be processed for surveying speed of 80km/hr or 22m/s and w=3m, l=2.20m frame dimensions, 1 frame must be selected from every 22 frames. for example, if the period of video is 1s (240 frames), the code will select 11 frames (1, 23, 45, 67, 89, 111, 133, 155, 177, 199, 221). these numbers apply only to the type of camera hero 8 black because they are calculated based on the characteristics of this camera. 4) change rgb frames to greyscale and then to binary this step is essential in enabling the code to work with only two colors. 5) regulate the frames to matrices 6) measure the standard deviation of each frame by utilizing std orders. 7) regulate the frames to to have the same pixel size 8) filtering to decrease the frame noise, the image should be filtered. in mpc, and after experimentation with many kinds of filters, the most useful filter that can be utilized is the gaussian filter. this kind of filter is dealing with almost all noises in the frame. 9) color conversion in order to differentiate undamaged pavement from the impairment area in the same image, the colors are converted to conclude the involved areas in white and black for the normal pavement. 10) edge detection edge detection is conducted by the canny algorithm. 11) total edge values total edge values are found for every column and every row in the frame. 12) finding the distress kind the values of total edges were compared to find the distress kind in the frame. the damage in the pavement and its severity are found by measuring the white to black ratio in the frame. 13) determine the pcr of the pavement iv. results and discussion the traditional method of assessment of pavement condition is to walk or drive down the road and collect the data manually. this way of road pavement surface detection depends on the experience level of the employees and it is time-consuming, hazardous, and subjective. therefore, an effort has been made to fully automate the data collection process. to examine the possibility of the program to identify the types of failures and their severity from different images, 50 failure images were obtained and processed. the program correctly identified 38 of them. in the remaining images, the program either failed to detect the crack, identified it incorrectly, or gave a wrong severity of the crack. so, the examined images have an accuracy percentage of about 76%. this medium accuracy may be caused by environmental factors like shadows, dust, or weather conditions. the accuracy percentage of the distress detection may be enhanced by taking clearer images and having criteria for proper capture of the images with a steady source of light. the proposed automated evaluation of pavement (aeop) method detects the defects of roads automatically and classifies the most common distresses (fatigue, transversal cracks, longitudinal cracks, and potholes) by using computer vision techniques and image processing. the obtained classification results contain distress name/class and severity level as demonstrated in figures 7-10. the manual method of assessment was conducted by the specialized department that is responsible for the evaluation and maintenance of city roads. the engineers did the manual assessment by using the engineering, technology & applied science research vol. 11, no. 5, 2021, 7702-7708 7706 www.etasr.com abbas & ismael: automated pavement distress detection using image processing techniques pavement condition index (pci) to quantify the condition of the road based on a scale from 0 to 100. they measured the pavement's integrity and surface condition and rated the sections as very poor, poor, fair, satisfactory, good, or excellent according to [27]. by comparing the automated with the manual survey for the 8 sections, the percentage of accuracy results of distress detection for this case study is 88.44%. table i. percentage differences between pci and aeop no. sections pci aeop 1 sec 1 68% 75.23% 2 sec 2 69% 78.03% 3 sec 3 71% 75.45% 4 sec 4 72% 80.26% 5 sec 5 75% 81.46% 6 sec 6 60% 76.25% 7 sec 7 65% 80.02% 8 sec 8 70% 75.34% fig. 5. percentage differences between pci and aeop surveying. in figure 5, we can see that the largest differences between the two methods occurred in sections 7 and 6. the smallest difference between the two methods occurred in section 3. when the two methods' results were compared, as shown in table i, the results are nearly similar with a small variation. the discrepancy in the results can be attributed to several factors, including the type of pavement evaluation method, or maybe due to other issues like environmental factors such as stains, lane marks of the road, adjacent vehicles, shadows of side road trees, or texture differences among different pavement surfaces that affect the results of the automated detection of the crack. among the most crucial comparisons to make is the difference in the time survey between the two techniques. the survey committee estimated the time required for the field survey and provided a report on the pavement's efficiency. the differences between the manual method and the automated approach are shown in table ii. table ii. time consumption no. time (min) section no. pci aeop 1 section 1 210 20 2 section 2 152 24 3 section 3 200 25 4 section 4 120 29 5 section 5 245 27 6 section 6 150 30 7 section 7 118 25 8 section 8 200 21 the time required to do a manual survey vs the aeop approach is significantly different. the aeop took less time than the manual method, as shown in figure 6. the time needed to finish the manual assessment of the 8 sections of the highway by the engineers of the maintenance department of the mayoralty of baghdad was about 23hr. and the time needed for finishing the automated way was about 3hr. fig. 6. required time for completing each method in each section. (a) (b) (c) (d) fig. 7. longitudinal crack: (a) original image, (b) binary image, c) after applying canny threshold, (d) result. (a) (b) (c) (d) fig. 8. alligator crack: (a) original image, (b) binary image, (c) after applying canny threshold, (d) result. engineering, technology & applied science research vol. 11, no. 5, 2021, 7702-7708 7707 www.etasr.com abbas & ismael: automated pavement distress detection using image processing techniques the cost of surveying is also an important issue to be evaluated. the manual method requires a committee with at least 3 experienced road engineers or technicians who work in road maintenance, and the use of these specialists means an augmented cost that will be spent on the evaluation of the road section. in addition, the evaluation of all the road sections requires a long time, and increasing time also means increased cost of the assessment of the whole road. on the other hand, the evaluation of the performance of the road’s pavement using the aeop method doesn't need committees or many workers. it requires just one person who knows how to use the code and a vehicle supplied with a camera. (a) (b) (c) (d) fig. 9. transverse crack: (a) original image, (b) binary image, c) after applying canny threshold, (d) result. (a) (b) (c) (d) fig. 10. pothole: (a) original image, (b) binary image, c) after applying canny threshold, (d) result. v. conclusions the presented results support the following conclusions: • it is useful to utilize the image processing approach for identifying pavement failures. the presented algorithm has a lot of promise in terms of automated crack and pothole detection, since it can provide quick, nearly precise, and cost-effective results, which is important in pavement management systems. • the suggested study is an encouraging solution for identifying cracks and potholes in asphalt pavements and sorting their severity by automated survey. by comparing the automated with the manual survey, the percentage of accuracy results of distress detection for this case study is 88.44%. • there is a very large difference in the time needed to conduct the two methods. the aeop required about 87% less than the manual method. • also, the automated method is much safer because it is generally conducted at prevailing traffic, it is easy to operate, it does not require committees, just one person to do it, and so it costs less than the manual method. • the automated technique can replace the traditional road measurements. improving the automated crack detection can be done by using a vehicle with more developed equipment like multiple sensors, or a lighted camera to overcome the shadowing problem. there is a need to develop the code through cooperation with artificial software experts who can add new algorithms and thresholds to the current code in order to increase its performance and make it more efficient in exploring more types of failures on paved roads. acknowledgement the authors would like to thank the engineers of the maintenance department of the mayoralty of baghdad for their cooperation. references [1] i. j. mrema and m. a. dida, "a survey of road accident reporting and driver’s behavior awareness systems: the case of tanzania," engineering, technology & applied science research, vol. 10, no. 4, pp. 6009–6015, aug. 2020, https://doi.org/10.48084/etasr.3449. 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[27] astm d6433-07(2007), standard practice for roads and parking lots pavement condition index surveys. west conshohocken, pa, usa: astm international, 2007. microsoft word etasr_v11_n4_pp7452-7457 engineering, technology & applied science research vol. 11, no. 4, 2021, 7452-7457 7452 www.etasr.com dalaf & mohammed: the impact of hybrid fibers on punching shear strength of concrete flat plates … the impact of hybrid fibers on punching shear strength of concrete flat plates exposed to fire ahmed naji dalaf department of civil engineering university of baghdad baghdad, iraq ahmed_naji.2007@yahoo.com shatha dheyaa mohammed department of civil engineering university of baghdad baghdad, iraq shatha.dh@coeng.uobaghdad.edu.iq abstract-this study presents an investigation about the effect of fire flame on the punching shear strength of hybrid fiber reinforced concrete flat plates. the main considered parameters are the fiber type (steel or glass) and the burning steady-state temperatures (500 and 600°c). a total of 9 half-scale flat plate specimens of dimensions 1500mm×1500mm×100mm and 1.5% fiber volume fraction were cast and divided into 3 groups. each group consisted of 3 specimens that were identical to those in the other groups. the specimens of the second and the third groups were subjected to fire flame influence for 1 hour and steady-state temperature of 500 and 600°c respectively. regarding the cooling process, water sprinkling was applied directly after the burning stage to represent the sudden cooling process. generally, the obtained results exhibited a significant increase in the punching shear capacity of the fiber-reinforced slabs as compared to the corresponding no fiber-reinforced slabs even at elevated burning temperatures 600°c. the ultimate load was increased by about 16.6, 19, and 21.5% at temperatures of 25, 500, and 600°c respectively, for steel fiber reinforced slabs and by about 13.9, 27.2, and 34.6% for slabs containing two mixed types of fibers (steel and glass), as compared with the reference specimen at the same temperatures respectively. in addition, the results indicated that fibers' presence in concrete resulted in gradually punching failure with more ductile mode, whereas the failure was sudden with a brittle mode in the slabs that did not contain fibers. keywords-steel fibers; hybrid fibers; punching shear i. introduction flat plates are reinforced concrete slabs supported directly on columns without beams or girder system. such slabs have a low capacity to transfer the shear loads to the columns due to their relatively small depth (thickness). as a result, most probable failure cases of flat plates are caused by higher shear stresses in the column connection. these failures are described as punching shear failures [1]. a punching shear failure takes place suddenly around the column in a particular collapse mechanism when a plug of concrete is pushed out from the slab immediately above the column [2]. punching failure may occur due to slab overloading, un-conservative design for the slabcolumn connections, and deterioration in the strength of concrete and steel reinforcement resulted from the exposure of the slabs to fire [3]. at elevated temperatures, both steel and concrete exhibit a significant reduction in their strength, stiffness, and physical properties [4-7]. some of these variables are not recoverable after sudden cooling, therefore, the punching strength of flat slabs subjected to fire is expected to be significantly affected [8]. recently, a new technique using different types of fibers to improve the performance of concrete has been proven to give advanced outcomes [9-15]. the main objective of this study is to investigate experimentally the effect of fire on the punching shear strength of flat plates and the effect of adding fibers to the concrete mix as a solution to increase the resistance and ductility of slabs and to control cracking during fire exposure. ii. literature review an experimental study about the effect of fire on some mechanical properties of concrete was carried out in [16]. the compressive strength of concrete was measured for 150mm cubes whereas the flexural strength was measured for 100×100×400mm prisms. the specimens were subjected to fire with temperatures between 25 and 700°c. three temperature levels of 400, 500, and 700°c were chosen with 4 different exposure durations (0.5, 1.0, 1.5, and 2.0h). the specimens were heated and cooled under the same regime and tested after exposure to fire. the results showed that the residual compressive strength ranged between 70% and 85% at 400°c, 59% and 78% at 500°c, and 43% and 62% at 700°c. the flexural strength was found to be more sensitive to flame exposure than the compressive strength. the residual flexural strength ranged between 67% and 78% at 400°c, 40% and 67% at 500°c, and 20% and 45% at 700°c. authors in [17] studied the behavior and capacity of steel fiber reinforced concrete (sfrc) flat slabs under punching shear force. the results showed that steel fiber improved the punching shear resistance of the slabs considerably. using steel fiber (30 to 60kg/m 3 ) increased punching shear resistance of the slabs from 9.0% to 39.8% and this increase was directly proportional to fiber volume fraction. steel fiber reduced significantly the average crack width of the slabs up to approximately 70.8%. iii. experimental work the experimental work comprised 9 half-scale two-way specimens of 1500×1500×100mm that were designed according to the aci-318m-2019 [18] requirements as a corresponding author: ahmed naji dalaf engineering, technology & applied science research vol. 11, no. 4, 2021, 7452-7457 7453 www.etasr.com dalaf & mohammed: the impact of hybrid fibers on punching shear strength of concrete flat plates … simply supported specimen over an effective span of 1400mm. the specimens were fiber reinforced by 1.5% volume fraction to investigate the effect of fire on the punching shear strength of fiber reinforced concrete flat plates. the geometrical layout and the reinforcement details are shown in figure 1. (a) (b) fig. 1. details of the tested specimens. the 9 specimens were divided according to the steady state temperature into 3 groups, where each group consisted of 3 specimens, as can be seen in table i, where nfc means no fiber content, sf1.5 means steel fiber with volume fraction of 1.5%, gf0.5-sf1 means a mix of glass 0.5% and steel fiber 1% and f500 or f600 represented the fire exposure at temperatures of 500 or 600°c respectively. table i. details of the specimens gro ups group no. slab designation steady state fire temperature ( o c) group 1 nfc-nf no fire effect sf1.5-nf no fire effect gf0.5-sf1-nf no fire effect group 2 nfc-f500 500 sf1.5-f500 500 gf0.5-sf1-f500 500 group 3 nfc-f600 600 sf1.5-f600 600 gf0.5-sf1-f600 600 the specimens in groups 2 and 3 were tested in punching conditions after being exposed to fire for 1h in order to study the effect of steady state temperature simultaneously with a uniform equivalent dead load (8kn/m 2 ) that represented 40% of the service design load (figure 2). after the burning process, sudden cooling by water sprinkling took place to reduce the temperature. fig. 2. burning setup. iv. materials and methods the concrete mix was made from cement (type i), coarse aggregates of 12mm maximum size and zone 2 fine aggregates. steel and glass fibers were added to the concrete mix. the specimens were covered with polythene sheets for 24h to avoid cracks caused by moisture loss, then they were cured by covering with damp canvases soaked with water continuously for 28 days to ensure good curing treatment. the characteristics of the considered fibers are reported in table ii. all the specimens were reinforced using deformed steel bars of 10mm diameter at 70mm c/c for each direction regarding the tension zone and at 150mm c/c for each direction in the compression zone. the steel yield strength was 470mpa. for each specimen, the compressive strength of concrete was measured for 3 standard 150×300mm cylinders subjected to the same burning conditions of the corresponding specimen. table iii shows the adopted concrete mixes proportions. table ii. properties of the steel and glass fibers. fiber type length (mm) diameter (mm) tensile strength (mpa) aspect ratio (lf/df) steel fiber 30 0.375 1700 80 glass fiber 30 0.6 1200 50 table iii. concrete mixes' proportions. mix type nfc msf (1.5) mgs (0.5&1) cement (kg/m3) 420 420 420 sand (kg/m3) 490 490 490 gravel (kg/m3) 1042 1042 1042 w/c 0.45 0.45 0.45 super plasticizer (l/m3) 3 3 3 steel fiber (% ) --1.5 1 glass fiber (% ) ----0.5 v. tested specimens and instrumentations the specimens of groups 2 and 3 were burned before the punching test, in a furnace with inner dimensions of 3500×2000×900mm used for the purpose. the fire source consisted of 20 methane burner nozzles distributed at the bottom of the furnace sides and the temperature was monitored by a digital thermometer reader of atp dt-612 model, and a thermocouple sensor wire type k as shown in figure 3. all the specimens were tested in punching test conditions as simply supported and loaded using one concentrated load applied at the center of the column. the vertical deflection at each engineering, technology & applied science research vol. 11, no. 4, 2021, 7452-7457 7454 www.etasr.com dalaf & mohammed: the impact of hybrid fibers on punching shear strength of concrete flat plates … loading stage was measured using mechanical dial gauges of 0.01mm sensitivity allocated at the center and at the quarter span in each direction. figure 4 shows the punching test setup. fig. 3. furnace and burning procedure. fig. 4. test setup. vi. results and discussion a. initial crack load (pcr) and ultimate punching load (pu) table iv shows the initial crack (pcr) and the ultimate punching (pu) loads. the results proved that adding fibers to the concrete mix increases the initial crack load and the ultimate load for all the tested specimens even at high elevated temperatures (600°c) since the fibers bridge the tensile cracks and allows the transferring of the stresses through the opposite sides of the cracks. this means that slab tension zone is still able to resist additional stresses. from the results of group 1 (table iv) it can be concluded that specimen sf1.5-nf of 1.5% steel fiber volume fraction presented the optimum improvement in the initial crack load and the ultimate load by about 40% and 16.6% respectively, as compared with the reference specimen nfc-nf. the highest improvement in the initial crack load and the ultimate load for the burned specimens was recorded in the models gf0.5-sf1-f500 and gf0.5sf1-f600 which contained two types of fibers (steel and glass fiber). the modification percentages reached 63.1% and 27.2% and 96.3% and 34.6% for steady state temperatures of 500 and 600°c respectively, as compared with the reference specimen of each group. the disadvantage behavior for the burned specimens sf1.5-f500 and sf1.5-f600 belongs to the considerable thermal expansion level of steel material (10×10 -6 /°c) compared with those of concrete and glass materials (10×10 -6 /°c and 4.9×10 -6 /°c respectively). the ratio (1.5%) of steel fibers resulted in a substantial reduction in the concrete compressive strength in comparison with the ratio (1%) due to the expansion damage effect of the steel fiber which was greater in the 1.5% specimen at the adopted burning temperatures (500 and 600°c). moreover, hybrid fibers of different sizes and styles provide different restriction conditions, and these conditions can be the result of the mechanical bond strength modification since each type can delay micro-crack formation and prevent their propagation [19]. table iv. initial crack and ultimate load results group specimens f 'c (mpa) pcr (kn) increase in pcr % pu (kn) increase in pu % 1 nfc-nf 35.52 50 --180 -- sf1.5-nf 40.32 70 40 210 16.6 gf0.5-sf1nf 39.2 68 36 205 13.9 2 nfc-f500 21.81 38 --147 -- sf1.5-f500 26.37 53 39.5 175 19 gf0.5-sf1f500 28.24 62 63.1 187 27.2 3 nfc–f600 18.36 27 --130 -- sf1.5-f600 21.83 40 48.1 158 21.5 gf0.5-sf1f600 25.85 53 96.3 175 34.6 b. load-deflection relationships figure 5 shows the load-deflection relationships for the unburned and burned specimens at 500 and 600°c respectively. two zones were recognized in the unburned specimens’ curves. the first refers to the behavior up to the initial crack load generation where the responses of all the tested specimens were similar and approximately linear. the second zone extended beyond the initial crack load generation during which other cracks were developed and the slope of the loaddeflection curves was decreased rapidly as a result of specimen stiffness reduction. different behavior in the burned specimens at 500°c was detected, i.e. the linear stage limit was reduced. moreover, in the case of 600°c, the behavior was completely nonlinear due to the increasing fire-induced damage. in figure 5(b)-(c), a strain hardening case can be observed in the reference specimens resulting from the highly fire damaged concrete which led to an increase of the steel reinforcement stresses. this case was prevented in the fiber reinforced specimens, since the steel fiber bridges the concrete parts and softens their tensile strength behavior. moreover, it can be observed that, at the same level of loading, fiber reinforced specimens (unburned and burned) had less deflection than that of the reference specimens (without fiber) since fiber enhances the stiffness of the specimens due to its bridging role between the two sides of cracks and this can be noticed more vividly beyond the cracking stage. for the same level of loading, the engineering, technology & applied science research vol. 11, no. 4, 2021, 7452-7457 7455 www.etasr.com dalaf & mohammed: the impact of hybrid fibers on punching shear strength of concrete flat plates … specimen of 1.5% steel fiber had the minimum deflection of group 1 (figure 5 (a)), whereas the specimens that contained two types of fibers showed less deflection (figure 5(b)-(c)). this usually reflects specimen stiffness modification. (a) (b) (c) fig. 5. loaddeflection curves: (a) group 1, (b) group 2, (c) group 3. table v symmetrizes the outcomes of the tested specimens including the ultimate punching loads and their corresponding ultimate deflections. the specimens were grouped according to the fiber’s type (no fiber, steel fiber, and mixed fibers). in general, there is a significant reduction in the punching shear resistance with an increase in the peak deflection of the burned specimens compared with the corresponding unburned specimens. the maximum drop (27.78%) in the punching load was detected at 600°c burning temperature by the specimen nfc-f600. this was improved to 24.76% when steel fiber was added whereas the optimum modification was presented by the specimen gf0.5-sf1-f600 in which the reduction percentage was 14.63%. the main reason for this is that the fire damage caused a reduction in the stiffness of the burned slabs. table v. variation in the ultimate load and deflection at different burning temperatures specimen temperature ( o c) pu (kn) reduction in pu% ultimate deflection ∆∆∆∆u (mm) increase in ∆∆∆∆u % nfc–nf 25 180 ---15.50 --- nfc-f500 500 147 18.33 16.76 8.13 nfc-f600 600 130 27.78 17.42 12.39 sf1.5-nf 25 210 ---17.22 --- sf1.5-f500 500 175 16.67 18.86 9.52 sf1.5-f600 600 158 24.76 19.65 14.11 gf0.5-sf1nf 25 205 ---16.95 --- gf0.5-sf1f500 500 187 8.78 19.33 14.04 gf0.5-sf1f600 600 175 14.63 20.28 19.65 c. crack patterns after the burning stage, there were hair cracks distributed randomly on the burned surface of the specimens as shown in figure 6. these hair cracks were more in number and more clearly observed in the burned specimens at 600°c. for all the tested specimens, additional cracks appeared around the column at the tension face of the tested specimen, during the loading stage. when the applied load was further increased, these cracks' were width and number increased and they were extended diagonally towards the specimens' edges causing failure in punching mode as shown in figure 7. (a) (b) fig. 6. hair cracks in the burned specimens at (a) 500°c, (b) 600°c. actually, fibers decreased the crack width for both unburned and burned specimens. the average maximum crack width in group 1 was 0.65mm for no fiber specimens and 0.50mm for fiber reinforced specimens. in group 2, it was 0.80mm for specimens without fibers and 0.60mm for fiber reinforced specimens, whereas in group 3, it was 0.95 and 0.70mm respectively. it was also noticed that the punching failure in the reference specimens (without fiber) was sudden with brittle mode, whereas the fiber reinforced specimens failed in a gradual way with a more ductile mode since the fiber presence in the concrete mix improved the specimens' ductility by increasing the ultimate deflection. the burned reference specimens nfc-f500 and nfc-f600 exhibited extensive cover spalling in the tension side of the specimens at failure stage resulting from the strength deterioration of concrete caused by burning. in the fiber reinforced specimens, the spalling in the concrete cover was more controlled. this indicates that fiber presence in the concrete mix contributes to the connection between the damaged concrete parts in the tension side of the specimens. engineering, technology & applied science research vol. 11, no. 4, 2021, 7452-7457 7456 www.etasr.com dalaf & mohammed: the impact of hybrid fibers on punching shear strength of concrete flat plates … (a) (b) (c) fig. 7. crack patterns in (a) group 1,(b) group 2, (c) group 3. d. area, perimeter, and angle of failure for all the tested specimens, the punching failure mode had approximately the shape of a pyramid. table vi illustrates the perimeter, the area, and the failure angle of the punching failure zone for the unburned and burned specimens. the failure angle was measured considering the dimensions of the crushed zone at the center line passing through the loaded area. several studies indicated that fiber reinforced concrete slabs had failure angle higher than that in the normal reinforced concrete slabs where the smaller value of failure angle means wider base for the failure pyramid zone that’s pushed out [20]. it can be concluded that, for both unburned and burned specimens, the failure angle for the fiber reinforced specimens was larger than that in the reference specimen in each group which means that the failure punching perimeter was smaller in the fiber reinforced specimens in comparison with the reference specimens. this usually belongs to the fiber contribution that prevents the disintegration in the concrete cover below the flexural steel reinforcement and helps to integrate the whole section. the results obtained in group 1 indicate that the specimens with 1.5% steel fiber volume fraction had the highest decrease in the punching failure perimeter by about 20.7% in comparison with the reference specimen (nsc-nf). on the other hand, specimens containing two mixed types of fibers (steel and glass) showed the optimum modification in the perimeter of the failure punching by about 22% and 21.3% for groups 2 and 3 respectively. table vi. perimeter, area and failure angle group specimen perimeter (mm) perimeter decrease (%) area (mm 2 ) failure angle (ø°) 1 nfc-nf 3080 --592900 17.9 sf1.5-nf 2440 20.7 372100 23.5 gf0.5-sf1nf 2600 15.6 422500 21.8 2 nfc-f500 3640 --828100 14.7 sf1.5-f500 3160 13.2 624100 17.3 gf0.5-sf1f500 2840 22 504100 19.6 3 nfc–f600 4120 --1060900 12.8 sf1.5-f600 3560 13.6 792100 15.2 gf0.5-sf1f600 3240 21.3 656100 16.8 vii. conclusions the following conclusions can be drawn from the experimental work outcome: • there is a reduction in the initial load crack and the ultimate load of the burned slabs compared with the corresponding unburned slabs. this reduction was improved by adding fiber to the specimens. • after burning, random hair cracks were observed on each slab. these hair cracks were multiplied and more clearly observed in the specimens burned at 600°c than in the specimens burned at 500°c. • adding fibers to the concrete has a significant effect on the punching failure perimeter zone, crack width, and concrete spalling for all the tested slabs (unburned and burned). • fiber reinforced slabs failed gradually in a more ductile mode. while the failure was sudden with brittle mode in slabs that contained no fibers. • steel fiber ratio 1.5% by volume had more effect in improving the response than the two mixed fibers (steel and glass) regarding the unburned specimens. for burned specimens, the two mixed fiber specimens had more improved response for both considered burning temperatures. references [1] m. k. jawad, "experimental study on shear heads in reinforced concrete flat plates," ph.d. dissertation, al-mustansiriya university, baghdad, iraq, 2005. 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[20] k.-k. choi, h.-g. park, and h.-m. kim, "shear strength model for slab-column connections," journal of the korea concrete institute, vol. 22, no. 4, pp. 585–593, aug. 2010, https://doi.org/10.4334/jkci. 2010.22.4.585. engineering, technology & applied science research vol. 7, no. 6, 2017, 2147-2155 2147 www.etasr.com askarizadeh and mohammadizadeh: numerical analysis of carbon fiber reinforced plastic (cfrp) … numerical analysis of carbon fiber reinforced plastic (cfrp) shear walls and steel strips under cyclic loads using finite element method nahid askarizadeh department of civil engineering faculty of engineering bandar abbas branch islamic azad university bandar abbas, iran mohammad reza mohammadizadeh department of civil engineering faculty of engineering hormozgan university bandar abbas, iran abstract—reinforced concrete shear walls are the main elements of resistance against lateral loads in reinforced concrete structures. these walls should not only provide sufficient resistance but also provide sufficient ductility in order to avoid brittle fracture, particularly under strong seismic loads. however, many reinforced concrete shear walls need to be stabilized and reinforced due to various reasons such as changes in requirements of seismic regulations, weaknesses in design and execution, passage of time, damaging environmental factors, patch of rebar in plastic hinges and in some cases failures and weaknesses caused by previous earthquakes or explosion loads. recently, fiber reinforced polymer (frp) components have been extensively and successfully used in seismic improvement. this study reinforces frp reinforced concrete shear walls and steel strips. cfrp and steel strips are evaluated by different yield and ultimate strength. numerical and experimental studies are done on walls with scale 1/2. these walls are exposed to cyclic loading. hysteresis curves of force, drift and strain of frp strips are reviewed in order to compare results of numerical work and laboratory results. both numerical and laboratory results show that cfrp and steel strips increase resistance, capacity and ductility of the structure. keywords-numerical analysis; shear wall; frp; lateral load; abaqus i. introduction polymer coatings used to improve concrete structures were first developed in 1980 in europe and japan. in europe, frp systems were used as an alternative to steel plates. connection of steel plates to tensile part of concrete members by epoxy resins is a common durable method to enhance bending strength of these members. steel plates are corroded and their corrosion leads to the collapse of steel plates with concrete. moreover, they are difficult to install, because they are installed by heavy machinery. thus, scientists tended to replace steel coatings by frp materials. with almost 20% of the weight of steel coatings, frp is approximately 8 to 10 times more resistant than steel. one of the problems with system structural calculations is the difficulty of computer modeling in the form of finite element. moreover, variation in effective parameters on behavior of these structures challenges laboratory methods due to high cost and time. numerical methods also require a correct understanding of non-linear behavior of reinforced concrete and frp [1]. this study develops suitable structural models and models non-linear behavior of concrete, reinforcement and frp. ii. problem description a. concrete damage plasticity the most important step in numerical modeling of reinforced concrete structures is the determination of concrete’s nonlinear behavior. in the finite element software abaqus, nonlinear behavior of brittle materials can be defined through three models: 1) smeared cracking, 2) brittle cracking and 3) concrete damage plasticity [2]. concrete damage model is the only model which can be used in both static and dynamic analysis. in this model, it is assumed that tensile cracking and compressive crushing are two main aspects of concrete failure mechanism. in modeling brittle material cracking under cyclic loading (alternating tension and compression), stiffness recovery is allowed during reciprocating loads [3]. in plastic damage model, elimination of elements and cracking are not allowed during analysis due to the lack of failure criterion, however, this model is able to predict location and direction of cracks. b. interpretation of moment curvature curve for reinforced concrete shear wall section unlike the simplicity in design and construction of reinforced concrete shear walls, the real response of these elements is rather complex. overall behavior of walls is influenced by bending, shear and axial responses. wall sections are against compressive axial forces caused by gravity loads and their own weight. axial pressure acting on the wall is estimated at 20% of product of concrete compressive strength, fc΄, in ag (gross concrete cross section) [4]. authors in [4] described the moment-curvature relationship in walls of highrise buildings against a unidirectional load. when bending moment is applied on the wall section, initial response of the wall is linear elastic with initial flexural stiffness. cracking engineering, technology & applied science research vol. 7, no. 6, 2017, 2147-2155 2148 www.etasr.com askarizadeh and mohammadizadeh: numerical analysis of carbon fiber reinforced plastic (cfrp) … occurs when moment exceeds initial elasticity and flexural stiffness is reduced by growth of the first crack and start of additional cracks. slope of this phase results from approximately parallel response of flexural stiffness of the cracked and deformed section. further increase in the applied moment leads to the weakening of steel and the section's capacity. it is thus considered essential to use non-linear analysis and theories of plasticity to simulate behavior of reinforced concrete shear wall. uniaxial stress-strain relationship of concrete under pressure and tension is an important parameter in importing concrete damage plasticity model to the software. to do this, the hognestad curve is used. equations (1) and (2) are used to import compressive stress of concrete versus compressive strain to the software. in these equations, ε0 is the corresponding strain to maximum stress. for specimens of which ε0 is unknown, this study uses the value 0.002, which is a rational value for conventional concretes [5]. in (2), ''cf is maximum stress in concrete element. the ks factor can be considered as portrayed in table i [5] for concretes with cylindrical compressive strength. descending branch of the modified hognestad curve is linear which extends from ''0 c, f to ''cε , 0.85fu . εu corresponds to ultimate corresponding strain to compressive failure of concrete, which has been reported from 0.003 to higher than 0.005. this study considers 0.0038. '' 2 0 0 2 ( )c cc cf f            (1) '' ' c s cf k f (2) table i. ks values in hognestad curve ' cf (mpa) 15 20 25 30 >35 s k 1 0.97 0.95 0.93 0.92 c. stress-strain under tension by using abaqussuggested equation concrete alone cannot tolerate tensile stresses and its tensile strength is low (7%-11% of compressive strength). steel rebar is usually used to compensate these problems. concrete tensile response begins with cracking and its expansion. thus, concrete behavior cannot be evaluated by considering tensile strain. instead, the crack should be evaluated. the concrete response under pressure is linear until it reaches its tensile strength which is associated with very fine cracks. the increase in loading decreases resistance and expands cracks to fracture under ultimate strain [6-7]. a straight line is usually used for softening part of tensile curve. moreover, tensile strength and ultimate strain are calculated by following equations [8-10]: ' '0.33 t cf f (3) * 0.001  (4) in periodic loading, stiffness decreases and cracks after each cycle emerge. unlike compressive cracks, these cracks are completely obvious and open [6]. the curves presented for the static scenario are in fact pushover curves of maximum stresses under periodic loading. d. damage parameter the slope of unloading curve is lower than the slope of the elastic curve in the softening part, which indicates damage. the reduced initial stiffness is shown by dt and dc (stiffness decline under tension, and stiffness decline under pressure respectively). it is assumed that these two variables are functions of plastic strain, temperature and other field variables [3].  , , 0 1plt t t i td d f d    (5)  , , 0 1plc c c i cd d f d    (6) where, cε pl and plt are corresponding plastic strains under pressure and tension, θ is the temperature, and fi is the field variable. in fact, concrete damage is determined by dt and dc in uniaxial stress-strain curves. these damage variables are expressed as follows:  , 01 t ce d e  (7) where e is the damaged module of elasticity, e0 is undamaged module of elasticity. it is important to select properties of damage, because excessive damage values have unsuitable effect on convergence rate. e. behavior of reinforcements there are many stress-strain models in finite element software. this study uses a bilinear elastoplastic model for reinforcement. in abaqus, longitudinal and transverse reinforcements are modeled by two-node truss element t3d2 which is only able to tolerate axial force and acts separately from concrete. f. stiffness recovery in abaqus stiffness recovery is an important discussion in the mechanical response of concrete in periodic loading. in abaqus, the user can directly import the stiffness recovery factors, wt and wc. in the majority of quasi-brittle materials such as concrete reflect improvement of compressive stiffness resulting from closure of cracks when loading shifts from tension to compression. on the other hand, tensile stiffness is not recovered by this shift after formation of microcracks under concrete crushing. this behavior which is related to wt=0 and wc=1 is default in abaqus. engineering, technology & applied science research vol. 7, no. 6, 2017, 2147-2155 2149 www.etasr.com askarizadeh and mohammadizadeh: numerical analysis of carbon fiber reinforced plastic (cfrp) … iii. specimens a. reinforced concrete shear walls specimens group a: five specimens of cfrp reinforced concrete shear walls tested by authors in [11] at scale of ½ are modeled in different arrangements of cfrp in abaqus. all specimens are 1000 mm in length, 100 mm in width and 1500 mm in height. all specimens are exposed to cyclic loading with drift control. group b: three specimens of cfrp reinforced concrete shear walls tested in [12] are modeled in different arrangements of cfrp in abaqus. all specimens are 1200 mm in length, 80 mm in width and 1045 mm in height. all specimens are exposed to cyclic loading with drift control and 48 kn compressive axial force and two axial forces, one compressive and the other tensile, in a distance which forms couple on top of the wall, as shown in (8) and (9). 24 1.115a cf f  (8)  , 01 t ce d e  (9) group c: four specimens of steel strip reinforced concrete shear walls tested in [13] at scale of ½ are modeled in different arrangements of steel strips in abaqus. all specimens are 1000 mm in length, 100 mm in width and 1500 mm in height. all specimens are exposed to cyclic loading with drift control b. specifications of materials group a: specimen 1 which is unreinforced is selected as reference specimen. four other specimens are determined (specimen 2, specimen 3, specimen 4 and specimen 5). all four reinforced specimens have a layer reinforced by cfrp strips [11]. group b: cw which is unreinforced is selected as reference specimen. two other specimens are determined (rw1 and rw2). all two reinforced specimens have a layer reinforced by cfrp strips [2]. group c: specimen 1 which is unreinforced is selected as reference. three other specimens are determined (specimen 2, specimen 3 and specimen 4). all three reinforced specimens have a layer reinforced by steel strips [13]. table ii shows 28-day resistance of concrete in all specimens. table iii shows yield and ultimate strength of rebar used in this experiment. values of shear modulus (g) are given in tables iv and v. iv. results a. group a figure 1 shows the force-drift hysteresis curve of numerical analysis for group a specimens under cyclic load [11]. figure 3 shows the strain-force hysteresis curve of cfrp materials in numerical analysis for group a specimens under cyclic load. table vi lists the experimental results and compares them to numerical results related to maximum strain. as shown, the numerical analysis is consistent with the experimental results. table ii. specifications of specimens group a: five specimens of cfrp reinforced concrete shear walls specimen5 specimen4 specimen3 specimen2 specimen1 15.6 15.9 15 15.7 15.5 'cf (mpa) a combination of mesh and horizontal and parallel strips at the top and bottom of specimen a combination of x-shaped, horizontal and parallel strips at the top and bottom of specimen an x-shaped layer horizontal and parallel strips fiber arrangement group b: three specimens of cfrp reinforced concrete shear walls rw2 rw1 cw 37 37 45 'cf (mpa) a crossed and a wrapping layer at the top and bottom of wall a vertical c-shaped layer in side edges and a wrapping layer around the wall fiber arrangement group c: four specimens of steel strip reinforced concrete shear walls specimen 4 specimen 3 specimen 2 specimen 1 18.5 17.8 18.2 15.5 'cf (mpa) a combination of horizontal and vertical strips horizontal and parallel strips a x-shaped layer arrangement of steel strips table iii. specifications of reinforcements group a: cfrp reinforced concrete shear walls ultimate strength (mpa) yield strength (mpa) reinforcement diameter (mm) 420 325 6 522 430 10 515 428 12 520 425 16 group b: cfrp reinforced concrete shear walls ultimate strength (mpa) yield strength (mpa) reinforcement diameter (mm) 550 450 10 720 620 6 group c: steel strip reinforced concrete shear walls tested ultimate strength (mpa) yield strength (mpa) reinforcement diameter (mm) engineering, technology & applied science research vol. 7, no. 6, 2017, 2147-2155 2150 www.etasr.com askarizadeh and mohammadizadeh: numerical analysis of carbon fiber reinforced plastic (cfrp) … 420 325 6 522 430 10 520 425 16 fig. 1. force-drift hysteresis curve under cyclic load, group a, specimens 1-5 a) experimental b) numerical table iv. specifications of cfrp group a: cfrp reinforced concrete shear walls ultimate strain (%) ultimate tensile stress (mpa) modulus of elasticity (mpa) thickness (mm) fiber 1.7 4100 231000 0.12 cfrp group b: cfrp reinforced concrete shear walls ultimate strain (%) ultimate tensile stress (mpa) modulus of elasticity (mpa) thickness (mm) fiber 1.6 3790 230 0.175 cfrp engineering, technology & applied science research vol. 7, no. 6, 2017, 2147-2155 2151 www.etasr.com askarizadeh and mohammadizadeh: numerical analysis of carbon fiber reinforced plastic (cfrp) … group c: steel strip reinforced concrete shear walls ultimate strength (mpa) yield strength (mpa) thickness (mm) steel strips 470 340 2.5 table v. input parameters for modeling fibers in abaqus group a: cfrp reinforced concrete shear walls 2 3g 1 3g 1 2g 2 3n u 1 3n u 1 2n u 3 e 2e 1e thickness layer fiber 9625 9625 96250 0.2 0.2 0.2 23100 23100 231000 0.12 1 cfrp group b: cfrp reinforced concrete shear walls 2 3g 1 3g 1 2g 2 3n u 1 3n u 1 2n u 3e 2e 1e thickness layer fiber 9583 9583 95833 0.2 0.2 0.2 23000 23000 230000 0.12 1 cfrp group c: steel strip reinforced concrete shear walls ultimate strength (mpa) yield strength (mpa) thickness (mm) steel strips 470 340 2.5 fig. 2. push comparison of hysteresis curves of experimental results and numerical analysis (group a) table vi. group a: comparison of maximum force num/ exp num exp specimen pull (kn) push (kn) pull (kn) push (kn) pull (kn) push (kn) 0.99 0.97 149.55 136.072 151.33 140 specimen1 1.05 0.91 267.57 225.62 254.72 250 specimen2 1.02 0.95 234.63 204.55 230.22 215 specimen3 1 1.05 239 273.69 238 260 specimen4 1.11 0.99 272.3 248.5 245 250 specimen5 table vii. group a: maximum cfrp strain num/exp exp num specimen specimen1 0.97 0.0075 0.0073 specimen2 0.89 0.0095 0.0085 specimen3 0.97 0.0088 0.0085 specimen4 0.96 0.0083 0.008 specimen5 b. group b figure 4 shows the force-drift hysteresis curve for group b: cw, rw1 and rw2 under cyclic load [12] (table vii). figure 5 compares push of force-drift hysteresis curves of specimens under cyclic load resulting from experimental numerical analysis. table viii lists experimental results and compares them to numerical analysis related to maximum forced obtained in reciprocating cycles. as shown, the numerical analysis for group b specimens is consistent with the experimental results. figure 4 shows the strain-force hysteresis curve of cfrp materials in numerical analysis for rw1 and rw2 under cyclic load. table ix compares the experimental and the numerical results which are shown to be consistent. engineering, technology & applied science research vol. 7, no. 6, 2017, 2147-2155 2152 www.etasr.com askarizadeh and mohammadizadeh: numerical analysis of carbon fiber reinforced plastic (cfrp) … fig. 3. strain-force curve of cfrp in group a, spesimens 1-5 a) experimental b) numerical table viii. group b: comparison of maximum force num/ exp num exp specimen pull (kn) push (kn) pull (kn) push (kn) pull (kn) push (kn) 1.075 1.04 64.52 62.53 60 60 cw 1.01 1.06 111.63 117.53 110 110 rw1 1.11 1.14 100.33 107.82 90 94 rw2 table ix. group b: maximum cfrp strain num/exp exp num specimen 1.04 5100 5300 rw1 0.93 4300 4000 rw2 engineering, technology & applied science research vol. 7, no. 6, 2017, 2147-2155 2153 www.etasr.com askarizadeh and mohammadizadeh: numerical analysis of carbon fiber reinforced plastic (cfrp) … fig. 4. force-drift hysteresis curve under cyclic load, group b, a) experimental b) numerical fig. 5. push comparison of hysteresis curves of experimental results and numerical analysis for group b specimens. (a) (b) fig. 6. strain-force curve of cfrp in group b, specimens rw1 and rw2 a) experimental b) numerical engineering, technology & applied science research vol. 7, no. 6, 2017, 2147-2155 2154 www.etasr.com askarizadeh and mohammadizadeh: numerical analysis of carbon fiber reinforced plastic (cfrp) … c. group c figure 7 shows force-drift hysteresis curve for group c specimens under cyclic load [13]. figure 8 compares the experimental and numerical push of force-drift hysteresis curves. table x lists the experimental results and compares them to numerical analysis related to maximum forced obtained in reciprocating cycles. as shown numerical analysis results are consistent with the experimental results. table x. comparison of maximum force num/ exp num exp specimen pull (kn) push (kn) pull (kn) push (kn) pull (kn) push (kn) 1 0.94 150 131.9 150 140 specimen1 1.04 1.004 254.07 239.15 245 238 specimen2 1.03 0.99 225.99 219.12 220 222 specimen3 1.09 0.96 228.65 215.73 208 225 specimen4 fig. 7. force-drift hysteresis curve under cyclic load, group c – specimens 1-4 a) experimental b) numerical engineering, technology & applied science research vol. 7, no. 6, 2017, 2147-2155 2155 www.etasr.com askarizadeh and mohammadizadeh: numerical analysis of carbon fiber reinforced plastic (cfrp) … fig. 8. push comparison of hysteresis curves of experimental results and numerical analysis (group c) v. conclusion close results of numerical analysis and experiments on specimens before and after frp reinforcement indicate that numerical modeling can be used as a scientific and inexpensive tool for analyzing the cyclic behavior of unreinforced and frp reinforced concrete shear walls. both numerical and experimental results showed that reinforcement of reinforced concrete shear walls, which have shear weakness under seismic loads by frp coating, is a suitable solution for increasing their resistance. adjustment of reinforced strips was effective on cyclic behavior of reinforced shear walls and failure mode. to compensate shear weakness of reinforced concrete shear walls, it is better to use horizontal strips along transverse reinforcements on both sides of the wall. to compensate bending weakness of reinforced concrete shear walls, frp plates are installed vertically along the height of shear wall parallel to longitudinal reinforcements. in general, results show that shear positions of fibers concentrated on edges increase bending and shear strength of the wall. both numerical and experimental results show that frp materials increase ultimate strength related to reinforced walls compared to unreinforced ones. references [1] a. kheroddin, h. naderpour, “nonlinear finite element analysis of r/c shear walls retrofitted using externally bonded steel plate and frp sheets”, 1st international structural specialty conference, pp. 2326, 2006 [2] s. soroshnia, h. najafi, m. mamaghani, m. mehrvand, the most complete practical reference of abaqus, 2nd ed., negarandeh danesh, 2014 [3] dassault systemes, abaqus analysis user’s manual, version 6-10, dassault systemes simulia corp., 2011 [4] i. m. m. ahmed, linear and nonlinear flexural stiffness models for concrete walls in high-rise buildings, phd thesis, university of british columbia, 2000 [5] d. mostofinejad, reinforced concrete structures, 12th ed, arkaneh danesh, 2010 [6] a. saedi-darian, h. bahram pour, h. arabzadeh, abaqus software comprehensive guide, angizeh, 2011 [7] j. lee, g. l. fenves, “plastic-damage model for cyclic loading of concrete structures”, journal of engineering mechanics, vol. 124, no. 8, pp. 892-900, 1998 [8] h. t. hu, f. m. lin, y. y. jan, “nonlinear finite element analysis of reinforced concrete beams strengthened by fiber-reinforced plastics”, composite structure, vol. 63, no. 3-4, pp. 271-281, 2004 [9] a. a. tasnimi, “strength and deformation of mid-rise shear walls under load reversal”, engineering structures, vol. 22, no. 4, pp. 311-322, 2000 [10] j. h. thomsen, j. w. wallace, “displacement-based design of slender reinforced concrete structural walls-experimental verification”, journal of structural engineering, vol. 130, no. 4, pp. 618-630, 2004 [11] s. altin, o. anil, y. kopraman, m. emin kara, “hysteretic behavior of rc shear walls strengthened with cfrp strips”, composites part b: engineering, vol. 44, no. 1, pp. 321-329, 2013 [12] h. el-sokkary, k. galal, “seismic behavior of rc shear walls strengthened with fiber-reinforced polymer”, journal of composites for construction, vol. 17, no. 5, pp. 603-613, 2013 [13] s. altin, y. kopraman, m. baran, “strengthening of rc walls using externally bonding of steel strips”, engineering structures, vol. 49 pp. 686–695, 2013 engineering, technology & applied science research vol. 8, no. 2, 2018, 2668-2672 2668 www.etasr.com hatem et al.: motivation factors for adopting building information modeling (bim) in iraq motivation factors for adopting building information modeling (bim) in iraq wadhah amer hatem baquba technical institute middle technical university baquba, iraq wadhah1970wadhah@gmail.com abbas mahde abd architecture engineering department diyala university of engineering baquba, iraq abbas.mahd@gmail.com nagham nawwar abbas civil engineering department diyala university of engineering baquba, iraq nagham.nawwar@gmail.com abstract—building information modeling (bim) is an integrated and comprehensive system including whatever is related to a construction project and its stages. it represents a unified database for all project data through which project documents are available to all stakeholders. this paper evaluates the factors driving the adoption of bim in iraqi construction projects in different ministries and adopts quantitative approach to collect data by using a questionnaire survey specially prepared for this purpose which was distributed to experts in the ministries of the iraqi construction sector. returned data were subjected to proper statistical analysis. results showed that the highest motivation for bim application is to include it in the educational curricula, raise awareness through courses and workshops and contracting with international experts with experience in bim field. keywords-construction project; building information modelling; bim; iraq; motivation factor i. introduction construction industry is witnessing a paradigm shift that tends to achieve higher productivity, efficiency, quality, sustainability and infrastructure value while reduces the life cycle costs and time [1, 2]. one of these techniques is building information modeling (bim) which is a technological and procedural shift in the construction industry [3]. actually, the evolution of computer science as well as information technology has caused a positive change in the processes of most industries [4]. bim is an advanced process consisting of a combination of virtual aspects, systems and concepts facilitated within a unified environment [5]. it includes the application and keeping of integrated digital representation of different information across different project stages [6, 7]. there are many bim applications [8] which can be used to support constructability, scheduling, analysis, cost estimating and sequencing [9]. bim as a new paradigm has a great potential for integration into the life cycle of construction projects [10, 11]. one of the main benefits of bim is the accurate geometrical representation of building parts within an integrated information environment [12]. furthermore, bim reduces the duration and cost of the project, improves maintenance management and increases the building value [7]. bim also improves communication between the different project parties [13]. on the other hand, bim as a new phenomenon seeks to renew the practices of the construction industry, so it is subject to several challenges facing its application [14]. for the implementation of bim, good planning and a coordinated approach with considerations for implementation and innovation management is required. ii. factors motivating the application of bim when authors in [15] investigated the factors that motivate the application of the bim, he concluded that the two most important factors were leadership and a supportive environment. author in [16] agreed on the importance of leadership as a key point in facilitating the application of bim. the government should take the leadership role in the implementation of the bim, but this is not enough. it should support and cooperate with other parties who have an impact on the development of iraqi projects, such as specialists in the private sector, contractors or other specialists [16]. making bim mandatory was considered by specialists as an effective way to motivate institutions to move to bim as this experience proved to be successful in the uk, usa, and singapore [16]. in the context of mentioning cooperation, authors in [17] pointed out that one of the most important points to facilitate the task of implementing the bim is the deployment of new cultures urging cooperation among stakeholders. providing adequate training and upgrading knowledge of bim will enhance its application [18, 19]. in the other hand, contracting with experienced bim and professional trainees for bim software is a step in facilitating the application and use of bim [20]. table i provides a summary of top bim motivation factors according to previous researchers’ studies. iii. research methodology this paper studies the factors motivating the application of bim in iraq. the data were collected using the field survey method through the design of a special questionnaire for this purpose and its distribution to the engineers working in the iraqi construction sector in both ministry of higher education and scientific research and ministry of construction, housing, municipalities and public works (in diyala governorate as a case study). engineering, technology & applied science research vol. 8, no. 2, 2018, 2668-2672 2669 www.etasr.com hatem et al.: motivation factors for adopting building information modeling (bim) in iraq table i. summary of bim motivation factors in previous studies country and reference motivation factors for bim adoption country and reference motivation factors for bim adoption usa [21]  strategies to reduce strong resistance  improve cooperation skills  acceptance of stakeholders to bim australia [22]  improvements in information technology (it) infrastructure  improvements in computer hardware and software  government interest through the adoption of bim for many demonstrator projects usa [18]  increase the level of knowledge of bim  provide adequate training  coordination among stakeholders in the project  provide adequate support by senior management for bim application. australia [23]  coordination among stakeholders in the project  provide adequate support by senior management for bim application  contribution of different parties (education providers, specialists, supply chain alliances) to develop broad lines towards application of bim uk [24]  adopting collaborative methods and approaches within the design team  provide staff with experience in the field of bim  provide contract forms that are suitable for use of bim  development of standards for use of bim korea [25]  organizational and individual confidence towards the use of new technology  provide adequate training  develop commitments to use bim within the organizations and firms  the government's obligation to use bim in projects china [26]  prepare validation for bim tools  pressure by government  coordination among stakeholders in the project malaysia [27]  compelling and supporting by the government  provide adequate training  provide adequate support by senior management for bim application australia [28]  provide adequate support by senior management for bim application.  develop higher strategies that encourage cooperative work, conflict resolution and reduce the strong resistance to change towards new technologies  develop a plan for bim adoption by the government.  not only training to expand knowledge of bim, but dealing with external organizations of investors and experts with expertise in the field of bim nigeria [29]  increase the level of knowledge of bim  expanding the scope of research related to bim  provide adequate support by senior management for bim application.  provide adequate training  facilitate educational facilities for the purpose of supporting their use  the government's obligation to use bim in projects a total of 130 questionnaires were distributed, 65 in the ministry of higher education and scientific research and 65 in the ministry of construction, housing, municipalities and public works. 114 were returned at a response rate of 87.7%. the questionnaire included two main parts: the first part is the personal information regarding the respondent: gender, age, academic qualification, specialization, group and work experience. the second part included 13 items representing the importance of motivation factors for the application of bim designed in the fivelikert scale [30] from 1 to 5, 1 being not important and 5 being very important. after the collection of the questionnaires, they were arranged, unloaded and analyzed using the statistical packaging for social science (spss) software, version 24. the statistical analysis represents the creation of some descriptive statistics such as frequency, percentage, mean and standard deviation and also calculated the value of the relative importance index (rii) in order to give ranks to the items. iv. results and discussion a. general information for respondents the demographic characteristics of target respondents are shown in table ii. b. statistical validity and reliability access to acceptable results within any research requires the use of accurate measurement instrument as one of the basic requirements. among the main objectives of the researcher is to design his research tool and make it characterized by three main qualities (be meaningful, be accurate, be efficient) [31]. therefore, validity and reliability tests were conducted on the obtained data from the pilot survey which was conducted before the main study. validity of instrument can be defined as the degree to which the instrument measures what it is supposed to measure [32, 33]. for the purpose of the test statistical questionnaire validity internal consistency was performed. through internal consistency correlation coefficients between each element in a particular part are measured with the part as a whole [34]. table iii shows the values of the spearman rho correlation and p-values for all items. results showed that correlation coefficients ranged from 0.496 to 0.755 and all p-values were less than 0.05 which indicates that the items are consistent and valid to measure what has been set to measure. reliability indicates the stability of the results when these are redistributed again for the same sample. one of the most common methods of calculating reliability and the value of the cronbach’s alpha constant from 0 to 1 and the closer to 1 indicates the high degree of reliability [35]. table iv represents a classification for the degree of reliability according to the value of the cronbach’s alpha coefficient. when the cronbach’s alpha method was conducted for the questionnaire, the results were shown within the good limits with 0.899 value. this result confirms the reliability of the questionnaire. i p c. of the th the the engineerin www.etasr information abo gender age (years) academic qualification specialization group (job) practical experien (years) table motivation fa m1 m2 m3 m4 m5 m6 m7 m8 m9 m10 m11 m12 m13 tab c motivation f this part con bim. these eir adaptation, hese items wer e results were e analysis of d ng, technology r.com table ii. ut cat m f 2 3 4 mor di ba m p o ar civil electric mechani o de con projec site o nce les 1 1 mor e iii. intern actors co c 0 0 0 0 0 0 0 0 0 0 0 0 0 c٭ c٭٭ ble iv. rel cronbach's alph α≥0.9 0.9>α≥0.8 0.8>α≥0.7 0.7>α≥0.6 0.6>α≥0.5 0.5>α factors of bim nsisted of 13 it items were ta modification re then subjec then analyzed data is the rela y & applied sci respondents p tegories male female 20-30 31-40 41-50 re than 51 iploma achelor master ph.d. other rchitect l engineer cal engineer ical engineer other esigner nsultant ct manager engineer other ss than 5 5-10 11-15 16-20 re than 20 nal questionnai orrelation coefficient 0.644** 0.751** 0.691** 0.773** 0.662** 0.683** 0.670** 0.679** 0.702** 0.714** 0.679** 0.625** 0.500** correlation is significan correlation is significan liability classif ha degree ex ac que una m adoption tems that moti aken from pre and integratio cted to the res d. one of the ative importan ience research hatem et al.: m profile percentage ( 77.2 22.8 32.1 24.7 32.1 11.1 1.8 75 11.6 10.6 1 6.3 64 9.9 14.4 5.4 14 9 10 56 11 19.5 24.8 15 24.8 15.9 re consistency sig. (2-tailed 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 nt at the 0.05 level (2-ta nt at the 0.01 level (2-ta fication [35] e of reliability xcellent good cceptable estionable poor acceptable ivate the appli evious studies on at certain p spondents' view techniques us nce index (rii) h v motivation fac (%) y d) ailed) ailed) cation s after points. w and sed in ). the pur par r whe com wei resp exe sing con med “sig whe thu sam was for ans the rela acc of edu edu resu lack of thro con con bim spe cou and app resu it is the imp vol. 8, no. 2, 20 ctors for adopti rpose of its use rt in the questio ( * ) w rii a n   5 5 5( ) 4( 5( n n rii n    ere w is th mponent (rang ight (which eq pondents. sign test is ecute based on gle sample th nditions and i dium value fo gn” for all the ether it is gre s gives a bino mple values [3 s performed w r the likert fiv swer is equal o descriptive s ative importan cording to (rii figure 1 show the thirteen i ucational base ucation in uni ult may have k a curriculum the study. m ough worksh nferences) too nstruction sect m. the third r ecialists with untries have p d the use of plication of b ults are less th s found that m bim motiv portant”. fig. 1. rela 018, 2668-2672 ing building in e is to give a r onnaire [36]: 4 3 2 4 3 2 1 ) 3( ) 2( ) ) n n n n n n n       he weight gi ging from 1 quals to 5) and equivalent to n dealing wit hat is not com its idea is ba or the distribut e values of sa eater or less th omial probabi 37]. the sign with a cut off ve point scale or more than 4 statistics sign nce index r i, mean and sta ws the values items. results for bim by m iversities) rep taken the top m related to bi 1 (promote lo hops and co ok second ran tor suffers fr rank is for m1 experience i revious exper their experts bim in iraq. han 0.05, and b more than 0.61 vation factors ative importance i nformation mod rank for each 1) ) n iven by resp to 5), a repr d n represents “one sample th the value o mplying with t ased on the a tion of the sam ample dependi han the hypot ility for the o test of bim value of 4 an e the assumpti . table v illus n test results, rii and the r andard deviati of the relative s showed that making it part resented the p rank because im, especially ocal awarenes urses as we nk, probably rom poor kno 13 (contracting in bim filed rience in the a has a positi since all p-v by the ratios s 1% of the resp s as “impor index (rii) for m 2670 deling (bim) in item in a parti (1) (2) pondents for resents the hi the total numb e t test” and of a medium the parametric assumption o mple and then ng on the val thesis medium observed patte motivation fa nd 61% percen ion is that 61% strates the valu the value o rank of the on). e importance i t m7 (establis t of the curric highest rank. e iraqi univer y in the early s ss of bim ben ell as specia because the owledge rega g with internat d), because m application of ive impact on values in sign shown in the t pondents evalu rtant” and “ motivations factor n iraq icular each ighest ber of it is for a c test of the n give ue of m and ern of actors ntage. % for ues of f the items index sh an culum this rsities stages nefits alized iraqi arding tional many bim n the n test table, uated “very rs engineering, technology & applied science research vol. 8, no. 2, 2018, 2668-2672 2671 www.etasr.com hatem et al.: motivation factors for adopting building information modeling (bim) in iraq table v. results of bim motivation factors statistical analysis no items sign test m ea n s d r ii % r a n k n observed prop. sig. 1tailed ≥4 <4 ≥4 <4 m1 promote local awareness of bim benefits through workshops and courses as well as specialized conferences 100 14 0.88 0.12 0.000 4.36 .82 87.19 2 m2 government policy is to make use of bim mandatory through developing special laws 83 31 0.73 0.27 0.006 3.93 .97 78.77 12 m3 provide government support for the implementation of bim in companies and firms 93 21 0.82 0.18 0.000 4.15 .86 83.16 7 m4 detailed analysis of project life cycle costs to convince the clients of financial returns from using bim 91 23 0.80 0.20 0.000 3.99 .92 79.82 11 m5 disseminate positive views to reduce strong resistance to change resulting from adhering to traditional practices and programs 92 22 0.81 0.19 0.000 4.01 .89 80.35 10 m6 raise the level of public-private partnerships 86 28 0.75 0.25 0.001 4.04 .85 80.88 9 m7 establish an educational base for bim by making it part of the curriculum education in universities 101 13 0.89 0.11 0.000 4.36 .77 87.19 1 m8 allocation of financial funding to support the costs of bim adoption 93 21 0.82 0.18 0.000 4.16 .83 83.16 6 m9 raise awareness of cooperation culture importance between different stockholders 88 26 0.77 0.13 0.000 4.05 .87 81.05 8 m10 development of contracts and legal rules governing the use of bim 83 31 0.73 0.27 0.005 3.93 .84 78.60 13 m11 raise the employment rate for fast-learning ages of engineers 95 19 0.83 0.17 0.000 4.20 .89 83.86 5 m12 develop skills of inexperienced engineers through specialized systematic programs 99 15 0.87 0.13 0.000 4.22 .94 84.56 4 m13 contracting with international specialists with experience in bim filed 94 20 0.82 0.18 0.000 4.28 .93 85.61 3 v. conclusion and recommendations this paper studied the factors that motivate the application of bim in iraq. this was discussed through a theoretical study that included a comprehensive survey of previous studies followed by analysis of the results of the survey that was prepared for this purpose and results showed that the highest three factors are “bim is to include it in the educational curricula”, “raise awareness through courses and workshops”, and “contracting with international experts with experience in bim”. a set of recommendations are needed to be considered including the need to update the curricula of civil engineering and architecture and these curricula should be working on student development in both modelling skills using bim tools as well as working skills within the bim collaborative environment. also, the need to raise the level of knowledge in bim by providing courses, conferences and training workshops about it, provide material and moral support by various organizations and finally the importance of attracting internationally individuals competent with extensive experience in the field of bim. references [1] y. arayici, f. khosrowshahi, a. m. ponting, s. a. mihindu, “towards implementation of building information modelling in the construction industry”, 5th international conference on construction in the 21st century, “collaboration and integration in engineering, management and technology”, istanbul, turkey, pp. 1342-1351, may 20-22, 2009 [2] s. azhar, a. nadeem, j. y. n. mok, b. h. y. leung, “building information modeling (bim): a new paradigm for visual interactive modeling and simulation for construction projects”, 1st international conference on construction in developing countries, karachi, pakistan, vol. 1, pp. 435-446, august 4-5, 2008 [3] b. succar, “building information modelling framework: a research and delivery foundation for industry stakeholders”, automation in construction, vol. 18, no. 3, p. 357-375, 2009 [4] c. t. w. chan, “barriers of implementing bim in construction industry from the designers’ perspective: a hong kong experience”, journal of system and management sciences, vol. 4, no. 2, pp. 24-40, 2014 [5] s. azhar, m. khalfan, t. maqsood, “building information modelling (bim): now and beyond”, construction economics and building, vol. 12, no. 4, pp. 15-28, 2015 [6] k. barlish, k. sullivan, “how to measure the benefits of bim—a case study approach”, automation in construction, vol. 24, pp. 149-159, 2012 [7] c. m. eastman, p. teicholz, r. sacks, k. liston, bim handbook: a guide to building information modeling for owners, managers, designers, engineers and contractors, john wiley & sons, 2011 [8] y. arayici, c. egbu, p. coates, “building information modelling (bim) implementation and remote construction projects: issues, challenges, and critiques”, journal of information technology in construction, vol. 17, pp. 75-92, 2012 [9] a. h. memon, i. a. rahman, i. memon, n. i. a. azman, “bim in malaysian construction industry: status, advantages, barriers and strategies to enhance the implementation level”, research journal of applied sciences, engineering and technology, vol. 8, no. 5, pp. 606614, 2014 [10] l. chen, h. qu, “evaluation for “economics and legislative factors influence the design team and contractor throughout a building project from inception to completion”, journal of system and management sciences, vol. 1, no. 6, pp. 94-108, 2011 [11] g. nagalingam, h. s. jayasena, k. a. t. o. ranadewa, “building information modelling and future quantity surveyor's practice in sri engineering, technology & applied science research vol. 8, no. 2, 2018, 2668-2672 2672 www.etasr.com hatem et al.: motivation factors for adopting building information modeling (bim) in iraq lankan construction industry”, 2nd world construction symposium, colombo, sri lanka, pp. 81-92, june 14-15, 2013 [12] crc for construction innovation, adopting bim for facilities management: solutions for managing the sydney opera house, cooperative research center for construction innovation, 2007 [13] w. a. hatem, a. kwan, j. miles, “comparing the effectiveness of face to face and computer mediated collaboration”, advanced engineering informatics, vol. 26, no. 2, pp. 383-395, 2012 [14] t. g. kekana., c. o. aigbavboa, w. d. thwala, “building information modelling (bim): barriers in adoption and implementation strategies in the south africa construction industry”, planetary scientific research center conference proceedings, vol. 76, pp. 109-111, 2014 [15] b. ozorhon, c. abbott, g. aouad, “innovation in construction: a project life cycle approach”, salford centre for research and innovation in the built environment (scri) research report 4, pp. 903-1012, 2010 [16] p. smith, “bim implementation–global strategies”, procedia engineering, vol. 85, pp. 482-492, 2014 [17] a. akintoye, j. goulding, g. zawdie, construction innovation and process improvement, john wiley & sons, 2012 [18] n. zikic, building information modeling uses for design in the architecture, engineering, and construction (aec) industry, msc thesis, pennsylvania state university, 2009 [19] a. a. latiffi, s. mohd, u. s. rakiman, “potential improvement of building information modeling (bim) implementation in malaysian construction projects”, in: product lifecycle management in the era of internet of things, pp. 149-158, 2015 [20] m. abubakar, y. m. ibrahim, k. bala, “contractors' perception of the factors affecting building information modelling (bim) adoption in the nigerian construction industry”, international conference on computing in civil and building engineering, pp. 167-178, june 2014 [21] w. kymmell, building information modeling: planning and managing construction projects with 4d cad and simulations (mcgraw-hill construction series): planning and managing construction projects with 4d cad and simulations, mcgraw hill professional, 2007 [22] c. furneaux, r. kivvits, bim–implications for government, crc for construction innovation, 2008 [23] j. mitchell, “bim & building simulation”, proceedings of building simulation vol. 12, 12th conference of international building performance simulation association, 2011 [24] d. sinclair, bim overlay to the riba outline plan of work, riba, 2012 [25] s. k. lee, j.-h. yu, “effects of intrinsic and extrinsic motivation factors on bim acceptance”, journal of the korea institute of building construction, vol. 13, no. 3, pp. 242-252, 2013 [26] t. kekana, c. aigbavboa, w. thwala, “building information modelling (bim): barriers in adoption and implementation strategies in the south africa construction industry”, international conference on emerging trends in computer and image processing, pattaya, 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basic review of the validity and reliability of measurement, createspace independent publishing platform, 2015 [32] j. pallant, spss survival manual: a step by step guide to data analysis using ibm spss, allen & unwin, 2016 [33] r. m. furr, v. r. bacharach, psychometrics: an introduction, sage publications, 2013 [34] g. garson, validity and reliability (statistical associates blue book series 12), kindle edition, statistical associates publishers, 2013 [35] r. d. yockey, spss demystified: a simple guide and reference, taylor & francis, 2016 [36] m. rajgor, c. paresh, p. dhruv, p. chirag, b. dhrmesh, “rii & impi: effective techniques for finding delay in construction project”, international research journal of engineering and technology, vol. 3, no. 1, pp. 1173-1177, 2016 [37] e. t. berkman, s. p. reise, a conceptual guide to statistics using spss, sage, 2011 microsoft word etasr_v11_n5_pp7673-7677 engineering, technology & applied science research vol. 11, no. 5, 2021, 7673-7677 7673 www.etasr.com truong et al.: application of an adaptive network-based fuzzy inference system to control a hybrid … application of an adaptive network-based fuzzy inference system to control a hybrid solar and wind grid-tie inverter dinh-nhon truong faculty of electrical and electronics engineering ho chi minh city university of technology and education ho chi minh city, vietnam nhontd@hcmute.edu.vn van-thuyen ngo faculty of electrical and electronics engineering ho chi minh city university of technology and education ho chi minh city, vietnam thuyen.ngo@hcmute.edu.vn mi-sa nguyen thi faculty of electrical and electronics engineering ho chi minh city university of technology and education ho chi minh city, vietnam misa@hcmute.edu.vn an-quoc hoang faculty of vehicle and energy engineering ho chi minh city university of technology and education ho chi minh city, vietnam hanquoc@hcmute.edu.vn abstract-in this paper, the application of an adaptive networkbased fuzzy inference system (anfis) to control a hybrid solar and wind grid-tie inverter in order to reduce power oscillations and enhance power quality is presented. to extract the maximum power from the pv system, a perturb and observe (p&o) algorithm is presented that tracks the maximum power point (mpp). time-domain simulation results of the studied system are performed in matlab/simulink under different operating conditions such as changing irradiation and short-circuit faults in the power grid. from the simulation results, it can be concluded that the designed anfis controller and the proposed p&o algorithm perform better than the traditional pi controller and improve transient responses under severe operating conditions. keywords-hybrid; grid-tie inverter; perturb and observe; anfis i. introduction sunlight and wind are the furthermost promising renewable energy sources. due to the randomness of the solar irradiance and the accessibility of the wind, a combination of solar and wind energy production configuration can be a highly reliable source of electrical energy. a general planning framework for integrating solar and wind energies in a hybrid power system (hps) was proposed to exploit the solar-wind complementarity and to stabilize the combined power output on a case study in pakistan in [1]. hps techno-economics for a single-family residence in the region of yambol, bulgaria was analyzed in [2] to determine optimum system configuration to minimize the excess energy produced. a hybrid optimization model for electric renewable software and its techno-economic feasibility to develop a hybrid wind-solar model was analyzed in [3]. the benefits of a water pumping power system using hps in order to supply water to remote areas and rural zones have been studied in [4]. to generate electricity for the power grid, an inverter is required. in [5], a 3-level inverter-based grid-tie hybrid solar and wind energy system was presented with the mitigation of power quality problems. for enhancing the power quality problems caused by the switching of the small-scale grid-tie inverter under the operation states of solar systems, some solutions have been mentioned in [6]. in terms of developing a grid-tie inverter, a shunt series switched grid tied inverter (sss-gti) was proposed in [7]. this inverter structure can operate in shunt or cascade-connected mode. another structure to improve efficiency by reducing the switching losses was introduced in [8]. research and application of inverter controllers make an important contribution to the quality of the power supplied to the power system. besides the traditional pi controllers [9, 10], a double closed-loop controller for voltage and current was adopted in [11], using sliding mode control [12]. also, new and modern control techniques have been applied, such as the fuzzy logic controller [13]. the purpose of this paper is to present the applicability of the adaptive network-based fuzzy inference system (anfis) controller to improve the stability of the hybrid grid-tie inverter. ii. studied system configuration the studied system configuration is introduced in figure 1. it includes a 5kwp rooftop solar pv system and a 3kw wind turbine system connected to the power grid through a hybrid grid-tie inverter [9, 14]. the mathematical models of the proposed system are described below. corresponding author: dinh-nhon truong engineering, technology & applied science research vol. 11, no. 5, 2021, 7673-7677 7674 www.etasr.com truong et al.: application of an adaptive network-based fuzzy inference system to control a hybrid … 5-kwp rooftop pv arrays grid-tie inverter power grid inverter controllers mppt controller dc c dcvdc v dc i d-ref i pwm i ,vg g 3-kw wind turbines fig. 1. block diagram of the studied system. a. pv array model an equivalent circuit diagram of the 5kwp pv array is referred to [13, 15]. in this paper, a sunpower spr-415ewht-d pv panel is selected. the i-v curve for a rated 5kwp pv system affected by irradiance is shown in figure 2. the rated parameters of this pv panel are: • maximum power: 414.8w • cells per module: 128 • voltage at maximum power point (mpp): 85.3v • short-circuit current: 6.09a • current at mpp: 5.69a fig. 2. irradiance effect on the i-v curve. b. the pmsg-based wind turbine model a small-scale permanent magnet synchronous generator (pmsg)-based vertical wind turbine was used in this paper. the equivalent voltage equation of the studied wind pmsg in per unit (p.u.) projected to the dq-axis was expressed in [16, 17]. in this research, the msfd5-3.000w wind turbine is selected with the following parameters: • rated power: 3.000w • max power: 3.500w • rated wind speed: 8m/s • generator type: three-phase pmsg • working voltage: 192v dc • power supply method: three-phase whole-wave bridge rectifier constant dc charger. iii. designed controllers a. p&o algorithm for mpp tracking for optimizing the efficiency of the pv system, an mpp tracker algorithm using the perturb and observe (p&o) controller is applied [18, 19]. its flowchart can be seen in figure 3. perturb in the opposite direction begin measure ipv, vpv calculate ppv perturb in the same direction ppv increases ? yesno fig. 3. flowchart of the p&o algorithm for mpp tracking. b. anfis controller for dc voltage control in this section, an anfis controller is proposed to replace the pi controller in the dc voltage controller block of the hybrid grid-tie inverter as presented in figure 4 [20, 21]. pi dc-ref invve v dc-meas v d-ref i pi e gi pmw modulation pwminv dc voltage controller current controller fig. 4. controllers for the hybrid grid-tie inverter. fig. 5. the designed anfis controller for dc voltage regulator. the structure of anfis can be seen in [22-24]. however, for enhancing the accuracy of this controller, besides the error of dc voltage (e), additional information from its derivative (de/dt) is added to train the anfis controller (see figure 5). as a result, after the training process, the minimal training root engineering, technology & applied science research vol. 11, no. 5, 2021, 7673-7677 7675 www.etasr.com truong et al.: application of an adaptive network-based fuzzy inference system to control a hybrid … mean square error is rmse = 0.000019. the surface rule is plotted in figure 6. the selected anfis information are: • number of nodes: 35 • number of linear parameters: 27 • number of nonlinear parameters: 18 • total number of parameters: 45 • number of training data pairs: 302.401 • number of fuzzy rules: 9 fig. 6. surface rule of the designed anfis. iv. simulation results to evaluate the effectiveness of the proposed controller simulations were performed in the time-domain of the studied hybrid solar and wind system under different operating conditions to compare the contributions of the designed p&o and anfis controllers to control the hybrid grid-tie inverter and thus enhance dynamic stability. the simulations were carried out in matlab/simulink. the mathematical model is shown in figure 7 and the parameters of the studied system using pi controllers are illustrated in figure 8. fig. 7. the mathematical model in simulink. figure 9(a) presents the response of the solar pv system when the solar irradiance changes and figure 9(b) shows the output power of the solar pv system. it is easy to observe that the p&o controller helps keeping the output power of the solar pv system close to the peak value of the maximum power. fig. 8. parameters of the inverter control block using the pi controller. (a) (b) fig. 9. responses of the studied system with changing irradiance. (a) irradiation, (b) active power of the solar pv system. the fuzzy rules designed in figures 10-12 show the comparative transient responses in the time-domain of the studied system with the pi controller (red lines) and with the designed anfis controller (blue lines) when a single-phase short-circuit fault occurs at the output of the inverter at 3.5s and at the power grid at 6.0s. the wind speed is 6m/s and the irradiation varies from 700w/m 2 to 600w/m 2 . engineering, technology & applied science research vol. 11, no. 5, 2021, 7673-7677 7676 www.etasr.com truong et al.: application of an adaptive network-based fuzzy inference system to control a hybrid … fig. 10. relationship between inputs and output of the anfis controller in the fuzzy rules. (a) (b) (c) fig. 11. response of the studied system when a single-phase short-circuit occurs. (a) active power of the wind system, (b) active power of the solar system, (c) voltage at the dc-link of the inverter. (a) (b) (c) fig. 12. response of the studied system when a short-circuit fault occurs at the power grid. (a) active power of the wind system, (b) active power of the solar system, (c) voltage at the dc-link of the inverter. it is shown from the comparative results that when the faults occurred, the responses of all parameters oscillated. however, transient fluctuations were better controlled with the proposed anfis controller than with the pi controller with regard to overshoot and settling time. v. conclusions in this paper, the comparative stability improvement of a hybrid grid-connected solar and wind system has been presented. to extract the maximum power from the solar pv system, a p&o controller is proposed for mpp tracking. furthermore, the anfis controller was designed to keep stable the dc voltage of the hybrid inverter. comparative timedomain simulation results of the studied system under severe faults were performed. it can be concluded from the results that the proposed p&o and anfis controller enhances the transient performance of the system with regard to overshoot and settling time reduction of the hybrid grid-tie inverter. engineering, technology & applied science research vol. 11, no. 5, 2021, 7673-7677 7677 www.etasr.com truong et al.: application of an adaptive network-based fuzzy inference system to control a hybrid … acknowledgment this paper was supported by the ministry-level science and technology program with the title "application of iot technology in monitoring, control, and management of integrated electrical systems", grant number ct.2019.04. references [1] a. naeem, n. ul hassan, and n. arshad, "design of solar-wind hybrid power system by using solar-wind complementarity," in 2020 4th international conference on green energy and applications (icgea), singapore, mar. 2020, pp. 100–105, https://doi.org/10.1109/ icgea49367.2020.239713. 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[20] m. y. allani, d. mezghani, f. tadeo, and a. mami, "fpga implementation of a robust mppt of a photovoltaic system using a fuzzy logic controller based on incremental and conductance algorithm," engineering, technology & applied science research, vol. 9, no. 4, pp. 4322–4328, aug. 2019, https://doi.org/10.48084/etasr.2771. [21] i. vairavasundaram, v. varadarajan, p. j. pavankumar, r. k. kanagavel, l. ravi, and s. vairavasundaram, "a review on small power rating pv inverter topologies and smart pv inverters," electronics, vol. 10, no. 11, jan. 2021, art. no. 1296, https://doi.org/ 10.3390/electronics10111296. [22] v.-t. bui and d.-n. truong, "improvement of anfis controller for svc using pso," in computational intelligence methods for green technology and sustainable development, 2021, pp. 293–302, https://doi.org/10.1007/978-3-030-62324-1_25. 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[24] v. h. nguyen, h. nguyen, m. t. cao, and k. h. le, "performance comparison between pso and ga in improving dynamic voltage stability in anfis controllers for statcom," engineering, technology & applied science research, vol. 9, no. 6, pp. 4863–4869, dec. 2019, https://doi.org/10.48084/etasr.3032. engineering, technology & applied science research vol. 7, no. 3, 2017, 1681-1684 1681 www.etasr.com soni and shah: design and analysis of qos routing framework integrated with olsr protocol … design and analysis of qos routing framework integrated with olsr protocol for multimedia traffic in mobile adhoc networks sunil soni computer engineering department marwadi education foundation, india and faculty of technology, r. k. university, india profsjsoni@gmail.com j. s. shah government engineering college gujarat, india jssld@yahoo.com abstract—manets (mobile ad-hoc networks) is the self organizing wireless structure of mobile hosts. wireless media is used for communication in manets. considering the developing requirements for multimedia and real-time traffic applications in real world, qos (quality-of-service) support is essential in manets. but most of the characteristics of manets make qos support a difficult problem. it is challenging to support qos routing in manet due to dynamic behavior and mobility of the hosts. the olsr (optimized link state routing) protocol can be efficiently used in manets to provide qos routing because of its dynamic mpr (multi point relay) selection criteria and proactive nature. in this paper, a design of qos routing framework integrated with olsr protocol is proposed and also analyzed using network simulator. proposed qos framework combines a bandwidth estimation algorithm with explicit resource reservation, qos routing and connection admission control (cac). olsr protocol is extended for qos framework to solve performance issues related to node mobility using cross layer approach. results after simulation conclude about efficiency of the proposed qos routing framework. keywordsqos; quality-of-service; qos routing; qos framework; bandwidth; delay; olsr; routing protocols; resource reservation i. introduction a mobile ad-hoc network (manet) is an infrastructureless, multiple hop wireless networks with mobile hosts. thus, a manet is self organizing and self configuring wireless network. in this network, connectivity among hosts or sometimes to other network is provided with the help of hosts themselves. attending qos support such as available bandwidth, end-to-end delay, probability of loss, rate of error and cost of links are extensively addressed in the perceptive of internet applications [2-3, 7-9]. internet applications are having very limited scope in manets due to the dynamic topology and bandwidth restriction. some qos routing solutions are proposed earlier for internet applications in spite of this limited applicability [4, 6, 10-12]. link state routing (lsr) looks more promising for qos routing support in manets as comprehensive information of connections is obtainable by all participating hosts. it enhances the opportunities to form a route by a host which meets up with the complete set of qos routing characteristics. in lsr protocol, participating nodes stores all the required information for routing. as a reason, olsr (optimized link state routing) as in [1] is used as a routing protocol in this proposed work. along with regular routing information olsr can be also used to store additional qos routing information like bandwidth and delay to select qos supported path formation. olsr provides a flexibility to select mpr (multi point relay) based on any specific qos parameter which can be extended for further mpr selections until it reaches to destination host. when a design for qos solution is thought of for manets to pursue bandwidth, delay, throughput, resource reservation, connection admission control should not be negotiated. protocols viz. olsr-etx [5], olsr-md [5], qos-olsr [9], cac-olsr [10], cld-olsr [13], qolsr [14], clq-olsr [17] etc. were very carefully designed, however they were found unable to attain various qos requirements. none of the above regulates the stipulation of focal points, channel assets and cross layering diagram for manets. so it is in fact prerequisite of a qos structure that can be successfully significant to whichever tradition and furthermore gives qos parts like cross layering, stream classifier, reservation flagging, association affirmation control etc. hence, it is emphasized to formally design and analyze qos requirement using welldefined framework. ii. review of qos frameworks in [18], authors presented a qos framework called insignia (in-band signaling with admission control). insignia is an ip (internet protocol) based framework that supports adaptive services for manets. authors have shown design, implementation and evaluation of insignia containing in-band signaling and soft-state resource management. these two factors of insignia are very suitable for mobility support and end-to-end qos route for highly dynamic topology change in manet. an independent network layer solution without use of mac layer is provided. the signaling data needed for qos support is encapsulated in data packets itself. so that framework becomes “lightweight”. engineering, technology & applied science research vol. 7, no. 3, 2017, 1681-1684 1682 www.etasr.com soni and shah: design and analysis of qos routing framework integrated with olsr protocol … the main drawback of presented framework is designed explicitly for awns (adhoc wireless networks) where there is no consideration of mobility and reservation of resources is also not deal with. in [19], authors presented a qos framework swan (service differentiation in stateless wireless adhoc networks) which is a stateless network system which utilizes distributed control computations to convey service separation in mobile wireless ad hoc networks in a basic, versatile and robust way. authors have utilized rate direction for tcp (transmission control protocol) and udp (user datagram protocol) bestexertion development, and source based affirmation control of udp enduring activity. swan utilizes explicit congestion notification (ecn) to progressively direct conceded ongoing activity even with system flow brought on by versatility or movement over-burden conditions. a novel part of swan is that it doesn't need the help of a qos-proficient mac (medium access control). on the other hand, soft real-time services are constructed by utilizing realistic best exertion wireless mac improvement. swan utilizes cross layering course of action that uses framework and association layers information and it relies on upon differentiated services considered for traditional wired frameworks. the major issue of swan is that it is not overseeing reservation of resources that is truly a significant piece of qos related controlling. in [20], authors proposed that it is basic to keep up qos progressively activity in manet since a large portion of the internet applications require ensured qos amid transmission. authors have proposed prtmac (proactive real time medium access control) framework to ensure guaranteed qos in the term of bandwidth and delay. it bolsters qos by the asset reservation instrument. once the assets are held, hubs get restrictive access on the asset. proposed technique concentrates on exceptionally specific mac protocols. it would require significant changes in the event of applying it on other routing protocols. in [11], a qos framework named brawn (bandwidth reservation over adhoc network) was presented. the principle thought behind brawn is to permit end-to-end reservation of data transfer capacity in an adhoc wireless network. reservation of resources is performed in an onrequest way, so at whatever point an end-client begins an application with particular qos needs, this application should work together with the reservation flagging module to set up a way before having the capacity to begin the information transmission. likewise the recommended internal plan of the given framework known as brawn has associations between the various modules for setting up a qos parameter. as observed with a few applications qos asks for thinking about the operation of the tradition and request the benefits through the reservation signaling module. major drawback of brawn to apply it on manets is it was proposed for static ad-hoc networks. mobility issue of manets is not considered in brawn. along these lines, so as to make brawn perfect with manet, mobility issue must be tended to. brawn is purely works on network layer, so cross-layer advantages cannot be achieved. brawn design simply relies upon bandwidth estimation; there is no arrangement for delay estimation. iii. comparison of proposed framework with other qos frameworks table i shows the most popular qos designs frameworks and their comparison for qos assurance in manets. as shown, no particular qos framework is capable to fully ensure qos for today’s real/non real time multimedia traffic flows in manets. so as a future work, a qos framework for manets could have been proposed by considering factors like crosslayer advantages, resource reservation, connection admission control (cac), multi-constrained qos parameters, hard qos assurance and proactive routing advantages. table i. comparison of qos frameworks qos criteria qos frameworks in si g n ia sw a n p r t m a c b r a w n pr op os ed f ra m ew or k mobility support yes yes yes no yes crosslayering no no yes no yes resource reservation yes no yes yes yes connection admission control yes yes no yes yes flow classifier no yes no yes yes qos parameters band width band width and delay throughput and delay band width band width and delay integrated routing protocol tora mac dsr aodv olsr type of traffic adaptive flows tcp and udp tcp cbr mpeg4 (cbr) the following observations are made that should be considered upon designing a new qos framework specifically for multimedia traffic in manet.  insignia can be extended for scalability issue in manets. in order to tackle multimedia traffic handsomely some features e.g. cross-layering, flow classifier could be added further in future work.  swan can be extended further by incorporating it with a proactive routing protocol (e.g. olsr) to get maximum benefit of cross-layered information and to support multiconstrained qos parameters.  prtmac can be incorporated with a proactive routing protocol and connection admission control and flow classifier can be also added.  brawn can be worked on in the future for dynamic mobile network (mobility) as it is just proposed and fitted for the static networks. there is no arrangement for checking delay estimation. it is single constraint engineering, technology & applied science research vol. 7, no. 3, 2017, 1681-1684 1683 www.etasr.com soni and shah: design and analysis of qos routing framework integrated with olsr protocol … architecture; not a multi-constraint one. it can be likewise improved for versatility perspective too. so there is a decent extent of research for amplifying its segments for offering almost hard qos ensures in manet where nodes are widespread or versatile. iv. design of proposed framework figure 1 shows an entire design of proposed framework which divided into various modules and presented in layered form. the main features of proposed framework are flow separation module, resource reservation, connection admission control (cac) and cross-layer design advantages. proposed framework is integrated with olsr protocol as in [1] and olsr protocol is assumed to be modified accordingly in design. non-multimedia apps directly forward data to the besteffort routes. no special treatment will be given to nonmultimedia apps. while flow separation module selects qos supported routes to forward multimedia apps data. multimedia apps will make a request of resources which generates signaling of resource reservation and gets qos route from olsr protocol. once qos route is formed by olsr protocol; resource reservation and connection admission control modules will remain in act until mpr selection reaches to destination host. the required information for calculating bandwidth and delay is obtained by taking support from mac/data link layer by olsr protocol on the basis of which the mpr selection is made. all major tasks of proposed framework are carried out in network layer. but qos related information will be taken out from mac/data link layer. fig. 1. a new qos framework proposal. v. analysis of proposed framework the entire proposed framework is simulated in network simulator 2 (ns2). in figure 2 the simulation scenario is given and as can be seen there are 50 nodes deployed within 1500x1500m2 coverage areas. the multimedia traffic (mpeg4, udp agent, constant bit rate traffic) starts at the beginning of the simulation time. until the end of the simulation time, part of this multimedia traffic flows between various pairs of connections. mpeg4 multimedia traffic is using video model based on ibp frames. the general list of parameters used in simulation is summarized in table ii. there are three different cases of routing protocols analyzed viz. naïve olsr protocol as in [1], brawn framework in dynamic (mobility) scenario as in [21] and proposed framework. all three cases are compared with different values of simulation time (100, 200, 300 sec) and number of connections (10, 15, 20 pairs). as shown in figures 3-5, delivery rate, end-to-end delay and throughput performance metrics are analyzed for naïve olsr, brawn framework with mobility scenario and proposed framework respectively. from the analysis of the results, it is concluded that: average delivery rate of 26.47% for proposed framework is better than naïve olsr and brawn framework with mobility scenario which are 17.98% and 23.11% respectively, average end-to-end delay which is 55.73 seconds for the proposed framework is better than naïve olsr and brawn framework with mobility scenario compared to 73.17 and 56.65 seconds respectively and average throughput of 1782.53 kbps for the proposed framework is better than naïve olsr and brawn framework with mobility scenario of 1217.20 and 1456.97 kbps respectively. fig. 2. simulation scenario with 50 nodes. table ii. simulation parameters parameters values coverage area 1500 x 1500 m2 number of nodes 50 transmission range 250 m type of traffic mpeg4 (udp agent, cbr traffic) video model ibp frames packet size 512 bytes routing protocols olsr, brawn, proposed framework simulation time 100, 200, 300 sec number of connections 10, 15, 20 pairs scripts awk vi. conclusion the difficulties confronted in qos frameworks in manets are discussed and a proficient design and analysis of novel qos framework of different qos routing parameters is presented in this paper. a olsr proactive routing protocol is integrated in the proposed qos framework and cross-layering is exploited to engineering, technology & applied science research vol. 7, no. 3, 2017, 1681-1684 1684 www.etasr.com soni and shah: design and analysis of qos routing framework integrated with olsr protocol … get multi-constrained qos metrics. along with this, resource reservation and admission control is also proposed in the framework by modifying olsr routing protocol. simulation results based on delivery rate, end-to-end delay and throughput conclude about efficiency of the proposed qos routing framework. fig. 3. comparison of delivery rate. fig. 4. comparison of end-to-end delay. fig. 5. comparison of throughput. references [1] t. clausen, p. jacquet, rfc 3626: optimized link state routing protocol (olsr), 2003 [2] a. tonnesen, implementing and extending the optimized link state routing protocol, msc thesis, university of oslo, 2004 [3] y. ge, quality-of-service routing in ad-hoc networks using olsr, msc thesis, carleton university, 2002 [4] a. huhtonen, “comparing aodv and olsr routing protocols”, hut t-110.551 seminar on internetworking, sjökulla, 2004 [5] a. pandey, m. baliyan, “performance analysis of olsr and modified version of olsr-etx/md/ml in mesh networks”, international journal of computer science & communication networks, vol. 2, no. 2, pp. 268-271, 2012 [6] d. passos, d. teixeira, “mesh network performance measurements”, 5th international information and telecommunication technologies symposium, 2006 [7] d. de couto, d. aguayo, “a high throughput path metric for multihop wireless routing”, mobicom ’03, usa, 2003 [8] p. jacquet, t. clausen, a. laouiti, a. quyyum, l. viennot, “optimized link state routing protocol for ad hoc networks”, ieee inmic 2001, international multi topic conference, pakistan, 30-30 dec. 2001 [9] a. munaretto, h. badis, a. agha, “a link-state qos routing protocol for ad hoc networks”, 4th international workshop on mobile and wireless communications network, sweden, 9-11 sept. 2002 [10] e. mineiro, d. muchaluat-saade, “admission control for qos provision in wireless mesh networks”, 2012 ieee symposium on computers and communications (iscc), turkey, 1-4 july 2012 [11] r. guimaraes, quality of service on ad-hoc wireless networks, phd thesis, universitat politècnica de catalunya, spain, 2008 [12] b. a. mohan, h. sarojadevi, “study of scalability issue in optimized link state routing (olsr) protocol”, international journal of advanced technology & engineering research, vol. 2, no. 4, pp. 4044, 2012 [13] t. sanguankotchakorn, s. k. wijayasekara, n. sugino, “a cross-layer design approach in olsr manet using ber and weighted connectivity index”, 19th ieee international conference on networks (icon), singapore, 11-13 dec. 2013 [14] g. rigazzi, v. palma, g.tamea, f. santucci, a. neri, “a cross-layer routing protocol with quality of service support for flexible deployment in manets”, 2012 ieee globecom workshops (gc wkshps), pp. 508-512, usa, 3-7 dec. 2012 [15] d. moad, s. djahel, f. n. abdesselam, “improving the quality of service routing in olsr protocol”, 2012 international conference on communications and information technology (iccit), tunisia, 26-28 june 2012 [16] s. banik, b. roy, b. saha, n. chaki, “design of qos routing framework based on olsr protocol”, 2010 international conference on advances in recent technologies in communication and computing (artcom), india, 16-17 oct. 2010 [17] y. peng, l. guo, q. gai, “cross-layer qos-aware routing protocol for multi-radio multi-channel wireless mesh networks”, ieee 14th international conference on communication technology (icct), china, 9-11 nov. 2012 [18] s. b. lee, g. s. ahn, x. zhang, a. t. campbell, “insignia: an ipbased quality of service framework for mobile ad hoc networks”, journal of parallel and distributed computing, vol. 60, pp. 374-406, 2000 [19] g. s. ahn, a. t. campbell, a. veres, l. h. sun, “swan: service differentiation in stateless wireless ad hoc networks”, twenty-first annual joint conference of the ieee computer and communications societies infocom 2002, usa, 23-27 june 2002 [20] g. u. devi, g. kavitha, “resource reservation using prtmac protocol in manet”, international journal of computer networks and wireless communications, vol. 2, no. 3, pp. 328-334, 2012 engineering, technology & applied science research vol. 7, no. 3, 2017, 1681-1684 1685 www.etasr.com soni and shah: design and analysis of qos routing framework integrated with olsr protocol … microsoft word etasr_v11_n5_pp7619-7623 engineering, technology & applied science research vol. 11, no. 5, 2021, 7619-7623 7619 www.etasr.com alsaedy & aljalawi: the effect of nanomaterials on the properties of limestone dust green concrete the effect of nanomaterials on the properties of limestone dust green concrete sajjad monther alsaedy department of civil engineering college of engineering university of baghdad baghdad, iraq s.naeem1901m@coeng.uobaghdad.edu.iq nada aljalawi department of civil engineering college of engineering university of baghdad baghdad, iraq nada.aljalawi@coeng.uobaghdad.edu.iq abstractportland cement is considered the most involved product in environmental pollution. it is responsible for about 10% of global co2 emissions [1]. limestone dust is a by-product of limestone plants and it is produced in thousands of tons annually as waste material. to fulfill sustainability requirements, concrete production is recommended to reduce portland cement usage with the use of alternative or waste materials. the production of sustainable high strength concrete by using nanomaterials is one of the aims of this study. limestone dust in 12, 16, and 20% by weight of cement replaced cement in this study. the study was divided into two parts: the first was devoted to the investigation of the best percentage of replacement of waste lime. the second part of the study evaluated the performance of concrete when adding nanomaterials. three percentages of cement replacement 0.5%, 1%, and 1.5% with nano-al2o3 were used. the most efficient content of hydrated lime used in this study which achieves sustainability and maintains the quality of concrete was (16%). on the other hand, it was found that the best percentage of nano-al2o3 as a partial replacement of cement is 1.5%. keywords-green concrete; limestone dust; nano al2o3 i. introduction concrete is a widely used construction material, with an annual production that exceeds 10 billion tons [2]. durability, fire resistance, water impermeability, cost efficiency, energy efficiency, and the ability to produce on-site are some of its advantages. however, cement manufacturing, which is the primary binder in concrete, necessitates a significant quantity of natural resources and energy. approximately 1.5 tons of raw ingredients are required to produce one ton of cement [3]. the need to reduce co2 emissions makes the search for alternative binders necessary. the necessity for more economical and environmentally friendly cement materials expanded the interest in other materials which can be used as substitutes to partially replace ordinary portland cement (opc) [4-6]. the cost of natural resources is increasing constantly, leading to the search for alternatives, such as recycled materials, rice husk ash, sawdust ash, tile powder, wood waste ash, silica fume, fly ash, coal bottom ash, limestone dust, porcelinite, etc. [7-12]. also, opc is related to several diseases [13-17]. limestone is the most prevalent type of calcium carbonate, often used in cement production. calcium carbonate (caco3), magnesium carbonate (mgco3), silica (sio2), alumina (al2o3), iron oxide (fe2o3), and sulphate (so3), are the principal components of limestone, with caco3 and mgco3 being its major components [18]. cements are primarily created by calcining a mixture of about 75% limestone and 25% clay to produce a calcium silicate clinker, which is then crushed and combined with a tiny amount of gypsum [19]. nanomaterials are important due to properties such as the high surface to volume ratio. as the surface area per mass of a material increases, a larger amount of the material can come to contact with neighboring particles, therefore nanomaterials have high reactivity [20]. the inclusion of ultrafine nanomaterial particles fills the holes in the concrete microstructure. the nanopowder increases the surface area of the pozzolanic reaction, resulting in a more cementitious product [21, 22]. in the present research, the effects of nanooxide (alumina) and limestone dust on concrete microstructure and mechanical properties are investigated. ii. material characterization opc produced by the tassloja cement factory, confirming to iraqi specification no.5/2019 was used in this research [23]. natural fine sand zone 2 (table i ), which is within the limits of the iraqi specification no. 45/1984 [24], was used as fine aggregates. coarse aggregates with size of 5-14mm were used to prepare concrete samples. the physical and chemical properties of fine and coarse aggregates are shown in tables ii and iii respectively. all concrete samples were produced with the same water to cement ratio (w/c) of 0.3. the concrete ingredients were mixed using 1:1.4:1.8 mixing ratio for cement, fine aggregates, and coarse aggregates respectively according to the british method for concrete mix design. limestone dust was obtained from a limestone quarry in karbala. it was finely ground in the form of dust, most of it passing the no.100 sieve. the chemical composition of the dust is given in table iv. it was used to partially replace cement in concrete. three different percentages (12%, 16%, and 20%) by weight were used to replace cement. corresponding author: sajjad monther alsaedy engineering, technology & applied science research vol. 11, no. 5, 2021, 7619-7623 7620 www.etasr.com alsaedy & aljalawi: the effect of nanomaterials on the properties of limestone dust green concrete table i. natural fine sand grading sieve size (mm) accumulative passing (%) accumulative passing (%) according to the limits of i.q.s no.45/1984 10 100 100 4.75 100 90-100 2.36 88.7 75-100 1.18 66.9 55-90 0.6 51.8 35-59 0.3 18.8 8-30 0.15 3.4 0-10 table ii. physical and chemical properties of fine aggregates properties of sand test results of sand limits of iqs no. 45/1984 fineness modulus 2.76 specific gravity 2.63 absorption 0.8% so3 0.23% ≤ 0.5% dry rodded density 1604kg/m³ table iii. physical and chemical properties of coarse aggregates properties of gravel test results of gravel limits of iqs no. 45/1984 specific gravity 2.652 absorption 0.7% so3 0.05% ≤ 0.1% dry rodded density 1640kg/m³ table iv. chemical analysis of limestone dust chemical composition constituent % silicon dioxide (sio2) 5.15 calcium oxide (cao) 52.1 aluminium oxide (al2o3) 0.66 ferric oxide (fe2o3) 0.08 magnesium oxide (mgo) 0.51 sulphur oxide (so3) 0.0 loss on ignition 41.49 fig. 1. nano al2o3 used in the research. the nanomaterial al2o3 shown in figure 1 was used as the partial replacement of cement. it was purchased from skyspring nanomaterials ltd and its physical analysis is shown in table v. three different percentages of 0.5, 1, and 1.5wt% of cement were used. table v. physical properties of nano al2o3 property specifications appearance milky white crystal structure and type alpha purity % 99 form powder density 3.5-3.9g/cm 3 iii. experimental program the experimental part consisted of 7 concrete mixes as shown in table vi (the concrete ingredients were mixed using 1:1.4:1.8 mixing ratio for cement, fine aggregates, and coarse aggregates respectively, according to the british method for concrete mix design). table vi. mix design details for concrete mixes mix symbol w/b hrwra (lt/100kg cement) cement (kg/m 3 ) limestone dust (kg/m 3 ) nano al2o3 (%) mr 0.3 2.5 500 0 0 ml1 440 60 0 ml2 420 80 0 ml3 400 100 0 mn1 417.9 80 0.5 mn2 415.8 80 1 mn3 413.7 80 1.5 iv. specimen preparation specimens in the shape of cube, prism, and cylinder were prepared to test compressive strength, flexural strength, and splitting tensile strength respectively. the steel molds were cleaned and their internal surfaces were lubricated with oil to prevent adhesion with concrete after hardening. the molds were filled with concrete in layers, and each layer was compacted by a vibrating table according to astm c 192/c192m [25], which is sufficient to remove any entrapped air. after compaction, the specimens were leveled by hand troweling, then left for 24 hours. the specimens were then removed from the molds, and were cured in water until the time of test. all specimens were cured in laboratory environment conditions according to aci 308r-01 [26]. v. results the tests performed on hardened concrete were the slump test, the compressive strength test, the flexural strength test, the splitting tensile strength test, and the sem test. a. workability (slump test) the workability of concrete mixes was measured directly after mixing, according to astm c143 [27]. the results are shown in table vii. b. compressive strength test the compressive strength of the concrete mixes was determined according to british standard bs 12390-3:2019 [28] on 100×100×100mm cubes. the cubes were tested as shown in figure 2 at the age of 7, 28, and 90 days. the average engineering, technology & applied science research vol. 11, no. 5, 2021, 7619-7623 7621 www.etasr.com alsaedy & aljalawi: the effect of nanomaterials on the properties of limestone dust green concrete result of three tested cubes was taken for each mix. the compressive strength for each cube was calculated as shown in (1): fcu = p/a (1) where fcu is the compressive strength (mpa), a the face area of the cube (mm 2 ), and p the compressive load at failure (n). the results are shown in table viii. table vii. slump test results mix symbol slump (mm) mr 102 ml1 116 ml2 122 ml3 125 mn1 117 mn2 111 mn3 107 fig. 2. compressive strength test. c. flexural strength test flexural strength was determined according to astm c 293-07 [29] by the center point method. the prism specimens with dimensions of 100×100×400mm were simply supported with 300mm span and were tested at the age of 7 and 28 days. the average of three prisms was taken for each mix. modulus of rupture was calculated with: fr. = 3pl/2bd² (2) where fr. is the flexural strength (mpa), p the maximum applied load indicated by the test machine (n), l the average length of the specimen (mm), b the average width of the specimen (mm), and d the average depth of the specimen (mm). the results are shown in table viii. d. splitting tensile strength test concrete cylindrical specimens with dimensions of 150×300mm were used in this test to determine the splitting tensile strength according to astm c 496-04 [30] using a compressive machine. in this test method, a diametric compressive force is applied along the side of a concrete cylindrical specimen until tensile failure occurs. the steel plate of the compressive machine is used to distribute uniformly the load applied along the length of the cylinder. the cylinders were tested at the age of 7 and 28 days, and the average of three cylinders was taken as the final result. splitting tensile strength was calculated by: τ = 2p / π ld (3) where τ the splitting tensile strength (mpa), p the maximum. applied load (n), l the length of the specimen (mm), and d its diameter (mm). the results are shown in table viii. fig. 3. compressive strength for all concrete mixes at the age of 28 days. fig. 4. flexural strength for ml2 and mn3 mixes at 7 and 28 days. fig. 5. splitting tensile strength for ml2 and mn3 at 7 and 28 days. e. dry density the specimens were tested according to the iraqi guide 274 [31]. the average result of three samples was calculated at 7, engineering, technology & applied science research vol. 11, no. 5, 2021, 7619-7623 7622 www.etasr.com alsaedy & aljalawi: the effect of nanomaterials on the properties of limestone dust green concrete 28, and 90 days for each mix after picking the cubes out of the curing water and drying their surfaces with a cloth. density (ρ) is the mass of a unit volume of hardened concrete expressed in kg/m 3 . the density was calculated from the specimen mass with volume of 100×100×100 mm obtained after air dry by: ρ = m / v (4) where ρ is the density(kg/m³), m the mass of specimen at the time of test (kg), and v the volume of the specimen calculated from its dimensions (m 3 ). the results are shown in table ix. table viii. summary of compressive, flexural, and tensile strength test results mix symbol compressive strength (mpa) flexural strength (mpa) splitting tensile strength (mpa) 7 days 28 days 90 days 7 days 28 days 7 days 28 days mr 43.8 56.6 68.5 ml1 40.6 53.3 66.0 ml2 39.1 51.3 63.6 6.2 8.6 3.5 5.4 ml3 34.2 44.7 60.1 mn1 40.4 51.8 64.9 mn2 44.0 53.2 65.8 mn3 46.1 55.5 69.0 8.3 11.8 4.9 6.1 table ix. dry density results mix symbol dry density(kg/m 3 ) 7 days 28 days 90 days mr 2511 2525 2536 ml1 2452 2476 2484 ml2 2449 2472 2481 ml3 2437 2459 2470 mn1 2523 2534 2541 mn2 2540 2548 2557 mn3 2556 2569 2580 f. scanning electron microscopy (sem) sem was used to observe the products of nanomaterials. figures 6 and 7 show the sem results of a sample from the mln concrete mix. for this observation, samples were taken from the cracked surface of the specimens of the concrete mixes. in figures 6, 7 the samples prepared with nano al2o3 show more density at c-s-h gel. g. result summary when adding limestone dust to the green concrete production, there was an improvement in workability and a slight decrease in the mechanical properties of concrete, but after adding nanomaterials, the properties begun to increase again, so green concrete containing waste material with high properties can be produced. the importance of this research lies in the possibility of replacing a good percentage of cement with waste material while maintaining the same properties. the results of this study are similar with the findings in [21, 32]. vi. conclusions based on the results obtained from the experimental investigation, the following conclusions can be drawn: • within certain ranges of strength and workability criteria, finely ground limestone dust can be recommended as a partial alternative for cement to produce green concrete. • the dry density of concrete with limestone dust is always lower than that of normal concrete made with opc only. when adding nano al2o3, the dry density increases with the increase in nano al2o3. • from all the tested mixes, 16% dust by weight was found to be most satisfactory as it exhibits optimum compressive, tensile, and flexural strength, and a remarkable increase in workability. fig. 6. sem image of concrete hydrated for 28 days with 1.5% nanoalumina. fig. 7. sem image of concrete hydrated for 28 days with 1.5% nanoalumina with different scale. • the compressive strength result of samples with nano alumina showed that the combination of nano-particles and micro-particles of limestone dust increased the compressive strength of concrete samples compared with the compressive strength of concrete with only limestone dust. engineering, technology & applied science research vol. 11, no. 5, 2021, 7619-7623 7623 www.etasr.com alsaedy & aljalawi: the effect of nanomaterials on the properties of limestone dust green concrete this observation indicates that nano alumina has a good filler effect and further distribution of the particles in the remaining voids lead to a more homogeneous concrete matrix which increases the compressive strength of the produced concrete. • homogeneity was found to be increased with nano particle addition. this was due to the smaller size of the particles leading to an improvement in the surface characteristics of concrete by smoothening the grain and closing the pores thus increasing concrete strength. • the addition of nano-alumina with limestone dust to the concrete mixture improved concrete properties and allows the 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[32] h. binici, h. kaplan, and s. yilmaz, "influence of marble and limestone dusts as additives on some mechanical properties of concrete," scientific research and essays, vol. 2, no. 9, pp. 372–379, sep. 2007, https://doi.org/10.5897/sre.9000594. engineering, technology & applied science research vol. 7, no. 6, 2017, 2118-2123 2118 www.etasr.com safaei et al.: enhancing the hvrt and lvrt capabilities of dfig-based wind turbine in an … enhancing the hvrt and lvrt capabilities of dfig-based wind turbine in an islanded microgrid arman safaei electrical engineering department amirkabir university of technology tehran, iran a.safaei@aut.ac.ir seyed hossein hosseinian electrical engineering department amirkabir university of technology tehran, iran hosseinian@aut.ac.ir hossein askarian abyaneh electrical engineering department amirkabir university of technology tehran, iran askarian@aut.ac.ir abstract—doubly fed induction generator (dfig) based wind turbines are very sensitive to grid voltage variations. therefore, low-voltage-ride-through (lvrt) and high-voltage-ride-through (hvrt) capabilities are employed to improve dfig performance during grid faults and voltage swell events. in this paper, a superconducting magnetic energy storage (smes) device with a pwm voltage source converter and a dc-dc chopper is proposed to enhance the dfig lvrt and hvrt capabilities in an islanded microgrid simultaneously. the simulation results demonstrate that the smes absorbs or releases energy from/to the microgrid during voltage swell events and fault condition respectively and consequently, improves the dfig performance and enhances the dfig lvrt and hvrt capabilities. the effectiveness of the proposed method is validated through detailed simulations in pscad/emtdc. keywords-doubly fed induction generator; microgrid; low voltage ride through (lvrt); high voltage ride through (hvrt); superconducting magnetic energy storage (smes) i. introduction the growth of renewable energy resources usage in the form of distributed generation is led to the introduction of the idea of microgrid. microgrids have significant advantages such as reducing environmental effects, increasing energy efficiency, increasing reliability of supply and reducing power losses. they can operate in both grid-connected and islanded operation modes and they usually include different distributed generation sources (dgs) such as wind and solar generation, energy storages and loads [1]. wind energy had a strong growth in the last decade among various renewable energy sources. in 2016, a capacity larger than 54.6 gw of new wind power has been installed and the world’s total installed wind capacity reached 486.8 gw at the end of 2016. global installed wind capacity is expected to reach 817 gw at the end of 2021 [2]. variable speed wind turbines with doubly fed induction generators (dfigs) are generally used to generate electrical power in microgrids. dfigs offer certain advantages such as, low converter capacity, high efficiency and ease controllability as they can operate under variable speed near their optimal turbine efficiency over a wide range of wind speed [3]. on the other hand, dfigs are very sensitive to grid voltage variations. the voltage dip caused by grid faults at the connection point leads to increase the rotor current which may damage the rotor side converter and dc link capacitor if no protection scheme has been implemented. also, voltage swell caused by unbalanced faults, large loads switching off and large capacitor banks energizing induce a big electromotive force (emf) and a surge current in the dfig rotor which will endanger the normal operation of the dfig [4, 5]. disconnecting the dfig from the grid during fault condition is the first solution that is used to protect the dfig. however, with large integration of wind generators in the power system, loss of significant part of wind generators following a fault may endanger the whole system’s stability. therefore, to ensure the reliable operation of the grid, dfig-based wts must tolerate grid turbulences and support the network. so, low voltage ride through (lvrt) and high voltage ride through (hvrt) schemes are implemented. different lvrt methods have been used to meet grid code requirements. usually to provide complete lvrt capability, additional circuits are required. the primary scheme to protect dfig converters from over current during fault conditions is short circuiting the dfig rotor windings by a system called crowbar [6]. however, with crowbar operation, the rotor side converter is deactivated and the dfig control is lost. the effectiveness of installing fault current limiters (fcls) on the lvrt capability of the dfig has been evaluated in [7, 8]. a modified flux-coupling-type superconducting fault current limiter (sfcl) is applied to improve the lvrt capability of dfig in [7] and the bridge-type fault current limiter (btfcl) impacts on the lvrt capability of dfig has been investigated in [8]. the effectiveness of facts devices such as dynamic voltage restorer (dvr), statcom and svc on the lvrt capability of the dfig has been studied in [9, 10]. dynamic voltage restorer (dvr) has been proposed to improve lvrt capability of the dfig in [9] and the statcom has been used to enhance dfig lvrt capability in [10]. however, these methods require more hardware which leads to a decrease in reliability and an increase in hardware costs. different smes configurations have been employed to enhance transient stability of the dfig [11, 12]. series and parallel compensation using smes has been used to improve power and voltage variations of the wind turbine in [11]. the coordinated control of the optimized resistive type superconducting fault current limiter (sfcl) and smes has been applied for transient stability enhancement in [12]. engineering, technology & applied science research vol. 7, no. 6, 2017, 2118-2123 2119 www.etasr.com safaei et al.: enhancing the hvrt and lvrt capabilities of dfig-based wind turbine in an … however, as the smes has no effect on the alleviation of dfig terminal voltage drop during fault condition, the lvrt capability cannot be guaranteed. various control strategies including virtual damping flux-based control, scaled current tracking control, and sliding mode control have been proposed to enhance dfig lvrt capability in [13-15]. however, these control schemes increase the complexity of the dfig control and the difficulty of coordination between normal and faulty conditions. recent researches only focus on the effects of grid voltage dip on the dfig while the effect of grid voltage swell has received less consideration. also, previous studies have mainly focused on improving the dfig lvrt capability in normal networks (not microgrids). therefore, the dfig lvrt capability during fault condition in an islanded microgrid is investigated in detail in this study. in this paper, important effort has been devoted to evaluate the effectiveness of applying the smes unit with a pwm voltage source converter and a dc-dc chopper on the dfig lvrt and hvrt capabilities in an islanded microgrid during faults and voltage swells. ii. system modelling a. dfig modeling the dfig consists of a back-to-back voltage-source converter including a rotor side converter (rsc) and a grid side converter (gsc). as shown in figure 1, the stator is directly connected to the constant frequency three-phase grid and the rotor winding is connected to a back-to-back converter. the rsc is used to regulate torque and reactive power injection of the dfig. also, the gsc is used to control the dc-link voltage. a capacitor is placed etween these two converters which is used to decrease the voltage ripple. fig. 1. doubly fed induction generator a vector controlled dfig based on [16], is used to investigate the impacts of smes on the dfig performance during fault and voltage swell events. current reference pwm (crpwm) and sinusoidal pwm (spwm) methods are used to control the rsc and gsc, respectively. as noted, the dfig rotor current is increased by occurring voltage dip at the dfig terminal which may damage the dfig converters. the general approach to solve this problem is making a short circuit in the rotor windings with the crowbar protection. in this paper, crowbar control strategy that is proposed in [17], is applied to protect dfig converters. in this method, the hysteresis comparator is used to compare the rotor current with the preset values of il and ih. as the rotor current becomes more than ih, the crowbar is activated and when the rotor current becomes less than il the crowbar is deactivated. the values of il and ih have been set to 1.9 pu and 2 pu, respectively. b. smes modeling smes is a dc current device capable of storing energy in the magnetic field which is generate by dc current flowing through it. the active and reactive power can be absorbed by (charging mode) or released from (discharging mode) the smes according to system situations. smes has some advantages compared to other types of storage devices, such as long lifetime, high response speed, high efficiency, etc. also, the main advantage of the smes is that it can release large amounts of power for a small period of time. also, the number of charging and discharging operations are unlimited. therefore, smes is applicable for wind generation application. different types of smes technologies and their control strategies have been proposed [18]. in this study, a smes unit with a pwm voltage source converter and dc-dc chopper is applied to investigate its effects on the dfig lvrt and hvrt capability. the smes consists of a transformer, a 6-pulse pwm voltage source converter (vsc), a two quadrant dc-dc chopper, a dc link capacitor, and an inductance as a superconducting coil as shown in figure 2. the stored energy in the smes can be calculated as follow: 21 2smes e l i (1) where esmes is stored energy, l is the inductance of the smes and i is the smes current. the capacity of the smes is depends on charging and discharging duration and the application of the smes. in this paper smes with 0.95mj capacity is used to evaluate its impacts on the lvrt and hvrt capability of the dfig. fig. 2. the smes topology the control of the vsc-based smes is based on [19]. the proportional integral (pi) controllers define the d-and q-axis reference currents by means of the difference between the dc link voltage and reference voltage, and the difference between terminal voltage and reference voltage, respectively. by converting dand q-axis voltages which are produced by the difference between reference d-q axes currents and their detected values, the reference signal for vsc is created. by comparing the reference signal which is converted to threephase sinusoidal wave with the triangular carrier signal, the pwm signal is produced for igbt switching. the control system is shown in figure 3. the dc-dc chopper is used to charge or discharge the superconducting coil. the dc-dc engineering, technology & applied science research vol. 7, no. 6, 2017, 2118-2123 2120 www.etasr.com safaei et al.: enhancing the hvrt and lvrt capabilities of dfig-based wind turbine in an … chopper is controlled to supply positive or negative voltage to superconducting coil in order to charge or discharge the stored energy. therefore, the superconducting coil is charged or discharged by regulating the average voltage across the coil which is determined by the duty cycle of the dc-dc chopper. then the reference signal is compared with the triangular signal to generate the pwm gate signals for the igbt of the chopper. 6  0.5 fig. 3. the control system of the vsc and dc-dc chopper iii. problem statement lvrt and hvrt requirements for wts define the disconnecting instruction of wt from the network. during the occurrence of a fault, the wts are required to remain connected for a specific amount of time before being allowed to disconnect. a curve rule for lvrt under the u.k. grid code can be found in [20]. according to it, for example, the wt should stay connected to the grid after the terminal voltage reaches 0% of nominal voltage within 0.14s and also it should stay connected to the grid after the terminal voltage reaches 80% of nominal voltage within 2.5s. in recent years, different countries such as spain, australia, denmark and usa have forced demanding voltage-time profiles for voltage swell situations. voltage swells could be initiated by unbalanced faults, large loads switching off and large capacitor banks energizing which may have different durations and magnitudes. this requirement is usually referred to as high voltage ridethrough (hvrt) capability. the hvrt capability curve for australia can be found in [21]. according to it, the allowed voltage is 1.3 pu for a duration of 0.06s [21]. as noted earlier, wts must stay connected to the power system in case of voltage dip and voltage swell, in compliance with lvrt and hvrt capability. however, dfig-based wts are very sensitive to grid voltage variations. therefore, the dfig rotor overcurrent caused by voltage dip may damage the rotor side converter and dc link capacitor if no protection scheme is taken into consideration. also, dfig rotor surge current caused by voltage swell may damage the dfig converters. therefore, to protect the dfig from the grid voltage dip and voltage swell events, low voltage ride through (lvrt) and high voltage ride through (hvrt) schemes are fundamentally required. iv. simulation results the islanded microgrid shown in figure 4, is simulated in pscad/emtdc to validate the effectiveness of installing the smes on the dfig lvrt and hvrt capability. the test system under study is based on [1] and consists of a 1 mw dfig wind turbine, one pv system and one synchronous generator. the voltage of the microgrid is 25 kv and the details of the system are stated in table i. fig. 4. microgrid model table i. microgrid parameters parameter value tr-1 0.69-25 kv, 2 mva tr-2 5.75-25 kv, 7 mva tr-3 0.23-25 kv, 2 mva frequency 60 hz dg-1 1 mw dg-2 5 mw dg-3 1 mw load-1 2 mw load 3, 5 1.5 mw load 4, 2 1 mw lines (20 km each) r=0.413 ω/km, l= 3.32e–3 h/km a. fault event in this section, simulation studies are carried out to evaluate the effectiveness of applying smes to enhance the dfig lvrt capability in an islanded microgrid. a three-phase fault is applied at t=10 s for a duration of 0.2 s at the dfig terminal. the dfig responses without the smes are compared with the case with the smes as shown in figure 5 and figure 6. figure 5, shows the dfig rotor current and crowbar operation with and without smes. it is obvious that, without smes, the dfig rotor current increases during fault condition as shown in figure 5(a). as noted, by increasing the dfig rotor current, the crowbar protection is activated. the number of crowbar operation in this case is about 47 times (figure 5(b)). figure 5(c) and figure 5(d), show the dfig rotor current and crowbar operation with smes. it is clear that by applying the smes, the rotor current and crowbar operation is decreased. in this engineering, technology & applied science research vol. 7, no. 6, 2017, 2118-2123 2121 www.etasr.com safaei et al.: enhancing the hvrt and lvrt capabilities of dfig-based wind turbine in an … case, the number of crowbar operations is about 34 times which lead to increase the dfig controllability during fault condition. 9 9.5 10 10.5 11 11.5 12 -3 -2 -1 0 1 2 3 time (sec) c ur re nt (p u) 9.6 9.7 9.8 9.9 10 10.1 10.2 10.3 10.4 0 0.2 0.4 0.6 0.8 1 1.2 time (sec) c ro w ba r o pe ra tio n 9 9.5 10 10.5 11 11.5 12 -3 -2 -1 0 1 2 3 time (sec) c ur re nt (p u) 9.6 9.7 9.8 9.9 10 10.1 10.2 10.3 10.4 0 0.2 0.4 0.6 0.8 1 1.2 time (sec) c ro w ba r o pe ra tio n (d) fig. 5. dfig responses to three-phase fault: a) rotor current without smes, b) crowbar operation without smes, c) rotor current with smes, d) crowbar operation with smes. figure 6(a), shows the dfig active power with and without the smes. the active power of dfig is decreased to zero during fault condition without the smes which causes to accelerate the rotor and increase the rotor speed accordingly. by applying the smes, it injects active power to the microgrid. so the dfig active power is increased to about 0.2 pu during fault condition. the absorbed reactive power of the dfig is about 0.22 pu at the fault clearance instant without the smes as shown in figure 6(b). by applying the smes, it injects reactive power to the microgrid during fault condition. therefore, the dfig absorbed reactive power is decreased to 0.13 pu which reduces the dfig terminal voltage drop and enhances the dfig lvrt capability. the dfig terminal voltage is shown in figure 6(c). it is clear that, the terminal voltage is reduced to zero during the three-phase fault without the smes. after connecting the smes, the voltage will drop to only 0.3 pu because the smes injects reactive power to the microgrid during fault condition. the simulation results show that by applying the smes, the crowbar operation of the dfig and the absorbed reactive power are decreased during fault condition. 9.6 9.8 10 10.2 10.4 10.6 10.8 -0.5 0 0.5 1 1.5 time (sec) a ct iv e po w er (p u) without smes with smes 9.6 9.8 10 10.2 10.4 10.6 10.8 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 time (sec) r ea ct iv e po w er (p u) without smes with smes 10.2 10.3 10.4 -0.2 -0.1 0 0.1 9.6 9.8 10 10.2 10.4 10.6 10.8 -1 -0.5 0 0.5 1 1.5 2 time (sec) v ol ta ge (p u) 9.9 10 10.1 10.2 10.3 0 0.2 0.4 without smes with smes fig. 6. dfig responses to three-phase fault with and without the smes: a) active power, b) reactive power, c) terminal voltage. so, the performance of the dfig is enhanced and the lvrt capability of the dfig is improved during fault condition in the islanded microgrid. therefore, effectiveness of the proposed approach is validated. figure 7, shows the transient responses of the smes during three-phase fault. before fault occurrence, the smes current is held constant at its rated value and the smes is in the standby mode and the maximum energy (0.95 mj) is stored within the smes. as fault occurrence at t=10s, discharging mode will take place and the smes current is decreased. in this condition the stored energy in the smes is being supplied to the microgrid. after fault clearance at t=10.2s, charging mode will take place and the smes current is increased. the energy is transferred from the microgrid to the smes until the maximum capacity of the smes is reached. so, the smes has a significant role to improve dfig lvrt capability during fault condition (a) (b) (c) (d) (a) (b) (c) engineering, technology & applied science research vol. 7, no. 6, 2017, 2118-2123 2122 www.etasr.com safaei et al.: enhancing the hvrt and lvrt capabilities of dfig-based wind turbine in an … 9.6 9.8 10 10.2 10.4 10.6 10.8 11 11.2 11.4 0.36 0.38 0.4 0.42 0.44 0.46 0.48 0.5 time (sec) c ur re nt (k a ) 9.6 9.8 10 10.2 10.4 10.6 10.8 11 11.2 11.4 0.7 0.8 0.9 1 1.1 1.2 time (sec) e ne rg y (m j) fig. 7. smes responses to three-phase fault: a) current, b) stored energy. b. voltage swell event in this section a voltage swell is applied to investigate the effectiveness of installing smes on the dfig hvrt capability. the voltage swell is applied by increasing the microgrid voltage to 1.25 pu at t=10s and lasts for 0.05s. the dfig responses to voltage swell event with and without the smes are shown in figure 8. figures 8(a) and 8(b), show the dfig terminal voltage without and with smes, respectively. by applying the smes, it absorbs surplus energy from the microgrid during voltage swell events. so, the dfig terminal voltage is decreased from 1.25 pu to 1.17 pu. the active power of the dfig is decreased to zero during voltage swell without the smes as depicted in figure 8(c). by applying the smes, fluctuation of dfig active power is decreased. therefore, the dfig active power is increased from zero to 0.1 pu with the smes. so, the stability of the dfig is improved during voltage swell event by installing the smes. figure 8(d), shows the dfig reactive power with and without the smes. the dfig will absorb reactive power about 0.28 pu without the smes. by installing the smes unit, the amount of absorbed reactive power is decreased from 0.28 pu to 0.18 pu. so, the voltage stability of the dfig is enhanced during voltage swell event by applying the smes. therefore, simulation results confirm that by applying the smes, the dfig hvrt capability is improved during voltage swell events. the transient responses of the smes during voltage swell event are shown in figure 11. before voltage swell occurrence, the smes is in the standby and the maximum energy (0.95 mj) is stored within the smes. as the voltage swell occur, the smes current is increased and charging mode will happen. in this condition the energy is transferred from the microgrid to the smes until the maximum capacity of the smes is reached (1.05 mj to allow for power modulation during voltage swell event). as the voltage swell clears at t=10.05s, discharging mode will take place and the smes current is decreased. so, the stored energy within the smes is transferred to the microgrid until the smes nominal energy capacity (0.95mj) is reached. therefore, the smes absorbs surplus energy from the microgrid and the dfig hvrt capability is enhanced. 9.6 9.8 10 10.2 10.4 10.6 10.8 0.8 0.9 1 1.1 1.2 1.3 1.4 time (sec) v ol ta ge (p u) 9.6 9.8 10 10.2 10.4 10.6 10.8 0.8 0.9 1 1.1 1.2 1.3 1.4 time (sec) v ol ta ge (p u) 9.6 9.8 10 10.2 10.4 10.6 10.8 -0.5 0 0.5 1 1.5 time (sec) a ct iv e po w er (p u) without smes with smes 9.6 9.8 10 10.2 10.4 10.6 10.8 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 time (sec) r ea ct iv e po w er (p u) without smes with smes 9.95 10 10.05 10.1 10.15 -0.3 -0.2 -0.1 0 0.1 fig. 8. dfig responses to voltage swell event with and without smes: a) terminal voltage without smes, b) terminal voltage with smes, c) active power, d) reactive power. v. conclusion in this paper, a new application of the smes is proposed to enhance the lvrt and hvrt capabilities of a dfig-based wind turbine in the islanded microgrid. the simulation results illustrate that dfig transient responses are improved and the dfig lvrt and hvrt capabilities are enhanced during faults and voltage swells. due to the recent development of high temperature superconductors, the proposed scheme is simple and easy to implement. also, the proposed approach has high response speed and high rotor current limitation capability. (a) (a) (b) (b) (c) (d) engineering, technology & applied science research vol. 7, no. 6, 2017, 2118-2123 2123 www.etasr.com safaei et al.: enhancing the hvrt and lvrt capabilities of dfig-based wind turbine in an … 9.6 9.8 10 10.2 10.4 10.6 10.8 11 11.2 11.4 0.42 0.425 0.43 0.435 0.44 0.445 0.45 0.455 0.46 time (sec) c ur re nt (k a ) 9.6 9.8 10 10.2 10.4 10.6 10.8 11 11.2 11.4 0.8 0.85 0.9 0.95 1 1.05 1.1 time (sec) e ne rg y (m j) fig. 9. smes responses to voltage swell event: a) current, b) stored energy. references [1] y. xu, w. zhang, g. hug, s. kar, z. li, “cooperative control of distributed energy storage systems in a microgrid”, ieee transactions on smart grid, vol. 6, pp. 238-248, 2015 [2] global wind energy council, global wind report 2016 – annual market update, available at: http://gwec.net/publications/global-windreport-2/global-wind-report-2016 [3] s. yang, t. zhou, l. chang, z. xie, x. zhang, “analytical method for dfig transients during voltage dips”, ieee transactions on power electronics, vol. 32, pp. 6863-6881, 2017 [4] z. xing, q. tingyu, x. zhen, c. renxian, “dynamic analysis of doubly fed induction generator during symmetrical voltage swells”, second international conference on mechanic automation and control engineering (mace), pp. 1245-1248, 2011 [5] c. feltes, s. engelhardt, j. kretschmann, j. fortmann, f. koch, i. erlich, “high voltage ride-through of dfig-based wind turbines”, 2008 ieee power and energy society general meeting conversion and delivery of electrical energy in the 21st century, pp. 1-8, 2008 [6] a. f. abdou, a. abu-siada, h. r. pota, “improving the low voltage ride through of doubly fed induction generator during intermittent voltage source converter faults”, journal of renewable and sustainable energy, vol. 5, no. 4, pp. 043110, 2013 [7] l. chen, c. deng, f. zheng, s. li, y. liu, y. liao, “fault ride-through capability enhancement of dfig-based wind turbine with a fluxcoupling-type sfcl employed at different locations”, ieee transactions on applied superconductivity, vol. 25, no. 3, pp. 1-5, 2015 [8] w. guo, l. xiao, s. dai, x. xu, y. li, y. wang, “evaluation of the performance of btfcls for enhancing lvrt capability of dfig”, ieee transactions on power electronics, vol. 30, no. 7, pp. 3623-3637, 2015 [9] a. o. ibrahim, t. h. nguyen, d. c. lee, s. c. kim, “a fault ridethrough technique of dfig wind turbine systems using dynamic voltage restorers”, ieee transactions on energy conversion, vol. 26, no. 3, pp. 871-882, 2011 [10] m. molinas, j. a. suul, t. undeland, “low voltage ride through of wind farms with cage generators: statcom versus svc”, ieee transactions on power electronics, vol. 23, no. 3, pp. 1104-1117, 2008 [11] t. kinjo, t. senjyu, n. urasaki, h. fujita, “terminal-voltage and output-power regulation of wind-turbine generator by series and parallel compensation using smes”, iee proceedings generation, transmission and distribution, vol. 153, no. 3, pp. 276-282, 2006 [12] i. ngamroo, s. vachirasricirikul, “coordinated control of optimized sfcl and smes for improvement of power system transient stability”, ieee transactions on applied superconductivity, vol. 22, no. 3, pp. 5600805-5600805, 2012 [13] q. huang, x. zou, d. zhu, y. kang, “scaled current tracking control for doubly fed induction generator to ride-through serious grid faults”, ieee transactions on power electronics, vol. 31, no. 3, pp. 2150-2165, 2016 [14] r. zhu, z. chen, x. wu, f. deng, “virtual damping flux-based lvrt control for dfig-based wind turbine”, ieee transactions on energy conversion, vol. 30, no. 2, pp. 714-725, 2015 [15] n. h. saad, a. a. sattar, a. e.-a. m. mansour, “low voltage ride through of doubly-fed induction generator connected to the grid using sliding mode control strategy”, renewable energy, vol. 80, pp. 583594, 2015 [16] h. geng, c. liu, g. yang, “lvrt capability of dfig-based wecs under asymmetrical grid fault condition”, ieee transactions on industrial electronics, vol. 60, no. 6, pp. 2495-2509, 2013 [17] y. ren, w.zhang, “a novel control strategy of an active crowbar for dfig-based wind turbine during grid faults”, ieee international conference on electric machines & drives conference (iemdc), pp. 1137-1142, 2011 [18] m. h. ali, b. wu, r. a. dougal, “an overview of smes applications in power and energy systems”, ieee transactions on sustainable energy, vol. 1, no. 1, pp. 38-47, 2010 [19] t. asao, r. takahashi, t. murata, j. tamura, m. kubo, y. matsamura, a. kuwayama, t. matsumoto, “evaluation method of power rating and energy capacity of superconducting magnetic energy storage system for output smoothing control of wind farm”, 18th international conference on electrical machines, vilamoura, pp. 1-6, 2008 [20] h. m. el-helw, s. b. tennakoon, “evaluation of the suitability of a fixed speed wind turbine for large scale wind farms considering the new uk grid code”, renewable energy, vol. 33, no. 1, pp. 1-12, 2008 [21] m. mohseni, s. m. islam, “review of international grid codes for wind power integration: diversity, technology and a case for global standard”, renewable and sustainable energy reviews, vol. 16, no. 6, pp. 38763890, 2012 (a) (b) engineering, technology & applied science research vol. 8, no. 2, 2018, 2770-2774 2770 www.etasr.com sohu et al.: significant mitigation measures for critical factors of cost overrun in highway projects … significant mitigation measures for critical factors of cost overrun in highway projects of pakistan samiullah sohu faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia sohoosamiullah@gmail.com abd halid abdullah faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia abdhalid@uthm.edu.my sasitharan nagapan faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia sasitharan@uthm.edu.my ashfaque ahmed jhatial faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia. aajhatial@hotmail.com kaleem ullah faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia gf150051@siswa.uthm.edu.my imtiaz ali bhatti faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia gf170069@siswa.uthm.edu.my abstract—stakeholders of the construction industry and academia are often facing problems of cost overrun. it has been observed that many constructions of highway projects are not completed at the approved cost due to certain factors. the objective of this research is to identify the cost overrun critical factors involved in highway projects with their significant mitigation measures. in this regard, literature review helped to identify 64 factors of cost overrun. based on these 64 common factors, a preliminary survey was carried out among 30 selected respondents of highway projects to identify the critical factors of cost overrun and its possible mitigation measures. results of the preliminary study reported 8 critical factors and 42 possible mitigation measures for the identified factors. another questionnaire was established on the findings of the preliminary survey and was distributed among 350 stakeholders of highway projects to identify the significant mitigation measures of finding critical factors of cost overrun. in total, 8 significant mitigation measures were identified as causative and critical factors of cost overrun. the findings of this research would be helpful for the construction practitioners who are dealing with cost overrun issues in the highway projects of pakistan. keywords-mitigation measures; critical factors; cost overrun; highway projects; pakistan i. introduction a project is successful when it is accomplished in the agreed cost, time fame and standard quality [1]. the definition of cost overrun according to [2] is “project is not successfully completed in the approved cost” [3]. cost overrun is a serious issue for both developed and developing countries like pakistan. pakistan construction industry is facing this issue for many decades and many projects are facing cost overrun exceeding beyond 100% of the initial cost [4]. according to [5], cost overrun has a draining effect on project parties including client, contractor and consultant. cost overrun creates issues related to litigation, cash flow, mistrust and arbitration in construction projects. according to [6], the construction projects do not perform as estimated in terms of costs. they reported that almost 9 out of 10 construction projects fall victim to significant cost overrun. the current literature review was conducted to find out studies supporting the impact of cost overrun on construction projects. not a single study has been carried to identify the mitigation measures of cost overrun in construction of highway projects in state of sindh, pakistan. the main aim of this research is to find out the significant mitigation measures for causative and critical factors of cost overrun in highway projects of pakistan particularly in the province of sindh. ii. literature review a. cost overrun many studies have been conducted on the identification of factors of project cost overrun. by carrying a survey approach, authors in [7] found the significant factors for cost overrun in indian construction projects. findings of their survey show that top significant factors of cost overrun in construction projects are high charges of transportation, change in materials specifications, escalation of materials price, lack of communication in the design phase, rework and changes in money exchange rates. authors in [8] identified the causes of cost overrun were bad weather impact, inflation, schedule delay and change in scope, the pressure of local government, strikes and technical faults. another survey was conducted among construction stakeholders in construction projects of pakistan [9]. results showed that significant factors which cause cost ov loc ina con qu eng cos sch ina app stu 15 res cos sho del un con au ov spe del du b. of mi pla pla fac (co res reg fac con int ma of and    div hel ba and ide engineerin www.etasr errun were th cation of a p accurate proje nstruction pro estionnaire wa gineers. the s st overrun wer hedule delay, accurate time proval of desi udy was carrie 0 construction sults of the sur st overrun na ortage of mate lay in work b availability o nstruction, lab uthors in [12] r errun in con ecifications by lay payment p e to contractor mitigation m a research w cost overrun f itigation meas anning of proj anning should ctor), appoi ontractor’s si sources in the gular coordina ctor). in [14] ntractors wer terviews. stu anagement, ap proper method d clear commu the objective to find out lead to cost o to determine critical factor to find out s i to attain the vided into tw lped us find t ased on the id d distributed entify the mos ng, technology r.com he unavailabi project, securi ect estimation. ojects of bah as developed survey outcom re construction , poor super e and cost e gn and drawin ed out by cond n industry ex rvey identified amely market erials, fluctuat by subcontract of skilled lab bor disputes an recognized the nstruction proj y clients, chang progress, chan r mistakes. measures was carried ou factors in mal sures for cost ect (project m be adopted (d intment of ite managem e construction ation between mitigation me re identified dy findings ppointment of d of constructi unication betw iii. resea es of this resea the most crit overrun in high e the possible rs of cost over significant miti iv. researc main objectiv wo stages. in the 64 most c entified factor among 30 e st critical facto y & applied sci sohu et al.: ility of suitab ity issues, low factors caus hrain were s and dispersed mes showed th n mistakes, ma rvision, poor estimates, del ngs at the time ducting a ques xperts in afg d the top ten s inflation, corr tion in price of tors, lack of p or, changes nd inadequate e major factor jects were ch ges in design d nge in the mat ut to identify m aysian constru t overrun fact management rel design and do experienced ment), develo n industry (lab n parties (com easures of cos by conducti were: prope experienced s ion, coordinati ween parties. arch objectiv arch are: tical and caus hway/road pro mitigation me rrun. igation measur ch methodol ves of this stu the first stage common facto rs a questionn experts of hi ors. after anal ience research : significant mi ble contractor w productivity ing cost overr studied in [1 d among 103 e hat major fact any design cha site manage lay in prepar e of tender. an stionnaire surv ghanistan [11] ignificant fact rruption in pro f selected mat roject coordin in drawing d number of wo s which cause hanges in ma during constru terial prices, re mitigation mea uction industry tors were: str lated factor), p cumentation r d sub-contr opment of h bor related fa mmunication r st overrun for ng semi-struc er supervision sub-contractor ion between p ves ative factors w ojects. easures of iden res. logy udy, this resea e, literature r ors of cost ov naire was deve ighway projec lysis of survey h v mitigation measu rs, the y and run in 0]. a expert tors of anges, ement, ration, nother vey on ]. the tors of ojects, terials, nation, during orkers. ed cost aterial uction, ework asures y [13]. rategic proper related ractors human actor), related small ctured n and rs, use arties, which ntified arch is review verrun. eloped cts to y data, a to a s the 30 for que surv gen the proj dete eac var imp resp res crit que que reje the vol. 8, no. 2, 20 ures for critica otal of 8 critic semi-structure 8 found critic experts for d the identified estionnaire wa vey. the surv neral informati mitigation m ojects. a fiv ermination of ch critical fact ried from 1 portant”. the pondents of h spondents wer tical factor of estionnaires we estionnaires w ected. a total e total valid re table i. type of o c con con t fig. 1. fig. 2. 018, 2770-2774 al factors of co cal factors wer ed questionnair cal factors and determination d factors. in as designed on vey consisted ion of the res measures for c ve-point like f significance or of cost ove for “not im questionnair highway proje re asked to ra f cost overrun ere received b were received l of 259 valid esponse was 74 summary of organization client nsultant ntractors total summary of status summary ost overrun in h re identified ou re was design d was distribute of possible m the second s n the findings d of two parts spondents whi cost overrun f ert scale wa level for mitig errun. the val mportant” to re was distrib ects of sindh ank each miti n. as shown back in a 3 mo with incompl d questionnair 4%. f questionnaire distributed q 6 1 1 3 f questionnaire dis y of distributed qu 2771 highway proje ut of the initia ned on the bas ed among the mitigation mea stage, a struc of the prelim s. part a incl ile part b incl factors in high as used for gation measur lues of likert 5 for “extre buted among h region (tab igation measu in figure 2, nth time perio lete data and res were anal e distribution questionnaires 61 101 188 350 stribution uestionnaires ects … al 64. sis of same asures ctured minary luded luded hway r the res of scale emely 350 le i). ure of , 281 od. 22 were lyzed. engineering, technology & applied science research vol. 8, no. 2, 2018, 2770-2774 2772 www.etasr.com sohu et al.: significant mitigation measures for critical factors of cost overrun in highway projects … v. reliability test the reliability test was carried out to check consistency and stability of collected data. it was conducted by cronbach's alpha method, which is mostly used by researchers. the reliability of data is considered low when the value of cronbach's alpha is less than 0.3 which means data is not acceptable and if the value of cronbach's alpha is more than 0.7 then the data would be considered acceptable and reliable [15]. in this study, spss v22 was used to calculate the value of cronbach's alpha, which gave a result of 0.837. this indicated that the collected data is reliable and acceptable. vi. results and discussion in the first survey, total 8 critical factors for cost overrun were identified and 43 possible mitigation measures were determined. there were several mitigation measures found to control each critical factor. however, the level of effectiveness for each critical factor was different. in the final survey, the findings of the significant mitigation measures of critical factors for cost overrun are shown in table ii. these measures are listed in ascending order according to their calculated mean values. in table iii the most significant mitigation measures are listed. these measures with highest mean value were selected as significant mitigation measures for each critical factor of cost overrun. table ii. mitigation measures of critical factors of cost overrun critical factor mitigation measures mean value critical factor mitigation measures mean value 1 . d el a y i n p ro ce ss o f p a y m en t b y c li en t 1. sufficient funds for project should be allocated. 4.529 2 . in a d eq u a te p la n n in g 1. client should make strategic planning before starting of project. 4.666 2. many changes in regulatory authority should be avoided. 4.000 2. the planning committee should visit project site before tendering. 4.475 3. forex restrict ration should be avoided. 3.529 3. competent staff should be appointed by the client. 3.936 4. client should stop influencing the projects politically. 3.508 4. cost of project should be estimated properly. 3.818 5. payment to contractor should be expedited by client 3.372 5.effective planning should be adopted for project. 3.598 6. the time duration of the project should be estimated properly. 3.460 3 . c li en t in te rf er en ce 1.favoured contractor should not be appointed by client. 4.691 4 . p o o r c o n tr a ct m a n a g em en t 1. contracts should be awarded on merit basis 4.607 2. approvals of work should be on time. 4.431 2. contract document should be clear to understand. 4.176 3. transfer of key posts in project should be avoided in top management. 4.004 3. well reputed and well-experienced consultant should be hired for the project. 3.558 4. political influence should be avoided by client. 3.717 4.contract documents should be well detailed. 3.333 5.policies of project should not be revised on basis of favouritism. 3.686 5. experienced staff should be employed for making comprehensive contract document 3.201 5 . d el a y i n d ec is io n m a k in g 1. proper decisions should be made on time. 4.356 6 . l a w s a n d r eg u la ti o n s o f f ra m ew o rk 1.general policies for all project should be adopted by client. 4.779 2. the competent and qualified team should be employed. 4.225 2. laws and regulations should be clear so that contractor can understand easily. 4.117 3. favouritism and nepotism should be avoided. 3.862 3. laws, regulations, and policies should be revised every year. 3.637 4.communication between parties should continue to take proper decisions. 3.759 4. law and regulations of different departments also be understood before starting of project. 3.411 5. client should arrange frequent meetings. 3.593 7 . c h a n g e in s co p e o f p ro je ct 1. proper assessment of construction site should be done. 4.150 8 . f in a n ci a l d if fi cu lt ie s f a ce d b y c li en t 1. adequate funds should be kept for each running project. 4.740 2. climatic conditions and environmental impacts of the site should be foreseen. 4.004 2 the donor should start a project on the availability of funds. 4.529 3. accessibility of different resources should be inspected. 3.710 3. funds should not be transferred to any other project. 4.009 4. political influence should be avoided 3.558 4. finance should allocate funds on time to the client. 3.764 5. the client should release funds to contractors as per work was done at the site. 3.436 a. delay in process of payment by owner the factor named “delay in process of payment by the owner” had five possible mitigation measures suggested by experts. among these five mitigation measures, the “sufficient allocation of each project” was found significant having maximum mean value of 4.53 contractor plays an important role in the completion of the project but unfortunately contractors always faces the problem of payment from the client. many projects have suffered from cost overrun due to delay in process of payment by the client [16]. b. poor planning the second factor “poor planning” had six possible mitigation measures suggested by experienced respondents. “client should make strategic planning before starting of project” is ranked as most significant with mean value of 4.67. engineering, technology & applied science research vol. 8, no. 2, 2018, 2770-2774 2773 www.etasr.com sohu et al.: significant mitigation measures for critical factors of cost overrun in highway projects … adequate planning is necessary for each project but unfortunately many projects have faced the problem of cost overrun due to inadequate planning in project by client [17]. table iii. significant mitigation measures for critical factors of cost overrun s. no. critical factor significant mitigation measures 01 delay in process of payment by owner sufficient funds for project should be allocated. 02 poor planning client should make strategic planning before starting of project 03 owner interference favoured contractor should not be appointed by client. 04 inadequate contract management contracts should be awarded on merit basis 05 delay in decisions proper decisions should be made on time 06 regulations of framework laws and regulations of framework 07 sudden changes in project scope proper assessment of construction site should be done 08 financial issues faced by client adequate funds should be kept for each running project c. owner interference five possible mitigation measures were recommended by experts for this factor of cost overrun. from these five measures “favored contractor should not be appointed by client” was observed as the most significant measure with mean value of 4.96. client interference which includes appointment of favored contractor, change in administrative posts, or changes in design on favoritism basis, leads to cost overrun in projects [18]. d. inadequate contract management for this factor highway experts advised five controlling measures. “contracts should be awarded on merit basis” mitigation measure was found most significant with mean value of 4.61. contract document should be clear to all stakeholders of the project and easy to understand. it has been observed that projects faced cost overrun because of poor contract management [19]. e. delay in descisions five mitigation measures were proposed by highway experts for this factor of cost overrun. among these “proper decisions should be made on time” had mean value of 4.36 and was identified as the significant one. most of the decisions are taken by client and consultants and delay may result in suspension of construction activities. delay in taking decisions may cause cost overrun in construction projects [20]. f. regulations of framework four mitigation measures were advised by highway experts for this factor. “general policies on all projects should be adopted by the client” was the most significant measure with mean value of 4.78. unclear policies, laws and regulations related to project may arise disputes during execution process, which could be another cause of cost overrun in construction projects [21]. g. sudden changes in project scope four potential mitigation measures were suggested by highly experienced respondents for this factor of cost overrun. out of four mitigation measures, “proper assessment of construction site should be done” was found most significant with mean value of 4.15. change in scope refers to bringing in activities during execution of the project which were never planned. this is commonly due to sudden demands from the client side. changes in the form of reduction, addition or modification, can consequentially effect on the overall cost of the project. changes in scope can influence the prime cost of materials and also lead the project in cost overrun [22]. h. financial issues faced by client experts of highway recommended five possible controlling measures for this factor. after analysis “adequate funds should be kept for each running project” was identified as the most significant mitigation measure with mean value of 4.74. availability of funds should be managed by client for each project. unfortunately, it has been observed that, in many construction projects the client has insufficient financial support which causes cost overrun in the project [23]. vii. conclusion in this research, an attempt was made to identify critical factors of cost overrun in highway projects in pakistan, particularly in sindh province. the study also helped in the determination of significant mitigation measures for these identified factors. based on the results of this research, the following recommendations are made to mitigate the critical factors of cost overrun in highway projects. 1. sufficient funds for the project should be allocated for successful completion of the project. 2. the client should make a strategic plan before initiating any highway project. 3. political influence should be avoided by the client in appointment of a contractor. 4. contract document should be clear enough to be understood by all parties involved. 5. communication between parties should be continuous. 6. general policies on all projects should be adopted by client. 7. proper assessment of construction site should be done by the client. 8. adequate funds should be kept for each running project. references [1] n. ejaz, i. ali, m. f. tahir, “assessment of delays and cost overruns during construction projects in pakistan”, available at: http://dl.lib.mrt.ac.lk/handle/123/9431, 2013 [2] i. avotos, “cost-relevance analysis for overrun control”, international journal of project management, vol. 1, no. 3, pp. 142–148, 1983 [3] n. azhar, r. u. farooqui, s. m. ahmed, “cost overrun factors in construction industry of pakistan”, first international conference on construction in developing countries, advancing and integrating engineering, technology & applied science research vol. 8, no. 2, 2018, 2770-2774 2774 www.etasr.com sohu et al.: significant mitigation measures for critical factors of cost overrun in highway projects … construction education, research & practice, karachi,, pakistan, pp. 499–508, august 4-5, 2008 [4] i. abdul rahman, a. h. memon, a. azis, a. asmi, n. h. abdullah, “modeling causes of cost overrun in large construction projects with partial least square-sem approach: contractor's perspective”, research journal of applied sciences, engineering and technology, vol. 5, no. 6, pp. 1963–1972, 2013 [5] a. alhomidan, “factors affecting cost overrun in road construction projects in saudi arabia”, international journal of civil & environmental engineering, vol. 13, no. 03, 2013 [6] a. c. devi, k. ananthanarayanan, “factors influencing cost over-run in indian construction projects,” matec web of conferences, vol. 120, p. 02023, 2017 [7] s. shanmugapriya, k. subramanian, “investigation of significant factors influencing time and cost overruns in indian construction projects”, international journal of emerging technology and advanced engineering, vol. 3, no. 10, pp. 734-740, 2013 [8] c. kaliba, m. muya, k. mumba, “cost escalation and schedule delays in road construction projects in zambia”, international journal of project management, vol. 27, no. 5, pp. 522-531, 2009 [9] i. zafar, t. yousaf, s. ahmed, “evaluation of risk factors causing cost overrun in road projects in terrorism affected areas pakistan–a case study”, ksce journal of civil engineering, vol. 20, no. 5, pp. 16131620, 2016 [10] h. a. m. abusafiya, s. m. a. suliman, “causes and effects of cost overrun on construction project in bahrain: part i (ranking of cost overrun factors and risk mapping)”, modern applied science, vol. 11, no. 7, pp. 20-27, 2017 [11] s. ahady, s. gupta, r. k. malik ,“a study of the causes of cost overrun in construction industry in afghanistan”, international journal of engineering development and research, vol. 5, no. 3, pp. 978–985, 2017 [12] p. jadhav, d. desai, a. gupta, “analysis of construction cost overrun causes-contractor’s view”, imperial journal of interdisciplinary research, vol. 2, no. 8, pp. 908–910, 2016 [13] a. a. ade, h. m. aftab, a. ismail, t. a. ahmad, “controlling cost overrun factors in construction projects in malaysia”, journal of applied science, engineering and technology, vol. 5, no. 8, pp. 2621–2629, 2013 [14] j. a. b. awolesi, j. k. fabi, o. a. akinseinde, “assessment of contractors’ mitigating measures for cost overrun of building projects in south-western nigeria”, journal of sustainable development, vol. 8, no. 9, pp. 139-146, 2015 [15] l. xin, w. rong, “survey research on relationship among service failure, service recovery and customer satisfaction”, international conference on management science and engineering, harbin, china, pp. 1121-1126, august 20-22, 2007 [16] s. sohu, a. h. abdullah, s. nagapan, a. fattah, k. ullah, k. kumar, “contractors perspective for critical factors of cost overrun in highway projects of sindh, pakistan”, aip conference proceedings, vol. 1892, no. 1, p. 080002, 2017 [17] a. senouci, a. a. ismail, n. eldin, “time and cost overrun in public construction projects in qatar procedia engineering, vol. 164, pp. 368– 375, 2016 [18] i. ismail, “risk assessment of time and cost overrun factors throughout construction project lifecycle”, phd thesis, universiti tun hussein onn malaysia, 2014 [19] z. shehu, i. r. endut, a. akintoye, “factors contributing to project time and hence cost overrun in the malaysian construction industry”, journal of financial management of property and construction, vol. 19, no. 1, pp. 55–75, 2014 [20] a. ambituuni, “five causes of project delay and cost overrun, and their mitigation measures”, msc thesis, the robert gordon university, 2011 [21] j. k. larsen, g. q. shen, s. m. lindhard, t. d. brunoe, “factors affecting schedule delay, cost overrun, and quality level in public construction projects”, journal of management in engineering, vol. 32, no. 1, p. 04015032, 2015 [22] r. o. asiedu, e. adaku, d. g. owusu-manu, “beyond the causes– rethinking mitigating measures to avert cost and time overruns in construction projects”, construction innovation, vol. 17, no. 3, pp. 363380, 2017 [23] a. h. memon, i. a. rahman, m. r. abdullah, a. a. a. azis, “factors affecting construction cost performance in project management projects: case of mara large projects”, international journal of civil engineering and built environment, vol. 1, no. 1, pp. 30-35, 2014 engineering, technology & applied science research vol. 8, no. 1, 2018, 2379-2384 2379 www.etasr.com el-morsy: wear analysis of a ti-5al-3v-2.5fe alloy using a factorial design approach and fractal … wear analysis of a ti-5al-3v-2.5fe alloy using a factorial design approach and fractal geometry abdel-wahab el-morsy mechanical engineering department faculty of engineering-rabigh king abdulaziz university saudi arabia mechanical engineering department faculty of engineering-helwan helwan university, cairo, egypt aalmursi@kau.edu.sa abstract—this paper describes the application of the full factorial experimental design technique to confirm the significance of the factors affecting the wear behavior of a recycled ti-5al-3v-2.5fe alloy with a minimum number of experiments. the fractal theory has been used to describe the worn surface state and to investigate the relationship between the fractal dimensions and the surface morphology. the experiments of the sliding wear have been performed under stresses in the range of 1-5 mpa and within sliding velocities range of 0.2–2.0 m/s. morphology of the worn surfaces investigations has been undertaken using a scanning electron microscope. from the analysis of variance and the nonlinear regression model, the results show that the applied stress has a higher contribution to the wear rate than the sliding velocity. keywords-dry wear; experimental design technique; ti-alloy; fractal geometry technique i. introduction titanium alloys are extensively used in critical applications such as biomedical and aerospace applications due to their attractive combination of high strength, low density, and good corrosion resistance [1-2]. for titanium alloys to be used in applications where wear resistance is largely concerned, such as orthopedic prostheses, sufficient wear resistance is required [3]. however, titanium alloys are well known to possess disreputable poor wear property [4-5]. when titanium products are manufactured considerable amounts of machining waste in the form of chips and discards are produced as an outcome. this certainly adds to the already high cost of titanium manufacturing. to add value to titanium manufacturing and reduce the cost, this scrap can be recycled by remelting, whereby some of the titanium is recovered and reutilized in production processes [6-9]. attention has grown in the wear characterization of titanium alloys in the past decades [10-14]. the rate of material loss or wear rate can be quantified. however, the description of the material deterioration or the wear worn surfaces is generally based upon visual examination. the wear rate has been recently quantified by utilizing fractal geometry to the micrographic features [15-17]. fractal geometry theory is finding its application in the wear morphology by characterizing the worn surface with fractal dimensions as the measure of heterogeneity of a set of points on a plane. fractal geometry is used also to designate complex two or three-dimensional surfaces such as wear worn surfaces. this study explores the wear characteristics of recycled ti-5al3v-2.5fe alloy machining chips. the full factorial experimental design technique has been used to clarify the influence of the wear parameters, applied stress and sliding velocity on the dry sliding wear of ti-5al-3v-2.5fe alloy. the micrographic images of the wear worn surfaces have been analyzed by fractal geometry using fourier analysis. ii. experimental procedure the experiments of the dry sliding wear tests have been conducted using titanium specimens containing 5.47% al, 3.35% v and 2.48% fe prepared by recycling of the machining chips of a ti-6al-4v alloy as part replacement of titanium sponge and expensive alloying elements [9]. the ingots of the ti-5.5al-3.5v-2.5fe alloy have been hot forged with 72.5% total reduction that is started in the -phase field and finished in the --phase field. figure 1 shows a schematic of the forging process and the heat treatment sequences. 0 200 400 600 800 1000 1200 t em p er at u re ( c ) time 950c/ 60 min rt 700c/ 120 min 1050c/ 30 min hot forging  50% hot forging  45%  phase  +  phase fig. 1. schematic diagram of the hot forging steps and the heat treatment sequence. engineering, technology & applied science research vol. 8, no. 1, 2018, 2379-2384 2380 www.etasr.com el-morsy: wear analysis of a ti-5al-3v-2.5fe alloy using a factorial design approach and fractal … the dry sliding wear tests have been performed using wear apparatus, pin-on-ring type [18]. the wear specimens have a diameter of 8 mm and a length of 12 mm. the wear experiments have been conducted in air at room temperature (25 ± 2)oc with dry conditions for a constant sliding distance of 1500 m. before and after each test, the specimens have been rinsed with acetone and have been dried in air. the wear tests have been conducted under different sliding velocities in the range of 0.2 2.0 m/s and applied stresses range of 1-5 mpa. weight loss of specimens (w) indicates the wear resistance of the material. w) is computed in the following manner: ab www   where: wb = weight of specimen before test and wa = weight of specimen after test. volumetric wear rate in mm3/m has been calculated by: s v l w wr     where:  = density of the material, ls = sliding distance . the experimentation of the dry sliding wear has been conducted with the full factorial experimental design technique by which the number of experiments required, mainly depends on the procedure employed for the design of experiments. the main merit of this technique is to realize the possible interaction between the parameters. in this work, a three-level full factorial design technique has been implemented to analyze the effect of wear parameters, namely, applied stress and sliding velocity, on the volumetric wear rate. the independent parameters and their levels used in this work are listed in table i. the complete experiment design matrix is summarized in table ii, which shows the experimental combinations of applied stress and sliding velocity. table i. independent parameters and their levels parameters level units i ii iii applied stress,  1 3 5 mpa sliding velocity, v 0.2 1.1 2.0 m/s table ii. experiment design matrix trail  (mpa) v (m/s) wear rate (mm3/m) 1 1 0.2 0.0206 2 1 1.1 0.0313 3 1 2.0 0.0438 4 3 0.2 0.0404 5 3 1.1 0.1141 6 3 2.0 0.1736 7 5 0.2 0.1026 8 5 1.1 0.1905 9 5 2.0 0.3644 a statistical analysis of variance (anova) has been conducted to recognize the wear parameters and their interactions. finally, a polynomial model has been developed for wear rate using regression analysis. the statistical analysis has been conducted using minitab 17 software. in order to explain the wear behavior, an overall investigation of the worn surfaces of some selected samples has been conducted using the scanning electron microscope (sem). worn morphologies have been studied using the image processing and the fractal geometry technique to reveal the effect of independent parameters on the specimen’s dry sliding wear. iii. results and discussion figure 2 shows the effect of independent parameters, applied stress and sliding velocity, on the volumetric wear rate. figure 2(a) shows the wear rate as a function of sliding velocity at constant applied stress. as shown, the wear rates increased with the increasing of the sliding velocity at all the applied stresses. at low applied stress of 1 mpa, the wear rate slightly increased as the sliding velocity increase. as shown, at low applied stress (1 mpa) the line is nearly horizontal and the parameter has a little effect. at 3 mpa applied stress, the wear rates presented a linear increase as a function of sliding velocity. at the highest applied stress of 5 mpa, the wear rate increased linearly until the sliding velocity reached 1.1 m/s. when the sliding velocity surpassed 1.1 m/s, the wear rate abruptly increased as a function of sliding velocity. in addition, the dependence of wear rate on the sliding velocity became marked and the variation is significantly different from the former. 2.01.10.2 0.4 0.3 0.2 0.1 0.0 531 0.4 0.3 0.2 0.1 0.0 applie d stre s s (mpa) sliding ve locity (m/s ) 1 3 5 0.2 1.1 2.0 (a) (b) fig. 2. interaction plot for wear rate, (a) effect of sliding velocity and (b) effect of stress. the influence of the applied stress on the wear rate at constant sliding velocity is shown in figure 2(b). the wear rate-applied stress relationship under varying sliding velocity exhibits that the wear rate increased linearly and rapidly as a function of applied stress until the highest applied stress. as the sliding velocity increased, the slope of the wear rate increased. the main effects plot for sliding parameters affecting the wear rate for the mean value is shown in figure 3. the highest point for each parameter shows the best level. as shown, the applied stress has higher inclination than the sliding velocity. from the inclination of the graph, the contribution of the applied stress on the output response, volumetric wear rate, is stronger than that of the sliding velocity. it is reported that a (a) (b) engineering, technology & applied science research vol. 8, no. 1, 2018, 2379-2384 2381 www.etasr.com el-morsy: wear analysis of a ti-5al-3v-2.5fe alloy using a factorial design approach and fractal … parameter with the greater effect on the line has the highest inclination [12]. the relationship between the wear parameters, sliding velocity, v, and applied stress,  and the output response, volumetric wear rate is obtained by nonlinear regression analysis. finally, the following polynomial model is fitted to the volumetric wear rate. from this model, it is confirmed that the most influencing parameter is the applied stress compared to the sliding velocity. the value of the determination coefficient, r2 = 0.997, for the wear behavior designates that less than 1% of the variance is not explicated, which indicates the high significance of the model. wrv = 0.042 – 0.0318 () – 0.0862 (v) + 0.115( × v) + 0.0081 ( 2) + 0.0328 (v 2) + 0.0089( 2× v 2) – 0.0184 ( 2× v) – 0.0406( × v 2) + 0.00014( 3) – 0.00001( 4) (3) fig. 3. main effects and their interaction plot for the wear rate. the significance of the model has been tested using 3d contour map (quadratic presentation) and the analysis of variance (anova) technique. figure 4 presents the interaction of the two-wear parameter for the response value of the volumetric wear rate using the polynomial model. to elucidate the previous relationship, the effect of each wear parameter on the wear rate has been reconstructed in the form of a contour map. the optimum combination of the wear parameters to enhance the response wear rate can be easily assessed from this figure. the sliding velocity, the applied stress, and the volumetric wear rate are considered as three perpendicular axes. the means of the normal probability plot of the residuals (the difference between the experimental values and the predicted values) has been used to evaluate the normality of the wear rate data as shown in figure 5. the normal probability plot reveals that the residuals points are very close to a straight line. this means the errors are negligible. the points randomly scattered in residual versus the fitted value graph determine that errors are negligible having constant variance. the relationship between the residuals and the observation order for a volumetric wear rate has been plotted to verify the independence of the wear data. the plot confirms that there is no expectable pattern observed because all the residues lay between the levels. these results are sufficient to show the adequacy of the polynomial model shown in (3). table iii shows the analysis of variance with the wear parameters percentage contribution. the applied load percentage (55.66 %) is the main controlling parameter on the volumetric wear behavior. in the case of interaction (12.88 %), they have less contribution in the output response. 1 2 3 4 5 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.2 0.5 0.8 1.1 1.4 1.7 2.0 w e ar r at e ( m m 3 / m ) ve locity (m/s) 0.35-0.40 0.30-0.35 0.25-0.30 0.20-0.25 0.15-0.20 0.10-0.15 0.05-0.10 0.00-0.05 0.2 0.5 0.8 1.1 1.4 1.7 2 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 w e ar r at e ( m m 3 /m ) stre s s (mpa) 0.35-0.40 0.30-0.35 0.25-0.30 0.20-0.25 0.15-0.20 0.10-0.15 0.05-0.10 0.00-0.05 fig. 4. contour surface of wear rate as a function of applied stress and sliding velocity. figure 6 shows the worn surface morphology after dry sliding wear at different wear conditions (different applied stresses and sliding velocities). it can be found from the series of images shown that many adhesive traces, grooves, debris, and ploughing marks are evident on all the worn surfaces. such topographies are features of abrasion causing wear by the removal of small fragments. the wear rate in the segmented area increases steadily as the wear parameters increases. once the applied stress is above 3 mpa, a sudden increase in the wear rate is notified. figure 6(f) shows the severely of wear rate on the worn surface tried at 5 mpa applied stress and 2.0 m/s sliding velocity. the sem micrograph images of the worn surfaces features in the grayscale at a magnification of x200 (scan area 622×416 m2) shown in figure 6 have been analyzed using the image processing and the fractal geometry technique based on fourier analysis and are shown in figure 7. the fitting curve has been applied to the data attained to (b) (a) engineering, technology & applied science research vol. 8, no. 1, 2018, 2379-2384 2382 www.etasr.com el-morsy: wear analysis of a ti-5al-3v-2.5fe alloy using a factorial design approach and fractal … interpret and correlate an evident linear relationship between log magnitude and log frequency. then the fractal dimension of all the samples has been calculated. the fractal values which can indicate the degree of complexity of the worn surface are varying between 2.06 at low independent wear parameters and 2.87 at high independent wear parameters. low fractal values indicate regularity surfaces and high fractal values indicate highly irregular surfaces. it can be found from the series of worn surfaces (the intensities of the grayscale image) shown in figure 7 that the segmented area (white pixel areas) increases steadily as the applied stress increases. once the applied stress is above 3 mpa, a rapid increase in the segmented area is notified. table iii. analysis of variance with the parameters contribution source df adj ss adj ms contribution stress 4 0.06377 0.015943 31.16 % velocity 4 0.11390 0.028475 55.66 % velocity*stress 16 0.026356 0.001686 12.88 % error 2 0.000614 0.000038 0.3 % total 26 0.20465 100 % fig. 5. the residual plots for the volumetric wear rate fig. 6. sem micrographs of the worn surfaces: (a) 0.2 m/s 1 mpa, (b) 0.2 m/s – 3 mpa, (c) 0.2 m/s – 5 mpa, (d) 2.0 m/s 1 mpa, (e) 2.0 m/s – 3 mpa, and (f) 2.0 m/s – 5 mpa. (b) (c) (a) (d) (e) (f) engineering, technology & applied science research vol. 8, no. 1, 2018, 2379-2384 2383 www.etasr.com el-morsy: wear analysis of a ti-5al-3v-2.5fe alloy using a factorial design approach and fractal … it is stated that the magnification can affect the physical interpretation regarding the structures and distributions of the worn surfaces [19]. therefore, the fractal values of the sem images of the wear samples under different magnifications, high magnification of x500 (scan area 229×171.5 m2) and low magnification of x200 (scan area 622×416 m2) have been analyzed to quantify the variations in the fractal dimensions. the fractal values of the wear samples under different magnifications are shown in figure 8. the figure demonstrates that the fractal dimension of the samples increases gradually with an increase of magnification ratios. under high magnification, the worn surface has higher fractal dimension compared with the value of low magnification. the samples at high applied load (5 mpa) have the highest fractal dimension values both under high magnification and under low magnification. fig. 7. analysis of worn surface using the image processing and the fractal geometry theory. iv. conclusions the wear behavior of the recycled ti-5al-3v-2.5fe machining chips sliding against stainless steel counterfaces has been investigated and interpreted. the experimentation of the dry wear tests has been conducted by the full factorial experimental design technique. the main findings are summarized as follows:  the relationship between the wear parameters, sliding velocity and applied stress, and the output response, volumetric wear rate is obtained by nonlinear regression analysis. the value of the determination coefficient of the polynomial model (r2 = 0.997) for the wear behavior (e) (f) (d) (c) (b)(a) engineering, technology & applied science research vol. 8, no. 1, 2018, 2379-2384 2384 www.etasr.com el-morsy: wear analysis of a ti-5al-3v-2.5fe alloy using a factorial design approach and fractal … indicates that less than 1% of the variance is not explicated, which indicates the high significance of the model.  it is clear from the analysis of variance that the applied stress has higher inclination than the sliding velocity. from the inclination of the graph, the contribution of the applied stress on the wear rate is stronger than that of the sliding velocity.  the sem image processing and fractal dimensions of the worn surfaces have been investigated for the purpose of wear monitoring. the results showed that the procedures are influential techniques since they are effective in characterizing the changes in the surface morphology. fractal dimension considers the difference in grayscale within a given scan area on different scales.  the results of the fractal dimension also exhibited that under high magnification, the worn surfaces had a higher fractal dimension (2.29-2.89) than the worn surfaces under the low magnification (2.06-2.87), which corresponded to higher complexity in the worn surface due to the existence of more such areas in the image. 2 .0 6 2 .2 9 2 .2 2 2 .8 6 2 .4 4 2 .4 5 2 .8 7 2 .8 9 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 f ra ct al v al u es 1 mpa 5 mpa fig. 8. fractal values of the worn surfaces under different magnifications. references [1] i. gurrappa, “characterization of titanium alloy ti-6al-4v for chemical, marine and industrial applications”, materials characterization vol. 51, no. 2-3, pp. 131-139, 2003 [2] i. v. gorynin, “titanium alloys for marine application”, materials science and engineering: a, vol. 263, no. 2, pp. 112-116, 1999 [3] j. bauer, s. cella, m. pinto, j. costa, a. reis, a. loguercio, “the use of recycled metal in dentistry: evaluation of mechanical properties of titanium waste recasting”, resources, conservation and recycling, vol. 54, no. 12, pp. 1312-1316, 2010 [4] p. jiang, x. he, x. li, l. yu, h. wang, “wear resistance of a laser surface alloyed ti–6al–4v alloy”, surface and coatings technology, vol. 130, no. 1, pp. 24–28, 2000 [5] c. martini, l. ceschini, “a comparative study of the tribological behaviour of pvd coatings on the ti-6al-4v alloy”, tribology international vol. 44, no. 3, pp. 297–308, 2011 [6] p. veronesi, s. gaiani, e. colombini, g. poli, r. tisu, “recycling of alpha-titanium technological scrap for exhaust system parts manufacturing”, journal of cleaner production vol. 53, pp. 332-340, 2013 [7] p. luo, d. mcdonald, s. zhu, s. palanisamy, m. dargusch, k. xia, “analysis of microstructure and strengthening in pure titanium recycled from machining chips by equal channel angular pressing using electron backscatter diffraction”, materials science and engineering: a, vol. 538, pp. 252-258, 2012 [8] p. luo, d. mcdonald, s. palanisamy, m. dargusch, k. xia, “ultrafinegrained pure ti recycled by equal channel angular pressing with high strength and good ductility”, journal of materials processing technology, vol. 213, no. 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vol. 473, no. 1-2, pp. 330-335, 2008 [19] k. liu, m. ostadhassan, “multi-scale fractal analysis of pores in shale rocks”, journal of applied geophysics, vol. 140, pp. 1–10, 2017 microsoft word etasr_v13_n3_pp10963-10968 engineering, technology & applied science research vol. 13, no. 3, 2023, 10963-10968 10963 www.etasr.com eldamaty et al.: gis-based multi criteria analysis for solar power plant site selection support in mecca gis-based multi criteria analysis for solar power plant site selection support in mecca tarek a. eldamaty civil engineering department, college of engineering and islamic architecture, umm al-qura university, saudi arabia tadamaty@uqu.edu.sa ayman g. ahmed civil engineering department, umm al-qura university, saudi arabia agahmed@uqu.edu.sa medhat m. helal civil engineering department, college of engineering and islamic architecture, umm al-qura university, saudi arabia | department of engineering mathematics and physics, zagazig university, zagazig, egypt mmhelal@uqu.edu.sa (corresponding author) received: 7 april 2023 | revised: 24 april 2023 and 25 april 2023 | accepted: 26 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5927 abstract one of the major sources of renewable energy, particularly electricity generation and water desalination, is solar energy. the national initiative to produce water and electricity started when the electricity consumption in saudi arabia begun to increase by about 5% per year. the current investigation aims to use a multicriteria gis technique to identify the best spatial location for solar energy collection in the mecca administrative district. the best locations for solar power plant construction were determined with the use of a set of factors and criteria, including planning and environmental criteria, and terrain calibrator. these criteria were defined through a thorough literature review. this information was then used to create a digital geographic database, which was incorporated into an integrated gis to produce a spatial fit model. according to the suitability data, most of mecca region is ideal for solar energy projects, with an applicability percentage ranging between 30% and 80%. these findings are encouraging and promising for mecca's renewable energy industry and they should be considered. it was discovered by examining these spatial locations and the level of suitability to the specifications that the lands with a sufficient share of more than 80% form an area of around 4000km 2 and makeup 3% of all suitable lands. the governorates of the mecca administrative area are home to most of these exceptionally suited locations. the taif governorate takes first place with 35% of the total area and the two governorates of turbah are placed second and third with 24% and 14%. in the mecca administrative area, the appropriate lands for solar energy projects are distributed spatially according to a digital map. the study proposes incorporating the findings into the saudi national plan for renewable energy sources. keywords-solar power; special analytics; multiple criteria; dss; gis i. introduction over the past two decades, the kingdom of saudi arabia's actual power generation capacity raised from 15,212mw to 51,302mw, with more than 7% mean annual growth. simultaneously, the portion of one subscriber increased from 23,928kwh to 33,936kwh. electricity is one of the most significant factors contributing to the rapid development and growth in all spheres of life on a global scale [8-11]. one renewable energy source that may be used anywhere and is free and endless, is solar energy. this form of renewable energy is clean and does not emit any pollutants, unlike the conventional energy sources. the strategies, methods, and processes for harnessing solar energy and turning it into electrical energy are becoming more and more popular on a global scale. over the past 15 years, the development of the electricity generation from solar energy led to a reduction in electricity cost by 4% per year [13-18]. high levels of solar radiation that can be converted into energy are present throughout the middle east, especially in the arab world. recently, countries in this region engineering, technology & applied science research vol. 13, no. 3, 2023, 10963-10968 10964 www.etasr.com eldamaty et al.: gis-based multi criteria analysis for solar power plant site selection support in mecca have tended to increase research, development, and investment efforts in solar energy. in the kingdom of saudi arabia, the interest in solar energy exists for forty years [25-27]. it should be mentioned that several studies in the kingdom have shown that, taking into consideration the economic value of the environmental and the health risks of oil use, the cost of producing power from solar energy is less than that of producing electricity from oil [13-17]. all the gulf cooperation council nations have begun investing in renewable energy sources, particularly solar energy, at a regional level [18-24]. geographic information systems (gis) are the best option for gathering, storing, processing, analysing, and displaying spatial and non-spatial data to come up with technological answers to multi-domain problems. a set of alternatives or solutions are presented to decision-makers after the multiparameter gis approach has studied the potential of a variety of natural, economic, and environmental criteria in a particular spatial location. this approach can be utilized in a wide variety of situations and it has been used to choose the optimal location for several projects, including solid waste treatment facilities, sewage treatment plants, agricultural development, and renewable energy projects. the kingdom of saudi arabia has used this approach in several different fields. this strategy, for instance, was used to determine the optimal locations in the for the construction of rainfall harvesting dams and flood control systems, to choose the optimum site for the construction of tourist facilities, and gis with multiple calibrations was used to determine the most suitable spatial locations for setting up solar collector projects in mecca area from kingdom of saudi arabia [1-7]. this study aims to provide solutions to help policymakers choose the most suitable locations to set up solar mining projects. ii. study area the mecca region spans a sizable area and is situated in the center of the western sector of the kingdom [29]. this region covers about 150km 2 , or 7% of the whole area of the kingdom. by 2025, the number of inhabitants is anticipated to reach 9.7 million [28]. iii. resources and techniques the initial data for the study came from several sources, and the requisite databases were later built. the information which was digitized came from [29]. development specialist mecca provided information on major cities, air terminals, electrical installation broadcasting classes and street organization. the ground elevation of the mecca specified area extends from -9m to 2586m, with a mean of 843m [29]. the highest mountains in the region are the al-hadab mountains in maysan belharith, which are nearly 2,500m above sea level. the sarawat-hijaz mountains extend from the northwest to the southeast, forming a group of hills that are characteristic of the topography of the mecca administrative region. these hills include the east al-sarawat plateau, which stretches from the city of taif in the north to the border of the al-baha region in the south, and the rakba plain's elevation, which stretches for around 400km and nearly 200km north to south. a collection of coastal fields arranged in the form of a run parallel to the ruddy sea's shore and varying in width from 15 to 25km are also included in the region's topography [27]. the major energy distribution network in mecca has a total length of about 900km while the main road network has a total length of over 7000km. the majority of the cities are grouped together in the west, near the shore. iv. data analysis the first procedures in data handling attempt to arrive at a group of criteria that have to be available in selecting the most appropriate geological areas for the use of the geographic data framework (gis) in order to facilitate the selection of the locations for sun-oriented energy plants [19–21], which results in choosing the best spatial sites for solar power plants. one of the most crucial factors is the amount of solar radiation [28], followed by the criterion of trends and the inclination direction, which has an impact on the setup and installation of the necessary equipment for solar power plants. fig. 1. optimal site selection criteria for solar cell construction. regarding the environment, picking the best places for solar energy projects involves the distance from major cities, airports, roads, electrical distribution networks, and beaches. seven criteria were chosen (see figure 1) and their relative weights were calculated (see table i). table i. criteria to be considered when selecting the best sites for solar power plants principle type principle result % planning towns and airfields 10 streets 10 shoreline 10 power networks 15 environment solar radiation 30 terrain calibrator inclination 10 inclination direction 15 engineering, technology & applied science research vol. 13, no. 3, 2023, 10963-10968 10965 www.etasr.com eldamaty et al.: gis-based multi criteria analysis for solar power plant site selection support in mecca for each of the stated criteria, a network layer representing the categorization of the criteria's values was derived [20-24]. these network layers were then reclassified according to scale ranging from 1 to 10 for simplicity of presentation and analysis. the final fit model was then obtained by applying the appropriate weights [28]. v. model builder the process of creating a model involves feeding it with raw data, such as street networks, towns and airfields, digital elevation model, power system, coastline. the digital elevation model was used to extract solar radiation, inclination, and inclination orientation. the weight for each cell was determined using the euclidean distance tool, and the street grid chart, power grid chart, town map, airfields, and shoreline map were created by reclassifying (or changing) the values in the raster, using the tool for weighted overlay [8]. the optimal location for solar power plants in mecca was identified using specific weights for each parameter (figure 2). fig. 2. the model builder will decide which locations are ideal for building solar plants. vi. results and analyses many initial models were built up matching the layers of the criteria values to the degree of spatial suitability for each criterion [8, 12]. figures 3-11 were made with the esri arc/gis software, version 10.3. figure 3 shows the territorial suitability for the sun powered radiation model, with the center and eastern areas having the most noteworthy esteem. since most cities are located on the western side of coastline and in connection to basis for separate shoreline, areas of appropriate height are those that are the most remote from the shoreline, as shown in figure 5 of the spatial appropriateness demonstrate for the cities and air terminals measure. fig. 3. solar radiation classification chart. fig. 4. classification of the distance to cities and airports. fig. 5. classification of the distance to the coastline. solar radiation classification chart engineering, technology & applied science research vol. 13, no. 3, 2023, 10963-10968 10966 www.etasr.com eldamaty et al.: gis-based multi criteria analysis for solar power plant site selection support in mecca fig. 6. degrees of conformity to the power line standard in locations in mecca. fig. 7. degrees of contormity to the road standard in in mecca. fig. 8. mecca's conformance map to slope standards. figure 6 outlines the spatial ampleness from the power dispersion. it should be noted that high altitude areas are those that are not distant from the control conveyance line. this model pertains to the criterion of distance from the electricity distribution network. additionally, the chart shows that the optimal areas are concentrated on the western portion of the research region for this criterion. figure 7 portrays the area suitability with regard to the proximity to the road network. fig. 9. map classifying orientation. fig. 10. best sites for solar power plants in mecca. figures 8 and 9 indicate that most of the authoritative locales have great suitability degrees with regard to slope and slope orientation, with the exemption of the centre fragment of the area, which has extraordinary slants. at the highest places the degree of suitability was medium and occasionally weak. to ensure that the sun's rays fall directly on the solar cells, it is ideal for the gradient to face south, southeast, or southwest. as a result, these restrictions were used in the final fit process, which can be seen in figure 10. mecca as a whole is ideal for the solar energy harvesting, with a reasonable rate between 30% and 80%. the findings of map of the degrees of conformity to the road standard in mecca mecca's conformance map to slope standards map classifying the orientation of mecca best sites for solar power plants site in mecca map of the degrees of conformity to the power line standard in mecca engineering, technology & applied science research vol. 13, no. 3, 2023, 10963-10968 10967 www.etasr.com eldamaty et al.: gis-based multi criteria analysis for solar power plant site selection support in mecca the current study are important for mecca's renewable energy sector. a detailed examination of the spatial zones and their level of compliance with the regulations shows that a 3% of the qualified lands that are defined by a satisfactory extent of more than 80% and cover a total area of about 4000km 2 . fig. 11. sitemap with relevance ≥ 80% in mecca. fig. 12. areas with at least 80% compliance. table ii. distribution of locations with spatial suitability greater than 80% percentage % area in km 2 governorate 24 1051 turubah 14 608 raneh 35 1521 taif 6 278 khorma 5 236 moyaha 1 48 kamil 5 211 jamom 9 403 maysaan 100 4356 total table ii and figures 11 and 12 show how these appropriate locations are distributed throughout the governorates of the mecca authoritative locale. the taif governorate has the most suitable areas, with 35% of the overall zones, followed by the two turbah governorates with 24% and the rania governorate with 14%. the governorates of maysan and al-khumra follow, each with 14%, and none of the other governorates have any place with a degree of compliance more than 80%. vii. conclusion the current research focuses on the mecca region of saudi arabia, mainly due to the promising prospects for international energy interconnection. the distribution of spatial phenomena varies between natural and human phenomena that spread on the lands of mecca governorate, such as road networks, electricity network, cities and airports, solar radiation, and tendencies. combined, these are criteria that the study relied on to design a model that determines the suitability for the application of solar energy projects. based on the investigation and analysis conducted in this study, it was found that the degree of spatial appropriateness varies, and the land area with a fit coefficient greater than 80% is about 5,000km 2 . mecca governorate's center region contains the majority of these areas. to evaluate the best locations for the deployment of photovoltaic power stations in the mecca region, this study considered various criteria (planning standards, environmental standards, terrain calibrator). the results showed that, with varying degrees ranging between 30% and 80%, the larger part of the mecca regulatory locale is suitable for establishing solar power 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[29] makkah city profile. riyadh, saudi arabia: ministry of municipal and rural affairs, 2012. microsoft word 3-lazizi.doc engineering, technology & applied science research vol. 4, no. 2, 2014, 605-611 605 www.etasr.com lazizi et al.: numerical simulation of tire reinforced sand behind retaining wall … numerical simulation of tire reinforced sand behind retaining wall under earthquake excitation amina lazizi habib trouzine aissa asroun farid belabdelouahab civil engineering dpt, djillali liabes university of sidi bel abbes, algeria lazizi_a18@yahoo.fr lgce laboratory, djillali liabes university of sidi bel abbes, algeria h_trouzine@yahoo.fr lgce laboratory, djillali liabes university of sidi bel abbes, algeria a_asroun@yahoo.fr enstp national high school of publics work, kouba, algiers, algeria belabdelouahabf@yahoo.fr abstract—this paper studies the numerical simulations of retaining walls supporting tire reinforced sand subjected to el centro earthquake excitation using finite element analysis. for this, four cases are studied: cantilever retaining wall supporting sand under static and dynamical excitation, and cantilever retaining wall supporting waste tire reinforced sand under static and dynamical excitation. analytical external stability analyses of the selected retaining wall show that, for all four cases, the factors of safety for base sliding and overturning are less than default minimum values. numerical analyses show that there are no large differences between the case of wall supporting waste tire reinforced sand and the case of wall supporting sand for static loading. under seismic excitation, the higher value of von mises stress for the case of retaining wall supporting waste tire reinforced sand is 3.46 times lower compared to the case of retaining wall supporting sand. the variation of horizontal displacement (u1) and vertical displacement (u2) near the retaining wall, with depth, are also presented. keywordswaste tire; sand; retaining wall; earthquake; simulation i. introduction with the rapid growth in automobile usage worldwide, approximately 2–3 billion tires are discarded annually [1-2]. algeria alone produces approximately 25918.50 tons/year of used tires [3]. the most common ways to recycle tires are burying, auxiliary fuel conversion, pyrolysis, reproduction, cutting and reprocessing, and reusing. applications in geotechnical engineering, highway engineering, soil and water conservation, and marine engineering use intact used tires. such applications which do not require complex processes are considered economical and eco-friendly [4-6]. the first research in france on soil reinforcements using old tires was commissioned in 1976. studies were conducted on reinforcement in the form of whole tires, sidewalls, or treads placed on edge or cut and laid flat [4-7]. the first project in england using scrap tires was the construction of an experimental gravity wall in west yorkshire [8]. an experimental research using a vibrating table was also undertaken from the “l’ecole nationale des ingénieurs de tunis” (enit) and the “laboratoire centrale des ponts et chaussés” (lcpc), whose objective was to protect the grenoble synchrotron road from vibrations. this study showed that used tires can attenuate vibration phenomena [9]. another full-scale experimentation was conducted in rouen in france; this research showed that tire reinforced soil can absorb and reduce pressure and acceleration [10]. in the seismic stability analysis, the magnitude of the dynamic force increment due to shaking is calculated using the mononobe-okabe (m.o) approach [11]. basha and babu in [12] presented a method to evaluate the internal stability of reinforced soil structures against tension and pullout modes of failures using pseudo-static methods for earthquake conditions. further, choudhury and ahmed in [13] presented the external stability of waterfront reinforced soil structures under seismic conditions using a pseudo-static method and a limited equilibrium approach. steedman and zeng in [14] developed the pseudo-dynamic method considering horizontal seismic acceleration and finite shear waves propagations using planar failure surface. in the present paper, a numerical simulation of tire reinforced sand behind retaining wall under earthquake using implicit and explicit methods is performed in order to study its dynamic behavior. ii. description of the numerical model a. geometry and ground conditions geometrically, the retaining wall is a reinforced concrete cantilever wall with 5.80 m of height and 0.50 m of wall stem thickness (figure 1). mechanically, the young’s modulus of the retaining wall is e=3.107 kn/m2, the poisson’s ratio is about 0.3 and its density is about 26.43 kn/m3. table i summarizes all the characteristics. the earthfill is a sandy soil with a semi-infinite length of 22.50 m. the surface of the backfill is plane and carries no surcharge. the seismic action is introduced in the form of the accelerogram acquired from the earthquake dated may 18, 1940 in el centro in the region of california. engineering, technology & applied science research vol. 4, no. 2, 2014, 605-611 606 www.etasr.com lazizi et al.: numerical simulation of tire reinforced sand behind retaining wall … fig. 1. geometric details of the wall. table i. model characteristics materials properties retaining wall ew = 3.e+7 kn/m² υw =0.25 ρw =26 430 kg/m 3 damping α =0.015 sand es = 100 000 kn/m² υs =0.25 ρs =18 260 kg/m 3 damping α =0.01 tire reinforced sand et = 100 000 kn/m² υt =0.25 ρt =17 940 kg/m 3 damping α =0.02 b. studied cases two distinct cases are studied; a reference case where the wall supports only the sand and a second case where the sand is reinforced by layers of waste tires. both cases are studied under static and dynamic loading. 1) case 1 : retaining wall supporting sand the backfill is wet sand with an average diameter of 1.10 mm, a density of 26.5 kn/m3, and a coefficient of curvature about 0.119 to 0.136. according to the unified classification (uscs), the soil is sp poorly graded clean sand. geotechnically, the cohesion is zero, and the angle of internal friction is 30°. mechanically, the young’s modulus e is 1.105 kn/m2, the poisson’s ratio is about 0.25 and its density is 18.40. the active earth pressure coefficient is determined using the rankine method, and it is about 0.333. the wall slip is considered with a coefficient of friction of 0.4. 2) case 2 : retaining wall supporting tire reinforced sand in this case, the same sand is reinforced with layers of light vehicle tires type flanks without treads on edge. the composite (tire-sand) is amended as multi layer, its young modulus and poisson’s ratio are determined using voigt reuss combined model: . /c vr me e       2 3m a a me v e e         1 3 1 31 .a m av e v       with: c vre  : the equivalent young’s modulus ,m ae e : the sand and waste tire young moduli c a c s v v v v   with ,c sv v : the sizes of tire and sand the tire height is 20 cm, and the layer of sand is 50 cm. the reinforcements are linear modeled as a superposition of the layer of sand and waste tire. the sand-rubber interaction is considered with a coefficient of sliding friction of 0.6; the rubber-wall friction coefficient is equal to 0.65. the active earth pressure coefficient is computed the same way as in the first case. iii. static and seismic loading for static loading, the weight of retaining wall is computed, and the active pressure is calculated using the rankine method and is about 86 kn in the first case and 85.4 kn in the second case. for seismic loading, the accelerogram of the el centro earthquake in california is introduced in the form of a table of two columns, the first for time, which is limited in 14 s, and the second for the values of acceleration [15]. rayleigh mass proportional damping factor is introduced for each element (wall, soil and tire-soil). fig. 2. the accelerogram of el centro california iv. results and discussion a. external stability analyses to calculate the lateral earth pressure, rankine’s theory is used. for the dynamic case the calculation is based on the pseudo-static method. 1) base sliding-static case the coefficient of rankine active earth pressure is given by:  2tan 45 2ak      engineering, technology & applied science research vol. 4, no. 2, 2014, 605-611 607 www.etasr.com lazizi et al.: numerical simulation of tire reinforced sand behind retaining wall … where ka is the active earth pressure coefficient and  is the angle of soil internal friction. the static earth pressure is given by: 20.5a a tp k h    where pa is the static earth pressure and t and h are respectively the total unit weight of backfill soil and the height of the retaining wall. the sliding resistance is provided by the friction between the concrete and the soil under the base of the wall. the frictional force between the concrete and the soil is computed using the following equation: tanf vf r    where ff is the frictional force between the concrete and the soil, rv is the vertical component of resultant force. fr is the force opposing the sliding and: r ff f   v totalr w   where wtotal is the resultant weight of the wall. the safety factor against sliding is equal to: s r af f p   2) base slidingdynamic case the pseudostatic earthquake force is given by [16]:  2max3 8 e t a p h g     where pe is the pseudostatic earthquake force and amax is the peak ground acceleration and: ae a ep p p    where pae is the sum of the static (pa) and the pseudo-static earthquake force (pe). the safety factor for sliding using both pseudostatic method and seed and whitman (1970) analysis is given by: 1tan s h e n f p p      where n is the sum of the weight of wall, the footing and the vertical component of the active earth pressure resultant force, δ1 is the friction between the bottom of the foundation and the soil backfill, and ph is the horizontal component of the active earth pressure resultant force with: sinan w p     cosh ap p    3) overturning static case the overturning and stabilizing moments may be calculated by taking moments about point o. the safety factor against overturning is therefore: st sr r m f m    where mst is the sum of moments that resist overturning and mr is the sum of overturning moments. 4) overturning dynamic case the safety factor for overturning using mononobe-okabe method is given as: . 0.333 cos sin s ae ae w a f p h ep      where a the lateral distance from resultant weight w of wall and footing to toe of footing, h the height of the retaining wall and e the lateral distance from the vertical component of the active earth pressure resultant force to the toe of wall with: sinv ap p    where pae is the sum of the static (pa) and the pseudostatic earthquake force (pe). if the conventional rule is applied, according to which the dynamic safety factor should not be less than 75%, the safety factor for sliding as well as for overturning should be in the range of 1.1 to 1.2. v. numerical analyses the finite element method (fem) has become the most popular method in both research and industrial numerical simulations. several algorithms, with different computational costs can be implemented in abaqus [17], which is a commonly used software for finite element analysis. understanding the nature, advantages and disadvantages of these algorithms is very helpful for choosing the right algorithm for a particular problem [18]. comparison of implicit and explicit methods for abaqus in nonlinear problems has been reported by rebelo in [19]. the unconditionally stable implicit method will encounter some difficulties when a complicated three dimensional model is considered. the reasons are as follows [18]: as the reduction of the time increment continues, the computational cost in the tangent stiffness matrix is dramatically increased and even causes divergence. local instabilities cause force equilibrium to be difficult to achieve. explicit techniques are thus introduced to overcome the disadvantages of implicit methods. for the explicit method, the cpu cost is approximately proportional to the size of the finite element model and does not change as dramatically as the implicit method. the drawback of the explicit method is that it is conditionally stable. the stability limit for an explicit operator is that the maximum time increment must be less than a critical value of the smallest transition times for a dilatational wave to cross any element in the mesh. secondly, the nature of the explicit method limits it to the analysis of short transient problems. if this method is used for quasi-static problems, the inertia effects must be small enough to be neglected. one way to assure this is to set the limit of the kinematic energy to be less than 5% of the strain energy. for dynamic problems, abaqus also offers some other methods such as a modal engineering, technology & applied science research vol. 4, no. 2, 2014, 605-611 608 www.etasr.com lazizi et al.: numerical simulation of tire reinforced sand behind retaining wall … dynamic algorithm. however, only direct integration methods implicit dynamics and explicit methods are suitable for nonlinear problems. most of the reported works on the comparison of implicit and explicit methods are on quasi-static nonlinear problems [18-20]. as it is well-known, the explicit integration operator is conditionally stable since the maximum stable time increment is limited by the minimum mesh size and the highest wave speed (courant stability condition) given by [21-22]:  e dt min l c  where el is the characteristic element length (e.g. minimum element dimension) and dc is the current effective, dilatational wave speed of the material. in other words, the time increment must be smaller than the minimum amount of time necessary for a wave to cross an element. the time step of t = 2.2.10-4 s has been found to be sufficiently powerful in obtaining an effective approximate computations of the quasistatic response [23]. it should be mentioned that the values of damping for each material is regrouped in table i. to get a clear comparison of the von mises stress distributions for the four studied cases, the von mises stress distributions are shown in figures 3, 4, 5 and 6. a. retaining wall supporting sand static case: according to the analytical computation, for this case, the safety factors for sliding as well as overturning are less than the default minimum values. fig. 3. the von mises stress distribution for retaining wall suporting sand under static loading von mises stress distribution change in the range of 7.416– 3528 kpa (figure 3). the lowest von mises stress values are observed near the ground level. von mises stress increases with depth. the higher von mises stress (3.5 mpa) is observed between the base slap and the stem of the retaining wall in the soil cover zone. figure 7 presents u1 and u2 displacements under static loading for the two studied cases. variations of u1 and u2 displacements of the wall with depth are presented in figures 9 and 10. case 1 and 2 make reference respectively to retaining wall supporting sand and retaining wall supporting reinforced sand. the displacement u1 is substantially constant with the depth (about 0.825 m). for u2 the maximum value is noted in the base slab and it’s about 0.0065 m. the minimum value is noted in the top of the wall and it’s about 0.0025 m. figure 5 presents the von mises stress distribution at 14 seconds (after 1023 time increments). for the second case, von mises stress distribution change in the range of 9.761 kpa to 13.95 mpa. the lowest von mises stress values (9.7 kpa) for this case are observed for backfill. the higher von mises stress (13.95 mpa) is observed in the wall between the base slap and the stem. the higher value of von mises stress for the dynamical case is 3.95 time higher than for the static case. figure 8 presents u1 and u2 displacements under static loading for the two studied cases. variations of u1 and u2 displacements with depth are presented in figure 11 and figure 12. u1 displacement is about 0.70 m for all the depth. for u2 displacement, the maximum value is about 0.0053 m and the minimum value is about 0.002 m. fig. 4. the von mises stress distribution for retaining wall suporting tirereinforced sand under static loading fig. 5. the von mises stress distribution for retaining wall suporting sand under seismic loading fig. 6. the von mises stress distribution for retaining wall suporting tirereinforced sand under seismic loading b. retaining wall supporting sand dynamic case: according to the analytical computation, for this case, the safety factors for sliding as well as overturning are greater than the default minimum values. engineering, technology & applied science research vol. 4, no. 2, 2014, 605-611 609 www.etasr.com lazizi et al.: numerical simulation of tire reinforced sand behind retaining wall … c. retaining wall supporting tire reinforced sand static case: according to the analytical computation, for this case, the safety factors for sliding as well as overturning are less than the default minimum values. for the third case, the von mises stress distribution change in the range of 7.930 to 3465 kpa (figure 4). the lowest von mises stress values are observed near the ground level. von mises stress increases with depth. the higher von mises stress is observed between the base slap and the stem of the retaining wall in the soil cover zone. there are not large differences between this case and the case of wall supporting sand for static loading. figure 7 presents u1 and u2 displacements under static loading for the two studied cases. variations of u1 and u2 displacements with depth are presented in figures 9 and 10. the value of u1 for this case is about 0.625 m, for u2 displacement the maximum value is about 0.005 m. fig. 7. displacements under static loading (a) u1 displacement for retaining wall suporting sand. (b) u2 displacement for retaining wall suporting sand. (c) u1 displacement for retaining wall suporting tire-reinforced sand. (d) u2 displacement for retaining wall suporting tirereinforced sand fig. 8. displacements under seismic loading (a) u1 displacement for retaining wall suporting sand. (b) u2 displacement for retaining wall suporting sand. (c) u1 displacement for retaining wall suporting tire-reinforced sand. (d) u2 displacement for retaining wall d. retaining wall supporting tire reinforced sand dynamic case: figure 6 presents the von mises stress distribution at 14 seconds (after 3869 time increments). for the fourth case, the von mises stress distribution change in the range of 2.829 kpa to 4.024 mpa. the lowest von mises stress values are observed near the ground level. von mises stress increases with depth. the higher von mises stress is observed between the base slap and the stem of the retaining wall in the soil cover zone. the higher value of von mises stress for this case is 3.46 times lower compared to the case of the retaining wall supporting sand with dynamic loading. figure 8 presents u1 and u2 displacements under static loading for the two studied cases. variations of u1 and u2 displacements with depth are presented in figures 11 and 12. (a) (b) (c) (d) (a) (b) (c) (d) engineering, technology & applied science research vol. 4, no. 2, 2014, 605-611 610 www.etasr.com lazizi et al.: numerical simulation of tire reinforced sand behind retaining wall … the u1 displacement is about 0.50 m and u2 displacement is about 0.0048 m. fig. 9. variation of u1 wall displacement with depth for static loading fig. 10. variation of u2 wall displacement with depth for static loading fig. 11. variation of u1 wall displacement with depth for seismic loading. fig. 12. variation of u2 wall displacement with depth for seismic loading vi. conclusion analytical analyses and implicit and explicit numerical methods are used to compare results of cantilever retaining wall supporting waste tire reinforced sand to the results of the same cantilever retaining wall supporting only sand, under seismic loading of el centro type. the following conclusions are drawn:  according to the analytical computation, the safety factors for sliding as well as for overturning are less than the default minimum values for all cases.  for the retaining wall supporting sand case: the lowest von mises stress value is about 9.7 kpa whereas the highest value is about 13.95 mpa and is observed in the wall between the base slap and the stem. the higher value of von mises stress for the dynamical case is 3.95 times higher compared to the static case.  for the retaining wall supporting waste tire reinforced sand under static loading case: the von mises stress distribution changes in the range of 7.930 to 3465 kpa and the lowest values are observed near the ground level. under el centro excitation, the higher von mises stress (4.024 mpa) is observed between the base slap and the stem of the retaining wall in the soil cover zone. this value is 3.46 times lower compared to the retaining wall supporting sand with dynamic loading.  for u1 and u2 displacements, the variations with depth are similar for each type of loading, but the values for the case of retaining wall supporting waste tire reinforced sand are slightly lower compared to the ones of the case of retaining wall supporting only sand. references [1] c. rothfuss, c. y. cha, “utilization of a scrap tire-waste oil derived carbonous residue as an asphalt modifier”, polymer recycling, vol. 2, no. 3, pp. 201–212, 1996 [2] c. y. wang, j. h. cheng, h. p. shih, j. w. chang, “ring columns as pier scour countermeasures”, international journal of sediment research, vol. 26, no. 3, pp. 353-363, 2011 engineering, technology & applied science research vol. 4, no. 2, 2014, 605-611 611 www.etasr.com lazizi et al.: numerical simulation of tire reinforced sand behind retaining wall … [3] h. trouzine, a. asroun, n. asroun, f. belabdelouahab, n. t. long, “problématique des pneus usés en algérie”, nature & technologie, vol. 5, pp. 28-35, 2011 [in french] [4] n. t. long, le pneusol: recherches-réalisations-perspectives, thèse de doctorat du lcpc, insa lyon, 1993 [in french] [5] m. r. hausmann, “slope remediation”, proceedings of the stability and performance of slopes and embankments conference, asce geotechnical special publication, vol. 2, pp. 1274–1317, 1990 [6] v. k. garga, v. o’shaughnessy, “tire-reinforced earthfill. part 1: construction of a test fill, performance, and retaining wall design”, canadian geotechnical journal, vol. 37, no. 1, pp. 75–96, 2000 [7] v. o’shaughnessy, v. k. garga. “tire-reinforced earthfill. part 2: pullout behaviour and reinforced slope design”, canadian geotechnical journal, vol. 37, no. 1, pp. 97–116, 2000 [8] wymcc, reuse of worn tyres in civil engineering construction, internal report. west yorkshire metropolitan county council, 1977 [9] n. b. romdhane, r. nasri, m. chaieb, n. t. long, “comportement dynamique du pneusol, etude sur modèle reduit tridimensionnel, essai sur table vibrante, actes des 4eme congres national afps, saint-rémy lés chevreuse, france, 1996 [in french] [10] y. guillard, n.t. long, p. ursat, j. c. valleux, “pneusol : essais de vibrations, actes des 2eme congres national afps, france, 1989 [in french] [11] s. l. kramer, geotechnical earthquake engineering, englewood cliffs, nj: prentice-hall 1996 [12] b. m. basha, s. g. l. babu, “reliability assessment of internal stability of reinforced soil structures: a pseudo-dynamic approach”, soil dynamics and earthquake engineering, vol. 30, no. 5, pp. 336-353, 2010 [13] d. choudhury, s.m. ahmad, “external stability of waterfront reinforced soil structures under seismic conditions using a pseudo-static approach”, geosynthetics international, vol. 16, no.1, pp. 1–10, 2009 [14] r. s. steedman, x. zeng, “the influence of phase on the calculation of pseudo-static earth pressure on a retaining wall”, geotechnique, vol. 40, no. 1, pp. 103–112, 1990 [15] a. k. chopra, dynamics of structures theory and applications to earthquake engineering, university of california at berkeley, prenticehall, 1995 [16] h. b. seed, r. v. whitman, “design of earth retaining structures for dynamic loads", asce specialty conference on lateral stresses in the ground and design of earth retaining structures, pp. 103-147, usa, 1970 [17] abaqus user's examples and theory manual, version 5.7. hibbitt, karlsson & sorensen inc., 1998 [18] j. s. sun, k. h. lee, h. p. lee, “comparison of implicit and explicit finite element methods for dynamic problems”, journal of materials processing technology, vol. 105, no. 1-2, pp. 110-118, 2000 [19] n. rebelo, j. c. nagtegaal, l. m. taylor, r. passmann, “comparison of implicit and explicit finite element methods in the simulation of metal forming processes”, numinform 92, international conference on numerical methods in industrial forming processes, pp. 99-108, 1992 [20] hibbitt, karlsson & sorensen inc., “application of implicit and explicit finite element techniques to metal forming”, journal of material process technology. vol. 45, pp. 649-656, 1994 [21] t. j. r. hughes, the finite element method – linear static and dynamic element analysis, englewood cliffs, (nj): prentice-hall, 1987 [22] t. belytschko, w. k. liu, b. moran, nonlinear finite element for continua and structures, chichester: john wiley & sons ltd, 2000 [23] l. siad, m. ould ouali, a. benabbes, “comparison of explicit and implicit finite element simulations of void growth and coalescence in porous ductile materials”, materials and design, vol. 29, no. 2, pp. 319–329, 2008 microsoft word etasr_v11_n4_pp7375-7380 engineering, technology & applied science research vol. 11, no. 4, 2021, 7375-7380 7375 www.etasr.com okello & sinde: development of a sensor-based heartbeat and body temperature monitoring system … development of a sensor-based heartbeat and body temperature monitoring system for remote chronic patients jimmy obira okello school of computational and communication sciences and engineering nelson mandela african institution of science and technology arusha, tanzania jobira32@gmail.com ramadhani sinde school of computational and communication sciences and engineering nelson mandela african institution of science and technology arusha, tanzania ramadhani.sinde@nm-aist.ac.tz abstract-the growing number of chronic diseases have stretched the healthcare sector. globally, more than 36 million deaths per year are attributed to chronic disease complications. this has increased the demand for telemedicine in managing chronic patients as they must be on continuous monitoring for a long time. the involvement of wireless sensor networks and cloud computing technology in the health sector is increasing due to the potential it possesses in remote sensing and monitoring applications. this paper presents a developed system prototype for monitoring the heartbeat rate and body temperature of chronic patients using sensors. the monitored data are sent to a cloud database in real-time via an internet connection using the esp8266 wireless module. the approach involves connecting a heart pulse sensor, an mlx90614 contactless temperature sensor, and the esp8266 module to the arduino development board. the goal of this work is to create a system that interfaces chronic patients and medical personnel in an attempt to avert the effects of insufficient health facilities, especially in rural africa. the patient’s data in the cloud database can also be retrieved by medical personnel anytime in order to track the patient’s conditions and to advise the patient accordingly. the sensed heartbeat and body temperature readings were processed, sent, and recorded in the cloud database effectively. keywords-arduino; sensor networks; esp8266 module; chronic diseases; pulse oximeter i. introduction the management of chronic diseases has become one of the biggest challenges that health sector faces nowadays. the healthcare sector is struggling to meet the needs of people with chronic diseases as they need continuous monitoring for a long time, commonly outside the health facilities [1]. a chronic disease is basically any condition that persists for a year or more requiring continuous medical care which may curtail an individual’s daily activities [2]. eighty percent of the world’s deaths from chronic diseases occur in low and middle-income countries [3] and although the biggest economic burden falls on the high-income countries, the burden on the low and middleincome countries is increasing along with population growth [4]. globally, over 36 million deaths per year are attributed to chronic disease complications. six out of ten adults in the usa have a chronic disease [3]. the challenges of chronic disease management have resulted to the increasing use of telemedicine. telemedicine is the involvement of information technology in providing healthcare services to patients who may be located away from the health facilities [5]. the integration of wireless communication, cloud computing, and sensor networks in the field of medicine has facilitated and promoted telemedicine. in the last decade, there has been a rapid growth in the use of low cost wireless communication protocols and sensors in healthcare which has greatly promoted the use of telemedicine [6]. sensor networks have also become a serious focus for research and deployment in the fields of oil and gas and agriculture [7, 8]. in this paper, some previous related works on remote patient management and monitoring were studied and analyzed to appreciate the trends and identify their gaps and a system that uses multiple sensors for collecting data, virtual instrument software for data processing, and wireless data transmission is proposed. a system that deploys wireless technology to detect any abnormalities in the patient bio signal and sends sms alerts to doctors using global system for mobile communication (gsm) has been proposed in [9]. a gsm based system that monitors the patient's health condition and passes messages to the doctor’s mobile phones has been developed in [10]. however, gsm technology is becoming obsolete in most countries. a mobile application based on android for remote patient monitoring system has been proposed in [11] that focuses in monitoring the body temperature of patients and displaying the data on a mobile application. however, this does not cater for users of other mobile phones that use different operating systems. a system that involves electrical signals to monitor heart disease has corresponding author: jimmy obira okello engineering, technology & applied science research vol. 11, no. 4, 2021, 7375-7380 7376 www.etasr.com okello & sinde: development of a sensor-based heartbeat and body temperature monitoring system … been developed in [12]. however, this system comes with a bulky strap that must be put around one’s chest making it a bit uncomfortable. a raspberry pi based system that automatically monitors patient’s heart rate, body temperature, respiration rate, and body movements has been proposed in [13]. however, the raspberry pi is an expensive and complex board to program and use, making it a costly approach. medical professionals use body temperature, heart beat rate, blood pressure, and pulse rate for the tracking of a patient’s health condition. body temperature is one of the main indicators of normal or abnormal body functioning. chronic patients require continuous monitoring of their body parameters, record keeping, and informing the doctors in case of any abnormality. this is sometimes a manual process and requires proper record keeping which is still a challenge as the doctors do not receive the data in real time for immediate response while sometimes the records are lost by patients. taking into consideration the challenges of monitoring, record keeping, and real time transfer of data, the authors of this paper found it extremely paramount to develop a system that monitors and relays chronic patient’s data in real time. some of the research carried out in this area of patient’s condition monitoring involves the use of expensive systems such as drones to capture data or gsm technology. however, little attention has been put on utilizing the low cost esp8266 wireless protocol, mlx90614 contactless temperature sensor and heart pulse sensors in patient remote monitoring, and the use of free cloud services for proper record keeping and virtualization. the present work brings in the element of using low cost, low power heart pulse sensor, mlx90614 contactless temperature sensor, esp8266 wireless module, and free cloud database. this developed system allows the extraction of a patient’s data in a spreadsheet document which facilities an offline analysis. the system allows real time transmission of a patient’s data to the database using a cheap wireless module thus allowing quick and easy response from the doctors. the major contribution of this paper is that the proposed system interfaces chronic patients and medical personnel that will help averting the effects of poor health facilities in areas such as the rural africa. ii. materials and methods this paper proposes a monitoring system that detects the body temperature and the heartbeat rate of chronic patients with the aim of improving timely intervention to patient’s conditions. the developed system prototype has two sides. on the patient’s side the readings are displayed on a liquid crystal display (lcd) screen whereas on the doctor’s side the readings are stored in the thingspeak cloud database. the developed system uses the arduino development board, a heartbeat sensor and a mlx90614 contactless temperature sensor, the esp8266 wireless module, and a cloud database. the sensors collect health indicators from the patient and transmit them to the thingspeak database using the esp8266 wireless module. the data from the cloud database can be retrieved any time by the doctors. the heartbeat sensor was connected to pin a0 of the arduino uno whereas the mlx90614 temperature sensor’s sda and scl were connected to the arduino’s sda and scl pins respectively. the arduino communicates with the thingspeak database remotely through an internet connection. the block diagram of the proposed system prototype is shown in figure 1. the system comprises of hardware and software components and their details are explained below. fig. 1. block diagram of the developed system. a. hardware requirements the hardware components of the system are summarized in table i. the heartbeat sensor detects the heartbeat rate whereas the mlx90614 sensor detects the body temperature of the patient. these sensors are attached to an arduino board where the collected readings are processed. the esp8266 wireless module is attached to the arduino board and is used to send the collected sensor data to the cloud database. table i. hardware requirements summary s/n required component quantity 1 arduino uno 1 2 heartbeat sensor 1 3 mlx90614 sensor 1 4 esp8266 module 1 5 breadboard 2 6 battery 2 7 jumper wires 1 packet 8 lcd 1 9 potentiometer 1 1) arduino uno arduino uno is an embedded development board having different pins for analog, pulse width modulation (pwm) and digital signal interfacing. it includes an integrated development environment (ide) for programing. the arduino development board is used to interface sensors which are used to collect data from the environment. the arduino board contains an atmega32 microprocessor which was programmed to sense body temperature and heartbeat. the arduino uno was used in this project because of its cost, simplicity, and availability. 2) heartbeat sensor pulse sensor is a heartbeat sensor designed for arduino. it can be used to incorporate heartbeat monitoring projects in real engineering, technology & applied science research vol. 11, no. 4, 2021, 7375-7380 7377 www.etasr.com okello & sinde: development of a sensor-based heartbeat and body temperature monitoring system … time. the sensor side with the heart logo is usually placed onto a fingertip or earlobe to take measurements of the heartbeat. the sensor has three jumper cables which are plugged into arduino pins. the sensor side contains the led indicator and an ambient light sensor. the light from the led strikes the fingertip, earlobe, or other body part and the reflected light is then used by the sensor in order to determine the heartbeat rate [14]. in this project, the sensor signal cable was connected to pin a0, the ground pin to gnd pin of the arduino, and the vcc pin was connected to the 3.3v pin of the arduino. 3) mlx90614 contactless temperature sensor the mlx90614 contactless temperature sensor measures ambient and target temperatures. it utilizes infrared (ir) to be able to detect the ambient and target temperature without coming into physical contact. it utilizes the inter-integrated circuit (i2c) serial communication protocol when communicating with microcontrollers or other devices. it consists of four pins: sda, vin, gnd, and scl. the sda pin is used for data transfer, the scl pin is used for clock transfer during i2c serial communication, and the vin pin is for power supply. this sensor can be used in a number of commercial, healthcare, and household applications. this sensor measures target temperature without making physical contact. all human beings emit ir energy and the mlx90614 sensor can calculate the temperature of a target from this emitted ir energy since the temperature is directly proportional to it. for this project, the sda pin was connected to the sda pin of arduino, the scl was connected to the scl of the arduino, while the vin pin was connected to 5v, and the gnd to the gnd of the arduino. 4) esp8266 wireless module the esp8266 module can be used as standalone host receiving internet connection from a router or as a master providing internet connection to other devices. when the esp8266 module is used to host application, it is booted directly from an external flash. it has on-chip memory to enhance the capacity of the developed applications. this module has a radio frequency (rf) antenna, filters, and power management mechanisms within a small board. esp8266 also integrates a 32-bit processor, on-chip static random access memory (sram) with the ability to communicate with external devices and sensors using the general purpose input output (gpio) pins. for this project the esp8266 wireless module was used and the pins were connected as follows: tx pin to pin 2 of arduino, rx to pin 3 of arduino, pins vcc and ch_en connected to 3.3v and reset and ground pins to the gnd of arduino. 5) liquid crystal display the lcd used for this project, is a 16×2 lcd which displays only 32 characters. this lcd is a 16 pin device which can display values when programmed with the help of liquid crystal library. the 16 pins include: vcc pin which is the power supply for the lcd and is usually connected to the arduino’s 5v, while the gnd pin goes to arduino’s ground pin (0v). the vo pin controls the contrast of the lcd and is connected to 5v for maximum brightness or to the signal pin of potentiometer for brightness adjustments. the register select (rs) pin is used to select between control command signals for lcd and data. the rs pin is connected to ground (low) to send command signals to the lcd and to 5v (high) to send data. read/write (r/w) pin is used to select read or write mode. connecting the pin to high reads data from the lcd whereas setting it to low sends data to the lcd. enable (en) pin is used to enable or disable the lcd using high and low signals respectively. anode (a) and cathode (k) pins are used to power the lcd backlight by connecting to vcc and gnd pins of arduino respectively. the data buses (d0-d7) pins are used to carry data and commands between the lcd and arduino. there are two modes used to send data, namely the 8bit and the 4-bit modes. for the 8-bit mode, a byte is sent at once in pins d0 to d7 whereas in the slower 4-bit mode, 4 bits are sent in pins d4 to d7 twice. in this project, a 4-bit mode connection was used in order to reduce the number of cables used. pin 1 was connected to the ground, vcc to 5v, vo to signal pin of potentiometer, r/w to the ground, en to pin 11, rs to pin 12, d7, d6, d5, d4 to arduino’s pins 4, 5, 6, 7 respectively, the anode to 5v and the cathode to ground. 6) potentiometer the potentiometer is a variable resistor, usually with 3 pins: gnd, vcc, and output. in this project, the brightness of the lcd was controlled by a 10k potentiometer. the potentiometer ground pin was connected to arduino’s gnd pin and the vcc to 5v of arduino while the output pin was connected to the vo of the lcd. 7) arduino integrated development environment the arduino ide is a software which includes code editor, compiler, and uploader to upload programs to a board. the text editor is used for coding and the codes are uploaded to the arduino hardware via serial communication. 8) thingspeak iot cloud database thingspeak is a web service that allows the collected sensor data to be stored in the cloud and aids the development of internet of things (iot) applications [15]. it works with different development boards like arduino, raspberry pi, and lpc1768. it uses rest api and http that allows working with various programming languages. the sensor data from the arduino are transferred to the cloud database for storage, processing, and visualization. thingspeak service also allows performing online analysis on the data. during this project, one channel called contactless sensor was set up in thingspeak having three fields. the first field is for the ambient temperature, the second field for body temperature, and the third field for heartbeat values. each channel has a unique channel identifier (id) and application programmable interface (api) write and read keys and must be included in the coding. the write api key allows data to be sent to a channel while the read api allows data from a personal channel to be viewed by others. for this project the write api "y2hq4zoyatcb8ee4" was used to allow sensor data get sent to the thingspeak database. b. validation validation is the procedure of checking key indicators aimed at verifying whether the specifications for the system engineering, technology & applied science research vol. 11, no. 4, 2021, 7375-7380 7378 www.etasr.com okello & sinde: development of a sensor-based heartbeat and body temperature monitoring system … match the intended purpose. it is meant to check whether the user specifications and requirements are realized [16]. for the developed system, different approaches were used for validation, including unit testing, integration testing, and system testing. the summary of the testing is shown in table ii. table ii. system testing summary requirement description score device powering up led indicator different devices are connected to the power supply and the power indicator led is observed. pass interfacing sensors with arduino board after programming, the output of the sensor measurements was checked on arduino serial monitor. pass lcd was added to the setup the measured readings from the sensor were programmed to be shown on the lcd and this was observed. pass visualization of data a hardware setup was interfaced with the iot cloud database. the sensor data were visualized in graphical form. pass excel report after visualization, the sensor data were extracted in excel format for further local analysis. pass validation of the accuracy of the readings the system readings were compared to the readings from other devices at the hospital. pass c. unit testing unit testing is a technique used to verify the functional correctness of each module of the system [17]. for the developed system, the following modules were tested: esp8266 module, heartbeat sensor, contactless temperature sensor, lcd, and potentiometer. each was tested for proper powering and the interfacing with arduino was checked for proper functionality. d. integration testing this is a testing technique that is used to verify whether the modules tested in the unit testing stage can be integrated to work smoothly and properly without problems [18]. different functional modules were integrated and tested to confirm whether they were able to work together properly. for instance, the two sensors were all connected in addition to esp8266, potentiometer and lcd in a bottom up approach and tested for any possible errors. the integration test was done by combining modules bit by bit to make sure they were working properly. e. system testing system testing is a technique of putting the system as a whole and carrying out tests to proof whether it is working as planned and that it meets the intended end user’s requirements. the combined outcome of all the modules was successfully tested during this testing stage. system testing does not look at the structural dimension of the program code but rather the visible functional correctness of the end product. the hardware was interfaced with thingspeak cloud database for data storage and virtualization. after the interfacing, the system was tested as a whole and was found to perform according to plan. iii. results and discussion the developed system prototype that monitors body temperature and heartbeat rate for chronic patients can be seen in figure 2. a thingspeak cloud database was utilized to store and virtualize the patients’ data. the aggregated data can also be extracted in excel format for offline analysis, allowing the doctors to track chronic patient’s data in real time and keeping track of the patient’s health conditions. a 16×2 lcd was used to display the patient’s body temperature and heartbeat readings. the patients can see their temperature and heartbeat readings while at the same time the readings are sent to the database. thingspeak was configured and 3 fields were created in order to receive ambient temperature, target temperature, and heartbeat readings from different remote sensors. the data were analyzed and organized in graphical form in terms of a line graph in different fields. the fields receive real time data from the sensor nodes corresponding to patient’s body readings. figures 3 and 4 show the body temperature and heartbeat data stored and visualized on thingspeak cloud database. fig. 2. developed system prototype. fig. 3. thingspeak capture of body temperature readings. seventy people were examined by the system and their body temperature and heartbeat readings were displayed on the lcd and at the same time sent to the cloud database. normal engineering, technology & applied science research vol. 11, no. 4, 2021, 7375-7380 7379 www.etasr.com okello & sinde: development of a sensor-based heartbeat and body temperature monitoring system … body temperature is 37°c and a person is said to have fever when the temperature is greater than 38.0°c [19] while body temperature between 35.5°c to 37°c is usually regarded as fine when assessing a patient’s condition. therefore, the temperatures taken by the developed system as shown in figures 3 and 5 mostly fall in the normal body temperature category. whenever the heart pumps blood, there is an increase in oxygenated blood whereas a decrease in oxygenated blood occurs when the heart relaxes. the heartbeat rate measured in beats per minute (bpm) is basically determined by the amount of time between the increase and decrease in the oxygenated blood. the normal bpm for adults is about 72, for children it is about 90, and for babies about 120 [12]. the bpm values shown in figures 4 and 6 were taken from adults and children only. fig. 4. thingspeak capture of heartbeat readings. fig. 5. temperature taken by the system prototype. fig. 6. heartbeats taken by the system prototype. iv. conclusion the scarcity of health facilities in rural areas, especially in africa, is a serious hindrance to healthcare access. this poses serious risks and is even more paramount in chronic patients. the advancement of wireless sensor networks and cloud computing technology has created an opportunity for adopting telemedicine. in this paper, a system capable of monitoring body temperature and heartbeat rate of chronic patients has been developed. this system is capable of sending patients' data to a cloud database in real time. this system will bridge the gap in healthcare access caused by the insufficient healthcare facilities and will further improve the way of managing chronic patients as well as dealing with any sudden changes in the patient’s health condition in order to avert health complications. the developed system consists of a heart pulse sensor, an mlx90614 contactless temperature sensor, an esp8266 wireless module, an arduino board, and a cloud database. the database virtualizes the received data in graphical and spreadsheet formats. the system has the potential of adding more health indicators for monitoring. policy makers, governments, and different stakeholders such as the internet service providers should increase the internet coverage to enable such systems to be used in rural areas where health facilities are usually distant. various stakeholders in the health sector should be able to sensitize the citizens on the use of telemedicine as an alternative to physical visits to health facilities. this will save time and enable quality services to reach even remote areas because telemedicine doctors will be able to serve patients from any location. in the future, more research can be done in the area of adopting sensors to improve remote patient monitoring. this system can be further improved by incorporating a dashboard pop up mechanism for immediate alerts. acknowledgment the authors wish to thank the center of excellence for ict in east africa (cenit@ea) and the nelson mandela african institution of science and technology (nm-aist) for their support. finally, the authors wish to thank the medical concierge group uganda. engineering, technology & applied science research vol. 11, no. 4, 2021, 7375-7380 7380 www.etasr.com okello & sinde: development of 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[19] m. sund levander, "accuracy when assessing and evaluating body temperature in clinical practice. time for a change?," in eat2012 book of proceedings, jan. 2012, vol. appendix 1, pp. 25–32. engineering, technology & applied science research vol. 7, no. 8, 2017, 1797-1801 1797 www.etasr.com tafti et al.: a study of the effective lifetime of aluminum buckets used in blood bank centrifuges a study of the effective lifetime of aluminum buckets used in blood bank centrifuges mohammad fallah tafti blood transfusion research center inst. of research & education in transfusion medicine tehran, iran m.falah@ibto.ir reza golestani sina ebtekar company, tehran, iran golestani@sinaebtekar.ir mahmoud salari dept. of mech. eng. imam hossein university tehran, iran msalari@ihu.ac.ir abstract—rotating parts of blood bank centrifuges are under heavy mechanical cyclic stresses due to their centrifugal loading conditions. estimating the effective lifetime for these parts is very important for their application. providing safety requirements for these components is mandatory in blood transfusion centers (btc). failure occurs in the engineering parts for both loading conditions of steady and cyclic. the fatigue phenomenon is the main reason for mechanical failures at least in 90 % of fractures during operation. in this paper, the effects of fatigue caused by centrifugal loadings on aluminum buckets produced by the iranian sina ebtekar company (iseco) are investigated experimentally. in this study, 48 aluminum buckets are chosen from a set of 500 buckets. the numbers of service of the samples are accounted for a period of 7 months. finite element analysis, fem, is done for an aluminum bucket and the relevant maximum stresses due to the rotating loads of centrifugation are determined. analyzing the numerical results and using the fatigue, lifetime diagrams according to the number of operating cycles is presented for the samples. a good consistency is observed between the experimental and numerical results. based on the results, a new correlation is presented for estimating the aluminum bucket’s lifetime made by iseco. keywords-failure; fem; fatigue; lifetime; aluminum buckets; blood bank centrifuges i. introduction the application of organized knowledge and skills in the form of devices, medicine, procedures and systems development to solve a health problem and improve quality of lives is referred as “health technology” [1]. the term “healthcare technology” describes the type of device or equipment used in health facilities. the blood bank centrifuges are machines used to separate blood components like platelet, plasma and red blood cells. they rotates the blood bags placed in swing aluminum buckets with a rotational speed of 4000 to 5000 rpm [2]. the process is conducted in blood bank centers. mechanical safety evaluation of rotating parts of the centrifuges is an important issue for designers, manufacturers of medical equipment and their operators. aluminum buckets used as parts in centrifuges are used for keeping the liners included blood bags. it is obvious that these rotating parts are under heavy mechanical stresses during the centrifuge process [3-7]. during blood processing, buckets and other parts with rotational motion are under continuous loading, which starts from zero and reaches to a maximum stress and works for a programmed time. after the separation process, through a braking function, the amount of bucket stress decreases to zero again. as a result, the assessment of load conditions indicated the dominant failure mechanism for these buckets would be the fatigue. in [8], authors reported that such loads, that may not cause failure of a structure in a steady state, may cause fracture when they are applied repeatedly on structures. failure may occur after a number of cycles of loading and unloading, usually a few millions of cycle, depending on the amplitude of the applied load. therefore the fatigue phenomenon can be also a main reason for failure of these type of parts [9–13]. this study tries to finds a method to estimate the lifetime of aluminum buckets used in blood bank centrifuges and to develop instructions for their preventative maintenance. stability and practically unlimited lifetime for engineering parts is a necessity because a sudden fracture can endanger peoples’ life and cause financial damages. there are different bases to investigate the lifetime of an engineering part. all topics from fracture progress theories in dynamical loading till creep analysis in static loading are developed for the purpose of estimating the lifetime of engineering parts. for metals, theoretical basis included fatigue; fracture and etc. are developed topics. some proposed topics in mechanical metallurgy [2] are theoretical basis of fracture, fatigue and creep. but according to the functional loading condition and environmental conditions for each engineering part the effective lifetime and exchanging time should be provided before occurring sudden fracture to avoid possible damages. the fatigue phenomenon is the main factor of fracture creation and destruction and thus the major factor that determines the bucket’s lifetime. because of the creep, the aluminum material in a temperature lower than 100 oc doesn’t have sensitivity and the creep process is not observed [14-17]. although stress release doesn’t occur suddenly but over time, it still may cause sudden and friable fractures in the part [18–21]. engineering, technology & applied science research vol. 7, no. 8, 2017, 1797-1801 1798 www.etasr.com tafti et al.: a study of the effective lifetime of aluminum buckets used in blood bank centrifuges other factors, usually considered are the effect of environmental corrosion, the effect of structure defects and the effect of structure tolerances. with regards to high rotational speed and weight of components during rotation in these devices, predicting the useful effective lifetime and estimating time to exchange buckets during operation is necessary, keeping in mind that fracture of buckets in these rotational speeds will cause irreparable damages [22–25]. ii. analysis method the present study focused on investigating the lifetime of 48 buckets in 3 blood bank centers in mashhad. it includes surveys undertaken in 7 months. it aims to determine the factors that adversely affect the operation, maintenance and disposal of the device. for analytical study of the lifetime of buckets, a chain of engineering steps were followed: a) determine loading conditions, b) model the system in a cad software, c) analyze stress in an fem software, d) extract lifetime results fatigue standard data based on maximum stress and finally e) use an innovative formula to construct some sample instructions for predicting the lifetime of buckets in a blood bank center and determine replacement time. to estimate the lifetimes of buckets, designed and manufactured by sina ebtekar company, one blood bank centrifuge from one of the six blood bank centers of ibto in mashhad was considered. the main reason for this selection was that the base of maintenance supplied unit of sina ebtekar company is in mashhad and the recording experimental results are a time consuming work and need the cooperation of these units. for this study, 48 aluminum buckets of the sina ebtekar plus brand were randomly selected from 500 buckets and the lifetimes of these buckets were studied for 7 months (from february 5 to august 21, 2014). normally the amount of load mass for each bucket during a cycle was about 2500 gr and the rcf was between 4500 and 5000 rpm. at the same time, with the gathering of the statistics of the 48 buckets, the lifetime of buckets was estimated. in this method by reviewing the loading conditions, determining the initial and boundary conditions and material characteristics of buckets and using the finite element method (fem) analyses, the maximum stress related to cyclic loads (repeated loading and unloading of accelerating and braking) was extracted (figure 1) and by mapping the maximum stress of buckets from fem analysis onto (s-n) fatigue life curve of the aluminum of bucket (figure 2) the safe zone for blood bank centrifuge’s bucket, was extracted and shown in figure 3 and the buckets lifetime was estimated (in cycles). a 3d modeling of the bucket was done using solid works modeling software and to obtain the maximum stress during cyclic loading, the finite element analysis was used. for this method, the cosmos software has been used. by simulating the operating conditions, the stresses on the body of bucket have been calculated. figure 4 shows the 3d model. in order to decrease the amount of unnecessary calculations, the 3d model was simplified in the region far from the stress concentration points. figure 1 shows the results of the finite elements analysis. fig. 1. the fem results of the stress contours occurred in a bucket during centrifuge process. fig. 2. s-n diagram for aluminum alloys fig. 3. the safe zone for blood bank centrifuge’s bucket. engineering, technology & applied science research vol. 7, no. 8, 2017, 1797-1801 1799 www.etasr.com tafti et al.: a study of the effective lifetime of aluminum buckets used in blood bank centrifuges fig. 4. three diensional model of the aluminum bucket for modeling blood bags in the liner, by considering weight and volume of bags, the irregular geometric square was used. according to material characteristics of liners, the mechanical property of liners for “static structural characteristics” has been considered as “linear elastic-isotropic” with elasticity modulus of 1.2gpa and poisson’s ratio of 0.41. loading has done as a centrifuge rotation with a rotational speed of 4000 rpm and the radius of the rotor has been considered 280 mm. these conditions caused 5000 units for rcf. it has been observed that maximum stress o is approximately 18 to 20 mpa. briefly, for the lifetime assessment analytically based on fatigue, following phases were done step by step: • the loading conditions were assessed. during this step the boundary conditions and initial conditions were defined. • cad model of the system was built in solidworks software and exported in standard cad format for finite element analysis. • the finite element model of the system was built in cosmos software. pyramid elements with four nodes and linear shape function were used. • material characteristics, boundary conditions and initial conditions were imposed to the finite element model and the problem was solved by using default setting. the most important result of the fem was the maximum stress in liner part during centrifugation operation. based on the results of fem and using fatigue data for the material of liner (co-polymer polypropylene) the lifetime of liners was estimated in cycles (the number of repeated loading and unloading that liner can bear to show the first sign of fracture). this result is adequate for any designer. but in order to prevent unwanted failure and loss of life, every technician of preventative maintenance system or technical staff of blood bank centers needs to know how many days the liners must be used and according to their own daily schedule when liners need to be replaced with new ones. finally, according to the plan for daily blood bags that are processed in each center, a simple but applicable formula was developed. it is useful for each machine, because some centers have more than one machine for blood processing. so it’s possible to know how many days a liner could be used. iii. results and discussion experimental and analytical results show that the prediction success rate reached 97%. about 3% of the buckets have a lifetime more or less than the predicted amount and 75% of the buckets have an effective lifetime between the lower and upper bound (13000 to 18000 cycles). about 22% of buckets have a lifetime larger than the predicted one. this is shown clearly in figure 1. as shown, if the lower bound is considered a success rate of 97% is achieved. if the upper bound is considered the success rate falls to 78%. here we presented a hypothetical formula which could be used to estimate the possible working time of copolymer buckets in the centrifuges of any blood bank with the same circumstance. the formula to calculate the number of operating days of buckets can be calculated as: number of operating days = 5 3 1 2 12x x x x where: x1: the number of centrifuging of each blood bag according to the statistic and existent reports x2: the number of blood bags in blood transfusion center bag according to the statistic and existent reports. the capacity of each centrifuge is 12 blood bags. x3: the number of centrifuge systems in blood transfusion center. x5: the useful lifetime of bucket by the number of operation according to bucket’ volume. this functions is hyperbolic (figure 5). comparing between the experimental and analytical lifetimes shows reasonably compatibility. the useful lifetime of buckets according to the fatigue analysis is between 13000 and 18000. according to the existent statistic, each blood bag centrifuges on average 2 times. table i shows the lower bound lifetime (13000 cycles) results for the “sina ebtekar plus” buckets. it’s advised that these amounts are considered as the ultimate lifetime of buckets. by this assumption you can prevent 97% of unwanted failure. in figure 5, the curves of “upper and lower fatigue life of liners” in days upon “the numbers of blood bags plus liners that processed daily in a blood bank center” are shown. the analytical results show that the lifetime should be between 13000 cycles (lower predicted bound) and 18000 cycles (upper predicted bound). curves are formed by output of the innovative formula with locating appropriate amount for variables. table i. the main instruction for replacement the buckets of sina ebtekar company in a preventative maintenance system. number of blood bags per day 50 60 80 100 lifetime (days) 192 160 120 96 engineering, technology & applied science research vol. 7, no. 8, 2017, 1797-1801 1800 www.etasr.com tafti et al.: a study of the effective lifetime of aluminum buckets used in blood bank centrifuges number of blood bags u se fu ll ife (d ay s) 500 1000 1500 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 1 centrifuge 3 centrifuge 5 centrifuge 7 centrifuge 9 centrifuge fig. 5. buckets lifetime (day) according to the number of blood bags and devices. a. mechanical properties of aluminum low special weight, low molting point, proper resistance to corrosion, good thermal and electrical conduction, being nonmagnetic and nontoxic, formability, high capacity of casting, proper stability, good appearance and color and proper cover ability make this metal to have a lot of application in automotive industry, building, maritime industry, petrochemical, food industry, electrical and electronics, military industry, aerospace, computer and etc. aluminum allays divided into two groups of casting alloys and wrought alloys. most of these consumable alloys are wrought which according to the aluminum association it divided into eight groups of 1xxx to 8xxx [27-28]. buckets in blood bank centrifuges because of their operating condition mostly are built by alloys of groups 2xxx and 7xxx which are respectively al-cu-mn and al-zn-mg alloys [27-28]. the mechanical properties of 2xxx and 7xxx alloys are shown in table ii. table ii. elastic properties of useful samples of alloys of groups 2000 and 7000[27]. material yield stress ultimate stress young's modulus shear modulus poisson's ratio 2014-t6 386.1 448.2 72 28 0.33 2014-t4 393 475.7 72 28 0.33 7075-t6 441.2 517.1 72 27 0.33 for engineering parts, two types of friable and soft fracture are possible. classification is conducted according to plastic transformation. soft materials typically have significant plastic transformation before fracture and also the energy absorption is high, but friable material usually have a little plastic transformation or don’t have any at all and absorb little energy before fracture. factors that cause friable fracture include temperature reduction, increasing strain rate, presence of sharp groove or grown crack and increasing sample thickness. fatigue is a kind of friable fracture that occurs in structures which are under dynamical or switching stresses like bridges, plane and rotational parts. under these conditions in stresses which are much lower than tensile or yield strength for static loading, friable stresses occur. the fatigue term is used because this type of fracture usually occurs after periodic numbers of stress-strain cycle. fatigue is important because it is one of the main reasons of metal’s fracture. about 90% of metals, ceramics and polymers are disposed to this type of fracture. furthermore such a fracture is sudden and unexpected and occurs without any pervious knowledge. even for a soft material in friable fracture process, a little plastic transformation occurs and the process stared by germination and crack growth and fracture surface is perpendicular to applied strain. there are three methods to determine the resistance to fatigue that the most important of them are stress-life method. in this method the fatigue information of metals is plotted in s-n diagram which is fracture stress versus stress period cycles [28]. surface under curve is the safe region from the perspective of design. for wrought alloys of aluminum s-n diagram is shown in figure 2. b. fatigue study in this paper, fatigue effects of centrifugal stresses on aluminum buckets of blood bank centrifuges was considered for determining the effective lifetime. by considering the number of permissible cycles until fatigue fracture of the bucket’s material, the number of the operating days of buckets determined by using the maximum stress cycles which calculated from finite element static analysis. c. 3d modeling of bucket and finite elements analysis 3d modeling of bucket was performed by solid works modeling software and ansys software was been used for finite element analysis. one of the important issues in bucket modeling is modeling connection of bucket to the rotor. for modeling this using joint is the easiest method and using the element contact is the most complete method to solve that. also there are different ways for modeling the mass because of blood bags, liners and balance weights but using additional mass because of simplicity is the most appropriate way and also its doesn’t have a noticeable difference in results in comparison with other methods. d. calculating the effective lifetime of blood bank centrifuge’s bucket it is mentioned that buckets with rotational equipment of blood bank centrifuge in each usage, are under continuous loading which starts from zero and reaches to a maximum stress and stays in that stress limitation for a specific time. and then by start braking, the stress decrease until reaches to the zero again. so applied stresses to the buckets can be divided into two groups: • stresses of staring and braking transient steps of device which addition of them in each operating cycle can be assumes as a one periodic cycle in constant direction. since it’s needed to have the amount of maximum cycle stresses for fatigue analysis, using the static analysis which is the determiner of maximum applied stress, is considered more valid. • loading can be assumed completely static as the operating temperature is under 22 oc and for this alloy, the minimum engineering, technology & applied science research vol. 7, no. 8, 2017, 1797-1801 1801 www.etasr.com tafti et al.: a study of the effective lifetime of aluminum buckets used in blood bank centrifuges temperature for creep is near 100 oc. so creep effects are not considered. in order to determine the number of operating cycle of bucket, according to the results of the numerical finite element analysis, maximum stress would be about 303mpa. considering a safety factor of 1.4, the stress in the maximum value it reaches 363 mpa which is equivalent of 52.6 ksi. in figure 3, the safe zone for designing of centrifuge bucket and the predicted lifetime has shown. it determines that the effective lifetime of buckets is between 13000 and 18000 stress cycles. according to the effective lifetime curves, obtained in this study, the exchanging timetable for isec’s buckets of blood bank centrifuges in each blood transfusion center was presented. for example, the maximum effective lifetime of a bucket, which used in a blood bank center with a capacity of centrifuge rate of 200 blood bags per a day, is 1400 working days or 46 months and if that mentioned centrifuge centrifuges maximum of 100 blood bags per a day, the lifetime of its buckets will be 2100 working days. iv. conclusion in summary, our hypothetically presented formula is working when buckets made by “sina ebtekar plus” are taken under centrifugal force with an rcf between 4500 and 5000 and temperature between 2 and 20 °c. other destructive factors like solvents and humidity were not considered in this investigation. fatigue effects of centrifugal stresses on polymer liners of blood bank centrifuges were considered for determining their effective lifetime. experimental tests were done to validate the analytical results. the results of this study can be useful for both the centrifuges designers and the blood banks maintenance staff. acknowledgement the authors thank the sina ebtekar company and the iranian blood transfusion organization for their support of this research. references [1] a. p. parker, “stress intensity factors, crack profiles, and fatigue crack growth rates in residual stress fields” in residual stress effects in fatigue, astm international, 1982 [2] g. e. dieter, d. j. bacon, mechanical metallurgy, vol. 3, mcgraw-hill new york, 1986 [3] h. pfister, k. h. braun, “induction of correct centrifugal 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fundamentals of biomechanics: equilibrium, motion, and deformation. springer science & business media, 2012 [9] u. beck, g. reiners, d. lerche, u. rietz, h. niederwald, “quantitative adhesion testing of optical coatings by means of centrifuge technology”, surf. coatings technol., vol. 205, pp. s182–s186, 2011 [10] j. c. q. amado, “manufacture and testing of lightweight tubes for rocketry and centrifuges”, light. compos. struct. transp. des. manuf. anal. perform., p. 421, 2016 [11] s. kamandulis, t. venckunas, a. snieckus, e. nickus, j. stanislovaitiene, a. skurvydas, “changes of vertical jump height in response to acute and repetitive fatiguing conditions,” science & sports, vol. 31, no. 6, pp. e163-e171, 2016 [12] m. tunali, h. özdemir, z. küçükodaci, s. akman, e. öncü, m. aydınbelge, m. akman, e. firatli, “a new centrifugation method for the improvement of platelet-rich fibrin products: a preliminary study”, br. j. med. med. res., vol. 13, no. 6, pp. 1–10, 2016 [13] s. kabir, t. i. yeo, “characterization of low-cycle fatigue parameters”, br. j. appl. sci. technol., vol. 12, no. 3, pp. 1–15, 2016 [14] m. r. mitchell, r. w. landgraf (eds), advances in fatigue lifetime predictive techniques, american society for testing and materials, 1993 [15] x. hai-jun, s. jian, “failure analysis and optimization design of a centrifuge rotor”, eng. fail. anal., vol. 14, no. 1, pp. 101–109, 2007 [16] h. kamata, h. mashimo, “centrifuge model test of tunnel face reinforcement by bolting”, tunn. undergr. sp. technol., vol. 18, no. 2, pp. 205–212, 2003 [17] w. a. take, m. d. bolton, “the use of centrifuge modelling to investigate progressive failure of overconsolidated clay embankments”, in constitutive and centrifuge modelling: two extremes, taylor & francis, 2002 [18] a. grm, m. batista, “on the coupling of analytical and fem solution in stress analysis around the polygonal hole shape in a finite twodimensional domain”, int. j. mech. sci., vol. 118, pp. 254–267, 2016 [19] s. m. jang, h. w. cho, s. k. choi, “design and analysis of a high-speed brushless dc motor for centrifugal compressor”, ieee trans. magn., vol. 43, no. 6, pp. 2573–2575, 2007. [20] p. jeanjean, “re-assessment of py curves for soft clays from centrifuge testing and finite element modeling”, offshore technology conference, 2009 [21] f. mckenna, m. h. scott, g. l. fenves, “nonlinear finite-element analysis software architecture using object composition”, j. comput. civ. eng., vol. 24, no. 1, pp. 95–107, 2009 [22] d. wang, d. j. white, m. f. randolph, “large-deformation finite element analysis of pipe penetration and large-amplitude lateral displacement”, can. geotech. j., vol. 47, no. 8, pp. 842–856, 2010 [23] i. anastasopoulos, g. gazetas, m. f. bransby, m. c. r. davies, a. el nahas, “fault rupture propagation through sand: finite-element analysis and validation through centrifuge experiments”, j. geotech. geoenvironmental eng., vol. 133, no. 8, pp. 943–958, 2007 [24] d. forsström, p. jonsén, “calibration and validation of a large scale abrasive wear model by coupling dem-fem: local failure prediction from abrasive wear of tipper bodies during unloading of granular material”, eng. fail. anal., vol. 66, pp. 274–283, 2016 [25] s. asiri, “modal and vibration analysis of functionally graded dental implant”, br. j. med. med. res., vol. 12, no. 7, pp. 1–14, 2016 [26] d. g. ullman, the mechanical design process, vol. 2. mcgraw-hill new york, 1992. [27] d. s. mackenzie, g. e. totten, analytical characterization of aluminum, steel, and superalloys. crc press, 2005 [28] j. e. shigley, shigley’s mechanical engineering design. tata mcgrawhill education, 2011 engineering, technology & applied science research vol. 8, no. 3, 2018, 2882-2886 2882 www.etasr.com memon et al.: effects of uncrushed aggregate on the mechanical properties of no-fines concrete effects of uncrushed aggregate on the mechanical properties of no-fines concrete muneeb ayoub memon department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan engr.muneebmemon@gmail.com muhammad aslam bhutto department of civil engineering ned university of engineering & technology karachi, pakistan mabhutto@neduet.edu.pk nawab ali lakho department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan nawablakho@gmail.com imtiaz ali halepoto department of computer systems engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan halepoto@quest.edu.pk ammaar noor memon department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan anmemon96@gmail.com abstract—concrete’s self-weight is a major aspect of a structure’s overall weight. recently, the use of lightweight concrete (no-fines, foamed and cellular concrete) has been increased. normally no-fines concrete is produced with crushed coarse aggregate of uniform gradation. this study aims to investigate experimentally the effects of the use of uncrushed coarse aggregates on unit weight, compressive and tensile strength of the no-fines (nfc) as well as conventional concrete (cc). in addition, the effects of coarse aggregate size on the mechanical properties were also studied. four gradations of uncrushed coarse aggregates ranging between (5.5-4.75) mm, (104.75) mm, (20-4.75) mm and (25-4.75) mm were used for preparing the concretes. the fixed cement-aggregate ratios of 1:6 (with w/c ratio=0.4) and 1:2:4 (with w/c ratio=0.5) were adopted for nfc and cc respectively. it was found that the gradation of uncrushed coarse aggregate has a significant effect on the mechanical properties of nfc. a maximum of 16% reduction in self-weight of the concrete without fines was obtained, as compared to that with fines. moreover, the compressive strength of no-fines concrete significantly improved by replacing crushed with uncrushed coarse aggregate. the compressive strength increased by 16% for the batch of (25-4.75) mm. keywords-no-fines concrete; uncrushed aggregate; unit weight; compressive strength i. introduction the self-weight of concrete is a major aspect of the overall weight of the structure. the lightweight concrete with sufficient strengths can be used for partition walls in framed structure, road pavings etc [1]. no-fines concrete is categorized as lightweight concrete. the no-fines concrete (nfc) is cast by mixing cement and only coarse aggregate [2]. the behaviour of nfc has been investigated by some researchers. authors in [3] replaced coarse and fine aggregates with clay and used aluminum-wastage as foaming agent for cement. in addition, compressive strength and thermal conductivity of no-fines cellular concrete were investigated. authors in [4] carried out an experimental study to determine the compressive strength of structural lightweight concrete by non-destructive ultrasonic pulse velocity method. they found that lightweight concretes with less porous aggregates are associated with lower ultrasonic pulse velocity and vice versa. authors in [5] experimented on the use of no-fines concrete as a building material and determined strength, durability properties of nofines concrete and checked corrosion protection of the embedded steel. they concluded that no-fines concrete could also be used in non structural elements such as reinforced panels. authors in [6] investigated some properties of no-fines polymer concrete, using 10mm maximum size of coarse aggregates. several concrete mixes with different cement aggregate ratios like 1:5, 1:6 and 1:7 were produced. the polymer was mixed in percentages by weight of cement as 5%, 7% and 10%. it was found that the density of no-fines concrete varies between 2030 and 2170kg/m3 and thermal conductivity was in the range recommended by aci 213-87 for structural lightweight concrete. author in [7] studied the hardened properties of no-fines concrete and used it as a lightweight concrete block masonry unit. in this study three different aggregate/cement ratios of 6:1, 8:1 and 10:1 and three different w/c ratios of 0.35, 0.4 and 0.45 have been used to determine the compressive strength, flexural strength and split tensile strength of nfc. results showed that for building application aggregate-cement ratio of 6:1 mix at 0.45w/c ratio is recommended. their 28 day compressive strength was found more when compared to other mixes, while the split tensile and flexural strength of no-fines concrete was found to range. authors in [8] carried out an experimental study to investigate engineering, technology & applied science research vol. 8, no. 3, 2018, 2882-2886 2883 www.etasr.com memon et al.: effects of uncrushed aggregate on the mechanical properties of no-fines concrete the performance of no-fines concrete in terms of compressive strength, porosity and permeability. the effect of aggregate gradation and use of fine aggregate in the mix proportion was also studied to evaluate the performance. the well graded sample was found suitable among various types of gradation. after that 0%, 2%, 4%, 6%, 8% and 10% fine aggregate (sand) was added in the well graded sample having water/cement ratio and aggregate/cement ratio 0.40 and 4.5:1, respectively. it was found that the addition of fine aggregate (sand) up to 10% increased the compressive strength about 56% but decreases porosity and permeability about 85% and 76%, respectively. author in [9] investigated the mechanical characteristics of no fines concrete with or without polypropylene fibers. the studied properties were unit-weight, compressive strength and tensile strength. results showed that the addition of polypropylene fibers in no-fines concrete can improve mechanical properties, especially tensile strength and compressive strength by 19% and 17% respectively compared with the concrete without fibers, with a slight effect on density. it was found that the strength of no-fines concrete is strongly related to its mixture proportion although sufficient research has been carried out to investigate the behavior of no-fines concrete, yet no attempt has been made to investigate experimentally the strength properties and unit weight of no-fines concrete with uncrushed aggregates. uncrushed aggregate is a waste obtained from the sieving of fine hill sand. the usage of waste in no-fines concrete makes it more economical when compared to conventional concrete. in view of the aforementioned issues, this study aims at investigating the effects of uncrushed coarse aggregate on unit weight, compressive and tensile strength of the no-fines (i.e. lightweight) concrete (nfc). in addition the effects of coarse aggregate size on mechanical properties were studied. compressive and tensile strength tests in specimens cast from four different batches of coarse aggregates were conducted. the results of nfc were compared with that of conventional concrete. ii. experimental part a. materials and mix proportions of concrete ordinary portland cement (opc) as per standard of astm c150 was used to prepare nfc and conventional concrete mix. to prepare conventional concrete mix design, locally available hill sand (i.e. passed from no. 16 sieve) was used. the hill sand was complying with astm c 778-02 (2002) and its gradation was according to specifications of astm c 33-03 (2003). the retained hill sand from no. 16 sieve was used as coarse aggregate for preparation of both no-fines and conventional concrete. the retained uncrushed coarse aggregates were smooth in surface texture. the smoothness of the coarse aggregates improves workability of both concretes. these different particle size aggregates were passed from different sizes of sieves (i.e. 4.75, 5.5, 10, 20 and 25mm) to obtain different batches of coarse aggregates. four different batches were formed ranging from 4.75 to 5.5mm, from 4.75 to 10mm, from 20 to 5.5mm and from 25 to 5.5mm. to be more specific, the aggregates retained in 4.75mm sieve and passed from 5.5 mm sieve in the first batch (from 4.75 to 5.5 mm). all the batches of the coarse aggregates are summarized in table i. tap water (suitable for drinking) was used while preparing conventional and no-fines concrete. a mixed proportion of 1:6 (cement: coarse aggregate) was used for the preparation of nofines concrete. whereas conventional concrete was prepared from a mixed proportion of 1:2:4 (cement: fine aggregate: coarse aggregate). table i. batches of coarse aggregates s. no. batch designation description 01 nfc / cc (5.5–4.75) un-crushedcoarse aggregates of size 5.5mm to 4.75mm 02 nfc / cc (10–4.75) un-crushed coarse aggregates of size 10mm to 4.75mm 03 nfc / cc (20–4.75) un-crushed coarse aggregates of size 20mm to 4.75mm 04 nfc / cc (25–4.75) un-crushed coarse aggregates of size 25mm to 4.75mm note: nfc= no-fines concrete; cc= conventional concrete b. specimen preparation cubes of conventional and nfc with standard size 150mm x 150mm x 150mm were prepared for compressive strength measurement of both concretes. for measuring tensile strength, cylinders of 100mm diameter and 200mm length were cast. in order to check accuracy and repeatability of the tests results, five specimens of each of cubes and cylinders were cast from each batch of coarse aggregates. cubic and cylindrical moulds made of steel were used to cast the specimens. the prescribed concrete mixes (i.e. 1:6 and 1:2:4 for no-fines and conventional concretes, respectively) were prepared from each batch of coarse aggregates. after each mix preparation, the concrete was poured into cubic and cylindrical steel moulds. before pouring, a thin oil layer was applied to the inside surfaces of the mould in order to prevent the bond development between the mould and the concrete. the conventional concrete was poured into moulds in three layers and then was compacted using vibration table. however, the nfc was poured in one layer and without compaction. the specimens were then demoulded after 24 hours curing in a controlled indoor environment. next, the samples were kept in a water tank for curing at 2710c until testing. some specimens of nfc are shown in figures 1 and 2. fig. 1. demoulded cubes of nfc engineering, technology & applied science research vol. 8, no. 3, 2018, 2882-2886 2884 www.etasr.com memon et al.: effects of uncrushed aggregate on the mechanical properties of no-fines concrete c. test methods before the specimens of no-fine and conventional concrete were tested for compressive and split tensile strength, each specimen’s unit weight was determined. all the specimens were weighed to calculate the unit weight before testing. to determine compressive strength, the cubes were tested in a universal testing machine (utm). the cubes were placed with the cast faces in contact with platens of the testing machine as shown in figure 3. then, the compressive load was applied gradually. because of the non-linearity in the behavior of the concrete, the strain rate was increased progressively as failure was approached. the ultimate load at the crushing failure of cube specimens was recorded. the load is divided by the cross sectional area of the cube to determine the ultimate compressive strength. as mentioned in section b, five specimens of cubes of each of no-fines and conventional concrete were cast from each batch. the ultimate compressive strength of each of the five specimens was measured. the average of the five values represents the ultimate strength of the cubes of their respective batch. cylinder tests were performed to determine the tensile strength of no-fines and conventional concrete. in this test the concrete cylinders were placed with their horizontal axis between the platens of the utm (figure 3) and the load increased until failure by indirect tension in the form of splitting along vertical diameter took place. at cylinder failure, the ultimate load was recorded and tensile strength was calculated from (1) ldpf 14.321    where f1=tensile strength, p=ultimate applied load l=cylinder length and d= cylinder diameter. fig. 2. demoulded cyliders of nfc fig. 3. a cyliderical specimen placed in utm iii. results and discussion a. unit weight the unit weight of each specimen of no-fines and conventional concretes was calculated before compressive and tensile strength tests. the average unit weight is given in table ii. it can be observed that the unit weight of the batch with larger size of uncrushed coarse aggregate was higher. for the batch 25-4.75mm, the maximum unit weight was 2152kg/m3 and 2527kg/m3 for no-fines and conventional concrete, respectively. figure 4 compares the unit weight of nfc with crushed and coarse aggregates. the unit weight of nfc with crushed aggregates for each batch was measured in [1]. it can be seen that nfc with uncrushed coarse aggregates is lighter than the nfc with crushed aggregates. the maximum 2152 kg/m3 and minimum 2038 kg/m3 unit weight of nfc with uncrushed coarse aggregates were measured for the batch of 5.5-4.75mm and 25-4.75mm respectively. the nfc with uncrushed coarse aggregates prepared from batch 5.5-4.75mm is 13% lighter than that with crushed coarse aggregates. figure 5 illustrates the comparison of the unit weight of no-fine concrete with that of conventional concrete for each batch with uncrushed coarse aggregates. it can be seen that the unit weight of the nfc is less than that of conventional concrete. this implies that the nfc is lighter than the conventional concrete. the nfc from batch 5.5-4.75mm was found to be 20% lighter than conventional concrete. table ii. average unit weight s. no. batch designation average unit weight (kg/m3) no-fines concrete conventional concrete 01 nfc / cc (5.5– 4.75) 2038.4 2426.64 02 nfc / cc (10–4.75) 2059.11 2451.95 03 nfc / cc (20–4.75) 2143.98 2522.62 04 nfc / cc (25–4.75) 2152.26 2527.34 b. compresive strength figure 6 shows the compressive strength of nfc with crushed and uncrushed coarse aggregate after 28 days. author in [1] measured the compressive strenght of nfc with crushed coarse from cubes after 28 days. therefore, a direct comparision can be made. it can be seen from the figure that nfc with uncrushed aggregate gives higher compressive strength than the concrete with crushed aggregate in each batch. the maximum compressive strength of was measured in the batch of 25-4.75mm. the magnitude of the maximum compressive strength is 10mpa which is 16% higher than that with uncrushed coarse aggregates. furthermore the size of coarse aggregates has significant effect on the compressive strength of no-fines concrete. the compressive strength increases with coarse aggregate size. the percentage increment of compressive strength of batch 25-4.75mm is 110 when compared to the strength of nfc of batch 5.5-4.75mm. figure 7 illustrates the compressive strength of nfc with uncrushed coarse aggregate and cc after 28 days. it can be observed that the strength of cc reduces significantly without fine aggregates (i.e. no-fines concrete). a maximum reduction of 72% was engineering, technology & applied science research vol. 8, no. 3, 2018, 2882-2886 2885 www.etasr.com memon et al.: effects of uncrushed aggregate on the mechanical properties of no-fines concrete measured. however, the compressive strength of both concretes increases with the increment of coarse aggregates size. this is the reason the nfc is used in non-structural applications (such as paving). 0 500 1000 1500 2000 2500 3000 5.5-4.75 10-4.75 20-4.75 25-4.75 a v er ag e u n it w ei gh t ( k g/ m 3 ) crushed coarse aggregate uncrushed coarse aggregate fig. 4. unit weight of nfc with crushed and uncrushed coarse aggregate 0 500 1000 1500 2000 2500 3000 5.5-4.75 10-4.75 20-4.75 25-4.75 a v er ag e u n it w ei g h t (k g /m 3 ) no-fines concrete conventional concrete fig. 5. unit weight of nfc and cc with uncrushed coarse aggregate 0 2 4 6 8 10 12 5.5-4.75 10-4.75 20-4.75 25-4.75 a v er ag e co m p re ss iv e st re n gt h ( m p a) crushed coarse aggregate uncrushed coarse aggregate fig. 6. compressive strength of nfc with crushed and uncrushed coarse aggregate 0 5 10 15 20 25 30 5.5-4.75 10-4.75 20-4.75 25-4.75 a v er ag e c o m p re ss iv e st re n gt h ( m p a) no-fines concrete conventional concrete fig. 7. compressive strength of nfc and cc with uncrushed coarse aggregate c. compressive and tensile strength figure 8 compares the compressive and tensile strength of nfc with uncrushed aggregates for all batches. it can be seen that the tensile strength is much smaller than the compressive strength of nfc for all batches. however, it is observed that tensile strength is same for all batches. it implies that the tensile strength is independent of the size of coarse aggregate in nfc. the maximum difference (i.e. 84% smaller) between tensile strength and compressive strength was found in the 254.75mm batch. engineering, technology & applied science research vol. 8, no. 3, 2018, 2882-2886 2886 www.etasr.com memon et al.: effects of uncrushed aggregate on the mechanical properties of no-fines concrete 0 1 2 3 4 5 6 7 8 9 10 5.5-4.75 10-4.75 20-4.75 25-4.75 s tr en gh t o f n o -f in es c o n cr et e batch compressive tensile fig. 8. comparision of compressive and tensile strength nfc with uncrushed coarse aggregate similar to compressive strength, the tensile strength of nfc is lower than that of conventional concrete with uncrushed coarse aggregates (as shown in figure 9). however, tensile strength of conventional concrete increased with the size of uncrushed coarse aggregates. for the batch 25-4.75mm, the tensile strength of nfc was measured 68% less than that of conventional concrete. 0 1 2 3 4 5 5.5-4.75 10-4.75 20-4.75 25-4.75 a v er ag e t en si le s tr en gt h ( m p a) no-fines concrete conventional concrete fig. 9. comparision of tensile strength of nfc and cc with uncrushed coarse aggregate iv. conclusion the compressive strength of nfc is significantly improved by replacing crushed with uncrushed coarse aggregate. the compressive strength increased by 16% for the 25-4.75 mm batch. on the contrary, the unit weight of the nfc with uncrushed aggregate decreased compared to that with uncrushed coarse aggregates. however, a maximum reduction percentage of 72% was achieved in compressive strength of the concrete without fines. the nfc with uncrushed coarse aggregates prepared from the 5.5-4.75 mm batch is 13% lighter than that with crushed coarse aggregates. the tensile strength of both concretes is in agreement with the standard values reported in the literature (i.e. 5% to 15% of respective compressive strength). the tensile strength of nfc was measured 20% of that of compressive strength. acknowledgment authors are grateful to the quaid-e-awam university of engineering, science and technology, nawabshah for providing the research facilities. references [1] z. a. tunio, experimental investigation of strength of no-fines concrete with various course aggregate gradation, m.e, quaid-e-awam univeristy of engineering scince & technology, 2015 [2] n. newman, p. owens, “properties of lightweight concrete”. in newman, j. and choo, b.s. 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2075-2079, 2016 [8] m. a. kabir, k. m. s. islam, “performance study on no fines concrete”, 3rd international conference on civil engineering for sustainable development (iccesd), kuet, khulna, bangladesh, 2016 [9] a. a. muttar, “improving the mechanical properties of nofines concrete”, journal of babylon university/ engineering sciences, vol. 21, no. 2, 2013 microsoft word etasr_v11_n3_pp7240-7246 engineering, technology & applied science research vol. 11, no. 3, 2021, 7240-7246 7240 www.etasr.com asrar et al.: facile coating of hap on ti6al4v for osseointegration facile coating of hap on ti6al4v for osseointegration shafaq asrar department of metallurgical engineering ned university of engineering and technology karachi, pakistan shafaqfara@neduet.edu.pk muhammad tufail ned university of engineering and technology karachi, pakistan mtufail@neduet.edu.pk ali dad chandio department of metallurgical engineering ned university of engineering and technology karachi, pakistan alidad@neduet.edu.pk abstract-ti6al4v alloy is a material with great strength, lowslung modulus, inferior density, and a virtuous blend of mechanical and exceptional corrosion resistance. however, it does not offer good osseointegration and bone development properties. conversely, hydroxyapatite (hap) is highly bioactive in nature to bind with the nearby bone tissues when implanted in the host body. in this work, we have extracted hap from bovine bones by using the thermal decomposition method. this was followed by its deposition onto the ti6al4v alloy using the electrophoretic deposition (epd) technique. tio2 is used as a bond coat layer to increase the adhesion between hap and ti6al4v alloy substrates. the coated samples after sintering exhibited excellent adhesion. this was followed by characterization using scanning electron microscopy (sem) and fourier transformed infrared spectroscopy (ftir). ftir and sem confirm the formation of hap and its presence after the immersion in sbf. vicker hardness tester confirms the increase in hardness value of coated samples up to 35%. potentiostat tests were conducted to compare the corrosion rate of both samples. in addition, the particle sizes were also identified by a laser particle analyzer, whereas x-ray diffraction (xrd) technique was also used to determine the crystalline phases of alloy and hap. keywords-corrosion; electrophoretic deposition; hydroxiapatite; simulated body fluid; ti6al4v alloy i. introduction materials having biotic nature or host tissue compatibility can be implanted into living organisms to augment or replace impaired parts. generally, metals, ceramics, polymers, and composites are materials widely used in biomedical applications. amongst them, titanium-based alloys are some of the most widely used as implant materials [1]. titanium and its alloys bear enhanced properties like excellent strength [2], optimum elastic modulus [3], low density [4], blend of other mechanical properties [5], and excellent corrosion resistance [6-12], needed for various applications including orthopedic [13], dental [14], and surgical implants [15], artificial joints [15], etc. it should be noted that the elastic modulus of titanium-based alloys is considerably close to bones' [16, 17] which makes it ideal for long term applications [18]. however, titanium based alloys do not possess good osseointegration [19] thereby requiring additional surface treatment. this means that there is a poor bond between titanium and bones causing implant loosening which is highly undesirable. therefore, surface modification plays a vital role in optimum osseointegration [15, 20]. there are several techniques used in this regard such as: sand blasting [21, 22], etching [23], electrochemical treatment [24], and thermal spray coatings [25]. amongst them, bio-ceramic coatings using, the hydroxyapatite (hap ca10(po4)6(oh)2) [26-28] are very promising for the modification of implant surfaces since they create strong bonding with bones [29-31]. one of the great advantages of the hap is its great lifespan [32, 33]. the calcium phosphate (cap) ratio of hap is 1.67 which is highly stable at a normal temperature and its ph ranges from 4 to 12. however, the properties and resultant applications of hap depend on morphology, size, chemical composition and crystallinity [31]. in addition, it provides speedy and durable fixation to the host bones and possesses osseoconductive properties [34], protecting the metal surfaces from the environmental effects and thereby reducing the discharge of metallic ions from the implant surface to the host body. the main advantage of cap is that it is already present in the bones and teeth of the vertebrates [35]. moreover, there are several methods to produce hap such as: dry methods, wet methods, microwave (mw)-assisted methods, ball-milling or ultrasound, etc. [36]. additionally, numerous coating strategies are available to coat hap on metallic alloys, for instance: plasma spraying [37, 38], sol gel [39, 40], electrophoretic deposition (epd) [11, 41-43], etc. amongst them the most economically viable technique is epd [44], offering a controlled coating composition with the process being highly pure [45], fast [41] corresponding author: ali dad chandio engineering, technology & applied science research vol. 11, no. 3, 2021, 7240-7246 7241 www.etasr.com asrar et al.: facile coating of hap on ti6al4v for osseointegration that could be used to coat complex shaped substrates [45]. in this study, hap was produced from bovine bones since they are an abundant and economical source. this was followed by the deposition of hap on chemically treated ti6al4v alloy. ii. experimental part a. materials the materials utilized in this research are shown in table i. all of them were of analytical grade and were used in as received condition. table i. materials/chemicals used s.no. chemicals / materials purity (%) supplier 1 ti-6al-4v 99.0 baoji north hongsheng industry & trade co., ltd. 2 sodium chloride 99.0 sigma aldrich 3 sodium bicarbonate 99.0 sigma aldrich 4 potassium chloride 99.0 sigma aldrich 5 di sodium phosphate tri hydrate 99.0 sigma aldrich 6 magnesium chloride hexa hydrate 99.0 sigma aldrich 7 hydrochloric acid 99.0 sigma aldrich 8 calcium chloride dehydrate 99.0 sigma aldrich 9 di sodium sulphate 99.0 sigma aldrich 10 cyano hydride tri methanol 99.0 sigma aldrich b. methods 1) preparation of hydroxyapatite hap was synthesized from bovine bones, purchased from the local market, by the thermal decomposition process. this was followed by their boiling in deionized water for about 3 hours to remove the unwanted fats. additionally, second boiling was carried out for the deproteinization of bones. thereafter, the bones were immersed in acetone for two hours in an ultrasonic bath for further cleaning. subsequently, the bones were dried and cut into smaller sizes by mortar and pestle. the resultant powder was placed into a box furnace and heated at 1100 o c at a heating rate of 5°c/min for 3 hours for the preparation of hap. later on, xrd and laser particle analysis were conducted to confirm the peaks and particle sizes of as-synthesized hap powders respectively. the process details are shown in figure 1. 2) activation of substrates titanium alloy ti6al4v was used as substrate in plate form, having a thickness of 2mm. the microstructure of the asreceived ti alloy was revealed by following the steps of grinding and polishing followed by etching for 20-25s in the kroll's reagent (96ml distilled water + 6ml hno3 + 2ml hf). a wet chemical etching process was carried out to enhance the surface available for coating at room temperature. several chemicals were used to immerse the electrode into the solution for the desired time and then it was ready to be used as a substrate for coating. next, we took an equal quantity of 5ml each for hydrochloric acid, nitric acid, hydrogen peroxide, sulfuric acid and introduced them into 30ml of distilled water followed by the immersion of substrates into the prepared solution for 3 hours. then, titanium substrates were placed in 5 molar naoh solutions for 72 hours at room temperature. in the next step, the substrates were annealed in the air using a box furnace at 600 ° c followed by holding for 1 hour. this process was used to create the small nano-sized pits on the surface of the substrates used for the coating purpose. the samples were then considered ready for the epd process. fig. 1. steps of producing hap from bovine bones, calcination cycle, and xrd pattern of successfully produced hap. 3) epd of hap for the enhancement of adhesion properties of hydroxyapatite, titania (tio2) was used as an intermediate layer between hap and titanium alloy substrate. the process flow chart is shown in figure 2. in this process, an electrolytic solution containing 0.5g tio2 and 0.5g hap was dissolved in 100ml ethanol solution followed by sonication for 15 minutes and was ultrasonically shook for 30 minutes. it was then left for settling for 20 minutes and was stirred again for 25 minutes at 40 ° c. the epd process was done at 20v for 5 minutes while keeping the distance between electrodes at 2cm. the resultant coating was sintered in the tube furnace at 800 ° c. finally, the samples were ready for characterization to further evaluate the properties of ti-6al-4v alloy coated with hydroxyapatite. fig. 2. process flowchart of coating hap on ti-6al-4v substrate. engineering, technology & applied science research vol. 11, no. 3, 2021, 7240-7246 7242 www.etasr.com asrar et al.: facile coating of hap on ti6al4v for osseointegration iii. results and discussion a. particle size analysis we used the bt-9300h laser particle analyzer for the determination of particle size of hap powder. the results are shown in figure 3. the average obtained particle size was 25.73 microns with respect to cumulative percentage. fig. 3. average particle size of hap powder synthesized by bovine bones. b. xrd analysis the x-pert pro xrd dy3313 xrd machine operating at 40kv and 30ma using cukα radiation was used to analyze the phase of the hap. the diffraction pattern was recorded over 2θ at the scanning rate of 0.1 and was performed over the angular range from 10° to 79°. figure 4 reveals the xrd spectra of bovine bones calcinated at 1100°c which is in good agreement with the standard hap pattern [46, 47]. the calcinated sample peak at 31.8 confirms the formation of hydroxyapatite powder. moreover, the xrd spectra of the chemically treated ti alloy surface show the presence of tio2 and coated alloy confirming the presence of the hap layer on the chemically treated ti6al4v. fig. 4. xrd pattern of synthesised hap, chemically treated surface and titanium alloy coated with hap powder after sintering. c. chemical composition the chemical composition of titanium alloy is found by using an x-ray fluorescence spectroscope (innov-x systems) which is comparable to astm f136 standard [48]. the results are presented in table ii. table ii. chemical composition using xrf analysis alloy titanium vanadium aluminum astmf136 balance 3.5-4.5 5.5-6.75 ti6al4v balance 4.17 6.12 d. microstructures the polarized light microscope olympus gx51 was used to reveal the microstructure of the as-received samples. it was found that the titanium alloy consists of two different phases: equiaxed alpha and transformed beta phase [49] which are shown in figure 5(a). figure 5(b) shows the sem image of the hap powder. the powder comprises of agglomerated fine particles while the shape of the particles is angular and nonspherical [50]. figure 5(c) shows ti6al4v alloy coated with hap after sintering which revealed that there was an enhanced linkage and the interconnection of hap powders that exist on the coated surface morphology [51]. figure 5(d) shows the hap coated on ti6al4v after the immersion in sbf [52]. (a) (b) (c) (d) fig. 5. (a) optical structure of as received sample. (b) sem image of the produced hap powder. (c) ti6al4v coated with hap and sintered at 800 o c. (d) after immersion in sbf solution. e. hardness micro vickers hardness tester (din en 6507) was used to examine the hardness of bare and coated ti6al4v alloy by applying a load of 500g with a dwell time of 10s. the results are shown in table iii. a significant increase in hardness value of 468hv was obtained for a coated sample as compared to the pristine sample with a hardness value of 340hv. the ti-based alloy produced a high hardness value which is a major requirement in being compatible with the body environment. table iii. hardness results alloy hardness (hv) ti6al4v (before coating) 340 ti6al4v (after coating) 468 engineering, technology & applied science research vol. 11, no. 3, 2021, 7240-7246 7243 www.etasr.com asrar et al.: facile coating of hap on ti6al4v for osseointegration f. corrosion behavior 1) immersion test of coated samples in sbf the coated samples of the hap were immersed in simulated body fluid (sbf) solution which was prepared according the procedure defined in [40]. the chemical composition of the sbf solution is shown in table iv. the characterization was based upon the ph scale. for comparative analysis, the ph of the solution was measured before immersion and was found to be 7.4. the sample was then immersed in the solution enclosed in a glass beaker at 37°c for 7 days. agitations and vibrations were provided to the beaker to create an artificial environment of fluid movement around the coating. after a passage of the prescribed time, the sample was removed from the solution. the solution ph was measured after the immersion and was found to be the same as before, i.e. 7.4. therefore it was confirmed that no exchange of ions took place between the sample and sbf. table iv. chemical composition of the sbf solution s.no. chemicals amount 1 sodium chloride 6.559g 2 sodium bicarbonate 2.26g 3 potassium chloride 0.3773g 4 di potassium phosphate tri hydrate 0.1496g 5 magnesium chloride hexa hydrate 0.3411g 6 hydrochloric acid 10ml 7 calcium chloride dehydrate 0.3635g 8 di sodium sulphate 0.0731g 9 cyano hydride tri methanol 6.0662g 2) ftir ftir (perkin elmer spectrum one system) was used to identify the functional groups of hap coated samples in the area of 400-4000cm −1 . the ftir spectra before and after the immersion in sbf solution is shown in figures 6 and 7. the po4 3 group displays peaks at 560 and 600cm -1 and at 1000– 1100cm -1 . the peak at about 2600–3600cm -1 links to the hydrated oh – ion of ha [53]. the peak from 2000 to 2200cm -1 shows the stretching of p-o-h [54]. the peak at 1490cm-1 matches co3 2 which specifies that hap is a carbonated-apatite (hca) [55]. the representative peaks of po4 3 appear at 1090, 1014, and 590cm -1 . the peak at 1650cm -1 shows the presence of h2o [54]. fig. 6. ftir spectra of titanium alloy coated with hap powder after the immersion in sbf solution. fig. 7. ftir spectra of the titanium alloy coated with hap powder before the immersion in sbf solution. 3) potentiostat test corrosion tests were conducted to find out the corrosion rate of the coated samples. the tests were conducted with a gamry potentiostat having a counter electrode (graphite) and a reference electrode (hydrogen) using tafel. the corrosion rate was determined in an artificially created human body environment called sbf. the tafel curve of the bare and coated sample is shown in figure 8. the samples (i.e. the working electrode) were prepared according to the standard astm g108-94 analyzed at 37 o c using voltage ranges between -0.3 and 0.3v. tafel curves were plotted at a rate of 1mv/sec to find the current density and potential. figure 8 also shows the potentiodynamic curve for bare ti6al4v alloy having a current potential of -240v and current density of 1.63×10 -4 µa/cm2. hence, the corrosion current density (icorr) in the passive zone shifted down from 252na to 701na and the corrosion potential (ecorr) from -0.24v to 0.25v. the corrosion rate for hap coated substrate was decreased as 11.95×10 -3 mpy from 33.53×10 -3 mpy for the bare ti6al4v alloy. the hap coating consequence on ti6al4v alloy infers that the coating shows minimum release of metallic ions in sbf solution [14]. fig. 8. tafel curve of coated and uncoated titanium alloy. g. adhesion for evaluating the adhesion of the coated samples we used the scratch tester machine m-tgn80 having diamond intender engineering, technology & applied science research vol. 11, no. 3, 2021, 7240-7246 7244 www.etasr.com asrar et al.: facile coating of hap on ti6al4v for osseointegration landed on the coated substrate producing an indent on the substrate surface up to a maximum load of 60n as shown in figure 9. the result shows an excellent strength for the coating [56]. the morphological measurements were taken in the stereo microscope under low magnifications (5x) which reveal the distances of the crack from various aspects. fig. 9. magnified scratch marked with the adhesion tester. iv. conclusion hydroxyapatite is the furthermost noticeable inorganic substance for biomedical applications. research showed that natural hap from bovine bones can be synthesized by using the thermal decomposition method. from this study, no significant difference was observed between bovine bonederived hap and naturally occurring hap. hap powder electrophoretically deposited on ti-6al-4v alloy was used as substrate. the characterization of the coated sample confirmed that the coating enhanced the osseointegration properties of the implant. moreover, the hardness of the coated samples was observed to be increased up to 35% as compared to the pristine samples. the corrosion rate for coated samples was found to be decreasing from 33.53×10 -3 mpy to 11.95×10 -3 mpy. therefore, the resultant structures show that our produced samples can be used for a wide variety of medical applications with minimal expenses. acknowledgment the authors wish to express their gratitude to the higher education commission of pakistan for the 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[55] h. gheisari and e. karamian, "preparation and characterization of hydroxyapatite reinforced with hardystonite as a novel bionanocomposite for tissue engineering," nanomedicine journal, vol. 2, no. 2, pp. 141–152, apr. 2015, https://doi.org/10.7508/nmj.2015.02.006. [56] l. mohan, d. durgalakshmi, m. geetha, t. s. n. sankara narayanan, and r. asokamani, "electrophoretic deposition of nanocomposite (hap+tio2) on titanium alloy for biomedical applications," ceramics international, vol. 38, no. 4, pp. 3435–3443, may 2012, https://doi.org/ 10.1016/j.ceramint.2011.12.056. authors profile shafaq asrar is currently serving as a lecturer, and a ph.d scholar in the department of metallurgy engineering, ned university. muhammad tufail is currently serving as a pro-vice chancellor of ned university. he has acquired his ph.d from the university of nottingham, uk ali dad chandio is currently serving as a chairman of the metallurgical engineering department, ned university. he has acquired his ph.d from the university of manchester, uk microsoft word rev-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 265-268 265 www.etasr.com musa and akinbode: utilizing rice husk briquettes in firing crucible furnace … utilizing rice husk briquettes in firing crucible furnace for low temperature melting metals in nigeria nicholas akhaze musa department of mechanical engineering auchi polytechnic, auchi edo state, nigeria madonick1@yahoo.com folorunsho olayiwola akinbode department of mechanical engineering university of abuja abuja, nigeria abstract— the search for alternative fuels for firing crucible furnace for low temperature melting metals has become mandatory, as a result of the pollution problem associated with the use of fossil fuels, the expense of electricity and also deforestation as a result of the use of charcoal. an agricultural waste, rice husk, in briquette form was used as an alternative fuel to fire crucible furnace to melt lead, zinc and aluminium. results showed that lead and zinc melted and reached their pouring temperatures of 3840c and 5300c in 70 minutes and 75 minutes respectively. aluminium was raised to a maximum temperature of 5200c in 75 and 100 minutes.the average concentration of the pollutants (co, so2and -ox) were found to be below the tolerance limit and that of tsp (total suspended particulates) was found to be within the tolerance limit stipulated by federal environmental protection agency (fepa) in -igeria. keyword:s rice husk briquettes; lead; zinc; aluminium; furnace. i. introduction traditionally, coal was used as solid fuel for firing melting furnace. however, it is hardly suitable because of its sluggish response to temperature control, the large space required for storage and associated health hazards [1]. in nigeria, especially in the rural areas, charcoal is widely used to fire non-ferrous melting furnace. these charcoals are produced from wood. the increase in demand for wood for the production of charcoal and other uses has caused a lot of deforestation. if the trend is not kept under control, nigeria will be depleted of wood at the expense of natural ecological settings. electricity is regarded as a clean energy source. however, the generation of electricity requires the use of energy from renewable and non-renewable sources, some of which are not environmentally friendly. in the operation of solid fuel (coal), fuel oil and gas fired furnaces, carbon dioxide, carbon monoxide, sulphur dioxide, oxides of nitrogen and tsp. these gases have adverse effect on both humans and the environment [2]. fossil fuels are also used for other purposes, for example in the manufacture of goods such as plastics or chemicals for agriculture and animal food stuff [3]. the increased use of fossil fuels leads gradually to their depletion. apart from the depletion and the environmental problem of the fossil fuel, the procurement cost is very high and this has adverse effect on the industries where non-ferrous products are produced. the problems of fossil fuels depletion, environmental pollution and high procurement cost are being dealt with in various ways. these include, among others, energy conservation and the search for alternative fuel sources that are environmentally friendly, available to all and sundry. agricultural waste is one of such alternative energy sources. rice husk, being such a waste, is thoroughly generated especially in rural areas of the country. rice husk has been used in loose form to supplement firewood for cooking, but with loss of fuel and pollution. in order to enhance its use the briquette form can be used. the rice husk briquettes has been investigated by many researchers. notable among them are, permchart and tenatvanit in [4], krongkaew, jurgen and christian in [5], musa in [6], and bhattacharya et al in [7].their results revealed the potential use of such briquettes in firing cooking and heating devices. the comparison of the use of traditional fuel to rice husk briquettes in terms of availability and quantities required, cost of the fuel etc are discussed as follows: a. availability and quantities required. traditional fuels such as diesel, liguefied petroleum gas (lpg) are not readily available in nigeria, as a result of diversion and irregularities being practiced by marketers. coal resources have been estimated to be 2.5 billion tonnes, but there is no serious effort by the government for their exploitation. the annual wood consumption in nigeria is about 88 million cubic meters and 80% is utilized as fuel (charcoal and fuelwood). the charcoal and fuelwood are readily available but the consumption rate exceeds the replenishment rate. from preliminary study, about 20.3 liters of diesel, 2.88kg of lpg, 22.4kg of charcoal and 21.18kg of coal are required to individually fire melting furnace to melt 12kg each of lead, zinc and aluminium in cottage industries in nigeria. etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 265-268 266 www.etasr.com musa and akinbode: utilizing rice husk briquettes in firing crucible furnace … the land mass used for rice cultivation in nigeria is about 1.8 million hectares. recently the quantity of rice produced was about 1900470.14 tonnes and 1520262.23 tonnes were milled as revealed by the national cereal research institute (ncri). the high quantity of rice husk generated can be estimated to be 168918.03 tonnes. when made into briquettes, such an amount will result in large quantities. in this work, the quantity required to fire the furnace to individually melt 12kg each of lead, zinc and aluminium is to be estimated. b. cost of the fuel the cost of diesel, lpg, charcoal and coal in nigeria are n120 per liter, n285 per kg, n125 per kg and n135 per kg. the rice husk briquettes cost n15 per kg. c. time required to attain the required temperature from preliminary study, the time required by diesel, lpg, charcoal and coal to reach the required combustion temperatures are 50, 45, 65 and 60 minutes respectively. rice husk briquettes are expected to reach their combustion temperature in a longer period. d. temperature requirement similarly, from preliminary survey, the combustion temperature requirement of diesel, lpg, charcoal and coal are 1701 0 c, 1782 0 c ,1110 0 c, and 1360 0 c respectively. e. labour utilization using diesel or lpg is less labor intensive because the fuel can be loaded at once. but using charcoal, coal and rice husk briquettes, requires periodical loading, especially in case of small furnaces, and evacuation of ash. further use of rice husk briquettes in firing crucible furnace for low temperature melting metals, is the aim of this study, with a view to find alternatives to other conventional fuel in firing melting furnace. ii. materials and method a. materials and equipment 50.5 kilogram of cylindrical rice husk briquettes with an average density of 524kg/m 3 and compaction pressure of 1471.5 kw/m 3 were used to fire the furnace. the following equipment was used to carry out various tests: • non-ferrous melting furnace designed and constructed for this purpose. • weighing scales (manufactured in china by dapeng) • gas alert micro and sample analyser (manufactured in canada by b.w technologies ltd). • gaztell portable toxic gas monitors ( supplied by ele international, england) • type –kthermocouple, (manufactured in china by nigbo taisuo tech. ltd • stop watch • nose mask b. types and composition of low melting metals (nonferrous) selected for study • lead (pb) – 99.97% (pb), 0.03% impurity level by weight • zinc (zn) – 99.99% (zn), 0.01% impurity level by weight • aluminium (al) – 99.59% (al), (cu), 0.04% (fe), 0.34 (si) c. experimental procedure 12kg of each of the test samples (lead, zinc and aluminium, were put in individual crucible. one of the crucibles containing one of the 12kg of the test sample is shown in figure 1. fig. 1. a crucible containing lead sample. these crucibles were individually put in the furnace. a thermocouple probe was inserted in the crucible to measure the melting temperature of the test samples. three type k thermocouple probes were positioned on a 340 mm diameter, spaced at 120 0 in the combustion chamber of the furnace, to measure the combustion temperature. the average of the temperature recorded by the three thermocouples, at a time was taken as the combustion temperature of the briquettes. this was in line with the works of grant in [8]. another type kthermocouple probe was inserted in the chimney, to measure the flue gas temperature. the furnace was loaded with individual briquettes. ignition was initiated by arranging waste paper between the briquettes and lit with a match stick. an air flow valve was gradually opened. figure 2 shows the crucible furnace being fired with rice husk briquettes. rice husk briquettes were used to fire the crucible furnace to melt lead, zinc and aluminium individually. the loading schedule for the crucible furnace is shown in table 1. the frequencies of loading were determined by the number of periods, the briquettes in the furnace got combusted with sudden drops in combustion temperature and melting temperature of the non-ferrous metal. temperature readings viz-a-viz melting temperature of the test samples, combustion temperature, and the flue gas temperature were taken in five minutes interval. the etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 265-268 267 www.etasr.com musa and akinbode: utilizing rice husk briquettes in firing crucible furnace … concentration of co and so2 were measured with gas alert micro sample analyzer (manufactured in canada by bw technologies ltd) and the concentration of nox was measured with gaztell portable toxic gas monitor, with the probes inserted in the exhaust pipe. the manometric deflection of the u-tube manometer fitted to the exhaust pipe were read and used to determine the flue extraction rates. adopting akeredolu and oyawale method as described in [9], a re-weighed 2µm cellulose filter paper was held in place by a filter holder to trap the particulate matter. this was re-weighed in five minutes interval during the test period. the tsp was estimated by the product of the extraction rates and the weight of the particulate matter. all the readings were carried out in an interval of five minutes. after each operation, the furnace was evacuated. the duration of the test depended on the time needed for the melting temperature to fall within the range of the pouring temperatures of individual non-ferrous. for aluminium whose melting and pouring temperatures could not be reached, the test was terminated after 150 minutes. fig. 2. the furnace being fired with rice husk briquette samples table i. schedule for rice husk briquettes loading of the furnace iii. results and discussion the variations of combustion, melting, flue gas temperatures with time and the average measured concentrations of the pollutants from rice husk briquettes fired furnace for melting lead, zinc and aluminium respectively, are shown in figures 3, 4 and 5 and table 2 respectively. it can be seen from figures 3, 4 and 5 that the combustion temperature increased with the heating temperature of the non ferrous metals, lead, zinc and aluminium, as well as the temperature of the flue gas. fig. 3. variation of combustion, lead melting and flue gas temperature (tf, tl and tg) with time using rice husk briquettes. fig. 4. variation of flame, zinc melting and flue gas temperature (tf, tz and tg) with time using rice husk briquettes. fig. 5. variation of combustion, aluminium melting and flue gas temperature (tf, ta and tg) with time using rice husk briquettes. the increase in temperature was low in the early stages of combustion, that is between 0 and 15 minutes, which was the smoldering stage. the increase in temperature was high in the later stages of the combustion, that is between 20 and 45 minutes for lead, 25 and 45 minutes for zinc, 20 and 45 minutes for aluminium. drops in combustion, melting and flue gas temperatures were experienced between 50 and 55 minutes for lead and zinc, 50 and 55 minutes, 80 and 85 minutes, 105 and 115 minutes, 135 and 140 minutes for aluminium. this could be attributed to an uneven combustion process of solid loading (kg) total time interval minutes types of non-ferrous 1 st 2 nd 3 rd 4 th 1 lead 10.5 4.5 15 50 2 zinc 10.5 4.5 15 50 3 aluminium 10.5 5.0 2.5 2.5 20.5 30 etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 265-268 268 www.etasr.com musa and akinbode: utilizing rice husk briquettes in firing crucible furnace … fuel and refueling of the furnace with the briquettes at those periods, where there were transitions from the flaming stage to the smoldering stage. however, the furnace fired with rice husk briquettes was able to melt lead and zinc in 40 and 60 minutes respectively, and bring them to their respective pouring temperature of 384 0 c and 530 0 c in 70 and 75 minutes. it could only raise the temperature of aluminium to a maximum temperature of 521 o c in 75 and 100 minutes. 15kg, 15kg and 20.5kg of briquettes were respectively used to attain a temperature of 1000 0 c for 70 minutes as shown in figure 1, 75 minutes as shown in figure 2 and 140 minutes as shown in figure 3. in 0 minutes, no emission of so2, nox and tsp occured. it should be noted that, at that time, combustion was just initiated. it was after 20 minutes that emissions of nox were experienced. however, the emission of nox was due to the oxidation of the nitrogen present in the briquettes and not atmospheric nitrogen, because the later oxidizes when the furnace temperature is about 1500 o c [10]. the furnace or combustion temperature of the rice husk briquette was found to be less than 1500 0 c. in a nutshell, as the temperature of combustion, melting metal and flue gas increased with time, emissions of so2 and nox also increased with time. but the emissions of co and tsp decreased with time. these values of the average concentrations of co, so2 and nox as depicted in table 2, were found to be below the environmental tolerance limit of 10-20ppm for co, 0.010.1ppm for so2 and 0.04-0.06ppm for nox. the values of the average concentration of the tsp estimated shown in table 2, was found to be within the limit of 0.2-0.6mg/m 3 stated by federal environmental protection agency of nigeria. table ii. average measured concentrations of the pollutants from rice husk briquette fired crucible furnace. concentration of pollutants types of melted -onferrous co (ppm) so2 (ppm) -ox (ppm) tsp (g/m 3 ) lead 7.3 0.08 0.014 0.00051 zinc 7.0 0.081 0.015 0.00055 aluminium 6.4 0.079 0.0135 0.00051 iv. conclusion the quantities of the briquettes used were sufficient but the heat released from the burning of the briquettes perhaps was not enough to melt aluminium whose melting and pouring temperatures are far higher than those of lead and zinc considered in this study. however, rice husk briquettes can be used to fire crucible furnace to melt low temperature melting metals such as lead, zinc and any other metal whose melting points and pouring temperatures are lower. it can also be used to preheat aluminium to about 531 0 c. the use of rice husk briquettes in firing crucible furnace for low temperature melting metals is environmentally friendly, partly solves the disposal problem, and serves as good alternative to other conventional fuel. references [1] h. a. monks, d. rochester, technician metallurgical process technology 2. macmillan publishing co. inc, 1980 [2] n. k. giri, automobile technology, khanna publishers, 2004 [3] t. d. eastop, a. mcconkey applied thermodynamics for engineering technologist. longman publishers, 1993 [4] w. permchart, s. tenatvanit, “preliminary investigation on combustion characteristics of rice husk in fbc”, world academy of science, engineering and technology, vol. 56, pp. 183-186, 2009 [5] l. krongkaew, h. jurgen, w. christian , “the production of synthetic diesel from biomass”, kmitl science technology journal. vol. 6, no 1, pp. 35-45, 2006 [6] n. a. musa, “full characteristics of some selected biomass briquettes” internationa journal of science and technology research. vol. 6, no 4, pp. 24-28, 2006 [7] s. c. bhattacharya, a. h. md, m. siddique, l. augustus, h. c. pham, c. p mahandari, “a study on improved institutional biomass stoves”, asian institute of technology journal, pp. 1-6, 2001 [8] b. t. grant, emissions of rural wood burning cooking devices. phd thesis faculty of engineering university of the witwatersrand johannesburg, 1997 [9] f. a. akeredolu, o. c. oyawale “monitoring combustion chamber”, journal of the nigerian society of chemical engineers, pp. 10-12, 2000 [10] p. k. nag, power plant engineering, tata mcgraw-hill publishing company ltd, 2001 microsoft word etasr_v12_n2_pp8259-8265 engineering, technology & applied science research vol. 12, no. 2, 2022, 8259-8265 8259 www.etasr.com ineza et al.: arctan-based robust droop control technique for accurate power-sharing in a micro-grid arctan-based robust droop control technique for accurate power-sharing in a micro-grid marie aimée ineza department of electrical engineering pau institute for basic sciences, technology and innovation, nairobi, kenya inezamarieaime@gmail.com michael juma saulo department of electrical and electronics engineering, technical university of mombasa (tum), mombasa, kenya michaelsaulo@tum.ac.ke cyrus wabuge wekesa school of engineering university of eldoret (uoe) eldoret, kenya cwekesa@uoeld.ac.ke received: 26 december 2021 | revised: 19 january 2022 | accepted: 25 january 2022 abstract-due to the inherent limitations of the traditional droop controller (tdc), an enhanced droop controller, known as robust droop controller (rdc) has been proposed in previous works. however, this controller cannot compensate for the error in measured frequency, which can potentially contribute to the errors in proper reactive power-sharing as well as degrade frequency regulation. this paper introduces an arctan-based robust droop controller (abrdc) that modifies the rdc for linverter to address this issue. the controller, rather than utilizing a linear function, utilizes an arctan-based function for power/frequency droop control. various simulations were performed in matlab/simulink to test the performance of the proposed abrdc. the results showed that it successfully reduces the frequency error, resulting in improved frequency regulation as well as adequate reactive load power-sharing. the comparative study showed that the abrdc scheme is more effective than the rdc scheme. keywords-parallel-operated inverters; robust droop control; arctan-based function; load power-sharing; frequency and voltage regulation i. introduction economic, environmental, and political concerns have increased the attention in green energy generation (ges). the micro-grid (mg) concept eases the introduction of ges. furthermore, it enhances the reliability of distribution networks, minimizes carbon dioxide (co2) emissions, transmission losses, etc.. an mg consists of distributed generation (dg) sources, storage devices, and loads [1-3]. power inverters are typically utilized as the link for dg sources, green energy sources (gess), and storage devices in an mg [4]. they are frequently connected in parallel to increase system reliability and performance and provide high power at a low cost. a vital challenge for parallel-operated inverters in mgs is how to obtain accurate power-sharing amongst them while retaining tight regulation of the mg frequency and voltage magnitude [5]. droop control is a technique that is often utilized in traditional energy generation systems [6-8]. its benefit is that there is no requirement for an external communication system between the inverters [5]. when using the traditional droop control (tdc) technique, the inverters operated in parallel ought to have the same per-unit impedance to distribute the load in proportion to their power ratings [9]. the droop controllers ought to produce the same voltage setpoint for the inverters as well. in practice, these requirements are challenging to satisfy, resulting in proportionate load power-sharing errors. for this reason, a new approach called robust droop control (rdc) strategy for r-inverters was presented [5] for achieving precise load power-sharing without fulfilling the above two conditions and reducing the voltage drop due to the load droop impact. the method only addressed the power-sharing errors caused by the errors in measuring load voltages. however, this method uses the linear function on the power-frequency droop. the droop based-linear function has a common limitation, the associated output range scaling factor does not affect system dynamics and steady-state condition [10]. if the frequency of the system is calculated using the droop controller based on this linear function, then it can deviate significantly from the nominal value [10, 11]. this results in high frequency errors which can potentially contribute to power-sharing errors, thus leading to inaccuracy in power-sharing amongst parallel operated-inverters and poor frequency regulation. this work intends to modify the rdc for the l-inverter. rather than using a linear-based function, it utilizes an arctan based function in power/frequency droop. the idea of using an arctan-based function for the power-frequency droop profile was first presented in [12]. implementing this arctan-based function offers natural frequency bounds, and enhances the mg's inverter small-signal stability. thus, incorporating an arctan function into rdc forms a controller that can provide accurate load power-sharing while stabilizing the frequency and pcc voltage regulations at their reference values in the mg of parallel-operated inverters. a. limitations of traditional droop control the form of a droop controller can vary depending on the inverter’s output impedance [13-15]. in this work, an inverter of inductive output impedance is considered. thus, the traditional droop controller is [16]: � �� = �� − ���� � = � − ���� (1) corresponding author: marie aimée ineza engineering, technology & applied science research vol. 12, no. 2, 2022, 8259-8265 8260 www.etasr.com ineza et al.: arctan-based robust droop control technique for accurate power-sharing in a micro-grid where �� and �� are the amount of real and reactive power delivered to the bus-bar from each inverter respectively, �� and �� are the nominal and output frequencies of the xth inverter, � is the nominal voltage, � is the rms value of the reference voltage of the x th inverter ����, and �� and �� are the voltage and frequency droop coefficients respectively. figure 1 illustrates the tdc diagram. fig. 1. traditional droop control diagram. when the mg is equipped with the tdc in a steady-state condition, the two inverters work at the same frequency, i.e. �� = �� and the relationship in (2) is satisfied. this ensures the active power-sharing accuracy for l-inverters [17] (or reactive power-sharing accuracy for rinverters [5]). ���� = ���� (2) in addition, the proportional reactive power for the linverters can be achieved when the relationship in (4) is satisfied. however, because of the presence of noise, disturbances, errors, and line impedance mismatches in the mg, the expressions in (3) are practically hard to satisfy [17]. � � = � ����� = ����� (3) b. limitations of robust droop control due to the inherent restrictions when utilizing the tdc for the mg-based inverters, the rdc was proposed in [5] to improve the accuracy of load power-sharing and voltage regulation. as presented in figure 2, the rdc of the l-inverter is: �� = �� − ���� (4) �� = �� � − �� − ���� (5) where � and � are an amplifier and the rms measured value of the output voltage �� . at the steady-state condition, (5) becomes: ���� = �� � − �� (6) as long as � is the same, the right part of (6) is always the same for all parallel-operated inverters [4]. thus: ���� = constant (7) which ensures accurate reactive power-sharing without using the same �. therefore, the accuracy of reactive power-sharing is no longer dependent on the output impedance of the inverter and is also resistant to disturbances and errors [4]. however, this method did not compensate for the frequency errors, potentially contributing to load-sharing errors and degradation of frequency regulation. fig. 2. robust droop control diagram. ii. the proposed droop control strategy a. design of the proposed droop controller the proposed arctan-based robust droop control (abrdc) strategy adopts the structure of rdc for l-inverter [5] and utilizes an arctan-based function in power frequency droop control rather than the linear function [18]. this controller gains the benefits of the two methods. this means that the rdc is responsible for eliminating the effect of line impedance mismatches, noise, disturbances, and sharing errors caused by the errors in measuring the load voltage, whereas the arctan-based droop control is responsible for removing the frequency error since a mg-based inverter equipped with arctan droop controller provides naturally frequency boundaries [10, 12]. as a result, the proposed controller is able to provide accurate load power-sharing while ensuring a tight voltage and frequency regulation. therefore, the �/& of the proposed droop controller is based on the arctan function, and can be expressed as: &� = &� − '() ∗ +,-.+/ 012�� − ����34 (8) or, as: �� = �� − 2-6 ∗ +,-.+/ 012�� − ����34 (9) the �/ of the proposed droop controller is based on the rdc methodology and it can be expressed as: �� = �� � − �� − ���� (10) where -6 is the multiplier, 1 is the coefficient, ���� is the actual power reference which is always equal to zero in the islanded mg, and the other parameters have already been specified. referring to (9) and (10), the proposed droop control diagram is illustrated in figure 3. the arctan-based function is inherently constrained in the frequency domain from 0&� 7 '(� 4 to 0&� − '(� 4 hz, which is one of the benefits of this method [12]. the multiplier -6 is mostly set to be 1 to keep the frequency within the limits of 50±0.5h. additionally, changing the multiplier directly affects the frequency variation boundaries due to the arctan function. as illustrated in figure 4, as the arctan bounding multiplier increases, the frequency variation increases [19]. furthermore, the coefficient 1 is used to control the concavity (and inherently over the gradient). the variation in real power may be imposed due to this coefficient, as shown in figure 5 [19]. engineering, technology & applied science research vol. 12, no. 2, 2022, 8259-8265 8261 www.etasr.com ineza et al.: arctan-based robust droop control technique for accurate power-sharing in a micro-grid fig. 3. proposed droop control diagram. fig. 4. the impact of variation of the arctan bounding multiplier, -6 [19]. fig. 5. the impact of variation of the arctan droop coefficient ρ [19]. the output voltage of the x th inverter can be expressed as: � = � − �89:; � (11) which can be kept within the predetermined range through selecting a big value of �. the proposed control strategy has excellent voltage regulation capability in addition to accurate power-sharing and excellent frequency regulation capability. figure 6 presents the schematic diagram of the proposed droop controller in mg of one dg unit. real (p) and reactive (q) power are computed utilizing the dq transformation for the 3ϕ current and voltage quantities. based on the computed power flux, the frequency is controlled using the arctan droop control algorithm, whereas the voltage is controlled using the rdc. the inverter's current and voltage outputs are stabilized utilising a cascaded system of the outer voltage and inner current control loops [19, 20]. a proportional integral (pi) controller is deployed to reduce the current error with quicker dynamic response and to ensure zero steady-state error [16, 2123]. it is also utilized to force the calculated q-axis voltage component to be zero and the calculated d-axis voltage component to be equal to the reference value [20]. b. performance comparison criteria of droop control strategies 1) power-sharing ratio criterion the load power-sharing ratio criterion is generally used to compare the capability of different droop control methodologies. if the relationship between the power and the droop coefficients of any two dgs in (12) is accomplished, proportionate power-sharing between parallel-operated inverters is acquired. > ?�?� = @�@� = ⋯ = ?8?8b� = @8b�@8���� = c�c� = ⋯ = �8�8b� = c8b�c8 (12) fig. 6. schematic diagram of the proposed droop control in one dg unit mg. engineering, technology & applied science research vol. 12, no. 2, 2022, 8259-8265 8262 www.etasr.com ineza et al.: arctan-based robust droop control technique for accurate power-sharing in a micro-grid 2) power-sharing ratio criterion apart from the load power-sharing ratio criterion, the load power-sharing error is also used to analyze and evaluate the capability of droop control techniques. low error values represent the ability of the control strategy to reduce the load power-sharing imbalances between the inverters, while large values represent a higher imbalance of load power-sharing among the inverters operated in parallel. the real and reactive load power-sharing errors are assessed based on (13): >d6� = @8∗e@8@8∗ f 100di� = c8∗ec8c8∗ f 100 (13) where d6� and di� are the active and reactive load powersharing errors of the jkl inverter in percentage respectively, ��∗ and ��∗ are the active and reactive power supplied by the jkl inverter when the active and reactive power-sharing is in exact proportion to their ratings, and �� and �� are the measured real and reactive power supplied by the jkl inverter. iii. simulated results and discussion a. simulation setup the performance of the developed droop control strategy is evaluated in a mg-based inverter. all models were created using the matlab/simulink toolbox. figures 7-8 depict the simulink model of the proposed droop controller in a standalone mg of two parallel-operated inverters and all submodels. table i shows the system parameters used during the simulations. table ii summarizes the investigated scenarios. table i. system parameters parameter value nominal voltage m =400 v dc bus voltage n' =850 v nominal frequency &� =50 hz inverter switching time op q�r��s�� =5 khz load1 �t� = 3ev var, �t� = 6ev w load2 �t� = 3ev var, �t� = 6ev w line1 impedance [t� = 0.7 ω, _t� = 0.005 h line2 impedance [t� = 0.8ω, _t� = 0.006 h filter c�� = c�� = 2.5eed f, _�� = _�� = 2eev h voltage and frequency droop coefficients �� = �� = 2.5eef v/var �� = α� = 6.25eef rad/sw arctan bounding multiplier -j� = -j� = 1 hz/w arctan droop coefficient 1� = 1� = 1eef rad/s.w. amplifier �� = �� =2 inner loops pi coefficients l6q = 0.15, lqq = 1.5, l6r = 20, lqr = 1000. table ii. operation scenarios time (s) operation 0-6 two dgs unit powers the load. 6-12 load 2 is added to the system 12-18 load 2 is removed from the system b. frequency and voltage stability analysis figures 9-10 present the frequency and pcc voltage stability when the abrdc technique is adopted. it can be seen that the abrdc can maintain the frequency and output pcc voltage during the steady-state condition to their reference values of 50hz and 400v. at the time t=6s, load 2 was added to the system and the frequency and output pcc voltage dropped from 50 to 49.99hz and from 400v to 396.10v respectively. at t=12s, load 2 was disconnected from the system and frequency and pcc voltage were reset to their previous values. as observed, the abrdc technique can retain the voltage and frequency at their reference values during the steady-state condition. it can also keep the voltage and frequency deviations within the allowed range according to ieee1547-2018 standards (the allowable range for frequency and voltage variation are ±1% and ±5% of the given reference values respectively) when a load change is added to the system. (a) (b) (c) (d) fig. 7. simulink submodel of : (a) p&q calculated, (b) abc to dqo transformation, (c) proposed droop controller, (d) cascade control loop. engineering, technology & applied science research vol. 12, no. 2, 2022, 8259-8265 8263 www.etasr.com ineza et al.: arctan-based robust droop control technique for accurate power-sharing in a micro-grid fig. 8. simulink model of the proposed droop controller in a stand-alone mg of two parallel-operated inverters. fig. 9. frequency variation for inverters using the proposed droop controller. fig. 10. voltage regulation at pcc using the proposed droop controller. c. active and reactive power-sharing analysis the load power-sharing capability of the abrdc in an mg of two parallel-operated inverters is also analyzed in this study. as depicted in figures 11-12, during the steady-state condition, the active and reactive load powers were correctly shared with ratios of α1: α2=p1:p2=3e 3 w:3e 3 w and β1:β2=1:1=q1:q2=1.5e 3 var:1.5e 3 var respectively. load 2 was introduced to the system at t=6-12s to verify the controller's performance as the load in the mg increases. the inverters kept distributing the active and reactive load power in a proportional manner, where the ratios were α1:α2=p1:p2=6e 3 w:6e 3 w for the real power and β1:β2=1:1=q1:q2=3e 3 var:3e 3 var for the reactive power. at t=12-18s, load 2 was disconnected from the system, the active and reactive power were also appropriately distributed, and the ratios were α1:α2=1:1=p1:p2=3e 3 w:3e 3 w and β1:β2=1:1 =q1:q2=1.5e 3 var:1.5e 3 var respectively. as seen, the abrdc technique satisfies the conditions of the load power-sharing in all scenarios, thus it ensures accurate power-sharing. engineering, technology & applied science research vol. 12, no. 2, 2022, 8259-8265 8264 www.etasr.com ineza et al.: arctan-based robust droop control technique for accurate power-sharing in a micro-grid fig. 11. the real power-sharing amongst two inverters operated in parallel utilizing the proposed controller. fig. 12. the reactive power-sharing amongst two inverters operated in parallel utilizing the proposed controller. d. comparative study analysis between the proposed and robust droop control techniques to validate the proposed droop control methodology, comparative analysis of the abrdc and rdc methodologies based on the frequency variation for the inverter, voltage regulation at pcc, and the active and reactive load powersharing amongst the inverters operating in parallel was performed. the frequency variation comparison of the two controllers is presented in figure 13. as seen, during the steady-state condition at t=0-6s, the abrdc technique can retain the frequency at the reference value of 50hz, whereas it drops to 49.81hz for the rdc. in figure 14, the voltage regulation at pcc when utilising abrdc and rdc techniques is compared. both abrdc and rdc techniques could regulate the output voltage at pcc to the reference value of 400v. at t=6-12s, load 2 was added to the system. the frequency decreases from 50 to 49.99hz for abrdc and from 49.81 to 49.63hz for rdc. the output voltage at pcc drops to 396.1v for both abrdc and rdc techniques. when the load 2 is removed from the system, the frequency is restored to 50hz for the abrdc technique, while for the rdc technique it was reset to its previous value. again, the output voltage at pcc was also restored to its reference value for both abrdc and rdc techniques. in brief, the abrdc provides better frequency and voltage regulation of 0.02% and 0.45%, respectively, whereas rdc has 0.36% and 0.45% respectively. as demonstrated, the abrdc technique reduced successfully the frequency error, leading to improved reactive load powersharing. the active power-sharing comparison between abrdc and rdc is presented in figure 15. it is noted that for all techniques, the real power-sharing ratio is p1:p2=1:1, which means each inverter delivers 50% of the total real power of the load in both cases. the reactive power-sharing comparison is seen in figure 16. the reactive load power-sharing when utilizing the abrdc technique is enhanced, where vsi1 supplied 49.98%, and vsi2 delivered 49.98% of the total reactive power of the load, whereas adopting rdc technique it is 52.48% and 47.52%. this enhancement in reactive load power-sharing when utilizing the proposed controller is due to its capability to reduce the system's frequency error. fig. 13. comparative analysis of the frequency variation for abrdc and rdc techniques. fig. 14. comparative analysis of the voltage regulation at pcc using abrdc and rdc techniques. fig. 15. comparative analysis of the real power-sharing using abrdc and rdc techniques. fig. 16. comparative analysis of the reactive power-sharing using abrdc and rdc techniques. table iii. power errors active and reactive load powersharing errors control strategy d@��%� d@��%� dc��%� dc��%� abrdc 0.04 0.09 0.64 0.76 rdc 0.05 0.10 -2.51 4.12 based on the power-sharing error criterion, a comparative study was performed to assess and analyze the capability and effectiveness of the proposed abrdc and the rdc. it is noted that the proposed droop controller minimizes power-sharing errors when compared to the rdc, resulting in improved power-sharing. table iii presents the active and reactive load power-sharing errors for the two strategies. engineering, technology & applied science research vol. 12, no. 2, 2022, 8259-8265 8265 www.etasr.com ineza et al.: arctan-based robust droop control technique for accurate power-sharing in a micro-grid iv. conclusion this paper proposes the arctan-based robust droop controller (abrdc) to provide tight frequency and voltage regulations as well as accurate load power-sharing amongst inverters operated in parallel. the proposed controller modifies the structure of the rdc for l-inverters. rather than using a linear function, it utilizes an arctan based function in power/frequency droop control. this means that the 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[23] e. pathan et al., "virtual impedance-based decentralized power sharing control of an islanded ac microgrid," engineering, technology & applied science research, vol. 11, no. 1, pp. 6620–6625, feb. 2021, https://doi.org/10.48084/etasr.3946. engineering, technology & applied science research vol. 8, no. 1, 2018, 2385-2388 2385 www.etasr.com cetin and daldaban: reducing torque ripples of the axial flux pm motors by magnet stepping and … reducing torque ripples of the axial flux pm motors by magnet stepping and shifting emrah cetin electrical and electronics engineering dpt erciyes university kayseri, turkey emrahcetin@erciyes.edu.tr ferhat daldaban electrical and electronics engineering dpt erciyes university kayseri, turkey daldaban@erciyes.edu.tr abstract—higher efficiency on electric machines is the research goal of many studies. an example is the axial flux permanent magnet machines. these machines have some advantages like their watt/kg efficiency and torque density. this study aims to develop the performance characteristics of the axial flux permanent magnet machines. a new rotor magnet poles design in axial flux machines is suggested to mitigate the torque ripples. the method of stepping and shifting of the magnets is used. two different designs are compared to verify the proposed approach. 3d finite element analysis is used for simulations. torque ripple and back electromotive force waveforms are obtained from computer analysis. as a conclusion, the suggested method is found to be useable and mitigates the torque ripples. in addition to that, back emf waveforms are turned to sinusoidal by the suggested design. keywords-axial flux machines; step and shift; rotor magnet poles; torque ripple; back emf; permanent-magnet machines i. introduction electric machine design became crucial since the necessities of higher efficiency constantly increase for many different applications. if the application is torque sensitive and of low acoustic noise, torque ripples must be eliminated. torque ripples must be taken into account in every machine design. torque ripple occurs in case of interactions between stator slots and rotor magnet poles. axial flux permanent magnet (afpm) machines have high power density, small volume and are convenient for many applications [1], but have particular problems in manufacturing [2]. moreover, afpm machines have torque ripples as many other permanent magnet machine types. most of the applications are torque sensitive, so torque ripples must be mitigated. torque ripples consist of two main components which are cogging torque and ripple torque. the cogging torque is produced by the interaction between the reluctance variation in stator and rotor magnetic flux. the ripple torque is mainly generated by the interaction of the stator current magnetomotive force and rotor magnetic flux distribution in the surface pm (spm) machines [3]. both the cogging and ripple torque are related to rotor magnetic flux distribution which is manipulated by the shape of pm in the spm machines. in the literature, various topologies were investigated in order to reduce torque ripple. the shaping of rotor magnet pole was realized by the skewing or displacing of magnet poles [4]. the stator slot shaping was proposed [5, 6]. many other torque ripple reducing approaches are summarized in [1, 7]. some researches focused on the predicting of torque ripple effects [8]. beyond the prediction and minimization, the manufacturing process is taken into account in [9, 10]. this paper suggests the two step on rotor magnet poles with a shift angle implementation. ii. proposed designs the single air gap axial flux machine is taken into account as the reference design (see figure 1 and table i for the studied motor reference parameters). design i, is a conventional axial flux permanent magnet machine model and the reference model for the study (figure 2(a)). this type of magnet can be found in the market easily. design ii, is the proposed model and it can be seen in figure 2(b). this design is the novel proposal for the axial flux machines. it is studied in order to determine its effect in reducing the torque ripples. the motor rotation was 2200 rpm. both transient and static analyses are performed. runtime process is done for 10 ms so motor turns more than one time during the simulation. the most used performance characteristics obtained from the analysis are moving torque and back emf waveforms. while moving torque values were taken with the current supply, back emf waveform were taken with zero current. m250-35a steel specifications were used for the defining of the steel parameters of the stator and the rotor. the cylindrical coordinate system is used to define the axial flux steel orientation. fig. 1. the studied afpm motor topology engineering, technology & applied science research vol. 8, no. 1, 2018, 2385-2388 2386 www.etasr.com cetin and daldaban: reducing torque ripples of the axial flux pm motors by magnet stepping and … all the permanent magnet poles are magnetized in z-axis and the all of the pm volumes, inner and outer diameters are the same for each pole design. magnet fill factor is 0.87 in each design. table i. reference parameters parameter value inner radius (ri) 40 mm outer radius (ro) 75 mm stator thickness 50 mm slot number 24 pole number 8 maximum current 175 a current waveform sinusoidal moving speed 2200 rpm magnet fill factor 0.87 magnet height 5 mm slot opening width 2 mm air gap 1 mm (a) design i (b) design ii fig. 2. magnet designs (a) solid magnet poles b) two-step magnet poles with shift angle iii. shifting angle the shifting angle means that inner rotor step magnets are displaced by an angle from the outer rotor magnets as seen in figure 2(b). one of the aims of this shifting method is the mitigation of the torque ripples. there are several analytical methods to define the best shift angle. one of them is the cogging torque period method described in [11]. but this method doesn’t give the best correct result for the axial flux permanent magnet machines. in this research, parametric analysis with 3-d fea is used to find the optimum shifting angle. the shifting angle defined as a variable and differs from 0º to 14º by 1º step. the moving torque values were taken into account for each result. figure 3 demonstrates the results of the parametric analysis. table ii shows each torque ripple and average torque value for each shifting angle. the simulation’s parametric analysis gave interesting results. if the torque ripple is the most important anchor of the application, the best result is the 11º shifting angle which produces 2.16 nm of peak to peak cogging torque. but if the average torque value is the most valued parameter, 3º shifting angle produce the highest average torque of 51.27 nm which is 1.3 nm higher than that of the 0º shifting angle. torque ripple drops from the shifting angle 1º to 11º, but after 11º it starts to rise again. fig. 3. defining the shifting angle by parametric analysis. table ii. parametric analysis results shift angle average torque torque ripple 0 49.95 5.52 1 49.77 6.23 2 51.24 6.04 3 51.27 5.44 4 50.58 5.59 5 50.21 5.11 6 50.46 5.02 7 50.00 4.51 8 49.35 4.34 9 49.47 3.77 10 48.46 2.98 11 48.32 2.16 12 47.37 3.06 13 45.81 3.25 14 45.25 4.04 iv. results static and dynamic simulations were run for each design. the stator was split out to four identical parts and, due to the symmetrical geometry and for reducing simulation time and one of them was studied (because of the 3d geometry, just one of the simulations takes nearly three hours). in the static analysis, the stator and the windings are stated fix. just rotor magnet poles and the rotor back iron are moving 90o with 15o steps. the simulation results can be seen at table iii which demonstrates the average values of the waveforms taken from each step. the magnetic force equals to the total magnetic force on the rotor side. it consists of three dimensional forces. the highest magnetic force value is taken from the simulation of the second design and the lowest data is taken from the first design. in dynamic analysis, pms having 11º shifting angle are used in design ii. moving torque and back emf waveforms are taken from the dynamic simulations. figure 4 shows the moving torque results of the two designs shown in figure 2. the engineering, technology & applied science research vol. 8, no. 1, 2018, 2385-2388 2387 www.etasr.com cetin and daldaban: reducing torque ripples of the axial flux pm motors by magnet stepping and … comparison of the two designs is demonstrated in table iv. we see that in design ii torque ripple and average torque reduced by 62,4% and 4,3% respectively. voltages induced in the windings are given by (1) obtained from faraday’s law. the left side of the equation is called transformer voltage and the right one is called back emf and is induced in the stator windings because of the magnet flux passing through the air gap. as seen in (1) back emf is directly proportional to the mechanical speed and the simultaneous changes of the inductance. the magnet shifting and stepping also influences the inductance. table iii. average values of magnetic force for each rotor magnet pole design design i design ii magnetic force (n) 743.47 1203 d dl wi dt di leind  (1) figure 5 illustrates the back electromotive force waveforms of each design. the smoothness of these waveforms is crucial in order to have more constant torque which means having lower torque ripple. design two has smoother back emf and lower torque ripple waveforms. flux density distributions are posed in figure 6 for the two designs which demonstrate the radial components of the flux density between the magnets and the stator steel. fig. 4. torque ripple mitigation results fig. 5. back emf results table iv. comparison of simulation results concerning average torque and torque ripple design i design ii average torque (at) 50.521 48.32 torque ripple (tr) 5.744 2.159 rate (tr/at) 0.114 0.045 at reduction ref. -%4.3 tr reduction ref. -%62.4 fig. 6. magnetic flux densities of the designs v. conclusion this study deals with the stepping and shifting effects of a novel design of the rotor magnets for the afpm machines considering torque ripple reduction. tr/at values prove that the proposed design has lower average torque and torque ripple than the reference design. the reference design (design i) is simulated in order to prove the stepping and shifting effects on performance characteristics. dynamic and static analysis are performed in this study and each design’s performance is discussed in the simulation results. also, a parametric analysis is fulfilled to determine the shifting angle correctly. the average magnetic force results are obtained from the static analysis. the highest magnetic force is created in the second design. the moving torque and the back emf waveforms are obtained from the dynamic analysis. magnetic flux density distribution waveforms show that the second design performs better in torque ripple mitigation due to the precision on constancy of moving torque. acknowledgement this study is supported by the tubitak (the scientific and technical research council of turkey). references [1] f. giulii capponi, g. de donato, f. caricchi, “recent advances in axial-flux permanent-magnet machine technology”, ieee transactions on industry applications, vol. 48, no. 6, pp. 2190-2205, 2012 [2] j. f. gieras, r. j. wang, m. j. kamper, axial flux permanent magnet brushless machines, springer science & business media, pp.3-19, 2005 [3] t. m. jahns, w. l. soong, “pulsating torque minimization techniques for permanent magnet ac drives a review”, ieee transactions on industrial electronics, vol. 43, pp. 321-330, 1996 [4] m. aydin, z. q. zhu, t. a. lipo, d. howe, “minimization of cogging torque in axial-flux permanent-magnet machines: design concepts”, ieee transactions on magnetics, vol. 43, no. 9, pp. 3614-3622, 2007 engineering, technology & applied science research vol. 8, no. 1, 2018, 2385-2388 2388 www.etasr.com cetin and daldaban: reducing torque ripples of the axial flux pm motors by magnet stepping and … [5] s. j. sung, s. j. park, g. h. jang, “cogging torque of brushless dc motors due to the interaction between the uneven magnetization of a permanent magnet and teeth curvature”, ieee transactions on magnetics, vol. 47, no. 7, pp. 1923 -1928, 2011 [6] d. g. dorrell, m. popescu, “odd stator slot numbers in brushless dc machines—an aid to cogging torque reduction”, ieee transactions on magnetics, vol. 47, no. 10, pp. 3012-3015, 2011 [7] m. aydin, t. a. lipo, “axial flux permanent magnet disc machines: a review”, speedam, pp. 61-71, 2004 [8] z. q. zhu, d. howe, “analytical prediction of the cogging torque in radial-field permanent magnet brushless motors”, ieee transactions on magnetics, vol. 28, no. 2, pp. 1371–1374, 1992 [9] l. gasparin, a. cernigoj, s. markic, r. fiser “additional cogging torque components in permanent-magnet motors due to manufacturing imperfections”, ieee transactions on magnetics, vol. 45, no. 3, pp. 1210 -1213, 2009 [10] m. a. khan, i. husain, m. r. islam, j. t. klass , “design of experiments to address manufacturing tolerances and process variations influencing cogging torque and back emf in the mass production of the permanentmagnet synchronous motors”, ieee transactions on industry applications, vol. 50, no. 1, pp. 346-355, 2014 [11] c. y. hsiao, s. n. yeh, j. c. hwang, “a novel cogging torque simulation method for permanent-magnet synchronous machines”, energies, vol. 4, no. 12, pp. 2166-2179, 2011 engineering, technology & applied science research vol. 7, no. 2, 2017, 1473-1477 1473 www.etasr.com taheri: a 4-4.8ghz adaptive bandwidth, adaptive jitter phase locked loop a 4-4.8ghz adaptive bandwidth, adaptive jitter phase locked loop hamidreza esmaeili taheri department of electronics engineering behbahan khatam alanbia university of technology behbahan, iran taheri@bkatu.ac.ir abstract—a low power, low phase noise adaptive bandwidth phase locked loop is presented in this paper. the proposed structure benefits from a novel lock status monitor unit (lsmu) that determines loop operation and loop bandwidth. the loop filter resistance and charge pump current are inversely proportional and bandwidth to reference frequency is maintained fixed. this structure is simulated in 0.18 μm cmos technology and simulation results are presented. keywords-low power; fast lock; adaptive bandwidth frequency synthesizer i. introduction the increasing demand for high speed, low power, small size and portable electronic and communication devices is growing more and more. this mounting exigency has forced many electronics engineers to confront with several challenging problems. one of the most important building blocks in many high-speed, high-performance systems is phase locked loop (pll). the basic duty of a pll is to eliminate the phase difference between input and output waveforms and produce a pure output waveform with desired frequency. however, in many applications, the resulted waveform is not ideal. the digression of produced output and the ideal form is expressed in terms of phase noise and jitter. there are several sources of noise in a pll system such as input reference noise, phase and frequency detector (pfd) noise, charge pump (cp) noise, divider noise and especially voltage controlled oscillator (vco) noise. in other words, each building block in a pll produces a signal which is not ideal. so the overall system will suffer from different sources of noise. mainly, these several sources are divided into two main categories: in-band and out-of-band phase noise [1]. in fact, it is shown in [1] that there are two different noise transfer functions for a pll, one for the noise due to vco (which is referred to output and has a high pass nature) and one for all other sources of noise (which is referred to input and has a lowpass nature). this means that for the frequencies inside the loop bandwidth, the loop will track the input referred noise and the vco noise will be suppressed. on the other side, for the frequencies outside the bandwidth, the pll noise approaches the vco noise and the other sources of noise will not have an important role in output noise [1]. thus, bandwidth choice will have an important role in determining the output noise of a pll. on the other hand, several pll characteristics such as settling behavior, stability and lock time are affected by pll bandwidth. the choice of pll bandwidth will appear more and more confusing when we look into the pll structure. a pll has a discrete-time nature and in order to be able to approximate it with a continues time system, the bandwidth to the reference frequency ratio should be sufficiently small. in other words, if the bandwidth of the pll is a significant fraction of the input frequency, continues time approximation will not be accurate [2]. so the first challenging step in the design procedure of a pll is bandwidth choice. however, it is possible to select an optimum pll bandwidth which satisfies all requirements. unfortunately, the loop bandwidth of a pll is a function of pvt variations and different loop parameters such as charge pump current, loop filter elements, vco oscillation frequency, and dividing ratio. this means that any change in one of these parameters will result in bandwidth change and the optimum designed operation will be lost. in order to maintain the optimum performance, adaptive bandwidth pll is a solution. the main idea in adaptive bandwidth pll is to reform the pll structure in such a way that the bandwidth to reference frequency ratio is kept fixed [2, 4]. this aim is usually reached using loop parameter variation according to loop conditions and dynamics. several architectures have been proposed to achieve bandwidth adaptivity. in this work a new architecture is proposed which achieves adaptivity using a lock status monitor unit. ii. a review on charge pump pll basically, a pll is a feedback system in which the phase difference between input and output signals is eliminated and thus, the output and input frequencies will be equal (in absence of a divider in feedback path) [3]. however, in many applications, it is not possible to remove phase difference completely but the constant phase difference will also result in frequency equality. inout inout inout dt d dt d cons     . (1) figure 1 depicts the basic structure of a charge pump pll. the pfd compares the frequency and phase of its two inputs and produces an "up" or "down" signal at its output. in fact, if engineering, technology & applied science research vol. 7, no. 2, 2017, 1473-1477 1474 www.etasr.com taheri: a 4-4.8ghz adaptive bandwidth, adaptive jitter phase locked loop the reference frequency is greater than the divided frequency, the output frequency of the vco should increase and an "up" signal is generated. on the other hand, if the divided frequency is more than the reference frequency, the output frequency of vco should decrease and a "down" signal is generated. according to the pfd output, the charge pump which basically consists of two totally matched current sources, will inject or draw current from the loop filter. the low pass filter (lpf) output, according to the sourced or sunk current, will force voltage controlled oscillator to increase or decrease its oscillation frequency. the divider will divide output frequency and deliver the result to the pfd. obtaining the transfer function of every building block in pll structure, one can show that the bandwidth of the pll is as shown in (2) where ωn and ξ are defined as (3) and (4) respectively. because of complexity in (2), the two approximations are presented in (5) and (6) [1] .in these equations, i, kvco, c1, n, and r are charge pump current, vco sensitivity, loop filter capacitance, divider ratio and loop filter resistance respectively. 24421 2423   ndb (2) 12 . nc ki vco n    (3) n ckir vco   2 .. 2 1 (4) )5.1(,23   forndb (5) )5.1(,)21(3   forndb (6) fig. 1. conventional pll structure several solutions have been proposed which have tried to achieve bandwidth to the reference frequency ratio. in [2], bandwidth adaptivity is obtained using two charge pumps and a ring oscillator. the key point in [2] is a symmetric load which is used in delay cells of the ring oscillator. the resistance of the symmetric load is changed using a control voltage that is generated using a bias generator. the proposed architecture in [2] exhibits ξ and ωn/ωref ratio that are determined using a ratio of capacitors and thus are fixed. in [4], using an averaging linear varactor, icp and ωosc 2 are inversely proportional together and in addition to the wide tuning range of lc-vco, bandwidth adaptivity is obtained. however, these are two of most important reports in the literature. in fact, these are two most important and reviewed works in the fields but, in spite of their nobel ideas, there seem to be more issues to be addressed. in [2], the solution presented is only applicable for ring vco based plls. however, in many high-performance systems, lc-vcos are prefered due to best jitter performance. on the other hand, the solution in [4] seems to be a complex way to achieve bandwidth adaptivity. iii. proposed adaptive bandwidth pll as mentioned previously, in order to achieve adaptive bandwidth pll, the ratio of bandwidth to the reference frequency should be kept fixed as much as possible. for many applications, the pll is employed in overdamped condition [4]. this means that bandwidth approximation in (5) will be appropriate. so n kir vco ndb   2 .. 23  (7) ref vco ref db n kir   2 ..3  (8) to maintain the best jitter performance, it is necessary to have fixed value for (8). with fixed values for n, ωref, and kvco, if loop filter resistance "r" and charge pump current "i" are changed inversely, the required ratio will be achieved. it is necessary to mention that fixed kvco requires a special vco design with linear varactor which is described in d. main building blocks of proposed structure are described in next subsections. a. phase frequency detector the main function of pfd is to compare the phase and frequency of the reference waveform and the divider output and generate a suitable signal for the charge pump. in this work, a modified tristate pfd which is shown in figure 2 is used. fig. 2. modified tristate pfd this circuit generates the reset signal (which is needed to prevent the unauthorized condition of "up=1 and down=1" in pfd) through a pass which does not include flip flops and so charge pump will not produce extra noise. one of the most important issues in pfd design is "dead zone". for small differences between pfd input signals, due to small differences engineering, technology & applied science research vol. 7, no. 2, 2017, 1473-1477 1475 www.etasr.com taheri: a 4-4.8ghz adaptive bandwidth, adaptive jitter phase locked loop between rise time of latch outputs and reset path delay, pfd will not detect the phase difference and will not respond properly. in the designed pfd, the dead zone is tried to be minimized as much as possible [1]. figure 3 depicts pfd characteristic. as it is obvious in figure 3, the pfd exhibits a dead zone less than 0.36 degrees. it means that for phase differences between -0.18 and 0.18 degree this pfd will not respond accurately. fig. 3. pfd characteristic b. charge pump circuit in order to implement a charge pump with perfectly matched charge-discharge currents, a basic topology shown in figure 4 was selected. this charge pump cell has two important advantages. first, in order to avoid channel length modulation effect and mismatch in output currents, an opamp is implemented in such a way that current mismatch issue is addressed. second, the controlling switches are moved out of the signal path and comparing to conventional charge pump circuits, the required headroom of the circuit is decreased [1]. actually, in order to have different charge pump current values, a charge pump with 5 cells similar to the circuit shown in figure 4 were applied which were controlled using a controller. this controller will decide whether a charge pump cell is activated or not. using this structure, an almost perfectly matched charge pump was obtained which plays an important role in adaptive bandwidth scheme and minimizing output jitter. figure 5 depicts the final structure of the charge pump circuit. note that all of the charge pump cells (cpcs) have the same structure but they do not produce the same current. c. loop filter in order to convert the charge pump current into vco control voltage and eliminate its high-frequency components, a low pass filter is required. in proposed architecture, in order to achieve bandwidth adaptivity, loop filter resistance should change inversely with charge pump current. figure 6 depicts proposed loop filter structure. note that loop filter controlling signals are the same ones with charge pump topology. in this simple structure, as the charge pump current rises more resistances are paralleled with each other and hence, loop filter resistance is diminished. in addition, the c2 capacitor is added in order to eliminate high-frequency ripple on the control line of vco and its chosen one-tenth of the value of c1 [1]. fig. 4. charge pump cell fig. 5. complete charge pump structure d. lc voltage-controlled oscillator a voltage controlled oscillator is a circuit that generates a periodic waveform that its frequency is determined by a control line. in pll, the control line is lpf output. basically, vcos are divided into two main categories, ring vco and lc vco. in high-performance systems, because of superior noise operation, lc vcos are preferred. the output frequency of a vco is defined as (9) where kvco, vctrl, ω0, l, and cv are vco engineering, technology & applied science research vol. 7, no. 2, 2017, 1473-1477 1476 www.etasr.com taheri: a 4-4.8ghz adaptive bandwidth, adaptive jitter phase locked loop sensitivity, control voltage, and free running frequency of vco respectively. 0.   ctrlvcoosc vk (9) as mentioned earlier, in order to achieve bandwidth adaptivity, a fixed kvco oscillator is required. we applied an lc-vco with linear mosfet varactor. in fact, an averaging varactor which is implemented using mosfets that are biased in inversion region, similar to [4] is used to obtain a fixed kvco architecture. figure 7 demonstrates the averaging varactor structure. the dc voltages of the gates are chosen so that the nonlinearity of inversion region mosfets is averaged and the overall input capacitance of the varactor exhibits linear variations with respect to vctrl. using this varactor in lc-vco circuit shown in figure 8, the resulted oscillator generates a sin waveform which its frequency varies from 4 to 4.8 ghz. table i demonstrates the main performance parameters of lc-vco. fig. 6. loop filter. e. lock status monitor unit the lock status monitor circuit is the key controller unit of this structure. it is required to control the charge pump current and the loop filter resistance regarding the lock status of the loop. the lsmu circuit is shown in figure 9. this circuit simply consists of four comparators. these comparators compare the control voltage of the lc-vco with four reference voltages and produce four controlling signals. the comparison levels of comparators circuits are chosen according to simulation results. in fact, a conventional pll with the same characteristics of our pll was simulated first and critical levels of comparators circuits were obtained. the resulting control signals will control the loop filter resistance and the charge pump current of the pll. iv. simulation results using all of the previously discussed building blocks, the final structure of adaptive bandwidth phase locked loop is shown in figure 10. in order to examine the functionality of the proposed idea, a pll with the same characteristics of proposed structure was simulated in matlab simulink and the idea was verified. figure 11 shows the bandwidth to the reference ratio of this pll for different values of the reference frequency. as its obvious from figure 11, the bandwidth to the reference frequency ratio variations is decreased significantly in this pll and consequently, the best jitter performance of the pll will be preserved. figure 12 depicts the rms cycleto-cycle jitter of this pll. as it is shown, not only the rms value of cycle-to-cycle jitter is reduced significantly, but also the jitter performance is maintained. this means that if the pll is designed to have the minimum output jitter, its best performance will not be affected by any change in bandwidth. figure 13 demonstrates the vco control line of the proposed pll when fref= 44mhz as an example. this pll consumes less than 35mw power from 1.8 v supply voltage. table ii describes the most important characteristics fo this pll. table i. lc-vco characteristics technology 0.18µm supply voltage (v) 1.8 current consumption (ma) 2.42 tuning range(ghz) 4 4.8 free running frequency (ghz) 3.9 kvco (ghz/v) 1.05 phase noise @ 1mhz offset -115 dbc/hz fig. 7. linear varactor. fig. 8. lc vco structure. engineering, technology & applied science research vol. 7, no. 2, 2017, 1473-1477 1477 www.etasr.com taheri: a 4-4.8ghz adaptive bandwidth, adaptive jitter phase locked loop fig. 9. lock status monitor unit (lsmu). table ii. adaptive pll characteristics. technology 0.18µm cmos supply voltage (v) 1.8 power consumption (mw) 47@ 4.8ghz cycle to cycle jitter (ps) 0.45 @ 4.8ghz lock time (μs) less than 10 (worst case) operating frequency (ghz) 4-4.8 fig. 10. proposed adaptive bandwidth pll structure. fig. 11. bandwidth to the reference frequency ratio vs. reference frequency for adaptive pll (dashed line) and conventional pll (dotted line). fig. 12. output cycle-to-cycle jitter vs. reference frequency; adaptive pll (dashed line) and conventional pll, (dotted line) fig. 13. vco control voltage vs. time @ fref=44mhz v. conclusion a 4-4.8 ghz adaptive bandwidth pll is proposed and simulation results are presented. to achieve adaptivity, the charge pump current and the loop filter resistance are inversely proportional and therefore, the ratio of bandwidth to reference frequency variation is minimized. a lock status monitor unit determines the lock status of the pll and decides about the amount of charge pump current and loop filter resistance. based on the simple adaptive scheme presented in this brief, the best jitter performance and bandwidth to the reference frequency ratio is preserved. references [1] j. rogers, c. plett, f. dai, integrated circuit design for high-speed frequency synthesis, artech house, 2006 [2] j. g. maneatis, “low-jitter process-independent dll and pll based on self-biased techniques”, ieee journal of solid-state circuits, vol. 31, no. 11, pp. 1723-1732, 1996 [3] b. razavi, design of integrated circuits for optical communications, mc graw hill, 2003 [4] t. wu, p. k. hanumolu, k. mayaram, u. moon, “method for a constant loop bandwidth in lc-vco pll frequency synthesizers”, ieee journal of solid-state circuits, vol. 44, no. 2, pp. 427 – 435, 2009 microsoft word etasr_v13_n4_pp11222-11229 engineering, technology & applied science research vol. 13, no. 4, 2023, 11222-11229 11222 www.etasr.com nguyen: combining fuca, curli, and weighting methods in the decision-making of selecting … combining fuca, curli, and weighting methods in the decision-making of selecting technical products anh-tu nguyen faculty of mechanical engineering, hanoi university of industry, vietnam tuna@haui.edu.vn (corresponding author) received: 6 may 2023 | revised: 25 may 2023 | accepted: 2 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6015 abstract determining the optimal one from the available alternatives is useful in numerous aspects of life. the process of selecting technical products from an available catalog also follows this pattern. this study was carried out to select the best from two types of technical products, the ones that serve in daily life at home, and products that are used in the agriculture field. air conditioners and washing machines are considered indispensable items in every household. these two types of products directly affect human lives and also indirectly influence labor productivity. unmanned aerial vehicles (uavs) are used in numerous tasks in the agriculture field, such as inspecting irrigation systems, checking for factors that can harm agricultural products, etc. however, making the decision to buy one of those three types of products may become complicated. this research was conducted to select the best alternative for each of those products. the different types of air conditioners, washing machines, and drones considered in this study were 9, 8, and 7, respectively. two methods, i.e. rs (rank sum) and piprecia (pivot pairwise relative criteria importance assessment) were used to determine the weights for the criteria of each product category. the fuca (faire un choix adéquat) method was used in combination with the two weighting methods mentioned above to rank the alternatives of each product category. the curli (collaborative unbiased rank list integration) method was used to complete this task. so, for each product category, there will be three different ranking results. an interesting thing has been achieved is that for each product category, these different ranking results gave the same best solution. keywords-mcdm; weighting method; fuca method; curli method i. introduction air conditioners and washing machines are nowadays considered indispensable items of our daily life. they also contribute directly to the improvement of labor productivity. however, choosing and buying these products can be complicated. a question that is often asked is how to buy "the best" product among various candidate products, since for each product, there are many different alternatives on the market. choosing a product based on only one or a few criteria can easily lead to bad purchases. to choose the best product, it is necessary to consider all the relevant criteria. this process is termed as multi-criteria decision-making (mcdm) [1]. such problems also occur in the selection of uavs for agricultural production. however, the authors of this study can state with certainty that up to now there have not been any studies applying mcdm methods to select air conditioners, washing machines, and uavs. up to now, there is not an exact estimation of how many mcdm methods there are, but certainly, they are more than one hundred [2]. in addition, over time, new mcdm methods are constantly being presented [3]. the mcdm methods are divided into two groups, the first group consists of methods that need to determine weights for the criteria, and the second consists of methods that do not [4]. fuca is a method that needs to determine weights for the criteria (the first group) [5, 6]. this method has a major difference from the methods in its class. the difference is that it does not need to perform data normalization [5, 6]. this method has been used for mcdm in many different fields, such as ranking companies [7-10], selecting chemical manufacturing process [11], selecting lathes [12], etc. however, to the best of our knowledge, the application of the fuca method in selecting air conditioners, washing machines, and uavs has not been conducted yet. as mentioned above, when using the fuca method, it is necessary to determine weights for the criteria. however, if the weights are only determined based on the classic numerical techniques, it could lose the objectivity of the mcdm problem as well as skip the importance of the expert’s opinions. for household items, it is important to consider the opinions of customers. piprecia is a criterion weighting method that considers the decision makers opinions. using this method, it is possible to determine criteria weights considering the opinions of different groups of individuals [13]. this method has also been used to calculate the criteria weights in several fields [12-18]. however, up to engineering, technology & applied science research vol. 13, no. 4, 2023, 11222-11229 11223 www.etasr.com nguyen: combining fuca, curli, and weighting methods in the decision-making of selecting … now, this method has not been used to determine the criteria weights for the of air conditioners, washing machines, and uavs. furthermore, if only the piprecia method is used to determine the criteria weights, the question whether the ranking results change when using a different weighting method needs to be answered. the decision makers can have a strong belief in an alternative when it is determined to be the best for various weighting methods. therefore, in addition to the piprecia, in this study, another weighting method was used, which is the rs weighting method [19]. this is a simple method to determine the weights for the criteria by only one formula. this method is used to determine the criteria weights based on the decision makers' opinion on the priority of the criteria. in recent times, it is also applied to determine the criteria weights in various different cases [20-25]. using the fuca method in combination with two weighting methods (piprecia and rs) is a solution that belongs to the first group of the mcdm methods. some methods that belong to the second group are the psi (preference selection index) method, the peg (paretoedgeworth grierson) method, and the curli method [26]. there is a difference between the curli method and the other methods of this group. when using the psi and peg methods, it is needed to perform data normalization, but when using the curli method, the data do not need to be normalized. which means that when using the curli method, the decision makers do not need to determine the criteria weights and normalize data, thus eliminating the problem of choosing a proper criteria weighting and data normalization method. recently, it has also been applied in mcdm in various different aspects [26-31]. in this study, the curli method will be applied to select air conditioners, washing machines, and uavs. ii. the used weighting methods to calculate the weight distribution by using the rs method, the criteria are first arranged in descending order of priority. this arrangement is made according to the opinions of the decision maker (buyer). after the criteria have been arranged in a descending order, their weights are calculated according to (1) [19]: �� = �(�� �)�(�� ) (1) where � is the number of criteria and is the order of the th criterion. the piprecia method was used to calculate the weights for the criteria in the following way [13]: step 1: select experts (buyers) and ask their opinions on the importance of the criteria. step 2: each expert will determine the relative importance of the criteria �� , starting from the second criterion. the criterion’s importance is expressed as (2): �� = � > 1 �ℎ�� �� > �� 1 �ℎ�� �� = �� < 1 �ℎ�� �� < �� (2) step 3: for each expert, determine the coefficient �� according to: �� = � 1 = 12 − �� > 1 (3) step 4: determine the recalculated weights of the criteria according to: �� = � 1 = 1���� � > 1 (4) step 5: calculate the weights of the criteria according to the opinion of each expert according to: �� = ��∑ �"#"$� (5) step 6: calculate the weights of the criteria according to (6) and (7), where k is the number of experts and the index r represents the %-th expert. ��∗ = '∏ ��)*)+ , /* (6) �� = .�∗∑ .�∗#�$� (7) iii. the used mcdm methods a. the fuca method the steps to rank the alternatives according to the fuca method are [5, 6]: step 1: rank the alternatives for each criterion ( %/� ). suppose there are m alternatives, the worst alternative will be ranked in the m-th place and the best alternative as first. step 2: calculate the score of each alternative according to: 0/ = ∑ %/� . ����+ (8) step 3: rank the alternatives according to the values of 0/ . the best alternative is the alternative with the smallest 0/ and vice versa. b. the curli method after having the decision matrix, the steps for ranking the alternatives using the curli method include [32]: step 1: scoring the alternatives for each criterion. the scoring result of each criterion is a square matrix of level m. so with n criteria, we will have n scoring matrices. some examples of scoring are:  if in the cell corresponding to column 1 and row 2, the value 2 is better than that of 2� , the score is equal to 1, which means 2�3 = 1.  if in the cell corresponding to column 2 and row 1, the value of 2� is worse than that of 2 , the score is -1, which means 2 3� = −1.  if in the cell corresponding to column 2 and row m, the value of 2� is equal to that of 24 , the score is 0, which means 24 3� = 0. engineering, technology & applied science research vol. 13, no. 4, 2023, 11222-11229 11224 www.etasr.com nguyen: combining fuca, curli, and weighting methods in the decision-making of selecting … scoring is performed for all the cells that do not lie on the main diagonal of the matrix. in the cells that lie on the main diagonal of the matrix, the score is 0 ( 2/ 3/ = 0 ), where 6 = 1 ÷ 8. this matrix is called the scoring matrix for each criterion (table i). table i. a scoring matrix example no. p1 p2 pi pm a1 a1p1 = 0 a1p2 = -1 a1pi = … a1pm = … a2 a2p1 = 1 a2p2 = 0 a2pi = … a2pm = … ai aip1 = … a1p2 = … aipi = 0 aipm = … am amp1 = … amp2 = 0 ampi = … ampm = 0 step 2: add all the scoring matrices for each criterion into a single matrix. thus, we get a matrix called the process scoring matrix. step 3: rearrange the rows and columns of the process scoring matrix so that the new matrix has the maximum number of cells with negative values above the main diagonal. after rearranging, the alternative that lies on the first row is considered as the best alternative. iv. selecting the best air conditioner, washing machine, and uav a. air conditioner selection nine types of air conditioner of the daikin brand were introduced by the supplier with product codes 1hp-msafc10crdn8, 1.5hp-gc-12is33, 1hp-atkc25uavmv, 1.5hp -ras-h13h4kcvg-v, 1hp-ftkb25wmvmv, 1.5hp-cu/ cs-pu12xkh-8m, 1hp-cu/cs-xu9xkh-8, 1.5hp-cu/csxu12xkh-8, and 1.5hp-ftkb35wmvmv. they are denoted by a1, a2, a3, a4, a5, a6, a7, a8, and a9 alternatives, respectively. ten criteria were used to evaluate each type of air conditioner, including:  c1: is the cost (dong). dong is the currency of vietnam, 1 usd is equivalent to about 23500 dongs.  c2: is the effective cooling area (m�).  c3: is the amount of electricity consumed (kw/h).  c4: is the average cooling speed (btu).  c5: is the power of device (hp).  c6: is the warranty period (month).  c7: is the maximum noise level of the indoor unit (db).  c8: is the maximum noise level of the outdoor unit (db).  c9: is the weight of the indoor unit (kg).  c10: is the weight of the outdoor unit (kg). a survey was carried out among 6 experts to determine the priority of the criteria. all the experts gave the same opinion. the criteria are arranged in descending order of priority as: c1 > c2 > c3 > c4 > c5 > c6 > c7 > c8 > c9 > c10. the data on the types of air conditioners are summarized in table ii. the criterion type (the larger the better, or the smaller the better) of each criterion is also summarized in the last row of this table. the most remarkable points from table ii are that c1 is the smallest at a1, c2 is the largest at a6 and a8, c3 is the smallest at a9, c4 is the largest at a4, and so on. hence, it is clear that the ranking could not be completed by relying solely on the obtained data in this table. all 10 criteria must be considered in order to identify the optimal alternative. this is the reason why applying mcdm methods is essential. table ii. types of air conditioner no. c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 a1 6590000 15 1.1 9000 1 36 39 51.5 7.4 21.7 a2 7390000 20 1.3 4095 1.5 36 32 50 8.5 21 a3 11590000 45 0.68 8500 1 12 38 47 8 23 a4 11990000 20 1.18 12000 1.5 24 24 48 9 21 a5 10990000 15 0.82 8500 1 12 36 47 8 19 a6 13890000 60 1.07 11900 1.5 12 28 48 8 23 a7 13490000 45 0.68 8700 1 12 19 47 10 18 a8 16890000 60 0.95 11900 1.5 12 19 48 10 23 a9 13490000 20 0.6 11900 1.5 12 37 47 8 22 type min max min max max max min min min min equation (1) was applied to calculate the weights of the criteria according to the rs method. accordingly, the weights of the criteria c1, c2, c3, c4, c5, c6, c7, c8, c9, and c10 have the values of 0.2929, 0.1929, 0.1429, 0.1096, 0.0846, 0.0646, 0.0479, 0.0336, 0.0211, and 0.0100, respectively. to calculate the weights according to the piprecia method, a survey was also carried out with the opinions of 6 experts and (2) was used. table iii is a summary of experts’ opinions on the relative importance of the criteria. applying the (3)-(7), the weights of the criteria were determined as shown in table iv. step 1 of the fuca method was applied to rank the alternatives for each criterion. the results are summarized in table v. step 2 of the fuca method was applied to calculate the score for each alternative with two different sets of weights (8). the results were summarized in table vi. step 3 of the fuca method was applied to rank the alternatives. the results are summarized in table vi. step 1 of the curli method was applied to score the alternatives for each criterion. the results are presented in tables vii xvi. the process scoring matrix was determined by applying the step 2 of the curli method as shown in table xvii. the process scoring matrix was rearranged according to step 3 of the curli method, and the results were shown in table xviii. engineering, technology & applied science research vol. 13, no. 4, 2023, 11222-11229 11225 www.etasr.com nguyen: combining fuca, curli, and weighting methods in the decision-making of selecting … table iii. expert opinions on the relative importance of the criteria �� criteria expert 1 expert 2 expert 3 expert 4 expert 5 expert 6 c1 c2 0.98 0.9 0.8 0.9 0.98 0.9 c3 0.96 0.96 0.96 0.9 1 1 c4 0.95 0.95 0.95 0.95 0.95 1 c5 0.94 0.94 0.9 0.9 0.95 0.94 c6 0.93 0.92 0.92 0.92 0.93 0.93 c7 0.9 0.9 0.9 0.9 0.9 0.9 c8 0.89 0.89 0.89 0.8 0.89 0.89 c9 0.85 0.6 0.5 0.8 0.8 0.75 table iv. the weights of the criteria determined using the piprecia method criteria c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 weight 0.1370 0.1259 0.1215 0.1167 0.1089 0.1013 0.0921 0.0819 0.0641 0.0508 table v. ranking the alternatives of each criterion no. c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 a1 1 8.5 7 5 7.5 1.5 9 9 1 5 a2 2 6 9 9 3 1.5 5 8 6 3.5 a3 4 3.5 2.5 7.5 7.5 6.5 8 2.5 3.5 8 a4 5 6 8 1 3 3 3 6 7 3.5 a5 3 8.5 4 7.5 7.5 6.5 6 2.5 3.5 2 a6 8 1.5 6 3 3 6.5 4 6 3.5 8 a7 6.5 3.5 2.5 6 7.5 6.5 1.5 2.5 8.5 1 a8 9 1.5 5 3 3 6.5 1.5 6 8.5 8 a9 6.5 6 1 3 3 6.5 7 2.5 3.5 6 table vi. alternative score and ranking with the fuca method no. rs weight piprecia weight vi rank vi rank a1 5.4545 8 5.4927 9 a2 5.3455 7 5.3288 7 a3 5.0182 6 5.2138 6 a4 4.6455 2 4.5532 2 a5 5.6182 9 5.3998 8 a6 4.7636 3 4.8387 4 a7 4.8636 5 4.7480 3 a8 4.8000 4 4.9445 5 a9 4.4909 1 4.4803 1 table vii. alternatives score for criterion c1 no. p1 p2 p3 p4 p5 p6 p7 p8 p9 a1 0 -1 -1 -1 -1 -1 -1 -1 -1 a2 1 0 -1 -1 -1 -1 -1 -1 -1 a3 1 1 0 -1 1 -1 -1 -1 -1 a4 1 1 1 0 1 -1 -1 -1 -1 a5 1 1 -1 -1 0 -1 -1 -1 -1 a6 1 1 1 1 1 0 1 -1 1 a7 1 1 1 1 1 -1 0 -1 0 a8 1 1 1 1 1 1 1 0 1 a9 1 1 1 1 1 -1 0 -1 0 table viii. alternatives score for criterion c2 no. p1 p2 p3 p4 p5 p6 p7 p8 p9 a1 0 1 1 1 0 1 1 1 1 a2 -1 0 1 0 -1 1 1 1 0 a3 -1 -1 0 -1 -1 1 0 1 -1 a4 -1 0 1 0 -1 1 1 1 0 a5 0 1 1 1 0 1 1 1 1 a6 -1 -1 -1 -1 -1 0 -1 0 -1 a7 -1 -1 0 -1 -1 1 0 1 -1 a8 -1 -1 -1 -1 -1 0 -1 0 -1 a9 -1 0 1 0 -1 1 1 1 0 table ix. alternatives score for criterion c3 no. p1 p2 p3 p4 p5 p6 p7 p8 p9 a1 0 -1 1 -1 1 1 1 1 1 a2 1 0 1 1 1 1 1 1 1 a3 -1 -1 0 -1 -1 -1 0 -1 1 a4 1 -1 1 0 1 1 1 1 1 a5 -1 -1 1 -1 0 -1 1 -1 1 a6 -1 -1 1 -1 1 0 1 1 1 a7 -1 -1 0 -1 -1 -1 0 -1 1 a8 -1 -1 1 -1 1 -1 1 0 1 a9 -1 -1 -1 -1 -1 -1 -1 -1 0 table x. alternatives score for criterion c4 no. p1 p2 p3 p4 p5 p6 p7 p8 p9 a1 0 -1 -1 1 -1 1 -1 1 1 a2 1 0 1 1 1 1 1 1 1 a3 1 -1 0 1 0 1 1 1 1 a4 -1 -1 -1 0 -1 -1 -1 -1 -1 a5 1 -1 0 1 0 1 1 1 1 a6 -1 -1 -1 1 -1 0 -1 0 0 a7 1 -1 -1 1 -1 1 0 1 1 a8 -1 -1 -1 1 -1 0 -1 0 0 a9 -1 -1 -1 1 -1 0 -1 0 0 according to the data in table xviii, the ranking order of the alternatives is: a9 > a6 > a8 > a3 > a4 > a7 > a1 > a2 > a5. figure 1 shows the ranking results of the air conditioners using the fuca method and the curli method. engineering, technology & applied science research vol. 13, no. 4, 2023, 11222-11229 11226 www.etasr.com nguyen: combining fuca, curli, and weighting methods in the decision-making of selecting … table xi. alternatives score for criterion c5 no. p1 p2 p3 p4 p5 p6 p7 p8 p9 a1 0 1 0 1 0 1 0 1 1 a2 -1 0 -1 0 -1 0 -1 0 0 a3 0 1 0 1 0 1 0 1 1 a4 -1 0 -1 0 -1 0 -1 0 0 a5 0 1 0 1 0 1 0 1 1 a6 -1 0 -1 0 -1 0 -1 0 0 a7 0 1 0 1 0 1 0 1 1 a8 -1 0 -1 0 -1 0 -1 0 0 a9 -1 0 -1 0 -1 0 -1 0 0 table xii. alternatives score for criterion c6 no. p1 p2 p3 p4 p5 p6 p7 p8 p9 a1 0 0 -1 -1 -1 -1 -1 -1 -1 a2 0 0 -1 -1 -1 -1 -1 -1 -1 a3 1 1 0 1 0 0 0 0 0 a4 1 1 -1 0 -1 -1 -1 -1 -1 a5 1 1 0 1 0 0 0 0 0 a6 1 1 0 1 0 0 0 0 0 a7 1 1 0 1 0 0 0 0 0 a8 1 1 0 1 0 0 0 0 0 a9 1 1 0 1 0 0 0 0 0 table xiii. alternatives score for criterion c7 no. p1 p2 p3 p4 p5 p6 p7 p8 p9 a1 0 1 1 1 1 1 1 1 1 a2 -1 0 -1 1 -1 1 1 1 -1 a3 -1 1 0 1 1 1 1 1 1 a4 -1 -1 -1 0 -1 -1 1 1 -1 a5 -1 1 -1 1 0 1 1 1 -1 a6 -1 -1 -1 1 -1 0 1 1 -1 a7 -1 -1 -1 -1 -1 -1 0 0 -1 a8 -1 -1 -1 -1 -1 -1 0 0 -1 a9 -1 1 -1 1 1 1 1 1 0 table xiv. alternatives score for criterion c8 no. p1 p2 p3 p4 p5 p6 p7 p8 p9 a1 0 1 1 1 1 1 1 1 1 a2 -1 0 1 1 1 1 1 1 1 a3 -1 -1 0 -1 0 -1 0 -1 0 a4 -1 -1 1 0 1 0 1 0 1 a5 -1 -1 0 -1 0 -1 0 -1 0 a6 -1 -1 1 0 1 0 1 0 1 a7 -1 -1 0 -1 0 -1 0 -1 0 a8 -1 -1 1 0 1 0 1 0 1 a9 -1 -1 0 -1 0 -1 0 -1 0 table xv. alternatives score for criterion c9 no. p1 p2 p3 p4 p5 p6 p7 p8 p9 a1 0 -1 -1 -1 -1 -1 -1 -1 -1 a2 1 0 1 -1 1 1 -1 -1 1 a3 1 -1 0 -1 0 0 -1 -1 0 a4 1 1 1 0 1 1 -1 -1 1 a5 1 -1 0 -1 0 0 -1 -1 0 a6 1 -1 0 -1 0 0 -1 -1 0 a7 1 1 1 1 1 1 0 0 1 a8 1 1 1 1 1 1 0 0 1 a9 1 -1 0 -1 0 0 -1 -1 0 it can be seen from figure 1 that the ranking orders of the alternatives are not completely the same when using fuca and curli. the ranking orders of the alternatives are also not the same when using rs and piprecia. this issue is consistent with the findings in [1]. however, in every performed case, a9 is always ranked as 1 st . accordingly, among the 9 considered types of air conditioners, the 1.5hp-ftkb35wmvmv is determined to be the best. table xvi. alternatives score for criterion c10 no. p1 p2 p3 p4 p5 p6 p7 p8 p9 a1 0 -1 1 -1 -1 1 -1 1 1 a2 1 0 1 0 -1 1 -1 1 1 a3 -1 -1 0 -1 -1 0 -1 0 -1 a4 1 0 1 0 -1 1 -1 1 1 a5 1 1 1 1 0 1 -1 1 1 a6 -1 -1 0 -1 -1 0 -1 0 -1 a7 1 1 1 1 1 1 0 1 1 a8 -1 -1 0 -1 -1 0 -1 0 -1 a9 -1 -1 1 -1 -1 1 -1 1 0 table xvii. the process scoring matrix no. p1 p2 p3 p4 p5 p6 p7 p8 p9 a1 0 -1 1 0 -2 4 -1 4 4 a2 1 0 2 1 -2 5 0 3 2 a3 -1 -2 0 -2 -1 1 -1 0 1 a4 0 -1 2 0 -2 0 -2 0 0 a5 2 2 1 2 0 2 1 1 3 a6 -4 -5 -1 0 -2 0 -1 0 0 a7 1 0 1 2 -1 1 0 1 3 a8 -4 -3 0 0 -1 0 -1 0 1 a9 -4 -2 -1 0 -3 0 -3 -1 0 table xviii. the process scoring matrix after rearrangement no. p9 p6 p8 p3 p4 p7 p1 p2 p5 a9 0 0 -1 -1 0 -3 -4 -2 -3 a6 0 0 0 -1 0 -1 -4 -5 -2 a8 1 0 0 0 0 -1 -4 -3 -1 a3 1 1 0 0 -2 -1 -1 -2 -1 a4 0 0 0 2 0 -2 0 -1 -2 a7 3 1 1 1 2 0 1 0 -1 a1 4 4 4 1 0 -1 0 -1 -2 a2 2 5 3 2 1 0 1 0 -2 a5 3 2 1 1 2 1 2 2 0 fig. 1. ranking of the air conditioner types. b. washing machine selection eight types of washing machines were introduced by the supplier with product codes ww80t3020ww/sv, wa90t5260by/sv, ww95ta046ax/sv, ww10t634dlx/ sv, ww10ta046ae/sv, ww90t634dln/sv, wa12t53 60bv/sv, and wa10t5260bv/sv. they are denoted by a1, a2, a3, a4, a5, a6, a7, and a8 alternatives, respectively. the 12 criteria used to evaluate each alternative were arranged in descending order of priority: 0 1 2 3 4 5 6 7 8 9 10 a1 a2 a3 a4 a5 a6 a7 a8 a9 fuca + rs fuca + piprecia curli r a n k engineering, technology & applied science research vol. 13, no. 4, 2023, 11222-11229 11227 www.etasr.com nguyen: combining fuca, curli, and weighting methods in the decision-making of selecting …  c1: is the mass of τηε fabric that can be processed in one wash (kg).  c2: is the cost (dong).  c3: is the efficiency of electricity use (wh/kg).  c4: is the maximum spin speed (rev/min).  c5: is the engine warranty period (years).  c6: is the cover material (stainless steel = ss, powder coated metal = pcm). according to experts’ opinions, ss is better than pcm.  c7: is the weight (kg).  c8: is the height (cm).  c9: is the width (cm).  c10: is the depth (cm).  c11: is the length of the water supply pipe (cm).  c12: is the length of the drainpipe (cm). the data for the 8 washing machines are summarized in table xix. each criterion type (the larger the better, or the smaller the better) is also listed in the last row. according to the data in table xix, c1 is the largest at a7, c2 is the smallest at a2, c3 is the smallest at a7, c4 is the largest at a4a6, etc. this demonstrates that mcdm methods are highly recommended for identifying the best alternative in this problem. the relative importance between the criteria was also obtained by surveying the opinions of 6 experts. the results are summarized in table xx. the weights of the criteria were calculated according to both rs and piprecia and are summarized in table xxi. table xix. washing machine types no. c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12 a1 8 6990000 12.6 1200 11 ss 58 83.7 59.5 49.3 106 165 a2 9 5990000 10.6 700 20 pcm 40 105 61 67.5 109 121 a3 9.5 10290000 11.9 1400 20 ss 65 84.3 60 60 212 145 a4 10 10990000 13.1 1400 20 ss 67 85 60 60.6 211 154 a5 10 8790000 13.1 1400 20 ss 65 85 60 55 195 140 a6 9 9990000 13 1400 20 pcm 67 84.2 60 61.5 214 131 a7 12 8390000 7.2 700 20 pcm 43 109 61 65.5 106 115 a8 10 7190000 8.8 700 20 pcm 41 108 60 65 106 115 type max min min max max ss is better than pcm max max max max max max table xx. experts’ opinion on the relative importance of the criteria s; criteria expert 1 expert 2 expert 3 expert 4 expert 5 expert 6 c1 c2 0.98 0.99 0.92 0.97 0.92 0.9 c3 0.94 0.95 0.94 0.92 0.97 0.95 c4 0.92 0.92 0.92 0.92 0.95 0.95 c5 0.97 0.98 0.98 0.95 0.95 0.95 c6 0.97 0.94 0.92 0.92 0.92 0.92 c7 0.96 0.96 0.96 0.94 0.94 0.94 c8 0.95 0.95 0.99 0.92 0.95 0.95 c9 0.99 0.92 0.92 0.92 0.92 0.92 c10 0.89 0.89 0.89 0.85 0.96 0.96 c11 0.88 0.9 0.9 0.85 0.9 0.95 c12 0.98 0.8 0.9 0.85 0.9 0.95 table xxi. criteria weights criteria c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12 rs weight 0.1538 0.1410 0.1282 0.1154 0.1026 0.0897 0.0769 0.0641 0.0513 0.0385 0.0256 0.0128 piprecia weight 0.1120 0.1064 0.1008 0.0942 0.0909 0.0851 0.0811 0.0773 0.0724 0.0663 0.0601 0.0535 ranking of the washing machines is conducted with steps similar to those of the precious section. the results are illustrated in figure 2. observing figure 2, it can be seen that the ranking orders of the alternatives are not completely the same when using fuca and curli. the ranking orders of the alternatives are also not completely the same when using the weighting methods rs and piprecia. however, all the cases determined that a7 is the 1 st alternative and a1 ranked 8 th . accordingly, wa12t5360bv/sv is the best type and ww80t3020ww/sv is the worst type among the 8 considered washing machines. after ranking the two product categories (air conditioner, washing machine) we can see that the best alternative determined by the curli method is always similar to the one determined when using the fuca method. also, when using the fuca method to determine the best alternative, that alternative does not depend on the weights for the criteria. c. uav selection seven types of agricultural uavs were considered [33-39]. their models are: u25l-4, u30l-6, d16l-4, u50 max, d72l8, agras t40, and agras t30. they are designated as the alternatives a1, a2, a3, a4, a5, a6, and a7. nine criteria are applied to evaluate each alternative. the criteria include engineering, technology & applied science research vol. 13, no. 4, 2023, 11222-11229 11228 www.etasr.com nguyen: combining fuca, curli, and weighting methods in the decision-making of selecting … maximum takeoff weight (kg), aircraft weight (kg), aircraft medicine box capacity (lt), flight altitude (m), max fly time (unloaded) (mins), fly time (loaded), max spray width (m), max spray flow (lt), min spray efficiency (hct/h). these criteria are denoted by c1-c9, in that order. among these criteria, c2 is defined as the cost factor; the remaining 8 criteria are defined as the benefit factors. the specific data of the uavs are indicated in table xxii. the opinions of six experts on the relative importance of the criteria were obtained. the results of the survey are summarized in table xxiii. fig. 2. ranking of the washing machine types. table xxii. uav specification [33-39] no. c1 c2 c3 c4 c5 c6 c7 c8 c9 a1 51 19 25 30 25 13 8 12 10 a2 66.5 24 30 30 30 13 12 10 10 a3 36 15 16 30 25 13 8 8 5 a4 82 42 40 30 20 15 10 4.5 6.8 a5 147 52 72 30 25 13 15 5 10 a6 90 50 40 45 18 6 11 12 10 a7 65 26.3 25 45 20.5 7.8 11 12 10 table xxiii. expert opinion on the relative importance of the criteria sj criteria expert 1 expert 2 expert 3 expert 4 expert 5 expert 6 c1 c2 0.98 0.97 0.99 0.97 0.97 0.94 c3 0.99 0.9 0.95 0.92 0.97 0.97 c4 0.96 0.95 0.99 0.9 0.92 0.95 c5 0.98 0.96 0.98 0.9 0.92 0.98 c6 1 0.99 0.97 0.95 0.95 1 c7 0.92 0.91 0.9 0.99 0.9 0.92 c8 0.98 1 0.91 0.92 0.95 0.95 c9 0.92 0.9 1 0.99 0.98 0.9 table xxiv. criteria weights criteria c1 c2 c3 c4 c5 c6 c7 c8 c9 rs weight 0.2000 0.1778 0.1556 0.1333 0.1111 0.0889 0.0667 0.0444 0.0222 piprecia weight 0.1314 0.1276 0.1215 0.1153 0.1102 0.1077 0.1001 0.0955 0.0909 fig. 3. the uav ranking results based on different mcdm methods. rs and piprecia were used to calculate the weights of the criteria. the results are presented in table xxiv. the ranking of alternatives in this case is implemented in the same way as above, and the results are illustrated in figure 3. figure 3 shows that the ranking results of the uavs are similar. specifically, the combination of the fuca method and the piprecia method gives ranking results that are completely consistent with those of the curli method. this result gives us a solid conclusion that a2 is the best alternative and a3 is the worst. accordingly, out of the 7 surveyed uav types, the u30l-6 is determined to be the best. v. conclusion ranking the alternatives to determine the best ones for three product categories, namely air conditioners, washing machines, and uavs was carried out for the first time in this study. four methods including rs, piprecia, fuca, and curli were applied simultaneously to accomplish this task. the main findings of this study are:  the best found alternative is the same regardless of the method used.  among the considered alternatives, 1.5hpftkb35wmvmv was the best air conditioner type.  the wa12t5360bv/sv is the best out of eight candidate washing 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[34] "30l pesticide spraying drone qingdao zhongfei intelligent technology co.,ltd." https://brouav.com/30l-pesticide-spraying-drone2-p.html. [35] "16l agriculture drone sprayer." https://brouav.com/16l-agriculturedrone-sprayer-p.html. [36] "u50 max." https://brouav.com/u50-max-c.html. [37] "72l agriculture drone farming." https://brouav.com/72l-agriculturedrone-farming-p.html. [38] "dji official website," dji official. https://www.dji.com/gr/t40/specs. [39] "high efficiency agras t30 drone sprayer 30kg agriculture sprayer agras t30 drone for spraying agricultural plant protection spraying drones," uav supplier-sinfox. https://www.ev-peak.com.hk/products/ high-efficiency-agras-t30-drone-sprayer-30kg-agriculture-sprayer-agrast30-drone-for-spraying-agricultural-plant-protection-spraying-drones. microsoft word 5-543-ed.doc engineering, technology & applied science research vol. 4, no. 4, 2014, 681-685 681 www.etasr.com dwidar and sharaf: statistical magnitude analysis and distance determination of the nearby f8v stars statistical magnitude analysis and distance determination of the nearby f8v stars hany r. dwidar astronomy, meteorology and space science dept. faculty of science, cairo university giza, egypt hanyryd@gmail.com adel sharaf department of astronomy faculty of science, king abdul aziz university jeddah, saudi arabia sharaf_adel@hotmail.com abstract—  the present paper is of three folds. first, to provide some basic descriptive statistics parameters for the apparent and absolute magnitudes of the nearby stars of spectral type f8v stars. second, to establish the frequency functions )(m and )(m of the absolute and apparent magnitudes for these stars. third, to compute the distance r of these stars as a system assuming that they scatter around a mean absolute magnitude in a gaussian distribution. the accuracy of the numerical results is satisfactory thus, the percentage error between r and the mean value is less than 0 .7%. keywords‐distance determinations; spectral types; frequency functions; statistical magnitude analysis  i. introduction an f-type main sequence star (f v), commonly called a yellow-white dwarf, is a main sequence (hydrogen-burning) star of spectral type f and luminosity class v. these stars have from 1.0 to 1.4 times the mass of the sun and surface temperatures between 6,000 and 7,600 k [1]. a star of spectral type f has a spectrum that shows strong absorption lines of ionized calcium, more prominent than the hydrogen lines. moderately strong lines due to iron and other heavier elements are also evident. the lines of neutral atoms for the stars of spectral type f are weak compared to those of ionized atoms. the hydrogen lines are stronger, attaining their maximum intensities in a-type stars. thereafter, these absorption lines gradually fade as the hydrogen becomes ionized [2]. main sequence f stars, of which procyon is an example, have a surface temperature of 5,800 to 6,900°c, a mass of 1.2 to 1.6 solar masses, and a luminosity of 2 to 6 times that of the sun. relatively nearby, late-type members of this category are generally included in the list of target stars for extra solar planet searches and targeted nasa seti programs. f-type super giants, of which canopus and polaris (the pole star) are examples, have a mass up to 12 solar masses and luminosity up to 32,000 times that of the sun. the importance of the distance of f8v stars derives from that if its moving stellar vertex and its distance of each member are known, then one can easily determine the velocity of the cluster, the position of its centre [3, 4] and also the distribution of the cluster’s members about this centre [5, 6]. modern observational astronomy has been characterized by an enormous growth in acquisition stimulated by the advent of new technologies in telescopes, detectors and computations. this new astronomical data give rise to innumerable statistical problems [7]. in the present paper we consider f8v stars and perform the following:  providing some basic descriptive statistics parameters for the apparent and absolute magnitudes of these stars  establishing the frequency functions ( )m and ( )m of the absolute and apparent magnitudes for these stars  computing the distance r of these stars as a system assuming that they scatter around a mean absolute magnitude in a gaussian distribution. the accuracy of the numerical results is satisfactory thus, the percentage error between r and the mean value is less than 0.7%. ii. basic materials a. data the source of data is (v/70 a) nearby stars [8] of (i/239) hipparcos and tycho catalogues [9, 10]. in table i of appendix a, the data for some f8v stars are listed. the columns of the table have the following meaning:  column 1: name with the following acronyms : o g1 [11]. o gj [12]. o wo [13]. o nn newly added stars (number added at cds)  column 2: vmag (unit mag): apparent magnitude  column 3: b-v(unit mag): color  column 4: u-b(unit mag): color  column 5: plx (unit mas  milli-second of arc): parallax  column 6: mv(unit mag): absolute visual magnitude b. the distance equation the following assumptions will be used to derive the distance equation [4]: engineering, technology & applied science research vol. 4, no. 4, 2014, 681-685 682 www.etasr.com dwidar and sharaf: statistical magnitude analysis and distance determination of the nearby f8v stars  all the members in a given cosmic group are at the same distance, r parsecs.  the frequency function for the absolute magnitudes of the members of the cosmic group is 2 2 0( ) / 2 1 ( ) 2 m mm e       (1) that is the members scatter around a mean absolute magnitude 0m in a gaussian distribution with dispersion  .  the mean apparent magnitude m of the members of the cosmic group and the limiting apparent magnitude 1m are related through the quantity  where 1m m    according to the above assumptions, the distance r and the frequency functions )(m of the apparent magnitude are given respectively by: 1 01 ( )/510 m m y r     (2) 2 2 0 1 ( 5 5log ) /2 ( ) 2 m r m m e          (3) where y is the solution of the transcendental equation: 2 1 / 2( ) 1 erf ( ) 0, 2 2 y yy y e                     (4) and, erf (z) is the error function defined by the integral 2 0 2 erf(z) d z te t    , (5) we call (4) the distance equation. the relation between 0 and m  is given by [3] 2 0 1.382 m m   (6) where m is the mean absolute magnitudes of the stellar group. c. empirical relation of vm versus 0( )b v an empirical relation between the absolute visual magnitude vm and 0( )b v is given in [14] in a tabular form (table ii of appendix a). from this empirical relation one can deduce an interpolating polynomial between 0( )b v and vm in the form [15]: 20 0 v 1 ( ) mj j b v q     (7) where q's are listed in table iii of appendix a. iii. numerical application a. procedure 1. compute the parallax p in second of arc from plx / 1000p  2. compute for each star of the group 0( )b v from its given value of vm using (7) 3. compute the absorption va for each star of the group from:  v 03 ( ) ( )a b v b v    4. compute the average v v of a a 5. correct the apparent magnitudes for absorption from vmag=vmagv a 6. compute the average value v m of the absolute magnitudes v m 7. compute the average value r of the individual distances ( 1 / ) j j j r r p 8. compute the median medianr of the individual distances 9. select start and end values of  ,say s  and e  respectively. in the present application, 0.5 s   and 2e  10. compute the optimum value of  as follows: a. for  = s  (0.01) e  perform the following calculations:  2 0 v m 1.382σm    compute the distance r (in parsec) of the stellar group from the values of 0vmag, and m  as obtained from the statistical method using the algorithm of [4].  compute the percentage error f in the mean from: | ( ) / | 100f r r r    compute the percentage error g in the median from | ( ) / | 100median mediang r r r   b. compute the value 1 that gives the minimum of the f's values c. compute the value 2 that gives the minimum of the g's values d. compute the optimum value of  as  =( 1  + 2  )/2. 11. compute some basic descriptive statistics parameters for the apparent and absolute magnitudes of the stellar group. 12. compute the measures of the central tendency for the individual distances 1 / j j r p of the stellar group, of these measures are :  the mean distance r (in parsec) of j r  the mode of j r  the median of j r  the harmonic mean of j r  the geometric mean of j r engineering, technology & applied science research vol. 4, no. 4, 2014, 681-685 683 www.etasr.com dwidar and sharaf: statistical magnitude analysis and distance determination of the nearby f8v stars 13. from the optimum values of 0m and  compute the frequency functions ( )m and ( )m of the absolute and apparent magnitudes [(1) and (3)] of the group. b. numerical results numerical results are obtained using mathematica 7 and are listed in appendix b throughout the following points:  statistics of the apparent and absolute magnitudes of the f8v group  graphical representations: a. histograms for the apparent and absolute magnitudes of the stellar group b. graphical representations for the percentage errors for the mean and median  optimum choice of   distance analysis  the frequency functions ( )m and ( )m of the absolute and apparent magnitudes for the f8v group   iv. conclusion the aim of the present paper is three fold. first, to provide some basic descriptive statistics parameters for the apparent and absolute magnitudes of the nearby stars of spectral type f8v stars. second, to establish the frequency functions ( )m and ( )m of the absolute and apparent magnitudes for these stars. third, to compute the distance r of these stars as a system assuming that they scatter around a mean absolute magnitude in a gaussian distribution. the accuracy of the numerical results is satisfactory thus, the percentage error between r and the mean value is less than 0.67%. this percentage error indicates the applicability of the used method for distance determination in the ranges of the considered stellar group. references [1] g. j. habets, j. w. heintze, "empirical bolometric corrections for the main-sequence", astronomy and astrophysics, vol. 46, pp. 193–237, 1981 [2] r. o. gray, r. f. garrison, "the early f-type stars: refined classification, confrontation with strömgren photometry, and the effects of rotation", astrophysical journal, vol. 69, pp. 301-321, 1989 [3] h. i. abdel-rahman, i. a. issa, m. a. sharaf, m. i. nouh, a. bakry, a. i. osman, a. s. saad, f. y. kamal, essam, "statistical gaussian distribution function as a distance indicator to stellar groups", journal of korean astronomical society, vol. 42, no. 4, pp. 71-79, 2009 [4] m. a. sharaf, i. a. issa, a. saad, "a method for the determination of cosmic distances", new astronomy, vol. 8, no. 1, pp. 15-21, 2003 [5] s. cassisi, r. de santis, a. m. piersimoni, "the distance to galactic globular clusters through rr lyrae pulsational properties", monthly notices of the royal astronomical society, vol. 326, no. 1, pp. 342348, 2001 [6] b. w. carney, b. c. chaboyer, d. dunca, t. grand, d. w. latham, a. layden, a. mcwilliam, a. sarajedini, m. shao, "anchoring the population ii distance scale: accurate ages for globular clusters and field halo stars", in american astronomical society meeting abstracts, vol. 33, 2001 [7] e. d. feigelson, g. j. babu (eds), statistical challenges in modern astronomy, springer-verlag, 1992 [8] w. gliese, h. jahreiss, preliminary version of the third catalogue of nearby stars, vizier online data catalog, vol. 5070, 1995 [9] esa, the hipparcos and tycho catalogues (esa 1997), vizier online data catalog, vol. 1239, 1997 [10] j. kovalevsky, "hipparcos and tycho catalogues," in encyclopedia of astronomy and astrophysics, p. murdin, ed.: encyclopedia of astronomy and astrophysics, 2000 [11] w. gliese, catalogue of nearby stars. edition 1969, veroeffentlichungen des astronomischen rechen-instituts heidelberg, vol. 22, 1969 [12] w. gliese, h. jahreiss, "nearby star data published 1969-1978", astronomy and astrophysics, vol. 38, pp.. 423-448, 1979 [13] r. van der riet woolley, catalogue of stars within twenty-five parsecs of the sun, herstmonceux, royal greenwich observatory, 1970 [14] d. mihalas, j. benney, galactic astronomy ,second edition. usa: freeman and company, 1981 [15] m. a. sharaf, "computations of the cosmic distance equation", applied mathematics and computation, vol. 174, no. 2, pp. 1269–1278, 2006 v. appendix a. appendix a: input data table i. data for some f8v nearby stars name vmag mag b-v mag u-b mag plx mas mv mag gl 34.1 5.07 0.51 0 55 3.77 gl 41 4.82 0.53 0.12 76 4.22 gl 55 4.96 0.58 0.1 82 4.53 gl 61 4.09 0.54 0.06 57.4 2.88 nn 3109 5.52 0.53 0 53 4.14 nn 3115 5.79 0.55 -0.01 49 4.24 g 81.3 6.1 0.48 -0.04 40 4.11 gl 87.1 5.67 0.56 0.07 34 3.33 nn 3161 6.02 0.54 0.04 44 4.24 nn 3175 5.78 0.52 0 45 4.05 gl 115 8.17 0.55 -0.01 61.9 7.13 gl 128 5.06 0.57 0.12 53.3 3.69 gl 147 4.28 0.57 0.08 59.4 3.15 wo 9181 7.17 0.54 0.01 27 4.33 gl 240.1 5.45 0.5 -0.02 47.5 3.83 nn 3443 5.86 0.48 -0.02 40 3.87 gl 296.2 6.57 0.58 0.01 37 4.41 gl 310.1 5.99 0.52 0.04 43.7 4.19 gl 379.1 6.15 0.6 0.16 46.7 4.5 gl 388.2 7.18 0.55 -0.04 30 4.57 gl 395 4.84 0.52 -0.01 78 4.3 gl 558.1 6.04 0.5 -0.02 39 4 nn 3880 5.63 0.5 0 41 3.69 gl 580.2 5.13 0.53 0.08 48.3 3.55 nn 3901 5 0.5 0.04 29.9 2.38 nn 3931 5.47 0.52 0.03 33.2 3.08 gl 615.2 5.64 0.51 0 44.4 3.88 gl 694.1 5.79 0.53 0.02 54.9 4.49 gl 743.1 4.87 0.52 0 68 4.03 gl 768.1 5.11 0.55 0.07 59 3.96 gl 773.4 5.66 0.49 -0.02 51.6 4.22 gl 794.2 5.12 0.53 0.01 55 3.82 gl 811 5.7 0.5 -0.04 45 3.97 gl 827 4.22 0.49 -0.12 115.5 4.53 wo 9829 6.49 0.54 -0.01 39 4.45 nn 4384 6.47 0.55 -0.06 36 4.25 engineering, technology & applied science research vol. 4, no. 4, 2014, 681-685 684 www.etasr.com dwidar and sharaf: statistical magnitude analysis and distance determination of the nearby f8v stars table ii. empirical relation between v m versus 0 ( )b v 0 ( )b v v m 0 ( )b v v m -0.30 -3.50 0.30 2.80 -0.25 -2.30 0.40 3.35 -0.20 -1.30 0.50 4.05 -0.15 -0.50 0.60 4.60 -0.10 0.30 0.70 5.20 -0.05 0.90 0.80 5.70 0.00 1.30 0.90 6.10 0.05 1.55 1.00 6.60 0.10 1.80 1.10 7.00 0.20 2.25 1.20 7.45 1.30 7.90 table iii. the q 's coefficients of (7) j qj j qj 1 -0.786498 11 0.769777 2 3.37819 12 -0.421287 3 -1. 96742 13 0.0908398 4 -10.6822 14 0.000500399 5 20.8088 15 -0.00573177 6 11.6107 16 0.00172542 7 -5.11632 17 -0.000284527 8 10.3234 18 0.0000296064 9 -5.29694 19 -1.94463 6 10   10 0.467069 20 7.40906 8 10   b. appendix b: output data b.1: statistics of the apparent and absolute magnitudes of the f8v stars  the average: for apparent magnitudes=5.63556 for absolute magnitudes=4.04944  the median (central value): for apparent magnitudes=5.65 for absolute magnitudes=4.08  the mode: for apparent magnitudes=5.79 for absolute magnitudes={3.69,4.22,4.24,4.53}  the geometric mean: for apparent magnitudes=5.576 for absolute magnitudes=3.9911  the harmonic mean: for apparent magnitudes=5.51804 for absolute magnitudes=3.93349  the root mean square: for apparent magnitudes=5.69684 for absolute magnitudes=4.1122  the quartiles: for apparent magnitudes={5.065,5.65,6.03} for absolute magnitudes={3.795,4.08,4.315}  the range: for apparent magnitudes=4.08 for absolute magnitudes=4.75  the unbiased estimate of the variance: for apparent magnitudes=0.714385 for absolute magnitudes=0.526863  the maximum likelihood estimate of the variance: for apparent magnitudes= 0.694541 for absolute magnitudes=0.512227  the unbiased estimate of the variance of the sample mean: for apparent magnitudes=0.019844 for absolute magnitudes=0.0146351  the unbiased estimate of the standard deviation: for apparent magnitudes=0.845213 for absolute magnitudes=0.725853  the maximum likelihood estimate of the standard deviation : for apparent magnitudes=0.833391 for absolute magnitudes=0.715701  the unbiased estimate of the standard error(standard deviation)of the sample mean: for apparent magnitudes=0.140869 for absolute magnitudes=0.120975  the mean absolute deviation: for apparent magnitudes=0.620247 for absolute magnitudes=0.442253  the median absolute deviation: for apparent magnitudes=0.525 for absolute magnitudes=0.255  the interquartile range: for apparent magnitudes=0.965 for absolute magnitudes=0.52  the quartiles: for apparent magnitudes={5.065,5.65,6.03} for absolute magnitudes={3.795,4.08,4.315}  the coefficient of skewness: for apparent magnitudes=0.679003 for absolute magnitudes=1.62311  pearson's first coefficient of skewness: for apparent magnitudes=-0.548185 for absolute magnitudes={1.48561,-0.704918,-0.787579,-1.98617}  pearson's second coefficient of skewness: for apparent magnitudes=-0.0512691 for absolute magnitudes=-0.126288  the quartile coefficient of skewness: for apparent magnitudes=-0.212435 for absolute magnitudes=-0.0961538  the kurtosis coefficient: for apparent magnitudes=4.00445 for absolute magnitudes=10.791  the kurtosis excess: for apparent magnitudes=1.00445 for absolute magnitudes=7.79101  the confidence interval of the population mean based on the normal distribution: for apparent magnitudes={5.35946,5.91165} for absolute magnitudes={3.81234,4.28655}  the confidence interval for the population variance based on the chisquare distribution : for apparent magnitudes={0.469961,1.21557} for absolute magnitudes={0.346598,0.896487} b.2 :graphical representations the histograms of the apparent and absolute magnitudes of the stellar group b.3: optimum choice of  graphical representations of the percentage errors for the mean and median engineering, technology & applied science research vol. 4, no. 4, 2014, 681-685 685 www.etasr.com dwidar and sharaf: statistical magnitude analysis and distance determination of the nearby f8v stars  the minimum value of the percentage error in the mean is 0.553121 and occurs at σ=1.  the minimum value of the percentage error in the median is 0.18854 occurs at σ=1.02  the optimum value of σ is 1.01 b.4: distance analysis  the value of 1 m is 9.64125  the value of m is 7.10681  the value of  is 1.01  the value of 0 m is 5.45922  the value of  is 2.50935  the value of y is 2.49132  the accuracy of the computed value of y is 7 4.42657 10    the distance r of the stellar group as obtained from the statistical method is 21.5357 parsec  the median of the individual distances is 21.233 parsec  the mode of the individual distances is {18.1818,22.2222,25.,25.641} parsec  the geometric mean of the individual distances is 20.761 parsec  the harmonic mean of the individual distances is 19.7835 parsec  the mean value of the individual distances is 21.6796 parsec  the percentage error between r and r̂ is 0.663949 b.5: frequency functions of the absolute and apparent magnitudes for the f8vstars 2 ( ) 0.398992 -0.490148 (-5.45922 ) m m e    2 ( ) 0.398992 -0.490148 (-7.12502 ) m m e    microsoft word 4-1781_s_ok_.docx engineering, technology & applied science research vol. 8, no. 3, 2018, 2646-2650 2646 www.etasr.com boztas et al.: design and analysis of multi-phase bldc motors for electric vehicles design and analysis of multi-phase bldc motors for electric vehicles gullu boztas electrical and electronics engineering dpt university of firat elazıg, turkey gboztas@firat.edu.tr merve yildirim electrical and electronics engineering dpt university of firat elazıg, turkey merveyildirim@firat.edu.tr omur aydogmus mechatronics engineering dpt university of firat elazıg, turkey oaydogmus@firat.edu.tr abstract—this paper presents a design and analysis of multiphase brushless direct current (bldc) motor for electric vehicles (ev). in this work, hub-wheels having 110nm, 900rpm rated values have been designed for the proposed ev. this ev can produce 440 nm without using transmission, differential and other mechanical components which have very high losses due to the mechanical fraction. the motors to be used in the ev have been designed as 3-, 5and 7-phase by infolytica/motor solve software to compare their performances at the same load conditions. the same rotor geometry has been utilized for the motors. however, slot numbers and dimensions of the stator have been determined by considering the motor phase number. performance curves of phase-currents, output powers, torques, efficiencies and power factors have been presented for these motors at the same operating conditions. it can be possible to use lower power switches in motor drive system thanks to the phase current reduction since the phase currents decrease proportionally to motor phase number. this work shows that the multi-phase bldc motors are a good alternative in order to obtain lower torque and lower power inverter structure than the 3-phase bldc motors which are used as standard. keywords-brushless direct current motor; multi-phase motor; electric motor design i. introduction interest on electric vehicles (ev) has increased recently because of their environmental advantages, high energy efficiency, and low noise [1]. significant properties of brushless direct current (bldc) motors for evs are high power density and high efficiency. besides, there are important advantages such as small size, high reliability, not having rotor copper losses and low maintenance cost due to not having brushes [2, 3]. therefore, bldc motors are commonly preferred in industry applications. in [4], a novel five-phase wheel hub motor which occurs from identical electromagnetic units with u-shaped electromagnets in the stator and permanent magnets in the rotor is designed. the electromagnetic torque of the motor is calculated and analyzed by finite element method (fem). torque ripple, average torque, torque per ampere and the ratio of torque to copper loss are examined for optimal design and speed regulation. authors in [5] propose a novel hub motor using variable electromagnetic (em) gearing to leverage torque and rotation speed based on driving conditions. the performance of the motor in terms of voltage/current ratings and energy conversion efficiency is compared with other conventional motors. it is seen that this motor is useful for vehicle propulsion applications. authors in [6] explain the design of permanent magnet (pm) bldc hub motor using fem analysis. the no-load and load characteristics are analyzed, torque and cogging torque of pm bldc hub motor are calculated by magnet software 7.4.1 for different temperatures. flux distribution and flux density in the core are also obtained. it is shown that pm bldc hub motor can be used for applications including less cogging torque than total torque. in [7], a design of three phase pm bldc hub motor which has high efficiency and power density and no cogging torque is realized for electrically powered two wheelers. some methods are used to reduce the cogging torque and increase the net torque. pm bldc motor is also analyzed by using 2d fem. the simulation results are tested by experimental results. it is seen that pm bldc hub motor has high efficiency and it is convenient for different scooter load and speed conditions. in [8], field oriented control based on hall-effect sensors of pm brushless hub motor is defined for four-wheel drive ev. the aim of the study is to obtain high efficiency and low torque ripple by a feedforward controller. results show that the feedforward field oriented control reduces the motor torque ripple. ironless axial flux pm in-wheel hub motor is designed by using multi-domain fem analysis [9]. 3d fem analysis is realized in different physical domains showing temperature distribution, cooling system heat flows and the motor is tested experimentally. results show that the designed in-wheel hub motor has high torque and high efficiency. different control methods for pm brushless hub motor of four-wheel drive ev are defined in [10]. bldc and pmsm control are combined. since the performance of the sinusoidal current control is very good and the torque ripple is much lower than that of the block commutation algorithm, this control is preferred at low speeds. on the other hand, the noise is high at middle and high speeds due to switching and harmonics. therefore, sinusoidal control or field oriented control and block commutation algorithm are used for low, middle and high speeds respectively. results show that low noise and successful performance are obtained engineering, technology & applied science research vol. 8, no. 3, 2018, 2646-2650 2647 www.etasr.com boztas et al.: design and analysis of multi-phase bldc motors for electric vehicles for four-wheel drive ev by the proposed approach. feedforward and feedback speed regulation control of hub motor for ev with in-wheel motor is explained in [11]. the linear feedforward control with the incremental pid feedback control is realized and these control methods can be switched easily considering the driving demand and the running condition. it is obtained from the results that this control method provides a good speed regulation and shows the drivability of the in-wheel ev. the control methods of an ev driven by two rear hub motors are defined to examine the ride quality of ev in [12]. vehicle dynamics with 11 degrees-offreedom are modeled by using matlab’s simulink. simulations with pid controller, fuzzy-pid controller and without controller are realized and compared with each other. according to the simulations, these control methods improve yaw rate and the stability of the ev based on the steering and contribute to evs with hub motors. in [13], computer aided design (cad) of a pm bldc hub motor is realized. designed pm bldc hub motor with 30w, 48v, and 310rpm is used for a fan application. flux density in the air gap and iron, stack length, slot space factor, length of the air gap and the number of the magnet poles are taken as design variables. furthermore, the parametric analysis of bldc hub motor is realized to develop the design in terms of the efficiency and size of the motor. by using fe analysis, designed algorithm is verified and the torque angle characteristics are obtained in the paper. in this paper, three different bldc motors have been designed for the comparison of motor performances based on the phase number. the slot numbers, dimension and geometry of the stator are changed to achieve a good comparison on the effect of the phase number. however, the rotor geometry of the compared motors is the same. it has been shown that the rated currents of the stator winding inversely decrease with the number of the phases. thus, it can be possible to use lower power switches in the motor drive systems. the output power, efficiency and power factor remain as constant values for the compared motors in this study. as a result, it can be observed that increasing of the motor phase number is an advantage in terms of the motor quality. in this work, the pole number and the slot numbers of the designed motors have been taken as 24 and 27 (3-ph), 55 (5-ph), 63 (7-ph), respectively. furthermore, torque and rated speed values of the motors are approximately 110nm and 900rpm, respectively. ii. modeling of bldc motor in modeling of a 3-phase bldc motor, armature winding and torque equations are used [14]. the equivalent circuit of bldc motor having trapezoidal back emf is shown in figure 1. back emf and torque constant is a function of the rotor position. as seen in the figure 1, the voltage equations within the armature windings based on the back emf can be given by (1) [14].                                                                    nnnn e e e i i i l i i i r v v v : : : :. : :. : : 2 1 2 1 2 1 2 1    (1) r1 l1 e1 r2 l2 e2 rn ln en 1.ph 2.ph n.ph fig. 1. bldc equivalent circuit where n is the phase number, v1, v2,….., vn are the supplied voltages to each phase r is armature winding resistance, i is phase current, l is inductance and e is back emf. there is a (360/n) phase angle between back emfs of each phase as follows [14] )(. ))1( 2 ( : : ) 2 ( )( )( : : )( )( 2 1 t n n k n k k te te te en en en n                                            (2) where ken is back emf constant of one phase of the n-phase motor. output torques of each phase are given by [14]: )1( 2 1 2 1 )( : : )( )( . ))1( 2 ( : : ) 2 ( )( )( : : )( )(                                                       ti ti ti n n k n k k tt tt tt ntn tn tn n      (3) where ktn is torque constant of a phase of the n-phase motor. total output torque can be defined as ne tttt  ...21 (4) where te is total output torque. iii. multi-phase motors design in motor design, nominal speed and torque values should be firstly determined. according to these two parameters, motor mechanical restrictions like motor dimension should be taken into consideration. it is also important to obtain a geometry for reducing torque ripples. generally, torque ripples can be reduced by increasing the bldc pole number. in this paper, three different motors have been designed: 3-phase, 5-phase and 7-phase. designed motors structure is shown in figure 2, in which while stator forms the interior of the motor, rotor is the outer of the motor. stator and rotor structures and flux lines and flux densities of bldc motors designed for different phases are shown in figures 3 and 4, respectively. flux lines and flux density of the three motors are illustrated in figure 4. ma cal sur and dif sta cur th of the res illu sig low nu engineerin www.etasr aximum flux lculated as 1.9 the designe rface mounted d outer rotor d fference is the ator slot area i rrent value c herefore, more the slot of 3-p e designed mo spectively. mechanical a ustrated in tab gnificantly red wer phase cur mber. in this ng, technology r.com density obtai 94 t. fig. 2. bldc (a) ed motors ha d with radial m diameters have number of slo is needed for l changes inve e coil area is o phase bldc m otors are 27, 5 and electrical ble i. as show duce inversely rrent will be o s way, both y & applied sci ined from sta c hub-motor struc fig. 4. f ave the same magnets per p e been taken a ots and the slo lower phase n ersely with th obtained by re motor. the num 55, and 63 for parameters of wn in table i, s y with the ph obtained by in cost and siz ience research boztas ator core has rotor core stator core coil magnet air gap shaft cture (b) flux lines and flu rotor structu pole and their as equal. their ot dimensions. number, since he phase nu educing the nu mbers of the sl r 3, 5, and 7-p f bldc moto stator phase cu hase number. ncreasing the ze will reduc h v et al.: design been fig. 3-ph ux density of the m ure as inner r only more phase umber. umber lots in phases ors are urrents thus, phase ce by dec to b equ the mot mot torq bld max rate app vol. 8, no. 3, 20 and analysis of 3. stator/roto h motors; a) 3-ph, b creasing the ra be used in driv ual output pow iv. the ability of rated speed r tor design. t tors are shown que in steady dc motor ar ximum power ed speed. t proximately ob 018, 2646-2650 of multi-phase b or structures of th b) 5-ph, a) 7-ph ated current va ve. bldc mo wers and torque multi-pha f the motor to range is one o torque-speed n in figure 5. y-state situatio e given in fi r and efficien the efficienc btained as 90% bldc motors f he designed moto (c) alues of semi-c otors have been es. ase motor ana o provide max f the importan curves of the . these motor on. pwm an igure 6. the ncy when the cy of the % in the region 2648 for electric veh ors: a) 7-ph, b) 5 conductor swi n designed to alysis imum torque nt results in b e designed b rs produce 110 nalyses of 3-p motor ensure motor reache bldc moto n above 50% sp hicles -ph, c) itches have up to bldc bldc 0 nm phase es the es the or is peed. mo has see bl bl mo mo the sa illu mo eff for bl inv val 70 engineerin www.etasr otor output po s been calcula tabl designe supply v rated c numbe rotor outer d stack he stator outer d stator inner d fig. 5. fig pwm analys en from the f ldc motor in ldc motor. a otor is lower otor is approx e motors tow ame performan ustrated in f otor is also obt ficiency and p r low and hig ldc motors versely propor lues of the mo a (7-ph) respe ng, technology r.com ower has incr ated as 0.58 un le i. desig d motors voltage (v) current (a) er of slots diameter (mm) eight (mm) diameter (mm) diameter (mm) torque-speed g. 6. pwm an sis of 5-phase figures 6 and n low speeds i at 100 rpm s than 71% wh ximately 82% wards rated s nce analysis is igure 8. des tained like the ower factor of gh speed regio are shown in rtional to the otor currents a ectively. y & applied sci reased to 10.3 nder full load c gned motor par 3-phase 5-p 96 164 1 27 300 3 80 274 2 115 1 curves of the desi nalysis for 3-phase motor is reali d 7, the perfo is worse than speed, the eff hile the efficie . however, th speeds are sig s realized for ired performa e other motors f the motors a ons. stator ph n figure 9. c number of t are 164a (3-ph ience research boztas 3 kw. power conditions. rameters phase 7-phase 96 96 102 70 55 63 300 300 80 80 274 274 170 189 igned motors e motor ized in figure ormance of 5that of the 3ficiency of 5ency of the 3he performanc gnificantly si 7-phase moto ance from 7. the output p are given in ta hase currents current value the phase. th h), 102a (5-ph h v et al.: design factor e 7. as -phase -phase -phase -phase ces of imilar. or and -phase power, able-ii of the es are e rms h) and thre pha as how pha the the vol. 8, no. 3, 20 and analysis of fig. fig. fig. 9. table ii. phase number p (k 3 1 5 1 7 1 the output t ee motors in f ase motors are the number wever, as see ase motor can phase numbe stator currents 018, 2646-2650 of multi-phase b 7. pwm ana 8. pwm ana stator phase cur comparison low speed reg (150 rpm) pout kw) eff. (%) 1.8 82 1.8 71 1.8 70 torque curve figure 10. the approximatel of phases in n in figure 1 n be regarded er by more tha s. bldc motors f alysis for 5-phase alysis for 7-phase rrents of the desig ns for low/high gion high pf pout (kw) 0.15 10.3 0.15 10.1 0.15 10.1 is separately e torque rippl ly 10%, 5% an ncreases, torqu 0, the result o as sufficient. an 5 is useful 2649 for electric veh motor motor gned motors speed regions h speed region (900 rpm) eff. (%) pf 95 0.58 92 0.51 92 0.51 examined fo es of 3-, 5an nd 6% respecti ue ripple red obtained by th hence, incre l only for redu hicles or the nd 7ively. duces. he 5asing ucing foc th fir mo th dim of by ana by cur and sam ob inc low sho ord ph and des ev bee th out inc sig mo ph per [1] [2] [3] [4] engineerin www.etasr in this study cus on compa hese motors u rstly, a 3-pha otor. this mot hen, 5-phase mensions of th the slots and considering alyses of the 3 infolytica/m rves of phase d power facto me operating served that a creases, the p wer power sw ows that multi der to use low ase bldc mo d power value signed motors v, total output en obtained as he other impo tput torque c creases, the gnificantly red otor are lower ase number rformance and x. fu, “a nov international c application, c m. yildirim, m motor types international p exposition, an s. m. jang, h. brushless dc m magnetics, vo c. sun, l. bai shaped electro ieee 9th co hangzhou, chi ng, technology r.com (a) fig. 10. v. co y three motors aring the effec used as wheel ase bldc hu tor has inner and 7-phase he base motor dimensions of the motor p 3-, 5-, and 7-p motor solve s e-currents, outp ors have been conditions. as the numbe phase currents witches in mo i-phase bldc wer power inv otors that are es have been c s. by consider t torque and o s 440 nm and ortant characte curve. as th torque ripp duces. howeve than that of o should be d usability whe refe vel design for flyw conference on int changsha, china, v m. polat, h. kuru and drives use power electronic ntalya, turkey, pp w. cho, s. k. ch motor for centrifu ol. 43, no. 6, pp. 2 , x. du, y. zhou omagnet working onference on in ina, pp. 1398-140 y & applied sci output torque a onclusions s have been d t of the phase l in evs are ub motor is d stator and ou motors havin have been des f the stator hav phase number. phase motors software pac tput powers, t presented for according to er of the ph reduce. this otor driving s c motors are a verter structure used as stand calculated as ring the use of output power h 41.2 kw in th eristic for bl he number of ple produced er, torque ripp ther motors. t evaluated in en considered erences wheel battery of telligent system d vol. 1, pp. 107-1 um, “a survey on ed for electric cs and motion c p. 218-223, septem hoi, “design and fugal compressor” 2573-2575, 2007 u, “a novel wheel g principle and ndustrial electron 03, june 9-11, 201 ience research boztas at steady-state con designed in ord e number on m called hub m designed as a uter rotor struc ng the same signed. the nu ve been determ . the perform have been obt kage. perform torques, efficie these motors o the results, ases of the s allows the u systems. this a good alternat e compared w dard. output t 110nm, 10.3k f four wheels have approxim he designed m ldc motors f the motor d by the m ples of the 5therefore, the n terms of commercially electric vehicles” design and engin 11, october 13-14 n comparison of vehicles”, ieee control conferen mber 21-24, 2014 analysis of a high ”, ieee transacti l hub motor based torque character nics and applic 14 h v et al.: design (b) nditions; a) 3-phas der to motor. motors. a base ctures. rotor umber mined mance tained mance encies at the it is motor use of work tive in with 3torque kw in for an mately motors. is the phase motors -phase motor cost, y. ”, ieee neering 4, 2010 electric e 16th nce and 4 h-speed ions on d on uristics”, cations, [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] vol. 8, no. 3, 20 and analysis of se bldc, b) 5-ph m. t. peng, s. high-torque-den propulsion”, i barcelona, spai s. abirami, s. m fem analysis” communication 6-8, 2014 s. ekram, d. optimization of fea”, internati seoul, south ko d. lu, j. li, brushless hub international c networking, ha o. winter, s. u wheel hub moto international s automation an 2012 d. lu, j. li, m. wheel drive el conference, ch h. yu m. huan feedback of h international c yichang, china y. chen, z. lu, ieee internatio china, pp. 627 k. r. rajagopa of a pm bld electronics, dr 12-15, 2006 y. s. jeon, h. simulation mod 7th workshop pp. 217-220, ju 018, 2646-2650 of multi-phase b hase bldc, c) 7h. chien, y. c. nsity and wide-sp eee electric v in, november 17m. bala, r. j. pr ”, ieee internati n and electrical e mahajan, m. fa f brushless perm ional conference orea, pp. 1476-14 j. gu, “field o motor in fou conference on f aikou, china, pp. ucsnik, m. rudo or design by using symposium on nd motion, sorre . ouyang, j. gu, “ lectric vehicle”, hicago, usa, sept ng, “speed regulat hub motor for m conference on a, pp. 4976-4979, , “study on contro onal conference o -632, june 20-23, al, c. sathaiah, “c dg hub motor” rives and energy s. mok, g. h. del of bldc mot on computers in uly 16-18, 2000 bldc motors f (c) phase bldc chung, t. s. liu peed-range hub m vehicle sympos -20, 2013 riya, “design of b onal conference engineering, coi azil, v. patwardh manent magnet h e on electrical m 480, october 8-11 oriented control ur-wheel drive future generation 128-131, decemb olph, c. kral, e. g multi-domain fi power electroni nto, italy, pp. 14 “research on hub ieee vehicle p tember 6-9, 2011 tion control comb motor-wheel driv electrical and september 16-18 ol of an two hubon information an 2010 computer aided d ”, international c systems, new d choe, d. k. ki tor with real back n power electron 2650 for electric veh ) u, t. j. flack, “a motor for electric v sium and exhi bldc hub motor on green com imbatore, india, han, n. ravi, “d hub motor drive machines and sy , 2007 of permanent m electric vehicle” n communicatio ber 20-23, 2014 schmidt, “ironle inite element anal ics, electrical d 474-1478, june b motor control o power and prop bining feedforwar ving electric veh control engine 8, 2011 motor electric veh nd automation, h design and fe an conference on delhi, india, dec im, j. s. ryu, “a k emf waveform nics, blacksburg, hicles a novel vehicle ibition, r using mputing march design using ystems, magnet ”, 8th on and ess inlyses”, drives, 20-22, f fourpulsion rd with hicle”, eering, hicle”, harbin, nalysis power cember a new m”, the usa, microsoft word moameni-f2-add-ans.doc etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 173-176 173 www.etasr.com moameni et al: the effect of measurement error on x-r fuzzy control charts the effect of measurement error on x̃-r ̃ fuzzy control charts m. moameni industrial engineering dpt science and research branch, islamic azad university tehran, iran m.moameni@srbiau.ac.ir a. saghaei industrial engineering dpt science and research branch, islamic azad university tehran, iran a.saghaei@srbiau.ac.ir m. ghorbani salanghooch pars special economic energy zone (pseez) boushehr, iran m.ghorbani@nioc.ir abstract— control charts are tools used for monitoring manufacturing processes. fuzzy set theory has found its way in control charts and new types of fuzzy control charts, with different capabilities, has been introduced. in this paper, a process in which the result of the measuring of each piece is imprecise is studied, and a x̃-r ̃ fuzzy control chart is used for monitoring. the aim is to study the effect of measurement error on the effectiveness of the fuzzy control chart to detect out of control situations. the model used in this research is a linear covariate model. arl parameters are used to study the performance of the fuzzy control chart when the parameters of covariate model is increased or decreased. keywordsprocess control; fuzzy control chart; average run length (arl); measurement error. i. introduction statistical process control includes a set of upcoming problems solving tools which is useful for creating stability in the process by decreasing the variability. control charts are powerful tools for monitoring manufacturing processes and the first samples of these type of tools were introduced by shewhart who introduced rx − control charts to monitor a process with continuous specifications. however, the application of control charts for monitoring continuous data is defined for situations in which the size of each piece is precisely determined and the result of measuring process can be presented as a crisp number. suppose that more than one expert are used for measuring each piece and all of them use a unique measurement tools or machine. if the mean of the values measured by the experts, through different measuring procedures is different, a measurement error is introduced, caused by the experts’ performance. if a system is subjected to such an error, control charts can not be used for monitoring the process. we can model the gauge or impreciseness in the size of product as a fuzzy number. some models of the fuzzy control charts are to be used for monitoring the processes with impreciseness or fuzzy data, and there is no limit in the amount of impreciseness or error. senturk and erginel [1] presented x̃-r ̃ fuzzy control charts. they aggregated all the results of different experts’ measuring in a fuzzy number and monitored the fuzzy number on an x̃-r ̃ fuzzy control chart. kaya and khahraman [2] introduced two different structures of control charts to monitor a process in which the size of each piece is expressed as a fuzzy number. assume that when a process is operating under an incontrol situation the true value of x index is dependant on the normal distribution with a known mean of µ and known variance of σ2p. but, for some reasons, the actual value can not me measured, and instead y index is monitored which has a linear relation with the x index. also assume that on the basis of the achievements of linna and woodall [3], the result of measuring process by each expert is determined by a linear covariate model as shown in (1) (1) +bx+a=y ε in this relation, a and b are constants and ε is the random error in the measurement system which is independent from x and is dependant on the normal distribution with a mean of zero and known a variance of σ2m. thus, variance of the observed value is equal to σ2p + σ 2 m. the results of undesirable effects of measurement error on control charts operation have been studied by different researchers. bennet [4] suggested that the variance of the measurement error (σ2m) can be considered insignificant if it is smaller than the variance of the process (σ2p). he studied the power of shewhart control charts when the measurement error variance is equal to the process variance and when it is twice the previous amount and he compared the achieved results with a state in which there is no measurement error. kanazuka [5] studied the power of rx − control chatrs when the measurement error affects the system. he showed that significant variance of the measurement error can decrease significantly the effectiveness of the control chart. he suggested that a bigger sample could solve the problem. etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 173-176 174 www.etasr.com moameni et al: the effect of measurement error on a x-r fuzzy control chart walden [6] measured the power of rxrx −&, control charts using average run length parameter, when the measurement error affects the system. linna [7] studied the effect of increasing the measurement error variance and slope of covariate model on shewhart control charts. maravelakis and et al. [8] studied the effect of measurement error on ewma charts. the purpose of this paper is to study the effect of measurement error on x̃-r ̃ fuzzy control charts [1], when the measured values by different experts are different. also, to show the effect of increasing the slope of linear covariate model on power of this kind of fuzzy control charts to detect undesirable changes. in the second part, the structure of x̃-r̃ fuzzy control charts is determined when there is an error in the measured values by the experts and measurement system influenced by linear covariate model simultaneously. simulation details are explained in the third part. the different conditions that may occur by changing noticeable parameters, are described in section four. finally in the fifth part, the effect of increasing the critical measurement parameter is estimated, using arl. ii. the structure of fuzzy control chart for covariate value we assume such a process that, under a controlled situation, the real value of x index follows a normal distribution with a known mean and variance of µ and σ2p, respectively. to design the structure of a control chart, under a controlled situation, we select some samples and ask experts to measure all of pieces. because of the fact that experts can only measure the value of y, we monitor y instead of x. but the values expressed by different experts are not necessarily equal. for each piece, all values expressed by different experts will be converted to a fuzzy number (ya, yb, yc). because of the measurement system error, we will have: (2) +b+a= , +b+a= , +b+a= cc bbaa ε εε yy yyyy a. the structure of fuzzy control chart when the process is operating under in-control situation, we choose m samples that each contains n pieces. ykij is the result of measuring the ith piece of the jth sample, by the kth expert. the mean for the jth sample will be calculated as follows: (3) m.,…1,=j ,,, 111 n y y n y y n y y n i cij cj n i bij bj n i aij aj ∑∑∑ === === where, n is the sample size. total mean for m samples, can be calculated as: (4) c,b,a,=k , 1 m y y m j kj k ∑ = = also, raj, rbj and rcj for each sample are defined as: (5) y-y=r cjmin,ajmax,aj (6) y-y=r bjmin,bjmax,bj (7) y-y=r ajmin,cjmax,cj ymax, aj and ymin,aj denotes the maximum and minimum values of ya in the sample. ymax,bj, ymin,bj, ymax,cj and ymin,cj also can be defined in the same way. the place of these parameters is shown on figure 1. for an n-pieces sample the general mean of ar , br and cr will be calculated as follows: (8) cb,a,=k, 1 m r r kj m j k ∑ = = finally the control limits of x ̃ fuzzy chart will be calculated as follows: (9) 2 αα α ca xmr yy cl + = − fig. 1. place of ymax, aj, ymin,aj, ymax,bj, ymin,bj, ymax,cj, ymin,cj . etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 173-176 175 www.etasr.com moameni et al: the effect of measurement error on a x-r fuzzy control chart (10) ) 2 ( αα αα ca xmrxmr rr aclucl + += −− (11) ) 2 ( αα αα ca xmrxmr rr acllcl + −= −− in which: (12) )( abaa yyyy −+= α α (13) )( bccc yyyy −+= α α and: (14) )( abaa rrrr −+= α α (15) )( bccc rrrr −+= α α and the control limits for the r ̃ fuzzy chart will be defined as follows: (16) 2 αα α ca rmr rr cl + = − (17) 3 4 αα αα rmrrmr rmrrmr cldlcl clducl −− −− ∗= ∗= where d3 and d4 are control chart coefficients [9]. the α yjmr s − for the jth sample is calculated as follows for the x ̃ control cart: (18) 2 )]()[()( bjcjajbjcjaj yjmr yyyyyy s −−−++ =− αα the α rjmr s − , for the jth sample is calculated as follows for the r ̃ control cart: (19) 2 )]()[()( bjcjajbjcjaj rjmr rrrrrr s −−−++ =− α α in case that the following limitations are effective, the process is under control, otherwise, the process is out of control:      ≤≤ ≤≤ −−− −−− ααα ααα rmrrjmrrmr xmryjmrxmr uclslcl and uclslcl (20) iii. simulation our aim is to simulate a condition in the system, in which there exists an error on the measured values by the experts and the measurement system has the linear covariate error model. for simplification, we have supposed that only three experts, measure the size of each product. let the mean of the true value of the product be µ and the mean of results achieved by experts a, b and c be µa, µb and µc, respectively such that µa ≤µb ≤ µc. in such a condition, the difference between the measured values of experts which is named d, averagely would be equal to (µc-µb). also, because of the presence of the measurement error, the observed value by each expert is calculated as y=a+bx+ε. the detection power of control charts is estimated by the average run length (arl) parameter. this parameter represents the average number of spc points (subgroups) that will pass before a signal or special cause is encountered. when the process is out-of-control, the aim is that the control chart can signal as soon as possible. therefore, smaller arl is a sign of better performance of a control chart. the model is simulated using matlab software for n=5, α=0.65 and 20000th loops. iv. study of different states a different view to the structure of the x̃-r ̃ fuzzy control charts shows that the notification to impreciseness or error resulted from the expert’s measurements can be decreased or increased by changing the value of α. the structure of control limits of x̃ & r ̃ control charts, shows that the ratio of significance of the opinion of expert b is α, and the ratio of significance of the opinion of experts a and c (together) is equal to (1-α). so: • if α =1, only the results achieved by expert b are used, and the opinions of experts a and c are not considered. • if α=1, a=0, b=1, σ2m=0, the chart will act as a traditional rx − control chart. • if α=1, a≠0 or b≠1 and σ2m≠0 the chart acts like a shewhart control chart, when the measurement error with linear covariate model affects the process. • finally, when α=0, the opinions of experts a and c is considered and the opinion of expert b is believed insignificant. v. effect of 2 m σ and b on x̃-r̃ control chart table (і) illustrates the effect of increase of (σ2m/ σ 2 p) on the power of the fuzzy x̃-r ̃ chart, when the results of measurements by different experts are varied about 0.2 unit (d=0.2) in average. the left side column shows the change of mean and the first row shows the amount of σ2m/ σ 2 p. the arl changes in rows show that there is a decreasing effect on power of fuzzy x̃-r ̃ control chart to detect the upcoming changes in the mean as the ratio of σ2m/ σ 2 p increases. etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 173-176 176 www.etasr.com moameni et al: the effect of measurement error on a x-r fuzzy control chart we can see that the achieved results are the same as the results linna & woodall achieved in their researches on shewhart control charts [3]. table i. estimated arl performance of x̃-r̃ control chart against several values of 22 pm σσ , under estimated limits: d=0.2, a=0, b=1 σ2m/σ 2 p |μ0-μ΄| 0.0 0.1 0.2 0.5 1.0 0.0 200.91 200.76 200.85 200.64 200.81 0.2 195.60 198.81 199.61 200.10 200.23 0.4 158.65 159.10 160.05 183.34 192.01 0.6 72.67 73.00 77.50 105.16 153.65 0.8 21.28 21.75 22.77 38.61 87.17 1.0 7.03 7.12 7.44 15.53 37.55 1.2 3.02 3.10 3.20 5.02 15.73 1.4 1.71 1.73 1.78 2.56 7.23 1.6 1.24 1.26 1.30 1.62 3.95 1.8 1.07 1.08 1.09 1.24 2.40 2.0 1.01 1.02 1.02 1.07 1.65 table ii. estimated arl against several values of b, for x̃-r̃ control chart under estimated limits d=0.2, a=0 and 2.022 = pm σσ b |μ0-μ΄| 1 2 3 4 0.0 200.85 200.82 200.78 200.81 0.2 199.61 199.55 199.15 199.07 0.4 160.05 159.68 159.43 158.77 0.6 77.50 76.93 76.23 74.69 0.8 22.77 22.32 21.14 21.37 1.0 7.44 7.28 7.20 7.07 1.2 3.20 3.14 3.08 3.03 1.4 1.78 1.78 1.70 1.74 1.6 1.30 1.28 1.27 1.23 1.8 1.09 1.08 1.07 1.06 2.0 1.02 1.02 1.01 1.01 table (іі) reports the estimated average run length (arl) to show the effect of the increase of b on the power of the fuzzy x̃-r̃ chart, when the results of the measured values by different experts is averagely different about 0.2 unit (d=0.2) and a=0. the first left side column shows the size of the shift in the mean value and the first row shows the value of b. as it can be seen in [3], increasing the value of b can result in an increase in the power of the x̃-r ̃ control chart in detecting the changes in the mean value. vi. conclusions in this research the effect of the measurement error on the x̃-r̃ fuzzy control chart is studied. the model used is a linear covariate model. the effectiveness of the control chart in detecting the changes in the mean value is calculated using the average run length (arl). it is shown that, when the mean values of measurements are different, a smaller value of measurements’ variance results to greater effectiveness of the x ̃ -r ̃ fuzzy control chart. also the alr changes show that in similar condition, the effectiveness of the control chart increases when the slope of the linear covariate model increases. references [1] s. senturk, n. erginel, "development of fuzzy x̃_r ̃ and x̃-s ̃ control charts using α-cuts", information sciences, pp. 1542-1551, 2009 [2] i. kaya, c. kahraman, "process capability analyses based on fuzzy measurements and fuzzy control charts", expert systems with applications, vol. 38, no. 4, pp. 3172-3184, 2011 [3] k. w. linna, w. h. woodall, "effect of measurement error on shewhart control charts", journal of quality technology, vol. 33, no. 2, pp. 213222, 2001 [4] c. a. bennett, "effect of measurement error on chemical process control", industrial quality control, vol. 10, no. 4, pp. 17-20, 1954 [5] t. kanazuka, "the effect of measurement error on the power of x-r charts", journal of quality technology, vol. 18, no. 2, pp. 91-95, 1986 [6] c. t. walden, an analysis of variables control charts in the presence of measurement error, mississippi state university, department of industrial engineering, 1990 [7] k. w. linna, control chart performance under linear covariate measurement processes, phd thesis, uiversity of alabama, 1991 [8] p. maravelakis, j. panaretos, s. psarakis, "ewma chart and measurement error", journal of applied statistics, vol. 31, no. 4, pp. 445-455, 2004 [9] d. c. montgomery, introduction to statistical quality control, john wiley & sons, inc., 1996 . microsoft word 01-753-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1212-1216 1212 www.etasr.com trstenjak et al.: adaptable web prediction framework for disease prediction based on the hybrid case… adaptable web prediction framework for disease prediction based on the hybrid case based reasoning model bruno trstenjak department of computer engineering medimurje university of applied sciences, cakovec, croatia btrstenjak@mev.hr dzenana donko department of computer science faculty of electrical engineering, sarajevo, bosnia and herzegovina ddonko@etf.unsa.ba zikrija avdagic department of computer science faculty of electrical engineering, sarajevo, bosnia and herzegovina zikrija.avdagic@etf.unsa.ba abstract—nowadays, we are witnessing the rapid development of medicine and various methods that are used for early detection of diseases. in order to make quality decisions in diagnosis and prevention of disease, various decision support systems based on machine learning methods have been introduced in the medical domain. such systems play an increasingly important role in medical practice. this paper presents a new web framework concept for disease prediction. the proposed framework is object-oriented and enables online prediction of various diseases. the framework enables online creation of different autonomous prediction models depending on the characteristics of diseases. prediction process in the framework is based on a hybrid case based reasoning classifier. the framework was evaluated on disease datasets from public repositories. experimental evaluation shows that the proposed framework achieved high diagnosis accuracy. keywords-disease prediction; web framework; hybrid model; case based reasoning i. introduction data mining and prediction in medical domain is gradually gaining significant importance. in order to ensure disease prevention and quality prediction of a potential disease, support systems based on a different prediction framework have become important tools in disease diagnosis. a “framework” is the environment where a prediction process is conducted. predicting a disease is a process of extracting hidden information from medical data and predicting the direction of disease development. for medicine purposes, many studies have been conducted with the aim to develop frameworks for disease prediction based on machine learning techniques.. each framework has embedded one or more machine learning techniques. today, for data prediction purposes various classification techniques are used, such as neural networks [1], support vector machines [2], naive bayes classifiers [3] and many others. a framework can also be implemented by using the hybrid prediction model. the hybrid classification model consists of several machine learning methods and provides a slightly different classification approach. techniques that are embedded in the hybrid prediction model supplement each other and contribute to the quality of prediction accuracy. a web framework is based on the hybrid cbr classification model. the hybrid model merges k-means technique for data clustering and case based reasoning (cbr) classification technique. in this paper, we propose a new concept of framework that allows online prediction and creation of different disease predictive models in a single environment. the study was conducted with the aim to develop a framework that will achieve a high degree of prediction accuracy regardless of the nature of the disease. the framework enables on-line creation of an autonomous prediction model based on disease features. the concept of the new prediction framework provides the existing medical decision support systems (mdss) connection on the framework and starts up the prediction process based on the selected disease model. the connected mdss, using standard web protocol, sends the collected data to the framework. based on the request sent, the framework performs prediction and sends the obtained result of prediction to mdss as a response to the request. in this way the adaptive web framework becomes completely independent of the medical system that uses it. ii. literature review implementation of different decision systems and frameworks for early disease prediction has become extremely important in the medicine domain and disease diagnosis. there is an increasing amount of research engaged in disease prediction using different machine learning techniques. with the development of machine learning techniques and hybrid models, different frameworks aiming to support disease prediction were simultaneously developed. for example, a framework based on the multi-layer classifier ensemble in the framework was presented in [4]. the proposed framework is based on the optimal combination of heterogeneous classifiers. the proposed model overcomes the limitations of conventional performance bottlenecks by utilizing an ensemble of seven heterogeneous classifiers. evaluation shows that the proposed framework dealt with all types of attributes and achieved high diagnosis accuracy. a new framework for prediction of heart disease based on the classification techniques like naive bayes and artificial neural networks was presented in [5]. the engineering, technology & applied science research vol. 6, no. 6, 2016, 1212-1216 1213 www.etasr.com trstenjak et al.: adaptable web prediction framework for disease prediction based on the hybrid case… authors used attribute filtering techniques like principle component analysis and information gain for feature selection in the given data set of heart disease symptoms. in [6], a support framework for heart disease prediction using majority vote based classifier ensemble was proposed. the five heterogeneous classifiers used to construct the ensemble model are as follows: naïve bayes, decision tree based on gini index, decision tree based on information gain, memory-based learner and support vector machine. comparison of proposed framework with individual classifiers shows an increase in average accuracy. in [7], an automatic classification and prediction of parkinson’s disease was proposed. support vector machine (svm) classifier and logistic regression are used for framework construction. the framework achieved high prediction accuracy. prediction improvements can be made by incorporating ensemble classifier instead of a single classifier. in [8], a prediction system and a new approach for detection of heart disease based on naive bayes classifier were presented. this prediction system classifies medical data into five different categories and also predicts the risk of the heart disease if unknown sample is given as an input. the evaluation results confirmed a good concept of the prediction system, the classification model has achieved a high degree of prediction accuracy, the accuracy in the amount of approximately 80%. in [9], a clinical decision support system for risk prediction of heart patients was presented. the proposed system uses weighted fuzzy rules and decision tree rules for prediction. risk prediction is performed in two phases: automated approach for generation of weighted fuzzy rules and decision tree rules; the second one is developing a fuzzy rule-based. in [10], a framework which can select the best model to predict liver disease caused by hepatitis c virus (hcv) was presented. the framework contains three phases: a preprocessing phase to prepare the data for applying data mining (dm) techniques, a dm phase to apply different dm techniques, and an evaluation phase to evaluate and compare the performance of the built models and select the best model as the recommended one. different dm techniques had been applied: associative classification, artificial neural network, and a decision tree to evaluate the framework. iii. research methodology and the proposed framework the objective of our study is to develop a web prediction framework based on the hybrid cbr model for disease prediction. in this section, firstly we explain the work principle of our proposed framework. we present the structure of the proposed framework and its major components. the second part of the section describes the structure of the hybrid cbr model and used machine learning techniques. a. case based reasoning (cbr) the hybrid prediction model is based on a case based reasoning (cbr) classifier. the principle of the cbr method is based on solving new problems by observing the similarity with the previously solved problems. the cbr method uses a problem-solving approach analogous to the way of problem solving by man when he draws on his experiences. each cbr system contains an embedded library of the cases that were resolved in the past. this is something like collecting life experiences in the domain of the problem. each case represents a description of the problem with its associated solution. the cbr method with a built-in function of similarities tries to find the most similar case from the library. the retrieved cases from the library are used to suggest a solution. if the proposed solution is not satisfactory, the method tries to revise selected cases and find a new solution. the method adds a new revised case to the cases library and thereby expands the knowledge base. the whole execution cycle of the algorithm can be divided into four main steps: retrieve, reuse, revise, retain [11]. cbr performs measurement of similarity on the local and global level. local similarity refers to the measurement of similarity between pairs of features. global similarity refers to comparison of similarity between all the features that make up the object. measuring similarity can be shown by:         n i i n i iij w wstf stsimilarity 1 1 , ),( (1) where t=target case, s=source case, n=number of features in each case, i=individual feature from 1 to n, f=similarity function for features i in cases t and s, w=importance weighting of feature i b. k-means k-means is one of the simplest unsupervised learning algorithms used for solving clustering problems. let x={xi, i=1,..,n} be a set of n dimensional objects, which should be classified into k clusters, c={cj, j=1,..,k}. the algorithm determines the quality of the clustering calculating square error between the mean of the cluster and points in the cluster. the goal of the algorithm is to minimize the sum of the squared error over all k clusters. the quality is determined by following the error function, as shown in [12]:    jcx ji k j xe 2 1  (2) where e is a sum of the squared error of all objects, µj indicates the average of cluster cj. |xi-µj| 2 is a chosen distance measure between data point xi and the centroids value. the algorithm can use different methods to calculate the distance (euclidean, manhattan, minkowski, etc.) [13]. c. techniques for ranking the features ranking the features is a procedure which determines the importance and influence of features on the final prediction result. due to different data types that can be used to describe a disease in the process of creating predictive model, three techniques of ranking features were used: information gain (ig) [14], gain ration (gr) [15] and correlation-based engineering, technology & applied science research vol. 6, no. 6, 2016, 1212-1216 1214 www.etasr.com trstenjak et al.: adaptable web prediction framework for disease prediction based on the hybrid case… feature selection (cfs) [16]. all these techniques use entropy as a basic measure for ranking the features. entropy is a measure of disorderliness of the system. ig method calculates the value of the features information. the value is defined as the amount of information, provided by the feature items for the class. ig uses the following expression for the calculation: ig (class, feature) = h (class) – h (class |feature) where h is entropy, which is defined by :    m j jj ppsentropy 1 2log)( (3) where p is probability, for which a particular value occurs in the sample space s. entropy value ranges from 0 to 1. value 0 means that all variable instances have the same value, value 1 equals the number of instances of each value. entropy shows how the attribute values are distributed and indicates the "purity" of features. gain ratio is a technique for selecting features created by extending the information gain technique using decision tree method. gain ratio takes number and size of tree branches into account when choosing a feature. gr corrects the information gain by taking the intrinsic information. intrinsic information is entropy of distribution of instances into branches (i.e. how much info we need to tell which branch the instance belongs to). attribute value decreases as intrinsic information gets larger [17]. )4( )(inf_ )( )( attributeintrinsic attributegain attributerationgain   cfs makes analysis and measures how strongly one attribute implies the other, based on the available data. the correlation between two variables is a goodness measure, a feature is good if it is highly correlated to the class but not highly correlated to any other feature. the evaluation measures the weight of the feature by measuring the correlation (pearson's) between it and the class. d. overview of the framework structure the framework is designed as a web environment that is accessed via the internet. figure 1 illustrates the framework components and their corresponding function in detail. the structure of frameworks is composed of two main components: a component for creating a model for the disease prediction according to disease characteristics, and another component which is responsible for performing the prediction on the basis of selected disease. creating a predictive model begins with uploading a dataset in the framework. the framework in the process of creating a predictive model uses four internal modules. all modules in figure 1 are marked with roman numbers: i: data preprocessing, ii: ranking dataset features, iii: data clustering, iv: cbr classification generator. data pre-processing includes data cleaning, normalization, transformation, feature extraction etc. this is a process of transforming raw data into a suitable format ready to be used by a data mining process. before starting the process of creating the prediction model, the correctness of input data should be verified. the quality of prediction of the future model directly depends on the quality of input data. in this step of creating a model, the framework verifies the syntax format of the input data and determines the data type of each feature. only in the case that data irregularity is not detected, the process of ranking the features begins. each disease is described by a set of properties. the input dataset, in standard csv format, contains instances composed of the features which describe the disease. if during the preprocessing irregularity in the input dataset is not detected, the framework begins with determining the weight values for disease features. weight values determine ranks of the features, their significance in the process of prediction. the ranking is performed using three techniques in the order to get more accurate values. after the rank module, follows a module for data clustering. the module has implemented k-means technique. to all instances from dataset, the framework determines the cluster label. the cluster instance label is determined according to similarity between instances. fig. 1. the framework structure. last of the modules in the framework is the module responsible for the generation of a cbr classifier. this is the most complex internal process in the framework. the module creates a case database and all the elements necessary for dynamic creation of the future cbr classifier. figure 1 shows a cbr classification model to which the case database, a cluster data component for clustering instance in the prediction process engineering, technology & applied science research vol. 6, no. 6, 2016, 1212-1216 1215 www.etasr.com trstenjak et al.: adaptable web prediction framework for disease prediction based on the hybrid case… and cbr data necessary for dynamic forming a classifier are connected. when the request for the disease prediction is sent by a user, the framework loads all these elements and adapts the cbr classifier according to the characteristic of the selected disease. the second component in the framework is intended to perform the prediction process. framework is not designed as a standard web portal, but as an environment to which various medical support systems can be connected. online connection between prediction frameworks and decision system is achieved via an internet protocol. medical decision system sends data, features values about the disease and the request of prediction. the framework on the base of selected disease and features values, performs prediction and sends a result to the medical system. the entire communication is carried out via the specially designed framework interface. iv. overview of the work principle the work principle of the framework is very simple. figure 2 illustrates the work flow of the prediction process in the framework. fig. 2. prediction process work flow. the prediction process begins with sending a packet of information about the disease to the framework. the user through the medical decision system enters data about the disease. medical decision system sends data to the framework in json data format. the framework creates received data into a new instance whose structure is adapted to the structure of case database of the selected disease. a newly formed instance is forwarded to a pre-processing process to verify the correctness of the features value. if irregularity in the instance structure is not detected, the framework begins the adaptation of the hybrid model based on the selected disease. the hybrid model loads the data necessary to form a cbr classifier, begins with initialization of the classification model and sets up the data about features weight values, mode of conducting the prediction, information about the structure of case database, etc. when the adaptation is completed, the framework starts with the clustering process of a new instance. based on the information about cluster centroids (cluster data), defined during the creation of the prediction model, the framework performs clustering of a new instance. the instance with additional information about the cluster label shall be forwarded to the classification. the cbr classification model, using the case database, performed the classification. the achieved result represents the result of prediction. the framework sends back prediction result to the medical support system by which the request was sent. v. experimental results and discussion a. dataset description in the development of the hybrid model and evaluation of the prediction quality, a large number of data sets was used. the majority of the experiments are performed on 15 well known medical data sets publicly available from the uci machine learning repository [18]. the decision to use these dataset is based on the tendency that the results of evaluation compare with the results achieved with a similar hybrid models. table i shows a list of used data sets in evaluation of prediction accuracy over different hybrid models. the following data sets were used: d1: breast cancer dataset retrieved from the university medical centre, institute of oncology, ljubljana, d2: breast cancer dataset retrieved from wisconsin clinical sciences centre, d3: diabetes datasets are named as pima indian diabetes dataset, d4: hepatitis disease dataset. b. evaluation of prediction accuracy the first part of the case study was focused on measuring the prediction accuracy of the framework. table i shows the achieved prediction results, where cbr is prediction accuracy, pr is classification precision and se is sensitivity achieved with the framework. during the evaluation the framework achieved a high degree of prediction accuracy and a high degree of sensitivity. table i. overview achieved prediction accuracy results. no dataset cbr pr se 1 d1 87.71 0.76 0.78 2 d2 100.00 1.00 1.00 3 d3 98.20 0.96 0.96 4 d4 91.33 0.85 0.90 in order to obtain complete details about the characteristics of the framework, our achieved results were compared with the results achieved by the following hybrid models: dtigp functional tree (ft) classifier [19], c4.5+nb decision tree + naive bayes classifier [20], gdadt genetic based data adaptation (gda)+ decision tree (dt) [21], bft best first tree [22], rep regression tree + information gain [22], ga+c4.5 genetic algorithm(ga) + decision tree (rgdt) engineering, technology & applied science research vol. 6, no. 6, 2016, 1212-1216 1216 www.etasr.com trstenjak et al.: adaptable web prediction framework for disease prediction based on the hybrid case… [22], srlpso + elm self-regulated learning capability of the particle swarm optimization (pso) algorithm with the extreme learning machine (elm) classifier [23], hmv hierarchical majority voting [4]. table ii. comparison results overview. model d1 d2 d3 d4 hybrid cbr 87.71 100 98.20 91.33 dtigp 71.70 94.70 72.65 83.20 c4.5+nb 71.66 95.77 75.79 80.98 gdadt 92.60 85.30 hmv 85.00 97.00 77.08 86.45 bft 69.58 72.65 80.64 rep 66.78 70.31 78.06 ga+c4.5 75.87 74.21 85.16 srlpso+elm 91.33 99.78 93.09 98.71 based on all achieved results noted in table ii, it may be seen that the framework with a cbr hybrid model achieved very good results compared to other hybrid models. with all used data sets the hybrid model achieved a high degree of prediction accuracy. analysing the results of other hybrid models, only a srlpso+elm model achieved similar results. the achieved results confirm the good concept of framework and implemented the prediction algorithm. vi. conclusion this paper has introduced a new approach for prediction framework. a new framework merges several machine learning methods in the cbr hybrid model. the results achieved by our experiments suggest that the proposed framework possesses good properties from the standpoint of quality. the concept of the framework provides the dynamic adaptation, depending on the disease characteristics. this research will be followed by additional testing of the framework in online environment. references [1] f. amato, a. lopez, e. m. pena-mendez, p. vanhara, a. hampl, j. havel, “artificial neural networks in medical diagnosis”, journal of applied biomedicine, vol. 11, pp. 47-58, 2013 [2] c. c. sady, a. l. p. ribeiro, “symbolic features and classification via support vector machine for predicting death in patients with chagas disease”, computers in biology and medicine, vol. 70, pp. 220-227, 2016 [3] m. -c. yang, c. -s. huang, j. -h. chen, r.-f. chang, “whole breast lesion detection using naive bayes classifier for portable ultrasound”, ultrasound in medicine & biology, vol. 38, no. 11, pp. 1870–1880, 2012 [4] s. bashir, u. qamar, f. h. khan, l. naseem, “hmv: a medical decision support framework using multi-layerclassifiers for disease prediction”, journal of computational science, vol. 13, pp. 10-25, 2016 [5] k. sudhakar, d. m. manimekalai, “propose a enhanced framework for prediction of heart disease”, int. journal of engineering research and applications, vol. 5, no. 4, pp. 1-6, 2015 [6] s. bashir, u. qamar, f. h. khan, m. y. javed, “mv5: a clinical decision support framework for heart disease prediction using majority vote based classifier ensemble”, arabian journal for science and engineering, vol. 39, no. 11, pp. 7771-7783, 2014 [7] 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algorithm”, advances in intelligent and soft computing, vol. 131, pp. 691-700, 2012 [14] b. azhagusundari, a. s. thanamani, “feature selection based on information gain”, international journal of innovative technology and exploring engineering, vol. 2, no. 2, pp. 18-21, 2013 [15] f. li, y. piao, m. li, m. piao, k. ryu, “positive impression of lowranking microrn as in human cancer classification”, in 4th international conference on computer science & information technology, sydney, australia, 2014 [16] r. priyadarsini, m. valarmathi, s. sivakumari, “gain ration based feature selection method for privacy preservation”, ictact journal on soft computing, vol. 1, no. 4, pp. 201-205, 2011 [17] r. tiwari, m. p. singh, “correlation-based attribute selection using genetic algorithm”, international journal of computer applications, vol. 4, no. 8, pp. 28-34, 2010 [18] c. l. blake, c. j. merz, uci repository of machine learning, university of california, department of information and computer science, 1998 [19] r. konig, u. johansson, t. lofstrom, l. niklasson, “improving gp classification performance by injection of decision trees”, wcci 2010 ieee world congress on computational intelligence, barcelona, spain, 2010 [20] l. jiang, c. li, “scaling up the accuracy of decision-tree classifiers: a naive-bayes combination”, journal of computers, vol. 6, no. 7, pp. 1325-1331, 2011 [21] r. g. ramani, l. balasubramanian, a. a. meenal, “a hybrid classification model employing genetic algorithm and root guided decision tree for improved categorization of data”, arpn journal of engineering and applied sciences, vol. 10, no. 21, pp. 9968-9975, 2015 [22] p. lakshmi, s. s. kumar, a. suresh, “a novel hybrid medical diagnosis system based on genetic data adaptation decision tree and clustering”, arpn journal of engineering and applied sciences, vol. 10, no. 16, pp. 7293-7299, 2015 [23] c. v. subbulakshmi, s. n. deepa, “medical dataset classification: a machine learning paradigm integrating particle swarm optimization with extreme learning machine classifier”, the scientific world journal, vol. 2015, article id 418060, pp. 1-12, 2015 engineering, technology & applied science research vol. 8, no. 2, 2018, 2731-2734 2731 www.etasr.com putra et al.: using length of bilge keel to length of waterline ratio to reduce ship rolling motion using length of bilge keel to length of waterline ratio to reduce ship rolling motion pringgo kusuma d. n. y. putra department of fisheries resource utilization faculty of fisheries and marine science bogor agricultural university bogor, indonesia pringgokusuma@gmail.com budhi h. iskandar department of fisheries resource utilization faculty of fisheries and marine science bogor agricultural university bogor, indonesia bhascaryo.iskandar@gmail.com yopi novita department of fisheries resource utilization faculty of fisheries and marine science bogor agricultural university bogor, indonesia yopi1516@gmail.com abstract-fishing vessels must have good stability and manoeuvrability. hull with round bottom shape has a relatively poor rolling duration compared to other forms. rolling duration reduction will improve the quality of stability of the ship which can be obtained with bilge keel installation. the objectives of this research are 1) to compare each parameter value on model ship by using bilge keel and 2) to determine the minimum ratio of bilge keel's length toward waterline length on the model ship which still has the ability to reduce rolling motion on the ship. the method used was giving treatment to model ship and observing its rolling motion with different lengths of bilge keel. based on the result of the research, it can be concluded that bilge keel installation with some length ratio toward length of waterline has different results significantly, and bilge keel with length ratio 0.2 still have effective capability in reducing the rolling motion of the model ship. keywords-bilge keel; rolling motion; round bottom; stability i. introduction fishing vessels are specifically used for fishing operations in the sea. these activities include operation of fishing gear, actual fishing and a place to store the catch. in order to support the success of fishing operations, fishing vessels have their own specifications when compared to other types of vessels [1]. fishing vessels must have good stability and manoeuvrability. stability factor and manoeuvrability of a vessel can be affected by the shape of the hull. the shape of the hull on fishing vessels in indonesia has different forms, namely u-bottom, round bottom, round flat bottom, hard chin bottom and akatsuki [2]. generally fishing vessels in indonesia use a round bottom or round flat bottom hull shape. the hull shape used in this study is round bottom which is commonly used in indonesia. however, this form of hull has the least stability compared to other forms [3]. the quality of the stability of a ship can be seen from the amount of rolling duration which occurs when the ship performs rolling motion, in which the ship’s stability lowers with the rising of the rolling duration. one effort to reduce the rolling duration of the ship is by installing a bilge keel on the hull of the ship. bilge keel is a fixed construction mounted on a ship that is almost perpendicular to the hull of the ship as a means to stabilize the vessel from the rolling motion [4]. in the sensitivity study of bilge keel, it was found that bilge keel was efficient in reducing the rolling motion on ships. the use of bilge keel can reduce the rolling motion on vessels by 20% in the irregular sea with a wind speed of 24 knots [5]. in addition, in more powerful seas with wind speed of 40 knots, rolling motion reductions can be as high as 13% [6]. in addition, the use of bilge keel can also support the stability of the vessel and may reduce the risk of overturn during motion. the placement and use of bilge keel's length will determine its ability to reduce ship rolling movement. the use of a longer and wider bilge keel will make it more effective in reducing rolling movement. however, the presence of bilge keels in large dimensions is feared to affect ship's resistance and obstructing fishing operation during setting and hauling of fishing gear. therefore, it is necessary to conduct a research on the minimum length of bilge keel which is optimal to reduce rolling motion. the length of bilge keel mounted on the hull will be compared with the highest length of waterline on the vessel. this is due to the placement of bilge keel at the highest length of waterline position will result in better stability of the vessel compared to the bilge keel installation at the lower position [7]. comparison on each parameter value was performed to determine the minimum ratio of bilge keel's length toward the length of the ship's waterline which still has the ability to reduce the ship's rolling movement. ii. method the method used in this research is experimental by using a ship in model scale because the experiment will be a lot easier to conduct in model scale and laboratories. the model ship is made with reference to the parameter values of ship operating encircling gear in some regions of indonesia [8]. the model ship has a round bottom hull shape (figure 1). a ship with this specification is prioritized for its speed, as in purse seine fishing gear. the model ship's dimensions are 51cmx16.7cmx10.9cm and bilge keel made of fiberglass with three different sizes. engineering, technology & applied science research vol. 8, no. 2, 2018, 2731-2734 2732 www.etasr.com putra et al.: using length of bilge keel to length of waterline ratio to reduce ship rolling motion fig. 1. lines plan model of ship with round bottom hull experiments were conducted on ship models that have been installed with bilge keels to obtain the following data types: 1) rolling angle value in each rolling motion of the ship. rolling angle is the angle formed by the sheer of a vessel as it moves to the right and to the left against the x axis. rolling angle formed from the rolling motion of each ship model will form a rolling motion pattern from each treatment. 2) rolling duration value of ship model in each treatment. rolling duration is the time required by the ship to return to its original position. the data were obtained by calculating the time duration of ship model from the first rolling motion until it returned relatively silent and upright. 3) rolling period value of ship model on each treatment. rolling period is the amount of time required by the ship to be upright after the ship is heeled over due to the forces working on it [9]. based on this understanding, the rolling period data is obtained by calculating the time duration of the model ship to perform the rolling movement from the left side to the right side until it returns to the left side or vice versa. 4) rolling frequency value of ship model in each treatment. rolling frequency is the number of heeled movement of a ship in one unit of time [4]. rolling frequency in this research is obtained by dividing total amount of rolling motion with rolling duration of each model ship in every treatment. treatment was the use of bilge keel with different length ratio of bilge keel toward length of waterline of ship model, namely:  without bilge keel (bk0), as the ship's reference at normal times  short bilge keel, with bilge keel length ratio of 0.2 (bk1) toward the length of waterline  medium bilge keel, with bilge keel length ratio of 0.3 (bk2) toward the length of waterline and  long bilge keel, with bilge keel length ratio of 0.4 (bk3) toward the length of waterline. illustration of bilge keel length ratio toward the length of waterline is presented in figure 2. (a) (b) (c) fig. 2. illustration of bilge keel length ratio toward length of waterline. (a) ratio 0.2 toward lwl (bk1), (b) ratio 0.3 toward lwl (bk2), (c) ratio 0.4 toward lwl (bk3) length. bilge keel is denoted with a. the obtained data will be processed to obtain the time, the amount of rolling motion, and the angle of rolling. the result is then processed in graphical form by making it as the x-axis and rolling angle as y-axis. to explain the values carried out on the graph, the values will be tabulated. data analysis used in this study was complete randomized design (crd) and numerical comparative. crd was performed to see if there is any significant difference in any treatment performed. this analysis is performed on all parameters by using f-test. numerical comparative method was performed to compare each rolling angle, rolling duration, rolling period, and rolling frequency of each treatment. iii. results and discussion a. rolling angle and rolling duration figure 3 shows the profile of ship's rolling motion for each treatment. this profile indicates that the momentum of rolling movement formed will be decreased with time. this indicates that the rolling motion is an oscillatory motion. the oscillation movement is an angular movement measured on the longitudinal axis [4]. in addition, figure 3 also shows that the installation of short bilge keel (bk1) on ship model can reduce the rolling angle by an average of 52%. similarly, moderate bilge keel (bk2) can reduce the rolling angle by 60% and long bilge keel (bk3) by 69%. this phenomenon occurs due to the number of water masses stuck by the area of bilge keel when the model ship experienced a rolling motion. therefore, the greater the area of bilge keel that resisted the rolling movement of ship model then the rolling angle will be smaller. authors in [6] stated that bilge keel installation would have a very engineering, technology & applied science research vol. 8, no. 2, 2018, 2731-2734 2733 www.etasr.com putra et al.: using length of bilge keel to length of waterline ratio to reduce ship rolling motion significant effect toward rolling motion on the ship. table i shows that the installation of short bilge keel (bk1) can reduce rolling duration of ship model by 44%. similarly, the treatment of ship models using medium (bk2) and long bilge keel (bk3) can reduce the rolling duration of ship models by 53% and 64%. these reductions of rolling duration is due to the addition of a bilge keel which causes a certain amount of water mass to be retained by the bilge keel when the ship is heeled over from one side to another [10]. results showed that a bilge keel with a length ratio of 0.2 toward length of waterline is still effective in reducing rolling movement produced by ship model. the result of statistical test showed that the value of rolling duration between treatments bk0 vs bk1, bk0 vs bk2, bk0 vs bk3, bk1 vs bk2, bk1 vs bk3, and bk2 vs bk3 have f-hit>f-tab. this means that the rolling duration value which generated between each treatment has a significant difference. this difference proves that the length of bilge keel can affect the value of rolling duration of the ship. table i. rolling duration value of model ship ( seconds) bilge keel treatment bk0 bk1 bk2 bk3 range 12.5-12.58 7.14-7.27 5.82-5.92 4.12-4.54 average 12.53 7.21 5.85 4.27 b. rolling period the values of rolling periods from the experiments are presented in table ii. table ii shows that bk3 has an average rolling period value of 0.73. this value shows that the average ship model with bk3 treatment can do 1 rolling motion in 0.73 seconds. in the table it can be seen that the treatment of bk0, bk1, bk2, and bk3 has smaller rolling period. this is due to the ship's initial stability moment getting bigger when compared to the vessel overturning moment [11]. the degree of rolling angle will affect the occurring rolling period [12]. table ii. rolling period value of model ship (seconds) bilge keel treatment bk0 bk1 bk2 bk3 range 2.39-2.4 2.61-2.65 2.7-2.75 2.85-2.93 average 2.39 2.64 2.73 2.88 fig. 3. ship model’s rolling motion profile this indicates that the reducing rolling period value of ship model can be attributed to the degree of rolling angle formed. in addition, the addition of bilge keel length not only will reduce the rolling angle and rolling duration but also can reduce the rolling period on the ship. this result is similar to the research in [13] which states that if the stability of a ship is low then the vessel has large rolling period. while on the contrary, if the rolling period, rolling duration and rolling angle are small then the ship will be more stable. however, if the rolling period produced by a ship is too small, it will have a negative effect toward the comfort of work on the deck [14]. the result of statistical test on rolling period between bk0 vs bk1, bk0 vs bk2, bk0 vs bk3, bk1 vs bk2, bk1 vs bk3, and bk2 vs bk3 showed the value of f-hit>f-tab. this means that rolling periods generated between treatments have significant differences. this difference proves that the length of bilge keel can affect the value of the rolling period of the ship. c. rolling frequency the results of the rolling frequency data in the experiments are presented in table iii. table iii shows that ship model with bk3 treatment can averagely produce almost 3 rolling motions in one second. in addition, it can be seen that the result of rolling frequency values from the treatment of bk0, bk1, bk2, and bk3, tend to have bigger rolling frequency. this result corresponds to the relation of period and frequency [12]. this indicates that the bk3 treatment produces fewer rolling motions and that the ship model did not take much time to return to its original upright position. this indicates that the effect of bilge keel installation can affect the value of rolling frequency. the longer the size of bilge keel used, the greater the value of rolling frequency generated and the ship will rapidly return to its stable position. therefore, bk3 treatment has better rolling frequency compared other treatments. the statistical tests results showed that on the value of rolling frequency between treatments bk0 vs bk1, bk0 vs bk2, bk0 vs bk3, bk1 vs bk2, bk1 vs bk3, and bk2 vs bk3 have f-hit>f-tab. this means that the value of rolling frequency has a significant difference between treatments. this proves that the length of bilge keel can affect the value of ship rolling frequency. table iii. rolling frequency value of ship model bilge keel treatment bk0 bk1 bk2 bk3 range 0.73-0.91 0.77-0.87 0.73-0.85 0.70-0.83 average 0.86 0.79 0.77 0.73 iv. conclusion comparison between each parameter value namely rolling angle, rolling duration, rolling period and rolling frequency gives significantly different results. this occurs due to the use of bilge keels with different ratio between bilge keel’s length and length of waterline on model ship. furthermore, bilge keel with length ratio toward length of waterline of 0.2 still has an effective performance in reducing rolling motion of model ship. acknowledgment authors would like to thank lembaga pengelola dana (lpdp-ri) scholarship for funding this research in bogor agricultural university. engineering, technology & applied science research vol. 8, no. 2, 2018, 2731-2734 2734 www.etasr.com putra et al.: using length of bilge keel to length of waterline ratio to reduce ship rolling motion references [1] y. novita, a. rahman, “the hull form, its influence towards hull resistance”, torani journal, vol. 18, no. 1, pp. 87-92, 2008 (in indonesian) [2] s. kruger, f. kluwe, “a simplified method for the estimation of the natural roll frequency of ships in heavy weather”, hansa international maritime journal, vol. 9, no. 8, pp. 1-7, 2008 [3] y. novita, a. d. ramadhan, m. imron, “influence of free surface area of liquid cargo towards rolling motion of a ship model”, journal of saintek perikanan, vol. 8, no. 2, pp. 44-51, 2013 [4] a. susanto, b. h. iskandar, m. imron, “fishing vessel design and stability evaluation in palabuhanratu”, marine fisheries: journal of teknologi dan manajemen perikanan laut, vol. 2, no. 2, pp. 213-221, 2011 (in indonesian) [5] b. h. iskandar, y. novita, the effect of hull forms on ship model toward its resistance (preliminary studies), department of fisheries resource utilization, 2006 [6] g. aloisio, f. di. felice, “piv analysis around the bilge keel of a ship model in free roll decay”, roma, italia, xiv convegno nazionale a.i.ve.la, pp. 1-11, 2006 [7] y. novita, b. h. iskandar, “relationship between hull form of fishing vessel model and its resistance”, bulletin psp, vol. 17, no. 3, pp. 315324, 2008 (in indonesian) [8] y. novita, “static stability comparison between western coast and eastern coast purse seiner in north sumatera”, bulletin psp, vol. 12, no. 1, pp. 1-9, 2003 (in indonesian) [9] m. gachet, j. g. kherian, “impact of linearization of bilge keel damping on the early assessment of vessel operability”, asme 27th international conference on offshore mechanics and arctic engineering, estoril, portugal, vol. 1, pp. 257-264, june 15-20, 2008 [10] d. saputra, a study of the size and position of bilge keel installation on the bottom hull of ship model toward its resistance, bogor agricultural university, 2007 (in indonesian) [11] r. bhattacharyya, dynamics of marine vehicles, john wiley & sons, 1978 [12] marjoni, b. h. iskandar, m. imron, “static and dynamic stability of a purse seiner at coastal fishing port in lampulo banda aceh nanggroe aceh darussalam”, marine fisheries: journal of teknologi dan manajemen perikanan laut, vol. 1, no. 2, pp. 113-122, 2010 (in indonesian) [13] e. d. lewis, r. o. brien, kapal, tira pustaka, 1983 (in indonesian) [14] n. liliana, y. novita, f. purwangka, “the type of cargo and its effect toward rolling period of ship model”, marine fisheries: journal of teknologi dan manajemen perikanan laut, vol. 20, no. 3, pp. 249-262, 2012 (in indonesian) microsoft word 6-704.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1067-1074 1067 www.etasr.com abid et al.: a pruning algorithm based on relevancy index of hidden neurons outputs a pruning algorithm based on relevancy index of hidden neurons outputs slim abid control & energy management lab (cem lab) national school of engineering of sfax university of sfax, tunisia abid_slim_enis@yahoo.fr mohamed chtourou control & energy management lab (cem lab) national school of engineering of sfax university of sfax, tunisia mohamed.chtourou@enis.rnu.tn mohamed djemel control & energy management lab (cem lab) national school of engineering of sfax university of sfax, tunisia mohamed.djemel@enis.rnu.tn abstract—choosing the training algorithm and determining the architecture of artificial neural networks are very important issues with large application. there are no general methods which permit the estimation of the adequate neural networks size. in order to achieve this goal, a pruning algorithm based on the relevancy index of hidden neurons outputs is developed in this paper. the relevancy index depends on the output amplitude of each hidden neuron and estimates his contribution on the learning process. this method is validated with an academic example and it is tested on a wind turbine modeling problem. compared with two modified versions of optimal brain surgeon (obs) algorithm, the developed approach gives interesting results. keywordspruning algorithm; obs approach; relevancy index; hidden neurons i. introduction the feedforward neural networks (fnns) [1, 2] have been successfully used to solve many problems, such as: dynamic system identification, signal processing, pattern classification [3, 4] and intelligent control [5]. one of the difficulties of a fnns applying process is the determination of the optimal network architecture. in general, if the network structure is too small, it may not be able to learn the training samples. on the other hand, large-sized networks learn easily but show poor generalization capacities due to over-fitting. thus, algorithms that can determine the appropriate network architecture automatically are highly desirable. research in this field can be classified in two categories: constructive [6] and pruning approaches [7]. recent interest has been growing on pruning strategies [8-10] that start with large-sized network and remove unnecessary hidden neurons or weights either during the training phase or after convergence to a local minimum. the most known methods are optimal brain damage (obd) [11] and optimal brain surgeon (obs) [12] which eliminate the neurons or weights with the smallest saliency one by one, which significantly increases the complexity of the procedure computation and the running time. in this paper, an improved pruning algorithm based on hidden neurons’ outputs is investigated and compared with two algorithms derived from the obs method. the rest of paper is organized as follows. section 2 presents briefly analysis of obs algorithm and the description of two modified versions of this algorithm namely (unit-obs) [13] and (fast-unit-obs) [14]. a pruning algorithm based on relevancy index of hidden neurons outputs is introduced in section 3. section 4 illustrates the obtained simulation results. finally, the conclusion is presented in section 5. ii. related works a simple (fnn)s with a single output is represented in figure 1 (the generalization to more outputs units is straightforward). fig. 1. feedforward neural network. this neural network is parameterized in terms of its weights, where:   mtm21 wwww  ,,,  (1) the training data consists of n patterns {xj,yj}, j=1, …, n. the error function for a given pattern is defined as: 2dp yy21j )(  (2) the global error function is described as:    n 1p pjn1j (3)  y xi x2 x1 wi 1 1  wi engineering, technology & applied science research vol. 6, no. 4, 2016, 1067-1074 1068 www.etasr.com abid et al.: a pruning algorithm based on relevancy index of hidden neurons outputs a. obs approch in [11], an obd method which calculates the saliency only with the pivot elements of the hessian matrix without retraining after the pruning process was introduced. to overcome this problem, the (obs) algorithm which determines and removes the weight that has the smallest effect on the neural network performance and adjusts the remaining weights according to the error function gradient was proposed [12]. the obs algorithm assumes that the network has been trained to a local minimum of the error, so the second-order taylor expansion of the error function with respect to the weights can be expressed as: )( 2 1 3 wowhww w j j t t           (4) where h denotes the hessian matrix composed by the coefficients of the second order derivatives of the error function. in order to minimize the error given by (3), obs algorithm deletes one of the weights having a value tending to 0 and removes the particular weight wq which satisfies the following equation: 0wwe qtq  (5) where eq represents the unit vector corresponding to weight wq qqt wew  . the corresponding expression for the minimum error is modified caused by changing a given weight depicted as:               0wwewhw21 qtqtq /..minmin (6) so as to resolve this constrained optimization problem, we introduce lagrange’s method which leads to find the corresponding optimum value of lagrange function l after deleting wq as:  qq1 2qq hw21l  (7) the remaining weights are updated according the following equation: q1qq1 q ehhww  ][ (8) with [h-1]qq denotes the diagonal element (q,q) of the inverse of the hessian matrix h-1. the obs algorithm needs inverse hessian matrix to update the weights which is the most disadvantage of this algorithm. it has been proposed a procedure to calculate h-1 based on a recursive method as [12]:     1n1nt1n 1n11n1n1n1n11n xhxp hxxhhh    (9) with  48pn0 1010ethhih   , . however, one of the main difficulties of obs approach is that it requires a great amount of computation and a huge time for pruning procedure. b. unit-obs algorithm the unit-obs pruning algorithm removes the unneeded neuron in one step with minimal increase in error [15]. this approach reduces both the computation complexity and the running time. the details of the unit-obs algorithm are as follows:  step 1: train the neural network to minimum error based on some local optimization method.  step 2: compute h-1.  step 3: for each neuron u:  compute the number of output weights for the neuron u and record it as m(u).  form the unit matrix m for neuron u which: ],,,[ )(uqm2q1q eeem  (10) where q1, q2,…, qm(u) denote the sequence number of each output weight with:     0010e itqi   ,,,, (11)  calculate the error deviation after deleting neuron u:   wmmhmmw21uj t11tt  )( (12)  step 4: find the neuron u0 that gives the smallest increase in error noted )( 0uj : if  t0 euj  )( then the algorithm will stop; otherwise go to step 5. where et indicates a preselected threshold.  step 5: remove neuron u0 and update the other weights using the following equation:   wmmhmmhw t11t1  (13) the unavoidable drawback for this algorithm is the complexity of computing the hessian matrix whose dimension is equal to the number of initial weights of the network. in order to overcome this disadvantage a modified version of unit-obs algorithm has been proposed in [14]. c. fast unit-obs algorithm in this case, the size of the hessian matrix depends on the number of hidden neurons. the relevance of each hidden neuron is described by the following equation:  uu1 2uu hw21l  (14) engineering, technology & applied science research vol. 6, no. 4, 2016, 1067-1074 1069 www.etasr.com abid et al.: a pruning algorithm based on relevancy index of hidden neurons outputs where the weight mean is given by:    m 1i uiu wm1w (15) where wui denotes the output weights for the hidden neuron u and m indicates the number of wui. the steps of the unit-obs-algorithm are as follows:  step 1: train the neural network to minimum error based on some local optimization method.  step 2: compute h-1.  step 3: for each hidden neuron u; compute the relevance lu and find the neuron u0 that gives the smallest value which will be noted l.  step 4: if l is greater than the preselected threshold lt, than go to step 5. otherwise:  delete the selected hidden neuron and adjust the other weights of the remaining neurons based on the following equation:   u1uu1u ehhww  (16) with :     0010e uu   ,,,, (17)  return to the step 2.  step 5: stop the pruning approach and it may be desirable to retrain the network at this stage. despite the improvements in algorithms unit-obs and fast-unit-obs which have reduced the computation time of the pruning procedure, these methods still need of calculating the inverse of the hessian matrix .to overcome this problem, a pruning algorithm that eliminates the hidden neurons having a low impact on learning performances without using the inverse of the matrix is proposed in the next section. iii. proposed algorithm the basic idea of the algorithm proposed in this paper has been inspired from the pruning approach in [16] which consists of estimating the sensitivity of the global error changes with respect to each connection during the training phase and removing the weight which presents the smallest sensitivity value. the neural network will be retrained and the pruning process will be executed as capacities learning are satisfactory. however, the success of this approach depends on the size of the initial neural structure. indeed, for the case of large-sized network, the number of weight increases hugely which degrades the performance of the approach significantly. the proposed method consists of finding the contribution of each hidden neuron in the network which reduces the complexity of the procedure and eliminates the one having the least effect on the cost function. this effect is estimated by calculating the relevancy index which depends on the output amplitude of each hidden neuron defined as follows:                 n 1p n1u pu puu c oon1ri (18) where puo indicates the output of the uth hidden node for a given pattern and nc denotes the number of hidden ones. the average value of relevancy index is defined as: c n 1u uavu nriri c   (19) each hidden neuron with a relevancy index smallest than the average value should be deleted. it is to be noted that we are interested in a multi input-single output (miso) model and the weights update law is based on the back-propagation algorithm which can explained as: wjw p (20) where  denotes the learning rate. the proposed pruning algorithm can be described as follows:  step 1: train the neural network based on the backpropagation algorithm to obtain a tolerated value of the training criterion noted jt.  step 2: calculate the relevancy index for each hidden neuron using equation (18).  step 3: remove each hidden neuron u which satisfies the following test: avuu riri  (21) if there is no neuron that satisfies the test (21), than go to step 5.  step 4: maintaining the same average value of the relevance index, train the obtained structure with a reduced number of iterations noted m and return to step 2.  step 5: stop the pruning approach and retrain the network at this stage. it can be seen that the proposed algorithm is based on a pruning strategy avoiding the computation the inverse of hessian matrix which consists the main contribution of this approach. iv. simulations results and discussions in this section, we present the simulation results. initially, the capacities of the proposed algorithm are verified on an academic example. then, we use this algorithm for wind engineering, technology & applied science research vol. 6, no. 4, 2016, 1067-1074 1070 www.etasr.com abid et al.: a pruning algorithm based on relevancy index of hidden neurons outputs turbine neural modeling. through two simulation examples the proposed algorithm will be compared with the unit-obs and the fast-unit-obs algorithms according to some performances criteria. a. first example the goal is to present the learning set to the studied algorithms and to show that they can determine a number of hidden neurons close to the one of the neural network used to generate the learning set. figure 2 shows the neural network generating the learning set with an input vector  )(),(),(),( 2ku1ku2ky1ky  , 3 hidden neurons and y as the output where the activation function in the hidden neurons and the output neuron is the sigmoid one. fig. 2. neural network generating the learning set. figures 3 and 4 represent the input signal used respectively for the training and validation sets. the efficiency of each algorithm is computed as: 100n 3n1eff cfc  % (22) with fcn indicates the final number of hidden neurons for the obtained structure after the pruning procedure. the initials values of weights and the numerical parameters are selected based on several simulations to obtain the best performances in terms of training capacities and convergence time. 0 50 100 150 200 250 300 350 400 450 500 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 fig. 3. training input signal. 0 20 40 60 80 100 120 140 160 180 200 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 fig. 4. validation input signal. the simulation results describing the performances of unitobs, fast-unit-obs and the proposed algorithms are given in table i where for each algorithm a set of initial neural structures has been considered. table ii shows the average of performances for the studied algorithms. it can be seen that the investigated approaches provide similar and satisfactory performances. on the other hand, the proposed algorithm avoids the complex calculation of the inverse of the hessian matrix which considers the main advantage of this method. to confirm these interpretations, we test the studied algorithms on neural modeling problem of wind turbine. b. second example in the last years, a growing interest in renewable energy has been evident [17]. wind energy has become competitive and considerable technological progress has been achieved in the field of wind turbines. the energy production depends on many factors essentially the choice of robust methods for controlling wind turbines [18]. this step can be accomplished as well as the model describes the system dynamics correctly, which shows the importance of the selection of modeling strategy. in this work, modeling of the turbine is provided via a neural model whose architecture is selected based on a pruning approach. the rigid model with only one degree of freedom [19-21] is given by: atgaat ktti  (23) the point (.) designates the first order time derivative, tg is the generator torque and ir, ig, kr, kg are the moment of inertia of rotor side masses, the moment of inertia of generator side masses, the mechanical damping in the rotor side and the mechanical damping in the generator side respectively, where: g2grt inii  is the total inertia of generator side masses, g2grt knkk  is the equivalent mechanical damping. for model (23) agg n  is satisfied, where: aa   is the rotor rotational speed and gg   is the rotational speed of the high speed shaft, while gn designates the gear ratio between the primary shaft and the secondary shaft, a and g are the azimuthally rotor position and the azimuthally position of the u(k) training samples k validation samples k u1(k) 1 6 7 2 4 8 5 3 y(k-1) u(k-1) u(k-2) 1 y(k-2) 9 y(k) engineering, technology & applied science research vol. 6, no. 4, 2016, 1067-1074 1071 www.etasr.com abid et al.: a pruning algorithm based on relevancy index of hidden neurons outputs high speed shaft. the captured aerodynamic torque ta is given in terms of the power coefficient cp(,) as:         ,pa 32a ckvr21kt (24) where  is the specific speed defined as: vr a (25) v is the effective wind speed,  is the air density, and r denotes the blades rotor radius. the power coefficient cp(,) is estimated using aerodynamic data obtained from wind tunnel measurements. it is generally represented under the form of an analytical formula which gives cp() for various values of the pitch angle . in the literature [22] one finds the following approximation:   ]exp[, bacp  (26) where:              2cc1g gcb cbcgca 3 32 6 541 (26) with the coefficients ci, i=1... 6 are identified from real cp curves. using the euler approximation and for small values of the sampling period, the discrete model describing the wind turbine can be expressed as follows:                 kiki kti kttk1k atttgtaaa (27) t denotes the sampling period. the goal of this study is to determine an adequate neural model of the wind turbine. this model should be able to learn nonlinear dynamics of the wind turbine and gives good generalization ability. table i. performances of the studied algorithms algorithm numerical simulation parameters cn fcn efficiency (%) generalization error run time unit-obs =0.6, et=8.10 -5, jt=0.003, =9.10-5 5 3 100 0.0036 0’11" 8 5 75 0.0032 0’11" 11 4 90.91 0.0035 0’18" 14 3 100 0.0035 1’11" 20 4 95 0.0037 1’12" 25 3 100 0.0035 2’08" fast-unit-obs =0.6, lt=jt=0.003, =10-8 5 3 100 0.0036 0’10" 8 3 100 0.0033 0’09" 11 4 90.91 0.0035 0’14" 14 2 92.86 0.0034 1’36" 20 5 90 0.0037 0’46" 25 4 96 0.0036 0’43" proposed algorithm =0.6, jt=0.003, m=20 5 2 80 0.0033 0’23" 8 3 100 0.0034 1’09" 11 3 100 0.0032 0’29" 14 3 100 0.0035 0’19" 20 5 90 0.0035 0’40" 25 5 92 0.0032 1’43" the wind turbine parameters used in simulations are the following [23, 24]:                   4.18cand10.636.9c,309082.0c ,10.003.0c,02.0c,10.1023.1c ,5.7,snmrad7.3k,snmrad5.1k ,1,kgm4.34i,kgm10.25.3i ,165.43n,m38.21r,kgm225.1 6 2 54 2 32 2 1 opt 1 g 1 r 2 g 25 r g 3    the input-output neural model describing the wind turbine is presented in figure 5. the model input vector is constituted by the actual and previous generator torque (tg(k) and tg(k-1)), the actual and previous rotor rotational speed (a(k) and a(k-1)) and the actual value of wind speed v(k). the model output is the future value of the rotor rotational speed a(k+1). the selection of the input vector and the value of the sampling period have been done after several simulations. the chosen mean wind speed was set to vmoy=12ms-1 and t=0.1s. figures 6 and 7 represent respectively the input signals tg(k) and v(k), used in the training (6.a and 7.a) and validation (6.b and 7.b) phases. it is to be noted that each training algorithms have been executed for different initial neural structures. the simulation results describing the performances of the algorithms studied in this paper are illustrated in table iii. it can be seen that the proposed algorithm provides better performances when compared to unit-obs and fast-unitengineering, technology & applied science research vol. 6, no. 4, 2016, 1067-1074 1072 www.etasr.com abid et al.: a pruning algorithm based on relevancy index of hidden neurons outputs obs algorithms. for better illustration of the results presented in table iii, they can be summarized in table iv which presents the average performance on final architecture, generalization capacities and convergence time. table iv shows the contribution of the proposed algorithm. in fact, we note that the algorithm based on relevancy index leads to the simplest neural structure and presents the least convergence time with satisfactory generalization abilities. moreover, the proposed method avoids the complex computation of the inverse of the hessian matrix which considers the major drawback of the obs approach. figure 8 gives the evolution of the identified neural model output for the training (8.a) and validation (8.b) sets using the proposed algorithm. fig. 5. input-output neural model. fig. 6. tg (k) used in the training and validation phases ((a): training, (b): validation). (a) (b) 0 100 200 300 400 500 600 5 10 15 20 k  0 20 40 60 80 100 120 140 160 180 200 5 10 15 20  k fig. 7. v(k) used in the training and validation phases ((a): training, (b): validation). fig. 8. training and validation performances for the proposed algorithm ((a): training, (b): validation). (a) (b) 0 100 200 300 400 500 600 7.5 7.6 7.7 7.8 7.9 8 8.1 8.2 8.3 8.4 real speed estimated speed 0 20 40 60 80 100 120 140 160 180 200 7.5 7.6 7.7 7.8 7.9 8 8.1 8.2 8.3 8.4 real speed estimated speed training validationv(ms -1) samples samples v(ms-1)  1ktg  ktg  ka  1ka  1 1   1ka   kv samples k a(rads-1) samples k a(rads-1) engineering, technology & applied science research vol. 6, no. 4, 2016, 1067-1074 1073 www.etasr.com abid et al.: a pruning algorithm based on relevancy index of hidden neurons outputs table ii. average of performances for the studied algorithms algorithm efficiency (%) generalization error run time unit-obs 93.49 0.0035 0’52" fast-unit-obs 95.11 0.0035 0’36" proposed algorithm 93.67 0.0033 0’47" table iii. algorithms performances for the wind turbine neural modeling problem. algorithm numerical simulation parameters cn fcn generalization error run time unit-obs =0.4, et=8.10-5 jt=0.01, =9.10-5 10 9 0.0058 1’42" 15 9 0.0080 2’01" 20 6 0.0056 2’44" 25 7 0.0048 2’41" fast-unit-obs =0.4, jt=0.01, lt= 0.002, =10-8 10 8 0.0044 1’53" 15 14 0.0048 1’34" 20 13 0.0057 2’37" 25 13 0.0067 2’02" proposed algorithm =0.4, jt=0.01, m=10 10 6 0.0063 1’34" 15 6 0.0084 1’39" 20 7 0.0048 2’04" 25 5 0.0084 1’52" table iv. average of performances. algorithm fcn generalization error run time unit-obs 8 0.0061 2’17" fast-unit-obs 12 0.0054 2’02" proposed algorithm 6 0.0070 1’47" v. conclusion this paper presents a pruning algorithm based on relevancy index that allows obtaining the adequate neural network structure. the main advantage of this method is that it avoids the calculating of the inverse of the hessian matrix which is indispensable for using any pruning algorithm based on the obs approach. to confirm the effectiveness of the developed algorithm, it has been applied on an academic example and on a wind turbine model. the simulation results demonstrated that the proposed algorithm, compared with the unit-obs and the fast-unit-obs algorithms, not only ensures the same training and generalization performance but also shortens the runtime and simplifies considerably the obtained neural structure after pruning process what proves the potential utility of this algorithm. references [1] p. mehra, b. w. wah, artificial neural networks: concepts and theory, ieee comput. society press, 1992 [2] j. m. zurada introduction to artificial neural systems, st paul, mn: west, 1992 [3] v. e. neagoe, c.t. tudoran, “a neural machine vision model for road detection in autonomous navigation”, u.p.b. sci. bull., series c, vol. 73, no. 2, pp. 167-178, 2011 [4] e. şuşnea, “using artificial neural networks in e-learning systems”, u.p.b. sci. bull., series c, vol. 72, no. 4, pp. 91-100, 2010 [5] a. mechernene, m. zerikat, s. chekroun, “indirect field oriented adaptive control of induction motor based on neuro-fuzzy controller”, j. electrical systems, vol. 7, no. 3, pp. 308-319, 2011 [6] d. liu, t. s. chang, y. zhang, “a constructive algorithm for feedforward neural networks with incremental training”, ieee transactions on circuits and systems. fundamental theory and applications, vol. 49, no. 12, pp. 1876-1879, 2002 [7] r. reed, “pruning algorithms-a survey”, ieee trans. neural net., vol. 4, no. 5, pp. 740-747, 1993 [8] h. honggui, q. junfei, “a novel pruning algorithm for selforganizing neural network”, international joint conference on neural networks, atlanta, georgia, usa, pp. 22-27, 2009 [9] d. juan, e. m. joo, “a fast pruning algorithm for an efficient adaptive fuzzy neural network”, 8th ieee international conference on control and automation xiamen, china, pp. 10301035, 2010 [10] z. zhang, j. qiao, “a node pruning algorithm for feedforward neural network based on neural complexity”, international conference on intelligent control and information processing, dalian, china, pp. 406410, 2010 [11] y. le cun, l. s. denker, s. a. solla, “optimal brain damage” in advances in neural information 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optimal wind energy systems development”, u.p.b. sci. bull., series c, vol. 74, pp. 223-230, 2012 [18] a. pintea. d. popescu, “a comparative study of digital imc and rst regulators applied on a wind turbine”, u.p.b. sci. bull., series c, vol. 74, no. 4, pp. 27-38, 2012 engineering, technology & applied science research vol. 6, no. 4, 2016, 1067-1074 1074 www.etasr.com abid et al.: a pruning algorithm based on relevancy index of hidden neurons outputs [19] p. christou, “advanced materials for turbine blade manufacture”, reinforced plastics, vol. 51, no. 4, pp. 22-24, 2007 [20] l. fingersh, m. hand, a. laxson, “wind turbine design cost and scaling model”, national renewable energy laboratory, technical report nrel/tp-500-40566, 2006 [21] y. d. song, b. dhinakaran, x. y. bao, “variable speed control of wind turbines using nonlinear and adaptive algorithms”, wind engineering and industrial aerodynamics, vol. 85, pp. 293-308, 2000 [22] k. reif, f. sonnemann, r. unbehauen, “nonlinear state observation using h∞-filtering filtering riccati design”, ieee transactions on automatic control, vol. 44, no. 1, pp. 203-208, 1999 [23] a. khamlichi, b. ayyat, m. bezzazi, l. el bakkali, v. c. vivas, c. l. f. castano, “modelling and control of flexible wind turbines without wind speed measurements”, australian journal of basic and applied sciences, vol. 3, no. 4, pp. 3246-3258, 2009 [24] s. abid, m. chtourou, m. djemel, “incremental and stable training algorithm for wind turbine neural modeling”, engineering review (er), vol. 33, no. 3, pp. 165-172, 2013 engineering, technology & applied science research vol. 7, no. 4, 2017, 1855-1862 1855 www.etasr.com asghari and rostami: the role of export entrepreneurship effective factors in export performance the role of export entrepreneurship effective factors in export performance elham asghari department of management, faculty of humanities south tehran branch, islamic azad university tehran, iran ali reza rezghi rostami department of management, faculty of humanities south tehran branch, islamic azad university tehran, iran abstract—this research aims to investigate the role of export entrepreneurship effective factors in export performance. research statistical population contains sales managers and top managers working in manufacturing companies of precious and decorative stones in firuzeh, a city in iran. in order to gather data, a questionnaire consisting of 32 questions has been used. the validity of the questionnaire was confirmed by supervisors and advisors and its reliability has been assessed (0.865) using cronbach’s alpha coefficient. five hypotheses have been proposed for this research. two methods of descriptive and inferential statistics have been used to analyze the data in this study. in the descriptive part, frequency number, frequency percentage, and frequency graph have been employed. statistical analysis on data collected show that the variables of management commitment, resources, and the intensity of competition have significant positive impact on export entrepreneurship while the variable market distance does not have significant positive impact on export entrepreneurship. in addition, export entrepreneurship has a significant positive impact on export performance. keywords-management commitment; resources and the intensity of competition; exports entrepreneurship; market distance i. introduction every country needs an export strategy to survive in the global markets and gain a larger share, or at least maintain its current position. in this regard, every country requires a identification of its market structure and its developments [1]. designing strategies for entering international markets is complex and difficult because of the dynamic nature and complexity of the issue as well as the impact of different variables. therefore, it is necessary to identify important variables determining strategies for entering international markets and export [2]. studies show that iran holds little contribution from international markets in spite of having a high potential for export. a major part of the country’s foreign exchange earnings is obtained from oil exports. this dependence is not desirable for several reasons.  oil price, and its export, is subject to severe fluctuations; the fluctuations have undesirable consequences on economic activities,  oil export is subject to international restrictions; an increase in its export does not necessarily lead to an increase in foreign exchange revenues,  oil is an exhaustible material; its export is like the export of capital and its export should not be regarded as the export of other goods. accordingly, export development is one of the main objectives of non-oil economy. the presence of knowledge, information, experience, and resources is essential for overcoming this problem for firms. moreover, export promotion programs should be defined meet this need and help the learning process in international competitive environment as well as motivating business environment toward export goals and providing the necessary infrastructure to facilitate export. besides, composition of exported goods requires reform and improvement. all these factors indicate lack of attention to export entrepreneurship in the country. with these lines, this research seeks to find the role of export entrepreneurship effective factors in export performance. spatial domain of the research is manufacturing companies of precious and decorative stones in firuzeh and the time domain in the year 2015. ii. theoretical foundations considering the research subject under study, theoretical literature of each key word in this study is as follows:  export: export is the easiest way to enter the foreign market. case export occurs when companies sell goods passively to buyers in foreign countries time to time due to having products in excess of domestic consumption. active export occurs when a company decides to export its products to the target country. in both cases, the company may produce the product in its own country and transform them for the target company, or export them in the same shape having been consumed in the domestic lands [3].  export marketing: it is an integrated marketing of goods and services supplied to customers in international markets. in general, export marketing contains all marketing activities carried out by a company to supply products outside the domestic markets [4]. engineering, technology & applied science research vol. 7, no. 4, 2017, 1855-1862 1856 www.etasr.com asghari and rostami: the role of export entrepreneurship effective factors in export performance  export entrepreneurship: ibeh and young [5] have defined export entrepreneurship (ee) as a process in which individuals will benefit from market opportunities in foreign markets by themselves or within the organization by considering available resources and environmental factors that effect on them. the definition highlights dependence of export entrepreneurship to internal resources as well as external and environmental factors.  export performance: classification of the determinants of export performance to internal and external factors is theoretically reasonable because internal determinants are founded based on resource-based theory and determining external factors are established based on industry structure theory. resource-based theory regards a company as a special package of touchable and untouchable resources (assets, competencies, processes, management characteristics, information, and knowledge). they are controllable by the company and enable the company to adjust strategies to improve its efficiency and effectiveness [6]. the theory argues that the resources within an organization are the determinants of export performance and corporate strategy. iii. literature review given the novelty of the subject, a study that examines all variables has not been found. however, there are some relevant studies inside and outside iran in this regard. in [7], authors studied the influence of uncertainty on marketing mix strategy elements in emerging business-to-business export-markets. they tried to find whether the degree and rate of compatibility and standardization depends on the management understanding of uncertainty and whether export entrepreneurship ability of a company (employment of networks, influences positively on the positive evaluation of environment. data collected from german companies that worked in international trading markets. the results show that the use of international entrepreneurship is more effective than using networks in reducing uncertainty. in [8], it was pointed out that export had a direct role in the development and economic growth; hence, using a variety of programs to encourage export, dozens of iranian government agencies and private companies take action to support their export activities. these programs aim to improve the export performance of companies or stimulating them to continue and initiate export activities. in order to evaluate the impact of these supportive programs on export performance of companies, a descriptive survey research has been carried out on exporting companies in the industrial area of khorasan razavi. the research sought to determine strategies to increase export performance for companies that intend to export goods or companies that recently have been on this path. the investigation presented a conceptual model through theoretical foundations in this regard. it analyzed the conceptual model constituted of one main hypothesis and five secondary hypotheses [8]. in [4], authors implied that uncertainty of host country, uncertainty of product market, competitive uncertainty, uncertainty of partner behavior, international experience, technical knowledge, marketing skills, total investment, competitive intensity, nature of foreign activity, attractiveness of location and business relatedness affect selecting foreign market entry strategies. moreover, attractiveness of location, language diversity and uncertainty of the host country are proved to be good manifests of the companies' strategic focus. uncertainty of host country, uncertainty of product market, competitive uncertainty, international experience, firm size, technical knowledge, marketing skill, total investment, business relatedness, and the nature of foreign activity are good manifests for the degree of control over their foreign activities [4]. iv. research hypotheses and research model the model is presented in figure 1. the model presents the relationships between research variables including management commitment, resources, competition intensity, market distance, export entrepreneurship, and finally export performance. this model provides principal and significant structures that have been proposed in the literature in a comprehensive way. accordingly, research hypotheses are as follows:  management commitment to export has a positive impact on export entrepreneurship.  company resources have a positive impact on export entrepreneurship.  intensity of competition has a positive impact on export entrepreneurship.  market distance has a negative impact on export entrepreneurship.  export entrepreneurship has a positive impact on export performance. v. statistical population and statistical sample research statistical population contains sales managers and top managers working in manufacturing companies of precious and decorative stones in firuzeh, a city in iran. random sampling is applied. all members of the community have equal chances to be selected. in other words, ii the number of community members is regarded n and the sample size is regarded n, the probability of selecting each member of society is equal to n/n. random sampling can be performed in two ways. first, draw; second, using a table of random numbers. this study has used the first method (draw). the research employs one of the most important and the most recent sample selection rules. the rule suggests for path model estimates of partial least squares method that the model size should be equal to or greater than the following items:  ten times the number of indicators of the scale with the largest number of formative indicators, or  ten times the largest number of structural paths directed at a particular construct in the inner path model [9]. considering research conceptual model and observing the above rules, the minimum required sample size for this study is 40. since some of the collected questionnaires may have inconsistent and unreliable data and many respondents refuse to fill the questionnaires, 70 questionnaires have been distributed. engineering, technology & applied science research vol. 7, no. 4, 2017, 1855-1862 1857 www.etasr.com asghari and rostami: the role of export entrepreneurship effective factors in export performance fig. 1. research conceptual model vi. research methodology this study can be considered an applied research according to its objectives because an applied research aims to develop practical knowledge in a particular field. moreover, it can be regarded as a descriptive-analytical research since it explains and develops the ways and reasons of the problem and its dimensions in addition to illustration of the facts. researchers need a strong argument to support for explaining and justifying reasons. the argument is acquired by searching the literature, theoretical discussions, formulation of general statements, and available propositions. the researcher connects logically his concerns with relevant general statements; then he makes a conclusion. it is noteworthy to state that each research is valuable in its own place. library based methods (books, articles and dissertations in english and farsi) have been used to collect information on the theoretical background of research; moreover, questionnaire has been used to gather data in the main part of the research. in the first phase, books, articles, theses, online surveys have been useful. parametric and nonparametric statistical methods have been used to analyze data in this research. variance-based structural equation with partial least squares method has been employed to describe data and explain demographic characteristics of descriptive statistics, data analysis, and testing hypotheses and conceptual model. vii. findings a. describing research variables with regard to conceptual model, research variables are market distance, intensity of competition, resources, management commitment, export entrepreneurship, and export performance. in order to address research variables in the software, the coding presented in table i has been used. table i. coding of dimensions and its related variables variable code variable mar market distance com intensity of competition res resources man management commitment ent export entrepreneurship per export performance b. reliability and validity of research data in the researches using partial least squares method, reliability should be calculated for both constructs and indicators. reliability of structures has been examined by cronbach’s alpha and dillon-goldstein's rho. the minimum acceptable value for the coefficients is 0.7. as specified in table ii, the values of cronbach’s alpha and dillon-goldstein's rho are higher than 0.7; it indicates very high reliability of constructs. table ii. the reliability of constructs dillon-goldstein's rho cronbach's alpha construct 0.9254 0.8984 intensity of competition 0.8891 0.8134 export entrepreneurship 0.8824 0.8237 management commitment 0.9248 0.9132 market distance 0.9501 0.9341 export performance 0.9261 0.8993 resources load factors have been tested to assess the reliability of indicators. in this examination, load factor of indicators should be higher than 0.7. coefficients of factor loadings for questions in the questionnaire are shown in tables iii-viii. engineering, technology & applied science research vol. 7, no. 4, 2017, 1855-1862 1858 www.etasr.com asghari and rostami: the role of export entrepreneurship effective factors in export performance table iii. load factor coefficients for the construct of market distance mark 5 mark 4 mark 3 mark 2 mark 1 questions 0.781 0.678 0.723 0.740 0.730 load factor mark 10 mark 9 mark 8 mark 7 mark 6 questions 0.725 0.784 0.759 0.71 0.789 load factor table iv. load factor coefficients for the construct of competition intensity com 5 com 4 com 3 com 2 com 1 questions 0.885 0.877 0.906 0.794 0.809 load factor table v. load factor coefficients for the construct of export entrepreneurship ent 3 ent 2 ent 1 questions 0.828 0.828 0.902 load factor table vi. load factor coefficients for the construct of management commitment man 4 man 3 man 2 man 1 questions 0.817 0.768 0.794 0.850 load factor table vii. load factor coefficients for the construct of export performance per 5 per 4 per 3 per 2 per 1 questions 0.814 0.911 0.891 0.898 0.939 load factor table viii. load factor coefficients for the construct of resources res 5 res 4 res 3 res 2 res 1 questions 0.878 0.891 0.875 0.890 0.680 load factor as seen in the above tables, most indicators have a load factor higher than 0.7. only indicators of res 1 and mark 4 have load factors less than 0.7. according to rule 1 and the average variance extracted of higher 0.5 for the related constructs, the indicators can be maintained. both convergent validity and discriminant validity must be calculated to assess assess the validity in the partial least squares model. the average variance extracted (ave) has been used to calculate the convergent validity; the results are represented in table ix. the value for average variance extracted for all variables is higher than 0.5522; it implies good convergent validity of the constructs. chen test has been used to evaluate discriminant validity of the constructs. square root of the average variance extracted for each construct must be higher than its correlation coefficient of the construct with other constructs. table x shows the results in this regard. as can be seen in the table, value of square root of the average variance extracted for all constructs is higher than its correlation coefficient with other constructs. it indicates good discriminant validity of the constructs. transverse loads have been tested to evaluate discriminant validity of the indicators transverse load for each construct must be higher than its transverse load for other constructs. the results of this test have been displayed in table xi. the results indicate good discriminant validity of the indicators because all indicators have higher load factors for their construct comparing to their load factors for other constructs. table ix. validity of constructs average variance extracted construct 0.7140 intensity of competition 0.7280 export entrepreneurship 0.6526 management commitment 0.5522 market distance 0.7925 export performance 0.7167 resources table x. correlation matrix and the square root of the average variance extracted (chen test) res per mar man ent com 0.8450 construct 0.8532 0.5948 intensity of competition 0.8078 0.5848 0.3800 export entrepreneurship 0.7431 0.1454 0.1235 0.1213 management commitment 0.8902 0.0255 0.4061 0.3720 0.4790 market distance 0.8466 0.2951 0.0299 0.5062 0.6051 0.3877 export performance c. results of path coefficient and determination coefficient in this section, hypotheses are investigated using pls algorithms and bootstrap with 500 su-samples. results of testing hypotheses are shown in figures 2 and 3. as observed in figures, the variables of management commitment, resources, and the intensity of competition have significant positive impacts on export entrepreneurship while the variable market distance does not have significant positive impact on export entrepreneurship. in addition, export entrepreneurship has a significant positive impact on export performance. the impact of variables in addition to path coefficient values, and t-statistics are seen in table xii. in general, table xii shows the relationships among research variables based on research hypotheses, conceptual model, and the software model. the important point in relation to the following table is confirmation of the relations with a p value less than 0.05. the relationships with a p value higher than 0.05 will not be confirmed. viii. conclusion this sections reviews research hypotheses and their confirmation or rejection results. moreover, each hypothesis will be discussed separately. the first research hypothesis evaluates the impact of management commitment to export on export entrepreneurship. as the results of extracting software indicate, the variable of management commitment to export has a significant positive impact on export entrepreneurship with a path coefficient of 0.281 and t-statistic of 3.502. therefore, one can assert in interpreting the test results that management commitment to export increases export entrepreneurship significantly. management commitment to export activities has a strong impact on manufacturers exporting success. to ensure development and maintain regular operations of export, understanding the attitude of foreign buyers and conducting advanced marketing activities are essential. management commitment to export is very important in order to build such capacity. engineering, technology & applied science research vol. 7, no. 4, 2017, 1855-1862 1859 www.etasr.com asghari and rostami: the role of export entrepreneurship effective factors in export performance fig. 2. the path coefficient of the model fig. 3. t-statistic for the model engineering, technology & applied science research vol. 7, no. 4, 2017, 1855-1862 1860 www.etasr.com asghari and rostami: the role of export entrepreneurship effective factors in export performance table xi. transverse loads res per mar man ent com 0.370538 0.361601 -0.100171 0.210616 0.452173 0.808864 com 1 0.210336 0.212294 -0.035270 0.283773 0.434538 0.737016 com 2 0.350460 0.472738 -0.061211 0.355679 0.519030 0.905673 com 3 0.349515 0.438944 -0.059501 0.358066 0.538961 0.877118 com 4 0.347376 0.500636 -0.239300 0.377591 0.554706 0.884975 com 5 0.587529 0.408352 -0.150027 0.526353 0.901601 0.574899 ent 1 0.375263 0.310033 -0.168686 0.455370 0.827784 0.540511 ent 2 0.576516 0.213427 0.014521 0.515148 0.828349 0.394513 ent 3 0.509294 0.294381 -0.114069 0.850458 0.554419 0.330068 man 1 0.353580 0.262652 -0.075471 0.793509 0.446526 0.186275 man 2 0.317498 0.470456 -0.174020 0.768097 0.364082 0.302122 man 3 0.421318 0.326220 -0.119855 0.817114 0.492648 0.399782 man 4 0.057823 0.032345 0.729878 -0.036422 -0.043716 -0.007590 mark 1 0.141535 -0.111845 0.739627 -0.070596 -0.083600 -0.061347 mark 2 -0.092055 0.131071 0.722593 0.010919 -0.030700 0.037430 mark 3 0.035685 -0.029481 0.678037 -0.020617 -0.032337 -0.120493 mark 4 0.012909 -0.024058 0.781277 -0.079448 -0.078857 -0.069033 mark 5 -0.041273 -0.066182 0.789494 -0.199506 -0.084601 -0.162362 mark 6 -0.082526 0.113268 0.714545 -0.009396 -0.100431 -0.096739 mark 7 -0.118420 0.062276 0.758813 -0.169506 -0.045785 -0.042854 mark 8 -0.144715 -0.033467 0.784284 -0.176939 -0.136596 -0.082887 mark 9 0.050241 -0.095895 0.725358 -0.153709 -0.123590 -0.151457 mark 10 0.259385 0.932932 -0.024334 0.344620 0.378028 0.486325 per 1 0.259746 0.898318 -0.068582 0.352620 0.287310 0.342009 per 2 0.229164 0.890702 -0.029938 0.437623 0.259890 0.415235 per 3 0.259302 0.911195 -0.012767 0.453082 0.380414 0.406063 per 4 0.287031 0.813563 0.014365 0.220652 0.317139 0.468594 per 5 0.680420 0.105936 0.278031 0.225557 0.369525 0.138157 res 1 0.889656 0.185475 0.013360 0.368959 0.543312 0.300394 res 2 0.875125 0.375439 -0.142781 0.543134 0.620019 0.404496 res 3 0.890697 0.231972 -0.144877 0.446623 0.494685 0.371461 res 4 0.877675 0.283636 -0.028835 0.502106 0.487709 0.375866 res 5 table xii. the result of the research hypothesis based on the results of structural models hypothesis result t-statistic path coefficient variables confirmed 3.502 0.281*** management commitment → export entrepreneurship confirmed 0.306 -0.029 market distance → export entrepreneurship confirmed 2.909 0.323** resources → export entrepreneurship confirmed 3.618 0.359*** intensity of competition→ export entrepreneurship confirmed 4.059 0.372*** export entrepreneurship → export performance * p < 0.05 ** p < 0.01 *** p < 0.001 management commitment is reflected in activities such as separate units of export, export control and planning, export market research, and regular inspections of the export market. management commitment to export points out to willingness of export decision makers in the company to allocate appropriate financial, human, and managerial resources. the tendency reduces export risk and obstacles that a company may be encountered in its activities. moreover, it attracts stronger support from foreign distributors. hence, results of testing hypothesis are consistent with the literature and confirm them. the second research hypothesis evaluates the impact of company resources on export entrepreneurship. resources have been evaluated with dimensions of experience and structure. results and outputs of the software in this study show that resource has a significant positive impact on export entrepreneurship with a path coefficient of 0.323 and t-statistic of 2.909. therefore, one can assert in interpreting the test results that increasing experience and structural resources of the company will increase, improve, and develop export entrepreneurship significantly. in terms of experience resources (experience in the organization), company must pay attention to the differences between basic experiences and international experiences. basic experiences refer to the relationships of knowledge in business activities in a competitive industry; it provides the foundation of internationalization process. on the contrary, international experience refers to knowledge about foreign markets. this type of experience will lead to the creation of specialized knowledge regarding export activities and it provides necessary information to adapt to foreign markets. having international experience reduces risk of exports and barriers to entry into international markets; besides, resource is one of the effective and important variables in export entrepreneurship. consequently, results of testing hypothesis are consistent with the literature and confirm them. engineering, technology & applied science research vol. 7, no. 4, 2017, 1855-1862 1861 www.etasr.com asghari and rostami: the role of export entrepreneurship effective factors in export performance the third research hypothesis evaluates the impact of company competition intensity on export entrepreneurship. results and outputs of the software in this study show that competition intensity has a significant positive impact on export entrepreneurship with a path coefficient of 0.359 and t-statistic of 3.618. in this regard, it can be asserted that increasing competition intensity will increase, improve, and develop export entrepreneurship significantly. intensity of industry competition shows the rivalry relationships among small, medium, and large firms. at first glance, it can be argued about industries with less competition intensity that companies try to employ the approaches leading to full control to exploit all benefits of investment. therefore, when competition increases, the companies prefer to contribute partners because it reduces their bargaining power is reduced. on the contrary, experimental findings have not confirmed this hypothesis. when competition increases in reality, companies prefer not to enter fully cooperative strategies because contribution reduces their assertiveness to respond quickly to competitors. with regard to contents extracted from the literature, the results of this hypothesis are in line with the available literature and confirm them. the fourth research hypothesis evaluates the negative impact of market distance on export entrepreneurship. results and outputs of the software in this study show that market distance has a negative impact on export entrepreneurship with a path coefficient of -0.029 and t-statistic of 0.306. accordingly, it can be stated that increasing market distance has an adverse effect on the development of export entrepreneurship. companies export their products to foreign markets to enjoy competitive advantages of a certain geographic region, to earn benefits of increase in market size, and to achieve a better position comparing to domestic and foreign rivals. market distance means the economic, legal, social, and cultural difference between the local market and foreign markets. market distance is one of the most remarkable barriers in the internationalization process of companies; it influences severely on the time and the way to enter foreign markets. thus, the more is the distance between domestic market and foreign markets, the less will be market and foreign markets; thus the activities to develop export entrepreneurship will be decreased and faded. therefore, the results of this hypothesis are in line with the available literature and confirm them. the fifth research hypothesis evaluates the positive impact of export entrepreneurship on export performance. export performance in this study has been evaluated by rate, speed, and scale. results and outputs of the software in this study show that export entrepreneurship (as a construct) has a positive impact on export performance with a path coefficient of 0.0372 and t-statistic of 4.059. export entrepreneurship is a process in which individuals will benefit from market opportunities in foreign markets by themselves or within the organization by considering available resources and environmental factors that effect on them. in fact, institutional entrepreneurs are individuals who are actively in search of export opportunities while keeping in mind establishment of innovation in product or market. export entrepreneurship is categorized in the group of programs and activities that are conducted to improve export performance. according to studies and literature, this variable has good impact on improving export performance. hence, the results of this hypothesis are in line with the available literature and confirm them. the result of testing first research hypothesis is consistent with the findings in [10, 11]. the second research hypothesis is in line with a part of results shown in [12, 13]. third research hypothesis results are in agreement with [14, 15]. fourth research hypothesis confirms the results [16, 17]. fifth research hypothesis is in accordance with [18, 19]. ix. suggestions for further studies it is suggested that a research is conducted for a longer period, for example some years, to study the impact of export entrepreneurship on export performance better; in this way, the results will be more sustainable. future studies can study the impact of other variables such as export problems, export incentives, export experience, etc. on export performance. references [1] m. haqiqi, m. firuzian, s. najafi majd, “identification of the determining factors of the export performance in the food industries”, iranian journal of business management, vol. 1, no. 4, pp. 12-43, 2008 [2] n. a. dehghan, “study, classification and selection of strategies for entering international markets”, second international conference on strategic management, iran: tehran, vol. 2, no. 3, pp. 10-12, 2007 [3] a. rosta, v. davar, e. abdolhamid, marketing management, tehran: samt publication, 2004 [4] h. rezvani, f. gol alizadeh, “evaluation and analysis of the strategies of food products entry to foreign markets”, strategic management journal, vol. 1, no. 2, pp. 71-100, 2011 [5] k. i. ibeh, s. young, “exporting as an entrepreneurial act—an empirical study of nigerian firms”, european journal of marketing, vol. 35, no. 2, pp. 566–586, 2001 [6] j. barney, “firm resources and sustained competitive advantage”, journal of management, vol. 17, no. 3, pp. 99-120, 1991 [7] r. helm, s. gritsch, “examining the influence of uncertainty on marketing mix strategy elements in emerging business to business export-markets”, international business review, vol. 23, no. 2, pp. 418428, 2014 [8] a. ghasemi, designing effective model of export incentives to improve export performance through dynamic capabilities of the organization, case study of small and medium industries in industrial region of khorasan razavi, 2013 [9] j. henseler, c. m. ringle, r. r. sinkovics, “the use of partial least squares path modeling in international marketing”, advances in international marketing, vol. 20, no. 3, pp. 277-319, 2009 [10] a. navarro, f. j. rondan, f. j. acedo, “the importance of an export oriented culture for export performance”, european journal of international management, vol. 7, no. 5, pp. 254 –277, 2013 [11] c. styles, t. ambler, “the impact of relational variables on export performance: an empirical investigation in australia and the uk”, australian journal of management, vol. 25, no. 2, pp. 261 –281, 2000 [12] e. ruzo, f. losada, a. navarro, j. a. díez, “resources and international marketing strategy in export firms: implications for export performance”, management research review, vol. 34, no. 2, pp. 496– 518, 2011 [13] f. vermeulen, h. barkema, “pace, rhythm, and scope: process dependence in building a profitable multinational corporation”, strategic management journal, vol. 23, no. 5, pp. 637 –653, 2002 [14] a. navarro, j. arenas, f. j. rondan, “external environment and the moderating role of export market orientation”, journal of business research, vol. 67, no. 2, pp. 740 –745, 2014 engineering, technology & applied science research vol. 7, no. 4, 2017, 1855-1862 1862 www.etasr.com asghari and rostami: the role of export entrepreneurship effective factors in export performance [15] j. d. mittelstaedt, w. a. ward, e. nowlin, “location, industrial concentration and the propensity of small us firms to export: entrepreneurship in the international marketplace”, international marketing review, vol. 23, no. 2, pp. 486 –503, 2006 [16] n. prime, c. obadia, i. vida, “psychic distance in exporter – importer relations hips: a grounded theory a pproach”, international business review, vol. 18, no. 3, pp. 184 –198, 2009 [17] c. m. sousa, f. bradley, “effects of export assistance and distributor support on the performance of smes the case of portuguese export ventures”, international small business journal, vol. 27, no. 2, pp. 681 –701, 2009 [18] e. nemkova, a. l. souchon, p. hughes, “export decision-making orientation: an exploratory study”, international marketing review, vol. 29, no. 5, pp. 349 –378, 2012 [19] k. s. powell, “profitability and speed of foreign market entry”, management international review, vol. 54, no. 3, pp. 1 –15, 2014 microsoft word 1-592-ed.doc engineering, technology & applied science research vol. 5, no. 5, 2015, 850-853 850 www.etasr.com erturk and jyoti: perspectives on a big data application: what database engineers and it students… perspectives perspectives on a big data application: what database engineers and it students need to know emre erturk senior lecturer, school of computing eastern institute of technology napier, new zealand eerturk@eit.ac.nz kamal jyoti postgraduate student, school of computing eastern institute of technology napier, new zealand erkamaljyoti@gmail.com abstract— cloud computing and big data are important and related current trends in the world of information technology. they will have significant impact on the curricula of computer engineering and information systems at universities and higher education institutions. learning about big data is useful for both working database professionals and students, in accordance with the increase in jobs requiring these skills. it is also important to address a broad gamut of database engineering skills, i.e. database design, installation, and operation. therefore the authors have investigated mongodb, a popular application, both from the perspective of industry retraining for database specialists and for teaching. this paper demonstrates some practical activities that can be done by students at the eastern institute of technology new zealand. in addition to testing and preparing new content for future students, this paper contributes to the very recent and emerging academic literature in this area. this paper concludes with general recommendations for it educators, database engineers, and other it professionals. keywords-information technology; database design; big data; mongodb i. introduction this paper discusses the latest emerging database technology and concepts. the content is aimed at information technology and cloud computing students as well as working database designers and administrators surveying professional and scholarly literature, and considering retraining. in order to demonstrate certain aspects of big data, it is first necessary to briefly review the qualities of modern cloud based databases. this also involves revisiting some of the fundamentals of database technologies. providing an instructional manual is not the purpose of this paper. the aim is to demonstrate the primary activities and concepts that current it students and database engineers need to know in order to work professionally with big data applications. then the paper relates the essential learning objectives and their relevance for industry practice and to the it sector in general. the following activities can be done in the database management systems and database administration courses. students in these two courses are not required to do extensive programming or create new applications. prior to the demonstrations in section iv, this paper covers the fundamentals of big data and mongodb in sections ii and iii with a literature review. finally, the paper summarizes and reflects on the authors’ technical experimentation along with conclusions and recommendations in section v. ii. cloud computing and the impact on big data cloud computing services operate on shared and remote resources on the internet rather than on an organization’s own local servers or on the end users’ own personal computers or devices [1-2]. as a result, cloud based services achieve greater availability, flexibility, and scalability. a wide range of platforms and applications are currently delivered under the banner of cloud computing. data management is an important issue in cloud computing as millions of people use cloud based hardware and software services that constantly store, update, and retrieve a great amount of data. big data is the term used to describe massive volumes of both structured and unstructured data [3]. it is difficult and inefficient to process this amount and type of data using traditional database applications [4]. one example of big data comes from the constantly expanding social media platforms and their users. another example is from the increasingly complex health care industry offering new devices and web based applications for the customers. all of this data is hosted on remote servers on the cloud. managing and running large and ‘live’ databases on the internet involves many technical aspects such as virtualization, concurrency control, operating systems, network administration, process scheduling, load balancing, transaction management, and database design. iii. understanding big data applications in order to manage big data, many nosql (not only sql) databases have been introduced in recent years. these nosql databases handle data in ways different from the tables and engineering, technology & applied science research vol. 5, no. 5, 2015, 850-853 851 www.etasr.com erturk and jyoti: perspectives on a big data application: what database engineers and it students… structured query language (sql) statements of traditional relational databases. there are many nosql document oriented databases, for example, couchdb and mongodb. document oriented databases store and retrieve data according to the meta-data definitions and tags found in their documents. mongodb was first developed by in 2009. it has versions that are compatible with different editions of windows, linux, solaris, and mac operating systems. mongodb is an open source and free database application, under the gnu affero general public license. it is currently the most popular application in the category of document oriented databases [5]. mongodb can store semi-structured and polymorphic data as well as structured data. much of the current big data exchanged on the internet does not follow clear cut structures, rigid schemas, or restrictions in terms of data type and length. this also means handling emails, forums, complicated large objects, and multimedia files [6]. mongodb allows users to flexibly define arrays within documents, and perform various operations on those array fields. furthermore, mongodb offers database querying functionality and supports high performance indexing. these are useful, for example, for text searches and manipulation of geospatial data. instead of sql join statements, mongodb users may reference a document from another or embed a document inside another document. it also features a powerful data aggregation and data analysis framework, for performing calculations on large data sets. mongodb aims to provide high performance, availability, and scalability, for cloud based information systems and big data environments. in order to ensure availability, sophisticated database systems create replicas of database files in different locations so that, if one location is down, then the user can access the information from another location. as shown in figure 1, a new machine becomes the primary server while the ‘heartbeat’ diagnostic program continues to check if the various replica servers are online and working properly. additionally, it is possible to automate the failover (switching from a server that is down to an available one) and data recovery processes. fig. 1. database replication and failover. scalability is the ability of databases to grow tremendously in size while maintaining usability or performance. there are very large databases that constantly accumulate data on the internet. in mongodb, more servers can be allocated to a database to balance the workload and increase performance; this is called horizontal scalability. sharding is the process in which a single database is divided into multiple components. these database components are stored on different servers. these servers may also be virtual machines or cloud based. iv. learning activities using mongodb one of the first skills that the database engineer needs is to be able to quickly install the mongodb server software on a given computer. a brief example in this paper is installing it on the microsoft windows operating system. after navigating to https://www.mongodb.org/downloads, the user needs to select the appropriate version from the menu, and clicks on ‘download msi.’ once the setup file is saved, the user can execute this, follow the instructions, and complete the steps. after this installation, the mongodb server can be run from the windows command prompt. however, the setup process does not complete all the requirements; the user needs to manually create a subfolder named ‘db’ in the ‘data’ folder of the hard drive to avoid potential error messages and run mongodb. although a database engineer can interact with this basic installation using the command line interface, the next recommended and useful task is to install a front-end graphical user interface application to manage the databases. figure 2 shows the configuration of the front-end application called nosql manager. the default port number for the mongodb server is 270017. fig. 2. connecting to mongodb using a front-end application. another optional tool for database students and trainees to be aware of is called mongodb management service (mms). engineering, technology & applied science research vol. 5, no. 5, 2015, 850-853 852 www.etasr.com erturk and jyoti: perspectives on a big data application: what database engineers and it students… this is a cloud based tool, and does not require an installation. mms offers a sophisticated database backup service, and can monitor up to thousands of online database deployments [7]. the second important area for learning mongodb involves the storage concepts and terminology. most trainees will already be familiar with relational database concepts and terms; therefore a good approach would be to explain to them the corresponding mongodb terms along with the similarities and differences. as seen in figures 3 and 4, a mongodb database is made up of collections, which may be viewed as two dimensional tables. on the other hand, given a similar business domain, relational database structures necessitate the creation of multiple tables to represent the data whereas the same design can be done with fewer collections in mongodb. not having to create joining tables for many-to-many relationships and handling one-to-many relationships within the same collection with are examples of reasons for this. each mongodb document is similar to an sql row; however mongodb’s bson (binary java script object notation) document format provides recursive functionality and allows more efficient database scanning. fig. 3. viewing sample data from mongodb. fig. 4. mongodb structure vs traditional sql. learning the syntax is essential for creating a mongodb database. advanced students and database professionals are already proficient in programming with sql using relational database applications, e.g. microsoft sql server or mysql. figures 5 and 6 compare statements in sql versus mongodb. in the case of an insert command that creates new data records, the mapping of the values is easier to understand. it can be explained as a transposition from sql’s horizontal coding (i.e. items and values are listed from left to right) to a vertical coding in mongodb where the document items and values are listed from top to bottom. in sql, the input row names are grouped together while their input values are also grouped together separately; these groups are implicitly corresponded based on their order within that table’s structure. in mongodb, the input values are written next to the field name, similar to xml (extensible markup language), and these fields can be listed vertically, each one on a new line. in the case of a read command (figure 6) that fetches data records, the difference is greater, between traditional sql select statements and mongodb (which uses the find method). first, the same kind of transposition or projection difference applies, going from horizontal groupings to vertical listings. on the other hand, in mongodb, the user needs to be careful to separate the fields involved in the query criteria from the fields included in the query output. furthermore, sql queries use intuitive boolean operators to define query criteria while mongodb queries use abbreviated tags, such as $gt (greater than). the value of ‘1’ also needs to be specified next to the field name(s) to show them in the output result. the publicly available instructional information on coding with mongodb is limited, with many of the resources written in a technical language that is not conducive to easier and faster learning. for this reason, the explanations offered above will be useful in a future training course by filling an educational gap. fig. 5. nosql vs traditional sql syntax. engineering, technology & applied science research vol. 5, no. 5, 2015, 850-853 853 www.etasr.com erturk and jyoti: perspectives on a big data application: what database engineers and it students… fig. 6. nosql vs traditional sql syntax. v. conclusion in order to implement these learning activities for students, it is necessary for instructors to cover the theoretical content in depth prior to the practical work. furthermore, the practical tutorials require initial familiarization, trouble-shooting, and self-guided technical learning. therefore it is important that instructors plan and allocate time to students so that they can understand what they need to do, and become prepared. in later stages of the course, once mongodb is installed on a server, students can access a cloud based mongodb using the lab computers and their own computers. in the course (that this paper targets), about thirty enrollments are expected. these students will be guided by one instructor. a recommendation for further research as well as training material development should be on understanding and improving the security of a mongodb database. this is important because many mongodb implementations have been done recently without setting up the correct access controls [8]. after the initial installation, all of the user profiles and authorizations have to be set up by the database administrator. secondly, hackers may try to exploit mongodb databases using code injections similar to the way sql injections have been used to target traditional relational database applications. future students who are doing additional training on mongodb security should review the syntax of the possible injections, and learn how these injections can be prevented from posing a risk. it needs to be emphasized that cloud computing and big data offer additional benefits together: capturing and analyzing much more information, making better business decisions, using the it infrastructure more efficiently, and enhancing disaster recovery. however, when selecting a database product, it needs to be kept in mind that each company should decide according to its own unique data and reporting requirements. however, in general, capturing and providing fast access to big data will continue to be crucial, with ever increasing numbers of connected mobile applications and new online systems [9]. as emphasized in this paper, the public awareness of big data applications and their benefits is increasing. as a result, more companies are looking for it professionals with the latest knowledge and skills in this area. these potential employers are not only software development companies but also include diverse organizations and companies from different sectors of the economy. references [1] v. beal, “cloud cmputing (the cloud)”, http://www.webopedia.com/term/c/cloud_computing.html [2] g. a. tarnavsky, e. v. vorozhtsov, “cloud computing in science and engineering and the “scishop.ru” computer simulation center”, engineering, technology & applied science research, vol. 1, no. 6, pp. 133-138, 2011 [3] v. inukollu , s. arsi1, s. ravuri, “high level view of cloud security : issues and solutions”, fourth international conference on computer science, engineering and applications, chennai, india, pp. 51-61, 2014 [4] a. shields, “why traditional database systems fail to support big data”, http://marketrealist.com/2014/07/traditional-database-systemsfail-support-big-data/ [5] solid it, “db-engines ranking of document stores”, http://dbengines.com/en/ranking/document+store [6] s. khan, v. mane, “sql support over mongodb using metadata”, international journal of scientific and research publications, vol. 3, no. 10, pp. 1-5, 2013 [7] j. roy, “mongodb: characteristics and future”, http://www.mongodbspain.com/en/2014/08/17/mongodb-characteristicsfuture [8] j. heyens, k. greshake, e. petryka, “mongodb databases at risk: several thousand mongodbs without access control on the internet”, saarland university center for it security, privacy, and accountability, https://cispa.saarland/wp-content/uploads/2015/02/mongodb_document ation.pdf [9] e. erturk, “an intelligent and object-oriented blueprint for a mobile learning institute information system”, international journal for infonomics, vol. 6, no. 3/4, pp. 736-743, 2013 [10] microsoft word etasr_v11_n6_pp7745-7749 engineering, technology & applied science research vol. 11, no. 6, 2021, 7745-7749 7745 www.etasr.com hyder ey al.: towards countering the insider reconnaissance using a combination of shuffling and … towards countering the insider reconnaissance using a combination of shuffling and diversity moving target defense techniques muhammad faraz hyder department of software engineering ned university of engineering & technology karachi, pakistan farazh@neduet.edu.pk waseemullah department of computer science and it ned university of engineering & technology karachi, pakistan waseemu@neduet.edu.pk muhammad umer farooq department of computer science and it ned university of engineering & technology karachi, pakistan umer@neduet.edu.pk abstract-moving target defense (mtd) has recently emerged as a significant cybersecurity technique. software-defined networking (sdn) has the capability to design efficient network architecture due to its programmability and centralized control management. in this paper, a mechanism for the protection against insider reconnaissance has been proposed using a combination of diversity and a shuffling-based approach of mtd. in order to implement the shuffling technique, ip shuffling is used in the insider network. the ip addresses of internal hosts are mapped via real to virtual ip mapping through random ip generation from a pseudo-random mechanism. for the diversity, a multiple servers’ platform is incorporated for different critical lan services like domain name system (dns), internal web services, etc. this combined diversity and shuffling approach significantly counters the insider reconnaissance targeting critical lan services. the proposed scheme also exploited open-source ids to block insider reconnaissance. the proposed solution was implemented using onos sdn controller, mininet simulator, snort ids systems. the experimental results substantiate effective protection against insider network reconnaissance at a low computational cost. keywords-diversity; ip shuffling; insider reconiccance moving target defense; software defined networking; virtual ip i. introduction threats emerging from malicious insiders that have quite a clear picture of the internal resources are becoming more and more common [1]. network reconnaissance is the initial stage of the cyber kill chain [2]. the notion is to collect information about the system and its attributes. many different solutions have been proposed for the protection against these types of attack [3]. however, the existing work for protection against the network reconnaissance is mainly focused on the external attackers and subsequently the reconnaissance traffic generated from outsiders. moving target is a cyber defense technique with the goal of constantly changing the attack surface in order to incommode the attacker to exploit the system [4-6]. this active cybersecurity has already drawn the attention of the research community in different domains including the security of cyber-physical systems [7, 8], network security [4], cloud security [9], iot security [10], etc. software-defined networking (sdn) [11] augments the mtd-based solution development due to its centralized network control, visibility, and separation of control and data planes. therefore, several mtd solutions are based on sdn [5, 12, 13]. in this paper, a mechanism for protecting the critical dns and web servers from reconnaissance attacks generating from inside the network has been developed. the notion of the work is the exploitation of the mtd mechanism for the protection of resources from insider reconnaissance. moreover, we have adopted a combination of two different mtd techniques, i.e. diversity and shuffling. the work provides a three-layer protection against insider reconnaissance. in the first line of defense, the ip addresses of the nodes are periodically mapped to virtual ip addresses. these addresses are generated using pseudo-random number generators in order to enhance the randomness. the mechanism provides the functionality of all internal communication happening via a virtual ip address. the second line of defense is the platform-level diversity of dns and web services. the third protection mechanism is the use of ids to detect and block malicious insiders generating reconnaissance traffic. these three approaches substantially counter the internal reconnaissance while ensuring that the information gained by the insider during the reconnaissance is not correct as it changes after a specific period. the fundamental motivation behind the mtd based system is to increase the uncertainty and confusion regarding the corresponding author: muhammad faraz hyder engineering, technology & applied science research vol. 11, no. 6, 2021, 7745-7749 7746 www.etasr.com hyder ey al.: towards countering the insider reconnaissance using a combination of shuffling and … information collected by attackers through constantly changing the attack surface [14]. it is an active cybersecurity technique with the objective of making cybersecurity an equal playing field for both the attacker and the defender. there are three broad categories of mtd, namely diversity, redundancy, and shuffling [15]. the diversity technique provides different platforms, software, programming languages, and networks. in the case of shuffling techniques, different system parameters are shuffled either periodically or on the basis of certain events. in redundancy, replicas of the resources are created. these replicated and redundant resources substantially increase the uncertainty for the attacker. most of the work in the domain of mtd exploits one of the basic three approaches. however, a combination of these approaches has not been exploited in detail. the amalgamations of these techniques will enhance the performance of the mtd solution and increase attacker uncertainty. sdn is getting popular in designing security solutions [16]. the centralized controlling attributes enable greater ease for designing the mtd solution. it’s also popular to design mtd for network security [17, 18], cyber-physical systems [7], ad hoc networks [19, 20], cloud security [9, 19], etc. insider attacks are gaining momentum [1, 20]. there is an initial level of work for the protection of the first stage of the cyber kill chain, i.e. reconnaissance [21]. authors in [22] proposed a scheme to counter external reconnaissance using sdn-based virtual topologies. in [23], the authors suggested a bio-inspired technique to mitigate insider reconnaissance attacks. insider threat detection based upon a reality gamebased approach was proposed in [24]. ii. the proposed scheme the proposed scheme has three levels of defense. the first one is the ip shuffling approach for different nodes and servers. the second one is based upon the diversity of platforms for web and dns servers. the third level of defense is the detection of insider reconnaissance via open-source ids solution and subsequently blocking the malicious hosts generating such traffic. the high-level diagram is depicted in figure 1. the mtd is created using the onos sdn controller that consists of multiple switches and different hosts connected. figure 2 depicts the communication between two hosts. it also presents the network flow between these hosts. the communication inside the network is happening via virtual ip addresses that are constantly changing. when a host initiates the traffic to other hosts in the network, then communication is mapped to their corresponding virtual ips. there are several steps involved in this communication. the application running in the controller will modify the ip address of the host to convert it into a virtual ip address. the frequency for ip shuffling is set to be 30 seconds for attaining a time-based mtd mechanism. the sdn controller injects the necessary flows based upon the new ip addresses for smooth communication inside the network. the second line of defense counters insider reconnaissance targeting specific services like dns and web servers. to protect against this type of attack, multiple platforms are used. in the case of dns, the server was prepared using bind9 and unbound dns. similarly, there are different platforms for web servers, like apache, nginx, and iis. within these platforms, different versions are also used to increase the uncertainty for the attackers. when the insider performs reconnaissance to gather information about the dns or the web servers, then they will get diversified platform information. fig. 1. the multi-layered defense approach against insider reconnaissance attacks. fig. 2. traffic flow sequence during ip mapping from real to virtual and vice versa. fig. 3. server platform diversification. engineering, technology & applied science research vol. 11, no. 6, 2021, 7745-7749 7747 www.etasr.com hyder ey al.: towards countering the insider reconnaissance using a combination of shuffling and … the proposed solution also utilized the open-source ids snort to detect and block the insider generating the reconnaissance traffic. this is the third line of defense against insider threats. figure 3 depicts the server platform diversification for dns and web servers. the attacker performing scanning will get different results of specific web and dns platforms. figure 4 represents the snort platform analyzing the traffic for detection of reconnaissance traffic. the graphical interface of the snort platform is depicted in figure 5. fig. 4. snort ids platform analyzing packets. fig. 5. graphical interface of the snort ids platform. iii. experimental setup we used onos sdn controller [25], mininet simulator [26], and snort ids [27]. regarding the server machines, we used different platforms for webserver implementation including apache [28], nginx [29], and iis [30], while dns implementation bind9 [31], unbound dns [32], and powerdns [33] packages were selected. on the sdn network, class a ip addresses were assigned. sflow [34] was used for collecting different statistical parameters of the network. the experimental setup was implemented on a dell server having 32gb ram. to generate the reconnaissance traffic, we have used nmap [35]. the experimental topology is depicted in figure 6. the attacker first generates the reconnaissance traffic against the other internal hosts. however, all internal transmission is based upon the mapping from real to virtual ip addresses mapping. this mapping also uses pseudo-random number generators to produce virtual ips. the information gained by the attacker in one iteration gets invalidated due to virtual ip randomization. in the second phase, the attacker targets the dns and web servers’ platforms. fig. 6. the experimental topology. iv. results and discussion we assumed that the attacker can perform a maximum of 10 scan probes at a time. table i represents the ip addresses on the network as observed by the attacker in different iterations. the attackers perform multiple reconnaissance attacks. the attackers observed different ip schemes and addresses due to the ip randomization through the proposed mtd scheme. this substantially increases the confusion for the attackers, because the knowledge gained in each iteration becomes void in the next. figure 7 illustrates the ip shuffling results for different iterations. the attackers discovered different number of ip addresses in different iterations. however, in different iterations attackers may correctly identify the previous ip addresses. the percentage of getting the same ip addresses in consecutive iterations is below 5%. we considered the generic case of i th and i th+1 iterations. table i. ip addresses discovered in different iterations of reconnaissance by the insider attacker ip addresses discovered in: 1 st iteration 2 nd iteration 3nd iteration 4 rth iteration 192.168.10.4 10.5.7.9 172.16.12.5 10.6.7.3 192.168.10.5 10.5.7.10 172.16.12.6 10.6.7.4 192.168.10.6 10.5.7.11 172.16.12.7 10.6.7.5 192.168.10.7 10.5.7.12 172.16.12.8 10.6.7.6 192.168.10.8 10.5.7.13 172.16.12.9 10.6.7.7 192.168.10.9 10.5.7.14 172.16.12.10 10.6.7.8 192.168.10.10 10.5.7.15 172.16.12.11 10.6.7.9 192.168.10.11 10.5.7.16 172.16.12.12 10.6.7.10 192.168.10.12 10.5.7.17 172.16.12.13 10.6.7.11 192.168.10.13 10.5.7.18 172.16.12.14 10.6.7.12 table ii depicts the diversified dns and web servers’ platform observed by the attackers while running probing traffic against these servers. since our scheme deploys diversified platforms, the attackers observe multiple platforms. this substantially increased the attacker confusion. engineering, technology & applied science research vol. 11, no. 6, 2021, 7745-7749 7748 www.etasr.com hyder ey al.: towards countering the insider reconnaissance using a combination of shuffling and … fig. 7. ip shuffling to counter insider reconnaissance. table iii indicates the ip addresses of the malicious insiders generating reconnaissance traffic being blocked by the third line of defense of our scheme i.e., the ids snort. the first column in table iii is the number of distinct attackers, the second column indicates the maximum number of probes generated by the attacker. the third column is the multiple of the first two, i.e. the total generated probes. the ids is able to detect and blocked on average approximately 85% of malicious attackers. overall, the proposed scheme successfully counters the insider reconnaissance using the three-level defense level mtd technique. table ii. platform diversity for web and dns services web server ip addresses web server platform detected dns server ip addresses dns server platform detected 192.168.10.10 apache 2.4.48 192.168.10.13 bind 9.12 10.5.7.15 10.5.7.18 172.16.12.11 nginx-1.21.1. 172.16.12.14 unbound 1.13.2 10.6.7.9 iis 10.0 express 10.6.7.12 powerdns 4.5.1 table iii. attacker ip addresses blocked by ids no. of malicious ip addresses generating scans no. of scans generated by an individual attacker total no. of insider reconnaissanc e attempts malicious ip addresses detected and blocked by the ids malicious ip addresses detected and blocked by the ids (%) n m t=n×m b % 10 10 100 8 80% 20 10 200 17 85% 30 10 300 26 87% 40 10 400 35 88% 50 10 500 42 84% 60 10 600 53 88% 70 10 700 60 86% 80 10 800 69 86% 90 10 900 76 84% 100 10 1000 86 86% v. comparison of the proposed scheme with stateof-the-art techniques table iv summarizes the comparison of the proposed scheme with the state-of-the-art existing solutions. the first advantage of our scheme is the exploitation of mtd for insider reconnaissance protection. the existing work in the literature [22-24] focuses on the protection of external reconnaissance. the second advantage of our technique is the combination of mtd techniques for insider reconnaissance protection. moreover, our scheme is based upon sdn which provides greater flexibility in designing mtd solutions. only the work presented in [22] exploited sdn-based mtd for probing traffic protection. however, their work focused on external reconnaissance protection only. hence our proposed sdnbased combination of mtd technique is quite an efficient one. table iv. comparison of the proposed implementation with existing solutions insider reconnaissance protection multiple mtd techniques sdn-based mtd solution proposed � � � [22] × × � [23] × × × [24] × × × vi. conclusion and future work in this paper, a protection mechanism against insider reconnaissance traffic has been developed by combining the randomization and diversification mtd approaches inside an sdn-based network along with ids-based detection. the work elaborated the effectiveness of the scheme for two important services, i.e. dns and web. the proposed scheme provides three levels of 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[35] g. f. lyon, nmap network scanning: official nmap project guide to network discovery and security scanning. sunnyvale, ca, usa: insecure. com llc, 2008. microsoft word etasr_v11_n2_pp7033-7040 engineering, technology & applied science research vol. 11, no. 2, 2021, 7033-7040 7033 www.etasr.com deptuła: application of the dependency graph method in the analysis of automatic transmission … application of the dependency graph method in the analysis of automatic transmission gearboxes adam deptuła department of management and production engineering faculty of production engineering and logistics opole university of technology opole, poland a.deptula@po.edu.pl abstract-the current article discusses the use of the dependency graph method to design and analyze automatic transmissions. different goals may be served by modeling an automatic transmission using graphs. the most important of them are: determining the gear ratios for gears and the analysis of speed and acceleration of the rotating elements. game tree-structure methods can be used to analyze the functional schemes of the selected gears. this paper describes the method of generating a system of kinematics equations for signal dependency graphs. this allows the generalization and extension of the algorithmic approach, and also further analyses and syntheses, such as checking the isomorphism of the proposed solutions and determining the validity of the structure and the operational parameters of the analyzed gears. keywords-computational model; computer aided design; optimization; graph theory; mechanical engineering i. introduction a machine as a system is a set of objects (blocks, elements), each of which is described by an appropriate mathematical model with indications of all connections existing between objects. system objects are usually individual devices: heat exchangers, extractors, compressors, etc. nowadays, the use of artificial intelligence, expert systems, or neural networks is increasingly utilized to solve many technical and engineering problems [1]. engineering practice requires a correct assessment of the mathematical model describing a given system by means of variables. models describe a given system with different accuracy. graphs and structural numbers play a role as models of mechanical systems [2-5] and are still systematically developed [6-11]. in addition, there are special stream graphs, e.g. in chemical and process engineering. many optimization methods are used in technical solutions to improve the efficiency of internal combustion and electric vehicles [12, 13]. unlike graphs, dendrite-tree structures do not have cycles, but there may be a different number of initial vertices. therefore, such structures are applicable to variant searching and optimizing the solutions of the designed system [6]. some of the functional requirements are transformed into the structural characteristics and incorporated in the generator as rules of enumeration. the generator enumerates all possible solutions using graph theory and combinatorial analysis. the remaining functional requirements are incorporated in the evaluator as evaluation criteria for the selection of concepts [14]. this results in a class of feasible mechanisms. finally, the most promising candidate is chosen for the product design. the process may be iterated several times until the final product is achieved. this methodology has been successfully applied in the structure synthesis of epicyclic gear trains, automotive transmission mechanisms, variable-stroke engine mechanisms, robotic wrist mechanisms, etc. generally, if a functional requirement can be written in a mathematical form, it should be included in the generator [2]. the current article presents the method of dependence graphs in the analysis of automatic transmission. the present work describes the algorithm of searching and generating parametric trees as outline graphs. the proposed method allows determining the optimal values of teeth, using only the relationships linking transmission elements with their presentation in the form of a graph. this allows a more accurate calculation of the number of teeth and an algorithmic approach to the problem. methods using graphs and structural numbers have long been used in mechanics. many previous works considered the theory of graphs as tools for studying system dynamics, both in the analysis and in the synthesis of complex mechanical systems. in particular, authors in [15, 16] focused on determining the power flow through closed kinematic chains. the circulating power dependency is used to analyze toothed gears. a graph describes the scalar product of the coupled graphs. the transmission system is described using kinematic chains, and the coupled toothed transmission system is described using block diagrams, which enables such systems to be analyzed in n degrees. in addition, from the diagrams (blocks) describing the coupled transmission systems, the authors constructed coupled graphs and pseudo-graphs. by varying the associated values, optimization is performed to minimize the load on a given kinematic chain of the transmission system. this is a different way of using dependency graphs than that described in the present work. the present methodology is based on input and output information (values). the graphs described in the cited works are not subject to decomposition or distribution over decision trees. in seeking optimum decisions (paths) it is desirable to define the properties of the structure in such a way that the nodes represent the sought parameter, and the leaves corresponding author: adam deptuła engineering, technology & applied science research vol. 11, no. 2, 2021, 7033-7040 7034 www.etasr.com deptuła: application of the dependency graph method in the analysis of automatic transmission … determine the output decision that is optimum at a given moment, as a response of the system to a particular change. decisions on the tree structure simulate a certain fictional "game" (mutual interaction) between the decision-maker (the decision taken) and the transmission system (the response to the decision). ii. graphic transmission models the objectives of gear modeling with graphs vary: dynamic analysis, kinematic analysis [4], synthesis [17], structure analysis [18], enumeration [19], optimization of gear sequences, automatic design, etc. are based on the so-called graph grammars. the advantage of modeling gears with graphs is that issues considered using graph models can be solved in an algorithmic manner, which allows the use of computer programs and widely understood integrated decision-making systems in a simple manner. in graph theory, a graph is associated with many other algebraic structures as arrays, matroids, structural numbers, and linear spaces of cutoffs. these objects enable the coding of the transmission structure, which allows the use of advanced artificial intelligence (evolutionary, genetic, or immunological) algorithms. an important advantage of modeling mechanical systems with graphs is that some considerations can be carried out in parallel in the field of mechanics and graph theory [20]. the relevance of the results is based on the transformation of knowledge between these two areas. at present, there is a considerable interest in graphical methods in optimization, and especially in modeling of gears, hydraulic systems, mechanisms, trusses and frames. among the methods of analysis of planetary gears, one can distinguish among others [5, 20-22]. in the case of hsu rules, the graph is built according to the following rules: geometrical dimensions are omitted and the considered kinematic pairs are: rotary, "planet-yoke", and meshing. the contour graph method was discussed in [6, 7, 22, 23] for the analysis of mechanical systems. it is particularly useful for considering mechanisms of various types (so-called planar, crossheads, etc.). in particular, it can be used in the analysis of planetary gears. in the analysis of planetary gears, the contour graph method is used. this method is based on distinguishing a number of subsequent rigid links of mechanisms that form a closed loop, the so-called contour. in particular, [21] concerns only outline graphs and their applications. unlike graphs, dendrite-tree structures do not have cycles, but there may be a different number of initial vertices. therefore, a different approach has been developed as a translation of a directed dependence graph, among others for game-tree structures. this approach is different from the previous literature on parametric automation machines and their applications, related to control systems, operating systems, importance analysis of construction and/or operating parameters, and gear analysis previously modeled using other graph types. various methodologies have been developed for the systematic enumeration of kinematic structures. a thorough understanding of the structural characteristics of a given type of mechanism is critical for the development of an efficient algorithm. during the '80s, some approaches for structural synthesis of kinematic chains were presented. authors in [24] presented a systematic approach for the kinematic analysis of multi degree of freedom robotic bevel-gear trains. in the '00s, authors in [25, 26] presented the structure synthesis of mechanisms. authors in [7] showed the kinematic, power flow, and efficiency analysis of epicyclic gear trains. authors in [27] presented a survey of works connected with the problem of gear modeling by means of versatile graph theory models. more recently, authors in [28] studied the kinematic, static force, power flow, and efficiency analysis of gear trains. other authors researched the topological synthesis of gear trains. the review analysis of the graph application issues in the transmission analysis can include kinematic analysis, torque analysis, power flow analysis, and mechanical efficiency analysis. the general algorithm for gear modeling with graphs can be described as: • selecting a problem for kinematic analysis or synthesis and considering the elements related to it (abstracting). • determining the relationships for the specified elements (e.g. listing kinematic rotational pairs and meshing). • listing the selected subgraphs based on the basic transmission graph and saving the codes. • generating of the equations describing the gearing on the basis of codes – which is an orderly (algorithmic) way and solving the obtained system of equations. iii. analysis of the automatic transmission gearboxes with game-tree structures a. automatic transmission gearboxes modern automatic transmissions are complex devices, consisting of several hundred elements of a mechanical hydraulic system and another several hundred in the electronic module. automatic planetary gearboxes belong to a special type of gearbox. there are several of them, each of which consists of a sun gear with external meshing, satellites, and a crown gear with internal meshing. the specified gear ratio is implemented by braking or connecting a sun wheel or satellites. brakes or clutches of individual planetary gears are controlled by hydraulic valves (transmission oil flow). the gearboxes are characterized by high durability and the ability to instantly change gears [29]. the current work is based on [6] concerning various possible developments of applications of graph methods in the analysis of gears. in particular, in [6] the concepts for describing the model of machine systems data using dependency graphs and signal flow were formulated. among other things, the authors in [30] developed a method for finding the optimal number of teeth without transforming the graph. the algorithm for generating equations and determining the optimal number of teeth is calculated directly from the dependency graph considered as a signal flow graph. this approach is different from other works on the application of the graph method in gear analysis. for example, in [31], the gear analysis uses the davie’s equations and the interdependencies of cylindrical gear alignment. in turn, authors in [32] used hypergraphs to determine the relationship between elements and generate kinematic equations. the use of graph grammars engineering, technology & applied science research vol. 11, no. 2, 2021, 7033-7040 7035 www.etasr.com deptuła: application of the dependency graph method in the analysis of automatic transmission … for the description of graph chains in the description of the gearboxes was used in [28, 33]. this is a different approach from that used in the works discussed above. the construction of contours in a graph begins in the supporting system and passes through successive rotating gear elements, each of which transfers rotary motion to the next. the contour is closed when we return in the analysis to the supporting system. to create a complete graph, all contours must be analyzed. the main goal of kinematic analysis of a toothed gear is to determine the transmission ratio and to identify any surplus gears. the analysis of automatic gearboxes is similar to the analysis of a single planetary gear. during the process of kinematic structure enumeration using graph theory, isomorphism identification of graphs is an important and complicated problem. there are many approaches to detect isomorphic graphs, and these approaches have been largely algorithmic. this path is formed by the corresponding edges of the gear graph. input and output are marked additionally. this path allows the analysis of the sequence of transmission of rotational motion by the subsequent elements of the transmission. in addition, it allows the detection of the socalled redundant elements for the given gear which is currently under consideration. the main purpose of the kinematic analysis of the planetary gear is to determine the kinematic ratio and possibly detect oversized gears. one of the methods of analysis, based on the use of the willis formula for any complex planetary gears, is described in detail in the [34], in which the theory of contour graphs was used for kinematic analysis. this method allowed not only to determine the kinematic ratio, i.e. the angular velocities of all wheels and gear yokes, but also to determine the angular accelerations of rotating gear elements. in addition, redundant (oversized) wheels could be detected when plotting contour graphs. individual gears were implemented using brakes, clutches and backstops (free wheels) as shown in table i [34]. table i. functional matrix of the a4ld gearbox position de (1 2 3 4) 2 nd gear 1 th gear reverse mt cl (− − x x) − − − cl1 (− − − −) x x x b1 (− − − x) − − − fw1 (x x x − ) x x x cl2 (− − x x) − − x cl3 ( x x x x) x x − b2 (− x − −) x − − b3 (− − − −) − x x fw2 (x − − −) − − − the object of the analysis is a complex four-speed automatic transmission with overdrive type a4ld [29, 34]. b. dependency graph and game-tree structures a graph is an ordered pair g = (v, e), in which v is a fine set of elements called the vertices of the graph, and e is a set of ( )( )i , j i , jv v v v v∈ pairs called the edges of the graph. to fully specify the graph, one must also specify the relationship p formed by the individual elements of the set of vertices v (g) and edges e (g). then the graph can be called an ordered three: ( ), ,=g v e p (1) where v is the set of graph vertices, e the set of edges (graph branches), and p is the three-member relationship which meets the following condition: there is such a pair of vertices x, y v∈ for each branch e, such that , ,x e y p∈ . if for branch e exist x,e, y p∈ and w,e,z p∈ then either x=w and y=z or x=y=z. a dependency graph is an ordered pair g=(x, r), in which x is a finite set of elements called vertices of the graph, and r is a set of pairs i j i j ( x ,x )( x ,x x )∈ called the edges of the graph. in the case of parametric graphs, the notation introduced in [34] defines the signs: g=(q, z), where z is a set of pairs ( , )( , ) i j i j z z z z z∈ . the oriented dependency (game) graph shown in figure 1 is composed of a set of vertices q: { }1 2 3 4 5, , , ,=q q q q q q (2) and of set of edges z: { }1 2 3 4 5 6 7, , , , , ,=z z z z z z z z (3) fig. 1. an example of a dependency graph. the path in the g=(q, z) is the edge sequence 1 2 2 3 1 ( , ),( , ),...,( , ) k ki i i i i i z z z z z z − in which each { } 1 2 3 j ji i j , ,...,k ( z ,z ) r − ∈ ∈ and vertices 1 2 ki i i q ,q ,...,q are different pairs. vertex 1i q is called the beginning of the pat, and the top ki q the end of the road. as a result of a graph distribution from the chosen vertex, a tree structure with cycles is obtained in the first step and then, a general game tree structure is obtained. each of them has an appropriate analytical formulation i g + and i g ++ . a game tree structures is a part of the systematic searching method. the algorithm of graph distribution of dependence on parametric structures has been presented, among others, in [35]. the expression describing the degree of inferiority of a given component graph is marked with a pair of parentheses, inside which the expression concerning the given component graph is written. when starting to build an analytical expression representing a graph (figure 1), first the starting vertex of the graph should be determined. in the case of starting the analysis from the initial vertex q1, we get the following expressions: engineering, technology & applied science research vol. 11, no. 2, 2021, 7033-7040 7036 www.etasr.com deptuła: application of the dependency graph method in the analysis of automatic transmission … 0 1 2 3 4 5 5 4 1 1 2 3 3 2 4 1 5 4 1 5 7 1 3 2 1 0 6 4 (1) ( ( ( ( , ( ( ) ) , ) ) ) ) q g q z q z q z q z q z q z q z q + = (4) 0 1 2 3 1 4 5 2 5 4 1 1 2 3 3 2 4 1 5 4 1 5 7 1 4 5 3 5 4 3 2 1 0 6 4 1 5 7 1 (1) ( ( ( ( , ( ( ) ) , ( ( ) ) ) ) ) ) q g q z q z q z q z q z q z q z q z q z q ++ = (5) iv. kinematic analysis of the gear with the use of dependency graphs power is transmitted through the torque converter, h1 yoke, free wheel fw1, cl3 and cl2 clutches, gears 6, 5, 4 and yoke h2 and in parallel through wheels 7, 8, 9 on the output shaft ii (thanks to the fw2 backstop activated), as can be seen in figure 2. the signal flow dependence graph of gears is shown in figure 3. fig. 2. power efficiency diagram for de1 gear. fig. 3. signal dependency graph for de. for the graph model, a system of contour equations of velocity i,i 1−ω , peripheral velocities 1i,i air−ω × , angular i,i 1−ε , tangential , -1i i airε × , and centripetal accelerations 2 i ai,ai 1r +ω ⋅ was generated and can be seen in (69): , 1 ( ) 6,0 5,6 2,5 0, 2 6,0 5,6 4,5 8,7 0,8 4,5 8,7 9,8 5, 2 6,0 5,6 2,5 8,9 0,8 , 1 ( ) 0 0 0 0 0 0 i i i h h h h ai i i i r − −  =   + + + =   + + + + =  + + + =  + + + + =   × =  ∑ ∑ ω ω ω ω ω ω ω ω ω ω ω ω ω ω ω ω ω ω ω ω (6) , 1 ( ) 6 5,6 4 5 2,5 6 5,6 4 4,5 7 8,7 9 9,8 4 4,5 7 8,7 9 9,8 4 5 5, 2 6 5,6 4 5 2,5 9 8,9 0 ( ) 0 0 ( ) 0 ( ) 0 −  × =   × + + × =  × + × + × + × =  × + × + × + + × =  × + + × + × =  ∑ ai i ii h h h r r r r r r r r r r r r r r r r r ω ω ω ω ω ω ω ω ω ω ω ω ω ω (7) 1 6 0 56 25 0 2 6 0 56 45 87 08 45 87 98 5 2 6 0 56 25 89 08 0 0 0 0 0 i,i( i ) , , h , ,h , , , , , , , , ,h , , h , , ,  =   + + + =  + + + + =  + + + =  + + + + =  ∑ ε ε ε ε ε ε ε ε ε ε ε ε ε ε ε ε ε ε ε (8) 2 1 1 6 5 6 4 5 2 5 6 5 6 4 4 5 7 8 7 9 9 8 4 4 5 7 8 7 9 9 8 4 5 5 2 6 9 6 0 9 0 6 5 6 4 5 2 5 9 8 9 0 0 0 0 0 ai i , j i ai ,ai ( i ) , h , , , , , , , , ,h , , , , h , , r r r ( r r ) r r r r r r r ( r r ) i / r ( r r ) r ε ω ε ε ε ε ε ε ε ε ε ε ω ω ε ε ε − +  × − ⋅ =   × + + × =   × + × + × + × =  × + × + × + + × =  = =  × + + × + × = ∑ (9) where 1i,i−ω is the relative angular velocity vector of the element i relatively to the previous element i-1, i,0ω is the vector of the absolute angular velocity of the element (relative to the fixed base), ai oair r= is the radius of the vector of point ai (point a on element i), and , 1 1ai ai ai air r r+ += − , 1i, jε − the vector of relative angular acceleration of the element relative to the previous element i-1. v. application of the signal flow graph method in calculating the number of gear teeth a new approach for the dependency graph can be obtained by using relationships that bind systems with their representation in the form of a dependency graph (in particular in relation to contour graphs). as mentioned above, a graph is an ordered pair g=(v, e), in which v represents its vertices and e its edges. the attached g ) search graph to a regular signal flow graph g is defined by replacing all g graph branches with the attached equivalents (figure 4). fig. 4. signal dependency graph for de1. engineering, technology & applied science research vol. 11, no. 2, 2021, 7033-7040 7037 www.etasr.com deptuła: application of the dependency graph method in the analysis of automatic transmission … a search graph g ) for linear branches is created by reversing the direction of the signal flow. for the non-linear branch described by the function j ijf ( v ,k ) ( ijk -number coefficient) in addition to reversing the direction of the branches, there is also a change in its description from j ijf ( v ,k ) to j ij jf ( v ,k ) / ( v )∂ ∂ , where the derivative is determined at the point vj corresponding to the solution of the graph g, i.e. searching the entire vertex j. this graph definition, which is the equivalent of the search circuit, allows to directly use the search graph method to calculate the sensitivity. the sensitivity of the vo output signal relative to the gain of the linear branch or nonlinear branch stick factor is determined on the basis of the solution of graphs g and g ) in the form of: ( , ) ∂ = ∂ ∂∂ = ∂ ∂ ) ) o i j ij j ijo i ij ij v v v a f v kv v k k (10) the sensitivity determination method applies to both coupled and unidirectional graphs. by minimally changing only the excitation value (e.g. the number of teeth) in the search graph g ) , the method can be adapted to determine the full gradient vector of the objective function [35]. the objective function will be expressed as the sum of squares of differences between the current values of the output signals voi and the set values di: 2 1 1 ( ) ( ) 2 m oi i i e w v d = = ∑ (11) where: 1 2 [ , ,..., ] t n w w w w= (12) the gradient e∇ is obtained as: 1 2 ... n e w e we e w ∂ ∂ ∂ ∂∇ = ∂ ∂ (13) where: 1 ( ) m oi oi i ij j ve v d w w= ∂∂ = − ∂ ∂ ∑ (14) the calculation of the j-th vector component of the gradient consists in the calculation of the derivative output signals voi and multiplying them by the appropriate difference: voi−di. the back propagation algorithm has been developed for use in unidirectional networks. its interpretation and generalization in the form of graphs applies to both directed graphs and recursive networks containing feedback cycles, e.g. a drawing with trees. it should be noted that in the case of unidirectional networks, it is easy to extract successive layers of neurons and search the signal flow between them, while in the dependence graphs this task is more complicated due to the existing cycles (feedback and contours). figure 5 shows an example of the implementation of the search graph. figure 6 shows the signal response for the selected graph vertices. fig. 5. implementation of a search graph for a gear. fig. 6. the signal response for selected graph vertices. the variables (z1, z2, z3, z4, z5, z6) in figure 5 are components of the input vector z. the output of the graph consists of neurons marked by their output signals (y1, y2, y3) and their corresponding set signals d1, d2, d3. when creating an attached g ) (figure 6), the output nodes of the normal graph are extracted, which are now available as input nodes for the g ) graph. input signal values can now be expressed as 1 1 1 y dε = − , 2 2 2 y d= −ε , 3 3 3 y dε = − . for searching, the range of values for the number of teeth searched are assumed as: z1, z2, z3, z4, z5, z6, z7, z8, z9: 1 (0,1,2,...,100),z ∈ 2 (0,1,2,...,100),z ∈ 9 ...... (0,1,2,...,100).z ∈ after steps t, the solution z1(t), z2(t), z3(t) ... is obtained, which can be considered as the solution to the search graph. in the case of engineering, technology & applied science research vol. 11, no. 2, 2021, 7033-7040 7038 www.etasr.com deptuła: application of the dependency graph method in the analysis of automatic transmission … a software solution, a discrete approach is used. in this way, with assumed startup conditions (selection of the initial graph vertex), an iterative string is created that leads to the correct solution. an analytical record of such a string for the initial vertices of graph from figure 6 can be represented by the analytical expressions (15)-(20), where gi is the iterative search string from the initial vertex i. 0 1 7 2 8 3 0 4 6 5 5 6 8 7 7 8 8 0 0 6 6 5 5 4 4 4 7 4 8 7 8 7 6 5 6 7 9 7 6 5 4 0 3 2 1 0 0 0 2 0 0 2 9 8 8 2 4 7 ( ( ( ( ( ( ( , ( ) ) , ( , ( ) ) ) ) , ) ) , ) ) ++ = a a z b h h h g g g g g g g g g g g h g h g g h g g ω ω ω ω ω ω ω ω ω ω ω (15) 0 1 6 2 5 3 8 4 8 5 0 0 6 6 6 5 5 4 4 4 8 0 0 6 6 2 9 7 9 8 8 8 8 7 6 5 4 4 7 4 3 5 2 1 8 8 0 0 9 9 0 0 4 7 8 8 2 ( ( ( ( ( ( , ( ( ( , ) ) , ) ) ) , ( ) ) , ) ) ++ = a b b z h h h g g g g g g g h h g g g g g g g g h ω ω ω ω ω ω ω ω ω ω ω ω (16) 0 1 5 2 8 3 8 4 0 5 6 5 0 5 5 5 4 4 4 8 0 0 6 6 5 5 2 9 6 9 7 8 8 7 6 5 4 3 3 7 3 2 8 8 0 0 9 9 0 0 4 7 8 8 5 1 0 2 ( ( ( ( ( ( ) , ( ( ( , ) ) , ) ) ) , ( ) ) , ) ) a b b z h h h g g g g g g g h h g g g g g g g g h ω ω ω ω ω ω ω ω ω ω ω ω ++ = (17) 0 1 9 2 8 3 0 4 6 5 5 6 7 7 7 9 9 8 8 0 0 6 6 5 5 4 4 4 7 8 8 8 7 8 7 6 5 6 6 5 4 0 3 8 2 1 0 4 8 0 0 2 2 9 0 0 2 9 9 2 9 ( ( ( ( ( ( ( ( ) , ( ) ) , ( , ) ) ) , ) , ) , ) ) ++ = a z b h h h g g g g g g g g g g g g h h g g h g h g ω ω ω ω ω ω ω ω ω ω ω ω (18) a b b ++ 0 1 8 2 0 3 6 4 5 5 8 6 7 z8 8 0 0 6 6 5 5 4 4 4 8 4 7 8 8 7 8 8 8 9 h 8 9 7 6 5 0 0 9 9 2 9 o 0 8 8 5 4 3 0 2 1 0 2 h 2 h 2 g =( g ( w g ( w g ( w g ( w g ( w g ,g g ( w g ( w g ,w g ( h g ( w g ) ,w g ) ) ) , w h ) ) ,w h ) ) ) ) (19) 0 1 0 2 6 3 5 4 8 5 8 5 5 7 0 0 6 6 5 5 4 4 4 8 0 0 4 7 8 8 6 8 7 9 8 8 7 8 6 5 4 5 3 2 0 1 0 9 9 8 8 9 2 0 0 0 0 2 ( ( ( ( ( ( ) , ( ( ( , ( ) ) , ) ) ) , ) ) , ) ) ++ = az b h h h g g g g g g g g g g g g g h g g h h ω ω ω ω ω ω ω ω ω ω ω ω (20) if we have a certain n-complex system, then the vertices of the search graph correspond to the teams in e and the set of arcs. { }1 2 2, ,..., −⊆ nz z z z (21) { }( , ) / ( , )= ∈ × ∈ ⇔i j i j i iu e e e e e e u u tests u in z (22) ultimately, the search graph is a function d g ( e ,u , f )= ) , where d f determines the optimal number of teeth. for a given gear design, there are groups of three gears with the same number of teeth: 1 4 7 2 5 8 3 6 9i : z z z ; ii : z z z ; iii : z z z= = = = = = . figures 7-9 show the examples of the graphical process of finding the optimal number of teeth z1-z9 with the help of computer software. the given values are: number of teeth z1=z4=z7=18, z2=z5=z8=27, module value m=2, input angular speed (after commissioning) ω6,0=377rad/s, input angular acceleration (during the 8s start-up) ԑ6,0=47.1rad/s 2 , output angular velocity ω9,0=153.2r/s, and ԑ9,0=19.15rad/s 2 . the analysis and calculations should be carried out for the other de1, de2, de3, de4 gears and for the reverse gear. in the general notation, the algorithm for generating the optimal number of teeth is presented in figure 10. fig. 7. the process of finding the optimal number for group i. calculated number of teeth n=36. fig. 8. the process of finding the optimal number for group ii. calculated number of teeth n=18. fig. 9. the process of finding the optimal number for group iii. calculated number of teeth n=27. engineering, technology & applied science research vol. 11, no. 2, 2021, 7033-7040 7039 www.etasr.com deptuła: application of the dependency graph method in the analysis of automatic transmission … fig. 10. flowchart of the general optimization algorithm of a transmission system with selection of the appropriate number of teeth. vi. conclusion the graph-based methods of analysis and synthesis of planetary gears provide an alternative for the accomplishing of the tasks in question. the automatic transmission presented in this article was modeled with the use of signal flow graphs. due to the use of the new modeling method, there is a need to analyze the technical risk of such a solution. an element necessary in the risk assessment process is to take into account the requirements of the engineering design methodology. in this regard, it is worth choosing a design methodology that meets the following criteria: • completeness of technical criteria. • adequacy of the set of parameters describing the designed object. the criteria formulated for assessment should be synthetic because this increases the objectivity of assessment of a given solution. designing facilities involves increasing efficiency (to some extent) while reducing the efficiency of another team. determining effectiveness consists in comparing the effects of a given measure with its expenditure. particularly in this respect, it should be ensured that the risk of the adopted boundary standards in the scope of e.g. costs is not exceeded. the current article presents the application of dependency graphs to determine the optimal number of gear teeth for an automatic transmission. each gearbox (automatic or manual planetary gear) can be additionally modeled with hsu graphs [36]. references [1] k. s. belkhir, "intelligent maximum power tracking control for a wind energy system based on magnetic gear generator," engineering, technology & applied science research, vol. 9, no. 4, pp. 4329–4333, aug. 2019, https://doi.org/10.48084/etasr.2851. 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[36] c.-h. hsu, "an analytic methodology for the kinematic synthesis of epicyclic gear mechanisms," journal of mechanical design, vol. 124, no. 3, pp. 574–576, aug. 2002, https://doi.org/10.1115/1.1485094. engineering, technology & applied science research vol. 8, no. 3, 2018, 3038-3040 3038 www.etasr.com zaman et al.: fabrication and characterization of organoclay reinforced polyester based hybrid … fabrication and characterization of organoclay reinforced polyester based hybrid nanocomposite materials noor zaman institute of chemistry shah abdul latif university khairpur, pakistan noorzamanshar@gmail.com shfique ahmed institute of chemistry shah abdul latif university khairpur, pakistan ashafique2010@gmail.com muhammad sanaullah institute of geology university of the punjab lahore, pakistan sana.ullah.geo@pu.edu.pk attique ur rehman institute of geology university of the punjab lahore, pakistan attique786aur@gmail.com abdul raheem shar institute of chemistry shah abdul latif university khairpur, pakistan saifiraheem3863920@gmail.com muhammad ramzan luhur dpt of mechanical engineering quest nawabshah pakistan ramzanluhur@yahoo.com abstract—synthesis and characterization of polyester nanocomposites was conducted in order to fabricate hybrid composite materials of polyester/montmorillonite (mmt). polyester based polymeric nanocomposite materials were synthesized by incorporating mmt nanoclay to produce polyester/mmt hybrid materials. successful efforts were made to fabricate hybrid nanocomposite materials based on matrix (polyester based) and reinforcement (organoclay) through sonication at 6 and 12 hours. synthesized nanocomposite polymers (polyester/mmt) showed different properties when compared to the properties of mmt and polyester, which confirmed the successful fabrication of the desired material. the finest incorporation of polyester with mmt was verified by uvvisible spectrophotometer, fourier tranform-infrared (ftir) and scanning electron microscopy (sem). the disappearance of the si-o characteristic peak was observed in the ftir spectrum justifying the fabrication of the desired composite materials. colored sem images were used to confirm the fine homogenous distribution of organoclay. black sem images showed the matrix and reinforcement together. sem, ftir and uv-visible spectroscopic techniques were used to analyze polyester based nanocomposite materials and organoclay was found randomly distributed in the polymeric matrix whereas on the surface was observed to be mostly uniform. keywords-polyester; nanocomposite; reinforcement; uv-visible spectrophotometer i. introduction nano devices are usually used to describe the structures in which nanomaterials are present [1, 2]. various subfields are included in nanomaterial field which in which studied substances possess exceptional properties arising from their nanoscale sizes [3]. nanoionics and nanoelectronics are associated to nanomaterials with speedy transport of ions. current applications of nanomaterials consist of biosensors, drug delivery and tissue engineering [4].various technologies are now able to produce nanomaterials smaller than 100nm which fell down from predictable solid state silicon methods for manufacturing microprocessors [5, 6]. it is due to nanotechnology that various products have become cheaper, faster and easier [7]. manufacturing and utilizing of nanomaterials on industrial scale may have multiple effects on human health and the environment as recommended by nanotoxicology investigations [8, 9]. composite materials can be produced by adding of two or more component substances which possess different physical and chemical properties, but on combination may give a substance possessing properties combining the ones of their individual constituents. within the ending product constituents remain isolate and discrete. rigidity is generally added by reinforcement which obstructs crack transmission to large extent. extremely high strength is provided by thin fibers. therefore overall properties of composites are progressed by mechanical mixing to the matrix. present study regards uv-visible and ftir spectra of the synthesized hybrid nanocomposite matrix. the synthesized composite will be subjected to sem in order to determine its surface morphology, distribution, compatibility and reinforcement. ii. methods experimental work was conducted to produce hybrid composite materials of polyester synthesis and their characterization. sonicator and centrifuge machine was used for the synthesis of polyester nanocomposite hybrid materials whereas uv-visible spectrophotometer, ftir and sem instruments were used for their characterization which revealed and verified the optimum incorporation of polyester with mmt. a. sam int suc hou 6, wa ver po b. of so wa c. for at ver to mo d. gen rel sho usi acc a. 40 the det b. wa attr am pea in the org pea pea str c. con thr int engineerin www.etasr synthesis of p for the sy mples the solu terval of 3 ho ccessful incorp urs and 12 ho 9, 12 hours. b as white whic rified the suc lyester. sonication it is also kno greater tha onochemistry e aves on chemic centrifuge centrifuge m r the purpose o the bottom wh ry high speed nano-scale l olecular weigh scanning ele better than 1 neral sem mo leased by ato owing the top ing a special cumulating sec i uv-visible s the hybrid c 0nm and the λ e absorbance termined using ftir charac the spectrum ave numbers ributed to the mine –nh2. th ak for the mm polymer matri e peak at 994 ganoclay pres ak broadening aks at 2850.8 retching (figur comparison ultrasonicat ftir spectra nfirm the inc rough the p terestingly, by ng, technology r.com polyester/mm ynthesis of p ution was soni ours until spl poration, clear ours, whereas before ultra-so ch was then ccessful inco own as ultraso an 20khz ar explains the c cal structure [ machines used of separating h hereas lighter centrifuge, fin level as well hts. ectron micros 1nm resolution ode is the dete oms excited pography of t detector, by condary releas iii. result spectroscopic composite solu λmax at was f of solutions g uv-visible cterization m revealed the at 994.4cme peaks of si-o he value of 994 mt organoclay ix through son 4cm-1 should ence in the po g justifies the p 8–2925cm-1 at re 2). of ftir spe tion time a of organocla corporation of presence of y increasing so y & applied sci zaman mt clay comp polyester/mmt icated for 3 to lendid experim r nanofabricat sample collec onication the altered to gr rporation of nication as ult re commonly chemical influe 11, 12, 13]. in the laborat heavy particles particles float ne particles m as molecule cope n is produced ermination of s by electron the sample su scanning the sed electrons. ts and discus measurement ution was scan found to be 34 of different spectrophotom characteristic 1and 3300-32 o stretch vibr 4.4cm-1 is the y. when the m nication at diff appear as th olymer matrix presence of h ttribute to the ectra of organ ay at different f mmt in the the si-o c onication time ience research et al.: fabricat posite t clay com 12 hours with mental results tion was foun ction was done color of the s rey jellylike w organoclay i trasonic freque y employed ences of ultra tories are emp s which settle t at the top [14 may be separate es having dif by sem [15] subsidiary ele beams. an urface is creat sample as w sion ts nned from 250 41nm. at this λ concentrations meter. c peak of organ 200cm-1 whic rations and pr major charact mmt is incorpo ferent time int he confirmati x. above 3400 h-bonding. how −ch3 asymm noclay at diff times of soni e polymeric m characteristic e the si-o int h v tion and chara mposite h time s. for nd at 9 e at 3, ample which in the encies [10]. asound ployed down 4]. by ed out fferent ]. the ctrons image ted by well as 0nm to λmax, s was noclay h are rimary eristic orated tervals ion of 0cm-1, wever metric fferent cation matrix peak. tensity dec mat stud wit and 360 mat fig. mate fig. poly vol. 8, no. 3, 20 acterization of o creases, furthe trix. this tren dies clearly in th the increase d increase of 00cm-1 proves terial. 1. concentra erials fig. 2 3. comparis yester at 6, 9 & 12 018, 3038-3040 organoclay rei er confirming nd is confirm ndicate the di of sonication –oh, nh2 a s the fabrica ation of 10, 20, 2. ftir spect on of ftir spect 2 hours of ultrason inforced polyes the dispersio med justified in ispersion of c time. the dec absorption pe ation of the 30, 40 and 50% trum of mmt org trum of mmt (or nication. 3039 ster based hybr on of clay into n sem. the clay homogen crease of si-o eaks from 340 desired comp % of hybrid com ganoclay rganoclay) incorp rid … o the sem ously peak 00 to posite mposite porated engineering, technology & applied science research vol. 8, no. 3, 2018, 3038-3040 3040 www.etasr.com zaman et al.: fabrication and characterization of organoclay reinforced polyester based hybrid … d. sem characterization sem images of mmts clearly indicate that it is homogeneous and its surface is smooth (figure 4). the white spots on the image show the presence of mmt, however the distribution is clustered and not uniform. black sem image shows the febricula distribution of organoclay over the polyester. the orange and cool blue sem images reveal the fine distribution of organoclay. sem images also show that the surface of mmt and polyester is homogeneous and smooth. therefore these samples are regarded as pure and fine. successful incorporation of organoclay mmt was observed which can be seen from sem images taken at different resolutions. the continuous trend of homogeneity, uniformity and exfoliation is observed at 12 hour of sonication. at 12 hours of sonication the incorporation of mmt organoclay was observed perfectly homogeneous and uniform (figure4). ftir spectra and sem images clearly indicate the incorporation of mmt organoclay regarding our purpose to fabricate hybrid nanocomposite materials based on matrix (polyester based) and inforcement (organic clay) through sonication. (a) (b) (c) (d) fig. 4. (a) sem images taken at different resolutions showing fine and pure mmts. sem images of mmt incorporated polyester at (b) 6 hours, (c) 9 hours and (d) 12 hours of ultra-sonication iv. conclusions regarding our aims and objectives, successful efforts were made to fabricate hybrid nanocomposite materials based on matrix (polyester based) and reinforcement (organic clay) through sonication. the desired nanocomposite hybrid materials were characterized by uv-visible, infra-red and sem spectroscopy. the ftir spectra, confirmed the incorporation of organoclay in the polymeric structure of polyester (the disappearance of si-o characteristic peak justifies the fabrication of desired composite materials). the colored sem images were used to verify the fine homogenous distribution of organoclay whereas black sem images showed the matrix and reinforcement together. the uv-v polymer spectra are different from the ones of the hybrid nanocomposite materials and on organoclay reinforcement the absorbance got decreased and then increased on increasing concentration of the desired composite material. the column and radar graph show the absorbance variations against concentration. references [1] f. allhof, p. lin, d. moore, what is nanotechnology and why does it matter, wiley-blackwell, 2010 [2] s. k. prasad, modern concepts in nanotechnology, discovery publishing house, 2008 [3] r. j. narayan, p. n. kumta, c. sfeir, d. h. lee, d. choi, d. olton, “nanostructured ceramics in medical devices applications and prospects”, jom, vol. 56, no. 10, pp. 38–43, 2004 [4] h. cho, e. pinkhassik, v. david, j. m. stuart, k. a. hasty, “detection of early cartilage damage using targeted nanosomes in a post-traumatic osteoarthritis mouse model”, nanomedicine, vol. 11, no. 4, pp. 939946, 2015 [5] p. kerativitayanan, j. k. carrow, a. k. gaharwar, “nanomaterials for engineering stem cell responses”, advanced healthcare materials, vol. 4, no. 11, pp. 1600–1627, 2015 [6] r. c. shetty, “potential pitfalls of nanotechnology in its applications to medicine: immune incompatibility of nanodevices”, med hypotheses, vol. 65, no. 5, pp. 998–9999, 2005 [7] m. h. kafshgari, n. h. voelcker, f. j. harding, “applications of zerovalent silicon nanostructures in biomedicine”, nanomedicine (lond), vol. 10, no. 16 pp. 2553–2271, 2015 [8] a. cavalcanti, b. shirinzadeh, r. a. freitas, l. c. kretly, “medical nanorobot architecture based on nanobioelectronics”, recent patents on nanotechnology, vol. 1, pp. 1–10, 2007 [9] m. boukallel, m. gauthier, m. dauge, e. piat, j. abadie, “smart microrobots for mechanical cell characterization and cell convoying” , . ieee transactions on biomedical engineering,vol. 54, no. 8, pp. 1536– 1540, 2007 [10] k. s. suslick, “sonochemistry”, science, vol. 247, pp. 1439–1445, 1990 [11] a. s. peshkovsky, s. l. peshkovsky, s. bystryak, “scalable high-power ultrasonic technology for the production of translucent nanoemulsions”, chemical engineering and processing process intensification, vol. 69, pp. 77–82, 2013 [12] a. golmohamadi, “effect of ultrasound frequency on antioxidant activity, total phenolic and anthocyanin content of red raspberry puree”, ultrasonics sonochemistry, vol.20, no. 5, pp. 1316–23, 2013 [13] n. s. deora, n. n. misra, a. deswal, h. n. mishra, p. j. cullen, b. k. tiwari, “ultrasound for improved crystallization in food processing”, food engineering reviews, vol. 5, no. 1, pp. 36-44, 2013 [14] s. r. mikkelsen, e. cortón, bioanalytical chemistry, ch. 13.centrifugation methods, john wiley & sons, pp. 247-267, 2004 [15] j. d. stokes, principles and practice of variable pressure environmental scanning electron microscopy (vp-esem), john wiley & sons, 2008 microsoft word etasr_v11_n5_pp7647-7652 engineering, technology & applied science research vol. 11, no. 5, 2021, 7647-7652 7647 www.etasr.com ali & fawzi: production of light weight foam concrete with sustainable materials production of light weight foam concrete with sustainable materials anowar wakaa ali department of civil engineering college of engineering university of baghdad baghdad, iraq a.ali1901m@coeng.uobghdad.edu.iq nada mahdi fawzi department of civil engineering college of engineering university of baghdad baghdad, iraq nada.aljalawi@coeng.uobaghdad.edu.iq abstractmost of the recent works related to the construction industry in iraq are focused on investigating the validity of local raw materials as alternatives to the imported materials necessary for some practical applications, especially in thermal and sound insulation. this investigation includes the use of limestone dust as partial substitution of cement in combination with foam agent and silica fume to produce sustainable lightweight foam concrete (lwfc). this study consists of two stages. in the first stage, trial mixes were performed to find the optimum dosage of foam agent. limestone dust was used as a partial replacement for cement. chemical analysis and fineness showed great similarity with cement. many concrete mixes were prepared with the content of lime dust powder being 10%, 14%, and 18% as partial replacement of cement by weight. the results indicate that the compressive strength at 7, 28, and 90 days of age was increased for specimens with 14% limestone dust. the best results in compressive strength show an increase at 7 days and a decrease at 28 and 90 days for concrete specimens with 14% limestone dust. in addition, the results show a decrease in dry density for concrete containing 14% lime dust. in the second stage, different percentages of polypropylene fibers were added to the concrete, all mixes, containing a constant content of limestone dust of 14% by weight of cement, were modified using different percentages of polypropylene fibers (1%, 1.5 %, and 2% by volume) and the best percentage was found to be 1%. the addition of polypropylene fibers enhances splitting tensile and flexural strength at 28 days by 14.55% and 55% respectively. keywords-lightweight concrete; foam concrete; sustainable materials; polypropylene fibers ;limestone dust i. introduction one of the disadvantages of conventional concrete is its high selfweight. the density of normal concrete is in the order of 2200 to 2600kg/m 3 . this heavy self-weight makes it, to some extent, an uneconomical structural material. attempts have been made in the past to reduce the self-weight of concrete in order to increase its efficiency. light-weight concrete (lwc) is a concrete whose density varies from 300 to 1850kg/m 3 [1]. there are many advantages of having low density. it helps in the reduction of dead load, increases the progress of building, and lowers haulage and handling costs. the weight of a building on the foundation is an important factor in design, particularly in the case of weak soil and tall structures. in framed structures, the beams and columns have to carry the load of floors and walls. if floors and walls are made of lwc, this will result in considerable cost decrease. another important characteristic of lwc is its relatively low thermal conductivity, a property which improves with decreasing density. in extreme climatic conditions and in the case of buildings where air-conditioning is to be installed the use of lwc with low thermal conductivity will produce considerable advantages from the points of thermal comfort and lower power consumption [2]. on the other hand, the cost of natural resources is increasing constantly, leading to the search for alternatives, such as recycled materials like rice husk ash, sawdust ash [3], silica fume, fly ash, coal bottom ash, limestone dust, marble powder, tile powder, millet husk ash, crumb rubber, etc. also, ordinary portland cement (opc), has been related to several diseases [4-5]. basically, there are three methods for making lwc. the first way is by using porous lightweight aggregates of low apparent specific gravity. this type of concrete is known as lightweight aggregate concrete. the second way is by introducing large voids within the concrete or mortar mass. these voids should be clearly distinguished from the extremely fine voids produced by air entrainment. this type of concrete is variously knows as aerated, cellular, foamed, or gas concrete. thirdly, by omitting the fine aggregates from the mix in such a way that a large number of interstitial voids are present. normal-weight coarse aggregates are generally used. this concrete is called no-fines concrete [2]. based on the purpose of use, there are three types of concrete. the first type is known as non-structural lwc. this is employed mainly for insulation purposes. with low unit weight, seldom exceeding 800kg/m³, its heat insulation value is high and compressive strength is low, from 0.69 to 6.89n/mm 2 [6]. the second type is moderate strength lwc. the use of this concrete requires a fair degree of compressive strength, and thus they fall about midway between the structural and low density concrete. this is sometimes designed as "fill" concrete. compressive strength varies approximately from 6.89 to 17.24n/mm², the insulation values are intermediate, and its density is between 800 to 1300kg/m 3 [7]. the third type is known as structural lwc. this type can be defined as a concrete with full structural efficiency containing aggregates which fall on the other end of corresponding author: anowar wakaa ali engineering, technology & applied science research vol. 11, no. 5, 2021, 7647-7652 7648 www.etasr.com ali & fawzi: production of light weight foam concrete with sustainable materials the scale. its minimum compressive strength is 17.24n/mm² [8]. most of structural lwcs are capable to produce concrete with excessive compressive strength. however, thermal insulation values for structural lwc are substantially better than nwc's. since the unit weight of structural lwc is considerably greater than that of low density concrete, the insulation efficiency is lower [9]. the compressive strength of insulating lwc increases with increasing density and watercement ratio [10]. as for polypropylene fibers, research has shown that they increase concrete's resistance to impact loads [11]. ii. materials and mix proportions a. cement opc type i, manufactured by al kubaisa cement factory, was used in 3.1.1 cement in all the mixes throughout this investigation. the chemical and physical properties of this cement are presented in tables i and ii respectively. the test results indicate that the adopted cement, type n 42.5mpa conforms to the iraqi specification no. 5/2019 [12]. table i. chemical composition of cement limits of [12] result oxide composition 62 lime (cao) 20.1 silica (sio2) 4.24 alumina (al2o3) 4.16 iron oxide (fe2o3) ≤ 2.8% if c3a>3.5 ≤ 2.5% if c3a<3.5 2.15 sulfate (so3) ≤ 5% 3.65 magnesia (mgo) ≤ 4% 3.42 loss on ignition (loi.) ≤ 1.5% 0.71 insoluble residue (ir) main compounds (bogues eq.) of cement 59.02 tricalcium silicate (c3s) 29.65 dicalcium silicate (c2s) 4.21 tricalcium aluminate (c3a) 12.65 tetracalcium aluminoferrite (c4af) table ii. physical properties of cement limits of [12] test result physical properties ≥ 250 m 2 /kg 295 specific surface area, blaine method, (m²/kg). ≥ 45 min ≤ 600 min 1:38 3:45 setting time -initial setting (min) -final setting (min) ≥ 10 n/m 2 ≥ 42.5 n/m 2 20.4 27.5 compressive strength of mortar (mpa) 2-days 28-days ≤ 0.8 0.35 soundness % (autoclave) table iii. grading of fine aggregates limits of [13] passing % of sand sieve size (mm) 100 100 10 90-100 100 4.75 85-100 100 2.36 75-100 100 1.18 60-79 67.57 0.6 12-40 36.73 0.3 0-10 4.33 0.15 b. fine aggregates natural sand supplied from al-ekhadir quarry was used in the concrete mixes. the physical and chemical properties of fine aggregates are shown in tables iii and iv. the test results indicate that the sand grading is within the limits specified by the iraqi standard no. 45/1984 [13] and lies in zone 4. table iv. physical and chemical properties of fine aggregates limits of [13] test results properties of sand 2.16 fineness modulus 2.61 specific gravity 0.8% absorption ≤ 0.5% 0.23 % so3 163.7 kg/m³ dry rodded density ≤ 5.0 2.6 materials finer than 75µm % c. foaming agent foaming agent for cellular concrete astm c796-97 [14] from dr. foamcrete was used to produce lwc by entraining a controlled amount of air bubbles to concrete mix. table v indicates the technical description of the foaming agent used throughout this investigation. table v. technical description of foaming agent (data taken from manufacture production report) liquid appearance yellow color 1.1 specific gravity nil nitrate content all types of portland cement compatibility with cement below 0ºc point water base flash point 3.5 loi d. mixing water water was used for mixing and curing of all concrete mixes conforming to standard iraqi specification 1703 [15]. e. fibers polypropylene fibers bought from belgian fibers manufacturing were used for reinforcement. the specifications and properties of the fibers used throughout the experimental work are illustrated in table vi according to the supplier. table vi. technical properties of polypropylene fibers length of fiber 6 mm diameter 34µm density 0.91gr/cm 3 young modulus 3750mpa melting point >164cº elongation 200% spinning oil 1% moisture max 3% tenacity 30cn/tex alkali resistance excellent conductivity very low engineering, technology & applied science research vol. 11, no. 5, 2021, 7647-7652 7649 www.etasr.com ali & fawzi: production of light weight foam concrete with sustainable materials f. silica fume silica fume commercially known as mega add ms(d) from the chemical company conmix was used as partial replacement of cement throughout this investigation. tables vii and viii illustrate its physical and chemical properties. the results show that the used silica fume satisfies the requirements of [16]. table vii. physical analysis of silica fume physical properties results requirements of [16] color grey percent retained 45µm (no.325) 10 ≤ 10 bulk density (kg/m3) 500 to 700 kg/m3 specific surface are (m²/gm) >15 > 15 specific gravity 2.2 > 105 table viii. chemical composition of silica fume oxides oxide content requirements of [16] sio2 89 min. 85% al2o3 0.4 fe2o3 1.2 mgo 2.5 cao 1.4 so3 1.0 na2o 1.2 g. limestone dust the limestone dust (figure 1) was obtained from a limestone quarry in karbal. it is finely ground in the form of a dust, most of it passing sieve no.100. the chemical composition of the lime dust conforming to [17] is given in table ix. fig. 1. the limestone dust used in the current research. table ix. chemical analysis of limestone dust chemical composition constituent(%) iqs 807 (%) silicon dioxide (sio2) 5.0 5 (max) calcium oxide (cao) 52.2 80 (max) aluminium oxide (al2o3) 0.66 5 (max) ferric oxide (fe2o3) 0.08 5 (max) magnesium oxide (mgo) 0.51 5 (max) sulphur oxide (so3) 0.0 loi 41.49 h. high-range water reducing admixture(hrwra) the hrwra master glenium 51 produced by basf company, satisfying the astm c 494/c 494m-17 [18] was used. the type f was used as concrete superplasticizer. the technical data of this type of admixture are shown in table x. table x. technical description of the superplasticizer properties technical description appearance viscous liquid. color light brown density 1.1kg/lt. ph 6.6 iii. mixing, casting, and curing the mixing procedure is important in order to obtain the required workability and homogeneity. mixing was performed with an electric mixer. the fine aggregates used were in saturated surface dry (ssd) condition. the mixing sequence was the following: the required quantity of dry cement was added to the fine aggregates, the mixing continued for one minute, then the two thirds of the required quantity of water were added to the dry materials. the remaining water and the required quantity of foaming agent were mixed. drill was used and in the head of the drill it was put the so-called mesh or paddle which rotates at high speed, 14000rpm, with a power supply of 220-240v/50hz. then the foam agent was added to mix. the mixer was stopped when a good homogeneous mix was produced. before casting, the mould sides and the base were oiled slightly to prevent mortar sticking to the surfaces. the casting was carried out to two layers. each layer was compacted by using a large vibrating table. the specimens were left under polyethylene sheets in the laboratory for one day after casting, then they were removed from the molds and kept in closed polyethylene bags for 7, 28, and 90 days until testing time. table xi. mix symbols symbols type content mr cube mortar + foam agent+ silica fume+ hrwra ml1 cube mortar + foam agent+ silica fume+ hrwra + lime dust 10% ml2 cube mortar + foam agent+ silica fume+ hrwra + lime dust 14% ml3 cube mortar + foam agent+ silica fume+ hrwra + lime dust 18% mf1 prism mortar + foam agent+ silica fume+ hrwra + lime dust 14% + polypropylene fiber 1% mf2 prism mortar + foam agent+ silica fume+ hrwra + lime dust 14% + polypropylene fibe1.5% mf3 prism mortar + foam agent+ silica fume+ hrwra + lime dust 14% + polypropylene fiber 2% mf4 cylinder mortar + foam agent+ silica fume+ hrwra + lime dust 14% + polypropylene fiber 1% a. mix proportions several mixes were tried in order to find the best mixing of cement to sand, and several ratios were used (1:2.25,1:2,1:3,1:1.5,1:2.5). the optimal ratio of 1:2 was used. experimental mixtures were then made by adding different amounts of foam agent to the water allocated to them (1, 3, and engineering, technology & applied science research vol. 11, no. 5, 2021, 7647-7652 7650 www.etasr.com ali & fawzi: production of light weight foam concrete with sustainable materials 5ml) where it was found that adding 3ml to the water gives the required consistency of the mortar. a reference mixture was made as described in table xii, three limestone dust ratios (10%, 14%, and 18%) were used. the best replacement rate of the weight of cement was found to be 14%. this percentage was used in a mixture in which three different ratios of polypropylene fiber (1%, 1.5%, 2%) were used. it was found that best fiber percentage was (1%). 10% silica fume was used as a partial replacement of cement and 1% of hrwra. table xii. details of concrete mixes mixes cement (kg/m 3 ) sand (kg/m 3 ) w/b silica fume (gm) foam agent (ml) hrwra (ml) fiber (gm) lime dust (gm) mr 300 600 0.4 30 3 1.5 ml1 300 600 0.4 30 3 1.5 30 ml2 300 600 0.4 30 3 1.5 42 ml3 300 600 0.4 30 3 1.5 54 mf1 300 600 0.4 30 3 1.5 17 42 mf2 300 600 0.4 30 3 1.5 26 42 mf3 300 600 0.4 30 3 1.5 34 42 mf4 300 600 0.4 30 3 1.5 17 42 iv. results and discussion a. determination of the consistency of mortar (flow test) the amount of water required for standard consistency of plain mortar or foamed mortar was determined by the flow test. the flow table was prepared according to [19]. the amount of mixing water was sufficient to produce a flow of 110±5mm expressed as a percentage of the original base diameter of the flow mould. the required amounts of water for standard consistency of mortars, expressed in terms of w/c ratio, are shown in table xiii. table xiii. details of the mortar mixes when using 1:2 mix flow 110 ± 5mm w/c foaming agent (ml) 106 0.4 1 112 0.4 3 117 0.4 5 fig. 2. the relationship between foam and flow. b. compressive strength test this test was conducted on 50×50×50mm cubes using an electrical testing machine with a capacity of 2000kn at fixed load according to [20] .the average of three cubes was recorded for each test conducted at ages of 7, 28, and 90 days as shown in table xiv. table xiv. compressive strength results mixes compressive strength (mpa) age (days) 7 28 90 mr 10.45 15.77 20.32 ml1 8.95 12.32 19.93 ml2 10.73 20.86 25.58 ml3 7.41 12.71 17.14 fig. 3. compressive strength at 7, 28, and 90 days. c. dry density test dry density was determined from the dried weight (105 o c for 24 hours) and the measured volume by a ruler. three cubes were measured in each tested sample. the density was found by weighting the specimens and dividing the weight by their measured volume. the dry density was tested at 7, 28, and 90 days as shown in table xv. table xv. dry density results mixes dry density (kg/m 3 ) age (days) 7 28 90 mr 1484 1623 1730 ml1 1478 1601 1679 ml2 1460 1572 1722 ml3 1354 1429 1620 fig. 4. density-age relationship. d. splitting tensile strength test splitting tensile strength test was performed according to [21] in which 100×200mm cylindrical specimens were used. they were tested using an electrical testing machine with a capacity of 2000kn. this test was conducted at 7, 28, and 90 days as shown in table xvi. engineering, technology & applied science research vol. 11, no. 5, 2021, 7647-7652 7651 www.etasr.com ali & fawzi: production of light weight foam concrete with sustainable materials table xvi. splitting tensile strength results splitting tensile strength (mpa) mix age (days) 90 28 7 ml2 2.04 1.65 0.82 2.21 1.89 1.01 ml4 fig. 5. splitting tensile strength at 7, 28, and 90 days. e. flexural strength test the flexural strength was determined according to [22] by using the center point method. the prism-shaped specimens with dimensions of 70×70×380mm were simply supported with 300mm span and were tested at the age of 7, 28, and 90 days as shown in table xvii. table xvii. flexural strength results mix flexural strength(mpa) age (days) 7 28 90 ml2 1.6 2.45 2.94 mf1 3.1 3.8 4.77 mf2 2.33 2.7 3.69 mf3 1.75 2.34 2.83 fig. 6. flexural strength at 7, 28, and 90 days. v. v. conclusion based on the results obtained from the experimental investigation, the following conclusions can be drawn: • the water requirement for lwc is decreased as the percentage of foaming agent increases and the maximum decrease in water for all concrete mixes was 0.4 as a percentage of cement weight. • lwc with 3ml foam agent gave better results of density and compressive strength. • compressive strength, flexural strength, and splitting tensile strength of lwc with limestone dust is slightly lower than those of normal concrete at all ages. • the added foam leads to an increase in the flow. three amounts of foam were added (1, 3, 5ml) and the flow rate was 106, 112, 117mm respectively. three percentages of foam (10%, 14%, and 16%) were added to concrete as partial replacement of cement to produce sustainable lwc. • flexural strength and splitting tensile strength of lwc with 1% polypropylene fiber are higher than those of lwc without fiber at all ages. • the best results were for specimens of lwc having a combination of polypropylene fibers (1%) and limestone dust (14%) due to the further physical effect of micro steel fibers in addition to the effect of limestone dust. the results of this research confirm that we can use limestone dust to produce green lwc and enhance its properties with polypropylene fibers. references [1] f. s. fulton, concrete technology, 7th ed. the portland cement institute, 1994. [2] m. s. shetty and a. k. jain, "chapter 12," in concrete technology: theory and practice, 8th ed., s. chand publishing, 2019. [3] n. bheel, a. w. abro, i. a. shar, a. a. dayo, s. shaikh, and z. h. shaikh, "use of rice husk ash as cementitious material in concrete," engineering, technology & applied science research, vol. 9, no. 3, pp. 4209–4212, jun. 2019, https://doi.org/10.48084/etasr.2746. [4] n. bheel, r. a. abbasi, s. sohu, s. a. abbasi, a. w. abro, and z. h. shaikh, "effect of tile powder used as a cementitious material on the mechanical properties of concrete," engineering, technology & applied science research, vol. 9, no. 5, pp. 4596–4599, oct. 2019, https://doi.org/10.48084/etasr.2994. [5] b. h. a. bakar, a. t. noaman, and h. m. akil, "cumulative effect of crumb rubber and steel fiber on the flexural toughness of concrete," engineering, technology & applied science research, vol. 7, no. 1, pp. 1345–1352, feb. 2017, https://doi.org/10.48084/etasr.854. 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[11] n. aljalawi, "behavior of polypropylene fiber reinforced concrete under impact loads and explosive," journal of the college of engineering of baghdad university, vol. 11, no. 3, pp. 59–68, sep. 2005. [12] iraqi standard no. 5: portland cement. baghdad, iraq: central organizationfor standardization and quality control, 2019. [13] iraqi specification, no. 45 aggregate from natural sources for concrete and construction. baghdad, iraq, 1984. [14] c09 committee, "astm c796 97: standard test method for foaming agents for use in producing cellular concrete using preformed foam," astm international. https://doi.org/10.1520/c0796-97. engineering, technology & applied science research vol. 11, no. 5, 2021, 7647-7652 7652 www.etasr.com ali & fawzi: production of light weight foam concrete with sustainable materials [15] iraqi specification, no .1703: water used in concrete. baghdad, iraq: central organization for standardization and quality control, 1992. [16] c09 committee, "astm c1240 03a: specification for silica fume used in cementitious mixtures," astm international. https://doi.org/ 10.1520/c1240-03a. [17] iraqi standard no. 807: lime used in construction and in the production of building materials. baghdad, iraq: central organization for standardization and quality control, 1982. [18] c09 committee, "astm c494 / c494m 17: standard specification for chemical admixtures for concrete," astm international. https://doi.org/10.1520/c0494_c0494m-17. [19] c01 committee, "astm c230 / c230m 21: standard specification for flow table for use in tests of hydraulic cement," astm international. https://doi.org/10.1520/c0230_c0230m-21. [20] c01 committee, "astm c109 / c109m 16a: standard test method for compressive strength of hydraulic cement mortars (using 2-in. or [50-mm] cube specimens)," astm international. https://doi.org/ 10.1520/c0109_c0109m-16a. [21] c09 committee, "astm c496 / c496m 11: standard test method for splitting tensile strength of cylindrical concrete specimens," astm international. https://doi.org/10.1520/c0496_c0496m-11. [22] c09 committee, "astm c293 / c293m 16: standard test method for flexural strength of concrete (using simple beam with center-point loading)," astm international. https://doi.org/10.1520/ c0293_c0293m-16. microsoft word article-format-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 190-195 190 www.etasr.com fakhouri et al: photoelastic analysis of the vertebral fixation system using different screws… photoelastic analysis of the vertebral fixation system using different screws photoelastic of the vertebral fixation system s. f. fakhouri department of biomechanics, medicine and rehabilitation of the locomotor apparatus, faculty of medicine of ribeirao preto, university of sao paulo, brazil sarahfakhouri@ yahoo.com.br m. m. shimano department of mechanical engineering federal university of triangulo mineiro uberaba, mg, brazil mmmshimano@ gmail.com c. a. araújo laboratory of mechanical projects professor henner alberto gomide school of mechanical engineering of federal university of uberlandia, brazil cleudmar@ mecanica.ufu.br h. l. a defino department of biomechanics, medicine and rehabilitation of the locomotor apparatus faculty of medicine of ribeirao preto, university of sao paulo, brazil hladefi@fmrp.usp.br a. c. shimano department of biomechanics, medicine and rehabilitation of the locomotor apparatus faculty of medicine of ribeirao preto, university of sao paulo, brazil ashimano@fmrp.usp.br abstract— the purpose of this study was to compare using photoelasticity, the internal stresses produced by two types of pedicular screws (synthes™) with three different diameters, when submitted to different pullout strengths. the fringe orders were evaluated around the screws using the tardy compensation method. in all the models analyzed, the shear stress was calculated. results showed that, independently of the applied load, the screw of smaller outer diameter had larger values of shear stress. according to the analysis realized, we observed that the place of highest stress was in the last thread, close to the head of the screws. keywords-photoelasticity; biomechanic, pullout strength, vertebral fixation system i. introduction resistance to the pullout of the pedicular screws is a value disseminated in the literature and a form of demonstrating, in an objective manner, the screws’ resistance to axial load [1-3]. it is one of the most important indices of interest to manufacturers and surgeons [4]. studies have been carried out by various researchers in order to assess the pullout strength and the factors that may influence it [5-9]. however, studies are usually carried out experimentally without a numerical study related to the strength and specific behavior during the screw pullout being available [10]. anchorage or support of the fixing systems by means of the screws is of basic importance to the performance of the biomedical functions of the implants applied to the spine. failure in the stability of the vertebral fixation system may be related to a mechanical failure of the implant or failure in the interface between the bone tissue and the implant [10]. dislocation of the screw in the bone tissue is a clinical problem commonly seen, caused by the pullout strength [11-12]. increase in the fixation and stability of the implant requires more pullout strength, reducing the incidence of failure by dislocation of the screw [13-14]. resistance to the pullout is related to various factors, such as the characteristics of the implants, bone density and insertion torque [4, 8, 15-17]. bone density is one of the most important factors for the fixation of the screw [8, 18]. when pullout strength is applied to the screw, it produces internal stress [19]. thus, photoelasticity has been used in scientific studies in order to determine the distribution of the stress in structural systems through qualitative and quantitative analysis by means of optical elements [20]. photoelastic analysis allows for the observation of the distribution of the stress in the whole structure, enabling a general perception of the behavior of the stress [21]. in this technique, the localization of the stress is observed inside an experimental model through fringes of different colorings. it is possible to infer the amount of deformation resulting from a specific strength comparing the stress observed, with the area which is free from stress. the optical stress law is related to the changes in the index of refraction, due to temporary birefringence, such as the stress state of the material. this relation is expressed in (1) [22,23]: (1) where: fσ is the optical constant of the material in n/mm fringe, � is the order of the fringe, h is the thickness of the model. the purpose of this study was to determine, analyze and compare the internal stress of photoelastic models under the influence of pedicular screws (uss i and uss ii synthes™) h �.fσ σ2σ1 =− etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 190-195 191 www.etasr.com fakhouri et al: photoelastic analysis of the vertebral fixation system using different screws… with difference external diameters, when submitted to pullout stress using plane transmission photoelasticity. ii. material and μethods pedicular screws of the uss i and uss ii system (synthes™) were used in this study as shown in figure 1. the uss i type screws are made of stainless steel, and their external diameter is of 5.0, 6.0 and 7.0 mm (groups g1, g2 and g3, respectively). on the other hand the uss ii type screws are made of titanium, and their outer diameter is of 5.2, 6.2 and 7.0 mm (groups g4, g5 and g6, respectively). fig. 1. uss i (a) and uss ii (b) vertebral fixation screws (synthes™). the photoelastic models were made of flexible photoelastic epoxy resin (polipox™). this resin has a young’s modulus of 4.51 mpa and poisson´s ratio of 0.4 v. for the making of these photoelastic models, two standard teflon™ moulds (polytetrafluorethylene) were used, as they allow for the reproducibility of the measurements and good finishing surface. the moulds were sealed using two acrylic plates, one on each side. between each acrylic plate and the mould, a silicone rubber plate was placed, prepared beforehand, in order for the acrylic plate not to adhere to the photoelastic resin as shown in figure 2. the whole set was fixed with pressure clamps. fig. 2. schematic of the fabrication of photoelastic epoxy resin models. the finished model measured 12 mm in thickness, 51 mm in width and 58 mm in length as shown in figure 3. twelve photoelastic models were made for the study. fig. 3. photoelastic models with screws type uss i (a) and uss ii (b) of 6.0 and 6.2 mm, respectively. these models were previously submitted to evaluation of the presence of residual stress, called “border effect”, before the application of the pullout strength on the screws under analysis. the photoelastic resin showed an optical constant of 0.375 n/mm fringe. this value of the constant was used to calculate the shear stress. a. photoelastic analysis the photoelastic analysis was carried out on a transmission polariscope by means of the application of pullout strength on the screw head, fixed to the photoelastic model. the model was fixed to an adjustable support which was positioned horizontally on the polariscope. a load cell coupled to a signal analyzer was used to measure the stress applied. the stress produced by the screws was assessed qualitatively and quantitatively. b. qualitative analysis in the qualitative analysis of the stress, observation was carried out at the starting point of the fringe orders in the model, the point of higher concentration of stress, the point of most sheer stress and the behavior of the stress distribution by means of the application of the different loads. c. quantitative analysis in the quantitative analysis, the sheer stress was measured, using a pullout strength of 1.4, 1.8, 2.4 e 3.3 kgf, registered by means of the use of a kratos  load cell, with a capacity of 10kgf. notwithstanding the type of the screw, 15 points at 1.5 mm distance around the contour of the screws were analyzed as shown in figure 4. the position of the points was standardized for both the uss i and uss ii type pedicular screws. the estimate for the sheer stress (τ) around the screw was carried out using tardy’s compensation method [22]. the values relating to the optical constant and the thickness of the photoelastic model used in the analysis were 0.375 n/mm fringe and 12.0 mm, respectively. etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 190-195 192 www.etasr.com fakhouri et al: photoelastic analysis of the vertebral fixation system using different screws… fig. 4. schematic of grid used to map showing the fifteen points analyzed in the pedicle screws. (a) uss i; (b) uss ii. iii. results a. qualitative analysis qualitative analysis was carried out on the photoelastic moulds correspondent to g1 to g6. in all groups it was possible to observe that the initial point of the fringe orders and the point of higher concentration were on the first threads of the screw, in the region near to the screw heads. groups g1 to g3 (cylindrical configuration screws) showed higher stress levels on the first threads of the screw than groups g4 to g6 (conical configuration screws). concerning the behavior of the stress distribution, it was possible to verify in all groups that the higher the load applied, the bigger the fringe formation along the body of the screw and consequently the bigger the stress in the most critical area (near the screw head) as shown in figure 5. the results obtained are in accordance with the model, the fixing conditions proposed and the screw dimensions. thus, as the pullout strength rises, stress gets higher, beginning on the first threads of the screw, located near the screw heads. fig. 5. pattern of isochromatic fringe orders obtained in the analysis of pedicle screw type uss i (a) and uss ii (b) with outer diameter of 6.0 mm and 6.2 mm, respectively, applying a load of 3.3 kgf. b. quantitative analysis by means of tardy’s compensation method, the sheer stress (τ) of the uss i type (groups g1, g2 and g3) and uss ii type (groups g4, g5 and g6) pedicular screws were determined, in four load intensities as shown in table 1. table i. mean ± standard deviation of the shear stress of the pedicle screws type uss i and uss ii in four levels of loading. group 1.4 kgf 1.8 kgf 2.4 kgf 3.3kgf uss i (kpa) g1 g2 g3 13.014±3.081 12.360±3.362 11.505±2.753 16.849±2.769 16.696±3.008 15.366±3.365 21.619±3.755 21.413±3.912 20.403±3.704 27.417±5.894 26.810±5.777 25.470±6.001 uss ii (kpa) g4 g5 g6 9.991±4.803 9.127±3.980 8.810±3.995 14.924±4.774 13.750±3.468 13.249±3.713 19.513±5.370 18.248±4.067 17.896±3.781 25.739±6.629 23.760±5.409 22.764±4.676 by means of these tables, it is possible to verify that the averages for the sheer stress of group g1 > g2 > g3, notwithstanding the load applied. the same behavior happens when analyzing using the averages of the sheer stress of group g4 > g5 > g6, notwithstanding the value of the load. group g1 has higher values for general average of sheer stress that group g4, in all the load values applied. the same happens with group g2 and g3 that shows higher average values than group g5 and g6, respectively. thus we have: g1 > g4, g2 > g5 and g3 > g6. iv. discussion the photoelasticity technique was discovered at the beginning of the 20th century and its application in the area of orthopedics and traumatology is still up to date. this line of experimental research has already got various articles published in this field of study, however, there are no scientific reports using this technique in the analysis of components of the vertebral fixation system. photoelasticity has shown itself to be an efficient technique, being able to evaluate in a quick and satisfactory manner the points of higher sheer stress due to the pullout strength. by means of this technique, photoelastic models were made with uss screws cast in the photoelastic resin. these models suggest a simulation of the bone-integrated screw during a chronic post-surgery period, as used in the clinical practice in surgeries with vertebral fixation system. the regular geometry of these photoelastic models allowed the analysis of the screws in vertebral fixation, comparing the outer diameters. in this case, possibly, geometry did not interfere in the results obtained by the photoelastic analysis. in this study, two types of analyses were carried out, a qualitative and a quantitative one. photoelasticity was efficient in the qualitative analysis carried out in this study, as it was possible to visualize, satisfactorily, the points of higher sheer stress around the screw, due to the pullout strength. in the general analysis, it was possible to verify that the initial point of the fringe orders and the most critical region was on the first threads of the screw, near the screw head. it is possible to see etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 190-195 193 www.etasr.com fakhouri et al: photoelastic analysis of the vertebral fixation system using different screws… also, that the shape of the fringe orders in the region of the tips of the screws were also different in the uss i and uss ii type screws. in the uss i type screws the shape of the fringe was pointed, accompanying their respective geometry; whereas on the uss ii type screws, the shape of the fringe was rounded according to their geometry. in the quantitative analysis, four loads were used in the pullout of the screws (1.4, 1.8, 2.4 and 3.3 kgf). for the 1.4 and 1.8 kgf load, the fringe orders formed were smaller, between 0 and 2; with a 2.4 kgf load the fringe orders formed were between 1 and 2 and with the 3.3 kgf load, the fringe orders formed were between 1 and 3. in this manner, the photoelastic models were analyzed using these four loads in order to observe their behavior due to the increase in the number of fringe orders that appeared with the increase of load, due to the increase in stress on the model. thus, with the increase of the pullout strength, the sheer stress was more critical, due to which there is an increase in the tendency of the screw to loosen itself. the strength values applied were low, as they served only to generate the pullout strength of the screw, seeing that the photoelastic epoxy resin has high sensitivity. the progressive increase in the strength values applied was important to observe the behavior of the photoelastic model due to the increase in the number of fringe orders. thus, with the increase in the pullout strength, the sheer stress became more critical and there is a tendency in the loosening of the screw. these conclusions are in accordance with the research carried out by fakhouri et al. [24]. it is necessary to highlight that the analyses of the stress levels in the models are comparative and that the behavior of the result of the stress on the screw and the bone would be similar, disregarding the effect of the bone geometry. the real load pullout values are higher that the values assessed in the photoelastic models, however the behavior of the result of the stress is similar. notwithstanding the value of the load applied, it was possible to verify that the values of the sheer stress in groups g1 and g4 were always higher than groups g2 and g5, which were higher than g3 and g6. when comparing the two types of pedicular screws, the uss ii type, correspondent to groups g4 to g6, showed lower values of sheer stress than the uss i type, correspondent to groups g1 to g3, disregarding the measurement of the outer diameter analyzed. thus, the pedicular screw type uss ii showed better stability and resistance to pullout. the point of the screw which is most susceptible to sheer is the first threads of the screw near the screw head, as it is the point of higher sheer stress. groups g1 to g3 are more susceptible to sheer, as they show more sheer stress in the first threads of the screw than groups g4 to g6. these results may be explained by the geometrical differences (internal, outer diameter, thread distance and height of the screw thread) and screw dimension. it was possible to verify that the uss ii type screws showed a smaller and more homogeneous formation of fringe orders in the region near to the point than the stress distribution observed in the uss i type screws. thus, the region near to the point of the uss ii type screws showed better stability due to a smaller concentration of stress. according to the quantitative analyses carried out on the screws with cylindrical configuration, it was possible to verify that the behavior of the 5.0 mm and the 6.0 mm screws was the most critical. when applying the same strength, higher rigidity means smaller displacement of the screw. rigidity depends on the material which is between the threads of the screw, in this case, the photoelastic resin, which has a much lower elasticity module than that of the bone. the 5.0 mm screw showed a bigger displacement and a smaller rigidity, compared to the 6.0 mm screw due to the outer and internal diameters of each screw of each screw. however, this difference is not so significant because the height of the screw threads and the distance between the screw threads are the same. this explains the fact that, in the graphs, the behavior of the sheer stress is similar in these screws. according to gayet et al. [25], the internal diameter does not have a significant effect in the pullout strength. the bigger the screw thread distance, the smaller the sheer stress between the threads and the bigger the height of the thread, the bigger the pullout strength. thus, the area between the threads is the point that opposes the pullout of the screw. the screws with a conical configuration (g4 to g6) offer more anchorage to the vertebra, demanding a higher pullout strength that the cylindrical configuration screws (g1 to g3) [13, 26]. conical screws present an increase of 17% in the pullout strength when compared to the cylindrical screws [13]. however, some authors did not find any difference in the fixation strength of these two types of screws [1, 27]. according to lill et al. [14], screws with a conical outer design may have inferior properties when compared to the cylindrical ones. notwithstanding the type of screw, the smallest outer diameter measurement is the most susceptible to possible clinical intercurrences, according to the dimensions of the screw and due to the fact that it shows a higher sheer stress value. according to barber et al. [28] and gayet et al. [25], as the outer diameter of the screw increases, the pullout strength also increases and it becomes more difficult to pull out the screw. thus, the conclusions obtained in this study are in accordance with these authors. based on their studies, kwok et al. [1] affirmed that the pullout strength depends on the outer diameter of the screws. the authors assessed the alterations produced in the pullout strength, based on the outer diameters and they observed that an increase from 5.0 to 6.0 mm in the outer diameter of the screw produces an increase of 47% in the pullout strength; an increase from 6.0 to 7.0 mm in the outer diameter of the screw increases in 65% its resistance to pullout and this increase reaches 143%, when increasing the outer diameter of the screw from 5.0 to 7.0 mm. in their study, de coster et al. [29] conclude that the screw thread has an important role in the pullout strength, in which the smaller and finer thread, even being small, generates a pullout effect. barber et al. [28] conclude that the performance of the screw is also influenced by its geometrical variation and that as the diameter of the screw increases, the pullout strength etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 190-195 194 www.etasr.com fakhouri et al: photoelastic analysis of the vertebral fixation system using different screws… also increases. the screw displacement before its fail may be related to the screw thread distance, in which its increase will increase the amount of displacement before the fail. the angulation of the screw has little effect on the pullout strength. these findings were the same as those reached in this study. the results observed in this study show that the higher concentrations of stress generated in the screws with the appliance of pullout strength happened in the first threads of the screw, near the head of the screw, due to the influence of the screw head. this result is in accordance with the study of daftari et al. [30], which, in studies carried out by means of mechanical pullout trials, observed that the diameter of the pilot hole near the screw head represented the most important point in the anchorage. with these studies, the authors suggest that the entrance point of the screw should be the most precise and tight-fitting as possible. v. conclusion photoelasticity showed itself to be an efficient technique, being able to evaluate quickly and satisfactorily the points of higher sheer stress due to pullout strength. in the photoelastic analyses carried out, geometry and the screw dimensions influenced in the results obtained. the pedicular uss ii type screw showed lower values of sheer stress than the uss i type, offering more vertebral anchorage and resisting better to pullout strength. notwithstanding the type of the screw, the one with the smallest outer diameter measurement was, probably, the most susceptible to pullout, as it showed higher values of sheer stress, and due to its geometrical dimensions. in all the analyses carried out, in both types of screws and in the different outer diameter measurements, it was observed that the point of higher concentration of stress was in the first threads of the screw, near the screw head, whatever load was applied. acknowledgements this research was supported by fapesp and capes. references [1] a. w. l. kwok, j. a. finkelstein, t. woodside, t. c. hearn, r. w. hu, “insertional torque and pullout strengths of conical and cylindrical pedicle screw in cadaveric bone”, spine, vol. 21, no. 21, pp. 24292434, 1996. 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[26] a. ono, m. d. brown, l. l. latta, e. l. milne, d. c. holmes, “triangulated pedicle screw construct technique and pull-out strength of conical and cylindrical screws”, journal of spinal disorders, vol. 14, no. 4, pp. 323-329, 2001. etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 190-195 195 www.etasr.com fakhouri et al: photoelastic analysis of the vertebral fixation system using different screws… [27] s. inceoglu, l. ferrara, r. f. mclan, “pedicle screw fixation strength: pullout versus insertional torque”, spine, vol. 4, no. 5, pp. 513-518, 2004. [28] j. w. barber, s. d. boden, t. ganey, w. c. hutton, “biomechanical study of lumbar pedicle screws: does convergence affect axial pullout strength?”, journal of spinal disorders, vol. 11, no. 3, pp. 215-220, 1998. [29] t. a. de coster, d. b. heetderks, d. j. downey, j. s. ferries, w. jones, “optimizing bone screw pullout force”, journal of orthopaedic trauma, vol. 4, no. 2, pp. 169-174, 1990. [30] t. k. daftari, w. c. horton, w. c. hutton, “correlations between screw hole preparation, torque of insertion, and pullout strength for spinal screws”, journal of spinal disorders, vol. 7, no. 2, pp. 139-145, 1994. engineering, technology & applied science research vol. 7, no. 4, 2017, 1850-1854 1850 www.etasr.com elashmawy et al.: heat transfer and fluid flow in naturally ventilated greenhouses heat transfer and fluid flow in naturally ventilated greenhouses mohamed elashmawy dept. of mechanical engineering college of engineering of hail hail city, saudi arabia & engineering science department, faculty of petroleum and mining engineering, suez university, suez, egypt arafat_696@yahoo.com abdullah a. a. a. al-rashed dept. of automotive and marine engineering technology college of technological studies, the public authority for applied education and training, kuwait aaa.alrashed@yahoo.com lioua kolsi dept. of mechanical engineering college of engineering of hail hail city, saudi arabia & unité de recherche de métrologie et des systèmes energétiques, enim, university of monastir, monastir, tunisia lioua_enim@yahoo.fr isam badawy dept. of industrial engineering college of engineering of hail hail city, saudi arabia isam149@gmail.com naim ben ali dept. of industrial engineering college of engineering of hail hail city, saudi arabia naimgi2@yahoo.fr shamas shoukat ali dept. of civil engineering college of engineering of hail hail city, saudi arabia ss.ali@uoh.edu.sa abstract—in this paper, heat transfer and fluid flow in naturally ventilated greenhouses are studied numerically for tow configuration according to the number and positions of the opening. the equations governing the phenomenon are developed using the stream function-vorticity formalism and solved using the finite volume method. the aim of the study is to investigate how buoyancy forces influence airflow and temperature patterns inside the greenhouse. rayleigh number is the main parameter which changes from 103 to 106 and prandtl number is fixed at pr=0.71. results are reported in terms of stream function, isotherms and average nusselt number. it is found that the flow structure is sensitive to the value of rayleigh number and the number of openings. also, that using asymmetric opening positions improve the natural ventilation and facilitate the occurrence of buoyancy induced upward cross-airflow inside the greenhouse. keywords-natural ventilation; open greenhouse,; heat transfer; fluid flow i. introduction ventilation plays a key role in ensuring good climate in a greenhouse and shear effort is conducted to ascertain the ventilation quality as a function of relevant parameters. the most unfavorable condition for greenhouse cooling is due to low wind speed, and natural ventilation is predominantly driven by buoyancy forces. the literature review reveals that previous studies focused on two dimensional ventilation models analysis. however, less research was attributed on the three dimensional characteristics of flow and temperature distribution in the greenhouse. furthermore, the extensive perception of the impact of asymmetric opening position and roof inclination on natural ventilation potential yet to be evaluated. for instance, the pioneer cfd work in [1], represented a 2d distribution of climate inside greenhouses. in [2], authors described the convective cells that appear inside a closed half-model scale mono-span greenhouse and showed that for low rayleigh numbers and during a transient regime, a flow pattern that takes the form of two counter-rotative air loops is initiated, whereas for higher rayleigh numbers in the permanent regime, this pattern is replaced by a single convective loop that takes up the whole volume. in [3], authors conducted 2d simulations of the convective and radiative transfers under night conditions. the researchers revealed that two counter-rotative cells developed inside the shelter and enhanced the homogenization of the temperature distribution. in [4], authors simulated two counter-rotative cells and probed that during the night, the warm air moved up from the ground along the central partition and reached the roof and moved don after cooling. in [5], authors anticipated the ventilation induced by thermal buoyancy in a greenhouse. the greenhouse was equipped with the openings located at the lower part of the roof, just above the gutter. authors compared a configuration with just one opening with the case of double symmetric vents by combining an experimental and a numerical approach. for both cases, the airflow was characterized by a single loop with higher velocities along the walls and ground, while the air was almost at rest at the center of the greenhouse. but in the case of the symmetric vents, one of the two openings played a engineering, technology & applied science research vol. 7, no. 4, 2017, 1850-1854 1851 www.etasr.com elashmawy et al.: heat transfer and fluid flow in naturally ventilated greenhouses dominant role in the air exchanges with the outside environment, and thus resulting in the cooling of the greenhouse. in [6], a single span greenhouse equipped with roof and side openings was considered. for low wind velocities, the results reported that fresh air entered the greenhouse through the side openings, moved horizontally along the ground where air got warmed, and moved up at the center of the building towards the roof openings where air was eliminated. in [7], authors carried out a two-dimensional numerical study of the same greenhouse but included the heat transfer occurring between the ground and the air inside the greenhouse. the researcher figured out that at zero external wind velocity, the qualitatively and quantitatively of velocity and temperature fields are in line with [6]. the capacity of cfd was estimated in [8] to predict greenhouse ventilation performance in order to optimize building design. the authors conducted 2d steady simulations, neglecting buoyancy effects and considering the wind as the main driving force. the study was focused on four configurations of a plastic tunnel greenhouse: (1) side openings only (roll-up type) at the middle of the walls; (2) identical to 1, along with side vents located on the upper part of the wall; (3) identical to 1, coupled with pivoting door type openings; and (4) identical to 1, but with an opening in the middle of the roof. since, the air exchanges per hour are twice as much for case 4 as for case 1, the investigator concluded that the configuration 4 was the most efficient, while configuration 1 turned out to be the least efficient. it was concluded that the velocity patterns inside the greenhouse and the air temperature difference between the inside and outside, in addition to the ventilation rate, must be considered in order to choose the best configuration. moreover, in all of the narrated cases, the temperature distribution follows the airflow patterns with high air temperatures in the greenhouse corners. similar flows were also observed in [9] in a single-span greenhouse with side wall and roof openings. the air renewal inside a multi-span pitched-roof greenhouse compartment was studied in [10] using tracer gas techniques. the aim of this study is to investigate buoyancy-driven natural ventilation inside greenhouse, for two configurations related to number and position of openings, using 2d numerical simulation based on fvm and stream function-vorticity formalism. ii. geometry, mathematical model and numerical method the physical model is presented in figure 1. the considered problem is two-dimensional buoyancy-driven natural ventilation inside greenhouses. two cases are considered according to the number of openings. tbottom of the greenhouse is considered at higher temperature th and all other walls are at cold temperature tc. the thermo-physical properties of the nanofluid are assumed to be constant except for the density variation in the buoyancy term, which is approximated by the boussinesq model. the stream functionvorticity formulation is used to express the governing equations for the laminar and unsteady state natural convection. scaling length, velocity and time by w, α/w and w2/α, and defining dimensionless temperature as    chc ttttt ''/''  , the governing equations in dimensionless stream functionvorticity form are:  vorticity x t ra yxy v x u t                               .prpr 2 2 2 2  (1)  energy                            2 2 2 2 y t x t y t v x t u t t (2)  kinematics               2 2 2 2 yx  (3) the foregoing dimensionless parameters are given as follows: f f   pr and ff f wtgra   . ... 3  the associated initial and boundary conditions for the problem considered are: for 0t : 0       t yx  (everywhere) for 0t : on the horizontal bottom wall: 0    y ; 1t on all other walls: 0    t n at open boundary: 0   x tctin  if 0. vn and 0  outx t if 0. vn local nusselt is given as follows: 0   yy t nu (4) the average values of nusselt number, on the hot wall is expressed by:  w av dxnunu 0 . (5) the governing equations (1)–(3) were discretized using the control-volume-finite-difference described in [11]. the central difference scheme for treating convective terms and the fully implicit procedure to discretize the temporal derivatives are retained. the grid is uniform in both directions with additional nodes on boundaries. the resulting nonlinear algebraic equations are solved using the successive relaxation-iterating scheme. the equation of radiative transfer is solved by repeatedly sweeping. the governing equations are represented by a general differential equation as follows: engineering, technology & applied science research vol. 7, no. 4, 2017, 1850-1854 1852 www.etasr.com elashmawy et al.: heat transfer and fluid flow in naturally ventilated greenhouses        s y v yx u xt                          (6) where  stands for either  or t with: 1 , pr , x t ras    .pr. 1t , 1t , 0ts cold hot open case ii (b) case i (a) fig. 1. studied configurations: (a): case i, (b) case ii. iii. convergence, grid testing and code validation an extensive mesh testing procedure was conducted to guarantee a grid independent solution. five different mesh combinations were used for the case of ra =105 and pr = 0.7. it is found that a grid size of 121x121 ensures an extremely grid independent solution. a time step of 10-4 is retained to carry out all numerical tests and all results are presented for a dimensionless time equal to 2. the solution is considered acceptable when the following convergence criterion is satisfied for each step of time: 51 3,2,1 1 10max max max      nini i n i n i n i tt   (7) a first validation (figure 2) test was made by comparing the present code results for ra = 105 and pr = 0.70 against the numerical simulation of khanafer et al. [12] in the case of differentially heated cavity. it is clear that the present code is in good agreement with other work reported in literature as shown in figure 2. fig. 2. nusselt number versus ra number; comparison with results of khanafer et al [12]. (a) ra = 103 (a) ra = 103 (b) ra = 104 (b) ra = 104 (c) ra = 105 (c) ra = 105 (d) ra = 106 (d) ra = 106 fig. 3. streamlines and velocity vectors profile for different ra; case i (left) and case ii (right) iv. results and discussion figure 3 shows for the two cases the stream function and the velocity profile for different rayleigh numbers. the fluid near the bottom wall is hotter than the fluid near the other walls. a density difference is formed due to this temperature difference. as a result, fluid rises from the heated portion and flows downwards to the cooled walls. for small values rayleigh number the buoyancy effects are not very much sensitive and, therefore, the streamlines are almost circular. it is noticed that for all case the increase of ra causes an intensification of the velocity at the opening and the higher region of the domain. it is shown that for case i the flow structure is perfectly symmetric with tow circulation cells. the position of these cells becomes nearest to the center of the greenhouse by increasing ra. for case ii the flow is more complex due to the non-symmetrical boundary conditions. in fact the flow is characterized by one principal and one secondary circulation engineering, technology & applied science research vol. 7, no. 4, 2017, 1850-1854 1853 www.etasr.com elashmawy et al.: heat transfer and fluid flow in naturally ventilated greenhouses cells. the size the secondary cell reduces by increasing ra due to the increase of the inflow air. (a) ra = 103 (a) ra = 103 (b) ra = 104 (b) ra = 104 (c) ra = 105 (c) ra = 105 (d) ra = 106 (d) ra = 106 fig. 4. temperature field for different ra: case i (left) and case ii (right) figure 4 presents isotherms respectively for cases i and ii. for low rayleigh numbers the conduction mode of heat transfer is dominant to convection and isotherms present a quasi-vertical central stratification. increasing ra isotherms are altered due to enhancement of the flow especially near of the openings and the stratification becomes quasi-horizontal. it is noticed that as the flow structure the isotherms are perfectly symmetric for case i and a dissymmetry is encountered for case ii especially for moderate ra (104 and 105) figure 5 presents the variation of average nusselt number versus ra at the bottom wall for the two cases. the heat transfer for case ii is clearly higher for about 22% due to the higher velocity near to this wall. 5 7 9 11 13 15 17 19 1000 10000 100000 1000000 n u a v ra case i case ii fig. 5. variation of average nusselt number versus ra for cases i and ii v. conclusion study of heat transfer and flow inside greenhouses remains a problem of highly practical interest. a great deal of experimental and numerical studies have been made in an effort to understand the fundamental of the fluid flow involved with the problem and propose practical solutions. through this research work, computational fluid dynamics (cfd) techniques have been used. it was found that in addition to rayleigh number the opening location affect the flow structure and heat transfer. acknowledgment the present work was undertaken within the research project (no: 0150282, 2015), funded by the deanship of scientific research, at the university of hail. this is gratefully acknowledged. nomenclature be bejan number cp specific heat at constant pressure (j/kg. k) g gravitational acceleration (m/s2) k thermal conductivity (w/m.k) n unit vector normal to the wall nu local nusselt number pr prandtl number ra rayleigh number t dimensionless time ( 2/'. lt  ) t dimensionless temperature [ )''/()''( chc tttt  ] ct dimensionless cold temperature (k) ht dimensionless hot temperature (k) engineering, technology & applied science research vol. 7, no. 4, 2017, 1850-1854 1854 www.etasr.com elashmawy et al.: heat transfer and fluid flow in naturally ventilated greenhouses w enclosure width and height x, y, z dimensionless cartesian coordinates greek symbols  thermal diffusivity (m2 /s)  thermal expansion coefficient (1/k)  density (kg/m3)  dynamic viscosity (kg./m.s)  kinematic viscosity (m2/s)  dimensionless stream function  dimensionless vorticity t dimensionless temperature difference subscripts av average x, y, z cartesian coordinates references [1] l. okushima, s. sase, m. nara, “a support system for natural ventilation design of greenhouse based on computational aerodynamics”, acta horticulturae, vol. 248, pp. 129–136, 1989 [2] m. a. lamrani, t. boulard, j. c. roy, a. jaffrin, “airflow and temperature patterns induced in a confined greenhouse”, journal of agricultural engineering research, vol. 78, pp. 75–88, 2001 [3] j. i. montero, p. munoz, a. anton, n. iglesias, “computational fluid dynamic modelling of night-time energy fluxes in unheated greenhouses”, acta horticulturae, vol. 693, pp. 403–410, 2005 [4] p. e. bournet, v. winiarek, g. chassériaux, “coupled energy radiation balance in a closed partitioned glasshouse during night using computational fluid dynamics”, international symposium on greenhouse cooling: methods, technologies and plant response, alméria, spain, 24–27 april, 2006 [5] t. boulard, r. haxaire, m. a. lamrani, j. c. roy, a. jaffrin, “characterization and modelling of the air fluxes induced by natural ventilation in a greenhouse”, journal of agricultural engineering research, vol. 74, pp. 135–144, 1999. [6] s. sase, t. takakura, m. nara, “wind tunnel testing on airflow and temperature distribution of a naturally ventilated greenhouse”, acta horticulturae, vol. 148, pp. 329–336, 1984 [7] a. mistriotis, c. arcidiacono, p. picuno, g. p. a. bot, g. scarasciamugnozza, “computational analysis of ventilation in greenhouses at zero and low-windspeed”, agricultural and forest meteorology, vol. 88, pp. 121–135, 1997 [8] t. bartzanas, c. kittas, “optimisation of greenhouses ventilation performance with computational fluid dynamics”, 2nd southeastern europe fluent users group meeting, bucharest romania, 2001 [9] j. i. montero, g. r. hunt, r. kamaruddin, a. anton, b. j. bailey, “effect of ventilator configuration on wind driven ventilation in a crop protection structure for the tropics”, journal of agricultural engineering research, vol. 80, no. 1, pp. 99–107, 2001 [10] c. kittas, b. draoui, t. boulard, “quantification of the ventilation of a greenhouse with a roof opening”, agricultural and forest meteorology, vol. 77, no. 1, pp. 95–111, 1995 [11] s. v. patankar, numerical heat transfer and fluid flow, hemisphere, mcgraw hill, new york. 1980. [12] k. khanafer, k. vafai, m. lightstone, “buoyancy-driven heat transfer enhancement in a two-dimensional enclosure utilizing nanofluids”, international journal of heat and mass transfer, vol. 46, pp. 3639– 3653, 2003 engineering, technology & applied science research vol. 7, no. 5, 2017, 1987-1995 1987 www.etasr.com soleimani and mazloum: considering facts in optimal transmission expansion planning considering facts in optimal transmission expansion planning koosha soleimani electrical engineering department shahid chamran university of ahvaz ahvaz, iran k-soleimani@stu.scu.ac.ir jalil mazloum electrical engineering department shahid sattari aeronautical university of science and technology tehran, iran abstract—the expansion of power transmission systems is an important part of the expansion of power systems that requires enormous investment costs. since the construction of new transmission lines is very expensive, it is necessary to choose the most efficient expansion plan that ensures system security with a minimal number of new lines. in this paper, the role of flexible ac transmission system (facts) devices in the effective operation and expansion planning of transmission systems is examined. effort was taken to implement a method based on sensitivity analysis to select the optimal number and location of facts devices, lines and other elements of the transmission system. using this method, the transmission expansion plan for a 9 and a 39 bus power system was performed with and without the presence of facts with the use of dpl environment in digsilent software 15.1. results show that the use of these devices reduces the need for new transmission lines and minimizes the investment cost. keywords-transmission; expansion;facts;9 bus; 39 bus; dpl i. introduction in order to provide reliable electrical energy to meet the demand, power grid equipment must have the required capacity and ability and several limiting factors are to be considered [1]. growth in consumer demand may cause the existing electrical grid to be inadequate and thus further research is needed to determine the time of adding new equipment and the actual pieces of equipment needed. expansion planning of electric power system is divided into three major parts including generation expansion planning (gep), transmission expansion planning (tep) and distribution expansion planning (dep). tep must lead to a system that is able to transport power with the necessary quality and reliability and maintain grid constrains in the occurrence of the event [2]. in [3], tep problem by considering consumption-based carbon emission accounting has been analyzed. in [4], a bi-level solving approach is presented. in [5], an approach based on constructive heuristic algorithms (cha) to solve nonlinear tep problems is presented. in [6] a stochastic multi-stage approach is proposed. a review of tep in deregulated environments can be found in [7]. authors in [8] suggested a fuzzy multi-objective optimization model that initially breaks down into several single-objective parts. authors in [9] presented a fuzzy approach. a further investigation on the relationship between the number of states and uncertainty is presented in [10]. authors in [11] have focused also on the economic aspect of tep. in this paper, transmission expansion planning in the absence and presence of facts devices is simulated by digsilent software. backward method is chosen in this paper as an effective approach to determine the optimal number and location of facts devices. ii. transmission expansion planning-tep generally, the purpose of tep is to offer an expansion plan for economic power supply in a way that the reliability of the system can be maintained or improved [12]. if the transmission system is not adequately expanded, the competition, which is one of the main characteristics of the power market, is flawed [13]. many researchers investigated classical and heuristic methods of solving tep [14-18]. tep problems is divided to four main sections: ‘input data’, ‘objective function’, ‘equality and inequality constraints’, and ‘planning criteria’ that are briefly discussed in the following sections. a. input data the input data includes network topology, characteristics of transmission lines and other transmission equipment, cost of power generation, construction costs for new equipment, estimated production and consumption in the period of planning studies [19, 20]. one of the most important input data for tep is estimated consumption in the future. b. the objective function the objective function is a cost function defined by what is important for tep planners. the aim of the objective function is the definition of the priorities of constructions. generally, in tep problems the objective function tries to minimize investment costs. c. equal and inequal constraints they include the restrictions and requirements, mainly technological and economical, which should be considered through tep planning. engineering, technology & applied science research vol. 7, no. 5, 2017, 1987-1995 1988 www.etasr.com soleimani and mazloum: considering facts in optimal transmission expansion planning d. planning criteria they include concepts such as the desired system voltage, thermal stresses, security, stability and short circuit levels. the common purpose of all these criteria is to guarantee the quality and reliability of the transmitted power in both normal and critical operation conditions. in this paper, thermal and voltage criteria are considered simultaneously. i. facts devices tep problem requires extensive costs and studies. therefore, it is better to try to postpone this by performing effective operation of the existing transmission system. production and control of reactive power in power systems is closely related to the tep problem. the usual method for producing reactive power is the installation of serial and parallel capacitors at the demand side. the semiconductor and power electronics industry, proposed the concept of flexible ac transmission systems (facts). using these devices leads to decrease the need for adding new lines and equipment and expands their capability in for short intervals [21]. applying facts devices in power system has many advantages compared to conventional methods of reactive power generation such as fast responding, strict control, and flexible curves. these devices compared to conventional methods have higher installation cost. facts devices such as svc, statcom, sssc and upfc are used to solve the tep problem. several studies have been done on the impact of facts devices in tep. it was shown that studies on how to increase the capacity of the transmission system and prevent excessive develop have been investigated by using the facts devices [22]. problem reports about the transmission systems development in the absence of facts is presented in [23]. facts equipment were introduced as an efficient tool that makes the tep more flexible [24]. ii. backward method to solve tep the backward method falls in the category of sensitivity analysis methods and can be implemented in any given power system by a large variety of software regardless of dimensions. thus, this method has no limitations in its implementation with any analytical software [25] which also means that it is rather faster compared to dynamical methods [25]. in backward method, all possible system elements are assigned an initial value and then by removing one of them at each algorithm’s step, the optimal point is obtained. this algorithm is an efficient tool in solving tep problems. according to this algorithm, at first all the lines are practically added to base power system and so, the primary power system is created. then, each of these lines should be separately removed one after another from primary power system temporarily. after each removal action the remaining terms of system will be examined in normal operation (no) and contingency operation (co) modes (in the event of “n-1” contingency). each time after evaluation of the remaining system, following conditions should be considered:  transmission lines whose removal from the primary system causes the isolation of any bus, cannot be removed.  transmission lines whose removal from the primary system causes the increase of loading in whether no or co, cannot be removed.  transmission lines whose removal from the primary system causes the treat of voltage stability, cannot be removed. each of these constrains leads to the impossibility to remove part of the lines in each stage. among the set of lines whose elimination did not conflict with any issues mentioned above, removal priorities are determined by the objective function. the same procedure will be repeated with each step. by removing each hypothetical line, the objective function corresponding to remaining lines is calculated in each stage. lines with smaller objective function value have priority to be removed from the primary system. this procedure is repeated among stages until the removal of any line in reduced power system leads to violation of at least one of these three constrains. in this stage, the developed power system is obtained at minimal investment cost which guarantees essential reliability of power system. iii. implementation of the proposed method in this paper, the backward method used to solve tep is a semi-dynamic method. it has been implemented on 9-bus and ieee-39-bus power systems. implementation of the objective function and constraints is achieved by using loop in loop dpl programming in digsilent software. implementing the proposed approach requires close scrutiny of buses voltage value, current flux of lines, etc, in normal operation and critical conditions (n-1). in reviewing the critical operation mode, it is necessary after removing each line to analyze parameters corresponding to the remaining elements. this procedure should be carried out through loop in loop dpl programming so that after removing each line the remaining parameters can be analyzed accurately. since the 9-bus standard system has a symmetric structure in comparison with other standard systems, the possibility of having equal construction cost for any lines is more than any other systems. in this paper, at first the transmission expansion of 9-bus system is examined, considering the costs of few lines are equal. in this particular case, the priority of construction is with a line or set of lines which balanced the power flow in no mode. for this purpose, through a series of lines with the same cost at each stage, loading of all remaining lines in no mode are evaluated. the line or set of lines whose construction leads to smaller amount of standard deviation corresponding to the loading of all lines in the system, and thereby more balanced power flow and reduced depreciation, has the priority and so will be constructed. the objective function and constraints of the proposed method are presented below. it should be noted that in all equations the loss of system is neglected. the objective function (when the line ‘t’ is removed):   1 ( ) . . ( ), ,r r x n f x c r l p x cr l o s s to ta l f a c t s to ta l     (1) 0 1  where: engineering, technology & applied science research vol. 7, no. 5, 2017, 1987-1995 1989 www.etasr.com soleimani and mazloum: considering facts in optimal transmission expansion planning n is the number of all candidates in each step after removing the line x, c(r) is total cost of investment for candidate r per km, lr is length of candidate line r [km], ploss, total(x) is the total real power losses in the power system after elimination the line x [mw] and cfacts, total is total cost of investment for construction facts device in each case. the α is used when the cost of two or more capable lines for installing are equal. the dimension of it is $/mw. the equations that describe the model have been represented in following.  power balance equations active power: no: i iij g d p p p  (2) co: i co co ij i dp p p  (3) reactive power: no: i iij g d q q q  (4) co: i co co ij i dq q q  (5) where: pij is active power flow in the line ij from the bus i, pgi is active power generated at bus i, pdi is active power consumed at bus i, qij is reactive power flow in the line ij from the bus i, qgi is reactive power generated at bus i and qdi is reactive power consumed at bus i.  thermal capacity constraints no: 2 2 ,nij ij l ij p q s        (6) co: 2 2 ,n co co ij ij l ijp q s        (7) where sln,ij is the nominal thermal capacity of the existing line between bus i and j.  voltage constraints no: min . , 0.95 pu l iv  (8) co: max . , 1.05 pu l iv  (9) where min ,vl i and max ,vl i are the minimum and maximum voltage amplitude in both no and co mode at the bus i, respectively.  frequency stability constraint : 0 , 2 ij ij ij p i         (10) where δij is the voltage angle deviation between bus i and j. mentioned procedure is applied once at the absence and another at the presence of facts in series and in parallel and the results of these two modes are compared. the planned 6.5 % annual growth in consumption for 20 years in a 9-bus system is divided to two 10-year periods. so that after the first 10 years the growth of production and consumption is 188 % and at the end of 20 years it will be equal to 352 % of the current value. then this method is applied to the ieee-39-bus power system in a 16-year period divided into two periods with a 6.5 % annual growth in consumption. in both 9 and 39 power systems, growth in consumption is uneven. construction of several power plants in several buses is also taken into consideration. also, the prices shown in the following content of this paper is the today’s equivalent of prices with interest rate of 10%. in relation to technical limitations of installing facts devices, it should be noted one of the undesirable impacts of facts devices on power system is the improper effects on distance relays existing in [26]. depending on mentioned distance relay, above undesirable effect may cause mistakes in diagnosis of fault location in some of distance relays. it is assumed in this paper that the aforementioned technical limitations force us to implement facts devices in particular buses and lines in power system, and not in all of them [27]. it is assumed according to mentioned technical limitation in 9-bus power system, buses 5 and 8, and lines 2-8 are capable of installing facts devices. also in 39-bus power system buses 4, 7, 12, 15 and 27, and lines 5, 7, 15, 25 and 32 are capable of installing facts devices. all calculated costs are in usd. iv. simulation results a. implementation on 9-bus power system figure 1 shows the basic system and figure 2 shows the primary system for the expansion planning. corrugated lines in figure 2 indicate the candidate lines for expansion of the power system. fig. 1. basic system 9-bus system engineering, technology & applied science research vol. 7, no. 5, 2017, 1987-1995 1990 www.etasr.com soleimani and mazloum: considering facts in optimal transmission expansion planning fig. 2. primary system for the expansion planning 1) tep without facts devices a) first expansion plan-no facts devices voltage violations and expanded transmission system at the end of first expansion plan is shown in figure 3. in this expansion, a total of 260 km of new 230 kv line is to be constructed. according to the loads and basic power system transformers, a 300 mva transformer in bus 1 and two 100 mva transformers in buses 2 and 3 should be added. b) second expansion with facts devices in this expansion, a total of 200 km of new 230 kv line is necessary to be constructed according to the loads and basic power system transformers, a 300 mva transformer in bus 1 and two 200 mva transformers in buses 2 and 3 should be added. 2) considering svc in tep results for optimal locating of svc using backward method is given in table i. expanded transmission system at the end of first expansion plan is shown in figure 5. a) first expansion plan considering svc the total cost of facts devices that have been constructed is 12 million. in this expansion, a total of 180 km of new 230 kv line is necessary to be constructed. according to the loads and basic power system transformers, a 200 mva transformer in bus 1 and two 100 mva transformers in buses 2 and 3 should be added. b) second expansion plan considering svc expanded transmission system at the end of second expansion plan is shown in figure 6. in this expansion, a total of 190 km of new 230 kv line is necessary to be constructed . according to the loads and basic power system transformers, a 300 mva transformer in bus 1 and two 200 mva transformers in buses 2 and 3 should be added. 3) considering statcom in tep results for optimal locating of statcom using backward method is given in table ii. fig. 3. expanded transmission system at the end of first expansion plan fig. 4. expanded transmission system at the end of second expansion plan fig. 5. expanded transmission system at the end of first expansion plan engineering, technology & applied science research vol. 7, no. 5, 2017, 1987-1995 1991 www.etasr.com soleimani and mazloum: considering facts in optimal transmission expansion planning table i. optimal location of svc using backward method in 9-bus power system. total cost total cost of second expansion total cost of first expansion location of svc 25972 187 bus 5 34472 272 bus 8 fig. 6. expanded transmission system at the end of second expansion plan table ii. optimal location of statcom using backward method in 9-bus power system total cost total cost of second expansion total cost of first expansion location of statcom 265 71 194 bus 5 350 71 279 bus 8 a) first expansion plan considering statcom expanded transmission system at the end of first expansion plan is shown in figure 7. the total cost of facts devices to be constructed is 20 million. in this expansion, a total of 180 km of new 230 kv line was necessary to construct . according to the loads and basic power system transformers, three 100 mva transformer in buses 1, 2 and 3 should be added. a) second expansion plan considering statcom expanded transmission system at the end of second expansion plan is shown in figure 8. in this expansion, a total of 190 km of new 230 kv line is necessary to be constructed. according to the loads and basic power system transformers, just two 200 mva transformer in buses 2 and 3 should be added and first transformer not to need for extending. 4) considering sssc in tep results for optimal locating of sssc using backward method is given in table iii. a) first expansion plan considering sssc expanded transmission system at the end of first expansion plan is shown in figure 9. the total cost of facts been constructed is 30 million. in this expansion, a total of 180 km of new 230 kv line is necessary to be constructed. according to the loads and basic power system transformers, a 400 mva transformer in bus 1 and two 100 mva transformers in buses 2 and 3 should be added. b) second expansion plan considering sssc expanded transmission system at the end of second expansion plan is shown in figure 10. in this expansion, a total of 110 km of new 230 kv line is necessary to be constructed . according to the loads and basic power system transformers, a 400 mva transformer in bus 1 and two 200 mva transformers in buses 2 and 3 should be added. fig. 7. expanded transmission system at the end of first expansion plan fig. 8. expanded transmission system at the end of second expansion plan table iii. optimal location of sssc using backward method in 9-bus power system total cost total cost of second expansion total cost of first expansion location of sssc 384.573 311.5l2 383.543.5 340l3 33643.5 292.5l4 33643.5 292.5l5 33643.5 292.5l6 250.543.5 207l8 5) considering upfc in tep results for optimal locating of upfc using backward method is given in table iv. optimal location of upfc was acquired by using backward method in the 9-bus power system. a) first expansion plan considering upfc expanded transmission system at the end of first expansion plan is shown in figure 11. the total cost of facts been engineering, technology & applied science research vol. 7, no. 5, 2017, 1987-1995 1992 www.etasr.com soleimani and mazloum: considering facts in optimal transmission expansion planning constructed is 40 million. in this expansion, a total of 180 km of new 230 kv line was necessary to construct. according to the loads and basic power system transformers, a 400 mva transformer in bus 1 and two 100 mva transformers in buses 2 and 3 should be added. fig. 9. expanded transmission system at the end of second expansion plan fig. 10. expanded transmission system at the end of second expansion plan fig. 11. expanded transmission system at the end of first expansion plan b) second expansion plan considering upfc expanded transmission system at the end of second expansion plan is shown in figure 12. in this expansion, a total of 110 km of new 230 kv line is necessary to construct . according to the loads and basic power system transformers, a 400 mva transformer in bus 1 and two 200 mva transformers in buses 2 and 3 should be added. overview of lines that should be constructed in various states of expansion is shown in table v. according to the results presented in table v, the devices include the series portion having a greater impact in reducing the need for construction of new lines on the power system. the occurrence indicated above reasons that it is possible to control the real and reactive power flow in the line containing a series of facts in order to effectively reach the desired size and angle of voltage. however, about devices that only include a parallel section, bus voltage measurements controlled until the injection of reactive power must be within the limits of their capacity otherwise they are unable to keep the voltage above the set value. following overview of power system total losses in different states of expansion is given in table vi. according to table vi, by considering facts devices in transmission system expansion planning, losses in expanded system are not decreased and in some cases, are increased. the current equivalent to the total cost of system expansion in each of the scenarios shown in figure 13. fig. 12. expanded transmission system at the end of second expansion plan table iv. optimal location of updfc using backward method total cost total cost of second expansion total cost of first expansion location of upfc series portion parallel portion 350 47.5 302.5 l4 bus 5 350 47.5 302.5 l5 260.5 43.5 217 l8 398.5 77 321.5 l2 bus 8 397.5 47.5 350 l3 350 47.5 302.5 l5 table v. lines that should be constructed in various states of expansion second expansion first expansion tep l2 – l5 l4 – l6 – l8 lack of facts l2 – l8 l4 – l6 considering svc l2 – l8 l4 – l6 considering statcom l2 l4 – l6 considering sssc l2 l4 – l6 considering upfc engineering, technology & applied science research vol. 7, no. 5, 2017, 1987-1995 1993 www.etasr.com soleimani and mazloum: considering facts in optimal transmission expansion planning table vi. total real and reactive power losses in the power system in the various states of expansion second expansion first expansion tep active losses (mw) reactive losses (mvar) active losses (mw) reactive losses (mvar) 44.12 279.31 16.55 402.27 no facts 44.32 271.84 16.58 102.9 svc 43.49 267.65 16.32 103.7 statcom 62.73 303.33 20.84 111.33 sssc 63.64 303.66 20.88 111.4 upfc fig. 13. overview of current equivalent to the amount of investment required for the expansion of the transmission section of 9 bus power system in different states. b. implementation of proposed method on 39-bus power system after the desired results were achieved in the previous for bus 9 power system, the proposed method was evaluated on the 39-bus power system overviewed in figure 14. planned 16year horizon is divided in two 8-year periods (first and second expansion plans). the results of the implementation of the proposed algorithm on power system bus 39 are shown below. 1) tep in the case of lack of facts devices for 39 bus power system. a) first expansion plan-no facts devices in this expansion, a total of 571 km of new 345 kv line is necessary to construct . in the expansion plan, it is necessary to expand a total of about 7100 mva in the transformer section. according to the results, the overall cost of the first expansion plan is 1026 million. b) second expansion with facts devices in this expansion, a total of 906 km of new 345 kv line is necessary to construct . in the expansion plan, it is necessary to expand a total of about 9400 mva done in the transformer section. the total cost of the second plan was 1617 million. the equivalent of today’s (with an interest rate of 10%) 754 million. today's equivalent of the sum of investments during the first and second expansion plans is 1.78 billion. 2) considering svc in tep a) the first expansion plan considering svc due to technical limitations the possibility of setting up to five svc devices in bus 4, 7, 12, 15 and 27 was assumed. it is important to optimize the number and location of the svc candidates to minimize the cost of the expansion. the locating of svc devices was done by using the proposed backward method and the steps of the process are given in table vii. it should be noted that during the 3rd stage of expansion the elimination of candidate 7 compared to the elimination of candidate 27 lead to 5mw smaller real power losses, so that's why the elimination of candidate 7 is a top priority. therefore, the optimal location in the first expansion plan is the construction of two svc in buses 12 and 15. in this expansion, a total of 489 km of new 345 kv line is necessary to construct. in the expansion plan, it is necessary to expand a total of about 5500 mva in the transformer section. in this plan, the total cost of facts devices has been 40 million. the total cost of the first expansion plan including the total cost of facts devices is 904 million. fig. 14. basic power system of 39 bus system table vii. locating of svc devices using backward method in first expansion plan stage eliminated candidate (svc) remaining candidates (svc) total cost for first expansion plan [m$] 1 initial state 4-7-12-15-27 945 2 4 7-12-15-27 928 7 4-12-15-27 933 12 4-7-15-27 957 15 4-7-12-27 991 27 4-7-12-15 933 3 7 12-15-27 916 12 7-15-27 978 15 7-12-27 974 27 7-12-15 916 4 12 15-27 928 15 12-27 962 27 12-15 904 5 15 12 950 12 15 916 6 15 no candidate 1026 b) the second expansion plan considering svc results for optimal locating of svc using backward method are given in table viii. engineering, technology & applied science research vol. 7, no. 5, 2017, 1987-1995 1994 www.etasr.com soleimani and mazloum: considering facts in optimal transmission expansion planning table viii. locating of svc devices using backward method in second expansion plan stage eliminated candidate (svc) remaining candidate (svc) total cost for first expansion plan [m$] 1 initial state 4-7-27 1632 2 4 7-27 1615 7 4-27 1620 27 4-7 1620 3 7 27 1608 27 7 1603 4 7 no candidate 1591 as result, none of the establishment of remaining svcs (candidates) cost will be reduced. so, the most economical mode of the second expansion plan, is not adding any more svcs to the svcs built in the first expansion. in this expansion, a total of 895 km of new 345 kv line was necessary to construct. it was necessary to expand a total of about 9000 mva in the transformer section. the total cost of the second plan was 1591 million. the equivalent of today’s (with an interest rate of 10%) of 742 million. today's equivalent of the investment sum during the first and second expansion plans was 1.646 billion. 3) considering sssc in tep a) first expansion plan considering sssc assuming the possibility that due to technical limitations, up to five sssc devices in lines 5, 7, 15, 25 and 32 could be set up. results for optimal locating of ssscs by using the backward method are given in table ix. thus, the optimal state in the first expansion plan, will be the construction of three sssc devices, in lines 5, 15 and 25. mentioned lines are between the buses 23-21, 19-15 and 29-24 respectively. in this expansion, a total of 398 km of new 345 kv line are necessary to construct. in the expansion plan, it is necessary to expand a total of about 6400 mva in the transformer section. the total cost of facts constructed was 90 million. the total cost of the first expansion plan including the total cost of facts was 825 million. table ix. locating of sssc devices using backward method in first expansion plan stage eliminated candidate (sssc) remaining candidates (sssc) total cost for first expansion plan [m$] 1 initial state 5-7-15-25-32 885 2 5 7-15-25-32 957 7 5-15-25-32 861 15 5-7-25-32 953 25 5-7-15-32 957 32 5-7-15-25 855 3 5 7-15-25 876 7 5-15-25 825 15 5-7-25 876 25 5-7-15 890 4 5 15-25 908 15 5-25 897 25 5-15 908 5 5 25 1056 25 5 1059 6 25 no candidate 1026 b) second expansion plan considering sssc results for optimal locating of sssc by using the backward method are given in table x. based on the results obtained, the optimal mode corresponding to the construction of a new sssc device will be in line 32 (between buses 6 and 8). in this expansion, a total of 528 km of new 345 kv line is necessary to construct. in the expansion plan, it is necessary to expand a total of about 9800 mva in the transformer section. the total cost of facts devices was 30 million. the total cost of the second plan was 961 million. the today’s equivalent of (with an interest rate of 10%) 448 million. today's equivalent of the sum of investments during the first and second expansion plans, is 1.273 billion. comparison of the costs of today's equivalent of total investments in various states of expansion (lack of facts, considering svc and sssc) for 39-bus power system is shown in figure 15. according to the results shown in figure 15, by the construction of two svc devices during the first eight years, and not adding devices during the second eight year period, the total economic savings of 134 million will be achieved. however, with the construction of three sssc devices during the first eight years, and the construction of one sssc during the second eight years, the total savings will rise up to 507 million. in addition to the above, by the increased reduction of lines, the occurrence probability occurrence of the undesirable n-1 contingency will also be reduced. table x. locating of sssc devices using backward method in second expansion plan stage eliminated candidate (sssc) remaining candidates (sssc) total cost for first expansion plan [m$] 1 initial state 7-32 991 2 7 32 961 32 7 115 3 32 no candidate 1117 fig. 15. today's equivalent of the total investment costs of the transmission section of 39-bus power system v. conclusion including facts devices in transmission system expansion planning leads to a more effective operation of the power system which results to a significant reduction in investment costs. series facts devices (sssc and upfc) seem to provide the best results due to the real power and reactive power flow control in line including the series portion of these devices. the optimal expansion of the transmission engineering, technology & applied science research vol. 7, no. 5, 2017, 1987-1995 1995 www.etasr.com soleimani and mazloum: considering facts in optimal transmission expansion planning system with the use of facts sometimes increases the need to expand the transformer sections but it is desirable because it is associated with a sharp decline of total costs in line constructions. however, a certain limit to this trade-off is to be considered. determining the optimal number and location of facts devices is essential for the optimization. this paper focuses on implementing a method based on sensitivity analysis to select the optimal number and location of facts devices, lines and other elements of the transmission system. the method was employed in a 9 and a 39 bus power system and results are shown and discussed. references [1] a. rouhani, s. h. hosseini, m. raoofat, “composite generation and transmission expansion planning considering distributed generation”, international journal of electrical power & energy systems, vol. 62, no. 1, pp. 792-805, 2014 [2] r. hemmati, r. a. hooshmand, a. khodabakhshian, “comprehensive review of generation and transmission expansion planning”, iet generation, transmission and distribution, vol. 7, no. 9, pp. 955–964, 2013 [3] y. sun, c. kang, q. xia, q. chen, n. zhang, y. cheng, “analysis of transmission expansion planning considering consumption-based carbon emission accounting”, applied energy, , vol. 193, pp. 232–242, 2017 [4] m. asensio, g. muñoz-delgado, j. contreras, “a bi-level approach to distribution network and renewable energy expansion planning 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b. human, and r.c. peterson, electric power planning, university of washington, 1998 [20] h. abdi, transmission expansion planning based on competitive electricity market, phd thesis, tarbiat modares university, 2006 [21] a. rouhani, m. r. safari tirtashi, r. noroozian, “combined design of pss and statcom controllers for power system stability enhancement”, journal of power electronics, vol. 11, no. 5, pp. 734-742, 2011 [22] r. a. hooshmand, m. banejad, g. isazadeh, “management of power flow of transmission lines in disturbed conditions using upfc”, australian universities power engineering conference, australia, 2007 [23] g. a. blanco, optimal transmission expansion planning with facts, in: electrical engineering, national university of san juan, argentina, 2010 [24] g. a. blanco, f. g. olsina, o. a. ojeda, f. f. garces. “transmission expansion planning under uncertainty: the role of facts in providing strategic flexibility”, ieee power tech, bucharest, 2009 [25] h.seifi, m. s. sepasian, electric power system planning, springer berlin heidelberg, pp.144-146, 2011 [26] m. arun bhaskar, a. indhirani, “impact of facts devices on distance protection in transmission system”, ieee national conference on emerging trends in new & renewable energy sources and energy management, chennai, pp. 52-58, 2014 [27] k. satyanarayana, b. k. v. prasad, k. saikrishna, “effect of series facts devices on distance protection”, international conference on sustainable energy and intelligent systems, pp. 36-41, 2011 microsoft word etasr_v12_n2_pp8241-8247 engineering, technology & applied science research vol. 12, no. 2, 2022, 8241-8247 8241 www.etasr.com maddah et al.: predictive regression models for the compressive strength of fly ash-based alkali… predictive regression models for the compressive strength of fly ash-based alkali-activated cementitious materials via machine learning hisham a. maddah department of chemical engineering king abdulaziz university rabigh jeddah, saudi arabia hmaddah@kau.edu.sa marwan kheimi department of civil engineering king abdulaziz university rabigh jeddah, saudi arabia mmkheimi@kau.edu.sa mahmoud abo el-wafa department of civil engineering king abdulaziz university rabigh jeddah, saudi arabia masayed@kau.edu.sa received: 22 december 2021 | revised: 8 january 2022 and 13 january 2022 | accepted: 18 january 2022 abstract-fly ash powders produced from pulverized carbon are a promising renewable and sustainable replacement for ordinary portland cement (opc) in concrete. however, quantifying the desired compressive strength threshold requires defining the ratio of fly ash (fa) to fine aggregates (s). this study presents two novel machine learning models to predict the mechanical properties of fa-based alkali-activated cementitious materials (aacms) using supervised regressors. the two models, slr and mgsvm, showed high prediction accuracy (~95%) based on raw compressive strength training datasets from aacms with mixed proportions of fa/s (0, 5, 10, 15, 20, 25, and 30%) for 28 days of curing. maximum compressive strength of ~67.5mp was observed at approximately 20% fa/s (spline interpolation), suggesting the attainment of high mechanical stability. having more than 30% fa/s indicates a high probability of recovering the original strength of 61mpa for pristine aacms. the nonlinear stress or strain patterns against fa/s confirmed the applicability of stress-strain relationships and elasticity laws. the pozzolanic properties of fa facilitate interaction with ca(oh)2 for aggregation linked to the non-linear behavior. this study provides generalized design models for correlating the mix proportions in opc-substituted aacms to the optimum compressive strength. keywords-regression; machine learning; compressive strength; fly ash; mechanical stability; cementitious materials i. introduction concrete consists of ordinary portland cement (opc), aggregates, water, and some other materials and chemical additives, such as superplasticizers. opc, as the primary binding material, plays a crucial role in determining concrete’s properties [1]. mineral admixtures are natural pozzolans (i.e. form cementitious compounds in a finely divided form in presence of water, combined with calcium hydroxide) like coal fly ash (fa) or fine aggregates (s), which can be obtained commercially from thermal power plants [2, 3]. the compressive strength of fa-based concrete was found to be strongly correlated with the blaine value [4], the pozzolanic reaction or cure age (high ca(oh)2 and the reaction of sio2+al2o3 in fa induce reaction rates), resulting in nonlinear relationships [5] and forming hydrate deposits (the decreased ca(oh)2 content and low ca 2+ concentration increase the deposition of c3s and cement hardness) [6-8]. physical parameters, including blaine (surface area) and particle size, along with other chemical processing parameters, such as c3s, c2s, c3a, c4af, and so3 contents, are some of the factors determining the compressive strength after 28 days of curing [9-11]. the compressive strength of fa concrete was predicted in [12] using the "particle model" according to the classification and the chemical information of fa particles. very high precision was obtained from the model with r2=0.99 to predict the compressive strength of 20% and 40% fa substitution (mass replacement) of cementitious materials with different curings from 3 to 180 days. this particle model applied machine learning (ml) classification algorithms, which classified fa particles into 9 different groups [13-14], allowing to build models and carry out regression analysis at different curing times giving empirical prediction models. these models were able to predict the compressive strength of fa concrete for 26 various fa sources (class c and class f based on astm c618 [15] for concrete mixtures made of opc). it should be noted that astm c618 asem was previously published as a widely accepted method to compare the performance of different fas [16]. type i portland cement consists mostly of cao (~63%), sio2 (~21%), and al2o3 (~4.6%) with other trace elements. the ratio of water-tocementitious material of 0.45 is a common practice when testing mixture proportions with a 20% or 40% fa replacement content. the identified strength performance of the mixtures based on 2000 particles of existing 11 elements (si, al, fe, ca, mg, s, na, k, ti, p, and sr) showed that the particle model was capable of building accurate predictive equations [16-18]. in [19], the unconfined compressive strength (ucs) of coal fa-based cement-based pastes, mortars, and concrete was predicted using ml models, showing a negligible mean square error of 5mpa according to mixtures following the european standards (35% for cement and 55% for concrete). these models described experimental data with ucs ranges of 32.5– 52.5mpa and 12–60mpa based on the european limits on corresponding author: hisham a. maddah engineering, technology & applied science research vol. 12, no. 2, 2022, 8241-8247 8242 www.etasr.com maddah et al.: predictive regression models for the compressive strength of fly ash-based alkali… cement and concrete respectively. mix composition data were trained for the generalization of the model [20] from neural network analysis (nna) and based on the defined input and output variables and the nonlinear relationships, concluding that the least influencing variables on strength were additives, being water or aggregates and cement, while the products and compositions of different amounts of fa were the detrimental variables. the development of sustainable concrete mixtures with optimal compressive strengths was also studied in [1, 2125] by combining linear regression with svm and artificial neural networks (anns), resulting in successful and precise models focused on the reduction of environmental impacts of concrete from information like aging time, contents, and ratios between contents. this study examined the impact of adding fa powders or s as a sustainable full replacement of opc in concrete from collected experimental datasets on the compressive strength of fa-based alkali-activated cementitious materials (aacms). an ml analysis was applied with supervised training and testing of mixed proportions data, using slr and mgsvm regression trainers from matlab toolboxes, for building accurate strength predictive models for 28-days cured aacms. the reliability and validity of the built models were evaluated using residual analysis to identify the models with minimum statistical error. the compression results obtained from data fitting and the prediction analysis using trained models were utilized to find the ideal fa/s ratio to maximize the compressive strength and mechanical stability. furthermore, changes in the mechanical properties were studied at high mixing ratios to check the effect of fa pozzolanic properties on particle aggregation and provide a generalized design model for opc-substituted aacms with optimum compressive strength. ii. methods and framework all aacm composite mixtures were prepared at room temperature at 20±1°c and 65±5% relative humidity and then were cured in steam condition. the studied parameters were slag cement (sl), with a constant quantity as the core binder for the full replacement of opc, combined with fa by partial replacement with s according to the previously mentioned ratios. alkali activator (al) to slag cement ratio (al/sl) of 20% and 50% water/slag cement ratio (w/sl) were used for all mixes to create an economically desirable performance with the complimentary benefits of meeting the sustainable development of high-performance systems [26-30]. the studied mixture proportions of aacms can be found in [26-28, 31], and the datasets were gathered from previous experimental works [26, 27, 31]. the collected datasets for 28-day curing included fa/s of 0, 5, 10, 15, 20, 25, and 30% to evaluate the optimum favorable mixture designs that improve the mechanical stability of aacms after steam curing with constant ratios of al and w to sl as the core binder. ml analysis was applied using supervised training and testing of mixed proportions data through the slr and mgsvm regression trainers from matlab toolboxes to build accurate strength predictive models. the original datasets containing 21 values were expanded to 105 using the earlier introduced concept of "in-between randomization" [32-35], by correlating randomly generated strength values between the three measured samples of each mixing ratio to the same fa/s proportion. this 5-fold expansion approach allows better ml training and testing analysis. the datasets were then divided randomly into two groups: 80% for training and 20% for testing to check the validity and reliability of the models in predicting the compressive strength. the supervised regression analysis was initiated from a selection of training data points (84) and testing data points (21) of the already curated and built datasets, based on raw experimental results (7 data points with 3 trials each). the model’s validity was examined using the testing datasets and by applying residual analysis to identify models with minimum statistical errors. the collected datasets included only fa/s as an independent input parameter and compressive strength as the only dependent variable, based on raw datasets taken from earlier works of aacms with 28-day steam curing [26, 27, 31, 36, 37]. various supervised regression learners from matlab’s toolbox [38] were selected for training and testing. linear and tree regression models as well as svm and gaussian process regression models (gprm) with a 50-fold cv were used to identify the optimal compression strength [38-41]. the training datasets consisted of four 84×1 matrices representing the input parameters and the compressive strength output. the compression results obtained from data fitting and prediction analysis were utilized to find the ideal fa/s ratio with the maximum compressive strength. furthermore, changes in the mechanical properties were studied at high mixing ratios to check the effect of the pozzolanic properties of fa on particle aggregation. it should be noted that each sample number was correlated with gradual-increasing ratios associated with the mixing proportions of fa/s 0, 5, 10, 15, 20, 25, and 30%, and their corresponding compressive strengths from experiments for both training and testing data points, which were originally forked from the raw datasets. it is quite common to measure a models' validity and prediction ability using various statistical metrics, including coefficient of determination (r2), mean square error (mse), root mean square error (rmse), mean absolute error (mae), and residual analysis. these metrics were respectively calculated using their mathematical definitions [42-44]: r� = �∑ ���, ��̅� ���, ��̅� � �� � � ∑ ���, ��̅� �� �� ×∑ ���, ��̅� �� �� (1) mse = ∑ ���, ���, �� �� � (2) rmse = �∑ ���, ���, �� �� � (3) mae = ∑ ���, ���, �� �� � (4) residual = #$ − #& (5) where #$,' and #$ are the observed values, #&,' and #&are the predicted by the ml model values, #̅$ is the average of the experimentally obtained values, #̅& is the average of the predicted values, and ( is the dataset size. rmse and mae allow the demonstration of more accurate prediction results, engineering, technology & applied science research vol. 12, no. 2, 2022, 8241-8247 8243 www.etasr.com maddah et al.: predictive regression models for the compressive strength of fly ash-based alkali… where more similarities arise between the trendlines of both experimental and predicted samples with higher r2 [45]. once the regression learners were trained, the statistical metrics obtained from the different models were compared. then, the best models (e.g. slr, fine trees, mgsvm, ensemble boosted trees, ensemble bagged trees, squared exponential gaussian process regression) were selected by checking if r2>0.7. only models that met the previous conditions were further examined to compare their predicted response patterns. finally, the mgsvm (r2>0.95) model was chosen for further analysis against the slr (r2>0.68). figure 1 depicts the process of selecting the optimal supervised ml models for the accurate prediction of strengths correlated to fa/s. fig. 1. flowchart for developing and selecting the optimal ml models for accurate prediction of compressive strength correlated with fa/s ratio. iii. results and discussion a. impact of adding fa/s the impact of adding fa/s content to the studied aacms was identified from the datasets. the selected testing data points showed a similar pattern, while an inspection of the experimental results shown in figure 2(a) confirms the reliability of the built ml models for accurate predictions. the cementitious materials showed a maximum compressive strength of ~67.5mp at ~20% fa/s ratio according to the raw data, as well as the spline interpolation fitting analysis using origin as illustrated in figure 2(b). without added fa or s, it appears that the cement cannot withstand high compressions greater than 61mpa, indicating the relatively poor mechanical strength before the addition of fa/s. however, increasing the fa/s ratio by more than 30% increases the probability of reaching a point where the original compression strength of 61mpa can be recovered, which is similar to the case of having pristine cement without additives. interestingly, these results were proved through experiments, supervised ml, and regression fitting. combining a core binder with a higher fa/s replacement ratio of up to 20% resulted in improved compressive strength by forming a denser binder matrix, which confirmed more released heat and higher initial mix temperature. however, the replacement ratios of fa/s over 25% reduced the composites’ compressive strength due to the lack of accessibility for hydration, as lowering produced heat inhibited dense binder formation, influencing the pozzolanic reactions and aacms mechanical properties. raw data suggest the addition of higher fa rates than those of fine aggregates to achieve high mechanical stability, as much as closer to the optimal point of ~20% fa/s ratio for the maximum mechanical and compression stability of the cementitious materials, as shown in figure 2. this could be achieved using training/testing dataset ranges of 0-300kg/m3 and 900-1200kg/m3 for fa and s additives, respectively. fig. 2. relationships between the fa and s content as mixed proportions against the compressive strength of aacms: (a) comparison between the selected trained/tested datasets used in the supervised ml, (b) experimental data of fa/s ratio against compression fitted by spline interpolation using origin. b. compression predictions from slr and mgsvm slr and mgsvm showed unexpectedly high prediction accuracy for the observed pattern, as shown in figure 3, compared to the other matlab supervised regression engineering, technology & applied science research vol. 12, no. 2, 2022, 8241-8247 8244 www.etasr.com maddah et al.: predictive regression models for the compressive strength of fly ash-based alkali… learners. the selection of training and testing data points from the already curated and built datasets, based on the raw data experimental results, led to the acquisition of training and testing trendlines of various samples against the observed compressive strength, as shown in figures 3(a) and (b), respectively. similar regression trends were generated when testing the model’s validity. it is worth noting that the sample number is correlated with gradual-increasing ratios associated with the various fa/s ratios and their corresponding compressive strengths. since both slr and mgsvm were capable of producing results very close to the experimentally observed pattern, they were both considered as the possible optimal available supervised models to predict the changing pattern of the experimental datasets, including training and testing data points originally forked from the raw datasets. fig. 3. results with slr and mgsvm and their comparison with the experiment c. exceedance probability for slr and mgsvm the exceedance probability is the probability that a certain value will be exceeded in a predefined future period [46, 47]: * = +,�-./ (6) where n is the total number of compressive strengths, m is the ranking from highest to lowest of observed, trained, and tested data separately. the observed (training) or predicted (testing) outputs were utilized to statistically characterize the compressive strength of aacms, as shown in figure 4. the values observed exceeded various percentages of the specified compressive strength. a 5% exceedance probability from both slr and mgsvm models means that a high compressive strength could exist and be exceeded by only 5% of all sampled records, whereas a 95% exceedance probability from sampled records is characterized with low compressive strength. fig. 4. observed vs. predicted compressive strength showing the exceedance probability of the ml models.. d. predictions accuracy and statistical errors a comparison between the training and testing datasets was used to build the ml regression prediction models, as shown in figure 5. the statistical analysis allowed checking the prediction accuracy of the built models. most of the observed versus the predicted training dataset points, either from slr or mgsvm models, were very close to the exact approximated compressions values and close to the drawn diagonal dotted line shown in figure 5(a). similarly, the same pattern was observed for the testing datasets, as shown in figure 5(b). fig. 5. observed vs. predicted compressive strength of aacm composites showing the prediction accuracy of the built ml models: (a) training, (b) testing. these results imply the correctness and the reliability of the model to be used for predicting the experimentally obtained compression results, without the need to conduct further experiments when dealing with similar cementitious materials. note that regardless of the number of used data for testing, one would get similar accurate model results if a minimum of 84 experimental data points were used in the model training session to ensure the model’s capability of producing high predictions. the statistical error parameters obtained for each built model, including rmse, r2, mse, and mae, are shown in table i. table i. statistical errors of regression models model fa/s = [0, 5, 10, 15, 20, 25, and 30%] slr mgsvm rmse 298.59 117.39 r2 0.68 0.95 mse 89158 13781 mae 230.64 84.75 slr=stepwise-linear-regression, mgsvm=medium-gaussian-svm; cross-validation (cv): 50-fold. considering that reliable models should have minimum mse or rmse with r2 > 0.70. e. residual analysis, stress/strain in fa-based composites residual statistic analysis is a method to check the reliability of the built ml models for their potential adoption by the scientific community. the compression strength results of the prediction analysis were compared, according to their calculated residuals which showed a very low residual range of ±1, indicating the high precision of the supervised models as shown in figure 6. the closer the determined residual points to the origin-line, the better the model accuracy becomes, indicating very low statistical errors. thus, it seems that the mgsvm outperformed the slr trained model due to its closer-to-the-zeroth-line points observed in the residual analysis. moreover, the tested results residuals were almost engineering, technology & applied science research vol. 12, no. 2, 2022, 8241-8247 8245 www.etasr.com maddah et al.: predictive regression models for the compressive strength of fly ash-based alkali… identical to those obtained from the training datasets, and this is only possible if the required compression of the aacms composites is for samples with mixed proportions or ratios of fa/s in the range 0–30%. such extrapolation may be possible if a huge selection of data points is available, which can be achieved from the in-between randomization and getting leverage of the inevitable experimental errors to create dataset inputs correlated to the same output ranges, yielding in much larger training datasets expanded for the possibility of predicting compression in mixed proportions with fa/s ratios beyond 30%. however, supervised ml models are ideal when analyzing inputs within the same provided experimental dataset constraints to ensure the correctness of the results without the need to conduct the experimental work. fig. 6. residual statistical analysis showing srl and mgsvm accuracy: (a) training datasets showing the low residual range of ±1 indicating high accuracy of the models, (b) testing datasets confirming the models’ ability to estimate experimental results with similar trained model high accuracy of ±1. the average stress and strain values were estimated using stress-strain relationships and elasticity laws for various fa/s ratios, confirming patterns that would follow non-linear behaviors of a polynomial function of third-order and secondorder for stress and strain, respectively, as shown in figure 7(a). furthermore, the approximate impact of high compression, or even stretch after the applied force is released on the material, on the designed fa-based composites was determined, shown as changes in the matrix length from the hook’s law analysis shown in figure 7(b). however, both stress and strain were found to follow a linear pattern when plotted against compressive strength, observed from the various fa/s ratios, as shown in figures 7(c) and (d) respectively. this indicates the possibility of directly applying common stress-strain relationships for the designed composites for further compression investigations. f. novelty, contribution, and significance of the results several ml models were used to predict the mechanical properties of fa-based aacms. the two presented models, slr and mgsvm, showed a high prediction accuracy of ~95%. maximum compressive strength of ~67.5mpa was observed at ~20% fa/s (spline interpolation), which suggests the attainment of high mechanical stability. a fa/s greater than 30% indicates a high probability of recovering the original strength of 61mpa from pristine aacms. this analysis showed the promise of using fa for a sustainable full replacement of opc in concrete validated by slr and mgsvm. the non-linear patterns of observed stress and strain against fa/s ratios were confirmed and linked to the pozzolanic properties of fa, facilitating interactions with ca(oh)2 for aggregation. a novel theoretical analysis was suggested to investigate changes in mechanical properties of various fa-based compositions and the impact of fa pozzolanic properties on particle aggregation to provide generalized design models for correlating mix proportions to optimum compressive strength. fig.7. impact of computed compressive strength on the stress and strain behavior of the fa-based aacms: (a) average stress and strain values for various fa/s ratios determined from stress-strain relationships and elasticity laws showing that the expected behaviors of stress and strain follow a polynomial function of third-order and second-order respectively. (b) the calculated changes in matrix length observed at high-stress values show the impact of possible compression or stretch of the composites according to hook’s law. (c)-(d) the obtained linear relationships between both stress and strain vs. the experimentally observed compressive strength. iv. conclusion this study presented two high-accuracy predictive models from collected experimental datasets on the compressive strength of fa-based aacms. the applied ml analysis was conducted using a supervised training and testing procedure on various proportions of fly ash (fa) to fine aggregate (s) ratios of 0, 5, 10, 15, 20, 25, and 30%. the analysis showed the promise of using fa as a sustainable full replacement of opc in concrete and was validated with slr and mgsvm regression trainers for 28-days of steam curing samples. this study aimed to evaluate the most optimum favorable mixture designs that would improve aacms’ mechanical stability and maximum compressive strength. the built models predicted the mechanical properties of fa-based aacms with high prediction accuracy (~95%) using mgsvm regressions that outperformed slr-trained models due to their closer-to-thezeroth-line points observed in residual analysis, translated as minimum statistical errors. the concept of "in-between randomization" was applied by taking advantage of inevitable experimental errors for expansion of raw datasets by 5-fold to obtain a better ml analysis, using strength as output and mix ratios as input. the results revealed a maximum compressive strength of ~67.5 mp at ~20% fa/s, obtained from data fitting using trained models, suggesting an optimal ratio for an economic desired compressive strength threshold and the engineering, technology & applied science research vol. 12, no. 2, 2022, 8241-8247 8246 www.etasr.com maddah et al.: predictive regression models for the compressive strength of fly ash-based alkali… attainment of high mechanical stability of the aacms. the non-linear patterns of the observed average stress and strain against fa/s ratios, but with linear patterns against strength, were confirmed indicating the applicability of stress-strain relationships and elasticity laws for the built composites. the pozzolanic properties of fa that facilitate interaction with ca(oh)2 for aggregation were linked to non-linear relationships. furthermore, the approximated impact of high compression on the designed composites was realized from the introduced changes in the matrix length from hook’s law. this study suggests a novel theoretical analysis to investigate the changes in the mechanical properties of various compositions based on fa and the impact of fa pozzolanic properties on particle aggregation. such works could offer generalized design models for optimum compressive strengths needed in engineering construction applications. acknowledgment this research work was funded by the institutional fund projects under grant no. ifpip: 610-829-1442. therefore, the authors gratefully acknowledge the technical and financial support from the ministry of education and the king abdulaziz university, dsr, jeddah, saudi arabia. references [1] h. naseri, h. jahanbakhsh, p. hosseini, and f. moghadas nejad, "designing sustainable concrete mixture by developing a new machine learning technique," journal of cleaner production, vol. 258, mar. 2020, art. no. 120578, https://doi.org/10.1016/j.jclepro.2020.120578. 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[47] h. kunreuther, "risk analysis and risk management in an uncertain world1," risk analysis, vol. 22, no. 4, pp. 655–664, 2002, https://doi.org/10.1111/0272-4332.00057. microsoft word etasr_v11_n5_pp7629-7634 engineering, technology & applied science research vol. 11, no. 5, 2021, 7628-7634 7628 www.etasr.com tariq et al.: investigation of the effects of distributed generation on protection coordination in a … investigation of the effects of distributed generation on protection coordination of a power system ayesha tariq department of electrical engineering ned university of engineering and technology karachi, sindh, pakistan ayesha_0405@hotmail.com krishan lal khatri department of electrical engineering ned university of engineering and technology karachi, sindh, pakistan engrkrishan@yahoo.com muhammad ibrar ul haque department of electrical engineering sir syed university of engineering and technology karachi, sindh, pakistan mihaque@ssuet.edu.pk muhammad amir raza department of electrical engineering ned university of engineering and technology karachi, sindh, pakistan amir.eed.neduet@gmail.com sadia ahmed department of electrical engineering sir syed university of engineering and technology karachi, sindh, pakistan sadiaa@ssuet.edu.pk muhammad muzammil department of electrical engineering sir syed university of engineering and technology karachi, sindh, pakistan muzammil@ssuet.edu.pk abstract-the rapid increase of the electrical power demand gave rise to many challenging situations for power system control engineers as the transmission lines are operating at their maximum capacity in most developing economies. to solve this, distributed generation (dg), i.e. the generation of electrical power in a distribution network that provides clean energy, is gaining popularity. there are several challenges the protection of distribution networks faces after dg installation, such as variations in short circuit levels, protection blinding, reverse power flow, protection coordination, change in fault impedance, recloser-fuse coordination, selectivity, unsynchronized reclosing, false tripping, etc. in this paper, an ieee 13-bus system radial distribution system is simulated using electrical transient analyzer program (etap), various scenarios of dg placement are considered, their impact on the protection system is analyzed, and different techniques are proposed to minimize the effect on protection coordination. the use of directional relays, current limiting reactors, and small magnitude dgs is tested and analyzed. the way this effect varies by changing the location of dg is also analyzed. keywords-distributed generation; protection coordination; relays; radial distribution network i. introduction in traditional power generation, large central generators at a remote end control the flow of power in transmission and distribution networks. duting the '90s, a revolution caused by the connection of power generators in the distribution network as distributed energy resources (ders) or distributed generators (dgs). dgs can be connected to voltages from 230v to 150kv. small power generators are coupled at smaller voltage networks. larger generators of capacity ranging around 100mw are connected to high voltage buses. with the insertion of dgs, the electricity supply by central generators reduces. dgs need additional facilities for the power system to function with fewer central generators being utilized [1]. there are several types of dgs, e.g. solar, wind, fuel cell, small hydro, and rotating machines [2]. the addition of distributed generation in a distribution network effects the power system protection coordination in several ways, e.g. fault currents and short circuit currents from the dg increase, but there are changes in power quality, increase of reliability, and changes in losses and the voltage profile. the contribution of short circuit current depends on the dg location and the location of the fault. the fault current supplied by the substation is decreased and relays are not able or take longer time to detect the fault, which reduces relay sensitivity. fault currents caused by rotating machine dgs are higher but those by inverter-based dgs are lower. to maintain power quality, line drop compensators (ldcs) or programmed timer distribution transformers (ptdts) are used to control voltage of distribution lines. step voltage regulators (svrs) are used to compensate the line voltage for dense power flow. these voltage regulators work properly if the feeder load is balanced. however, if many dgs are located on a particular line, the power flow gap widens between the feeder lines due to back power flow and results in voltage corresponding author: krishan lal khatri engineering, technology & applied science research vol. 11, no. 5, 2021, 7628-7634 7629 www.etasr.com tariq et al.: investigation of the effects of distributed generation on protection coordination in a … fluctuations. the reliability of system increases due to the addition of dg sources as they locally inject power into the system. however, dgs' power flows in reverse direction and affects usual power flow, which can cause underor over voltage problems in the network. on the other hand, reduction in losses is one of the major positive impacts. the location of distributed generation units is a major issue that needs consideration in order to result in performance enhancement of the system with fewer losses. in general, the placement of dgs in the network is like placing capacitors, the only difference is that dgs provide both active and reactive power unlike capacitors that provide reactive power only [3]. in this work, the impact of the addition of dgs to a distribution network is analyzed mainly with regard to protection coordination of relays and the sizing and placement of dgs in ieee 13-bus system is suggested with regard to the demand that there is minimum impact on protection coordination. ii. literature review authors in [4] proposed an expert system, tested it on a 22kv distribution network, and proposed multiple coordination settings to prevent the ill effects of dg placement. the system operates on microsoft windows, the interface modules and knowledge base are in microsoft access via open data base connectivity (odbc). the expert system is used for the modification of protection settings. the method of "adaptive inverse time over current protection" was proposed in [5]. the authors suggested the calculation of newer values of plug setting multiplier (psm) by taking information from over current, fault current, voltage drop, and zero sequence fault current in the network. however, their results are not valid in changing network conditions. authors in [6] simulated the tunisian distribution network using directional relays and changing coordination settings on etap. directional over current relays were used for correct tripping and to ensure time grading between primary and backup relay and the settings of over current relays were revised. to avoid the miss coordination problem of relays after the dg insertion, a directional feature was employed in relays. relays and recloser settings were updated. the 11kv distribution feeder of elgharbia was simulated on etap in [7]. the directional protection scheme with relays of microprocessor type offered in [8] was used and the islanded mode with distributed generation was discussed. for achieving least-disturbance optimal protection settings and failure timings, the time coordination method was introduced. with the new dgs, a new relay setting is generated and proposed every time on the ring system for achieving zero interruption frequency and supply failure rate [9]. voltage sag coordination technique is based on disconnecting the dg when the voltage falls in the system to 0.5pu in less than 6 cycles. this technique is limited to small dgs [10, 11]. a method based on neutral networks and fuzzy logic was proposed in [12]. the neuro-fuzzy protection scheme was based on finding the optimal settings of inverse definite minimum time (idmt) relays constructed on the position of dg and also on power system network conditions. by this technique, the results were improved through a current and voltage phasor-based discrete fourier transform (dft) algorithm. a genetic algorithm (ga) method based on finding the optimum time multiplier setting (tms) values of over current relays and circuit breaker’s operating time for proper coordination of relays after dg insertion was proposed in [13]. this method is not suitable if the relays are conventional and they should be replaced by new relays which are costly. in [14], sizes and locations of dgs were found on matlab by using the ga on a 33-node system by allowing the relays to work on their conventional settings. the effect of three different sources (induction machines, wind turbine, and synchronous machines) on distribution network’s fault current was checked on etap. by adding dgs, "blind zones" are created and different fault currents by different dgs were observed on a 4-bus system in [15]. some major challenges in distribution systems were discussed in [16], including protection blinding, false tripping, fuse-recloser coordination, impedance variations during fault, unsynchronized reclosers, change in power flow’s direction, loss of mains, deviations in levels of short-circuit currents, and the selection of a protection device. fault current limiters (fcls) were added to the system to limit the level of fault current and to avoid miss coordination issues [17]. in a nutshell, some methods that have been proposed work on changing protection device’s settings after the dgs' insertion in the system. methods that are used for solving coordination issues like directional relays, and fcl work with small dgs and will be discussed in detail below. iii. research methodology we used the etap 12.6 simulation software to analyze the impact of the addition of dg units on the protection coordination of the network. etap is specialized software used for the analysis, monitoring, simulation, control, automation, and optimization of electrical systems. etap software in electrical engineering has the most complete collection of combined power system enterprise solutions. an ieee 13-bus radial test system, as shown in figure 1, is used in this study. the system is first modeled on etap and load flow analysis is executed on the network to find out the power ratings of system. short circuit analysis is done for finding the systems’ behavior during fault conditions. standard ieee 13 bus is a radial feeder system with a small number of components, however it contains numerous features and can be used as an exemplary to find out the performance of power system. this system contains underground and overhead lines, distributed and spotted loads, a 500 kva transformer, and capacitor banks. the following assumptions are considered: • the voltage regulator at bus 650 is not considered. • the loads that were distributed between bus 671 and 632 are not considered. • all the loads are three phase and constant impedance loads differentiate from one motor load. for the protection of ieee 13 bus system, fuses and over current relay devices are used. current transformers (cts) are used for current measurement. high voltage circuit breakers (hvcbs) and low voltage circuit breakers (lvcbs) are used as interrupting devices at 4.16kv and 0.4kv respectively. to engineering, technology & applied science research vol. 11, no. 5, 2021, 7628-7634 7630 www.etasr.com tariq et al.: investigation of the effects of distributed generation on protection coordination in a … find the overall behavior of the system, and for the selection of ratings of fuses, relays, and circuit breakers, load flow analysis and short-circuit analysis is performed. maximum 3-phase and minimum single line-to-ground short circuit currents are considered and further studied because maximum short circuit current is used for protection device’s selection (devices should be capable to withstand short circuit current without damage). minimum values are used so that protection devices should not mal-operate at minimum short circuit current. the pickup current of relays should be more than the overload current in the system and less than single line-to-ground (slg) fault current. for the selection of protection devices slg and 3phase fault current values are calculated on the buses as shown in figure 2 [17]. fig. 1. standard ieee 13 bus system. fig. 2. fault current at different bus. as per calculations, maximum short circuit current is seen at bus 634. bus 634 is the bus with the 500kva transformer 4.16/0.48 and is rated at 0.48kv while all the remaining buses are operating at higher voltage of 4.16kv. fault current level is low at higher voltage levels. inverse time over-current relays are used for feeder protection. fuses are used for load protection. these relays operational time is inversely proportional to the fault current as shown (1)-(3). the different types of iec curves are shown in (1), (2), and (3). standard inverse (si) relays are used for the coordination of relays and the time of operation can be found with (1) [17]. alstom p125 relay is used in the network. as psm is required in (1), it can be calculated by (4) whereas the pickup current in (4) is calculated by (5). relays should operate when current in the cts exceeds the 25% of normal current. time dial setting (tms) varies from 0.025 to 1 in steps of 0.025. the operating time of the circuit breaker is considered as 0.4s and 10% overshoot is considered for proper coordination between the primary and the backup relay. the time of operation of backup relays should be greater than the time of operation of the primary relay and the operating time of circuit breaker [18, 19]. table i. iec 60255 characteristic curves relay types equation standard inverse (si) top � 0.14 ∗ tms psm�.�� � 1 (1) very inverse (vi) top � 13.5 ∗ tms psm � 1 (2) extremely inverse (ei) top � 80 ∗ tms psm� � 1 (3) psm � ����� ������� �� ����� � �� !��"�# ������� (4) pickup current � rated secondary current of ct ∗ ps (5) psm � top2p3 4 0.4 4 10%top2b3 4 0.4 (6) in (6), top(p) is the primary relay's operating time and top(b) is backup relay's time of operation. an arrangement of thirteen over-current relays is used on etap. the tms of relays that are closest to the load is 0.1s and the tms of other relays is found by (1) and (6), making sure that the difference of 0.4s is maintained between the primary and the backup relay. in order to find out the impact of dg on the power system, different scenarios will be considered. • scenario 1: the impact on protection coordination of distribution network with the addition of dgs in the system. • scenario 2: the impact on protection coordination of distribution network with non-directional relays replaced by directional relays. • scenario 3: the addition of small dgs in the system instead of larger dgs. • scenario 4: the use of current limiting reactors or fault current limiters to limit the impact on protection coordination. iv. results and discussion the standard system with supply from the grid only is considered. the protection of the ieee 13-bus system is done by fuses and over current relays. setting of fuses and relays is done on etap. system is perfectly coordinated before the placement of dgs in the system as verified on etap. a. scenario 1: the effect on protection coordination when adding dgs directly connected motors and generators are spinning as usual and supply a high amount of fault current. this extremely engineering, technology & applied science research vol. 11, no. 5, 2021, 7628-7634 7631 www.etasr.com tariq et al.: investigation of the effects of distributed generation on protection coordination in a … high short circuit current is dangerous because it may over stress equipment that is being used in the network to break the current, such as circuit breakers. if the value of short circuit current is very small, then it is also of concern, because fault will not be detected if this is too low and there is a possibility that protection devices will not operate correctly. reliable fault detection from gds can be difficult due to their small ratings. designing the scheme of dg protection should be done carefully [1]. when the size of dg increases, the contribution of upstream fault current from grid will decrease which can cause a decrease in protection device sensitivity. short circuit current increases in the downstream network as the size of dg increases or location of the dg is moved closer to the fault location. this may cause false tripping of relays. some such examples are considered below. the relay settings are the same. 1) 3 mw dg at bus 611 in this case, when a fault occurs at bus 692, relay 12 should operate primarily to isolate the fault. however, what happens in the system is that relay 16 is operated first as shown in figure 3 [16] because of the dg interconnection at bus 611. maloperation of relays has occurred, and protection coordination is lost. the coordination time interval (cti) between relays is below 0.3s. fig. 3. 3mw dg at bus 611. fig. 4. 4 dgs at three different buses. 2) three 1.5mw dgs at bus 611, 675, and 646 in this case, 3 different dgs, each of 1.5mw are placed at 3 different points, 611, 675, and 646. a fault near bus 692 is shown in figure 4. false tripping occurs in this case as fault current is coming from 4 different points (the grid and the 3 dgs). the condition worsens by increasing the number of dgs in the system. selectivity and sensitivity between the relays is disturbed. it is concluded that by the addition of dg in the system, the protection system is no more perfectly coordinated and some changes in relay settings are required. the following three techniques can be used for solving the protection coordination issues. • conventional (non-directional over current) relays should be replaced by directional relays. • adding small dgs in the network in order to have minimum effect on the protection. • use of fault current limiter. engineering, technology & applied science research vol. 11, no. 5, 2021, 7628-7634 7632 www.etasr.com tariq et al.: investigation of the effects of distributed generation on protection coordination in a … b. scenario 2: conventional (non directional over current) relays replaced by directional relays electromechanical relays were used for protection in the above scenario. with the advancement of technology, microprocessor (numerical) based devices are utilized today but there are still a lot of conventional power systems utilizing electro-mechanical relays. a directional feature can be added in modern microprocessor-based relays, but our simulation system doesn’t have this capability. hence, we used digital relays: three 1.5 mw synchronous (diesel) dgs at buses 611, 675, and 646. the rest of the scenario is the same with the one considered above. conventional non-directional relays were replaced by directional relays. the system is perfectly coordinated during the fault. for the 3-phase fault in the system between fuse 9 and lump 5 as shown in figure 5, fault current is as high as 7.5ka in fuse 9 which operated primarily at 15.8ms, then relay 12 at 680ms, and finally relay 11 at 1138ms. this can make relays insensitive for fault detection or to distinguish between load and fault current. by the addition of the directional feature in over current relays, the selectivity and all other protection issues are solved. there are certain situations where coordination interval can be disturbed. to correct this, relay settings need to be changed if there is any such coordination issue. fig. 5. fault placed at bus 692. c. scenario 3: addition of small dgs in the network replacement of conventional relays by the addition of each dg in the network is not possible sometimes due to cost and system redesign issues. another solution is adding small dgs that have overall very small impact on the fault currents of the system. in order to penetrate distributed generation into the network for this scenario, power flow is performed on the network so that the voltage range is not violated. as it is discussed above, over-voltages occur on the nodes by the addition of dgs in the network. thermal limits should not be violated, any of the equipment should not be overloaded by the addition of dgs. protection coordination and cti should not be violated. we analyzed dgs in the range of 100kw~10mw with a step size of 100kw. bus 632 cannot be considered for the addition of dg because of it is connected to the grid. maximum increase, of the order of 100%, in short circuit current is observed on bus 634, hence it is also not considered for the addition of dg. the required conditions to maintain power quality and system integrity are: • voltage range should be within limits, i.e., 95%-105%. • the thermal limit of equipment should not be exceeded. • the protection devices should be perfectly coordinated. small synchronous dgs are installed in the system at buses 611, 633, 645, 692, and 671 simultaneously. the total load connected in the distribution system is of 3.5mw. to meet the total load demand, 3.5mw of generation which consists of small dgs are added in the system and the impact on protection coordination is checked and verified as shown in figures 6 and 7. small dgs are installed at distant buses having low tms values as the fault current of dg increases. increased fault current has maximum impact on the relay that has low tms because the time of operation of the relays is proportional to tms as shown in (7). fig. 6. fault near bus 675. fig. 7. sequence of operation for the fault near bus 675. time of operation 2top3 � tms ∗ psm (7) dgs are installed at 4.16kv buses and should not be installed at 0.48kv bus 634 as it shows the highest impact on the system. this is because of the placement of the step down transformer between buses 633 and 634. the over-voltages on buses are within the allowed range. the system is coordinated as observed in the two different examples discussed above and the operating time of protection devices is checked. d. scenario 4: use of fault current limiter (fcl) working with small dgs is costly and technically challenging. large dgs can be placed in the system in the presence of fcls. we used current limiting reactors (clrs) that limit the fault current. a clr is used for limiting current engineering, technology & applied science research vol. 11, no. 5, 2021, 7628-7634 7633 www.etasr.com tariq et al.: investigation of the effects of distributed generation on protection coordination in a … because it produces small loss in real (active) power. however, the use of fcl has limitations because of the power loss it causes in normal conditions. an example is considered, and the results are shown below with and without the presence of fcl in the system. in figure 8, a dg of 3.5mw at bus 684 with a reactor is shown. for a fault near bus 611, the time of operation without fcl is shown in figure 9. relay 17 operates as a backup of relay 16. after relay 16 any other relay should operate after a time interval of 0.4s but in this case relay 12 is operating simultaneously with relay 17. this can be restricted by using fcl in series with the dg. when we did this, the relays operated sequentially as shown in figure 10. fig. 8. 8 dgs of 3.5mw with clr. fig. 9. sequence of operations without the clr. v. conclusion and recommendations in this paper, the effect caused by dgs on the power system’s protection network is analyzed and possible techniques for the addition of dgs to the distribution network have been proposed that result in minimum impact on protection coordination in the ieee 13-bus system. since it is costly and technically challenging to improve the settings of original relay systems or to upgrade the relays, the proposed techniques would help network operators install dgs with minimum impact on the distribution network. different scenarios have been established in order to investigate the effects of dg and to find solutions to the emerging issues. fig. 10. sequence of operations with the clr. coordination issues and other problems related to protection can be solved by the use of directional over current relays in the network. the drawback is the difficulty of replacement of the conventional electromechanical relays that are already installed in the system. this will not be the case for numerical relays. another solution is using small dgs with very low power ratings and low fault currents. this will have minimum impact on protection system coordination and very few protection coordination issues will arise. however, it can be economically and technically challenging due to the issue of protection blinding. the third method proposed is using fcls to limit the current from the dg. fcls can be used in the network for limiting the fault current from the dgs. for this optimal value, clrs need to be calculated as they produce power loss in normal conditions also. by using fcls in the network, dg selection is based on the trade between minimum impact on protection coordination with low real power loss in normal conditions. vi. future work simple clrs were analyzed in this work and their effects on protection coordination of relays were studied on etap software. by the use of limiters in the network, working with dgs of different types and sizes will have minimum impact on system in terms of current injection from the devices. however, it results in a tradeoff in terms of power loss in usual network operation. with the recent advances in conductor materials, advanced technologies have been introduced for limiting currents from dgs such as the use of superconducting materials. super conducting fcls have very small resistance and have almost no impact on normal real 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[19] m. a. raza, k. l. khatri, k. rafique, and a. s. saand, "harnessing electrical power from hybrid biomass-solid waste energy resources for microgrids in underdeveloped and developing countries," engineering, technology & applied science research, vol. 11, no. 3, pp. 7257–7261, jun. 2021, https://doi.org/10.48084/etasr.4177. engineering, technology & applied science research vol. 7, no. 3, 2017, 1633-1637 1633 www.etasr.com boukendakdji et al.: comparative study of prestress losses comparative study of prestress losses mustapha boukendakdji college of engineering department of civil engineering university of hail hail, saudi arabia m.boukendakdji@uoh.edu.sa mabrouk touahmia college of engineering department of civil engineering university of hail hail, saudi arabia m.touahmia@uoh.edu.sa belkacem achour college of engineering department of civil engineering university of hail hail, saudi arabia b.achour@uoh.edu.sa abstract— this paper compares the prestress losses as calculated by four different design codes; british standard cp110, comite europeen du beton 70 and 78, american concrete institute 77 and the prestressed concrete institute method (pci). the comparison is done by determining the total losses which take place in a rectangular prestressed concrete beam for both pretensioning and post-tensioning systems. the results show that total losses calculated for the post-tensioning method are higher than those calculated for the pre-tensioning method, which is not the usual case. it seems that the pci method may be required for special structures or for simply supported slender members which may be sensitive to small changes in deflections. however, for non-special structures, or where actual losses have little effect on the design, it is better to compute losses by the aci method because it is simple and does take into considerations interactions between the various sources of losses. however, it is not possible to conclude which method gives the more accurate prediction of shrinkage and creep without direct co-relation to realistic insitu data. keywords-losses; prestress; pre-tension; post-tension; creep; shrinkage; relaxation i. introduction prestressed concrete is a particular form of reinforced concrete. prestressing involves the application of an initial compressive load to the structure to reduce or eliminate the internal tensile force and, thereby, control or eliminate cracking [1]. it has long been recognized that the prestress introduced into concrete, does not remain constant but decreases gradually with the progress of time. it is therefore necessary for the designer to estimate the losses of prestress throughout the anticipated life of the structure and to provide an initial prestress which is sufficiently high so that the structural integrity will not be impaired as the losses take place. in a pretensioned member, the major components of prestress losses are those due to elastic, creep and shrinkage deformation of concrete and that due to relaxation of steel. in a post-tensioned member, additional losses due to friction take place. relaxation is theoretically defined as the decrease of stress in the prestressing element when it is restrained to a constant length. in the pre-tensioning process, part of the loss due to relaxation occurs before transfer. shrinkage is the shortening of the concrete due to loss of water which results in loss of the prestressing stress. after an initial high rate of drying shrinkage, concrete continues to shrink for a long period of time but at a continuously decreasing rate. in general drying shrinkage is directly proportional to the water-cement ratio and inversely proportional to the aggregate-cement ratio. for a given water-cement ratio shrinkage increases with increasing cement content [2]. creep is the time dependent deformation of concrete due to sustained compressive stresses in the fibres. one of the difficulties in determining these losses accurately is the assumption that the stress remains constant. this is not true because there is gradual reduction in stress during the life of the structure. creep of concrete is influence by many factors, such as: aggregate and cement content and water-cement ratio [3-4]. many method and design recommendations have been developed to predict prestress losses. a notably one is the time step method. the basis of this method is to divide the service life into small time intervals during which the stress relaxation, creep strain and shrinkage strain can be assumed to be independent of each other. in each small time interval prestress loss due to stress relaxation and strain changes due to creep and shrinkage are calculated. the stress levels at the end of each time interval are used in the next succession time interval. this procedure is continued until the required service life of the structure is reached. the aci-209r-82 model [5], the ceb-fip model code 1990 [6] and the b3 model [7] are recent and are based on extensive research as well as experimental studies. the measured creep and shrinkage strains were compared with different code predictions. in [8], authors observed that cebfip model code [6], slightly over predicts at an early age but matches well at a later age. an error in computing losses can affect service conditions such as camber, deflection and cracking. the underestimation of losses might result in cracking. the main purpose of this research is a comparative study of the loss of prestress to four different design codes; british standsrd cp110 [9], comite europeen du beton 70 [10] and 78 [11], and american concrete institute 77 [12]. the latter recommends pci [13] and aci [12] methods for calculating prestress losses. the comparison is done by determining the total losses which take place in a rectangular prestressed concrete beam for both pre-tensioning and post-tensioning systems. engineering, technology & applied science research vol. 7, no. 3, 2017, 1633-1637 1634 www.etasr.com boukendakdji et al.: comparative study of prestress losses ii. comparative study of losses the comparison is performed by determining the total losses which take place in a rectangular prestressed concrete beam for both pre-tensioning and post-tensioning systems. ceb 70 [10] and ceb 78 [11] are supposed to predict shrinkage and creep more accurately than aci [12] and cp110 [9] methods because they use some graphs to take into account some factors such as relative humidity, temperature of curing, time of loading and theoretical thickness. a. beam data the beam is of rectangular cross section 200 mm wide by 380 mm deep. it contains 6 wires (diameter=7 mm) 40 mm from the soffit, six wires 75 mm from the soffit and three wires 25 mm from the top. each wire is tensioned by a force of fi=47 kn before transfer which corresponds to a total force of f=705 kn. the following apply:  es=modulus of elasticity of steel=200 gpa.  eci=modulus of elasticity of concrete at transfer=31 gpa.  ec=modulus of elasticity of concrete at 28 days=35 gpa.  fcu=characteristic concrete cube strength=50 mpa  fci =concrete strength at transfer=40 mpa.  f’c=compressive strength of concrete at 28 days (cylindrical specimens)=40 mpa.  f’ci=initial concrete compressive strength at transfer (cylindrical specimens)=32 mpa.  ap=area of presetressing tendons=577.2 mm2.  fpi=prestressing stress at the jacking end=1221 mpa.  a area of concrete=79 145 mm2  yb=distance of lowest point from centroid of concrete section=187 mm.  i =area second moment of concrete section=9.759x108 mm4.  zb=section modulus for lowest point in concrete section=13.941x106 mm3.  zt=section modulus for highest lowest point in concrete section=5.056 x 106 mm3.  zc=section modulus for the tendons level=13941x106 mm3.  e=eccentricity of prestressing force with respect to centroid of concrete section.=70 mm.  mdl=dead load moment at midspan=12.825 kn.m.  fpu=characteristic strength of prestressing steel=1750 mpa.  fpi/fpu=0.7  age of loading (transfer)=13 days. losses due to friction in the duct are calculated from the following expression:   kxf eff  1  where x=3.75 m (distance from the end of the beam to midspan) and k=0.0033 (constant depending on the type of duct). the loss of prestress computed by ceb 78 method (comite europeen du beton) [11] is the sum of the losses which occur before the concrete has been prestressed, the instantaneous losses, and the losses due to time dependent deformations. the evaluation of the time dependent losses due to shrinkage and creep of the concrete and relaxation of the steel must take account of the interdependence of these phenomena as follows:           po scp relpscpp    ,,,,,, 21 (2) in which  ,, scp denotes the loss of prestress in steel due toa shortening of the concrete as a result of creep and shrinkage. the aci (american concrete institute) method was developed to estimate the losses from time dependent effects without having to break the life history of the beam into several time intervals. the interactions between the various sources of losses have been considered in setting the various coefficients which are used, thus it is significantly better than summing up individual estimates for loss of steel stress from elastic shortening, creep, and shrinkage of concrete together with relaxation of the steel. loss of prestress due to creep is computed for bonded members from the following expression:   cdscir c s cr ffe e kcr         in which kcr=2.0 for pre-tensioned members and kcr=1.6 for post-tensioned members. loss of prestress due to shrinkage is given by:  rh s v eksh ssh 015.05.106.0110550 6          where v/s : volume to surface ratio, rh: average relative humidity surrounding the concrete member, ksh: 1.0 for pretensioned members. iii. results and discussion the losses of prestress for the beam in the pre-tensioning and post-tensioning processes are given in tables i and ii respectively. it is assumed that half of relaxation occurs before transfer. total losses calculated for the post-tensioning method are higher than those calculated for the pre-tensioning method (figure 1), which is not the usual case. this is due to the fact that prestress losses caused by anchorage set are very high. the effect of anchorage set losses is more pronounced with short tendons (i.e. beam span=7.5 m). this loss can be overcomed by overstressing each wire or (but not greater than engineering, technology & applied science research vol. 7, no. 3, 2017, 1633-1637 1635 www.etasr.com boukendakdji et al.: comparative study of prestress losses 80 % ultimate tensile strength) or re-stressing and placing shims behind each anchor. usually losses determined for the post-tensioning method are smaller than those determined for the pre-tensioning method because:  losses due to elastic shortening, in the case of posttensioning, are less than half than those for pre-tensioning.  there is no loss due to relaxation before transfer.  the effect of shrinkage of concrete before transfer is not taken into account in the case of post-tensioning. however, losses after transfer calculated for the posttensioning method are lower than those calculated for the pretensioning method (figure 2). table i. prestress losses in the pre-tensioning process for cp110, ceb 70,78 and aci methods in mpa losses due to cp110 ceb70 ceb 78 aci half relaxation 15.25 15.26 15.26 15.26 elastic deformation 73.35 73.35 73.35 63.68 at transfer 88.60 88.60 88.60 78.94 half relaxation 14.1 31.7 39 17.87 shrinkage 60.0 44.0 52.4 41.6 creep 106.1 155.2 186.6 114.00 after transfer 180.2 229.7 278 173.47 total losses 268.8 318.3 366.6 252.42 % of losses 22.0% 26.07% 30.0% 20.65% table ii. prestress losses in the post-tensioning process for cp110, ceb 70,78 and aci methods in mpa losses due to cp110 ceb70 ceb78 aci friction 15.60 15.60 15.60 14.85 anchorage set 131.60 131.6 131.60 131.60 elastic deformation 32.30 27.80 32.32 31.0 at transfer 179.5 175.0 179.51 177.45 relaxation 26.04 29.2 36.3 9.77 shrinkage 40.0 44.0 47.8 32.66 creep 69.76 142.4 170.4 86.06 after transfer 135.80 215.6 254.5 128.49 total losses 315.30 390.6 434.0 305.94 % of losses 25.8% 32.0 % 35.5% 25.34% fig. 1. comparison of total losses between pre-tension and post-tension. fig. 2. comparison of losses after transfer between pre-tension and post-tension. this is due to the fact that the effect of shrinkage of concrete before transfer is not taken into account in the case of post-tensioning. the shrinkage in the case of post-tensing method is less than those of pre-tensioning method as shown in figures 3 and 4. fig. 3. losses due to creep and shrinkage in the case of pre-tension for different codes. fig. 4. losses due to creep and shrinkage in the case of post-tension for different codes. engineering, technology & applied science research vol. 7, no. 3, 2017, 1633-1637 1636 www.etasr.com boukendakdji et al.: comparative study of prestress losses in cp110, the value of shrinkage in post-tensioning is approximately two thirds of those given in pre-tensioning (table iii). losses calculated by cp110 are smaller than those calculated by ceb 70 or and this is due to the fact that ultimate shrinkage and creep strains given by cp110 are smaller than those predicted by both other methods (table iii). table iii. predicted shrinkage by different codes codes shrinkage in micro strain per unit length pre-stression post-tension cp 110 300 200 ceb 70 220 220 ceb 78 262 239 it seems that cp110 underestimates shrinkage and creep for thin sections (theoretical thickness 130 mm) because cp110 gives only one value of shrinkage for all concrete members even though it is known that shrinkage varies with the size of the member. thus if another example were done with a larger member, cp110 may give higher losses than those given by ceb70nor ceb78 method because both methods take into account size of the member. the higher value of predicted shrinkage and creep strains by ceb 78 causes the losses of prestress to be higher than those of ceb 70. for example in pre-tensioning process; ceb 70 predicts a shrinkage strain of 220 microstrain and a creep strain of 776 microstrain per unit length, and ceb 78 predicts 262 and 933 microstrain for shrinkage and creep strain respectively (figure 5). it is not possible to conclude which method of these two gives the more accurate prediction without direct co-relation to realistic in-situ data, but according to [14], the ceb 70 methods yields a slightly greater accuracy than that of the ce78. so it is preferable to use the ceb 70method for predicting creep and shrinkage. a general comment is that the ceb78 method makes no use of composition factors such as cement content and water cement ratio. also the effect of age at loading upon drying creep is not represented. fig. 5. creep in microstrain per unit length for different codes. since prestress losses due to steel relaxation and creep and shrinkage of concrete are inter-dependent and are time dependent, the pci method (or step-by-step procedure) can be used in order to account for changes which occur in successive time intervals. it is recommended that a minimum of four time intervals be used. the losses of prestress calculated by the pci method in the pre-tensioning and post-tensioning processes are given in tables iv and v respectively. the losses calculated by the pci method are lower than ceb 70 and 78 methods in both the pre-tensiong and post-tensioning process (figures 1 and 2). table iv. losses of prestress in the pret-tensioning process for pci methods in mpa stages periods losses (mpa) 1 tensioning steel to transfer (0-13 days) 81.27 2 1330 days 57.36 3 30 days to one year 81.53 4 one year to 40 years 35.40 total losses 255.56 % of losses 21.10 % table v. losses of prestress in the post-tensioning process for pci methods in mpa stages periods losses (mpa) 0 elastic shortening + friction + anchorage set 177.52 1 1330 days 55.92 2 30 days to one year 65.12 3 one year to 40 years 32.07 total losses 330.63 % of losses 27.38 % iv. conclusion although the aci method is a very simple method for predicting losses without having to break the life history of the beam into several time intervals and taking into account the various sources of losses gives nearly the same amount of losses as given by the pci method (step by step method) which is considered as a lengthy method. the aci method gives a constant value of creep which is independently of relative of humidity or volume to surface ratio. it seems that this method underestimates creep for high volume to surface ratio and high relative humidity. determination of prestress loss in accordance with the pci method (step by step method) is a lengthy and laborious procedure because the rate of loss due to one factor, such as relaxation of tendons, is continually altered by changes in stress due to other factors such as shrinkage and creep of concrete. rate of creep is, in turn, altered by the change in tendon stress. many of these factors are further dependent upon such uncertainties as material properties, time of loading, method of curing of concrete, environmental conditions and construction details. therefore, this method may be required for special structures or for simply supported slender members which may be sensitive to small changes in deflections. for non-special structures, or where actual losses, greater or smaller than the estimated, have little effect on the design, it is better to compute losses by aci method because it is simple and does take into considerations interactions between the various sources of losses, than simply summing up individual estimates of losses. engineering, technology & applied science research vol. 7, no. 3, 2017, 1633-1637 1637 www.etasr.com boukendakdji et al.: comparative study of prestress losses acknowledgment the research reported herein was funded by the deanship of scientific research at the university of hail, saudi arabia, under the contract (0150209). the author would like to extend his gratitude to the deanship of scientific research and to the college of engineering at the university of hail for providing all facilitations required for this research. references [1] r. i. gilbert, n. c. mickleborough, g. ranzi, design of prestressed concrete to as 3600-2009, crc press, 2016 [2] j. j. brooks, “30-year creep and shrinkage of oncrete”, magazine of concrete research, vol. 57, no. 9, pp. 545–556, 2005 [3] a. m. neville, w. h. dilger, j. j. brooks, “creep of plain and structural concrete”, construction press, london, pp. 361, 1984 [4] j. j. brooks, p. j. wainwright, m. boukendakdji, “influences of slag type and replacement level on strength, elasticity, shrinkage and creep of concrete”, 4th inter. conf. on the use of fly ash, silica fume, slag and natural pozzolans in concrete, vol 2, istanbul, turkey, aci spec. publ., pp 1325-1341, 1992 [5] aci committee 209, “guide for modeling and calculating shrinkage and creep in hardened concrete”, aci report 209.2r-08, farmington hills, 2008 [6] ceb-fip model code “model code for concrete structures”, thomas telford services ltd., london, great britain; also published by comité euro-international du béton (ceb), bulletins d'information no. 213 and 214, lausanne, switzerland, 1990 [7] z. p. bazant, q. yu, “excessive long-time deflections of prestressed box girders”, asce j. of structural eng., vol. 138, no. 6, pp. 676-696, 2012 [8] k. jayakumar, a. upadhyay, n. m. n. bhandari, “artificial neural network for predicting creep and shrinkage of concrete”, journal of advanced concrete technology, vol. 6, no. 1, pp.135-142, 2008 [9] cp110, the structural use of concretepart 1, britsih standard code of practice ,1972 [10] ceb-fip, international recommendations for the design and construction of concrete structures principles recommendations, european concrete committee , 1970 [11] ceb-fip, model code for concrete structures, comitee european du beton, fedeation internationale de la precontraite, paris, 1978 [12] aci committee 318, building code requirements for reinforced concrete (aci 318-77), american concret institute, detroit, 1977 [13] pci committee on prestress losses, “recommendations for estimating prestress losses”, prestressed concrete institute journal, vol. 20, no. 4, pp. 43-75, 1975 [14] f. m. abdellatif, long-term prediction of deformation of plain concrete, msc thesis, department of civil engineering, leeds university, 1982 microsoft word 1-605-ed.doc engineering, technology & applied science research vol. 5, no. 6, 2015, 871-875 871 www.etasr.com wu: developing situation of tea harvesting machines in taiwan developing situation of tea harvesting machines in taiwan chia-chang wu tea machinery tea research and extension station taoyuan, taiwan, r.o.c. tds311@ttes.gov.tw abstract—in recent years rapid social change and industrial and commercial development in taiwan has lead to migration of rural labor, population ageing, high wages and labor shortages, which resulted in significant problems for the tea industry. thus, mechanization in the tea industry emerges as the direction for the future. according to a survey, tea harvesting and tea manufacturing use 87% and 5% of available labor, so the mechanization of tea harvesting is a priority. the application and development of tea harvesting machines worldwide and especially in taiwan in recent years is investigated in this paper. recommendations are made for the implementation of tea harvesting machinery in taiwan in the future. this report may also used as a reference for the use of mechanical harvesting. keywordstea; plucking; machine; tea harvesting i. introduction taiwan is the sole producer of non-fermented tea, partially fermented tea and completely fermented tea in the world. in 2013, the value of primary processed tea was nt$6.7 billion. the sum of the value of tea-related marketing and connected industry (such as, leisure, arts, cultural and creative and tourism) of bonus is estimated to be more than nt$30 billion. with canned tea drinks and tea shops, the total is more than nt$70 billion. in recent years tea has become the most competitive agricultural product. social changes have affected the industry and migration of young people from the countryside resulted to a gradual ageing of the labor pool and a labor shortage in tea producing areas. wages have also increased, so the production and manufacturing costs have increased. therefore, the introduction of machinery emerges as a necessity for the tea harvesting industry in order to reduce the dependence on labor and costs. tea production, manufacturing and marketing are highly labor-intensive. harvesting and transportation labor is intensive in the tea production process, including tea plantation reclamation, planting, cultivation, irrigation, fertilization, pest and disease control, weed control and pruning. in tea leaf processing, fresh leaves are withered in the sun, set and tossed indoors, fermented, stirred, rolled, dried, de-stemmed, roasted and packaged, which requires much labor and capital. according to a chinese academic report, the cost in working hours for tea harvesting accounts for 45% and 50-60% of tea production and management [1]. according to a survey by the taiwan tea experiment station in 2014, the tea industry is especially in need of labor. the manual harvesting of tea accounts for 87% and tea manufacturing accounts for 5%. the greatest shortage of labor occurs in april and may, so there is a seasonal lack of labor. the report also shows that tea production costs account for 40%, with labor expenditure for tea harvesting accounting for 80%. the time at which tea is harvested affects the quality and price of tea, so labor availability. labor shortages, aging workforce and increasing wages result to mechanical harvesting becoming rather important for the tea production and manufacturing processes. japan has the highest penetration of tea harvesting machines. in taiwan, the mingjian tea area in nantou and the northern part of the pinglin tea area have used mechanical harvesting for many years with good results. in china, sri lanka and india mechanical harvesting also increased gradually. this study focuses on the tea producing countries of the world, the harvesting machinery and its use for systemic collation. the study shows that taiwanese tea plantations should increase their mechanical harvesting in the future. this paper aims to serve as a reference for agricultural authorities during policy setting and also as a guide for tea plantations managers and farmers. ii. the study and application of tea harvesting machines taiwan, china, japan, india and kenya are the major producers of tea harvesting machinery. japan is the biggest and most advanced producer. japan was the first country to use mechanical plucking for tea, when the big scissor was introduced in 1910. in 1915 the patent was approved and in 1920 the spreader big scissor was used in tea plantations. in 1960, a self-propelled tea plucking machine and a ride-on tea plucking machine were designed. some more specialized teas in the yulu tea plantation were still hand-plucked, but the mechanical plucking of tea accounted for almost 90 % of all tea plucked in japanese tea plantations. by 1980, tea plantations were commonly using tea plucking machines and the quantity engineering, technology & applied science research vol. 5, no. 6, 2015, 871-875 872 www.etasr.com wu: developing situation of tea harvesting machines in taiwan of tea plucking machine reached 10, 0000 [2-4]. using tea plucking machines significantly increased the productivity, reduced the dependence on labor and the production costs. in 1960, china began to consider the use of tea plucking machines and later studies concerned the cutting, fracture, folding and rolling of plucked tea leaves. manual, saddlemaneuvered and manually dragged tea machineries were subjected to experiments. by the 1980s, chinese manufacturers began to study double type plucking machines. however, single and double tea plucking machinery remains all imported [3]. in 1929, russia imported plucking shears from japan and in 1930 developed a reciprocating cut tricycle-type tea plucking machine. in 1953, studies began to focus on tea plucking machines and in 1965 a self-propelled tea plucking machine was developed but it was only suitable for use on plains with gradients less than 10 degrees and on gently sloping tea plantations. therefore, it could only be used in 40% of plantations. in 1970, a cutting tea plucking machine was developed. taiwan began to use the big scissor in 1951. it replaced the manual plucking of tea leaves and was being widely used in longtan and yangmei, in northern taiwan, by 1957. the big scissor only allowed 120kg of leaves to be plucked, and it was a difficult task, so its use was not that widespread [5]. the tea experiment station in pingzhen (the predecessor of taiwan tea experiment station) introduced a single burden japanese tea plucking machine in 1964. the farmer used the single tea plucking machine instead of the big scissor for tea leaf plucking. funding came from the joint commission on rural reconstruction (the predecessor of council of agriculture) and 42 japanese single reciprocating tea plucking machines were introduced in 1970. in 1973, experiments took place involving reciprocating and rotary type double tea plucking machines. these machines plucking replaced manual plucking in tea plantations in dongshan, pinglin and lugu counties from 1983 to 1985 [4]. in order to reduce the operating costs for the double type plucking machine, the taiwan tea experiment station introduced a japanese rail operating system in 1992. at the same time the rail operating material and the operation vehicles were localized and the system was used in the mingjian tea plantation [6]. iii. mechanical tea harvest experiments a comprehensive analysis of the literature on tea harvesting machine experiments from 1996-2014 follows. the harvesting efficiency of different harvesting machines, the pruning operation period, the cost of management operations for machine harvesting and manual harvest of tea and the efficiency of rail mounted machines are detailed. this is a comprehensive and authoritative guide to the use of harvesting machines in tea plantations. a. a comparison of the harvesting efficiency of different harvesting machines chang [7] compared the efficiency of manual plucking and machine plucking (big scissor, ochiai type tea plucking machine, uchida type tea plucking machine and fujimi type tea plucking machine) for different types of tree crown (mountain type, semicircular type and level type). the weight of the tea harvest for different plucking methods was determined and it was found that the harvesting efficiency of power plucking machines is greater than that for manual plucking (table i). the results showed that the ochiai type tea plucking machine (rotary cutting type), the uchida type tea plucking machine and the fujimi type tea plucking machine were 5-8 times more efficient than manual plucking. the fujimi type plucking machine rotates more slowly than the ochiai type tea plucking machine (rotary cutting type) and the uchida type tea plucking machine. the results show that manual tea plucking is more labor intensive and incurs greater production costs than machine plucking. these studies clearly show that in tea plantations, mechanization improves harvesting and increases production. the best results were obtained using a dynamic tea plucking machine that used the reciprocating cutting method. this increased the quality of tea bud selection and avoided coarseness that is associated with old leaves (data not shown). the report stated that the intense vibration of the machine induced operator fatigue so improving the performance of tea plucking machines would be crucial. table i. a comparison of the efficiency of different harvesting methods in g/min (source: an adaptation of [7]) plucking surface manual harvest plucking shears orgiaii plucking machine ugita plucking machine fuji plucking machine triangular plane 21.64* 74.11 142.00 132.75 110.50 hemispherical plane 17.42 67.53 159.00 144.25 94.67 horizontal plane 24.00 83.10 162.00 176.25 99.78 b. the effect of a transition from manual plucking to mechanical plucking in terms of yield and tea quality hung et al. [8] evaluated the transition from manual plucking to mechanical plucking in pinglin and mingjian. the feasibility of a tea plantation’s transition from manual to mechanical plucking is shown in the second year’s data. manual plucking of tea after shaping was necessary before mechanical plucking, because the density of tea buds must be uniform, so the yield of fresh tea leaves increased (table ii). in terms of quality, tea buds do not grow uniformly in the pinlin tea area, so the tea evaluation scores after manufacturing were lower than those for the mechanical plucking experimental area, but the scent was similar for manually harvested and mechanically harvested tea in both areas (tables iii and iv). mechanical plucking allows more centralization and fresh tea leaves can be withered indoors, so leaf moisture evaporates uniformly, which results in a better fragrance. for a large area and flat terrain in the mingjian tea area, manual plucking and mechanical plucking should produce more significant differences. hung et al. concluded that a transition from manual plucking to mechanical plucking was possible, but its feasibility depended on the manner in which the tea was grown and mechanical plucking required the formation of a curved plucking crown [8]. engineering, technology & applied science research vol. 5, no. 6, 2015, 871-875 873 www.etasr.com wu: developing situation of tea harvesting machines in taiwan table ii. the effect of different harvesting methods on the weight of fresh tea leaves harvested in kg/experiment area (source: an adaptation of [8]) pyng len ming jian crop season machine harvest manual harvest machine harvest manual harvest spring 37.3 29.7 108.4 120.0 summer 26.1 16.8 109.4 94.4 autumn 34.5 30.0 90 80 winter 22.8 21.6 47 42 table iii. the effect of different harvesting methods on the quality of tea (pyng len) (source: an adaptation of [8]) crop season harvest appea rance (20%) color (20%) color of liquid (10%) aroma &taste (30%) tea dregs (10%) total scores (100%) machine 16.0 15.5 16.2 24.2 8.3 80.5 spring manual 16.5 16.5 16.5 24.5 8.5 82.5 machine 13.5 13.0 14.5 19.5 6.8 67.3 summer manual 14.2 14.2 15.0 20.0 7.5 70.9 machine 14.0 14.0 15.5 19.5 7.2 70.2 autumn manual 14.6 14.5 15.0 21.5 7.2 72.2 machine 15.0 15.0 16.0 22.0 7.8 75.8 winter manual 14.0 14.5 15.2 20.5 7.2 71.4 table iv. the effect of different harvesting methods on the quality of tea (ming jian) (source: an adaptation of [8]) crop season harvest appea rance (20%) color (20%) color of liquid (10%) aroma &taste (30%) tea dregs (10%) total scores (100%) machine 15.0 15.0 15.0 22.8 7.8 74.6 spring manual 15.5 15.5 15.0 23.0 7.8 76.8 machine 14.8 15.0 14.8 21.3 6.8 72.7 summer manual 15.0 15.2 15.0 21.8 7.2 74.2 machine 15.8 16.0 15.5 22.5 7.5 77.3 autumn manual 15.8 15.5 14.8 21.0 7.2 74.3 machine 15.8 16.2 15.8 23.0 7.5 78.3 winter manual 15.6 15.8 15.8 23.5 7.5 78.2 c. the effect on leaf quality of pruning at different times lee [9] investigated the effects of pruning tea at different times: in winter (a week after the winter solstice) and spring (a week after spring tea plucking). the crown continued to be pruned (depth of pruning is 5cm) at chin shin oolong (camellia sinensis (l.) o. kuntz) tea plantation and the height and growth of the crown were measured during the harvesting period. table v shows the results for crown pruning operations in winter and spring. the height of the tea plant and the crown in the manual plucking experimental tea area show less significant differences. the experimental area that used machine plucking for pruning operations in winter or spring, also showed less significant differences in the height of the tea plant and the crown. the height of the plant increased by 1.21.5cm, and the crown was larger by 2.1-2.7cm in the mechanical plucking area than in the manual plucking area. the density of tea buds affects yield and quality, so this must be controlled within a certain range. a large number of tall plants could cause a nutrient shortage, which would result in smaller tea buds and thinning. a smaller density of buds can result excessive vegetative growth in plant and the quality of the fresh leaves is lower. table v. a comparison of the height and width of tea bushes in cm (source: an adaptation of [9]) after pruning the previous year before pruning current year total growth treatment bush height bush width bush height bush width bush height bush width manual harvest prune after winter tea 54.2 106.8 59.5 111.8 5.3 5.0 prune after spring tea 54.6 104.8 60.0 108.9 5.4 4.1 machine harvest prune after winter tea 54.9 104.3 61.7 111.4 6.8 7.1 prune after spring tea 53.3 103.5 59.9 110.3 6.6 6.8 table vi shows the results for pruning in the spring. both the manually plucked and mechanically plucked buds retain a high density after pruning operations in winter and the density of the tea buds increased by 24% per annum. for 2 3 harvests in each area, tea bud density in winter was not affected by pruning in winter or spring, either for manual or mechanical plucking methods. table vii shows the results for tea after pruning in winter, to study the yield of tea leaves either for manual or mechanical plucking and compares these with those for significant pruning in spring. after pruning in winter, thinning of the spring buds significantly reduces yield but balancing autumn and winter tea produces less than significant differences. table vi. a comparison of the density of tea shoots for different seasons in bud/900 cm2 (source: an adaptation of [9]) crop season treatment spring tea summer tea 2nd summer tea autumn tea winter tea manual harvest prune after winter tea 87.1 95.2 101.5 75.3 90.0 prune after spring tea 117.9 73.5 89.8 70.8 99.1 machine harvest prune after winter tea 93.9 87.2 95.4 74.7 97.3 prune after spring tea 118.9 69.1 88.8 69.6 96.9 table vii. a comparison of the yield of fresh tea lea leaves for different pruning and harvesting methods in different seasons in kg/40m length of tea bush (%) (source: an adaptation of [9]) crop season treatment spring tea summer tea 2nd summer tea autumn tea winter tea manual harvest prune after winter tea 15.5 (66.8) 15.6 (219.7) 18.5 (149.2) 12.5 (112.6) 13.5 (95.7) prune after spring tea 25.0 (107.8) 10.3 (145.0) 13.8 (111.3) 11.8 (106.3) 14.7 (104.3) machine harvest prune after winter tea 16.2 (69.8) 12.2 (171.8) 15.7 (126.6) 14.1 (127.0) 13.2 (93.6) prune after spring tea 23.2 (100.0) 7.1 (100.0) 12.4 (100.0) 11.1 (100.0) 14.1 (100.0) engineering, technology & applied science research vol. 5, no. 6, 2015, 871-875 874 www.etasr.com wu: developing situation of tea harvesting machines in taiwan in order to maintain yield and quality in the chin shin oolong (camellia sinensis (l.) o. kuntz) tea plantation, shaping operations (pruning) were necessary. to maintain the density and growth of buds and to give an increased yield in spring after the winter tea season partially fermented tea was produced in spring and winter. when the chin shin oolong (camellia sinensis (l.) o. kuntz) tea plantation underwent shallow pruning, the experimental results show that pruning after spring is more favorable. the total yields for the spring and winter seasons with pruning in winter are 29-37% greater. d. a comparison of the management of manual plucking and machine plucking a comparison of the management of tea plantations in the lugu tea area (manual plucking) and the mingjian tea area (machine plucking) is considered next. since 1980, the mingjian tea area has implemented machine plucking. in this area the altitude is 100-200m and the topography is flat. however, in the lugu tea area tea plucking is still primarily dine manually. in this area the altitude is 300-1,500m and the topography is mountainous. the tea plantation working hours and production costs in mingjian and lugu tea areas in 1989 are summarized in table viii. table viii. the labor and cost for tea production for different types of tea cultivation (source: an adaptation of [10]) lugu ming jian items time (hour) cost of production (dollar/ hectare) time (hour) cost of production (dollar/ hectare) weeding* 582 (16.9) *** 32,837 (10.6) 448.6 (35.0) 23,269 (14.9) fertilizing 244 (7.1) 24,145 (7.8) 204 (15.9) 13,417 (8.6) pest control 362 (10.5) 33,923 (10.9) 257 (20.1) 19,621 (12.6) tea harvest 2080 (60.4) 173,000 (55.6) 220 (17.2) 40,400 (26.0) others** 174 (5.1) 46,999 (15.1) 151 (11.7) 58,881 (37.9) total 3,442 (100) 310,904 (100) 1280.6 (100) 155,588 (100) note: *, includes weeding, mowing by machine, herbicides and artificial grass. **, includes deep, mulching, pruning, machinery depreciation and maintenance, fuel costs, wages and depreciation, irrigation, irrigation equipment and other operations. in the lugu tea area, manual plucking working hours constitute 60.4% of operation hours and manual plucking accounts for 55.6% of production costs. in the mingjian tea area, manual plucking working hours constitute 17.2% of operation hours and manual plucking accounts for 26.3% of production costs. huang [10] determined the cost of plucking tea. in the mingjian tea area (machine plucking), the cost per hectare was nt$ 40,400 and in the lugu tea area (manual plucking) the cost per hectare was nt$ 173,000 [10]. the wage for manual plucking of fresh leaves was nt$ 40-60 per kilogram and the cost of machine plucking per hour was nt$ 1000-1200, giving an average cost per kilogram of nt$ 2.5 3.0 [10]. huang [10] compared the results for the different production methods and confirmed that the tea harvest accounted for the highest percentage of tea plantation management costs [10]. therefore, it is concluded that mechanical plucking is more profitable than manual plucking. over a full year, mechanical plucking significantly reduces production costs. e. the effect of different plucking methods on yield and operational efficiency huang et al. [11] found that rail type mechanical plucking reduces double type plucking machine labor costs. the tea plantation was pruned in winter and the yield and efficiency for the next year for aril type plucking machine harvest, double type plucking machine and manual plucking were determined [6]. table ix shows the yield for manually harvested leaves is significantly less than that for a rail type plucking machine or a double type plucking machine. rail type and double type plucking machine give similar yields. table x shows the comparison of the yield of tea shoots and plucking time for a rail type plucking machine, a double type plucking machine and manual plucking. the data only concerns labor, collection and transport costs ignored. rail type plucking machine harvesting requires only one person and double type plucking machine operations requires two people. each experimental row was only 30m so the rail type plucking machine had to stop and change direction, which increases the operating time. table ix. a comparison of the yield of fresh tea (source: an adaptation of [6]) crop season plucking spring crop autumn crop winter crop rail machine 24.8* 21.4 24.0 double type machine 23.1 24.3 22.3 hand 15.7 17.9 15.1 ` note: *, kg/4rows×30m length. table x. a comparison of the yield of tea shoots and plucking time (source: an adaptation of [6]) plucking labor (people) time (hour) total time (hour) total time per hectare (hour) cost of harvest (nt$) rail machine 1 0.42 0.42 23.3 6,990 double type machine 2 0.20 0.40 22.2 6,660 hand 16 1.57 25.12 1359.6 140,000 hung et al. [11] suggested increasing the length of the tea row to reduce the overall operating time by reducing mechanical shutdown and changes of direction. table x shows that the harvest weight of fresh leaves for the rail type plucking machine and double type plucking machine are both significant higher than that for manual plucking, mainly because manually plucked tea plantations have a lower growth density. there is no significant difference in the density of tea buds and the harvest weights between the rail type plucking machine harvest and a double type plucking machine harvest. lee [12] used imported semi-self-propelled and self-propelled plucking machine in a tea plantation to reduce the physical burden on the engineering, technology & applied science research vol. 5, no. 6, 2015, 871-875 875 www.etasr.com wu: developing situation of tea harvesting machines in taiwan operator, but this requires the coordination of two people. the efficiency and effectiveness are no greater than that for a double type plucking machine. these two types of plucking machines impose restrictions on the width, slope and length of rows and a self-propelled plucking machine is expensive, so it is not generally feasible. a self-propelled plucking machine was found to be suitable only for long rows with minimal gradient. the cost of self-propelled plucking machine machines is now $nt 1,000,000-4,000,000 and there is an additional need to allot the space for mechanical rotating operations, so they are only suitable for very large tea plantations. iv. conclusions harvesting tea involves a large expenditure on seasonal labor. labor shortages in the labor and an aging workforce mean that traditional manual plucking of tea leaves must be replaced by mechanical plucking. the mechanical plucking of tea leaves is quite common in japan and argentina. the mechanical plucking of tea leaves has been used for many years and the mechanical plucking technology has improved in the mingjian tea area of nantou, taiwan. china, sri lanka and india are also currently mechanically plucking tea leaves. the mechanical plucking of tea leaves of tea gives 8-15 time better harvesting efficiency than manual harvesting. compared with manual plucking, mechanical plucking reduces production costs by 50-70%. mechanical plucking also leads to time saving and superior quality since tea leaves arrive in less time (and thus are fresher) to the factory. however, it should be noted that manual plucking causes fewer tea leaves to be lost during plucking, and thus improves tea quality, and that mechanical plucking requires a pre-classification of tea leaves to get a superior quality tea. in order to reduce the production costs and to address the labor shortage in taiwan, the development of the mechanical plucking of tea leaves is inevitable. however, machine plucking over a long time, causes the tea buds to germinate and there is an excessive increase in density. tea leaves with a density greater than 900cm² have more than 140 buds and the shoot is thin. this causes the tea buds to develop facing-leaves, the leaves become thin and tea quality is reduced. therefore, during the tea leaf harvest, there must be an appropriate control of the mechanical blade and suitable pruning operations. in the future, tea plantations that use mechanical plucking will require more planning of the selection of the correct tea variety and cultivator, deep plowing, fertilization, irrigation, disease and pest management, tree crown pruning, machinery and tea manufacturing techniques so that the tea is robust vigorous and has an even branch size and distribution. the tea bud germination density must be appropriate and there must be tidy growth, to allow mechanical plucking and to maintain tea leaf quality. mechanized tea plucking in taiwan will require coordination between tea plantations and automation, so that production costs are reduced and competitiveness is improved. to increase mechanization, the agricultural authorities must provide mechanical means and management technology and assistance for machine purchases by farmers, to ensure that the taiwanese tea industry remains internationally competitive and to allow sustainable development. references [1] z. f. mao, d. b. chen, “discussion of the excellent tea on plucking mechanized”, china tea, vol. 3, no. 1, pp. 4-5, 2006 [2] s. l. tsai, china encyclopedia of agriculture, tea volumes, agriculture publishing house, beijing, china, pp. 7-8, 1988 [3] z. m. chen, zhong-guo chajing, shanghai culture publishing house, shanghai, china. pp. 353-354, 1992 [4] y. han, h. xiao, g. qin, z. song, w. ding, s. mei, “developing situations of tea plucking machine”, engineering, vol. 6, pp. 268-273, 2014 [5] j. m. chang, “a study of effect on the growth and quality of tea bush with mechanical plucking”, journal of chinese agricultural engineering, vol. 12, no. 1, pp. 1-10, 1996 [6] c. l. lee, t. f. huang, “development and application of rail management system for tea field management machines”, taiwan tea research bulletin, vol. 19, pp. 29-36, 2000 [7] j. m. chang, “the province of implemented general situation on tea garden mechanization ”, tea newsletter, vol. 346, pp. 87, 1971 [8] t. f. huang, c. l. lee, y. k. chang, “study and extension on mechanical plucking of hand plucking tea area”, taiwan tea research bulletin, vol. 5, pp. 15-30, 1986 [9] c. l. lee, “technical improvement mechanical plucking in chin-shin oolong tea gardeneffects of plucking periods and depths on tea yields of different tea crop seasons”, taiwan tea research bulletin, vol. 10, pp. 115-127, 1991 [10] t. f. huang, “development of hand-pluck tea garden mechanized in the future”, development and promotion of taiwan tea research seminars monograph. taoyuan, taiwan, pp. 38-43, 2001 [11] t. f. huang, c. l. lee, y. k. chang, “study on using the rail mechanical plucking management system in hand plucking tea area”, taiwan tea research bulletin, vol. 22, pp. 79-86, 2003 [12] c. l. lee, “study and promotion on tea plucking mechanization”, tea production technology seminars monograph, taoyuan, taiwan, pp. 115-124, 1992 microsoft word etasr_v12_n1_pp8129-8135 engineering, technology & applied science research vol. 12, no. 1, 2022, 8129-8135 8129 www.etasr.com el gharbi: a distributed control approach for demand response in smart grids a distributed control approach for demand response in smart grids atef el gharbi faculty of computing and information technology northern border university rafha, saudi arabia institut national des sciences appliquées et de technologie (insat), lisi carthage university tunisia atef.gharbi@nbu.edu.sa abstract-the smart grid is a new concept that has been developed during recent years to improve the intelligence and efficiency of electric power system management. traditional electricity systems are combined and integrated with information technology, communication technology, and intelligent control technology in the smart grid. demand response (dr) refers to the changes in consumers' electricity consumption behavior in response to dynamic pricing or financial incentives. based on the control manner, dr methods are classified as centralized or distributed. in distributed techniques, customers communicate with the other consumers and provide data to the power utility about the overall use. in this paper, we focus on the distributed approach of dr using the shifting method for a short-term horizon. to be more specific, three well-known solutions were studied: the resource allocation with legitimate claims, the constrained fair-splitting dispatch, and real-time pricing. finally, we compare the different techniques of dr distributed approaches based on the control mechanism. keywords-demand response; distributed approach; resource allocation with legitimate claims; constrained fair-splitting dispatch problem; real-time pricing i. introduction demand response (dr) is a technique describing the way the demand side responds to the supply-side price techniques or incentive measures [1-3]. dr leads to modifications in end-use customer consumption patterns as a result of the changes in electricity pricing over time or incentive payments designed at encouraging lesser energy use during periods when the market prices are higher or when system reliability is affected. dr is a cost-effective way to minimize power usage, and the cost of putting it in place is less than the cost of adding more generation capacity to get the same result [4]. the fundamental advantage of dr is that it improves power system use by establishing a closer relation between customers' consumption and the electricity price [5]. dr is becoming increasingly crucial in the interaction between supply and demand, which is the most critical aspect of the smart grid compared to traditional power systems. when consumers participate in dr programs, they are more likely to decrease their electricity use during critical peak periods or shift some peak demand to offpeak periods [6]. as a result, the economy and security of the electricity systems are improved. customers can react to high prices in one of the following methods [7]: • foregoing is a method for limiting electricity consumption during times of high prices, but not consuming it thereafter. • shifting is a technique to reschedule power usage from high-priced periods to other times. • onsite generation is a method where some users have backup emergency generators that can be used to respond partially or totally to their use demands. in this paper, we are interested in the shifting method as it is the most used in dr. dr methods are classified as centralized and distributed, based on their control mechanism. in the centralized approach, costumers interact directly with the power utility, without communicating with each other. in the distributed approach, consumers communicate with the others and inform the power utility about its use [8]. the main contributions of this paper are: (1) the introduction and exhibitions of results of the most famous distributed solutions for dr using the short-term horizon shifting method, (2) addressing a comparison between the distributed solutions. ii. background dr methods are classified as centralized or distributed, based on the control mechanism. in centralized dr, the response decisions for energy assignment or load scheduling are solely handled by the power utility, based on groups formed by sets of customers. in this method, each consumer participates without having to be aware of the other customers in the group's involvement [9]. furthermore, fixing the problems centrally necessitates transferring all the consumers' personal data to the aggregator, resulting in significant communication overhead and privacy problems. this central strategy, on the other hand, always entails a large computational load along with the privacy issue. in the corresponding author: atef al gharbi engineering, technology & applied science research vol. 12, no. 1, 2022, 8129-8135 8130 www.etasr.com el gharbi: a distributed control approach for demand response in smart grids distributed approach, the power utility's key role is the delivery of pricing information, depended on the total system consumption. customers can manage directly with one another to accomplish aggregated load reduction. unlike a central authority which collects data to make decisions, the decentralized control ensures scalability and protection of consumer privacy [10]. in the literature review, there were found two primary families on distributed dr approaches. the first group includes techniques that treat energy uses as continuous [11] which makes the underlying dr issue convex and hence computationally feasible. the second group includes techniques representing energy uses as a combination of discrete and continuous uses [12]. the interaction between consumers and providers can be divided into 3 approaches based on the time scale: long-term horizon, medium-term horizon, and short-term horizon. pricebased demand response is concerning customers' energy consumption changes in reaction to changes in their purchase prices [13]. this category includes real-time pricing (rtp), time-of-use (tou), and critical-peak pricing (cpp). for rtp, electricity prices are set for a short-term horizon of time, usually one hour [14], to match fluctuations in wholesale electricity prices. customers are frequently given price information a day or hour ahead of time. tou defines different costs for medium-term horizon of time, which are commonly established in 24-hour increments [15]. cpp is a combination of tou and rtp, and it is more difficult to implement [16]. the base program is tou, and under certain circumstances, substantially higher peak pricing is used (e.g. whenever the system reliability is affected or when power costs are very elevated). incentive-based programs (ibps) control consumption without using power costs. instead, customers agree to reduce their load during crucial circumstances and to be paid for that [17]. the load can be controlled in two ways. it might be the utility that guides the load and takes appropriate actions, or it could be the consumers the ones who take appropriate actions in the event of an emergency. classic programs and market-based programs [18-20] are the two types of incentive-based programs. to the best of our knowledge, no research has been published about the evaluation of the different dr techniques in a distributed way using the shifting method for a short-term horizon. in this paper, the assessment of three different distributed dr techniques is conducted. the scope is to provide a very contribution in the awareness of the best approach based on specific criteria. iii. distributed dr control algorithms in a centralized solution, the dr procedure is controlled by only one unit, which gathers the demand information from the customers and then makes decisions for demand scheduling. in distributed dr, demand information is not centrally gathered and customers have direct access to grid state meters. with this information, consumers are able to react based on the system’s state, if it is critical. in this section, we present the most important techniques related to dr of smart grid as distributed approach. a. resource allocation with legitimate claims (ralc) in ralc, the provider agent must determine how much energy , in i t π each customer agent should be assigned, taking into account certain limits. as a result, the energy demand allocation problem is to consider how much energy should be allocated to each customer agent , in i t π . the proposed allocation method is based on distributive fairness and is self-organized [21]. customer agents agree on the criteria for conducting the allocation. any of the provider agents then computes this allocation. the allocation is done pursuant to a set of canons in distributive justice. to this purpose, we propose the following mechanism for agreeing on load allocation at a certain time t (hour): 1. information about the load l(t) is available at the provider agent (t). 2. every customer agent i sends a request to the provider agent asking the desired power , in i t π as well as the constraints min ,i t π and max ,i t π . 3. the provider agent calculates the total amount of power requested min max , , t t t π π π . there could be a variety of scenarios: • min t t l π= : if the equality holds, all customer agents are given the smallest amount of authority, min , , in i t i t π π= . • min max t t t lπ π≤ ≤ : customer agents are assigned power within their needed range. each customer agent's power is assigned by the provider agent based on a rank attributed according to a set of weights. weights are assigned to all customer agents after they reached an agreement a set of canons. in this case, every customer receives power , in i t π such that: min min min , , , , , min( , ) in i t i t t i t i t i t lπ π π π π← + − − • max t t l π≥ the customer agent obtains the exact amount of power required, , , in i t i t π π= . 4. the provider agent provides each customer agent with the computed allocation , in i t π . 5. each customer agent must pay , in t i t λ π× in accordance to the provided energy , in i t π . the second protocol in step 3 is crucial, as it requires the customer agents to agree on the way the load will be divided. to do so, the rescher's canons are used as voting functions f* for the allocation, and the relevance of each function is decided by its associated weight w*. the process of determining the way the load is divided is essentially an allocation procedure that is frequently applied. the weights' initial value is set at * 1 w m = (where m represents the functions number), and the procedure proceeds as follows: a consensus on a particular ranked list of customer agents should be reached in order to proceed with the allocation. the engineering, technology & applied science research vol. 12, no. 1, 2022, 8129-8135 8131 www.etasr.com el gharbi: a distributed control approach for demand response in smart grids borda count protocol is used as a consensus-based voting approach. in the borda count process, each function f∗ is considered as a voter. each vote in borda count voting sorts the candidates based on a specific criterion. each candidate in the list is given borda points: for example, if we have n customer agents, then the rank k receives n k + 1 borda points. the borda points obtained from each vote are added together to give a total borda score for every agent. the candidate having the highest borda score gains the borda count procedure, however it is possible to find several "winners," therefore we construct a borda point queue in decreasing order and assign electricity to the head of the queue until there are no more to allocate. under a set of functions f, the borda score b of candidate i is calculated by: * * * 1 ( , ) ( ( )) f b i f w bpts f i = = ×∑ (1) where f∗(i) determines each f∗'s rank order for candidate i, bpts() computes the borda points for that rank, and w∗ is the weight associated with the function f∗. the borda count function returns the borda_ptq list after computing the borda score b for each agent i. algorithm 1 presents the main idea explained above, where a is a set of n consumer agents, and f is a set of m voting functions f∗, each with its own weight w∗. algorithm 1. resource allocation with legitimate claims. 1: for each time slot t ∈ t do 2: 0 t π ← , min 0 t π ← 3: for each customer agent i ∈ n do 4: ,t t i t π π π← + 5: min min min ,t t i t π π π← + 6: end for 7: lt ← update(lt) 8: if lt > tπ then 9: for each customer agent i ∈ n do 10: , , in i t i t π π← 11: end for 12: else if lt > min t π // lt < tπ 13: rank orders ← [ ] 14: for every voting function f∗ ∈ f do 15: rank orders ← rank orders ∪ f∗(a) 16: end for 17: borda_ptq ← borda count(rank orders, f) 18: repeat 19: i ← head(borda_ptq) // customer i 20: borda ptq ← tail(borda_ptq) 21: min min min , , , , , min( , ) in i t i t t i t i t i t lπ π π π π← + − − 22: , in t t i t l l π← − 23: until (borda_ptq = null) 24: else // lt = min t π then 25: for each customer agent i ∈ n do 26: min , , in i t i t π π← 27: end for 28: end if 29: end for 30: end as a running example, figure 1 depicts the agents ranked by a group of voters, each of whom creates its own rank list. borda points are assigned to each rank in a list and then are combined together in a weighted sum to produce a single final rank list and final borda score for each agent. fig. 1 the borda count voting mechanism in a simple form. b. constrained fair-splitting dispatch (cfsd) sfsd is the most famous dr method. at first, we consider a direct graph g = {v, e} where each customer i can possibly transmit information to other customers called its neighbors ni. the customers sending data (respectively receiving data) to the customer i are called the in-neighbors (respectively outneighbors) of i and are represented by the set i n − (respectively i n + ) = {j ∈ v: (i, j) ∈ e}. the number of in-neighbors (respectively out-neighbors) of agent i is called the in-degree (respectively out-degree) and is denoted by i d − (respectively i d + ). π denotes the total amount of power that the system should collectively deliver, i.e.: 1 n i i π π = = ∑ . the ratio consensus technique is explained below. consider the exchange of data between customers in a direct graph where each customer i in the graph keeps two values, yi and zi, called internal states, which are independent and updated as a linear combination of customer i's prior internal states and the past internal states of its in-neighbors respectively. for each k ≥ 0, each customer i updates yi and zi, in the following way [22]: 1 ( 1) ( ) i i j j n j y k y k d− + ∈ + = ∑ (2) 1 ( 1) ( ) i i j j n j z k z k d− + ∈ + = ∑ (3) ∀ k, customer i computes: ( ) ( ) ( ) i i i y k k z k γ = (4) engineering, technology & applied science research vol. 12, no. 1, 2022, 8129-8135 8132 www.etasr.com el gharbi: a distributed control approach for demand response in smart grids lemma 1: for every customer i, it is demonstrated in [22] the convergence of ( ) i kγ to some constant γ. then, each customer i asymptotically obtains: 1 1 (0) lim ( ) (0) n j j k i n j j y k z γ γ =→∞ = ∑ = = ∑ (5) without loss of generality, we assume that the total resource amount π is known to a power entity v, who is able to exchange data with specific customers v + (having a number m). besides, the initial conditions in (2) are set to (0) i y = π / m− min i π if i ∈ v+, and (0) i y = − min i π otherwise. moreover, the initial conditions in (3) are set to max min (0) i i i z π π= − , ∀ i. then, as long as min max 1 1 n n i i i i π π π = = ≤ ≤∑ ∑ , we conclude from lemma 1 that the i-th node can asymptotically determine its contribution i π as: min max min ( ) i i i i π π γ π π= + − (6) where: min 1 max min 1 ( ) lim ( ) lim (0) ( ) n j ji k i k n i j j j y k k z π π γ γ π π = →∞ →∞ = − ∑ = = = −∑ (7) note that (6) satisfies min max i i i π π π< < , ∀ i, and also 1 n i i π π = =∑ . additionally, every customer i can independently declare infeasibility if γ > 1 or γ < 0. the solution in (6) is not considered as the optimal solution, but it ensures a "fair" splitting of the total amount of resource π proportional to the "excess" capacity of each node. as a running example, figure 2 depicts the convergence of ( ) i kγ for j = 1, .., 4 over 30 iterations. we can conclude from the graph that after about 13 iterations, all customers obtain a common value γ = 0.9. as a result, the customers decide the solution is possible and update their output in accordance with (6), obtaining x = [0.279, 0.129, 0.364, 0.228] t . fig. 2 convergence of constrained fair-splitting dispatch algorithm. c. real-time pricing (rtp) algorithm the provider agent modifies its energy supply tactics in every iteration, based on the consumer agents' energy consumption strategies, whereas the consumer agent i adjusts its energy consumption based on real-time costs (see figure 3). we present here the optimal rtp algorithm based on the utility maximization for smart grid [23] in which: * , t i j π is the optimal requested power by the consumer agent i to the provider agent j, t j λ is the updated price by the provider agent j, * ( ) t t l λ is the capacity update, and t j µ the coordination parameter. the requested power is: min max , , , * , , , , ( ) u( , ) argmax t i j i j i j t t t t t i j j i j i t j i j ππ π π πλ λ πω ≤ ≤ = (8) and the price update is provided by: ( )1 * *, 1 ( ) ( ) n t t t t t j j i j j t j i lλ λ λ λπγ + + =  = + −∑   (9) where [�] + = max{�, 0}. the capacity update is given by: min max * ( ) ( )argmax t j j j t t t t t j j j j t j l l l l l c lλ λ ≤ ≤ = (10) and the coordination parameter by: ( )1 *, 1 ( ) n t t t t i i i j j i i bµ µ γ λπ + + =  = − −∑   (11) 1) real-time pricing formulation algorithm 2: executed at consumer agent i. 1: for every t ∈ t 2: receive the new price t j λ from the provider agent j. 3: compute the consumption value * , t i j π using (8). 4: send the updated * , t i j π to the provider agent j. 5: calculate the coordination parameter t i µ by (11). 6: end for algorithm 3: performed by the provider agent j. 1: repeat 2: if time t ∈ t 4: calculate the new electricity price t j λ by solving (9). 5: send the new price t j λ to each consumer i. 6: else 7: update the capacity value ( ) t t j l λ using (10). 8: receive * ,i t π from all the consumer agents i ∈ n. 9: update the total load * , t i j i n π ∈ ∑ accordingly. 10: end if 11: until the end of planned period. the pricing mechanism proposed in this study aims to align social benefit with individual welfare, i.e. to find a suitable pricing so that the locally optimal solution is the same as the engineering, technology & applied science research vol. 12, no. 1, 2022, 8129-8135 8133 www.etasr.com el gharbi: a distributed control approach for demand response in smart grids globally optimal solution. from the algorithm 2, the consumer agents are regarded independent agents who are responsible for their own well-being. to improve their benefits and contentment, each consumer agent requires a specific quantity of power. the mission of a smart grid is to manage the coordination of the customer agents to cover the requested power, so that there is a balance between energy production and consumption. form the algorithm 3, it is clear that the provider agent is trying to fulfill the consumer agents' requests or facilitate the coordination between customer agents so that they can guarantee the total requested power and maintain a balance between energy production and consumption (in accordance with the consumer agents' needs and constraints). the following characteristics are included in the proposed algorithms. • algorithms 2 and 3 are considered distributed algorithms in which each utility company and user solves the subproblems locally to allocate energy. there is no requirement for a central controller or a third party. • each user helps energy allocation by coordinating the demand from several power entities to satisfy his need. • the distributed algorithms 2 and 3 protect power entities' and customers' privacy. however, this leads to a more complicated solution. figure 3 depicts the communication between the utility company and the user in a multiseller–multibuyer system. the electricity pricing and energy demand are the two pieces of information that must be exchanged between the utility provider and the customer. algorithms 2 and 3 summarize the distributed algorithms at each utility business and each user respectively. each utility business adjusts its supply in response to the electricity price. each utility company determines the price of power depending on its supply and demand from all customers. the price is then made public to all users. the electricity price and the user's coordination parameter are used to update each user's demand. fig. 3 information exchange between the provider and the consumer agents. 2) running example figure 4 depicts the relationship between the provider's hourly fee and the consumed electricity. customers actually lower their use during peak hours (as shown in the figure at hours 18 and 19) because the price is doubled. furthermore, clients determine the optimal consumption at the lowest price (in the figure at hours 11 and 12): this is illustrating the most significant benefit of the rtp algorithm. fig. 4 total power consumed with rtp algorithm. iv. numerical results through this section, we study the features of each technique: dr with ralc, cfsd, and the rtp algorithm. some numerical results illustrating the results of each are provided and compared. for the purposes of simulation throughout our research, we will use a network with c = 7 companies and u = 150 clients. figures 5 and 6 show the customers' average utility and energy usage as functions of the timeslots required for all comparative frameworks to converge to the steady customers' association with power companies. the results show that the rtp algorithm produces the highest consumer utility (figure 5) and the lowest customer electricity consumption (figure 6). this trend is the result of the use of (8)-(10), including both monetary and electricity-related aspects, as described above. furthermore, the ralc, which is self-organized and based on distributive fairness, delivers acceptable outcomes in terms of consumers' utility and electricity consumptions. cfsd, on the other hand, does not optimize the electricity consumption and achieves the lowest customers’ utility and high electricity consumption. when compared to the other two algorithms, the rtp algorithm outperforms both, demonstrating the huge benefit of using optimization in the overall process. the results reveal that: (a) the cfsd applies no optimization. users choose time periods at random to place their schedulable loads. (b) the ralc is a greedy algorithm, in which everyone strives to reduce its total electricity cost by lowering the base price. this one simulates a scenario in which there is no cost fluctuation fee and users do not collaborate while making judgments. (c) the rtp algorithm provides optimal results. engineering, technology & applied science research vol. 12, no. 1, 2022, 8129-8135 8134 www.etasr.com el gharbi: a distributed control approach for demand response in smart grids fig. 5 customers’ average utility. fig. 6 customers’ total energy consumption. v. conclusion dr is an important subject in smart grid implementations, allowing better system operation and extension, and increased market efficiency. it can be used to lower the overall load in response to peak power constraints as well as for auxiliary services like frequency regulation, which has a faster scale reaction time. in this paper, we studied the most widely known techniques in distributed dr, namely ralc, cfsd, rtp. we compared these techniques based on two criteria: customers' average utility and energy usage. the results show that the rtp technique is the best as it ensures the highest consumer utility as well as the lowest customer electricity consumption. for future work, it is possible to extend the distributed algorithms to make them robust to faulty consumers. references [1] m. e. bendib and a. mekias, "solar panel and wireless power transmission system as a smart grid for electric vehicles," engineering, technology & applied science research, vol. 10, no. 3, pp. 5683–5688, jun. 2020, https://doi.org/10.48084/etasr.3473. 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tunisia abdelkader.mami@fst.utm.tn abderrahman el mhamedi iut of montreuil, university of paris 8 paris, france a.elmhamedi@iut.univ-paris8.fr el mouloudi dafaoui iut of montreuil, university of paris 8 paris, france e.dafaoui@iut.univ-paris8.fr received: 21 april 2022 | revised: 16 may 2022 | accepted: 18 may 2022 abstract-the economic emission dispatch (eed) is a multiobjective optimization problem that seeks to find the optimal balance between the reduction of the generation costs and the pollutant emissions of power thermal plants while respecting power balance and several operational restrictions. this balance could be carried out by proper scheduling power generation of the committed units to fulfill the power demands considering emissions. this paper presents a novel application of the conventional levenberg-marquardt algorithm (lma) optimization approach to solve the eed problem with the integration of renewable energy. wind and solar energy were chosen to be injected into the system’s power balance constraint. the combined eed objective function with valve point effects (vpe) consideration was modeled using price penalty and weight factors. this study showed the effectiveness of the chosen optimization technique and the influence of injecting renewable energy along with traditional power resources on reducing total cost and pollutant emissions. the proposed method was applied to the ieee 9-bus test system and tested in matlab. keywords-economic emission dispatch; levenberg-marquardt algorithm; wind; solar; valve point effects i. introduction more than 80% of total consumed energy is derived from fossil fuels such as oil, coal, and gas [1]. fossil fuels are expensive to extract, finite, and their use emits a variety of harmful pollutants [2]. thermal power plants can respond to sharp and sudden power demands quickly. economic dispatch (ed) is a necessary task in fuel-based power production systems. it is a computational optimization problem where the overall required generation is distributed among the commuted thermal power units to minimize the total generation cost, no matter the harmful emissions produced. however, alternative strategies are required to respond to the increasing demands for environmental protection [3]. economic emission dispatch (eed) is one of these strategies that has received considerable attention. eed aims to simultaneously reduce total generation costs and pollutant emissions, such as so2, nox, and co2. emissions could be considered within the economic dispatch problem by being incorporated as a constraint [4, 5], or as a weighted quantity within the objective function of the problem. renewable energy is environment-friendly and sustainable with low production cost. once built, renewable facilities cost very little to operate. however, it is difficult for renewable energy to generate power on the same large scale as fossil fuels. the most common renewable resources are solar and wind. both these energy sources are intermittent, as they depend on climate parameters such as solar radiation, temperature, and wind speed and they are challenging to schedule [6]. several tools have been explored considering renewable energy in the eed problem. in [7], eed with solar and wind power was solved using harmony search. the results were carried out for one level of power demand and the influence of integrating renewable energy was studied. artificial neural networks were applied in [8] to predict and solve eed with the integration of renewable energy, reaching an optimum in real-time. the effectiveness of the pso-based strategy was shown in [9] by solving the eed problem by considering vpe and including wind energy sources for a 10unit system. the results were investigated for both cases, with and without wind power penetration. among the various existing optimization techniques to solve power system problems, this study investigated the use of the levenberg-marquardt algorithm (lma) [10-12]. lma is a hybrid numerical optimization approach that uses both the corresponding author: tawba dridi engineering, technology & applied science research vol. 12, no. 4, 2022, 8850-8855 8851 www.etasr.com dridi et al.: application of the levenberg-marquardt algorithm in solving the economic emission … gauss-newton algorithm and the steepest descent search to converge to the optimal solution. this technique is particularly effective in solving systems with non-linear equations [12]. this paper proposes a novel application to lma for solving the static lossy non-convex multi-objective eed problem with solar and wind power penetration. the results showed the influence of integrating renewable energy to reduce total production costs and pollutant emissions. this method was tested and simulated on an ieee 9-bus system via the matlab environment. ii. eed formulation with wind and solar power two objective functions were considered: minimization of the total generation cost and of the nox emissions of the committed power units. a. objective functions the eed problem is defined as a constrained multiobjective optimization problem that minimizes simultaneously total power cost and emissions of pollutant gases while satisfying power balance and operational constraints. 1) cost function with vpe the basic form of the thermal generation units’ cost function was approximated by a smooth quadratic function, as in [13]. however, in practice, multiple steam valves exist in large turbines, whose role is to maintain the power balance in thermal units by being opened and closed to reach a specific load. this operation contributes to the non-convexity of the fuel cost function, which is known as valve-point loading effects (vpe) and is modeled as an additional sinusoidal component [14]. the fuel cost curve with vpe is illustrated in figure 1. fig. 1. fuel cost curve with and without valve point effects. the total generation cost of thermal power units can be expressed as: minimize��� � ∑ ���� �� � (1) where fr is the total generation cost function, c(pgi) is the cost of the th i generation unit, pgi is the real power output of the th i generation unit, and ng is the number of dispatchable generation units. ���� � � � � �� � � �� � � �� ����� ��� � � � �� �� (2) where ai, bi, and ci are the cost coefficients of the th i generation unit, and di, ei are the valve-point effects coefficients of fuel cost for the th i generation unit. 2) emission function nox is a serious global concern. in this study, it is one of the numerous dangerous gases generated by the production units. the emission function is a quadratic function, described as [15]: minimize��� � ∑ �� !��� �� � (3) where et is the total emission function measured in kg/h, and enox(pgi) is the nox emission of the th i generation unit. �� !��� � " � # �� � $ �� � (4) where ai, βi, and γi are the nox emission coefficients of the th i generation unit. the above bi-objective combined economic emission dispatch problem was converted into a single optimization problem by introducing a price penalty factor. the weighted objective function is represented as: �% � &����� � ℎ�1 � & ����� (5) where ω is the weight factor in the range of [0,1], used to balance cost and emissions. h is the price penalty factor which is the ratio between the maximum fuel cost and the maximum emissions of the corresponding generator [16]: ℎ � )�*�+ ,-. /01.�*�+ ,-. (6) b. modeling renewable energy 1) solar power the maximum power a solar panel can deliver (ps) is determined as [7-8]: �2 � ���341 � ���56 � 56789 : (7) where ec is solar radiation, tjref is the reference temperature of the panels in 25°c, and tj is the cell junction temperature (°c). k1 represents the characteristic dispersion of the panels and is between 0.095 to 0.105, and k2=0.47%/°c is the drift in panels temperature. including a third parameter p3 in the solar power equation improves the results: �2 � ���341 � ���56 � 56789 :��; � �3 (8) having only 3 constant factors p1, p2, and p3 and a simple equation, this simplified model can predict the maximum power generated by a group of solar panels, given the panel temperature. a thermal solar power plant is made up of a solar system that generates heat and feeds it to turbines in a thermal cycle to generate electricity. 2) wind power the power provided by a wind turbine pw is expressed as [7-8]: �< � � � =�>?@ ;10b; (9) engineering, technology & applied science research vol. 12, no. 4, 2022, 8850-8855 8852 www.etasr.com dridi et al.: application of the levenberg-marquardt algorithm in solving the economic emission … where a is the area traversed by the wind (m 2 ), ρ is the air density (1.225kg/m 3 ), v is the wind speed (m/s), and cp is the efficiency factor which depends on the wind speed and the architecture of the system. wind turbines should be built considering a mechanical adjustment to develop nominal power from a nominal wind speed in a way to avoid mechanical overloads. c. problem constraints the objective function is minimized under the following operational constraints. 1) power balance constraint the total generation power must meet demand while also accounting for transmission losses. solar and wind power are injected into the system power balance constraint, where pren is the sum of solar and wind power and pd is the power demand. ∑ �� � �78� � �c � �d � 0�� � (10) the transmission lines’ network power loss pl could be calculated by solving the power flow problem [17]. the total real power losses can be calculated using the total net injected real power at all buses using [18]: �d = ∑ ef�g � + g6� − 2g g6 �i�(j − j6)��kf � (11) where nl is the number of transmission lines, gk is the conductance of the k th line that connects bus i to bus j, vi is the voltage magnitude at bus i, and δi is the voltage angle at bus i. 2) real power operating limits to ensure reliable operation, each unit's power generation should be provided concerning its minimal and maximal boundaries. �� � � ≤ �� ≤ �� �m! (12) using the lagrange function, the above-constrained optimization problem was converted into an unconstrained problem. the objective function henceforth is expressed as: n(�� ,p) = �% + p∑ (�� + �78� − �c − �d)�� � (13) iii. levenberg-marquardt algorithm lma is a mathematical-based optimization approach based on a combination of the directions of the gauss-newton algorithm and the gradient descent search. v(x) is assumed to be the function to minimize considering the parameters vector x. newton’s update for this vector is [19]: qfr� = qf − 4s�g(q):b�sg(q) (14) where s�g(q) is the hessian matrix and sg(q) is the gradient. the function v(x) is assumed to be a sum of squares function: g(q) = ∑ � �(q)� � (15) where e(x) is the difference between the target and the network output. then it can be shown that: ∇g(q) = u�(q)�(q) (16) and s�g(q) = u�u + v(q) (17) the jacobian matrix j(x) is: u(q) = ⎣⎢ ⎢⎢ ⎢⎢ ⎢⎡ z8[(!) z![ z8\(!) z!\ . . . z8^(!) z!^ z8\(!) z![ z8\(!) z!\ . . . z8^(!) z!^. . . . . . . . . .. . z8^(!) z![ z8^(!) z!\ . . . z8^(!) z!^ ⎦ ⎥⎥ ⎥⎥ ⎥⎥ ⎤ (18) and v(q) = ∑ � (q)s�� � � (q) (19) the gauss-newton method assumed that s(x)=0, so the equation becomes: qfr� = qf − 4u�(q)u(q):b�u�(q)�(q) (20) the levenberg-marquardt modification to the gaussnewton method is modeled as follows, where the characteristic μk is generally set to 0.01 as a starting point: qfr� = qf − 4u�(q)u(q) + bfc:b�u�(q)�(q) (21) qfr� = qf − 4d(q) + bf:b�∇g(q) (22) this algorithm sets μk at 0.01 as a starting point and then it’s multiplied by 10 whenever a step results in an increased v(x), otherwise, if v(x) decreases μk is divided by 10. to adapt lma to this problem, q = 4�� ,p: and g(q) = n(�e ,p). a. levenberg-marquardt algorithm • step 1: read the given data cost coefficients (ai, bi, ci), vpe coefficients (di, ei), nox coefficients (αi, βi, γi), power demand (pd), and unit’s power limits (�� � �,�� �m!). • step 2: read the forecasted wind and solar power (pren), where pren<0.3pd. • step 3: run power flow analysis and calculate transmission lines' power losses (pl). • step 4: set the initial values of the lagrangian multiplier λ 0 , the active generated power �� f , and the levenbergmarquardt characteristic μ0. • step 5: calculate the lagrange function l(pgi, λ). • step 6: calculate the jacobian matrix: u(�e ,p) = ⎣⎢ ⎢⎢ ⎢⎢ ⎢⎢ ⎡ gd[g*h[ gd[ g*h\ . . . gd[ g*h^ gd[ gi gd\ g*h[ gd\ g*h[ . . . gd\ g*h^ gd\ gi . . . . . . . . . .. . . . . gd^ g*h[ gd^ g*h[ . . . gd^ g*h^ gd^ gi ⎦⎥ ⎥⎥ ⎥⎥ ⎥⎥ ⎤ (23) • step 7: calculate the hessian matrix: d(�e ) = u�(�e )u(�e ) (24) engineering, technology & applied science research vol. 12, no. 4, 2022, 8850-8855 8853 www.etasr.com dridi et al.: application of the levenberg-marquardt algorithm in solving the economic emission … • step 8: update the power generation following (23): j�e (kl[)p(fr�) m = j �e (k) p(f) m − n� o �e p p (25) • step 9: calculate the new value of lk+1(pgi, λ) for each generating unit. • step 10: update the levenberg-marquardt characteristic μk: if lk+1≥lk set μ=μ×10 else if lk+1<lk set μ=μ/10. • step 11: check generation limits for each unit: set �� = �� � � if �� q �� � � set �� = �� �m! if �� r �� �m! • step 12: calculate the power mismatch δpg n�e = ∑ �e �h � − �78� − �s − �d (26) • step 13: if δpg≤ ε, where ε is the convergence criteria set to 0.01, then stop the calculation and move to step 15. otherwise, go to the next step. • step 14: repeat the procedure from step 5. • step 15: calculate the cost function and the emission quantity using the optimal values of pgi and λopt. iv. results and discussions dispatch simulation was carried out for 3 different cases: • case study 1: ed with vpe consideration. • case study 2: eed without vpe consideration. • case study 3: eed with vpe consideration in the presence of renewable energy. the performance of lma was tested on an ieee 9-bus system for these cases. the considered network system consists of 9 buses, 3 power generators, 3 power transformers, 6 transmission lines, and 3 loads, as shown in figure 2. table i shows the units’ data for all cases. the proposed approach was programmed using matlab. fig. 2. ieee 9-bus system. table i. ieee-9 bus cost and emissiondata [20] network data generating unit 1 2 3 cost coefficients a 0.001562 0.001940 0.004820 b 7.920 7.85 7.97 c 561 310 78 d 300 200 150 e 0.0315 0.0420 0.0630 nox coefficients " 0.043732540 0.055821713 0.027731524 # -9.4868099 e-05 -9.7252878 e-05 -3.5373734 e-04 $ 1.4721848 e-07 3.0207577 e-07 1.9338531 e-06 unit’s limit (mw) �� � � 100 100 50 �� �m! 600 400 200 a. case study 1 in this case, the single-objective ed problem was solved by setting the weight factor to ω=1, thus considering only the cost function. the power demand to be met by the 3 generating units was 850mw, and the transmission lines’ power losses were neglected. the ed results using the lma and other methods are presented in table i. lma was compared with sde [21], ga [22], and mpso [23]. lma succeeded in finding the generation outputs that give the minimum cost while meeting the total power demand. from table ii, it is clear that the proposed approach reported the global optimum solution over other algorithms. table ii. result comparison for case study 1 unit method sde [21] ga [22] mpso [23] lma tuv[mw] 400.0000 400.000 400.0000 402.4788 tuw[mw] 300.2669 300.000 300.2700 312.5117 tux [mw] 149.7331 150.000 149.7400 135.0095 cost [$] 8241.50 8234.60 8234.07 8232.50 b. case study 2 in this case, the multi-objective eed problem was solved without considering vpe, which means that the cost function was considered in its convex form. the power demand to be met by the 3 generating units was 850mw, and the transmission lines’ power losses were taken into account. table iii shows the best compromise solutions to reduce simultaneously cost and nox emissions found by lma, csa [24], and nsga ii [15]. table iii. result comparison for case study 2 unit method csa [24] nsga ii [15] lma tuv[mw] 470.9502 470.957 442.2904 tuw[mw] 280.7243 280.663 306.8524 tux[mw] 113.6211 113.675 116.1568 ty[mw] 15.2950 15.2940 15.2996 cost [$] 8349.722 8349.72 8339.80 nox emissions [kg/h] 0.09654 0.09654 0.09770 the best solution for lma was determined by running the program for all possible values of the weight factor in the range of [0, 1] with a step of 0.1. lma provided a profit of 9.92$/h in terms of cost. csa and nsga reported a minimum solution engineering, technology & applied science research vol. 12, no. 4, 2022, 8850-8855 8854 www.etasr.com dridi et al.: application of the levenberg-marquardt algorithm in solving the economic emission … for nox emissions with a profit of 0.1% compared to lma. it seems that lma converged to a near-global solution in this scenario. c. case study 3 in this case, the multi-objective eed problem considering vpe and the presence of renewable energy was resolved for different demand levels. hence, power demand was randomly changed at the different network load buses in a wide range of units’ power limits. the first step consisted of performing newton-raphson power flow analysis to calculate the power losses of the transmission lines using the generators and the data of the lines from [25]. the penetration of solar and wind power was randomly generated in a way to be limited to up to 30% of power demand due to the stochastic availability of these resources. the weight factor was set to 0.5 to give the same importance to the two objective functions considered. several levels of power demand were generated with intermittent renewable energy power. for each level of power demand, the lma was run to converge to the optimum values of generating power, and λopt, cost, and emissions quantities were calculated. the proposed approach structure is illustrated in figure 3. the lma solutions for various values of power demand are presented in table iv. since there is a lack of studies with the same criteria (multiobjective, vpe, power losses, wind and solar power, ieee-9 bus system), the simulation results were compared only with and without the presence of renewable energy. fig. 3. the proposed lma architecture flowchart. table iv shows that both cost and emissions decrease significantly when integrating renewable energy. it is obvious that when the penetration of renewable energy is high, the reduction in cost and emission is more considerable. as an example, for the case of 761mw power demand, penetration of renewable energy led to a reduction in cost and nox emissions of about 60% and 21%, respectively. therefore, the enhancement of the eed problem is more efficient with the presence of renewable energy. table iv. eed with vpe using lma with/without renewable energy penetration for ω=0.5 power demand [mw] tz{| [mw] tuv[mw] tuw[mw] tux [mw] cost [$] profit in cost [%] emission [kg/h] profit in emissions[%] 451 162.1612 193.0458 102.0527 7.3932e+03 17.3% 0.0923 1.2% 15.0481 176.1747 169.8884 96.1484 6.1163e+03 0.0912 505 168.3291 224.7244 119.8273 8.5375e+03 51.8% 0.0943 2.0% 62.8873 161.8538 203.5875 84.552 4.1135 e+03 0.0924 615 229.0195 283.5452 116.0003 1.3820e+04 40.3% 0.0950 0.84% 20.132 319.0071 141.7072 147.7186 6.2000e+03 0.0942 761 241.5953 350.9251 198.3037 3.2606e+04 62.0% 0.1219 21.0% 53.6624 347.9706 316.3517 72.8395 1.2377e+04 0.0961 835 326.6593 368.3790 195.3959 5.2899e+04 38.8% 0.1219 8.3% 195.0715 271.5196 225.4007 198.4422 3.2358e+04 0.1118 v. conclusion this paper presented a new application of the mathematical-based method levenberg-marquardt for solving the static multi-objective non-convex eed problem for the ieee 9-bus network incorporating solar and wind energy. the proposed approach was applied to two other case studies. the results provided by lma were compared with those obtained by sde, ga, mpso, csa, and nsga ii. the comparison showed that lma provided a better solution for the case of the single-objective problem. for the multi-objective problem, 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[25] p. m. anderson and a. bose, "stability simulation of wind turbine systems," ieee transactions on power apparatus and systems, vol. pas-102, no. 12, pp. 3791–3795, sep. 1983, https://doi.org/10.1109/ tpas.1983.317873. microsoft word etasr_v12_n1_pp7974-7981 engineering, technology & applied science research vol. 12, no. 1, 2022, 7974-7981 7974 www.etasr.com tahzeeb & hasan: a neural network-based multi-label classifier for protein function prediction a neural network-based multi-label classifier for protein function prediction shahab tahzeeb dept. of computer & information systems engineering ned university of engineering & technology karachi, pakistan stahzeeb@neduet.edu.pk shehzad hasan dept. of computer & information systems engineering ned university of engineering & technology karachi, pakistan shasan@neduet.edu.pk abstract-knowledge of the functions of proteins plays a vital role in gaining a deep insight into many biological studies. however, wet lab determination of protein function is prohibitively laborious, time-consuming, and costly. these challenges have created opportunities for automated prediction of protein functions, and many computational techniques have been explored. these techniques entail excessive computational resources and turnaround times. the current study compares the performance of various neural networks on predicting protein function. these networks were trained and tested on a large dataset of reviewed protein entries from nine bacterial phyla, obtained from the universal protein resource knowledgebase (uniprotkb). each protein instance was associated with multiple terms of the molecular function of gene ontology (go), making the problem a multilabel classification one. the results in this dataset showed the superior performance of single-layer neural networks having a modest number of neurons. moreover, a useful set of features that can be deployed for efficient protein function prediction was discovered. keywords-gene ontology; molecular function term; multi-label classification; neural network; protein function prediction i. introduction understanding proteins’ functions plays a vital role in acquiring insights of the molecular mechanisms operating in both physiological and ailing medical conditions. as a result, this understanding substantiates the discovery of drugs in different diseases [1]. however, predicting protein functions is an arduous task. the fact is markedly implied by the incredibly large number of unannotated protein entries hosted by the most comprehensive protein database, the universal protein resource knowledgebase (uniprotkb) [2]. this is mainly due to the reliance on traditional experimental annotation techniques carried out by molecular biologists. the gap between reviewed and unreviewed protein sequences is widening due to the data deluge from high-throughput state-ofthe-art sequencing techniques [1, 3-5]. the pressing demands for computational methods on the functional annotation of proteins have paved the way for significant contributions by computer science researchers. many computational techniques employing machine learning for functional annotation of proteins have been utilized in the literature. the principal difference between various approaches lies in the set of features pursued by different investigators. this section presents a brief summary of some of the most prominent efforts in this area. an ensemble of deep neural networks (dnns) was proposed in [1], where each dnn worked on a different set of features from the dataset. the predictions of different dnns were then voted to arrive at the final protein function prediction. a dnn for the hierarchical multilabel classification of protein functions designed to perform well even with a limited number of training samples was presented in [3]. in [4], a dnn was introduced to learn features from word embedding of protein sequences, based on the concept of natural language processing (nlp), using sequence similarity profiles as additional features to locate proteins. authors in [5] established the efficacy of exploiting any interrelationships among different functional terms. for instance, different functional classes were found to coexist with some proteins suggesting a mutual relationship. furthermore, a quantification model of these relations was proposed, using a functional similarity measure and a framework to capitalize on it for the eventual prediction of protein functions. a classification technique based on a neural network coupled with a support vector machine (svm) was demonstrated in [6], utilizing a bidirectional long short-term memory (lstm) network to generate fixed-length protein vectors out of variable-sized sequences and deal with the challenges posed by the variable length of protein sequences. in [7], protein sequence motifs were used to build a deep convolutional network and predict protein function, while the authors claimed to have built the best performing model for the cellular component classes. the significance of protein-protein interaction (ppi) and timecourse gene expression data as powerful predictors for the prediction of protein function was shown in [8]. a method, called dynamic weighted interactome network (dwin), was proposed, that in addition to ppi and gene expression data, took also into account information related to protein domains and complexes to improve the prediction performance. in [9], clustering was applied on a ppi network for the prediction of protein function. a protein graph model was shown in [10], constructed of protein structure, with each node representing a cluster of amino acid residues. however, the idea of using an accuracy metric for evaluation is generally misleading. in [11], an active learning approach was explored for the prediction of corresponding author: shahab tahzeeb engineering, technology & applied science research vol. 12, no. 1, 2022, 7974-7981 7975 www.etasr.com tahzeeb & hasan: a neural network-based multi-label classifier for protein function prediction protein function using a ppi network. this method operated in two phases: spectral clustering was used to cluster the ppi network followed by the application of the betweenness centrality measure for labeling within each cluster, and then the labeled protein data were used by a classification algorithm. associations between functions in a ppi network were used in [12], stating that multiple function labels assigned to proteins were not independent and their coexistence could be used effectively to predict protein function. a deep semantic text representation was presented in [13], with various pieces of information extracted from protein sequences such as homology, motifs, and domains. protein function prediction was carried out using a consensus between text-based and sequence-based methods. in [14], a classifier using cumulative iterations was proposed, based on its semantic similarity with the term gene ontology (go). each prediction was followed by updating and optimizing scores of characteristic terms in the set of go annotations, which, in turn, led to improved future predictions. the dissimilarity of protein functions, rather than conventional similarity measures, was used in [15] to segregate rare and frequently occurring classes of functions. this technique worked well for imbalanced datasets. the notable contributions cited above are just a handful of numerous praiseworthy efforts towards the prediction of protein function. these endeavors differ in terms of the protein information utilized by the corresponding systems and the computational or time complexities of the classification models. the current paper presents a neural network-based multi-label classifier for the prediction of protein function by training and testing several neural networks on a large dataset [16]. the results indicate that a neural network with a single hidden layer achieved remarkable prediction performance with nominal computational complexity. this makes its implementation viable on systems with modest hardware capabilities. consequently, the time required for the classification task is in the order of seconds. ii. materials and methods a. dataset the dataset adopted from [16] includes 121,378 protein instances. these labeled protein examples were extracted from uniprotkb [2], a comprehensive worldwide repository of protein information. these protein entries pertain to 9 bacterial phyla, namely actinobacteria, bacteroidetes, chlamydiae, cyanobacteria, firmicutes, fusobacteria, proteobacteria, spirochaetes, and tenericutes. each instance in the dataset had 9,890 features. these features included the sequence of amino acids making up the corresponding protein, compositions of amino acids, dipeptides and tripeptides; compositions of five groups of amino acids, i.e. aliphatic, aromatic, positively charged, negatively charged, uncharged, and various structural and physiochemical properties derived from the amino acid sequence. in addition, some features quantify conjoint triads. a conjoint triad is a unit of three successive amino acids such that each amino acid in the unit belongs to one of the seven groups formed on the basis of the dipole and volume scale [17]. these characteristic values indicate the strength of interaction between the amino acids of these 7 groups. the feature set also contains pseudo amino acid compositions for the corresponding protein. as suggested in [18], these numbers overcome the loss of sequence order effect in a protein caused by considering just plain amino acid compositions. moreover, there are also 541 motifs included in the features. these are small segments in proteins’ tertiary structure that are frequently found in different proteins. these similar patterns are associated with the structural or functional roles of proteins. there are 1,739 binary labels associated with each protein instance. these labels correspond to go terms belonging to the molecular function (mf) category. the go is a categorization of biological functions using three broad classes, i.e. molecular function (mf), cellular component (cc), and biological process (bp), generally referred to as go terms [19]. the molecular function term specifies a biochemical activity performed by a gene product, without taking into account the time and space dimensions of this activity. the enzyme is an example of the mf term. the cc refers to the location of the biochemical activity of a gene product in the cell. ribosome and nuclear membrane are two such examples. bp, an allencompassing term, defines a biological objective to which activities of various gene products contribute. cell growth and maintenance serve as examples the bp term. b. data preprocessing the comma separated values (csv) files for 9 different bacterial phyla were combined to obtain a single pandas’ data frame object using the pandas data analysis library in python [20]. duplicate rows were removed from the data frame, which was then converted to an array using the scientific computing library numpy in python [21]. the feature values were then scaled using the standard scaler available in the scikit-learn library in python [22]. data scaling was investigated using normalization and robust scaler, but these data scaling techniques proved inferior to the standard scaling technique. c. features partitioning the neural networks were trained on 3 sets of features. the objective of partitioning features into various subsets was to test the hypothesis that compositions of amino acids, dipeptides, and tripeptides are sufficient to predict protein functions. f = {f1, f2, f3} represented the set of features used to train different models, where f1 was the entire set of 9,890 features, and f2 was the set of 8,420 features that contained only compositions of amino acids, dipeptides, and tripeptides. the set f3=f1–f2 contained 1,470 features consisting of various properties and characteristics derived from proteins as described in subsection a. d. neural networks a variety of neural networks was selected, differing in the number of hidden layers and neurons in each layer to train the protein function classification system on datasets corresponding to each feature set f1, f2, and f3. the experimental results are given in section iii. it was observed that the simplest neural network containing a single hidden layer demonstrated better performance on this dataset compared to neural networks having more hidden layers. the optimal number of neurons in this single hidden layer was experimentally determined to be just 5% of the total input and output neurons for feature sets f1 and f2 for the best performing engineering, technology & applied science research vol. 12, no. 1, 2022, 7974-7981 7976 www.etasr.com tahzeeb & hasan: a neural network-based multi-label classifier for protein function prediction neural network. however, for the f3 feature set, the optimal number of neurons in the single hidden layer of the best performing neural network turned out to be 50% of the total of input and output neurons. once the optimal number of neurons in a single hidden layer was determined, the addition of another hidden layer was utilized to observe any potential boost in performance. the number of neurons in the second hidden layer was chosen to be 50% of the first hidden layer. this was done to ensure that the network captured the most important features for prediction. table i summarizes various single-hidden layer neural networks trained and tested on the f1 feature set, i.e. the entire set of features from the dataset. the reference computer for all time and memory size measurements presented is a core i78700 at 3.2 ghz 6-core processor. table i. single-hidden layer models trained on the f1 feature set model neurons 1 size (mb) training time (sec) predictiontime (sec) m1 1 16 1950 2.25 m2 5 77 2655 6.03 m3 10 154 3920 7.51 m4 15 232 4860 9.75 m5 25 386 8820 13.6 m6 50 773 12175 21.8 m7 75 1130 15400 31.6 1. expressed as percentage of input + output neurons table ii presents the m8 neural network with two hidden layers trained on f1. this model was constructed by adding another hidden layer to the best performing single-hidden layer neural network m2 to explore any performance gain. the second hidden layer had 50% neurons of the first hidden layer in an attempt to capture the optimal features best suited for the prediction task. table ii. two-layer model trained on the f1 feature set model size (mb) training time (sec) prediction time (sec) m8 74 2120 5.52 table iii summarizes various single-hidden layer neural networks trained and tested on the f2 feature set, i.e. the compositions of amino acids, dipeptides, and tripeptides in the protein sequence. table iii. single-hidden layer models trained on the f2 feature set model neurons 1 size (mb) training time (sec) prediction time (sec) m9 5 60 2760 5 m10 10 118 3480 6.31 m11 25 295 7920 11.1 m12 50 590 15000 17.8 m13 60 708 15855 20.4 1. expressed as a percentage of input + output neurons table iv presents the m14 neural network containing two hidden layers and trained on f2. this model was developed by adding another hidden layer to the best performing single hidden layer neural network m9, to investigate any improvements in the classifier performance. the second hidden layer had 50% neurons of the first hidden layer to exploit the predictors best suited for the prediction task. table iv. two-layer model trained on the f2 feature set model size (mb) training time (sec) prediction time (sec) m14 56 2050 4.76 table v summarizes several single-hidden layer neural networks trained and tested on the f3 feature set, i.e. features consisting of various properties and characteristics derived from proteins. table v. single-hidden layer models trained on f3 feature set model neurons 1 size (mb) training time (sec) predictiontime (sec) m15 5 6 2750 1.33 m16 10 12 3200 1.58 m17 25 30 5200 2.92 m18 30 35 5270 3.05 m19 50 60 6630 4.20 m20 60 71 7320 4.59 1. expressed as a percentage of input + output neurons table vi presents the m21 neural network having two hidden layers and trained on f3. this model was generated by adding another hidden layer to the best performing single hidden layer neural network m19 to discover any potential performance enhancement. the number of neurons in the second hidden layer was chosen to be 50% of the first hidden layer to capitalize on the features best suited for the classification. table vi. two-layer model trained on the f3 feature set model size (mb) training time (sec) prediction time (sec) m21 58 5720 4.64 for each network, we employed the relu activation for the hidden layers, the sigmoid activation for the output layer, the he_uniform kernel initializer for the hidden layers, and the adaptive moment estimation (adam) optimizer with a learning rate of 0.00001. e. performance evaluation since a protein example in this dataset can be mapped to more than one binary label, the prediction of protein function is a multilabel classification problem. the dataset is also highly imbalanced due to the overwhelming number of negative examples for each label. evaluation of such a classification model cannot simply rely on the accuracy of prediction [23, 24]. for example, if a negative class is abundantly prevalent among all examples in an imbalanced dataset, then a naive classifier predicting this class for all examples will easily achieve very high accuracy. the challenge of this inflated accuracy measure becomes aggravated in the case of multilabel classification of imbalanced datasets. this problem was engineering, technology & applied science research vol. 12, no. 1, 2022, 7974-7981 7977 www.etasr.com tahzeeb & hasan: a neural network-based multi-label classifier for protein function prediction addressed by defining more meaningful performance measures, namely precision, recall, f1 score, zero-one loss, hamming loss, and matthews correlation coefficient. these measures are defined here. 1) precision precision is defined as the fraction of positively classified instances that are, in effect, positive. this gives a clear picture of a classifier’s strength in predicting positive classes. letting tp and fp respectively denote the count of true and false positives, precision is calculated as: ��������� = � �� � (1) the precision of predict-majority-class-for-all classifier is thus 0 judiciously penalizing for its shortcoming at predicting the positive minority class. however, any classifier that makes just one positive prediction and ensures its correctness would have 100% precision despite its failure to predict other positive examples. this calls for another classification metric, called recall, also known as sensitivity. 2) recall recall is defined as the fraction of positive examples in the dataset classified as positive. letting fn denote the number of false negatives, the recall is given by: ������ = � �� � (2) this measure penalizes a classifier that attempts to achieve high precision simply by making a few correct positive predictions. 3) f1 score precision and recall are combined in a single performance measure called f1 score, which is their harmonic mean. �1 ����� = 2 ∗ ���������∗���� �������������� (3) as the harmonic mean is biased towards lower values, f1 score can have a higher value only in the case when both precision and recall have high values. in multi-label classification, there are several ways to average the aforementioned performance metrics on all labels [25, 26]. these are the micro average, macro average, weighted average, and samples average as defined below. as usual, the f1 score is the harmonic mean of the corresponding precision and recall in each case. 4) micro average this is calculated by counting the number of true positives (tps) across the entire set of target labels. if there are n samples in the dataset and each sample has l binary target labels, then the micro averages of precision and recall are calculated as: ���������!���� = ∑ #$_&��'( ∧ $_*�+�( , -∗. (/0 ∑ $_&��'( -∗. (/0 (4) ������!���� = ∑ #$_&��'( ∧ $_*�+�( , -∗. (/0 ∑ $_*�+�( -∗. (/0 (5) where y_pred and y_true are the predicted and actual target labels, respectively. the conjunction operator ∧ ensures the inclusion of only those label instances that are positive in both y_pred and y_true, i.e. tps. 5) macro average this averages the precision and recall scores of the individual target labels, giving equal weights to all of them. ���������!���� = 1 2 ∑ ∑ #$_&��'(3∧ $_4567 (3, (/0 ∑ $_&��' (/0 (3 2 891 (6) ������!���� = 1 2 ∑ ∑ #$_&��'(3∧ $_4567 (3 , (/0 ∑ $_*�+� (/0 (3 2 891 (7) 6) weighted average this averages the precision and recall scores of the individual target labels, using the number of positive instances of each label in the set y_true as their weight. ���������:��;<*�' = 1 ∑ :3 . 3/0 ∑ ∑ #$_&��'(3∧ $_4567(3,∗:3 (/0 ∑ $_&��' (/0 (3 2 891 (8) ������:��;<*�' = 1 ∑ :3 . 3/0 ∑ ∑ #$_&��'(3∧ $_4567(3,∗:3 (/0 ∑ $_*�+� (/0 (3 2 891 (9) where wj denotes the weight, also known as the support of the j-th label. 7) samples average it averages the precision and recall scores across the samples. �����������!& �� = 1 � ∑ ∑ #$_&��'(3 ∧ $_4567(3, . 3/0 ∑ $_&��' . 3/0 (3 � �91 (10) ��������!& �� = 1 � ∑ ∑ #$_&��'(3∧ $_4567 (3, . 3/0 ∑ $_*�+� . 3/0 (3 � �91 (11) this is the most faithful as well as the most conservative performance indicator of the multi-label classifier as it reflects, on the average, how well the classifier performed on each sample. therefore, the sample averages were used to gauge the performance of the models. 8) zero-one loss for a multi-label classification problem, this measure credits a prediction as correctly classified only when all labels are correctly classified. the loss is zero for a correct prediction. however, if the classifier fails to make a correct prediction even for just one target label, the corresponding loss is 1. it follows that the zero-one loss is truly a conservative and highly penalizing performance measure. =���>/1 = 1 � ∑ ∏ #a_b��c�8 ⊕ a*�+� �8, 2 891 � �91 (12) the combination of the product operator π and the exclusive-or operator ⊕ ensures that any mismatch between l predicted and target labels generates a loss of 1 for any given sample. otherwise, the loss is zero for a complete match between all predicted and target labels for a given sample. engineering, technology & applied science research vol. 12, no. 1, 2022, 7974-7981 7978 www.etasr.com tahzeeb & hasan: a neural network -based multi-label classifier for protein function prediction 9) hamming loss this gives the fraction of all incorrectly predicted labels by quantifying the number of incorrect predictions of all labels rather than penalizing individual examples. hence, if a multilabel classifier incorrectly predicts 1 out of 10 labels for a given instance, the hamming loss for that example is just 1/10 as compared to 1 in the case of zero-one loss. it follows that hamming loss is lenient compared to the stringent zero-one loss. e= = 1 �∗2 ∑ #a_b��c� ⊕ a_f�g��, �2 �91 (13) 10) matthews correlation coefficient the matthews correlation coefficient (mcc) is a binary version of pearson’s correlation coefficient [27]. however, multiclass classification problems can also benefit from its extended version [28]. mcc compares ground truth and predicted vectors, considering all possibilities of prediction, i.e. true positives (tp), true negatives (tn), false positives (fp), and false negatives (fn). therefore, it gives a balanced evaluation of the performance of the classifier. the correlation coefficient lies in the range [-1, +1], with -1 for false prediction, 0 for random prediction, and +1 for correct prediction. hii = �∗ �j �∗ � k# �� �,# �� �,# �� �,# �� �, (14) the mcc was calculated for every example and its average was used to assess the performance of the classifier on the entire dataset. 11) consolidated performance metric for the sake of an all-encompassing and more realistic comparison of performance, the aforementioned metrics were combined in a single consolidated performance metric (cpm) as follows: i�h = 1 l����∗mnn 2���0/1∗p2 (15) the cpm was constructed in the higher, the better way. iii. results table vii shows the performance details of the neural networks (m1 to m21) as the samples averages of precision (p), recall (r), f1 score (f1), zero-one loss (zol), hamming loss (hl), mcc, and cpm. a wide variety of neural networks was trained and tested on a large dataset of proteins. for feature sets f1 and f2, it was observed that 5% of the total input and output neurons in the single hidden layer networks exhibited better prediction performance than other single-layer models. these models were designated as m2 and m9, respectively. however, for the feature set f3, the optimal count of neurons in the hidden layer emerged as 50% of the total input and output neurons. this model was designated as m19. the bar graphs in figures 1-3 compare the cpm for various neural networks that work on a specific feature set. in each case, the best performing singlelayer network was extended by adding a second hidden layer to assess any performance edge. neurons in the second hidden layer were the 50% of the first hidden layer to ensure that the most relevant features for prediction play their due role. the blue bars in figures 1-3 represent the performance of the best performing single-layer networks, while yellow bars show the performance of 2-layer neural networks. table vii. performance of neural networks model p r f1 zol hl mcc cpm m1 0.96 0.95 0.95 12.25 0.0159 0.9518 4.6423 m2 0.96 0.96 0.96 11.36 0.0120 0.9576 6.7437 m3 0.96 0.96 0.95 11.64 0.0122 0.9571 6.4028 m4 0.96 0.96 0.95 11.76 0.0122 0.9566 6.3341 m5 0.96 0.96 0.95 11.90 0.0123 0.9568 6.2100 m6 0.96 0.96 0.95 12.55 0.0129 0.9546 5.6016 m7 0.96 0.96 0.95 12.61 0.0132 0.9539 5.4442 m8 0.96 0.95 0.95 12.21 0.0128 0.9535 5.7959 m9 0.94 0.94 0.93 15.85 0.0173 0.9341 3.1681 m10 0.94 0.94 0.93 16.47 0.0179 0.9329 2.9429 m11 0.93 0.94 0.93 16.70 0.0180 0.9318 2.8828 m12 0.93 0.94 0.93 17.30 0.0186 0.9298 2.6873 m13 0.93 0.93 0.93 17.07 0.0183 0.9297 2.7678 m14 0.93 0.93 0.92 17.17 0.0188 0.9279 2.6446 m15 0.96 0.95 0.95 12.43 0.0129 0.9535 5.6492 m16 0.96 0.96 0.96 11.34 0.0117 0.9591 6.9396 m17 0.97 0.96 0.96 10.43 0.0108 0.9614 8.1935 m18 0.97 0.96 0.96 10.66 0.0110 0.9614 7.8709 m19 0.97 0.96 0.96 10.34 0.0107 0.9625 8.3516 m20 0.97 0.96 0.96 10.39 0.0108 0.9621 8.2310 m21 0.97 0.96 0.96 10.95 0.0114 0.9593 7.3775 fig. 1. neural networks’ comparison on f1 feature set. fig. 2. neural networks’ comparison on f2 feature set. engineering, technology & applied science research vol. 12, no. 1, 2022, 7974-7981 7979 www.etasr.com tahzeeb & hasan: a neural network -based multi-label classifier for protein function prediction fig. 3. neural networks’s comparison on f3 feature set. f. optimal feature set the experiments also focused on exploring an optimal set of features for the prediction of protein function. as it was noticed, the f3 feature set proved to be the best predictor for this multi-label classification. figure 4 shows a comparison of the best-performing models for each feature set, where m19 on f3 achieved the best performance. fig. 4. performance comparison of the best performing single-layer models on different feature sets. f3 proves to be the best predictor set. g. classification threshold the impact of the classification threshold on the performance of a classifier was examined. the models predict the probability of each target label associated with every instance. these probability values quantify the chance for a given instance to belong to a particular class. these probability values should be translated into binary labels 0 and 1 before the final evaluation of the model. this conversion to binary labels required a threshold or probability cutoff value below which all values are classified as class 0 and equal or greater values are classified as class 1. classifier performance metrics are profoundly influenced by the choice of this threshold. the impact of the threshold is more pronounced for imbalanced datasets. as the examined dataset is skewed towards more negative examples of each label, the performance of the models was evaluated for various values of thresholds. figures 5 and 6 show two example plots of samples averages of p, r, and f1 score for models m2 and m19, respectively, against a range of classification thresholds. fig. 5. performance curves of m2 for the f1 feature set. the choice of classification threshold plays an important role in improving the performance of the classifier. fig. 6. the performance curves of model m19 for the f3 feature set. h. confusion matrix the confusion matrix is a visualization of a classifier’s performance, as it gives the count of tp, fp, tn, and fn class predictions. fig. 7. confusion matrices of the best-performing model m19 for f3. only labels having support more than 1,000 are included. engineering, technology & applied science research vol. 12, no. 1, 2022, 7974-7981 7980 www.etasr.com tahzeeb & hasan: a neural network-based multi-label classifier for protein function prediction figure 7 presents the confusion matrices of select labels in the test dataset for the model m19 that performed best in the f3 feature set. to highlight the strength of the classifier, only labels whose support exceeded 1,000 in the dataset were chosen iv. discussion the performance comparison of different neural networks on a large protein dataset showed that neural networks having a single hidden layer and a modest number of neurons achieved superior performance on this specific dataset than relatively more complex networks. the number of neurons in the single hidden layer was empirically determined. the rigorous experimentation revealed that only 5% of the total input and output neurons were adequate in single-hidden-layer models operating on f1 and f2 feature sets. however, this count was 50% for a single-layer model on f3. this disparity in the number of neurons was because these models for the f1 and f2 feature sets had 9,890 and 8,420 neurons, respectively, in their input layers. therefore, even 5% of the total input and output neurons were adequate to effectively train the model for 1,739 labels. however, for f3, the number of input neurons was barely 1,470, and consequently, more neurons were needed for better prediction performance. this justifies a 50% count of neurons in the single hidden layer for this network. in any case, the training time, prediction time, and model size of these models were much better than those of other competing models. these models showed much better performance (f1 score: 0.96) compared to the deep learning ensemble [1] (f1 score: 0.79) on the same dataset. this was also achieved with a much lower computational complexity. a. best predictors the findings highlight the impressive role of the physiochemical properties and motifs in proteins, pseudo amino acid compositions, and other properties derived from the protein sequences in predicting protein functions. the proposed model for this feature set was extremely efficient as it had better performance and lower computational complexity. b. sufficiency of amino acid, dipeptide, and tripeptide compositions the results were suggestive of the sufficiency of amino acid, dipeptide, and tripeptide compositions in predicting protein functions. although the performance metrics for this particular feature set had lower values than other feature sets, it can be used for a sufficient and tolerable approximation. this could save time spent in engineering features from existing features of the dataset consisting of bare compositions of amino acids, dipeptides, and tripeptides. v. conclusions this study culminated in two significant findings regarding the examined protein dataset. the first one pertains to the exceptional performance of single-layer neural networks on this dataset, alhough the number of neurons in this single hidden layer must be empirically determined as a percentage of 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[28] p. baldi, s. brunak, y. chauvin, c. a. f. andersen, and h. nielsen, "assessing the accuracy of prediction algorithms for classification: an overview," bioinformatics, vol. 16, no. 5, pp. 412–424, may 2000, https://doi.org/10.1093/bioinformatics/16.5.412. engineering, technology & applied science research vol. 8, no. 1, 2018, 2555-2561 2555 www.etasr.com gupta and mohan: color channel characteristics (ccc) for efficient digital image forensics color channel characteristics (ccc) for efficient digital image forensics surbhi gupta computer science & engineering faculty i. k. gujral punjab technical university kapurthala, india royal_surbhi@yahoo.com neeraj mohan computer science & engineering faculty i. k. gujral punjab technical university kapurthala, india erneerajmohan@gmail.com abstract-digital image forgery has become extremely easy as lowcost image processing programs are readily available. digital image forensics is a science of classifying images as authentic or manipulated. this paper aims at implementing a novel digital image forensics technique by exploiting an image’s color channel characteristics (ccc). the cccs considered are the noise and edge characteristics of the image. averaging, median, gaussian and wiener filters along with sobel, canny, prewitt and laplacian of gaussian (log) edge detectors are applied to get the noise and texture features. a complete, no reference, blind classifier for image tamper detection has been proposed and implemented. the proposed ccc classifier can detect copy-move as well as image splicing accurately with lower dimensionality. support vector machine is used for classification of images as authentic or tampered. experimental results have shown that the proposed technique outperforms the existing ones and may serve as a complete tool for digital image forensics. keywords-image tampering; noise discrepancies; feature extraction; edge textural information; statistical evaluation i. introduction wide digital image usage has led to their intended manipulation. some manipulations can make the image more informative and useful. these manipulation types are called image enhancements. other manipulations could change the content of the image altogether. such manipulations are termed as image forgeries [1]. image forgery is usually achieved using copy-move or image splicing operations [2-3]. when a subpart of an image is cropped, processed and then pasted into the original image the manipulation is called copy-move. when two or more images are required in order to build a new image it is called image splicing.imaging forensic techniques are applied to distinguish and classify authentic and manipulated images. these techniques utilize the image data to locate whether the questioned image is authentic or manipulated. some of these techniques try to define the origin of the image, whereas others try to compare it with some reference images. some techniques extract features to check inconsistencies present in the image itself. an image may be expressed using different color models like rgb, ycbcr, l*a*b etc. each color model has three channels. the image intensity information is spread in these three channels. the color information distribution among channels depends on the model used. in rgb model, red, green and blue channels contain equal amount of intensity information. but the human vision system cannot utilize rgb color for its apprehension. luminance or brightness of color is the most important information which human vision system uses for understanding colors. other models like l*a*b (luminance, red minus green, green minus blue) and ycbcr (luminance, chrominance blue, chrominance red) are based on luminance. in these models, most of the intensity information is present in luminance channel. another popular color model is hsv (hue, saturation and value) model which is based on the human color perspective. it has hue, saturation and value channels for the distribution of intensity data. different channels in these examples are capable to illustrate and bring out different features of an image. color channel characteristics (ccc) for various models could be a genuine aid inimage analyzing. various image forensic techniques have been proposed and analyzed in the last two decades. the author in [4] proposed a blind, noise based, passive image quality assessment model to transform the heuristics into noise structures. mathematical models were developed to measure the edge sharpness, the random noise and the structural noise in an image objectively, without any reference image. authors in [5] proposed image quality measures (iqm) to expose compression and steganography using image statistical analysis. a linear regression classifier was used for image classification of original and manipulated images. sequential floating forward search (sffs) algorithm was applied for feature selection. the achieved accuracy was 91% and 80% for large and small manipulated regions of the image, respectively. further, authors in [6] used noise variance of overlapping blocks to estimate manipulation in images, but this method did not execute well when images with high quality factors were spliced and resaved at a lower quality. binary similarity measures (bsm) were introduced in [7]. bsm are based on correlation and texture features of the image. feature selection was applied to attain an accuracy of 90% using joint feature sets. the major limitation of the approach was that its accuracy decreased when the image manipulated region was small. authors in [8] proposed statistical noise feature extraction engineering, technology & applied science research vol. 8, no. 1, 2018, 2555-2561 2556 www.etasr.com gupta and mohan: color channel characteristics (ccc) for efficient digital image forensics using de-noising, wavelets and likelihood of neighbors. the classifier was 90% effective in classifying direct camera outputs from tampered versions. authors in [9] proposed splice detection based on the measuring of statistical differences by using discrete cosine transform (dct) and image quality measures. authors in [10] performed block-wise wavelet analysis followed by tiling sub-band hh1and noise variance estimation for detecting manipulations. the main limitation of the algorithm was that it could not be used as an individual forgery detector and needed human intervention as well. authors in [11] compared features from chroma and rgb channels for inserted objects’ edge sensitivity and sharpness. but the outcomes were not illustrated for images at different quality factors. authors in [12] used blocking, activity and zero crossing characteristics from ycbcr channels for locating the tampered area in manipulated images. authors in [13] proposed the use of variance based noise estimation in forged images using principal component analysis (pca) from hue, saturation and value channels with high accuracy. recently, authors in [14] used sobel operator to detect sharp-edged areas of foreign objects to localize the manipulated regions in the image efficiently. other significant contributions used natural model [15], markov features [16], gabor filters [17], multi-scale weber local descriptors [18] and textural features [19] for image forensics. these algorithms achieved high accuracy, but induced a big number of features and high computation time.moreover, the execution of these techniques was not evaluated extensivelyfor various jpeg images at different qualities. a forensic classifier for different quality jpeg images with high accuracy and low dimensionality is still required. literature study reveals that various color model channels have different data and hence different characteristics. these characteristics are named as color channel characteristics (ccc). this paper aims to propose ccc and further implement a ccc based image classifier with high accuracy and low computation time. ii. ccc based feature extraction a forged image may be produced by copy-move, splicing or various other post processing operations. only a robust technique can reveal such technical image forgeries.the proposed method uses statistical estimation of image noise and edge texture variation based on ccc. every tampering operation leaves its traces on the image. these traces differentiate the tampered image from original one. the first and second order derivatives are obtained from different color channels to capture the discontinuities and highlight image tampering. the proposed feature set is extracted using rgb and ycbcr planes of the image. a ccc based classification model is presented in figure 1. a. analysis of rgb color channel characteristics for feature extraction rgb image is also denoted as a true color image. for each pixel it gives the value of red, green, and blue color component. hence, the intensity of the image element is obtained by combining the three color components at a particular pixel location. useful information drawn for rgb channels could be used for discriminating forged images from the original. noisebased features could play a substantial role in differentiating direct camera images from their tampered version. one can elicit and analyze features from red, green and blue plane to highlight tampering. in the current study, statistical noise features from rgb channels are extracted and their use has been explored to differentiate tampered images from the original ones. the original image in most cases is not available, but it can be approximated by the use of a de-noising filter. the filter will get rid of the noisy sharp features of the available image. the filtered image will now be close to the original image. this de-noised image is compared with the tampered image to get the discontinuities. authors in [8] extracted features using de-noising filtering and used them for detecting cropped regions in the image. various de-noising filters, i.e. averaging a(x,y) , median m (x,y) , gaussian g(x,y) and wiener filters w(x,y) of 3x3size are considered for image forgery detection. a(x,y) , m (x,y) , g(x,y) and w(x,y) are defined as (1), (2), (3), and (4) respectively. a(x,y) = .∑ ∑ f(x,y) (1) wheref(x,y) represents the intensity at pixel location (x,y). m(x,y) = median{f(x,y)} (2) where (x,y) ∈ w and w represents a neighborhood defined by the user, centered on location x,y in the image. gaussian low pass filter, with standard deviation 0.5, is explored for image forensics application in this work. g(x,y) = .e ( )/ (3) where x and y are the distances from the origin in the horizontal and vertical axis. σ is the standard deviation of the gaussian distribution. weiner filter filters the image to estimate the local image mean and standard deviation. w(x,y) = μ + .(f(x,y) − μ) (4) where µ and estimate the local mean and variance around each pixel and v denotes noise variance. this study is based on the features extracted from r, g and b channels individually. the tampered image in every image channel, e.g. red, is filtered using de-noising filter and then the original red channel image is subtracted from the red filtered image. the absolute difference image is then analyzed. first order derivatives, i.e. mean and standard deviation are extracted as features using (5) and (6). μ = ∑ ∑ f(x,y) (5) σ = ∑ ∑ (f(x,y) − μ) (6) the algorithm used for noise based statistical feature extraction is presented below: step 1: consider an image i and extract its rgb values. ( , ), ( , ) and ( , ) represent the intensity values for red, green and blue planes respectively. step 2: apply one of (1)-(4) 3x3 filters, e.g. gaussian filter, to obtain filtered image ( , ). let gr(x,y), gg(x,y), gb(x,y), engineering, technology & applied science research vol. 8, no. 1, 2018, 2555-2561 2557 www.etasr.com gupta and mohan: color channel characteristics (ccc) for efficient digital image forensics represent the gaussian intensity value for red, green and blue planes respectively. step 3: calculate the absolute difference ( , ) between ( , ) and ( , ) by using. (7): ( , ) = | ( , ) − ( , )| (7) then, compute the base-2 logarithm of ( , ) using (8) ( , ) = ( ( , )) (8) step 4: calculate mean and standard deviation as first order image derivatives using (5) and (6). step 5: repeat step 3 and step 4 for green and blue channels to obtain 3x2=6 features. four different filters are used in the experiment, which means 4x6=24 features. original and 10 tampered (t1-t10) images from miccf220 [20] database have been utilized for experimentation. table i shows the results obtained for the mean and standard deviation for rgb channels and de-noising median filter. figure 2 shows the values obtained for mean and standard deviation features for median filter. results indicate a clear difference in values obtained from original and tampered images. the value of the mean and standard deviation for all filters and all rgb planes is low as compared to its tampered versions. figure 3 shows the scatter plots for mean and standard deviation features extracted from median filtering. a total of 12 features of the three r, g and b channels for four filters are calculated as mean and standard deviation features. it is evident from the scatter plots that value of features of original image differs significantly from the value of the features of tampered images while tampered images have similar values. fig. 1. ccc based model for image forensics (a) mean (b) standard deviation fig. 2. representation of mean and standard deviation feature extracted from median filtering table i. feature extraction from median filtering of original and tampered images mean standard deviation image red green blue red green blue original 0.9414 0.9372 0.9486 1.4216 1.4229 1.4265 t1 0.9644 0.9591 0.9701 1.4338 1.4348 1.4380 t2 0.9667 0.9607 0.9713 1.4319 1.4328 1.4362 t3 0.9683 0.9626 0.9731 1.4321 1.4330 1.4360 t4 0.9667 0.9609 0.9714 1.4319 1.4328 1.4362 t5 0.9700 0.9648 0.9754 1.4370 1.4380 1.4409 t6 0.9719 0.9668 0.9773 1.4391 1.4400 1.4428 t7 0.9723 0.9671 0.9773 1.4393 1.4402 1.4431 t8 0.9711 0.9664 0.9766 1.4381 1.4391 1.4419 t9 0.9735 0.9678 0.9782 1.4358 1.4368 1.4397 t10 0.9785 0.9731 0.9836 1.4388 1.4397 1.4427 b. noise feature extraction from ycbcr planes for image forensics each color model has specific characteristics to indicate the image forgery. most of the splice detection methods ignore the chroma component, but use the luminance component of the image to detect forgery. nevertheless, image chroma (saturation) is very useful for color image splicing detection. in the ycbcr color model, y represents the luminance component and cb and cr are the bluedifference and red-difference chroma components. cb (or cr) component has little image content while most of image content is preserved in y component. engineering, technology & applied science research vol. 8, no. 1, 2018, 2555-2561 2558 www.etasr.com gupta and mohan: color channel characteristics (ccc) for efficient digital image forensics (a) mean (b) standard deviation fig. 3. scatter plot for feature extracted from median filtering as discovered in [11], the edge analysis in chroma channel is especially useful. authors utilized chroma channels for extracting edge texture features from forged images. they demonstrated that chroma channels are specifically useful as they catch the crisp edges of spliced region. gray level co-occurrence matrix (glcm) for immediate neighbors was used to extract features. in present study, four edge detectors namely, canny, prewitt, sobel and laplacian of gaussian have been explored for extracting features from y, cb and cr channels. figure 4 depicts the edge extraction using these different edge detectors.it is evident that edges of foreign objects, e.g. zebra in this image, have sharper edges as compared to the edges of other natural objects present in the image. the obtained images are used for extracting second order derivatives using glcm. glcm [22] is very useful in the study of pixel pair's relationship to examine image texture. it computes how many times a pair of intensity values occur in a particular neighborhood in an image. an example of glcm extraction has been presented in figure 5. an original image may contain many pixel pair relationships. all possible pixel pair relationships for image in figure 5a are presented in figure 5b. for each pair, the number of its occurrence is counted and listed in figure 6c. for example, value ‘2’ in the first cell of figure 6c means that the pair (0,0) occurs twice in the example image. further, second order statistical features, i.e. for energy, correlation, contrast and homogeneity (ecch) are extracted. contrast measures the confined variations in the gray-level co-occurrence matrix. correlation gives the joint probability occurrence of specific pixel pairs. energy gives the sum of squared elements in the glcm. homogeneity denotes that how closely the factors in the glcm are distributed to the glcm diagonal. a) original b) canny c) log (d) prewitt (e) sobel fig. 4. edge images obtained from dehrominance channel for different edges fig. 5. extracting glcm matrix engineering, technology & applied science research vol. 8, no. 1, 2018, 2555-2561 2559 www.etasr.com gupta and mohan: color channel characteristics (ccc) for efficient digital image forensics table ii. example of ecch feature extraction from canny edge of original image and its tampered versions energy correlation contrast homogeneity y cb cr y cb cr y cb cr y cb cr original 0.6991 0.7626 0.8331 0.4035 0.4371 0.4649 0.1176 0.0883 0.0594 0.9412 0.9558 0.9703 t1 0.7131 0.7953 0.8272 0.4161 0.4575 0.4675 0.1102 0.0739 0.0613 0.9449 0.963 0.9693 t2 0.7114 0.7951 0.8252 0.4158 0.4585 0.4696 0.111 0.0739 0.0619 0.9445 0.963 0.969 t3 0.7103 0.7935 0.8232 0.4172 0.4591 0.4716 0.1112 0.0744 0.0625 0.9444 0.9628 0.9688 t4 0.7104 0.794 0.825 0.4161 0.4583 0.4699 0.1113 0.0743 0.062 0.9443 0.9628 0.969 t5 0.7132 0.7964 0.8267 0.4145 0.4566 0.4673 0.1104 0.0736 0.0615 0.9448 0.9632 0.9692 t6 0.7126 0.7961 0.8272 0.4134 0.4557 0.4645 0.1108 0.0738 0.0616 0.9446 0.9631 0.9692 t7 0.7123 0.7967 0.8261 0.4124 0.4538 0.4633 0.1111 0.0737 0.0621 0.9445 0.9631 0.969 t8 0.7119 0.7964 0.8256 0.4121 0.4517 0.4624 0.1113 0.0741 0.0623 0.9444 0.963 0.9688 t9 0.711 0.7946 0.826 0.4144 0.4568 0.4684 0.1113 0.0742 0.0617 0.9443 0.9629 0.9691 t10 0.7097 0.7931 0.8246 0.4106 0.453 0.4634 0.1123 0.0751 0.0626 0.9438 0.9624 0.9687 (a) (b) (c) (d) fig. 6. representation of a) contrast, b) energy, c) correlation and d) homogeneity feature extracted from median filtering contrast: ∑ ∑ ( − ) (9) energy: ∑ ∑ (10) correlation: ∑ ∑ ( ∗ )∗ (11) homogeneity: ∑ ∑ | | (12) where i, j denotes a pixel pair. the algorithm used for texture based statistical feature extraction is: step 1: consider an image i and extract its ycbcr channels. ( , ), ( , ) ( , ) represent the intensity values for different channels. step 2: apply edge detector to ( , ), to obtain a binary edge image ( , ) and then obtain glcm matrix for edge image ( , ). step 3: further, second order derivative features ecch are calculated by using (9), (10), (11) and (12). step 4: repeat steps 2 and step 3for the other two channels to obtain 4x3=12 features. repeat algorithm steps 2 and 3 for another three edge operator to obtain 12x4=48 features. engineering, technology & applied science research vol. 8, no. 1, 2018, 2555-2561 2560 www.etasr.com gupta and mohan: color channel characteristics (ccc) for efficient digital image forensics table ii indicates the results obtained from ecch features for the canny edge operator. features are extracted from y, cb and cr channels of original and 10 tampered (t1-t10) images. figure 6 demonstrates the values obtained for these features for original and tampered images. a clear deviation can be observed for the feature values of original and tampered images. figure 7 shows the relevant scatter plots. it is evident that the value of the features of tampered images differs significantly from the value of the features of the original image. ccc based first and second order derivatives are used together for features extraction for classification of images. as shown above, a total of 24+48=72 features is extracted. the computational complexity of the algorithm is linear as every pixel is accessed only once. fig. 7. scatter plot for canny edge detector iii. experimental results the experimental results of the proposed method have been obtained using a popular image dataset casia v2.0 [23]. this dataset consists of 7,491 authentic and 5,123 tampered images. tampered images are produced using crop-paste and spliced image region(s). these images are pre-processed with resizing, rotation or other distortions. images are post-treated with operations such as blurring to finish crop-and-paste operations. different sizes (small, medium and large) of spliced regions have been studied. experiment with 3 and 10 fold crossvalidation approach has been conducted to assess the operation of the proposed method. machine learning is achieved using support vector machines (svm). svm offer high accuracy and avoid over-fitting. svm can perform comfortably even if data is not linearly separable in the base feature space. kernel choice is crucial. the rbf kernel of svm gives the best results for binary classification. so, libsvm [24] classifier with radial basis function kernel is applied. the grid search method is used for choosing the penalty parameter c. all the experiments are tested on the mentioned dataset with libsvm classifier. the software platform used was matlab r2012a. hardware was a pc with 2.10 ghz intel core 2 duo processor. the efficiency of the classifier is evaluated on the basis of accuracy, feature dimensionality, feature selection and computation time. a classifier’s accuracy is determined by the right image classifications. dimensionality denotes the number of features used for the categorization. lesser dimensionality means fewer features and less evaluation time. feature selection is a technique used for the reduction of the number of used features. the non-contributing features may be ignored using feature selection procedure, but increases the evaluation time of the algorithm. the computation time is the time taken for feature computation and feature selection. the performance of the proposed method is investigated for different jpeg compression quality factors as illustrated in table iii. the proposed classifier is further compared with existing state of the art classifiers. accuracy, dimensionality and need for feature selection are compared and tabulated in table iv. comparison of computation time has been illustrated in table v. the main features of ccc classifier are:  the classification accuracy of ccc classifier is better when authentic and forged images are of different quality. the classifier accuracy drops slightly when the spliced image is of high quality.  ccc classifier’s accuracy is superior compared to natural image model (nim) [15], markov features (mf) [16] and multi-scale wld [18]. the comparison is illustrated in figure 8.  ccc classifier has low dimensionality. the accuracy of ccc classifier is similar to textural feature-based classifier [19] but with lower dimensionality.  ccc classifier does not require feature selection. classifier presented in [17] has a marginally higher accuracy compared to the proposed ccc classifier, but it additionally requires feature selection.  ccc classifier computes the features of the complete image as a unit and does not involve image blocks for feature extraction. moreover, feature selection is not commanded. this reduced the time as well as the space requirement for the proposed technique. table v indicates that the computation time for ccc classifier is much lower compared to nim [15] and mf [16] classifiers. fig. 8. accuracy comparison of the proposed ccc classifier with existing classifiers engineering, technology & applied science research vol. 8, no. 1, 2018, 2555-2561 2561 www.etasr.com gupta and mohan: color channel characteristics (ccc) for efficient digital image forensics table iii. accuracy (%)at various jpeg quality factors jpeg image quality factor accuracy obtained authentic image quality factor spliced image quality factor accuracy (%) at 3-fold accuracy (%) at 10-fold qf100 qf60 100 100 qf100 qf80 93.5 96.40 qf100 qf100 94.7 95.70 qf80 qf60 94.7 99.30 qf80 qf80 92.4 95.00 qf80 qf100 92.3 97.00 qf60 qf60 94.2 94.60 qf60 qf80 93.2 100 qf60 qf100 95.8 98.20 average 94.53 97.36 table iv. performance comparison method accuracy (%) dimensionality feature selection proposed method 97.36 72 not required natural image model [15] 84.86 266 not required markov features [16] 89.76 100 required multi scale wld [18] 96.61 960 not required textural feature [19] 97.73 96 not required gf+dct [17] 97.9 70 required table v. computation time comparison method feature computation time(s) feature selection time(s) total computation time(s) proposed method 1.4 1.4 natural image model [15] 4.3 4.3 markov features [16] 2.2 2.1 4.3 iv. conclusion in this work, machine learning based blind jpeg classifier for detecting forged images using ccc based noise and edge characteristics is proposed and implemented. statistical discriminating ccc features from original and tampered images are extracted. the original and spliced jpeg images at various quality factors are considered to train and test the classifier. the proposed classifier gives better efficiency in terms of higher accuracy and lower dimensionality. moreover, its performance is high even for low quality jpeg images. the only limitation of ccc classifier is that the classification accuracy decreases slightly for high quality spliced image. the proposed classifier could be extended to detect copy move, seam carving, steganography and other types of image tampering and serve as a complete tool for image forensics. references [1] a. rocha, w. scheirer, t. boult, s. goldenstein, “vision of the unseen: current trends and challenges in digital image and video forensics”, acm computer survey, vol. 43, no. 4, pp. 26:1–42, 2011 [2] h. farid, “detecting digital forgeries using bispectral analysis”, technical report aim-1657, ai lab, massachusetts institute of technology, 1999 [3] g. k. birajdar, v. h. mankar, “digital image forgery detection using passive techniques: a survey”,digitalinvestigation,vol. 10, no. 3, pp. 226-245, 2013 [4] x. li, “blind image quality assessment”, ieee international conference on image processing,vol. 1, pp. i-449-i-452, 2002 [5] i. avcibas, s. bayram, n. memon, m. ramkumar, b. sankur, “a classifier design for detecting image manipulations”, international conference on image processing, pp. 2645–2648, 2004 [6] c. popescu, h. farid, exposing digital forgeries by detecting duplicated image regions, technical report tr2004-515, dartmouth college, 2004 [7] s. bayram, i. avcibas, b. sankur, n. memon, “image manipulation detection”, electron imaging, vol. 15, no. 4,pp. 041102:1–17, 2006 [8] h. gou, a. swaminathan, m. wu, “noise features for image tampering detection and steganalysis”, international conference on image processing, pp. 97–100, 2007 [9] z. zhang, j. kang, y. ren, “an effective algorithm of image splicing detection”, international conference on computer science and software engineering, pp. 1035–1039, 2008 [10] b. mahdian, s. saic, “using noise inconsistencies for blind image forensics”, image and vision computing, vol. 27, no. 10, pp. 14971503, 2009 [11] w. wang, j. dong, t. tan, “effective image splicing detection based on image chroma”, 16thieee international conference on image processing, pp. 1257-1260, 2009 [12] f. battisti, m. carli, a. neri,“image forgery detection by means of noreference quality metrics”, 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the ieee, vol. 67, no. 5, pp. 786-804, 1979 [23] j. dong, w. wang, “casia tampered image detection evaluation database”, ieee china summit & international conference on signal and information processing (chinasip), july 6-10, 2013 [24] c. chang, c. j. lin, “libsvm: a library for support vector machines”, acm transactions on intelligent systems and technology, vol. 2, pp. 27:1-27, 2011 engineering, technology & applied science research vol. 7, no. 6, 2017, 2222-2230 2222 www.etasr.com hojjati et al.: logit model of computer-based data-driven creative idea generation in the industry … logit model of computer-based data-driven creative idea generation in the industry and service sectors sanaz nikghadam hojjati department of information technology management science and research branch islamic azad university tehran, iran sanaznik@hotmail.com ali rajabzadeh ghatari department of management tarbiat modares university tehran, iran alirajabzadeh@gmail.com mahmood alborzi department of information technology management, science and research branch islamic azad university tehran, iran mahmood_alborzi@yahoo.com gholamreza hassanzadeh department of anatomy, school of medicine tehran university of medical sciences tehran, iran hassanzadeh@tums.ac.ir abstract—organizational creativity and employee idea generation have become important and essential elements of an organization’s success, as creativity results to increased performance. the need of increased creativity is evident in industrial and service companies. the main idea behind this paper is to analyze and demonstrate if accessing various types of data in certain ways and/or situations affects creative idea generation by the people involved in different industrial/service sectors, considering that now most of the employees use digital data. the current paper discusses how seven different factors are related to digital data affect creativity. keywords-idea; generation; computer-based; data-driven; creativity; competitive; environment; business i. introduction in today’s highly competitive environment the goal of each organization is to gain sustainable competitive advantage to defeat the competition and stabilize its operation [1]. companies must create conditions for sustainable advantage under fierce competition. in [2] three conditions for sustainable advantage are indexed: 1) hierarchy of source, 2) number of distinct sources, and 3) constant improvement and upgrading. organizational creativity is a means to build sustainable competitive advantage, among other things because it includes these three conditions. creative thinking, idea generation and behavior is widely recognized as an important human skill and behavior in 21st century [3-5]. modern problems demand new forms of problem solving, and hence creativity becomes more important. while some companies do not give enough attention to creativity, a survey conducted by ibm, in which more than 1,500 ceos from 60 countries and 33 industries were interviewed, showed that creativity is what is needed for success [6]. creativity has also been defined as a key source for competitive advantages for long lasting organizations. in [7] it was showed that 82% of companies believe that there is a strong connection between creativity and business results. according to this report, companies that actively foster creative thinking outperform their rivals in revenue growth, market share and competitive leadership. modern accounts of creative cognition stress the central role of combining pre-existing knowledge components or materials [8]. even exceptionally creative products have incorporated pre-existing material [9], such that some of these materials and components have never been used in relation to the subject matter. awareness of the existence of these materials and/or components in different ways and in certain circumstances can help divergent thinking and creative idea generation [10-12]. accordingly, accessing various data in different forms from their own specialized field along with data from other fields may help creative idea generation. in this regard, the present study intends to study the impact of accessing various data types in certain ways and situations on creative idea generation by people involved in different industrial/service sectors. it applies a logistic regression model and presents a logit model for these factors. the main contribution of this paper is therefore the discussion of how various types of data and ways of accessing it contribute to improve creativity. the empirical analysis presented here is based on a large sample of computer users and employs a set of explanatory variables. engineering, technology & applied science research vol. 7, no. 6, 2017, 2222-2230 2223 www.etasr.com hojjati et al.: logit model of computer-based data-driven creative idea generation in the industry … ii. theoretical background a. creativity creativity has been defined in different ways by different people [13, 43]. for instance, creativity was defined as a developing process for novel and imaginative views about different situations [14]. some researchers state that creativity is the combining of ideas and individual and group approaches in a new way [15]. in [16] creativity is defined as a process composed of three main steps. the first step is becoming sensitive to problems, shortages, gaps in knowledge, pressures, lack of harmonies etc. the next step is finding new solutions for the previously identified problems as well as presenting hypotheses and testing them. in the last step the obtained results are communicated. creativity covers different levels, from employee level to organizational level. this process encompasses employees being creative in their own work, which aid further development of the creative idea that is then passed through others to enhance the organization’s creativity [17]. therefore, understanding what causes creativity to flourish and what may inhibit it, is beneficial for organizations and a very important thematic for organizational research. both personal and contextual factors [18] can affect creative performance, so organizational psychology has placed most of its focus on determining which factors promote creative ideas. on the one hand, there are many individual and organizational barriers to creativity [19-22]. on the other hand, organizational climate, culture, leadership, resources, skills, organizational structures and systems [23], inherent risk [24], job design [25, 26], support [27, 28], diversity [29, 30], safety [31, 32], resources [30, 33], dynamics [31, 32], personal characteristics and individual [34-41], structural and system [23, 42] motivation can motivate individual, group and organizational creativity. researchers in [11, 13, 27, 44] offered a theoretical perspective and understood creativity as the production or generation of novel and valuable ideas, products, or processes by individuals or groups. on the other hand, researchers’ oriented to cognitive approach [45] offer a holistic vision of creativity, which includes non-cognitive factors (personal and social) in creative production. this approach views creative ideas as being the natural result of applying basic mental operations to existing knowledge structures. for instance, authors in [46] described and measured creativity by fluency, flexibility, originality and elaboration while and some others like editors in [47] emphasized the role of the environment, the person, and intrinsic motivation on creativity. b. data and creativity according to [48], knowledge and information are outcomes of human action that engages signs, signals, and artefacts in social and physical settings. knowledge builds on an accumulation of experience and information, which depends on the data aggregation. authors in [49] describe “data” as chunks of facts about the state of the world. they believe data may be either quantitative or qualitative in nature. when thinking of data most people seem to emphasize the quantitative form that is easily stored and manipulated in computer systems. author in [50] reiterated that “data are material facts”. data, information, knowledge, and relative technologies have effect on creativity at all levels [51-59]. this is why these subjects became an interesting topic for individual, group and organizational creativity researchers (e.g. [60-83]). authors in [60] have designed and implemented an innovative creativity support system. authors in [74] considered the relation between computational creativity and computing. they stressed the important role of a knowledge base in creative computing system. authors in [73] examined the relation between information technology use by children and their creativity. these researchers considered the use of 4 types of information technology: 1) computer, 2) internet, 3) video games and 4) mobile. authors showed that playing video games has a significant effect on children creative behaviour. the researchers suggested that video game designers should consider various aspects of stimulating creativity such as visual and audio features. authors in [81] stated that creative work is often achieved in distributed groups. therefore, information exchange is frequently facilitated by groupware systems. in order to reduce losses inherited in group work and to best support creative group processes (cgp), they proposed a framework which combines: a) the stages of the creative process, b) the potential losses of creative group processes and c) different media characteristics drawn from the media synchronicity theory to formulate groupware design principles . authors in [84-89], are among the researchers in the field of neurology and medicine that examined the effect of different data types (visual, audio and textual data) on human brain and its idea generation process. iii. concepts and approach a. fundamental concepts the seven fundamental concepts defined in the context of this work are:  various visual data (vvd)  various textual data (vtd)  various audio data (vad)  data related to the performance of various creative persons who are dealing with similar issues (drc)  data presentation speed (dps)  presentation of various data with different combinations and various arrangements, frequently in a variety of time periods (dpcad)  presentation of various data to users on the left side of the screen so that the left eye receives them (pdls) computer users from industrial or service companies deal with different data types which may affect creative idea generation in varying degrees. thus, it is necessary to carefully define the data types considered. computer users often interact with computer’s output data using visual perception and auditory perception. the data received by eyesight is often separating into two different data types: visual and textual. the engineering, technology & applied science research vol. 7, no. 6, 2017, 2222-2230 2224 www.etasr.com hojjati et al.: logit model of computer-based data-driven creative idea generation in the industry … fundamental concept definition about three data types derives from this. 1) various visual data (vvd) various visual data refer to a set of the offered data to the users in the form of images, charts, or movies. these types of data are recognized by users’ visual perception. patterns, trends and correlations that might go undetected in text-based data can be exposed and recognized easier with data visualization software. 2) various textual data (vtd) various textual data refer to systematically collected material consisting of written, printed, or electronically published words, typically either purposefully written or transcribed from speech. these types of data are recognized by users’ visual perception and demand reading and writing skills. 3) various audio data (vad) various audio data refer to a set of offered data to users through acoustic, frequencies, and they are commonly understandable by auditory human sense. computer users from industrial or service companies receive/process data with different content. not all contents are suitable to improve creative idea generation. thus, it is necessary to carefully define what data contents are being considered. 4) data related to the performance of various creative persons dealing with similar issues (drc) audio, visual and/or textual data presented to a user, which describe how other creative people performed similar activities, can conduct the behavior, feeling and thought of the user to be more creative. 5) data presentation speed (dps) while sensitive to the speed of receiving data, the human brain reacts differently to data obtained at different speed, therefore it is necessary to carefully define the data presentation speed. theoretically, humans’ eyes and brain can perceive image and texts with a maximum speed of 1000 frames per second (fps). however, to the untrained, this speed is commonly reduced to 150 fps. in this research passing speed of various textual and visual data from human eyes is between 1 to 150 fps. 6) presentation of various data with different combination and various arrangements, frequently in a variety of time periods (dpcad) different combinations and various arrangements of the received data can lead users to different understandings and different outcomes. employees computer users are frequently exposed to different combinations and various arrangements, frequently in a variety of time periods. 7) presentation of various data to users on the left side of the screen so that the left eye receives these data (pdls) visual and textual placement in users’ vision range can affect the user’s perception. computer users receive data in different visual range positions. not all ranges are suitable to improve creative idea generation. to do this it is necessary to carefully define the vision range being considered. this variable refers to presenting various visual and textual data on the left side of the screen so that data are received outside the central vision (angle of 40 to 60 degrees) and the right half of the left eye much more than other places of both eyes. b. approach the main question behind this research is if data type, content and properties effectively contribute to creative idea generation. one important issue to be discussed is why these seven data related factors were considered relevant enough for this study. it is consensual, that a data flood is created every day by the billions of people interactions using information and communication technologies. researchers and policymakers are already realizing the potential of this torrent of data to identify needs, provide products and services, and predict and prevent crises for the benefits of individuals, organizations and societies. people need to access appropriate data in a specific situation and form in order to improve their ability of creative idea generation. organizations which need to access creative ideas should provide and support appropriate data in a specific situation and form for their employees. inappropriate data in inappropriate situation and form can prevent people, organizations and societies from accomplishing their goals [90]. thus, identifying the appropriate type of data, the appropriate form and mixture of content, the appropriate way of presenting data and appropriate situations of presenting and accessing data are important in order to cause the generation of creative ideas for individual, organizational and social objectives. iv. research method a. research scheme this research is decision-oriented. the data collection method is a descriptive survey, and data analysis is correlational research. the dependent variable “creative idea generation” is related to independent variables vvd, vtd, vad, drc, dps, dpcad, pdls (see section iii.a for definitions). these independent variables were chosen based on the literature. table i indicates the research works supporting the choice of these independent variables. the theoretical framework for this research considers the following set of hypotheses:  h1: there is meaningful relationship between vvd and computer-based data-driven creative idea generation.  h2: there is meaningful relationship between vtd and computer-based data-driven creative idea generation.  h3: there is meaningful relationship between vad and computer-based data-driven creative idea generation.  h4: there is meaningful relationship between drc and computer-based data-driven creative idea generation.  h5: there is meaningful relationship between dps and computer-based data-driven creative idea generation. engineering, technology & applied science research vol. 7, no. 6, 2017, 2222-2230 2225 www.etasr.com hojjati et al.: logit model of computer-based data-driven creative idea generation in the industry …  h6: there is meaningful relationship between dpcaf and computer-based data-driven creative idea generation.  h7: there is meaningful relationship between pdls and computer-based data-driven creative idea generation. table i. researches that support the considered independent variables independent variables researches support independent variables vvd [84], [87], [91], [92] vtd [84], [87], [91], [92] vad [84], [87], [91], [92] drc [91], [93] dps [94], [95], [96] dpcaf [91], [94], [95], [96] pdls [87], [91] a questionnaire based on the theoretical framework indicated above was developed. it was designed to be answered on a likert scale with a few demographic questions, and one cross-examination question placed between demographic questions. the study has a cronbach’s alpha coefficient of 0.713 indicating high reliability. the data were collected with an online questionnaire. an aspect worth to highlight is the large number of samples used, higher above the 384 that the cochran formula considers as the minimum for unlimited community samples. the dependent variable is creative idea generation. figure 1 displays the research variables and the related dimensions considered in the theoretical framework. fig. 1. theoretical framework b. research participants to assess and validate the above hypotheses, two types of computer users from different domains were considered to fill the questionnaire: 1) industry/service, and 2) academics (university professors). the responses to this electronic questionnaire were anonymous and without any monetary incentives. the data was gathered in a time period of 6 months. a total of 929 individuals answered the questionnaire. the collected questionnaires were filtered in two stages:1) in the first stage the questionnaires whose participants did not answer all questions were removed, 2) in the second stage those questionnaires whose cross-examination question made the questionnaire unreliable were also removed. as a rule, if the difference between the answer of the cross-examination question and the answer of a dependent variable was more than 2 levels, then, that questionnaire was considered unreliable. eventually, after this two-step screening we obtained 871 valid questionnaires. v. results a. descriptive research findings the number of participants for this study is 871 computer users of whom 60.8% were male and 39.2% female. the most prevalent age interval is the 21-30 years old range with 42.1% of the participants. the data frequency distribution shows that 29.7% of the participants use computer and information systems daily for a period of 5-10 hours, while 22% use daily their computers for a period of 3-5 hours. moreover, 78.1% of the users believe they are capable of creative idea generation while 21.9% believe they are not. further details can be seen in table ii. table iii represents the descriptive analysis for dependent and independent variables. frequency distribution of dependent variable data show that 30.1% of participants admit that “sometimes” they generate computer-based data-driven creative ideas; 18.9% found it “most of times”; 17.1% “very rarely”;16.9% “rarely”; and finally, 7.2% of the participants in this research believed it happens “always”. table ii. frequency distribution and percentages of demographic variables frequency percent valid percent cumula tive percent gender female 341 39.2 39.2 39.2 male 530 60.8 60.8 100 total 871 100 100 age (y.o.) <20 31 3.6 3.6 3.6 21-3o 367 42.1 42.1 45.7 31-40 339 38.9 38.9 84.6 41-50 114 13.1 13.1 97.7 51-60 17 2.0 2.0 99.7 >60 3 0.3 0.3 100 total 871 100 100 comput er and informa tion systems usage per day (hrs) <1 111 12.7 12.7 18.6 1-3 181 20.8 20.8 39.4 3-5 192 22.0 22.0 61.4 5-10 259 29.7 29.7 91.2 >10 77 8.8 8.8 100 no idea 51 5.9 5.9 5.9 total 871 100 100 871 creative idea generat ion ability yes 680 78.1 78.1 78.1 no 191 21.9 21.9 100 total 871 100 100 yo: years old, hr: hours engineering, technology & applied science research vol. 7, no. 6, 2017, 2222-2230 2226 www.etasr.com hojjati et al.: logit model of computer-based data-driven creative idea generation in the industry … table iii. frequency distribution and percentages of dependent and independent research variables frequency percent valid percent cumulative percent vvd no idea 46 5.3 5.3 5.3 very low 147 16.9 16.9 22.2 low 189 21.7 21.7 43.9 middle 295 33.9 33.9 77.7 high 157 18.0 18.0 95.8 very high 37 4.2 4.2 100 total 871 100 100 vtd no idea 19 2.2 2.2 2.2 very low 66 7.6 7.6 9.8 low 126 14.5 14.5 24.2 middle 259 29.7 29.7 54.0 high 310 35.6 35.6 89.6 very high 91 10.4 10.4 100 total 871 100 100 vad no idea 50 5.7 5.7 5.7 very low 316 36.3 36.3 42.0 low 218 25.0 25.0 67.0 middle 181 20.8 20.8 87.8 high 88 10.1 10.1 97.9 very high 18 2.1 2.1 100 total 871 100 100 drc no idea 78 9.0 9.0 9.0 very low 204 23.4 23.4 32.4 low 252 28.9 28.9 61.3 middle 228 26.2 26.2 87.5 high 97 11.1 11.1 98.6 very high 12 1.4 1.4 100 total 871 100 100 dps no idea 53 6.1 6.1 6.1 very low 77 8.8 8.8 14.9 low 149 17.1 17.1 32.0 middle 413 47.4 47.4 79.4 high 152 17.5 17.5 96.9 very high 27 3.1 3.1 100 total 871 100 100 dpcaf no idea 100 11.5 11.5 11.5 very few 106 12.2 12.2 23.7 few 206 23.7 23.7 47.3 middle 307 35.2 35.2 82.5 high 125 14.4 14.4 96.9 very high 27 3.1 3.1 100 total 871 100 100 pdls no idea 143 16.4 16.4 16.4 very low 126 14.5 14.5 30.9 low 224 25.7 25.7 56.6 middle 241 27.7 27.7 84.3 high 118 13.5 13.5 97.8 very high 19 2.2 2.2 100 total 871 100 100 cig* no idea 85 9.8 9.8 9.8 very rarely 149 17.1 17.1 26.9 rarely 147 16.9 16.9 43.7 sometimes 262 30.1 30.1 73.8 most of times 165 18.9 18.9 92.8 always 63 7.2 7.2 100 * cig: creative idea generation b. results of analytical research since the sample size of this study is large (871 persons), the distribution of data is normal (note: based on central limit theory plus some simulations if sample size is bigger than 30 (n≥30) then sample is assumed as “large sample” and the sampling distribution is considered normal [97]). given that this distribution is normal for all variables in the society, the pearson correlation coefficient was used to analyze the relationship between variables. the results of computing the correlation coefficient between the variables are shown in table iv. given that the “sig” is less than the significance level (0.01), significant relationship between the variables in the model is proved. to analyze the impact of each independent variable to predict the dependent variable linear regression equation for the relationships outlined in the model is calculated. according to table v, the durbin-watson d = 1.764 is between the two critical values of 1.5 < d < 2.5 and therefore we can assume that there is no first order linear autocorrelation in the data. also, we found that the adjusted r² of our model is 0.237 with the r² = 0.244 that means that the linear regression explains 24.4 % of the variance in the data. table iv. pearson correlation test for research variables correlations creative idea generation vvd pearson correlation 0.365** sig. (2-tailed) 0.000 n 871 vtd pearson correlation 0.312** sig. (2-tailed) 0.000 n 871 vad pearson correlation 0.098** sig. (2-tailed) 0.004 n 871 drc pearson correlation 0.360** sig. (2-tailed) 0.000 n 871 dps pearson correlation 0.215** sig. (2-tailed) 0.000 n 871 dpcaf pearson correlation 0.243** sig. (2-tailed) 0.000 n 871 pdls pearson correlation 0.234** sig. (2-tailed) 0.000 n 871 ** correlation is significant at the 0.01 level (2-tailed). table v. model summary table model r r2 adjusted r2 std. error of the estimate durbin-watson 1 0.493 0.244 0.237 1.233 1.764 this low p value / high r2 combination indicates that changes in the predictors are related to changes in the response variable and that their model explains a lot of the response variability. the explanation for this rather high r2 is that, like most human related studies, some factors like genetic, environmental, cultural and economic ones were de facto not considered. also, one has to remember that people are unpredictable. if this research was to consider all the things that might affect someone’s creative idea generation it would be expected for these seven special variables to be minor contributors. putting all possible factors into the model would engineering, technology & applied science research vol. 7, no. 6, 2017, 2222-2230 2227 www.etasr.com hojjati et al.: logit model of computer-based data-driven creative idea generation in the industry … indeed give better results. but the goal of this research was to see if there was a small, but reliable relationship between the specific variables and the creative idea generation. small effect sizes require larger samples to find significance which is the case of this research, as it involved the participation of 871 users. table vi indicates the f-test. the linear regression's ftest has the null hypothesis that there is no linear relationship between the two variables (in other words r²=0). with f = 39.685 and 863 degrees of freedom the test is highly significant, thus we can assume that there is a linear relationship between the variables in our model table vii shows the regression coefficients, the intercept and the significance of all coefficients and the intercept in the model. we find that our linear regression analysis estimates the linear regression function to be: 0.443 + 0.228(vvd) + 0.127(vtd) – 0.107(vad) +0.274(drc) + 0.097(dps) + 0.083 (dpcaf) +0.128(pdls) = y (1) in table vii, the coefficients for the variables are shown. all have p-value smaller than 0.05. the intercept is significantly different from 0 at the 0.05 alpha levels. table vi. the linear regression’s f-test anova model sum of squares df mean square f sig. 1 regression 421.993 7 60.285 39.685 0.000 residual 1310.951 863 1.519 total 1732.944 870 table vii. simple linear regression coefficients coefficientsa model unstandardized coefficients standardized coefficients t sig. b std. error beta 1 (constant) 0.443 0.155 2.857 0.004 vvd 0.228 0.041 0.199 5.625 0.000 vtd 0.127 0.042 0.106 3.034 0.002 vad -0.107 0.038 -0.090 -2.806 0.005 drc 0.274 0.041 0.231 6.757 0.000 dps 0.097 0.040 0.078 2.461 0.014 dpcaf 0.083 0.036 0.075 2.276 0.023 pdls 0.128 0.033 0.121 3.861 0.000 vi. conclusion the main idea behind this paper was to analyze and demonstrate if accessing various types of data in certain ways and situations affects creative idea generation in people involved in different areas of the industry and services. as computer-based data-driven creativity becomes more and more recognized as one key factor for long term organization and business sustainability the present study contributes to understanding if various types and forms of data can improve the sustainability of computer related tasks in industry. considering the importance of data in current societies it was considered relevant to analyze if this environmental factor was effectively improving creativity. to verify this relation, a questionnaire was developed with answers using the likert scale. to make the study more credible the chosen target population were highly skilled computer users for two main reasons:  computer users are much more familiar with various data types in certain ways and situations than most of other population  most of creative industrial/services jobs are using intensively computers nowadays, so most of target creative population are computer users the findings from the questionnaires showed that the defined variables have a positive and meaningful relationship with creative idea generation, demonstrating the validity of hypotheses 1 to 7 defined in the research method section (section iii.a). moreover, the variable “various audio data” (vad) has a negative and meaningful relationship with creative idea generation, indicating in this way the validity of the hypothesis 3 defined in the research method section (section iii.a). like most other research, this one is not complete and several limitations that need to be solved in future work are indicated below:  only three separated general types of data (visual, textual and audio data) were considered as types of data in this research. it is also recognized that adding more specific types of data may contribute to creative idea generation. however, it was decided to focus on these three general types because of their widespread usage in today’s organizational computer systems.  on the data content, only those contents that were related to the performance of various creative persons which were dealing with similar issues were considered. however, it is still necessary to investigate if other types of contents can indoctrinate and encourage creative idea generation between employees or provide clues for motivating divergent thinking or out of the box thinking for improving creative idea generation processes.  the authors only considered if various data with different combinations and various arrangements, will impact a creative idea generation. but, they did not discuss the kind of data, the combination, arrangement and frequency. thus, future research must address these issues.  the validation by the end users was mainly qualitative in the sense that their answers were based on their individual perception and not on real quantitative data. the main aspect here is that when users were answering if factors improved their creativity they answered based on qualitative perception and not on data that measure quantitatively how effectively they became more creative. despite these limitations the fundamental conclusions from this work are:  research departments should encourage the use of vvd, drv and vtd to improve creativity. on the other hand, dps, dpcaf, pdls and vad have little importance. the engineering, technology & applied science research vol. 7, no. 6, 2017, 2222-2230 2228 www.etasr.com hojjati et al.: logit model of computer-based data-driven creative idea generation in the industry … use of various audio data (vad) is even not recommendable.  there are business opportunities for companies to develop new applications targeting specifically creative idea generation following the identified aspects discussed in this paper.  the results obtained with this work are important to increase the competitive advantage of companies and their survival in today’s dynamic and complex business environment. 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et al.: modified numerical modeling of axially loaded concrete-filled steel circular-tube … modified numerical modeling of axially loaded concrete-filled steel circular-tube columns phu-cuong nguyen advanced structural engineering laboratory faculty of civil engineering ho chi minh city open university ho chi minh city, vietnam cuong.pn@ou.edu.vn, henycuong@gmail.com thanh-tuan tran institute of offshore wind energy kunsan national university kunsan city, cheollabuk-do, republic of korea tranthanhtuan@kunsan.ac.kr duc-duy pham advanced structural engineering laboratory faculty of civil engineering ho chi minh city open university ho chi minh city, vietnam duy.pd@ou.edu.vn trong nghia-nguyen faculty of civil engineering ho chi minh city open university ho chi minh city, vietnam nghia.nt@ou.edu.vn abstract—predicting the behavior of concrete in a concretefilled steel tubular (cfst) column is challenging due to the sensitivity to input parameters such as the size of the crosssection, the material modeling, and the boundary conditions. the present paper proposes a new modified finite element model to predict the behavior and strength of a cfst subjected to axial compression. the development is based on the concrete damaged plasticity model, with its stress-strain relationship revised from the available model. the predicted accuracy of the modified model is verified via a wide range of experimental tests. the proposed model has more accuracy than the available models in predicting the ultimate compression strength. the results show good agreement with the test data, allowing its use in modeling cfst columns. keywords-cfst columns; axial compression; finite element modeling; stress-strain relationship; steel; concrete i. introduction concrete-filled steel tubular (cfst) columns are widely used in modern constructions. many studies have been conducted in order to understand the behavior of these composite columns, either experimental [1, 2] or analytical [3, 4]. based on the outcomes from these investigations, different guidelines and codes have been published for the design procedure [5, 6]. cfst columns combined with steel-framed structures [7, 8] form very powerful structures. authors in [9] used fiber reinforced polymer tubes filled with recycled materials and concrete for pile foundations. using finite element (fe) models has become a popular technique to model cfst via software such as ansys and abaqus. this approach can model the interaction between concrete core and steel tube accurately. in this study, the fe software abaqus is used to fe model cfst. recently, authors in [10] studied the influence of geometric and material properties on the behavior of the concrete-filled double skin steel tube (cfdst) member with m16 studs under bending. the material model is an input parameter that is mainly affected by the behavior of cfst. several concrete and steel stress-strain � − � models have been developed [11-16]. almost all models are developed from experimental data based on regression analysis. authors in [17, 18] proposed fe modeling for analyzing box and circular cfst columns. authors in [16] developed a simplified model to calculate the capacity of the cross-section and the axial force via the load-deformation � − � curve based on 50 test data of self-consolidating concrete (scc) filled hollow structural steel (hss) stub columns. similarly, authors in [14, 15] proposed a simple and effective model for cfst subjected to extreme loadings. in [11], the steel � − � relationship was revised based on the available models by [19]. in the present study, the concrete � − � curve developed in [12] is revised via the modification of the plateau branch to represent the actual behavior of the material. this paper aims to develop an fe model of circular cfst columns under axial compression loading. a modified � − � model is proposed for the concrete material. the purpose of this study is to improve the accuracy of the fe model using abaqus. the accuracy and effectiveness of the new model are verified against the test data from [3, 20]. in the future, focus may be given to the behavior of cfst with steel fiber reinforcement [21], concrete using fly ash [22], or concrete with cement paste including silica oxide nanoparticles. ii. development of the material models a. steel material model in this study, the material model proposed in [19] is adopted for the characteristics of the stress-strain curves, as illustrated in figure 1. the relationship of � − � can be expressed as follows: corresponding author: phu-cuong nguyen engineering, technology & applied science research vol. 11, no. 3, 2021, 7094-7099 7095 www.etasr.com nguyen et al.: modified numerical modeling of axially loaded concrete-filled steel circular-tube … � � �� � � �� 0 � ���� �� � �� �� − ��� − �� � � � �� ���� ��� � � �� � �� �� � � �� (1) where � is young’s modulus of steel, �� is the yield strength corresponding to the yield strain �� � ���� , �� is the ultimate strength corresponding to the ultimate strain �� , ! is the hardening exponent that can be calculated as: ! � � � ��� ����� ��� � (2) where � is the initial elastic modulus at the onset of strain hardening, and can be taken as 0.02es. yield strain �� and ultimate strain �� can be expressed based on the range of yield strength �� which is 200mpa-800mpa: ε# � $ 15 � �� �� 300(15 − 0.018��� − 300�+ � �� �� � 300 (3) ε, � $ 100 � �� �� 300(100 − 0.15��� − 300�+ � �� �� � 300 (4) fig. 1. constitutive model of steel. b. concrete material model characteristics of stress-strain curves for concrete have been studied in [1, 24]. most researchers focused on the development of a � − � model based on the experimental results. for example, in [25], � − � cuves for the fiber model of concrete have been developed to predict the monotonic and cyclic force-deformation behavior of cfst columns. similar studies have been performed in [2, 26]. in these works, empirical models were proposed for the strain-softening response for cfst. in this paper, the damaged plasticity model of concrete material is utilized. this model is available in abaqus and can be easily used by defining some key material parameters. these factors are calibrated and verified with the extensive test results of [27-29] and they are briefly introduced as follows: young’s modulus of concrete is predicted based on the concrete strength -�./0 [30]: . � 47003�4′ (5) according to [31], the ratio of compressive strength under biaxial loading to the uniaxial compressive strength -�67 /�./0 is obtained based on the available data in the literature as follows: �9:�;< � 1.5 � -�./0�7.7=> (6) the fracture energy -?@ 0 that is defined as the tensile softening response beyond the failure stress, depends on the maximum coarse aggregate size -abcd) and concrete strength -�./0. the following equation can be deduced to determine ?@ [32, 33]: ?@ � -0.0469 � aghij − 0.5 � abcd k 260 m�;<n7o 7.= (7) authors in [29] stated that the compressive meridian -p.0 that is used to determine the yield surface of the material model, varied in the range from 0.5 to 1, and it is expressed as a function of equibiaxial concrete strength -�670 and concrete strength -�./0 [34]: p. � >.>��9:3��4′ k5��q0 (8) the dilation angle -ψ0 factor is used to define the plastic flow potential. this parameter is affected by the confining stress and plastic deformation of the material [27]. the factor ψ is determined as the function of the confinement factor -r.0 based on regression analysis [1]: ψ � $56.3 � -1 − r.0 r. 0.56.672sm t.uu.vuwx;o r. y 0.5 (9) in which the confinement factor is calculated as: r. � z� ��//z. �./, where z� and z. are the cross-sections of the steel tube and concrete respectively. for the strain hardening–softening rule, authors in [12] proposed a � − � curve for confined concrete through the tests. this model is revised in the present paper. the details of the proposed model are described below. c. the proposed stress-strain relationship for concrete the � − � model developed in [12] is modified to describe the effective � − � relationship of confined concrete by the steel tube, as illustrated in figure 2. the model includes three main stages, corresponding to ascending branch (oa), plateau branch (ab), and descending branch (bc). the initial stage oa is described as follows: [ �;< � c\ ]6 \ ^ n]-c�j0\]-6]n0\ ^ if 0 b � �.7 (10) where co x ε ε = , c and q are factors that are defined in (11): c � �;�;:�;< , q � -c �n0 ^ 7.>> − 1 (11) engineering, technology & applied science research vol. 11, no. 3, 2021, 7094-7099 7096 www.etasr.com nguyen et al.: modified numerical modeling of axially loaded concrete-filled steel circular-tube … the parameter �.7 of the unconfined concrete is expressed based on the regression analysis of over 100 test data from 17 references [35], in which the uniaxial compressive strength �./ ranges from 10 to 100mpa: ( )' 7 0 0.00076 0.626 4.33 10 c c fε − = + − × (12) fig. 2. the constitutive model of confined concrete. the ultimate strain εcc of the confined concrete is expressed using the model of [12]. in this model, εcc depends on the compressive strength �./ , and confining stress at the point b, �e: �;;�;: � s f g � -2.9224 − 0.00367 � �./0 m�h�;< o 7.injj]7.77j��;< (13) it is worth mentioning that the confining stress only happens before and after the yielding location of the material. in this study, the confining stress of the circular column is determined based on the regression analysis as follows: �e � n]7.7ijj���k:.:^l^ �mn (14) the constant value of confining stress �e remains from �.7 to �../ corresponding to the plateau branch (ab) that represents the increment of the peak strain of the concrete due to confinement. for the last stage of the concrete model (bc), the model of [36] is used, which is expressed as follows: σ � �pq k -�./ − �pq0 � exp u− m� ��;;v o w x y� � y �.. (15) where �pq is the residual stress [1] and z and { are factors determining the shape of the softening stage. the parameter { can be taken as 1.2 [1], and z is calculated as follows: z � 0.04 − 7.7i|n]qv .:}x; ~�.u� (16) iii. numerical modeling a. finite element modeling the current paper used the available model developed in [37]. the diameter and length of the cfst are 300mm and 900mm respectively. the thickness of the steel tube is 3.2mm. concrete with 27.2mpa compressive strength and 0.351 of ultimate strain is assigned for the concrete core, while steel with yield strength of 232mpa is assigned for the steel tube. (a) (b) fig. 3. modeling of a cfst column. (a) axisymmetric model, (b) full 3d model. the finite element model of figure 3 is developed in abaqus. the steel tube and concrete are simulated by a 4node bilinear element with reduced integration with hourglass control (cax4r). the mesh size of each element ranges from d/20 to d/10 which can provide accurate simulation. for the interaction between the steel tube and the concrete core, the surface-to-surface contact with hard contact condition is used to model linear behavior, and the column friction model is used to simulate the nonlinear behavior with a coefficient of 0.6 [3]. for boundary condition, the bottom surfaces are assumed to be fully fixed against all degrees of freedom. the incremental load is applied on the top of the column using the displacement control method to solve. engineering, technology & applied science research vol. 11, no. 3, 2021, 7094-7099 7097 www.etasr.com nguyen et al.: modified numerical modeling of axially loaded concrete-filled steel circular-tube … b. effect of the mesh size on finite element analysis the accuracy and required computing time of the fe model are investigated in this section. different meshing approaches, including the axisymmetric model and 3d model, are generated. figure 4 illustrates the stress distribution from each model under the axial force. it can be seen that there is no obvious effect on the predicted von mises stress for the cfst column. for better consideration, the axial load-strain -� − �0 relationship is obtained, as shown in figure 5. the predicted responses from the two meshing approaches are almost the same as those from the experiment-tested cu-070 [20]. an important finding is that the computational time in the axisymmetric model is only 22sec which is less by a factor of 20 when compared to the 3d model. it can be concluded that the fe axisymmetric model can give accurate and efficient computation. (a) (b) fig. 4. stress distribution of different models. (a) axisymmetric model, (b) full 3d model. fig. 5. influence of the meshing and element types. iv. verification and discussion a. ultimate strength the data of 663 circular cfst columns from the previous studies are selected for validation. the ultimate strength �� is defined as the peak load of the � − � curve. in this paper, the ultimate strength from the proposed model ��� is compared with those obtained from the available models in [3, 20]. ��� is normalized with the measured ultimate strength ��b, which is denoted as ��� /�.b. the comparison is summarized in table i. it can be seen that the result obtained from the fe model is more conservative than those produced from the available models. additionally, the smallest value of standard deviation for the proposed model is found to be 0.055. the results indicate that the predicted outcomes from the current fe model are more reasonable than the previous models. table i. ultimate strength obtained from the proposed and other models [3] [20] proposed mean 0.975 0.980 1.011 std. 0.090 0.129 0.055 b. � − � curves of the cfst column in terms of the prediction of the � − � curves, the proposed model is compared to the available models from [3, 20]. the comparison is performed for different specimens obtained from [2, 16, 20]. figure 6 illustrates the predicted � − � relationship of normal cfst, with its modeling parameters taken from [20]. the observed result from the fe model agrees with the experiment very well. fig. 6. n–ε curves of cfst column for normal specimens. fig. 7. n–ε curves of cfst column with 21.7 �/� 150. 0 500 1000 1500 2000 2500 3000 3500 0 5000 10000 15000 20000 25000 a x ia l lo a d n (k n ) axial strain εεεε (µεµεµεµε) test proposed model han et al hsuan-teh hu et al specimen cu-070: d = 280.00 mm; t = 4.00 mm; l = 840.00 mm; fc' = 31.15 mpa; fy = 272.60 mpa; ξξξξc= 0.52 0 1000 2000 3000 4000 0 5000 10000 15000 20000 25000 a x ia l lo a d n (k n ) axial strain εεεε (µεµεµεµε) test proposed model han et al specimen cc8-a-8: d = 108.00 mm; t = 6.50 mm; l = 324.00 mm; fc' = 77.00 mpa; fy = 853.00 mpa; ξξξξc = 3.22 engineering, technology & applied science research vol. 11, no. 3, 2021, 7094-7099 7098 www.etasr.com nguyen et al.: modified numerical modeling of axially loaded concrete-filled steel circular-tube … figure 7 shows the prediction of the � − � curve of the specimen reported in [2]. in this test, the ratio �/� varies from 21.7 to 150. as can be seen, the unsafety in the prediction is obtained for the model in [3] in the post-yielding strength branch. on the contract, the modified fe model gives a better prediction with the test. furthermore, the predicted � − � relationship was also performed for specimens with thin-walled steel tube and high-strength, as shown in figure 8. the test curve is shown in [16]. the results indicate that the prediction from the fe modeling matches very well with those obtained from han et al.’s model [16] and the test. in contrast, hu et al.’s model [20] is an unsafe prediction in the post-yielding strength stage. the above discussion leads to the conclusion that the developed fe model can be used in simulating the cfst column under axial compression for accuracy, effectiveness, and safety predictions. fig. 8. n–ε curves of the cfst column with thin-walled and high-strength steel. v. conclusion the current paper developed a fe modeling for axially loaded circular concrete-filled steel tube columns. the proposed model is compared with the available models in terms of accurate prediction. a new fe model is used to analyze the cfst subjected to axial compression. the model revised the � − � curve in [12]. the proposed model is more accurate than the models in [3, 20]. in predicting the ultimate strength. the predicted � − � curve from the new model matches well with the test data, for both normal materials and thin-walled steel tubes, which indicates the versatility of the developed modeling in calculating the load-deformation curves. regarding future work, the behavior of cfst columns with steel fiber reinforcement [21], concrete using fly ash [22], concrete with cement paste with including silica oxide nanoparticles [20], etc. can be studied by performing fem simulation. acknowledgment the authors gratefully acknowledge the financial support provided by the scientific research fund of ho chi minh city open university, vietnam. 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[37] m.-x. xiong, d.-x. xiong, and j. y. r. liew, "axial performance of short concrete filled steel tubes with highand ultra-highstrength materials," engineering structures, vol. 136, pp. 494–510, apr. 2017, https://doi.org/10.1016/j.engstruct.2017.01.037. microsoft word etasr_v11_n4_pp7515-7521 engineering, technology & applied science research vol. 11, no. 4, 2021, 7515-7521 7515 www.etasr.com zainurin et al.: a review of battery charging discharging management controller: a proposed … a review of battery charging discharging management controller: a proposed conceptual battery storage charging – discharging centralized controller nur ariana zainurin faculty of electronic and computer engineering universiti teknikal malaysia melaka (utem) melaka, malaysia m022020034@student.utem.edu.my siti aisyah binti anas faculty of electronic and computer engineering universiti teknikal malaysia melaka (utem) melaka, malaysia aisyah@utem.edu.my ranjit singh sarban singh faculty of electronic and computer engineering universiti teknikal malaysia melaka (utem) melaka, malaysia ranjit.singh@utem.edu.my abstract-this paper describes the development of a centralized controller to charge or discharge the battery storages that are connected to renewable energy sources. the centralized controller is able to assist, control, and manage the battery storage charging when excessive power is available from renewable energy sources. at the same time, the centralized controller also performs battery storage discharging when the connected load requires a power source, especially when the renewable energy sources are unavailable. background studies regarding battery storage charging-discharging are presented in the introduction section. also, generally developed chargingdischarging methods or techniques were applied at the system level and not specifically to the battery storage system level. due to the limited study on battery storage system chargingdischarging, this paper reviews some of the similar studies in order to understand the battery storage charging–discharging characteristics as well as to propose a new conceptual methodology for the proposed centralized controller. the battery storage state-of-charge (soc) is used as the criterion to develop the conceptual centralized controller, which is also used as a switching characteristic between charging or discharging when only the battery energy storages are supplying the output power to the connected load. therefore, this paper mainly focuses on the conceptual methodology as well as explaining the functionality and operationality of the proposed centralized controller. a summarized comparison based on the studied charging– discharging systems with the proposed centralized controller is presented to indicate the validity of the proposed centralized controller. keywords-management controller; centralized controller; battery charging/discharging; dynamic charging/discharging controller i. introduction a battery is an energy storage device, which is considered not usable if it is unable to perform the energy storage functionality and to discharge the stored energy source. batteries are used in electronic devices, electric cars, renewable energy systems, etc. as batteries are used into various applications, energy management when the battery is performing charging – discharging is gaining attention. renewable energy systems are known as highly dependent systems to battery storages, which allows them to store the produced energy into the connected batteries [1-3] and optimize the battery charging-discharging operation [4, 5]. looking at the gaining popularity of the renewable energy systems, especially the microgrid renewable energy systems, battery storage charging and discharging [1, 6-11] are equally crucial for the renewable energy system in both islanded and non-islanded modes. both modes need to ensure the reliability of the output energy with little to no disruption to the connected load during the operation hours [12]. furthermore, the modes also need to ensure the battery storages can perform better and improve the utilization of renewable energy systems [9, 13-15]. looking at the importance of battery storage charging – discharging, methods or mechanisms such as the adaptive neuro-fuzzy inference system (anfis) [6, 16, 17], backtracking search algorithm [10, 18, 19], non-simultaneous charging and discharging [20], genetic algorithm [4, 21], particle swarm optimized fuzzy controller [22-27], model predictive control [28-32], dynamic optimal power flow [3336], and grey model and genetic algorithms [37] are commonly used to perform the battery storage charging and discharging. the used methods or mechanisms also conduct system corresponding author: ranjit singh sarban singh engineering, technology & applied science research vol. 11, no. 4, 2021, 7515-7521 7516 www.etasr.com zainurin et al.: a review of battery charging discharging management controller: a proposed … optimization to reduce the stress on the battery storages as well as protect the batteries from being damaged. optimal scheduling was introduced in [38] to reduce the battery aging effects on batteries that are frequently charged. similarly, authors in [39] proposed an optimization model for charging and discharging which again resulted in the improvement of the battery aging effects. in [40-45], the maximum power point tracking (mppt) method is applied with different schemes, based on the perturb and observe (p&o) algorithm [40, 41], incremental conductance (inc) algorithm [42, 43], fractional open circuit voltage (focv), or fractional short circuit current algorithm (fcc) [44, 45]. all these schemes allow the mppt method to maximize the harvesting process as well as analyze the behavior of the variantion during the harvesting which results to output power reduction. indirectly, all these schemes are actually contributing to the battery charging process if the power system is connected to the battery storages. on the contrary, it is also important to have battery storage charging – discharging when these schemes are operating at the maximum capacity. even though the mentioned algorithms, methods, or mechanisms perform the battery storage charging – discharging decisions such as to charge or to stop battery storages charging, a systematic or spontenously decision such as to assist, manage, or control the battery storages charging – discharging is not effectively implemented and also has the probability to damage the battery storages. in [46], a mathematical modelling to study the lithium-ion battery charging – discharging behavior is proposed. the developed mathematical model focuses on the lithium-ion battery charging – discharging voltage as well as on the temperature of the lithium-ion battery. this mathematical model can be used to conduct battery optimization process but yet unable to intelligently control or manage the charging – discharging process. similar to the mathematical model, the electrochemical model (em) [47] were proposed in [48] to study the lithium-ion battery state-ofcharge (soc) estimation. the single particle model and nernst equation were employed in this research and the charging – discharging of the battery were correctly measured to achieve an accurate soc. the results of this study show that the em for soc estimation can be used to estimate the lithium-ion battery’s soc as well as its state of health (soh), but the em method is not able to assist, manage, and control in terms of effective battery storage charging – discharging. various methods, meachnisms, or techniques have been used in renewable energy systems, but not specifically to assist, manage and control the battery storages charging – discharging. mostly these methods, mechanisms, or techniques were applied to smooth the performance, especially in diversifying and stabilizing the overall system. limited study also has been conducted to specifically study an apprioprite method, mechanism, or technique that can effectively assist, manage and control the battery storage charging – discharging. also, looking into the critical situation, when one resource is not available, the decision making for the system to assist, manage, and control the battery storages in terms of charging – discharging has not specifically been implemented. therefore, it is necessary to have a system that can assist, manage, and control the battery storage charging-discharging. hence, selected papers such as [1, 6, 9] were extensively studied to understand the battery storage charging-discharging management systems. the studied papers were used to develop the conceptual methodology battery storage chargingdischarging strategy proposed in this review paper. the main contributions of this paper are: (1) a study of the available battery storage charging-discharging controller management methodologies, (2) the summarization and proposal of a conceptual methodology for a centralized controller for battery storage charging discharging that can be integrated into renewable energy systems while simultaneously assisting, managing, and controlling the effectiveness of battery storage charging – discharging based on battery soc. ii. a study of selected battery charging/discharging management methodologies a microcontroller was used in [1] to control the hybrid energy system and the charge discharge of the battery storages. figure 1 shows the architecture of the developed system and explains the system operation. first, the system reads the vdc and idc of the connected direct current (dc) sources. then, if the dc sources are equal to or greater than 80% of the vdc, idc, all the switches connecting to the connected load are switched off. the dc sources are used to charge the battery storages if their capacity is less than 80%, otherwise, the battery storage will be connected to the load for discharging. the system returns to the start process and continuously checks on the available vdc, idc from the dc sources. fig. 1. microcontroller embeded algorithm-battery charging-discharging. in a similar research [6], an intelligent algorithm based on anfis was developed to simultaneously perform two different tasks: to protect the connected battery against overcharging and deep discharging. the anfis algorithm that has been engineering, technology & applied science research vol. 11, no. 4, 2021, 7515-7521 7517 www.etasr.com zainurin et al.: a review of battery charging discharging management controller: a proposed … developed in this research measures the vpv, ipv, soc of the battery storage and volt direct current (vdc). this measurement is vital to find the maximum power point (mpp) from the resources and control the battery storage charging discharging. figure 2 presents the algorithm process that controls the battery storage charging discharging based on the power condition (pc), battery soc minimum (socmin) and battery soc maximum (socmax). when the measured vpv and ipv input from the photovoltaic panel is equal to the maximum, the photovoltaic power is compared with the initial pc before starting the charging process. based on the calculation, when the photovoltaic panel power (ppv ) is equal to maximum photovoltaic power (pmax), then the ppv is equal to pc. otherwise, the anfis algorithm keeps searching for pmax. start pc, socmin, socmax anfis learning ppv = pmax ppv = pc soc < socmax socmin < soc soc = socmax ppv = pc mode 1 mode 4 mode 1 mode 5 mode 3 mode 2 vpv ipv soc vdc yes noyes yes yes no no yes no no fig. 2. anfis algorithm – battery charging-discharging based on soc. figure 2 shows the battery storage charging discharging process according to the battery soc conditions. based on the process, three different operation modes are controlled by three relays that act as switches, as presented in table i. during mode 1, the logic state for r1 and r2 relay switches equals to 1. the power generated from the photovoltaic generator (ppv) is greater than zero, sufficient to source the connected load and batteries. during mode 2, the logic state for r2 and r3 relay switches equals to 1. during this mode, the power generated by the photovoltaic generator is insufficient (0 < ppv < pc). in this case, the battery power is utilized to satisfy the additional required power demand, this mode is also known as battery compensation mode. during mode 3, the logic state for the r3 relay switch is equal to 1. the energy stored in the batteries is fed to the connected load. during this operation mode, the photovoltaic generator is unavailable to produce power, ppv <0. during mode 4, the logic state for the r2 relay switch is equal to 1. the photovoltaic generator, ppv = pc and the batteries are fully charged. therefore, in this mode it is required to disconnect the batteries from being overcharged. during mode 5, none of the relay switches is equal to 1. this condition shows that the photovoltaic generator ppv is equal to zero, and the batteries' soc is equal to socmin. therefore, both the available recourses are disconnected from the connected load. table i. modes of operation based on relay logic state relay switches operation mode 1 mode 2 mode 3 mode 4 mode 5 r1 1 0 0 0 0 r2 1 1 0 1 0 r3 0 1 1 0 0 start battery management system (bms) photovoltaic mppt & battery voltage + current parameters photovoltaic power & battery soc estimation check photovoltaic supply (p), load demand (d) & battery soc p − d = 0 battery islanding end p − d > 0 check battery status check battery status soc > 80% charging battery islanding soc < 40% discharging battery islanding end no noyes fig. 3. entire system and battery charging-discharging operation. in another similar recent research [9], the intelligent power control shown in figure 3 was developed to improve battery reliability and operational life. the power control operates in two control modes: 1) mppt mode and 2) battery management system (bms) mode. the soc estimation technique incorporates the back-propagation neural network (bpnn) algorithm, which manages the battery’s charging discharging and islanding approaches, which helps prolong the battery's lifespan. the developed system is divided into stages of operation. firstly, the available photovoltaic power, battery’s engineering, technology & applied science research vol. 11, no. 4, 2021, 7515-7521 7518 www.etasr.com zainurin et al.: a review of battery charging discharging management controller: a proposed … voltage, and current information are collected. in the second stage, the photovoltaic power supply is compared with the load demand. if the photovoltaic power supply and load demand are zero, then the battery is connected to islanding mode. if the photovoltaic power supply is higher than the load demand, the battery soc status is checked. if the battery soc is more than 80%, then the battery is connected to the islanding mode. otherwise, if the battery soc is between 40% to 80%, then the battery is connected for charging. if the battery soc is less than 40%, battery discharging is not allowed, and the battery is connected to islanding mode. iii. summary of the reviewed and proposed charging/discharging management controllers this section summarizes the most recent battery storage charging discharging methods, mechanisms, or techniques. the battery storage charging discharging process shown in figure 1 starts to operate when the connected dc source is equal to or greater than 80% of the generated dc input. otherwise, the proposed process is deactivated from all the connected loads. therefore, if the dc is equal to or more than 80%, the proposed system checks on the battery soc. if the battery soc is above 80% and the dc source is equal to or more than 80%, only the battery source is connected to the discharging and connected load. therefore, the developed system functionality is restricted and dependent on the dc source supply. if the battery source is sufficient, the system should be connected to the load. the battery storage charging discharging shown in figure 2 shows the overall proposed process simultaneously sensing and measuring the voltage, current, battery soc, and direct current battery voltage. this information is used to calculate either the solar photovoltaic system power output or to analyze the total power condition. the proposed process operates fully only when the solar photovoltaic system power output is equal to the maximum power required and the power condition. the proposed system operates entirely when these conditions are satisfied. otherwise, the system strictly follows the five mode conditions that have been explained in section ii. furthermore, the proposed system can only operate unidirectionally, and the initial conditions need to be met for the battery energy storages to operate. the presented battery storage charging – discharging shown in figure 3, operates when the photovoltaic power supply and load demand are equal to zero and the battery is connected into islanding condition. when the photovoltaic power supply is more than the load demand, only the battery status is checked for either charging discharging or islanding. the proposed process shows that the battery can only operate when the battery’s soc is consistently above 80%, which also explains that the system needs to be installed at a location where solar irradiance is always available. the proposed system also shows that the functional period of the battery is only limited to 20%, which explains why the system needs to be installed at a location where continuous solar irradiance is available. the study of three different processes of battery storage charging discharging shows that each proposed process has its own methodology, operationality, and functionality. in the following, a hierarchical soc based battery storage charging discharging system is proposed. the conceptual system fundamentally explains the methodology applied for battery storage charging discharging and the proposed idea has the ability to extend the battery lifespan. figures 4-6 show the conceptual hierarchical soc battery storage charging discharging methodology process that is divided into three parts as depicted in table ii. table ii. battery charging-discharging conditions relay switches operation a batteries' soc = 100% b batteries' soc = 60% to 80% c batteries' soc = 40% figure 4 (part a) shows the hierarchical soc battery storage charging discharging when the proposed methodology measures the soc of two batteries. if both batteries' soc is equal to 100%, battery b will be connected for discharging and will be discharged at 20% of its soc. when the soc of battery a is more or equal to battery b, the discharging is switched to battery a. at the same time, battery b is connected for charging only if the charging source is available. if battery b is connected to the charging process, the battery b's soc is measured and compared with battery a's soc. if the soc of charging battery b is more or equal than discharging battery a's soc (20%), battery b is switched to the discharging process. the part a methodology process only happens when both batteries' soc are between 80% to 100%. start initialization battery system and capacity of battery a and battery b battery a = battery b = 100% discharged battery b battery a ≥ battery b (20%) discharged battery a b a charged battery b battery b ≥ battery a (20%) charge battery a no yes s ta te o f c h a rg e (s o c ) → 1 0 0 % yes no fig. 4. hierarchical soc battery charging-discharging: battery soc = 100% (part a). engineering, technology & applied science research vol. 11, no. 4, 2021, 7515-7521 7519 www.etasr.com zainurin et al.: a review of battery charging discharging management controller: a proposed … figure 5 (part b) shows that the hierarchical soc battery starts to charge/discharge when the battery' socs are between 60% and 80%. when battery a is being discharged, as shown in figure 4, when the measured soc is less or equal to battery b (20%), then discharging is switched to battery b, otherwise, it remains. suppose the measured battery a soc is less or equal to battery b (20%). in that case, battery b will be connected to the discharging process while battery a to the charging process, only if the charging source is available. the charging of battery a will continue until the battery a's soc is more or equal than the 20% of discharging battery b's soc. additionally, if the measured battery a soc is more than or equal to 20% of battery b at 60% soc condition, the discharging of battery b will be switched to battery a. battery b will be connected for the charging process when a charging source is available. during the battery b charging, the soc of battery b will be continuously measured and compared with the soc of battery a. if the soc of battery b more or equal to the soc of battery a (20%), discharging will be switched to battery b, otherwise, it remains. figure 6 (part c) occurs when both batteries' soc is equal to 40%. the halt condition is required to prevent the battery from fully discharge, which will cause damage to the batteries. therefore, the discharging process of the batteries is halted when both socs are equal to 40%. at the same time, battery a will also be connected to any available charging source to start charging until the soc of both batteries is at least 60%. when both batteries' soc is at 60%, then the hierarchical soc battery charging/discharging methodology process is activated. a battery b ≥ battery a (20%) charge battery a b discharge battery b battery a ≥ battery b (20%) charging battery b battery a ≥ battery b (20%) charge battery b discharge battery b battery b ≥ battery a (20%) charging battery a d no yes c no yes c no yes no yes s ta te o f c h a rg e (s o c ) → 8 0 % s ta te o f c h a rg e (s o c ) → 6 0 % fig. 5. hierarchical soc battery charging-discharging: soc battery equal to 60% or 80% (part b). d battery a = battery b (40%) halt s ta te o f c h a rg e (s o c ) → 4 0 % fig. 6. hierarchical soc battery charging-discharging: soc battery equal to 40% (part c). iv. conclusion the reviewed and presented battery storage charging discharging methodology processes have limitations in continuous provision of power source supply to the connected load when the battery capacity is at soc equal to 80%. hence, the proposed hierarchical soc battery storage charging discharging presents the ability of the batteries to perform continuous power source supply to the connected load until their remaining soc is equal to 40%. also, the hierarchical soc battery storage charging discharging shows its ability to perform continuous battery charging when the source is available. with this ability, the hierarchical soc battery storage charging discharging functionality to supply power to the connected load continuously can be extended as well as maintained longer. acknowledgement the authors wish to acknowledge the support from the ministry of higher education of malaysia (mohe), the advanced sensors and embedded control (asecs) research group, the centre for telecommunication research & innovation (cetri), the fakulti kejuruteraan elektronik dan kejuruteraan komputer (fkekk), and the universiti teknikal malaysia melaka (utem). references [1] t. pangaribowo, w. mulyo utomo, a. bakar, and d. khaerudini, “battery charging and discharging control of a hybrid energy system using microcontroller,” indonesian journal of electrical engineering and computer science, vol. 17, no. 2, pp. 575–582, feb. 2020, https://doi.org/10.11591/ijeecs.v17.i2.pp575-582. 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[48] l. liu, j. zhu, and l. zheng, “an effective method for estimating state of charge of lithium-ion batteries based on an electrochemical model and nernst equation,” ieee access, vol. 8, pp. 211738–211749, 2020, https://doi.org/10.1109/access.2020.3039783. engineering, technology & applied science research vol. 7, no. 2, 2017, 1455-1459 1455 www.etasr.com javadpoor and nazarpour: modeling a pv-fc-hydrogen hybrid power generation system modeling a pv-fc-hydrogen hybrid power generation system shabnam javadpoor department of electrical engineering, faculty of engineering, urmia branch, islamic azad university urmia, iran dariush nazarpour department of electrical engineering, faculty of engineering, urmia branch, islamic azad university urmia, iran abstract—electrical grid expansion onto remote areas is often not cost-effective and/or technologically feasible. thus, isolated electrical systems are preferred in such cases. this paper focuses on a hybrid photovoltaic (pv)-hydrogen/fuel cell (fc) system which basic components include a pv, a fc, alkaline water electrolysis and a hydrogen gas tank. to increase the response rate, supercapacitors or small batteries are usually employed in such systems. this study focuses on the dynamics of the system. in the suggested structure, the pv is used as the main source of power. the fc is connected to the load in parallel with the pv by a transducer in order to inject the differential power while reducing power generation in relation to power consumption. an electrolyzer is used to convert the surplus power to hydrogen. this study studies a conventional hybrid photovoltaichydrogen/fuel cell system to evaluate different loading behaviors. software modeling is done for the suggested hybrid system using matlab/simulink. keywords-dynamic modeling; fuel cell; generated power; hybrid; photovoltaic system; electrolyzer; hydrogen; simulink i. introduction solar systems that convert sunlight directly into electricity are sustainable, silent, low-maintenance, eco-friendly, clean and efficient independent of the size of generator. photovoltaic (pv) cells can be used connected to the grid or as isolated power sources. electrical energy of photovoltaic systems is injected to electricity grid using electrical equipment of dc to ac voltage transducer as well as inverters connected to the grid. functionally, the power generated by solar pv generators considerably changes due to climate changes; this may cause many problems such as extreme frequency deviation in the grid. considering the significance of system reliability, it is proposed that pvs must be associated with another power source or backup unit, particularly in grid-independent systems, for continuous power generation. one solution to the problem of hybrid pv units and other energy sources such as diesel generators is the use of fuel cells (fc) or a backup battery [1]. diesel generator guarantees continuous power generation [2]. a fuel cell is an electrochemical system which converts chemical energy directly into electrical energy. the efficiency of fuel cells is higher than that of internal combustion engines.. fuel cells are a rather interesting option for hybrid pv generators due to their good efficiency, proper response time, production in modules and packs, and flexibility. the system studied in this paper is a hybrid off-grid system based on pvs, fcs, alkaline water electrolysis and hydrogen gas storage tanks. the required hydrogen is achieved through electrolysis [3]. results for a full day's supply of disposable and grid-independent load are acquired and discussed. ii. introduction to pv systems the dynamics model of a photovoltaic system is given by: shdphs iiii  (1) where iph is the flow of each photon in the solar cell photovoltaic systems, id is diode current losses and ish is the shunt current in the electrical equivalent circuit of a solar cell. cell short circuit current is determined by i-v characteristic of the solar cell for the output current of zero i0=0 (no-load). ( ) ( )1 2 0 3 01 (2)ph s s ji pe p e e p t té ù= + + -ê úë û in (2), p1, p2, p3 are the empirical constants, where p1 is the photon current generation area in sunlight and p2, p3 are the correction coefficients in relation to the type of sunlight and ambient temperature. in (2), tj can be considered as the connection heat of the cells provided by (3). [5] ( )20 800 s j a e t t noct= + (3) where ta is the ambient temperature and noct is the normal cell performance temperature. 0. exp . 1 (4)s s s d sat f s j e u ri i i a n k t é ùæ ö+ ÷çê ú÷ç= -÷ê úç ÷ç ÷÷çê úè øë û equation 4 is about the amount of the losses in diode, where in this regard isat is the saturation current, ns the is number of cells in series and k is boltzmann's constant, as the saturation current equation is shown in the form of (5) [6]. 3 4 exp (5)g sat j j e i pt kt æ ö÷ç ÷ç= ÷ç ÷ç ÷÷çè ø where eg is the gap energy and value for ish can be ultimately written as in (6). rsh is the shunt resistor value [7]. engineering, technology & applied science research vol. 7, no. 2, 2017, 1455-1459 1456 www.etasr.com javadpoor and nazarpour: modeling a pv-fc-hydrogen hybrid power generation system (6)s s s sh sh u ri i r + = iii. pv modeling the different equations presented previously were modeled in simulink through various models depicted in figures 1 to 6 (representing the equations presented previously). fig. 1. the pv saturated currents model fig. 2. the pv diodes losses model fig. 3. the pv current model fig. 4. the pv shunt current model fig. 5. the pv overall current output model fig. 6. the model of ambient air and pv cells’ heat iv. models and results a. pv modeling results results of the modeling of photovoltaic system were considered overnight (model output). regarding the existence of heat in the temperature and sunlight radiation during 2000060000 seconds (overnight), the output curves show the sunlight radiation condition and ambient temperature (figure 7). in addition, the overnight results were considered as 86400 seconds [8-9]. the extracted curve shows the result of sunlight condition, as the existed curves represent the sunlight condition at different times overnight and another one shows the thermal conditions at the ambient temperature around the cell. figure 8 shows the generated current, voltage and power through the solar cell overnight. as shown, when the rate becomes higher or lower, the values changes accordingly. fig. 7. status of sunlight radiation and ambient temperature overnight engineering, technology & applied science research vol. 7, no. 2, 2017, 1455-1459 1457 www.etasr.com javadpoor and nazarpour: modeling a pv-fc-hydrogen hybrid power generation system fig. 8. graph of output current, voltage and power generated by the solar cell during a day b. fuel cell model the dynamic model of a fuel cell is given by: (7) open circuit voltage of the fuel cell is considered as a change in gibbs free energy for the reaction of hydrogen and oxygen [10-11].              2/3 0 2/1 20 2 22 15.2982297.1 p pp in f rt f s tu oh ocv (8) in the above equation, uocv is related to the activation potential of a cell of fuel cell caused by the reaction at the electrode surface [12].      actact rtfrtf eejj  /12/20  (9) the model of the hybrid system is presented in figure 9 and the two subsystems are further shown in figures 10 and 11. c. results the polarization curve represents a comparison between the simulation and theoretical values (figure 12). the graph shows the differences between these outputs and a good agreement is shown. figure 13 shows the current at the outlet of the fuel cell depending on its maximum and minimum performance. comparison of the predicted output power and the response of the output power measured from the fuel cell system at the same conditions is shown in figure 14. comparison of both curves also shows good agreement. further, the sample load or the consumed power connected to fuel cell is just 900 watts whereas the power generated by a fuel cell may reach 6000 watts. figure 17 shows the output values of current, voltage and power of the fuel cell when the fuel cell is used as a power source. d. electrolyzer model the voltage model for the electrolyzer system is shown in figure 16. figure 17 shows the input/output model. figure 18 shows the dynamics of the ohmic potential in the electrolyzer system, directly affected by the value of hydrogen generated in electrolyzer. fig. 9. the fc model with electrolyzer system and hydrogen storage tank fig. 10. the electrolyzer model fig. 11. the hydrogen storage tank system model fig. 12. values for current, voltage and output power in the polarization curve of experimental and predicted results ohmconcactocvfc uu   engineering, technology & applied science research vol. 7, no. 2, 2017, 1455-1459 1458 www.etasr.com javadpoor and nazarpour: modeling a pv-fc-hydrogen hybrid power generation system fig. 13. the extracted value of the current obtained by the fuel cell at the maximum and minimum times of the system performance fig. 14. comparison of the predicted output power and the response of the output power measured from the fuel cell system at the same conditions fig. 15. values of the current output, voltage and power at during turning on and off of the fuel cell system fig. 16. the model of the actual voltage in the electrolyzer system fig. 17. the electrolyzer input/output model fig. 18. the electrolyzer ohmic potential model e. results the electric dynamics of the electrolyzer is shown in figure19. figure 20 represents the hydrogen flow at the time of production and consumption through the electrolyzer and a fuel cell. figure 21 shows the volume of hydrogen flow and pressure alterations in the liquid hydrogen tank at the storage and consumption times. fig. 19. electrical dynamics of the electrolyzer system fig. 20. velocity of hydrogen flow at the times of production and consumption via electrolyzer and fuel cell engineering, technology & applied science research vol. 7, no. 2, 2017, 1455-1459 1459 www.etasr.com javadpoor and nazarpour: modeling a pv-fc-hydrogen hybrid power generation system fig. 21. volume of the hydrogen flow and pressure alterations in the liquid hydrogen tank at the times of storage and consumption v. conclusion the presented study focuses on modeling an isolated hybrid power generation system. the suggested structure used pv as the main power source. a fuel cell is connected to in parallel in order to compensate the power balance. an electrolyzer was used to convert the surplus power to hydrogen. the produced hydrogen is stored in tanks and used as fuel in the fuel cell. the theoretical basis and simulink models are shown and results are presented and discussed. references [1] k. agbossou, m. kolhe, j. hamelin, t. k. bose, “performance of a stand-alone renewable energy system based on energy storage as hydrogen”, ieee transactions on energy conversion”, vol. 19, no. 3, pp. 633-640. 2004 [2] c. wang, m. h. nehrir, “power management of a stand-alone wind/photovoltaic/fuel cell energy system”, ieee transactions on energy conversion, vol. 23, no. 3, pp. 957-967, 2008 [3] k. s. tam, s. rahman, “system performance improvement provided by a power conditioning subsystem or central station photovoltaic fuel cell 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[10] a. d. hansen, p. e. sorensen, l. h. hansen, h. w. bindner, models for a stand-alone pv system, technical university of denmark, 2001 [11] t. esram, j. kimball, p. krein, p. chapman, p. midya, “dynamic maximum power point tracking of photovoltaic arrays using ripple correction control”, ieee transactions on power electronics, vol. 21, no. 5, pp. 1282-1291, 2006 [12] eg&g technical services, inc., fuel cell handbook, u.s. department of energy, 2004 microsoft word etasr_v12_n2_pp8335-8341 engineering, technology & applied science research vol. 12, no. 2, 2022, 8335-8341 8335 www.etasr.com alqethami et al.: disease detection in apple leaves using image processing techniques disease detection in apple leaves using image processing techniques sara alqethami college of computers and information systems umm al-qura university makkah, saudi arabia s44286527@st.uqu.edu.sa walla alzhrani college of computers and information systems umm al-qura university makkah, saudi arabia s44285472@st.uqu.edu.sa badriah almtanni college of computers and information systems umm al-qura university makkah, saudi arabia s44285875@st.uqu.edu.sa manal alghamdi college of computers and information systems umm al-qura university makkah, saudi arabia maalghamdi@uqu.edu.sa received: 28 december 2021 | revised: 26 january 2022 | accepted: 1 february 2022 abstract-the agricultural sector in saudi arabia constitutes an essential pillar of the national economy and food security. crop diseases are a major problem of the agricultural sector and greatly affect the development of the economies in various countries around the world. this study employed three prediction models, namely cnn, svm, and knn, with different image processing methods to detect and classify apple plant leaves as healthy or diseased. these models were evaluated using the kaggle new plant diseases database. this study aims to help farmers detect and prevent diseases from spreading. the proposed method provides recommendations for the appropriate solutions for each type of recognized plant disease based on the classification results. keywords-plant disease; apple; deep learning; machine learning i. introduction agriculture plays a substantial role in modern life and contributes to the development of the economy by providing food security [1]. the agricultural sector in saudi arabia constitutes an essential pillar of the national economy and food security [2]. crop diseases are one of the main problems of the agricultural sector and significantly affect the economic development in various countries, as they affect both quantity and quality of crops [3]. as a result, crop damage results in significant productivity loss, affecting the economy. according to the food and agriculture organization [4], the world population will increase to more than 9.1 billion by 2050. the food growth rate should increase by 70% to meet the nutritional needs of such a vast global population. crop diseases can be challenging to diagnose. some types can be dangerous, especially scab, black rot, and cedar rust, and they could spread fast to other parts of the leaf if left untreated, leading to the death of entire crops [5]. in addition, the diagnosis of crop diseases can be expensive, takes a long time, and is often prone to errors due to the difficulty of analyzing each plant individually [6]. furthermore, it is expensive for many farmers to consult an expert about their crop disease problems, especially in developing countries. hence, it is crucial to detect and recognize these diseases in their initial stages to prevent them from spreading. the continuous development of computer vision (cv) and digital image processing (dip) have tremendously impacted the detection of diseases, as they are used to improve image quality and aid diagnosis [7,8]. the improvement of the accuracy of diagnostic techniques through image processing and classification methods is crucial to address the challenges of manual diagnosis of plant diseases [9,10]. several researchers were inspired to build efficient algorithms using machine learning (ml) and deep learning (dl) models to provide accurate diagnoses of plant leaf diseases [11, 12]. this study employed three prediction models, namely cnn, svm, and knn, to detect apple plant leaf photos and classify them to healthy or diseased. several image pre-processing methods were also applied to improve the quality of the images and remove any noise that could affect the classification results. segmentation techniques were also used to detect the correct disease spot and extract the most convenient features to obtain the best result, while the proposed models were evaluated in a large and reliable database. ii. related work the methodologies used by previous researchers to classify plant diseases are separated into two categories: dl-based and ml-based approaches. in [8], several ml-based classifiers were proposed for the detection and classification of plant diseases. a dataset of 14956 images was used, classified into 38 distinct classes. the highest accuracy was achieved by the corresponding author: manal alghamdi engineering, technology & applied science research vol. 12, no. 2, 2022, 8335-8341 8336 www.etasr.com alqethami et al.: disease detection in apple leaves using image processing techniques rf model, with performance up to 73%, which was better than any other method. several studies evaluated the performance of various dl methods in detecting plant diseases. some studies used multiple cnn architectures such as alexnet, googlenet, inceptionv3, resnet-101, resnet-50, resnet-34, resnet-18, and vggnet-16 to detect and classify apple plant diseases. in [13, 14], a vgg-incep model was proposed, combining vggnet-16 with inceptionv3, to detect apple leaf diseases. this model had higher accuracy than several prominent deep cnns. in [15], ml methods, namely svm and transfer learning, were used with dl techniques, such as densenet, vgg, resnet, and googlenet, to detect apple plant diseases. the result showed that svm had low accuracy while transfer learning models had the highest. the plant village dataset with 1821 labeled images of apple plant leaves classified into 3 disease and one 1 classes, was utilized. deep cnns built on the alexnet platform were used in [16] to detect apple leaf diseases. the dataset had a total of 13,689 images and the highest accuracy was 97.62%. in [17], deep cnn network architectures and ml methods, such as svm and knn, were evaluated. the used dataset had a total of 54,000 images of different plant diseases, and the highest accuracy was achieved by the svm model. in [18], a cnn segmentation model trained on tomato leaf images was proposed, and a smartphone application was deployed, that can be used for real-time diagnosis and detection of diseases and monitor and manage early tomato growth stages. in [19], a hybrid framework of dl and svm was proposed, where the results showed that the svm classifier models outperformed the softmax function. iii. basic steps for disease detection recent developments in dl and ml appear to enhance the accuracy potential of plant disease detection [20]. the main stages of the proposed model are shown in figure 1. it starts with pre-processing and enhancing the input images, followed by segmentation, feature extraction, and classification. fig. 1. stages of the research. a. image pre-processing the first step in any cv-based system is to pre-process raw images [21]. image preprocessing is necessary to ensure equality and uniformity between all images, making the following segmentation and feature extraction steps more accurate and effective. for this reason, the noise in the background should be removed to enhance images and color space conversions, helping to properly focus on the region of attention of an image [22]. all plant images were converted from rgb to lab color space, as the latter decouples color and lightness, enhancing object detection [23]. 1) cielab color model cielab is a color space and color characterization system based on human vision, released by the international commission on illumination (cie) in 1976. it is considered one of the most common and accurate color space systems used for detecting affected areas in plants. these affected areas have different colors, relying on the color without intensity [24, 25]. the following equations were used to convert the images from rgb to cie xyz [26]: � � 0.4124� 0.3576� � 0.1805 � � (1) � � 0.2126 � 0.7152� � 0.722� � (2) � � 0.0193� 0.1192 � � 0.9505 � � (3) cielab uses a three-dimensional system where l represents brightness, a represents a range of colors from green to red, and b represents the colors ranging from blue to yellow [25]. the formula of the lab color model is defined as [27]: � � 0.2126� 0.7152� � 0.0722 � � (4) � � 1.4749� �0.2213 � � 0.3390� � 0.1177 � �� 128 (5) � � 0.6245� �0.1949� 0.6075� � � �0.8006 � �� 128 (6) figure 2 shows the rgb to lab color conversion. fig. 2. converting rgb color image to lab color. b. image segmentation in many cases, images contain parts or problems that affect the detection results, such as an unwanted background [28]. for this reason, it is important to manipulate image segmentation approaches to detect the correct disease spot, which also helps the feature extraction process [22]. image segmentation is a method used to divide data into groups with comparable properties or qualities to make it simpler for analytical operations [29]. many image segmentation techniques have engineering, technology & applied science research vol. 12, no. 2, 2022, 8335-8341 8337 www.etasr.com alqethami et al.: disease detection in apple leaves using image processing techniques been developed, such as region-based, clustering, edge detection, mask r-cnn [30, 31], and k-means clustering [32]. k-means clustering segmentation categorizes pixels by decreasing the average squares of the distance between the objects and the clusters they belong to [33]. the segmentation stage consisted of three steps. at first, k-means clustering was used to detect and classify pixels and objects into k classes based on the feature set [34]. subsequently, the flood fill method was used to fill the empty spaces in binary images and match the color of the hole space of connected pixels with the same color [35]. finally, the resulting image was applied as a mask to the original to obtain the image section containing the required characteristics [36]. the mask images were obtained after the flood fill algorithm combined with the original rgbbased image, which gives a background-free image. figure 3 shows the steps of the image segmentation process. the last image presents only the leaf, as the background containing all unnecessary information was eliminated. fig. 3. steps of the image segmentation process. c. feature extraction feature extraction is a critical step in any cv system based on ml. several feature extraction methods are used to obtain significant features that can be used in the disease classification stage. some of the essential features adopted in plant disease detection are color, shape, and texture features [37-39]. many researchers used techniques such as grey-level co-occurrence matrices and lbp for the extraction of texture features [40, 41]. this study focused on texture because it is the most common and important feature used to detect different plant diseases. the local binary pattern (lbp) method [8] was used to extract the features, considering the texture and color of any image [41]. d. classification method based on machine learning classification is a supervised ml approach used in many applications such as disease prediction, classification, etc. [42], where the algorithms learn from the dataset how to classify. for evaluation purposes of the apple classifier, two ml algorithms were executed: svm and knn. svm is a popular classifier algorithm that has been used to handle plant disease detection and classification [19, 42]. the svm process determines whether plants are diseased or healthy by optimizing a hyperplane. this algorithm creates a separate set of features that classifies the data sample into two different classes. at first, the segmented images are used to extract the lbp features, and then the svm is trained on the extracted features. knn is another classifier algorithm that has been used in plant disease classification [18]. its implementation includes the following steps: • finding the closest neighbors using the distance measure. • derive a classification from knn using the distance rule. • how many neighbors does the new sample require? plants are classified as diseased or healthy based on the knn process by determining and calculating the nearest point to a new sample. if the nearest neighbor is diseased, then the plant indicates disease. considering the k value to be small, k values of 1, 3, or higher are commonly employed to assist in minimizing noisy data sets. finally, the knn is trained on lbp features extracted from the previous stage. e. classification method based on deep learning in dl, cnns are most commonly used for image recognition and classification [43]. in contrast to the traditional feature extraction approaches, cnns have been demonstrated to automatically learn robust and level features from raw images and outperform hand-extracting specific features. pooling, convolution, and full connection layers are the main components of a cnn architecture. this study used one of the most popular cnn models, the googlenet architecture [43]. this model has been used successfully in cv challenges [14]. the goal is to employ these structures to improve the plant disease detection results. googlenet is a 22-layer deep cnn variation of the inception network, developed at google [43]. the inception network employs parallel convolutions in conjunction with a max-pooling layer. this feature allows it to capture multiple features at the same time. however, googlenet was modified for this dataset and the classification procedure and trained on the segmented testing data. the parameters of some layers of the network were changed as per requirements. iv. experiments to evaluate the performance, a large publicly available dataset of crop leaf images called new plant diseases was obtained from kaggle. this dataset consists of 54,306 images of 14 different plant leaves. for this study, 240 images of apple leaves were extracted, where 60 images were classified as healthy and 180 as diseased. the dataset contained images with noise, rotation, tilt, different lights, and backgrounds. table i shows the description of the dataset. the accuracy is defined as: �������� � !"#$ !"#!"#$" $ (7) where tp, tn, fp, and fn represent true positive, true negative, false positive, and false negative respectively. the experiments were carried out on matlab r2020b, on a pc with an amd ryzen 5 3500u 2.10ghz cpu with radeon engineering, technology & applied science research vol. 12, no. 2, 2022, 8335-8341 8338 www.etasr.com alqethami et al.: disease detection in apple leaves using image processing techniques vega mobile gfx, 8gb of ram, running windows 10 64-bit. a training dataset was used to train the ml and dl models, and a validation dataset was used to avoid overfitting. the original dataset was divided into 70% for training and 30% for validation. table i. dataset description class no. new plant diseases dataset apple train sample val sample 1 scab (diseases) 30 30 2 black_rot (diseases) 30 30 3 cedar_rust (diseases) 30 30 4 healthy 30 30 5 total 240 v. results and discussion a. classification methods during the experiment, multiple dl and ml models were implemented to evaluate their performance and determine which fits best this dataset and is most effective and efficient at classifying plant diseases. these models included cnn, knearest neighbor, and svms. accuracy and the area under the curve (auc) were used to analyze and compare the performance of these models. figures 4-6 show the confusion matrices for the validation dataset of these models. figures 7-9 show the auc for the google net, svm classifier, and knn classifier models, respectively. fig. 4. confusion matrix for googlenet. fig. 5. confusion matrix for svm. fig. 6. confusion matrix for knn. fig. 7. auc for googlenet. fig. 8. auc for svm classifier. table ii presents the comparison of the three models based on accuracy, training time, and auc. table i. comparison of the three models accuracy training time auc googlenet 98.5% 184 min 0.95 svm 82.25 101.68 sec 0.91 knn 70.3% 5.52 sec 0.72 engineering, technology & applied science research vol. 12, no. 2, 2022, 8335-8341 8339 www.etasr.com alqethami et al.: disease detection in apple leaves using image processing techniques fig. 9. auc for knn classifier. the maximum accuracy of 98.5% was achieved with googlenet. the dl classifier outperformed the ml because it was less complex, and there is no need to extract features before the classification process. feature extraction is a necessary step before classification in ml methods. the dl classifier was also faster than the ml classifiers as the size of the dataset increased. ml algorithms such as knn and svm became slower as the dataset grew. on the other hand, svm works better for binary classification, while knn works based on majority voting, and dl learns to classify the 4 classes of apple leaves accurately on its own. table iii presents a comparison with similar works. many studies have been conducted to diagnose plant diseases using ml and dl, but as most of them used different datasets and evaluation measurements, it is objectively difficult to compare the results. table ii. comparison with related works models study accuracy this study’s accuracy google net [13] [14] [15] [16] 94.12% 94.85% 94% 95.69% 98.5% svm [15] 50% 82.25% in [13] a dl-googlenet architecture was introduced for the identification of apple leaf diseases and the results showed an accuracy of 94.12%. several deep convolution networks, one of which was the googlenet, were utilized in [14] for the detection of apple leaf diseases, and their results were evaluated through accuracy performance. the accuracy achieved by googlenet in this study was 94.85%. ml-based classifiers and several dl models were utilized in [15], where svm and googlenet achieved accuracies of over 50% and 94%, respectively. a method to identify apple leaf diseases, based on the googlenet architecture, was presented in [16], which obtained an accuracy of 95.69%. authors in [8, 17] used different datasets comprising of apple and other plant diseases, so it is difficult to compare their results. ml-based classifiers, namely svm and knn, were presented in [8] to detect and classify plant leaf diseases, obtaining accuracies of 67.27% and 63.20%, respectively. an svm classifier was presented in [17] for the detection and classification of plant leaf diseases, depending on feature extraction using lbp and obtaining an accuracy of 80.6%. these results show that the proposed method performed better than the others, as it attained 98.5% accuracy on googlenet, 82.25% on svm, and 70.3% on knn. therefore, image processing, extracting, and important features acquisition play an important role in increasing the accuracy and effectiveness of the models. moreover, as these approaches [8, 13-17] have a higher computational cost, the proposed method is more successful and efficient for classifying plant diseases. b. plant disease detection system a graphical user interface (gui), shown in figure 10, was built for the proposed system to help users detect plant diseases and get appropriate recommendations for pesticides to treat any found disease. the screen is divided into three sections: the left part (input panel) to load or delete an image, the middle section displays the image after loading, and the right part (output panel) shows the classification result and the appropriate pesticides for the disease. figure 11 presents a sample of results. as shown, the system detected apple scab disease and recommends sulfur pesticide to treat it. figure 12 shows the result if no disease is detected and no pesticide is required. the user can press the delete button to test other images. fig. 10. plant disease detection system. fig. 11. detection of apple scab disease. engineering, technology & applied science research vol. 12, no. 2, 2022, 8335-8341 8340 www.etasr.com alqethami et al.: disease detection in apple leaves using image processing techniques fig. 12. detection of a healthy apple leaf. vi. conclusion this study aimed to detect and prevent the spread of apple leaf diseases by detecting them in the early stages. to achieve that, 240 images were obtained and categorized as healthy and diseased. the images were pre-processed to improve the quality, and the local binary pattern (lbp) method was 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[43] c. szegedy et al., "going deeper with convolutions," presented at the proceedings of the ieee conference on computer vision and pattern recognition, boston, ma, us, 2015, pp. 1–9. microsoft word etasr_v13_n4_pp11153-11156 engineering, technology & applied science research vol. 13, no. 4, 2023, 11153-11156 11153 www.etasr.com ranjan & kumar: economic earthquake resistance construction of high-rise buildings economic earthquake resistance construction of high-rise buildings raushan ranjan department of civil engineering, national institute of technology patna, india raushanr.phd18.ce@nitp.ac.in (corresponding author) ajay kumar department of civil engineering, national institute of technology delhi, india sajaydce@gmail.com received: 17 april 2023 | revised: 26 april 2023 and 6 may 2023 | accepted: 10 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5930 abstract the economic perception of earthquake resistance construction for mediumto high-rise rcc buildings is examined in this paper. the conventional way of creating high-rise buildings is not financially viable without a shear wall to withstand seismic energy. framed structures with irregular floor plans that vary in size, shape, and geometry are also expensive. many studies have been conducted recently on the coupling ratio (cr). the current analysis investigates the behavior of the coupled shear wall and the cr for an affordable earthquake resistance construction including the shear wall within a range of 30 % to 45 %. the study shows that shear walls could be reduced at 40–50 % and at 60–70 % of the base height for regular and irregular buildings, respectively. the current study also comes to the conclusion that coupled shear wall earthquake-resistant construction is more practical than the conventional approach because couple beams can be repaired with ease. keywords-coupled shear wall; non-linear dynamic analysis; sap2000 i. introduction in developing countries like india, the population density of cities is increasing rapidly. the most common used practice to mitigate the problem is the construction of low to medium rise load bearing structures or framed structures, mainly for economic reasons. also, according to [1], the size of population has significant positive association with the fatalities during an earthquake [2]. the opted solution is to construct the maximum number of low cost, mediumto high-rise earthquake resistant structures that are affordable to the maximum number of people. the study area of this paper is an indian city near the himalaya. the area has faced many significant earthquakes in the past, due to its proximity to the himalayan mountain range [3, 4]. it was observed that after the 2015 gorkha earthquake, the rc frame buildings were less damaged than masonry infill and mud structures. load bearing and frame structures for high-rise buildings are unfeasible against earthquakes because columns, beams, and slabs are not enough to provide the expected lateral stiffness. in this, paper we used a series of shear walls connected with beams. this system is known as coupled shear wall and the connecting beam is called the coupling beam. properly detailed coupling beams can dissipate large amounts of energy at the ends of the beam by the formation of plastic hinges before any hinging occurs at the wall base. damaged connected beams are easier to repair than walls. for developing countries, the process of urbanization is generally associated with the growth of vulnerable infrastructures and buildings [5], since the relearnt construction codes may be deficient [6]. the cities in developing countries are expending with very fast rates [7] and the location of these cities in earthquake-prone zones is up to the 31% of globally infrastructure built-up areas [8]. many studies are available regarding the theoretical and experimental studies of coupled shear walls. authors in [9] created curves from the continuum theory for the rapid evaluation of the stresses and maximum deflections. authors in [10] developed a technique where the beams made using uniform openings having vertical arrangements inside the walls had been replaced by minute elastic laminas of similar stiffness. authors in [11] presented a method that the connecting beams applied to develop axial, flexure, shear, and torsion resistance have been considered as slender elastic members. authors in [12] studied the frame method application of nodal rotational degree of freedom and shear deformation while analyzing the coupled wall frame structures. authors in [13] gave the idea of single band openings of asymmetrical coupled shear walls and two band openings of symmetrical arrangement. authors in [14] present coupling beams used to transfer forces between wall piers. the upper limit of 66% coupling ratio (cr) was proposed in [15]. the cr range from 30 % to 45 % has been proposed in [16]. the competent design has been proposed [17] for 30-story reinforced concrete structure, with the structures having cr value of 67% and 78%. engineering, technology & applied science research vol. 13, no. 4, 2023, 11153-11156 11154 www.etasr.com ranjan & kumar: economic earthquake resistance construction of high-rise buildings the coupled shear wall concept for the earthquake resistance design of structures is very useful because the coupled beams fail before the rest of the building during an earthquake, and they can be easily repaired. the knowledge gap filled in this paper is the curtailment of shear walls to maintain the cr within the limit of 30-45 %, thus reducing the cost of the building. in this paper, we present the positioning of coupled shear walls of different shapes of rcc structure. the main objective of this paper to investigate the brittle failure of coupling beams and to show that the damage of buildings before the coupling beams depends on the cr. so, we can provide 40-50 % coupled shear walls for the regular sections and 60-70 % for the irregular sections of the total building height to maintain the cr within limits for good-performing and economical earthquake resistant structure design. ii. methodology we modeled a 10-story rcc building with 30 m × 30 m coupled shear walls, with coupled shear width of 14.5 m and thickness of 25 cm (figures 1-2). the dimensions of the primary beams are assumed as 50 cm × 60 cm, of the secondary beam as 35 cm × 45 cm, of the columns as 50 cm × 50 cm, and of opening in the coupled shear wall as 4.5 m × 2 m. m25 concrete and fe 500 tmt rebar were used. all the provisions laid down in is 13920:2021 deals with the flexural strength and boundary elements required for shear walls. fig. 1. cross section and channel section. the time history method was used. we have taken the ground motion of patna, bihar for non-linear dynamic earthquake analysis of different shape of structure from [18]. in this, the base shear (vb) is obtained by sap2000 and the shear at each floor is calculated manually as: �� = � � �� � ∑ � � � � � (1) if the manually calculated force is greater than the forces calculated by sap2000, then the ratio of the force calculated manually and the sap2000 generated forces is multiplied by a scale factor (sf) and the building effects are observed. the followed steps are:  distribute the base shear along the height of the building at various levels and calculate the over turning moment (otm).  calculate the equivalent triangular load on the coupled shear wall.  calculate the shear force and moment in coupling beams by using figure 3. the shear reactions at the bases of the wall piers are resisting the base shear. the proportion of overturning moment (otm) resisted by the couple is defined as the cr. cr = �� �� ��� x100 (2) over τurning μoment (otm) = 61361.33 kn.m m = ��� � w= �� �� , w=204.54 kn fig. 2. cross section plane. fig. 3. coupling beam. engineering, technology & applied science research vol. 13, no. 4, 2023, 11153-11156 11155 www.etasr.com ranjan & kumar: economic earthquake resistance construction of high-rise buildings table i. story shear and lateral forces of the regular section floor weight (kn) height (m) wixhi2 storey shear (kn) fxh (knm) 7107.19 0 0 0 0 7107.19 3 63964.71 6.904511177 20.71353 7107.19 6 255858.8 27.61804471 165.7083 7107.19 9 575682.4 62.14060059 559.2654 7107.19 12 1023435 110.4721788 1325.666 7107.19 15 1599118 172.6127794 2589.192 7107.19 18 2302730 248.5624024 4474.123 7107.19 21 3134271 338.3210477 7104.742 7107.19 24 4093741 441.8887153 10605.33 7107.19 27 5181142 559.2654053 15100.17 iii. results table ii shows the displacement and drift of the regular section, while figure 4 exhibits the drift and displacement versus height. table ii. height, displacement, and drift of the regular section height (m) displacement (mm) drift (mm) 0 0 0 3 0.32 0.32 6 0.92 0.6 9 1.7 0.77 12 2.64 0.95 15 3.6 0.95 18 4.43 0.84 21 5.22 0.79 24 5.98 0.76 27 6.68 0.7 30 7.3 0.62 (a) (b) fig. 4. height vs (a) displacement, (b) drift (regular section). the maximum drift of the stories of the regular section is 0.95 mm. so, the actual drift is less than the value of the allowable drift (12 mm). table iii and figure 5 and table iv and figure 6 show the displacement and drift of the cross section and channel section, respectively. table iii. height, displacement, and drift of the cross section height (m) displacement (mm) drift (mm) 0 0 0 3 0.288 0.288 6 0.84 0.55 9 1.56 0.72 12 2.39 0.83 15 3.23 0.84 18 4.1 0.87 21 4.96 0.86 24 5.73 0.77 27 6.44 0.71 30 7.07 0.63 (a) (b) fig. 5. height vs (a) displacement, (b) drift (cross section). table iv. height, displacement, and drift of the channel section height (m) displacement (mm) drift (mm) 0 0 0 3 0.3 0.3 6 0.85 0.55 9 1.6 0.75 12 2.41 0.81 15 3.26 0.85 18 4.14 0.88 21 5 0.86 24 5.79 0.79 27 6.52 0.73 30 7.17 0.65 the maximum drift of the stories of the channel section is 0.88 mm. so, the actual drift is less than the allowable drift value (12 mm). the maximum story displacement in the engineering, technology & applied science research vol. 13, no. 4, 2023, 11153-11156 11156 www.etasr.com ranjan & kumar: economic earthquake resistance construction of high-rise buildings regular structure was found to be equal to 7.3 mm, whereas relatively to the regular structure, the maximum displacement in the cross section and the channel section were 6.19 mm and 6.2 mm, respectively, but after separate analysis of the sections, the maximum displacement in cross section and channel section were found to be 7.07 mm and 7.17 mm, respectively. from this it can be concluded that the regular structure performed well during the earthquake as compared to the irregular structure and the performance of the cross section was better than that of the channel section during the earthquake. iv. conclusions according to [16], systems with coupling ratios of 30 % to 45 % perform the best and are the most cost-effective since they need less steel and concrete. the traditional method for mediumto highrise building construction and repairing are uneconomical without placing coupled shear walls against earthquake forces because the coupled shear walls reduce the moment. if an earthquake's force exceeds the design level, the connected beams will sustain damage first and withstand the structure collapse. story drift is directly correlated with flexibility (fs). maximum story drift is 0.89 mm at a height of 12 m above the ground, 0.88 mm at 18 m, and 0.87 m at 18 m for the regular plan, channel section, and cross section, respectively. therefore, the regular plan dissipates more energy than the irregular plan, and the cross section dissipates more energy than the channel section. based on the limited study of the current paper, we can say that regular buildings performed well during earthquakes as compared to buildings with irregular plans. regarding the performance with irregular plans, it was observed that the cross section structure performed better than the channel section. in order to keep the coupling ratio within acceptable bounds for effective earthquake resistance structure design and structure beam economy, we propose the use of 40–50 % coupled shear walls for the regular sections and 60–70 % for the irregular plans of the overall building height. if the cr is within the range of 30 % to 45 %, then the coupling beam will fail first. these beams can be repaired easily at a low cost. the findings of this paper may assist engineers, researchers, and designers in creating earthquake-resistant structures that are both efficient and cost-effective. references [1] g. chen et al., "global projections of future urban land expansion under shared socioeconomic pathways," nature communications, vol. 11, no. 1, jan. 2020, art. no. 537, https://doi.org/10.1038/s41467-020-14386-x. [2] m. đorđević, a. radivojević, r. dragović, and i. filipović, "exposure to earthquakes distribution and change of the world’s population with regard to disposition of seismic activities," journal of the geographical institute "jovan cvijic" sasa, vol. 66, no. 3, pp. 353–370, 2016, https://doi.org/10.2298/ijgi1603353d. [3] t. boudina, s. bounouni, and n. allout, "a comparative analysis of seismic site response in time and frequency domains," engineering, technology & applied science research, vol. 13, no. 2, pp. 10414– 10418, apr. 2023, https://doi.org/10.48084/etasr.5701. [4] i. c. thakur and l. b. roy, "soil liquefaction potential in different seismic zones of bihar, india," engineering, technology & applied science research, vol. 12, no. 6, pp. 9471–9476, dec. 2022, https://doi.org/10.48084/etasr.5292. [5] t. a. nguyen, n. m. pham, t. c. vo, and d. d. nguyen, "assessment of shear strength models of reinforced concrete columns," engineering, technology & applied science research, vol. 12, no. 6, pp. 9440–9444, dec. 2022, https://doi.org/10.48084/etasr.5248. [6] a. aitsi-selmi, s. egawa, h. sasaki, c. wannous, and v. murray, "the sendai framework for disaster risk reduction: renewing the global commitment to people’s resilience, health, and well-being," international journal of disaster risk science, vol. 6, no. 2, pp. 164– 176, jun. 2015, https://doi.org/10.1007/s13753-015-0050-9. [7] l. jiang and b. c. o’neill, "global urbanization projections for the shared socioeconomic pathways," global environmental change, vol. 42, pp. 193–199, jan. 2017, https://doi.org/10.1016/j.gloenvcha.2015.03. 008. [8] m. pesaresi et al., atlas of the human planet 2017: global exposure to natural hazards. luxembourg: publications office of the european union, 2017. [9] a. coull and r. d. puri, "analysis of coupled shear walls of variable thickness," building science, vol. 2, no. 2, pp. 181–188, jun. 1967, https://doi.org/10.1016/0007-3628(67)90018-7. [10] t. paulay, "coupling beams of reinforced concrete shear walls," journal of the structural division, vol. 97, no. 3, pp. 843–862, mar. 1971, https://doi.org/10.1061/jsdeag.0002848. [11] a. c. heidebrecht and r. d. swift, "analysis of asymmetrical coupled shear walls," journal of the structural division, vol. 97, no. 5, pp. 1407–1422, may 1971, https://doi.org/10.1061/jsdeag.0002901. [12] a. k. h. kwan, "analysis of coupled wall/frame structures by frame method with shear deformation allowed.," proceedings of the institution of civil engineers, vol. 91, no. 2, pp. 273–297, jun. 1991, https://doi.org/10.1680/iicep.1991.14983. [13] n. k. subedi, a. k. marsono, and g. aguda, "analysis of reinforced concrete coupled shear wall structures," the structural design of tall buildings, vol. 8, no. 2, pp. 117–143, 1999, https://doi.org/10.1002/ (sici)1099-1794(199906)8:2<117::aid-tal124>3.0.co;2-7. [14] g. xuan, b. m. shahrooz, k. a. harries, and g. a. rassati, "a performance-based design approach for coupled core wall systems with diagonally reinforced concrete coupling beams," advances in structural engineering, vol. 11, no. 3, pp. 253–268, jun. 2008, https://doi.org/10.1260/136943308785082580. [15] k. a. harries, "ductility and deformability of coupling beams in reinforced concrete coupled walls," earthquake spectra, vol. 17, no. 3, pp. 457–478, aug. 2001, https://doi.org/10.1193/1.1586184. [16] s. el-tawil and c. m. kuenzli, "pushover of hybrid coupled walls. ii: analysis and behavior," journal of structural engineering, vol. 128, no. 10, pp. 1282–1289, oct. 2002, https://doi.org/10.1061/(asce)07339445(2002)128:10(1282). [17] k. a. harries and d. s. mcneice, "performance-based design of highrise coupled wall systems," the structural design of tall and special buildings, vol. 15, no. 3, pp. 289–306, 2006, https://doi.org/10.1002/ tal.296. [18] r. ranjan and a. kumar, "forecasting ground movement of patna region, india," earthquakes and structures, vol. 20, no. 5, pp. 487–494, may 2021, https://doi.org/10.12989/eas.2021.20.5.487. engineering, technology & applied science research vol. 8, no. 1, 2017, 2477-2484 2477 www.etasr.com taghikhani and farahani: a reactive power based reference model for adaptive control strategy in … a reactive power based reference model for adaptive control strategy in a seig mohammad ali taghikhani department of engineering imam khomeini international university qazvin, iran amir davoudabadi farahani department of engineering imam khomeini international university qazvin, iran abstract—in this paper, a new control strategy is proposed for a three-phase squirrel-cage self-excited induction generator (seig) connected to a variable speed wind turbine in autonomous mode. in order to improve the dynamic performance of the mentioned vector control system, a model reference adaptive controller is used for online rotor time constant estimation. thus, the main drawbacks of this method, which include the effects of the changes in machine parameters on rotor flux estimation, slip speed, the creation of instability problems and the system leaving vector control mode, are resolved. in this control strategy, a pi controller is used to control the dc voltage and three similar hysteresis current controllers (hcc) are used to control the switching of igbts. the results of the dynamic simulation indicate the desirable performance of the proposed system. keywords-self-excited induction generator (seig); rotor flux oriented (rfo) vector control; model reference adaptive system (mras) i. introduction using capacitor-excited squirrel-cage induction generators in small hydropower or wind power plants in areas far from the grid has always attracted interest in order to electrify isolated areas. some of the advantages of induction generators include the simple and sturdy structure (due to the squirrel-cage rotor), simpler operation, low price, lesser safety and measurement equipment, higher reliability, self-protection against errors, high power-to-weight ratio, adequate dynamic response, no need for synchronization and excitation adjustment. also, the lack of rings, commutators, brushes and a separate dc source for excitation lead to reduced repair and maintenance costs. in addition, since wind speed varies in different times, the use of induction generators has attracted a lot of attention, because these generators are able to convert mechanical to electrical energy in a wider range of rotor speed changes. poor regulation of voltage and the required reactive power are the two main drawbacks of an induction generator. in order to use an induction generator in autonomous mode, we need a proper control system to maintain a constant dc-bus voltage [1-3]. some solutions are presented in various articles in order to control the terminal voltage of seigs. in [4], a rotor flux oriented vector control is proposed by taking into account the effects of core losses and magnetic saturation. but no solution is offered for the sensitivity of the system to rotor resistance changes. authors in [5] propose a stator flux oriented (sfo) vector control. the main advantage of this control method is that it’s not sensitive to the changes of the generator leakage inductance. however, the main drawback is the system’s dependency on stator resistance changes which can reduce the precision of flux estimation in low voltages. in [6], seig steady state characteristics are proposed by series and shunt capacitors. the results show that short shunt generator has the best characteristic and is a good candidate for static power supply. a seig transient characteristic with series compensation that feeds a dynamic load such as induction motor has been studied in [7]. in addition, the steady state and transient behavior in different operational conditions, such as seig voltage generation under no load condition and sudden connection of induction motor to seig with and without series compensation, has been analyzed through mathematical modeling. however, series capacitor may cause sub synchronous resonance (ssr) in seig-im, such that create overvoltage, over current, induction motor speed and torque unstable oscillations. in [8], a self-controlled static reactive power compensator with a fixed-capacitor thyristor-controlled reactor (fc-tcr) is used to adjust the terminal voltage and frequency of induction generators. a model predictive controller (mpc) is used in order to control the svc’s fire angle. magnetization inductance has the main role in seig voltage generation and stability in no-load and under load conditions. therefore, to have a real and accurate model for seig dynamic analysis, it is required to evaluate magnetization inductance. an estimation method of magnetization inductance is proposed in [9]. in [10], the authors proposed a control strategy to obtain the maximum possible energy from wind turbines and also to simultaneously adjust the terminal voltage of the generator against the original load and wind speed changes. this strategy is based on the principles of fuzzy logic control using an electronic load controller (elc) connected to a voltage source inverter. a current controlled voltage source inverter with a suitable control algorithm could be used as a static synchronous compensator (statcom). statcom performance principle and control strategy for seig terminal voltage regulation is proposed in [11-15]. statcom could be considered as a required reactive power source for seig terminal voltage regulation in variable load conditions. in this strategy, seig engineering, technology & applied science research vol. 8, no. 1, 2017, 2477-2484 2478 www.etasr.com taghikhani and farahani: a reactive power based reference model for adaptive control strategy in … supplies the required active power of the load, while the required reactive power of the load and seig are supplied through statcom. in addition to compensating reactive power, the statcom is employed to compensate the unbalanced currents caused by single-phase loads that are connected across the two terminals of the three-phase seig, and also suppresses the harmonics injected by consumer loads. however, this method is not able to regulate seig frequency under variable load conditions. in [16], a decoupled voltage and frequency controller (dvfc) is proposed which causes seig to feed linear and nonlinear loads in constant voltage and frequency by regulating them separately. hence, the dvfc is a combination of a static synchronous compensator for regulating the voltage and an elc [17] for controlling the power which maintains the system frequency constant. however, this procedure includes a pi controller for regulating active power in the elc and two other pi controllers for ac and dc voltage control are also set in statcom controller which regulating these controllers cause practical problems in the design of dvfc. ii. studied system description the main structure regarding the execution of the vector control system is illustrated in figure 1. the main components of the studied system are a vector control system and a threephase induction generator. the generator’s shaft is connected to the wind turbine through the gear box, its stator terminal is connected to a current-controlled voltage source inverter, and an excitation capacitor, battery and resistive load exist in its dc-link. in this paper, the dynamic model for seigs proposed in [18] is used to design the vector control system due to high precision and reduced amount of calculations, which needs less hardware and software requirements and lower costs. the effects of saturation and iron losses are both taken into account in this model in a way that the iron loss resistance is a function of synchronization frequency and flux, and the magnetizing inductance is a function of magnetizing current. the effects of the magnetizing flux on iron losses are expressed by the corresponding current of iron losses irm. the equivalent circuit of the seig in a stationary reference frame is illustrated in figure 2. all the variables along the q axis are similar to the variables of the d axis with a 90-degree phase shift, therefore, only the equivalent circuit of the d axis is actually illustrated. if we substitute the dashed area by its thevenin equivalent, we will obtain the equivalent circuit of figure 2(b), in which the iron loss resistance is included in the variable resistance of the stator. the values of the magnetizing inductance and iron loss used in the simulation are calculated online by look-up tables [4], as shown in figure 3. the thevenin equivalents for the stator current/voltage and resistance are calculated in the following. s m st s m s m r r r r r r r    ‖ (1) m std sd s m r u u r r   (2) m stq sq s m r u u r r   (3) fig. 1. system description fig. 2. the equivalent circuit of the seig fig. 3. the online calculation of lm and rm since the structure of the equivalent circuit shown in figure 2 is similar to the lossless seig model, we can maintain the structure of the lossless model within the model with losses using the following substitution. the equations of the lossless model will also be valid and the first-order differential equations are preserved, resulting in a lower amount of calculations: , , , , s st sq stq sd std sq stq sd stdr r u u u u i i i i    the seig model illustrated in figure 2 (b) can be perfectly described through the following four first-order differential equations by choosing the rotor and stator currents as state variables. engineering, technology & applied science research vol. 8, no. 1, 2017, 2477-2484 2479 www.etasr.com taghikhani and farahani: a reactive power based reference model for adaptive control strategy in … s m sd std sd m m r r u i i r r    (4) sqs m stq sq m m ur r i i r r    (5) 21 ( ) std m r stq r st std s r m r r rq m r rd r std m rd s i l i l r i l l l l i l r i l u l k           (6) 21 ( ) stq r st stq m r std s r m r rq m r r rd r stq m rq si l r i l i l l l r i l l i l u l k           (7) 1 ( ) rd s r m stq m st std s r s r r rq s r rd m std s rd si l l i l r i l l l l i l r i l u l k           (8) 1 ( ) rq m st stq s r m std s r s r rq s r r rd m stq s rq si l r i l l i l l l r i l l i l u l k          (9) iii. field-oriented vector control (foc) in a dc machine, the axes of the field and the two armature coils are perpendicular and the mmf forces caused by their currents do not interact with each other if we disregard core saturation. therefore, the controlling variables of the machine, the vectors of the armature current ia and the excitation current if, can be regarded as stationary and orthogonal in space, each of which can be controlled independently. in general however, controlling a three-phase induction machine is not as easy and simple as controlling a dc machine because the rotor and stator fields obey the operating conditions, and their spatial directions lack the 90-degree phase difference, so they interact with each other. if the equations and block diagram of an induction machine are studied in a reference frame at synchronous speed, then the stator current is expressed by two components ids and iqs which can be used as controlling tools for the induction machine. in the vector control of induction machines, the ids current is similar to the if current and acts as the component of flux and the iqs current is similar to the ia current and acts as the component of torque. therefore, the performance of a dc machine can be extended to an induction machine using this control strategy. in vector control, the control strategies are implemented in a two-phase reference frame fixed on the rotor or a stationary reference frame with an excitation frequency. we are looking to convert all the variables from the three-phase a-b-c system to a two-phase stationary reference frame and then convert them again from the stationary reference frame to a synchronous rotating reference frame. in this situation, all sinusoidal signals seem like dc values in the steady state (like a dc machine). after applying field-oriented vector control on the d and q components of the stator current, the variables need to be converted to the a-b-c system, which is done using inverse transformations [19]. these transformations, which are usually in series, are shown in figure 4 [19]. fig. 4. vector control transformations vector control is a mathematical control strategy based on space vector theory which is performed in a synchronous reference frame with current and phase angle control. in the vector control strategy, we try to put the space vectors of the stator’s flux and current in the hands of the controller, so that by tracing the space vector, the d and q components of the stator current are separated and controlled properly. direct and indirect strategies are proposed based on the calculation of the solid angle of the induction machine’s flux in the vector control algorithm. in direct vector control strategy, the positioning of flux is done by measuring flux signals through the hall effect sensor. however in the indirect strategy, parameters such as the speed signal ωr and the slip frequency ωsl are used. in vector control analysis, all vector quantities must be in the same basis and frame reference in order for a correct and significant analysis. basically, three reference frames are considered in vector control: the magnetizing flux, rotor flux and stator flux oriented reference frames. in this paper, an indirect rotor flux oriented vector control strategy is used. we have chosen the indirect vector control strategy because of the shortcomings of the direct technique, namely the need for a flux sensor which results in the high volume and high costs. in the stator flux oriented strategy, we need a decoupling circuit in the flux control loop due to the coupling of the variables. we also need pi controllers and more amplitude limiters at the output which results in higher complexity in comparison with the rotor flux oriented strategy. therefore, the rotor flux reference frame is chosen among other types of reference frames due to the simplification of the equations of the induction machine and simpler performance. according to the vector control diagram illustrated in figure 5, the de axis of the rotating reference frame overlays the rotor flux vector λr in the rotor flux oriented strategy. in other words, the rotor flux vector is considered as a reference of measurement for the other vectors. in this case, the q component of the rotor flux would be zero and the flux in the d axis would be equivalent to the total rotor flux in the induction machine. therefore, the conditions of validity for the rotor flux oriented vector control can be expressed as [20]: e dr r  (10) 0eqr  (11) 0 e qrd dt   (12) engineering, technology & applied science research vol. 8, no. 1, 2017, 2477-2484 2480 www.etasr.com taghikhani and farahani: a reactive power based reference model for adaptive control strategy in … . fig. 5. the rotor flux oriented vector control diagram the ds – qs axes are fixed and the de – qe axes rotate with the synchronous speed ωe. the angle of the rotating de axis relative to the fixed ds axis is equivalent to θe which is the sum of the rotor angle θr and the slip angle θsl. r r dt   (13) sl sl dt   (14) e sl r    (15) the rotor voltage equations of an induction machine in a synchronous reference frame are:   0 e e edr r dr e r qr d r i dt        (16)   0 e qr e e r qr e r dr d r i dt        (17) the rotor currents are obtained from the equations of the d and q components of the rotor flux in the synchronous reference frame: e e e dr m ds dr r l i i l    (18) e e qr m qse qr r l i i l    (19) substituting (18) and (19) in (16) and (17), we can obtain the rotor voltage equations in terms of rotor flux and stator currents. 0 e e e edr mr dr r ds sl qr r r d lr r i dt l l        (20) 0 e qr e e emr qr r qs sl dr r r d lr r i dt l l        (21) substituting (12) to (19), which describe the conditions of validity of the rotor flux oriented vector control, in (20) and (21), we obtain the following: er r r m ds d t l i dt    (22) em sl qs r r l i t    (23) in which sl e r    and r r r l t = r represent the slip speed and the time constant of the rotor respectively. in the steady state, the rotor flux is constant and therefore, (22) can be expressed as below: e r m dsl i  (24) substituting the above equation in (23), we obtain: 1 eqs sl e r ds i t i   (25) as seen in the above equations, the rotor flux oriented vector control strategy controls the variables separately; because the rotor flux depends only on the d axis current. however, the main drawback of this strategy is the variability of the machine parameters, because the rotor resistance may vary with temperature and the skin effect, and also the rotor inductance might vary with the level of the core magnetic saturation. this drawback leads to the presence of noise in the reference slip estimation which ultimately leads to the coupling of the variables. thus, the system exits vector control mode. in this paper, the model reference adaptive system is proposed for the compensation and the online adjustment of the rotor resistance in order to resolve this problem. iv. model reference adaptive system (mras) so far, various programs have been presented for the online estimation of machine parameters. these programs can be classified as: the signal injection strategy, the model reference adaptive system, the observer-based strategy [21] and other strategies. the model reference adaptive system is a strategy that has attracted a lot of interest due to its relatively simple execution. the main idea of the system is based on the calculation of one quantity in two different ways. the first value is calculated by the references within the control system and the second value is obtained from the measured signals. one of these two values is independent of the studied quantity. in this paper, the model reference adaptive system is designed on the basis of the reactive power, in a way that it eliminates all demands for the estimation of stator resistance and flux in the calculation process. the main structure of the mras block is illustrated in figure 6. this structure contains a reference model and an adjustable model which calculate the momentary reactive power (qref) and the steady state reactive power (qest), respectively. the reference model is independent of the slip speed (rotor resistance or time constant) while the adjustable model is dependent on this quantity. the error signal caused by the difference between these two values ( )ref estq e = q implies the error in the resistance of the rotor used in the control system which is the input of the adaptation mechanism block (i or pi engineering, technology & applied science research vol. 8, no. 1, 2017, 2477-2484 2481 www.etasr.com taghikhani and farahani: a reactive power based reference model for adaptive control strategy in … controller). the output of the block is the estimated slip speed ωsl,est which can be used to calculate rotor resistance. fig. 6. the main structure of the model reference adaptive system the d and q components of the stator voltage in the rotating synchronous reference frame ωe can be expressed as follows: e m ds s ds e s qs qr r ds m dr s r l v = r i l i + l di l d l + dt l dt       (26) e m qs s qs e s ds dr r qs qrm s r l v r i l i l di dl l dt l dt            (27) the momentary reactive power (q) can be expressed as below: 1 qs ds ds qsq v i v i  (28) substituting equations (26) and (27) in equation (28), we obtain a new equation for q: 2 2 2 qs ds s ds qs e m qr qs dr ds r e s ds qs qrm dr ds qs r di di q l i i dt dt l i i l l i i dl d i i l dt dt                               (29) if we take the derivative segment to be zero in the steady state, and substitute equation (24) and the conditions of validity for rotor flux oriented vector control (equations (10) to (12)), we can simplify the (29) as: 2 2 2 2 2 m e s ds qs e ds r l q l i i i l        (30) where e r sl    and the equation for q2, which is independent of the rotor flux and stator resistance and dependent on slip speed, can be regarded as the adjustable model and the equation for q1, which is independent of slip speed, can be considered as the reference model. v. simulation results in order to use an induction machine as an autonomous generator for wind energy conversion, we need a proper control system. figure 7 illustrates the details of the implementation of the proposed vector control strategy in an autonomous induction generator. in this article, we use the rotor flux oriented vector control strategy in order to control the flux of the induction machine and maintain a constant dc-link voltage. the vector control algorithm contains two loops that work in parallel. the first loop allows us to control the flux and also the d component of the reference current. that’s how we control the flow of reactive power in the system. the second loop lets us control the dc voltage and thus the q component of the reference current. therefore, the flow of active power from the generator to the dc circuit can be controlled. the reference current on the rotating qe axis in the rotating synchronous reference frame ( )*qsi is obtained from the dc voltage controller output but the d component of the reference current in the rotating synchronous reference frame ( )*dsi is obtained if we divide the rotor flux amplitude by the magnetizing inductance, according to (24). the reference slip sl can be calculated by (25). in the next step, the value of e and thus the value of θe, the position angle of the rotating area which is the heart of the vector control system, are calculated with high precision using the values of slip and rotor speeds. the simulation has been performed in matlab simulink in order to evaluate the efficiency of the proposed vector control strategy. the rated values and parameters of the induction machine are brought in table i. table i. machine parameters parameter value shaft power : pn 5.5 kw stator phase voltage: un 200 v base speed: ωn 690 rpm stator resistance: rs 1.0713 ω rotor resistance: rr 1.2951 ω rotor inertia : j 0.230 kg.m2 rotor friction coefficient: d 0.0025 n.m/rad pole pairs: p 4 frequency: f 50 hz at first, the rotor of the induction machine gains speed until it reaches the synchronous speed. we now investigate the performance of the proposed system with a 10% increase in rotor speed in 6 seconds using different variables. the rotor speed of the induction machine is illustrated in figure 8 in which the machine reaches the synchronous speed in 0.5 engineering, technology & applied science research vol. 8, no. 1, 2017, 2477-2484 2482 www.etasr.com taghikhani and farahani: a reactive power based reference model for adaptive control strategy in … seconds. figure 9 displays the changes of the rotor flux. the rotor flux reaches its reference value in 1.26 seconds without overshoot. the rotor flux follows the changes of speed rapidly and therefore it passes the noise generated in the speed and returns to its reference value immediately. the dc voltage wave in the inverter output is illustrated in figure 10 which reaches its reference value in 1.127 seconds with a poor overshoot of about 2.14%. the response of the dc voltage to the generated noise is exactly similar to that of the flux. figure 11 shows the d and q components of the stator currents which can be controlled separately. the isq current wave is similar to the rotor flux. in other words, isq shows the changes of speed which in turn imply the changes of the electromagnetic torque in the induction generator, illustrated in figure 12. fig. 7. the proposed control strategy fig. 8. rotor speed fig. 9. changes in rotor flux engineering, technology & applied science research vol. 8, no. 1, 2017, 2477-2484 2483 www.etasr.com taghikhani and farahani: a reactive power based reference model for adaptive control strategy in … fig. 10. the generated dc voltage fig. 11. changes in the d and q components of the stator current fig. 12. changes in the electromagnetic torque vi. conclusion in this paper, a new control strategy is proposed for an autonomous self-excited induction generator (seig) connected to a variable speed wind turbine which is based on the principles of vector control in order to maintain a constant dcbus voltage. the proposed control strategy uses indirect rotor flux orientation (irfo) which doesn’t need a decoupling circuit and is less complex and easier to perform than the stator flux oriented strategy. the indirect strategy is chosen because of the shortcomings of the direct technique, namely the need for a flux sensor which results in the high volume and high costs. in order to design the vector control system, the effects of core losses and saturation are both taken into account in the dynamic model of the induction machine in a way that the iron loss resistance is a function of synchronization frequency and flux, and the magnetizing inductance is a function of magnetizing current. this leads to high precision and low calculation complexity while maintaining the simplicity. it also reduces the hardware and software requirements and thus the cost. in order to improve the dynamic performance of the studied vector control system, a model reference adaptive system (mras) is used for the online estimation of the rotor time constant. this resolves the main drawbacks of this strategy which are the effects of changes in machine parameters on the estimation of the rotor flux and slip speed, the creation of instability problems and the system leaving vector control mode. the simulation results indicate that the proposed controller has displayed optimal performance in the adjustment of the voltage of the induction generator in autonomous mode. references [1] r. choudhary, r. k. saket, “critical review on the self-excitation process and steady state analysis of an seig driven by wind turbine”, renewable and sustainable energy reviews, vol. 47, no. 12, pp. 344–353, 2015 [2] s. meddouri, l. a. dao, l. ferrarini, “performance analysis of an autonomous induction generator under different operating conditions using predictive control”, ieee international conference on automation science and engineering, pp. 1118-1124, 2015 [3] m. basic, d. vukadinovic, “online efficiency optimization of a vector controlled self-excited induction generator”, ieee transactions on energy conversion, vol. 31, no. 1, pp. 373-380, 2016 [4] m. basic, d. vukadinovic, “vector control system of a self-excited induction generator including iron losses and magnetic saturation”, control engineering practice, vol. 21, no. 1, pp. 395–406, 2013 [5] d. vukadinovic, m. basic, “a stand-alone induction generator with improved stator flux oriented control”, journal of electrical engineering, vol. 62, no. 2, pp. 65–72, 2011 [6] m. h. haque, “comparison of steady state characteristics of shunt, short-shunt and long-shunt induction generators”, electric power systems research, vol. 79, no. 23, pp. 1446–1453, 2009 [7] b. singh, m. singh, a. k. tandon, “transient performance of seriescompensated three phase self-excited induction generator feeding dynamic loads”, ieee transactions on industry applications, vol. 46, no. 4, pp. 1271-1280, 2010 [8] m. ahmed kassem, “robust voltage control of a standalone wind energy conversion system based on functional model predictive approach”, international journal of electrical power and energy systems, vol. 41, no. 6, pp. 124–132, 2012 [9] l. kalamen, p. rafajdus, p. sekerak, v. hrabovcova, “a novel method of magnetizing inductance investigation of self-excited induction generators”, ieee transactions on magnetics, vol. 48, no. 4, pp. 16571660, 2012 [10] s. a. deraz, f. e. abdel kader, “a new control strategy for a standalone self-excited induction generator driven by a variable speed wind turbine”, renewable energy, vol. 5, no. 2, pp. 263–273, 2013 [11] b. singh, s. s. murthy, s. gupta, “a stand-alone generating system using self-excited induction generators in the extraction of petroleum products”, ieee transactions on industry applications, vol. 46, no. 1, pp. 94-101, 2010 [12] b. singh, s. s. murthy, r. s. r. chilipi, “statcom-based controller for a three-phase seig feeding single-phase loads”, ieee transactions on energy conversion, vol. 29, no. 2, pp. 320-331, 2014 [13] y. k. chauhan, s. k. jain, b. singh, “a prospective on voltage regulation of self-excited induction generators for industry applications”, ieee transactions on industry applications, vol. 46, no. 2, pp. 720-730, 2010 [14] y. k. chauhan, s. k jain, b. singh, “operating performance of static series compensated three-phase self-excited induction generator”, international journal of electrical power and energy systems, vol. 49, no. 3, pp. 137-148, 2013 [15] r. s. r. chilipi, b. singh, s. s. murthy, “performance of a self-excited induction generator with dstatcom-dtc drive-based voltage and frequency controller”, ieee transactions on energy conversion, vol. 29, no. 3, pp. 545-557, 2014 [16] g. k. kasal, b. singh, “decoupled voltage and frequency controller for isolated asynchronous generators feeding three-phase four-wire engineering, technology & applied science research vol. 8, no. 1, 2017, 2477-2484 2484 www.etasr.com taghikhani and farahani: a reactive power based reference model for adaptive control strategy in … loads”, ieee transactions on power delivery, vol. 23, no. 3, pp. 966973, 2008 [17] b. singh, s. s. murthy, s. gupta, “analysis and design of electronic load controller for self-excited induction generators”, ieee transactions on energy conversion, vol. 21, no. 1, pp. 285-293, 2006 [18] m. basic, d. vukadinovic, g. petrovic, “dynamic and pole-zero analysis of self-excited induction generator using a novel model with iron losses”, international journal of electrical power and energy systems, vol. 42, no. 6, pp. 105–118, 2010 [19] y. oguz, m. dede, “speed estimation of vector controlled squirrel cage asynchronous motor with artificial neural networks”, energy conversion and management, vol. 52, no. 3, pp. 675–686, 2011 [20] b. k. bose, modern power electronics and ac drives, prentice hall. 2001 [21] t. abbasian nadjafabadi, f. rajaei salmasi, “a flux observer with online estimation of core loss and rotor resistances for induction motors”, international review of electrical engineering, vol. 4, no. 5, pp. 816-824, 2009 engineering, technology & applied science research vol. 7, no. 6, 2017, 2240-2250 2240 www.etasr.com ravindra and srinivasa rao: sensitive constrained optimal pmu allocation with complete … sensitive constrained optimal pmu allocation with complete observability for state estimation solution m. ravindra electrical and electronics engineering department jawaharlal nehru technological university, kakinada kakinada, india ravieeejntu@gmail.com r. srinivasa rao electrical and electronics engineering department jawaharlal nehru technological university, kakinada kakinada, india srinivas.jntueee@gmail.com abstract—in this paper, a sensitive constrained integer linear programming approach is formulated for the optimal allocation of phasor measurement units (pmus) in a power system network to obtain state estimation. in this approach, sensitive buses along with zero injection buses (zib) are considered for optimal allocation of pmus in the network to generate state estimation solutions. sensitive buses are evolved from the mean of bus voltages subjected to increase of load consistently up to 50%. sensitive buses are ranked in order to place pmus. sensitive constrained optimal pmu allocation in case of single line and no line contingency are considered in observability analysis to ensure protection and control of power system from abnormal conditions. modeling of zib constraints is included to minimize the number of pmu network allocations. this paper presents optimal allocation of pmu at sensitive buses with zero injection modeling, considering cost criteria and redundancy to increase the accuracy of state estimation solution without losing observability of the whole system. simulations are carried out on ieee 14, 30 and 57 bus systems and results obtained are compared with traditional and other state estimation methods available in the literature, to demonstrate the effectiveness of the proposed method. keywords—sensitive; bus; observability; phasor; measurement; pmu; state; estimation; zero; injection; zib i. introduction state estimation plays a vital role in real-time control of power system providing security and reliability. it acts as a filter between the received information and application functions that need reliable data. in power systems, supervisory control and data acquisition (scada) systems are used to collect the raw data (bus voltage magnitudes, currents and complex power flows) of the transmission network and this data is processed for state estimation solution. however, this information is not sufficient to estimate the accurate states of voltage and phase angles at every bus in the system. one of the recent developments in real time analysis of power systems is an implementation of synchrophasor in the state estimation process. synchrophasors or pmus are used to directly measure phase angles associated with voltages and currents with respect to an absolute time reference. this absolute reference is provided by common timing signal by high accuracy clocks to coordinated universal time (utc) such as global positioning systems (gps) [1]. a phasor measuring unit is a device used to store synchronized measurement data and to communicate the same to a control center through gps. allocation of pmus at every bus to measure the complete data of the system is not a feasible solution from economic perspective. hence, in order to get complete observability and identify gross errors in measurement set, pmus must be placed optimally at sensitive nodes by considering zib in the network. in a power system network, some of the buses are sensitive to sudden load changes that may lead to a blackout. blackouts occur in power grid predominantly due to inadequate generation and state predictability of the system [2]. prior knowledge of the states of a system at sensitive buses can be very useful in avoiding blackouts. different types of sensitive indices are proposed in the literature for various applications in the performance analysis of power system [3-7]. in this paper voltage sensitive indices are used to identify sensitive buses for the placement of pmus. several approaches are proposed in literature for optimal pmu placement. initial work on phasor measurements using synchrophasors to measure phasor voltage and currents is proposed in [8]. authors in [9] proposed a linear programming based measurement system for maintaining observability when a single line outage occurs in the network. authors in [10] used ga with the immune operator to select optimal sites for pmu placement to achieve observability with improved converging speed and execution time. authors in [11] implemented nondominated sorting genetic algorithm (nsga) in pmu placement problem and simultaneously optimized two conflicting objectives such as minimization of number of pmus and maximization of the measurement redundancy and obtained pareto-optimal solutions. authors in [12] developed an integrated model to show the effect of zib and conventional measurements in pmu allocation to enhance system observability by considering single branch and single pmu outage contingencies separately and simultaneously. authors in [13] proposed a method for multi-staging of pmus by modeling zero injection constraint as a linear model in integer linear programming approach with two indices such as bus observability index (boi) and system observability redundancy index (sori). author in [14] proposed a generalized linear integer programming approach for redundant engineering, technology & applied science research vol. 7, no. 6, 2017, 2240-2250 2241 www.etasr.com ravindra and srinivasa rao: sensitive constrained optimal pmu allocation with complete … pmu placement, full and incomplete observability, with and without zero injections and showed that accuracy, redundancy, and robustness of state estimation solution will be enhanced with pmu placement. authors in [15] considered the pmu placement problem as a quadratic minimization problem with continuous decision variables and solved the problem using non-linear weighted least squares approach. authors in [16] proposed a binary search algorithm to determine the minimum number of pmus for observability under normal conditions and single branch outage conditions. authors in [17] introduced the concept of time-synchronized measurements for pmu placement and solved the problem using integer quadratic programming to minimize the total number of pmus and to increase the redundancy at power system buses. in [18], authors formulated a binary integer linear programming approach with binary decision variables to locate pmus at each bus by integrating possibility of single or multiple pmu loss in the decision strategy while preserving observability and the lowest metering economy. authors in [19] introduced a hybrid constrained state estimator in which conventional and synchrophasor measurements are incorporated simultaneously in the problem without using any measurement transformation and shown that solution converges faster with small uncertainty. authors in [20] introduced a multistage state estimation procedure to include synchrophasor measurements without disturbing existing scada system. this procedure requires more pmus which opposes the economic criteria. authors in [21] investigated three different methods to include pmu measurements into state estimation problem. in this paper, a sensitive constrained integer linear programming approach is used for optimal pmu allocation considering sensitive buses along with zibs. the pmus are placed at sensitive buses which are identified based on voltage stability index with complete observability. the method is tested with different test cases and results are presented. the rest of the paper is organized as follows: section ii deals with traditional state estimation method; section iii covers optimal pmu allocation considering sensitive buses; section iv presents state estimation with conventional and pmu measurements. section v provides results and analysis and section vi gives conclusions. ii. traditional state estimation the traditional state estimation method collects data from scada systems to find states of power systems. for a given set of measurements, weighted least squares state estimation [22] can be represented as: 2 m 1k kkw krmin  (1) subjected to: kkk rxhz  )( , k=1….m (2) where rk = zk-hk(x) is residual value of measurement k calculated from the difference of the measured zk and a nonlinear function hk(x) related to measurement state vector (x). the residual vector 2kr is weighted by kkw = 2 k which is calculated from the standard deviation of respective measurements and m is the number of measurements. the gain matrix is formed for better accurate state estimation, formulated with jacobian h matrix and covariance }......,{ 222 2 1 mdiagr  . the jacobian matrix for traditional state estimation is defined as                                                v v v qq v pp v qq v pp h mag flfl flfl inin inin 0     (3) the gain matrix is defined as zrhxg t  1)( (4) where hrhg t 1 and )(xhzz k from (4), the solution is obtained by updating the state vector xxx tt 1 (5) the convergence of the state estimation algorithm is obtained when δx becomes smaller than the tolerance value 105. in state estimation process observability of the system can be obtained numerically by finding the rank of the jacobian matrix or through topological bus connectivity matrix. if jacobian matrix h has full rank the system is numerically observable otherwise is not observable. in this paper topological observability is considered, each bus is checked with redundancy index (ri) and total system with complete system observability redundancy index (csori) to show complete observability of the system. iii. optimal pmu allocation considering sensitive buses a. formulation for the optimal pmu allocation problem the proposed approach is formulated as an optimization problem of allocating pmus in the network with highest preference at sensitive buses for complete observability considering cost criteria which produce accurate state estimation solution. the optimization problem for optimal allocation of pmus is formulated as: n k k 1 f kmin x   (6) subject to bax  and eqeq bxa  (7) engineering, technology & applied science research vol. 7, no. 6, 2017, 2240-2250 2242 www.etasr.com ravindra and srinivasa rao: sensitive constrained optimal pmu allocation with complete … where fk is cost coefficient of pmu installed at bus k, aeq is matrix of order n×n consisting of sensitive buses, whose entries are all equal to one and for other buses it is zero, n is number of buses,  tnxxxxx ...321 is a decision variable vector, b and beq is observability constraints matrix which can be written as  tn 11....1 1 1 1  , kx is binary decision variable and a is incidence matrix of order i×j which are defined as     otherwise 0 busat installed is pmu if 1 k xk      otherwise 0 other each toconnectedor if 1 , ji a ji proper identification of sensitive buses in the system and optimal placement of pmus at these buses accurately estimate the states of state estimation problem. b. identification of sensitive buses from experiences of major blackouts occurred in india, failure of the supply occurred due to either sudden removal of generation or overloading beyond safety limits leading to dip in system voltage. in order to determine the most sensitive buses in a system which are prone to load changes, voltage stability indexes (vsi) at each bus are formulated by increasing the load from 5 to 50%.    n i avg iv n v 1 )( 1 (8) 0vvvsi avg  (9) where, v0 is the vector of true bus voltages obtained from the base load, vavg is calculated from average of voltages obtained with increased load and n is the number of load samples. vsi is calculated from the difference of average voltage and true bus voltage. the bus with the highest vsi value among buses is considered as the highest sensitive bus in the system. the calculated values of vsi for 14-bus test case system are shown in table i. from table i data, sensitive buses are arranged in descending order i.e., b14 > b9 > b10 > b4 > b7 > b5 > b11 > b13 > b12, where b1 is slack bus b2, b3, b6, and b8 are generator buses, b7 is zib and remaining are load buses. b14 and b9 buses are the most sensitive buses (in that order) affected by load change. in this paper, sensitive buses are considered as constraints for optimal pmu allocation. the procedure to compute voltage stability index (vsi) and sensitive buses at each bus is presented in figure 1. table i. vsi data obtained from load flows bus no b1 b2 b3 b4 b5 b6 b7 vsi 0 0 0 0.0062 0.0059 0 0.0062 bus no b8 b9 b10 b11 b12 b13 b14 vsi 0 0.0095 0.0094 0.0055 0.0036 0.0051 0.0115 fig. 1. flowchart to estimate sensitive buses c. sensitive constrained optimal pmu allocation placement of pmu at each and every bus increases the number of pmus in the system which is a drawback from economic perspective. hence, in order to optimize the number of pmus and to allocate pmus at sensitive buses for accurate state estimation solution, the problem is formulated as follows using an eight-bus network as shown in figure 2. fig. 2. eightbus system network diagram the optimization problem can be expressed as 1 2 3 8..........min x x x x   (10) subject to observability constraints bus 1: 121  xx (11) bus 2: 15321  xxxx (12) bus 3: 1352  xxx (13) bus 4: 154  xx (14) bus 5: 15432  xxxx (15) bus 6: 176  xx (16) bus 7: 18765  xxxx (17) bus 8: 187  xx (18) engineering, technology & applied science research vol. 7, no. 6, 2017, 2240-2250 2243 www.etasr.com ravindra and srinivasa rao: sensitive constrained optimal pmu allocation with complete … where }1,0{kx in sensitive constrained integer linear programming formulation. for instance, consider bus 5 and 7 are the most sensitive buses in the eight-bus system. in order to allocate pmu at sensitive buses, locations suggested are 1,1 75  xx . as a result of substituting these values in observability constraints (11-18), inequalities for buses 2, 3, 4, 5, 6, 7, 8 are satisfied. after eliminating satisfied constraints, residual observable constraints subjected to optimization are shown below. the sensitive constrained optimization problem is written as   8 1k kxminimize (19) subjected to observability constraints 121  xx (20) with application of integer linear programming the solution  01010010 which means pmus need to be allocated at 2, 5, 7 to make the system completely observable. d. optimization of sensitive constrained pmus allocation with zero injection (zi) modeling in a power system when there is no generation or load at any particular bus, power injection to rest of the network is zero. such buses are considered as zibs. when zibs are considered, the size of connectivity matrix will be reduced, thus it is possible to minimize the number of pmus in the network. in this problem of zero injection modeling, every bus connected to zib is considered. permutation matrix p is formulated from an array of the vector that includes buses not associated with zib and array of buses associated with zib. zib constraint matrix is formulated with the number of buses not associated with zib and buses associated with zib. the buses associated with only zib can be written as zas. zib constraint matrix is written as 0 0 l l m as i z z       (21) where il×lis identity matrix of l number of buses not associated with zib. the bus connectivity matrix developed for optimal allocation of pmu can be presented as * *pmu mz a p z (22) where, a is bus incidence matrix defined from the bus system, p is permutation matrix of the bus system and zm is zib constraint matrix formulated in (21). bus constraint matrix bcon is defined as the vector of buses (not associated with zib which are all equal to one) and the number of buses associated with each zib. bus constraint matrix is vector formed to check observability of the system. the optimization of sensitive constrained pmus with zero injection modeling is formulated as n k k 1 f kmin x   (23) subjected to observability constraints pmu conz x b (24) eq eqa x b (25) where: x=[x1 x2 …… xn] t, xkє(0,1), k=1,2,3,….,n , zpmu is bus connectivity matrix defined in (22), bcon and beq is bus constraint matrix formed to check observability of the system. aeq is a matrix of n×n order which consists of sensitive bus elements whose entries are equal to one and for other bus elements it is zero. equation (25) ensures that xk variable must be one for sensitive buses in the system. it gives priority to sensitive buses for allocation of pmus in the bus network. for instance, in figure 2, bus-2 is a zib which is optimized with modeling of bus connectivity matrix. permutation matrix of the system is                            00010000 00000100 00000010 00000001 10000000 01000000 00100000 00001000 p from (21) zib constraint matrix is written as                  11110000 00001000 00000100 00000010 00000001 mz bus constraint matrix is developed such that every bus of the system is measured by at least two pmus. t conb ]31111[ from (22), bus connectivity matrix for optimal allocation of pmus can be calculated as                  01031342 11110000 11110000 01100000 00011000 pmuz bcon, aeq, f, zpmu and number of nonzero elements in aeq are inputs for sensitive constrained integer linear programming method, which results in a decision variable vector [0 0 0 0 1 0 1 0]. this gives optimal allocation of pmus at 5 and 7 buses. e. optimization of sensitive constrained pmus allocation under single line contingency the optimization of sensitive constrained pmus with zero injection modeling in case single line contingency is formulated as engineering, technology & applied science research vol. 7, no. 6, 2017, 2240-2250 2244 www.etasr.com ravindra and srinivasa rao: sensitive constrained optimal pmu allocation with complete … n k k 1 f kmin x   (26) subjected to observability constraints 2pmu conz x b (27) eq eqa x b (28) in case of single line contingency, the problem is formulated in such a way that each network bus is observed by at least two pmus f. complete observability of the system the performance of optimization method depends on the observability of the power system. the performance of every bus of the system is measured by bus observability index (boi). the maximum boi is limited to maximum connectivity (χ) of the bus plus one [13]. 1k k   (29) for bus-k, (  ) boi gives the number of times the bus is observed by the pmu. to know the performance of the total system, complete system observability redundancy index (csori) is determined and it can be presented as the sum of boi of every bus in the system. 1 n k k csori    (30) maximum redundancy of the bus can be formulated as 1 n t k pmu k k max b z x   (31) subjected to following constraints 0 1 n k k x    (32) pmuz x b (33) where μ0 is the minimum number of pmus obtained for complete system observability, zpmu is bus connectivity matrix obtained from the proposed sensitive constrained approach. b is the vector of observability constraints which is written as transpose of vector [1 1 1 1 . . .1]. iv. state estimation with conventional and optimal sensitive constrained pmu measurements newton-raphson load flow is considered for calculation of conventional measurements and true state values (vtru, δtru) of the system. for integration of pmu measurements into state estimation, the method followed in this paper is widely investigated in [19], [21], [25-27] and this process exhibits good results. for the joint optimality of pmu and scada measurements, the optimization method used for solving nonlinear equations is wls method in which the errors are weighted with standard deviation. the proposed method includes optimal pmu measurements at sensitive buses along with zibs obtained from sensitive constrained ilp approach formulated in this paper. the procedure to find states of the power system with sensitive constrained state estimation method is presented in figure 3. the measurement function for state estimation is written as kkk rxhz  )( (34) where zk is a vector of conventional and optimal pmu measurements, x is state vector, hk is the measurement vector of non-linear function related to state vector x and rk is measurement error vector. the residual vector obtained from the measurement function can be written as rk = zk-hk(x) , k=1,2….m (35) the objective function for sensitive constrained state estimation is formulated as 2 1 ( ( )) ( ) m k k k kk z h x j x min r    (36) rkk is diagonal matrix formed with inverse of variances of conventional and pmu measurements which is written as rkk=diagonal of 2 2 2 1 21 / ,1 / ,.......1 / m     (37) where 2m is covariance of the measurements. the state estimation method integrates pmu measurements with conventional measurements by designing jacobian matrix i.e. first order derivatives of pmu and conventional measurements are formulated in the state estimation process. the jacobian matrix with pmu measurements at sensitive buses and conventional measurements can be formulated as 0 0 in in in in fl fl fl fl pmu pmu pmu rpmu rpmu ipmu ipmu p p v q q v p p v q q v h v v i i v i i v                                                                (38) engineering, technology & applied science research vol. 7, no. 6, 2017, 2240-2250 2245 www.etasr.com ravindra and srinivasa rao: sensitive constrained optimal pmu allocation with complete … fig. 3. flow chart for state estimation with optimal allocation of pmus considering sensitive buses gain matrix is defined for the best solution of the system state accuracy which is written as 1( ) tpmu pmug x h r r    (39) where 1tpmu pmu pmug h r h  , ( )r z h x   . state estimation solution is obtained by updating state vector which is defined as 1 1 1( ) ( ( ))t t tpmu pmu pmux h r h h r z h x      (40) 1 1 1 1( ) ( ( ))t t t t tpmu pmu pmux x h r h h r z h x       (41) where xt is the vector of state variables at tth iteration. the convergence tolerance (ε) for state estimation is selected as 10-5 and state error is obtained from the difference of estimated states (vest, δest) and true values of the system. voltage magnitude error (verr) and phase angle error (δerr) are written as err est truv v v  , err est tru    (42) v. results and analysis in order to allocate pmus and estimate the states of a power system, the proposed method is applied to 14, 24, 30 and 57-bus test systems. the single line diagrams of 14 and 57-bus system are shown in figures 4 and 5 respectively. simulations are carried out on the test systems with matlab and results are presented and compared. matlab programs are run on intel(r) core(tm), i3 processor at 2.20 ghz with 4 gb of ram. table ii shows the zero injection buses, and sensitive buses generated from formulation (8), (9). fig. 4. sensitive constrained pmu locations in 14 bus network table ii. sensitive and zero injection buses ieee test systems sensitive buses zib buses 14 bus 14,9 7 24 bus 22,21 11,12,17,24 30 bus 30,26,24,19 6,9,22,25,27,28 57 bus 31,33,29,32,25 4,7,11,21,22,24,26,34, 36,37,39.40,45,46,48 fig. 5. sensitive constrained pmu allocation for 57 bus system. engineering, technology & applied science research vol. 7, no. 6, 2017, 2240-2250 2246 www.etasr.com ravindra and srinivasa rao: sensitive constrained optimal pmu allocation with complete … a. optimal pmu allocation with sensitive constrained integer linear programming general optimal pmu locations without sensitive constraints using bilp method [30] is shown in table iii. table iii. pmu allocations without sensitive constraints ieee test systems no. of pmus pmu locations 14bus 4 2,6,7,9 24 bus 7 2, 3, 8, 10, 16 , 21,23 30 bus 10 1,7,9,10,12,18,24,25,27,28 57 bus 17 1,4,6,13,19,22,25,27,29,32,36,39,41,45,47,51,54 binary integer programming is used to model sensitive constrained ilp method for optimization. using bus constraint vector matrix and bus connectivity matrix, zero injection modeling is framed in sensitive constrained ilp to optimize pmu allocation in the network. the sensitive buses are arranged according to the priority of higher sensitive buses. table iv shows sensitive constrained pmu allocation with and without out zero injection modeling. table v shows sensitive constrained pmu allocation with and without zero injection modeling under single line contingency. with zib modeling, allocation of pmus in the network is reduced to meet the cost criteria. the method’s performance is analyzed through the system redundancy. redundancy index (ri) measures the observability of each bus of the system covered under pmus. system redundancy increases with the optimal location of pmus in the system. tables vi and vii show the redundancy index of sensitive constrained pmu locations under no line and single line contingency. it can be observed from table vi that under single line contingency pmus are placed in the network in a way that each branch is observable by at least 2 pmus. table viii shows the comparison of csori that is observable with the optimal number of pmus under no line and single line contingency in the system. table iv. sensitive constrained pmu allocations with and without zi modeling ieee test systems without zi modeling with zi modeling no. of pmus pmu locations no. of pmus pmu locations 14bus 5 2,6,7,9,14 4 2,6,9,14 24 bus 8 3,4,8,10,16,21,22,23 7 1,4,6,8,19,21,22 30 bus 10 3,6,7,9,10,12,19,24, 26, 30 9 3,6,7,10,12,19,24, 26,30 57 bus 20 1,4,9,12,20,24,25,28, 29,31,32,33,36,38,39, 41,45,46,50,53 17 3,4,9,12,15,20,24, 25,29,31,32,33,36, 38,50,54,56 table ix shows the number of pmus allocated with proposed method and other methods [10, 12-17]. the proposed approach optimizes and allocates pmus at sensitive buses that are prone to load changes. pmu allocation at sensitive buses is given the highest preference to provide accurate states of the system. all other methods cited in [10, 12-17] optimized the pmus without considering the constraints of the buses and allocation of pmus at sensitive buses which results in inaccurate system measurements. table v. sensitive constrained pmu allocations with and without zi modeling under single line contingency ieee test systems without zi modeling with zi modeling no. of pmus pmu locations no. of pmus pmu locations 14bus 10 2,4,5,6,7,8,9,11,13,14 8 2,4,5,6,9,10,13,14 24 bus 15 1,2,3,7,8,9,10,11,15, 16, 17,20,21,22,23 12 1,2,7,8,9,,10,16, 18,19,21,22,23 30 bus 21 1,2,3,5,6,8,9,10,11,12, 13,15,16,18,19,22,24,25, 26,27,30 17 1,3,5,6,7,10,12,13, 15,17,19,20,22,24, 26,27,30 57 bus 33 1,3,4,6,9,12,15,19,20, 22,24,25,27,28,29,31,32, 33,35,36,37,38,39,41,43. 45,46,47,50,51,53,54,56 30 1,2,4,6,9,12,15,18, 20,22,24,25,28,29, 30,31,32,33,35,36, 38,41,45,48,49,50, 51,53,54,56 table vi. ri of bus with sensitive constrained pmu allocations bus no b1 b2 b3 b4 b5 b6 b7 ri 1 1 1 3 2 1 2 bus no b8 b9 b10 b11 b12 b13 b14 ri 1 3 1 1 1 2 2 table vii. ri of bus with sensitive constrained pmu allocations under single line contingency bus no b1 b2 b3 b4 b5 b6 b7 ri 2 3 2 5 4 4 4 bus no b8 b9 b10 b11 b12 b13 b14 ri 2 4 2 2 2 3 3 table viii. csori for sensitive constrained pmu locations ieee test systems no line contingency single line contingency csori with zi modeling csori without zi modeling csori with zi modeling csori without zi modeling 14 bus 18 22 36 42 24 bus 24 33 48 62 30 bus 39 43 67 82 57 bus 72 79 120 128 table ix. comparison of optimization methods for complete observability methods 14 bus system 24 bus system 30bus system 57bus system generalized ilp programming[14] 4 10 17 wls[15] #4 #10 #17 integer quadratic [17] 4 10 17 bilp [18][30] 4 10 17 cro[28] 4 10 17 bpso[29] 4 10 17 bgo[31] 4 10 proposed sensitive constrained ilp *4 7 *9 *17 * optimal number of pmus allocated at sensitive buses. # optimal number of pmus obtained solely with pmu measurements. engineering, technology & applied science research vol. 7, no. 6, 2017, 2240-2250 2247 www.etasr.com ravindra and srinivasa rao: sensitive constrained optimal pmu allocation with complete … b. state estimation with sensitive constrained pmu allocations in state estimation process, load flow solution is considered as a true case for generating measurements with errors. measurement noise (gaussian random variable) has been added to measurement function to limit the noisy measurements. to obtain measurement accuracy for each measurement, the error variance of the measurements is added to each type of the measurement. the gaussian measurement noise is set to 10-4. in this proposed state estimation method, voltage phasors are measured in polar coordinates and current flow measurements are measured in rectangular coordinates. as current flow measurements in polar coordinates lead to very large and uncertain for a certain range of terminal voltages and phase angles that result in an ill condition of the state estimation gain matrix [21]. hence current measurements are considered in rectangular coordinates in the following test cases. 1) test case 1: 14-bus system to define the accuracy of estimation with pmu allocation at sensitive buses and to show the difference between with and without sensitive bus locations, state estimation method integrating pmu measurements without sensitive buses is shown. three scenarios i.e., traditional state estimation without pmu allocations, state estimation integrating pmu measurements and state estimation with proposed sensitive constrained pmu allocations are compared. in the state estimation method without considering sensitive buses, four pmus are allocated at 2, 6, 7 and 9 to obtain 38 measurements. total 85 (38+47) measurements are used in state estimation method without considering sensitive buses. in this 14-bus system shown in figure 4, four pmus are allocated at bus 2, 6, 9 and 14 to obtain 36 measurements and 47 conventional measurements to make the system completely observable. the traditional state estimation method is performed with 47 conventional measurements and state estimation method with proposed sensitive constrained pmu locations utilizes a total of 83 (36+47) measurements to get the accurate performance of the state estimation. (i) conventional measurements: power injections: {1, 2, 3, 4, 7, 8, 10, 11, 12, 14} power flows: {1-2, 3-2, 3-4, 4-2, 4-7, 4-9, 5-2, 5-4, 5-6,613, 7-9, 11-6, 12,-13} (iii) pmu measurements without considering sensitive buses: voltage phasors: {2, 6, 7, 9} current flows: {2-1, 2-3, 2-4, 2-5, 6-5, 6-11, 6-12, 6-13, 7 4, 7-8, 7-9, 9-4, 9-7, 9-10,9-14} (iii) pmu measurements considering sensitive buses: voltage phasors: {2, 6, 9, 14} current flows: {2-1, 2-3, 2-4, 2-5, 6-5, 6-11, 6-12, 6-13, 94, 9-7, 9-10, 9-14, 14-9, 14-13} state estimation accuracy of the system depends on variance of the estimated states. the smaller variance value implies better accuracy. for the proposed state estimation, variances of power injections and power flows are set to 0.0001, and 0.00064. for pmu measurements, variance for voltage phasors is set to 0.00001 and for real and imaginary current flows it is set to 0.001. the state estimation solution with optimal pmu allocations converged after 6 iterations. voltage magnitude error and phase angle error are obtained from the difference of estimated and true values (load flow calculated values are considered as true values). the voltage magnitude error and phase error obtained using traditional state estimation method without pmus (scenario 1) and proposed state estimation with pmu (scenario2) and state estimation with proposed sensitive constrained pmu locations (scenario 3) is presented in figure 6 and 7 respectively. allocation of pmus at sensitive buses has impact on measurement accuracy with complete observability of the system. that can be observed with voltage and phase angle errors obtained and presented in scenario 3. state estimation with pmu allocation at sensitive constrained buses i.e. at 2, 6, 9, and 14 shows very small angle error deviation when compared to traditional state estimation method and state estimation without sensitive constrained locations as shown in figure 7. comparison of scenarios 1, 2 and 3 presented in figures 6 and 7 gives better accuracy results for complete observability of the system with the proposed sensitive constrained state estimation. fig. 6. comparison voltage magnitude error of 14-bus system fig. 7. comparison of phase angle error of 14-bus system 2) test case 2: 57-bus system the topology of the 57-bus system with pmus is shown in figure 5. the optimal pmus obtained are 17 and are located at {3, 4, 9, 12, 15, 20, 24, 25, 29, 31, 32, 33, 36, 38, 50, 54, 56} with sensitive constrained ilp method to make system completely observable. there are a total of 145 conventional measurements (voltage, power flow, and power injection engineering, technology & applied science research vol. 7, no. 6, 2017, 2240-2250 2248 www.etasr.com ravindra and srinivasa rao: sensitive constrained optimal pmu allocation with complete … measurements) and with 17 pmus allocated in the network, 140 measurements (voltage phasor measurements and real and imaginary current flow measurements) are obtained to get the accurate performance of the state estimation. pmu locations obtained through ilp method with and without sensitive constrained locations are shown as follows. (i) conventional measurements: power injections: {1, 2, 3, 4, 5, 6, 7, 8, 9, 14, 15, 16, 20, 25, 32, 33, 37, 40, 50, 53, 56} power flow measurements: {2-1, 2-3, 3-4, 3-15, 4-5, 4-18, 5-6, 6-7,6-9, 7-8, 7-29, 9-10,10-12,10-51,11-13,11-41,11-43, 12-17, 13-49, 14-46, 15-45, 18-19, 19-20, 21-22, 22-23, 23-24, 24-25, 24-26, 27-28, 28-29, 29-52, 30-31, 32-33, 34-35,35-36, 36-40, 37-38, 37-39, 38-48, 39-57, 41-42, 41-43, 44-45, 46-47, 47-48, 48-49,50-51, 52-53, 54-55, 57-56} (ii) pmu measurements obtained through general ilp method voltage phasors: {1, 4, 6, 13, 19, 22, 25, 27, 29, 32, 36, 39, 41, 45, 47, 51, 54} current flows: {1-2, 1-15, 1-16, 1-17, 4-3, 4-5, 4-6, 4-18, 64, 6-5, 6-7, 6-8, 13-9,13-12,13-14,13-15, 13-49,19-18,1920,22-21,22-23,22-38, 25-24, 25-30, 27-26,27-28, 29-28, 2952, 32-31, 32-33, 32-34, 36-35, 36-37, 36-40,39-37,39-57,4110,41-11,41-42,41-43,41-56,45-15,45-44,47-48,47-46,4749,51-10,51-50,54-53,54-55} (iii) pmu measurements obtained through sensitive constrained ilp method voltage phasors: {3, 4, 9, 12, 15, 20, 24, 25, 29, 31, 32, 33, 36, 38, 50, 54, 56} current flow measurements: {3-2, 3-15, 4-3, 4-5, 4-6, 4-18, 9-10, 9-11, 9-12, 9-13, 9-55, 12-9, 12-13, 12-16, 12-17, 15-3, 15-1,15-13, 15-14, 15-45,20-19, 20-21, 24-23, 24-26, 25-24, 25-30, 29-7, 29-28, 29-52, 31-32, 31-30, 32-33, 32-34, 3332,33-34,36-35, 36-37,36-40, 38-22, 38-37, 38-44, 38-48, 3849,50-49, 50-51, 54-55, 54-53, 56-57, 56-41,56-42, 56-40} the pmu measurements obtained through general ilp method are 140 and with including conventional measurements, total measurements are 285 (145+140). with the integration of pmu measurements obtained through sensitive constrained ilp and conventional measurements, we obtain total 278 (145+133) measurements to perform state estimation. for the proposed method, variances of power injections, power flows and voltage phasors of pmu measurements are set to 0.00001 and for real and imaginary current flow measurements it is set to 0.001. the state estimation solution with optimal pmu allocations converged after 7 iterations. the voltage magnitude error and phase error obtained for 57 bus system using traditional state estimation method without pmus (scenario 1), state estimation with pmu (scenario 2) and state estimation with proposed sensitive constrained pmu allocation (scenario 3) is presented in figures 8 and 9 respectively. with pmus allocation at sensitive buses, state error obtained in the measurement is very low which means improved accuracy of the state estimation. fig. 8. comparison voltage magnitude error of 57-bus system phase angle measurement is very important in power system state estimation, as a small deviation of angle leads to instability of the system. comparison of scenario 1 (traditional state estimation without pmu), scenario 2 (state estimation with pmu) and scenario 3 (state estimation with proposed sensitive bus constrained pmu allocation) in figure 9 shows the state estimation method with sensitive constrained pmu allocation (scenario 3) results in very small phase angle error deviation showing the impact of pmu measurement accuracy with complete observability of the system. fig. 9. comparison of phase angle error of 57-bus system c. performance of state estimation with proposed sensitive constrained allocation with root mean square error (rmse) indicator in order to quantify accuracy and performance of state estimation, an rmse is formulated and error is computed. the states of 14and 57-bus systems with optimal sensitive constrained pmus allocation are examined with rmse and compared with traditional state estimation and state estimation method without considering sensitive buses. rmse is formulated as rmse    n k truest kxkx n 1 2))()(( 1 (43) engineering, technology & applied science research vol. 7, no. 6, 2017, 2240-2250 2249 www.etasr.com ravindra and srinivasa rao: sensitive constrained optimal pmu allocation with complete … where xest is estimated state, xtru is the true state of the system, and n is the number of buses in the system. rmse for voltage and phase angles are computed separately because the scale of measurements is different in each case. rmse measures the accuracy of state estimation voltage and phase angle errors of the system. rmse with pmu for the proposed sensitive approach has better accuracy compared to traditional state estimation and all other methods. rmse values of 14and 57bus systems are shown in table x. when compared to state estimation solution given in [19, 21, 26, 27], the solution with proposed method is better. table x. comparison of rmse index of proposed method with other methods methods rmse of voltage (p.u) ieee 14-bus system ieee57bus system traditional state estimation method[22] 0.0006 0.007 ref[19] 0.000076 0.002 ref[21] 0.00011 ref[27] 0.00099 proposed sensitive constrained state estimation method 0.000027 0.0009 vi. conclusion this paper presented a sensitive constrained integer linear programming approach 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a. g. phadke, “hybrid linear state estimation utilizing synchronized phasor measurements”, ieee lausanne power tech, pp. 1665-1669, 2007 engineering, technology & applied science research vol. 7, no. 6, 2017, 2240-2250 2250 www.etasr.com ravindra and srinivasa rao: sensitive constrained optimal pmu allocation with complete … [27] g. n. korres, n. m. manousakis, “state estimation and observability analysis for phasor measurement unit measured systems”, iet generation, transmission & distribution, vol. 6, no. 9, pp. 902-913, 2012 [28] j. xu, m. h. f. wen, v. o. k. li, k. c. leung, “optimal pmu placement for wide-area monitoring using chemical reaction optimization”, ieee pes innovative smart grid technologies conference, pp. 1-6, 2013 [29] a. ahmadi, y. alinejad-beromi, m. moradi, “optimal pmu placement for power system observability using binary particle swarm optimization and considering measurement redundancy”, expert systems with applications, vol. 38, no. 6, pp. 7263-7269, 2011 [30] m. ravindra, r. srinivasa rao. “dynamic state estimation solution with optimal allocation of pmus in presence of load changes”, ieee international conference on intelligent control power and instrumentation, pp. 163-168, 2016 [31] k. jamuna, k. s. swarup, “multi-objective biogeography based optimization for optimal pmu placement”, applied soft computing, vol. 12, no.5, pp. 1503-1510, 2012 engineering, technology & applied science research vol. 7, no. 4, 2017, 1741-1745 1741 www.etasr.com fakhim: an investigation of the effect of different nanofluids in a solar collector an investigation of the effect of different nanofluids in a solar collector hamed agabalaie fakhim department of mechanical engineering, tabriz branch, islamic azad university, tabriz, iran hamedfakhim@iaut.ac.ir abstract—in this article, we examine the use of different nanofluids in a solar collector in a parabolic form. temperature, thermal efficiency and outlet average temperature for a conventional parabolic collector and a collector with nanofluid are compared. the effect of various parameters (concentration ratio, volume fraction of nanoparticles, absorption and fluid velocity) are studied. results are discussed and it is shown that nano fluid increases the efficiency of the collector. keywordsnanofluid; water; solar collector; thermal efficiency; numerical analysis i. introduction the importance of solar energy is widely recognized and is of increased significance for countries where favorable weather conditions permits increased exploitation through pvs and solar collectors [1-2]. however, the potential is often larger than the amounts of energy actually used. in iran, the potential is calculated to be about 4,000 times its energy consumption [3]. researchers have made different experiments and simulations to evaluate the performance of collectors. an experimental investigation can be in conjunction with the plate coverage [4]. the two-dimensional finite element method has been employed in order to investigate the collector’s performance [5]. another numerical simulation of the flat plate solar collector in which water has streamed showed good agreement with experimental results [6]. an effort to optimize a parabolic solar collector was conducted in [7] that included a comprehensive mathematical model of thermal and optical performance conditions of the collector. a considerable improvement in reducing radiation convection losses was reported [7]. the natural flow inside a waveform solar collector with the use of two nanofluids, using the finite element method, was investigated in [8]. it was concluded that the silver-water nanofluid had a better effect on increasing the heat transfer rate [8]. in this paper, the effect of nanofluids (water-silver and silver-copper) on the performance of a parabolic concentrator collector is examined. to improve the efficiency of the system, the nanoparticles are added to the fluid in the absorbing tube and as a result direct heat transfer is possible. this study numerically models the flow of nanofluid in the solar collector and describes its difference with a common collector. ii. design of solar systems solar collectors work out as a heat exchangers in which a form of energy, solar energy, converts to another form of energy [9]. in general, it can be said that solar collectors absorb the solar radiation energy and convert it to heat. an essential part of the set up is anti-corrosion and the use of water and/or water with some additives such as antifreeze [10]. there are various different schemes that can be roughly categorized as active and passive, direct and indirect, full and back gravity systems. passive systems include the use of very few moving and no electronic equipment. in these systems, storage and heat circulation are supplied with thermosiphon or cold input water pressure. in active systems, electricity is used to supply the pump and the controllers. these systems are also known as mandatory rotation and have better management potential and performance on absorbed solar heat. thermal, economic, environmental efficiency and lifetime of solar water heaters of thermosiphon type have been examined in various works (e.g. [11]). an additional issue is the choice of solar collectors. flat plate solar collectors are widely used due to their lower price, however vacuum tube collectors gain increased attention due to their improved characteristics. iii. model parameters figure 1 shows the basic scheme of a solar collector, a water storage tank, heat exchangers and back tubes. collector includes the absorber plate, glass coverage and side plates. cube is with 1.2 length and 120 mm lateral distance. height of absorbent to glass is 240 mm and insulator thickness under the absorbent is 30 millimeters. pipe diameter inside the collector is 1.2 mm which passes from the adsorbent. tubes on the parts outside the collector and the water tank are all assumed to be adiabatic. in the exact modeling, production of a precise computational grid is required for the geometric range. the control volume forms should be in a way to reduce computational error. the accuracy of the computational results in fluid dynamics depends heavily on the grids. further, regular engineering, technology & applied science research vol. 7, no. 4, 2017, 1741-1745 1742 www.etasr.com fakhim: an investigation of the effect of different nanofluids in a solar collector computing grids that include cubes controls volume increase the accuracy of the results and reduce the number of grids. the level of radiation in experiments has been obtained by averaging the amount of radiant energy on the top and bottom of the absorber tube. to evaluate the thermal performance of vacuum solar water heaters, a closed system instead of an open system is used. the thermal performance of a vacuum tube solar water heater is obtained via (1) ga tcm c p    (1) in (1), m represents the rate of mass flow of water heater inside the tank (via incoming and outgoing tank), cp represents the thermal capacity of the working fluid, δτ represents the average increase in the temperature of the working fluid between the tank inlet and the outlet, ac represents the tube absorber level and g represents the average solar radiation. for closed systems, the mass of the fluid inside the tank is used instead of m. 3d components related to the workspace are considered to only appear in the time of activity performance in simulation. temporary activities were corresponding to the construction resources in three categories: materials, machinery or equipment and manpower. for each of the resources, an attributed space was designed that covered the main resource in the form of transparent and geometric volumes. the workspace of the construction resource was defined to produce the building components of one day and it is appeared daily and continuously besides building components and is hidden in the end of that day. actually, after the construction of one day's workspace were hidden and then the corresponding volumes with 3d building components were appeared and remained to the end. in (2), t represents the increase in the average temperature of the fluid inside tank, g represents the average solar radiation per tube and time represents the time of the experiment. gtime tcm pk , tan   (2) fig. 1. display of solar water heating system iv. mathematical modeling to evaluate and analyze the theory of parabolic collector, the radiation source, nanofluids and concentrator have been numerically modeled. the spectral distribution of radiation by a black object is a function of wavelength and temperature which has been defined by the planck distribution, in (3) [12].              1exp 2 ),( 0 2 0 sumb sumb tk hc hc ti     (3) in this equation, tsum represents the solar surface temperature, h is planck's constant, kb represents boltzmann's constant, c0 represents the speed of light in a vacuum and λ the wavelength. spectral radiation intensity is calculated via (3). energy emission wavelength is considered between 0.2-6 μm. in this research, the adsorbent is modeled as geometric and in form of a circular channel which has placed along linear parabolic concentrator. water tank has been designed 10 liters regarding single-tube collector. to simplify the model, it is assumed that the absorber has a transmittance coefficient equaled to 1. nanofluid is modeled as a half-transparent environment, moving with constant speed. in this modeling, the radiation landing and then the energy transmission are considered through the absorption and rayleigh scattering methods [13]. received radiation in the water is due to absorption but received radiation caused by the interaction of nanoparticles is due to both scattering and absorption. the concentrator in figure 1 converges the radiations caused by solar energy on adsorbent and a parameter called concentration ratio is defined to determine the convergence size [14]. for ease of severity, received radiation caused by solar energy is assumed in the radial direction. to receive and calculate radiation at various radiuses, the corrected form of bayes equation in form of (4) is used. rikrikk dr rid esa ...).( ).(     (4) in (4), kaλ represents the absorption coefficient of the spectrum, ksλ represents the spectral scattering coefficient and keλ represents the coefficient of received scattering. the tube inside collector has been made of copper with a thickness of one millimeter and a diameter of 1.27 cm. it has been assumed that the inner surface of the collector is lined with black tubes to increase the absorption of radiation; tube as opaque surface has the absorption coefficient of 0.94. the intensity of the radiation received in the nanofluid is caused by the effect of base fluid and nano-particles. when radiation passes through the water, received radiation takes place through absorption; received radiation takes place through scattering and absorbing incoming radiation in nanofluids. in the proposed model, the average diameter of the nanoparticles is about 8 nm thus the overall received coefficient is expressed in (5) via riley equation. d q k meesnanopartice 2 3 ),( )(      (5) engineering, technology & applied science research vol. 7, no. 4, 2017, 1741-1745 1743 www.etasr.com fakhim: an investigation of the effect of different nanofluids in a solar collector in (5), ϕ represents the volume fraction of nanoparticles and qeλ represents the received efficiency and d represents particle diameter. α represents particle size and m represents the relative refractive index of particles obtained in (6) [7-15].    d   (6) fluid particles n m m   (7) received efficiency in computing is obtained via (8). 2 2 2 4 2 22 2 22 2 2 1 1 3 8 } 32 3827 1 1 15 1 1 1 {4                              m m m mm m m m m iq me     (8) the ratio of the total received radiation for the nanofluid is obtained by the superposition of received base fluid and nanofluid coefficient. thus, in order to obtain the relationship between the radiation flows in the flow system, the placement of this amount in the bayes equation is used. in the software, time-dependent equations in terms of both time and space are discrete. in (9), the amount of energy production (egn) in the overall energy balance equation is expressed. .... stgenoutin eeee   (9) in (9), ėin, ėout, ėgen, ėst represent the energy transmission to system, power transmission from system, power generation and energy storage respectively. to find the temperature field for the two-dimensional steady-state from the overall equation of equilibrium temperature, (9) is used. after obtaining the overall nanofluid temperature, average outlet temperatures, optical efficiency, thermal efficiency, etc. are calculated. a. equations governing the flow to study and analyze the behavior of flows, the conservation of mass equations are used. for compressible flows or flows of heat transfer, energy conservation equations are solved. under turbulent flow, turbulence modeling equations should be used. the purpose of calculating flows, especially turbulent flows, is to determine the terms such as reynolds stress, turbulent mass flux or turbulent heat flux by linking the mentioned amounts to the average flow quantities and especially existing gradients at average flow [9]. mass conservation equation is written in (10). 0)()( 11      uu xt i    (10) by considering (10), the equation of momentum is written in (11). vpguu xdt vd j i 2)(       (11) energy equation is written in (12).                                  11 1 1 1 1 1 2 x u x u x u x u tuc x t k xdt td c jj j p i p    (12) v. numerical solution to solve this set of equations, finite difference method is used, so that the total volume is decomposed to the initial controls volume with grids at their centre [10]. absorbent with radius and length of 40 mm and 2.5 mm decomposes along radial direction. the size of the nodes along radial direction of axis r equals 0.5 mm and 1.2 mm. the size of the grids is selected so that solutions are stable and convergent in iterations from simulation. fluid temperature incoming the environment and the collector temperature are considered 25°c. further, convective heat transfer coefficient is equal to 6.75w/m2k. incoming solar radiation flux to system is also considered be 1000w/m2k [11]. in this calculation, the diameter of the nanoparticles and the volume fraction (ϕ) have been considered 8 nm and 0.03 wt%, respectively. to obtain effective thermophysical properties of nanofluid, the rule of mixture is used [12]. (1 )nanofluid particle basedfluidp p p     (13) vi. study on results the results of two-dimensional field for collectors with nanofluid and conventional collectors are displayed in figure 2 and the comparison of the two collectors is shown in table i. the results of the simulation in table i show that the nanofluid collector outperforms the conventional collector under the same working conditions. table i. comparison of two collectors in the proposed model optical efficiency (%) thermal efficiency (%) average outlet temperature (k) working fluid 322.5 27.8 33.2 pure water 331.72 95.2 97.8 nanofluid to optimize the proposed model, working parameters such as concentration ratio, volume fraction, the adsorbent and the flow rate were varied and their impact on the performance index is evaluated. the impact of nanofluid volume fraction (ag/water, al/water) on the temperature of the fluid in the tube is shown in figures 3 and 4. as shown, the temperature engineering, technology & applied science research vol. 7, no. 4, 2017, 1741-1745 1744 www.etasr.com fakhim: an investigation of the effect of different nanofluids in a solar collector difference will be about 2 degrees. if different percentage of nanoparticles is added to the base fluid, inlet and outlet temperature difference with respect to the used volume percent varies. fig. 2. results from the two-dimensional field for collectors with nanofluid and conventional collectors fig. 3. the impact of the volume fraction of nanofluids (ag/water) on the temperature of the fluid in the tube fig. 4. the impact of the volume fraction of nanofluids (al/water) on the temperature of the fluid in the tube considering table i, it is specified that independent optical and thermal efficiency are the ratio of concentration, but the outlet temperature changes linearly with concentration ratio as shown in figure 5. a change of the volume fraction has a significant impact on all three performance indicators. as shown in figure 6, the average outlet temperature increases rapidly with increasing volume fraction to reach a certain speed and then it is almost constant. indeed, there is a certain amount of volume fraction, after which certain progress does not occur in the average temperature outlet. figure 7 shows the comparison of the temperature of the absorber plate and the working fluid along the tube using nanofluid with the same volume percentage. in case of using water as the fluid, the difference in the inlet and outlet temperature of water has the least temperature, and also the temperature difference between the beginning and end of the absorber plate has the highest amount, so that we will witness less efficiency using water as fluid. in case of nanofluid, there will be the highest difference on inlet and outlet temperature and lowest difference on the absorber plate. the black lines display fluid temperature with nanoparticles and red lines display the temperature of the flowing water. fig. 5. average outlet temperature of nanofluid based on collector concentration ratio fig. 6. average outlet temperature in terms of volume fraction of nanoparticles fig. 7. comparison of the temperature of the absorber plate and the working fluid along the tube as shown in figure 8, the average outlet temperature increases by increasing the absorber. this behavior is because of the fact that the duration at which a specific amount of working fluid passes absorber increases by constant flow speed and increased absorber, the fluid has more time to warm up along tube. on the contrary to figure 8, thermal efficiency reduces by increasing the absorption. this increases due to increased absorber and thereby increased the time spent in the working fluid and heat loss increases through convection. on the other hand, by increasing the flow rate, the elapsed time in the adsorbent decreases, or in other words, less time is spent to increase temperature through radiation. thus, with increasing speed, the average temperature of outlet reduces. by increasing the flow rate of heat loss, convection reduces and thermal efficiency increases (figure 9). engineering, technology & applied science research vol. 7, no. 4, 2017, 1741-1745 1745 www.etasr.com fakhim: an investigation of the effect of different nanofluids in a solar collector fig. 8. average outlet temperature in terms of absorber fig. 9. heat efficiency in terms of flow speed fig. 10. average outlet temperature in terms of collector concentration ratio. vii. conclusion in this research, the effect of different nanofluids (ag/water, al/water) on a parabolic solar collector performance is discussed. the results of the simulations demonstrate that adding a small amount of nanoparticles, not only improves its absorption characteristics, but also improves the efficiency of the collector. an increase in the volume fraction will increase collector efficiency and fluid speed to a certain range. further, by increasing the absorption, average outlet temperature increases but thermal efficiency decreases. on the contrary, this governs the speed increase so that the average temperature was reduced by increasing flow rate, but the heat efficiency increases. overall, using nanofluids as the base fluid is shown to increase collector efficiency and outlet temperature. viii. references [1] a. w. badar, r. buchholz, f. ziegler, “experimental and theoretical evaluation of the overall heat loss coefficient of vacuum tubes of a solar collector”, solar energy, vol. 85, pp.1447–1456, 2011 [2] i. budihardjo, g. l. morrison, m. behnia, “natural circulation flow through water in glass evacuated tube solar collectors”, solar energy, vol. 81, pp. 1460–1472, 2007 [3] f. jorge, o. armando, “numerical simulation of a trapezoidal cavity receiver for a linear fresnel solar collector concentrator”, journal of renewable energy, vol. 36, pp. 90–96, 2011 [4] k. sopian, m. syahri, s. abdullah, m. y. othman, b. yatim, “performance of a non-metallic unglazed solar water heater with integrated storage system”, renewable energy, vol. 29, pp.1421–1430, 2004 [5] r. s. r. gorla, “finite element analysis of a flat plate solar collector”, finite elements in analysis and design, vol. 24, pp. 283-290, 2010 [6] m. selmi, m. j. al-khawaja, a. marafia, “validation of cfd simulation for flat plate solar energy collector”, renewable energy, vol. 33, pp. 383-387, 2008 [7] a. kahrobaian, h. malekmohammadi “exergy optimization applied to linear parabolic solar collectors”, journal of faculty of engineering, vol. 42, no. 1, pp. 131-144, 2008 [8] t. p. otanicar, p. e. phelan, r. s. prasher, g. rosengarten, r. a. taylor, “nanofluid-based direct absorption solar collector”, journal of renewable and sustainable energy, vol. 2, no. 3, p. 033102, 2010 [9] t. yousefi, f. veysi, e. shojaeizadeh, s. zinadini, “an experimental investigation on the effect of ph variation of mwcnt–h2o nanofluid on the efficiency of a flat-plate solar collector”, solar energy, vol. 86, no. 2, pp. 771-779, 2012 [10] m. f. modest, radiative heat transfer, academic press, 2003 [11] a. kasaeian, a. mohmmadkarim, a. kaabinejadian, “performance investigation of solar evacuated tube collector using trnsys in tehran”, international journal of renewable energy research, vol. 4, no. 2, pp. 497-503, 2014 [12] f. p. incropera, d. p. de witt, fundamentals of heat and mass transfer, wiley and sons, new york, 2007 [13] h. tyagi, p. phelan, r. prasher, “predicted efficiency of a lowtemperature nanofluid-based direct absorption solar collector”, asme journal of solar energy engineering, vol. 131, no. 4, pp. 0410041 0410047, 2009 [14] s. k. das, s. u. choi, w. yu, t. pradeep, nanofluids: science and technology, wiley and sons, new york, 2008 [15] z. li, c. chen, h. luo, y. zhang, y. xue, “all-glass vacuum tube collector heat transfer model used in forced-circulation solar water heating system”, solar energy, vol. 84, pp. 1413-1421, 2010 microsoft word etasr_v11_n6_pp7938-7943 engineering, technology & applied science research vol. 11, no. 6, 2021, 7938-7943 7938 www.etasr.com angın & albrka ali: analysis of factors affecting road traffic accidents in north cyprus analysis of factors affecting road traffic accidents in north cyprus mehmet angın department of civil engineering near east university nicosia, cyprus mehmet.angin@neu.edu.tr shaban ismael albrka ali department of civil engineering near east university nicosia, cyprus shabanismael.albrka@neu.edu.tr abstract-road traffic accidents are a global issue. north cyprus exhibits a similar trend to the rest of the world. urbanization and the increasing number of vehicles come along with the increase of road traffic accidents. the objectives of the current study are to draw attention to the issue of road traffic accidents and to identify which factors are the main causes of road traffic accidents in north cyprus. this article follows a two-stage study to examine the causes of this critical issue. in the first stage, a survey was conducted to determine local public opinions. the participants were asked about how environmental factors, vehicle factors, human factors, and road factors impact accidents. according to the survey outcomes, human factors and road factors have the most significant impact. in the second stage of the study, official data from official statistics were considered. the number of accidents, fatalities, and injured people are indicated initially followed by the causes of accidents. negligent driving and speeding were identified to be the most frequent causes within the studied period. at the end of the study, the common causes of accidents in official statistics and in survey results were specified. negligent driving and over-speeding were the major causes of road traffic accidents according to the results. keywords-accidents; environmental factors; vehicle factors; human factors; road factors i. introduction and background road traffic accidents (rtas) represent an important and well-known global problem. they are considered a substantial public health threat in terms of injuries, disabilities, and fatalities. deaths caused by rtas have increased to 1.35 million a year, while up to 50 million injuries are caused by such incidents. in other words, approximately 3,700 people lose their lives every day in rtas. rtas are the eighth leading cause of death for people of all ages and the leading cause of death for children and young adults between 5 and 29 years of age. the death rates are three times higher in low-income countries than in high-income countries according to a global status report on road safety published in 2018 [1]. globally, the total number of vehicles has increased during the last decade [2]. the increase in vehicle numbers and growth in urbanization have led to traffic congestion in urban centres and subsequently to the occurrence of more rtas. the importance of traffic safety measures has emerged as a result of the increasing number of vehicles as well as the growth in urbanization [3]. moreover, the problem of improving road quality and all concerned traffic safety equipment is a key factor of minimizing rtas [4]. on the other hand, it has been proven that stress and environmental factors play a vital role in causing rtas. other important factors such as vehicle age, human error, safety measures and place and time of accident decide the seriousness of the accidents [5]. another previous study presents an alternative solution that smartphone-based road accident determination and reporting systems can improve drivers’ awareness on road safety and save lives in road accidents [6]. in north cyprus, 478 people lost their lives and 12,551 were injured as a result of rtas between 2007 and 2018 [712]. this study aimed to discover the main causes of rtas in north cyprus. the research aim was addressed by taking into consideration a combination of local public opinions and real data. the current article includes three main sections. the first section introduces the status of rtas globally and provides different examples of past studies about rtas. in the second section, the study area and the acquisition of data are defined. the concluding aspects are presented in the last section, in which all human and road factors were identified to have a significant impact on rtas in the survey. on the other hand, the individual, vehicle, and environmental factors were found to have variable impact. negligent driving and over-speeding came to the fore according to the official statistics. most of the rtas were recorded in 2008 and most of the accidents that caused fatalities and injuries happened in 2012 based on the same statistics. authors in [13] conducted a study in turkey in which they used multinomial logit analysis to determine the risk factors that influence the severity of traffic injuries. the results showed that factors such as primary-educated drivers, singlevehicle accidents, drivers over the age of 65, accidents occurring on provincial roads, highways, or state routes and the existence of pedestrian crosswalks increase the likelihood of fatal injuries. moreover, accidents with private vehicles or cars reach a peak level in the evenings. fatal injuries decrease in the presence of traffic lights or under clear weather conditions on local city streets. authors in [14] found that general driving errors and casual pedestrian behavior cause deaths or injuries as a result of rtas. however, they emphasized in the corresponding author: mehmet angın engineering, technology & applied science research vol. 11, no. 6, 2021, 7938-7943 7939 www.etasr.com angın & albrka ali: analysis of factors affecting road traffic accidents in north cyprus importance of road safety education. authors in [15] analyzed both severe and non-severe rtas on dry and wet highways. they used crash records of the 2010-2014 period. they used four different sets of crash data obtained from urban highways and four-lane rural roads in the state of alabama. the four datasets include severe crashes on wet pavements, non-severe crashes on wet pavements, severe crashes on dry pavements and non-severe crashes on dry pavements. it was found that the rate at which younger drivers were involved in crashes was higher than the one of older drivers, except for non-severe crashes that occurred on wet pavements. in terms of the correlation between non-severe and severe crashes and gender, crash involvement rates for younger and older female drivers were found to be higher on wet pavement surfaces than dry pavement surface conditions. authors in [16] examined the relationships between drunk driving or being under the influence of drugs and driver-related risk factors, which are known as factors that contribute to fatal road traffic crashes. norwegian road traffic crash registries and forensic toxicology databases were utilized. the relation between impairment and driver-related risk factors according to specific substance groups was calculated. according to the study, drug/alcohol use among car or van drivers is associated with speeding, not having a valid driver license, and not using a seatbelt. moreover, a relationship was found between motorcycle/moped drivers and not having a valid driver license as well as not using a helmet. authors in [17] analyzed rtas involving young drivers in urban areas. the study aimed to demonstrate measures that would reduce the number of rtas involving young drivers. the authors stated the importance of starting to instil knowledge of traffic culture from an early age in order to develop safe, defensive, and attentive drivers. the educational process results in the creation of responsible drivers, which will also reduce the frequency of rtas and indirectly the number of fatalities and casualties. authors in [18] studied the impact of various risk factors on rtas. the authors aimed to identify the impact of different risk factors on rtas in the city of shenyang, china and discuss the different common factors that affect non-motor vehicle and pedestrian accidents. time of year, administrative division, and age were the three most common factors for pedestrian and non-motor vehicle accidents. factors affecting pedestrian and non-motor vehicle accidents also had different orders of importance. the authors used data from 1,227 traffic crashes in which pedestrians and drivers of non-motor vehicles were victims in shenyang between 2015 and 2017. administrative division, age, and season were the most common influencing factors. for pedestrian accidents, the season was the most important influencing factor, whereas for non-motor vehicle accidents, the administrative division was the most important influencing factor. authors in [19] published an article about public health issues connected to road traffic crashes. the study analyzed the factors that contribute to road traffic crashes and made some recommendations. ii. methodology a. study area and data collection cyprus is an island situated in the eastern basin of the mediterranean sea [20]. north cyprus amounts to around one third of the island, and is divided into six districts: nicosia, famagusta, kyrenia, morphou, trikomo, and lefka [21]. official statistics books were used to determine the actual number of accidents, number of injured people and number of fatalities. additionally, a survey was conducted via google forms to obtain the thoughts of the local community regarding rtas. the survey included personal information, trip characteristics, and suggested accident reasons. the evaluation of the survey results and then the compiled official data are presented in this research paper. at the end of the study, the compatibility between public opinion and the actual data is presented. b. questionnaire design the survey was conducted using an online method and questions were asked to members of the local community including pedestrians, passengers, and drivers. a total of 114 people participated in the survey. three different groups of questions were included in the survey, which included personal information, daily trip characteristics and causes of rtas above. the first two sections of the survey include short answers or multiple-choice type questions. the third part of the survey asked the respondents to state the degree of impact (1=no impact, 2=impact, 3=great impact) of the rta causes. the last part of the survey is divided into four sections, namely human factors, vehicle factors, road factors, and environmental factors. each section has its own specific questions. participants were asked to choose the most appropriate impact factor based on their aspects. c. personal information the personal information section is the first step of the survey. it includes questions about age, gender, job, education level, and workplace location. the respondents were in different age categories. the youngest respondents were 19 years old, and the oldest was 69 years old. the majority of the respondents were 22 years old (9.50%). on the other hand, in terms of the gender of the participants, 68.80% of the respondents were males and 31.20% of them were females. the respondents were from different occupational fields and educational levels. the last question of the personal information part is about the workplace location. this question is a multiple-choice question with the possible choices of nicosia, famagusta, kyrenia, morphou, trikomo, or lefka, and not towns or villages. although the majority of the participants worked in nicosia, people who worked in other cities also participated in the survey, except for trikomo, see figure 1. therefore, the opinions of people working in different districts were obtained through this study. d. trip characteristics this section includes workdays per week, time taken to drive to the workplace, and driving experience. each participant wrote his/her own answers. afterwards, all the provided responses were reviewed and clarified with the engineering, technology & applied science research vol. 11, no. 6, 2021, 7938-7943 7940 www.etasr.com angın & albrka ali: analysis of factors affecting road traffic accidents in north cyprus following distributions. the majority of the respondents stated that they worked 5 days per week with a ratio of 45.20%. this may be a sign that many of the participants constantly encounter traffic. the second question of the trip characteristics was about trip time. it was a short-answer type of question. thus, each person wrote a different duration. according to the responses, the maximum duration was seven and a half hours and the minimum was a minute. in the last part of the trip characteristics section, the driving experience of the respondents was examined. the driving experience distribution of the respondents is shown in figure 2. workplace distribution of the respondents. fig. 1. driving experience distribution of the respondents. fig. 2. e. road traffic accident causes this part of the survey is directly related to the detection of the causes of rtas. the survey participants chose the impact factor that suited their views. each cause has three different types of options, namely no impact, impact, and great impact, as mentioned in the questionnaire section. the first part of this subsection is about human factors, which includes negligent driving, drunk driving, inexperienced drivers, over-speeding, driving while sleepless and tired, and using a mobile phone while driving. all these reasons were considered to be risk factors that may cause rtas and were regarded by the respondents as having a significant impact on rtas. it should be noted that this category achieved the highest vote ratio. the distribution of these reasons is shown in figure 3. negligent driving has the highest percentage with 80.20%. therefore, this demonstrates the awareness among the local community about the risks of negligent driving effect in terms of crashes. despite negligent driving having the highest percentage, over-speeding, and using a mobile phone while driving have an effect on rtas. over-speeding was selected by 78% and using a mobile phone while driving was chosen by 76.6% of the respondents with regard to having a significant impact. furthermore, drunk driving and driving while sleepless or tired worsened the human-induced risk factors on rtas. the effect of inexperience on road traffic accidents received the least percentage. human factors distribution of the respondents. fig. 3. the second part of the causes of the accidents in the survey considers vehicle factors. those factors include bad tire usage, insufficient lighting, breakdown of engines, breakdown of gearboxes, and poor brakes. three types of impact factors were observed for different reasons in this section. figure 4 describes the moderate impact distribution of bad tyre usage and insufficient lighting. the bad tire usage had the highest percentage with 50%. on the other hand, insufficient lighting had a moderate impact on rtas with 44.1%. moderate impact vehicle factors. fig. 4. no impact vehicle factors. fig. 5. furthermore, the breakdown of engines and gearboxes were considered to be factors that have no impact on rtas according to the results. the results displayed in figure 5 show engineering, technology & applied science research vol. 11, no. 6, 2021, 7938-7943 7941 www.etasr.com angın & albrka ali: analysis of factors affecting road traffic accidents in north cyprus the distribution of these factors. the breakdown of gearboxes has the highest percentage with 50.50% while the breakdown of engines received 50% with regard to having no impact. lastly, poor brakes was the only factor that had a great impact for vehicles in rtas according to the survey with a percentage 42.70%. the third part of the survey was based on road factors. the great impact choice was selected for all the reasons. poor road surface, poor road lighting, poor road signing, speed humps and roadway geometry, are included in this part. with 68.50%, poor road lighting had the highest impact percentage among these reasons. the distribution of the answers is shown in figure 6. the last part of the survey is concerned with environmental factors. the participants were asked about the impact degree of slick road surfaces and weather conditions. according to the results, slick road surfaces have a great impact with 49.10% and weather conditions have a moderate impact with 50%. distribution of road factors. fig. 6. f. road traffic accident data in this section of the study, the actual data of the north cyprus collected via official statistics are presented. the data period is from 2007 to 2018. the official accident reasons are presented to be compared with the survey outcomes. regarding the data, the number of rtas, number of fatalities and injuries were obtained. most of the traffic accidents occurred in 2008, whereas most of the fatal accidents and most injuries happened in 2012, as shown in figures 7 and 8. there are fluctuations across the time period. number of rtas and injuries between 2007-2018. fig. 7. figures 9-11 exhibit all the factors that contributed to rtas in north cyprus with consideration of the actual data of the 2007 2018 period. negligent driving, speeding, and drunk driving are dominant factor, as were and in the survey part of the study. figures 8-10 also show the striking effect of lack of compliance with traffic signs and not keeping a safe distance while driving on rtas. number of fatalities between 2007-2018. fig. 8. accident reasons between 2007-2010. fig. 9. accident reasons between 2011-2014. fig. 10. engineering, technology & applied science research vol. 11, no. 6, 2021, 7938-7943 7942 www.etasr.com angın & albrka ali: analysis of factors affecting road traffic accidents in north cyprus accident reasons between 2015-2018. fig. 11. iii. discussion and conclusions the current study explores different factors to determine the reasons for rtas in north cyprus. the necessary information was obtained by conducting an online survey and researching official statistics. as a result of the evaluation of these two sources, the main risks that cause rtas have been identified. the fact that the statistical data and the results of the survey are in accordance shows the awareness of the local community about rtas. in addition, this situation increases the reliability of the study. the opinions of 114 respondents who answered the survey's questions were presented with charts. human and road factors are the primary reasons for rtas based on the conducted online survey. human factors such as negligent driving, over-speeding, and using a mobile phone while driving were selected as primary. other factors like poor road surface and poor road lighting are seen as the most important road factors. furthermore, poor brakes under vehicle factors and slick roads under environmental factors were evaluated as the main causes of rtas in north cyprus. according to the recorded data, rtas increased in 2018 compared to 2007, and the number of accidents causing injuries and fatalities decreased. when we examine the distribution of accident causes in the graphs, we see that the major factors that cause accidents are negligent driving, noncompliance with traffic signs, over speeding and not keeping a safe distance while driving. when both aspects are examined, it is observed that negligent driving and over-speeding, are common. these are the main factors that cause rtas in north cyprus. the results of this study can be used by policy makers to ensure traffic safety. based on the study findings, the following conclusions can be made: • human factors are the major causes of rtas. • consistency of the survey and real data has been observed. negligent driving and over speeding were major reasons in both parts of the research. thus, the main causes of traffic accidents in north cyprus are negligent driving and over speeding. • vehicle factors have 3 types of impact factors on rtas based on the conducted survey result. • road factors have a great impact on the rtas from the perspective of the north cyprus society. • environmental factors have great or moderate impact on rtas from the perspective of the local public. • the number of rtas increases continuously since 2014. • there was a decrease in rta-related fatalities and injuries in 2018 compared to 2007 in north cyprus. • this study could be used for developing new mitigation strategies about rtas in north cyprus. these strategies can achieve success via education, awareness, and engineering solutions. references [1] global status report on road safety 2018. geneva, switzerland: world health organization, 2018. 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[online]. available: https://en.wikipedia.org/w/index.php?title=cyprus&oldid= 1053625350. engineering, technology & applied science research vol. 8, no. 3, 2018, 2887-2891 2887 www.etasr.com gmati and amiri: a global online handwriting recognition approach based on frequent patterns a global online handwriting recognition approach based on frequent patterns chekib gmati lr-siti laboratory national engineering school of tunis el manar university tunis, tunisia chekibgmt2007@gmail.com hamid amiri lr-siti laboratory national engineering school of tunis el manar university tunis, tunisia hamidlamiri@gmail.com abstract—in this article, the handwriting signals are represented based on geometric and spatio-temporal characteristics to increase the feature vectors relevance of each object. the main goal was to extract features in the form of a numeric vector based on the extraction of frequent patterns. we used two types of frequent motifs (closed frequent patterns and maximal frequent patterns) that can represent handwritten characters pertinently. these common features patterns are generated from a raw data transformation method to achieve high relevance. a database of words consisting of two different letters was created. the proposed application gives promising results and highlights the advantages that frequent pattern extraction algorithms can achieve, as well as the central role played by the “minimum threshold” parameter in the overall description of the characters. keywords-frequent features; mining frequent patterns; spatiotemporal relations; minimum threshold; online handwriting recognition i. introduction the performance of the online handwriting recognition process is considered as an important characteristic in mobile devices [1]. further, it could be a source of interesting information in several scientific fields. indeed, in the field of medical data processing, a lot of tests have been done concerning the analysis of the muscular and neurological assessment of patients [2], such as the analysis of the relationship between learning motor skills, handwriting and reading [3]. other research focuses on the detection of alcohol intoxication [4] or the analysis of the writing performance of dysgraphic children [5], biometrics, graphology, etc. technological developments used in the conception of electrical devices like tablets, mobile phones and touchsensitive notebooks demonstrate the need of human interactions using handwriting recognition algorithms [6, 7]. the online handwriting signal is a trajectory of a pen and could be represented by a sequence of coordinates of points ordered in time. this description of the signal highlights the spatiotemporal aspect and the intervention of the writer. indeed, the variability of the writing by the same or several writers leads us to think extracting invariant and relevant characteristics that neglect parasitic and useless data. in this sense, a uniform description seems to be ideal to achieve this objective. however, in case of a signal carrying temporal information through sequential points, an elementary modeling is essential. afterward, we pass from an elementary modeling to a global description through the extraction of frequent features. ii. recognition system architecture online handwriting recognition is a four step process (figure 1): online acquisition of the signal from an input device, pre-processing, primitives extraction and finally classification and recognition. the key step in this process is feature extraction. the nature of the handwriting is simply a temporal sampling applied to the incoming signal during the movement of the stylus tip on a touch screen; the result is a sequence of coordinates (x, y) of points. fig. 1. the handwriting recognition process. these points cannot be equidistant because the speed varies during writing. their positions and the relationships that may exist between them depend on the movements of the writer. between the sampling frequency and the writer's movement, several points will be recorded and can be considered as outliers in relation to all the points representing the object. moreover, pre-processing (raw data normalization and smoothing) is essential in solving this problem. actually, this step prepares the data in an adequate way and makes them appropriate for the rest of the process. unnecessary and duplicated pixels as well as small arcs and hooks and all data that can represent noise, are eliminated. then the character can be resized and centered to finalize the normalization phase. in addition, interpolation is used to recover missing pixels and detect sharp points to complete the relevant characteristics of the character. these techniques are further investigated in [810]. however, authors do not take into account the case where engineering, technology & applied science research vol. 8, no. 3, 2018, 2887-2891 2888 www.etasr.com gmati and amiri: a global online handwriting recognition approach based on frequent patterns some brackets and other delated data in the preprocessing step may belong to the specific characteristics of the character. indeed, the writer can add to the object ligatures and brackets that will be considered as part of the model of the character and therefore they can contribute to the overall recognition process. before starting feature extraction, a segmentation step is applied to contribute directly in the modeling of the signal. in [11], authors presented a method to modify the dispersion of the points on the trajectory which tends to be concentrated on the areas where the speed of writing decreases. this is done based on spatial frequency analysis. authors in [12] proposed a segmentation method that is however found unable to divide connected objects. authors in [13] helped to address this difficulty by introducing the freeman's coding, and by referring to the connection points as two opposing strokes. but this method is not applicable on complicated objects that we may encounter in online handwriting. on the other hand, several approaches adopt the segmentation-recognition method to solve the problem of handwriting online recognition [14]. several approaches have been proposed in the literature based on online segments to extract satisfactory structural characteristics [15, 16]. geometric feature extraction methods are applied such as line segment directions, line length [17], line order, spatial relationship between strokes, distances between consecutive points [18], tangents [19] and connection angles [20, 21]. authors in [22] proposed an approach based on delaunay triangles to describe the line segments. this makes it possible to select more “significant” groups (i.e. triangles) to represent the global characteristics and to use the temporal and topological characteristics of the handwritten forms. other approaches are based on the freeman code to code the direction of writing. an approach proposed in [21] is based on the levenshtein distance computation. the characteristics are generated from a quantization of the contour. this quantification takes place in 8 zones with respect to the center of the character. it will then cover 360 degrees around the center. the contour will be coded according to this quantization method, and then two features will be added to the generated code chain. the first characteristic represents the value of the horizontal distance between the coordinate x of a point at time t and the coordinate of the starting point, respectively. the second characteristic represents the value of the vertical distance between the coordinate y from the same point at time t and the coordinate of the starting point. relations between two points on the contour, distant in time, can be considered as characteristic, which would be added to the characteristic vector in relevance [22]. feature extraction is a crucial step in the recognition process as it directly affects the efficiency of classification algorithms. several classification methods have been proposed for online handwriting recognition such as neural networks, fuzzy logic, hidden markov models (hmm), etc. [23]. hmm is a very popular classification method in online handwriting recognition systems. in [25], authors used an ergodic standard model with finite explicit statements (dhmm) for recognition of arabic characters online. each character is represented by a sequence of radial distances, and then a time distribution matrix in each state is defined. state duration modeling by dhmm improved discrimination by up to 12% compared to conventional hmms. the disadvantages of hmm lie in the huge learning time and computing cost. a comparative study was carried out in [26] between hmm and svm, a new feature extraction method based on the discrete wavelet transform. the results showed a very low learning time when using svm compared to that of hmm. authors of [27] used a bayesian network algorithm for learning and adopted an approach based on positional relationships between strokes. this induces a spatial dependence between strokes, which represents a much better characteristic than the geometric one, but it is not adopted for online recognition. the modeling is done based on a hierarchy of points and strokes. the relationships between strokes and between points are explicitly and statistically modeled. in [30], authors introduced a method based on grammars from a hierarchical structure of handwritten kanji characters and used the hmm approach in the same context [31]. the method proposed in [28] is a hybrid approach that combines hmm and multilayer perceptron neural networks. the input signal is segmented in a continuous line, a characteristic vector is generated by the multilayer perceptron neural network based on ten characteristics. this generated vector is better adapted for the hmm, the approach was applied on the adab database [29]. iii. frequent itemsets mining data mining is a technique that extracts frequent patterns and it is a step of knowledge discovery in databases (kdd). the purpose of this step is to analyze the raw data, to extract useful information and to help make decisions [17]. in the knowledge discovery process, we found several steps that are proportional to the steps present in the process of online handwriting recognition systems. the first step, called data selection, is to clean the data to improve its qualities. this improvement also concerns the modification of the data to make them suitable for data analysis [15, 16]. then, a cleaning step can be performed to eliminate redundancy, inconsistent or incorrect values. regarding the preprocessing step, it can be applied to prepare the data for a transformation step, in order to refine the data quality. after this, we reach the stage of data mining, this step is crucial, because the quality of the generated models directly affects the efficiency of the system and influences the final decision. fig. 2. kdd process. a. definition let i be a set of items i={i1 , i2 , i3 , …, im} and d a set of transactions d= {t1 , t2 , t3 , …, tn}, where m is the number of engineering, technology & applied science research vol. 8, no. 3, 2018, 2887-2891 2889 www.etasr.com gmati and amiri: a global online handwriting recognition approach based on frequent patterns all items and n is the number of all transactions. let x be another itemset of i, xi and t a transaction of d, with tx the set of transactions containing x [18]:  txdtt  /x   note that the support of x, supp(x), is only the ratio of the number of transactions containing x and the total number of all transactions in the database d. b. minimum threshold to be able to generate frequent itemsets, an essential parameter must be taken into account, it is a minimum threshold called minimum support and is named as minsupp. indeed, an itemset is defined to be frequent if: supp(x)  minsupp. c. anti-monotony the main property that allows an optimal pattern extraction is the property of anti-monotony. extraction techniques rely heavily on anti-monotonicity property to optimize extraction by reducing the number of items and candidates that are likely to be frequent [18]: let x’ and x’’ be two different itemsets, if x’  x’’ then supp(x’)  supp(x’’) . therefore, if x’ is not frequent then x’’ is not frequent. this property was very useful when generating frequent itemsets. we will present two methods of extraction of the frequent pattens, the frequent and closed itemsets and maximal itemsets:  closed patterns: a pattern x’ is defined as closed if no other pattern x’’ exist and has the same support of x’, with x’  x’’ [19].  maximal patterns: a pattern x’ is maximal if no other pattern x’’ exists and is frequent, with x’  x’’ [20]. iv. proposed method a. data selection and preprocessing we created a new dataset that contains the two characters. this dataset contains repetitive data that should be eliminated because it represents noise. saving the same coordinates of a point for multiple times can produce a noise. this is due to the phase shift which can occur between the speed of the writing and the recording or sampling frequency of the signal. on the other hand, we will not remove small hooks because we want to prove we can achieve a good recognition rate while reducing the preprocessing step. moreover, we want to prove that the characteristics relating to the sample still exist without eliminating strokes of the raw “form” of the character. besides, to be able to describe the signal, we segment the trajectory into elementary strokes. each of these elementary strokes is composed of 4 points in the chronological order of writing. b. extraction of frequent data in the feature extraction step, the goal is to achieve a relevant representation of the object. in our approach we aim at extracting the frequent data, which are therefore dominant, in each object class of the database. indeed, what we want to say is that we must extract the characteristics of the combination of all the letters of each word. this representation is interested in the relevant and discriminating part of all the data available in the class of each word, since there are several samples for each two-letter word. figure 3(b) shows the strokes that share common characteristics. in fact the most frequent, or dominant features, will be extracted from the base of the samples of the same word, but also from the word itself. (a) (b) fig. 3. (a) two-letter word: ‘ad’, (b) strokes that have common characteristics in a single word are surrounded by the same color. to apply the extraction of frequent patterns we must group the calculated characteristics into three classes. regarding major and minor axes, they will have the class “small”, “medium” and “large”. the directions will also have three classes: “up”, “down” and “horizontal”. similarly, for the positions of the elementary strokes, they will have the classes “right”, “left” and “continual”. these classes are retrieved by computing the threshold values delimiting the groups after applying a clustering algorithm (kmeans). thus, after the application of closed and maximal pattern extraction methods, we will obtain frequent itemsets of various sizes representing each object in the database. we must then normalize these vectors to obtain a matrix that we will compress to have a characteristic vector. we apply the standard deviation in a vertical manner to each matrix generated, i.e. according to the columns. v. results and interpretations the database of words we collected consists of several combinations of two latin letters. the input device that we used was a graphics tablet. recordings of the coordinates of touch points with the touch surface were performed every 10 milliseconds from the first pen-down. in tables i-iii, we present the characteristic and the classification algorithms that we used to test the relevance and efficiency of closed and maximal patterns in the description of objects bearing spatial and temporal information. we have varied the value of the minsupp to highlight the frequent itemsets from the point of view of relevance. in figures 4 and 5, we get a peak when minsupp is equal to 0.55 or 55%, i.e. that we have obtained frequent motives of more than 55% and more relevant to the data set. on the other hand, the use of a closed pattern extraction algorithm (charm) showed a better performance than that of the maximum pattern extraction algorithm (charm mfi). similarly for figures 6 and 7, we note that the recognition rates exceed the previous results with a minimum of 50%. the values of the minimum thresholds are very close (50% and 55%), which demonstrates the validity of our approach regarding the relevance of frequent characteristics engineering, technology & applied science research vol. 8, no. 3, 2018, 2887-2891 2890 www.etasr.com gmati and amiri: a global online handwriting recognition approach based on frequent patterns that can be discriminatory. moreover, closed patterns are more efficient than the maximal one; this is confirmed through the trend curves in the figures. table i. description of characteristics features description usefulness major and minor axes these are the values of the axes of an elliptical box applied to each elementary stroke. these values give us the characteristics of the elementary strokes at the length and curvature level. directions the direction relative to the vertical axis. we consider it a major feature position of elementary strokes this is the position of each elementary stroke compared to the preceding one. gives information on the orientation of writing while preserving invariance with respect to rotation and translation. table ii. correct classification rate (charm algorithm) threshold minsupp multilayer percerptron svm k-nearest neighbor naive bayes 0.20 70.620 50.340 63.630 54.540 0.25 68.530 57.340 65.730 57.340 0.30 74.120 62.230 69.930 57.340 0.35 76.920 65.730 67.123 64.330 0.40 71.320 63.630 66.433 66.430 0.45 75.520 69.230 65.734 67.830 0.50 79.020 62.930 79.021 62.230 0.55 69.230 73.420 63.630 71.320 0.60 73.020 60.130 65.030 60.130 0.65 65.030 53.850 60.830 50.340 table iii. correct classification rate (charm mfi algorithm) threshold minsupp multilayer percerptron svm k-nearest neighbor naive bayes 0.20 58.741 51.748 61.538 55.944 0.25 62.237 54.545 59.440 57.342 0.30 66.433 51.049 61.538 57.342 0.35 66.433 49.650 65.734 51.049 0.40 76.223 60.139 58.042 60.139 0.45 72.727 60.139 63.636 62.937 0.50 68.531 60.839 66.433 64.335 0.55 70.629 65.734 62.237 69.230 0.60 67.132 57.342 69.930 60.839 0.65 62.237 51.049 62.937 52.447 fig. 4. correct classidfication rate (naïve bayes algorithm). fig. 5. correct classidfication rate (svm algorithm). fig. 6. correct classidfication rate (multilayer perceptron algorithm). fig. 7. correct classidfication rate (k-nearest neighbor algorithm). increasing the value of the minsupp, data will be overlooked. when we get a peak at 50% or 55%, we can deduce that the noisy data are eliminated. the curves show that we can find relevant characteristics at values lower than 50%. it is true that this is not very remarkable, but it draws our attention to the cause of this phenomenon. the variations that we observe in all the figures show that there is an overlap between the discriminating characteristics and the characteristics that represent noise, and also show that the closed frequent motifs are more relevant because there is no loss in the generation of these patterns. we think the purpose of our proposed work is achieved, but these points need to be improved: engineering, technology & applied science research vol. 8, no. 3, 2018, 2887-2891 2891 www.etasr.com gmati and amiri: a global online handwriting recognition approach based on frequent patterns  to make the size of the elementary stroke adapted to the size of the object in a number of points to guarantee invariance in the case where the samples vary in size.  compression performed at frequent patterns by applying the standard deviation may not be sufficient to preserve the useful information that the frequent patterns generated. vi. conclusions through our approach, we generate characteristic vectors that contain dominant elements based on frequent pattern extraction algorithms. it has been proved that frequent closed patterns are more relevant with a minimum threshold value of 50% and 55%. the overall representation we have obtained can be remarkably improved if we focus on data fusion methods to preserve the useful information we have extracted. we noticed that the larger the database we have, the more the frequent patterns are discriminating. thus, we are planning to prepare a massive database for handwritten character recognition online. besides, we find that we need to introduce sequential pattern extraction algorithms to take advantage of temporal information that can be modeled through these algorithms. references [1] i. degtyarenko, o. radyvonenko, k. bokhan, v. khomenko, “text/shape classifier for mobile applications with handwriting input”, international journal on document analysis and recognition, vol. 19, no. 4, pp. 369-379, 2016 [2] n. dounskaia, a. w. van gemmert, b. c. leis, g. e. stelmach, “biased wrist and finger coordination in parkinsonian patients during performance of graphical tasks”, neuropsychologia, vol. 47, no. 12, pp. 2504-2514, 2009 [3] m. s. julius, r. meir, z. shechter-nissim, e. adi-japha, “children's ability to learn a motor skill is related to handwriting and reading proficiency”, learning and individual differences, vol. 51, pp. 265-272, 2016 [4] j. shin, t. okuyama, “detection of alcohol intoxication via online handwritten signature verification”, pattern recognition letters , vol. 35, pp. 101–104, 2014 [5] v. paz-villagrán, j. danna, j.-l. velay, “lifts and stops in proficient and dysgraphic handwriting”, human movement science, vol. 33, pp. 381-394, 2014 [6] t. deselaers, d. keysers, j. hosang, h. a. rowley, “gyropen: gyroscopes for pen-input with mobile phones”, ieee transactions on human-machine systems, vol. 45, no. 2, pp. 263-271, 2015 [7] m. young, the technical writer’s handbook. mill valley, ca: university science, 1989 [8] b. q. huang, y. b. zhang, m. t. kechadi, “preprocessing techniques for online handwriting recognition”, seventh international conference on intelligent systems design and applications (isda 2007), rio de janeiro, brazil, pp. 793-800, october 20-24, 2007 [9] m. a. abuzaraida, a. m. zeki, a. m. zeki, “online recognition system for handwritten hindi digits based on matching alignment algorithm”, 3rd international conference on advanced computer science applications and technologies, amman, jordan, pp. 168-171, december 29-30, 2014 [10] m. e. mustafa, h. a. a. alshafy, “characters' boundaries based segmentation for online arabic handwriting”, international conference on computing, electrical and electronic engineering (icceee), khartoum, sudan, pp. 306-310, august 26-28, 2013 [11] c. de stefano, m. garruto, a. marcelli, “a multiresolution approach to on-line handwriting segmentation and feature extraction”, ieee 17th international conference on pattern recognition (icpr 2004), vol. 2, pp. 614-617, 2004 [12] y. jiang, x. wang, x. ao, g. dai, “online recognition of handwritten chemical formula”, 2nd joint conference on harmonious human machine environment. hangzhou, china, pp. 111-115, 2006 [13] l. zhao, h. yan, g. shi, j. yang, “segmentation of connected symbols in online handwritten chemical formulas”, international conference on system science, engineering design and manufacturing informatization (icsem), yichang, china, pp. 278-281, november 12-14, 2010 [14] m. cheriet, n. kharma, c. liu, c. suen, character recognition systems: a guide for students and practitioners, john wiley & sons, 2007 [15] o. maimon, l. rokach, data mining and knowledge discovery handbook, springer science+business media, inc, 2005 [16] u. m. fayyad, g. piatetsky-shapiro, p. smyth, r. uthurusamy advances in knowledge discovery and data mining, aaai press, 1996 [17] s. mitra, t. acharya, data mining multimedia, soft computing and bioinformatics, john wiley & sons, 2003 [18] r. agrawal, t. imielinski, a. swami, “mining association rules between sets of items in large databases”, in: sigmod '93: proceedings of the 1993 acm sigmod international conference on management of data, pp. 207-216, acm, 1993 [19] m. j. zaki, c.-j. hsiao, “charm: an efficient algorithm for closed itemset mining”, in: 2002 siam international conference on data mining, pp. 457-473, siam, 2002 [20] l. szathmary, “symbolic data mining methods with the coron platform”, phd thesis, henri poincaré university, 2002 [21] s. dutta chowdhury, u. bhattacharya, s. k. parui, “online handwriting recognition using levenshtein distance metric”, 12th international conference on document analysis and recognition, washington dc, usa, august 25-28, 2013 [22] m. mori, s. uchida, h. sakano, “global feature for online character recognition”, pattern recognition letters, vol. 35, pp. 142-148, 2013 [23] s. dewangan, p. k. gupta, u. k. sahu, i. k. verma, “realtime recognition of handwritten words using hidden markov model”, international journal of technological synthesis and analysis, vol. 1, no. 1, pp. 7-9, 2012 [24] v. vuori, m. aksela, j. laaksonen, e. oja, “on-line recognition of handwritten characters”, in: biennial report, laboratory of computer and information science, neural networks research centre, helsinki university of technology, 2003 [25] n. b. amara, a. belaïd, n. ellouze, “utilisation des modèles markoviens en reconnaissance de l'écriture arabe : état de l'art”, colloque international francophone sur l'ecrit et le document cifed'00, lyon, france, july, 2000 [26] k. p. primekumar, s. m. idiculla, “on-line malayalam handwritten character recognition using hmm and svm”, international conference on signal processing, image processing and pattern recognition (icsipr), coimbatore, india, february 7-8, 2013 [27] s.-j. cho, j. h. kim, “a bayesian network approach for on-line handwriting recognition”, in: digital document processing. advances in pattern recognition, pp. 121-141, 2007 [28] n. tagougui, h. boubaker, m. kherallah, a. m. alimi, “a hybrid mlpnn/hmm recognition system for online arabic handwritten script”, world congress on computer and information technology (wccit), sousse, tunisia, june 22-24, 2013 [29] h. el abed, m. kherallah, v. margner, a. m. alimi, “on-line arabic handwriting recognition competition: adab database and participating systems”, international journal on document analysis and recognition, vol. 14, no. 1, pp. 15-23, 2011 [30] i. ota, r. yamamoto, s. sako, s. sagayama,“on-line handwritten kanji recognition based on inter-stroke grammar”, ieee 9th international conference on document analysis and recognition (icdar 2007), vol. 2, pp. 1188-1192, 2007 [31] f. alvaro, j.-a. sanchez, j.-m. benedí, “recognition of on-line handwritten mathematical expressions using 2d stochastic context-free grammars and hidden markov models”, pattern recognition letters, vol. 35, pp. 58-67, 2014 microsoft word 5-706.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1062-1066 1062 www.etasr.com matin: identifying the effective factors for cost overrun and time delay in water construction … identifying the effective factors for cost overrun and time delay in water construction projects danial mirzai matin sharif university of technology, international campus kish, iran danial.mrzmtn@hotmail.com abstract—water construction projects in iran frequently face problems which cause cost overrun and time delay, the two most common issues in construction projects in general. the objective of this survey is to identify and quantify these problems and thus help in avoiding them. this survey represents a collection of the most significant problems found in the literature, classified into 11 groups according to their source. the questionnaire form used contains 84 questions which were answered by random engineers who work in water construction projects. the relative importance weight (riw) method is used to weight the importance of each one of the 84 problems. the focus of this survey is on overall top ten issues which are: bureaucracy in bidding method, inflation, economical condition of the government, not enough information gathered and surveys done before design, monthly payment difficulties, material cost changes, law changes by the government, financial difficulties, mode of financing and payment for completed work and changes made by the owner. a section for each of these issues provides additional information about them. in the full text of this survey the same weighting method is used to classify the main groups, and the results show that issues related to the groups of government, owner and consultant has the most significant impact. the last part of this survey describes the point of view of the engineers who took part in this survey and the recommendations they made. keywords-construction projects; water construction projects; iran construction projects; time delay; cost overrun i. introduction project success can be defined by achieving successful technical performance, staying on planned schedule and not exceeding the initial budget or the anticipated time. in lots of construction projects across the world especially in the developing countries, most of the projects participants cannot reach their goal as finishing the project on time and without additional cost. delay in time and cost overrun are the two most common issues that occur in a construction project. however, cost overrun is more common than time delay. it should be noted that time delay can have a different impact on the contractor and the owner, from losing money to losing other projects due to the delay. delivering without additional time or cost depends on many factors such as personnel performance, owner, contractor, consultant, labors and design team, availability of material and other sources, contractual relations and etc. project management techniques play an important role in having a complete organized project which covers managing the materials, people, machinery, budget and methods used. this study, investigates factors that affect the time and cost in water construction projects specifically in iran by the means of identifying and ranking them according to their importance. the outcome can help all practitioners to develop a more complete view of the factors causing cost overrun and time delay for constructing water projects, and provide guidance and some recommendations for efficient solution for construction managers. ii. aim and objectives the objectives of this work is an attempt to show the common causes of delay and cost overrun in construction projects in developing countries and identify and examine these factors according to engineers that participate in water construction projects in iran. to summarize the main objectives of this survey: • to study the factors that developing countries other than iran, face in construction projects (especially water construction projects) • to identify the main issues that influence the time and cost schedule of water construction projects in iran • to examine the importance of the studied issues • to identify which group is more responsible about delay and overrun in a given project • to give some information and recommendation about the top ten of this list iii. literature reviews because of the nature of groundwater projects the main factors for time delay and cost overrun are generally the following: • bad planning that causes poor technical performance • not enough procurement procedures. engineering, technology & applied science research vol. 6, no. 4, 2016, 1062-1066 1063 www.etasr.com matin: identifying the effective factors for cost overrun and time delay in water construction … • schedule not updated frequently • not enough attention to resources allocation (human, financial and material resources) • lack of management experience from contractors • financial difficulties (owner/contractor) • design changes literature reviews are selected from countries which are somehow similar to iran in terms of weather, geographical location or being a developing country. the considered countries are nigeria, ghana, saudi arabia, vietnam and pakistan. a. nigeria [1] a problem that surfaces is that most of the projects are given to the lowest bidder and lots of these bidders have a lack of experience in management and neglect the importance of contractor’s plan, cost control and site management. an added reasoning in [1] is that many contractors are entrepreneurs who are in business of making money instead of good management. material procurement and poor technical support are two other top-ranked problems in [1]. b. ghana [2, 3]. the information for the study in ghana was collected by questionnaire from three groups: 1. owners as key decision-makers 2. consultants from groundwater projects 3. contractors from drilling projects results show that there are several factors that may cause cost overrun and time delay. the top five of these factors which are agreed between owners, consultants and contractors can be name as monthly payment difficulties from agencies, poor contractor management, material procurement, poor technical performance and change in the price rate of material. however, there are some disagreements between owners, contractors and consultants in the rankings. for example contractors and consultants are unhappy with the monthly payments (but not the owners). another example of this disagreement can be the poor contract management according to the study of university of sydney [2]. the lack of experience is also hinted in this case. in addition to what mentioned above, weather and geological factors are also mentioned, as the main interest in ghana is on groundwater construction projects. c. saudi arabia [4] saudi arabia was able to deliver only 31 out of 76 projects on scheduled time in the water and sewage section between 1985 and 1994. the first thing that should be considered in sewage projects is that most of these projects are in urban areas so special adjustments and safety activities should be considered. in this case, the main problems are the size of the project and finding the best bidder. in large projects, delay should be considered more possible. most of the responsibilities of delays in construction projects fall on the contractors, thus finding the best bidder for a project surfaces as an important factor. the solution of the government of saudi arabia is to divide the contractors into five different groups considering their abilities and size and then allow contractors only from specific groups (i.e. with certain background) to bid on certain projects. d. vietnam [5-6] vietnam raised its activities in the field of construction management since 2000. vietnam has similar weather condition to ghana (high temperature, heavy tropical rain which causes problems in the speed of the workers and material and machinery delivery). in addition, vietnam as a country which has the history of great wars faces some not so ordinary problems, as unknown facilities and unknown war equipment may be found in construction areas. e. pakistan [7-8] pakistan is considered mainly regarding two dam projects (kuram tangi and demer-bahshi). in the first case, the delay caused by changing the design of this project (increasing the height and width of the dam) caused a significant increase in the cost of the project. in the second case, due to government delays there was also a significant additional cost. iv. factors to avoid delay a list of factors that can help minimize the project delays according to [9] is given below: 1. continuous meeting between different groups of a construction project 2. using reasonably modern equipment 3. proper material procurement 4. sufficient and clear information 5. keeping the record of every project’s issues v. research methodology a list of 84 issues which are more common and repeated throughout the considered cases (and iran) are collected to make a questionnaire form. a total number of 55 people asked to fill the questionnaire forms were random engineers involved in iranian construction companies that have experience in water construction projects as consultants, contractors or owners. analysis was made and recommendations to help minimizing delay and cost overrun are given according to the top 10 issues. vi. questionnaire design the questionnaire of this survey contains 84 issues which are found repeated, important and common in such projects. these issues are classified into 11 groups which are project (problems that can refer to more than one groups), owner, contractor, consultant, design team, material, equipment, labor, land/weather, government and extra issues (accidents, cultural and social). each engineer was asked to rank the issues engineering, technology & applied science research vol. 6, no. 4, 2016, 1062-1066 1064 www.etasr.com matin: identifying the effective factors for cost overrun and time delay in water construction … according to the frequency and importance from very low to very high (very lowlowmediumhighvery high). vii. data analysis method the method used in analyzing the results of the questionnaire forms is the relative importance weight (riw). this method is used to show the importance of each factor by weighting them with the means of summing up the scores that each person gave to the issues. every single issue can be ranked between very low to very high (very low, low, medium, high, and very high). relative importance weight (riw) equation is: 100 . 1 5 1      n j j i ii x na riw where ai refers to the coefficient of each answer (a1=1 for “very low” to a5=5 for “very high”) and ni refers to the number of responses for each score (n1=1 for “very low” to n5=5 for “very high. n refers to the number of issues which is 84 in this project. j refers to the issue number (1, 2, 3… n). xj refers to the summation of all the answers to issue number j. in the full text of this survey this method has been used to rank all 84 problems, classify them in each group and at last analyzing the importance of each group. viii. findings and results the results are shown in table i. the overall results show the top 10 most important issues in water construction projects in iran: 1. bureaucracy in bidding methods (owner): iran like lots of over countries has the problems of finding the best contractor. in iran there are 3 ways of choosing a contractor: • public tender: for small projects advertisement is given to the television and newspaper to inform the contractors of the project • restricted tender: a list of trusted and qualified contracted is prepared by the owner and they will be contacted to be informed and the winner will be the lowest bidder • no bidding: in most of the large construction projects there will be no bidding procedure and the project goes to a known and accepted contractor 2. inflation (government): inflation has a serious impact on employment, when the inflation rate is high companies have to reduce the number of their workers and thus the quality of their works [10]. the inflation in iran has a couple of big changes from 1980 till this day due to the oil shock in middle east in 1985 and 1986, the great war against iraq for 8 years from 1980 and implementing the economic reform program between 1989-1993. in 1995 the inflation in iran reached 49.5% which was the highest recorded and the rate of inflation is now twice as it was in 2010 (almost 25% ) [11]. 3. economical condition of the government (government): iran has the government as the major owner of big construction projects and when the government faces economical problem this affects these construction projects. 4. not enough surveys and information done and collected before the beginning (design team): in a high-populated country like iran the speed of work is important so unfortunately some design teams only do preliminary survey on the site. this lack of time for proper survey is able to cause further problems in the project. 5. monthly payment difficulties (owner): because of the economical problems in iran contractors are not sure that they will be paid on schedule so they ask their money for watch section beforehand. this may cause problems since an inability of the owner to make these payments will result to contractors being less motivated to complete their task with the best quality and at exact time. 6. inconstancy of the price of the materials (material): due to the fast change of exchange rates, preparing the proper material for a big construction site may be tricky and any change in the rates can result to a project costing way more than its original budget. 7. changes in the government laws (government): such changes is usually to compensate the damage and delay (mostly beneficial but not always). 8. financial difficulties (contractors): contractors poor management causes them financial problems which force them to work non-constructional on the side to compensate. 9. mode of financing the project and the disbursement for the completed project: most of the owners try to stay in the zone of their anticipated budget and most of the time it is possible to pay the debt to the contractor from it. 10. changes that is done by the owner in the middle of project process (owner): according to what mentioned in number 4 of the issues design problems may force the owner to take some new decisions and this may take significant time. the same weighting method is used to pin point the groups that are more responsible for these issues (table ii). based on the information gathered from engineers, issues related to the government are labeled as the most significant for time delay and cost overrun in water construction projects in iran, followed by the owner and consultants groups. ix. conclusion this report investigates the problems related to water construction projects in iran through the use of a questionnaire designed for this project which includes 84 problems divided into 11 groups according to their source. the impact of each issue was ranked from “very low” to “very high”. in the last section of questionnaire form an space was given for additional ideas. these questionnaires were filled by random engineers who had a background in water construction projects in iran. engineering, technology & applied science research vol. 6, no. 4, 2016, 1062-1066 1065 www.etasr.com matin: identifying the effective factors for cost overrun and time delay in water construction … similar problems from countries somehow similar to iran were considered to form the questionnaire. the questionnaire form results were scored by the relative importance weight method which shows the importance of each issue according to their weight. comparing the results leads the reader to the top issues in water construction projects in iran in the view of iranian engineers. top overall issues are: bureaucracy in bidding method, inflation, governments economical condition, not enough survey and information before design, difficulties in owners’ monthly payment, instability of the material prices, change in government laws, financial difficulties, mode of financing and order changes by the owner. in general, preventing ideas and considerations found on other countries are: holding continuous meetings between members, using best equipment and methods, avoid using insufficient and unclear methods, using information and educated guesses for the exact time and cost of a project. the last preventing activity can be considered to be record keeping (keeping records of previous similar projects issues and considering them in new projects). table i. riw of issues in water construction projects in iran issues riw issues riw bureaucracy in bidding method 5.1 high cost of maintenance of machinery 3.459 inflation 4.947 low level of efficiency from the equipment 3.459 economical condition of the government 4.947 mistakes and reworks wanted for them during construction 3.437 not enough information collected and surveys done before design 4.422 lack of sufficient contact between consultant and other groups 3.437 monthly payment difficulties 4.356 low level of experience in design team 3.415 inconstancy of the price of materials 4.356 effect of hot/cold weather on the construction and the materials 3.415 changes in the laws provided by the government 4.356 disagreement between consultant and design team 3.393 financial difficulties 4.334 domination of construction industry by foreign firms and aids 3.393 mode of financing and payment for completed work 4.312 high number of public holidays (negative effect on incentives for contractor for finishing on time) 3.371 sudden order change by owner during construction (incessant variation order) 4.268 wrong consideration about the owners requirements 3.349 poor contract management 4.225 lack of variety of materials in market 3.327 poor supervision on the site 4.225 traffic facilities 3.262 insufficient scheduling of project by contractor 4.203 shortage of technical and qualified personnel 3.196 low-speed decision making process 4.115 taxes on the construction utility and equipment (electricity, water, telephone, etc.) 3.196 delay in decision making for deciding the final materials selected of many available types 4.072 suspension 3.174 delay in delivering the site to contractor 4.049 shortage of equipment 3.174 problems in sub-contractors schedule for finishing the project 4.028 low level of qualification and technical staff 3.13 not having enough experience by consultant 4.028 high cost of the qualified personnel 3.13 delay in accepting and performing the changes in the scope of the project by consultant 3.984 effect of subsurface condition 3.13 unstable cost and delay in preparing special materials 3.962 sub-contractor delay work 3.087 delay in delivering the imported materials 3.919 effect of precipitation on the construction activities 3.065 rigidity of consultant (not able to be flexible) 3.875 third party final inspection and certification delay by a third party 3.065 delay in producing and completing the design documents 3.875 ground problems 3.021 contrast and poor communication between contractor and consultant/owner 3.831 delay in site mobilization 2.977 late preparation of the materials 3.809 unexpected geological condition/ natural disaster 2.977 poor communication and coordination with other parties 3.787 waste on site 2.955 lack of proper mechanical equipment/machinery 3.765 domination of construction industry by foreign firms and aids 2.933 unclear information on the drawings 3.743 materials damage on the site while they are needed 2.89 unsuitable methods for construction 3.7 sub-contractor change (cause of insufficient work) 2.846 inadequate contractor work/ low bid 3.7 lack of harmony between contractor and sub-contractor 2.824 interest rate changes (on the loans from banks) 3.7 accidents during construction 2.824 short contract duration 3.699 machinery breakdown 2.758 having complexity in the documents 3.656 ineffective delay penalties 2.736 high transportation costs 3.656 not using the best proper software in design 2.736 delay in reviewing and accepting the design documents 3.634 need of import because of lack of raw materials in country 2.715 late action in inspection and testing by consultant 3.634 level of creativity of the labors 2.583 delay in gaining the needed permissions from municipality 3.612 nationality of the labors 2.561 contrast between joint-ownership of the project 3.568 delay in providing the utilities on the site 2.496 change of the types of selected materials during the construction 3.503 late revision of the documents and approving them 2.473 lack of skilled people in using the equipment 3.503 legal argument between different parts 2.408 delay in accepting the materials and drawings 3.502 contrast between technical person and labors 2.408 change in the documents because of mistake 3.459 unavailability of utilities 2.255 engineering, technology & applied science research vol. 6, no. 4, 2016, 1062-1066 1066 www.etasr.com matin: identifying the effective factors for cost overrun and time delay in water construction … table ii. ranking of responsible groups for issues groups riw government 336.666 owner 331.911 consultant 309.114 material 302.851 design team 297.500 contractor 295.84 project 274.429 equipment 269.772 additional 267.272 weather and land 258.333 labor 231.386 x. views and recommendations considering the point of view of the engineers, the most significant points are discussed below along with a proposal to overcome each one. in the full text of this report 9 more views and recommendations are given. 1. choosing the bidding winner in water construction project is not as easy as other construction projects due to the size issue. most of very large sized projects are given to big contractors and consultants. however, the bidding methods are limited because of the financial and inflation status and trust issues arise. proposal: lowest and highest bidders may be neglected and the bidding winner can be chosen from the remaining bidders. 2. inflation is the main cause of material and equipment costs rises. proposal: the government (the most usual customer) may compensate the contractor by adjusting the price lists. 3. economic problems in 3rd world countries. proposal: the contractors should follow the government directives about changing prices 4. hastiness is one of the major problems for the design teams at the start of the project.. proposal: the project should be divided into a couple of sections and when a section is under construction the next phase is studied. 5. monthly payments due to economic problems has an impact on most of the projects as contractors usually do not risk their assets to provide further finance in a given month (when needed) and that reduces the overall speed of the process. proposal: the length of the contract may be extended in such cases but no compensation should be given. 6. material cost change is possible in countries with unstable economic conditions. a change the material cost will change the whole project cost estimation. proposal: there are a couple of solutions for this matter: cutting cost of smaller projects to obtain the budget for the bigger and more important ones and collect all the needed material before implementation. further, it is sometimes more advantageous for the owner to start its own factory for producing the needed material and machinery (tehran water agencies and gilan water agencies use this method). 7. changes in country laws mostly happen due to government changing, which are considered to compensate the damages or delays. these changes are mostly beneficial, but not all of them. contractors’ financial problems, mostly due to their poor management or economical conditions. this has led the contractors to work on other projects (non-constructional) to compensate. staying in the zone of budget estimation is important for the owners. proposal: the owner keeps 10% of each section of the contractors work as a guarantee that the project will be done according to the estimated time and cost. references [1] s. o. ogunlana, p. o. olomolaiye, “a survey of site management practice on some selected sites in nigeria”, building and environment, vol. 24, no. 2, pp.191-196, 1989 [2] y. frimpong, project management in developing countries: causes of delay and cost overruns in construction of groundwater projects, masters research project, university of technology, sydney, australia. 2000 [3] y. frimpong, j. oluwoye, l. crawford, “causes of delay and cost overruns in construction of groundwater projects in a developing countries; ghana as a case study”. international journal of project management, vol. 21, no. 5, pp. 321-326, 2003 [4] m. i. al-khalil, a. a. mohammed "delay in public utility projects in saudi arabia." international journal of project management, vol. 17, no. 2, pp. 101-106, 1999 [5] l. le-hoai, y. dai lee, j. y. lee, “delay and cost overruns in vietnam large construction projects: a comparison with other selected countries”, ksce journal of civil engineering, vol. 12, no. 6, pp. 367-377, 2008 [6] s. a. assaf, s. al-hejji, “causes of delay in large construction projects”, international journal of project management, vol. 24, no. 4, pp. 349-357. 2006 [7] wapda, kurram tangi dam project, available at: http://www.wapda.gov.pk/index.php/projects/water-sector/future/ kurram-tangi-dam [8] wapda, diamer bhasha dam, available at: http://www.wapda.gov.pk/index.php/projects/hydro-power/on-going/ diamer-basha-dam [9] cousins business law, 5 methods for resolving construction disputes, available at: https://www.business-lawfirm.co.uk/blog/5-methods-forresolving-construction-disputes.aspx [10] h. armesh, h. salarzehi, n. mohammad, “causes of inflation in the iranian economy”, international review of business research papers, vol. 6, no. 3, pp. 30-44. 2010 [11] indexmundi.com iran inflation rate (consumer prices) economy. 2012. engineering, technology & applied science research vol. 8, no. 2, 2018, 2685-2688 2685 www.etasr.com sohu et al.: determining the critical success factors for highway construction projects in pakistan determining the critical success factors for highway construction projects in pakistan samiullah sohu department of civil engineering quaid-e-awam university college of engineering, science & technology larkano, sindh, pakistan sohoosamiullah@gmail.com ashfaque ahmed jhatial department of civil engineering mehran university of engineering and technology, szab campus khairpur mirs, sindh, pakistan aajhatial@hotmail.com kaleem ullah faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia gf150051@siswa.uthm.edu.my muhammad tahir lakhiar faculty of civil and environmental engineering universiti tun hussein onn malaysia parit raja, johor, malaysia gf170030@siswa.uthm.edu.my jam shahzaib department of civil engineering quaid-e-awam university college of engineering science & technology larkano, sindh, pakistan jam_shahzaib@hotmail.com abstract—the success of construction projects is not only crucial to stakeholders but also for the country’s economic and social development. critical success factors (csfs) are considered as key to project management practices wich can lead to a construction project success. the aim of this research is to determine and rank the csfs of highway construction projects in pakistan. a deep literature review was carried out to determine a set of csfs for construction projects. after that, a questionnaire based on found csfs was designed and distributed among construction experts working in highway construction projects of pakistan. out of 250 distributed questionnaires, 130 were received completed and validated. gathered data was analyzed through statistical software spss, and critical success factors were ranked based on their mean value. as a result, experienced project management team, effective site management, commitment of all parties to the project, experienced design team, and proper project planning have been determined as the top five critical success factors for highway projects in pakistan. the findings of this research would help construction practitioners in understanding csfs and to improve project performance. keywords-critical; success; factors; highway; construction; projects; pakistan i. introduction a vibrant construction industry plays a vital role in the economic growth and social development of any country. however, due to its complex nature and other uncertainties, construction projects are experiencing several problems and the highway projects of pakistan are no exception. for productive construction industry, project success is essential [1]. project success can also be defined as “when a project achieves more results than the excepted or normally obtained in terms of quality standards, cost, time, and safety measures” [1]. a construction project is considered successful when the project is completed on schedule time, within planned budget and satisfying quality standards [2]. there are many factors which influence the project performance and can lead to construction project success. according to [3] there are certain factors which are more important than others and are called “critical success factors”. author in [4] used the term critical success factors (csfs) in projects management perspective for the first time and defined it as “csfs are the few main areas of activity in which auspicious results are definitely compulsory for a particular manager to reach his or her goals”. csfs directly affect the main parameters which measures project success i.e. cost, time, quality and safety. authors in [5] state that csfs are helpful in productive decision making. thus, determining and ranking of csfs of construction project is important. the aim of this research is to determine and rank csfs of highway construction projects. most construction projects including highways projects in pakistan are facing problems of delay [6, 7], cost overrun [8, 9], quality [10] and failure in safety performance [11]. this research has focused csfs of highway construction projects in pakistan. the results of this research can influence success of highway construction projects. ii. objectives 1) to determine csfs of highway construction projects in pakistan. 2) to rank csfs of highway construction projects applying their mean values. iii. literature review in previous researches, a number of factors influencing the success of the construction projects project were identified. engineering, technology & applied science research vol. 8, no. 2, 2018, 2685-2688 2686 www.etasr.com sohu et al.: determining the critical success factors for highway construction projects in pakistan authors in [12] studied the csfs of construction projects in thailand. a questionnaire based on csfs grouped into nine categories was distributed among construction practitioners. the survey results showed that proficiency of project management team, proper quality control, good relationship among project members, regular maintenance of equipment required for the project, capable supervisors, effective communication among project stakeholders, and durability of the completed work were the most csfs in each category. authors in [13] investigated the csfs of public-private partnership highway project in malaysia. the study was carried out through conducting interviews with ten public sector clients working in highways projects and through a real case study of highway project. the top five csfs were effective communication, proper project planning and commitment from public and private sectors, fair procurement process and potential to delegate authority. authors in [14] discussed the csfs for construction projects in iran. a literature based questionnaire was designed. questionnaire was prepared with respect to project success criteria measures i.e. time, cost, quality and safety and was distributed to construction experts. the findings of the study showed that efficient project planning, allocating suitable finance, multidisciplinary project team, adequacy of resources required for project, effective project monitoring, qualified and experienced project management team, tender awarded to competent contractors, the urgency of completing the project, correct and reliable estimates of project costs, clear contracts and project goals, and support from senior management of the project were the dominant csfs. another research in iran [15], found that availability of resources, skilled project management team, strategic project planning, on-time decision making, and effective project monitoring were the top csfs for construction projects. in libya, authors in [16] investigated the most csfs of construction projects. the research was conducted through quantitative approach by distributing questionnaires in construction professionals from both public and private sector. research concluded that efficient project monitoring, effective coordination, timely decision making, proper site management, and experienced design team are the main factors influencing project success. author in [17] obtained the csfs for large construction projects through conducting interviews with project managers from four nordic countries. the findings of the study showed that experienced project management team, availability of resources, and effective communication were main csfs of large construction projects. authors in [18] studied csfs for public private projects in uk construction industry using a questionnaire survey comprised of 18 csfs. factor analysis revealed that strong private consortium, proper risk allocation and risk sharing, availability of finance, commitment of both public/private sectors, and competitive procurement process are the main csfs. authors in [3] studied construction csfs in pakistan by applying a quantitative approach. the main csfs were proper communication system, effectiveness of decision making, experienced project management team, skillful contractors, effective supervision, and proper planning. from the literature review the following csfs were identified: experienced project management team, effective site management, effective communication and coordination, commitment of all parties to the project, on time decision making, good relationship among project participants, experienced design team, availability of resources required for project, effective quality control system, adequacy of raw materials, allocating appropriate funds, availability of equipment, capable supervisors, experienced sub-contractors, use of environment friendly equipment, support from senior management, implementation of safety management system, regular equipment maintenance, utilization of advanced technology, clear project goals, proper project planning, competitive procurement process, multidisciplinary project team, and correct estimation of project cost. iv. research method in this research both literature review and field survey were used to gather data. literature review resulted in the identification of 24 csfs. a questionnaire containing these 24 csfs was design, consisting of two parts. part a aimed to know the demography of survey participants while part b aimed to get the perception of construction professionals on csfs for highway projects in pakistan. five-point likerd scale was used to assess the csfs from 1 for “not significant” to 5 for “extremely significant”. before the questionnaire survey, content analysis of the designed questionnaire was carried out. for content analysis the questionnaire was checked with five construction experts of highway projects. the experts were asked whether csfs given in the questionnaire were relevant to highway projects or not. according to them, all proposed csfs provided were relevant. after content analysis the questionnaire was disturbed to 250 construction professionals of highway projects in pakistan. v. data analysis and discussion a total of 130 completed questionnaires were collected, showing a response rate of 52%. respondents of the questionnaire survey were from different organization backgrounds. figure 1 shows the results of the survey participants based on their organizations. the majority of the survey respondents are from clients (50) followed by contractors (44). only 28% of the survey respondents were from the consultants group. respondents experience and educational level are important aspects in questionnaire survey. figure 2 shows the academic qualification of the exports participated in the surrey. a large number of participants (i.e. 70 of 130) have obtained bachelor degree. thirty-five respondents of the survey had master’s degree and twenty-five 25 had diploma degree. overall survey respondents had sufficient education level. apart from education level, experience of the respondents in highway projects is vital in deciding the critical success factors for highway projects. figure 3 shows the experience of survey participants in highway projects. collected data were analyzed using spss. cronbach’s alpha was used to measure the internal consistency, to know how well the items in the questionnaire are correlated to each other. it is suggested that cronbach’s alpha value is strong if more than or equal to 0.7 [19]. the cronbach’s alpha of this research is 0.785, showing acceptable internal consistency of the survey instrument. the critical success factors were ranked based on their mean value. csf ranking engineering, technology & applied science research vol. 8, no. 2, 2018, 2685-2688 2687 www.etasr.com sohu et al.: determining the critical success factors for highway construction projects in pakistan enabled the identification of the main csfs of highway projects in pakistan. table i shows the ranking of the csfs of highway projects in pakistan. fig. 1. type of respondents’ organization fig. 2. respedents’ academic qualification fig. 3. respondent’s experience table i. csfs ranking critical success factors mean value ranking experienced project management team 4.54 1 effective site management 4.50 2 commitment of all parties to the project 4.46 3 experienced design team 4.31 4 proper project planning 4.25 5 effective communication and coordination 4.19 6 allocating appropriate funds 4.10 7 equipment availability 3.94 8 effective quality control system 3.92 9 availability of resources 3.90 10 implementation of safety management system 3.83 11 experienced sub-contractors 3.82 12 adequacy of raw materials 3.59 13 capable supervisors 3.57 14 competitive procurement process 3.54 15 good relationship among project participants 3.52 16 on time decision making 3.50 17 multidisciplinary project team 3.48 18 correct estimate of project cost 3.46 19 clear project goals 3.45 20 support from senior management 3.32 21 utilization of advanced technology 3.25 22 use of environment friendly equipment 3.21 23 regular equipment maintenance 3.14 24 table i shows respondents ranked the “experienced project management team” as the most significant with mean value of 4.50. experienced project management team is key to project success. effective site management ranked 2nd, followed by “commitment from all participants of project” with mean scores 4.50 and 4.46 respectively. the respondents ranked “experienced design team” as fourth significant csf. design team plays an important role as their work involves from beginning to completion on a project. competent designers can influence success of construction projects. utilization of advanced technology, use of environment friendly equipment, and regular equipment maintenance ranked next. vi. conclusion the quality completion of highway construction projects within cost and time is the top priority for the stakeholders. in this research, csfs of highway projects have been studied. the most important csfs found to be experienced project management, effective site management, commitment of all parties to the project. the scope of this research is limited to highway projects in pakistan. the results of this research can contribute construction professionals to achieve successful projects. references [1] n. ramlee, n. j. tammy, r. m. noor, a. a. musir, n. a. karim, h. b. chan, s. r. m. nasir, “critical success factors for construction project”, aip conference proceedings, vol. 1774, no.1, pp. 030011-1030011-7, 2016 [2] a. p. c. chan, d. scott, e. w. m. lam, “framework of success criteria for design/build projects”, journal of management in engineering, vol. 18, pp. 120–128, 2002 engineering, technology & applied science research vol. 8, no. 2, 2018, 2685-2688 2688 www.etasr.com sohu et al.: determining the critical success factors for highway construction projects in pakistan [3] m. saqib, r. u. farooqui, s. h. lodi, “assessment of critical success factors for construction projects in pakistan”, first international conference on construction in developing countries, karachi, pakistan, pp. 392–404, august 4-5, 2008 [4] j. f. rockart, “the changing role of the information systems executive: a critical success factors perspective”, sloan management review, vol. 24, no. 1, pp. 3–13, 1982 [5] z. alias, e. m. a. zawawi, k. yusof, a. abra, “determining critical success factors of project management practice: a conceptual framework”, procedia-social and behavioral sciences, vol. 153, pp. 61– 69, 2014 [6] s. sohu, n. a. memon, s. a. abbasi, m. a. pahore, k. ullah, “causes of delay in highway projects in pakistan”, 8th international civil engineering congress, karachi, pakistan, pp. 35–40, december 23-24, 2016 [7] s. haq y. rashid, m. s. aslam, “effects of delay in construction projects of punjab-pakistan : an empirical study”, journal of basic and applied scientific research, vol. 4, no. 4, pp. 98–104, 2014 [8] i. zafar, t. yousaf, s. ahmed, “evaluation of risk factors causing cost overrun in road projects in terrorism affected areas pakistan–a case study”, ksce journal of civil engineering, vol. 20, no. 5, pp. 1613– 1620, 2016 [9] a. r. nasir, h. f. gabriel, r. m. choudhry, “cost and time overruns in highway projects of pakistan”, sixth international conference on construction in the 21st century, kuala lumpur, malaysia, pp. 69–76, 2011 [10] m. abas, s. b. khattak, i. hussain, s. maqsood, i. ahmad, “construction projects evaluation of factors affecting the quality of construction projects”, technical journal, university of engineering and technology, vol. 20, no. 2, pp. 115–120, 2015 [11] r. farooqui, f. arif, s. f. a. rafeeqi, “safety performance in construction industry of pakistan”, first international conference on construction in developing countries, karachi, pakistan, pp. 74–87, august 4-5, 2008 [12] s. homthong, w. moungnoi, “critical success factors influencing construction project performance for different objectives: operation and maintenance phase”, international journal of advances in mechanical and civil engineering, vol. 3, no. 3, pp. 84–95, 2016 [13] f. e. m. ghazali, s. a. rashid, a. m. sadullah, “the critical success factors for public-private partnership highway construction project in malaysia”. journal of engineering and technology, vol. 8, no. 1, pp. 69–84, 2017 [14] a. i. maghsoodi, m. khalilzadeh, “identification and evaluation of construction projects ’ critical success factors employing fuzzytopsis approach”, ksce journal of civil engineering, pp. 1–13, 2017 [15] a. pakseresht, “determining the critical success factors in construction projects: ahp approach”, interdisciplinary journal of contemporary research in business, vol. 4, no. 8, pp. 383–393, 2012 [16] a. omran, m. a. abdulbagei, a. o. gebril, “an evaluation of the critical success factors for construction projects in libya”, journal of economic behavior, vol. 2, pp. 17–25, 2012 [17] h. szentes, “success factors in large construction projects”, proceedings of tg65 and w065-special track. 18th cib world building congress, pp. 423–433, 2010 [18] b. li, a. akintoye, p. j. edwards, c. hardcastle, “critical success factors for ppp / pfi projects in the uk construction industry”, construction management and economics, vol. 23, no. 5, pp. 37–41, 2005 [19] m. s. litwin, a. fink, how to measure survey reliability and validity, thousand oaks, sage, 1995 engineering, technology & applied science research vol. 7, no. 3, 2017, 1719-1724 1719 www.etasr.com soliman and karia: antecedents for the success of the adoption of organizational erp among higher … antecedents for the success of the adoption of organizational erp among higher education institutions and competitive advantage in egypt mohamed soliman operations department, school of management universiti sains malaysia, usm, malaysia, 11800 usm penang, malaysia soliman2002s@yahoo.com noorliza karia operations department, school of management universiti sains malaysia, usm, malaysia, 11800 usm penang, malaysia noorliza@usm.my abstract-although the enterprise resource planning (erp) system has long been acknowledged in higher education institutions (heis) to improve their performance and efficiency, there are not many heis in egypt that adopt erp system and those that do are in an early stage. the research on erp system in hei is still limited and in the immature stage, hence little is known about the success factors for the adoption stage of erp systems. consequently, this article aims to understand what are the success factors for erp adoption and further develop a conceptual model that explains the successful implementation of erp in heis and its impact on competitive advantage. based on previous studies, this paper identifies and conceptualizes success factors for erp and further develops the proposed model for the adoption of erp system in heis. this article contributes to the development of the theoretical framework of the successful implementation of the erp system to explain the competitive advantage of hei by merging information system (is) success and diffusion of innovation (doi) theories with the success factors for the adoption stage of erp systems. the current study will provide recommendations and guidelines for both the potential adopters and the vendors on the successful erp system adoption. keywords-adoption; enterprise resource planning; is success model; doi; erp; heis; critical success factors; competitive advantage; higher education; egypt i. introduction the adoption of the erp system in universities was intended to create progressive levels of efficiency and performance so that colleges, departments, and schools can improve on their education and research at a low or practical cost [3]. the erp system is defined as the innovative technology within the heis due to its benefits [4]. due to substantial benefits of the erp system, several universities have allocated an investment of more than five billion dollars for the system [5]. however, some erp projects might have some flaws due to the complexity of the implementation process, the misfit between erp system and organizational business processes, the lack of skilled human capital, crossfunctional coordination issues, inappropriate planning and project management, and incompetent consultants [6]. all the listed reasons for the flaws confirmed that it is essential to have a deep understanding on the innovation process in the effort to achieve the success in erp projects [7]. furthermore, most of the erp literature reviews concentrated on the implementation phase such as the implementation of csfs to erp in particular [8, 9]. this trend has resulted in a relatively limited understanding of the other stages of erp innovation process such as adoption, use, and retirement [10]. hence, it is important to avoid this “one size fit all” approach and any conceptual that overlap between the implementation and other stages of the erp innovation process [11]. the adoption stage is the decision-making stage in the innovation process [1]. therefore, a great understanding of csfs relating to the adoption stage enable the organizations to save on the costs and time, as well as diminishing the risks of any failures by creating an ideal environment and adequately preparing themselves [12]. due to the limited research on csfs relating to erp adoption, the first objective of this research is to close the gap by determining the factors that are critical to the success of adoption phase. there are limited studies conducted on erp settings in egyptian universities. in a recent research, the result indicates that the erp implementation success rate is relatively poor in the egypt organizations compared to the western organizations [13]. the same author also reported that nearly 50 per cent of the erp implementation failed in egyptian enterprises. consequently, the second objective of this research is to investigate the factors that can influence the adoption success of erp in egyptian organizations, especially in heis. as a result, this research aims to construct a research model by extending the most popular is success theory [14] with doi theory [1] and some independent csfs. within the egyptian context, there are not many studies done that examine the determining factors of erp adoption among heis. the literature revealed that the application of erp system in egypt focuses on two phases: pre-implementation and engineering, technology & applied science research vol. 7, no. 3, 2017, 1719-1724 1720 www.etasr.com soliman and karia: antecedents for the success of the adoption of organizational erp among higher … implementation [15, 16]. in [17], authors clarified that the higher education sector in egypt is enormous and includes public, private, and foreign universities, besides institutions of technical and skilled training. there are a lot of problems that occurred in the higher education institutions, and the erp system can emphatically contribute to the changes, as well as diminishing the impacts of these issues. however, the total utilization of erp has not been embraced by the largest sector of heis in egypt. in conclusion, this research is among the few research that focus on the determinants of erp adoption in the higher education sector in egypt. this research will answer three research questions: 1) how can is success model, doi theory, and csfs be utilised for the success of the adoption of erp among heis in egypt? 2) to what extent can is success model, doi theory, and csfs influence the success of the adoption of erp among heis in egypt? 3) what is the factor that can influence the success of the adoption of erp among heis in egypt? ii. theoretical background a. previous studies on is success model in [14], authors posited that system quality and information quality have the ability to jointly and separately affect the use and users’ satisfaction, which can have resulted in individual impact and subsequent organizational impacts. further research on this model had led to the addition of dimensions such as service quality, intention to use, and net benefits (replacing organization impact construct) [18]. many erp studies incorporated this is success model to measure the success, performance, and net benefits of erp adoption and implementation [19-26]. b. previous studies on diffusion of innovation (doi) theory in [1], the innovation process was defined in terms of individual and organizational lenses by focusing on the attributes that can affect the process. it was explained that the innovation process within the organization comprised of five stages: two-stage of initiation sub-process, namely agendasetting and matching; and three-stage implementation subprocess, namely redefining/restructuring, clarifying and routinizing. these innovation models have been tested in crossdisciplinary contexts. many scholars have also presented updates, extensions, and revisions relating this model. doi model was termed as being too formulaic and lacking in realism [27]. given the scope of this research, the authors employed the doi theory as it has the ability to achieve the objectives of the research. c. critical success factors csfs in [28], authors developed the concept of csfs as “characteristics, conditions, or variables that when properly sustained, maintained, or managed, can have a significant impact on the success of a firm that is competing in a particular industry”. the current research adopts this view and definition as its fundamental concept. the determination of csfs is vital to organizations as it is used to constantly and sufficiently focus on activities in the already identified key areas or identify key areas in achieving improvements of the performance [11]. the csfs are assumed to provide a positive and beneficial effect on the outcome; thus, knowing a greater number of csfs pertaining to a specific innovation process has been considered as critical to the success of the process [29]. despite the fact that csfs are linked to the performance impacts of the firms, there is still a very significant gap in the literature in terms of understanding the true role of csfs. generally, the previous studies on csfs seemed to conceptualize them as an independent object that is relevant to a certain process. the investigations were done without examining the importance of csf on performance improvements. this situation requires further examination of the role of csfs in their interactive effect on performance improvements of the firms [11]. iii. research model and hypotheses there is the lack of research effort in linking the is success model and doi theory with the independent csfs. several studies were done to prove the significant impact of the broader concept of technology adoption. therefore, one of the contributions of this research is to cover the gap in the literature by linking these theories and examining the impact of the factors on the success of erp adoption among heis in egypt. this research also investigates the attributes that are critical to the adoption of erp and their effect on competitive advantage. consistent with the broad category of attributes that was identified in the is success theory, this research uses innovation related, organizational and is success related factors to create a hypothetical model as shown in figure 1. fig. 1. proposed research framework a. perceived information quality the information quality within any information system is referred to the measures of its output, and it has been measured engineering, technology & applied science research vol. 7, no. 3, 2017, 1719-1724 1721 www.etasr.com soliman and karia: antecedents for the success of the adoption of organizational erp among higher … in terms of accuracy, output precision, output reliability, information timeliness, information relevance on decisions, completeness, format, and understanding ability and many more [18, 30]. information quality has been found to be positively linked to user satisfaction [30]. this shows that erp information quality is critical to the success of adoption of the system. additionally, erp system is recognized to provide reliable, accurate, and timely information. hence, it is confirmed that the quality of erp’s perceived information is a positive contributing factor towards the decision of adoption.  h1: the erp’s ability to provide quality information can positively influence the success of erp adoption among heis. b. perceived system quality according to [18], system quality dimension has been found to be one of the most important enablers of is success. system quality has been measured in many ways, including convenience of access, integration capabilities, reliability, ease of learning, resource utilization, investment utilization, flexibility of the system, response time, and usefulness of specific function. [18, 30]. it is also perceived as a key factor for erp implementation besides being positively associated with user satisfaction [30]. the erp system is supposed to provide integration, flexibility, and optimum resource utilization, which can lead to high system quality. thus, the erp’s capabilities in system quality is an important factor that can affect the success of adoption among heis.  h2: the erp’s ability to provide system quality can positively influence the success of erp adoption among heis. c. perceived service quality a revised model was provided in [2] by adding a service quality dimension to the model due to the fact that this dimension can capture the quality of services that a particular information system provides to an organization. moreover, it also integrates the individual impact and organizational impact dimensions into a new dimension called net benefits, besides adding the intention to use dimension. as a result, information systems can affect the individual user or the organization as well the work group, inter organizational units, intra organizational units, consumers, and society.  h3: the erp’s ability to provide quality service can positively influence the success of erp adoption among heis. d. organisational readiness in [31], authors defined organizational readiness as “the ability of a firm to successfully adopt, use, and benefit from information technologies”. earlier studies have used several measures to investigate readiness as the following: awareness of benefits and risks of innovation; availability of human resources skills and capabilities; availability of technological, business and financial resources, commitment and support by top management; fit between innovation and organizational structure; as well as goals and values of organization [31, 32]. based on the findings of the structural contingency theory of fit, [33] the assessment of ‘readiness’ for an organization to adopt a certain technology is an important criterion for the success of the implementation and performance impact. organizational readiness can positively impact the adoption of technological innovations [32]. hence, the internal organizational awareness is critical to the success of erp adoption.  h4: organisational readiness can positively influence the success of erp adoption among heis. e. perceived benefits the perceived erp benefits is referred to what extent can the new erp system provides more benefits than the conventional ones [34]. the importance of expected benefits in pre-adoption and post-adoption performance has been identified in technology research [35, 36]. moreover, many empirical studies have validated that positive perceptions of benefits or relative advantages of new information and communication technologies can drive an incentive for their acceptance and utilization [37, 38]. perceived benefits are one of key determinants of e-business technology adoption as it covers factors such as enhancing competitiveness of the firm [39], increasing efficiency and effectiveness of information flow [40], reducing operating cost of technology [41], and improving manufacturing flexibility, system integration and process innovation [42]. in addition, [43] indicated that firms that have greater perceived relative advantage of enterprise systems are predicted to become adopters of these systems. kim and garrison [44] revealed that perceived benefits of rfid have a significant role in its adoption and implementation in south korea. [45] and [46] they also validated that the expected benefit of e-business is a vital factor that shapes the e-business diffusion. previous argument mentioned that the potential benefits of new enterprise technology can motivate firms to increase their readiness level in implementing the technology.  h5: the expected erp benefits can positively influence the success of erp adoption among heis. f. top management support in [47], it was affirmed that the initial direction of a business in an erp initiative is to gain full commitment from senior executives. researchers often hypothesize that the attitude of the top management to change has a significant influence on the adoption outcomes [48]. the active involvement, vision, and direction of high-level executives can provide the drive needed to sustain the implementation of erp systems [49]. top management must direct strong signals to different parts of the organization on the significance of a project [50]. the support from the top management can lead to the realization of organizational benefits and provide credibility to the functional managers who are responsible for the implementation and use of erp [51].  h6: the degree of top management support on the adoption of erp system has a positive relationship with the success of erp adoption among heis. engineering, technology & applied science research vol. 7, no. 3, 2017, 1719-1724 1722 www.etasr.com soliman and karia: antecedents for the success of the adoption of organizational erp among higher … g. business process re-engineering the erp system is designed for best practices in specific industries [49]. nevertheless, this system may not be essentially fit for the operating practices in the institution. accordingly, the erp software package can either be customized to better fit a company’s needs or the company must change its business processes to adapt to the erp software package requirements [52]. most of erp experts confirmed that the customization of the erp software can lead to higher implementation costs and time consumption. therefore, companies should keep the erp package “as it is” as much as possible and re-engineer their business processes to conform to the package [53, 54]. an organization that reengineers processes to the best practices of erp will experience benefit as a result of the implementation. besides that, the organization will most likely to experience a smoother implementation of the system, which will maximize the stakeholder’s satisfaction.  h7: the degree of re-engineering to the best practices of erp system has a positive relationship with the success of erp adoption among heis. h. training it is important to give training to the users due to the inherent complexity of erp system [53]. one of the greatest advantages of erp is the integration of data, which can also be a double-edged sword when the system experienced any errors. an error in the upstream can instantly affect the flow down the line; consequently, the employees should be aware of these type of problems for any mistakes that can occur [55]. it is clearer that the training to the users of erp systems results in greater achievement in terms of organizational performance measures. moreover, the allocation of the essential resources for training can enhance the users’ satisfaction.  h8: the employees’ level of training on the erp system has a positive relationship with the success of erp adoption among heis. i. the success of erp adoption and competitive advantage (ca) in [56], authors reported that “a company achieves competitive advantage by implementing a value creating a strategy that is not being implemented by competing firms”. therefore, the adoption of strategic information system such as erp has been linked to achieving capabilities as the following: 1) agility in offering innovative products and services; 2) effective leveraging of resources; 3) raising entry barriers for new competitors; 4) achieving increased bargaining power with suppliers and customers; and 5) changing the dynamics of competition [57]. furthermore, heis can gain a competitive advantage through the adoption of erp system due to the higher quality of educational services for a lower cost; erp system can also enable them to effectively use their resources [58]. on the other hand, erp system might not provide a competitive advantage when directly adopted, although the information can be provided through faster processing of data and given the access at the right time [59]. there is a gap in the knowledge regarding how the adoption and implementation of erp system can contribute to competitive advantage, especially in the higher education sector, particularly in egypt.  h9: the success of erp adoption is positively linked to the competitive advantage for the heis. iv. discussion and conclusion to conclude, this research is designed to understand the success of the determinants of erp adoption among heis in egypt. also, it can contribute to the literature review of it adoption, erp and higher education by 1) improving our understanding on the adoption stage of erp within the higher education context unlike previous studies that examined erp adoption among other contexts, 2) identifying factors of the successful erp adoption among heis to gain a competitive advantage, and 3) extending the use of is success model, doi theory, and some csfs within erp adoption among heis. this contribution might eliminate or reduce the risk of failure, as well as improving the chances of success of their erp projects. moreover, this research also provides a better understanding of whether the csf’s role is limited to influencing the outcome of the relevant stage in an innovation process or also has the ability to influence the competitive advantage. practically, this research can help erp vendors to understand the needs of potential erp adopters, so that they can formulate their marketing and product development activities to increase their market share as well as adopting a new theoretical framework of ‘successful adoption’ of erp. however, this research has several limitations such as limited number of antecedents pertaining to erp adoption stage. hence, there is the need for future research in investigating more factors in order to get an agreeable set of csfs. the outcomes of this research are also limited due to the geographical focus on egyptian heis. overall, this research is important in helping heis to achieve competitive advantages through the adoption of erp. acknowledgement this research is supported by usm fellowship from institute of postgraduate studies (ips) in universiti sains malaysia (usm). the authors would like to thank the school of management for providing these facilities for this research. references [1] e. m. rogers, diffusion of innovations, 5th edition: free press, 2003. 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grover, "types of information technology capabilities and their role in competitive advantage: an empirical study”, journal of management information systems, vol. 22, pp. 253-277, 2005 [58] m. soliman, n. karia, "enterprise resource planning systems in higher education context: functionalities and characteristics”, international journal of innovative research in science, engineering and technology, vol. 4, pp. 10408-10413, 2015 [59] b. johansson, m. newman, "competitive advantage in the erp system's value-chain and its influence on future development”, enterprise information systems, vol. 4, pp. 79-93, 2010 microsoft word 04-swankar.doc etasr engineering, technology & applied science research vol. 1, �o.3, 2011, 70-75 70 www.etasr.com swarnkar et al: effect of adaptation gain in model reference adaptive controlled… effect of adaptation gain in model reference adaptive controlled second order system pankaj swarnkar dept of electrical engineering maulana azad national institute of technology bhopal, india shailendra jain dept of electrical engineering maulana azad national institute of technology bhopal, india r. k. nema dept of electrical engineering maulana azad national institute of technology bhopal, india abstract— adaptive control involves modifying the control law used by the controller to cope with the fact that the parameters of the system being controlled change drastically due to changes in environmental conditions or in system itself. this technique is based on the fundamental characteristic of adaptation of living organism. the adaptive control process is one that continuously and automatically measures the dynamic behavior of a plant, compares it with the desired output and uses the difference to vary adjustable system parameters or to generate an actuating signal in such a way so that optimal performance can be maintained regardless of system changes. the nature of the adaptation mechanism for controlling the system performance is greatly affected by the value of adaptation gain. it is observed that for the lower order systems, wide range of adaptation gain can be used to study the system’s performance. as the order of the system increases the applicable range of adaptation gain becomes narrow. this paper deals with application of model reference adaptive control (mrac) scheme to second order systems with different values of adaptation gain. the rule which is used for this application is the mit rule. simulation is done in matlab and simulink and the results are compared for varying adaptation mechanisms due to variation in adaptation gain. keywords- model reference adaptive control, mit rule, adaptation mechanism, adaptation gain i. introduction a control system is in the broadest sense, an interconnection of the physical components to provide a desired function, involving some type of control action with it. the requirement of high performance control systems for industrial applications has produced great research efforts for the application of modern control theory and, in particular, adaptive control. adaptive control is a rather recent class of control technique, although research in adaptive control has a long and vigorous history. in 1950s, it was motivated by the problem of designing autopilots for aircraft operating at wide range of speeds and altitudes. consequently, gain scheduling based on some auxiliary measurements of air speed was adapted. kalman [1] developed the concept of a general self tuning regulator with explicit identification of the parameters of a linear, single-input, single-output system and he used these parameters’ estimation to update an optimal linear quadratic controller, and other researchers (most significantly lyapunov and parks) further advanced the concept. nowadays the adaptive control schemes are making their place where the conventional control system is not able to cope-up with the situation, like: • loads, inertias and other forces acting on the system, change drastically. • possibility of unpredictable and sudden faults. • possibility of frequent or unanticipated disturbances. the conventional pid controllers with fixed gain are unable to cope up with the problems discussed above. however, advanced fuzzy pid controllers [2-9] have been recently developed to deal with such problems for electrical and mechanical systems. also the concept of neural network has been applied [10-12] in order to enhance the dynamic characteristics of the pid controllers. still, to obtain the complete adaptive nature, specific adaptive control techniques are needed. adaptive control changes the control algorithm coefficients in real time to compensate for variations in environment or in the system itself. it also varies the system transfer function according to situation. in practical cases, a model reference adaptive control system is generally best implemented with a digital computer, owing to the complexity of the controller. out of many adaptive control schemes, this paper mainly deals with the model reference adaptive control approach based on mit rule [13-17]. in mrac [13-24], the output response is forced to track the response of a reference model irrespective of plant parameter variations. the controller parameters are adjusted to give a desired closed-loop performance. here the controller parameters are estimated to cause the desired change in plant transfer function so that its performance can be made similar to the reference model. apart from the mit rule there are some other design techniques in model reference adaptive control system, like lyapunov theory [23-24] and the theory of augmented error [25]. in this paper the emphasis is given to mit rule only for developing the mrac scheme. the system response is calculated for different values of adaptation gain. ii. model reference adaptive control this technique of adaptive control falls under the category of non-dual adaptive control. a reference model describes the etasr engineering, technology & applied science research vol. 1, �o.3, 2011, 70-75 71 www.etasr.com swarnkar et al: effect of adaptation gain in model reference adaptive controlled… system’s performance. the adaptive controller is then designed to force the system (or plant) to behave like the reference model. model output is compared to the actual output, and the difference is used to adjust feedback controller parameters. mras has two loops: an inner loop (or regulator loop) that is an ordinary control loop consisting of the plant and the regulator, and an outer (or adaptation) loop that adjusts the parameters of the regulator in such a way as to drive the error between the model output and plant output to zero, as shown in figure 1. fig. 1. model reference adaptive controller iii. components of model reference adaptive controller reference model: it is used to specify the ideal response of the adaptive control system to external command. it should reflect the performance specifications in control tasks. the ideal behavior specified by the reference model should be achievable for the adaptive control system. in this paper the critically damped second order system is taken as the reference model. controller: it is usually parameterized by a number of adjustable parameters. in this paper, two parameters θ1 and θ2 are used to define the controller law. the control law is linear in terms of the adjustable parameters (linear parameterization). adaptive controller design normally requires linear parameterization in order to obtain adaptation mechanism with guaranteed stability and tracking convergence. the values of these control parameters are mainly dependent on adaptation gain which in turn changes the control algorithm of adaptation mechanism. adaptation mechanism: it is used to adjust the parameters in the control law. adaptation law searches for the parameters such that the response of the plant which should be same as the reference model. it is designed to guarantee the stability of the control system as well as conversance of tracking error to zero. mathematical techniques like mit rule, lyapunov theory and augmented error theory can be used to develop the adaptation mechanism. in this paper the mit rule is used for this purpose. iv. the mit rule this rule was developed in massachusetts institute of technology and is used to apply the mrac approach to any practical system. in this rule the cost function or loss function is defined as f (θ) = e 2 / 2 (1) where, e is the output error and is the difference of the output of the reference model and the actual model, while θ is the adjustable parameter known as the control parameter. in this rule the parameter θ is adjusted in such a way so that the loss function is minimized. therefore, it is reasonable to change the parameter in the direction of the negative gradient of f, that is: dθ/dt = γ ∂f / ∂θ (2) = γ e ∂e / ∂θ (3) the partial derivative term ∂e/ ∂θ, is called the sensitivity derivative of the system. this shows how the error is dependent on the adjustable parameter, θ. there are many alternatives to choose the loss function f. for example, it can also be taken as mode of error. similarly dθ/dt can also have different relations for different applications. sign-sign algorithm: dθ/dt = γ sign (∂e / ∂θ) sign e (4) or it may be chosen as : dθ/dt = γ (∂e / ∂θ) sign e (5) where sign e = 1 for e › 0 = 0 for e = 0 = -1 for e ‹ 0 in some industrial applications it is found that the choice of adaptation gain is critical and its value depends on the signal levels. so mit rule has to be modified as follows: dθ/dt = γ ζ e (6) where ζ = ∂e / ∂θ also dθ/dt = γ ζ e / (β + ζ t ζ) (7) where β › 0 is introduce to avoid the zero division when ζ t ζ is small. this paper uses the mit rule defined by equations (1), (2) and (3) for developing the control law. v. mathematical modelling in this paper model reference adaptive control scheme is applied to a second order system using mit rule. it is a well known fact that an under damped second order system is oscillatory in nature. if oscillations are not decaying in a limited time period then they may cause system instability. so, for stable operation, maximum overshoot must be as low as possible (ideally zero). this can automatically reduce the transient period of the system and improve the system’s performance. a critically damped second order system gives a characteristic without any oscillations and this characteristic is similar to the first order system. but it is not feasible to achieve such system practically. in this paper a second order under damped system with large settling time, very high maximum overshoot and with intolerable dynamic error is taken as a plant. the object is to improve the performance of this system by using adaptive control scheme. for this purpose, a critically adjustment mechanism plant controller reference model etasr engineering, technology & applied science research vol. 1, �o.3, 2011, 70-75 72 www.etasr.com swarnkar et al: effect of adaptation gain in model reference adaptive controlled… damped system is taken as the reference model. let the second order system be described by: d 2 y/dt 2 = -a (dy/dt) -by+ b u (8) let a=8 and b=600 where y is the output of plant (second order under damped system) and u is the controller output or manipulated variable. the transfer function can be written as: y(s)/u(s)=600/(s 2 +8s+600) (9) similarly the reference model is described by: d 2 ym/dt 2 = -am dym/dt bm ym + bm r (10) take am =8 and bm=16 where ym is the output of reference model (second order critically damped system) and r is the reference input (unit step input). the transfer function is written as: ym(s)/r(s)=16/(s 2 +8s+16) (11) here the object is to compare the actual output (y) and the reference output (ym) and, by applying model reference adaptive control scheme, to improve the overall output. let the controller be described by the law: u(t) = θ1 r(t) θ2 y(t) (12) the controller parameters are chosen as: θ1 = bm / b and θ2 = (ama) / b (13) the update rule for the controller parameters using mit rule is described by: dθ1/dt = γ e ∂e / ∂ θ1 =γ e [b r / (p + am)] =-α e[am r / (p + am)] (14) and dθ2/dt =α e [am y / (p+ am)] (15) where α = γ b/am is the adaptation gain and error e=yym. fig. 2. simulated model for mit rule vi. simulation and results in this paper the model reference adaptive control model is simulated in matlab and simulink. here the mit rule is applied to the second order system. the simulation model is shown in figure 2. the time response characteristics for the plant and the reference model are shown in figure 3, with out using any control technique. it can be observed that the characteristic of the plant is oscillatory with high value of overshoot and undershoot whereas the characteristic of the reference model is smooth without any oscillation. there is a large dynamic error between these two and this error has to be reduced to zero by using model reference adaptive control scheme. now if the adaptation gain (α) is varied in a range from 0.1 to 5 then according to equations (14) and (15) it changes the values of control parameters θ1 and θ2. figure 4 and figure 5 show the variation of control parameters with time for different values of adaptation gain. it can be seen from figure 4 and figure 5 that control parameters converge to a constant value in each case. now these values of control parameters are used to improve the plant parameters (a and b). etasr engineering, technology & applied science research vol. 1, �o.3, 2011, 70-75 73 www.etasr.com swarnkar et al: effect of adaptation gain in model reference adaptive controlled… 0 1 2 3 4 5 6 7 8 9 10 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 time o u tp u t ym y fig. 3. time response curve (without any control) 0 2 4 6 8 10 12 14 16 18 20 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 time c o n tr o l p a ra m e te r 1 alpha=0.1 alpha=1 alpha=2 alpha=5 fig. 4. variation of control parameter θ1 for different values of α 0 5 10 15 20 25 30 -0.35 -0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 time c o n tr o l p a ra m e te r 2 alpha=0.1 alpha=1 alpha=2 alpha=5 fig. 5. variation of control parameter θ2 for different values of α now by using equation (13) the estimated plant parameters come out to be b ’ = bm / θ1 and a ’ = am b ’ θ2 figure 6 shows the output characteristic (response curve) for the system with model reference adaptive control scheme. it can be seen that the characteristic of the plant has improved drastically. there is no oscillation in the system response. also the effect of adaptation gain is shown in figure 6. the better response can be achieved for the higher values of adaptation gain. the best result is obtained for α equal to 5, for the selected range of adaptation gain. finally the error curve is shown in figure 7. the dynamic error is reducing with the increment in adaptation gain. it implies that by mrac the plant output is following the desired output which was the main aim behind the control action. 0 1 2 3 4 5 6 7 8 9 10 0 0.2 0.4 0.6 0.8 1 1.2 1.4 time o u tp u t ym alpha=0.1 alpha=1 alpha=2 alpha=5 fig. 6. effect of α on time response characteristic 0 1 2 3 4 5 6 7 8 9 10 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 time e rr o r alpha=0.1 alpha=1 alpha=2 alpha=5 fig. 7. error versus time curve vi. conclusion as compared to conventional fixed gain controllers (pid controllers), the adaptive controllers are very effective to etasr engineering, technology & applied science research vol. 1, �o.3, 2011, 70-75 74 www.etasr.com swarnkar et al: effect of adaptation gain in model reference adaptive controlled… handle the situations where the parameter variations and environmental changes are frequent. this fact is demonstrated clearly in the results. also the use of pi control mainly improves the steady state performance by reducing the steady state error whereas pd controller improves the transient period by reducing the maximum overshoot. but in case of adaptive control the entire dynamic characteristic of the system is improved. here the controller parameters are adjusted to give a desired closed-loop performance throughout the working of the system. the adaptive controller maintains constant dynamic performance in the presence of unpredictable and immeasurable variations. application of mit rule in a model reference adaptive controller results clearly to an improvement in system’s performance. the tracking error is tending to zero and the performance of the actual plant is approaching the performance of the reference model. table i shows that without any control, plant performance was very poor with very high values of overshoot and undershoot. whereas the application of mrac by using mit rule reduces the values of overshoot and undershoot directly to zero. this paper mainly emphasis on the effect of adaptation gain on the system’s performance. table i shows that with the increment in adaptation gain the settling time is reducing. also the control parameters vary in the direction to improve the system performance with the increment in adaptation gain. but beyond the chosen range of adaptation gain (0.1< α < 5), system performance is very poor. the system may even become unstable for the wrong choice of adaptation gain. therefore, it is shown that for suitable values of adaptation gain, the mit rule can make the plant output as close as possible to the reference model in model reference adaptive control scheme. table i time response specifications with and without mrac for different adaptation gain with mrac without any control α = 0.1 α = 1 α = 2 α = 5 peak time (second) 0.135 0 0 0 0 maximum overshoot (%) 60% 0 0 0 0 undershoot (%) 34% 0 0 0 0 settling time (second) 1.7 28 4 3.6 2 θ1 ……. 0.722 0.8 0.832 0.86 θ2 …….. -0.227 -0.2 -0.168 -0.14 references [1] d. simon, “kalman filtering with state constraintsa survey of linear and nonlinear algorithm”, control theory and application, iet, vol. 4, no. 8, 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[2] rey-chue hwang, huang-chu huang, wei-shen chi, “a new fuzzy pid-like controller”, ieee international conference on systems, man and cybernetics, nashville, vol. 5, 2000. [3] k. s. tang, kim fung man, guanrong chen, sam kwong, “an optimal fuzzy pid controller”, ieee transactions on industrial electronics, vol. 48, no. 4, pp. 757-765, 2001. [4] k. l. lo and m. o. sadegh, “systematic method for the design of a full-scale fuzzy pid stability controller for svc to control power system”, ieee transaction on generation transmission and distribution vol. 150, no. 3, pp. 297 – 304, 2003. [5] e. m. jafarov, m. n. a. parlakçı, and y. istefanopulos, “a new variable structure pid-controller design for robot manipulators”, ieee transactions on control systems technology, vol. 13, no. 1, pp. 122 130 , 2005. [6] tae-yong choi, kap-ho seo, jin-ho shinü, ju-jang lee, “the hybrid sof-pid controller for a mimo nonlinear system”, proceedings of the 2005 ieee/asme, international conference on advanced intelligent mechatronics monterey, california, usa, pp. 825 830, 2005. [7] b. jia, g. ren, g. long, “design and stability analysis of fuzzy switching pid controller”, 6th world congress on intelligent control and automation, dalian, china, pp. 3934 3938, 2006. [8] a. rubaai, m. j. castro-sitiriche, a. ofoli, “dsp-based implementation of fuzzy-pid controller using genetic optimization for high performance motor drives”, ieee international conference on industry applications, new orleans, la, pp. 1649 – 1656, 2007. [9] a. rubaai, m. j. castro-sitiriche, a. ofoli, “dsp-based laboratory implementation of hybrid fuzzy-pid controller using genetic optimization for high-performance motor drives”, ieee transactions on industry applications, vol. 44, no. 6, pp. 1977 – 1986, 2008. 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[24] kuo-kai shyu, ming-ji yang, yen-mo chen, yi-fei lin, “model reference adaptive control design for a shunt active-power-filter system”, ieee transactions on industrial electronics, vol. 55, no. 1, pp. 97 – 106, 2008. [25] k. j. astrom, bjorn wittenmark, “adaptive control”, 2nd ed. pearson education asia, pp. 185-225, 2001. [26] pankaj swarnkar, “automatic control system”, 3 rd ed. satya prakashan, new delhi, 2010. authors profile pankaj swarnkar received the b.e. degree from govt. engineering college, jabalpur, india in 1998 and the m.tech degree from maulana azad national institute of technology, bhopal, india in 2004. currently he is an assistant professor in maulana azad national institute of technology, bhopal and pursuing the phd degree. his field of interest includes control system, network analysis and power systems. he is the author of five technical books. s. k. jain received the b.e. degree from samrat ashok technological institute, vidisha, india, in 1990, the m.e. degree from sgsits, indore, india, in 1994, and the ph.d. degree from the indian institute of technology, roorkee, india, in 2003. currently he is an assistant professor in the department of electrical engineering, national institute of technology, bhopal, india. his research interests include power electronics, electric drives, active power filters, and high-power factor converters. dr. jain received the aicte—career award for young teachers for the year 2003–2004. r. k. ;ema received the b.e. degree from barkatullah university, bhopal, india, in 1986, the m.e. degree from barkatullah university, bhopal, india, in 1992, and the ph.d. degree from bhopal university, india, in 2004. currently he is an associate professor in the department of electrical engineering, national institute of technology, bhopal, india. his research interests include power electronics, electric drives and dsp. engineering, technology & applied science research vol. 7, no. 6, 2017, 2200-2204 2200 www.etasr.com hashemi and dehghanian: a survey and analysis of the relationship between human resources … a survey and analysis of the relationship between human resources management and organizational performance seyed ahmad hashemi department of government management e-campus islamic azad university tehran, iran farideh dehghanian department of government management e-campus islamic azad university tehran, iran abstract—this study aims to evaluate the relationship between human resources management and organizational performance with emphasis on the mediating role of organizational innovation. the study methodology is descriptive-correlation and structural equations modeling. the study population is employees of the electricity distribution company of tehran city. the reliability and validity of measures were evaluated using cronbach’s alpha and confirmatory analysis and the results showed the acceptable reliability and validity of measures. for data analysis, pearson correlation coefficient and structural equations method with lisrel software were used. the results showed that the effect of organizational innovation mediating variable was indirectly 0.17 meaning that if human resources management is increased as 1%, the organization performance with the mediating role of organizational innovation is increased as 16%. this study evaluates the relationship between human resources management and organizational performance with emphasis on the mediating role of organizational innovation. keywords-human resources management; organizational innovation; organizational performance. i. introduction in most organizations, leaders and managers attempt to promote and improve their performance. previous studies results emphasized on the role of human resources management and organizational innovation in the improvement of organizational performance. a few studies evaluated the direct and indirect effects of mentioned variables on the framework of structural equations modeling on organizational performance. thus, the evaluation of these is necessary. nowadays, non-assurance, complexity, globalization and increasing technological changes are considered important features. innovation, creativity and problem solving capability are key skills [1]. creativity and innovation are required for the durability of each organization and non-innovative organizations are eliminated over time [2]. the organization that can present new thoughts can accept changes well and can also act as a factor of making changes. thus, it is necessary for organizations to use creativity and innovation or else they are threatened with elimination from the competition. thus, it is necessary to identify the predictors and outcomes of organizational innovation. electricity distribution company of tehran attempts to use new strategies, including the use of a proposition system and its active use in decision making process, maximum use of existing human resources, development of participation in all levels, recognition, development and prosperity of existing human resources, increase of empathy and collaboration, qualitative and quantitative improvement of activities and the increase of satisfaction and innovation of employees. the increase of motivation, improvement of human relationships, achieving optimal service providing methods, decision making, saving in organization, accepting the positive changes and implementation of productivity techniques can improve the performance of this company. based on the necessity in the approach of electricity industry to use new advanced technologies to improve performance, the innovation of employees is of great importance. based on the electricity distribution company of tehran, we can say low level of innovation of employees in an organization can endanger its performance. the important role of human resources management for the organization’s survival can oblige the electricity distribution company of tehran to adapt to the increasing complexities and rapid changes. under such spaces, the organizations with high creativity can respond rapidly to the environmental challenges and they have better performance compared to that of non-creative organizations. thus, due to the importance of performance and innovation, the identification of effective factors on these variables is of great importance. the present study evaluates the relationship between human resources management and organizational performance with emphasis on the mediating role of organizational innovation [3]. ii. theoretical basics  human resources management: human resources management is defined as the arrangement and activities of planned human resources model with the goal that the organization is enabled to achieve its goals [4]. engineering, technology & applied science research vol. 7, no. 6, 2017, 2200-2204 2201 www.etasr.com hashemi and dehghanian: a survey and analysis of the relationship between human resources …  education: education is experience based on learning. normally, it is said that education can lead to the change of skills, knowledge, attitude and social and organizational behavior [5].  employees’ participation: creating a space in which all organization employees collaborate and participate in decision making process and resolving the organization problems with the management [3].  performance assessment: performance assessment refers to the measurement of employee performance [3].  job analysis: job analysis refers to the definition of responsibilities and job position of employees and revision in those responsibilities under necessary conditions [3].  employee’s development: employees development refers to the opportunities provided by the organization for the employees to progress in their job [3].  organizational innovation: organizational innovation refers to the development or acceptance of a new idea or behavior in business operation [6].  innovation production: innovation production refers to presenting new ideas for job improvement, using new methods, new work techniques and coming up with new solutions [6].  innovation improvement: innovation improvement refers to stimulating innovative ideas [6].  innovation execution: innovation execution refers to turning the innovative thought to useful methods [6].  organizational performance: performance means the result and amount of work. in another definition, it is the amount of results achieved by a person, team organization or process [4]. iii. research basics authors in [7] evaluated the correlation of human resources strategies based on the model of allen yelsi with the organizational performance of the employees of ayatollah kashani hospital of shahre kord. the results showed that there was a significant correlation between human resources strategy and organizational performance. authors in [8] conducted a study to evaluate the impact of knowledge management strategies on innovation and organizational performance. the results showed that knowledge management had positive impact on organizational innovation and performance. in addition, organizational innovation had positive and direct impact on organizational performance. authors in [9] evaluated the relationship between human resources strategic management and firm performance. the study findings showed that the companies following the activity of human resources strategic management have better performance compared to the companies that don’t. author in [3] evaluated the relationship between human resources management, organizational innovation and organizational performance in the framework of structural equations in the companies with high performance. the results showed that human resources management was effective on organizational innovation and performance. in [4], authors evaluated the impact of human resources strategic management on organizational performance, based on the mediating role of organizational learning processes in korean organizations. it was found that the strategic management of human resources had a positive and significant impact on the organizational learning processes and organizational performance. the organizational learning processes had positive and significant impact on organizational performance. authors in [10] evaluated the relationship between knowledge management, strategic orientation, organizational innovation and organizational performance. it was found that knowledge management had a direct impact on strategic orientation but the relationship between other variables was not significant. authors in [6] evaluated the relationship between innovation, organizational learning and performance. the results showed that innovation and organizational learning had positive impact on commercial performance and organizational learning had positive impact on organizational innovation. iv. study population, sample size and sampling method the study population of the present study is the 250 employees of the electricity distribution company of tehran. based on the sample study, to determine the sample size, cochran’s formula is used: 2 2 2 2 2 t s n d t s n n   thus, 151 employees of electricity distribution of tehran are selected as the study sample. the sampling method in the present study is simple random method. a. introduction of study measures the variables of the present study are the methods of human resources management, organizational innovation and organizational performance. to evaluate each of the variables, standard questionnaires were used.  human resources management: to measure human resources management, the questionnaire presented in [11] is applied. this questionnaire is composed of 19 items. the questions are scored based on likert scale (totally disagree=1, totally agree=5).  organizational innovation: to measure organizational innovation a questionnaire composed of 9 items is applied. the questions are scored based on likert scale (totally disagree=1, totally agree=5). b. determine validity and reliability of study measures the measure validity and reliability are the most important factors in a study. to determine the test reliability in this study, cronbach’s alpha is used. this method is used to calculate the internal consistency of measures measuring the different attributes. to calculate cronbach’s alpha coefficient, at first we should calculate the variance of scores of each sub-set of engineering, technology & applied science research vol. 7, no. 6, 2017, 2200-2204 2202 www.etasr.com hashemi and dehghanian: a survey and analysis of the relationship between human resources … questions of questionnaire and total variance. then, by the following formula, alpha coefficient value is calculated.  2 1 21 )1 n j j s j r j s     in this study, alpha above 0.7 is a suitable for the reliability. thus, measurement of reliability is performed using cronbach’s alpha and spss 18 software. to evaluate validity of measures, besides the content validity, confirmatory factor analysis is used. c. data analysis methods to analyze the data of this study, descriptive and inferential tests were used. in descriptive section, percent, mean and standard deviation and in inferential section, pearson correlation and structural equations modeling were used. for data analysis, spss, lisrel software were used. v. study results a. evaluation of the demographic features of study sample study findings show that 19.86% of respondents are women and 80.14% men. 42.47% have a diploma, 48.63% ba and 8.90% ma and above. 31.51% of the respondents are at the age group of 30-40 years, 43.83% at 41-50 and 24.66% are above 51 years old. the respondents with 10-15 years of experience are 7.53%, 64.39% have 16-20 years of experience and 28.08% above 20 years. b. descriptive indices of study variables table i shows the indices of descriptive statistics for the study sample as mean and standard deviation for the studied variables. table i. the descriptive indices of study variables variables mean sd human resources management 3.09 0.72 organizational innovation 2.74 1.06 organizational performance 2.86 0.94 c. evaluation of normality of data at first, the normality and non-normality of data is determined and then the study hypotheses are evaluated. to evaluate data normality, kolmogorov-smirnov test was used. as shown in table ii, kolmogorov-smirnov test for all variables is not significant. thus, the study variables are normal and pearson correlation and structural equations modeling are used for stud hypothesis testing. the results of correlation coefficient are shown in table iii. the results show that correlation coefficient of human resources management with organizational innovation (r=0.51) and organizational performance (r=0.53) is significant and positive at the level p<0.01. the correlation coefficient of organizational innovation with organizational performance (r=0.48) is significant and positive at the level p<0.01. figure 1 shows the tested model with the standardized values on each path. the results show that the effective of human resources management on organizational innovation and organizational performance is positive and significant. the effect of innovation on organizational performance is positive and significant. figure 2 shows the t-valued of tested model. t-values above ±1.96 to 2.58 are significant at the level 0.05 and t-values above ±2.58 are significant at the level 0.01. as shown in figure 2, t-values show that all coefficients are significant. table iv shows the path coefficients of study variables. d. correlation coefficient of variables after determining the validity of measures, the identification of the relationship between the variables is the next step. to identify the relationship between the presented variables, pearson correlation coefficient is used. as shown in table iv, the direct effect of human resources management on organizational innovation (β=0.59) and organizational performance (β=0.44) is positive and significant at the level 0.01. the direct effect of organization innovation (β=0.28) on organizational performance is positive and significant. the indirect effect of human resources management on organizational performance via organizational innovation (β=0.17) is positive and significant at the level 0.01. the 41% variance of organizational performance and 34% variance of organizational innovation are explained by the existing variables in the present study. the fit indices of the tested model in table v show that rmsea index in the estimated model with 0.023 is acceptable and other fit indices as cfi, gfi, nfi, agfi are 1, 0.96, 0.99 and 0.93 respectively, which is at suitable level. this shows that the study data have good fit with the factor structure. table ii. kolmogorov-smirnov test of study variables variables z significance level human resources management 0.740 0.644 organizational learning 1.292 0.071 organizational performance 0.913 0.375 table iii. the correlation matrix of study constructs variables 1 2 3 human resources management 1 organizational innovation **0.51 1 organizational performance **0.53 **0.48 1 * p < 0.05 ** p < 0.01 table iv. path coefficients of study variables. path direct effect indirect effect total effect explained variance on organizational performance from 41% organizational innovation **0.28 **0.28 human resources management **0.44 **0.17 **0.61 on organizational innovation from 34% human resources management **0.59 **0.59 * p < 0.05 ** p < 0.01 engineering, technology & applied science research vol. 7, no. 6, 2017, 2200-2204 2203 www.etasr.com hashemi and dehghanian: a survey and analysis of the relationship between human resources … fig. 1. the tested model of study (* p < 0.05 ** p < 0.01) fig. 2. t-value of tested model of study (* p < 0.05 ** p < 0.01) table v. the fit indices of fitted model agfi nfi gfi cfi rmsea x/df 0.93 0.97 0.96 1 0.023 1.09 e. hypothesis test overall results hypothesis test are shown in table vi. 1) first hypothesis: there is a significant relationship between human resources management (education, participation, job analysis, performance evaluation and employee development) with organizational performance (executive and market). the results of structural equations showed that the effect of human resources management on organizational performance was positive and significant. this result is consistent with the results of [12] and [3]. the continuous employee education, the teaching of new skills, the consideration of employee’s opinions, the initiative encouragement, the objective employee evaluation, the offered career opportunities are among the things making the employees to have high motivation to improve personal and therefore organizational performance. table vi. study hypotheses test hypothesis path coefficient supported/ rejected there is a significant relationship between human resources management with organizational performance 0.44 supported there is a significant relationship between human resources management with organizational innovation 0.59 supported there is a significant relationship between organizational innovation and organizational performance 0.28 supported organizational innovation in the relationship between human resources management and organizational performance has a mediating role. 0.17 supported 2) second hypothesis: there is a significant relationship between human resources management (education, participation, job analysis, performance evaluation and employees development) with organizational innovation (production, promotion and engineering, technology & applied science research vol. 7, no. 6, 2017, 2200-2204 2204 www.etasr.com hashemi and dehghanian: a survey and analysis of the relationship between human resources … execution of innovation). the results of structural equations showed that the effect of human resources management on organizational innovation was positive and significant. thus, the involvement of human resources in varied duties is effective on organizational innovation. the goal of investment in human resources management is the emphasis on the employee improvement with continuous learning and education. this result is consistent with [13] stating that the organizations by using effective strategies of human resources can create some features and behavior in the employees which are necessary for the organization success. today, the importance of human factor and its unique role as a strategic source is increased. today, the organizations use human resources with rapid growth, continuous improvement, efficacy, effectiveness, flexibility, preparation for the future and excellent position in their activities. organizations without these qualities, organizations enter the competition with a handicap. via human resources management methods, the organizations can create organizational innovation. 3) third hypothesis: there is a significant relationship between organizational innovation (production, promotion and execution of innovation) and organizational performance (executive and market). the results of structural equations showed that the effect of organizational innovation on performance is positive and significant. we can say innovation is the source of system change for progress. via innovation the organization equips itself with new tools, methods and techniques and it is aware of the latest progress and knowledge and by using them, optimization is improved leading to the improvement of organizational performance [14]. 4) fourth hypothesis: organizational innovation (production, promotion and execution of innovation) in the relationship between human resources management (education, participation, job analysis, performance evaluation and employee development) and organizational performance (executive and market) has a mediating role. the results of structural equations showed that the indirect effect of human resources management on organizational performance was positive and significant. this result emphasizes on the mediating role of organizational innovation in the relationship between human resources management and organizational performance. vi. conclusion the results showed that the direct and indirect effect of human resources management on organizational performance was positive and significant. thus, the results of study emphasize on the role of organizational innovation as an important mediator. if human resources management applies education, participation of employees, job analysis, objective evaluation of performance and development of employees, organizational innovation is provided affecting the organization performance. the human resources management methods should be applied in creating organization’s processes, services and products. if the organization cannot use the human resources management, it cannot achieve competitive advantages. vii. recommendations it is proposed to the managers of the electricity distribution company of tehran to use competence methods of human resources in human resources management, i.e. to apply improvement opportunities and job development for the employees, provide learning opportunities, support good decision making and evaluate employees based on their performance. these can affect the organizational innovation and organizational performance. it is proposed to the managers of electricity distribution of tehran to provide the conditions in which the employees are encouraged to present new ideas and solutions, to search new tools, methods and techniques, to support innovative ideas, to attempt to turn innovative thought to useful methods, to relate innovative thought with the work and to evaluate the effectiveness of innovative thought by which organizational performance is improved. references [1] a. monavarian, n. asgari, organizations in the age of industry, information and knowledge, tehran publication, 2009 [2] h. mohammadi, m. tabari, “institutionalize creativity and innovation in organization”, journal of tadbir, vol. 1, no. 1, pp. 201202, 2008 [3] k. lu, j. zhu, h. bao, “high-performance human resource management and firm performance: the mediating role of innovation in china”, industrial management & data systems, vol. 115, no. 2, pp. 353-382, 2015 [4] i. h. s. chow, s. t. teo, i. k. chew, “hrm systems and firm performance: the mediation role of strategic orientation”, asia pacific journal of management, vol. 30, no. 1, pp. 53-72, 2013 [5] m. silberman, c. auerbach, metody aktywizujące w szkoleniach, wolters kluwer polska, 2009 [6] d. jimenez-jimenez, r. sanz-valle, “innovation, organizational learning, and performance”, journal of business research, vol. 64, no. 4, pp. 408-417, 2011 [7] m. nasiri, m. heidari, s. shahbazi, e. ansari, “correlation of human resource strategies based on allen ylsy model with organizational performance staff in aiat allah kashani hospital”, journal of health promotion management, vol. 2, no. 3, pp. 36-44, 2013 [8] h. safarzadeh, a. tadayon, m. hormohammadi, “the evaluation of effects of knowledge management strategy on organizational innovation and performance (a case study in community health centers of north part of fars province)”, the journal of toloo-e-behdasht, vol. 11, no. 1, pp. 65-76, 2012 [9] s. a. efje, m. esmailzade, “the evaluation of the relationship between human resources strategic management and performance of firms”, development and change management, vol. 1, no. 2, pp. 20-25, 2009 [10] a. a. ferraresi, c. o. quandt, s. a. dos santos, j. r. frega, “knowledge management and strategic orientation: leveraging innovativeness and performance”, journal of knowledge management, vol. 16, no. 5, pp. 688-701, 2012 [11] j. e. delery, d. h. doty, “modes of theorizing in strategic human resource management: tests of universalistic, contingency, and configurational performance predictions”, academy of management journal, vol. 39, no. 4, pp. 802-835, 1996 [12] j. bae, j. j. lawler, “organizational and hrm strategies in korea: impact on firm performance in an emerging economy”, academy of management journal, vol. 43, no. 3, pp. 502-517, 2000 [13] r. s. schuler, s. e. jackson, “linking competitive strategies with human resource management practices”, the academy of management executive, vol. 4, no. 1, pp. 207-219, 1987 [14] h. zarei matin, advanced organizational behavior management, tehran, agah publication, 2009 microsoft word etasr_v12_n3_pp8718-8722 engineering, technology & applied science research vol. 12, no. 3, 2022, 8718-8722 8718 www.etasr.com syed et al.: prioritization of occupational accident causes in the automotive manufacturing prioritization of occupational accident causes in the automotive manufacturing muhammad zain syed department of industrial engineering and management, dawood university of engineering and technology karachi, pakistan syedmzain1@gmail.com aaraiz khalique department of industrial engineering and management, dawood university of engineering and technology karachi, pakistan aaraizkhalique@gmail.com muhammad dawood idrees department of industrial engineering and management, dawood university of engineering and technology karachi, pakistan muhammad.dawood@duet.edu.pk atif jamil department of computer systems engineering, dawood university of engineering and technology karachi, pakistan atif.jamil@duet.edu.pk abdul sami department of electronic engineering, dawood university of engineering and technology karachi, pakistan. dr.abdulsami@duet.edu.pk arif abdullah department of electronic engineering, dawood university of engineering and technology karachi, pakistan arif.abdullah@duet.edu.pk nawal sajid department of industrial engineering and management, dawood university of engineering and technology karachi, pakistan nawal_3211@hotmail.com kanzal khan department of industrial engineering and management, dawood university of engineering and technology karachi, pakistan kanzalkhan96@gmail.com safdar rizvi department of computer sciences bahria university karachi campus karachi, pakistan safdar.bukc@bahria.edu.pk received: 23 january 2022 | revised: 19 march 2022 and 5 april 2022 | accepted: 18 april 2022 abstract-the automotive industry is a significant contributor to the economy. additionally, it is prone to occupational accidents. the current study focuses on organizational accidents in highrisk activities, particularly occupational accidents in the automobile and manufacturing industries. this investigation aims to rank and quantify the causes of occupational accidents. these reasons are identified through a literature review and are investigated utilizing the analytical hierarchy process (ahp). an ahp model is built based on a literature review. this model created a questionnaire and its evaluation via a survey of experts' opinions. this study shows that the most significant and dominant elements in accidents are human and organizational factors since they receive roughly equal weighting, whereas environmental factors weigh less. keywords-analytical hierarchy process (ahp); automotive; occupational accidents; high-risk operations i. introduction management commitment to safety culture varies from organization to organization. organizational and psychological factors increasingly influence the accident rate [1]. according to a quantitative survey of 225 complaints, dangerous activities constitute the top cause of occupational accidents. additionally, hazardous circumstances and elements associated with machines and equipment significantly impact occupational accidents. additionally, it is essential to develop new plans and programs for assessing workers' occupational health to take preventative measures against health risks [2-4]. in turkey's metal production industry revealed that the majority of workplace fatalities are caused by risky activities and lack of training [5, 6]. additionally, at an italian steel manufacturing company, it was shown that working in a hypercritical atmosphere results in occupational accidents and disease. the study noted that working at a high temperature and being exposed to environmental conditions such as noise, vibration, poor air quality, and a demanding workload may result in severe injuries and burns [6]. similarly, factors that contribute to occupational stress, lack of a reward system, and worker health may also contribute to occupational sickness and job stress results in an increase of dangerous behaviors [7]. numerous factors have been identified as contributing to occupational mortality. these ambiguous situations occur due to a variety of personal characteristics, behaviors, and organizational circumstances [8, 9]. this partiality and bias in safety management contribute to the development of flawed policies. while doing a safety review, operators' psychological behavior, religious and cultural beliefs must be considered when examining fatality reports [10-12]. this aids in corresponding author: muhammad dawood idrees engineering, technology & applied science research vol. 12, no. 3, 2022, 8718-8722 8719 www.etasr.com syed et al.: prioritization of occupational accident causes in the automotive manufacturing understanding their risk perception along with the cause of death [13]. numerous manufacturing companies employ the six sigma methodology to enhance their product quality and operational efficiency, and to increase security. it is an organization's responsibility to safeguard the operator's safety. workplace accidents occur mostly due to unsafe working conditions and behaviors, low visibility, and a hazardous atmosphere. these variables can result in life-threatening illness, accidents, lifelong disability, or death [14]. the conclusion of [15] indicates that these accidents have certain characteristics. there is a greater probability of limited exposure, and most injuries are caused by power machinery. these judgments would predate programs on accident prevention in the automotive industry. human factor engineering is concerned with ensuring that the design of the man-machine system does not exceed the human capacity for information processing. emotional stress affects one's ability to digest information, as defined by reception and feedback time. these indicators focus on employee safety, particularly preemployment screening and stress management practices. it is the company's responsibility to give stress management training. additionally, monitoring, interpreting, and interfering in employees' risky activities prevents accidents [16]. the evaluation of circumstances is a systematic tool used in occupational safety to ascertain the reasons of accidents. conducting this type of study can assist a company in forecasting future occurrences. the analytical report is deficient in detail due to the absence of examining the variables associated with the workplace conditions. also, a systematic model for evaluating workplace accident causes is required and a database containing accident statistics. numerous studies have been conducted to improve the quality of accident analysis models and procedures to reduce the number of accidents. however, the increasing number of accidents motivates analysts to conduct additional research in this field. numerous sectors have implemented continuous improvement systems to increase worker safety, productivity, and quality. however, just a few occupational publications examine using the research's standardized recommended criteria. this chasm will have been closed by addressing the training and skills of the professionals responsible for compiling an accident investigation report. similarly, to ensure the validity of accident cause reports, the firm must implement monitoring mechanisms to ensure the methodology is being followed [17]. ii. methodology this research conducts a thorough analysis of the occupational accident causes in the automobile industry. it has been discovered that occupational deaths are caused by three distinct cause categories: environmental, human, and organizational factors. these factors have sub factors as shown in figure 1. these factors and sub factors have been identified through an extensive literature review [8-12]. this process results in the development of a model based on these criteria and sub-criteria under the supervision of safety specialists and academic experts. the ahp approach determined the relative importance of many causes in an occupational accident or sickness. fig. 1. criteria and sub-criteria of occupational accidents cause in the automotive industry. decisions are usually quick and even have to be made at the instant. however, these decisions require time, tools, and techniques to resolve many situations. sometimes it is challenging to quantify many alternatives to make a judgment. in such circumstances, executing these judgments requires logical, systematic, and mathematical tools through which decisions would be obtained. numerous decision-making approaches and procedures have been proposed and ahp [18] is one of these methods. there are many reasons to use ahp in decision-making, and one of them is to prioritize factors. this method necessitates the establishment of an objective or goal, classifying various criteria, selecting a scale, evaluating preferences, conducting a consistency test, and aggregating the resultant weights of sub-criteria about the primary criterion. figure 2 summarizes the entire study hierarchy. the pairwise comparison questionnaire requires an assortment of a scale. the pairwise comparison of different alternatives was assessed by employing the saaty scale [18, 19] to conduct the examination. before evaluation, the design of the questionnaire was validated by academic professionals. the standardized procedure of ahp requires a pairwise comparison of one criterion to another through a questionnaire and results in a ranking of the factors. the geometric mean was applied to the whole sample size and was further evaluated for consistency in order to prioritize the causes leading to the objective. iii. results this analysis included 5 automobile manufacturers in pakistan and 220 participants. to ensure the reliability of the results, the primary focus during sample collection was on engineering, technology & applied science research vol. 12, no. 3, 2022, 8718-8722 8720 www.etasr.com syed et al.: prioritization of occupational accident causes in the automotive manufacturing safety management specialists. as a result, safety management specialists and automobile industry experts discussed and responded to the questionnaire. the comprehensive literature assessment on occupational accident causes follows a logical structure and focuses on diverse developed and developing countries. the complete analysis, conducted using microsoft excel, is summarized in table i, including pairwise comparisons of the major risk factors for occupational accidents. fig. 2. research flow diagram. table i. pair-wise comparison of oac oac e h o e 0.250569035 0.315352748 0.199831687 h 0.300700026 0.378444924 0.442300229 o 0.448730939 0.306202328 0.357868084 similarly, as shown in table i, the study obtained results for the sub-criteria of environmental, human, and organizational aspects. finally, the results, as shown in table ii of occupational accidents indicated that ecological variables (e) had a 26% weighting, human factors (h) had a 37% weighting, and organizational factors also had a 37% weighting on the accident rate, as illustrated in figure 3. the complete results in table ii also contain the weights of sub-criteria at the local and global levels. according to table ii, the leading environmental factor that causes an occupational accident or illness is excessive occupational noise (e1) with 8% weightage. the human factors that cause occupational accidents are unsafe acts (h2) with 13% weightage, job stress (h4) with 9% weightage, and personal physique (h3) with 8% weightage. finally, the most significant organizational elements that contribute to the accident occurrence are the lack of safety training and education (o2), which account for 10% of the weight, and the physical conditions of the workplace which account for 8%. fig. 3. weightage of oac. table ii. lo cal and overall weights of o ac main criteria local weights sub-criteria local weights global weighs overall weights e 0.255 e1 0.303 0.08 26% e4 0.211 0.07 e3 0.228 0.06 e2 0.258 0.05 h 0.374 h2 0.194 0.13 37% h4 0.349 0.09 h3 0.212 0.08 h1 0.245 0.07 o 0.371 o2 0.157 0.10 37% o5 0.274 0.08 o4 0.159 0.07 o1 0.193 0.06 o3 0.216 0.06 total 1.00 1.00 1.00 iv. conclusion this study discusses important occupational accident causes in car production, including environmental, human, and organizational factors. the ahp approach categorizes and prioritizes the primary causes of occupational accidents. identifying these factors encourages the prevention of the leading causes. based on past research, a logical assessment of the literature on various ergonomic and managerial variables was conducted, and a new model was built. human and organizational variables are the most significant and dominant components in accidents, since they receive approximately equal weighting, while environmental factors receive less weighting. appendix research survey name: organization/industry: email: do you have experience with the health & safety department in the automotive sector? engineering, technology & applied science research vol. 12, no. 3, 2022, 8718-8722 8721 www.etasr.com syed et al.: prioritization of occupational accident causes in the automotive manufacturing instructions • if you think criterion 1 is more important than criterion 2, you must pick a number from the left side. let's suppose you think criterion 1 is five times more important than criterion 2, so you can circle 5 from your left. • similarly, if you think criterion 2 is more important, you can mark 5 from the right. • circle only one number in each comparison. criterion 1 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 criterion 2 questionnaire pair-wise comparison of occupational accident causes q1) pair-wise comparison of occupation al accident causes e 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 h e 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 o h 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 o q2) pair-wise comparison of environmental factors e1 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 e2 e1 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 e3 e1 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 e4 e2 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 e3 e2 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 e3 e3 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 e4 q3) pair-wise comparison of h uman factors h1 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 h2 h1 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 h3 h1 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 h4 h2 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 h3 h2 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 h3 h3 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 h4 q4) pair-wise comparison of o rgan ization al factors o1 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 o2 o1 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 o3 o1 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 o4 o1 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 o5 o2 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 o3 o2 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 o4 o2 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 o5 o3 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 o4 o3 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 o5 o4 9 8 7 6 5 4 3 2 1 2 3 4 5 6 7 8 9 o5 references [1] s. clarke, "safety culture: under-specified and overrated?," international journal of management reviews, vol. 2, no. 1, pp. 65–90, 2000, https://doi.org/10.1111/1468-2370.00031. 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[19] h. bain, n. howard, and t. l. saaty, "using the analysis of options technique to analyze a community conflict," the journal of conflict resolution, vol. 15, no. 2, pp. 133–144, 1971. microsoft word etasr_v13_n4_pp11406-11411 engineering, technology & applied science research vol. 13, no. 4, 2023, 111406-11411 11406 www.etasr.com kumar & ponnusamy: robust medical x-ray image classification by deep learning with multi-versus … robust medical x-ray image classification by deep learning with multi-versus optimizer thirugnanam kumar department of computer and information science, annamalai university, india kumarddeau@gmail.com (corresponding author) ramasamy ponnusamy department of computer and information science, annamalai university, india povi2006@gmail.com received: 16 june 2023 | revised: 24 june 2023 | accepted: 29 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6127 abstract classification of medical images plays an indispensable role in medical treatment and training tasks. much effort and time are required in the extraction and selection of classification features of medical images. deep neural networks (dnns) are an evolving machine learning (ml) method that has proved its ability in various classification tasks. convolutional neural networks (cnns) present the optimal results for changing image classification tasks. in this regard, this study focused on developing a multi-versus optimizer with deep learning enabled robust medical x-ray image classification (mvodl-rmxic) method, aiming to identify abnormalities in medical x-ray images. the mvodl-rmxic model used the cross bilateral filtering (cbf) technique for noise removal, a mixnet feature extractor with an mvo algorithm based on hyperparameter optimization, and bidirectional long-short-term memory (bilstm) for image classification. the proposed mvodl-rmxic model was simulated and evaluated, showing its efficiency over other current methods. keywords-medical x-ray images; biomedical imaging; image classification; deep learning; multi-versus optimizer i. introduction automated systems to detect abnormalities in medical xray images have become a challenge in the ml domain [1]. the expansive anatomical varieties for individual patients are one of the most severe problems in radiograph projection with superimposed frameworks [2]. radiologists apply practical knowledge and their skills to analyze x-ray images and detect fractures in bones [3]. the quality of medical images captured with image capture tools is often poor. therefore, it is challenging for physicians to identify abnormalities, and a potentially automated computer aided detection (cad) mechanism was devised in [4] to overcome this issue. therefore, automated recognition of abnormalities in x-ray images can be helpful for physicians in identifying numerous clinical problems such as osteoporosis, arthritis, bone cancer, infection fracture, and dental decay [5]. researchers in artificial intelligence (ai) make a large contribution to data processing [6]. advances in ai can transform healthcare by considering medical treatments and diagnostics as data problems. deep learning (dl) is a subdivision of ml that extracts detailed features from data and has been proven to be very effective in many data processing tasks [7]. dl is becoming an eminent solution for a wide range of text processing or natural language processing (nlp), speech recognition and synthesis, computer vision (cv) tasks, and signal analysis [8]. cnn, a multi-layered neural network (nn), is essential in several digital image processing tasks such as segmentation, object recognition, pattern detection, classification, and feature extraction in many kinds of images, including healthcare images [9]. dl needs a plethora of data to achieve suitable results and is resource-hungry. transfer learning (tl), which is an ml method, has been proposed to solve this problem. tl repurposes a technique trained on a single task on a second relevant task. to achieve maximum accuracy, pre-trained approaches were re-trained on small data with fewer trainable variables [10]. based on the selected method and data, pre-trained methods were optimally tuned to attain promising results. this study developed the multi-versus optimizer with deep learning enabled robust medical x-ray image classification (mvodl-rmxic) method, using the cross bilateral filtering (cbf) approach for noise removal, a mixnet feature extractor with an mvo algorithm based on hyperparameter optimization, and the bidirectional long short-term memory (bilstm) method for image classification. a far-reaching simulation process was carried out to evaluate the effectiveness of the proposed mvodlrmxic method. engineering, technology & applied science research vol. 13, no. 4, 2023, 111406-11411 11407 www.etasr.com kumar & ponnusamy: robust medical x-ray image classification by deep learning with multi-versus … ii. related works in [11], a chest x-ray (cxr) imaging categorization method of covid-19 artifacts under altered real-time conditions was presented, using a new cnn based on bayesian optimization. this method used cnn to extract and learn deep features and bayesian-based optimization to tune cnn hyperparameters based on the primary function. in [12], a fractalcov-net infrastructure was established using fractal blocks and u-net to segment chest ct images to detect areas of lesion. a similar fractalcov-net setting was also used to classify cxr images using tl. different approaches were used, such as fcn, u-net, segnet, denseu-net, and resnetunet. classification results were compared with different algorithms, namely vgg16, resnet5, xception, densenet, and inceptionresnetv2 structures. in [13], cxr imaging was used to detect covid-19 and pneumonia in a 3-stage process. the main stage involved segmented raw x-ray imaging using a conditional generative adversarial network. in the second phase, pulmonary image segmentation was performed as a novel pipeline, integrating key point extraction approaches and a dnn trained to extract discrimination factors. in [14], stateof-the-art techniques were used to classify x-ray images of potential tuberculosis patients. a vital improvement was observed if coarse-to-fine data transfer can be used to fine-tune the method using several data augmentation systems. in [15], a novel method was presented to detect covid-19, using a c-gan to generate synthetic images to increase the restricted count of accessible data, presenting two dl techniques. this study focused on either a binary classifier for covid-19 vs a normal case or a multiclassifier that contains a tertiary class for bacterial pneumonia. in [16], an ml system was introduced to recognize covid-19 in cxr images. the features extracted by hog and cnn in x-ray images were fused for classification with a vggnet cnn. the madf system can be used to optimally preserve edges and decrease noise from the image. a watershed segmenting system can be used to mark a critical fracture part from the input x-ray image. iii. the proposed model this paper presents the mvodl-rmxic method to detect and classify medical x-ray images. the proposed model aimed to identify abnormalities in medical x-ray images, encompassing cbf noise removal, mixnet feature extraction, mvo-based tuning process, and lstm-based classification. figure 1 illustrates the block model of mvodl-rmxic. a. stage i: image filtering process cbf was used for noise removal, as it can decide the range distancing through the captured guide image in diverse photographic circumstances instead of the target image [17]. this method may alleviate quality loss whenever the image is too noisy and has pseudoor unsharp edging. the theoretical variances among the original and cross-bf appear to be insignificant. bf plays a significant role in smoothing tasks by appropriately substituting guides and target images. consider the bf enforced on a 2d grayscale image x. let � ∈ �� denote a neighboring pixel of �, where � ∈ �� signify the location of the target pixel, �� ⊂ �� is the neighboring pixel set at � , which is a rectangle domain assisted in a filter window, and � ∈ ℝ� designates its pixel intensity. using such notation, bf can be given as follows: ����: = ∑ ������ ��,��⋅�����,�� ⋅!�∑ ������ ��,��⋅�����,�� (1) where "� is one of its neighboring pixels, and "� is a target pixel in the guide image. this definition was equal to the novel bf if it is self-guided, i.e., "� = � and "� = � . fig. 1. block diagram of the mvodl-rmxic model b. stage ii: feature extraction process in this phase, the mvodl-rmxic method used a mixnet feature extractor, as shown in figure 2. fig. 2. structure of the mixnet model. mixed depthwise conv (mixconv) kernels would extend vanilla depthwise convolution through several kernel sizes in a single conv [18]. mixconv merges several kernel sizes in one conv by dividing the input of conv into groups and implementing diverse kernel sizes in all groups. unlike vanilla depthwise conv, mixconv can capture various paradigms from conv input at several resolutions. similarly, it needs some parameters and is more computationally effective than employing one kernel. for example, using several kernels [(3, 3),(5, 5),(7, 7)] is more computationally effective than using a engineering, technology & applied science research vol. 13, no. 4, 2023, 111406-11411 11408 www.etasr.com kumar & ponnusamy: robust medical x-ray image classification by deep learning with multi-versus … 7×7 single kernel. then, it uses various kernels for all groups, and finally, the three results are linked to generate the last complex result. figure 2 presents the structure of mixnet. then, the mvo algorithm was used, which is based on hyperparameter optimization [19]. mvo is a populace-based technique stimulated by the big-bang theory. the proposed method performed the search process using two stages: (i) exploration and (ii) exploitation. the concept of black holes and white holes was used to explore the search space, and the wormhole concept was used to introduce the exploiting stage. in multiverse theories, a black hole attracts everything. a wormhole connects different places in the universe and plays the role of interconnecting tunnels among diverse universes. every universe has its inflation rate. the mvo attributes every resolution with an inflating rate corresponding to the fitness function. according to mvo, the subsequent rules are used in optimization:  a high rate of inflation in the universe is making it have additional white holes, and, on the other hand, the probability of consisting black holes dropping.  contrary to a universe with a smaller inflation rate, a universe with a huge inflation rate is prone to dispatching objects to others via a white hole. in contrast, the universe with the lowest inflating rate tends to obtain objects through black holes.  despite the rate of inflation, the object transmits arbitrarily toward a better universe through a wormhole. in mvo, the object (search agent) moves among diverse universes via white or black holes. a roulette wheel approach is applied for mathematical modeling, and the black/white hole tunnel transmits the procedure of objects among universes. initially, many universes are constructed to create a multiverse. next, using the iterative method, the universe is sorted according to its inflation rate. then, the universe is carefully chosen to possess a white hole through the roulette wheel. the optimizing procedure begins by producing various universes. in the optimization method, two variables dictate solution changes and can be evaluated to update the solution: (i) traveling distance rates (tdrs) and (ii) wormhole existence probability (wep). #$% = & + ( × *+,-. / (2) 012 = 1 − 5 6/�.6/� (3) where a and b are the minimum and maximum numbers (a = 0.2 and b = 1), and t and t indicate the maximum and the existing iteration amounts, respectively. consider that there are n candidate solutions and d variables that are the number of universes. after defining wep and tdr variables, the position of the solution was upgraded according to the following: 89�:;�,�,…,=�>�>;�,�,…,?� = ⎩⎪⎨ ⎪⎧def + 012 × *�ghf − ihf × jk + ihf / ; rn < 0.5ef − 012 × *�ghf − ihf × jk + ihf / ; jn > 0.5 j� < w$% 9f j� ≥ w$% (4) where 9f specifies the v-th parameters of the i-th universe, xj denotes the j-th variable of the better universe, lbj and ubj denote the low and high limiting of the j-th variables correspondingly, and r2, r3, and r4 indicate three random number ranges within [0, 1]. c. stage iii: x-ray image classification process the bilstm method was used for image classification. lstm proposed a particular memory cell for temporal dataset storage. this architecture allows recalling long-range features more than conventional rnns [20]. through multi-layer models, the cell component at the i-th time step at the l layer in the forward direction is carried out by the following: w9x = y�#�z�x ℎ\⃗ :x,� + �̂z�x ℎ\⃗ :,�x + h�z�x (5) 89x = y�#�9�x ℎ\⃗ :x,� + �̂9�x ℎ\⃗ :,�x + h�9�x (6) 09x = y�#�_�x ℎ\⃗ :x,� + �̂_�x ℎ\⃗ :,�x + h�_�x (7) "9x = tanh �#���x ℎ\⃗ :x,� + �̂��x ℎ\⃗ :,�x + h���x (8) d9x = w9x ⊙ d9,�x + 89x ⊙ "9x (9) ℎ\⃗ 9x = 09x ⊙ tanh �d9x (10) in these expressions, w9x refers to forget gate, 89x denotes the input gate, 09x signifies the output gate, "9x implies the hidden state, and d9x is a candidate gate. σ and hyperbolic tangent functions were used as activating functions, # x denotes the weighted matrix among layer cells �i − 1� − i, ℎ\⃗ 9x indicates the sigmoid function, ^ x signifies the weight matrix amongst sequential i layer cells, h x denotes the bias vector in the total layers, ⊙ represents component-wise multiplication, and f x the dimension vector magnitude. the sequence length distributes the bias value and weight matrix in a cell, thereby reducing the comprehensive amount of weights and hidden neurons in the network. a blstm will process the data in the backward and forward directions with two different lstm layers. the ℎ\⃗ :x , forward hl is computed through the abovementioned formula, and the back-state, ℎ⃖\9x is concatenated and then fed into the subsequent layer: ℎ⃡9x = iℎ\⃗ :x ,ℎ⃖\9x j (11) where i = 0 indicates the input layer. blstm is good at achieving the correlations among components in a whole sequence through information instead of recalling the features in one direction. furthermore, using the variable sharing model, blstm needs less memory to resolve problems compared to the fnn and cnn mechanisms. iv. performance validation the proposed mvodl-rmxic method was simulated using python 3.6.5 on an i5-8600k, 16gb ram, geforce 1050ti 4gb, 250gb ssd, and 1tb hdd pc, with the following parameters: dropout: 0.5, batch size: 5, epoch count: 50, learning rate: 0.01, and activation function: relu. the covid-19 radiography dataset [21] was used to evaluate the engineering, technology & applied science research vol. 13, no. 4, 2023, 111406-11411 11409 www.etasr.com kumar & ponnusamy: robust medical x-ray image classification by deep learning with multi-versus … method, which has images in three categories: normal, covid, and viral pneumonia (vp). figure 3 shows some sample images and figure 4 shows the confusion matrix of the mvodl-rmxic method on the x-ray image classification process. fig. 3. (a) covid, (b) normal, and (c) vp. fig. 4. confusion matrix of the mvodl-rmxic method (a-b) 80:20 tr/ts, and (c-d) 70:30 tr/ts. the output of the mvodl-rmxic method was effective in all classes. table i shows the classification results of the mvodl-rmxic method in an 80:20 proportion for tr and ts of the dataset. figures 5 and 6 show the classification results of the mvodl-rmxic method on the 80% tr and the 20% ts of the dataset, respectively, demonstrating its efficiency in all cases. in the covid class, the mvodlrmxic model obtained an increased accuy of 99.42% and 99.50%, precn of 99.50% and 98.98%, recal of 98.76% and 99.49%, fscore of 99.13%, and 99.23% and mcc of 98.69% and 98.86%, for 80% tr and 20% ts of the dataset, respectively. table i. output analysis of mvodl-rmxic under 80:20 tr:ts data labels accuy precn recal fscore mcc training (80%) covid 99.42 99.50 98.76 99.13 98.69 normal 99.12 99.24 98.13 98.68 98.03 vp 99.04 97.65 99.50 98.57 97.86 average 99.19 98.80 98.79 98.79 98.19 testing (20%) covid 99.50 98.98 99.49 99.23 98.86 normal 99.50 99.49 98.99 99.24 98.87 vp 99.67 99.51 99.51 99.51 99.26 average 99.56 99.33 99.33 99.33 99.00 fig. 5. evaluation of mvodl-rmxic system under 80% tr dataset. fig. 6. evaluation of mvodl-rmxic method in 20% ts dataset. table ii shows the classification results of mvodlrmxic in a 70:30 tr/ts proportion of the dataset, demonstrating its efficiency in all cases. in the covid class, the mvodl-rmxic method had accuy of 98.95%, precn of engineering, technology & applied science research vol. 13, no. 4, 2023, 111406-11411 11410 www.etasr.com kumar & ponnusamy: robust medical x-ray image classification by deep learning with multi-versus … 97.73%, recal of 99.14%, fscore of 99.43%, and mcc of 97.65%. similarly, in standard class, the mvodl-rmxic approach attained an increased accuy of 98.81%, precn of 98.84%, recal of 97.57%, fscore of 98.20%, and mcc of 97.32%. in the vp class, the mvodl-rmxic method achieved an increased accuy of 99.19%, precn of 98.86%, recal of 98.72%, fscore of 98.79%, and mcc of 98.18%. table iii shows a comparison of mvodl-rmxic with other methods [22, 23]. the results show that the squeezenet and vgg19 models showed the least accuy values of 92.96% and 93.30%, respectively, followed by the tl_squeezenet and resnet1with 96.44% and 97.23%, respectively. in contrast, the tl_resnet-2 method showed a considerable accuy of 98.44% but the mvodl-rmxic model reached a higher accuy of 99.56%. table ii. evaluation of mvodl-rmxic model under 70:30 tr:ts of the dataset labels accuy precn recal fscore mcc training (70%) covid 98.95 97.73 99.14 98.43 97.65 normal 98.81 98.84 97.57 98.20 97.32 vp 99.19 98.86 98.72 98.79 98.18 average 98.98 98.48 98.48 98.47 97.72 testing (30%) covid 99.33 99.67 98.36 99.01 98.51 normal 99.44 98.68 99.67 99.17 98.76 vp 99.67 99.32 99.66 99.49 99.24 average 99.48 99.22 99.23 99.22 98.84 table iii. relative evaluation of mvodl-rmxic with other methods models accuy precn recal squeezenet 92.96 91.73 95.10 tl_squeezenet 96.44 96.08 96.84 vgg_19 93.30 91.78 94.73 tl_resnet2 98.44 97.97 97.94 resnet1 97.23 96.74 97.43 mvodl-rmxic 99.56 99.33 99.33 v. conclusion this study developed a novel mvodl-rmxic method for detecting and classifying medical x-ray images, aiming to identify abnormalities. the proposed mvodl-rmxic method used the cbf technique for noise removal, a mixnet feature extractor with an mvo algorithm based on hyperparameter optimization, and the bilstm model for image classification. a wide-ranging simulation analysis was carried out, showing the effectiveness of mvodl-rmxic and its improved performance over other current methods. in future work, hybrid dl classifiers could be integrated to boost the performance of the mvodl-rmxic method. references [1] j. i. z. chen, "design of accurate classification of covid-19 disease in x-ray images using deep learning approach," journal of iot in social, mobile, analytics, and cloud, vol. 3, no. 2, pp. 132–148, jun. 2021. 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[23] m. ragab, s. alshehri, n. a. alhakamy, w. alsaggaf, h. a. alhadrami, and j. alyami, "machine learning with quantum seagull optimization model for covid-19 chest x-ray image classification," journal of healthcare engineering, vol. 2022, mar. 2022, art. no. e6074538, https://doi.org/10.1155/2022/6074538. engineering, technology & applied science research vol. 7, no. 4, 2017, 1759-1764 1759 www.etasr.com rezki and griche: simulation and modeling of a five -level (npc) inverter fed by a photovoltaic … simulation and modeling of a five -level (npc) inverter fed by a photovoltaic generator and integrated in a hybrid wind-pv power system m. rezki department of electrical engineering faculty of sciences and applied sciences university of bouira bouira, algeria mohamedrezki197@yahoo.fr i. griche department of electrical engineering faculty of sciences and applied sciences university of bouira bouira, algeria griche_issam@yahoo.fr abstract—a distributed hybrid coordinated wind photovoltaic (pv) power system was proposed in this paper. as oil and coal reserves are being depleted whilst at the same time the energy demand is growing, it is important to consider alternative energy generating techniques. today, the five-level (npc) inverter represents a good alternative for several industrial applications. to take advantage of the five-level inverter topology and the benefits of renewable energy represented by a photovoltaic generator, a new scheme of these controllers is proposed in this work. this paper outlines the design of a hybrid power system consisting of a solar photovoltaic (pv) and a wind power system. the system is modeled in matlab simulink and tested for various conditions. the model and results are discussed in this paper. keywords-five-level inverter; solar pv; wind energy; hybrid power system i. introduction the limited reserves of fossil fuel and environmental pollution have significantly increased the interest in renewable energy sources. hybrid wind-pv power systems as a distributed generation network structure have received considerable attention. such a system has the merit of supplying the difference in time and zone between wind power system and pv system. hybrid wind-pv systems have become a promising power generation form, as they can improve power reliability in certain remote areas such as deserts, plateaus etc. the hybrid wind-pv generation systems can achieve optimal performance by designing the rational system structure and choosing the coordinated optimization algorithm [1, 2]. active power filter (apf) is the modern solution used to eliminate the undesired current components by injection compensation currents in opposition to them [3]. the universal power converter topology used is the “two level voltage source inverter” [4-6]. due to power handling capabilities of power semiconductors, these converters are limited to low power applications. principally, the design of any apf system pass through three essentials criteria: power inverter topology, current controller and strategy control. multi level inverters are successfully used in medium and high power applications [7, 8]. instantaneous power theory [9] and synchronous reference frame detection method [10] have also been widely used. these techniques provide good results under different voltage source conditions but present some drawbacks such as a large calculations number, complex mathematical transformation and difficult practical implementation. the synchronous current detection method is another interesting method. it is concise and requires less computational calculations compared to the two other methods. in this work, the synchronous current detection technique is adopted using a five-level (npc) inverter after some necessary modifications. ii. the hybrid photovoltaic-wind system a schematic presentation of the proposed hybrid energy conversion system is given in figure 1. the system consists of the following elements: a doubly fed induction generator (dfig), a wind turbine, a pv generator and an inverter of fivelevel npc vsi. the wind turbine converts the wind kinetic energy into mechanical energy, which is transformed in electrical by the dfig and transmitted to the network. the dfig rotor is connected to the inverter. the purpose of the multilevel converter is to synthesize a sinusoidal form of the voltage with less harmonic distortion. however, it presents a fluctuating potential of mid-point inducing instability of its input voltages, and then instability of its output voltages. different pwm algorithms for the five-level npc vsi are available with the vector modulation strategy with four bipolar carriers [3, 4] to be considered one of the best. fig. 1. pv-wind hybrid system. engineering, technology & applied science research vol. 7, no. 4, 2017, 1759-1764 1760 www.etasr.com rezki and griche: simulation and modeling of a five -level (npc) inverter fed by a photovoltaic … iii. hybrid system modeling a. modeling of the aeroturbine the wind model used has been developed at risø national laboratory based on the kaimal spectra [11]. the wind speed is calculated as an average value of the fixed-point wind speed over the whole rotor, and it takes the tower shadow and the rotational turbulences into account. a main component in this model is the normally distributed white noise. therefore, in order to obtain the same wind time series in all considered simulation tools used in the simulation platform, some investigations have been done. it has been found that the builtin white noise generator from different simulation tools uses a different algorithm and thus a different wind time series is obtained. in order to validate the new white noise generator model, some comparisons have been done. a wind time series for 3600 sec with 0.05 sec sample time is shown in figure 2. 0 500 1000 1500 2000 2500 3000 3500 6 7 8 9 10 11 12 13 14 time (s) sp ee d (m /s ) wind profile fig. 2. the wind profile. the aerodynamic model of the wind turbine (wt) rotor is based on the torque coefficient qc or the power coefficient pc . the torque coefficient qc is used to determine the aerodynamic torque directly by using: 30.5wt qt r v c  (1) ςhere  is the air density, r is the blade radius ,v  is the wind speed, qc is the torque coefficient. alternatively, the aerodynamic torque can be determined using the power coefficient pc based on: 2 30.5wt pt r v c  (2) it is important to underline that both coefficients pc and qc can be function of the tip speed ratio  for passive-stall wind turbines or function of tip speed ratio  and pitch angle  for active stall and variable pitch/speed wind turbines. the parameters for this model are: blade radius, air density, cut-in and cut-out wind speeds, as shown in appendix. using a reduced look-up table in respect with the variation of the torque coefficient/power coefficient with the pitch angle ( 10 10 )     , the model for the active-stall wind turbine is obtained. imposing a zero value for the pitch angle  the model for passive stall wind turbine can be obtained. the equivalent model of a wind turbine drive train is presented in figure 3. the masses correspond to a large mass of the wind turbine rotor, masses for the gearbox wheels and a mass for generator respectively. [12] fig. 3. model of a wind turbine drive train taking into account the stiffness and the damping factors for both shafts, the dynamic equations can be written as follows:  1wtrwtr wtr wtr wtr swtr wtr d t j d k dt         (3)  11 1 1 1wtr swtr wtr d t j d k dt         (4)  2 22 2 2gen sgen gen d d t j d k dt dt         (5)  2gengen gen gen gen sgen gen d t j d k dt          (6) 2 1 1 gear t t k   (7) such as: wtr wtr d dt    , gengen d dt    ; ; 1, 2ii d i dt     ; 2 1geark   , (8) where: wtrt is the wind turbine torque, 1t is torque that goes in the gearbox, 2t is the torque out from the gearbox, wtrj is the wt moment of inertia, wtr is the wt mechanical speed, swtrk is the spring constant indicating the torsion stiffness of the shaft on wind turbine part, gent is the generator torque, genj is the generator moment of inertia, gen is the generator mechanical speed, sgenk is the spring constant indicating the torsion stiffness of the shaft on generator part. b. modeling of the dfig some of the machine inductances are functions of the rotor speed, whereupon the coefficients of the state-space equations (voltage equations), which describe the behavior of the induction machine, are time varying (except when the rotor is at stand-still). a change of variables is often used to reduce the complexity of these state-space equations. there are several engineering, technology & applied science research vol. 7, no. 4, 2017, 1759-1764 1761 www.etasr.com rezki and griche: simulation and modeling of a five -level (npc) inverter fed by a photovoltaic … changes of variables, which are used but there is just one general transformation [8]. this general transformation refers the machine variable to a frame of reference, which rotates at an arbitrary angular velocity g . in this reference frame, the machine windings are replaced with some equivalent windings as shown in figure 4. fig. 4. induction machine windings in the dq0reference frame the basic equation of the machine is:         d v r i dt     (9) based on (9) and using the general transformation, the voltage equations in the arbitrary reference frame can be written as:          dv r i dt      (10) the relation between the linkage fluxes and currents is given by:     l i  (11) the electromagnetic torque can be obtained starting from eq. (11) and multiplying it from the left with the transpose of the currents vector:                   t t t td i v i r i i i dt      (12) where:    tip i v is the instantaneous power.      t copperp i r i are the copper losses in the machine blades.    tmag d p i dt   is the magnetic power stored in machine (due to the variation in time of the magnetic energy) and     tmp i   is the mechanical power. the electromagnetic torque is then:  3 2 m m e sd sq sq sd r r p p t p p i i        (13) with p is the number of pole pairs and r is the mechanical speed of the rotor. c. flux oriented control of the dfig the principle of the vector control requires the knowledge of the exact position of the stream to orient at all times and make it coincide with the direct axis "d" at the same synchronous rotating speed. to achieve this, two approaches are possible to know the direct control and indirect control [13, 14]. in this work, the indirect control is used. • choice of reference by choosing two axes d-q repository related to rotating stator field and aligning the stator flux s illustration with axis d, we can write: 0 ds s qs      (14) therefore, the torque electromagnetic of dfig is given by: em sd rq s m c p i i l   (15) and the currents in the stator and rotor are: s ds dr s s dr qr s m i i l l m i i l      (16) the active and reactive powers are given by: s qr s s s s dr s s m p v i l v v m q i l l       (17) in steady state, the terms involving the derivatives of the two-phase rotor currents disappear. we can therefore write: 2 2 ( ) ( ) dr r dr s r qr s s dq r dq s r qd s s s s m v r i g l i l mvm v r i g l i g l l            (18) • indirect vector control the indirect method is to replicate reverse the block diagram of the system to be controlled. this builds a block diagram for expressing the rotor voltages functions and powers. the proportional-integral (pi) controller is used to control the dfig. fig. 5. indirect control block diagram without power loop engineering, technology & applied science research vol. 7, no. 4, 2017, 1759-1764 1762 www.etasr.com rezki and griche: simulation and modeling of a five -level (npc) inverter fed by a photovoltaic … figure 5 shows a closed loop system corrected by a pi controller given in the equation: ( ) ip k r s k s   (19) where pk : is the proportional gain controller and ik : is the integral controller gain. fig. 6. block diagram of the current control d. modeling of the pv module among the modeling methods of pv module, the two-diode model is known to be an accurate model as depicted in figure 7 [15]. the output current of the module can be described as: 1 s pv d p v ir i i i r          (20) where: 1 01 1 1 exp 1sd t v ir i i av            (21) and: 2 02 2 2 exp 1sd t v ir i i a v            (22) where pvi is the generated current by the incidence of light; 01i and 02i are the reserve saturation currents of diode 1 and diode 2, respectively. the term 02i is introduced to compensate for the recombination loss in the depletion region as described in [9]. other variables are defined as follows: 1tv and 2tv (both equal to /sn kt q ) are the thermal voltages of the pv module having sn cells connected in series, q is the electron charge ( 191.60217646 10 c ), k is the boltzmann constant ( 231.3806503 10 /j k ) and t is the temperature of the p n junction in kelvin. the variables 1a and 2a represent the diode ideality constants; 1a and 2a represent the diffusion and recombination current component, respectively. fig. 7. two-diode model of pv cell although greater accuracy can be achieved using this model than the single diode model [16], it requires the computation of seven parameters, namely pvi , 01i , 02i , pr , sr , 1a and 2a . recently, a fast and simple two-diode model is proposed in [17]. the simplified current equation is given as:  0 2 spv p p v ir i i i i r           (23) where: exp exp ( 1) s s p t t v ir v ir i v p v               (24) and 21p a  (25) iv. five -level inverter multilevel inverters are being investigated and recently used for active filter topologies. five-level inverters are becoming very popular today for most inverter applications, such as machine drives and power factor compensators. these advantages are the reduction of the harmonic content generated by the active filter and the decrease the voltage or current ratings of the semiconductors. figure 8 shows the circuit topology of a diode-clamped five-level inverter based on the six main switches (t11, t21, t31, t14, t24, t34) of the traditional two-level inverter, adding two auxiliary switches (t12, t13, t22, t23, t32, t33) and two neutral clamped diodes on each bridge arm respectively. the diodes are used to make the connection with the point of reference to obtain midpoint voltages. such structure allows the switches to endure larger dc voltage input on the premise of not raising the level of their withstand voltage. moreover, take phase-a as example, three kinds of voltage level udc/2, 0 and−udc/2. fig. 8. five level inverter npc engineering, technology & applied science research vol. 7, no. 4, 2017, 1759-1764 1763 www.etasr.com rezki and griche: simulation and modeling of a five -level (npc) inverter fed by a photovoltaic … v. case study –results and discussion figure 9 illustrates a schematic representation in its most simple form of hybrid energy conversion chain. this chain is made up of elements, which are: • a doubly fed induction generator (dfig). • a wind turbine converts energy of wind into mechanical energy injected directly to the rotor of dfig. • four photovoltaic solar panels that provide a dc voltage from solar energy. each panel consists of 36 cells connected in series. • a three-phase voltage inverter with five levels in npc structure whose role is to convert the dc voltage of the photovoltaic panels into an alternating voltage supplied to the stator of dfig. the schematic model of hybrid system is implemented in matlab / simulink. figure 10 shows the performance of the vector control and reactive power in the stator applied to a doubly fed induction machine. note that the active and reactive and current (ird, irq) are identified with their references powers. proportionality appears between the rotor current quadrature iqr and active power, and between direct current idr and reactive power. the quadrature component of flux is almost zero in steady state, which confirms the hypothesis of the vector control. note the effect of coupling between the two powers p and q, because that pref pass (0 to -800) to (t = 1s) there is a small oscillation in the graph of the reactive power q. it can be noted that the electromagnetic torque reacts spontaneously when there is a demand for active power, reactive power independent. in addition, the voltage response time issued by the panel is big. the voltage va is a consequence of the input voltage of the pv panel. we see an appearance of ripples levels of the stator flux, the rotor current and the electromagnetic torque. this is due to the nature of the voltage of the solar panel. figure 10 shows the performance of the vector control and reactive power in the stator applied to a doubly fed induction machine. note that the active and reactive and current (ird, irq) are identified with their references powers. proportionality appears between the rotor current quadrature iqr and active power, and between direct current idr and reactive power. the quadrature component of flux is almost zero in steady state, which confirms the hypothesis of the vector control. note the effect of coupling between the two powers p and q, because that pref pass (0 to -800) to (t = 1s) there is a small oscillation in the graph of the reactive power q. it can be noted that the electromagnetic torque reacts spontaneously when there is a demand for active power, reactive power independent. in addition, the voltage response time issued by the panel is big. the voltage va is a consequence of the input voltage of the pv panel. we see an appearance of ripples levels of the stator flux, the rotor current and the electromagnetic torque. this is due to the nature of the voltage of the solar panel. fig. 9. case study ( a) ( b) fig. 10. simulation results without mppt and a) without and b) with vector control) engineering, technology & applied science research vol. 7, no. 4, 2017, 1759-1764 1764 www.etasr.com rezki and griche: simulation and modeling of a five -level (npc) inverter fed by a photovoltaic … vi. conclusions a distributed coordinated hybrid wind-pv system structure based on dfig representing an isolated renewable energy site is investigated in this paper. five-level (npc) inverter neutralpoint diode clamped topology with the integration of a pv generator is proposed to provide a great improvement in the quality of the output voltages. the doubly-fed induction machine for the five level inverter is flux oriented controlled in order to improve the inverter’s performance. for future work, it is recommended to examine the performance of the proposed methodology by using other techniques such as fuzzy logic and sliding mode controller. references [1] o. vodyakho, t. kim, s. kwak, “comparaison of the space vector current controls for shunt active power filters”, iet power electronics, vol. 2,no. 6, pp. 653–664, 2009 [2] u. khruathep, s. premrudeepreechacharn, y. kumsuwan, “implementation of shunt active power filter using source voltage and source current detection”, iciea 2008, 3rd ieee conference on industrial electronics and applications, singapore, 3-5 june 2008 [3] e. e. el-kholy, a. el-hefnawy, h. m. mahrous, “three-phase active power based on current controlled voltage source inverter”, electric power and energy systems, vol. 28, pp. 537-547, 2006 [4] n. g. apte, v. n. bapat, a. n. jog, “a shunt active filter for reactive power compensation and harmonic mitigation”, ieee 7th international conference on power electronics, pp. 672-676, 2008 [5] s. bhattacharya, t. m frank, d. m divan, b. banerjee, “active filter system implementation”, ieee transactions on industry applications, vol. 4, no. 5, pp. 47-63, 1998 [6] m. routimo, m. salo, h. tuusa, “comparaison of voltage source and current source shunt active power filter”, ieee transactions on power electronics, vol. 22, no. 2, pp. 636-643, 2007 [7] o. vodyakho, c. c. mi, “three-level inverter-based shunt active power filter in three-phase three-wire and four-wire systems”, ieee transactions on power electronics, vol. 24, no. 5, pp. 1350-1363, 2009 [8] o. vodyakho, d. hackstein, a. steimel, t. kim, “novel direct currentspace vector control for shunt active power filters based on three-level inverters”, ieee transactions on power electronics, vol. 23, no. 4, pp. 1868-1873, 2008 [9] r. h. herrera, p. salemeron, h. kim, “instantaneous reactive power theory applied to active power filter compensation: different approaches, assessment, and experimental results”, ieee transactions on industrial electronics, vol. 55, no. 1, pp. 184-196, 2008 [10] s. bhattachrya, d. divan, “synchronous frame based controller implementation for a hybrid series active filter systems”, ieee thirtieth ias annual meeting industry applications conference ias '95, vol. 3, pp. 2531-2540, 1995 [11] a. shaltout, “analysis of torsional torques in starting of large squirrel cage induction motors”, ieee transactions on energy conversion, vol. 9, no. 1, pp. 135-141, 1994 [12] a. s. neris, n. a. vovos, g. b. giannakopoulos, “a variable speed wind energy conversion scheme for connection to weak ac systems”, ieee transactions on energy conversion, vol. 14, no. 1, pp. 122-127, 1999 [13] t. petru, t. thiringer, “modeling of wind turbines for power system studies”, ieee transactions on power systems, vol. 17, no. 4, pp. 1132–1139, 2002 [14] s. seman, s. kanerva, j. niiranen, a. arkkio, “transient analysis of wind power doubly fed induction generator using coupled field circuit model”, 16th international conference on electrical machines icem 2004, cracow, poland, september 5-8, 2004 [15] d. s. h. chan, j. c. h. phang, “analytical methods for the extraction of solar-cell singleand double-diode model parameters from i-v characteristics”, ieee transactions on electron devices, vol. 34, no. 2, pp. 286-293, 1987 [16] k. ishaque, z. salam, h. taheri, “simple, fast and accurate twodiode model for photovoltaic modules,” solar energy materials and solar cells, vol. 95, no. 2, pp. 586-594, 2011 [17] kc200gt high efficiency multicrystal photovoltaic module datasheetkyocera, available at http://www.kyocera.com.sg/products/ solar/ pdf/kc200gt.pdf engineering, technology & applied science research vol. 8, no. 3, 2018, 2923-2930 2923 www.etasr.com opanuga et al.: hall current and joule heating effects on flow of couple stress fluid with … hall current and joule heating effects on flow of couple stress fluid with entropy generation abiodun a. opanuga department of mathematics covenant university ota, nigeria abiodun.opanuga@covenantuiversity.edu.ng sheila a. bishop department of mathematics covenant university ota, nigeria sheila.bishop@covenantuiversity.edu.ng hilary i. okagbue department of mathematics covenant university ota, nigeria hilary.okagbue@covenantuiversity.edu.ng olasunmbo o. agboola department of mathematics covenant university ota, nigeria ola.agboola@covenantuiversity.edu.ng abstract—in this work, an analytical study of the effects of hall current and joule heating on the entropy generation rate of couple stress fluid is performed. it is assumed that the applied pressure gradient induces fluid motion. at constant velocity, hot fluid is injected at the lower wall and sucked off at the upper wall. the obtained equations governing the flow are transformed to dimensionless form and the resulting nonlinear coupled boundary value problems for velocity and temperature profiles are solved by adomian decomposition method. analytical expressions for fluid velocity and temperature are used to obtain the entropy generation and the irreversibility ratio. the effects of hall current, joule heating, suction/injection and magnetic field parameters are presented and discussed through graphs. it is found that hall current enhances both primary and secondary velocities and entropy generation. it is also interesting that joule heating raises fluid temperature and encourages entropy production. on the other hand hartman number inhibits fluid motion while increase in suction/injection parameter leads to a shift in flow symmetry. keywords-hall current; joule heating; entropy generation; couple stress fluid; adomian decomposition method i. introduction the study of hydromagnetic flow has been extensively investigated in the past years due to its applications in mhd generators, flow control, shock damping in car absorbers, nuclear reactors, plasma studies, purifications of metal from non-metal enclosures, geothermal energy extractions, polymer technology and metallurgy. relevant investigation was pioneered in the first half of the twentieth century. thereafter several studies have been conducted. author in [1] investigated the spontaneous magnetic field in a conducting liquid in turbulent motion. in [2], magnetohydrodynamics at high hartmann numbers were investigated. author in [3] considered the effect of a uniform magnetic field on the eckman layer over an infinite horizontal plate at rest relative to an electrically conducting liquid rotating with uniform angular velocity about a vertical axis while authors in [4] analyzed the combined effect of free and forced convection on mhd flow in a rotating porous channel, authors in [5] investigated the radiation effect of magnetohydrodynamics flow of gas between concentric spheres. in [6], authors considered the radiative effect on velocity, magnetic and temperature fields of a magnetohydrodynamic oscillatory flow past a limiting surface with variable suction in [7], author considered the hydromagnetic natural convection flow between vertical parallel plates with time-periodic boundary conditions, authors in [8] studied convection heat and mass transfer in a hydromagnetic flow of second grade fluid in the presence of thermal radiation and thermal diffusion. in the studies above where the effect of magnetic field is reported, small and moderate values of the magnetic field are assumed. however, the current trend of research is geared toward a strong magnetic field and a low density gas due to its numerous applications such as in space flight, nuclear fusion research, magnetohydrodynamic generators, refrigeration coils, electric transformers, hall accelerators and biomedical engineering (e.g. cardiac mri and ecg). hall current occurs when the applied magnetic field is very strong or gas is ionized with low density leading to a reduction in conductivity normal to the magnetic field, as a result of the free spiraling of electrons and ions around the magnetic lines of force before collisions. this then induces a current in the direction of both electric and magnetic fields. this is referred to as hall effect, the induced current is called hall current [9-15]. in this study, the hall current and joule heating effects on the flow of couple stress fluid with entropy generation is considered. the study is essential due to the fact that entropy generation occurs in moving fluid with high temperature which can lead to loss of resources and effort if the inherent irreversibility in the fluid flow is not well addressed. authors in engineering, technology & applied science research vol. 8, no. 3, 2018, 2923-2930 2924 www.etasr.com opanuga et al.: hall current and joule heating effects on flow of couple stress fluid with … [16] submitted that all processes that produce, convert and consume energy must be re-examined very carefully and all available-work destruction mechanisms must be removed. to the best of our knowledge similar study has not yet been reported in literature, although various factors responsible for the entropy production have been studied, for instance in [17] authors considered effects of velocity slip and temperature jump on the entropy generation in mhd flow over a porous rotating disk. also, authors in [18] presented entropy generation on mhd nanofluid blood flow due to peristaltic waves. recently, authors in [19] studied the thermodynamic analysis of hydromagnetic third grade fluid flow through a channel filled with porous medium. in [20], the effect of thermal radiation on the entropy generation of hydromagnetic flow through porous channel was investigated. more studies on the factors responsible for entropy production are reported in [21-26]. several techniques such as homotopy perturbation [27], differential transform method [28-29], variational iteration technique [30], finite difference technique [31] etc. are available in literature. however, the adomian decomposition method is applied in this work due to its simplicity in application and rapid convergence, (see tables i and ii). furthermore, the method has been used to analyze various linear and nonlinear problems such as the fractional-order differential equations [32], the time dependent edem–fowler type equation [33], the navier–stokes equations [34], the evolution model [35], the flierl–petviashivili equation [36], the fourth-order wave equation [37], the peristaltic transport model [38], the fokker–planck equation [39] and the bratu’s problem [40]. ii. problem formulation fully developed, steady, incompressible and electrically conducting couple stress fluid between two parallel plates of distance h apart has been investigated. the coordinate system is taken such that the x-axis is along the lower plate in the flow direction, the y-axis is normal to the xy-plane while z-axis is made perpendicular to the plates. a constant pressure gradient is induced along the x-direction. hot fluid is injected into the channel wall at the lower plate and sucked off at the upper plate with the same velocity. following [41], the generalized ohm’s law with hall current is 0 ( ) ( )e ej j b e q b b        (1) it is further assumed that if (jx, jy, jz) are the components of the current density j, the equations of conservation of electric charge 0j  shows that jz is constant which is assumed to be zero because jz=0 at the plates which are electrically nonconducting. it then implies that jz=0, everywhere in the flow. furthermore, the electrical field e=0 [42]. following the given assumptions, (1) becomes: 0x yj mj wb  (2) 0y xj mj ub   (3) note that e em   represents the hall parameter. solving (2) and (3) for jx and jy gives:  0 21x b j w mu m     (4)  021y b j mw u m     (5) the governing equations for the flow following [43-44] are: momentum equation along axis x:   * 2 * 4 * * *2 *4 2 * * 2 2 * 2 * * * *2 *2 ; 1 (0) (0) 0 ( ) ( ), du dp d u d u dy dx dy dy m u mw m d u d u u u h h dy dy               (6) momentum equation along axis y:   * 2 * 4 * 2 * * * *2 *4 2 2 * 2 * * * 2 2 ; 1 (0) (0) 0 ( ) ( ), dw d w d w m w mu dy dy dy m d w d w w w h h dy dy             (7) energy equation:  2 2 2* 2 * * * 0 * *2 * * 2 22 * 2 * 2 *2 * 0*2 *2 * * ; (0) ( ) 0. p dt d t du dw c v k dy dy dy dy d u d w b w u dy dy t t h                                            (8) introducing the following dimensionless variables, ** * * 2 0 0 0 0 0 2 0 0 0 , , , , , , , , h h t ty u w h dp y u w g h v v t t v dx t t v hh a v s t v                     (9) equations (6), (7) yield the following dimensionless form;   2 4 2 2 2 4 2 2 2 2 2 1 , 1 (0) (0) 0 (1) (1), du d u d u m s g u mw dy dy a dy m d u d u u u dy dy           (10)   2 4 2 2 2 4 2 2 2 2 2 1 , 1 (0) (0) 0 (1) (1), dw d w d w m s w mu dy dy a dy m d w d w w w dy dy          (11)   2 22 2 2 22 2 2 2 2 2 2 ; (0) 0, (1) 1. r d d du dw sp br dy dy dy dy br d u d w jh u w a dy dy                                            (12) engineering, technology & applied science research vol. 8, no. 3, 2018, 2923-2930 2925 www.etasr.com opanuga et al.: hall current and joule heating effects on flow of couple stress fluid with … where 2 2 2 0 2 2 2 2 2 0 pr , , , ( ) ( ) , . p g h h c t h e br ns k k t t k t t b h jh brm m               (13) iii. adomian decomposition the adomian decomposition method is applied by writing (10), (11) and (12) in integral form as:   32 1 2 2 2 0 0 0 0 2 ( ) 3! , 1 y y y y b u y b y y du d u s g dy dy dydydydy m u mw m                   (14)   32 1 2 2 2 2 0 0 0 0 ( ) 3! , 1 y y y y f w y f y y dw d w m s w mu dydydydy dy dy m             (15) and   3 4 2 2 2 22 2 2 2 2 0 0 2 2 ( ) pr + . y y y b b y d du dw s br dy dy dy br d u d w dydy a dy dy jh u w                                                    (16) using the partial sum in (17) and the adomian polynomials for the non-linear terms in (18), (14)-(16) yield (19)-(21). the final stage for the implementation of adm is the coding of equations (19)-(21) in symbolic mathematica software, which yields a very large symbolic solution. 0 0 0 ( ) ( ), ( ) ( ), ( ) ( ), n n n n n n u y u y w y w y y y              (17) 2 2 2 0 0 1 0 1 2 1 0 2 2 2 2 0 0 1 0 1 2 1 0 2 : , 2 , 2 . : , 2 , 2 n n a u a u a u u a u u u b w b w b w w b w w w              (18)   32 1 0 2 2 2 0 0 0 0 2 ( ) 3! , 1 r n n y y y y b u y b y y du d u s g dy dy dydydydy m u mw m                     (19)   32 1 0 2 2 2 2 0 0 0 0 ( ) 3! , 1 r n n y y y y f w y f y y dw d w m s w mu dydydydy dy dy m               (20)   3 4 0 2 2 2 22 2 2 2 2 0 0 ( ) pr + . r n n y y n n y b b y d du dw s br dy dy dy br d u d w dydy a dy dy j a b                                                      (21) a. results verification the approximate solution obtained by adm can be verified by comparing our result and the one in [44] as displayed in table i. b. entropy generation analysis the local entropy generation expression [35] for the flow is given as  2 2 2 2 2* * * 2 * * * 0 0 2 2 22 * 2 * * *0 *2 *2 0 0 g k dt du dw e t dy t dy dy bd u d w w u t dy dy t v                                              (22) using (9) in (22) yields   2 2 2 2 22 2 2 2 2 2 2 d br du dw ns dy dy dy br d u d w jh w u a dy dy                                             (23) entropy generation within the flow can be analysed by letting   2 2 2 1 2 2 22 2 2 2 2 2 2 , d br du dw n n dy dy dy br d u d w jh w u a dy dy                                             (24) if bejan number (be) is less than one-half, irreversibility due to viscous dissipation dominates entropy generation and when (be) is greater than one-half irreversibility due to heat transfer dominates the fluid flow. bejan number (be) equal to one-half indicates that both contribute equally to entropy generation. the bejan number can be written as: fig br (j) vel y i the fro inc eff ma dem tre suc shi is du usu tha the par tem ho flu engineerin www.etasr 1 1 1s n be n    tabl g=1, s=0.1, s/n 0 0.1 0.0 0.2 0.0 0.3 0.0 0.4 0.0 0.5 0.0 0.6 0.0 0.7 0.0 0.8 0.0 0.9 0.0 1 2.20 table ii. s/n 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 i this section gures 1-13 by r=0.5. to expla ), suction/inje locity profile, s presented in e influence of om these figur creases. this i fect of the lo agnetic field monstrate that end is revers ction/injection ift in flow sym in figures 3 displayed. we ue to the fact ually generate at retards fluid e variation in rameter is d mperature is r wever hall cu uid temperature ng, technology r.com 2 1 , . n n    le i. resul α=1, μ=0 uadm 0 − 03714182 07024039 09612623 11255559 11818879 11257781 09616293 07027825 03716603 02672×10-11 results (exact g = 1, s = 0 uexact 6.94e-15 0.003714182 0.007024039 0.009612623 0.011255559 0.011818879 0.011257781 0.009616293 0.007027825 0.003716603 9.98e-15 iv. result n presents res fixing parame ain the effect o ection (s) and the non-dime n figures 1 to f hall current res that fluid m is due to the f orentz resistiv on fluid m t fluid motion sed at the n parameter ( mmetry. (a) and 3(b), m e can see that that applicati es a resistive ty d flow. the r hall parame epicted in f educed for di urrent does no e. y & applied sci op lts for velocity [44 uexact −3.91321×10−14 0.00371418 0.00702404 0.00961262 0.0112556 0.0118189 0.0112578 0.00961629 0.00702782 0.0037166 3.91321×10-14 t solution) for 0.1, a = 1, m = 0 uadm 0 0.00371418 0.00702404 0.00961262 0.01125556 0.01181888 0.01125778 0.00961629 0.00702782 0.0037166 2.0267e-11 ts and discus sults of the a eters pr=0.71, of hall curren d magnetic ( ensional veloc 3. figures 1(a on fluid velo motion is enha fact that hall ve force impo motion. figur accelerates at upper wall (s>0) increase magnetic effe t fluid motion ion of transve ype of force c response of tem eter, joule hea igures 4-6. i fferent values ot have much s ience research panuga et al.: h (25 y profiles 4] uadm 0 0.00371418 0.00702404 0.00961262 0.0112556 0.0118189 0.0112578 0.00961629 0.00702783 0.0037166 -7.66586×10-18 velocity profil 6.94e-15 1.20e-12 2.22e-12 2.91e-12 3.05e-12 2.44e-12 8.78e-13 1.87e-12 6.13e-12 1.22e-11 2.03e-11 sion analysis as plo m=0.5, jh=2, nt (m), joule he (m) paramete city u and w a a) and 1(b) illu ocity. it is app anced as hall c current reduc osed by the ap res 2(a) and t the lower wa with injectio es, this indica ect on fluid ve is inhibited, t erse magnetic called lorentz mperature pro ating and ma in figure 4, s of hall param significant effe h v hall current an 5) les ots in , g=1, eating ers on against ustrate parent urrent es the pplied 2(b) all, the on as ates a elocity this is c field z force file to gnetic fluid meter, fect on fig. diffe fig. for d vol. 8, no. 3, 20 nd joule heatin 1. (a) primar erent m 2. (a): prima different s 018, 2923-2930 ng effects on f ( ry velocity profile ( ary velocity profil flow of couple (a) (b) e and (b) second (a) (b) le and (b) second 2926 stress fluid w dary velocity profi dary velocity profi with … file, for iles for fig diff engineerin www.etasr g. 3. (a) prima ferent m fig. fig. ng, technology r.com ary velocity profi 4. temperatu . 5. temperat y & applied sci op (a) (b) ile and (b) secon ure profile for dif ture profile for dif ience research panuga et al.: h ndary velocity pro fferent m fferent j h v hall current an ofile for incr effe tem mag hea fig hea gen hal fig and cor in s whi phe rep vol. 8, no. 3, 20 nd joule heatin fig. 6 figure 5 dem rease in the j ect of varying mperature. it i gnetic field in ating which e gures 7-9 rep ating and su neration. entro ll current and gures 7-8. joul d hartman num rresponding ris suction/injecti ile opposite enomenon is orted in figur fig. fig. 018, 2923-2930 ng effects on f 6. temperatur monstrates th joule heating g values of m is observed th ncreases, due enhances trans resent the in uction/injection opy generation d joule heat le heating is th mber, increase se in entropy g on parameter trend is obs attributed to es 2a and 2b. 7. entropy ge 8. entropy g flow of couple re profile for diffe at fluid temp parameter. fi magnetic field p hat temperatu to the increas sfer of heat t nfluence of h n parameters n is enhanced w ting paramete he product of e in the param generation. in retards fluid f served at pl the change i eneration for diffe generation for diff 2927 stress fluid w ferent m perature rises igure 6 depict parameter on ure is enhance se in fluid vis to the bound hall current, on the en with the increa ers as depicte f brinkman nu meters result i n figure 9, inc flow at plate y ate y = 1. in flow symm erent m ferent j with … with ts the fluid ed as scous daries. joule ntropy ase in ed in umber in the crease y = 0 this metry suc dis be suc jou tha ent jou bee non tec engineerin www.etasr finally, the ction/injection splayed in fig ejan number ction/injection ule heating an at both viscou tropy generati fig. 9. f f an analytica ule heating on en conducted ndimensionali chnique. the ng, technology r.com influence o n and magnetic gures 10–13. reduces as t n parameters v d magnetic pa us dissipation on. entropy gene fig. 10. bejan n fig. 11. bejan v. c al investigation n entropy gene d. the gover ised and solve solution obtai y & applied sci op of hall curre c parameters o figures 10 the values of vary while the arameters incre n and heat tra eration profile for number for differe number for differ conclusion n of the effects eration of a cou rning equatio ed using adom ined is used t ience research panuga et al.: h ent, joule he on bejan numb and 13 revea f hall curren trend is rever ease. it is conc ansfer contribu r different s ent m rent j s of hall curren uple stress flu ns were obt mian decompo to compute en h v hall current an eating, ber are al that nt and sed as cluded ute to nt and uid has tained, osition ntropy gen exp     vol. 8, no. 3, 20 nd joule heatin neration and plain the physi from the resu hall current i while the tem increase in temperature, e hartman nu temperature a both viscous entropy gener f fi u' w' μ p t' t0 k br g θ u, w v0 s 018, 2923-2930 ng effects on f irreversibility ics of the flow ults it is conclu increases fluid mperature and b joule heatin entropy genera umber retards and bejan num s dissipation a ration. ig. 12. bejan n g. 13. bejan nu nomen velocity c velocity c dy flu initia thermal c br dimensio dimen the dim constant veloc suction flow of couple y ratio. plots . uded that: d velocity and bejan number ng paramete ation and beja s fluid flow mber. and heat tran number for differe umber for differen nclature component along component along ynamic viscosity fluid pressure uid temperature al fluid temperatur conductivity of the rinkman number onless pressure gra sionless temperat mensionless veloci city of fluid suctio n/injection parame 2928 stress fluid w are presente entropy gener are reduced. r enhances an number. w, increases sfer contribut ent s nt m x-axis y-axis re e fluid adient ture ities on/injection eter with … ed to ration fluid fluid tes to engineering, technology & applied science research vol. 8, no. 3, 2018, 2923-2930 2929 www.etasr.com opanuga et al.: hall current and joule heating effects on flow of couple stress fluid with … (s>0 is suction and s<0 is injection) v kinematic viscosity ns dimensionless entropy generation rate be bejan number eg entropy generation parameter ω temperature difference parameter cp specific heat at constant pressure η fluid particle size effect due to couple stresses h channel width ρ fluid density β0 uniform transverse magnetic field μ magnetic field parameter jh joule heating parameter a couple stress parameter pr prandtl number m hall current parameter references [1] g. k. batchelor, “on the spontaneous magnetic field in a conducting liquid in turbulent motion”, proceedings of the royal society of london. series a, mathematical and physical sciences, vol. 21, no. 1066, pp. 406-416, 1950 [2] j. c. r. hunt, j. a. shercliff, “magnetohydrodynamics at high hartmann number”, annual review of fluid mechanics, vol. 3, 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applied mathematics, vol. 34, no. 1, pp. 293–307, 2015 [45] a. bejan, entropy generation through heat and fluid flow, wiley, new york, 1982 engineering, technology & applied science research vol. 8, no. 3, 2018, 3048-3053 3048 www.etasr.com oad et al.: flexural stress-strain behavior of rc beams made with partial replacement of coarse … flexural stress-strain behavior of rc beams made with partial replacement of coarse aggregates with coarse aggregates from old concrete part 1: 1:2:4 ratio mahboob oad department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan engrmahboob04@gmail.com abdul hafeez buller quaid-e-awam university of engineering, science & technology nawabshah, pakistan engrabdulhafeezbuller@gmail.com bashir ahmed memon department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan bashir_m@hotmail.com noor ahmed memon department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan nahmedmemon@gmail.com abstract—occupancy, particularly in urban areas, requires more space than ever. space constraints need erection of high rise buildings in place of short height buildings. this need demolishing of old structures which creates huge quantities of demolished concrete. one of its best disposals is its use in new concrete. therefore, this research work uses 50% replacement of natural coarse aggregates with coarse aggregates from old concrete to study the flexural stress-strain behavior of reinforced concrete beams. total of 12 reinforced concrete beams (900x150x150 mm) were cast with 2#4 bars in tension and 2#4 bars in compression zones. ordinary portland cement with hill sand and crush aggregate was used in 1:2:4 proportions. water cement ratio used is 0.54. the beams were cast in two batches, one with 100% natural aggregates and another with 50% natural coarse aggregates replaced with coarse aggregates from old concrete. in each batch 3 beams were cured for 7 and 28 days respectively. after curing all beams were tested with central point load. the beams were monitored at regular intervals for load, displacement, strain and load until first crack. the beams under study were compared with the controlled specimen. the results were in good agreement with the normal concrete specimen. maximum reduction in flexural stress is recorded as 8.8% for 7-day cured beams and 5.52% for 28-day cured specimen. thus, the use of coarse aggregates from demolished concrete in new concrete is proved to be promising partial replacement of coarse aggregate in terms of flexural stress-strain relationship. keywords-flexural stress; green concrete; old concrete; recycled coarse aggregates; strain i. introduction migration from rural areas to city centers due to attractive opportunities of jobs and living style has posed a serious problem of accommodation around the globe. due to limited residential space and limited space for associated facilities, construction industry is forced to opt for vertical construction instead of short height buildings. to this end, demolishing of short height buildings generates huge quantities of demolishing waste. this needs proper disposal, generally by dumping in reserved areas. the city centers already lack such space thus the problem of proper disposal emerges. one way of dealing this waste is by making use of it in new construction as whole or partial replacement of ingredients of new concrete. this will not only reduce the problem of waste management but also will help in saving the natural aggregates. attempts have been made to make use of various ingredients of construction waste by screening or detailed reprocessing. re-use of bricks, glass, wood, old concrete, etc. has been done and it was observed that utilization of these materials as an aggregate in new constructions has promising effects. it was believed that filler portion of concrete is 70% to 80% of total concrete volume. this filler is believed to be the coarse aggregates. also, it is believed that it has little effect on finished product, but research in the field reports differently. it reports that this component contributes much in determining stability, workability, durability and strength of the concrete. two main issues with conventional concrete remain hot. first engineering, technology & applied science research vol. 8, no. 3, 2018, 3048-3053 3049 www.etasr.com oad et al.: flexural stress-strain behavior of rc beams made with partial replacement of coarse … is the finding of alternative ingredient or material to enrich the strength and second is the use of waste obtained from demolishing of existing concrete structure. earlier, recycled aggregates were used mainly in low utility applications such as general fill. recently, these aggregates are used for intermediate utility application such as building foundations, roads etc. construction industry still has reservations on using recycled aggregates mainly due to doubts related to recycling methods, cost, machinery used in the process and the confidence in finished product. it is improving with time as research provides good insight of the use of such materials from different angles. however, it is also observed that scatter in reported observations in making use of recycled materials in concrete still demands more research in the area. therefore, in this research paper, flexural stress-strain behavior of reinforced concrete beams made by using coarse aggregates from old concrete as partial replacement of coarse aggregates is studied. the research work is basically divided into two parts. the first part outcome is this research article, which deals with 1:2:4 mix and the second part will deal with rich concrete mix. old concrete is collected from nawabshah city. large pieces of old concrete are then hammered to smaller pieces followed by sieving through 25mm sieve. using ordinary portland cement, hill sand, 50% crushed aggregates and 50% coarse aggregates from old concrete, 12 reinforced concrete beams were prepared using 1:2:4 mix (m15 grade concrete). 2#4 deformed bars were used in tension and compression zone respectively. #3 deformed bars were used as stirrups at 150mm center to center spacing throughout the length of beam. six beams were prepared with 50% replacement of recycled coarse aggregates and six beams are prepared using 100% natural coarse aggregates to compare the results. three beams of each group are cured for 7 days and three beams for 28 days in water. after curing time all beams were tested using central point load up to failure. load, deflection and strain are recorded at regular intervals. the load at which the first crack is appeared is also recorded. the flexural stress is then computed using empirical methods. obtained results are analyzed and presented in both tabular and graphical form. ii. literature review researchers remained actively engaged for a long time in finding alternative materials, which may be used as full or partial replacement of ingredient of concrete. to this end, glass, jute, husk, ash, old concrete, demolishing waste, polymers etc. have been studied by several scholars. but scatter in results is one of the key barriers to reach a solid conclusion for making use of these materials. this shows that there is still room for further research in the field. use of demolished waste of old structures has been studied by different scholars but the difficulties associated with the use of demolished waste in new concrete demands more work to understand its behavior. following literature review depicts the state of the art of the related work. author in [1] in a research paper on recent developments on the use of demolished concrete as coarse aggregates presented the details of the possibilities of use of demolished concrete as coarse aggregates and difficulties associated with the use of demolished concrete. author concludes that the use of demolished concrete as partial replacement of natural coarse aggregates has promising effect. author also concludes that if existing government policies are made more liberal and opportunities are introduced then the use of demolished concrete will increase. authors in [2, 3] made use of demolished concrete as partial replacement of natural coarse aggregates in preparation of concrete cylinders of standard size. they used 50% replacement of natural coarse aggregates with aggregates from demolished concrete. in one study, authors developed relationship between the tensile strength versus weight of concrete while in the other study they evaluated and compared the tensile strength of concrete cylinders with concrete cylinders made with 100% natural coarse aggregates. they concluded that with the use of demolished concrete results in loss of only 5% tensile strength of the tensile strength of concrete cylinders made with 100% natural coarse aggregates. authors in [4] studied the compressive strength of concrete cylinders using partial replacement of natural coarse aggregates with coarse aggregates from demolished concrete collected from nawabshah city. they made seven batches of concrete cylinders by replacing 0%, 5%, 15%, 25%, 35%, 45% and 50% natural coarse aggregates with mix ratio of 1:2:4 and 0.45–0.60 w/c ratio. they used a total of 54 cylinders with natural aggregates and 324 cylinders with recycled aggregates at curing age of 7, 14 and 28 days. based on laboratory test results, they observed maximum decrease in compressive strength equal to 26% with 50% replacement of natural aggregates. therefore, they concluded that demolished concrete can effectively be used as coarse aggregates in new concrete works of low load. authors in [5] studied the flexural behavior of beams made with partial replacement of natural coarse aggregates with coarse aggregates from demolished concrete. they used beams with 1:2:4 concrete mix and 0.45-0.55 water cement ratio. 2#4 deformed bars were used as main reinforcement and #2 bars were used as stirrups. the beams were cast with 50%, 60%, 70% and 80% replacement of natural coarse aggregates with coarse aggregates from demolished concrete. all beams were cured for 28 days followed by testing using central point load for flexural strength and cracking behavior. from the test results they observed minimum and maximum reduction in flexural strength equal to 12% and 26.6% respectively in comparison to beams made with 100% natural aggregates. based on the research findings they concluded that 88% strength can be achieved with 50% replacement of natural aggregates with demolished waste concrete aggregates. therefore, it can effectively be used in the areas of moderate or low load. authors in [6] studied the flexural behavior of reinforced lightweight concrete beams made with oil palm shell. they used 6 underweight reinforced concrete beams with steel reinforcement ratios from 0.52% to 3.9% to study deflection characteristics, ductility, cracking behavior and end rotations. from the test results, they observed that the proposed product compares well with other lightweight concrete models. in [7], flexural behavior of reinforced concrete beams using foamed glass was carried out. authors used foamed glass as partial replacement of coarse aggregates from 0% to 100% with engineering, technology & applied science research vol. 8, no. 3, 2018, 3048-3053 3050 www.etasr.com oad et al.: flexural stress-strain behavior of rc beams made with partial replacement of coarse … increment of 25%. in each beam 2 bars of 8mm size were used to reinforce it. authors observed that the density and compressive strength decreased with increase in dosage of foamed glass. based on the test results they concluded that the presence of foamed glass in reinforced concrete beams improved the flexural load at which first crack appears but the deflection at failure was observed more than in the control concrete beams. authors in [8] studied the flexural behavior of reinforced concrete beams made with low calcium fly ash-based geo polymer as replacement of opc. they tested four beams of 3m length up to failure under static load. based on test results they concluded that the use of the proposed material improves the flexural strength of reinforced concrete beams. authors in [9] studied analytically and experimentally the flexural behavior of concrete beams using gfrp bars. they tested 10 beams with dimensions 2800mmx300mmx120mm under four-point load up to failure. using the test results and regression analysis, authors presented an empirical equation to evaluate the effective moment of inertia for frp reinforced concrete beams. the proposed equation is compared with different code provisions and previous models for predicting. based on the comparison they concluded that the developed equation was good for frp reinforced concrete beams at high loads. author in [10] used cfrp-nsm technique to retrofit the reinforced concrete beams and studied their flexural behavior. based on the experimental observations he concluded the near surface mounted–carbon fiber reinforced polymer plates give better results than other techniques. authors in [11] studied the flexural behavior of reinforced self-compacting concrete containing ggbfs. their study used simply supported beams 2mx0.1mx0.1m with hysd bars with different percentages of ggbfs (0%, 30%, 40% and 50%) as partial cement replacement. they compared the test results with the results of control concrete specimens and found that the new product has promising effects on the strength and flexural behavior of reinforced concrete beams. authors in [12] used steel fibers to study the enhancement in flexural capacity of reinforced high strength concrete beams. they used 35mm long and 0.5mm diameter steel fibers in dosage of 1% and 2% to cast and test high strength concrete beams. the test results showed the improved properties of their proposed model. in [13] ggbs is used as partial replacement of opc to study the flexural behavior of rc beams. authors used 8 reinforced concrete beams with and without ggbs in dosage of 40% with glenium b-233 super plasticizer. the test results of specimen cured at 28 and 56 days revealed comparable results with control concrete beams. iii. model description and testing in this research work a total of twelve reinforced concrete beams with dimensions of 900mmx150mmx150mm are cast. out of these beams, six were prepared using old demolished concrete in 50% proportion, whereas the other six beams were cast using 100% natural coarse aggregates to compare the results. old concrete in the shape of large pieces is collected from nawabshah city (figure 1(a)). these large pieces are then hammered to size approximately equal to 25mm (figure 1(b)), followed by sieving of the material through 25mm sieve. both natural coarse aggregates and coarse aggregates from old concrete with hill sand and ordinary portland cement are proportioned in 1:2:4 ratio. water cement ratio used is 0.54. 2#4 deformed bars are used in both tension and compression zones respectively along with stirrups of #3 deformed bars at 150 mm center to center. the beams b1, b2, b3 (with 50% rca) and b7, b8, b9 (with 0% rca) were cured for 7 days. the beams b4, b5, b6 (with 50% rca) and b10, b11, b12 were cured for 28 days. after curing period, strain dumic pads were fixed on the sides of the beams in three positions i.e. one at center and two layers one above and one below the center layer with38 mm gap between layers (figure 2). the beams were tested in universal load testing machine with central point load (figure 3). load, deflection and strain were measured at regular intervals. flexural stress is then computed using numerical expression for flexural strength. (a) (b) fig. 1. (a) old concrete, (b) rca hammered to 25mm fig. 2. dumic pads fig. 3. beam under central point load iv. results and discussion all the beams are tested using a universal load testing machine with central point load applied gradually. load, deflection and strain were recorded at regular intervals of engineering, technology & applied science research vol. 8, no. 3, 2018, 3048-3053 3051 www.etasr.com oad et al.: flexural stress-strain behavior of rc beams made with partial replacement of coarse … approximately 2500n. load is applied till beam failure. all beams were carefully monitored during the loading process and the load at which first crack appeared was recorded. figure 4 shows the first crack in 3 beams. the crack appeared near support with diagonal orientation. similar pattern of first crack is observed in the other beams but with different locations between supports. after the first crack the load was increased till beam failure. failure of almost all beams started with widened crack starting from center and progressed diagonally up to support location. figure 5 shows the failure of selected beams. crack pattern shows beams failed in shear. from recorded load flexural stress is then evaluated by numerical expression given bellow 2 3 2 f pl bd   (1) where p is the central point load on beam, l is the length, b is breadth, d is depth of beam and f denotes flexural strength. fig. 4. first crack in beams b1, b3 and b4 fig. 5. failure of beams dial readings for strain at all locations were converted into strain by multiplying dial constant, followed by evaluation of average strain for all beams. deflection values recorded at intervals of approximately 2500n except for failure load were also recorded. flexural stress and strain are plotted in figure 6 for beams cast with 50% coarse aggregates from old concrete and cured for 7 days. the plot shows similar pattern of flexural stress versus strain, however, beam b2 showed slight downward jerk in strain between flexural stress values of 15n/mm2 and 20n/mm2. the cause could be that the coarse aggregate from old concrete is weaker. the jerk is less than 5% and therefore was ignored. the maximum flexural stress observed in this b3 was 30.16n/mm2 which was about 16.73% higher than that of beam b1 and 13.35% higher than that of beam b2. the deflection observed in all three beams was in the range of 5.1–5.2mm. the value obtained is 2%-4% higher than the approximate value given by aci-318 provisions (l/180). flexural stress versus strain for beams b4 to b6, cast with 50% coarse aggregates from old concrete and cured for 28 days, is plotted in figure 7. fig. 6. flexural stress-strain behavior of beams b1–b3 (7 days of curing with 50% rca) fig. 7. flexural stress-strain behavior of beams b4–b6 (28 days of curing with 50% rca) the pattern of all graphs is approximately the same with approximately same maximum value. maximum flexural stress in all three beams is recorded as 28.81n/mm2. maximum deflection in beams is recorded equal to 4.17mm which is within permissible values of aci 318 provisions. figures 8 and 9 show the flexural stress versus strain of beams cast with total natural aggregates and cured for 7 and 28 days respectively. three beams in each group were used. figure 10 presents the flexural stress and strain for 7-day cured beams made with 50% rca and 7-day cured beams made with 100% natural aggregates. it is clear from the figure that beams made with allnatural aggregates obtained more flexural stress and less strain than beams made with 50% rca. peak values of maximum load, deflection, flexural stress, strain and load at which first crack appeared are given in table i for beams made with 50% rca (7-day curing) and table iii presents the same for beams made with all-natural aggregates. the average of these values and the difference percentage with control specimen are given in table v. it can be noticed that beams made with 50% rca and cured for 7 days showed 8.8% reduction in maximum load and 20.47% less deflection. the same percentage reduction in flexural stress was recorded. however, these beams showed 12.99% more strain than control specimen. the first crack appeared in these beams at 8.97% lesser load than control specimen. figure 11 presents the same comparison as in figure 10 but for 28-day cured beams. peak values of parameters under consideration are given in tables ii and iv for 50% rca engineering, technology & applied science research vol. 8, no. 3, 2018, 3048-3053 3052 www.etasr.com oad et al.: flexural stress-strain behavior of rc beams made with partial replacement of coarse … beams and 0% rca beams respectively. average values of these parameters along with percentage difference are given in table vi. the beams made by 50% replacement of coarse aggregates showed 5.53% reduction in maximum load compared to beams made with 100% natural coarse aggregates. although this is surprising, these beams showed 40.8% less deflection than the control specimen. a reduction of 5.52% was recorded in flexural stress. also, these beams showed 12.25% more strain than control specimen. these beams showed first crack at 18.52% less load than beams made with all-natural coarse aggregates. fig. 8. 7 days cured beams (0% rca) fig. 9. 28 days cured beams (0% rca) fig. 10. flexural stress – strain comparison of all beams (7-day curing) fig. 11. flexural stress-strain comparison of all beams (28-day curing) table i. peak values of 7 days cured 50% rca beams beam max load (n) deflection (mm) stress (n/mm2) strain load at first crack (n) b1 65098 5.13 25.01 0.00305 50031 b2 65069 5.12 26.03 0.00314 45018 b3 75401 5.22 30.16 0.00302 55322 table ii. peak values of 28 days cured 50% rca beams beam max load (n) deflection (mm) stress (n/mm2) strain load at first crack (n) b4 72030 4.17 28.81 0.00338 55043 b5 68038 3.85 27.22 0.00336 50031 b6 69890 3.96 27.96 0.00326 55041 table iii. peak values of 7 days cured 0% rca beams beam max load (n) deflection (mm) stress (n/mm2) strain load at first crack (n) b7 74606 6.46 29.84 0.00271 55000 b8 73985 6.46 29.59 0.00272 55080 b9 73980 6.53 29.59 0.00272 55105 table iv. peak values of 28 days cured 0% rca beams beam max load (n) deflectio n (mm) stress (n/mm2) strain load at first crack (n) b10 73506 6.71 29.40 0.00295 45000 b11 72810 6.74 29.12 0.00295 45021 b12 75925 6.79 30.37 0.00300 45070 table v. average values of 7 day cured beams # beam max load (n) deflection (mm) stress (n/mm2) strain load at first crack (n) 1 b1 67665.00 5.16 27.07 0.00307 50123.67 b2 b3 2 b7 74190.33 6.48 29.68 0.00272 55061.67 b8 b9 % value 91.20 79.53 91.20 112.99 91.03 % difference 8.80 20.47 8.80 -12.99 8.97 engineering, technology & applied science research vol. 8, no. 3, 2018, 3048-3053 3053 www.etasr.com oad et al.: flexural stress-strain behavior of rc beams made with partial replacement of coarse … table vi. average values of 28 day cured beams # beam max load (n) deflection (mm) stress (n/mm2) strain load at first crack (n) 1 b4 69986.00 3.99 28.00 0.00333 53371.67 b5 b6 2 b10 74080.33 6.75 29.63 0.00297 45030.33 b11 b12 % value 94.47 59.20 94.48 112.25 118.52 %difference 5.53 40.80 5.52 -12.25 -18.52 from the obtained results it is concluded that the coarse aggregates from old concrete have promising effect on the strength of new reinforced concrete members. although the water absorption of these aggregates is higher than the natural coarse aggregates yet the percentage reduction in flexural strength is only 8.8% which even can be improved by controlling water-cement ratio or steel quantity. it is also observed that beams made with 50% replacement of natural coarse aggregates with coarse aggregates from old concrete observed about 41% less deflection than control specimen with no further reduction in flexural strength. this phenomenon shows better performance of the beams but needs further indepth evaluation and analysis of this effect with larger numbers of beams and considering water cement ratios. these beams also showed about 13% more strain when compared with control specimen. this is also a very good sign as it proves the ductility of the members and it will give more warning time before failure. the appearance of first crack is recorded at about 9% less load than that of control specimen but the reduction in flexural strength, peak load and failure mode of beams are in good agreement with the control specimen (figure 12). therefore, 50% replacement of natural coarse aggregates may comfortably be used initially in those areas where less load is applied on the structural members. fig. 12. peak load for 0% and 50% rca beams. (a) 7-day curing, (b) 28day curing v. conclusion this research paper presents experimental evaluation of reinforced concrete beams made with 50% replacement of natural coarse aggregates with coarse aggregates from old concrete. twelve reinforced concrete beams were prepared in two groups. in one group beams were cast with 50% rca, whereas in the second group, beams were prepared with allnatural aggregates and were termed as control specimen for result comparison. in each group three beams were cured for 7 days and the other three for 28 days. peak load, flexural strength, strain, deflection, load at which first crack occurs and failure mode were studied by testing beams under central point load. load was applied gradually up to failure. comparison and analysis of results showed that the beams observed maximum of 8.8% average reduction in flexural strength for cured beams for 7 days and average reduction of 5.52% for cured beams for 28 days. minimum strain gain of 12.25% was observed in 28day cured beams. the average deflection in these beams was recorded lower than the control specimen’s. this parameter needs further study for better conclusions. although first crack appeared at lower load than control specimen, yet cracking pattern and failure mode are in good agreement with the control specimen. therefore, it is concluded that the use of coarse aggregates from old concrete has promising impact on parameters studied in this research work and can be used comfortably initially in low loads. references [1] b. a. memon, “recent development on use of demolished concrete as coarse aggregates”, international journal of emerging technology and innovative engineering, vol. 2, no. 1, pp. 1–11, 2016 [2] s. tanwani, b. a. memon, “relationship between weight and tensile strength of concrete cylinders made by partial replacement of coarse aggregates from old concrete”, international journal of engineering inventions, vol. 5, no. 06, pp. 1-9, 2016 [3] s. tanwani, b. a. memon, “tensile strength of concrete cylinders made by partial replacement of natural coarse aggregates with coarse aggregates from old concrete”, international journal of emerging technology and innovative engineering, vol. 1, no. 4, 2015 [4] m. oad, b. a. memon, “compressive strength of concrete cylinders using coarse aggregates from old concrete”, 1st national conference on civil engineering (ncce 2013-14)-(modern trends and advancements), april 28–29, 2014 [5] b. a. memon, g. s. bhatti. “flexural behavior of beam made by partial replacement of natural aggregates with coarse aggregates from old concrete”, international journal of engineering sciences & research technology, vol. 3, no. 5, pp. 52-61, 2014 [6] d. c. l. teo, m. a. mannan, j. v. kurian, “flexural behavior of reinforced light weight concrete beams made with oil palm shell”, journal of advanced concrete technology, vol. 4, no. 3, pp. 459-468, 2006 [7] j. m. khatib, s. shariff, e. m. negim, “effect of incorporating foamed glass on the flexural behavior of reinforced concrete beam”, world applied sciences journal, vol. 19, no. 1, pp. 47-51, 2012 [8] s. kumaravel, s. thirugnanasambandam, “flexural “behavior of reinforced low calcium fly ash based geopolymer concrete beam”, global journal of researches in engineering civil and structural engineering, vol. 13, no. 8, pp. 8-13, 2013 [9] m. a. adam, m.said, a. a. mahmoud, a. s. shanour, “analytical and experimental flexural behavior of concrete beams reinforced with glass fiber reinforced polymers bars”. construction and building materials, vol. 84, pp. 354-366, 2015 [10] s. al-obaidi, behavior of reinforced concrete beams retrofitted in flexure using cfrp-nsm technique, msc thesis, portland state university, 2015 [11] m. mithra, p. ramanathan, p. muthupriya, r. venkatasubramani, “flexural behavior of reinforced self compacting concrete containing ggbfs”. international journal of engineering and innovative technology, vol. 1, no. 4, pp. 124-129, 2012 [12] n harsha vardan, k. kartheek babu, a. annadurai, “enhancing flexural capacity of steel fiber reinforced high strength concrete beams”, international journal of scientific research engineering technology, vol. 2, no. 2, pp. 57-61, 2016 [13] s. p. sangeetha, p. s. joanna, “behavior of reinforced concrete beams with partial replacement of ggbs”, american journal of engineering research, vol. 3, no. 1, pp. 119-127, 2014 (a) (b) microsoft word etasr_v12_n1_pp8157-8163 engineering, technology & applied science research vol. 12, no. 1, 2022, 8157-8163 8157 www.etasr.com anas et al.: designing an iot agriculture monitoring system for improving farmer’s acceptance of … designing an iot agriculture monitoring system for improving farmer’s acceptance of using iot technology siti aisyah binti anas faculty of electronics and computer engineering universiti teknikal malaysia melaka malacca, malaysia aisyah@utem.edu.my ranjit singh sarban singh faculty of electronics and computer engineering universiti teknikal malaysia melaka malacca, malaysia ranjit.singh@utem.edu.my nur adilah binti kamarudin electrical electronic validation, engineering validation, r&d engineering perusahaan otomobil nasional sdn bhd shah alam, selangor, malaysia nuradilah@proton.com abstract-this paper describes agri-snaps, an internet of things (iot) agriculture monitoring system designed to improve farmers’ acceptance of using iot technology in their farm field. agri-snaps consists of four dedicated sensor circuit modules that integrate magnetic pogo pin connectors for easier assembly with the controller circuit module. this work investigated how such a design can enable the farmers to understand how 1) to assemble, 2) self-troubleshoot, and 3) maintain the monitoring system independently without requiring expertise on the farm site. userexperience testing was conducted with ten participants to validate agri-snaps’s viability. the results showed that those participants positively rated agri-snaps as attractive, easy to understand and assemble, exciting, and innovative compared to the typical agriculture monitoring systems. keywords-internet of things; agriculture; industrial design; sensors; embedded system; human-computer interaction i. introduction internet of things (iot) is driving change in agriculture. it enables sensors on a farm to remotely monitor and give realtime data to the farmer, such as detecting the current environmental conditions [1]. the implementation of iot also allows the farmers to increase farm production effectively throughout the year. in line with the fourth industrial revolution (ir 4.0), farmers are always encouraged to implement smart farming using iot technology for better decision making [2, 3]. unfortunately, most farmers are still hesitant to adopt iot on their farm sites and prefer traditional farming practices, resulting in lower crop yields [4]. a deeper investigation revealed 4 main reasons why farmers were not ready to implement iot in their farm fields [2, 5]: 1) the level of education required to become familiar with the technology, 2) the lack of engineering skills needed to install the system, 3) the troubleshooting process required to sustain the system, and 4) the high cost of implementing the system. while previous studies focus on the benefits of implementing iot in the agriculture sector, to the best of our knowledge, there are no studies on improving the farmers’ acceptance of using iot technology. hence, this work focuses on how a typical iot agricultural monitoring system can be enhanced to enable the farmers to implement the system without requiring particular skills. with an improved design, farmers can easily understand how to self-integrate, self-troubleshoot and self-maintain the iot environmental monitoring system without requiring expertise on the farm site. as a result, it can increase the farmers’ willingness to accept innovative iot technology and help them gain control over growing crops. in the end, such technology will allow them to run a more predictable, efficient, and profitable agribusiness [4]. ii. background in previously conducted research, authors in [6, 7] developed an automatic iot environmental control system to optimize mushroom production. the developed system enables the farmer to remotely monitor and analyze the environmental conditions of the mushroom production house. based on the analyzed data, the system will automatically control the irrigation system to ensure the temperature level is optimum. this smart mushroom system has proven to optimize the mushroom’s quality and productivity. authors in [8] developed an automatic web-based iot agriculture fertigation system that allows the farmers to remotely set the fertigation schedule. the system also enables the farmers to formulate the fertilizer composition. in this way, the farmers can virtually manage their automated fertigation system by accessing the website using their mobile devices. authors in [9] proposed an iot corresponding author: siti aisyah binti anas engineering, technology & applied science research vol. 12, no. 1, 2022, 8157-8163 8158 www.etasr.com anas et al.: designing an iot agriculture monitoring system for improving farmer’s acceptance of … smart farming framework of cotton crops that supports smart reasoning based on the data streams from the embedded sensors deployed inside the cotton field. as a result, the framework provided real-time results that helped farmers make efficient event detection decisions. in addition, authors in [1012] developed an automatic iot irrigation system that measured and maintained the moisture content in the soil. through the system, the farmers can optimize the usage of water fertilizers while maximizing the yield of the crops. to summarize, all the mentioned iot research related to agriculture enables the farmers to increase the crop yield compared to conventional methods. this nonetheless proved that iot technologies help to improve agricultural and farming industries. while previous research focused on the benefits of implementing iot technology, there are no studies on the willingness of the farmer to accept, adopt and sustain the iot system. therefore, this work focuses on designing and developing a simple and intuitive iot agriculture monitoring system that allows the farmers to understand how to implement it without much effort. such a design could improve the farmers’ acceptance of iot technology in their farm fields. iii. design and implementation a typical iot agricultural monitoring system is generally built with a complex architecture and is difficult for farmers to comprehend [13]. therefore, the complex architectural design of the iot agricultural monitoring system needs to be separated into two modules: 1) the controller module and 2) the sensor modules. the following sections will describe how the two modules are designed and developed to improve farmers’ acceptance of implementing iot technology in the farm field. a. 3d enclosure design one key design decision was to allow the farmers to clearly understand how to assemble and easily set up the iot weather monitoring system independently. figure 1 shows 3d enclosures uniquely designed to house the controller and the sensor modules. the controller enclosure is designed to fit the system’s brain (esp8266 wi-fi module). four sensor enclosures were designed to fit: the humidity sensor (esp01), the rain index sensor, the light intensity sensor, and the temperature sensor (ds18b20). color-coded schemes [14] and emboss sensor icons [15] were also integrated into the designed enclosure for easy differentiation and understanding. for example, the blue enclosure with the water drop emboss icon represents the humidity sensor. slot joints were also added to create a joint between two modules. therefore, by referring to the matched emboss icon, such a design allows the user to easily assemble the system by inserting the sensor module into the controller module slot joint, respectively. screw-fastened covers were also integrated to protect the electronic circuits placed inside the enclosure. figure 2 shows the microcontroller and the circuit sensor modules placed inside the 3d printed enclosures to ensure the electronic components are protected in any environment. however, putting the sensors inside the enclosures can result in an inaccurate sensor reading that might directly lead to substantial risks [16]. therefore, each of the sensors used for this system is mounted outside of the enclosure to provide a better and more accurate sensor reading. fig. 1. 3d casing design of agri-snaps. fig. 2. agri-snaps’s 3d printed enclosures. b. pogo pins and magnets the electronic connection of agri-snaps was inspired by the work of bdeir on littlebits [17]. like littlebits, pogo pins were used, specifically at the slot joint, to allow the current/signal to flow from the controller module to the sensor module and vice versa (figure 3). strong magnets were also used to enable a solid connection between the controller and the sensor modules. therefore the current/signal can flow smoothly throughout the system. figure 3 shows the placement of the pogo pins and magnets that are embedded into the designed enclosure. each sensor module enclosure is integrated with different magnetic poles combinations as a safety precaution. such combinations will protect the system if the user accidentally inserts the sensor module at the wrong slot joint, damaging the system’s circuit. for example, as shown in figure 5, magnets will repel each other when inserting a light intensity sensor module at the temperature slot joint. engineering, technology & applied science research vol. 12, no. 1, 2022, 8157-8163 8159 www.etasr.com anas et al.: designing an iot agriculture monitoring system for improving farmer’s acceptance of … fig. 3. pogo pins and magnets as an enabler mechanism to allow current/signal to flow from the controller to the sensor module and vice versa. fig. 4. integration of pogo pins and magnets into the 3d printed enclosures. fig. 5. magnets will push the sensor module away if the user tries to insert the sensor module at the wrong slot joint. c. power supply a typical 5v dc power connector is used to power the agri-snaps. it operates at 3.3v and has a maximum current draw of 70ma with a power consumption of 231mw. generally, agri-snaps will consume 2.024kwh over the year, and the electricity bill will only cost around 7 usd per year. therefore, implementing agri-snaps will not going to break the user’s bank. d. assembling procedures agri-snaps can be easily assembled. first, the user needs to match the emboss icon on top of the enclosures (figure 6(a)). then, the magnets will snap the sensor module into the controller module’s joint slot (figure 6(b−e)). any 5v dc power supply can be used to turn on agri-snaps. as shown in figure 6(f), a usb power supply cable connected to a waterproof solar power bank and plugged into the power slot is used to power up agri-snaps. afterwards, the user can decide where to integrate the system appropriately, as shown in figure 7. fig. 6. assembling procedure of the agri-snaps. fig. 7. agri-snaps placed directly in the farm field. e. iot data visualizations thingspeak is a web-based open api iot source information platform that can store sensor data and graphically present it on the web. agri-snaps uses the esp8266 nodemcu microcontroller to send the humidity, rain index, light intensity, and temperature data to the thingspeak platform over the internet. as shown in figure 8, thingspeak allows the farmers to visualize a live data stream from any web browser or mobile device and help them make accurate and proactive decisions. fig. 8. data visualization on thingspeak. engineering, technology & applied science research vol. 12, no. 1, 2022, 8157-8163 8160 www.etasr.com anas et al.: designing an iot agriculture monitoring system for improving farmer’s acceptance of … another key design was allowing the farmers to easily troubleshoot the system when required. suppose two of the sensor modules are not functioning properly due to broken, ageing or similar reasons (figure 9). in that case, agri-snaps will alert the user through the thingspeak platform. therefore, the user simply needs to snap out the broken sensor modules and buy new modules from the supplier. apart from that, agrisnaps can be customized following the user’s requirements. for example, the system will understand and function accordingly if the user decides to use humidity and temperature sensors in a certain situation, as shown in figure 10. fig. 9. notification of defect sensor modules. fig. 10. notification of unconnected sensor modules. iv. user-experience testing before testing, a typical iot agriculture monitoring system (figure 11) was developed to allow the users to use both the typical system and the agri-snaps. the user-experience testings for both system designs were compared and analyzed at the end of the testing. fig. 11. a typical iot agriculture monitoring system. a. participants within-subjects testing was designed to involve 10 farmers (7 males, 3 females, age range: 25 to 45). the farmers were evenly separated into two groups of 5 participants, groups a and b. b. procedures each participant was required to experience using the typical system for group a for 7 days. after that, they were asked to fill out a set of questionnaires. then, the procedure was repeated again by letting the participants in group a experience agri-snaps. after 7 days, they filled out the same set of questionnaires again. the same procedures were implemented for group b, except they were experiencing using agri-snaps initially and then the typical system. these procedures were designed to eliminate the ordering effects that might affect the testing’s outcome [18]. c. measurement the user experience questionnaire (ueq) [19] was used to measure the subjective impression of users towards a product (figure 12). the ueq questionnaire consistsed of 26 items divided into 6 individual scales: 1) attractiveness indicated the overall impression of the product, 2) perspicuity which measured the difficulty of participants to get familiar and learned how to use the product, 3) efficiency was the ability of participants to realize how to use the product without unnecessary effort, 4) dependability refers to the predictability when using the product, 5) stimulation shows participants’ excitement and motivation to use the product, and 6) novelty indicated whether the product was innovative, creative, and able to catch the participant’s interest. items 1, 12, 14, 16, 24, 25 were related to the attractiveness scale, items 2, 4, 13, 21 were related to the perspicuity scale, items 9, 22, 23 were related to the efficiency scale, items 8, 11, 17, 19 were related to the dependability scale, items 5, 6, 7, 18 were related to the stimulation scale, and items 3, 10, 15, 26 were related to the novelty scale. participants must express their experience with both the typical system and agri-snaps by marking each item of the ueq questionnaire with a 6-point likert scale. fig. 12. the user experience questionnaire (ueq). engineering, technology & applied science research vol. 12, no. 1, 2022, 8157-8163 8161 www.etasr.com anas et al.: designing an iot agriculture monitoring system for improving farmer’s acceptance of … d. results and discussion all the measured items have been summarized according to the scale as tabulated in table i. the unshaded rows were the percentage of the participants’ rating towards agri-snaps. the shaded rows were the percentage of the participants’ rating towards the typical circuit. to better understand the participants’ responses, figure 13 shows the overall mean values of the ueq questionnaire for each scale. the ueq scale mean ranges from −3 (horrible bad) to +3 (extremely good), with values between −0.8 and 0.8 indicating a neutral assessment [19]. table i. percentage of participants that rated each of the items according to the scale scales items -3 -2 -1 0 1 2 3 a tt r a c ti v e n e ss annoying/ enjoyable 50% 50% 20% 10% 40% 10% 20% bad/ good 40% 60% 20% 30% 20% 30% unlikeable/ pleasing 10% 90% 20% 40% 20% 10% 10% unpleasant/ pleasant 20% 80% 10% 10% 30% 50% unattractive/ attractive 20% 40% 40% 30% 10% 30% 30% unfriendly/ friendly 40% 60% 10% 30% 40% 20% p e r sp ic u it y not understandable/ understandable 20% 60% 20% 30% 10% 20% 10% 30% difficult to learn/ easy to learn 50% 50% 30% 40% 30% complicated/ easy 10% 60% 30% 30% 40% 20% 10% confusing/ clear 50% 50% 10% 30% 30% 10% 10% 10% e ff ic ie n c y slow/ fast 10% 60% 30% 10% 10% 60% 20% inefficient/ efficient 20% 40% 40% 20% 30% 30% 10% 10% impractical/ practical 20% 60% 20% 10% 40% 40% 10% cluttered/ organize 20% 40% 40% 20% 20% 40% 10% 10% d e p e n d a b il it y unpredictable/ predictable 40% 60% 10% 20% 30% 40% obstructive/ supportive 10% 10% 50% 30% 10% 10% 40% 30% 10% not secure/ secure 20% 20% 50% 10% 10% 10% 40% 30% 10% not meet expectation/ meet expectation 10% 20% 50% 20% 10% 20% 40% 30% s ti m u la ti o n inferior/ valuable 10% 60% 30% 20% 60% 20% boring/ exciting 40% 60% 20% 30% 40% 10% not interesting/ interesting 50% 50% 10% 30% 30% 20% 10% demotivating/ motivating 30% 50% 20% 10% 30% 30% 20% 10% n o v e lt y dull/ creative 50% 50% 40% 20% 20% 20% conventional/ inventive 10% 10% 60% 20% 20% 10% 30% 10% 20% 10% usual/ leading-edge 50% 50% 20% 10% 30% 40% conservative/ innovative 80% 20% 10% 30% 20% 20% 10% 10% unshaded rows: the collected results for agri-snaps shaded rows: the collected results tor the typical system based on the results, the scales mean values show very positive impressions for agri−snaps, ranging from 1.53 to 2.38 for all aspects of user experience. this indicates that the participant’s judgment of agri-snaps was that it was attractive, easy to understand, efficient, reliable, stimulating, and innovative. in contrast, the scales mean values for the typical iot agriculture system leaned towards negative impressions, with the scores ranging from −0.83 to −1.23. this result validates that although the typical system provided useful agriculture monitoring data, the participants seemed demotivated to depend on and use it when compared to agrisnaps. they felt the typical system was unattractive, difficult to understand, less efficient, unreliable, uninteresting and failed to grab their attention. fig. 13. overall results for ueq items, per scale. for agri-snaps, dependability was the least positively rated scale among the participants (m=1.53). the results suggested that participants may have difficulty predicting where the sensor modules should be snapped together with the controller module as 40% of participants rated agri-snaps as neither unpredictable nor predictable, 10% found it to be neither obstructive nor destructive and neither meet their expectation or not, and 20% felt agri-snaps as neither insecure nor secure. it can be speculated that the icon embossed on top of the controller and sensor module enclosures was not clearly visible to the user. therefore, instead of referring to the embossed icon, the design of agri-snaps can be improved by changing the color of the controller module slot joint. instead of using a white color scheme, the controller module slot joint should be matched with the color of the sensor modules. for example, the blue color slot joint at the controller module is to be attached with the blue color sensor module. this design approach will allow the user to instantaneously rely on the color scheme when assembling the agri-snaps. nonetheless, 50% of the participants rated agri-snaps as supportive, secure, and meeting their expectations, whereas 60% of the participants found the design of agri-snaps as predictable. in contrast, stimulation was the most positively evaluated scale (m=2.40), in which 60% (+2) of the participants found it to be exciting and 50% (+2) of them rated agri-snaps as motivating. also, half of the participants found the design of agri-snaps was positively interesting (+3). the results proved that agri-snaps has improved the way the participants perceived the iot system as more valuable than the typical system. although both systems were able to produce the same iot data visualization, the enhanced design of agri-snaps made the participants feel more motivated and interested in implementing the iot system in their farm field. perspicuity was the second most positively evaluated scale (m=2.38). 60% of the participants found agri-snaps as understandable and easy (+2). whereas 50% of the participants rated agri-snaps as easy to learn and clear (+3). this indicated that when compared to the typical system, the intuitive design engineering, technology & applied science research vol. 12, no. 1, 2022, 8157-8163 8162 www.etasr.com anas et al.: designing an iot agriculture monitoring system for improving farmer’s acceptance of … of agri-snaps managed to develop a better understanding of how to assemble, self-troubleshoot, and maintain the system independently without much effort. it should be noted that allowing the farmers to have a thorough understanding and a firm knowledge of the system is critical in order to galvanize and sustain their interest in the use of iot. attractiveness and efficiency were the third and fourth positively evaluated scales with m=2.28 and m=2.15 respectively. these results indicated that the participants liked agri-snaps and could practically assemble the system without unnecessary effort. this was reflected when 60% of participants rated agri-snaps as fast to assemble and practical (+3). also, 80% of the participants rated agri-snaps’s design as efficient and organized (+2 to +3). moreover, 90% of the participants found agri-snaps as pleasing (+3), whereas 60% rated the design of agri-snaps as friendly and good (+3). novelty was the participants’ second least positively rated scale (m=1.93), in which 20% of the participants found agrisnaps’s design as conventional (−1 to −2). the results suggested that despite agri-snaps’s inventive design, only 4 sensors were integrated into the system, limiting its capability to detect other changes in environmental conditions. however, it is a good starting point to investigate whether the design of agri-snaps can improve the farmers’ acceptance of using iot technology in their farm field. nonetheless, based on figure 13 and table i, the design of agri-snaps has been positively accepted among the participants compared to the typical iot agriculture monitoring system. v. future work and conclusion future work should further improve the design of agrisnaps by integrating more sensor modules, as illustrated in figure 15. the variety of sensors allows the farmer to choose which sensor modules are required to cater the crop grown on their farm field. in conclusion, the design of agri-snaps successfully allows the user to easily understand how to assemble, self-troubleshoot, and maintain the system independently without requiring an extensive understanding of iot technology and electronic concepts. these features enable the farmers to improve their acceptance towards implementing iot technology in their farm fields. fig. 14. the design concept of agri-snaps with more sensor modules integration. acknowledgement the authors wish to acknowledge the support from the ministry of higher education of malaysia (mohe), advanced sensors and embedded control (asecs) research group, centre for telecommunication research & innovation (cetri), fakulti kejuruteraan elektronik dan kejuruteraan komputer (fkekk), universiti teknikal malaysia melaka (utem), hang tuah jaya, durian tunggal, melaka, malaysia. this work was financially supported by utem internal grant (pjp/2020/fkekk/pp/s01759) references [1] v. narayanamurthy and f. samsuri, "perspectives of a farmer 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[19] m. schrepp, j. thomaschewski, and a. hinderks, "construction of a benchmark for the user experience questionnaire (ueq)," international journal of interactive multimedia and artificial intelligence, vol. 4, no. 4, pp. 40–44, jun. 2017, https://doi.org/ 10.9781/ijimai.2017.445. engineering, technology & applied science research vol. 8, no. 1, 2018, 2568-2571 2568 www.etasr.com umar et al.: taxonomy of fuzzy multi-attribute decision making systems in terms of model, inventor … taxonomy of fuzzy multi-attribute decision making systems in terms of model, inventor and data type rusydi umar department of informatics engineering universitas ahmad dahlan yogyakarta, indonesia rusydi_umar@rocketmail.com sunardi department of electrical engineering universitas ahmad dahlan yogyakarta, indonesia sunardi@mti.uad.ac.id yasinta bella fitriana department of informatics engineering universitas ahmad dahlan yogyakarta, indonesia yasintabella13@gmail.com abstract—decision support systems are one of the choices decision-makers make in an attempt to cope with the problems related to the time length required in decision-making process. such systems are known to improve the efficiency and accuracy in the decision-making processes. in developing a decision support system, a certain calculation method is required as part of its processing. one of the most commonly used methods is fmadm. this research discusses the clustering of decision support system using fmadm in an attempt to provide a taxonomy of decision support system based on fmadm. keywords-artificial intelligence; decision support system; fuzzy; taxonomy i. introduction a decision support system (dss) is a computerized system that will provide results in the form of ranking based on the assessment aspects determined by decision makers. dsss are derived from expert systems and are part of the artificial intelligence (ai) field and of the applications that aim to help solving common knowledge-based cases [1]. dsss are systems that try to gather and exploit human knowledge and experience in artificial intelligence systems so that they may assist in, or even perform, decision making [2]. some examples of research on expert systems are stroke detection [3], animal disease identification [4, 5] and motor engine damage detection [6]. one of the algorithms used in dsss is the multiple criteria decision making (mcdm) algorithm. however, mcdm is divided into several types. this paper, following a similar approach to the one in [7], provides a short literature review on mcdm taxonomy focusing on multi attribute decision making (madm) aiming to provide a taxonomy of fuzzy multi-attribute decision making systems in terms of model, inventor, and data type methods. ii. result and discussion mcdm is a decision-making method that can be used to establish the best choice from a number of alternatives based on certain criteria, e.g. size, standard etc [8]. however, mcdm has a minor disadvantage: if the data provided by the decision maker or the attribute of the data is incomplete, then the resulting decision will contain uncertainty. the problem of uncertainty can be caused by several things, namely: 1. information that cannot be calculated, 2. incomplete information, 3. unclear information and 4. partial abandonment [9]. to solve these problems, some research on the use of fuzzy mcdm began to be conducted in order to find methods that proved to have excellent performance. fmcdm can be divided into 2 models: fuzzy multi objective decision making (fmodm) and fuzzy multi attribute decision making (fmadm). fmadm model then can be further divided into 2 models namely the yager and the baas & kwakernaak model. based on the type of data, fmadm can be divided into 3 types, namely fuzzy data, crisp data, fuzzy and crisp data [10]. while based on the method of application, fmadm can be divided into 3 types, namely saw method, wp method and topsis. fmadm taxonomies are shown in figures 1-4 and are presented below. a. fmadm inventor-based taxonomy 1) yager model the yager model fmadm is the standard form of fmadm. according to [11],yager model has 5 completion stages, which are: 1. set a pairwise comparison matrix between attributes m based on saaty’s hierarchy procedure. 2. determine the consistent weight of wj for each attributes for each attribute based on the eigenvector method of saaty. 3. calculate the value of 4. determine the intersection of all 5. select with the largest membership degree in , and set the optimal alternatives. one of the researches related to dss using yager method is [12] which emphasize on theapplication of dss to solve cases about the determination of families as poor. a similar research, [13], was conducted to solve the best customer selection case. both researches resulted in a desktop-based decision support system that was able to assist the decision-making process in their respective cases. mo oft th ran set the wh of bro b. engineeri www.etas fig 2) baas in contrast odel is not a ften used by s he baas &kw nking of som ts[14].accord e following ste 1. evaluate follows: here w = (w1, f μzi is defined m through the ought to a fuzs the value 2. the best ∈ | ̅ fmadm da 1. crisp dat obtained their re considere ing, technology sr.com fig. 1. fm g. 2. fmadm & kwakernaa to the yager standard form some research wakernaak mod me aspects ding to[11]baa eps: each alterna ∑∑ ... , wm ; r1, .. as follows : in ,.. g function, th zy set sup ̅ ̅) is an alternative is ̅ ,∀ ∈ ata-type-base ta, also called directly from spective attr ed less suitabl gy & applied sc umar et al.: t madm taxonom inventor-based ta ak model r model, the m of fmadm hers for furthe del is a metho of an altern as and kwaker ative ai, thro .. , rm ). the m , ,.. he fuzzy set, with m n alternative en chosen as foll , and 1, ed taxonomy d standard data m the source [ ributes. use le. cience research taxonomy of f my axonomy baas &kwak m, but the con er developmen od that describ native using rnaakmodel co ough function (1 membership fu (2 , membership fun (3 nd value ai. lows: …, . (4 a is the origin [15] and grou of crisp d h fuzzy multi-att kernaak ncept is nt [10]. bes the fuzzy ontains n g as ) unction ) will be nction: ) ) nal data uped by data is c. th m we att no all [1 alt th pr th co w de de ra att ca w cr vol. 8, no. 1, tribute decision 2. fuzzy d overcom request. been tran generaliz function members fig . fmadm ap 1) simp saw[17] is he most comm multi-attribute eighted sum o tributes[10]. ormalizing the l alternative ju 8] : where rij is ternatives in t he preference ∑ a larger v referred/chose 2) weig the wp me he rating of orresponding a∏ where i = 1,2, enotes the crit enotes the crit ank for the att tribute of cos an be given as ∏∏ where v denote riteria, and w d 2018, 2568-25 n making syste data, this dat me the problem in this case th nsformed into zation of th , the fuzzy se ship value bei g. 3. fmadm pplicator-base ple additive w s known as th monly used val decisions. t of performanc saw meth e decryption m udgments. the the normaliz the attributec value for each vivalue indic n. ghted product ethod [19] uses each attribute attribute weigh ..., m, s repre terionvalue, w teria number. tribute of gain st. the relativ : ∗ es alternative denotes the we 71 ems in terms of ta is chosen m of uncerta he fuzzy data o fuzzy set. th he concept t has an uncle ing in the rang data-type-based ed taxonomy weighting (saw he linear weigh uation method the basic con e ratings on e hod requires matrix (x) to a e normalized zed performan cj; i = 1,2, ..., h alternative (v cates that th t (wp) s the normaliz e must be ra hts. this proce esents an alte w denotes the the rank wj n, and is nega ve preferences preferences, x eight of criteri 2569 of model, inven as the solu ain decision m is crisp data t he fuzzy set [ of a charac ear boundary w ge 0 to 1 [15]. taxonomy w) hting combina ds for making ncept is to ach alternativ s the proce scale proporti formula is as ( nce rating of m and j = 1, vi) is given as (6) he ai alterna zation process aised first w ess is given by (7 rnative prefer criterion’s we is a positive atively valued s of each alte (8 x denotes the v ia. ntor … ution to maker’s that has 16] is a cteristic with its ation or g simple find a e on all ess of ional to follows (5) f the ai ,2, ...,n. s: ative is s, where with the y (7). 7) rence, x eight, n -valued for the ernative 8) value of ide lim alt po ne de on wh sol ba wh wh sol sol engineeri www.etas 3) techn eal solution (t topsis is a mited alternat ternative mus ositive solutio gative solutio sribed as follo 1. create a 2. create a 3. determe matrices 4. determin alternativ negative 5. determin topsis req n each of the n ∑ here i =1, 2, lution a+ and ased on the nor here i = 1, 2, .. a+ = 1 , 2 a= 1 , 2 whereas and herej = 1,2,...n the distance lution is formu ∑ 1 the distance lution is formu ∑ the preferen ing, technology sr.com nique for or (topsis) a multi-criteri tives. the ba st have the s on and the f on [17]. in g ows [10]: normalized de weighted norm the matrix of negative id ne the distan ve with posi ideal solution ne the preferen quiresperforma normalized cj c ∑ ..., m; and j the ideal nega rmalized weig ..., m; and j = 2 ,… , 2 ,… , ; ; ; ; n. e between alte ulated as: 2 ; e between alte ulated as: ; nce value for e gy & applied sc umar et al.: t rder preferen ia method to asic principle shortest dista furthest distan general, top ecision matrix malized decisi of positive deal solutions; nce between itive ideal s n matrix; nce value for e ance rating of criteria, namel = 1, 2, ..., n ative solution ghted rating (y 1, 2, ..., n. ernative ai wi 1, ernative ai wi each alternativ cience research taxonomy of f nce by simila identify soluti is that the ance from the nce from the sis procedur x ion matrix ideal solution the value o olution matri each alternativ f each alterna ly: (9 n.the ideal p a-can be dete yij) as: (1 (1 (1 (1 (1 ith the ideal p ,2,… , (1 ith the ideal n 1,2,…, (1 ve (vi) is given h fuzzy multi-att arity to ions of chosen e ideal e ideal res can ns and of each ix and ve. ative ai ) positive rmined 0) 1) 2) 3) 4) positive 5) egative 6) n as: de in de is of m [1] [2] [3] [4] [5] [6] [7] [8] [9] [10 [1 [12 vol. 8, no. 1, tribute decision a largervi s fig the mcdm ecision making nformation is eveloped as a presented in f fuzzy multimodel, inventor ] e. d. rikh mendiagnosa dempster sha 1–10, 2013 ] y. n. istiqom saluran penc sarjana tekni ] p. wijayanti, stroke mengg informatika, v ] m. j. wahy penyakit uda sarjana tekni ] s. triyanto, kelinci berba 1, pp. 701-71 ] s. purnama, kerusakan telecommuni pp. 33–38, 20 ] r. umar, su system base journal of inn pp. 206–211, ] o. e. turban, intelligent sy andi publishe ] c. chen, c. m problems”, fu 0] s. kusumade attribute dec 1] h. -j. zimme academic pub 2] d. kartini, a madm yage miskin (studi tanah laut)”, 191–198, 201 2018, 2568-25 n making syste ; score indicates g. 4. fmadm iii. c m method is g due to the u provided. f solution to th this paper in -attribute deci r and data type re hiana, a. fadlil penyakit dalam afer”, jurnal sarja mah, a. fadlil, “s cernaan menggun ik informatika, v , a. fadlil, “sis gunakan metode vol. 2, no. 1, pp yudi, a. fadlil, ang galah deng ik informatika, v a. fadlil, “sist asis web”, jurna 1, 2014 f. firdausy, a mesin motor ication computin 007 unardi, y. b. fi ed on software novative science 2017 , j. e. aronson, t ystems (sistem p er, 2005 m. klein, “an ef uzzy sets and sys ewi, s. hartati, cision making (fu ermann, fuzzy s blishers, 1991 a. saputra, o. er pada sistem p i kasus : desa k , seminar ilmiah 5 71 ems in terms of 1,2,…, s that ai altern applicator-based conclusion s not conside uncertainty in uzzy mcdm hat issue. a sh an attempt to ision making e. ferences l, “implementas m pada manusi ana teknik infor sistem pakar untu nakan metode d vol. 1, no. 1, pp. 3 stem pakar men certainty factor p. 691–700, 2014 “sistem pakar gan metode the vol. 1, no. 1, pp. tem pakar untuk al sarjana teknik a. yudhana, “s menggunakan ng electronics an itriana, “taxonom and calculation and research t t. -p. liang, dec endukung keput fficient approach stems, vol. 88, n a. harjoko, r. uzzy madm), sets theory and soesanto, “impl pendukung keput karang rejo keca nasional teknol 2570 of model, inven (1 natives are pre taxonomy ered appropri results if inco m method ha hort literature provide a tax systems in te si sistem paka a menggunakan rmatika, vol. 1, n uk mendiagnosa dempster shafer 32–41, 2013 ndiagnosa jenis r”, jurnal sarjan untuk mengid eorema bayes 1 11–20, 2013 k mendiagnosa k informatika, vo sistem pakar pe borland del nd control, vol. my of decision n method”, inte echnology, vol. cision support sy tusan dan sistem to solving fuzzy no. 1, pp. 51–67, wardoyo, fuzz graha ilmu, 2006 its applications lementasi metod tusan penentuan amatan jorong k logi komputer, v ntor … 17) eferred. iate for omplete as been review xonomy erms of ar untuk n metode no. 1, pp. penyakit r”, jurnal penyakit na teknik dentifikasi ”, jurnal penyakit ol. 2, no. endeteksi lphi 7”, 5, no. 1, support ernational 2, no. 9, ystem and m cerdas), y madm 1997 zy multi6 s, kluwer de fuzzy keluarga kabupaten vol. 1, pp. engineering, technology & applied science research vol. 8, no. 1, 2018, 2568-2571 2571 www.etasr.com umar et al.: taxonomy of fuzzy multi-attribute decision making systems in terms of model, inventor … [13] r. b. permana, “pemilihan pelanggan terbaik dengan model yager pada pt. aesha surabaya”, available at: http://ppta.stikom.edu/upload /upload/file/04410100234makalah_ta.pdf [14] h. kwakernaak, “an algorithm for rating multiple-aspect alternatives using fuzzy sets”, automatica, vol. 15, no. 5, pp. 615–616, 1979 [15] e. prasetyo, “fuzzy database”, available at: http://www.slideserve.com /moeshe/fuzzy-database, 2012 [16] c. praseptyo, a. pujiyanta, “media pembelajaran himpunan fuzzy berbasis multimedia”, jurnal sarjana teknik informatika, vol. 2, no. 2, pp. 1176-1185, 2014 [17] i. kaliszewski, d. podkopaev, “simple additive weighting—a metamodel for multiple criteria decision analysis methods”, expert systems with applications, vol. 54, pp. 155-161, 2016 [18] y. melia, “multi attribute decision making using simple additive weighting and weighted product in investment introduction”, international academic institutefor science and technology, vol. 3, no. 7, pp. 1–15, 2016 [19] a. ahmadi, d. t. wijayanti, “implementasi weighted product (wp) dalam penentuan penerima bantuan langsung masyarakat pnpm mandiri perdesaan”, seminar nasional aplikasi teknologi informasi, pp. α19–α22, 2014 engineering, technology & applied science research vol. 7, no. 5, 2017, 1967-1973 1967 www.etasr.com eslami et al.: a probabilistic approach for the evaluation of fault detection schemes in microgrids a probabilistic approach for the evaluation of fault detection schemes in microgrids r. eslami department of electrical engineering amirkabir university of technology tehran, iran reza.eslami@aut.ac.ir s. h. h. sadeghi department of electrical engineering amirkabir university of technology tehran, iran sadeghi@aut.ac.ir h. askarian abyaneh department of electrical engineering amirkabir university of technology tehran, iran askarian@aut.ac.ir abstract—an important challenge in protection of a microgrid is the process of fault detection, considering the uncertainties in its topologies. equally important is the evaluation of proposed methods as their incorrect performances could result in unreasonable power outages. in this paper, a new fault detection and characterization method is introduced and evaluated subject to the uncertainties of network topologies. the features of threephase components together with the positive, negative and zero sequences of current and voltage waveforms are derived to detect the occurrence of a fault, its location, type and the engaged phases. the proposed method is independent of the microgrid topology. to evaluate the performance of the proposed method in various network topologies, a monte carlo scheme is developed. this is done by computing the expected energy not-supplied reliability index and the percentage of successful performance of the fault detection. simulation results show that the proposed method can detect faults in various microgrid topologies with a very high degree of accuracy. keywords-fault detection; reliability; network sequences; stransform; signal energy i. introduction despite the benefits counted for the microgrids, their designs remained at the laboratory level because of various technical reasons. one of the most important technical issues is the challenge of protecting these networks [1]. the dynamic behavior of microgrids in which a distributed generation (dg) is connected or disconnected from the network at any time and also the performance of the microgrids in both normal and isolated modes create the most important problems in protecting these networks [2]. the dynamic behavior of microgrids leads to diversity in magnitudes and the current directions which encounters the fault detection procedure with major problems. this issue signifies the necessity of studies in the field of determining the appropriate protection method for the microgrids [3]. the authors in [4-6] have introduced the protection challenges of microgrids. in [3, 4, 7, 8], authors categorized the various methods for solving this problem. these methods included voltage analysis, harmonic analysis, wavelet analysis, and s analysis. in this respect, authors in [9] suggested monitoring output voltage of distributed generations and transferring them from abc axis to dq axis and then determining threshold value in dq axis for detecting fault in the microgrids. in [10], authors detected faults using created spectrums from the harmonic impedance and their comparison by the central server. using wavelet transform analysis and s analysis was suggested in [11, 12] and deriving signal energy was investigated in [13]. all these studies considered only a certain topology for the microgrid so the effectiveness of these methods may face challenge in other topologies. in [14], the fault is detected by monitoring the thd of the output voltage of distributed generations and its comparison with a threshold value. in [15], authors used harmonic analysis for fault detection and the proportion of zero sequence current to positive sequence current in the fifth harmonic is used and only single phase to ground faults could be detected by it. lack of attention to the dynamic topology of microgrids, difficulty in detecting various faults (regular faults and high impedance) and inability to identify the transient states from the persistent faults were examples of problems seen in the previous studies. thus, in this paper a new method is suggested for fault detection in microgrids and is evaluated by means of monte carlo simulation. s-transform, positive, negative and zero sequences of current and voltage waveforms are used to detect faults. the presented method can respond to all dynamic topologies of microgrids. as it was mentioned, the new method is evaluated using monte carlo simulation. to do this, the performance accuracy of this method in detecting various faults is evaluated by means of expected energy not-supplied reliability index (eens) and percentage of successful performances. validation results of the suggested method for the persistent and transient faults properly show that this method has acted very well with very high reliability in detecting various faults in different topologies. in addition, this method can distinguish the difference between the persistent faults and transient states of microgrids. engineering, technology & applied science research vol. 7, no. 5, 2017, 1967-1973 1968 www.etasr.com eslami et al.: a probabilistic approach for the evaluation of fault detection schemes in microgrids ii. problem statement due to the short lines in microgrids, the fault occurrence in a point of network can lead to disturbance in other points of the network. to show this, figure 1 is presented. based on occurred fault in point f of figure 1, figure 2 shows the current signals seen in the various line modules in the network. as seen in figure 2, by a fault occurring at f, the current waveform of the faulted line is in overlap with the current waveforms of the sidelines. this issue bears difficulty in detecting the exact location of fault using traditional methods. meanwhile, this issue which the previous studies only emphasized the detection of fault occurrence is not true because inaccuracy in determining the fault location and fault type can lead to unnecessary switching in the safe lines and as a result reduction in protection system reliability. fig. 1. a sample microgrid another issue that challenged the previous microgrid protection methods is their inability to detect different fault types in the network. as mentioned before, short circuit current has high diversity in microgrids. the low amount of this current even encounters challenges of detecting regular faults. however, high impedance faults are of the important possible faults in the electricity networks in which the fault current produced is very low [16]. therefore, this type of faults requires very accurate methods for detection. this issue caused the authors in [16] to present a new relay design for detecting these types of faults. the new presented relay in [16] can only detect the high impedance faults and neglects the low impedance faults. therefore, it is obvious that to increase reliability, protection systems have to be designed in such a way that they could effectively protect the network in the all operational structures. meanwhile, protection has to be able to detect various possible faults (not one special fault) plus their exact locations by using various specifications of turbulent signals. iii. introduction and evaluation of the proposed fault detection method a. required substructure for the implementation of the proposed method figure 3 shows the required context for implementing the proposed method in this paper for fault detection in microgrids. as shown in figure 3, fault detection modules ( 1 :m m ) are installed at the beginning of network lines which have connection with a central server through communication links. the modules continuously take samples from voltage and current signals and deal with the proposed fault detection method to determine the occurrence of a fault, its type, and the line within it occurs. it is worth noting that in order to increase the accuracy of fault detection, the proposed strategy, for detection of fault occurrence, fault location, fault type and the engaged phases, is to use standard deviation (std) and signal energy obtained from the analysis of positive, negative and zero sequences and meanwhile three-phase components of voltage and current signal. this paper suggests using stransform to calculate the std and energy of voltage and current signals. fig. 2. fault current signals in different modules of figure 1 for fault f fig. 3. the required platform for the implementation of the proposed method b. fault detection process and its validation using monte carlo since the parameters and uncertainties vary through time, sequential monte carlo simulation is used to implement the proposed method. details have been presented in [17]. during simulation, the intended reliability indices are evaluated due to the possibility of fault occurrence in various network lines and dynamic behavior of microgrid topology. in this respect, implementation flowchart has been shown in figure 4. as shown, seven subroutines have been considered for implementing the suggested. it is worth noting that the performance accuracy of the proposed method has been evaluated in these subroutines based on the occurrence of permanent faults and transient distortions (including lines switching on and dgs switching on or off). subroutine 1: fixing faulty elements step 1: check whether the line is fixed due to repair rate. engineering, technology & applied science research vol. 7, no. 5, 2017, 1967-1973 1969 www.etasr.com eslami et al.: a probabilistic approach for the evaluation of fault detection schemes in microgrids step 2: if a line had been fixed, it should be switched on. step 3: implement changes of microgrid topology in the network. step 4: if the network topology is changed go to subroutine 2; otherwise go to subroutine 3. subroutine 2: simulation of transient state. step 5: simulate the transient state as a result of topology change (repaired lines switching on or dgs switching on or off) and then go to subroutine 4. subroutine 3: random numbers for determining the faulty lines. step 6: compare generated random numbers with the failure rate of lines, if there is a fault in a line, go to step 7; otherwise go to the step 1 in the next simulation. subroutine 4: fault detection step 7: sample three-phase current and voltage in different points of the network. signals are sampled by interval time of t and total sampling number being n. step 8: calculate positive, negative and zero sequences based on three-phase components for sampled signals. step 9: apply discrete s-transform to different signals as follows, , 1 2 [ , ] ( ). (( ) , ).exp( ) n m m u q q k n n j kn s lt u kt k l t nt nt n       (1) in which  is a running gaussian function window, 1 :m m , 0 1 2, , , , ,q seq seq seq a b c and ,u i v ; i and v indicate the current and voltage signals respectively. step 10: s-matrix, s , m u q , is the s-transform output as (2), , , , , , , , , , , , , , 1 2 1 [ , ] [ , ] [ , ] 1 2 1 [2 , ] [2 , ] [2 , ] [ , ] 1 2 1 [3 , ] [3 , ] [3 , ] 1 2 1 [ , ] [ , ] [ , ] m m m u q u q u q m m m u q u q u q m m m mu q u q u q u q m m m u q u q u q s t s t s t nt nt t s t s t s t nt nt t n s lt s t s t s tnt nt nt t s nt s nt s nt nt nt t                                    (2) step 11: calculate the energy matrix, e , m u q , whose elements are the square of the amplitude of the respective elements in the smatrix. step 12: calculate the signal energy, , m u qe , as follows, 2 , , 1 1 | [ , ] | n n m m u q u q e g g e s et nt     (3) step 13: calculate the standard deviation of signal, , m u qstd , as follows, 2 , 1 12 2 2 , 2 1 1 , 2 | [ , ] | (| [ , ] | ( )) n n m u qn n e gm u q e gm u q g s et ntg s et nt n std n           (4) step 14: compare std and signal energy values of voltage and current signals for positive, negative and zero sequences with threshold values. step 15: if all four values of each sequence at step 14 are above threshold values, it means a fault happened. otherwise; no fault occurred. if the last simulation was a result of topology change, go step 6. subroutine 5: detection of fault location step 16: calculate 1k index for modules which detected fault as follows, 0 1 2 0 1 2 0 1 2 0 1 2 1 1 1 , , , 2 2 2 , , , 3 3 31 , , , , , , 2 2 2 2 i seq i seq i seq i seq i seq i seq i seq i seq i seq l l l i seq i seq i seq e e e e e e k e e e e e e                               (5) step 17: determine two modules with the largest k1. step 18: determine current sign for these two modules (if the crossing current from a module is entering the line of that module, the sign of sensing current is positive. otherwise; the sign of sensing current is negative). step 19: if current sign of these two modules have the same mark, go step 20. otherwise; fault location is between these two modules. step 20: if there is another line at current flow path, go step 21. otherwise, the fault is at the last line of this path. step 21: determine the next module at current flow path and analyze whether this module detects fault occurrence or not. if it is detected, go step 22. otherwise; the fault is at the previous passed line of this path. step 22: if current sign of this module changed, fault location is at the line where this module locates. otherwise, go step 21. subroutine 6: detection process of fault type step 23: calculate m2k  and m3k  indices for module ( m m ) having the highest 1k index value as follows, 0 02 , , m m m i seq v seqk e e     (6) 1 2 2 1 3 , , , , 1( )m m m mi seq i seq v seqm v seq k e e e e         (7) step 24: determine fault type as follows, (8)double phase fault 2 2 m thk k  , 3 31 m thk k  engineering, technology & applied science research vol. 7, no. 5, 2017, 1967-1973 1970 www.etasr.com eslami et al.: a probabilistic approach for the evaluation of fault detection schemes in microgrids three phase fault  2 2 m thk k  , 3 31 m thk k  single phase fault  2 2 m thk k  , 3 32 m thk k  double phase to ground fault  2 2 m thk k  , 3 32 m thk k  step 25: determine the engaged phases in the fault using the energy values of the a , b , and c phase current waveforms, knowing that the faulty phases have larger energy values. subroutine 7: calculating reliability indices step 26: execute load flow and calculate and save not-supplied energy. step 27: if simulation state relates to a transient state, go step 6. otherwise, go step 28. step 28: if simulation time is lower than 8760 hours (one year), go step 1; otherwise calculate the eens. step 29: compare simulation time with 1000 years. if lower than this value, go subroutine1; otherwise calculate ens and percentage of successful performances as the final result. based on the mentioned steps, implementing of the proposed method is shown in figure 4. iv. simulation results to evaluate the proposed method, it was implemented on a sample microgrid which is presented in figure 5 having the substructure pointed earlier, the same to the one used in [18]. this microgrid is connected to upstream network through bus 1. four dgs are connected in buses 4, 5, 6, and 9. specifications for network load are presented in table i. based on the table i, loads are categorized into three types of residential, commercial and industrial. blackout cost for each load is extracted from [19]. in addition, daily load curve for loads is based on the patterns in [20]. considering the dynamic state of microgrid topology, like study [20] it was supposed that dgs in each feeder connect to the network when the feeder load reaches 97% load peak. table i. characteristics of the network loads load type reactive power (mvar) active power (mw) bus number commercial 1.5 4.8 2 industrial 2.5 4.5 3 municipal 0.8 2.7 4 municipal 0.5 2.5 5 industrial 0.7 2.2 6 commercial 4 3.4 7 municipal 1 2 8 municipal 1 3 9 for simplicity of calculations, it was assumed that all lines have the same repair and failure rates, and their values were 3 hours per fail and 0.8 fails per year respectively. it is worth noting that dgs’ reliability assumed 100%. the system studied is analyzed in two different scenarios. in the first scenario, it is assumed that fault is detected using traditional methods (high current value of a threshold value) by the central server. in the second scenario, according to the algorithm, the new method is used for fault detection. the results of these scenarios are then compared. it is worth noting that ens reliability index and percentage of successful performance of protection system calculated and analyzed for both scenarios. in both scenarios, transient states resulted from entering and exiting dgs and entering lines are assumed as the transient states. it is necessary that the proposed method does not react for these transient states because some of loads will not be power supplied due to the wrong reaction of the protection system. as the results in table ii represent, the proposed method has more appropriate indices for fault detection than those of the traditional methods. the reason is that the new methods have extraordinary accuracy in detecting faults with limited current. see table iii for more explanation. according to this table, while microgrid is working on isolated mode and only dg1 exists in the network, a fault in line 7 occurs. as it is clear, since one protected setup can be saved, therefore in the traditional methods, covering all faults is not possible. this issue is clear in table iii; while module 6 has been set up on 4ka performance current, and only dg1 exists in the network, the provided fault current by this dg will be 1.96ka. therefore, the fault is not detected by the main protection system and this issue will increase power outages. that’s why in table ii both ens index and percentage of successful performance of the proposed method are higher than that those of the traditional methods of fault detection. to do so, the behavior of proposed method versus double phase to ground fault, f1, on phases a and b with 100 ω fault resistance on line 2 of sample microgrid of figure 5 will be analyzed. to determine the values of the energy and the std thresholds of voltage and current signals for zero, positive and negative sequences, the worst situations that could challenge the proposed method which may interrupt the performance of detection algorithm are considered. these worst case scenarios are determined in such a way that fault detection algorithm can detect all the occurred faults and become indifferent for the transient stable states occurred in the network. the values for the normalized energy thresholds and also the normalized std thresholds for the voltage and current signals for zero, positive and negative sequences are presented in table iv and also based on the network topology, all possible fault types in various locations of the microgrid are simulated and the values of 2 thk , 31 thk , and 32 thk are found to be 0.458, 0.465, and 1.221, respectively. table v includes the values for the normalized energy and the standard deviation for zero and negative sequences of voltage and current signals obtained from s-transform for all modules after fault f1 is occurred. based on table v, fault occurrence is detected by 1, 2, 3, 5, and 6 modules. to find out the location of fault, table vi includes energy values of zero, positive and negative sequences of current waveforms for the modules which detected the fault. based on table vi, it is observed that the values of 1k at sensing modules 2 3m and are greater than the other ones and based on algorithm of fault location in figure 4, the detection algorithm has correctly detected the fault location on line 2. engineering, technology & applied science research vol. 7, no. 5, 2017, 1967-1973 1971 www.etasr.com eslami et al.: a probabilistic approach for the evaluation of fault detection schemes in microgrids fig. 4. evaluation algorithm of the proposed method using mont carlo simulation engineering, technology & applied science research vol. 7, no. 5, 2017, 1967-1973 1972 www.etasr.com eslami et al.: a probabilistic approach for the evaluation of fault detection schemes in microgrids table ii. reliability indices using the proposed method the new proposed method traditional scenario 113400 213000 ens (mwh/yr) 8010 7459 the number of occurred faults 15301 14746 the number of stable transient states 99.438 51.963 percentage of successful operation table iii. fault evaluation using traditional methods fault detection threshold magnitude fault current fault location unsuccessful 4ka 1.96ka line 7 table iv. normalized threshold values magnitude parameter magnitude parameter 0.028683 0, th i seqstd 0.045428 0, th i seqe 0.044978 1, th i seqstd 0.128013 1, th i seqe 0.029851 2, th i seqstd 0.061538 2, th i seqe 0.047726 0, th v seqstd 0.032678 0, th v seqe 0.077512 1, th v seqstd 0.07199 1, 1 th v seqe 0.060298 2, th v seqstd 0.040853 2, th v seqe table v. obtained normalized magnitudes by different modules after occurred fault f1 current signal voltage signal module number std energy std energy zero sequence negative sequence zero sequence negative sequence zero sequence negative sequence zero sequence negative sequence 0.379362 0.039851 0.123389 0.09009 0.159037 0.063072 0.093733 0.165176 1 0.781557 0.113859 0.353886 0.195613 0.216125 0.142548 0.247754 0.595129 2 0.147892 0.072361 0.220038 0.13365 0.238648 0.084298 0.1834 0.383602 3 0.032486 0.020524 0.042004 0.058979 0.213662 0.105177 0.118865 0.102636 4 0.145174 0.03576 0.093558 0.097953 0.183455 0.070036 0.036288 0.156191 5 0.048626 0.032323 0.075094 0.08735 0.048201 0.045436 0.063322 0.050916 6 0.020046 0.013267 0.016833 0.040954 0.041121 0.028792 0.025332 0.026994 7 0.012456 0.00498 0.007304 0.022525 0.035604 0.020386 0.009474 0.016614 8 table vi. calculated magnitudes of different parameters by modules which detect the occurred fault f1 current sign k1 energy of positive sequence of current waveform module number + 0.470175 0.133308 1 + 1.148062 0.244677 2 0.739419 0.165693 3 + 0.378299 0.09323 5 + 0.319105 0.081567 6 fig. 5. the microgrid studied by comparing the above values with the values of 2 0.476 thk  , 32 1.232 thk  and using 2, 0.674645i ae  , 2 , 0.783688i be  , and 2 , 0.341458i ce  , based on (8), it is concluded that the occurred fault type is double phase to ground on phases a and b . to determine the fault type, using the values of 0 2 , 0.353886i seqe  , 1 2 , 0.244677i seqe  , 2 2 , 0.195613i seqe  , 0 2 , 0.247754v seqe  , 1 2 , 1 0.468523 v seqe  , and 2 2 , 0.595129v seqe  , the values of fault detection indices of 22 0.60164k  and 2 3 1.503942k  are calculated. it is worth noting that figure 6 shows the way of convergence in ens reliability index for both methods. as it is clear, monte carlo algorithm reaches convergence after 1000 years in both methods and the proposed method created better ens value than traditional methods. this issue shows that the reliability of the proposed method is strongly higher than traditional methods. it is necessary to note that, in addition to the particular accuracy of the presented method in detecting various permanent network faults, the results show that this method has had the appropriate reaction toward the transient states. the percentage of successful operations in table ii represents the appropriate performance of the methods for both scenarios of permanent and transient faults occurred. fig. 6. monte carlo simulation convergence in both proposed scenarios engineering, technology & applied science research vol. 7, no. 5, 2017, 1967-1973 1973 www.etasr.com eslami et al.: a probabilistic approach for the evaluation of fault detection schemes in microgrids v. conclusions since the most important challenge of developing microgrids is the matter of fault detection, the scope of this paper is to present a new method for fault detection. the new proposed method uses the signal’s energy and std which has been derived form s-transform. to evaluate the method and determine its performance accuracy versus traditional methods, monte carlo simulation was used. using this simulation, ens reliability index and performance percentage of proposed method was compared with those of the traditional methods. the evaluations show that the proposed method has strongly higher reliability in contrast to reliability obtained by the transitional fault detection methods. correct performance of the proposed method was 99.44% in contrast to the 51.96% correct performance for traditional methods which represents a significant increase. it is worth noting that the performance accuracy of the intended methods is measured based on their proper reaction against permanent faults and the transient states. being independent from the topology is one of the advantages of the proposed method for fault detection, since the most important challenge in past designs was their severe dependence on the network topology. therefore, by using the new proposed method, microgrids can be protected in different topologies with very high reliability. references [1] t. liang, c. schwaegerl, s. narayanan, z. jian hui, “from laboratory microgrid to real markets challenges and opportunities”, ieee 8th international conference on power electronics and ecce asia (icpe & ecce), pp. 264-271, 2011 [2] t. s. ustun, c. ozansoy, a. zayegh, “modeling of a centralized microgrid protection system and distributed energy resources according to iec 61850-7-420”, ieee transactions on power systems, vol. 27, pp. 1560-1567, 2012 [3] w. jiang, z.-y. he, z. bo, “the overview of research on microgrid protection development”, international conference in intelligent system design and engineering application, pp. 692-697, 2010 [4] a. a. memon and k. kauhaniemi, “a critical review of ac microgrid protection issues and available solutions”, electric power systems research, vol. 129, pp. 23-31, 2015 [5] z. kai-hui, x. ming-chao, “impacts of microgrid on protection of distribution networks and protection strategy of microgrid”, international conference on in advanced power system automation and protection (apap), pp. 356-359, 2011 [6] m. a. redfern and h. al-nasseri, “protection of micro-grids dominated by distributed generation using solid state converters”, 9th international conference on developments in power system protection, pp. 670-674, 2008 [7] s. a. hosseini, h. a. abyaneh, s. h. h. sadeghi, f. razavi, a. nasiri, “an overview of microgrid protection methods and the factors involved”, renewable and sustainable energy reviews, vol. 64, pp. 174-186, 2016 [8] p. basak, s. chowdhury, s. halder nee dey, s. p. chowdhury, “a literature review on integration of distributed energy resources in the perspective of control, protection and stability of microgrid”, renewable and sustainable energy reviews, vol. 16, pp. 5545-5556, 2012 [9] h. al-nasseri, m. a. redfern, f. li, “a voltage based protection for micro-grids containing power electronic converters”, ieee power engineering society general meeting, 2006 [10] s. a. hosseini, h. askarian abyaneh, s. h. h. sadeghi, f. razavi, m. karami, “presenting a new method for identifing fault location in microgrids, using harmonic impedance”, iranian journal of science and technology, vol. 39, pp. 167-182, 2015 [11] a. m. el-zonkoly, “fault diagnosis in distribution networks with distributed generation”, electric power systems research, vol. 81, pp. 1482-1490, 2011 [12] s. a. saleh, r. ahshan, m. a. rahman, m. s. a. khaizaran, b. alsayed, “implementing and testing d-q wpt-based digital protection for microgrid systems”, ieee industry applications society annual meeting (ias), pp. 1-8, 2011 [13] s. r. samantaray, g. joos, i. kamwa, “differential energy based microgrid protection against fault conditions”, ieee pes in innovative smart grid technologies (isgt), pp. 1-7, 2012 [14] h. al-nasseri and m. a. redfern, “harmonics content based protection scheme for micro-grids dominated by solid state converters”, 12th international middle-east in power system conference, pp. 50-56, 2008 [15] m. petit, x. le pivert, l. garcia-santander, “directional relays without voltage sensors for distribution networks with distributed generation: use of symmetrical components”, electric power systems research, vol. 80, pp. 1222-1228, 2010 [16] m. a. zamani, t. s. sidhu, a. yazdani, “a protection strategy and microprocessor-based relay for low-voltage microgrids”, ieee transactions on ppower delivery, vol. 26, pp. 1873-1883, 2011 [17] r. billinton, a. sankarakrishnan, “a comparison of monte carlo simulation techniques for composite power system reliability assessment”, ieee conference proceedings on communications, power, and computing in wescanex 95, vol. 1, pp. 145-150, 1995 [18] w. k. a. najy, h. h. zeineldin, w. l. woon, “optimal protection coordination for microgrids with grid-connected and islanded capability”, ieee transactions on industrial electronics, vol. 60, pp. 1668-1677, 2013 [19] g. wacker, r. billinton, “customer cost of electric service interruptions”, ieee proceedings, vol. 77, pp. 919-930, 1989 [20] m. gilvanejad, h. a. abyaneh, k. mazlumi, “estimation of the overload-related outages in distribution networks considering the random nature of the electrical loads”, iet generation, transmission & distribution, vol. 7, pp. 855-865, 2013 microsoft word etasr_v12_n1_pp8168-8174 engineering, technology & applied science research vol. 12, no. 1, 2022, 8168-8174 8168 www.etasr.com sadeghi et al.: a simple and fast computation equivalent circuit model to investigate the effect of … a simple and fast computation equivalent circuit model to investigate the effect of tape twisting on the ac loss of hts cables alireza sadeghi department of electrical engineering shahrood university of technology shahrood, iran alisadeghi380@yahoo.com seyyed mesysam seyyed barzegar department of electrical engineering shahrood university of technology shahrood, iran seyyedbarzegar@shahroodut.ac.ir mohammad yazdani-asrami james watt school of engineering university of glasgow glasgow, uk m.yazdaniasrami@gmail.com abstract-this paper aims to evaluate the ac loss of a high temperature superconducting (hts) cable with respect to the twisting angle while considering mechanical constraints in an iterative approach. a 1km 22.9kv ac hts cable was selected in this study to assess the impact of the twisting angle alterations. the electromagnetic behavior of the selected hts cable was modeled using an equivalent circuit model (ecm). after the implementation of this model in matlab/simulink, a series of simulations were performed without the consideration of mechanical limits. they showed that the increase in the twisting angle leads to the decrease of the ac loss. afterwards, simulations were conducted to reduce the ac loss, while mechanical limits were taken into account. this could reduce the ac loss by 27.41% with a much lower computation time than finite element methods (fems). keywords-hts cables; power cables; twisting; magnetic field; ac loss i. introduction since the discovery of superconductors in 1911 by h. k. onnes, many investigations were initiated to enhance the critical temperature of superconductors. in 1986, j. g. bednorz and k. a. müller have introduced new superconductors with a critical temperature near 30k [1]. this has led to the rapid development in the manufacturing of high temperature superconducting (hts) tapes and wires. ever since the application of superconductors in power systems is gaining interest. consequently, numerous investigations were funded to take the advantage of hts materials in various apparatuses of power systems [2-9]. among them, hts cables are the most investigated components. they can be applied in common power systems as transmission or distribution lines [7]. they also play a significant role in future power systems with renewable energy resources and even smart grids [10-14]. accordingly, multiple studies have dedicated their efforts and funding to improve and model the electromagnetic and thermomechanical characteristics of hts cables. altogether, the main objective of these studies is to attain the proper behavior of hts cables and increase their efficiency. one of the most significant parameters which could entirely impact the characteristic of cables is ac loss. along with the passing of an ac current through hts tapes of a superconducting cable, alternating magnetic fields are generated in the hts cable [15]. the ac current and the generated fields induce losses in hts cables which are known as transport current loss and hysteresis loss respectively [16]. these losses increase the heat load of the cooling system and consequently, the efficiency of the cable is reduced [17, 18]. to avoid such consequences, numerous attempts were conducted to reduce the ac loss of cables. in [19] the ac loss of a 66kv hts cable was studied and reduced by the variation in the topology of the hts cable. this change is based on the increase of the radius of the former. by doing this, the number of hts tapes is increased in each layer and a lower current passes through each tape. however, this method increases the total cost and weight of the cable. in [20], the ac loss is reduced by the reduction of tape thickness. the thickness of tapes directly impacts their engineering current density and so, ac loss. a sensitivity analysis was conducted in [21] to reduce the ac loss of the cable by the variation of the twisting angle. this method is very effective and can reduce ac loss significantly. nonetheless, there is a lack of an iterative algorithm in this method to guarantee the certainty of the results. authors of [22] have also used the twisting angle increase to suppress the ac loss. however, they did not consider any types of mechanical constrain on the hts tapes. twisting angle was also used for the sake of gaining a uniform corresponding author: seyyed mesysam seyyed barzegar engineering, technology & applied science research vol. 12, no. 1, 2022, 8168-8174 8169 www.etasr.com sadeghi et al.: a simple and fast computation equivalent circuit model to investigate the effect of … current distribution in hts cables, without any attention to ac loss [23, 24]. the novelty of this paper is the reduction of the ac loss by varying the twisting angle in an iterative method while the mechanical limits of the hts tapes are considered to avoid mechanical issues. a 22.9kv hts cable with a length of 1km is opted to apply variations of twisting angle and the design improvement. all simulations were carried out in matlab/simulink. the results show that the twisting angle has a significant impact on the value of the ac loss. ii. structure of the hts cable and simulation procedure a. description of the hts cable and ecm to analyze the proposed method, a 22.9kv coaxial hts cable was considered [25]. figure 1(a) illustrates the structure of the chosen cable and table i tabulates the most important parameters of the cable. according to figure 1(a), the superconducting tapes of the cable are 2g hts tapes. more detailed information about these tapes is listed in table ii. the selected hts cable is a connection between the 22.9kv generation units and a 50 mva load at 50hz frequency. in this study, an ecm is put to work to simulate the behavior of the selected hts cable. (a) (b) fig. 1. the structure of (a) hts cable, (b) equivalent circuit model of the understudied cable. compared to fems, ecms not only have a lower simulation time but also can provide a more complex test power system with different buses, lines, and generation units for the simulation of an hts cable. so, an ecm for 22.9kv hts cable was provided which is shown in figure 1(b). in this figure, the subscript “hts” is devoted to the resistances and inductances of superconducting layers in each phase while “f” is related to former layers. there are also mutual inductances which are not shown in figure 1(b) to avoid complexity. however, self-inductances, mutual-inductance, and capacitances were calculated according to [26]. table i. information of the selected hts cable item value and type voltage/power (kv/mva) 22.9/50 tape ybco operational temperature (k) 70 insulation layer pplp primary pitch angle in each phase [a1 a2 b c] [18.1 o -16.3 o 30.7 o 45.8 o ] former radiuses [a b1 b2 c] (mm) [17 20 21 28] coolant ln2 table ii. ybco tape characteristics parameter value tape type ybco width and thickness (mm) 4.4 & 0.1 stabilizer thickness 50 (25 upper stabilizer and 25 lower stabilizer) upper shield thickness (µm) 2 lower shield thickness (µm) 1.8 ybco thickness (µm) 1 substrate thickness (µm) 45.2 b. modeling formulation the passing current through the cable induces a magnetic field with perpendicular and parallel components. these components vary with respect to the twisting angle and the pitch length. according to biot-savart law, these components of the magnetic fields are computed as follows [27]: ��� � �� �∑ �� �� � � � ������� ������� � �� �� � ���� � (1) ��� � �� � ������ ∑ � � � ������� ������� � ������� ��� �� � (2) �� � � ��� !"#� � ���"$%#� (3) �� ∥ � ���"$%#� � ��� !"#� (4) where �� �is the perpendicular component of the magnetic field in ith layer and �� ∥ is the parallel magnetic field, #� is the twisting angle, ��� states the axial magnetic field, and ��� expresses the azimuthal magnetic field. equations (5-8) represent the formulations of the pitch length in each layer of the cable [28]: ℓ(,� � *+�,-(,-., -/0 (5) ℓ(,� � 1*+�,-(, -., -/0 (6) ℓ.,� � *+�,-(,-., -/0 (7) engineering, technology & applied science research vol. 12, no. 1, 2022, 8168-8174 8170 www.etasr.com sadeghi et al.: a simple and fast computation equivalent circuit model to investigate the effect of … ℓ/,� = *+2(-(, -.,-/) (8) where ℓ(./,� is the primary twisting pitch of th ith layer of the three phases and rabc is the radii of the formers in each phase. as it can be seen, the twisting length is a function of the former radius. by accessing the pitch length of the phases, the calculation of the primary pitch angle of the hts cable is conductible according to (9) [29]: # = tan�� ℓ����� (9) the calculated twisting length and the twisting angle of the understudied cable based on (5-9) are tabulated in table i as simulation initial values. by having the magnetic field and the current distribution in each tape, the ac loss could be attained according to [30-32]: 67(8 = 9 �:;� < => ?�2 @� a� < 1�:;�<=> (�?� − �2?�d)@� a� > 1f (10) �� = g���� +���� (11) a� = ;�=>hi. (12) 6j�(�k = =>:�i�<�� l(2 − n�)n� + 2(1 − n�)ln (1 − n�)p (13) n� = �q��i� (14) where 67(8 is the magnetization loss in tapes, 6j�(�k is the transport current loss of superconducting layers, f is the frequency, �� is the permeability of vacuum, @� is a crosssection of layer i, rsis critical current density, b is the half width of hts tapes, �s� is critical current of the ith layer, and �t� is the peak value of the current. according to (10-14), twisting angle has a remarkable impact on the magnetic field and on ac loss [33]. as a matter of fact, the ac loss of a superconducting cable could be reduced by changing the initially calculated twisting angles. however, changing the twisting angle could jeopardize the mechanical stability of the tapes and this could lead to malfunctions in the hts cable. to attain the mechanical limits, firstly strain must be calculated. the strain is a function of twisting pitch and the calculation point of strain. this could be conducted as expressed in (15). if the mechanical limits surpass the threshold value, the critical current abruptly becomes zero. the correlation between the strain and the critical current of tapes is expressed in (15-19) [34]: *(u,ℓ) = 2v� �w<�x<y<�ℓ< (15) �/(z,*) = �/7(z)[1 − \(z) |* − *7(z)|�^ ∀* ≤ *����/(z,*) = 0 ∀* > *��� (16) \(z) = \� + ubcd(bz) (17) *7(z) = ϝz − *7� (18) �/7(z) = �/f> �1 − ggiy�7 (19) in (16), *��� is the maximum strain value of tapes. the other parameters are tabulated in table iii [34]. table iii. parameters of (16-19) parameter value hijk 1282 lmn 94 m 1.45 ok 3122 d 4.3e-4 e 0.201 pjk 0.44 f 5.1e-5 pqrr 1.1 figure 2 illustrates the normalized value of the critical current in different locations while the strain is varied. as shown in figure 2, the maximum value of strain in phase a is about 0.5%, while this value for phase b is about 0.95% and in phase, c is 1%. so, the angle of phase c should not be increased any further or the mechanical collapse will occur in this phase. on the other hand, in phases a and b, the maximum induced strain is lower than *��� and so, their angle can be changed. after analyzing the resulting critical current of different phases, it can be observed that the tapes of phase a are operating way lower than *��� and the angle of this phase could be further increased to reduce the ac loss of the system. the tapes of phase b have the maximum strain value of 0.95% and could be twisted a little further. c. simulation procedure of the proposed method to this section, the formulation, structure of the test system, the geometry of the hts cable, and the structure of ecm are discussed. this section is presented to characterize the proposed modeling procedure and the ac loss reduction. figure 3(a) represents the simulink model of the test system. it can be seen that hts cable with 1km length is used to connect the upstream grid and the load. the hts cable model is shown in figure 3(b). each phase of the cable is modeled by a variable resistance for hts tapes, a constant resistance for the former layer, and a matrix of self and mutual inductances between all layers. each variable resistance consists of multiple parallel superconducting tapes. one of these tapes is illustrated in figure 3(c). in this figure, rybco is the resistance of the superconducting layer of tape, rag is the resistance of a silver layer of the tape, and rcu and rsolder imply the resistivity of the copper stabilizer layer and solder, respectively. these resistances along with the resistivity of the former and the inductances are calculated in each iteration and inserted into the system. the procedure is shown in figure 4. the first step is to feed the model with the former radii and to calculate the twisting characteristics as an initial value for the model. after that, the iteration number is set to 1 and after inserting the values of resistances and inductances, the simulink model is run. after that, the strain for the calculated twisting angle is computed. in the next step, the computed strain is compared with the maximum irreversible strain of hts tapes. if the strain is lower than this limit, a value as ∆α is added to the last twisting angle and another time simulink model is run. this procedure continues until the strain overpasses the irreversible engineering, technology & applied science research vol. 12, no. 1, 2022, 8168-8174 8171 www.etasr.com sadeghi et al.: a simple and fast computation equivalent circuit model to investigate the effect of … strain limit and that results in stopping the algorithm. ∆α plays an important role in the speed of the proposed method. the smaller this value is, the higher the computation time would be. (a) (b) (c) fig. 2. normalized critical current value with respect to strain for the primary angle of tapes: (a) of phase a, (b) of phase b, (c) of phase c. (a) (b) (c) fig. 3. simulink model used as the test system of the proposed method: (a) system model, (b) cable model, (c) hts tape model. fig. 4. the general flowchart for implementing the proposed method. i c (n o rm ) engineering, technology & applied science research vol. 12, no. 1, 2022, 8168-8174 8172 www.etasr.com sadeghi et al.: a simple and fast computation equivalent circuit model to investigate the effect of … iii. results and discussion a. sensitivity analysis of twisting in an hts cable without consideration of mechanical limits the twisting angle impacts the parallel and perpendicular components of the magnetic field. figure 5 shows the changes of parallel and perpendicular components of the magnetic fields of each phase. according to figure 5, the parallel component of the magnetic field is maximum for twisting angle of 0 o , whereas the maximum perpendicular magnetic field occurs in 90 o . the values of figure 5 are calculated by neglecting the mechanical limits of the tapes. (a) (b) fig. 5. (a) parallel, (b) perpendicular magnetic field variation with respect to angle. ac loss reduction is the most important target of this paper. ac loss is reduced by the increase in twisting angle with respect to parallel and perpendicular magnetic fields. figure 6 illustrates the behavior of ac loss with respect to pitch angle alterations. according to figure 6, a twisting angle of 90 o produces the minimum ac loss, near-zero, however, this led to the mechanical collapse of the tapes. fig. 6. ac loss variations with respect to twisting angle. b. the results of the proposed method in the reduction of the ac loss of the hts cable with consideration of the mechanical limits in order to reduce the ac loss of the hts cable, the twisting angle of the hts cable could undergo some changes. the proposed ecm in this paper can analyze the aforementioned electromechanical problems at a significantly faster time (than fem) with high accuracy while the mechanical limits are considered. firstly, the twisting angles of hts tapes in phase a (two layers of tapes), phase b, and phase-c are increased according to the procedure of figure 4 with a ∆α step, and pitch lengths are recalculated. after gaining these parameters of the hts cable, the strain is computed in each iteration to avoid the downgrading of the critical current to zero. the basic value of the ac loss without any changes in twisting angle is about 3.125w/m/ph. to reduce this value and change the twisting angle, multiple ∆α are presented in table iv. according to this table, the smaller ∆α leads to a more precise solution. however, the simulation time increases significantly. this means that for a 0.0644% further reduction in ac loss, computation time is 886.3333 times increased. table iv. angle variation impact on ac loss reduction ∆α (degrees) 0.05 0.005 0.0005 0.00005 final αngle (degrees) 35.3612 35.2332 35.2292 35.2284 ε (%) 1.105761 1.099339 1.099065 1.099059 hm(p)hm(k) 0.899 0.8988 0.8965 0.8963 maximum ac loss (w/m/ph) 2.25168 2.25043 2.25026 2.25023 iteration 159 1593 15927 159263 time (s) 0.03 0.32 2.72 26.59 improvement (%) 27.9462 27.9862 27.9917 27.9926 table v shows the comparison results bewtween the proposed method and other previously published methods. the conducted studies in [21, 22] have also aimed to reduce the ac loss by the variation of the twisting angle. the maximum reduction of the ac loss in [21] is about 19.66% while the mechanical limits were also considered. however, the current paper uses sensitivity analysis to gain the results and does not a c l o ss (w /m ) engineering, technology & applied science research vol. 12, no. 1, 2022, 8168-8174 8173 www.etasr.com sadeghi et al.: a simple and fast computation equivalent circuit model to investigate the effect of … present any iterative method. on the other hand, in [22] the ac loss is reduced by 12 to 14%, but the mechanical limits were neglected. table v. comparison between the proposed method and [21, 22] reference maximum reduction mechanical limits iterative method [21] 19.66% yes no [22] 12-14% no no proposed 27.99% yes yes iv. conclusion ac loss is investigated in this paper, as a significant parameter in the performance of superconducting cables, with its reduction being the main target. this paper has utilized an ecm to analyze the impact of the twisting angle increment on the efficiency improvement of the selected hts cable. for this purpose, firstly a sensitivity analysis was conducted to analyze the electromagnetic behavior of the cable which results in: • the parallel magnetic field was reduced along with the increment of twisting angle, while the perpendicular magnetic field was increased. • the ac loss of the cable in all phases was either decreased to a minimum value for the angle of about 90 degrees. in order to reduce the ac loss of the cable, another study was accomplished. according to this study: • the ac loss in the improved design of the hts cable is 0.356 times of the ac loss in the preliminary design. • the ac loss could be further decreased if the reduction step of the twisting angle is selected to be smaller, but we would end up needing a much better computer system to handle the high computation cost. references [1] j. chigvinadze, v. tavkhelidze, g. mamniashvili, g. donadze, j. v. acrivos, and d. gulamova, "vibrating reed study of superconducting cuprates fabricated by superfast melt quenching in a solar furnace," engineering, technology & applied science research, vol. 9, no. 4, pp. 4495–4499, aug. 2019, https://doi.org/10.48084/etasr.2948. 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[34] j. fleiter, m. sitko, and a. ballarino, "analytical formulation of ic dependence on torsion of ybco and bscco conductors," ieee transactions on applied superconductivity, vol. 23, no. 3, pp. 8000204– 8000204, jun. 2013, https://doi.org/10.1109/tasc.2012.2228292. engineering, technology & applied science research vol. 7, no. 3, 2017, 1713-1718 1713 www.etasr.com gashti et al.: detection of spam email by combining harmony search algorithm and decision tree detection of spam email by combining harmony search algorithm and decision tree mehdi zekriyapanah gashti department of computer engineering payame noor university iran gashti@pnu.ac.ir abstract—spam emails is probable the main problem faced by most e-mail users. there are many features in spam email detection and some of these features have little effect on detection and cause skew detection and classification of spam email. thus, feature selection (fs) is one of the key topics in spam email detection systems. with choosing the important and effective features in classification, its performance can be optimized. selector features has the task of finding a subset of features to improve the accuracy of its predictions. in this paper, a hybrid of harmony search algorithm (hsa) and decision tree is used for selecting the best features and classification. the obtained results on spam-base dataset show that the rate of recognition accuracy in the proposed model is 95.25% which is high in comparison with models such as svm, nb, j48 and mlp. also, the accuracy of the proposed model on the datasets of ling-spam and pu1 is high in comparison with models such as nb, svm and lr. keywordsspam email; harmony search algorithm; decision tree i. introduction spam spotting is a significant task for all web actions and especially for email clients [1]. spam emails consume a considerable amount of traffic volume and also may carry viruses [2]. since the security of computer systems is based on the three principles of prevention, diagnosis, and response, if all the security risks were identified and prevented, there obviously would be no need for reaction. hence, identification is a vital method for providing email users’ security and it can be the front defensive line of for any computer system. spam senders are always using more complicated tools and methods for getting through the spam filters. hence, emails’ security against attacks on email servers and the trial for accessing valid usernames or email addresses through accessing mail servers is a critical requirement [3]. one way for keeping unauthorized access to users’ email accounts is a two-step verification of identity. two-step verification is a security mechanism that uses a second keyword or phrase in addition to the password [4]. spotting spam email is mainly based on characteristics and features written in the subject field of emails. most spams use similar subjects. therefore, this is a unique feature for identifying. the present work utilizes the spam-base dataset [5] including the two classes spam and non-spam for the purpose of spam identification based on a combination of hsa [6] and id3 [7]. in addition, the ling-spam [8] and pu1 [8] datasets were used for assessment and comparison. hsa was used for selecting characteristics, increasing accuracy in the final solution, and for determining the features that take the fitness function to its optimal situation. id3 was used for class recognition and final categorization. ii. related works various techniques have been introduced for identifying spams, including statistical techniques, expert systems, bayesian networks, neural networks, fuzzy logic, and collective intelligence algorithms. a radial basis function (rbf) model is set forward alongside with support vector machines (svm) technique for identifying spam emails in [9]. rbf, an artificial neural network model, is used for training and testing data; and svm, a classification technique, is used for mapping the features. assessment is done on double bounce email, a linear dataset. in addition, preprocessing and determining the frequency of words according to (1) is carried out by use of tfidf. results show an identification accuracy of approximately %84. )1( }:{1 log)( )( 1 )( 1 ),,(            dtdd d tf tf idftf tf ddtidftf d t d t d in [10], a bayesian additive regression trees (bart) model was carried out on ling-spam, pu1, and spam-base. bart model is a binary dt with linear regression correlations at every end node that are able to predict numerical values. the most important and main criterion for assessment of the dt is the error rate created in the tree. for calculating the total error rate of the tree the weighted total of the error rate of the leaves is calculated. in order to prevent low quality laws being created, some branches are pruned. although this pruning causes a higher error rate, it will stop inefficient laws being created. results show that in the models cbart, random forests (rf), bart, and classification and regression trees (cart) the accuracy on ling-spam and pu1 is 100%. also, on spam-base, the highest amount in rf model is 98.61%. engineering, technology & applied science research vol. 7, no. 3, 2017, 1713-1718 1714 www.etasr.com gashti et al.: detection of spam email by combining harmony search algorithm and decision tree cart model reduces the error rate by 2.2% in comparison with bart. an enhanced genetic algorithm (ega) model was used in [11], which is an enhanced version of genetic algorithm (ga) through combination with simulated annealing (sa), is proposed for spotting spam emails. assessment is carried out on spam corpus with 54 characteristics. in ega, 15 chromosomes are used with 54 characteristics and 1000 generations. results suggest an accuracy of 99.73% and 99.86% for ga and ega respectively. therefore sa has been very effective in enhancing ga, and has improved its operators, and increased its accuracy. a particle swarm optimization (pso) model, a population based algorithm, has been proposed for identification of spam emails in [12]. gpu technology is used for running pso model. gpu processes tasks in parallel and processes many tasks better and faster than cpu. assessment is made on trec 2015 with 48360 spam emails and 36450 non-spam emails. the probability of identifying spam emails is calculated with (2). results suggest an accuracy of 99% in spotting non-spam emails and an accuracy of 66% to 99% in spotting spam emails. )2( )pr()|pr()pr()|pr( )pr()|pr( )|pr( hhwssw ssw ws    a bayesian classification was done on three datasets with 1000, 1500, and 2100 emails in [13]. bayesian classification identifies and predicts data according to probabilities. bayesian model includes the steps of preprocessing, training, testing, and classification. results show that the accuracy in dataset1, dataset2, and dataset3 is 93.98, 94.85, and 96.46 respectively. in addition, the processing time for dataset1 is less than the other two datasets. identification of spam emails was performed on rfc2822 with 9189 emails according to vertex dependency [14]. in this model, the neighboring vertices relationships are used for prediction. the data similarity distance between the vertices is calculated with (3). results point to a maximum accuracy of 93.78%. in addition, the accuracy in identification of spam email is 80.72% and for nonspam emails, it is 98.01%. )3( )()( . 1 2 1 2 1        n i i n i i n i ii ba ba ba ba sim a combined model pso+k-means in [15] was performed on spam-base with 57 characteristic for spam email spotting. in pso+k-means model, pso is used for characteristic selection and k-means is used for data clustering. in k-means algorithm, k members are selected out of n members randomly as cluster centers. afterwards, the remaining n-k members are allocated to the closest clusters. once all members added to clusters, cluster centers are calculated again and members are allocated to clusters anew according to the new cluster centers. this process is carried on until the cluster centers are fixed. distance factor according to equation (4) is used for clustering. results suggest that the maximum accuracy of the model is 94.62%. )4(),( 1 2    n i ii yxyxdis a combined model multi-layer perceptron artificial neural (pso-mlpnn) was proposed for spam email identification in [16]. pso algorithm is used for characteristic selection and mlpnn model is used for training, data testing. in pso-mlpnn model the perceptron neural function is used with sigmoid activation function for the hidden layer; %80 of the data is used for training and %20 for testing. the number of the hidden layers in mlp model is considered to be between 3 and 15; and the repetition of pso algorithm for characteristic selection is 200. assessment was done with 481 spam emails and 2171 non-spam emails on ling-spam and 6000 email samples on spam-assassin. assessment done on spamassassin and ling-spam suggests that the accuracy in psomlpnn model is respectively 99.98 and 99.79. comparison shows that pso-mlpnn model is more accurate in identification than svm and bpnn. in table i, a comparison of the proposed models for spam emails identification is presented. table i. comparison of proposed models for spam detection time complexity correlation fs classifier preprocessing data set models low high √ √ x ●double bounce rbf [9] svm [9] medium medium √ x √ ●ling-spam ●pu1 ●spam-base bart [10] low medium √ x √ ●spam corpus ega [11] low medium √ x ●trec 2015 pso [12] medium high x √ x ●dataset1=1000 ●dataset2=1500 ●dataset3=2000 bayesian [13] high medium x x x ●rfc2822 vertex dependency [14] medium high √ √ √ ●spam-base pso+kmeans [15] low high √√ √ ●ling-spam ●spamassassin psomlpnn [16] engineering, technology & applied science research vol. 7, no. 3, 2017, 1713-1718 1715 www.etasr.com gashti et al.: detection of spam email by combining harmony search algorithm and decision tree iii. proposed model in the proposed model, first the data in spam-base dataset is preprocessed. at the preprocessing level, data are controlled; because the data in the dataset might not be controlled enough and inapplicable, repeated, or erroneous values may result in invalid output. presence of inapplicable data in most results in dysfunctions in conclusion obtained from the data. in the next step, primary vectors form in hsa. each vector is comprised of 57 characteristic. in the vectors, a number of characteristics are selected based on hsa memory randomly and transferred to id3. in id3 tree classification rules according to characteristics are carried out. characteristics that are influential in identification accuracy are saved in hm memory and used for later fs steps. assessment function in hsa does a complete and exhaustive search in the space of the subset of characteristics until it finds the best combination of characteristics. the most important step in the id3 tree is setting the rules. according to the root of the tree, rules are set and characteristics are compared. the most important criterion for the root node is the data rate of the tree. the characteristic that has the highest data rate is chosen as the root node and the id3 tree is expanded based on it. afterwards, training and testing of data is carried out. testing is done in order to assess data and its validity. in figure 1, the flowchart of the proposed model is shown. fig. 1. flowchart of the proposed model in hsa [6] harmony memory (hm) is used to maintain the best of the previous solutions. hm works as a matrix as done in equation (5) with a solution in every line. therefore, the number of the columns in this matrix actually shows the dimensions of the solution. the last column in the matrix is set for saving the value of the fitness function for every line. the amount of answer vectors in hm is shown using harmony memory size (hms). output value of the fitness function for each vector is shown using f(x). )5( )( ... )( )( ... ... ... ... 2 1 21 22 2 2 1 11 2 1 1                hmshms n hmshms n n xf xf xf xxx xxx xxx hm in hsa, first all hm lines are made and the value of the fitness function for each line is calculated and saved in the last column of the hm matrix. then, based on the number of necessary repetition or the time repetition is finished, the entire hm is scanned and for each line the suitable value for each entry is set according to hsa parameters. afterwards, if the value for the fitness function is better than the worst solution present in hm, replaces it. eventually, the solution that produces the optimal value in the fitness function is chosen as the best available solution. in hsa, any value can select values randomly. randomization is in fact utilized for increasing the variety of solutions. id3 tree [7] is a method for presenting a set of rules that result in a group or a value. in id3 tree, a statistical value is used called data rate for clarifying how much a character is effective in the final identification. in id3 tree, at first, the amount of disorder for every characteristic is calculated using entropy; and using its value for each characteristic, the data rate is calculated. entropy displays the randomness as a mathematical figure. if the set s includes positive and negative samples of a set, the entropy of s in relation to boolean categorization is defined as (6). )6(loglog)( 22  ppppse in (6), p⊕ is the ratio of positive samples to the all the samples, and p⊖ is the ratio of negative samples to the all the samples. the decision of which characteristic is to be in the root of the tree depends on the data rate of each characteristic. equation (7) is used for calculation of the data rate [7]. )7()()(),( )(    avaluesv v v se s s seasig in (7), the values (a) parameter denotes sum of the a values and sv is a subset of s for which a gives value v. the criteria used for the assessment of the proposed model are precision, recall, f-measure, and accuracy; accuracy is the most important item among those criteria [17, 18]. )8( fptp tp precision   )9( fntp tp recall   )10( )( **2 recallprecision recallprecision measuref   )11( )( )( fnfptntp tntp accuracy    )12(2/                     fptn tn fntp tp auc engineering, technology & applied science research vol. 7, no. 3, 2017, 1713-1718 1716 www.etasr.com gashti et al.: detection of spam email by combining harmony search algorithm and decision tree tn represents the number of records that factually pertain to the negative set and were identified correctly as negative by the algorithm. tp represents the number of records that factually pertain to the positive set and were identified correctly as positive by the algorithm. fp represents the number of records that factually pertain to the negative set and were identified wrongly as positive by the algorithm. fn represents the number of records that factually pertain to the positive set and were identified wrongly as negative by the algorithm. iv. evaluation and results assessment and results of the proposed model are obtained in matlab 2015 on spam-base. spam-base dataset includes 4601 samples with 57 characteristics. in addition, in order to illustrate its efficiency and accuracy, the proposed model was run on ling-spam and pu1 datasets and was compared with other models. ling-spam datasets includes 481 spam and 2412 non-spam emails. pu1 dataset includes 481 spam and 618 non-spam emails. the maximum repetition in hsa is 150 and to the end of maintaining variety and optimal solutions, the technique of unfit vectors omission was put to use. in table ii, assessment of the proposed model on spam-base dataset with different number of characteristics is shown. as could be seen in table ii, the number of characteristics is very influential in identification accuracy; also, the type of the chosen characteristic is influential in the accuracy of the results. in figure 2, the comparison of the number of characteristics in identification accuracy in the dataset spambase is shown in a graph. in table iii, the comparison of the proposed model with other models is presented. as can be seen in table iii the accuracy of the proposed model is 95.25%. the proposed model has a higher accuracy than models such as naive bayes (nb), svm, j48, and most other models; but it also has a lower accuracy than random forest and random tree models. in table iv the comparison of the proposed model with other models on ling-spam dataset is presented. the accuracy of the proposed model in ling-spam dataset is 99.80%, which is higher than models nb, svm, nnet, and lr. table ii. assessment of the proposed model on spam-base with different number of characteristics fs precision recall f-measure accuracy 15 94.66 97.30 95.96 98.05 17 94.54 95.65 95.09 97.65 20 94.21 92.15 93.17 98.00 23 93.84 95.80 94.81 95.08 28 93.99 94.77 94.38 94.15 30 95.31 93.10 92.70 96.72 33 91.48 94.48 92.96 98.32 35 92.03 93.41 92.71 96.61 38 94.69 95.34 95.01 94.90 40 93.11 90.57 91.82 93.11 45 92.89 93.68 93.28 96.46 50 93.34 94.35 93.84 95.12 53 95.78 92.22 93.97 93.15 57 90.15 91.23 90.69 95.25 fig. 2. comparison graph of the influence of the number of characteristics on detection accuracy on spam-base table iii. comparison of the proposed model with other models on spam-base percentage of comparisons accuracy (%) models refs 4.03 91.22 nsa-pso [19] 13.93 81.32 pso 26.39 68.86 nsa 15.93 79.3 nb [20] 5.25 90 svm [21] 24.25 71 dfs-svm [22] 9.25 86 ann [23] 8.35 86.9 type-2 fuzzy set [24] 2.7 92.55 pso-fuzzy [15] 0.63 94.62 12.05 83.20 nsa-pso [25] 6.69 88.56 bayes net [26] 5.55 89.7 logic boost 3.71 91.54 random tree 2.93 92.32 jrip 2.91 92.34 j48 1.97 93.28 mlp 1.69 93.56 kstar 5.06 90.19 nb [27] 0.8 94.45 logistic 1.41 93.84 kstar 2.49 92.76 filtered classifier 1.34 93.91 part 2.28 92.97 j48 16.32 78.93 nb [28] 2.54 92.71 bayes net 8.71 86.54 svm -0.29 95.54 ft -0.4 95.65 j48 -4.29 99.54 random forest -4.46 99.71 random tree 1.32 93.93 simple cart 95.25 proposed model in table v, the comparison of the proposed model with other models on pu1 dataset is presented. the accuracy of the proposed model in pu1 dataset is 97.12%, which is higher than models nb, and nnet. in table vi, the comparison of the proposed model with other models is shown on the dataset spam-base. in the proposed model the accuracy in the dataset spam-base is 93.25%, which is higher than nb models. engineering, technology & applied science research vol. 7, no. 3, 2017, 1713-1718 1717 www.etasr.com gashti et al.: detection of spam email by combining harmony search algorithm and decision tree table iv. comparison of the proposed model with other models on ling-spam ref models precision recall f-measure auc [29] cbart 100.00 100.00 100.00 100.00 rf 100.00 99.57 99.78 100.00 bart 100.00 100.00 100.00 100.00 svm 98.39 93.00 94.35 99.63 nnet 96.97 46.22 62.18 99.68 cart 100.00 100.00 100.00 100.00 lr 99.28 97.86 98.54 99.77 nb 100.00 33.48 49.71 66.55 proposed model 98.77 99.35 99.06 99.80 table v. comparison of the proposed model with other models on pu1 ref models precision recall f-measure auc [29] cbart 100.00 100.00 100.00 100.00 rf 99.36 100.00 99.68 100.00 bart 100.00 100.00 100.00 100.00 svm 97.94 94.78 95.92 99.25 nnet 94.71 55.13 69.51 95.09 cart 100.00 100.00 100.00 100.00 lr 98.83 96.82 97.78 98.16 nb 99.02 37.86 54.58 68.97 proposed model 96.90 98.88 97.88 97.12 table vi. comparison of the proposed model with other models on spam-base ref models precision recall f-measure auc [29] cbart 95.24 92.72 93.96 96.40 rf 95.42 92.64 93.99 98.61 bart 94.78 88.43 91.48 97.60 svm 93.04 90.88 91.92 97.83 nnet 93.17 92.89 93.01 97.77 cart 88.38 85.82 87.05 94.73 lr 92.32 88.98 90.60 97.19 nb 57.52 95.54 71.81 88.74 proposed model 90.15 91.23 90.69 95.25 v. conclusion and future works spam emails consume a huge bulk of email storage and compromise users’ security. therefore, measurements such as identification filters should be adopted. content based filters that use emails’ content are the main and most common type of spam filters. in most content based methods, machine learning and data mining are used. in addition, many identification filters scrutinize the content and subject of emails for existence of key words or phrases used in spam emails frequently. in conclusion, at first identification is the best method for avoiding spams. in the present paper, a model for spam identification was proposed based on the combination of hsa and id3. assessment was carried out on datasets spam-base, ling-base, and pu1. results suggest that the proposed model has higher identification accuracy in comparison with models svm and nb; and compared to most models increases the identification accuracy up to 15%. in spam email identification one of the main problems faced is selection of the type of the characteristic. in conclusion, in order to eliminate the problem, algorithms should be used that are capable of fs and can enhance identification accuracy. references [1] s. liu, y. wang, j. zhang, c. chen, y. xiang, “addressing the class imbalance problem in twitter spam detection using ensemble learning”, computers & security, 2016 (in press) [2] a. heydari, m.a. tavakoli, n. salim, z. heydari, “detection of review spam: a survey”, expert systems with applications, vol. 42, no. 7, pp. 3634-3642, 2015 [3] t. ouyang, s. ray, m. allman, m. rabinovich, “a large-scale empirical analysis of email spam detection through network characteristics in a stand-alone enterprise”, computer networks, vol. 59, pp. 101-121, 2014 [4] n. perez-diaz, d. ruano-ordas, j. r. mendez, j. f. galvez, f. fdezriverola, “rough sets for spam filtering: selecting appropriate decision rules for boundary e-mail classification”, applied soft computing, vol. 12, no. 11, pp. 3671-3682, 2012 [5] https://archive.ics.uci.edu/ml/datasets/spambase [6] z. w. geem, j. h. kim, g. v. loganathan, “a new heuristic optimization algorithm: harmony search”, simulation, vol. 76, no. 2, pp. 60-68, 2001 [7] j. r. quinlan, induction of decision trees, machine learning, vol. 1, no. 1, pp. 81-106, 1986 [8] http://www.csmining.org/index.php/spam-email-datasets-.html [9] s. ali, s. ozawa, j. nakazato, t. ban, j. shimamura, “an autonomous online malicious spam email detection system using extended rbf network”, 2015 ieee international joint conference on neural networks (ijcnn), pp. 1-7, 2015 [10] s. abu-nimeh, d. nappa, x. wang, s. nair, “bayesian additive regression trees-based spam detection for enhanced email privacy”, ieee third international conference on availability, reliability and security, pp. 1044-1051, 2008 [11] s. salehi, a. selamat, m. bostanian, “enhanced genetic algorithm for spam detection in email”, ieee 2nd international conference on software engineering and service science, pp. 594-597, 2011 [12] m. prilepok, t. jezowicz, j. platos, v. snasel, “spam detection using compression and pso”, ieee fourth international conference on computational aspects of social networks (cason), pp. 263-270, 2012 [13] s. b. rathod, t. m. pattewar, “content based spam detection in email using bayesian classifier”, ieee international conference on communications and signal processing (iccsp), pp. 1257-1261, 2015 [14] m. prilepok, m. kudelka, “spam detection based on nearest community classifier”, ieee international conference on intelligent networking and collaborative systems, pp. 354-359, 2015 [15] s. salehi, a. selamat, o. krejcar, k. kuca, “fuzzy granular classifier approach for spam detection”, journal of intelligent & fuzzy systems, vol. 32, no. 2, pp. 1355-1363, 2017 [16] a. r. behjat, a. mustapha, h. nezamabadipour, m. nasir sulaiman, n. mustapha, “a pso-based feature subset selection for application of spam/non-spam detection”, in soft computing applications and intelligent systems, communications in computer and information science, vol. 378, springer, berlin, heidelberg, 2013 [17] r. s. michalski, i. bratko, m. kubat, machine learning and data mining: methods and applications, new york: wiley, 1998 [18] d. francois, binary classification performances measure cheat sheet, 2009 [19] i. idris, a. selamat, “improved email spam detection model with negative selection algorithm and particle swarm optimization”, applied soft computing, vol. 22, pp. 11-27, 2014 [20] y. zhang, h. y. li, m. niranjan, p. rockett, “applying cost-sensitive multiobjective genetic programming to feature extraction for spam email filtering”, lecture notes in computer science, genetic programming, berlin/heidelberg, springer, vol. 4971, pp. 325-336, 2008 [21] t. fagbola, s. olabiyisi, a. adigun, “hybrid ga-svm for efficient feature selection in e-mail classification”, comput. eng. intell. syst, vol. 3, no. 3, pp. 17-28, 2012 [22] a. k. uysal, s. gunal, “a novel probabilistic feature selection method for text classification”, knowl. based syst., vol. 36, pp. 226-235, 2012 engineering, technology & applied science research vol. 7, no. 3, 2017, 1713-1718 1718 www.etasr.com gashti et al.: detection of spam email by combining harmony search algorithm and decision tree [23] l. ozgur, t. gungor, f. gurgen, “spam mail detection using artificial neural network and bayesian filter:, in: z. yang, h. yin, r. everson (eds.), intelligent data engineering and automated learningideal 2004, springer, berlin/heidelberg, 2004, pp. 505-510, 2004. 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[28] m. rathi, v. pareek, “spam mail detection through data mining-a comparative performance analysis”, international journal of modern education and computer science, vol. 12, pp. 31-39, 2013 [29] s. abu-nimeh, d. nappa, x. wang, s. nair, “bayesian additive regression trees-based spam detection for enhanced email privacy”, ieee third international conference on availability, reliability and security, pp. 1044-1051, 2008 microsoft word etasr_v11_n4_pp7291-7295 engineering, technology & applied science research vol. 11, no. 4, 2021, 7291-7295 7291 www.etasr.com farooq et al.: estimation of traffic occupancy using image segmentation estimation of traffic occupancy using image segmentation muhammad umer farooq department of computer science and it ned university of engineering and technology karachi, pakistan umerora1@gmail.com shariq mahmood khan department of computer science and it ned university of engineering and technology karachi, pakistan shariq@neduet.edu.pk afzal ahmed department of urban and infrastructure engineering ned university of engineering and technology karachi, pakistan afzalahmed@neduet.edu.pk muhammad bilal nawaz department of urban and infrastructure engineering ned university of engineering and technology karachi, pakistan mbilalnawaz91@gmail.com abstract-increased traffic flow results in high road occupancy. traffic road occupancy is often used as a parameter for the prediction of traffic conditions by traffic engineers. although traffic monitoring systems are based on a large number of technologies, challenges are still present. most of the methods work efficiently for free-flow traffic but not in heavy congestion. image processing techniques are more effective than other methods, as they are based on loop sensors and detectors to monitor road traffic. a huge number of image frames are processed in image processing hence there is a need for a more efficient and low-cost image processing technique for accurate vehicle detection. in this paper, a novel approach is adopted to calculate road occupancy. the proposed framework has robust performance under road conjunction and diverse environmental conditions. a combination of image segmentation threshold technique and shadow removal technique is used. the study comprised of segmenting 1056 images extracted from recorded videos. the obtained results by image segmentation were compared with traffic road occupancy calculated manually using autocad. a final percentage difference of 8.17 was observed. keywords-image segmentation; road occupancy; shadow removal i. introduction precise and accurate calculation of basic traffic flow parameters is a major step towards the successful planning and management of a traffic system. real time traffic flow can be used to enhance the capacity of a traffic system. traffic road occupancy is often used to determine traffic congestion and related characteristics. it is the ratio of the area occupied by vehicles to the total area of the road in a traffic scenario. road occupancy has been a subject of interest for traffic management and planners over time [1, 2]. a consequence of traffic density is road congestion and the enhanced probability of accidents. there is an exponential increase in the number of total vehicles globally during the last decade. traffic monitoring is a difficult task due to the high traffic occupancy and issues such as shadows, occlusion etc. for the advancement of traffic monitoring systems, different methods and techniques have been applied. however, obtaining traffic road occupancy for heterogeneous traffic (e.g. the traffic of the city of karachi) is a difficult task due to the variety of traffic modes in the traffic composition, the ranging in area and size, and little to no lane discipline. so, a method needs to be developed for obtaining road occupancy [3]. image processing has been used in a number of ways to obtain real time traffic in terms of both model flow and density. however, the accuracy of the models generated is highly traffic dependent and occlusion reduces greatly the accuracy of the models [4]. for heterogeneous traffic, occlusion affects accuracy and real time traffic management systems cannot be adopted [3-5]. a spatio-temporal markov random field algorithm for traffic images at intersections was developed in [6]. this algorithm traces each pixel of the image on the x-y plane versus the time axis. the authors also developed an extended recognition system based on hidden markov models. this system has the ability to learn and keep track of events, thus it can be used to identify events like illegal u-turns or reckless driving. a novel framework was developed to explore multidimensional data of road traffic to examine different patterns of traffic and anomaly detection in [3]. the framework was implemented on a collection of road traffic datasets gathered from different areas of the city. a three step method was ormulated for vehicle counting in images with multiple vehicle occlusions in [7]. the first step involves the deduction of vertices for each vehicle from the camera configuration. in the second step, a contour description model is used to determine the vanishing contours with their directions to determine vehicle counts, and finally, in the last step, a resolvability index is assigned to each occluded vehicle to find out the dimensions of the occluded vehicles. another methodology was purposed [8] to perform video analysis for corresponding author: muhammad umer farooq engineering, technology & applied science research vol. 11, no. 4, 2021, 7291-7295 7292 www.etasr.com farooq et al.: estimation of traffic occupancy using image segmentation counting vehicles. the methodology involved the formulation of a bounding box to detect the vehicles and then the use of a kalman filter and adaptive background subtraction to count vehicles. a study for the number plate recognition of cars moving on the road in saudi arabia was conducted in [9]. in the proposed mechanism, a camera captures the image of the car and uses image segmentation algorithms to obtain the special letters. this mechanism was tested on 610 images taken under different illumination conditions. image segmentation plays an essential role in understanding of image, investigation of medical images, video surveillance, image compression, etc. [10-12]. the objective of image segmentation is the clustering of pixels into image regions. these regions refer to individual objects, surfaces or parts of objects. most research has been done in the field of vehicle detection, vehicle tracking, vehicle recognition, and vehicle behavior understanding [4, 13]. beside these, the estimation of traffic occupancy is also essential in improving traffic management systems. in this research, image segmentation is used for the estimation of traffic occupancy. for complex traffic scenarios, image processing techniques are playing an important role in a wide range of applications. image segmentation deals with the image processing and refers to the segregation of an image into various regions based on texture, color, or intensity. image segmentation can be performed by different techniques and algorithms. among these techniques we have chosen the color threshold technique to obtain road occupancy. this technique does not require prior knowledge of the image, has simple calculations, and fast operating speed. the videos were recorded during daytime, therefore the shadows of vehicles cause inaccuracy in the results. this issue is tackled by adopting a novel combination approach of color threshold with shadow removal. threshold segmentation algorithm otsu, which is an interclass variance method is used [14]. the results showed that this approach minimizes the error due to the shadows of vehicles and leads to a better estimation of road occupancy. ii. research methodology a. otsu’s thresholding thresholding plays an important role in the segmentation of an image into various regions and in pattern recognition. some grayscale values are selected automatically as threshold and the image is classified into different regions. among various thresholding techniques, we have chosen otsu’s thresholding method [14] for this research, which is a globally accepted threshold method. through this method, maximum separation of classes can be obtained and histogram image thresholding can be performed automatically. it is assumed that in otsu’s algorithm, an image consists of two classes, foreground (��) and background (��), and based on probability density function a normalized histogram is constructed. the probability density function is: �� �� � � � , � � 0,1,2,…. . ,� � 1 (1) where n is the total pixels of the image, � is the pixel having intensity level � , and � is the maximum intensity level of the image. center point between the minimum and maximum intensity level in the image is known as the initial threshold. if � is the initial threshold, then the set of pixels ��� has levels �0,1,……. . ,m � 1� and the set of pixels ��� has levels �m,m � 1,……. . ,n� 1�. the extension of otsu’s method for multilevel thresholding is given as: �� � !��"� �"# � � !��"� � "# � (2) where: !� � ∑ � �� %&� '� (3) !� � ∑ � �� (&� '% (4) "� � ∑ �� �� /!� %&� '� (5) "� � ∑ �� �� /!� *&� '� (6) "# � ∑ �� �� *&� '� (7) the optimal threshold value can be achieved by +�,�+-�� . b. traffic occupancy estimation by otsu’s thresholding in order to perform image segmentation, videos were recorded on the project site, which is the university road of karachi near the federal urdu university. for an accurate occupancy calculation the camera needs to be parallel with the road. the more the camera is titled beyond 180 0 angle, more error will be observed. due to site limitation and in order to attain maximum height, the camera was installed on the 5 th floor of a building. the research methodology is shown in figure 1. videos were recorded for different times of the day in order to have samples from all traffic conditions for analysis. the videos were cropped to obtain frames having road surface and vehicles only. after the extraction of image frames, image segmentation was performed in matlab. the obtained results were compared with manual road occupancy results obtained in autocad. finally, the results were displayed by plotting graphs of image segmented occupancy and original occupancy obtained from autocad. fig. 1. proposed framework. c. data collection and analysis using matlab, frames were extracted from videos at an interval of 3 frames per minute. the camera recorded the videos at 30fps (frames per second). every minute had 1800 engineering, technology & applied science research vol. 11, no. 4, 2021, 7291-7295 7293 www.etasr.com farooq et al.: estimation of traffic occupancy using image segmentation frames, so the 600 th , 1200 th , and 1800 th frames of every minute were analyzed. matlab offers multiple functions and tools to perform image segmentation. original image and threshold image are shown in figure 2. a binary filter was applied after thresholding to convert the image in two parts, background (black) and foreground (white). the mask created was exported to matlab script where operations were defined including image import and applying the created mask. in order to render the small pixel areas left within the image, such as the windscreens of the cars, they were filled using the hole filling option. finally, the total number of white and black pixels was obtained. a ratio of sum of all white pixels and a sum of all pixels gave the occupancy. (a) (b) (c) (d) fig. 2. (a), (b) original and (c), (d) segmented images. fig. 3. autocad calculating original occupancy values. in order to calculate the accuracy of the procedure, these images were imported to autocad and the object areas were calculated by drawing a boundary around all vehicles in the image. figure 3 is a pictorial presentation of the calculation of the original occupancy values. a ratio of the sum of the area of all the objects to the total area of the image was computed to calculate the total occupancy. d. shadow removal in order to minimize the errors due to the formation of shadows on the road by the passing vehicles, it is necessary to devise a technique for the shadow removal. due to the resemblance of the shadows with the dark color objects in an image often the detection and removal of shadows turns out to be a difficult task. in order to remove shadows another mask was defined in matlab. l*a*b color space is the tool used to define the shadow removal mask. here, l* is for the lightness and a* and b* for the green–red and blue–yellow color components. original and shadow detected images are shown in figure 4. (a) (b) (c) (d) fig. 4. (a), (b) original and (c), (d) shadow detected segmented images. iii. results a total of 1056 image frames were analyzed. based on the comparison of the average of the real occupancy calculated with autocad vs the occupancy calculated by matlab, a percentage difference of 33.18 was observed before the application of shadow removal mask between the actual and matlab occupancy. after the shadow removal mask the observed difference percentage was found to be 8.17. the results are given in table i whereas figure 5 exhibits the difference percentage between the calculated and the observed occupancy. during the research, a large difference percentage was observed for a few frames. this can be explained by the small value of occupancy in these frames. even a small difference between the two occupancy values can result in a considerable percentage difference. iv. validation in order to validate the masking techniques proposed in this research, multiple frames were extracted. the results for the difference percentage in occupancy obtained by the masking techniques showed an average difference of 8.17 with 19.156 maximum and 0.906 minimum difference obtained. engineering, technology & applied science research vol. 11, no. 4, 2021, 7291-7295 7294 www.etasr.com farooq et al.: estimation of traffic occupancy using image segmentation (a) (b) (c) (d) (e) (f) (g) (h) fig. 5. difference between actual and image segmented road occupancy. table i. result comparison of traffic occupancy obtained from image segmentation with and without shadow removal image name area of objects by autocad area of individual image actual road occupancy occupancy by image segmentation without shadow removal difference occupancy by image segmentation after shadow removal difference 600 0.060 0.343 17.539 21.706 23.761 18.689 6.55 1200 0.057 0.343 16.608 21.366 28.647 16.810 1.21 1800 0.074 0.343 21.785 27.317 25.390 19.670 -9.70 2400 0.056 0.343 16.433 13.913 -15.338 15.089 -8.18 3000 0.036 0.343 10.529 13.781 30.883 12.082 14.746 3600 0.077 0.343 22.484 17.289 -23.102 20.635 -8.223 4200 0.070 0.343 20.418 23.861 16.859 17.634 -13.638 4800 0.070 0.343 20.418 25.128 23.062 18.785 -7.997 5400 0.079 0.343 23.240 21.249 -8.567 19.861 -14.540 6000 0.062 0.343 18.091 23.017 27.227 19.846 9.698 6600 0.045 0.343 13.118 16.633 26.795 15.147 15.473 7200 0.058 0.343 16.986 17.337 2.063 15.938 -6.170 7800 0.040 0.343 11.721 14.305 22.037 13.238 12.934 8400 0.071 0.343 20.564 24.648 19.861 18.466 -10.202 9000 0.049 0.343 14.252 16.643 16.778 14.641 2.7286 9600 0.051 0.343 14.950 21.641 44.752 17.624 17.887 10200 0.068 0.343 19.982 17.990 -9.970 20.183 1.006 10800 0.062 0.343 18.179 21.314 17.247 18.215 0.198 11400 0.064 0.343 18.848 20.038 6.313 17.825 -5.426 12000 0.057 0.343 16.783 23.327 38.992 20.406 21.591 12600 0.080 0.343 23.356 21.914 -6.176 20.654 -11.570 13200 0.081 0.343 23.676 27.571 16.449 24.417 3.130 13800 0.075 0.343 22.047 23.497 6.573 19.817 -10.115 14400 0.103 0.343 30.046 32.189 7.133 27.933 -7.033 15000 0.068 0.343 19.837 22.631 14.087 20.795 4.831 15600 0.072 0.343 20.942 23.478 12.107 21.581 3.053 16200 0.078 0.343 22.833 25.101 9.935 21.300 -6.713 v. conclusion based on the observed results, it can be concluded that image segmentation can be effectively used to calculate the occupancy of the road segments, while being a cost effective solution. results can be obtained at a very quick interval compared to the convenient methods of finding occupancy. moreover, the occlusion will have minimal effect on the calculated occupancy. it is worth mentioning that the camera angle with the road surface plays an important role on the accuracy. the closer is the angle with the road to 180 0 and the placed camera in the middle lane, the better the result will be. references [1] m. won, "intelligent traffic monitoring systems for vehicle classification: a survey," ieee access, vol. 8, pp. 73340–73358, 2020, https://doi.org/10.1109/access.2020.2987634. engineering, technology & applied science research vol. 11, no. 4, 2021, 7291-7295 7295 www.etasr.com farooq et al.: estimation of traffic occupancy using image segmentation [2] n. k. jain, r. k. saini, and p. mittal, "a review on traffic monitoring system techniques," in soft computing: theories and applications, singapore, 2019, pp. 569–577, https://doi.org/10.1007/978-981-130589-4_53. [3] m. umer, n. ahmed, and m. ali, "unsupervised video surveillance for anomaly detection of street traffic," international journal of advanced computer science and applications, vol. 8, no. 12, pp. 270– 275, jan. 2017, https://doi.org/10.14569/ijacsa.2017.081234. [4] b. tian et al., "hierarchical and networked vehicle surveillance in its: a survey," ieee transactions on intelligent transportation systems, vol. 18, no. 1, pp. 25–48, jan. 2017, https://doi.org/10.1109/tits. 2016.2552778. [5] a. detho, s. r. samo, k. c. mukwana, k. a. samo, and a. a. siyal, "evaluation of road traffic accidents (rtas) on hyderabad karachi m-9 motorway section," engineering, technology & applied science research, vol. 8, no. 3, pp. 2875–2878, jun. 2018, https://doi.org/ 10.48084/etasr.1920. [6] s. kamijo, y. matsushita, k. ikeuchi, and m. sakauchi, "traffic monitoring and accident detection at intersections," in proceedings 199 ieee/ieej/jsai international conference on intelligent transportation systems (cat. no.99th8383), tokyo, japan, oct. 1999, pp. 703–708, https://doi.org/10.1109/itsc.1999.821147. [7] c. c. c. pang, w. w. l. lam, and n. h. c. yung, "a method for vehicle count in the presence of multiple-vehicle occlusions in traffic images," ieee transactions on intelligent transportation systems, vol. 8, no. 3, pp. 441–459, sep. 2007, https://doi.org/10.1109/ tits.2007.902647. [8] e. bas, a. m. tekalp, and f. s. salman, "automatic vehicle counting from video for traffic flow analysis," in 2007 ieee intelligent vehicles symposium, istanbul, turkey, jun. 2007, pp. 392–397, https://doi.org/10.1109/ivs.2007.4290146. [9] m. sarfraz, m. j. ahmed, and s. a. ghazi, "saudi arabian license plate recognition system," in 2003 international conference on geometric modeling and graphics, 2003. proceedings, london, uk, jul. 2003, pp. 36–41, https://doi.org/10.1109/gmag.2003.1219663. [10] j. n. saeed, "a survey of ultrasonography breast cancer image segmentation techniques," academic journal of nawroz university, vol. 9, no. 1, pp. 1–14, feb. 2020, https://doi.org/10.25007/ajnu. v9n1a523. [11] w. s. chowdhury, a. r. khan, and j. uddin, "vehicle license plate detection using image segmentation and morphological image processing," in advances in signal processing and intelligent recognition systems, manipal, india, 2018, pp. 142–154, https://doi.org/10.1007/978-3-319-67934-1_13. [12] s. bargoti and j. p. underwood, "image segmentation for fruit detection and yield estimation in apple orchards," journal of field robotics, vol. 34, no. 6, pp. 1039–1060, 2017, https://doi.org/ 10.1002/rob.21699. [13] k. k. santhosh, d. p. dogra, and p. p. roy, "anomaly detection in road traffic using visual surveillance: a survey," acm computing surveys, vol. 53, no. 6, pp. 119:1-119:26, dec. 2020, https://doi.org/ 10.1145/3417989. [14] f. garcia-lamont, j. cervantes, a. lópez, and l. rodriguez, "segmentation of images by color features: a survey," neurocomputing, vol. 292, pp. 1–27, may 2018, https://doi.org/10.1016/j.neucom. 2018.01.091. microsoft word etasr_v11_n5_pp7571-7577 engineering, technology & applied science research vol. 11, no. 5, 2021, 7571-7577 7571 www.etasr.com chati et al.: moist air flow analysis in an open enclosure. part a: parametric study moist air flow analysis in an open enclosure. part a: parametric study tounsi chati laboratory of development in mechanics and materials ziane achour university of djelfa djelfa, algeria t.chati@univ.djelfa.dz kouider rahmani modeling, simulation and optimization of real complex systems research laboratory,university of djelfa djelfa, algeria kouiderrah2@yahoo.fr toufik tayeb naas gas turbine joint research team ziane achour university of djelfa djelfa, algeria toufiknaas@gmail.com abdelkader rouibah modeling, simulation and optimization of real complex systems research laboratory,university of djelfa djelfa, algeria rouibah_a@yahoo.fr abstract-heat and mass transfer in many systems is widely accomplished by applying natural convection processes due to their low cost, reliability, and easy support. typical applications include different mechanisms in various fields such as solar energy, solar distillers, stream cooling, etc. this paper examines the turbulent natural convection and mass transfer in an open enclosure for different aspect ratios (ar = 0.5, 1, and 2) with humid air. mass fraction and local nusselt number were examined to investigate the heat and mass transfer. heat flux boundary conditions were subjected to the lateral walls, the bottom one was an adiabatic wall while the top area was a free surface. the effects of rayleigh numbers (106 ≤≤≤≤ �������� ≤≤≤≤ 108) on natural convection and mass flow behavior were analyzed. the governing equations were solved using the cfd fluent code based on the simple algorithm. results showed that a cavity with an aspect ratio of ar=2 enhanced the rates of both heat and mass transfer. maximum heat transfer rates were observed when the rayleigh number increased due to the more vigorous fluid flow. however, mass transfer improved when the rayleigh number decreased. keywords-rayleigh number; turbulent flow; moist air; cfd; free convection i. introduction thermal turbulent flow is used in multiple applications of different mechanisms and systems such as solar energy collectors and evaporation, drying, distillation, and cooling processes of electronic compounds [1-9]. mass and heat transfers induced by temperature and concentration gradients, are generally applied in physical processes that involve the convective and diffusive transport of chemical substances. thereby, these heat and concentration gradients are considered to assist or oppose the performance of a system, depending on the boundary conditions of a problem. many researchers tried to analyze extensively solutions on the heat transfer flow within closed or open cavities [10-17]. some studies used heat flux or temperature gradient fields to the cavity walls as boundary conditions [18-20]. several investigations and experiments were conducted for various structural configurations, such as rectangular and square cavities [21-25], and non-structure enclosures such as sinusoidal and inclined protuberances [14, 16, 19, 26]. the effects of rayleigh [17, 24] and reynolds numbers on the behavior of free, forced, and mixed convection were studied in [24-29]. furthermore, various studies were conducted on the conditions of mass transfer and heat fluid motion for square cavities and rectangular shapes in a closed system [7, 30-36]. the heat and mass transfer induced by natural convection in a steady-state square cavity was studied in [31], proposing a two-dimensional cavity with different heated walls. the effects of the solute momentum on the rates of heat and mass transfer and lewis number on fluid motion were investigated, suggesting correlations between the properties of dimensional quantities and rates of thermal and mass transfer. the natural double diffusion convection in a square cavity with horizontal walls was examined in [32], characterizing the mass transfer parameters through the local and global nusselt and sherwood numbers on all walls. the 3d aspect was compared to the 2d in [37], finding a satisfactory agreement for low values of the rayleigh number. several researchers chose the rectangular configuration area to study the heat and mass transfer in natural convection [3840]. the effect of humidity on the natural heat flow and their characteristics between vertical walls in a differentially heated cavity was discussed in [4, 41, 42]. a cfd study of heat and mass transfer by natural convection in a 2d area with an airco2 mixture was presented in [43-44]. the effect of the buoyancy ratio on mass and heat transfer was investigated in [44] for different contexts. the thermal air quality behavior of higher co2 concentration in the vertical walls was analyzed under assisted and opposite flow conditions, considering different values for the rayleigh number. τhe temperature corresponding author: tounsi chati engineering, technology & applied science research vol. 11, no. 5, 2021, 7571-7577 7572 www.etasr.com chati et al.: moist air flow analysis in an open enclosure. part a: parametric study gradient inside the cavity for turbulent flow was observed more homogeneous for all flow cases. the effect of mass on heat transfer with radiation on the double diffusion problems has been examined for newtonian and non-newtonian fluids in [45] and [46] respectively concluding that the radiative heat transfer inside the enclosure gave better thermal results and did not affect the mass transfer process. the humid air transfer for natural convection in a 2d rectangular surface with a solid section was investigated in [35], dealing with a set of different variables: rayleigh thermal number, partition thickness, inclination, and buoyancy ratio. in [47], the impact of a heated plate on double-diffusive free convection in a square closed cavity was examined. the vertical walls maintained low temperatures while the horizontal walls were adiabatic, and the vortex viscosity values reduced both heat and mass transfer rates. a new vision on the mass transfer behavior of moisture under the buoyancy-driven effect for low turbulent flows was carried out in [35], using different values of mass fraction and varying temperature gradients between 20 and 60°c. the study concluded that the vapor content in the humid air had an important impact on heat and current fields inside the enclosure, and the variation of the vertical wall temperature gradients showed the effect of moisture concentration inside the cavity. the percentage of the difference in heat transfer changed significantly depending on the mass fraction of air moisture and the heat gradient between the vertical sides. the air-steam mixture flow of the natural convection inside a square cavity with vertical wall temperature and concentration gradients was investigated in [48], proposing a prandtl number equal to 1.32 and a rayleigh number equal to 4.05×105. the influence of species spread was investigated with soret and dufour mixture effects, finding that these effects had little contribution for this binary mixture. a parametric study of a differentially heated enclosure to treat the natural convection flows that contained a mixture of air and carbon dioxide was conducted in [49], analyzing the effect of change in buoyancy rate on the mass transfer for a laminar system. a new procedure for a solar system was proposed in [3], considering a latent heat source of evaporation condensation in the energy equation. the results proved that the properties were uniformly distributed. the relative humidity was almost 100% in the whole enclosure which implied that the air was saturated everywhere. however, the sudden change in the temperature or mass fraction was near the evaporating surface. the free convection of thermo-solute with mass lines and thermal flow in a rectangular area was investigated in [36], where the vertical sides were isotherms and the others adiabatic. the study examined prandtl number, rayleigh number, buoyancy ratio, and lewis number, finding that these parameters significantly affect the overall rates of heat and solute transfer. in [50], an experimental study was conducted to examine the combined thermal flow caused by mass transport and buoyancy in an open enclosure for various aspect ratios. the results of retained condensate on mass movement areas due to water's thermal stability were also examined with no remarkable impacts. in [51], the heat and mass transfer inside a ventilated cavity in laminar flow was examined for fluid of air-co2 mixtures. a comparative study was conducted to examine the thermal behavior and the air quality inside a cavity, considering the exit space location of the fluid mixture and three different values for the co2 contaminant (1000, 2000, 3000ppm). the air inlet space was located below the right vertical side of the cavity, and the location of the mixture outlet was considered in four different positions. in [33], double diffusion natural convection for open square enclosures was investigated with constant concentrations and temperatures imposed along the right and the left walls. results showed that the top thermal flow was the most effective for heat transfer, while the middle heating was the most stable for mass transfer. the effects of buoyancy ratio, rayleigh number, soret and dufour coefficients, and lewis number on heat and mass transfer in an open cavity were simulated in [52]. the results showed that changing the lewis number had little influence on sherwood and nusselt numbers, but when the rayleigh number increased lewis number increased gradually. despite the importance of mass transfer flow, there are only a few research efforts on the natural convection of open cavities, especially with moist air as a working fluid. this paper investigates the natural convection inside an open cavity through humid-air passes for turbulent flow to examine the impact of rayleigh number and aspect ratios on the heat and mass transfer at heat flux subjected to the vertical walls. ii. mathematical modeling a. geometrical description the considered physical problem is shown schematically in figure 1. humid-air occupies a two-dimensional rectangular enclosure. the vertical parallel walls are subjected to uniform flux (q) and the bottom side is considered impermeable and adiabatic. the top domain is defined as a free surface. the dimension of the open fluid at the bottom left wall was equal to 20% of the enclosure's height. different cases of aspect ratios (ar=h/l=0.5, 1, and 2) were proposed. fig. 1. a schematic representation of an open cavity. b. governing equations the governing equations for heat and mass transfer inside this open cavity are the continuity, momentum, energy, and concentration of humid-air liquid equation for natural convection [30]: engineering, technology & applied science research vol. 11, no. 5, 2021, 7571-7577 7573 www.etasr.com chati et al.: moist air flow analysis in an open enclosure. part a: parametric study • continuity equation: �� �� + �� �� = 0 (1) • momentum equations: �� �� + �� �� + � �� �� = − � � �� �� +�� ��� ��� + ��� ���� (2) �� �� + �� �� + � �� �� = − � � �� �� +�� ��� ��� + ��� ���� +���� − ��� (3) • energy equation: �� �� + �� �� + � �� �� = �� ��� ��� + ��� ���� (4) • concentration equation: �� �� + �� �� +� �� �� = � ��� ��� + ��� ���� (5) where υ is the kinematic viscosity, β is the thermal expansion coefficient, p is the fluid pressure, α and d are the thermal and mass diffusivity, respectively. all the governing equations of heat and mass transfer in the proposed open cavity were solved in a turbulent regime using the cfd code. a second-order upwind scheme was selected to solve the concentration and momentum equations. the computations were simulated to be converged at 10−7 of root mean square residual values. c. turbulence model a standard simple model of turbulence was proposed in [53], named k−ε, which is based on the turbulent kinetic energy equations k and the rate of dissipation of turbulent kinetic energy ε. this model was used to analyze the flow and heat transfer calculations due to its robustness, and consistent precision. the generic form of this model is [16]: # #$�%&�+ # #'�%& � = # #()*+ + +� ,.#&#(/ +0+ 01 − %2 −34 +5 (6) # #$�%2� + # #'�%2 � = # #()*+ + +� ,6 . #2#(/+ 76�. 2 &�0+76901�− 76:% 2: & +56 (7) where µt is the eddy viscosity, σk and σε are the turbulent prandtl numbers for k and ε, sk and sε are user-defined source terms, gk represents the kinetic energy production of turbulence due to velocity gradients, gb is the kinetic energy production of turbulence due to buoyancy, ym represents the contribution of the expansion of fluctuations, cµ=0.09, cε1=1.44, cε2=1.92, σk=1, and σε=1.3. d. boundary conditions the boundary conditions associated with the problem were: ���� ' = 0; 0 ≤ ( ≤ 0.1?: = � = 0, b = 5d, 7 = 1 ���� ' = 0; 0.1? ≤ ( ≤ 0.3?: = � = 0, b = 0, 7 = 0 � = ��, f = f� ���� ' = 0; 0.3? ≤ ( ≤ ?: = � = 0, b = 5d, 7 = 1 ���� ' = g; 0 ≤ ( ≤ ?: = � = 0, b = 5d, 7 = 1 ���� ( = 0; 0 ≤ ' ≤ g: = � = 0,#� #(⁄ = 0,#7 #(⁄ = 0 ���� ( = ?; 0 ≤ ' ≤ g: = � = 0, b = 5d 7 = 0 � = ��, ∆f = %�? the following variables are dimensionless: j∗ = ' g⁄ , 3∗ = ( g⁄ , �∗ = �� −��� ��l −���⁄ e. meshing sensitivity analysis the region was covered with a meshing grid having a further refinement in vertical sides. different grids were used: 140×140, 160×160, 180×180, and 200×200 for a cavity with aspect ratio ar=1. from table i, it is clear that the 180×180 mesh produced more satisfactory results than the others, for a maximum error of 0.02% and maximum values for the velocity components u and v. table i. mesh sensitivity test for maximum x, yvelocities, and temperature. 140×140 160×160 180×180 200×200 umax (m/s) 0.100652 (0.03%) 0.100668 (0.01%) 0.100673 (0.00%) 0.100678 vmax (m/s) 0.087004 (0.05%) 0.086937 (0.03%) 0.0869814 (0.02%) 0.086962 tmax (k) 304.914 (0.005%) 304.92 (0.003%) 304.9246 (0.001%) 304.929 iii. results and discussion the effects of aspect ratios (ar=0.5, 1 and 2) and rayleigh number (106 ≤ �� ≤ 108) on heat and mass transfer of turbulent humid-air flow for an open enclosure were investigated parametrically. the thermophysical properties of the working fluid were [54]: • %� = 1.15 mkg.mq9r • 7s� = 1005 mj.kgq�.kq�r • u� = 2.65.10q: mw.mq�. sq�r • +� = 1.85.10q[ mkg.mq�.sq�r • = 2.59.10q[ mm:. sq�r. a. validation the flow visualization of isotherms, streamlines, and isoconcentration results for the heat and mass transfer (ra=107 with different buoyancy ratios) were compared with those obtained by [49], as shown in figure 2. a second validation was investigated with results from [31, 37, 51], concerning the nusselt number as a function of the buoyancy ratio (n). the validations were satisfactory exhibiting good agreement, as shown in table ii. engineering, technology & applied science research vol. 11, no. 5, 2021, 7571-7577 7574 www.etasr.com chati et al.: moist air flow analysis in an open enclosure. part a: parametric study isotherm streamlines isoconcetrations n=1 present work [49] n=-5 present work [49] fig. 2. qualitative validation: comparison of isotherm, streamline and iso-concentration contours for ra=107 and n=1 and -5. table ii. quantitative validation; nusselt number as function of buoyancy ratio. nu n -0.5 -0.8 -5.0 present work 13.6 10.3 23.2 [51] 13.6 10.6 23.7 [37] 13.5 10.5 23.5 [31] 13.6 10.6 23.7 err % for [51] 0.7% 1.9% 1.2% b. discussion isotherms, streamlines, and mass fraction of η2ο visualizations are illustrated in figures 3, 4, and 5 to examine the hydrodynamic behavior and the heat transfer characteristics for ar=0.5, 1, and 2, respectively. the main flow tended to cross the cavity in a semi-vertical direction, creating a strong vortex at the bottom right wall of each configuration and indicating an accelerating mass transfer. the heat transfer efficiency for the natural convection of humid-air inside open enclosures was influenced by the rayleigh number at the lateral walls for all aspect ratios. for ar=0.5, the small cell found at the middle of the free surface was lost by the effect of enhanced buoyancy forces. another clockwise small rotating vortex was created at the left bottom wall, where its size became increasingly powerful, while the high temperatures were localized in close spaces near the humid left wall, which corresponded to the concentration of the thermal boundary layer. for the square enclosure, three cells started to develop compared to ar=2 geometries. the contours of the h2o mass fraction for all aspect ratios showed that the mass transfer dominated more as the rayleigh number decreased. a close observation of the isotherms and hydrodynamics contours remarks that the mass and heat transfer processes were less concentrated at the top free surface. the concentration of h2o increased significantly on the left wall of the enclosure, especially for ar=2. fig. 3. contours of isotherms (left), streamlines (middle), and mass fraction of h2o liquid (right) at ar = 0.5 for different rayleigh numbers (106≤ra≤108). fig. 4. contours of isotherms (left), streamlines (middle), and mass fraction of h2o liquid (right) at ar = 1 for different rayleigh numbers (106≤ra≤108). the effect of the rayleigh number with a fixed wall heat flux on the enhancement of thermal flow and mass transfer are presented in figures 6 and 7 respectively. the local nusselt number and mass fraction indicate the efficiency of the heat and mass transfer processes. as the height of the cavity has a significate role, the greater heat and mass transfers were found at ar=2. for low values of the rayleigh number, the mass fraction of the humid-air increased while the nusselt number decreased due to the slowly moving fluid. the heat transfer increased with the rayleigh number, showing optimum thermal performance due to the vigorous turbulent flow. engineering, technology & applied science research vol. 11, no. 5, 2021, 7571-7577 7575 www.etasr.com chati et al.: moist air flow analysis in an open enclosure. part a: parametric study fig. 5. contours of isotherms (left), streamlines (middle), and mass fraction of h2o liquid (right) at ar=2 for different rayleigh numbers (106≤ra≤108). fig. 6. evolution of local nusselt number as a function of rayleigh number with different aspect ratios (ar= 0.5,1, and 2). iv. conclusions this paper examined the effective mass and heat transfer efficiency for the natural convection of humid air inside open enclosures, concluding the following: • heat transfer efficiency for natural convection of humid air inside open enclosures is influenced by the rayleigh number at the lateral walls for all aspect ratio cases. the mass transfer decreases because of vaporization. moreover, as the rayleigh number increased the flow visualization revealed that the vortex created in each enclosure had more vigorous intensity. fig. 7. mass fraction of h2o for various rayleigh numbers with different aspect ratios (ar = 0.5, 1, and 2). • the opening surface enhanced the mass transfer, while the bottom wall was the most stable for a few mass transfers. • the mass transfer was reduced for the square cavity compared to the preferable enclosure at aspect ratio ar=2. furthermore, higher rates of the rayleigh number increased the thermal enhancement rate and decreased the mass fraction of humid air. • as a consequence, the thermal and mass transfer performance in the cavity with ar=2 was greater than in the other configurations for moist air as a working fluid. acknowledgment this research was funded by 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[54] b. e. poling, j. m. prausnitz, and j. p. o’connell, properties of gases and liquids, fifth edition, 5th ed. new york, ny, usa: mcgraw-hill education, 2001. microsoft word etasr_v11_n6_pp7957-7963 engineering, technology & applied science research vol. 11, no. 6, 2021, 7957-7963 7957 www.etasr.com ozalp et al.: investigation of a digital hydraulic valve operated by servo motors investigation of a digital hydraulic valve operated by servo motors adem fatih ozalp department of mechanical engineering karabuk university karabuk, turkey ademfatihozalp@karabuk.edu.tr refik polat department of mechanical engineering karabuk university karabuk, turkey refikpolat@karabuk.edu.tr celalettin cetinkaya department of mechanical engineering karabuk university karabuk, turkey c.cetinkaya06@hotmail.com muhammet huseyin cetin department of mechanical engineering konya technical university konya, turkey mhcetin@ktun.edu.tr abstract-this paper describes a new type of digital hydraulic valve run by two servo motors. digital hydraulics is a cuttingedge technology, which saves more exhausted energy than conventional hydraulic valves. it includes conventional valves, but its working principle is different. similar or different size valves constitute a digital hydraulic valve assembly. when the assigned valves are opened, a certain amount of flow is obtained from the output of the valve assembly. to control a digital hydraulic valve, pulse number modulation (pnm) control technique is used for equal valve flow rates, while pulse code modulation (pcm) is used for different valve flow rates. valves are exerted by independently launched electric coils. previous studies used controller board and external power booster circuits for coils. in this study, a new type of digital hydraulic valve is designed, manufactured, and tested with the pnm method. the studied valve body has two different valve groups. every group includes 16 equal valves and 1 camshaft rotated by 1 servo motor. the servo motors are controlled by a plc. the calculated performance index is found to be 5.1ms which is similar to the results of previous studies. the experimental results showed that the cam and servo motor controlled digital hydraulics is applicable to variable speed control hydraulic systems. keywords-hydraulic control; digital hydraulics; position control; valve design i. introduction hydraulic cylinders and hydraulic motors are used for lifting and turning heavy loads. elevators, presses, excavators, buckets, and dams are common areas of use. when precise position control is required for lifting heavy or light loads, and the lifting system has limited space, hydraulic systems are applied instead of electric actuators. proportional and servo valves are used for precise position control with a hydraulic cylinder. however, these high cost valves can easily break down due to contamination in the oil. this paper presents a hydraulic valve which can be used in precision position control applications, can work in the performance of servo and proportional valves, is resistant to oil contamination, and saves more energy than the conventional valves. the proposed valve is tested for speed and position control with a hydraulic cylinder. pressurized flow valves have been highly investigated in order to increase the performance of a system. pressure and flow rate change during the operation greatly affect the behavior of the system [1, 2]. on-off directional valves, proportional valves, servo valves are often used for a single hydraulic cylinder or a single motor. authors in [3] used two independent proportional valves each for one port of a hydraulic cylinder, reducing the energy losses by 15%. authors in [4] increased the controllability of the system by running the inlet and outlet ports of a hydraulic cylinder by 5 separate proportional valves. in addition, the efficiency of the system has increased. the lines to and from the cylinder were controlled by 4 proportional valves. another valve saves the potential load energy that the cylinder lifts and increases the system efficiency by connecting the return line of the hydraulic cylinder to the system. authors in [5] proved that parallelconnected on-off valves can be used as servo valves in the digital hydraulic method. in this method, the hydraulic system using water as fluid is operated with valves located in parallel. the valves have different flow rates and are controlled by the binary coding method. the data obtained in the experiment showed that velocity and position graphs are similar to the servo valve actuated system. however, it was found that the pressure shocks in the system are high. proportional and servo valves alone are generally used with a hydraulic cylinder, and a spool of the valve regulates the amount of flow through the valve. however, in digital hydraulics, the on-off valves just open and close and are more than one. the flow rate of each valve is a small amount of the total flow of the system. the flow rate of each valve may be corresponding author: adem fatih ozalp engineering, technology & applied science research vol. 11, no. 6, 2021, 7957-7963 7958 www.etasr.com ozalp et al.: investigation of a digital hydraulic valve operated by servo motors different or equal to the others'. if the valve flow rate is desired to be the same, valves with a very small flow rate are required in order to increase their accuracy, so the number of valves increases. if the valve flow rate is selected in multiples of 2 by the binary coding method, four valves will be sufficient instead of sixteen equal valves. the sensitivity will be 1/16 times. the fibonacci (1: 1: 2: 3: 5) method is similar to the binary coding method and the flow rates are chosen using different coefficients. in this way, when the valve flow rate is selected as a coefficient of some numbers, pressure shocks occur during the opening and closing of the valves at system pressure. these pressure shocks cause undesirable results in system control, hydraulic system parts and make it difficult for the system to operate linearly [6]. authors in [7] evaluated the hydraulic systems required in the iter fusion reactor. they stated that the hydraulic system to be used in the reactor would take a narrow space, work in high radiation, and should carry high reliability and high sensitivity. they mentioned that the digital hydraulic method would be suitable for this because the system is capable of tolerating errors. when they compared the servo hydraulic system to the digital hydraulic system, they obtained similar position tracking results. however, the digital hydraulic system made oscillation movements when servo systems gave more linear results at low speeds. they stated that using more on-off valves should be used to solve the pressure fluctuation causing oscillations. when separate valves are placed differentially in the a and b pressure and tank lines to the system, all four flow lines can be controlled independently. controller systems using 2-5 independent proportional valves instead of only one proportional valve are called programmable, multifunctional, independent line, and distributed line. since the valve system is used differentially, these systems are energy efficient, and their losses are minimized. when a single proportional valve is used, the valve spool regulates the flow to the pressure line and tank line equally [8-10]. digital hydraulic control method is superior compared to proportional and servo systems. in the case of a digital hydraulic system, when a valve fails, the system is capable of continuing operation. digital hydraulics systems are cheaper compared to proportional and servo systems and can cost even less if they are mass manufactured. they have the advantages of not requiring spool feedback as the proportional or servo valves [11-13]. the model-based controller system is used to control the digital hydraulic system. the controller operates based on a steady-state model and does not require dynamic modeling, so it does not make many calculations during the operation of the system. in this method, the control technique is based on reducing the previously calculated estimates in an optimal way by using the cost function method. during the operation of the system, the best reference command is determined by comparing the measurements taken from the position, pressure, and flow sensors with the estimated data to be operated with minimum energy, and the system is controlled according to [14-15]. authors in [16, 17] conducted the experiments of a hydraulic system powered by a fixed displacement pump, working with a four-zone secondary controller and variable displacement hydraulic motor. in this system, it is not possible to produce a hydraulic cylinder with a variable piston similar to its variable displacement motor in today's conditions. instead, authors in [16] used telescopic independent pistons and cylinders. the cylinder is connected to a boom arm and has loads of 200kg, 150kg, 100kg, and 50kg on the arm. the system shows 60% reduction in energy losses compared to systems operated by proportional and servo valves. this system is well controlled at high speeds but faces problems at low speeds. in contrast to the previous systems, a safety valve and a second flow sensor outside the pump line are installed to measure energy efficiency. it was found that the energy saving of this experimental system is increased by reducing the energy loss in the pressurized flow to the tank. authors in [18] operated a three-part hydraulic cylinder with 3 digital hydraulic control units including 8 on-off valves each. this system is operated by digital hydraulics and its energy loss is reduced by 66%. in the experimental system, the hydraulic cylinder is connected to a single degree of freedom lever, and the lever is required to keep fixed permanently. authors in [19] tested a lever mechanism with an electronic load sensing pressure system, a distributed digital hydraulic control unit, and a pressurized tank line. the system had a hydraulic accumulator connected to the tank line. the flow from the system to the tank was pressurized by a relief valve. the studied system's energy losses decreased by 53% to 71% compared to the proportional valve systems. authors in [20] examined a system of miniature valves to lift a load of 50kg. their system worked successfully for 15mm, 50mm, and 100mm position displacement. the coefficient found by dividing the derivative of the position error over time by velocity was determined as a success. their obtained coefficient was 1.7ms which is much better than the 5.3ms found in [21]. in the newly developed digital hydraulic method, instead of a servo valve, simple on-off poppet valves with equal fluid flow rate are used. the total number of the poppet valves is at least 2. in order to reduce the total number of poppet valves, valves with different flow rates are selected in multiples of two (binary coding). thus, instead of 16 openclose valves, the same process can be applied with 4 on-off valves. in the digital hydraulic control method, when one of the valves breaks down, the system continues to operate, and the operation of the system is not disrupted at all [19]. controlling four or more valves at the same time with binary coding in pcm method causes undesired pressure fluctuations in the system. other pnm methods use equal flow rate commercial valves that require more valves and more space in digital valve assembly. to solve that, custom made miniature valves are produced. this type of assembly is smaller compared to the commercially used valve assembly. either commercial or custom-made valves require high performance electronic control cards and additional valves are added to the system to show a damping effect. therefore, the complexity of the system increases [19, 21-24]. the above mentioned digital hydraulic valves involve independent control components for each small valve flow rate and that makes it even more complicated. the proposed valve has one camshaft and a servo motor for 16 same flow rate valves, which is better coordinated to control the valves. engineering, technology & applied science research vol. 11, no. 6, 2021, 7957-7963 7959 www.etasr.com ozalp et al.: investigation of a digital hydraulic valve operated by servo motors ii. conctrol principle the steady state model and the cost function presented in [5] are used to control the suggested valve. for the extending movement of the steady state, the equations of the system are: q n,p = ∑ upi qn,pi npi=1 (1) q p =q n,p �up��ps-pa= aa (2) q t =q n,t �ut��pb= ab (3) f=aapaabpb (4) z = �q n,p �up�� / �qn,t�ut�� (5) � = �� / �� (6) pa= z2ps+ γ 2f/ab z2+ γ3 (7) �� = � � ���� ���/�� ��� �� (8) v = qn,p�up� ab � γ psf/ab z2+ γ3 (9) w = q p .ps (10) for the retracting movement of the steady state, the equations of the system are: pa= γ2ps+ γ 2f/ab z-2+ γ3 (11) pb= γ3psz -2f/ab z-2+ γ3 (12) v = qn,t�ut� ab � ps+ f/ab z-2+ γ3 (13) where q n,p (up) and qn,t(ut) are the nominal flow coefficients of the tank side and the pressure side that change with up and ut which are the element vectors of qn,p and qn,t. f is the force applied by the cylinder, ps is the supply pressure, pa is the piston side pressure of the hydraulic cylinder, pb is the rode side pressure of the hydraulic cylinder, w is system energy and � is the hydraulic cylinder velocity. every poppet valve has an equal flow rate. also, the elements of vectors of q n,p and q n,t consist of the flow rates of these valves. the system is controlled with the steady state equations and the cost function. the least error control input calculated from the cost function is applied to the servo motors. this function can be written as: j�k�=�vr�k����k� 2+kpd�pdr�k�-p�d�k� 2 + k1�p��!k-1$-p���k� 2& k 2 �p��!k-1$-p���k� 2 (14) where j(k) represents the calculated error for the given combination of input, vr is the reference velocity, "^" circumflex is used to represent the calculated values of the below symbol, p dr represents the downstream reference pressure, kpd is the weight of downstream pressure error, and k' and k( are the weights of pressure variation for the a and b sides of the cylinder. the least error combination shows us the best control switch to achieve less error output. this combination has error vectors that correspond to the vector of q n,p (up) and q n,t (ut) in the same row and column. thus, less calculated error for the given reference value is applied to the system. hydraulic systems are sensitive to disturbance and a closedloop controller is efficient to obtain better results [26]. a closed-loop controller is used which can be written as: vrc= vr+ kp (yr-y) (15) where vrc is closed-loop velocity reference, kp is closed-loop gain, y r is position reference, and y is the actual position. a closed-loop controller is used to decrease velocity error (figure 3). the studied valve is not able to change the direction of the piston, therefore a commercial directional valve is added to the system as shown in figures 1, 4. the direction signal is shown as udir in figure 3. iii. design of the valve the studied hydraulic valve has two camshafts, and each one is driven by 1 servo motor. each camshaft has 16 cams and is used to actuate the valve spools instead of 16 different coils independent of each other. its rode and piston ports are connected to a commercial 4-way valve to channel the pressurized flow to the pump and tank ports of the used digital hydraulic valve. the studied digital valve has 2 groups of valves. each group includes 16 equal rate poppet valves and 1 servo motor to exert the spool of the poppets. the studied valve cannot use the binary coding method because the camshaft is able to open the valves one after another while the binary coded method needs to open different flow rate valves independently. for example, the pcm method might run 4 valves, and these are placed as 1x, 2x, 4x, and 8x flow rate valves in a line. it will open 1x, 2x, 4x, and 8x flow rate valves to have 15x flow rate or will open 1x and 8x flow rate valves to have 9x flow rate. however, the used camshaft will open 16 pieces of 1x flow rate valves respectively to supply the 16x flow rate to the system, and the studied valve cannot be used for binary coding method. in addition, for binary coding method, a hydraulic system has a lot of pressure fluctuations while different flow rate poppets are opened. instead, the studied valve will open the equal flow rate poppets successively by the servo motor with camshaft and the pressure shocks which are produced with the opening and closing of different flow rate valves will be decreased. thus, pressure shocks that reduce the life and operating accuracy of the system will be prevented. two servo motors through camshafts exert the poppet spools in the valve group one by one and each camshaft has 16 different angled cams mounted. as shown in figure 2, each cam makes an angle of 11,25° with the next cam. so, for every 11,25° turn of the camshaft, one poppet in the valve group opens. the valve poppet is pressed down by a running cam lobe and is lifted by spring force. engineering, technology & applied science research vol. 11, no. 6, 2021, 7957-7963 7960 www.etasr.com ozalp et al.: investigation of a digital hydraulic valve operated by servo motors fig. 1. test setup. fig. 2. the valve assembly. in figure 2, each camshaft faces two identical valve bodies, below and above. the left sides of the upper and lower body are for the pressure line and the right sides are for the tank line. each valve body has 2 plates and spools fitted into them. the red color valve plate houses the higher pressurized line, and the orange color plate houses the lower pressurized line. plates are connected to each other with bolts. also, two plates hold up each valve body, camshafts, and servo motors from the sides with bolts. to minimize the valve, two opposite valve bodies are used. iv. test setup the test setup is shown in figure 1. loads are placed on the plate, which is attached to the vertical cylinder rode end. steel frame houses the manufactured valve on the right side and a directional valve on the left side. the vertical hydraulic cylinder is set in the middle of the steel frame. pressure transducers are connected to the hydraulic cylinder end ports and a linear position sensor is attached to the hydraulic cylinder rode end. a hydraulic pressure supply unit is connected to the valve with hydraulic hoses. the schematic of the hydraulic circuit is shown in figure 4. the studied valve body (8, 9) and an on-off valve (10) are attached side by side on a frame. a double-acting hydraulic cylinder (ø40 mm / ø25 mm × 400 mm) is placed in the center of the frame to lift up loads. its ports are from the pump and tank ports of the studied valve manifold. hydraulic hoses are used to connect valves, cylinder, and hydraulic supply to each other. a separate hydraulic supply unit includes a 5.5kw electric motor and a 32.5lt/min fixed displacement pump (1) is used. servo motors are run by an omron plc unit. measurements are taken by the same plc unit. two pressure transducers (6) are added to the rod pressure line and piston pressure line of the hydraulic cylinder (11) to measure the pressure of the cylinder chambers. to see the flow rate of the pump, a flowmeter (4) is used. hydraulic cylinder displacement is measured with a linear position sensor (7). tank (12), check valves (2), relief valve (3), and mechanic pressure gauge (5) are the other system components. fig. 3. block diagram of the closed loop control system. v. experimental results fifth-order polynomial is used for reference generation. three different trajectories are chosen, namely 25mm, 50mm, and 100mm back and forth displacement with 2s movement time. each trajectory is performed 4 times and integral of square error (ise) and maximum position error measurements are compared to see the performance of the system as shown in table i. after several tests to acquire better cost function parameters kpd, k1, and k2, they were found to be 5×10 -16. nominal flow coefficients qn,p1 and qn,t1 are 1×10 -8m3/(s√pa) and 0.9×10-8m3/(s√pa) respectively. replaceable orifice cavity is designed on the valve manifold and the flow rate of the valve can be changed by using different diameter bores inside the orifices. however, it is hard to find the desired diameter commercial orifices, so commercial setscrews are drilled and used for the required orifices. it is highly difficult to drill the desired bore below ø1mm diameter in high strength commercial setscrews. closed-loop gain is kp = 35/s and the used load mass is 50kg. output data are filtered with a low-pass filter. for each position tracking experiment, position, position error, velocity, cylinder port pressures, and states of valve engineering, technology & applied science research vol. 11, no. 6, 2021, 7957-7963 7961 www.etasr.com ozalp et al.: investigation of a digital hydraulic valve operated by servo motors openings are measured. figure 5 depicts that 25mm position error is bigger than in longer distance trajectories. both pressure outputs oscillate at maximum speed peak point. maximum position error is 0.29mm at the speed stop point on back forward movement. fig. 4. hydraulic circuit diagram. figure 6 presents the 50mm position tracking. the position error is better than the 25mm error. there are some pressure fluctuations at extending movement. retracting movement makes more valve openings than the 25mm retracting movement. to decrease cavitation, the t port flow rate is smaller than the p port flow rate. due to the area difference between the rod and piston side, more valve openings occur with a larger speed. figure 7 shows the pressure fluctuations with both extending and retracting movement of 100mm displacement results. these fluctuations happen when it is getting closer around maximum speed peak point. moreover, the valve opening number increases with speed. besides, the best maximum position error by speed is 0.51mm. previous studies compared their experiments with a performance index method calculated by dividing maximum position error by speed. fig. 5. 25mm displacement tracking results. table i. values of ise and maximum error for position trajectory ise (mm 2 /s) ∆x (mm) 25 mm 0.14 0.29 50 mm 0.19 0.38 100 mm 0.26 0.51 vi. conclusion in this study, a cam operated digital hydraulic valve is designed, manufactured, tested, and discussed. it is proven to be applicable to solenoid operated digital hydraulic valves, proportional, and servo operated valves. engineering, technology & applied science research vol. 11, no. 6, 2021, 7957-7963 7962 www.etasr.com ozalp et al.: investigation of a digital hydraulic valve operated by servo motors fig. 6. 50mm displacement tracking results. the results show promising values: the 100mm trajectory performance index is 5.1ms, which is similar to the value of 5.3ms found in [21]. on the other hand, the 25mm trajectory position error is not as good as the 100mm trajectory response because valve flow rates are chosen with a wide range which affects the speed and the position error. however, the valve is self-designed and manufactured allowing orifice change, and hence proper flow rates can be applied to the desired systems. fig. 7. 100 mm displacement tracking results. the 50mm tracking response error can also be tolerated by changing orifices. also, by increasing valve number and using smaller flow rate valves, 25, 50, and 100mm tracking responses can give good results. on the other hand, the studied valve uses a vertically placed cam, and this results in a wider valve manifold with more valves. cam operated valves cannot be placed crosswise like solenoid operated digital hydraulic valves. it can be concluded that the valve can present great engineering, technology & applied science research vol. 11, no. 6, 2021, 7957-7963 7963 www.etasr.com ozalp et al.: investigation of a digital hydraulic valve operated by servo motors performance for bigger systems due to manufacturing limits. an essential result is achieved because cheaper components than the solenoid-operated digital hydraulic valves are used. it is possible to obtain smoother movement with smaller flow rate of valves. this comes with a larger volume, but with a smaller price. in summary, our first digital hydraulic valve is not as superior as the previously studied digital hydraulic valves due to the used cam and servo motor, but it can be improved with a smaller design and more valves while it has already showed its potential with inexpensive components. acknowledgment this study was funded by the scientific and technological research council of turkey (tubitak) ardeb 1002 grant no 218m256. references [1] k. a. venkataraman, k. kanthavel, and b. n. kumar, 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[26] s. babesse, "design of two optimized controllers of a hydraulic actuator semi-active suspension: a comparison study," engineering, technology & applied science research, vol. 9, no. 4, pp. 4561–4565, aug. 2019, https://doi.org/10.48084/etasr.2836. engineering, technology & applied science research vol. 8, no. 2, 2018, 2796-2798 2796 www.etasr.com lakhiar et al.: effect of river indus sand on concrete tensile strength effect of river indus sand on concrete tensile strength muhammad tahir lakhiar faculty of civil and environmental engineering universiti tun hussein onn malaysia gf170030@siswa.uthm.edu.my noridah mohamad faculty of civil and environmental engineering universiti tun hussein onn malaysia noridah@uthm.edu.my muhammad abu bakar shaikh department of civil engineering mehran university of engineering and technology pakistan muhammad.abubakar@faculty.muet.edu.pk anees ahmed vighio department of civil engineering, mehran university of engineering and technology pakistan aneesahmedvighio08@gmail.com ashfaque ahmed jhatial faculty of civil and environmental engineering universiti tun hussein onn malaysia aajhatial@hotmail.com abdul aziz abdul samad faculty of civil and environmental engineering universiti tun hussein onn malaysia azizs@uthm.edu.my abstract—in the development of pakistan construction industry, the utilization of river indus sand in concrete as fine aggregate has expanded tremendously. the aim of this research is to study the effect of indus river sand on the tensile strength of various grades of concrete when it is utilized as fine aggregate. concrete samples of m15, m20 and m25 grade concrete were cured for 7, 14, 21 and 28 days. based on the results, it is found that concrete became less workable when indus river sand was utilized. it is recorded that tensile strength of concrete is decreased from 5% up to 20% in comparison with hill sand. the results were derived from various concrete grades. keywords-tensile strength; workability; river indus sand; hill sand i. introduction concrete is broadly utilized as building material because of it is highly durable, easily accessible and economical [1]. basically, concrete is a blend of binder, aggregates (coarse and fine), water and admixtures [2-3]. fine aggregate is an important ingredient in concrete occupying 25% to 35% of its volume. it is utilized as filler in concrete. the composition, shape, and size of the fine aggregates have great influence on the fresh and hardened properties of concrete [4-5]. in indus river there is a siltation problem which causes negative effects on storage capacity, water quality and subsequently, reduces power and irrigation capability [6]. normally, hill sand is used as fine aggregate in pakistan construction industry, which makes the concrete un-economical in northern areas of sindh. to overcome this problem, in this research river indus sand was used as fine aggregate to make the concrete economical and solve the siltation problem. in the experimental work, hill sand was fully replaced by indus river sand. the workability and tensile strength of concrete were examined with comparison to the conventional concrete which used hill sand as fine aggregates. ii. literature review authors in [7] analyzed the m25 grade concrete at different curing regimes (7, 14 and 28 days). foundry sand replaced natural sand with 10%, 20%, 30%, 40% and 50% by weight of fine aggregate. the results indicated that the compressive strength increased up to 30%. however, further increment of replacement percentage showed a decrease in compressive strength. authors in [8] experimented with the mechanical properties of concrete at different proportions of 0%, 15%, 25% and 35% where natural sand was replaced by foundry sand. the results concluded that the optimum percentage was 25 % which gave the maximum strength. authors in [9] studied m25 grade concrete at different curing regimes (7, 14 and 28 days). the sea sand was partially replaced by river sand at different percentages of 20%, 40%, 60%, 80% and 100%. the results demonstrated that the compressive strength of this concrete was decreased up to 6.5% compared to that of conventional concrete. authors in [10] replaced natural sand at different percentages 10%, 20% and 30% with foundry sand to manufacture m20 grade concrete. the results concluded that the compressive strength increased significantly as the replacement percentage increased. meanwhile, the tensile strength was maximum at 20% replacement. iii. materials and methods a. materials ordinary portland cement cem i 42.5 n that complies with astm c0150-04ae01, branded name as falcon cement was engineering, technology & applied science research vol. 8, no. 2, 2018, 2796-2798 2797 www.etasr.com lakhiar et al.: effect of river indus sand on concrete tensile strength selected for this research work. in this research, the two types of fine aggregates (hill sand and river indus sand) were used. material properties like specific gravity, water absorption, fine modulus and color of hill sand and river indus sand are shown in tables i and ii. table i. properties of hill sand s.no particulars of test test results 1 specific gravity 2.56 2 fineness modulus 3.01% 3 water absorption 1.2% 4 color light orange table ii. properties of indus river sand s.no particulars of test test results 1 specific gravity 2.50 2 fineness modulus 2.04% 3 water absorption 3.8% 4 color dark grey b. test parameters and mixture proportions three grades of concrete mixtures (m10, m15 and m20) were studied for this research. two different kinds of concrete mix were cast, namely conventional concrete using hill sand as fine aggregate and concrete using indus river sand as fine aggregate. hill sand was fully replaced with indus river sand. the cylinders were tested for concrete tensile strength at curing ages of 7, 14, 21, 28 days. mixing was carried out using a rotary mixer. the concrete mix workability was checked by standard slump test using standard slump cone and procedure according to astm c 143. all the cylinders were extracted from the molds after 24 hours and cured for the required age of testing. the concrete tensile strength was tested using the universal testing machine available in the civil engineering department, muet jamshoro, and followed the overall procedure described in astm c496/c496m-17. iv. results and discussion a. slump test (astm c 143) for slump test, the astm c 143 standard was followed. the workability results of both concretes are shown in table iii. it is seen that the indus river sand concrete is low workable when compared to the conventional concrete. table iii. workability values of concrete mixes mixture slump value (mm) conventional concrete (m15) 31.75 river sand concrete (m15) 25.4 conventional concrete (m20) 50.8 river sand concrete (m20) 43.18 conventional concrete (m25) 63.5 river sand concrete (m25) 50.8 b. tensile strength tensile strength test was conducted according to the astm c496/c496m-17 standard. the tensile strength results of both concretes are shown in table iv and figures 1-3. the results showed that there was a reduction in the tensile strength of river sand concrete because of the improper material bonding due to the larger amount of clayey particles present in river indus sand. after 7 days curing, the tensile strength of m15, m20 and m25 river sand concrete decreased by 12.72%, 10.21% and 5.88%, respectively. after 14 days water curing, the tensile strength of m15, m20 and m25 river sand concrete decreased by 6.87%, 3.87% and 2.79% respectively. at 21 days water curing, the tensile strength of m15, m20 and m25 river sand concrete decreased by 2.06%, 2.77% and 1.63%, respectively. at 28 days water curing, the tensile strength of m15, m20 and m25 river sand concrete decreased by 1.90%, 1.68% and 1.08%, respectively. table iv. tensile strength of m15, m20 and m25 grade concrete. mixture t en si le s tr en g th a t 7 d a y s (m p a ) t en si le s tr en g th a t 1 4 d a y s (m p a ) t en si le s tr en g th a t 2 1 d a y s (m p a ) t en si le s tr en g th a t 2 8 d a y s (m p a ) conventional concrete (m15) 1.24 1.71 1.98 2.13 river sand concrete (m15) 1.10 1.60 1.94 2.09 conventional concrete (m20) 1.51 1.92 2.22 2.41 river sand concrete (m20) 1.37 1.85 2.16 2.37 conventional concrete (m25) 1.80 2.21 2.48 2.80 river sand concrete (m25) 1.70 2.15 2.44 2.77 fig. 1. tensile strength vs curing regimes of m15 grade concrete fig. 2. tensile strength vs curing regimes of m20 grade concrete engineering, technology & applied science research vol. 8, no. 2, 2018, 2796-2798 2798 www.etasr.com lakhiar et al.: effect of river indus sand on concrete tensile strength fig. 3. tensile strength vs curing regimes of m25 grade concrete v. conclusion concrete becomes less workable when indus river sand is utilized as fine aggregate. for better results of workability, certain admixtures will be required. the results showed the tensile strength of indus river sand concrete 1% to 2% lower than the tensile strength of conventional concrete. hence, it is concluded that m25 grade concrete gave better results for concrete with indus river sand as fine aggregate. references [1] e. aprianti s., “a huge number of artificial waste material can be supplementary cementitious material (scm) for concrete production – a review part ii”, journal of cleaner production, vol. 142, no. 4, pp. 4178-4194, 2017 [2] z. li, advanced concrete technology, john wiley and sons inc., 2011 [3] a. m. neville, properties of concrete, prentice hall, 2011 [4] j. p. mclaughlin, k. b. woods, r. c. mielenz, n. c. rockwood, “distribution, production, and engineering characteristics of aggregates, section 16”, in: highway engineering handbook, mcgraw-hill, 1960 [5] c. s. poon, z. h. shui, l. lam, h. fok, s. c. kou, “influence of moisture states of natural and recycled aggregates on the slump and compressive strength of concrete”, cement and concrete research, vol. 34, no. 1, pp. 31-36, 2004 [6] a. omoregie, o. e. alutu, “the influence of fine aggregate combinations on particle size distribution, grading parameter, and compressive strength of sandcrete blocks”, canadian journal of civil engineering, vol. 33, no. 10, pp. 1271-1278, 2006 [7] a. d. raval, a. pamnani, a. i. kachwala, “foundry sand: utilization as a partial replacement of fine aggregate for establishing sustainable concrete”, international journal of engineering sciences & research technology, vol. 4, no. 1, pp. 308-311, 2015 [8] d. r, bhimani, j. pitroda, j. j. bhavsar, “used foundry sand: opportunities for development of ecofriendly low cost concrete”, international journal of advanced engineering technology, vol. 4, no. 1, pp. 63-66, 2013 [9] d. chaurasiya, k. koli, s. chaudhari, v. more, p. c. satpute, “utilization of foundry sand: an art to replace fine sand with foundry sand”, international journal on theoretical and applied research in mechanical engineering, vol. 5, no. 1, pp. 44-48, 2016 [10] k. p. salokhe, d. b. desai, “application of foundry sand in manufacture of concrete”, second international conference on emerging trends in engineering (sicete), jaysingpur, india, pp. 43-48, 2015 microsoft word etasr_v13_n4_pp11400-11405 engineering, technology & applied science research vol. 13, no. 4, 2023, 11400-11405 11400 www.etasr.com zisopol et al.: dimensional accuracy of 3d printed dog-bone tensile samples: a case study dimensional accuracy of 3d printed dog-bone tensile samples: a case study dragos gabriel zisopol mechanical engineering department, petroleum-gas university ploiesti, romania zisopol@zisopol.ro alexandra ileana portoaca mechanical engineering department, petroleum-gas university ploiesti, romania alexandra.portoaca@upg-ploiesti.ro (corresponding author) maria tanase mechanical engineering department, petroleum-gas university ploiesti, romania maria.tanase@upg-ploiesti.ro received: 23 may 2023 | revised: 11 june 2023 | accepted: 26 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | https://doi.org/https://doi.org/10.48084/etasr.6060 abstract three-dimensional (3d) printing technology has revolutionized manufacturing by enabling the rapid production of complex objects. however, ensuring dimensional accuracy in 3d printed parts remains a significant challenge due to various factors, including the selection of appropriate parameters during the fused deposition modeling (fdm) process. achieving dimensional accuracy is crucial in determining the reliability of a printing machine to produce objects that meet the expected results. this study aims to investigate the influence of fdm parameters (filling percentage and layer thickness) on the final dimensions of 3d printed parts made from polylactic acid (pla) through a systematic experimental and statistical approach. the goal is to identify the optimal process parameter settings that minimize the error percentage in the dimensions of the printed parts using the taguchi method. overall higher dimensional accuracy was obtained, influenced mainly by the layer thickness parameter (in the case of y direction dimensions) and by the filling percentage (in the case of z direction dimensions – corresponding to sample thickness). the findings of this study provide valuable insight into identifying the optimal configuration for producing pla 3d-printed components. keywords-3d printing; fdm; pla; dimensional accuracy; printing process parameters i. introduction 3d printing is a modern technology that offers numerous possibilities for creating complex-shaped objects by utilizing a computer-aided design (cad) model [1, 2]. this technology has already had a significant impact across various industries [3-13]. one of the commonly used additive manufacturing techniques is fused deposition modeling (fdm), which involves depositing thermoplastic filaments layer by layer through extrusion. fdm has gained immense popularity as a manufacturing technology primarily because of its affordability, versatility in material selection, and the ability to customize printed parts. however, the fdm has certain limitations such as printing time and surface quality that can be adjusted based on the specific requirements of the intended application through process parameters such as layer height, infill percentage, printing speed, etc. abs, pla, petg, and pc are among the most popular thermoplastic materials used in fdm [14]. the mechanical properties of fdm-printed components are greatly influenced by the design and processing conditions of the printing process [3, 14-19]. while extensive research has been conducted on the impact of the process parameters on the mechanical properties of printed parts [3, 14-16, 18, 21-30], only limited studies [1, 13, 15, 17, 31-38] have focused on the dimensional accuracy of 3d printing and its relationship with the process settings. authors in [1, 27, 32] showed that the layer thickness has the most significant influence on the dimensional characteristics of 3d printed parts. the main objective of [36] was to identify the 3d printing technology that results in the highest level of accuracy among three different methods. the geometric analysis showed that for simple shapes, the fdm and sls technology had much lower accuracy than the mj technology (polyjet method). authors in [13, 16, 26, 28] investigated the influence of parameters such as filling percentage, layer thickness, printing direction, on the dimensional accuracy of 3d printed spur gears made of different materials (pla, nylon, abs, petg). authors in [17] compared the dimensional accuracy of spur engineering, technology & applied science research vol. 13, no. 4, 2023, 11400-11405 11401 www.etasr.com zisopol et al.: dimensional accuracy of 3d printed dog-bone tensile samples: a case study gears produced using fused filament fabrication (fff) technology with two different polymeric materials, pla and nylon-pa6. the findings indicate that the pla exhibits better overall dimensional accuracy. furthermore, the gears printed with nylon, which had a lower infill ratio compared to pla, showed less form errors. very important findings are highlighted in [14], in which a statistical calculation is used to establish the influence of fdm parameters (height of the deposited layer at one pass and filling percentage) on the dimensions of the shaft diameter and the bore diameter of cylindrical spur gears made of pla, revealing that the filling percentage has a greater influence on the dimensional accuracy of cylindrical spur gears made of pla. in the this article a novel approach was used by examining the impact of fdm parameters (layer thickness and filling percentage) on the dimensional accuracy of dog-bone tensile test pieces manufactured from pla. consequently, the obtained dimensional measurements for the test pieces (thickness and width) were compared against their respective nominal values to determine the accuracy percentage. the results of the current work have a significant contribution in the identification and quantification of the predominant influence between the two parameters under investigation, through rigorous measurements and statistical analysis. ii. materials and methods the present study was performed using the working methodology shown in figure 1. fig. 1. working methodology. a. sample preparation for the experimental study, a total of 40 samples (fabricated with pla) were printed, consisting of 5 samples for each combination of 2 different layer thicknesses (0.10 mm and 0.20 mm) and 4 filling percentages (25%, 50%, 75% and 100%). the shape and dimensions of the samples are shown in figure 2. fig. 2. tensile test specimen dimesional details. a raise e2 3d printer was used, which has a volume capacity of 330×240×240 mm. the printing parameters are presented in table i. table i. 3d printing parameters constant parameters variable parameters build orientation: x-y layer thickness: lt = 0.10 and 0.20 mm print speed: 80 mm/s filling percentage: fp = 25%, 50%, 75%, 100% deposition temperature: 200 °c infill model: lines, 45°orientated the indicated dimensions from figure 2 were measured for all samples. the width and thickness were measured at both ends of the section (ow1, ow2, respectively t1 and t3) as well as the middle (w1, w2, w3, respectively t2). since the most important part for the dog-bone tensile test specimen is the gauge section, three measurements were made in this area, for each specimen. b. statistical analysis of the measured data in order to establish the influence of printing parameters on the dimensional accuracy of the printed samples, statistical calculations were performed, determining (for each dimension presented in figure 1) the arithmetic mean �̅ , standard deviation �, and dispersion �� [39, 40]: �̅ = ���� �...���� (1) � = ∑�����̅� � (2) �� = �� ∑��� − �̅�� (3) the results were analyzed with the minitab software, in order to identify the importance of the printing parameters and their influence on the dimensional accuracy of the 3d pla printed samples. the considered factors were the filling percentage and the layer thickness and the standard deviation of the results was considered. interpreting the standard deviation for dimensional accuracy involves understanding that a higher standard deviation indicates greater variability or inconsistency in the measurements. this means that the printed objects may have more significant deviations from the desired dimensions, with some measurements being larger and others smaller than the target value. on the other hand, lower standard deviation suggests that the measurements are closer to the desired dimensions, indicating a higher level of accuracy and consistency in the printing process. therefore, when assessing dimensional accuracy, a smaller standard deviation is desirable as it reflects a more precise and reliable printing process with minimal variations in the printed objects dimensions. so, the quality characteristic "smaller is better" was taken into account engineering, technology & applied science research vol. 13, no. 4, 2023, 11400-11405 11402 www.etasr.com zisopol et al.: dimensional accuracy of 3d printed dog-bone tensile samples: a case study for the analysis of the signal-to-noise (s/n) ratio and the optimum level of the two investigated factors was selected based on the s/n ratio plots. iii. results and discussion the dispersion values for the measured dimensions indicated in figure 2, for the printing parameters investigated, are presented in figures 3-6. fig. 3. the dispersion values for ow1 dimension. fig. 4. the dispersion values for w2 dimension. fig. 5. the dispersion values for t1 dimension. for exemplification, in the case of dimensions w2 and t2, figures 7 and 8 were used to select the best values of process parameters. the plot displays the average values of a response variable for different factor levels. interpreting the main effect plot for "smaller is better" means supposes focusing on minimizing the response variable. the plot helps identifying which factor levels or combinations of levels result in smaller values of the response variable. the optimum combination of printing parameters is filling percentage 100% and layer thickness 0.2 mm (for the w2 dimension) and filling percentage 75% and layer thickness 0.1 mm (for the t2 dimension). fig. 6. the dispersion values for t2 dimension. fig. 7. main effect plot for w2 dimension. fig. 8. main effect plot for t2 dimension. in order to identify the most significant factors that lead to smaller standard deviation, the pareto chart (figures 9 and 10) can be used. therefore, in the case of the w2 dimension (y direction) the term influencing significant the dimensional accuracy is layer thickness, while in the case of the t2 engineering, technology & applied science research vol. 13, no. 4, 2023, 11400-11405 11403 www.etasr.com zisopol et al.: dimensional accuracy of 3d printed dog-bone tensile samples: a case study dimension (z direction) the most significant factor is filling percentage. the same problem was investigated in [14], but on pla spur gears. it was observed that filling percentage has a greater influence on the dimensional accuracy of 3d printed parts. fig. 9. pareto chart for the w2 dimension. fig. 10. pareto chart for the t2 dimension. fig. 11. interaction plot between data means (w2 dimension). the interaction plots in figures 11 and 12 reveal that the target dimensions values are obtained with 0.2 mm layer thickness, excepting at 100% filling percentage (in the case of the w2 dimension) and 0.1 mm layer thickness in most cases (in the case of the t2 dimension). in both cases, if 50% infill percentage is applied, then larger layer thickness is recommended in order to obtain smaller dimensional errors. in order to quantify the level of accuracy achieved for each measured dimension, the average percentage deviation was calculated and is graphically represented in figure 13. fig. 12. interaction plot between data means (w2 dimension). fig. 13. average percentage deviation. in figure 13, a reasonably accurate printing process can be highlighted, as the deviation is relatively small (on average, the measured dimensions of the 3d printed parts deviate by approximately 1.64% from the expected dimensions). the biggest values of the average percentage deviation were obtained for the w1, w2 and w3 dimensions (y direction) and the smallest for the t1, t2 and t3 (z direction), suggesting a directional influence on the accuracy of the printed parts (the printing process is more prone to dimensional variations in the y direction compared to the z direction). also, it can be seen that the average deviation percentage values are positive (the real measured values are bigger than the nominal values) for all the analyzed dimensions, except ow1 and ow2 dimensions (representing the width of the external area of the samples) which recorded negative values. the results are in accordance with the findings in [1], where the accuracy of dog-bone test specimens ranged between 97% and 99% and in [37] where the dimensional error values ranged from 0.82% to 2.60%. another engineering, technology & applied science research vol. 13, no. 4, 2023, 11400-11405 11404 www.etasr.com zisopol et al.: dimensional accuracy of 3d printed dog-bone tensile samples: a case study important aspect is that, overall, the dispersion values were smaller for 0.20 mm than for 0.10 mm layer thickness, indicating 0.20 mm for less variability and higher accuracy. these results confirm the statement from [1] that as the number of layers increases (the thickness of the layer decreases), the dimensional accuracy of the 3d printed part tends to decrease. the same conclusion was mentioned in [37], where cubic parts were 3d-printed using pla and fdm, observing that layer height of 0.25 mm resulted in lower dimensional errors compared to 0.05 mm layer height. iv. conclusions in this paper, theoretical-experimental analysis was conducted in order to evaluate the influence of the printing parameters layer thickness and filling percentage on the dimensional accuracy of 3d-printed pla dog-bone tensile samples, while the results were compared with those of other similar studies. the positive average percentage deviations for most dimensions indicate that, on average, the measured dimensions of the 3d printed parts are larger than the expected or intended dimensions. the highest accuracy was obtained for thickness dimensions t1, t2, t3. a remarkable influence was noticed for the layer thickness parameter on the accuracy of dimensional characteristics, observing that is better to increase the layer thickness. adjusting the layer thickness can improve the dimensional accuracy in the y direction, while varying the filling percentage can have a notable effect on the dimensional accuracy in the z direction. by focusing on 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[40] d. zisopol, "the place and role of value analysis in the restructuring of production (case study)," economic insights – trends and challenges, vol. 1, no. 4/2012, pp. 27–35, jan. 2012. microsoft word etasr_v12_n4_pp8891-8895 engineering, technology & applied science research vol. 12, no. 4, 2022, 8891-8895 8891 www.etasr.com khmailia et al.: design of a low power cmos inverter with the vbb stack approach design of a low power cmos inverter with the vbb stack approach samah khmailia department of physics faculty of science university of tunis el manar tunis, tunisia samehkhmailia@gmail.com jilani rouabeh department of technology faculty of science university of tunis el manar gafsa, tunisia rouabeh.jilani@yahoo.com abdelkader mami department of physics faculty of science university of tunis el manar tunis, tunisia abdelkader.mami@fst.utm.tn received: 12 february 2022 | revised: 21 february 2022 | accepted: 16 april 2022 abstract-due to the exponential advancement in nanotechnology devices, low energy consumption has become a significant concern of researchers and vlsi designers. in this paper, the variable body bias (vbb) and the stack approach are used simultaneously to reduce the leakage power of a cmos inverter in standby mode. this new technique is called the vbb stack approach. the simulations have been conducted on the lt spice simulator. the power evaluation has been determined and compared between the conventional approach, the stack approach, and the vbb stack approach. the results have demonstrated the performance of the vbb stack approach. the power consumption in the vbb stack approach has decreased by 23% compared to the conventional approach and by 10% compared to the stack approach. keywords-cmos inverter; vlsi; power dissipation; leakage current; low power; vbb stack approach i. introduction the continuous demand for lightweight portable devices such as laptops, tablets, and smart phones has increased the need to reduce the processor size [1, 2]. vlsi designers have made possible to put millions of transistors on a single chip while maintaining good device performance [3]. the oxide thickness of transistor has been shrinking. the channel length has also become short, but produces increased leakage current in standby mode. with the continuous decreasing of technology size, the leakage power in standby mode is becoming the main contributor of total power consumption. the high power dissipation has become a major issue in digital circuit design with each new technology emergence [4]. the main effect of high leakage power is the increase in temperature, which in some cases leads to device breakdown [5]. power optimization has become an important research field for vlsi designers. many techniques have been proposed, each one delivering a new way to decrease power leakage, but the shortcomings of each push researchers to try to discover a better approach. in this work, the stack approach and the vbb approach are used simultaneously to ensure the best power optimization of a cmos inverter. the proposed technique is called the vbb stack approach. ii. literature review at all levels of vlsi design steps, many approaches heve been proposed to reduce power dissipation. authors in [6] presented low power half adder, full adder, half substractor, and full substractor using the cmos technology. authors in [7] developed a full adder design using the modified gdi technique to reduce power consumption. authors in [8] analyzed a mos transistor to decrease leakage current in standby mode based on forward and reverse body biasing techniques. authors in [9] used the substrate biasing technique to reduce the standby leakage power of a nanometer scale cmos circuit. the substrate biasing vsb of a cmos transistor has a direct effect on the threshold voltage vth, which can be controlled by varying the substrate potential. the equation that shows the impact of substrate biasing on threshold voltage is: ��� = ���� + �( |2∅ − �� | − |2∅ |) (1) where ∅ is the flatband voltage, � is the substrate effect coefficient, ���� is the threshold voltage with zero body biasing, and �� is the source to substrate voltage. the threshold voltage is directly proportional with the body potential vbb (vsb). figure 1 illustrates the conventional cmos connections and the vbb connections. corresponding author: samah khmailia engineering, technology & applied science research vol. 12, no. 4, 2022, 8891-8895 8892 www.etasr.com khmailia et al.: design of a low power cmos inverter with the vbb stack approach fig. 1. body connections: (a), (b) conventional bias, (c), (d) vbb technique. commonly, the body (substrate) of an nmos transistor is connected to the ground and the body of the pmos transistor is connected to vdd [10]. with the vbb technique, the body terminal of pmos is connected to the positive voltage, and the body terminal of nmos is connected to the negative voltage to increase the threshold voltage. authors in [11] presented the stack technique as a method to reduce leakage power. this method is based on the principle that each transistor can be replaced by two half size transistors associated in series [11, 12]. fig. 2. the stacking technique. if only one transistor "n" is in standby mode, the potential in the source node is zero, hence there is not a self-reverse bias effect and the leakage current increases. when both transistors n1 and n2 are in standby mode, a low drain current occurs. a positive potential vn appears. the gate to source voltage (vgs1) of transistor n1 reduces because the sub-threshold current reduces which has as effect an increase to the threshold voltage. this effect is known as the stacking effect [13]. authors in [11] used the sleepy stack approach to reduce the power consumption of a cmos inverter. the sleepy stack approach consists of dividing each transistor into two half size transistors. a sleep transistor is placed in parallel to one of the transistors. during the standby mode, the sleep transistors are put off. the threshold voltage increases and the leakage current reduces. the increase of area is the major penalty of this approach. authors in [14] used the mtcmos technology to design of a low power xnor gate. this method is based on adding two sleep high threshold voltage transistors to the principal circuit. while low threshold transistors are active to realize the principal function, the high threshold transistors are turned on. during the stand-by mode, the high threshold transistors are turned off, hence the subthreshold leakage current is cut off and the static power decreases. the mtcmos technique reduces the leakage current but increases the propagation delay time. fig. 3. the sleepy stack approach. fig. 4. the mtcmos technique. authors in [15] proposed the use of the lector technique to cut down the leakage current of a nand gate [17]. in this approach, two leakage control transistors lc1 and lc2 are introduced between the pull up and pull down network. the source of each leakage transistor controls the gate terminal of the other. the introduction of leakage control transistors increases the resistance between vdd and gnd, thus reducing the leakage current. the lector technique reduces the leakage current but increases the area and the propagation delay time. iii. low power inverter using the vbb stack approach the inverter is the basic design element of digital circuits. a good understanding of its behavior is necessary in order to build more complex circuits. it has one input and one output. engineering, technology & applied science research vol. 12, no. 4, 2022, 8891-8895 8893 www.etasr.com khmailia et al.: design of a low power cmos inverter with the vbb stack approach the output is always the complement of the input. which means a logical 0 at the input produces a logical 1 at the output and vice versa [10, 11]. generally, a cmos logic circuit consists of a symmetrical and complementary pairs of pmos blocks placed on the circuit as a pull up network (pun) and a nmos block connected as a pulldown network (pdn). the conventional cmos inverter consists of two complementary transistors connected to the same input. fig. 5. the lector technique. fig. 6. the conventional cmos inverter. in active mode, the transistors behavior is comparable to that of switches. when the input is at low logic level (0), the pmos transistor is conductive and acts like a closed switch, the current flows from the vdd supply to the output. when the inverter input is at high logic level (1), the pmos transistor is cut off, disconnecting the output from the positive voltage vdd and the n-mos transistor is conductive and acts like a closed switch, pulling the output to low level (0). the power dissipation in the cmos inverter consists of two components, the dynamic and the static power. dynamic power permits to charge and discharge the load during the active mode [12]: 2 dyn l dd p c v f= ∗ ∗ (2) where �� is the load capacitance, ��� is the supply voltage. ideally a pmos transistor must be in standby mode when vgs < vth (static power), vgs is the voltage from the gate to the source, and vth is the threshold voltage. due to reduced transistor size, the gate oxide and the channel length become short which produces leakage power or static power. as reported by vlsi designers, static power may in the future dominate the total power consumed by cmos devices as technology size continue to shrink [10, 16] ������� = ��� ∗ �������� (3) where �� !"!# is the leakage current during the standby mode. a major part of the leakage current is caused by the subthreshold current [12]. ��$% = ��$%� &'()&*+ ,&.1 − )&0(&1 (4) where �2340 is the zero bias electron mobility: �2340 = 6 77. �9: ;<= > . �?2 (5) where �? is the thermal voltage, vth is the threshold voltage, η is the subthreshold swing coefficient, vgs is the transistor gate to source voltage, vds is the drain to source voltage, μeff is the electrons mobility, �9: is the gate oxide capacitance per unit area, and < and = are the width and length of the channel respectively. (a) (b) fig. 7. low power cmos inverter (a) stack method, (b) vbb method. the subthreshold current isub is inversely proportional to the threshold voltage ��� . therefore, an improvement of the threshold voltage may resolve the problem of growing leakage power. the stack and vbb techniques are frequently used to improve the threshold voltage in consequence decrease the leakage power in vlsi circuits and devices. each method engineering, technology & applied science research vol. 12, no. 4, 2022, 8891-8895 8894 www.etasr.com khmailia et al.: design of a low power cmos inverter with the vbb stack approach increases the substrate potential in a different way which decreases the substrate leakage current. to take advantage of the stack and vbb approaches, we have used them together in the same circuit. the new technique is called the vbb stack approach. each transistor in the conventional inverter is divided into two equal transistors. a positive potential is applied on the body terminal of pmos transistors. a negative potential is applied on the body terminal of nmos transistors. a self-reverse bias potential appears in all transistors, thus the threshold voltage increases and the leakage current decreases. the schematic circuit design and the simulation of the inverter with the vbb stack approach have been done on the lt-spice tool. fig. 8. design of the inverter using the vbb stack approach. iv. results and discussion to evaluate the performance of the proposed method, the inverter is simulated on the lt-spice with supply voltage variation from 0.2v to 1v. simulations have been carried out for the inverter in the conventional approach, the stack approach, and the vbb stack approach. power dissipation and delay have been calculated with variation in vdd . table i. power dissipation and delay variations as fuctions of the supply voltage supply voltage (v) 0.2 0.4 0.6 0.8 1 conventional approach power dissipation (nw) 111 615 1604 3044 4897 delay (ns) 7.757 7.757 7.510 7.493 7.441 stack approach power dissipation (nw) 82 443 1214 2460 4197 delay (ns) 7.645 7.561 7.544 7.510 7.491 vbb stack approach power dissipation (nw) 71 368 997 2036 3535 delay (ns) 7.634 7.562 7.561 7.527 7.508 from the obtained results, it is observed that power dissipation increases simultaneously when the supply voltage increases. power dissipation in the vbb stack approach is minimal in comparison with the other techniques, but the delay increases slightly due to the increase in the threshold voltage of the device. we can observe from table i that by using the stack technique we can save 27% power as compared to the conventional method, but in this case the delay is increased slightly. by using the proposed vbb stack technique, power dissipation is approximately 37% less than in the conventional method, but with a slight increase in delay of 2%. figure 9 shows the power dissipation characteristics as functions of the supply voltage. fig. 9. power dissipation characteristics. the main achievement is the inverter with the proposed vbb stack approach is that it shows much better performance in terms of consumed power as compared to the conventional and stack methods. hence, the proposed vbb stack approach technique is an optimum alternative method to realize low power devices with accepted performance in vlsi design. v. conclusion the demand for low power vlsi circuits increases due to the continuous development of wireless technologies which require a limited source of power. power dissipation is becoming a major issue in today’s digital circuits. so, the main objective of vlsi designers is to reduce power consumption as much as possible. in this paper, the vbb stack approach is presented as a solution to prevent the problem of leakage power. a comparative analysis of logic cmos inverters that were designed with the conventional technique, the stack technique, and the vbb stack technique was conducted in this paper. to evaluate the performance of the vbb stack approach, all cmos inverter designs have been simulated in lt-spice, with supply voltage variation from 0.2v to 1v. from the experimental results, it is observed that power dissipation in the vbb stack technique is much less than in the other techniques with a minor increase in delay. references [1] h. ghabri, d. b. issa, and h. samet, "performance optimization of 1-bit full adder cell based on cntfet transistor," engineering, technology & applied science research, vol. 9, no. 6, pp. 4933–4936, dec. 2019, https://doi.org/10.48084/etasr.3156. [2] m. ma, z. li, and z. yao, "current-mode cmos active inductor with applications to low-voltage oscillators," engineering, technology & applied science research, vol. 3, no. 6, pp. 540–543, dec. 2013, https://doi.org/10.48084/etasr.317. [3] w. w. kai, n. binti ahmad, and m. h. bin jabbar, "variable body biasing (vbb) based vlsi design approach to reduce static power," engineering, technology & applied science research vol. 12, no. 4, 2022, 8891-8895 8895 www.etasr.com khmailia et al.: design of a low power cmos inverter with the vbb stack approach international journal of electrical and computer engineering, vol. 7, no. 6, pp. 3010–3019, dec. 2017, https://doi.org/10.11591/ijece.v7i6. pp3010-3019. [4] b. l. dokic, "a review on energy efficient cmos digital logic," engineering, technology & applied science research, vol. 3, no. 6, pp. 552–561, dec. 2013, https://doi.org/10.48084/etasr.389. [5] m. j. rani and s. malarkkan, "analysis of pseudo-nmos logic with reduced static power in deep submicron regime," international journal of advances in electronics engineering, vol. 2, no. 3, pp. 233– 236, dec. 2012. [6] a. a. beltran jr, k. nones, r. l. salanguit, j. b. santos, j. m. r. santos, and k. j. dizon, "low power nand gate–based half and full adder / subtractor using cmos technique," journal of robotics and control, vol. 2, no. 4, pp. 252–257, jul. 2021, https://doi.org/10.18196/jrc.2487. [7] h. pasha, "design and analysis of low power high speed full adder cell using modified gdi technique at 90nm technology," vol. 4, no. 8, pp. 43–48, aug. 2016, https://doi.org/10.17148/ijireeice.2016.4810. [8] p. kalyani, m. m. latha, and p. c. sekhar, "analysis of mos transistor behavior with forward and reverse body biasing in subthreshold region," vol. 13, no. 19, pp. 14236–14240, 2018. [9] j. w. chun and c.-y. r. chen, "leakage power reduction using the body bias and pin reordering technique," ieice electronics express, vol. 13, no. 3, 2016, art. no. 13.20151052, https://doi.org/10.1587/elex. 13.20151052. [10] m. zabeli, "the most significant mosfet parameters impact in cmos inverter switching characteristics," international journal of circuits, systems and signal processing, vol. 12, pp. 565–572, may 2018. [11] l. kumre, b. p. shrivastava, and n. rai, "comparative analysis of cmos inverter for low leakage power," international journal of scientific & technology research, vol. 8, no. 9, pp. 1598–1601, sep. 2019. [12] m. v. ramanaiah, s. alluri, b. r. naik, and n. s. s. reddy, "transistor sizing of cmos vlsi circuits in deep submicron technology," international journal of innovative technology and exploring engineering, vol. 8, no. 11s2, pp. 15–29, oct. 2019, https://doi.org/ 10.35940/ijitee.k1004.09811s219. [13] m. gangele and k. p. patra, "comparative analysis of lector and stack technique to reduce the leakage current in cmos circuits," international journal of research in engineering and technology, vol. 4, no. 7, pp. 92–100, jul. 2015, https://doi.org/10.15623/ijret.2015. 0407015. [14] s. nehra and p. k. ghosh, "design of a low power xnor gate using mtcmos technique," advance in electronic and electric engineering, vol. 3, no. 6, pp. 701–710, 2013. [15] n. hanchate and n. ranganathan, "lector: a technique for leakage reduction in cmos circuits," ieee transactions on very large scale integration (vlsi) systems, vol. 12, no. 2, pp. 196–205, oct. 2004, https://doi.org/10.1109/tvlsi.2003.821547. [16] s. i. padma, m. shamila, p. rahima, and m. a. devi, "leakage power reduction techniques for nanoscale in cmos vlsi systems using microwind eda tool," international research journal of engineering and technology, vol. 7, no. 5, pp. 2835–2840, may 2020. engineering, technology & applied science research vol. 7, no. 6, 2017, 2256-2259 2256 www.etasr.com ehteshami et al.: improving the power quality in tehran metro line-two using the ant colony algorithm improving the power quality in tehran metro line-two using the ant colony algorithm hossein ehteshami electrical engineering dpt kashan branch, islamic azad university kashan, iran saeid javadi electrical engineering dpt amirkabir university of technology tehran, iran seyed mohammad shariatmadar electrical engineering dpt naragh branch, islamic azad university naragh, iran abstract—this research aims to survey the improvement of power quality in tehran metro line 2 using the ant colony algorithm and to investigate all the factors affecting the achievement of this goal. in order to put tehran on the road of sustainable development, finding a solution for dealing with air pollution is essential. the use of public transportation, especially metro, is one of the ways to achieve this goal. since the highest share of pollutants in tehran belongs to cars and mobile sources, relative statistical indicators are estimated through assuming the effect of metro lines development and subsequently reduction of traffic on power quality index. keywords-power; quality; improvement; tehran; metro; ant colony; algorithm; index i. introduction in the last two decades, a remarkable growth in rail transport systems has occurred. the world's fastest passenger rail vehicles are made in france and japan [1]. new rail lines in transport and fleet are important in terms of dynamic interaction. the type and quality of rail lines play a significant role in this field. rail lines range in various groups of power. trains’ power of movement is a decisive parameter from the aspect of mobility comfort, resisting forces and dynamic interaction of wheel and rail. in addition, it should be mentioned that any range of power requires its own control system necessities [2]. since the first passenger trains [3], heavy rail transit systems usually refer to the underground and elevated rails. in these lines, high capacity electric trains move on routes separated from other transport systems. subway stations have great length and height and electric energy consumption is usually supplied through the third rail. suburban transport system areas are constructed between urban rail transportation systems and residential and commercial centers hence they are also called metro links [4]. in suburban lines, the distance between stations is high (3 to 6 miles); therefore, the power of movement is larger than that of the urban rail systems (about 80 km/hr). the suburban trains are usually scheduled for peak commute hours. usually any rail transportation system using only one independent rail is called monorail. commonly the rails are in a height, but there are intersections or underpasses. the wagons can be hanged from the rails or move on them. in terms of movement and control, monorail system is in the category of automated guide way transit (agt) [5]. tehran metro line 2 is a completely urban line with 26 km length and 22 stations, 8 of which are also connected to other lines. with the operation of line 2, the move time from east of tehran to the west decrease to 40 minutes. ii. improvement of power quality power quality is one of the most important issues of electric loads. any noise in voltage, frequency and current losses can damage electrical equipment [6]. retail markets must set the natural transmission of electricity (transmission and distribution) and other services contracted with the consumers in order to supply their demand. the subject is the improvement of power quality indexes, better voltage regulation and modification of power factor from the advantages of dgs usage which is not possible in central systems of production. there isn’t any voltage adjustment in the power systems because of the enhancement of the transmission power. there are also other parameters such as economic and biological problems which influence the structure of power network. there are many factors which affect the inclination of using smart networks. these factors are: reduction of lines losses, enhancement of voltage profile, reduction of the issuance of emissions, development of network security, enhancement of power quality, development of efficiency, increase of security of the sensitive loads and enhancement of the capacity of transmission and distribution system [7]. one of the most important problems is supplying the quality which is accepted by the consumers [8]. frequently, the following issues are presented about the electronic quality discussion: • gradual development of general output. • the possibility of distortion • misfunction of electronic devices. iii. analysis method first, we should review the power equations to analyze the power quality in the train. engineering, technology & applied science research vol. 7, no. 6, 2017, 2256-2259 2257 www.etasr.com ehteshami et al.: improving the power quality in tehran metro line-two using the ant colony algorithm 3 21 ( , ) 2 m air p p v r c    (1) m m m p t (2) m p v p c p  (3) m r v    (4) where pm is the mechanical power of the train, pair is the air density, v is the wind power, m is the power of rotation,  is the blade angle, tm is the mechanical torque, and r is the radius of the turbine. curve power (cp) for a given peak power and also m r v    are given by manufacturer. note that cp should not exceed the upper limit theory [9]. 16 / 27 0.59 max p c   iv. the ant colony algorithm an assembly of ants, bees and/or all kind of social insects is a distributed system that despite the simplicity of each of them creates a highly structured social organization. the ant colony can perform complex tasks which are beyond the capabilities of individual ants [10]. the subject of “ant colony” reviews the derived samples of the actual behavior of ants and uses these samples as a source of inspiration for the design of new algorithms [11]. the algorithm was suggested for solving the vendor issue with 75 cities in 1991 and was called ant system which was the prototype ant colony algorithm. this algorithm had three features: • versatility: same issues could be solved with the algorithm such as using the vendor symmetric algorithm for solving vendor asymmetric issues. • capabilities: with modifying algorithm, other problems can be solved in hybrid optimization. the algorithm is not affected by parametric changes. • population-based: allows the algorithm to have a positive feedback mechanism for finding correct answer rapidly. it also allows parallel execution. in addition, it will prevent convergence and get caught in the initial optimal solution due to the decentralized computing. the process of the algorithm is the following: • determine the initial value for pheromone function and innovative function • insert the city of origin on the blacklist for each ant • calculate the probability function to select the next town for each ant in each city • modify urban populations for each course • adding the selected city to blacklist for each ant • determine the best route • update v. functions and elements of ant colony algorithm a. the function of pheromones  t, t 1 /kij ijq d   (5)     1 , 1 , 1 m k ij k t t t t       ij (6) in the first equation, the pheromones amount of k-th ant is calculated on dij and in second equation the total pheromone is calculated on the edge with the passage of m ants. b. routing algorithm based on ant colony this algorithm shows the details of routing scheme for manets which includes route discovery and support mechanisms. the route discovery will be completed by reaching the pioneer ant and reversing links to the destination. this mechanism looks like the aodv algorithm. routes primarily are kept by data packets. this means that if a path fails, it temporarily creates a package and sends it to alternate links. otherwise, it returns to the previous hop for simulation. if the package eventually returns to the origin, finding the new direction has been created sequentially. c. ant routing algorithm each node in the grid keeps a record of destination package which passes through the node. according to the information in the table, the first movement of pioneer ant makes a decision for next hop which wants to take the node. the pioneer ant collects all information about the nodes and time. in future, this information will be updated. the next move to reach the neighbor node is calculated by a simple formula:  ij ad q s / ij ijb  (7) for reaching the destination, the score of the trip is calculated and the pioneer ant becomes a secondary ant. the secondary ant comes back through the captured path and uses the queue of the data packet. the secondary ant uses priority queues. the simulation can be summarized as: the topology shows the origin and then calculates the time delay. after confirming the ant algorithm on the current topology, the likelihood will be applied on routing tables, and it will recalculate the delay [12]. if the new delay was better, it will change the origin node for pioneer ant. then it accepts the new solution. the comparison between the delays indicates the best one. when tant is over but tsimul is not over yet, the new topology of the grid will be simulated based on mobile models of rwm and bsam till the tsimul gets over. vi. problem optimization by ant colony ant colony optimization algorithm is highly efficient in combinatorial optimization problems [13]. the ant algorithm is a good example of collective intelligence where agents with low capabilities work together and create very good results. this algorithm is useful to solve optimization problems, for engineering, technology & applied science research vol. 7, no. 6, 2017, 2256-2259 2258 www.etasr.com ehteshami et al.: improving the power quality in tehran metro line-two using the ant colony algorithm example the train movement behavior for the distance between two stations. in current case we study the power profile of a train movement for a route of tehran subway line 2. initially we need route information like: • the start point of train movement in first station: xmin=200m • the endpoint of the route in second station: xmax=1450m with respect to the information we have, line slope of the start and end of the route is 0 and in the distance between start and end the slope is 0.03 percent. • the point that the slope changes after train starts movement: x1=430m • the point that the slope becomes 0 before the train reaches to final station: x2=1315m with respect to the route information mentioned above, the train has 0 slope from the movement start point in xmin=200m to the first point that slope changes in x1=430m, and from this point to the distance of x2=1315m the slope is 0.03%. from this point to the end of the route the slope is again 0 (slope 0 means that the train continues movement in a horizontal path). horizontal paths that are at the start and end of the route show the points in which the train reaches to passengers platforms. the other information that we need to study the train power profile is the limitation of train movement power. • power limitation from the start point to the point x=505m is equal to: v=65km/h • power limitation from the point x= 505m to the point x=705m is equal to: v=50km/h • power limitation from the point x=705m to the end of the path xmax=1450m is equal to: v=65km/h the optimal time the train passes the distance between these two stations is equal to 110 seconds. the first repetition of the algorithm is shown in figure 2. point p1 shows the start moment of train movement with power 0. point p2 shows the point of the path slope change. the train power decreases after reaching this point because it enters a steep path. point p3 is the path strategic point in which the train changes from acceleration state to neutral state. point p4 is where the train experiences the slope change again. in p5 the train brakes while entering the station to stop in p6 which shows the platform. the blue diagram is related to the train movement and the yellow diagram shows power limitation. it is obvious that in the first repetition using imperialist competitive algorithm, the power limitation is not observed and the train power exceeds the allowed power, therefore we need the other operations of this program to observe the power range. with the second repetition the results in figure 2 are obtained for train power profile. in figure 2 the profile of the train movement power is decreased and along the total cost is decreased, but again the power limitation condition is not observed in second repetition, therefore the program enters its third repetition. using the following relationship, energy consumption for train movement is obtained: total energy consumption= time of acceleration / required electrical power for acceleration. fig. 1. power profile for determined path with the first repetition with one variable. fig. 2. power profile after applying second repetition with one variable. fig. 3. power profile for the third acclivity path with one variable vii. conclusion in order to find an optimal power profile we have to look for points of modifying strategy. this means to determine numbers in allowed range for strategy change variables that optimize the power profile. numerous points could be engineering, technology & applied science research vol. 7, no. 6, 2017, 2256-2259 2259 www.etasr.com ehteshami et al.: improving the power quality in tehran metro line-two using the ant colony algorithm effective. in other words, we study each path using different numbers of variables and finally we choose the highest response. we used the ant colony algorithm to compare the gathering results. in fact, we changed the train problem into a mathematical problem: to find a minimum point in ‘n’ dimensions environment for an anonymous function. by generating random numbers and combining them, the ant colony algorithm method tries to find the optimal point to create new numbers. fig. 4. power profile for the third acclivity path with three variables. references [1] s. shiee, m. omidi, “planning land use around stations of tehran subway line2 with emphasis on transitoriented development”, national conference on architecture, new urban development, vol. 1, no. 2, pp. 10-15, 2015 [2] m. montazeri, b. rahnavard, “supporting domestic manufacturers of subway industry equipments using strategic alliance model”, 15th international conference on traffic and transportation engineering, vol. 1, pp. 5-7, 2014 [3] m. niksirat, m. ghatee, s. mehdi hashemi, “multimodal k-shortest viable path problem in tehran public transportation network and its solution applying ant colony and simulated annealing algorithms”, applied mathematical modelling, vol. 36, no. 11, pp. 5709-5726, 2012 [4] h. seifi, m. s. sepasian, electric power system planning: issues, algorithms and solutions, springer science & business media, 2011 [5] m. h. almasi, a. sadollah, s. kang, m. r. karim, “optimization of an improved intermodal transit model equipped with feeder bus and railway systems using metaheuristics approaches”, sustainability, vol. 8, no. 6, pp. 537-563, 2016 [6] r. dehini, s. sefiane, “power quality and cost improvement by passive power filters synthesis using ant colony algorithm”, journal of theoretical and applied information technology, vol. 23, no. 2, pp. 70-79, 2011 [7] r. s. parpinelli, h. s. lopes, a. a. freitas, “data mining with an ant colony optimization algorithm”, ieee transactions on evolutionary computation, vol. 6, no. 4, pp. 321-332, 2015 [8] y. h. song, c. s. chou, t. j. stonham, “combined heat and power economic dispatch by improved ant colony search algorithm”, electric power systems research, vol. 52, no. 2, pp. 115-121, 2014. [9] r. s. parpinelli, h. s. lopes, a. a. freitas, “an ant colony algorithm for classification rule discovery” in: data mining: a heuristic approach, pp. 191-208, idea group publishing, 2012 [10] d. niu, y. wang, d. d. wu, “power load forecasting using support vector machine and ant colony optimization”, expert systems with applications, vol. 37, no. 3, pp. 2531-2539, 2010 [11] m. dorigo, g. di caro, l. m. gambardella, “ant algorithms for discrete optimization”, artificial life, vol. 5, pp. 137-172, 1999 [12] l. slimani, t. bouktir, “economic power dispatch of power systems with pollution control using artificial bee colony optimization”, turkish journal of electrical engineering & computer sciences, vol. 21, no. 6, pp. 1515-1527, 2014 [13] b. yu, z. z. yang, b. yao, “an improved ant colony optimization for vehicle routing problem”, european journal of operational research, vol. 196, no. 1, pp. 171-176, 2015 microsoft word etasr_7-1_1413-1419.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1413-1419 1413 www.etasr.com teymournejad and elghaei: effect of transformational leadership on the creativity of employees… effect of transformational leadership on the creativity of employees: an empirical investigation kaveh teymournejad faculty of management, central tehran branch islamic azad university tehran, iran reza elghaei faculty of management, central tehran branch islamic azad university tehran, iran abstract—considering the accelerated pace of developments and advancements in the current era, organizations which have innovative, change-oriented managers and leaders with a longterm vision are more likely to survive the competitive environment. undoubtedly, leadership behavior and style considering creativity and innovativeness of employees within the organization as an incentive of organizational change considerably influence employee needs and knowledge. the purpose of this study is to determine the effect of transformational leadership involving idealized influence, intellectual stimulation, inspirational motivation and individualized considerations on organizational creativity of employees in the maskan bank in tehran. this study is an applied research using descriptive data analysis. data is collected by questionnaires. correlation is used to analyze the hypotheses. the studied population includes all managers and employees of the maskan bank in tehran province. using cochran formula, 127 employees are selected as a sample. validity and reliability of the questionnaire are calculated by using expert opinion and cronbach alpha. the normal distribution of variables is determined by using kolmogorov-smirnov test and confirmatory factor analysis; hypotheses are tested by using linear structured relationships. all hypotheses are confirmed; that is, transformational leadership as a whole and each of its dimensions, such as idealized influence, intellectual stimulation, individualized consideration and inspirational motivation have a significant and positive effect on creativity of maskan bank employees. keywords-transformational leadership; creativity; idealized influence; intellectual stimulation; individualized consideration; motivational inspiration i. introduction modern organizations are facing changing dynamic environments; in these circumstances, those organizations which are consistent with developments in modern society, predict future changes and direct these changes for favorable developments for a better future are more likely to be successful and efficient [1]. continuous change within organizations requires a change in individuals who underlie a business [2]. undoubtedly, leadership behavior and style considering the creativity of employees within the organization as an incentive of organizational change considerably influence employee needs and knowledge. leadership has been emphasized in change management process by the fact that change, by definition, needs a new system to institutionalize new approaches [3]. in fact, leadership in organizations plays an important role in shaping creativity, attitude and responsiveness of employees to organizational change and acceptance of innovations. therefore, individualized consideration of attitude, creativity and organizational changes, which implies to the degree of attention and support to each subordinate, is an important dimension of transformational leadership. bank is a competitive financial organization in which managers particularly focus on surpassing the competitors. therefore, identification and deployment of transformational leaders in the banking system highly motivates employees to achieve organizational goals. considering the important role of transformational leadership on organizational creativity, this study determines the effect of transformational leadership (idealized influence, intellectual stimulation, inspirational motivation and individualized consideration) on organizational creativity of maskan bank employees in tehran. ii. theoretical background and literature review quiescent leadership cannot survive for long. obviously, traditional leadership will not survive in the third millennium. the world will need transformational leaders. transformational leadership allows companies to compete in a turbulent and unpredictable environment and improve their performance. to transform the organization into a creative and innovative organization, proper local procedures, strategies and models are required to accelerate environmental changes; organizations are required to adapt to these changes to survive in this competitive environment. organizations require creativity and innovation for this reconstruction. leadership style is one of the factors effective on creativity of employees, directly and indirectly. in general, recent studies on leadership theories can be categorized in six main schools including leadership qualities, behavior or leadership style, contingency, leadership competencies, emotional intelligence and charismatic or inspirational leadership. there are many definitions of leadership. some describe leadership as an influence on people to perform their duties willingly. others define leadership as an influence on subordinates [4]. in another definition, leadership is the process of guidance and influence on activities of the engineering, technology & applied science research vol. 7, no. 1, 2017, 1413-1419 1414 www.etasr.com teymournejad and elghaei: effect of transformational leadership on the creativity of employees… group and members of the organization [5]. there is a consensus that leadership is an effective process which helps groups and individuals approach to set goals [6]. leadership style refers to how the leader uses his power and influence. power bases are position and personal [7]. transformational leadership transforms the society through words and actions and considerably influences its followers [8]. with the respect and trust of followers or by expressing a vision beyond the current mission, transformational leadership informs personnel of the goals, directs people from individual thinking to group thinking and motivates them to make efforts for the public interest [9]. the main behaviors which characterize transformational leadership include idealized influence, inspirational motivation, intellectual stimulation and individualized considerations. the first dimension of transformational leadership is charisma or idealized influence, describing the leaders who act as strong models. they are deeply revered by followers, they are reliable and they direct followers to fulfill the vision and mission [10]. inspirational motivation is to motivate and raise the motivation of followers by appealing to their emotions. inspirational motivation emphasizes on emotion and inner motivations rather than daily interactions of the leader and followers. intellectual stimulation is to stimulate followers by the leadership to discover new solutions and new thinking for solving organizational problems by the followers. individualized consideration is to consider individual differences of followers, communicate with them and stimulate them by assigning responsibilities for learning and experiencing. people are supported by leaders and leaders demonstrate concerns for their personal feelings and needs [8]. another variable which needs to be addressed is creativity. many definitions have been proposed for creativity; some consider creativity and innovation equivalent to adaptation and change. some others consider creativity and innovation as something beyond change and adaptation [11, 12]. creativity refers to new valuable achievements based on an idea which exists in all people more or less [13]. creative organizations share some qualities including complete and intensive competition, culture, access to management, respect for people, community service, teamwork, permanent and long-term relationships of employees with these organizations and change acceptance of managers [14]. creativity involves following procedures: 1) attraction: the first step is to attract to a subject which often requires new data; 2) inspiration: this phase happens very fast and it is difficult to consider; that is, one is unaware of the change before it happens, and in some cases, it is associated with an idea or solution after investigations with the raw material; 3) experiment: the formed idea is tested to determine whether it is beneficial and productive; 4) refinement: practicality of the idea is evaluated (the third and fourth phases are time-consuming, as edison said ‘genius is one percent inspiration and ninety-nine percent perspiration’); 5) sales: the final phase of creativity is sales which can neutralize most creativities; this phase must occur first within the organization; authorized people should buy or adopt the idea, commit to it and present to outsider customers. transformational leadership was introduced in the leadership literature by burns as a new leadership model which pays more attention to the start of changes among subordinates and transforms personal values and organizational culture of subordinates [15]. transformational leadership has been studied by many researchers under different topics [16-19]. generally, these studies have described behaviors and characteristics of transformational leaders as warmth and empathy, need for power, eloquence and good articulation skills, intelligence and caring for others. these leaders are able to motivate followers, inspire them, gain commitment of their followers and change beliefs, attitudes and goals of people and organizational norms. transformational leaders let their subordinates to feel that they are seen as human beings and help people see issues in a new way. in [20], the authors evaluated the role of transformational leadership on tendency for organizational creativity. their results show that creativity, as a competitive advantage, is one of the most important factors of organizational success. in this regard, employee creativity can emerge as an important competitive advantage in the light of transformational leadership. the main objective of this study is to examine the relationship between transformational leadership and creativity of employees (teachers). in [21], the authors experimentally studied the effects of transactional and transformational leaderships on creativity of groups. in this study, participants in both real and nominal groups performed a brainstorming task. evaluation of their performance in terms of eloquence and fluency and flexibility showed that nominal participants in transformational leadership outperformed their real peers in transactional leadership. iii. materials and methods in general, this study determines whether dimensions of transformational leadership including: 1) idealized influence; 2) motivational inspiration; 3) intellectual stimulation and 4) individualized considerations have a significant effect on organizational creativity. hence, the conceptual model and hypotheses are as follows. idealized influence intellectual simulation inspirational motivation individualized consideration employee creativity fig. 1. conceptual model hypotheses are formed based on the conceptual model, as follows: engineering, technology & applied science research vol. 7, no. 1, 2017, 1413-1419 1415 www.etasr.com teymournejad and elghaei: effect of transformational leadership on the creativity of employees…  hypothesis 1: transformational leadership has a significant positive effect on creativity of maskan bank employees.  hypothesis 1.1: idealized influence has a significant positive effect on creativity of maskan bank employees.  hypothesis 1.2: intellectual stimulation has a significant positive effect on creativity of maskan bank employees.  hypothesis 1.3: inspirational motivation has a significant positive effect on creativity of maskan bank employees.  hypothesis 1.4: individualized considerations has a significant positive effect on creativity of maskan bank employees. this study is an applied research using descriptive data analysis. data is collected by questionnaires. correlation is used to analyze hypotheses. archival studies are used to develop the theoretical model and extract literature. to collect data, field studies (questionnaire) are used in order to test the hypotheses. the questionnaire used is a 5-point likert scale based on which hypotheses are tested. to ensure validity of the questionnaire, qualitative methods, including expertise of professors and theories of experts, are used and similar questionnaires, articles and textbooks are reviewed to make necessary modifications in the questionnaire. to determine reliability of the questionnaire, cronbach's alpha is calculated by the spss software. the studied population includes 500 managers and employees of maskan bank in tehran. the cochran formula is used to determine the sample size (217); the samples are selected by simple random sampling. descriptive and analytic statistics (modeling and sem) are used to analyze the data. normal distribution of variables is determined by using kolmogorov-smirnov test, confirmatory factor analysis and linear structured relationships to test the hypotheses by lisrel software. table i shows validity and reliability. given that cr >0.7 [22] and ave >0.5 [23] for all latent variables, reliability and convergent validity can be confirmed. table i. convergent validity and reliability latent variables combined reliability (cr> 0.7) average variance extracted (ave> 0.5) idealized influence 0.941 0.801 intellectual stimulation 0.898 0.689 individualized considerations 0.853 0.660 inspirational motivation 0.811 0.519 creativity 0.785 0.620 iv. results a. normal distribution of variables one way to determine normal distribution of variables is to use kolmogorov-smirnov test. the results of this test are listed in table ii. according to table ii, test distribution is normal. as the results show, sig>0.05. based on the central limit theorem, spss confirms normal distribution of variables; thus, the null hypothesis, which implies that variables are normal, is confirmed. table ii. normal distribution of variables variable ks sig. idealized influence 0.664 0.770 intellectual stimulation 0.966 0.308 individualized considerations 1.565 0.075 inspirational motivation 1.313 0.064 creativity 1.023 0.820 b. measurement model for dimensions of transformational leadership figure 2 shows the measurement model of the independent variable (transformational leadership) with standardized estimates. as the figure shows, membership of all the factors examined in this variable is confirmed. figure 2 shows factor loadings with standard estimate of the effect of each variable in explaining variance of the variable. in other words, factor loading indicates correlation of each observer variable (question) with the latent variable. for example, factor loading of the idealized influence is 0.76 in the first question. measurement model of transformational leadership is calculated by using significant factor analysis. given that sig <1.96 or sig >1.96, all the coefficients obtained are significant. fig. 2. measurement model of transformational leadership using standard cfa c. measurement model for employee creativity figure 3 shows measurement model of the dependent variable (employee creativity) with standard estimate. as the figure shows, membership of all the factors examined in this variable is confirmed. figure 3 shows factor loadings with standard estimate of the effect of each variable in explaining variance of the variable. for example, factor loading of employee creativity is 0.37 in the first question. measurement model of employee creativity is calculated by using significant factor analysis. given that sig <-1.96 or sig >1.96, all the coefficients obtained are significant. engineering, technology & applied science research vol. 7, no. 1, 2017, 1413-1419 1416 www.etasr.com teymournejad and elghaei: effect of transformational leadership on the creativity of employees… fig. 3. measurement model of employee creativity using standard cfa d. hypothesis testing structural analysis of hypothesis 1 shown in figures 4 and 5 indicates that transformational leadership has a significant positive effect on creativity of maskan bank employees (sig = 5.43). e. hypothesis testing by linear structured relations once the measurement models are determined, hypotheses are tested by structural equation modeling (sem) to evaluate the conceptual model and ensure the presence or absence of a causal relationship between variables and fit of the observed data to the conceptual model. the results are reflected in figures 6 and 7. testing hypotheses by sem, the software output indicate that the structural model is well fitted for testing hypotheses. moreover, χ2/df < 3 which is optimal; rmsea = 0.065 which indicates that the structural model is well fitted. in other words, the observed data match the conceptual model to a large extent. the calculated nfi, ifi, rfi, nnfi and cfi are higher than 91%, which indicate high fit of the model. fig. 4. measurement model of hypothesis 1 with standard estimates fig. 5. measurement model of hypothesis 1 with significant estimates fig. 6. overall measurement model and results of hypothesis testing with standard estimate fig. 7. overall measurement model and results of hypothesis testing with significant estimate engineering, technology & applied science research vol. 7, no. 1, 2017, 1413-1419 1417 www.etasr.com teymournejad and elghaei: effect of transformational leadership on the creativity of employees… table iii. fit indices of the conceptual model result model value optimal fit index well fitted 1.36 <3.00 χ2/df well fitted 0.95 >0.90 gfi(goodness of fit index) well fitted 0.91 >0.90 agfi(adjusted goodness of fit index) well fitted 0.022 >0.90 rmr(root mean square residual) well fitted 0.91 >0.90 nfi (normed fit index) well fitted 0.93 >0.90 nnfi (non-normed fit index) well fitted 0.94 >0.90 ifi(incremental fit index) well fitted 0.94 >0.90 cfi (comparative fit index) well fitted 0.038 <0.08 rmsea(root mean square error of approximation) f. results of statistical analysis results of lisrel (figure 8) show that χ2/df < 3 and other fit indices confirm the fit of the model. fig. 8. output of the conceptual model testing v. discussion the main hypothesis of this study claims that transformational leadership has a significant positive effect on the creativity of maskan bank employees. as statistical analysis shows, sig = 5.43; since sig > 1.96, hypothesis 1 is confirmed. this is consistent with [20, 24]. they showed a positive relationship between transformational leadership and employee creativity and strength of this relationship is subject to coordination with the leader and existence of an innovative atmosphere. the first sub-hypothesis claims that idealized influence has a significant positive effect on creativity of maskan bank employees. according to results, sig=8.10; since sig>1.96, hypothesis 1.1 is confirmed. furthermore, since sig is positive, this effect is direct. as the size of the effect of idealized influence on employee creativity is equal to 0.67, it can be concluded that one unit of variation in idealized influence will be followed by 0.67 unit of variation in employee creativity. this is consistent with [25]. therefore, there is a positive relationship between idealized influence and creativity of employees. this relationship is stronger when the leaders are supportive of employees and support their tasks and work. the second sub-hypothesis claims that intellectual stimulation has a significant positive effect on creativity of maskan bank employees. according to results, sig=9.51; since sig>1.96, hypothesis 1.2 is confirmed. furthermore, since sig is positive, this effect is direct and one unit of variation in intellectual stimulation will be followed by 0.83 unit of variation in employee creativity. this is consistent with [20, 26]. their results show that employee creativity, as an important competitive advantage, can emerge in the light of intellectual stimulation. this is also consistent with [21]. the third sub-hypothesis claims that individualized consideration has a significant positive effect on creativity of maskan bank employees. according to results, sig=3.40; since sig>1.96, hypothesis 1.3 is confirmed. furthermore, since sig is positive, this effect is direct and one unit of variation in individualized consideration will be followed by 0.90 unit of variation in employee creativity. this is consistent with [25]. their results show that the significant effect of individualized considerations on employee creativity can provide a competitive advantage for the organization and ultimately improve organizational performance. the fourth sub-hypothesis claims that inspirational motivation has a significant positive effect on creativity of maskan bank employees. according to results, sig=2.14; since sig>1.96, hypothesis 1.4 is confirmed and one unit of variation in inspirational motivation will be followed by 0.58 unit of variation in employee creativity. this is consistent with [20, 25, 26]. their results indicate significant effect of inspirational motivation on employee creativity. finally, transformational leadership can predict employee creativity. this is also consistent with [27]. vi. conclusions and remarks managers are recommended to utilize the characteristics of transformational leadership and provide employees with the opportunity to present their suggestions, ideas and new solutions for new banking services, new markets, and increasing sales and motivate creativity among organizational members by encouraging ideas of creative people. in addition, leaders can create an environment to facilitate production and implementation of creative knowledge and encourage learning and creative ideas. planning is also recommended to adapt the tools needed for expected processes of transformational leadership. to play a more effective role, transformational leadership should improve the infrastructures required for creative processes:  by emphasizing vision and mission and empowering people, management should encourage employees to act based on information and support changes for employee creativity.  by creating vision, leaders let followers to commit to the goals, establish relationships between employees and let them fulfill their deepest demands and achieve their goals.  by establishing trust and respect, leaders should encourage followers to learn internal and external information and consider moral consequences of their creative decisions. engineering, technology & applied science research vol. 7, no. 1, 2017, 1413-1419 1418 www.etasr.com teymournejad and elghaei: effect of transformational leadership on the creativity of employees… bank managers should use the tools and technologies required for employee creativity as an opportunity to improve their capabilities (however, this requires modern technologies); moreover, a clear vision of how to encourage creative ideas among employees can also develop effective leadership and knowledge management within the organization. it is recommended to encourage new solutions by rewarding fresh and innovative ideas. moreover, delegation of authority and empowerment of employees can be effective. employees should be trained to evaluate organizational problems from different angles; for this purpose, emphasis is required on creative motivation techniques, such as brainstorming. finally, intellectual stimulation of employees can lead to creativity and innovative solutions. it is recommended to consider needs of employees and provide opportunities for their promotion to higher levels of personal development by determining the level of people to participate in training courses. it is also recommended to use proper techniques and practices to motivate employees to participate in these courses. it is recommended to prepare a workshop for implementing scientific knowledge of employees and provide the tools required to implement creative ideas.a clear vision of how to transfer and exchange creative ideas among employees can develop effective leadership and knowledge management within the organization. thus, managers can communicate with employees to understand and meet their needs in order to develop their creative capabilities and increase commitment and effectiveness of employees. management should be aware of the pygmalion effect in the sense that high expectations and assignment of challenging responsibilities to employees will improve their performance. it is essential to involve employees in developing the future vision, mission and strategies in order to attract more participation in achieving the goals and encourage creative and optimistic thinking about the future. in addition to the above, managers can consider the following suggestions to improve the effect of employee creativity on organizational performance: management should provide an environment in which people accept change. members of the organization must believe that this change will be beneficial to them and the organization. usually, this belief appears when members participate in decision making. management should promote new beliefs. managers should show respect for new ideas. for this purpose, management should show interest in suggestions of subordinates and implement promising ideas. management should allow members to interact. an open creative atmosphere is promoted when people and members of different groups are allowed to communicate with each other more closely. this interaction will lead to the exchange of useful information, feedback and new perspectives about organizational problems between members. transformational leadership can influence employees and present new methods to achieve different tasks; this leads to an increase in creativity and innovation. management should set specific goals and allow members to achieve them. members require purpose and direction to show their creativity. management should eliminate limitations in creativity of members. management also should control the time and money spent on new ideas. management should value creative and hard-working people. creative people have a very strong motivation. hence, they never stop trying and working hard. however, they are also human and should be encouraged in this way and be rewarded properly for their good work. by encouraging creative people, management should appreciate their work. references [1] m. nasiri, motivation for change. management development, vol. 47, pp. 35-37, 2003 [2] m. neiestani, h. choupani, h. gholamzadeh, m. zare-khalili, “the relationship between transformational leadership and empowerment of employees”, industrial management, vol. 9, no. 1, pp. 12-23, 2012 [3] r. eisenbach, k. watson, r. pillai, “transformational leadership in the context of organizational change”, journal of organizational change management, vol. 12, no. 2, pp. 80-89, 1999 [4] b. shirzad-kebria, f. shabani-zanganeh, “the relationship between leadership style of senior managers”, educational administration research quarterly, vol. 2, no. 4, pp. 105-124, 2011 [5] m. r. redmond, m. d. mumford, r. teach, “putting creativity to work: effects of leader behavior on subordinate creativity”, organizational behavior and human decision processes, vol. 55, no. 1, pp. 120-151, 2010 [6] k. boal, r. hooijberg, “strategic leadership research: moving on”, leadership quarterly, vol. 11, pp. 515-549, 2009 [7] l. epitropaki, r. martin, “the moderating role of individual differences in the relation between transformational/transactional leadershipperceptions and organizational identification” leadership quarterly, vol. 16, pp. 569-589, 2005 [8] c. s. long, l. y. thean, “relationship between leadership style, job satisfaction and employees’turnover intention: a literature review”, research journal of business management, vol. 5, no. 3, pp. 91-100, 2011 [9] b. m. bass, p. steidlmeier, “ethics, character, and authentic transformational leadership behavior”, leadership quarterly, vol. 10, pp. 181-217, 2007 [10] s. abraham, “stretching strategic thinking”, strategyand leadership, vol. 33, pp. 5-1, 2005. 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organizational health”, methodology in curriculum development, vol. 1, no. 25, pp. 136-137, 2010 [26] k. ghahraman-tabrizi, f. tondnevis, a. amirtash, p. kadivar, “the relationship between organizational culture and creativity”, physical and sportive sciences, vol. 3, no. 6, pp. 139-150, 2005 [27] m. javdani, the relationship between transformational leadership and organizational commitment, msc thesis, shiraz university, iran, 2002 microsoft word etasr_v12_n4_pp8910-8915 engineering, technology & applied science research vol. 12, no. 4, 2022, 8910-8915 8910 www.etasr.com allal et al.: improved optimization of the charge simulation method for the calculation of the electric … improved optimization of the charge simulation method for the calculation of the electric field around overhead transmission lines using statistical methods abdalali allal laboratoire de recherche en electrotechnique ecole nationale polytechnique algiers, algeria abdelali.allal@univ-djelfa.dz ahmed boubakeur laboratoire de recherche en electrotechnique ecole nationale polytechnique algiers, algeria ahmed.boubakeur@g.enp.edu.dz adnan mujezinović faculty of electrical engineering university of sarajevo sarajevo, bosnia and herzegovina am14618@etf.unsa.ba received: 21 april 2022 | revised: 3 june 2022 | accepted: 4 june 2022 abstract-in order to decide the appropriate arrangements of fictitious charges in the charge simulation method, the use of the monte carlo method is proposed for the estimation of the probability density function of two variables, the radius ratio, and the angle ratio. τhe scale and shape parameters of the weibull's distribution are determined by the maximum likelihood estimator. the obtained results are used to calculate the electric field at arbitrary points in the neighborhood of high voltage transmission lines. the comparisons between the results computed by this method, the results calculated by the genetic algorithm, and those measured, confirm the effectiveness and accuracy of the proposed method. keywords-charge simulation method; monte carlo method; optimization; genetic algorithm; high voltage transmission lines; electric field calculation i. introduction designing any high voltage device and analyzing discharge phenomena requires complete knowledge of electric and magnetic field distribution [1]. the potential surface gradient is a critical design parameter for planning and designing overhead lines (insulation or discharge) [2, 3]. the electric fields can be calculated using several analytical and numerical methods. the most used is the charge simulation method (csm) [4-9]. the csm was introduced in 1969 [4]. its basic concept is to replace the distributed charge of conductors and the polarization charges on the dielectric interfaces with a large number of fictitious discrete charges. the magnitudes of these charges have to be calculated so that their integrated effect satisfies the boundary conditions precisely at a selected number of points on the boundary. the principle of this method is to simulate an actual field with a field formed by a finite number of simulation charges (point and line charges of infinite and semiinfinite length [11]) placed outside the region where the field is to be calculated. the values of the discrete charges are determined by satisfying the boundary conditions at a selected number of contour points: ���� = ������ � (1) where [vb] is the vector of contour point voltages, [qs] is the vector of unknown simulation charges, and [p] is the matrix of potential coefficients calculated by contour points and simulation charges. for overhead lines consisting of n parallel conductors placed above the ground, the elements of the matrix of potential coefficients are given by the following relation: 0 1 ln 2π ij ij ij d p dε   =       (2) where ε0 is the electric permittivity of vacuum ≈8.854 10 -12 f/m, dij, dij are respectively the distance between the jth point charge and the image of the ith point charge and the distance between the jth point charge and the ith point charge. based on the laplace equation (3), the superposition theorem and image charge theory, the components at an arbitrary point in the plane y-z plane produced by n point charges m(y,z) can be calculated by (4) and (5): corresponding author: abdelali allal engineering, technology & applied science research vol. 12, no. 4, 2022, 8910-8915 8911 www.etasr.com allal et al.: improved optimization of the charge simulation method for the calculation of the electric … ∆ = − ��� (3) �� ��, �� = ∑ ������ � ���� ��� + ! ������� " # $%� (4) �& ��, �� = ∑ ������ � &�&� ��� + ! &'&���� " # $%� (5) where γ is the reflection coefficient of soil's surface, ($ is the distance between the arbitrary point m(y,z) and the ith point charge, yi and zi are the coordinates of the ith contour point, and qi is the ith fictitious charge. the reflection coefficient of the soil can be approximated as ! = −1. the current paper aims to optimize csm parameters using stochastic optimization employing the monte carlo method (mcm). this optimization is based on estimating the probability density functions (pdfs) of the polar coordinates of the simulation charges where the relative mean square error of the voltage on the conductor surface is less than a threshold. to ensure the accuracy of this method, a comparison is made with the measured values of the electric field at arbitrary points near high voltage transmission lines with standard dimensions of the tower on the 40kv line ss sarajevo 10 –ss sarajevo 20 [10]. ii. related work since 1969, when the csm was used for the first time [4], it has been applied and developed in many cases. some of the main contributions, in chronological order, are: authors in [12] used csm combined with the rosenbloom’s method to solve the potential distribution of the rod-plane. authors in [13] calculated the field distribution for multi-phase ac sources or in configurations including volume resistance. authors in [5] simulated the sheathed three cores belted power cable using the complex fictitious charges. authors in [14] combined csm with the genetic algorithm (ga) to optimize the csm for a 2d electrode system with an asymmetrical structure. authors in [15] used csm-ga to calculate the electric field of a 35kv vacuum interrupter (vi). ga has been utilized to compute the electric field [16], to model the horizontal sphere gap [17], and to model the horizontal sphere gap above the ground plane [18]. authors in [19] calculated the electric field around the head of a transmission tower and its composite insulators by coupling csm with bem. authors in [20] used an optimization strategy to arrange the simulated charges in the thin electrode. authors in [21] combined csm with ga to solve the inverse problem in electric-fields of high voltage insulators. authors in [22] combined csm with hashing integrated adaptive ga (haga) to the contour design of support insulators. authors in [23] used csm combined with the gold section method to calculate the conductors' surface electrical field of ±800kv uhvdc transmission lines. authors in [24] used csm-ga to enhance the computation precision of electric fields associated with plate‐type electrostatic separators. an adapting particle swarm optimization (pso) combined with csm was used for calculating the field distribution with non-axial symmetry resulting from a floating spherical conductor between the spheres in [25]. authors in [26] improved the calculation accuracy of the electric fields associated with electrostatic plate separators by using csm-ga. for the optimization of high voltage electrode surfaces, authors in [27] used csm combined with a biogeography-based algorithm. authors in [28] used csm-pso for sphere-plane gaps. 3d calculation of electric field intensity under transmission lines with csm-pso and csm-ga was conducted in [29]. authors in [30] made a comparison between the performance of pso, ga, and grey wolf optimizer (gwo) in 3d quasi-static modeling of the electric field produced by high voltage (hv) overhead power lines. to optimize the ion flow field calculation, authors in [31] used csm combined with the flux tracing method (ftm). iii. the proposed algorithm a. intoduction the proposed algorithm is based on stochastic optimization (so) methods. the so methods generate and use random variables [32]. they are used in many areas, including aerospace, medicine, transportation, finance, electrical engineering, and many more science and engineering fields. so can rely on sampling methods such as mcm [33], latin hypercube sampling [34], or the quasi-monte carlo method (qmcm) [35]. the algorithm aims to optimize the location of fictitious charges by generating a bivariate distribution of n×n random variables 〈cr, ca〉 which are respectively the ratio between , and , , .and . according to (6)-(8). as shown in figure 1, the contour points are arranged at equal distances on the perimeter of the conductor and are determined by their polar coordinates rc and θ k b according to (7)-(8). the simulation charges are also arranged at an equal distance on the perimeter of a virtual circle inside and are determined by their polar coordinates , and .-/. . / = �0/#1 �2 − 1� , 2 = 1 34 5 (6) ,= 67 , (7) .-/ = . / + 68 . �0:1 (8) where rb is the radius of the conductor, θ k b the angle of the k th contour point, nc the number of contour points, rc the radius of the virtual circle that contains simulation charges, θ k c the angle of the k th fictitious charge, and cr and ca the radius and angle ratios ranging between 0 and 1. fig. 1. arrangement of contour points, fictitious charges, and test point. engineering, technology & applied science research vol. 12, no. 4, 2022, 8910-8915 8912 www.etasr.com allal et al.: improved optimization of the charge simulation method for the calculation of the electric … b. the algorithm for each iteration, we have a set of coordinates of fictitious charges, denoted by �67$ , 68$ � such that: the set of all coordinates is: ℇ � 〈67 , 68 〉 and the set of acceptable coordinates is ℇ< � 〈6=7 , 6=8 〉. the work is carried out in two steps. 1) step 1: extraction of the set of solutions ℇ< data: the electrical and geometric parameters of the line such as the potential of point contour vb, the number of conductor nc, the number of fictitious charges nc, the objective function threshold fobjthreshold,, the number of iterations n which generate n random (cr,ca) pairs. from i=1 to n do calculate nc*nc coordinates of fictitious charges with (6) and (7). calculate the potential created by these fictitious charges with (2). calculate the fictitious charges with (1). calculate the potential created by these fictitious charges: � > � � ��> ����� calculate the objective function fobj: ?@ab � 1c d� > � � compare fobj with fobjthreshold if fobj > fobjthreshold then (cr,ca) is rejected. else add (cr,ca) to the ℇ< 2) step 2: statistical study the followed steps are: 1. establish the histograms of cr and ca 2. estimate the weibull law parameters a and b with the maximum likelihood estimator (mle). 3. calculate the mean and standard deviation of cr and ca the above algorithm is executed for a simple geometry problem (figure 2) where nc=2, nc=3, n=100, fobjthreshold=4×10 -12 , h=11m, d=2m, rb=7cm, and v=400kv. after the iterations are completed, there are 26 accepted bivariates (cr,ca) and their histograms are shown in figures 3 and 4. it is quite obvious that the greatest pdf is concentrated around 0.95 for cr and 0.49 for ca. from the obtained results, it should be noted that the shapes of the two histograms are asymmetrical. the obtained data of the first histogram are grouped near the upper limit and incline to the left towards the lower values. on the other hand, in the second histogram, the data are grouped towards the center, which leads to estimating the two parameters of the weibull distribution as follows. fig. 2. histogram geometry problem. fig. 3. histogram of cr. fig. 4. histogram of ca. the weibull distribution is used in reliability studies, for example, to study the voltage breakage of electric circuits [36]. the weibull distribution has two parameters, denoted in the following equation: e�f|h, i� � i. h�j f j��k �l m no p (10) where a> 0 is the scale parameter and b > 0 is the shape parameter of the distribution. the maximum likelihood estimator (mle) [37] estimates the weibull parameters a and b. the results are given in table i and the estimate distributions are shown in figures 5 and 6. table i. estimated weibull parameters data a b 67 relative radius 0.968882 31.02033 68 relative angle 0.507651 27.0408 engineering, technology & applied science research vol. 12, no. 4, 2022, 8910-8915 8913 www.etasr.com allal et al.: improved optimization of the charge simulation method for the calculation of the electric … fig. 5. estimate distribution of cr. fig. 6. estimate distribution of ca. the estimated distributions shown in figures 6 and 7 agree with the histograms obtained in figures 3 and 4. the estimated distributions have mean and variance μr=0.9519, σr=0.0015 for the relative radii cr, and μr=0.9519, σr=0.0015, μa=0.4975, σa=5.2887 10 -4 for the relative angular distribution ca. the optimum position of the coordinates of the fictitious charges obtained are cr є [μr–σr, μr+σr] and ca є [μa –σa, μa+σa] with respective mean [0.9505; 0.9534] and [0.4970; 0.4980]. for example, for cr=0.95 and ca=0.49 the optimum arrangement of the fictitious charges is shown in figure 7. fig. 7. optimum arrangement cr=0.95 and ca=0.49. to verify this approach, an example of the electric field calculation around an overheadtransmission line, already treated in the literature [10] is examined below. iv. result comparison the considered example is a 400kv line with a horizontal conductor configuration, as shown in figure 2. measurements were taken at 1m height according to recommendations [38], and were performed in the middle of the range between the two adjacent transmission line towers. the electric field is calculated without considering the effect of conductor end, arc sag, and the influence of the tower. in addition, the electromagnetic fields caused by the overhead transmission lines can be approximated by quasi-static fields [39], where quasi-static field displacement current and changes in the magnetic flux are negligible, so the electric field has exactly the same characteristics as the static one. it is assumed that the component of the electric field vector in the x direction is equal to zero, and the electric field vector in an arbitrary point, caused by the n point charges, can be calculated using (7) and (8). the application of csm with a relative radius cr=0.95 and relative angle ca=0.497 normally leads to optimum results close to the measured results, but to ensure its effectiveness it must be compared with another method already used with csm. the choice fell on the ga because it is the most used with csm as shown above. also, it has been widely used in the field of electrical engineering [40-43]. figure 8 illustrates the graphs of the electric fields calculated by this method, by csm-ga, and the measured values (the values are listed in table ii). it can be seen that the field calculated with the proposed method is closer to the measured field than the field calculated with csm-ga. fig. 8. distribution of the electric field. table ii. comparison of measured and calculated results distance (m) measured (kv/m) csm-mcm csm-ga 0 4.13 17.69% 02.50% 5 4.45 02.50% 06.86% 10 5.93 01.44% 03.17% 10.8 6.09 01.11% 03.50% 15 5.81 03.20% 07.66% 20 3.84 01.75% 06.26% 25 2.30 00.99% 03.61% 30 1.39 04.69% 00.04% 35 0.81 16.11% 10.90% mean 04.38% 04.95% engineering, technology & applied science research vol. 12, no. 4, 2022, 8910-8915 8914 www.etasr.com allal et al.: improved optimization of the charge simulation method for the calculation of the electric … v. conclusion a new approach for optimizing the charge simulation method using the mcm has been presented in this paper. the proposed algorithm aims to determine the pdfs of the classes of polar coordinates for which the error is minimal. the two pdfs follow weibull's law. the pdf of relative radius (cr) is asymmetric and concentrated near 1, while the pdf of the relative angle (ca) is symmetric and is slightly centered at 0.49. the proposed algorithm offers excellent flexibility and accuracy in determining the optimal locations of simulation charges. accurate results are achieved for the electric field calculation around the overhead transmission lines. in addition, the solution is not a single element (ca,cr) like the results of other methods, but a range distributed according to the weibull distribution whose parameters are calculated. this work aims at an optimal calculation of the electric field by cms by arranging the fictitious charges so that they are very close 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[43] d. m. falcao, "genetic algorithms applications in electrical distribution systems," in congress on evolutionary computation. cec’02 (cat. no.02th8600), honolulu, hi, usa, dec. 2002, vol. 2, pp. 1063–1068, https://doi.org/10.1109/cec.2002.1004390. engineering, technology & applied science research vol. 7, no. 5, 2017, 2017-2021 2017 www.etasr.com ayed et al.: software in the loop simulation for robot manipulators software in the loop simulation for robot manipulators mossaad ben ayed ces laboratory, sfax university, tunisia and al majmaah university, ksa mm.ayed@mu.edu.sa, mossaad_benayed@yahoo.fr lilia zouari ces laboratory sfax university, tunisia lilia6enis@yahoo.fr mohamed abid ces laboratory sfax university, tunisia mohamed.abid@enis.rnu.tn abstract—in the last decades, the classical verification of robotic software component is postponed until the code is developed enough to function in real hardware. for this reason, the verification of code at early stages is essential to reduce development costs and necessary time for embedded systems such as robot manipulator. therefore, software in the loop (sil) simulation may be realized in the early stages of software development. it offers the possibility to execute tests before the hardware is available and thus detect errors. in this paper, we propose a software in the loop (sil) test for robot manipulator driven by a brushless dc motor without a target system hardware. simulation results prove the rapidity and the good performance of the developed code for the controller’s part by the validation of the behavior of robot manipulator software. keywords-software in the loop (sil); robot manipulator; controllers; s-function i. introduction the engineering of software and digital electronics represent an important place in the process of the design and the verification of the electronic systems [1, 2]. the levels of electronic components integration, the complexity and the size of embedded code are continually growing and this growth is accompanied by great sensitivity to the disturbance and uncertainties [3, 4]. the number of possible combinations states poses a problem of combinatorial explosion that led to huge numbers of possible states due to the complexity of mechatronic systems [5, 6]. this complexity is a challenge for dependability [1, 5, 7]. indeed, new robotic applications representing the most known mechatronic system have required the lightest and most precise robots that can be driven with small amounts of energy [8-10]. unfortunately, the flexibility of these robots leads to an oscillating behavior at the end of the link. obtaining a precise trajectory tracking is an arduous task that requires a complex control in closed-loop [11-14]. to achieve the control objectives, such as the accuracy of the position and vibration suppression, many control techniques were applied to these flexible joint manipulators [15-18]. thus, we consider the entire robotic system including actuator dynamics and flexibility in the joint. to guarantee a high performance of the control system, a flexible joint manipulator which is highly nonlinear, strongly coupled and uncertain is used [19-21]. the embedded systems in the robotic industry must accomplish high safety requirements [22]. therefore, verification step is essential to verify the behavior of the proposed system and to detect and correct the errors at earlier stage without any hardware or physical environment [23]. this paper presents the sil simulation technique for robot manipulator driven by brushless dc motor (bdcm). in section i, some related works were detailed. the second section described the manipulator control system. the third section defined the sil simulation technique. the fourth section was devoted for sil implementation method shown the speed and torque controller and the current hysteresis controller. finally, simulation results in matlab/simulink are shown in section v. extracted simulation time prove the role of the sil technique to accelerate the simulation and prevent the risks. ii. related works the software in the loop (sil) approach allow us to integrate software component with an environment simulation [23-24]. besides, this approach allows testing different scenarios and control algorithms very quickly and benefit from its flexibility. in [25], authors realized a sil environment for the development of control strategies for hybrid vehicles. this environment allows the evaluation of different vehicle dynamic behavior for each additional masses and each position of gravity center of the vehicle. in [26], authors described the sil validation of a flight control system needed to develop low cost unmanned aerial vehicles (uav). moreover, this technique allows modeling, linearizing and decoupling of the highly nonlinear six degrees-of-freedom dynamics of the vehicle. in [27], authors presented a low cost sil simulation to evaluate performance of control law for quadricopter using matlab/simulink for control law and xplane for vehicle dynamics and flight environment. in [22], authors described a cost effective sil simulation methodology for mobile nodes representing large-scale pervasive system. this methodology permits deploying the real code once and replicating environments and over virtual devices as often as they wish. in [28], authors used the high level simulation framework open virtual platforms (ovp) for sil simulation of embedded control applications to benefit from rapid prototyping in early stages of the development cycle. this approach was applied for two cases which are the motor control application and the image processing application. in [29], authors described sil simulators for autonomous engineering, technology & applied science research vol. 7, no. 5, 2017, 2017-2021 2018 www.etasr.com ayed et al.: software in the loop simulation for robot manipulators navigation algorithms of planetary rovers due to temporarily unavailable hardware. this simulator is necessary to facilitate the continued algorithms development even in the absence of hardware. in [30], authors studied sil technique for flying robots. in fact, the high production expenses need the validation of such system by simulation to predict the robot reactions in various flight modes. this technique was realized using matlab for control part and adams for structural design. nowadays, validating complex systems in early stages needs a good simulation technique. this paper proposes the sil simulation for robot arm driven by bdcm. the development of robot control algorithms for robot arm driven by bdcm often hinges on access to robot hardware that its access is usually very limited. in order to facilitate the continued development of these algorithms, the sil simulation was used to integrate each algorithm change at low cost. iii. manipulator control system to implement control algorithms for the proposed manipulator, it is essential to check and study the performance of the manipulator in the matlab/simulink environment. in fact, we focus on the implementation of the dynamic model of the proposed manipulator taking into consideration the controllers studied in the matlab/simulink. figure 1 presents the block diagram of the proposed manipulator. based on figure 1, we distinguish three blocks describing the proposed system:  the model of the system,  the controllers,  the reference trajectory. iv. sil technique designing a system with its controller requires mathematical model followed by adjusted certain parameters. recently, the x in the loop approach is often used to check the system in the middle stage of the design [31]. this approach is an effective way to produce a fast and reliable short-time system. in the x in the loop approach, there are two levels of the simulation configurations based on the pc shown in figure 2: model in the loop (mil) and sil [31]. each configuration provides certain levels of progress and reduced the gap in the development process between the mathematical model and the proposed platform [31, 32]. indeed, these techniques are essential to predict possible risks before the implementation phase and to accelerate the simulation time. thus a check is made by exploiting several verification techniques. mil simulation refers to the model verification in the modeling environment such as matlab/simulink. check system at mil means that the model and its controllers are simulated in the modeling framework without physical hardware. when checking the implementation of complex systems models, it is necessary to distinguish between the verification of modules and the check of the overall system. this technique verifies the system at an earlier stage of the realization. in this step, any problem of the mathematical model of the controller can be quickly found and fixed [33]. in sil simulation, the used model is replaced by executable code running on the same computer platform of a fixed-point arithmetic way. this step allows the developer to quickly find some bad choices of memory size and to ameliorate the controller code performance. checking system in sil level means that embedded software is verified in a simulation environment, but without any hardware such as mechanical or hydraulic components or sensors or actuators [33]. normally, these two steps are performed using a single integrated platform in a pc [33]. fig. 1. block diagram of the proposed manipulator engineering, technology & applied science research vol. 7, no. 5, 2017, 2017-2021 2019 www.etasr.com ayed et al.: software in the loop simulation for robot manipulators fig. 2. different simulation techniques v. sil implementation method after the algorithms in mil stage operate as designed, the model of the controller can be converted into c code with a coder as simulink coder and targetlink. the exported code can as well be connected to the external sources of code. the created code can first be tested in simulink and also communicated with other systems and subsystems. in this section, we will present the modeling of the control part and simulation via sil simulation. in sil, the used model in mil technique is replaced with executable code running on the same computer platform in a fixed-point arithmetic way. this step is performed using an integrated platform in a single computer. figure 3 presents the block diagram of the proposed manipulator replacing the control block by the adequate sfunction block to communicate with the executable code as well as an image of the c code area. to perform a sil simulation, the flexible joint manipulator with brushless dc motor must be modeled. the control part to be replaced by the equivalent c code is articulated on two controllers that are the speed and torque controller and the current controller. stills from the fuzzy logic pi controller code and hysterisis controller in c code are shown in figure 4. for the speed and torque control part, the inputs are: the speed error (rad/s) and the position error (rad) and the output is the amplitude of the reference current. in order to obtain a compromise in performance between the simulation time and the reliability of the studied controllers and simulation results on previous works [34-25], we adopt the fuzzy pi controller. for the current control part that uses the hysteresis controller, the inputs are the current errors in the 3 phases (a) and the outputs are the states of igbts (s1-6) (1 or 0). in this part, the states of igbts applied to the inverter through the hysteresis controller will be verified through the sil simulation replacing it by its equivalent c code. vi. simulation results in order to implement these control algorithms of the studied manipulator, it is essential to check and study as a first step the controllers of the manipulator driven by bdcm in matlab/simulink environment. to evaluate the effectiveness and performances of sil simulation technique for different controllers, we are interested to the following principal variables: speed (rad/sec), position (rad), position error (rad), speed error (rad/sec), control law and simulation time. the system parameters are given in table i. figure 5 represents respectively the evolution of the speed, the position, the error of the position and speed and the electromagnetic torque in the case of fuzzy logic pi controller. to evaluate the performance of the sil technique, we adopted the simulation results given on the matlab/simulink environment specifying the execution time of the various controllers’ codes. after checking the control algorithm in matlab/simulink, sil technique produces the same results in the case of mil simulation by reaching the desired speed and position. the simulation time is decreased compared to those of mil simulation technique. table ii represents a simulation time recapitulation for each system for both mil and sil simulation techniques. table i. system parameters symbol description numeric value r resistance 0.625 ω l inductance 1.595e-3 h jm du motor inertia 1e-5kg/m 2 m1 manipulator mass 0.8619 kg l1 length of manipulator 0.3 m j1 inertia of the manipulator 0.0065 n/m2 n reduction ratio 74 η transmission efficiency 0.72 f friction 1.164e-3 kgm/s2 kt torque constant 0.0382 ke electromotive constant 0.0382 table ii. simulation time of systems for mil and sil simulation techniques system mil sil motor 6 mn 40 sec 4 mn 40 sec manipulator 18 h 9 mn 34 sec 15 h 13 mn 55 sec vii. conclusion this work was developed within the sil simulation technique for the verification of the proposed robot manipulator driven by brushless dc motor at an earlier stage. in such a complex system, the sil simulation can guarantee the verification of software component i.e. c code without any hardware and benefit from its flexibility to validate different controller algorithms. so, the manipulators including their controllers have been presented. then, the sil technique has been defined. also, sil implementation method has been detailed. finally, simulation results have shown that the sil simulation technique leads to high performance at low cost and time and allows detecting errors code before implementation. engineering, technology & applied science research vol. 7, no. 5, 2017, 2017-2021 2020 www.etasr.com ayed et al.: software in the loop simulation for robot manipulators fig. 3. different speed and torque controllers opted for the proposed manipulator (left) and the code area (right) fig. 4. fuzzy logic pi controller code (left) and hysterisis controller in c code (right) fig. 5. simulation results for fuzzy logic pi controller engineering, technology & applied science research vol. 7, no. 5, 2017, 2017-2021 2021 www.etasr.com ayed et al.: software in the loop simulation for robot manipulators references [1] l. zouari, m. b. ayed, m. abid, “embedded control of robot arm driven by brushless dc motor on fpga”, complex systems (wccs), second world 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schutter, m. verhaegen, “development of advanced driver assistance systems with vehicle hardware-in-the-loop simulations”, vehicle system dynamics, vol. 44, no. 7, pp. 569–590, 2006 [34] l. zouari, h. abid, m. abid, “sliding mode and pi controllers for uncertain flexible joint manipulator”, international journal of automation and computing, vol. 12, no. 2, pp.117–124, 2015 [35] l. zouari, h. abid, m. abid, “backstepping controller for electrically driven flexible joint manipulator under uncertainties” international journal of applied engineering research, vol. 12, no. 8, pp. 19885– 19896, 2015 microsoft word 4-467-ed.doc engineering, technology & applied science research vol. 4, no. 4, 2014, 677-680 677 www.etasr.com www.etasr.com ikhlef et al.: effect of cement and compaction on the physicochemical behavior of a material… effect of cement and compaction on the physicochemical behavior of a material in the region of sidi bel abbes n. s. ikhlef laboratory of civil engineering and environment djillali liabès university sidi bel-abbès 22000, algeria ikhlefsaidnour@yahoo.fr m. s. ghembaza laboratory of civil engineering and environment djillali liabès university sidi bel-abbès 22000, algeria sm_gou@yahoo.fr m. dadouch laboratory of civil engineering and environment djillali liabès university sidi bel-abbès 22000, algeria mokhtardaddouche@yahoo.fr abstract— soil treatment describes the procedure under which a soil acquires certain characteristics that did not originally have. this paper is focused in the field of road earthworks and the treatment of a material found in the region of sidi bel abbes, algeria. this material has poor characteristics that do not meet the standards used in road geotechnics. to remedy this, firstly, the proctor standard characteristics of this material were improved using mechanical treatment that increased the compaction energy. then a chemical treatment was employed, adding some cement dosages, and results show that the material classified in the a1h class, for an increased maximum dry density and a reduction in water content. a comparative study is made on the optimal properties of the material between the two modes of treatment. on the other hand, after treatment, one finds a decrease in the plasticity index and the methylene blue value. this material exhibits a change of class. therefore, soil class cl turned into a soil class cl-ml (silt of low plasticity). this observation allows the material to be used as backfill or subgrade. keywords-treatment of soil; cement; methylene blue value; embankment; subgrade i. introduction using local materials of poor quality that are generally ignored in favor of good soils provides obvious economical advantages. different mechanical or chemical methods are used in the treatment of soil compaction [1-2], pre-loading [3] and chemical treatment [4-9]. today hydraulic binders treatment extends to an increasingly large number of soils: silt, clay, marl, sandy material, sandy-gravelly and gravelly etc... cement appears to be a very effective stabilizer product. on the other hand, it has a high cost and requires a particular implementation. the cement stabilization develops from cementing ties between the hydration products of calcium silicate and aluminate and soil particles [10]. the addition of cement in clay soils reduces the liquid limit, plasticity index, swelling potential and increases the withdrawal limit and the shear strength [6, 11]. this work contributes to the treatment procedures employed to improve the physical properties of a material by adding cement. this method can be applied to fill and shape layers constituting the pavement structure in accordance with the standard/technical guide followed [12]. the processing technique is based on the formulation of mixtures at different percentages of cement and poor materials, in order to have a good quality material that is both economical and easy to implement. ii. characteristics of the considered materials the considered material was collected in a site located 50 km west of sidi bel abbes, algeria in a depth of about 65 cm. its physical and chemical properties are shown in table 1. the result of the grading curve shows that the material is very fine silty and sandy. according to [12-13], it is classified in the heading of fine soils rated class a with dmax≤50 mm and passing of 80µm>35%. the subclass may be determined according to the methylene blue value: vbs equal to 1.23 which gives the subclass a1 [14]. for atterberg limits we refer to [15]. the frequently water "wet" condition of the soil characterized by a relative sensitivity to water does not allow efficient compaction. the treatment with cement is particularly suitable for less plastic soils, which are a priori unsuitable for lime treatments because of their low clay content. the adjustment of water status is determined by the natural water content (wn): 0.9·wopn≤wn≤1.1·wopn with wn = 18.86% [16]. from this analysis, it was considered useful to improve the characteristics of the material by a chemical treatment with cement in order to meet the requirements in terms of load capacity and deformation in pavement structures. the cement used is portland cement artificial (cem i) from the cement works of chlef, algeria. the physical and chemical properties of the cement are summarized in table 2. engineering, technology & applied science research vol. 4, no. 4, 2014, 677-680 678 www.etasr.com www.etasr.com ikhlef et al.: effect of cement and compaction on the physicochemical behavior of a material… table i. properties of the considered material plasticity wl % ip % 33,00 11,97 particle size analysis < 80 m (%) cc = d30 2/ d10. d60 cu = d60/ d10 56,80 37,94 0,84 characteristics opn wopn (%) d /w 16,40 1,68 grain density (s /w) methylene blue value specific surface area (cm2/g) 2,55 1,23 25,75 natural water content (%) 14,86 chemical properties silica (%) lime organic matter iron oxide alumina oxide caco3 (%) 38,86 27,01 1,35 1,36 52 table ii. properties of the cement used physical characteristics values specific surface area (cm2/g) consistance (%) curing time (h, mn) warm dough expansion (mm) 3500 19 2:13 1,51 chemical characteristics values insoluble (%) loss on ignition (%) free cao (%) sio2 fe2o3 cao mgo so3 0,97 5,14 0,70 20,71 3,47 62,07 1,12 1,66 iii. exprimental procedure the processing procedure begins by drying the samples in the oven at 60°c for 24 h, then the dry material is thoroughly mixed for about 15 min with different percentages of cement (2%, 3% and 4% by [17]). the mixing is done using a mixer with knives and optionally distilled water, until a homogeneous material is achieved. atterberg limits and blue tests were performed on natural samples and treated in accordance with [14, 15]. iv. result and discussion a. effect of the cement on the liquid limit atterberg limits of soil samples found in the natural state and mixed with different percentages of cement are shown in figure 1. there is a strong limit liquidity passing 33% to 29.34% decrease. this decrease is due to the variation of water content with increasing cement content. this observation is in good agreement with the results in [6, 18-20]. similar trends of the liquid limit have been observed by other researchers on materials treated with lime and pozzolan [9, 21], and on materials treated with fly ash [22-24]. the implication of this reduction in soil plasticity, with an increasing amount of cement is attributed to the process of exchange of cations between the soil and stabilizers [6]. other authors [4, 25] explained that the cation exchange, flocculation of clay particles and reaction sintering process are the main physico-chemical mechanisms responsible for the improvement of mechanical properties of soils when treated with lime. in contrast, an increase in liquid limit when increasing the percentage of cement has been shown in [26]. we can say that this difference depends on the nature of the soil: namely an increase can occur for kaolinitic clay soils and a decrease may occur for clay montmorillonite [27]. 0 2 41 3 5 cement percent, (%) 28 30 32 34 29 31 33 l iq u id l im it , w l ( % ) 20 22 24 21 23 p la s ti c it y l im it , w p ( % ) fig. 1. variation of the liquid limite and plasticity varius percentage of cement. b. effect of the cement on the plastic limit regarding the plastic limit wp, the treated samples showed an increase of the limit with the increase of the amount of cement (figure 2). this limit increased from 21% to 23.93%. the same trends have been observed on materials treated with lime [28] and on materials treated with limestone [5]. the same behavior was also observed in [9, 22, 29-30]. it has been shown that the addition of fly ash at low calcium soil swelling causes an increase in the plasticity limit, this is due to the replacement of the fine particles by the larger particles [7, 9]. however, some authors have shown a decrease in the plastic limit, when the material is treated with a mixture of lime-pozzolana with a high content of lime (> 10% lime) [9]. c. effect of the cement on the plastic index the variation of the plasticity index based on the percentage of cement is shown in figure 2. it shows a decrease in the plasticity index when the cement content increases. this means an improvement in the behavior of the plastic material. the same trend was observed in [5, 31]. engineering, technology & applied science research vol. 4, no. 4, 2014, 677-680 679 www.etasr.com www.etasr.com ikhlef et al.: effect of cement and compaction on the physicochemical behavior of a material… 0 2 41 3 binder percent, (%) 4 6 8 10 12 5 7 9 11 13 p la s ti c it y i n d e x , ip ( % ) 0 0.40 0.80 1.20 1.60 v b s , (g /1 0 0 g ) plasticity index vbs fig. 2. influence of cement on the plasticity index and the methylene blue value d. effect of the cement on the methylene blue value the methylene blue test [18], identifies the reactivity of the clay fraction (<2 microns) present in a material by measuring the ability of the fine particles to absorb methylene blue. after several attempts to blue on samples treated and untreated cement, there has been a significant change in measurements of blue with increasing percentage of cement. the results shown in figure 2 show a decrease in the blue value from 1.23 to 0.59 (g/100 g) with the increase of the cement content. this highlights the insensitivity of the material after water treatment. e. effect of the cement on the classification of the material the different results of tests on atterberg limits, natural material and treated are shown in the diagram of plasticity of casagrande (figure 3). according to this diagram, the untreated material is associated with the class of so-called low plasticity clay loam (cl) materials. after adding different percentages of cement, the material exhibits a change of class and is positioned below the a-line. therefore, soil class of cl turned into a soil class of cl-ml (silt of low plasticity). these class changes are assigned by the flocculation of the material when the cement stabilized. in addition, changes in plasticity characteristics of the treated material, allow therefore its use in roadworks (subgrade). even after treatment we found that the material remains in the same family group (a1) according to [12]. despite the considerable decrease in the blue value and the plasticity index, similar results were found in [9]. f. effect of the cement on the properties of optimum proctor in our case, the material to be treated contains a large proportion of fine particles (56.80%) and an organic matter content of about 1.35%. the selected additive is artificial portland cement (cem i). treatment with cement according to [17] is made. doses vary from 2 to 4% by weight of dry soil. the soil cement mixture is homogenized for about 15 min. however, we proceed in the same way to the standard proctor test in cbr mold. the results before and after treatment are shown in figure 4. it is found that the dry density significantly increases the dry side of the optimum and remains substantially equal to the wet side of the optimum for different percentages of cement imposed. this leads us to say that the maximum dry density increases with increase in the percentage of cement in a cbr mold. in contrast, the corresponding optimal water content decreases as the addition of cement is important. 0 10 20 30 40 50 60 70 80 90 100 liquid limit, wl (%) 0 10 20 30 40 50 60 p la s ti c it y i n d e x , ip ( % ) used material naturel material 2% cement 3% cement 4% cement line a ip = 0.73 ( wl 20 ) ch line u ip = 0.9 ( wl 8 ) cl ml cl-ml ml cl oh ol mh organic and inorganic silts silty clays of low plasticity rock dust; fine sand clay or silty or or fig. 3. diagram of plasticity of casagrande : case of the material studied we can say that the behavior during the compaction of soil treated with hydraulic binder is slightly modified compared to treatment with lime. it should be noted that the optimum water content is shifted to the higher water content and dry density is equal to or slightly lower, the optimum moisture content is decreased and dry density is increased when treating a ground hydraulic binder. the addition of a binder in the soil causes a change in its water content. this effect is more significant with the lime than with hydraulic binders. it should also be noted that, for a given water content of the wet side of the optimum resistance measured using the cbr test are lower for samples that are subjected to high energy compaction (case of modified proctor). 12 16 20 2414 18 22 water content (%) 15.00 16.00 17.00 18.00 14.50 15.50 16.50 17.50 18.50 d ry u n it w e ig h t (k n /m 3 ) standard proctor soil+0% ciment soil+2% cement soil+3% cement soil+4% ciment sr = 1 0.900.8 d max = 16.37 kn /m 3 wopn = 18.4 % sr = 83 % proctor tests made in the cbr mold 56 shots fig. 4. influence of cemnt on the optimal properties engineering, technology & applied science research vol. 4, no. 4, 2014, 677-680 680 www.etasr.com www.etasr.com ikhlef et al.: effect of cement and compaction on the physicochemical behavior of a material… v. conclusions the objective of the study was to characterize a material to be used in road construction, relying on a process of recovery, taking into account treatment with reasonable dosages of cement with normal compaction. results allow the consideration of the use of the material as subgrade in a body floor. improving material properties by a significant energy compaction is not an effective solution as it required an increase of the maximum dry density of 1.1 kn/m3 which is not consistently seen in the measurement tolerance specified by the standards. it is therefore best to follow a different path, aiming to improve the geotechnical properties of soils by adding a chemical compound such as cement strength class 32.5 (cem i) and proceed to a standard compaction (opn). the amount of treatment product is expected to be 3% cement and it is expected to reduce the water content due to hydrations phenomena and improve the dry density. according to the results of this study, the cement can be a good treatment for a class a1h material. the pattern of results show a slight reduction in the liquid limit, an increase of the plastic limit, and therefore, a reduction of the plasticity index. as shown, when applying a certain amount of cement to the soil it passes brutally from a plastic state to the crumbly state. the analysis reveals a difference of the soil’s behavior in regards of the way of treatment (mechanical or chemical). the major difference between the two types of treatment relates to the size of the mold, which on site, may result to less roller passes and thus avoidance of over-compaction. references [1] a. l. bell, “the development and importance of construction technique in deep vibratory ground improvement” in ground 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[14] afnor nf p 94-68, sols: reconnaissance et essais, mesure de la capacité d'adsorption de bleu de méthylène d'un sol-détermination de la valeur de bleu de méthylène d'un sol par l'essai à la tâche, 1998 [15] afnor nf p 94-51, sols: reconnaissance et essais, détermination des limites d'atterberg limite de liquidité à la coupelle-limite de plasticité au rouleau, 1993 [16] afnor nf p 94-50, sols: reconnaissance et essais, détermination de la teneur en eau pondrale des matériaux-méthode par étuvage, 1995 [17] afnor nf p 94-100, sols: reconnaissance et essais, matériaux traités à la chaux et/ou aux liants hydrauliques-essai d'évaluation de l'aptitude d'un sol au traitement, 1999 [18] d. t. davidson, r. l. handy, “lime and lime applications” in highway engineering handboo, pp. 23–98, m.c graw hill, new york, 1960. [19] o. l. lund, w. j. ramsey, “experimental lime stabilization in nebraska”, highway research board bulletin, vol. 231, pp. 24–59, 1965 [20] h. newbauer, m. thompson,. stabilization properties of uncured limetreated fined-grained soils. highway research record, vol. 381, pp. 20– 26, 1972 [21] j. manasseh, a. i. olufemi, “effect of lime on some geotechnical properties of igumale shale”, electronic journal of geotechnical engineering, 13a, pp. 1-12, 2008 [22] d. turker, e. cokca, “effects of addition of fly ash on swell potential of an expansive soil”, in expansive soils-recent advances in characterization and treatment, pp. 453-463, taylor & francis, london, uk, 2006 [23] n. degirmenci, a. okucu, a. turabi, “application of phosphogypsum in soil stabilization”, building and environment, vol. 42, no. 9, pp. 3393-3398, 2007 [24] a. reyes, m. pando, “evaluation of cfbc fly ash for improvement of soft clays”, world of coal ash (woca), covington, kentucky, usa, may 7-10, 2007 [25] m. r. thompson, “lime-treated soils for pavement construction”, journal highway division, vol. 94, no. 2, pp. 59–67, 1965 [26] r. n. yong, v. r. ouhadi, “experimental study on instability of bases on natural and lime/cement stabilized clayey soils”, applied clay science, vol. 35, no. 3-4, pp. 238-249, 2007 [27] n. o. attoh-okine, “lime treatment of laterite soils and gravelsrevisited”, construction and building materials, vol 9, no. 5, pp. 283287, 1995 [28] f. g. bell, “lime stabilization of clay minerals and soils”, engineering geology, vol. 42, no. 4, pp. 223-237, 1996 [29] a. s. muntohar, g. hantoro, “influence of rice husk ash and lime on engineering properties of a clayey subgrade”, electronic journal of geotechnical engineering, vol. 5a, pp. 1-9, 2000 [30] e. a. basha, r. hashim, a. s. muntohar, “effect of the cement-rice husk ash on the plasticity and compaction of soil”, electronic journal of geotechnical engineering, vol. 8a, pp. 1-8, 2003 [31] r. l. parsons., e. kneebone, “field performance of fly ash stabilized subgrade”, ground improvement, vol. 9, no. 1, pp. 33-38, 2005 engineering, technology & applied science research vol. 8, no. 1, 2018, 2595-2597 2595 www.etasr.com bangwar et al.: an improvement in the bond strength of rice husk ash concrete by incorporating … improving the bond strength of rice husk ash concrete by incorporating polymer a new approach daddan khan bangwar dpt of civil engineering quaid-e-awam university of engineering, science & technolgy nawabshah, pakistan daddan@quest.edu.pk mohsin ali soomro dpt of civil engineering quaid-e-awam university of engineering, science & technolgy nawabshah, pakistan drmohsin@quest.edu.pk nasir ali laghari energy environmental engineering dpt quaid-e-awam university of engineering, science & technolgy nawabshah, pakistan mashaalnasirlaghari@gmail.com mukhtiar ali soomro dpt of civil engineering quaid-e-awam university of engineering, science & technolgy nawabshah, pakistan eng.soomro@gmail.com ahsan ali buriro dpt of civil engineering quaid-e-awam university college of engineering, science & technology larkana, pakistan ahsanone@gmail.com abstract—this paper gives an insight of how to improve the bond strength of cement in which concrete is replaced with rice husk ash. a concrete mix was prepared and was used in different types of mixes i.e. control mix, 10% cement substituted concrete with rice husk ash and polymer modified concrete by incorporation different dosages of polymer in the 10% cement substituted concrete. a bar of 12mm diameter, 300mm in length was placed in the center of the cylindrical specimens for pull out test. it was observed that the bond strength between concrete and steel decreases with the replacement of cement with ash, conversely the bond strength improves with the addition of polymer dosages. keywords-polymer; bond strength; rha; cement replacement i. introduction several pozzolanic materials are used for cement replacement and rice husk ash (rha) is one of them. various concrete properties are affected when cement is substituted. authors in [1] made various cement replacements with rha starting from 5 to 30% replacement and concluded that bond strength increased up to an optimum level of cement replacement beyond which it started decreasing. a good repair system is supposed to provide a satisfactory bond between the repair material and old concrete. ideally the bond between the composite concretes behaves as a monolithic. the most notably factors that have an adverse effect on bond strength are the characteristics of original concrete, surface conditions, preparation and characteristics of repair system, workmanship and environmental circumstances [2]. importance of interfacial bond and surface preparation of concrete substrate prior to embarking on actual repair will be the single most important factor in repair viability as it is well documented in [3, 4]. the inclusion of the latexes to mortars and concretes improves their adhesion or bond strength to various substrates like pastes, mortars, concretes, tiles, bricks, steel, wood and stone in comparison to the un-modified mortars and concretes [2]. the higher adhesion of the latex-modified mortars and concretes is due to higher adhesion of polymers present in them. the adhesion is usually affected by the polymer-cement ratio, and the properties of substrates used. adhesion or bond between latex-modified mortars and reinforcement has been investigated in [5] in which bond strength kept on increasing with an increase of polymer to cement ratio of 10 to 15%. authors in [6] developed an economical polymer-based repair material by blending epoxy acrylate, methyl methacrylate and polyurethane prepolymer. they utilized interpenetrate polymer network technology and conducted a chain of experiments on the bonding response of the developed material to be used for concrete structure crack repairing. the experimental outcomes revealed that the developed repairing material possessed a long lasting ability to repair concrete cracks with wanting operability, bonding agent strength and cracking resistance. authors in [7] conducted different tests on concrete latex based polymer-modified concrete in green as well as in hardened stage. the dosage of polymer to cement was 2.5, 5 and 7.5%. the utmost effects of polymer modification are on the enhancement of concrete tensile strength, ductility, bond between reinforcement and concrete, and on improvement of properties contributing to the durability of reinforced structures. engineering, technology & applied science research vol. 8, no. 1, 2018, 2595-2597 2596 www.etasr.com bangwar et al.: an improvement in the bond strength of rice husk ash concrete by incorporating … ii. methodology a laboratory pan mixer for concrete preparation was used. the moulds were lightly coated with mineral oil before use [8]. rha, eva powder and aggregates were dry-mixed for 2 minutes, followed by the addition of water and then mixed for 1 minute as per jis a 1171 (method of making test samples of polymer-modified mortar in laboratory). five specimens of each of the control mix and the 5 different mix types were cast making the total number of 30 cylindrical, sized 100 mm x 200 mm, specimens, by using the mix design shown in table i. table i. specimen mixes s. no concrete mix cement kg/m3 rha kg/m3 rpp kg/m3 t.binder kg/m3 plasticize r kg/m3 water kg/m3 f.a kg/m3 c.a kg/m3 slump mm 1 cm 346 0 0.0 346.0 0.0 190.3 692 1038 2550 2 rhamm 311.4 34.6 0.0 346.0 0.0 205.8 692 1038 3 rhapmm1 311.4 34.6 3.1 349.1 2.79 205.8 692 1038 4 rhapmm2.5 311.4 34.6 7.8 353.8 2.83 205.8 692 1038 5 rhapmm5 311.4 34.6 15.6 361.6 2.89 205.8 692 1038 6 rhapmm7.5 311.4 34.6 23.4 369.4 2.95 205.8 f692 1038 a bar of 12 mm diameter, 300 mm length, was placed in the specimens’ center for pull out test, as shown in figure 1. after 24 hours the samples were de-moulded and were kept for curing. the control mix (un-modified) and rha modified concrete mix samples were cured for 28-days in moist curing as per astm c 192 and polymer-modified concrete mix samples were first kept in wet curing for 7-days and then kept in the air for 21-days for air dry curing as per jis a 1171-2000. at the end of the curing period, the reinforcing bar was pulled with the help of a universal load testing machine (utm) until failure and the force was recorded as pull out strength [1]. the bond stress was calculated by (1): ld p    (1) where p is the required force to pull the embedded bar out of concrete specimen, l is the anchorage length of the bar in concrete specimen and d is the bar diameter. the average value of the five samples was recorded as concrete bond strength. fig. 1. samples for pull out test iii. results and discussion a. workability workability is one of the most important factors governing concrete strength. results in figure 2 show the workability of control mix, optimum rha-modified mix and rha polymermodified mixes. from the figure, the addition of rha as a supplementary cementing material causes a reduction in slump and a stiffer mix compared to control mix. for enhancing workability, keeping the water to cement ratio constant, 0.8 percent of super plasticizer is added. furthermore, it was noticed that with polymer addition into the mix the slump increased, because the polymer has air entrapping quality. such findings are lined up with [9, 10]. fig. 2. workability b. bond strength results in figure 3 show the behavior of bond/adhesion between the tensile reinforcement and concrete in control mix, 10% cement replaced with rha concrete and rha polymermodified concrete (rhapmc). upon the cement replacement with rha a weak bond is observed compared to control mix. bond strength between reinforcement and rha modified concrete decreases from 4.47mpa to 4.45mpa (i.e. 0.447% less) compared to the bonding behavior of control mix. this is because the cement substitute, i.e. rha, is not so dense as cement. however adhesion characteristic significantly increases with the addition of rpp from 1 to 7.5% dosages when compared to control mix. at 5% dosages of rpp in the rha modified concrete maximum bond strength is 4.49mpa (0.89% increase) compared to rha modified concrete. the increase in the adhesion is primarily due to the increase in the tensile property. the constituents in polymer-modified concrete are compactly joined with each other due to the presence of interweaving polymer films [11]. such findings are validated by the researchers in [2, 6, 12, 13]. engineering, technology & applied science research vol. 8, no. 1, 2018, 2595-2597 2597 www.etasr.com bangwar et al.: an improvement in the bond strength of rice husk ash concrete by incorporating … fig. 3. bond strength of cm, rhamm and rhapmm with steel bar iv. conclusions on the basis of the experiment results the following conclusions can be drawn:  the fluidity of the concrete with substituted cement with rha is increased with the addition of polymer dosages.  the bond strength between the reinforcement and rha modified concrete decreases by 0.447% when compared to the bonding behavior of control mix. however adhesion characteristic significantly increases with the addition of rpp from 1 to 7.5% dosages compared to control mix. at 5% dosage of rpp in the rha modified concrete, maximum bond strength is increased by 0.89% when compared to rha modified concrete. acknowledgment the authors express their thanks to the civil engineering department quest nawabshah for the necessary support. references [1] v. saraswathy, h. -w. song, “corrosion performance of rice husk ash blended concrete”, construction and building materials, vol. 21, no. 8, pp. 1779-1784, 2007 [2] y. ohama, “principle of latex modification and some typical properties of latex-modified mortars and concretes adhesion; binders (materials); bond (paste to aggregate); carbonation; chlorides; curing; diffusion”, materials journal, vol. 84, no. 6, pp. 511-518, 1987 [3] a. m. vaysburd, g. sabnis, p. h. emmons, j. e. mcdonald, “interfacial bond and surface preparation in concrete repair”, indian concrete journal, vol. 75, no. 1, pp. 27-34, 2001 [4] b. v. bhedasgaonkar, “surface preparation for application of patch repairs, sealers and coatingsindian approach”, indian concrete journal, vol. 75, no. 1, pp. 83-86, 2001 [5] y. ohama, handbook of polymer-modified concrete and mortars: properties and process technology, william andrew, 1995 [6] h. wu, m. zhu, z. liu, j. yin, “developing a polymer-based crack repairing material using interpenetrate polymer network (ipn) technology”, construction and building materials, vol. 84, pp. 192200, 2015 [7] r. j. folic, v. s. radonjanin, “experimental research on polymer modified concrete”, materials journal, vol. 95, no. 4, pp. 463-469, 1998 [8] astm c192 / c192m 16a. standard practice for making and curing concrete test specimens in the laboratory, astm international, 1988 [9] y. ohama, “polymer-modified mortars and concretes”, in: concrete admixtures handbook: properties, science & technology, william andrew, 1984 [10] j. b. kardon, “polymer-modified concrete: review”, journal of materials in civil engineering, vol. 9, no. 2, pp. 85-92 ,1997 [11] m. u. k. afridi, y. ohama, k. demura, m. z. iqbal, “development of polymer films by the coalescence of polymer particles in powdered and aqueous polymer-modified mortars”, cement and concrete research, vol. 33, no. 11, pp. 1715-1721, 2003 [12] y. ohama, k. demura, h. nagao, t. ogi, “adhesion of polymermodified mortars to ordinary cement mortar by different test methods”, in: adhesion between polymers and concrete / adhésion entre polymères et béton, springer, 1986 [13] y. ohama, h. ibe, h. mine, k. kato, “cement mortars modified by sb latexes with variable bound styrene”, rubber chemistry and technology, vol. 37, no. 3, pp. 758-769, 1964 engineering, technology & applied science research vol. 7, no. 5, 2017, 1946-1952 1946 www.etasr.com shahgholian and fattollahi: improving power system stability using transfer … improving power system stability using transfer function: a comparative analysis ghazanfar shahgholian department of electrical engineering najafabad branch, islamic azad university najafabad, iran shahgholian@iaun.ac.ir arman fattollahi smart microgrid research center najafabad branch, islamic azad university najafabad, iran fattollahi@iaun.ac.ir abstract—in this paper, a small-signal dynamic model of a singlemachine infinite-bus (smib) power system that includes ieee type-st1 excitation system and pss based on transfer function structure is presented. the changes in the operating condition of a power system on dynamic performance have been examined. the dynamic performance of the closed-loop system is analyzed base on its eigenvalues. the effectiveness of the parameters changes on dynamic stability is verified by simulation results. three types of pss have been considered for analysis: (a) the derivative pss, (b) the lead-lag pss or conventional pss, and (c) the proportional-integral-derivative pss. the objective function is formulated to increase the damping ratio of the electromechanical mode eigenvalues. simulation results show that the pid-pss performs better for less overshoot and less settling time compared with the cpss and dpss under different load operation and the significant system parameter variation conditions. keywords-power system stabilizer; pid controller; lead-lag controller; stability. i. introduction modern power systems are complex, nonlinear and often exhibit electromechanical oscillations due to inadequate system damping [1, 2]. power systems continuously experience changes during abnormal operating conditions due to variations in generation or load and a wide range of disturbances. power system stability improvements have been considered an important problem for secure system operation over many years [3, 4]. low frequency electromechanical oscillations are a characteristic of the power system and they are inevitable. these oscillations can be observed in most power system variables like line current, bus voltage, synchronous generator power and speed. generally, the damping control methods of power system oscillations can be divided into two broad groups: damping control at generator locations (such as excitation control) and damping control in the transmission path (such as line reactance control). because of the complexity of the network evolved from the interconnected large transmission systems and heavy generations, the use of the power system stabilizer (pss) has become common by the utilities today. pss plays an important role to suppress the electromechanical oscillation, increase the system positive damping and improve the steady-state stability margin and improve the stability in power system [5]. generally, pss control design methodologies can be categorized as (a) classical method, (b) adaptive and variable structure methods, (c) robust control approaches, (d) intelligent techniques and (e) digital control schemes [6, 7]. a number of studies have been performed about the pss parameters design and its applications to improve the dynamic stability of power systems [8, 9]. an adaptive fuzzy pss based on robust synergetic control theory and terminal attractor techniques is developed in [10], which fuzzy logic systems are used to approximate the unknown power system dynamic functions without calling upon usual model linearization and simplifications. in [11] a pss designed using the improved simple adaptive control based on quadratic performance, which this approach can track the reference model and decrease the control increment. a method of designing fixed parameter decentralized pss for interconnected multi-machine power systems is proposed in [12]. a technique for designing fixed parameter decentralized psss for interconnected power systems is proposed in [13], which local information available at each machine in the multi-machine environment, is used to tune parameters of pss. a modified fruit fly optimization algorithm combined with a probabilistic approach to coordinate and optimize the parameters of pss and svc damping controller for improving the probabilistic small signal stability of power systems is proposed in [14]. a space recursive least square algorithm developed for tuning of pss parameters on smib power system based pid is proposed in [15] to meet the vulnerable conditions. an objective function and algorithm to obtain a set of optimal pss parameters that include a feedback signal of a remote machine and local and remote input signal ratios for each machine in a multi-machine power system under various operating conditions in proposed in [16]. a robust pid based pss to properly function over a wide range of operating conditions is proposed in [17]. the objective of this paper is to investigate the effects of pss based pid controllers on power system electromechanical oscillation damping. the synchronous generator is represented by the third-order model. the parameters of pss are determined based on a linearized model of the power system around a nominal operating point where they can provided good performance. the effectiveness of the proposed pss in engineering, technology & applied science research vol. 7, no. 5, 2017, 1946-1952 1947 www.etasr.com shahgholian and fattollahi: improving power system stability using transfer … increasing the damping of low-frequency oscillation is demonstrated in a smib for different operating conditions of the power system. ii. power system description power system stabilizer is used to enhance damping of power system oscillations, mainly through excitation control. the ieee type-st1 is used for the voltage regulator excitation system [18]. the dynamic model in state-space form of the linearized smib power system model around an operation point can be expressed as [19]: rb dt d      m m ' q m r m i m r t j e j k j d j k dt d  121    f' do ' q' do ' do ' q e t e tkt k e dt d  11 3 4    f a ' q a a a a r a a f e t e t kk t kk u t k e dt d  165    where the state variables are angle load (), field voltage (ef), angular velocity (r) and voltage proportional to direct axis flux linkages (e'q). also, jm is the generator inertia constant, di is the inherent damping constant, t'do is the d-axis open circuit transient time constant, and b is the base electrical angular velocity. the primary inputs to the generating unit are the mechanical torque deviation (tm) and reference terminal voltage deviation (ur), which are supplied from a higher level of control. k1 and k2 are the constant derived from electrical torque, k3 and k4 are the constant derived from field voltage equation, and k5 and k6 are the constant derived from terminal voltage magnitude. the parameters kl-k6 are constants for a particular operating point (peo, qeo, uto) but they are sensitive to power system network parameters and generator operating conditions. figure 1 shows the functional block diagram of the smib power system based on control transfer function (between the output electrical torque and load angle), hq(s), and the electrical loop transfer function (between exciter input and the output electrical torque), ge(s). also gm(s) is the transfer function of the dynamic machine. fig. 1. block diagram of the open loop smib power system based on control and electrical loop transfer functions iii. system control scheme a two-input two-output process be represented by the block diagram of the smib power system shown in figure 2. the transfer functions hst(s), htt(s), hsu(s) and htu(s) show the ratio output variables r and te to input variables tm and ur in open loop system. when the speed deviation is used to input signal of pss, the transfer function hsu(s) is important in pss parameter design. but if electrical torque is used for pss input signal, the transfer function htu(s) is important in pss parameter design. a system without pss, will have:  fig. 2. block diagram of the open loop smib power system based on transfer functions s ttj kk )s()s(u )s( )s(h a ' dom a or r su 21      ) j d s(s tt kk )s()s(u )s(t )s(h m i a ' do a or e tu  21     where o(s) is the open loop characteristic polynomial in power system. it has four eigenvalues. therefore, the characteristic equation of the open loop smib power system is given by:  01 2 2 3 3 4 pspspsps)s(o    by varying the operating point, the coefficient parameter values p0 through p3 also vary. a. conventional lead-lag pss the conventional lead-lag pss (cpss) transfer function is given by the following [20]:  ) st st ( st st k)s(g g d w w cl     1 1 1   where tw is the washout time constant and kc is the pss pure gain. td is the lead time constant and tg is the lag time constant. the selection of the tw value depends upon the type of mode under study [21]. figure 3 show the phase frequency response characteristics of cpss (tg=0.05) according to the variation of td. the figure shows that the maximum phase lagging of the gl(s) happens on c:  gd c tt 1    engineering, technology & applied science research vol. 7, no. 5, 2017, 1946-1952 1948 www.etasr.com shahgholian and fattollahi: improving power system stability using transfer … fig. 3. phase frequency response characteristics of the cpss b. derivative pss the block diagram of the derivative power system stabilizer (dpss) with gain kd and time constant td used in this paper is depicted in figure 4. the transfer function of the derivative pss (dpss) as shown in is given by:  st st st t k)s(g d d d d dd   11   bode plot of the dpss for different values of td are shown in figure 5. the figure shows that the maximum amplitude of the gd(j) at m=1/td is kdtd/2. also, in this frequency, the phase of the gd(j) is zero. the time constant of the dpss should optimally determine to compensate for phase lag between the exciter input and the generator electrical torque. c. proportional-integral-derivative pss a pid controller is commonly used by industrial utilities. it can be represented in transfer function form as [22, 23]:  sk s k k)s(g d i pc    fig. 4. the structures of a dpss where kp represents the proportional gain, ki represents the integral gain, and kd represents the derivative gain. the phase angle diagram of the pid controllers for different values of gains are shown in figure. 6. the pid-pss as shown in figure 7 with rotor deviation as input have the following transfer function: ( ) ( ) ( ) 1 w i p g p d w t k g s k k k s t s s       d. close-loop transfer function the linearized model of the close-loop in a smib power system has six eigenvalues. the transfer functions in close loop system (with pss) are given by the following:  )s(g)s(h )s(h )s(u )s( )s(h psu su r r sv    1     )s(g)s(h )s(h )s(u )s(t )s(h psu tu r e er   1    to increase the system damping, the eigenvalue-based objective function is considered as follows:  [ ( )]ij max real    where i is the i th electromechanical mode eigenvalue. in the optimization process, it is aimed to minimize j in order to shift the poorly damped eigenvalues to the left in s-plane.  (a) (b) fig. 5. bode plot of the dpss for various times constant fig. 6. phase angle diagram of the pid controller fig. 7. block diagram of pid power system stabilizer (pid-pss) engineering, technology & applied science research vol. 7, no. 5, 2017, 1946-1952 1949 www.etasr.com shahgholian and fattollahi: improving power system stability using transfer … e. characteristic equations the characteristic equation of the close loop power system with dpss s defined as:  01 2 2 3 3 4 4 5 5 6 asasasasasas)s(d    where the coefficients a0 through a6 are given by:                            020 1201 22102 2 32213 2324 35 1 12 12 12 12 2 p t a p t p t a p t p t pa tt kk kp t p t pa t p t pa t pa d dd dd ' doa a d dd dd d   according to this equation, all coefficients are depending on td, but a3 only depend on the kd. the characteristic equation of the close loop smib power system equipped with pid-pss is given by:  )dsdsdsdsds(s)s(p 01 2 2 3 3 4 4 5    where the coefficients d0 through d4 are given by:                        w ' dom ig w ' dom pg w ' dom dg w w t p d tj kkk t p pd tj kkk t p pd tj kkk t p pd t pd 0 0 20 11 21 22 22 33 34 1    the characteristic equation of the close loop smib power system equipped with cpss is given by:  01 2 2 3 3 4 4 5 5 6 msmsmsmsmsms)s(l   where the coefficients m0 through m5 are given by the next equation according to which, the time constant t1 only effected on m3 and gain kp only effected on m3 and m2.                          2 0 0 2 0 2 1 1 2 2 0 2 1 2 2 2 2 12 1 2 2 2 3 3 2 2 3 2 4 3 2 5 11 11 11 111 11 tt p m ) tt (p tt p m t k ttj kk p) tt (p tt p m t tk ttj kk p) tt (p tt p m p) tt (p tt m p tt m w ww p ' doam a ww p ' doam a ww ww w   iv. simulation results the small signal stability analysis of a smib power system is examined by the eigenvalues of the state matrix. to assess the effectiveness of the proposed controllers, three different loading conditions nominal, light and heavy as shown in table i are considered for eigenvalue analysis. the data of the system is given in table ii. the constants k1 to k6 for the three operating points considered are given in table iii. note that the constant k5 is only positive for light loading. the system modes and damping ratio for electromechanical mode without pss are given in table iv. note that the system without pss is slightly damped only in light loading. the system response without applying any pss is more oscillatory in heavy load condition. the maximum phase lagging of the open loop system in the hq(s) is approximately -100 degree and in the ge(s) is approximately -140 degree at 10 rad/s, respectively. therefore, one first-order blocks will be used to achieve the desired phase compensation. also, the proportional and integral gains of pid controller are positive. the undamped natural angular frequency (n) is n=5.4741 rad/s. the pss parameters time-constants tw, td, tg and gain kc are to be optimized. tw=10s and tg=0.05s are chosen. the required phase-lead can be obtained by choosing the value of time constant td. the transfer function ge(s) in the jn is 1.2516-62.9522. therefore, td=0.8049s is obtained which provides the desired phase-lead of 62.9522. the optimal parameters of the pss base on phase compensation design are shown in table v. the system eigenvalues with the stabilizer for three different operating conditions are given in tables vi, vii and viii. the damping ratio of the electrometrical mode eigenvalue for different loading of the power system without pss and pss are shown in table ix. table i. different loading operation normal load operation peo=0.8, qeo=0.6, uto=1 heavy load operation peo=1.3, qeo=1.0, uto=1 light load operation peo=0.3, qeo=0.1, uto=1 engineering, technology & applied science research vol. 7, no. 5, 2017, 1946-1952 1950 www.etasr.com shahgholian and fattollahi: improving power system stability using transfer … table ii. smib power system parameters generator jm=10s, t'do=6s, xd=1.6, x'd=0.32, xq=1.55, f=50hz ieee type-st1 excitation system ka=50, ta=0.05 transmission line reactance re=0, xe=0.4 table iii. constants k1-k6 for different loading conditions parameters nominal loading light loading heavy loading k1 0.9538 0.7334 0.7803 k2 0.9445 0.6526 1.0833 k3 0.3600 0.3600 0.3600 k4 1.2081 0.8353 1.3867 k5 -0.0539 0.0573 -0.1989 k6 0.4674 0.5154 0.4359 table iv. system modes in power system without pss operating points mechanical mode electrical mode nominal loading 0.1028j5.5022 -14.2975, -6.3710 light loading -0.1787j4.6571 -13.4839, -6.6216 heavy loading 0.6068j5.3140 -14.4917, -7.1848 table v. optimal parameters setting for pss cpss kc=12.0458, tw=10, td=0.8049, tg=0.05 pidpss kg=1, tw=10,kp=19.4623, ki=2.4753, kd=11.2516 dpss kd=2.03, td=0.30 table vi. system modes for power system with pss under normal loading cpss pidpss dpss -1.55033.2201 -4.323411.4349 -28.7149 -0.1007 -1.5376±j3.1204 -8.6940±j12.3729 -0.0997 0 -1.3566±j5.3300 -2.7562±j4.6203 -16.8229 -2.0811 table vii. system modes for power system with pss under heavy loading cpss pidpss dpss -1.26083.3534 -4.256411.7692 -29.4278 -0.1007 -1.2518±j3.2023 -8.9798±j13.1208 -0.0997 0 -0.4622±j5.1017 -3.4194±j4.8032 -17.2650 -2.1013 table viii. system modes for power system with pss under light loading cpss pidpss dpss -1.32083.0888 -5.35319.8632 -27.1145 -0.1006 -1.3473±j2.9787 -8.8843±j10.1524 -0.0997 0 -0.4622±j5.1017 -3.4194±j5.1017 -17.2650 -2.1013 a comparative between the conventional pss and dpss with pidpss in damping power system oscillation under normal operating conditions is shown in figures 8, 9 and 10. the step response of the angular speed deviation under heavy operating conditions has been shown in figure 11. the results show the superiorly of pidpss and cpss over dpss in increasing the damping of low frequency oscillations. table x shows the summary of the system dynamic characteristics such as settling time (ts), peak time (tp) and percent overshoot (mp). it is seen from these simulation studies that the pid-pss is more effective than the cpss and dpss in damping the electromechanical oscillations under various loading conditions and its damping speed is much faster. table ix. damping ratio of electromechanical mode for power system under different operation conditions loading without pss cpss dpss pidpss normal loading -0.0187 0.4338 0.2467 0.4420 heavy loading -0.1135 0.3519 0.0902 0.3641 light loading 0.0383 0.3932 0.0902 0.4121 fig. 8. step response of the angular speed deviation v. nonlinear simulation the scenario was simulated that a 0.10 pu step change in the input mechanical power occurred at 0 s. the simulation results are shown in figures 12-14. the simulation results show that the pid-pss achieved better damping effects than the derivative pss and conventional pss. fig. 9. step response of the electrical torque deviation engineering, technology & applied science research vol. 7, no. 5, 2017, 1946-1952 1951 www.etasr.com shahgholian and fattollahi: improving power system stability using transfer … fig. 10. step response of the pss output signal deviation fig. 11. step response of the angular speed deviation under heavy loading table x. system dynamic characteristic pss ts tp mp% cpss 7.9621 1.2576 106.8231% dpss 2.6399 s 0.6156 s 126.5998% pidpss 1.9988 0.8094 126.2119% fig. 12. pss output response to a 10% mechanical power change vi. conclusion the main function of power system stabilizer is suppressing the low-frequency oscillation of the power system to improve its dynamic stability. the dynamic response of a smib power system with pss based on transfer function at various operating conditions has been investigated in this paper. three types of pss have been considered for analysis. the pid-pss performs better for less overshoot and less settling time compared with the cpss and dpss under different load operation and the significant system parameter variation conditions. fig. 13. rotor speed response to a 10% mechanical power change fig. 14. electrical power response to a 10% mechanical power change references [1] g. shahgholian, m. maghsoodi, a. movahedi, “fuzzy proportional integral controller desing for thyristor controlled series capacitor and power system stabilizer to improve power system stability”, revue roumaine des sciences techniques, vol. 61 no. 4, pp. 418-423, 2016 [2] g. shahgholian, k. khani, m. moazzami, “frequency control in 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vol. 2, no. 1, pp. 21-30, 2017 engineering, technology & applied science research vol. 12, no. 1, 2022, 8143-8150 8143 www.etasr.com pylarinos: using google my maps as a geospatial ticket management system for scheduling … using google my maps as a geospatial ticket management system for scheduling and monitoring power distribution network works case study of patras area’s distribution network engineering & construction section d. pylarinos patras area’s distribution network engineering & construction section department of peloponnese-epirus region hellenic electricity distribution network operator s. a. greece d.pylarinos@deddie.gr abstract-the need to ensure the long-term ability of power distribution systems to meet demands means that upgrades and alterations/expansions, as well as inspection and maintenance works, are constantly necessary. this paper presents an approach to use custom google maps as a ticket management system for scheduling and monitoring such works. a geospatial representation is rather useful in networks that are great in length and follow irregular routes (which is typically the case for power distribution networks). however, acquiring a representation of such networks, especially for the low voltage side, is an enormous task. this paper presents a cost-free and easy-to-implement approach that can be used in the absence of a full geospatial representation of the network. this approach utilizes an assign-to-the-feeding-transformer (for all low voltage issues) and assign-one-indicating-point (for each middle voltage issue) scheme, thus, requiring a minimum amount of data easily retrieved from the network. this approach provides a georeferenced ticket management system that can be employed for improved monitoring and scheduling through a user-friendly and free-to-use web-based application which use requires no additional costs or training. the presented approach has been applied in the area of patras, greece and initial results, showing a significant improvement in productivity, ranging from 10% to 42%, are further presented and discussed in this paper along with background information. keywords-power distribution network; google maps; custom; ticket management system; geospatial; georeference. i. introduction electrical networks and installations are generally divided in three main categories: production, transmission and distribution [1]. the distribution system (network) includes all medium voltage (mv) and low voltage (lv) equipment used to carry electricity to the final consumer whereas the transmission system includes all hv equipment used to carry hv between hv substations [1]. a distribution system operator (dso) is an entity responsible for operating, maintaining and developing the power distribution system in a given area [2]. the number of dsos within a specific country as well as their exact nature, their inner structure, the level of involvement of outside contractors and their general mode of operation varies from country to country [3-6]. in greece, hedno [7] is currently the sole dso for the whole distribution network throughout the country with over 7.5 million customers and a network length that exceeds 240.000 km (with the low voltage network holding a marginal majority of this sum) and over 163.000 installed medium/low voltage transformers [8]. to measure the reliability and quality of services provided by dsos, two values are widely used: saifi and saidi. the system average interruption frequency index (saifi) is the average number of interruptions that a customer would experience within one year whereas the system average interruption duration index (saidi) is the average interruption duration within one year for each customer served [6]. in saifi and saidi terms, hedno scores rather low in comparison with other european dsos [4] but well better than the median world value [9]. although there is always room for improvement, it should be noted that comparing such values between different areas and countries may be misleading as local conditions vary (e.g. the weather, the landscape, the age of the network etc.). network expansions and upgrades as long as the initial network design have a significant impact on the performance of a network (and thus of its operator) [10-11]. the followed inspection and maintenance strategies are also key factors [1215]. this paper presents and discusses an approach to improve ticket managing, and thus scheduling and monitoring of works, using geospatial data. the use of geospatial data has proven a rather useful tool in a variety of cases [16] including various applications in the power network industry [17-22]. however, the ticket-management aspect is often neglected. at the moment, hedno is running a major project aiming to incorporate gis technology in the core of its functions, expected to be completed in late 2022 [23]. this paper presents an intermediate step undertaken meanwhile from the hedno’s network engineering & construction section (necs) of patras area, greece in an effort to increase the section’s corresponding author: d. pylarinos engineering, technology & applied science research vol. 12, no. 1, 2022, 8143-8150 8144 www.etasr.com pylarinos: using google my maps as a geospatial ticket management system for scheduling … productivity and to familiarize its personnel with the use of digitized and geospatial data. a major initial goal was that no additional cost (in terms of software, equipment, personnel or training) should be required at any time. the proposed approach does not require a detailed geospatial representation of the network either. thus, it can easily be followed by other organizations under similar conditions. ii. case study and background a. traditional naming scheme for network components traditionally, in the absence of gis systems and of geospatial data, simple naming rules had to be employed in order for the personnel to be able to navigate and work on the network. for example, in this particular case, mv lines were named after the high voltage substation they are connected to, along with an arithmetic value. if a line splits, then each subsection was named adding a dash and another arithmetic value. mv poles are also numbered and thus a third dash and arithmetic value was added to the naming scheme. these data were maintained in numerous hard copy maps and sheets depicting the network in various zoom scales. of course, the network changes over time (e.g. mv poles may be added or removed at any time), which creates similar issues with the ones mentioned in [20]. however, unlike what happens with transmission towers [20], pole numbering is not indicated on the actual poles in the field. only key network components (e.g. mv/lv transformers) are equipped with indicating signs. mv/lv substations are traditionally named using local toponyms (city areas, village names or general location names), although not always accurately, followed by an arithmetic value. substations were then used as starting points to pin-point other lv network components such as lv poles or spans, that do not bear a specific name tag. however, the traditional naming scheme for key network components such as mv/lv transformers is soon to be abandoned since jurisdiction areas are gradually merging and this means that components with the same name would ultimately be found in the same jurisdiction (as there are numerous places and villages with identical toponyms throughout greece). b. area and network data the case study area covers over 1,500 km2 and includes more than 200,000 customers connected to over 3,000 mv/lv transformers. the area is depicted in figure 1 (in red) and, in more detail, in figure 2 with the mv lines shown in solid green color. it should be noted that mv lines are mostly overhead, with small parts (mostly within major cities) being underground. in comparison, larger parts of the lv network are underground, but again these are to be found mostly within major cities (mostly in the city of patras). this means that the larger part of the network is subjected to open-air environmental stress and thus its inspection and maintenance is essential for the system’s reliability. c. inspection and ticketing standard procedure within hedno is for the area’s network operation & maintenance section (noms) to perform yearly inspections of the network and note down all potential issues, including potential upgrade works, as judged by them on site. issues that fall under the necs’s jurisdiction are forwarded in the form of hard-copy notes (tickets) for further consideration. these tickets are given a unique number for all future reference. each ticket describes the issue and its location by using the traditional naming schemes previously described. the necs is then expected to prioritize the received tickets and schedule on-site visits and consequent studies. finally, the studies are handed to an outside contractor and the necs is then responsible for inspecting and monitoring the contractor’s works. it should be noted however that all hedno personnel is allowed (and expected) to report any potential issues they spot at any time (e.g. when working on other projects or even when not on duty). hedno also receive reports from citizens about potential issues. needless to say that these reports do not use the internal naming scheme described earlier to provide location information. fig. 1. a view of greece with the case studied area (screenshot from google earth. map data: data sio, noaa, u.s. navy, nga, gebco. image landsat/copernicus). fig. 2. a closer view of the studied area with the mv distribution lines in green solid color (screenshot from google earth. map data: data sio, noaa, u.s. navy, nga, gebco. image landsat/copernicus, data ldeocolumbia, nsf, noaa). engineering, technology & applied science research vol. 12, no. 1, 2022, 8143-8150 8145 www.etasr.com pylarinos: using google my maps as a geospatial ticket management system for scheduling … d. network expansions and alterations the necs has to study and perform network expansions and alterations that are requested by network customers and land owners. this is because according to greek legislation (e.g. laws 1468/50, 1672/51, 2941/2001, 4001/2011), the dso is allowed to install mv and lv installations in private and public properties. however, contrary to the legislation in effect for transmission installations [24], no expropriation or easement is applied on the properties. thus, any land owner can receive a building permit without informing or consulting the dso, regardless of the existence of mv and lv on the property. after acquiring the permit, the land owner notifies the dso who is then required to alter the network in a fashion that would allow the safe construction (and continuing existence) of the building. land owners can also quote a variety of reasons (e.g. works that do not require specific permits) to request network alterations. connecting new customers to the grid may also demand extended works as there are no limitations regarding the distance/position etc. finally, necs receives guidelines from within the dso regarding standard desired upgrades, strategic expansions etc. the result of the above is that there is a constant flow of requests to the necs for network alterations and expansions. e. weaknesses and effects on scheduling 1) trying to cope with hard copy tickets as explained earlier, after receiving the tickets/notes, the necs has to schedule on-site visits and network studies, if needed, as a follow up. during scheduling, one has to consider the distance and routes between different locations, the nature and importance of each issue, general guidelines, deadlines etc. in an attempt to achieve this, hard copy tickets and notes were kept in different stacks related to their priority status and their general location. the personnel would then have to go through the stacks in an attempt to formalize a schedule. as new requests were received almost daily, this meant that the time consuming, and prone to errors process of going through the hard-copy stacks also had to be repeated almost daily. 2) multiple tickets and narrow data view a significant weakness in the scheme described above, is the inability to identify multiple tickets and/or requests on the same issue. hedno is currently equipped with different software to monitor the progress of studies and the finances/logistics of construction works but none of them can be used effectively for managing the prior stage (ticketmonitoring and assigning), i.e. they are not designed to keep track of tickets/requests that do not ultimately result to a study or construction work. the available software is also unfitting to provide a wider view of the data. instead, they are more oriented towards a case by case approach, i.e. they are rather useful when the user searches for a specific information but tend to be rather time consuming and not user friendly when the user tries to acquire a wider view of the data. simple queries can be submitted but the return time is significant and their functions are not easily (or at all) customized. a user often has to use multiple software, perform multiple queries, go through several entries and move between multiple screens to actually get the needed information. 3) naming scheme issues the naming approach for mv/lv transformers described in previous sections, suffers from the fact that toponyms may provide a rough idea of the approximate location of a given group and its proximity to other groups but not of the proximity of specific group members to others. this means that e.g. two transformers belonging in the same group may actually have a greater distance between them compared to the distance each of them has with neighboring substations belonging to different groups. the issue worsens if one considers that the overall shape of a group following a toponym is bound to be irregular. this means that even though e.g. group a may be closer to group b in general, and this can be understood by the respected toponyms, a specific transformer belonging to group a may actually be closer to a transformer from another group instead. a simple example is depicted in figure 3. fig. 3. a simple example of the traditional naming convention scheme. the image shows six different groups (a-e) of mv/lv transformers, with each group using the same toponym for all transformers in the group. group a is adjacent to groups b, c, e and f. however, the far right transformer of group a is closer to a transformer of group d than to any of the transformers in groups b, f and e. further, certain transformers within all groups are closer to transformers of adjacent groups than to transhormers in their own group. (screenshot from google earth, map data: google earth) 4) other issues other obvious issues caused by the lack of geospatial representation is not considering the actual routes between different points (a minor issue for distribution networks however compared to transmission systems [20]), having a lengthier learning curve for new personnel and being unable to easily correlate outside reports (e.g. when they use street addresses) with specific network works and components. iii. utlizing the available geospatial data during a process similar to the one described in [20], geospatial data (i.e. coordinates) for all mv/lv transformers as well as the route of mv lines had been acquired previously. these data could then be utilized to provide a geospatial representation of all tickets, studies and works that should engineering, technology & applied science research vol. 12, no. 1, 2022, 8143-8150 8146 www.etasr.com pylarinos: using google my maps as a geospatial ticket management system for scheduling … improve overall scheduling and, thus, productivity. however, a key goal that was set was that no additional cost (in terms of software, equipment, personnel and even additional training) should be required at any time. an approach similar to [20] was judged unsuitable due to the nature of the application and of the available data. free to use software such as google earth, maps.me and mantisbt previously used by the author in transmission applications [20, 25] were also found unsuitable. a ticketing system without a geospatial representation, such as mantisbt, could solve the multiple-ticketing issue but would do little to improve scheduling whereas geospatial representation software that had to function locally, such as google earth, was also found to be unsuitable as several different employees needed to have access to the information. thus, it was decided to use custom google maps (google my maps) [26] instead and try to work within its restrictions. a. restrictions and solutions google my maps enforces certain limitations to custom maps created by users. these are related to the number of layers, the number of points-of-interest (pois) per layer and per map, the size of imported files etc. also, unlike google earth, google my maps does not provide a pop-up function when two pois superimpose one on top of the other. regarding the discussed case study, the routes of mv lines had to be redrawn and different line sections or parts had to be united (e.g. at the bus of the high voltage substation or before and after a mv component) in order to follow the restrictions (figure 4). it should be noted however that the actual route of mv lines is not necessary for the system’s function and it is only added as a visual aid. the spreadsheet with all mv/lv transformers and their coordinates also had to be split into smaller spreadsheets to comply with google my maps restrictions. fig. 4. a printscreen from the custom map showing the mv lines layer (screenshot from google my maps, map data © 2021 by google maps). b. pois, custom icons and representation for the mv network, it was decided that one poi would be created for each ticket, even if the ticket referred to a line section (in such a case, the poi would be inserted in the approximate middle of the section). for the lv network, each ticket is assigned to the poi depicting the mv/lv transformer that feeds the corresponding circuit (one poi for all tickets fed by the same transformer). it was decided to import pois for all transformers in the map, even for the ones with no active tickets. this way, map editing would be easily conducted within google maps, the maps would present a better view of the network and they could also be used for navigation purposes. custom made icons were developed for the pois with different icons representing different types of issues and with different colors representing a different status and/or prioritization. examples of custom made icons and of map parts are depicted in table i and figure 5 respectively. table i. examples of custom made poi icons lv poi (lv/mv transformer) without active tickets lv poi with active ticket(s) (low priority) lv poi with active ticket(s) (at least one of high priority) lv poi with active ticket(s) (assigned) mv poi with active ticket(s) (low priority) mv poi with active ticket(s) (high priority) mv poi with active ticket(s) (assigned) mv poi with all tasks completed fig. 5. a simple example of how pois appear in th the custom maps (at a remote location). the image has been slightly edited to erase placenames (screenshot from google my maps, map data © 2021 by google maps). c. additional pois in general, additional icons can be created and used to depict different types of tickets, depending on the application. for example, in this case, tickets related to street addresses (and not feeding transformers) such as tickets related to the urban underground network and tickets reported by people outside the dso are depicted with different icons. to avoid overpopulating the map, such pois can be deleted when engineering, technology & applied science research vol. 12, no. 1, 2022, 8143-8150 8147 www.etasr.com pylarinos: using google my maps as a geospatial ticket management system for scheduling … completed or they can be merged with existing pois. for example, tickets regarding customer requests can be imported in different layers and when concluded, can be merged as a text comment in existing lv pois. iv. working with custom maps a. split into two maps it was decided to construct two custom made maps: one for onsite visits/studies (the so-called “studies map”) and one for construction (the so-called “constructions map”). this was done to comply with the internal structure of the necs and the overall organization scheme but also in order to avoid internal confusion and to avoid showing redundant data to employees (as different employees work in the respected subsections). b. create new pois, edit existing pois, monitor past tickets in order for pois to have the desired number of metadata categories, they were created by importing spreadsheets to the custom maps. new pois however can then be created from within google my maps and inherit the structure of a given group. each poi in a certain group was equipped with several metadata fields (description, comments, alphanumeric codes, styling etc). using the styling option, a user can link the appearance of a poi with a certain metadata field and just edit this field to alter the way the poi appears (figure 6). by editing a poi’s metadata, the user can also move a ticket’s description/number from an active field to an inactive one. it should be noted that the built-in search function considers all text within all fields. thus, the maps retain a list of past works/tickets, with all data being easily searchable and retrievable. this feature is then used to identify redundant or overlapping tickets. c. removing duplicates the first group of tickets to be inserted into the studies map was consisted of 489 tickets. 327 tickets out of the 489 were part of the 2021 yearly inspection whereas the remaining 162 were low-priority tickets left over from previous years (17 tickets from 2018, 79 tickets from 2019 and 67 tickets 2020). a total of 33 tickets were removed as duplicates. 14 of these, were tickets that were identical with other tickets from the same yearly inspection whereas 19 were identical with tickets from previous years. an additional 13 were tickets referring to issues that had been solved since (studied or declined) without reaching the construction stage. an additional 4 tickets were found to be identical with works in the construction stage (and map). thus, through the process of entering the data in the two maps, the number of tickets was reduced from 489 to 439. d. scheduling for scheduling, one has to consider the priority status, the location, the available routes, the proximity with other tickets and customer requests, the weather in each area etc. the user can see the geospatial representation of issues and click on pois (figure 6) to acquire more information in order to construct an optimal working schedule. figure 7 shows a part of the map in an urban location (an area with a significantly larger network and issue density compared to figure 5). an important additional function is that tthe search function can be employed to identify all the pois that fall under the same mv line (or subsection) as shown in figure 8. this way the user can also consider electrical connections when scheduling works (e.g. a construction work at a certain section of a mv line can be combined with works at the lv circuits of mv/lv transformers that are fed by this mv line section). this also means that depicting the actual lines is of no particular importance for this system’s functionality (provided that the correct and full data for each poi are used). fig. 6. an example of the metadata of a lv poi as shown in the custom maps. the user can simply edit the metadata by clicking the pencil icon in the bottom of the pop up window. the number (and name) of categories in the metadata correspond to the number (and names) of columns of the initial spreadsheet. (screenshot from google my maps, map data © 2021 by google maps). fig. 7. an example of an urban location as shown in the custom maps. the map has been manually edited to erase placenames. (screenshot from google my maps, map data © 2021 by google maps). engineering, technology & applied science research vol. 12, no. 1, 2022, 8143-8150 8148 www.etasr.com pylarinos: using google my maps as a geospatial ticket management system for scheduling … fig. 8. using the search function to see all the pois belonging to a certain mv line (a narrower search using a line subsection would return the pois in this specific subsection). the map has been manually edited to erase placenames. (screenshot from google my maps, map data © 2021 by google maps). v. results assessing (and documenting) the effect in productivity is not an easy task as there are a number of outside factors that may have an impact on the final results. the main question regarding this case study, is if the proposed scheme will help the necs cope with yearly inspection tickets faster (before the next yearly inspection and ideally within 6 months) while not causing any delays to any of its other works. so, one has to consider not only the trend regarding the inspection tickets but also the overall numbers. these should be considered not only in terms of their absolute value but also in terms of their total cost (as some tickets may require far more work than others) in order to acquire a correct view of the effect of the proposed approach. a. inspection tickets the first results regarding inspection tickets show a rather significant improvement as depicted in figure 9. a week after the application, a new group of 58 tickets (corresponding to a certain mv line section that had just been inspected) were submitted to the necs increasing the total number of initial tickets to 497. considering the studies map, the actual initial number of active pois was 473 (24 of the 497 tickets were assigned to the same mv/lv transformers). this number fell to 371 after a month (a reduction of 102 active pois per month). this means that, with this rate, the number of active pois (and thus inspection tickets), should be expected to fall to zero within 5 months since the application of the custom maps (and within 3 months for each following year, as this group of tickets included 163 tickets from previous years). fig. 9. a summary of the results regarding inspection tickets and pois. b. number of studies and respective costs the number of studies and their total cost also increased significantly in the first month of the application of the proposed scheme. the average number of cases studied per month for the previous 36 months were 82 with an average total predicted cost per month of 376 thousand euros. the first month after the application of the proposed scheme, these numbers increased to 108 cases studied with a total cost of 414 thousand euros, an increase of 31.71% and 10.11% respectively. in terms of construction, the average number of constructed studies for the past 36 months was 74 and the average total final cost per month was 133 thousand euros. these numbers also increased the first month of the application of the proposed scheme to a total of 96 constructed studies with a total cost of 190 thousand euros, an increase of 29.73% and 42.86% respectively. it should be stated that the constructed studies of each month are not necessarily the same studies studied within this month or even the month before. apart from this, the gap between the predicted costs and the actual final costs should be largely attributed to the bidding procedure followed in greece (the cost of public works is generally calculated using standard prices whereas outside contractors bid by proposing discount rates on the standard prices and the works are assigned to the bidder offering the largest discount). a summary of the results is shown in table ii. table ii. number of studies and costs (before and after) monthly average (past 36 months) after 1 month with custom maps +/(%) cases studied 82 108 +26 (+31.71%) predicted cost of studies (rounded) 376,000 € 414,000 € +38,000 € (+10.11%) constructed studies 74 96 +22 (+29.73%) actual cost of constructed studies (rounded) 133,000 € 190,000 € +57,000 € (+42.86%) vi. discussion the initial results presented in the previous section show a significant improvement in all fronts. however, there are several limitations regarding this approach that should be stated. first of all, there is no easy way to extract the pois and edit their structure (e.g. to a spreadsheet), as only kmz and kml exportation is supported. this means that to add an extra category in the metadata of pois or to change the name of a metadata category, one has to actually work with the exported kml/kmz files, which requires specialized software and/or knowledge. performing any type of statistical or meta-analysis is also an issue. backing up is also not user-friendly as the user can either extract the data in kml/kmz files or save a copy of the entire map. neither option is suitable to monitor the progress of works in the long term. saving copies of the maps does not allow easy comparisons between them. reimporting a previously exported kml/kmz file as a new layer to an existing map could solve this but the limit to the number of layers per map and the limit to the size of kml/kmz files to be imported, means that the user would eventually have to extract and engineering, technology & applied science research vol. 12, no. 1, 2022, 8143-8150 8149 www.etasr.com pylarinos: using google my maps as a geospatial ticket management system for scheduling … reimport one kml/kmz file per layer, which is rather time consuming and would result to a vast number of locally kept files. another significant disadvantage is that google my maps is a rather unforgiving application with limited “undo” capabilities, which means that a human error is not easily spotted or fixed. finally, it should be noted that although the custom maps are easily viewed by multiple users, a refresh of the web page is needed to acquire the latest edition of the map. so, a no-simultaneous editing policy is required to avoid overlapping between different users. on the other hand, if the map developer maintains a strategy that considers all limitations (both of the software and of a specific case study), it is possible to produce a scheme with significantly more pros than cons. google my maps is currently a free application that is designed for the ordinary user, which means that no extra software, staff or specialized training of any kind is required to develop or maintain the maps. also, following the proposed approach, map editing is rather fast and requires minimum effort and time in terms of everyday work. it should be noted that although geospatial representations have been incorporated in various applications, the proposed approach differs in that it provides a geospatial ticket-managing approach which is cost-free, easy to implement/maintain, and does not require a detailed geospatial representation of the network. thus, it can be implemented in a variety of cases with similar characteristics, especially in the absence of a more sophisticated gis system or in case the installed gis system does not offer a ticket-management capability (which is often the case with specialized gis software). vii. conclusion this paper presents the approach followed by the patras area’s distribution network engineering & construction section in an attempt to acquire a free and user-friendly geospatial representation of works related to the power distribution network of the area. the presented scheme uses google my maps effectively as a geospatial ticket management system to monitor and schedule works. given the rather userfriendly nature of google maps, this scheme requires no additional training to develop or maintain. gathering the data also requires a minimum effort, as lv issues are assigned to the transformer that feeds the corresponding circuits and a single indication point is used for each mv issue. the bulk of points (i.e. the lv/mv transformers) are imported from available spreadsheets that are customized to suit the needs of the users. custom icons are used to depict pois of different categories and different colors to depict their condition or priority. adding new points and editing existing ones is easily conducted within google my maps. the main initial goal for this approach was to improve the speed with which the section coped with issues recorded during network inspections. initial results showed a significant improvement to this but at the same time also showed a significant increase in overall productivity, ranging from 10% to 42% depending on the aspect considered each time. this approach can easily be implemented by other utilities in the absence of a gis system and of detailed geospatial data of the network, as it is rather easy to implement and maintain, requires no additional cost at any level and offers a significant improvement to traditional hard copy based approaches or to ticket management systems that do not incorporate a geospatial representation. acknowledgment the author wishes to acknowledge the help of f. kotzampigikis from the department of electrical and computer engineering of the university of peloponnese, in the repetitive task of joining different line parts in order to comply with google my maps restrictions. the author also wishes to thank all hedno personnel within the patras area and within the department of peloponnese-epirus region for their cooperation and especially s. 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[26] "google my maps." https://www.google.com/intl/el/maps/about/ mymaps/ (accessed dec. 27, 2021). microsoft word etasr_v12_n2_pp8266-8272 engineering, technology & applied science research vol. 12, no. 2, 2022, 8266-8272 8266 www.etasr.com antar et al.: automatic number plate recognition of saudi license car plates automatic number plate recognition of saudi license car plates rayana antar department of computer science umm al-qura university jeddah, saudi arabia s44286241@st.uqu.edu.sa shimaa alghamdi department of computer science umm al-qura university makkah, saudi arabia s44286664@st.uqu.edu.sa johara alotaibi department of computer science umm al-qura university jeddah, saudi arabia s44285136@st.uqu.edu.sa manal alghamdi department of computer science umm al-qura university jeddah, saudi arabia maalghamdi@uqu.edu.sa received: 30 december 2021 | revised: 21 january 2022 | accepted: 25 january 2022 abstract-automatic license plate recognition has become a significant tool as a result of the development of smart cities. during the experiment studied in the current paper, 50 images were used to detect saudi car plates. after the preprocessing stage, the canny edge method to detect the car edges and different threshold techniques were used to reduce noise. horizontal projection was applied in the segmentation process to split the plate. after that, a masking technique was utilized to locate and separate the region of interest in the image. ocr was applied to the processed images to read the characters and numbers in english and arabic separately. then, combining the english and arabic text, after using the re-shaper for the arabic letters. finally, rendering of the results of text on images down the plate regions took place. the canny algorithm with projection technique with a proper preprocessing for images produces results with accuracy of 92.4% and 96% for arabic and english language respectively. keywords-computer vision; edge detection; segmentation; ocr; license plates; recognition system i. introduction traffic regulation and traffic violations are major issues. the flow of traffic is regulated by a network of cameras placed across the streets. since these cameras capture immediate images of cars, sophisticated software is required to recognize vehicles license plates [1]. in order to automatically record and recognize license plates, license plate recognition (lpr) or automatic number plate recognition (anpr) are extensively employed in entrance/exits, parking lots, road traffic, security control of restricted areas, and traffic surveillance [2]. many image processing applications have become more reliable and effective as a result of the usage of computer image processing. one of them is anpr. several recent studies detected vehicle's plates by applying different computer vision techniques. authors in [3] proposed a new security system to trace stolen vehicles by capturing the plate numbers. they used canny edge detection to detect the plate and applied the multi-layer perceptron artificial neural network model. the result was displayed as text. their proposed model achieved 97.8% accuracy in detecting multi-style arabic characters. authors in [4] proposed an identification system based on vehicle license and number plate recognition. the system's lnpr software employs a series of image processing algorithms to recognize number plates and identifies the vehicle from a database. the median filter was employed to minimize the image's visual noise. authors in [5] provided a sobel edge detection technique and morphological operation for anpr. the bounding box method was utilized to segment the numbers and letters on the plate. to distinguish numbers and characters after segmentation, a template matching technique was employed. authors in [6] introduced the iseecarrecognizer, an automated recognition system for reading vietnamese registration numbers using boundary line-based technique integrating the hough transform and the contour algorithm in the vlp detection module. for segmentation, horizontal and vertical projections were used to separate plate numbers. finally, an optical character recognition (ocr) module based on a hidden markov model detects the plate number. authors in [7] cropped 9021 license plate (lp) images of 5 different countries. image segmentation was used with a cnn to detect the language and the country of the lp with 99.5% accuracy. the secondary positioning (sp) model was utilized in [8]. a plate number localization technique was presented and evaluated using locally obtained data. the position of a plate number was determined by scanning the red light areas in hsv color space, and the plate number was localized by determining the plate number's vertical edge. a correction coefficient was generated between the templates and the testing pictures and template matching was used to recognize individual characters with a precision of about 75% and 70%. corresponding author: manal alghamdi engineering, technology & applied science research vol. 12, no. 2, 2022, 8266-8272 8267 www.etasr.com antar et al.: automatic number plate recognition of saudi license car plates italian-style automobile registration plate recognition was conducted in [9]. to determine the plate and character locations, images were acquired from a toll gate camera and were preprocessed via a quick and robust 1-d dft method. a multilayer neural network using the recently presented brls learning method was used to classify characters. authors in [10] designed a smart system for recognizing license plates, by applying canny edge detection to identify the lp location. the images were collected locally with a camera and the output was segmented into numbers and letters by the binary k-means algorithm, with 90% accuracy for english lp recognition. authors in [11] proposed an automatic iraqi car lp identification model by utilizing ocr. the model can extract the plates' features by dividing the numbers and words into sub-images and achieved 86.6% accuracy. authors in [12] proposed an improved automatic lp recognition system, in which 500 jordanian vehicle images were processed. in the detection stage, histogram vertical-edge analysis and potential region size estimation were performed. during the segmentation, the mismatched license plate images were derotated and the feature extraction results of the plate's letters reached 91.5% accuracy. the purpose of this paper is to collect a dataset of cars in the kingdom of saudi arabia (ksa) and to perform recognition of saudi car plates with the use of edge detection, segmentation, and contouring techniques. in addition, a preprocessing technique of the collected images is utilized. after that, ocr is utilized to extract letters and numbers from the processed images. the proposed approach aims to detect different car plate shapes and recognize the plate in both arabic and english texts. ii. methodology the basic tasks of the lpr system are to find the lp and to recognize the lp characters. number plate identification algorithms are classified into many categories depending on the different methodologies they use [13]. the following variables should be considered while detecting vehicle number plates: • the size of the car plate may vary in size from one image to another. • the location of the plate on the vehicle. • the background color of a plate might vary depending on the vehicle. • a plate might have a screw or motto or symbol, which could be regarded as a character. the flowchart of the proposed system is shown in figure 1. the following methodologies were used in lpr. a. license plate extraction the image processing stage is important for the enhancement of images [14]. resizing, scaling, and rotation were performed on the images. the input images were converted to grayscale, the rgb values were transformed from 24-bit onto 8-bit gray level values by adding or removing the alpha channel. the brightness of a grayscale picture pixel value varies from 0 to 255 [14]. moreover, to create a smoother image, the interpolation method was used in image processing. in picture interpolation, the rule is to utilize a source image as a reference to create a new or interpolated/scaled image [15]. the size of the produced image is determined by the specified interpolation proportion. when we execute the interpolation, we produce empty areas in the original image and fill them with the proper pixel values. as a result, the interpolation processes provide varied outcomes. we used the nearest neighbor approach to replace empty areas with the next nearby image pixels. fig. 1. recognition system flowchart. filters are primarily used to reduce the high frequencies within a picture [16]. the bilateral filter technique is used to preserve the edges of images. the basic idea is to include a photometric weight into a regular gaussian filter. this weight has the effect of canceling the spatial connections between pixels with significant intensity differences. suppose a photometric weight wp is incorporated as a factor of the spatial weight wi. the bilateral filter produces the picture f from the source image e as follows: ���� � ∑ � �| |���� ��������� ������ ��∈��∑ � �| |�������������� ���∈�� (1) where im represents a square window [-m,m] × [-m,m], wi is a decreasing symmetrical function of the distance kt from the center of im, and wp is decreasing the intensity of the function. the edge information of an image explains the target boundaries, the location inside the region of interest [17], and other significant details [18]. first derivatives, such as sobel, are used to detect the gradient by calculating the minimum and maximum in the first derivative input images [19], which are very sharp edges [20]. the canny edge, which is utilized in the experiment, is a multi-stage process used in edge detection. it has minimum error rate and reduces noise [22]. the algorithm involves the following steps: • converting the original image to grayscale. • applying gaussian blurring to remove high-frequency noise that may be detected as false edges. engineering, technology & applied science research vol. 12, no. 2, 2022, 8266-8272 8268 www.etasr.com antar et al.: automatic number plate recognition of saudi license car plates • compute the gradients along the x and y axes (gx1,gy) independently. • the final gradient over the whole image can be computed using the follow equation [20]: ���� +��� (2) where the gx and gy are the mask values of the operator [21] as shown in table i. table i. max values of gx and gy mask values of gx mask values of gy �−! " !−# " #−! " !$ � ! # !" " "−! −# −!$ • non-maximum suppression is conducted, where only pixels that constitute a local maximum in their neighborhood are considered, and the other pixels are set to zero. this results in a binarized image. • hysteresis thresholding follows, where the two threshold values are high and low threshold. all pixels with intensity values higher than the high threshold are picked as strong edges, and all intensity values lower than the low threshold are discarded. pixels with values between the two thresholds are only picked if they are connected to a strong edge. in practice, the picture's edges represent a small portion of the image information. in photos with less edge information, the mean gradient magnitude and standard deviation of most of the pixels are placed in a limited range [23]. because the gradient magnitude distribution of those non-edge pixels is concentrated, a good threshold can help pick edge pixels out. equation (3) is the threshold selection approach for photos with little edge information [24]: %& � %' /2 (3) where ti and th represent the low and the high threshold respectively [23]. after that, contours were used to detect lines and polygons. we utilized a contour with 4 points like the plates' shape, to find the shape from the edge information. b. license plate recognition after extracting the plate, the projection profile is generated independently for each axis. the projection profile approach is primarily used for text object segmentation within the text [25]. the horizontal projection feature is the picture's projection profile along the horizontal axis. for each row, the horizontal projection profile is determined as the sum of all column pixel values within the row [25]. to turn printed words of the preprocessed images into editable text, the ocr technology is used. image preprocessing and segmentation processes can have an impact on ocr accuracy [25]. character recognition necessitates the matching of the resulting binary format with the existing template. a matching track-sector matrix must be produced, defining the number of pixels in each region and the matrix's center [27], by calculating the radius via distance equations to identify the pixel with the greatest distance from the center as in (4): * � + �,� −,-��+��� − �-��� (4) the size of each track matrix is identified via calculating number of 1’s in each intersection of sector and track [27]. c. evaluation mertrics the evaluation metrics that were employed in this study to evaluate the performance are precision, recall, f1-score, and mean average precision (map) to measure the detector performance for english and arabic text separately. when the costs of false positives (fp) are substantial, precision is a suitable metric to use [29]. precision is defined as: ./0123245 � 6767�87 (5) when there is a large cost related to false negatives (fn), the recall measure is used to identify the optimum model, and it's calculated as: 901:;; � 676< => ?@ a=> 7<bc cdeb (6) for instance, a correct plate number (actual positive) passes the test but is predicted to be incorrect (i.e. fn). if the car was stolen, the cost of fn will be exceedingly significant. f1 is a function of precision and recall and is calculated as in (7). whenever we want to strike a balance among precision and recall, the f1-score achieve this balance. �1 � 2 x 7he@cbc<i � je@=>>7he@cbc<i�je@=>> (7) accuracy is the simplest basic performance metric, which is just a ratio of accurately outcome expectations to the total number of samples, and is calculated by: k11l/:1, � 67�6m67�87�6m�8m (8) iii. experiments this section contains a summary of the obtained data as well as information about saudi traffic laws and the automobile lp system. furthermore, the framework configuration is described in depth. d. dataset the dataset contains 50 images of various parked cars. an iphone 12 pro max camera was used to capture the images, which has a resolution of 1284×2778 pixels. the pictures were taken from different positions (front and back), different angles, various time intervals, and different light conditions. in addition, these images were captured inside/outside the parking as shown in figure 2, representing a sample of the collected dataset. the saudi car plates have two sizes (w×h), namely 30cm×16cm and 53cm×14cm. also, the lps combine arabic and english characters and numbers. the top part of the plate contains the arabic language (the top right has 3 arabic characters and the top left has 4 arabic numbers), whereas the bottom part contains 3 english characters at the right and 4 numbers at the left as shown in figure 3. engineering, technology & applied science research vol. 12, no. 2, 2022, 8266-8272 8269 www.etasr.com antar et al.: automatic number plate recognition of saudi license car plates fig. 2. dataset images that were collected during (a) the morning, (b) the afternoon, and (c) the night periods, and (d) various tilt angles. additionally, saudi arabia doesn't support all arabic letters for security purposes. for example, there are two similar letters, غ and ع. some criminals may take advantage of these and just remove the color from the dot and change the plate. another reason is the need to match the number of arabic letters with the number of english letters. figure 4 depicts the arabic and english characters that are used in saudi plates. fig. 3. some saudi license plates. fig. 4. approved letters in the saudi license plates. e. experimental setup the experiment was conducted on the jupyter program [28]. jupyter notebook is an open-source software that allows collaborative data science, used to organize, and execute models, which were written in python. the specification of the device on which these programs are installed is windows 10 operating system on an intel core (tm) i7-1065g7 cpu 1.50ghz with 16gb ram to test the algorithm's effectiveness. f. plate detection and localization to detect the plate location, proper scaling of images that helps reduce the number of pixels in the photos is performed. figure 5 depicts different interpolation methods for resizing. the interpolation nearest method was chosen. fig. 5. different interpolation techniques. after that, the images were convolved using gaussian blur to remove the high frequencies with a kernel size of 5×5. a bilateral filter technique transforms a filter into a bilateral picture. the intensity, noise and smoothing values were set to 60, 80, and 30 respectively, and the output is shown in figure 6. the parameters for intensity, noise and smoothing should be set very high because when using a small value, the other details appear. fig. 6. the output of the bilateral filter. in canny detection, the parameter was set very low in order to not detect other areas like floor and car details, so 20 was chosen for all images as shown in figure 7. we can observe that other details are shown (figure 8) if we set the parameter too high. morphological gradient was performed to find the outline of an object as shown in figure 9. moreover, the contours were used to detect within lines and polygons. we used contours with 4 points like the plates' shape. in addition, we utilized masking to separate the remaining edges to transfer engineering, technology & applied science research vol. 12, no. 2, 2022, 8266-8272 8270 www.etasr.com antar et al.: automatic number plate recognition of saudi license car plates the pattern. the plate should generate a blank mask. the final image is presented in figure 10. some of the images in the contouring process could not detect the complete plate, but only a part of it due to lighting, angles and texturing conditions. figure 11 shows the result of the detected plate. fig. 7. canny detector with low parameter value. fig. 8. canny detector with high parameter value. fig. 9. the output of the morphological gradient. fig. 10. detecting the care plate. fig. 11. displaced detection cases. g. plate number recognition before placing the images into the ocr model as inputs, the plate needs to be divided into rows, so horizontal projection is performed. figure 12 shows the result of the projection on the plate. fig. 12. horizontal projection. figure 13 represents the supervised segmentation by thresholding with different threshold values over the plate. the threshold value 3 was chosen since it does not show the nails. after the processing and noise reducing, the images are ready to be inserted into the ocr reader without training. we utilized the engine mode (–oem) of the ocr model. for the arabic language, a re-shaper is needed to show the letter correctly when rendering text on the images. the final render result is shown in figure 14. fig. 13. various threshold values on processed plates. engineering, technology & applied science research vol. 12, no. 2, 2022, 8266-8272 8271 www.etasr.com antar et al.: automatic number plate recognition of saudi license car plates fig. 14. rendering text result on the original image. h. comparison with related works according to the conducted review, some researchers used techniques like artificial neural networks (ann) and machine learning (ml) for the purpose of reading the characters and numbers in various languages. the findings are shown in a detailed comparison in table ii, whereas the authors in [3] achieved a high accuracy ratio for arabic plates with the use of the multi-layer perceptron (mlp) approach. table ii. result comparison reference techniques used dataset result [3] canny edge detection with mlp arabic 97.8% [8] ann english 75% [10] canny edge. k-means algorithm english 90% [9] multilayer ann english 90% [17] yolov2 detector with resnet5 to detect lps only 5 languages 99.5% table iii depicts the comparison of the results regarding plates in arabic. authors in [12] achieved 91.5% accuracy but our model obtained 92.4% on our collected dataset. regarding lps in english, table iv compares the results of similar works with our proposed method. our proposed method (consisting of the canny method, along with a projection approach and with the suitable image processing techniques that we applied), outperforms the others by achieving 96% accuracy. figures 15 and 16 exhibit the average precision result for lps in english and arabic respectively. table iii. arabic lp recognition result comparison reference techniques used dataset result [4] ocr by comparing with the records on a database iranian [11] ocr arabic 86.6% [12] canny edge detection & sobel edge detection arabic 91.5%. current study canny edge detection with horizontal projection ocr arabic 92.4% table iv. english lp recognition result comparison reference techniques used dataset result [5] sobel edge. morphological operation english [6] boundary line-based technique. contour algorithm. ocr english 92.85% current study canny edge detection with horizontal projection ocr english 96.0% fig. 15. average precision for english lps. fig. 16. average precision for arabic lps. iv. conclusion in the current paper, after the preprocessing stages, the canny edge approach was used to detect the plate edges, and multiple threshold strategies were employed to minimize the image noise. the plate was divided into rows using vertical projection during the segmentation process. after that, the masking technique was used to find and divide the image's regions of interest. the letters and numerals in english and arabic are read individually using ocr on the processed pictures. then, the re-shaper for the arabic characters was used, combining english and arabic text. finally, the effects of the text on images were rendered along with the plate areas. the canny method, along with a projection approach and suitable picture preparation, results in an accuracy of 92.4% for arabic and 96% for english texts on lps. future work will concern training the model in various conditions to increase the obtained accuracy results and increasing the dataset size. also, the model could be developed to recognize all types of cars' plates by using different digital cameras to get good results. in addition, training the model with natural language processing on the arabic letters to increase the speed of operation in real-time applications will be considered. engineering, technology & applied science research vol. 12, no. 2, 2022, 8266-8272 8272 www.etasr.com antar et al.: automatic number plate recognition of saudi license car plates acknowledgment we wish to thank the car owners who allowed us to take photos of their cars, the completion of our study would not have been possible without their support. references [1] n. o. yaseen, s. ganim saeed al-ali, and a. sengur, "development of new anpr dataset for automatic number plate detection and recognition in north of iraq," in 1st international informatics and software engineering conference, ankara, turkey, nov. 2019, pp. 1–6, https://doi.org/10.1109/ubmyk48245.2019.8965512. 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[29] b. ahmed, g. ali, a. hussain, a. baseer, and j. ahmed, "analysis of text feature extractors using deep learning on fake news," engineering, technology & applied science research, vol. 11, no. 2, pp. 7001–7005, apr. 2021, https://doi.org/10.48084/etasr.4069. microsoft word etasr_v11_n6_pp7836-7840 engineering, technology & applied science research vol. 11, no. 6, 2021, 7836-7840 7836 www.etasr.com saad & al-baghdadi: evaluation of rutting in conventional and rubberized asphalt mixes … evaluation of rutting in conventional and rubberized asphalt mixes using numerical modeling under repeated loads dhuha ameir saad department of civil engineering college of engineering university of baghdad baghdad, iraq d.saad1901m@coeng.uobaghdad.edu.iq hayder a. al-baghdadi department of civil engineering college of engineering university of baghdad baghdad, iraq baghdadi.hayder@coeng.uobaghdad.edu.iq abstract-this research aimed to predict the permanent deformation (rutting) in conventional and rubberized asphalt mixes under repeated load conditions using the finite element method (fem). a three-dimensional (3d) model was developed to simulate the wheel track testing (wtt) loading. the study was conducted using the abaqus/standard finite element software. the pavement slab was simulated using a nonlinear creep (time-hardening) model at 40°c. the responses of the viscoplastic model under the influence of the trapezoidal amplitude of moving wheel loadings were determined for different speeds and numbers of cycles. the results indicated that a wheel speed increase from 0.5km/h to 1.0km/h decreased the rut depth by about 22% and 24% in conventional and rubberized asphalt mixes, respectively. moreover, increasing the number of cycles from 7,500 (15,000 passes) to 15,000 (30,000 passes) under constant speed increased the rut depth by about 25% and 30% in conventional and rubberized asphalt mixes, respectively. furthermore, the addition of crumb rubber (cr) to the asphalt reduced its rut depth by 55% compared to conventional asphalt. keywords-rutting; finite element method; rubberized asphalt; repeated load; creep i. introduction rutting distress is one of the most common types of failure in flexible pavements. it is generated by accumulated permanent deformations in the wheel path as a result of repeated axle loads [1]. the rutting depth is an important factors to assess a pavement's condition [2]. pavements are complex systems that include several variables that affect their performance [3]. the behavior of non-linear asphalt mixtures is divided into two types: viscoelastic and viscoplastic, which are associated with recoverable and non-recoverable deformations, respectively [4, 5]. temperature is one of the most critical factors affecting the resistance of asphalt pavement to rutting. temperature variations allow the asphalt pavement to expand and contract, altering the asphalt mixture's characteristics and resulting in pavement deformation [6]. moreover, the increasing number of loading cycles affects the asphalt paving, as the rutting develops gradually and usually appears in the wheel tracks as a longitudinal drop with small side upheavals [7]. lower vehicle speed results in a longer load period and lower frequency, having a greater effect on permanent deformation compared to higher speeds for the same number of passes [8]. hot asphalt mixture at low temperatures and high loading speed are considered as a liquid plastic thermoplastic, while high temperatures and slow loading appear as a viscous liquid and elastic solid. this classic duality necessitates the improvement of the asphalt binder's performance to reduce cracking stresses at low temperatures and plastic deformations at high temperatures. one method to achieve the specified pavement performance standards is to use a polymer-modified asphalt binder [9]. it is therefore imperative to enhance the properties of the conventional asphalt content, as well as the advancement of successful asphalt mix design technology [10, 11]. overall, crumb rubber modifier (crm) additions appear to improve the maximal initial strength of conventional asphalt [12]. crm is a powder produced by crushing and grinding vehicle waste tires [13]. to anticipate permanent deformation, a variety of analytical methods are available such as multilayer elastic theory, finite difference method (fdm), and finite element method (fem) [14]. there are several advantages of using finite element analysis. these advantages include the modeling capabilities on the model geometry designs that are irregularly shaped or complex, various loading options, representation of an unlimited number of materials, unlimited boundary conditions, and finally a study of large deformations with nonlinear behavior of viscoplastic response [15]. fem depends on inputs obtained from the experimental data of bituminous materials. this study used the parameters adopted in [16]. the main objective of the current research was to study the effect of repeated wheel loading under the influence of different speeds and the number of loading cycles. to investigate the impact of the assumptions on rutting predictions, a wheel tracking test (wtt) was simulated in a 3d finite element model generated from rubberized and conventional asphalt mixtures. the abaqus software was utilized, as it includes a creep power-law model that simulates the viscoplastic behavior of the asphalt layer. corresponding author: dhuha ameir saad engineering, technology & applied science research vol. 11, no. 6, 2021, 7836-7840 7837 www.etasr.com saad & al-baghdadi: evaluation of rutting in conventional and rubberized asphalt mixes … ii. method the wtt was simulated as an illustration of how rutting forecasts are affected by repeated wheel loading assumptions at different speeds and numbers of passes. a three-dimensional fem model was constructed using flexible pavements made from conventional and rubberized asphalt mixtures. the asphalt layer was modeled as a viscoplastic substance using the creep power-law model (time-hardening) of the abaqus software. iii. creep power-law a constitutive model of viscoplastic deformation for flexible pavements developed in the abaqus software [18] was adopted, which, despite its simplicity, is used to solve complex problems [17]. the model is given by: ɛᵥ � ��ⁿ�ᵐ (1) where ɛᵥ is the creep strain rate, σ is the equivalent stress, t is the time of loading, and a, n, and m are the model's parameters. the parameters were obtained from laboratory tests by using the dynamic creep test [16] listed in table i. an important assumption in this analysis is the use of the creep power-law model to depict the nonlinear behavior of the asphalt concrete mixture. the hardening time assumption available in the abaqus library was used. creep is the time-dependent behavior of a solid material to deform under constant stress less than the yield stress of the material. all non-recoverable components must be included during asphalt mix permanent deformation analysis, particularly viscous deformation. there are three stages to typical nonlinear creep behavior: primary, secondary, and tertiary, as shown in figure 1. fig. 1. te three stages of plastic strain in repeated load creep testing. table i. law parameters of the creep model mix type temperature (°c) a(e-5) n m rubberized asphalt 40 4.2 1.5 -0.609 conventional asphalt 40 7.3 1.5 -0.570 iv. fem simulation this section describes the 3d finite element simulation of asphalt slab in a wtt, the employed wheel loading assumptions, and a synopsis of an analysis technique to determine the material properties associated with the presented constitutive model. fem has been proven to be suitable for analyzing the complex nonlinear behavior of composite pavement materials and has been effectively applied to flexible pavement performance analysis [19]. numerical simulation in pavement engineering is an efficient and effective way to verify the pavement's response and performance under moving vehicle loads. it is an easy, inexpensive, and time-reducing method, in addition to the versatility and flexibility required for wtt simulation [18]. abaqus was adopted to simulate the paving structure, as it is a powerful fem software that can easily solve complicated problems by using nonlinear analysis for the realization of the basic concept. the software includes a library with many finite elements and different behavior models of materials. abaqus can automatically select reasonable increments and logical defaults. a. geometry, boundary conditions, and meshing defining the physical model is the first step of fem. figure 1 presents the geometry of the studied wtt. its dimensions were 300×300×50mm in length, width, and depth respectively as shown in figure 2. these dimensions were chosen to correspond with the wtt specimens [16]. fig. 2. three-dimensional slab modeling. the model's boundary conditions were modeled by specimen circumstances in wtt. boundary conditions have a major influence on expected responses since they have a strong influence on the reaction of the form. the bottom surface of the bituminous wheel tracking test slab was assumed to be fixed and restrained in all directions to have a completely fixed end. the nodes at the bottom were unable to move horizontally or vertically, simulating the experimental conditions, while the upper surface of the sample was free to move. the side edges were constrained in the horizontal but not in the vertical direction, as shown in figure 3. the body was divided into 960 small, discrete finite elements (fes), which were all resolved at the same time for all simulations. these fes were connected to 1581 common shared nodes. the mesh was formed by combining nodes and elements, as shown in figure 4. the size of the element mesh has a significant impact on numerical accuracy, while the fine mesh size requires a longer time for model analysis. engineering, technology & applied science research vol. 11, no. 6, 2021, 7836-7840 7838 www.etasr.com saad & al-baghdadi: evaluation of rutting in conventional and rubberized asphalt mixes … fig. 3. boundary conditions, temperature distribution, and loading along the wheel path. fig. 4. mesh of 3d finite element model. b. employed material parameters the viscoplastic permanent deformation properties of the flexible pavement materials are usually determined using the dynamic creep test. abaqus is efficient in analyzing complex time rate-dependent and viscoplastic problems. the timehardening version of the power-law creep model is most suitable when the stress state remains essentially constant. temperature is an important factor affecting the corrosion resistance of all mixtures. all materials' model parameters used in the simulation, the elastic modulus, and poisson’s ratio were collected from laboratory results [16]. an elastic modulus of 3,800mpa and a poisson's ratio of 0.35 were also obtained from laboratory results. c. characterization of moving wheel load amplitude a 150kpa uniform vertical tire pressure was adopted in the simulation of a moving load. the moving load was applied along the test path with a length of 230±10mm. under the influence of a 40°c temperature applied to the entire model, the contact pressure will be equal to the tire pressure when the stiffness effect of the tire wall is neglected, according to the national cooperative highway research program (nchrp), where the load was simplified and assumed as a rectangular area and distributed evenly on the loading footprint of 50mm and 30mm in length and width respectively [20]. to simulate the gradual loading of the test wheel back and forth, the loading path was divided into 8 regions, depending on the length of the wheel path and the tire footprint, and then each region was having one-third of the wheel loads. this load was applied repeatedly overlapping to the wheel path. the repeated load was applied with trapezoidal amplitude and the loading time for one pass at 0.5km/h was 1.728s, as shown in figure 5. fig. 5. repeated loading amplitude of one pass. v. sensitivity analysis sensitivity analysis was carried out to study how the wheel speed and the number of loading cycles affect the reaction of flexible pavements, depending on the mixture type. a. wheel speed hot mix asphalt (hma) is a time-dependent material. as a result, wheel speed, which is proportional to loading duration, is likely to affect the reactivity of hma mixes. when it increases, loading time and rut depth decreases, and vice versa. this explains the rutting in the pavement in crossroads and other places where vehicles move slowly. rut depths predicted for 10,000 loading cycles (20,000 passes) at 0.5 and 1.0km/h wheel speeds are shown in figures 6 and 7 for rubberized and conventional asphalt pavements, respectively. the decrease in crack depth when increasing speed from 0.5km/h to 1.0km/h is about 22% and 24% in the conventional and rubberized mixture, respectively, as shown in figure 8. (a) (b) fig. 6. predicting rutting under repeated loading for rubberized asphalt pavement at 20,000 passes at different speeds, (a) 0.5km/h, (b) 1.0km/h. engineering, technology & applied science research vol. 11, no. 6, 2021, 7836-7840 7839 www.etasr.com saad & al-baghdadi: evaluation of rutting in conventional and rubberized asphalt mixes … (a) (b) fig. 7. predicting rutting under repeated loading for conventional asphalt pavement at 20,000 passes at different speeds, (a) 0.5km/h, (b) 1.0km/h. fig. 8. comparison of rutting under repeated load for conventional and rubberized asphalt pavements at 20,000 passes with different speeds. b. number of cycles the major cause of rutting in wheel paths can be correlated to wheel load repetitions. the accumulation of permanent deformation, which rises with the number of loading cycles, is the basic mechanism of rutting. larger loading stress causes more rutting at steady temperatures and speeds. figure 9 indicates that increasing the number of passes increases the rutting values of asphalt samples. on the other hand, rubber asphalt reduces rutting values compared to ordinary samples. vi. conclusion this paper presented a study on the permanent deformation of conventional and rubberized asphalt mixes based on repeated loads. a three-dimensional viscoplastic model was developed to simulate the wtt. the creep behavior of such mixtures was investigated based on creep power-law parameters. the following conclusions were obtained: (a) (b) fig. 9. rutting with different numbers of passes in the model of wtt, (a) rubberized asphalt, (b) conventional asphalt. • rubber crumbs improve the rutting performance of asphalt specimens, as they reduce the rut depth of the rubberized asphalt by 55%. • the results showed that the proposed numerical models portrait satisfactorily the rut behavior at various operating speeds and cycle numbers. • speed has a significant effect on rutting depth. when increasing the wheel speed from 0.5 to 1.0km/h (100%), the rut depth decreases about 22% in the rubberized and 24% in the conventional asphalt mixtures. • the number of cycles has a significant effect on the rutting depth. when the number of cycles increases from 7500 to 15000, the rut depth increases by about 25% in rubberized and 30% in conventional asphalt mixtures. acknowledgment sincere thanks to the staff at the university of baghdad, department of civil engineering, college of engineering, for their assistance in completing this research. references [1] m. saleh and m. ghorban ebrahimi, "finite element modeling of permanent deformation in the loaded wheel tracker test," transportation research record, vol. 2641, no. 1, pp. 94–102, jan. 2017, https://doi.org/10.3141/2641-12. [2] f. alzaidy and a. h. k. albayati, "a comparison between static and repeated load test to predict asphalt concrete rut depth," engineering, technology & applied science research, vol. 11, no. 4, pp. 7363–7369, aug. 2021, https://doi.org/10.48084/etasr.4236. [3] j. wu, j. liang, and s. adhikari, "dynamic response of concrete pavement structure with asphalt isolating layer under moving loads," journal of traffic and transportation engineering (english edition), vol. 1, no. 6, pp. 439–447, dec. 2014, https://doi.org/10.1016/s20957564(15)30294-4. engineering, technology & applied science research vol. 11, no. 6, 2021, 7836-7840 7840 www.etasr.com saad & al-baghdadi: evaluation of rutting in conventional and rubberized asphalt mixes … [4] harold l. von quintus, "performance prediction models in the superpace mix design system," strategic highway research program, washington, d.c., usa, shrp-a-699, aug. 1994. accessed: oct. 30, 2021. [online]. available: https://trid.trb.org/view/406369. [5] a. c. collop, a. (tom) scarpas, c. kasbergen, and a. de bondt, "development and finite element implementation of stress-dependent elastoviscoplastic constitutive model with damage for asphalt," transportation research record, vol. 1832, no. 1, pp. 96–104, jan. 2003, https://doi.org/10.3141/1832-12. [6] j. ji, l. chen, z. suo, y. xu, and y.-l. han, "effect of high temperature and heavy load on deformation resistance of dclr modified asphalt mixture," jiaotong yunshu gongcheng xuebao/journal of traffic and transportation engineering, vol. 19, pp. 1–8, feb. 2019. [7] m. m. pradhan, "permanent deformation characteristics of asphaltaggregate mixtures using varied materials and molding procedures with marshall method," ph.d. dissertation, montana state university, bozeman, mt, usa, 1995. [8] e. g. epifanio and l. gan, "validation of a pavement performance model for flexible pavements based on," m.s. thesis, chalmers university of technology, gothenburg, sweden, 2009. [9] i. a. mahmoud, "performance modification of saudi asphalt binders using sabic polymers," m.s. thesis, king fahd university of petroleum & minerals, dhahran, saudi arabia, 2002. [10] h. ziari, a. goli, and a. amini, "effect of crumb rubber modifier on the performance properties of rubberized binders," journal of materials in civil engineering, vol. 28, no. 12, dec. 2016, art. no. 04016156, https://doi.org/10.1061/(asce)mt.1943-5533.0001661. [11] a. amini, h. ziari, and a. goli, "investigating the performance of rubberised binders used in iran based on multiple stress creep recovery and performance grading systems," road materials and pavement design, vol. 19, no. 4, pp. 803–818, may 2018, https://doi.org/ 10.1080/14680629.2016.1274676. [12] k. jadidi, m. khalili, m. karakouzian, and s. amirkhanian, "toughness, tenacity and maximum initial strength of rubber modified asphalt binders," engineering, technology & applied science research, vol. 9, no. 1, pp. 3765–3769, feb. 2019, https://doi.org/10.48084/etasr.2526. [13] m. bekhiti, h. trouzine, and a. asroun, "properties of waste tire rubber powder," engineering, technology & applied science research, vol. 4, no. 4, pp. 669–672, aug. 2014, https://doi.org/10.48084/ etasr.439. [14] m. arabani, r. jamshidi, and m. sadeghnejad, "using of 2d finite element modeling to predict the glasphalt mixture rutting behavior," construction and building materials, vol. 68, pp. 183–191, oct. 2014, https://doi.org/10.1016/j.conbuildmat.2014.06.057. [15] j. hua, "finite element modeling and analysis of accelerated pavement testing devices and rutting phenomenon," ph.d. dissertation, purdue university, west lafayette, in, u.s., 2000. [16] b. bakhshi and m. arabani, "numerical evaluation of rutting in rubberized asphalt mixture using finite element modeling based on experimental viscoelastic properties," journal of materials in civil engineering, vol. 30, no. 6, jun. 2018, art. no. 04018088, https://doi.org/10.1061/(asce)mt.1943-5533.0002116. [17] t. d. white, j. e. haddock, a. j. t. hand, and h. fang, "contributions of pavement structural layers to rutting of hot mix asphalt pavements," transportation research board national research council, washington, d.c., usa, 468, 2002. accessed: oct. 31, 2021. [online]. available: https://trid.trb.org/view/710690. [18] "abaqus 6.11 scripting user’s manual," dassault systèmes simulia, 2011. [19] f. bai, x. yang, and g. zeng, "a stochastic viscoelastic–viscoplastic constitutive model and its application to crumb rubber modified asphalt mixtures," materials & design, vol. 89, pp. 802–809, jan. 2016, https://doi.org/10.1016/j.matdes.2015.10.040. [20] y. h. huang, pavement analysis and design. englewood cliffs, n.j., u.s.: prentice-hall, 1993. engineering, technology & applied science research vol. 7, no. 4, 2017, 1802-1810 1802 www.etasr.com razmyar and eslami: geotechnical characterization of soils in the eastern and western areas of tehran geotechnical characterization of soils in the eastern and western areas of tehran arash razmyar department of civil engineering amirkabir university of technology (tehran polytechnic) tehran, iran abolfazl eslami department of civil engineering amirkabir university of technology (tehran polytechnic) tehran, iran abstract—tehran is placed in a high seismic risk zone with specific natural hazards. the resources to deal effectively with a possible crisis are limited, so proper preparation is a necessity. therefore, the identification of geotechnical design building features based on local and environmental conditions plays a fundamental role in improving the construction quality. thus, given the increase of population in tehran, the concentration in certain areas and the need to better identify soil characteristic for safer construction in these areas, a zoning study is performed in this study. the results showed that soils in regions 4 and 22 belong to b tehran formation and are coarse. because the soil is coarse-grained in these areas, earthquake liquefaction is not expected. given the shear wave velocity in the 4 and 22 areas, the soil mass is characterized as dense or too dense. keywords-field testing; geotechnical testing; coarse grain; shear wave velocity; young's modulus i. introduction quaternary as an area of human activity and expansion of urban issues, industry and agriculture is increasingly considered and the quaternary role is considered in all fields, especially in natural hazards and retrofitting civil structures and most of all in the preservation and management of land and environment. determination of geological geotechnical characteristics of the deposits can be a suitable tool for basic information of the projects related to the earth's surface. with increasing population growth and rapid urbanization and pollution in the environment, the importance of zoning maps and municipal engineering geology has become clear. with the rapid growth of construction in cities and considering events such as earthquakes, neglecting geological and geotechnical engineering issues has brought many problems. the geophysical methods in addition to being incapable of providing complete geotechnical data, also face numerous disturbances in urban areas and it is impractical in urban centers [1]. aerial and satellite images also can't provide information. it seems that the best way to evaluate and interpret geotechnical properties of a place, especially in urban areas is the use of borehole data. often boreholes are drilled in cities for various purposes and mechanical soil tests are conducted at different depths of the earth that can provide useful information for geotechnical mapping and zoning. geotechnical investigations and zoning can be used to retrofit buildings and engineering structures and reduce risks. in [2], authors investigated geotechnical and seismic properties in zanjan using geotechnical and geophysical data and usage maps drawn in gis environments [2]. the geotechnical properties in arak using geotechnical data was investigated in [3] and gis maps were also drawn. in [4], authors investigated geotechnical zoning based on information obtained from boreholes in guwahati in the northeast of india. another study was based on information from 200 boreholes with a depth of 30 meters drilled in the city and considered the results of certain field tests such as lofran, spt, geophysical test results and experimental results to draw gis geotechnical zone maps [5]. in [6], authors investigated the geotechnical properties within pakistan's lahore using geotechnical and geophysical data. using information obtained from boreholes drilled in the city, they investigated geotechnical properties of different soils at various depths to be explored in the city and then using data from geotechnical boreholes zoning maps were drawn in terms of geotechnical parameters. in [7], authors examined and draw geotechnical maps for basre using geotechnical data and gis. using data obtained from 105 boreholes drilled in the southern city of basra geotechnical zoning maps were drawn. since tehran is in a high risk seismic zone and due to its specific natural hazards and the limited resources to deal effectively with a possible crisis, proper preparation is a necessity. construction rise in tehran has caused new buildings to have more floors and basements, increasing the risk factor. therefore, the identification of geotechnical design features for buildings based on local and environmental conditions plays a fundamental role in improving the quality of construction. thus, given the increase in the population of tehran in recent decades and the concentration of population in certain areas of tehran, especially in the eastern and western regions (zones 4 and 22) and the need for a better understanding of soil properties, for engineering and safe construction proposes, a zoning study is carried out in this paper. engineering, technology & applied science research vol. 7, no. 4, 2017, 1802-1810 1803 www.etasr.com razmyar and eslami: geotechnical characterization of soils in the eastern and western areas of tehran ii. material and methods a. used data in this study, data from geotechnical boreholes drilled by different companies in the considered area were used. in figures 1 and 2, the boreholes’ locations are shown. borehole names in zone 4 includes bh boreholes and p series boreholes and the t series boreholes. boreholes were named based on gathered data series. boreholes are drilled between the depths of 15 to 36 meters. in this study, the depth of the boreholes is considered in a way that allowable stress under the foundation for eastern region (zone 4) and western region (zone 22) could be considered. in zone 22, the names of these boreholes include ch series boreholes and h series and o series boreholes are shown in the map of their location. these boreholes have been drilled between the depths of 40 to 70 meters and in the northern part of the region due to mountainous and less height construction in area, so in this section drilled boreholes were less and many drilling is focused in the center. fig. 1. shows the position of the drill holes used in the area fig. 2. shows the position of the drill holes used in zone 4 b. data analysis the considered boreholes were drilled for investigations of construction projects in the area. data are analyzed using information from these boreholes. data indicates that materials at area 4 include gw, gm, gc, gp, sc, sw-sc, gp-gc, gw-gm, gp-gm, sp-sc, sw-sm, sm, gw-gc, sw, sp, sp-sm and particle-size analysis shows that the material in zone 4 is coarse and is a part of unit b of tehran. figures 3 and 4 show the percentage of each soil sample in the region, according to information obtained from boreholes. as shown, the gw soil has the highest percentage equal to 25 percent of fourth area's soil and soils sp-sm, sp, sw with the frequency of each approximately equal to 0/43 percent, the lowest frequency. in zone 22 the highest percentage is equal to 22/1 percent for gm soil and sw, gw-gc, sp, sp-sm with a frequency of approximately below 0/4 percent have minimum frequency. fig. 3. percentage of different soils in the zone 4 fig. 4. percentage of different soils in zone 22 c. exploration drilling in this study exploratory boreholes drilled in zones 4 and 22 of tehran to identify the layers is used. exploratory bore holes drilled with a diameter of 101, aim of drilling these boreholes in addition to identifying the undersurface, was inside borehole tests such as spt, cpt, permeability tests lofran and down hole geophysical study methods and obtaining undisturbed sample for laboratory tests such as particle-size analysis, atterberg limits, consolidation, direct shear and triaxial test. while drilling, exploratory borehole tests, including in situ inside borehole tests such as spt or engineering, technology & applied science research vol. 7, no. 4, 2017, 1802-1810 1804 www.etasr.com razmyar and eslami: geotechnical characterization of soils in the eastern and western areas of tehran cpt, lofran and geophysical down whole method are conducted. d. laboratory tests to complete the characterization studies and to obtain the technical and mechanical properties of subsurface materials different physical and mechanical tests were performed in the laboratory. the samples used for testing were disturbed samples of karbali and samples from spt sampler and shelby samples. tests conducted on samples were according to astm and aashto standards. the experiments included moisture content test, particle-size analysis, natural density and direct shear test as discussed below. 1) soil moisture content determination test this test is done based on the astm d2216 standard. soil moisture is available water in soil to the weight of its solid components. (%) w d w w w  in most soils natural moisture content is one of the important physical properties which characterizes soil behavior in comparison with atterberg limits [5]. 2) particle-size analysis this test is done based on the astm d421 standard. most natural soils consist of a mixture of gravel, sand, silt and clay, respectively. there are also soils which contain organic substances as well. soils can be classified according to their different properties in a way that they have the same engineering properties. particle-size analysis is based on particle size and percentage of grains in the soil mass and is the simplest soil test [5, 8, 9]. mechanical particle-size analysis is vibrating soil samples on a series of sieve that their size decreases respectively from top to bottom. this test is used for soils that their particle diameter is larger than 0/075 mm [5, 8, 9]. 3) atterberg limits based on the astm d4318 standard, other physical parameters such as soil liquid limit, plastic limit and plasticity index have important role in soil classification and behavior determination. the relationship between changes in volume due to moisture change is known as atterberg limits. liquid limit (ll) is minimum soil moisture that soil behaves as liquid and plastic limit (pl) is minimum soil moisture that then becomes plastic. the difference between them is the plasticity index (pi) that is one of the most important factors in classification of fine grained soils [4-7]. 4) direct shear test this test is done based on the astm d3080-72 standard. on all issues related to soil stability such as the design of foundations, retaining walls and embankments, having data about soil strength is essential. soil shear strength is the internal resistance of the soil surface that can withstand rupture and slip along each internal surface. the amount of soil shear strength is important for issues such as bearing capacity of foundations slope stability, and effective horizontal pressure on the earth retaining structures (retaining walls). this test is performed on disturbed samples from boreholes. to determine the mechanical properties and shear strength parameters for soil in drained condition (c,  ) what should be noted is that the adhesion (c) and internal friction angle (ø) of soil are not fixed properties and vary with different factors [5, 8, 9]. e. obtaining data bank in the geotechnical data bank, created in tehran for the regions 4 and 22 only a geotechnical perspective is considered on a conceptual level while some other perspectives, including geotechnical, geological and environmental each separately can be used as a part of or all of the bank in line with its objectives. for the geotechnical database, a relational database management system is used. relational database management systems are based on a common language and set of rules. in this study according to the database features of geotechnical database, information is classified and then analyzed. provided geotechnical database contains several important components. these components include:  borehole position (position and altitude)  drilling type (manual or machine)  groundwater level  depth  profile classification of soils at various depths  atterberg limits at different depths (including ll, pl and pi)  permeability at different depths  shear strength parameters c and φ in direct shear at different depths  elastic parameters at different depths in the loading page  nspt at different depths  n60 and n70 at different depths  soil density (in normal, dry and saturated) at different depths  moisture content at different depths in table i, the properties and the number of holes in each region are shown and in tables ii to iv, the number of tests and parameters used in this study are shown. table i. information about boreholes specifications. zone 4 zone 22 depth 55 30 lower than 15 35 40 15 to 25 meter 40 36 25 to 35 meter 50 24 35 to 50 mete 0 50 deeper than 50 180 180 total sum engineering, technology & applied science research vol. 7, no. 4, 2017, 1802-1810 1805 www.etasr.com razmyar and eslami: geotechnical characterization of soils in the eastern and western areas of tehran table ii. field information spt test lefran test plat load test direct shear test depth zone 4 zone 422 zone 4 zone 22 zone 4 zone 22 zone 4 zone 22 1260 1260 900 900 900 900 900 900 < 15 625 750 375 450 375 450 375 450 15-25 450 550 270 330 270 330 270 330 25-35 350 520 250 370 250 370 250 370 35-50 500 350 350 350 > 50 2685 3580 1795 2400 1795 2400 1795 2400 total sum table iii. laboratory information sieve analysis density water content aterberg limit depth zone 4 zone 22 zone 4 zone 22 zone 4 zone 22 zone 4 zone 22 1260 1260 900 900 900 900 900 900 < 15 625 750 375 450 375 450 375 450 15-25 450 550 270 330 270 330 270 330 25-35 350 520 250 370 250 370 250 370 35-50 500 350 350 350 > 50 2685 3580 1795 2400 1795 2400 1795 2400 total sum table iv. number of the borehole seismic information zone 4 zone 22 depth 900 900 < 15 375 450 15-25 270 330 25-35 250 370 35-50 350 > 50 1795 2400 total sum f. geotechnical zoning using arc gis software digital data prepared for city map, geology and topography of tehran provided by a mapping agency was used. for this study, a digital map of tehran is prepared and after the correction and the scaling, basic gis mapping is provided by collecting information from geotechnical boreholes at zones 4 and 22 and entering this data in arc gis software [1]. another positive feature of this research, is the ability to be updated in subsequent complementary studies and research. with the addition of geotechnical data in future the geotechnical parameters estimation can be presented even more accurately. g. analysis using spss software now it is necessary to specify the parameters of each soil in the area. thus, an analysis was carried out in spss for each parameter. the number of samples used in statistical tables (n), the difference between the maximum and minimum data (rang), the maximum data (max), minimum data (min), average data (mean), standard deviation (variance), the tilt disruption (skewness) and the elongation (kurtosis) were considered. iii. analysis a. atterberg zoning maps according to the information obtained from boreholes at different depths of zones 4 and 22, maps are drawn which include atterberg changes maps, plasticity limits changes and plasticity index to a depth of 10 meters. in the depths of 10 meters in zone 4 atterberg limits vary between 0 to 34% and the largest coverage area is about atterberg limits between 20 and 30 percent. also in zone 22 in depth of 10 meters deep the atterberg limit vary between 0 to 36% and the largest coverage area is about atterberg limits from 20 to 36 percent (figure 5 and figure 6). in figures 7 and 8, plasticity limits zoning maps are shown. in the depths of 10 meters in zone 4 the plasticity limit ranges between 0 to 25%. the largest portion of the area has a plasticity limit less than 10%. in zone 22, plasticity limits range between 0 to 24 % and the largest portion of the area has approximately zero plasticity, as well as 10 to 20 percent plasticity. in figures 9 and 10, plasticity index zoning maps are shown. in the depths of 10 meters in zone 4 plasticity index ranges between 0 to 13% and the largest coverage area has the plasticity index between 4 and 7%. in zone 22 plasticity index ranges between 0 to 13% and the largest coverage area is with the plasticity index of zero as well as 4 to 7 percent. b. density maps in figure 11 and figure 12 dry density zoning maps are shown. in the depths of 10 meters in the zone 4 dry density varies between 1.87 to 2.02 grams per cubic centimeter and maximum dry density in area varies between 1.90 to 1.98 grams per cubic centimeter is. in zone 22 dry density varies between 1.9 to 2.05 grams per cubic centimeter and maximum dry density in area varies between 1.95 to 2.0 grams per cubic centimeter. fig. 5. the atterberg limits zoning map at a depth of 10 meters of zone 4 engineering, technology & applied science research vol. 7, no. 4, 2017, 1802-1810 1806 www.etasr.com razmyar and eslami: geotechnical characterization of soils in the eastern and western areas of tehran fig. 6. atterberg limits zoning map at a depth of 10 meters of zone 22 fig. 7. zoning map of plasticity limit at a depth of 10 meters of zone 4 fig. 8. zoning map of the plasticity limit at a depth of 10 meters in zone 22 fig. 9. plasticity index zoning map at a depth of 10 meters in zone 4 fig. 10. plasticity index zoning map at a depth of 10 meters in zone 22 fig. 11. the dry density zoning map at a depth of 10 m of zone 4 fig. 12. the dry density zoning map at a depth of 10 meters from zone 22 wet density zoning maps is shown in figures 13 and 14. in the depths of 10 meters in zone 4, wet density varies between 1.96 to 2.13 grams per cubic centimeter and the largest coverage area has density between 0.2 to 1.2 grams per cubic centimeter. in zone 22 wet density ranges between 1.96 to 2.12 grams per cubic centimeter and the largest coverage area has wet density of 0.2 to 1.2 grams per cubic centimeter. engineering, technology & applied science research vol. 7, no. 4, 2017, 1802-1810 1807 www.etasr.com razmyar and eslami: geotechnical characterization of soils in the eastern and western areas of tehran fig. 13. wet density zoning map at a depth of 10 m of zone 4 fig. 14. wet density zoning map at a depth of 10 meters of zone 22 c. zoning map of the shear parameters figures 15 and 16 show the cohesion zoning maps. in the depths of 10 m of zone 4 cohesion varies between 0 and 0.06 mpa and maximum coverage area is between 0.01 to 0.03 mpa. in zone 22 cohesion varies between 0 to 0.07 mpa and the largest coverage area is between 0 to 0.03 mpa. in figures 17 and 18, the zoning maps of internal friction angle are shown. in the depths of 10 meters in zone 4 internal friction angle ranges between 30 and 35.8 degrees and maximum coverage area between 33 to 34 degrees. in zone 22 internal friction angle ranges between 31 to 35.5 degrees and large portion of area has friction angle from 33 to 35 degrees. fig. 15. cohesion zoning map at a depth of 10 meters in zone 4 fig. 16. cohesion zoning map at a depth of 10 meters in zone 22 fig. 17. internal friction angle zoning map at a depth of 10 m in zone 4 fig. 18. internal friction angle zoning map at a depth of 10 meters in zone 22 d. elasticity modulus zoning map these results have been obtained on the basis of information from plate load test, figures 19 and 20 show elasticity modulus zoning maps. in the depths of 10 meters in zone 4 elasticity modulus ranges between 250 and 650 mpa and the largest coverage area elasticity modulus is between 300 to 350 mpa. in zone 22 elasticity modulus ranges between 250 to 650 kilograms per square centimeter and the largest coverage area has elasticity modulus between 300 to 350 kilograms per square centimeter. engineering, technology & applied science research vol. 7, no. 4, 2017, 1802-1810 1808 www.etasr.com razmyar and eslami: geotechnical characterization of soils in the eastern and western areas of tehran fig. 19. elasticity modulus zoning map at a depth of 10 m of zone 4 fig. 20. elasticity modulus zoning map at a depth of 10 m of zone 22 poisson ratio zoning maps are shown in figure 21 and figure 22. poisson ratio varies between 0.3 and 0.35 at the depths of 10 meters in zone 4. poisson ratio varies between 0.3 and 0.35 in zone 22 and the largest covering area has a poisson ratio between 0.32 and 0.34. e. wave velocity zoning map longitudinal wave velocity zoning maps are shown in figure 23 and figure 24. in the depths of 10 meters in zone 4 longitudinal wave velocity varies between 700 to 1520 meters per second and the largest covering area has wave length of 900 to 1000 meters per second. in zone 22, longitudinal wave velocity varies between 330 to 1300 meters per second and the largest covering area has longitudinal wave velocity of 600 to 850 meters per second. fig. 21. poisson's ratio zoning map of a 10 meters depth in zone 4 fig. 22. poisson's ratio zoning map of a 10 meters depth in zone 22 fig. 23. longitudinal wave velocity zoning map of a 10 meters depth in zone 4 fig. 24. longitudinal wave velocity zoning map of a 10 meters depth in zone 22 shear wave velocity zoning maps is shown in figure 25 and figure 26. in the depths of 10 meters in zone 4 shear wave velocity ranges between 300 to 990 meters per second and maximum coverage area varies between 600 to 700 meters per second. in zone 22, shear wave velocity ranges between 230 and 800 meters per second and maximum coverage area is between 400 to 550 meters per second. f. spt zoning map one of the quickest and cheapest tests to determine the relative density of granular soils, especially sandy is using standard penetration test or simply be spt. with regard to the materials in this area and gravelly coarse aggregate all the engineering, technology & applied science research vol. 7, no. 4, 2017, 1802-1810 1809 www.etasr.com razmyar and eslami: geotechnical characterization of soils in the eastern and western areas of tehran results obtained in this area has shown nspt more than 50 hits and in many cases nspt value of 100 is reached. spt and nspt zoning maps are shown in figure 27 and figure 28. as shown, spt is more than 45 in this area and can be seen in most depths more than 50. based on spt results soil is dense to very dense and another reason for high spt is coarse grain of area. fig. 25. shear wave velocity zoning map of a 10 meters depth in zone 4 fig. 26. shear wave velocity zoning map of a 10 meters depth in zone 22 fig. 27. nspt zoning map of a 10 meters depth in zone 4 g. permeability zoning map geotechnical zoning maps is shown in figure 29 and figure 30. based on existing maps the permeability in zone 4 is between 4-10 and 2-10 cm per second. in zone 22 permeability is between 3-10 and 5-10 centimeters per second. fig. 28. nspt zoning map of a 10 meters depth in zone 22 fig. 29. permeability zoning map at a depth of 10 meters in zone 4 fig. 30. permeability zoning map at a depth of 10 meters in zone 22 iv. conclusion in this paper, iranian geotechnical data bank, analysis of engineering geology and geotechnical properties of quaternary engineering, technology & applied science research vol. 7, no. 4, 2017, 1802-1810 1810 www.etasr.com razmyar and eslami: geotechnical characterization of soils in the eastern and western areas of tehran deposits of west and east of tehran, statistical analysis of the data, gis maps of different geotechnical zoning system for zones 4 and 22 of tehran and basic knowledge of the properties of these regions are associated to optimize costs and time. examples of statistical results including values of minimum, maximum, mean, standard deviation, etc. are investigated in order to provide an overview of the regional characteristics of zones 4 and 22 of tehran. preparation of gis micro-zonation maps of zones 4 and 22 provides the possibility to estimate the geotechnical parameters in any given point of these maps. this system enables the user to simultaneously display and analyze the map and tabular data and the ability to provide high services in various fields. according to the soil of zones 4 and 22, it's seen that soil materials in the area of formation are coarse-grained type b. materials in zones 4 and 22 don’t have high liquid or plastic limits. according to low ll in coarse-grained soils inflation phenomena do not occur. due to the coarse-grained soils of these areas, earthquake liquefaction will not happen and plasticity index of soils is usually in the category of non-plastic to the low plastic. also, due to a friction angle between 30 and 37 degrees, coarse grain and relative density is considered medium to large. references [1] a. deg, intuitive concepts of arcgis and gis, publish cultural institute, university of north sustainable north, 1982 [2] h. alilahi, h. mojtabazade, “a review of studies on seismic geotechnical zoning and micro-zoning urban areas”, journal of novel applied sciences, vol. 4, no. 2, pp. 190-196, 2015 [3] m. karbasi ravari, “geotechnical city zoning relying on gis”, civil ninth international congress, isfahan, iran, 2002 [4] b. sharma, s. k. rahman, “use of gis based maps for preliminary assessment of subsoil of guwahati city”, journal of geoscience and environment protection, vol. 4, no. 5, pp. 105-106, 2016 [5] r. ajal louain, s. farrashi, “geotechnical city zoning using the gis”, fourth international conference on geotechnical and soil mechanics, tehran, iran, 1986 [6] m. ahmad, q. iqbal, f. a. khan, “profiling and zoning of geotechnical sub-soil data using geographic information system”, science international, vol. 25, no. 3, pp. 15-20, 2013 [7] k. s. namir, m. al-saoudi, m. kadhim, “digital geotechnical maps of basrah cityusing geographical information systems technique”, eng. & tech journal, vol. 31, no. 4, pp. 8-10, 2013 [8] w. n. s. wan-mohamad, a. n. abdul-ghani, “the use of geographic information system (gis) for geotechnical data processing and presentation”, procedia engineering, vol. 20, no. 1, pp. 397-406, 2011 [9] m. juárez-camarena, g. auvinet-guichard, e. méndez-sánchez, “geotechnical zoning of mexico valley subsoil”, ingeniería, investigación y tecnología, vol. 17, no. 3, pp. 297-308, 2016 engineering, technology & applied science research vol. 8, no. 2, 2018, 2805-2808 2805 www.etasr.com elboughdiri: concentration and temperature on extraction yield of phenolic compounds … effect of time, solvent-solid ratio, ethanol concentration and temperature on extraction yield of phenolic compounds from olive leaves noureddine elboughdiri chemical engineering department college of engineering university of hail saudi arabia and chemical engineering process department national school of engineering gabes university of gabes tunisia ghilaninouri@yahoo.fr abstract—this study aims to determine the factors affecting the process of extraction of phenolic compounds from olive leaves. two methods of extraction were used in this work and different tests were implemented with the aim of optimizing the recovery of phenolic compounds from olive leaves. the factors considered were the extraction time, temperature, solvent-solid ratio and the ethanol concentration. obtained results show that the recommended optimal conditions for the extraction of the total phenolic compounds from olive leaves were found at 40°c with a solvent/solid ratio of 30:1 and ethanol concentration of 80% (v/v) when the dried olive leaves are stored at -21°c at the beginning of the experiments. keywords-solvent extraction; total phenolics; olive leave; optimization i. introduction the olive leaves have been used in traditional medicine in some mediterranean regions. many recent studies indicate that olive leaves contain significant amounts of phenols possessing strong and high antioxidant capacity [1], whose concentration are near to those of olive oil. utilizations of olive leaves to produce health promoting products and food ingredients have great potential for pharmaceutical and food industries. there are many methods for the extraction of antioxidants from olive leaves, and solvent extraction is the most common one. the solvents frequently used for the extraction of phenolic compounds and derivatives from olive leaves are methanol or hexane and water mixtures. however, the toxicity of both solvents limits their industrial exploitation in order to obtain antioxidants for human use [2]. in this paper, it is aimed to define the optimum extraction conditions for phenolic compounds from dried olive leaves which allows the evaluation of different process variables such as solvent composition, temperature, time and solvent to solid ratio effects on total phenolic compound content in the extract. ii. literature review the extraction yield is strongly influenced by the solvent, due to the different polarity and different antioxidant potential of compounds extracted [3]. therefore, organic solvent of higher polarity is more effective in quantitative recovery for phenolic compounds. non-polar solvent and methanol were reported in many studies as a good solvent for extraction of phenolic compounds from the plants including olive leaves. however, it may lead to unacceptable levels of toxic residues in the final extracts. ethanol and water are most widely employed as solvents for safety and abundances reasons [3]. authors in [4] revealed that pure ethanol was not effective as a solvent for extraction of phenolic compounds from olive leaves, and water has important role in extraction process by increasing the diffusion of phenolic compounds through plant tissues. changes in ethanol concentration modify the physical properties of the solvent such as density, dynamic viscosity, and dielectric constant. solubility of compounds would also be modified by changes in the ethanol concentration, and this may influence the extraction of phenolics [5]. authors in [6] used 40%, 50% and 60% ethanol (v/v) in their study to investigate the effect of ethanol concentration on total phenolics yield. ethanol, methanol, ethyl acetate, boiling water, hexane, diethyl ether, chloroform and butanol were the main solvents used by researchers. of these solvents, aqueous methanol or ethanol was most commonly used and the concentration of solvent varied between 40% and 80% (v/v). extraction with 80% methanol (v/v) was reported as the most effective method for olive leaves polyphenols [7]. authors in [2] suggested 80% aqueous ethanol (v/v) was the optimum solvent for extraction of the targeted phenolics from olive leaf and it can be used as engineering, technology & applied science research vol. 8, no. 2, 2018, 2805-2808 2806 www.etasr.com elboughdiri: concentration and temperature on extraction yield of phenolic compounds … replacement of toxic solvents (methanol, diethyl ether, chloroform ) to obtain bioactive phenols for human use. the temperature has impact on solubility, diffusion coefficient and the stability of phenolic compounds. an increase in temperature and a decrease of viscosity significantly increase the diffusion rate. however, high temperature may degrade the phenolics [8]. a range of extraction temperatures and time were employed by researchers in the extraction of phenolic compounds from olive leaves. generally less extraction time is required with increasing temperature. when ethanol was used as a solvent, the extraction process took place either at room temperature or elevated temperatures of 40°c for 2 days under agitation where water bath was used to achieve required temperatures [9]. with boiling water, 8 to 29 minutes extraction time was reported [7]. this kind of extraction is purely a static process and easy to operate. many studies indicate that the solvent to solid ratio is normally expressed as the ratio of the volume of solvent (mm3) to the weight of extraction sample (gram) and considered an important factor in extraction of phenolic compounds from olive leaves. the solvent to solid ratio employed by the researchers for olive leaf extraction varied hugely from 4 to 100, but a ratio between 10 and 50 was mostly reported in the literature [9-10]. iii. materials and methods the olive leaves were collected from a region in north tunisia in august 2017. after collection, the leaves were transferred to the laboratory, the twigs were removed from leaves, and the fresh leaves were washed with tap water. the clean leaves were air dried at 20°c for 5 hours before continuing drying at 30°c in an incubator for 2 days [11]. before each extraction, the dried olive leaves were ground in a coffee grinder to become fine powder and stored n2 gas purged glass jars covered with aluminum foil at 0ºc until the extraction. analytical grade methanol and absolute ethanol was purchased from thermofisher scientific. distilled water was used for preparing a solution of ethanol/water 80:20 (v/v), 70:30 (v/v), 60:40 (v/v) and 50:50 (v/v). the prepared extracts were used for total phenols determination. colorimetric reaction was measured by uv spectrophotometry and the folin ciocalteau reagent was used as an oxidizing agent. dried olive leave samples were stored at -21°c, in order to ensure the minimum change or variability between samples used for extraction experiments and to avoid degradation of phenolic compounds. total phenolic contents of the controlled samples were monitored every 5 days. iv. results and discussion a. stability of dried olive leaves figure 1 shows the changes of the controlled sample values during the extraction experiments. we see that the total phenolic content remained constant. the result suggests that dried olive leaves are relatively stable when stored at -21°c. according to [12], there was no significant degradation of total phenolics during experimental period. 0 2 4 6 8 10 12 14 16 18 20 22 24 0 5 10 15 20 25 to ta l p he no lic s (m g c af fe ic ac id /g d ry m at te r) days fig. 1. variation of total phenolic content of dried olive leaves with storage time at -21°c b. the effect of extraction time on extraction yield figure 2 shows the effect of extraction time on total phenolics content obtained in olive leaves extracts. two extreme treatment conditions were tested in order to determine the optimum extraction time: the first treatment was carried out using 60% aqueous ethanol (v/v) at a solvent to solid ratio of 20 (w/w) and temperature of 20°c, and the second treatment was using 80% aqueous ethanol (v/v) at a solvent/solid ratio of 30 (w/w) and temperature of 40°c. significantly higher level of total phenolic content was observed after 20 hours duration for both treatments. comparing total phenolics obtained by the two treatments, it can be seen that significantly higher values of total phenolic compounds were found in the leave extract of the second treatment. it gives an indication that higher level of phenolic compounds may be recovered with increasing ethanol concentration, temperature and solvent to solid ratio. 0 5 10 15 20 25 30 35 10 20 30 40 50 to ta l p he no lic s (m g ca ffa ei c ac id / g dr y m at te r) extraction time (hours) treatment 1 treatment 2 fig. 2. changes of total phenolic content in olive leaves extracts vs extraction time for two different treatments engineering, technology & applied science research vol. 8, no. 2, 2018, 2805-2808 2807 www.etasr.com elboughdiri: concentration and temperature on extraction yield of phenolic compounds … c. the effect of extraction temperature on extraction yield the impact of three extraction temperatures (20°c, 30°c, 40°c) on extraction yield was investigated. these temperatures were frequently used in previous studies [9-13]. table i shows the effect of temperature on total phenolics extracted and indicates that the values were significantly affected by temperature. as can be seen in table i, total phenolic compounds extracted at 40°c are significantly higher than those extracted at 20°c and 30°c. table i. variation of total phenolics vs. extraction temperatures parameter value temperature (°c) 20 30 40 total phenolics (mg caffeic acid/g dry matter) 21 23 25 increasing temperature favored extraction by enhancing both the solubility and the diffusion coefficient from a solid matrix to a liquid matrix as mentioned earlier in the literature review [16]. as a consequence, much higher values of the total phenolics content are observed at 40°c than 20°c. the results confirm that extraction temperature influences greatly the extraction yield. increasing temperatures also affects the stability of phenolic compounds [17]. when extracting phenolic compounds from olive leaves at higher temperature, both effects need to be considered. d. the effect of solvent-solid ratio on extraction yield in this study, three different solvent-solid ratios (20%, 25% and 30%) were investigated. result analysis for total phenolics indicates that total phenolics are significantly affected by solvent-solid ratio. the distribution of mean values of total phenolics for 5 extractions is shown in table ii. the higher the solvent to solid ratio (30%), the higher the total phenolics obtained (24.5mg caffeic acid/g dry matter), suggesting that the solvent-solid ratio has a positive effect on the extraction yield. this is consistent with mass transfer principles. the driving force during mass transfer is the concentration gradient between the solid and the bulk of the liquid, which is greater, when, a higher solvent to solid ratio is used [5-14]. table ii. variation of total phenolics vs. solvent: solid ratio parameter value solvent: solid ratio (w/w) 20 25 30 total phenolics (mg caffeic acid/g dry matter) 22 23.5 24.5 e. the effect of ethanol concentration on extraction yield the influence of ethanol concentration on extraction yield was investigated. ethanol concentrations of 50%, 60%, 70% and 80% (v/v) were used in this study, which are the mostly reported concentrations in previous studies [9-15]. as shown in figure 3, there was no significant difference in total phenolics obtained using ethanol at four different concentrations. optimum ethanol concentration for olive leaves extraction reported in previously published studies varies. authors in [6] used 40%, 50% and 60% ethanol (v/v) to extract phenolic compounds from olive leaves and they discovered that the ethanol concentration had a biphasic effect, as an intermediate ethanol level (50%) appeared to provide the lowest yield. higher concentration of total phenolics was obtained in extracts using 40% and 60% ethanol (v/v). it was suggested that decreasing or increasing the ethanol concentration both favored extraction of phenolics from olive leaves. 10 12 14 16 18 20 22 24 50 60 70 80 to ta l p he no lic ss (m g ca ffe ic ac id /g d ry m at te r) ethanol concentraion (%) fig. 3. variation of total phenolics vs ethanol concentration authors in [18] suggested that 80% aqueous ethanol (v/v) was the optimum solvent for extraction of the targeted phenolics from olive leaves. v. conclusions olive leaves are a good and cheap source of phenolic compounds. the recovery of phenolic compounds from olive leaves could be achieved by solvent extraction. the solvent should be of low toxicity, economical and easily recycled by evaporation. in this study, the time, temperature, solvent to solid ratio and ethanol concentration were investigated to identify optimum extraction conditions. it was found that higher total phenolic content is obtained by increasing temperature and solvent to solid ratio. the results show that good recovery of phenolic compounds can be achieved using 80% ethanol (v/v) at 40°c and solvent to solid ratio of 30. the olive leaf extract is recommended to be stored under -21°c. three months storage at room temperature for liquid olive leaves extracts can lead to considerable loss of phenolic compounds, and thus prolonged storage should be avoided for liquid olive leaves extracts. olive leaves are a promising source for exploitation in terms of its total phenolic content. current study results could be the first step for the implementation of the process on a large scale, being an adequate starting point for further studies regarding the optimization of the continuous process, of major interest from an industrial point of view. references [1] m. h. aludatt, i. alli, k. ereifej, m. n. alhamad, a. alsaad, t. rababeh, “optimisation and characterisation of various extraction engineering, technology & applied science research vol. 8, no. 2, 2018, 2805-2808 2808 www.etasr.com elboughdiri: concentration and temperature on extraction yield of phenolic compounds … conditions of phenolic compounds and antioxidant activity in olive seeds”, natural product research, vol. 25, no. 9, pp. 876-889, 2011 [2] r. japon-lujan, j. m. luque-rodriguez, m. d. l. decastro, “multivariate optimisation of the microwave-assisted extraction of oleuropein and related biophenols from olive leaves”, analytical and bioanalytical chemistry, vol. 385, no. 4, pp. 753759, 2006 [3] e. b. seda, “the effects of time, temperature, solvent:solid ratio and solvent composition on extraction of total phenolic compound from dried olive (olea europaea l.) leaves”, the journal of food, vol. 35, no. 6, pp. 4-7, 2010 [4] e. altiok, d. baycin, o. bayraktar, s. ulku, “isolation of polyphenols from the extracts of olive leaves (olea europaea l.) by adsorption on silk fibroin”, separation and purification technology, vol. 62, no. 2, pp. 342-348, 2008 [5] j. e. cacace, g. mazza, “optimization of extraction of anthocyanins from black currants with aqueous ethanol”, journal of food science. vol. 68, no. 1, pp. 240-248, 2003 [6] s. mylonaki, e. kiassos, d. p. makris, p. kefalas, “optimisation of the extraction of olive (olea europaea) leaf phenolics using water/ethanolbased solvent systems and response surface methodology”, analytical and bioanalytical chemistry, vol. 392, no. 5, pp. 977-985, 2008 [7] n. s. a. malik, j. m. bradford, “recovery and stability of oleuropein and other phenolic compounds during extraction and processing of olive (olea europaea l.) leaves”, journal of food agriculture and environment, vol. 6, no. 2, pp. 8-13, 2008 [8] d. l. luthria, “influence of experimental conditions on the extraction of phenolic compounds from parsley (petroselinum crispum) flakes using a pressurized liquid extractor”, food chemistry, vol. 107, no. 2, pp. 745752, 2008 [9] k. kiritsakis, m. g. kontominas, c. kontogiorgis, d. hadjipavloulitina, a. moustakas, a. kiritsakis, “composition and antioxidant activity of olive leaf extracts from greek olive cultivars”, journal of the american oil chemists society, vol. 87, no. 4, pp. 369-376, 2010 [10] a. p. pereira, i. ferreira, f. marcelino, p. valentao, p. b. andrade, r. seabra, j. a. pereira, “phenolic compounds and antimicrobial activity of olive (olea europaea l. cv. cobrancosa) leaves”, molecules, vol. 12, no. 5, pp. 1153-1162, 2007 [11] o. h. lee, b. y. lee, j. lee, h. b. lee, j. y. son, c. s. park, y. c. kim, “assessment of phenolics-enriched extract and fractions of olive leaves and their antioxidant activities”, bioresource technology, vol. 100, no. 23, pp. 6107-6113, 2009 [12] i. mourtzinos, f. salta, k. yannakopoulou, a. chiou, v. t. karathanos, “encapsulation of olive leaf extract in beta-cyclodextrin”, journal of agricultural and food chemistry, vol. 55, no. 20, pp. 8088-8094, 2007 [13] r. japon-lujan, p. janeiro, m. d. l. decastro, “solid-liquid transfer of biophenols from olive leaves for the enrichment of edible oils by a dynamic ultrasound-assisted approach”, journal of agricultural and food chemistry, vol. 56, no. 16, pp. 7231-7235, 2008 [14] m. pinelo, m. rubilar, m. jerez, j. sineiro, m. j. nunez, “effect of solvent, temperature, and solvent-to-solid ratio on the total phenolic content and antiradical activity of extracts from different components of grape pomace”, journal of agricultural and food chemistry, vol. 53, no. 6, pp. 2111-2117, 2005 [15] h. jemai, m. bouaziz, i. fki, a. elfeki, s. sayadi, “hypolipidimic and antioxidant activities of oleuropein and its hydrolysis derivative-rich extracts from chemlali olive leaves”, chemico-biological interactions, vol. 176, no. 2-3, pp. 88-98, 2008 [16] t. v. gabbay alves, r. silva da costa, b. aliakbarian, a. a. casazza, p. perego, m. s. pinheiro arruda, j. o. carréra silva júnior, a. converti, r. m. ribeiro costa, “bioactive compounds and antioxidant potential for polyphenol-rich cocoa extract obtained by agroindustrial residue”, natural product research, vol. 11, no. 10, pp. 4-7, 2017 [17] x. u. cong-cong, b. wang, p. u. yi-qiong, t. jian-sheng, t. zhang, “advances in extraction and analysis of phenolic compounds from plant materials”, chinese journal of natural medicines, vol. 15, no. 10, pp. 721-731, 2017 [18] r. japon-lujan, l. decastro, “superheated liquid extraction of oleuropein and related biophenols from olive leaves”, journal of chromatography a, vol. 1136, no. 2, pp. 185191, 2006 engineering, technology & applied science research vol. 8, no. 2, 2018, 2709-2714 2709 www.etasr.com ramadan: interface structure and elements diffusion of as-cast and annealed ductile iron/stainless … interface structure and elements diffusion of as-cast and annealed ductile iron/stainless steel bimetal castings mohamed ramadan mechanical engineering department college of engineering university of hail saudi arabia and central metallurgical research and development institute (cmrdi) cairo, egypt mrnais3@yahoo.com abstract—bimetal casting is considered to a promising technique for the production of high performance function materials. heat treatment process for bimetal castings became an essential tool for improving interface structure and metallurgical diffusion bond. molten iron alloy with carbon equivalent of 4.40 is poured into sand mold cavities containing solid 304 stainless steel strips insert. specimens are heated to 7200c in an electrical heating furnace and holded at 720 0c for 60min and 180min. for as-cast specimens, a good coherent interface structure of ductile cast iron/304 stainless bimetal with four layers interfacial microstructure are obtained. low temperature annealing at 720oc has a significat effect on the interface layers structure, where, three layers of interface structure are obtained after 180min annealing time because of the complete dissolving of thin layer of ferrite and multi carbides (layer 2). low temperature annealing shows a significant effect on the diffusion of c and otherwise shows slightly effect on the diffusion of cr and ni. plearlite phase of layer 3 is trsformed to spheroidal shape instead of lamallar shape in as-cast bimetals by low tempeature annealing at 720oc. the percent of the performed spheroidal cementit increases by increasing anneaaling time. hardness of interface layers is changed by low temperauture annealing due to the significant carbon deffussion. keywords-annealing; interface; bimetal; stainless steel; ductile iron; composite i. introduction the demand for excellent physical, chemical and mechanical properties and for long life time of spare parts is still an issue in many industrial applications. a single material cannot satisfy all the high performance needs of long lifetime spare parts. in some applications, both high strength and high impact toughness are need. in other applications, wear resistance and corrosion resistance are needed. bimetallic materials have been considered as advanced functional materials for their unique physical and mechanical properties. referring to the species of application, the physical and mechanical properties of constituent metals should be considered for selecting high quality metals. the wettability, diffusion, melting temperature, thermal conductivity and thermal expansion of constituent metals should be suitable in order to bond with each other [1-4]. bimetallic materials can be fabricated by joining of both similar and dissimilar metals. the selection of working surface layer and base of bimetallic material usually are depending on the proposed application. for bimetal materials, the two metals play different roles. the exterior alloy may be resistant to corrosion or wear and the interior alloy is the one with better machining or toughness properties. nowadays, the bimetals have wide applications in fields such as radiators, reservoirs, bearings, pistons etc. [5– 10]. ductile cast irons (known as spheroidal graphite irons), are mainly heat treated to create certain matrix microstructures for specific mechanical properties that are not readily obtained in the as-cast conditions. matrix microstructures usually consist of ferrite or pearlite or combinations of both in its as-cast condition, that mainly depending on cast section size, cooling rate and/or alloy composition. if maximum ductility and good machinability are desired and high strength is not required, ductile iron castings are generally given a full ferritizing annealing process. the microstructure is thus converted to ferrite, and the excess carbon is deposited on the existing nodules [11]. fabrication of bimetal material that has both of higher impact toughness on one hand and corrosion resist (304 stainless steel) on the other, can serve in many industrial applications. however, the transition zone between metals has a great effect on the fabricated bimetal performance. previous researches [12–13] stated that the properties of bonding bimetal products are greatly affected by the properties of a very thin transition zone of the metallurgical bonding interface, which is mainly influenced by the element diffusion behavior through it [14–17]. the influence of low temperature annealing on interface structure of gray iron/stainless steel bimetallic castings was investigated in [18]. it was found that low engineering, technology & applied science research vol. 8, no. 2, 2018, 2709-2714 2710 www.etasr.com ramadan: interface structure and elements diffusion of as-cast and annealed ductile iron/stainless … temperature annealing at 760oc changed interface structures [18]. however, influence of low temperature annealing on interface structure of ductile iron/ stainless steel bimetal casting is still ambiguous. in current study, the effect of low temperature annealing at 720oc on interface structure and elements diffusion of ductile iron/stainless steel bimetal casting composites are investigated. ii. experimental methods a. materials the iron alloy is melted in a medium frequency induction furnace. the molten iron alloy is inculcated with fe–si alloy and spherodized with fe-si-mg alloy. οpen mold cavities of 25.4x25.4mm2 cross section and 250mm long were made in sand molds. 304 stainless steels strips of cross section of 5x 25.4mm width and 250mm long were grinded with 400 mesh emery papers and inserted in sand mold. molten iron alloy with carbon equivalent of 4.40 was poured into the cavities that contained solid 304 stainless steel strips inserts. the chemical composition of final fabricated bimetal ductile cast iron (di) and 304 stainless steels strips (304ss) are showing in table i. table i. chemical composition of ductile cast iron and 304ss strips, wt% c si mn p cr ni mg mo di 3.55 2.51 0.62 0.03 0.08 0.02 0.04 304ss 0.03 0.45 1.51 0.03 18.8 8.74 0.04 b. processing all samples were cut from the bottom parts of solidified bars. specimens of approximate dimensions 12.5x25.4x25.4 mm3 were cut for low temperature annealing heat treatment as well as microstructure examination and microhardness measurements. specimens were heated to 720oc in an electrical heating furnace with heating rate of 8.5oc/min. for ferritizing annealing and to study the effect of holding time at 720oc, specimens are dividied in to two groups. specimens are holded at 720oc for 60min heating time (group 1) and for 180 min heating time (group 2). all speciemens were subjected to controled furnace cooling to 290oc tempeartue with low cooling rate of 1.67oc/min. specimens were leter further subjected to furnace cooling to room tempeartue. the heating/cooling sequence is shown in figure 1. fig. 1. schematic illustration showing low temperature annealing heat treatment processes applied for bimetal castings. c. material testing and characterization specimens in both as-cast and heat treated conditions were grinded, polished and etched with a solution of 4% nital. microstructural observations were performed using an optical microscope connected with advanced digital camera. as-cast and heat treated microstructural changes and interface structures were observed with scanning electron microscope (sem) with energy dispersive x-ray spectrometry (eds). microhardness tests were performed using 0.25kgf loads. iii. results and discussion a. microstructure for higher strength with reasonable ductility, ductile iron region in bimetal ductile iron/304 stainless steel composite, annealing cycle can be varied to produce structures containing variety of percentages of mixed pearlite and ferrite matrices using reduced annealing times in the temperature range of 700°c to 720°c [11, 19]. figure 2 shows the microstructure of ductile iron region of bimetal casting for as-cast and heat traeted ductile iron for annealing times of 60min and 180min respectively. it is clear that the matrix structure of as-cast ductile iron contains higher percentage of pearlite phases that changed to ductile iron with higher feritte percentage by increasing the holding time. frrite percent increares with increasing annealing time due to dissociation of cemintite in pearlite phase to iron and carbon. fig. 2. microstructure of ductile iron region of bimetal casting for a) ascast, b) 60min annealing time, c) 180min annealing time. structure of interface region of as-cast and annealed bimetal casting are shown in figures 3 and 4. four layers interface in ductile iron/304 stainless steel bimetal casting are performed (see figure 3a)). from stainless steel side, layer1 (austenite+carbide), layer 2 (ferrite+carbides), layer 3 (pearlite+carbide) and layer 4 (pearlite+ledeburite) are formed due to the diffusion of c, cr and ni from higher concentration sides to lower concentration ones (see figure 5). unlike the interface of gray iron/stainless steel bimetal casting [16] that contains a martensite layer, the current interface of ductile iron/stainless steel bimetal casting contains a pearlite layer. low temperature annealing of ductile iron/304 stainless steel bimetal casting significantly effects on layer1, layer 2, and layer 3, for 60min. and 180min annealing time (see figure 3b), 3c) and figure 4 at higher magnification). layer 4 is not affected by low temperature annealing. the annealing processes of ductile cast iron are mainly depended on the amount and type of carbides in matrix structure. eutectic cementite in layer 4 needs a relatively higher temperature and longer time to be dissolved [11]. (a) (b) (c) engineering, technology & applied science research vol. 8, no. 2, 2018, 2709-2714 2711 www.etasr.com ramadan: interface structure and elements diffusion of as-cast and annealed ductile iron/stainless … a) c) layer 1 layer 2 layer 3 layer 4 fig. 3. microstructure of interface region of bimetal casting for a) as-cast, b) 60min annealing time, c) 180min annealing time. a) b) c) layer 2 partially dissolved l2 completely dissolved l2 spheroidized cementite l3 fig. 4. differences in annealed interface microstructures: a) as-cast, b) 60min annealing time, c) 180min annealing time. layer 2 (ferrite+carbides) partially dissolved and changed to discontinuous layer after 60min annealing time (see figure 4). by increasing the annealing time to 180min, layer 2 completely dissolved. pearlite morphology in layer 3 changed to be of spheroidal shape instead of the lamellar one that was presented in as-cast bimetal interface microstructure. subcritical anneal that convert pearlite to ferrite by heating and holding single metal ductile iron at 705°c to 720°c [11] does not have the same effect in bimetal casting layer 3. whereas, the current layer (layer 3) has a carbon content of 1.28%wt that considered as being hypereutectoid steel contains pearlite and some secondary cementite. referring to previous research work [20] and by applying 720°c annealing temperature and maximum 180min annealing time, the microstructure of the typical lamella pearlite that performed in as-cast bimetal microstructure will be changed to spheroidized cementite pearlite. the percent of lamella pearlite that changed to spheroidal often increases by increasing annealing time. low temperature annealing of ductile iron / 304 stainless steel does not show a significant effect on the microstructure of layer 4 (pearlite+ledeburite). eutectic cementite and/ or primary cementite usually need relatively higher temperatures and longer time to dissolve to ferrite and graphite. in order to heat treat ductile iron with carbides present, full annealing by heating and holding at 900°c to 925°c for minimum 2h and longer for heavier sections followed by controlled furnace cooling should be applied [11]. the structural changes occurring in the transition zone of ductile cast iron/stainless steel bimetals result from diffusion and redistribution of elements in the solid phase. it is well known that many reactions and processes important in the treatment of materials rely on the transfer of mass within a specific solid or from a liquid or another solid phase. the diffusion is a material transport by atomic motion. figure 6 shows the interface of c, cr and ni distribution for studied ascast and annealed ductile cast iron/stainless steel bimetal casting. it is clear that low temperature annealing at 720oc has a significant effect on carbon diffusion in the transition zone between ductile cast iron and 304 stainless steel bimetal casting. by increasing annealing time from 60 to 180mins the diffusion rate of carbon from ductile cast iron side to 304 stainless steel side increases. on the other hand, the low temperature annealing does not show a significant effect on the diffusion of cr and ni from stainless steel side to ductile iron side. there are two models for atomic motion in metallic materials. one mechanism involves the interchange of an atom from a normal lattice position to an adjacent vacant lattice site or vacancy and the other (model of diffusion) involves atoms that migrate from an interstitial position to a neighboring one that is empty. this latter mechanism fits the inter diffusion of carbon, nitrogen, and oxygen, as they have atoms small enough to fit into the interstitial positions. this can explain the significant effect of low annealing temperature on carbon atom form ductile iron side to stainless steel side. layer 1 (austenite+carbide) in 304 stainless steel microstructure of bimetal casting for as-cast and low temperature annealing (720oc for 60 and 180min, furnace cooling) is shown in figure 7. it is clear that low temperature annealing has a significant effect on the structure and thickness of layer 1. like the previous research on gray iron/stainless steel [18, 21], layer 1 thickness increases by increasing annealing time. carbon interstitially diffused in austenite, which migrates from the (b) engineering, technology & applied science research vol. 8, no. 2, 2018, 2709-2714 2712 www.etasr.com ramadan: interface structure and elements diffusion of as-cast and annealed ductile iron/stainless … whole volume of  phase and after saturation to the grain boundaries and in connection with cr vacancy diffusion from near border grain areas, cr23c6 chromium carbides are achieved [21]. besides the presence of this border carbides, they occur in the central areas of austenite grains. layer 1 is easy to difine using nital etching metallographic specimens that appear explicitly in those areas due to decreasing of the corrosion resistance of containing cr23c6. b. hardness hardness of interface layers of as-cast and annealed ductile cast iron/stainless steel bimetal casting is shown in figure 8. it is clear that annealing at 720oc for 60 and 180min increases the hardness of layer 1 and decreases the hardness of layer 3 and layer 4. the relativelly high diffusion of c from ductile iron side to stainless steel side is the reason of these changes in hardeness measerments of bimetal interface. iv. conclusion casting and low temperature annealing heat treatment at 720oc of bimetallic castings of ductile cast iron and 304 stainless steel were investigated, which led to the following conclusions:  good coherent interfaces with multi-layers (4 layers) with different interfacial microstructure bimetal castings are produced.  three layers of interface structure are obtained after 180min annealing time due to the complete dissolving of the thin layer 2 (ferrite+multi carbides).  low temperature annealing shows a significant effect on the diffusion of c and slightly effect on the diffusion of cr and ni.  in layer 1, c (carbon) interstitially diffused in austenite in whole volume of  phase and after saturation migrates to the grain boundaries and in connection with chromium vacancy diffusion from near border grains areas.  plearlite phase of layer 3 for as-cast condition is transformed to spheroidal one by low tempeature annealing at 720oc. the percentage of spheroidal cementite increases by increasing the anneaaling time.  annealing at 720oc for both 60 and 180min increases the hardness of layer 1 and decreases the hardness of layer 3 and layer 4 due to the significant carbon deffussion . a) b) c) d) e) f) fig. 5. eds analysis for interface layers of as-cast ductile cast iron/stainless steel bimetal casting, a) as-cast interface microstructure, b), c), d), e) and f) are the point 1, 2, 3, 4 and 5 eds analyses respectively. (a) (b) (c) (d) (e) (f) engineering, technology & applied science research vol. 8, no. 2, 2018, 2709-2714 2713 www.etasr.com ramadan: interface structure and elements diffusion of as-cast and annealed ductile iron/stainless … -120 -100 -80 -60 -40 -20 0 20 40 60 80 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 interface line stainless steel ductile cast iron c ar b o n c o n te n t, w t% distance, m as-cast annealed for 60 min. annealed for 180 min. -120 -100 -80 -60 -40 -20 0 20 40 60 80 0 5 10 15 20 25 interface line sainless steel ductile cast iron c r co n te n t, w t% distance, m as-cast annealed for 60 min. annealed for 180 min. -120-100 -80 -60 -40 -20 0 20 40 60 80 0 2 4 6 8 10 interface line stainless steel ductile cast iron n i co n te nt , w t% distance, m ascast annealed for 60 min. annealed for 180 min a) b) c) fig. 6. interface c, cr and ni distribution for as-cast and annealed ductile cast iron/stainless steel bimetal casting; a) c%; b) cr% c) ni%. fig. 7. stainless steel region of bimetal casting for a) as-cast; b) 60min annealing time and 760oc annealing temperature and c) 180min annealing time and 760oc annealing temperature. fig. 8. hardness measurments of interface layers of as-cast, annealed for 60min and annealed for 180min bimetal casting. acknowledgement author would like to thank the technical staff of foundry technology laboratory of central metallurgical r&d institute, cmrdi, egypt, for their kind help in the sample preparation of this study. references [1] h. danesh manesh, a. karimi taheri, “bond strength and formability of an aluminum-clad steel sheet”, journal of alloys and compounds vol. 361, no. 1-2, pp. 138–143, 2003 [2] m. paramsothy, n. srikanth, m. gupta, “solidification processed mg/al bimetal macrocomposite: microstructure and mechanical properties”, journal of alloys and compounds, vol. 461, no. 1-2, pp. 200–208, 2008 [3] b. kurt, c. adnan, “interface structure of diffusion bonded duplex stainless steel and medium carbon steel couple”, materials characterization, vol. 60, no. 9, pp. 1035–1040, 2009 (a) (b) (c) a) b) c) engineering, technology & applied science research vol. 8, no. 2, 2018, 2709-2714 2714 www.etasr.com ramadan: interface structure and elements diffusion of as-cast and annealed ductile iron/stainless … [4] b. xiong, z. xu, q. yan, b. lu, c. cai, “effects of sic volume fraction and aluminum particulate size on interfacial reactions in sic nanoparticulate reinforced aluminum matrix composites”, journal of alloys and compounds, vol. 509, no. 4, pp. 6700–6704, 2011 [5] l. guobin, w. jianjun, l. xiangzhi, l. guiyun, “the properties and application of bi-metal hot-forging die”, journal of materials processing technology, vol. 75, no. 1-3, pp. 152–156, 1998 [6] l. mehnen, h. pfutzner, e. kaniusas, “magnetostrictive amorphous bimetal sensors”, journal of magnetism and magnetic materials, vol. 215–216, pp. 779–81, 2000 [7] j. nakano, y. miwa, t. tsukada, m. kikuchi, s. kita, y. nemoto, h. tsuji, s. jitsukawa, “characterization of 316l(n)-ig ss joint produced by hot isostatic pressing technique”, journal of nuclear materials, vol. 307-311, no. 2, pp. 1568–1572, 2002 [8] o. yilmaz, h. celik, “electrical and thermal properties of the interface at diffusion-bonded and soldered 304 stainless steel and copper bimetal”, journal of materials processing technology, vol. 141, no. 1, pp. 67–76, 2003 [9] b. v. krishna, p. venugopal, k. p. rao, “co-extrusion of dissimilar sintered p/m preforms—an explored route to produce bimetallic tubes”, materials science and engineering: a, vol. 407, no. 1-2, pp. 77–83, 2005 [10] m. simsir, l. cenk kumruoglu, a. ozer, “an investigation into stainless-steel/structural-alloy-steel bimetal produced by shell mould casting”, materials and design, vol. 30, no. 2, pp. 264–270, 2009 [11] asm, asm handbook, volume 4:heat treating, asm international, 1991 [12] x. gomez, j. echeberria, “microstructure and mechanical properties of carbon steel a210–superalloy sanicro 28 bimetallic tubes”, materials science and engineering: a, vol. 348, no. 1-2, pp. 180–191, 2003 [13] n. masahashi, s. watanabe, n. nomura, s. semboshi, s. hanada, “laminates based on an iron aluminide intermetallic alloy and a crmo steel”, intermetallics, vol. 13, no. 7, pp. 717–726, 2005 [14] l. y. sheng, f. yang, t. f. xi, c. lai, h. q. ye, “influence of heat treatment on interface of cu/al bimetal composite fabricated by cold rolling”, composites part b: engineering, vol. 42, no. 6, pp. 1468– 1473, 2011 [15] c. y. sun, l. li , m. w. fu, q. j. zhou, “element diffusion model of bimetallic hot deformation in metallurgical bonding process”, materials and design, vol. 94, pp. 433–443, 2016 [16] m. ramadan, “interface characterization of bimetallic casting with a 304 stainless steel surface layer and a gray cast iron base”, advanced materials research, vol. 1120-1121, pp. 993-998, 2015 [17] t. wrobel, “characterization of bimetallic castings with an austenitic working surface layer and an unalloyed cast steel base”, journal of materials engineering and performance, vol. 23, no. 5, pp. 1711–1717, 2014 [18] m. ramadan, k. m. hafez k. s. abdel halim, n. fathy, t. chiba, h. sato, y. watanabe, “influence of heat treatment on interface structure of stainless steel/gray iron bimetallic layered castings”, applied mechanics and materials, vol. 873, pp. 3-8, 2017 [19] asm, asm handbook, volume 15: casting, asm international, 1991 [20] m. ramadan, m.takita, h. nomura, n. el-bagoury, “semi-solid processing of ultrahigh-carbon steel castings”, materials science and engineering: a, vol. 430, no. 1-2, pp. 285–291, 2006 [21] t. wróbel, “bimetallic layered castings alloy steel–grey cast iron”, archives of materials science and engineering, vol. 48, no. 2, pp. 118125, 2011 engineering, technology & applied science research vol. 7, no. 4, 2017, 1843-1849 1843 www.etasr.com rajabi et al.: a numerical study of gas injection and caprock leakage from yort-e-shah aquifer in iran a numerical study of gas injection and caprock leakage from yort-e-shah aquifer in iran maysam rajabi faculty of mining and metallurgical engineering amirkabir university of technology tehran, iran hossein salari rad faculty of mining and metallurgical engineering amirkabir university of technology tehran, iran mohsen s. masoudian nottingham centre for geomechanics, university of nottingham university park, united kingdom abstract—in order to mitigate the adverse effects of global warming due to anthropogenic co2 emission into the atmosphere, geological sequestration of co2 into subsurface formations has been investigated by many studies over the last decade. however, selection of formations and sites for any field application is still open to debate. the most important properties of a formation suitable for carbon sequestration are those which impact the fluid flow processes. the injection or extraction of gas can change the pore pressure within the reservoir, which in turn results in redistribution of the stress field. these events may cause considerably leakage of the fluid into the surrounding geological formations or ground surface. the main objective of this paper is to evaluate the potential of yort-e-shah aquifer for co2 storage, through a series of analyses with a simplified numerical model. the numerical results suggest that the optimum injection pressure in yort-e-shah aquifer is about 15.51 mpa with a safety factor of about 1.7. the results of the fluid pressure and gas plume expansion are presented. also, an analysis was carried out for a case with leak through cap rock. when there is no leak, the pressure within the aquifer is stable, while on the other hand, the pressure in case of leakage is slightly smaller. in case of leakage, the pressure is lowest in the middle of the reservoir, mainly because the nodes at the middle of the aquifer are influenced by all the leakage points, while around the wellbore or near the end of gas plume, are affected less due to their longer distance to leakage points. keywords-numerical model; fluid flow; co2 sequestration; optimum gas pressure; leakage through cap rock i. introduction global warming has a direct effect on climate patterns and this includes the increasingly frequent occurrence of extreme weather events such as heat waves, floods, storms, droughts and bushfires [1,2]. the increase in the global surface temperature from 1956 to 2005 is 0.13 oc per decade and eleven of the twelve years between 1995 and 2006 rank among the twelve warmest years since 1850 [3, 4]. scientists have suggested several options through which the amount of greenhouse gas emissions into the atmosphere can be reduced. among these, geological sequestration of carbon dioxide has received a lot of attentions over the last decade [5, 6], and different formations may be suitable for co2 storage. the estimated capacity of co2 storage in geological formations are listed in table i, where it can be seen that saline aquifers offer the highest potential storage capacity. the feasibility of storage in aquifers has been extensively studied [7] and it has exhibited some technological and economic attractiveness. the main parameters in selecting an aquifer for co2 storages, are its size, porosity, permeability and depth [8, 9]. in addition, an overlying formation is required to cover the aquifer which provides an impermeable seal to prevent the leakage of gas into the atmosphere. the injected co2 stored in aquifer by a combination of three mechanisms, namely immobilization in traps, dissolution in water, and geochemical interaction with reservoir rocks. in order to assess the suitability of the reservoir for gas storage purposes, a great number of theoretical, numerical, and analytical approaches have been employed [1014] and strategies for site selection have been proposed [15]. since the first co2 injection into saline aquifer (in the 90s), many progresses have been made and many pilot and filed scale projects have been planned and/or are being undertaken. table i. global storage capacity for geological sequestration options reservoir type storage capacity (gt co2) lower estimate upper estimate oil and gas fields 675a 900a unmineable coal seams (ecbm) 3-15 200 deep saline formation 1000 uncertain,but possibly 10000 a these numbers would increase by 25% if undiscovered oil and gas were included in this assessment in iran, dating back at the 70s, different areas were studied to shortlist suitable locations. based on the results of the primary studies, the yort-e-shah region in varamin was chosen for further studies by the national iranian oil company [16]. therefore, yort-e-shah aquifer can be alternatively considered for gas storage. this paper provides the results of numerical simulations where the potential of yort-e-shah aquifer for carbon sequestration is investigated. in order to achieve this, a simplified numerical model was employed where the radial flow is considered around a single vertical wellbore. through a series of simulations the optimum injection pressure and the storage capacity of yort-e-shah aquifer is determined. also, an analysis is carried out for a case engineering, technology & applied science research vol. 7, no. 4, 2017, 1843-1849 1844 www.etasr.com rajabi et al.: a numerical study of gas injection and caprock leakage from yort-e-shah aquifer in iran with leaking through cap rock. it should be noted that the model taking into account the numerical study of co2 injection and leakage through caprock, has been modified and verified compared with the previous study [17, 18]. the results of this study, however, are advantageous to many projects involving gas injection into subsurface formations, enhanced oil and gas recovery. ii. geological studies of yort-e-shah aquifer in varamin yort-e-shah aquifer is in the form of an anticline and is located 70 kilometers southeast of tehran and 40 kilometers south of varamin. yort-e-shah anticline was formed in 4 stages by extension during middle alpine movements, then stagnation and reactivated extension by late middle alpine movements, and finally compressions by late alpine movements [16]. detailed geological studies of this aquifer, started in 1997, for the purpose of natural gas storage. the primary phase of the project carried out by establishing descriptive wellbores number 2 and 3 by kbb. then, sofregaz was responsible for drilling wells number 4 and 5, and also performed supplementary studies. from the geological point of view, there are three formations in the region as listed in table ii. the upper red formation is a sequence of sandstone, clay stone and anhydrite, below which qum formation contains sequences of anhydrite, gypsum and limestone. below qum formation, there is a volcanic formation. qum formation has shown promising properties for storage of gas, while the upper red formation has shown high potential to prevent gas leakage and is considered as a suitable cap rock, given its very low permeability and porosity measured from laboratory analysis, as listed in table iii [16]. iii. modeling in order to model and evaluate the capacity of storage in yort-e-shah aquifer, a simplified numerical model is employed. the model considers a vertical wellbore in the middle of the aquifer, through which gas can be injected. the gas plume, which is the only phase and the component, can flow in the radial and angular direction through the uniform thickness of the aquifer, while the cap rock provides a seal to the storage site. this ideal conditions are depicted in figure 1. table ii. properties of yort-e-shah geological formations upper depth in well no. 4 (m) upper depth in well no. 3 (m) upper depth in well no. 2 (m) geological sequence formation name 33 20.50 16 sequence of sandstone, clay stone and anhydrite upper red formation 948 1002.50 575.10 sequence of anhydrite, limestone and gypsum qum formation 1273 1396.8 804.9 porphyry andesite volcanic formation table iii. laboratory analysis of caprock sample number depth (m) brine permeability (m2) gas drive pressure (mpa) permeability(m2) 14v 571.45 7.007∙10-21 3.445 no flow 5.516 no flow 6.895 no flow 11.032 no flow 13.790 no flow 17.926 no flow 26.890 1.974∙10-23 20v 585.8 3.948∙10-21 3.445 no flow 5.516 no flow 6.895 no flow 11.032 no flow 13.790 no flow 17.926 no flow 26.890 no flow 29v 618.75 4.935∙10-20 3.445 no flow 5.516 no flow 6.895 no flow 11.032 no flow 13.790 no flow 17.926 no flow 26.890 <9.869∙10-23 39v 635.70 1.875∙10-20 3.445 no flow 5.516 no flow 6.895 no flow 11.032 no flow 13.790 no flow 17.926 no flow 26.890 <9.869∙10-23 fig. 1. idealized schematic illustration of gas storage in the aquifer. the outer periphery of the aquifer is impervious to gas flow, as is the underlying rock formation. there is an axial symmetry around the single vertical injection wellbore. the well is subject to a variable pressure which was known as function of time. the viscosity of the gas is assumed to be constant, while its density slightly increases with pressure, i.e. slightly compressible gas. it is also assumed that the flow of gas is an isothermal process, an assumption which is made in many of reservoir simulation works. in order to assess the conditions under which the imperfection of the cap rock seal leads to gas leakage from the reservoir, a leakage rate has also been employed. the leakage rate is assumed to only depend on the local pressure of the gas plume and its spatial position. to describe the mathematical foundation and governing equations for gas flow, we start with darcy’s law as below: r k p v r     (1) engineering, technology & applied science research vol. 7, no. 4, 2017, 1843-1849 1845 www.etasr.com rajabi et al.: a numerical study of gas injection and caprock leakage from yort-e-shah aquifer in iran k p v       (2) where p is local pressure in the gas plume, k is the intrinsic permeability of the aquifer, μ is gas viscosity, vr is superficial radial velocity component, νθ is superficial angular velocity component. the equation of continuity, taking into account radial and angular flows, accumulation due to density change and leakage through the cap rock, gives: t mv r rv rr              )( 1 ),( 1 (3) where ρ is the gas density, φis the porosity of the aquifer and t is the injection time. note that m is the leakage parameter that defines the mass flow rate of gas per unit surface area of cap rock per unit depth of the aquifer. in other words, the leakage rate has been added as a sink term into the flow equation. following [19], parameter m is defined as a function of gas pressure as below: ll ppppkm  ),( * (4) lppm  ,0 (5) where pl is the threshold pressure beyond which the leakage through cap rock occurs, and k* is a coefficient that defines how the leakage rate depends on the gas plume pressure. in other words, the leakage rate is dined as a piecewise function whose value is zero when the gas pressure is below the leakage threshold, and it is linearly related to the differential pressure across leakage, when the gas pressure is beyond the leakage threshold. the gas is considered to be slightly compressible and hence follows this simple equation: cp (6) where c is the rock compressibility. substituting darcy’s law into the equation of continuity yield the basic flow equation as below: t p kkc mp r p r p r p r p r p r p p                              2 22 2 2 2 2 2 1 (7) it is convenient to introduce the dimensionless flow equation, using the following non-dimensional variables: 0p p p  (8) 1 0 r tkp t   (9) 2 0 2 1 kcp rm m   (10) 1r r  (11) where, p0 is the initial uniform pressure throughout the aquifer, r1 is the radius of injection well and r2 is radius of gas plume within the aquifer. equation (7) will then become: t p m ppppppp p                            2 22 2 2 2 2 2 1  (12) equation (12) is a non-linear second-order partial differential equation that mathematically explain the transient diffusion of pressure within the radial and angular positions distance within the aquifer. this equation can be solved using a finite difference scheme. for the purpose of a more convenient finite difference solution, we can change the radial distance variable into the following logarithmic variable:       1 2ln r rr (13) the flow equation then becomes as follows: t p uq pp p r p r p p                         2 2 22 2 2  (14) where rmetrqq 2),,(   (15) reruu 2)(  (16) to simplify this relationship, equation (14) can be solved for one vertical half of the gas plume, i.e. in the semi-circular region. both the curved boundary at r=ln(r2/r1), i.e. the gas/water interface, and the meridian plane represented by θ=0 and θ=π will be effectively impervious to gas flow. an approximation to the solution of (14) and its associated initial and boundary conditions can be obtained by a finite difference technique. we introduce a series of grid points spaced uniformly by a dimensionless radial increment δr and an angular increment δθ. subscripts i and j may then be used to denote that grid point having coordinates r=iδr and θ=jδθ. details of this model are presented in [19]. in order to verify the numerical model, its results can be compared with the results of an analytical model. assuming an incompressible fluid is injected at constant rate, q, into a horizontal homogenous isotropic reservoir with an infinite extent and initial pressure of p0, through a vertical wellbore at its center, an analytical solution can be found following [6].              fff ff f r c tk r ei hk q ptrp    44 ),( 2 0 (17) where h is thickness of the aquifer and ei is the exponential integral function, which can also be defined for any positive y using ei, as below:     1 1 )()( dyy e yeiyei y (18) an example was analyzed by both the numerical and analytical solutions, and the pressure predictions exhibit perfect match, as depicted in figure 2. iv. results and discussion the main problem investigated in this study, is to determine the optimum injection pressure and time needed to fill the aquifer with gas. as such, the potential capacity of gas storage in the aquifer can be assessed. the optimum injection pressure engineering, technology & applied science research vol. 7, no. 4, 2017, 1843-1849 1846 www.etasr.com rajabi et al.: a numerical study of gas injection and caprock leakage from yort-e-shah aquifer in iran and time, can be estimated following the concept developed in [19]. in order to do that, the properties of yort-e-shah aquifer is used as an input for the numerical model, as listed in table iv. the case was then simulated for different gas injection pressures. for each case, the injection time required for the gas pressure within the aquifer to nearly reach the injection pressure is estimated. the injection pressure under which the shortest injection time, with suitable safety factor, was achieved considered to be the optimum injection pressure. this approach was employed for wellbores number 2 to 4 in yort-eshah aquifer. the results of these analyses are shown in table v. table iv. properties of yort-e-shah aquifer used in numerical simulation parameters symbol value units reference averaged porosity in wellbore no. 2 φf 0.086 [16, 20] averaged porosity in wellbore no. 3 φf 0.069 [21, 22] averaged porosity in wellbore no. 4 φf 0.08 [18, 23] averaged permeability in well wellbore no. 2 kf 1.59∙10 -15 m2 [16, 20] averaged permeability in wellbore no. 3 kf 5.05∙10 -15 m2 [21, 22] averaged permeability in wellbore no. 4 kf 2.44∙10 -15 m2 [18, 23] gas viscosity μf 1∙10-4 pa s [24] reference gas density 0f 955.3 kg/m3 from real gas equation of state initial reservoir pressure pi 9.7 mpa [21, 22] radius of the reservoir r0 500 m [21, 22] radius of the wellbore rw 0.13 m [21, 22] reservoir depth in wellbore no. 2 dr 804.9 m [21, 22] reservoir depth in wellbore no. 3 dr 1396.8 m [21, 22] reservoir depth in wellbore no. 4 dr 1273 m [18, 23] reservoir thickness wellbore no. 2 tr 229.8 m [21, 22] reservoir thickness in wellbore no. 3 tr 394.3 m [21, 22] reservoir thickness in wellbore no. 4 tr 325 m [18, 23] numerical time step δt 0.1 days table v. relationship between gas pressure and injection time well no. 4 injection time (day) well no. 3 injection time (day) well no. 2 injection time (day) injection pressure (mpa) 635 184 1195 13.448 623 165 1170 13.789 610 152 1145 14.478 595 145 1115 15.168 586 141 1090 15.513 612 175 1160 15.858 597 152 1120 16.547 585 145 1095 17.237 579 150 1095 18.616 555 140 1065 19.305 from the data presented in this table, it can be seen that increasing pressure generally leads to shorter injection time, regardless of injection well. to determine the optimum injection pressure, however, it is essential to consider the leakage threshold. the leakage threshold was assumed to be 27 mpa (according to the table iii). fig. 2. pressure profiles at different times predicted by the analytical solution and numerical simulation in order to reduce the risk of leakage a safety factor of 1.7 is chosen, based on which, the optimum gas injection pressure is determined to be 15.5 mpa. assuming no leakage through the cap rock, the simulations were repeated for each depth within the reservoir, considering the corresponding engineering, technology & applied science research vol. 7, no. 4, 2017, 1843-1849 1847 www.etasr.com rajabi et al.: a numerical study of gas injection and caprock leakage from yort-e-shah aquifer in iran permeability and porosity and an injection pressure of 15.5 mpa applied for 330 days. figures 3-5 depict the typical variations of gas pressure as a function of depth for the storage wells no. 2 to 4. it can be seen that for wellbore no. 4, the maximum gas pressure within the reservoir was achieved at a depth of about 1034 m. also, it can be seen that in the maximum pressure was achieved at a depth of 623 m and 1344m for wellbore no. 2 and wellbore no. 3, respectively. from the results given in figures 3-5, no relationship between depth, porosity, permeability and maximum injection pressure can be concluded, as this is mainly due to the variability of the reservoir. to study the effect of leakage through cap rock, on pressure distribution within the reservoir, a case was considered in which a cascade of leaking points contributed to the leakage (figure 6). in this case, injection was simulated at a depth of 1041.15 m in wellbore no. 4, while the leakage threshold was assumed to be pl=14.8 mpa and the leakage coefficient was considered to be k*=0.0047 kg/cu.m.day.pa. the same simulation was performed without leakage and the results are summarized in figure 7. the results for the case with leak are also summarized in figure 8. as expected, when there is no leak, the pressure within the aquifer is stable, while on the other hand, the pressure in case of leakage is slightly smaller. in case of leakage, the pressure is lowest in the middle of the reservoir, mainly because the nodes at the middle of the aquifer are influenced by all the leakage points, while around the wellbore or near the end of gas plume, are affected less due to their longer distance to leakage points. fig. 3. gas pressure, porosity and permeability as a function of depth at wellbore no. 2 fig. 4. gas pressure, porosity and permeability as a function of depth at wellbore no. 3 engineering, technology & applied science research vol. 7, no. 4, 2017, 1843-1849 1848 www.etasr.com rajabi et al.: a numerical study of gas injection and caprock leakage from yort-e-shah aquifer in iran fig. 5. gas pressure, porosity and permeability as a function of depth at wellbore no. 4 fig. 6. location of leak in the aquifer fig. 7. gas pressure within aquifer at depth of 1041.15 m in wellbore no. 4 (no leak) fig. 8. the gas pressure in depth 1041.15 m of wellbore no. 4(leaky condition) v. concluding remarks to reduce the adverse effects of global warming, geological sequestration has been suggested, which includes capturing and pumping anthropogenic the yort-e-shah aquifer near tehran, was investigated in this study as a potential candidate for gas storage. one of the main practical aspects for gas storage is to determine the optimum gas pressure and injection time. no particular relationship was found to connect the optimum injection pressure with the depth of the injection within the reservoir. the results of this study showed that an optimum pressure of about 15.5 mpa, provides a leakage safety factor of 1.7. a comparative analysis was also conducted to study the effect leakage on pressure distribution within the aquifer. the leakage, as expected, resulted to a lower pressure level within the aquifer. to determine the suitability of this site for gas storage or co2 sequestration, further studies are needed, including a more rigorous parametric study. in addition, more exploratory wellbores are needed to understand the extent of variability in the reservoir characteristics. in addition, to evaluating the leakage potential through cap rock, more comprehensive field and experimental investigations are required, where the hydro-mechanical properties of the cap rock are examined. the results of this preliminary study provide some useful first-hand estimation of the gas pressure distribution within the reservoir, with or without leakage potential. the model provided in this paper, can also be further engineering, technology & applied science research vol. 7, no. 4, 2017, 1843-1849 1849 www.etasr.com rajabi et al.: a numerical study of gas injection and caprock leakage from yort-e-shah aquifer in iran developed to include the geomechanical response of the reservoir to gas injection. references [1] j. hansen, d. johnson, a. lacis, s. lebedeff, p. lee, d. rind, g. russell, “climate impact of increasing atmospheric carbon dioxide”, science, vol. 213, no. 4511, pp. 957-966, 1981 [2] a. dai, “drought under global warming: a review”, wiley interdisciplinary reviews: climate change, vol. 2, no.1, pp. 45-65, 2011 [3] d. a. lashof, d. r. ahuja, “relative contributions of greenhouse gas emissions to global warming”, nature, vol. 344, no. 6266, pp. 529-531, 1990 [4] r. k. pachauri, a. reisinger, contribution of working groups i, ii and iii to the fourth assessment report of the intergovernmental panel on climate change (ipcc), geneva, 2005 [5] m. s. masoudian, “multiphysics of carbon dioxide sequestration in coalbeds: a review with a focus on geomechanical characteristics of coal”, journal of rock mechanics and geotechnical engineering, vol. 8, no. 1, pp. 93-112, 2016 [6] m. s. masoudian, d. airey, a. el-zein, “mechanical and flow behaviours and their interactions in coalbed geosequestration of co2”, geomechanics and geoengineering: an international journal, vol. 8, no. 4, pp. 229-243, 2013 [7] j. k. eccles, l. pratson, r. g. newell, r. b. jackson, “physical and economic potential of geological co2 storage in saline aquifers”, environmental science & technology, vol. 43, no. 6, pp. 1962-1969, 2009 [8] m. bentham, g. kirby, “co2 storage in saline aquifers”, oil & gas science and technology – revue d'ifp energies nouvelles, vol. 60, no. 3, pp. 559-567, 2005 [9] ipcc (intergovernmental panel on climate change), the ipcc special report on carbon dioxide capture and storage, cambridge: cambridge university press, 2005 [10] s. bachu, j. m. nordbotten, m. a. celia, “evaluation of the spread of acid gas plumes injected in deep saline aquifers in western canada as an analogue to co2 injection in continental sedimentary basins”, in proceedings of 7th icggct, vol. 1, 2005 [11] k. pruess, “on co2 fluid flow and heat transfer behavior in the subsurface following leakage from a geologic storage reservoir”, environmental geology, vol. 54, no. 8, pp. 1677-1686, 2008 [12] s. l. bryant, s. lakshminarasimhan, g. a. pope, “buoyancy-dominated multiphase flow and its impact on geological sequestration of co2”, spe journal, vol. 13, no. 4, pp. 447-454, 2006 [13] z. zhang, r. k. agarwal, “numerical simulation and optimization of co2 sequestration in saline aquifers for vertical and horizontal well injection”, computational geoscience, vol. 16, no. 4, pp. 891-899, 2012 [14] l. nghiem, p. sammon, j. grabenstetter, h.ohkuma, “modeling co2 storage in aquifers with a fully-coupled geochemical eos compositional simulator”, spe/doe symposium on improved oil recovery, tulsa, april 17–21, p. 51–67, 2004 [15] s. bachu, “sequestration of co2 in geological media in response to climate change: road map for site selection using the transform of the geological space into the co2 phase space”, energy conversion and management, vol. 43, no. 1, pp. 87-102, 2002 [16] d. powell, lab investigation of yort-e-shah aquifer: petrophysical core analysis study of exploration well no. 2, task report a10, vol. 3, kbb group, hannover, 1998 [17] m. rajabi, h. tavakoli, m. shafiei, “prediction of optimum gas pressure and injection time in underground gas storage reservoirs”, proceedings of 3rd iranian mining engineering conference, yazd, january 26–29, p. 72–79, 2010 [18] p. werner, drilling program for yort-e-shah well no. 4, task report a2.1, sofregaz group, paris, 2006 [19] e. brooks, j. ellis, g. grow, e. hedges, c. stout, t. walsh, new concepts in underground storage of natural gas, report po-50, university of michigan, ann arbor, 1966 [20] k. wiechart, lab investigation of yort-e-shah aquifer: petrophysical core analysis study of exploration well no. 2, task report a10, vol. 2, kbb group, hannover, 1998 [21] d. powell, lab investigation of yort-e-shah aquifer: petrophysical core analysis study of exploration well no. 3, task report a10, vol. 3, kbb group, hannover, 1999 [22] k. wiechart, lab investigation of yort-e-shah aquifer: petrophysical core analysis study of exploration well no. 3, task report a10, vol. 2, kbb group, hannover, 1999. [23] m.r. esfahani, e. kazemzadeh, j. vali, routine core analysis report for well no. 4 of yort-e-shah field, core research department, exploration & production research division, research institute of petroleum industry (ripi), tehran, 2006 [24] a. fenghour, w.a. wakeham, v. vesovic, “the viscosity of carbon dioxide”, journal of physical chemistry reference data, vol. 27, no. 1, pp. 31–44, 1998 microsoft word 7-707.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1075-1079 1075 www.etasr.com vadhi et al.: image fusion technique based on hadamard transform using hvs an image fusion technique based on hadamard transform and hvs radhika vadhi department of ece, university college of engineering, jntuk, kakinada, andhra pradesh, india. radhikav139@gmail.com veera swamy kilari department of ece, qis college of engineering and technology, ongole, andhra pradesh, india. kilarivs@yahoo.com s. srinivas kumar department of ece, university college of engineering, jntu, kakinada, andhra pradesh, india. samay_ssk2@yahoo.com abstract—the main endeavor of image fusion is to obtain an image that contains more visual quality information than any one of the source images. in general, the source images may be multi focus, multi modality, multi resolution, multi temporal, panchromatic, satellite images considered for fusion. this paper discusses image fusion using hadamard transform (ht). in this work, human visual system (hvs) is investigated for image fusion in the ht domain. the proposed fusion process contains three important parts, (1) divide source images into sub images / blocks and transform them into ht domain. (2) multiply transformed coefficients with hvs based weightage matrix of ht and select the highest value from them (3) fuse the corresponding block of selected coefficients from source images in to an empty image. the utility of hvs makes the coefficients more significant. the performance of the proposed method is analyzed and compared with discrete wavelet transform (dwt) based image fusion technique. implementation in ht domain is simple and time saving when compared with dwt. keywords-hadamard transform; ht; human visual system; hvs; discrete wavelet transform; dwt; image fusion i. introduction image fusion is a process of combining information from two or more source images of a scene in to a single composite image that is more informative and more suitable for visual perception or machine processing. the concept of image fusion has been used in a wide variety of applications like medicine, remote sensing, machine vision, automatic change detection, biometrics, robotics, microscopic vision etc. an image fusion algorithm [1-6] should require entire salient information contained in the input images. fusion process should not introduce any artifacts or inconsistencies which can distract images. image fusion must be reliable, robust, tolerant to noise or misregistrations. generally fusion algorithms can be categorized into spatial domain fusion and transform domain fusion. the spatial domain fusion algorithms can use the local spatial features such as mean, variance, gradient, spatial frequency, and local standard deviation. the spatial domain techniques are simple and less complex, but not robust. because of this, multi resolution transforms are used to represent the sharpness and edges of an image in the design of fusion algorithms. the transformed coefficients provide the information of an image that can be used to select the blocks from source images to the fusion image. wavelet transforms have been successfully used in fusion algorithms due to their advantages such as increased directional information and the absence of blocking artifacts that often occur in discrete cosine transforms (dct) and hadamard transform (ht). however, wavelet transform implementation takes more time and the process is more complex. a major problem with dwt is its shift variant nature caused by sub-sampling which occur at each level. a small shift in the input signal results in a completely different distribution of energy between dwt coefficients at different scales [16-21]. to overcome the shift variant problem, block based transforms are preferred. human visual system (hvs) is also used to suppress the blocking artifacts. hence, ht with hvs is explored for image fusion in this manuscript. hvs model is easy to adapt to the specified resolution for viewing. implementation of hvs models with block based transform is easy than multi-resolution transforms like dwt, curvelet, and contourlet. the elements of the basis vectors of the ht [7] take only the binary values ±1 and are, therefore, well suited for digital hardware implementations of image processing algorithms. hadamard transform offers a significant advantage in terms of a shorter processing time as the processing involves simple integer manipulation (compared to floating point processing with dct and dwt) and easier hardware implementation than any common transform techniques. so it is computationally less expensive than many other orthogonal transforms. this paper is organized as follows. the hvs model and design considerations are discussed in section ii. computation of 2d-ht and its inverse is discussed in section iii. the proposed fusion algorithm using hvs model is presented in section iv. the experimental results are given in section v and the conclusions in section vi. engineering, technology & applied science research vol. 6, no. 4, 2016, 1075-1079 1076 www.etasr.com vadhi et al.: image fusion technique based on hadamard transform using hvs ii. mathematical analysis a. human visual system the hvs has been investigated by several researchers [811]. the visual sensitivity and selectivity are the important requirements for the development of hvs. the hvs is based on the psychophysical process that relates psychological phenomena (luminance, contrast and brightness etc.) to physical phenomena (light sensitivity, spatial frequency and wavelength etc.) [9]. the hvs is complicated, as it is a nonlinear and spatial varying system. putting its multiple characteristics into a single equation, especially one that is linear, is not an easy task. the work in [8] may be first breakthrough to incorporate the hvs in image coding. hvs as a nonlinear point transformation followed by the modulation transfer function (mtf) is given by )1()))((exp()()( dfccfbafh  where, f is the radial frequency in cycles/degree of the visual angel subtended and a, b, c and d are constants. hvs model proposed in [15] is applied for generating the quantization table for image compression applications. this hvs model is a modified version of the one in [8] with a=2.2, b=0.192, c=0.114 and d=1.1 respectively. the mtf of hvs has been successfully applied to the optimal image half toning [9, 10]. the mtf as reported in [15] is )2( otherwise f; > v)(u,f if . 0.1 ),(114.0(exp(.),(114.0192.02.2 ),( 1.1                vufvuf vuw where (u,v) is radial spatial frequency in cycles/degree and f is the frequency of 8 cycles/degree at which the exponential peak. to implement this, it is necessary to convert discrete horizontal and vertical frequencies, {f (u), f (v)} into radial visual frequencies. for a symmetric printing grid, the horizontal and vertical discrete frequencies are periodic and given in terms of the dot pitch δ and the number of frequencies n by: )3( 1 )(, 1 )( n v vf n u uf       converting these to radial frequencies, and scaling the result to cycles/visual degree for a viewing distance (dis) in millimeters gives )4()()( 1 1 arcsin180 ),( 22 2 vfuf dis vuf     finally, to account for variations in visual mtf as a function of viewing angle, θ, these frequencies are normalized by an angular-dependent function, s(θ (u, v)), such that )5( )),(( ),( ),( vus vuf vuf    where, s (θ (u, v)) is given in [15] as: )6( 2 1 )),(4cos( 2 1 )),((         vuvus b. hadamard transform in series form the transform pair becomes forward hadamard transform for a 2-d signal f(m, n) is defined as: )7()1)(,( 1 ),( 1 0 1 0 )()()()( 1 0         n m n n lnkm bbbb nmf n lkf iii n i i where 1...,,1,0,10,0,0  nk,lnnm the inverse hadamard transform is defined as:          1 0 1 0 )()()()( )8()1)(,( 1 ),( 1 0 n k n l lnkm bbbb lkf n nmf iii n i i where m, n=0, 1, …, n-1. bi(l) represents the ith (from lsb) bit of the binary value of n decimal number represented in binary. the ht [7] has been used in image processing, image compression, and image fusion. let f(m, n) represents the original image and f(k,l) the transformed image. the ht is given by )9( )],([ n hnmfh f(k,l) nn where nh represents an n x n hadamard matrix, with element values either +1 or -1. the hadamard transform is real, symmetric, and orthogonal that is )10(1  n t nnn hhhh the inverse transformation is )11( )],([ ),( n hlkfh nmf nn the hadamard matrix of the order n is generated in terms of hadamard matrix of order n-1 using kronecker product ‘⊗’ given by         11 11 2 1 1h )12(11 hhh nn   ht matrix has its ac components in a random order. the processing is performed based on the 8x 8 sub-blocks of the whole image, the third order ht matrix h3 is used. by applying h3 becomes: engineering, technology & applied science research vol. 6, no. 4, 2016, 1075-1079 1077 www.etasr.com vadhi et al.: image fusion technique based on hadamard transform using hvs )13( 11111111 11111111 11111111 11111111 11111111 11111111 11111111 11111111 8 1                                  iii. proposed method given hadamard matrix, the number of sign changes in each row of the hadamard transform matrix is given as 0,7, 3, 4, 1, 6, 2 and 5 in the rows 1 to 8 respectively. the number of sign changes in each column of the hadamard transform matrix is given as 0, 7, 3, 4, 1, 6, 2 and 5 in the columns 1 to 8 respectively. the number of sign changes is referred to as sequence. the concept of sequence is analogous to frequency for the fourier transform. therefore, r = [0 7 3 4 1 6 2 5], c=[0 7 3 4 1 6 2 5]. the horizontal and vertical discrete frequencies in the hadamard domain are given in equation (12) n ur uf 2 )( )(   for u =1,2,…….n n vc vf 2 )( )(   for v=1,2,…….,n (14) the dot pitch (δ) of the high resolution computer display is about 0.25mm. high resolution computer display is about 128 mm height and 128 mm width to display a 512x512 pixel image. the appropriate viewing distance is four times of height. hence, distance is considered as 512 mm. constant ω is a symmetric parameter, derived from experiments and set to 0.7. thus, the human visual frequency weighting matrix w(u, v) of (2) is calculated for ht using (3) and (4) as given in table i [11]. table i. hvs weighting matrix for ht 1.0000 0.6571 1.0000 0.9599 1.0000 0.7684 1.0000 0.8746 0.6571 0.1391 0.4495 0.3393 0.6306 0.1828 0.5558 0.2480 1.0000 0.4495 0.7617 0.6669 1.0000 0.5196 0.8898 0.5912 0.9599 0.3393 0.6669 0.5419 0.9283 0.930 0.8192 0.4564 1.0000 0.6306 1.0000 0.9283 1.0000 0.7371 1.0000 0.8404 0.7684 0.1828 0.5196 0.4940 0.7371 0.2278 0.6471 0.2948 1.0000 0.5558 0.8898 0.8192 1.0000 0.6471 0.9571 0.7371 0.8746 0.2480 0.5912 0.4564 0.8404 0.2948 0.7371 0.3598 the human visual frequency weighting matrix w(u, v) indicates the perceptual importance of the transform coefficients. after multiplying the 64 hadamard coefficients with human visual frequency weighting matrix the weighted hadamard coefficients contribute the same perceptual importance to human observers. fig. 1. experimental results with different images the fusion algorithm is given as:  both the input images are first divided into non overlapping 8 x 8 blocks.  for each block apply ht using (7) results t(u, v).  all the transform coefficients are multiplied with weighting matrix w(u, v) results r(u,v). )15(),(),(),( 8 1 8 1     i j vuwvutvur  select the corresponding block from each source images, according to the highest r(u,v)                    vurvurvut vurvurvut vut bb bb f ,,, ,,, , 212 211 where rb1(u,v) and rb2(u,v) are the corresponding blocks with highest r(u,v) from each source images. tf(u, v) is the selected block from source images for fusion.  fuse the corresponding blocks in to the empty image. iv. experimental results three multi focused images from [16] are used as source images. to compare the results, dwt method with maximum selection rule is tested [3]. )16()],(),([ )1)(1( 1 1 0 1 0 2        n i m j jifjis mn mse where n is the number of total pixels and s(i,j) and f(i,j) are the pixel values in the original and fused image. )17( 255 log10 2 10        mse psnr the mutual information (mi) [13] is also one important measure to test the fused image quality. mutual information between the source images s1, s2 and the fused image f is )18( 21 21 fsfs ss f iim  consider k can be 1 or 2, then fski is  k k k kk sf ksf kfs kfskfs spfp sfp sfpsfi , )()( ),( log),(),( where fskp is the jointly normalized histogram. engineering, technology & applied science research vol. 6, no. 4, 2016, 1075-1079 1078 www.etasr.com vadhi et al.: image fusion technique based on hadamard transform using hvs the edge strength and orientation preservation [14] values can be calculated as               )19( ,, ,,,, 1 1 1 1/ 21 2211 21          n n m m ss n n m m sfssfs fss mnwmnw mnwmnqmnwmnq q  mnq fsk , represents the edge strength and orientation strength, w represents weight. feature similarity (fsim) [12, 18] index can be measured as: )20( )(. )().(     x m x ml xpc xpcxs fsim where ω means the whole image spatial domain, mpc means phase congruent structure, ls is the similarity depends upon the gradient measure. the usable gray level values range from 0 to 255. the other quality parameter is normalized cross correlation (ncc) is given as: )21( ),(),(),(),(( )),(),()(,(),(( 22                  i ji j i j jifjifjisjis jifjifjisjis ncc where, ),( jis indicates the mean of the original image and ),( jif indicates the mean of the fused image. psnr and ncc are commonly used as a measure of quality of fused image with respect to the ground truth image. typical psnr values are 20 to 50 db, where higher is better. ncc is one of the methods used for template matching; a process is used for finding incidences of a pattern or object within an image. the above mentioned metrics evaluate the amount of information transferred from source images to fused image. from the information point of view mutual information statistically depend on two random variables. the metric qs1s2/f evaluates the edge information. with the feature similarity metric phase congruent and edge information between source images and fused image can be obtained. other metrics considered to assess the fused images are mutual information (mi) [13], objective image fusion performance [14], and feature similarity index measure (fsim) for image quality assessment [12]. objective quality assessment depends on the edge strength and orientation preservation (esop). experiments are performed with different images and different metrics. proposed method gives better performance than dwt in terms of all metrics. experimental results are presented in table ii. experimental results clearly indicate that the proposed method gives better results in terms of subjective and objective assessment. a bar chart related to the psnr values is shown in figure 2. experimental results clearly indicate that the proposed method gives better results in terms of subjective and objective assessment. mi measure is objective, concise, meaningful, and explicit. in the proposed method, considerable improvement in mi values is observed. fsim concentrate on gradient measure. esop concentrates on edges in the fused image. from table iii, it is observed that the proposed method ht+hvs is surpasses the other statistical methods such as ht+average, ht+variance [17]. psnr values for the existing method and the proposed method are shown in figure 2. more than 7 db improvement is observed in psnr values using the proposed method. fig. 2. graphical representation of psnr and mi v. conclusions in this paper, ht with human visual system for image fusion is presented. the proposed algorithm is efficient than dwt fused method. experimental results indicate that, hvs based fusion gives better quality over traditional fusion rules. further, more than 7db improvement is observed in psnr values with the proposed method. hvs based methods can be extended for image fusion using other transforms also. ht offers a significant advantage in terms of a shorter processing time as the processing involves simpler integer manipulation (compared to floating point processing with dct and dwt) and the ease of hardware implementation engineering, technology & applied science research vol. 6, no. 4, 2016, 1075-1079 1079 www.etasr.com vadhi et al.: image fusion technique based on hadamard transform using hvs table ii. experimental results table iii. experimental results image no. metric ht+average ht+variance ht+hvs [proposed] 1 mi 3.0699 4.4407 4.5343 esop 0.8063 0.9076 0.9148 fsim 0.9477 0.9997 0.9997 ncc 0.9898 0.9989 0.9992 2 mi 2.9045 2.8182 3.1300 esop 0.8623 0.9716 0.9753 fsim 0.9597 0.9651 0.9896 ncc 0.9929 0.9937 0.9970 3 mi 2.8385 3.0513 3.8318 esop 0.9664 0.9644 0.9753 fsim 0.9345 0.9376 0.9872 ncc 0.9706 0.9708 0.9943 references [1] a. garzelli, 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liang, “remotely sensing image fusion based on wavelet transform and human visual system”, international journal of signal processing, image processing and pattern recognition, vol. 8, no. 7, pp. 291-298, 2015 [21] y. yang, w. zheng, s. huang, “effective multifocus image fusion based on hvs and bp neural network”, the scientific world journal, vol. 2014, article id 281073, pp.1-8, 2014 image no fusion rule psnr mi esop ncc fsim 1 dwt 24.3543 2.0754 0.4643 0.9226 0.8846 ht+hvs proposed 30.4657 3.6681 0.9148 0.9829 0.9693 2 dwt 21.5123 1.6946 0.4467 0.9056 0.8467 ht+hvs proposed 34.2161 3.1300 0.9753 0.9970 0.9896 3 dwt 23.7146 2.0732 0.4766 0.9366 0.8967 ht+hvs proposed 33.2027 3.5307 0.9753 0.9920 0.9774 engineering, technology & applied science research vol. 8, no. 1, 2018, 2499-2507 2499 www.etasr.com naveen et al.: a cloud associated smart grid admin dashboard a cloud associated smart grid admin dashboard p. naveen wong kiing ing michael kobina danquah faculty of engineering and science curtin university miri, sarawak, malaysia navp80@gmail.com faculty of engineering and science curtin university miri, sarawak, malaysia faculty of engineering and science curtin university miri, sarawak, malaysia amandeep s. sidhu a. abu-siada faculty of engineering and science curtin university miri, sarawak, malaysia department of electrical and computing engineering curtin university perth, australia abstract—intelligent smart grid system undertakes electricity demand in a sustainable, reliable, economical and environmentally friendly manner. as smart grid involves, it has the liability of meeting the changing consumer needs on the dayto-day basis. modern energy consumers like to vivaciously regulate their consumption patterns more competently and intelligently than current provided ways. to fulfill the consumers’ needs, smart meters and sensors make the grid infrastructure more efficient and resilient in energy data collection and management even with the ever-changing renewable power generation. though cloud acts as an outlet for the energy consumers to retrieve energy data from the grid, the information systems available are technically constrained and not user-friendly. hence, a simple technology enabled utilityconsumer interactive information system in the form of a dashboard is presented to cater the electric consumer needs. keywords-admin dashboard; cloud; smart grid i. introduction electrical energy has progressed as a vital part of modernday life. the major portion of the energy produced comes from fossil-fueled power stations and the rest from atomic and renewable energy sources. due to rapid industrialization, urbanization, cultural changes and modern human lifestyle, the electrical energy demand has increased exponentially and it becomes a challenging task to the electric energy providers and distributors. particularly, the peak power demand management is one of the principal concerns even though it lasts for a short period of a day [1-3]. this management task involves a high marginal cost to maintain the fast responding (fossil-fuelled) standby power plants. besides, additional costs are involved in overcoming the environmental issues caused by the standby units. peak demand charges can be often more than 30 percent of an industrial consumer’s monthly utility bill [4, 5]. the electric consumption charges are based on the highest capacity desired for the duration of the billing period, normally, a 15minute interval through that billing cycle. due to advancement in real-time monitoring systems, energy usage can be easily monitored, hence energy demand peaks become more obvious. inappropriately automated building management systems and mechanical system letdowns are collective causes of higher than required energy peaks. the prime share of the energy production cost is the fuel cost for fossil-fuelled power plants; hence, the frequent escalation of the fuel cost is a risk for investors on achieving the return on their investments [5, 6]. utilities suffer from limited/uncertain fuel supplies and cash collection from the government and energy sector. moreover, the availability of intermittent forms of renewable generation, storage, and backup issues, the unattractive energy buyback policies and energy cost, and their high capital investment with limited funding resources are further challenges in terms of higher energy cost. the energy consumers are not satisfied with the high-energy cost, supply interruptions, and impact to environment. a change in the energy systems was inevitable and thus smart grid came into existence [7-10]. energy management is the usual technique of monitoring, controlling, and conserving energy [11], whereas, in smart grid, energy management is the foremost concern. it is crucial for resource conservation, environmental protection and economic considerations without conceding functional processes by optimally coordinating many energy sources. to gain benefits through energy management, the smart grid (sg) energy management system (ems) integrates building energy management system (bems), demand side management (dsm), home energy management (hem), and demand response (dr). bems is a classy technique envisioned to monitor and control building services like heating, ventilation, and air conditioning (hvac), lighting or security measures, ensuring the building operates at maximum efficiency by avoiding energy wastage. it will adjust electrical load automatically according to the demand response events communicated by the energy provider [12]. dsm signifies the development, executing, and monitoring activities of electric utilities, which are premeditated to reassure consumers to amend their quantity and pattern of electricity usage. as a result, the utility gets to benefit from the shifting of energy consumption from peak to non-peak hours. dsm programs engineering, technology & applied science research vol. 8, no. 1, 2018, 2499-2507 2500 www.etasr.com naveen et al.: a cloud associated smart grid admin dashboard [13] inspire the end-user to be energy efficient through lighting retrofits, building automation advancements, hvac enhancements, variable frequency drives, etc. dsm is essential in sg to maintain grid stability and to integrate new sources of energy generation for capacity addition and environmental friendliness. hem is a technology platform [14] that permits the end-user to monitor energy consumption and generation and to physically regulate and/or automate the use of energy within a home. hem systems provide information to end-users about how they use energy in their premises and/or alert them remotely via a smartphone or web service or based on a set of rules, which can be planned or augmented based on end-user behavior. dr is a significant demand-side management technique. it encourages end-users [12, 15] to carry out shortterm reductions in their energy use in response to (i) a price signal from the electricity hourly market, or (ii) an incentivebased trigger initiated by the grid administration. the evolved sg system accomplishes electricity demand in a sustainable, dependable and economical manner. it involves all kinds of electric power generating resources ranging from conventional to all types of renewable energy sources and residential, commercial and industrial electric consumers. renewable energy resources being practiced successfully like solar are weather dependent and the power generation varies continually, hence the power generation must frequently adjust to match supply against demand. henceforth, heaps of sensors and smart meters are being employed [16-18]. these incorporated sensors produce a huge amount of data instantaneously, which are gathered, and processed in order to produce control decision to progress efficiency and reliability of the power grid. to manage the masses of sensors and smart meters electric utilities need to comprehend the bilateral messaging network management system to a distributed data center [19]. in this respect, cloud computing is envisioned to perform significant tasks in the modernization process of the existing sg. cloud computing is an evolving expertise for empowering trustworthy and necessity-based access to various computing sources, which can rapidly provide an economical way to the service providers [20, 21]. it offers new-fangled openings to the ict industry permitting businesses to contract out their it services to cloud providers and circumvent costly open investments of launching their own infrastructure and subsequent costs of maintenance and upgrades [22, 23]. it is evident that cloud computing forms a bridge between the sg and the energy consumers. the information systems available to consumers are technically constrained. moreover, such resources are limited in quantity and not user-friendly to all consumers. hence, a simple technology enabled utilityconsumer interactive information system is preferable to cater the needs of the electric consumers. ii. related research work the greatest challenge to an up-and-coming sg lies in engaging consumer support. without it, the sg cannot be existent and it cannot provide its assured benefits. eventually, the consumer is paying for the sg, which on one hand does yield imperative benefits for consumers, but on the other, they come at a substantial cost and, at the individual level, the need for these benefits may feel immediate. the german smart grid developed smart meter gateway (smgw) to speed up the processing of data acquisition, energy consumption monitoring, supply-demand management, and secured communication between energy consumers and external bodies [24]. the smgw is not a hardware, but it has a built-in hardware security module for protecting the important materials and cryptographic operations. the smgw administrator plays the technical role of configuring tariffing profiles, issuing and controlling smgw certificates, and embedded firmware updates to regulate the tasks of various hardware devices and systems, but he cannot access to the end-users’ energy consumption data. the extension of smgw to household becomes a major concern for all residential consumers and the associated cost of the maintenance and up keeping of the gateway. the smart grid administration of european r&d smart grid projects is facing challenges in the administration and handling of user rights. discern [25] offers an expressive web-based tool concept with the objective of re-using sg data from both field trials and simulations by (european) sg projects, expediting the reuse of prevailing sg solutions, associating the present and upcoming sg projects and, thus, facilitating the assimilation of real-world trials and simulations. the dashboard primarily focuses on the user access rights to handle data as well as historical data in the context of information security management systems. the comprehensive sg dashboard system facilitates a user to upload and store a data object in the dashboard. the user can retrieve the stored data and can transfer to third parties. the dashboard has messaging options and data analyzing facilities. since the dashboard has multitasking amenities, it has room for rear-enders in the sg dashboard system when more than one user with write or manage rights want to edit the same data object at the same time. the sg dashboard system should be able to manage multi-editing of the data objects. the gujarat state government in india has initiated a sg dashboard concept for its consumer’s convenience in 2013 [26]. it facilitates its consumers to participate in various programs such as demand side management and energy cost forecast. this helps the planning of their energy-related activities based on the tariff forecast in an economical way. the dashboard sends real-time messages to alert them about their energy consumption trends, planned supply interruptions, past energy consumption statistics, monthly energy consumption bills etc. the security and reliability of the dashboard were not yet ascertained and the consumers’ feedback on the usage of the dashboard would justify its suitability at a large scale. in ireland and northern ireland, eirgrid plc [27] gets involved in electric energyrelated activities such as transmission, distribution and marketing. to enhance its services, eirgrid group developed a web-based smart grid dashboard. it empowers the users to outlook and parallel the power system information and graphs in one location. in addition, the users can visualize the realtime energy data with the time-varying energy cost. it is userfriendly and has no need for log in because the information provided is general and not user specific. this paper presents a cloud-based sg admin dashboard that provides real-time data of the sg for the benefit of the utilities, renewable energy investors, independent power producers, and engineering, technology & applied science research vol. 8, no. 1, 2018, 2499-2507 2501 www.etasr.com naveen et al.: a cloud associated smart grid admin dashboard end-users for their energy-related activities and suitable actions. while designing the dashboard, equal importance was given to the electric utility and the consumer. iii. cloud for smart grid management smart grid encompasses conventional power plants such as thermal power stations (coal, oil, and gas, etc.) and renewable energy sources. it forms a hybrid combination of both conventional and renewable energy sources to achieve economic as well as environmental benefits. the power generated has been delivered to the consumers through long transmission and distribution networks. all the data will be stored and updated periodically by the electric utility data management system (i.e. in every 20 minutes) and simultaneously passed on to the cloud network. since sg has the two-way communication facility, the utilities and cloud network are connected on real-time web services for the exchange of information. it is worth noticing that there is no power flow between the utilities and the cloud. instead, the power flow is only from the utilities to the consumers (end users). a rudimentary formation of sg and cloud architecture has been presented in [28, 29], and based on that work, a modified sg and cloud architecture has been proposed as shown in figure 1. fig. 1. proposed smart grid and cloud architecture a. the electric consumers (end-users) the chief groupings of electric consumers are of industrial, commercial and residential type. they are interconnected with utilities through smart meters and intelligent sensors. these smart meters measure the energy consumption at their end and communicate with the sensors. the incorporated sensors produce a mass of data instantaneously and they take control decisions in order to improve efficiency and consistency of the power grid. from the smart meters’ and sensors’ communications, the total energy consumption scaled load demand (power demand) is determined. the consumers’ expectation is the availability of electric supply as and when they need it. through the cloud network services, consumers can schedule their power requirement well in advance since they are informed far ahead about the availability of electric supply, the probable electricity unit cost, the power supply’s planned shut-down, the probable outages due to weather conditions, system faults, and blackout due to threats. b. the cloud network this is a rather recent and advanced addition in sg to enhance its performance. it is a junction for the communication flow between the utilities and the consumers. sg communications networks are used to observe the load variations, power generations, weather forecast, consumers’ expectations, security threats, etc. to optimize the real-time functioning of the system and envisage faults prior to their occurrence [28, 29]. cloud computing platforms provide the possibility to exploit huge amounts of resources, both in terms of data storage and in the capability of flexible and scalable data processing. c. dashboard the cloud-based smart grid system needs to have the capability to monitor electrical power consumption in kwh, unit energy costs, weather conditions, renewable energy generation etc. in deregulated power market, there should be provision for end-users to participate in market transactions and to optimize their energy consumption and energy cost, and to avail environmental credit wherever possible. end-users can be encouraged by power market price signals for decision-making and intermingle with power generation companies and the power grid. to accommodate certain features as discussed, a web-based user-friendly dashboard is presented in the next section. iv. data acquisition network the sg data are obtained from the system technical network support as:  all energy resources, backup storage systems and all load points (industrial, commercial and residential) are connected to sensors, preferably wireless. these sensors aid higher precision of inflow predicting, the actual energy consumption by the end-users and the load forecast.  these sensors are then connected to controllers for monitoring. data from the sensors are inputs and are handled and related to the rules and settings prescribed by the administrator. if the input data is within an acceptable range, then it will be passed on to the sg admin dashboard through modems. data outside an acceptable range trigger the control system to issue commands to change the status of the controlled device.  the data communication to sg admin can be done through lan, wan, can, han or satellite communication depending upon the sg structure.  all collected data are stored in the cloud server, and are retrievable.  the sg admin can control the on and off status of the der or re sources on the consumer side. if any alert on instability in sg operation occurs, the administrator can engineering, technology & applied science research vol. 8, no. 1, 2018, 2499-2507 2502 www.etasr.com naveen et al.: a cloud associated smart grid admin dashboard switch off or isolate the source to maintain the stable operation. v. smart grid admin dashboard a web-based smart grid admin dashboard (sgad) has been developed for administrative purposes and for the planning of consumer energy-related activities. the proposed dashboard involves cloud for data storage and exchange of information. theccloud has generally three models: infrastructure as a service (iaas), platform as a service (paas), and software as a service (saas). paas as a service model offers computing platforms that classically contain operating systems, programming language execution environment, database, and web server. it is the second layer on top of iaas. windows azure, google app engine, and apache stratus are some common examples of paas. paas is preferred for the smart grid services because of its technical suitability and flexibility. the dashboard of the sg system is presented in pictorial form. the homepage for the sg system has the main navigation panel and its options as seen in figure 2. the sgad-visualizer (figure 3) facilitates the registered operators (both administrators and end-users) to monitor the existing data of the sg system by providing the ip address, start date or time, and end date or time. there are two categories of ip addresses: one for the system admin and the other for the endusers. the system admin can control, monitor, and manipulate the data of all end-users, whereas the end-user is entitled to visualize the information and data relevant to him/her only. the visualizer has three display options: two options in tabular format (online monitor tabular and data tabular) and the other in graphical format dashboard). fig. 2. a portion of the home page fig. 3. smart grid admin dashboard-visualizer the data visualized through the online monitor tabular and the data tabular are shown in table i.  the online monitor tabular once the admin logs in, the online monitor tabular displays the latest data of the sg system. the information is meant for the administration purpose only, and not visible to the end-user.  data tabular a) for system admin if no search option is chosen, the data tabular displays all the data available in the sg system. if ip address option is chosen, it displays the data relevant to that ip address available in the sg. if start/end date or time options are chosen, it displays the relevant data available in the sg. b) for end-user if no search option is chosen, the data tabular displays all the data available in the sg system relevant to his/her ip address. if start/end date or time options are chosen, it displays the corresponding ip address relevant data. the end-user does not have the privilege of visualizing other end-users’ information. engineering, technology & applied science research vol. 8, no. 1, 2018, 2499-2507 2503 www.etasr.com naveen et al.: a cloud associated smart grid admin dashboard  dashboard for graphical display the dashboard has three components and they are provided with additional sub-components. the admin or the end-user can select any one of the sub-components from the factor component as presented in figure 4. the sub-components vary from the system demand, the system generation, the unit cost of energy, the solar and wind power generation (by the end-users), the system frequency and the lighting and power loads of the end-users. the dashboard provides a special option to save the retrieved information for the end-user reference in later days without log in again. the next component is the chart duration and it has the options for viewing the data from a day to year as seen in figure 5. there are options namely line chart and column chart in the chart type component as in figure 6. the line chart is preferable to compare changes over the same period for more than one data group. column charts are ideal to compare stuff between different data groups or to track changes over time (day, week, month, and annual). table i. visulaized data sg load data load demand (kw) energy consumption (kwh) sg generation data power generation (kw) energy produced (kwh) system frequency (hz) unit energy cost ($/kwh) solar power data power generation (kw) energy produced (kwh) wind power data power generation (kw) energy produced (kwh) consumer load status lighting load (on/off) power load (on/off) fig. 4. factor sub-components fig. 5. chart duration sub-components fig. 6. chart type sub-components vi. sgad displays though several options are provided in the sgad for the admin’s and end-users’ data retrieval and visualization, only a few displays are presented here, and the data retrieval and visualization through other options follow the same operation logic. when the admin logs in, the latest data entry from the sg system will be displayed as in figure 7. this information is not visible to any end-users. the entry of an end-user ip address by the system admin displays the relevant data of that user as well as the latest system data (figure 8). if the system admin wants to visualize the entire energy-related activities of all the endusers on a specific date, it is possible by entering the date of interest on the start date. a portion of the data for few endusers on september 2, 2017 s presented in figure 9. the end-user can monitor his/her energy activities on a day during different timings by providing the date and duration. figure 10 shows the energy activities of the end-user with ip address 192.168.1.220 on march 19, 2016 during the time 01:17:21 – 01:18:16. end-users want to know the unit energy cost to regulate their energy consumption and to plan for their future demand in a cost-effective manner. the user can select the sub-component – unit energy cost, $/kwh option from the factor component as presented in figure 4. the dashboard provides the relevant information for the end-user as seen in figures 11 (a) (line chart) and 11 (b) (bar chart). consumers having their own renewable energy sources like the wind and/or solar power can plan their energy usage according to their own power generation, and their excess engineering, technology & applied science research vol. 8, no. 1, 2018, 2499-2507 2504 www.etasr.com naveen et al.: a cloud associated smart grid admin dashboard power can be exported to the grid. the dashboard supports them to participate in load shedding and load shifting solutions, and to shift among several competing energy providers based on greenhouse gas emissions or social goals. the dashboard has the option of visualizing their import and export nature of energy by on and off controls as seen in figure 9. it can also display the unit energy cost variations during a period as in figures 11 (a) and (b). the sg admin can control the on / off status of the der or re sources on the end-user side. if any alert on instability occurs the administrator can switch off or isolate the source to maintain stability. these dashboard displays are on a real-time basis providing energy-related activities in a user-friendly way. the system admin can practice the dashboard to identify system performance matters, and the end-users to optimize their energy consumption in a costeffective manner. fig. 7. latest data visualization by admin fig. 8. data visualization by ip address fig. 9. data visualization of many end-users engineering, technology & applied science research vol. 8, no. 1, 2018, 2499-2507 2505 www.etasr.com naveen et al.: a cloud associated smart grid admin dashboard fig. 10. data visualization by an end-user (a) (b) fig. 1. unit energy cost visualization: (a) line chart, (b) column chart vii. superiority of the proposed dashboard it is significant to compare the performance of the proposed dashboard against the earlier discussed dashboards [24-27]. the primary objective of the german sg developed smart meter gateway (smgw) is to speed up the processing of data acquisition, energy consumption monitoring, supply-demand management, and secured communication between energy consumers and external bodies [24]. here, the end-user has limited scope for interaction with the smgw administrator. in addition, the extension of smgw to household becomes a major concern for all residential consumers along with the associated cost of the maintenance and up keeping of the gateway. whereas the proposed dashboard is user specific, and all types of registered end-users such as residential, industrial, and commercial can make use of the dashboard. the dashboard in [25] focuses on the user access rights to handle data as well as historical data in the context. it facilitates the users to upload and store a data object in the dashboard. the users can repossess the stored data and can transfer to third parties. the dashboard has multi-tasking amenities, however, it has room for data trafficking in the system when more than one user with write or manage rights want to edit the same data object at the same time. the sg dashboard system should be able to manage multi-editing of the data objects, and the data traffic congestion should be reduced. the proposed sgad has no such restriction on the number of registered users, and the data can be stored and retrieved without any such data trafficking. cloud computing platforms provide the possibility engineering, technology & applied science research vol. 8, no. 1, 2018, 2499-2507 2506 www.etasr.com naveen et al.: a cloud associated smart grid admin dashboard to exploit huge amounts of resources, both in terms of data storage and processing. the sg dashboard in [26] enables its consumers to participate in several programs such as demand side management and energy cost forecast. this supports to plan their energy-related activities based on the tariff forecast in an economical way. the dashboard sends real-time messages to alert them about their energy consumption trends, planned supply interruptions, past energy consumption statistics, monthly energy consumption bills etc. however, there is no feedback on the status of the security and reliability of the dashboard. the presented sgad has all the above attractive features. in addition, sgad has the capability to monitor renewable energy generation at consumer sides and utility side, which assists the end-users to take part in market transactions and optimize their energy consumption and energy cost and to avail environmental credit wherever possible. it encourages the end-users by the power market price signals for decisionmaking and intermingles with power generation companies and the power grid. the dashboard developed by eirgrid plc [27] deals with energy data relevant to their energy groups. it is very general and not user specific. it empowers the users to outlook, parallels their associated power system information, and graphs in one location. in addition, the users can visualize the realtime energy data with the time-varying energy cost. it is userfriendly and with no need for log in. since there is no need to log in, the information provided is general and not user specific. the proposed admin dashboard is scalable and securable. only registered users can log in, hence it assures data protection of its registered users. viii. conclusions the conventional power system needs to be informative, innovative, and intelligent by integrating the information and communication technology with its electricity infrastructure. with such expectations, sg comes into existence partially in several parts of the world. hence, the electric utilities and consumers are aware of information such as the power generation level, power demand, unit energy cost, the planned load shedding, the weather forecast, emission level, any cyber threat etc. on real-time basis. though this information is very helpful for the consumers, the technological constraints of the sg and the amount of information often provide incovenient results. hence, a simple technology enabled utility-consumer interactive information system in the form of a dashboard is presented to cater the needs of the electric consumers. the dashboard provides real-time smart grid operating status, power supply and demand, unit energy cost etc. with the support of cloud services. the experience with this dashboard shows its technical suitability of its use and its userfriendliness. the presented dashboard can be extended to various consumers with additional data such as emission credit, monthly electricity bill visualization, feed-in-tariff information etc. references [1] g. andersson, p. donalek, r. farmer, n. hatziargyriou, i. kamwa, p. kundur, n. martins, j. paserba, p. pourbeik, j. sanchez-gasca, r. schulz ,a. stankovic, c. taylor, v. vittal, “causes of the 2003 major grid blackouts in north america and europe, and recommended means to improve system dynamic performance”, ieee transactions on power systems, vol. 20, no. 4, pp. 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attributes distinguish cloud computing services, gartner, stamford, ct, 2009 [29] s. bera, s. misra, j. j. p. c. rodrigues, “cloud computing applications for smart grid: a survey”, ieee transactions on parallel and distributed systems, vol. 26, no. 5, pp. 1477-1494, 2015 authors profile p. naveen was born in tamil nadu, india, on january 5, 1980. she completed her bachelor of engineering and master of engineering in computer science from anna university, chennai, india and master of business administration from madurai kamaraj university, india. she worked as a lecturer in brunei darussalam for 4 years and currently she is pursuing her ph.d. in electrical and computer science engineering with curtin university, sarawak, malaysia. she has published two research papers in ieee transactions and two in other reputed journals and conferences. her areas of interest include cloud computing, networking, artificial intelligence, and development of application packages in interdisciplinary areas. wong kiing ing was born in sarawak, malaysia in 1975. he received b. eng. (hons) degree from the university of manchester in 1999 and ph.d. degree from the university of southampton in 2003. in his ph.d. program, he investigated the electrical aging phenomena of polyethylene materials using electroluminescence technique. he has successfully measured the phase resolved electroluminescence of polyethylene using a charge couple device (ccd) camera for the first time. michael k danquah is a chartered engineer (ceng), a chartered scientist (csci) and a fellow of the institution of chemical engineers (icheme), uk. he is also a chartered professional engineer (cpeng) and a chartered member (mieaust) of engineers australia. professor danquah is currently a full professor in the department of chemical engineering and the associate dean (research & development) of the faculty of engineering and science, curtin university, malaysia. he previously worked as a senior lecturer in the department of chemical engineering and the principal research fellow of the bio engineering laboratory, monash university, australia. he completed his ph.d. in biochemical engineering from monash university after obtaining a bsc. hons (first class) degree in chemical engineering from knust (ghana). amandeep sidhu’s research has resulted in over 60 publications that have been cited over 450 times till date. he has an h-index of 12 and an average of 28.80 cites per year. he was awarded the highest indian diasporic award granted to non-resident indian citizens by the government of india for his contributions to academia in january 2014. he is the editor for data, semantics and cloud computing subseries of springer-verlag. he is also the editor in chief of the international journal of semantic and infrastructure services. he holds a ph.d. in computing from la trobe university during which he developed the world’s first protein ontology that is now part of national center for biomedical ontologies at national institute of health, usa. he received the research thesis merit citation award for his ph.d. thesis in 2008. prior to joining curtin sarawak, he worked at curtin university’s bentley campus since 2007. there, in collaboration with microsoft, he led the development of an hpc & cloud facility for data intensive science projects. he is the recipient of the curtin business school’s new researcher of the year award for 2007. he is also a senior member of ieee and is actively involved in many ieee activities in the areas of bioinformatics, semantic web, data management and cloud computing. a. abu-siada received his b.sc. and m.sc. degrees from ain shams university, egypt and the ph.d. degree from curtin university, australia, all in electrical engineering. currently, he is an associate professor in the department of electrical and computer engineering at curtin university. his research interests include power system stability, condition monitoring, power electronics, and power quality. he is the editor-in-chief of the electrical and electronic engineering international journal and a regular reviewer for ieee transactions on dielectrics and electrical insulation and ieee transactions on power electronics. microsoft word etasr_v12_n2_pp8321-8327 engineering, technology & applied science research vol. 12, no. 2, 2022, 8321-8327 8321 www.etasr.com ha et al.: t-type multi-inverter application for traction motor control t-type multi-inverter application for traction motor control vo thanh ha faculty of electrical and electronic engineering university of transport and communications hanoi, vietnam vothanhha.ktd@utc.edu.vn pham thi giang faculty of electrical engineering university of economics-technology for industries hanoi, vietnam ptgiang@uneti.edu.vn vu hoang phuong school of electrical engineering hanoi university of science and technology hanoi, vietnam phuong.vuhoang@hust.edu.vn received: 29 january 2022 | revised: 10 february 2022 | accepted: 13 february 2022 abstract-the structure and principle of the t-type 3-level reverse voltage source that will be fed to three-phase induction motors will be presented in this study. the implementation of space vector pulse width modulation (svpwm) and the math models of the induction motor, the stator currents, and the speed controller design of the electric traction drive system based on field-oriented control (foc) will be also shown. this three-level t-type inverter in the foc structure decreases total harmonic distortion (thd) more than the previous two-level inverters. by combining the foc control structure with the t-type 3-level inverter, the speed and torque responses necessary for railway traction motor load were improved. finally, matlab/simulink will be used to demonstrate the correctness of the t-type multilevel inverter theory. keywords-multilevel inverter; t-type inverter; induction motor; field oriented control; railway traction motor i. introduction since the '90s, most asynchronous motors have been replaced, mainly by dc motors. the induction motor outperforms the dc motor in maintenance cost, mechanical stability, and energy efficiency, whereas it can also work in the flux-weakening mode [1-4]. thus, the induction motor is widely used for railway traction motors. nowadays, traction electric transportation systems are widely used in developed and developing nations to alleviate traffic congestion in major cities. traction power systems typically employ big capacity (200kw-300kw), and traction motors are driven from high voltage (25kv, 50hz) to low voltage (1500v-750v, 50hz) [5]. furthermore, since the traction drive system runs at high voltage, a voltage source inverter is required to power the traction motor and assure 100% harmonic distortion of the stator current and, low voltage, standard sine phase voltage, and appropriate controls (torque, speed) for traction electric motor and train operating characteristics. in the control structure of traction power transmission systems, 2-level voltage source inverters with power circuits including 6 semiconductor valves and the pwm svm technique are often used. however, compared to a multi-level inverter, this 2-level inverter has greater thd [6]. according to [7], the multi-level inverter comprises semiconductor valves and a dc voltage source, and the output voltage is in the form of wavelengths. therefore, the output voltage of a multi-level inverter may be made sinusoidal with low thd by increasing the number of voltage levels. currently, clamp diode (npc), variable capacitor (fc), h-bridge stage (chb), and t-type multi-level inverters are extensively used in industry and transportation (such as pumps, fans, wind energy, and traction motors for electric trains, electric vehicles, etc.). based on the literature review [8], the npc-type multi-level inverter offers benefits over the standard 2-level voltage inverter, such as reduced stator current harmonic distortion and lower tdh voltage. however, because of the npc's construction, increasing the number of voltage levels will increase the number of diodes and igbts, making it impossible to raise further the number of voltage levels [9]. the fc variable-capacitor multi-level inverter has seen a lot of applications. this multi-level inverter has the same construction as the npc multi-level inverter. instead of diode transistor valves, a capacitor is used, resulting in different voltages. this benefit allows semiconductor valves to operate without requiring continuous switching. thd is lower than that of the npc set, resulting in higher efficiency of the fc multilevel inverter than in the npc set. however, this multi-level inverter costs more than the npc multi-level inverter [10, 11]. in addition, it has been shown [12, 13] that a multi-level inverter structure of h-bridge cascade (chb) employs an igbt semiconductor and a separate dc source (electrolytes). the voltage is provided via several output transformers or corresponding author: vo thanh ha engineering, technology & applied science research vol. 12, no. 2, 2022, 8321-8327 8322 www.etasr.com ha et al.: t-type multi-inverter application for traction motor control capacitors for industrial applications. this multi-level inverter's power circuit (staged semiconductor phases) is simple to build, replicate, and install in order to increase the number of voltage levels as required. compared to npc and fc, a chb multilevel inverter has this benefit. furthermore, the chb multilevel inverter works with medium and high voltages. however, since this multi-level inverter structure requires dc balancing to assure output voltage quality, the control structure must propose a voltage balance management algorithm. moreover, scientists have been researching the t-type multi-level inverter because it has more benefits than the chb structure, such as employing just one dc source and preventing dc voltage imbalance across phases [14, 15]. besides, authors in [16] shown that the t-type multi-level inverter has the advantage of reducing the number of semiconductor valves and capacitors while increasing the voltage level. the current article's research, analysis, and assessment focus will be applied to the t-type three-level inverter for traction motor control power supply in a high-capacity, highvoltage traction power transmission system. in addition, the file-oriented control structure of a traction electric drive system using a t-type 3-level inverter combined with torque speed pi controllers is also provided. again, this controller is designed so that the responses are accurate. ii. svm structure and modulation of the t-type 3level inverter a. control structure the 3-phase 3-level t-type inverter structure is developed from the standard 3-phase 2-level voltage source structure. each phase includes 8 semiconductor valves, such as 4 igbt valves (sa1-sa4) and 4 diodes (d1-d4). the three-phase design of a three-level t-type converter is shown in figure 1. the t-type 3-level inverter works on 2 dc capacitors to divide the input voltage into two voltage components vdc/2 and create a virtual neutral point. properly adjusting and switching of the semiconductor valves will give a wire voltage of 5 levels: −vdc, −vdc/2, 0, vdc/2, vdc. thus, the output phase voltage has the form of 3 levels: −vdc/2, 0, vdc/2. based on the working principle of this 3-level t-type inverter, the switching status table is built as shown in table i. fig. 1. 3-phase t-type inverter structure power circuit. table i. t-type 3-level inverter switch ing status status ���� sa1 sa2 sa3 sa4 p +vdc/2 on off on off o 0 off off on on n −vdc/2 off on off on b. pulse width modulation svm with a multi-level inverse scheme, the number of subtriangles on the vector plane increases rapidly as the number of levels (m) increases. the calculation becomes more straightforward if we use the system's symmetry in every sixth angle vector space shown on three-six quadrant vector plane coordinate systems (z1x, z1y), (z2x, z2y), (z3x, z3y), where: 1 ( ) 3 a b c v v v v v α β =   = −  (1) z1x z1y z2xz2y 13 4 5 2 6 z3x z3y fig. 2. coordinate systems (z1x, z1y), (z2x,z2y) and (z3x,z3y). the number of sub-triangles in the spatial vector diagram will increase as the degree increases. the calculation becomes much easier using the symmetry property of the space vector system in each arc. the coordinate systems (z1x, z1y), (z2x, z2y) and (z3x, z3y) are shown in figure 2. first, we determine the projection of the desired voltage vector on the upper coordinate system (z1x, z1y), (z2x, z2y) and (z3x, z3y) then we define three transformation matrices, m1, m2 and m3 described as: 1 2 3 1 1 2 1 1 0 3 3 3 ; ; 2 1 1 0 1 1 3 3 3 m m m       −           = = =       − − −            (2) according to [6], pwm svm is performed according to the following calculation steps: 1) step 1: locating the reference vector the number of sectors s (s = i, ii, ···, vi) is determined by table ii. table ii. lo cating the hex agons z1x.z1y < 0 z1x.z1y ≥ 0 z2x.z2y < 0 z2x.z2y ≥≥≥≥ 0 z1x<0 z1x≥≥≥≥0 z3x<0 z3x≥0 z2x<0 z2x≥0 sec iii sec vi sec v sec ii sec iv sec i 2) step 2: determining the duty cycle in this step the three nearest vectors are determined based on the three vertices of the modulation triangle, the duty cycle of the three most similar defined vectors is calculated, and the switching states of the semiconductor valves are chosen. with the assumption shown in figure 3, the sum of the output voltage vector is as follows: the vector is represented by the vectors in (3): engineering, technology & applied science research vol. 12, no. 2, 2022, 8321-8327 8323 www.etasr.com ha et al.: t-type multi-inverter application for traction motor control ( ) ( ) ( ) 1 1 2 1 3 1 1 2 3 v p p p p p 1 p p p g h g h g h m m m m m m = + − + − = − − + + r r r r r r r r r (3) ( )( ) ( )( ) ( ) ( ) ( ) 2 4 3 4 2 4 4 3 2 1 1 1 1 1 g h g gh h v p m p p m p p m m p m p m p = + − − + − − = + − + − + − r r r r r r r r r (4) the coefficients mg and mh are determined as follows: 1 1 1 1 1 1 g x x x g h y y y h m z z z k m z z z k  = −   = −    = − = −   (5) with g 1x h 1y k z , k z =   =    . 0 m g m h z1y z1x 2 p(kg+1,kh) rrrr 1 v rrrr 2 v rrrr 4 p(kg+1,kh+1) rrrr3 p(kg,kh+1) rrrr 1 p(kg,kh) rrrr fig. 3. synthesizing the output voltage vector from the 3 vertex vectors of the sub-triangle. 3) step 3: determining the switching state if ka = k, the coefficient k must satisfy this condition: m 1 m 1 k 2 2 − − − ≤ ≤ . the coordinates of the state vector in the (a, b, c) coordinate system are given by (6): 1 1 1 1 1 an x bn x y cn x y k k k k k k k k k k k        ≈ = −          − −    (6) equation (6) shows the relationship between [k1x, k1y] coordinates (i = 1,2,3) and (a, b, c) coordinates. 4) step 4: balancing the voltage on the two dc capacitors using svm modulation for multi-level inverters, voltage balancing for dc capacitors is always a challenge. although just one dc source is utilized in the t-type inverter construction, voltage imbalance on the two capacitors in series is conceivable for a variety of reasons, including: • the dc capacitor's value is inaccurate in this case. • due to inefficient circuit switching, the discharge and charge times of two capacitors differ. as a result, dc voltage will deteriorate the harmonic quality of the inverter output voltage, which is impossible. thus, multi-level inverters in general, and t-type inverters in particular, must address this issue. the steps for balancing the capacitor voltage are: • step 1: measure the voltage on the capacitors vdc1, vdc2. • step 2: compare the two voltages. • step 3: discharge voltage on capacitor c1 and charge capacitor c2 if vdc1 > vdc2. • step 4: discharge voltage on the capacitor c2 and charge c1 if vdc2 > vdc1. table iii. order of the vector switches sector triangle shape switching order case of unbalance 1 1 (0 0 0) (1 0 0) (1 1 0) – (1 0 0) vc1>vc2 ( -1 -1 -1) – (0 -1 -1) – (0 0 -1) – (0 -1 -1) vc2>vc1 2 (1 0 0) – (1 0 -1) – (1 -1 -1) – (1 0 -1) vc1>vc2 (0 -1 -1) (1 -1 -1) (1 0 -1) (1 -1 -1) vc2>vc1 3 (1 0 0) (1 1 0) -(1 0 -1) (1 1 0) vc1>vc2 (0 -1 -1) (0 0 -1) (1 0 -1) (0 0 -1) vc2>vc1 4 (1 1 0) (1 1 -1) (1 0 -1) (1 1 -1) vc1>vc2 (0 0 -1) (1 0 -1) (1 1 -1) (1 0 -1) vc2>vc1 table iii shows the changing of the switching order in sector one to balance the voltage on the capacitor. we follow the same procedure in the remaining sectors. the voltage imbalance between the two capacitors c1 and c2 may be determined using the state table, and control can be used to balance the voltage on the two capacitors. iii. mathematical models a. mathematical model of induction motor the foc approach is used to regulate the induction motor, hence, the induction motor's mathematical model (based on [4]) is: 1 1 1 1 1 1 1 1 1 sd sd s sq sd s r r s sq s sd sq m sq s r s rd m rd sd r r p rd sq l di i i u dt t t t l di i i i u dt t t l d l i dt t t zd k i m dt j ω σ σ ω σ σ σ σ σ σ ω ω σ σ σ σ ψ ψ ω ψ    − −   =− + + + +       − −   =− − + − +      =− + = − (7) with 2 2 3 ; 2 sq p mm s r r rd r i z ll k t l j ωω ω ω ω ψ = + = + = . the equation represents the im's mechanical equation: m t jd m m dt ω = + (8) b. mathematical model of the traction motor load traction motor load includes load torque and drag forces. the drag force of the electric traction motor is a characteristic engineering, technology & applied science research vol. 12, no. 2, 2022, 8321-8327 8324 www.etasr.com ha et al.: t-type multi-inverter application for traction motor control quantity for the train's movement, including two main components, essential and auxiliary resistance. 1) basic drag the main factors that cause drag are friction and impact between the wheel and the rails, between the locomotive and the air, and between the locomotive parts. the essential parts of frictional resistance between the bearing and the wheel hub are: rolling resistance, sliding, shock and shock, and air. from the above factors, it can be seen that the factors affecting the essential unit resistance are very complex and, in practice, it is challenging to use theoretical formulas to calculate. therefore, empirical formulas are often used, related to the square of train speed. the general form of the procedure for calculating essential train resistance is: 2 0 w a bv cv= + + (kn) (9) the primary resistance of the locomotive when operating traction and when running momentum is not equal, so for all types of locomotives, it is necessary to find a formula for calculating separately the two primary resistances, which are the unit essential resistance ' 0ω and the elemental resistance when running momentum ' 0cdω . the general formula for calculating the unit resistance of the locomotive is: 2 ' 0 127.5 6.37 0.98. 0.1. 10 0.1. . 10 v ca v q i q ω   = + + +     (10) the basic formula for calculating resistance when running momentum (generally used for locomotives) is: ' 2 0 2.4 0.1. 0.00035. cd v vω = + + (11) 2) secondary drag slope resistance is the principal source of secondary drag. auxiliary resistance differs from elemental resistance: it is less impacted by the locomotive or wagon type. because route circumstances determine it, the additional damper does not differentiate between locomotives and wagons but is computed per train. the unit ramp resistance is calculated as: ( ) 1000.sin . i i w p q g ω θ= = + (12) iv. simulation results a control structure for traction motors driven by a 3-level t-type inverter is depicted in figure 4, based on the above findings. the simulation results for electric traction motors using the 3-level t-type inverter and induction motor specifications are shown in table iv. table iv. parameter table parameters symbol value dc voltage dcu 1000 frequency of modulation fs 2000hz power dmp 270 kw rated speed dmn 2880 rpm rated voltage dm u 400v pole pair p 1 power factor cosφ 0.9 stator resistance rs 0.0138ω rotor resistance rr 0.00773ω rotor inductance lr 0.0078h mutual inductance lm 0.0077h voltage 750 vdc maximum speed for the train 80km/h im a b c train resistances traction motor and load sje ϑ 3 2 tu tv tw usαusd usq isα isu svm isq isd sje ϑ− usβ isv isw s ϑ speed measurement isβ *ω (-) * sq i * sd i rω 3-level t-type w h e e l gear i r mhtt (-) r ψ k ac dc e l e c t r i c g r i d electric traction substation + resistance brake dc link rd tmω rd ψ * dc u rd ψ * rd ψ fig. 4. control structure of traction motor fed by t-type 3-level inverter. engineering, technology & applied science research vol. 12, no. 2, 2022, 8321-8327 8325 www.etasr.com ha et al.: t-type multi-inverter application for traction motor control to evaluate the effectiveness of the 3-level t-type inverter, the stator current controller will be selected as pi in the control structure, with the adjustment parameters chosen as: 0 .3 85; 0 .0 52 p i k t= = . in addition, the speed controller is a pi controller with parameters 4 .1; 0.8 2 p i k t= = . a. case 1: simulation and εvaluation of the 3-level t-τype ιnverter with τwo classic levels at 50hz with no load the phase voltage response and thd are displayed in figure 5. figure 6 depicts the dc voltage response on the two capacitors of a t-type 3-levels inverter. through the simulation results (figure 5), it was found that the output voltage of the 3level t-type inverter has a wavelength with the three required voltage levels. in addition, the current is sinusoidal with lower thd (7.53%) than a two-voltage level inverter (thd = 11.39%). in addition, the difference in dc voltage between the two capacitors is not significant, with the most notable change being vcmax = 3v (0.6%), demonstrating that the balancing procedure is successful. furthermore, owing to the voltage balancing technique on capacitors, svm modulation considerably reduces the voltage imbalance on the two dc capacitors. consequently, the svm modulation produces acceptable voltage and current quality with a thd of 7.53%. b. case 2: simulation and evaluation of traction drive system using the 3-level t-type inverter traction electric motor will operate according to the following simulation scenario: • from t = 0.5s to t=2.3s, the im is operating at pull process with: t0.5s =0 (km/h), t1s=50 (km/h), and t2.3s=73 (km/h). • from t = 2.3s to t = 4.5s, the im is operating at coasting process with: t2.3s =73 (km/h), t4.5s =73 (km/h). • from t = 4.5s to t = 8s, the im is operating at braking process with: t7s =13 (km/h) and t8s=0 (km/h). the simulation results are shown in figure 7. (a) (b) (c) (d) (e) (f) fig. 5. line voltage and thd of the t-type multi-level inverter and the classic 2-level inverter. (a), (b) t-type 3-level voltage inverter, (c), (d) inverter 2 voltage levels, (e) 3-phase current response using the 3-level t-type, (f) classic 2-level inverter current response. engineering, technology & applied science research vol. 12, no. 2, 2022, 8321-8327 8326 www.etasr.com ha et al.: t-type multi-inverter application for traction motor control fig. 6. the dc voltage response on two capacitors of a t-type 3-level inverter. (a) (b) (c) (d) fig. 7. (a) speed response, (b) torque response, (c) single phase voltage, (d) tdh when rr is constant. figure 7 shows that the output voltage of the 3-level t-type inverter has a wavelength with the required 3 voltage levels. furthermore, the current is sinusoidal, resulting in decreased thd. in addition, the torque and speed controllers have been effective. thus, the actual speed response closely reflects the reference speed response with a rapid reset time. on the other hand, the torque controller provided the required torque at each operating moment of the railway traction drive. as a result, boosting the voltage level and applying a nonlinear control approach to the controllers is a challenge that has to be handled in the future to assure minimal thd and minor torque pulsation. v. conclusion the design and assessment of the control structure of a traction motor foc driven by a 3-level t-type inverter were effectively suggested in this study. according to the simulation results, the harmonic distortion diminishes as the voltage level rises, resulting in increased inverter performance. the design and computation of this multi-level inverter, on the other hand, is complicated, mainly when the number of voltage vectors grows fast with voltage level. furthermore, since the torque response still exhibits strong torque pulsation, a more straightforward voltage modulation method is required when the power level rises and the torque pulsation reduces. this is a promising area for future research, as methods to enhance the control quality of traction powertrains are developed. references [1] l. frederick and g. k. dubey, "ac motor traction drives—a status review," sadhana, vol. 22, no. 6, pp. 855–869, 1997. [2] m.-ş. nicolae and i.-r. bojoi, "a control strategy for an induction motor used for vehicular traction and/or positioning systems with variable speeds," in 2012 international conference on applied and theoretical electricity (icate), craiova, romania, jul. 2012, pp. 1–6, https://doi.org/10.1109/icate.2012.6403425. [3] a. fathy abouzeid et al., "control strategies for induction motors in railway traction applications," energies, vol. 13, no. 3, jan. 2020, art. no. 700, https://doi.org/10.3390/en13030700. [4] n. p. quang and j. a. dittrich, vector control of three-phase ac machines, 2nd ed., vol. 2. hedelberg, germany: springer, 2015. vc1 vc2 δ vcmax engineering, technology & applied science research vol. 12, no. 2, 2022, 8321-8327 8327 www.etasr.com ha et al.: t-type multi-inverter application for traction motor control [5] a. steimel, electric traction motive power and energy supply: basics and practical experience. munich, germany: oldenbourg industrieverlag, 2008. [6] c. m. van, t. n. xuan, p. v. hoang, m. t. trong, s. p. cong, and l. n. van, "a generalized space vector modulation for cascaded h-bridge multi-level inverter," in 2019 international conference on system science and engineering (icsse), dong hoi, vietnam, jul. 2019, pp. 18–24, https://doi.org/10.1109/icsse.2019.8823465. [7] s. pradhan, "multilevel inverter based electric traction motor," m.s. thesis, national institute of technology, odisha, india, 2013. [8] n. b. mohite and y. r. atre, "neutral-point clamped multilevel inverter based transmission statcom for voltage regulation," in second international conference on emerging trends in engineering (sicete), jaysingpur, india, 2010, pp. 31–35. [9] f. z. peng and j.-s. lai, "dynamic performance and control of a static var generator using cascade multilevel inverters," ieee transactions on industry applications, vol. 33, no. 3, pp. 748–755, feb. 1997, https://doi.org/10.1109/28.585865. [10] j. rodriguez, s. bernet, b. wu, j. o. pontt, and s. kouro, "multilevel voltage-source-converter topologies for industrial medium-voltage drives," ieee transactions on industrial electronics, vol. 54, no. 6, pp. 2930–2945, sep. 2007, https://doi.org/10.1109/tie.2007.907044. [11] m. rezki and i. griche, "simulation and modeling of a five -level (npc) inverter fed by a photovoltaic generator and integrated in a hybrid wind-pv power system," engineering, technology & applied science research, vol. 7, no. 4, pp. 1759–1764, aug. 2017, https://doi.org/10.48084/etasr.1271. [12] p. guerriero et al., "three-phase pv chb inverter for a distributed power generation system," applied sciences, vol. 6, no. 10, oct. 2016, art. no. 287, https://doi.org/10.3390/app6100287. [13] y. gopal, k. p. panda, d. birla, and m. lalwani, "swarm optimizationbased modified selective harmonic elimination pwm technique application in symmetrical h-bridge type multilevel inverters," engineering, technology & applied science research, vol. 9, no. 1, pp. 3836–3845, feb. 2019, https://doi.org/10.48084/etasr.2397. [14] d. a. tuan, p. vu, and n. v. lien, "design and control of a three-phase t-type inverter using reverse-blocking igbts," engineering, technology & applied science research, vol. 11, no. 1, pp. 6614–6619, feb. 2021, https://doi.org/10.48084/etasr.3954. [15] h. p. vu, d. t. anh, and h. d. chinh, "a novel modeling and control design of the current-fed dual active bridge converter under dpdps modulation," engineering, technology & applied science research, vol. 11, no. 2, pp. 7054–7059, apr. 2021, https://doi.org/10.48084/ etasr.4067. [16] l. g. franquelo, j. rodriguez, j. i. leon, s. kouro, r. portillo, and m. a. m. prats, "the age of multilevel converters arrives," ieee industrial electronics magazine, vol. 2, no. 2, pp. 28–39, jun. 2008, https://doi.org/10.1109/mie.2008.923519. engineering, technology & applied science research vol. 7, no. 3, 2017, 1595-1599 1595 www.etasr.com khodadadi et al.: designing an optimal lightning protection scheme for substations using shielding … designing an optimal lightning protection scheme for substations using shielding wires abolfazl khodadadi electrical engineering department amirkabir university of technology tehran, iran a.khodadadi@aut.ac.ir mohammad hassan nazari electrical engineering department amirkabir university of technology tehran, iran nazary@aut.ac.ir seyed hossein hosseinian electrical engineering department amirkabir university of technology tehran, iran hosseinian@aut.ac.ir abstract—an optimal lightning protection scheme for a substation using shielding wires is investigated in this paper through computer software analysis. an economic approach is utilized by choosing a reasonable trade-off between protection, the number of shielding wires and the heights of them from the ground. this study is initially applied to a simple two-wire system and then extended to a sample substation. the solution for each problem is executed in matlab and 3-d realization is shown. keywords—substation protection; lightning stikes; shielding wires; computer aid analysis i. introduction faults and damages in substations are the culmination of sundry factors each of which play a significant role in the shielding failures among which lightning is one of the most important one. this phenomenon as a probabilistic event may cause severe consequences like power supply interruptions and economic losses [1–5]. therefore, a lightning protection system is required for reducing the probability of a fault against direct lightning stroke to the objects and buses within the substations [6, 7]. for more illustration on the lightening progress phenomenon, a brief description is presented in [8]. in the lightening, the stepped leader moves toward earth in stopping steps of about 50 meters. after each step, the stepped leader pauses, then proceeds along one or more paths. the time for each step is about 50μs near the base of the cloud but decreases to about 13μs as it approaches the earth. the velocity of the stepped leader is slow, about 0.1% of the speed of light. as this stepped or downward leader reaches near the earth, an upward leader or return stroke start progressing to meet the downward leader. the speed of this stoke is about 10 to 30% of light which makes it possible to be observed by naked eye. the amplitude of this upward channel is more than 200 ka with a median value of 33 ka. the total length of the downward leader or the upward channel is about 5 to 6 km. the above description illustrates the mechanism of the first stoke of a lightning flash. one flash may consists of up to 54 stokes; however, the average is three stokes per flash in order to apply protection to the equipment, three different methods can be utilized: shielding wires, masts and combination of these two. each of the aforementioned methods for shielding a substation has its own advantages and disadvantages. however, the application of shielding wires is much more recommended due to its wide range of protection area [9]. in addition, the approach which is applied for lightning protection can be obtained from various equations, such as young’s equations, love’s equations, brownwhitehead, ieee-1992 and ieee-1995 [8], [10]. for young’s equations only a small modification for the value of the strike distances is required and for love’s equations and ieee-1995, there is no need for any adjustment. however, utilizing brownwhitehead and ieee-1992 needs significant changes in the value of different strike distances. in this paper, for the case of generality, young’s equations are employed. matlab is employed in this paper for simulation. the economic aspect of the design is also considered and a trade-off between cost and level of security is proposed. thus, this paper applies specific criteria for achieving the design with minimum possible cost. ii. methodology different distances are used for defining the strike distance: (1) the strike distance to the shielding wire or shielding mast, rs (2) the strike distance to the object to be protected, rc , and (3) the striking distance to the ground, rg [11]. all of these distances are shown in figure 1. this figure also specifies the areas on which lightning strokes will be terminated. the following equations have been derived from the electromagnetic model to calculate the strike distance equations [8]: s s g c c gr r r r   (1) in which γs and γc are coefficients which will be defined by young’s equations: 0.3227 444 for 18 otherwise 1 462 444 for 18 otherwise 1 462 g s s c c r i h m h y m y              (2) engineering, technology & applied science research vol. 7, no. 3, 2017, 1595-1599 1596 www.etasr.com khodadadi et al.: designing an optimal lightning protection scheme for substations using shielding … where i is the design current in ka and rs, rg and rc are strike distances in meters. design current is an important factor that highly affects the output parameters of the design. for practical designs, the design current value for voltages below 230 kv is usually considered to be 5 ka and for voltages above 230 kv is considered to be 10 ka [8], which is the value used in this paper. in substations, the height of devices can vary from zero to the height of the shielding wires. thus, the location of the objects and wires should be determined in such a way that a minimum number of shielding wires cover the entire area of the substation. each shielding wire has a specific protection zone. for instance, consider a single wire as depicted in figure 1. the actual area of the final protective zone depends on the number of shielding wires that have been employed. in order to clarify this issue, two cases are investigated as follows. h y rc rs rg strike to wire strike to ground strike to ground strike to object a a0 rpc fig. 1. strike distances ( front view ) a. one shielding wire in this case one shielding wire will be used in order to protect a specified zone. assume that there is an object with height y and a shielding wire at height h. now if the position of the object from the shielding wire is known, with the following equations, the height of the shielding wire may be determined (see fig. 1). 2 2 0 2 2 0 ( )po c g po g s r r r y a a r h r r a         (3) where in these equations 0a is the distance from the shielding wire to the object (figure 2). b. two sheilding wires the shielding zone which is introduced by two shielding wires is shown in figure 3. the highlighted zone in this figure shows the protected area by two shielding wires. having an object with the height of y, the horizontal distance of the protection, a, will be calculated as it follows: 2 2 2 2( ) ( )c g c ga r r h r r y      (4) also the equations for calculating the horizontal protective distance between two shielding wires can be evaluated by (5) and is depicted in figure 4. 2 2 2 2( )pc c s c c c pc r r h y r r a r r        (5) h a0 a h y rpc y=0 a0 y fig. 2. protective zone of a single wire ( upper view ) rg rc rcrg ymc sg a y hy fig. 3. protected zone of the two shielding wires the minimum height of the protection level is in the middle of the distance between two wires as shown in figure 3 and it can be derived by setting the rpc equal to zero in (5), that is: 2 2 mc c s cy h r r r    (6) however, it should be mentioned that if the distance between two wires increases, the value of the ymc equals to zero and the configuration which is depicted in figures 3 and 4 will not hold true, but the equations can be utilized. sg hy rpc ac rs rc rc fig. 4. protective zone between two shield wires engineering, technology & applied science research vol. 7, no. 3, 2017, 1595-1599 1597 www.etasr.com khodadadi et al.: designing an optimal lightning protection scheme for substations using shielding … to clarify and visualize the shielding protection area by two wires, 3-d realization of figure 4 is depicted in figure 5. 100 50 horizontal distance (m) 0 -50 0 50 depth (m) 0 10 20 30 40 100 h ei gh t (m ) 0 2 4 6 8 10 12 14 16 18 20 22 shielding wires stands fig. 5. 3-d visualization of shielding protection zone c. economic analysis the overall cost of the design should be calculated in a cost effective manner. so, a software should be employed to solve the problem with specific technical and economic constraints (number of wires and height are considered as parameters). as the height of the wires increases, the number of them decreases. an equation that can be applied for economic constraint can be defined as follows. . n .costfunction h   ($) (7) where α is a constant which transfers the number of wires, n, into monetary unit ($/number) and β is another constant which transfers the height of the wires (in meter) into monetary unit ($/height). a person who is expert in this field should define these constants in order to have reasonable and economic solution. iii. simulation results a. case study information any sample substation can be analyzed by the algorithm utilized for this paper. for instance, consider a substation which its front view is shown in figure 6. the first part isa 345 kv transformer which its height is 30 feet (approximately 10 meter) or second part a 500 kv ehv gas circuit breaker [12]. b. simulation algorithm at the first stage, the algorithm puts two wires in the beginning and the end of the specified area at minimum acceptable height. then it proceeds to calculate the shielding zone between these two wires. it is obvious that these placement cannot guarantee the full protection of the equipment between them. then, it brings one of the wires closer to the other one in order to increase the height of the protection level between them. this process continues until the position of the second wire reaches a position ensuring that all of the equipment between them will be completely protected. the user can define the specific margin between the highest part of the equipment and the protection level defined by shielding wires. in this problem, the aforementioned margin is set one meter above the highest equipment. after determining the position of the second wire, this process continues until the protection area of the last wire reaches the end of the defined area. the process which has been mentioned however, above will solve problem for a specific height. next step is to increase the height of the wires and then repeat the same process. as the height of the wires increases, the number of them will decrease. therefore, the economic criteria will be considered for the final scheme selection. h ei gh t ( m ) fig. 6. front view of the sample substation c. simulation results in the first part of the simulation, the minimum height of the wires is selected and the algorithm calculates the complete protection as depicted in figure 7. as it was stated before, this design has been performed in a way that all equipment has at least one meter margin from the shielding area provided by the wires. in this case five shielding wires have been used and the height of the wires is 11.5 meter from the ground. the 3-d realization is shown in figure 8. h ei gh t ( m ) fig. 7. protection level provided by wires 100 50 0 10090807060 50403020 100 22 4 8 2 0 10 12 6 16 18 20 14 h ei gh t ( m ) depth (m) width(m) fig. 8. 3-d realization of shielded area engineering, technology & applied science research vol. 7, no. 3, 2017, 1595-1599 1598 www.etasr.com khodadadi et al.: designing an optimal lightning protection scheme for substations using shielding … selecting deferent cost function constants is a variable that can be depended on the various factors based on the region in which the shielding design is performed, such as monetary factors or availability of specific materials. according to this, a table with different constants and their consequent costs based on (7) is provided (table i). this table is based on the first scenario in which the height of the wires is the minimum possible height and five wires are employed according to the computer software solution. increasing the height of the wires leads to a decrease in their number. in this problem, in order to protect all the equipment with just two wires, the final result will be as depicted in figure 9. table i. costs of the first scenario ($) α 10 20 30 40 50 β 10 170 220 270 320 370 20 290 340 390 440 490 30 410 460 510 560 610 40 530 580 630 680 730 50 650 700 750 800 850 h ei gh t(m ) fig. 9. protection with two wires in this scenario, the final cost of designing this protection system is stated in table ii. table ii. cost of the second scenario ($) α 10 20 30 40 50 β 10 420 440 460 480 500 20 820 840 860 880 900 30 1220 1240 1260 1280 1300 40 1620 1640 1660 1680 1700 50 2020 2040 2060 2080 2100 the optimal configuration derived is based on α=40 and β=10 which are obtained by an expert in the region in which the substation has been located. the final output of the algorithm is depicted in figure 10. in this design, three shielding wires have been applied and the height of the wires from the ground is 15 meters. thus, the total cost of this design is found to be the lowest. as a final step, 3-d realization of figure 10 is depicted in figure 11. h ei gh t ( m ) fig. 10. optimal shielding protection design depth (m) 100 50 010080 width (m) 6040 200 15 10 0 5h ei gh t(m ) fig. 11. 3-d realization of the optimal design iv. conclusion in this paper, an algorithm has been developed in matlab in order to design a lightning shielding protection system for substations using shielding wires. young’s equations are employed to determine the value of the different strike distances in the design process. as a significant factor in design, an economic constraint has been defined and this factor determines the number of the shielding wires to be employed and their height from the ground. finally, the algorithm has been applied to a sample substation and simulation results are shown and discussed. references [1] p. sen, “understanding direct lightning stroke shielding of substations”, power syst. eng. res. center, pserc seminar, colorado, november 6, 2001 [2] f. a. m. rizk, “modeling of substation shielding against direct lightning strikes”, ieee trans. electromagn. compat., vol. 52, no. 3, pp. 664– 675, 2010 [3] k. l. v. dung, “lightning protection systems design for substations by using masts and matlab”, international journal of mathematical, computational, physical, electrical and computer engineering, vol. 4, no. 5, pp. 562-566, 2010 [4] f. a. m. rizk, “exposure of overhead conductors to direct lightning strikes: modeling of positive streamer inhibition”, ieee trans. power deliv., vol. 26, no. 2, pp. 1156–1165, 2011 [5] s. dedeoglu, s. yilmaz, “design and implementation of a programmable high-voltage impulse measurement system”, turkish journal of electrical engineering & computer sciences, vol. 22, pp. 262-275, 2014 engineering, technology & applied science research vol. 7, no. 3, 2017, 1595-1599 1599 www.etasr.com khodadadi et al.: designing an optimal lightning protection scheme for substations using shielding … [6] a. m. mousa, “shielding of high-voltage and extra-high-voltage substations”, ieee trans. power appar. syst., vol. 95, no. 4, pp. 1303– 1310, 1976 [7] a. m. mousa, r. j. wehling, “a survey of industry practices regarding shielding of substations against direct lightning strokes,” ieee trans. power deliv., vol. 8, no. 1, pp. 38–47, 1993 [8] a. hileman, insulation coordination for power systems, crc press, 1999 [9] a. h. a. bakar, c. k. tan, a. z. abidin, p. j. khai, h. mokhlis, h. a. illias, “comparative study on substation shielding due to direct lightning strokes”, j. power energy eng., vol. 2, no. 4, pp. 600–611, 2014 [10] a. mousa, “a computer program for designing the lightning shielding systems of substations,” ieee transactions on power delivery, vol. 6, no. 1, pp. 143-152, 1991 [11] j. mcdonald, electric power substations engineering, crc press, 2012 [12] ieee std 998-1996, ieee guide for direct lightening stroke shielding of substations, 1996 microsoft word etasr_v13_n4_pp11505-11510 engineering, technology & applied science research vol. 13, no. 4, 2023, 11505-11510 11505 www.etasr.com alraddadi: a survey and a credit card fraud detection and prevention model using the decision tree … a survey and a credit card fraud detection and prevention model using the decision tree algorithm abdulaziz saleh alraddadi college of computer science and engineering at yanbu, taibah university, saudi arabia alraddadi1@yahoo.com (corresponding author) received: 17 june 2023 | revised: 27 june 2023 | accepted: 1 july 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6128 abstract today, many people prefer online payment methods due to the rapid growth in cashless electronic transactions. credit and debit cards are the most popular electronic payment methods but are prone to fraud due to the nature of their use and the tendency of fraudsters to access their details. this study proposes a theoretical credit fraud detection and prevention model using a decision tree algorithm (dca). moreover, a survey questionnaire was used to investigate students' perceptions of credit card fraud incidents. data were collected from 102 students from different universities and countries around the world. the results showed that 95.9% of the respondents knew how credit/debit card fraud occurs, while 4.1% of them did not. finally, 81.6% expressed their willingness to use a tool based on the proposed model to prevent or detect credit/debit card fraud incidents. keywords-online payment; credit card fraud; decision tree algorithm (dca); survey i. introduction cybercrime is one of the most serious threats cyberspace users and the global economy face. according to european and international organizations, it is considered one of the most significant security challenges of the 21st century [1]. numerous studies have attempted to investigate or prevent cybercrime methods. such studies contain database schemes [2], automation [3], avoiding cyberbullying [4], wireless networks [5-6], cloud safety [7-8], smart iot [9-10], drone domain and mobile areas [11], and the health field [12-20]. companies and organizations monitor consumers' or users' spending patterns to identify and prevent fraudulent activities. credit cards are becoming increasingly popular as a payment method in both online and conventional transactions. fraud detection involves the identification and capture of fraudulent activities and events. in recent decades, many modern methods have been developed to prevent frauds related to credit card transactions. several approaches can be used to detect and prevent fraudulent transactions, including machine learning, data mining, sequence alignment, fuzzy reasoning, genetic programming, and fuzzy reasoning [21-22]. fraud occurs when goods, services, or money are acquired illegally. there are many situations in which frauds occur when there is criminal intent present, but it is often obscure. in addition to credit cards, there are many other fraud targets. credit card fraud is a general term for theft, fraud, and other similar payment methods used fraudulently to fund a transaction. credit card fraud is becoming a growing problem. as it can be challenging to identify credit card fraud using standard procedures, the development of prevention models is now crucial for academic and commercial institutions. furthermore, with the development of technology over the past few decades, fraud methods have changed dramatically. credit card fraud is one of the greatest obstacles for business and commercial enterprises. credit card fraud is the use of another person's credit card for private reasons without the person who owns the card or the card issuer being aware of it [23-24]. credit card fraud can be eliminated, and financial risks can be reduced using many systems, models, procedures, and preventive measures. although the number of people using credit cards is quickly increasing, very few feel secure and confident in using them for regular purchases [23, 25]. credit card fraud is expanding around the world along with advancements in communication channels and information technology, leading to significant losses. this study investigated the extent to which students have been victims of credit card fraud and focused on a model to detect and prevent credit card fraud on campuses. to address this objective, four research questions (rq) were formulated as follows:  rq1: have you ever heard of or been involved in credit card fraud before?  rq2: how do you think it does happen?  rq3: how do you think it can be mitigated?  rq4: would you use a solution based on the proposed model that prevents credit card fraud? the main contribution of this study is the proposal of a theoretical framework for a model to prevent credit card fraud. engineering, technology & applied science research vol. 13, no. 4, 2023, 11505-11510 11506 www.etasr.com alraddadi: a survey and a credit card fraud detection and prevention model using the decision tree … moreover, this study investigated students' perceptions of how credit card fraud occurs and can be prevented or detected using a survey questionnaire. finally, it was determined that the students would be willing to use such a system. ii. related works in [26], an algorithmic framework was developed using a decision tree and a combination of luhn's and hunt's algorithms to prevent credit card fraud. frauds were detected using luhn's algorithms in incoming transactions, which were assessed based on address mismatches and degrees of outliers to determine how far they deviate from the typical customer profile. bayes' theorem was applied to strengthen or weaken the general belief, and a more sophisticated combinatorial heuristic was applied to combine the probable fraud with the original belief. in [27], three methods were proposed, using machine learning algorithms to identify fraudulent transactions. many metrics can be used to assess how well a classifier or predictor performs, such as the vector machine, the random forest, and decision trees. it is important to note that these measures depended on prevalence [28]. in [29], a comparative study was conducted among the different methods of detecting credit card fraud. in [30], three security levels were introduced in the concept of credit card fraud detection based on a hidden markov model (hmm). in [31], hmms were used to detect fraudulent card payments in two stages using dynamic random forest and k-nearest-neighbor algorithms. in [32], advanced data mining techniques were investigated to combine with a neural network based on real-time credit card data to offer even stronger predictive capabilities. in [33], two kinds of random forest methods were used to train features that represent normal or abnormal transactional behavior. in [34], supervised algorithms were used for the same purpose, including deep learning, logistic regression, nave bayesian, support vector machines (svm), neural networks, artificial immune systems, k-nearest neighbor, decision trees, data mining, and fuzzy logic-based systems. in [27, 35] prediction, clustering, and outlier identification were compared in machine learning techniques. random forests were used to train a classifier to recognize the behavioral characteristics of credit card transactions. the following methods were used to train the genuine and fraudulent "behavior feature": cart-based random forest and random forest based on random trees. transactions were grouped into relevant sliding window groups, and various window features were retrieved to discover consumer behavioral patterns. there are features such as the maximum or minimum amount of a transaction, average amounts in the windows, and even the time elapsed [36]. systems generate fraud scores for specific transactions using a variety of instructions and algorithms. in [37], deep neural network techniques were proposed for fraud detection. the preparation approach is a significant setback in addressing data skew issues in a dataset. there are numerous methods to assess whether a transaction is legitimate or fraudulent [24]. the drawback of supervised learning is that it depends on people to optimize its settings. on the contrary, decision trees can be built more quickly than other techniques and do not require the user to set any parameters [26]. although internet payments are more convenient, adequate, and easy to use, losses related to electronic commerce should not be ignored. there are many security frameworks for businesses and banks, but fraudsters change their subtle strategies over time to bypass them. therefore, it is essential to improve methods for detection and prevention [28]. understanding the way a fraud is carried out is essential for effective fraud prevention. a credit card fraud detection tool should depend on the fraud technique itself [38-39]. in [40-42], machine learning-based methods were used to detect fraud in financial transactions and analyze research gaps to uncover research trends in the area. in [46], some unsupervised credit card fraud detection methods were proposed with the aid of behavioral outlier identification methods. most likely, fraud incidents will be discovered as anomalous spending patterns and transaction frequency. table i. summary of existing works. ref focus [26] credit cards were validated using the credit card number (input). incoming transactions were assessed based on address mismatches and degrees of outliers to determine how far they deviate from the typical customer profile. [27] many metrics were used to evaluate the performance of a classifier or predictor. [30] three levels of security were introduced using a hmm [31] dynamic random forest algorithms and k-nearest neighbor algorithms were used to detect credit card fraud in two stages [32] the possibility of improving prediction by combining advanced data mining techniques with a neural network based on real-time credit card data was investigated. [33] two types of random forest methods were used. trainning features represent normal and abnormal transaction behavior iii. the proposed model this study used design science research [43] to propose a credit fraud detection and prevention model, using a decision tree algorithm (dca). the development process consisted of three main stages, as shown in figure 1. fig. 1. research methodology. engineering, technology & applied science research vol. 13, no. 4, 2023, 11505-11510 11507 www.etasr.com alraddadi: a survey and a credit card fraud detection and prevention model using the decision tree … these stages were: collecting data, filtering the collected data, and selecting detection models for implementation. in the first stage, common search engines were used to retrieve relevant articles using the keywords "fraud prevention" and "fraud detection" for the period 2014-2023, and kaggle was used to retrieve several credit card transaction datasets with labels for fraudulent credit card transactions. only journal and conference papers written in english were collected. the datasets had several credit card transactions, with an additional binary field called that indicated whether a transaction was fraudulent (1) or not. the datasets also included transaction features, such as amount, time, frequency, geographic location, merchant information, cardholder information, transaction type, and device type and information. in the second stage, the collected data were filtered. a dca was used in the design of the credit fraud detection and prevention model based on common features, as shown in figure 2. fig. 2. the proposed credit card fraud detection and prevention model. the model used supervised learning, specifically dca. dca tree-structured classification starts with a root node and divides the dataset's features into internal nodes that represent dataset features, decision instructions, and results [44]. a decision tree simply poses a query and divides it into subtrees depending on the response. although dca can resolve classification and regression problems, it is mostly applied to the former. the method starts its search at the top of the tree to locate the dataset classes. to reach the next node, it calculates the branch based on the relations and matches the base trait with the record attribute [45]. as shown in figure 2, the proposed model was designed to work on the user's device as a client-side implementation to forecast the possibility of fraud. based on the forecast made by the model, the user gets realtime feedback regarding the transaction risk level. if the model detects a high likelihood of fraud, the user may receive a warning. the model should be compatible with android, ios, and pc operating systems. credit or debit card transactions were assumed to take place over the internet, at a sales point, or in a mobile application. at the initiation of the transaction, the card status is checked, and the transaction proceeds if the card is valid. the model uses dca, the expected score is generated, the investigation is carried out, and the appropriate decision is taken. if the score is appropriate, the card status is further checked. if a fraudulent trace is noticed, it automatically rejects the transaction, otherwise it is executed and outputs successfully. the second phase used a questionnaire that was distributed through the whatsapp platform, targeting a population of 450 students. the adopted questionnaire design was vetted by an expert and 102 responses were recovered within 48 hours. the purpose of the survey was to obtain responses that will provide answers to research questions. the proposed model was discussed with the respondents before sending the questionnaires. iv. survey the survey was carried out among computer science students. figure 3 shows the ages of the respondents, where 79.6% were 21-30 years old, and 20.4% were 11-20 years old, and figure 4 shows the degree levels of the participant students. fig. 3. ages of respondents. fig. 4. respondents' degree levels. engineering, technology & applied science research vol. 13, no. 4, 2023, 11505-11510 11508 www.etasr.com alraddadi: a survey and a credit card fraud detection and prevention model using the decision tree … figure 5 shows that 95.9% of the respondents had knowledge of how frauds occur through credit or debit cards, while 4.1% of them did not. on the other hand, as shown in figure 6, 67.3% answered "others" for the sources of fraud incidents. however, 20.4% responded that it occurs online and 12.3% agreed that it often happens through pos, atm, and mobile applications. fig. 5. knowledge about credit card fraud. fig. 6. medium for credit card fraud. fig. 7. students that believe in the use of a solution that prevents credit card fraud. figure 5 answers rq1, while figure 6 answers rq2. as shown in figure 7, the vast majority of respondents agreed that a method that can prevent or detect debit/credit card fraud is needed. developing a solution is one thing, but using it is another. figure 7 shows that 63.3% of the respondents expressed their willingness to use such a method based on the proposed model to prevent or detect credit/debit card fraud, while 30.6% of the respondents strongly welcome such a solution. meanwhile, 7.1% did not believe that such a solution could minimize the risk of credit card fraud. these results answer rq4. below are the solutions suggested by the students that can help in resolving the issue of credit card fraud in addition to the proposed model, providing further answers to rq3:  developing a system that uses fingerprint before card details are requested to identify the user of the mobile application or on-site.  other personal details of the user should be required in online transactions rather than the serial number of the card and cvv.  cyber-security awareness should be consolidated for everyone, including students and business owners.  individuals should be careful when using credit cards online, especially when certain malware can be easily installed unknowingly, such as keyloggers or spyware.  the ability of access to customers' details after a withdrawal at pos centers should be disabled.  educating people about not disclosing their details and avoiding visiting sites that are not secure. v. conclusion credit card fraud is an issue that has received a lot of attention during the recent years. this study presented a theoretical model to minimize the challenges associated with credit card fraud and surveyed the perspectives of university students. this study also provides insight into the willingness of the respondents to use a method that will provide such prevention measures. as a result of the study, information was obtained from selected university groups of students and the results indicate that students are very positive about using a method based on the proposed model. furthermore, the study offers suggestions that could help prevent 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[46] r. j. bolton and d. j. hall, "unsupervised profiling methods for fraud detection," imperial college, london, uk. engineering, technology & applied science research vol. 7, no. 5, 2017, 2073-2082 2073 www.etasr.com armaki et al.: a hybrid meta-learner technique for credit scoring of banks’ customers a hybrid meta-learner technique for credit scoring of banks’ customers ali ghasemy armaki mir feiz fallah mahmoud alborzi amir mohammadzadeh department of management qazvin branch islamic azad university qazvin, iran alghasemy@yahoo.com tehran central branch islamic azad university tehran, iran fallahshams@gmail.com information technology management department science and research branch islamic azad university tehran, iran mahmood_alborzi@yahoo.com department of management qazvin branch islamic azad university qazvin, iran amn_1378@yahoo.com abstract—financial institutions are exposed to credit risk due to issuance of consumer loans. thus, developing reliable credit scoring systems is very crucial for them. since, machine learning techniques have demonstrated their applicability and merit, they have been extensively used in credit scoring literature. recent studies concentrating on hybrid models through merging various machine learning algorithms have revealed compelling results. there are two types of hybridization methods namely traditional and ensemble methods. this study combines both of them and comes up with a hybrid meta-learner model. the structure of the model is based on the traditional hybrid model of ‘classification + clustering’ in which the stacking ensemble method is employed in the classification part. moreover, this paper compares several versions of the proposed hybrid model by using various combinations of classification and clustering algorithms. hence, it helps us to identify which hybrid model can achieve the best performance for credit scoring purposes. using four real-life credit datasets, the experimental results show that the model of (knn-nn-svmpso)-(dl)-(dbscan) delivers the highest prediction accuracy and the lowest error rates. keywords-credit scoring; hybrid machine learning models; stacking; deep learning i. introduction owing to the recent global financial crisis and european sovereign debt crisis, credit risk assessment has turn out to be an increasingly vital issue for banks and credit institutions throughout the world. also, the sharp competition in financial sector has caused a large decline in banking profit. this leads banks toward more consumer loans to make higher interest profits. however, the expected profitability depends on the quality of consumer loans issued by the banks, which requires a vigilant credit scoring process. it is worthwhile to mention that even 1% enhancement on the accuracy of credit scoring system would significantly increase the profit of banks and other financial institutions [1]. traditionally, credit decisions were made by human experts based on past experiences, historical performances, and some guidelines specially the classic five c’s of credit: character, capacity, capital, collateral and conditions [2]. but this approach suffers from some drawbacks including inconsistent decisions, repeated incorrect decisions, and high training costs. therefore, with the quick development in credit industry, various credit scoring techniques are being used for the credit evaluation. the credit scoring models have been developing at a fast pace to distinguish bad credit applicants from good ones through their associated features such as gender, age, education, income, job and marital status or based on their historical credit performance. the advantages of credit scoring models can be enumerated as cost reduction of credit analysis, faster credit decisions, higher rate of credit collections, efficient performance monitoring of the model, mitigating possible risks and changes in economic conditions or policies can simply be integrated into the model [3-5]. even a minor betterment in the accuracy of credit scoring models may diminish a significant amount of credit risks and generate noteworthy future savings. due to both the impacts of financial crisis and soaring risk appetite, the number of non-performing loans has sharply intensified along with banks giving more credits to applicants without sufficient assessments. thus, the use of efficient credit scoring models seems to be inevitable for the banks and other credit institutions. there are several approaches employed by financial institutions over the past decades to model the credit risk which are mainly classified into two groups of statistical and artificial intelligence (ai) techniques. generally, the statistical methods include logistic regression (lr) and linear discriminant analysis (lda). on the other hand, ai approaches mainly comprise of machine learning techniques such as support vector machines (svm), artificial neural networks (ann), decision trees (dt) and so many other machine learning (classification and clustering) algorithms. there are some pros and cons associated with these methods. for instance, lda assumes a normal distribution of the variables and a linear relationship between explanatory variables but it is unable to verify fulfillment of these assumptions [4, 5]. lr is used for forecasting on a dataset with binary outcomes. although, the normality assumption is not required by lr, but linear relationship among variables is a basic assumption for both models. therefore, some researchers [4-7] are having doubts about predictive performance of these models for credit scoring. in contrast, artificial intelligence techniques recently draw attention from many scholars for coping with credit scoring problems. these techniques are best known for their higher predictive accuracy compared to statistical models and usually do not require abovementioned engineering, technology & applied science research vol. 7, no. 5, 2017, 2073-2082 2074 www.etasr.com armaki et al.: a hybrid meta-learner technique for credit scoring of banks’ customers assumptions. for example, ann which simulates the human brain’s mechanism on the computer environment does not need any assumptions and in the field of credit scoring, it performs much better than its classical rivals including lr and lda [813]. in general, it can be said that ai methods are superior to traditional ones [14-16]. in recent years, many researchers have focused on the development of machine learning techniques for credit scoring applications. one of the methods that they are using to improve the performance machine learning algorithms is the hybridization. these researchers believe that the credit scoring models which are built by combing classification (supervised learning) and clustering (unsupervised learning) techniques have the ability to outperform sole machine learning methods [12, 17-20]. in this study, a new hybrid method is introduced for credit scoring which is based on a combination of traditional hybrid and stacking ensemble methods. the idea comes from the traditional hybrid model of classification plus clustering. this is because clustering is considered as an unsupervised learning method and it cannot differentiate data precisely like supervised methods. accordingly, a classifier or set of classifiers can be trained first, and then its output is used as the input for the clustering method to enhance the clustering outcomes [21]. in this model, instead of using a single classification algorithm in the first part of the hybrid model, we adopt a stacking ensemble method and in the second part several clustering algorithms will be interchangeably used. also, this model benefits from a deep learning algorithm as the meta-learner classifier. it is believed that the superior learning capacity of deep learning can improve the predictive accuracy of the new hybrid credit scoring model. this study has chosen various types of classifiers and clusterers to be used in this hybrid model. in the relevant literature, many studies have developed hybrid credit rating models only by choosing single learning algorithms as the baselines (traditional hybrid models) but this study adopts the stacking ensemble method as the baseline of the hybrid model. moreover, this paper tries to compare several versions of the proposed hybrid model by using various combinations of classification and clustering algorithms. thus, it helps us to identify which hybrid model can achieve the best prediction accuracy for credit scoring purposes. the structure of the paper is as follows: section ii reviews the literature in terms of different hybrid and ensemble credit scoring models. section iii explains the data and methodology of the study and section iv presents the experimental results and analysis. finally, section v concludes the study and discusses future work opportunities. ii. literature review in this section, the literature of machine learning in the field of credit scoring will be reviewed. when banks want to grant credit to their customers, they evaluate their credit. through adopting a good credit scoring system, banks can classify their customers in terms of risk (probability of default), so offer them risk adjusted loans with different interest rates and collateral conditions. therefore, optimal credit decisions can be made based on the outputs of the credit scoring models. since the emergence of ai systems like neural networks, genetic algorithm and expert systems, these methods have been increasingly used in financial researches and also implemented by many financial institutions specially banks. authors in [22] adopt the four different types of traditional hybrid machine learning techniques to identify which method can achieve the best predictive results. they combine different classification and clustering algorithms such as naïve bayesian, decision tress, logistic regression, neural network, k-means and expectation maximization. then, they apply these hybrid models on a real credit dataset from taiwan. comparative results show that the “classification + classification” hybrid model outperforms the other hybrid models. this model utilizes logistic regression and neural network as the first and second classifiers (lr + nn), respectively. they state that these hybrid credit scoring models can help financial institutions make more correct decisions for issuing consumer loans with high confidence in the future. authors in [23] study the behavior of imbalanced credit scoring datasets by different machine learning methods. data imbalances take place when the number of defaulting customers in a dataset is typically much lower than the number of non-defaulting ones. they tested various models on five real-world credit datasets. finally, they showed that when datasets are imbalanced, machine learning methods like decision trees, knn, linear discriminant analysis (lda) do no perform well. on the other hand, models such as gradient boosting and random forests have much better predictive performance. although, decision trees (dt) is one of the most popular algorithms used in machine learning and credit scoring, it suffers from two drawbacks: 1) it’s very sensitive to noise and 2) redundant features may falsify the learning process. hence, authors in [24] suggest two ensemble methods namely bagging-rs dt and rs-bagging dt to deal with these problems. in these models they adopt random subspace (rs) and bootstrap aggregating (bagging) strategies. they test these two models on australian and german credit datasets and results show that these two models perform better than other base models. author in [25] introduces a new solution for credit scoring problems which is based on a modified version of svm. he mentions that since most of real credit datasets are pretty big, the use of conventional nonlinear svms even with high levels accuracy are computationally suboptimal. consequently, he proposes a clustered support vector machine (csvm) to cope with this problem. he concludes that the csvm, despite gaining similar prediction performance, can stay relatively cheap from computational point of view. in another attempt to create an optimal credit scoring model, authors in [26] have proposed the ensemble classification based supervised clustering (ecsc) method. the main idea behind this model is that data samples from the identical class might have dissimilar characteristics or patterns. by means of supervised clustering, samples with similar characteristics or patterns are categorized into the same cluster. hence, the training subsets, formed by mixture of clusters from diverse classes, could well express various patterns of samples, which is beneficial to enhance the variety and accuracy of base classifiers. in this paper they use base classifiers such as logistic regression, decision trees, svm and also k-means for supervised clustering. they have applied this model along with random subspace bagging (rs-bagging), bagging-rs, and dynamic classifier ensemble using classification confidence (dce-cc) on german and australian engineering, technology & applied science research vol. 7, no. 5, 2017, 2073-2082 2075 www.etasr.com armaki et al.: a hybrid meta-learner technique for credit scoring of banks’ customers credit datasets. results show the ecsc is relatively more accurate than other models. one of the heuristic methods used for credit scoring is fuzzy svm based on support vector data description (svdd) which is introduced in [27]. svdd is based on the svm classifier, which looks for a spherical-shaped border around a dataset to identify outliers or unique data. this approach uses svdd to mitigate the impact of outliers and noisy data in order to improve the fuzzy svm learning rate. authors adopted this model to test against the ordinary linear and nonlinear fuzzy svm on the australian and german credit datasets. what can be drawn as a conclusion is that although the best result is obtained by the svdd-fsvm its superiority is negligible. in a recent study, authors in [28] introduced a model based on the combination of hybrid and ensemble methods. they believe that merging filtering and feature selection methods can perform as an effective pre-processor for machine learning models. for this reason, they have combined multivariate adaptive regression splines (mars) and gabriel neighborhood graph editing (gng) in the hybrid modeling stage. as base classifiers, they have selected decision trees, ann, random forests, bayesian network and svm. they have applied these models on seven real world credit datasets. results illustrate that the authors’ proposed model relatively improves the predictive performance relative compared with base learners. iii. methodology this section describes the procedure of developing the credit scoring system introduced by this study. generally, there are two ways to establish a hybrid machine learning model which are traditional and ensemble methods. the traditional hybridization method offers four different ways to combine machine learning algorithms. these options are (1) merging two classification algorithms, (2) merging one classification algorithm with one clustering algorithm, (3) merging one clustering algorithm with one classification algorithm, and (4) merging two clustering algorithms [22, 29]. on the other hand, ensemble methods offer sophisticated ways of hybridizing machine learning techniques. employing ensembles is beneficial as they can overcome the three problems of base learning algorithms namely statistical, computational, and representational problems [30]. when the size of a dataset is too small compared with the potential space of hypotheses, a learning algorithm may select to yield a hypothesis from a group having the equal predictive accuracy on the training data. thus, the statistical problem emerges in such cases if the selected hypothesis is unable to forecast new data. when a learning algorithm is trapped in an incorrect local minimum rather than finding the best hypothesis within the hypotheses space, the computational problem will arise. lastly, the representational problem occurs when no hypothesis inside the hypotheses space is a good estimate to the correct function [31]. there are several forms of ensembles including bagging, boosting, and stacking. these techniques are frequently used in the literature of machine learning and credit scoring. findings suggest that ensemble methods usually achieve superior predictive performance compared to other single algorithms or traditional hybrid models [26, 28, 32-36]. unlike the bagging and boosting which are used in many papers, few researchers have employed the stacking method. stacking (stacked generalization) is designed to enhance predictive performance through combining the predictions of several machine learning algorithms [37]. it consists of training a combiner algorithm to amalgamate the predictions of various learning algorithms. first, an ensemble of classifiers (base classifiers) is trained using the available data via bootstrapped sampling (tier 1 classifiers). then the output of base classifiers are used as an input to train a meta-classifier (tier 2 classifier) [36]. in other words, stacking trains a set of classifiers parallelly and then learning is done by a meta-learner. author in [38] emphasizes that classifiers which are functioning in a collaborative way can significantly outpace those working separately, showing the importance of using such a model. the meta-learner (meta-classifier) in the stacking algorithm generates a vector of weight distribution by assigning a weight to each base classifier that is proportional to their performances [31]. stacking can be considered as a fully customizable hybrid machine learning system as it hosts various types of baseand meta-classifiers. also, it has been successfully employed on both supervised and unsupervised learning tasks [39-41]. in a recent study [32] is showed that a hybrid ensemble machine learning system with stacking is superior to other types of ensemble methods. the proposed hybrid meta-learner model is built based on the combination of traditional hybrid and ensemble modeling of credit scoring systems. the foundation of the model is based on the traditional hybrid model of “classification+clustering” which uses a classification technique as a pre-processor for the clustering algorithm. the only difference is that this paper adopts the stacking ensemble method in the first part instead of using a single classification method. also, several classification and clustering techniques are used in this study which are briefly described in following sub sections. a. classification techniques classification (or supervised learning) methods are capable of mapping input vectors into one of various preferred output classes through learning by examples. a classifier can be learned by computing the rough distance between input–output instances and correctly labeling outputs out of training set. this procedure is named as the model generation stage. after generating the model, the resulting classifier is able to classify an unidentified example based on the learned classes in the training set. various classification techniques are employed in this paper which are artificial neural network (nn), automated multilayer perceptron (amlp), decision tree (dt), k-nearest neighbors (knn), logistic regression (lr), naïve bayesian (nb), support vector machines (svm), and support vector machines optimized by particle swarm optimization (svm-pso). b. clustering techniques clustering (or unsupervised learning) methods can be viewed as the way toward combining similar examples into a cluster. unlike the classification, labeled examples are not available in clustering. the main aim of clustering approach is engineering, technology & applied science research vol. 7, no. 5, 2017, 2073-2082 2076 www.etasr.com armaki et al.: a hybrid meta-learner technique for credit scoring of banks’ customers to increase the resemblance between the group members. moreover, the data between different clusters should have the highest dissimilarity. conversely, the highest data similarity should exist within each cluster [42]. there are two categories for clustering algorithms, which are partitional and hierarchical clustering algorithms but the former is much more popular [43]. partitional clustering has been widely implemented in many credit scoring problems. k-means and expectation maximization are two renowned partitional clustering algorithms. in contrast, hierarchical clustering generates clusters according to a hierarchy by means of the accumulation algorithm. then, a different single cluster will be merged individually until fulfilling some rules. the outcome will create a series of branching partitions. this study uses five clustering algorithms namely expectation maximization (em), k-means (km), fuzzy c-means (fcm), density-based spatial clustering of applications with noise (dbscan), and self-organizing maps (som). c. the hybrid meta-learner model this study introduces a new hybrid method for credit scoring which is a mixture of traditional hybrid and stacking ensemble methods. the idea comes from the traditional hybrid model of “classification plus clustering” due to the fact that clustering is an unsupervised learning method and it is unable to distinguish data accurately like supervised approaches. therefore, a classifier or set of classifiers can be trained first, and then the output can be used as the input for the clustering technique to improve the clustering results. in this process, instead of using a single classification algorithm in the first part of the hybrid model, a stacking ensemble method will be used. this stacking model utilizes three different base classifiers (level 0 generalizers) to train the meta-classifier (level 1 generalizer). in the second part, several clustering techniques will be interchangeably used in order to find which combination of algorithms yield the best results. one of the advantages on this hybrid system is placing a deep learning algorithm (dl) in the heart of the proposed model as the metalearner. owing to the great learning ability of dl, the predictive performance of the model is expected to improve significantly. for the first time, the concept of dl is proposed in 2006. this algorithm is defined in the framework of deep belief networks (dbn). later, dl has caused considerable amount of scientific researches in several fields [45-47]. this algorithm as a feature selection technique, tries to get feature abstractions at the high-levels through learning various feature structures in the training process. every dl iteration is an unsupervised learning process for feature extraction, and the mix of different layers has the ability to create a deep supervised predictor [48]. dl has various theoretical frameworks, but this study utilizes the h2o version, which is based on the feedforward architecture. as shown in the figure 1, the main part of the dl model is the neuron which is inspired by the human neural system. in this model, the weighted mix of input signals (α) is combined, and then an output signal f(α) conveyed by the connected neuron. the nonlinear activation function and neuron’s activation threshold (bias) are denoted by f and b, respectively [49]. fig. 1. the neuron architecture in the deep learning model the weights which are connecting neurons and biases with other neurons define the output of the whole network. the error on the labeled training data should be minimized through weight adjustment procedure in order to make learning possible. specifically, the aim is to minimize the loss function of l(w; b | j) for every training example j [49]. dl as the meta-learner in the stacking algorithm creates a vector of weight distribution by giving a weight to each base classifier that is proportional to their performances. stacking can be seen as a completely customizable hybrid machine learning technique since it embraces various types of baseand metaclassifiers. this study employs different types of classifiers and clusterers to be used in this hybrid model. in the literature, many works have been done by developing hybrid credit rating models only by choosing single learning algorithms as the baselines but this study adopts the stacking ensemble method as the baseline of the hybrid model. furthermore, the aim is to compare several versions of the proposed hybrid model by selecting various mix of classification and clustering algorithms in order to find the best model. figure 2 illustrates the framework for the proposed hybrid meta-learner model. fig. 2. the hybrid meta-learner model engineering, technology & applied science research vol. 7, no. 5, 2017, 2073-2082 2077 www.etasr.com armaki et al.: a hybrid meta-learner technique for credit scoring of banks’ customers after collecting the desired datasets, the pre-process treatment should be applied on the data. in this stage, those data points which are considered as outliers or anomalies should be removed from datasets. for this reason, a distancebased outlier detection algorithm is used to identify n outliers in the given dataset based on the distance to their k nearest neighbors [50]. also, those examples with missing feature values are removed from datasets. then, a combination of three classifier algorithms is interchangeably selected out of various classifiers as the base learners. as mentioned before, the stacking model is equipped with dl algorithm as the metalearner. the stacking model uses the results of base learners (level 0 generalizers) to train the meta-learner (level 1 generalizers). in the next step, the results of the dl as the processed data are fed into the clustering unit. hence, it is expected to see significant improvement in the prediction accuracy of the model. the performances of models are compared after applying 10-fold cross-validation with stratified sampling during the training and testing stages. therefore, each dataset is divided into 10 unique subsets (strata), in which any 9 of the 10 subsets are used for training and the leftover for testing. in other words, each model will be trained and tested 10 times. d. data financial institutions need to have a system for evaluating the credit risk of their customers when granting loans. but before that, they need to make sure that the accuracy of their system is at the acceptable level. since, it is very difficult to assess the performance of a credit scoring system against private datasets, it is necessary to measure its performance against some benchmark datasets. as a result, we study four real-life datasets to evaluate the predictive power of our proposed hybrid meta-learner model. table i displays the characteristics of the datasets. particularly, the first three datasets are considered as benchmark datasets in the literature. they are related to consumer credit card loans from australia, germany, and japan; and collected from the ucsd data repository. the last dataset is related to consumer loans in iran and collected from mellat bank. table i. characteristics of the data sets data set #attributes #good #bad total source australian (aus) 14 307 383 690 uci machine learning database repository german (ger) 24 700 300 1000 uci machine learning database repository japanese (jpn) 15 296 357 653 uci machine learning database repository iranian (ira) 12 9351 649 10000 mellat bank e. evaluation strategies in order to assess the predictive power of the developed models, prediction accuracy rate and f-measure which is the harmonic mean of precision and recall are taken into account. precision shows the accuracy degree of classification results and recall is the success rate of identifying classification results. moreover, besides from these evaluation methods, type i and ii errors are also shown for the best model in each dataset (table ii). these evaluation methods can be calculated as follows: table ii. confusion matrix for a credit scoring problem good applicant bad applicant predicted as good tn fn predicted as bad fp tp note: positive class is bad. iv. empirical results a. the single baseline classifiers table iii shows the prediction accuracy, f-measure and average rank of single baseline classifiers. in order to rank the performance of the models, we choose the average rank method as presented in [23]. table iii. accuracy, f-measure and average rank of the single baseline models model accuracy f-measure average rank aus ger jpn ira aus ger jpn ira accuracy f-measure svmpso 97.54 93.90 98.47 98.92 97.15 88.68 98.62 91.54 1.00 1.00 nn 87.54 81.20 87.29 98.66 86.65 66.19 87.70 89.25 3.00 3.00 amlp 87.10 77.40 87.90 98.57 85.53 65.65 88.47 88.62 3.75 3.75 lr 87.68 73.40 88.82 96.21 86.82 64.53 89.62 76.65 4.00 3.25 dt 86.81 68.00 86.68 98.89 86.32 46.67 86.80 90.65 5.00 4.50 svm 85.51 77.90 86.52 94.75 85.03 55.71 86.67 48.58 5.50 6.50 knn 73.33 74.80 74.89 95.48 63.35 37.31 77.66 54.34 6.75 7.50 nb 80.72 74.40 80.40 93.29 75.77 60.25 83.55 52.11 7.00 6.50 note: all the numbers are in percentage form. the analyses are carried out in rapidminer 7.2 program. this method helps us compare various model performances and identify the top performers. as shown, the svmpso has shown the best predictive accuracy and f-measure and it is ranked first among the other baseline classifiers. svms are first introduced by authors in [51] as a form of linear classifiers. svms can be utilized for twofold classification with the aim of generating a best hyperplane (line) that sorts the input information into two classes (bad or good credit) [52]. as a engineering, technology & applied science research vol. 7, no. 5, 2017, 2073-2082 2078 www.etasr.com armaki et al.: a hybrid meta-learner technique for credit scoring of banks’ customers population-based stochastic optimization approach, particle swarm optimization (pso) works via simulating the birds’ behavior inside a flock. this algorithm is introduced by authors in [53] and [54]. pso can be used to improve the accuracy of svms through identifying the best hyperplane which separates two classes. as can be seen from the results, the svm-pso is one of the highly accurate heuristic classifiers but only few studies have applied this method. according to the results, the second and third best performers are nn and amlp. conversely, the worst predictive performance on average belongs to nb. here, f-measure shows the overall performance of the model via combining precision and recall values. b. the hybrid meta-learner models table iv represents the prediction accuracy, f-measure and average rank of the best hybrid meta-learner models. as it is shown in this table, the (knn-nn-svmpso)-(dl)(dbscan) model has achieved the best accuracy rate and fmeasure compared with other hybrid models on all credit datasets. it is interesting that other high performing models also have the same stacking combination as the best model. it is obvious that employing an optimized version of support vector machine, svmpso, has a significant role in improving the accuracy of the results. moreover, among the clustering algorithms, dbscan has highest performance and followed by som and fcm. dbscan is a data clustering algorithm introduced in [55] and it is a density-based clustering algorithm that groups data points which are closely located together. dbscan is known as one of the top performing clustering algorithms in the literature. the advantages of dbscan algorithm can be enumerated as follows:  unlike the k-means, dbscan does not need the number of clusters in the dataset to be specified a priori.  it has the ability to detect clusters which are arbitrarily shaped. it can even discover a cluster entirely bounded by (but not linked to) a different cluster. table iv. accuracy, f-measure and average rank of the best hybrid models model accuracy f-measure average rank aus ger jpn ira aus ger jpn ira accuracy f-measure (knn-nn-svmpso)-(dl)-(dbscan) 99.71 99.80 99.85 99.90 99.67 99.67 99.86 99.23 2.00 2.00 (knn-nn-svmpso)-(dl)-(som) 99.86 99.70 99.85 99.80 99.84 99.50 99.86 98.45 2.13 2.13 (knn-nn-svmpso)-(dl)-(fcm) 99.71 99.70 99.85 99.74 99.67 99.50 99.86 97.99 3.25 3.25 (knn-nn-svmpso)-(dl)-(em) 99.86 99.60 99.69 99.78 99.84 99.33 99.72 98.29 3.50 3.50 (knn-nn-svmpso)-(dl)-(km) 99.71 99.70 99.69 99.72 99.67 99.50 99.72 97.82 4.13 4.13 (dt-knn-nn)-(dl)-(fcm) 95.65 97.70 94.33 99.48 95.07 96.19 94.71 95.95 11.88 11.38 (dt-knn-nn)-(dl)-(km) 95.94 97.90 93.88 99.48 95.39 96.45 94.30 95.91 12.13 13.50 (knn-nn-svm)-(dl)-(fcm) 95.22 98.10 94.33 99.46 94.60 96.82 94.78 95.78 15.00 14.63 (nb-knn-nn)-(dl)-(fcm) 95.65 97.80 94.03 99.43 95.03 96.33 94.42 95.61 16.00 16.75 (knn-nn-svm)-(dl)-(dbscan) 95.80 97.70 94.03 99.42 95.25 96.10 94.48 95.53 16.50 15.38 (knn-nn-lr)-(dl)-(som) 95.65 97.60 94.18 99.42 95.07 95.99 94.54 95.44 17.25 17.63 (dt-knn-nn)-(dl)-(em) 95.80 97.10 93.87 99.55 95.27 95.09 94.40 96.45 17.38 16.75 (dt-knn-nn)-(dl)-(dbscan) 95.36 97.80 93.72 99.55 94.61 96.28 94.12 96.51 17.75 18.50 (nb-knn-nn)-(dl)-(em) 95.36 97.40 94.49 99.45 94.70 95.65 94.87 95.74 17.88 18.00 (knn-nn-amlp)-(dl)-(em) 96.52 95.90 94.03 99.46 96.03 92.79 94.45 95.73 17.88 18.25 (knn-nn-amlp)-(dl)-(fcm) 95.51 95.70 94.49 99.47 94.99 92.77 94.99 95.80 17.88 17.75 (knn-nn-amlp)-(dl)-(dbscan) 93.91 98.20 94.49 99.41 93.02 97.01 94.89 95.28 18.87 19.50 (knn-nn-amlp)-(dl)-(km) 95.51 96.00 94.18 99.47 94.82 93.22 94.49 95.87 19.00 20.13 (knn-nn-amlp)-(dl)-(som) 94.93 98.30 94.33 99.39 94.14 97.12 94.78 95.27 19.63 19.13 (knn-nn-lr)-(dl)-(dbscan) 95.51 98.10 94.18 99.37 94.89 96.85 94.69 95.17 19.63 18.00 (dt-knn-nn)-(dl)-(som) 95.07 97.30 94.03 99.52 94.48 95.43 94.42 96.23 20.13 20.88 (knn-nn-lr)-(dl)-(km) 95.36 97.50 94.03 99.44 94.81 95.83 94.53 95.71 20.50 18.88 (nb-knn-nn)-(dl)-(km) 95.65 97.50 93.72 99.43 95.15 95.81 94.23 95.48 21.13 21.00 (knn-nn-lr)-(dl)-(fcm) 95.80 97.20 93.87 99.42 95.19 95.29 94.32 95.47 21.25 21.88 (nb-knn-nn)-(dl)-(dbscan) 95.51 96.90 94.18 99.41 95.06 94.70 94.60 95.52 22.75 19.88 (knn-nn-lr)-(dl)-(em) 95.51 97.00 93.87 99.43 95.01 94.92 94.43 95.52 23.63 22.38 (lr-nn-amlp)-(dl)-(km) 95.65 95.40 93.11 99.46 95.03 91.87 93.58 95.76 23.88 24.38 (knn-nn-svm)-(dl)-(km) 95.36 97.70 93.42 99.41 94.82 96.10 94.07 95.39 24.38 24.13 (knn-nn-svm)-(dl)-(em) 95.65 97.50 93.87 99.37 95.02 95.77 94.32 95.00 24.38 25.88 (nb-knn-nn)-(dl)-(som) 95.36 97.20 93.87 99.41 94.74 95.38 94.33 95.39 25.88 25.63 (lr-nn-amlp)-(dl)-(em) 93.04 97.70 92.50 99.45 92.23 96.17 93.17 95.62 26.50 26.75 (knn-nn-svm)-(dl)-(som) 95.22 97.50 93.72 99.40 94.53 95.83 94.22 95.41 27.00 26.13 (lr-nn-amlp)-(dl)-(dbscan) 93.33 97.60 92.8 99.43 92.51 96.00 93.41 95.47 27.75 28.62 (lr-nn-amlp)-(dl)-(som) 93.91 97.20 94.03 99.39 92.91 95.29 94.44 95.15 28.00 28.63 (lr-nn-amlp)-(dl)-(fcm) 93.91 97.60 93.42 99.36 93.16 95.86 93.99 94.94 30.75 30.75 (dt-nb-lr)-(dl)-(km) 94.49 89.30 90.66 99.38 93.75 83.56 91.30 95.07 35.88 35.63 (dt-nb-lr)-(dl)-(fcm) 93.62 88.80 91.27 99.39 92.59 82.22 91.80 95.07 36.25 37.38 (dt-nb-lr)-(dl)-(dbscan) 94.20 88.50 91.27 99.38 93.38 80.21 91.82 95.02 36.25 36.50 (dt-nb-lr)-(dl)-(em) 93.33 89.20 90.81 99.39 92.65 80.99 91.71 95.12 37.00 37.25 (dt-nb-lr)-(dl)-(som) 93.48 89.60 91.73 99.36 92.66 82.61 92.22 94.83 37.13 37.25 note: see table iii engineering, technology & applied science research vol. 7, no. 5, 2017, 2073-2082 2079 www.etasr.com armaki et al.: a hybrid meta-learner technique for credit scoring of banks’ customers  it is robust to outliers so it can successfully deal with noises in datasets. table v compares the best baseline and hybrid models in terms of accuracy, f-measure, type i and ii errors. the best hybrid model has improved the accuracy rate and f-measure results of the best baseline model by 2.68% and 5.97% on average, respectively. in contrast, the best hybrid model has reduced the type i and ii errors by 79.84% and 95.16% on average, respectively. furthermore, as we have included three public real-world credit datasets in this study, it is easy to compare the predictive performance of our hybrid models with other studies in the literature. table vi presents a comprehensive summary of credit scoring performances of various models which are used in the literature by several researchers. as the australian and german credit data sets are the most frequently used datasets in the relevant literature, we also collected the results of the papers which have used these two datasets as their benchmarks. as shown, different authors have applied different models in their studies and they found various results in terms of predictive performance. it is interesting that the best performing hybrid model of this study is placed in the first rank based on the prediction accuracy measure. this hybrid credit scoring model has reached to an astonishing 99.71% and 99.80% accuracy on australian and german datasets, respectively. table v. average performance comparison of the best baseline and hybrid models best baseline best hybrid svmpso (knn-nn-svmpso)-(dl)-(dbscan) accuracy f-measure error i error ii accuracy f-measure error i error ii aus 97.54 97.15 0.00 5.54 99.71 99.67 0.26 0.33 ger 93.90 88.68 0.00 20.33 99.80 99.67 0.14 0.33 jpn 98.47 98.62 3.38 0.00 99.85 99.86 0.34 0.00 ira 98.92 91.54 0.46 10.02 99.90 99.23 0.03 1.08 average 97.21 94.00 0.96 8.97 99.82 99.61 0.19 0.43 improvement 2.68 5.97 -79.84 -95.16 note: “improvement” shows the percentage growth rate for the accuracy and f-measure. it also show the type i and ii error reduction rates in percentage. table vi. performance comparison of various credit scoring models in the literature model australian german rank author(s) year (knn-nn-svmpso)-(dl)-(dbscan) 99.71 99.80 1 (this study) 2017 mc-lr (intersection) 99.11 99.18 2 tsai,hsu [56] 2013 hybrid som-km-nn 97.98 98.46 3 hsieh [17] 2005 mlp + fs 97.20 4 analide [57] 2011 libsvm 86.38 94.00 5 peng, kou, shi,chen [58] 2008 hybrid nn 91.61 87.45 6 tsai,hung [59] 2014 ammlp 92.75 84.67 7 marcano-cedeno, marin-de-la-barcena, jiménez-trillo, pinuela,andina [60] 2011 gaussian classifier 92.6 83.80 8 somol, baesens, pudil,vanthienen [61] 2005 ann 97.32 78.97 9 tsai,wu [62] 2008 vbdtm 91.97 81.64 10 zhang, zhou, leung,zheng [63] 2010 deepsvm 88.98 83.70 11 qi, wang, tian,zhang [64] 2016 pso-svm 91.03 81.62 12 lin, ying, chen,lee [65] 2008 svm 85.70 13 martens, baesens, van gestel,vanthienen [66] 2007 clc 86.52 84.80 14 luo, cheng,hsieh [67] 2009 mlp 90.20 79.11 15 tsai [68] 2008 2sgp 89.17 79.49 16 huang, tzeng,ong [69] 2006 gng + mars 88.10 79.00 17 ala'raj,abbod [28] 2016 rs-bagging dt 88.17 78.36 18 wang, ma, huang,xu [24] 2012 genetic programming 88.27 77.34 19 ong, huang,tzeng [16] 2005 parallel random forest 89.40 76.20 20 van sang, nam,nhan [70] 2016 ls-svm 90.40 74.60 21 baesens, van gestel, viaene, stepanova, suykens,vanthienen [71] 2003 fa-mlp 86.08 78.76 22 tsai [72] 2009 svm + ga 86.90 77.92 23 huang, chen,wang [73] 2007 svdd-fsvm 87.25 77.30 24 shi,xu [27] 2016 rbf-svm 87.52 76.60 25 ping,yongheng [74] 2011 genetic fuzzy classifier 88.60 75.00 26 lahsasna, ainon,wah [11] 2010 mixture-of-experts network 87.25 76.30 27 west [5] 2000 lda + svm 86.52 76.70 28 chen,li [75] 2010 bayes 86.70 76.00 29 hoffmann, baesens, mues, van gestel,vanthienen [76] 2007 gr-ga-svm 86.84 75.75 30 liu, fu,lin [77] 2010 rs-lmnc 87.05 74.67 31 nanni,lumini [78] 2009 adopted cba 86.96 74.40 32 lan, janssens, chen,wets [79] 2006 hga-nn 78.90 33 oreski, oreski,oreski [80] 2012 ecsc 86.86 70.60 34 xiao, xiao,wang [26] 2016 note: the above models are ranked based on their average performances on australian and german credit datasets. engineering, technology & applied science research vol. 7, no. 5, 2017, 2073-2082 2080 www.etasr.com armaki et al.: a hybrid meta-learner technique for credit scoring of banks’ customers v. conclusion as financial institutions are exposed to credit risk when issuing consumer loans, developing reliable credit scoring systems is crucial for them. since, machine learning methods have demonstrated their applicability and merit, this study develops and compares several hybrid machine learning approaches for the credit scoring problem. in this paper, a novel framework is proposed for hybrid meta-learning to improve the predictive performance of credit scoring models. based on the selected datasets, the results show that the hybrid meta-learner model of (knn-nn-svmpso)-(dl)-(dbscan) outpaces all the literature’s baseline classifiers in terms of accuracy rate and type i/ii errors. this model also outperforms the best models used in the relevant literature in terms of accuracy rate with a significant margin. the findings of this study give us the insight to realize which type of hybrid machine learning techniques is capable of achieving higher accuracy and lower error rates in the case of credit scoring. also, it is clear that the optimized version of support vector machine, svmpso, and deep learning algorithms have significant roles in enhancing predictive power of the proposed models. as a result, it is believed that using the best credit scoring model identified by this study can help financial institutions to make more accurate and confident credit decisions in the future. for further studies, several issues can be studied in the future. one of them can be the reduction of feature dimensionality. to be precise, the pre-process treatment of selected datasets for dimensionality reduction or feature selection can be beneficial to achieve better prediction precision [72]. although, this paper is quite rich in terms of employing various machine learning algorithms, there are other techniques which can be applied for further comparisons especially those 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kerman, iran abstract—this paper focuses on solving the fluid flow and heat transfer equations inside a two-dimensional square enclosure containing three hot obstacles affected by gravity and magnetic force placed on a ramp using boltzmann method (lbm) applying multiple relaxation times (mrt). although, the lattice boltzmann with mrt is a complex technique, it is a relatively new, stable, fast and high-accurate one. the main objective of this research was to numerically model the fluid flow and ultimately obtaining the velocity field, flow and temperature contour lines inside a two-dimensional enclosure. the results and their comparisons for different types of heat transfer revealed that free or forced heat transfer has a considerable impact on the heat transfer and stream lines. this can be controlled by modifying the richardson number. it is revealed that changing the intensity of the magnetic field (hartman number) has an appreciable effect on the heat transfer. keywords-lattice boltzmann; multiple relaxation times; twodimensional enclosure; hot obstacles; ramp; hartmann number i. introduction in fluid flow analysis, three types of techniques may be applied: microscopic, mesoscopic and macroscopic ones. microscopic techniques are not that effective for solving engineering problems. macroscopic techniques are common in computational fluid dynamics but they often do not have analytical solutions. they are rather solved through numerical methods such as finite differences, finite volume and finite element in which the values of velocity, temperature and pressure are obtained in the different situations and times. mesoscopic techniques lie between the previous two, involving a set of molecules as a particle rather than a single particle or molecule of fluid. these particles can move in the specified directions, so that their equations of motion can be statistically expressed by the distribution equations. the lattice boltzmann is one of the most important mesoscopic techniques in fluid flow analysis. in the recent years, due to its simplicity of programming, high capability and precise simulation, the lattice boltzmann method has been adopted for the various problems including the single-phase flows, multi-phase flows, non-steady flows, flow in porous media and many other problems as a new approach to solving complex problems related to fluid dynamics. the multiple relaxation time model was initially proposed in [1].this method is widely used in many important and complex engineering problems including multiphase flows [2], incompressible flows [3, 4] the passing flows through porous media [5]. in [6], authors examined the bounce back boundary condition in the boltzmann method demonstrating that the bounce back is suitable for the non-slip boundary condition on stationary walls. this method was developed and problems were solved through a complex geometry [7, 8]. in [9], authors numerically studied the natural convection of an electric fluid in a rectangular enclosure in presence of a magnetic field. they found that convection effect is reduced in the presence of strong magnetic field. this was apparent as heat transfer by an increasing hartmann number. in [10], authors examined the effect of uniform magnetic field on the natural convection in a nano-fluid. the results obtained confirmed the previous results and the only difference lied in the solution and the choice of three functions for flow, heat and magnetic field. in [11], authors conducted an experimental investigation on forced convective heat transfer of magnetic fluids in the presence of an alternating magnetic field. they concluded that the alternative magnetic fields are more influential than the uniform ones in the heat transfer. in [12], authors simulated a square enclosure containing a water-aluminum nano-fluid affected by a magnetic field using lattice boltzmann. the differences of their works were related to the temperature depending on the walls. they concluded that increasing the rayleigh number results in the greater heat transfer and as the hartman number increases the heat transfer decreases. in [13], authors examined a container with a removable lid influenced by a forced convection with the obstacles. in [14], authors examined a compartment with more than one obstacle engineering, technology & applied science research vol. 7, no. 3, 2017, 1647-1657 1648 www.etasr.com keshtkar and ghazanfari: numerical investigation of fluid flow and heat transfer inside a 2d … influenced by a magnetic field. in [15], authors carried out an experimental study to investigate the convection heat transfer of fe3o4/water nanofluid through a porous metal foam tube with uniform heat flux under the influence of constant magnetic field. in [16], authors focused on magnetite nanoparticles that were prepared via the solvothermal technique for further application as a nanofluid in heat transfer studies. the results showed that heat transfer properties of the examined magnetite nanofluids based on various concentrations of water and ethylene glycol were significantly enhanced under the influence of an alternating magnetic field. the hall and mhd effects on peristaltic flow of carreau-yasuda fluid in a convectively curved configuration was studied in [17]. thermal radiation, soret and dufour effects were also accounted. physical behaviors of velocity, temperature, concentration and streamlines were discussed with the help of graphical representation. in [18], authors investigated the hydro-thermal characteristics of ferrofluid (water and fe3o4) in a rib-channel exposed to several non-uniform transverse magnetic fields generated by an electric current going through several wires located perpendicularly in the flow between ribs. in [19], authors investigated the heat transfer characteristics and the entropy generation rate of hybrid graphene-magnetite nanofluids under a forced laminar flow that were subjected to the permanent magnetic fields. the effect of magnetic field on the nanofluid flow inside a sinusoidal two-tube heat exchanger was investigated numerically in [20]. this study focuses on the influence of variable magnetic field in the heat transfer of heat exchanger while mixture is single phase. the effect of a permanent magnetic field on the heat transfer characteristics of hybrid graphene-magnetite nanofluids (hybrid nanofluid) under forced laminar flow was experimentally investigated in [21]. the experimental heat-transfer results indicated that the heat transfer enhancement of the hybrid nanofluid compared to the control fluid (distilled water) was negligible when no magnetic field was applied. in [22], authors studied entropy generation due to natural convection in entrapped trapezoidal cavities filled with nanofluid under the influence of magnetic field was numerically. the convective heat transfer characteristics of fe3o4/water (3 vol%) nanofluids were investigated under a parallel constant and uniform magnetic field in [23]. a rise in the heat transfer coefficient was observed when the temperature of the nanofluids was high, so compared with the effect of the chain-like structure, it was reported that the nanoparticle’s brownian motion had a major effect on the nanofluid heat transfer performance under a weak magnetic field. in [24], authors reported the magnetic field effect on natural convection heat transfer in a curved-shape enclosure. the obtained results were depicted in terms of streamlines and isotherms which showed the significant effects of hartmann number on the fluid flow and temperature distribution inside the enclosure. fe3o4–water nanofluid flow in a cavity with constant heat flux was investigated using a control volume based finite element method (cvfem) in [25]. effects of rayleigh and hartmann numbers and volume fraction of fe3o4 (nano-magnetite, an iron oxide) on flow and heat transfer characteristics were analyzed. according to the authors’ knowledge, the lbm-mrt method has not been used for the investigation of the effects of the magnetic field on a ramp with three hot obstacles in cavity with these boundary conditions. also, the novelty of this study lies on the investigation of the effects of different richardson numbers (ri) (type of heat transfer mechanism) and the various hartmann numbers (ha) at different angles (λ) on hydrothermal behavior of mentioned problem. ii. geometry and problem statment the problem includes a two-dimensional square enclosure with the length and width of 100 mm in which the left and right boundaries are isolated while the upper and lower boundaries have constant temperatures (τc=0). the enclosure is located on a ramp and inside the enclosure there are three hot obstacles by dimensions of 12.5×12.5mm with constant temperature (th=1). the spaces between the obstacles have been filled by fluids with prandtl of 0.7. all dimensions are shown in figure 1. the fluid in the enclosure is assumed to be newtonian, incompressible, and laminar. the momentum equation is written in the boussinesq approximation. the thermophysical properties of fluid are constant. analyzing this problem requires to solve momentum and energy equations by the lbm-mrt formulation. fig. 1. schematic view of the problem iii. governing equations the governing equations are mass, navier-stokes and the energy equations and are written as follows: 2 0 . u 0 1 . ( ) . .( ) u u u p u f t t u t t t                       (1) the discrete form of kinetic equation for lattice boltzmann is formulated as follows: engineering, technology & applied science research vol. 7, no. 3, 2017, 1647-1657 1649 www.etasr.com keshtkar and ghazanfari: numerical investigation of fluid flow and heat transfer inside a 2d … ( , ) ( , ) ( , ) ( , ) . 1 ( , ) ( , ) i i i i i eq i i f x t t f x t f x x t t f x t t c t x f x t f x t f                     (2) where, ci is the velocity of the particle and fiis distribution function. then, the distribution function represents the type of problem, which can vary depending on the problem. to solve the above equation, there are two steps, the first of which involves the impact obtained through the distribution function at equilibrium  eqif . the distribution function at equilibrium state is obtained through the following equation: 1 2 3 4( ( . ) ( . ) ( . )) eq i i i if k k c u k c u k u u     (3) the d2q9 method is used to solve the equation of momentum (figure 2). hence, there are 9 discrete velocities and 9 functions. the term c represents the discrete velocity of particles, which are obtained according to the method of choice in (4). fig. 2. d2q9 layout                     0 1 2 3 4 5 6 7 8 , , 0, 0 , 1, 0 , 0,1 , 1, 0 0, 1 , 1,1 , 1,1 , 1, 1 , 1, 1 i ix iyc c c c c c c c c c c c                 (4) in (3) weighting function  is as follows: 4 0 9 1 1, 2, 3, 4 9 1 5, 6, 7, 8 36 i i i      (5) where the constant terms in (3) are obtained by the following equations: 1 2 3 42 4 2 1 1 1 1, , , (2 ) 2cs cs cs k k k k c c c      (6) the speed of sound ( )csc can be obtained from the following equation: 3cs c c  (7) fluid velocity vector is u  and given as follows: i ju u v   (8) according to (2), f is the external force, which is the total force from gravity and magnetic force affecting the enclosure. because of the slope of the surface, the external force should be placed on the main directions equal to the following [26]: 2 2 2 2 2 2 ( ) sin sin cos sin ( ) cos sin cos cos x m y m ha f g t t v u h ha f g t t u v h                           (9) the first term in the above equations represent the influence of gravity and the second term represents the effect of magnetic field analyzed based on the arrangement on the ramp in x and y directions. the hartmann number represents a measure of the relative importance of mhd flow. moreover, the various problems can be solved through mrt based on transfer matrix (m). this matrix helps us arrive at a quicker solution by the moment vector space (m). equations (10) and (11) represent the transfer matrix and the moment space matrix:  , , , , , , , ,x x y y xx yym e j q j q p p  (10)  , , , , , , , , tx x y y xx yym e j q j q p p  (11) the transfer matrix to solve the momentum equation is obtained as follows (in d2q9 scheme) [27]: 1 1 1 1 1 1 1 1 1 4 1 1 1 1 2 2 2 2 4 2 2 2 2 1 1 1 1 0 1 0 1 0 1 1 1 1 0 2 0 2 0 1 1 1 1 0 0 1 0 1 1 1 1 1 0 0 2 0 2 1 1 1 1 0 1 1 1 1 0 0 0 0 0 0 0 0 0 1 1 1 1 m                                             (12) with attention to the above equations, solving process begin from time step of t=0. after determining the initial engineering, technology & applied science research vol. 7, no. 3, 2017, 1647-1657 1650 www.etasr.com keshtkar and ghazanfari: numerical investigation of fluid flow and heat transfer inside a 2d … values for vertical and horizontal speed and density, equilibrium distribution functions are obtained. the next stage is collision in which it is transferred to momentum space from the discrete space by the transfer matrix (m) in the method of multiple-relaxation-time. the aim of this work is reduction of numerical errors. collision stage in the lattice-boltzmann method with multiple-relaxation-time has the following steps:  conversion of the distribution functions f from speed space to momentum space as m=mf.  collision in the momentum space, ( )eqm m m m     .  conversion of distribution functions from the momentum space (m+) to speed space (f+) as 1f m m   . after solving this stage and applying (2) (streaming step), boundary conditions applied to the problem. convergence condition (or a specified number of repetitions) is executed and the desired output is given. furthermore, the transfer matrix to solve the energy equation is obtained as follow (in d2q5 scheme) [26]: 1 1 1 1 1 0 1 0 1 0 0 0 1 0 1 4 1 1 1 1 0 1 1 1 1 n                 (13) these steps carried out for determination of the temperature filed, similarity. for the more information of exerting of the lbm-mrt readers can be refer to the references [27-28]. iv. boundary conditions if the problem boundary conditions imply that the enclosure walls are fixed and solid, the bounce back will be used on all the walls to solve the momentum equation. when solving the energy equation, we are faced with two boundary conditions: insulation boundary condition used for left and right insulation surfaces and constant temperature boundary condition used for the upper and lower surfaces. fig. 3. exerting bounce back in the momentum equation solving through d2q9 table i displays the boundary conditions based on the distribution functions when d2q9 has been used. the formulation for insulated surfaces such as bounce back is done in the flow equation, whereas the boundary conditions for surfaces with constant temperature are formulated by the given relations in table ii. table i. boundary conditions (bounce back) for momentum equation [27] top boundary f(4,:,ly)=f(2,:,ly) f(7,:,ly)=f(5,:,ly) f(8,:,ly)=f(6,:,ly) bottom boundary f(2,:,1)=f(4,:,1) f(6,:,1)=f(8,:,1) f(5,:,1)=f(7,:,1) right boundary f(3,lx,:)=f(1,lx,:) f(6,lx,:)=f(8,lx,:) f(7,lx,:)=f(5,lx,:) left boundary f(1,1,:)=f(3,1,:) f(8,1,:)=f(6,1,:) f(5,1,:)=f(7,1,:) table ii. boundary conditions for energy equations [26] top boundary ( constant temperature ) g(4,1:lx,ly)=0-g(0,1:lx,ly)-g(1,1:lx,ly)g(2,1:lx,ly)-g(3,1:lx,ly) bottom boundary ( constant temperature ) g(2,1:lx,1)=0-g(0,1:lx,1)-g(1,1:lx,1)g(3,1:lx,1)-g(4,1:lx,1) right boundary ( insulation ) g(3,lx,:)= g(1,lx,:) left boundary ( insulation ) g(1,1,:)= g(3,1,:) for the obstacles with the constant temperature (th=1), the boundary conditions should be formulated. to solve the momentum equations, the same bounce back is applied due to the solid surfaces. to solve the energy equation, the obstacle surfaces of the boundary condition for constant temperature are as follows [27]: ( , ) ( , ) 2 3ci i hg x t t g x t t     (14) where, a and th are the thermal diffusion coefficient and obstacle temperature, respectively. v. results a. independency of grid from meshing to show independency from the mesh, this problem was examined for four different mesh modes and the following results were obtained : table iii. comparison of average nusselt number in different meshing modes meshing average nusselt number 71×71 3.6631 101×101 3.6705 121×121 3.6109 151×151 3.6421 one can conclude that the results are independent of the meshing. in this study, a 101 × 101 mesh was used to reduce the truncation error. b. results and discussion to ensure the correctness of the code, the results were compared with various references from the beginning of the process of solving, until sufficient confidence was built about engineering, technology & applied science research vol. 7, no. 3, 2017, 1647-1657 1651 www.etasr.com keshtkar and ghazanfari: numerical investigation of fluid flow and heat transfer inside a 2d … the accuracy of the final results. the results obtained were compared with different references [28, 29] results and the entire accuracy of the code was assured. table iv. comparison of average nusselt in present work and various references. grashof number khanafar’s study[28] theoretical research[29] present 104 4.0430 4.1069 105 4.102 4.0068 all results in the present study were based on forced ( 0.1ri  ) and natural ( 10ri  ) convection heat transfers in reynolds number of 100 and 0ha  , 10 and 50 on the ramp at angles of 0  , 30 and 60 degrees as displayed in figures 4 to 11. as shown, at 0  increasing the hartmann number results in the more vortices formed between the lower obstacles. in contrast, there are no velocity contour lines at 0ha  (magnetic field is negligible) and there are zones with zero velocity. transformation of velocity contour lines with the hartmann number in a specified angle was evident for all states, especially for a hartman number of 50 which was quite distinct. this indicates the high influence of the angulations on the enclosure at the high hartmann number. when the hartmann number is zero, there is little change in the overall shape of the velocity contour by changing the angle of the ramp especially for 30  and 60. however, 10ha  (weak magnetic field) led to more visible changes as high speed lines tended towards the center of the vortex enclosure near the upper obstacle. at 50ha  , increasing the slope, results in stretching the angle of velocity contour lines which tend to form the third and fourth vortices at the upper right corner and bottom right corner of the enclosure. moreover, increasing the slope of the ramp in forced convection was associated with the increase in velocity as shown in the pictures. at 0  , increasing the hartmann number causes the main vortex becomes gradually smaller while the lateral vortex around lower obstacles grows. by the angulations of the enclosure, at the first glance, the effect of the hartmann number on the stream lines on the ramp is evident. in fact, the higher hartmann number , the greater the angularity in the behavior of stream lines is; as if the center of the upper vortex is located on the left side of the higher obstacle as the vortex has been spun to the angle of the ramp anti-clockwise. this is more evident when the hartman number is 50. the flow field around the obstacles is created near the cold wall of the enclosure due to temperature difference between the hot and cold walls and then hits with adiabatic walls leading to change its direction toward the upper cold sidewall and then hits with the another cold wall. this recycles movement causes to produce the major vortices around the hot obstacles at the lower section of enclosure. the comparison between figures 4 and 6 visibly indicates that velocity contours in the free and forced convections are similar, and a high speed vortex around the upper obstacle is formed. in this case, it is noteworthy that as convection progresses towards free, these high speed lines are dragged towards the lower section of the enclosure. also near the lower obstacles, a vortex is formed in the opposite direction of the previous vortex. it can be found in all two forms so that the richardson number increases as velocity increases in stationary conditions. when the magnetic field effect is significant (i.e. 50ha  ), the lorentz force due to magnetic field effect becomes higher than the buoyancy force due to the natural convection effect which leads to decrease the flow circulation strength and as a result the convection effect diminishes. as shown in figure 7, in the free convection, the earlier facts applied and therefore the conditions do not change so drastically. however, a fundamental change occurs in the behavior of stream lines for 0ha  and 10ha  . this change involves the formation of small vortices in the lower section of the enclosure between the two obstacles in where the vortices are eliminated with increased ramp angle to 0  degrees, turning into a vortex. in addition, the effect of angularity in this state is higher for 0ha  and 10ha  than the previous states. however, this angle is not even close to the minimum angle of the ramp and is far smaller than that. the formation of a small vortex at an angle of 0  at the top of the enclosure is due to the impact of the stream lines with the upper wall of the enclosure. in figure 8, it can be seen that the arrangement of the isothermal temperature contour lines for forced convective heat transfer is the same in all cases. this reveals that changing the forced convective heat transfer into the hartman number and angle of the ramp has very little effect on the behavior of the isothermal lines. figure 9 shows clearly that the slope angle and the hartman number have very little impact on changing trend of nusselt number in forced convective heat transfer. increasing the hartman number influences the addition of the maximum nusselt and increasing the ramp angle influences slightly the asymmetry of the forms. another point is that the graphs are similar at 0  for all three modes. this reveals that changing the hartmann number influences slightly the forced convective heat transfer. figure 10 indicates that in the free convection heat transfer, changing the hartmann number and the angle of the ramp has the higher effect than the forced heat transfer in such a way that in the certain circumstances the overall shape is totally transformed. as the enclosure angle increases the value of heat transfer increases. on the contrary, increasing the hartman number for constant angle heat transfer will reduces. figure 11 indicates that when the angle of the ramp is zero, the nusselt number graphs have three extreme points on a regular basis and symmetrically shaped. with the angularity of the enclosure, however, the trend gradually alters and the maximum values of nusselt number are closer to the right wall and the graph drifts apart from the symmetric mode. another interesting point is the great similarity of nusselt variations trend for 0ha  and 10ha  . this reflects the fact that when the hartman number becomes larger, the effect of changing the angle of the ramp on the nusselt number is lower than when the hartmann number is small. also, this figure shows that, the values of nusselt number decreases when the hartmann number increases for 0, 30  and increases for 60  . this is due to the effect of magnetic field becomes very important. with increasing hartmann number the flow circulation strength decreases and the temperature gradient reduces and for this reason the nusselt number decreases. engineering, technology & applied science research vol. 7, no. 3, 2017, 1647-1657 1652 www.etasr.com keshtkar and ghazanfari: numerical investigation of fluid flow and heat transfer inside a 2d … σφάλμα! τα αντικείμενα δεν μπορούν να δημιουργηθούν από την επεξεργασία κωδικών πεδίων. fig. 4. velocity contour in forced convection for different conditions. fig. 5. stream lines in forced convection for different conditions. 60  0ha  30  0  50ha  60  30  0  0ha  10ha  10ha  50ha  engineering, technology & applied science research vol. 7, no. 3, 2017, 1647-1657 1653 www.etasr.com keshtkar and ghazanfari: numerical investigation of fluid flow and heat transfer inside a 2d … fig. 6. velocity contour speed in free convection for various conditions fig. 7. stream lines in free convection for different conditions. 50ha  0  60  30  10ha  0ha  0  30  60  50ha  0ha  10ha  engineering, technology & applied science research vol. 7, no. 3, 2017, 1647-1657 1654 www.etasr.com keshtkar and ghazanfari: numerical investigation of fluid flow and heat transfer inside a 2d … fig. 8. temperature contour in forced convection for different conditions. fig. 9. nusselt number variations in forced convection for different conditions. 10ha  0  60  30  50ha  0ha  60  10ha  50ha  0ha  30  0  engineering, technology & applied science research vol. 7, no. 3, 2017, 1647-1657 1655 www.etasr.com keshtkar and ghazanfari: numerical investigation of fluid flow and heat transfer inside a 2d … fig. 10. temperature contour in free convection for different conditions. fig. 11. nusselt number variations in free convection for different conditions. 0ha  10ha  50ha  0  0  0ha  10ha  50ha  60  30  30  60  engineering, technology & applied science research vol. 7, no. 3, 2017, 1647-1657 1656 www.etasr.com keshtkar and ghazanfari: numerical investigation of fluid flow and heat transfer inside a 2d … vi. conclusions the problem includes a two-dimensional square enclosure with a length and width of 100 mm in which the left and right boundaries are isolated while the upper and lower boundaries have constant temperatures. the enclosure is located on a ramp and inside the enclosure there are three hot obstacles with constant temperature. the results can be listed as follows:  for a hartman number of 50, the type of heat transfer (free or forced) does not have much impact on the shape of the velocity contour.  the impact of the ramp angle on the stream lines for a hartman number of 50 can be seen as much greater compared to lower hartman numbers.  in free convection heat transfer, the effect of changing the angle of the slope is much greater than that of the forced convection.  in the forced convection heat transfer, a change in the angle of the ramp or a change in the hartman number left little impact on the behavior of the temperature contour lines.  in the free convection heat transfer, for a hartman number of 0 and 10, as the angle of the slope increases, there will be greater heat transfer. for a hartman number of 50, as the slope increases, there will be lower heat transfer.  the rate of heat transfer in free convection is much higher than that in forced convection. nomenclature b magnetic field c lattice velocity g gravitational acceleration, _ 2m s gr grashof number, 3 2( )s mgr g t t l   h enclosure length, m ha hartmann number, ha bh   k thermal conductivity, 1 1wm k  nu nusselt number, nu hl k pr prandtl number,   ra rayleigh number, .prra gr re reynolds number, v l  ri richardson number, 2 2( ) res mri g t t l v gr   t dimensionless temperature, k u, v dimensionless velocities components in x and y direction, 1m s v characteristic velocity, 1m s x, y dimensionless cartesian coordinates, m greek symbols  thermal diffusivity, 2m s  thermal expansion coefficient, 1k  electrical conductivity, -1sm  kinematic viscosity, 2 1m s subscripts c cold f fluid h hot m mean w wall references [1] d. h. rothman,s. zaleski, “lattice-gas model of phase separation: interfaces, phase transitions, and multiphase flow”, rev. mod. phys., vol. 66, no. 4, pp. 1417-1479, 1994 [2] s. chen, g. doolen, “lattice boltzmann method for fluid flows”, ann. rev. fluid mech., vol. 30, pp. 329-364, 1998 [3] s. succi, the lattice boltzmann equation for fluid dynamics and beyond, clarendon, oxford, 2001 [4] g. bella, s. ubertini, m. bertolino, “computational fluid dynamics for low and moderate 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secure data encryption through a combination of aes, rsa and hmac secure data encryption through a combination of aes, rsa and hmac eman salim ibrahim harba computer unit and internet college of arts, university of baghdad baghdad, iraq emanharba_121212@coart.uobaghdad.edu.iq abstract—secure file transfer based upon well-designed file encryption and authorization systems expend considerable effort to protect passwords and other credentials from being stolen. transferring and storing passwords in plaintext form leaves them at risk of exposure to attackers, eavesdroppers and spyware. in order to avoid such exposure, powerful encryption/authentication systems use various mechanisms to minimize the possibility that unencrypted credentials will be exposed, as well as be sure that any authentication data that does get transmitted and stored will be of minimal use to an attacker. in this paper we proposed a method to protect data transferring by three hybrid encryption techniques: symmetric aes algorithm used to encrypt files, asymmetric rsa used to encrypt aes password and hmac to encrypt symmetric password and/or data to ensure a secure transmitting between server-client or client-client from verifying in-between client and server and make it hard to attack by common attacked methods. keywords: cryptography; data encryption; aes; rsa; hmac i. introduction key based encryption can be categorized into two types: symmetric key and asymmetric key [1]. the algorithms of symmetric-key, known as one-key, single-key, and private key encryption are a type of cryptography that uses a public and private algorithm to implement encryption/decryption. commonly used symmetric algorithms include blowfish, des, tea, tdes, idea, cast5, aes (rijndael), rc6, two fish, mars and serpent. the asymmetric key algorithms, also referred to as public key encryption, use two keys, one called the public key and on called the private key. common asymmetric algorithms include: rsa, pgp, ssh and ssl [2]. in addition to the previous two types of encryption, there is a third type called hash which focuses on securing authentication. however traditional algorithms of this kind (such as sha and md5) have gradually become obsolete. in spite of their improvements, once an attacker is able to get a hash and successfully provide it to the authentication server, he can assume whatever security identity is associated with this hash [3]. to protect stored hashes, various tool have been proposed typically based on using lsa (local security authority). several works focus on enhancing hashing security, mainly employing message authentication code commonly known as mac. typically, mac is used between two sides that share a secret key in order to verify transferred data. this method is known as hmac (hash-based message authentication code) [4]. hmac provides the client and server with a private and public key. the public key is known, while the private key is known only in the specific server and client. the client generates a specific hash or hmac for each request via combing the hashing and request data together with a private key and then transmitting it as portion of a request to server. when the server receives this request it will regenerate a unique hmac. the client authorization is based on the comparison of the two hmacs. this technique is usually known as secret handshake [3]. the reason that makes hmac safer compared to mac is that the message and the key are hashed in separate steps. the sender appends an authentication tag to the data calculated as a function of shared key and the data. at the receiver side, the receiver recomputes and compares the authorization tag on the message received [4]. an effective wireless application protocol called wtls has been presented in [5]. in [5], hmac has been used in wtls to support the unique demands for verification with security of high-level strength. the presented design is based upon used hash function type sha-1. the results of the implementation of both the sha-1 and hmac are compared with other relevant studies, and it is shown that the proposed system performs better. in [2], authors provided an extensive comparison analysis of several existing symmetric cryptographic algorithms based upon their limitation, scalability, reliability, security, flexibility and their architecture. through that analysis it was noticed that aes algorithm perform the best in terms of encryption performance, flexibility, security and memory usage. although the other algorithms were also competent, most of them had a tradeoff between memory usage and the time required for encryption. in [6], authors implemented image and text encryption along with decryption. the text encryption uses 128-bit key size and also plaintext. every word or space is changed into an 8-bit sequence. thus, maximum overall 16 positions are identified by this code. aes encryption algorithm in cfb mode is used for image encryption. the pkcs5padding method is used. results verify the superior speed of aes. in [1], authors presented a comparison study of encryption standards aes, des and rsa considering different parameters engineering, technology & applied science research vol. 7, no. 4, 2017, 1781-1785 1782 www.etasr.com harba: secure data encryption through a combination of aes, rsa and hmac including memory usages and computation time. a cryptographic tool has been used for testing. depending on the text files used and the experimental result it is shown that aes and des algorithm uses minimum encryption time compare to rsa. in addition, des has the lowest memory usage, and the time of encryption between aes and des algorithm has a very minor difference. when data size increases then the asymmetric cryptographic algorithm performs slower compare to the symmetric algorithm. in [7], authors presented a new approach to saving files in the cloud. they used rsa and aes algorithms for protecting data and connection based upon various keys in encryption and decryption. they also used an sha1 algorithm to protect the hash table of data. their model handles the total cloud system security to protect data. aes is used for signing in and rsa to encrypt data on storage. the sha1 function is used to hash the key on the system. a key managing center is used as a third party to send out keys in all stages. in the present paper, three methods are combined: a symmetric-key algorithm type (aes) has been used to encrypt data, standard type asymmetric cryptography (rsa) has been used to encrypt aes key and hash type (hmac) has been used in between the two sides (that share a secret key) in order to authenticate transferred information. ii. theoretical background a symmetric key algorithm is an encryption technique where both receiver and sender share the same key. des and aes are the general types of symmetric-key algorithms. ciphers are performed as either stream or block ciphers. a block cipher considers inputs in blocks of plaintext rather than individual characters [8]. the main advantages of symmetric cryptography are strength (due to its speed it can encrypt vast amount of data) and availability whereas its main weaknesses are key implementation and management and limited distribution security [9]. other block ciphers have been released and several have already been broken (e.g. feal [10]). the des algorithm is a block cipher with a a 56-bit key and 64-bit block size. it involves 16-rounds of permutation and substitution. in every round, key and data bits are xored, permutated, shifted, and sent through a group of lookup tables. decryption is basically the same process, performed backwards [6]. it is considered vulnerable to attacks employing linear cryptanalysis, differential cryptanalysis and brute force. the aes algorithm is a ‘symmetric block cipher’ that can be decrypted using the original encryption key. aes uses 10, 12 or 14 rounds that involve mixing, substitution permutation, and key adding [11]. the size of the key may be 128 bits, 192 bits or 256 bits. it main weaknesses are cipher limitations, requiring additional code and cycles to be implemented on a smart card and the use of numerous tables and large code in terms of software. it is considered vulnerable to the xls attack. an asymmetric cryptography algorithm uses two keys which are often called public and private. the public one is utilized for encryption function and the private one is utilized for decryption. both of these keys are mathematically related. the public key may be revealed without compromising system security [8]. its main advantages are its strength and that it offers efficient scalability and that it allows the distribution of the public key. its main weakness is that it is computationally intensive and slow (thousand times or more slower than the symmetric). an rsa algorithm is a generally used public key algorithm. it is the most commonly used asymmetric cryptography algorithm. it can be used for the encryption of small blocks of data or in key exchange digital signatures. rsa uses a variable key size and a variable encryption block size. the key pair come from a highly large number, which is the product of 2 prime numbers whose selection is based on special rules. rsa is commonly used for developing secure communication channels and for digital signatures [6]. its main disadvantages are the large number of bits required and the fact that if one knows enough of the parameters used, he can calculate the others. rsa is used in security protocols like: ssh-terminal connection security, email security (pgp), data security ipsec/ike-ip, service security (silc-conferencing) and web security transport data security (tls/ssl). it is considered vulnerable to lattice based attacks such as attacks on small secret keys, attacks on stereotyped messages, factoring with a hint and factorization attacks. hash cryptography is a technique that does not use a key. instead, a fixed-length hash value is computed based on the plaintext which makes it impossible to be recovered for either length of the plaintext or the contents. hash algorithms are generally employed to produce a digital fingerprint of a file's contents. it is generally used by several os to encrypt passwords [3]. sha includes a variety of algorithms such as sha-1 (sha160), sha256, sha385 and sha512, in which the number is the hash length in bits. sha is used widely in several algorithms of public-key cryptographic, such as in digital signature algorithm (dsa) [12]. the hmac algorithm is a method to modify hash functions to give cryptographic security. basically, a unique part of data is hashed together with a key in many steps so that increased effort will be required to reverse the function. the advantages of hmac is that data can be authenticated through a certain key among the inputs to the function. in normal hash function, the result is always the same for a specific input, nevertheless because a hmac uses the key as an additional input the output depends upon both the data and the key [4]. an hmac can be used to check if some a part of the data has been modified or not. whenever the parties share a key, they compute the hmac of the data using this key each before transmitting and after reception. if hmac of received message meets the expected value, then the key (or data) won't be modified and could be considered authentic and if hmac is different from the expected value, then the key (or data) seems to have changed. the attacker can’t easily customize the data and recalculate the hmac even when simple hash functions are used. if the key is properly chosen, hmac can be a rather powerful method [13]. iii. system model the proposed model depends on three hybrid functions that are combined with each other to produce a strong system engineering, technology & applied science research vol. 7, no. 4, 2017, 1781-1785 1783 www.etasr.com harba: secure data encryption through a combination of aes, rsa and hmac protection. the aes function is used to encrypt the data symmetric aes algorithm to encrypt files, asymmetric rsa to encrypt aes password and hmac to encrypt the authentication between server-client or client-client [14]. figure 1 illustrates the system. fig. 1. block diagram of the proposed system. as shown, the data runs under three levels of security using the three algorithms in combination: • receiver uses the rsa algorithm to generate the key pairs (public and private keys), and send the public key value to the sender. • sender uses the aes algorithm to encrypt data using cipher keys of 256 bits length. • asymmetric-key algorithm (rsa algorithm) is used to encrypt the symmetric key with receiver’s public key. • a hmac sha256 is used to calculat4 the mac that includes a hash function combination with a secret cryptographic key. • the ciphertext produced by encrypting the plaintext then appends mac from the encrypted plaintext. • receiver uses the stored key (private key) to decrypt the aes key, and after that decrypt data using the aes key. aes is usually high speed and requires low ram, so it is very useful for encrypting data, but since it’s the same key for both encryption and decryption, there is a big problem of key transport from the encryption side (sender) to the decryption side (receiver). rsa is used to protect the encryption key. instead of using an expensive rsa provider we generated a stand-alone rsa algorithm that generates two key (private and public). private key stays on the receiver side and the public key is sent to the sender side. the sender will use this key to encrypt data. this will be useful against passive attackers but not against active attacks, so mac is used to protect encrypted data. supposing the mac shared secret hasn't been compromised, we need to be capable to deduce if a given ciphertext is definitely authentic or has been forged. so, the flexibility of the cipher scheme ensures the elimination (through the mac code) of any invalid cipher text. mac doesn't give any information on the plaintext due to the fact that the output of the cipher appears randomly. basically, it does not carry any structure from the plaintext to the mac code. the basic steps of the algorithm are as follows: 1. insert data for encryption. 2. generate rsa key pair 3. insert encryption key 4. use random salt to block pre-generated weak password attacks. the salt bit size is 64. at first salt1 is created then derived and used for crypto key in aes and also slat2 is created then derived and used for authentication key for hmac. 5. apply aes with a 128 block bit size and 256 key bit size. 6. aes encryption and hmac authentication of data iv. results the sender and receiver operation is simulated by first using the rsa algorithm to generate the two keys (public and private) and save each one as two files. figure 2 shows the values of the aes key, the rsa public key and the hmac key. the encrypted key results are shown in figure 3. the encryption program used (figure 4) uses aes & hmac algorithms to encrypt data. on the other hand, the symmetric key itself is encrypted through a key-encryption program by uploading the public key to it. the size and encryption time request is tested by using a text file or by typed text. the size in bytes is firstly calculated and then the results after applying aes algorithm with the defined symmetric key and then by applying hmac algorithm. figure 4 shows the text data before encryption and the result after applying aes and hmac algorithm. as shown, size of the text has increased from 144 bits to 784 and the encryption time is under 1 second. fig. 2. keys values of the three algorithms. server client public key client data aes & hmac data aes & hmac data aes key aes key aes key encryp tion encryp tion encryption engineering, technology & applied science research vol. 7, no. 4, 2017, 1781-1785 1784 www.etasr.com harba: secure data encryption through a combination of aes, rsa and hmac fig. 3. encrypted data value and uploading the public key. fig. 4. text data size. up: before aes-hmac encryption and down: after aes-hmac encryption. in the second test, a large text file (136800 byte) was used figure 5shows the text data before encryption and after applying aes and hmac algorithm. from figures 4 and 5, it can be seen that there is a change in size due to adding encryption which is 256bit aes and 256bit hmac, but the change in size is still very small and near the aes encryption size. the time requests are also near the aes encryption of the same condition. fig. 5. text data size. up: before aes-hmac encryption with and down: after encryption with aes-hmac.\ fig. 6. conclusion in this work, it three types of encryption have been combined in order to exploit the advantages of each one to build a high security system. aes is used to encrypt sent data, exploiting its high encryption speed and its low ram requirements. rsa is used to protect the encryption key from getting stolen by generating two keys (a private and a public one). mac is used to protect the encrypted key or the data. the key and encrypted data are sent to the receiver and get decrypted by using the private. the overall encryption run is engineering, technology & applied science research vol. 7, no. 4, 2017, 1781-1785 1785 www.etasr.com harba: secure data encryption through a combination of aes, rsa and hmac simple and fast with low computational requirements and provides high system security. references [1] p. prajapati, n. patel, r. macwan, n. kachhiya, p. shah, “comparative analysis of des, aes, rsa encryption algorithms”, international journal of engineering and management research, vol. 4, no. 1, pp. 292-294, 2014 [2] m. ebrahim, s. khan, u. bin khali, “symmetric algorithm survey: a comparative analysis”, international journal of computer applications, vol. 61, no. 20, pp. 12-19, 2013 [3] g. c. kessler, “an overview of cryptography” in the handbook on local area networks, auerbach, 1998 [4] p. jungles, m. simos, b. godard, j. bialek, m. bucher, c. waits, w. peteroy, t. garnier “defending against pass-the-hash attacks, mitigating pass-the-hash and other credential theft”, the microsoft security intelligence report (sir), microsoft corporation, 2014. [5] r. berry, k. berry, a. kumar, “review on network security and cryptography”, international journal of innovative research in technology, vol. 3, no. 7, pp. 44-53, 2016 [6] g. selimis, n. sklavos, o. koufopavlou, “vlsi implementation of the keyed-hash message authentication code for the wireless application protocol” 10th ieee international conference on electronics, circuits and systems, united arab emirates, december 14-17, 2003 [7] m. s. abutaha, a. a. amro, “using aes, rsa, sha1 for securing cloud”, international conference on communication, internet and information technology, madrid, spain, 2014 [8] v. agrawal, s. agrawal, r. deshmukh, “analysis and review of encryption and decryption for secure communication”, international journal of scientific engineering and research, vol. 2, no. 2, art. no. j2013115, 2014. [9] n. settia, “cryptanalysis of modern cryptographic algorithms”, international journal of computer science and technology, vol. 1, no. 2, pp. 166-169, 2010. [10] a. j. menezes, p. c. van oorschot , s. a. vanstone, handbook of applied cryptography, crc press, 2001 [11] d. p. joseph, m. krishna, k. arun, “cognitive analytics and comparison of symmetric and asymmetric cryptography algorithms” international journal of research studies in computer science and engineering, vol. 2, no. 3, pp. 63-68, 2015 [12] y. s. solanki, “performance based design and implementation of a sha-1 hash module on fpga”, international journal of emerging technology and advanced engineering, vol. 2, no. 12, pp. 391-393, 2012 [13] c. knopf, cryptographic hash functions, thesis, leibniz universität, hannover institut für theoretische informatik, 2007 [14] nist, secure hash standard, federal information, processing standards publication 180-2, 2002 microsoft word idach_ed_p.doc etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 237-240 237 www.etasr.com idachaba and idachaba: robust e-health communication architecture for rural communities… perspectives robust e-health communication architecture for rural communities in developing countries francis idachaba dpt of electrical and information engineering covenant university ota nigeria idachabafe@yahoo.com ejura idachaba covenant university health center covenant university ota nigeria. idachabaejura@yahoo.com abstract— the lack of access to quality healthcare and the lack of sufficient manpower, especially doctors, in rural areas is a major healthcare challenge faced by dwellers in rural communities in most developing countries. the intervention of governments, which range from the introduction of training programs aimed at producing health workers from schools of health technology and nursing to the recalling and deployment of retired nurses to rural areas, has still not been able to generate the desired improvement in healthcare delivery, as outbreaks of epidemics are still being reported in such areas. this work presents an e-health architecture which utilizes low cost sensors and communication devices to link the doctors in the urban areas with the patients in rural areas enabling doctors-patients interaction. the system enables accurate and timely diagnosis of the patients and facilitates proper treatment plans. it also incorporates an epidemic alert which enables the tracking of diseases and the early detection and control of epidemics. keywordsdoctors; e-health; epidemic; rural areas; vital signs i. introduction the current healthcare challenges faced by developing nations especially in the african continent is deepened by the lack of sufficient manpower, especially doctors, and this is felt the most in rural areas. uneven distribution of health personnel is judged to be a greater problem than actual shortage of supply. the concentration of a high percentage of personnel in large cities depletes services to rural areas [1]. medical schools keep producing doctors yearly, but these doctors are reluctant to go to rural areas due to the challenges associated with such areas [2, 3]. nigeria has one of the largest stocks of human resources for health (hrh) in africa: 28 doctors (as at 2007, currently 40) and 170 nurses per 100,000 population. this compares with a sub-saharan average of 15 doctors and 72 nurses per 100,000 population. despite the large stock of hrh, there are great disparities in health status and access to health care among different population groups in nigeria. for example, the under-five mortality rate in rural areas is estimated at 243 per 1,000 live births, compared with 153 per 1,000 in urban areas. while 59% of women in urban areas deliver with a doctor, nurse, or midwife, only 26 percent of women in rural areas do so [4]. the hrh assessment indicated that the major reason for the great disparities in health status and access to health care among different population groups in the country is the misdistribution of health workers [4]. the government, over the years, has introduced training programs aimed at producing more low level medical and health workers from schools of health technology and schools of nursing. retired nurses are currently being recalled from retirement and sent to rural communities to improve the health care delivery. these strategies, however, have still not been able to generate appreciable improvement in health care delivery as outbreaks of epidemics in remote areas are still being recorded [5-12]. this gap in the healthcare service delivery due to the inadequate number of healthcare personnel often leads to the problem of quackery as quacks and charlatans rise up to provide alternatives which, in most cases, result in unaccounted fatalities. the current shortages in health workers and especially doctors is most acute in sub-saharan africa which is home to the 11% of the world’s population and accounts for 24% of the global disease burden but has only 3% of the world’s health workers [13, 14]. this paper presents an ehealth architecture [15] which will enable doctors in urban areas to interact with patients in rural areas. the system also incorporates an epidemic alert which will enable the tracking of diseases and the early detection and control of epidemics. ii. methodology the system utilizes sensors to capture the vital signs of the patients. these signs include patient’s weight, height, temperature and blood pressure. the data is digitized and sent as an electronic mail through the communication network to the doctor in the urban hospital. the system utilizes audio/visual equipment to provide both audio and video feed in order to enable doctors to have both audio and visual interaction with patients. an onsite health attendant manages the health center and provides language translation between the etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 237-240 238 www.etasr.com idachaba and idachaba: robust e-health communication architecture for rural communities… doctor and the patient and also performs physical examination under the guidance of the doctor. the doctor’s prescription is sent to the remote health center and printed out for the patient for onward transmission to the pharmacy. this architecture provides to rural dwellers an access to high-quality medical expertise available in the cities, without demanding them to physically be there, except in extreme cases. iii. technology description from the system architecture in figure 1, each village or hamlet is provided with a health center manned by the onsite health attendant. a number of health centers transmit to one collation center. the collation center collates the transmissions from the health centers and transmits the data via satellite to the doctor in the urban area. the doctor, upon receipt of the patient’s details, commences the interactions with the patient. these interactions (both audio and video) are stored on the doctor’s end. only the final prescriptions are sent back to the health center for printing and delivery to the patient. a. transmission between collation center and hospital in urban area video communications has high quality of service (qos), high bit rate and hence high bandwidth demands [16, 17]. in video transmissions, the transmission paths and the receivers have different capacities and multilayer transmission is used to solve the problem of varying bandwidth in multimedia multicast applications. a multilayered video encoder compresses a raw video sequence into one or more streams or layers with different priorities. the highest priority layer is called the base layer as it contains the most important data of the video while the other layers are called enhancement layers as they contain refinements of the base layer [18]. when a network link is congested, the lower priority packets get discarded. a number of compression algorithms are currently in use, the most popular being the mpeg2, mpeg4 and the motion jpeg 2000(mj2). the mj2 utilizes jpeg2000 for the compression, in order to generate frame by frame independent code streams. the absence of inter frame dependencies as used in mpeg2 and mpeg4 reduces the processing complexities of the compression process [16]. to achieve an optimum video quality during high error rates, a robust and error rate adaptive link layer transport is required and, thus, the second generation digital video broadcast (dvb-s2) [19] has been adopted as the satellite link layer transport mechanism. it offers enhanced error protection and flexible input data stream format. using adaptive coding and modulation enables the operation within a carrier to noise ratio of -2.4db to +16db. during high link error, the data field length (dfl) in each physical frame is reduced to allow more fec codes. the dvb-s2 is optimized for high definition tv, news gathering and interactive services [20]. the dvb-s2 modem is combined with encoders and multiplexers, as shown in figure 2, to allow the transmission of multiple streams of signals from the health centers onto one carrier frequency for transmission through the satellite to the hospital in the urban area and back to the rural area. fig. 1. system architecture fig. 2. transmission diagram from village health centers to collation center b. point to point link between the health center and the collation center point-to-point digital microwave radio (dmr) is a digital transmission technology that provides a wireless radio link operating at microwave frequencies between two points. a terminal at one end of the link communicates exclusively with a complementary terminal at the other end of the link. each terminal is fitted to a parabolic dish antenna and communication is by line-of-sight beams between the dishes. communication distances can be as short as a few meters (e.g. across the street between city buildings) or very long (up to 80km) in the country. to achieve line-of-sight, the antennas are typically mounted on rooftops, on hills or on towers. links can also be daisy-chained to avoid major obstructions or to cover virtually endless communications distances. dmr links can be used to carry a wide variety of traffic [21]. c. the health center the block diagram of the health center is shown in figure 3. it comprises of the following: 1. digital sensors for taking patients vital signs: these sensors include weight and height sensors, sphygmomanometers for blood pressure measurement and thermometers for temperature measurement. these sensors can be linked to the computer system either using wires or wirelessly (using bluetooth). however the manual methods of data capture can still be used with the onsite attendant taking the readings and inputting them into the computer system for the transmission to the doctor. etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 237-240 239 www.etasr.com idachaba and idachaba: robust e-health communication architecture for rural communities… 2. audio visual equipment: this equipment includes a camera and a microphone/ speaker system. they are used for the doctor-patient interactions. 3. computer system: the computer system collates all the sensor data. the onsite attendant ensures that the patients are properly positioned for the data to be captured. it serves as the gateway by linking the health center to the doctor and managing the two way communication between the doctor and the health center. 4. power supply: the power supply for the health center is based on renewable energy. solar and wind energy coupled with back up batteries are used to provide electric energy for the health center. the choice between solar or the wind is determined by the availability of each source in the rural location. the sensors (data capture devices) are individually powered by rechargeable batteries which can be recharged in the health center. the onsite health attendant will be required to be able to communicate in the local languages of the area and will be required to populate the patient’s information sheet and forward the same to the doctor before the video sessions commence. the digital video signal is compressed using an mpeg software encoder, and then wrapped in an ip packet for transmission [22] as shown in figure 4. fig. 3. block diagram of the health center fig. 4. video compression and packaging for transmission. the video sessions can be implemented using any video stream management software, an example being the cisco stream manager video surveillance solutions [23]. the video surveillance provides real-time monitoring and observation of the patient by the doctor in the urban center hospital and it also enables the doctor to guide the onsite health attendant to perform any physical examination required. it also provides a recording of the sessions in the event that there is a need for second opinions in serious cases. the recording and documentations, however, are subject to the doctor-patient confidentiality and can only be transferred with the patient’s consent. the microwave link can be implemented by a wide variety of available equipment. the generic equipment lists include an indoor unit, an outdoor unit, two antennas, surge protectors, grounding kits and cables. typical power consumptions of the equipment in the health center are listed in table 1. table i. typical health center equipment and power consumption. equipment use typical power consumption values thermometer sphygmomanometer weigh scale meter rule vital signs nil desktop computer system 50w microwave transmission system communication 100w antennas nil web camera nil ethernet switch communication 20w surge protectors protective devices nil solar panels, inverter and deep cycle batteries power supply as shown in table 1, the power consumption is below 200w and solar power supplies capable of generating in excess of 500w are readily available. the opex of the system is very low due to the use of renewable energy. such equipment is readily available in the market and can be set up by anyone with basic it training in networking, vsat installation, expertises also readily available. the doctors and onsite health attendants given basic computer appreciation courses can comfortably and efficiently utilize the system iv. results the main results generated by this system includes the diagnosis and prescription from the doctors in the urban areas for patients in the rural areas which results in better treatment plans for these patients. the system will greatly reduce complications arising from misdiagnosis or wrong diagnosis of a number of health conditions. the epidemic alert system which monitors the different diagnosis of all doctors triggers an alert message to all the predefined relevant government agencies at any time the number of treated cases of a particular disease by different doctors for specific locations exceeds a threshold value. this will help to reduce the occurrence of epidemics and its associated negative consequences. a database of the prescription, diagnosis and the transcripts of the entire process are maintained and can be used when second opinions or expert advice is required for any patient. v. system benefits the benefits of this system are outlined below. etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 237-240 240 www.etasr.com idachaba and idachaba: robust e-health communication architecture for rural communities… 1. it enables early and accurate diagnosis of ailments and facilitates the early commencement of appropriate treatment. reports have shown that most terminal diseases are actually curable if detected early. 2. it facilitates rapid access to second opinions. this system will enable doctors to seek a second opinion for cases that require such. both the visual and audio transcripts of the doctor patient interactions can be forwarded to different specialists located in different parts of the world at the same time for their opinion. 3. it enables a higher utilization factor of the government hospitals in the urban areas as more doctors can be employed and based in the urban areas to provide coverage to the rural areas. 4. it is cost effective in the sense that the sensors and the systems located at the rural areas are low cost resulting in a low total cost of ownership, low capex and opex. 5. this system will reduce the effect of quackery as it will provide access to qualitative health care delivery to the rural dwellers 6. the epidemic alert will enable government manage cases of epidemics and contain it before it starts/spreads. the database generated by this system will help governments in proper planning of the health care delivery systems for the rural areas and also track other environmental issues as it affects the public health of the rural dwellers. 7. the doctors and onsite health center attendants require basic computer appreciation training to be able to utilize the system. vi. conclusion this system has the capability of improving the patients/doctor ratio for rural areas without the actual relocation of doctors to such areas. it also provides access for the rural dwellers to qualitative health care available in the urban centers without the cost and inconvenience of travel to urban hospitals. the limitation of bandwidth costs and transmission outages associated with this system can be reduced by the use of multiplexing/collation centers where traffic from a large number of health centers are collated and transmitted together using appropriate technologies. this will reduce the average transmission cost per center and the limitation of transmission outage can be mitigated by the use of suitable transmission frequencies which are resistant to rain attenuation and the use of automatic gain compensating networks which ensures that transmission is maintained regardless of the weather conditions. references [1] k. ojo, “the crisis in the distribution of health personnel in nigeria” health policy and planning, vol. 5, no. 1, pp. 60-65, 1990 [2] m. kamien, w. cameron, “solving the shortage of general practitioners in remote and rural australia: a sisyphean task”, the medical journal of australia, vol. 185, no 11, pp. 652-653, 2006 [3] “health care in india”, www.wikipeadia.org/wiki/healthcare_in_india [4] g. kombe, s. chankova, h. nguyen, d. chipanta, a. onoja, k. ogungbemi, a. taye, “confronting hiv/aids, tb, and malaria: a situation analysis of human resources health in nigeria: emerging challenges and opportunities”, health systems 20/20, usaid 2007 [5] i. a. adeoye, m. d. dairo, l. v. adekunle, h. o. adedokun, j. makanjuola, “investigation of measles outbreak in a rural nigeria community the aladura experience”, african journal of microbiology research, vol. 4, no. 5, pp. 360-366, 2010 [6] i. h. kara, a. ceylon, h. acemoglu, “measles epidemic in turkey and developing countries: review of the literature”, middle east journal of family medicine, vol. 5, no. 5, 2004. [7] f. j. spenser, “epidemic shigellosis in a rural area”, public health reports, vol. 76, no. 3, pp. 219-222, 1961 [8] world health organization media center, “african trypanosomiasis or sleeping sickness”, http://www.who.int/mediacentre/factsheets/fs259/en/ [9] world health organization, “who supports malaria epidemic prevention and control in pakistan”, www.who.int/entity/hac/crises/pak/releases/12october2010 [10] a. m. prentice, “the emerging epidemic of obesity in developing countries”, international journal of epidemiology, vol. 35, no. 1, pp. 93-99, 2005 [11] d. smith, “cholera kills more than 1500 people in nigeria”, the guardian, 26 th october, 2010 [12] united nations institute for training and research. briefing report. unitar/unfpa/iom, key migration issues workshop series: new york. 2006, available at: www.un.org/esa/population/meetings/fourthcoord2005/p06_unitar.p df [13] world health organization. “the global shortage of health workers and its input”. fact sheet no. 302, 2006 [14] united nations population facts, “health workers, international migration and development”, no. 2010/2/e/rev, 2010, available at: http://www.un.org/esa/population/publications/popfacts/popfacts_20102rev.pdf [15] s. ouma, m. e. herselman. “e-health in rural areas: case of developing countries”, international journal of biological and life sciences, vol. 4, no. 4, pp. 194-200, 2008 [16] h. k. sellapan, l. sacks, “intelligent dropping scenario for motion jpeg2000 transmission over satellite networks”, available at: http://www.ee.ucl.ac.uk/lcs/previous/lcs2005/23.pdf [17] s. dogan, a. h. sadka, a. m. kondoz, “video transmission over mobile satellite systems”, international journal of satellite communications, vol. 18, pp. 185-205, 2000. [18] l. patil, video transmission over varying bandwidth links. m.tech desertation. indian institute of technology bombay, 2006, availablr at: www.it.iitb.ac.in/~sri/students/laxmikant-thesis.pdf. [19] etsi final draft en 302307 (v1.1.1) digital video broadcasting (dvb) second generation framing structure, channel coding and modulation systems for broadcasting interactive services, news gathering and other broadband satellite applications(dvb-s2). 2005. www.etsi.org [20] y. mostovoy, “maximizing satellite transmission efficiency with dvb-s2”, scopus, available at: http://www.scopus.ru/files/maximizing_satellite_transmission_efficien cy_with_dvb-s2.pdf [21] codan, “introduction to digital microwave radio technology”, available at: http://codan.ru/upload/file/codan/en/3p4.pdf [22] telecommunication handbook for transportation professionals: the basics of telecommunications, final report. us department of transportation, federal highway administration, 2004. [23] cisco, “stream manager video surveillance solutions reference network design”, cisco systems 2007. microsoft word etasr_v12_n2_pp8284-8288 engineering, technology & applied science research vol. 12, no. 2, 2022, 8284-8288 8284 www.etasr.com sahito et al.: workstation evaluation regarding ergonomic awareness and work-related … workstation evaluation regarding ergonomic awareness and work-related musculoskeletal disorders among coal mine workers wasayo sanam sahito civil engineering department college of engineering and islamic architecture umm al-qura university makkah, saudi arabia smsahito@uqu.edu.sa rabeea w. bazuhair civil engineering department college of engineering and islamic architecture umm al-qura university makkah, saudi arabia rwbazuhair@uqu.edu.sa hebah mimesh mississippi state university mississippi, usa hmimesh@hotmail.com received: 4 december 2021 | revised: 26 january 2022 | accepted: 1 february 2022 abstract-mining is often associated with the risk of workrelated musculoskeletal disorders (wrmsds). despite being a coal-rich country, pakistan’s mining sector stays behind in terms of occupational health and safety. only a few research studies have been conducted on ergonomics in the mining industry. the current study aimed at evaluating workstations for wrmsds and ergonomic factors among coal mine workers. survey data were gathered from a total of 103 workers using a structured questionnaire. information on the incidence of musculoskeletal disorders was obtained using the standardized nordic questionnaire. the questions about ergonomics awareness, workstation, environment, demands, and risks were based on the available literature studies. the association between the incidence of wrmsds and age was explored using chi-square analysis. the results showed a high rate of uneducated workers with a lack of ergonomics awareness. back, shoulders, and legs were the most vulnerable body areas to wrmsds. a significant association between workers’ age and wrmsds was found. the workers’ opinion towards workstation was at a very low level. the current work conditions were found to have risks of potential hazards and economic losses. ergonomic interventions are suggested to be developed and implemented to improve workplace conditions.. keywords-musculoskeletal disorders; coal mine workers; ergonomics; workstation evaluation; work environment; work demands i. introduction any engineering project encounters several risks during its life cycle [1]. risk management is based on the management of health, safety, and the environment of the personnel. risk is a process that has an uncertain and unknown outcome in each field [2]. longwall mining is a highly automated, very powerful and productive way to mine. in the absence of longwall mining, other technologies can be applied, named highwall mining or coal mining of flat-laying coal seam technology which solves the same problem as high wall mining, but does not require any specialized equipment [3]. mining is often associated with high rates of work-related musculoskeletal disorders (wrmsds) that have adverse effects on the health of workers. coal is a major energy source of the economic development of a country [4-5]. however, its mining is believed to be a dangerous task, as it poses many health problems to workers [6-9]. the health issues include manual tasks, working in awkward postures, and for long durations, increasing the risk of developing wrmsds [10]. wrmsds are one of the major cost occurring disorders [11] and are related to discomforts in muscles, joints, nerves, blood vessels, and supporting structure. they include both workrelated and non-work exposures [12, 13]. wrmsds have become one of the most serious problems in industries, causing one-third of the total sickness absenteeism [14]. regardless of the work nature and the involvement of high physical efforts, wrmsds are very common in virtually all job categories and are among the major causes of workers’ pain, disability, absenteeism, low productivity, and high financial costs [15-20]. studies suggest a causal relationship between wrmsds with occupational and non-occupational physical risk factors. numerous mining-related physical risk factors such as manual material handling, repetitive movements, high exertion, working in awkward postures, and changes of workplace circumstances are some reasons for the development of wrmsds [21, 22]. wrmsds are contributed by many risk factors in the mining industry, and a variety of positions and postures like kneeling, squatting, and stooping can enhance the occurrence of musculoskeletal disorders [23]. from an corresponding author: wasayo sanam sahito engineering, technology & applied science research vol. 12, no. 2, 2022, 8284-8288 8285 www.etasr.com sahito et al.: workstation evaluation regarding ergonomic awareness and work-related … ergonomic perspective, disorders or injuries are caused by carrying out the activities incorrectly. the risks and hazards in the mining comprise of the design of equipment and vehicles, high job demands, work pressure, job rotation, overtime, improper rest, recovery time, and breakdowns [24]. working in low working heights (in low-seam mines) causes multiple forms of discomforts and injuries attributed to working in kneeling and squatting postures [25, 26]. the workers are often exposed to these risks, therefore risk potential should be identified and reduced [27]. in pakistan, the coal is still being extracted using conventional mining methods, thus wrmsds have become the most common health problems [28, 29] in this industry. the mining industry in pakistan is not technologically advanced [30]. therefore, the present study has been carried out to evaluate ergonomic factors and assess wrmsds with the aim to address the key issues that contribute in their development. the focus of this study is the assessment of a representative sample of pakistan’s coal mining industry workforce. the study will help the government and mining enterprises to promote the health of workers by developing and implementing proper ergonomic interventions. ii. methodology the study has been carried out to explore wrmsds and to evaluate workstations for ergonomic conditions in lakhra coal mines, sindh, pakistan. the data were obtained from the workers of 18 different underground coal mine sites. the study sample consisted of 103 underground coal mine workers, which were selected with randomize sampling technique. the data were gathered through a structured questionnaire. the prevalence of musculoskeletal disorders was measured using the nordic musculoskeletal questionnaire [31]. the questions regarding ergonomic awareness, workstation evaluation, work environment, work demands, and risks at work were based on the contents of [32-34]. a 5-point likert scale was used, from 1 for strongly disagree to 5 for strongly agree. spss version 23 was used for data analysis. data obtained from the workers were summarized in frequency, percentage, mean, and standard deviation. the association between the prevalence of wrmsds and the age of coal mine workers was evaluated with the chi-square test. the alpha (α) level was set at 0.05. iii. results a. demographic data the demographic description of the respondents is presented in table i. the study sample comprised of only males, as women do not work in the mining industry in pakistan. b. work-related musculoskeletal disorders according to the data on pain during the last 12 months, the results show that a high number of workers were suffering from wrmsds. the overall measurement results are summarized in table ii. figure 1 shows the percentage of wrmsds among workers. the prevalence of wrmsds complaints during the last 12 months was significantly associated with workers’ age. the back-pain complaint (88%) was the most commonly reported and leading complaint among the workers and it was highly significantly associated with the workers’ age (p < 0.001). shoulder pain (76%) and leg pain (67%) were ranked as the second and third most commonly reported wrmsds. the prevalence of wrmsds was found consistently associated with age. table i. demographic characteristics of respondents variable description (%) age (years) 18–33 38 (36.9) 34–49 36 (35.0) ≥50 29 (28.2) marital status single 12 (11.7) married 78 (75.7) other 13 (12.6) education level uneducated 55 (53.4) primary 36 (35.0) secondary 12 (11.7) nature of job coal cutter 21 (20.4) hand trolley man 9 (8.7) haulage operator 14 (13.6) worker 28 (27.2) loader 11 (10.7) surface collie 7 (6.8) underground transporter 13 (12.6) total experience (years) <1 5 (4.9) 1–10 17 (16.5) 11–20 45 (43.7) 21–30 28 (27.2) >30 8 (7.8) table ii. msds and their association with age body part prevalence (%) mean (sd) p shoulder 76.7 3.79 (0.75) 0.008* forearm 48.6 3.36 (0.93) <0.001* back 88.4 3.94 (0.50) 0.045* legs 67.0 3.57 (0.94) <0.001* foot / toe 63.1 3.58 (0.99) 0.011* *significant at p < 0.05 level fig. 1. percentage of wrmsds among workers. c. ergonomic awareness table iii presents information about ergonomics awareness among the workers. more than 86% of them were unaware of the ergonomic body of knowledge in their daily work. only 32% of the survey population realized the effects of neglecting ergonomics in their life. besides that, only 7.8% of the total respondents ever attended an ergonomic seminar. d. workstation evaluation the ergonomic analysis showed a low level of respondents’ perception of their workstation. the results presented in table iv are the responses to questions on workstation evaluation. more than 59% of the respondents reported that the engineering, technology & applied science research vol. 12, no. 2, 2022, 8284-8288 8286 www.etasr.com sahito et al.: workstation evaluation regarding ergonomic awareness and work-related … workstation was not clean and comfortable to work. the majority (72%) of the respondents stated that the workstation did not have suitable space to carry out routine work. most (64%) of the respondents felt uneasy to work due to the congested workspace. more than 50% of the respondents were not provided with the necessary equipment. e. work environment the results of overall perception towards work environment are shown in table v. around 52.5% of the respondents reported the problem of gases in mines and 65% complained about improper lighting. the workers did not extensively report any difficulty to work due to noise, temperature, and humidity, and 71% of them reported the problem of coal dust and more than half (56%) were not satisfied with the overall ventilation system of the mine. f. work demands from the results shown in table vi, we can see that a low percentage of the workers work overtime (40%). according to 58% of the respondents, their job involved a high degree of repetitiveness. the muscular strength requirement was high for 66% of the respondents, the work of 54% of the respondents was done manually, 52% of the respondents required bending and twisting, most of the respondents (68%) were dealing with carrying, lifting, or lowering heavy physical loads, 51% of the respondents required pushing/pulling/dragging the material with no aid of machinery, 47% had to climb up or down and 41% had to kneel or squat to perform their work. g. risks at work the data in table vii indicate that errors in work are associated with risks of personal injury and economic losses. about 91% of the respondents were at risk of personal injury and 86% stated that their work is associated with risk of economic losses. iv. discussion this study was carried out in order to analyze the rate of wrmsds and their associations with respondents’ age. in addition, ergonomics awareness at work was considered. workers’ perception towards workstation, work environment, and work demands was analyzed. the risks associated with work were also explored. the results showed that more than half of the respondents were uneducated (53%), 35% had primary education, and less than 12% had secondary education. the back pain complaint was mostly reported, and it was found significantly associated with workers’ age. the back pain became more prevalent with the increase of age. pain in shoulders and legs ranked second and third respectively. the likelihood of developing body pain was caused by the adoption of uneasy working positions. the prevalence of all wrmsds complaints was significantly associated with the age of the workers. lack of ergonomic knowledge was observed and at the moment there was no safety and health program running at the workplaces. the majority of the respondents were unaware of the ergonomic issues. this implies that they had no knowledge of ways to avoid the wrmsds. approximately 68% of the respondents even did not realize the effects of ergonomics on their health, implying that the mine management was inefficient in providing ergonomic awareness. only 7.8% of the respondents stated that they have been informed about ergonomics before the conduct of this survey. the respondents’ opinion towards workstation was at a very low level. workstations were reported as unclean and uncomfortable, space was not suitable for routine activities and the workers felt uneasy to move during their work. the appropriate equipment was not provided to many of the workers, which could also be a factor of causing wrmsds. there was a moderate level between satisfaction and dissatisfaction of the workers towards mine environment. the coal mines were having adequate air, comfortable temperature and humidity with a reduced level of noise. the presence of gases, improper lighting, and dust were the most reported problems, therefore, the workers’ opinion towards overall ventilation was not satisfactory. the ventilation is the fundamental element involved in occupational safety and health (osh) of the workers. the current state of work demands was found to have potential health hazards. although a low percentage of workers work overtime, the problems of manual material handling and the requirement of high muscular strength were common. a high percentage of the workers had to repeatedly bend and twist, push, pull, drag, climb, kneel, squat, and carry heavy physical loads. the results show that errors in work were associated with the risk of personal injury and economic losses. the analysis of risk factors showed a mean score of 3.96 and a standard deviation of 0.84. there is no doubt that coal miners are engaged in a heavy and repetitive task and they carry out monotonous work, which makes them highly vulnerable to wrmsds, which is reflected in the prevalence of wrmsd rates in this study. table iii. workers' perception towards ergonomic awareness item yes n (%) no n (%) mean (sd) ergonomic knowledge 14.0 13.6 89 86.4 1.86 (0.34) knowing the effects of neglecting ergonomics 33 32 70 68 1.68 (0.47) attended ergonomic training 8 7.8 95 92.2 1.92 (0.27) overall 1.82 (0.36) table iv. workers' perception towards workstation item n (%) n (%) n (%) n (%) n (%) mean (sd) clean and comfortable work pace 3 2.9 14 13.6 44 42.7 35 34 7 6.8 3.28 (0.89) suitable space for routine activities 18 17.5 33 32 23 22.3 26 25.2 3 2.9 2.64 (1.13) ease of movement in work space 8 7.8 26 25.2 32 31.1 31 30.1 6 5.8 3.01 (1.05) appropriate aid equipment provided 2 1.9 6 5.8 44 42.7 44 42.7 7 6.8 3.47 (0.79) overall 3.1 (0.97) engineering, technology & applied science research vol. 12, no. 2, 2022, 8284-8288 8287 www.etasr.com sahito et al.: workstation evaluation regarding ergonomic awareness and work-related … table v. workers' perception towards work environment item n (%) n (%) n (%) n (%) n (%) mean (sd) mine gases 10 9.7 7 6.8 32 31.1 44 42.7 10 9.7 3.36 (1.07) lighting 14 13.6 17 16.5 36 35 28 27.2 8 7.8 2.99 (1.14) noise 3 2.9 14 13.6 16 15.5 51 49.5 19 18.4 3.67 (1.02) temperature and humidity 4 3.9 15 14.6 20 19.4 48 46.6 16 15.5 3.55 (1.05) dust 12 11.7 11 10.7 50 48.5 27 26.2 3 2.9 2.98 (0.98) overall ventilation 19 18.4 16 15.5 23 22.3 34 33 11 10.7 3.02 (1.29) overall 3.26 (1.09) table vi. workers' perception towards work demand item n (%) n (%) n (%) n (%) n (%) mean (sd) working overtime 3 2.9 24 23.3 35 34 33 32 8 7.8 3.18 (0.98) tasks with a high degree of repetitiveness 3 2.9 8 7.8 32 31.1 52 50.5 8 7.8 3.52 (0.86) muscular strength requirements 2 1.9 12 11.7 21 20.4 54 52.4 14 13.6 3.64 (0.93) manual material handling 7 6.8 8 7.8 32 31.1 49 47.6 7 6.8 3.40 (0.97) bending and twisting 12 11.7 12 11.7 25 24.3 41 39.8 13 12.6 3.30 (1.19) heavy physical load (carrying, lifting or lowering loads) 2 1.9 10 9.7 21 20.4 58 56.3 12 11.7 3.66 (0.88) pushing/ pulling/ dragging 10 9.7 13 12.6 28 27.2 44 42.7 8 7.8 3.26 (1.09) climbing up or down 2 1.9 11 10.7 31 30.1 54 52.4 5 4.9 3.48 (0.83) kneeling or squatting 3 2.9 14 13.6 44 42.7 35 134 7 6.8 3.28 (0.89) overall 3.41 (0.96) table vii. workers opinion about risks associated with work item 1 n (%) 2 n (%) 3 n (%) 4 n (%) 5 n (%) mean (sd) are errors in your work associated with a risk of personal injury? 2 1.9 3 2.9 4 3.9 69 67 25 24.3 4.09 (0.76) are errors in your work associated with the risk of economic losses? 5 4.9 7 6.8 2 1.9 75 72.8 14 13.6 3.83 (0.92) overall 3.96 (0.84) v. conclusion this study aimed to assess wrmsds and analyze the ergonomic conditions at workstations associated with underground coal mine workers in pakistan. the results showed that back, shoulders, and legs were the most exposed body regions to wrmsds. every respondent was found with at least one msd, while the workers themselves had a very low level of ergonomic awareness. inefficient organization setting and low-technology environment are the main reasons for the high prevalence of wrmsds. it is recommended that the current mining method employed should be investigated and immediate changes should be applied. concentrated steps should be taken, and proper strategies must be developed and 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[34] s. a. mustafa, s. kamaruddin, z. othman, and m. mokhtar, "ergonomics awareness and identifying frequently used ergonomics programs in manufacturing industries using quality function deployment," american journal of scientific research, vol. 3, pp. 51– 66, 2009. microsoft word etasr_v11_n5_pp7714-7719 engineering, technology & applied science research vol. 11, no. 5, 2021, 7714-7719 7714 www.etasr.com nuanmeesri & sriurai: multi-layer perceptron neural network model development for chili pepper … multi-layer perceptron neural network model development for chili pepper disease diagnosis using filter and wrapper feature selection methods sumitra nuanmeesri faculty of science and technology suan sunandha rajabhat university bangkok, thailand sumitra.nu@ssru.ac.th wongkot sriurai faculty of science ubon ratchathani university ubon ratchathani, thailand wongkot.s@ubu.ac.th abstract-the goal of the current study is to develop a diagnosis model for chili pepper disease diagnosis by applying filter and wrapper feature selection methods as well as a multi-layer perceptron neural network (mlpnn). the data used for developing the model include 1) types, 2) causative agents, 3) areas of infection, 4) growth stages of infection, 5) conditions, 6) symptoms, and 7) 14 types of chili pepper diseases. these datasets were applied to the 3 feature selection techniques, including information gain, gain ratio, and wrapper. after selecting the key features, the selected datasets were utilized to develop the diagnosis model towards the application of mlpnn. according to the model’s effectiveness evaluation results, estimated by 10fold cross-validation, it can be seen that the diagnosis model developed by applying the wrapper method along with mlpnn provided the highest level of effectiveness, with an accuracy of 98.91%, precision of 98.92%, and recall of 98.89%. the findings showed that the developed model is applicable. keywords-chili pepper diseases; feature selection; multi-layer perceptron neural network; wrapper i. introduction chili peppers are plants used and consumed by thai people in many forms. they are fundamental spices that can enhance the flavor, odor, and color of food. chili peppers are considered unique due to their nutritional and medical benefits, flavors, and colors, so they cannot be replaced by other plants, hence, they are highly economically important in thailand [1]. chili peppers must be appropriately stored and maintained before being sold. many farmers usually face problems in chili pepper plantations. these include inevitable natural disasters, weeds, and pests. therefore, the farmers need to be educated about chili pepper diseases in order to protect their plants appropriately. multi-layer perceptron neural networks (mlpnns) have been broadly applied to diagnose diseases. for example, such models were developed in [2] and in [3] for predicting lung cancers and heart diseases respectively. these two studies developed disease diagnosis models which were more than 90% effective. the current research aims to apply mlpnns to diagnose chili pepper diseases. it also employs the filter and wrapper feature selection methods to develop the diagnosis model. the feature selection methods will select only significant features for synthesizing the model rapidly and classifying data more effectively [4]. the most effective model in terms of data classification will be further applied to the development of a chili pepper disease diagnosis system that can assist the farmers in diagnosing the diseases and treat their plants timely and adequately. ii. literature review a. filter feature selection methods filter feature selection methods are the processes that evaluate the level of effectiveness of each feature regarding its compatibility with data analysis. these processes do not rely on any learning approach. these filter methods select the data by ranking each feature in a priority queue. the priority list is based on the number specified by the user or the threshold of the selected feature. the advantages of these methods are rapid data processing and independence from learning methods [4]. this research applies two types of filter feature selection methods, namely the information gain (ig) and gain ratio (gr), as follows. 1) information gain (ig) ig is a measure used for classifying data by calculating the gain value of each attribute. if any attribute has the highest gain value, it will be selected as a subset with classification power, as shown in (1) [5]. equation (1) demonstrates the calculation of entropy, while (2) explains the calculation of the gain value [5]. 1 2 0 ( )log ( ) c i i i entropy p t p t − = = −∑ (1) ( ) 1 ( ) (parent) k i i i n v gain entropy entropy v n = = −∑ (2) where c refers to the number of classes, ( )ip t refers to the frequency value of class i for node t, entropy(parent) refers to corresponding author: sumitra nuanmeesri engineering, technology & applied science research vol. 11, no. 5, 2021, 7714-7719 7715 www.etasr.com nuanmeesri & sriurai: multi-layer perceptron neural network model development for chili pepper … the entropy of the parent node, k refers to the total number of feature values, n refers to the total amount of data of the parent node, and n(vi) refers to the total amount of instances of child node i. 2) gain ratio (gr) gr is a measure that uses the gain ratio as the indicator for dividing datasets into sub-datasets based on the ig value. however, when the ig value is used for classifying datasets, there would be the occurrence of bias in favor of attributes with large numbers of values. thus, the gr can be derived from the gain value divided by the splitinfo value that is calculated in (3) [6], where k refers to the total number of split data. therefore, the gr is calculated in (4) [5]: 2 1 ( ) ( ) log k i i i n v n v splitinfo n n= = −∑ (3) gain gr splitinfo = (4) b. wrapper feature selection wrapper feature selection methods are processes that select subsets from all features. they explore the feature subsets which specifically match a learning approach. therefore, these methods can increase the effectiveness of the learning process to the greatest extent. this research applies an evolutionary wrapper for selecting features. the features, which are predictor variables, are randomized into the equation each by each. then, their effectiveness in prediction is tested. if the level of effectiveness in prediction increases, the effective features will be maintained. in contrast, if the level of effectiveness in prediction decreases, the ineffective features will be removed [7]. c. multi-layer perceptron neural network mlpnn is a form of perceptron neural network with multiple layers. it is suitable for complex computational tasks. it consists of 3 layer lavels, namely the input layer, the hidden layer, and the output layer. the hidden layer could be composed of many layers, but there must be at least one layer in it [6, 8]. the data are the input of the input layer. the output is sent out from the output layer. the summation function of mlp is calculated in (5): 1 k i i i n p w b = = +∑ (5) where n is the total sum gained from the summation function, pi is the input of neuron i, wi is the weight of neuron i, k is the number of input layer neurons, and b is the bias value. the mlpnn model is illustrated in figure 1. d. model’s effectiveness evaluation the model’s effectiveness was evaluated by the confusion matrix, which can calculate the precision, recall, and accuracy of the model [9-12]. e. related works authors in [2] developed a model to predict lung cancer using the mlpnn, comparing the efficacy of disease classification with the k-nearest neighbor (knn) technique. the results showed that the disease classification model using the mlpnn was more effective. authors in [3] applied the mlpnn to predict heart diseases. the efficacy of the heart disease classification model was compared with 9 classification methods and the results showed that the mlpnn was the most effective. authors in [13] applied the wrapper method to select feature data to classify cardiac arrhythmias. the model’s effectiveness was tested using 10-fold cross-validation, comparing 5 modeling techniques. the results showed that the model used to classify cardiac arrhythmias using wrapper combined with mlp had the best performance. authors in [14] developed an mlp model by applying the correlation-based feature selection (cfs) and ig to analyze thai water buffalo diseases. the experimental results showed that the developed model by cfs and mlp was efficient with accuracy, precision, and recall greater than 99.0%. fig. 1. multi-layer perceptron neural network model. iii. methods in this work, a mlpnn model for chili pepper disease diagnosis was developed using filter and wrapper feature selection methods. six 6 processes were involved: data collection, data preparation, feature selection, modeling, evaluation, and deployment. a. data collection primary data were collected from 5 agricultural professionals and 33 chili pepper farmers in ubon ratchathani province of thailand with the use of questionnaires. this is a significant chili pepper cultivation area in 3 districts, namely muang sam sip district, mueang district, and khueang nai. the secondary data were collected from the review in [15]. an analysis of the data revealed 14 diseases in chili peppers in those plantations, as shown in figure 2. the details of the data are illustrated in table i. b. data preparation at the data preparation stage, the selected data were prepared before being applied to the model. the data were prepared in the following steps: 1) data selection, 2) data cleaning, and 3) data transformation. ultimately, 863 questionnaires were processed, and were divided into 80% for training and 20% for testing. the data used for developing the chili pepper disease diagnosis model are illustrated in table ii. engineering, technology & applied science research vol. 11, no. 5, 2021, 7714-7719 7716 www.etasr.com nuanmeesri & sriurai: multi-layer perceptron neural network model development for chili pepper … fig. 2. sample image of 14 chili peppers diseases. table i. data used in this research no. data 1 types of chili pepper diseases 2 causative agents 3 infected areas 4 growth stages of infection 5 conditions for diseases 6 symptoms 7 fourteen types of chili pepper diseases: 1. bacterial wilt 2. southern wilt 3. collar and root rot 4. frog-eye leaf spot 5. powdery mildew 6. bacterial spot 7. wet rot 8. gray leaf spot 9. anthracnose 10. cucumber mosaic virus 11. chili veinal mottle virus 12. chili leaf curl virus 13. capsicum chlorosis virus 14. tomato mosaic virus table ii. features used for developing the chili pepper disease diagnosis model no. data features 1 types of chili pepper diseases non: nonliving (abiotic) agents liv: living (biotic) agents 2 causative agents bac: bacterial agents fung: fungal agents vir: viral agents 3 infected areas s1: stems f2: fruits r3: roots l4: leaves st5: stems and roots lf6: leaves and fruits ls7: leaves and stems fs8: fruits and stems sl9: stems, leaves, and fruits 4 growth stages of infection g1: early stage of growth g2: flowering g3: harvest g4: at all stages 5 conditions for diseases c1: poorly drained soil c2: humidity and rain consecutive days c3: rains and wet soil c4: strong and dry winds c5: frost and strong winds c6: overcrowded sprouts; poor ventilation c7: thrips c8: tobacco whiteflies 6 symptoms s1: browned vessels s2: white powdery coating or brown pellets appearing on the lower surface s3: water soaked lesions on stems and stalks s4: midget growth s5: severely spotted leaves turn yellow and drop s6: black narrow elongated lesions or streaks developing throughout the stems to the top of the plant s7: bleached, pale veinlets s8: wet, macerated stalks with black-ended silvery hair covering the lesions s9: distorted, irregular, curly leaves s10: yellowing of lower leaves at the front and back s11: a dark ring and a yellowish halo around the ring, forming a "frog-eye" appearance on the leaves 7 types of chili pepper diseases (classes) bw1: bacterial wilt sw2: southern wilt cr3: collar and root rot fl4: frog-eye leaf spot pm5: powdery mildew bs6: bacterial spot wr7: wet rot gr8: gray leaf spot an9: anthracnose cm10: cucumber mosaic virus cv11: chili veinal mottle virus cl12: chili leaf curl virus cc13: capsicum chlorosis virus tm14: tomato mosaic virus once the data in table ii had been collected, the research team verified their accuracy. then, they were converted into a csv file to be computed in weka 3.9, as illustrated in figure 3. after converting the data, the authors input the data into weka to select features by applying ig, gr, and wrapper. engineering, technology & applied science research vol. 11, no. 5, 2021, 7714-7719 7717 www.etasr.com nuanmeesri & sriurai: multi-layer perceptron neural network model development for chili pepper … fig. 3. a sample of the data used in model development. c. modeling the data were divided into 4 datasets, namely 3 datasets undergoing the feature selection process and 1 original dataset used for mlpnn modeling. the research team specified the parameters for the mlpnn modeling as follows: hidden layer = 2, training time = 500, learning rate = 0.3, and momentum = 0.2. these parameters provided the best results. d. evaluation the effectiveness of the chili pepper disease diagnosis model was evaluated by 10-fold cross-validation with the test dataset (20% of the total data). in addition, it was measured by examining the precision, recall, and accuracy of the developed models [6]. e. deployment after constructing the model, the most effective sample was applied to develop the chili pepper disease diagnosis prototype system. this system can diagnose chili pepper diseases timely and suggest proper treatments for each disease rapidly. the research model framework is illustrated in figure 4. fig. 4. the research model framework. iv. results the chili pepper disease diagnosis model was developed by applying filter and wrapper methods along with mlpnn. the number of features remaining after the feature selection process is shown in table iii. table iii. remaining features after feature selection feature selection method number of features remaining ig 7 gr 7 wrapper 6 the effectiveness of the models was evaluated by 10-fold cross-validation. the research results showed that the model developed by wrapper and mlpnn (wrapper+mlp) provided the highest results with accuracy of 98.91%, precision of 98.92%, and recall of 98.89%. next in the rankings were ig+mlp, gr+mlp, and mlp (original data), as shown in table iv and figure 5. furthermore, compared to other studies that detected or classified chili pepper diseases (table v), the developed model by the wrapper+mlp method gave the highest effectiveness result. table iv. effectiveness evaluation results method precision (%) recall (%) accuracy (%) mlp (original data) 92.60 92.54 92.52 ig+mlp 96.50 96.42 96.45 gr+mlp 93.34 93.20 93.26 wrapper+mlp 98.92 98.89 98.91 fig. 5. comparison between the models' effectiveness evaluation results. table v. comparison with other research studies method no. of classes accuracy (%) hsv model feature extraction [16] 2 80.00 hyperspectral image + mlp [17] 2 83.26 deep belief network [18] 2 91.96 deep learning + support vector machine [19] 7 92.10 fuzzy c-means segmentation [20] 5 97.56 wrapper + mlp (this study) 14 98.91 v. conclusion and discussion this research aimed to develop a chili pepper disease diagnosis model by applying filter and wrapper feature engineering, technology & applied science research vol. 11, no. 5, 2021, 7714-7719 7718 www.etasr.com nuanmeesri & sriurai: multi-layer perceptron neural network model development for chili pepper … selection methods along with the mlpnn. the data used for classifying the 14 considered chili pepper diseases were processed by 3 feature selection techniques, namely ig, gr, and wrapper. once the feature selection process was completed, the selected data were applied to develop the chili pepper disease diagnosis model with the use of the mlpnn the experimental results indicated that the diagnosis model developed by the wrapper method and the mlpnn provided the highest level of effectiveness, with an accuracy of 98.91%. this result means that the developed model can be used in a chili pepper disease diagnosis system, suggesting chili pepper disease prevention and treatment. the results of this research conform to the study conducted in [3], in which the authors applied the mlp method to develop a disease diagnosis model which proved to perform better than other known techniques. the research findings also conform to the findings in [13]. the authors employed the wrapper method and the mlp to classify the symptoms of cardiac arrhythmia. their research results showed that the wrapper feature selection method could increase the effectiveness of the classification process. in general, a disease on chili peppers can be identified by its symptoms. most research is focused on image processing [16, 17, 20] and deep learning [18, 19] disease analysis from chili pepper leaves that require large image datasets to train the model. however, some symptoms that appear on chili pepper leaves may be similar, resulting in discrepancies in the efficiency and accuracy of classification. in addition, the disease identification of chili peppers from leaves is limited to some diseases with distinctive features appearing on the leaves. it is often necessary to analyze symptoms in other parts of the chili pepper plant, such as roots, stems, leaves, and fruits. therefore, this study used the information presented on plants throughout the chili pepper life cycle and considered the environmental conditions to help identify 14 occurring diseases. besides, the wrapper feature selection process proved to be more efficient than the ig, and gr, and the classification without feature selection. acknowledgment the authors are grateful to the institute for research and development, suan sunandha rajabhat university, and the faculty of science, ubon ratchathani university for supporting this research. references [1] k. lertrat, "production, planting, processing, marketing, and chili pepper products in thailand," research community, vol. 73, pp. 15–20, may 2007. [2] s. potghan, r. rajamenakshi, and a. bhise, "multi-layer perceptron based lung tumor classification," in 2018 second international conference on electronics, communication and aerospace technology (iceca), coimbatore, india, mar. 2018, pp. 499–502, https://doi.org/ 10.1109/iceca.2018.8474864. [3] k. subhadra and b. vikas, "neural network based intelligent system for predicting heart disease," international journal of innovative technology and exploring engineering, vol. 8, no. 5, pp. 484–487, 2019. [4] k. sutha and j. j. tamilselvi, "a review of feature selection algorithms for data mining techniques" international journal on computer science and engineering, vol. 7, no. 6, pp. 63–67, jun. 2015. [5] p.-n. tan, m. steinbach, a. karpatne, and v. kumar, introduction to data mining, 2nd ed. new york, usa: pearson education, 2019. [6] p.-n. tan, m. steinbach, and v. kumar, introduction to data mining, 1st ed. boston, massachusetts, usa: addison-wesley, 2005. [7] y. b. wah, n. ibrahim, h. a. hamid, s. abdul-rahman, and s. fong, "feature selection methods: case of filter and wrapper approaches for maximising classification accuracy," pertanika journal of science & technology, vol. 26, no. 1, pp. 329–340, jan. 2018. [8] b. karlik and a. v. olgac, "performance analysis of various activation functions in generalized mlp architectures of neural networks," international journal of artificial intelligence and expert systems, vol. 1, no. 1, pp. 111–122, 2011. [9] s. nuanmeesri, s. chopvitayakun, p. kadmateekarun, and l. poomhiran, "marigold flower disease prediction through deep neural network with multimodal image," international journal of engineering trends and technology, vol. 69, no. 7, pp. 174–180, jul. 2021, https://doi.org/10.14445/22315381/ijett-v69i7p224. [10] s. nuanmeesri, l. poomhiran, and k. ploydanai, "improving the prediction of rotten fruit using convolutional neural network," international journal of engineering trends and technology, vol. 69, no. 7, pp. 51–55, jul. 2021, https://doi.org/10.14445/22315381/ijettv69i7p207. [11] a. n. saeed, "a machine learning based approach for segmenting retinal nerve images using artificial neural networks," engineering, technology & applied science research, vol. 10, no. 4, pp. 5986–5991, aug. 2020, https://doi.org/10.48084/etasr.3666. [12] m. b. ayed, "balanced communication-avoiding support vector machine when detecting epilepsy based on eeg signals," engineering, technology & applied science research, vol. 10, no. 6, pp. 6462–6468, dec. 2020, https://doi.org/10.48084/etasr.3878. [13] a. mustaqeem, s. m. anwar, m. majid, and a. r. khan, "wrapper method for feature selection to classify cardiac arrhythmia," in 2017 39th annual international conference of the ieee engineering in medicine and biology society, jeju, south korea, 2017, pp. 3656–3659, https://doi.org/10.1109/embc.2017.8037650. [14] s. nuanmeesri and w. sriurai, "thai water buffalo disease analysis with the application of feature selection technique and multi-layer perceptron neural network," engineering, technology & applied science research, vol. 11, no. 2, pp. 6907–6911, apr. 2021, https://doi.org/10.48084/etasr.4049. [15] s. sudhi-aromna et al., a guide to chili pepper pests, nonthaburi, thailand: the agricultural co-operative federation of thailand, ltd., 2014. [16] d. p. patil, s. r. kurkute, p. s. sonar, and s. i. antonov, "an advanced method for chilli plant disease detection using image processing," in 52nd international scientific conference on information, communication and energy systems and technologies, niš, serbia, 2017, pp. 309–313. [17] m. ataş, y. yardimci, and a. temizel, "a new approach to aflatoxin detection in chili pepper by machine vision," computers and electronics in agriculture, vol. 87, pp. 129–141, 2012, https://doi.org/10.1016/ j.compag.2012.06.001. [18] s. jana, a. r. begum, and s. selvaganesan, "design and analysis of pepper leaf disease detection using deep belief network," european journal of molecular & clinical medicine, vol. 7, no. 9, pp. 1724–1731, 2020. [19] n. n. ahmad loti, m. r. mohd noor, and s.-w. chang, "integrated analysis of machine learning and deep learning in chili pest and disease identification," journal of the science of food and agriculture, vol. 101, no. 9, pp. 3582–3594, 2021, https://doi.org/10.1002/jsfa.10987. [20] s. das chagas silva araujo, v. s. malemath, and k. m. sundaram, "symptom-based identification of g-4 chili leaf diseases based on rotation invariant," frontiers in robotics and ai, vol. 8, 2021, art. no. 650134, https://doi.org/10.3389/frobt.2021.650134. engineering, technology & applied science research vol. 11, no. 5, 2021, 7714-7719 7719 www.etasr.com nuanmeesri & sriurai: multi-layer perceptron neural network model development for chili pepper … authors profile sumitra nuanmeesri received her ph.d. in information technology at the king mongkut’s university of technology north bangkok, thailand. she is an assistant professor in the information technology department, faculty of science and technology at suan sunandha rajabhat university, thailand. her research interests include speech recognition, data mining, deep learning, image processing, mobile application, supply chain management system, internet of things, robotics, augmented reality, and virtual reality. wongkot sriurai received her ph.d. in information technology at the king mongkut’s university of technology north bangkok, thailand. she is an assistant professor in the mathematics, statistics and computer department, faculty of science, ubon ratchathani university, ubon ratchathani province, thailand. her research interests include data mining, text mining, web mining, recommender system, information filtering, information retrieval, decision support systems, expert systems, multimedia technology, and computer education. engineering, technology & applied science research vol. 8, no. 2, 2018, 2741-2744 2741 www.etasr.com ali et al.: comparison of mechanical properties of lightweight and normal weight concretes … comparison of mechanical properties of lightweight and normal weight concretes reinforced with steel fibers ahsan ali department of civil engineering quaid-e-awam university of engineering, science & technology larkana, pakistan ahsanone@gmail.com zuhairuddin soomro department of civil engineering quaid-e-awam university of engineering, science & technology larkana, pakistan zuhairuddin@quest.edu.pk shahid iqbal department of civil engineering cecos university peshawar, pakistan shahid.iqbalmce@gmail.com nadeem-ul-karim bhatti department of civil engineering quaid-e-awam university of engineering, science & technology larkana, pakistan knadeem_b@yahoo.com ahmed faraz abro department of civil engineering, quaid-e-awam university of engineering, science & technology larkana, pakistan a.faraz.abro@outlook.com abstract-compared to conventional concrete, lightweight concrete is more brittle in nature however, in many situations its application is advantageous due to its lower weight. the associated brittleness issue can be, to some extent, addressed by incorporation of discrete fibers. it is now established that fibers modify some fresh and hardened concrete properties. however, evaluation of those properties for lightweight fiber-reinforced concrete (lwfc) against conventional/normal weight concrete of similar strength class has not been done before. current study not only discusses the change in these properties for lightweight concrete after the addition of steel fibers, but also presents a comparison of these properties with conventional concrete with and without fibers. both the lightweight and conventional concrete were reinforced with similar types and quantity of fibers. hooked end steel fibers were added in the quantities of 0, 20, 40 and 60kg/m3. for similar compressive strength class, results indicate that compared to normal weight fiber-reinforced concrete (nwfc), lightweight fiber-reinforced concrete (lwfc) has better fresh concrete properties, but performs poorly when tested for hardened concrete properties. keywords-lightweight; steel fibers; density; elastic modulus; ductility i. introduction structural lightweight concrete is defined as the one with minimum 28-days compressive strength of 17mpa and equilibrium density between 1120 and 1920kg/m3[1], whereas a cubic meter of conventional concrete weighs around 2300kg. compared to conventional concrete, structural lightweight concrete generally weighs 25% to 35% less [2]. this reduced weight not only imparts favorable effects on foundations, but also lowers the seismic inertial mass [3]. wide acceptance of the lightweight concrete by the construction industry in the past has been hindered by multiple factors including the lower strength of lightweight aggregates, the aggregate availability, the extra attention required during designing and making of lightweight concrete due to its higher water absorption and most importantly due to its higher brittleness associated with the material compared to the conventional concrete. nevertheless, current consumption trends show that structural lightweight concrete is getting momentum [4], as an increasing number of industrial plants have been set up for production of artificial aggregates addressing the aggregates’ availability issue. design engineers now have the choice of selecting among varieties of artificial aggregates such as expanded clay and expanded shale etc. moreover, development of mineral and chemical admixtures and improvement in particle strength of the artificial aggregates over the years have made it possible to produce lightweight aggregate concrete with better mechanical and rheological properties. as for the concerned brittleness issue, studies suggest that discrete fibers can be used to make concrete a more ductile material. use of fibers in concrete has been found to affect the properties of fresh and hardened concrete [5-7]. this effect so far has been quantified mostly for the conventional concrete and its test results have been made part of different committee reports and code sections[8, 9]. our understanding, however, regarding the influence of fibers on fresh and hardened lig in des con [10 is gu con exp and inc a. com con b. 1 den as 12 wo wa exa wo sta non c. ela engineering www.etasr ghtweight conc initial stage, sign of memb ncrete, wherea 0] is available therefore esse idelines that ncrete is fir perimental pro d hardened corporation of materials us one of the mpressive str ncrete, therefo exp h experimenta 1) fresh tested fresh nsity. fresh stm method 350-5 [13] orkability of a as chosen ove ample, it beco orkability usin andard, the sam n-fibrous conc fig. 1. mix hardened co all hardene astic modulus g, technology & r.com crete propertie for example ers produced u as a compreh for normal w ential for the the behavior rstly well un ogram was de lightweight f steel fibers. ii. experim sed major objec rength for bot ore ordinary p type p panded clay gravel sand shape hooked-end al tests concrete tes concrete prop concrete dens [12]. germa were follow all the used mi er other meth omes easy to q ng german di me din stand crete mixes. (a) xes at the end of sl oncrete tests ed concrete t and splitting t & applied scien ali e s and the mate there are no c using lightwei ensive commi weight fiber rei development r of lightweig nderstood. co evised for the concrete pro mental prog tives was to th lightweigh portland ceme particle size range 2-10 2-8 0-2 fl [mm] 35 ts perties include sity test wer an standard g wed for the ixes (figure 1 hods due to quantify the ef in standard, s dard can be u lump flow test (a) tests, i.e. com tensile strengt nce research et al.: compari erial behavior code guidelin ight fiber-reinf ittee report by inforced concr of any such d ght fiber-reinf onsidering th evaluation of operties after gram attain comp ht and conven ent (cem-1/4 table i. e [mm] bulk d ed workability e performed guidelines din determinatio 1). this test m its simplicity ffect of fibers o since unlike a used for fibrou (b) ) nwfc (b) lwf mpressive str th tests were c vol ison of mechan is still nes for forced y aci rete. 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march, nforced merican ensity, c 128astm method tric )”, e test”, ence of ht high 12, pp. h steel vol. 18, fraction on and ship of rials in l fibre 2005 -based microsoft word etasr_v11_n4_pp7321-7325 engineering, technology & applied science research vol. 11, no. 4, 2021, 7321-7325 7321 www.etasr.com hyder et al.: performance evaluation of rsa-based secure cloud storage protocol using openstack performance evaluation of rsa-based secure cloud storage protocol using openstack muhammad faraz hyder department of software engineering ned university of engineering and technology karachi, pakistan farazh@neduet.edu.pk syeda tooba department of computer science & it ned university of engineering and technology karachi, pakistan stooba1314@gmail.com waseemullah department of computer science and it ned university of engineering and technology karachi, pakistan waseemu@neduet.edu.pk abstract-in this paper, the implementation of the general secure cloud storage protocol is carried out and instantiated by a multiplicatively homomorphic encryption scheme (hes). the protocol provides a system for secure storage of data over the cloud, thereby allowing the client to carry out the operational tasks on it efficiently. the work focuses on the execution of five major modules of the protocol. we also evaluate the performance of the protocol with respect to the computation cost of these modules on the basis of different security parameters and datasets by conducting a series of experiments. the cloud was built using openstack and the data were outsourced from the client’s system to the cloud to study the security features and performance metrics when adopting the cloud environment. keywords-cloud computing; openstack; rsa; homomorphic encryption; privacy i. introduction cloud computing has become an evolving field in research and development because it can considerably lower computation cost. it has become a demanding and tempting technology that provides various services of storage, computation, and availability of data from anywhere and at any time [1]. as cloud computing is used to store a huge amount of data that reside on servers that are not physically in the reach of the users and they are transferred to and from the servers, security has therefore become an issue that obstructs the deployment of the cloud environment in an affirmative way [23]. the advancements in cloud computing are taking place at a very fast pace as the majority of the it firms have either already developed it products aligned with the cloud computing paradigm or are planning to move their infrastructure over it. this leads to a greater emphasis on improving security policies and measures. thus, there has been a rapid emergence in the security domain of cloud computing. storage facilities are provided by the cloud to store the data on the servers, but users are not able to verify whether their data are kept secure. detailed overviews of the core issues concerning privacy and security in cloud computing can be seen in [4-7]. to perform operations on the encrypted data stored on the cloud requires the cloud to send data to the client. the client then needs to decrypt them and perform the required operations. next, the data must then be encrypted again by the client before they are outsourced to the cloud. obviously, this increases the overhead at the client and the cloud side as well and is neither a feasible nor an efficient system. it implies the need for such a system that allows the client to directly perform operations on the outsourced data without decryption. this is what we call homomorphic encryption schemes (hess) [8]. simply encrypting the data using hess does not cater to the demands of data security. besides, maintaining the integrity of data sent over to the cloud, it must also allow the client to detect any forgery and recover the original data. in this paper, the implementation of the general secure cloud storage protocol instantiated by rsa-based hes has been carried out and evaluated. the cloud was built using openstack and data from the client’s system were outsourced to the cloud. also, the performance of the protocol was evaluated with respect to the computation cost of these modules on the basis of different security parameters and datasets by conducting a series of experiments. this work also gives an overview to understand the practicality of the rsa-scs protocol to overcome the threats and issues posed to the data stored on the cloud. authors in [9], studied the execution of gradient-based algorithms that belong to a class of distributed projected algorithms. they proposed he-based schemes that can attain accuracy by concurrently maintaining the state and coefficient of the respective member. authors in [10], dealt with a privacypreserving distributed big data analytics framework for cloudbased applications that performs analysis tasks on encrypted data with end-to-end data protection. the framework employs corresponding author: muhammad faraz hyder engineering, technology & applied science research vol. 11, no. 4, 2021, 7321-7325 7322 www.etasr.com hyder et al.: performance evaluation of rsa-based secure cloud storage protocol using openstack bgv as a fully hes. authors in [11] reviewed hess and also presented an implementation of the paillier phe using python library for paillier's phe. the extension module gmpy2 was used for carrying out the arithmetic operations and calculations. authors in [12] discussed the enhanced fhe with a focus on the dynamic structure of fully hess that are symmetric in nature. regarding secure outsourced calculations using he, the authors in [13] discussed the encrypted data processing protocols by applying he over addition and proxy cryptography. their system aimed to attain the secrecy of the user data while preserving the intermediary and final results security under the semi-honest model. to process encrypted data, non-interactive protocols were designed. authors in [14] discussed the security of multiparty computations. sometimes, the users of cloud infrastructure have to sustain the computation overheads although these must be outsourced. ii. rsa based secure cloud storage protocol to work out on the performance evaluation of the protocol, we have used rsa-based hes to instantiate the general cloud storage protocol discussed in [15]. the g-scs system model rsa-based hes is partially homomorphic over multiplication [16]. a. the rsa-scs protocol the chief aspects of the rsa-based hes are: • keygen �1�� → �sk, pk�. by considering the value of λ, this module is required to generate two prime integers p and q which must be large enough [17]. • the multiplicative homomorphic property of rsa can be computed using the technique presented in [18]. • rsa can be used to evaluate the general cloud storage protocol as rsa-scs which consists of five modules each corresponding to a module as in the g-scs but with the different parameters and enc( ), dec( ). [15]. b. rsa-scs workflow it is evident that to validate the integrity of the data stored on the cloud, the relationship expressed in [15] can be easily used by the client. the comprehensive approach to describe the modules and the steps the in rsa-scs are mentioned below. • keygen �1�� → �sk, pk� . this module is required to generate two integers p and q, where both of these should be prime numbers and the number of bits in the product of p and q must be ≥ λ. • outsource �d; sk� → d�. the client needs to split data d to m data segments such as �d�, d�, … … , d��, where di ∈ zn* (and zn* denotes {0,1, …, n-1}) for each value of i, before outsourcing its own data,. • audit �1�� → σ. as g-scs protocol provides two types of auditing. the client can perform either deterministic auditing, which is comparatively simpler, or randomized auditing. • in the former, the user spawns another key k2 whose length of bits is λ, to compute prf using this key value. now the auditing query σ = k2 and it is then sent to the cloud. • in the case of randomized auditing, the client selects l values (i1, i2, . . ., il) from znm (znm denotes m numbers chosen from the set {0,1, …, n-1}) and also generates k2, whose length of bits is λ to compute prf ��� (·). now, auditing query σ = [(i1, i2, . . ., il), k2] and both of these are sent. • prove �σ, d′; pk� → г. the proof generated by the cloud is also of two types depending on the type of audit query sent by the client. this is the output of the ‘verify’ module. iii. openstack cloud implementation openstack is one of the most popular open-source cloud ecosystems. we implemented the openstack using 3-node architecture as depicted in figure 1. the architecture consists of compute, controller, and network nodes. these nodes are installed using the ubuntu server 16.04. the openstack cloud was implemented in order to emulate the performance of the protocol in cloud environment. the data transfer and encryption for the instance running in the openstack cloud environment provided a realistic approach for the implementation of the protocol. figure 2 presents the dashboard screen of the installed openstack cloud. fig. 1. openstack core components. iv. experimental setup to perform the experiments on the rsa-scs, we implement this protocol in java using netbeans ide on a system with 1.7 intel(r) core(tm) i5-8500 cpu running at engineering, technology & applied science research vol. 11, no. 4, 2021, 7321-7325 7323 www.etasr.com hyder et al.: performance evaluation of rsa-based secure cloud storage protocol using openstack 3.00ghz and 16gb ram. the evaluations were carried out using 3 different values for security parameter λ, i.e. 512, 1024, and 2048 bits on two data sets that are text files of 10 and 16kb. as the security of the rsa encryption scheme requires the product of two primes to be sufficiently large [17], therefore the biginteger datatype is used to store the values for computation of the subsequent modules. aes is used as a pseudo-random function and the keys for the prf are generated by the client. fig. 2. openstack dashboard. each experiment was carried out 10 times and the average value was obtained as the result. to outsource the data, the ubuntu machine was used and the instances were generated with the flavor m1.small having 2gb ram and 20gb hard disk. the launched instances were accessed through the putty software by using the key pair generated. v. results and discussion we have implemented the cloud using openstack. the ubuntu 16.04 system was used to carry out the experiment. the keystone service was used to establish the connection using the dashboard. the method involves creating new instances on the compute node and then transferring the data over the cloud. the reason for the data values being larger in the results is that the experiment is carried out using the gui of the instance created in the openstack. the computation costs in seconds of the 5 modules of the rsa-scs with respect to the 3 security parameter values when outsourcing a file of 16kb size are shown below. the values in tables i and ii signify that there is a direct correspondence between the outsourced data and the time cost of all the modules of the protocol. it can be seen from the results that running the keygen algorithm takes a longer time as the client generates 2 prime numbers initially and then other 3 integers to compute the pair of keys that are required for encryption and decryption. also, the user has to generate a random number with a bit length of λ as the prf key. the outsourcing time of keygen is much less than that of rsa and is linearly dependent on the size of the data, as we have carried out deterministic auditing. an audit is basically the time used to generate k2 for the prf as the audit query is equal to k2. the computation cost for rsa-scs is comparatively higher than that of rsa-scs, since it has to parse the outsourced data and generate the values of α and β using the exponential function. referring to table i, the cost of rsa-scs is as large as expected. to check whether the cloud has maintained the integrity of the data that are sent to it, the client has to carry out exponentiation and modular multiplication and then a comparison of each computed result with the corresponding value of α. therefore, the time for this module is sufficiently large. table i. computation cost of file1.txt for varying bitlengths security parameter (λ) keygen (s) outsource (s) audit (s) prove (s) verify (s) 512 12.326 0.209 0.103 0.698 12.248 1024 85.788 0.780 0.793 1.587 84.952 2048 404.51 8.330 25.819 28.087 404.336 table ii. computation cost of file2.txt for varying bitlengths security parameter (λ) keygen (s) outsource (s) audit (s) prove (s) verify (s) 512 15.423 0.314 0.312 0.956 16.738 1024 102.88 1.764 0.993 3.485 104.512 2048 503.32 11.234 40.819 54.486 604.334 figures 3 to 7 represent the comparative analysis of different parameters for 2 different file sizes, i.e. 10 and 16kb. as evident from these graphs, the time required for different parameters increases linearly with the increase in file size. fig. 3. comparative analysis of keygen parameter for different file sizes. fig. 4. comparative analysis of outsource parameter for different file sizes. engineering, technology & applied science research vol. 11, no. 4, 2021, 7321-7325 7324 www.etasr.com hyder et al.: performance evaluation of rsa-based secure cloud storage protocol using openstack fig. 5. comparative analysis of audit parameter for different file sizes. fig. 6. comparative analysis of prove parameter for different file sizes. fig. 7. comparative analysis of verify parameter for different file sizes. table iii shows the comparison of the proposed approach with the existing solutions. the proposed scheme was implemented using openstack cloud. vi. g-scs implementation: secure against risks the data stored on the cloud face threats such as insider attacks, data leakage/loss, data alteration, malicious cloud providers, and lack of data recovery [19, 20]. the implemented openstack based g-scs provides security against these types of risks and threats posed to the cloud data and users. table iii. comparision of the proposed implementation with existing solutions implementation on open-source cloud platform third party auditing security model proposed � � standard [9] × × rom [11] × × rom [14] × � standard a. loss of data integrity the openstack based secure cloud storage protocol implementation offers its clients verification of the integrity of the data stored on the cloud through the auditing mechanism, thereby sending the proof against the audit query which can be verified as mentioned above. the cloud cannot cheat its client since a minor change in data results in a proof which when verified by the client, leads to output 0 rather than 1. b. malicious cloud provider this is one of the major threats to cloud computing. it can include a malicious insider/employee or the provider itself [21]. the implemented gscs-rsa outsource initially requires a pseudorandom function which must be secure enough so that the overall protocol becomes secure. as discussed in [15], if the cloud provider is malicious, it generates more than one (legitimate) proofs. even then, the number of unknown quantities is greater than the total number of equations thus generated and hence the malicious cloud is unable to discover the secret key because of the prf being used. c. lack of data recovery the data recovery algorithm provides an efficient way to reconstruct the data in case of data loss. for this, the client needs to generate a special audit query for which the cloud sends the proof. if this proof is verified by the client, he then computes enc�d�� by calculating β ! enc�d�� "# mod t . finally the outsourced data �d�, d�, … … , d�� can easily be recovered from enc�d��. vii. conclusion and future work in this paper, we have carried out an evaluation on the performance metrics and studied the security properties of the general sloud storage protocol under various circumstances that can occur in any hes. we have instantiated this protocol by a hes that is multiplicatively homomorphic, i.e. rsa, and thus assessed the computation cost of rsa-scs using various parameter values and data sets in a series of experiments. the carried out analysis left us with the conclusion that although the evaluated protocol is secure and efficient, its computation costs can be lowered. as the experiments were conducted on varying bitlengths of the security parameter, it was found that, the higher the value of λ, the greater the security achieved, but the computation cost increases. on the other hand, a 1024 bitlength can help us attain more or less the same security but with a greater impact on the computation cost. the computation costs of the 5 modules with respect to different values of security engineering, technology & applied science research vol. 11, no. 4, 2021, 7321-7325 7325 www.etasr.com hyder et al.: performance evaluation of rsa-based secure cloud storage protocol using openstack parameters are found by applying this algorithm on two datasets which led us to the optimization of the rsa-scs protocol. there is always a door towards improvement, therefore we can further take steps to make this protocol operate more securely while maintaining its efficiency. moreover, since rsa is a partially hes, we can further extend the protocol so that it is instantiated by an encryption scheme that is fully homomorphic. although fully hess are required in real-life applications and cloud infrastructure, their cost, whether that of computation or performance, is high. therefore, as future work, we can consider this aspect and make progress in this regard that can lead us to achieve a secure as well as lightweight scheme. in the future, we will also implement the proposed scheme in a federated cloud environment. references [1] m. a. 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[21] md. t. khorshed, a. b. m. s. ali, and s. a. wasimi, "a survey on gaps, threat remediation challenges and some thoughts for proactive attack detection in cloud computing," future generation computer systems, vol. 28, no. 6, pp. 833–851, jun. 2012, https://doi.org/10.1016/ j.future.2012.01.006. engineering, technology & applied science research vol. 7, no. 6, 2017, 2124-2131 2124 www.etasr.com teeparthi and vinod kumar: dynamic power system security analysis using a hybrid pso-apo … dynamic power system security analysis using a hybrid pso-apo algorithm kiran teeparthi department of electrical engineering national institute of technology warangal warangal, india kiran.t39@gmail.com d. m. vinod kumar department of electrical engineering national institute of technology warangal warangal, india vinodkumar.dm@gmail.com abstract—in this paper, a novel hybrid particle swarm optimization and artificial physics optimization (hpso-apo) algorithm is proposed to solve the dynamic security constrained optimal power flow (dscopf) problem for enhancing system security. the dynamic security assessment deals with contingency analysis which is carried out using a performance index. dscopf recommends preventive control actions like generator rescheduling to alleviate an existing credible contingency in the system while ensuring minimal operating cost. the opf problem is a highly nonlinear differential one and becomes more complex when considering the rotor dynamics of the system. the apo algorithm has the capability to reach a near global optimum value. however, it suffers from convergence problem. on the other hand, pso exhibits premature convergence characteristics, but it may get trapped at a local optima value. the proposed hpso-apo algorithm combines both individual algorithm strengths, to get balance between global and local search capability. the proposed method has been evaluated on a standard ieee six-generator, 30-bus system and a new england ten-generator, 39-bus test system. the proposed hpso-apo algorithm gives an efficient and robust optimal solution of dscopf problem compared to standard pso and apo methods. keywords-dynamic security assessment; overload alleviations; security enhancement; hybrid evolutionary algorithm; stability limits. i. introduction power system security assessment and enhancement are two major concerns in the energy management centers (emc) [1]. whenever a system is subjected to sudden disturbances (e.g. line outages or generator outages or short circuit faults), it can be lead to an insecure state. security assessment is the analysis carried out to determine the level in which a power system is safe from unforeseen disturbances (contingencies). the bottleneck of the security assessment is contingency analysis. it accesses the impact of a set of contingencies and identifies potential harmful contingencies that cause operating limit violations. security constrained optimal power flow (scopf) enhances system security by implementing the preventive or corrective control actions like generation rescheduling, phase shifter positions, switching of facts devices, hvdc line mw transfer and load shedding during the contingencies so that no contingencies will result to violations. power system security is classified into static and dynamic security. static security detects any overloading lines or out of limit voltages following a given list of contingencies. dynamic security evaluates the system dynamic behaviour in terms of transient stability or voltage stability when subjected to perturbations [2]. to illustrate the transient dynamic behavior of the system, a large group of nonlinear differential algebraic equations is involved. these equations are solved by approximate or full simulation algorithms like numerical integration methods e.g. runge-kutta, euler methods or direct methods such as lyapunov method [3-4]. the overall architecture of the dscopf problem is shown in figure 1. initialize system input data simulate (n-1) contingencies and compute transient stability index(tsi) minimum production cost (objective) security assessment rank the contingencies based on tsi and select top harmful contingencies dynamic security constrained opf perform the proposed hybrid pso-apo algorithm base case study optimal values of generators security enhancement fig. 1. architecture of dscopf problem. in static scopf problem, the dynamic constraints like rotor angle limits are excluded. moreover, the base case of optimal power generations may or may not be able to sustain the transient stability when the system is in contingency condition. dscopf is a highly nonlinear differential opf problem because of generator rotor angle dynamics. it aims to reschedule the generator active power outputs to bring back the system to the normal operating state under the consideration of static and dynamic constraints. the main challenge to solve the dscopf problem is choosing an effective optimization algorithm. over the last years, various conventional (mathematical based) algorithms have been implemented to solve the opf problem [5-6], however, these methods could be trapped at local optima solutions and also lack in handling the inequality constraints. in recent years, many researchers have tended to apply several heuristic methods for solving the opf and transient stability opf (tsopf) problems like simulated engineering, technology & applied science research vol. 7, no. 6, 2017, 2124-2131 2125 www.etasr.com teeparthi and vinod kumar: dynamic power system security analysis using a hybrid pso-apo … annealing (sa) [7], genetic algorithm (ga) [8], differential evolution algorithm (dea) [9-10], evolutionary programming method (ep) [11], particle swarm optimization (pso) [12-13], ant colony optimization (aco) [14], improved group search optimization (igso) [15], chaotic artificial bee colony (cabc) [16] and grey wolf optimization method [17]. however, these algorithms have some limitations regarding convergence issues and optimal setting of control parameters. as a way to cope with these drawbacks, hybrid heuristic optimization methods are implemented in practical and academic problems. the best results are found with hybrid methods [18-20]. a hybrid ts/sa optimization method has been implemented for solving the opf problem using facts devices in [21]. a new fuzzy adaptive artificial physics optimization algorithm (faapo) has been proposed for solving the scopf problem with the wind and thermal generators [22]. a novel hybrid particle imperialist competitive algorithm and teaching learning algorithm (hicatla) is proposed to solve the opf problem with nonsmooth cost functions [23]. in [24], a modified tla algorithm is implemented to solve the optimal dispatch reactive power problem. the main aim of heuristic optimization algorithms is to balance the exploitation and exploration capabilities in order to find an optimum solution with faster convergence. some algorithms were good at exploiting but may be trapped at the local minimum point. some are good at global search but poor in convergence. the main contribution of this paper is to formulate a novel hybrid optimization algorithm with combining standard pso and apo (hpso-apo) algorithms to solve the dscopf problem. the standard pso method may trap at local minima and fails to reach near global optimum value whereas apo gives the near optimal value due to its strong searching ability. however, it exhibits poor convergence characteristics. the proposed hybrid pso-apo algorithm combines both individual algorithm strengths to get balance between exploration and exploitation. the apo algorithm improves the diversity in the search space of the pso algorithm so as to avoid trapping in local optima. the validity of the proposed hpso-apo method is tested on well-known standard ieee test systems. ii. mathematical formulation dynamic security constrained opf is a special type of opf problem to minimize the objective function subjected to static and dynamic constraints by choosing the optimal control variables like phase-shifter angles, active and reactive power generations, transformer tap positions and voltages at pv buses. the general mathematical equation of objective function subject to the constraints is as follows: min ( , )f x u (1) subject to ( , ) 0e x u  (2) ( , ) 0i x u  (3) where, ( , )f x u represents the objective function, ( , )e x u and ( , )i x u are two nonlinear equality and inequality constraints. the vector x consists of active powers for all generators except the ref/slack bus and vector u consists of all dependent variables like slack bus real power, reactive power generations, and load bus voltages. minimization of fuel cost (fcost) subjected to network static and dynamic constraints is the main aim of dscopf and it is expressed as follows [16]. 2 cos 1 fuel cost ( ) = ; 1, 2 ../ .$ ... gn t i gi i gi i g i f a p b p nhc i     (4) where pgi is the real power generation of the ith generator, ng is the available generators, and ai, bi and ci are the generator fuel cost coefficients. dscopf problem includes both static as well as dynamic constraints like generator rotor angle limits. the equality and inequality constraints for dscopf problem is elucidated in the following subsections [16]. a. equality constraints (static and dynamic) the basic power flow equations give voltage magnitude and phase angle at each bus which is given by (5) and (6). , , 1 ( ) cos( ) 0 bn gen i load i i k ik ik ik k p p v v y        (5) , , 1 ( ) sin( ) 0 bn gen i load i i k ik ik ik k q q v v y        (6) where vi and vk represent bus voltage magnitudes, pgen,i and qgen,i are specified as the real and reactive power generation of ith bus, pload,i and qload,i are the real and reactive power loads of ith bus, nb represents total number of buses, δik and θik are voltage and admittance phase angles between i-k buses, and yik is the bus admittance matrix. in this work, a classical generator model has been considered. it comprises a constant voltage source in series with a transient. the swing equation of ith generator is expressed as follows [25]: 2 2 2 1, 2......i i mi ei g s h d p p i n w dt     (7) where, hi is the inertia constant of ith generator, ws is the angular speed, δi is the load angle, pei is the electrical power output, and pmi is the mechanical power input of ith generator. during the fault condition, the electrical output power ( feip ) is expressed in (8) and state space variable model for each generator is given in below: ' ' 1 cos( ) ; 1, 2...... gn f ei i j ij ij ij g i p e e y i n      (8) 1 2 , 1 , 2 ( ) ( ) ( ) i i r i s i i r i s fo i mi ei i x x x f x p p h                           (9) where, x1(=δi) and x2(=δωi) represent the state variables, δωi is the difference between the rotor speed ωr,i and synchronous engineering, technology & applied science research vol. 7, no. 6, 2017, 2124-2131 2126 www.etasr.com teeparthi and vinod kumar: dynamic power system security analysis using a hybrid pso-apo … speed (ωs) of the ith generator. the modified euler method is implemented to solve the state space equations because of its simplicity. b. inequality constraints (static and dynamic) the lower and upper limits of each element of power system inequality static and dynamic constraints are expressed as follows: min max 1, 2......gi gi gi gp p p i n   (10) max 1, 2......i i lines s i n  (11) min max 1, 2......i i i bv v v i n   (12) min max 1, 2......gi gi gi gq q q i n   (13) min max 1, 2......i i i tft t t i n   (14) 1 1 maxmax 1, 2......( 1)i gi n       (15) generally, a penalty function approach is used for solving the constrained optimization problem. the optimization problem is converted into unconstrained one from constrained problem by penalizing the equality and inequality constraints and building a single fitness function which is given in (16). 2 2 cos 1 ( , ) ( ( ) )+ [0, ( , ) ] ; for j 1, 2....., neq t j j i inequal min f x u f e x i x u n        (16) where ei(x,u) and ij(x,u) represent static and dynamic equality and inequality constraints, λ is the penalty factor and the value has considered as 1000. c. dynamic security assessment (dsa) the dynamic contingency analysis plays a vital role in dsa. the contingency ranking and selection has been done based on performance index [26-28] and identify the top harmful contingencies based on transient stability index (tsi). the dynamic contingency evolution has been done by euler’s method. the tsi is defined by max max (360 ) tsi 100 ; -100 < tsi < 100 (360 )          (17) where, δmax is the maximum allowable relative rotor angle and its value is fixed based on operational experience. for a real world power system, the δmax value is set to 100-120o. iii. proposed hybrid pso-apo algorithm to solve dscopf problem the apo and pso methods are two optimization methods inspired by basic physics and the behavior of bird flocking respectively. in pso method, each bird is treated as the particle and each particle having its own position, velocity and fitness value [29]. similarly, in apo, each particle constitutes mass, position, and velocity. based on the attractive and repulsive forces, each particle tends to larger masses close to global solution [30]. in recent years, hybrid heuristic optimization methods are implemented in practical and academic problems. a classifications of hybrid optimization methods is presented in [31]. according to [31], hybridization can be done at a low or a high level with relay or teamwork with heterogeneous or homogeneous approaches. in this paper, a low level with teamwork heterogeneous approach is used. the proposed hybrid algorithm combines both individual algorithm strengths, to get balance between global and local search capability. the general steps involved in finding the optimum values of generations subject to static as well as dynamic constraints are shown in figure 2. the following steps are implemented to solve the dscopf problem by the hpso-apo algorithm. step 1: (a) first, read the input data of dscopf problem.e., line data, bus data, and generator limits. also, initialize the apo and pso control parameters. (b) generate an initial population randomly within the given search space. step 2: compute the fitness for each particle using (16) and update the best and worst values. step 3: evaluate mass (mi(t)) and calculate the total force (fi(t)) on each particle iteratively using apo algorithm. ( ) ( ) ( ) exp ( ) ( ) i i best t fit t m t worst t best t        (18) ( ) ( )( ( ) ( )) ( ) ( ); ( ) ( ) ( )( ( ) ( )) ; ( ) ( ) i j j i j i ij i j j i j i gm t m t x t x t fit t fit tif f t gm t m t x t x t if fit t fit t        (19) , ( ) ( ) pop i ij j best j i f t f t     (20) step 4: update particle’s velocity and positions iteratively. the modified velocity equation of pso is as follows. finally, the positions of all particles are updated by using (22). ' 1 ' 2 ( 1) ( ) () ( ( ) / ( )) () ( ( )) i i i i i v t w v t c rand f t m t c rand gbest x t           (21) ( 1) ( ) ( 1)i i ix t x t v t    (22) step 5: check for maximum iterations count. if yes print the final results (fuel cost and active power generations) otherwise go to step 2. read input data and set the parameters of both pso and apo algorithms generate initial population in the given search space fitness evaluation and updating best and worst values evaluate mass(m) and forces for all particles using apo algorithm update modified pso velocity and position for all particles meeting end criterion? return the best values yes no fig. 2. flowchart of the proposed hybrid pso-apo algorithm. engineering, technology & applied science research vol. 7, no. 6, 2017, 2124-2131 2127 www.etasr.com teeparthi and vinod kumar: dynamic power system security analysis using a hybrid pso-apo … iv. simulation results and discussion in order to analyze the effectiveness of the proposed hybrid pso-apo method, the standard ieee six generator, 30-bus system and the new england ten generator, 39-bus system were considered. the obtained test results are compared with standard individual apo and pso methods. the total simulation time is 3.0 s for observing generator rotor oscillations and the time step adopted is 0.01s. for each case 20 independent trail runs are performed to validate the effectiveness of the proposed hybrid algorithm. the proposed hpso-apo algorithm is coded in matlab environment and all simulations were run on an intel, core i5-4210u processor, and 2.40 ghz personal computer. the following case studies are considered to evaluate the robustness of hpso-apo algorithm. (a) base case and (b) (n-1) contingency cases in the first case i.e. base case, the proposed hybrid optimization algorithm is employed to reschedule the active power generations under normal conditions. in the next case i.e. (n-1) contingency case, the proposed method is utilized to solve the dscopf problem to alleviate the line overloads by taking preventive control action like generator rescheduling. the control parameters used for the standard apo and pso are listed in table i. the simulation results for both base case and contingency cases are elaborated in the following sub-sections. table i. control parameters of apo and pso apo pso population size = 50; max. iteration number = 100 gravitational constant (g) = 0.01 swarm size = 50; max. iteration number = 100 acceleration constants, c1 = c2= 2; w=1 a. ieee 30-bus system the test data (line data, bus data and generator limits) along with network topology are taken from [32]. the test system comprises of six-generators and 41 transmission lines. the total real power demand on the system is 189.2 mw. 1) case a: base case the results for the base case that are obtained by using the proposed hybrid and apo, and pso methods are shown in table ii. the optimal fuel cost attained by the proposed hybrid method is 576.62 $/h. figure 3 shows the comparison convergence characteristic. the results reveal that pso algorithm was trapped at local optimum point, however, exhibits faster convergence characteristic. whereas apo attains the near global optimum point, but exhibits poor convergence characteristic. the proposed hybrid optimization method was superior and robust compared to apo and pso algorithms in terms of getting near global optimum point and faster convergence. 2) case b: (n-1) contingency case a set of contingency scenarios are created by implementing three phase short circuit faults at each bus on the system. the dynamic security assessment was done on the basis of transient stability index (tsi) [28], which is determined by timedomain simulation. the top-ranked contingency scenarios are listed in table iii. table ii. ieee 30-bus system: optimal generation (mw) for base case generator bus number proposed hybrid method apo pso g1 43.69 44.03 33.24 g2 58.16 58.61 48.73 g13 17.62 18.17 12.80 g22 23.21 23.34 24.75 g23 16.76 15.98 17.94 g27 32.69 32.00 55.00 fuel cost ($/h) 576.62 576.73 577.32 cpu time (s) 48.90 49.20 58.20 fig. 3. convergence characteristic of base case for 30-bus system. the thermal and voltage limits are considered as 120% and ± 5% of the base case values respectively. the δmax value is set to 120o. the proposed optimization algorithm is implemented to solve the dscopf problem with preventive control actions like generator rescheduling to bring the system into normal operating conditions. the relative rotor generator angles with respect to ref/slack generator obtained by the proposed hybrid method are shown in figures 4(a), 4(b). it is revealed that the relative rotor angles have not violated their maximum allowable limits after the rescheduling of active power generations. hence it can be said that the system is dynamically secured during the various contingency scenarios. the fuel costs along with optimal active powers obtained by the proposed as well as other reported methods are shown in table iv. only the top two severe contingency cases are presented in detail. the fuel cost of thermal generators obtained by the proposed hybrid optimization method for a line outage between buses 1-2 and 2-5 are 603.90 $/h and 593.98 $/h respectively. the proposed method gives a better global optimal fuel cost than the standard apo and pso methods. the comparison of convergence characteristics of the proposed hybrid pso-apo algorithm, as well as for other reported algorithms for line outage between buses 1-2 and 2-5, is shown in figures 5 and 6. the cpu times for completion of hundred iterations are listed in tables ii and iv. the computational time of the hpso-apo is faster than apo and pso methods. hence, the proposed hybrid optimization method is superior and more robust than the standard apo and pso algorithms in terms of getting near global optimum point and faster convergence. the performance engineering, technology & applied science research vol. 7, no. 6, 2017, 2124-2131 2128 www.etasr.com teeparthi and vinod kumar: dynamic power system security analysis using a hybrid pso-apo … measure (mean and standard deviation) and statistical (pvalues) results obtained over 20-independent runs by the proposed as well as standard apo and pso algorithms are shown in table v. the p-values are obtained from wilcoxon’s rank sum test. the results indicate that the proposed hpsoapo algorithm achieves the statistically best final accuracy over standard algorithms. fig. 4. generator relative rotor angles for 30-bus system – proposed hybrid algorithm (a) contingency-1 (between buses 1-2) (b) contingency-2 (between buses 2-5). fig. 5. convergence characteristic of contingency-1 (between buses 1-2) for 30-bus system. fig. 6. convergence characteristic of contingency-2 (between buses 2-5) for 30-bus system. table iii. dynamic contingency ranking for 30-bus system faulted bus number line outage between buses transient stability index (tsi) rank 1 1-2 -87.62 1 2 2-5 -87.18 2 27 27-29 -85.32 3 23 15-23 -10.60 4 22 10-22 -7.67 5 table iv. ieee 30-bus system: optimal rescheduling of generation (mw) for contingency case generator bus number line outage between buses proposed hybrid method apo pso 1-2 2-5 1-2 2-5 1-2 2-5 g1 10.80 45.39 10.58 46.46 10.51 63.83 g2 65.33 30.71 74.94 30.55 68.91 12.66 g13 24.15 24.08 21.35 25.44 20.44 22.04 g22 26.50 25.79 25.47 25.64 24.40 43.12 g23 21.76 20.43 20.36 22.31 26.36 6.55 g27 43.28 45.67 39.16 41.60 41.33 44.05 fuel cost ($/h) 603.90 593.98 604.92 594.07 605.10 596.25 cpu time (s) 103.2 105.7 112.5 113.9 123.8 125.6 b. new england 39-bus system the line data, bus data, and generator limits along with network topology are taken from [16]. the system comprises 10-generators, 46-transmission corridors, and 29-load buses. the total load on the system is 6098.0 mw. the δmax value is considered as 120o. 1) case a: base case the optimal active power generations along with fuel costs for the proposed hybrid as well as standard apo and pso methods are shown in table vi. as shown, the proposed hpso-apo algorithm outperforms the apos and pso algorithms and gives a fuel cost of 60917.68 $/h. the convergence characteristic of the best trail for the three algorithms is shown in figure 7. the results reveal that the proposed method provides better results in terms of reaching near global optimum point and faster convergence characteristic when compared to standard individual algorithms like pso and apo. fig. 7. convergence characteristic of base case for 39 bus system. 2) case b: (n-1) contingency case the hpso-apo algorithm is employed for the dscopf problem by rescheduling generators to minimize the severity during contingency conditions. the contingency ranking is (a) (b) engineering, technology & applied science research vol. 7, no. 6, 2017, 2124-2131 2129 www.etasr.com teeparthi and vinod kumar: dynamic power system security analysis using a hybrid pso-apo … based on tsi using t-d simulations and the five top ranked harmful contingencies are listed in table vii. the optimal values of active power generations along with fuel costs are shown in table viii. the minimum fuel cost obtained by hpso-apo for line outage between buses 17-27 and 4-5 are 60964.60 $/h and 61151.16 $/h respectively. the active power generations of all generators are rescheduled subjected to system static and dynamic constraints. the results reveal that the proposed hpso-apo algorithm achieves a near-optimal value when compared to the standard pso and apo algorithms. the relative rotor generator angles are shown in figure 8. table v. ieee 30-bus system: performance and statistical comparison of different algorithms for base case and contingency cases cost ($/h) base case line outage between buses 1-2 line outage between buses 2-5 proposed hybrid method apo pso proposed hybrid method apo pso proposed hybrid method apo pso best 576.62 576.73 577.32 603.90 604.92 605.10 593.98 594.07 596.25 worst 576.75 576.83 578.08 604.61 605.81 609.42 594.29 596.54 598.71 mean 576.66 576.78 277.41 604.28 605.21 607.65 594.16 595.22 597.36 standard deviation 0.039642 0.040029 0.538858 0.360026 0.383541 1.649737 0.116148 1.220495 0.792447 p-values na 2.14e-04 1.32e-04 na 1.28e-04 1.29e-04 na 3.86e-04 1.28e-04 table vi. new england 39-bus system: optimal generation (mw) for base case generator bus number proposed hybrid method apo pso g30 247.44 256.74 262.18 g31 560.07 545.76 650.00 g32 653.84 637.88 678.27 g33 654.41 600.59 387.71 g34 498.45 476.38 556.61 g35 673.97 615.86 750.00 g36 528.48 623.74 673.89 g37 542.59 530.83 423.82 g38 841.17 856.63 747.34 g39 940.55 995.39 994.64 fuel cost ($/h) 60917.68 60999.79 61165.77 cpu time (s) 134.40 137.80 142.40 table vii. dynamic contingency ranking for 39-bus system faulted bus number line outage between buses transient stability index (tsi) rank 27 17-27 -90.83 1 5 4-5 -88.92 2 17 16-17 -88.78 3 10 10-13 -86.78 4 8 8-9 -85.94 5 the convergence plots of the proposed hpso-apo, pso and apo algorithms for the both contingency scenarios are shown in figures 9 and 10. as shown, the proposed hpsoapo method has quite faster convergence characteristics compared to existing reported methods. the proposed hybrid algorithm integrates the strength of both algorithms to get a balance between exploration and exploitation. the relative rotor angles obtained by the proposed hpso-apo and reported methods are shown in figure 9 (a, b). this confirms the relative rotor angles have not violated their maximum limits during the alleviation of contingency. hence, the system is dynamically secured after the rescheduling of active power outputs during the contingency scenario. the cpu time for completion of hundred iterations of the proposed hybrid algorithm for both the cases is tabulated in tables vi and viii. it shows that the proposed hpso-apo method is faster compared to the standard apo and pso methods. the performance measure (mean and standard deviation) and statistical results (p-values) comparison of the proposed hpso-apo as well as standard apo and pso algorithms for both base case and contingency cases are tabulated in table ix. the results indicate that the proposed hpso-apo algorithm achieves the statistically best final accuracy over standard apo and pso algorithms. table viii. new england 39-bus system: optimal rescheduling of generation (mw) for contingency case generator bus number line outage between buses proposed hybrid method apo pso 17-27 4-5 17-27 4-5 17-27 4-5 g30 238.87 275.02 231.35 151.37 255.20 202.52 g31 541.74 550.20 544.87 460.21 430.39 374.84 g32 653.72 628.50 692.26 489.19 589.12 650.90 g33 648.93 609.63 623.85 715.13 659.12 750.00 g34 483.92 456.97 505.35 546.79 474.14 502.86 g35 697.01 750.00 615.82 745.53 711.40 644.71 g36 565.44 555.15 557.19 750.00 637.58 680.30 g37 530.09 502.31 579.45 548.52 608.21 477.18 g38 804.45 900.00 718.25 864.54 832.05 900.00 g39 975.22 914.74 1067.05 885.02 949.12 965.77 fuel cost ($/h) 60964.60 61151.16 61055.45 61201.75 61250.78 61373.37 cpu time (s) 182.35 185.26 192.89 193.25 210.78 212.65 engineering, technology & applied science research vol. 7, no. 6, 2017, 2124-2131 2130 www.etasr.com teeparthi and vinod kumar: dynamic power system security analysis using a hybrid pso-apo … fig. 8. generator relative rotor angles for 39-bus system – proposed hybrid algorithm (a) contingency-1 (between buses 17-27) (b) contingency-2 (between buses 4-5) fig. 9. convergence characteristic of contingency-1 (between buses 1727) for 39-bus system. fig. 10. convergence characteristic of contingency-2 (between buses 4-5) for 39-bus system. table ix. new england 39-bus system: performance and statistical comparison of different algorithms for base case and contingency cases cost ($/h) base case line outage between buses 17-27 line outage between buses 4-5 proposed hybrid method apo pso proposed hybrid method apo pso proposed hybrid method apo pso best 60917.8 60999.7 61165.7 60964.6 61055.4 61250.7 61151.1 61201.7 61373.5 worst 60946.2 61057.5 61230.2 60990.2 61109.8 61315.1 61182.1 61373.3 61404.1 mean 60928.5 61027.5 61205.7 60979.0 61070.7 61263.9 61162.9 61287.4 61391.0 std 11.25619 23.68506 27.75061 11.80751 21.37535 30.23327 13.26959 17.31354 16.43638 p-values na 1.884e-04 1.872e-04 na 1.92e-04 1.89e-04 na 1.23e-04 1.23e-04 v. conclusions a novel hybrid pso-apo algorithm is employed in this paper to solve the dynamic security constrained optimal power flow (dscopf) problem in order to enhance system security. the proposed hybrid optimization algorithm integrates the strengths of both algorithms to get a balance between exploration and exploitation. the proposed method is demonstrated on standard test systems like the ieee sixgenerator, 30-bus system and the new england ten-generator, 39-bus system. simulation results revealed that the proposed hybrid pso-apo algorithm is shown to be superior and more robust compared to the standard apo and pso algorithms in terms. references [1] b. stott, o. alsac, a. j. monticelli, “security analysis and optimization”, proceedings of the ieee, vol. 75, no. 12, pp. 1623–1644, 1987 [2] k. morison, w. lei, p. kundur, “power system security assessment”, ieee power and energy magazine, vol. 2, no. 5, pp. 30–39, 2004 [3] y. zhang, l. wehenkel, p. rousseaux, m. pavella, “sime: a hybrid approach to fast transient stability assessment and contingency selection”, international journal of electrical power & energy systems, vol. 19, no. 3, pp. 195–208,. 1997 [4] f. allella, d. lauria, “fast optimal dispatch with global transient stability constraint”, ieee proceedings-generation, transmission 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“hybridizing genetic algorithm with differential evolution for solving the unit commitment scheduling problem”, swarm and evolutionary computation, vol. 23, pp. 50-64, 2015 [19] m. mehdinejad, b. mohammadi-ivatloo, r. dadashzadeh-bonab, k. zare, “solution of optimal reactive power dispatch of power systems using hybrid particle swarm optimization and imperialist competitive algorithms”, international journal of electrical power & energy systems, vol. 83, pp. 104–116, 2016 [20] j. polprasert, w. ongsakul, v. n. dieu, “optimal reactive power dispatch using improved pseudo-gradient search particle swarm optimization”, electric power components and systems, vol. 44, no. 5, pp. 518–532, 2016 [21] w. ongsakul, p. bhasaputra, “optimal power flow with facts devices by hybrid ts/sa approach”, international journal of electrical power and energy systems, vol. 24, no. 10, pp. 851–857, 2002 [22] k. teeparthi, d. m. vinod kumar, “security-constrained optimal power flow with wind and thermal power 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pp. 541–564, 2002 [32] r. d. zimmerman, c. e. murillo-sanchez, matpower: a matlab power system simulation package, available at http://www.pserc.cornell.edu/ matpower/, 2005 microsoft word 3-606-ed.doc engineering, technology & applied science research vol. 5, no. 6, 2015, 885-890 885 www.etasr.com siad et al.: fea based on 3d micro-ct images of mesoporous engineered hydrogels fea based on 3d micro-ct images of mesoporous engineered hydrogels l. siad j. jing j. braux m. dubus f. velard d. laurentmaquin university of champagne, france larbi.siad@ univ-reims.fr university of champagne, france jing.jing@ univ-reims.fr university of champagne, france julien.braux@ univ-reims.fr university of champagne, france marie.dubus@ univ-reims.fr university of champagne, france frederic.velard@ univ-reims.fr university of champagne, france dominique.laurentmaquin@ univ-reims.fr s. c. gangloff h. kerdjoudj r. rahouadj j. -f. schmidt j. -f. ganghoffer university of champagne, france sophie.gangloff@ univ-reims.fr university of champagne, france halima.kerdjoudi@ univ-reims.fr university of lorraine, france rachid.rahouadj@ univ-lorraine.fr university of lorraine, france jean-francois.schmidt@ univ-lorraine.fr university of lorraine, france jean-francois.ganghoffer@ univ-lorraine.fr abstract —the objective of this computational study was to propose a rapid procedure in obtaining an estimation of elastic moduli of solid phases of porous natural-polymeric biomaterials used for bone tissue engineering. this procedure was based on the comparison of experimental results to finite element (fe) responses of parallelepiped so-called representative volume elements (rev) of the material at hand. to address this issue a series of quasi-static unconfined compression tests were designed and performed on three prepared cylindrical biopolymer samples. subsequently, a computed tomography scan was performed on fabricated specimens and two 3d images were reconstructed. various parallelepiped revs of different sizes and located at distinct places within both constructs were isolated and then analyzed under unconfined compressive loads using fe modelling. in this preliminary study, for the sake of simplicity, the dried biopolymer solid is assumed to be linear elastic. keywords-porous biomaterials; finite element; micro-ct; elasticity. i. introduction polysaccharides fall into the category of biopolymers derived from natural sources; their properties make them suitable for various biomedical and pharmaceutical applications [28, 37] including, e.g., tissue engineering purposes. the success of polysaccharides like chitosan for these applications stems from the fact that they are natural, abundant, and renewable polymers (originate from, e.g., algae and plants). furthermore, they are biocompatible and biodegradable [22, 38]. in addition, polysaccharides are characterized by a wide variety of structures that lead to peculiar properties that can hardly be matched, if necessary, by synthetic materials. on the other hand, considerable attention has been focused on microcomputed tomography (micro-ct), a non-destructive technique, which yields 3d information of the material analyzed through high-fidelity models constructed from data images. besides, nowadays image-based meshing offers interesting opportunities based on microstructures scan data to computational continuum micromechanics methods for material characterization [7, 25, 27]. this approach turns out to be very attractive in materials science where the link between macroscopic properties and the micro-structure of a material is sought. ii. polymeric gels a brief overview polymeric gels consist of physically or chemically crosslinked polymer chains that are able to absorb large amounts of solvent molecules (for instance, biological fluid) without dissolving [11, 16, 26, 29, 31]. they are called hydrogels when the solvent is water. hydrogels have the capability to mimic the extracellular matrix and their soft nature matches that of biological tissues. subsequently, they are hence highly desirable as 3d scaffolds for cells encapsulation [2]. based on the bonding type of the crosslinks, polymeric gels are classified into chemical gels (covalent bonds) or physical gels (cohesion forces existing between polymer segments, e.g., ionic bonding, van der waals forces …). the strong chemical bonds enable the polymeric gel to keep its shape after a large deformation. the high solvent content and elasticity yield a resemblance to biological tissue, creating extensive biomedical applications. at the same time, many tissues consist of elastic network and mobile molecules; the elasticity enables the tissues to retain shapes and deform, while mobile molecules enable the tissues to transport nutrients and wastes [18, 19, 20, 36]. engineering, technology & applied science research vol. 5, no. 6, 2015, 885-890 886 www.etasr.com siad et al.: fea based on 3d micro-ct images of mesoporous engineered hydrogels the deformation of polymeric gels (swelling) can be affected by many external factors (stimuli) like forces, temperature, electrical or magnetic fields, ph values, ionic concentration, many other types of stimuli. their response to these stimuli is generally a transient process involving solvent diffusion and deformation coupled via the chemo-mechanical interactions of polymer network and present solvent. such stimuli-responsive gels have become a good material choice in numerous applications. among them one could specifically name scaffolds for tissue engineering, drug delivery applications, and model of ecm for biological studies. it is believed that precisely because polymeric gels are responsive to various types of stimuli due to different mechanisms, a unified constitutive model that covers all of them seems to be very tedious to construct. generally speaking, the three main components of the polymeric gels synthesis are monomers, initiator, and crosslinkers which have good solubility in solvent at hand [11, 16, 23, 26]. nowadays, it is possible to design the structure of polymeric gels for a specific application by selecting proper starting materials and processing techniques. indeed, more and more polymeric gels have been engineered with tunable microstructures, mechanical properties, and also degradable rates. fig. 1. the 3d structure of a covalently cross-linked polymeric gel is a result of polymer cross-linking that forms an insoluble structure within the fluid environment where the network of polymer chains swell. constitutive models based on deformation, chemical diffusion, and transformation mechanisms of the chemical and mechanical energy of polymeric gels are receiving more and more attention. the thermodynamics of swelling dates at least back to gibbs [6] who formulated an equilibrium theory for the deformation of an elastic solid that absorbs a fluid. biot [15] used thermodynamic theory and darcy’s law to model the mass transport in a porous solid. as a matter of fact, these early works were not specific for polymeric gels. flory and rehner [12, 13] and flory [14] developed a statistical-mechanical model for gels. based on these seminal works, continuum models accounting for, amongst others, chemically induced volume transition, diffusion of a fluid, and inhomogeneous swelling in elastomeric gels are formulated and analyzed in [4, 5, 8, 10, 19, 20]. suo, hong and their coworkers [18, 19, 20, 36] modified the flory-rehner model for neutral gel by adopting the interaction parameter as a function of temperature and concentration. with a specific material model, such a theory enables analysis for the deformation of temperature-responsive polymeric gel under different geometric and mechanic constraints. as a model material, the polymeric gel is characterized by a helmholtz free-energy density function proposed by flory and others. this free-energy function accounts for, at the very last, the stretching of the polymer network and mixing of the polymer network and the solution. indeed, in neutral (as opposed to ionic) polymeric gels, there are two competing energies within the system. the energy that resists the solvent migration comes from the entropy of stretching the polymer chains and the energy that drives the influx of solvent is from the entropy of mixing. when solvent molecules migrate into a neutral polymeric gel, the possible arrangements of the system increase, leading to greater entropy of the mixture compared with the separated components, [16, 19, 20]. the interaction between the polymer network and solvent results in the heating of the mix. if the density of the crosslinks is very low, the effect of crosslinks on mixing can be reasonably neglected. in this circumstance, it is reasonable to assume that the free-energy density function of the polymeric gel is simply written as the sum stretch mixw w w  , where stretchw and mixw are the contributions from stretching the polymer network and mixing the polymers network and the solvent, respectively, [12, 13, 14]. this model (classical) is still being widely used to describe various approximate behaviours of polymeric gels. in order to trace the deformation of the polymeric gel, the dried polymer network under no mechanical load is taken as the reference state. each marker is named by its coordinate x in the reference state. in the current state at time t, the marker x moves to a place with coordinate x (x, t) . the local stretching state of the polymer network near marker x can be described by the deformation gradient f (x, t) . in addition, the solvent molecules constantly change their neighbors and migrate freely in and out of the polymeric gel. to account for the mobile species, we define the field of nominal solvent concentration c (x, t) , so that c dv is the number of solvent molecules in a volume element in the current state. for neutral one species of polymer chains and one species of solvent molecules, both being electroneutral polymeric gel, the two commonly used field variables are the deformation gradient and the nominal solvent concentration, in situations of isothermal processes (the temperature is deleted from the list of state variables): w w(f, c) . the free energy of a surface or interface is disregarded. a simple form of the helmholtz freeenergy density function is stretch mixw(f, c) w (f, c) w (c)  (1) the scope of polymeric gels applications is often severely limited by their mechanical properties, in particular their low elastic moduli. in the current paper, we limit our investigation to small deformation and to the linear elastic response of the engineering, technology & applied science research vol. 5, no. 6, 2015, 885-890 887 www.etasr.com siad et al.: fea based on 3d micro-ct images of mesoporous engineered hydrogels dried polymer network ( c 0 ). as a result, the strain energy density function of stretching the dried polymer network, in terms of infinitesimal strain tensor ε, is 2 ij kk ij ij 1 e e w( ) 2 (1 )(1 2 ) (1 2 )                  (2) where e is the young’s modulus and ν is the poisson’s ratio of the material at hand. this is the st. venant-kirchhoff model which is the simplest example of a hyperelastic material. it should be kept in mind that this st. venant-kirchhoff material has been found to be of little practical use beyond the small strain domain. iii. uniaxial compression tests three-dimensional mesoporous scaffolds have been manufactured according to the freeze-drying procedure. for a detailed description of the used process allowing the preparation of the mesoporous polymeric biomaterial, we refer the reader to the paper by brun et al. [3]. the porosity of the investigated cylindrical samples, measured by the liquid displacement method, was estimated to range from 80 to 91 % with a pore size of 50 to 150 µm. the uniaxial (or unconfined) compression test is often chosen to characterize porous materials because of the simplicity of the testing configuration and the specimen test shape. a typical compression test involves influence of specimen size, influence of porosity, and strain rates effects on mechanical response of the material [9]. usually compression data including, for example, young's modulus, yield stress and poisson's ratio, is obtained from the measured force versus the displacement curve. in this preliminary work, unconfined compression tests were carried out first in order to obtain an appraisal of the young's modulus e of built scaffolds circular cylindrical samples with about 10.0 mm in diameter and 9.0 mm in height were subject to unconfined compression through an universal testing machine at a strain rate of 3 120 10 s  (figure 2). both chemical crosslinked and uncrosslinked scaffolds were tested. in this paper the focus is only on the former biomaterial for which figure 3 displays the obtained stress-strain curves due to loading (increasing strain) and unloading (decreasing strain) for three distinct samples. the curves seem to be linear for stresses up to about kpa100 . the mean experimental values of young' moduli of the tested samples were measured as the slopes of linear elasticunloading curves, using the approximate expression: (figure 4) exp oe h h       , (2) (1)    , (2) (1)h h h   (3) in this way, for the considered crosslinked scaffold it has been found that expe 19.20 mpa . fig. 2. prepared crosslinked scaffold for compression tests. a) uniaxial compression stress state; b) specimen typical failure mode. fig. 3. nominal stress versus true strain curves for crosslinked scaffolds. the 3 curves correspond to 3 distinct samples. fig. 4. used technique for the determination of the mean value of the young’s modulus from experimental results. engineering, technology & applied science research vol. 5, no. 6, 2015, 885-890 888 www.etasr.com siad et al.: fea based on 3d micro-ct images of mesoporous engineered hydrogels iv. finite element modeling high-resolution three-dimensional micro-ct scan data of cylindrical samples were obtained and the data were straightforwardly segmented using threshold and flood fill tools in simpleware's scanip software [35]. the pixel size was 8.85 m . the 3d connectivity of the dried biopolymer turns out to be practically totally interconnected (figure 2). as a trade-off, various parallelepiped specimens having the same cross section oa (0.345 × 0.345, 0.522 × 0.522, 0.699 × 0.699 and 0.965 × 0.965 2mm ) with increasing thickness oh (0.345, 0.531, 0.708 and 0.965 mm ) were used in this preliminary investigation. they were extracted from the 3d image as shown in figure 5. fig. 5. various parallelepiped rves for uniaxial compression simulations. typical example of rve size: 60×89×60 voxels; one pixel = 8.85 µm. the corresponding 3d micro-ct image data are converted into fe models. the parallelepiped specimens were meshed with the same mesh density. the anti-aliasing techniques implemented in this software are volume, topology and geometry preserving. mixed hexahedral and tetrahedral elements were generated. the element parameters were adjusted to the software recommended aspect ratio in order to ensure the highest mesh quality possible [35]. the various samples were subject to compression tests along the z-direction. to this goal, a displacement which amplitude depends on the considered sample is imposed on top faces perpendicular to the z-direction, whereas the bottom faces were fixed along z-direction and the four other faces remain free. we made the assumption that the behavior of the solid phase of the considered porous biomaterials remains linear elastic during the whole process of deformation. a series of fe analyses using abaqus [1] were carried out under compression loading conditions up to approximately 30 % strain. it is believed that this is high enough to observe local deformation. by way of illustration, figure 6 shows a typical mesh geometry created from tomographic images using simpleware [35]. prior to simulation as such, a wide number of analyses were performed in order to get insight of the sensitivity of numerical predictions to mesh density and segmentation parameters. vertical total reaction force zf of the top moving face and its vertical displacement zu were recorded during the simulated compression test. the nominal compression stress  was calculated as the ratio of zf on its initial total area oa : z of / a  . the engineering strain  is given by o o(h h ) / h   . fig. 6. fe mesh of a parallelepiped created from tomographic images [9]. the fe model includes about 920 940 hexahedral and tetrahedral elements. fig. 7. 3d visualization of the contour plot of the z-displacement. v. results and discussion the whole simulated parallelepiped specimens exhibited a similar mechanical trend under compression loading. by way of example, figure 7 displays a deformed contour plot of the zu component of the displacement u calculated using the procedure described above. as regard our first simulation, the used values of young's modulus and poisson's ratio of the porous biomaterials at hand were obtained from a literature review dealing with chitosan, e.g., [23, 32, 38]: e 380 mpa , y 110 mpa  . it emerged that using these values yields a large overestimation of the young' moduli in comparison to experimental results. engineering, technology & applied science research vol. 5, no. 6, 2015, 885-890 889 www.etasr.com siad et al.: fea based on 3d micro-ct images of mesoporous engineered hydrogels the foregoing fe modelling is used, thanks to the linearity of the problem under consideration, to obtain an estimation of the young's modulus of the chemical crosslinked biomaterials which preparation is described in [3]: pge 27.73 mpa for µct construct sample 1 and pge 45.51 mpa for µ-ct construct sample 2. after which these values have used in order to get an estimation of the apparent young's modulus ae , for a fixed volume size of considered rves. the obtained results are shown in table i, figure 8 and table ii, figure 9, respectively. one has to notice that when the size of the simulated specimen is smaller than the rve of the material, the properties that can be computed are not necessarily the effective properties but merely apparent properties of the investigated volume, [17, 21, 24, 34]. the computer used throughout the present study is a standard pc. within the context of random heterogeneous materials, it should be kept in mind that larger computer facilities would be necessary in order to analyze specimens with larger sizes. table i. computed apparent young's modulus as a function of the thickness oh of the simulated rve; epg = 27.73 mpa. µct construct 1 ho (µm) 345.2 522.2 699.2 964.7 ea (mpa) 16.94 17.48 17.81 19.20 µct construct 2 ho (µm) 345.2 345.2 345.2 522.2 522.2 692.2 964.5 ea (mpa) 15.42 12.99 13.42 15.91 13.26 14.02 13.76 fig. 8. computed apparaent young’s modulus a e as a function of the thickness oh of the simulated parallelipiped rve; epg = 27.73 mpa. table ii. computed apparent young's modulus as a function of the thickness oh of the simulated rv; epg = 45.51 mpa µct construct 1 ho (µm) 345.2 522.2 699.2 964.7 ea (mpa) 23.65 24.40 24.86 26.80 µct construct 2 ho (µm) 345.2 345.2 345.2 522.2 522.2 692.2 964.5 ea (mpa) 18.73 18.14 21.53 18.51 22.22 19.57 19.20 fig. 9. computed apparaent young’s modulus ae as a function of the thickness oh of the simulated parallelipiped rve; epg = 45.51 mpa. vi. conclusion and future prospects the foregoing numerical model accounts for the micro architecture of the porous polymeric biomaterials at hand. this and prior work highlights that fe models based on an accurate 3d model from micro-ct data are an essential tool to quantify the effects of pores in complex material systems such as polymeric biomaterials. the ease with which models can be generated would allow us to account for, e.g., the hyperelastic and the viscoelastic behaviour of the materials at hand. these constitutive models can be coupled with fe biomechanical simulations to analyse the behaviour of chitosan-hyaluronic acid based materials used as scaffolds for tissue engineering. these extensions are contemplated as future works. references [1] abaqus/standard, simulia, providence, ri, 2013 [2] e. m. ahmed, “hydrogel: preparation, characterization, and applications: a review”, journal of advanced research, vol. 6, pp. 105121, 2015 engineering, technology & applied science research vol. 5, no. 6, 2015, 885-890 890 www.etasr.com siad et al.: fea based on 3d micro-ct images of mesoporous engineered hydrogels [3] v. brun, c. guillaume, s. mechiche alami, j. josse, j. jing, f. draux, s. bouthors, d. laurent-maquin, s. c. gangloff, h. kerdjoudj, f. velard, “chitosan/hydroxyapatite hybrid scaffold for bone tissue engineering”, biomed. mater. eng., vol. 24, pp. 63-73, 2014 [4] s. baek, a. r. srinivasa, “diffusion of a fluid through an elastic solid undergoing large deformation”, int. j. non-linear mech., vol. 39, pp. 201-218, 2004 [5] s. baek, t. j. pence, “inhomogeneous deformation of elastomer gels in equilibrium under saturated and unsaturated conditions”, j. mech. phys. solids, vol. 59, pp. 561-582, 2011 [6] m. a. biot, “general theory of three-dimensional consolidation”, j. appl. phys., vol. 12, pp. 155-164, 1941 [7] s. k. boyd, "image-based finite element analysis" in c. w. sensen, b. hallgrimson, editors, advanced imaging in biology and medecine, pp. 3-25, springer, berlin, 2009 [8] s. a. chester, l. anand, “a coupled theory of fluid permeation and large deformations for elastomeric materials”, j. mech. phys. solids, vol. 58, pp. 1879-1919, 2010 [9] s.c. cowin, s.b. doty, tissue mechanics, springer, berlin, 2007. [10] j. delbow, e. fried, h. ji, "chemically induced swelling of hydrogels", j. mech. phys. solids, vol. 52, pp. 51-84, 2004 [11] m. djabourov, k. nishinari, e. schacht, physical gels from biological and synthetic polymers, cambridge university press, 2013 [12] p. j. flory, j. rehner, “statistical mechanics of cross-linked polymer networks i. rubberlike elasticity”, j. chem. phys., vol. 11, pp. 512-520, 1943 [13] p. j. flory, j. rehner, “statistical mechanics of cross-linked polymer networks ii. swelling”, j. chem. phys., vol. 11, pp. 521-526, 1943 [14] p. j. flory, principles of polymer chemistry, cornell university press, ithaca, 1953 [15] j. w. gibbs, the scientific papers of j. willard gibbs, dover publication, new york, 1961. digital copy of the book is freely available at http://books.google.com/ [16] f. horkay, g. b. mckenna, “polymer network and gels”, in j. e. mark, editor, physical properties of polymers handbook, pp. 497-523, springer, berlin, 2007 [17] s. hazanov, c. huet, “order relationships for bcs effect”, j. mech. phys. solids, vol. 42, pp. 1995–2011, 1994 [18] w. hong, “continuum models of stimuli-responsive gels”, in s. li, b. sun, editors, advances in soft matter mechanics, pp. 165-196, springer, berlin, 2012 [19] w. hong, x. zhao, j. zhou, z. suo, “a theory of coupled diffusion and large deformation in polymeric gels”, j. mech. phys. solids, vol. 56, pp. 1779-1793, 2008 [20] w. hong, z. liu, z. g. suo, “inhomogeneous swelling of a gel in equilibrium with a solvent and mechanical load”, int. j. solids struct., vol. 46, pp. 3282-3289, 2009 [21] c. huet, “application of variational concepts to size effects”, j. mech. phys. solids, vol. 38, pp. 815–831, 1990 [22] i.-y. kim, s.j. seo, h.s. moon, m. k. yoo, in-y. park, b.-c. kim, c. s. cho, “chitosan and its derivatives for tissue engineering applications”, biotechnology advances, vol. 26, pp 1-21, 2008. [23] r. jin, p.j. dijstra, “hydrogels for tissue engineering applications”, in r. m. ottenbrite, k. park, t. okano, editors, biomedical applications of hydrogels handbook, pp. 203-225 , springer, berlin, 2010 [24] t. kanit, s. forest, i. galliet, v. mounoury, d. jeulin, "determination of the size of the representative volume element for random composites: statistical and numerical approach", int. j. solids struct, vol. 40, pp. 3647–3679, 2003 [25] d. lacroix, a. chateau, m. p. ginebra, j. a. planell, “micro-finite element models of bone tissue engineering scaffold”, biomaterials, vol. 27, pp. 5326-5334, 2006 [26] h. li, smart hydrogel modelling, springer, berlin, 2009 [27] e. maire, p. j. withers, "quantitative x-ray tomography", international materials reviews, vol. 59, pp. 1-43, 2014 [28] m. a. meyer, p.-y. chen, biological materials science, cambridge university press, 2014 [29] h. omidian, k. park, “introduction to hydrogels”, in r. m. ottenbrite, k. park, t. okano, editors, biomedical applications of hydrogels handbook, pp. 1-16, springer, berlin, 2010 [30] m. l. oyen, "mechanical characterisation of hydrogel materials", international materials reviews, vol. 59, pp. 44-58, 2014 [31] n. a. peppas, hydrogels in medicine and pharmacy, vol. 1, crc press, florida, 1987 [32] b. d. ratner, a. s. hoffman, f. j. schoen, j. e. lemons, biomaterials sciences, 3rd edition, app. 8: properties of soft materials by m. c. l. martins, elsevier inc., 2013 [33] b. van rietbergen, r. huiskes, f. eckstein, p. rüegsegger, “trabecular bone tissue strains in the healthy and osteoporotic human femur”, j. bone miner. res., vol. 18, pp. 1781-1788, 2003 [34] h. shen, l. c. brinson, “representative volume element size for porous titanium”, j. mech. mater. structures, vol. 1, pp. 1179–1204, 2006 [35] simpleware ltd., exeter, uk, http://www.simpleware.com, 2014 [36] suo, http://imechanica.org/node/987, http://imechanica.org/node/538 [37] a. steinbuchel, editor, biopolymers, vols. 5-6, wiley, weinheim, 2006 [38] s. k. wang, j. li, f. yao, "application of chitosan-based biomaterials in tissue engineering", in k. yao, j. li, f. yao, y. yin, editors, chitosan-based hydrogels. functions and applications, pp. 407-468, scrc press, 2012 engineering, technology & applied science research vol. 7, no. 5, 2017, 2022-2025 2022 www.etasr.com modi et al.: fmfinder: a functional module detector for ppi networks fmfinder: a functional module detector for ppi networks manali modi computer engineering department marwadi education foundation rajkot, gujarat manalim.21@gmail.com navjyotsinh jadeja information technology department marwadi education foundation rajkot, gujarat noon2night88@gmail.com kirtirajsinh zala marwadi education foundation rajkot, gujarat kirtirajzala@gmail.com abstract—bioinformatics is an integrated area of data mining, statistics and computational biology. protein-protein interaction (ppi) network is the most important biological process in living beings. in this network a protein module interacts with another module and so on, forming a large network of proteins. the same set of proteins which takes part in the organic courses of biological actions is detected through the function module detection method. clustering process when applied in ppi networks is made of proteins which are part of a larger communication network. as a result of this, we can define the limits for module detection as well as clarify the construction of a ppi network. for understating the bio-mechanism of various living beings, a detailed study of fmfinder detection by clustering process is called for. keywords-functional modules; protein; ppi network; detection methods; inferring ppi network i. introduction one of the major applications of biotechnology is in the field of bioinformatics especially when working with organic data. analysis of biological processes is the primary objective of bioinformatics. the primary research revolves around hereditary connections, structural alignment of proteins, various protein to protein interaction methods and evaluation methods. large part of bioinformatics is concerned with various biological processes which are part of protein-protein interaction (ppi). ppi network, is a network of proteins interacting with each other to carry out various biological processes inside an organism. hence it is very important to study and analyze how these protein modules interact to perform and carry out various metabolic activities. systematical examination of the properties which are concerned with proteins which give concise depictions of consistent structures in wellbeing and diseases is known as proteomics [1]. normally, protein infrequently goes about as a solitary isolated component. proteins, including those in the indistinguishable cell forms, regularly associate with one another to consolidate into an extensive atom to perform the organic capacities. for example, absorption framework, quality outpouring control, cell spread, cell signal transduction, the ways of action and movements of gsc and cell apoptosis depend on ppi. as needs be, the examination of ppi frameworks frequently serves as the reason to a better comprehension of cell affiliation, strategies, and limits and thusly elucidation of protein correspondence which is a central issue in science [1]. ii. ppi major datasets the postgenomic period is recognized by the accessibility of colossal measure of organic information sets which are truly heterogeneous in nature and hard to examine. vast scale ppi network throughput such as tandem affinity purification and yeast two hybrid give associations stable as well as transient in nature [4]. ppi networks also have mass spectrometry showing the protein edifices [4]. these datasets, notwithstanding being inadequate, additionally comprise of false positives, and, thusly, the cooperation found in different information sets may not concur with one another. owing to this difference, it is basic to make utilization of statistic techniques to induce the ppi arranges by discovering solid and reproducible connections and anticipate the associations not discovered yet in the accessible data. iii. inferring ppi network this segment depicts the statistical techniques that are utilized to discover solid and complete protein-protein association systems. the inference of ppi systems can be done in sundry courses, for example, phylogenetic profiling and id of basic examples. it is to be noticed that in contrast with quality systems, a great deal of work can be flawed in a protein-protein system surmising utilizing the probabilistic strategies. in a living life form, a few proteins cooperate to do different undertakings framing a protein complex. a large sum of protein-protein interaction information compromises the interaction and it is extremely uncommon the discovering communications amongst large protein numbers. subsequently, recognizable proof of protein buildings is of prime significance to pick up a superior comprehension of the cell system. distinguishing protein edifices is a crucial zone of investigation of protein systems, for which different grouping techniques were connected. one of the different methods for recognizing engineering, technology & applied science research vol. 7, no. 5, 2017, 2022-2025 2023 www.etasr.com modi et al.: fmfinder: a functional module detector for ppi networks the protein buildings incorporate diagram division, where the chart is grouped into subgraphs utilizing expense based pursuit calculations. another methodology is extensively ordered as protection crosswise over species, where arrangement devices are utilized to discover the edifices that are normal in numerous information sets originating from distinctive species. the conclusion of human genome sequencing in turn makes proteomic examination a standout amongst the most critical of life science processes. a systematical investigation procedure in which various properties concerned with are investigated. this investigation helps in representing the structure, capacity and the control of natural frameworks defining health and sickness [1]. at times proteins go about as single disengaged elements. on the other hand, proteins included in the same cell regularly associated with one another to join into an extensive particle. case in point, the methods and exercises of the hereditary substance duplicate, quality declaration control, cell signal transduction, digestion system, cell proliferation are related to ppi. they are the foundation of organic courses of action occurring in life forms. consequently, the examination of ppi systems commonly serves as the premise to a superior comprehension of cell association, courses of action, capacities and subsequently to the explanation of protein communication which is a focal issue in science [2]. last decade saw ppi information dissected by high throughput test systems. such as two hybrid frameworks, protein chip innovation and mass spectrometry. established approach to focus protein capacity is to discover homologies between an unannotated protein and other protein utilizing grouping comparability calculation [3]. numerous coordinated ppi systems have performed identification processes. the huge size of ppi system information becomes a tedious task to effectively distinguish various organic modules as well as essential examination subject in genomic time. there are various organic trial systems to identify functional modules in ppi systems. a. module detection survey [1] the authors have dissected existing issue and present metrics for distance. also they categorized the overall arrangement of practical module discovery as well as execution of numerous calculations by using known values. final execution in the current scenario is the investigating of the network system. essential idea driving the research is to distinguish utilitarian modules from existing network. by organizing and utilizing diverse bunching routines with distinctive calculation. in the current research different problems are introduced to assess the discovery of module and its quality and also counting location system's execution. parameters are sensitivity, precision, f-measure, recall, accuracy and positive predictive value, and p-value measure. this research portrays procedures which recognize utilitarian module in comparison with current network. b. dfm-cin algorithm [2] the authors have presented a novel structure which identifies protein complexes. this paper also proposes practical approach by acclimatizing hereditary component statement information into datasets of ppi. dfm-cin is the proposed method which calculates revelation of useful module in view of the distinguished edifices. authors developed protein protein interaction network as a part of static systems of tsns. the proposed structure not only calculates but can also recognize protein complexes and modules. the research findings of the authors recommend functional modules identification with the help of protein complexes. c. protein function prediction using ann [3] authors have built a model by using weighted graph for protein interactions. this acts as a base to put forward and reflect facts related to small world network property. this property filters protein interaction network reliably. in certain situations, individual protein has multiple functions. this makes it an issue of multi labeling in a weighted graph problem. the procedure shows very high reliability amongst the connections of protein in the network. the suggested approach has been tested on mips datasets showing high performance in terms of precision and recall while using ann. d. mofinder algorithm for overlapping modules [4] mofinder for large ppi networks is proposed by the authors in [4]. ppi data file is primarily converted into sparse matrix in this approach. then this sparse matrix is processed with global approximate minimum degree ordering as well as local amd. local sparse matrix and local amd are generated using sliding window protocol along the diagonal. clustering coefficient for this matrix is required to be calculated and if found higher than the cutoff then we save the sub modules. else they are discarded. finally sliding window goes diagonally to fetch remaining modules. detection of small modules is not possible with this algorithm. e. overlapping modules mining using lgt [5] authors proposed a method in which they have used line graph transformation for discovering utilitarian modules from large network as well as accumulate ones identifying protein module structure. resulting modules are identified with projected algorithm which shows high scope among fly, yeast, and worm network of proteins. investigation on yeast protein networks recommends enormous protein modules which have been found with association of capacity annotation, localization as well as buildings blocks of proteins. f. coach algorithm [6] in this paper authors promoted coach method for anticipating constructions with the help of recognizing protein complexes as well as containing protein associations. they measured and investigated protein groups from different viewpoints. from first view, they execute widespread correlation among projected method as well as present approaches with consideration of expected groups in contradiction of targeted protein structures. second, they admit focal point linking edifices exploiting dissimilar biological evidence as well as learning. g. fuzzy clustering algorithm [7] authors have proposed a method in which they have secluded the capacity of q fluffy cluster. this means they have engineering, technology & applied science research vol. 7, no. 5, 2017, 2022-2025 2024 www.etasr.com modi et al.: fmfinder: a functional module detector for ppi networks applied grouping strategy in order to discern the covering group structure. the research shows the higher efficiency of the new algorithm in detecting appropriate number of clusters and good clustering. h. functional module detection using metrices [8] authors have addressed various problems arising while developing protein protein connections and resultant issues of protein communication information. hence, they advised for usage of betweenness commonality decomposition for calculating customs edge shared trait and for the recognizing of practical modules from the extensive networks. fig. 1. intferring ppi network iv. proposed framework all the above procedures devised some shortcomings with the reference of quantity of practical module recognition. hence, fmfinder approach is designed for amending enactment of prevailing procedure. the steps for the proposed flow of the algorithm are shown in figure 2. for the proposed fmfinder, ppi file in terms of protein network and clustering coefficient 0.45 are the inputs and in turn functional modules from the human and yeast database are the production of the protein networks. figure 3 shows the proposed algorithm fmfinder for functional module detection. v. implementation and comparison with existing techniques human ppi dataset and yeast ppi dataset were used to perform fmfinder algorithm based implementation. interacting protein data is stored in these datasets. human dataset was collected from human protein release dataset (hprd). yeast dataset was collected from dataset of interacting proteins (dip). 1800 protein interactions are included in the yeast dataset and 39200 interactions of proteins are found in human ppi network. fmfinder algorithm processes on these datasets to detect functional modules. analysis and comparison with earlier algorithms and approaches along with their limitations are described in table i. table ii depicts modules identified with its major modules for human dataset. table iii depicts modules identified with its major modules for yeast dataset. from this review it is obvious that fmfinder outflanks when applying to yeast and human datasets for overlapping module detection. this relative study will be helpful for the examination of the diverse algorithm which is valuable for the detection of protein modules. despite the fact that lpcf has most anticipated proteins and covered proteins it has less utilitarian rate. figure 5 shows modules that are predicted and covered proteins by the algorithm in human database. as shown in the figure 5 and table ii fmfinder algorithm has highest predicted proteins and covered proteins as compared to other algorithms for human database. figure 6 shows functional percentage of identifying modules from the large network by different algorithms in yeast database. it can easily seen from the figure 6 and table iii that fmfinder shows highest functional percentage for detecting functional modules for yeast database. thus fmfinder has highest accuracy for discovering overlapping modules from ppi complex network. fig. 2. proposed flow of fmfinder algorithm fig. 3. proposed algorithm engineering, technology & applied science research vol. 7, no. 5, 2017, 2022-2025 2025 www.etasr.com modi et al.: fmfinder: a functional module detector for ppi networks fig. 4. flow of mmd algorithm table i. algorithmic analysis algorithm description limitation mcode identifies densely connected group of proteins detects only connected graphs of proteins within the ppi network dpclus based on the agglomerate and divisive algorithm unable to detect overlapping functional modules mofinder identifies functional modules, specially overlapping modules detects only small size of modules, less than 12, from human and yeast database fmfinder identifies functional modules detects 256 modules from human database and 109 modules from yeast database. major size module is 4. table ii. functional modules identification on human database algorithm modules identified major module size mcode 21 3 dpclus 102 8 mofinder 221 12 fmfinder 265 4 table iii. functional modules identification on yeast database algorithm modules identified major module size mcode 15 3 dpclus 54 8 mofinder 90 3 fmfinder 109 3 fig. 5. comparision graph for human database vi. conclusion the current paper portrays different methods which are exploited as a part of reviling functional modules from a large database. we examined each dataset, inferred ppi network, analysis of existing algorithms and its covered proteins and functional percentage of modules which are actually identified from the existing algorithms. results show that the fmfinder proposed algorithm outperforms previous algorithms (mcode, dpclus, mofinder) by detecting more modules of proteins in both human and yeast databases. fig. 6. comparision graph for yeast database fig. 7. graph comparison between fmfinder and mofinder references [1] j. ji, a. zhang, c. liu, x. quan, z. liu, “survey: functional module detection from protein-protein interaction networks”, ieee transaction on knowledge and data engineering, vol. 26, no. 2, pp. 261-273, 2014 [2] m. li, x. wu, j. wang, y. pan, “towards the identification of protein complexes and functional modules by integrating ppi network and gene expression data”, bcm bioinformatics, pp. 1-12, 2012 [3] l. shi, y. r. cho, a. zhang, “prediction of protein function from connectivity of protein interaction network”, international journal of computational bioscience, vol. 1, pp. 1-5, 2010 [4] q. yu, g. h. li, j. f. huang, “mofinder: a novel algorithm for detecting overlapping modules from protein-protein interaction network”, journal of biomedicine and biotechnology, vol. 2012, pp. 110, 2012 [5] ] s. zhang, h. w. liu, x. m. ning, x. s. zhang, “a hybrid graphtheoretic method for mining overlapping functional modules in large sparse protein interaction networks”, international journal of data mining and bioinformatics, vol. 3, no. 1, pp. 68–84, 2009 [6] m. wu, x. li, c. k. kwoh, s. k. ng, “a core-attachment based method to detect protein complexes in ppi networks”, bmc bioinformatics, vol. 10, pp. 1-5, 2009 [7] s. zhang, r. s. wang, x. s. zhang, “identification of overlapping community structure in complex networks using fuzzy c-means clustering”, physica a, vol. 374, no. 1, pp. 483– 4490, 2007 [8] c. wang, c. ding, q. yang, s. r. holbrook, “consistent dissection of the protein interaction network by combining global and local metrics”, genome biology, vol.8, no.12, pp. 1-10, 2007 engineering, technology & applied science research vol. 8, no. 2, 2018, 2689-2692 2689 www.etasr.com far et al.: assessment of health, safety and environmental risks of zahedan city gasoline stations assessment of health, safety and environmental risks of zahedan city gasoline stations somayeh yadollahi far zahedan university of medical sciences zahedan, iran ramazan mirzaei social determinants of health research center, mashhad university of medical sciences mashhad, iran mobina bakoei katrini faculty of engineering and technology, zahedan branch islamic azad university zahedan, iran mahin haghshenas environmental & occupational health center ministry of health, treatment and medical training tehran, iran zoleikha sayahi national iranian oil products distribution company, khuzestan region (ahvaz) ahvaz, iran abstract—the purpose of this study was to assess the risk and determine the health, safety and environmental status of fuel stations in zahedan. in this study, failure mode and effects analysis (fmea) method was used for risk assessment in accordance with the hse guidelines, national and international standards and laws. in this cross-sectional study, 2 governmental stations and 6 active private stations were evaluated after the necessary coordination with the relevant units. as a result of risk assessment, 27 health risks, 55 safety risks and 22 environmental risks were identified. from among all the identified risks, 67 risks had a risk priority number (rpn) of less than 91, 31 risks had an rpn ranging between 91 and 201, and 6 risks had an rpn of over 201. the findings of the study indicated that compliance with the hse requirements was 51.85%, in the area of health, 47.57% in the area of safety and 27.45% in the environmental area. overall compliance with the hse requirements was 42.54%. in order to distribute fuel considering health, reducing risk and increasing compliance with the requirements for safety improvement, health and environmental conditions of fuel supplies are essential. keywords-fuel station; health; safety; environment i. introduction the supply chains are important parts of the fuel distribution and supply [1]. a gas station is a place licensed by the national oil distribution company of iran and has standard reservoirs for storing oil products [2]. the purpose of the construction and operation of gas stations is to complete the production to consumption cycle of oil products, including gasoline [3]. the occurrence of any mistake or incident at the stations can destroy the result of a long-term endeavor in the fields of exploration, drilling, extraction, refining, distribution, etc. in recent years, these cases have included other dimensions, which could have irreparable effects on the environment and the residents. in particular, we are faced with a huge amount of chemicals that are considered to belong to toxic and hazardous groups [4]. properties such as high flammability of oil products have caused the most attention to stations. generally, oil industries attract attention in terms of providing security and maintaining financial and human resources and taking care of potential risks for the environment and health of the people. there are always environmental and health risks during the stations’ operation [3, 5]. fire and explosions at the city gas stations which are near the buildings are considered to be a threat, and people outside the gas station, including personal drivers and passengers, have augmented increase vulnerability to fire. by increasing the gas station staff and the quality of the limitations, the fire safety problem becomes seriously faced [6]. the existence of multiple risks, including the above, indicates the importance of risk assessment at gas stations. the risk management assessment is based on the management of the health, safety and environment of the personnel. “risk” is a process that has an uncertain and unknown outcome in each field. the main purpose of risk analysis and risk assessment is to determine the degree of uncertainty of the study system, its cost, and the proposed reduction strategies, as well as the cost of the corresponding solution [8]. risk identification and determining its positive and negative outcomes are of particular importance to the objectives of the project [9]. the more accurate the risk identification is, the better the system performance [10]. making a system safe, without the primary identification of risks or controlling risks is practically impossible. one of the common mistakes in safety engineering is ignoring this stage or paying insufficient attention to it. the next stage is the identified risks analysis. risk analysis is a technique for studying the causes and consequences of a potential risk in the system [11]. among the risk assessment techniques, the fmea method is the only analytical method in risk assessment that can assess the potential risks within the assessment ranges and also identify and classify the causes and effects associated with it. among the benefits of this approach we can refer to its appropriateness in quantitative risk assessment and the reliability of this approach to predict engineering, technology & applied science research vol. 8, no. 2, 2018, 2689-2692 2690 www.etasr.com far et al.: assessment of health, safety and environmental risks of zahedan city gasoline stations problems and identify the most effective risk prevention solution [12]. fmea is a systematic and a completely mental preventive approach based on teamwork which is used in defining, identifying, assessing, preventing, eliminating or controlling the states, causes and effects of potential errors in a system, process, project, or service (before a final product or service reaches its customer), and the prediction of errors and the way to prevent them is the prerequisite [13-15]. on the other hand, the hse management system provides guidance for all work guidelines such as research and development, design, construction, operation, transportation and distribution, product management and work which is performed by employees and contractors in accordance with the health and safety standards [16]. in the oil products distribution company, the hse guideline of oil products supply network have been prepared based on national and international standards for preventing accidents and creating safe conditions for performance and enhancement of safety factors [2]. this research was carried out with the aim of determining the health, safety and environmental risks of zahedan fuel stations using the fmea method. health, safety and environmental aspects of fuel stations are provided in order to investigate their compliance with the hse requirements of the stations particularly in the field of exploiting and identifying risks. ii. methodology in this cross-sectional study, the health, safety and environmental risks in the fuel stations of zahedan city were investigated using the fmea method. the status of the stations’ compliance with the requirements of hse was also investigated. at the time of the research, there were 11 stations in zahedan, namely 3 government and 8 private stations. from among these stations, 1 governmental and 1 private station were under reconstruction, and 1 station was not ready to cooperate. eventually, this study was conducted in 2 governmental and 6 private operational stations. in order to assess risk through the fmea method, fuel stations were first supervised and the way they act was carefully monitored. information on the collection process and all environmental, equipment, material, human, etc. risks that threaten health, safety and the environment were listed. in the next steps, the causes of risk, the effects of each risk, and then the existing control processes were examined. for this purpose, the conditions in the fuel stations were compared to the standards, requirements and rules governing the work environment. rate of deterioration, probability of occurrence, rate of probability of risk discovery/call rank was determined and the rpn (risk priority number) was calculated based on them. in the last step, the risks were ranked based on the rpn [17]. in reviewing the requirements of the hse, the basis for investigating was the hse guidelines for the fuel products supply networks of the national oil refinery company which includes three parts of the requirements for construction, operational requirements, and considerations for the referrals. based on this, a checklist was designed whose validity was confirmed by experts. iii. results table i indicates the number of risks in the three areas of health, safety and the environment in fuel station processes, and table ii indicates the division of risks into three acceptable, tolerable and unacceptable categories. also, in figure 1, the number of risks is displayed based on the specified ranges in the three domains. table i. the number of risks identified in gas stations based on different parts of the process risk rpn emptying refueling lighting total health 11 16 27 safety 20 30 5 55 environmental 12 10 22 table ii. risk situation decision table row risk number decision type 1 1 to 90 acceptable 2 91 to 200 unacceptable-tolerable 3 more than 201 intolerable fig. 1. comparative diagram of the number of health, safety and environmental risks based on the rpn rates in assessing the risks of the oil product stations through fmea, the highest levels of risks in the three considering areas are:  health: car traffic (rpn: 486)  safety: use of cigarettes during refueling and the lack of continuous sampling of product vapors (rpn: 280)  environment: lack of assessing the thickness of tanks (rpn: 112) based on the investigation results, the hse requirements had the average compliance of 51.85% in health area, 47.57% in the safety area and 27.45% in the environmental area. the results of this assessment indicated that, there is 42.54% of compliance in the studied stations and 57.46% of the noncompliance with the checklist requirements. chi-square test was used to determine the compliance with the requirements at the stations and the results indicated that there are significant differences between the criteria and the positions in four stations (p-value <0.05). engineering, technology & applied science research vol. 8, no. 2, 2018, 2689-2692 2691 www.etasr.com far et al.: assessment of health, safety and environmental risks of zahedan city gasoline stations iv. discussion according to the results of the risk assessment, the most identified risks are related to safety, health and environment fields respectively. risks with rpn of more than 100 are subject to the above order. in a study conducted on fire safety in 22 gas stations in zanjan using the national review list, the findings of the analysis revealed that, on average, 70% of safety tips in these stations have been respected [18]. this is while the safety situation in the stations studied in zahedan were consistent with an average of 47.57% of the criteria set out in the hse guidelines for the fuel products supply network. also, in assessing the environmental risks of oil products storage facilities through the fmea method the risk number for oil tanker 210 was obtained [12]. according to the present research, the environmental risk number of this activity at fuel stations is 72. in [19], the use of a proper ventilation system and the proper equipment maintenance in order to prevent leakage in the joints and the reduction of people exposure, have been proposed as control measures in confronting chemicals. in this study, leakage from the valves, pipes and tanks at fuel stations also result in the introduction of pollutants into the environment, thereby increasing the risk of fuel leaks. according to [20], the lack of a three-way catalytic converter system on cars, the average car age, the low respect for regulatory requirements such as technical vehicle inspection, high engine set-up and spare parts costs, gasoline spills, new car prices, the low number of petrol stations in comparison to the car number are some of the main factors of pollution increasing near gas stations [20]. the results of this study indicated that the lack of attention to the hse requirements of the stations and the existing regulations in this field resulted in increasing various health, safety and environmental risks. in a study in a petrochemical industry, benzene earned a risk level of 5 with a coefficient of 5-6.5 [21]. this level indicates high risk and the need for corrective actions. however, in [22], conducted at shiraz gas stations, the average exposure of gas station workers to btx does not exceed the exposure limit values of these compounds, and the exposure to lead-free gas did not seem to be evident with blood damage. in [23] the average concentration of benzene in the air was higher than the one proposed by the national technical committee on occupational health (0.5 ppm) at the gas station in yazd. at the same time, the concentration of toluene, ethyl benzene and xylene was lower than the allowed limit [23]. in [24], which was conducted regarding gas stations in ahwaz downtown, the results indicated that the concentration of benzene in the gas stations and the surrounding streets was averagely higher than that of respiratory air. in [3], the calculations indicated that about 14 tons of gasoline (ordinary and super) is evaporated from the reservoirs of tehran's vali'asr gas station per year. this rate of evaporation can have an impact on the air pollution in the surrounding environment and increases health, safety and environmental risks. according to the results of this study, increasing control measures to reduce exposure to benzene in zahedan fuel stations is necessary. according to [25], conducted at gas stations in kenya, the employers and customers are encouraged to adhere to standards that ensure the safety of the workplace. however, our study indicated that in total, 57.46% of the studied stations have noncompliance with the checklist requirements, and in terms of compliance with the hse guidelines for the fuel products supply networks, the visited stations are almost identical. v. conclusion there are various health, safety and environmental risks, and numerous cases of non-compliance with the criteria under consideration, something that clarifies the need for more supervision on the stations at construction time and during operation. the use of technical and managerial methods to eliminate and reduce risks is recommended. holding training classes in all three areas of health, safety, and environment in a compiled form for staff, internal auditing, continuous maintenance, installation of instructions, guiding and warning boards and general training of the drivers of all types of vehicles will be helpful. in general, compliance with the health, safety and environmental requirements of the hse guidelines for fuel supply networks can be effective in risk reduction. the attention of experts to the implementation of the requirements is as necessary as the attention of the authorities. it should be noted that the use of proposed solutions in each of the health, safety and environmental areas can also be effective in other areas and ultimately lead to a general reduction of risks. acknowledgment this study was supported by islamic azad university, zahedan, iran. authors would like to particularly thank the management and staff of zahedan city gasoline stations. references [1] national iranian oil products distribution company, office of health, safety and environment, environmental considerations product supply stations, public relation publication, (in persian), 2008 [2] national iranian oil products distribution company, instructions hse ducts supply of petroleum products, (original in persian), 2010 [3] a. karbasi, f. kavyanifar, “estimate the rate of heavy due to gasoline evaporation in the stations via software, case study: the valiasr”, technical seminar on oil ,gas and the environment, iran, vol. 1, no. 4, pp. 23-35, 2008 [4] f. ahmadi, gasoline vapor recovery, national iranian oil engineering company, 2006 [5] r. d. harbinson, m. m. bourgeois, g. t. johnson, hamilton & hardys industrial toxicology, mosby, 1998 [6] epa, preventing leaks and spills at service stations: a guide for facilities, available at: https://www3.epa.gov/region9/waste/ust/ pdf/servicebooklet.pdf, 2003 [7] d. hillson, effective opportunity , management for projects – exploiting positive risk, marcel dekker, 2004 [8] v. t. covello, j. menkes, j. mumpower, risk evaluation and management, plenum press, 1986 [9] r. yarahmadi, p. moridi, “risk assessment and management of health, safety and environment in vitro research sites”, occupational health and safety, vol. 3, no. 3, pp. 11-26, 2012 [10] a. jafari, “job safety analysis in abadan oil refining company”, 2nd national conference on safety engineering and hse management, iran, 2007 [11] n. j. bahr, system safety engineering and risk assessment, crc press, 2014 [12] s. naghavi, d. salehi rahmatollah “environmental risk assessment of fmea storage facilities”, sixth national conference and specialized engineering, technology & applied science research vol. 8, no. 2, 2018, 2689-2692 2692 www.etasr.com far et al.: assessment of health, safety and environmental risks of zahedan city gasoline stations exhibition of environmental engineering, iran, vol. 1, no. 8, pp. 201236, 2012 [13] j. s. krouwer, “an improved failure mode effects analysis for hospitals”, archives of pathology & laboratory medicine, vol. 128, no. 6, pp. 663-667, 2004 [14] m. g. gressel, j. a. gideon, “an overview of process hazard evaluation techniques” american industrial hygiene association journal, vol. 52, no. 4, pp. 158-63, 1991 [15] r. j. cody, “anticipating risk for human subjects participating in clinical research: application of failure mode and effects analysis”, cancer investigation, vol. 24, no. 2, pp. 209-214, 2006 [16] hse management system, sustainability report, available at: http://www.inpex.co.jp/english/csr/pdf/sustainability2014-e12.pdf, 2014 [17] e. habibi, applied safety and performance indicators in the industry, fanavaran publishing, 2005 [18] s. arghami, h. zahiriangh, a. ruhani, m.aflatooni, “presentation of a practical approach for prioritizing preventive actions”, seventh national conference on health occupational, 2011 [19] m. jahangiri, m. jalali, c. h. saeidi, “assessment of occupational exposure exposure to chemicals in order to provide control strategies (case study in polyurethane foam industry)”, occupational medicine, vol. 5, no. 4, pp. 33-41, 2012 [20] a. bahrami, a. heydari jafari, “single-ring aromatic compounds are taxi drivers exposured compared with emissions to petrol pump stations in the city of hamedan”, ninth national conference on environmental health, iran, 2006 [21] f. golbabaee, d. eskandari, m. rezazadeh azari, m. jahangiri, a. rahimi, “health risk assessment of exposure to chemical pollutants, with emphasis on the risk of leukemia at a petrochemical industry”, iran occupational health journal, vol. 9, no. 3, pp. 11-21, 2012 [22] m. neghab, k. hoseinzadeh, j. hasanzadeh, “assessment hematotoxic effects of occupational exposure to unleaded gasoline”, iran occupational health journal”, vol. 9, no. 4, pp. 1-12 , 2012 [23] m. mosadegh mehrjerdi, n. tahmasbi, a. barkhordari firoozabadi, h. falahzadeh, s. esmaeel, k. soltanizadeh, “evaluation of exposure to benzene, toluene, ethylbenzene and xylene (btex) by solid phase micro extraction and gas chromatography in the gas station city of yazd”, south medical, vol. 16, no. 6, pp. 419-427, 2013 [24] m. fooladi, g. h. goodarzi, m. mohamadi roozbahani, “measuring and comparing the composition btex of the filling stations in the city of ahvaz in the morning and afternoon and assessing their infection transmission radius”, second national conference on planning and environmental protection, iran, 2013 [25] m. james, i. m. fedha, safety and health assesment in kenyan petrol station: case study of nairobi highway stations, mechanical engineering conference on sustainable research and innovation, vol. 4, no. 3, pp. 211-213, 2012 engineering, technology & applied science research vol. 8, no. 1, 2018, 2577-2584 2577 www.etasr.com soomro et al.: 3d numerical modeling of pile group responses to excavation-induced stress release ... 3d numerical modeling of pile group responses to excavation-induced stress release in silty clay mukhtiar ali soomro department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan eng.soomro@gmail.com abdul salam brohi department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan eng.armaan@gmail.com mohsin ali soomro department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan drmohsin@quest.edu.pk daddan khan bangwar department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan skb_khan2000@yahoo.com shahzad ali bhatti department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan shahzadalibhatti72@gmail.com abstract—development of underground transportation systems consists of tunnels, basement construction excavations and cut and cover tunnels which may encounter existing pile groups during their construction. since many previous studies mainly focus on the effects of excavations on single piles, settlement and load transfer mechanism of a pile group subjected to excavationinduced stress release are not well investigated and understood. to address these two issues, three-dimensional coupledconsolidation numerical analysis is conducted by using a hypoplastic model which takes small-strain stiffness into account. a non-linear pile group settlement was induced. this may be attributed to reduction of shaft resistance due to excavation induced stress release, the pile had to settle substantially to further mobilise end-bearing. compared to the sp of the pile group, induced settlement of the single pile is larger with similar settlement characteristics. due to the additional settlement of the pile group, factor of safety for the pile group can be regarded as decreasing from 3.0 to 1.4, based on a displacement-based failure load criterion. owing to non-uniform stress release, pile group tilted towards the excavation with value of 0.14%. due to excavation-induced stress release and dragload, head load of rear piles was reduced and transferred to rear piles. this load transfer can increase the axial force in front piles by 94%. keywords-multipropped excavation; pile group; tilting; loadtransfer i. introduction in dense urban environments where buildings are closely spaced, deep excavation for basement construction and other underground facilities such as mass rapid transit station sand cut-and-cover tunnels is unavoidable. as these excavations are usually carried out close to existing buildings, a major concern is to prevent/minimize the damage to adjacent buildings and underground utilities [1, 2]. thus, it is important for designers to estimate potential damage resulting from nearby deep excavations to existing piles. most researches estimated the buildings settlement and tilting considering wall movements and ground surface settlement trough using empirical approaches. the performance of pile group depends on the stress state in the soil and surrounding sub-surface soil movements [3]. in addition, deep excavation in soft clay induces negative excess pore water pressure [4] which induces long term pile group settlement with the dissipation of excess pore water pressure. therefore, it is essential to investigate the pile group response mechanism adjacent to deep excavation in soft soil. authors in [1, 2] reported case studies in granular soil and alluvium residual soil respectively. they demonstrated that lateral soil movements due to excavation can be detrimental to nearby existing piles. in both the reported case studies pile toe levels were much deeper than the excavation level and they reported only the lateral pile behavior. apart from field monitoring, a number of centrifuge tests were also conducted to investigate the response of single pile [5] and pile group in soft kaolin clay [6]. they concluded that the induced bending moment and lateral deflection of piles were highly influenced by distance from wall and pile head condition. in studies, lateral response of end bearing piles without initial applied load was reported. in reality, pile group in soft clay behaves as floating pile group and subjected to initial applied load from superstructure. in the presence of initial applied load, soil surrounding the pile group experiences higher stress level before the commencement of adjacent excavation. authors in engineering, technology & applied science research vol. 8, no. 1, 2018, 2577-2584 2578 www.etasr.com soomro et al.: 3d numerical modeling of pile group responses to excavation-induced stress release ... [7-8] conducted centrifuge tests to investigate the effects of an unpropped excavation on the behavior of nearby single piles and pile groups in dry dense toyoura sand. it was found that the distance from the pile to the retaining wall and pile head conditions had a large influence on the induced pile bending moment and lateral deflection. authors in [9] reported the results of three centrifuge tests which were carried out to study the effects of a multipropped deep excavation in-flight on the behavior of single piles in dry toyoura sand. piles were laterally restrained in terms of rotation and deflection right at or above ground surface in the three different tests. it was concluded that lateral restraints imposed on the pile head have a significant influence on induced pile bending moment. induced bending moment due to excavation can exceed the pile bending capacity. authors in [10] developed design charts to compute the lateral behavior of a single pile adjacent to deep excavation in soft ground. they performed two staged analysis considering plane strain conditions and linear elastic soil model. similar work was conducted by authors in [11] using finite element method. in both these studies the lateral response of single pile was investigated. the settlement behavior of pile and development of excess pore water pressure and consolidation settlement were not investigated. authors in [12] proposed an analytical method to investigate the capacity reduction and settlement increase of a nearby pile during excavation. it was reported that pile settlement due to excavation depends on the percentages of end bearing and shaft friction of the pile, the soil movement pattern, and the distribution of the maximum shaft friction with depth. however, shaft resistance in these methods is calculated on the assumption that horizontal stress acting on the piles does not change during excavation. this assumption may not be valid and the pile settlement may be underestimated using the preceding methods, leading to a non-conservative prediction. most of the previous studies focused on the lateral response of single pile foundation. the vertical response of floating pile group combined with working load adjacent to deep excavation in soft clay has not been studied. in this study, to investigate the settlement, tilting, load transfer and load redistribution of a elevated (2×2) pile group affected by nearby excavation, a three-dimensional coupledconsolidation finite element analysis (fea) was carried out in saturated silty clay. ii. three-dimensional coupled consolidation analysis it is well-known fact that the stress-strain relationship of soils is highly nonlinear even at very small strain. the stiffness of most soils decreases as strain increases and depends on the recent stress or strain history of the soil [13-14]. owing to nonlinear soil behavior, an excavation can cause reduction in the ground stiffness. therefore, it is vital to investigate the pile responses to adjacent excavation in silty clay. to obtain a satisfactory numerical model of the pile group responses to excavation-induced stress relief, the analysis needs to take account of the small strain non-linearity of soil. to gain new insights into pile group responses to a nearby multipropped excavation in saturated silty clay, this study conducts a 3d coupled consolidation numerical analysis. figure 1(a) shows the elevation view of the configuration of numerical simulation in which a multipropped excavation was carried out adjacent to a loaded elevated (2×2) pile group. the final depth of the excavation (he) was 10m. the embedded length (lp) and diameter (dp) of the piles were 18m and 08 m respectively. the heads of all four piles were rigidly embedded into a 4.5m × 4.5m ×1.0m (length×width×thickness) pile cap. the pile spacing was 3.2dp. the pile cap was elevated by 1m from the ground surface. the modeled pile represents a cylindrical reinforced concrete (grade 40, reinforcement ratio=1) with a bending moment capacity of 800knm. the clear distance between diaphragm wall and the front pile row was 3.0m (0.3he). the excavation was supported by 0.6m thick diaphragm wall. the ratio of wall penetration depth to excavation depth is typically 0.5-0.2 in engineering practice [15-16], and thus a value of 0.5 was adopted in this study. the retaining wall was supported by three levels of props, at 1.0, 4.0 and 7.0 m depth. the props were modeled as soft with axial rigidity of 81 × 103knm [15]. horizontal spacing of props was 10m. figure 1(b) illustrates the plan view of the configuration of the numerical simulation. the length of the excavation is 12m. due to symmetry, only half of the excavation was simulated. a monitoring section was selected at the transverse centerline of the excavation. in addition to this simulation, a pile load test (l) was conducted numerically in “greenfield” conditions (i.e., without excavation) to obtain the ultimate capacity of the pile in silty clay. based on this, the working load was then calculated with a factor of safety of 3.0. the obtained working load was applied to the pile in the analysis simulating excavation. ground water table working load (3.44 mn) silty clay prop 1 (1.0 m) prop 2 (4.0 m) prop 3 (7.0 m) p la n e o f sy m m et ry excavation level 1 (3.0 m) excavation level 2 (7.0 m) formation level (10.0 m) embedded length = 18 m diameter = 0.8 m diaphragm wall thickness = 0.6 m depth = 14.0 m 3.0 m (2×2) pile group (4.5m×4.5m×1m) pile cap (a) monitoring section 50m 20m p la ne o f sy m m et ry 0.6 m thick diaphragm wall prop prop 10m 6m 1.0 m thick pile cap (b) fig. 1. configuration of the numerical run (a) elevation, (b) plan view engineering, technology & applied science research vol. 8, no. 1, 2018, 2577-2584 2579 www.etasr.com soomro et al.: 3d numerical modeling of pile group responses to excavation-induced stress release ... iii. finite element mesh and boundary conditions figure 2 shows an elevation view of a finite element mesh used to analyze the excavation effects on the pile group. the size of the mesh for numerical runs is 50m×20m×40m. these dimensions were sufficiently large to minimize boundary effects in the numerical simulation as further increment of the finite element mesh dimensions did not lead to any change in the computed results. regarding the element size in the mesh, it is found that further halving the adopted mesh size only leads to a change of computed results of no more than 0.2%, suggesting the mesh is sufficiently fine. eight-noded hexahedral brick elements were used to model the soil, the pile and the diaphragm wall, while two-noded truss elements were adopted to model the props. roller and pin supports were applied to the vertical sides and the base of the mesh, respectively. therefore, movements normal to the vertical boundaries and in all directions of the base were restrained. the water table was assumed to be at ground surface. initially, the pore water pressure distribution was assumed to be hydrostatic. free drainage was allowed at the top boundary of the mesh. the excavation process was simulated by deactivating soil elements inside excavation zone. in the meantime, the truss elements representing the props were activated. fig. 2. three dimensional finite element mesh and boundary conditions iv. constitutive model and model parameters used in finite element analysis the basic hypoplastic model was developed to capture the non-linear behavior (upon monotonic loading at medium to large-strain levels) of granular materials [19-20]. the basic model consists of five parameters  r and ,,, ** cn  . the parameters n and * define the position and the slope of the isotropic normal compression line in the ln(1+e) versus lnp’ plane [21], where e is the void ratio and p’ is mean effective stress. the parameter * defines the slope of the isotropic unloading line in the same plane. φc is the critical state friction angle and the parameter r controls the large strain shear modulus. to account for the strain-dependency and pathdependency of the soil stiffness (at small strains), authors in [22] further improved the basic hypoplastic model by incorporating the concept of intergranular strain. the intergranular strain concept requires five additional parameters  rtr mmr and ,,,  : r controlling the size of the elastic range, βr and χ controlling the rate of stiffness degradation. the parameters mt and mr control the initial shear modulus upon 180° and 90° strain path reversal, respectively. in this study, all the model parameters for silty clay reported in [23] are adopted and summarized in table i. the coefficient of lateral earth pressure at rest, ko is estimated through (1) [24]:      sin0 sin1 ocrk (1) table i. silty clay model parameters adopted [23] description parameter effective angle of shearing resistance at critical state: ’ 33o parameter controlling the slope of the isotropic normal compression line in the ln(1 + e) versus lnp plane, * 0.103 parameter controlling the slope of the isotropic normal compression line in the ln(1 + e) versus lnp plane, * 0.015 parameter controlling the position of the isotropic normal compression line in the ln(1 +e) versus lnp plane, n 1.31 parameter controlling the shear stiffness at mediumto large strain levels, r 0.3 parameter controlling initial shear modulus upon 180 strain path reversal, mr 12 parameter controlling initial shear modulus upon 90 strain path reversal, mt 12 size of elastic range, r 2×10-5 parameter controlling the rate of degradation of the stiffness with strainr 0.09 parameter controlling degradation rate of stiffness with strain 0.7 initial void ratio, e 0.7 dry density (kn/m3) 1615 coefficient of permeability, k (m/s) 1×10-9 the concrete pile, the diaphragm wall and the props were assumed to be linear elastic with young's modulus of 35gpa and poisson's ratio of 0.25. the wall thickness was taken as 0.60m. the concrete unit weight was taken as 24kn/m3. the parameters for the piles and the diaphragm wall are summarized in table ii. table ii. concrete parameters adopted in finite element analysis description parameter young's modulus, e 35 gpa poisson's ratio,  0.3 density,  2400 kg/m3 v. numerical modeling procedure each numerical analysis is modeled according to the following steps: step 1: set up the initial boundary and initial stress conditions (i.e., static stress conditions with varying k0 with depth). step 2: activate the brick elements representing pile group (modeled as “wished-in-place”). engineering, technology & applied science research vol. 8, no. 1, 2018, 2577-2584 2580 www.etasr.com soomro et al.: 3d numerical modeling of pile group responses to excavation-induced stress release ... step 3: apply the working load (determined from numerical pile load test) on the pile. step 4: allow excess pore pressure, which generated in result of application of working load on the pile, to dissipate. step 5: activate the brick elements representing the diaphragm wall. step 6: staged multipropped excavation was simulated. after excavating to 3m depth, the first level of props was installed at 1m below ground surface. soil was then excavated to 7m below ground surface, followed by the installation of the second level of props at 4m depth. finally, excavation was extended to the target level of 10m depth with installation of the third level of props at 7m. vi. interpretation of computed results a. determination of working load for the pile group the study’s objective was to investigate a pile group (subjected to a working) load responses to an adjacent excavation. prior to the simulation of the excavation, it was necessary to determine the ultimate axial load carrying capacity of the pile group. the working load can then be obtained using a factor of safety (fos) of 3.0. therefore, a numerical pile load test was carried out on a different finite element mesh to obtain the load settlement relationship and the capacity of the pile group without excavation. the load applied on the pile group was gradually increased to 11mn over a period of 24h. the resulting pile load-displacement curve for the simulated pile group is shown in figure 3. the ultimate axial load capacity was determined based on a displacement-based failure criterion proposed in [25]. this failure criterion is expressed as follows: ,max 1 0.045 2 h p ph p p p p l d a e    (2) where δph,max is the maximum pile head movement which defines the ultimate load, ph is the pile head load, lp is the pile length, ep is the pile shaft elastic modulus, ap is the crosssectional area of the pile, and dp is the pile diameter. based on the failure criterion, the ultimate bearing capacity of 10.34mn was calculated. with a factor of safety (fos) of 3.0, the working load was determined to be 3.44mn. owing to the applied working load, the pile group settled by 0.85%dp (figure 3). b. progressive pile settlement and apparent loss of the pile capacity during excavation figure 4 shows the incremental settlement (sp) of the pile with different excavation stages. construction stages of the excavation are indicated by the depth (i.e., h) from the ground surface. sp and h are normalized by the pile diameter (dp) and the final excavation depth (he) respectively. the measured induced single pile settlement due to excavation in centrifuge modeling reported in [9] and computed excavation-induced settlement of a single pile reported in [27] are also shown in the figure for comparison. the centrifuge test was carried out to investigate the effects of a multipropped deep excavation (final depth of excavation=8m in prototype) in-flight on the behavior of single pile (diameter of the pile=1.25 m in prototype) in dry toyoura sand (i.e. dr=70%). fig. 3. computed load settlement curve from the pile group load test without excavation fig. 4. normalised pile cap settlement during excavation the embedded depth of the pile and clear distance between the pile and model wall is 20m and 3m (in prototype) respectively. the configuration of their numerical analysis (i.e., excavation depth, pile diameter and length and clear distance between pile and diaphragm wall) are the same as those of the numerical model in this study. it can be observed from the figure that induced settlement with increasing excavation depth was approximately bilinear. during the first two excavation stages (i.e., h/he=0.3 and h/he=0.7), the pile settled almost linearly. after that, the pile settlement occurred at an increased rate during last excavation stage (h/he=1.0). this may be attributed to reduction of shaft resistance. due to excavation induced stress release, the pile had to settle substantially to further mobilise end-bearing. similar settlement characteristics of a single pile due to excavation observed from the centrifuge test reported in [9] and the computed results in [27]. however, induced settlement of the single pile was larger than that of the pile group after excavation. the total settlement of the pile (including settlement due to working load and excavation) was engineering, technology & applied science research vol. 8, no. 1, 2018, 2577-2584 2581 www.etasr.com soomro et al.: 3d numerical modeling of pile group responses to excavation-induced stress release ... 19.5mm (i.e., 2.5% pile diameter). this value satisfies a reliability-based serviceability criterion (i.e. 56mm), which was developed based on 95 composite (i.e., reinforced concrete and steel) buildings subjected to settlement [26]. this conclusion may not be applicable to scenarios in which the ground conditions or excavation depth are different from those adopted in this study. c. reduction of factor of safety after excavation the pile capacity is often determined using displacement based criteria. the induced settlement can be regarded (conveniently but approximately) as an additional load on the pile cap. to investigate the reduction of an equivalent factor of safety (fos) of the loaded pile group due to tunneling, an additional pile cap settlement of 12.75mm (1.6% pile diameter) after excavation is considered as the cause of the reduction in pile capacity when a displacement-controlled failure load acceptance criterion as given in (1) [25] is used. due to the initial applied working load (pile cap displaced vertically by 6.8mm or 0.85 pile diameter) and the excavation effects, the pile group is settled by 19.5mm in total. it is possible to consider that the pile cap is subjected to an equivalent axial load of 7.3mn including the excavation effects, resulting in a 19.5mm pile head settlement (see the pile-load displacement curve in figure 3). as the applied working load of the pile increases from the original of 3.44mn to an equivalent applied working load of 7.3mn, this means that an equivalent fos of the pile drops from 3.0 to 1.4 due to the excavation effect. however, it should be pointed out that the calculated reduction of the equivalent fos does not really mean that the ultimate load capacity is physically reduced due to the excavation. the reduction of the equivalent fos just simply means that designers should be reminded that the serviceability limit state of the pile group can be violated as a result of additional excavation-induced pile settlement. d. transverse tilting of pile cap during excavation figure 5 illustrates computed transverse tilting of the pile cap during excavation. each tilting is determined as a ratio of differential settlements measured at two edges of the pile cap to the distance between them. a positive value means the pile cap tilts towards the first tunnel and vice versa. it can be seen from the figure that during the excavation, the transverse titling of the pile group increases non-linearly with tunneling stages. the rate of the tilting increases as during entire process of the excavation. this is because the front pile row experienced larger stress release that that of the rear pile row. the computed tilting of the pile cap during the first, second and final excavation stage (i.e. h/he equal to 0.3, 0.7 and 1.0) is 0.02%, 0.07% and 0.14% respectively. all the values do not exceed the allowable tilting limit (0.2%) suggested by eurocode 7 for typical commercial and residential buildings. owing to same stress release along longitudinal direction of the excavation, no longitudinal tilting of pile cap was observed. e. computed load redistributions among piles in the group in order to study the load transfer mechanism during excavation, figure 6 shows the changes in load at the pile head within the 2×2 pile group at various excavation stages. in the figure, the change in head load due to tunneling (p) is normalized by the computed head load of each pile before excavation (pi). before excavation, the applied working load is equally shared by each pile. it can be observed from the figure that the head loads carried by the front row piles increased linearly with excavation stages. it was expected that head loads carried by the front row pile would decrease due to excavationinduced stress release as the pile cap tilted towards excavation. on the contrary, the head loads of piles p1 and p2 decreased due to substantial drag load resulting from excavation-induced soil movement (discussed in section f). to support the constant working load acting on the pile cap, the head load of pile p2 as well as that of piles p4 decreased as a result of load redistribution from piles p1 and p3. owing to load redistribution among piles, the front row piles experienced the most significant increase of 32% in head load. 0.00 0.05 0.10 0.15 0.20 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 t il ti n g : % normalised excavation depth (h/he) pile group pile group ground surface forma tion level wall p1 p2 p3 fig. 5. computed transverse tilting of the pile cap during excavation f. changes in axial load distribution since load redistribution in the front row of piles (piles p1 and p3) and rear row of piles (piles p2 and pile p4) is the same, only one pile is selected from each row to discuss axial load distribution along the pile length. figure 7 shows the axial force distribution along the front pile (p1) and rear pile (p2) with normalized depth (z/lp) below the ground surface after completion of the excavation. the axial load distribution before excavation (after applying the working load) is also included in the figure as a reference. the applied working load on pile cap including weight of pile cap 4,000kn, was shared equally by each pile before excavation. the load taken by each pile is 1000kn. before excavation, the pile carried approximately 61% of the working load (i.e., 607kn) with its shaft resistance and the remainder with its end-bearing resistance. the load distribution along the pile shaft started to alter when the excavation commenced. it can be seen from the figure that the computed load increased along the entire pile length of p1 after completion of the excavation. on the other hand, the load decreased along the upper portion (z/lp≥0.3) of p2 and increased along the remaining length of the pile at the end of the excavation. the maximum increment in the axial force 94% and 33% of that engineering, technology & applied science research vol. 8, no. 1, 2018, 2577-2584 2582 www.etasr.com soomro et al.: 3d numerical modeling of pile group responses to excavation-induced stress release ... working load was computed in p1 at z/lp=0.43 and in p2 at z/lp=0.51 respectively. by inspecting the axial load distribution it is observed that along the upper portion of both piles (z/lp≥0.47), negative skin friction (nsf) is mobilized resulting from soil movement due to excavation induced-stress release. this suggests that this portion of the pile is subjected to “dragload” by the surrounding soil. consequently, the load transferred to the lower portion of the pile as well as load redistribution occurred within pile group. to maintain equilibrium, the pile had to settle (see figure 4) to further mobilize the end-bearing and shaft resistance along the lower portion of the piles (z/lp>0.47). the percentage increment of the end-bearing of p1 and p2 were computed as 74% and 37% respectively. -40 -30 -20 -10 0 10 20 30 40 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 n o rm al is ed c h an ge o f p il e h ea d lo ad ( δ p /p i): % normalised excavation depth (h/he) pile p1 pile p2 pile p3 pile p4 e x ca v at io n pile p1 pile p2 pile p3 pile p4 fig. 6. computed load-redistributions among piles (p1, p2, p3 and p4) in the group 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 300 500 700 900 1100 1300 1500 1700 1900 n o rm al is ed p il e d ep th ( z /l p ) axial force: kn at working load pile p1 pile p2 e x ca v at io n pile p1 pile p2 fig. 7. computed axial load distribution along the length of piles p1 and p2 due to excavation g. mobilized shaft resistance during excavation to further understand the load transfer mechanism, the mobilized shaft resistance in pile p1 and p2 after the application of the working load (i.e. before the excavation) and during the excavation is shown in figure 8. the depth below the ground surface (z) is normalized by the pile length (lp). the computed average mobilized unit shaft resistance f(z) at various depths was calculated based on the following equation: ( ) ( ) zf f z s    (3) where δf is the difference between the computed axial loads at two consecutive depths, δz is the vertical distance between the two consecutive depths, and s is the pile perimeter. as expected, after working load application, the positive shaft resistance (i.e. soil supporting the pile) is mobilized along the pile entire length. the mobilized positive shaft resistance increased along pile depth with maximum shaft resistance of 26kpa near the pile toe. on the completion of the excavation, the mobilized shaft resistance at the upper portion of the both piles (z/lp<0.5) decreased to negative and increased below formation level (0.5<z/lp<1.0). this caused negative skin friction (nsf) mobilization at the upper part of the pile shafts (z/lp<0.5) due to stress release and soil movement due to excavation. this implies that this portion of the pile group is “dragged” down by the surrounding soil, which settles due to excavation. to maintain vertical equilibrium of the pile, the soil surrounding the upper part of the pile resists from settling, by mobilizing psf at the soil–pile interface. the neutral plane, where the zero shaft resistance is mobilized, is located at depth z/lp=0.5 (above formation level). this location is consistent with the depth where the maximum axial load was induced (see figure 7). consequently the load was transferred to the lower part of the piles. to support the applied working load and “dragload” resulting from nsf, the pile group settled substantially to mobilize its end-bearing resistance (see figure 7). h. computed change in vertical stress below the pile group to substantiate the previous section discussion, figure 9 shows the computed change in vertical effective stress ('v) in the soil immediately below the toe of the pile during various excavation stages (h/he=0.3, 0.7 and 1.0). after first excavation stage the vertical effective stress ('v) under both piles p1 and p2 increased. this suggests a further mobilization of the end-bearing resistance of the pile group to compensate for the reduction in mobilized shaft resistance. the last two excavation stages led to further increase in 'v underneath both piles p1 and p2. after the excavation, ('v) underneath both piles p1 and p2 increased by 64 and 37kpa respectively. the non-uniform change (140kpa) in vertical effective stress caused differential settlement between the two piles and hence tilting of the pile group (see figure 5). engineering, technology & applied science research vol. 8, no. 1, 2018, 2577-2584 2583 www.etasr.com soomro et al.: 3d numerical modeling of pile group responses to excavation-induced stress release ... 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -40 -30 -20 -10 0 10 20 30 40 50 60 70 n o rm al is ed p il e d ep th (z /l p ) mobilised shaft resistance: kpa at working load (before excavation) pile p1 pile p2 formation level fig. 8. mobilized shaft resistance along the pile length at various stages of excavation 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 c h an ge in v er ti ca l e ff ec ti v e st re ss : k p a normalised distance (x/d) h/he = 0.3 h/he = 0.7 h/he = 1.0 p1 p2 a a p1 p2 fig. 9. computed change in vertical effective stress below the pile group during excavation vii. summary and conclusions this study reports a 3d coupled consolidation numerical analysis (using a hypoplastic model, which considers straindependent and path-dependent soil stiffness) investigating pile group responses to an adjacent excavation in saturated silty clay. based on the ground conditions and geometries, the following conclusions can be drawn:  owing to the degradation of the stiffness of the clay surrounding the piles in the group and the reduction of shaft resistance due to excavation induced stress release, a nonlinear pile group settlement was induced.  compared to the sp of the pile group, induced settlement of the single pile is larger with similar settlement characteristics.  based on a displacement-based failure load criterion proposed in [25], the factor of safety for the pile group can be regarded as decreasing from 3.0 to 1.4 due to the additional pile group settlement.  owing to non-uniform stress release, pile group tilted towards the excavation by 0.14%.  due to excavation-induced stress release and dragload, head load of rear piles away from the excavation was reduced and transferred to front piles. this load transfer can increase the axial force in front piles by 94%.  the non-uniform change (140kpa) in vertical effective stress caused differential settlement between the two pile rows and hence tilting of the pile group. references [1] r. j. finno, s. a. lawrence, n. f. allawh, i. s. harahap, “analysis of performance of pile groups adjacent to deep excavation”, journal of geotechnical and geoenvironmental engineering, vol. 117, no. 6, pp. 934-955, 1991 [2] a. goh, k. wong, c. teh, d. wen, “pile response adjacent to braced excavation”, journal of geotechnical and geoenvironmental engineering, vol. 129, no. 4, pp. 383–386, 2003 [3] s. w. jacobsz, j. r. standing, r. j. mair, t. hagiwara, t. sugiyama, “centrifuge modelling of tunnelling near driven piles”, soils and foundations, vol. 44, no. 1, pp. 49-56, 2004 [4] s. y. lam, ground movements due to excavation in clay:physical and analytical models, phd thesis, university of cambridge, 2010 [5] d. e. ong, c. e. leung, y. k. chow, “pile behavior due to excavationinduced soil movement in 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modeling of pile group responses to excavation-induced stress release ... conference on soil mechanics and foundation engineering, vol.3, pp. 915-956, 1991 [15] b. c. b. hsiung, “a case study on the behaviour of a deep excavation in sand”, computer and geotechnics, vol. 36, no. 4, pp. 665–675, 2009 [16] c. w. w. ng, y. hong, g. liu, t. liu, “ground deformations and soilstructure interaction of a multi-propped excavation in shanghai soft clays”, geotechnique, vol. 62, no. 10, pp. 907-921, 2012 [17] n. loganathan, h. g. poulos, d. p. stewart, “centrifuge model testing of tunnelling-induced ground and pile deformations”, geotechnique, vol. 50, no. 3, pp. 283-294, 2000 [18] a. m. marshall, r. j. mair, “tunneling beneath driven or jacked endbearing piles in sand”, canadian geotechnical journal, vol. 48, no.12, pp. 1757-1771, 2011 [19] d. masin, “a hypoplastic constitutive model for clays”, international journal for numerical and analytical methods in geomechanics, vol. 29, no. 4, pp. 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m. zhang, a. m. y. ng, “probabilistic limiting tolerable displacements for serviceability limit state design of foundations”, geotechnique, vol. 55, no. 2, pp. 151-161, 2005 [27] m. a. soomro, k. f. memon, m. a. soomro, a. memon, m. a. keerio, “single pile settlement and load transfer mechanism due to excavation in silty clay”, engineering, technology and applied science research, vol. 8, no. 1, pp. 2485-2492, 2018 microsoft word etasr_v12_n4_pp8884-8890 engineering, technology & applied science research vol. 12, no. 4, 2022, 8884-8890 8884 www.etasr.com abbas & al‐zuhairi: flexural strengthening of prestressed girders with partially damaged strands … flexural strengthening of prestressed girders with partially damaged strands using enhancement of carbon fiber laminates by end sheet anchorages hayder qays abbas department of civil engineering university of baghdad baghdad iraq haider_q@yahoo.ocm alaa hussein al‐zuhairi department of civil engineering university of baghdad baghdad iraq alaalwn@coeng.uobaghdad.edu.iq received: 23 april 2022 | revised: 13 may 2022 | accepted: 21 may 2022 abstract-this paper examines the impact of flexural strengthening on the percentage of damaged strands in internally unbonded tendons in partially prestressed concrete beams (0, 14.28%, and 28.57%) and the recovering conditions using cfrp composite longitudinal laminates at the soffit, and end anchorage u-wrap sheets to restore the original flexural capacity and mitigate the delamination of the soffit of longitudinal carbon fiber reinforced polymer (cfrp) laminates. the composition of the laminates and anchors affected the stress of the cfrp, the failure mode, and thus the behavior of the beam. the experimental results revealed that the usage of cfrp laminates has a considerable impact on strand strain, particularly when anchors are employed. the eb-cfrp laminates increased the flexural capacity by approximately 13%, which corresponds to strand damage of 14.28%, while flexural capacity increased by 9.3%, strand damage increased by 28.57% for members strengthened with laminates only, and around 21.58% and 16.85% for members reinforced with laminates and end anchorings. quasi-experimental equations have been proposed to estimate the actual stress of untethered tendons considering the effect of cfrp laminates and final fixation winding. keywords-cfrp laminates; debonding; post-tensioned girder; strand damage; unbonded strand i. introduction recent destructive failures of pre-stressed (ps) concrete bridges have prompted a reassessment of the condition of several ps members [1], giving rise to new postings and, in some cases, emergency closure. some of these failures are the result of terrorist attacks involving explosives [2], which damage ps bridge members or tendons [3]. the losing strands on the concrete member have a great effect on the design ps force which reflects a reduction of the nominal capacity and lack of serviceability [4]. one of the strengthening findings that will be investigated in this paper is the evaluation of the use of cfrp laminates with and without end anchorages for strengthening enhancement. cfrps are increasingly being used to strengthen and repair reinforced concrete (rc) structures. the advantages of using fiber-reinforced polymer (frp) include the application's ease to use, the high ultimate strength, and corrosion resistance. the experimental results show that due to premature cfrp debonding from the concrete substrate, the maximum capacity of ps externally reinforced beams with cfrp sheets is not always completely realized. external frp composites have emerged as a viable alternative to strengthening methods. frp composites have been used for ps girder structures. it is not easy to determine strain and stress in unbonded tendons at ultimate flexural capacity due to the tendons' slip relatively to the surrounding concrete [5]. in practice, it is preferable to prevent the brittle failure mode by either eliminating it or shifting it to a more ductile mode. anchoring the laminates to the concrete substrate with metallic or cfrp anchors may be a practical way to accomplish this [4]. cfrp u-wrapped anchors or other mechanical anchor systems have demonstrated high effectiveness in delaying the delamination process and increasing the strengthening efficiency. this study, along with [15], is a part of the ongoing investigating research regarding the efficiency of strengthening techniques that are conducted at baghdad university (civil engineering lab). the current paper focuses on the strengthening techniques using externally bonded cfrps. ii. material properties and methodology a. design of the tested member all tests were conducted in the laboratory of the college faculty of baghdad university under 4 points of loading as shown in figures 1 and 4. seven girders, as illustrated in table ii, have been used in this paper, spanning 3000mm and resting on simply supported ends of 2800mm apart. the specimens were reinforced with 2φ16mm at the bottom and 2φ10mm at the top whereas φ10mm bars were used for stirrups. two unbonded strands were used inside the 22.5mm pvc duct with end grips, and the strand extended by 0.45m from each side. cfrp laminates (bf=50mm and tf=1.2mm) were attached to the soffit to strengthen the specimen in addition to two cfrp sheets at the end for anchorage purposes with tf =0.167mm, set up on u wrapping shape as shown in figure 2. corresponding author: hayder q. abbas engineering, technology & applied science research vol. 12, no. 4, 2022, 8884-8890 8885 www.etasr.com abbas & al‐zuhairi: flexural strengthening of prestressed girders with partially damaged strands … fig. 1. specimen and strand damage details. fig. 2. strengthening types considered in this study. b. properties of the tested beams the design of the concrete mixture consisted of: portland cement c45 with densities of 412kg/m 3 for cement, 1030kg/m 3 for aggregates, 548kg/m 3 for coarse sand, and 245kg/m 3 for fine sand (f’c=44.60n/mm 2 and ft=5.80n/mm 2 ), while 5.46lt/m 3 of superplasticizer were used. the yield, ultimate, strain, and area of steel bars are 518.20n/mm 2 , 658.970n/mm 2 , 12.20%, and 77.21mm 2 respectively for d10 bars and 577.30n/mm 2 , 710.74n/mm 2 , 13.40%, and 199.10mm 2 for d16 bars (es=200000mn/m 2 ). nominal area, ultimate strength, yield strength, and ultimate strain were 98.7mm 2 , 1860.00mn/m 2 , 1725.00mn/m 2 , and 5.00% respectively for the 7 wires of grade 270 unbonded tendons (es=197.5gpa). the manufacturer provided the carbon fiber fabrics' mechanical properties in addition to the resin, in which the nominal thickness, tensile strength, and ultimate elongation were 1.2mm, 3100mn/m 2 , and 0.02 respectively for laminates (ef=170gpa), and 0.167mm, 3500mn/m 2 , 1.59% for unidirectional sheets (ef=220gpa). the first letter b in the specimens' designation in table ii stands for beam, and the numbers 1 and 2 after the second letter designate the 14.25% and 28.57% strands damage groups, respectively. the letter r corresponds to individual group references, s to cfrp laminate strengthening, and w to laminate and end anchorage wrapping strengthening. table i. properties and locations of strain gauges usage type ω adhesive type qty, location steel flab–6–11 118.5±0.5 cn 2 @ tension bars strand yeflab-2-3 119.5±0.5 cn 3 concrete pl-60-11 120±0.5 cn-e 2 @ 5cm below the top cfrp bflab-5-3 119.5±0.5 cn 2 c. recording gauges and setup all members were tested using a unidirectional electrical resistance strain gauge attached at the middle span to measure strain in the strand, frp, concrete, and steel (table i). d. experimental testing the steel cages were instrumented with strain gages of electric type before being placed in wood forms for concrete casting, using ready-mixed concrete. in addition to the dial gauge for measuring camber, the strain gauge wires were linked to a data logger to capture the strain of the strands during the pre-stressing process, as shown in figure 3. fig. 3. post-tensioning process. fig. 4. test setup. table ii. tested girder details group girder id d (%) aps (mm 2 ) laminate (lf) sheets (sf) ρρρρp ρρρρs tlf blf llf tsf bsf lsf (mm) (%) ref. b0 0 197.40 0.490 0.810 b1 b1r 14.28 169.20 0.385 b1s 1.2 50 2.7 b1sw 1.2 50 2.7 0.167 250 76 b2 b2r 28.57 141.00 0.320 b2s 1.2 50 2.7 b2sw 1.2 50 2.7 0.167 250 76 two 1cm thick end steel plates were used at the ends of each specimen with the incision at one of the endplates to protect and guide the strain gauge’s wires during the prestressing process. τhe 2 endplates were punched with 2.2cm diameter ps ducting. for anchorage at the unbonded strands, 2 pieces of split-wedge anchor grips (barrel-type) were used. the grips were attached to the ends of the strands, which were then marked using a permanent marker to determine the pre-strain level that was applied in each strand. (∆l=15.5cm as per the member design required). the first strand was pulled out to the requisite pre-stressing value in two stages: initial for starching the strand and final to the preferred pre-stressing value. then the piston was released. the procedure was then repeated with the second strand, with pressure gauge readings from the hydraulic jack used in the post-tensioning procedure [6]. two engineering, technology & applied science research vol. 12, no. 4, 2022, 8884-8890 8886 www.etasr.com abbas & al‐zuhairi: flexural strengthening of prestressed girders with partially damaged strands … dial gauges were attached to each end of the strand to find out the slipping of the strand slip during the loading process. four lvdts were used to measure the deflection of the 2 specimens near the support, one under the point load, and the other under the quarter point. all lvdts were set up to zero strain at the start of testing as shown in figure 4. to progressively raise the load, a 50-ton hydraulic jack was installed to a load cell with a maximum capacity of 50ton. increments of 15kn were added until the cracking load was reached. the load was then applied in 30kn increments until failure occurred. each beam took approximately 2 to 3 hours to complete the test. the load cell was used to monitor the applied load from the frame of the test and to collect the reading data. the applied cracks were signified for each load step after the appearance of the first crack. the fracture pattern on the 2 sides of the cross-section was captured on camera after the test. the modes and ultimate loads of failure were reported. during testing, the first crack and crack propagation were monitored as well as the load deflection. iii. results the test girders' performance was measured in terms of maximum load-bearing capability. all the reference girders failed in the compression zone due to flexure tensile steel reinforcing yielding, whereas the strengthened beams failed by laminate debonding followed by sudden compression and tension of concrete and steel bars (figure 6). the first flexural crack appeared in the midspan of sub-reference girders pc1r, and pc2r, with respective cracking loads approximately 94%, and 85% of the reference girder’s cracking load. the cracking propagation is typically shown in figure 5 at the end of the test members in the various test series. fig. 5. representative beam crack patterns. when the specimens were subjected to the externally applied load, the cracking patterns were quite similar and typical of flexural members. during the initial cyclic loading between pmin and pmax, the first flexural cracks appeared within the constant moment zone. table iiii shows the cracking loads pcr for the various members before frp application. as the applied load increased, the number of cracks increased as they began to form within the shear zone. the cracks tended to separate as the load increased and additional flexural cracks were formed. table iii contains a summary of the members' modes of failure. unbonded pc specimens failed due to concrete crushing, cfrp ultimate strain (rupture), cfrp debonding, or combinations of these modes. the propagation of interface cracks in the concrete near the cfrp in a horizontal direction along with the embedded tension reinforcement until connecting with the vertical flexural cracks caused peeling off of the concrete cover, indicating frp debonding failure. the control girder failed in a more brittle mode than the strengthened girders, which was evidenced by faster crack propagation and fewer cracks but with wider widths, whereas the control girder showed a more brittle mode [7]. that is explained by the propagation of fewer and faster cracks in wide widths. a large number of cracks with smaller widths occurred for girders strengthen by carbon fibers. fig. 6. representative beam failure modes. a. flexural capacity and load deflection the tested members were investigated at 3 different load levels: cracking loads, post cracking elastic stage, and peak loads as shown in figure 7. the cfrp laminates and tendons had almost no influence on the member behavior when the applied load did not reach the cracking load. the findings demonstrate that group 1 and 2 exhibited more strength than the undamaged member. however, the strengthened members with laminates exhibited an increase in flexural capacity of 139% for groups 1 and 2 and 21-16% for laminates with anchors when compared to the undamaged girders of the same group as illustrated in figure 7, indicating the effect of the end anchorage on strength and ductility. the stiffness of the reference girders decreases slightly and the strengthened girders did not significantly differ from the damaged reference girders of the same group. when the applied load exceeded the cracking load, the damaged members exhibited a relatively high rate of stiffness deterioration [8] due to the absence of a portion of the pre-stressing force, which increases the development rate of crack and displacement. likewise, the flexural-strengthening cfrp eb of the laminates exhibited their ability to postpone the fracture formation and deterioration of the stiffness of the strengthened girders [9], and the girders strengthened with laminates and anchors were observed to be superior to the girders strengthened with laminates only. the deflection is at the same value as the applied load which is equal to 0.79 of the ultimate load. the serviceability limitation for deflection (span over 250) is considered and the corresponding value is used in this paper, as b b1sw engineering, technology & applied science research vol. 12, no. 4, 2022, 8884-8890 8887 www.etasr.com abbas & al‐zuhairi: flexural strengthening of prestressed girders with partially damaged strands … per the result of control, the deflection at the serviceability limit is 1.12cm and this value is referred to as the permissible load which is about 79% of the ultimate load. the displacement of the strengthened girders was slightly reduced by 9–18% for b1s and b2s whereas almost the same amount (11-19%) of reduction occurred for b1sw and b2sw. it should be noted that in each case, the member with the end anchorage had a smaller drop in the value of the load, higher strength, and much more stiffness [10]. the cfrp girders strengthened with cfrp laminates and u-wrapping of cfrp sheets demonstrated increased deflection at the maximum load due to the absence of a relatively gradually load drop after the initiation of partial debonding. the ability of the members with an anchor to preserve their ductile response was exhibited. the ultimate displacement increased significantly when the specimen strengthened with laminates only and laminates with end anchorage, and the increment reached 18.16% and 11.39% respectively for b1sw and b2sw in comparison with b1s and b2s. table iii. summary of specimen testing and results girder id cracking load (kn) cracking load concerning control (%) ultimate load (kn) mid-span deflection at ultimate load (mm) pcr/pult (%) change in flexural strength (%) failure mode b0-control 55.03 166.240 26.9 33.10 sf, cc b1r 52.05 94.5 157.250 25.5 33.10 5.410 r sf, cc b1s 62.79 14.06 187.990 24.1 33.40 13.080 i sf, cc-dl b1sw 66.78 25.9 202.120 28.5 33.00 21.580 i sf, cc-cd b2r 47.00 85.38 148.710 29.9 31.60 10.540 r sf, cc b2s 58.37 6.09 182.420 23.8 32.00 9.730 i sf, cc-dl b2sw 62.16 21.21 194.250 26.5 32.00 16.850 i sf, cc-cd sf, steel failure at tension zone, cc crushing of concrete, dl, delamination of cfrp laminate. cd covers delamination, a negative sign is for reduction, and a positive sign is for increasing. r is for reduction, and i is for increase fig. 7. load deflection curves. b. applied load and strain for the cfrp laminates the cracks in cfrp laminates before the cracking load are minimal and nearly equal (figure 6). after the load reaches the cracking load, the strain clearly increases, and after the bonded steel reinforcement yields, the strain increment rate increases significantly. the increased rates of strain in the cfrp laminates, with and without the end anchors, were almost similar but the maximum strain of the strain increases in cfrp laminates end by anchors was much higher. at the serviceability load limit, the rise in a strain of strengthened members b1s and b2s was 0.265% and 0.346%, in comparison with the 13.25% and 17.3% of the ultimate strain of laminate capacity (εffu =2%) with no significant change to the strengthened specimens with laminates and anchorage sheets, b1sw and b2sw. the strain increase at the ultimate load was 0.830% and 0.90% corresponding to 41.5% and 45.1% of the ultimate strain of the fiber capacity of b1s and b2s. the b1sw and b2sw specimens achieved more strain at the ultimate load, which is about 1.0235% and 1.033% corresponding to the 51% of the laminate strain capacity. furthermore, the use of frp laminates with end u-wrapping anchorage sheets had a significant impact on the compressive concrete strain. the cfrp laminates, as previously mentioned, were able to stop the development of cracks in their path. c. applied load and effect on the strands strain because of the minor strain increases, the strand did not contribute to flexural strength before the first crack. the increase in the strand strain was calculated by subtracting the post-tensioning initial strain from the actual strain (figure 8). during this loading stage, the strand exhibited the same behavior in all the tested members. the strain increases in the strand for the references groups 1 and 2 were greater than the control girder's, whereas the strand strain increases in the members strengthened with laminates was less than in the same group members without strengthening. at the serviceability load limits, the increase in the strand strain for b1r and b2r was 7500με and 89501με, representing an increase of 8.5% and 29.5% from the control member. similarly, the strain increases in the strands of the strengthened girders b1s and b2s were 6750με and 7620με, with a reduction of 14.670% and 14.860%. the references' strand strain increments were much smaller in the loading stage after the load in the serviceability manner in the strengthened members b1s and b2s at the same loading level. the lessening of the tendon strain increases in the member strengthened with end anchors was 14.67% and 17.88% for b1sw and b2sw girders. the above results prove that the cfrp strengthened with laminates, including the end u-wrapped anchors, have a great influence on the behavior of the strands. as previously mentioned, the cfrp laminates were able to delay the cracks, prevent their development, and slow down the degradation of the member stiffness. engineering, technology & applied science research vol. 12, no. 4, 2022, 8884-8890 8888 www.etasr.com abbas & al‐zuhairi: flexural strengthening of prestressed girders with partially damaged strands … fig. 8. cfrp and strands load-strain. iv. evaluating the nominal moment capacity of the member a. the increased strain in the strands determining the increase in a strain of unbonded strands is a critical case in estimating the flexural strength of unbonded post-tension members strengthened with cfrp laminates. regrettably, the design guidelines, such as [11] have only suggested one approach to evaluate the increase in the strain of bonded post-tendons and pre-tension members strengthened with eb-cfrp sheets, whereas the correlating approaches for unbonded strands in members strengthened with cfrp laminates were not included. additionally, the result of the experimental work exhibited that cfrp laminates significantly influence the unbonded tendons' behavior [5]. the increase in the strain of the strand of the unbonded post-tension member strengthened with cfrp was evaluated using the equations for unbonded tendons in normal reinforced concrete members, as below [12]: for members without end cfrp u-wrapped sheet anchors: ∆���,��� �� ���� �� � � �1 � 100 �� �� ��� �� ���� ! ".$% (1) for members with end cfrp u-wrapped sheet anchors: ∆���,��� �� ���� �� � � �1 � 100 �& �& �&' �� �� �&((� ).*$ (2) the overall strain of the unbonded strands ∆���,��� is calculated as: ���,��� ��+ � ∆���,��� (3) where εfe is the initial strain of a strand not including strain losses = fp/ (ep ap), fp (n) is the actual tensile force in a strand, ap (mm 2 ) and ep (mpa) are the cross-sectional area and elasticity modulus of a strand respectively, ∆���,��� is the increase in a strain of strands, ψ is "the length of the plastic zone divided by the height of the compressive concrete zone": ψ = 10.50 [13] for un-cracked, simply supported unbonded post-tensioned members, reinforced with cfrp laminates, and ψ = 9.80 [14] for pre-cracked unbonded post-tensioned members reinforced by eb-cfrp, � is the maximum strain at the concrete compression fiber [11], dp, (mm) is the distance between the compressive concrete fiber's furthest point and the centroid of the strands' cross-sectional area, c (mm) represents the compression zone height [6], l0 (mm) represents the effective span of the member, and εfe represents the actual strain in cfrp laminates at the ultimate applied load. b. evaluation of the proposed formula the suggested equations (2)–(4) were applied for the estimation of flexural strength of the 23 unbonded post tensioned members reinforced with cfrp laminates including the 7 simply supported members reinforced with eb-cfrp laminates investigated in this manuscript and the 16 slabs and beams of [7]. the theoretical (predicted) flexural strength, mu,pred, was calculated as per [11] considering 1.0 as the factor of strength reduction, as below: • step # 1: estimation of the compression concrete zone depth. the depth of the neutral axis, c (mm), is initially assumed as depth/10 [11]. • step # 2: evaluate the strain in cfrp laminates, concrete, and strands. the cfrp laminate strain, �,+ , for failure detected by concrete crushing is: �,+ � ���� � . �/0 1 �,� (4) where df is the effective cfrp laminate depth, εcu is the concrete’s ultimate compressive strength which is equal to 0.003, and �/0 represents the initial strain in the substrate: ε34 ����� �� �1 � + 56 78 � � 9:;56 <��� (5) where fp is the initial prestressing force (n) after excluding the losses, e (mm) represents the prestressing force's eccentricity engineering, technology & applied science research vol. 12, no. 4, 2022, 8884-8890 8889 www.etasr.com abbas & al‐zuhairi: flexural strengthening of prestressed girders with partially damaged strands … concerning the concrete cross-centroid section, yb (mm) represents the distance from the gross-centroidal section (ignoring steel rebars) to the farthest bottom fiber, r (mm) represents the radius gyration of the member section = (ic/ac) 0.5 , ic (mm 4 ) represents the moment of inertia of concrete cross concerning the neutral axis, mdl (n.mm) is the applied dead load’s moment, and εfd is the strain’s debonding, defined by: �,� 0.41 ∗ ? ,� @ a��b� 1 0.9�,, (6) where fc′ is the concrete strength, εffu, tf, and ef are the ultimate strain, thickness, and elasticity modulus of cfrp respectively, and n represents the cfrp layer’s numbers. the strain in cfrp laminate, εfe, for failure detected by the rupture of prestressing strands is: �,+ d��. ��0 e ���� � . �/0 1 �,� (7) where εpu is the strand rupture strain which is equal to 0.05 and εpi is the strand initial strain, which can be estimated as: ��0 ���� �� � �� �� �� �1 � + 8 78 � (8) • step # 3: estimation of the steel rebars strain, εs: �� d�,+ � ��0 e � �� ��� ! (9) • step # 4: the depth of c must be recalculated, using the summation of forces equal to zero. f ��,�gh�g,gh��,��ij,�@kj/ (10) where ffe (mpa) is the cfrp laminate stress = ef × εfe, fps (mpa) is the strand’s stress = ep × εps,cfrp ≤ fpy, and fs (mpa) is the tensile rebars’ stress = es × εs ≤ fy. • step # 5: checking the c for the depth of the compressive concrete zone. now, when the assumed value of c (cassumed) and the calculated through the above equations (ccalculated) meet the presented criterion of convergence in (11), the appropriate value of c is obtained. if not, another cassumed value is calculated, and the process is iterated starting at the second step until convergence is achieved. criterion of convergence | wgg � �wx| wgg 1 0.1% (11) • step # 6: evaluating the flexural strength of eb-cfrp strengthened member. the flexural strength of the eb-cfrp strengthened unbonded prestressed concrete member, mu,pred can be calculated as: z-,�7+� [�\�� �]� . kj ^ � � [, \,+ �], . kj ^ � � [� \� �] . kj ^ � � [�_ \�_ � kj ^ . ]_� (12) fig. 9. flexural capacity predictions and experimental results comparison. table iv. theoretical and predicted value comparison members from [7] members from this study member mu-p mu-e mu-p/mu-e member mu-p mu-e mu-p/mu-e ub1_h_f1 41.778 41.800 0.999 b0 90.706 91.43 0.99 ub1_h_f2 51.381 54.300 0.946 b1r 85.734 86.49 0.99 ub1_p_f1 34.749 41.400 0.839 b1s 103.774 103.39 1.00 ub1_p_f2 51.678 55.600 0.929 b1sw 104.61 111.17 0.94 ub2_h_f1 54.846 50.500 1.086 b2r 80.498 81.80 0.984 ub2_h_f2 63.855 65.500 0.975 b2s 100.0175 100.33 1.00 ub2_p_f1 50.787 58.500 0.868 b2sw 100.7985 106.84 0.94 ub2_p_f2 58.905 63.300 0.931 average m 0.979 us1_h_f1 22.374 21.400 1.046 standard deviation sd 0.026 us1_h_f2 27.324 26.900 1.016 cov 2.63% us1_p_f1 19.701 21.600 0.912 us1/p/f2 28.314 30.100 0.941 us2_h_f1 25.443 26.600 0.957 us2_h_f2 30.690 35.800 0.857 totals us2_p_f1 27.423 29.800 0.920 m 0.953 us2_p_f2 31.680 37.400 0.847 sd 0.063 average m 0.942 cov 6.56% sd 0.071 mu-p is the theoretical (predicted) and mu-e is the experimental value cov 7.5% engineering, technology & applied science research vol. 12, no. 4, 2022, 8884-8890 8890 www.etasr.com abbas & al‐zuhairi: flexural strengthening of prestressed girders with partially damaged strands … the predicted-to-experimental flexural strength ratios are illustrated in table iv and figure 9. the mean value of 0.953 and the coefficient of variation (cov) of 6.56%, describe the precision of the theoretical flexural strength values and their applicability for predicting the flexural strength of the ebcfrp reinforced unbonded prestressed concrete members with and without wrapped sheet anchorages. v. conclusion • beams outfitted with the proposed u-anchor had an about 15% higher debonding load, as well as companion beams with the anchor have a higher maximum load and corresponding deflection. anchors experienced greater cfrp strain than their counterpart members without anchorages, and the maximum strain is much more than the theoretical strain-based [11] the anchorage was discovered to be effective in restricting the extent of debonding of the laminate, thus indirectly contributing to member flexural stiffness by restricting the crack width. • for the same loading level, the flexural capacity of posttensioned girders decreases as the strand damage ratio increases, whereas the displacement of girders increases the damaged strands ratio. the test results exhibited flexure capacity losses up to 5.4% for b1r and 10.54% for b2r at midspan for damaged strands, and for a strengthened member the flexural capacity gained back the lost strength due to the strand's damage and increased it by (13.08%, 26.47%, for b1s and b1sw, whereas for b2s and b2sw the enhancement was 9.73% and 25.25% respectively). • prestressed concrete element members with more than 20% damaged strands must meet the serviceability requirements before using enhancing procedures. • the proposed equations for tendon strain in unbonded prestressed reinforced concrete members reinforced with eb-cfrp laminates, provide flexural capacity predictions with high precession and minimal variation with a mean equal to 0.95 and cov equal to 0.067. references [1] a. m. al-hilali, a. f. izzet, and n. oukaili, "static shear strength of a non-prismatic beam with transverse openings," engineering, technology & applied science research, vol. 12, no. 2, pp. 8349–8353, apr. 2022, https://doi.org/10.48084/etasr.4789. [2] b. f. abdulkareem, a. f. izzet, and n. oukaili, "post-fire behavior of non-prismatic beams with multiple rectangular openings monotonically loaded," engineering, technology & applied science research, vol. 11, no. 6, pp. 7763–7769, dec. 2021, https://doi.org/ 10.48084/etasr.4488. [3] h. m. hekmet and a. f. izzet, "performance of segmental postτensioned concrete beams exposed to high fire temperature," engineering, technology & applied science research, vol. 9, no. 4, pp. 4440–4447, aug. 2019, https://doi.org/10.48084/etasr.2864. [4] g. razaqpur and a. b. mostafa, "c-anchor for strengthening the connection between adhesively bonded laminates and concrete substrates," technologies, vol. 3, no. 4, pp. 238–258, dec. 2015, https://doi.org/10.3390/technologies3040238. [5] l. nguyen-minh et al., "flexural-strengthening efficiency of cfrp sheets for unbonded post-tensioned concrete t-beams," engineering structures, vol. 166, pp. 1–15, jul. 2018, https://doi.org/10.1016/j.engstruct.2018. 03.065. [6] aci committee 318, aci code-318-19: building code requirements for structural concrete and commentary. farmington hills, mi, usa: aci, 2019. [7] f. el meski and m. harajli, "flexural behavior of unbonded posttensioned concrete members strengthened using external frp composites," journal of composites for construction, vol. 17, no. 2, pp. 197–207, apr. 2013, https://doi.org/10.1061/(asce)cc.1943-5614. 0000330. [8] a. a. abdulhameed et al., "the behavior of hybrid fiber-reinforced concrete elements: a new stress-strain model using an evolutionary approach," applied sciences, vol. 12, no. 4, jan. 2022, αρτ. νο. 2245, https://doi.org/10.3390/app12042245. [9] a. h. al-zuhairi, a. h. al-ahmed, a. a. abdulhameed, and a. n. hanoon, "calibration of a new concrete damage plasticity theoretical model based on experimental parameters," civil engineering journal, vol. 8, no. 2, pp. 225–237, feb. 2022, https://doi.org/10.28991/cej2022-08-02-03. [10] a. h. al-zuhairi and a. i. taj, "effectiveness of meso-scale approach in modeling of plain concrete beam," journal of engineering, vol. 24, no. 8, pp. 71–80, jul. 2018, https://doi.org/10.31026/j.eng.2018.08.06. [11] aci committee 440, aci prc-440.2-17: guide for the design and construction of externally bonded frp systems for strengthening concrete structures. farmington hills, mi, usa: aci, 2017. [12] a. tam and f. n. pannell, "the ultimate moment of resistance of unbonded partially prestressed reinforced concrete beams," magazine of concrete research, vol. 28, no. 97, pp. 203–208, dec. 1976, https://doi.org/10.1680/macr.1976.28.97.203. [13] f. t. k. au and j. s. du, "prediction of ultimate stress in unbonded prestressed tendons," magazine of concrete research, vol. 56, no. 1, pp. 1–11, feb. 2004, https://doi.org/10.1680/macr.2004.56.1.1. [14] f. el meski and m. harajli, "evaluation of the flexural response of cfrp-strengthened unbonded posttensioned members," journal of composites for construction, vol. 19, no. 3, jun. 2015, art. no. 04014052, https://doi.org/10.1061/(asce)cc.1943-5614.0000516. [15] a. j. daraj and a. h. al-zuhairi, "the combined strengthening effect of cfrp wrapping and nsm cfrp laminates on the flexural behavior of post-tensioning concrete girders subjected to partially strand damage," engineering, technology & applied science research, vol. 12, no. 4, pp. 8856–8863, aug. 2022, https://doi.org/10.48084/ etasr.5008. engineering, technology & applied science research vol. 7, no. 4, 2017, 1833-1837 1833 www.etasr.com sarjou and shabakhty: effect of the improved pall friction damper on the seismic response of steel frames effect of the improved pall friction damper on the seismic response of steel frames parviz hosseini sarjou department of civil engineering, higher educational complex of saravan, iran. naser shabakhty department of civil engineering, iran university of science and technology, tehran, iran. abstract—energy-absorbing dampers are used to reinforce structures which are vulnerable to earthquakes. this study evaluates the performance of improved pall frictional dampers (ipfd) which is a type of pall frictional damper (pfd). for this purpose, this study compares the performances of steel frames with concentric steel bracing reinforced by ipfd and steel frames with concentric steel bracing with no damper. frames with different stories and pans were modelled in sap2000 and exposed to accelerograms of earthquakes for non-linear time history analysis. results of analysis were studied; parameters such as story displacement, base shear and absorbed energy were compared in steel frames with damper and without damper. keywordspall; damper; energy absorption i. introduction during an earthquake, a great deal of energy is applied to the structure. different methods are used to confront this energy applied to the structure; these methods usually control damage to the structure. one of the conventional structure control methods is that structural elements remain elastic during an earthquake. since the magnitude of a future earthquake is not clear, this design is not economical and costeffective. as noted in the regulations, a structure should not be damaged considerably by a moderate earthquake and collapsed during a massive earthquake. however, prevention of collapse is no longer a criterion in modern buildings; during an earthquake, functional and non-structural elements of some structures are more valuable than the structures themselves and they need to be maintained during an earthquake. these structures include hospitals, police stations and nuclear plants. seismic response and damage control will be improved by controlling energy applied to the structure and dissipating a major part of this energy by a mechanism independent of structural elements. as show in (1), an increase in ed reduces the energy applied to other parts of the structure. for this purpose, new techniques including energy absorption systems have been developed in engineering society [1]. k s h de e e e e    (1) where, e is the energy applied to the structure during an earthquake, ek denotes absolute kinetic energy, es denotes elastic strain energy, eh denotes energy dissipated by the structural system itself and ed is the energy dissipated by energy absorption systems [2]. there are three types of energy dissipation systems including: 1) active and semi-active control systems; 2) passive control systems; and 3) hybrid control systems. in active control systems, some particular sensors are used in the building to determine changes in displacement, velocity and acceleration of the building. using data analysis, a deterrent force is exerted by a stimulus in an opposite direction of the exerted force. in other words, active control systems tend to control behaviour of the building during an earthquake by exerting an external energy [3]. in passive control system, vibration-controlling element is well located in the structure; the control system which is passive before stimulation (earthquake) starts to control during stimulation and again becomes passive after earthquake. many techniques are used in passive systems; these techniques include base isolators, viscoelastic dampers, metal dampers, tuned mass dampers and friction dampers. in a hybrid controlling system, both active and passive control systems are used simultaneously. once stimulation begins, vibrations are reduced by the passive system; shortly after, the active system starts to operate. then, the passive system may continue or stop working, if necessary [4]. this study examines the seismic behavior of a frame equipped with improved pall friction damper which is a passive system. ii. materials and methods as noted earlier, friction dampers are passive control systems. these dampers work based on friction mechanism between two rigid objects, one slipping over another. in fact, friction is a distinctive feature of energy dissipation. previously, this idea has been used in automatic brakes (brake pads) of automobiles to dissipate kinetic energy. currently, this technology is used to control a structure against earthquake. in general, friction tools well perform against earthquake and their response is independent of loading range, frequency and number of loading cycles [5]. friction dampers are usually available in four types including: 1) pall friction damper system; 2) sumitomo friction damper system; 3) gap–screw connection damper; and 4) rotational friction damper [3]. a. pall friction damper (pfd) a pall damper is installed in the intersection of cross, chevron and single diagonal bracings [7]. this type of damper has been used in countries such as canada, india, usa and china. pall dampers have been approximately used in more engineering, technology & applied science research vol. 7, no. 4, 2017, 1833-1837 1834 www.etasr.com sarjou and shabakhty: effect of the improved pall friction damper on the seismic response of steel frames than 90 buildings over the world; different types of pall dampers have been suggested. a simple schematic can be found in [3]. a pall damper consists of a series of steel plates made of special material which are interconnected by highresistance screws and well perform for friction. pall dampers are widely used in cross bracings [8]. hysteresis curves of several passive energy dissipation systems can be found in [1]. energy absorption and dissipation is higher in the friction damper than in the other dampers due to the large area under the friction damper curve. it means that fewer devices are required for a certain level of earthquake; thus, it is costeffective [1]. pall damper is considered better than other energy dissipation systems because 1) it is easy and cost-effective to build a pall damper, 2) a pall damper performs reliably against an earthquake, 3) energy dissipation is very high in a pall damper due to its large hysteresis loop, 4) this damper performs independently from changes in velocity and temperature, 5) pall dampers do not usually require considerable repair after the earthquake, 6) they can be hidden in blades, 7) due to rectangular hysteresis loop, these dampers are easily modelled in a computer [1]. in [8], authors introduced a new type of pall damper which is used in cross bracings. these dampers are similar to pfds, with a difference that their central core is tshaped. this type of damper was called an improved pall friction damper (ipfd). a schematic can also be found in [7]. the mechanical performance of both dampers is entirely similar and they both absorb an equal amount of energy. most of pall’s assumptions for pfd are true for ipfd. however, ipfd is considered better than pfd because 1) its configuration is easier, 2) its motor function is better, 3) its analysis is simpler, and 4) its construction costs lower. b. optimum slip load the most important step in designing pall systems (pfd and ipfd) is to determine optimum slip load of design. structure response to vibrations is usually expressed by energy applied to the structure and energy dissipated by the structure. accordingly, optimal vibration response occurs when there is minimal difference between energy applied to the structure and energy dissipated by the structure [9]. slip load considered for pall damper should fulfil following requirements [1]:  dampers should not slip during severe wind.  dampers should slip during a severe earthquake before yield of structural elements.  energy absorbed in the structure should be maximized by friction. there are different methods used to determine optimum slip load; one of the most effective methods is non-linear timehistory analysis. in this method, a range of slip loads is selected based on existing standards; then, a series of non-linear dynamic analyses are done to determine slip load corresponding to minimum response as design slip load. structural response may be based on items such as roof displacement, base shear, dissipated energy, etc. c. damper modeling in computer sap2000 was used to analyse the models [11]. there are generally two methods for modelling pall damper; these methods include simple method and accurate method. the simple method was suggested by pall; in this method, damper and bracings are replaced in the computer model only by simple bracing systems which yield under tension and pressure [10]. in this method, friction damper is modelled easily, because hysteresis loop of the friction damper is similar to rectangular loop of a full elasto-plastic material. therefore, elastic bracings-friction dampers can be replaced by bracings which yield in slip load and damper slip load is considered as yield force of bracings [12]. in the second method suggestedin [9], all elements including bracings and damper links are defined by using linear elements and their stress-strain curve. this study used pall’s method for computer modelling. d. the studied frames the studied frame had 6 stories (3 m in height) and 3 openings (4 m in width). figure 1 shows a schema of this cross-braced frame. loading of this frame was based on the sixth topic of national construction regulations according to which 0.8 ton/m live load and 2.4 ton/m dead load were applied to the stories. since this study tended to compare dynamic behavior of frames, the frame with damper was considered similar to the frame without damper; only the damper was located in the structure. it is noteworthy that ipe and ipb profiles and double channel were used for columns, beams and bracings, respectively. fig. 1. the frame used in this study e. selection and scaling of accelerograms based on the 2800 standard four accelerograms of kobe, naghan, tabas and sanfernando earthquakes were used for dynamic time-history analysis of frames. the accelerograms were modified and engineering, technology & applied science research vol. 7, no. 4, 2017, 1833-1837 1835 www.etasr.com sarjou and shabakhty: effect of the improved pall friction damper on the seismic response of steel frames scaled based on the iran seismic code (the standard 2800) [13]. figures 1 and figure 2 show the scaling procedure. fig. 2. mean acceleration spectrum fig. 3. scale of accelerograms and design spectrum then, 53% scale factor was selected for two 6-story structures with and without dampers. this factor is given to the application. f. selection of optimum slip load for dampers the frame with friction damper was exposed to different accelerograms. roof displacement was plotted versus different slip loads. as shown in figure 4, the structure under 12-ton slip-load had the lowest response (lowest displacement) in all accelerograms. thus, optimum slim-load was 12ton. fig. 4. roof displacement under different accelerograms versus different slip loads iii. result a. time-history non-linear analysis of cross-braced frames in this section, the cross-braced frame was modelled in sap2000 and exposed to non-linear dynamic analysis under tabas, naghan, kobe and sanfernando earthquakes with 53% scale factor. some results are shown in figures 5 and 6. these results include maximum roof displacement and base shear. fig. 5. maximum roof displacement fig. 6. maximum base shear b. time-history non-linear analysis of frames with ipfd damper the frame with ipfd damper was modelled in sap2000 and exposed to tabas, naghan, kobe and sanfernando earthquakes with 53% scale factor and 12-ton damper slip-load. figures 7 to 10 show the results of analysis including maximum base shear, maximum roof displacement, damper hysteresis diagram and energy absorbed by the dampers. fig. 7. maximum roof displacement engineering, technology & applied science research vol. 7, no. 4, 2017, 1833-1837 1836 www.etasr.com sarjou and shabakhty: effect of the improved pall friction damper on the seismic response of steel frames fig. 8. maximum base shear fig. 9. hysteric behavior of ipfd under tabas earthquake fig. 10. input energy and energy absorbed by ipfd under tabas earthquake c. analysis of results figures 11 and 12 compare base shear and maximum roof displacement in two frames with and without dampers. iv. conclusion this study compared the performance of steel frames with concentric steel bracing reinforced by ipfd and steel frames with concentric steel bracing with no damper. frames with different stories and pans were modelled in sap2000 and exposed to accelerograms of earthquakes for non-linear time history analysis. final conclusions are achieved as follows:  ipfd significantly reduces base shear in the frame.  ipfd reduces total and relative displacement in stories.  damper outperforms in severe earthquakes such as kobe and tabas earthquakes.  dampers dissipate a great deal of energy; in absence of dampers, this energy damages other parts of the structure.  in a structure, energy dissipated by a damper varies considering its location in the structure and the load applied to it during an earthquake. fig. 11. comparison of roof displacement in frames fig. 12. comparison of base shear in frames references [1] a. pall, “performance-based design using pall friction dampers-an economical design solution”, 13th world conference on earthquake engineering, vancouver, bc, canada, 2004 [2] m. c. constantinou, “principles of friction, viscoelastic., yielding steel and fluid viscous dampers: properties and design”, in passive and active structural vibration control in civil engineering, springer vienna, 1994. [3] v. ruiz, k. walsh, m. m. abdullah, investigating the energy dissipating properties of passive friction devices, florida state university, tallahassee, florida; tokyo institute of technology, tokyo, japan, 2005 [4] j. marko, d. thambiratnam, n. perera, “influence of damping systems on building structures subject to seismic effects”, engineering structures, vol. 26, no. 13, pp. 1939-1956, 2004 [5] l. di sarno, a. s. elnashai, “seismic retrofitting of steel and composite building structure”,. mid-america earthquake center cd release 02-01, 2002 [6] m. c. constantinou, m. d. symans, experimental and analytical investigation of seismic response of structures with supplemental fluid engineering, technology & applied science research vol. 7, no. 4, 2017, 1833-1837 1837 www.etasr.com sarjou and shabakhty: effect of the improved pall friction damper on the seismic response of steel frames viscous dampers, buffalo, ny: national center for earthquake engineering research, 1992 [7] . f. f. miguel, r. h. lopez, “simultaneous optimization of force and placement of friction dampers under seismic loading”, engineering optimization, vol. 48, no. 4, pp. 582-602, 2016 [8] b. wu, j. zhang, m. s. williams, j. ou, “hysteretic behavior of improved pall-typed frictional dampers”, engineering structures, vol. 27, no. 8, pp. 1258-1267, 2005 [9] a. s. pall, c. marsh, “response of friction damped braced frames”, journal of structural engineering, vol. 108, no. 9, pp. 1313-1323, 1982 [10] a. filiatrault, s. cherry, “comparative performance of friction damped systems and base isolation systems for earthquake retrofit and aseismic design”, earthquake engineering & structural dynamics, vol. 16, no. 3, pp. 389-416, 1988 [11] a. ravitheja, “seismic evaluation of multi storey rc buildings with and without fluid viscous dampers”, global journal of research in engineering, vol. 16, no. 1, pp. 10-15, 2016 [12] s. k. lee, j. h. park, b. w. moon, k. w. min, s. h. lee, j. kim, “design of a bracing-friction damper system for seismic retrofitting”, smart structures and systems, vol. 4, no. 5, pp. 685-696, 2008 [13] l. h. najafi, m. tehranizadeh, “ground motion selection and scaling in practice”, periodica polytechnica, civil engineering, vol. 59, no. 2, pp. 232-233, 2015 microsoft word etasr_v11_n6_pp7846-7852 engineering, technology & applied science research vol. 11, no. 6, 2021, 7846-7852 7846 www.etasr.com hussain et al.: design and analysis of a dual rotor multiphase brushless dc motor for its application … design and analysis of a dual rotor multiphase brushless dc motor for its application in electric vehicles mujtaba hussain department of electrical power engineering u.s.-pakistan center for advanced studies in energy national university of sciences and technology islamabad, pakistan mujtaba.hussein@gmail.com abasin ulasyar department of electrical power engineering u.s.-pakistan center for advanced studies in energy national university of sciences and technology islamabad, pakistan abasin@uspcase.nust.edu.pk haris sheh zad department of mechanical & manufacturing engineering pak-austria fachhochshule institute of applied sciences and technology haripur, pakistan haris.shehzad@fcm3.paf-iast.edu.pk abraiz khattak department of electrical power engineering u.s.-pakistan center for advanced studies in energy national university of sciences and technology islamabad, pakistan abraiz@uspcase.nust.edu.pk shibli nisar military college of signals national university of sciences and technology islamabad, pakistan shiblinisar@mcs.edu.pk kashif imran department of electrical power engineering u.s.-pakistan center for advanced studies in energy national university of sciences and technology islamabad, pakistan kashifimran@uspcase.nust.edu.pk abstract-the main objective of this paper is to study the effect of phase numbers in the dual rotor brushless dc (bldc) motor for its application in electric vehicles (evs). the performance of two novel 5-, and 7-phase dual rotor bldc motors is compared against the standard 3-phase dual rotor bldc motor. the proposed motors combine the positive characteristics of multiphase bldc motor and the dual rotor bldc motor thus achieving better fault tolerance capability, high power density, and less per phase stator current. finite element method (fem) was used to design the 3-, 5-, and 7-phase dual-rotor bldc motors. the design parameters and operating conditions are kept the same for a fair comparison. the stator current and torque performance of the proposed motors were obtained with fem simulation and were compared with the standard 3-phase dual rotor bldc motor. it is possible to use low power rating power electronics switches for the proposed motor. the simulation results also validate low torque ripples and high-power density in the proposed motors. finally, the fault analysis of the designed motors shows that the fault tolerance capability increases as the phase number increases. keywords-dual rotor; brushless dc (bldc); electric vehicle (ev); multiphase; finite element method (fem) i. introduction electric vehicles (evs) are the future of road transportation. extensive research has been conducted on the drive system of evs to provide low-cost and energy-efficient solutions. the electric motor is an integral part of its propulsion system along with the transmission system, the power electronics, and the battery [1]. the basic requirements of the electric motor for ev applications include high torque and power density, varied speed range (high speed cruising and low speed crawling), high efficiency over wide torque and speed ranges, wide constant power operation region, high intermittent overload capability, and high reliability and robustness [2-6]. the main advantages of the brushless dc (bldc) motor are its small size, the absence of rotor copper losses due to yhe absence of rotor windings, and its low maintenance cost [7]. the bldc motor offers high efficiency, high power, and torque density, but the conventional bldc motor topologies do not provide all the requirements for ev application [8-10]. the dual-rotor bldc machine promises high torque density and high efficiency. this motor consists of an outer rotor, an inner rotor, and a stator between them. in other words, two separate motors share the same stator nested between them corresponding author: abasin ulasyar engineering, technology & applied science research vol. 11, no. 6, 2021, 7846-7852 7847 www.etasr.com hussain et al.: design and analysis of a dual rotor multiphase brushless dc motor for its application … [11-12]. since both sides of the stator are used as compared to single rotor permanent magnet (pm) bldc, this structure improves the torque density. the topology reduces the copper quantity, which in turn reduces the winding resistance. thus, the copper losses are reduced, and efficiency is improved. the reduced copper usage also cuts down the cost [13-15]. the next important requirement for pm bldc machines used in ev applications is fault tolerance which is the ability of a system to continue working even if a fault occurs. the faulttolerant capability of the pm bldc motors can be enhanced by increasing the number of stator phases (more than threephase). in a multiphase pm bldc drive system, increasing the phase number also increases the number of power electronic switches while it reduces the converter rating required per phase [16-17]. the multiphase pm bldc motors have low torque ripple and high torque density as compared to the threephase electric motors [18-20]. it is now evident that dual-rotor pm bldc and multiphase pm bldc topologies offer unique advantages for ev application. these two topologies can be combined to get the positive characteristics of multiphase pm bldc machines and dual-rotor pm bldc machines. in our research work, two dual rotor bldc motors with 5, and 7 phases are designed for ev application. these motors are fed with square wave currents and have trapezoidal back emf waveform unlike the sinusoidal pmsm motors. the characteristics of these two motors are compared against the standard 3-phase dual rotor bldc motor. they combine the positive characteristics of the dual rotor and multiphase bldc motors, thus achieving less per phase stator current, high power and torque density, and better fault tolerance capability. the main contributions of the current paper are: • two new dual rotor multiphase bldc motors as 5-, and 7phase are designed to drive an ev. the characteristics of these motors are compared with the standard 3-phase dual rotor bldc motor. finite element method (fem) based two-dimensional models of the motors were developed with the jmag designer. • load and no-load analysis of the three designed motors were performed. • fault analysis of the three motors is provided to compare their fault tolerance. open circuit faults, high-impedance faults, and demagnetization of the permanent magnets are studied. ii. analytical study the main design parameters of the bldc motor are the diameter of the armature, the stack length, and the air-gap length, through which the energy conversion process is completed. the calculation of these three design parameters is a fundamental step in any electric motor design. bldc motor’s electromagnetic loading comprises of the specific electrical loading and the specific magnetic loading. these loads define torque, efficiency, and other mechanical characteristics of the motor. even though the motors in this study have two rotors, the design of any bldc motor starts with the general sizing equation. the sizing equation gives the relationship between the main design parameters and the electromagnetic load of the dual-rotor bldc motor. the main design specifications of the dual-rotor bldc motor are derived as follows. ��� � 11. � . �. ��. ������� . ����� . �� (1) where ��� is the apparent power, � is the stator’s stack length, d is the armature’s diameter, � is the specific magnetic loading, and �� is the specific electrical load. the rated speed of the motor represented by �� and � is a constant which depends on the pole arc of the motor. the bldc motor having trapezoidal back emf is modeled using the equivalent circuit shown in figure 1. the voltage of the single phase can be derived as: �� � ���� � �� ����� �� � !� (2) where �� is the phase voltage, �� is the phase resistance, �� is the phase inductance, !� is the generated back emf, and �� is the phase current. the generated back emf and torque constant are functions of the relative rotor position. the voltage equation for multiple phases based on the back emf is expressed as: "# ## $���%⋮⋮�' () )) * � +�� 0 … 00 �% … 0⋮0 ⋮0 ⋱ ⋮⋯ �'0 "## #$���%⋮⋮�'() ))* � ��� "## #$���%⋮⋮�'() ))* � "## #$!�!%⋮⋮!'() ))* (3) fig. 1. equivalent circuit of the n-phase bldc motor. for single phase, the expression for the current is derived as a function of supplied voltage, phase inductance, and back emf as: ��� �� � �1�� 22�%% � �%4 5 3���� � ∅89��52!�: � !%: � !4: ; (4) where <� is the rotational speed, 8 is the pole pair number, and ∅ is the induced flux. the phase inductance is considered constant as the relative rotor position does not affect it. the following equation shows phase inductances bldc motor: engineering, technology & applied science research vol. 11, no. 6, 2021, 7846-7852 7848 www.etasr.com hussain et al.: design and analysis of a dual rotor multiphase brushless dc motor for its application … �� � ��� 5 = �% � �%% 5 = . . . �' � �'' 5 = (5) where = is the mutual inductance, �' is the phase inductance for the n-phase and �'' is the self-inductance. from (3) and (5), the equation for phase voltages can be rewritten as: "# ## $���%⋮⋮�' () )) * � +�� 0 … 00 �% … 0⋮0 ⋮0 ⋱ ⋮⋯ �'0 "## #$���%⋮⋮�'() ))* � + �� 0 … 00 �% … 0⋮0 ⋮0 ⋱ ⋮⋯ �'0 ��� "## #$���%⋮⋮�'() ))* � "## #$!�!%⋮⋮!'() ))* (6) the back emf of the motor depends on rotor speed, rotor relative position, magnetic field intensity, and the number of turns. for a n-phase bldc motor, the phase angle difference is (360/n) for each phase of the back emf. so, the back emf of each phase is: "## #$!�!%⋮⋮!'() ))* � "# ### #$ >?@�a >?@ a 5 �b' �⋮⋮>?@ ca 5 �b' �� 5 1 d() ))) )* . < (7) in (7), the back electromotive force constant of one phase of n-phase bldc motor is represented by >?@. the per phase output torques are derived as: "# ## $e�e%⋮⋮e'() )) * � "# ### #$ >f@�a >f@ a 5 �b' �⋮⋮>f@ ca 5 �b' �� 5 1 d() ))) )* . "# ## $g�g%⋮⋮g'() )) *h� (8) where >f@ is the torque constant of one phase of the n-phase bldc motor. the total electromagnetic torque is given as: e� � e� � e% � ⋯ � e' (9) iii. dual rotor multiphase bldc motor design a. structure of the dual rotor bldc motor figure 2 represents the cross-section of the 2d cad model of a dual rotor bldc motor. the motor consists of a stator sandwiched between two (outer and inner) rotors. the magnets of both rotors are polarized in the same direction. the flux generated by the outer magnets goes through the outer teeth of the stator and the flux driven by the inner magnets goes through the inner teeth of the stator. this structure enables the motor to have low overall volume and improved torque density. with this structure, high torque to volume ratio is obtained, which is critical for ev applications. in the designed dual-rotor multiphase bldc motor, full-pitched concentrated windings are used. this winding configuration reduces the requirement of greater stator slot numbers and reduces the use of copper. fig. 2. structure of the proposed dual rotor bldc motor. b. determination of motor power the first step in any motor design is to determine the motor toque and the nominal speed. two parameters define the motor dimensions, motor radius and stack length. the required power to drive the vehicle can be deduced as [21]: 8�� i jkl28�, 8�, 84; (10) where 8� is the maximum power of the motor when the vehicle achieves maximum speed, 8� is the maximum power of the motor when the vehicle is at highest gradient, and 84 is the maximum power of the motor when the vehicle achieves maximum acceleration. 8�, 8� and 84 are defined by (11), (12) and (13) respectively: 8� � no�p1q�rs jtu � vwxnoy ��.�z � (11) 8� � n[1q�rs jtu \]^���_ � jt ^�����_ � vwxn[y ��.�z � (12) 84 � �1q���rs c `j n�y�a�� � jtu n��.z b� � vwxn�c��.�z∗�.z b�d (13) where e� is the initial velocity, e��_ is the maximum velocity, e� is the final velocity, and ` is the mass conversion coefficient of the vehicle. the maximum speed ���_ of the motor is calculated as: ���_ � no�p∗��c���bf (14) the nominal speed �� is related to maximum speed as: ���_ � g�� (15) where g is the coefficient of constant power meter. increasing the value of g will increase the generated torque. its value ranges between 2 and 4. a large size power converter is needed to achieve a greater value of g. engineering, technology & applied science research vol. 11, no. 6, 2021, 7846-7852 7849 www.etasr.com hussain et al.: design and analysis of a dual rotor multiphase brushless dc motor for its application … c. machine design and comparison to study the effect of different phase numbers on the performance of motors, three different bldc (3-phase, 5phase, and 7-phase) motors were designed. to allow a fair comparison of the three motors, similar materials were used and most of the geometric parameters were kept the same. the three motors were analyzed with fem. table i shows the design parameters of the three dual rotor bldc motors. the cross sections of the simulation models for the three motors are shown in figure 3. (a) (b) (c) fig. 3. cross section of the simulation models. (a) 3-phase dual rotor motor, (b) 5-phase dual rotor motor, (c) 7-phase dual rotor motor. table i. design parameters designed motors 3ph 5ph 7ph number of poles (p) 20 20 20 number of turns 35 35 35 number of slots 27 40 63 outer diameter(mm) 110 110 110 stack length (mm) 50 50 50 current density (a/mm 2 )) 5 5 5 rated speed 900rpm 900rpm 900rpm magnetic loading (t) 0.8 0.8 0.8 magnets ndfeb ndfeb ndfeb iv. no load operation in dual rotor bldc motor, two independent flux loops are formed in the outer and inner air gaps as displayed in figure 1. the flux flows from one magnet in the outer rotor through the outer air gap to the teeth of the outer stator. following the core of the outer stator, the flux flows back to the opposite polarity of the magnet and thus completes a loop. in a similar fashion, a flux loop is created in the lower air gap between the inner rotor and the stator. a different amount of flux is generated in each air gap and two independent back emfs are generated in each stator. at no-load conditions, no current flows in the armature winding, and a magnetic field is generated by the permanent magnet. the no-load characteristics of the motor are obtained by running the motor without input current. cogging torque is generated due to the interaction of magnets and coils at no load. the cogging torques of the three designed motors were compared. the conventional three-phase bldc motor demonstrated a greater cogging torque as compared to the two proposed motors. furthermore, the 7-phase dual rotor bldc motor indicated a reduction in cogging torque than the 5-phase dual rotor bldc motor. fig. 4. cogging torque of the 3-phase bldc motor. fig. 5. cogging torque of the 5-phase bldc motor. fig. 6. cogging torque of the 7-phase bldc motor. c o g g in g t o rq u e ( n m ) c o g g in g t o rq u e ( n m ) c o g g in g t o rq u e ( n m ) engineering, technology & applied science research vol. 11, no. 6, 2021, 7846-7852 7850 www.etasr.com hussain et al.: design and analysis of a dual rotor multiphase brushless dc motor for its application … v. load operation to analyze the dual rotor multi-phase motors under load conditions, they were driven by a trapezoidal current source. a logic commutation was developed for each motor [22]. the interaction of permanent magnets and the magnetic field of the stator coils produce torque. for an n-phase dual rotor bldc motor, one phase is positively energized, another phase is negatively energized, and the remaining phases are not energized. (a) (b) fig. 7. stator winding configuration: (a) 5-phase motor (b) 7-phase motor. as shown in figure 8, each phase of the n-phase bldc motor is star-connected using 2n switches, where n is the number of phases. since all three dual rotor bldc motors are designed with the same electric and magnetic loading, the per phase rms current of the three-phase motor is the largest. as shown in figure 9, the peak value of the 3-phase motor is 86a, of the 5-phase motor is 45a, and of the 7-phase motor is 32a. fig. 8. winding diagram of the n-phase bldc motor. fig. 9. stator phase current waveforms. figures 10-12 show the wave forms of the steady state output electromagnetic torques of the three motors. the torque ripples of the 3-phase motor are the highest, whereas the torque ripples are reduced with increasing number of phases. however, the torque ripples of the 5-phase motor can be considered satisfactory. hence, a phase number greater than 5 is only necessary to reduce the stator current. fig. 10. torque waveform of the 3-phase motor. fig. 11. torque waveform of the 5-phase motor. fig. 12. torque waveform of the 7-phase motor. c u rr e n t (a ) t o rq u e ( n m ) t o rq u e ( n m ) t o rq u e ( n m ) engineering, technology & applied science research vol. 11, no. 6, 2021, 7846-7852 7851 www.etasr.com hussain et al.: design and analysis of a dual rotor multiphase brushless dc motor for its application … vi. fault analysis this section analyzes the transient process of the three designed dual rotor bldc motors under various fault conditions. the performance of the three motors under various short and open circuit faults was analyzed. figure 13 shows the comparison of the average output torque of each motor under different faults. the figure shows either an open circuit fault or short circuit faults by phase number. to simulate these faults, a fault was introduced at certain time using switches. at the time of the fault, there was a sudden dip in the average torque and the torque ripples were increased. fig. 13. average torque under various open or short circuit fault conditions. high impedance faults occur due to broken strands of the motor winding. the most common type is the high resistance fault. this fault was simulated using extra resistance in series with the phase winding. the value of this resistance is obtained from: ��_�f� � ��h h ���'�n4�if � ��'� (16) where j defines the percentage of the broken wires. tables iiiv compare the effect of this fault on the three motors. increasing the phase number makes the motor more prone to broken strand faults. table ii. high impedance fault condition in 3-phase motor condition average torque percentage of normal torque normal condition 30 100% 20% broken strands 21.708 72.36% 35% broken strands 20.319 67.3% 65% broken strands 14.469 48.23% table iii. high impedance fault condition in 5-phase motor condition average torque percentage of normal torque normal condition 30 100% 20% broken strands 26.41 88.04% 35% broken strands 23.54818966 76.8% 65% broken strands 20.15 67.17% table iv. high impedance fault condition in 7-phase motor condition average torque percentage of normal torque normal condition 30 100% 20% broken strands 28.43 84.76% 35% broken strands 26.02 86.73% 65% brokens strands 23.72 79.06% extreme temperature and high electrical loading can cause demagnetization of the bldc motors, decreasing the average output torque. the designed motors were studied under different demagnetization conditions. when all magnets were demagnetized by 4%, the average torque decreased by 12.7%, 8.3%, and 6.6% for the 3-phase, 5-phase, and 7-phase bldc motors respectively. vii. comparison with the available literature the combination of the characteristics of the dual rotor and multiphase permanent motors is available in literature for permanent magnet synchronous motors (pmsm) [23-24]. in [23], a dual-rotor pmsm was designed, a motor with sinusoidal back emf, to get high torque density and good fault tolerance capability. the performance and fault tolerance of the same dual-rotor five phase pmsm is investigated in [24]. to the best of our knowledge, no literature is available with regard to the dual-rotor multiphase bldc motors. in the current research work, two dual rotor bldc motors with 5 and 7 phases were designed for ev application. these motors were fed with square wave currents having trapezoidal back emf waveforms unlike the sinusoidal back emf in pmsm motors. the characteristics of the two proposed motors were compared against the standard 3-phase dual rotor bldc motor. the designed motors have the advantages of the dual rotor and multiphase motors, thus achieving less per phase stator current, high power and torque density, and better fault tolerance capability. viii. conclusion considering the requirements of a high torque ev, two new dual rotor bldc motors were designed and studied in this paper. the dual-rotor pm bldc motor promises high torque density and high efficiency. this machine consists of an inner rotor, an outer rotor, and a stator between the two rotors. three motors: 3-phase, 5-phase, and 7-phase have been designed and fem was utilized to analyze their performance. the main design parameters and materials are preliminarily decided by standard methods. analytical modeling of the multiphase bldc motor has been presented. the performance of the 5 and 7-phase dual rotor bldc motors has been evaluated under load and no-load conditions and the results were compared with the standard 3-phase dual rotor bldc motor. to allow a fair comparison, most of the design parameters and operating conditions of the motors were kept the same with the ones of the base motor. the number of stator slots for each motor has been determined by the phase number. the cogging torque and back emf waveforms were obtained at no load. average torque and stator current waveforms were obtained at loaded conditions. the results show that increasing the phase number decreases phase current. this enables the use of low rating power electronic switches. the output torque can also be increased per rms current for the same volume of the motor. torque ripples also decreased as the number of phases increased. finally, fault analysis of the three motors has been performed to analyze their performance under fault conditions. it was found that the increased phase number makes the motor more fault tolerant and increases reliability. engineering, technology & applied science research vol. 11, no. 6, 2021, 7846-7852 7852 www.etasr.com hussain et al.: design and analysis of a dual rotor multiphase brushless dc motor for its application … references [1] p. zheng, y. liu, y. wang, and s. cheng, "magnetization analysis of the brushless dc motor used for hybrid electric vehicle," ieee transactions on magnetics, vol. 41, no. 1, pp. 522–524, jan. 2005, https://doi.org/10.1109/tmag.2004.838746. [2] j. a. sanguesa, v. torres-sanz, p. garrido, f. j. martinez, and j. m. marquez-barja, "a review on electric vehicles: technologies and challenges," smart cities, vol. 4, no. 1, pp. 372–404, mar. 2021, https://doi.org/10.3390/smartcities4010022. [3] k. t. chau, c. c. chan, and c. liu, "overview of permanent-magnet brushless drives for electric and hybrid electric vehicles," ieee transactions on industrial electronics, vol. 55, no. 6, pp. 2246–2257, jun. 2008, https://doi.org/10.1109/tie.2008.918403. [4] w. cai, x. wu, m. zhou, y. liang, and y. wang, "review and development of electric motor systems and electric powertrains for new energy vehicles," automotive innovation, vol. 4, no. 1, pp. 3–22, feb. 2021, https://doi.org/10.1007/s42154-021-00139-z. [5] a. eldho aliasand and f. t. josh, "selection of motor foran electric vehicle: a review," materials today: proceedings, vol. 24, pp. 1804– 1815, jan. 2020, https://doi.org/10.1016/j.matpr.2020.03.605. 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[24] j. zhao, x. gao, b. li, x. liu, and x. guan, "open-phase fault tolerance techniques of five-phase dual-rotor permanent magnet synchronous motor," energies, vol. 8, no. 11, pp. 12810–12838, nov. 2015, https://doi.org/10.3390/en81112342. engineering, technology & applied science research vol. 7, no. 6, 2017, 2109-2112 2109 www.etasr.com hota et al. : a standalone pv system with a hybrid p&o mppt optimization technique a standalone pv system with a hybrid p&o mppt optimization technique shubhakam hota department of electrical engineering, centre for advanced post graduate studies, biju patnaik university of technology, odisha, india shubhakam143@gmail.com manoj kumar sahu department of electrical engineering, centre for advanced post graduate studies, biju patnaik university of technology, odisha, india, manojsahu.bls@gmail.com j. m. rao malla department of electrical engineering, centre for advanced post graduate studies, biju patnaik university of technology, odisha, india, mallajagan@gmail.com abstract—in this paper a maximum power point tracking (mppt) design for a photovoltaic (pv) system using a hybrid optimization technique is proposed. for maximum power transfer, maximum harvestable power from a pv cell in a dynamically changing surrounding should be known. the proposed technique is compared with the conventional perturb and observe (p&o) technique. a comparative analysis of powervoltage and current-voltage characteristics of a pv cell with and without the mppt module when connected to the grid was performed in simulink, to demonstrate the increment in the efficiency of the pv module after using the mppt module. keywords-maximum power point tracking; mppt; photo voltaic; perturb and observe; p&o; optimizaton i. introduction a solar photo voltaic (pv) cell converts solar energy directly into electrical energy. the solar cell is fabricated with the use of semiconductor devices that produce voltage from solar irradiance. the efficiency of a solar cell is small as it converts 30%-40% of solar irradiance into electrical energy but the nature of the application provides obvious advantages. to overcome the efficiency problem, the maximum power point tracking (mppt) technique is used, which increases the efficiency about 20% 30%. a mppt system is defined as an electronics device which guides the pv cell in a manner that all the power produced by the pv cell will be delivered to the load. generally mppt is used to transfer maximum power either with higher voltage & lower current or with lower voltage & higher current and mppt is installed between the pv cell and the load. an appropriate mppt algorithm is required to reach the mpp, as the mpp varies with the solar irradiance and cell temperature. mppt algorithm gives the point where the actual power output of the pv cell reaches to its maximum value when the source impedance is equal to the load impedance. a boost converter is employed to the pv system which increases the output voltage. the boost converter matches the impedance by changing its duty cycle. a boost converter is connected between the pv cell and the load [1-2]. there are a number of mppt techniques used for maximum power point tracking [3-4]. this paper considers the p&o (perturb and observe) algorithm and provides comparison with and without mppt that demonstrates the improvement in efficiency. the block diagram of the proposed model is shown in figure 1. it consists of a pv cell, the mppt, the boost converter and the load. first the voltage and current are fed to the mppt controller, and then the mppt generates the required gate pulse to the boost converter, so as to maintain the output voltage across the load irrespective of temperature and solar irradiance. fig. 1. block diagram of the p&o method. ii. characterstics of a pv system a. basic characteristics of a pv cell a solar cell is based on the photoelectric effect i.e., the ability of a matter to emit electrons when light falls on it. a solar pv cell is a pn junction diode. when the photo current (iph) falls on the solar cell, the valance band electron (free electron) in the n-type semiconductor get energized and moves to the p-side to fill up the holes. so the holes moves opposite to the electron and treated as direction of current. if there is no load i.e. rse=0, then a short circuit condition occurs that means the short circuit current iph=isc=imax. so that net current iph = 0. if a load is connected, then a voltage produces across the load i.e. (vrse), which is the diode voltage and this voltage(vrse), forwards bias the pn diode. so a diode current (id) flows opposite to the photon current (iph). so the net current is given as i=iph=id (always id<iph). if rse=0, then iph=0, and at this condition, the diode voltage is given as vd=vmax=voc. engineering, technology & applied science research vol. 7, no. 6, 2017, 2109-2112 2110 www.etasr.com hota et al. : a standalone pv system with a hybrid p&o mppt optimization technique b. equivalent circuit of a pv cell photo voltaic cells have non-linear characteristics as the output power changes directly with the temperature of the pv cell and solar irradiance [6]. the equivalent circuit of a pv cell is a single diode model. here gallium arsenide is taken as the semiconductor material, which have the band gap energy=1.12. the equivalent circuit of a pv cell is shown in figure 2. fig. 2. equivalent circuit of a pv cell. the equivalent circuit consists of a diode, the photo current, the shunt field resistance and the series diode resistance. the net current is given as: shdph iiii  (1) the photo current is given as:   refopscroph ttkiii  1 (2) where, iro=references irradiations=1000, isc=short circuit current=3.8 amp, k1= current coefficient=22.2·10 -3, top=operating temperature=25+273.15 oc, tref=reference temperature=25+273.15oc. diode current can be written as: exp 1 exp 1d dd s s opt v v i i i ktv q                                               1exp op d s kt qv i                      1exp op se s kt irvq i    e x p 1s es t q v i r i v                             1 ... exp st se psd ncv irv nii  so, exp 1 . . se s s d s p t irv n n i i n v c                       (3) where: η=ideality factor=1.36, k=boltzmann’s constant, q=charge in electron, c=number of cells=36, ns=np=1, number of series and parallel paths. reverse saturation current is given as 3 1 1 * * exp * gop s rs ref op ref qet i i t t t k                       (4) where, reverse saturation current at operating temperature is given as 1exp        op oc i rs kct qv i sc  (5) where: voc=open circuit voltage=21.1 v and isc=short circuit current=3.8 a. now the shunt field current is given as sh irv sh r i se  (6) where v the output voltage, rse the series field resistance, rsh the shunt field resistance. now putting the values of (2), (3) and (6) in (1), the net current of the pv cell can be obtained. figures 3 and 4 show the i-v and p-v curve of pv cell with the temperature variation and change in solar irradiance. fig. 3. i-v curve of a pv cell without mppt. fig. 4. p-v curve of pv cell without mppt. engineering, technology & applied science research vol. 7, no. 6, 2017, 2109-2112 2111 www.etasr.com hota et al. : a standalone pv system with a hybrid p&o mppt optimization technique iii. characteristics of a boost converter a boost converter has an important role for mppt. it maintains the output voltage of pv cell by changing its duty cycle [3, 7]. so voltage at which maximum power obtained is determined. the duty cycle of the boost converter is given as t t d on and the output voltage is given as d v v inout   1 . if d=0 then vout=vin and if d=1 then vout=  . so the value of duty cycle varies from 0 to 1. by adjusting the duty cycle, the output voltage as well as the output power can be adjusted. figure 5 shows the basic boost converter circuit. the circuit contains an inductor, a capacitor, a diode, a switch (mosfet/ igbt) and the load. when the switch is on, the mosfet/igbt is short circuited and the entire current goes through the path as shown in figure 6. at this time the inductor is charging and the diode act as reverse biased, so the output circuit cut from the input circuit. when the switch is off, the mosfet/igbt is open circuited and the diode d1 is forward biased. now the inductor discharges and the capacitor stores the charge. so a higher voltage (vin+vl), minus a small voltage drop across the diode, appears across the load. after the initial start-up when the switch is off, capacitor discharges each time and the current across the load maintains as the same current. so the output voltage across the load is almost maintaining the steady voltage. figure 7 shows the current path when the switch is off. fig. 5. basic boost converter circuit. fig. 6. boost converter operation at switch on. fig. 7. boost converter operation at switch off. iv. p&o and its application in mppt design due to the simple structure and convenience of the p&o method, it is generally used to track the maximum power [8-9]. it finds the maximum power point of pv cell by iteratively comparing and observing the generated power of the pv cell. in this algorithm, the maximum power point is obtained by changing the terminal voltage and output power of the pv cells. the terminal voltage and output power can change by adjusting the load. by comparing and observing the previous and current value of voltage and power, we can conclude on the maximum power point (figure 8). fig. 8. the flow diagram of the p&o method. one disadvantage is that oscillation occurs near the maximum operating point [10]. the magnitude of oscillation determined from variation of the output voltage. from the figure 9, starting point is point a, and a +δv voltage perturbation moves the operating point a to b, causing a power drop with steady weather condition. according to the p&o method the voltage will change -δv in the opposite direction to maintain the output power. if the sun irradiance increases, power curve moves from p1 to p2 and operating point moves from a to c. fig. 9. separation diagram of mpp for p&o. v. simulation result in this paper, soft switching boost converter for pv system interface has been implemented to reduce ripples at input engineering, technology & applied science research vol. 7, no. 6, 2017, 2109-2112 2112 www.etasr.com hota et al. : a standalone pv system with a hybrid p&o mppt optimization technique current and switching losses in the converter. figure 10 represents power vs voltage characteristics. as shown with an open circuit voltage of 1000 v and short circuit current of 47 a maximum power that can be tracked is 30 kw. from the i-v characteristic (figure 11), it is clear that with an increase in voltage, initially current decreases gradually but there is a drastic decrease in current just after maximum power point. results are shown in table i. fig. 10. pv curve of p&o mppt. fig. 11. i-v curve of p&o mppt. table i. perfomance comparison of the proposed p&o mppt method for 1s1p configuration shading pattern maximum power from pv module (kw) tracking techniques maximum power (kw) tracking efficiency 1s1p 32 without mppt 14 43.75 1s1p 32 p&o 30 93.75 vi. conclusion the classical mppt tracking method has been simulated showing the increased tracking ability of a stand-alone pv system with the p&o mppt technique. the pv simulation system used in this paper is simulated in matlab/simulink. the model of pv modules used in the simulation is established according to the electrical specifications of industrial pv modules. after accomplishing the model of pv modules, the models of dc-dc boost converter and mppt systems are combined with it to complete the pv simulation system with the mppt function. the accuracy and execution efficiency for the mppt algorithm can then be simulated under different weather conditions. under normal environmental condition maximum achievable power is 30 kw. references [1] m. azab, “a new maximum power point tracking for photovoltaic systems”, world academy of science, engineering and technology, vol. 2, no. 8, 2008 [2] d. y. jung, y. h. ji, s. h. park, y. c. jung, c. y. won, “interleaved soft-switching boost converter for photovoltaic power generation system”, ieee transaction on power electronics, vol. 26, no. 4, pp. 1137-1145, 2011 [3] p. thounthong, p. sethaku, s. rael, b. davat, “design and implementation of 2phase interleaved boost converter for fuel cell power source”, 4th iet international conference on power electronics, machines and drives, pp. 91-95, 2008 [4] g. shobana, p. sornadeepika, r. ramaprabha, “global maximum power point tracking of photovoltaic array under partial shaded conditions”, international journal of engineering research, vol. 2, no. 3, pp. 219233, 2013 [5] h. a. c. braga, i. barbi, “a 3-kw unity-power-factor rectifier based on a two-cell boost converter using a new parallel connection technique”, ieee transactions on power electronics, vol. 14, no. 1, pp. 209-217, 1999 [6] c. larbes, s. m. ait cheikh, t. obeidi, a. zerguerras, “genetic algorithms optimized fuzzy logic control for the maximum power point tracking in photovoltaic system”, renewable energy vol. 34, no. 10, pp.2093–2100, 2009 [7] b. subudhi, r. pradhan, “a comparative study on maximum power point tracking techniques for photovoltaic power systems”, ieee transactions on sustainable energy, vol. 4, no. 1, pp. 89-98, 2012 [8] m. s. ait cheikh, c. larbes, g. f. tchoketch kebir, a. zerguerras, “maximum power point tracking using a fuzzy logic control scheme”, revue des energies renouvelables, vol. 10, no. 32, pp. 387 – 395, 2007 [9] m. j. m. rao, m. k. sahu, p. k. subudhi, “pv battery based hybrid power generator system”, journal of materials today: proceedings, 2016 [10] t. a. binshad, k. vijayakumar, m. kaleeswari, “pv based water pumping system for agricultural sector”, frontiers in energy, vol. 10, no. 3, pp. 319-328, 2016 microsoft word etasr_v12_n2_pp8444-8451 engineering, technology & applied science research vol. 12, no. 2, 2022, 8444-8451 8444 www.etasr.com salah: performance of hybrid castellated beams performance of hybrid castellated beams prediction using finite element modeling wael a. salah civil engineering department college of engineering, northern border university arar, saudi arabia and civil engineering department faculty of engineering, al azhar university cairo, egypt wael.khalil@nbu.edu.sa received: 12 february 2022 | revised: 28 february 2022 | accepted: 2 march 2022 abstract-in the current study, the up to failure behavior of the hybrid castellated beams (hcbs) is predicted with the use of a developed finite element (fe) model. both material and geometric nonlinearities are considered in the numerical simulations. the accuracy of the fe model was validated using the experimental test results presented in the literature. the results of the fe analysis had a close agreement with the experimental work in predicting the failure load and failure mode pattern. a parametric study was conducted to investigate the influence of some parameters on hcbs’ ultimate strength. these parameters included slenderness of compression flange, beam span-to-depth ratio, and laterally unbraced length of compression flange. a design formula is proposed to estimate the inelastic lateral-distortional strength of both homogeneous and hybrid material castellated beams. keywords-castellated beams; finite element analysis; failure load; lateral-distortional; unbraced length; slenderness i. introduction beams with web openings have been widely involved in various large-scale steel structure projects such as hyper markets, car parking buildings, and storage facilities. the economic cost and the authentic appearance in addition to the provided facility to pass the services through web openings, have encouraged the designers to involve these opened-web steel elements in their designs. the utmost number of carried out researches on hot-rolled steel elements are directed to plain-web elements either in a simple beam or in a frame system as presented in [1-5]. on the other hand, during the last two decades, extensive studies focused on the investigation of the performance of perforated-web beams fabricated from hotrolled elements. many researchers focused on the determination of the loading capacity of bar steel opened-web beams [6-12] and steel-concrete composite opened-web beams [13-17], whereas the possible instability failure modes of perforated-web beams were highlighted in [18-22]. recently, various endeavors have been made to improve the performance of steel beams. one of these efforts was to increase the depth of the i-profile steel beam by cutting its web in a special pattern and re-welding the two split parts to form what is known as the castellated beam (cb) or perforated-web beam. the load strength of cbs could be increased by utilizing a higher-grade steel material for the entire beam. however, higher-grade steel can be specified only for certain parts of the steel beam forming what is known as a hybrid beam. commonly, higher-grade steel is used for flanges whereas relatively lower-grade is used for web plates. since cb is a combination of two welded rolled beam halves, it is very convenient to combine two alternate halves from two different rolled beams, each with a specific steel grade to form an hcb. this method causes no losses of steel materials and, in the same time, may raise the cb load strength. concerning hybrid steel beams, most of the carried out studies focused on the performance of hybrid solid-web beams [23-26]. a simple design formula was suggested to determine the bending resistance of hybrid beams in [27]. the flexure strength and the ductility of hybrid high-performance beams, have been evaluated in [28]. an analytical method for determining the biaxial bending stress through the unsymmetrical hybrid beams was proposed in [29]. the distortional buckling capacity of built-up-cold-formed hybrid double-i-box beams was experimentally and numerically investigated in [30]. furthermore, it has been demonstrated that the flexure strength, rotation capacity, and failure mode pattern of a simply supported hybrid beam are substantially affected by the applied moment, whether gradient or uniform [30]. one of the earlier recorded research projects in hcbs, was [31]. in that study, hybrid beams with one rectangular web opening at mid-span failed due to the flexural deformation. after a while, the same researchers introduced an analytical solution for calculating the bending strength of both homogeneous and hcbs [32]. however, less attention, if any, has been paid in reviewing the performance of hcbs fabricated by welding two halves of iprofile beams with different grade materials. this study focuses on the evaluation of the load strength of hcbs formed from two i-profile beams of different steel grades. fe analysis was utilized to investigate the behavior of hcbs. the developed fe model was calibrated with the experimental results from the relevant literature. the results of the fe model agree with the experimental results. this gave a corresponding author: wael a. salah engineering, technology & applied science research vol. 12, no. 2, 2022, 8444-8451 8445 www.etasr.com salah: performance of hybrid castellated beams strong confidence to employ the validated fe model in predicting the ultimate load strength of hcbs. furthermore, the developed fe model has been utilized to apply a parametric study to examine the effect of certain parameters on the strength of hcbs. the considered parameters were slenderness ratio of compression flange, beam-span-to-depth ratio, and laterally unbraced length of compression flange. ii. finite element modeling a 3d fe model was developed in abaqus [33], to study the behavior of cbs. flanges, web, and support stiffeners of cbs were modeled using the four-node general-purpose doubly-curved shell elements with reduced integration, s4r. the mid-span point load was applied through a steel block of 100×100×40mm to avoid any kind of stresses concentration at the point of load application. the external steel block was modeled using c3d8r elements and it was connected to the top flange through the surface-to-surface contact option available in abaqus. small sliding contact interface was applied between the bottom surface of the steel block and the top surface of the top flange and a 0.2 friction coefficient was applied between the two contacted surfaces. the end beam vertical support was modeled by restraining a line of nodes at the bottom flange, located at the beam end-support, from the translation in both vertical and lateral directions. the nodes of beam flanges, at a distance of 165mm from the end-support, were precluded against any lateral translation. the steel block was rigidly constrained to a reference point positioned at its top surface center. this assigned reference point was restrained not to move in the two horizontal directions. both material and geometric nonlinearities were considered in the fe analysis. steel was modeled as elastic-plastic with strain hardening. young’s modulus, e, of 210gpa and poisson’s ratio, ν, of 0.3 were used to model the elastic material behavior. the true stress-strain was considered to represent the material nonlinearity. the initial geometric imperfection was introduced to the fe model by scaling the first eigenmode obtained from the conducted elastic buckling analysis by a factor of lb/1000, where lb is the effective laterally unbraced length of the compression flange [34]. iii. validation of the finite element model in order to validate the developed fe model, the acquired fe results were compared to those of previously tested beams in the literature. six simply supported beams tested in [22] were numerically simulated using the present fe model. the results of tensile coupon tests [22] were converted to true stress-strain values to represent the material nonlinearity behavior. figure 1 depicts the conducted comparison between the results of fe analysis and the tested specimen c210-3600. the first and second numbers refer to the section height and beam’s span length respectively. the results are presented in terms of load to lateral displacement. in the experimental program, the lateral displacements were recorded at three points along the mid-span section, namely t4, t5, and t6 to represent respectively top, middle, and bottom of the considered section. the developed deformations at the end of the experimental test and at the ultimate load of fe analysis of the specimen c210-4400 are compared in figure 2. table i exhibits the numerically and experimentally achieved ultimate loads for all tested specimens. the applied comparison indicates that the developed fe model can predict the ultimate load of all tested cbs. however, the relative discrepancy in tracing load to lateral-displacement relation in specimen c2103600 attributes to the applied initial geometric imperfection at the beginning of the fe analysis. the partial lateral restrains provided by the friction developed between the surfaces of steel block and top-flange of the tested specimens should be added to that. the carried out validation for the developed fe model, gives a strong confidence to employ this fe model in a parametric study. fig. 1. load-lateral displacement comparison (c210-3600). fig. 2. resulted deformations of specimen c210-4400 (a) at failure load through the test and (b) fe analysis. table i. fe analysis and test results comparison specimen ptest (kn) pfe (kn) pfe / ptest c180-3600 21.58 22.052 1.02 c180-4400 15.63 16.29 1.04 c180-5200 25.92 i 12.926 0.499 c210-3600 37.22 37.69 1.01 c210-4400 39.94 ii 29.788 0.746 c210-5200 24.9 25.198 1.01 i initial geometric imperfections of this tested specimen resulted in a higher failure load than the expected value [22]. ii observed developed frictional restraint at the loading point during the test, led to a higher beam strength compared to the other tested c210 beams [22]. iv. parametric study the parametric study was carried out to scrutinize the performance of cbs fabricated from two different steel grades (hybrid beams). hybrid steel i-beams, are usually built up from two flanges with a steel grade higher than that of web plate. cbs are typically fabricated from hot-rolled profile by welding two components, the top part (cbt) and the bottom part engineering, technology & applied science research vol. 12, no. 2, 2022, 8444-8451 8446 www.etasr.com salah: performance of hybrid castellated beams (cbb). one of the economical alternatives to enhance cbs load carrying capacity, is to combine the two welded beam parts from two i-profiles with different steel grades. the current parametric study aims to investigate certain cb parameters such as the slenderness ratio of beam flanges, the span-to-depth ratio, and the length of unbraced compression flange on hcbs ultimate load. the suggested beam layout is shown in figure 3 while the beam section, and the distribution of web openings are shown in figure 4. the proposed cb was built up from the ub152×89×16 beam profile. steel grades s275, s355, s420, and s460 [35] were adopted for the materials of numerically analyzed beams. lateral horizontal displacement is completely restrained at the point of load application. fig. 3. layout of fe analyzed castellated beam. fig. 4. opening distribution and section details of an fe analyzed castellated beam. a. compression flange slenderness the slenderness of compression flange has a great impact on the ultimate load of cbs. the effect of flange slenderness was examined numerically through 7 beam groups, with 4 cbs in each group. the cb groups were modeled. the beams in the first 3 groups were hcbs and homogeneous in the last 4 groups. each group consisted of 4 beams: cb-1, cb-2, cb-3, and cb-4. hybrid beams were formed from two halves, cbt and cbb, that appertained to two rolled i-profiles with different steel grades. for all hybrid beams, the material of cbb was always of grade s275, whereas steel grades s355, s420, and s460, were assigned to cbt of the hybrid beam groups, gr-1, gr-2, and gr-3 respectively. steel grades s275, s355, s420, and s460 were assigned, in order, as the material properties for the last 4 homogeneous beam groups, gr-4, gr-5, gr-6, and gr-7. the compression flange of all cbs was laterally restrained only at end supports and at beam mid-span point of load application. the results of cbs in the group gr-4, homogeneous cbs of steel grade s275, were used to normalize the corresponding beam result within the other beam groups. to study the effect of flange slenderness, λf, on the cb ultimate load, thickness values of 4, 6, 8, and 10mm were assigned to the cb flanges cb-1, cb-2, cb-3, and cb-4 respectively in each group from gr-1 to gr-7. the above assigned thickness values of beam flanges, resulted in slenderness ratios of 11, 7.4, 5.56, and 4.45 correspondingly. the lowest scaled eigenmode, picked up from the conducted eigenvalue buckling analysis, was introduced to each fe model typifying the initial geometric imperfection. modified riks method [28] was used to predict the nonlinear response of the cbs. the fe models' notation, i.e. all_s275, all_s355, all_s420, and all_s460 refer to the analyzed homogeneous beams with steel material grades of s275, s355, s420, and s460 in order, whereas the notations top_s355, top_s420, and top_s460 refer to the fe models of hcbs with cbt assigned material grades of s355, s420, and s460 respectively. the results of fe analysis are presented in figures 5 and 6. considering homogeneous cbs, it is conspicuous that using higher-grade steel, has increased cb ultimate load. however, the influence of the material grade has degraded as the compression flange slenderness increased. likewise, specifying higher-grade material to cbt in hcbs, increased the ultimate strength of hcbs. figures 5 and 6 clearly reflect that utilizing a higher-grade material, whether for the entire homogeneous beam or for the hybrid beam's top half, has almost the same effect on the beam's achieved ultimate strength. these results can be interpreted by investigating hcb stress distribution by approaching failure load. figure 7 maps the von mises stress distribution of hcb top_460 at failure load. it can be observed that the beam failed in the instability mode of lateral torsionaldistortional buckling. hence, particular zones of the laterally displaced compression flange have achieved the yield stress whereas the stress in the bottom flange was still below yielding. therefore, raising the limit of the yield stress of the beam’s top-half, increased the entire castellated beam load strength. hence, the failure load of the hcb is only controlled by the top compression flange. the analyzed hcbs with a steel grade s460 employed to cbt and with a flange slenderness ratio equal to 11, sustained more than 13% higher ultimate load compared to that of homogeneous beams with steel of grade s275. however, this gained load ratio was increased to 19% when the slenderness of the compression flange shifted to 4.45. b. span-to-depth ratio beam span-to-depth ratio plays a non-trivial impact on the cb strength. to examine the effect of span-to-depth ratio on the cb ultimate strength, 7 groups, gr-8 to gr-14, were numerically simulated. these beam groups are indistinguishable from the prior introduced groups, gr-1 to gr7, in the same order considering the utilized materials, root iprofile, web openings distribution, and compression flange lateral restraints. the cross-section of all beams in this study part is invariant and matched to that of the original considered i-profile shown in figure 4. the considered span-to-depth ratios for castellated beams cb-1, cb-2, cb-3, and cb-4 in the gr-8 to gr-1428 groups are 30, 32, and 34. varying span-todepth ratios were generated by changing the beam span length. the numerically achieved ultimate strengths of the homogeneous and hybrid beams with disparate span-to-depth ratios, are shown in figures 8 and 9. the presented fe results show that a larger span-to-depth ratio leads to a lower beam ultimate strength for both homogeneous and hybrid beams with the same cross-section for all utilized steel grades. since all engineering, technology & applied science research vol. 12, no. 2, 2022, 8444-8451 8447 www.etasr.com salah: performance of hybrid castellated beams beams of this subsection have failed in the instability mode of lateral torsional-distortional buckling, the top flange has reached the yield stress earlier than the bottom flange. thus, for all considered span-to-depth ratios, specifying a higher steel grade for the top-half of hcbs, resulted in greater ultimate load strength that could be attained before failure. fig. 5. ultimate loads of homogeneous castellated beams with various values of flange slenderness. fig. 6. ultimate loads of hybrid castellated beams with various values of flange slenderness. fig. 7. von mises stresses distribution at failure load of analyzed hcb with λf=5.56, top_s460. c. unbraced length of compression flange this part of the paper intends to study the effect of unbraced compression flange length (lb) on the ultimate strength of hcbs. two different arrangements of hcbs were considered. hcbs scrutinized types are: 1) higher-grade steel to be assigned to cbt, 2) higher-grade steel to be assigned to the castellated beam’s flanges (cbfs). fig. 8. effect of span-to-depth ratio on the failure load of homogeneous castellated beams using various steel grades. fig. 9. effect of span-to-depth ratio on the failure load of hybrid castellated beams considering various steel grade for the top-half beam section. 1) applying higher grade steel to the top-half of the castellated beams seven groups of cbs, gr-15 to gr-21, identical to the earlier introduced gr-1 to gr-7 groups, have been created. all modeled beams had a constant thickness of flange plate out from the used base, i-profile. each beam group included 4 matching cbs, namely cb-1, cb-2, cb-3, and cb-4 but with only customizing the unbraced length of compression flange (lb). the lateral unbraced lengths of compression flange l/2, l/4, l/8, and l/∞ were utilized for cb-1, cb-2, cb-3, and cb4 respectively. the fe results are shown in figures 10 and 11. concerning the homogeneous beams, it is obvious from the presented comparisons that using higher-grade steel has increased cbs’ failure load for all considered unbraced lengths of compression flange. 60% higher ultimate load has been achieved when using steel grade s460 with lb = l/8 compared to the ultimate load of the same cb with s275 steel grade. the relatively close distance between the provided lateral supports, prevented the compression flange to move perpendicular to the web plate plane. such lateral restraints have stiffened cbs against failure in the instability lateral-distortional buckling mode. therefore, the stresses at the critical cross section, midspan section, reached the material ultimate strength as long as no local buckling was observed during the analysis. hence, the employed steel grade has a great impact in the final attained ultimate load for cbs with lb = l/8 or lb = 0. engineering, technology & applied science research vol. 12, no. 2, 2022, 8444-8451 8448 www.etasr.com salah: performance of hybrid castellated beams in the case of hcb and relatively nearby lateral restraining points, the beam didn’t have any kind of lateral instabilities, either lateral torsional or lateral torsion-distortional buckling. since the bottom beam’s half has a lower steel grade than the top half, the mid-span bottom flange reached the yield stress whereas the top flange was still much below its nominated material’s yield stress, as depicted in figure 12. the analysis of these hcbs with lb = l/8 or lb = 0, was terminated because the mid-span bottom flange reached its ultimate strength. moreover, stress concentration was recorded at the mid-span opening’s corner by achieving the beam’s ultimate load. the early failure of hcb with comparatively short lb before the top flange achieves ultimate stress, demonstrates the grounds of a low ratio of acquired ultimate load shown in figure 11. consequently, using higher-grade steel only in the cbt with relatively short lb, has a rather low impact on the beam’s load carrying capacity. considering the analyzed cbs with lb = l/4, the beams have failed in the mode of instability lateral-distortional buckling. the ultimate load strength of homogeneous beams with l/4 unbraced length, has been achieved as the top flange was fully yielded whereas the bottom flange was partially yielded. such stress distribution of both beam flanges points out that the employed steel grade has a substantial impact on the beams’ ultimate strength, agreeing with the results shown in figure 10. furthermore, at the ultimate load of the analyzed hcbs, the mid-span bottom flange, with a lower steel grade, was fully yielded whereas the top flange had limited yielded areas compared to the homogeneous beams. this explicates the relatively low ultimate strength achieved when compared to a commensurate homogenous beam. also in this case, stress concentration was observed at the top corner of the web opening next to the middle web post of hcb. however, applying relatively distant lateral supporting points to the compressed flange, resulted in a lateral torsion-distortional buckling failure with full yielding of the top flange. therefore, using higher-grade steel for the cbt delayed hcb’s failure and allowed carrying higher load than the homogeneous beam with s275 steel grade. since the failure of these cbs has commenced before any yielding initiation at the bottom flange, the acquired load strength ratios were indistinguishable for the same utilized higher-grade steel, either in homogenous or in hybrid beams. as a result, higher-grade steel has almost identical effects on the cb gained strength of homogeneous and hybrid beams. 2) applying higher grade steel to the flanges of castellated beams in this form of hcbs, higher-grade steel was applied to the beam flanges instead of the top-half part. three hcb groups, gr-22, gr-23, and gr-24 similar to the earlier presented groups gr-1, gr-2, and gr-3, were created except that material grade s275 was assigned to the beam’s web plate, and the highergrade steel was assigned to the flanges. the values of lb, i.e. l/2, l/4, l/8, and l/∞ were utilized in 4 beams: cb-1, cb-2, cb-3, and cb-4 in each group. hcb fe models of the flange plate's material grades of s355, s420, and s460 are referred to respectively as flange_s355, flange_s420, and flange_s460. the analysis results are shown in figure 13. the gained strength using beam flanges with higher-grade steel was close to that obtained from the corresponded homogeneous beams with the same steel grade. fig. 10. ultimate load of homogeneous castellated beams using various steel grades. fig. 11. ultimate load of hybrid castellated beams, with higher garde steel assigned to the top part of the beam. fig. 12. von misses stresses of numerically analyzed beam with l/4 unbraced length. v. analytical study since castellated beams are deeper and slenderer than the original root i-profile rolled sections, and because of the existing web openings, castellated beams are sensitive to lateral buckling, whether lateral-torsional or lateral-distortional. such engineering, technology & applied science research vol. 12, no. 2, 2022, 8444-8451 8449 www.etasr.com salah: performance of hybrid castellated beams behavior was dominant in the tested castellated beams and among most of the numerically analyzed beams as well. therefore, finding out a relation able to predict the inelastic distortional-buckling moment (mid) of simply supported castellated beams loaded with mid-span point load, became essential. many formulas dealing with buckling of beams with web openings, have focused on determining the elastic lateraltorsional buckling of a simply beam under various load types as provided in [36, 37], whereas castellated beam elastic lateraltorsional and elastic lateral-distortional were analytically determined in [38]. fig. 13. failure loads of hybrid symmetric castellated beams considering flanges with various steel grades. based on the fe results of the conducted parametric study, the inelastic distortional buckling, mid, of a simply supported castellated beam, whether homogeneous or hybrid, loaded by concentrated load at mid-span can be obtained by: ��� �� � � � (1) where mp is the cross-section plastic moment, and α, are constants equal to 0.77 and 1.6 respectively. r and mp are given by: � � ���� � , �� � �� �� (2) where fy is the yield stress of the homogeneous castellated beam or the yield stress of castellated beam top-half in case of hcb, and �� is: �� � �� ��� � ���� � � � ! �! "# $ �!% (3) the used notations are declared in figure 14. the elastic critical distortional moment, mcr, derived by [38], is modified to fulfill the castellated beam case: �&' � () *+, -. /� 012 31 � 567 (4) () � 1.36 � 0.02=6 $ 0.171= (5) = � , � ?@ a@ (6) where l is the beam’s span length, e is the modulus of elasticity, iy is the y-axis moment of inertia; c is a coefficient which can be taken as [30]: ( � 2.95 $ 1.143 56 � 4.07 5 (7) 5 � +, � e*�f ghf (8) ecwe and gje are the effective warping and torsion rigidities in order. (�2 � *�ij'@�� kl�m� nijo@k p , r!� � ?@?� s 2 (9) where (t is the warping constant. the effective torsion constant, je, can be calculated by: 12 � 6 h@ "i6w� , �% 3+��7 / �2 0 1! � "i6w� ,�% 3+��7 � (10) where 1y is the flange torsion constant and dw is: z� � e ?� [ i63i�\�7 (11) where ] is the poisson ratio = 0.3. fig. 14. cross-section employed notations. fig. 15. elastic critical distortional moment determined by both of modified equation and fe analysis. mcr in (4), can predict the elastic critical distortional moment to an acceptable precision degree compared to all numerically analyzed cbs with lateral supports at the mid-span and at the end. the closeness of the elastic critical distortional engineering, technology & applied science research vol. 12, no. 2, 2022, 8444-8451 8450 www.etasr.com salah: performance of hybrid castellated beams moment determined by (4), to that obtained numerically, varies from 97.40% to 102.45%. figure 15 shows the close agreement between the elastic distortional moment of cbs achieved numerically and by (4). figure 16 presents a comparison between the moment determined by the proposed equation and that evaluated using fe analysis. the comparison conducted in figure 16, proves that (1) can anticipate, with an acceptable accuracy, the inelastic moment capacity of cb fails in the lateral-distortional buckling mode. moreover, this equation can be used for both homogeneous and hybrid cbs. fig. 16. inelastic distortional moment from the proposed equation and numerical analysis. vi. conclusions hcbs formed from two rolled-profiles of varying steel grades, could represent an alternative to strengthen cbs. the current study aimed to find out the advances of hcbs formed from various hot rolled profiles with different steel grades. the close agreement between the results of fe analysis and of experimented cbs, considering both attained ultimate strength and final developed deformations, allowed to employ the developed numerical model in a further parametric study. the conducted parametric study put some light on the influence of specific factors, i.e. slenderness degree of compression flange, beam span-to-depth ratio, and length of unbraced compression flange on the ultimate strength of hcbs. in general, replacing the top-half part of simply supported homogeneous cbs with higher-grade steel, leads to the formation of hcbs with remarkably greater ultimate strength. the carried out numerical analysis has confirmed that applying higher steel grade to the top-half part of cb is more significant when considering a relatively compact top compression flange. the substantially higher proportion of a beam span-to-depth ratio, has a worse effect on the ultimate strength of both cbs and hcbs. both homogeneous cbs and hcbs with the same steel grade, have an indistinguishable impact on the beam load capacity for all considered values of flange slenderness or beam-span-to-depth ratio. the lb of compressed flange has a significant impact on the cb strength. in the view of numerically simulated cbs with lb less than or equal to l/4, the carried-out fe analysis proved that employing a higher-grade material has a positive influence on the beam strength. the maximum load capacities have been achieved in the homogeneous cbs, whereas these load values were shifted down about 10% in the case of higher-grade material assigned to beam’s flanges. compared to the previous two cb types, the minimum acquired ultimate load has been recorded in the case of hcbs with higher-grade steel being employed to cbt. for rather distant lateral restraining points, lateral instabilities were highly expected and the gained load capacities were very close between all analyzed cbs, including hcbs. therefore, whenever lateral instability of simply supported cb is anticipated, it is recommended to utilize hcbs to raise beam's load capacity up to 25% depending on the beam's geometry and applied transverse restraints. based on the results of the 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[39] d. sonck and j. belis, "lateral-torsional buckling resistance of castellated beams," journal of structural engineering, vol. 143, no. 3, mar. 2017, art. no. 04016197, https://doi.org/10.1061/(asce) st.1943-541x.0001690. microsoft word 03-769-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1221-1226 1221 www.etasr.com hemmati and hosseini: effect of it application on project performance focusing on the mediating… effect of it application on project performance focusing on the mediating role of organizational innovation, knowledge management and organizational capabilities mahdi hemmati department of computer engineering iran university of science and technology tehran, iran hassan hosseini department of industrial engineering k.n. toosi university of technology tehran, iran abstract—the purpose of this study is to examine the effect of it application on project performance focusing on mediating role of organizational innovation, knowledge management and organizational capabilities using sem. for this purpose, 194 managers, supervisors and experts of software developer companies participated in this study. participants were asked to complete a questionnaire on each subject. sem was used to analyze data using the lisrel software. results are thoroughly discussed in this paper and the findings support the role of it application , organizational innovation, knowledge management and organizational capabilities on project performance and project benefits. keywords-information technology; organizational innovation; knowledge management; organizational capabilities; project performance i. introduction in the past two decades, performance has been the subject of many interesting discussions and has led to theoretical and practical innovations [1]. project performance is an area of performance evaluation. for improved project implementation, project managers need to identify the factors that affect project performance. successful project management, along with certain processes, is definitely associated with a successful project and auditing can measure this success. however, one of the main weaknesses of project-based organizations is the lack of proper indicators to audit the project and information technology assets are increasingly used for aid. information technology (it) is as a very broad science involving both hardware and software components as well as network communications between two personal computers to the largest private and public networks [2]. the term it is used to describe technologies used in capture, storage, processing, retrieval, transmission and reception of information. this term involves recent technologies such as computers, fax transmission, remote communications, and microelectronics as well as older technologies such as document filing systems, mechanical computing machines, printing and engraving. in other words, it refers to production of services, issues and factors related to receiving, collecting, storing, processing, retrieving, and managing data and information in computer systems. it infrastructure, generally defined as the collective application of electronic devices, telecommunications, software, decentralized computer stations, and integrated media, has deeply influenced spatial distance and consequently other systems. it promotes dynamism, flexibility of services and monetary flows and often provides the opportunity for increased performance and efficiency [3]. various advances in it capabilities have quickly transformed the industry over the past decade. adoption of it and its efficient implementation can improve the cooperation between supply chain members through fast, accurate information transfer and distribution and application of information systems and finally improve the supply chain efficiency [4]. ii. information technology aspects a. knowledge management with the advent of knowledge-based economy, global economy has been integrated into a single global economy through it [5], resulting in a massive economic science. in this new situation, firms must continually adapt to the process of change and new economic realities. in this economy, knowledge is the most important factor of production and the most important competitive and strategic advantage of organizations [6]. therefore, knowledge management is a strategic objective in managing organizational projects [7]. knowledge management is a strategic effort through which an organization attempts to achieve superiority in competition by using intellectual assets of employees and customers. obtaining, storing and distributing knowledge will lead employees to work more intelligently, reduce duplication and ultimately provide more innovative products and services which better meet customer needs [8]. the purpose of knowledge management is to identify and pursue collective engineering, technology & applied science research vol. 6, no. 6, 2016, 1221-1226 1222 www.etasr.com hemmati and hosseini: effect of it application on project performance focusing on the mediating… knowledge to meet strategic goals and help organizations to compete and survive in the global arena [9]. although many studies have addressed knowledge management as one of the factors effective in improving organizational performance [1013], very few studies have focused on the effect of knowledge management on project performance. b. organizational innovation innovation is crucial for individuals, institutions, and in total, for all societies because of its relationship with flexibility and performance [14]. innovation is a continuously planned process which increases competitive advantage of organizations by reducing costs and price of products, increases quality, efficiency and effectiveness of products and services and ultimately increases revenue and publicity of the organization [15]. innovation refers to value creation of new technology or new business activities in terms of new products or processes [16]. more innovative organizations will be more successful in changing environments by developing new capabilities which allow them to achieve better performance [17]. it is not accidental that innovation is currently noted as the most important factor of sustainable competitiveness [18]. c. organizational capabilities organizational capabilities refer to the ability of an organization to use assets and capital. in fact, capabilities act as a link between asset and capital and allow these assets to be used profitably by the firm [19]. capabilities are different from assets, because one cannot give them a monetary value. capabilities are so deeply integrated in procedures that they are not interchangeable or imitable [20]. capabilities and processes of an organization are closely tied together, as it is the capabilities of an organization which allows activities required for various processes of the organization to be carried out in an appropriate manner [21]. a review of empirical literature (table i) suggests that no study has been conducted on the relationship between it, organizational innovation, knowledge management, organizational capabilities, project performance and project benefits within the framework of structural equation modeling. therefore, the main problem addressed in this study is the effect of it application on project performance focusing on the mediating role of organizational innovation, knowledge management and organizational capabilities. d. conceptual model according to the theoretical literature, the conceptual model is illustrated in figure 1. obviously, it is independent variable; mediating variables include knowledge management, organizational capabilities and organizational innovation. project performance and project benefits are also dependent variables. therefore, the hypotheses of the present study are listed as follows: 1. it application is effective on knowledge management. 2. it application is effective on organizational capabilities. 3. it application is effective on organizational innovation. 4. knowledge management is effective on organizational innovation. 5. organizational capability is effective on organizational innovation. 6. knowledge management is effective on project performance. 7. knowledge management is effective on project benefits. 8. organizational capability is effective on project performance 9. organizational capability is effective on project benefits. 10. organizational innovation is effective on project performance. 11. organizational innovation is effective on project benefits. table i. studies conducted on the current variables reference results [22] organizational dynamics is one of the most important mechanisms effective on organizational performance. [4] results showed that it capabilities had a significantly positive effect on knowledge absorption capacity and performance. [7] it has a positive, significant direct effect on knowledge management. knowledge management has a significant direct effect on project success. direct effect of it was not significant on project success. [23] knowledge management has a direct effect on strategic orientation; however, there are no significant relationships between other variables. [25] results showed that it can be effective in improving knowledge management. [24] results showed a significant relationship between it and knowledge management. [26] results showed no significant relationship between itc infrastructure and knowledge creation. [27] results showed a significant positive relationship between it components and knowledge management. iii. materials and methods this study uses a descriptive (non-trial) methodology using correlation and structural equation modeling; in this study, the relationships between variables are examined through a causal model. a. participants participants of the current study included managers, supervisors and experts of software developer companies in tehran, among whom 220 questionnaires were distributed. out of 203 questionnaires returned, nine questionnaires were excluded due to the high number of questions which were not answered. finally, 194 questionnaires were included in the analysis. engineering, technology & applied science research vol. 6, no. 6, 2016, 1221-1226 1223 www.etasr.com hemmati and hosseini: effect of it application on project performance focusing on the mediating… fig. 1. conceptual model b. data collection instrument 1) it application the questionnaire developed in [7] was used to measure it application . this questionnaire involves 12 items measuring basic it tools (4 items) and advanced it tools (8 items). questions are scored on a likert scale from strongly disagree (1) to strongly agree (5). internal consistency of the questionnaire is estimated at 0.90 using cronbach’s alpha. moreover, gfi=95, agfi=0.92 and rmsea=0.066, indicating that the model is well fitted to data [7]. 2) knowledge management the questionnaire developed in [7] was used to measure knowledge management. this questionnaire involves 9 items measuring knowledge integration and storage (4 items) and knowledge sharing and application (5 items). questions are scored on a 5-point likert scale from strongly disagree (1) to strongly agree (5). internal consistency of the questionnaire is estimated at 0.88 using cronbach’s alpha. moreover, gfi=0.93, agfi=0.90 and rmsea=0.051, indicating that the model is well fitted to data [7]. 3) organizational innovation the questionnaire developed in [7] was used to measure organizational innovation. this questionnaire involves 4 questions scored on a likert scale from strongly disagree (1) to strongly agree (5). internal consistency of the questionnaire is estimated at 0.84 using cronbach’s alpha. moreover, gfi=0.98, agfi=0.96 and rmsea=0.026, indicating that the model is well fitted to data. 4) organizational capability the questionnaire developed in [11] was used to measure organizational capability. this questionnaire involves 7 questions scored on a likert scale from strongly disagree (1) to strongly agree (5). internal consistency of the questionnaire is estimated at 0.92 using cronbach’s alpha. moreover, gfi=95, agfi=0.94 and rmsea=0.047, indicating that the model is well fitted to data [11]. 5) project performance the questionnaire developed in [7] was used to measure project performance. this questionnaire involves 12 items measuring planning performance (3 items), cost performance (3 items), quality performance (3 items) and security performance (3 items). questions are scored on likert scale from strongly disagree (1) to strongly agree (5). internal consistency of the questionnaire is estimated at 0.96 using cronbach’s alpha. moreover, gfi=0.95, agfi=0.93 and rmsea=0.057, indicating that the model is well fitted to data [7]. 6) project benefits the questionnaire developed by yang et al (2012) was used to measure project benefits. this questionnaire involves 4 items. questions are scored on a likert scale from strongly disagree (1) to strongly agree (5). internal consistency of the questionnaire is estimated at 0.88 using cronbach’s alpha. moreover, gfi=96, agfi=0.94 and rmsea=0.037, indicating that the model is well fitted to data [7]. c. data analysis by calculating descriptive indexes of the variables, pearson coefficient of correlation and structural equation modeling (sem) are used to examine the causal relationships between variables. spss and lisrel are used to analyze data. iv. results matrix of correlation is the cornerstone of analysis of causal relationships. table ii presents the matrix of correlation, mean and standard deviation of the studied variables. according to table ii, there is a significant positive correlation between it and knowledge management (r=0.64), organizational capability (r=0.46), organizational innovation (r=0.46), project benefits (r=0.49) and project performance (r=0.60). there is a significant positive correlation between knowledge management and organizational capability (r=0.44), organizational innovation (r=0.40), project benefits (r=0.41) and project performance (r=0.60). there is a significant positive correlation between organizational capability and organizational innovation (r=0.68), project benefits (r=0.53) and project performance (r=0.55). there is a significant positive correlation between organizational innovation and project benefits (r=0.44) and project performance (r=0.51). figure 2 shows the fitted model. the numbers on the paths are standardized parameters. according to figure 2, all path coefficients are significant, except for the path from knowledge management to organizational innovation. since this study evaluates the mediating role of knowledge management, organizational innovation and organizational capability in the relationship between it application and project performance and project benefits, table iii lists the coefficients of direct effect, indirect effect, total effect, variance explained and significance level of the variables. as shown in table ii, the direct effect of organizational innovation (β=0.31), organizational capability (β=0.38) and knowledge management (β=0.48) is significant and positive on project performance (p<0.01). the direct effect of organizational innovation engineering, technology & applied science research vol. 6, no. 6, 2016, 1221-1226 1224 www.etasr.com hemmati and hosseini: effect of it application on project performance focusing on the mediating… (β=0.30), organizational capability (β=0.42) and knowledge management (β=0.18) is significant and positive on project performance (p<0.01). the direct effect of it application (β=0.27) and organizational capability (β=0.51) is significant and positive on organizational innovation (p<0.01). however, the effect of knowledge management is not significant on innovation. effect of it application is significant and positive on knowledge management and organizational innovation. the indirect effect of it application is significant and positive on project performance and project benefits (p<0.01). in total, the model explains 47% of variance in project performance, 30% of variance in project benefits, 35% of variance in organizational innovation, 37% of variance in knowledge management and 24% of variance in organizational capabilities. fit indexes of the path analysis are listed in table iv. according to table iv, χ2/df=1.62, gfi=0.94, agfi=0.91 and rmsea=0.057; thus, the fitted model is well fitted. v. discussion this study examines the effect of it application on project performance focusing on the role of organizational innovation, knowledge management and organizational capabilities using sem. the results show that the proposed model is well fitted to the data and can explain 47% of variance in project performance and 30% of variance in project benefits. sem results show that it application has a positive significant effect on knowledge management. this is consistent with other works [7, 11, 24, 27]. this finding suggests that the role of it in knowledge management is important for those organizations which tend to use technologies to manage their intellectual capital. it influences knowledge management process in different ways as follows: 1) it facilitates fast knowledge collection, storage and transfer; 2) the advanced information technologies merge discrete knowledge flows, which eliminates the barriers in communication between different parts of the organization; 3) it improves and develops different methods of knowledge production (socialization, internalization, externalization and combination) and it is not limited to explicit knowledge transfer [28]. table ii. matrix of correlation and descriptive indexes of variables variables 1 2 3 4 5 6 1. it 1 2. knowledge management 0.64** 1 3. organizational capability 0.46** 0.44** 1 4. organizational innovation 0.46** 0.40** 0.68** 1 5. project benefits 0.49** 0.41** 0.53** 0.44** 1 6. project performance 0.60** 0.60** 0.55** 0.51** 0.66** 1 mean 3.19 2.82 2.91 2.93 3.05 2.89 standard deviation 0.75 0.80 0.92 0.94 0.93 0.95 ** p<0.01 fig. 2. fitted model engineering, technology & applied science research vol. 6, no. 6, 2016, 1221-1226 1225 www.etasr.com hemmati and hosseini: effect of it application on project performance focusing on the mediating… table iii. estimation of standardized coefficients of direct effect, indirect effect, total effect and variance explained of the model path direct effect indirect effect total effect variance explained project performance vs organizational innovation organizational capability knowledge management applying it .031** 0.38** 0.48** 0.16** 0.04 0.62** 0.31** 0.54** 0.52** 0.62** 47% project benefits vs organizational innovation organizational capability knowledge management applying it 0.30** 0.42** 0.18* 0.15** 0.04 0.49** 0.30** 0.57** 0.22** 0.49** 30% organizational innovation vs organizational capability knowledge management applying it 0.51** 0.12 0.27** 0.32** 0.51** 0.12 0.59** 35% knowledge management vs applying it 0.61** 0.61** 37% organizational capability vs applying it 0.49** 0.49** 24% ** p<0.01; *p<0.05 table iv. fit indexes of sem χ2/df rmsea gfi agfi cfi nfi 1.62 0.057 0.94 0.91 0.99 0.98 the results show that it application has a significant positive effect on organizational capabilities. this finding suggests that it is a key facilitator of business activities in organizations. other results show that it application has a positive significant effect on organizational innovation. this finding suggests that it application promotes the knowledge and capability of the organization and leads to considerable technological foundations which influence innovation. it application leads to the tendency for finding the causes of problems and producing best solutions, thus promoting innovation [29]. as shown. knowledge management has no significant effect on organizational innovation but organizational capability has a significant positive effect on organizational innovation. organizational capability influences organizational innovation by developing abilities, knowledge and organizational strength, whereby it improves project performance. knowledge management has a significant positive effect on project performance. this finding is consistent with other works [23, 7, 30] and indicates that knowledge management promotes organizational knowledge and thus enhances the operation of an organization. sem results show that knowledge management has a significant positive effect on project benefits. this finding is consistent with [7]. in line with this finding, authors in [31] suggested that knowledge management helps different groups to work together, facilitates the exchange of knowledge among them, promotes learning in the organization and improves the ability to fulfill individual and organizational goals, thereby it provides advantages for project success [31]. the results show that organizational capabilities have a significant positive effect on project performance. this finding is consistent with [22].thus, project performance will be promoted if the organization pursues environmental changes to identify the factors effective on the project, evaluates effectiveness of environmental changes on the project, assesses the project to ensure that correct implementation of procedures, make efforts to use new technologies in the project, acquires new knowledge, has better integration capabilities than similar organizations, develops resources ideally, matches business and specialized processes, and has better communication skills and adaptability than similar organizations [24]. the results also show that organizational capabilities have a significant positive effect on project benefits. to explain this finding, one can say that organizational capability refers to the ability of an organization to use assets and capital. in fact, capabilities act as a link between asset and capital and allow these assets to be used profitably by the firm. it is also shown that organizational innovation has a significant positive effect on project performance. this finding suggests that organizational innovation influences project performance by providing financial resources for research and projects and providing new forms of services and new solutions for problem solving. the organization which can provide new ideas and apply them properly is flexible to changes; this organization also can act as a factor of change in its environment. the results also show that organizational innovation has a significant positive effect on project benefits. this finding suggests that an innovative organization using new technologies can deal with problems, provide new solutions and thus gain advantages for the project success. sem results also show that knowledge management has a significant positive effect on organizational innovation. this finding is consistent with other works [23, 32, 33]. vi. conclusion the results presented in this paper show that it application influences project performance and project benefits through knowledge management, organizational innovation and organizational capabilities. therefore, knowledge management, organizational innovation and organizational capabilities play a mediating role in the relationship between it application and project performance. this study addressed a sample of experts and managers of software developer companies; 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with applications, vol. 37, no. 2, pp. 1096-1103, 2010 microsoft word etasr_v11_n6_pp7776-7781 engineering, technology & applied science research vol. 11, no. 6, 2021, 7776-7781 7776 www.etasr.com korich et al.: a novel mppt design for a partially shaded pv system using spotted hyena … a novel mppt design for a partially shaded pv system using spotted hyena optimization algorithm belkacem korich laadi laboratory department of sciences and technology ziane achour university of djelfa djelfa, algeria kor_belkacem@yahoo.fr amar benaissa laadi laboratory department of sciences and technology ziane achour university of djelfa djelfa, algeria benaissa_am@yahoo.fr boualaga rabhi lmse laboratory department of sciences and technology university of biskra biskra, algeria boualaga@yahoo.fr derradji bakria laadi laboratory department of sciences and technology ziane achour university of djelfa djelfa, algeria bakriaderradji@gmail.com abstract-partial shading is a common problem in photovoltaic (pv) systems, known for its difficulty. numerous attempts have been conducted to mitigate this problem. some of these efforts deploy metaheuristic optimization with a view to tracking the multiple-peak p–v curve in a partial shading pv system. hence, this paper proposes a novel metaheuristic algorithm to track the maximum power point of pv systems using the spotted hyena optimization (sho) algorithm. when evaluated, the sho algorithm proved to be very fast, robust, and accurate in standard conditions, partial shading conditions (pscs), and irradiance variations. also, the results reveal a remarkable improvement in the performance when we compare the sho algorithm with the grey wolf optimization (gwo) algorithm and the perturb and observe (p&o) algorithm. keywords-photovoltaic system; maximum power point tracking; partial shading condition; sho optimization i. introduction photovoltaic solar energy is a renewable energy that is characterized by great development potential. some of the advantages of this energy that it comes from an inexhaustible, clean source and the great safety it offers when used. nevertheless, the two main problems that limit the use of pv systems are the high cost of installation and the low efficiency in energy conversion. we can only get up to 20% efficiency when we convert solar energy into electrical energy. hence, the remaining of the solar energy is lost in the environment as it is not converted into useful electrical energy. as in many renewable energy systems, maintaining maximum efficiency remains a big challenge, especially when rapid changes occur in weather conditions. researchers have concentrated on three basic topics in order to increase the efficiency of pv systems [1]: designing solar irradiance tracking systems, implementing efficient power converters, and developing maximum power point tracking (mppt) algorithms. the latter has the advantage that it can be deployed in both new and existing pv systems, whereas the two first can be implemented only during the design and installation of new pv systems [2]. to increase the output electrical power of a pv system, an mppt algorithm must be adjusted to the operating point, whereas the connection of the pv system to the load is done by a dc-dc boost converter [2]. the output of mppt algorithms can be the reference voltage, the reference current, or the duty cycle of the pulse width modulation (pwm) controller, and the pv systems' operating point can be controlled and adjusted via these parameters. under uniform irradiance, there is a unique mpp in the power-voltage curve that changes according to temperature and irradiance variations and the mppt algorithm is responsible to find new optimal operating points according to these changes. part of the conventional mppt algorithms involve the perturb and observe (p&o) algorithm [3], the incremental conductance algorithm, and the extremum-seeking control algorithm [4, 5]. cloud movement, big buildings, and tree shadows may generate lower irradiance received by some elements of the pv systems. such a condition is called a partial shading condition (psc). under psc, there are various mpps in the p-v curve of the system: a cluster of local maximum power points (lmpps) with one global maximum power point (gmpp) [6]. under psc, it was discovered that the conventional mppt algorithms have low performance, especially when assuming just one mpp on the p-v curve. in reality, due to their poor global search performance, methods such as the p&o method are often trapped in lmpps and they cannot guarantee the convergence to the gmpp [7]. due to the limitations of the classical mppt algorithms, several algorithms based on corresponding author: belkacem korich engineering, technology & applied science research vol. 11, no. 6, 2021, 7776-7781 7777 www.etasr.com korich et al.: a novel mppt design for a partially shaded pv system using spotted hyena … artificial intelligence and stochastic optimization, have been presented, many of which have been reviewed in [8, 9]. in this paper, the spotted hyena optimization (sho) algorithm is utilized to design a fast, robust, and precise mppt algorithm for pv systems [10, 11]. the sho algorithm is a new and powerful method that proved to be efficient in solving different optimization problems with many local optimum points. a pv system was simulated, and the performance of the suggested method was examined in various environmental conditions. ii. system modeling and description a. the pv system model the pv cell is the principal element of a pv system that directly products electrical power from sunlight. we can represent this device by a single diode model because of its simple structure. the mathematical model for the currentvoltage characteristic of a pv cell is [13, 14]: ��� � ��� ���� �� �exp����������� � 1�� ����� �� (1) where ipv is the pv current source, rs is the series equivalent resistance, rp is the equivalent parallel resistance, ipvn is the photocurrent, i is the difference between ipvn and ��, �� is the diode current, �� is the saturation current, �� is the thermal voltage, nss is the number of cells connected in series, and npp is the number of cell connected in parallel. in the present article, we used the kc200gt module (table i) to examine the simulation [15] and a dc-dc boost converter (table ii). table i. kc200gt module characteristics parameter value model kc200gt maximum power 200.143w mpp voltage 26.3v mpp current 7.61a open-circuit voltage 32.9v short-circuit current 8.21a kv -0.123v/ºc ki 0.003a/ºc cells per module 54 table ii. parameters of the dc-dc boost converter element value inductance 300µh output capacitor 100µf ( !) load 100ω switching frequency 10khz figure 1 displays the p-v characteristic of the kc200gt pv panel obtained through simulation at changing irradiation and constant temperature. we notice the effect of insolation on the efficiency of the pv module whenever the value of insolation decreases. the extracted power from the pv module also diminishes. fig. 1. p-v characteristics of the kc200gt pv module at changing irradiation and constant temperature. fig. 2. the structure of the studied system. b. system description pv modules are grouped in series and in parallel in order to increase the power of the pv system according to the demand requirements. a rapid and dynamic insolation change may appear on the panels during pscs or in cloudy days. then, multiple peaks are viewed in the curve of p–v characteristic as shown in figure 3 (local and global mpps) because of the bypass diodes’ existence [8]. during pscs, the existence of the bypass diode aids to reduce the possibility of hot-spot occurrence. this makes the shaded module to behave like as if it is loading power instead of generating it. fig. 3. p-v characteristics for shade patterns. more importantly, the gmpp is changing, mainly depending on the shade pattern (figure 3). therefore, under engineering, technology & applied science research vol. 11, no. 6, 2021, 7776-7781 7778 www.etasr.com korich et al.: a novel mppt design for a partially shaded pv system using spotted hyena … partial shading, gmpp tracking is important in order to improve the power generation efficiency. as shown in figure 2, in our operating scenario of the pv system, an array of 3 kc200gt pv modules in series is simulated in matlab/simulink. we remark the immense effect of insolation on the extracted power of the three modules (figure 3). the first case (pattern 1) shows that the insolation applied on the three modules was the same (1000w/m 2 ) and the outcome of the global power was estimated as 600.42w. in the two other cases, the insolation changed (pattern 2: 1000/800/400, pattern 3: 900/700/300) and new lmpps and gmpp occurred for each case. the power of gmpp was estimated as 333.4w and 291.7w respectively. in all these patterns, the temperature did not change. iii. a review of p&o and gwo algorithms a. p&o algorithm the mppt that can be generated from a pv system is maintained due to the use of the p&o mppt algorithm [16]. this method is considered as the most useful technique due to its simple simulation and easy implementation [4]. firstly, the p&o algorithm senses the voltage and current, and after it calculates the power. based on the change of the power, this algorithm generates a variation in the dc–dc converter’s duty cycle as presented in (2): "# $% � #�&' ( ∆# *+,. -�&'/# $% � #�&' ∆# *+,0 -�&'/ (2) the flowchart of p&o is presented in figure 4 [4]. fig. 4. flowchart of the p&o algorithm. b. gwo algorithm in 2014, mirjalili formulated the social hierarchy and the hunting behavior of the grey wolf packs as an optimizer to deal with many optimization problems [17, 18]. a pack of grey wolfs is composed of an alpha (α), a beta (β), and a delta (δ) wolf, while the rest of the pack are omega wolves. α, β, and δ are the dominating wolves. they are responsible for decision making and discipline in the pack. during the hunt, the omega wolves update their locations and surround the area determined by α, β, and δ. the hunt will continue until the prey stops moving, and finally the hunt will end by attacking the prey. the mathematical model of the aforementioned behaviors is detailed in [17, 18]. gwo-based mppt design for pv system has been presented in [18, 19]. the duty cycle has been considered as a grey wolf that tries to find the optimum solution related to the mpp. the flow chart of the gwo-based algorithm is presented in figure 5 [18]. fig. 5. flowchart of the gwo algorithm. iv. the sho algorithm a. spotted hyena optimizer (sho) the sho was first presented in 2017 [11]. this bioinspired optimization technique imitates the social hierarchy and the group hunting behavior of the spotted hyenas in the purpose of solving various optimization problems. for more details see [11, 12, 20]. the pack of spotted hyenas can contain more than 100 members working together in an organized way. it is a hunting technique that can be divided into 4 main behaviors which are: • searching for prey • encircling prey • hunting • attacking prey engineering, technology & applied science research vol. 11, no. 6, 2021, 7776-7781 7779 www.etasr.com korich et al.: a novel mppt design for a partially shaded pv system using spotted hyena … b. application of sho for mppt figure 6 represents the diagram of the sho algorithm. our optimization problem is the maximization of pv output power. the duty cycle (d) of the pwm signal (which controls the switch of the boost converter) is defined as a hyena [12]. the sho algorithm, which is used for the first time in this field in the current paper, is proved to be applicable when racking the gmpp in the case of partial shading fault in pv systems. fig. 6. flowchart of the sho algorithm. v. simulation and analysis to examine the performance of the proposed sho mppt algorithm, we compared its performance with the p&o and gwo algorithms'. the structure of the pv system under study (figure 2), has been simulated in matlab/simulink. the kc200gt pv model module was used in the simulations. a. performance under standard conditions in this situation, the proposed method’s performance is evaluated throughout the pv system simulations under standard conditions. the levels of irradiance of the 3 pv modules are set as 1000w/m 2 . the modules’ temperature is 25°c as shown in figure 3 (pattern 1). figures 7-9 show pv output’s power, voltage, and current of the 3 algorithms. p&o, gwo, and sho took approximately 0.53s, 0.58s, and 0.50s respectively, to arrive at the mpp. we note that the time response of sho is better than that of p&o and gwo. moreover, the steady-state output power of the sho algorithm is about 600.41w which is closer to the pv's maximum power, i.e. 200.143×3=600.43w when compared to the other methods. fig. 7. performance of p&o algorithm under standard conditions. fig. 8. performance of gwo algorithm under standard conditions. fig. 9. performance of sho algorithm under standard conditions. engineering, technology & applied science research vol. 11, no. 6, 2021, 7776-7781 7780 www.etasr.com korich et al.: a novel mppt design for a partially shaded pv system using spotted hyena … thus, we can conclude that the sho algorithm is more efficient than the formerly mentioned algorithms. b. performance under pscs in this test, the pv modules have 3 irradiance values, set as follows: 900, 700, and 300w/m 2 . their temperature is at 25°c as shown in figure 3 (pattern 3). we observe the existence of a gmpp at 291.78w and two lmpps at 168.35w and 201.29w. figures 10-12 show the pv output power, pv output voltage, and pv output current of the three algorithms. in this state of shading condition, both sho and gwo algorithms are able to find the gmpp. the sho algorithm came to 291.7w while gwo reached 291.06w. hence, it is affirmed that for reaching the gmpp (291.78w), the sho proved to be more valid than the gwo. it should be noted that the p&o algorithm converges to an lmpp (201.22w). this result shows that power losses due to wrong tracking of the gmpp are significant. to arrive at the gmpp, gwo takes 0.6s and sho 0.5s. as a result, the sho algorithm proved to be more effective than the gwo algorithm. fig. 10. p&o algorithm under psc. fig. 11. gwo algorithm under psc. fig. 12. sho algorithm under psc. c. performance under fast changing solar irradiance in this condition, all 3 modules of the simulated array are used under standard conditions (t=25°c, g=1000w/m 2 ). at 1s, we applied a step variation to the solar irradiance (the irradiances of the second and third modules are decreased to 800 and 400w/m 2 (see figure 3, pattern 2) respectively, while the irradiance of the first module remains as before to test and examine the performance and precision of the sho in comparison with the gwo algorithm, when solar irradiance changes rapidly. in this case, at 1s we got a new curve that involves a gmpp at 333.41w and two lmpps (187.94w and 269.94w). in figures 13, 14, the trajectories of the solar array for gwo and sho algorithms are displayed. fig. 13. gwo tracking trajectories under rapid solar irradiance change. as can be seen in figures 13 and 14, after applying a step change of the solar irradiance, the presented sho algorithm has absolutely detected the gmpp (333.24w) and converged with a proper speed, while gwo reached it satisfactorily (332.1w). the time of convergence has increased by about 0.48s after a fast change of solar insolation. when observing engineering, technology & applied science research vol. 11, no. 6, 2021, 7776-7781 7781 www.etasr.com korich et al.: a novel mppt design for a partially shaded pv system using spotted hyena … the obtained simulations results, it can be noted that the gmpp tracking can be reached with more accuracy with the proposed sho algorithm than with other literature results [6-8]. fig. 14. sho tracking trajectories under rapid solar irradiance change. vi. conclusion with the aim of designing an mpp tracker for pv systems, sho has been presented in this research paper and it is proposed for working under pscs. the performance of the sho algorithm was tested and compared with gwo and p&o algorithms. according to the test results, it was concluded that sho proved to be efficient in tracking the gmpp with high fidelity, mainly under pscs. the proposed algorithm exhibits fast, robust, and accurate performance. as a final result, this work confirmed that this optimization exhibited superior performance when compared with the two other tested methods, especially in terms of tracking ability. references [1] h. yatimi and e. aroudam, "assessment and control of a photovoltaic energy storage system based on the robust sliding mode mppt controller," solar energy, vol. 139, pp. 557–568, dec. 2016, https://doi.org/10.1016/j.solener.2016.10.038. 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[14] s. hota, m. k. sahu, and j. m. r. malla, "a standalone pv system with a hybrid p&o mppt optimization technique," engineering, technology & applied science research, vol. 7, no. 6, pp. 2109–2112, dec. 2017, https://doi.org/10.48084/etasr.1374. [15] "kc200gt high efficiency multi-crystal photovoltaic module datasheet." kyocera, 2011. [16] s. latreche, a. e. badoud, and m. khemliche, "implementation of mppt algorithm and supervision of shading on photovoltaic module," engineering, technology & applied science research, vol. 8, no. 6, pp. 3541–3544, dec. 2018, https://doi.org/10.48084/etasr.2354. [17] s. mirjalili, s. m. mirjalili, and a. lewis, "grey wolf optimizer," advances in engineering software, vol. 69, pp. 46–61, mar. 2014, https://doi.org/10.1016/j.advengsoft.2013.12.007. [18] s. mohanty, b. subudhi, and p. k. ray, "a new mppt design using grey wolf optimization technique for photovoltaic system under partial shading conditions," ieee transactions on sustainable energy, vol. 7, no. 1, pp. 181–188, jan. 2016, https://doi.org/10.1109/ tste.2015.2482120. [19] m. valan rajkumar, m. mahakumar, m. manojkumar, m. hemaraj, and e. kumaravel, "a new dc-dc converter topology with grey wolf mppt algorithm for photovoltaic system," international journal of emerging technologies in engineering research, vol. 5, no. 4, pp. 54– 59, apr. 2017. [20] g. dhiman and v. kumar, "spotted hyena optimizer for solving complex and non-linear constrained engineering problems," in harmony search and nature inspired optimization algorithms, singapore, 2019, pp. 857–867, https://doi.org/10.1007/978-981-130761-4_81. microsoft word 1-612-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1115-1118 1115 www.etasr.com mavromatakis et al.: modeling photovoltaic power modeling photovoltaic power fotis mavromatakis department of electrical engineering technological educational institute of crete heraklion, crete, greece fotis@staff.teicrete.gr, yannis franghiadakis department of electrical engineering technological educational institute of crete heraklion, crete, greece pvjfra@staff.teicrete.gr frank vignola solar radiation monitoring laboratory 1274 university of oregon eugene, oregon 97403-1274, usa fev@uoregon.edu abstract—a robust and reliable model describing the power produced by a photovoltaic system is needed in order to be able to detect module failures, inverter malfunction, shadowing effects and other factors that may result to energy losses. in addition, a reliable model enables an investor to perform accurate estimates of the system energy production, payback times etc. the model utilizes the global irradiance reaching the plane of the photovoltaic modules since in almost all photovoltaic (pv) facilities the beam and the diffuse solar irradiances are not recorded. the airmass, the angle of incidence and the efficiency drop due to low values of solar irradiance are taken into account. currently, the model is validated through the use of high quality data available from the national renewable energy laboratory (usa). the data were acquired with iv tracers while the meteorological conditions were also recorded. several modules of different technologies were deployed but here we present results from a single crystalline module. the performance of the model is acceptable at a level of 5% despite the assumptions made. the dependence of the residuals upon solar irradiance temperature, airmass and angle of incidence is also explored and future work is described. keywords-photovoltaic power; modeling; data analysis; spectral effects; low irradiance losses i. introduction the monitoring of the performance of a pv system is important for the detection of possible problems during the operational life time of a photovoltaic system. several models are available in the literature that provide estimates of the pv power based on a number of parameters [1]. in the approach used in this study, simple mathematical functions are utilized to describe the effects of the light traveling path through the atmosphere, angle of incidence, low irradiance and inverter efficiency [2, 3]. dust losses can be included if they are known. the above functions can be determined experimentally or adopted from the literature. a minimum number of input parameters was used to keep the approach as simple as possible while providing quality performance estimates. despite the fact that during the nrel experiment all solar irradiance components were independently measured, the model incorporates only the global irradiance as this is actually measured in typical photovoltaic installations. the performance of the model is discussed along with the factors that affect it and how it can be improved. ii. experimental data a. maintaining the integrity of the specifications the model assumes that the solar irradiance affects the power production in two distinct ways. the first is the known linear dependence of photovoltaic power and the short circuit current, while the second involves the known reduction in efficiency ([3] and references there in). the cell temperature is assumed to be measured through the backside temperature. if it is not available, then it can be determined through measurements of the air temperature and the wind speed along with the global solar irradiance. however, the dependence of power on this term is much reduced due to the temperature coefficient of maximum power at stc conditions which is typical around -0.4%/c for crystalline modules. this coefficient is obtained from the manufacturer’s data otherwise it can be determined from actual measurements. the angle of incidence effects for any given module can be determined through measurements of the short circuit current, the incident beam and diffuse irradiance, and the temperature of the module [4]. the way of performing such measurements is described in detail in [4]. typically, such measurements are taken over a short period of time, e.g. around solar noon where the incoming solar radiation is not varying. it is then possible to separate the aoi effects from airmass/spectral effects. currently this model assumes that the response of a module to the beam and diffuse irradiances is the same. it is known that the nominal or peak power of a photovoltaic module is given at standard test conditions (stc). these conditions assume a solar irradiance of 1000 w/m2 at normal incidence, a cell temperature of 25 degrees celsius and an air mass of 1.5. however, it is clear that these conditions rarely hold outdoors, especially during the winter period in northern latitudes. the electromagnetic radiation coming from the sun is affected as a function of wavelength due to its propagation through the atmosphere. rayleigh scattering is the dominant scattering mechanism under cloudless skies. this mechanism displays a strong wavelength dependence affecting mainly uv/optical wavelengths. it is evident that the module performance will also be affected. since the spectral response of thin film modules lies mainly in the optical regime, these will be more affected than mono or polycrystalline modules. air mass effects are studied through engineering, technology & applied science research vol. 6, no. 5, 2016, 1115-1118 1116 www.etasr.com mavromatakis et al.: modeling photovoltaic power measurements of the short circuit current according to the method described in [4]. the data are reduced to stc conditions by correcting for the temperature and the instantaneous solar irradiance acquired during the measurements. such measurements are especially useful since photovoltaic modules can be used to assess the spectrally averaged solar irradiance incident upon the module. the dependence of the produced dc power upon the air mass is examined through this function to a first approximation. fig. 1. the ratio of normalized power to normalized short circuit current is related to the efficiency of the module. data are from a single crystalline module during its deployment at cocoa, fl. it is also known that at low light levels photovoltaic efficiency is reduced in a nonlinear way. the effect of the shunt resistance becomes important since the total resistance of the module during operation approaches the value of the shunt resistance. the percentage loss of power due to the shunt resistance increases at low solar irradiances. in order to study the effect of the change of the efficiency of a module as a function of solar irradiance stainless steel meshes of various transmittances were constructed. these meshes when used in various combinations allow us to vary the incoming solar irradiance by a factor of 10. the backside module temperature is recorded along with the solar irradiance with and without the mesh. the unobstructed solar irradiance in front of the mesh is used to assess the stability of the ambient conditions. the resulting data can be used to model the performance of modules of the same technology, e.g. single or multi crystalline, amorphous si, etc. another simplified approach utilizes good quality iv curves of a module under different solar irradiances as in the nrel data. it relies on the fact that the short circuit current under typical conditions is not affected by the shunt resistance and that the power is affected by air mass and angle of incidence in the same way as the short circuit current. the selected data satisfy the following conditions: air mass less than 2, angle of incidence less than 60 degrees and global irradiance less than 1000 w/m2. the instantaneous maximum power and short circuit current are corrected for temperature and normalized to their stc values. subsequently, the two quantities are divided to form a ratio independent of airmass and angular effects. the ratio is plotted as a function of normalized incoming solar irradiance as in figure 1. iii. validation data currently, the model takes into account the solar irradiance, the cell temperature, the angle of incidence, and the low irradiance performance. runs are conducted with and without the air mass correction which to a first approximation is assumed to be that of the short circuit current. high quality validation data are required to check the performance of the model. nrel carried out a field campaign at three different sites in the united states and with several pv modules of different technologies at different climatic conditions [5]. quality assessment methods were implemented by nrel to create a reliable data base that can be used by scientists for validation and performance purposes. the regular maintenance of the experiment along with the quality of the measurement equipment provided specific measurement errors. in this work data acquired from a single-crystalline silicon module are processed. the module was first deployed at a tilt of 28o.5 and an azimuth of 180o in cocoa, fl (subtropical climate) for more than one year. during this time i-v traces were recorded every five minutes along with several environmental parameters. the same module was then deployed at eugene, or (marine climate) at a tilt of 44o and an azimuth of 180o. nrel performed indoor performance measurements at standard test conditions (stc) of the deployed modules. the adopted stc power used in the calculations is 83 watts. the data from the two different sites mentioned above offer an excellent tool to study the effects of diverse climates upon the performance of a module. iv. discussion a first version of the model has been presented in [3] along with the mathematical expressions describing the various factors that affect the photovoltaic power. as already mentioned the model can be improved if diffuse and beam solar irradiance data are available. the model adopts the spectral function that describes the effects of the propagation of sunlight through the atmosphere upon the short circuit current as given in [4] and [6]. a fourth degree polynomial is determined through measurements of the short circuit current at various air masses during a day. it is noted that actual atmospheric conditions are not stable during the day leading to differences before and after solar noon. formally, maximum power point measurements should be conducted but these should be corrected for the low irradiance losses. a separate function refers to the effect caused by the fact that light does not enter the module at normal incidence. a generic curve normalized to unity at zero angle of incidence can be adopted from [4, 6] or separate measurements can be carried out using the module under study. the model also takes into account the reduction in efficiency of a cell or module when operating under solar irradiances significantly less than that of the standard test conditions. the influence of other effects can be included in the model if their functions are known. seasonal dust effects can be included to the model if related data are available from independent sources. a fixed factor may be engineering, technology & applied science research vol. 6, no. 5, 2016, 1115-1118 1117 www.etasr.com mavromatakis et al.: modeling photovoltaic power used to account for the aging of the modules. if the module is new, this factor can be set to 1. nrel provides error estimates for all the data available from this experiment. the relative errors on the mppt photovoltaic power and the solar irradiance, among other parameters, were calculated. in the current analysis the selected data are characterized by relative errors of less than 2% in both pv power and solar irradiance. two data sets were created for the model validation, one for each of the sites with experimental data adopting the constraint of 2%. the data set from eugene, or contains 21552 different measurements, while the data set from cocoa, fl contains 24776 measurements. the ratio between model and measured or experimental data is calculated as pmodel/pdata, while the percent difference between the model and the measured data is calculated as (pmodel-pdata)/pdata. histograms of the percentage difference are created and fit with gaussian profiles to determine the sigma of the distribution. figure 2 shows the histogram of the percentage difference between modeled and observed values of pv power for cocoa, fl. figure 3 shows the corresponding plot for eugene, or. a gaussian fit to the cocoa, fl histogram results in a sigma of 0.012, while the sigma for the eugene, or data is 0.016. the one sigma limit is accompanied by a possibility of 68% which is not large enough to confidently limit a parameter. adopting the three sigma confidence limit, the typical uncertainty of the model is around 0.05 or 5%. examination of the actual power produced by the module and that estimated by the model shows a linear relation with the scatter increasing at the lower values of the power (figure 4). a number of reasons may explain this behavior. the variation of efficiency as a function of solar irradiance should be determined by laboratory measurements at predetermined conditions. however, such detailed data are not available in the data sheet. usually, the reduction in efficiency at a level of e.g. 200 w/m2 is quoted by the manufacturers. the air mass effect is more complicated than the polynomial expression adopted in the calculations and its unique dependence upon the elevation of the sun. precipitable water and the aerosol content of the atmosphere are expected to affect the performance of a module. note also that the atmospheric conditions are not stable during the day but this effect cannot be modeled in the absence of detailed data as is generally the case, e.g. a grid connected photovoltaic power facility. in addition, the air mass effect is less important in single or multi crystalline modules because their spectral response is less affected by the scattering of light in the atmosphere. amorphous si or cdte modules are more affected due to their bluer response. the nrel data include modules of different technologies including cdte, cigs, a-si which will be strongly affected by the spectral distribution of light during low sun elevation angles. different functions will be required to account for the actual implications of the atmospheric conditions upon the power production. a simple model using a small number of input parameters is validated against quality data from an experiment carried out at different climatic conditions in usa. the current analysis suggests an accuracy of the model of around 5%. the full analysis of all module technologies will provide an even better assessment of its performance. fig. 2. the histogram of the percentage difference between modeled and measured photovoltaic power for cocoa, fl. fig. 3. the histogram of the percentage difference between modeled and measured photovoltaic power for eugene, or. fig. 4. a one to one plot of the measured and modeled photovoltaic power from the single crystalline module under consideration. engineering, technology & applied science research vol. 6, no. 5, 2016, 1115-1118 1118 www.etasr.com mavromatakis et al.: modeling photovoltaic power acknowledgment this project is implemented through the operational program "education and lifelong learning", action archimedes iii and is co-financed by the european union (european social fund) and greek national funds (national strategic reference framework 2007 2013). the authors would also to thank b. marion for providing the nrel test’s facility data. the eugene data used in this project was generated under the nrel subcontract number afu-2-220721. references [1] k. ding, z. ye, t. reindl, “comparison of parameterisation models for the estimation of the maximum power output of pv modules”, energy procedia, vol. 25, pp. 101-107, 2012 [2] f. mavromatakis, g. makrides, g. georghiou, a. pothrakis, y. franghiadakis, e. drakakis, e. koudoumas, “modelling the photovoltaic potential of a site”, renewable energy, vol. 35, pp. 1387-1390, 2010 [3] f. mavromatakis, f. vignola, y. franghiadakis, “modelling photovoltaic power”, 10th international conference on deregulated electricity market issues in south eastern europe (demsee), budapest, hungary, 24-25 september, 2015 [4] d. l. king, j. a. kratochvil, w. e. boyson, “measuring solar spectral and angle-of-incidence effects on photovoltaic modules and solar irradiance sensors”, 26th ieee photovoltaic specialists conference, anaheim, california, usa, september 29 october 3, 1997 [5] w. marion, a. anderberg, c. deline, s. glick, m. muller, g. perrin, j. rodriguez, s. rummel, k. terwilliger, t. j. silverman, user’s manual for data for validating models for pv module performance, national renewable energy laboratoy, technical report, vtp-5200-61610, 2014 [6] a. h. fanney, m. w. davis, b. p. dougherty, d. l. king, w. e. boyson, j. a. kratochvil, "comparison of photovoltaic module performance measurements”, transactions of the asme, vol. 128, pp. 152-160. 2006 microsoft word 5-1857_s_ok_.doc engineering, technology & applied science research vol. 8, no. 2, 2018, 2651-2655 2651 www.etasr.com aich: 3d buoyancy induced heat transfer in triangular solar collector having a corrugated … 3d buoyancy induced heat transfer in triangular solar collector having a corrugated bottom wall walid aich mechanical engineering department university of hail, saudi arabia research unit of materials, energy and renewable energies (meer) faculty of sciences of gafsa, tunisia aich_walid@yahoo.fr abstract—a numerical study of the natural convection heat transfer and fluid flow in 3d triangular solar collector having a corrugated bottom wall has been carried out using finite volume method. the aim of the study is to investigate how buoyancy forces influence airflow and temperature patterns inside the collector heated from below and cooled on its inclined walls while vertical ones are assumed to be perfect thermal insulators. rayleigh number is the main parameter which changes from 103 to 105 and prandtl number is fixed at pr=0.71. results are reported in terms of particles trajectories, iso-surfaces of temperature, velocity magnitude and mean nusselt number. it has been found that the flow structure is sensitive to the value of rayleigh number and that heat transfer is enhanced with increasing of this parameter. keywords-natural convection; heat transfer; solar collector; rayleigh number; nusselt number i. introduction a prodigious importance has been given to the natural convection heat transfer phenomena which can be seen in many energy-related applications, such as thermal insulation of buildings using air gaps, solar energy collectors, furnaces and fire control in buildings and so on. these applications are reviewed by many authors in the literature [1–4]. the shape of the enclosure is the most effective parameter for natural convection studies in enclosure. the enclosures encountered in these applications are highly diverse in their geometrical configuration and the most investigated enclosures include the annulus between horizontal cylinders, the spherical annulus, the hollow horizontal cylinder, the closed rectangular cavity, and the closed triangular cavity. pioneers studied natural convection in triangular cavities in [5-7]. authors in [8, 9] modeled the winter and summer day boundary conditions inside a roof of triangular cross-section. assuming a geometric symmetry through the midplane of an isosceles triangular cavity, author in [10] examined a right angled triangular cavity with a heated bottom wall, cooled hypotenuse, and insulated vertical wall. various aspect ratios and preselected rayleigh numbers were used for the reduced right-angled triangular cavity filled with air or water. solutions of the time-dependent conservation equations were obtained using two different numerical techniques, which while yielding different numerical values for the velocity and temperature fields, did not alter the flow structure pertinent to a single convective cell for low rayleigh number and to a multicellular regime for high rayleigh number. authors in [11] carried out the natural convection problem with flush mounted heater on one wall of a triangular cavity. governing parameters on heat transfer and flow fields are triangle aspect ratio, heater location, heater length and rayleigh number. they observed that the most important parameter on heat transfer and flow field is the heater position which can be a control parameter for their system. authors in [12] analyzed a numerical study of heat and mass transfer due to natural convection inside a triangular enclosure. the governing equations of the two-dimensional flow problem consist of a velocity–pressure (uvp) formulation along with the energy and concentration flow equations. these equations are solved numerically by control volume based finite element method using the equal-order method without pressure correction. they found that the buoyancy ratio and the lewis number values have a profound influence on the thermal, concentration and dynamic fields. steady state laminar natural convection in right triangular and quarter circular enclosures was investigated in [13]. the presented results showed that both aspect ratios and rayleigh number have a strong influence on the streamline patterns and isotherms. a sizable amount of other related studies can be found in the literature review [1425]. only limited attention has been paid to the study of threedimensional transverse flow which is primordial when dealing with the enhancement of heat transfer. the paramount aim of this work has been to numerically investigate the diffusive natural convection heat transfer and fluid flow in a threedimensional triangular solar collector heated from its corrugated bottom wall. ii. mathematical formulation a. physical model the considered physical model is presented in figure 1 with its specified coordinate system and boundary conditions. the model is a triangular shape solar collector with a corrugated bottom wall. the gravity acts in the negative y axis engineering, technology & applied science research vol. 8, no. 2, 2018, 2651-2655 2652 www.etasr.com aich: 3d buoyancy induced heat transfer in triangular solar collector having a corrugated … and the cavity is formed by the heated corrugated absorber plate, the two cooled inclined glass covers and the two vertical adiabatic walls. fig. 1. schematic of the problem with domain and boundary conditions. b. governing equations and numerical solution as numerical method we used the vorticity-potential vector formalism )(    which allows, in a three-dimensional configuration, the elimination of the pressure, which is a delicate term to treat. to eliminate this term one applies the rotational to the equation of momentum. more details on this 3d formalism can be found in [26]. the potential vector and the vorticity are respectively defined by the two following relations: ' 'v     and ' 'v      (1) after nondimensionalization, the system of equations controlling the phenomenon becomes as: 2      (2) ( . ) ( . ) .pr . ; 0; t t v v ra t z x                          (3) . t v t t t        (4) with:   pr and   . ... 3ltg ra   boundary conditions for considered model are given as follows: temperature: 1t at the corrugated absorber, 0t at inclined glass covers and 0   z t on vertical walls (adiabatic). velocity: 0 zyx vvv on all walls. the average nusselt at the hot corrugated wall is given by: 21 0 0 t dxdznuav n      (5) where n   is the unit vector normal to the hot corrugated wall. the mathematical model described above was written in a fortran program. the control volume finite difference method is used to discretize governing equations. the centraldifference scheme is used for treating convective terms while the fully implicit procedure is used to discretize the temporal derivatives. the grids are considered uniform in all directions with clustering nodes on boundaries. the successive relaxation iteration scheme is used to solve the resulting non-linear algebraic equations. a computer program written for a regular grid was improved to handle the irregularly shaped computational domain using the blocked-off method as described in [27]. in this technique, the whole region is divided into two active and inactive (blocked-off regions) parts. thus the surface of inclined step in present analysis is approximated by a series of fine cubic steps. it is obvious that using fine grids in the interface region between active and inactive zones causes to have an approximate boundary which is more similar to the true boundary. according to the blocked-off technique, known values of the dependent variables must be established in all inactive control volumes. if the inactive region represents a stationary solid boundary as in this case, the velocity components in that region must be equal to zero, and a known temperature (isothermal boundaries) must be established in the inactive control volumes. the control volumes, which are inside the active region, are designated as 1 and otherwise they are 0. the time step (10-4) and spatial mesh (81 81 81) are utilized to carry out all the numerical tests. the solution is considered acceptable when the following convergence criterion is satisfied for each time step: 11,2,3 1 4 max max 10 max n n i i n n i in i i t t           (6) iii. results and discussion particle trajectories for different rayleigh number values are illustrated in figure 2. it is noted that prandtl number is fixed at pr=0.71 for the whole work and the rayleigh number which is the main parameter changes from 103 to 105. as it can be seen, the flow strength is very low for ra=103 and two opposite rotating vortexes are formed showing poor convective heat transfer. flow strength increases with increasing of rayleigh number. indeed the fluid takes up heat energy from the bottom heated absorber and becomes lighter to induce a convective current. lighter fluid goes up and due to the symmetric nature of colder glass covers, the colder portion of fluid follows the line traced by the colder walls. as a consequence, a significant change in convection is observed and strongest flow pattern is achieved for ra=105. in figure 3 shows the effect of varying rayleigh number on iso-surfaces of temperature inside the enclosure. at ra=103, convection is not significant at all and the iso-surfaces of temperature are parallel to each other and are densely distributed near the bottom heated absorber. the parallel nature of iso-surfaces of temperature shows the domination of conductive heat transfer. however, plumelike distribution on temperature field is observed at ra=104 due to the starting of convection regime. iso-surfaces are seen to be densely packed along the boundaries showing that convection is very strong in those regions. at the corners these iso-surfaces are more and more densely packed showing the presence of a strong conduction heat transfer. the temperature distribution assumes a distorted shape near the engineering, technology & applied science research vol. 8, no. 2, 2018, 2651-2655 2653 www.etasr.com aich: 3d buoyancy induced heat transfer in triangular solar collector having a corrugated … middle and the top due to increasing of effectiveness of convection heat transfer. strong convection occurred for ra=105 and stronger plumelike distribution is observed. (a) (b) (c) fig. 2. particles trajectory for different ra values: (a) 103, (b) 104, (c) 105 the velocity magnitude of the fluid flow inside the enclosure is presented in figure 4 for different rayleigh number values. at the lowest value of this parameter and due to the domination of conduction regime of heat transfer, the fluid is almost at rest in the enclosure with negligible motion at the middle far from boundaries. by increasing ra, the heated and rising fluid leads to formation of the thermal boundary layer at the upper part of the inclined walls and there is a strong convective current in the middle of the cavity while corners remain as stagnant zones. this result supports our observations made during the discussion on the particles trajectory and temperature distribution. the highest magnitude of velocity occurred for ra=105 and a very strong double plumelike distribution is observed due to increasing of effectiveness of convection heat transfer and fluid flow at the middle of the collector. it is noticed that the heat transfer rate inside the enclosure is measured in terms of the overall nusselt number. figure 5 shows the variation of the average nusselt number with the rayleigh number ra. it is obvious that for low values of ra and when the conduction is the dominant mode of heat transfer, this variation is insignificant. however, for ra>104 heat removal from the heated corrugated absorber increases by means of increasing ra and the maximum rate is obtained for the highest ra as expected. the corrugated form of the bottom of the collector is found to enhance heat transfer due to increasing of heated surface when compared with simple plane wall. (a) (b) (c) fig. 3. iso-surfaces of temperature for different ra values: a) 103, (b) 104, (c) 105 iv. conclusion three-dimensional numerical investigation has been carried out to simulate buoyancy induced heat transfer and fluid flow inside a triangular enclosure with corrugated bottom wall. results are presented for different values of rayleigh number which is the main parameter of the study. some of the drawn conclusions are:  for lower values of ra conduction is the primary mode of heat transfer and the flow strength is very low due to poor convective heat transfer.  flow strength increases with the increasing of ra and a strong convective current is noticeable in the middle of the enclosure far from boundaries.  the flow structure and the magnitude of velocity are sensitive to the value of ra.  overall nusselt number at the heated surface increases with increasing value of ra indicating a maximum heat transfer rate at ra=105.  even at high ra the symmetry of the flow is not broken contrary to results of many previous studies in 2d cases. further study may include the effect of filling the enclosure with nanoparticles in water based fluid under the effect of magnetic field. engineering, technology & applied science research vol. 8, no. 2, 2018, 2651-2655 2654 www.etasr.com aich: 3d buoyancy induced heat transfer in triangular solar collector having a corrugated … (a) (b) (c) fig. 4. velocity magnitude for different ra values: a) 103, (b) 104, (c) 105 fig. 5. variation of mean nusselt number on hot corrugated wall with rayleigh number. acknowledgment author would like to express his deepest gratitude to dr. ali amri and his institution, “the english polisher” for their meticulous and painstaking review of the english text of the present paper. references [1] g. de vahl davis, “natural convection in a square cavity: a benchmark numerical solution”, international journal for numerical methods in fluids, vol. 3, no. 3, pp. 249–264, 1983 [2] t. fusegi, j. m. hyun, k. kuwahara, b. farouk, “a numerical study of three dimensional natural convection in a differentially heated cubical enclosure”, international journal of heat and mass transfer, vol. 34, no. 6, pp. 1543–1557, 1991 [3] s. c. tzeng, j. h. liou, r. y. jou, “numerical simulation-aided parametric analysis of natural convection in a roof of triangular enclosures”, heat transfer engineering, vol. 26, no. 8, pp. 69-79, 2005 [4] a. omri, j. orfi, s. ben nasrallah, “natural convection effects in solar stills”, desalination, vol. 183, no. 1-3, pp. 173–178, 2005 [5] r. d. flack, “the experimental measurement of natural convection heat transfer in triangular enclosures heated or cooled from bellow”, journal of heat transfer, vol. 102, no. 4, pp. 770–772, 1980 [6] d. poulikakos, a. bejan, “natural convection experiments in a triangular enclosure”, journal of heat transfer, vol. 105, no. 3, pp. 652–655, 1983 [7] d. poulikakos, a. bejan, “the fluid dynamics of an attic space”, journal of fluid mechanics, vol. 131, pp. 251–269, 1983 [8] h. asan, l. namli, “numerical simulation of buoyant flow in a roof of triangular cross-section under winter day boundary conditions”, energy and buildings, vol. 33, no. 7, pp. 753–757, 2001 [9] h. asan, l. namli, “laminar natural convection in a pitched roof of triangular cross-section: summer day boundary conditions”, energy and buildings, vol. 33, no. 1, pp. 69–73, 2000 [10] h. salmun, “convection patterns in a triangular domain”, international journal of heat and mass transfer, vol. 38, no. 2, pp. 351–362, 1995 [11] y. varol, a. koca, h. f. oztop, “natural convection in a triangle enclosure with flush mounted heater on the wall”, international communications in heat and mass transfer, vol. 33, no. 8, pp. 951– 958, 2006 [12] i. hajri, a. omri, s. ben nasrallah, “a numerical model for the simulation of double-diffusive natural convection in a triangular cavity using equal order and control volume based on the finite element method”, desalination, vol. 206, no. 1-3, pp. 579–588, 2007 [13] e. fuad kent, e. asmaz, s. ozerbay, “laminar natural convection in right triangular enclosures”, heat and mass transfer, vol. 44, pp. 187– 200, 2007 [14] m. m. rahman, h. f. oztop, a. ahsan, m. a. kalam, y. varol, “double-diffusive natural convection in a triangular solar collector”, international communications in heat and mass transfer, vol. 39, no. 2, pp. 264–269, 2012 [15] e. fuad kent, “laminar natural convection in isosceles triangular roofs in wintertime conditions”, heat transfer engineering, vol. 31, no. 13, pp. 1068–1081, 2010 [16] e. fuad kent, “numerical analysis of laminar natural convection in isosceles triangular enclosures”, proceedings of the institution of mechanical engineers, part c: journal of mechanical engineering science, vol. 223, no. 2, pp. 1157–1169, 2009 [17] e. h. ridouane, a. campo, “formation of a pitchfork bifurcation in thermal convection flow inside an isosceles triangular cavity”, physics of fluids, vol. 18, no. 7, p. 074102, 2006 [18] e. h. ridouane, a. campo, m. hasnaoui, “benefits derivable from connecting the bottom and top walls of attic enclosures with insulated vertical side walls”, numerical heat transfer, part a, vol. 49, no. 2, pp. 175–193, 2006 [19] e. fuad kent, “numerical analysis of laminar natural convection in isosceles triangular enclosures for cold base and hot inclined walls”, mechanics research communications, vol. 36, no. 4, pp. 497–508, 2009 engineering, technology & applied science research vol. 8, no. 2, 2018, 2651-2655 2655 www.etasr.com aich: 3d buoyancy induced heat transfer in triangular solar collector having a corrugated … [20] y. varol, h. f. oztop, i. pop, “influence of inclination angle on buoyancy-driven convection in triangular enclosure filled with a fluidsaturated porous medium”, heat and mass transfer, vol. 44, pp. 617– 624, 2008 [21] e. h. ridouane, a. campo, m. mc garry, “numerical computation of buoyant airflows confined to attic spaces under opposing hot and cold wall conditions”, international journal of thermal sciences, vol. 44, no. 10, pp. 944–952, 2005 [22] e. h. ridouane, a. campo, “heightened thermal convection as a result of splitting a square cavity diagonally in half”, journal of electronic packaging, vol. 128, no. 3, pp. 251–258, 2006 [23] t. basak, s. roy, c. thirumalesha, “finite element analysis of natural convection in a triangular enclosure: effects of various thermal boundary conditions”, chemical engineering science, vol. 62, no. 9, pp. 2623– 2640, 2007 [24] s. roy, t. basak, c. thirumalesha, c. murali krishna, “finite element simulation on natural convection flow in a triangular enclosure due to uniform and non-uniform bottom heating”, journal of heat transfer, vol. 130, no. 3, p. 032501, 2008 [25] e. h. ridouane, a. campo, j. y. chang, “natural convection patterns in right-angled triangular cavities with heated vertical sides and cooled hypotenuses”, journal of heat transfer , vol. 127, no. 10, pp. 1181– 1186, 2005 [26] l. kolsi, a. abidi, m. n. borjini, n. daous, h. ben aissia, “effect of an external magnetic field on the 3-d un steady natural convection in a cubical enclosure”, numerical heat transfer, part a, vol. 51, no. 10, pp. 1003–1021, 2007 [27] s. v. patankar, numerical heat transfer and fluid flow, crc press, 1981 microsoft word etasr_v12_n1_pp8151-8156 engineering, technology & applied science research vol. 12, no. 1, 2022, 8151-8156 8151 www.etasr.com iliass et al.: dft investigation of the structual and optoelectronic properties of alkali metal hydrides … dft investigation of the structual and optoelectronic properties of alkali metal hydrides mh (m=li, na) taieb iliass materials science and informatics laboratory faculty of science, university of djelfa djelfa, algeria iliasstaieb@yahoo.com hamza ziani materials science and informatics laboratory faculty of science, university of djelfa djelfa, algeria hamza_ziani@yahoo.com ahmed gueddim materials science and informatics laboratory faculty of science, university of djelfa djelfa, algeria ahmed_gueddim@yahoo.fr a. djamel guibadj laboratory of physical chemistry of materials faculty of science, university of laghouat laghouat, algeria d.guibadj@gmail.com abstract-this paper presents ab initio calculations within the density functional theory (dft) for the structural and optoelectronic properties of the alkali metal hydrides lih and nah in rocksalt structure (b1). this study used the generalized gradient approximation (gga) of wu-cohen to consider the electronic exchange and correlation interactions. in addition, the tran-blaha modified becke-johnson exchange potential was used with the gga approach (gga-tbmbj) to calculate the band structure with high accuracy. the structural properties, namely the lattice parameter, the bulk modulus, and the pressure derivative of the bulk modulus were determined and found to be generally in good agreement with other research findings. furthermore, the energy band gaps, the density of states (dos), the static and high-frequency dielectric constant, along the refractive index were addressed and analyzed. these results could be useful for hydrogen storage purposes. keywords-hydrogen storage; lih; nah; ab initio; mbj-gga i. introduction the energy transition is necessary in order to meet the increasing energy needs and cope with global warming. the main drivers for this transition are the adoption of responsible consumer practices and the increased use of renewable sources of energy. this transition also requires efficient processes for production, conversion, storage, and transport of energy. many scientific and technological challenges exist in each of those axes. as the problem of suitable materials is ubiquitous, materials science is at the heart of this research. the challenge is to obtain and optimize materials having specific properties to fulfill the requirements of renewable energy. hydrogen is a transportable, storable, and convertible energy medium and has great potential to become the ultimate solution that combines energy security, resource availability, and environmental compatibility. however, the greatest challenge in the development of hydrogen-based technologies is how to store hydrogen safely, effectively, and economically [1-5]. depending on the physical state of hydrogen, three different routes are currently used for its storage: compressed gas, liquid, and solid-state. hydrogen stored as a solid-state material has potential advantages in terms of volumetric density and safety, compared to compressed gas or liquid [611]. in the case of solid-state, the bonds between hydrogen and the host material can be of different kinds and strengths. both van der waals weak and chemisorptive strong bonds can be involved [11]. it is possible to increase the density of hydrogen, as it is packed with h-h distances up to 170kg/m 3 in many hydride-type materials. this value is higher than the density of hydrogen in a liquid state [12]. numerous studies have been conducted to determine and design the most suitable materials with convenient gravimetric and volumetric densities for hydrogen storage. these materials span a large class, from conventional metal hydrides to complex hydrides, microporous materials, and clathrate hydrates. this study addresses some fundamental properties of lih and nah using the first principles calculations to utilize the density functional theory (dft). such calculations are of great interest before the synthesis procedure, which is a very time-consuming effort. the structural properties along with their electronic and optical features are explored and analyzed for the materials under load in the rock-salt (b1) structure. the comparison with experimental and theoretical data, when possible, shows satisfactory agreement in general. ii. computational methodology this study used the full potential linearized augmented plane wave (fp-lapw) method, based on the dft [13] that constitutes the core of the wien2k code [14]. exchangecorrelation energy was calculated using the wc-gga [15] when dealing with structural properties. the exchangecorrelation functional mbj [16] was applied to determine the electronic and other optical characteristics. in the fp-lapw corresponding author: ahmed gueddim engineering, technology & applied science research vol. 12, no. 1, 2022, 8151-8156 8152 www.etasr.com iliass et al.: dft investigation of the structual and optoelectronic properties of alkali metal hydrides … method, the wave function and the potential are developed as sums of spherical harmonic functions inside non-overlapping spheres, surrounding the atomic sites (muffin-tin spheres), and a set of plane waves in the interstitial region. a plane wave cutoff of rmt.kmax=7 (where rmt is the smallest muffin-tin radius in the unit cell) was used. rmt’s were chosen to be 1.7, 2.1, and 2.5a.u. for h, li, and na, respectively. the k-sampling over the brillouin zone was performed up to a 13×13×13 monkorstpack [17-20] mesh for both considered materials. the number of k-points and the plane wave cut-off energy varied in such a manner as to obtain total energy convergence. the convergence of these self-consistent calculations was considered to be obtained within an error of 10 −5 ry on the total energy of the crystals studied. iii. results and discussion the total energy was calculated from the wc-gga approach as a function of the volume of lih and nah in the rocksalt structure. at first, the total energy for some selected lattice parameter values was calculated. the results obtained were then written according to murnaghan’s equation of state [21]. this allowed determining the equilibrium lattice parameter a0, the zero pressure bulk modulus b0, and the firstorder pressure derivative of the bulk modulus b ́ for the ground-state. these results are summarized in table i with experimental and theoretical data from other researches for comparison. the wc-gga lattice parameter in this study is generally closer to the experiment than those of the gga or lda approaches [27-29]. the a0, calculated for both lih and nah from wc-gga, agrees quite well with those reported in [22, 23]. the same remark can be drawn for the bulk modulus b0, which agrees within a few percent with other experimental or theoretical values [22, 24-26]. table i. a0, b0, and b' for lih and nah in b1 structure using gga and wc-gga along with the values reported in the literature. material ��(å) �� (gpa) �′ lih 3.9934 a 4.0153 b 4.012 c 3.92 d 38.1840 a 41.1635 b 36.228 c 36.60 e 34.7 f 3.9913 a 3.0976 b 3.51 c 3.40 e nah 4.8051 a 4.8347 b 4.833 c 4.775 d 25.9068 a 23.0855 b 23.546 c 19.40 f 22.9 g 4.1001 a 6.560 b 3.90 c 4.40 f a. present calculation using wc-gga, b. present calculation using gga, c. [22], d. [23], e. [24, f. experimental value quoted in [25], g. [26] the formation energy is an important thermodynamic quantity that permits one to characterize and classify hydrogen storage materials. formation energy is defined as the difference between the sum of the total energies of the products and the reactants: ∆� � ∑ � � ����� �� � ∑ � ����� �� �� (1) the formation of mh (m=li, na) materials from their constituting elements is given as: � � � → �� (2) the formation energy can be written as: ∆� � ������� � ������ � ������ (3) the total energies of lih, nah, li, na, and h were calculated. the formation energies of lih and nah were found to be -88.91kj.molh2 and -109.054kj.molh2, respectively. the desorption temperature of hydrides was estimated using the standard gibbs energy: �� � �� � �� (4) where ∆h and ∆s are the enthalpy of formation and the standard entropy of the reaction respectively. at equilibrium, the standard gibbs energy ∆g is zero. therefore, the desorption temperature can be expressed as: � � � !"!# (5) the calculated desorption temperature was 680.33k for lih and 834.38k for nah. the gravimetric hydrogen storage capacity can be determined as: $%� % � ' ( ) *+ ,) ,)-./0()*+,) 1 1004 (6) where h/m is the hydrogen to material atom ratio, mh is the molar mass of h, and mhost is the molar mass of the host material. the hydrogen storage capacities calculated for lih and nah were 22.5% and 8.06%, respectively. (a) (b) fig. 1. electron band structure calculated using tb-mbj-gga along high symmetry directions for (a) lih and (b) nah. engineering, technology & applied science research vol. 12, no. 1, 2022, 8151-8156 8153 www.etasr.com iliass et al.: dft investigation of the structual and optoelectronic properties of alkali metal hydrides … the electronic and optical properties of the materials are classically described by their electronic band structure [30-33]. accurate knowledge of the band parameters of a given material provides precious information regarding its synthesis and devices fabrication [34-37]. the results of using the ggatbmbj approach to compute the electronic band structure of rocksalt lih and nah are plotted in figure 1. it should be noted that, from a qualitative point of view, the same picture is observed for all the reported band structures. the fermi level energy does not cross any energy bands for all questioned crystal materials. therefore, lih and nah in the rocksalt structure can be considered respectively as semiconductor and insulating materials. according to figure 1, the valence band maxima and the conduction band minima are located at the same high symmetry point x in the brillouin zone. the band gaps of these materials are direct in nature, agreeing with the results of [22]. the fundamental difference between the band structures arises from the magnitude of their fundamental energy band gap, which differs from one band structure to another. the calculated fundamental direct band gap (x-x) for the rocksalt lih and nah were 3.05 and 3.65ev respectively. (a) (b) fig. 2. density of states (dos) calculated using tb-mbj-gga for (a) lih and (b) nah. the properties of semiconductors can be related to the electron configuration shown by the molecules. the densities of states (dos), total and projected, were computed for the rocksalt lih and nah using the tb-mbj approach to show how the electrons are distributed on different orbitals. the results are shown in figure 2. an inspection of lih (figure 2(a)) shows that the first region of the dos is the most tightly bound energy band. the contribution of the li-s electrons is predominant for the energy bands near the fermi level of the lih crystal. hence, the li-s electrons are useful for the conductibility of the crystal of interest. the dos at these regions consist essentially of li-s and li-p states. the contribution of the h-s states was remarkably weak. figure 2a also shows that the bonding peaks ranged from about -5 to 0ev. these peaks were mainly formed by the li-s state. for nah (figure 2b), it is observed that the intensity of the h-s orbitals in the valence band constitutes the dominant contribution to the dos. the na-p and na-s states have a minor contribution to the dos compared to the h-s orbitals. the bonding peaks ranged from about -3.75 to 0ev. moreover, the optical properties, such as the dielectric function, were examined. the computed optical response functions, real ε1(ε) and imaginary ε2(ε), for lih and nah are displayed in figures 3 and 4 respectively, where e is the photon energy. the main peak of the real parts of lih and nah occurs around e=2.94ev and e=4.58ev respectively. fig. 3. real part of the dielectric function calculated using tb-mbj-gga. fig. 4. imaginary part of the dielectric function calculated using tb-mbjgga. based on the optical transition mechanisms, the optical spectrum of a given crystal is usually classified into several photon energy regions [38]. in general, three spectral regions are distinguished. the first one is known as the reststrahlen region and is characterized by the interactions between the radiation field and the fundamental lattice vibrations [38]. for very low energies, the real part of the dielectric function tends to the static or low-energy dielectric constant ε0. the ε0 for lih and nah materials were determined as: engineering, technology & applied science research vol. 12, no. 1, 2022, 8151-8156 8154 www.etasr.com iliass et al.: dft investigation of the structual and optoelectronic properties of alkali metal hydrides … 56�78�� � 4.55 (7) 56�<��� � 3.21 (8) regarding the ε0 of lih, this result is different from the quoted in [39]. to the best of our knowledge, no data regarding ε0 for nah has been reported so far. thus, this result could serve as a reference. the optical constant that relates the socalled reststrahlen region to the near-infrared region is commonly known as the high-frequency dielectric constant ε∞. for these materials, the calculations gave: 5?�78�� � 7.84 (9) 5?�<��� � 10.82 (10) the calculated ε∞ for lih shows reasonable agreement with the one reported in [34]. for nah, the calculation in [40] gave a value of 3.71, which is too low compared to this result. the general shape of ε1 was expected for a harmonic oscillator with resonant frequencies of about 8.39 and 5.71ev for lih and nah, respectively. it is generally accepted that the resonance frequency is a fundamental property of a given material. this quantity allows the expression of the average energy that separates the levels of bonding and anti-bonding [30]. the absorption for the imaginary part of the dielectric function starts at about 2.04 and 3.09ev for lih and nah, respectively. similar behavior was reported in [41, 42] for znte1-xox alloys. knowledge of the refractive index of semiconductors in the energy range below or near the fundamental absorption edge is mostly interesting in device design [43-48]. this refractive device (n) can be easily derived from the dielectric function ε(ε). the n values obtained for lih and nah were: ��78�� � 2.8 (11) ��<��� � 3.29 (12) the n value for lih is in reasonable agreement with the value of 1.47 reported in [49]. the calculated spectral dependence of n(e) for lih and nah is shown in figure 5. fig. 5. refractive index calculated using tb-mbj-gga for lih and nah. from this spectrum, it can be noted that clear peaks are present. these peaks are due to the excitonic transitions at the e0 edges. excitonic effects are believed to be responsible for the enhancement of the oscillator strength at the critical points m0 and m1 [50]. since the total strength of the oscillator is proportional to the number of valence electrons, it should be ''conserved'' in some way. this means that as the oscillator strength at the critical points m0 and m1 is enhanced due to excitonic interactions, some losses occur elsewhere to achieve strength conservation. the strongest peaks in the n(e) spectra can be explained as the result of the 2d exciton transition (e1). iv. conclusion this study examined the structural, electronic, and optical properties of the alkali metal hydrides lih and nah, using the fp-lapw technique within dft in the wc-gga for structural properties and tb-mbj-gga for electronic and optical features. the crystal structure of both investigated materials investigated was rocksalt (b1). results regarding the lattice constant, bulk modulus, and pressure derivative for lih and nah were reported and compared, where possible, with the available experimental and theoretical data. in general, a reasonably good agreement was found between the results of this study and the literature. the electron band structure, the density of states, and the dependence of the real and imaginary parts of the dielectric function along the refractive index of the materials under load were also studied and analyzed. the results derived from the present study could be useful for hydrogen storage purposes. references [1] l. schlapbach and a. züttel, 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[50] p. y. yu and m. cardona, fundamentals of semiconductors. berlin, heidelberg, germany: springer, 2010. engineering, technology & applied science research vol. 7, no. 6, 2017, 2160-2166 2160 www.etasr.com yilmaz and turan: fahamecv1:a low cost automated metaphase detection system fahamecv1:a low cost automated metaphase detection system hakan yilmaz computer programming department tobb tech. sciences vocational school karabuk university karabuk, turkey hakanyilmaz@karabuk.edu.tr m. kamil turan biology and genetics department faculty of medicine karabuk university karabuk, turkey kamilturan@karabuk.edu.tr abstract—in this study, fahamecv1 is introduced and investigated as a low cost and high accuracy solution for metaphase detection. chromosome analysis is performed at the metaphase stage and high accuracy and automated detection of the metaphase stage plays an active role in decreasing analysis time. fahamecv1 includes an optic microscope, a motorized microscope stage, an electronic control unit, a camera, a computer and a software application. printing components of the motorized microscope stage (using a 3d printer) is of the main reasons for cost reduction. operations such as stepper motor calibration, are detection, focusing, scanning, metaphase detection and saving of coordinates into a database are automatically performed. to detect metaphases, a filter named metafilter is developed and applied. average scanning time per preparate is 77 sec/cm2. true positive rate is calculated as 95.1%, true negative rate is calculated as 99.0% and accuracy is calculated as 98.8%. keywords-automation; metaphase detection system; focus; image processing; 3d printing; fahamecv1 i. introduction analysis of metaphase plate images by a computer aided application is a main method used in hospitals and laboratories. in this stage, accuracy plays an important role. automatic metaphase detection and retrieval with high objective resolution for image analysis is quite beneficial [1]. cytogenetic analysis includes two stages: detection of metaphase and karyotype analysis [2]. it is essential that all chromosomes are monitored and classified with high accuracy. these monitoring and classification processes are usually performed by clinical experts. this situation causes humandriven mistakes, wrong diagnosis and loss of time and thus automated systems are bound to be employed. metaphase detection system is a system which automatically scans, detects and monitors metaphases [3]. a metaphase detection system generally includes a camera attached to the ocular piece and a computer controlled motorized microscope. in addition to this, artifacts of other cells and paint residues exist. removing these artifacts and residues is the first step of a high qualified analysis [4]. the improving of diagnostic accuracy and consistency has been studied in [5, 6]. researchers have developed many systems to detect metaphases [1-3, 7-11]. authors in [1] have developed a system which detects metaphases painted with fish and uses a fluorescent light source. authors in [2] have released a metaphase detection system named metafer2 which registers x-y-z coordinates of metaphases. authors in [3] have produced a low-cost system to detect metaphases using morphological operations. authors in [4] have utilized artificial neural network to identify metaphases and nuclei. in [10], author used a trained classifier to separate metaphases with non-metaphases. authors in [12] have applied and test computer aided methods such as classical statistical methods, artificial neural networks, knowledge based fuzzy logic systems. authors in [13] tested the performance of four commercial systems. there are two groups considered in metaphases detection systems assessment, the true positives (tp) and true negatives (tn). while tp stands for areas including metaphases, tn stands for areas not including metaphases. under ideal conditions, these two groups are independent. however, independence is inattentive at metaphase detection systems since object detection is a complicated process. consequently, results obtained by applications are evaluated by a clinical expert [14]. in this study, a metaphase detection system named fahamecv1 consisting of hardware and software has been implemented. fahamecv1 is low cost and modular, can be connected with different microscopes, provides high accuracy and high scan speed. most components of fahamecv1 are printed by a 3d printer and can be reprinted and easily modified. fahamecv1 can be connected with a manual microscope in a fast manner. all components used in fahamecv1 are composed of single, independent and easily provided parts. in addition to hardware properties of fahamecv1, an application has been developed to selfcalibrate, perform focus, detect metaphases and save coordinates of detected metaphases in a database. a filter named metafilter was developed in this study and is applied to detect metaphases. fahamecv1 excels among other systems because of the easy use of hardware and software, low cost, high scan speed and high accuracy. engineering, technology & applied science research vol. 7, no. 6, 2017, 2160-2166 2161 www.etasr.com yilmaz and turan: fahamecv1:a low cost automated metaphase detection system ii. system materials fahamecv1 is composed of an optic microscope, a motorized microscope stage, an electronic control unit, a camera, a computer and an application. figure 1 depicts an overview of the system. fig. 1. overview of fahamecv1. a. camera a digiretina16 usb camera produced by tucsen is used to obtain images from the microscope. images are captured using 25 frames per second (fps), 4 megapixel (mp) resolutions, auto white balance and auto exposure time. b. microscope the produced stage is connected to binocular soif optic microscope. this microscope is selected because of its low cost. 4x, 10x, 40x and 100x objectives exist on the microscope and 10x ocular is attached. it is a manual microscope which has a halogen light source, focus and coaxial screws. the produced microscope stage is connected to the microscope by removing its original microscope stage. halogen light source is replaced with led light source since halogen light source brings about noises on images. 10x objective is preferred as an active objective to scan. 0.45x connection mount is used to attach camera with ocular. c. electronic control unit and computer an electronic control unit is located in a metal box which has a 12 cm diameter fan. a socket structure is used. hence, it is assured that fahamecv1 is easily assemblied and disassemblied in case of failure or transport. a power supply with output properties of 12v and 5a is selected. a4988 stepper motor drivers are selected to control stepper motors. arduino mega 2560 is selected as a main control card. commands of the control card are sent by the application. “#” symbol is put between the numbers of the activated stepper motor, count of steps, delay time for steps and direction of rotation. the “$” symbol is put at the end of the command line. hence, the command shown in figure 2 is sent to the control card as a single command. fig. 2. the command line sent to the control card. the used computer has an intel i7 2.50 ghz cpu and 8 gb ram. c and c# programming languages are preferred for the developing of the application. c programming language is used in arduino ide and c# programming language is used in microsoft visual studio 2015. d. produced motorized microscope stage the automated motorized microscope stage produced in this study is composed of stepper motors, ball screws and nuts, miniature rails and runner blocks, end-stop modules, carrier component, main table, preparates carrier and connection materials. the main table is produced using aluminum materials by laser cutting. the carrier component used at the bottom to provide connection of motorized microscope stage to the microscope and the other plastic parts are produced using pla materials by the 3d printer. 12 mm diameter ball screws, 4mm nuts and the stepper motors whose types are nema17 and 200 steps for a rotation are used. heights of the miniature rails and the runner blocks which provide the main table with slipping on y axis are 10 mm. limited space between the microscope objective and the light source is effectively used. the motorized microscope stage height is 26 mm (figure 3). as a result of this, enough space for focus is created. single and triple preparates can be scanned. the end-stop modules exist on each axis to identify home location. the modules are selected as mechanic switches. the focus screw and shaft of the stepper motors are composed by a coupler (printed on 3d printer) to make z axis move. fig. 3. overview of the 3d drawing of the produced motorized microscope stage. e. preparates the preparates used in this study are not highly qualified for analysis, idle and need to be reprepared. images are engineering, technology & applied science research vol. 7, no. 6, 2017, 2160-2166 2162 www.etasr.com yilmaz and turan: fahamecv1:a low cost automated metaphase detection system captured at 2304x1728 resolutions using the preparates. size of the preparates is 76x26 mm. the painted areas whose widths on the preparates are 28 mm are used for patient information and brand labels. the 48x26 mm2 areas on the preparates are transparent. 36x16 mm2 areas on the preparates are accepted as active scanning areas. the remaining areas are accepted as inactive areas and are not scanned because metaphases whose chromosomes are either rarely or excessively spread exist on inactive areas. iii. methods the application was developed at four stages: scanning preparation, focus, detection of metaphases and saving coordinates of metaphases. the application automatically brings preparates to the initial point, communicates with the electronic control unit, calibrates axis, performs focus, detects metaphases and saves coordinates of metaphases in a database. a scanning name is the only one necessary parameter needed for one to start scanning. during scanning, metaphase images and parameters such as the number of detected metaphases, metaphase coordinates and frame scanning time are monitorized synchronously. one of the interfaces provides access to enter properties as: full step number for a rotation of the stepper motors, micro step levels of the stepper motor drivers and size of the ball screw pitch. a. scanning preparation the application sets a rectangle as the current scanning area. the rectangle width is 1.2 mm on x axis and the rectangle height is 0.9 mm on y axis. to scan preparates, it is needed to scan 30 different image areas on x axis and 18 different image areas on y axis. hence, the preparates are split to a grid which contains 540 cells of 18 rows and 30 columns. the application detects metaphases by scanning each cell. an end-stop module which identifies home location on each axis is used. the application sets all coordinates to zero by moving to home location before each scanning. therefore, fahamecv1 calibrates itself automatically. b. converting the stepper motor steps as metric units a specified step number is necessary for a full rotation. although the stepper motors take 200 full steps for a rotation, the stepper motor drivers provide 3200 steps for a rotation. this rotation movement is converted to linear movement by the ball screws and can be used with different pitches. however, value of steps for a rotation is changed after either the stepper motors, the stepper motor drivers or the ball screws is replaced. thus, it is needed to calculate metric changes of the preparate on x-y-z axis. micro step level as m, full steps for a rotation as fs, distance as d and ball screw pitch as sp are used to obtain the equation which finds how many steps should be taken by the stepper motor (1). this equation explains how the application controls the stepper motors. this control is performed until the stepper motor moves to 0.01 mm on x-y axis and 0.001 mm on z axis. steps = (m x fs x d) / sp (1) c. focus since blurred images can directly affect diagnostic accuracy, it is critical to obtain focused high-resolution microscopic images efficiently. thus, an autofocus technique is required for high efficiency microscopic system in clinical practice [15]. capturing images and detecting metaphases with high accuracy depends on performing proper focusing. in the application, there are two focus functions: one-way focus and two-way focus. there are also first focus, main focus and short focus which are components of one-way and two-way focuses. fahamecv1 automatically decides which focus component should be applied. first focus and main focus use one-way focus function. short focus uses two-way focus function. first focus is applied at the beginning of scanning. short focus is applied once at every 10 cells. main focus is applied when short focus fails, because short focus runs at a limited distance while main focus runs from home location of z axis. all focus components are applied automatically by fahamecv1. histograms of captured images are investigated at red, green, blue and intensity bands. it is proved that the best result is obtained at intensity band when the thresholding method is applied (figure 4). focus value is calculated when a comparison between all pixel counts and white pixel counts is made. focus position is identified when the focus value is calculated as maximum. when main focus is performed, z axis is located at home location and the stepper motor starts rotating counter-clockwise. the focus value is calculated at each 0.002 mm. when a new focus value is calculated, it is compared with the current focus value. if the new focus value is higher than the current focus value, the new focus value is replaced with the current focus value. when the new focus value is lower than the current focus value, calculation of focus value is stopped. as a result, the stepper motor rotates clockwise and is located at maximum focus position. hence, necessary focus process is completed before fahamecv1 starts scanning (figure 5). the shape of the preparate carrier can be deformed due to the ambient temperature changes because materials used as preparate carriers are produced using pla materials. in this case, short focus is necessary to be applied. while short focus is applied, the stepper motor rotates until obtaining an image and a first local focus value is calculated as maximum of this period. after that, the stepper motor rotates by changing direction until obtaining a second image and a second local focus value is calculated as maximum of the second period. the two local maximum focus values are compared and the higher one is identified as a short focus value. z axis is located at short focus position. therefore, the best qualified image is obtained (figure 6). d. detection of metaphases after focus is performed, fahamecv1 starts scanning cells. the images are converted to intensity band and contrast stretching method is applied. bradley local thresholding method is applied on the images [16]. sobel edge detection method, erosion and dilation processes are applied. as a result of that, metaphases and non-metaphases stay on the images. metafilter is applied to detect metaphases and eliminate nonmetaphases (figures 7-8). engineering, technology & applied science research vol. 7, no. 6, 2017, 2160-2166 2163 www.etasr.com yilmaz and turan: fahamecv1:a low cost automated metaphase detection system fig. 4. original image, b. image view of r band and its histogram graph, c. image view of g band and its histogram graph, d. image view of b band and its histogram graph, e. image view of intensity band and its histogram graph. fig. 5. main focus graph(upper), overview of main focus (lower). fig. 6. short focus graph. fig. 7. a. original image, b. contrast stretching and grayscale, c. bradley local thresholding, d. sobel, e. morphological operations, f. metafilter. e. saving coordinates of metaphases center coordinates of detected metaphases are calculated and saved in a database. relocation can be applied for each detected metaphase whose coordinates are saved. thus, preparations for chromosome scanning with 100x objective are to be completed. iv. results and discussion this study is evaluated according to customizability, scanning time, cost, loss of relocation and accuracy. the fact that fahamecv1 can easily connect and disconnect with other microscopes enhances fahamecv1’s ease of use. fahamecv1 is faster than noncommercial systems based on scanning time per preparate. it is presented that fahamecv1 is quite cheap when the camera, the microscope and the computer are not considered. a. customizability the stepper motors, the stepper motor drivers and the screw balls can be changed in case of failure. when the same materials cannot be found, different types of stepper motors, stepper motor drivers and screw balls can be used. by using one of the interfaces, properties of the different types of materials can be entered and saved. hence, fahamecv1 continues scanning without data loss. the fact that many components are specially printed by a 3d printer makes material supply easier. the connection of fahamecv1 with the manual microscope is performed by using four screws for carrier components and one screw for z axis. it is also possible that the microscope can be restored by removing the five screws. if fahamecv1 is requested to connect with another microscope, it can be done easily by suitable printed carrier components (figure 9). b. scanning time time interval is between 34 and 78 milliseconds per image during all image processing operations. the time interval is between 384 and 506 sec to perform scanning on active scanning areas (36x16 mm2). during scanning, focus is performed 54 times on average. the time passing while performing focus is included total scanning time. fahamecv1 needs 77 sec average time to scan per cm2. the average scanning speed of fahamecv1 is measured as 1.29 mm2/sec. engineering, technology & applied science research vol. 7, no. 6, 2017, 2160-2166 2164 www.etasr.com yilmaz and turan: fahamecv1:a low cost automated metaphase detection system fig. 8. the flow chart of metafilter. fig. 9. the carrier component. c. cost low cost materials are selected to produce fahamecv1. the expenditure was 600 dollars for the microscope, 1285 dollars for the camera, 285 dollars for the electronic control unit, 22 dollars for the filament used in 3d printer, 71 dollars for laser cutting and 28 dollars for other expenses. total expenditure was 2291 dollars including taxes (table i). d. loss of relocation the screw balls, the nuts, the miniature rails and the runner blocks used to produce the motorized microscope stages are generally preferred in industry area. therefore, loss of relocation occurs when measurements in micron level are performed. the effect of these measurements on 100 micron steps is measured and modeled with a microscope micrometer (figure 10). spearman, kendall tau and pearson correlation analysis are performed on obtained measurements. as a result of these analyses, coefficient of correlation is obtained as close to zero and p-values are very close to each other (table ii). table i. costs unit price all system camera, microscope, automatic motorized microscope stage automatic motorized microscope stage computer 700 + microscope 600 + + camera 1285 + + electronic control unit and automatic motorized microscope stage 285 + + + 3d printing 22 + + + laser cutting 71 + + + other 28 + + + total 2991 2291 406 all prices are in u. s. dollars fig. 10. modeling of measured relocationing values. table ii. table of correlations and p-values. test name correlation p-value spearman -0.060 0.52 kendall tau -0.046 0.51 pearson -0.096 0.34 when the measurements obtained on x and y axis are investigated at the time-series plot and scatter plot of x versus y, no correlated results are found. hence, the obtained errors of relocation are not systematic and increased. besides, it is seen that the obtained errors were realized randomly in a specific area (figure 11). e. accuracy a total of 3018 objects obtained as a result of scanned images and are randomly selected and evaluated by a cytogeneticist. 184 of 3018 objects are identified as metaphases by the application. 155 of 184 objects as metaphase and 29 of 184 objects as non-metaphase are marked by a cytogeneticist. true positive rate (tpr) is calculated as 95.1% and true negative rate (tnr) is calculated as 99.0%. positive predictive value (ppv) is calculated as 84.2%. negative predictive value (npv) is calculated as 99.7%. the fact that tnr, ppv and npv are quite high brings the application to the fore of detecting objects as a metaphase and a non-metaphase. engineering, technology & applied science research vol. 7, no. 6, 2017, 2160-2166 2165 www.etasr.com yilmaz and turan: fahamecv1:a low cost automated metaphase detection system accuracy is calculated as 98.8% and f1 score is calculated as 0.893 (table iii). fig. 11. time series plot of x and y(upper), scatter plot of x versus y (lower). table iii. confusion matrix of scanning results. total population= 3018 human (cytogeneticist) metaphase nonmetaphase fahamecv1 metaphase 155 29 nonmetaphase 8 2826 accuracy = 98.8% tpr, sensitivity= 95.1% tnr, specificity= 99.0% f1 score= 0.893 fdr=15.8% npv= 99.0% ppv= 95.1% fnr, miss rate= 4.9% fpr= 1.0% v. discussion the ball screws, the nuts, the miniature rails and the runner blocks used in fahamecv1 are selected from products used for solution of industrial type. the loss of relocation can be reduced by choosing more sensitive products. the scanning time obtained in fahamecv1 is compared with the scanning time in the literature in table iv. the accuracy obtained in fahamecv1 is compared with the literature in table v. the main reason why tpr is low in fahamecv1 is the obtaining of images using low-qualified preparates. paint artifacts, metaphases which cannot be spread and paint loss are considered to be the causes. in future versions, all fixed parts will be produced with a 3d printer instead of laser cutting materials. thus, the cost of fahamecv1 will be further reduced. the height and weight of the motorized microscope stage can be reduced by choosing thinner ball screws. the stepper motors can be replaced with smaller ones thus reducing the total weight and power consumption. vi. conclusion a low cost and high accuracy solution for metaphase detection is investigated in this paper. the proposed system, fahamecv1, is described and the various aspects of its operation are investigated and compared to other systems described in the literature. results show that fahamecv1 provides a fast, highly accurate and low cost solution. acknowledgment this work was supported by scientific research projects coordination unit of karabük university. project number: kbü-bap-15/2-dr-024 table iv. time comparison metaphase detection system scanning speed (mm2/sec) average time per preparate (sec) [1] 0.16 * [7] 0.18 * [3] 0.10 * [10] 1.50 * [9] 0.45 * [8] * 1500 [2] * 1050 fahamecv1 1.29 445 *: not reported table v. accuracy comparison metaphase detection system true positive rate (tprsensitivity) false positive rate (fpr) accuracy [10] * 20.0% 80.0% [17] 84.0% 17.0% * [7] * 14.0% * [1] * 9.3% * [14] 74.0% 6.0% 89.0% [9] * 5.0% * [11] * 3.0% * [4] 91.8% 2.9% * fahamecv1 95.1% 1.0% 98,8% *: not reported references [1] j. piper, m. poggensee, w. hill, r. jensen, l. ji, i. poole, m. stark, d. sudar, “automatic fluorescence metaphase finder speeds translocation scoring in fish painted chromosomes”, cytometry, vol. 16, no. 1, pp. 7–16, 1994 [2] r. huber, u. kulka, t. lorch, h. braselmann, m. bauchinger, “automated metaphase finding: an assessment of the efficiency of the metafer2 system in 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2014 [7] l. roy, v. durand, m. delbos, i. sorokine-durm, f. soussaline, p. voisin, “a new image analysis system for biological dosimetry by fluorescent in situ hybridization. step 1: metaphase finder and engineering, technology & applied science research vol. 7, no. 6, 2017, 2160-2166 2166 www.etasr.com yilmaz and turan: fahamecv1:a low cost automated metaphase detection system automatic metaphase acquisition validation”, journal of radiation research, vol. 42, no. 2, pp. 165–177, 2001 [8] k. odawara, k. yamamoto, h. kato, m. hara, k. shigefumi, f. kishida, a. yoshitake, i. nakatsuka, “a new semi-automated chromosome analysis system for in vitro chromosomal aberration tests”, mutation research/genetic toxicology and environmental mutagenesis, vol. 389, no. 2–3, pp. 207–212, 1997 [9] a. furukawa, “the project of another low-cost metaphase finder”, radiation protection dosimetry, vol. 172, no. 1–3, pp. 238–243, 2016 [10] k. r. castleman, “the psi automatic metaphase finder”, journal of 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“evaluations of auto-focusing methods under a microscopic imaging modality for metaphase chromosome image analysis”, analytical cellular pathology, vol. 36, no. 1-2, pp. 37–44, 2013 [16] d. bradley, g. roth, “adaptive thresholding using the integral image”, journal of graphics tools, vol. 12, no. 2, pp. 13–21, 2007 [17] g. corkidi, l. vega, j. márquez, e. rojas, p. ostrosky-wegman, “roughness feature of metaphase chromosome spreads and nuclei for automated cell proliferation analysis”, medical & biological engineering & computing, vol. 36, no. 6, pp. 679–685, 1998 engineering, technology & applied science research vol. 8, no. 1, 2018, 2493-2498 2493 www.etasr.com el-morsy et al.: effect of friction stir welding parameters on the microstructure and mechanical … effect of friction stir welding parameters on the microstructure and mechanical properties of aa2024-t4 aluminum alloy abdel-wahab el-morsy mohamed m. ghanem haitham bahaitham faculty of engineering, rabigh branch king abdulaziz university, saudi arabia and faculty of engineering, helwan university cairo, egypt central metallurgical research and development institute cairo, egypt faculty of engineering rabigh branch king abdulaziz university saudi arabia abstract—in this work, the effects of rotational and traverse speeds on the 1.5 mm butt joint performance of friction stir welded 2024-t4 aluminum alloy sheets have been investigated. five rotational speeds ranging from 560 to 1800 rpm and five traverse speeds ranging from 11 to 45 mm/min have been employed. the characterization of microstructure and the mechanical properties (tensile, microhardness, and bending) of the welded sheets have been studied. the results reveal that by varying the welding parameters, almost sound joints and high performance welded joints can be successfully produced at the rotational speeds of 900 rpm and 700 rpm and the traverse speed of 35 mm/min. the maximum welding performance of joints is found to be 86.3% with 900 rpm rotational speed and 35 mm/min traverse speed. the microhardness values along the cross-section of the joints show a dramatic drop in the stir zone where the lowest value reached is about 63% of the base metal due to the softening of the welded zone caused by the heat input during joining. keywords-friction stir welding; welding parameters; 2024-t4 aluminum alloy; mechanical properties i. introduction due to many outstanding characteristics of aluminum (al) and its alloys, such as excellent corrosion resistance, high strength-to-weight ratio and ease of fabrication, al-alloys are finding a wide range of application in aircrafts, ships, automobiles, storage facilities and heat exchangers building industries [1]. the utilization of al-alloys in such industries is highly affected by their weldability factor. in order to achieve maximum joint efficiency, the al-alloys weld joints should have exceptional levels of their mechanical properties while maintaining minimal levels of weld-defect density. the use of conventional fusion welding process in joining al-alloys, especially the high-strength and heat-treatable ones, is considered less efficient due to the high possibility of forming hot cracks, segregation, and porosities welding defects during the fusion and solidification phases of the process [2]. in addition, the traditional welding process often leads to deterioration of mechanical properties and degradation of corrosion resistance in the joint because of phase transformations and the dissolution of strengthening precipitates during the fusion welding process [3-4]. to eliminate the distortions, particularly in thin sheets, and the problems associated with the traditional fusion welding processes, friction stir welding (fsw) has been developed. as a solid state joining process, fsw is a promising and a viable welding technique that can produce high-quality, defect-free, and low-cost joints particularly in the joining of high-strength al-alloys such as highly alloyed 2xxx and 7xxx series [3, 5, 6]. in addition, fsw is considered to be the most remarkable and viable welding technique for several materials such as alalloys [2-8], mg-alloys [9-10], ti-alloys [11], ni-base alloys [12], cu-alloys [13], and steels [14, 15]. moreover, fsw has the possibility of creating dissimilar joints with excellent mechanical characteristics [16-17]. during fsw process, using an inappropriate level of welding parameters can cause defects in the joint and worsen its mechanical properties [18]. thus, it is very important to choose the optimum levels of these welding parameters in order to get a weld of appropriate quality. the present study addresses the effect of traverse and rotational speeds on the quality of al-alloys joints produced by fsw process through analyzing the microstructure and mechanical properties of 1.5 mm 2024-t4 aluminum alloy. the mechanical properties that have been explored include microhardness distributions, bending, and tensile strength of the welded joints. ii. experimental procedure to study the effects of rotational speed and traverse speed on the quality of friction stir butt welded joints of al-2024-t4 al-alloy, sheets with a thickness of 1.5 mm have been utilized. chemical composition and mechanical properties of these sheets are presented in table i. using sawing machines, the sheets have been cut into 90×150×1.5 mm3 strips. the fsw process has been conducted by a vertical milling machine equipped with a high-speed stirring tool, which moves perpendicular to the rolling direction. in table ii the tool geometry is illustrated along with the ranges of rotational speeds and traverse speeds applied in the fsw process. engineering, technology & applied science research vol. 8, no. 1, 2018, 2493-2498 2494 www.etasr.com el-morsy et al.: effect of friction stir welding parameters on the microstructure and mechanical … table i. chemical composition and mechanical properties of al-2024-t4 chemical composition si fe cu mn mg zn ti al 0.5 0.5 4.1 0.6 1.2 0.25 0.15 bal. mechanical properties hardness tensile strength yield stress 160 hv 417 mpa 276 mpa table ii. welding parameters and tool geometry rotational speed (rpm) traverse speed (mm/min) tool 560 35 cylindrical pin tool geometry 700 900 1400 1800 900 11 18 28 35 45 the joint performance has been determined by conducting optical microscopy and mechanical testing (microhardness, tensile and bend tests). the metallography samples for microstructural characterization have been taken perpendicular to the welding direction for each welded sheet. the samples have been etched using killer’s reagent base with the following chemical composition: 1.5 ml hcl, 2.5 ml hno3, 1 ml hf and 95 ml distilled water. after being immersed for few seconds in the etching solution, the samples have been water-washed and dried in order to have them checked by the optical microscope. the hardness variation across the stirred zones of the joints has been obtained by conducting the vickers microhardness test on the traverse cross section of fsw samples joints. the mechanical performance of the joints has been determined through tensile testing where the ultimate tensile strength, the yield stress, and the percentage of elongation of several sets of specimens have been recorded and compared with those obtained from the base metal (bm) specimens. the specimens’ sets have been prepared according to astm e8m-13a standard [19] where each set contains three specimens made by the predetermined settings of rotational and traverse speeds considered in the study. the bending tests have been carried out as per astm e290 for welded specimens to check the joints performance and weld consolidation [20-21]. for each joint, bends have been checked with mandrel diameter. in order to conduct the test, 1.5×20×180 mm3 specimens have been bent around mandrel diameter 4t. the joint surface of the specimens has been examined for cracks and imperfections after reaching 180 bend by applying enough force to make the specimens’ legs parallel. figure 1 shows schematic illustration of the fsw joints and the transverse testing specimens. iii. results and discussion the bm microstructure, presented in figure 2, is mainly consisting of α-solid solution of cu-al (the bright contrast) and secondary phases with different morphologies precipitated in the matrix (the dark contrast). as shown in the figure, the cladding layer of pure al is rolled with the alloy to give high corrosion resistance by a layer of al-oxide which cannot be penetrated by o2 and prevents further attack. fig. 1. schematic illustration of the fsw and the traverse testing specimens. fig. 2. optical microstructure of the base metal. figures 3-6 show the morphology overviews of the traverse cross sections of fsw samples at different welding conditions covering the predetermined levels of rotational and traverse speeds. in all presented cases, the joints were split into several distinct regions: bm, stir zone (sz), heat affected zone (haz) and the narrow transition region which is commonly called thermo-mechanically affected zone (tmaz). figure 3 shows the optical micrograph of sz at 900 rpm rotational speed and 11 mm/min traverse speed. it is observed that the clad layer has been damaged and forced into weld nugget. the indiscernible shape found in the sz could be due to inadequate flow of metals and mixing in that zone. the improper heat applied during the fsw process has caused the void or groove-like defect to occur in both zs and tmaz in addition to causing some pinholes which have been observed at the bottom side of the joint. the observed kissing bond has been formed under the pin shoulder during the fsw process due to the severities of the oxide with some absorbed air on the specimens’ surface [9]. the optical micrograph of the welded sample at 900 rpm rotational speed and 35 mm/min traverse speed is shown in figure 4. despite the few microvoids observed in the sz, it can be claimed that almost sound joints have been successfully produced by applying these levels of rotational and traverse engineering, technology & applied science research vol. 8, no. 1, 2018, 2493-2498 2495 www.etasr.com el-morsy et al.: effect of friction stir welding parameters on the microstructure and mechanical … speeds. this is mainly because of the sufficient heat input applied during the fsw process which has elevated the temperature and promoted the plastic flow of materials around the pin tool in an effective manner. fig. 3. a micrograph of the joints at 11 mm/min traverse speed and 900 rpm rotational speed. fig. 4. a micrograph of the joints at 35 mm/min traverse speed and 900 rpm rotational speed. optical micrograph of welded sample at 710 rpm rotational speed and 35 mm/min traverse speed is shown in figure 5. as in the case of 900 rpm and 35 mm/min, few microvoids have been observed on the retreating side of sz and tmaz. the overall area percentage of the microvoids to the welding nugget is less than 1% indicating that the porosity level is still quite low. the cross-section of a typical fsw joint for the rotational speed of 1400 rpm and the traverse speed of 35 mm/min is shown in figure 6. voids have been obviously seen in the sz and that could be attributed to the excess amount of heat generated by the high rotational speed of the pin tool. in addition, the excess heat input applied during the fsw has softened the metal and, as a result, has caused a large mass of flash to be ejected to the outside [22]. figure 7 shows the ultimate tensile strength of the joints compared to the bm. figure 7a presents the tensile strength of joints obtained at traverse speed of 35 mm/min and different rotational speeds, whereas part b of the figure presents the tensile strength of the joints obtained at rotational speed of 900 rpm and different traverse speeds. both parts of this figure show that the tensile strength of the fsw joints is much lower than that of bm. the stated findings agree with findings in [23]. from the experimental results shown in figure 7a, the tensile strength of the joints has a tendency to increase when rotational speed increases until it reaches 900rpm. rotational speeds higher than this value cause the tensile strength to decrease due to the higher temperatures experienced in the sz. of the five rotational speeds shown, 700 rpm and 900 rpm rotational speeds enhanced the tensile strength of the joints substantially but the other rotational speeds (560, 1400, and 1800 rpm) deteriorated tensile strength of the joints analyzed. fig. 5. a micrograph of the joints at 35 mm/min traverse speed and 700 rpm rotational speed. fig. 6. a micrograph of the joints at 35 mm/min traverse speed and 1400 rpm rotational speed. when varying the traverse speed at constant rotational speed (900rpm), as shown in figur 7b, the tensile strength is decreased but with a magnitude lower than the one observed when varying the rotational speed at constant traverse speed. this coincides with findings in [24, 25] as they report that temperature and rotational speed are significantly affecting the strength and microstructure of joints. figure 8 shows the tensile strength performances of the joints obtained at different rotational and traverse speeds. the strength performances are defined as the ratios of the tensile strength of the joints to those of the bm. the tensile strength performances of the joints vary with the welding condition. for the joints obtained at a traverse speed (35 mm/min) and different rotational speeds, the strength performances are varying between 54.9% at 560 rpm and 86.3% at 900 rpm. for the joints obtained at constant rotational engineering, technology & applied science research vol. 8, no. 1, 2018, 2493-2498 2496 www.etasr.com el-morsy et al.: effect of friction stir welding parameters on the microstructure and mechanical … speed (900 rpm) and different traverse speeds, the strength performances are varying between 74.8% at 45 mm/min and 86.3% at 35 min/min. the best results were obtained at a traverse speed of 35 mm/ min for all tool rotational speeds. fig. 7. tensile strength of joints at different rotational and traverse speeds compared to bm. (a) at 35mm/min traverse speed and (b) at 900 rpm rotational speed. figure 9 shows the microhardness profiles across the weld cross-section of the fsw joints at 35 mm/min traverse speed and various rotational speeds. as illustrated, the bm in the initial condition has an average microhardness value of about 160 hv. this value is gradually decreasing in haz and tmaz until it reaches its lowest level in the sz. the minimum microhardness value observed in the sz is 101 hv which is 63% of the bm value at 560 rpm rotational speed. such reduction of the microhardness value within the welded zone is attributed to the softening of the welded zone caused by the excess heat input during joining. similar microhardness behavior of other friction stir-joined al alloys has also been reported by other researchers [3, 24, 26]. however, the effect of the excess heat generated during the fsw process on the microhardness level is highly affected by the rotational speed applied. the microhardness value has increased to 119 hv in the sz at 700 rpm and to 117 hv at 900 rpm while it has decreased at 1400 and 1800 rpm rotational speeds. this reduction in the microhardness value at higher rotational speeds is due to grain growth resulting from higher temperatures experienced during the fsw process [27]. such observation coincides with findings in [21] which state that the rotational speed must be moderate enough to avoid grain growth. fig. 8. tensile strength performances of joints at (a) at 35mm/min, and (b) at 900 rpm. figure 10 shows the microhardness profiles across the weld cross-section of the fsw joints at 900 rpm rotational speed and two traverse speeds, 11 mm/min and 35 mm/min. as seen in the figure, the low traverse speed has decreased the microhardness value within the welded area by about 42.5% while the high traverse speed has decreased it by 26.8% of the bm microhardness value. with decreasing traverse speed, the time of exposure to the heat is increased and leads to grain growth. the mechanical resistance and the ductility of all joint specimens have been addressed using bending tests. these tests are very sensitive to defects near the surface of the welded zone. the welded specimens are loaded until they take a u-shape or a failure is observed. the bending tests were performed on the welded specimens obtained at different rotational and traverse speeds and the surface photographs of tested specimens are shown in figure 11. as shown in figure 11a, the welds presented good ductility, allowing for very high bend angles and no cracks or failures were observed on the welded specimens at the rotational speeds of 560, 700, and 900 rpm. on the other hand, cracks and failures are found in the welded zones on the specimens that have been welded at the rotational speeds of 1400 and 1800 rpm. the photographs of tested specimens in figure 11b show that that the surface of most of the welded specimens seems to be good. solely one specimen was observed to fail in the bend testing at the (a) (a) (b) (b) engineering, technology & applied science research vol. 8, no. 1, 2018, 2493-2498 2497 www.etasr.com el-morsy et al.: effect of friction stir welding parameters on the microstructure and mechanical … traverse speed of 45 mm/min. table iii presents a summary of the conducted bend testing parameters and results fig. 9. microhardness profile across the stirred zone at 35 mm/min traverse speed. fig. 10. microhardness profile across the stirred zone at 900 rpm rotational speed and two different traverse speeds (11 mm/min and 35 mm/min). (a) (b) fig. 11. the bending results of joints at different traverse and rotational speeds. (a) at 35mm/min and (b) at 900 rpm. iv. conclusions in this study, the friction stir butt weldability of aa2024t4 aluminum alloy was studied. the tensile, bending and microhardness tests, as well as microstructure analysis were conducted to determine the mechanical properties and the welding performances of joints. the following conclusions were drawn:  the almost sound joints were successfully produced at the rotational speeds of 900 rpm and 700 rpm and traverse speed of 35 mm/min. for the rotational speed of 1400 rpm.  as a result of the tensile test it was observed that the maximum welding performance of joints was found to be 86.3% with a 900-rpm rotational speed and a 35 mm/min traverse speed. the tensile value is reached to 360 mpa in the welded sample. however, it is seen that the tensile strength values are decreased under the highest traverse speed (45 mm/min) and under the highest rotational speeds (1400 and 1800 rpm).  the microhardness profile of all the welded sheets clearly shows a dramatic drop in microhardness measurements within the sz. the hardness increases relatively quickly from the sz through the haz toward the bm. the welded sheet at low traverse speed (11 mm/min) demonstrates a more abrupt microhardness value compared with the welded sheet at high traverse speed (35 mm/min).  most of the welds presented good ductility, allowing for very high bend angles and no cracks were observed. table iii. experimental bending results of welded samples at different traverse and rotational speeds traverse speed (mm/min) rotational speed (rpm) remarks 35.5 560 no cracks 710 no cracks 900 no cracks 1400 cracks 1800 cracks 11.2 900 no cracks 18 no cracks 28 no cracks 35.5 no cracks 45 cracks references [1] t. dursun, c. soutis, “recent developments in advanced aircraft aluminium alloys”, materials & design, vol. 56, pp. 862–871, 2013 [2] p. kah, r. rajan, j. martikainen, r. suoranta, “investigation of weld defects in friction-stir welding and fusion welding of aluminium alloys”, international journal of mechanical and materials engineering, vol. 10, no. 1, p. 26, 2015 [3] h. aydın, a. bayram, a. uguz, s. akay, “tensile properties of friction stir welded joints of 2024 aluminum alloys in different heat-treated state”, materials & design, vol. 30, pp. 2211–2221, 2009 [4] w. xu, j. liu, g. luan, c. dong, “temperature evolution, microstructure and mechanical properties of friction stir welded thick 2219-o aluminum alloy joints”, materials & design, vol. 30, pp. 1886– 1893, 2009 [5] p. cavaliere, r. nobile, f. panella, a. squillace, “mechanical and microstructural behaviour of 2024–7075 aluminium alloy sheets joined by friction stir welding”, international journal of machine tools and manufacture, vol. 46, no. 6, pp. 588–594, 2006 [6] h. aydın, a. bayram, i. durgun, “the effect of post-weld heat treatment on the mechanical properties of 2024-t4 friction stir-welded joints”, materials & design, vol. 31, pp. 2568–2577, 2010 [7] j.-h. cho, w. j. kim, c. g. lee, “texture and microstructure evolution and mechanical properties during friction stir welding of extruded engineering, technology & applied science research vol. 8, no. 1, 2018, 2493-2498 2498 www.etasr.com el-morsy et al.: effect of friction stir welding parameters on the microstructure and mechanical … aluminum billets”, materials science and engineering: a, vol. 597, pp. 314–323, 2015 [8] l. karthikeyan, v. s. senthilkumar, k. a. padmanabhan, “on the role of process variables in the friction stir processing of cast aluminum a319 alloy”, materials & design, vol. 31, pp. 761–771, 2010 [9] j. chen, r. ueji, h. fuji, “double-sided friction-stir welding of magnesium alloy with concave-convex tools for texture control”, materials & design, vol. 76, pp. 181–189, 2015 [10] x. cao, m. jahazi, “effect of welding speed on the quality of friction stir welded butt joints of a magnesium alloy”, materials & design, vol. 30, pp. 2033–2042, 2009 [11] s. ji, z. li, y. wang, l. ma, “joint formation and mechanical properties of back heating assisted friction stir welded ti–6al–4v alloy”, materials & design, vol. 113, pp. 37-46, 2017 [12] k. song, h. fuji, k. nakata, “effect of welding speed on microstructural and mechanical properties of friction stir welded inconel 600”, materials & design, vol. 30, pp. 3972–3978, 2009 [13] n. xu, r. ueji, y. morisada, h. fuji, “modification of mechanical properties of friction stir welded cu joint by additional liquid co2 cooling”, materials & design, vol. 56, pp. 20–25, 2014 [14] h. li, s. yang, s. zhang, b. zhang, z. jiang, h. feng, p. han, j. li, “microstructure evolution and mechanical properties of friction stir welding super-austenitic stainless steel s32654”, materials & design, vol. 118, pp. 207–217, 2017 [15] m. hajian, a. abdollah-zadeh, s. rezaei-nejad, h. assadi, s.m. hadavi, k. chung, m. shokouhimehr, “microstructure and mechanical properties of friction stir processed aisi 316l stainless steel”, materials & design, vol. 67, pp. 82–94, 2015 [16] p. avinash, m. manikandan, n. arivazhagan, k.d. ramkumar, s. narayanan, “friction stir welded butt joints of aa2024 t3 and aa7075 t6 aluminum alloys”, procedia engineering, vol. 75, pp. 98– 102, 2014 [17] m. ahmed, s. ataya, m. e. seleman, h. r. ammar, e. ahmed, “friction stir welding of similar and dissimilar aa7075 and aa5083”, journal of materials processing technology, vol. 242, pp. 77–91, 2017 [18] c. meran, o.e. canyurt, “the effects of tool rotation speed and traverse speed on friction stir welding of aisi 304 austenitic stainless steel”, international journal of materials research, vol. 102, no. 4, pp. 420– 428, 2011 [19] astm e8 / e8m-13, standard test methods for tension testing of metallic materials, astm international, west conshohocken, pa, 2013 [20] astm e190-14, standard test method for guided bend test for ductility of welds, astm international, west conshohocken, pa, 2014, www.astm.org [21] astm e290-14, standard test methods for bend testing of material for ductility, astm international, west conshohocken, pa, 2014, www.astm.org [22] y. g. kim, h. fuji, t. tsumura, t. komazaki, k. nakata, “three defect types in friction stir welding of aluminum die casting alloy”, materials science and engineering: a, vol. 415, pp. 250–254, 2006 [23] k. elangovan v. balasubramanian, “influences of post-weld heat treatment on tensile properties of friction stir-welded aa6061 aluminum alloy joints”, mater. charact., vol. 59, no. 9, pp. 1168-1177, 2008 [24] l. karthikeyan, v. senthilkumar, v. balasubramanian, s. natarajan, “mechanical property and microstructural changes during friction stir processing of cast aluminum 2285 alloy”, materials & design, vol. 30, pp. 2237–2242, 2009 [25] r. palanivel, p. k. mathews, n. murugan, i. dinaharan, “effect of tool rotational speed and pin profile on microstructure and tensile strength of dissimilar friction stir welded aa5083-h111 and aa6351-t6 aluminum alloys”, materials & design, vol. 40, pp. 7–16, 2012 [26] p. cavaliere p. p. demarco, “friction stir processing of a zr-modified 2014 aluminum alloy”, materials science and engineering: a, vol. 462, pp. 206–210, 2007 [27] m. azizieh, a. h. kokabi, p. abachi, “effect of rotational speed and probe profile on microstructure and hardness of az31/al2o3 nanocomposites fabricated by friction stir processing”, materials & design, vol. 32, pp. 2034–2041, 2011 microsoft word etasr_v12_n2_pp8300-8305 engineering, technology & applied science research vol. 12, no. 2, 2022, 8300-8305 8300 www.etasr.com shah et al.: power quality improvement using dynamic voltage restorer with real twisting sliding … power quality improvement using dynamic voltage restorer with real twisting sliding mode control muhammad shahzaib shah electrical engineering department university of engineering and technology taxila, pakistan mshahzaib.shah@students.uettaxila.edu.pk tahir mahmood electrical engineering department university of engineering and technology taxila, pakistan tahir.mehmood@uettaxila.edu.pk asad ur rehman electrical engineering department university of engineering and technology taxila, pakistan asadur.rehman3@students.uettaxila.edu.pk muhammad qasim manan mechatronics engineering department wah engineering college, university of wah wah cantt, pakistan qasim.manan@wecuw.edu.pk mian farhan ullah electrical engineering department wah engineering college, university of wah wah cantt, pakistan farhan.ullah@wecuw.edu.pk received: 3 january 2022 | revised: 22 january 2022 | accepted: 25 january 2022 abstracthigher power quality (pq) is a common demand of sensitive industrial customers. pq issues are gaining attention from both end-users and electrical utility companies since they are generating significant economic losses to sensitive industrial loads. voltage sags/swells are the most significant and usually occurring pq issues in a secondary distribution system. dynamic voltage restorer (dvr), is a fast, flexible, effective, and dynamic custom power device (cpd), that can be used to eliminate voltage sags and swells. its performance is mostly determined by the control strategy established for switching voltage source converters (vscs). this research work develops a fused control method for vsc of dvr based on the real-twisting algorithm (rta) and sliding mode control (smc) that successfully eliminates the impacts of voltage sags/swells. rta along with the conventional smc reduce the effect of chattering, which is a disadvantage of smc while retaining its additional qualities like robustness, quicker response time, and insensitivity to load variations. to evaluate the performance of the proposed control approach, the matlab/simulink simpower system toolbox was employed. according to the simulation findings, the real twisting sliding mode controller (rtsmc) for dvr can detect and mitigate voltage sags/swells within 2.5ms which is much lower than the allowable limit of 20ms as per semiconductor industrial equipment voltage sag immunity standard (semi f-47 standard) for sensitive loads. total harmonics distortion (thd) is determined to be less than 5% in all simulated instances. a comparative study is also performed between the conventional smc and the suggested rtsmc, revealing that the proposed method outperforms the classical smc. keywords-dynamic voltage restorer; power quality issues; sliding mode control; real-twisting algorithm; voltage sag/swell i. introduction power quality (pq) is a key problem of today's power systems, since it may have an impact on sensitive loads and utilities [1-2]. most of the industrial devices are typically based on electronic devices like the programmable logic controller, microprocessors, computers, and adjustable speed drives that are very sensitive to variations such as voltage sags/swells and harmonics [3]. as the distribution system (ds) is the weakest link in a power system, these pq problems have a higher impact on it [4-5]. to mitigate these issues, custom power devices (cpds) like the dynamic voltage restorer (dvr), the active filter (af), the unified power quality conditioner (upqc), and the distribution static synchronous compensator (dstatcom) are some of the most often utilized power devices [6]. dvr, due to its superior performance, is regarded as the best solution for minimizing the pq issues. it is a fast, dynamic, and efficient technology that is employed to effectively mitigate voltage magnitudes [7]. several control schemes, e.g. state feedback, self-tuning, instantaneous reactive power (irp) theory, direct quadrature (dq), reference adaptive model, phase shift control, vector template method, pcc regulated voltage, instantaneous symmetrical components, dc-link with proportional-integral (pi) controller, synchronous reference frame (srf) theory, feedback, feedforward, phase shift control, pi resonant, p + resonant, corresponding author: mian farhan ullah engineering, technology & applied science research vol. 12, no. 2, 2022, 8300-8305 8301 www.etasr.com shah et al.: power quality improvement using dynamic voltage restorer with real twisting sliding … artificial neural network (anns), fuzzy controller (fc) are used as vscs of the dvr [8-11]. all these control schemes have advantages and disadvantages, when it comes to generating a clean sinusoidal ac waveform at the dvr's vsc output. they're constructed for creating a highly precise linearized mathematical model of the system that performs well under certain operating circumstances. on the other hand, these control techniques are unable to provide optimal performance when system parameters change. as a result, an efficient and robust control system is required, capable of performing functions with high precision and stability in dynamic conditions. the smc for dvr overcomes these problems because it is not sensitive to changes in system parameters and does not require an exact mathematical model of the system, but it has an important disadvantage, named the chattering effect [12]. in order to avoid the chattering effect, some algorithms such as real-twisting, super-twisting, optimal, suboptimal, global, integral, and state-observer algorithm have been used [4, 13-15]. among these algorithms, the realtwisting algorithm has the upper hand due to its stability, robustness, and high tracking accuracy with less chattering effect. in this research, an smc control strategy based on the second order rta for vsc of dvr is presented, which can successfully prevent the impacts of voltage sags/swells in distribution systems and decrease chattering, which is a drawback of the traditional smc. rtsmc and dvrs can successfully minimize the percentage of thd and voltage disturbances according to [16], using the matlab/ simulink software platform. ii. mathematical modeling of dvr in a distribution system a dvr is a power electronics switching device, connected in series with the distribution line in order to inject the desirable controlled voltage. figure 1 depicts the generalized dvr model as well as the way it is linked to the grid. dvr essentially consists of an energy storage unit and a control system, with a vsc linked in series with grid through a boosting injection transformer. fig. 1. generalized single line model of dvr in the distribution network. the equivalent circuit diagram of dvr is shown in figure 2, where load voltage is represented by vl and source voltage is represented by vsource, so the voltage inserted by dvr vdvr can be written as: l source dvr v v v= + (1) cfc and lfc are the filter parameter as shown in figure 2. the filter capacitor current ifc can be defined as: dvr fc fc dv i c dt = (2) fig. 2. equivalent circuit diagram of dvr. now, kcl is applied at node (al) in the given figure 2, the result is: 0 s fl fc i i i− + = (3) in (3), is represents the source current, while ifl and ifc are representing the filter inductor and capacitor current respectively. now, putting the value of ifc in (3), gives (4) and after simplification, we get (5): 0dvr s fl fc dv i i c dt − + = (4) ( )fl sdvr fc i idv dt c − = (5) the dvr first state equation is produced in (5). to generate the second state equation, kvl is applied in figure 2 at closed loop. so: – 0v v v dvr fl in + = (6) where vin is the output ac voltage of vsc, vdvr is the voltage injected by the dvr, and vfl is the voltage across the inductor, given in (7). by putting (7) in (6), we get (8), and, after simplification, we get (9): fl fl fl di v l dt = (7) engineering, technology & applied science research vol. 12, no. 2, 2022, 8300-8305 8302 www.etasr.com shah et al.: power quality improvement using dynamic voltage restorer with real twisting sliding … 0 fl dvr fl in di v l v dt + − = (8) ( )fl in dvr f di v v dt l − = (9) therefore, the state space model of the series connected dvr is shown in (10): 1 1 0 0 1 1 0 0 fl flfl lf s dvr dvr in fc fc l li i id v v vdt c c −                = +        −                 (10) where ifl and vdvr are the state variables while is and vin.are the the input variables. iii. designing the second order rtsmc two steps are necessary for the implementation of smc. the first is selecting the sliding surface. the dvr displays the desired performance when the state trajectory is pushed on the specified sliding line. the second stage is to drive the system's state to reach and remain on the chosen sliding surface in a finite period. hence, the difference between the reference voltage and the voltage inserted by the dvr is the standard for the suggested procedure for the sliding surface as given in (11). after this, a comparator is applied on the sliding surface (s) with ±c reference quantity. after the comparator, the produced value is passed through the multiplexer. the aim of passing a signal via a multiplexer is to apply the law of switching to a single signal, and then to apply the control law to the surface. err err d s v k v dt = + (11) to bring the state variable on the sliding surface and to ensure the existence of operation, the given conditions must be satisfied: 0s = (12) 0s =& (13) the switching law can be written as: ( ) 1 1 if s c x t if s c + > + =  − < − (14) in (14,) x(t) is the switching control, and c is a constant. if we get x(t) =+1 then two switches sw1 and sw2 are on. if we get x(t) =-1 then the other two switches, sw3 and sw4, are on. on the bases of this control law, a gating signal is produced for the vsc. the vsc produced the required magnitude of voltage and inserted it with the help of the injection transformer. thus the control strategy used in this paper senses and corrects faults like sags and swells in a short time, i.e. 2.5ms. the state trajectory in an ideal smc is aimed at the sliding manifold with an infinite switching frequency. on the other hand, real power converters cannot work at an infinite switching frequency. as a result, the state trajectory does not go to the origin s=0 and instead follows a discontinuous surface with undesirable oscillations, also known as chattering. the system's unmodeled dynamics can be stimulated by such oscillations. therefore rta is utilized in smc to remove the chattering effect. the block diagram of smc along rta is shown in figure 3. fig. 3. sliding mode block diagram. by applying the rta on the sliding surface, the switching law gives the modified input of control z as given in (15): ( )1 2 ( ) z n sign s n sign s • = − − (15) to remove the undesirable switching components, two tuning constants, n1 and n2, are used in the control law of rta. the sliding manifold term sign(s), removes the switching frequency of the components to increase the life of switches. when the designed sliding surface s is greater or less than zero, the sign function sign(s) of the sliding manifold gives the +1 and -1 output respectively. the total effect of rta on smc results in less chattering effect, faster response, and robustness against external parameter variations. iv. simulation results and discussion to test the efficiency of the rtsmc for dvr in matlab/simulink, a test system was developed. the parameter details are given in table i. figure 4 depicts the suggested distribution system that was used to model and simulate the dvr using the rtsmc. three-phase programming source produces voltage sags/swells in the distribution test system which are then corrected by the dvr. the following analysis is carried out to evaluate the effectiveness of the suggested control approach. • voltage sag/swell mitigation. • total harmonic distortion. engineering, technology & applied science research vol. 12, no. 2, 2022, 8300-8305 8303 www.etasr.com shah et al.: power quality improvement using dynamic voltage restorer with real twisting sliding … rs ls lf cf injection transformer dvr ida il s1 s2 s3 s4 lf cf injection transformer idb s5 s6 lf cf injection transformer idc s9 s10 ls ls rs rs vdc vdc vdc s7 s8 s11 s12 three phase load (vla, vlb, vlc) three phase voltage source (vsa, vsb, vsc) vda vdb vdc rtsmc switching signal vda vdb vdc (vla, vlb, vlc) fig. 4. a three phase system with connected dvr. table i. parameters of the distribution test system parameter description values grid voltage(phase-phase) 400 v frequency of the system (fo) 50 hz impedance of line (rs, ls) 0.8929 ω, 16.58 mh loads rating (3ø) linear load: p = 10 kw, q = 1 kvar switching constant ±c 0.1 energy storage(dc) 40v lc-filter: lf, cf 1.8 mh, 5.5 µf power rating for coupling transformer 100 kva control action rtsmc smc gain γ 0.142 µ switching frequency (fs) 10 khz solver for simulation ode23tb (stiff/tr-bdf2) time of sampling 5 µsec filter cutoff frequency 405 hz rtsmc tuning gains, n1 and n2 0.5 and 0.5 the rtsmc does not provide any switching signal to run the dvr when the system voltage does not change (normal state). when the voltage of the system deviates from its tolerated range, the controller begins to operate. rtsmc operates in the following manner: • detect voltage sags/swells. • compute the voltage sags/swells (percentage). • determine the signal of the switching control. • generate the switching signal (pwm) for vsc to activate source and load voltage. • generate the necessary switching signal uninterruptedly to ensure that voltage sags/swells are compensated. • terminate the switching pwm signal, when the voltage sag/swell is resolved. a. voltage sag mitigation due to the sudden switching on of the sensitive load at the supply-side, a three-phase balanced voltage sag of 30% occurs. this sag starts at 0.1s and ends at 0.2s, as displayed in figure 5(a). the controller is used to correct the disturbance. during normal operation, if there is no sag then no voltage is inserted. once a fault occurs (voltage sag), the controller will detect it and evaluate its magnitude. fig. 5. voltage sag waveform before and after mitigation: (a) source voltage with 30% sag, (b) voltage injected by the dvr to mitigate the sag, (c) the compensated load voltage. fig. 6. thd value of the compensated load voltage under voltage sag for phase a. the fault (voltage sag) is corrected in a very small duration of time (2.5ms) as compared to the allowable limit of ieee standard that is 20ms. figure 5(b) shows that dvr injects only the missing value to eliminate the unnecessary high frequency element by utilizing a low pass filter. the pure and sag free compensated system voltage is shown in figure 5(c). the compensated voltage thd value is given in table ii and figure 6. the harmonic content which is present in load voltage is lower than 5% which is proposed by the ieee standard 1159-1995. b. voltage swell compensation due to the switching off of sensitive load, a 30% swell is produced in the three-phase source voltage, which starts at 0.1s and ends at 0.2s as shown in figure 7(a). the simulation result engineering, technology & applied science research vol. 12, no. 2, 2022, 8300-8305 8304 www.etasr.com shah et al.: power quality improvement using dynamic voltage restorer with real twisting sliding … shows that the good and quick feedback of sliding mode retains the load voltage of the sensitive load according to the itic standard. due to the voltage swell, the distortion in the supplyside voltage is corrected in 2.5ms which is very small time duration, as shown in figure 7(b). after the compensation, the system voltage is shown in figure 7(c) with a magnitude of 1pu. the compensated voltage thd value is given in table ii and figure 8. this value is less than the ieee standard value. fig. 7. voltage swell waveform before and after mitigation: (a) source voltage with 30% swell, (b) voltage injected by dvr to mitigate swell, (c) compensated load voltage. fig. 8. thd value of compensated load voltage under voltage swell for phase a. table ii. thd values before and after compensation disturbances phase a phase b phase c thd when voltage sag occurs 10.59% 11.83% 11.82% thd when voltage sag is resolved 1.13% 4.62% 4.05% thd when voltage swell occurs 8.70% 9.71% 9.69% thd when voltage swell is resolved 1.83% 4.91% 4.51% in this research, an smc control scheme based on a second order rta for vsc of dvr is proposed and implemented, which can successfully prevent the impacts of voltage sags/swells in distribution systems and decrease chattering, which is a major drawback of the traditional smc. rtsmc with dvrs successfully minimizes the percentage of thd and voltage disturbances as per ieee standards. in table iii, the proposed rtsmc is compared with the classical smc, revealing that the proposed method with smc outperforms the classical smc in terms of voltage sag/swell recovery, thd, transients, and multimode oscillations. table iii. proposed rtsmc-smc comparison parameter rtsmc smc voltage sag/swell recovery (p.u.) excellent good voltage sag/swell recovery (s) 2.5 ms 4 ms thd between 1% to 4% between 2% to 8% transients fewer more robustness excellent excellent multi-mode oscillations fewer observed v. conclusion in this paper, an smc technique based on rta for threephase dvr is presented. the suggested control mechanism eliminates chattering, while attains constant switching frequency. as a result of using rta in dvr control, a continuous control input is generated, which can be contrasted to the triangular carrier signal to generate pulse width modulation signals. to evaluate the performance of the suggested control approach, the matlab/simulink simpower system toolbox is employed. according to the simulation outcome, the designed rtsmc for dvr effectively corrects voltage sags/swells and provides the required power within 2.5ms with thd less than 5% for sensitive loads using the itic curve and the semi-f-47 standard. the suggested control approach provides faster response, less disturbances, and better of sag/swell voltage adjustment. a comparative study was performed between the conventional smc and the suggested rtsmc, 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[15] u. riaz, m. tayyeb, and a. a. amin, "a review of sliding mode control with the perspective of utilization in fault tolerant control," recent advances in electrical & electronic engineering, vol. 14, no. 3, pp. 312–324, nov. 2021. [16] ieee recommended practice for monitoring electric power quality, ieee std 1159-2019 (revision of ieee std 1159-2009), ieee, 2019, https://doi.org/10.1109/ieeestd.2019.8796486. engineering, technology & applied science research vol. 8, no. 1, 2018, 2438-2446 2438 www.etasr.com rajabi et al.: a numerical model for caprock analysis for subsurface gas storage applications a numerical model for caprock analysis for subsurface gas storage applications maysam rajabi faculty of mining and metallurgical engineering amirkabir university of technology tehran, iran m_rajabi@aut.ac.ir hossein salari rad faculty of mining and metallurgical engineering amirkabir university of technology tehran, iran salarih@aut.ac.ir mohsen s. masoudian nottingham centre for geomechanics university of nottingham university park united kingdom mohsen.masoudian@nottingham.ac.uk abstract—in considering a site for gas storage, it will be important to evaluate the effects of gas storage on the formation, so as to minimize the risk of a breach occurring in the system. gas injection will result in an increase in formation fluid pressure, especially around the injection source, which in turn results in redistribution of the stress field. the induced deformations within the reservoir can potentially result in a damage zone within the caprock formation. this mechanical failure may involve shear along many of the existing fractures or creation of new fractures that reduce the sealing properties of the caprock system. the main objective of this paper is to develop a model to estimate the growth and extension of cracks in the caprock. in order to achieve this, the smeared crack approach is used to model the process of cracking in the caprock. smeared cracking is a continuum approach for damage mechanics which is based on the idea that a crack is modeled by modifying the strength and stiffness of the material. the main model presented in this paper has three sub-models, which are the reservoir model, the caprock model and the smeared crack model. the reservoir model is a simplified coupled hydro-mechanical model that numerically simulates the radial fluid flow and analytically estimates the associated stress and strain within the reservoir. the results of the reservoir model are used as boundary conditions for the caprock model that estimates the stress and strain within the sealing caprock due to the deformation of the reservoir. using the calculated stress and strain, the smeared crack model predicts the growth and extension of cracks within the caprock. the caprock is assumed to be initially crack free and impermeable. the developed model is then used to study the yort-e-shah aquifer caprock in iran to predict the growth and extension of cracks. keywords-caprock integrity; smeared crack; reservoir geomechanic;yort-e-shah aquifer i. introduction changing the pore fluid pressure and temperature in a reservoir will result in the generation of mechanical stresses in the vicinity of the reservoir [1, 2]. the potential exists for these stresses to induce a failure in the reservoir’s bounding seal. these failure events may result in relatively permeable flow paths that enable leakage of the reservoir fluids into the surrounding geological formations, and potentially to ground surface or into shallow aquifers. as such, when evaluating the suitability of a reservoir for gas storage, it is important to recognize the types of failure mechanisms that may occur, and their likelihood. authors in [3] have categorized typical geomechanical risks that may lead to leakage by influencing the hydraulic integrity of caprock during and after gas injection in three different sections: storage-induced, storage-activated and tectonic activity. in their research, storage-induced section includes capillary leakage, hydraulic fracturing and shear fracturing. storage-activated section includes fault reactivation and reactivation of pre-existing fractures. tectonically active regions are considered separately, and may be avoided by locating the project site in non-seismic regions. there are a great number of studies investigating the caprock integrity from different perspectives such as rock-fluid interactions [4, 5], geomechanical failure [6, 7], induced seismicity [8] and fault slip [9]. a summary of the research activities in the area of caprock integrity has been provided in a number of review papers [10-12]. among all parameters influencing the hydromechanical integrity of caprocks, a number of studies have highlighted the importance of crack growth and extension on sealing performance of the caprock [10]. despite a long history of studies on crack initiation and propagation in rock mechanics, especially in the area of hydraulic fracturing, it remains a challenging topic where there is no consensus on an optimized unified approach and different mechanisms and methodologies have been employed [13-17]. to analyze the initiation and propagation of cracks in several structural problems, numerical studies such as finite element and boundary element methods have been used. there are generally three approaches in solid mechanics when modeling cracks: discrete crack, interface elements and smeared crack. although, discrete crack approach reflects the fracture development phenomenon most closely, it does not fit the nature of numerical methods and it can be computationally expensive [18]. with the development of cracks, each node is replaced by more nodes, which entails re-definition of finite element mesh and hence augments the need for computational resources. on the other hand, the smeared crack approach assumes that the cracked solid is a continuum and permits the description of the medium in terms of conventional stress-strain engineering, technology & applied science research vol. 8, no. 1, 2018, 2438-2446 2439 www.etasr.com rajabi et al.: a numerical model for caprock analysis for subsurface gas storage applications equations. although this may conflict with the nature of the cracking phenomenon, it simplifies significantly the computational process. the smeared crack approach can model the crack development in any direction and it is independent of finite element discretization. within the smeared crack framework, small cracks formed in the band are gradually connected to each other and also one or more cracks may be defined for each gauss point of each element. there are a number of comparative studies investigating the advantages and disadvantages of different approaches. in this paper, we employ the smeared crack approach to avoid the need for remeshing the finite elements, and to enhance the computational efficiency of the model. the idea of smeared cracks was first introduced by in [19] and was later named smeared crack approach in [20]. the results of this study are advantageous to many projects involving gas injection into subsurface formations, namely co2 sequestration, enhanced oil and gas recovery. in order to numerically study the crack development in an initially intact caprock following gas injection in an aquifer, an integrated reservoir-caprock model was developed. the reservoir modeling is a simplified single phase flow model coded in fortran which also estimates the geomechanical response of the reservoir rock to gas injection. the spatial and temporal deformation distribution of the reservoir is then used as a boundary condition for the bottom of the caprock model constructed in abaqus. the model includes the elastoplastic behavior which is coupled with a smeared crack model. the smeared crack model provides an efficient tool to estimate the density and orientation of developed crack in all elements of the caprock. the developed model is then used to simulate the crack development within the caprock of yort-e-shah aquifer. the results of this study can have a significant impact on improving the current methodologies for caprock integrity assessments in geological storage activities. ii. theory and governing equations a. elasto-plasticity in caprock in this paper, cracking is assumed to be the most important aspect of caprock behavior, and it dominates the modeling. cracking is assumed to occur when the stresses reach a failure surface, which can be named as crack detection surface. this failure surface is taken to be a simple coulomb line written in terms of the first and second stress invariants, p and q. the smeared crack model does not track individual macro-cracks but rather constitutive calculations are performed independently at each integration point of the finite element model. the presence of cracks enters into these calculations by the way the cracks affect the stress and material stiffness associated with the integration point. when the principal stress components are dominantly compressive, the response of the caprock is modeled by an elastic-plastic theory, using a simple form of yield surface written in terms of the first two stress invariants. associated flow and isotropic hardening are used. this model significantly simplifies the cracking and compression responses of caprock incorporated in the model. when caprock is loaded in compression, it initially exhibits elastic response. as stress increases, some inelastic straining occurs, and the response of the material softens. an ultimate stress is reached, after which the material softens until it can no longer carry any stress. note that the hysteresis of loading and unloading is not considered in this paper. when a uniaxial specimen is loaded into tension, it responds elastically until, at a stress that is typically 7–10% of the ultimate compressive stress, cracks are initiated very quickly. in order to model these phenomena, we employ a softening mechanism by which the developments of cracks results in a damage effect. in this framework, the open cracks are represented by the loss of elastic stiffness. in other words, we neglect permanent strains associated with cracking. in multi-axial stress states these phenomena can be generalized through the concept of surfaces of failure and of ultimate strength in stress space, which are defined by fitting to the experimental data. the crack model used in this paper is the built-in smeared crack model of abaqus that is originally used for the cracking of concrete. a brief summary of the mathematical implementation of the model is given in this section, while further theoretical background of smeared crack model can be found in the literature [21-26]. this model considers a “compressive” yield/flow surface to model the caprock response in compressive stress states, along with damage elasticity to represent cracks that have occurred at a material calculation point. the occurrence of cracks is defined by a “crack detection” failure surface. following the classical theory of plasticity, the mechanical strain rate dε can be decomposed into elastic and plastic components as below: el pl c d d d        (1) where eld  is the elastic strain rate of un-cracked rock which can be estimated from classical elasticity theory. pl c d  is the plastic strain rate associated with the “compression” surface. the “compression” surface, fc is: 033 0  cc paqf  (2) where p is the effective compressional stress, defined as: )( 3 1 tracep  (3) and q is the mises equivalent deviatoric stress: ssq : 2 3  (4) where pis  is the deviatoric stress, the colon (operator “:”) is applied for matrix multiplication, 0a is a constant defined using the ratio of triaxial peak strength, u bc to the uniaxial compressive strength, u c (i.e. u c u bcbcr    ) as below:   bc bc r r a 21 1 30    (5) engineering, technology & applied science research vol. 8, no. 1, 2018, 2438-2446 2440 www.etasr.com rajabi et al.: a numerical model for caprock analysis for subsurface gas storage applications also ( )c c  is a hardening parameter, where c is the size of the yield surface on the q -axis at 0p . note that surface is a straight line in p-q space and provides a good match to experimental data over a fairly wide range of pressure stress values [25]. ) 3 2 3 1 ( 0 a bc c    (6) where σbc is the magnitude of each nonzero principal stress. the model uses associated flow rule in where the plastic strain rate is defined as below:      c c c pl c fp cdd ))(1( 20 (7) note that, c0 is a constant defined as: )432()()3( ) 2 3()3( 9 0 2 0 00 0 arar aar c bcbc bc      (8) where 11 11( ) / ( ) pl bc pl c bc c cr    is the ratio of the plastic strain in triaxial, 11( ) pl bc c , and uniaxial compression tests, 11( ) pl c c . when the stress state is tensile, cracking is the dominant form of failure, and hence the “crack detection” surface in stress space is used to estimate the spatial distribution of cracks. damage elasticity is then used to describe the postfailure behavior of the rock. the behavior of the cracked rock is defined using a brittle fracture concept derived from [22]. thus, the elastic strain rate in (1), eld  can be further decomposed into elastic, el dd  and plastic strains rates in cracked rock, pl td  as below: el el pl d t d d d    (9) considering an associated flow rule, the plastic components of strain in cracked rock can be written as: pl t t t f d d      (10) in which ft is a coulomb-type tensile failure envelope as: 0) 3 2(ˆ)3(ˆ 00  tu t t u t t t b pbqf      (11) where t and u t are the tensile stress and uniaxial tensile strength, respectively. also, b0 is a constant defined as: )1(1 )(1)2(1 3 2 0 fr frfrrf b t ttt      (12) where uc u ttr    . also the associated plastic multiplier (hardening parameter) is defined as: 11 02 3 t pl t t u t d ( d ) b ( )       (13) following crack detection, the damage elastic theory is used to relate the stress and strain in the failed rock: el d :  (14) where d is the stiffness matrix of the rock, in which the effect of poisson’s ratio is neglected. it should be noted that cracking is assumed to be irrecoverable and that no more than three cracks can occur at any given point. b. reservoir model the reservoir model is a simplified coupled hydromechanical model that numerically simulates the radial fluid flow and analytically estimates the associated stress and strain within the reservoir [27]. gas is injected into an axisymmetric disc-shaped reservoir through a vertical wellbore at its center. the reservoir is treated as a homogeneous and deformable system whose porosity is filled with a single phase, single component and slightly compressible gas. it is a rather simplified model, but this paper is focused on the applicability of smeared cracking approach for caprock integrity and hence, using a simple reservoir model would be sufficient. following the approach employed in [27, 28], the coupled flow equation can be expressed as below: 0 2 2 0 1 ( ) ( ) ( ) ( ) 1 f f f f f f f f f f v ff f f f f ff μ c p(r ,t) p(r ,t) p(r ,t) k t r r r ε (t, r )μ αμ q(r ,t) ρ [ c (p p )]k k t                (15) where t is time, rf is the radial distance from the wellbore, p is the gas pressure within the reservoir, kf is the intrinsic permeability, f is the gas viscosity, f is the porosity of the reservoir, cf is the compressibility of the fluid, 0f is the density of gas at reference pressure of 0p ,  is the biot’s coefficient, and v is the volumetric strain of the reservoir that is determined from the elastic constitutive relations. the term q is the mass rate of gas diffusing into and/or out of matrix blocks, i.e. matrix–fracture transfer function, defined as below: ave f f q ( x ,t) q ( x ,t) t     (16) where qave is the mean value of the gas concentration inside the reservoir matrix and is determined by integration over the volume of the matrix block as below: 1 m ave f m f m v q (x ,t) q (t, x , x )dv v   (17) where vm is the volume of matrix block and q is the gas concentration which is a function of time, t, global fracture coordinate, xf , and local matrix coordinate xm. engineering, technology & applied science research vol. 8, no. 1, 2018, 2438-2446 2441 www.etasr.com rajabi et al.: a numerical model for caprock analysis for subsurface gas storage applications assuming an isotropic poroelastic reservoir, the incremental change in horizontal effective stress becomes: prr       1 (18) where υ is the poisson’s ratio, σ΄ is the effective stress and subscripts of r and θ represent the radial and tangential directions in global coordinates, respectively. the overbars in this equation and throughout this paper denote incremental values of parameters with respect to time. also, note that the biot’s definition of effective stress is employed. the assumption of uniaxial vertical deformation has been widely used in reservoir geomechanics studies as a helpful simplification for reservoir and geomechanical coupling. using the classical elasticity theory, the incremental strain can be determined as: 1 1 2 m s v zz zz zz rr θθ ε ε ε ε υ(σ σ ) ( υ)αp e           (19) where e is the young's modulus of reservoir, mzz and s zz are the mechanical and chemical strains in vertical direction, respectively. also, assuming that the displacement is zero at the bottom of the reservoir, the displacement at the top of the reservoir, zu can be calculated as below: 0 rh z zz r zzu dz h   (20) where hr is the thickness of the reservoir. a backward implicit finite difference scheme was applied to the flow equation (15), while the incremental mechanical stresses and deformations are calculated at each time step. further discussions on features of the employed coupled hydro-mechanical model of the reservoir can be found in [27-29]. c. computational workflow as explained earlier, the integrated reservoir– caprock model used in this paper is constructed by coupling a reservoir model with an abaqus model for elasto-plastic deformation of the caprock which includes the built-in smeared crack subroutine. the reservoir model calculates distributions of pore pressure and stress within the reservoir, using which the displacement of the top of the reservoir is estimated. the reservoir model uses a finite difference scheme coded in fortran, the results of which are validated against an analytical solution as presented in [27]. the estimated displacement is then used as a condition for the lower boundary of the caprock model, where a bonded (frictional) interface is assumed, i.e. the displacement of the top of the reservoir is the same as the displacement of the bottom of the caprock. the caprock model constructed in abaqus, will then estimate distributions of stress and strain within caprock using a finite element scheme. using these estimated stress and strain, the crack model checks the crack criterion within all elements of the caprock. upon crack initiation in each element, the constitutive equations for the cracked rock are employed to estimate the stress and strain within the rock. results of the caprock model have been validated against the ones obtained from the analytical method of solution [30, 31].the flowchart of the integrated model is given in figure 1. d. model construction in order to set up the model, a disk shape reservoir is considered underlying a caprock of the same shape, while their thickness can be independent of each other. since the reservoir model only provides the displacement of the top of the reservoir as a boundary condition to the caprock model, the constructed model in abaqus includes a three dimensional representation of the overlying caprock. considering isotropic reservoir and caprock, an axial symmetry around the wellbore can be assumed and the problem of disk can be reduced to a quarter. the spatial discretization of the caprock model in abaqus is illustrated in figure 2a. the boundary conditions for the model are depicted in figure 2b. as explained earlier, the displacement calculated for the top of the reservoir is used as the displacement of the bottom of the caprock which defines the condition for the bottom side of the model. the side faces are fixed in the normal direction, which means there would be only vertical and radial displacement on these surfaces. for the wellbore in the center of the disk, the pressure is assumed to be equal to the injection pressure to simulate an uncased wellbore. the total vertical stress applied at the top of the models is assumed to be constant during the whole injection time, and considered to be equivalent to the weight of the overburden. also, the initial horizontal stress is assumed to be equal to the total vertical stress. the model is a representation of the yort-e-shah aquifer in iran which is located 70 km southeast of tehran and 40 km south of varamin. the geological studies of the formations in the region revealed that the aquifer is formed of limestone and gypsum, while the caprock is formed of anhydrite [32]. the reservoir and caprock properties for yort-e-shah aquifer are mainly available from the site investigation reports as listed in tables i-iii. the radius of the caprock is considered to be 500 m, and the thickness is 60 m from depth of 240 m to 300 m. data from [33] is used when relevant parameters are not available for yort-e-shah region. table i. properties of overburden material used in calculation of in-situ stress reference units value symbol parameters [34, 35] m 240 hb overburden thickness [33] kg/m3 2500 bdensity [34, 35] m 500 rb radius of the overburden iii. numerical results using the parameters introduced above, a numerical analysis was conducted. the result of reservoir simulation is shown in figure 3, where it can be seen that the pressure increase as injection continues. the outer boundary of the reservoir is assumed impermeable which means the pressure engineering, technology & applied science research vol. 8, no. 1, 2018, 2438-2446 2442 www.etasr.com rajabi et al.: a numerical model for caprock analysis for subsurface gas storage applications within the reservoir is built up with time until the whole reservoir reaches a uniform pressure. the same trend is observable for displacement at the top of the reservoir, as expected. these results are used as a boundary condition for the bottom of the caprock at every time step. fig. 1. flowchart of the integrated reservoir – caprock model (a) (b) fig. 2. the caprock model in abaqus; (a) spatial discretisation and (b) applied boundary conditions engineering, technology & applied science research vol. 8, no. 1, 2018, 2438-2446 2443 www.etasr.com rajabi et al.: a numerical model for caprock analysis for subsurface gas storage applications table ii. properties of caprock of yort-e-shah-aquifer reference units value symbol parameters [33] 3101  f initial porosity [33] m2 22101  kf initial intrinsic permeability [34, 35] m 240 dcap caprock depth [34, 35] m 60 hcap caprock thickness [33] 0.35 υ poisson’s ratio [33] gpa 31.3 ecap young's modulus [33] kg/m3 2700 cap density [34, 35] m 500 rcap caprock radius equivalent to the weight of the overburden mpa 5.886 v initial vertical stress equal to initial vertical stress mpa 5.886 h initial horizontal stress [33] mpa 129.2 c compressive strength [33] 0.005 c strain in peak strength [33] mpa 124.2 y yield stress [33] mpa 9.0 ft tensile strength [26] 1.16; 0 .07; 1.29 failure ratios (abaqus input data) table iii. reservoir properties in yort-e-shah region reference units value symbol parameters [32,36] 0.05 f initial porosity [32,36] m2 9.87×1 0-16 kf initial intrinsic permeability [37] pas 1×10-4 f gas viscosity from real gas equation kg/m3 955.3 0f reference gas density [32,36] mpa 10 p0 reference gas pressure [32,36] 0.35 υ poisson’s ratio [32,36] gpa 27.2 e0 initial young's modulus depleted reservoir mpa 0 pi initial reservoir pressure [34, 35] mpa 10 pwell injection pressure [34, 35] m 500 r0 reservoir radius [34, 35] m 0.13 rw wellbore radius [34, 35] m 300 dr reservoir depth [34, 35] m 325 hr reservoir thickness 501 no. of grid points [34, 35] days 330 tmax injection time days 0.1 t numerical time step the results of the simulations using the assumed conditions and reservoir outputs show that some limited cracks are developed within the caprock around the injection wellbore after 330 days. the locations of these cracked elements in the model are shown in figure 4. the distribution of the maximum principal stresses within the caprock is depicted in figure 5. as shown, the caprock is cracked where the elements are under tensile stress regime. the profile of the displacement at the bottom of the caprock is depicted in figure 6. it can be seen that the caprock moves upward as injection continues, while the absolute magnitude of the uplift is larger near the injection well (note that all upward vertical displacements in the caprock are considered negative in this paper). by gas injection, the pressure in the reservoir rises gradually. by increasing of gas pressure in the reservoir, the effective stress reduces, therefore, the upward moving will be seen in caprock. the orientation of the cracks developed within caprock is illustrated in figure 7. note that these are collected at the integration points of the finite elements of the model. it can be seen that the crack planes are directed perpendicular to the minimum principal stress. this is in agreement with what is widely known [38]. also note that this is the case around the whole circumference of the wellbore, which is an indication of the fact that the major and minor principal stresses are following wellbore’s geometry in an axisymmetric manner. this is the case because an isotropic caprock has been assumed in this model, while developing anisotropic model can lead to a non-axisymmetric stress distribution, but the orientation of cracks are still expected to be perpendicular to the minor principal stress. (a) (b) fig. 3. results of reservoir model at different injection times; (a) pore pressure distribution and (b) vertical displacement of the reservoir ceiling engineering, technology & applied science research vol. 8, no. 1, 2018, 2438-2446 2444 www.etasr.com rajabi et al.: a numerical model for caprock analysis for subsurface gas storage applications fig. 4. the layout of the cracked elements fig. 5. distribution of maximum principal stress within the caprock fig. 6. distribution of vertical displacement within the caprock the results of the caprock model have been validated against the ones obtained from the analytical method. a simplified uniaxial vertical displacement model is used to estimate the vertical displacement of the caprock bottom due to gas injection by (19) [30, 31]: (1 )(1 2 ) (1 )r h p h e           (21) where δp is the change in pore pressure and ∆h is the vertical displacement. ε, υ, α, and hr parameters were defined in section ii. equation (21) can be used to calculate vertical displacement with the change in reservoir pore pressure. the vertical displacement of the caprock bottom due to gas injection, computed from the analytical solution and the numerical scheme are shown in figure 8, after 99 and 330 days. there are differences between analytical and numerical results. when the maximum pore pressure change at the reservoir-caprock interface near injection well zone from the numerical result was used, the calculated vertical displacement from (21) was about 45.4 mm after 99 days of injection, which is 4 mm higher than the numerically calculated value (41.4 mm). the uniaxial analytical model overestimates the vertical displacement in comparison with a real case or the numerical results because the pore pressure is not distributed uniformly in the reservoir, unlike the assumption used in (21). another reason is that the overburden stiffness, which is apt to restrict vertical deformation in a real 3d situation, is not considered in the uniaxial strain model of (21) [7, 31]. fig. 7. distribution and orientation of cracks developed within elements fig. 8. vertical displacement profiles at different times predicted by the analytical solution and numerical simulation iv. conclusion the integrity of a caprock is an important feature of storage sites. this paper presents preliminary results of a model for caprock integrity where smeared crack approach is employed. changes in reservoir pressure change the stress conditions of the reservoir and the surrounding rocks and result in redistribution of stress within the caprock. the paper presented the hydro-mechanical coupling of a reservoir model and the caprock model. the latter included the use of smeared crack engineering, technology & applied science research vol. 8, no. 1, 2018, 2438-2446 2445 www.etasr.com rajabi et al.: a numerical model for caprock analysis for subsurface gas storage applications module of abaqus which was determined to be a computationally effective tool in modeling crack development within the caprock and the algorithm of the developed model was presented. the model was employed to analyze the crack development within the caprock of yort-e-shah aquifer in iran. results suggest that the caprock in this aquifer can help a safe storage since there is only a limited zone around wellbore prone to crack development. however, this conclusion is limited to the conditions assumed in this paper. further investigation is required to assess the integrity of caprock under different injection pressure, loading and deformation conditions and assumptions. further studies are being undertaken to include the impact of different boundary and initial condition, as well as different injection plans to assess the suitability of yort-e-shah aquifer subsurface gas storage. references [1] m. s. masoudian, d. w. airey, a. el-zein, “mechanical and flow behaviours and their interactions in coalbed geosequestration of co2”, geomechanics and 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262-275, 2016 [6] j. rutqvist, j. t. birkholzer, c. f. tsang, “coupled reservoir– geomechanical analysis of the potential for tensile and shear failure associated with co2 injection in multilayered reservoir–caprock systems”, international journal of rock mechanics and mining sciences, vol. 45, no 2, pp. 132-143, 2008 [7] m. karimnezhad, h. jalalifar, m. kamari, “investigation of caprock integrity for co2 sequestration in an oil reservoir using a numerical method”, journal of natural gas science and engineering, vol. 21, no. 1, pp. 1127-1137, 2014 [8] d. dempsey, s. kelkar, r. pawar, e. keating, d. coblentz, “modelling caprock bending stresses and their potential for induced seismicity during co2 injection”, international journal of greenhouse gas control, vol. 22, no.1, pp. 223-236, 2014 [9] b. orlic, b. wassing, “a study of stress change and fault slip in producing gas reservoirs overlain by elastic and viscoelastic caprocks”, rock mechanics and rock engineering, vol. 46, no. 3, pp. 421–435, 2013 [10] r. shukla, p. ranjith, a. haque, x. choi, “a review of studies on co2 sequestration and caprock integrity”, fuel, vol. 89, no. 10, pp. 26512664, 2010 [11] o. r. harvey, n. p. qafoku, k. j. cantrell, g. lee, j. e. amonette, c. f. brown, “geochemical implications of gas leakage associated with geologic co2 storage—a qualitative review”, environmental science & technology, vol. 47, no. 1, pp. 23-36, 2013 [12] j. song, d. zhang, “comprehensive review of caprock-sealing mechanisms for geologic carbon sequestration”, environmental science & technology, vol. 47, no. 1, pp. 9-22, 2013 [13] e. detournay, “propagation regimes of fluid-driven fractures in impermeable rocks”, international journal of geomechanics, vo. 4, no. 1, pp. 35-45, 2004 [14] a. bunger, e. detournay, r. jeffrey, “crack tip behaviour in nearsurface fluid-driven fracture experiments”, comptes rendus mecanique, vol. 333, no. 4, pp. 299-304, 2005 [15] e. dontsov, “propagation regimes of buoyancy-driven hydraulic fractures with solidification”, journal of fluid mechanics, vol. 797, no. 1, pp. 1-28, 2016 [16] t. mohammadnejad, j. andrade, “numerical modeling of hydraulic fracture propagation, closure and reopening using xfem with application to in-situ stress estimation”, international journal for numerical and analytical methods in geomechanics, vol. 40, no. 15, pp. 2033-2060, 2016 [17] a. abdollahipour, m. fatehi marji, a. yarahmadi bafghi, j. gholamnejad, “dem simulation of confining pressure effects on crack opening displacement in hydraulic fracturing”, international journal of mining science and technology, vol. 26, no. 4, pp. 557-561, 2016 [18] j. g. rots, j. blaauwendraad, “crack models for concrete, discrete or smeared? fixed, multi-directional or rotating?”, heron, vol. 34, no. 1, pp. 3-59, 1989 [19] y. r. rashid, “ultimate strength analysis of prestressed concrete pressure vessels”, nuclear engineering and design, vol. 7, no. 4, pp. 334-344, 1968 [20] c. meyer, h. okamura, finite element analysis of reinforced concrete structures, asce, new york, 1986 [21] m. a. hussain, s. l. pu, j. underwood, strain-energy-release rate for a crack under combined mode i and mode ii, astm-stp-560, pp. 2– 28, 1974 [22] a. hillerborg, m. modeer, p. e. petersson, “analysis of crack formation and crack growth in concrete by means of fracture mechanics and finite elements”, cement and concrete research, vol. 6, no.6, pp. 773–782, 1976 [23] c. betegon, j. w. hancock, “two-parameter characterization of elasticplastic crack-tip fields”, journal of applied mechanics, vol. 58, no. 1, pp. 104–110, 1991 [24] y. hu, g. chen, w. cheng, z. yang, “simulation of hydraulic fracturing in rock mass using a smeared crack model”, computers and structures journal, vol. 137, pp. 72-77, 2014 [25] s. esperancinha, “fracture potential of evaporite seals”, european regional conference and exhibition, lisbon, portugal, 2015 [26] abaqus, cae user's guide, and abaqus analysis user's guide, version 6.13, dassault systemes simulia corp., providence, ri, u.s.a, 2015 [27] m. s. masoudian, d. w. airey, a. el-zein, “the role of coal seam properties on coupled processes during co2 sequestration: a parametric study”, greenhouse gases: science and technology, vol. 6, no. 4, pp. 492-518, 2016 [28] m. s. masoudian, d. w. airey, a. el-zein, “modelling stress and strain in coal seams during co2 injection incorporating the rock–fluid interactions”, computers and geotechnics, vol. 76, no. 1, pp. 51–60, 2016 [29] m. s. masoudian, d. w. airey, a. el-zein, “a chemo-poro-mechanical model for sequestration of carbon dioxide in coalbeds”, geotechnique, vol. 63, no. 3, pp. 235-243, 2013 [30] e. fjaer, r. m. holt, p. horsrud, a. m. raaen, r. risnes, petroleum related rock mechanics, 2nd edition, elsevier, 2008 [31] j. lee, k. b. min, j. rutqvist, “probabilistic analysis of fracture reactivation associated with deep underground co2 injection”, rock mechanics and rock engineering, vol. 46, no. 4, pp. 801-820, 2013 [32] p. werner, drilling program for yort-e-shah well no. 4, task report a2.1, sofregaz group, paris, 2006 [33] s. hangx, c. spiers, c. peach, mechanical behaviour of anhydrite caprock and implications for co2 sealing capacity, journal of geophysical research, vol. 115, no. 7, pp. 1-22, 2010 engineering, technology & applied science research vol. 8, no. 1, 2018, 2438-2446 2446 www.etasr.com rajabi et al.: a numerical model for caprock analysis for subsurface gas storage applications [34] d. powell, lab investigation of yort-e-shah aquifer: petrophysical core analysis study of exploration well no. 2, task report a10, vol. 3, kbb group, hannover, 1998 [35] k. wiechart, lab investigation of yort-e-shah aquifer: petrophysical core analysis study of exploration well no. 2, task report a10, vol. 2, kbb group, hannover, 1998 [36] m. r. esfahani, e. kazemzadeh, j. vali, routine core analysis report for well no. 4 of yort-e-shah field, core research department, exploration & production research division, research institute of petroleum industry (ripi), tehran, 2006 [37] a. fenghour, w.a. wakeham, v. vesovic, “the viscosity of carbon dioxide”, journal of physical chemistry reference data, vol. 27, no. 1, pp.31–44, 1998 [38] r. j. twiss, e.m. moores, structural geology, 2nd ed, w. h. freeman and company, san fransisco, 2006 microsoft word etasr_v11_n6_pp7788-7792 engineering, technology & applied science research vol. 11, no. 6, 2021, 7788-7792 7788 www.etasr.com jakhrani et al.: analysis of the physicochemical characteristics of distillery wastewater at habib sugar … analysis of the physicochemical characteristics of distillery wastewater at habib sugar mills, nawabshah nasir hussain jakhrani environment engineering department quest nawabshah, pakistan engrnasirhussain@gmail.com kishan chand mukwana environment engineering department quest nawabshah, pakistan kcmukwana@quest.edu.pk muhammad aslam bhutto civil engineering department ned university of engineering and technology karachi, pakistan mabhutto@neduet.edu.pk dur muhammad mangi environment engineering department quest nawabshah, pakistan dm_mangi@yaho.com memoona hafeez institute of chemistry university of sindh jamshoro, pakistan memoonahafeez88@gmail.com abstract-the aim of this study is to perceive the level of significant physicochemical characteristics of distillery wastewater (dww) at habib sugar mills, nawabshah, pakistan. five locations in the mill namely spent wash, digester tank, distillery, primary treatment, and secondary treatment were selected for analysis of ph, total dissolved solids (tds), total suspended solids (tss), and chemical oxygen demand (cod) of the samples. the samples were taken on a weekly basis for four succeeding months, from january 2021 to april 2021 and the experiments were carried out in the laboratory by adopting standard procedures. the results revealed that the ph of the samples from spent wash was the lowest, whereas secondary treatment samples had the highest. on the contrary, the highest concentrations of tds, tss, and cod were found in the samples taken from the spent wash and the lowest from the secondary treatment. the ph values were found abruptly increasing in the digester tank due to the addition of calcium carbonate in the stream of wastewater after the spent wash. the cod concentration was found to rapidly decrease, from more than 106000mg/l in the spent wash to around 35000mg/l in the digester tank samples, and then to gradually decrease up to the final point of disposal. overall, tds, tss, and cod values were higher during april, january, and february and lower during march. the level of ph was extremely low in the spent wash and did not meet the lower limits of standards and the other examined parameters exceeded the upper limits of who standards. keywords-chemical oxygen demand; distillery wastewater; sugar mill effluents; physiochemical characteristics i. introduction around 75% of the earth’s crust is covered with water. about 97% of the total available water is saline, which is confined in oceans, 2% is entwined in glaciers, ice caps, mud and air. the remaining less than 1% is usable freshwater for the general public [1, 2]. the quality and quantity of water has great importance as a basic need [3, 4]. the discharge of untreated effluents should be within the safety limits [5]. water is used for many purposes such as drinking, washing, bathing, cooking, agriculture, industry, and generation of electricity. in average, global agricultural withdrawals of all freshwater sources is about 70%. agricultural inputs, especially fertilizers, pesticides, and other chemicals used for increasing the production of crops deteriorate the quality of water [6, 7]. moreover, industries and municipal sewage pollute water sources when discharged directly into the water bodies without treatment. polluted water causes many ailments, which are either direct or indirect [8]. sugar industries are quite common globally due to their availability in more than 65% of sovereign countries. they are processing cane to produce raw sugar [9]. these industries generate byproducts such as bagasse, press mud, molasses and wastewater [10]. the production of 1kg sugarcane crop requires about 210lt of water. besides crop requirements, water is also needed to run different processes in sugar mills and generates varying quantities and qualities of wastewater. in the sugar industry, water is normally obtained during the cane processing and the refinery processes [11]. sugarcane crop contains about 70–80% moisture and approximately 1m 3 of wastewater is generated when 1ton of sugarcane is processed in sugar industry [9, 12]. a. distillery industry sugar industries can be categorized into three main groups, namely those that produce only raw table sugar, those that produce only ethanol, and those that produce a combination of corresponding author: nasir hussain jakhrani engineering, technology & applied science research vol. 11, no. 6, 2021, 7788-7792 7789 www.etasr.com jakhrani et al.: analysis of the physicochemical characteristics of distillery wastewater at habib sugar … both [9, 13]. approximately 90% of sugar industries belong to the third category, whereas, 7% produce only ethanol and 3% only sugar [14]. the increasing population has forced the enhancement of the development of distillery industry that produces ethanol, industrial chemicals, and bio-fuels. the processes used in distillery industry leads to the generation of distillery wastewater (dww), stillage, or spent wash. on average, 1lt of alcohol production generates about 13lt of dww depending on the used methods of distillation and waste treatment [15]. thus, typical large distillery plants produce about 1950m 3 of dww. b. characteristics of distillery wastewater the sugar mill dww is highly polluted wastewater due to the presence of various organic compounds. it has dark color, low ph, high temperature, and extreme level of chemical oxygen demand (cod), bod, total dissolved solids (tds), sludge, press mud, and bagasse [16]. dww has a ph of 4.0– 4.6, bod 25,000–35,000ppm tds 85,000–110,000ppm and cod 85,000–110,000ppm [17]. authors in [18] found the ratio of bod and cod index in sugar industry to be 0.60 and 0.25. authors in [10] found that dww has a ph of 4.0 to 4.3 with high rates of bod (52-58kg/m 3 ), cod (92-100 kg/m 3 ), and total suspended solids (tss) (2.0-2.5kg/m 3 ). authors in [19, 20] reported the characteristics of dww as dark brown color, 5.4-4.5 ph, 40,000 to 50,000mg/l bod, and 80,000 to 100,000mg/l cod. the high concentration of cod and bod of dww were attributed to the composition of input material used for the production of ethanol [21, 22]. high pollution load and the volume of dww cause significant environmental issues [23] but now due to statutory restrictions, it cannot be used without meeting standards [24], as it may lead to alteration of the soil structure and can cause eutrophication of water bodies [21, 25, 26]. from the literature review, it is perceived that dww is one of the most polluted waste materials and must be disposed of with care as it is of low ph, dark brown color, high content tds, tss, and cod. if dww is disposed of without proper treatment, it can deteriorate the receiving water bodies and affect the general environment. this study was conducted in order to analyze the physicochemical characteristics of dww and to check the level of pollutants in dww and whether it meets standards or not. ii. materials and methods a. study area habib sugar mills was selected for this case study. it is located in the nawabshah city. the sugarcane crushing capability of the mill is around 11,000ton per day. the refine productions of the mill are sugar and methanol, and the raw wastes are bagasse and molasses [27]. b. sampling and collection a total of 5 wastewater sampling locations, namely spent wash, digester tank, distillery unit, primary treatment, and secondary treatment plant were selected in order to investigate the characteristics of sugar mill dww. the samples were collected weekly for a period of four months. the samples were kept in cleaned plastic bottles. all bottles were washed properly with distilled water. the capacity of each bottle was 5lt. the samples were collected from the exit points of each location. precaution and standard protocols were adopted during the entire sampling period. c. analysis of the physicochemical characteristics of sugar mill distillery wastewater some physicochemical parameters of dww were measured on the spot, while others were examined in the laboratory using the standard protocols. the instruments and methods used for the analysis of the physicochemical characteristics of dww are tabulated in table i. iii. results and discussion four physicochemical parameters, namely ph, tds, tss, and cod of sugar mill dww were analyzed as per astm standards from january 2021 to april 2021. the results obtained from the experimental work are presented in figures 1-8. table i. methods used for the analysis of physicochemical characteristics of dww s. no. parameter instrument method 1 ph ph meter, hi 2211 ph/orp meter astm e70-19 astm d1293-18 2 tds (mg/l) tds digital meter astm d5907-18 astm d5907-10 3 tss (mg/l) tss digital meter astm d5907-18 astm d5907-10 4 cod (mg/l) titration method astm d1252-06 (2020) a. ph level the determined ph value of the samples taken from different locations and the monthly average values are presented in figures 1 and 2. the ph value of spent wash wastewater samples was 4.3, 4.5, 4.3, and 4.3 for each month from january to april respectively with an average value of 4.3. similarly, the ph value of digester tank was 7.6, 7.9, 7.8, and 7.6 with an average value of 7.7. likewise, the ph level of distillery wastewater sample was 8.0, 8.0, 8.0, and 7.9 with an average of 7.9. the ph of the samples taken from primary treatment was 8.1, 8.1, 8.1, and 8.1 with an average of 8.1 and from secondary treatment it was 8.3, 8.2, 8.2 and 8.2 with an average value of 8.2. the maximum and minimum ph values of spent wash, digester tank, distillery wastewater, primary treatment and secondary treatment were 4.5 and 4.4, 7.9 and 7.6, 8.0 and 7.9, and 8.3 and 8.2 respectively. the mean monthly average values of ph from all sampling locations were 7.3, 7.3, 7.3, and 7.2 from january to april respectively. the maximum and minimum mean monthly average values of ph were 7.3 and 7.2 in february and april respectively. overall, the maximum ph values were observed in the secondary treatment samples, and the minimum from the spent wash wastewater samples. it was observed that 4 wastewater samples were slightly closer to the upper limit of the standard and only 1 sample was highly acidic which was taken from the spent wash. engineering, technology & applied science research vol. 11, no. 6, 2021, 7788-7792 7790 www.etasr.com jakhrani et al.: analysis of the physicochemical characteristics of distillery wastewater at habib sugar … b. tds concentration the levels of tds in dww samples are shown in figure 3 and the monthly average in figure 4. the tds of spent wash wastewater was 34525, 34400, 34050, and 34675mg/l each month from january to april with an average of 34412mg/l. the tds of the digester tank samples was 26775, 27150, 26890 and 27062mg/l respectively with an average of 26969mg/l. similarly, the tds concentration of distillery wastewater was 20675, 21962, 21420 and 21825mg/l with an average of 21470mg/l and from the primary treatment 14637, 14837, 14550, and 14887mg/l with an average of 14728mg/l. the tds concentration of the samples taken from the secondary treatment was 11775, 11250, 11230, and 11362mg/l with an average value of 11404mg/l. the maximum and minimum tds concentration of spent wash, digester tank, distillery wastewater, primary treatment, and secondary treatment was 34675 and 34050, 27150 and 26775, 21962 and 20675, 14887 and 14550, and 11775 and 11230mg/l respectively. the monthly mean values of tds from all sampling locations were 21677, 21920, 21628, and 21962mg/l from january to april respectively. fig. 1. ph values. fig. 2. average monthly ph level. the monthly maximum average value of tds was 21962mg/l during april and the minimum was 21628mg/l in march. the higher tds values were shown in spent wash samples and the lower values in secondary treatment water samples. all wastewater samples were higher than the who standards. fig. 3. tds values of all samples from different locations. fig. 4. average monthly level of tds in different months c. total suspended solids concentration the concentrations of tss in the samples taken from different locations are given in figure 5 and their average monthly level is displayed in figure 6. the level of tss in spent wash wastewater samples was 11630, 11370, 11246, and 11315mg/l for each months from january to april respectively with an average of 11390mg/l. the respective tss level of digester tank samples was 8292, 8337, 8264, and 8305mg/l with a monthly average of 8300mg/l. the tss concentration of distillery wastewater samples was 6822, 6852, 6808, and 6695mg/l with an average of 6794 mg/l. similarly, the primary treatment samples had tss level of 2917, 2970, 2968, and 2990mg/l with a monthly average of 2961mg/l. the tss level in the samples taken from the secondary treatment was 1892, 1872, 1854, and 1847mg/l with an average of 1866mg/l. the higher and lower tss concentrations of spent wash, digester tank, distillery wastewater, primary treatment, and secondary treatment were 11630 and 11246, 8337 and 8264, 6852 and 6695, 2990 and 2917, and 1892 and 1847mg/l respectively. the monthly mean values of tss from all sampling locations were 6311, 6280, 6228, and 6230mg/l from january to april respectively. the highest observed monthly mean of tss was 6311mg/l in january and the lowest was 6228mg/l in march. overall, the higher tss concentrations were found in spent engineering, technology & applied science research vol. 11, no. 6, 2021, 7788-7792 7791 www.etasr.com jakhrani et al.: analysis of the physicochemical characteristics of distillery wastewater at habib sugar … wash samples and the lower in the samples taken from the secondary treatment location. it was also observed that all examined samples showed higher values than the who standards. d. cod concentration the levels of cod in the examined samples are shown in figure 7 and their average monthly values in figure 8. the cod value of spent wash samples for the months from january to april were 104763, 108370, 106052, and 106112mg/l respectively with an average of 106324mg/l. the cod values of the samples taken from the digester tank were 36250, 34448, 34510, and 34375mg/l respectively with an average of 34896mg/l. the monthly values of the samples taken from the distillery were 23175, 23225, 22640, and 23750mg/l respectively with an average of 23197.50mg/l. likewise, the primary treatment samples values were 14012, 13982, 14270, and 14700mg/l respectively with an average of 14241mg/l. correspondingly, the cod of secondary treatment samples for the months from january to april were 8400, 8705, 8320, and 8375mg/l respectively with an average of 8450mg/l. fig. 5. tss values of all samples. fig. 6. average monthly level of tss. the maximum and minimum cod concentration in spent wash, digester tank, distillery wastewater, primary treatment, and secondary treatment were recorded as 108370 and 104763, 36250 and 34375, 23750 and 22640, 14700 and 13982, and 8705 and 8320mg/l respectively. the maximum mean monthly average value of cod was 37746mg/l in february and the minimum 37158.4 mg/l in march. generally, it was found from the analysis that the spent wash samples showed the highest cod concentration, whereas the samples taken from secondary treatment location displayed the lowest values. however, all examined samples showed higher cod values than the who standards. fig. 7. cod values of all samples. fig. 8. average monthly level of cod. iv. conclusion weekly samples of sugar mill dww were taken from 5 locations, namely spent wash, digester tank, distillery wastewater, primary and secondary treatment, and analyzed for four consecutive months from january 2021 to april 2021 by observing 4 physicochemical characteristics, namely ph, tds, tss, and cod. it was found from the analysis that the ph values of spent wash samples were the lowest, whereas the values from the secondary treatment samples were the highest. the highest concentrations of tds, tss, and cod were found from the samples taken from the spent wash and the lowest from the secondary treatment location. the authorities of sugar mill add calcium carbonate to increase the level of ph up to standards, thus its values were sharply increased in the next sampling place, i.e. in the digester tank, and then were slowly increasing up to the final disposal point. 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[27] "company history," habib sugar mills ltd. http://www.habibsugar. com/company-history (accessed oct. 16, 2021). engineering, technology & applied science research vol. 8, no. 1, 2018, 2393-2398 2393 www.etasr.com achour et al.: buckling of hybrid composite carbon/epoxy/aluminum plates with cutouts buckling of hybrid composite carbon/epoxy/aluminum plates with cutouts belkacem achour djamel ouinas mabrouk touahmia mustapha boukendakdji college of engineering university of hail hail, saudi arabia b.achour@uoh.edu.sa faculty of engineering university of mostaganem mostaganem, algeria douinas@netcourrier.com college of engineering university of hail hail, saudi arabia m.touahmia@uoh.edu.sa college of engineering university of hail hail, saudi arabia m.boukendakdji@uoh.edu.sa abstract—structural instability becomes an important concern in the composite plate safe and reliable design. in this research, a resistance analysis is carried out on plates made of hybrid composite material with and without elliptical cutouts using the finite element method. the carbon/epoxy/aluminum laminated plates are arranged in the following ordered manner [al/(θ/θ)/al]. the hybrid plate resistance to buckling submitted to uniaxial compression is highlighted. results indicate that given a structural geometry, boundary and loading condition and stacking sequence, the buckling resistance of such plates is strongly influenced by the ply orientation, the anisotropy ratio, and the cutout presence, position and size. the critical load reduction is found to decrease linearly with the decrease of the geometric ratio a/b. when b=8a, the reduction factor n* increased from 1.8% to 7% when φ=90ο and φ=0ο respectively regardless of the ply orientation. maximum reduction of the buckling critical load is important when the elliptical cutout is located in the middle of the plate. regardless of the declination of the elliptical cutout, maximum reduction of the critical buckling stress is obtained when the ratio e2/e1=1. keywords-elliptical cutout; buckling; hybride composite; finite element analysis i. introduction composite materials in the form of laminated plates or shells, have found a growing use in many industrial applications due to their high resistance to fatigue and corrosion and therefore their satisfactory durability. in addition, the minimization of the structural mass in the aeronautical industry leads directly to reducing the aircraft fuel consumption which constitutes an important technological advancement. these shell structures however present cutouts that serve as access pathways, windows which require some kind of reinforcement to overcome the local deformations and stresses around them. in addition, these structures may be subjected to compressive loadings something that requires an understanding of their buckling response in order to determine effective designs [1]. designing structures of this type needs tools to model their more and more sophisticated mechanical behavior and consideration of their specificities. numerical methods and in particular the finite element methods are essential for sizing these complex composite structures. analysis of laminated plate behavior always remains an open research problem, due to its complexity [2]. the structural instability becomes an important concern in the safe and reliable design of composite plates. several studies of laminated plate stability have been concentrated on rectangular plates [3-6]. it is known that the rectangular plate resistance to buckling depends on the boundary conditions, the orientations of the plies and the geometrical ratios [7-10]. the widely used thin walled composite structures become unstable when subjected to mechanical or thermal loadings leading to buckling. accordingly, their behaviors in buckling are significant factors in safe and reliable design [11]. to predict the buckling load and the deformation mode of a structure, linear analysis remains a valid evaluation technique [12]. in general, the laminated plate analysis is more complicated than the analysis of an isotropic and homogeneous material [10]. in [13] authors performed a buckling analysis of a laminated composite rectangular plate having a circular hole at the centre. authors in [14] studied the influence of a cutout on the behavior to buckling of symmetrically crossed composite laminated rectangular plates having a polymer matrix (pmc) using the finite element method. authors in [15] studied the effect of fiber orientation on the critical load of buckling of a symmetrical laminated composite plate having a crack emanating from a circular cutout. they indicated that the buckling critical load reaches its maximum values when the plies were oriented in an interval varying from 50° to 90°. in [16], authors studied the effect of the presence of an elliptical notch on the buckling of laminated boron/epoxy plates arranged anti-symmetrically [(θ/-θ]. in this study the buckling of composite plates made of hybrid carbon/epoxy/ aluminum material with and without elliptical cutouts is analyzed using the finite element software abaqus 6.11. the effects of the cutout size, position, orientation with respect to x-axis, the orientation of plies and the rigidity ratio e2/e1 on the buckling load have been examined. ii. finite element model a thin square plate made of hybrid carbon/epoxy/aluminum composite material, with length and width 2h=100 mm and 2w=100 mm respectively and having an elliptical cutout at the center is considered. total thickness is e=1.162 mm. plate’s engineering, technology & applied science research vol. 8, no. 1, 2018, 2393-2398 2394 www.etasr.com achour et al.: buckling of hybrid composite carbon/epoxy/aluminum plates with cutouts lower edge is fixed and the displacement on the upper edge is assumed to be free along the y-axis. the plate is subjected to a uniaxial compression in the vertical direction under the load per unit length σ=1ν/mm. to solve the problem numerically, the finite element tool abaqus 6.11 was used with 33328 s8r quadrilateral elements and 397 stri65 elements with a refined mesh at the vicinity of the cutout. the plate was composed of eight plies, six of carbon/epoxy and two of aluminum alloy. carbon/epoxy layer’s thickness is 0.127 mm and the plies were symmetrically crossed in an orderly alternate manner according to an angle of θ and -θ respectively. aluminum layers were outside the plate and each had 0.2 mm thickness. several mesh sizes were used in the numerical calculation to examine the accuracy and the convergence of a test case chosen where the ratio of the elliptical cutout is b/a=3, and the orientation of the layers is [-45/45]3. a uniform loading was applied taking into account the boundary conditions. the classical model theory of laminates was implemented using the shell elements s4r, s8r of abaqus with the composite layup option. the linear and quadratic elements with reduced integration s4r and s8r are generally well suited for the calculation of semi-thick or thin shells. mechanical properties of the hybrid composite plate are given in table i. table i. mechanical properties of the hybrid composite plate property aluminium 2024t3 carbon/epoxy e1 (mpa) 72.4 145 e2 (mpa) 0 v12 0.33 0.25 v23 0.25 g12 (mpa) 27 7 g13 (mpa) 7 g23 (mpa) 3.7 in real life applications, cutouts could be of different forms, according to the design needs. cutout’s shape has been assumed primarily to be an elliptical hole at the centre of the plate. however, the effect of different positions for the elliptical cutout on the buckling load is highlighted. these positions are represented by an angle between the major axis of the cutout which is the x-axis by 0°, 15°, 30°, 45°, 60°, 75°, and 90°. the dimensions of the main diameters of the ellipse are represented by a and b. parameters a and b vary with respect to several chosen ratios. accordingly, the effect of the circular cutout was also analyzed as a special case when a=b. a buckling analysis has been performed for various elliptical and circular cutouts using different models. in addition, particular attention was paid to the number of alternate cross over plies of the laminated plate as well as the plies orientation. iii. results and discussion a. effect of the cutout geometric ratio on the buckling load the influence of the ratio a/b of the elliptical cutout on the buckling variation parameter is illustrated in figure 1 for various declinations of the cutout with respect to the x-axis. three configurations of the hybrid composite material were studied, namely [al/(0)3/al], [al/(45/-45)3/al] and [al/(90)6/al]. in this case, the ellipse major axis is maintained constant (2b=20 mm) and the minor axis (a) variable. (a) (b) (c) fig. 1. effect of the ratio a/b on the buckling parameter for (a) [al/(0)3/al], (b) [al/(45/-45)3/al] and (c) [al/(90)6/al] configurations. figure 1 shows that the buckling load decreases gradually in a linear manner with regard to the increase of the ratio of the elliptical cutout. this decrease is noticed regardless of the declination angle φ of the cutout. the minimum value obtained corresponds to the largest ratio a/b=1, i.e. for a circular cutout, and it is almost identical for all cases, while the maximum values are obtained for the lowest ratio a/b. this means that the engineering, technology & applied science research vol. 8, no. 1, 2018, 2393-2398 2395 www.etasr.com achour et al.: buckling of hybrid composite carbon/epoxy/aluminum plates with cutouts increase of the cutout radius produces the lowest critical buckling loads in the plates subjected to compression, which makes the bearing capacity of the structure diminish. the slope of the trends increases with the increase of φ. therefore, the angle of declination of the elliptical cutout influences the buckling critical factor evolution which in turns influences the buckling critical load. as the cutout major axis tends to be parallel to the applied load, the critical load becomes more important. this indicates that an elliptical cutout whose major axis is parallel to the applied load does not significantly affect the panel’s stability. an inverse behavior occurs for the size of the elliptical cutout. in this case, the buckling load importance lessens with the augmentation of the cutout size, in other words, the buckling load decreases with the increase of the cutout size (increase of a/b) which shows that the resistance of the laminated composite plate will be reduced. the influence of the ratio a/b on the reduction of the buckling critical load for different declinations of the cutout with regard to the x-axis is shown in figure 2. the reduction factor is defined by: wtc wc n n n  1* (1) where nwc and nwtc are the buckling loads for the hybrid plate with and without the elliptical cutout respectively. it is to be noted that the maximum reduction in the critical load is marked for the maximum ratio a/b=1 regardless of the configuration of the laminated hybrid composite material [al/(0)3/al], [al/(45/-45)3/al] and [al/(90)6/al]. however, the value of the maximum reduction of the critical load is found for the plies orientation (45/-45) in the configuration [al/(45/45)3/al]. it is of the order of 10% in comparison with a plate without an elliptical cutout. the critical load’s reduction decreases linearly with the decrease of a/b. when this equals to 0.125 (b=8a), the reduction parameter n* passes from 1.8 % to 7% when φ = 90οand φ = 0ο respectively, therefore the elliptical cutout oriented at 0°, reduces the maximum load four times more than that when it is oriented at 90o. this observation is noticed for all ply orientations cases. b. influence of the cutout position in this part, the buckling load variation as a function of the position of the elliptical cutout center with regard to the applied load is shown in figure 3. the effect of the declination of the cutout with regard to the x-axis is highlighted for the three configurations of the hybrid laminated composite material al/(0)6/al], [al/(45/-45)3/al] and [al/(90)6/al]. the size of the elliptical cutout is considered constant; ie. a/b=1/3. it should be noticed that regardless of the position (h) of the cutout, there are two peaks indicating the critical buckling stress in the range 20-30mm and 70-80mm, that is to say in the bottom and top ends respectively close to the fixed boundary and applied load, and a peak of minimum critical stress obtained in the middle of the plate (h= 50mm). it is clear that the presence of a cutout in the middle of the plate reduces the bearing capacity of the hybrid composite plate. it is noticeable that the curves are sinusoidal and symmetrical about the plate axis. also, it is worth mentioning that the increase of the angle of declination φ of the cutout leads to the increase of the critical buckling load where the largest values are obtained for φ = 90ο. better plate resistance is attained when the cutout minor axis is perpendicular to the applied load compared to the case where the cutout minor axis is parallel to the applied load (φ=0ο). the extremum values have the tendency to be amplified when the ply orientation angle θ tends toward 90o. for a clear illustration of this phenomenon, the reduction parameter of the buckling load as a function of the height h is drawn in figure 4 where it could be noticed that the reduction trends of the critical load are reversed in comparison with those shown in figure 3. (a) (b) (c) fig. 2. effet of the ratio a/b on the critical buckling load reduction for (a) [al/(0)3/al], (b) [al/(45/-45)3/al] and (c) [al/(90)6/al] configurations. the maximum reduction of the buckling critical load is important when the elliptical cutout is located in the middle of engineering, technology & applied science research vol. 8, no. 1, 2018, 2393-2398 2396 www.etasr.com achour et al.: buckling of hybrid composite carbon/epoxy/aluminum plates with cutouts the plate. it reaches 7%, 7.5% and 8.5% respectively for θ values of 0ο, 45οand 90o when the cutout is oriented at 0° (φ=0ο). μinimum reduction is attained for the orientation of the plies at 90o. the smallest reductions of the critical load occur when the cutout is oriented at 90o (φ=90ο) of the order of 2%, 3.5% and 2.5% regardless of the hybrid plate configuration. (a) (b) (c) fig. 3. effect of the height h on the buckling parameter for (a) [al/(0)6/al], (b) [al/(45/-45)3/al] and (c) [al/(90)6/al] configurations. (a) (b) (c) fig. 4. effect of the height h on the buckling load reduction for (a) [al/(0)6/al], (b) [al/(45/-45)3/al] and (c) [al/(90)6/al] configurations. c. influence of the rigidity ratio the effects of the young modulus ratios are also studied for different orientations of the laminated structure with and without the presence of the elliptical cutout. three cases of cutout position φ are studied: 00, 45o and 90o. as shown in figure 5, the buckling load increases exponentially with the importance of the ply orientations when the young modulus ratios are less than 0.4. beyond this value, the buckling load trends tend to be more and more parabolic. in other words, the maximum buckling load will be almost identical for θ=0ο and engineering, technology & applied science research vol. 8, no. 1, 2018, 2393-2398 2397 www.etasr.com achour et al.: buckling of hybrid composite carbon/epoxy/aluminum plates with cutouts θ=90ο for a ratio ε2/ε1=1, and the minimum load is obtained for θ=45ο. (a) (b) (c) fig. 5. buckling load for modulus ratio versus ply orientation angles for φ: (a) 00, (b) 45o and (c) 90o. it is worth mentioning that the maximum value is obtained for θ=90ο regardless of the cutout position. when the orientation angle of the elliptical cutout is φ=0ο, the values of the critical buckling load are generally lower compared to the other orientations, which shows that in that case, the cutout presents a greater risk of damage. in the absence of a cutout, the hybrid laminated composite plate is more resistant. when the two properties e1 and e2 are nearly equal, the critical load increases on both sides of the ply orientation angle θ=45ο. the critical load decreases with the decreasing value of the ratio e2/e1. emphasizing on the effect of the ratio of the young's modulus on the evolution of the buckling parameter, the amplification n* as a function of the fiber orientations for different ratios of rigidity is plotted and shown in figure 6. (a) (b) (c) fig. 6. effect of the ratio e2/e1 on the buckling amplification parameter for φ: (a) 00, (b) 45o and (c) 90o. it should be noted that for e2/e1=1, all the peaks are attained when θ=45ο. regardless of the declination of the engineering, technology & applied science research vol. 8, no. 1, 2018, 2393-2398 2398 www.etasr.com achour et al.: buckling of hybrid composite carbon/epoxy/aluminum plates with cutouts elliptical cutout, the maximum reduction of the critical buckling stress is obtained when e2/e1=1. thus, the maximum reduction is obtained when the cutout is oriented at 0° while it is minimum when it is at 90°. this shows that the cutout at 0° reduces the structure capacity more. the maximum reduction of the plate bearing capacity is of the order of 8.5%, 5% and 3% respectively for the cutout orientations 00, 45o and 90o of φ. iv. conclusion in this study, the buckling response of a hybrid composite square plate in the presence of an elliptical cutout was investigated. the effects of the orientation angle of the elliptical cutout, the cutout geometry, the orientation of the plies of the composite material, the position of the elliptical cutout and the rigidity ratio of the material on the variation of the buckling load were highlighted leading to the following findings:  the buckling load increased exponentially with regard to the increase of the orientation angle of the composite material plies. this increase was much faster and more important for θ≥45ο.  for all the laminated hybrid composite configurations used, the more the size a/b of the cutout is important the less is the buckling load.  the critical load reduction is found to decrease linearly with decreasing geometric ratios a/b. when b=8a, the reduction factor n* increased from 1.8% to 7% respectively for φ=90ο and φ=0ο regardless of the ply orientations. when the elliptical cutout is declined by 0°, it reduces the maximum load four times more than when it is declined by 90o.  regardless of the hybrid plate configuration, the maximum reduction of the critical buckling load is important when the elliptical cutout is located in the middle of the plate. it reaches 7%, 7.5% and 8.5% respectively for θ=0ο, 45ο and 90ο when the cutout is oriented at φ=0°.  when the two properties e1 and e2 are nearly equal, the critical load increases on both sides of the ply orientation angle θ=45ο, while the critical load decreases with decreasing values of the ratio e2/e1. acknowledgment this research was funded by the deanship of scientific research at the university of hail, saudi arabia, under the contract (e-2-ce). authors would like to express their gratitude to the deanship of scientific research and to the college of engineering at the university of hail for providing all required facilitations. references [1] h. allahbakhsh, a. dadrasi, “buckling analysis of laminated composite panel with elliptical cutout subject to axial compression”, modelling and simulation in 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and composites, vol. 24, no. 11, pp. 1119–1130, 2005 [12] i. shufrin, o. rabinovitch, m. eisenberger, “buckling of laminated plates with general boundary conditions under combined compression, tension, and shear-a semi-analytical solution”, thin-wall structures, vol. 46, no. 7-9, pp. 925–938, 2008 [13] b. o. baba, a. baltaci, “buckling characteristics of symmetrically and antisymmetrically laminated composite plates with central cutout”, applied composite materials, vol. 14, no. 4, pp. 265-276, 2007 [14] s. a. m. ghannadpour, a. najafi, b. mohammadi, “on the buckling behaviour of cross-ply laminated composite plates due to circular/elliptical cutouts”, composite structures, vol. 75, no. 1-4, pp. 3-6, 2006 [15] n. hamani, d. ouinas, n. benderdouche, m. sahnoun, “buckling analyses of the antisymetrical composite laminate plate with a crack from circular notch”, advanced materials research, vol. 365, pp. 56-61, 2012 [16] d. ouinas, b. achour, “buckling analysis of laminated composite plates [(θ/-θ)] containing an elliptical notch”, composites part b: engineering, vol. 55, pp. 557-579, 2013 microsoft word etasr_v12_n1_pp8210-8216 engineering, technology & applied science research vol. 12, no. 1, 2022, 8210-8216 8210 www.etasr.com sahli et al.: efficient hybrid algorithm solution for optimal reactive power flow using the sensitive … efficient hybrid algorithm solution for optimal reactive power flow using the sensitive bus approach zahir sahli quere laboratory electrical engineering department university ferhat abbas setif 1 setif, algeria sah_zah@yahoo.fr abdellatif hamouda quere laboratory optics and fine mechanics institute university ferhat abbas setif 1 setif, algeria a_hamouda1@yahoo.fr samir sayah quere laboratory electrical engineering department university ferhat abbas setif 1 setif, algeria samir.sayah@univ-setif.dz damien trentesaux lamih-umr cnrs university of valenciennes valenciennes, france damien.trentesaux@univ-valenciennes.fr abdelghani bekrar lamih-umr cnrs university of valenciennes valenciennes, france abdelghani.bekrar@univ-valenciennes.fr abstract-this paper presents the design and application of an efficient hybrid algorithm for solving the optimal reactive power flow (orpf) problem. the orpf is formulated as a nonlinear constrained optimization problem where the active power losses must be minimized. the proposed approach is based on the hybridization of particle swarm optimization (pso) and tabu-search (ts) technique. the proposed pso-ts approach is used to find the settings of the control variables (i.e. generation bus voltages, transformer taps, and shunt capacitor sizes) which minimize transmission active power losses. the bus locations of the shunt capacitors are identified according to sensitive buses. to show the effectiveness of the proposed method, it is applied to the ieee 30 bus benchmark test system and is compared with pso and ts without hybridization, along with some other published approaches. the obtained results reveal the effectiveness of the proposed method in dealing with the highly nonlinear constrained nature of the orpf problem. keywords-optimal reactive power flow; active power loss minimization; hybrid methods; particle swarm optimization; tabu search; sensitive bus i. introduction due to their complex construction and operation, electrical power networks encounter several challenges. in modern power system operation and planning, optimal reactive power flow (orpf), which is a specific optimal power flow (opf) and a highly constrained large-scale non-linear optimization problem, has emerged as one of the major problems and intensively explored topics. the goal of orpf is to find the optimal settings for a power system under some imposed equality and inequality constraints, in order to optimize its active power loss objective [1, 2]. the objective of orpf in power systems is to minimize real power losses while satisfying a given set of operating and physical constraints. the orpf then provides optimal control variables settings such as generator bus voltages, output of static reactive power compensators, transformer tap-settings, shunt capacitors, etc. [3, 4]. due to its influence on the secure and economic operation of power systems, orpf has attracted increasing interest from electric power suppliers. many classical approaches for solving the orpf problem have been reported such as the gradient based approach [5, 6], linear programming [7], non-linear programming [8, 9], quadratic programming [10], and interior point [11]. however, these methods have some disadvantages in solving complex orpf problems, namely premature convergence, algorithmic complexity, and the local minima entrapment [12]. in order to overcome these drawbacks, researchers have applied corresponding author: zahir sahli engineering, technology & applied science research vol. 12, no. 1, 2022, 8210-8216 8211 www.etasr.com sahli et al.: efficient hybrid algorithm solution for optimal reactive power flow using the sensitive … evolutionary and meta-heuristic algorithms such as the genetic algorithm (ga) [13], differential evolution (de) [14], artificial physics optimization (apo) [15], sunflower optimization (sfo) [16], evolutionary programming (ep) [17], stud krill herd algorithm (skha) [18], whale optimization algorithm (woa) [19] and particle swarm optimization (pso) [20, 21]. pso in particular has received increased attention from researchers because of its searching capability. it was developed through simulations of a simplified social system, and has been found to be robust in solving continuous non-linear optimization problems. generally, pso has a more effective global searching ability at the beginning of the run and a local search near the end of the run [1]. pso can generate high-quality solutions and has a more stable convergence than other stochastic methods. however, when solving complex multimodal problems, pso can be trapped in local optima [22]. to overcome this drawback, pso performance can be enhanced with a few adjustments. hybridization is one of these modifications or techniques which, is applied to evolutionary algorithms in order to increase their efficiency and robustness [23]. hybrid pso has provided promising results for problems such as the power loss minimization problem [24, 25]. the novelty of this paper is that an efficient hybrid pso with tabu search (pso-ts) method is implemented to solve the orpf problem by minimizing active power losses. the optimal locations of shunt capacitors have been identified based on sensitive buses. to demonstrate the superiority of the proposed technique, the obtained results were compared to those given by standalone pso and ts and some other published approaches. simulations were performed with matlab using the ieee 30-bus benchmark system. ii. orpf problem formulation the purpose of orpf in a power system is to find the optimal settings of the reactive power control variables, which mainly include the generator voltages (vg), the transformer tapsettings (t), and the shunt capacitors/reactors (qsh), to minimize the real power loss (ploss) while satisfying a given set of constraints. these comprise the power flow equations, the upper and lower limits of the control variables and the dependent variables, including mainly the pq-bus voltages (vpq) and the reactive power out-puts of generators (qg). the orpf mathematical model can be written as [14]: �min ���, subject tog��, = 0ℎ��, ≤ 0 (1) where j(x,u) represents the transmission active power losses, g and h are the sets of equality and inequality constraints respectively, x is the state or dependent variables vector, and u is the control or independent variables vector. in this study, all control variables have been considered as continuous variables. the objective to be minimized is the system transmission active power losses. this objective function is expressed as [1]: ���, = ∑ ������ + � � − 2��� #$%&� '(�)* (2) where nl is the number of transmission lines, vi and vj represent the voltage magnitude at buses i and j respectively, �� is the conductance of branch k between buses i and j, and &� is the voltage angle difference between bus i and bus j. the elements of the state variables vector x are load bus voltage (vl), generators' reactive power output (qg), and lines' apparent power flow (sl). the control variables vector u includes the generation buses voltage (vg), the transformer tap settings (t), and the shunt var compensators (qc). accordingly, the x vector can be written as: �+ = [�-. … �-012 ,34. … 3405 , 6-. … 6-0(] (3) where ng is the number of generators, npq is the number of pq buses (load buses). u can be expressed as: + = [�4. … �405 , 8* … 8'9, 3:. … 3:0;] (4) where nt is the number of tap regulating transformers and nc is the number of shunt var compensation. the minimization of the above function is subject to a number of equality and inequality constraints [1] which will be detailed below: a. equality constrains these constraints reflect the physical laws governing the electrical system, known as power flow equations. they are the expression of the balance between load demand (power loss included) and generated power. the power flow equations are: p=> − p?> − v> ∑ va�g>a cosθ>adea)* + b>a sin θ>a = 0 (5) q=> − q?> − v> ∑ va�g>a sin θ>adea)* − b>a cos θ>a = 0 (6) where pgi, qgi are the active and reactive power of the i th generator, pdi, qdi are the active and reactive power demand at bus i, nb is the total number of buses, and bij, gij are the real and imaginary parts of the (i,j) th element of the bus admittance matrix. b. inequality constraints 1) inequality constraints on security limits some limits are imposed for security purposes: • active power generated at the slack bus: h4,ijkl�m�n ≤ h4,ijkl� ≤ h4,ijkl�mko (7) • load bus voltage: �-pm�n ≤ �-p ≤ �-pmko q ∈ stu (8) • generated reactive power: 34�m�n ≤ 34� ≤ 34�mko q ∈ s4 (9) • thermal limits: the apparent power flowing in line "l" must not exceed the maximum allowable apparent power flow value (6-mko): 6≤ 6-mko , v ∈ s (10) engineering, technology & applied science research vol. 12, no. 1, 2022, 8210-8216 8212 www.etasr.com sahli et al.: efficient hybrid algorithm solution for optimal reactive power flow using the sensitive … 2) inequality constraints on control variable limits the different control variables are bounded as follows: • generator voltage limits: �4pm�n ≤ �4p ≤ �4pmko q ∈ stw (11) • transformer tap limits: 8�m�n, ≤ 8� ≤ 8�mko q ∈ s+ (12) • shunt capacitor limits: 3:pm�n ≤ 3:p ≤ 3:pmko q ∈ s: (13) where pg,slack is the real power generation at the slack bus, vgi is the voltage magnitude at generator bus i, ti is the tap ratio of the transformer i, qci is the reactive power compensation source at bus i, and npq is the number of pq bus. (.) max and (.) min are the upper and lower limits of the considered variables respectively. the objective functions of equality and inequality constraints, are non-linear functions and they depend on control variables. therefore, orpf is a constrained non-linear optimization problem with multiple local minima [26]. the equality constraints given by (5) and (6) are met by solving the load-flow problem. the inequality constraints given by (11)(13) should be maintained during the solution evolution, while (7)-(9) should be handled by additional techniques. iii. the proposed hybrid algorithm hybridization is a way of combining two techniques in a judicious manner, so that the resulting algorithm contains the positive features of both algorithms. the success of the metaheuristic optimization algorithms depends to a large extent on the careful balance between the two conflicting goals: exploration (diversification) and exploitation (intensification). in order to achieve these two goals, the algorithms use local search techniques, global search approaches, or integrations of both, commonly known as hybrid methods [23]. for the orpf problem, different hybridizations with pso have been used to improve the algorithm’s performance by avoiding premature convergence. for instance, pso has been hybridized with the linear interior point method [27], fuzzy logic [28, 29], pareto optimal set [30], grey wolf technique [31], de [32], multiagent systems [1], imperialist competitive algorithm [33], ga [34], and chaotic bat algorithm [35]. tabu search was used to solve opf [36] and it is hybridized with harmony search algorithm to solve the reactive power flow problem [37]. both algorithms (pso, ts) and their hybridization (pso-ts) for solving the orpf problem are discussed below. a. particle swarm optimization pso is a population-based evolutionary computation technique. the main idea is to evolve the population (particles) of initial solutions in a search space in order to find the best solution. this evolution is an analogy of the behavior of some species as they look for food, like a flock of birds or a school of fish [38]. these particles move through the search domain with a specified velocity in search of the optimal solution. each particle maintains a memory which helps it in keeping the track of its previous best position. the positions of the particles are distinguished as personal best and global best. the swarm of particles evolves in the search space by modifying their velocities according to the following equations [23]: x��y* = z�x�� + #*[\]^ × `abc%d� − ���e + #�[\]^ ×`�bc%d − ���e (14) where x�� is the current velocity of particle i at iteration k, z� is the inertia weight, rand is a random number between 0 and 1, #* and #� are the acceleration coefficients, abc%d� is the best position of the current particle achieved so far, �bc%d is the global best position achieved by all informants, and ��� is the current position of particle i at iteration k. the new position of each particle is given by: ���y* = ��� + x��y* (15) the inertia weighting factor for the velocity of particle i is defined by the inertial weight approach [24]: z� = zmko − fghijfgpk�lmnghi × o (16) where itermax is the maximum number of iterations, k is the current iteration number, and wmax and wmin are the upper and lower limits of the inertia weighting factor. the efficiency of pso has been proved in a wide range of optimization problems. however, constrained non-linear optimization problems have not been widely studied with this method. the authors in [39] were the first to try to adapt pso to constrained non-linear problems. the penalty function approach is used in this paper due to its simplicity of implementation and its proven efficiency for many constrained non-linear optimization problems. the orpf objective function is then modified as follows [22]: p+ = p + qt`h4,ijkl� − h4,ijkl�j�m e� + qw ∑ `�-p −'12�)*�-pj�me� + qu ∑ `34� − 34�j�me� + qr ∑ `6-p − 6-pj�me�'(�)*'5�)* (17) where f is the total active power loss given by (2), kp, kv, kq and ks are the penalty factors of the slack bus generator, bus voltage limit violation, generator reactive power limit violation, and line flow violation respectively. h4,ijkl�j�m , �-pj�m, 34�j�m and 6-pj�m are defined as follows: h4,ijkl�j�m = s h4,ijkl�m�n qt h4,ijkl� < h4,ijkl�m�n h4,ijkl�mko qt h4,ijkl� > h4,ijkl�mko (18) �-pj�m = s �-pm�n qt �-p < �-pm�n �-pmko qt �-p > �-pmko (19) 34�j�m = s34�m�n qt 34� < 34�j�m 34�mko qt 34� > 34�mko (20) 6-pj�m = s 6-pmko qt 6-p > 6-pmko 0 qt 6-p ≤ 6-pmko (21) b. the tabu search method ts is a meta-heuristic proposed in 1986 that guides a local heuristic search procedure to explore the solution space beyond engineering, technology & applied science research vol. 12, no. 1, 2022, 8210-8216 8213 www.etasr.com sahli et al.: efficient hybrid algorithm solution for optimal reactive power flow using the sensitive … local optimality. this technique uses an operation called "move" to define the neighborhood of any given solution. one of the main components of ts is its use of adaptive memory, which creates a more flexible search behavior [40]. the simplest of these processes consists in recording in a tabu list the features of the visited regions on the space search, which provides a means to avoid revisiting already inspected solutions and thus avoid becoming trapped in local optima. c. the hybrid pso-ts approach applied to orpf several arguments support the hybridization of pso with ts. firstly, pso is a global population-based algorithm while ts proposes a fast local search mechanism. secondly, the incorporation of ts into pso enables the algorithm to maintain population diversity. finally, ts is integrated to prevent pso from falling into local optima. to this end, ts is proposed to serve as a local optimizer of the best local solutions (pbest). the pbest solutions of pso are the inputs of the ts diversification procedure. for each solution s, a neighborhood list is defined. candidate solutions from the list are examined and the best one becomes the new current solution that replaces s. the move leading to the solution s is saved in the tabu list, called best_list. this process is repeated to produce successive new solutions until a defined stopping criterion is satisfied. the neighborhoods of a solution s are defined by hyper-rectangles introduced in [41]. a hyper-rectangle of s with a radius r is the space containing solutions s’ such that the distance between s and s’ is less than r. to generate m neighbors for the solution s, m hyper-rectangles centered on s are created, and a point is randomly chosen from each of them. the best of the m chosen points then replaces s. the search procedure of pso-ts algorithm will terminate whenever the predetermined maximum number of generations is reached, or whenever the global best solution does not improve over a predetermined number of iterations. the diversification procedure is outlined in the algorithm in figure 1, while the general flowcharts of the proposed pso-tabu search are given in figure 2. fig. 1. tabu search procedure (diversification). fig. 2. flowchart of the proposed pso-ts algorithm. iv. simulation results in this study, the proposed pso-ts based reactive power optimization approach was applied to the ieee 30-bus power system shown in figure 3 with 12 control variables. two cases were considered. in the first case, we kept the shunt capacitors on their initial buses [24]. in the second case, the capacitors were installed at the most sensitive buses. a sensitive bus is a load bus which requires the installation of a shunt capacitor. to identify this type of buses and their number, we removed the load from each load bus and calculated the active power losses (ploss) each time. the bus giving the least active power losses was considered as the most sensitive bus. table i shows the classification of the sensitive buses according to the new values of the active power losses when the loads of these buses were eliminated. from this table we can see that the most sensitive buses are: 7, 21, 30, 24, and 19. therefore, the 2 available shunt capacitors will be installed at buses 7 and 21. all inequality constraints (7)-(13) were taken into consideration. the simulations were carried out in matlab 7.3 on a pentium® 3.4ghz computer with 1gb total memory. the pso-ts parameter selection is a challenging task not only for this algorithm but also for other meta-heuristic algorithms. the parameter settings used in the proposed pso-ts algorithm, namely initial inertia weight, acceleration factors, number of generations, swarm size, tabu list length, total number of neighborhoods, and neighborhood radius are shown in table ii. inputs pbest; // best historical solution of particles pbestval; solutions values m; //neighborhood size r; //radius of hyper-rectangles eps; //threshold for accepting new solution best_list =( pbest,r); // initializing the tabu list best_list repeat for each solution s(vgi ,ti ,qci) in pbest //generation of m neighbors i=1 while i <= m generate the hyper-rectangle of radius r*i around s, choose randomly a solution ns in the hyper-rectangle if ns ∉ best_list then add the move to best_list; if eval(ns)-pbestval(s) ≤ eps then update pbestval and pbest s = ns, end if i=i+1; end while until (stopping criteria) engineering, technology & applied science research vol. 12, no. 1, 2022, 8210-8216 8214 www.etasr.com sahli et al.: efficient hybrid algorithm solution for optimal reactive power flow using the sensitive … fig. 3. single-line diagram of the ieee 30 bus test system. table i. classification of the sensitive buses load bus new ploss (mw) load bus new ploss (mw) 7 4.787 10 5.696 21 4.816 14 5.707 30 5.040 23 5.769 24 5.271 18 5.771 19 5.306 16 5.838 17 5.487 20 5.850 15 5.517 3 5.944 12 5.670 29 5.944 4 5.691 table ii. control parameter settings parameters value initial inertia weight w 0.9 and decreased to 0.4 acceleration factor c1 2 acceleration factor c2 2 maximum number of generations (pso) 200 swarm size 20 tabu list length 7 number of neighborhoods 3 neighborhood radius 0.1 maximum number of generations (ts) 1000 this system contains 6 generator units connected to buses 1, 2, 5, 8, 11, and 13. four regulating transformers are connected between the line numbers 6–9, 6–10, 4–12, and 27– 28 and two shunt compensators were connected to buses 10 and 24. the transmission feeder number is 41. the generator voltages, transformer tap settings, and var injection of the shunt capacitors were considered as control variables. the voltage magnitudes of all the buses were between 0.95 and 1.1pu, transformer tap settings were within the range of 0.91.1pu and shunt capacitor sizes were within the interval from 0 to 30mvar [24]. there are 12 control variables in this case, namely 6 generator voltages, 4 transformer taps and 2 capacitor banks. the initial total ploss before optimization was 5.2783mw. in the first case study, the shunt capacitors are installed at buses 10 and 24 as in [24]. in the second case study, the shunt capacitors are placed at the most sensitive buses, namely 7 and 21. table iii summarizes the results of the optimal settings and the system power losses obtained by the proposed pso-ts approach, standalone pso and ts, and the methods reported in [24, 25], namely ca, ip-opf, lpac, gpac, and bbo. for the case 1, the results show that the dispatch optimal solutions determined by the pso-ts led to better results. the achieved active power losses are lower than those found by the other methods. using the pso-ts algorithm, power losses decrease from 5.2783mw to 4.6304mw, indicating a reduction of 12.27%, while standalone pso and standalone ts reduce power losses by only 1.03% and 5.61% respectively. for the other optimization algorithms, the best result is given by the bbo algorithm [25] which reduces losses by 5.93%. the convergence characteristic of power loss objective function for this case is plotted in figure 4. from figure 5, it is clear that the results obtained in case 2 are better than those obtained in case 1. this amelioration is due to the installation of shunt capacitors at the most sensitive buses. the active power losses obtained by the pso-ts method in case 2 decrease from 5.2783mw to 4.6095mw, indicating a reduction of 12.67% which is better than the reduction obtained in case 1. it can be concluded that the proposed pso-ts method is able to determine a near-global optimal solution. at the same time, the proposed method succeeded in keeping the dependent variables within their limits. the convergence characteristics of power loss objective function for this case is plotted in figure 6. as the hardware and the software environment significantly affect the computational time, it is not possible to compare the computational time requirements of the different methods unless all the methods are run on the same hardware and are programmed using the same environment. as a rough guide, however, the average time taken by pso-ts is 19s. fig. 4. convergence characteristic of the power losses (case 1). fig. 5. comparative graph of the power losses. engineering, technology & applied science research vol. 12, no. 1, 2022, 8210-8216 8215 www.etasr.com sahli et al.: efficient hybrid algorithm solution for optimal reactive power flow using the sensitive … table iii. experimental results of the proposed and other known algorithms control variables ca ip-opf lpac gpac bbo ts pso pso-ts (case 1) pso-ts (case 2) v1 1.02282 1.10000 1.02342 1.02942 1.1000 1.0684 1.1000 1.0992 1.0990 v2 1.09093 1.05414 0.99893 1.00645 1.0943 1.0933 1.0943 1.0948 1.1000 v5 1.03008 1.10000 0.99469 1.01692 1.0804 1.0893 1.1000 1.0766 1.0687 v8 0.95000 1.03348 1.01364 1.03952 1.0939 1.0853 1.1000 1.0977 1.1000 v11 1.04289 1.10000 1.01647 1.03952 1.1000 1.0017 0.9505 1.0837 1.1000 v13 1.03921 1.01497 1.01101 1.04870 1.1000 1.0780 1.1000 1.0754 1.1000 t6–9 1.07894 0.99334 1.04247 1.04225 1.1000 0.9979 1.0547 0.9257 0.9072 t6–10 0.94276 1.05938 0.99432 0.99417 0.9058 0.9008 1.1000 1.0291 0.9399 t4–12 1.00064 1.00879 1.00061 1.00218 0.9521 1.0337 0.9000 0.9265 0.9000 t27–28 1.00693 0.99712 1.00694 1.00751 0.9638 0.9441 0.9468 0.9422 0.9149 qsh10 0.15232 0.15253 0.17737 0.17267 0.2891 0.1395 0.3000 0.2864 qsh24 0.06249 0.08926 0.06172 0.06539 0.1007 0.1838 0.0000 0.1363 qsh07 0.1285 qsh21 0.2052 ploss (mw) 5.09209 5.10091 5.09212 5.09226 4.9650 5.2240 4.9819 4.6304 4.6095 fig. 6. convergence characteristic of the power losses (case 2). v. conclusion in this paper, a new efficient hybrid pso-ts strategy was successfully implemented to solve the orpf problem. this problem was formulated as a highly constrained non-linear optimization problem where all realistic constraints were taken into consideration. the proposed hybrid algorithm combines the exploration ability of the pso algorithm and the exploitation 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[40] f. glover and m. laguna, "tabu search," in handbook of combinatorial optimization, d.-z. du and p. m. pardalos, eds. boston, ma, usa: springer, 1998, pp. 2093–2229. [41] r. chelouah and p. siarry, "enhanced continuous tabu search: an algorithm for optimizing multiminima functions," in meta-heuristics: advances and trends in local search paradigms for optimization, boston, ma, usa: springer, 1999, pp. 49–61. engineering, technology & applied science research vol. 7, no. 4, 2017, 1771-1774 1771 www.etasr.com rezai and zahedi: dealing with wormhole attacks in wireless sensor networks through discovering … dealing with wormhole attacks in wireless sensor networks through discovering separate routes between nodes farzad rezaei department of computer engineering, college of technical and engineering, kermanshah branch, islamic azad university, kermanshah, iran. farzad_65sh@yahoo.com abdolhamid zahedi department of electrical engineering kermanshah university of technology kermanshah, iran zahedi@kut.ac.ir abstract—one of the most common attacks against wireless sensor networks is the wormhole attack. in this attack, the enemy deploys two malicious nodes in two different areas of the network and establishes a high-speed dedicated channel between these two. this will cause the normal nodes in two different areas wrongly think that they are two-hop neighbors. therefore, this attack will greatly affect the routing algorithms. in this paper, a new distributed algorithm is provided to deal with the wormhole attack. the main idea of the proposed algorithm is to discover separate routes between pairs of two-hop neighboring nodes. the proposed algorithm was implemented and evaluated in terms of true and false detection rate by performing a series of experiments and the results were compared with the base algorithm. the test results showed that the proposed algorithm has desirable efficacy. keywords-wireless sensor networks; security; wormhole attack i. introduction today, wireless sensor networks have an increasing application in military, environment, urban services, discoveries and monitoring fields. since, sensor nodes have very limited computational, memory and radio capabilities, and according to the application of such networks in critical regions especially military, establishing security in such networks is very essential and has attracted the attention of many researchers [1-3]. one of the most dangerous known attacks against such networks is wormhole attack [4]. in this attack, as shown in figure 1, the enemy deploys two malicious nodes in the network and establishes a high-speed dedicated communication channel between these two nodes. these two nodes receive messages from a part of network from a low latency link and relay them in another part of the network. thus, this attack greatly affects the routing algorithms [5]. many algorithms have been provided to cope with this attack in wireless sensor networks until now. in [5], an algorithm is proposed based on probability distribution of the number of neighboring nodes called wapn to cope with wormhole attacks. this algorithm requires no special hardware and simply attempt to identify the wormhole attack according to the number of neighbors. one of the well-known algorithms benefiting from beacon nodes to detect the wormhole attack is provided in [6]. in this algorithm, in addition to the conventional sensors, a number of beacon nodes are released in the network constantly. these beacon nodes are aware of their location and detect the wormhole attack by sending a series of probe messages for each other. since the wormhole attack causes these probe messages reach other beacon nodes with fewer steps, so beacon nodes use this to detect the wormhole attack. in [7], a general mechanism called packet leashes is proposed to cope with wormhole attack. a leash is in fact any type of information added to a packet to limit the allowed maximum transmission distance of packet. two types of geographical and temporal leashes are introduced in this study. a geographical leash ensures that the packet receiver is in a determined distance from the transmitter. a temporal leash ensures that the packet has an upper bound on its’ lifetime which limits the maximum moving distance, because the packet can move at a maximum speed of light. these two types of leashes ware used in [8] to provide a protocol to cope with wormhole attack. in [9], the impacts of wormhole attack on localization protocols based on dv-hop have been analyzed. also, a safe localization protocol based on label has been provided. the main idea of this protocol is to produce a list of quasi-neighbors for each beacon node and use all lists of quasineighbors receiving from neighboring beacon nodes to categorize all attacked nodes in a different group and then label all neighboring nodes (including all sensors and beacons). based on the labels of neighboring nodes, each node will prevent from communication with its neighbors treated by wormhole attack. in [10], an algorithm based on another beacon called wrl was presented. wrl is a localization algorithm resistant to the wormhole attack benefiting from dvhop methods. in [11] a group-based expansion has been provided to cope with wormhole attack. in this method, sensor nodes are spread in the environment in group form and they are aware of the location of their group. during the establishment of the route, the location of group between sensors is exchanged and a link between two sensor nodes is created only when the location distance of the group of these two nodes are engineering, technology & applied science research vol. 7, no. 4, 2017, 1771-1774 1772 www.etasr.com rezai and zahedi: dealing with wormhole attacks in wireless sensor networks through discovering … close enough. in [12], a clustering-based mechanism is proposed to cope with wormhole attack. in this algorithm, a series of beacon nodes is used between clusters in order to detect the wormhole attack. in [13, 14] additional algorithms are provided to deal with wormhole attack which uses the connection information to search for forbidden infrastructures in the connection graph. these algorithms are completely local and require no special hardware. in [15], a lightweight ids (intrusion detection system) framework called lidea has been proposed to cope with wormhole attack. in this system, the nodes hear the communication of their neighboring nodes and cooperate with each of them for successful infusion detection [16]. in [17], a secure routing protocol called serwa has been provided to cope with wormhole attack. this algorithm also requires no specialized hardware such as directional antennas. this protocol takes advantage of discovering single-hop neighbors and also the original route to cope with this attack. in [18] also another algorithm has been presented which benefits from local and neighborhood information to detect the wormhole attack. this algorithm uses the message broadcasting to two-hop neighbors through special single-hop neighbors to detect the wormhole attack. fig. 1. wormhole attack model in this article, a new distributed algorithm is presented to deal with the wormhole attack in order to solve the disadvantages of previous algorithms desirably. the main idea of the proposed algorithm is to discover separate paths between pairs of nodes. for instance, as shown in figure 1, the existence of wormhole attack causes the n1 and n2 nodes wrongly think that they are neighbors, while these two nodes are much far from each other and they are real neighbors. in the proposed algorithm, node n1 can realize occurring of a wormhole attack between itself and node n2 which appears to be neighbor by discovering all separate routes with maximum stride length α (e.g. 2 or 3) between them. as there is only one path with maximum stride length 3 between these two nodes. this is while if these two nodes were real neighbors, then there would be more separate routes (depending on the destination of the network) between them. thus, the proposed algorithm can easily estimate the possibility of wormhole attack and its’ occurring location in the network with great accuracy. ii. system assumptions • a sensor network contains n sensor nodes which are randomly distributed in a two-dimensional region. • the network is homogenous. • after expansion in the network environment, the nodes remain constant in terms of location status. • each node has a unique identifier and not aware of their location status which means they don’t need gps. • radio range of nodes is constant and identical. • each node is aware of approximate density of the network or the average of the number of single-hop neighbors, d. • the nodes communicate with each other via wireless radio channel and use broadcasting by omni-directional method. • it is also assumed that the sensor network is expanded in a hostile environment. so, the network is insecure and the enemy can start the wormhole attack. • the two nodes setting up the wormhole attack are called malicious enemy nodes. iii. the proposed algorithm the main idea of the proposed algorithm is to discover separate paths between each pairs of nodes u and v to detect the wormhole attack. since the existence of wormhole attack causes the two legal nodes u and v, which are far from each other, to consider to be two-hop neighbors, so there would be only one unique route with stride length of 2 or even 3 between these two legal nodes. hence, the wormhole attack can be detected by discovering separate routes between these two nodes. the proposed algorithm is made of three phases of 1: discovering single-hop neighbors, 2: discovering two-hop neighbors and 3: discovering separate routes which will be described in continue. a. discovering single-hop neighbors after expansion of nodes in environment, each u node releases a “hello” message. all nodes located in radio range u will receive its’ hello message and consider the u node as their single-hop neighbor. the first phase is carried out simultaneously by all nodes in the network. b. discovering two-hop neighbors after the phase of discovering one-hop and two-hop neighbors, the third phase is implemented. as mentioned earlier, the wormhole attack in a specific area of the network causes the number of two-hop neighbors of legal nodes located in that region become much more than normal. thus, in this phase, if each u node find that the number of two-hop neighbors is more than the threshold t1, it will doubt to the existence of a wormhole attack in its’ neighborhood and consequently, it runs the third phase. the threshold t1=β·d is set up. the parameter βis a constant value larger than 1. in this status, the u node send a route discovery message for v destination to its’ one-hop neighbors per each v existing in its’ two-hop-neighbor so that to discover the possible routes to v node. figure 2 has indicated the form of discovery packets. in source field, there is the id of each source or the same node producing the packet of route generation, in destination field, engineering, technology & applied science research vol. 7, no. 4, 2017, 1771-1774 1773 www.etasr.com rezai and zahedi: dealing with wormhole attacks in wireless sensor networks through discovering … there is the id of destination node or the same node of two-hop neighbor, in intermediate field, there is the id of intermediate nodes from source to destination route and the lifetime is in ttl field. the u node produce and publish a route generation packet with <<u,v,{},2>> value. each w node receiving this message, first reduce a unit from ttl, add its’ id in intermediate part and then publish the packet. but if ttl is equal to zero, the w node ignores the received packet. the v node returns a confirmation message (containing the id of intermediate nodes) with ttl=2 per each received route discovery packet to reach the u source node. if the source node receive only one separated confirmation message with completely different intermediate, it will add a unit to its’ counter field. the u node repeats this process per all its’ two-hop neighbors. after that, if the u node find its’ counter value higher than the threshold t2, it will realize that a wormhole attack is set up in its’ neighborhood. hence, it will release a warning message in the network and turn off its’ radio and stop its’ operation. the value of the threshold t2=d-a will be calculated; 0≤a<d will be set up. iv. simulation results the proposed algorithm has been implemented by the c ++ language. then, its efficiency was evaluated by performing several tests in form of true and false detection rates. also, the efficacy of the proposed method has been compared with the base algorithm [5]. • true detection rate: a percentage of legal nodes is the neighbor of malicious nodes of wormhole attack which have succeed to detect an attack in their neighborhood. • false detection rate: a percentage of legal nodes that have wrongly detected a wormhole attack in their neighborhood. in tests implementation, the network contains n nodes distributed randomly in an area of 1000 x 1000 m. the radio range of nodes is set to r=40 m. the proposed algorithm has been implemented by the c ++ language. then, its’ efficiency was evaluated by performing several tests in form of true and false detection rates. also, the efficacy of the proposed method has been compared with the base algorithm [5]. • true detection rate: a percentage of legal nodes is the neighbor of malicious nodes of wormhole attack which have succeed to detect an attack in their neighborhood. • false detection rate: a percentage of legal nodes that have wrongly detected a wormhole attack in their neighborhood. in tests implementation, the network contains n nodes distributed randomly in an area of 1000 x 1000 m. the radio range of nodes is set to r=40 m. the parameter β=2 and α=0~5 are set. each test has been repeated 500 times and the final results is obtained from the average of the results of this 500 iterations. it is assumed that there is a wormhole attack in the network so that the distance of its’ two malicious nodes is 500 m from each other. a. first test in this test, we want to evaluate the efficacy of the proposed algorithm per change in the parameter α. in this test, we will have n=2000 in the network and the parameter α=0~5 has changed. the result of this test is given in figure 3 in form of true and false detection rates. the results of this test show that the threshold t2 is reduced. consequently, if a legal node has less two-hop neighbors and has discovered only one separate route to them, it reports the wormhole attack with lower value for counter. this will increase both criteria. as can be seen from the results of this test, a suitable value for this parameter is α=1 which leads to true detection rate of 95% and false detection rate of 7%. b. second test this test aims to evaluate the parameter n on efficacy of the proposed algorithm and compare the results with algorithm [5]. in this test, the parameters α=1 and n=500~3000 have been changed. figure 4 has indicated the results of this test in form of respectively true and false detection rates. the results of this test show that the true detection rate of both algorithms is increased by increasing the number of nodes in the network. because, by increasing this parameter, there would be the possibility of increasing the number of legal nodes neighboring malicious nodes. as a result, the detection rate will be increased. however, the false detection rate of the proposed algorithm is a bit higher than the base algorithm, but it is tolerable compared with the improvement rate obtained in true detection rate. fig. 2. the effect of parameter on efficacy of the proposed algorithm (n=2000) fig. 3. the impact of n parameter on efficacy of the proposed algorithm (a=1) and comparing with the base algorithm engineering, technology & applied science research vol. 7, no. 4, 2017, 1771-1774 1774 www.etasr.com rezai and zahedi: dealing with wormhole attacks in wireless sensor networks through discovering … v. conclusion in this paper, a new distributed algorithm was proposed to deal with the wormhole attack. the main idea of the proposed algorithm was to discover separate routes between pairs of twohop neighboring nodes. the proposed algorithm was implemented and evaluated by a series of tests for its efficacy in terms of true and false detection rates and the results were compared with wapn algorithm. test results showed that the proposed algorithm offers superior performance. references [1] j. yick, b. mukherjee, d. ghosal, “wireless sensor network survey”, computer νetworks, vol. 52, no. 12, pp. 2292-2330, 2008 [2] a. j. goldsmith, s. b. wicker, “design challenges for energyconstrained ad hoc wireless networks”, ieee wireless communications, vol. 9, no. 4, pp. 8-27, 2002 [3] i. f. akyildiz, i. h. kasimoglu, “wireless sensor and actor networks: research challenges”, ad hoc networks,vol. 2, no. 4, pp. 351-367, 2004 [4] k. sharma, m. k. ghose, d. kumar, r. p. k. singh, v. k. pandey, “a comparative study of various security approaches used in wireless sensor networks”, international journal of advanced science and technology, vol. 17, no. 2, pp. 31-44, 2010 [5] f. r. kong, c. w. li, q. q. ding, g. z. cui, b. y. cui, “wapn: a distributed wormhole attack detection approach for wireless sensor networks”, journal of zhejiang university science a, vol. 2, no. 4, pp. 279-289, 2009 [6] h. ronghui, m. guoqing, w. chunlei, f. lan, “detecting and locating wormhole attacks in wireless sensor networks using beacon nodes” world academy of science, engineering and technology, vol. 55, no. 31, pp. 10-15, 2009 [7] y. c. hu, a. perrig, d. b. johnson, “packet leashes: a defense against wormhole attacks in wireless networks. in infocom 2003”, 22nd annual joint conference of the ieee computer and communications. ieee societies, vol. 3, no. 1, pp. 1976-1986, 2003 [8] j. wu, h. chen, w. lou, z. wang, z. wang, “label-based dv-hop localization against wormhole 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[13] r. maheshwari, j. gao, s. r. das, “detecting wormhole attacks in wireless networks using connectivity information”, ieee infocom 2007-26th ieee international conference on computer communications, spain, may 6-12, 2007 [14] d. dong, m. li, y. liu, x. liao, “connectivity-based wormhole detection in ubiquitous sensor networks”, journal of information science & engineering, vol. 27, no. 1, pp. 65-78, 2011 [15] t. giannetsos, t. dimitriou, n. p. prasad, “state of the art on defenses against wormhole attacks in wireless sensor networks”, ieee 1st international conference on wireless communication, vehicular technology, information theory and aerospace & electronic systems technology, wireless vitae 2009, denmark, may 17-20, 2009 [16] i. krontiris, t. giannetsos, t. dimitriou, “lidea: a distributed lightweight intrusion detection architecture for sensor networks”, 4th international conference on security and privacy in communication networks acm, turkey, september 22 25, 2008 [17] s. madria, j. yin, “serwa: a secure routing protocol against wormhole attacks in sensor networks”, ad hoc networks, vol. 7, no. 6, pp. 10511063, 2009 [18] w. znaidi, m. minier, j. p. babau, “detecting wormhole attacks in wireless networks using local neighborhood information”, ieee 19th international symposium on personal, indoor and mobile radio communications, france, september 15-18, 2008 engineering, technology & applied science research vol. 7, no. 4, 2017, 1874-1878 1874 www.etasr.com shayan and iscioglu: an assessment of students’ satisfaction level from learning management … an assessment of students’ satisfaction level from learning management systems: case study of payamnoor and farhangian universities parisa shayan department of computer and instructional technology teacher education, eastern mediterranean university (emu), famagusta, cyprus ersun iscioglu department of computer and instructional technology teacher education, eastern mediterranean university (emu) famagusta, cyprus abstract—learning management systems (lms) have played a significant role in education. the purpose of this study is to investigate the acceptance level of lms amongst students of two universities in tehran, payamnoor and farhangian. the total number of participants was 200. this study was directed based on a quantitative research method and data collection from a questionnaire which was then interpreted according to accurate statistical procedures through spss software. results show that most students, regardless their gender, age, and department were satisfied with the usage of payamnoor and farhangian lmss. however, a student’s grades seem to play a significant role regarding his or hers level of satisfaction from the lms. keywords-e-learning; lms; tam; learners i. introduction learning management system (lms) is an application software that has played a significant role in education. such a software can be designed to augment and facilitate instructional activities including registration and management of education courses, analyzing skill gaps and reporting and delivery of electronic courses simultaneously [1]. in the private section, an lms can also be helpful to maintain and develop the business by training employees. since an education system needs to have mechanisms of access control, communication and results monitoring, an lms can be considered as a solution. an lms operates as an infrastructure in order to administer and distribute the instructional content, classify and evaluate learning objectives, follow the development of training goals, and collect data for managing the education process [2]. it is a platform with diverse resources and various educational activities that is embedded within courses. it provides opportunities to monitor each learner’s activities with different types of tests, assignments, and documents. moreover, it provides easy communication and collaboration between instructors and students via discussion forums [3]. lms allows instructors to create online courses, and training courses. along with creating, managing and delivering e-courses to their learners, instructors can also track their learners’ progress by accessing detailed reports and statistics. another important aspect of an lms is that it provides learners with online classrooms where they can interact and learn in an interactive environment. to create such an environment, lms allows instructors to upload all their courses and training materials such as videos, presentations, pdfs or even live web content such as wikis and blogs to a central location, i.e. the online classroom [4]. an lms has also some features to help instructors to manage their students better. for instance, they can organize students into groups or classes to centralize reporting and assignment or quizzes. with advanced reports and statistics, tracking the progress of large groups or individual learners would be easy. moreover, instructors save valuable time in grading tests, and assessing the results. as the lms automates the grading of hundreds of test papers and students can instantly see the results [5]. clarity may be an added benefit that can be achieved through its capability of accepting proposals from the users regarding additional characteristics [6]. most experts believe that an lms should be more based on peer interaction so that learners can improve their skills by learning from each other and taking advantages of other students’ knowledge [7]. in considering the above, in iran universities, students can easily interact with professors and curriculum planners through discussion forums in the lmss. for examples, payamnoor and farhangian lmss, two of the most powerful lmss in iran, facilitate the exchange of information and communication between the students and instructors at anytime. although both have been successful in e-learning, there are still some technical issues in using them. it is in light of this fact that the different viewpoints of iranian students about payamnoor and farhangian lmss are investigated [8]. the present study aims to provide an in-depth understanding of the current position of lmss in iranian universities by examining the level of students’ satisfaction from lmss in farhangian and payamnoor universities. ii. theoretical background an lms is a term utilized to describe a web-based technology in order to design, implement and evaluate a particular learning process. an lms is usually used as a platform and interface to set e-learning materials to the net. generally, an lms enables instructors to create and deliver instructional content, monitor students’ activities, and evaluate students’ performance [9] or, as elsewhere described, a software that automates the administration of training events engineering, technology & applied science research vol. 7, no. 4, 2017, 1874-1878 1875 www.etasr.com shayan and iscioglu: an assessment of students’ satisfaction level from learning management … [10]. all lmss manage registered users log-ins, manage course catalogs, record data from learners and provide reports to the management. lmss have been extensively used particularly in the realm of modern education. regardless of the education approach, distant or traditional, lmss have contributed considerably to the progress of higher education in colleges and universities. with the advent of lmss as well as the increasing growth of using computers in both personal and professional areas, numerous students and instructors have been attracted to e-learning [11]. lmss have greatly focused on students’ learning needs and instructors’ requests related to instructional tasks [12]. the concept of technology acceptance model (tam) was introduced in [13] in order to examine students’ acceptance of lmss in the university. this model is designed and built upon the theory of reasoned action (tra) which is considered as a foundation for both the technology acceptance model (tam) and the theory of planned behavior (tpb). tpb explains the influence of a belief on attitudes towards forming, directing and dictating of behaviors [14]. generally, tam consists of five main components: pu, peu, atut, bit, and atu [15-17]. according to [13], perceived ease of use (peu), perceived usefulness (pu), and attitude towards using technology (atut) have a considerable impact on actual technology use (atu). behavioral intention to use technology (bit) and actual technology use (atu) are additional parameters. iii. research background nowadays, most universities have invested in lms to deliver course materials and content to students. an increase in student satisfaction and a decrease in costs and in dropout rates has been reported [18-20]. it has been reported that there is no significant relationship between students’ satisfaction level of using lms and their gender [21, 22] and age [23, 24]. however, some other researchers believe that older respondents are more satisfied with lms [21]. on the other hand, most researches show that students’ grades play a major role on their satisfaction level [24, 25]. the department has no remarkable impact on students’ gratification level [25, 26]. some studies show that there is no considerable relationship between gender [27, 28] or age [23, 24] and students’ perceived usefulness. however, the latter is disputable [29]. τhe students’ grades have a significant effect on perceived usefulness [24, 25], but not the department [25, 30]. there is no substantial difference between male and female students’ perceived ease of use [27, 28]. however, age has a significant impact [29, 31] and there is a remarkable effect of students’ grades [24, 25]. the department has no noteworthy impact [25, 30]. there is no considerable relationship between the students’ gender [27, 28], age [23, 24, 30], grades [32, 33] and department [25, 30] and the students’ behavioral intention to use the lms]. further, that there is no considerable relationship between gender [21, 22], age [23, 24, 30] or department [25, 26] and the students’ attitude toward using the lms. whereas, there is a significant impact of between students’ grades [24, 25]. no considerable relationship between gender [21, 22], age [22-24] or their department [25, 30] and the students’ actual technology use. however, there is a significant effect of students’ grades [24, 34 iv. research questions 1) what is the lms satisfaction level of the students according to the current lms model? 2) is there any relationship between lms level satisfaction of students and gender? 3) is there any relationship between lms level satisfaction of students and age? 4) is there any relationship between lms level satisfaction of students and grade? 5) is there any relationship between lms level satisfaction of students and department? 6) what is the lms satisfaction level of the students according to perceived usefulness? 7) what is the lms satisfaction level of the students according to perceived ease of use? 8) what is the lms satisfaction level of the students according to behavioral intention to use technology? 9) what is the lms satisfaction level of the students according to attitude toward using technology? 10) what is the lms satisfaction level of the students according to actual technology use? v. research method a. population and sampling the population of this study were iranian students from two universities in tehran (farhangian and payamnoor) in the academic year of 2015-2016, fall semester. the total population was over 700 people and the total number of candidates was 200 iranian students who already had the experience of working with an lms. 29.5% (59) of the candidates were female and 70.5 % (141) of them were male. 91 % (182) of them were in the age range of 20 to 30, 3.5 % (7) of them were in between 31 to 40, and 5.5 % (11) of them were over 40 years old. as it can be seen, 4.5 % (9) of the candidates were freshman, both 2nd and 3rd grade students comprise the same portion of the sample, by 31.5 % (63) participants, while 19.5 % (39) of the candidates were senior and the population of the graduate students was 13 % (26). b. research questionnaire in order to collect quantitative data, a close-ended questionnaire was used. in this study, the applied questionnaire was divided into two parts: the first one contained demographic information (gender, age, grade, and department) and the second part was extracted from [17]. it consisted of 30 items using a five point likert scale. the likert scale items comprised strongly disagree (1), disagree (2), agree (3), strongly agree (4) and neutral (5). as shown in table i, for each construct cronbach alpha was >0.7 and cronbach alpha for our sample was 0.846 as well. similarly, the total amount of cronbach alpha was 0.923, which means that the questionnaire is acceptable in terms of reliability. consequently, all constructs are considered reliable [17]. engineering, technology & applied science research vol. 7, no. 4, 2017, 1874-1878 1876 www.etasr.com shayan and iscioglu: an assessment of students’ satisfaction level from learning management … table i. statistics result overview ave composite reliability r square α atu 0.585232 0.908027 0.418542 0.882350 atut 0.608817 0.903059 0.612458 0.871126 bit 0.595598 0.854259 0.424390 0.771428 peu 0.624012 0.892189 0.848471 pu 0.608465 0.902827 0.870218 c. data analysis quantitative data gathered from the questionnaire was analyzed through spss, version 22.0. autonomous sample ttests were also conducted to determine the differences between genders [35]. in order to test the relationship between each variable in contrast to the student’s status, anova and lsd were employed. vi. results 1) question1: as table ii illustrates, the minimum score is 30, while the maximum score is 120. as shown , the satisfaction level of the students is 63.53 (52.93 %). the result is consistent with [1820]. table ii. students’ satisfaction levels n min max x sd students’ satisfaction 200 30 200 63.53 24.2 2) question 2 as shown in table iii, there was no significant difference between male or female students’ degree of satisfaction in which, t (70)=1.78 and p=0.079>0.05. therefore, it can be said that there was no considerable relationship between students’ satisfaction degree and gender which is supported by other investigations in the literature [21, 22]. table iii. students’ satisfaction level based on gender gender n x ss sd t p female 59 43 28.4 70 1.78 0.079 male 141 58.5 23.9 3) question 3 a one-way anova was applied to examine the statistical relationship among the students’ different age groups and their satisfaction level of using lms. table iv provides the descriptive statistics of satisfaction level based on age and the results are shown in table v. table iv. descriptive statistics of satisfaction level based on age age n x std. deviation 20-30 182 62.5055 24.37727 31-40 7 64.4286 27.21432 41 + 11 79.8182 11.90645 total 200 63.5250 24.19933 table v. students’ satisfaction level based on age variance source sum of squares sd mean square f p. between groups 3115.030 2 1557.515 within groups 113420.845 197 575.740 2.705 0.069 total 116535.875 199 as shown, age has no significant impact on students’ level of satisfaction [f (2.197)=2.71, p=0.69>0.05]. these findings are consistent with [22-24]. however, it has been stated that older respondents are generally more satisfied with lmss [21]. 4) question 4 a one-way anova was conducted to test students’ satisfaction level based on their grades. descriptive statistics of satisfaction level associated with age groups is given in table vi and the results are shown in table vii. table vi. descriptive statistics of satisfaction level based on grade grade n x std. deviation 1 9 43.0000 28.39454 2 63 58.5079 23.87256 3 63 64.0952 21.63533 4 39 74.3846 23.57141 master and phd 26 65.1154 24.12853 total 200 63.5250 24.19933 table vii. students’ satisfaction level based on grade variance source sum of squares sd mean square f p significant difference between groups 10062.816 4 2515.704 4.607 0.001 3 / 1 within groups 106473.059 195 546.016 4 / 1 total 116535.875 199 master and phd / 1 as shown, students’ grades play a significant role on their satisfaction level (p<0.05) [f (4.195)=4.61, p=0.001]. post hoc comparisons with the lsd test specified that the mean score for the 3rd grade students group (x=64.09, sd=21.64) was dramatically different from the 1st grade students group (x=43.00, sd=28.39). moreover, the mean score for the 4th grade students group (x=74.38, sd=23.57) was significantly different from that of the 1st grade students group (x=43.00, sd=28.39). in addition, there was a considerable difference between the master and phd group (x=65.12, sd=24.13) and the 1st grade students group (x=43.00, sd=28.39). generally, it can be concluded that the higher the grade, the more the satisfaction level in using the lms. as it can be seen, master and phd groups as well as 4th grade student group had the highest satisfaction level in using lmss. these findings are also supported by [24-25]. 5) question 5 the study in a one-way anova test was applied to examine the statistical relationship between different faculty engineering, technology & applied science research vol. 7, no. 4, 2017, 1874-1878 1877 www.etasr.com shayan and iscioglu: an assessment of students’ satisfaction level from learning management … groups and satisfaction level of using lms. descriptive statistics are shown in table viii and results in table ix. table viii. descriptive statistics of satisfaction level based on department department n x std. deviation science 76 64.6316 23.89301 engineering 123 62.7724 24.54264 total 200 63.5250 24.19933 table ix. students’ satisfaction level based on department variance source sum of squares sd mean square f p between groups 234.565 2 117.282 within groups 116301.310 197 590.362 0.199 0.820 total 116535.875 199 as shown, the department has no significant impact on students’ satisfaction level [f (2.197)=0.199, p=0.82>0.05] which is consistent with [25, 26]. 6) questions 6-10: in this part, lms satisfaction dimensions including pu, peu, bit, atut, and atu were examined. as it can be seen in table x, pu had 6 items (min=6, max=24), peu had 5 items (min=5, max=20), bit 4 items (min=4, max=16), atut had 8 items (min=8, max=32), and atu had 7 items (min=7, max=28), respectively. table x. satisfaction dimensions’ scores dimensions n x % std. deviation perceived usefulness 200 12.74 53.08 6.15 perceived ease of use 200 10.22 51.1 5.05 behavioral intention to use technology 200 9.04 56.5 4.26 attitude toward using technology 200 17.63 55.09 8.08 actual technology use 200 13.90 49.64 6.50 according to table x, most of the students were satisfied with the lms dimensions. the students’ satisfaction level is 12.74 (53%) at lms perceived usefulness. similar results can be seen in the research in [36]. in [37] it was indicated that in order to reach effective and efficient results on lmss, pu should be precisely examined. the students’ satisfaction level is 10.22 (51.1%) at lms dimension perceived ease of use. similar results can be seen in [36]. therefore, it can be said that lmss actually influenced students’ progress [37]. the students’ satisfaction level at behavioral intention to use the technology of lmss is 9.04 (56.5%). similarly, in [32], it was mentioned that students’ intention to use technology has a positive effect on user satisfaction. in [38], it was that bit had a significant effect on the students’ satisfaction. the students’ satisfaction level is 17.63 (55%) at attitude toward using technology of lms in accordance with [39, 40]. the students’ satisfaction level at actual technology use of lmss is 13.90 (49.64%), in accordance to [41, 42]. vii. discussion and conclusion payamnoor and farhangian lmss attempt to provide a user-friendly environment for learners with the aim of 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ali and arshad: perspectives of students’ behavior towards mobile learning (m-learning) in egypt… perspectives perspectives of students’ behavior towards mobile learning (m-learning) in egypt: an extension of the utaut model reham adel ali school of computer sciences, universiti sains malaysia penang, malaysia reham_akwah@yahoo.com muhammad rafie mohd arshad school of computer sciences, universiti sains malaysia penang, malaysia rafie@cs.usm.my abstract—the rapid development of third-generation (3g) mobile technologies has led to the emergence of a new kind of learning called mobile learning (m-learning). m-learning means the use of mobile devices to access learning materials at anytime and anywhere with the aid of mobile terminals and networks. this paper explores the possibility of applying m-learning for schools in egypt through a proposed model of acceptance factors that may affect the students’ intentions to adopt m-learning. we use the original model of unified theory of acceptance and use of technology (utaut) and extended it with three new factors mobility, interactivity, and enjoyment. keywords-behavioral intention; enjoyment; interactivity; mobility; mobile learning; students; utaut i. introduction with the continued development in the field of mobile technology and the introduction of the third generation of mobile telecommunications technology, the mobile device becomes a multi-functions device. a variety of services (financial, health tracking, news, information sharing, etc) are added. a new mechanism for training and learning known as mobile learning or m-learning has also appeared. according to, mobile learning can be used as a way to overcome many educational problems. mobile learning definition can be varying. according to [2], m-learning is using mobile technologies to facilitate learning. in [3] m-learning is considered an e-learning by using of mobile devices. the perception of mobility is the most important aspect of mlearning, not the technology itself [4]. in this sense, it is considered that m-learning refers to learning processes supported by the use of mobile and wireless information and communication technologies which have as a fundamental characteristic the students’ mobility, who may or may not be physically or geographically remote from formal educational places, such as classrooms, workplace, instruction and training rooms [4]. m-learning has many advantages that increase the attraction of educators and learners. the most important advantage of mobile learning against traditional education approaches is mobility [5, 6] as it enables users to exchange information anytime and anywhere. hence, the problem of locality and the requirement that students travel to access learning is removed. m-learning supports collaborative learning through interaction. mobile devices help achieve interaction and access learning materials anytime and anywhere [7]. interaction in m-learning can happen between students themselves or between student and educator or between student and content [8, 9]. interaction encourages learners to exchange information, knowledge and ideas between them [10]. through m-learning, students can combine between education and enjoyment through a collection of edutainment tools such as e-book, educational games, e-drawing. that makes education fun and helps alleviate the pressures of studying. m-learning supports situated learning; students can capture their own material using their mobiles phones with cameras or video and transfer to other students and lecturers. the learners like to take an active role in their education, rather than a passive role, through scheduling, monitoring, and assessment their own learning [11, 12]. m-learning encourages a sense of responsibility and selfmanaging of learning. hence, the students become the center of the learning process and have more control on their own learning. according to [4], there are different types of mlearning applications. some of them are simple applications and others more complicated:  interacting with colleagues and teachers using sms. it is also possible to contribute in conversation forums or video classes via cell phones. engineering, technology & applied science research vol. 6, no. 4, 2016, 1109-1114 1110 www.etasr.com ali and arshad: perspectives of students’ behavior towards mobile learning (m-learning) in egypt…  students can answer questions through a mobile phone; after watching a video, listening to an audio track or accessing previously defined content in a mobile [13].  learning through access a mobile learning management system that include interaction with colleagues, search for materials anywhere and sharing knowledge [14-16].  learn by using mobile games.  applications that allow students to capture and organize information that occur in specific places.  applications that allow learners to access different third dimension virtual worlds (tdvw) via mobile devices.  exchange information for informal learning activities such as access social networks  listen to podcasts presenting comments or lecture syntheses recorded by a teacher or classmate, after a class [14, 17].  learn in context. for example, one can visit a historical place and receive important information about events that happened in that place [18].  support in attendance teaching. for instance, some schools already demand that newly enrolled students own a tablet to attend the classes. egypt is an african developing country with a population of 86 million people [19]. according to [20], the egyptian telecommunications sector is one of the most developed in the middle east/north africa region and it is expected to continue growth in the next few years. additionally, egypt is one of the most rapidly growing mobile markets in africa [20]. a study by gsma and docomo [21] indicates that egyptians children between the ages of eight and 18 are familiar with mobile devices. they have believed that the ownership of the mobile device increases their confidence. m-learning in egypt is still in its infancy. according to [22], the current trends that could last for two-five years in egypt is e-learning practices such as open source learning applications, social media, etextbooks, and so on. for mobile learning, it is not expected to be adopted in egypt before five years [22]. additionally, the studies that analyze the acceptance of mobile technology in learning in egypt are limited. for these reasons, and in order to support m-learning in egypt, it is important to investigate the factors that may affect students’ intentions to adopt mobile technology. in this paper, the authors will extend the utaut acceptance model to examine students’ intentions to adopt mobile learning in egypt. ii. theoretical background a. technology acceptance model (tam) technology acceptance model (tam) is one of the robust models used in explaining the acceptance of information technology [23]. in [24], tam was developed by proposing two factors, the perceived usefulness (pu) and perceived ease of use (peu), are basic factors for explaining the adoption of new technology. pu is defined as the extent to which a person believes that using the system will enhance his or her job performance and peu is defined as the extent to which a person believes that using the system will be free of effort. according to tam, external variables can affect on pu and peou. hence these two key factors (pu and peou) are mediated the effect of external variables on intention [17, 25]. tam states that actual use of a system is determined by behavioral intention to use a system, where the intention to use the system is determined by the attitude of a person toward using the system. person’s attitude towards using the system is affected by perceived usefulness (pu) and perceived ease of use (peu). b. unified theory of acceptance and use of technology (utaut) in [26], a model known as the unified theory of acceptance and use of technology (utaut) was proposed. the researchers designed utaut by consolidating eight significant theories in behavior prediction. utaut has four independent variables (performance expectancy, effort expectancy, social influences, and facilitating conditions) are determinants of behavioral intention or use behavior. according to [26], performance expectancy and effort expectancy in utaut are similar to perceived usefulness and perceived ease of use in tam, social influences is similar to the factor ‘‘subjective norm’’ in tam2, an extension of tam and facilitating conditions is having the same meaning of compatibility construct from diffusion of innovation theory (doi). utaut also considers the moderating variables (gender, age, experience, and voluntariness of use) are essential in understanding the effect of users’ characteristics on the technology adoption. many studies in different domains have adopted the utaut model, including 3g mobile communication [27, 28], mobile banking implementations [29, 30] and organizational learning systems [31, 32]. also utaut applied as a framework in training in health care systems [33]. with regard to the utaut, the selection of this model for this study is justified by its global and comprehensiveness approach. the constructs of utaut have been adopted from eight other user acceptance models [26]. this model covers almost the main factors that influence user acceptance of technology such as technology factors that describes the characteristics of a technology and environment factors that includes organization characteristics [26, 34]. additionally, utaut defined an experience, age, and gender as individual differences which may influence the attitudes of a person about a given technology. utaut could successfully predict the adoption of information technology in approximately 70 percent of the cases, but other user adoption models could do so in about 40 percent of the cases [17, 26]. moreover, utaut is considered a new theoretical framework and needs more investigation to validate its robustness [35]. iii. research model and hypotheses a. performance expectancy (perceived usefulness) performance expectancy (pe) is defined as the degree to which an individual believes that using the new technology will aid him/her to achieve benefits in job performance [26]. according to [26], age and gender moderated the relationship between performance expectancy and behavioral intention to engineering, technology & applied science research vol. 6, no. 4, 2016, 1109-1114 1111 www.etasr.com ali and arshad: perspectives of students’ behavior towards mobile learning (m-learning) in egypt… use an information technology. in the context of mobile learning, there are many studies that suggest performance expectancy (pe) has a positive influence on behavioral intention to use m-learning [36-39]. adapting this scheme (performance expectancy) to examine the acceptance of mobile learning by students suggests that they will accept mobile learning if they believe that the technology improves their performance. regarding the gender and age moderating, this study presents whether the gender of the students will moderate the relationship between performance expectancy and students intention to use mobile learning. we will investigate the behavioral intention of mobile learning for students from the same age group, so we have omitted the age moderator. therefore, the following hypotheses are stated:  h1: performance expectancy has a positive effect on student intention to use m-learning.  h2: the impact of performance expectancy on intention to use m-learning will be moderated by gender. b. effort expectancy (perceived ease of use) effort expectancy (ee) is defined as the degree to which an individual believes the new technology will be easy to use [26]. in [26] age, gender and user experience were identified as a moderating variables for the relationship between effort expectancy and behavioral intention. there are many studies that suggest that effort expectancy has a significant influence on user intention to use m-learning technology [36, 39-43]. adapting this construct (effort expectancy) to examine the acceptance of mobile learning by students suggests that they will accept mobile learning if they believe that the technology is easy to use. it is the interest of the study to find out whether the relationship between effort expectancy and students intention to mobile learning is moderated by gender and students’ experience. we will investigate the behavioral intention of mobile learning for students from the same age group, so we have omitted the age moderator. therefore, the following hypotheses are stated:  h3: effort expectancy has a positive effect on student intention to use m-learning.  h4a: the effect of effort expectancy on student intention will be moderated by gender.  h4b: the effect of effort expectancy on student intention will be moderated by experience. c. social influence social influence is defined as the degree to which an individual feel others’ belief on the importance of the use of the new technology [26]. age, gender, and experience have moderated the effect of social influence on behavioral intention to use m-learning [26]. many kinds of literature indicate that the social influence has a significant influence on behavioral intention to use m-learning [36, 40, 42, 43]. for young students, the intention to use mobile learning is affected by beliefs of the parents and teachers about the important of the use mobile technology in education [6]. social influence was adapted in this study to suggest that the acceptance of mobile learning is determined by the opinions of teachers and parents on the use of the technology. it is worth to find that whether the relationship between social influence and the students’ intention to use mobile learning will be moderated by gender and experience. therefore, the following hypotheses are stated:  h5: social influence has a positive effect on student intention to use mobile learning.  h6a: the relationship between social influence and student intention will be moderated by gender.  h6b: the relationship between social influence and student intention will be moderated by experience. d. facilitating conditions according to [26], the facilitating condition is defined as the degree to which an individual believes that an organizational and technical infrastructure will support the use of new technology. many works of literature indicate that the facilitating condition has a positive effect on behavior intention to use mobile technology [20, 42, 44]. the essential requirement for implementing mobile learning for young students is students’ ownership of a mobile device that support the activities of learning [6]. schools in egypt don’t have enough budgets to buy a mobile device for each student. therefore, the parents’ support is important to implement mobile learning in schools. additionally, parents’ agreement for their children to interact with mobile devices at home [6]. adapting this construct to mobile learning suggests that students perceive that availability of devices, learning materials, parents’ support and suitable infrastructure will enable them to use mobile learning without any problem, and to interact with other students and teachers. therefore, the following hypothesis is stated:  h7: facilitating conditions has a positive effect on student intention to use mobile learning. e. mobility mobility (also known as ubiquity) means access mobile services, such as mobile banking, anytime and anywhere with the aid of mobile terminals and networks [30]. mobility is additional construct added to the utaut and has not been tested previously by this model. students in egypt suffer from the issue of drop out, especially females, to avoid the cost of transportation [45]. additionally, the students face the problem of increasing classroom density and limited availability of classrooms. with mobility, learning process take place virtually anywhere and anytime [28]. as well, mobility provides teachers and students with much more flexibility than a lab model because small laptops can be used anywhere, so students don’t need to consume time in the movement to and from classrooms and labs [46] and this also will decrease in the number of rooms. therefore, mobility is necessary for the acceptance of m-learning system in egypt because it can overcome the problem of schools drop out and the limited number of classrooms. engineering, technology & applied science research vol. 6, no. 4, 2016, 1109-1114 1112 www.etasr.com ali and arshad: perspectives of students’ behavior towards mobile learning (m-learning) in egypt… many studies have indicated that mobility of learners has a strong effect on the adoption decision for the acceptance of mlearning. in [47], it was found that individual mobility has a positive effect on user intention. in [48], the tam model was extended to include perceived enjoyment (pe) and perceived mobility value (pmv) to explore users’ behavior towards ubiquitous m-learning in private and government higher learning institutions in malaysia. the study revealed that perceived mobility value has an effect on behavioral intention. other studies suggested that mobility has an indirect impact on user intention to use m-learning through perceived usefulness (performance expectancy) [49-51]. therefore, the following hypotheses are stated:  h8: mobility has a positive effect on performance expectancy.  h9: mobility has a positive effect on student intention to use mobile learning. f. enjoyment motivational model (mm) proposes that extrinsic motivation and intrinsic motivation as strong predictors of user intention to use particular information technology [52]. extrinsic motivation refers to the extent to which the user believes that using a system will enhance his/her job performance (similar to performance expectancy in the utaut). almost all information and communication technology studies indicated intrinsic motivation as enjoyment [53]. intrinsic motivation has been defined as the degree to which a user believes that using the particular system will be enjoyable [54]. the process of traditional learning may cause a sense of stress and pressure, especially in egypt. the parents put pressure on their children and require them to obtain the highest scores. some parents send their children to private tutoring when they’re still in a kindergarten school. with mlearning technology, the process of learning becomes more interesting and enjoyable. therefore, we extend the utaut model to include the enjoyment construct. in the context of mobile learning, perceived enjoyment is defined as the degree to which a student believes that using mlearning will be enjoyable. according to the information and communication technology literature, system enjoyment has a significant impact on user intention to use m-learning. for example, a study was conducted to understand the factors affecting m-learning acceptance [55]. it was found that perceived enjoyment has a significant effect on user behavioral intention to use m-learning. in [43], another study was conducted to investigate the determinants and age and gender differences in the acceptance of mobile learning. it was found that a significant relationship between perceived playfulness and intention to use m-learning exists. additionally, a study to explain and predict the acceptance of mobile learning (mlearning) revealed that perceived enjoyment can predict user intentions of using m-learning as antecedents of the behavioral intention [49]. in relation to this study, students will adopt mobile learning if they perceive that using the technology and the courses will be enjoyable. therefore, the following hypothesis is stated:  h10: enjoyment has a positive effect on student intention to use mobile learning. g. interactivity according to [56], interaction plays an important role in students’ contentment and learning levels. moreover, interactivity and active learners have a great impact upon successful learning; but the lack of interaction has no the learning motivation of the students. interactivity is an additional element added to the utaut. the process of learning in most schools in egypt depends on memorization and rote learning, and thus considered boring [45]. a student in most of the time is passive and the teacher transfers knowledge to learners without any participation from the students. mlearning can change the role of students from inactive learners to active learners through the interaction between students such as share knowledge with peers. also, the teacher can use mobile devices for interactive activities with the students by having a quick survey or quiz in subjects. hence, the interactivity is necessary for the acceptance of m-learning in egypt. in [57], a study was conducted to understand users’ attitudes toward mobile learning environment. the study revealed that interactive learning environment variable has an effective indirect impact on user intention to use mobile services through the perceived usefulness (performance expectancy). in [58] it was suggested that system interactivity factor was an effective antecedent variable of the perceived usefulness and perceived ease of use that influences the intention to use e-learning system. in [17] it was found that perceived usefulness and perceived ease of use are completely mediated the effect of system characteristics on user intention to use e-mail technology. therefore, the following hypothesis is stated:  h11: interactivity has a positive effect on performance expectancy. h. proposed model with the above literature review, a research model is proposed with seven independent variables and two moderators. altogether, we generated 11 hypotheses as discussed above. the model proposed is presented in figure 1. as shown in figure 1, unified theory of acceptance and use technology (utaut) were adopted as the basis of this study. some modifications were applied to the traditional utaut model to include the properties of mobile technologies. mobile learning is considered a new technology especially in egypt and there is no system that actually use. this study investigates the factors that may affect the future acceptance of mobile learning. therefore, the behavioral intention was used as a dependant variable of mobile learning acceptance and use behavior construct was removed. additionally, this study will investigate the acceptance of mobile learning for students from the same age and in totally voluntary usage context, so we have removed age and the voluntariness of use moderators. engineering, technology & applied science research vol. 6, no. 4, 2016, 1109-1114 1113 www.etasr.com ali and arshad: perspectives of students’ behavior towards mobile learning (m-learning) in egypt… fig. 1. proposed research model, key: pe= performance expectancy, ee= effort expectancy, si= social influence, fc= facilitating conditions, bi= behavioral intention iv. conclusion and future work the education in most schools in egypt is facing some challenges and we need an innovative technology to overcome these issues. from the literature, mobile learning can be used as an innovative technology to support traditional education. the successful implementation of mobile learning in schools is dependent on many factors including the acceptance of mobile learning by students. in egypt, the research in m-learning is still very new and there are limited studies have analyzed the acceptance of mobile technology in learning. this paper provides a roadmap the factors that may affect acceptance of mobile learning in schools by students in egypt through a proposed model and certain hypotheses. the future work is to test the proposed model by using mobile learning application among students from several schools in egypt to measure if this model can better explain the students’ intention to use mobile technology in learning. acknowledgment this research is supported by usm fellowship from institute of postgraduate studies (ips) in universiti sains malaysia (usm). the authors would like to thank the school of computer science for providing the the facilities for this research. references [1] d. m. west, “mobile learning: transforming education, engaging students, and improving outcomes”, center for technology innovation at brookings, mobile learning, pp. 1-17, 2013 [2] g. j. hwang, c. c. tsai, “research trends in mobile and ubiquitous learning: a review of publications in selected journals from 2001 to 2010”, british journal of educational technology, vol. 42, pp. e65e70, 2011 [3] j. traxler, “the evolution of mobile learning. en: r. guy (ed.), the evolution of mobile teaching and learning (pp. 1-14). santa rosa”, ed: ca: informing science press, 2009 [4] a. freitas, e. 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huan.vnp@ou.edu.vn phu-cuong nguyen advanced structural engineering laboratory structural engineering department faculty of civil engineering ho chi minh city open university ho chi minh city, vietnam cuong.pn@ou.edu.vn abstract—the shaft-grouted method has been applied on highrise buildings in ho chi minh city for the purpose of increasing the bearing capacity of barrette piles. the exim bank building foundation, using two kinds of shaft-grouted barrette piles, was 65m (tp1) and 85m (tp2) in depth. to assess the bearing capacity, this project assembly used the o-cell tools installed at 49m depth below the pile head level. shaft grouting was performed from -25m to the tp1 pile toe level and -65m to the tp2 pile toe level. this work is based on the data from the o-cell experiments at the construction site and the results of finite element simulation in plaxis software. the effectiveness of shaft grouting was analyzed and the length and position of the ejector were evaluated and compared in order to find the best solution for applying shaft grouting with the aim to ensure safety and mitigate economic problems. keywords-bearing capacity; barrette pile; shaft grouting; o-cell test; plaxis i. introduction high-rise building foundations in ho chi minh city are constructed by using bored piles and barrette piles to ensure the total loads of structures. the shaft resistance using the grouting method has been reported in [1-3, 7, 8, 11]. authors in [7] carried out laboratory tests in sand to find the behavior of density, soil gradation, and stress on the shaft resistance in grouting methods. the increase of shaft resistance was indicated by the low mobility grout. authors in [2, 3] studied the bored piles in ho chi minh city. in the results, the shaft resistance development in bored piles gains maximum resistance after a movement of only 3mm to 4mm. the osterberg test (o-cell test) in principle is exactly the same as the static compression test, and it is dedicated to bored piles and barrettes. the testing principle is to apply the load directly on the pile tip or the pile body using a device called osterberg cell. it is quite possible to use the pile load, the lateral soil friction, and the tip resistance as counterweights to increase the load. the osterberg test method will give a result in which the two curves of load and displacement at the pile tip and pile head are built independently. the purpose of this paper is to evaluate the effectiveness of shaft grouting method on the barrette piles in ho chi minh city and compare it with the no shaft-grouted method in order to find the best position to install the ejector using the finite element method (fem). ii. project information the eximbank building is located at district 1, ho chi minh city. it consists of 5 basements and 40 storys with a construction area of 3518m 2 . its design adopts 2 barrette test piles of 2800×800mm size and 15mn load [3]. the tp1 pile is 65.3m in depth near the borehole no. 2. the tp2 pile is 85.3m in depth near the borehole no. 8. their designed to be grouted lengths are 40m for tp1 and 21m for tp2 respectively from their upward tips. the geological survey report states the soil condition at the test piles as follows: soft clay stratum at a depth of 7m, sandy stratum at the tips at 41m, mixed clay at 52m and finally a dense and very dense sandy stratum. o-cell hydraulic jack is installed 16m from the pile tip and strainometers are installed along its body as shown in figure 4 of [3]. figure 1 shows how to install the equipment on the cross-sectional area of the two piles in which the main 32-dia steel bar of each pile is joined with the loop reinforcement to its frame. the total main steel bar area of the pile is 289cm 2 and the pile cross-sectional area is 2.24m 2 . the grout pipe with a diameter of 60mm is mounted around the perimeter of the steel frame throughout the length of the pile and 39.7m and 21.2m lower than the lengths of tp1 and tp2 respectively. the grout pipe must be perforated to allow the grout to escape and it can be capped to ensure a secure grouting. fig. 1. cross section and details of installation equipment for piles. corresponding author: phu-huan vo nguyen engineering, technology & applied science research vol. 11, no. 5, 2021, 7653-7657 7654 www.etasr.com nguyen &nguyen: effects of shaft grouting on the bearing behavior of barrette piles: a case study in … iii. pile load-bearing analysis a. test results in site the results of the force-displacement relationship curve of the o-cell test performed on the two test piles tp1 and tp2 can be seen in figure 7 of [3]. the force acting on the o-cell is evaluated and adjusted subjecting to the pile self-load and the water pressure at the depth of the o-cell placement. after the duration of holding the maximum load is over, the displacement values of the lower o-cell are 9.0mm and 5.9mm, and the pile tip displacement values are 4.6mm and 2.2mm respectively. the displacement values of the upper o-cell are 6.7mm and 6.9mm and the pile end displacement values are 1.2mm and 0.8mm. b. fem analysis the determination of the input data for the model is made on the basis of the correlation equations and empirical researches [9, 12-14] as follows: • the young’s modulus, e50ref, is determined from the drained 3-dimensional (3-d) consolidation test with the selected chamber pressure level σ3 in accordance with the actual state of the soil profile. • drained shear strength parameters are taken from the drained 3-dimensional consolidation test or as the effective shear strength values in the undrained 3-d consolidation test. for the soil profile without the 3-d cu test, cd can be obtained from the direct shear strength test, but its reliability is not high. the undrained shear strength parameter also does not take the friction angle of the ground soil, φu = 0, into account but only the adhesion force of the soil cu. cu values are obtained through the undrained 3-d test, the in-situ shear vane test, or the 1-dimensional unconfined compressive test. • for dense layers of sand or over-consolidated layers of clay, the expansion angle ψ exists. normally, according to the instructions of plaxis software, ψ = φ 30 0 . in other cases, the expansion angle is equal to 0. the parameters of the hardening soil model are determined directly from the geological survey report test results or from the correlation equations of the previous researches to obtain the values summarized in table i. table i. soil parameters in fem no. backfill layer 1 layer 2 layer 3 layer 3b layer 4 layer 6 type hs hs hs hs hs hs hs γunsat (kn/m 3 ) 18.56 14.61 18.42 18.35 19.23 20.38 19.93 γsat (kn/m 3 ) 18.80 15.59 19.31 19.21 19.94 20.66 20.62 e ref 50 (kn/m 2 ) 11210 4000 18000 60000 80000 95000 90000 e ref oed (kn/m 2 ) 11210 4000 18000 60000 80000 95000 90000 e ref ur (kn/m 2 ) 56030 20000 90000 250000 370000 350000 330000 m 0.75 1 0.85 0.5 0.5 0.75 0.6 νur 0.2 0.2 0.2 0.2 0.2 0.2 0.2 c (kn/m 2 ) 22.41 13.77 36 4.1 4.1 218.4 1.7 φ (o) 0 0 4.8 32.49 32.49 0 37.00 ψ (o) 0 0 0 2.49 2.49 0 7.00 rinter 0.85 0.7 0.7 0.85 0.85 0.85 0.85 to make load capacity comparison easier, the 4 used models in plaxis 2d software were: • model 1: tp1 pile with grouting • model 2: tp1 pile without grouting. • model 3: tp1 pile with grouting only from -26.3m to -48.5m. • model 4: tp1 pile with grouting only from -48.5m to -65.5m. firstly, the tp1 pile with grouting will be simulated, because it is most similar to the actual observation. after obtaining its results (note that the load level is gradually adjusted until failure) the parameters change. pile tp1 becomes a non-grouted pile, and also from that model, the set of parameters change in order to simulate the models 3 and 4 (the grouting length from -26.3m to -48.5m and -48.5m to -65.5m respectively). the obtained results are used to draw the relationship graph of the curve and the load of the four investigated models. we convert the test load of the osterberg method into the conventional static test load using an equivalent method, from which we have enough basis to evaluate the increase in the load capacity of the tp1 pile according to the four different models. fig. 2. movement and load curves obtained from actual and simulated observations. the o-cell upper displacement is 7.44mm/9.82mm on site. the o-cell lower displacement is -10.08mm/-6.27mm on site. the total strain of the o-cell is 17.52/16.09mm. this result from figure 2 shows that the measured results and the finite element modeling have high accuracy. however, in terms of displacement between the upper and lower o-cells, there is an inversion. the field displacement value is smaller than that of the plaxis model, i.e. 7.44/9.82mm. it should be noted that the lateral friction is enhanced due to the better grouting ability (regarding the safety issue). for the lower o-cell, in fact, the tip resistance has not been applied to the load-carrying capacity of the pile, so the actual displacement is larger than that of the plaxis model -10.08/-6.27mm). iv. disscusion this analytical model is rather similar to the investigated field, so the authors take this set of soil parameters to continue to simulate the remaining models with the condition of engineering, technology & applied science research vol. 11, no. 5, 2021, 7653-7657 7655 www.etasr.com nguyen &nguyen: effects of shaft grouting on the bearing behavior of barrette piles: a case study in … increasing load until the failure of the pile. the results of models 1-4 are displayed in figures 3-6. fig. 3. model 1. the tp1 pile with grout reaches 305% of maximum load. fig. 4. model 2. the tp1 pile without grout reaches 255% of maximum load. fig. 5. model 3. the tp1 pile with grout from -26.3m to -48.5m reaches 280% of maximum load. fig. 6. model 4. the tp1 with grout from -48.5m to -65.5m reaches 280% of maximum load the ultimate load capacity is determined based on the shape of the load-displacement relationship curve: s = f(p), logs = f(logp) (1) in many cases, it is necessary to combine with other curves like: s = f(logt), p = f(s/logt) (2) with the load-displacement relationship curve, the ultimate load-carrying capacity is determined as follows: • case 1: the p-s relationship curve has a clear bending point. the ultimate load-carrying capacity is determined directly on the curve, the load corresponding to the point where the curve begins to change suddenly or the curve is closely parallel to the displacement axis. • case 2: the p-s relationship curve changes slowly. it is quite difficult or impossible to accurately determine the bending point. the ultimate load-carrying capacity is determined by different graphical methods. the analysis and evaluation of the test results by the osterberg method are still based on the principles of conventional static testing, in which the q-s relationship curve is an important tool of the quantitative analysis of the loadcarrying capacity of the piles that a mechanical problem usually covers. the goal of load testing in most cases is not only to determine the bearing capacity of the pile foundation, but also to get a more specific view than the one from the general theory and the calculated results about the interaction between the pile and the composing ground so that we can offer more appropriate behaviors in the design of the pile foundation and in the future construction processing. we can build a load-settlement curve (similar to a conventional static compression test curve) in the following way: at any displacement s, the downward force affecting the soil is: q’↓ = q↓ + w2’ (3) where q↓ is the downward force by the o-cell at the displacement s and w2 is the self-load of the pile from the ocell downwards (buoyancy must be taken into account if we are below the groundwater level). at the same displacement s, the upward force carried by the soil is: q’↓ = (q↓ w1’) × f (4) where w1’ is the self-load of the pile from the o-cell upwards (buoyancy must be taken into account if we are below the groundwater level) and f is the coefficient that takes into account the difference in the lateral friction between the normal static compression and the osterberg compression. with f = 1.00 for the pile in the rock and f = 0.95 for the pile in the loose soil. at the displacement s, the sum of the upward and downward forces will be subjected by the soil: p = q’↓ + q’↓ = q↓ + w2’ + (q↓ w1’) × f (5) engineering, technology & applied science research vol. 11, no. 5, 2021, 7653-7657 7656 www.etasr.com nguyen &nguyen: effects of shaft grouting on the bearing behavior of barrette piles: a case study in … however, in the case of downward compression, the soil is already partially imposed by the self-load of the pile, so the applied load at the top of the pile is: pe = p – w1’ – w2’ = q↓ + (q↓ w1’) × f – w1’ (6) at a load of pe (loading downwards), the settlement of the pile is s + ∆δ where the increment ∆δ refers to the elastic compressive strain of the pile. repeating the above steps with different positions s, we can draw a static compression curve corresponding to the data pair (pe, s + ∆δ). if at a certain position that goes beyond the range of a curve (for example, the lateral resistance curve of the pile segment on the jack), we choose one of the following two solutions: • take the upward force as constant (regarded as the extreme value) and equal to the tested maximum lateral resistance. • extrapolating the next segment of the lateral resistance curve. however, this extrapolation has errors, because if the pile body is very rough (convex), then the lateral resistance reaches its ultimate value more slowly. conversely, the less convex and concave the pile body is, the faster the lateral resistance reaches its ultimate value. fig. 7. load capacity of the pile in the models 2 and 4. fig. 8. load capacity of the pile in the models 1 and 3. from the above analysis, we will convert equivalently the test results of the osterberg method into those of the conventional test method to plot the p-s relationship curve from the data pair (pe, s +∆δ) and then use the graphical method to determine the load capacity. the results of the shape of the load-displacement relationship curve are displayed in figures 7-9. fig. 9. summary of the pile load-carrying capacity of the 4 models. v. conclusion through the experimental study from the o-cells of the tp1 pile in the eximbank building on the ability to improve the load-carrying capacity of the lateral walls, the following conclusions can be drawn: • improvement of the bearing capacity of the pile by the lateral grouting method is highly effective with results of 61.7mn and 41.8mn with and without grout respectively. the friction performance of the pile body with grouting increases by 1.48 times. it is different from the previous studies that we compared the analytical equations and the field results. • grouting of each segment at depths of 22.2m (from -26.3m to -48.5m) and 16.8m (from -48.5m to -65.3m) corresponding to the maximum load of 59.2mn and 59.4mn is evaluated as being similar to the load-carrying capacity. the fem simulation results show that the bigger grouting length and the bigger grouting depth will give higher values of bearing capacity. simulating grouting in each segment is very beneficial for the design of allowable loads, both in terms of safety and cost aspects. • the fem (plaxis) can simulate and evaluate the o-cell and the lateral grouting tests of piles. this method can be used for computational correction after the field results are available for detailed design. acknowledgment the current research is supported by the ho chi minh city open university (project no. e2019.08.3). references [1] b. h. fellenius, "tangent modulus of piles determined from strain data," presented at the foundation engineering: current principles and practices, 1989, pp. 500–510. [2] b. h. fellenius, "analysis of results of an instrumented bidirectional-cell test," geotechnical engineering journal of the seags & agssea, vol. 46, no. 2, pp. 64–67, 2015. [3] h. m. nguyen, b. h. fellenius, a. j. puppala, p. aravind, and q. t. tran, "bidirectional tests on two shaft-grouted barrette piles in mekong delta, vietnam," geotechnical engineering journal of the seags & agssea, vol. 47, no. 1, pp. 15–25, mar. 2016. [4] l. m. zhang and l. f. chu, "calibration of methods for designing large-diameter bored piles: ultimate limit state," soils and foundations, vol. 49, no. 6, pp. 883–895, dec. 2009, https://doi.org/ 10.3208/sandf.49.883. engineering, technology & applied science research vol. 11, no. 5, 2021, 7653-7657 7657 www.etasr.com nguyen &nguyen: effects of shaft grouting on the bearing behavior of barrette piles: a case study in … [5] "report on barrtte load testing tp2eximbank tower, ho chi minh city, viet nam," 138131–2, sep. 2013. [6] "pile foundation design standard," national standards, vn 10304: 2014. [7] s. pooranampillai, s. elfass, w. vanderpool, and g. norris, "large scale laboratory testing of low mobility compaction grouts for drilled shaft tips," geotechnical testing journal, vol. 33, no. 5, pp. 397–409, sep. 2010, https://doi.org/10.1520/gtj102658. [8] g. d. plumbridge, b. d. littlechild, s. j. hill, and m. pratt, "full-scale shaft grouted piles and barrettes in hong kong–a first," in proceedings of the nineteen annual seminar of the geotechnical division of the hong kong institution of engineers, hong kong, china, 2000, pp. 159– 166. [9] t. nguyen, v. q. lai, d. l. phung, and t. p. phan, "shaft resistance of shaft-grouted bored piles and barrettes recently constructed in ho chi minh city," geotechnical engineering, vol. vol. 50, no. 3, pp. 155–162, sep. 2019. [10] j. zhou, x. gong, and r. zhang, "model tests comparing the behavior of pre-bored grouted planted piles and a wished-in-place concrete pile in dense sand," soils and foundations, vol. 59, no. 1, pp. 84–96, feb. 2019, https://doi.org/10.1016/j.sandf.2018.09.003. [11] x. zhao, g. zhou, g. zhao, l. kuang, and x. hu, "fracture controlling of vertical shaft lining using grouting into neighboring soil deposits: a case study," soils and foundations, vol. 57, no. 5, pp. 882–891, oct. 2017, https://doi.org/10.1016/j.sandf.2017.08.018. [12] n. mangi, d. k. bangwar, h. karira, s. kalhoro, and g. r. siddiqui, "parametric study of pile response to side-by-side twin tunneling in stiff clay," engineering, technology & applied science research, vol. 10, no. 2, pp. 5361–5366, apr. 2020, https://doi.org/10.48084/etasr. 3290. [13] t. a. rind, h. karira, a. a. jhatial, s. sohu, and a. r. sandhu, "particle crushing effect on the geotechnical properties of soil," engineering, technology & applied science research, vol. 9, no. 3, pp. 4131–4135, jun. 2019, https://doi.org/10.48084/etasr.2730. [14] a. h. bhutto et al., "mohr-coulomb and hardening soil model comparison of the settlement of an embankment dam," engineering, technology & applied science research, vol. 9, no. 5, pp. 4654–4658, oct. 2019, https://doi.org/10.48084/etasr.3034. microsoft word etasr_v13_n4_pp11338-11343 engineering, technology & applied science research vol. 13, no. 4, 2023, 11338-11343 11338 www.etasr.com nguyen et al.: 3d finite element model and measurement comparison for roller compaction induced … 3d finite element model and measurement comparison for roller compaction ιnduced vibration: the case study of a ring road in hanoi, vietnam ngoc long nguyen university of transport and communications, vietnam nguyenngoclong@utc.edu.vn chau lan nguyen university of transport and communications, vietnam nguyenchaulan@utc.edu.vn (corresponding author) tien thanh bui university of transport and communications, vietnam btthanh@utc.edu.vn hong lam dang university of transport and communications, vietnam dang.hong.lam@utc.edu.vn received: 29 may 2023 | revised: 17 june 2023 | accepted: 24 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6070 abstract vietnam is currently constructing many transportation and infrastructure projects in urban areas. during the construction process of road foundations such as pile driving and vibratory compaction often causes vibrations that can affect nearby structures. therefore, it is necessary to study the impact of vibrations induced by construction activities. a study was conducted to investigate the impact of roller compactioninduced vibration on the buildings and structures of ring road no.2 in hanoi, vietnam. the study also applied a 3d fem method to evaluate the impact of vibration on surrounding structures. the results showed a good correlation between finite element calculations and field measurements. keywords-3d plaxis; vibration; fem; soil structure dynamics i. introduction the construction of ring road no.2 in hanoi was executed in 2018 and consisted of two sections: an elevated section and a lower section. the elevated section is over 5 km long, starting from the southern connection point of vinh tuy bridge and ending at the intersection with nga tu so street. the lower extension, which links to vinh tuy bridge at the starting point, is approximately 3 km long and terminates at the nga tu vong intersection. this is a road with high traffic density, and there are many buildings around it. the use of vibrating rollers for road foundation construction raises concerns about their impact on nearby buildings and historic structures. therefore, it is necessary to assess and monitor the effects of this construction activity on the structures placed along the ring road no.2. construction activities in city sites can cause significant disturbances to nearby structures such as differential settlement, even collapse [1-5]. the vibration sources are soil excavation, pile driving, and compaction using vibratory equipment [2-4, 6-10]. these sources can cause vibrations in the surrounding soils, which will be transmitted to nearby buildings and structures. for example, a resonance in multistory buildings at distances close to 200 and 500 m from dynamic sources was observed. in addition, a frequency of 26 hz from a vibratory sheet pile can generate ground vibrations below 5 mm/s and vertical floor vibrations higher than 51 mm/s in two-story houses and can cause architectural damage [11]. the impact of these vibrations on existing structures is typically measured by particle vibration velocity. most standards and guidelines set an allowable vibration level based on peak particle velocity (ppv) [12, 13]. bs 5228: part 4: engineering, technology & applied science research vol. 13, no. 4, 2023, 11338-11343 11339 www.etasr.com nguyen et al.: 3d finite element model and measurement comparison for roller compaction induced … 1992, which is a code of practice for managing noise and vibration during piling operations, also offers direction on the permissible levels of vibration in structures. according to this standard, a cautious limit of ppv for intermittent vibration should be set at 10 mm/s, while for continuous vibrations it should be 5 mm/s, to avoid minor or cosmetic damage [6]. experimental and numerical analysis are commonly used to solve wave propagation induced by impact pile driving [4, 7, 8, 14-17]. authors in [18] performed a 2d numerical analysis to estimate the soil deformation induced by vibrations of the piling hammer. authors in [15] evaluated the seismic loading of nearby structures according to the czech technical standards. authors in [6] focused on the study of field monitoring of roller vibrations during the compaction of subgrade soil. previous studies in vietnam have investigated the effects of construction vibrations on buildings and structures [19, 20]. authors in [21] focused on controlling vibrations on existing buildings in the metro line 3 project. the monitoring and numerical analysis (plaxis 3d) results showed the minimum distance of 4 m between the vibration source and the existing building and the grab drop height of 1 m of grab shock for the metro line 3 project. however, other construction activities, such as vibrating rollers, have not been studied carefully regarding the effect on nearby buildings on the construction site in hanoi. therefore, this study aims to use the finite element method (fem) to address wave propagation in non-homogeneous ground conditions in hanoi due to a vibrating roller, and to compare the results obtained from the fem with the experimental data of the ring road no.2 construction project. ii. method a. soil investigation the geological soil profile of borehole 1, which is close to the measurement points, is shown in figure 1. for a detailed geological investigation, standard penetration tests (spts) were conducted at every 2 m depth. it is observed that the stratigraphy consists of 7 layers. the 1 st layer is filled soil (layer 1) with thickness of about 1.2 m. below, there is a yellow/brown soft to medium sandy clay (cl) layer with an average thickness of 4.4 m and uncorrected nspt = 6~16. the 3rd layer is fine sand (layer 3) with about 1.2 m thickness. the 4 th layer is also yellow/brown, soft sandy clay (cl) with a thickness of about 3.7 m and uncorrected nspt = 5~6. layer 5 is brown soft sandy clay (cl) with some gravels (layer 5), with thickness of 10.8 m and nspt = 10~23. the 6 th layer is also yellow/brown, soft sandy clay (cl) with a thickness of about 7.5 m and uncorrected nspt = 8~11. the 7 th layer is also yellow/brown, stiff sandy clay (cl) with a thickness of about 7.5 m and uncorrected nspt = 14~15. soil samples were retrieved for the conduction of laboratory tests, such as physical property tests (water content, soil distribution, atterberg limit, etc.) and mechanical property tests (consolidation test, hydraulic conductivity test, triaxial test). the physical and mechanical properties results for soil layers were collected and were considered as input parameters for plaxis 3d model. they are presented in table i. fig. 1. spt value for soil profile in borehole 1. table i. soil parameters in plaxis 3d contents layer 1 layer 2 layer 3 layer 4 layer 5 layer 6 layer 7 type of model mc mc mc mc mc mc mc unit weight γ (kn/m 3 ) 18 18.6 13.4 19 17.3 19.7 18 saturated unit weight γsat (kn/m 3 ) 18.5 18.68 13.84 19.5 17.3 19.89 18.5 cohesion, c' (kpa) 15 23 8.8 1 15.8 27.3 20 friction angle, ’(o) 20 12.91 8.18 28.23 18.5 15.76 20 ν 0.32 0.3 0.3 0.3 0.3 0.3 0.3 eoed (mpa) 21.46 26.92 4.815 40.38 21.46 26 26.92 e (mpa) 15 20 3.0 30 15 26 20 vs (m/s) 55.65 63.7 28.52 77.18 56.76 80.46 64.75 vp (m/s) 108.2 119.2 59.37 144.4 110.3 113.8 121.1 rinter 0.65 0.7 0.7 0.7 0.65 0.8 0.65 note: c' and ’are taken from the consolidated undrained triaxial test. b. monitoring accelerometers or geophones can be utilized to measure the vibration velocity (ppv) in mm/s and assess the impact of construction activities on a plane that requires compaction using a vibrating roller [6, 7]. the vibrating roller hamm 20t generates vibrations with a frequency range of 27 hz to 30 hz and applies a centrifugal force of 250 kn to 330 kn (figure 2). the significant impact produced by the roller compaction can cause soil particles to displace and compress, leading to a reduction in soil porosity and resulting in ground vibrations that may affect nearby structures. to determine the magnitude of the impact caused by the roller compaction vibrations, acceleration sensors placed on steel anchors were used to record the ground's dynamic response during the construction process. the devices used for vibration monitoring are depicted in figure 3. four sensors, namely 31, 32, 35, and 36 were used in this study with highly sensitive accelerometers and vibration detection sensors. sensors 31 and 35 monitored vertical acceleration, while sensors 32 and 36 measured horizontal acceleration for point 1 and point 2, respectively. the measuring frequency range of the sensors is 0.15 ÷ 1000 hz. the sensitivity of the sensors is approximately 10000 mv/g equal to 1019.4 mv/(m/s 2 ) and their non-linearity is less than 1%. engineering, technology & applied science research vol. 13, no. 4, 2023, 11338-11343 11340 www.etasr.com nguyen et al.: 3d finite element model and measurement comparison for roller compaction induced … fig. 2. vibration source hamm 20t. (a) (b) fig. 3. test setup: (a) acceleration sensors, (b) data accquisition and computer analysis. the vibrating work was carried out along the road. the experiment was conducted to measure ground vibration for a 3story building (figure 4). the distance from the vibration machine to point 1 and point 2 are shown in figure 1. the vibration measuring device was attached to a 30 cm length of steel pile at the foundation of the building. during the operation of the roller compactor, vibration measurements were taken. then, the measured data were processed and analyzed with the elasto-dynamic program for comparison and evaluation. fig. 4. monitoring point setup for a 3-story building. c. 3d plaxis model in this study, the wave propagation from roller compaction was modeled with plaxis 3d dynamic finite element code. the dimensions of the model is shown in figure 5. soil conditions and shear wave velocity are included in the model (table i) with the profile shown in figure 1. the soil layers were modeled using the mohr-coulomb (mc) model in plaxis with the input parameters presented in table i. the transversal and longitudinal seismic wave propagation velocities were automatically determined in plaxis 3d by: ��������� =� ��� � � ��� � (1) �� � � � (2) the three-story building was modeled with plate elements. its input parameters are presented in table ii. table ii. input parameters for 3-story building in plaxis 3d contents unit type of model elastic γ kn/m3 24.5 e1 kpa 26+e6 e2 kpa 26+e6 g12 kpa 11.67+e6 ν12 0.2 the plaxis 3d has a calculation dynamic module that allows for solving dynamic problems using fem. the elementary equation for calculating time-dependent deformation changes under dynamic loading in matrix notation for the entire area under consideration is: 0 ' ' sin( )f f m t   (3) where �� is the amplitude multiplier, �� is the input value of the load, � � 2π� with � being the frequency in hz, �� is the initial phase angle, and ���� is the amplitude of the dynamic load. for hamm 20t vibrating roller, the ���� is taken as 330 kn, the frequency is obtained as f =30 hz and the initial phase angle is equal to 0. fig. 5. plaxis 3d model of a 3 story building. setup 4 setup 5 31,32 35,36 31,32 ring road no.2 3-storey-building 7.28m3.69m24.579m 11.529m vibration machine (hmamm 20t) point 2point 1 point 3 setup 4 point 2 point 1 point 3 engineering, technology & applied science research vol. 13, no. 4, 2023, 11338-11343 11341 www.etasr.com nguyen et al.: 3d finite element model and measurement comparison for roller compaction induced … iii. results a. monitoring results the obtained vibration velocities are shown in figures 6-9. fig. 6. vertical velocity versus dynamic time at point 31. fig. 7. horizotal velocity versus dynamic time at point 32. fig. 8. vertical velocity versus dynamic time at point 35. fig. 9. horizontal velocity versus dynamic time at point 36. b. plaxis 3d results the vibration velocities obtained from plaxis 3d are shown in figures 10-13. fig. 10. vertical velocity versus dynamic time at point 31. fig. 11. horizotal versus dynamic time at point 32. fig. 12. vertical velocity versus dynamic time at point 35. fig. 13. horizotal velocity versus dynamic time at point at point 36. engineering, technology & applied science research vol. 13, no. 4, 2023, 11338-11343 11342 www.etasr.com nguyen et al.: 3d finite element model and measurement comparison for roller compaction induced … the monitoring data and 3d plaxis results are summarized in table iii. table iii. comparison of monitoring data and fem 3d results point vibration direction distance to the vibration source (m) monitoring data ppv (m/s) fem 3d ppv (m/s) s32 horizontal 3.7 4×10 -5 4.1×10 -5 s31 vertical 3.7 1.8×10 -5 1.88×10 -5 s35 vertical 12.5 8.5×10 -5 8.3×10 -5 s36 horizontal 12.5 2.5×10 -5 2.3×10 -5 the waveform records of the vibration velocities (horizontal component vx, and vy, vertical component vz) are shown in figures 10-13. the maximum vertical velocity (vz), as can be seen in table iii, is about 8.5×10 -5 mm/s. this finding is consistent with previous research [2, 5, 6]. it is observed that the maximum measured velocity values were similar to the values derived from the numerical analysis. normally, the maximum ppv for buildings and structures with masonry or concrete construction should not exceed 12.5 mm/s for shortterm exposures and 5 mm/s for long-term exposures. similarly, the international organization for standardization (iso) recommends a maximum ppv of 10 mm/s for buildings and structures. therefore, the ppv value is still lower than standard requirements, which means that the house still is not affected by vibrations induced by roller compaction in this case. figure 14 presents the vertical displacement of the soil due to the vibration of the roller. a small value of displacement was observed and it had no effect on the settlement of the house. fig. 14. vertical displacement due to roller vibration. iv. conclusion this paper presents the results of experimental measurements and 3d fem modeling of the roller compaction effects during the construction of the ring road no.2 in hanoi, vietnam. the fem dynamic analysis (plaxis 3d) of roller compaction-induced vibration based on the hanoi conditions was studied. the results show that the velocity decreases with the increase in distance from the roller. the fem results are in good agreement with the actual velocity measurements and frequency dominant structure responses due to ground-borne vibration. acknowledgment this research is funded by the university of transport and communications (utc) under grant number t2022-ct009tđ. references [1] m. e. bayraktar, y. kang, m. svinkin, and f. arif, "evaluation of vibration limits and mitigation techniques for urban construction," florida department of transportation, tallahassee, fl, usa, fdot contract no.: bdk80 977-22, oct. 2013. 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[21] h.-l. dang, v.-q. nguyen, and t.-h.-m. vo, "a study of 3d modelling the vibrations induced from grab shock at the metro line 3 project in hanoi," journal of materials and engineering structures, vol. 9, pp. 557–562, 2022. microsoft word etasr_v12_n2_pp8402-8409 engineering, technology & applied science research vol. 12, no. 2, 2022, 8402-8409 8402 www.etasr.com tran et al.: load shedding in high-integrated wind energy power systems using voltage electrical … load shedding in high-integrated wind energy power systems using voltage electrical distance tung giang tran electrical and electronics department hcmc university of technology and education ho chi minh city, vietnam giangtt@hcmute.edu.vn thai an nguyen electrical and electronics department cao thang technical college ho chi minh city, vietnam nguyenthaian@caothang.edu.vn minh vu nguyen hoang hcmc university of architecture ho chi minh city, vietnam vu.nguyenhoangminh@uah.edu.vn ngoc au nguyen electrical and electronics department hcmc university of technology and education ho chi minh city, vietnam ngocau@hcmute.edu.vn tan thien tran electrical and electronics department cao thang technical college ho chi minh city, vietnam trantanthien@caothang.edu.vn received: 26 january 2022 | revised: 16 february 2022 | accepted: 27 february 2022 abstract-this paper presents a load shedding method for power systems with high integration of wind energy, considering their frequency response. the minimum load shedding power needed to restore system frequency to operational limits can be determined by using the modified frequency response model along with secondary frequency control. the voltage electrical distance method can then be applied to appropriately distribute the shedding power to load buses. this method brings selectivity to the problem and minimizes the impact caused by load shedding. the proposed method was validated using simulations on the ieee 37-bus test system with a modified wind power generator model. keywords-modified frequency response (fr) model; load shedding; voltage electrical distance (ved); secondary frequency control (sfc) i. introduction the impact of the high integration of renewable energy, especially wind power plants, into classical power systems raises concerns [1-3]. accordingly, stability issues should be studied and solved in power systems with high-integrated wind energy [4-7]. when a disturbance occurs in an integrated wind power system and causes a power imbalance, the problem is more serious if the generating capacity is less than the load demand, which requires the system to take measures to rebalance the power and stabilize its frequency [8-10]. in [1113], virtual frequency controls with frequency response models of wind power systems were proposed to solve these stability issues. however, when all control efforts have been taken and the frequency does not return to normal or within the allowable range, load shedding is the final option for preventing a system blackout. load shedding methods based on priority for wind energy integration were proposed in [14]. higher priority loads powered by reliable wind power were prevented from being shed under redundancy conditions, such as high load demand. a method to improve the recovery period of underfrequency transients was demonstrated in [15]. in the rate of frequency change for wind turbine power generation, virtual inertia control was applied under frequency contingency. the main focus of these studies was to evaluate the response of the system to disturbances and to consider wind power as a reliable energy source to prevent shedding loads. an effective load shedding strategy requires the lowest amount of shedding power, which means that the system’s control capabilities and transmission system operators’ (tsos) actions will provide the appropriate amount of additional power to the grid. this study deployed a modified frequency response (fr) model to analyze the frequency characteristics of the system considering wind energy, along with the secondary frequency control action of tsos to obtain the minimum power for the load shedding strategy. the goal is to bring the system's frequency within normal operating limits and minimize the impact caused by load shedding. in addition, the voltage electrical distance method was used to distribute the shedding power and obtain selectivity. furthermore, this study carried out simulations on the ieee 37-bus system with a corresponding author: tung giang tran engineering, technology & applied science research vol. 12, no. 2, 2022, 8402-8409 8403 www.etasr.com tran et al.: load shedding in high-integrated wind energy power systems using voltage electrical … modified wind turbine model using the powerworld simulation platform to validate the effectiveness of the suggested method. the results were then analyzed and compared with a traditional load shedding method. ii. primary frequency control for wind power assessing the controllability of wind turbine generators (wtgs) when frequency disturbances occur is an important issue, especially with the high penetration of wind energy into the traditional power systems. most wtgs are connected to the system entirely or partly through power converters, so the frequency control support in the form of the inertia of a wtg is negligible, even though there is a small amount of inertia reserve in its mechanical parts (blades, rotor generator). therefore, using the virtual inertia (vi) controller, the kinetic energy stored in the wtg can be quickly released to adjust power and prevent a rapid drop in frequency when a large disturbance occurs. in addition, the droop controller helps to adjust the wtg's generation power to restore the system frequency within the normal operation range during the wtg's primary frequency control. to generate more power for primary frequency control when there is a sudden increase in load demand, the wtg cannot operate in the maximum power point (mpp) mode but needs to be deloaded to reserve a certain amount of power. therefore, the pitch controller will enter the stage of deloading power from the wtg by mechanical power. the power system with high participation of wtg should apply this control method to get a good response to frequency disturbances. therefore, the wtg's dynamic frequency control strategy applied in this study was based on vic combined with the pitch angle deload control method. the control diagram is shown in figure 1 of [16]. the parameters used in the primary frequency controller are: ∆f and ∆β are the frequency and pitch angle deviations respectively, ηω is the equivalent inertia time constant of the wtg, pe, te, and tm are the wind turbine’s active output power, electrical, and mechanical torque respectively, kb is the gain constant of the pitch controller, kω is the proportional gain, and rω is the droop constant. a. frequency regulation using droop and virtual inertia control the additional electrical power control signal combined with the droop controller is expressed as: δ������ = − ��� + ���� δ���� (1) b. the pitch angle-based deloaded control for wtgs when deloading is neglected, wtg operates in the mpp mode with the mechanical and electromagnetic torque expressed as: �� = ����� � � (2) �� = ���� (3) where cp is the optimal power coefficient of the turbine depending on wind speed, rotor speed, and blade angle and kp is the factor representing the maximum generating power at the rated condition. the deloaded power of the wtg is accomplished by setting the blade angle β to a nonzero value, depending on the desired amount of power for reservation. and with the pitch angle-based deload controller, the blade angle will be regulated according to the frequency deviation [16]. iii. frequency response representation of the highintegrated wind energy power system this section elaborates the system frequency response representation of the control method to evaluate the model's efficiency and determine the shedding power in the secondary frequency control. using small-signal analysis, the reordered dynamic model of wtgs is presented as a small-signal linear transfer function. a modified fr model for a high-integrated wind energy power system will be obtained and the frequency response features will be evaluated. in addition, the stability of the closed-loop control system will be analyzed. a. dynamic transfer function of the wtg the electromagnetic power pe of the wtg is regulated through the primary controller (virtual inertia and droop controllers), while the mechanical power pm is regulated by the pitch angle controller [16]. the total change of electromagnetic torque according to the frequency deviation using these control methods can be written as: δ����� = − � � ����� � !δ���� + 2���δ���� (4) using a small signal stability analysis and the linearization method, the change in mechanical torque ∆tm due to the frequency deviation δf and wind speed variation δv can be given as: #����� = $%&$' #���� + $%&$( #)��� + $%&$� #���� = ���*�+�,� #���� + .���/0 12�� � − ���3��4012 � 5#)��� + ����67�� − ��7.89: �' �� ! #���� (5) where �� = $��$4 and �< = $�� $< will be considered constant in this study, based on the dynamic power characteristic of the turbines. the swing equation in the frequency domain is: 2=��δ���� = δ����� − δ����� (6) joining (2), (3), and (4), the correlation relating the change of output power to frequency fluctuation can be expressed as: δ����� = 6> �� δ)��� − ?� ��?� �?@ > �� δ���� (7) where: a = �b���c� ��,�(,�/0 12d�e�(� f = ����,(�g.�/0 12d�e4012h��,�(,�/0 12d�e�(� i� = �b���c�c� ��,�(,�/0 12d�e�(� (8) engineering, technology & applied science research vol. 12, no. 2, 2022, 8402-8409 8404 www.etasr.com tran et al.: load shedding in high-integrated wind energy power systems using voltage electrical … i� = �b�����c� d����� ��,�(,�/0 12d�e�(� + �� ij = − �� � �������*�+(�� ��,�(,�/0 12d�e�(� + � �� b. the modified fr model for high-integrated wind energy power system a widely used fr model was developed in [17] for a traditional power system, focusing on the response of thermoelectric generators. however, with the highly integrated large-scale wind energy into the power system and with the different characteristics from traditional generators, this fr model cannot be applied in this study. based on the combination of the wtg’s de-ordered dynamic model in (7) and the model proposed in [17], the modified fr model for high-integrated wind energy power systems was derived and is shown in figure 1. the model in figure 1 was applied to the system containing conventional and wind power generators. therefore, the parameters of the model were modified using the equalization method presented in section iv. tr is the time constant, fh is the generating power fraction of the thermoelectric generator, r is the characteristic constant of the governor (droop control), h is the system equivalent inertia time constant, d is the self-regulation coefficient of the load, and α is the participation factor of wind energy in the power system. fig. 1. the modified fr model for high-integrated wind energy power systems. the input signals of the modified fr model are the fluctuations in load demand ∆pl and in wind speed δv, where the frequency variation δf is the output of the proposed model. as seen in figure 1, the modified fr output signal is influenced by the variation in both power demand and wind speed. in this study, the total power of the system is constant, and wtgs connected to the power grid are converted to the single-machine model. the superposition principle was used to analyze the impact of each input disturbance on the frequency variation of the system [18]. more specifically, when assessing the influence caused by the change in load demand to the frequency, the wind speed will be set as constant, and vice versa when evaluating the effect of wind speed variation. the transfer function of frequency deviation to fluctuations in load and wind speed for the high-integrated wind energy power system is: δ���� � kl9m 6 > �� l(m n o� ��o� �o@ p, ,�p� ��p� �p@ (9) qj � a�� q� � a �� qj � 1 s. � ti��� 2�1 t�=a�� s� � �1 t�u2=�a ��� va��w ��dx�yb>%� � t�i� i���� s� � �1 t�u2= v�a ���w ��dx��>�yb%�� � t�i� ij��� sj � �1 t�v �1 t�/[ tij (10) where ∆pd and ∆vd represent the disturbances in load demand and wind speed per unit. according to the initial/final value theory, the initial rate of change of frequency (ircf) and the steady-state frequency deviation (ssfd) of the system are obtained by: \[8] = ^_`abjc s#��d� sd = ^_` b�∞��#���� = ∆�p q�s� = #�p t�� + 2�1 t�= (11) ee]v � ^_` ab�∞ #��d� = ^_` bjc�#���� = �#�p + f#)p� qjsj f = #�p + f#)p�1 − t�v + �1 − t�/[ + tij (12) the results from (11) and (12) were used to evaluate the frequency controllability of the power system with high wind energy penetration under disturbance conditions. the natural response of the system against disturbances can be defined as the primary control process of the system. the ssfd value will be the basis to decide whether or not to perform load shedding to stabilize the frequency within an allowable range. iv. equivalent conversion of system's parameters a. equivalent wind power generators model the uncertainty of wind power sources due to their dependence on weather and geometric conditions, as wind farms consist of many turbines, causes each turbine to behave inconsistently, leading to changes in the total generating power and the parameters of the whole wind farm. therefore, having an equivalent conversion model of all or a part of the wind farm is essential to create homogeneity among the generating sources and to obtain the equivalent parameters used for the modified fr model. the method of equivalent transform proposed in [19] helps converting the wind farm into a singlegenerator model. the advantage of this method is that due to its simple implementation and equivalent model, it can be applied engineering, technology & applied science research vol. 12, no. 2, 2022, 8402-8409 8405 www.etasr.com tran et al.: load shedding in high-integrated wind energy power systems using voltage electrical … to many problems. in addition, the equivalence method converts the wind farm into multiple generators and helps improving accuracy. a detailed equivalence method was proposed in [20] to analyze the location and wind speed data of each turbine to develop the wind farm model. the accuracy of the equivalent model is further enhanced by updating the data values. due to the objective of this study, the equivalent method of a single-generator model will be used for simplicity. b. equivalence method for system parameters to evaluate the system's frequency response to disturbances using the modified fr model, the parameters of a classical power plant such as the inertia time constant h and the selfregulating coefficient d are needed. the equivalence procedures of the parameters of a power system considering wind power sources were presented in [21] and are applied as: =�gh = ∑ jkl+,k nk ∑ l+,knk = ∑ jkl+,knk loo (13) where hequ and hi are the equivalent and individual inertia time constants, stt is the total apparent power of the system, sb,i is the apparent power of the individual conventional generator, and n is the total conventional generating units. if m conventional generating units are replaced by wtgs with an equivalent amount of power, the system's inertia time constant is given as: =p�gh = ∑ jkl+,k nq&k ∑ l+,k�lrstnq&k = �1 − t)=�gh (14) v. determining minimum load shedding power α generator failure or severed load disturbance in a highintegrated wind energy power system causes an imbalance between generating power and load demand leading to a frequency deviation. in this case, the modified fr model shown in figure 1 defines the response of the system, the initial rate of frequency change is calculated by (11), and the frequency deviation of the new steady state is calculated by (12). the normal operation of the power system frequency is ∆fallow=±0.5% [22-23]. for the case of disturbances decreasing frequency, when the system returns to a new steady-state with ssfd less than -0.5%, the second frequency control must be enabled by the tsos to elaborate maximum power injected into the grid to restore the frequency into normal limits. if the frequency does not return to normal limits, through secondary control actions, load shedding must be deployed to prevent system blackouts. modifying (12) to restore the frequency deviation within normal limits, the maximum power for the secondary control stage and the minimum power for load shedding can be derived as: #�?uuvw = �x9m�x9y13znm{0| 3zno0z} &{~d9�� &kn��6∆�m��dx�����dx�/��x?@ (15) where ∆psecondary control max is the maximum power available for secondary control. the minimum power for load shedding is given as: ��l min = #�p − #�secondary control �?� −∆�?uuvw k�1 − t)v + �dx� +tijn (16) vi. distribution power method for load shedding the ved method can be elaborated by the following steps [24-27]. • step 1: convert all buses to load buses (change all pv buses into pq buses). • step 2: determine [��/��] in all buses. this inverse of the jacobian matrix indicates the relationship between the reactive power injection at one bus to the voltage variation of the neighboring buses as follows: #�� = −[���/���]#�� = −���d�#�� (17) where, ���d� is the sensitivity matrix [���/���]. • step 3: calculate t�� using the sensitivity matrix in step 2. then the voltage variation relationship between bus i and bus j is given as: #�� = [���d�/���d�]#�� = t��#�� (18) where, t�� is defined as [���d�/���d�]. • step 4: calculate the ved using the cross product of t���t�� × t��� which is reflected by the symmetrical distance: v��_, �� = v���, _� = −���gtij × t��h (19) where, t�� is defined as[���d�/���d�]. the load shedding power is then given as [21]: ��l� = ��,1� ��,&k .��l��o (20) where plsi is the shedding power needed at bus i (mw), plsmin is the minimum power for optimal load shedding (mw), dvmi is the ved value of the corresponding load bus i to the fault bus, and dv,eq is the equivalent ved value of all load buses to the fault bus. in addition, the physical-electrical relationship of the buses in the system is presented by the ved values. equation (17) shows that the closer the distance, the smaller the dv or the larger the t�� is. on the other hand, (16) evaluates the voltage interactions between buses i and j, with a higher value of t�� the voltage attenuation is more severe at bus i when a disturbance occurs at bus j. thus, when a disturbance occurs such as tripping of a generator unit, the amplitude of the voltage fluctuation near this generator is large, leading to an attenuation voltage at nodes with increasing in ved. to ensure that the voltage profile returns to its stability margin, the load shedding power at each bus can be determined on the principle that the smaller the ved, the larger the load shedding power is and vice versa. with: dv(k,1) < dv(k,2) < dv(k,3) < …< dv(k,n), the priority in load shedding is: load 1� load 2� load 3� … � load n. vii. case study and simulation results the ieee 37-bus test system consists of 8 conventional generators and an equivalent capacity wind farm replacing the generator on bus no.28 with the name elm345#1 to maintain engineering, technology & applied science research vol. 12, no. 2, 2022, 8402-8409 8406 www.etasr.com tran et al.: load shedding in high-integrated wind energy power systems using voltage electrical … power balance. this system was used to evaluate the suggested method. the single-line diagram of the system is shown in figure 2, where the total load capacity is 1032mw. the ratio of wind power to the total system capacity is 15% (α=0.15). table i presents the parameters of conventional generators. fig. 2. the ieee 37-bus test system with modified wind power generator model used in the simulation. table i. parameters of the conventional generators bus no. bus name h (s) d min mw max mw min mvar max mvar 14 redbud69 1.328 0.848 10 35 0 5 28 elm345#2 11.16 3.384 0 150 -60 60 31 slack345 18.75 6.5 0 220 -90 120 44 peach69 4.352 2.72 0 150 -20 40 48 cedar69 1.71 1.197 16 52 -14 26 50 birch69 3.4 0.7905 38 80 -18 33 53 pear138 9.3 2.175 22 140 0 45 54 pear69 4.6 2.5645 15 110 -20 60 table ii. equivalent parameters of the wind power plant wtg hw = 3 kw = 0.2 rw = 0.05 kp = 0.73 α = 0.15 kb = 250 kc = 0.0771 kβ = -0.1422 table iii. classical power system parameters classical power system r = 0.05 d = 1 tr = 7 fh = 0.3 the parameters of the equivalent converting model of the wind power plant are shown in table ii. the disturbance factor used in the simulation is the sudden tripping of generator elm345#2 at bus 28, which equals 14% of total power capacity (δpu = 0.14pu) and neglects the disturbance factor from wind speed variation (δv = 0). using (14), the equivalent system inertia time constant was h = 4.60849. table iii presents the other parameters of the traditional power system. the modified fr model was used to analyze the frequency response of the system. the initial rate of frequency change and the steady-state frequency deviation can be obtained from (11) and (12). the simulation result of the system frequency variation is shown in figure 3. \[8] = j.�¡j.�¢×j.�����dj.�¢�ס.£j¤¡¥ = 0.0178©ª = 1.068hz ee]v = j.�¡��dj.�¢�×���q@.�®@.@® �j.�¢×�¥.¥�£¢ = 0.0067©ª = 0.4031hz engineering, technology & applied science research vol. 12, no. 2, 2022, 8402-8409 8407 www.etasr.com tran et al.: load shedding in high-integrated wind energy power systems using voltage electrical … fig. 3. the system frequency after the response of the fr modifies the model and performs secondary control. the maximum power of the secondary control depends on the generator’s capability to inject additional power into the system. after the primary frequency control of the system applies the modified fr model, the additional power that can be transmitted to the system from each generating unit is shown in table iv. table iv. the capability of generators in secondary frequency control bus no. bus name status available power for secondary control (mw) 14 redbud69 closed 17.05 28 elm345-1 closed 0 28 elm345-2 closed 0 31 slack345 closed 0 44 peach69 closed 0 48 cedar69 closed 0 50 birch69 closed 0 53 pear138 opened 0 54 pear69 closed 0 using (16), the minimum shedding power to restore the frequency within normal operating limits is calculated as: ��l min + δ�secondary control �?� � 0.14 j.. £j k�1 0.15� � 1 �dj.�¢ j.j¢ 0.15 � 19.9165n � 0.0358 pu � 36.96 mw ��l min � 36.96 ∆�secondary control �?� � 36.96 17.05 � 19.91mw applying the optimum load-shedding power distribution method, the voltage electrical distance values from the load buses to the bus containing the fault generator elm345#2 are shown in figure 4. the shedding power at each load bus is shown in table v. the under-frequency load shedding (ufls) relay method [28] was employed to evaluate the effectiveness of the proposed method. according to [28], with an initial frequency change rate of 1.068hz, the total load shedding capacity will be 9% of the entire system, corresponding to 92.88mw shedding power. figure 6 presents a comparison chart of the frequency response between the conventional and the proposed method. the results show that the ufls method has a better recovery frequency of 59.84hz, while the proposed method has a recovery frequency of 59.7hz. however, the shedding power of the ufls method is higher than 72.97mw, which increases cost. this is an advantage of the proposed shedding method. fig. 4. the ved from elm345#2 generator to load buses. table v. shedding power at each load bus distributed according to voltage distance bus no. load shedding power (mw) 3 0.854823 5 0.761556 10 0.589216 12 0.74109 13 0.539807 14 0.824023 15 0.707635 16 0.681851 17 0.600648 18 0.695548 19 0.567426 20 0.805271 21 0.600106 24 0.732919 27 0.676369 30 1.340028 33 1.024133 34 0.800958 37 0.67662 44 1.009286 48 0.640163 50 0.847997 53 0.645239 54 0.696382 55 0.557964 56 1.292943 total 19.91 figure 6 shows a comparison of the voltage magnitude with and without the use of the proposed shedding method. the results show that the steady-state voltage in load shedding is higher than without load shedding. this improvement in voltage magnitude comes from the amount of load power removed from the system. in addition, the suggested method of engineering, technology & applied science research vol. 12, no. 2, 2022, 8402-8409 8408 www.etasr.com tran et al.: load shedding in high-integrated wind energy power systems using voltage electrical … distributing the shedding power to the load buses gives more selectivity than the ufls because it is based on the ved of the fault bus to the load buses. fig. 5. the recovery frequency of the system after performing load shedding according to the proposed and the ufls method. fig. 6. voltage comparison with load shedding based on the proposed method and no load shedding at bus pine69. viii. conclusion applying the modified fr model to a high-integrated wind energy power system demonstrated the system's frequency response when interference occurs and proved its effectiveness. this model is suitable for a traditional power system increasingly integrated with renewable energy sources. the calculation of the minimum load shedding power considering the modified fr model and the system's secondary frequency control helped reduce power for load shedding and restore frequency to the normal operation range, lessening the impact caused by load shedding. this demonstrates the feasibility of controlling a traditional power system with the integration of renewable energy sources. the ved method was applied to distribute the shedding power to the load buses, making load shedding more selective and providing a fast recovery in the system frequency. the effectiveness of the proposed method was evaluated through simulation on the ieee 37-bus test system with a modified wind power generator. in the future, optimization issues for load shedding in high-integrated wind energy power systems considering costs of power generation and penalty charges from load shedding will be studied, optimization algorithms will be applied, and the rank of priority of the loads will also be taken into account. acknowledgment this study belongs to the project with grant no: t202159td funded by the ho chi minh city university of technology and education, vietnam. references [1] s. eryilmaz and c. kan, "reliability based modeling and analysis for a wind power system integrated by two wind farms considering wind speed dependence," reliability engineering & system safety, vol. 203, aug. 2020, art. no. 107077, https://doi.org/10.1016/j.ress.2020.107077. 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[28] florida reliability coordinating council, "frcc regional frequency load shedding (ufls) implementation schedule," in frcc handbook, jun. 2011. engineering, technology & applied science research vol. 7, no. 4, 2017, 1791-1796 1791 www.etasr.com milic and stojanovic: egosense: a framework for context-aware mobile applications development egosense: a framework for context-aware mobile applications development eleonora milić department of computer science faculty of electronic engineering, university of niš niš, serbia eleonora.milic@elfak.rs dragan stojanović department of computer science faculty of electronic engineering, university of niš niš, serbia dragan.stojanovic@elfak.ni.ac.rs abstract—this paper presents a context-aware mobile framework (or middleware), intended to support the implementation of context-aware mobile services. the overview of basic concepts, architecture and components of context-aware mobile framework is given. the mobile framework provide acquisition and management of context, where raw data sensed from physical (hardware) sensors and virtual (software) sensors are combined, processed and analyzed to provide high-level context and situation of the user to the mobile context-aware applications in near real-time. using demo mobile health application, its most important components and functions, such as these supposed to detect urgent or alarming health conditions of a mobile user and to initiate appropriate actions demonstrated. keywords-context; context-awareness; mobile services; personal health monitoring; i. introduction context-aware systems take into account the current state of a user and, in addition, his environment, enabling a mobile device and the application to adjust in an appropriate way. the development of affordable sensors with low power consumption (such as accelerometer, gyroscope, digital compass, light sensor etc.) and their integration into modern mobile devices coupled with the recent advances in machine learning, enabled the creation of a more extensive model of user context often used for health monitoring [1]. usage of context in remote medical monitoring is considered as an important innovation for reducing healthcare delivery costs and improving the responsiveness of health care. remote healthcare monitoring involves the use of smart devices which aggregate data from multiple sensors and transmit the data to the remote server in order to generate high level context. existing solutions collect patient’s sensor data and transmit that data without any local processing to the remote server for real-time or offline analysis. to significantly reduce the flow of high volumes of collected data and in order to reduce the processing of that data on the remote server we propose a mobile context-aware framework for android smart devices where context data processing and analysis is performed locally on the device itself and appropriate actions are initiated based on defined changes in the user’s context. only necessary context data is sent to the remote server for further use. our goal is to collect data from physical and virtual sensors on mobile devices which provide the basic context and enable storage, process and analysis of contextual data locally in order to detect the context of a higher level and the situation of users on mobile devices. the subject of this paper, and its realization in practice, is the study of methods and techniques for gathering and detecting user context on smartphones, based on sensors integrated in a mobile device (such as gps, accelerometers, temperature, motion detector and sensors for activity recognition etc.), user’s preferences, his/her environment and activities. the framework for context data collection, organization, processing and analysis, needed for generation of high-level context information, is developed. the appropriate techniques and components within the framework are implemented on android smart devices, as support for the development of context-aware mobile applications and services. to provide usefulness and effectiveness of the proposed framework we implemented a demo mobile health monitoring application for android platform, based on funf 1 and asper2 open source technologies, as well as sensors for physical activity, pulse, pressure, temperature and motion detection. egosense framework and personal health monitoring android application are supposed to detect urgent or alarming health conditions of a mobile user and initiate appropriate actions by using the implemented framework and background services. ii. problem statement and related work the notion of context is defined in numerous fields of science, such as: linguistics, philosophy, knowledge representation and problem-solving in artificial intelligence and communication theory. there are different definitions of context. according to the free online dictionary of computing, context is something which encircles and provides the meaning for something else. another definition of context is from the field of distributed and mobile computing, where the person is that “something”, and context is comprised of information of that person’s environment, such as the location and identity of people and objects surrounding him/her. the 1 http://funf.org/about.html 2https://github.com/mobile-event-processing/asper engineering, technology & applied science research vol. 7, no. 4, 2017, 1791-1796 1792 www.etasr.com milic and stojanovic: egosense: a framework for context-aware mobile applications development context can be used to characterize the state of an entity. the entity is a person, a place or an object that is considered relevant in user-application interaction. it is necessary to identify what kind of information fits this definition, the structure of information, the way to present it and how to use context in a specific application. context includes information such as: location, time, status of application, resources, network flow, user’s intentions and desires, activity and environmental conditions [2]. user’s activity is an important part of user context since it directly influences the possibility of the user to interact with a mobile device. context-aware systems are agents and applications that use different levels of contexts and adjust their behavior according to current contexts. in order to gather the context, a context-aware service has to ask for specific information the context provider or to monitor events sent by the context providers. in order to construct contextaware services, specific actions are most often defined to run according to a set of rules each time when the current context changes. solution architects can write a set of rules without major problems and to specify which method will be run when a condition is fulfilled. all the rules are memorized in a file and become part of the context understanding process. this is the principle used in services for energy saving and many other services provided by smart devices [4]. context interpreters are components responsible for context processing based on logical reasoning. context processing may include: deriving higher level context from a low level context, knowledge discovery, maintaining consistency of knowledge and resolving conflicts. in order to provide an effective infrastructural support for the development of context-aware services in pervasive computing environment, a general architecture of a context-aware framework has been designed and described in [4]. it is a distributed middleware which transfers context from a physical into a semantic space, where the access to context can be easily divided among contextaware services. it is comprised of the following mutually independent components: context providers, context data base, context-aware services and a service for context service locating (a mechanism where context providers and interpreters can sign up their presence so that the application or users can locate them). in [6], authors proposed contextdroid as a framework for context-aware android phone applications. it was designed in order to provide developers all the necessary services for easier development of context-aware applications, all the while taking into account the battery usage. contextdroid integrates several context phrases, so it generally requires applications that use the least resources possible [6]. queries are transmitted from the application to the service and then forwarded to the sensor. the sensor then sends the acquired data back to the service, which further reasons the received data and notifies the application if needed. it was explained how the contextual information are modeled, acquired, reasoned and, in the end, delivered to the application. framework is implemented for android platform. contextphone [8] is a software platform comprised of four different connected modules realized through a set of open source c++ libraries. contextphone was running on symbian os and was developed using an iterative human-centered design strategy. it was developed for the researches who want to acquire data in a way that is not intrusive for a user and it requires minimal control and maintenance. all the acquired data are stored in local file and periodically updated. aware [9] is the android framework developed for context measuring, inference, logging and sharing, and it was built for developers, researchers and regular smartphone users. aware records hardware, software and data based on user’s actions in its local memory. these data are further analyzed using plug-ins and are transformed into information that a user can understand. wawelite [11] is a framework for situational awareness in environment monitoring. its goal is to provide and organize situational knowledge by acquiring data from sensors in the environment. some examples of such sensors are those that monitor air pollution, aerosols, cloudiness etc. applications that use this framework, written in java, observe the data acquired from certain sensors on specific location and for a specific time period. samurai [12] is an expandable, eventbased architecture which integrates and demonstrates wellknown software modules for event processing (esper), machine learning (weka) and knowledge representation (parliament), as restfull services. it acquires, aggregates, represents and distributes contextual information. its main characteristics include:  conversion of low-level data and events into characteristics which are easier to analyze and compare.  aggregation of data from various sources in order to increase accuracy of deduced conclusions.  identification of frequent activities in event flow in order to produce patterns that could be of interest. wildcat [13] is a generic framework for the development of context-aware applications, which is based on sensor-based monitoring and data aggregation. data are presented hierarchically, as in unix file system, and are updated dynamically. it acquires, models, represents, understands and delivers context. data browsing is performed synchronously and asynchronously, using pull and push methods. esper is used for data processing, more specifically cep (complex event processing) engine and language similar to sql in order to create queries over data. camf [14], or context-aware framework for machine learning developed for android devices, combines machine learning and context-aware computing to provide services based on patterns of mobile devices usage coupled with the context surrounding a specific user. components that this framework is comprised of are used for acquiring, modeling, representing, understanding and interpretation of the context. camf is developed so to hide physical sensors in order to ensure expandability and reusability, as well as the possibility for application to work offline. framework consists of three major levels. the first level provides contextual information, the second one records data and the third level provides weka machine learning used over contextual information. caredroid [19] is a framework that is designed to decouple the application logic from the complex adaptation decisions in android context-aware applications. caredroid, as part of the android runtime system, monitors the context of the physical environment and intercepts calls to sensitive methods, activating only the blocks engineering, technology & applied science research vol. 7, no. 4, 2017, 1791-1796 1793 www.etasr.com milic and stojanovic: egosense: a framework for context-aware mobile applications development of code that best fit the current physical context. caredroid allows applications developers to develop context-aware applications without having to deal directly with context monitoring and context adaptation in the application code. system architecture is comprised of three levels: context sensors that provide context information, system layer for monitoring and adaptation and application layer. harmoni middleware [20] includes a light-weight event engine that runs on the mobile device, and processes incoming sensor data streams using rules that are appropriate for the current context. research suggests that appropriate contextaware filtering can significantly reduce the volume of transmitted medical data. there are four main components: event engine which processes the data readings, data adaptation component for converting sensors proprietary data formats into a standard sensor stream format, the rule manager and rule server on the backend interact with each other to dynamically alter the processing rules, data transmission component for transmitting compressed data to the backend infrastructure and local action manager component responsible for manipulating settings on the local device. cenceme [21] middleware inferres physical and social context and shares information through social network applications. social context detected locally on the device is transferred to a backend server to match common shared social contexts to raise social awareness. classification can be done on the phone with the support of the backend servers, or entirely on the phone. empath (emotional monitoring for pathology) [22] is a middleware to remotely monitor emotional health for depressive illness. patients’ diagnosis and therapeutic treatment planning were supported by reports generated by aggregating context such as sleep, weight, activities of daily living, and speech prosody. the behavior analysis routines run on the server and results would be displayed on the touch screen fixed station at patients’ homes. systemsens [23] middleware captures usage context of mobile phones. usage context is the collection of users’ interactions with research applications. the users’ interactions include battery, call, cpu usage, cell location, data connection active and traffic and telephony information events. most of the related researches, except [8], are implemented as a framework for android smart devices. common to all platforms is the general architecture of context-aware framework where the first level provides contextual information (sensing), the second records data (storing) and the third level usually is the application that reacts to a specific, deducted user’s situation or provides weka machine learning used over contextual information (processing and reasoning). also common is the usage of built-in sensors, while in [11] data is acquired form sensors in the environment. then usually sensors send the acquired data to the service, which further reasons the received data and notifies the application if needed. unlike most of the listed works, context-aware systems/frameworks presented in [8-10] use local memory for storing acquired data. in order to process data in [12] and [13] integration and demonstration of software modules for event processing (esper) is featured. [12] and [14] propose combination of machine learning and context-aware computing in order to provide services. in the most of the proposed solutions mobile devices serve only as event sources and event filters, while the complete event processing and machine learning is done on a backend server. they don’t include advanced processing and analysis of contextual data, nor generating a higher level of context and situation. the built-in sensors of smart devices provide applications with a continuous stream of context data. event processing rules are used to aggregate and correlate the sensor data to more abstract and more meaningful situation data. until a few years ago mobile operating systems were rather inefficient and the computing resources of mobile devices were very limited. along with the rise of computing power of mobile devices the cep for processing data streams is developed for mobile devices. the execution of sophisticated event processing rules directly on the mobile device is still a rather new approach. also performing the event handling of embedded built-in sensors with cep on the mobile device itself can be considered as a rather new approach. complete event processing and machine learning should be server-independent and could be processed locally. our solution showed that collected sensor data should be processed and stored locally on device, and notifications for the application u/i or data transmissions to the remote server are only necessary for events considered as warning or dangerous health conditions. iii. egosense – a framework for context processing and analysis to support the development of mobile context-aware applications we developed a framework for context-aware services and implemented a demo application with impact on health care domain. developed framework integrates components for: collecting data from sensors, complex events processing, reasoning and storing important data on resource limited devices. events considered as important are presented to the user as notification of dangerous health condition and sent to the remote server for further processing and presentation. evaluation and demonstration of the proposed framework is done by the development of a demo android application for mheatlh. the framework is designed in a way that the layers are totally independent and customizable depending on user needs. applications of services in this area are highly interesting now days and particularly relevant for health care applications. actions taken by the highest level in the architecture in a safe and reliable way are informing the user and other interested parties about the alarming situation related to the user's health condition. figure 2 presents the organization and the architecture of the system. the architecture consists of four basic layers, service executed in the background and u/i component for adjustment of variable parameters of context-aware service. the architecture of the system is comprised of three major, mutually connected subsystems: sensing, thinking and acting. sensing subsystem consists of sensors that are being used, situations that need to be recognized and information that is going to be acquired. after that, techniques for context understanding are being realized. finally, appropriate actions engineering, technology & applied science research vol. 7, no. 4, 2017, 1791-1796 1794 www.etasr.com milic and stojanovic: egosense: a framework for context-aware mobile applications development are defined according to a specific need. sensors at the bottom of the architecture acquire data which are then sent to the layer for data retrieval and preprocessing. layer for context understanding as a result produces contextual information as needed by the application and services. management layer can further perform queries over retrieved context information and distribute updated values to the background service and application. the first level in the architecture retrieves data from physical sensors via sensor provider. by using funf framework [15], application gets the information of user’s location. accelerometer and google play services send the notification of physical activity and the position of the user. motion detector provides information that is used to calculate speed of a user’s motions, and sensors provide information about the temperature, pulse (heart rate) and cardiac pressure of a user. sensors data are retrieved over a certain period of time or after the change of values has been detected. furthermore, it is possible to ask for the current value from a specific sensor using the implemented methods, if there is a need for it. all the data are deserialized in dto, i.e. objects for data transfer, and are propagated to the next level that gathers them and prepares them for further processing. the next level for acquiring and analysis of contextual data from sensors, accepts retrieved data and classifies them in previously defined objects for storing values that are used for analysis of specified contexts. one object stores contextual data from specified sensors and every time one sensor retrieves and pushes a new value a specified object updates its previously stored values and raises event for the next level in order to notify it that the change in sensor values has occurred. fig. 1. system architecture. cep (complex event processing) is a software technology that provide processing of continuous streams of data in near real-time. when applied on android smart phones, cep use phone sensors and additional contextual information available on smart phones in real time. cep is used for processing generated data flow from sensors and detected events. this level, after receiving notification and detecting the event, initiates appropriate actions based on received information by using asper. asper detects every change on sensors, generates a new event, executes a query on event flow which should check whether any of the conditions are fulfilled and notifies the next level every time when one of the above mentioned user cases is realized. the highest level (monitoring level), generates a appropriate message if a condition for warning or alarm is fulfilled. it further propagates the message to the background service responsible for sending a notification to a user, sending notification via web service and sending a text message to all interested parties. service is automatically run after an android device is turned on and, for variable parameters in cited user cases, sets predefined values stored in device’s memory. if there is a need to change parameters using the user interface component, the user can add desirable values and the changes will again be stored in devices memory. iv. implementation of egosense framework all the values acquired from sensors are joined with the location of the user and current time. in order to make this data readable to the end user and usable by mobile applications, it was necessary to develop a context management framework for acquiring, processing and analyzing these data so that their functionality can be used by mobile applications via the developed api. this framework was developed with the aim to provide context information of a higher level, that would enrich user’s location with his/her situation and circumstances. it was shown how to process and analyze the data acquired from various physical sensors in order to generate the context, situation, behavior and activity of a higher level user, which could allow services to send contextual information to the interested parties. a demo android application was developed using the framework that represents personal health monitoring, and it should detect urgent or alarming health condition of a mobile user and initiate appropriate actions. android application is based on funf, asper and google play services libraries that have been included in this android project in order to integrate their functionalities. for gathering sensors data and user’s activities which make up the context, funf open sensing framework has been used together with sensors for motion, activity, pulse, pressure and temperature detection. for context processing, interpretation and understanding, cep (asper as android port of esper) has been used. the appropriate techniques and components for user context detection and processing on android smart devices are implemented, all of which is brought together in a contextaware mobile service based on previously developed components. the following use cases have been selected and if some of these actions are detected, notifications to a user, notifications via web services and text message of a warning to other interested parties are activated:  the user is still (he/she lies), pulse is higher than p, blood pressure is higher than k, and cardiac pressure is higher than s -> warning! rule : "warning" select warningevent from pattern[every warningevent = warningevent (userisnotwalking(iswalking), pulseishigherthannormal(pulse, p), systolicpresureishigherthannormal(systolicpresure, k), engineering, technology & applied science research vol. 7, no. 4, 2017, 1791-1796 1795 www.etasr.com milic and stojanovic: egosense: a framework for context-aware mobile applications development diastolicpresureishigherthannormal(diastolicpresure, s))]  the user is moving, the speed is higher than s, temperature of the environment (body) is above the limit t, and pulse is increased by 30% in the last minute. user’s current location is in coordinates: x, y -> user is in danger! rule : "danger" select dangerevent from pattern[every condition = dangerevent -> (timer:interval(60 sec) and dangerevent = dangerevent(pulseincreasedby30percent(condition.pulse), !userisnotwalking(iswalking), bodytemperatureishigherthannormal(temperature, t), movingspeedishigherthen(speed, s), curentlocationin(location, x, y)))] in the demo application we developed a set of methods for organizing and preserving context data gathered from sensors. all processing happens in a background service which is invisible to the user. for example, every time user’s blood pressure changes that sensor data is being transferred to the application layer that deals with gathering and context data organization. if that change has an influence on processed use cases then client’s android application generates high-level context in order to inform user if alarming condition has occurred. in case of detecting urgent health condition actions like sending text messages to the interested parties (phone numbers are preconfigured in the application for every user), displaying notification on user’s smartphone and sending notification via web service to web server occur one after the other. interested parties in those notifications can see explanations, with exact time and date, about the problem originated in a given moment regarding the state of health of the user and current monitored health parameters which led to that health condition. restful web service is developed in order to be responsible for sending the notifications related to detected events in android application to the web server. web application is developed in order to store alarming health conditions in sql database for every user. also web application is used for visualization and analysis of critical events detected by the user’s smart phone. with simple architecture containing application layer (service layer) and data access layer, mvc web api on server side receives client’s notifications in form of http post requests. received data are used later for generating all kind of reports for every user (for example how much disturbing health changes the user had during every night in this month). in addition the web server also sends email messages to preconfigured addresses (email addresses are stored in a database for every user separately) for every user when notification of his alarming health condition has been received. the android application is tested by several test users on real mobile devices which run android operating system with api level 2.3.5 (gingerbread) and above. server application was hosted on microsoft azure cloud server and database was hosted on sql server 2012. the system was active and reliable 24/7. with an active internet connection, the application was able to send notifications to the web server and, of course, to send text messages and display notifications to the user. when there was no internet connection text messages were sent to the interested parties and notifications were displayed on the user’s smartphone. from the database hosted on web server reports were generated for specific user for specified date and time intervals in order to monitor disturbing changes in their health conditions. v. evaluation the client application has been developed with the android application framework that provides access to the local device resources like hardware sensors of the device and processing the data by using cep. so if the screen consumption is taken into consideration, and having in mind that the core of android operating system consumes 34.9% of processor resources, it can be said that by testing developed context-aware service on four different smartphone devices which run different versions of android os we concluded that implemented activity recognition system does not influence consumption and processor usage in any significant way. it is proved that the presented architecture of context-aware service, implemented through a demo application for the android operating system, could be implemented, without any difficulty, for any other operating system running on smartphones by using similar open source technologies specialized for use on the selected operating system. the proposed architecture offers advantages like reduced network traffic and exploiting local processing power. to be more specific, sensor data is processed directly on the mobile device. cloud server is used for preserving logs related to alarming health conditions. because the sensors of potentially many users may produce high volumes of data, the overall network traffic is reduced significantly. also processing data on the smart devices exploits only the processing power of mobile devices. fig. 2. amount of transmitted data to the remote server from figure 2, we see that appropriate filtering of sensor data results in a significant reduction in the amount of data transmitted to the remote (cloud) server. thus, we conclude that context-aware events filtering can lead to a significant reduction in the amount of data that must be transmitted by a mobile device. in many sensor environments, a large fraction of the collected data conforms to expected patterns, and data transmissions are only necessary for notification about the warning or danger events for user’s health condition. that behavior can allow locally performing an accurate and continuous analysis of the users’ health status by minimizing network transmission and maintaining appropriate levels of security and privacy by using https protocol for communication with the cloud server. engineering, technology & applied science research vol. 7, no. 4, 2017, 1791-1796 1796 www.etasr.com milic and stojanovic: egosense: a framework for context-aware mobile applications development cpu utilization regarding developed context-aware service seems to be appropriate and it doesn’t have a significant influence on the performance of smart devices because events processing and reasoning use very small fragments of available resources. also, we observed the memory usage of the reasoning system on the four mobile devices considered. as further consideration, it is possible to note that memory usage does not significantly vary depending on the mobile device used. as the number of collected sensor data increases by time, the overall memory usage of application grows up which increase the pattern matching time and the overall reasoning time. fig. 3. personal health monitoring application screen shots. in the health care domain, the presented platform proved to be secure and reliable, because it operates in the background and it is very reliable from the standpoint of the values obtained with built-in sensors. the technologies used to handle sensor data are free and open source, so they can be adapted for handling users’ specific requests. the user does not need to interact with the service or to have any technical knowledge, because the service will perform all the work and inform him of the alarming situation regarding his health condition. vi. conclusion possibilities of applying context-aware systems are perhaps the greatest in the field of health care, where we can see an increasing interest in the systems that can detect human activities. the methods for activity tracking currently used, often require a lot of time and resources, and are usually in the form of an additionally paid person who is in charge of monitoring the patient and reporting his/her condition or in the form of making a patient independently notify a doctor about his/her condition in prescribed time intervals. an automatic activity recognition system would lower the risk of mistakes and, in addition, it would increase the quality of health care, since it would save the time that medical staff usually spends in acquiring and sorting the data. furthermore, non-invasive monitoring will enable people to live their everyday lives undisturbed while, at the same time, they would offer their doctors a more precise presentation of their activities. another possibility of application is social networks which are becoming an important part of everyday life. existing communication services allow a simple exchange of textual messages, photos, videos, etc. with the use of sensors, a richer user context could be shared with friends in a much more natural and easier way. automatic activity recognition would enable users to share their current physical activity with their friends via social networks. the results of this research work show that it is possible to develop mobile context-aware applications which would adapt to a user using his/her current context and which would, in accordance with the general context, access services in order to acquire or deliver adjusted information and services. references [1] a. k. dey, “understanding and using context”, personal and ubiquitous computing journal, vol. 5, no. 1, pp. 4-7, 2001 [2] s. loke, context-aware pervasive systems: architectures for a new breed of applications. auerbach (crc press), 2006 [3] m. baldauf, s. dustdar, f. rosenberg, “a survey on context-aware systems”, international journal of ad hoc and ubiquitous computing, vol. 2, no. 4, pp. 263-277, 2007 [4] t. gua, h. k. pung, d. q. zhang, “a service-oriented middleware for building context-aware services”, journal of network and computer applications, vol. 28, pp. 1–18, 2005 [5] j. koolwaaij, a. tarlano, m. luther, p. nurmi, b. mrohs, a. battestini, r. vaidya, “context watcher ─ sharing context information in everyday life”, iasted conference on web technologies, applications and services (wtas), 2007 [6] b. van wissen, n. palmer, r. kemp, t. kielmann, h. bal, contextdroid: an expression-based context framework for android, phonesense 2010, zurich, switzerland, 2010 [7] t. hasu, contextlogger2a tool for smartphone data gathering, hiit technical reports 2010-1, aalto university, finland, 2010 [8] m. r. h. toivonen, r. p. a. oulasvirta, “contextphone: a prototyping platform for context-aware mobile applications”, pervasive computing, vol. 4, no. 2, pp. 51-59, 2008 [9] aware android mobile context instrumentation framework, 2014, http://www.awareframework.com/ [10] j. dunkel, r. bruns, s. stipković, “event-based smartphone sensor processing for ambient assisted living”, 2013 ieee eleventh international symposium on autonomous decentralized systems (isads), hannover, germany, march 6-8 , 2014 [11] m. stocker, m. ronkko, m. kolehmainen, “abstractions from sensor data with complex event processing and machine learning”, 7th intl. congress on env. modelling and software, san diego, ca, usa, 2014 [12] d. preuveneers, y. berbers, “samurai: a streaming multi-tenant context-management architecture for intelligent and scalable internet of things applications”, international conference on intelligent environments, shanghai, 2014 [13] wildcat, http://wildcat.ow2.org/ [14] a. i. wang, q. k. ahmad, camf – context-aware machine learning framework for android, institutt for datateknikk og informasjonsvitenskap, 2010 [15] funf open sensing framewok, http://www.funf.org/about.html [16] android activity recognition, https://tsicilian.wordpress.com/2013/09 /23/android-activity-recognition/ [17] low-power sensors, https://developer.android.com/about/versions/ kitkat.html [18] event processing with esper and nesper, http://esper.codehaus.org/ tutorials/tutorial/tutorial.html [19] s. elmalaki, l. wanner, m. srivastava, “caredroid: adaptationframework for android context-aware applications”, mobicom '15 the 21st annual international conference on mobile computing and networking, 2015 engineering, technology & applied science research vol. 8, no. 2, 2018, 2745-2749 2745 www.etasr.com ali et al.: prediction of corner columns’ load capacity using composite material analogy prediction of corner columns’ load capacity using composite material analogy ahsan ali department of civil engineering quaid-e-awam universityof engineering, science & technology larkana, pakistan pakistanahsanone@gmail.com zuhairuddin soomro department of civil engineering quaid-e-awam university of engineering, science & technology larkana, pakistan zuhairuddin@quest.edu.pk shahid iqbal department of civil engineering cecos university peshawar, pakistan shahid.iqbalmce@gmail.com nadeem-ul-karim bhatti department of civil engineering quaid-e-awam university college of engineering, science & technology larkana, pakistan knadeem_b@yahoo.com ahmed faraz abro department of civil engineering quaid-e-awam university of engineering, science & technology larkana, pakistan a.faraz.abro@outlook.com abstract-there are numerous reasons for which concrete has become the most widely used construction material in buildings, one of them being its availability in different types, such as fiberreinforced, lightweight, high strength, conventional and selfcompacting concrete. this advantage is specially realized in highrise building construction, where common construction practice is to use concretes of different types or strength classes in slabs and columns. columns in such structures are generally made from concrete which is higher in compressive strength than the one used in floors or slabs. this raises issue of selection of concrete strength that should be used for estimating column capacity. current paper tries to address this issue by testing nine (09) sandwich column specimens under axial loading. the floor concrete portion of the sandwich column was made of normal strength concrete, whereas column portions from comparatively higher strength concrete. test results show that aspect ratio (h/b) influences the effective concrete strength of such columns. a previously adopted methodology of composite material analogy with some modifications has been found to predict well the capacity of columns where variation in floor and concrete strength is significant. keywords-composite material analogy; sandwich columns; corner columns; axial loading i. introduction there are many reasons for which concrete has become the most widely used building construction material. concrete’s ability to shape into any structural form, easy accessibility of its constituent materials and liberty of selecting among its various types, for example, fiber-reinforced, lightweight, high strength, conventional and self-compacting are few worth mentioning reasons. this choice of selection of different grades/types of concrete favors its application also in high-rise building construction. concrete compressive strength used in construction has been increasing over the years and strengths up to 20ksi (138mpa) and more have been used in the industry, especially in columns of high-rise buildings [1]. the use of high strength concrete column sections along the height, with higher-strength concrete placed in lower stories, results in additional savings associated with repetitive use of formwork. compared to columns, high strength concrete is not required in floor/slab region of a framed structure. also, economy and space requirements in high-rise building construction force designers to select concretes of different types/strength classes for slabs and columns. in such a state, presence of two different grades of concrete in slab-column region raises issue of selection of concrete strength 'cf to be used in (2) for estimating column capacity. aci-318 [2] addresses the issue of variation in strengths of column and floor concretes in its section 10.12, where it recommends no special measures as long as the ratio of column to floor concrete strength ' 'cc csf f is limited to 1.4. requirements of aci are based on [3] and state: when ' ' 1.4cc csf f £ (1-a) ' ' ce ccf f= (for interior, corner & edge columns) when ' ' 1.4cc csf f > (1-b) ' ' ce csf f= the maximum concentric load carrying capacity of the column can be obtained by adding the contribution of the engineering, technology & applied science research vol. 8, no. 2, 2018, 2745-2749 2746 www.etasr.com ali et al.: prediction of corner columns’ load capacity using composite material analogy concrete, calculated by '( )0.85g st ca a f, and the contribution of the steel ( )st ya f . the value of '0.85 cf instead of 'cf is used in the calculations. aci recommends this value on the basis of 564 tests on columns carried out during 1927 to 1933 at lehigh and illinois universities [4]. the nominal concentric load capacity of a column po can be expressed as: ( )'0.85o c g st st yp f a a a f= + (2) rearranging (2), effective strength of concrete 'cef can be defined as ( ) ' 0.85 o st y ce g st p a f f a a = in [3, 5-10], researchers tried to address this subject and proposed different expressions and solutions. few of these studies are discussed here to justify the proposed solution presented later in the paper. author in [5] tested six specimens with aspect ratio h/b of 0.7 to understand the load transfer mechanism of high strength concrete column through a layer of lower strength slab concrete and to determine the effects of confinement on behavior of slab concrete. treating the specimens as composite materials, he used mechanics of materials approach for developing (3) to calculate the effective concrete strength. ' ' ' ' ' 2.0 cc csce g cc cs f f f f f l= + (3) where, 0.9,1.0,1.25gl = for corner, edge & interior columns respectively. authors in [11] proposed (4) for computing effective concrete strength of a sandwich column and concluded that current aci provisions for ' ' 1.4cc csf f > are overly conservative for edge and corner columns. their results were based on tests conducted on 54 sandwich column specimens. ( )' ' ' 'ce cs cc csf f a f f= + (4) where 1 0.4 2.66 a h b       . authors in [7] investigated the effects of aspect ratio h/band column rectangularity on the effective concrete strength 'cef of high strength concrete corner columns intersected by weaker slabs. the aspect ratio varied from 0.3 to 1.14 with maximum 12600psi (87mpa) concrete strength. they concluded that it would be inaccurate to not consider aspect ratio in estimating the effective compressive strength of joint. using mechanics of material approach like [5], authors in [12] suggest (5), a design expression for prediction of interior column capacity. they are of the opinion that the composite material analogy can be effectively applied for the theoretical analysis of the problem associated with estimating column capacity. however, like [5], their suggested equation also does not acknowledge the effect of aspect ratio. ' '3 3 '3 ' '3 3 2.0 cc csce g cc cs f f f f f l ´ = + (5) where 1.07gl = . all mentioned studies signify the importance of aspect ratio h/b and composite material analogy approach. expressions proposed by some researchers are based on this approach but are independent of aspect ratio, whereas expression proposed in[11] is based on regression analysis rather mechanics of material approach. ii. experimentalprogram and test setup the experimental program included the testing of nine sandwiched column specimens in direct compression, as these specimens adequately model the corner column slab joint [5, 7]. specimens were divided into three groups a, b and c, having three specimens in each group, each group had different ratio of column to floor concrete strength. specimens in each group had slab/floor layer of 4, 6 and 8 inches (102, 152 and 203mm). slab portions were sandwiched between two column ends made up of comparatively lower strength concrete than the one used in column ends. specimen with 4 inch (102mm) thick slab layer had aspect ratio h/b of 0.67 typical to that of flat plate floor system, whereas those with 6 inch (152mm) and 8 inch (203mm) thick layer developed an aspect ratio of 1 and 1.33 respectively. figure 1 shows the rest of the features of specimens in all groups. all specimens were tested in axial compression in a 2000kn capacity compression testing machine. first, the test specimens were installed in the testing machine, centered carefully to avoid any flexural stresses resulting from accidental eccentricity. strain gauges applied to main reinforcement in slab region to monitor their performance under load were connected to the data logger. three cylinders cast from the column concrete and slab concrete batches were tested first to obtain the axial compressive strength. this was followed by compressive testing of sandwich column specimens. before testing, elastic pads were placed between specimen and machine loading plates to avoid damage to column ends. the load was applied in increments of 50kn. during the test, specimen behavior was carefully monitored, cracks were marked on their appearance along with load readings. strain gauge readings were also recorded after each load increment. after specimen failure, the crushed concrete around the failure area was removed to observe the behavior of the reinforcement. a typical test setup is shown in figure 2(a). iii. test results test results confirm the established behavior of axially loaded columns, specimens in current experimental work failed due to buckling of the longitudinal bars and crushing of slab concrete. the buckling of longitudinal bars and crushing of slab concrete (see figure 2(b)) took place almost simultaneously and suddenly. although, at the beginning, sm of cau pro sp sug thu tes com mo is t beh co fav [13 (rv ele sim eac 3(c hig asp “b” em bet or as eff req mu dis engineerin www.etasr maller cracks ap testing machi use of failure ogressed verti pecimens with ggesting that a us confirming st results for al fig. 1. l iv. proposed equ mposite mat odifications is that the colum have like com omposites are vorable proper 3]. figure 3(a rve) having d ementary mec milarities of r ch other, along c)) with effec ghlighted in f pect ratio (h/b ”. unlike fibro mbedded by w tween stronge sandwich colu shown in fi fective transv quires that the ust be equal splacements in using definit ng, technology r.com ppeared in the ine, however appeared late ically until a higher aspect aspect ratio do the findings ll specimens ar longitudinal& cro composite uation (3) in terial. the presented her mn with two di mposite materia preferred fo rties fibrous a) shows the dimensions “b chanics of ma rve and a san g with equival ctive transvers figure 3. ack b), rve is ass ous composite weaker matrix er column ends umn is subjec igure 3(a), th verse modulu e total transve to the sum n the fibers fyd cybe e= tion of hook’s ' ' y fy y fy f f e e = ´ y & applied sci e column ends the cracks wh er in the floor after spalling ratios (h/b) fa oes influence t of previous s re presented in oss sectional deta e material an [5] is based o same appro re. the basic p ifferent grades al made of tw or application composite is o e representativ b” and simple aterials mode ndwich column lent homogeno se modulus o knowledging signed dimens e (rve), wher x, weaker sla s in this analo cted to transve he response i us ey. geom erse composit of the corres and the matrix fy f my ml le e+ s law: ' f my my l f b e ´ + ´ ience research ali et al.: pre s near loading hich were the r concrete are of cover con ailed at lower the column cap studies [7, 10] n table i. ails of specimens nalogy on the princip oach with principle or an s of concrete s o kinds of ma n as they res one typical ex ve volume el e states of str els. comparis n (figure 3(b) ous material (f f elasticity the significan sions of unit re fibers are h abs are sandw ogy. when the erse normal st s governed b metric compat te displacemen sponding trans x myd . ml myl b ´ v ediction of corn plates e main ea and ncrete. loads, pacity ]. the ples of some nalogy should aterial. ult in ample ement ess in on or ) with figure are nce of width held or wiched e rve tressσy by the tibility nt cyd sverse fibe stre mu mat sim bec com littl stre ' cef whe com it is colu cor diff ac valu con or e ac fig prev 318 draw with fou gre new app pre pro exis vol. 8, no. 2, 20 ner columns’ l if we assume er are all equal 1 ye b = from figure esses is valid st be equal fo trix blocks h mplifying and comes: modulus of e mpressive stren le margin of e ength i.e. ce a ( ' ' cc e cc bf h f f = ere (h/b≤1). mposite action s believed tha umn slab join rner columns ferent research ci-318 recomm ue of concre ncrete strength equal to 1.4, n results of ef ci approach an gure 4 shows vious samples 8 and propose wn to these p h overall test t und to be too c ater than 1.5. wly proposed parent strength dicted ration oposed design sting code equ 018, 2745-2749 load capacity cy fye e= ´ e that the stres l then above e f m fy l l e b e + ´ ´ 3, it would se because equi or the series a have equal ar d using sand (y c e h e = elasticity is pr ngth. here for error, it is tak ' cf or ' cf . ) ' ' ' c cs cs cs f f f b+  condition of n to exist. v. resu at sandwich co nts. therefore have been u hers [3, 5-6, 1 mends the us ete strength, i hs ' 'cc csf f exc no measures ar ffective concr nd the propose apparent co s plotted again ed equation. t lots along wit to prediction r conservative, the effective (7) has sho h 'cpf of tested of 1.29 and equation app uation. 9 using composi f my l b e´ + ´ ses in the com quation reduce my mye eem that the as ilibrium requi arrangement a reas normal t dwich column ) s cc c s s be e e e+ roportional to r the sake of s ken proportion ( ' ce c f h f b  = f h/b≤1 is im ults analysis olumns adequa previous data used for ana 11-12, 14]. fo se of puddle if the ratio o eeds 1.4. if th re suggested. rete strength f ed one are pre oncrete streng nst the calculat the theoretical th the data poi ratio of 1.38, t particularly fo strength calcu own good co samples. with standard devi pears to be m 2747 ite material an ml b mposite, matrix es to: (6) ssumption of res that the f and both fiber to the y-direc n’s notations b the square ro simplicity and nal to compre ) ' ' ' ' ' cc cs cc cs cs f f f f+ mposed to (7 s ately model c a of sandwich alysis purpose or corner colu concrete or l of column to his ratio is less ' cef , following esented in tab gth of current ted values by l line at 45o is ints. from tab the aci equati or ratios of 'ccf ulated 'cef usin orrelation with h an average t iation of 0.28 much safer tha nalogy x and equal forces r and ction. , (6) oot of d with essive s (7) 7) for orner h and es by umns, lower slab s than g the ble ii. t and acis also ble ii ion is ' c csf ng the h the test to 8, the an the engineerin www.etasr s concre strength psi (mp tp ' cpf ng, technology r.com fig. 3. specimen ete h pa) top column slab bottom column lb kn psi mpa ' ' cc csf f ' ' cp csf f h/b y & applied sci fig. (a) . (a) rve (b) sca4 60 27 60 182700 812.69 3665.47 25.27 1.34 0.67 ience research ali et al.: pre (a) 2. (a) test se sandwich colum tabl sca-6 s 082 (41.93) 725 (18.79) 020 (41.51) 177244 17 788.42 7 3480.81 33 24 2 2.22 1.28 1 fig. 4. v ediction of corn etup, (b) failure o ( mn as composite m le i. test r ca-8 scb-4 73692 19474 72.62 866.25 360.59 4073 23.17 28.08 1.23 1.81 1.33 0.67 concrete stren vol. 8, no. 2, 20 ner columns’ l f specimen in slab (b) material (c) equiva results 4 scb-6 7754 (53.46) 2249 (15.51) 7105 (48.99) 1 190545 5 847.59 3931 8 27.10 3.3 1.75 1 ngth graphs 018, 2745-2749 load capacity b region alent homogenou scb-8 scc 187115 171 832.33 761 3814.9 327 26.3 22. 1.696 1.1 1.33 0.6 9 using composi (b) (c) s material c-4 scc-6 5342 (36.84 2857 (19.7) 5556 (38.32 163 165195 .37 734.82 75 3073 59 21.19 1.91 15 1.08 67 1 2748 ite material an scc-8 4) ) 2) 163865 728.91 3028 20.88 1.06 1.33 nalogy engineering, technology & applied science research vol. 8, no. 2, 2018, 2745-2749 2749 www.etasr.com ali et al.: prediction of corner columns’ load capacity using composite material analogy table ii. ratio of apparent to effective concrete strength specimen series ' ccf (psi) ' csf (psi) ' cpf (psi) aci 318-11 proposed ' cef (psi) ' ' cp cef f ' cef (psi) ' ' cp cef f a 6051 2725 3666 2725 1.35 3329 1.10 6051 2725 3481 2725 1.28 2725 1.28 6051 2725 3361 2725 1.23 2725 1.23 b 7430 2249 3815 2249 1.70 2921 1.31 7430 2249 4073 2249 1.81 2249 1.81 7430 2249 3931 2249 1.75 2249 1.75 c 5449 2857 3275 2857 1.15 3389 0.97 5449 2857 3073 2857 1.08 2857 1.08 5449 2857 3028 2857 1.06 2857 1.06 mean 1.38 1.29 standard deviation 0.28 0.28 vi. conclusions analysis and discussion of test results leads to the following conclusions:  specimens of all series confirm that the effective strength of an axially loaded column intervened by lower strength concrete floor is influenced by its aspect ratio h/b.  as the aspect ratio increases, the effective strength of the joint decreases.  the aci 318, section 10.12, provisions for ' ' 1.4cc csf f > are overly conservative for corner columns.  mechanics of composite materials can be used to predict the response of slab-column joints to axial loads. the proposed expression (7) can safely be used for predicting the effective concrete strength of axially loaded corner columns. denotation table ag gross area of column cross section lf length of fiber ast area of deformed bar lm length of matrix b least column dimension po nominal concentric load capacity of column ecc modulus of elasticity of column concrete pt axial test load applied to column ecs modulus of elasticity of slab concrete ρ reinforcement ratio ey effective modulus of elasticity in y-axis direction δcy axial displacement of composite in ydirection ' ccf compressive strength of column concrete δfy axial displacement of fiber in y-direction ' cef effective compressive strength of column δmy axial displacement of matrix in y-direction ' cpf apparent concrete strength of column cy e strain in composite in y-direction ' csf compressive strength of slab concrete fy e strain in fiber in ydirection yf yield strength of deformed bar my e strain in matrix in ydirection h thickness of slab column joint l length of specimen references [1] aci committee 363, “report on high-strength concrete (aci 363r10)”, in: aci manual of concrete practice, american concrete institute, 2013 [2] aci 318-14, building code requirements for structural concrete and commentary, american concrete institute, 2014 [3] a. c. bianchini, r. e. woods, c. e. kesler, “effect of floor concrete strength on column strength,” aci journal, vol. 31, no. 11, pp. 1149– 1169, 1960 [4] j. k. wight, reinforced concrete : mechanics and design,pearson, 2016 [5] m. k. kayani, “load transfer from high-strength concrete columns through lower strength concrete slabs”, university of illinois, 1992 [6] j. h. lee, y. s. yoon, w. d. cook, d. mitchell, “benefits of using puddled hsc with fibers in slabs to transmit hsc column loads”, journal of structural engineering, vol. 133, no. 12, pp. 1843–1847, 2007 [7] s. c. lee, p. mendis, “behavior of high-strength concrete corner columns intersected by weaker slabs with different thicknesses”, aci structural journal, vol. 101, no. 1, pp. 11–18, 2004 [8] a. a. shah, y. ribakov, “estimation of rc slab-column joints effective strength using neural networks”, latin american journal of solids and structures, vol. 8, no. 4, pp. 393–411, 2011 [9] i. shahid, s. h. farooq, n. a. qureshi, k. r. kayani, h. mumtaz, “effective concrete strength within slabcolumn joint”, international journal of engineering and technology vol. 7, no. 3, pp. 965–972, 2015 [10] j.-h. lee, y.-s. yoon, “prediction of effective compressive strength of corner columns comprising weaker slab–column joint”, magazine of concrete research, vol. 64, no. 12, pp. 1113–1121, 2012 [11] c.-c. shu, n. m. hawkins, “behavior of columns continuous through concrete floors”, aci structural journal,vol. 89, no. 4, pp. 405–414, 1993 [12] a. a. shah, j. dietz, n. v tue, g. koenig, “experimental investigation of column-slab joints”, aci structural journal, vol. 102, no. 1, pp. 103– 113, 2005 [13] r. f. gibson, principles of composite material mechanics, mcgraw-hill, 1994 [14] p. j. mcharg, w. d. cook, d. mitchell, y. s. yoon, “improved transmission of high-strength concrete column loads through normal strength concrete slabs”, structural journal,vol. 97, no. 1, pp. 157–165, 2000 microsoft word revised paper-etasr-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 232-236 232 www.etasr.com sabzpoushan and faghani ghodrat: role of sodium channel on cardiac action potential role of sodium channel on cardiac action potential s. h. sabzpoushan department of biomedical engineering iran university of science and technology (iust) tehran, iran sabzposh@iust.ac.ir a. faghani ghodrat department of biomedical engineering iran university of science and technology (iust) tehran, iran alireza.faghani.ghodrat@gmail.com abstract—sudden cardiac death is a major cause of death worldwide. in most cases, it's caused by abnormal action potential propagation that leads to cardiac arrhythmia. the aim of this article is to study the abnormal action potential propagation through sodium ion concentration variations. we use a new electrophysiological model that is both detailed and computationally efficient. this efficient model is based on the partial differential equation method. the central finite difference method is used for numerical solving of the two-dimensional (2d) wave propagation equation. simulations are implemented in two stages, as a single cardiac cell and as a two-dimensional grid of cells. in both stages, the normal action potential formation in case of a single cell and it's normal propagation in case of a twodimensional grid of cells were simulated with nominal sodium ion conductance. then, the effect of sodium ion concentration on the action potential signal was studied by reducing the sodium ion conductance. it is concluded that reducing the sodium ion conductance, decreases both passing ability and conduction velocity of the action potential wave front. keywords: action potential; sodium channel; partial differential equation; arrhythmia; reentrant i. introduction information transmission in the form of propagating waves of electrical excitation is the fastest form of long-range internal communications available to living organisms. in the heart, the electrical waves initiate contractions of the cardiac muscle. abnormal propagation of the electrical excitation wave has serious medical consequences. regarding the brain, it is believed to be associated with epilepsy. regarding the heart it leads to cardiac arrhythmia. among the various types of cardiac arrhythmias, reentrant ventricular arrhythmia is considered the most dangerous. reentrant arrhythmia which frequently occurs, is caused mainly due to abnormal reentrant propagation of excitation waves and is considered very dangerous too [1]. modeling studies have a long-standing tradition and play a very significant role in cardiac electrophysiological research. mathematical models and computer simulations play an increasingly important role in cardiac arrhythmia research. ionic (electrophysiological) models include complete detailed descriptions of cardiac cells processes and can be used for accurate studies in cellular level. one of the most important application of these theoretical studies is the simulation of the human heart, which is rather important for a number of reasons. firstly, the possibilities for doing experimental and clinical studies are very limited. secondly, animal hearts used for experimental studies may differ significantly from the human heart in terms of size, heart rate, action potential (ap), shape, duration and restitution, vulnerability to arrhythmias, etc. finally, cardiac arrhythmias, especially those occurring in the ventricles, are three-dimensional phenomena whereas experimental observations are still largely constrained to surface recordings. some of the above mentioned problems can be bypassed using computer simulations of arrhythmias in the human heart [1-2]. the propagation of a wave front in an excitable media requires a sufficient number of na ions that can diffuse into adjacent resting cells and raise the membrane potential to the firing threshold. na channels become rapidly inactivate, so they participate only briefly in the wave front expansion and therefore must be replaced with newly recruited channels in order to keep the wave front from collapsing. the process of charge diffusion, subsequent regional depolarization and opening of na channels characterizes the recruiting process [3]. the recruiting capacity reflects the density of non-inactivated and unblocked na channels adjoining the leading edge of the wave front. the status of an impulse arising from stimulation is thus determined by the ability of the wave front to recruit sufficient na channels from adjacent cells such that the resulting inward current maintains an active region comparable in size to the liminal length. the inward na current (ina) is responsible for the initial upstroke of the action potential. equations for ina are of the type first formulated by beeler and reuter [4]. the steady-state activation and inactivation curves used in the model are based on recent patch clamp experiments in rat ventricular myocytes [5]. the basic kinetic characteristics of ina are similar in ventricular cells across different species [6]. therefore, the time constants for activation and inactivation were adapted from the guinea pig ventricular cell model [7], and were scaled for room temperature [8]. the maximum na conductance (gna) was adjusted to generate an appropriate value for the action potential amplitude and the maximal upstroke velocity (dv/dtmax). recent clinical reports of gene mutations, drugs and cardiac disease link a variety of often lethal conditions with the loss of cardiac na channel function (nalof) and reentrant proarrhythmia. etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 232-236 233 www.etasr.com sabzpoushan and faghani ghodrat: role of sodium channel on cardiac action potential ii. method a human cardiac cell model that is both detailed and computationally efficient is needed in order to study human heart activities and the way these activities are linked to (sub)cellular processes such as ion channel mutations. in this work, we use a new electrophysiological model that is both detailed and computationally efficient [2]. the action potential generation and propagation was described using the following differential equation [9]: m ion stim v c i i d v t ∂ = + + ∇ ∂ (1) where v is the transmembrane potential, cm is the membrane capacitance, d is the diffusion coefficient, iion denotes sum of the currents constituted by various ions across the cell membrane and istim is the external current signal. the nominal value of sodium ion conductance is 15 ms/cm 2 . for the numerical solving of the two-dimensional (2d) wave propagation, the central finite difference method [10] is used with a time step of 0.02 millisecond and a space step of 0.25 millimeter. we assume c=1µf/cm 2 , d=0.00154 cm 2 /ms in two-dimensional grid of cells simulations to obtain a maximum planar conduction velocity (cv) of 68 cm/s consistent with measurements in human ventricular tissue [2], and d=0 cm 2 /ms for single cells. simulations of cardiac action potential are implemented in two stages, as a single cardiac cell and as a two-dimensional grid of cells. normal action potential formation in case of a single cell and it's normal propagation in case of a twodimensional grid of cells are simulated with nominal sodium ion conductance. the effect of sodium ion concentration on the action potential is studied by reducing the sodium ion conductance. computer simulations are implemented using delphi . iii. results the inward na current (ina) is responsible for the upstroke of the action potential signal. in this section, we initially show the effect of sodium ion conductance on the action potential amplitude in case of a single cell and we investigate this effect on both amplitude and conduction velocity(cv) of the action potential wave in a two-dimensional grid of cells. a. single cell the single cell model was constructed and simulated according to tusscher’s myocardial cell model [2]. the typical cardiac action potential has 5 phases from 0 up to 4 including: (0) depolarization or upstroke phase, (1) partial repolarization or notch phase (2) plateau phase (3) repolarization phase and (4) resting membrane potential phase. in mammalian heart, depolarization phase (phase 0) results from a rapid inward pulse of sodium ions to a positive potential. in this section, the action potential response of a single cell is simulated with the nominal value of gna, as shown in figure 1. five phases for the action potential signal are observable. the vertical axis shows the transmembrane voltage in millivolts (mv) and the horizontal axis shows the time in milliseconds (ms). at the next step, we decrease the gna from its nominal value. figures 2 and 3 show that when gna was reduced to 70 and 50 percent of its nominal value, the action potential upstroke was decreased from 38mv to 30mv and 25mv respectively. fig. 1. action potential of the single cell with the nominal value of gna fig. 2. action potential of the single cell after decreasing gna to 70% of its nominal value fig. 3. action potential of the single cell after decreasing gna to 50% of its nominal value etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 232-236 234 www.etasr.com sabzpoushan and faghani ghodrat: role of sodium channel on cardiac action potential b. two-dimensional grid of cells the two dimensional (2d) grid is a mxm grid of cells, where m is the number of cells. we test the 2d action potential propagation with different sodium ion conductances and show the effect of this operation on action potential propagation. the nature of grid connection are based on the physiological conditions, i.e. in reality, cardiac cells communicate with the maximum possible number of connected neighbors. the simulations are performed in a square excitable medium with 80 cells in both x and y direction. at first, a 15 ms/cm 2 conductance is employed and parameters are kept at the nominal value. an external stimulus is applied at the left down corner of our excitable medium. this external stimulus current (es1) is required in order to generate an action potential. the normal action potential propagates in the medium from the left down corner to the right top corner. the snapshots of normal action potential propagation are shown in figure 4. fig. 4. 2d action potential propagation with nominal value of gna (series of snapshots 0, 0.5, 2, 4, 6, 8, 10, 12, 14 milliseconds after the start of propagation, from top row to bottom row respectively and in each row from left side to right side) in the next study, the sodium ion conductance is decreased to 70 percent of its nominal value. the amplitude of the action potential wave front has decreased consequently, after the passing ability of the wave front has been reduced. moreover according to the snapshots represented in figure 5, the propagating wave front needs more time compared to the previous state to traverse across the medium whereas the conduction velocity of the wave front is reduced. in the final state, we decrease the sodium ion conductance to 50 percent of its nominal value. figure 6 depicts that both amplitude and conduction velocity of the action potential wave front has been further decreased compared to the two previous states. in figures 4-6, the dark color shows the medium resting state and the light color represents the medium depolarized state. fig. 5. 2d action potential propagation after decreasing gna to 70% of its nominal value(series of snapshots 0, 0.5, 2, 5, 7, 9, 12, 14, 16 milliseconds after the start of propagation, from top row to bottom row respectively and in each row from left side to right side) fig. 6. 2d action potential propagation after decreasing gna to 50% of its nominal value (series of snapshots 0, 0.5, 2, 4, 7, 10, 13, 16, 18 milliseconds after the start of propagation, from top row to bottom row respectively and in each row from left side to right side) as a next step, we study the effect of obstacles on the action potential propagation in our represented excitable medium. in the normal heart, rhythmic cardiac contractions are coordinated through nonlinear electrical waves of excitation that smoothly propagate through the cardiac tissue. reentrant waves are a common cause of cardiac arrhythmias. the term re-entry was coined to describe a wave front that re-enters and hence re-excites the same tissue again and again as opposed to the normal planar wave front emitted by the sinus node that etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 232-236 235 www.etasr.com sabzpoushan and faghani ghodrat: role of sodium channel on cardiac action potential excites all tissue only once. in the two dimension tissue, reentry can be caused by a wave front curved around an obstacle [11-13]. the dead regions of the cardiac tissue play the role of obstacles. in this study we create some local obstacles as dead tissues considering the sodium ion conductance equal to zero in the excitable medium. as shown in figure 7, three rectangular obstacles in the medium are considered. the considered obstacles that exist in the passing way of action potential wave disorder wave front. this perturbation causes changes in the normal action potential propagation in the grid, which disturbs the normal cardiac rhythmic pattern and arrhythmia status occurs. the cumulative effect of the disturbance in the abnormal cardiac rhythmic pattern forms a re-entry in the location of the obstacle. re-entry is formed because the dead region of the tissue acts as an obstacle for the normal action potential propagation. as time elapses, the re-entry waves move to all regions of the grid and thus cause a total arrhythmic pattern. in figures 4-7, it is clearly observed that sodium ion concentration plays a vital role in the propagation of the action potential wave front in an excitable medium. fig. 7. considering gna equal to zero for creating obstacles which cause anatomical reentrant and consequently cardiac arrhythmia iv. discussion in order for a wave front to successfully expand in tissue, recruitment of an adequate supply of charge carriers (e.g. na) is required. the carriers should be able to diffuse down a concentration and voltage gradient into adjacent resting cells, depolarizing the local membrane potential to the na channel opening threshold. since recently recruited na channels inactivate, they must be rapidly replaced with newly recruited channels in order to prevent wave front collapse. the process of charge diffusion and subsequent opening of resting na channels adjacent to the wave front is referred as a recruiting process [3, 14]. the amount of recruited charge, as determined by the recruiting range and the restored na conductance density within this range, are critical determinants of not only whether propagation can be sustained but also of the propagation velocity. in this work, an efficient pde model was used to study the action potential formation and its propagation. the effect of sodium ion concentration, which is one of the reasons behind arrhythmias, was well studied in case of a single cell and in case of a 2d grid of cells. this was achieved by decreasing the sodium ion conductance step by step. the effects of the change were studied in each stage. in the final stage, we investigated the effect of obstacles on the action potential propagation. we considered three obstacles in the different points of the represented excitable medium by assigning 0 to gna. the obstacles played the role of dead regions of cardiac tissue and caused reentrant waves formation leading to cardiac arrhythmia v. conclusion results portrayed in this paper, confirmed that action potential propagation in an excitable media requires a sufficient number of na ions that can diffuse into adjacent resting cells and raise the membrane potential to the firing threshold. it is concluded that decreasing the sodium ion conductance decreases both the passing ability and the conduction velocity of the action potential wave front. sodium ion concentration plays a vital role in controlling arrhythmia, hence further research should be focused on studying the effects of this channel on formation and control of cardiac arrhythmias. references [1] k. h. w. j. ten tusscher, “spiral wave dynamics and ventricular arrhythmias”, phd thesis, university of utrecht, 2004. [2] k. h. w. j. ten tusscher, a. v. panfilov, “cell model for efficient simulation of wave propagation in human ventricular tissue under normal and pathological conditions”, phys. med. biol., vol. 51, pp. 6141-6156, 2006. [3] c. frank starmer , a. o. grant, t. j. colatsky. “what happens when cardiac na channel function is compromised? 2-numerical studies of the vulnerable period in tissue altered by drugs”, cardiovascular research, vol. 57, no. 4, pp. 1062–1071, 2003. [4] g. w. beeler, h. reuter, “reconstruction of the action potential of ventricular myocardial fibres”, j. physiol., vol. 268, no. 1, pp. 177–210, 1977. [5] h. c. lee, t. lu, n. l. weintraub, m. vanrollins, a. a. spector, e. f. shibata. “effects of epoxyeicosatrienoic acids on the cardiac sodium channels in isolated rat ventricular myocytes”, j. physiol., vol. 519, pp. 153–168, 1999. [6] d. a. hanck, “biophysics of sodium channels. in cardiac electrophysiology: from cell to bedside”, d. p. zipes and j. jalife, editors. w. b. saunders co., philadelphia, pp. 65–74, 1995. [7] c. luo, y. rudy, “a dynamic model of the cardiac ventricular action potential i simulations of ionic currents and concentration changes”, circ. res., vol. 74, pp. 1071-1096, 1994. [8] t. j. colatsky, “voltage clamp measurements of sodium channel properties in rabbit cardiac purkinje fibres”, j. physiol., vol. 305, pp. 215–234, 1980. [9] j. keener, j. sneyd, “mathematical physiology”, springer, 1998. [10] g. c. everstine, “ numerical solution of partial differential equations” , lecture notes, george washington university, 2010. etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 232-236 236 www.etasr.com sabzpoushan and faghani ghodrat: role of sodium channel on cardiac action potential [11] n. wiener, a. rosenblueth, “the mathematical formulation of the problem of conduction of impulses in a network of connected excitable elements, specifically in cardiac muscle”. arch. inst. cardiol. mex, vol. 16, no. 3, pp. 205–265, 1946. [12] a. t. winfree, “the geometry of biological time”. springer-verlag, new york, usa, 1980. [13] v. s. zykov, “simulation of wave processes in excitable media”. manchester university press, manchester, uk, 1987. [14] c. f. starmer, t. j. colatsky, a. o. grant. “what happens when cardiac na channels lose their function? 1-numerical studies of the vulnerable period in tissue expressing mutant channels”, cardiovascular research, vol. 57, pp. 82–91, 2003. microsoft word 4-776-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1130-1132 1130 www.etasr.com rojas-renteria et al.: an electrical energy consumption monitoring and forecasting system an electrical energy consumption monitoring and forecasting system j. l. rojas-renteria engineering dpt, autonomous university of queretaro, mexico luis_rojasr@ hotmail.com t. d. espinoza-huerta faculty of accounting and administration, autonomous university of queretaro, mexico tdespinoza@ mail.itq.edu.mx f. s. tovar-pacheco industrial maintenance and construction dpt, technological university of san juan del rio, mexico fstovarp@ utsjr.edu.mx j. l. gonzalez-perez linking dpt, polytechnic university of santa rosa jauregui, mexico gpjluismx@ hotmail.com r. lozano-dorantes engineering dpt, anahuac university mexico raullozanodorantes@ hotmail.com abstract—electricity consumption is currently an issue of great interest for power companies that need an as much as accurate profile for controlling the installed systems but also for designing future expansions and alterations. detailed monitoring has proved to be valuable for both power companies and consumers. further, as smart grid technology is bound to result to increasingly flexible rates, an accurate forecast is bound to prove valuable in the future. in this paper, a monitoring and forecasting system is investigated. the monitoring system was installed in an actual building and the recordings were used to design and evaluate the forecasting system, based on an artificial neural network. results show that the system can provide detailed monitoring and also an accurate forecast for a building’s consumption. keywords-power consumption; energy monitoring; heuristic methods i. introduction the problem of electric energy consumption, and its forecast, is an issue of growing interest. the growth in industrial, commercial and housing sectors result in increased electricity consumption whereas the nature of the loads has shifted towards a nonlinear nature. however, the overall consumption of buildings is lately recognized as an important characteristic, now increasingly considered and implemented in the building’s calculated worth. in this situation, new challenges surfaced. the energy efficiency of electrical and control devices is constantly sought to be improved [1], but the most significant means of optimization are related to the power network (generation, transmission, distribution) [2]. of course, the optimization of the network is of great interest to power companies. nowadays, the distribution companies need to monitor and correct problems in energy quality for the benefit of their users, real-time plot the average values of the programmed energy production and make adjustments according to the demand of the day [3]. thus, detailed consumption monitoring systems is of great interest to power distribution companies. however, it has also proved to be valuable for consumers. the energy profile of buildings is now increasingly considered during the buildings’ design and the overall reduction in energy consumption results to increased power quality [6-7]. further, close monitoring may be used by consumers to alter their consumption routine and thus exploit flexible rates provided by power companies and general reduce their consumption. recent research has shown that the traditional periodic measurements have been ineffective in changing users’ behavior. however, detailed monitoring (and electronic feedback) has been more efficient in that area [4]. in [5], it was concluded that close monitoring captures the attention of the audience, gains participation and it is credible and useful to users. although it is not simple to unfold the information, what matters the most at this stage is that these information motivates consumers to save energy. in [8], a study regarding the benefits of an interactive connection information system of energy consumption for residential buildings was conducted. a comparison of energy consumption before and after the installation of the system revealed a reduction in the total consumption of electricity. information about the energy consumption is also very useful for detecting abnormalities [5]. the next generation of predictive load schemes however, will require an increased amount of information and the ability to make an accurate forecast will be a significant benefit of monitoring systems. this paper focuses on a system that is able to monitor and forecast the electricity consumption of a building. the forecast part is based on an artificial neural network (ann) and it uses actual consumption data as recorded from the monitoring system installed in an actual building. being able to provide accurate forecasts of future consumption is obviously a matter of great importance for power companies. consumers may also benefit from such a system in the future as smart grids may bring about flexible rates linked to overall consumption thus making an accurate forecast rather useful. engineering, technology & applied science research vol. 6, no. 5, 2016, 1130-1132 1131 www.etasr.com rojas-renteria et al.: an electrical energy consumption monitoring and forecasting system ii. consumption monitoring technological advances in networking, communications, data management, and measurement technology have combined to reduce significantly the cost of energy monitoring systems (ems), and to increase the capacity of these systems and include energy quality data. traditional measuring instruments used individual analog circuits to measure and calculate the energy parameters. a power monitoring system can currently perform all measurements on a single chip. as the level of integration increases, the gauge of the future will be smaller, more capable and less expensive. in [9], a list of intelligent building components is provided, in which power management systems (sae) are the most important. sae allows a user to control and monitor energy consumption of a building locally or remotely. for proper operation of a sae, accurate energy consumption values are necessary [10]. the energy consumption data considered in this paper, were obtained from the main substation at the technological university of corregidora from january 29 to november 3, 2015. a building management system (bms) was designed and installed in the control room of the building, embedded on a web server. this bms is based on a microcontroller module that allows the monitoring of the building’s energy consumption in real time via the internet (figure 1). it should be noted that since monetary relations are based on meter readings, production, sale and use of these instruments are subjected to strict regulations and specification. the threephase analyzer used in this system complies with ansi/isa s82.01-1994. figure 2 shows a part of monitoring data obtained. fig. 1. the bms scheme fig. 2. measurement of energy monitoring iii. forecast scheme and results the proposed forecasting model is based mainly on an artificial neural network. this network was used to select the best average of the absolute differences between measured and estimated values, expressed as a percentage of the measured values. the ann implemented in this study is a multilayer perceptron (mlp) with an input layer of 3 nodes (the inputs are kw, hr and day), a hidden layer with a variable number of hidden nodes (several networks with variable number of hidden nodes were implemented and tested) and an output layer with only one node (the result of the forecast). the basic description of the algorithm is as follows: • determine the input and output variables • include a set of data describing the relationship between input-output model • divide the data set into 2 parts: the training and validation set (used to determine the parameters of the ann) and the test set (used to evaluate the model). 80% of the data is used to train the network, 10% is used for the validation and the remaining 10% is used for generalization. • develop a conventional model to train the network with the data set • estimate the relationship between inputs and outputs of the neural network (i.e. define the ann). these steps are repeated to find the appropriate number of hidden nodes, using different training parameters for the network. the ann was implemented in matlab. several models were evaluated for a structure of 7000 hrs. the error of the mean absolute percentage (mape) was used to evaluate the performance of the different anns. the results for each tested ann are shown in table i. as shown, the 3-3-1 ann performed best. figure 3 shows the approximation curve. a data analysis tool called hypothesis testing was employed to accept or reject the found values. a threshold of 95% confidence level has been set and an added probability factor is considered to make sure that the results are statistically significant. figure 4 shows a screenshot from the data analysis procedure. fig. 3. approximation curve electricity consumption engineering, technology & applied science research vol. 6, no. 5, 2016, 1130-1132 1132 www.etasr.com rojas-renteria et al.: an electrical energy consumption monitoring and forecasting system table i. comparison of the estimated error for different models of neural networks model r2 mape sep 3-1-1 0.9015 0.0628 0.0959 3-2-1 0.9270 0.0617 0.1788 3-3-1 0.9310 0.0537 0.0849 3-4-1 0.9264 0.0563 0.1094 3-5-1 0.9003 0.0662 0.1134 3-6-1 0.9153 0.0650 0.1073 3-7-1 0.9023 0.0631 0.1126 3-8-1 0.9010 0.0571 0.1094 iv. conclusion an electricity consumption forecast system based on an artificial neural network (ann) is investigated in this paper. actual values recorded from a monitoring system installed in the main substation of a university building were used to design and evaluate the system. hypothesis testing was employed and a threshold value of 95% was used to ensure that the results are statistically significant. several architectures were tested and the best results showed an estimated error (mean absolute percentage) of 0.0537. fig. 4. data analysis references [1] p. soderholm, “the political economy of international green certificate markets”, energy policy,vol. 36, no. 6, pp. 2051– 2062, 2008 [2] n. truong, l. wanga, p. k. c. wong “modelling and short-term forecasting of daily peak power demand in victoria using twodimensional wavelet based sdp models”, electrical power and energy systems, vol. 30, pp. 511-518, 2008 [3] j. k. w. wong, h. li, s. w. wang, “intelligent building research: a review”, automation in construction, vol. 14, pp. 143–159, 2009 [4] g. wood, m. newborough, “energy-use information transfer for intelligent homes: enabling energy conservation with central and local displays”, energy and buildings, vol. 39, no. 4, pp. 495-503, 2006 [5] j. e. seem, “using intelligent data analysis to detect abnormal energy consumption in buildings”, energy and buildings, vol. 39, no. 1, pp. 52-58, 2006 [6] j. l. rojas-renteria, g. macias-bobadilla, r. luna-rubio, c. a. gonzalez-gutierrez, a. rojas-molina, j. l. gonzalez-perez “control response of electric demand by means of fuzzy logic using programmable logic controller (plc)”, international journal of physical sciences, vol. 8, no. 20, pp. 1058-1067, 2013 [7] y. s. kim, k. s. kim, “simplified energy prediction method accounting for part-load performance of chiller”, building and environment, vol. 42, no. 1, pp. 507-515, 2007 [8] j j. l. rojas-renteria. r. luna-rubio, j. l. gonzalez-perez, c. a. gonzalez-gutierrez, a. rojas-molina, g. macias-bobadilla, “estimated electric power consumption by means of artificial neural networks and autoregressive models with exogenous input methods”, international journal of physical sciences, vol. 8, no. 14, pp. 585-592, 2013 [9] h. doukas, k. d. patlitzianas, k. iatropoulos, j. psarras, “intelligent building energy management system using rule sets”, building and environment, vol. 42, no. 10, pp. 3562-3569, 2007 [10] j. k. pal, f. c. huff, “advantages of an electrical control and energy management system”, isa transactions, vol. 39, no. 1, pp. 103-114, 2000 authors profile j. l. rojas-rentería received the ph.d. degree in the division de estudios de posgrado at es, autonomous university of queretaro. received the b.e degree in automation and instrumentation in industrial processes control, the m.s. degree in quality engineering from the engineering school (es), autonomous university of queretaro (uaq). he joined the es as assistant professor in 2010 and at the technological university of corregidora as a research professor in 2012. he has 22 years of experience in different types of industrial mechanic and electric maintenance, as well as industrial machinery facilities. his current research interests are focused on building management systems for intelligent buildings, control of energy demand response, and forecasting of electrical power energy. t. d. espinoza-huerta is a research professor in the department of industrial engineering from the technological institute of queretaro and autonomous university of queretaro. f. s. tovar pacheco is a director of the division of production systems, industrial maintenance and construction of the technological university of san juan del rio. j. l. gonzalez-perez is a software engineer and software quality consultant (software testing and audit processes). he has worked with capability maturity model integration (cmmi), model for the improvement and evaluation of processes for development, maintenance and operation of software systems. he has worked as a research professor at the polytechnic university of santa rosa jauregui (upsrj) and other universities in mathematics, computer algorithms, embedded software, expert systems, computer vision and digital image processing. r. lozano-doantes received a master's degree from the department of engineering and control of process of the autonomous university of queretaro. his research interests include develop computational and control of process of multivariable tank, evolutionary computation, time series of this modeling prototipe and control numeric of drill automatic forecasting, and develop of machinery bend process and welding. microsoft word etasr_v12_n1_pp8101-8106 engineering, technology & applied science research vol. 12, no. 1, 2022, 8101-8106 8101 www.etasr.com deaconescu et al.: the dynamics of the radiated field near a mobile phone connected to a 4g or 5g … the dynamics of the radiated field near a mobile phone connected to a 4g or 5g network delia-bianca deaconescu doctoral school of electrical engineering technical university of cluj-napoca cluj-napoca, romania deliadeaconescu@yahoo.com andreea maria buda nicolae balcescu land forces academy politehnica university of bucharest bucharest, romania budaandreeea98@yahoo.com david vatamanu nicolae balcescu land forces academy lucian blaga university sibiu, romania davidvatamanu@yahoo.com simona miclaus dept. communications, it & cyb. def. nicolae balcescu land forces academy sibiu, romania simo.miclaus@gmail.com abstract-characterizing the time variations of signals emitted by mobile terminals provides complementary information to health authorities, especially with the increase of frequency and energy of radiation towards millimeter waves. this experimental work aimed to quantify and classify the time variability of the electric field level measured at 10cm from a mobile phone connected sequentially to a 4 th and 5 th generation mobile network. statistic analysis was performed on data from real-time spectrum analyzers, while self-similarity was computed by first recurrence plots of the radiated emissions, corresponding to five different types of mobile applications. moreover, specificities to the communication standard and the type of application were identified. keywords-human exposure; 5g nr; lte; mobile phone; field variability i. introduction massive mobile phone use has led to a tremendous data traffic increase in wireless networks. the fifth-generation (5g) of mobile communication technology, called new radio (nr), has been proposed and developed to provide sufficient data speeds [1-2], as the 4 th generation (4g) reached its limits. the core features of 5g technology are low communication latency, higher download speeds, higher cell density, ultrareliability, etc. [3]. compared to the 4g mobile communication standard, called long term evolution (lte), that uses frequencies lower than 6ghz [4], the 5g nr standard uses two sets of frequency ranges: frequency range f1 (fr1) [5] has a maximum of 6ghz and an extension up to 7.125ghz, and frequency range f2 (fr2) from 24.25 to 52.60ghz [6]. the spread of such technologies has raised continuous public worries about the associated health risks. this study aims to examine and compare the time-variability of the radiated emissions on these networks. 4g lte involves the use of orthogonal frequencydivision multiplexing (ofdm) and single carrier-frequency division multiple access (sc-fdma) for downlink (dl) and uplink (ul) transmissions respectively [7]. two frame types are delivered [8]: type 1 uses frequency division duplex (fdd), while type 2 uses time division duplex (tdd). in fdd mode, the 4g frame has a duration of 10ms and contains 10 subframes or 20 slots. in tdd mode, the frame has the same duration but is divided into 2 halves of frames with a length of 5ms. the minimum resource that can be used in ul and dl is called resource block (rb), which lasts 0.5ms, occupies 180khz, and contains 12 subcarriers with a spacing of 15khz [9]. the number of subcarriers and symbols differ for each rb, depending on the length of the cyclic prefix and the spacing of the subcarriers. the slots consist of 6 ofdm symbols in an extended cyclic prefix and 7 symbols in a normal cyclic prefix. 5g nr adopts, similar to 4g, the fdd and tdd techniques, while the signals are ofdm modulated. 5g uses a grid structure consisting of subcarriers in the frequency domain and ofdm symbols in the time domain [10]. for services requiring low latency and high frequencies, 5g supports subcarrier spacings of 30, 60, 120, and 240khz, based on the subcarrier of 15khz, whereas the subcarrier spacing in 4g is 15khz [11]. in the time domain, ofdm symbols are used to construct slots, subframes, and frames. a frame is 10ms long and consists of 10 subframes. in the extended cyclic prefix, a slot consists of 12 ofdm symbols, while in the case of a normal cyclic prefix a slot consists of 14 symbols [12]. in the frequency domain, rb consists of 12 consecutive subcarriers. the access in 5g is based on a procedure that involves the detection of the synchronization signal (ss). similarly to 4g, the ss in 5g consists of two signals: the primary synchronization signal (pss) and the secondary synchronization signal (sss). one of the biggest differences between 4g and 5g is that in 5g the ss blocks are transmitted as a directional signal with a high periodicity, while in 4g the cell-specific reference signal (crs) is distributed in frames corresponding author: delia-bianca deaconescu engineering, technology & applied science research vol. 12, no. 1, 2022, 8101-8106 8102 www.etasr.com deaconescu et al.: the dynamics of the radiated field near a mobile phone connected to a 4g or 5g … and is transmitted throughout the cellular network. an ss/pbch block consists of a physical broadcast channel (pbch) and de-modulation reference signals [13]. like in 4g, random access in 5g is performed in 4 steps. at first, the user equipment (ue) identifies the ssb within the ss burst set by using part of the time index carried by the pbch and transmits a physical random access channel (prach). the 5g standard defines 13 prach formats, some with fixed and others with variable subcarrier spacings, that can fit into an nr slot. when a base station uses beamforming and different beams are applied to multiple ss/pbch block transmissions, prach resources are associated with ss/pbch blocks. in this way, ue transmits a prach [14] to randomly initiate the access. therefore, the base station figures out which ss/pbch block was received by the ue based on the received prach resources. in the next random access procedure, the base station can use transmission/reception beamforming directed to the ue. a major improvement in 5g networks is the use of active antennas that can synthesize many beams pointing to different directions in continuous dynamic [15-16]. beamforming is achieved by combining elements in an antenna array. massive multiple-input multiple-output (ma-mimo) exploits the resources in the space dimension and enables users connected to the same base station to use the same time and frequency resources. this ability is defined by a 3gpp antenna port and is associated with a specific set of signals that allow the reuse of time-space resources of the channel. mimo transmission is based on two different physical phenomena, polarization multiplexing and spatial multiplexing [17]. with the advent of 5g, one of the concerns of mobile technology users is related to the impact of radiation on human health. as the 5g nr standard is characterized by the use of different technical features (advanced tdd, beam-forming, beam steering, and ma-mimo), the classical method of measuring the emitted power density of a mobile device, as applied in 4g, cannot be used as such. in [18], a measurement method was proposed based on the evaluation of extrapolation factors associated with beam sweeping and tdd access mode, which can be used to estimate the instant maximum and the total power transmitted during a 5g radio frame. as 5g systems have unprecedented beam management flexibility, maximum permissible exposure (mpe)-specific measurements are applied in unknown beam states. a solution to solve this problem was proposed in [19] using a beam-forcing technique of ues, concluding that using a ue capable to interact actively with the base station forces the system into a suitable mode for measurement. an electromagnetic field (emf) level estimation technique was proposed in [20], derived from a base station tested in single-user mimo (su-mimo) coding. the efficiency of using the extrapolation technique for 5g technology was demonstrated. the number of multiplexed subchannels increased by using multi-user mimo (mumimo) systems, and the spatial variation of the field could be exploited. this approach expands beam-forming and spatial filtering and allows the reuse of time and frequency resources with a low level of user interference. optimization of the antenna array to obtain maximum performance in line-of-sight (los) propagation condition was explored in [21], introducing a predictor factor for beam-forming losses and a way to use it in mu-mimo systems. moreover, grating lobes did not have a negative impact in mu-mimo systems, while using larger inter-element spacings can be advantageous. in [22], the first experimental measurement session made in a 5g site was presented. a five-step procedure was applied to assess in-situ the exposure of people due to emissions of 5g base stations. additional factors such as the temporal duty cycle, the spatial duty cycle, and a tdd factor, were added to the description of the theoretical maximum exposure level following iec standard 62232: 2017 [23]. furthermore, the levels of the e-field per resource element were measured and extrapolated to a theoretical maximum strength, while all reported values were below the icnirp reference level [24]. in 5g systems, beamforming may represent a health risk due to the momentary intense increase of the radiated power and the dynamics of these variations. so far, no scientific evidence has been reported to sustain this aspect. some recent studies reported the possibility of reducing exposure by adopting the beamforming technique [25]. in [26], a scenario was considered to evaluate the impact of pencil beamforming, as a strong reduction in human exposure was observed when the tuning of traffic beams integrated localization information. when the localization uncertainty was lower, the synthesized beams were narrower, and the emf exposure decreased. as stated above, emf human exposure from cellular network devices originates from two sources: dl (base stations) and ul (own or a nearby person’s handset/terminal). the actual power output of ue is set by the network at the lowest level, while the power transmitted by a base station varies with the area it serves. over time, small cells increased the network capacities and lowered the power. it is reported that more than 70 million small cells will be installed worldwide by 2025, with one-third belonging to 5g systems [27]. very few papers quantified the radiation emitted by a mobile terminal in 5g networks [28]. this study aims to highlight the time-variation peculiarities of the radiated field near a ue operating in either a 4g or 5g network. the objective was the comparison of the dynamics of the emitted field strength during the use of several mobile applications types, to expand the knowledge on the variation of the user exposure in time. the dynamics of rf exposure may be important in triggering biological responses at the cell membrane level [29]. since a new approach is proposed for the increasing frequencies towards millimeter-wave range [30], paving the way to the experimental findings on the timevariability of the emitted radiation may represent a valuable complementary instrument in expo-dosimetry of new mobile technologies. ii. materials and methods a motorola smartphone model g 5g plus (xt 2075-3), connected sequentially to 4g and 5g in fr1, was used as the source of emf exposure. in both connections, the location of the base station was the same related to the ue, at 75m distance, in non-los propagation as ue was located inside a building. the main characteristics of the ul signals (both networks used tdd) were: a) in 4g, the central frequency was f1=2.59ghz and the channel bandwidth was bw1=20mhz, b) engineering, technology & applied science research vol. 12, no. 1, 2022, 8101-8106 8103 www.etasr.com deaconescu et al.: the dynamics of the radiated field near a mobile phone connected to a 4g or 5g … in 5g, the connection used band n77 with central frequency f2=3.7ghz and channel bandwidth bw2=40mhz. ue could deliver a maximum transmitted power of 23dbm for 4g and 5g. a line parallel to the ue upper edge was chosen to capture the radiated electric e-field level in far-field conditions of propagation near the phone, at a 10cm distance, where three efield probes were located at the same distance between them. the following measuring instruments were used (figure 1): three identical portable real-time spectrum analyzers type spectran 5 aaronia (hf 80120 v5 x model), three small psb e1 e-field probes connected to the analyzers, and laptops. fig. 1. measurement ensemble with electric field probes, real-time spectrum analyzers, laptops, and the motorola one 5g phone. the time-series data of emitted power were synchronously recorded and retrieved using aaronia rtsa suite pro and aaronia mcs spectrum analysis. five mobile applications were used as sources of the emf emissions on both networks: video call, voice call, file upload, file download, and streaming. three measurements (r1, r2, r3) were performed on each mobile application and probe (p1, p2, p3). each power level stream was recorded continuously for 25s and the sampling periodicity was 100ms. the spectral analyzer was set to a realtime bandwidth span (rtbw) of 88mhz, for 4g and 44mhz for 5g. after collecting the evolution of the signal spectrum in time, the channel power was calculated every 100ms, by: ��� � � ���� �� ����� � ���� ��� ����� �� (1) where f start and f stop are the limits of the spectrum in the channel, fft bin(f) is the power level of each of the spectral components (440 frequency bins were used), and window bandwidth wb is the resolution bandwidth (195khz for the 4g and 98khz for the 5g). once the power levels were determined, the e-field strengths in air, at 10cm from the ue and their time-evolution was calculated, using the field probe calibration files. based on these time series of e-field strength values, the descriptive statistics of field levels per each emission type were calculated and represented in poincare plots for all 90 situations (5 mobile applications × 2 communication standards × 3 field probes × 3 repetitions). the idea of capturing the selfsimilarity of the emission dynamics was implemented over the time series in the form of a two-dimensional recurrence map called poincare plots, which was applied for the first time in [31] for wireless local area network emissions. standard descriptors were used to quantify the poincare ellipse geometry: the ellipse axes, namely sd1 (short-term variability) and sd2 (long-term variability). sd1 represents the standard deviation of the distances of points from axis 1, and sd2 represents the dispersion of points along the axis. the areas of ellipses were calculated to emphasize the differences between the standards, which indicate the total variability and the sd1/sd2 ratios showing the randomness of the time series of the radiated e-field strengths. all the calculations were made to observe the differences in the electromagnetic time-print of the emissions between 4g and 5g. iii. results and discussion the mean, median and interquartile ranges (iqr) of the efield strengths, measured in the air at the three points where the probes p1…p3 were situated can be seen in figure 2. the outliers are represented in the emissions of the 5 mobile applications and can be observed as prominent during streaming and voice calls. three repetitions are shown for each probe, each of the same color. figure 2 contains 5 graphs corresponding to each mobile application marked on the abscissa. the first nine boxplots of each graph correspond to 4g, while the second nine correspond to 5g emissions. upload in 4g presented the largest iqr in which e-field strengths spread. iqr is a measure of the variability around the median, indicating the range of the middle half (50%) of the data. all 4g transmissions during upload, download, and video call showed visible iqr intervals with few outliers. the 5g transmissions on these applications had multiple outliers, indicating that the e-field levels were too far from the central values. another difference was observed between the 4g and 5g field-level spread for video calls. voice call and streaming had outliers in both 4g and 5g, indicating that field variability is the highest during such activities. on the other hand, upload and video call in 4g caused more exposure than in 5g. download and voice call cause lower exposure in 4g, while streaming showed similar exposure levels in both communication standards. however, in these measurements made 10cm from the phone, the field levels were far beyond the icnirp safety limits guidelines [24]. figure 3 shows four characteristic poincare maps of the time distribution of e-field strength values, measured during video call and file download in 4g and 5g. it can be observed that short-term variability is lower than long-term during an application running in 4g, while the variabilities are vice versa in 5g. in each network, the radiated field level tends to have a certain scatter pattern for all applications, so the self-similarity in the time variation of the signals depends on the communication standard. moreover, specificities could be observed between the type of mobile applications. in this sense, figure 4 shows the ratios between the ellipse axes, the sd1/sd2 ratios, and the average of the results for all probes. engineering, technology & applied science research vol. 12, no. 1, 2022, 8101-8106 8104 www.etasr.com deaconescu et al.: the dynamics of the radiated field near a mobile phone connected to a 4g or 5g … fig. 2. boxplots with outliers of e-field strength distributions for all mobile applications, all probes, and repetitions in 4g and 5g networks. fig. 3. poincare maps of e-field strength near the phone in 4g (left) and 5g standard (right) during two applications. the results of the ellipse axis ratio for r2 and r3, are presented for the 5 applications on both networks. the lowest ratio between shortand long-time variabilities was found in upload on 4g. the highest ratio between shortand long-time variabilities was found in the 5g download. for all 5g applications, the randomness of the emitted field was higher in the shortthan the long-term, as compared to the respective 4g. the poincare ellipse areas, shown in figure 5, indicate that the largest variability of the radiated field corresponds to file upload and video call in 4g. figure 5 indicates the average areas for two repetitions of the measurements. the total variabilities of the emitted fields were higher in 5g than in 4g for file download, streaming, and voice call. however, upload and video call in 4g had at least one order of magnitude larger variability than the other applications in both standards. as this specific feature confirms that file upload and video call led to the highest exposure levels in 4g, as deduced from figure 2, it engineering, technology & applied science research vol. 12, no. 1, 2022, 8101-8106 8105 www.etasr.com deaconescu et al.: the dynamics of the radiated field near a mobile phone connected to a 4g or 5g … can be concluded that these applications could be the most interesting for further biological dosimetry research. in 5g, the largest variabilities of the radiated field were observed for voice calls and file download. these high variabilities may be due to the higher field levels in 5g for these two mobile applications. therefore, at least voice calls deserve special attention in future dosimetric studies devoted to the biological effects of 5g signals. fig. 4. average ratios sd1/sd2 of e-field strength ellipses for all mobile applications in 4g and 5g in two repetitions: r1 (up), r2 (down). fig. 5. areas of the poincare maps of e field strength for all applications in 4g and 5g in two repetitions: r1 (up), r3 (down). previous findings, extracted by applying a different methodology but still based on real-time spectrum analyzers and small and sensitive field probes, emphasized specific features of the time variability of signals emitted by a 4g phone [28]. in line with those findings, this study allowed a step further in extracting the main peculiarities of the time dynamics of the emitted radiation, by comparing the 4g and 5g sub-6 ghz band networks using the same phone model. the novelty of this research was the approach of a complementary characterization of human exposure by the energy fluence rate adapted to the ghz frequency range. based on this quantity, it was shown that a prediction is possible based on differentiating chaotic behavior from true randomness of 4g and 5g emitted signals evoked by recurrence quantification. iv. conclusions this study aimed to identify the differences in the time variability of signals emitted by a mobile phone when sequentially connected to a 4g-lte or 5g-nr network. the main reason behind this study was the need of describing not only the dose of radiation absorbed by a human body while using a phone but also the average or the momentary dose rate. while the present safety exposure standards do not yet expressly require such knowledge, increasing the frequency towards tens of ghz in 5g networks means an increase in the energy of the radiation so it might need a time-dependent description similar to the ionizing radiation. moreover, the averaging time used to describe the biological impact of the field is also very important to accurately describe the safety of people exposed to very short and quasi-stochastic pulses [31]. by experimentally determining the e-field strength variation during the 25s usage of 5 different mobile communication activities in either 4g or 5g networks, which allowed tdd technique and respectively had 20 and 40mhz bandwidths for the transmission, streams of 250 field values were gathered and treated as time-series. the boxplot representations of these data allowed obtaining descriptive statistic distributions, while the poincare plots showed selfsimilarity by first recurrence means. the results showed that: a) more intensive dynamics are encountered generally in 5g ul signal than in 4g, b) the time variability is dependent not only on the communication standard but also on the type of mobile application used, c) short-term variability is lower than longterm when using a 4g application, as compared to 5g where the short-term variability of field level is higher than the longterm, d) the lowest ratio between shortand long-time variabilities was encountered for file upload in 4g, while the highest ratio was encountered for file download in 5g, and e) the largest total variabilities in 4g were associated to upload and video call, while in 5g they were noted during voice call and file download. these results provide important knowledge that completes the picture of amplitude-time variation of human exposure to near-the-body used mobile devices. references [1] s. parkvall, e. dahlman, a. furuskar, and m. frenne, "nr: the new 5g radio access technology," ieee communications standards magazine, vol. 1, no. 4, pp. 24–30, dec. 2017, https://doi.org/10.1109/ mcomstd.2017.1700042. engineering, technology & applied science research vol. 12, no. 1, 2022, 8101-8106 8106 www.etasr.com deaconescu et al.: the 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[28] s. m. and p. bechet, "non-stationary statistics with amplitude probability density function for exposure and energy density reporting near a mobile phone running 4g applications," progress in electromagnetics research m, vol. 89, pp. 151–159, 2020, https://doi.org/10.2528/pierm19110706. [29] m. simkó and m.-o. mattsson, "5g wireless communication and health effects—a pragmatic review based on available studies regarding 6 to 100 ghz," international journal of environmental research and public health, vol. 16, no. 18, jan. 2019, art. no. 3406, https://doi.org/10.3390/ijerph16183406. [30] e. neufeld, t. samaras, and n. kuster, "discussion on spatial and time averaging restrictions within the electromagnetic exposure safety framework in the frequency range above 6 ghz for pulsed and localized exposures," bioelectromagnetics, vol. 41, no. 2, pp. 164–168, 2020, https://doi.org/10.1002/bem.22244. [31] s. miclaus, a. sarbu, and p. bechet, "using poincare plots for feature extraction of the dynamics of electromagnetic field exposures when using different protocols of wi-fi communications," in 2021 8th international conference on wireless communication and sensor networks, new york, ny, usa, jan. 2021, pp. 32–38, https://doi.org/10.1145/3461717.3461723. microsoft word etasr_v12_n3_pp8488-8491 engineering, technology & applied science research vol. 12, no. 3, 2022, 8488-8491 8488 www.etasr.com minhl et al.: analysis of leakage inductances in shunt reactors: application to high voltage … analysis of leakage inductances in shunt reactors: application to high voltage transmission lines tu pham minh school of electrical and electronic engineering hanoi university of science and technology hanoi, vietnam tu.phamminh@hust.edu.vn hung bui duc school of electrical and electronic engineering hanoi university of science and technology hanoi, vietnam hung.buiduc@hust.edu.vn vuong dang quoc school of electrical and electronic engineering hanoi university of science and technology hanoi, vietnam vuong.dangquoc@hust.edu.vn received: 12 february 2022 | revised: 1 march 2022 | accepted: 16 march 2022 αbstract–inductance is one of the main parameters directly related to the reactive powers of shunt reactors (srs) in electrical systems. thus, the definition and computation of leakage inductances and the ratio of leakage to total inductances play an extremely important role in the design and manufacturing of srs. in this study, a finite element approach was developed to compute leakage and total inductances and define a relationship between them with different sr powers and high voltage levels. the expanded method is presented with the magnetic vector potential formulations. keywords-shunt reactor; leakage inductance; magnetic vector potential formulation; finite element method i. introduction in long-distance high voltage transmission lines, capacitances occur between the phase voltage and earth or between phase voltages, leading to large reactive power in the electrical system [1-3]. in general, when a system operates on a full load, the reactive power is absorbed by the inductance load and lines. on the other hand, if the system works on low or no load, the voltage along lines increases, leading to overload voltage at the end of the line and affecting directly the electrical devices. therefore, to overcome these drawbacks and maintain voltage stability in the electrical system, a shunt reactor (sr) is proposed to absorb the generated reactive powers [1-9]. the total inductance values, consisting of fringing and leakage inductances, are needed to compute and analyze the reactive power capacity of an sr. fringing inductances have been recently proposed in [4, 10]. in this study, a finite element approach was developed with magnetic vector potential formulations to calculate and analyze the leakage inductances of an sr. based on the obtained results, a relation of the shape factors of an sr, between inductance leakages and total inductance, was proposed to help researchers and designers to select suitable leakage inductances for computing and designing. ii. magnetodynamic problems a. maxwell’s equations a canonical magneto-dynamic problem is defined in a domain �, with boundary: �� = � = �h ∪ �e maxwell’s equations, considered in the frequency domain and behavior laws, are written in the euclidean space ℝ� as [11-12]: �� � = �� (1-a) �� � = −�� � (1-b) ��� � = 0 (1-c) � = �� (2-a) � = �� (2-b) where h is the magnetic field (a/m), b is the magnetic flux density (t), e is the electric field (v/m), js is the current density (a/m 2 ), and µ and σ are the relative permeability and electric conductivity (s/m), respectively. the boundary conditions (bcs) defined on γ are expressed as [11-12]: � × �|�� = 0 (3-a) � ∙ �|�! = 0 (3-b) where n is the unit normal exterior to �, with � = �" ∪ �# ". the domains �" and �# " are the conducting and non-conducting regions, respectively. the equations (1-a) and (1-b) were solved with bcs taking into account the tangential component of h in (3-a) and the normal component of b in (3-b). corresponding author: hung bui duc engineering, technology & applied science research vol. 12, no. 3, 2022, 8488-8491 8489 www.etasr.com minhl et al.: analysis of leakage inductances in shunt reactors: application to high voltage … the fields h, b, e, and j are defined to satisfy tonti’s diagram [12]. this means that � ∈ %& '�� ; �) , � ∈ %* '�� ; �) , � ∈ � '���; �) , and � ∈ %* '���; �) , where %& 'curl; ω) and %* 'div; ω) are function spaces containing bcs and the fields defined on �& and �3 of the studied domain �. fig. 1. tonti’s diagram [12]. the field b in (1-c) is derived from a vector potential a such that: � = curl 4 (4) combining (4) with (1-b), leads to the definition of an electric scalar potential v such that: � = −�5 4 − 6 7� 8 (5) b. magnetic vector potential weak formulations based on the weak form of ampere’s law (1-a), the weak formulation of magnetic problems is written as [11-13]: 9 : ∮ '�� 4 ∙ �� <)�� � = � ∮ '�5 4 ∙=> �� <)��" ? � ∮ '6 7� @ ∙ �� <)��" ?=> a '� � �) ∙ <�� � ∮ '�� ∙ <)���=b , ∀ < ∈ %* e'�� , �) (6) where %* e'�� , �) is a function space defined on � and containing the basis functions for 4 and the test function t. the surface integral term 〈� × �, <〉 γ� on γ& in (6) accounts for the natural bcs and can be given in (3a-b). the energy density (hi) is defined via the post-processing, i.e: hj = 9 k ∮ h ∙ b n dω (7) finally, the inductance value (l) is computed via (7), being: o = kpq rs (8) iii. analysis of the practical test the practical test problem was a single-phase sr of 35mvar (500/ √3 kv and 50hz). a simple model of this single-phase sr is presented in figure 2. the typical parameters are given in table i [4]. the percentage of the leakage inductance to the total can be defined as: vi% = xy!z[z\! x]^]zy × 100 (9) where oi*`a`b* (h) and o5c5`i (h) are the leakage and total inductances of the sr respectively. the distribution of the magnetic vector potentials due to the current following in the winding is presented in figure 3. the percentage ratio of oi*`a`b* to o5c5`i (kl %) for different reactive powers and voltage levels is shown in figure 4. fig. 2. model of a single-phase shunt reactor. table i. typical parameters of the sr parameters notations values reactive power q (mvar) 35 rated voltage u (kv) 500/√3 rated current i (a) 121.24 totalinductance l (h) 7.5788 core dimension dc (mm) 701 height of core hc (mm) 1793 total air gap length lg (mm) 386 turn number n (turn) 2018 fig. 3. distribution of magnetic vector potentials. fig. 4. ratio of oi*`a`b* to o5c5`i (kl %) for diferent voltage levels. hc dc hw ww hy dy wy engineering, technology & applied science research vol. 12, no. 3, 2022, 8488-8491 8490 www.etasr.com minhl et al.: analysis of leakage inductances in shunt reactors: application to high voltage … as can be noted, at the same voltage level, when the reactive power increases, the ratio of leakage inductance to total inductance also increases. from the obtained results, a polynomial function of the leakage inductance, power, and voltage, is expressed via the lagrange interpolation method [14]. according to the lagrange interpolation theory, it is possible to determine a polynomial function p(x) of degree less than or equal to n satisfying the conditions p(xi) = yi, for i =1…n+1. the general formula is written as: d'e) = ∑ gh ij9 hk9 ∏ mnmo mpnmo qrh (10) where xi can be considered as the voltage (u), power (q), and yi is the ratio of the total value of leakage flux. based on (10), the polynomial leakage inductance according to power and voltage is defined as: %oi*`a`b* = s't, u) = '−9.913 × 10 n9euk ? 6.116 � 10nyu � 3.451 � 10n|)tk ? '1.329 � 10nyuk � 8.83 � 10n�u ? 9.037 � 10nk)t � '9.008 � 10nyuk ? 3.002 � 10n�u � 8.289) (11) where q (mvar) is the reactive power and u (kv) is the voltage. polynomial (10) allows determining the percentage of leakage inductance at different reactive powers and voltage values. in addition, leakage inductance depends significantly on the winding factor (kw) in the magnetic core’s window. it is shown that kw is the basis to determine the overall shape of the magnetic core. for each value of different reactive power and voltage, the value of oi*`a`b* is computed with the different value of kw (kw= 4� 12) for a change step of 0.2, as shown in figure 5. a polynomial function of the leakage inductance value at the high voltage level of 110 kv is defined as: vi '99ea�)% = s'vp , t) = '−4.753 × 10 n�tk ? 10.61 � 10n|t ? 0.1136)vp k ? '1.127 � 10n|tk � 2.627 � 10nkt � 2.704)vp ? '�9.091 � 10n|tk ? 0.2223 � 10nkt ? 20.85) (12) fig. 5. calculation of the leakage inductance with the change of winding factor. in the same way, the leakage inductance value at the high voltage level of 220kv is expressed as: vi 'kkea�) % = s'vp , t) = '−5.069 � 10 n�tk ? 10.3 � 10n|t ? 0.1068)vp k ? '1.154 � 10n|tk � 2.517 � 10nkt � 2.567)vp ? '�8.932 � 10n|tk ? 0.2135 � 10nkt ? 20.15) (13) for the extra high voltage level of 500kv, the leakage inductance is computed as: vi '�eea�) % s'vp , t) '�4.823 � 10 n�tk ? 9.908 � 10n|t ? 0.1046)vp k ? '1.11 � 10n|tk � 2.432 � 10nkt � 2.521)vp ? '�8.535 � 10n|tk ? 0.2063 � 10nkt ? 19.94) (14) based on the polynomial functions given in (12), (13), and (14), the percentage of leakage inductance to total inductance vi '%) according to vp at different reactive powers and voltage levels is shown in figures 6-8. fig. 6. the value of vi'%) flowing to vp with different powers at 110kv. fig. 7. the value of vi'%) flowing to vp with different powers at 220kv. based on the results shown in figures 6-8 and the polynomial functions of the leakage inductance according to the winding factor at different reactive powers and voltage levels, this method can be a basis for researchers, designers, and manufacturers to choose and look up leakage inductance values when calculating the design, and thus reduce the number of the needed virtual object models. engineering, technology & applied science research vol. 12, no. 3, 2022, 8488-8491 8491 www.etasr.com minhl et al.: analysis of leakage inductances in shunt reactors: application to high voltage … fig. 8. the value of vi '%) flowing to vp with different powers at 500kv. iv. conclusion a finite element approach was developed with the magnetic vector potential formulations. based on the development of the formulation, the leakage and total inductance values according to the winding factor were defined at different reactive powers and voltage levels of 110kv, 220kv, and 500kv. the proposed method and the obtained results could help designers and manufacturers to make a suitable selection of the leakage inductance during the design or manufacturing of the srs. the obtained results also show that there is a very good agreement on standardizing the type of leakage inductances in the sr. acknowledgment this study was funded by the hanoi university of science and technology (hust) under grant number t2021-pc-006. the authors also gratefully acknowledge the quy nhon university, which provided favorable conditions for the use of the copyright-supported ansys electronics desktop v19.r1. references [1] z. norouzian, "shunt reactors: optimizing transmission voltage system," abb transformers and reactors, oct. 2016. [2] z. lubośny, j. klucznik, and k. dobrzyński, "the issues of reactive power compensation in high-voltage transmission lines," acta energetica, no. 23, pp. 102–108, jun. 2015, https://doi.org/ 10.12736/issn.2300-3022.2015210. [3] a. s. nunes, p. kuo-peng, and m. g. vanti, "air core reactor analysis based on rnm method," presented at the compumag 2013 19th international conference on the computation of electromagnetic fiels, budapest, hungary, jul. 2013, art. no. 3. [4] t. p. minh et al., "finite element modeling of shunt reactors used in high voltage power systems," engineering, technology & applied science research, vol. 11, no. 4, pp. 7411–7416, aug. 2021, https://doi.org/10.48084/etasr.4271. [5] t. pham minh, h. bui duc, t. tran van, d. dang chi, and v. dang quoc, "investigating effects of distance air-gaps on iron-core shunt reactors," in advances in engineering research and application, cham, 2022, pp. 545–557, https://doi.org/10.1007/978-3-030-92574-1_57. 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[9] r. p. hutahaean and g. sianipar, "transient analysis of 150 kv shunt reactor at bulukumba substation," in proceedings of the 2011 international conference on electrical engineering and informatics, bandung, indonesia, jul. 2011, pp. 1–6, https://doi.org/10.1109/ iceei.2011.6021818. [10] h. b. duc, t. p. minh, t. p. anh, and v. d. quoc, "a novel approach for the modeling of electromagnetic forces in air-gap shunt reactors," engineering, technology & applied science research, vol. 12, no. 1, pp. 8223–8227, feb. 2022, https://doi.org/10.48084/etasr.4692. [11] v. d. quoc, "robust correction procedure for accurate thin shell models via a perturbation technique," engineering, technology & applied science research, vol. 10, no. 3, pp. 5832–5836, jun. 2020, https://doi.org/10.48084/etasr.3615. [12] v. d. quoc, "accurate magnetic shell approximations with magnetostatic finite element formulations by a subdomain approach," engineering, technology & applied science research, vol. 10, no. 4, pp. 5953–5957, aug. 2020, https://doi.org/10.48084/etasr.3678. [13] r. v. sabariego, "the fast multipole method for electromagnetic field computation," ph.d. dissertation, university of vigo, vigo, spain, 2004. [14] r. l. burden, j. d. faires, and a. m. burden, numerical analysis. boston, ma, usa: cengage learning, 2015. microsoft word sifis-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 226-231 226 www.etasr.com bagheri: security analysis of zipper hash against multicollisions attacks security analysis of zipper hash against multicollisions attacks nasour bagheri electrical engineering department, shahid rajee teacher training university (srttu) tehran, iran nbagheri@srttu.edu abstract— in this paper, the existence of multicollisions in zipper hash structure, a new hash structure which was introduced to strengthen the iterated hash structures, is presented. this study shows that finding multicollisions, i.e. 2kway collision, in this hash structure is not much harder than finding such multicollisions in ordinary merkle damgard (md) structure. in fact, the complexity of the attacks is approximately n/2 times harder than what has been found for md structures. then, these large multicollisions are used as a tool to find d-way preimage for this structure. the complexity of finding 2k-way multicollisions and 2k-way preimages are ( )( )/ 2/ 2 1 2no k n× + × and ( )/ 2/ 2 2 2 2n no k n× × + × respectively. similar to what has been proved by joux for md, it is shown in this paper that this structure could not be used to create a hash function with 2n-bit length by concatenating this structure with any other hash structure by hash’s output length of n-bite. it is also shown that time complexity of finding a collision for this concatenated structure is ( )( )2 / 2/ 2 2no n × which is much smaller than what was expected from generic-birthday attack which would be ( )2nω . in addition, it is shown that increasing the number of rounds of this hash function can not improve its security against this attack significantly and the attacker can find multicollisions on this hash function which means that this hash function has a structural flaw. keywordszipper hash structure; hash function; multicollision attack; joux attack; preimage attack; r-way collision i. introduction a. background in a recent paper by joux [1], it was shown that there is a k 2 -way collision attack for the classical iterated hash function based on a compression function, { } { }nnmf 1,01,0: →+ , where the attack has a complexity of ( )2/2nko × . this complexity is much smaller than the complexity for the generalized birthday attack which is ( )2 1 22 k k n o −         [2] this is the basic idea of joux’s attack. the main strategy of joux’s attack is to first find k successive collisions by performing k successive birthday attacks using a collision finder oracle machine c. the attack works as follows: – let 0 h be equal to the initial value iv of h. – for i from 1 to k do: • call c and find i m and i m ′ such that ( ) ( ) iiiiii mmandmhfmhf ′≠′= −− ,, 11 . • let ( ) iii mhfh , 1−= . – pad and output the k 2 messages of the form ( )paddingmmm k ,,...,, 21 (where i m is one of the two blocks of i m or i m ′. clearly, the 2 k different messages built as above all reach the same final value. a schematic representation of these 2 k messages together with their common intermediate hash values is drawn in figure 1. since birthday attack is a probabilistic attack, there is some positive reason that joux’s attack fails. in following proposition, it is shown that an attacker needs more effort to achieve k-way collision than what has been claimed by joux. proposition 1. the complexity of finding 2 k –way collision in joux’s attack is ( )2/1 22 nkko ×× − . proof: assume that probability of each chain in joux’s attack, shown in figure 1, equals toε . hence, the success probability of those messages to lead to collision would be kε . on the other hand, in ordinary 2 k -way collision birthday attack on an ideal hash function, for the success probability of 2 1 , the complexity would be (2 1) 22 k k n o −        [2]. hence, if one aims to compare the joux’s attack to the ordinary birthday attack, he should improve the joux’s attack in order for the success probability to reach 2 1 . to improve the success probability of etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 226-231 227 www.etasr.com bagheri: security analysis of zipper hash against multicollisions attacks joux’s attack the attack may be repeated several times. the success probability for “�” repetition of attack, pr � , could be determined as follows: ( )pr 1 1 2 � k � −= − − where for 1 pr 2 � = the value of n should be 2k-1. recall that the complexity of original joux’s attack is ( )2/2nko × , the total complexity of finding k-way collision following the joux’s attack would be ( )2/1 22 nkko ×× − . proof has been completed. fig. 1. schematic representation of joux multicollision construction. after introducing this attack, many structure have been proposed to strength iterated structure against this type of attach such zipper hash [3], 3c and 3c+ [4,5], sfrh and mfrh[6], wph and dph [7], l-pipe[8], etc. most of these structure have tried to strengthen against multicollision attack. among this new hash structure, in this paper the strength of zipper hash [3] against multicollision attack is investigated. b. related work and contribution in [9] lin et. al have presented a multicollision attack for zipper hash. however, their attack work when the underling compression functions are weak while there is such assumption on compression function and the adversary has oracle access to compression functions. hence, this hash function is analyzed on random oracle model for compression functions and the results are more general in comparison with the results of [9]. in addition, it is shown that even if this structure is repaired, the attacker can find multicollision for this hash function. it means that this hash function is not suitable for general deployment and it has structural flaw. c. paper organization in this paper an attack for this previously believed secure hash structure is presented. for this purpose a brief description of zipper hash function is given in section 2. section 3 contains an explanation of the attack for finding multicollision on this structure, whereas section 4 presents a preimage attack for it. in section 5 it is clarified why zipper hash could not be used as a primitive for 2n-bit concatenated hash function. in section 6 it is shown that even if structure is repaired by employing more functions, the attacker can find multicollision on it, which means that it is not suitable for general deployment. conclusion will be presented in section 7. ii. zipper hash structure the zipper hash structure can be considered as a general hash function construction. to build an n-bit hash function, two independent ( ) bitkm −, compression functions 0 f and 1 f are needed. these functions can be seen as a{ } { }kmk 1,01,0 →+ mapping. same as all hash structures, this one needs a padding function p and an initialization vector iv. for function p(x) for input x, it is guaranteed to return a padded value such that p(x) is a string that can be broken down into m-bit length blocks, and for all ( ) ( )mpmmpmmm ≠≠ '',' . moreover it uses a finalization function { } { }nkg 1,01,0: → . given all these pieces, the zipper hash function works as follows[3]: 1. let l mm ,..., 1 be m-bit strings such that ( )mpmmm l =,..., 1 . 2. 1 h is computed as ( )ivmf , 10 , and l hh ,..., 2 are computed iteratively as ( ) 10 , −= iii hmfh . 3. 1 h′is computed as ( ) ll hxf , 1 , and l hh ′′,..., 2 are computed iteratively as ( ) 111 , −+− ′′=′ iili hmfh . 4. final output ( ) ( ) l hgmh ′= . since existence of g function is not affecting the attack, in the rest of the paper, without losing generality, it is assumed that output length of functions 0 f and 1 f are equal to n therefore these functions can be seen as { } { }nmn 1,01,0 →+ mapping. figure 2 depicts the zipper hash construction. fig. 2. the zipper hash structure. iii. multicollision attack on zipper hash zipper hash structure was developed as a strengthen structure against multicolission attack. in this section, we show that constructing multicollisions in zipper hash function can be done in a efficient way. in particular, constructing k 2 collisions costs 2/nk × times as much as building ordinary 2-collisions and 2/n times as much as building multicollisions in ordinary md structure. if collisions between messages of the same length are considered, the etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 226-231 228 www.etasr.com bagheri: security analysis of zipper hash against multicollisions attacks blocks of padding are identical, the padding process can be ignored and this is the case study in this paper. moreover, if the intermediate hash chaining values collide at some point in the hash computation of two messages, the following values remain equal as soon as the ends of the messages are identical. thus, on messages of the same length, collisions without the padding clearly lead to collisions with the padding. although this attack could be applied for any length of message block and chaining value, for simplicity of proof, it is assumed that the size of the message blocks is bigger than the size of the chaining values. however, the attack can be easily generalized. it is also assumed that one can access two collision finding machines c and 'c . c is a machine that, given as input a chaining value h , outputs two different blocks m and 'm such that ( ) ( )',, 00 mhfmhf = and 'c is such a one that given 2/ 2 n different messages of length 2n blocks and h as chining value, finds the multiblocks ψ and 'ψ among them such that ( ) ( )',, 11 ψ′=ψ′ hfhf where ( )ψ′, 1 hf is ordinary compressed value of ψ by applying 1 f as compress function and h’ as initial value where illustrated in figure 3. these collision finding machines may use the generic birthday attack or any specific attack based on a weakness of 0 f and 1 f multicollision attack on ordinary md. the most relevant property is that c and 'c should work properly for all chaining values. it’s clear that most of these assumed conditions for the scenario investigated in this paper is similar to what considered in [1]. ( ) 2/122/12/ ... njjnjnj mmm +++=ψ ( ) ( )jjnnj hfh ψ′=′ + ,2/2/1 fig. 3. the ( ) jj hf ψ′, 1 function structure. we now claim that we can generate k 2 equal collisions by only ( )/ 2o k n× calls to the c oracle machine and ( )ko calls to c′ oracle machine which is much less than what we expected from birthday paradox ( ) ( )( )( )kkno 2122/2 −× . assuming that, l is the number of message blocks and is equal to 12 +× nk , the attack works as follows: 1 let 0 h be equal to the initial value iv of zipper hash. 2 for i from 1 to 2nk × do: a. call c and find i m and i m ′ in such a way that ( ) ( ) iiii mhfmhf ′= −− ,, 1010 . b. set ( ) iii mhfh , 10 −= . 3 since 12/ +×nkm is the padded message block determine ( ) 12/2/012/ , +××+× = nknknk mhfh and ( ) 12/12/11 , +×+×=′ nknk mhfh 4 for j from 1 to k do: a. call 'c to find jψ and 'jψ among 2/ 2 n different messages of 2n blocks length and ( ) ( ) 112/ +−×′ jnh in such a way that ( ) ( )( ) ( ) ( )( )jjnjjn hfhf ψ′′=ψ′ +−×+−× ,, 112/1112/1 . 5 output the k 2 messages of form ( )1 / 2 1,..., ,k knmψ ψ + where j ψ will be one of the two multi blocks j ψ or ' j ψ . obviously, all k 2 different messages generated in this way result to the same value of hash. the third step of this algorithm finds ( )2/ 2 nk× different multicollisions for the forward part of the zipper hash which uses 0 f as the compress function and the fourth step finds k 2 different multicollisions for the reverse part of the zipper hash which uses 1 f as the compress function. the time complexity of the attack is equal to all attempts done by the adversary. it is equal to ( ) 2/22 nnk ×× for finding a 2-way collision in the forward path of the attack and 2/ 2 n k × for finding a 2-way collision in the reverse path. figure 4 is a schematic illustration of these k 2 multiblocks messages together with their common intermediate hash values. 1ψ 1ψ′ 2ψ 2ψ′ k ψ k ψ′ fig. 4. schematic representation of multicollision attack on zipper hash structure. iv. finding k-way second-preimage attack on zipper hash in reference [1] joux puts forward the attack method called k-way which is applicable for finding the second preimage of an output of a hash function based on the md structure. for a given hash target value ( ) { }0,1 k y h m= ∈ , at first the attackers find 2 r collisions on r-block messages 1 2 2 , ,..., rm m m making ( ) ( ) ( )1 2 2... rrh h m h m h m= = = = . then, to find the block 1r m + such that ( )1,r rf h m y+ = . in this way, the attackers succeed in finding 2 r second preimages with the message m. obviously, the time complexity of this attack is ( )/ 22 2n no r + . etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 226-231 229 www.etasr.com bagheri: security analysis of zipper hash against multicollisions attacks for the hash function based on the zipper hash structure, we show that theadversary can find 2 r -way preimage and second preimage with cost of ( ) ( )( )/ 21 / 2 2 2 2n no r n+ × + × . for this purpose, as mentioned in [3], it is assumed that g function is a identical function. the attack works as follows: 1. fixed 1 h with some random value. 2. for i from 2 to 12 +×= nrl do: a. call c and find i m and i m ′ in such a way that ( ) ( ) iiii mhfmhf ′= −− ,, 1010 . b. set ( ) iii mhfh , 10 −= 3. since 12/ +×nkm is the padded message block determine ( ) 22/12/022/ , +×+×+× = nrnrnr mhfh and ( ) 22/22/11 , +×+×=′ nknk mhfh 4. for j from 1 to k do: a. call 'c to find jψ and 'jψ among 2/ 2 n different messages of length 2n blocks and ( ) ( ) 112/ +−×′ jnh in such a way that ( ) ( )( ) ( ) ( )( )jjnjjn hfhf ψ′′=ψ′ +−×+−× ,, 112/1112/1 . 5. find 1 m in such a way that ( )( ) 112/1 , mhfgy nr +× ′= . 6. find iv in such a way that ( ) 101 , mivfh = . obviously, all k 2 different messages generated in this way lead to value y as a hash result. this procedure can be divided in two parts. fist part of the attack is finding the r 2 -way collision whose cost is ( ) 2/22 nnr ×× and the second part, described in steps 5 and 6, is related to finding two preimages to guarantee the successes of the attack with cost n 22× . hence, the total complexity of the attack equals to the claimed value. by applying a similar procedure, the adversary can find a r 2 -way second preimage with identical cost of time complexity which is far from ideal value nr 22 × . clearly this kind of attack can not be used for the original version of zipper hash structure which use prefixed iv value, but it shows that this structure is far from ideal structure. v. zipper hash in 2n-bit concatenated structure a natural construction to build large hash values is to concatenate several smaller hashes. for example, given two hash functions f and g, it seems reasonable given a message m to form the large hash value ( ) ( )( )f m g m . in this construction, f and g can either be two completely different hash functions or two slightly different instances of the same hash function. in [1] joux has shown that if at least one of these hash function is a md iterated hash function, the complexity of finding a collision for this structure is slightly more than finding collision for one branch and it is equal to ( )/ 2/ 2 2no n × . the basic idea in this attack is to find a / 22 n -way collision for md structure and find a collision among this / 22 n different messages for the second hash function. clearly this collision is applicable to booth branches. a similar attack can be applied to find a collision on the “2n-bit” hash construction ( ) ( )( )f m g m when one replaces either f or g, namely f, by the zipper hash structure. the attack complexity includes the complexity of finding / 22 n -way collision on zipper hash which is ( ) ( )( )/ 2/ 2 / 2 2no n n× × plus the complexity of finding a collision on g which is ( )/ 22no . hence, the total complexity would be ( ) ( )( )/ 2/ 2 1 / 2 2no n n+ × × .” vi. increasing the rounds of the zipper hash assume that someone tries to protect the zipper hash by adding another layer to this structure. figure 5 has illustrated this modified version of zipper hash. in general it is assumed that 2 0 f f≠ and 2 1 f f≠ . the following theorem shows that this structure is vulnerable to multicollision attack. to finding multicollision in this new structure we introduce an new oracle machine c′′ which is such a one that given 2/ 2 n different messages of length ( ) 2 2 n blocks, i.e. / 2 2 n messages of form ( )1 2 ,..., n ψ ψ where j ψ will be one of the two multi blocks j ψ or j ′ψ , and h′ as the chining value, to find the multiblock ϒ and ′ϒ among them such that ( ) ( )2 2, ,f h f h′ ′ ′ϒ = ϒ where ( )2 ,f h′ ϒ is ordinary compressed value of ϒ by applying 2 f as compress function and h′ as initial value. these collision finding machines may use the generic birthday attack or any specific attack based on a weakness of 2 f . the most relevant property is that c′′ should work properly for nay chaining values. fig. 5. schematic representation of multicollision attack on zipper hash structure. etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 226-231 230 www.etasr.com bagheri: security analysis of zipper hash against multicollisions attacks we now claim that we can generate 2 k equal collision by only ( )( )2/ 2o k n× calls to the c oracle machine, and ( )2no k × calls to c′ oracle machine and ( )o k calls to c′ oracle machine which is much less than what we expected from birthday paradox ( ) ( )( )( )kkno 2122/2 −× . assuming that, l is the number of message blocks and is equal to 12 +× nk , the attack works as follows: 1 let 0 h be equal to the initial value iv of zipper hash. 2 for i from 1 to ( ) 2 2k n× do: a. call c and find i m and i m ′ in such a way ( ) ( )0 1 0 1, ,i i i if h m f h m− − ′= . b. set ( )0 1,i i ih f h m−= . 3 since 12/ +×nkm is padded block fined ( )/ 2 1 0 / 2 / 2 1,k n k n k nh f h m× + × × += and ( )1 1 / 2 1 / 2 1,k n k nh f h m× + × +′ = 4 for j from 1 to 2 nk × do: a. call 'c to find jψ and 'jψ among 2/ 2 n different messages of 2n blocks length and ( ) ( ) 112/ +−×′ jnh in such a way ( ) ( )( ) ( ) ( )( )1 1/ 2 1 1 / 2 1 1, ,j jn j n jf h f h× − + × − +′ ′ ′ψ = ψ . 5 for l from 1 to 2 nk × do: a. call c′′ to find j ϒ and j ′ϒ among 2/ 2 n different messages of ( ) 2 2n blocks length and ( ) ( ) 112/ +−×′ jnh in such a way ( ) ( )( ) ( ) ( )( )1 1/ 2 1 1 / 2 1 1, ,j jn j n jf h f h× − + × − +′ ′ ′ϒ = ϒ 6 output the k 2 messages of form ( )1,..., kγ γ where jγ will be one of the two multiblocks j γ or j γ ′ . obviously, all k 2 different messages generated in this way result to the same value of hash. the third step of this algorithm finds ( ) ( ) / 2 / 2 2 2 k n n× × different multicollisions for the first round of the zipper hash which uses 0 f as a compress function, the fourth step finds ( ) / 2 2 k n× different multicollisions for the second round of the zipper hash which uses 1 f as a compress function and the fifth step finds 2 k different multicollisions for the third round of the zipper hash which uses 2 f as a compress function. the time complexity of the attack is equal to all attempts done by the adversary. it is equal to ( ) 2 / 2 2 2 n k n× × for finding 2-way collision in the first round of attack, ( ) / 22 2nk n× × for finding 2-way collision in the second round and / 22nk × for finding 2-way collision in the third round. this approach can be easily extended to zipper hash with extra rounds. in similar way, it can be shown that the complexity of finding 2 k -way collision in zipper hash with i round is ( )( )/ 2/ 2 2i no k n . this approach can be easily extended to zipper hash with extra rounds. following the given algorithms to find 2 k -way collision on the zipper hash with two and three rounds that have the complexities of ( )( )/ 2/ 2 2no k n and ( )( )/ 2/ 2 2i no k n respectively, it can be shown that the complexity of finding 2 k -way collision in zipper hash extended to “i” rounds would be ( )( )1 / 2/ 2 2i no k n − . whenever this complexity reaches the birthday bound to find a 2 k -way collision on an ideal hash function, ( ) ( )( )2 1 2 2 k k n o × −      , the extended zipper hash would be strengthen to the multicollision attack. to determine a bound for “i” we do as follows: ( ) ( )( ) ( ) ( ) 2 1 21 1/ 2 / 2 1 / 2 2 / 2 / 2 2 2 / 2 2 2 / 2 2 / 2 log 1 k k ni in n n i n n k n k n n i n × −− − − ≥ ⇒ ≥ ⇒ ≥ ⇒ ≥ × + this means that, in oracle model of compression function, the extended zipper hash to “i” rounds, for 2 / 2 / 2 log 1 n i n≥ × + , is not vulnerable to the multicollision attack. vii. conclusion in this paper, it is shown that multicollisions in zipper hash structure are not much harder to find than finding multicollisions in the md one. it is also shown that finding 2 r way preimages and second preimages on this structure are not really harder to find than ordinary preimages and second preimages. another important result is the fact that zipper hash structure can not be used as a building block for creating 2n-bit concatenated hash structure because of its strength against collision which is much less than the ideal one. the study shows that although this structure is slightly more secure than iterated hash function, it is really far from an ideal hash function. it is shown that modifying the zipper hash by an extra round can not make it resistant to this attack. finally, it is shown that in oracle model of compression function, the extended zipper hash to “i” rounds, for 2 / 2 / 2 log 1 n i n≥ × + , is not vulnerable to the multicollision attack reference [1] a. joux, “multicollisions in iterated hash functions. application to cascaded constructions”, advances in cryptology-crypto ’04, springer-verlag, pp. 306–316, 2004 [2] m. nandi, d. r. stinson, “multicollision attacks on some generalized sequential hash functions”, ieee transactions on information theory, vol. 53, no. 2, pp. 759-767, 2007 [3] m. liskov, “constructing an ideal hash function from weak ideal compression functions”, 13th international conference on selected areas in cryptography, pp. 358-375, 2007 [4] p. gauravaram, w. millan, e. dawson, k. viswanathan, ”constructing secure hash functions by enhancing merkle-damgard construction”, lecture notes in computer science, vol. 4058, pp. 407–420, 2006. [5] p. gauravaram, w. millan, e. dawson, k. viswanathan, ”constructing secure hash functions by enhancing merkle-damga°rd construction etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 226-231 231 www.etasr.com bagheri: security analysis of zipper hash against multicollisions attacks (extended version). ” information security institute (isi), queensland university of technology (qut), number qut-isi-tr-2006-013, http://www.isi.qut.edu.au/ research/ publications/technical/qut-isi-tr2006-013.pdf, july 2006. [6] s. su, y. yang, b. yang, s. zhang ,”the design and analysis of a hash ring-iterative structure”, available: http://eprint.iacr.org/2006/384.pdf [7] s. lucks, “a failure-friendly design principle for hash functions”, advances in cryptology asiacrypt 2005, 11th international conference on the theory and application of cryptology and information security, chennai, india, 2005 [8] w. r. speirs, j. molly, ”making large hash functions from small compression function”, available:http://eprint.iacr.org/2007/239.ps. [9] p. lin, w. wu, c. wu1, t. qiu, "analysis of zipper as a hash function”, lecture notes in computer science, vol. 4991, pp. 392-403, 2008 engineering, technology & applied science research vol. 7, no. 6, 2017, 2113-2117 2113 www.etasr.com shahgholian et al. : impact of pss and statcom devices to the dynamic performance of a ... impact of pss and statcom devices to the dynamic performance of a multi-machine power system ghazanfar shahgholian department of electrical engineering, najafabad branch islamic azad university najafabad, isfahan, iran esmaeil mardani smart microgrid research center najafabad branch islamic azad university najafabad, isfahan, iran arman fattollahi smart microgrid research center najafabad branch islamic azad university najafabad, isfahan, iran abstract—this paper studies the impact of leveraging both static synchronous compensator (statcom) and power system stabilizer (pss) on multi-machine power systems. considering a standard ieee 9-bus test power network, classic and intelligent controllers are applied to achieve the desirable system performance. simulated tests show the usefulness of statcom on network power quality in terms of voltage profile. in addition, it is shown that it can significantly improve the damping oscillations of synchronous generator under normal and abnormal network conditions. as shown, the pss also contributes to improving the synchronous generator parameters. it is also observed that using intelligent controllers with statcom and pss leads to a better performance relative to the classic controllers. keywords-power quality; intelligent controller; pss; statcom; neuro; fuzzy; anfis i. introduction the mission of network managers, manufacturers and distributors of electrical energy, is to deliver the highest possible quality of electrical power and ensure maximum reliability [1, 2]. in order to achieve such goals, comprehensive information and studies of the power network are required. in normal working conditions, various parameters are important. these include the bus voltage level, the loss of active network, freeing capacity increase of network load, etc. [3, 4]. in critical situations such as sudden withdrawal of large loads, symmetrical and asymmetrical short circuit faults, etc., the situation is more complex. at first, network instability (increase in power angle and the frequency oscillation amplitude) must be prevented and parameters such as voltage fluctuations, the frequency and power angle have to be gradually returned to the desired level [5, 6]. figure 1 shows different techniques to damp power oscillation. generally, facts controllers can be divided into four major groups as shown in figure 2: series controllers such as tcsc and sssc, shunt controllers such as svc, statcom and statcom with energy-storage system, combined series-shunt controllers such as upfc and tcps, and combined series-series controllers such as ipfc [7-16]. in power production and transmission, facts devices are considered highly important and have been studied in several researches [8, 9]. to reduce active power losses and to raise the voltage, the placement of reactive power injection [10, 11] and facts devices controller [12, 13], has been considered. fig. 1. strategies to damp power oscillations parallel facts devices such as statcom and svc [14, 15] have been considered for the supply of reactive power, intense voltage drop compensation and sustained improvement in severe transients whereas facts devices such as tcsc and sssc series have been considered for dynamic stability improvements [16, 17]. however, the high costs of construction and installation of facts devices is always to be considered. the power system stabilizer (pss) element is undeniable and very effective [18, 19]. this equipment is used in production units with synchronous generators, and a significant portion of the risks to the network is eliminated or significantly reduced. in this context, there have been many studies on the impact of pss on power oscillation damping and frequency [20, 21]. this equipment as well as other power network controllable equipment has been implemented with various classic and nonlinear controllers [22, 23]. in this paper, the 9-bus and 3-mashine power system is considered as a test network. statcom and pss devices are considered in several positions under normal and abnormal conditions (a three-phase short circuit fault that caused voltage drop, frequency swinging and power angle swinging in engineering, technology & applied science research vol. 7, no. 6, 2017, 2113-2117 2114 www.etasr.com shahgholian et al. : impact of pss and statcom devices to the dynamic performance of a ... generating units). a classic pi controller and a neuro-fuzzy controller optimized by anfis are employed to control the equipment in each of the above scenarios. simulations are performed in matlab and results are shown and discussed for each scenario. fig. 2. classification of facts devices ii. system under study the ieee 9-bus standard system consists of 3 synchronous machines with ieee type-1 exciters as shown in figure 3. there are 12 buses, 6 transformers and 3 constant impedance loads. it contains 6 lines connecting the bus bars in the system with the generator connected to network through step-up transformer at 230kv transmission voltage. the total load demand is 315 mw and 115 mvar. for this power system generator, lines and load parameters are given in [24]. fig. 3. system under study iii. simulation results a. normal conditions the network is simulated based on the results of load flow analysis. the results of the network simulation in the initial state (without statcom and pss) are given in figures 4 and 5. as shown in figure 4, bus 5 voltage is lower than all buses voltage, so the statcom is placed at bus 5. fig. 4. voltage buses in the initial state (without pss and statcom) fig. 5. angular velocity of generators 2 and 3 according to time (without pss and statcom and the controller) b. statcom placement in bus 5 in this section the pi controller is used, to control the statcom device in order to achieve the desired voltage (1.02 pu) at bus 5, and the optimal ratio controller (kp=92.2 and ki=9.1) are obtained using a ga. results of are shown in figures 6 and 7. with the presence of statcom at bus 5, in addition to the voltage on the bus already reaching to 1.02pu, the rest of the buses voltage (except pv generator buses) are in a better mode than before. also, improvement in angular velocity damping is achieved. fig. 6. voltage buses in the bus 5 with statcom. fig. 7. angular velocity of generators 2 and 3 with statcom (without controller). engineering, technology & applied science research vol. 7, no. 6, 2017, 2113-2117 2115 www.etasr.com shahgholian et al. : impact of pss and statcom devices to the dynamic performance of a ... c. placing pss now pss are added to generators 2 and 3. the results of the simulation are presented in figures 8 and 9. with the presence of pss no change in network voltage profile is found. so the pss in normal working condition has no effect on the parameters of the network such as voltage and therefore can’t reduce network losses, and improve the lines capacity release. but, in the presence of pss, rotor angular velocity fluctuations are reduced and damped with a better speed. in the case of a statcom connected to bus 5, rotor angular velocity damping in terms of time is improved. the pss has better effect in this regard than the statcom. fig. 8. the voltage buses with the presence of pss fig. 9. the angular velocity of generators 2 and 3 according to time. d. case of circuit fault without statcom or pss in this case, the network is simulated under a three-phase short circuit fault of 200ms (10 cycles, 50 hz frequency) on the line between buses 5 and 7 (closer to bus 5). the results of this simulation without the presence of statcom and pss are shown in figures 10 and 11. when the fault occurs all buses experience a sharp drop and voltage did not recover after fault clearance. the 5 and 7 bus voltage, dropped more than other buses. it can be seen that the angular velocity fluctuations of the synchronous generators at the time of fault increased and after it was fixed, the time was spent for the damping of oscillations. e. placing statcom the statcom is placed on bus 5. the controller is again the pi controller, with coefficients optimized by ga. the results of the simulation of statcom on bus 5, in the presence of a short circuit fault are shown in figures 22 and 33. because of the presence of statcom at bus 5 and the reactive power injection to the network, all buses voltage consist of less drop and buses are shown to have the ability to restore the voltage. in figure 13 we observe that with the presence of statcom, not only fluctuations in angular velocity generator have been dramatically reduced, but also the damping of fluctuations happened sooner. fig. 10. the buses voltage in the presence of three-phase short circuit fault according to time (without pss and statcom). fig. 11. rotor angular velocity of generator (2) and (3) in the presence of three-phase short circuit fault according to time (without pss and statcom). f. placing pss next, instead of placing statcom in bus 5, according to different controllers (pd optimization and fuzzy control) [25], we will place pss in generators 2 and 3 and compare the results. these results were compared in figures 14-16. as shown in figure 14, with the presence of pss, the buses voltage during and after the error has not changed much and voltages in addition to a sharp drop in the voltage level during the fault, did not reach an acceptable level. in figure 15 we observe that in the presence of optimized classic controllers, the impact of statcom in damping of oscillations in the angular velocity of the synchronous generators have been better than pss. the results in figure 16 show that with the presence of the intelligent controller, pss performs better than statcom in terms of damping the frequency oscillations. iv. conclusion in this paper, the impact of statcom and pss in power quality is studied. the 9 bus-ieee standard network was chosen as the test network and normal operation and operation during a fault scenarios were simulated in matlab. engineering, technology & applied science research vol. 7, no. 6, 2017, 2113-2117 2116 www.etasr.com shahgholian et al. : impact of pss and statcom devices to the dynamic performance of a ... fig. 12. the buses voltage in the presence of three-phase short circuit fault according to time (with statcom). fig. 13. rotor angular velocity of generator (2) and(3) in the presence of three-phase short circuit fault according to time (with statcom). fig. 14. the buses voltage in the presence of three-phase short circuit fault according to time (based on optimized pd controller for pss). fig. 15. rotor angular velocity of generator (2) and (3) 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301–307, 2013 engineering, technology & applied science research vol. 7, no. 6, 2017, 2194-2199 2194 www.etasr.com ghaffari et al.: assessing market development and innovation project management factors using … assessing market development and innovation project management factors using the picea-g hybrid evolutionary multi-criteria decision technique the calcimine company case study saeed ghaffari department of industrial engineering payam-e-noor university tehran, iran saeed.ghaffari68@gmail.com amir najafi department of industrial engineering zanjan branch islamic azad university zanjan, iran asdnjf@gmail.com meisam jafari eskandari department of industrial engineering payam-e-noor university tehran, iran meisam_jafari@pnu.ac.ir abstract—project management includes the consideration of complex decision modes used in modern decision support techniques. the aim of this paper was to prioritize such factors and evaluate their effects on project management and optimal control. their effect on management and optimal project control are evaluated in frame of a statistical hypothesis. a new algorithm, "ipicea-g" is proposed for the assessment. a questionnaire is used for data collection distributed between 56 employees of the calcimine company. t-test, two-sentence test, anp method, fuzzy seamatel and the ipicea-g hybrid algorithm, are employed for data analyzing. results are further discussed and conclusions are drawn. keywords-management; control; projects; hybrid; algorithm; ipicea-g; deamatel; fuzzy; anp; marketing; development i. introduction project management uses two main strong arms: project planning and project control and it is widely accepted as an area of interdisciplinary nature. the central core of all project management activities is project control which is the main factor for distinguishing it from other areas of management [1]. a set of conditions and limitations are employed to make use of management knowledge in the field of project management while avoiding the creation of additional concepts or a new body of knowledge which would have little difference from their original version. the interference trend of project management can be investigated in three zones: production of project management knowledge, solutions for enterprise resource planning and mobility of human resources [2]. the current paper investigates management elements for an optimal implementation in the case of calcimine company with the purpose of identifying and assessing such factors. authors in [3] investigated the affecting factors in delays of development projects. authors in [4] studied the affecting factors on the success of knowledge management projects. authors in [5] provided a model of such factors in the construction industry and explained the relationship between them. author in [6] discussed the dynamic modeling of projects execution time and explored influencing factors on the delay through a system dynamics approach in both micro and macro levels. in [7], the harmonization of knowledge and project management was studied. a model in which the success of change initiatives is explained by the quality of project management, which in turn is determined by the quality of the knowledge integration, was presented. in [8] the viewpoints of shareholders about cost estimates in project management are discussed. the aim of this study was to identify key issues and provide a conceptual model. in [9], the issue of comprehensive systematic thinking in the innovative project management was investigated. authors in [10] examined the integration of project management office role in the forefront of innovation. the effect of communications management on construction project performance was investigated in [11]. authors in [12] investigated the project risk management approach in small companies. in [13], authors provided a new method for controlling projects under uncertainty with regard to returning to first principles. authors in [14] employed framework analysis to evaluate the success of the knowledge-based project approach. ii. research methodology the method of study is descriptive and in terms of achieving results is focused on the explorations. information is collected through questionnaires sent to experts and engineers of the calcimine company local market and project engineering, technology & applied science research vol. 7, no. 6, 2017, 2194-2199 2195 www.etasr.com ghaffari et al.: assessing market development and innovation project management factors using … characteristics were considered for the selection of factor for the conceptual model (figure 1). fig. 1. the conceptual model two questionnaires were sent to each of the 56 managers of the calcimine company selected to participate in this study. of these, 11 were senior managers and 45 r & d project managers. the first questionnaire follows a five-item likert method that includes 11 questions in terms of organizational criteria, 12 questions in relation to performance criteria, 14 questions regarding personal standards and 8 questions regarding personal–group criteria. the second questionnaire contained 7 questions regarding organizational criteria, 10 questions in relation to performance metrics, 9 questions in relation to individual criteria, and 6 questions in relation to the criteria of the individualgroups and was designed considering the results from the first questionnaire. in terms of reliability and validity the cranach’s alpha coefficient of the questionnaire is shown in table i. to study and analyze questionnaire answers the t-test and binomial test were employed. then through a combination of anp and fuzzy methods the weights of the objective functions were determined and finally through the implementation of the ipicea-g hybrid algorithm, the prioritization of factors was achieved. spss and matlab were the software used for the analysis. table i. the reliability scale of affecting factors on project management row subscale cranach’s alpha coefficients 1 organizational 0.82 2 functional 0.79 3 individual 0.77 iii. computational results a. descriptive statistical results 19.6% of the cases were female and 80.4% were male, 25% were under 30, 41.1% were from 30 to 35 years old, 10.7% from 36 to 40, 8.9% were from 41 to 45 and 14.3% from 46 and over. 32.1% owned a bachelor degree or less, 50% a master's and 17,9% owned a phd. as for the work experience 35.7% of people had work experience of 5 years and less, 23.2% 6 to 10 years, 25% 11 to 15 years, and 16.1% of them had work experience longer than 16 years. b. results of criteria and indicators monitoring and evaluation 0 1 : 0.5 : 0.5 h p h p        the proportion of people who agree with the standard x, less than the average. the proportion of people who agree with the standard x, more than the average. : : h h    0 1 according to the binomial test, the most important affecting factors on project management and optimal control are shown in table ii. according to the binomial test, the main criteria for the effective functioning on the management and optimization control of project are shown in table iii. according to the binomial test, the most affecting individual measures on the management and optimization control of project are shown in table iv and the most important affecting individual group measures on the management and optimization control of project are shown in table v. table ii. organizational affecting factors on project management and optimal control id knowledge competence c1 understanding of project characteristics c2 understanding of the assessment process and the feasibility of the project c3 understanding of project structures c4 understanding the topic of project resources c5 understanding the concept of project time c6 understanding the budget issues and project costs c7 understanding the topic of project resources table iii. performance criteria for effective management and optimal control of project id functional competencies c8 project documentation c9 determining the project scope, registration and approval c10 choosing project structures c11 resource planning, registration and approval c12 select of qualified contractors and vendors c13 estimating project costs c14 directing, managing of registration process and executing contracts c15 investigate, identify and implementation of necessary changes in project c16 coordination between different units and issuing guidelines which related to projects c17 funding, resources and equipment needed to start the project table iv. affecting individual measures on the management and optimization control of project id behavioral competencies c18 hard work c19 the spirit of achievement c20 initiative and innovation c21 self confidence c22 result oriented c23 being regulated c24 having strategic perspectives c25 spirit of competition c26 having systematic approaches engineering, technology & applied science research vol. 7, no. 6, 2017, 2194-2199 2196 www.etasr.com ghaffari et al.: assessing market development and innovation project management factors using … table v. affecting individual group measures on the management and optimization control of project id behavioral competencies c27 sociability c28 having the leadership and guidance behavior of the project team c29 influence and impact on group projects c30 spirit of unity and empathy c31 motivate of project individuals c32 communication and fair treatment with employees, customers and stakeholders c. results the initial monitoring criteria were 45 which were later narrowed down to 32. the results of distribution variables in kolmogorov-smirnov test are shown in table vi. as shown, the assumption of normality for all variables is confirmed. therefore, t-test can be used to test the hypothesis and the results are shown in table vii. results show that individual factors, individual-group factors, performance factors, organizational factors are found to be effective. table vi. results of kolmogorov-smirnov test variable frequency avera ge sd statistic of z level of signific ance organizational factors 56 3.02 0.506 0.954 0.322 performance factors 56 3.14 0.56 1.19 0.09 individual factors 56 3.49 0.454 1.47 0.11 individualgroup factors 56 3.63 0.38 1.34 0.52 table vii. results of hypotheses testing ci number of items degrees of freedom signifi cance quantity of t sd avera ge large scale and subscale upper line low line 3.507 3.170 9 55 0.000 39.748 0.628 3.339 individual 3.464 3.137 6 55 0.000 40.498 0.610 3.301 individualgroup 3.512 3.326 10 55 0.000 47.259 0.533 3.369 performance 3.529 3.164 7 55 0.000 36.663 0.683 3.346 organizational d. hybrid meta-heuristic ipicea-g method results the ipicea-g hybrid meta-heuristic method is a multiobjective optimization algorithm based on non-dominated relationships and the brushing technique. to implement this algorithm, we need multiple objective functions and the algorithm searches the objective answers to achieve optimal solution space. if factors are defined as x1, x2, x3 and x4 we define objective functions as follows: max z1 = w1x1 max z2 = w2x2 max z3 = w3x3 maxz4 = w4x4 where, w1, w2, w3 and w4 are the weights or importance of individual, individual-group, performance and organizational. the objective is to determine the values of x1, x2, x3 and x4, in a range from 0 to 1. the values of x1, x2, x3 and x4 represent the final rank of the factors obtained by the proposed algorithm. to solve the functions with the proposed algorithm, the initial weights w1, w2, w3 and w4 were determined by combining fuzzy anp-deamatel and ipicea-g. 1) the hybrid fuzzy anp-deamatel approach performance evaluation steps are described below. a) formation of decision network the network consisted of 3 levels that are used because of computing limited super matrixes and rate of incompatibility. b) implementation of dematel fuzzy method results are shown in table viii. language assessments are changed to corresponding triangular fuzzy numbers and converted to absolute numbers through cfcs (converting fuzzy data into crisp scores) and (1) to (9). the primary direct matrix is normalized by (10) and the overall relationship matrix t is calculated by (11). afterwards, the matrix t, is placed in super matrixes as matrix w22. table viii. linguistic variables and corresponding fuzzy numbers linguistic variable final equivalent fuzzy equivalent (a) fuzzy equivalent (b) very low 0 (0, 0.1,0.3) (0, 0, 0.25) little 1 (0.1, 0.3, 0.5) (0, 0.25, 0.5) average 2 (0.3, 0.5, 0.7) (0.25, 0.5, 0.75) very 3 (0.5, 0.7, 0.9) (0.5, 0.75, 1) very much 4 (0.7, 0.9, 1) (0.75, 1, 1) 1 max min min k k ij k k ijl ij l l xl      (1) 1 max min min k k ij k k ijk ij m l xm      (2) 1 max min mink kij k k ijk ij r l xr      (3) engineering, technology & applied science research vol. 7, no. 6, 2017, 2194-2199 2197 www.etasr.com ghaffari et al.: assessing market development and innovation project management factors using … max min max min k k ij ijr l  (4) 1 k ijk ij k k ij ij xm xls xm xl    (5) 1 k ijk ij k k ij ij xr xls xr xm    (6) (1 ) 1 k k k k k ij ij ij ij ijk ij k k ij ij xls xls xrs xrs xrs x xrs xls       (7) 11 k k k ij ij k a bnp k     (8) max minmin k k k ij ij ijbnp l x   (9) x s a  (10a) 1 1 1 1 min , max \ \ max \ \ n n i ij j ijj j s a a            (10b) to obtain matrix t, the following formula is used: t=x+x2+…+xk=x(i+x+x2+…+xk-1)(1-x)(1-x)-1 =x(1-xk)(1-x)-1 (11a) if limk→∞xk=[0]nxn, the overall relationship matrix is obtained by the following equation t=x(1-x)-1 (11b) c) fuzzy anp process and its combination with fuzzy deamatel the data collection phase is based on paired comparison questionnaire. for example, a combination of expert opinions for paired comparison of finance criteria perspective is calculated and recorded by using (12). then, by using the cfcs method, defuzzification was performed and by using (13) the weight of secondary criteria is obtained (incompatibility rate at this point is zero). for the other main criteria, there are similar calculations and the weights of these comparisons are recorded in a column titled local weight of minor factors. the weights as matrix w32 are in the initial super matrix. the main factors will pair. thus, the initial matrix will form with calculation of w11, w22 and w23. 0 j ij i n c t     (12) 0 i ij j n r t     (13) d) prioritization of key factors and sub-factors and identify of cause-effect factors to perform the required analysis, prioritization of factors is based on limited weights of super matrix. at the specific table the weight and prioritization of factors are recorded. to identify the causal factors, ri, cj, ri-cj are calculated by using (12) and (13) and their values are recorded. the first step is the formation of decision network and in next stage we described deamatel fuzzy technique for the forming of overall relationship matrix. the deamatel fuzzy relationship matrix obtained by the method is shown in table ix. as can be seen in table ix, individual and individual–group dimensions are the reasons and organizational and performance factors are the effects. as mentioned, this matrix w22 is used in initial super matrix of fuzzy anp method. to the formation of the super matrix we need to form the w32 and w11 matrixes. the w32 matrix was obtained from the comparison of secondary factors. after cfcs defuzzification, the weight for each factor group is calculated with (13). tables x-xiii show the calculated weight of sub-factors. the weight of calculated factors in tables x and xiii is used to form the initial matrix w32. after preparing the matrices w22, w32 and w11, the super initial matrix is prepared and then the limited super matrix is formed. the weight of factors and their prioritization is shown in table xiv. to identify causal relationships, ri, cj, ri-cj are calculated and the results are shown in the table xv. table ix. the overall relationship matrix (output of dematel fuzzy) individual individualgroup perfor mance organiza tional ri individual 0.0742 0.475 0.565 0.297 1.411 individualgroup 0.842 0.803 0.955 0.838 3.438 performance 0.142 0.384 0.088 0.082 0.695 organizational 0.172 0.332 0.379 0.936 1.818 cj 1.230 1.993 19999 .997 2.153 ri-cj 0.181 1.445 1.338 0.335 type of factor reason reason effect effect table x. weight of the individual sub-indices index name weight hard work 0.222 the spirit of achievement 0.0401 initiative and innovation 0.210 self confidence 0.0506 result oriented 0.177 being regulated 0.114 having strategic perspectives 0.087 spirit of competition 0.008 having systematic approaches 0.0913 table xi. weight of individual sub-groups indicators index name weight sociability 0.103 having the leadership and guidance behavior of the project team 0.223 influence and impact on group projects 0.303 spirit of unity and empathy 0.0809 motivate of project individuals 0.109 communication and fair treatment with employees, customers and stakeholders 0.1811 engineering, technology & applied science research vol. 7, no. 6, 2017, 2194-2199 2198 www.etasr.com ghaffari et al.: assessing market development and innovation project management factors using … 2) the final results of ipicea-g the ipicea-g algorithm determines the optimal values of x1, x2, x3 and x4 ensuring they are less than 1. to implement the algorithm in this study, a structure for the presentation of the answers with an one-dimensional matrix and a row with 4 cells was used. the values of this matrix represent the values of model variables and they are between 0 and 1. the basic steps of the algorithm are as follows:  first a certain number of answers are produced as the first generation.  secondly, with the use of non-dominated solutions they are arranged and ranked.  third, using the combination operator, the solutions are combined and produce new solutions.  in the fourth step, solutions are leveled and according to the number of population size, we select nextgeneration solutions.  in the fifth step, the solutions identified to optimize border and then the algorithm returns to the second step. it should be noted that the above actions are repeated until the maximum number of iterations of the algorithm is reached. a single-point crossover operator is also employed. the ipicea-g algorithm took 500 iterations and after its implementation, 75 responses were reported as optimal solutions. mean values were calculated as the final weights factors shown in table xvi table xii. weight of the sub-indices of operating performance index name weight project documentation 0.0701 determining the project scope, registration and approval 0.0225 choosing project structures 0.173 resource planning, registration and approval 0.121 select of qualified contractors and vendors 0.0205 estimating project costs 0.193 directing, managing of registration process and executing contracts 0.0419 investigate, identify and implementation of necessary changes in project 0.112 coordination between different units and issuing guidelines which related to projects 0.1675 funding, resources and equipment needed to start the project 0.0785 table xiii. weight of the sub-indices of organizational factors index name weight understanding of project characteristics 0.223 understanding of the assessment process and the feasibility of the project 0.0998 understanding of project structures 0.104 understanding the topic of project resources 0.0752 understanding the concept of project time 0.298 understanding the budget issues and project costs 0.109 understanding the topic of project resources 0.091 table xiv. main factor weights and their priorities individual individual group performance organizational main factors 0.0013 0.0041 0.0009 0.0016 main factors weight table xv. determine the causal factors type of factor ri-cj cj ri factor reason 0.0034 0.0066 0.01 individual reason 0.0186 0.0129 0.0315 individual-group effect 0.0043 0.0114 0.007 performance effect 0.0177 0.0301 0.0125 organizational table xvi. the final weight of the ipicea-g algorithm individual individual group performance organizational main factors 0.318 0.487 0.287 0.409 weight v conclusion project management decisions are influenced by many correlated factors and thus multi-criteria decision-making processes and group decision-making are necessary. the purpose of this paper is to prioritize the factors that have a significant effect on project management. four different factor groups were identified and evaluated. the data were gathered through questionnaires handed out to expert employees of a certain company. results are shown and discussed. references [1] a. enshassi, adnan, s. mohamed, s. abushaban, saleh, “factors affecting the performance of construction projects in the gaza strip”, journal of civil engineering and management, vol. 15, no. 3, pp. 269280, 2009 [2] a. saedghi, a. kalanaki, a. noktehdan, a. s. samghabadi, f. barzinpour, “using bees algorithm to solve the resource constrained project scheduling problem in psplib”, theoretical and mathematical foundations of computer science, pp. 486-494, 2011 [3] d. mirzai matin, “identifying the effective factors for cost overrun and time delay in water construction projects”, engineering, technology & applied science research, vol. 6, no. 4, pp. 1062-1066, 2016 [4] s. milovanovic, “aims and critical success factors of knowledge management system projects”, economics and organization, vol. 8, no 1, pp. 31–40, 2011 [5] z. alias, e. m. a. zawawi, k. yusof, n. m. aris, “determining critical success factors of project management practice: a conceptual framework”, procedia social and behavioral sciences, vol. 153, pp. 61-69, 2014 [6] j. m. lyneis, d. n. ford, “system dynamics applied to project management: a survey, assessment, and directions for future research”, system dynamics review, vol. 23, no. 2-3, pp. 157-189, 2007 [7] jonas soderlund, “knowledge entrainment and project management: the case of large-scale transformation projects”, international journal of project management, vol. 28, no. 2, pp. 130-141, 2010 h. k. doloi, “understanding stakeholders' perspective of cost estimation in project management”, international journal of project management, vol. 29, no. 5, pp. 622-636, 2011 engineering, technology & applied science research vol. 7, no. 6, 2017, 2194-2199 2199 www.etasr.com ghaffari et al.: assessing market development and innovation project management factors using … [8] m. kapsali, “systems thinking in innovation project management: a match that works”, international journal of project management vol. 29, no. 4, pp 396–407, 2011 [9] k. artto, i. kulvik, j. poskela, v. turkulainen, “the integrative role of the project management office in the front end of innovation”, international journal of project management, vol. 29, no. 4, pp. 408421, 2011 [10] x. meng, “the effect of relationship management on project performance in construction”, international journal of project management, vol. 30, no. 2, pp. 188-198, 2012 [11] s. marcelino-sadaba, a. pérez-ezcurdia, a. m. echeverría lazcano, p. villanueva, “project risk management methodology for small firms”, international journal of project management, vol. 32, no. 2, pp. 327340,2014 [12] f. acebes, j. pajares, j. manuel galán, a. lopez-paredes, “a new approach for project control under uncertainty. going back to the basics”, international journal of project management, vol. 32, no. 3, pp 423-434, 2014 [13] m. l. todorovic, d. c. petrovic, m. m. mihic, v. l. obradovic, s. d. bushuyev, “project success analysis framework: a knowledge-based approach in project management”, international journal of project management, vol. 33, no. 4, pp. 772-7832015 microsoft word etasr_v11_n6_pp7944-7949 engineering, technology & applied science research vol. 11, no. 6, 2021, 7944-7949 7944 www.etasr.com darem: anti-phishing awareness delivery methods anti-phishing awareness delivery methods abdulbasit darem computer science department northern border university arar, saudi arabia basit.darem@nbu.edu.sa abstract-phishing attacks are increasingly exploited by cybercriminals, they become more sophisticated and evade detection even by advanced technical countermeasures. with cybercriminals resorting to more sophisticated phishing techniques, strategies, and different channels such as social networks, phishing is becoming a hard problem to solve. therefore, the main objective for any anti-phishing solution is to minimize phishing success and its consequences through complementary means to advanced technical countermeasures. specifically, phishing threats cannot be controlled by technical controls alone, thus it is imperative to complement cybersecurity programs with cybersecurity awareness programs to successfully fight against phishing attacks. this paper provides a review of the delivery methods of cybersecurity training programs used to enhance personnel security awareness and behavior in terms of phishing threats. although there are a wide variety of educational intervention methods against phishing, the differences between the cybersecurity awareness delivery methods are not always clear. to this end, we present a review of the most common methods of workforce cybersecurity training methods in order for them to be able to protect themselves from phishing threats. keywords-anti-phishing awareness; phishing; phishing attack; awareness delivery methods; cybersecurity threats i. introduction advances in technology have transformed the way people work, communicate, and socialize quite dramatically. this has also exposed people and companies to various threats, one of which is phishing. phishing attacks form one of the most common cybersecurity threats that individuals and businesses face around the world, costing victims billions of dollars. phishing is described as a potent attack vector by which cybercriminals gain access to networks and systems to deliver malicious payloads (e.g. ransomware) or siphon off valuable and sensitive information (e.g. login credentials for online banking or e-commerce sites) from potential victims. phishing primarily depends on the perception of authenticity normally enacted through authentic-looking emails and spoofed websites purportedly from a legitimate and trusted source. it also masquerades hidden malicious payloads, such as ransomware, as authentic products or services. figure 1 shows the unique fake websites and phishing emails detected by apwg just in the first quarter (q1) of 2020, which are significantly higher than during the previous years [1]. many fake websites are exact copies of the genuine websites, which make it difficult for people to recognize them as illegitimate websites. these malicious websites usually remain on-line for a short time only. fig. 1. unique phishing websites and emails in q1 of 2020. in addition to the usual fake websites and phishing emails, cybercriminals rely on social engineering techniques to exploit human psychology to deceive people. the prevalent human weaknesses cybercriminals exploit include the inability of the people to differentiate real enterprise websites from spoofed ones, the way people interact with systems, the way people understand various alert messages and clues, and so forth. in addition, the attackers frequently use factors such as urgency or intimidations to compel the potential victims. the unsuspecting users are lured to click on a malicious link embedded in emails, which may activate a trustworthy looking spoofed website to disclose sensitive personal or financial information. cybercriminals use sensitive information illegally harvested from victims for illicit purposes that include identity theft, financial fraud, and corporate espionage [2]. ii. phishing threat landscape with th e advances in technical countermeasures making penetration of corporate networks quite difficult, cybercriminals are shifting their focus to exploiting the easier human vulnerability to perpetrate an attack. this shift has made phishing threats prevalent and costly. according to the anti-phishing working group (apwg), phishing attacks have consistently increased over the last ten years [1]. as phishing threats are gaining prominence and techniques to prevent them are developing, phishers are getting more creative by coming up with new tactics and crafting sophisticated messages to corresponding author: abdulbasit darem engineering, technology & applied science research vol. 11, no. 6, 2021, 7944-7949 7945 www.etasr.com darem: anti-phishing awareness delivery methods evade detection by both people and the anti-phishing measures in place. until recently, phishing attacks were largely dependent on spoofed websites and emails. currently, the phishers are also taking advantage of varied channels, in addition to the conventional email messages, such as social media, sms/text phishing (smishing), business email compromise (bec), and voice phishing (vishing). figure 2 shows the recent phishing attack distribution based on specific channels [3]. the study is based on approximately 50 million simulated phishing attacks. it showed bec-based and social media-based phishing attacks taking prominence over other platforms [3]. for example, with a 176% perennially increase in phishing uniform resource locator (url), facebook has become the favor platform for phishing attacks [4]. recently, social network sites with malicious links masked as fake news are used [5] fig. 2. phishing attack channels. another channel being quietly exploited by cybercriminals is the https (hypertext transfer protocol secure) protocol. exiting web browsers use the https protocol to alert users when they are attempting to access an "unsecure" website. an increasing practice by cybercriminals is to set up phishing sites that use the https protocol. currently, almost 60% of phishing websites use https [1] to give a false sense of security to unsuspecting victims. since the fake websites use https protocol, the web browsers may not flag the fake website as unsecured to the end users. this makes it very difficult for the end users to recognize it as fake. therefore, fake https-based websites have become so prevalent that solely relying on conventional representations of internet security is no longer trusted. mobile-based [ 6 ] and usbbased [7] phising attacks are other channels that are increasingly exploited by cybercriminals. for example, sms phishing that targets consumers (e.g. major bank customers) and enterprises is on the rise. with 84% of the customers reporting sms/text phishing attacks [7], smishing volume is clearly on the rise. a study was carried out in [8] in order to see if people would take a usb flash drive left on various locations of a university campus and plug it to their computer. they found that 45% of people did plug them into their device, as well as opened a file on that usb. this problem is becoming a concern as a recent study shows that 81% of businesses in the study had suffered from malicious usb drops [7]. cybercriminals are introducing innovative techniques to increase the success rate of phishing attacks and defeat the antiphishing tools and the effectiveness of intervention programs. the growth of the phishing attack variety and techniques further highlights the shift of the burden of action from an automated exploit or tool to a human intelligence. iii. phishing threat challenges the main challenge cybersecurity professionals face is finding ways to defend enterprise networks effectively and efficiently against attacks that manipulate human frailty. addressing this challenge is very important for several reasons. in particular, with phishing attacks known to be the most frequent first step in penetrating the defenses of a firm network, the sooner a phishing attempt is detected in the attack chain, the higher the chances of stopping, containing and responding to the attack are. normally, corporations have technical defenses in place to detect and stop phishing messages before they reach the inboxes of the employees. however, cybercriminals are innovating new tactics and are refining their attack techniques. as a result, phishing attacks are becoming more sophisticated and evading detection even by advanced technical countermeasures [9-11]. the literature discusses several possible ways to identify phishing attempts based on various clues that are visible with the naked eye. these clues include the absence of https in browsers url, the content of web browsers, the warning signs displayed by browser toolbars, the various signs for valid certificates (e.g. verisign certificates), and the content and the context of the email message. unfortunately, many people are unaware of security warnings and clues that are displayed on web browsers, or simply disregard them [12 ]. in addition, it is not easy for average online users to recognize phishing signs or visually identify a spoofed website [13]. phishing attacks can be identified just by looking at the uniform resource locator (urls), even though recognizing an impersonated url from a real one just by looking is not easy [14]. fig. 3. reasons for acting on phishing emails. there are various reasons for the reaction of people to phishing messages, which make dealing with phishing threats very challenging. for example, curiosity, anti-phishing countermeasures, knowledge of the sender, and interest in validating the message are some of the reasons that compel users to act on phishing emails [15] (figure 3). authors in [15] engineering, technology & applied science research vol. 11, no. 6, 2021, 7944-7949 7946 www.etasr.com darem: anti-phishing awareness delivery methods found that 34% of the participants opened emails because they were curious about the content of the message followed by 27% by the urge to find out the validity of the email message. the appearance of a name known to the receiver in the email body impersonating as the sender (even though the sender addresses are different) as well as the trust on the existence of technical anti-phishing measures are some of the reasons that make users to act on phishing emails. to summarize, with cybercriminals resorting to more sophisticated phishing techniques, strategies, and different channels, phishing is becoming a harder and harder problem to solve. therefore, the main objective is to minimize the success of phishing and the consequences through complementary means to advanced technical countermeasures. specifically, phishing threats cannot be controlled by technical controls alone, thus it is imperative for businesses to complement their cybersecurity with awareness programs that successfully fight against phishing attacks. iv. delivery methods' comparison in this section, we analyze the various delivery methods along with various factors as shown in table i. regarding face-to-face delivery methods such as lectures and workshopbased methods, the training time, place, and topic of training are well known in advance. in the self-based class of delivery methods, such as the web-based, the time and place are decided by the trainee while the topic of the training may be known in advance. lecture and workshop-based delivery methods are generally moderated by an expert with different levels of involvement. the training is conducted onsite (e.g. classroom) thus the learners and the instructors are required to be physically present in the classroom. all other delivery methods are conducted in a virtual classroom without the physical presence of the instructors and learners. normally the content in the self-directed delivery methods tends to be generic often developed with a one-size-fits-all scenario. on the other hand, the content in lecture-based training can be adjusted by the instructors to cater to the requirements of the learners. the instructors can also adapt lesson plans to the specific requirements of the learners. the main difference between the story-based method and the other methods, is that the content of the lesson is always written from the perspective of real experiences on an individual, whereas in the other methods, it is written from the perspective of experts. embedded training is an ongoing real-time training and thus does not require allocation of training timetable [16-17]. as the lecture and workshop-based training methods are highly customizable, it is possible to tailor them to meet the needs of a workforce in a specific division. the trainers in the lecture-based and workshop-based training have an active presence while the instructor is passive in self-directed approaches. a marked difference between the lecture-based and workshop-based methods is the way the knowledge is transferred. in the lecture based method, the transfer is from the instructor to the trainees, while, in workshop-based training, the knowledge is generated and shared by the participants with occasional contribution from the instructors. also, the instructor in the lecture-based training has an active involvement in the delivery of the training content, whereas the involvement of the instructor in the workshop-based training is restricted almost to an observer level. because employees have to be away from their regular work for the duration of the training, lecture-based and workshop-based trainings tend to be held infrequently. additionally, both may require more time to complete than the other delivery methods. in the lecture-based training, the communication between the instructor and the learners is one way. in contrast, the communication in the workshop-based delivery method is many-to-many because the method is based rather on dialogue than on instructions. communication in all other methods is one-to-one, meaning there is no direct instructor involvement but the communication with the content prepared by the lectures. the problem with the later delivery methods is that if the learners want to apply what they have learnt to specific examples, they must do so on their own. another obvious drawback is the absence of interaction with other learners and instructors, which means that learners must research and find out on their own what is not clear to them. with the provision to start studying at a time of their choice and proceed at their own pace, learners in self-directed methods must be able to self-motivate in order to finish the lesson. as learners advance through their training program, it is necessary to track a range of metrics (e.g. participation rate, course completion rate), monitor progress, and reporting. all delivery methods except story-based and embedded-based are capable of tracking the participation rate and the completion rate. note that in the story-based and embedded-based, an intervention for the end-users who fail the simulated phishing test is prescribed. there is no mechanism to ensure that the end users successfully complete the recommended intervention. but the end-users may or may not follow the recommendations. only the web-based training method and the video-based and game-based delivery methods have real time reporting to answer queries regarding how many employees have completed the lesson and how many are in the progress. the lessons in the lecture-based and workshop-based delivery methods have a fixed time to start and end, and thus they are not self-paced. the lecture-based training runs approximately 45 minutes in a classroom. for example, it run for 45 minutes in [18] and for 30 to 45 min in [13]. since the lecture-based and workshop-based delivery methods are generally moderated by an expert, the pace is determined by the lecturer. in the story-based and the embedded-based delivery methods, the training must be done immediately after the instantiation of the lesson, and thus there is no specific time limit. the self-directed delivery methods allow the learners to choose the pace, sequence, and content of their training material. video-based learning is flexible, and users could watch and rewatch the videos as they wish [31]. this is generally true for game-based learning. some game-based learning progresses are controlled in such a way that the learner must achieve certain threshold in terms of correctly identifying phishing and genuine urls [18]. feedback is a core component in providing an effective learning experience to learners. the lecture-based delivery method, due to the active presence of the instructor during the training, offers real-time feedback [19]. the workshop-based engineering, technology & applied science research vol. 11, no. 6, 2021, 7944-7949 7947 www.etasr.com darem: anti-phishing awareness delivery methods and the game-based [20] delivery methods also offer real-time feedback for the same reason. the embedded delivery method provides quick and useful feedback to the end users at the very moment when they make mistakes [21]. the story-based delivery method that implements the embedded training [22] also provides instant feedback. however, text-based delivery does not offer feedback or other interactive elements due to the static nature of the content format. video-based delivery also does not provide feedback. v. analysis of the delivery models the current research suggests that different training delivery methods have different outcomes on the learners' ability to recognize and mitigate phishing threats [18, 21]. with this in mind, we reviewed some of the user studies with a focus on those that consider two or more delivery methods. this will shed some light on the delivery methods that are most effective in enabling learners to identify and mitigate phishing threats. table i summarizes the various research results we considered. table i. comparative an alysis o f the delivery methods delivery method satisfaction communication tracking r ef er en ce l ec tu re w o rk sh o p s to ry t ex t w eb v id eo g am e e m b ed d ed p re fe re n ce c li ck r at e f al se n eg at iv e f al se p os it iv e s el fef fi ca cy m an ym an y p ar ti ci p a te c om p le te d r ep or ti n g [27] × √ √ × × √ √ × √ × × √ √ √ √ × [2] × × × √ × √ √ × √ × × × × × × × [16] × × × √ √ √ √ √ √ × √ √ × × √ √ × [28] √ × × √ × √ √ × × √ × √ √ × × √ [29] × × × × √ × √ × × √ × √ √ × × √ [30] √ × × √ × × √ × × √ × √ √ × × √ [31] × × √ × √ × × × × √ × √ √ × × × [32] × × √ × √ × × × × √ × √ √ × × × authors in [23] tested the efficacy of embedded phishing with a web-based training page to see if it improves the phishing awareness of the users. the study considered 1,359 corporate employees. the authors organized the outcome of the evaluation in terms of click rate as: people who always clicked (always) irrespective of previous training about phishing, people who clicked at least once (once), people who clicked after training (trained), and people who never clicked (never). the result showed that anti-phishing education works as demonstrated by nearly 63% reduction of the click rate after the training. this study revealed that there are people who ignore security training and advice. the main reasons for the end user's decision to accept or ignore security advices are investigated in [24-25]. the authors revealed that perceived trust of the security advice sources as the main reason for accepting it while factors such as inconvenience, privacy concerns, and excessive information are grounds for rejecting the security advice. authors in [26] determined that fear of consequences of clicking or not clicking as the main driver for people to act on phishing emails. a summary of the results of the works of wash and cooper [31], marsden et al. [32] and caputo et al. [23] in terms of click rate by the study subjects is shown in figure 5. the results of these studies show that there is a correlation between the performance of the training and the different class of subjects. therefore, it is paramount to consider the demographic information of the subjects when designing and delivering intervention training. several user studies that measure the efficacy of gamebased training method as compared to other delivery methods exist. authors in [29] evaluated the effectiveness of gamebased delivery method in raising phishing attack awareness. they compare it to a webbased delivery method (i.e. tutorial information given in apwg website on phishing). in terms of recognizing fake websites, the result showed that the end-users trained with game-based delivery method were able to recognize a fake site with a higher rate of accuracy than the participants who were trained using a website. fig. 4. participants click rate characteristics. authors in [16] evaluated the efficacy of embedded training to improve end user susceptibility to phishing threats using the false positive (fp) and false negative (fn) metrics. a fp happens if a user identifies a genuine website as a phishing one while a fn occurs if a user wrongly identifies a phishing website as a genuine website. different training delivery methods, namely game-based, web-based/videobased, and text-based were considered. the participants received several simulated phishing emails. a remedial training is randomly offered from the list of the four embedded training methods to the end users who clicked on the embedded link in the simulated emails. after the training, another set of simulated phishing emails were sent to the same end users and then it was behaviorally measured whether they fell victims to engineering, technology & applied science research vol. 11, no. 6, 2021, 7944-7949 7948 www.etasr.com darem: anti-phishing awareness delivery methods the phishing attacks or not. the outcome of the study is summarized in table ii. the overall result shows that the end users correctly recognize phishing links in a significantly better rate after the training. participants trained with gamebased delivery method performed better overall. this may be due to the fact that they performed the post-training test immediately after training. the result also shows that training with game-based methods is as good as the web-based in regard to fn but better in terms of fp. although the gamebased delivery method is able to decrease fp from an original 30% to 14%, as well as fn from the original 34% to 17%. unfortunately, the result shows that a significant number of end users are still susceptible to phishing threats. table ii. embedded train in g perfo rman ce an alysis evaluation text-based game-based web-based fp fn fp fn fp fn pre-training 27% 43% 30% 34% 30% 38% post training 21% 19% 14% 17% 41% 12% authors in [27] conducted a user study of game-based delivery method and compared it against web-based [33] using 39 students at cornell. the game used in study was what.hack [27] and the web-based training material [33]. the participants were given a pretest, training, and a posttest, in that sequence. the effectiveness was measured using the correctness percentage (click rate). the result of the experiment shows a significant improvement for game-based delivery method from 65% before training to 89% after training (about 37% improvement) in correctly recognizing phishing attempts. the performance of the web-based delivery methods of wash et al. [31] and wen et al. [27] is compared in figure 5. fig. 5. web-based delivery method outcome. the result shows that training reduces the susceptibility to phishing threats but incorporating lecture-based training does not have significant changes. following training, both groups substantially reduced the threat. the authors also considered the confidence level of the participants after training. the learners’ self-confidence based on self-assessment showed that the learners showed strong confidence in their ability to recognize phishing emails. the result also suggested that preference for lecture-based delivery method is higher than the other methods. table iii. combined train ing performance an alysis evaluation group a group b click rate data divulge click rate data divulged pre-training 13.2% (9/68) 77.77% (7/9) 3.1% (2/56) 50% (1/2) post training 1.5% (1/68) 100% (1/1) 1.6% (1/56) 100% (1/1) reduction 11.4% 51.6% vi. conclusion this paper provides a review of the delivery methods of cybersecurity training programs aimed at improving personnel's awareness and behavior of information security in the context of phishing. the phishing landscape and challenges were addressed. the delivery methods were analyzed to shed some light on the delivery that is most effective in enabling learners to identify and mitigate phishing threats. the delivery methods along with their various factors were analyzed. in face-to-face delivery methods, such as lecture and workshopbased methods, training time, place, and topic of training are well known in advance. in the self-based class of delivery methods such as the web-based, the time and place are decided by the trainee while the topic of the training may be known in advance. the web-based delivery method performance for several studies was compared to observe that after training, the click rate decreases by 21% which suggests that training does decrease susceptibility to phishing threat to certain extend. the result also suggested that the preference for the lecture-based delivery method is higher than for the other methods. references [1] apwg, phishing activity trends report, 1st quarter. anti-phishing working group, 2020. 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[33] barracuda networks inc, "click thinking content," barracuda campus. https://campus.barracuda.com/product/phishline/doc/79463828/clickthinking-content/ (accessed nov. 23, 2021). microsoft word etasr_v11_n5_pp7564-7570 engineering, technology & applied science research vol. 11, no. 5, 2021, 7564-7570 7564 www.etasr.com samreen et al.: exploring the relationship between foreign investments and carbon emission … exploring the relationship between foreign investments and carbon emission: a bound test analysis for pakistan hina samreen department of mathematics and statistics institute of business management karachi, pakistan hina.samreen@iobm.edu.pk shahida wizarat department of economics institute of business management karachi, pakistan shahida.wizarat@iobm.edu.pk zafar mehdi department of management & hr institute of business management karachi, pakistan zafar.mehdi@iobm.edu.pk rizwan ahmed department of mathematics and statistics institute of business management karachi, pakistan rizwan.ahmed@iobm.edu.pk abstractin this study, the theoretical and empirical effects of foreign investment, openness to trade, urbanization, and economic development on carbon dioxide emission levels (co2) in pakistan were examined. annual time series for 38 years 19702018 were utilized. the auto regressive distributed lag (ardl) bound test has been used to estimate the model which indicates the presence of cointegration among the variables. long-run and short-run relationships were observed between foreign direct investment (fdi) and co2 emission levels revealing that increase in fdi results in increased co2 emission levels contributing to environmental degradation. this endorses the theory of pollution haven hypothesis (phh) in the case of pakistan. to achieve the goal of sustainable economic development, it is imperative to consider the possible negative effects of foreign investment on the environment. the study suggests limiting co2 emissions by adopting more advanced low carbon technologies to ensure growth and a sustainable environment. strict implementation of environmental laws for foreign and domestic firms both by defining co2 emission limits, installation of proper waste management plants, and imposing a pollution tax are crucial steps for the improvement of environmental quality. keywords-fdi; pakistan; co2; emissions; environment; bound test; phh i. introduction environmental pollution, climatic change, and globalwarming are some of the most concerned topics in scientific research. the last century witnessed a significant change in climate as revealed by different indicators. it is reported that there is a 0.41° increase in average recorded global temperature from 1998 to 2007 as compared to the 1961 to 1990 period [1]. this weather change is a big ecological issue that has caught the attention of researchers, policy makers, international institutions, and environmentalists. according to the intergovernmental panel for climate change (ipcc), increased human activity due to the economic liberalization and industrialization has warmed the earth by 1° centigrade since the pre-industrialization era. furthermore, the ipcc 2018 reported that the effects of global warming have been felt in many parts of the world. nonetheless, they are not spread consistently over the globe, with different areas experiencing the impacts unexpectedly and unevenly. among various effects, it is resulting in heavy rainfall in certain areas, especially in the high latitudes of the northern hemisphere, raising the risk of flooding. further increase in global warming may aggravate the situation due to the rapid melting of glaciers, the liquefication of ice masses, and, consequently, the rising of the sea level [2]. carbon dioxide (co2) emerges as a main contributor to global warming [3]. co2 diffuses into the environment through the extraction, refining, and consumption of petroleum products and fossil fuels. there are several factors which have contributed to the rise in temperature over the last century and energy demand is one of them. a rapidly growing economy has huge energy requirements for power generation, transportation, and industrial production. because of the onset of globalization in the early 1990s, free capital inflows along with the increase in international trade intensified the movement of foreign investment in less developed countries in various sectors [4]. there is substantial evidence that foreign direct investment (fdi) enhances the productivity of host countries and promotes economic growth. foreign investment brings capital, technology, and skill development and provides access to new markets and greater opportunities to exports [5]. the industrial sector is a key sector of an economy, vastly contributing to economic growth. foreign resource mobilization is crucial for industrial production and growth [6]. corresponding author: hina samreen engineering, technology & applied science research vol. 11, no. 5, 2021, 7564-7570 7565 www.etasr.com samreen et al.: exploring the relationship between foreign investments and carbon emission … the existing literature on fdi and co2 emissions adopts two different approaches. the pollution haven theory, which is the major focus of attention in this study, has a hypothesis referred to as "pollution haven hypothesis" (phh) stating that foreign investment moves towards countries with poor environmental laws and conditions and less environmental taxes. the hypothesis explains that multi-national corporations (mncs) relocate the industries which are more pollution intensive in nature to less developed countries (ldcs) with flexible environmental regulations to avoid high environmental costs in terms of environmental taxes. this results in increasing pollution level in the host country thus becoming a pollution haven [7]. the environmental quality is critical for human health. poor environmental conditions pose a serious risk to human wellbeing in various ways [8]. according to the world health organization (who) global health observatory, poor environmental quality causes roughly 200 deaths per 100,000 people in pakistan. indoor air pollution induced by residential biomass fuel combustion causes about 30 deaths per 100,000 people, whereas outdoor pollution causes around 25 deaths per 100,000 people. rapid increase in population growth, number of vehicles, unplanned and rapid urbanization, and industrialization cause air pollution, particularly particulate matter (pm) pollution. traffic congestion, open air combustion of untreated solid waste, and improper management of construction and demolition waste are the main sources of air pollution in urban areas [9]. considering the importance of foreign investment in development, growth, and prosperity, the objective of the current study is to explore if the fdi is a possible major cause of environmental degradation, and if so, ways to design a policy framework that is sustainable for economic development with minimum hazards for the environment. numerous empirical researches often aimed to study the direct relationship of economic growth and carbon emission [10-12] and fdi and greenhouse gas (ghg) emissions [13, 14], while in the current study, we analyze the indirect impact of foreign investment to ghg emissions through its direct relationship with economic growth, urbanization, and trade openness. the goal of this study is to look at the evidence of this indirect relationship and see if there is a significant effect, and if so, to quantify it. this paper contributes to earlier research on foreign investment inflow and its possible harmful effects on carbon emissions to help policy makers to design policies that combat carbon emissions but not at the cost of economic growth. ii. pollution haven hypothesis environmental pollution is the result of human activities which the environment cannot deal with naturally. fdi is considered as a main contributor to this environmental destruction as it accelerates economic activity that results in economic growth on one hand but it also causes an increase in ghg emissions, deforestation, and biodiversity loss on the other. authors in [15] used a non-linear estimation method to check if there is any association between environmental devastation and foreign investment in the case of the malaysian economy for the 1965-2010 period. the results confirm that fdi results in great environmental degradation. phh asserts that a host country with weak environmental regulation attracts more foreign investments, as profit-oriented companies try to evade costly regulatory compliance in their home countries by relocating their dirty industries in developing countries [16]. the nexus between weak environmental laws and capital inflows of polluting industries is explored in [17]. the authors considered cross-sectional data for 7 developing economies and 15 developed countries for the period from 1985 to 1990 and found that poor environmental laws in the host country encourage fdi inflow in the industries that pollute environment, while for the less polluting sector, the results were insignificant. authors in [18] tried to explore whether private sector involvement is beneficial to the environmental quality. the study considers co2 emission as a measure of environmental pollution, along with other variables like financial market scope, industrial sector composition, and foreign investment. the study found that greater involvement of the private sector in a developing economy resulted in environmental quality improvement. earlier, authors in [19] analyzed the case of asean economies to study the impact of capital inflow on the environmental degradation. the study used the ardl model and time series data for 31 years (19702001). thailand, malaysia, and the philippines are the countries where a significant relationship between fdi and pollution is observed. it has been observed that foreign capital inflows do not contribute to increasing pollution levels in indonesia, while for singapore no significant results were found. authors in [20] studied the long run relationship between capital inflows, pollution level, and output for malaysia using the granger causality test. the research employed annual per capita gdp as a proxy for income and annual co2 emission per capita as a proxy for pollution. the study found that fdi granger-causes gdp growth and pollution level in the short run, while in the long run, causal relationship was observed for output and fdi inflows. authors in [21] studied the association between foreign investment and environmental policy considering 33 countries. the study found that foreign investment can influence environmental policy only if there is a sincere effort from local government to design and implement environmental rules. the study concludes that the flexibility of environmental policy depends on the degree of corruption of government officials. the authors recommended the adoption of a political economic model with imperfect product market competition along with the application of pollution tax to combat pollution. authors in [22] used data from 112 countries to study the relationship between foreign inflows and the level of pollution. granger causality test was employed to test the results. the authors report that for lower income groups, co2-levels granger-cause foreign investment inflows. also, for middle income groups, fdi granger-causes co2 emissions, whereas for higher income groups there is no evidence of granger causality. to confirm the phh for asean countries, authors in [23] used the ardl method on time series data for the 1970-2008 period. in the case of the philippines, the results indicated that all the regression coefficients except for per capita gross national income are significant. mixed results were reported in the cases of thailand and indonesian economies. authors in [24] found that economies with liberalized trade policies contribute more to pollution intensity than those following engineering, technology & applied science research vol. 11, no. 5, 2021, 7564-7570 7566 www.etasr.com samreen et al.: exploring the relationship between foreign investments and carbon emission … more restrictive policies. authors in [25] tried to explore whether free trade agreements are affecting the environment of the countries that are bound by these agreements. the gravity model framework was used to analyze the impact of free trade agreements on bilateral co2 emissions. the study found that weak environmental standards prevailing in low income countries result in greater pollution effect of free trade agreements, whereas, high income countries shift dirty industries to the countries where there is weak or no implementation of environmental policy, hence confirming the pollution haven theory. the export volume of china is a sign of greater economic activity, but also generates an enormous amount of co2 [26]. the author calculates the size of co2 emission by 18 exporting industries of china from 2001 to 2010 using the i-o framework. the study concludes that the increase in the volume of exports is a major contributor to the increment of the co2 level of a country. the study did not confirm china as a pollution haven for developed countries. authors in [27] empirically explored the link between energy consumed by the transport sector, co2 emission, economic development, foreign investment, and urbanization. ardl and vecm were used for estimation over the period from 1990 to 2015. the study found transport sector energy consumption as a significantly strong determinant of co2 emissions in pakistan. the study also confirms the contribution of foreign investment in co2 emission, whereas economic growth and urbanization were found to be insignificant determinants of co2 emission. the study recommends that the government should play a more active role in improving environmental quality by providing energy efficient solutions in the transport sector with less adverse effects on economic growth. the author in [28] selected per capita gdp in real terms, energy consumption, urbanization, transport sector intensive-energy along with fuel prices as key determinants of pollution level in tunisia during the period from 1980 to 2014. the author claimed that the reliance of the road transport system mainly on fossil fuel usage is a major cause of co2 emissions. the study supported the ekc theory by confirming the presence of an inverse u-shaped curve indicating the relationship between economic development and co2 level from the transport sector. iii. data sources and model specification data on economic and other key indicators were collected from world development indicators (wdi) over the time span from 1970 to 2018 [29]. as a determinant of environmental quality, we have used co2 emission per capita (co2pcap), in metric tons. we have also considered other economic indicators due to the limited availability of carbon emission data. gross domestic product per capita (gdpcap) was used to define the level of economic development (in constant 2010 us $). fdi is the net inflow of investments as a percentage of gdp (fdipgdp). the urbanization variable (urban) is calculated as a percentage of urban to total population. trade to gdp ratio is a proxy for a liberal economy (topeness) and was also taken from the wdi. to explore how capital inflows affect co2 emission levels in pakistan, the following model has been specified using eviews. log�co2pcap = β� +β� �log�gdpcap + β��log�topenness + β� �log�fdipgdp +β� �log�urban + ϕ (1) ardl-bound test estimation method, proposed in [30, 31] has been used to explore the relationship between co2 emissions with foreign investment, gdp per capita, urbanization, and trade openness. ardl estimation generates results in two steps. the first is the ecm results and the second is the bounds test results. when co-integration exists, it is recommended to also report the ecm results, in case of no cointegration, we conclude with the ardl model. iv. data analysis and diagnostic test tables i and ii report the descriptive statistics and the correlation matrix for the variables considered in the current study. to confirm the robustness of the results, different diagnostic tests are employed which are discussed in the following section. to examine the stationarity of variables, both augmented dickey-fuller (adf) test and phillips & peron (pp test) were applied. table iii shows the findings. it is revealed from unit roots tests that initially, level following variables are non-stationary like per capita co2 emission, foreign investment, and per capita gdp, but become stationary after taking the first difference, whereas the remaining variables are stationary. table i. descriptive measures variable mean std. dev. min max fdipgdp 0.7606914 0.7968646 -0.063242 3.668323 urban 31.16394 3.422316 24.81700 36.44200 gdpcap 2.191195 2.162259 -2.218736 8.385496 topeness 32.55893 4.043413 19.93229 38.90950 co2pcap 0.6512522 0.2209307 0.3083813 0.9878324 table ii. correlation matrix fdipgdp urban gdpcap co2pcap topeness fdipgdp 1.0000 urban 0.5683 1.0000 gdpcap 0.0003 -0.0657 1.0000 co2pcap 0.6382 0.9795 -0.0628 1.0000 topeness 0.2612 0.1392 -0.0446 0.0783 1.0000 table iii. augmented dickey fuller unit root test variable adf at level pvalue adf at first difference (p-value) order of integration pp test at level pp test at first difference lnco2pcap 0.8561 0.000 i(1) 0.9221 0.0000 ln fdi 0.0816 0.0000 i(1) 0.1138 0.000 ln urban 0.0144 i(0) 0.0000 lngdpcap 0.8550 0.0000 i(1) 0.9435 0.0000 lntopenss 0.0112 i(0) 0.0097 an optimal lag length selection is the first step in ardl estimation. table iv reports various lag selection criteria available in the literature. except schwartz information criterion (sic) all three-information criteria suggest that we should consider a maximum lag length of two in this study. the * sign in table iv defines the selected lag order by the chosen criterion. in the second step we proceed with the estimation of the ardl model, which requires the computation and analysis of f-statistics using ardl bound test methodology. engineering, technology & applied science research vol. 11, no. 5, 2021, 7564-7570 7567 www.etasr.com samreen et al.: exploring the relationship between foreign investments and carbon emission … table iv. lag length selection lag logl lr fpe aic sic hq 0 87.99601 na 0.001465 -3.688711 -3.487971 -3.613878 1 100.7045 22.02806 0.000871 -4.209089 -3.968201 -4.119288 2 103.1279 4.092887* 0.000819* -4.272352* -3.991316* -4.167585* 3 103.9750 1.393006 0.000825 -4.265557 -3.944372 -4.145822 4 103.9809 0.009329 0.000864 -4.221371 -3.860039 -4.086670 table v reports the calculated f-statistic and its critical values. the f-statistic (17.773) is found to be greater than the upper bound critical value (5.06) at 1% significance level which helps us reject the null hypothesis of no long-run association at 1% level of significance. long run elasticities for both the dependent variable (carbon emissions) and the independent variables (foreign investment, per capita gdp, urbanization and trade openness) are summarized in table vi. the coefficients for fdi, urbanization and trade liberalization are found to be significant at the 1% level of significance in the long run, while the coefficient on per capita gdp is found to be significant at the 10% level of significance. as expected, the estimated coefficients of all the explanatory variables carry the expected positive sign. foreign investment opens the door to infrastructure and technological and human development in the host country [32]. a significant and positive coefficient on fdfi describes investment opportunities available at the cost of environmental degradation. a 1% increase in foreign investments causes a 0.0418% increase in co2 emissions. the coefficient on urbanization is also found to be a positive and significant determinant of carbon emissions. high urbanization means that more people are settled in urban areas resulting in increase in human and economic activities. this result is in line with the findings in [33]. table v. ardl bound test f-statistic 17.773*** critical values bound significance lower bound upper bound 1% 3.74 5.06 5% 2.86 4.01 10% 2.45 3.52 table vi. long run estimates variable coefficient std. error t-statistic prob. log(fdipgdp) 0.041811 0.007119 5.873148 0.0000 log(gdpcap) 0.232906 0.133448 1.745300 0.0895 log(urban) 1.951081 0.329676 5.918186 0.0000 log(topeness) 0.186990 0.041948 4.457692 0.0001 log(co2pcap) -9.122096 0.480991 -18.965208 0.0000 a continuous growth in urbanization is responsible for the increase in the pollution level of a country causing damage to the environment, not only in industrialized nations, but also in developing economies [34]. people migrate to cities to find better health, education, and employment opportunities. this growth in urban population creates numerous challenges for urban areas due to the increase in demand and the limited resources. this unplanned population growth brings new challenges in various ways. better infrastructure and transport facilities form a need for growing urban population. to provide transport facilities to a large urban population results in increase in the number of vehicles, resulting in more vehicular emissions. rapid growth in urban population also exerts pressure on the availability of clean water and proper wastage and sewerage system [33]. as expected, we observed a positive and significant coefficient (0.2329) for per capita gdp growth and co2 emissions in the long run, namely 1% increase in per capita gdp growth contributes to 0.2329% increase in co2 emissions. this phenomenon may reflect in more economic activities and the number of vehicular emissions [35]. the coefficient (0.1869) of trade openness is also found to be positive and significant determinant of co2 emission levels. this is a significant result explaining why pakistan experiences a comparative advantage in the production of goods that are harmful for the environment. this result helps to conclude that in the absence of strict environmental protection laws, greater trade openness does not lead to the path of sustainable growth in the long run. since we found evidence for a long run relationship we further tested for short run relationship by adopting the ecm-ardl approach. the results are given in table vii. the adjustment coefficient (-1.0307) has the expected negative sign and is statistically significant. table vii also provides the short run estimates of regressors and co2 emissions. table vii. shortrun estimates variable coefficient std. error t-statistic prob. dlog(co2pcap (-1)) 0.060852 0.148354 0.410180 0.6842 dlog(co2pcap (-2)) 0.040098 0.106818 0.375383 0.7097 dlog(fdipgdp (-1)) 0.017003 0.009797 1.735437 0.0917 dlog(fdipgdp (-2)) -0.000999 0.007147 -0.139768 0.8897 dlog(gdpcap (-1)) 0.425215 0.261891 1.623635 0.1137 dlog (gdpcap (-2)) 0.315363 0.308304 1.022896 0.3136 dlog(urban (-1)) -5.003957 9.281719 -0.539120 0.5933 dlog(urban (-2)) 5.684971 8.876761 0.640433 0.5262 dlog(topenes s(-1)) 0.123089 0.050503 2.437276 0.0202 dlog(topenes s(-2)) 0.017732 0.037870 0.468230 0.6426 ecm(-1) -1.030749 0.277675 -3.712069 0.0007 r-square 0.560200 the optimal lag length is found to be 2 for every variable thus all the short run estimates given in the table show 2 lags for every variable. all explanatory variables are found to be insignificant, except for the coefficient on trade openness, which means trade openness contributes significantly to carbon engineering, technology & applied science research vol. 11, no. 5, 2021, 7564-7570 7568 www.etasr.com samreen et al.: exploring the relationship between foreign investments and carbon emission … emission only in the short run. the error correction (ecm) term is found to be significant with the expected negative sign (-1.0307) which explains that whenever per capita carbon emission is above or below the equilibrium level, it automatically adjusts by 103% and the speed of adjustment occurs within the first year. the value of r square shows that the fitted model is a good fit and explains that the 56% variability in the model is due to the included explanatory variables. the high p-values of urbanization and trade openness coefficients are evident that no short run causal relationship exists between the explanatory variables and the dependent variable. whereas a significant value of fdi at 1% and per capita gdp at 10% indicates that there is an evidence of short run causal relation from explanatory variables to the dependent variable. the highly significant ecm term (p-value 0.0007) in table vii is evident of the causality among variables. generally, the co-integration analysis is used to observe the possible causal relationship between the variables, at least unidirectional. but it does not provide the direction of causality. thus, to examine the direction of causality among the variables the next step is to run a granger causality test. table ix provides the results. two-way causality is observed between carbon emission and fdi. a very interesting finding of the granger causality test is the uni-directional causality from fdi to co2 emission per capita gdp growth, urbanization, and trade openness. this validates the hypothesis of the study that foreign investment stimulates the economic activity reflected in terms of urbanization and per capita gdp growth but also explains the environmental degradation in terms of hazardous emissions. table viii. wald test variables probabilities fdi 0.000 gdpcap 0.0992 urban 0.5730 topeness 0.1144 table ix. vecm granger causilty test hypothesis probability log(fdipgdp) does not granger-cause log(co2pcap) 0.0058 log(co2pcap) does not granger-cause log(fdipgdp) 0.0981 log(gdpcap) does not granger-cause log(co2pcap) 0.0002 log(co2pcap) does not granger-cause log(gdpcap) 0.1487 log(urban) does not granger-cause log(co2pcap) 1.e-05 log(co2pcap) does not granger-cause log(urban) 0.0433 log(topeness) does not granger-cause log(co2pcap) 0.0273 log(co2pcap) does not granger-cause log(topeness) 0.4636 log(gdpcap) does not granger-cause log(fdipgdp) 0.2950 log(fdipgdp) does not granger-cause log(gdpcap) 0.0055 log(urban) does not granger-cause log(fdipgdp) 0.4332 log(fdipgdp) does not granger-cause log(urban) 0.0296 log(topeness) does not granger-cause log(fdipgdp) 0.7558 log(fdipgdp) does not granger-cause log(topeness) 0.0003 log(urban) does not granger-cause log(gdpcap) 0.0820 log(gdpcap) does not granger-cause log(urban) 0.1818 log(topeness) does not granger-cause log(gdpcap) 0.4591 log(gdpcap) does not granger-cause log(topeness) 0.5039 log(topeness) does not granger-cause log(urban) 0.0045 log(urban) does not granger-cause log(topeness) 0.7983 in table ix we also observe that per capita gdp growth causes carbon emissions in the long run. this result also suggests that a stimulated economic activity may harm the environment if certain protective measures are not adopted. no long run causality was observed in the reverse direction which means that co2 emission does not granger-cause economic growth, therefore a unidirectional causality is observed. this result is in contrast to the findings of [1], who asserted that any measure to control co2 emissions may have different implications for developed and developing countries. measures to limit or control co2 emissions are more harmful for developing countries as compared to developed countries. to test the stability of the model, the cumulative sum of recursive residuals (cususm) test was applied and the result is explained with the help of figures 1 and 2. the plots of cusum test explain the stability of the ecm model. the straight lines in both figures describe the critical values at 5% level of significance. the cusum and cusumsq plots lie within the drawn critical values confirming the model is stable. -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1985 1990 1995 2000 2005 2010 2015 cusum of squares 5% significance fig. 1. cusum plot. -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1985 1990 1995 2000 2005 2010 2015 cusum of squares 5% significance fig. 2. cusumq plot. further diagnostic tests are applied to the ecm model and the results are presented in table x. the results suggest that the ardl model fits well and passes the breusch-pagan-godfrey heteroscedasticity test and breusch-godfrey lm test for serial correlation. engineering, technology & applied science research vol. 11, no. 5, 2021, 7564-7570 7569 www.etasr.com samreen et al.: exploring the relationship between foreign investments and carbon emission … table x. diagnostic test results breusch-pagan-godfrey for heteroscedasticity f-value 1.034710 prob. f (14,30) breusch-godfrey lm test of serial correlation f-value 1.178700 prob. f (2,28) v. conclusion in the neoliberal economic model, foreign investment is a major contributor to development through the introduction of new knowledge and technology and the creation of opportunities for employment and income growth. therefore, the governments in host countries give lucrative offers to attract foreign investors. our results confirm that increasing fdi causes an increase to co2 emissions, thus contributing to environmental degradation. a positive association between co2 emissions and fdi corroborates the phh for pakistan. the study suggests that before signing an agreement with the investor, host governments need to consider the possible adverse effects of fdi on the environment. host governments should ensure that the investor company/country would adopt a clean energy technology that would reduce the pollution level. thus, there is a need to set standards for industrial pollutants and emissions. to achieve the object of sustainable economic growth and development, governments should focus on strict implementation of policies that are more environmentally friendly and limit emissions to an ideal level. a sustainable approach is one that is low carbon in nature, such as wind and solar energy and aimed at reducing emissions but not at the cost of economic growth. fig. 3. flow chart of the research. this study establishes the understanding that a stimulated economic activity coupled with rapid urbanization results in more dependence on fossil fuel consumption and ultimately results in harmful emissions. environmental degradation not only disturbs human life, but also puts pressure on economic activities in the long term. urbanized activities are more energy intensive in nature. dependence on fossil fuel consumption to cater for demands of the urban sector (electricity generation, heating, and transport) results in increased levels of pollution. with the growing population, it is difficult to limit the energy demand, hence awareness programs for the public are needed to be designed. to reduce the negative effects of urbanization, governments should monitor the technology transfer process and set standards to ensure environmental quality. introduction of more ecofriendly and energy efficient automobiles and provision of better public transport in the urban sector are some steps governments should adopt. there is a need to explore long term investment options that are cleaner in nature and provide sustainable solutions both for economic development and the environment. moreover, to attract foreign investors with more ecofriendly transfer of technology, strict environmental policy, improved infrastructure, and human capital development are crucial. figure 3 exhibits the flow chart of the research conducted to determine if there is a relationship between carbon emissions and fdi. appendix list of acronyms ipcc intergovernemental panel for climate change fdi forgien direct investment co2 carbon dioxide phh pollution haven hypothesis mncs multinational corporations ldc's less developed countries who world health organization pm particulate matter ghg greenhouse gas emissions asean association for south east asian nations ecm error correction model ardl autoregressive distributed lag model sic schwartz information criteria fdipgdp net inflow of investement as a percentage of gdp gdpcap per capita gdp topeness trade openness co2pcap carbon dioxide emissions per capita urban urbanization cusum cumulative sum control chart references [1] f. bilgili, e. kocak, and u. bulut, "the dynamic impact of renewable energy consumption on co2 emissions: a revisited environmental kuznets curve approach," renewable and sustainable energy reviews, vol. 54, pp. 838–845, feb. 2016, https://doi.org/10.1016/j.rser. 2015.10.080. 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[30] h. pesaran and y. shin, "an autoregressive distributed lag modeling approach to co-integration analysis," econometncs and economic theory in the 20st century: the ragnar frisch centennial symposium, vol. 31, feb. 1995, https://doi.org/10.1017/ccol0521633230.011. [31] m. h. pesaran, y. shin, and r. j. smith, "bounds testing approaches to the analysis of level relationships," journal of applied econometrics, vol. 16, no. 3, pp. 289–326, 2001, https://doi.org/10.1002/jae.616. [32] h. mahmood, "fdi, population density and carbon dioxide emissions: a case study of pakistan," iranica journal of energy & environment, vol. 3, no. 4, pp. 354–360, jan. 2012, https://doi.org/10.5829/ idosi.ijee.2012.03.04.09. [33] r. ali, k. bakhsh, and m. a. yasin, "impact of urbanization on co2 emissions in emerging economy: evidence from pakistan," sustainable cities and society, vol. 48, jul. 2019, art. no. 101553, https://doi.org/ 10.1016/j.scs.2019.101553. 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[35] k. hamid, "is foreign direct investment a cause of environmental degradation in pakistan? an ardl approach to cointegration," journal of management and research, vol. 3, no. 2, pp. 60–76, dec. 2016, https://doi.org/10.29145/jmr/32/0302003. microsoft word 8-723.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1080-1083 1080 www.etasr.com mafakheri et al.: design of the administrative building of kuhsar city under a sustainable architecture … design of the administrative building of kuhsar city under a sustainable architecture concept approach hamid reza mafakheri department of architecture, hidaj branch, islamic azad university, hidaj, iran. amir hosin hejazi department of architecture, abhar branch, islamic azad university, abhar, iran. mehran dashti department of architecture, hidaj branch, islamic azad university, hidaj, iran. abstract—this study investigates a sustainable approach in the design of the administrative building of the municipality and islamic council of kuhsar city, iran. the initial design is inspired by a flower bud and the various stages of the design are described using actual images, 2-d plans and 3-d models. an extra focus is given to sustainable elements. overall the design aims to deliver an energy sufficient yet aesthetically pleasing building. keywords-sustainable architecture; city council; municipality; building; energy retention; administrative i. introduction in most countries, experts try to formulate urban controlling rules, building rules and environmental ranking systems to promote sustainable development [1]. in the early 21th century, shortage of natural resources, population growth and concerns about pollution obliged cities to review environmental plans and determine goals for the future. issues such as greenhouse gas, using water, urban waste, recycle, land use and environment quality are considered in this process [2]. sustainable architecture is the manifestation of sustainable development in construction. in sustainable architecture, buildings are not just adapted regarding the climatic conditions of the region, but establish a mutual relationship with it [5]. the goal of design of such buildings is the reduction of damage on environment, energy resources and nature [4]. the important point of this paper is the sustainable architecture approach to environmental issues. however, it is difficult to separate this issue from other economic, cultural and social aspects. further, although current critical results are identified well, most of presented solutions are inefficient. considering the importance of fossil energy consumption, pollution and climatic change, the full re-evaluation and possible reform of buildings under construction emerges as a necessity. sustainable architecture in iran, in residential and non-residential areas, is not that much followed and existing buildings, especially public establishments, are mainly energy consumers. to respond to the climatic needs of each region in iran, traditional architecture should also be considered. this study aims to investigate sustainable environmental and sustainable architecture theories in an attempt to help in policy definition. ii. famous examples of sustainable buildings a. hsbc building in shangai the hsbc building in shanghai is designed under the unique styles of norman foster. it stands 180 m above ground with four basements levels. there are 47 floors with a rectangle plan approximately 54*70 m. the middle atrium is 52 m. lifts stop at certain floors only and floors are connected via escalators. the structure of the building is visible mainly due to maintenance principles. sea water is used as an initial cooler for the ventilation system, as well as for the washing system and wc. to increase the lighting in central space solar mirrors following sun movements are used [3]. b. guggenheim museum the museum has a statue-oriented form of simple design. it has an approximate height of 250 m and dome ceiling with a 12-angle spider web skylight. a central inverse cone atrium is saturated with natural light. c. swiss re building swiss re building has 41 floors and an overall area of 76400 m2. in this tower, some ideas a new rapport between nature and the work place, is its energy-conscious enclosure resolving walls and roof of a continuous triangulated skin. the tower has a radial plan with a circular perimeter. from halfprofile, this is widened to top and then its width is reduced and it is minimized at the end. iii. case study a. location kuhsar city is located in iran (figure 1). due to the limited extension of this city, the existing height difference has no effect on weather conditions. the highest height in kuhsar city is observed in the north end of the city with a height of 1640 m and lowest height is found south west with a height of 1310 m. the center of kuhsar city is located at a height of 1450 m from sea level. based on the topography conditions of the region, engineering, technology & applied science research vol. 6, no. 4, 2016, 1080-1083 1081 www.etasr.com mafakheri et al.: design of the administrative building of kuhsar city under a sustainable architecture … savojbolagh town can be divided into mountainous, foothills and plain area. about 25% of town area is mountainous. the foothills area is in the southern range of the taleghan mountain. the average temperature there is higher compared to the mountainous area. three factors play an important role also: the kavir plain, the alborz mountains and the humid west winds. according to long-term statistics (1985-2005), the annual average of air temperature (dry air) is 15.8 oc. july and august with 28.4 and 28.2 oc have the highest and january and february with 2.2 and 4.4 oc, have the lowest temperature. (a) (b) fig. 1. a) aerial photo of kuhsar city (b) the map of savojbolah and kuhsar city generally, the selection of building location depends upon some factors as natural condition of earth, the need to private spaces, reduced noise, wind and sun. southern direction is usually considered optimum as it can result to achieving highest solar energy in winter and lowest in summer. the total annual rainfall (2007) in the synoptic station of karaj, the closest station to kuhsar town, is 393.5 mm. maximum relative humidity in 2007 was 91% and minimum relative humidity in the same year was 15%. the dominant wind in the region is northwestern and its geographical direction is 315° between north and west. the historical review of earthquake shows a relatively high risk [6]. figure 2 show the master plan of kuhsar city and its border. (a) (b) fig. 2. a) the city border map of kuhsar b) master plan of kuhsar city the selected site is located in a mixed-use zone of kuhsar city (commercial, administrative , service and residential) with a density of 240%. most offices (electricity offices, health houses, urban services etc.) are located in this area and there is a suitable access via two streets. a third road is under construction in close proximity. the site is located at a height of 1400 m and in a distance of 12 km from the karaj-qazvin highway (figure 3). figure 4 shows some images of the site. fig. 3. aerial photo of the site (a) (b) (c) fig. 4. (a): north to south site (b): south to north site (c): south to north site b. idea and concept the concept of the project is based on a flower bud as shown in figure 5. several instants from the design trend are shown in figure 6. the designs for each floor are shown in figure 7 fig. 5. project concept fig. 6. design trend of the project engineering, technology & applied science research vol. 6, no. 4, 2016, 1080-1083 1082 www.etasr.com mafakheri et al.: design of the administrative building of kuhsar city under a sustainable architecture … fig. 7. plans from the project c. using a central atrium such intermediate spaces, atriums, are used for natural lighting, internal comfort, mild and spatial sub-climate. the skylights may be of different dimensions and forms and have glass-covered ceiling and lateral walls with various materials, usually different from plain building materials. an atrium is suitable to absorb solar energy and facilitate heat storage (in winter) and air circulation (in summer) (figure 8). d. using external louvers the highest solar energy absorption in summer is done via windows. to do this, external vertical louvers can be installed in the east and south of the building, and horizontal louvers in the west (figure 9). fig. 8. image of the central atrium fig. 9. image of external louvers e. using external skin in city council for sustainable architecture creating skin as a secondary will increase the shading of the building and thus reduce the absorbed heat. in the winter it will help protect the building from the cold north west winds (figures 10 and 11). fig. 10. the external wall fig. 11. overview of the building engineering, technology & applied science research vol. 6, no. 4, 2016, 1080-1083 1083 www.etasr.com mafakheri et al.: design of the administrative building of kuhsar city under a sustainable architecture … f. looking over the city the terrace overlooking the city serves two additional purposes as it will allow employees to gaze upon the city and also provide a feeling of reassurance to the citizens (figure 12). fig. 12. looking over the city g. application of urban matrix in site design finally, the main streets of the city have been incorporated in the design of the building providing easy access and pleasant walking routes along fountains and green areas (figures 13 and 14). fig. 13. urban matrix extraction trend from city passages fig. 14. figure 14-urban matrix image in site design iv. conclusion this paper presents the design of the municipality and islamic council building of kuhsar city under a sustainable approach. the site’s location is also presented and a walkthrough of the design is given, focusing on the most important, and unique, aspects. actual images as well as 2-d designs and 3-d models are given. the building was inspired by a flower bud and certain elements of sustainable architecture have been implemented (a central atrium, external louvers, a second skin external wall). this design aims to deliver a practical, energy saving and aesthetically pleasing building. references [1] a. rezvan, “sustainable development”, architect news iran, 2012 [2] s. e. sayadi, s. m. mahdavi, “sustainable architecture”, journal of architecture and urbanization in iran, vol. 20, no. 68. [3] m. golabchi, the investigation of works of norman foster. tehran university publication. 2010. [4] y. gorji, mahlabani, a. yaran, solutions of sustainable architecture of gilan with comparison with japan architecture. fine arts journal. 41, 2010. [5] m. mahmoudi, the development of housing consistent with sustainable development. tehran university publications. spring. 2013. [6] consulting engineers studies of spadana. p. 20, 2009. microsoft word etasr_v11_n6_pp7782-7787 engineering, technology & applied science research vol. 11, no. 6, 2021, 7782-7787 7782 www.etasr.com al-baghdadi & sabah: behavior of rc beams strengthened with nsm-cfrp strips subjected to fire … behavior of rc beams strengthened with nsmcfrp strips subjected to fire exposure a numerical study hayder a. al-baghdadi department of civil engineering college of engineering university of baghdad baghdad, iraq baghdadi.hayder@coeng.uobaghdad.edu.iq anwer sabah department of civil engineering college of engineering university of baghdad baghdad, iraq anwer.ali1801m@coeng.uobaghdad.edu.iq abstract-the use of near-surface mounted (nsm) carbonfiber-reinforced polymer (cfrp) strips is an efficient technology for increasing flexural and shear strength or for repairing damaged reinforced concrete (rc) members. this strengthening method is a promising technology. however, the thin layer of concrete covering the nsm-cfrp strips is not adequate to resist heat effect when directly exposed to a fire or at a high temperature. there is clear evidence that the strength and stiffness of cfrps severely deteriorate at high temperatures. therefore, in terms of fire resistance, the nsm technique has a significant defect. thus, it is very important to develop a set of efficient fire protection systems to overcome these disadvantages. this paper presents a numerical study that investigates the fire behavior of thermally insulated rc beams flexurally strengthened with nsm-cfrp strips and subjected to fire exposure according to the iso 834 standard. the numerical study considered three-dimensional finite element models in the abaqus software that have been developed to simulate and predict the performance (thermal and structural response) of fire endurance tests on strengthened, uninsulated strengthened, and thermally insulated beams strengthened with nsm-cfrp strips, which were exposed to fire and had different fire insulation schemes. the insulation used was plaster from local material with a thickness range of 25 to 50mm. the variation of the thermal and mechanical properties with the temperature of the constituent materials was considered. all beams' mechanical and thermal responses were adequately simulated using numerical models. the results of the numerical simulations were in good agreement with the experimental data. the fire behavior of the nsm-cfrp strengthened rc beams was examined and particularly the efficiency of the nsm strengthening system during the fire. the behavior in the fire of the nsm-cfrp strengthening system on the rc beams thermally protected with different fire insulation schemes was assessed. finally, the effectiveness of fire insulation was studied. keywords-near-surface mounted (nsm); carbon fiber reinforced polymer (cfrp); rc beams; fire exposure i. introduction strengthening technologies based on fiber-reinforcedpolymer (frp) composites have recently emerged as a possible alternative to infrastructure issues. frp materials are appealing to civil engineers because of their resistance to electrochemical corrosion, their high ratio of strength to weight, and their fabrication pliability. frp is a modern type of building material made up of resin-saturated fibers (polymeric matrix). frps have high tensile strength, low thermal conductivity, corrosion resistance, residual stress strength, availability in a variety of configurations, lower maintenance costs, ease of installation, and mechanical fixing. since the '90s the frps have seen widespread use in civil constructions [1]. frp materials are highly susceptible to the consequences of high temperatures. at a temperature close to the polymer adhesive matrix's glass transition temperature (��) substantial mechanical and/or bonding degradation can be predicted. this raises the possibility of a sudden and disastrous collapse during a burn. furthermore, the majority of organic polymer matrix products are flammable. also flame spread, smoke production, and toxicity must be considered [2]. near-surface mounted (ndsm) frp reinforcement is used in a growing number of applications. this system is based on the concept of embedding frp reinforcements (e.g. bars or laminates) into grooves created by slotting the concrete members’ surface with an adhesive (organic or inorganic) in the concrete cover of the elements to be strengthened. externally bonded frp reinforcement (ebr frp) has several advantages over the nsm system: (a) it is possible to reduce the needed amount of site installation work. (b) nsm bars can be easily anchored into adjacent members to prevent debonding failures. (c) nsm reinforcement can be pre-stressed more easily. this feature is particularly appealing in the flexural strength. the frp reinforcement in nsm is slitted instead of being externally bonded. this provides additional fire safety opportunities. (g) the nsm system has better bonding properties and protects the frp bars or strips from accidental impact, mechanical damage, fire, and vandalism, due to the concrete cover. the polymer binder in these composites does not have the same fire resistance as the fibers used in frps. as a result, fires damage concrete buildings reinforced with frps. in reality, when compared to the ebr, the nsm technique provides better effectiveness and anchoring capacity because the strengthening material is within the concrete cover [3-9]. corresponding author: hayder a. al-baghdadi engineering, technology & applied science research vol. 11, no. 6, 2021, 7782-7787 7783 www.etasr.com al-baghdadi & sabah: behavior of rc beams strengthened with nsm-cfrp strips subjected to fire … ii. description of the finite element models a. geometry and element types the studied three-dimensional (3d) finite element (fe) models simply support rc beams flexturally strengthened with nsm-cfrp strips. an nsm-cfrp strip strengthened rc beam was modeled as a reference. the geometry, dimensions, and configuration of the beams were identical to the tested specimens. the insulated modeled rc beam is 1850mm in length and has a rectangular cross-section of 225mm and 130mm in depth and width respectively, and a concrete cover of 20mm. two 8mm diameter steel rebars were used to model the top and bottom internal steel reinforcement. the transverse stirrups were identical, made from steel with 8mm diameter and the distance between stirrups kept constant at 60mm. the beam was strengthened with two cfrp strips that have a crosssection of 15mm (width)× 1.2mm (thickness) and a total length of 1450mm was applied on the beams’ grooves according to the nsm technique. the adhesive layer was modeled as a fully bonded model. plaster with a thickness ranging from 25mm to 50mm was used to insulate the three sides and ends of the rc beam as shown in figure 1. it should be noted that an anchorage length of approximately 550mm was determined [10]. two concentrated static loads, spaced 550mm apart, were applied to the beam, giving it a shear span of 500mm. the fe models included unburned and burned beams. the unburned beam comprised of 4 parts. these parts were concrete, longitudinal and stirrup steel reinforcements, the steel rods of loading and the supports, and the cfrp strips. concrete, steel rods of loading, and supports, were modeled with the c3d8r 3d 8-node linear brick solid element with reduced integration (r), whereas steel reinforcement bar and stirrup elements were modeled using the 3-d 2-node truss element t3d2. the cfrp was modeled using the 3d 4-node shell element termed s4r. fig. 1. assemby of the whole insulated and strengthening rc beam parts, fem analysis. for the burned uninsulated beam, concrete was modeled using the 3d 8-node linear heat transfer brick solid element titled dc3d8, while the heat transfer 2-node dc1d2 was the selected link element as the steel reinforcement. the cfrp was modeled using the heat transfer quadrilateral ds4 3d 4-node shell element. for the burned insulated beams, an additional part was modeled: the linear3d 8-node hexahedral heat transfer brick dc3d8 element was selected as the insulation element. the overall brick element mesh is shown in figure 2. fig. 2. meshing for brick elements, fem analysis. b. material properties at ambient temperature concrete was modeled as an elastic and isotropic material. abaqus requires the identification of 2 parameters: modulus of elasticity and poisson's ratio. equation (1) in [11] was used to determine the modulus of elasticity of concrete. a value between 0.15 and 0.2 was used for the poisson's ratio for concrete based on [12]. moreover, to simulate the inelastic behavior of concrete, the concrete damage plasticity model (cdpm) is used. five parameters are required for cdpm to be defined: the dilation angle (ψ), the flow potential eccentricity (e), the ratio of initial equibiaxial compressive yield stress to the initial uniaxial compressive yield stress (��� /���� , the parameter (k) which is used to define the multi-axial behavior of concrete, and the viscosity (µ). �� 4700 ��� (1) table i lists the cdpm parameters adopted in this study. the data for the compressive and tensile behavior of concrete come from the uniaxial compression and uniaxial tension tests in [12]. table i. cdpm parameters adopted in this study specimen description reinforced concrete beams strengthened with cfrp parameters ψ e ���/��� k µ values 40 0.1 1.16 0.667 1e-4 specimen description reinforced concrete beams strengthened with cfrp (loading after burned) parameters ψ e ���/��� k µ values 50 0.1 1.16 0.667 1e-4 the steel reinforcement and stirrups were modeled using an elastic-perfectly plastic material, with modulus of elasticity and poisson's ratio of 200000mpa and 0.3 respectively, which defined the linear isotropic part, while yield stress and plastic strain determine the bilinear isotropic part. steel bearing rods and support rods were modeled as isotropic linear materials. the linear isotropic part is specified by the steel rods' modulus of elasticity and the poisson's ratio, which are 200000mpa and 0.3 for each rod. as facilitation, the cfrp strips were modeled as a linear elastic isotropic brittle material. the poisson’s ratio of 0.3 was assigned to cfrp components at an ambient temperature [13], ��� was 2800mpa, the modulus of elasticity ����� was 160gpa according to the manufacturer’s specifications of sika ® carbodur ® plates. the adhesive was also treated as a linear elastic isotropic brittle material [14]. a plaster made from local materials was used as the fire engineering, technology & applied science research vol. 11, no. 6, 2021, 7782-7787 7784 www.etasr.com al-baghdadi & sabah: behavior of rc beams strengthened with nsm-cfrp strips subjected to fire … insulation system, with a thickness ranging from 25 to 50mm. it was applied on the three surfaces of the beam. the fire insulation system presents variable thickness along the beam’s length, being typically thicker at the anchorage zones of the cfrp strips. the thermal conductivity and the specific heat capacity of the plaster at room temperature are λ = 0.15w/(m.k), and �� = 1000j/(kg.k) respectively [15]. c. temperature-dependent material properties due to the considerable effect of temperature on the structural and thermal response of the cfrp-strengthened rc beams subjected to fire, the dependency of all material properties on temperature was taken into account in the models. the variation of concrete specific heat capacity, density, and thermal conductivity with temperature was provided in [15]. the concrete’s density is taken to have a constant value of 2400kg/m 3 , and a constant emissivity value of 0.7 was considered. classical concrete was adopted in simulations. the mechanical properties of concrete at room temperature were: average cylinders’ compressive strength: ��� =21mpa, maximum tensile strength: ��� � =1.512mpa, and average modulus of elasticity: ��=21538mpa. it was assumed that the reduction of these properties with temperature would follow the relationships indicated in [16]. the reduction with temperature of reinforcement steel mechanical properties suggested in [15] was included in the present models. the steel's density was taken as 7800kg/m 3 . the variation of the thermal properties of cfrp strips with temperature was determined by the data provided by [17]. according to [18], a constant with temperature cfrp emissivity of 0.7 was assumed. the cfrp bonding adhesive was modeled as a fully bonded model. the variation of the plaster properties with temperature was considered as reported in [16]. the variation of the plaster density and specific heat with temperature was determined according to [16] and a constant with temperature emissivity value of 0.7 was considered. the mechanical contribution of the fire protection schemes is expected to be negligible, consequently, it was not considered. iii. thermal and structural boundary conditions a. temperature-dependent material properties 1) thermal boundaries to closely match the environments occurring during fire, the bottom face and the two lateral faces of the beams’ models were directly exposed to fire according to the heating rate of iso 834 standard fire curve. figure 3 shows the thermal applied loads on the models, which represent the furnace temperature measured at the fire test, whereas the top face was submitted to the temperature of the air above the top face of the beam. the lateral faces were thermally insulated during the tests. the boundary conditions correspond to the thermal exposure of beams (adopted in the tests). radiation and convection heat transfer modes were considered on top, bottom, and the two lateral faces, a convection coefficient ���) of 25w/m 2 °c (constant with temperature) was adopted, as suggested in [16]. the initial temperatures of the models were defined according to the recorded data of the beams test ranging between 10 and 20°c. fig. 3. thermal applied loads on bshp-25 and bshp-50 beams’ models. 2) structural boundaries the beams were subjected to a mechanical load applied in a 4-point bending configuration. simply supported boundary conditions were assigned to the beam-ends. these supports were simulated by elastic supports. one support provided restraint to both vertical and longitudinal displacements (directions y and z), while it permitted rotations around the (xaxis), (pinned support). the second support provided restraint to only vertical displacements, (direction y) while still enabling longitudinal displacements and rotations about the x-plane axis, (roller support). these supports were initially applied on concrete beams subjected to concentrated load. an identical simplification was adopted for the applied load, each rod has equal to (1/2) of the actual applied load (p). for all beams, the same increment of the experimentally applied load was adopted. it is worth pointing out that the beams’ self-weight was not considered. iv. results and discussion several comparisons between the numerical and the experimental findings are presented. these comprise the effect of elevated temperature, load-deflection relation under the applied load of the references, and post-fire reinforced beams. the temperature of the nsm-cfrp strengthened rc beams subjected to fire exposure was recorded at the opposite anchorage zone (thermocouples t1 and t2) and the mid-span section (thermocouple t3). a. thermal response (temperature vs duration of fire exposure) the comparison of the predicted (numerical) and recorded (experimental) temperatures as a function of the duration of fire exposure at various places are shown in figures 4-6. for the uninsulated beam, it was noted that the fe model underestimated the temperatures along the central zone of the bonded interface. the differences are most likely due to the high difficulty of simulating the behavior of nsm-cfrpstrengthened rc members in fire (because of the thermal gradient that exists along the depth of the slits causing nonuniform thermal deterioration throughout its depth) and because the effect of concrete spalling on heat transfer indepth, which was not considered by the models. for the insulated beams, it was also found that the numerical model underestimated the temperatures along the center zone of the bonded interface. these variations are most likely the result of engineering, technology & applied science research vol. 11, no. 6, 2021, 7782-7787 7785 www.etasr.com al-baghdadi & sabah: behavior of rc beams strengthened with nsm-cfrp strips subjected to fire … modeling without taking into account the impacts of plaster cracks and fall-off (which were seen in the experimental fire test) in simulations due to their high complexity. falling off is an outcome of the formation of diverse discrete cracks in the gypsum. gypsum fall-off in fire strongly influences the fire resistance of the insulated beams. however, modeling this phenomenon is exceedingly complex, and no scientific effort has yet been published that uses numerical methods to solve this problem [15]. fig. 4. comparison of temperatures recorded at various locations of the bsh beam. fig. 5. comparison of temperatures recorded at various locations of the bshp-25 beam. in comparison to their experimental counterparts, the predicted time-temperature curves show a more uniform temperature rise. the predicted temperature curves did not show any plateau (such as those recorded on the timetemperature curves in actual tests). this means that the influence of moisture content was not entirely captured by the thermal characteristics. there are some differences between the measured and the predicted temperatures. this might have occurred because the actual thermal characteristics of concrete and plaster utilized in the beams at increased temperatures differ from those included in the fe models. despite the abovementioned deviations, generally all models gave a satisfying accuracy of the temperature development in the respective beams, demonstrating the fe models' capacity to correctly predict the thermal behavior of uninsulated and insulated nsm-cfrp beams exposed to fire. the comparison of the time the epoxy adhesive required to reach t is listed in table ii and shown in figures 7 and 8. fig. 6. comparison of temperatures recorded at various locations of the bshp-50 beam. table ii. required time comparison for epoxy adhesive to reach tg beam code time required to reach !" of epoxy adhesive (min.) central zone anchorage zones exp. num. exp. num. bsh 3 6 7 7 bshp-25 20 13 21 14 bshp-50 44 26 56 35 fig. 7. comparison of the time required to reach �� of epoxy adhesive at the central zone. fig. 8. comparison of the time required to reach �� of epoxy adhesive at the anchorage zones. engineering, technology & applied science research vol. 11, no. 6, 2021, 7782-7787 7786 www.etasr.com al-baghdadi & sabah: behavior of rc beams strengthened with nsm-cfrp strips subjected to fire … b. structural response (load vs mid-span displacement) figures 9-12 show the measured and predicted mid-span displacement increments of all beams. from the fe analysis result, it can be seen that the models are stiffer than the experimental specimens. some influences may be the cause for higher stiffness in fe analysis results. micro-cracks resulting from the drying shrinkage and curing are found in the concrete during the experiment and after burning and cooling. these would decrease the actual specimens' stiffness. modeling of these micro-cracks hasn't been conducted in fe models. also, the bond between concrete and steel reinforcing or cfrp in the fe analysis is assumed perfect. this assumption is not totally true for real specimens. when bond-slip happens, composite work is lost between concrete and steel reinforcing. therefore, the overall stiffness of the real specimens can be lower than the one expected from fe analysis. fig. 9. comparison of load vs deflection curves for bsr beam. fig. 10. comparison of load vs deflection curves for bsh beam. fig. 11. comparison of load vs deflection curves for bshp-25 beam. fig. 12. comparison of load vs deflection curves for bshp-50 beam. there are differences between the real temperature effects on materials' mechanical properties and those included in the models. all beams' mechanical responses were adequately simulated using numerical models. in terms of load versus deflection curves, strength, and stiffness, the results of numerical simulations were in good agreement with the experimental data. table iii lists the ultimate load and deflection, as found in fe analysis and the experimental work for all specimens under static test. all failure loads obtained from fe analysis (except bsr and bshp-50) show an overestimation of the real experimental values. table iii. comparison between the numerical and experimental ultimate load and deflection of the tested specimens beam code ultimate load(kn) ultimate deflection (kn) exp. num. exp. num. bsr 73.72 70.46 16.21 16.75 bsh 53.71 54.37 16.68 17.79 bshp-25 57.73 59.85 14.25 15.59 bshp-50 68.82 65.16 16.81 17.32 v. conclusion the conclusions from the findings of the current study can be summarized as: • the numerical models were able to estimate the thermal behavior of the insulated rc beams that strengthened nsm-cfrp that were exposed to fire adequately. in addition, the flextural responses of the fe models for all beams were in good agreement with the experimental findings. • the structural performance of reference beams, uninsulated and insulated nsm cfrp-strengthened rc beams subjected to static load after being exposed to fire according to the standard fire curve was adequately predicted. • from the fe analysis result, it can be seen that the models are stiffer than the experimental specimens. • the numerical results indicate that using thicker insulation in the cfrp anchoring zones (applied using nsm methods) reduced the required time the adhesive temperature needs to reach glass transmission temperature ��. engineering, technology & applied science research vol. 11, no. 6, 2021, 7782-7787 7787 www.etasr.com al-baghdadi & sabah: behavior of rc beams strengthened with nsm-cfrp strips subjected to fire … • the predicted time-temperature curves show a uniform temperature rise, while the predicted temperature curves did not show any plateau (such as those recorded on the timetemperature curves in actual tests). this shows that the influence of moisture content is not entirely captured by the thermal characteristics. • the numerical models underestimated the temperatures along the center zone of the bonded interface. these variations are most likely the result of modeling without taking into account the impacts of plaster cracks and fall-off (which were seen in the experimental fire test) in simulations due to their higher complexity. acknowledgments the authors would like to express their gratitude to the staff of the civil engineering department of the university of baghdad for their scientific and professional help. the authors would also like to thank the staff of the civil engineering department's structural laboratory of the university of baghdad for their support. references [1] n. t. k. al-saadi, a. mohammed, r. al-mahaidi, and j. sanjayan, "a state-of-the-art review: near-surface mounted frp composites for reinforced concrete structures," construction and building materials, vol. 209, pp. 748–769, jun. 2019, https://doi.org/10.1016/j.conbuildmat. 2019.03.121. [2] v. k. r. kodur, l. a. bisby, and m. f. green, "preliminary guidance for the design of frp-strengthened concrete members exposed to fire," journal of fire protection engineering, vol. 17, no. 1, pp. 5–26, feb. 2007, https://doi.org/10.1177/1042391507061956. [3] r. el-hach, s. rizkalla, and r. kotynia, "modelling of reinforced concrete flexural members strengthened with near-surface mounted frp reinforcement," in 7th int. symp. on fiber reinforced polymer (frp) reinforcement for concrete structures, jan. 2005, pp. 1681– 1700. [4] j. a. o. barros, s. j. e. dias, and j. l. t. lima, "efficacy of cfrpbased techniques for the flexural and shear strengthening of concrete beams," cement and concrete composites, vol. 29, no. 3, pp. 203–217, mar. 2007, https://doi.org/10.1016/j.cemconcomp.2006.09.001. [5] r. seracino, n. m. jones, m. s. ali, m. w. page, and d. j. oehlers, "bond strength of near-surface mounted frp strip-to-concrete joints," journal of composites for construction, vol. 11, no. 4, pp. 401–409, aug. 2007, https://doi.org/10.1061/(asce)1090-0268(2007)11: 4(401). [6] l. de lorenzis and j. g. teng, "near-surface mounted frp reinforcement: an emerging technique for strengthening structures," composites part b: engineering, vol. 38, no. 2, pp. 119–143, mar. 2007, https://doi.org/10.1016/j.compositesb.2006.08.003. [7] m. a. j. hassan and a. f. izzet, "experimental and numerical comparison of reinforced concrete gable roof beams with openings of different configurations," engineering, technology & applied science research, vol. 9, no. 6, pp. 5066–5073, dec. 2019, https://doi.org/10.48084/etasr.3188. [8] h. m. hekmet and a. f. izzet, "numerical analysis of segmental post tensioned concrete beams exposed to high fire temperature," engineering, technology & applied science research, vol. 9, no. 5, pp. 4759–4768, oct. 2019, https://doi.org/10.48084/etasr.3059. [9] a. h. buller, m. oad, b. a. memon, and s. sohu, "24-hour fire produced effect on reinforced recycled aggregates concrete beams," engineering, technology & applied science research, vol. 9, no. 3, pp. 4213–4217, jun. 2019, https://doi.org/10.48084/etasr.2764. [10] aci-committee-440.2r-17, aci prc-440.2-17: guide for the design and construction of externally bonded frp systems for strengthening concrete structures. west conshohocken, pa, usa: aci, 2017. [11] aci-committee-318-19, aci 318-19: building code requirements for structural concrete. west conshohocken, pa, usa: aci, 2019. [12] y. dere, "nonlinear fe modeling of reinforced concrete," international journal of structural and civil engineering research, vol. 6, no. 1, pp. 71–74, 2017, https://doi.org/10.18178/ijscer.6.1.71-74. [13] j. p. firmo and j. r. correia, "fire behaviour of thermally insulated rc beams strengthened with ebr-cfrp strips: experimental study," composite structures, vol. 122, pp. 144–154, apr. 2015, https://doi.org/10.1016/j.compstruct.2014.11.063. [14] z. s., "behaviour, and modelling of rc beams strengthened in flexure with near-surface mounted frp strips," ph.d. dissertation, hong kong polytechnic university, hong kong, china, 2012. [15] i. rahmanian, "thermal and mechanical properties of gypsum boards and their influences on fire resistance of gypsum board based systems," ph.d. dissertation, university of manchester, manchester, uk, 2011. [16] une en 1992-1-2:2011/a1:2021 eurocode 2: design of concrete structures part 1-2: general rules structural fire design. 1992. [17] c. a. griffis, r. a. masumura, and c. i. chang, "thermal response of graphite epoxy composite subjected to rapid heating," journal of composite materials, vol. 15, no. 5, pp. 427–442, sep. 1981, https://doi.org/10.1177/002199838101500503. [18] j. r. miller and p. m. weaver, "temperature profiles in composite plates subject to time-dependent complex boundary conditions," composite structures, vol. 59, no. 2, pp. 267–278, feb. 2003, https://doi.org/10.1016/s0263-8223(02)00054-5. microsoft word etasr_v12_n1_pp8217-8222 engineering, technology & applied science research vol. 12, no. 1, 2022, 8217-8222 8217 www.etasr.com lipej: challenges in the numerical analysis of centrifugal pumps challenges in the numerical analysis of centrifugal pumps energetic, cavitation, and dynamic characteristics andrej lipej faculty of mechanical engineering university of novo mesto novo mesto, slovenia andrej.lipej@fs-unm.si abstract-pumps are energetic devices that are present in a wide range of industries. their installed power varies from a few tens of watts up to hundreds of megawatts. as the energy consumption is connected with global warming and climate change, the development of pumps that have good characteristics is very important. theoretical and experimental methods have long been utilized in the development of pumps, but recently much research has been carried out with the help of computational fluid dynamics (cfd) analysis. certain numerical analyses can be of high quality and accurate, but special operational phenomena still occur, where special attention is required when performing analysis. this category includes operating regimes outside the best efficiency point (bep), the formation of inlet recirculation, cavitation, and the influence of wall roughness on all the above characteristics. the current paper presents the main problems that developers face when numerically analyzing the above-mentioned special operating regimes. both numerical and experimental results are considered. keywords-pump; computational fluid dynamics; operation characteristics; cavitation i. introduction pumps are used in all branches of industry. depending on the different requirements for the basic characteristics of the head (h) and the flow rate (q), piston pumps [1] or centrifugal pumps [2] are used. centrifugal pumps are developed to operate at a calculation point, but in reality, they operate over a wider range. the service life of a pump and the probability of various damages depend on its operating range [2]. pumps have a theoretically defined recommended operating range, but it is not always feasible for this condition to be met. from the efficiency point of view, the pump is recommended to operate most of the time near the best efficiency point (bep). for accurate knowledge of the kinematics of the flow conditions in the pumps, the best option is to use computational fluid dynamics (cfd). the use of numerical methods is an indispensable tool for the development of pumps. numerical simulations of flow conditions are more or less accurate, depending on the operating range. at the same time, high accuracy of calculations and analysis of various characteristics in the widest possible range of operation must be achieved during the development. stationary calculations are sufficient for some characteristics, but in some special cases, it is necessary to use non-stationary calculations. the current article aims to present various problems that arise when using numerical methods in the development phase of centrifugal pumps and reversible pump turbines. the problems are mainly related to instabilities in pump operation and numerical instabilities. comparisons between the measured results and the cfd analysis results are needed to better understand the problems and validate non-standard numerical procedures. the results of model measurements for most presented cases in the paper were done based on international standards [3]. in some cases, it was necessary to analyze specific properties that are rarely discussed in the literature. one such example is the consideration of wall roughness, which may be due to different influences in the operation of the pumps [4]. to the best of our knowledge, there is no literature relevant to the link between roughness and the use of a suitable turbulent model with a proper computational grid. in such cases, certain studies need to be performed for fairly fundamental properties, such as boundary layer flow analysis [5]. the influence of wall roughness on pump operation is presented in [6]. the research in the paper was focused on issues where it is necessary to perform non-usual procedures in numerical simulations. the first example is related to the instability of h (q) characteristics of different types of pumps. the stability of pump characteristic is the most important and complex design criterion. some research has already been done in this area. a detailed description of the numerical simulation of a reversible pump turbine in pump mode is presented in [7]. a similar topic is addressed in [8], where more focus is given on the analysis of guide vanes geometry. there have been quite a few articles dealing with experimental research [9]. another example is associated with unstable operation as a consequence of inlet recirculation. a numerical simulation of the causes and consequences of inlet recirculation is presented in [10]. inlet recirculation has various consequences, including cavitation [11] and rotating stall [12], which can occur regardless of favorable standard cavitation characteristics. input recirculation analysis in most cases requires the selection of a suitable turbulent model for nonstationary calculations, which is presented in [13]. corresponding author: andrej lipej engineering, technology & applied science research vol. 12, no. 1, 2022, 8217-8222 8218 www.etasr.com lipej: challenges in the numerical analysis of centrifugal pumps the numerical analysis results presented in this paper are the result of the author's many years of research in the field of centrifugal pump development. ii. instability of pump characteristics centrifugal pumps operate under different operating conditions, depending on the magnitude of the flow q and the head h. the relationship of the two variables is given by a function known as the h-q characteristic. theoretically, this function decreases with increasing flow. the shape of the function is influenced by many operating parameters, so it is not trivial to identify possible instabilities in the operation of the pump. by measurements on the model or prototype, it is possible to determine very precisely the shape of the above characteristic, but without detailed measurements of the kinematics, it is not possible to determine the possible causes of unstable areas during pump operation. by using cfd it is possible to determine the exact characteristic and also predict the causes for the formation of the so-called unstable regions in the h-q characteristic. since the flow conditions in the pumps are very demanding, mainly due to the diffuser effect in the fluid flow through the impeller, it is necessary to be very careful when preparing computational grids, choosing a turbulent model, determining boundary conditions, and deciding on stationary or nonstationary analysis. all numerical analyses are based on the solution of reynolds-averaged navier-stokes system of equations, i.e. continuity equation and momentum equation. since a region of instability in the h-q characteristic occurs in areas where the flows are smaller than the qbep, the flow conditions in this region are associated with several different causes of instability. the inlet angles and consequently the velocity triangles at the inlet to the pump indicate a mismatch of kinematic and geometric angles, which affects the flow conditions inside the impeller and also in the area in front of the impeller. fig. 1. axial velocity component at the inlet of the impeller. in the front of the impeller, the so-called inlet recirculation can occur, which continues downstream through the runner. the recirculation area can be detected accurately enough if quality computational grids are used. a sufficiently dense computational grid must be considered, one that provides orthogonality and all recommendations regarding the individual relationships between sides within elements and regarding the size of the adjacent elements. since the above phenomena are always associated with temporal changes, it is necessary to determine whether the stationary calculation is sufficiently accurate or whether a much more time-consuming non-stationary calculation needs to be used. in the presented case, it was found that stationary calculations are not the most appropriate, because they cannot describe all the effects of operating conditions on flow conditions. cavitation and inlet recirculation of the centrifugal pumps have a significant impact on the operation and the service life of the pump. partial flow recirculation directly affects the reliability of the pump and limits the operating range. damage to the pressure side of the inlet blade rotor due to cavitation due to recirculation may occur. the hydraulic design of the pump should prevent many of the negative effects of cavitation due to recirculation in the pumps. the basic criterion for free-range recirculation is the suction specific speed (ss) of the pump. fig. 2. hump zone analysis. measurement, steady and unsteady state simulation results. figure 2 shows the measurement and numerical analysis results in the case where the pump characteristic has a welldefined area of instability. the results of numerical analysis differ considerably if we perform a stationary or nonstationary calculation. a comparison of the results shows that in this case, it is very important to use a non-stationary calculation that predicts the characteristics of the pump with sufficient accuracy, which is also confirmed by the comparison with the measurement results. in the case of efficiency analysis, there are no such pronounced differences between stationary and non-stationary calculations, but a slightly better result can still be observed compared to the measurement results if a nonstationary calculation is used (figure 3). since the numerical and experimental results agree quite well in stationary calculations, such results can mislead us and it is possible to obtain a bad result for the h(q) characteristic. if the kinematics of the flow at the inlet to the impeller is monitored in parallel, it can be roughly determined when non-stationary calculations should be started. the turbulent model k-ω sst is recommended for stationary calculations and the scale-adaptive simulation (sas-sst) for non-stationary analysis. engineering, technology & applied science research vol. 12, no. 1, 2022, 8217-8222 8219 www.etasr.com lipej: challenges in the numerical analysis of centrifugal pumps fig. 3. efficiency comparison. iii. numerical instability the numerical simulations according to different operating conditions can basically be divided into 3 main areas. the first area is near the bep. the two others are at part load and at full load. large differences can be observed between these 3 results if continuous monitoring of the efficiency convergence during the calculation is running. due to the favorable flow conditions at the impeller inlet, the convergence is very stable in the optimal mode, which can be seen well in the upper curve in figure 4. the other 2 curves represent the operating range at partial and at maximum flows. at partial flows, a small fluctuation in the efficiency of about 2% is observed and at maximum flows the instability of convergence is more than ± 15%. in particular, this must be taken into account when it is necessary to accurately predict numerically the efficiency characteristic in the wider operating range of the pump. by simultaneously monitoring the convergence of different variables, it can be determined when it is necessary to use nonstationary instead of stationary calculation. in any case, this is not always the same for all types and specific rotating pump speeds, so continuous monitoring can greatly simplify and shorten the development time of a new pump. from these results, it can be concluded that standard convergence monitoring with residual monitoring can lead to erroneous conclusions. therefore, it is advisable to always monitor the convergence of individual variables that are important for the calculation. fig. 4. efficiency comparison. iv. inlet recirculation in pumps inlet recirculation (figure 5) in the pumps can cause many side effects with harmful consequences such as vibration, noise, and erosion damage. the probability of damage depends on the specific rotational speed, cavitation characteristics, and the suction energy level at the inlet. fig. 5. inlet recirculation. fig. 6. npsh characteristics of pump with safe range of operation. by improving the characteristics associated with the inlet recirculation, the area where the pump operates without the risk of cavitation is increased. the maximum flow that determines non-cavitation operation is determined where the npsha and npshr curves intersect. however, by reducing the inlet vortices, it can be determined what the minimum flow must be such that there is no danger of cavitation due to the inlet recirculation. the results of the safe area of the pump, in which there will be no cavitation are presented in figure 6. with the optimized geometry, in the case shown above, the npsh characteristic is slightly worse, but the area at part load is significantly increased. the flow conditions at the inlet vary greatly depending on the operating regime of the pump. figure 7 shows two situations without and with inlet recirculation. under unfavorable conditions at the inlet, this is also transferred to the space between impeller blades, where various vortices are observed (figure 8). a novelty in the numerical analysis of the inlet recirculation is the cognition that in terms of cavitation engineering, technology & applied science research vol. 12, no. 1, 2022, 8217-8222 8220 www.etasr.com lipej: challenges in the numerical analysis of centrifugal pumps characteristics it is not enough to analyze the npsh parameters but the parameters related to the inlet recirculation must be also considered. only in this way it is possible to obtain a correct assumption about the interval of the operating area without cavitation. fig. 7. flow conditions in front of impeller – without (left) and with inlet recirculation (right). fig. 8. flow inside the impeller – vortices. v. wall roughness the pumps are made of different materials and with different technological processes. as a result, wetted surfaces have different roughness values. in most cases, this fact does not greatly affect the performance characteristics, but there are cases where the surface roughness of the rotor blades can affect the performance characteristics. since numerical flow analysis (cfd) has been widely used in the development of pumps in recent times, it is necessary to determine how accurately it is possible to numerically analyze the influence of wall roughness on the energy and cavitation characteristics of pumps. the first step in the numerical analysis of the flow along rough surfaces is to determine which turbulent model enables satisfactory results and how the characteristics of the computational grids affect these results (figure 9). figure 9 shows the difference between the theoretical and the numerical results when using different sizes of the non-dimensional parameter y + . it is known that the influence of roughness is closely related to the modeling of the fluid in the boundary layer and therefore such a preliminary analysis is very welcome. from the obtained results, it was seen that the values of y+ significantly influence the final calculation results. to analyze the use of appropriate parameters of computational grids, a numerical analysis of 2 simple examples was performed, where it was possible to compare the numerical with the theoretical results. the need to consider roughness in numerical simulations can be seen in figure 10, where a comparison of numerical and experimental results for two smooth and rough walls is shown. these findings were used in the analysis of various pumps, where it was confirmed that even with numerical analyzes, where surface roughness is considered, it is possible to obtain useful results in the analysis of energy and cavitation characteristics. fig. 9. influence of y + on the numerical analysis accuracy. fig. 10. comparison of numerical and experimental results – smooth walls and rough walls. in numerical analysis, the so-called sand grain equivalent should be considered instead of the classical roughness data. another problem is the appropriate definition of computational networks in the roughness range. for the appropriate selection of the y+ parameter, a method based on a comparison with the theoretical results was presented, which differs from the classical comparison between measurements and numerical analysis. engineering, technology & applied science research vol. 12, no. 1, 2022, 8217-8222 8221 www.etasr.com lipej: challenges in the numerical analysis of centrifugal pumps vi. cavitation cavitation is a physical phenomenon that occurs during the operation of various energy and working machines. this can be a particular problem with centrifugal pumps, as cavitation characteristics are very important when choosing a suitable machine in a particular system. since cavitation also affects many other characteristics, such as operation stability, maintenance costs, and the service life of pumps, it is necessary to pay close attention to this phenomenon during the development of new machines. as engineers increasingly use cfd analysis, it is necessary to know the main pitfalls that arise in the numerical predictions of all the operating characteristics of centrifugal pumps. qualitative numerical prediction of cavitation is performed almost routinely, which means that numerical simulations can predict the position, the size of the area, and the intensity of cavitation, but it is not always possible to accurately obtain quantitative results of certain characteristics as a result of cavitation. determining the critical cavitation coefficient can be an even more challenging task. figures 11 and 12 show the location and intensity of the cavitation cloud, for two different values of suction height. it can be observed that the sizes of the steam clouds vary, as at higher suction heights (figure 12) the risk of cavitation formation is higher. in both images, it can also be observed that the cavitation intensity varies from individual impeller blades, although the geometry of the blades is identical. fig. 11. cavitation inside the impeller – low suction head. this means that there are no uniform conditions at the pump inlet or that the situation changes greatly over time. the consequence of the above-mentioned observations is the fact that it is not always possible to obtain concretely useful results using stationary calculations, but we have to use non-stationary calculations. these require significantly longer computational times, thus extending the entire development cycle. the influence of wall roughness on cavitation characteristics was also considered during the research. when predicting the efficiency by considering roughness, the obtained numerical results were quite satisfactory. a larger problem arises in the numerical simulation of cavitation considering the roughness of the walls. figure 13 shows the results of numerical analysis of cavitation at 3 different suction heights for smooth and rough walls. fig. 12. cavitation inside the impeller – high suction head. fig. 13. influence of roughness on the cavitation intensity – smooth wall (top), rough wall (bottom). fig. 14. comparison of npsh characteristics for two different roughness – numerical analysis and experimental results. in the case of rough walls, a slightly larger size of the cavitation cloud is observed, which is not observed in all similar situations. in some cases, the ground plan size of the cloud remained the same or even decreased, but the thickness of the cavitation cloud increased. in the figure, the color scale indicates the thickness of the cavitation cloud. roughness also engineering, technology & applied science research vol. 12, no. 1, 2022, 8217-8222 8222 www.etasr.com lipej: challenges in the numerical analysis of centrifugal pumps affects the npsh characteristic. figure 14 shows a comparison between the measurement results and the numerical results. the absolute results do not match very well, but the right trends of considering roughness in the numerical calculations are observed on the graph. in linking cavitation and roughness, it was found that it is important to consider the thickness of the cavitation area and not only the size of the cavitation clouds. vii. conclusion the pump is one of the most important working machines in the industry. pumps are major energy consumers and therefore special attention needs to be paid to their development phase. the pumps should operate to as high as possible efficiency without significant energy losses. they must also operate reliably with the lowest possible operating cost and their service life must be reasonably long. as numerical methods are increasingly used in the development of pumps, development engineers are facing various problems. the current article presents some of the problems that arise in the development phase when cfd analysis is used in the design. for accurate instability analysis in pump characteristics, it is recommended to analyze the kinematics of the flow at the pump inlet. when the first input vortices are observed, nonstationary calculations must be used. the k-ω sst turbulent model is recommended for stationary calculations and the sas-sst for non-stationary analysis. where operating conditions are far from optimum, numerical instabilities occur. it can be concluded that standard convergence monitoring with residual monitoring cannot lead to the right conclusions. therefore, it is recommended to monitor the convergence of several variables that are important for the qualitative result in numerical analysis. the often-overlooked consideration of wall roughness in numerical calculations has proven to be an important factor to consider at the development stage if the properties of the materials and the surface treatment technology are known. detailed analysis revealed which computational grids are suitable for the numerical simulation of rough surfaces. instead of the classical roughness parameters, the so-called sand grain equivalent should be considered in cfd analysis. for the appropriate selection of the y+ parameter, a method based on the comparison with the theoretical results should be used, which differs from the classical comparison between the experimental and the numerical results. the results show that the roughness affects the efficiency and the npsh characteristics of the pumps. the surface roughness increases the wall shear stress in the turbulent boundary layer. sometimes the numerical results match very well with the experimental ones but in many cases the difference is still relatively big. the comparison of the numerical and experimental results shows a slight improvement of the results if wall roughness is considered. in linking cavitation and roughness, it was found that it is important to consider the thickness of the cavitation area and not only the size of the cavitation clouds. in fact, all the above phenomena are intertwined and interdependent, so in most cases, consideration and analysis of all the physical phenomena presented in the article should be done during the development phase of a new centrifugal pump. by presenting the results of individual numerical analyses and some recommendations on how to perform them most optimally, we are far from covering all the problems that arise in numerical analysis of centrifugal pumps. however, it can be concluded that any contribution that enables development engineers to work more successfully in the development process is very welcome. references [1] m. elashmawy, "3d-cfd simulation of confined cross-flow injection process using single piston pump," engineering, technology & applied science research, vol. 7, no. 6, pp. 2308–2312, dec. 2017, https://doi.org/10.48084/etasr.1561. [2] d. florjančič, trouble-shooting: handbook for centrifugal pumps : sources, diagnoses, recommendations. ljubljana, slovenia: turboinštitut, 2008. [3] iec 60193 hydraulic turbines, storage pumps and pump-turbines – model acceptance tests. iec, 2009. [4] f. b. mainier, a. m. coelho, and e. f. barros, "corrosivity evaluation of copper-nickel alloy (90/10) in pumps used in offshore platforms for seawater pumping," engineering, technology & applied science research, vol. 9, no. 5, pp. 4636–4639, oct. 2019, https://doi.org/10.48084/etasr.3016. [5] f. b. mainier, a. m. coelho, and e. f. barros, "velocity boundary layer analysis of a flat plate heat exchanger in laminar flow: a case study," engineering, technology & applied science research, vol. 2, no. 6, pp. 310-314, dec. 2012, https://doi.org/10.48084/etasr.251. [6] a. lipej, s. muhič, and d. mitruševski, "wall roughness influence on the efficiency characteristics of centrifugal pump," journal of mechanical engineering, vol. 63, no. 9, pp. 529–536, 2017, https://doi.org/10.5545/sv-jme.2017.4526. [7] u. ješe, "numerical study of pump-turbine instabilities: pumping mode off design conditions," ph.d. dissertation, université grenoble alpes, grenoble, france, 2015. [8] j. jia, j. f. zhang, y. f. qu, h. k. cai, and s. b. chen, "study on hump characteristics of pump turbine with different guide vane exit angles," iop conference series: earth and environmental science, vol. 240, mar. 2019, art. no. 072038, https://doi.org/10.1088/17551315/240/7/072038. [9] j. yang, g. pavesi, s. yuan, g. cavazzini, and g. ardizzon, "experimental characterization of a pump–turbine in pump mode at hump instability region," journal of fluids engineering, vol. 137, no. 5, may 2015, https://doi.org/10.1115/1.4029572. [10] a. lipej and d. mitrusevski, "numerical prediction of inlet recirculation in pumps," international journal of fluid machinery and systems, vol. 9, no. 3, pp. 277–286, sep. 2016, https://doi.org/10.5293/ijfms.2016.9.3.277. [11] p. limbach, t. müller, m. blume, and r. skoda, "numerical and experimental investigation of the cavitating flow in a low specific speed centrifugal pump and assessment of the influence of surface roughness on head prediction," presented at the international symposium on transport phenomena and dynamics of rotating machinery, honolulu, hi, usa, apr. 2016. [12] j. vesely, l. pulpitel, and p. troubil, "model research of rotating stall on pump-turbines," presented at the hydro 2005, villach, austria, 2005. [13] c. wang, y. x. zhang, j. y. zhang, z. w. li, and a. xu, "comparative research on various turbulence closure models for unsteady cavitation flows in the ultra-low specific speed centrifugal pump," iop conference series: earth and environmental science, vol. 240, mar. 2019, art. no. 062038, https://doi.org/10.1088/1755-1315/240/6/062038. engineering, technology & applied science research vol. 8, no. 2, 2018, 2799-2804 2799 www.etasr.com carosso et al.: a new modular control board for pulse-jet cleaning of dust collector filter bags a new modular control board for pulse-jet cleaning of dust collector filter bags lorenzo carosso department of electronics and telecommunications, politecnico di torino, italy lorenzo.carosso@polito.it daniel gaiki department of electronics and telecommunications, politecnico di torino, italy daniel.gki@gmail.com silvano bertoldo department of electronics and telecommunications, politecnico di torino, italy silvano.bertoldo@polito.it marco allegretti department of electronics and telecommunications, politecnico di torino, italy marco.allegretti@polito.it abstract–this work presents a timing system modular control board to be used for pulse-jet cleaning of dust collector filter bags or pneumatic conveying systems. many systems of this kind are already available on the market but only some of them have the ability to operate in full range alternating current power supplies. the presented versatile and innovative control board can control the electro valves, either the ones operating with alternating current and those in direct current (since they are both used in the industrial plants). for the same reason, the designed prototype system can be powered with different voltages, widening the number of potential industrial applications. the electronic board has as main advantage the ability to fully automate the cleaning cycle. it can drive many electro valves simultaneously since it is possible to connect more control boards together if needed. it also allows the user to separate the control section of the system from the section dedicated to the actuation of the electro valves. the electro valves can be controlled from a pc terminal via ethernet. the work describes the adopted solutions and the steps made for the design of the entire prototypal modular board, with particular focus on the innovative timing system. keywords-pulse jet baghouse; pulse jet electro valve; pulse jet cleaning; electro valve actuator; remote monitoring bag house; ac electro valves control; dc electro valves control; prototypal timing system i. introduction surface filter systems are heavily applied in air filtration processes for industrial applications and the use of a bag (filter media) cleaning subsystem by using compressed air jets is widespread as well. the pulse-jet type of dust filter was invented and developed and introduced on the market in the late 1950´s [1]. the basic device patent has expired and there are now many manufacturers of pulse-jet collector type [2]. core business of industries using pulse-jet fabric filtration (pjff) regard power generation, incineration, chemical, steel, cement, food, pharmaceuticals, metal working, aggregates and carbon black [3]. the research group of remote sensing and innovative sensors development of the department of electronics and telecommunications (det) of politecnico di torino, has a great interest in designing new prototypes and new solutions for both academic research purposes and industrial innovative applications. adopted solutions were always realized considering keeping the cost as low as possible for industrial applications. they cover a large range of applications highlighting the multidisciplinary attitude and interests of the research group. during the year some environmental monitoring sensors have been developed such as a microwave radar for rain monitoring [4], sensors and techniques for forest fire monitoring [5, 6] etc. starting from the first multipurpose board realized in 2012 [7], a large number of industrial projects have also been realized. they include a new anti-theft alarm systems for photovoltaic panels [8], a wireless sensor network (wsn) for smart gas metering (which was also documented by the italian patent for utility model no. 0000279556) and more recently rfid tags and readers to be installed on unmanned aerial vehicles (uavs) [9] and sensors for health structure monitoring [10]. exploiting the high expertise of the research group in of sensor board realization, this work presents the realization of a new low cost and versatile solution for modular control board for pulse-jet cleaning of dust collector filter bags. considering the energy costs involved in pressurizing air to clean the filter media, the proper design of an innovative adhoc cleaning system is of high interest. a widely used system for implementing an automatic cleaning of an air-jet dust collector consists of a differential pressure gauge and a programmable controller. the differential pressure gauge measures the pressure difference between the dirty air side and the clean air side of the bag filters in the baghouse: our system is based on this consideration. clean filter systems are called “reverse pulse jet”. in the filter media cleaning subsystem, high pressure gas injections and short duration are used in the reverse direction of the pressure gradient and cause a loosening of the dust layer from the surface of the bag: the dust layer is then collected in the dust tank located at the bottom of the filter housing (see figure 1). such systems work in countercurrent by compressed air jets controlled by solenoid valves, which in turn are activated according to a predefined program [11]. the impulse type and the pause time between two consecutive pulses are programmed with the sequencer, according to a predefined and not modifiable structure. this procedure causes an excessive wear of the sleeve of the filter. the operating principle of the sequencers available on the market is the following: first, the cleaning cycle is activated. the sequencer engineering, technology & applied science research vol. 8, no. 2, 2018, 2799-2804 2800 www.etasr.com carosso et al.: a new modular control board for pulse-jet cleaning of dust collector filter bags detects the first available electro valve and, on the basis of the pre-set working time, the electro valve is opened to recall a specific amount of compressed air required to clean the filter until the completion of a cleaning cycle. then, after a pause interval, the sequencer automatically recalls and opens the following available electro valve to start a new cleaning cycle. fig. 1. lateral view of bag house chamber. therefore, it is not possible to directly check the correct working of the cleaning system or the degree of cleanliness achieved by the filter when a single cleaning cycle is completed (i.e. when a single electrovalve has been activated). since it is not possible to interact directly with the sequencer, the control procedure is performed usually from time to time by means of external instrumentation. based on the obtained results, it is then possible to re-calibrate the time necessary for carrying out a whole cleaning cycle. evidently, the described technique has a set of undesired effects, the most important of them being:  the lack of a real time control of the degree of cleanliness achieved by the air/gas/steam that passes through the single filter. this limitation could be dangerous in the case of treatment of dangerous substances.  the need of a qualified operator to work on the sequencer (even remotely) to adapt the system to the new conditions found during the subsequent checks performed with external instrumentation.  the impossibility to obtain real time reports during the filters’ working operations.  the impossibility to understand in real time the potential causes of malfunctioning. therefore, it is not possible to intervene promptly to avoid more filter damage and even to the complete industrial process. the innovation implemented here concerns a new modular control unit to optimize the cleaning process. specifically, such unit performs multiple tasks:  managing the plurality of voltages input (including ac or dc) from the solenoid valves, thus allowing system adaptation to different industrial processes.  performing the automation of the cleaning cycle. the automatic re-definition of the pulse and pause interval can be obtained according to the cleaning results achieved and measured inside the filters.  the possibility of operation with either fixed or variable cleaning cycle. it is possible to set the “cleaning cycle” operational mode according to the pressure difference between filter input and output (see section ii).  the possibility to correlate the generated pulse and the pause interval to the residual capacity in compressors that are supplying air jets. air shots too long and close to each other air shots can drastically decrease the pressure in input. ii. functional logic description of the system the operations performed by the prototypal system presented in this work can be better illustrated using the scheme represented in figure 2. the baghouse is divided horizontally in four sectors and each one contains four electro valves, represented by the ev# codes, and vertically in two sections: the clean chamber, where the cleaned air comes out of the filters, and the dirty chamber, where the air is introduced to be cleaned. the electro valves are responsible to control a specific air pulse jet for a group of bags that clean the dirty air through the bag cages. fig. 2. baghouse division on 4 sectors. each sector contains 4 electrovalves. depending on the size of the filter, the number of sections and valves may vary. only one electro valve at a time is excited, the wash cycle is completed when all the valves are energized progressively. with this prototypal system, a large set of programmed sequences of electro valve activations is also possible. however, a good rule is to avoid to fire electrovalves placed consecutively. since each cleaning cycle causes a reduction of the filter lifetime, to avoid excessive wear on the filter elements, the washing system must be optimized to act only when necessary. in that case, the electro valve shooting time and the interval between a shot and the next may vary depending on the values measured by the pressure sensor inside the filter chamber. usually, for a single electro valve the time to shoot can vary from 80ms to 140ms. the time interval between two consecutive shots of the same valve may be defined in two ways and depends on whether it chooses a “fixed cycle” or “variable cycle” operational mode, described below. both cycle types can be programmed with the boards realized in this project. evidently, both the shot duration and the interval period must be proportional to the capacity of compressors that provide compressed air: shots too long and close can drastically decrease the air pressure in input, reducing the quality of filtering operation. a. fixed cycle operational mode the “fixed cycle” operational mode sets the number of cycles to be run during a specific time interval. let us assume, engineering, technology & applied science research vol. 8, no. 2, 2018, 2799-2804 2801 www.etasr.com carosso et al.: a new modular control board for pulse-jet cleaning of dust collector filter bags for instance, that a number of 3 washing cycles is needed during one hour. it means that all 16 valves (if the bag filter is made by a set of 16 electro valves) must shoot 3 times in one hour. as a result, the system will calculate the time interval between 2 consecutive shoots as reported in (1): = ∙ ∙ /∙ / (1) where: tinterval [s] is the time interval between two consecutive wash cycles, tshot [s] the time interval between electro valve drives, nvalve the total number of valves and ncycle/hour [cycle/hour] the total number of cycles in one hour. b. variable cycle operational mode with the “variable cycle” operational mode, the shooting range time depends on the difference in pressure (dp) between the “clean chamber” and the “dirty chamber” of the filter, measured through a differential pressure sensor. at first it is necessary to determine the desired dp to be maintained and this value is used as a set-point to trigger a new cleaning cycle. with this information, the system automatically evaluates the time interval between two consecutive shots. of course, if dp is greater than the set-point, the system increases the washing frequency, thus decreasing the time between two consecutive shots. otherwise, if the dp is lower than the set-point, the time between two shots needs to be increased. at specific intervals (usually 30-100 seconds) the system controls the dp and compares it to the set-point; if it is greater than a preset threshold (called “dead band”), the system changes the interval time at a fixed percentage (1%-10%), otherwise it stays unchanged. if the dp is very low and the filter already has a very long interval time (usually limit values are set a priori), the washing cycle can be stopped. it is resumed when dp is greater than a certain threshold. c. general notes usually, the factory set of the pulse frequency can range from a few seconds to a few minutes; this clearly depends on the number of valves and the filter size. the number of valves inside a filter can vary from 10-16 up to 180-200. if the filter is stopped for low dp or low compressed air by the compressors, when it is resumed it must restart from the valve next to the one where it was previously stopped. in this way, all the sleeves of a filter are washed the same number of times. specific sensors can measure the cleaning results inside the filter and according to the programmed settings, a potential re-definition of the pulse and pause interval between consecutive pulses can be automatically obtained. iii. electronic blocks description the system is made by a set of different electronic blocks. their description and their functionalities are presented below, according to the different subsystems of the modular control board for pulse-jet cleaning of dust collector filter bags:  power supply  human machine interface  output and input of the controller board (the subsystem that supervises the whole modular system and can be programmed to automatically re-configure the operational model)  output of the electro valves driver board (the board that directly controls the electro valves activation which is directly linked with the controller board). a scheme of the connection between control board and electro valve output control boards using a serial interface is shown in figure 3. a. power supply industrial pulse jet timer controllers (pjtcs), commonly used for baghouse filters, established that control boards that use a universal alternating current (ac) input in a full range power supply 115/230 vac. these control boards usually have on-board power supplies. it means that whenever there is a problem with the circuit power supply, the entire control board must be replaced and the new control board must be properly reprogrammed. the developed solution aims to separate the different possible problems and to make the solution more flexible and versatile. together with common full ac range power supply, a system that has a 24 v dc power supply is included. it adds robustness to the system and, if failure occurs, the power supply can easily be substituted without need of reprogramming the entire system, giving thus a noteworthy advantage in terms of cost, materials and time saving. b. human-machine interface a large part of timer controller has an interface that operates fully integrated on board without the possibility of sending or receiving data from a remote management system. for instance the cement industry routinely implements human machine interface (hmi) and supervisory control and data acquisition (scada) interfaces for a wide range of processes, maintenance and environmental compliance requirements. these sophisticated systems do not offer the possibility to adapt to specialized systems dedicated to particulate matter (pm) control and associated with advanced baghouse diagnostics. pm and baghouse specific systems are certified with fieldbus ports to communicate with existing plcs and dcs systems to enable seamless integration with most of the existing plant equipment. a common and versatile family of standards and technologies that can be used in innovative electronic boards is the industrial ethernet (ie). it consists on the use of ethernet technologies in an industrial environment with protocols that provide determinism and realtime control (e.g. ethercat, ethernet/ip, profinet, powerlink, sercos iii, cc-link ie, and modbus/tcp [12, 13]). using ie, data collected on the filter bag can be stored and displayed on a dashboard, and by sharing them on a shared platform it is possible to compare them with others collected by other systems. moreover, using devices connected to a network and a centralized interface capable to get data and send commands to all devices, it is possible to control the electro valves using different information acquired by other sensors distributed on the industrial plant. in order to overcome the above difficulties, the proposed control board is equipped with an ie controller, thus giving the board the whole set of described advantages, including the possibility to remotely reprogramming the systems, if needed. engineering, technology & applied science research vol. 8, no. 2, 2018, 2799-2804 2802 www.etasr.com carosso et al.: a new modular control board for pulse-jet cleaning of dust collector filter bags c. outputs of the controller board the control systems available on the market to integrate everything on the same board present several inputs and outputs. it is possible to find boards with 8/16/32 outputs to control solenoid valves. this could be a problem when having in mind to further expand the system. if it is necessary to control more electro valves and if the system has a limited number of outputs, it should be replaced and reprogrammed, leading to extra working time and adjustments. the proposed electronic board is actually a modular system. it is possible to add more output modules to the solenoid valves as needed, without changing the control board, by simply adding new expansion boards in which the actuation drivers are placed. this modularization allows the separation of the actuation modules (also referred to as electro valve driver board) from the control module. when a failure in one of the actuation modules occurs, any of the actuation modules may be substituted without modifying the setup and configurations in the control module. the board control that drives the solenoid valves is controlled by a serial interface. even if the serial communication interface is not a recent one, it allows increasing the number of outputs without compromising many pins of the microcontroller and, at the same time, giving robustness to the system. the serial communication used is then a “synchronous serial communication” where each actuating board of the solenoid valve has a shift register circuit that can trigger sequentially each valve. each shift register circuit has 8 outputs that are used for the control of the electric valves. it is possible to increase the number of outputs by simply linking several registers together. other outputs of the control board are the alarm signals. they can be programmed according to a predefined setup or depending on specific inputs coming from dedicated sensors aiming to trigger the alarm signals. these outputs can be used to give a visual feedback on the system-operating situation or to communicate the presence of a possible problem detected by an external sensor. the alarm output is an optically isolated transistor that can trigger an external device (e.g. acoustic or visual alarm signaling devices). d. input sensors of the controller board a dp sensor is commonly used as input of the timing control board. the developed system is engineered to allow both the input of the dp sensors and the input of a second control based on another sensor that can be chosen according to specific needs of the industrial process. the automation of the system is made according to the input of all those sensors. e. outputs of the electro valve driver board due to the existence of different types of electronic valves in the market, a board with a power interface operating in both dc and ac has been designed, thus increasing the system’s versatility. another possibility given by the present modular system is the use of ac or dc solenoids using the same circuit. considering a large set of electro valves available on the market, it is possible to find electro valves with voltages that range in the interval of 115v-230v ac and 24v dc, which are generally widespread in the industry. two common types of control boards for electro valves are commercially available. they are different on the basis of the circuit used as actuator for the solenoid valves. generally the control boards that control ac electro valves use relay or triac (triode for alternating current). the disadvantage of the circuits using triac is that they work only for ac thus losing the probability to control dc electro valves. in this work, a circuit is proposed that can operate with both ac and dc valves. it uses a bidirectional electronic switch based on mosfets (a type of circuit widely used in solid-state relays). by using this topology is possible to design a robust circuit at low cost (very similar to a simple and standard circuit based on common relays). figure 4 illustrates two bi-directional switches used to control two different electrovalves separately. in this case the signals defined by in1 and in2 are connected in phase with respect to the signal considering ac or at the positive signal in case of dc. the outputs defined by pout1 and pout2 are connected to the returns that feed the solenoid valves. this circuit has the possibility to use both ac and dc without the need to change the power supply modules. through the shunt resistors (represented in figure 4 as shunt 1-4) the electric current that supplies the electro valves can be monitored, thus controlling if some valve is disconnected or damaged. if a short circuit occurs, the activation of a specific electro valve may be canceled and in this case an alarm signal can be generated as output of the modular control board and sent to the system that controls the industrial plant exploiting the ie communication. fig. 3. connection between control board and electro valve output control boards using a serial interface fig. 4. bidirectional switches used to control two separated electro valves. iv. installation the proposed modular electronic board can be integrated with a large number of systems commonly and widely present in a large number of industrial plants. generally, other systems must be installed together with the air filtration system and they already have their own power supplies. on the diagram represented in figure 5 it is possible to note the presence of two engineering, technology & applied science research vol. 8, no. 2, 2018, 2799-2804 2803 www.etasr.com carosso et al.: a new modular control board for pulse-jet cleaning of dust collector filter bags different circuits: the proper control board of the entire system and the board devoted to electro valve controlling (electro valve driver board). it is evident that supplying the circuits directly with the 24v source, if available, could be optional or to supply them with the standard ac provided by the power grid. at the same time, it is possible to activate electro valves of both types, as described above. figure 6 represents an example of realization of a modular installation using the realized boards. the smaller board on top is the control board (figure 7), the other three are the electro valve driver boards (figure 8). it is evident that multiple control boards can be interconnected to each other. fig. 5. wiring diagram of the installation of the boards on the system. fig. 6. example of assembled system with 1 controller board and 3 electrovalves driver boards. fig. 7. the realized control board. fig. 8. picture of the realized driver board. v. conclusion present work presents the prototypal realization of a modular low cost control board for a system for baghouses cleaning. some advantages have been already described in the introduction. however, the improvements introduced by these boards compared to the usual practice are mainly related to their possible integration with already existing commercial systems and to the versatility of the system itself. the same board allows the automation of the cleaning cycle according to measured parameters acquired by dedicated sensors and the possibility of operation with both fixed and variable cleaning cycles. the modular structure of the boards allows users to install them in any desired number without difficult operations of reprogramming the entire systems. the possibility to connect different drive boards together, controlled by a single control board, allows a wide number of drive outputs, widening the number of potential applications. the possibility to automatically reprogram the entire system using the information provided by sensors devoted to check the state and the “health” of the filter to be cleaned is very significant. the configuration and the programming of the control board can be easily made by using a common pc. it is possible to setup the number of valves to be activated and the system can be configure remotely, since the board is equipped with an ie that allows the system itself to be accessible within a company network and even in the world of internet (of course, only for authorized users). for what concerns the electric drive, it is important to highlight that the proposed prototypal board allows using the same drive circuit for different types of electro valves, thanks to its high versatility. references [1] r. e. frey,t. v. reinauer, “new filter rate guide”, air engineering, vol. 30, 1964 [2] e. bakke, “optimizing filtration parameters”, journal of the air pollution control association, vol. 24, no. 12, pp. 1150-1154, 1974 [3] a. k. choudhary, a. mukhopadhyay, “particulates: selection of cleaning pulse pressure for pulse jet fabric filtration”, filtration + separation, vol. 50, no. 4, pp. 28-30, 2013 [4] m. gabella, r. notarpietro, s. bertoldo, a. prato, c. lucianaz, o. rorato, m. allegretti, g. perona, “a network of portable, lowcost, x-band radars”, in: doppler radar observations weather radar, wind profiler, ionospheric radar, and other advanced applications, intech, 2012 [5] a. losso, l. corgnati, s. 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(ed.), industrial communication technology handbook, crc press, 2014 microsoft word etasr_v12_n2_pp8296-8299 engineering, technology & applied science research vol. 12, no. 2, 2022, 8296-8299 8296 www.etasr.com alamri et al.: face recognition and gender detection using sift feature extraction, lbph, and svm face recognition and gender detection using sift feature extraction, lbph, and svm hanaa alamri department of computer science umm al-qura university makkah, saudi arabia s44286207@st.uqu.edu.sa eman alshanbari department of computer science umm al-qura university makkah, saudi arabia s44286515@st.uqu.edu.sa shouq alotaibi department of computer science umm al-qura university makkah, saudi arabia s44286616@st.uqu.edu.sa manal alghamdi college of computer and information systems umm al-qura university makkah, saudi arabia maalghamdi@uqu.edu.sa received: 4 january 2022 | revised: 31 january 2022 | accepted: 4 february 2022 abstract-face recognition and name and gender identification are challenging processes, especially when identifying perpetrators and suspects or when used in authentication systems. machine learning and computer vision technologies are used in many fields, including security, and play an important role in face recognition and gender detection, offering valuable information to officials to rectify a situation in less time. this study used a few machine learning methods in the labelled faces in the wild (lfw) database to examine their facial recognition and gender detection capacities. the lfw dataset was used to train and evaluate the scale invariant feature transform (sift) feature extraction method along with the support vector machine (svm) classifier and the local binary pattern histogram (lbph) method. the result comparison from the current and other studies showed that the proposed lbph method had higher accuracy in face recognition, while its accuracy in gender detection was very close to the ones of other, relevant studies. keywords-face recognition; gender detection; svm; sift; lbph i. introduction face recognition is one of the most important computer vision techniques [1, 2] and is considered a machine learning process. the ability to recognize human faces is complex in many circumstances, while it has been widely applied for personal identification, smart home access systems, and more. gender classification is a hereditary technique to identify a person as male or female. gender recognition is certainly a tough process for computers. current work focuses on facial recognition and gender classification, which is a binary classification [3]. the current paper studies the use of scale invariant feature transform (sift) to extract features from face images and the application of support vector machine (svm) to classify face images and obtain a face recognition model [4]. moreover, the local binary pattern histogram (lbph) [5] feature extraction method was applied to the extracted object to create an intermediate image that describes better the original. ii. related work in [6], a new learning-based encoding method was used to encode the microstructures of a face using unsupervised learning approaches, unlike many previous manually created encoding methods (e.g. lbp or sift). the associate-predict (ap) is a model proposed in [7], built on a separate generic identity dataset that included numerous photos for each identity with a significant intra-personal variation. this study followed strictly the restricted protocol, which included pca learning and svm training. a new supervision objective method named "uniform loss" was presented in [8] to learn deep equidistributed representations for face recognition. most existing methods encourage large interclass distances and small intra-class variations to learn discriminative face features, while the softmax loss function has been also widely applied. throughout the experiments, this study used the mxnet package and resnet as the cnn architecture for all sets. in [9], the widely used sift and surf algorithms were employed, which are widely used in face recognition due to their outstanding ability to handle a wide range of tasks. in [10], a better method was proposed for identifying human faces at various angles, side stances, and tracking during human motion. furthermore, this study presented the lr500 dataset for training and classification and used the architecture of the lbph algorithm. in [11], gender prediction was evaluated from ocular images captured in a mobile environment, using several textural descriptors in combination with svm and multi-layer perceptron (mlp) on a publicly available large-scale visob corresponding author: manal alghamdi engineering, technology & applied science research vol. 12, no. 2, 2022, 8296-8299 8297 www.etasr.com alamri et al.: face recognition and gender detection using sift feature extraction, lbph, and svm dataset captured using mobile devices. the problem of detecting gender from faces in real-world images was studied in [12]. faces from images were extracted, aligned, and represented using the lbph and a face detector. adaboost was used to select discriminative features and the boosted lbp features were applied to train an svm with a recognition rate of 93.29%. the fdrenet for face detection through the histogram of oriented gradients was proposed in [13], using a siamese technique and contrastive loss to train the deep learning architecture embednet. face detection and recognition were performed using viola-jones, pca-lda, and square euclidean distance. svm and knn clustering were also applied in various types of data. a facial recognition application for a biometric system was introduced in [14], based on a convolutional neural network. this study presented a deep learning model structure that can improve current state-of-the-art precision and processing time. this method and the proposed cnn achieved high-accuracy performance. iii. methodology this study applied different algorithms for face recognition and gender detection. at first, the sift feature extraction was used to extract features from face images and then svm was applied to recognize faces. moreover, the lbph algorithm was applied for face recognition. two different algorithms were used for gender detection: svm and lbph. figure 1 shows the steps of the methodology. fig. 1. steps for face recognition and gender prediction using sift, lbph and svm. a. scale invariant feature transform (sift) feature extraction feature extraction is an essential part of a computer vision application that recognizes objects in an image [15]. sift was used to extract features from face images, and then svm was applied to classify the face images and get the face recognition model. sift locates the local features of an image that are not affected by operations like object scaling and rotation, by taking an image as input and converting it into a large group of local feature vectors commonly known as the key points [16]. the extracted features are scale and orientation invariant, and they are highly distinguishing the image. this process includes four steps. the first step detects the maxima and minima of a set of difference of gaussian (dog) filters applied at different scales all over the image to compute the locations of probable interest spots with a total of 26 neighbors for each pixel (key point). the positions are then refined by removing low-contrast points. then, each key point is given an orientation based on local image attributes [17]. finally, a local feature descriptor is computed for each key point. a sift feature extractor was created using the function cv2.feature2d_sift() and then 128 features from the face image were calculated. b. local binary pattern histogram (lbph) the lbph method was proposed in 2006 and is widely used due to its discriminative power and computational simplicity [18]. the lbp histograms from each sub-region are concatenated into a single histogram with spatial advanced characteristics, defined as: ��,� � �� � �, ��,�� � �� ����,������, � � 0,…,� � 1, � � 0,…,� � 1 the lbph method was used to train the face recognition model. an lbph recognizer was created using the function cv2.face.lbphfacerecognizer_create() and trained with the training dataset. after training, the accuracy of the model was tested. c. support vector machine (svm) classifier svms are a collection of supervised learning algorithms for classification and regression that are members of the generalized linear classification family [19]. svm is a binary classification approach that uses the concept of structural risk reduction to identify the best linear decision surface. the decision surface is a weighted mixture of the training set's features [20]. after extracting the features using sift, gridsearchcv was used to find the best parameters in the svm method, and then the svm model was trained for face recognition. d. gender detection this detection model was used on the lfw dataset from the scikit-learn package. at first, the images from the dataset were read to increase the accuracy of the model, and only images of people who had more than five images were used. the svm and the lbph models were used with different datasets. the first step in the implementation was to create two separate lists for males and females, and the second step was to detect the gender: if the output was 0, it was male, while if it was 1, it indicated a female. iv. experiments this section describes the framework setup and the lfw data overview, which includes information on each attribute, feature correlations, and data pre-processing. a. experimental setup all algorithms were executed in a pc having ms windows os and an intel core i7-10510u processor at 1.80ghz. the jupyter notebook is a non-profit open-source software that has grown to support collaborative data science. the python engineering, technology & applied science research vol. 12, no. 2, 2022, 8296-8299 8298 www.etasr.com alamri et al.: face recognition and gender detection using sift feature extraction, lbph, and svm programming language was used to manage and execute the models using jupyter [21]. the numpy libraries offer highperformance, easy-to-use data structures, and data processing resources for python. numpy was used to convert string to numerical values [22]. in addition, scikit-learn, a widely used python-based machine learning library, was used to split the dataset into training and testing [23] sets. as a result, the data were split into 75% for training and 25% for testing. b. data description the labeled faces in the wild (lfw) database was designed to study the problem of unconstrained face recognition [24]. the database contains 13,233 face images collected from the web. each image is labeled with the name of the person. the database contains images of 5749 different people, while 1680 people have two or more images in the database. these images are available in 250×250 pixel jpeg files. most images are in color, although a few are in grayscale. all images are the result of detections using the viola-jones face detector [25]. c. data pre-processing the train-test split is a strategy for testing the output of a machine-learning algorithm and can be used with any supervised learning algorithm for classification or regression problems [26]. the sift feature extractor calculated 128 features from each face image. there were no needless or null images that needed to be removed from the dataset. to increase the accuracy of the face recognition model, a subset of the original dataset, that contains people with more than 70 images, was used. on the other hand, in order to increase the accuracy of the gender detection model, a subset of the original dataset was used containing people with more than 5 images. after pre-processing, the dataset was split into the training (75%) and testing (25%) subsets. v. results and discussion a. experimental results after data-preprocessing, the face recognition and gender detection algorithms were applied: • the sift feature extraction and svm classifier were used in face recognition, achieved 65% accuracy in 1288 samples, extracting 128 features from each face image, and using 7 classes. • the lbph was applied in face recognition, achieving an accuracy of 88%. • svm was applied to detect the gender from the images. the number of samples was 5985, having 2 classes, and the model achieved an accuracy of 82%. • the lbph algorithm was used for gender detection, on the same samples, and achieved an accuracy of 91%. b. comparison with previous works table i shows the result comparison for face recognition and gender detection techniques of the current and previous studies. comparing the acquired results with the ones of previous studies showed that lbph had the highest accuracy of 88% on face recognition, while the same method showed a very close to [12] accuracy (91%) on gender detection. the lack of many images per person in the dataset caused some difficulties during face recognition while using svm, as the method requires a large number of images per person to train. table i. result comparison feature extraction and face recognition paper methodology accuracy% [7] pca 84.45% [8] pca svm 86.83% [9] cnn 79.98% [10] sift 71.1% current study sift svm 65.8% lbph 88% gender detection [12] lbp svm 93.29% current study svm 82.8% lbph 91% vi. conclusion an accurate implementation of facial recognition can recognize human faces for identification or authentication purposes and be utilized in many areas, such as security systems. this study used the lfw dataset to evaluate the use of the sift feature extraction technique with the svm and the lbph method for face recognition and gender detection. the results showed an accuracy of 65% for sift with an svm classifier, while the use of lbph had an accuracy of 88% in face recognition, outperforming previous studies. 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[22] j. reback et al., pandas-dev/pandas: pandas 1.3.4. zenodo, 2021, https://doi.org/10.5281/zenodo.5574486. [23] l. buitinck et al., "api design for machine learning software: experiences from the scikit-learn project," arxiv:1309.0238 [cs], sep. 2013. [24] university of massachusetts, "lfw face database labeled faces in the wild." http://vis-www.cs.umass.edu/lfw/. [25] p. viola and m. j. jones, "robust real-time face detection," international journal of computer vision, vol. 57, no. 2, pp. 137–154, feb. 2004, https://doi.org/10.1023/b:visi.0000013087.49260.fb. [26] j. brownlee, "machine learning mastery," machine learning mastery. https://machinelearningmastery.com/ (accessed feb. 11, 2022). engineering, technology & applied science research vol. 7, no. 5, 2017, 1914-1917 1914 www.etasr.com mozhdegani and afhami: using ecotech architecture as an effective tool for sustainability in …. using ecotech architecture as an effective tool for sustainability in construction industry azam sadat mozhdegani department of architecture islamic azad university kerman branch kerman, iran reza afhami department of architecture islamic azad university kerman branch kerman, iran abstract—ecotech architecture can be used as an effective strategy to minimize energy consumption and enhance the satisfaction of construction industry beneficiaries in the middle east. the use of ecotech principles has been employed in different parts of the world. however, following a universal approach is not possible as local conditions are always to be considered applications and examples of ecotech architecture are investigated in this paper. a proposed building design for the cheetgar region in tehran is also briefly demonstrated. a further insight on masdar city in abhu dabi is provided. an overall discussion is made and key conclusions are drawn. keywords-architecture; ecotech; persian gulf; cheetgar; architectural form; masdar city; energy consumption; environment. i. introduction sustainable strategies are gradually implemented in the construction industry. such a strategy requires the phasing out of conventional technologies and replacing them with sustainable ones, more compatible with the environment [1]. efficient use of water resources is one of the most important approaches to achieve clean architecture and move towards to the principles of ecotech. from one perspective, environmental based design defines the foundation of ecotechonogical architecture. planning to construct buildings with special characteristics in a specific area requires a comprehensive and systemic approach [2]. although these definitions define the scope of environmental management in architecture effectively, it is closely related to equipment and facilities. it is very important to develop suitable strategies for environmental management by adjusting the temperature, good ventilation, sound level, etc. all these define the real conditions of comfort for the people and residents through construction and engineering [3]. energy consumption and greenhouse gases emission of buildings have been investigated in [4]. increasing energy efficiency is essential to change the pattern of world energy consumption [5] and thus reduce greenhouse gas emissions. according to com 815 program that is a subject of emphasis by european union, all eu members are seeking to reduce of energy consumption by 20% and limit and reduce annual cost per household to less than 1000 euros. therefore, the saving can create more than two million jobs by 2020 in eu countries. despite the recognition of this approach by all eu members, the results of the field surveys are disappointing and few effective efforts are done to achieve potential reduction identified in the outlined vision [6]. energy performances of buildings are defined according to different rules and mechanisms. one way in this regard is near zero energy buildings (nzeb). this goal seems very ambitious and it needs the cooperation of several sectors and different fields. using this strategy seems evidently in ecotech architecture. considering all the aspects and difficulties of this law, the members are less likely to implement its provisions. applying ecotech architecture is suggested firstly for public buildings because of its high cost and the need for specific and innovative technologies as well as the obligation to have a systematic and comprehensive perspective. different countries should reach near-zero energy buildings standards in public applications through special ecotech architectural principle and utilizing environmentally efficient thermal insulation by the year 2018. ii. ecotech architecture examples modern architecture focuses on the construction of structures with natural ventilation and light, employing various technologies and techniques including computer simulation [7]. apparently, failure to meet users' demands in modern buildings is the cause of changes [8]. a yeast production building in malta (location very similar to tehran) sets a good example covering all american and european requirements in the field of air conditioning and energy in an industrial building. this building is very different from other similar plants. the application of massive ventilation towers has made it a good sample of modern industrial buildings. placing the ventilation openings in the roof of the building provides the possibility of conditioning half of the air from the internal area within an hour. with regard to exothermic process of yeast production and chemical conversion fitting the proliferation, it is essential to keep ambient temperature always between 5 and 7° c. uncoated additional facades are used to enhance temperature regulation, allowing the building to “breathe” normally [8]. in any ecotech architecture approach the aim is to balance diverse engineering, technology & applied science research vol. 7, no. 5, 2017, 1914-1917 1915 www.etasr.com mozhdegani and afhami: using ecotech architecture as an effective tool for sustainability in …. factors such as urban development, design, attention to function, appearance and the response to users’ needs [9]. the first executive steps about new attitude to ecology and architecture can be seen in the complex form buildings of willis -faber dumas-norman foster in ipswich. creating a small glazed area to the building and designing deep plans maintain most of the energy inside the building. the introduction of a central atrium enhances the use of sunlight. the presence of glass walls suspended in facades also helps absorbing sunlight in offices. a garden with short plants and grass has been created on the roof and the employees can enjoy it in rest hours [9]. the stansted terminal at london airport has similar advances in the use of sunlight. the outer shell of the building depicts a new approach to the design transportation buildings in europe. properly designed forms for columns have created the focus in the ceiling with tree-like structures [10] (figure 1). fig. 1. a view of the interior space of the stansted terminal. another building that represents the process of ecotech architecture is found in duisburg, germany. the city was dependent on the steel and coal industry that ran into serious decline. to regenerate itself it looked at the introduction of the microelectronic industry as a new form of industry for the city, and thus producing an overall master plan for an inner city center, which led to a group of three buildings. the first of those is the telematic center, a flagship building to show how the city could rework itself. in some ways, the external appearance of this has some similarities with the willis-faber in ipswich, a sheer glass wall. the overall energy strategy is based on solar collectors on the roof and the city’s main gas supply provides the rest of the energy. the gas is turned into energy through a cogenerator producing the electricity for all the power and lighting requirements and also heat which, when linked with the solar collectors on the roof, transformed it into the cooling system through the absorption cooling machine, that cooling taking the form of a chilled water system in the ceiling [10] (figures 2 and 3). the most important and most successful example of ecotech architecture is the changes and improvements on the dome of reichstag. many changes have been done in this old building to respond new demands and new applications. moreover, this place is regarded as the symbol of berlin, hence, it has become a special and different place. using a dome as the main part of the air conditioning and skylight for the first time. besides, a movable cover on the dome follows the path of the sun. solar cells on the side of the dome design provide the required electrical energy supply [11]. airflow applies a negative force on the dome and pulls hot air out. in addition to sunlight, the consumed energy is supplied by natural fuels such as sunflower. the reichstag building produces 94% less carbon dioxide than buildings of similar volume. the energy reservoir is a water reservoir and it is located at a depth of 300 meters which is used to regulate the building’s temperature [11]. fig. 2. interior and shallow of the plan space inside the shell, a three-layer the building. fig. 3. exterior view of the building and its transparency. iii. a promising design for tehran, iran it is observed from the latest developments in tehran that there is a gap between the ecotech principles and the actual situation. increasing population growth, geographical expansion, ethnic diversity, uneven development and the lack of attention to environmental issues and renewable energies will reflect a great transformation in physical transformation of tehran. however, ecotech design is a major priority for tehran with cheetgar region providing the capability to be introduced as a pattern for other regions due to its local characteristics and optimal access. a proposed ecotech building structure has three engineering, technology & applied science research vol. 7, no. 5, 2017, 1914-1917 1916 www.etasr.com mozhdegani and afhami: using ecotech architecture as an effective tool for sustainability in …. upper floors and an underground one that has various functions according to requirements and needs. instances from the design are shown in figures 4-8. fig. 4. cross-section of the proposed building fig. 5. outside view fig. 6. main entrance fig. 7. basement view fig. 8. from the entrance to the first floor terrace iv. the case of masdar city, abu dhabi in the ecotech and energy field, the following major issues should be considered: • innovation and experience. innovation requires creative talents and money usually (not always) is regarded as an essential and motivating factor for it. therefore, it has been accepted traditionally that authorities must invest for accomplishment of creative people’s capabilities. • engaging in clear and worthwhile goals. energy supply and benefit from it will form a complex system whose complexity will be increased by the inclusion of conditions and methods of financing. comprehensive attention and understanding of the system is essential. otherwise serious problems will be imposed on the system [14]. the infrastructures and supply needs are of particular importance. • balance. establishing economic, social, and environmental balance are recognized as dimensions of ecotech architecture and as critical factors. masdar city is in abu dhabi, uae and it is indeed a carbon neutral city with minimum waste emission. it indicates the application of ecotech architecture in middle east, on an independent desert city. the city will be the home of 50.000 residents and 1.500 businesses upon completion. it will present 70 thousand jobs [12]. masdar city has a great advantage in terms of attracting talented people (e.g. students and traders) as resources are generously provided by the government. such an approach would identify the city as an international laboratory for suitable investors. in this way, it facilitates attracting talents and new investments [13]. public spaces include landscaping and water flow as evaporative cooling. a multi-functional complex includes various sections such as laboratories, accommodations, variety of social spaces like gyms, restaurant, cafes, research centers, and meeting halls. apartments are designed in one-room, two-room, and three-room complexes constructed with high density blocks [11]. despite the expected objectives and benefits, the city design is facing serious challenges as a work in project [15]. a deeper insight on masdar city and the application of multi-functional buildings as a complex provides valuable conclusions that may be classified in the following general groups: • the use of accurate and update equipment is very important for measuring greenhouse gas emissions and reducing fossil engineering, technology & applied science research vol. 7, no. 5, 2017, 1914-1917 1917 www.etasr.com mozhdegani and afhami: using ecotech architecture as an effective tool for sustainability in …. fuel consumption in order to monitor the process of constructing sustainable cities. • the creation of sustainable forms of transportation, agriculture, environment, and energy can bring economic interests. with investments of around five billion dollars in sustainable cities, a three-time return on investment can be experienced in six years. masdar city is trying to reduce operating costs with the help of selling materials resulting from filtration and carbon dioxide recovery. • the sharp decline in oil prices brings forth financing problems for any large-scale construction project in middle east. these should be solved through proper management of portfolio and using rational strategic plans. • using multi-functional urban experiences in hot and dry area with obstacles and problems such as water shortages and overproduction of carbon dioxide can be important and administrative strategies to reduce the pollution in cities around the world. v. discussion the ecotech approach aims to pay particular attention to energy, environment, and social and economic aspects of modern architecture. the main problem in this regard is the lack of standards and principles for how to do things. a short investigation of major ecotech projects reveals the following key points: • enforcing an ecotech architecture approach on a city can cause a construction boom and also improve the life of residents, attract investments and tourism. • there are no standard ecotech design guidelines that can be implemented on all cases. each region needs a different strategy according to its own climatic, historical, and economic situation. • tehran has a high potential for such applications, having a large population and high density as well as warm and dry climate and varied architectural styles. considering average income and per capita costs, the construction of ecotech buildings seem suitable for investors. vi. conclusion ecotech architecture is a topic of major interest for the construction industry in middle east due to the local environmental factors such as the climate, in combination with certain factors that demand the consideration of strategies to minimize energy consumption. in this paper, a short investigation in such applications is provided. a discussion is conducted and some key conclusions are drawn. references [1] m. asif, “growth and sustainability trends in the buildings sector in the gcc region with particular reference to the ksa and uae”, renewable and sustainable energy reviews, vol. 55, no. 3, pp. 1267-1273, 2016 [2] w. pan, “system boundaries of zero carbon buildings”, renewable and sustainable energy reviews, vol. 37, no. 2, pp. 424-434, 2014 [3] s. marczak, d. damian, “how interaction between roles shapes the communication structure in requirements-driven collaboration”, 19th ieee international requirements engineering conference, pp. 47-56, 2011 [4] s. lechtenbohmer, a. schuring, “the potential for large-scale savings from insulating residential buildings in the eu”, energy efficiency, vol. 4, no. 2, pp. 257-270, 2011 [5] e. e. roadmap, 2050—com (2011) 885/2. brussels: european commission, 2011 [6] european commission, communication on energy 2020: a strategy for competitive, sustainable and secure energy, com (2010) 639/3, european commission, brussels, 2010 [7] m. i. sayyadzadeh, i. shiravi, ibrahim, h. sadeqi, a. sadeqi, “effect of using heat recovery ventilation system in the building”, 1st biennial conference on persian gulf oil, gas and petro chemistry, 2016 [8] m. iommi, “the natural light in the italian rationalist architecture of ex gil of mario ridolfi in macerata. the virtual reconstruction and the daylight analysis of the original building”, energy and buildings, vol. 113, no. 1, pp. 30-38, 2016 [9] h. niroumand, j. a. barcelo, c. j. kibert, m. saaly, “evaluation of earth building tools in construction (ebtc) in earth architecture and earth buildings”, renewable and sustainable energy reviews, 2016 [10] a. scott, dimensions of sustainability, e & fn spon, 1998 [11] m. golabchi, technology and architecture: a study of faster norman works, tehran university press, iran, 2012 [12] s. e. lee, p. braithwaite, j. m. leach, c. d. rogers, “a comparison of energy systems in birmingham, uk, with masdar city, an embryonic city in abu dhabi emirate”, renewable and sustainable energy reviews, vol. 65, no. 2, pp. 1299-1309, 2016 [13] f. cugurullo, “how to build a sandcastle: an analysis of the genesis and development of masdar city”, journal of urban technology, vol. 20, no. 1, pp. 23-37, 2013 [14] d. r. lombardi, m. caserio, r. donovan, j. hale, d. v. hunt, c. weingaertner, l. jankovic, “elucidating sustainability sequencing, tensions, and trade-offs in development decision making”, environment and planning b: planning and design, vol. 38, no. 6, pp. 1105-1121, 2011 [15] d. reiche, “renewable energy policies in the gulf countries: a case study of the carbon-neutral masdar city in abu dhabi”, energy policy, vol. 38, no. 1, pp. 378-382, 2010 microsoft word etasr_v11_n4_pp7311-7320 engineering, technology & applied science research vol. 11, no. 4, 2021, 7311-7320 7311 www.etasr.com barutcu: examination of the chance constrained optimal wt penetration level in distorted … examination of the chance constrained optimal wt penetration level in distorted distribution network with wind speed and load uncertainties ibrahim cagri barutcu department of electricity and energy çölemerik v.h.s. hakkari university hakkari, turkey ibrahimcagribarutcu@hakkari.edu.tr abstract-harmonic penetration can be problematic by the growing interconnection of wind turbines (wts) in distribution networks. since the active power outputs of wts and loads in the distribution system have uncertainties, the optimal wt penetration level problem can be considered to have a stochastic nature. in this study, this problem is taken into account in the stochastic optimization method with the consideration of uncertainties in wind speed and distribution network load profile. chance constraint programming is taken into account in the determination of optimal wt penetration levels by applying the genetic algorithm (ga) along with monte carlo simulation (mcs). the harmonic power flow analysis based on the decoupled harmonic load flow approach is employed in the distorted distribution network. chance constraints are considered for the harmonic issues such as the total harmonic distortion of voltage (vthd), individual harmonic distortion of voltage (vihdh), and root mean square of voltage (vrms). keywords-chance constraint programming; wind turbine; distribution network; stochastic optimization i. introduction wind turbines (wts) are gaining importance with the increase in power demand in distribution systems [1]. these dg systems, which are integrated to distribution systems with power electronics converters, have a wide range of applications. although wts meet the power demand in the distribution networks, they can also have negative effects. the fact that the penetration levels of wts have increased significantly causes problems in terms of power quality issues related to harmonic distortion in distribution systems [2–4]. these types of problems result from the power electronics converter interfaces that provide the interconnection between the wts and the distribution network. currents and voltages are increasingly diverging from their sinusoidal shapes since power electronics devices have been widely used in distribution networks. this situation negatively affects the quality of the power transmitted to the consumers. as a result of high installation of wts in distribution networks with nonlinear loads, high levels of harmonics cause negative results in terms of efficiency and reliability of distribution systems. in this manner, it is useful to optimize the penetration level of wts in the network by taking the harmonic parameters into consideration. therefore, the examination of the influence of wts on the harmonic issues of power systems is a vital problem [5]. on the other hand, the investigations on the harmonic impact of wts on the distribution systems require information about the harmonic characteristics of their output currents. in this manner, the increasing penetration of wts plays an important role in the evaluation of the harmonic influences of these systems. wind speed variations give rise to changes in the operating points of wts. this in turn influences the harmonic distortions caused by the output current of the wind system. in general, the problem concerning the impacts of wind speed changes on harmonic power quality of the utility grid is considered in the planning of optimal placement and capacity of wts on distorted distribution networks. some studies consider the effects of wind speed on the behavior of harmonic power quality of the power system [6– 10]. in [6], the harmonic influences of wind system on the grid power quality have been examined, and it has been shown that variable speed conditions cause greater total harmonic distortion (thd) current when compared to constant speed operation. while installing the wts at power grids, the assessment of harmonic power quality of the power network is a very important issue due to wind speed variations. in [7, 8], the output current of the doubly fed induction generator (dfig) type of wt has been examined in case of instantaneous variations in wind speed. it has been determined that the harmonic frequency currents have stochastic behavior due to the uncertainty in wind speed conditions. it is important to note that the dependency of harmonic problems on wind turbine operation conditions such as wind speed variations is a vital problem in the literature. in [9], the impact of these conditions on the harmonic output currents of the wt has been investigated. it has been concluded that these harmonic currents can be represented by probability distributions because of the random characteristics based on the changes in the wind speed. the harmonic current components of a wind farm have been analyzed by taking into account the relations between the corresponding author: ibrahim cagri barutcu engineering, technology & applied science research vol. 11, no. 4, 2021, 7311-7320 7312 www.etasr.com barutcu: examination of the chance constrained optimal wt penetration level in distorted … harmonic injection currents and the output powers of the wts in [10]. optimal planning of inverter-based dgs considering harmonic penetration is generally performed using deterministic optimization procedures [11]. on the other hand, the random nature of problems may not be taken into account in the deterministic approaches, which present conservative behavior in terms of optimization solutions. however, the random characteristics of environmental conditions and distribution system load profile make the optimization problems to have probabilistic nature. the optimization outcomes can be represented by the probability distributions within the determined region by utilizing the probabilistic approaches. in this manner, monte carlo simulation (mcs) is a well suited method for handling the probabilistic and harmonic related problems [12–14]. in [12], an optimization problem has been investigated by the mcs method with the consideration of confidence intervals for thd current limits in distribution system with background harmonics. chance constrained programming plays important role in performing the planning of distorted distribution systems. in [13], mcsbased genetic algorithm (ga) optimization has been applied to determine the optimal planning of passive harmonic filters considering the confidence intervals for harmonic constraints. in [14], a method incorporating ga and mcs has been proposed for optimal planning of passive harmonic filters taking into account chance constraint for vthd in a distribution network, consisting of pv systems and nonlinear loads. however, the optimization framework for planning the wt penetration level by simultaneously considering the chance constraints for the harmonic power quality indices, which are vthd, vihdh and vrms has not been taken into account in these studies. in the present paper, these literature gaps have been handled in detail. in the current paper, the optimal wt penetration level problem is taken into account in the stochastic optimization method with the consideration of wind speed and load uncertainties in the distribution system. chance constraint programming is considered in the determination of optimal wt penetration levels by performing ga along with mcs. the harmonic power flow analysis based on decoupled harmonic load flow method is employed. the chance constraints are considered for vthd, vihdh, and vrms. ii. harmonic power flow as the penetration levels of wts increase in distorted distribution networks with nonlinear loads, harmonics also increase. wt harmonics negatively affect devices in distribution networks with higher background harmonics. as the interconnection of wts in the distribution system rises, the total harmonic distortions in the voltage and current cause the lifetime of devices to decrease. in this context, the harmonic issues must be considered when integrating wts into distribution networks, which are distorted. harmonic distortions in electricity distribution networks increase due to the inverter interfaces in the structures of wts resulting from the installation of these sources into the distribution grids. in addition, nonlinear loads, which are widely used in distribution systems, have an important role in these harmonic distortions. as a result of the constantly increasing energy demands, power quality is a major issue. the nonlinear loads and the variability of wt active power capacities, which depend on wind speed, may affect the power quality in distribution systems. in this context, harmonic power flow analysis studies play an important role in terms of analysing and designing distribution systems considering harmonic distortions. in this manner, thd becomes higher when the wts meet all the power demands in the distribution network, with nonlinear loads also connected. therefore, harmonic analysis study is inevitable for the examination of power quality issues. in this paper, the harmonic analysis based on decoupled approach is utilized [15]. the harmonic power flow can be solved by taking into account the following equation for each harmonic order of interest: h bus h bus h bus vyi = (1) where h busy represents the bus admittance matrix, h busv shows the bus voltage vector, and h busi denotes the total harmonic current injection vector of wind turbines and nonlinear loads. iii. optimization framework in this article, ga [16] is carried out to maximize the optimal wt penetration level based on the constraints. this problem can be considered to have stochastic nature since the active power outputs of wts and loads in the distribution network have uncertainties. thus, the chance constraints are taken into account for the vthd, vihdh, and vrms limits. the determination of the optimal wt penetration levels based on chance constraint programming is handled by performing ga along with mcs. the objective function can be presented as: 100(%) 1 , x total p pl mva nc k kwt∑ == (2) where nc is the amount of wt candidate buses, kwtp , is the wind turbine capacity at bus k, mva total shows the total system mva of the distribution system, and pl(%) denotes the total penetration level of wts. the chance constraints for the power quality indices are given by: { }k k ,max vthdpr vthd (%) vthd (%) α≤ ≥ (3) { }k k ,max vihdhpr vihdh (%) vihdh (%) α≤ ≥ (4) { }k ,min k k ,max vrmspr vrms vrms vrms α≤ ≤ ≥ (5) where: 2 1 100 h h,k hk ,k v vthd (%) x v = ∑ (6) engineering, technology & applied science research vol. 11, no. 4, 2021, 7311-7320 7313 www.etasr.com barutcu: examination of the chance constrained optimal wt penetration level in distorted … 1 100 h,k k ,k v vihdh (%) x v = (7) 2 2 1 h k ,k h,k h vrms v v= +∑ (8) 1,k v , h,k v , vthd k , vihdh k , and vrms k , denote fundamental frequency voltage, harmonic frequency voltage, total harmonic distortion of voltage, individual harmonic distortion of voltage, and root mean square of voltage at bus k, respectively. h and h are the harmonic order of interest and maximum harmonic order respectively. vthd α , vihdh α , and vrms α show the confidence levels (cl) for vthd k , vihdh k , and vrms k respectively. the overall objective function has been determined considering the chance constraint violations in harmonic parameters with the utilization of penalty function approach [17]: ( ) ( ) ( ) 1 1 1 1 100 1 1 1 nc wt ,k k overall mva tb k vthd vthd vthd k tb h k vihdh vihdh vihdh k h tb k vrms vrms vrms k p f x total pm pm pm ϕ α ϕ α ϕ α = = = = = + − − + − − + − − ∑ ∑ ∑∑ ∑ (9) where: { }1k k k ,maxvthd pr vthd (%) vthd (%)ϕ = − ≤ (10) { }1k k k ,maxvihdh pr vihdh (%) vihdh (%)ϕ = − ≤ (11) { }1k k ,min k k ,maxvrms pr vrms vrms vrmsϕ = − ≤ ≤ (12) where vthd pm , vihdh pm , and vrms pm represent the penalty multipliers in case of the violations in chance constraints corresponding to vthd, vihdh, and vrms respectively and k vthd ϕ , k vihdh ϕ , and k vrms ϕ are the probabilities of limit violations in vthd, vihdh, and vrms respectively. tb is the total amount of nodes in the distribution network. as illustrated in (9), the wt penetration level is maximized provided that the probabilities of violations are within the corresponding limits. when the probabilities of violations exceed their limits, the penalty factors are utilized. therefore, the optimization algorithm explores a more suitable solution, when the overall objective function becomes larger due to the violations in chance constraints. in this paper, ga is utilized to handle the stochastic optimization problem illustrated in (9). the solution representing the optimal active output powers of wts at each candidate node of distribution network is presented as follows: ( )1wt , wt ,k wt ,ncx p ,...,p ,...,p= (13) the lower and upper limits of wind turbine capacities are presented as in: max,,min, wtkwtwt ppp ≤≤ (14) the main steps of the overall methodology, which is performed by applying ga in conjunction with mcs, are: 1. input the parameters that belong to the distribution system. 2. input the harmonic spectrums of the wt system and nonlinear loads. 3. generate 1000 different wind speed and load states from the corresponding probability distributions. 4. generate the initial population representing the candidate solutions randomly. 5. start the mcs for the t th state (t = 1, 2, … , 1000), otherwise, if t is greater than 1000, go to step 10. 6. determine the active power outputs of wt systems and get the load data corresponding to the t th state. 7. implement the decoupled harmonic power flow method for the t th state. 8. evaluate the vthd, vihdh, and vrms at each bus of the distribution system for the t th state. 9. go to step 5. 10. determine the probability density functions of distributions of vthd, vihdh, and vrms at all buses of the distribution system by considering all states. 11. calculate the probabilities of limit violations in vthd, vihdh, and vrms by taking into account the probability density functions of these parameters. in this step, the probabilities of violations are determined by integrating the probability density functions over the intervals of limit violations for vthd, vihdh, and vrms at every bus of the distribution system [18]. as an example, this process is illustrated in figure 1 for the harmonic power quality parameters at bus k of the distribution network. the total and individual harmonic distortions of voltage have been limited by 5% and 3% respectively [19], according to the ieee 519 standards. the root mean square value of voltage has the lower and upper bounds of 0.9pu and 1.1pu respectively. the shaded areas under the probability density functions represent the probability of limit violations, except for the shaded areas which illustrate the confidence level for the harmonic parameters. 12. check the chance constraints whether they are within their limits or not. the chance constraints are satisfied when the areas under the probability density functions of vthd, vihdh, and vrms over the corresponding intervals of engineering, technology & applied science research vol. 11, no. 4, 2021, 7311-7320 7314 www.etasr.com barutcu: examination of the chance constrained optimal wt penetration level in distorted … limit violations are less than 1 vthd α− , 1 vihdh α− , and 1 vrms α− respectively. 13. calculate the objective function for each chromosome considering the chance constraints related to the harmonic power quality indices. 14. evaluate the objective function by taking into account the penalty function method, if the chance constraints are not met. 15. print the optimal active power outputs of wts if the optimization criteria are satisfied, otherwise go to step 4. 16. test the optimization results considering the chance constraint violations for harmonic power quality parameters. (a) (b) (c) fig. 1. the probability density functions of (a) vthd, (b) vihdh, (c) vrms at bus k. the chance constrained optimization method is utilized for the probabilistic optimization problems, the constraints of which have random characteristics. determination of the optimal solution means that the stochastic constraints are within their limits for the defined confidence interval. in this context, mcs is a well suited method for dealing with the probabilistic problems. the flowchart of ga optimization methodology along with mcs is demonstrated in figure 2. the flowchart of the approach for testing the optimization results by taking into account the chance constraints is given in figure 3. fig. 2. the flowchart of the proposed method. engineering, technology & applied science research vol. 11, no. 4, 2021, 7311-7320 7315 www.etasr.com barutcu: examination of the chance constrained optimal wt penetration level in distorted … fig. 3. the flowchart of the approach for testing the optimization results. in this paper, the 1000 different wind speed and load states have been firstly generated from their corresponding probability distributions. then, the ga optimization process has been initiated by randomly generating initial populations representing the candidate solutions. the mcs approach, which has been embedded in the optimization algorithm, has been applied for all wind speed and load states. the decoupled harmonic power flow method has been implemented to evaluate vthd, vihdh, and vrms at each bus of the distribution system by considering the active power outputs of wt systems and load data for all states in the mcs algorithm. after the mcs process has been completed, the probability density functions of vthd, vihdh, and vrms have been determined. after that, the probabilities of limit violations in these harmonic parameters have been calculated taking into account the probability density functions. the objective function has been evaluated with the consideration of limit violations in chance constraints. if the chance constraints have not been met, the objective function has been calculated by considering the penalty function method. ga optimization approach has been iteratively carried out by considering reproduction, mutation, crossover, and the new population generation stages until the optimization criteria were satisfied. after the optimization process presented in figure 2 has been completed, the optimization results have been tested to determine the probabilities of violations in chance constraints by using the method illustrated in figure 3. iv. modeling of uncertainties the uncertainties of load demand and wind speed are gaining importance in the stochastic power flow analysis of distribution networks with the growing interconnection of wind turbines to these power systems. the probabilistic approaches, in which these uncertainties are taken into account, are inevitable for the evaluation of the stochastic behavior of distribution systems, to which the wts are interfaced. in that manner, it is very important for stochastic approaches that the random variables in the problem have some probability distributions [12]. since the consumptions and renewable power productions in distribution systems have probabilistic framework, these are included in the stochastically modeled approaches. the outcomes, which are determined by the probabilistic approach, also show stochastic behavior and follow a probabilistic distribution. the output random variables of stochastic process performed on the problem have uncertainties and probabilistic features as the input ones have these properties [20]. the distribution functions are generally utilized to express the uncertainties of load demand and wind speed in probabilistic methods. in this paper, the wind speed is considered to have a rayleigh distribution [21]. the probability density function (pdf) of wind speed is given as in the following: ( )                 −        = 2 , 2 , , exp 2 c v c v vf kwtkwt kwt (15) where c represents scale index and kwtv , shows the wind speed on the wind turbine at bus k of the distribution network. the wind turbine capacity depends on wind speed, and can be evaluated as [21]: 0 0 0 wt ,k c,i c,i wt ,k wt ,n c ,i wt ,k wt ,n c ,i wt ,nwt ,k wt ,n wt ,n wt ,k c,o c,o wt ,k v v v v p v v v v vp p v v v v v ≤ ≤   − ≤ ≤  −=    ≤ ≤  ≤ (16) where nwtv , represents the nominal speed of wt, ocv , shows the cut-out speed of wt, icv , illustrates the cut-in speed of wt, and nwtp , is the nominal active power output of wt. in this study, the load uncertainty of the distribution network has been modelled by normal distribution [12]. the normal distribution pdf is given as follows: engineering, technology & applied science research vol. 11, no. 4, 2021, 7311-7320 7316 www.etasr.com barutcu: examination of the chance constrained optimal wt penetration level in distorted … ( ) ( )         − −      = 2 2 ,,, , 2 exp 2 1 σσπ meankdkd kd pp pf (17) where d,k p illustrates the active power load at bus k of distribution system, d,k ,mean p is the load profile mean value at bus k, and σ is the standard deviation. v. simulation results in this study, ga parameters are selected as: 10 -6 for the tolerance of fitness function, 200 for the maximum number of generation, 30 for population size, and 0.8 for the crossover fraction. the study simulations have been implemented on a pc with 2.80ghz cpu. in this study, the optimal penetration levels of wts have been determined based on the uncertainties of load powers on the distribution network and wind speed on wts. the chance constraints for harmonic issues have been considered in the stochastic planning of active output powers of wts. the wt penetration levels have been maximized by ensuring chance constraint limits and considering a probabilistic framework of load powers and wind speed. the wts have the installed capacity of 500kw at each candidate bus of the distribution system. a 33 bus distribution network [22] has been used to perform the simulations. this system, which has the total capacity of 6mva, is given in figure 4. the chosen wt candidate buses are 5, 11, 16, 17, 19, 22, 24, 25, 26, 28, 30 and 32. fig. 4. 33 bus radial test system. different states have been generated for the load profile of the distribution system. the active powers of original load in the grid are regarded as the mean values. the generated load cases have 10 % standard deviation with respect to the mean values. the total distribution system active load profile is given in figure 5. the proposed methodology considers the examination of harmonic power quality indices on wts integrated distribution system based on the uncertainties in the probabilistic optimization framework. nominal, cut – out, and cut – in speeds of wts have been regarded as 16m/s, 25m/s, and 4m/s respectively [23]. the wind speed states have been generated based on the rayleigh distribution in the proposed method. the uncertainties in wind speed conditions, which in turn affect the wt power generation, give rise to the probabilistic generation in wt systems. as a result of wind speed uncertainties in wt systems and load uncertainties in distribution systems, the probabilistic approaches are applied. by the aid of the probabilistic model, the different cases of random variables can be considered in the active distribution network, which is examined. the probabilistic approach requires handling the input random variables, which are represented by distribution functions, by performing deterministic approaches for different states. by implementing the probabilistic method with the inclusion of input random variables, the output variables, which also follow a distribution function, can be determined. the wind speed states, which are generated from the corresponding probability distribution, are illustrated in figure 6. fig. 5. the total load states of the distribution system. fig. 6. the wind speed states. the installation nodes and the capacities of nonlinear loads are presented in table i. the harmonic current components of wts and nonlinear loads are demonstrated in table ii [11, 15]. table i. nonlinear load powers in the distribution system buses active power (kw) reactive power (kvar) 2 45 27 6 27 9 14 54 36 19 40.5 18 23 40.5 22.5 27 27 11.25 33 27 18 the optimal active power outputs of wts are shown for different confidence levels in table iii by performing ga with mcs in chance constraint optimization framework. the optimal values of wt penetration levels have been determined engineering, technology & applied science research vol. 11, no. 4, 2021, 7311-7320 7317 www.etasr.com barutcu: examination of the chance constrained optimal wt penetration level in distorted … as 44.79%, 40.86%, and 36.28% for 0.7, 0.8, and 0.9 confidence levels respectively. the ga success rates [24] determined for 0.7, 0.8, and 0.9 confidence levels are depicted in figure 7. the ga optimization approach, where mcs is embedded, has converged to the optimal solutions in 26556.55s at 89 iterations for 0.7 confidence level, in 25189.85s at 94 iterations for 0.8 confidence level, and in 38654.93s at 143 iterations for 0.9 confidence level respectively. table ii. harmonic current components harmonic order magnitudes (%) wind turbine nonlinear load 1 100 100 5 4.00 23.52 7 4.00 6.08 11 2.00 4.57 13 2.00 4.20 17 1.50 1.80 19 1.50 1.37 23 0.60 0.75 25 0.60 0.56 29 0.60 0.49 31 0.60 0.54 35 0.30 37 0.30 41 0.30 43 0.30 47 0.30 49 0.30 table iii. optimal wt output powers for different confidence levels buses ���,� (kw) for 0.7 cl for 0.8 cl for 0.9 cl 5 379.33 396.67 78.39 11 59.53 59.88 261.31 16 274.82 374.02 371.44 17 128.11 4.05 83.66 19 327.05 83.26 178.25 22 137.18 208.05 55.33 24 382.04 243.40 217.03 25 133.48 138.96 18.91 26 197.78 343.86 235.66 28 308.93 288.38 250.29 30 225.41 211.59 215.29 32 134.13 99.58 211.32 fig. 7. the iteratively depicted optimal wt penetration levels. as presented in table iii, the optimal wt penetration levels decrease with the increase of confidence levels. the main reason is that the optimization process is more conservative in higher confidence levels. since the optimal penetration levels of wts in lower confidence levels are less than those at the higher levels by the chance constraints, the optimal wt penetration levels are increasing by the decrease of confidence levels. the upper limits and optimal values of wt active power outputs for different confidence levels have been interconnected to the distribution network to test violations in chance constraints related with harmonic power quality parameters. the violations in chance constraints for these parameters are presented in table iv. as seen in table iv, chance constraint violations of vthd, vihd5, vihd7, and vrms are observed when the nominal capacities of wt output powers are connected to the distribution system. the optimal active power outputs by the proposed methodology cause considerable minimization in the violations. these optimal output powers of wts ensure that the violations in the chance constraints of harmonic related issues comply with their corresponding limits for each confidence level. the chance constraint violations of vihd7 are not observed for the optimal solutions of wt output powers for all confidence levels. the violations in chance constraints for power quality parameters are satisfied with the corresponding confidence levels, in which the probabilistic optimization procedure has been applied. according to [25], meaningful results can be determined by using 1000 states in the mcs process. low accuracy can be increased by increasing the number of states. this in turn does not require the utilization of a greater number of states. in this study, the wind speed states in figure 6 and the load states in figure 5, which are considered in the ga optimization process, are also taken into account in the testing of the optimization results. the chance constraints are satisfied by the ga optimization results for these data sets. it can be concluded that the load and wind speed data sets, which are taken into account in the optimization algorithm, illustrate the chance constraint handling ability of the optimization process when they are used as test sets. by the increase of wt integration into the distribution systems, harmonic distortions cause negative effects in these networks. the connection of these renewable energy resources to the grids with nonlinear loads leads the distribution system planners to research on ensuring harmonic power quality. in this context, determining the optimal wt penetration levels in active distribution networks, where high harmonic currents and voltages are observed, is a major issue. optimal penetration levels of wts obtained based on the harmonic limits specified in the ieee 519 standards become important for the continuity of harmonic power quality in the distribution systems. maintaining power quality is inevitable for the efficiency and reliability of power transferred to the end users in the distribution network. in this manner, the occurrence of harmonic problems in the distribution systems requires that each phase of planning for the optimal penetration levels of wind turbines should be made correctly. engineering, technology & applied science research vol. 11, no. 4, 2021, 7311-7320 7318 www.etasr.com barutcu: examination of the chance constrained optimal wt penetration level in distorted … table iv. violation probabilities buses violation probabilities in harmonic power quality parameters for ���,��� ���,� for 0.7 cl ���,� for 0.8 cl ���,� for 0.9 cl vthd vihd5 vihd7 vrms vthd vihd5 vrms vthd vihd5 vrms vthd vihd5 vrms 1 0.5073 0.8984 0.1610 0.0007 0.0748 0.0379 0.0111 2 0.5083 0.9131 0.1617 0.0007 0.0750 0.0380 0.0111 3 0.5437 0.9146 0.1835 0.0008 0.0859 0.0447 0.0145 4 0.5469 0.9155 0.1855 0.0009 0.0978 0.0522 0.0168 5 0.5503 0.9288 0.1877 0.0010 0.0984 0.0525 0.0169 6 0.5875 0.9410 0.1916 0.0011 0.1277 0.0003 0.0706 0.0235 7 0.5890 0.9408 0.2137 0.0012 0.1450 0.0003 0.0812 0.0278 8 0.5964 0.9508 0.2193 0.0014 0.1659 0.0008 0.1066 0.0391 9 0.6315 0.9513 0.2228 0.0016 0.1886 0.0017 0.1216 0.0543 10 0.6368 0.9595 0.2504 0.0019 0.2389 0.0022 0.1383 0.0636 11 0.6377 0.9596 0.2511 0.0019 0.2392 0.0022 0.1384 0.0637 12 0.6388 0.9597 0.2520 0.0019 0.2396 0.0022 0.1564 0.0639 13 0.6736 0.9667 0.2568 0.0026 0.2976 0.0031 0.1990 0.0001 0.0867 0.0001 14 0.6771 0.9669 0.2593 0.0002 0.0026 0.2990 0.0005 0.0034 0.1998 0.0011 0.0001 0.1000 0.0009 15 0.6791 0.9669 0.2611 0.0004 0.0026 0.2992 0.0013 0.0034 0.1999 0.0026 0.0001 0.0998 0.0017 16 0.6814 0.9668 0.2634 0.0008 0.0026 0.2994 0.0022 0.0034 0.2000 0.0083 0.0001 0.0996 0.0033 17 0.6849 0.9664 0.2672 0.0015 0.0026 0.3000 0.0068 0.0034 0.2000 0.0215 0.0001 0.0993 0.0089 18 0.6849 0.9664 0.2672 0.0015 0.0026 0.3000 0.0093 0.0034 0.2000 0.0288 0.0001 0.0993 0.0123 19 0.5086 0.9132 0.1619 0.0007 0.0750 0.0380 0.0126 20 0.5099 0.9137 0.1629 0.0007 0.0747 0.0376 0.0126 21 0.5104 0.9139 0.1632 0.0007 0.0745 0.0375 0.0125 22 0.5115 0.9002 0.1638 0.0007 0.0742 0.0371 0.0125 23 0.5445 0.9150 0.1840 0.0009 0.0862 0.0448 0.0145 24 0.5461 0.9156 0.1850 0.0008 0.0862 0.0448 0.0145 25 0.5166 0.9158 0.1856 0.0008 0.0862 0.0446 0.0145 26 0.5881 0.9412 0.1921 0.0011 0.1279 0.0003 0.0812 0.0279 27 0.5889 0.9414 0.2140 0.0011 0.1282 0.0003 0.0814 0.0279 28 0.5906 0.9421 0.2157 0.0013 0.1463 0.0005 0.0819 0.0280 29 0.5921 0.9425 0.2169 0.0013 0.1470 0.0005 0.0939 0.0332 30 0.5930 0.9428 0.2176 0.0013 0.1473 0.0005 0.0940 0.0333 31 0.5943 0.9430 0.2183 0.0014 0.1675 0.0008 0.1075 0.0394 32 0.5949 0.9522 0.2186 0.0014 0.1679 0.0008 0.1077 0.0394 33 0.5952 0.9523 0.2187 0.0014 0.1898 0.0008 0.1080 0.0465 harmonic studies carried out in distribution networks, are a major issue these networks face. studies which find applications of wts in different areas, are increasingly gaining importance in power quality researches. optimal connection of wts to the distribution networks is important in order to keep harmonic distortions within the allowable limits. however, the increase in the installation of these sources in the distribution networks leads to violations of the harmonic limits specified in ieee 519 standards. in this manner, the optimal penetration levels of wts should be determined taking into account the harmonic parameters. in this study, the probabilistic optimization approach is proposed to achieve optimal wt penetration levels by considering load uncertainty and wind speed variability in active distribution systems considering harmonic distortions. this approach is important for proper network planning. the cumulative distribution functions for the power quality parameters at node 18, which is the most vulnerable bus to harmonic currents, are given in figure 8 for different confidence levels. as presented in figure 8, the vthd at bus 18 has been observed above 5% with probabilities of 0.0026, 0.0034, and 0.0001, while the vihd5 at bus 18 has been determined beyond the limit of 3% with probabilities of 0.3, 0.2, and 0.0993 for 0.7, 0.8, and 0.9 confidence levels respectively. moreover, the vrms has violated its corresponding limits with 0.0093, 0.0288, and 0.0123 probabilities for the confidence intervals of 0.7, 0.8, and 0.9. within the scope of this study, probabilistic harmonic analysis studies considering distorted active distribution networks to which wts and nonlinear loads are connected have been carried out, and optimal penetration levels of these sources have been evaluated by considering the harmonic power quality issues with respect to wind speed. in wt connected distribution networks, changes in wind speed may cause violations of the harmonic parameters. in this manner, the probabilistic nature of harmonic parameters based on wind speed variations should be included in the constrained optimization problem while determining the optimal wt penetration levels by considering harmonic distortions in distribution networks. the probabilistic dependence of harmonic power quality parameters on changes in wind speed is an important research subject in the wt-integrated active distribution networks. in this study, the vthd, vihdh, and vrms in distribution system vary stochastically depending on the wind speed due to the changes in operating points. therefore, the effects of wts on the harmonic parameters in the distribution networks are taken into consideration for variable wind speed in the harmonic analysis performed in the study. engineering, technology & applied science research vol. 11, no. 4, 2021, 7311-7320 7319 www.etasr.com barutcu: examination of the chance constrained optimal wt penetration level in distorted … (a) (b) (c) fig. 8. the cumulative distribution functions for (a) vthd, (b) vihd5, (c) vrms at bus 18. the assessment of harmonic power quality issues due to the wt presence for various wind speed states is a prominent topic considered in applications. in addition, determining the optimal output powers and penetration levels of the wts integrated in the distribution networks is a promising problem in terms of keeping the vrms, vihdh, and vthd values obtained from harmonic power flow analyses within the desired limits for the continuity and reliability of power quality. in this manner, the load profile of the distribution network, the variability of the capacity of the wts depending on wind speed, and the harmonic constraints specified in the standards increase the importance of the problem of determining the optimal interconnections of the wts in the distribution networks. vi. conclusions in this study, the uncertainties of wind speed and load profile in the distribution network are considered while dealing with the optimal wt penetration level problem in the stochastic optimization framework. the dependency of harmonic power quality problems on wind speed is handled in the wts installed grid by the proposed method. by implementing ga along with mcs, the optimal wt penetration levels are determined by utilizing chance constraint programming. harmonic power quality indices such as vthd, vihdh, and vrms, which are considered while writing the chance constraints, are calculated by harmonic power flow analysis. based on the results, the optimal capacities of wts ensure that the violations in the chance constraints of the harmonic issues comply with the corresponding limits for each confidence level. since the optimization process is more conservative in higher confidence levels, the optimal wt penetration levels decrease with the increase of confidence levels. the load uncertainty of distribution networks and the variability of wind speed on wts encourage network operators to probabilistic planning studies. the main reason is that the stochastic optimization problem, which needs to be solved, has a complex structure due to the changes in load profile and wind speed. the dependence of the harmonic power quality of the grid on the operating points and wind speed adds a new dimension to this probabilistic optimization problem. based on these points, the stochastic planning of optimal wt penetration levels in distribution networks brings the work done in the literature to a new level in terms of maintaining the power quality by minimizing the harmonic distortions. therefore, the probabilistic planning on optimal wt penetration levels within the scope of this study has an important place in the relevant literature. acknowledgment the author would like to thank assoc. prof. dr. engin karatepe for his valuable and constructive comments to this paper. references [1] g. mustafa, m. h. baloch, s. h. qazi, s. tahir, n. khan, and b. a. mirjat, "experimental investigation and control of a hybrid (pv-wind) energy power system," engineering, technology & applied 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[24] a. sehgal, h. m. la, s. j. louis, and h. nguyen, "deep reinforcement learning using genetic algorithm for parameter optimization," in 2019 third ieee international conference on robotic computing, naples, italy, feb. 2019, pp. 596-601, https://doi.org/10.1109/irc.2019.00121. [25] a. faza, "a probabilistic model for estimating the effects of photovoltaic sources on the power systems reliability," reliability engineering & system safety, vol. 171, pp. 67-77, mar. 2018, https://doi.org/10.1016/ j.ress.2017.11.008. authors profile ibrahim cagri barutcu received his b.s. (in 2011) degree from the department of electrical – electronics engineering in eskisehir osmangazi university, eskisehir, turkey, his m.s. (in 2014) and ph.d. (in 2020) degrees from the electrical – electronics engineering department in ege university, izmir, turkey. he is currently an assisstant professor in the department of electricity and energy at hakkari university. his research interests are harmonic power quality in active distribution networks, renewable energy resources, distributed generation planning and optimization methods. microsoft word etasr_v12_n1_pp8164-8167 engineering, technology & applied science research vol. 12, no. 1, 2022, 8164-8167 8164 www.etasr.com minh et al.: electromagnetic and thermal analysis of interior permanent magnet motors using filled … electromagnetic and thermal analysis of interior permanent magnet motors using filled slots and hairpin windings dinh bui minh school of electrical engineering hanoi university of science and technology hanoi, vietnam dinh.buiminh@hust.edu.vn hung bui duc school of electrical engineering hanoi university of science and technology hanoi, vietnam hung.buiduc@hust.edu.vn nguyen huy phuong school of electrical engineering hanoi university of science and technology hanoi, vietnam phuong.nguyenhuy@hust.edu.vn vuong dang quoc school of electrical engineering hanoi university of science and technology hanoi, vietnam vuong.dangquoc@hust.edu.vn abstract—this paper analyzes the electromagnetic and thermal design of interior permanent magnet motors using filled slots and hairpin windings for electric vehicle applications. two models of ∇∇∇∇ shape of the interior permanent magnet motors have been proposed to evaluate the temperature distribution and cogging torque performance. a narrow opening slot of the interior permanent magnet of 48 slots/8 poles with the filled winding has been designed to investigate the electromagnetic torque because the cogging torque depends on opening stator slots. a parallel– rectangle slot of the interior permanent magnet with the hairpin winding has been also implemented with finite element analysis to evaluate their performances. normally, the slot opening of the interior permanent magnet stator equals the slot width, it is greater than the size of hairpin windings, and the cogging torque is increased significantly with a bigger slot opening. the main advantage of the hairpin winding design is the high slot fill factors. hence, the lower the current density, the higher torque, and efficiency are, than the normal design with the same geometry parameters. to improve the cogging torque due to the wide slot opening, the step–skew rotor slices have been arranged to minimize the torque ripple with different skewing angles. keywords-interior permanent magnet; finite element analysis; ansys maxwell; speed software; hairpin windings i. introduction hairpin-type windings are gaining increasing popularity [1, 2], especially in automotive traction motors due to advantages which include reduced manufacturing time, high fill factor, shorter end-winding overhang, and better high voltage protection. moreover, with respect to the random nature and the packing style of traditional distributed windings, hairpin windings consist of a plurality of accurately placed stator bars [1, 3]. however, the cogging torque is very high with a wider slot opening, and it is also very complicated to manufacture. thus, in order to improve the torque ripple, a novel design of a step-skew v shape magnet has been presented for interior permanent magnet (ipm) motors of 150kw (48 slots/8 poles). the stator stepped slot-openings with optimal shift angles have been implemented for the ipm motors in [4-6]. cogging torque reduction has become an increasingly important issue in ipm motors. effective methods for reducing the cogging torque, such as skewing slots, step-skewing rotor, and magnets are possible for the slot-filled windings. for the hairpin windings, only step-skewing rotor can be applied to improve the torque ripple. in this paper, a stepped skewing shift magnet rotor method for reducing the cogging torque of ipm motors, which can avoid the drawbacks of the wider slot opening of stator slots, is proposed. the electromagnetic torque and efficiency performance of the ipm motor are significantly affected by winding topology. the electromagnetic performance of multilayered ipm motors keeping in mind their potential use in electric vehicle (ev) applications. the torque and back electromagnetic force (emf) waveforms are verified with different step skewing models. the torque harmonics have been compared for different topologies. finally, an ipm motor with a step-skewing magnet rotor is manufactured to verify the results of finite element analysis (fea) [9-12]. ii. hairpin and slot fill winding designs the designed ipm motor with ∇ shape of permanent magnet rotor with slot filled and hairpin windings is presented in figure 1. the stator slot parameters are pre-determined in and are shown in table i. the slot-filled winding has an opening width of 1.2mm, which is greater than the wire diameter of 1mm (figure1(a)) and the stator slot opening of the hairpin winding is 5mm, bigger than the rectangle bar sizes of 4.3×3.3mm (figure 1(b). corresponding author: dinh bui minh engineering, technology & applied science research vol. 12, no. 1, 2022, 8164-8167 8165 www.etasr.com minh et al.: electromagnetic and thermal analysis of interior permanent magnet motors using filled … (a) (b) fig. 1. (a) slot filled winding and (b) hairpin winding. table i. slot filled and hairpin winding parameters parameter unit slot filled winding harpin winding stator lamination diameter mm 250 250 stator bore ds mm 175 175 airgap mm 1 1 stator slot opening width (ts) mm 1.2 5 mechanical opening angle (0) 0.55 2.22 motor length mm 240 240 stator lam length mm 120 120 magnet length mm 120 120 magnet segments 6 6 rotor lam length mm 100 100 ewg overhang [f] mm 55 37 ewg overhang [r] mm 55 37 copper size mm φ 0.85 4.3×3.3 number strands 15 1 phases 3 3 turns 6 6 throw 5 5 parallel paths: 2 2 the two ipm motors have 48 slot/8poles, the stack length is 51mm, the diameter of stator and rotor is 250mm and 175mm respectively, the air-gap length is 1mm, the thickness of the electrical steel sheet is 0.2mm, the continuous phase current amplitude is 400a, the continuous rated power is 150kw, and the maximum speed of the machines is 12000rpm. the main differences are winding overhang, slot opening, and the copper sizes of 15 (φ 0.85) and 4.3×3.3mm. the slot opening is 1.2mm in slot filled and 5mm in hairpin designs. in both models, the slot openings are arranged along the motor axis and the central position of the slots remains the same. the cogging torque of ipm motors results from the interaction between the stator teeth and rotor magnetic poles, which can be expressed in fourier series [6-8]: ��� � ∑ ��,� sin� ��� � ��� (1) where i is the order of the cogging torque harmonics, tci is the amplitude of i order cogging torque component, and n is the least common multiple between the number stator slots and rotor poles. the mechanical angle of the stator opening θ is: � � 360 �� ��� (2) where ts is slot opening width, ds is the stator diameter. the cogging torque of slot filled winding with 1.2mm (0.55 0 ) opening is 2.8n.m, while the cogging torque of hairpin winding with 5mm opening width (2.22 0 ) is 8n.m, which is three times bigger than the slot filled winding designs. (a) (b) fig. 2. (a) cogging torque of slot filled and (b) hairpin winding. iii. cogging torque and thermal analysis to eliminate the cogging torque by the stator slot-openings, the step-skewing rotor has a shift angle of β mechanical degrees. the cogging torque can be transformed as [6]: ���� � ∑ ��� sin� ��� � ��� � ��� (3) if the rotor is divided into segments along the motor axial direction, and the relative shift angle between the adjacent two rotor poles is δn mechanical degrees, the resultant cogging torque can be expressed as [6]: ���� � ∑ ��� ∑ . �� !�� sin� ��� � "���� � �� (4) the above equation can be simplified to: ���� � � ∑ ��� #�� $%&'' ( #�� $%&' ( sin� ��� � "���� � �� (5) hence, for eliminating the i-th order cogging torque component, the theoretical shift angle βn must fulfill the following requirements: sin �)*'� + =0 (6) by applying the cogging torque for straight skewing and vshape skewing magnet model, the conventional skewing model with straight skewing has a smaller shift angle than the v-shape skewing model with the same total skewing angle. the v shape magnet model has more advantages than the straight skewing because two harmonic orders can be eliminated together. for example, the harmonic orders with mechanical degrees of 1 0 or 3 0 are reduced to zero if they fulfill (6). the cogging torque of the 3 models is shown in figure 3. the cogging torque of the v shape skewing design is the lowest value because the second order harmonics are eliminated in this model. the back emf harmonic of the 3 models has been analyzed by fourier transform from the electromagnetic force waveform with the harmonic order from the first to the 15 th order. the back emf amplitude versus harmonic order was implemented by the engineering, technology & applied science research vol. 12, no. 1, 2022, 8164-8167 8166 www.etasr.com minh et al.: electromagnetic and thermal analysis of interior permanent magnet motors using filled … matlab function to obtain the results shown in figure 5. from the back emf harmonic result, the total harmonic distortion tdh of model 3 with v skewing is the smallest about 4.2%. (a) (b) fig. 3. (a) straight skewing and (b) v-skewing. fig. 4. cogging torque of the 3 models. fig. 5. back emf harmonic order analysis of the models. the temperature distribution of slot fill and hairpin winding designs is depicted in figure 6. the hot spot of hairpin winding is 105.7 0 c, which is lower than 111.5 0 c. based on these results, the ipm v skewing with the hairpin winding design is preferable for ev applications. the efficiency map of hairpin winding design is shown in figure 7, with a speed range of 12000rpm and a current density of 8.9a/m 2 . iv. skewing rotor desing the prototype with the 6-segmented magnets has been manufactured and is shown in figure 8. each segment with a thickness of 20mm is skewed by 1.5 mechanical degrees. to insert the six segments simply, every segment block is designed with one guide pin to fix the correct position when all segments assembly together. (a) (b) fig. 6. (a) slot fill, (b) hairpin winding designs temperature distribution. fig. 7. efficiency map of hairpin winding design. (a) (b) fig. 8. (a) rotor lamination, (b) six step-v skew magnet slices assembly. engineering, technology & applied science research vol. 12, no. 1, 2022, 8164-8167 8167 www.etasr.com minh et al.: electromagnetic and thermal analysis of interior permanent magnet motors using filled … the whole hardware of the ipm motor has been assembled as in figure 9. the high accurate torque transducer is used to measure the torque and speed values under different load conditions. the measured no-load phase emf at 1500rpm of ipm is shown in figure 10. to verify the electromagnetic performance, the 48 slot/8 pole proposed pm machine is built. distributed windings were adopted. it should be noted that the pm motor is a prototype. the no-load back-emf is carried out by using a voltage sensor. the simulated and measured results are exhibited in figure 10. one circle of the back emf has been measured by the oscilloscope and the data were recorded for plotting those curves. fig. 9. back emf measurement of the ipm motor system. fig. 10. back emf comparison of ipm motor system. v. conclusion the obtained performance of ipm with slot filled and hairpin windings in the wide speed range has been presented in this paper and the effect of slot opening width on the cogging torque has been discussed. the thermal simulation of the two designs has been investigated to find out the hot spot or maximum temperature of hairpin and slot filled windings. a significant contribution of this study is the analytical calculation of the v skewing angle for the elimination of the second order harmonics of the cogging torque. a prototype of the v skewing magnet shape of the ipm hairpin winding has been manufactured and assembled. the simulation results achieved peak torque of 300n. m at the base speed of 5500rpm. the back emf waveforms obtained from the fea are close to the measured ones. acknowledgement this research was supported by the institute for control engineering and automation-icea which provided the high processing speed computer needed to run the simulations. references [1] c. liu et al., "experimental investigation on oil spray cooling with hairpin windings," ieee transactions on industrial electronics, vol. 67, no. 9, pp. 7343–7353, sep. 2020, https://doi.org/10.1109/tie. 2019.2942563. [2] j.-w. chin, k.-s. cha, m.-r. park, s.-h. park, e.-c. lee, and m.-s. lim, "high efficiency pmsm with high slot fill factor coil for heavy-duty ev traction considering ac resistance," ieee transactions on energy conversion, vol. 36, no. 2, pp. 883–894, jun. 2021, https://doi.org/10.1109/tec.2020.3035165. [3] j.-g. lee, h.-k. yeo, h.-k. jung, t.-k. kim, and j.-s. ro, "electromagnetic and thermal analysis and design of a novel-structured surface-mounted permanent magnet motor with high-power-density," iet electric power applications, vol. 13, no. 4, pp. 472–478, jan. 2019, https://doi.org/10.1049/iet-epa.2018.5322. [4] j. zhao, j. wang, l. zhou, w. huang, y. ma, and z. zhang, "cogging torque reduction by stepped slot-opening shift for interior permanent magnet motors," in 2019 22nd international conference on electrical machines and systems (icems), harbin, china, dec. 2019, https://doi.org/10.1109/icems.2019.8921448. [5] s.-k. lee, g.-h. kang, j. hur, and b.-w. kim, "stator and rotor shape designs of interior permanent magnet type brushless dc motor for reducing torque fluctuation," ieee transactions on magnetics, vol. 48, no. 11, pp. 4662–4665, aug. 2012, https://doi.org/10.1109/ tmag.2012.2201455. [6] x. ge, z. q. zhu, g. kemp, d. moule, and c. williams, "optimal stepskew methods for cogging torque reduction accounting for threedimensional effect of interior permanent magnet machines," ieee transactions on energy conversion, vol. 32, no. 1, pp. 222–232, mar. 2017, https://doi.org/10.1109/tec.2016.2620476. [7] g. pellegrino, a. vagati, and p. guglielmi, "design tradeoffs between constant power speed range, uncontrolled generator operation, and rated current of ipm motor drives," ieee transactions on industry applications, vol. 47, no. 5, pp. 1995–2003, sep. 2011, https://doi.org/ 10.1109/tia.2011.2161429. [8] g. pellegrino, a. vagati, p. guglielmi, and b. boazzo, "performance comparison between surface-mounted and interior pm motor drives for electric vehicle application," ieee transactions on industrial electronics, vol. 59, no. 2, pp. 803–811, oct. 2012, https://doi.org/ 10.1109/tie.2011.2151825. [9] m. barcaro, n. bianchi, and f. magnussen, "design considerations to maximize performance of an ipm motor for a wide flux-weakening region," in the xix international conference on electrical machines icem 2010, rome, italy, sep. 2010, https://doi.org/10.1109/ icelmach.2010.5607926. [10] v. d. quoc, "robust correction procedure for accurate thin shell models via a perturbation technique," engineering, technology & applied science research, vol. 10, no. 3, pp. 5832–5836, jun. 2020, https://doi.org/10.48084/etasr.3615. [11] d. b. minh, l. d. hai, t. l. anh, and v. d. quoc, "electromagnetic torque analysis of srm 12/8 by rotor/stator pole angle," engineering, technology & applied science research, vol. 11, no. 3, pp. 7187–7190, jun. 2021, https://doi.org/10.48084/etasr.4168. [12] d. b. minh, v. d. quoc, and p. n. huy, "efficiency improvement of permanent magnet bldc motors for electric vehicles," engineering, technology & applied science research, vol. 11, no. 5, pp. 7615–7618, oct. 2021, https://doi.org/10.48084/etasr.4367. microsoft word 439-ce-r2.doc engineering, technology & applied science research vol. 4, no. 4, 2014, 669-672 669 www.etasr.com bekhiti et al.: mechanical properties of waste tire rubber powder properties of waste tire rubber powder melik bekhiti habib trouzine aissa asroun civil engineering department, djillali liabes university of sidi bel abbes, algeria bkheti.melik@yahoo.fr civil engineering department, djillali liabes university of sidi bel abbes, algeria h_trouzine@yahoo.fr civil engineering department, djillali liabes university of sidi bel abbes, algeria a_asroun@yahoo.fr abstract—scrap tires are abundant and alarming waste. the aggregates resulting from the crushing of the waste tires are more and more used in the field of civil engineering (geotechnical, hydraulic works, light concretes, asphaltic concretes, etc.). depending on the type of the used tires, dimensions and possible separations and treatment, the physical and mechanical characteristics of these aggregates might change. some physical, chemical and direct shear tests were performed on three gradation classes of waste tire rubber powder. the tests results were combined with data from previous studies to generate empirical relationships between cohesion, friction angle and particle size of waste tire powder rubber. a cubic (third order) regression model seems to be more appropriate compared to linear and quadratic models. keywords-rubber powder; waste tires; experimental; polynomial regression i. introduction in recent decades, the worldwide growth of the automobile industry and the increasing use of cars as the main means of transport have tremendously boosted tire production. this has generated massive stockpiles of used tires. extensive research projects were carried out on how to use used tires in different applications [1]. the scrap tires in algeria are estimated at approximately 25,918 tones/year [2].waste tires need a larger storage space than other waste due to their large volume and fixed shape. they are unlikely to be decomposed, as burying the waste tires would shorten the service life of the burial ground and have low economic benefit; in addition, buried waste tires often emerge from the burial ground surface or destroy the anti-leakage cover of the burial ground and the exposed waste tires accumulate water that may breed bacteria, molds, insects or mice. in case of fire, waste tires generate toxic gases, such as dioxin, that could result in severe pollution problems [3-4]. in order to properly dispose these millions of tires, the use of innovative techniques to recycle them is important. the use of scrap tires including tire chips or tire shreds comprised of pieces of scrap tires, tire chip/soil mixtures, tire sidewalls, and whole scrap tires in civil engineering applications is the object of the standard astm d 6270. these materials can be used in lightweight embankment fill, lightweight retaining wall backfill, drainage layers, thermal insulation to limit frost penetration beneath roads, insulating backfill to limit heat loss from buildings, and replacement for soil or rock in other fill applications [5]. rubber tires can also be used in civil and non-civil engineering applications such as in road construction, in geotechnical works, as a fuel in cement kilns and incineration for production of electricity or as an aggregate in cement-based products or in geotechnical field [6-7-8]. astm d 6270 studied the properties of shredded waste tires (practical size of 2 mm and more), but not waste tire rubber powder. the objective of this paper is to present experimental work on the waste tire rubber powder. further, a polynomial regression analysis of the cohesion and friction angle versus the particles size is proposed. ii. materials and methods a. tire rubber powder scrap tire rubber powder can be obtained from tires through two principal processes: (1) ambient, which is a method in which scrap tire rubber is ground or processed at or above ordinary room temperature and (2) cryogenic, a process that uses liquid nitrogen to freeze the scrap tire rubber until it becomes brittle and then uses a hammer mill to shatter the frozen rubber into smooth particles [9]. for this study, the rubber powder was produced from three used automobile tires by mechanical shredding at ambient temperature. steel was removed by magnetic separation and one part of textile fiber was removed by density. a photograph of the used scrap tire rubber sample is shown in figure 1. fig. 1. used rubber powder. a less than 0.08 mm, b size of 1 mm and c size of 1.6mm. engineering, technology & applied science research vol. 4, no. 4, 2014, 669-672 670 www.etasr.com bekhiti et al.: mechanical properties of waste tire rubber powder b. physical characteristics of the rubber powder the used specimens don’t contain steel but contain less than 2% of textile fiber. since it was not possible to determine the gradation curve of the rubber powder as for normal aggregates, a microscope examination was done. dimensions of rubber powder vary from 1.6 mm to 0.8 mm with an average particle size of 1 mm. the density of the rubber powder is determined using helium pycnometer and it’s about 0.83. rubber powder is also characterized by an insignificant water absorption less than 3%.table i resumes some characteristics of the used waste tire powder rubber. table i. rubber powder characteristics properties rubber powder density 0.83 size 80 µm – 1.6 mm elongation (%) 420 rate of steel fiber 0% c. chemical analysis the tire is made up mainly by rubber. its constitution varies a little between the car tires and heavy truck tires. rubber consists of a complex mixture of elastomers, polyisoprene, polybutadiene and stirene-butadiene. stearic acid (1.2%), zinc oxide (1.9%), extender oil (1.9%) and carbon black (31.0%) are also important components of tires [10-11]. in table ii, chemical composition of the used rubber powder is presented. the quantity of steel is generally about 15%, and it’s more important for the heavy trucks tires. for this study steel and one part of textile were removed by magnetic separation and density. table ii. rubber powder characteristics material/element mass percentage rubber 54% carbon black 29% textile 2% oxidize zinc 1% sulfur 1%. additives 13% d. direct shear test the tests were performed according to astm d 3080 standard [12]. the direct shear test is a laboratory testing method used to determine the shear strength parameters of rubber powder. to achieve reliable results, the test is often carried out on three or four samples of rubber powder. the sample is placed in a shear box for round specimens (60 mmdiameter and 20 mm height). the shear box is composed of an upper and lower box. the limit between the two parts of the box is approximately at the mid height of the sample. the sample is subjected to a controlled normal stress and the upper part of the sample is pulled laterally at a controlled strain rate or until the sample fails. the applied lateral load and the induced strain are recorded at given internals. these measurements are then used to plot the stress-strain curve of the sample during the loading for the given normal stress. results of different tests for the same rubber powder are presented in figures with peak stress on the horizontal axis and normal (confining) stress on the vertical axis. a linear curve fitting is often made on the test result points. the intercept of this line with the vertical axis gives the cohesion and its slope gives the peak friction angle. e. preparation of test specimens for practical consideration, specimens were separated to three gradation classes. class a: less than 0.08 mm, class b: size between 1.6 mm and 1 mm and class c: size more than 1.6 mm f. tests the specimens are round (60 mm diameter and 20 mm high). the realized test is an unconsolidated un-drained test (uu). the normal constraints (normal stress) used are: 100, 200 and 300 kpa. the speed of shearing is about 0.5 mm/min. the sample is placed between two half-boxes that can move relatively to each other. moreover, a piston permits to exert a normal constraint in the plan of shearing. the inferior half-box is involved horizontally at a constant speed. the total force of shearing f is to be measured using a fixed ring at the superior half-box. iii. results and discussion figure 2 presents the results of the shear strength tests (curve intrinsic), the cohesion and the internal friction angle of the waste tire rubber powder, value relatively important if compared to some experimental values of the literature. fig. 2. direct shear tests of rubber powder. the waste tire rubber powder is strongly compressible, moreover the surface quality of the powder produced by mechanical crushing with ambient temperature is irregular. the mohr-coulomb shear strength parameters obtained from direct shear tests by these studies are presented in (1). : 6.5 25 : 10 25 : 50 8 c tg class a tg class b tg class c tg                 (1) it’s observed that the cohesion values vary from 6.5 to 50 kpa, and fewer values were observed for class a and b sizes. engineering, technology & applied science research vol. 4, no. 4, 2014, 669-672 671 www.etasr.com bekhiti et al.: mechanical properties of waste tire rubber powder friction angles vary from 8 to 25° and it’s increasing with particle size. iv. polynomial regression the following table gives values of cohesion c and friction angle ø according to the average size of the rubber particles t according to the literature [10-11-13-16-17] and this work. table iii. experimental results references size (mm) c (kpa) ø (°) conditions of test <1.06 4.78 30 1.016-4.064 3.3516 31 black and shakoor, 1994 [10] 4.064-6.858 6.224 27 dry density about 0.33 2 0 25.8 benda 1995 [11] 2 0 36 rate of deformation 10% rate of deformation 20% massad et al, 1996 [13] 4.572 81.97 15 rate of deformation 20% wu et al, 1997 [14] 2 0 45 no steel fiber bekhiti et al 2012 [15] 0.405 77 8.5 no steel fiber 1.6 6.5 25 1 10 25 present work 0.08 50 8 no steel fiber the graph in double y of figure 3 represents the principal results of c and ø according to the average particles sizes according to the literature and this work. the values of cohesion vary from 0 to 81.97 kpa, for the friction angle the values vary from 8.5 to 45°. in order to estimate a relations ships among variables (t, c and ø), polynomial regressions analysis of c versus t and ø versus t using linear, quadratic and cubic models were used. only results of cubic models will be presented here, since coefficients of determination seems to be interesting. fig. 3. values the angle internal fraction and the cohesion according to decimal logarithm of the average size of waste tire rubber particle according to the literature and this work. a. variation of cohesion according to the rubber powder particle size the cubic model gives a rather faithful image of the situation compared to the linear and quadratic ones. the polynomial regression using cubic model is given by (2), with s=21.0599, and r-sq (multiple coefficient of determination) = 72.3%. r-sq (adjusted) value is about 58.4%. the fitted line plot is presented in figure 4. 2 387.25 132.4 59.22 6.48c t t t     where c: the cohesion (kpa) and t: the particle size in (mm). fig. 4. fitted line plot of cohesion versus particle size. b. variation of friction angle according to the rubber powder particle size for friction angle versus particle size, the polynomial regression using cubic model is given by (3), with s=5.186, and r-sq (multiple coefficient of determination) = 80.1%. rsq (adjusted) value is about 70.2%. the fitted line plot is presented in figure 5. the regression for this case is more representative than for c versus t. fig. 5. fitted line plot of internal friction angle versus particle size.. 2 31.557 36.90 14.39 1.548t t t      where: ø: friction angle in (°); t: the particle size in (mm). v. conclusion waste tire rubber powder is used in a variety of civil and non-civil engineering applications. some properties of rubber powder resulting from crushing of light vehicles waste tires with no steel fiber have been determined in this work: the particle size, the density, the chemical composition as well as the cohesion and friction angle by direct shear test. rubber powder, crushed mechanically in ambient temperature, showed engineering, technology & applied science research vol. 4, no. 4, 2014, 669-672 672 www.etasr.com bekhiti et al.: mechanical properties of waste tire rubber powder has a very low density of about 0.83, cohesion varied from 6.5 to 50 kpa. friction angle varied from 8 to 25° according to the average size rubber particle. using the results from this study along with previous results from other studies, cubic regressions is proposed. cohesion as well as friction angle versus particle size using cubic model give respectively for the coefficient of determination values of 72.3 and 80.1%. references [1] e. ganjian, m. khorami, a. a. maghsoudi, “scrap–tyre–rubber replacement for aggregate and filler in concrete”, construction and building materials, vol. 23, no. 5, pp. 1828-1836, 2009 [2] h. trouzine, a. asroun, n. asroun, f. belabdelouhab, n.t. long, “problem of waste tires in algeria”, nature & technologies, vol. 5, pp. 28-35, 2011[in french] [3] rubber manufacturer’s association, us scrap tire markets 2003 edition, washington (dc), rubber manufacturer’s association, 2004 [4] r.k. dhir, m.c. limbachiya, k.a. paine, recycling and reuse of used tyres, thomas telford publishing–thomas telford ltd, london, 2001 [5] astm d 6270-98 (reapproved 2004), standard practice for use of scrap tires in civil engineering applications, astm international, west conshohocken, usa [6] v. corinaldesi, g. moriconi, “durable fiber reinforced selfcompacting concrete”, cement and concrete research, vol. 34, no. 2, pp. 249–254, 2004 [7] v. corinaldesi, a. mazzoli, g. moriconi, “mechanical behaviour and thermal conductivity of mortars containing waste rubber particles”, materials & design, vol. 32, no. 3, pp. 1646–1650, 2011 [8] h. trouzine, m. bekhiti, a. asroun, “effects of scrap tyre rubber fibre on swelling behavior of two clayey soils in algeria”, geosynthetics international, vol. 19, no. 2, pp. 124-132, 2012 [9] california department of transportation, asphalt rubber usage guide, caltrans, state of california, department of transportation, sacramento, ca, usa, 2003 [10] b.a black, a. shakoor, “a geotechnical investigation of soil/tire mixtures for engineering applications”, proceedings on the first international conference on environmental geotechnics, pp. 617623, 1994 [11] c. c. benda, “engineering properties of scrap tires used in geotechnical applications”, report n° 95-1, vermont agency of transportation, montpelier, v.t., 1995 [12] astm d 3080–03 standard test method for direct shear test of soils under consolidated drained conditions, astm international, west conshohocken, usa [13] e. massad, r. taha, c. ho, t. papagiannakis, “engineering properties of tire /soil mixtures as a lightweight fill material”, geotechnical testing journal, vol. 19, no. 3, pp. 297-304, 1996 [14] w. y. wu, c. c. benda, r. f. cauley, “triaxial determination of shear strength of tire chips”, journal of geotechnical and geoenvironmental engineering, vol. 123, n. 5, 479-482, 1997 [15] m. bekhiti, h. sellaf, h. trouzine a. asroun, “propriétes mécaniques des granulats de caoutchouc issus du broyage des pneus uses”, 1st international conference on civil engineering, 8-9 may 2012, laghouat algeria [in french] engineering, technology & applied science research vol. 7, no. 5, 2017, 1996-2004 1996 www.etasr.com alizadeh et al.: an investigation of the effect of ventilation inlet and outlet arrangement on … an investigation of the effect of ventilation inlet and outlet arrangement on heat concentration in a ship engine room ε. alizadeh malek ashtar university of technology (mut) fereydunkenar, iran ealizadeh@mut.ac.ir α. maleki malek ashtar university of technology (mut) fereydunkenar, iran amaleki@gmail.com α. mohamadi malek ashtar university of technology (mut) fereydunkenar, iran abstract—τhe ventilation in the ship engine rooms is an essential issue concerning finest performance of engines and diesel generators as well as electric motors. the present study has aimed at the analysis of temperature distribution inside the ship main engine room. in the same way, attempts have been made to identify those points with considerable thermal concentration in main engine room space, so that proper ventilation systems could be engineered and utilized and favorable thermal conditions could be realized. the cfd approach has been utilized in order to analyze impact of the designed ventilation system on the temperature distribution pattern. the inlet layout and area have been analyzed under a variety of scenarios in order to decrease the average temperature and eliminate the heat concentrations in various points of the engine room. the temperature distribution and location and area of ventilation air inlet have been studied in different modes resulted in temperature distribution pattern, heat concentration outline and average volumetric temperature level in each mode. the results indicated that considerable circulating air volume is required compared to those levels suggested by common practices, calculations and standards in order to eliminate the heat concentration. keywords-surface ship; engine room ventilation; thermal analysis; heat analysis; naval i. introduction main and auxiliary engine rooms are of the main areas in a military floating ship containing lots of equipment, machineries, electrical gears and major engines and thus require proper ventilation under various severe weather conditions. ventilation of engine rooms is essentially important and follows a series of objectives including supply of air to engines for combustion purposes, heat transfer through convection and airflow for recovery and outflow of undesirable heat, fixing the temperature in a specific interval so that crews could operate there and electrical appliances be kept away from substantial thermal exposure [1]. there are few studies conducted on application of cfd in ventilation of marine engine rooms despite the importance of such analysis. authors in [2] estimated the thermal profile of a marine ship's engine room through simulation techniques and measuring approaches using in-field data gathering. the experimental data were integrated to cfd model for a thermal analysis under various applications. they made use of cfd approach for modeling of the ventilation system in a marine ship under operation in order to monitor the systems performance improvement (under severe weather conditions) that had the potential of higher efficiency of its engines and generators. they were focused on inlets and outlets to conduct the air flow and accordingly convection process in the room in order to enhance the efficiency of the engines and generators. operation conditions and average temperature suitable for crews as well as efficiency level of the engines had been selected as the performance indicators in their study. authors in [3] have conducted 3d simulation of the ventilation system in a closed engine room using cfd. their test results were in accordance with the estimations generated through the experimental formulations. authors in [4] conducted the ventilation analysis in a ship engine room. cfd analysis was included in the study in order to estimate the air flow in the engine room and use of results as a reference for locating the smoke sensors. internal air flow pattern could be resulted from analysis output. author in [5] also analyzed the simulation and optimization of ventilation system of a ship engine rooms. theory-based principles were applied in ventilation system design of the study. in addition, the cfd approach was utilized to investigate the conditions of engine room ventilation. the study analyzed and simulated the flow and temperature patterns in the engine room and resulted in an optimum design for the ventilation system. author in [6] simulated the temperature and flow pattern in the ship engine room. the study was conducted using the cfd approach in a ship engine room. simulation of the ventilation system resulted in flow rate and temperature distribution pattern in the engine room. in [7], author applied the numerical simulation approach to analyze the air flow distribution in the marine engine room. analyzing a ship engine room as a research objective, he simulated the ventilation system using cfd and analyzed the simulation results in detail. authors in [8] utilized cfd for air flow engineering, technology & applied science research vol. 7, no. 5, 2017, 1996-2004 1997 www.etasr.com alizadeh et al.: an investigation of the effect of ventilation inlet and outlet arrangement on … analysis in the ship engine room. the simulation presented in their study provides a clear view of the airflow distribution in the engine room. there are other similar studies conducted in the field of cfd analysis in the engine room including research and investigations made by authors in [9-12]. objective of the present study is to investigate the temperature distribution in the engine room; hence attempts have been made here to identify points with high level of heat concentration so that appropriate ventilation systems could be designed in order to realize a proper temperature condition. the cfd approach is also utilized in the present study to investigate the impact of ventilation system design on the temperature distribution pattern. ii. numerical and geometrical modeling of the engine room a. engine room geometry the ship studied in the present paper has two engine rooms equipped with 2850 kw diesel generator and 19500 kw turbocompressor. figure 1, shows one of the engine room interior arrangements with main engine and auxiliary equipment. fig. 1. equipment arrangement in ship engine room in this engine room expect of main engines and their exhaust pipes, there is some auxiliary machinery that includes fuel pumps and purifier, lubrication pumps and purifier, firefighting pump, air compressor etc. b. engine room heat source all engines and auxiliary equipments are source of heat that can be released to engine room space. each engine heat transfer to the space is described as follows. a) electric generators considering 97% efficiency level of the main engines (turbine & diesel) water cooled generators, there is 3% capacity loss. since 0.25% of the capacity loss in the watercooled generators has been released to engine room [13], it could be concluded that the heat transfer equals to 48 kw and 7 kw. b) diesel engine considering the diesel engine catalogue presented by caterpillar company, the heat radiation to the engine room equals to 128 kw. c) gas-turbine gas turbine structure differs considerably from diesel engine. gas turbine equipment is located in a box with specific air inlet and outlet. the inlet air serves as the cooling agent for the gas turbine in addition to supply of the air required in the combustion chamber. it should be noted that the box input air for turbine needs is supplied through a specific vent that has nothing to do with the engine room’s air inlets. gas turbine box is internally (thermal & acoustic) isolated. considering various electrical appliances exist in the gas turbine box, the temperature level is somehow stable. structure of turbine box and this air inlet and outlet is showed in figure 2. each side of the gas turbine has its own temperature which is calculated through simulation and varies between 308k and 317k and the average amount is 310k. table i. heat radiation of diesel engine to atmosphere fig. 2. gas turbine box and inlet and outlet of air. to assess the shell temperature of the turbine module, turbine box is modeled in the gambit which is called later in the fluent. it is assumed that the air flows through the module under 308 k temperature and 3 kg/s mass rate. following the simulation process, the average temperature contour of the module shell could be illustrated as figure 3. d) exhaust pipes the heat emissions from two exhaust pipes are determined from the curve presented in iso8861 [1]. according to the total lengths of exhaust pipes, the total heat emission to the engine room is calculated to be 5 kw. engineering, technology & applied science research vol. 7, no. 5, 2017, 1996-2004 1998 www.etasr.com alizadeh et al.: an investigation of the effect of ventilation inlet and outlet arrangement on … e) auxiliary machineries auxiliary machinery and equipment in the engine room operate under 100kw nominal capacity. by considering iso8861, there is a 20% loss of capacity assumed in the engine room (i.e. 20kw) that is added to loss of diesel engine. f) sum of heat radiations calculated heat radiations from engines, generators and other heat sources in engine room are listed in table ii. fig. 3. gas turbine module temperature contour table ii. thermal radiation of engine room auxiliary machineries equipment heat radiation (kw) generator (for turbine) 45 generator (for diesel) 7 gas turbine 8.9 diesel engine 128 exhaust pipes 5 auxiliary machineries 20 sum of heat radiation 205.6 c. boundary condition boundary condition of ventilation air inlet and outlet identifies velocity inlet and pressure outlet. the lateral and side walls of the ship engine room known as “wall” are exposed to convection heat transfer. since part of the side wall is in contact with water and the other part is in touch with air, it is analyzed separately. wall boundary condition of the diesel generators, turbine generators and diesel engines are the system walls with heat flux. constant temperature on the side wall is set as the turbine wall boundary condition. wall of the turbine and diesel engine exhaust pipe are set as the boundary condition shell with a 6 mm insulation thickness. bundary conditions and their description are shown in table iii. d. governing equations in this study; continuity equations, momentum conversation equations and energy conversation equations for steady state and incompressible flows in conjunction with buoyancy effects from boussinesq approximation are used for the analysis. table iii. boundary condition description boundary condition type condition value air inlet velocity inlet 5 m/s air outlet pressure outlet 1 atm side wall wall convection heat transfer coefficient for 10 w/m2.k and 15 w/m2.k for air and water respectively lateral wall wall symmetry diesel engine surface wall (constant flux) 1316(w/m2) gas turbine surface wall (constant temperature) 310k generator (for diesel) wall (constant flux) 133.48 (w/m2) generator (for turbine) wall (constant flux) 732.6 (w/m2) exhaust surface wall (constant temperature) 350k (gas turbine), 343k (diesel engine) continuity equation: . 0v   (1) momentum conversation equation:   2.        v v p v s (2) energy conversation equation:    2.   p tc v t k t s (3) where: s is the buoyancy force which affects the fluids and is derived from the boussinesq approximation:  1 refs g t t        (4) for ventilation of engine room, iso8861 [1], proposes some equations. equation (5) defines the total amount of air needed for the ventilation: c hq q q  (5) h hq c t     (6) d g a d c p m q    (7) q in (5) is the total volume of air needed for the ventilation of engine room, qc and qh are the total air volume for combustion and for evacuation of heat emission respectively. φh is the total amount of thermal emission from all equipment which is given in table ii. ρ, c, δτ are the density of air, specific heat capacity of air and the difference between inlet and outlet air at design conditions. pdg is the power of the engine room and mad is the air requirement for diesel engine combustion, in kilograms per kilowatt second. for investigating the thermal concentration in engine room, a dimensionless parameter, η, is defined as below: engineering, technology & applied science research vol. 7, no. 5, 2017, 1996-2004 1999 www.etasr.com alizadeh et al.: an investigation of the effect of ventilation inlet and outlet arrangement on … . . h h t m v t v t   (8) vh is the volume of space in engine room in which the temperature exceeds 55 oc (hot zones), th is the temperature in hot zones, vt is the total volume of engine room and tm is the average temperature of the engine room. considering iso 8861, temperature difference between air flow inlet and outlet in the engine room (while engines and other auxiliary are operating) should not exceed 12.5oc. it should be noted that the input air temperature has been set on 37 oc in the present study due to the ship’s geographical coordination. table iv. sum of the airflow for engine room ventilation equipment cooling airflow (m3/s) combustion airflow(m3/s) diesel engine 8.97 5.31 gas turbine 0.62 generator (for diesel) 0.5 generator (for turbine) 3.15 exhaust pipe 0.35 auxiliary machinery 1.4 iii. simulation initial inlet arrangement should be identified in advance to start the simulation process. the engine room is first simulated regardless of any vents in order to provide us with the best initial proposal so that warmer areas could be identified and accordingly initial vent layout could be arranged close to the proposed points. at the first phase the engine room is modeled regardless of any inlet and outlet air vent in order to identify critical and heat zone. the modeling showed that critical point and hot zones are close to the main heat sources. considering the first phase approach (without vents), the temperature level above the diesel engine is higher than other zones. in addition, since the combustion air of the engine diesel is directly supplied through the air exits in the engine room, most of the engine manufacturers/vendors suggest that the air inlet should be positioned close to the diesel engine super charger. it should be noted that a variety of positioning and sizes of the inlet and outlet have been considered in the present study for the ventilation of the engine room. the simulation is carried out with an inlet and an outlet vent and accordingly various scenarios have been analyzed in this case based on changes in the layout. initial layout has been arranged in accordance with the heat concentration pattern as shown in figure 4. the scenarios mentioned above will be analyzed further in detail. a. single inlet area of 4.5 m2 a) case 1 inlet is located above the diesel engine and outlet is located close to the diesel engine on the engine room ceiling (figure 5). in this case, highly heat concentration levels are observed above the diesel engine and the associated generator. on the other hand, the generator is exposed to heat concentration due to its distance from the vent. thus the vent is positioned to another point in the next layout to be located somewhere closer to both generator and top of the diesel. so the vent is positioned on the ceiling center and somewhere between the generator and diesel generator. however, it should be noted that considerable heat concentration does not increase again and exceed acceptable level. hence this task is carried out with care in multiple stages. in the next step the vent position is closer to the ceiling center and the turbine generator. fig. 4. isometric view of temperature contours of engine room with no inlet and outlet fig. 5. isothermal contours of temperature and mesh of case 1 b) case 2 inlet is located in the ceiling center and outlet is at corner near the diesel engine (figure 6). average temperature level in this case is 4 degrees lower compared to the previous case however heat concentration above the generator (for diesel) and generator (for turbine) remained the same. decrease in the average temperature indicates that increase in distance between vents inlet and outlet leads to better circulation of the air enter in the engine room and accordingly decrease in the average temperature. however, heat concentration above the generator (diesel & turbine) has remained the same. therefore, attempts have been made in the next step to increase the distance even more compared to the case 2, so the next position could be suggested above the turbine generator. engineering, technology & applied science research vol. 7, no. 5, 2017, 1996-2004 2000 www.etasr.com alizadeh et al.: an investigation of the effect of ventilation inlet and outlet arrangement on … fig. 6. isothermal contours of temperature and mesh of case 2 c) case 3 inlet is located above the generator (for turbine) and output is located close to the diesel engine on the engine room ceiling (figure 7). average temperature in this case is lower than the two cases mentioned above, however the only drawback to this layout could be stated as the increase in the heat concentration around the diesel engine where supplies the air required for combustion purposes. increase in air temperature around the diesel engine and accordingly increase in the combustion air temperature leads to loss of engine efficiency. simulation of cases 1, 2 and 3 shows that it is unlikely to eliminate heat concentration in all points. positioning the inlet above the diesel engine leads to heat concentration in south part of the generator (for turbine) and above the generator (for diesel) & generator (for turbine). considering the velocity contours, heat concentration takes place in the south part of the generator (for turbine) due to improper circulation of the input air in the area. positioning the inlet vent in the middle of the ceiling decreases the average temperature compared to the case 1. considering larger distance between inlet & outlet in this case and better air circulation in the engine room, this issue is both feasible and justifiable. besides, heat concentration in the south part of the generator (for turbine) is disappeared though it stays the same in the area above the machineries and equipment. positioning the inlet vent above the generator (for turbine) decreases the average temperature again while removing the heat concentration above the generator (for turbine). however, increase in heat concentration in the north part of the generator (for diesel) may lead to loss of the diesel engine efficiency. in addition, heat concentration above the generator (for diesel) stays the same. simulation results in this case are listed in table v. table v. results for cases 1-3 parameter/case c.1 c.2 c.3 inlet velocity (m/s) 5 5 5 inlet area (m2) 4.5 4.5 4.5 outlet area (m2) 2 2 2 average temperature (k) 318.5 314.5 312.4 heat concentration 0.18 0.1 0.14 considering the simulations mentioned above, it could be concluded that the 4.5 m2 single inlet case study does not meet the engine room requirements. therefore, the inlet area is divided into two equal parts in the next step to evaluate various positioning and layouts. there are two inlets for the ventilation air, each of which is 2.25 m2 for simulation of this case that conduct the 308 k air to the engine room. fig. 7. isothermal contours of temperature and mesh of case 3 b. two inlet areas of 2,25m2 a) case 4 both inlets are above the engine diesel and in middle of the room and outlet’s output is located close to the diesel engine on the engine room ceiling (figure 8). although the heat concentration in this case has been considerably removed, the concentration above two generators and among machineries and equipment stay the same. next vent positioning is suggested in the middle of the ceiling and above the generator (for turbine) to decrease the temperature level around the generator (for turbine). fig. 8. isothermal contours of temperature and mesh of case 4 b) case 5 inlets are in the middle of the ceiling and above the generator (for turbine) and outlet’s output is located close to the diesel engine on the engine room ceiling (figure 9). heat engineering, technology & applied science research vol. 7, no. 5, 2017, 1996-2004 2001 www.etasr.com alizadeh et al.: an investigation of the effect of ventilation inlet and outlet arrangement on … concentration points around the diesel engine still exist in this case due to lack of a vent above the diesel engine. therefore, inlets are positioned in the diesel engine and the generator (for turbine) in the next positioning layout. fig. 9. isothermal contours of temperature and mesh of case 5 c) case 6 inlets are on the generator and diesel engine and outlet is located close to the diesel engine on the engine room ceiling (figure 10). although average temperature in this layout has shown a little bit increase compared to case 2, heat concentration is decreased and limited to east part of the diesel engine due to inlets positions far away from the ceiling center. analysis of the double-vent case with total area of 4.5m2 indicates that the heat concentrations are not eliminated and there are at least some parts of the engine room deprived from input air circulation for ventilation purposes. results of simulations in these cases are listed in table vi. fig. 10. isothermal contours of temperature and mesh of case 6 considering results of the 4.5m2 single inlet case and three different positioning layouts, it was shown that positioning the inlet above the diesel engine and in the middle of the ceiling are better cases. considering the double vent case with total area of 4.5m2, the heat concentration inside the engine room is not eliminated totally. part of the engine room is deprived of the intake air flow required for cooling purposes. considering 6 simulations made with a total vent area of 4.5 m2 it could be concluded that the proposed 4.5m2 area (obtained through iso 8861) is not enough for cooling purposes of the mmr2 engine room. so the entrance vent area will be increased until the desired results are achieved. hence the next two cases are simulated in the case of 6m2 vent inlet area. if the proper outcome is not resulted from the 6m2 single vent, the area could be further increased. table vi. results for cases 4-6 with double inlet parameter/case c.4 c.5 c.6 inlet velocity (m/s) 5 5 5 inlet area (m2) 4.5 4.5 4.5 outlet area (m2) 2 2 2 average temperature (k) 315.9 313.4 314.5 heat concentration 0.19 0.14 0.18 c. inlet area of 6m2 a) case 7 inlet is positioned on the diesel engine and outlet is outlet vent is located close to the diesel engine on the engine room ceiling (figure 11). there is a considerable heat concentration around the generator shell due to distance of the inlet from the generator. fig. 11. isothermal contours of temperature and coordination of inlet and outlet for case 7 b) case 8 inlet is positioned in the ceiling center and outlet is located close to the diesel engine on the engine room ceiling (figure 12). both maximum and minimum temperature levels are decreased in this case compared to the previous one. inlet positioning in the ceiling center still creates heat concentration between equipment and lateral walls of the engine room. compared to the 4.5m2 inlet area and analysis of the 6m2 single inlet indicates that despite the improvements made earlier, thermal condition has not become desirable yet considering 6 m2 single or double inlet vent, although the average temperature in the engine room decreases, the heat concentration in some points is not eliminated as shown in table vii. therefore, various cases of single & double vents (with total area of 8m2) with various arrangements are analyzed in the next section. engineering, technology & applied science research vol. 7, no. 5, 2017, 1996-2004 2002 www.etasr.com alizadeh et al.: an investigation of the effect of ventilation inlet and outlet arrangement on … fig. 12. isothermal contours of temperature and coordination of inlet and outlet for case 8 d. inlet area of 8m2 a) case 9 inlet is positioned on the diesel engine and located close to the diesel engine on the engine room ceiling (figure 13). although average temperature in this case is decreased compared to the similar cases of 4.5m2 and 6m2, heat concentration has remained the same between equipment and the side walls of the engine room. fig. 13. isothermal contours of temperature and coordination of inlet and outlet for case 9 table vii. results for cases 7 8 parameter/case c.7 c.8 inlet velocity (m/s) 5 5 inlet area (m2) 6 6 outlet area (m2) 2 2 average temperature (k) 316.9 312.9 heat concentration 0.15 0.07 b) case 10 inlet is located in the ceiling center and outlet is located close to the diesel engine on the ceiling (figure 14). in spite of the decrease in the average temperature compared to the previous and similar cases with 4.5 & 6-m2 inlet area, there is a considerable heat concentration above the two generators and between generator (for turbine) and side walls as well. results of simulations in this case are listed in table viii. fig. 14. isothermal contours of temperature and coordination of inlet and outlet for case 10 table viii. results for cases 9 10 parameter/case c.9 c.10 inlet velocity (m/s) 5 5 inlet area (m2) 40 40 outlet area (m2) 2 2 average temperature (k) 314.5 312 heat concentration 0.062 0.058 e. two inlet areas of 4m2 simulations in these cases require two inlets for ventilation air (308 k) each of which 4m2. there are four layouts considered for simulation of double inlets as follow. a) case 11 inlets are positioned in the middle of the room above the diesel engine and outlet located close to the diesel engine on the engine room ceiling (figure 15). average temperature level is decreased in this case same as the similar aforesaid 4.5m2 case, however the heat concentration remains the same between diesel and generator (turbine) and the side walls of the engine room and above the generators as well. fig. 15. isothermal contours of temperature and coordination of inlet and outlet for case 11 engineering, technology & applied science research vol. 7, no. 5, 2017, 1996-2004 2003 www.etasr.com alizadeh et al.: an investigation of the effect of ventilation inlet and outlet arrangement on … b) case 12 inlets are positioned in the ceiling center and above the generator (for turbine) and outlet is located close to the diesel engine on the engine room ceiling (figure 16). heat concentration above the diesel engine and generator (for turbine) is considerably decreased in this case however the concentration has remained the same above the generator. c) case 13 inlets are positioned above the generator (for turbine) and diesel engine and outlet vent is located close to the diesel engine on the engine room ceiling (figure 17). heat concentration on the diesel engine is completely removed. it is insignificant on the generator however there is considerable heat concentration above the generator (for diesel). d) case 14 considering outlet vents were close to the diesel engine in all the aforesaid cases, in case 14 inlets are positioned on the diesel engine and turbine (with total area of 8m2) while the outlet is positioned close to the generator (for turbine) (figure 18). heat concentration exists in the south part of the generator (for diesel) and generator (for turbine) in this case while it shows considerable decrease in temperature above the equipment and machineries. further distances between input and output vents, displacement of larger air volumes and better air circulation in the engine room are among the advantages of such layout. iv. analysis and conclusion positioning the inlets on the diesel engine leads to heat concentration around the generator (for turbine) in the single inlet cases while considering position of the outlet vent, input air is not circulated properly. in cases of relocating the inlets to the ceiling center there is a heat concentration in areas between the engine and the room walls as well as zones between generator (for turbine) and the room walls. analyzing the temperature contours show that air flow is not circulated adequately in such zones. positioning the inlets above the generator (for turbine) is the optimum case concerning lower average temperature level which is resulted through farther distance between inlet and outlet vents in this case which exposes the engine room to considerable inlet air circulation. however, heat concentration around the diesel engine increases in this case may lead to loss of engine efficiency due to the hot air entering the combustion chamber. the 8m2 single vent positioned in the ceiling center has shown better conditions compared to other cases. considering temperature and flow current contours in double inlet cases, average temperature and its level of concentration are lower compared to the single inlet case due to proper circulation of the ventilation air and sweeping hot air away in highly concentrated areas. on the other hand, there are some heat concentrations in case of the double inlet so that it could be shown that the flow rate and current velocity decrease in such areas and ventilation air flow is not properly circulated and accordingly heat concentration increases. figures 19 and 20 show the parameter η and the average temperature of the above studies cases respectively. although impact of layout, single and double positioning and inlet areas are integrated together, considering aforesaid issues, it could be concluded that the double inlets layout with two 4m2 inlet area above the turbine and diesel engine has shown better results with respect to heat concentration and flow current pattern compared to all other simulations elaborated earlier in the present study. in the same way heat concentration in this case has shown better improvements compared to other cases fig. 16. isothermal contours of temperature and coordination of inlet and outlet for case 12 fig. 17. isothermal contours of temperature and coordination of inlet and outlet for case 13 fig. 18. isothermal contours of temperature and coordination of inlet and outlet for case 14 engineering, technology & applied science research vol. 7, no. 5, 2017, 1996-2004 2004 www.etasr.com alizadeh et al.: an investigation of the effect of ventilation inlet and outlet arrangement on … table ix. results for cases 11 14 with double vent parameter/case c.11 c.12 c.13 c.14 inlet velocity (m/s) 5 5 5 5 inlet area (m2) 8 8 8 8 outlet area (m2) 2 2 2 2 average temperature (k) 313.1 310.5 311.3 310.7 heat concentration 0.08 0.05 0.06 0.05 fig. 19. the graph of η for each case fig. 20. graph of average temperature for each case references [1] bs en iso 8861:1998, shipbuilding engine-room ventilation in diesel engined ships design requirements and basis of calculations, british standards, 1998. [2] w. newton, m. lewis, d. carswell, n. lavery, b. evans, d. bould, j. sienz, “investigating the thermal profile of a marine vessel engine room through simulation with field measurements”, applied thermal engineering, vol. 73, no.1, pp. 1360-1370, 2014 [3] s. jiang, x. xu, “three-dimensional numerical simulation of the ventilation system in closed engine rooms based on cfd”, chinese journal of ship research, vol. 2, no. 2, pp. 80-83,89, 2013 [4] h. lee, h, k. seo, “ventilation analysis for an engine room of a ship”, journal of the society of naval architects of korea, vol. 41, no. 5, 2004 [5] y. c. liang, simulation analysis and optimization of ship engine room ventilation system, msc thesis, shanghai jiaotong university, 2012 [6] w. j. he, numerical simulation of temperature and velocity fields in vessel engine room, msc thesis, 2006 [7] y. jiang, numerical simulation of airflow distribution in marine engine room ventilation, msc thesis, harbin engineering university 2013 [8] j. h. ding, c. b. ni, y. p. he, “cfd application in airflow field analysis for lng ship engine room”, proceedings of the 11th pacific/asia offshore mechanics symposium, pp. 225-229, 2014 [9] x. j. li, r. p. zhou, d. konovessis, “cfd analysis of natural gas dispersion in engine room space based on multi-factor coupling”, ocean engineering, vol. 111, pp. 524–532, 2016 [10] j. a. perez, j. a. orosa, t. grueiro, “a three-dimensional cfd simulation study to reduce heat stress in ships”, thermal engineering, vol. 94, pp. 413–421, 2016 [11] j. c. ramos, m. beiza, j. gastelurrutia, a. rivas, r.anton, g. s. larraona, i. de miguel, “numerical modelling of the natural ventilation of underground transformer substations”, applied thermal engineering, vol. 51, no. 1-2, pp. 852-863, 2013 [12] p. rohdin, b. moshfegh, “numerical modelling of industrial indoor environments: a comparison between different turbulence models and supply systems supported by field measurements”, building and environment, vol. 46, no. 11, pp. 2365 2374, 2011 [13] man diesel & turbo, man v 28/33d stc project guide, 2014 engineering, technology & applied science research vol. 7, no. 6, 2017, 2313-2318 2313 www.etasr.com jayakumar and kulkarni: a simple measuring model for evaluating the performance of small block … a simple measuring model for evaluating the performance of small block size accesses in lustre file system naveenkumar jayakumar department of computer engineering bharati vidyapeeth deemed university college of engineering pune 43, india naveenkumar@bvucoep.edu.in anuja kulkarni department of computer engineering bharati vidyapeeth deemed university college of engineering pune 43, india anukul2009@gmail.com abstract—storage performance is one of the vital characteristics of a big data environment. data throughput can be increased to some extent using storage virtualization and parallel data paths. technology has enhanced the various sans and storage topologies to be adaptable for diverse applications that improve end to end performance. in big data environments the mostly used file systems are hdfs (hadoop distributed file system) and lustre. there are environments in which both hdfs and lustre are connected, and the applications directly work on lustre. in lustre architecture with out-of-band storage virtualization system, the separation of data path from metadata path is acceptable (and even desirable) for large files since one mdt (metadata target) open rpc is typically a small fraction of the total number of read or write rpcs. this hurts small file performance significantly when there is only a single read or write rpc for the file data. since applications require data for processing and considering in-situ architecture which brings data or metadata close to applications for processing, how the in-situ processing can be exploited in lustre is the domain of this dissertation work. the earlier research exploited lustre supporting in-situ processing when hadoop/mapreduce is integrated with lustre, but still, the scope of performance improvement existed in lustre. the aim of the research is to check whether it is feasible and beneficial to move the small files to the mdt so that additional rpcs and i/o overhead can be eliminated, and read/write performance of lustre file system can be improved. keywords-big data; metadata; lustre; active storage; small file i. introduction the quantity of data generated and consumed by hpc (high-performance computing) applications is increasing exponentially. current i/o paradigms and file system designs are often overwhelmed by this deluge of data. to improve the i/o throughput to a certain extent, parallel file systems incorporate features such as data striping, sharing resources, etc. file systems such as lustre, afs, nfs use a single metadata server to manage globally shared file system namespace. while simple, scalability can’t be achieved by this design, having as result the metadata server to become a bottleneck and a single point of failure. in big data environment, most of the files (70%) are small, and most data (nearly 90%) is placed in big files. the number of small files is big though used space is not. small files consume more resources and produce big slowdown. also, the latency of access to small files is important. the problem is studied by considering lustre file system as a use case. lustre file system is open source, most widely used in hpc environment and easy to implement. lustre is a general public licensed (gnu), open-source distributed, parallel file system. it is developed and maintained by sun microsystems inc. lustre is supported by linux operating system, and it presents a posix interface to its clients with which shared file objects can be accessed in parallel. the key features offered by the lustre file system are, among others, scalability, high-performance, posix compliance, high availability, interoperability. lustre is an object-based file system with three main components: object storage servers (osss), metadata servers (mdss), and clients. when a client wants to write a file to the lustre file system, first it communicates with the mds with a write request. the mds checks for the user authentication and the intended file location. depending on the file system settings or the directory settings, the mds sends back a list of osts that can be used by the client to write the file. once the reply is sent by the mds, the client can now directly interact with the assigned osts without any contact with the mds. this is applicable for any file regardless of size, whether it's a few bytes or a few terabytes [1]. the main advantage of lustre file system over storage area network (san) file system and network file system (nfs) is that it provides: a global name space, the ability to distribute very large files across multiple storage nodes, wide scalability, in performance as well as storage capacity. since large files are distributed across many nodes in the cluster environment, lustre file system is best suited for high-end hpc cluster i/o systems. lustre servers are equipped with multiple storage devices which provide high-availability. engineering, technology & applied science research vol. 7, no. 6, 2017, 2313-2318 2314 www.etasr.com jayakumar and kulkarni: a simple measuring model for evaluating the performance of small block … lustre can handle and serve up to tens of thousands of clients. the high-availability mechanism should enable any cluster file system to handle server failures or reboots transparently. the lustre failover mechanism is robust and transparent, and it allows servers to be upgraded without the need to take the system down. accessing small files on the lustre is not efficient. the read/write performance of lustre file system is currently optimized for large files, i.e. files more than few megabytes in size. to access any file, client has to send initial open rpc to the mdt and after that, to fetch the data from the osts, there are separate read/write rpcs to the osts. in addition to this, there are separate rpcs to perform disk i/o on mdt and ost. this functionality separation is desirable for large files since one open rpc to mdt requires less execution time compared to total number of read/write rpcs to osts, but this affects overall performance of small file significantly when there is only one read or write rpc to the osts for accessing file data. one possible way to improve small file performance in lustre is to put the data for small files only on the mdt where metadata also resides so that additional rpcs and i/o overhead can be eliminated. this research aims to check whether it is feasible and beneficial to move the data from ost to mdt and if yes how much data can be pushed onto the mdt. ii. background a. lustre: component view on architecture lustre file system is supported by linux operating system, and it presents a posix interface to its clients with which shared file objects can be accessed in parallel. lustre is an object-based file system with three main components: object storage servers (osss), metadata servers (mdss), and clients. lustre components are as shown in figure 1. fig. 1. lustre: component view on architecture b. lustre components  metadata server (mds) metadata servers provide metadata services. correspondingly the metadata client (mdc) is a client of those services that makes metadata available to the lustre clients. file metadata, such as file names, access permissions, directory structures, is stored on the metadata target (mdt).  management server (mgs) the management server, stores configuration information for all available lustre file systems in a cluster. lustre clients and lustre target contacts the mgs to retrieve and provide information respectively. the mgs can have a separate disk for storage, or it can share a disk with a single mdt.  object storage server (oss) the oss exposes block devices and serves data to the client. correspondingly, object storage client (osc) is a client of the services. each oss manages one or more osts (object storage targets). osts are used to store file data in the form of objects. c. lustre functionality the collection of mds/mgs and oss/ost are referred to as lustre server front ends and ldiskfs, fsfilt as lustre server back ends. in lustre, file operations like create, open, write, read, etc. require metadata information which is stored on mds. this service provided by mds is accessed through client interface module, known as metadata client (mdc). fig. 2. basic lustre i/o operation from the mds point of view, every single file is composed of numerous data objects, and these objects are striped across one or more osts. each data object is assigned with a unique object id. mds stores normal file metadata attributes like inode with some additional information known as extended attributes (ea). extended attribute is used to store file objects layout information (also called as striping ea) which is used to map file object id with corresponding osts. consider one example, if a file p has a stripe count of three, then its ea will be : ea  <obj id x, ost a> <obj id y, ost b> <obj id z, ost c> stripe size and stripe width before reading the file stored on the osts, client will communicate with mds via mdc (metadata client) and collect the information about osts where the objects of the file are stored. according to the example, the objects of the file are stored on ost a, ost b and ost c. at client side, this information is structured in lov (logical object volume). now the client can communicate with corresponding osts through a client module interface known as osc (object storage client). lov is the software layer in the client stack and it is used to direct the pages towards the correct oscs and then the engineering, technology & applied science research vol. 7, no. 6, 2017, 2313-2318 2315 www.etasr.com jayakumar and kulkarni: a simple measuring model for evaluating the performance of small block … oscs assemble a vector of pages, group them and send them to ost through poratlrpc and lnet. iii. rpc mechanism in native lustre in lustre file system, the communication between client and server is coded as an rpc (remote procedure call) request and response. this middle layer is known as ptl-rpc i.e., portal rpc which translates the file system request in the form of rpc request and response and the lustre networking (lnet) provides network infrastructure to put that down onto the wire. a. rpc to mds let's assume client c1 wants to open the file /lustre/d1/d2/test.txt to read. here /lustre is the mount point. the first rpc request is lock_enqueue with lookup intent. this request is sent to mds for the lock on d1. the second rpc request is also lock en-queue with lookup intent. this request is also sent to mds asking inodebits lock for d2. the inodebits lock will be returned with its resources represented by the fid of d1 and d2. the third rpc request is a lock_enqueue with open intent, but it is not asking for lock on test.txt. the file content is provided by ost, and hence it can be opened and read without a lock form mds. now the lock is requested from an ost. b. rpc to oss after getting the ea structure from the mds, the client can communicate with oss. consider one example with one client and four osts. client c1 reads file p. the file p is striped across four osts with data objects p1, p2, p3, and p4. first, client c1 sends lock enqueue requests to all four osts in parallel, asking for read lock with intent flag set. if any of the objects client c1 is asking has a blocking request, then the corresponding osts don't grant the lock. instead, they just return the information described by a data structure lvb (lustre value block). lvb contains the information like file size, modification time, etc. if there are no any conflicts, the read locks on the entire file objects will be granted to c1 with lock mode pr. 1) when client c1 wants to access a file stored on osts, it sends lookup rpc to mds 2) at the mds side, after receiving rpc from client c1, the lock manager will grant the lock for the resource requested by the client. now client c1 sends the second rpc to the mds with the intent to create or open the file. 3) so, at the end of step 2, c1 will get the lock, extended attribute (ea) information and other metadata details which the client needs to communicate with osts. 4) once the client gets the lock and ea information, it can perform i/o operations. 5) mds maintain queue to track the allocated resources. when multiple clients try to access the same file then the new client has to wait in the waiting queue till the time the current owner of the lock releases the lock. once the lock is released, the mds will then hand over the lock to the new client. 6) for example, client c2 wants to access the same file which was earlier opened by c1 then c2 will be placed in the waiting queue. mds will send a blocking ast to c1 to revoke the lock granted. on receiving the blocking ast, c1 will release the lock. in some scenario where client c1 is down or something goes wrong, mds will wait for a ping timeout of 30 seconds after which it will revoke the lock. 7) once the lock is revoked, the mds will grant a lock handle and ea for the file to c2. c2 can proceed with i/o once it gets the lock handle and ea information. c. rpc mechanism in proposed system this research aims to improve the performance of small files by putting small files data only on mdt so that the additional read/write rpcs to the osts can be eliminated. this allows the improving of small file performance. the mdt storage is configured with raid 1+0 which is well-known for high-iops. data on mdt can be used in conjunction with dne (distributed namespace) to improve the efficiency. to store file data on the mdt, system administrators or users must explicitly specify a layout that will allow storing the data on mdt at the time of file creation. the maximum file size for which data can be stored on mdt must be specified by the administrator so that users cannot store large files on mdt which will cause problems to other users. if the layout of a file specifies to the client to store the data on the mdt, but the file size reaches to the maximum size specified by the administrator, then the data will be migrated to ost. in native lustre architecture, the small file data is present on the ost. whenever the client wants to access data from small files, it has to send rpcs to both mds and oss. as the number of rpcs get increased the overall latency increases which affects the i/o performance. in the proposed system, the data for small files will be stored on mdt instead of osts. since the data and metadata are present on mdt, the client has to send rpc to mds only. as the number of rpcs decreases the overall latency also decreases and i/o performance for the small files can be improved to some extent. iv. core methodology a. lustre setup figure 2 shows the proposed system architecture in which two virtual machines are created. the virtual machines are formatted with centos 6.7 operating system and kernel is patched with lustre 2.7.0 software release. one virtual machine is configured with mds (metadata server) having single mdt (metadata target) and other with oss (object storage server) with two osts (object storage target). lustre clients are connected to the server over ethernet connection, and they are also formatted with centos6.7 operating system. lustre file system contains two types of servers, a metadata server (mds) and one or more object storage servers (osss). since the mds is the starting point for all posix file system operations, it must quickly handle many remote procedure calls (rpcs). to access the file from a lustre file system, lustre client needs to query to the metadata target via the mds to engineering, technology & applied science research vol. 7, no. 6, 2017, 2313-2318 2316 www.etasr.com jayakumar and kulkarni: a simple measuring model for evaluating the performance of small block … obtain the file attributes (e.g., file type, owner, access permission) along with the file data layout. fig. 3. system architecture the io operations on the mdt are mostly small and random. if more data is cached into memory, then the mds can respond to client queries faster. therefore, the mds needs a large amount of ram to cache the working set of files, and powerful cpus to handle the simultaneous inquiries. the amount of memory required by the mds depends on a number of clients and the number of files accessed by them in their working set. apart from 1 gb memory required by the operating system and 4 gb memory needed for the file system journal, nearly 0.1% of the mdt size is needed for the mdt file system's metadata cache. the remaining ram is available for caching the file data for the client/application file working set. the file working set cached in the ram is not used by the clients actively all the time, but it should be kept hot to reduce io latency and avoid adding extra read io/s to the mdt which is under load. for the kernel data structure approximately 2 kb of ram is needed, to keep a file in the cache without a lock. for the ldlm (lustre distributed lock manager) lock every client requires 3 kb of ram for each file in the cache. b. lustre benchmarking tools native lustre performance can be monitored by using different benchmarking tools. the iozone [2] tool is used to test the read/write performance of small files on lustre platform. ior [3] test is conducted to benchmark the speed of read/write operations on mdt and ost. data duplicator [4] command is implemented to monitor whether it is beneficial to move small file data on mdt to minimize the number of rpcs. the dd command is used to check the feasibility of the proposed model. it is not possible to put the data on mdt and test the small file performance directly as the file layout must be specified before accessing any file. 1) iozone: iozone is the benchmarking tool for the file system. the benchmark measures a variety of file operations (read, write, etc.) and generates the results accordingly. iozone runs under multiple operating systems. iozone is useful for performing file system analysis broadly, and it tests file i/o performance for the following file operations: read, write, re-write, re-read, fread, fwrite, read backwards, random read, read strided, mmap, pread, aio_read, aio_write. 2) ior: ior (interleaved or random) is designed to measure i/o performance of parallel file system at both the mpi-io and posix level. the ior benchmark is developed by llnl (lawrence livermore national laboratory), and it tests system performance by considering parallel/sequential read/write operations. the ior_survey script is used to test the performance of the lustre file system. it uses various interfaces and access patterns to test the performance of a parallel file system. mpi is used for process synchronization. under the control of constants defined at compile time, i/o is done via mpi-io. the data is written and read using parallel transfers of blocks of contiguous bytes. these blocks are of equal size, and they do not overlap each other. the test consists of three main operations creating a new file, writing the data in it, then reading the data block. there are two ways to run ior: (a) interactive command line with arguments. for example: ior -w -r -o filename this performs write and read to the specified file. (b) interactive command line with scripts. for example: ior -w -f script. this performs all tests in the script to check write data performance. 3) dd (data duplicator) command: the dd command stands for "data duplicator". it is used for data copying and converting. it is a very powerful utility for linux which is used for multiple applications like –backup. it can restore a partition or the entire hard disk, backup of master boot record (mbr) and is also used by linux kernel make file to make boot images. improper usage of dd command can lead to data loss, hence it must be run by the super user. the syntax for dd command is dd if=<source file name> of=<target file name> [options]-[4]. n the syntax above ' if 'stands for input-file and ' of ' stands for output-file. the 'source file name' and 'target file name' in the syntax can be disks, partitions, files or devices from which data can be read or written. to test the native lustre performance, ‘dd’ command can be run on lustre client node. ‘dd’ command is used to monitor the write performance of disk device. v. result analysis a. small file performance on native lustre platform the iozone test is conducted on lustre client node to check the i/o performance of read/write file operations in native lustre platform and also the impact of record size on i/o performance. a set of iozone tests is executed on the client to find out the influence of record size. to evaluate the read/write performance with iozone, the file size is set to 2g with stripe size 4m and data striped across 2 osts. figure 4 shows the results of the tests. the vertical axis is the read/write bandwidth (data transfer rate in bits/sec), and the horizontal axis is the record size. the red line shows write performance, and the blue line shows read performance. engineering, technology & applied science research vol. 7, no. 6, 2017, 2313-2318 2317 www.etasr.com jayakumar and kulkarni: a simple measuring model for evaluating the performance of small block … fig. 4. small file performance in lustre as shown in figure 4, the trend of the two lines is almost the same, but when the record size is 128k, 256k, and 1m, the performance is better than others. for the record size 4k or 8k, most of the rpc packets contain only one or two pages and hence the i/o efficiency is much lower. from the graph above, it can be concluded that for small record size less number of rpcs are required and the overall i/o performance gets affected when there is only one read or write rpc to the osts for accessing the file data. this shows that in the native lustre platform small files get processed slowly with less record size which will decrease the overall i/o performance. b. feasibility check of the proposed system the write performance of ost and the write performance of mdt are compared by running dd command on client node and mdt. as shown in figure 5, when dd command is run on the client, the latency is more, compared to latency achieved when dd command is run on mdt. this means, when the client accesses small file data stored on ost, it has to send rpcs to both mds and oss and thus the time required to perform read/write operation increases. as the client has to send rpcs to both mds and oss, the network overhead gets increased. fig. 5. latency comparison when the dd command is run on mdt, the latency is less. this means that if the small files get stored on the mdt, they can be accessed very fast with the minimal number of rpcs. in this case, since the data and metadata will both get stored on mds, there is no need to send rpcs to the oss. considering the results above, it can be concluded that, it is feasible to move small file data on mdt in order to increase small file io performance. one more important factor that must be considered here is the maximum block size of file for which the data can be moved to mdt. the maximum block size for which data can be stored on mdt can be obtained by evaluating the results of latency test on mds for different block sizes. figure 6 shows the results achieved by running dd command on mdt. here, the latency is less for the block size of up to 8kb. for the block size of 16 kb and above the latency increases exponentially. if the latency is high for the block size of 16 kb and above then it is not beneficial to store the file data on mdt because the small files are more latency sensitive. for the maximum of 8 kb block size, the latency is very low. fig. 6 latency test for maximum block size so it can be concluded that in lustre file system with 2 gb ram for mdt, maximum 8 kb record size files can be stored on mdt. these files require minimum latency without impacting the system performance and that way the i/o performance of the small files increases. vi. conclusion the read/write performance of lustre file system is currently optimized for large files. the read/write performance depends on the number of lookup rpcs between client to ost and client to mdt. to access any file, client has to send initial open rpc to the mdt and after that, to fetch the data from the osts, there are separate read/write rpcs to the osts. this functionality separation is desirable for large files, but this affects the overall performance of small files significantly when there is only one read or write rpc to the osts for accessing the file data. also, the small files are more latency sensitive. one possible way to improve small file performance in lustre is to put the data for small files only on the mdt where metadata also reside so that additional rpcs and i/o overhead can be eliminated. in the current work, the native lustre i/o performance is tested by different benchmarking tools (iozone, ior) and it is evaluated and proposed that storing small file data on the mdt is feasible and the maximum record size for which data can be stored on mdt with 2 gb ram is 8kb. the scope of this research is not limited to lustre file system. it can also be applied to other parallel distributed file systems (for example ceph, hdfs) that store data and metadata on separate servers. lustre file system is most widely used in big data environment in which most of engineering, technology & applied science research vol. 7, no. 6, 2017, 2313-2318 2318 www.etasr.com jayakumar and kulkarni: a simple measuring model for evaluating the performance of small block … the files (70%) are small, and most data (nearly 90%) is placed in big files. the number of small files is big though used space is not. small files consume more resources and produce big slowdown. also, the latency of access to small files is important. this research is very helpful in big data environment to handle small files and to increase the read-write performance of small files. references [1] f. wang, s. oral, g. shipman, o. drokin, t. wang, i. huang, understanding lustre filesystem internals, national center for computational sciences, oak ridge national laboratory, 2009 [2] iozone filesystem benchmark, http://www.iozone.org [3] nersc, ior test, https://tinyurl.com/jnmdo8u [4] the linux juggernaut, 12 linux dd command examples, https://tinyurl.com/ycg6acpm microsoft word 1-434-ce.doc engineering, technology & applied science research vol. 5, no. 1, 2015, 739-747 739 www.etasr.com ahmad et al.: a research on synchronization of two novel chaotic systems based on a nonlinear… a research on the synchronization of two novel chaotic systems based on a nonlinear active control algorithm israr ahmad azizan bin saaban adyda binti ibrahim mohammad shahzad school of quantitative sciences university utara malaysia, malaysia & college of applied sciences nizwa, oman iak_2000plus@yahoo.com school of quantitative sciences, university utara malaysia, malaysia azizan.s@uum.edu.my school of quantitative sciences, university utara malaysia, malaysia adyda@uum.edu.my college of applied sciences, nizwa, oman shehzad.niz@cas.edu.om dmsinfinite@gmail.com abstract— the problem of chaos synchronization is to design a coupling between two chaotic systems (master-slave/driveresponse systems configuration) such that the chaotic time evaluation becomes ideal and the output of the slave (response) system asymptotically follows the output of the master (drive) system. this paper has addressed the chaos synchronization problem of two chaotic systems using the nonlinear control techniques, based on lyapunov stability theory. it has been shown that the proposed schemes have outstanding transient performances and that analytically as well as graphically, synchronization is asymptotically globally stable. suitable feedback controllers are designed to stabilize the closed-loop system at the origin. all simulation results are carried out to corroborate the effectiveness of the proposed methodologies by using mathematica 9. keywords-synchronization; lyapunov stability theory; nonlinear control; routh-hurwitz criterion i. introduction synchronization of chaotic systems is a process where two (or many) chaotic systems eventually progress identically for different initial conditions in all future states. this means that the dynamical state of one of the system is completely dictated by the dynamical state of the other system [1]. chaos synchronization between two chaotic systems is one of the most primary procedures in complex systems’ control and has wide potential applications in different fields [2-6]. after a pioneering work on chaos synchronization [1], synchronization of chaotic dynamical systems has received a great interest among researchers in nonlinear sciences for more than two decades [7]. until now, diverse techniques have been proposed and applied successfully to synchronize two identical (or nearly identical) as well as nonidentical chaotic systems [8-13]. notable among those, the nonlinear control algorithm [7, 9] is one of the effectual techniques for synchronizing two chaotic systems [7]. nonlinear control techniques take the advantage of the given nonlinear system dynamics to produce highperformance designs. no lyapunov exponents or gain matrix are required for its execution. these qualities allow the designer to focus on the synchronization problem, leaving troublesome model manipulations [9]. edward lorenz, a meteorologist and mathematician, is known to be the pioneer of chaos theory. in the 1960s, lorenz made his historical discovery by observing weather phenomena particularly in convections of fluids [14]. lorenz took different mathematical models of fluid convection and simplified them into a system of ordinary differential equations and came up with a 3-d chaotic attractor for the first time, what is now known as the popular lorenz equations [14]. after the exceptional discovery of e. lorenz on chaotic attractor, chaos has become an interesting topic for many researchers. during the last three decades, remarkable research has been done on chaos which explored its different applications, features and fundamental properties [15]. the significance of the 3-d differential equations is that relatively simple systems could exhibit rather complex or specifically chaotic behavior. the 3-dimensional chaotic systems have many potential applications in different scientific fields such as chemical reactions, secure communications, biological systems and nonlinear circuits [15]. due to a wide range of applications of 3-d chaotic systems, various systems such as the chen system, rossler system, liu system, qi system, tigan system and lu system [16-19] have been proposed and applied successfully to many practical systems and have shown some effective outcomes. recently, a new 3-d autonomous chaotic system based on a quadratic exponential nonlinear term and a quadratic cross product term has been proposed and studied [20]. a quadratic exponential nonlinear term was added to the third equation while eliminating the second term from the second equation and a nonlinear term from the third equation of the lorenz system [20]. the new 3-d chaotic system is topologically different from the lorenz system. the two-scroll attractor from the new system exhibits multiplex chaotic dynamics. the nonlinear dynamical properties of the new engineering, technology & applied science research vol. 5, no. 1, 2015, 739-747 740 www.etasr.com ahmad et al.: a research on synchronization of two novel chaotic systems based on a nonlinear… chaotic system such as equilibrium points, phase portraits, lyapunov exponents, bifurcation diagram, and poincare mapping was also extensively studied [20]. a new three dimensional chaotic system on the same construction patterns of chen, liu and qi chaotic systems was proposed in [21]. an exponential term was added, the quadratic nonlinear term to the third equation of the liu system was eliminated and a new 3-d chaotic system was proposed, topologically different from those of chen, liu and qi systems and with more complex dynamics. the main objective of this research work is to utilize the non-linear active control technique to synchronize two new chaotic systems introduced in [20, 21]. based on the lyapunov stability theory [22] and using the non-linear active control technique, a class of appropriate feedback controllers are designed to achieve globally asymptotic synchronization. numerical simulations and graphs are furnished to show the performance and effectiveness of the proposed schemes. the remainder of the paper is organized as follows: section ii discusses the problem statement and the proposed methodology. in section iii global chaos synchronization of two novel 3-d chaotic systems is investigated. in section iv numerical results are imparted and finally, the summary and the concluding remarks are provided in section v. ii. desigin of nonlinear active control certain synchronization algorithms belong to the driveresponse systems arrangement. the drive-response systems arrangement means that the two chaotic systems are coupled in such a manner in which the output of the response system asymptotically follows the output of the drive system and the drive system is not influenced by the exertion of the response system. thus let us consider a drive-response systems configuration for a chaotic system given as: 1 1 ( )x a x b g x  (drive system) (1) and 1 2 (y) ( )y a y b h t   (response system) (2) where, 11 1 1 1[ , ,...., ] , [ , ,...., ] t t n n nx x x x y y y y r    are the corresponding state vectors, 1 2, n na a r  are the matrices and 1 2, nb b r are the vectors, , : n ng h r r are the nonlinear continuous functions of the drive and response systems respectively and 1 1 2( ) [ ( ), ( ),...., ( )] t n nt t t t r      is an injected additive nonlinear controller to the controlled system. if 1 2 1 2( ) ( ) / ,and og h r a a b b   , then x and y are the states of two identical (nearly identical) chaotic systems. if 1 2 1 2( ) ( ) / ,and og h r a a b b   , then x and y are the states of two nonidentical chaotic systems. the error dynamics for the synchronization of (1) and (2) can be described as: ( ) ( , , ) ( )e t h x y e t  (3) where ( , , )h x y e that contains linear terms and nonlinear terms of the drive and response systems, and ( ) ( ) ( )i i ie t y t x t  is the errors dynamics. for the two (identical or nonidentical) chaotic systems in the absence of a proper controller i (μ =0) if the initial conditions,  1 2 1 2(0), (0),...., (0) (0), (0),...., (0)d d nd r r nrx x x y y y , then the trajectories of the two chaotic systems will quickly bifurcate from each other in all future states and will become uncorrelated. hence, the role of a proper feedback controller for the synchronization problem is to restrict the error dynamics converges to zero for all initial conditions [7], i.e., lim ( ) lim ( ) ( ) 0i i i t t e t y t x t      , for all (0) nie r , then the two chaotic systems (1) and (2) are said to be synchronized. let us assume the following theorem. theorem 1[9]. the trajectories of the two (identical or nonidentical) chaotic systems (1) and (2) for any initial conditions  1d 2d nd 1r 2r nrx (0),x (0),....,x (0)¹y (0),y (0),....,y (0) will be synchronized asymptotically globally with appropriate nonlinear regular stabilizing feedback controller, 1 1 2( ) [ ( ), ( ),...., ( )] t n nt t t t r      proof: let us define a candidate lyapunov errors function as ( ) tv t e ae (4) where the matrix 1 2( , ,......., )na diag a a a is a positive definite matrix [9]. further it is assumed that all the variables and parameters of the drive and response systems are available and measureable. it may be noticed that : n nv r r is a positive definite function by construction. it may achieve the synchronization by selecting a suitable non-linear controller ' ( )t ' to make (t) tv e be  , a positive definite function (i.e., the matrix b is also a positive definite matrix), then by the lyapunov stability theory [21], the states of both drive and response systems will be asymptotically globally synchronized. iii. synchronization a. identical synchronization of a new chaotic system [20] system description: fey yu, et.al, [20] proposed and studied a new 3d autonomous chaotic system. the differential equations describing the new chaotic systems are given as: engineering, technology & applied science research vol. 5, no. 1, 2015, 739-747 741 www.etasr.com ahmad et al.: a research on synchronization of two novel chaotic systems based on a nonlinear… ( ) x y x a y x y b x c x z z e d z             (5) where , , nx y z r are the state variables and , ,a b c and d are the system parameters. the new system exhibits chaotic attractor for a = 10, b = 40, c = 2 and d = 2.5 with initial condition (2.2, 2.4, 28). for the dynamics properties such as equilibrium points, lyapunov exponents, phase portraits, bifurcation diagram etc for the system (5), one may refer to [20]. to achieve identical synchronization for chaotic system (5), let us consider the drive-response systems arrangement is described as: 1 1 1 1 1 1 1 1 1 1 1 ( ) x y x a y x y bx cx z z e dz             (drive system) (6) and 2 2 2 2 2 1 2 2 2 2 2 2 2 3 ( ) x y x a y x y bx cx z z e dz                   (response system) (7) where 1 1 1, , nx y z r are the state variables of the drive system with , ,a b c and d as the system parameters and 2 2 2, , nx y z r as the state variables of the corresponding response system and 1 2 3( ) [ ( ), ( ), ( )] tt t t t    as the nonlinear stabilizing feedback controller that yet to be designed. from (6) and (7), the error dynamics can be described as: 2 2 1 1 2 1 1 1 2 2 2 3 3 3 1 2 1 1 ( ) ( ) x y x y e be c x z x z e de e a e e e e                       (8) where 1 2 1 2 2 1 3 2 1 , , e x x e y y e z z      the aim of the synchronization problem is to design a feedback controller ' μ(t) ' such that: lim ( ) 0, (0 ) ni i t e t for all e r    . the main focus of this section is to investigate and study the synchronization problem of (6) and (7) by designing a suitable feedback controller that when synchronizing the two chaotic systems, the effect of nonlinearity of chaotic systems does not neglect and the error signals of the two identical chaotic systems converges to the equilibrium point asymptotically globally with less control effort and sufficient transient speed. for these motivations, we assume the following theorem. theorem 2. the two controlled chaotic systems (6) and (7) will achieve asymptotically globally synchronization for all initial conditions ( (0), (0), (0)) ( (0), (0), (0))d d d r r rx y z x y z with the following nonlinear feedback controllers: 1 1 2 2 1 2 1 2 2 2 1 1 3 ( ) 0 ( ) 2 ( ) ( ) x y x y t t be ae c x z x z t e e                 (9) proof: replacing (9) in (8), we have: 2 1 2 1 1 2 3 3 ( ) e be ae e de e a e e               let us construct a lyapunov errors function candidate as: ( ) , 1, 2, 3ti iv e e ae for i  (10) where: 1 0 0 0 0.125 0 0 0 0.5 a           is a positive definite matrix with ( ) 0v e  and considering a=0, b=40, c=2 and d=2.5. now the time derivative of the lyapunov errors function (10) is given as: ( ) 2v e aee   ( ) 2 ( ), 1, 2, 3i iv e ae e for i   1 1 2 2 3 3( ) 2 [ ( ) ( ) ( )]v e a e e e e e e       1 2 2 1 2 3 31 1 0 0 ( ) 2 0 0.125 0 [ ( ) ( ) ( )] 0 0 ) 0.5 (v e e e be ae ea e ee d                2 2 2 1 2 3 2 0 0 ( ) 2 0.5 0 0.5 0 0 0 0 t a v e ae ae de e a e d                 i.e., ( ) 0v e  . therefore, ( ) tv e e be  and the matrix: 20 0 0 0 10 0 0 0 2.5 b           engineering, technology & applied science research vol. 5, no. 1, 2015, 739-747 742 www.etasr.com ahmad et al.: a research on synchronization of two novel chaotic systems based on a nonlinear… is also a positive definite matrix. hence, based on lyapunov stability theory, the error dynamics (8) of the two identical chaotic systems converges to the origin asymptotically. thus, the two chaotic systems (6) and (7) are asymptotically globally synchronized. b. nonidentical synchronization of [20] and lu systems to analyze the switching synchronization between two nonidentical chaotic systems [20] and lu [19] using the nonlinear control algorithm, it is assumed that the new chaotic system [20] drives the lu chaotic system [19]. therefore, the drive-response systems arrangement is given as: 1 1 1 1 1 1 1 1 1 1 1 ( ) x y x a y x y bx cx z z e dz             (drive system) (11) and 2 2 2 1 2 2 2 2 2 2 2 2 2 3 ( )x y x y y x z z z x y                        (response system) (12) where 1 1 1, ,x y z ϵ r n and 2 2 2, ,x y z ϵ r n are the corresponding state vectors of drive and response systems respectively, a, b, c, d are the system parameters of the drive system and α, β and γ are the system parameters of the response system respectively and 1 1 2 3( ) [ ( ), ( ), ( )] t nt t t t r      is the non-linear controllers. the lu system describes a chaotic attractor for the parameters value, α = 36, β = 3 and γ = 20. from (11) and (12), the error dynamics can be described as: 1 1 1 2 2 1 1 2 2 1 1 2 3 3 1 2 2 1 1 1 2 1 3( ( ) ) x y e e y bx x z cx z e e d z x y e e e a x y ay                                      (13) the main objective of this part is to investigate and study the switching synchronization between (11) and (12) by designing such a feedback controller that when synchronizing the two chaotic systems, the effect of nonlinearity of chaotic systems should not be neglected and the error signal of the two nonidentical chaotic systems converges to the equilibrium point asymptotically globally with less control effort and sufficient transient speed. to achieve these goals, we presume the following theorem. theorem 3. the trajectories of the two chaotic systems (11) and (12) will achieve asymptotically globally synchronization for all initial conditions ( (0), (0), (0)) ( (0), (0), (0))d d d r r rx y z x y z with the following control law: 1 1 1 2 2 1 1 2 2 1 1 3 1 1 1 2 2 2 ( ) ( ) 2 ( ( ) ( ) ) x y t t y y bx x z c a x x z t d z x y e y ay                         (14) proof: let us construct a lyapunov errors function candidate as: 1( ) ( ), 1, 2, 3 2 t i iv e e e for i  now the time derivative of the lyapunov errors function is, 2 2 2 2 2 2 1 2 3 1 2 3( ) ( ) 0v e e e e e e e              therefore, ( ) 0v e  . hence based on lyapunov stability theory, the error dynamics of two nonidentical chaotic systems (11) and (12) converges to the origin asymptotically. thus the two chaotic systems (11) and (12) are asymptotically globally synchronized. c. identical synchronization of a new chaotic system [21] system description: recently, chunlai li et.al, [21] proposed and investigated a new three dimensional autonomous chaotic systems. the dynamics of the new chaotic systems is given by the following system of nonlinear differential equations, 2 ( ) ( ) x p y x yz y r p x xz ry z qz sy                 (15) where , , nx y z r are the state variables and ,, aq ndp r s are the parameters of the new system. the new system exhibits a chaotic attractor for parameter values, [0,140, 5, 30 0]ar n sp q d    with the lyapunov exponents 1 2 33.88, 0.00, 25.52l l l    . in this section, the aim of the study is to achieve asymptotically globally synchronization between two identical chaotic systems using a nonlinear active controller. to achieve this objective, let us consider the drive-response systems arrangement for the new chaotic system [21] which is described as: 1 1 1 1 1 1 1 1 1 1 2 1 1 1 ( ) ( ) x p y x y z y r p x x z ry z qz sy                 (drive system) (16) and engineering, technology & applied science research vol. 5, no. 1, 2015, 739-747 743 www.etasr.com ahmad et al.: a research on synchronization of two novel chaotic systems based on a nonlinear… 2 2 2 2 2 1 2 2 2 2 2 2 2 2 2 2 3 ( ) ( ) x p y x y z y r p x x z ry z qz sy                       (response system) (17) where 1 1 1, , nx y z r the state variables of the drive system with , , aq ndp r s as the system parameters and 2 2 2, , nx y z r the state variables of the corresponding response system and 1 1 2 3( ) [ ( ), ( ), ( )] t nt t t t r      the nonlinear active feedback controller. from (17) and (18), the error dynamics can be described as: 1 2 1 2 1 1 2 2 1 2 1 2 2 1 2 2 2 3 3 2 1 1 3 ( ) ( ( ) ) ( ) e r p e re x z x z e qe e p e e y y z s y y z                           (18) where 1 2 1 2 2 1 3 2 1 and ,e x x e y y e z z      . the theme of this section is to investigate and study the synchronization of (16) and (17). to accomplish this goal, let us presume the following theorem. theorem 4. the trajectories of the two chaotic systems (16) and (17) will achieve asymptotic global synchronization for any initial values ( (0), (0), (0)) ( (0), (0), (0))d d d r r rx y z x y z with the following control law: 1 1 1 2 2 2 2 2 2 1 2 13 2 1 2 ( ) ( ( ) 2) ) ( x z x z t y z y z t t s y y re             proof: it is assumed that all the variables and parameters of the drive and response systems are available and measurable. let us construct the same lyapunov errors function as in (10) and selecting the positive definite matrix a as, 1 0 0 20 1 0 0 5 0 0 1 a                  now the time derivative of the lyapunov errors function is, 2 2 2 1 2 3 4 0 0 ( ) 4 12 10 0 12 0 0 0 0 10 tv e e e e e e                 therefore, ( ) tv e e be  and: 4 0 0 0 12 0 0 0 10 b           is also a positive definite matrix. hence, based on lyapunov stability theory, the origin of the error dynamics of the two identical chaotic systems converge to the origin asymptotically. thus the two chaotic systems (16) and (17) are asymptotically globally synchronized. d. nonidentical synchronization of [21] and lu systems to achieve nonidentical synchronization for [21] using nonlinear active control strategy, it is assumed that [21] drives the lu chaotic system [19]. therefore, the drive-response systems configuration is given as; 1 1 1 1 1 1 1 1 1 1 2 1 1 1 ( ) ( ) x p y x y z y r p x x z ry z qz sy                 (drive system) (19) and 2 2 2 1 2 2 2 2 2 2 2 2 2 3 ( )x y x y y x z z z x y                        (response system) (20) where 1 1 1, ,x y z , 2 2 2, ,x y z ϵ r n are the corresponding state vectors of drive and response systems respectively, , ,p q r and s are the system parameters of the drive system and a, β and γ are the system parameters of the response system respectively and 1 1 2 3( ) [ ( ), ( ), ( )] t nt t t t r      is the nonlinear controller that yet to be designed. from systems of equations (19) and (20), the error dynamics can be described as; 1 2 2 1 1 2 2 1 1 1 2 2 3 3 2 2 2 2 1 2 1 2 3 1 1 1 ( ) ( ) ( ) e e r y r p e pe p a x x z x z x y e qe qz z x py y y sy z                                    (21) the main contribution of this section is to achieve asymptotically globally synchronization between (19) and (20) by designing such a feedback controller that [21] is forced to track the lu system [19] and the two systems show similar behavior for all future states. to achieve this objective let us assume the following theorem. theorem 5. the two chaotic systems (19) and (20) will achieve asymptotically globally synchronization for any initial values ( (0), (0), (0)) ( (0), (0), (0))d d d r r rx y z x y z with the following control law: engineering, technology & applied science research vol. 5, no. 1, 2015, 739-747 744 www.etasr.com ahmad et al.: a research on synchronization of two novel chaotic systems based on a nonlinear… 21 2 2 1 1 2 2 1 1 2 3 2 1 1 2 1 2 1 2 ( ) ( ) 2 ( ( ) ) ( ) ( ) ( ) t t y r y p r x x z x z t q z x p a y s x y py y y z                           (22) proof: let us assume that the parameters of the drive and response systems are known and the states of both chaotic systems are measurable. substituting the proposed controllers (22) in (21), we have: 1 1 2 2 3 3 e pe e e e qe               (23)  1 1 2 2 3 3 0 0 0 0 0 0 e p e e e e q e                             it can be seen that the error system (23) is a linear system of the form, e ae . thus by linear control theory, the system matrix a is hurwitz [23], and so the all the eigenvalues of the system matrix a has negative real parts. i.e., 40 0 0 0 20 0 0 0 5 a          is hurwitz. hence, the above system (23) is asymptotically stable, which implies that the two nonidentical chaotic systems (19) and (21) are synchronized asymptotically globally. iv. numerical simulations numerical results are provided to justify the effectiveness of the proposed approaches. the parameters for [20] are taken as, 10, 40, 2 2.5a b c and d    , with initial conditions: 1 1 1( (0), (0), (0)) (1.2,1.2, 29)x y z  and 2 2 2( (0), (0), (0)) (2.2, 2.4, 28)x y z  . the parameters for [21] are selected as, 40, 5, 3 [0,10]0, sp q r    , with initial conditions (3, -3, 3) and (-4, -7, 4). for the lu system, the parameters are taken as, 36, 3, 20     , with initial conditions (6, 3, 4) and (5, 2, 2). for the above chosen values, the time series of states variables for identical systems [20] and [21] is shown in figures 1-3 & 9-11 and for nonidentical systems [19] and ([20], [21]) in figures 5-7 & figures 13-15. figures 4 & 12 illustrate the synchronization errors of two identical new chaotic systems [20, 21] and figures 8 & 16 show the synchronization errors of two completely different chaotic systems ([20, 21]) and lu) respectively. for the two different chaotic systems ([20, 21] and lu systems), that contain parameters mismatches and different structures, the controllers were used to synchronize the states of drive and response systems asymptotically globally when the controls are switched on at t = 0 s. it has been shown that the new systems are forced to track the lu systems and the states of two different systems show similar behavior, which shows that the error systems (figures 8 & 16) are feedback stabilized and the investigated controllers are more robust to accidental mismatches in the transmitter and receiver. figure 17 illustrates the derivative of lyapunov errors functions of identical chaotic systems [20 & 21] and nonidentical [20] and lu chaotic systems. fig. 1. time series of states x1[t] and x2[t] (identical systems [20]) fig. 2. time series of states y1[t] and y2[t] (identical systems [20]) fig. 3. time series of states z1[t] and z2[t] (identical systems [20]) engineering, technology & applied science research vol. 5, no. 1, 2015, 739-747 745 www.etasr.com ahmad et al.: a research on synchronization of two novel chaotic systems based on a nonlinear… fig. 4. time series of error states (identical systems [20]) fig. 5. time series of x1[t] and x2[t] (non-identical systems [19, 20]) fig. 6. time series of y1[t] and y2[t] (non-identical systems [19, 20]) fig. 7. time series of z1[t] and z2[t] (non-identical systems [19, 20]) fig. 8. time series of error states (non-identical systems [19, 20]) fig. 9. time series of x1[t] and x2[t] (identical systems [21]) fig. 10. time series of y1[t] and y2[t] (identical systems [21]) fig. 11. time series of z1[t] and z2[t] (identical systems [21]) engineering, technology & applied science research vol. 5, no. 1, 2015, 739-747 746 www.etasr.com ahmad et al.: a research on synchronization of two novel chaotic systems based on a nonlinear… fig. 12. time series of error states (identical systems [21]) fig. 13. time series of x1[t] and x2[t] (non-identical systems [19, 21]) fig. 14. time series of y1[t] and y2[t] (non-identical systems [19, 21]) fig. 15. time series of z1[t] and z2[t] (non-identical systems [19, 21]) fig. 16. time series of error states (non-identical systems [19, 21]) fig. 17. time series of v(t) v. conclusion this paper investigated the global chaos synchronization of two novel chaotic systems. based on the lyapunov stability theory and using the nonlinear control algorithm with different approaches, a class of nonlinear controllers was designed to achieve the global stability of the error dynamics. since the lyapunov exponents or gain matrix are not required for its execution, nonlinear control algorithm is an efficient technique to synchronize identical as well as nonidentical chaotic systems. all graphical as well as analytical results showed that the proposed schemes have excellent transient performances and that the synchronization is asymptotically globally stable. this study focused on selecting a suitable lyapunov errors functions candidate that ensured asymptotically global stability. it was also shown that the error signals converge to the origin very smoothly with minimum rate of decay and sufficient transient speed. in addition, the synchronization with negative derivative of the lyapunov errors functions allows large synchronizable intervals, which is significant especially for engineering applications. it should be mentioned however that in practice environmental or internal noise may provide disturbances. hence, future work should focus on the effect of noise present on practical implementations. engineering, technology & applied science research vol. 5, no. 1, 2015, 739-747 747 www.etasr.com ahmad et al.: a research on synchronization of two novel chaotic systems based on a nonlinear… vi. acknowledgement the authors would like to express their gratitude to mr. saif said al bimani (deptt. of english, college of applied sciences, nizwa, ministry of higher education, sultanate of oman) who suggested many worthwhile changes to improve the language of the manuscript. references [1] l. m. pecora, t. l. carroll, “synchronization in chaotic systems”. physical review letters, vol. 64, no. 8, pp. 821–824, 1990 [2] m. shahzad, i. ahmad, “experimental study of synchronization & antisynchronization for spin orbit problem of enceladus”, international journal of control science and engineering, vol. 3, no. 2, pp. 41-47, 2013 [3] x. f. wang, z. q. wang, “synchronization of chua's oscillators with the third state as the driving signal”, international journal of bifurcation and chaos, vol. 8, no. 7, pp. 1599-1603, 1998 [4] k. miyakawa, t. okabe, m. mizoguchi, f. sakamoto, “synchronization in the discrete chemical oscillation system”, the journal of chemical physics, vol. 103, no. 22, pp. 9621-9625, 1995 [5] a. n. pisarchik, f. t. arecchi, r. meucci, a. digarbo, “synchronization of shilnikov chaos in a co2 laser with feedback”, laser physics, vol. 11, no. 11, pp. 1235–1239, 2001 [6] o. moskalenko, a. a. koronovskii, a. e. hramov, “generalized synchronization of chaos for secure communication: remarkable stability to noise”, physics letters a, vol. 374, no. 29, pp. 2925-2931, 2010 [7] a. saaban, a. ibrahim, m. shahzad, i. ahmad, “global chaos synchronization of identical and nonidentical chaotic systems using only two nonlinear controllers”, international journal of mathematical, computational, physical and quantum engineering, vo. 7, no. 12, pp. 1182-1188, 2013 [8] i. ahmad, a. saaban, a. ibrahim, m. shahzad, “global chaos identical and nonidentical synchronization of a new 3-d chaotic system using linear active control”, asia journal of applied sciences, vol. 2, no. 1, pp. 1-12, 2014 [9] h. k. chen, “global chaos synchronization of new chaotic systems via nonlinear control”, chaos, solitons & fractals, vol. 23, no. 4, pp. 12451251, 2005 [10] 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[12] a. saaban, a. ibrahim, m. shahzad, i. ahmad, “identical synchronization of a new chaotic system via nonlinear control and linear active control techniques: a comparative analysis”, international journal of hybrid information technology vol.7, no.1, pp. 211-224, 2014 [13] i. ahmad, a. saaban, a. ibrahim, m. shahzad, “global chaos synchronization of two different chaotic systems using nonlinear control”, international journal of sciences: basic and applied research, vol. 14, no. 1, pp. 225-238, 2014 [14] e. lorenz, “deterministic nonperiodic flow”, journal of the atmospheric sciences, vol. 20, no. 2, pp. 130–141, 1963 [15] s. boccaletti, c. grebogi, y. c. lai, h. mancini, d. maza, “the control of chaos: theory and applications”, physics reports, vol. 329, no. 3, pp.103-109, 2000 [16] l. s. tee, z. salleh, “dynamical analysis of a modified lorenz system”, journal of mathematics, vol. 2013, article id 820946, 2013 [17] g. qi, g. chen, a. a. van wyk, b. j. van wyk, y. zhang, “a four-wing chaotic attractor generated from a new 3-d quadratic autonomous system”, chaos, solitons & fractals, vol. 38, no. 3, pp. 705-721, 2008 [18] g. tigan, d. opris, “analysis of a 3d chaotic system”, chaos, solitons & fractals, vol. 36, no. 5, pp. 1315-1319, 2008 [19] j. lu. g. chen, “a new chaotic attractor coined”, international journal of bifurcation and chaos, vol. 12, no. 3, pp. 659-662, 2002 [20] f. yu, c. wang, “a novel three dimensional autonomous chaotic system with a quadratic exponential nonlinear term”, engineering, technology & applied science research, vol. 2, no. 2, pp. 209-215, 2012 [21] c. li, l. wu, h. li, y. tong, “a novel chaotic system and its topological horseshoe”, nonlinear analysis: modelling and control, vol. 18, no. 1, pp. 66–77, 2013 [22] h. k. khalil, non linear dynamical systems. prentice hall, 3rd edi, nj, 07458, usa, 2002 [23] r. c. dorf, r. h. bishop, modern control systems, 9th ed. princeton hall, usa, 2001 engineering, technology & applied science research vol. 7, no. 3, 2017, 1619-1622 1619 www.etasr.com al-jarrah et al.: effect of applied pressure on the mechanical properties of 6061 aluminum alloy welded… effect of applied pressure on the mechanical properties of 6061 aluminum alloy welded joints prepared by friction stir welding jawdat a. al-jarrah mechanical engineering department engineering college northern border university arar, saudi arabia jawdatj@yahoo.com masoud ibrahim chemical and material science engineering dpt, engineering college, northern border university, arar, saudi arabia and industrial engineering dpt, faculty of engineering, fayom university egypt ibrahim_64@yahoo.com salameh swalha mechanical engineering dpt, engineering college northern border university arar, saudi arabia and mechanical engineering dpt faculty of engineering, al-balqa applied university jordan sawalhasalameh84@yahoo.com abstract—this paper investigates the effect of axial force on the surface appearance and mechanical properties of 6061 aluminum alloy welded joints prepared by friction stir welding. the applied pressure varies from 1.44 to 10.07 mpa. the applied pressure was calculated from the axial force which exerted by a spring loaded cell designed for this purpose. defect free joints obtained at an applied pressure of 3.62 mpa. the mechanical properties of the welded joints were evaluated through microhardness and tensile tests at room temperature. from this investigation, it was found that the joint produced with an applied pressure of 5.76 mpa exhibits superior tensile strength compared to other welded joints. the fracture of this joint happened at the base material. keywords-friction stir welding; aluminum alloys; applied pressure; mechanical properties i. introduction since 1930s aluminum alloys have been the material of choice for aircraft construction. nowadays 6xxx aluminum used in a variety of applications including aircraft fuselage skins and automobile body panels and bumpers, instead of more expensive 2xxx and 7xxx alloys, after appropriate heat treatments [1]. 6xxx alloys have numerous benefits including medium strength, formability, weldability, corrosion resistance, and low cost [2]. aluminum 6061 is a precipitation hardening alloy containing magnesium and silicon as its major alloying elements [3]. this alloy is highly weldable by tungsten inert gas welding and by metal inert gas welding. however, certain welding defects appear, such as solidification cracking porosity, heat-affected zone (haz) degradation [4]. solid state welding techniques such as friction stir welding (fsw) developed by twi, cambridge, in 1991 [5] have received great attention in the last years. the process requires lower energy than conventional fusion welding processes [6] and no consumables such as electrodes and protecting gases are needed [7]. fsw has different process parameters that affect the welding process such as tool geometry, axial force, rotational speed, traverses speed and, tool tilt angle as well as base material properties [8-10]. there have been many efforts to understand the effect of process parameters on material flow behavior, microstructure formation and mechanical properties of friction stir welded joints as well as realize their influence on the welding properties [11]. the main two fsw parameters receive interest from researchers are tool rotational speed and welding speed. it is well documented that quality of welded joints increases with increase in tool rotational speed to a maximum value, further increase in tool rotational speed leads to the decrease in quality of welded joints [7]. welding speed also has a significant effect on joints quality. an increase in welding speed leads to an improvement in mechanical properties up to a maximum limit and further increase result to a decline in mechanical properties. it is well documented that fs welded joints produced under the effect of extrusion process [12], in which the applied axial force and the motion of the tool pin propel the material after it has undergone the plastic deformation. the shoulder force is directly responsible for the plunge depth of the tool pin into the work piece and load characteristics associated with linear friction stir welding [13]. many research works have demonstrated the effect of axial force in the friction stir welding process which can be concluded in: (a) the material flow in the weld zone during the process and (b) its role in heat input to the welding area. in other word axial force affect the temperature and hydrostatic pressure which is responsible for producing defect free joints [6]. however, the effect of applied pressure on the welding quality of welded joints obtained by fsw is investigated along with other parameters of the fsw engineering, technology & applied science research vol. 7, no. 3, 2017, 1619-1622 1620 www.etasr.com al-jarrah et al.: effect of applied pressure on the mechanical properties of 6061 aluminum alloy welded… process. in this paper, the effect of applied pressure on the quality of welded joints produced by fsw is solely investigated. other fsw parameters like rotational speed, welding speed, shoulder diameter, pin shape and size, were called from an optimal fsw process from previous work [8]. ii. experimental work two rectangular 6061 aluminum alloy plates of 300x150 mm size were butt-welded by friction stir welding process and 6 mm thickness was used. the compositions of base materials used in this investigation are given in table i. a conventional vertical milling machine was used for the friction stir welding process, by using a fixture. the fixture is tightly fixed on the milling machine table to prevent vibration from occurring as a result of the frictional forces of the welding process. a welding tool with flat shoulder of 24 mm diameter and 20 mm height, made of high carbon steel was used. a 6 mm square pin profile was used to carry out the welding process. a spring-loaded unit was used to change the pressure applied on the shoulder face of the welding tool against the upper surface of the work piece. the calculated pressure values exerted on the shoulder face used in this investigation are 1.44, 3.62, 5.76, 7.92 and 10.07 mpa. the welding process was carried out using a rotational speed of 1000 rpm and a welding (traverse) speed of 1.5 mm/sec. single stir pass was applied during the dry welding process. microstructure examinations were performed using an optical microscope. the specimens, which were taken from the middle of the stirred zone, were prepared by standard metallographic techniques and etched with keller’s reagents to reveal the grain structure. vickers microhardness was measured with 0.5 kgf load and a dwell period of 10 s. several measurements were done for each hardness value. in addition, a tensile test on a universal tensile testing machine was carried out to measure the tensile strength of the welded plates, according to astm: e8. the tensile test specimens had a gauge diameter of 12 mm and gauge length of 90 mm. table i. chemical composition of the alloy used (%wt). si mg cu fe mn ti zn cr al 0.75 0.9 0.5 0.5 0.15 0.05 0.03 0.03 rest iii. results and discussion a. welding appearance surface images were collected for the welded pieces under different values of applied pressure. figure 1 shows the effect of applied pressure on surface appearance of the welds in plates joined by fsw. the rotational speed and welding speed are kept constant at 1000 rpm and 1.5 mm/sec respectively. at low pressure, 1.44 mpa, the material has poor flow beneath the shoulder face, reducing material loss at retreating side as shown in figure 1a. defect free welds were successfully obtained at applied pressure of 3.62 mpa, and the plate surface becomes more smoother at 5.76 mpa, as shown in figures 1b and 1c respectively. however, at an applied pressure of 7.92 mpa, the welding tool would sink to the weld gradually, and a wavy burr starts forming at the edge of the weld region due to the increased heat input to the welding region as shown in figure 1d. with a further increase of the applied pressure to 10.07 mpa, semicircle streaks appear clearly and more wavy burrs are formed at the weld regions as shown in figure 1e. a low heat input during the fsw process at a low applied pressure, 1.44 mpa, in addition to lack of stirring, reduces the fluidity of aluminum substrate in the stir zone [14]. the microstructure of 6061 aluminum alloy joined by friction stir welding was studied by employing optical microscopy. the microstructure samples are collected from the stir zone. the evolution of the microstructure in the stir zone depends on the recrystallization temperature and the cooling rate of the welding region [15]. the heat input during the welding process controls the temperature in the welding area. the stir zone of the butt-welded plates was cooled by ambient air. the most of the heat generated during friction stir welding arises from the friction at the surface of the tool shoulder, which is proportional to the applied pressure [16]. figure 2 shows the evolution of the microstructure at the stir zone at different applied pressures. at a low pressure of 1.44 mpa, where the induced heat is very small, the microstructure grain of sz is fine and equiaxed as shown in figure 2(a). the heat generated during the fsw process depends on the applied pressure on the surface of the welding tool, increasing further in the applied pressure to 3.62 and 5.76 mpa and produces coarsen and deformed grains as shown in figures 2b and 2c. the rate of heat generated during the welding process is directly proportional to the applied pressure. as the heat input increased, the temperature of the stir zone increased, which means relatively prolong heat dissipation. this gives the grains more time to growth [17]. figure 2d shows that at higher applied pressure of 10.07 mpa, the microstructure has elongated grains due to deformation under the surface of welding tools at the same time the grains become more coarsen. fig. 1. appearance of top surface welded at (a) 1.44mpa, (b) 3.62 mpa, (c) 5.76 mpa, (d) 7.92 mpa and (e) 10.07 mpa. fig. 2. microstructure of stir zone at (a) 1.44mpa, (b) 3.62 mpa, (c) 5.76 mpa and (d) 10.07 mpa (a) (b) (c) (d) (e) (a) (b) (c) (d) engineering, technology & applied science research vol. 7, no. 3, 2017, 1619-1622 1621 www.etasr.com al-jarrah et al.: effect of applied pressure on the mechanical properties of 6061 aluminum alloy welded… b. mechanical properties the microhardness of specimens prepared from all the welded joints at different levels of applied pressure at the welding region are recorded. the average of five readings at the stir zone was taken. the input heat to the welding area during the welding process increases as the applied pressure increased. figure 3 shows that the microhardness of sz decreases as the applied pressure increased from 1.44 to 5.76 mpa, and then reduced with a further increase in applied pressure. figure 4 shows the microhardness profile. the readings were taken from base metal to base metal crossing the sz under different applied pressure. it has been shown that at low applied pressures there is no significant change in the microhadness in the welding area. however, the microhardness of the stir zone is higher than that of the base metal. this is because the as received parent material was in the homogenized condition wherein all the precipitates are dissolved, thus accounting to a lower hardness due to the absence of strengthening precipitates. in the stir zone, which experiences higher temperatures than the remaining regions, the dissolved precipitates do re-precipitate subsequently. here the precipitates are finer and uniformly distributed in the stir zone [18]. applied pressure, mpa 0 2 4 6 8 10 12 m ic ro ha dn es s of s tir z on e, h v 30 40 50 60 70 80 rotational speed 1000 rpm welding speed 1.5 mm/sec fig. 3. the variation of microhardness with applied pressure for the stir zone the tensile properties such as the tensile strength and the elongation of friction stir welded 6061 aluminum alloy joints were evaluated. under each condition three specimens were tested and the average of the results is recorded. the variety of mechanisms that alter the strength of materials includes work hardening, solid solution strengthening, precipitation hardening, and grain boundary strengthening. in this study, the effect of applied pressure on the strength of aluminum-welded joints was investigated. figure 5 reveals the effect of applied pressure on ultimate tensile strength of the welded joints. it has been found that the strength of joint produced with an applied pressure of 5.76 mpa, exhibits a superior strength more than that of the base material as shown in figure 5. while the other welded joints have a strength lower than that of the base material. the frictional forces between the mating faces (surface of the welding shoulder tool and the welding plates) increased as the applied pressure increases leading to introduce more heat to welding area. the welded joint produced at 5.76 mpa, has the highest hardness value as shown in figure 3, in addition to having a fine grain microstructure [19]. it has been shown that uts increased as the applied pressure increases up to 5.76 mpa. but at higher applied pressures, excess of heat is introduced to the welding joint, which leads to a decrease on ultimate tensile strength as applied pressure increases to values above 5.76 mpa [8]. it was reported that gp-zones observed only at low temperature, and assumed that β' phase is formed directly from the solid solution at temperatures above 100120°c [20]. this precipitate hardening of 6061 aluminum alloy, leads to fabricate welded joints have superior strength more than that of the base material as shown in figure 6. for the welded joints when the fracture happened outside the welding zone, this joint has more elongation than other joints where the fracture occurred in welding zone as shown in figure 6. this joint gives the base metal to elongate freely to its own ductility, while other joints fractured before the elongation of the base metal reached. distance from welding line, mm -20 -15 -10 -5 0 5 10 15 20 m ic ro -h ar dn es s, h v 20 40 60 80 100 1.44 mpa 3.62 mpa 5.76 mpa 7.92 mpa 10.07 mpa fig. 4. hardness profile of fsw joint welded at 1000 rpm and 1.5 mm/sec applied pressure, mpa 0 2 4 6 8 10 12 u ts , m p a 170 180 190 200 210 220 230 rotational speed 1000 rpm welding speed 1.5 mm/sec bm as as as sz fracture location as: advancing side bm: base metal sz:stir zone fig. 5. variation of ultimate tensile strength with fsw applied pressure in this investigation, the joints fractured under tension advancing side near the sz, except the joint prepared at 5.76 mpa of applied pressure where the fracture occurred at the base metal as shown in figure 5. this may be due to the difference in microstructure between the sz and tmaz. the sz is engineering, technology & applied science research vol. 7, no. 3, 2017, 1619-1622 1622 www.etasr.com al-jarrah et al.: effect of applied pressure on the mechanical properties of 6061 aluminum alloy welded… composed of fine-equiaxed recrystallized grains, while the tmaz consists of coarse deformed grains. therefore, the interface between the sz and tmaz becomes the poorest location in the tensile test [8]. applied pressure, mpa 0 2 4 6 8 10 12 e lo ng at io n, m m 4 6 8 10 12 14 rotational speed 1000 rpm welding speed 1.5 mm/sec bm as as as sz as: advancing side sz: stiring zone bm: base metal fig. 6. elongation of the welded joints prepared at different applied pressures iv. conclusions in this study, fsw of 6061 aluminum sheets welded at different applied pressures was investigated. we concluded the following:  at a low applied pressure of 1.44 mpa, the flow of plasticized metal under shoulder face is not sufficient, leading to a loss of metal in the retreating side.  the microhadness of the sz increases as the applied pressure increases from 1.44 to 5.76 mpa and then starts decreasing for further increase of pressure.  the ultimate tensile strength increases to an optimum value then it starts decreasing.  at an applied pressure of 5.76 mpa, the welded joints have a superior tensile strength compared to the base metal.  due to the changes in the microstructure size as moving from zs to tmaz, the failure of the test specimens occurred near the welding line in the advanced side. acknowledgment the authors wish to acknowledge the approval and support of this research study by grant 434-16 from deanship of scientific research in northern border university, arar, kingdom of saudi arabia. references [1] l. p. troger, e. a straka, “microstructural and mechanical characterization of superplastic 6xxx aluminum alloy”, material science and engineering, vol. a277, no.1, pp. 102-113, 2000 [2] t. evern, b. ogel, “influence 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word etasr_v12_n4_pp8856-8863 engineering, technology & applied science research vol. 12, no. 4, 2022, 8856-8863 8856 www.etasr.com daraj & al-zuhairi: the combined strengthening effect of cfrp wrapping and nsm cfrp … the combined strengthening effect of cfrp wrapping and nsm cfrp laminates on the flexural behavior of post-tensioning concrete girders subjected to partially strand damage abbas jalil daraj department of civil engineering university of baghdad baghdad, iraq abbas19asdi@gmail.com alaa h. al-zuhairi department of civil engineering university of baghdad baghdad, iraq alaalwn@coeng.uobaghdad.edu.iq received: 23 april 2022 | revised: 11 may 2022 | accepted: 15 may 2022 abstract-the studies on unbonded post-tensioned concrete members strengthened with carbon fiber reinforced polymers (cfrps) are limited and the effect of strengthening on the strain of unbonded pre-stressed steel is not well characterized. estimating the flexural capacity of unbound post-tensioned members using the design methodology specified in the design guidelines for frp strengthening techniques of bonded posttensioned members does not provide a reliable evaluation. this study investigates the behavior of unbonded post-tensioned concrete members with partial strand damage (14.3% and 28.6% damage) and strengthened with cfrp laminates using a nearsurface mounted technique with and without u-wrap anchorages. the experimental results showed that the use of cfrp laminates significantly affects strand strain, especially with the use of anchors. the cfrp reinforcement affected flexural strength, crack width, and midspan deflection. however, the flexural stiffness of strengthened members during the serviceability phases is critical as strand damage ratios increase. in comparison with the nondamaged girder, the nsm-cfrp laminates enhanced the flexural capacity by 11% and 7.7% corresponding to strand damage of 14.3% and 28.6% respectively. additionally, semiempirical equations were proposed to predict the actual strain of unbonded strands whilst considering the effects of frp laminates. the suggested equations are simple to apply and provide accurate predictions with little variance. keywords-nsm-cfrp laminates; post-tensioned concrete; strand damage; strengthening i. introduction most standard investigations on the repair and strengthening of prestressed concrete members utilizing cfrp materials have recently concentrated on pre-tensioned concrete (pc) members, especially deteriorated or damaged due to corrosion or collision from overheight vehicles [1-3]. according to experimental tests, the use of cfrp strengthening techniques enhanced the stiffness and flexural strength of pc members, and reduced crack spacing and crack width [4-7]. the frp reinforcement design guidelines cover two types of techniques. the first kind is external bonded (eb), which involves bonding cfrp sheets or laminates to the tension surface of the concrete member. the second is the near-surface mounted technique, which requires extending cfrp bars or laminates into concrete cover grooves and attaching them with epoxy [8, 9]. the above techniques have many advantages, the most notable of which is that they are light-weight and improve flexural capacity, the near-surface mounted (nsm) technique is gaining popularity since it is less prone to weather fluctuations and has the potential to delay or prevent frp debonding [10]. the aci 440-r of frp strengthening has extensively documented the strengthening of prestressed concrete members, including bonded post-tensioned and pretensioned members, but unfortunately, these guidelines did not cover unbonded concrete members on the one hand, and these guidelines for strengthening were limited to the externally bonded technique on the other [11]. unlike bonded posttensioned members, which use the same concepts of equilibrium and strain compatibility to determine the strains in each of the pre-stressing steel, concrete, and cfrp components, the challenge for unbonded post-tensioned members is determining the pre-stressing steel strain increase due to the loss of strain compatibility between the pre-stressing steel and the surrounding concrete. nonetheless, several researchers were able to develop methodologies that allowed them to predict the strain increase in unbonded post-tensioned members strengthened with eb techniques [4, 5, 12, 13]. the use of nsm-cfrp is commonly accompanied by the concrete cover separation, which limits the reinforcing elements' contribution to increasing flexural capacity and reducing ductility. as a result, the use of u-wrap anchorages, which prevent the concrete cover from separating, is effective in increasing the strains of each of the reinforcing elements, resulting in considerably improved flexural behavior of the reinforced concrete members [10, 14, 15]. corresponding author: abbas j. daraj engineering, technology & applied science research vol. 12, no. 4, 2022, 8856-8863 8857 www.etasr.com daraj & al-zuhairi: the combined strengthening effect of cfrp wrapping and nsm cfrp … the current study is a part of an investigating research regarding the efficiency of strengthening techniques that is performed at baghdad university (civil engineering lab) [20]. this paper focuses on the strengthening with the use of cfrp near-surface mounted technique. ii. material properties and methodology a. design of the tested girder the experimental program includes 7 upcs simply supported girders with heights (h) of 300mm, widths (b) of 200mm, lengths (l) of 3000mm, and an effective length (lo) of 2800mm. the concrete cover was 25mm, except for tensile rebars, which use a cover of 35mm. compressive and tensile strength, and the modulus of elasticity of concrete were obtained according to astm c39, astm c496-04, and astm c469 respectively. the compressive and tensile strengths of the concrete estimated in 10 concrete cylinders (150mm×300mm) were 44.6mpa and 5.1mpa. the concrete had a slump of 118±10mm (table i). four girders strengthened with cfrp laminates using the near-surface mounted technique were tested along with a nondamaged reference girder (ref) and two sub-reference girders (pc1r and pc2r) with damaged strand ratios (sdr) of 14.3% and 28.6%. the patterns of strand damage are illustrated in figure 1. two types of steel reinforcement with diameters of 16mm and 10mm, as shown in table ii, were used for all girders in tension and compression zones respectively. the appropriate amount of steel was used for shear reinforcement to avoid the occurrence of shear failure before flexural failure. accordingly, closed stirrups with a diameter of 10mm and a spacing of 100mm c/c were placed along a length of 500mm from the girder’s edges and 200mm c/c for the remaining middle length. two seven-wire low relaxations strands with 12.7mm diameter and grade 270 were used for each upc girder (table ii) with a constant eccentricity of 70mm extended inside pvc tubes as unbonded pre-stressing steel. strand wires were carefully damaged as a result of the spiral form by fastening the two ends of the strand with metal cages and using an electric saw to achieve the specific ratio. wedge-anchored prestressing strands were directly supported on a steel bearing plate (200mm [width] × 80mm [depth] × 12mm [thickness]) attached to the ends of the girder. two holes were formed on the steel plate to facilitate the application of prestressing. the steel plate was then installed on the formwork before pouring the concrete to ensure the centrality of strands and achieve complete contact with the concrete. four damaged girders were strengthened using the nearsurface mounted technique utilizing two cfrp laminates with dimensions of 1.2mm width, 25mm depth, and 2000mm length (table iii)cfrp properties. in addition, two of these girders were strengthened with cfrp u-wrap sheet anchors at the ends of the cfrp laminates with 250mm width and 280mm height (table iv). the details of the tested girders are presented in figures 2-4 and table ivcfrp properties. girders were posttensioned by strands (according to the specific damage ratios of each strand) with a straight trajectory after 28 days of casting and immediately before the strengthening process. the initial jacking stress in each strand was 0.6fpu (figure 5). the cfrp laminates were installed one day after the tensioning of girders and before installing the strengthening material, groove locations are first marked on the girders, which have been turned upside down. the concrete was cut to the required dimensions with a concrete saw. an air and water pressure jet was subsequently used to remove the remaining concrete particles in the grooves. cfrp laminates were then inserted after the application of an adhesive layer. the adhesive was leveled with the concrete surface with a scraper (figure 6). each strengthened girder contained grooves with dimensions of 30mm (depth) × 6mm (width), as recommended by the aci 440.2r-17 [11]. the cross-sectional edges of the girders were rounded to a radius of approximately 13mm before applying the carbon panels. using a grinder, the surface of the specimens was cleaned and prepared for installation. this was done to get rid of laitance and open up the pores in concrete. after that, a primer was used to seal all the possible openings and cracks, and the cfrp sheets were applied using adhesive, according to the manufacturer's instructions (figure 6). fig. 1. patterns of damaged strands in the tested girders. fig. 2. details of steel reinforcement and girder profile for the tested girders (all dimensions are in mm). fig. 3. details of cfrp-nsm strengthened girders (all dimensions are in mm). fig. 4. details of the cfrp-nsm strengthened girders with u-wrap anchorages (all dimensions are in mm). engineering, technology & applied science research vol. 12, no. 4, 2022, 8856-8863 8858 www.etasr.com daraj & al-zuhairi: the combined strengthening effect of cfrp wrapping and nsm cfrp … fig. 5. posttensioning process of the tested girders. fig. 6. strengthening stages of the tested girders. table i. concrete properties table ii. steel reinforcement properties table iii. cfrp properties material thickness (mm) tensile modulus (gpa) tensile strength (n/mm²) ultimate elongation (%) laminates 1.2 170 3100 2 sheets 0.167 220 3500 1.59 b. instrumentation and testing procedures the upc girders were examined under two-point loading, as presented in figure 7. the load was applied at a distance of 1100mm from the closest support. the strain of the cfrp laminate was detected using strain gauges (with resistance of 119.5±0.5ω), which were glued to the surface of the cfrp laminate at midlength. the tendon strain was measured using three strain gauges (119.5±0.5ω) mounted at midlength and loading locations. notably, grooves were cut in the steel plate before installing anchors to prevent damaging the strain gauge wires. the strain of steel reinforcement was measured using one strain gauge (118.5±0.5ω) glued at the midlength, whilst two strain gauges (120±0.5ω resistance and 60mm gauge length) were surface-attached at compression and tension zones to monitor concrete strain. in addition, lvdts were used to determine the girders' deflection. the data were automatically collected using a computerized data collecting system. to progressively raise the load, a hydraulic jack with 50-ton capacity was used. a load cell with a 50-ton capacity was used to detect the load. the load was applied in increments of 15kn until the cracking load was reached. then the load was applied in increments of 30kn until failure. each beam took 2 to 3 hours to complete the test. two dial gauges were used, one at the end of each strand, to check whether any strand slip occurred during the loading process. fig. 7. test setup of the experimental girders. table iv. summary of the test parameters girder id sdr (%) aps (mm 2 ) ρρρρp (%) ρρρρs (%) cfrp laminate n× (bf ×hf) (mm) u-wrap anchor wf hf ref 0.0 197.4 0.49 0.81 ------ pc1r 14.3 169.2 0.39 ------ pc1n 169.2 2×1.4×25 ---- pc1ne 169.2 2×1.4×25 250 280 pc2r 28.6 141.0 0.32 ------ pc2n 141.0 2×1.4×25 ---- pc2ne 141.0 2×1.4×25 250 280 note: sdr:strand damage ratio; n, bf, and hf : width, and height of cfrp laminates; wf and hf : width and height of sheet anchors iii. results and discussion a. failure mode flexural failure was observed in reference and subreference girders, with tensile steel reinforcing yielding, followed by concrete crushing in the compression zone, as shown in figures 8(a)-8(c). compared with the strengthened girders, cracks develop faster, in fewer numbers, and with a wider crack width in the reference and sub-reference girders. the first flexural crack appears in the midspan of sub-reference girders pc1r, and pc2r, with cracking loads of the reference girder’s cracking load at approximately 94%, and 85% respectively. it was noticed that the cracking load decreases with increasing strand damage ratio (sdr). the failure modes of the nsm-cfrp-strengthened girders were yielding of the tensile steel reinforcement and concrete cover separation after that (figures 8(d)-8(f)error! reference source not found.). the failure of this type of strengthening showed higher brittleness, more cracks, and smaller crack widths than the corresponding sub-reference girders (figure 9). the first flexural crack appears at the midspan of nsm-cfrpstrengthened girders pc1n, and pc3n, with an increase in the cracking load of 11%, and 13% respectively, compared with those of sub-reference girders. similar to the reference girders, the strengthened girders with end cfrp u-wrap sheet anchorages failed due to tensile steel reinforcement yield compressive strength ��� (mpa) tensile strength ��� (mpa) modulus of elasticity �� (mpa) 44.6 5.1 31,220 type dia (mm) yield strength (mpa) ultimate strength (mpa) maximum elongation (%) modulus of elasticity (gpa) rebar 10 518.2 658.97 12.2 200 rebar 16 577.3 710.74 13.4 200 strand 12.7 1725 1860 5 197.5 engineering, technology & applied science research vol. 12, no. 4, 2022, 8856-8863 8859 www.etasr.com daraj & al-zuhairi: the combined strengthening effect of cfrp wrapping and nsm cfrp … followed by concrete crushing in the compression zone with more ductility as a result of exploiting the greatest amount of high tensile stress in cfrp laminates before concrete crushing (figures 8(e), 8(g)). the cfrp u-wrapped anchors, on the other hand, did not affect the tested girder's cracking load. in comparison to the sub-reference girders, flexural cracks arise in the mid-span of the girders pc1ne and pc3ne, with a 13.5% and 13% increase in cracking load. the cfrp u-wrap sheet anchors change the failure mechanism of cfrp nsm laminates significantly. without cfrp u-wraps, all nsm strengthened girders failed by separating the concrete cover, whereas cfrp u-wraps shift the failure mode to crushing concrete in the compressive zone. a crushing sound indicated the debonding of the cfrp laminate at approximately 85% of the ultimate load. however, the separation of the concrete cover occurred close to the end of cfrp laminates and developed rapidly along the shear span. according to the observations, concrete cover separation was caused by the significant increase of diagonal shear cracks that caused slip along the longitudinal steel reinforcement and the concrete cover. concrete cover separation or cover delamination and debonding of frp from the concrete substrate are two failure modes associated with frp strengthening. they are discussed in detail in [11]. fig. 8. failure patterns of the tested girders. fig. 9. concrete cover separation and debonding of cfrp laminates. b. load–deflection response the flexural behavior of the studied girders, as shown in figure 10, was investigated at 3 loading stages: elastic uncracked, allowable load at the serviceability state, and ultimate load. the load-displacement relationship of the studied girders exhibited an elastic linear behavior up to the cracking load. during this stage, as the ratio of damaged strands grows, the stiffness of the reference girders decreases slightly, whereas there was no noticeable change in the stiffness of the strengthened girders compared to their counterparts from the sub-reference girders. however, when the applied load exceeds the crack load, the sub-reference girders exhibit a significantly higher rate of stiffness degradation as a result of the reduction in the pre-stress force, and thus an increase in the rate of crack development, increasing deflection. meanwhile, the flexuralstrengthening cfrp nsm laminates demonstrated their effectiveness in delaying the development of cracks and postponing the degradation of the strengthened girders' stiffness [16, 17]. as a result, for the same level of applied load, the strengthened girders showed lesser deflection than the reference girders. the applied load of the reference girder was pser,ref= 0.79pu,ref when it increased to a load level that caused a deflection corresponding to the permissible deflection (lo/250=11.2mm) at the serviceability state. this load is denoted by the allowable load at the serviceability state (pser,ref). at the service load (pser,ref), the deflection of subreference girders pc1r and pc2r increases by 6.2% and 30.4% respectively, over the reference girder ref. in comparison with their sub-reference counterparts, the deflection of pc1n and pc2n nsm strengthened girders without anchors was reduced by 15.5% and 17.2% respectively, whereas the deflection of pc1ne and pc2ne strengthened girders with anchors was reduced by 14 % and 25% respectively. the flexural strength of the strengthened girders was much higher than that of the reference girder (table v) and the strength increased with the use of cfrp uwrap anchorages. during this period, the cfrp u-wrapped anchorage system eliminated the relative slippage and concrete cover delamination of the cfrp laminates and thus significantly enhanced the frp-strengthening effectiveness and the flexural strength of the girders. in comparison with the reference girder, the flexural capacity of girders pc1r and pc2r was reduced by 5.7% and 11.8% respectively. compared to their counterparts from the sub-reference girders, the flexural capacity of the strengthened girders without anchors increased by 17.3% and 20.4% respectively, and the flexural capacity of the strengthened girders with anchors increased by 27.9% and 30.1% respectively. it is evident from the results that the effectiveness of the frp-strengthening increases with the increase in the ratio of damaged strands. it is essential to compare the behavior of the strengthened girders and the reference girder because it was found that after cracking load, the strengthened girders pc1n and pc1ne (with an sdr of 14.3%) behave similarly to the reference girder until the steel reinforcement yields, resulting in a significant increase in deflection in the reference girder due to the rapidly increasing crack width, while pc1n and pc1ne engineering, technology & applied science research vol. 12, no. 4, 2022, 8856-8863 8860 www.etasr.com daraj & al-zuhairi: the combined strengthening effect of cfrp wrapping and nsm cfrp … maintain a large portion of their stiffness even after yielding of the reinforcing steel until concrete cover separation occurred. moreover, the deflection of the strengthened girders pc2n and pc2ne (with an sdr of 28.6%) after cracking load is larger than that of the reference girder at the same load level for a load of 85% of the reference girder’s ultimate load, which is approximately equal to the yield load of the reinforcing steel. this finding suggests that evaluating the serviceability requirements of prestressed concrete members with more than 14% of damaged strands before implementing repair techniques is crucial despite the restoration of flexural capacity. fig. 10. load-deflection relationships at mid-span of the tested girders. table v. summary of the test parameters girder id pcr (kn) pu (kn) δu,mid (mm) mu (kn.m) reduction in fs relative to rfp (%) increase in fs relative to rfp (%) failure mode ref 55 166.24 26.9 91.43 ----sy-cc pc1r 52 157.25 25.5 86.49 5.7 --sy-cc pc1n 58 184.56 23.4 101.51 --11 sy-ccscc pc1ne 59 201.20 26.9 110.66 --21 sy-cc pc2r 47 148.72 29.9 81.80 11.8 --sy-cc pc2n 53 179.10 25.4 98.51 --7.7 sy-ccscc pc2ne 53 193.62 28.1 106.49 --16.5 sy-cc pcr: f irst cracking load, pu: ultimate load, δu: ultimate deflection, mu: ultimate load, fs: flexural strength, sy: bonded steel yielding, cc: concrete crushing, and ccs: concrete cover separation c. strain in cfrp laminates load versus strain of cfrp laminates is presented in figure 11. before the breaking load, the strain in cfrp laminates is minimal and roughly equal, and it is independent of the fastening systems. after the cracking load, the strain rises noticeably and the rate of strain development increases dramatically after the bonded steel reinforcement yields. on the other hand, the strain increases in cfrp laminates with and without anchors were nearly the same, whereas the maximum strain in cfrp laminates with anchors was substantially higher than in those without anchors. the maximum strain of the cfrp laminates in the girders without anchors, pc1n and pc2n, was 0.667% and 0.86% respectively, corresponding to 33.35% and 43% of the rupture strain from coupon tests (εffu=2%). on the other hand, the maximum strain of the cfrp laminates in the girders with anchors, pc1ne and pc2ne, was 0.78% and 0.96% respectively, corresponding to 39% and 48% of the rupture strain from the coupon tests. furthermore, the use of frp strengthening had a considerable influence on concrete strain. cfrp laminates, as previously stated, successfully reduced cracks and delayed their development. this behavior resulted in a higher compressive concrete zone height for nsm-cfrp-strengthened specimens, resulting in lower concrete strain in the strengthened girders at the same loading level as sub-reference girders. d. strain in strands and influence of cfrp laminates the flexural strength remained unaffected by the strands before the occurrence of the first crack because of the small strain increases. notably, the strand strain increase was determined by subtracting the initial strain (≈0.46%) from the actual strain, as illustrated in figure 11. the behavior of strands was very similar amongst the investigated specimens during this stage. the strain of strands began to increase significantly after cracking. the increase in strand strain of sub-reference specimens was higher than that of the reference girder. however, at the same loading level, the increase in strand strain of nsm-cfrp specimens was less than that of the subreference specimens. at the reference girder's permissible load (pser-ref), the increase in the strand strain was about 0.0693% whereas the corresponding increase in strand strains in subreference girders, pc1r and pc2r, was 0.0752% and 0.0896% respectively, which showed an increase of 8.6% and 29.5% in comparison with the reference girder ref. similarly, the strand strain increase in strengthened girders without anchors, pc1n and pc2n, was 0.0651% and 0.0731%, with a reduction of 15% and 22% compared with their counterparts in the subreference girders. on the other hand, the strand strain increases in strengthened girders with anchors, pc1ne and pc2ne, was 0.0621%and 0.0712%, with a reduction of 20.7% and 26% compared with their counterparts in the sub-reference girders. in the loading phase, after the allowable load at the serviceability state, the strand strain increase in the strengthened girders was much smaller than that in the reference girder at the same loading level. for instance, at the maximum load of the reference girder (pu,ref), the strand strain increase in the strengthened girders without anchors, pc1n and pc2n, was smaller by 42% and 25.5%. similarly, the strand strain increase in the strengthened girders with anchors, pc1ne and pc2ne, was smaller by 52.6% and 29%. the cfrp laminates and cfrp u-wrapped anchorages have a considerable influence on the behavior of the strands. again, the cfrp laminates were able to arrest cracks and delay crack development and they slowed down the degradation of the girder stiffness. δδδδser=11.2mm 0 50 100 150 200 250 0 10 20 30 40 l a o d ( k n ) deflection (mm) ref pc1r pc2r pc1n pc1ne pc2n pc2ne engineering, technology & applied science research vol. 12, no. 4, 2022, 8856-8863 8861 www.etasr.com daraj & al-zuhairi: the combined strengthening effect of cfrp wrapping and nsm cfrp … fig. 11. load-strain curves of cfrp laminates and strands. iv. strain increase of the strands determining the increase in a strain of unbonded strands is a critical case in estimating the flexural strength of unbonded post-tensioned members strengthened with near-surface mounted cfrp laminates. unfortunately, the design guidelines have only proposed one approach to evaluate the increase in the strain of bonded strands in bonded post-tensioned and pretensioned members strengthened with eb-cfrp sheets, whereas the corresponding approaches for unbonded strands in members strengthened with nsm-cfrp laminates are not included. additionally, the experimental results have exhibited that nsm-cfrp laminates significantly influence the unbonded tendons' behavior. the strand’s strain increase of the unbonded post-tensioned members strengthened with cfrps was evaluated using tam and pannell's equations for unbonded tendons in normal reinforced concrete members. for members without end cfrp u-wrapped sheet anchorages, we have: ∆� ,� �� = ω�� ������� � × �1 + 100 ! "! �!# $ "$�!%%& '.)* (1) for members with cfrp u-wrapped sheet anchorages: ∆� ,� �� = ω�� ������� � × �1 + 100 + "+ �+, $ "$ �+--� ../) (2) after that, the overall strain of the unbonded strands ∆� ,� �� is calculated as: � ,� �� = � 0 + ∆� ,� �� (3) where εfe is the initial strain of strands not including strain losses = fp/(ep ap), fp (n) is the actual tensile force in strands, ap (mm 2) and ep (mpa) are the cross-sectional area and the elasticity modulus of a strand respectively, ∆� ,� �� is the increase in the strain of strands, ψ is the length of the plastic zone divided by the height of the compressive concrete zone: ω = 10.5 [18] for simply supported unbonded post-tensioned members which are un-cracked and reinforced with cfrp laminates, and ω = 9.8 [4] for the pre-cracked unbonded posttensioned members reinforced by eb-cfrp sheets. �� is the maximum strain at concrete compression fiber as per aci 440.2r-17 [11], dp (mm) is the distance between the compressive concrete zone's furthest point and the centroid of the strand cross-sectional area, c (mm) is the compressive concrete zone's height as per [19], l0 (mm) is the effective span of the members, and εfe is the actual strain in cfrp laminates at the ultimate applied load. v. the proposed formula's evaluation equations (1)–(13) were applied to the estimating flexural strength of the 23 unbonded post-tensioned members reinforced with cfrp laminates including the 7 simply supported members reinforced with eb-cfrp laminates investigated in this manuscript and 16 slabs and girders from [4]. the predicted flexural strength, mu,pred was calculated as per aci 440.2r-17 [11] considering the materials and strength reduction factors to be equal to 1.0, as follows: step #1: estimation of the compressive concrete zone depth (c). the depth of the neutral axis, c (mm), is initially assumed, which could be h/10 as per [11], where h is defined as the concrete cross-section height. step #2: evaluating the strain in cfrp laminates, concrete, and strands. the cfrp laminate strain �10, for failure detected by concrete crushing is given by: �10 = ��2 ��!��� � − �45 ≤ �1� (4) where df is the effective cfrp laminates depth, εcu is the concrete’s ultimate compressive strain which is equal to 0.003, c is the compressive concrete zone depth, and �45 is the initial strain in substrate: �45 = � �"$ $ �1 + 0 78 9: � + ;<=78 >$ $ (5) where fp (n) is the initial prestressing force after excluding the losses, e (mm) is the prestressing force's eccentricity concerning the concrete cross-centroid section, yb (mm) represents the distance from the gross-centroidal section (ignoring steel rebars) to the farthest bottom fiber, r (mm) represents the radius gyration of the member section = (ic/ac) 0.5, ic (mm 4) represents the moment of inertia of concrete cross concerning the neutral axis, mdl (n.mm) is the applied dead load’s moment, and εfd is the strain’s debonding described by: initial strain in stran≈≈≈≈4590 micro strain strand yield strain =8485 micro strain 0 50 100 150 200 250 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 l o a d ( k n ) strain (micro strain) loadstrain curves for strand & cfrp laminatepc1 (14.3% sdr) strand-l/2-ref strand-l/2-pc1r strand-l/2-pc1n cfrp-l/2-pc1n cfrp-l/2-pc1ne strend-l/2-g1ne initial strain in stran≈≈≈≈4590 … strand yield strain =8485 … 0 20 40 60 80 100 120 140 160 180 200 0 2000 4000 6000 8000 10000 12000 l o a d ( k n ) strain (micro strain) load-strain curves for strand & cfrp laminates-pc2 (28.6% sdr) strand-l/2-ref strand-l/2-pc2r strand-l/2-pc2n cfrp-l/2-pc2n cfrp-l/2-pc2ne strand-l/2-pc2ne engineering, technology & applied science research vol. 12, no. 4, 2022, 8856-8863 8862 www.etasr.com daraj & al-zuhairi: the combined strengthening effect of cfrp wrapping and nsm cfrp … �1� = 0.41@ 1$ a b"$c! ≤ 0.9�112 (6) �1� = 0.7 �112 (7) where fc′ is the concrete strength, εffu, tf, and ef are the ultimate strain, thickness, and elasticity modulus of cfrp respectively, and n represents the cfrp layers numbers. according to [11], (6) is replaced by (7) to determine the debonding strain of nsm-cfrp in this study. the strain in cfrp laminates, εfe, for failure caused by rupture of strands is: �10 = f� 2 − � 5 g ��!��� � − �45 ≤ �1� (8) where εpu is the strands rupture strain which is equal to 0.05 and εpi is the strand initial strain, which can be estimated as: �45 = �"$ $ + � "$ $ �1 + 0 : 9: � (9) step #3: estimation of the steel rebars strain εs: � = f�10 + �45 g � ����!��& for tensile rebars (10) step #4: recalculation of the depth of the compressive concrete zone c using the equilibrium of forces: h = �1�ij i1ij !1!#kl1$aml4 (11) where ffe (mpa) is the cfrp laminates stress = ef × εfe, fps (mpa) is the strands stress = ep × εps,cfrp ≤ fpy, and fs (mpa) is the tensile rebars stress = es × εs ≤ fy. step #5: checking the depth of the compressive concrete zone c. if the assumed value of c (cassu) and re-calculated one (ccalc) meet the presented convergence criterion in (12), the appropriate value of c is obtained. if not, the value of cassu is recalculated and the process is repeated starting at the second step until convergence is achieved. criterion of convergence= |�oii%��$op| �oii% ≤ 0.1% (12) fig. 12. experimental vs. predicted values of flexural capacities. step #6: evaluating the flexural strength of nsm-cfrp strengthened members. finally, the flexural strength of nsmcfrp strengthened unbonded post-tensioned members, mu-p , can be calculated as per (13): r2�� = s t �u − ml�v � + s1 t10 �u1 − ml� v � + s t �u − ml�v � (13) the predicted-to-experimental flexural strength ratios mu-p /mu-e are illustrated in table vi and error! reference source not found.figure 12. the mean value is 0.948 and cov=0.066 (coefficient of variation). they describe the accuracy of the theoretical strand strain values and their suitability for the prediction of the flexural strength of the nsm-cfrp unbonded post-tensioned members with and without anchorages. table vi. table i: the predicted and experimental flexural capacities eb cfrp-strengthened upc members el meski and harajli specimens mu-p mu-e mu-p / mu-e girders ub1_h_f1 41.36 41.80 0.99 ub1_h_f2 51.38 54.30 0.95 ub1_p_f1 34.75 41.40 0.84 ub1_p_f2 51.68 55.60 0.93 ub2_h_f1 54.85 50.50 1.09 ub2_h_f2 63.86 65.50 0.97 ub2_p_f1 50.79 58.50 0.87 ub2_p_f2 58.91 63.30 0.93 slabs us1_h_f1 22.37 21.40 1.05 us1_h_f2 27.32 26.90 1.02 us1_p_f1 19.70 21.60 0.91 us1_p_f2 28.31 30.10 0.94 us2_h_f1 25.44 26.60 0.96 us2_h_f2 30.69 35.80 0.86 us2_p_f1 27.42 29.80 0.92 us2_p_f2 31.68 37.40 0.85 average 0.941 standard of deviation 0.070 cov 0.075 nsm-cfrp strengthened upc girders (current study) ref 90.72 91.43 0.992 pc1r 85.72 86.49 0.991 pc1n 99.88 101.51 0.984 pc1ne 100.65 110.66 0.909 pc2r 80.50 81.80 0.984 pc2n 96.05 98.51 0.975 pc2ne 96.79 106.49 0.909 average 0.964 standard of deviation 0.038 cov 0.039 for all members average 0.948 standard of deviation 0.062 cov 0.066 mu-p is the predicated moment capacity and mu-e is the experimental moment capacity vi. conclusions the behavior of post-tensioned concrete girders subjected to partial strand damage and strengthened by nsm-cfrp laminates with and without cfrp u-wrap sheet anchorages 0 20 40 60 80 100 120 0 20 40 60 80 100 120 m u -p ( kn .m ) mu-e (kn.m) current-beam meski-beam meski-slab engineering, technology & applied science research vol. 12, no. 4, 2022, 8856-8863 8863 www.etasr.com daraj & al-zuhairi: the combined strengthening effect of cfrp wrapping and nsm cfrp … was researched and evaluated in this work. the following conclusions are derived from this study's experimental results: • the flexural capacity of post-tensioned girders reduces as the sdr increases. the flexural strength was reduced by 6% and 12% for girders with strand damage of 14.3% and 28.6% respectively. on the other hand, at all loading stages, the deflection increases as the sdr increases. • near-surface mounted techniques using cfrp laminates enhance flexural capacity by controlling crack development. in comparison with the nondamaged girder, the nsm-cfrp laminates enhanced the flexural capacity by 11% corresponding to strand damage of 14.3%, whereas the flexural capacity increased by 7.7%, corresponding to strand damage of 28.6%. • the use of u-wrap anchorages eliminates the cover separation and effectively enhances the flexural strength for strengthened girders. in comparison with the nondamaged girder, the nsm-cfrp laminates enhanced the flexural capacity by 21% corresponding to strand damage of 14.3%. whereas the flexural capacity increased by 16.5%, corresponding to strand damage of 28.6%. • the cfrp laminates significantly affect the behavior of the strands. at the same loading level, the strain increase of the strands in the strengthened girders was much smaller than that of the damaged girder. for example, at the service load of the undamaged reference girder, the increase in strand strain of the strengthened girders is reduced by 15% and 22% respectively, compared to the increase in strand strain of the corresponding damaged girders. on the other hand, this effect increases considerably when using u-wrap anchorages. • the proposed procedure for predicting strand strain rises in unbonded post-tension girders enhanced with nsm-cfrp laminates, effectively predicts flexural strength with high accuracy and minimal variation (average = 0.956 and cov = 0.064). references [1] c. e. reed and r. j. peterman, "evaluation of prestressed concrete girders strengthened with carbon fiber reinforced polymer sheets," journal of bridge engineering, vol. 9, no. 2, pp. 185–192, mar. 2004, https://doi.org/10.1061/(asce)1084-0702(2004)9:2(185). 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[16] a. h. al-zuhairi, a. h. al-ahmed, a. a. abdulhameed, and a. n. hanoon, "calibration of a new concrete damage plasticity theoretical model based on experimental parameters," civil engineering journal, vol. 8, no. 2, pp. 225–237, feb. 2022, https://doi.org/10.28991/cej2022-08-02-03. [17] a. a. abdulhameed et al., "the behavior of hybrid fiber-reinforced concrete elements: a new stress-strain model using an evolutionary approach," applied sciences, vol. 12, no. 4, jan. 2022, art. no. 2245, https://doi.org/10.3390/app12042245. [18] a. tam and f. n. pannell, "the ultimate moment of resistance of unbonded partially prestressed reinforced concrete beams," magazine of concrete research, vol. 28, no. 97, pp. 203–208, dec. 1976, https://doi.org/10.1680/macr.1976.28.97.203. [19] aci committee 318, aci code-318-19: building code requirements for structural concrete and commentary. west conshohocken, pa, usa: aci, 2019. [20] h. q. abbas and a. h. al‐zuhairi, "flexural strengthening of prestressed girders with partially damaged strands using enhancement of carbon fiber laminates by end sheet anchorages," engineering, technology & applied science research, vol. 12, no. 4, pp. 8884–8890, aug. 2022, https://doi.org/10.48084/etasr.5007. engineering, technology & applied science research vol. 8, no. 1, 2018, 2537-2541 2537 www.etasr.com syafrina et al.: stochastic modeling of rainfall series in kelantan using an advanced weather generator stochastic modeling of rainfall series in kelantan using an advanced weather generator a. h. syafrina department of mathematics faculty of science universiti putra malaysia serdang, selangor, malaysia syafrina@upm.edu.my a. norzaida utm razak school of engineering and advanced technology universiti teknologi malaysia kuala lumpur, malaysia zaida.kl@utm.my o. noor shazwani utm razak school of engineering and advanced technology universiti teknologi malaysia kuala lumpur, malaysia noorshazwaniosman@gmail.com abstract—weather generator is a numerical tool that uses existing meteorological records to generate series of synthetic weather data. the awe-gen (advanced weather generator) model has been successful in producing a broad range of temporal scale weather variables, ranging from the highfrequency hourly values to the low-frequency inter-annual variability. in malaysia, awe-gen has produced reliable projections of extreme rainfall events for some parts of peninsular malaysia. this study focuses on the use of awe-gen model to assess rainfall distribution in kelantan. kelantan is situated on the north east of the peninsular, a region which is highly susceptible to flood. embedded within the awe-gen model is the neyman scott process which employs parameters to represent physical rainfall characteristics. the use of correct probability distributions to represent the parameters is imperative to allow reliable results to be produced. this study compares the performance of two probability distributions, weibull and gamma to represent rainfall intensity and the better distribution found was used subsequently to simulate hourly scaled rainfall series. thirty years of hourly scaled meteorological data from two stations in kelantan were used in model construction. results indicate that both probability distributions are capable of replicating the rainfall series at both stations very well, however numerical evaluations suggested that gamma performs better. despite gamma not being a heavy tailed distribution, it is able to replicate the key characteristics of rainfall series and particularly extreme values. the overall simulation results showed that the awe-gen model is capable of generating tropical rainfall series which could be beneficial in flood preparedness studies in areas vulnerable to flood. keywords-weather generator; flood; rainfall intensity; probability distribution; northeastern monsoon i. introduction weather generator is a numerical tool that uses existing meteorological records to produce a series of long daily synthetic weather data that is often short and non-continuous [1-2]. various weather generators have been built throughout the years, such as the weather generator (wgen) [3-4], climate generator (cligen) [5], long ashton research station-weather generator (lars-wg) [6]. weather generators are often based on empirical statistical relationships that maintain the autocorrelation and correlation properties of the various variables. according to [7], the simulated time scales range from daily to annual periods. however, one of the drawbacks of daily weather generators is that they underestimate monthly and inter-annual variances due to the lack of consideration in estimating low-frequency component of climate variability. authors in [8] used a monthly generator (based on first-order autoregressive model) to adjust the low frequency capability based on the daily wgen model. even though the results are well simulated, this model is not able to capture the inter-annual variability. in [9], authors introduced a method for pairing of two different time scales modeled stochastic hydrological time series model. two resembling time series were produced where one preserves important statistical properties on a finer time scale while the other is on a coarser scale of time. the adjustment is then made on a series of finer time scales so that the series is consistent with a series of coarser time scales. the results show that the coupling method can produce a series of daily rainy days which preserves some important statistical properties on daily, monthly and yearly scales. other studies of weather generator (e.g. [10-13]) were conducted to address daily weather generator related problems. authors in [14] compared the performance of different stochastic weather generators for long term climate data simulation. in particular, climate generator (cligen), long ashton research station weather generator (lars-wg), and weather generators (weagets) were compared in terms of their ability to capture vital statistics features. the observed daily monitoring statistical features and minimum as well as maximum daily air temperatures are well simulated using both cligen and lars-wg models. these generators can also simulate maximum growth periods and increasing degree days, making them ideal for plant growth simulation. however, weagets model is not quite capable of capturing the descriptive statistics, output value distributions, and evaluate extreme variables. on the other hand, the advanced weather generator (awe-gen) model, developed by authors in [15], has been successful in producing a broad range of temporal scale weather variables from the high-frequency hourly values to the low-frequency inter-annual variability. in malaysia, the model engineering, technology & applied science research vol. 8, no. 1, 2018, 2537-2541 2538 www.etasr.com syafrina et al.: stochastic modeling of rainfall series in kelantan using an advanced weather generator had demonstrated its ability in producing projections of extreme rainfall events for peninsular malaysia [16]. in this study, the awe-gen model is used to analyze rainfall activities in kelantan using meteorological data from selected stations. embedded within the awe-gen model is the neyman scott rectangular pulse (nsrp) model, developed in [17]. nsrp model uses parameters to denote the physical rainfall characteristics, thus it is highly crucial to appoint the correct probability distributions representing the parameters to allow reliable results to be produced. in malaysia, several types of distributions have been tested for rainfall intensity and the results varied according to the models used. for instance, generalized pareto [18], mixed exponential [19, 20] were used. this study compares the performance of two probability distributions, weibull and gamma to represent rainfall intensity. the distribution with the best fit will be used to simulate hourly scaled rainfall series. weibull is a heavy-tailed distribution which could capture the extreme rainfall events, frequently experienced in the studied region, while gamma distribution has been successfully employed in [15] in awegen to assess rainfall in tucson airport, arizona, usa. ii. data malaysia lies within the equatorial belt with high temperatures and rains all year long. its rainfall distribution is influenced by the monsoon regime and lately, is inconsistent from year to year. there are two main monsoon winds seasons, the southwest monsoon (between may to september) and the northeast monsoon (from november to march). the east coast of peninsular continues to be affected by the northeast monsoon which brings more rain. the studied region, kelantan is located in the north east and is highly susceptible to monsoon flood almost on a yearly basis. in this study, the awe-gen model is constructed based on 30 years (1975-2005) of historical meteorological data. data on hourly scale such as rainfall amount, temperature, relative humidity and wind speed are taken from two selected rainfall stations (see table i). figure 1 shows the location of the rainfall stations in this study. iii. model development within the awe-gen model is the nsrp model to assess the intra-annual variability. work by authors in [20] and [21] indicated that the neyman scott methodology is suitable to be used in malaysia. parameters describing the physical characteristics of rainfall in the nsrp model are given in table ii. further description of nsrp model and theoretical formations could be found in [19]. as mentioned before, appointing the correct probability distributions in representing the parameters of nsrp model is critical. hence in this study, the performance of gamma and weibull in representing cell intensity is compared. the gamma distribution that is associated in nsrp is as follows,                   0,0 0, 1 )( 1 x xex xp x   (1) where  is the scale parameter  0 ,  is the shape parameter  0 and x is the hourly rainfall amount. fig. 1. map of peninsular malaysia with location of rainfall stations table i. station data station id name of station lat (o) lon (o) 4819027 gua musang, kelantan 2.92 101.37 5120025 balai polis bertam, kelantan 3.43 101.18 meanwhile, the weibull distribution is as follows,                                  x e x )x(p 1 (2) where  and  are the scale and shape parameters, respectively. the first phase of this study individually fits gamma and weibull distributions to the data of the selected stations. generated rainfall amount of each station are then compared with the observed data. the performance of both distributions are judged using root mean square error (rmse), rmse = ∑ − (3) where n is the total number of data, iy is the i-th actual rainfall amount and ˆiy is the simulated rainfall amount. lower value of rmse denotes the more efficient distribution at a particular station. the second phase of the study involves generating rainfall series using the identified distribution representing rainfall intensity at each rainfall station. in order engineering, technology & applied science research vol. 8, no. 1, 2018, 2537-2541 2539 www.etasr.com syafrina et al.: stochastic modeling of rainfall series in kelantan using an advanced weather generator to validate the model, the simulated hourly rainfall was divided into two non-overlapping periods. these periods are (i) 1975 to 1989 and (ii) 1990 to 2005. the first period is the reference period where a multiplicative factor is computed based on the simulation output and the high resolution observational data. next, the changing factors were then used to amend the biases of the simulation output from 1990 to 2005. the revised hourly rainfall is then compared to the observation from the identical period of 1975-1989. table ii. rainfall parameters of the nsrp model param. meaning λ mean storm origin arrivals (h) β mean waiting time for cell origins after the origin of the storm (h) η mean duration of the cell (h) μc mean number of cell per storm α, θ shape and scale parameters of rainfall intensity using gamma γ, θ shape and scale parameters of rainfall intensity using weibull iv. results and discussion table iii shows the rmse values for both distributions at each rainfall station. there is not much difference in the values between gamma and weibull, but overall, gamma has the better fit for rainfall intensity at both stations with a lower value of rmse. the nsrp model parameters with gamma representing intensity are displayed in table iv. table iii. rmse values of gamma and weibull distributions station id name of station rmse gamma weibull 4819027 gua musang 216* 224.7 5120025 balai polis bertam 238.7* 240.0 * indicates lowest rmse value table iv. estimated nsrp parameters of the awe-gen model with gamma station 4819027 month   c    jan 0.005 0.02 22.25 2.39 0.43 8.10 feb 0.005 0.02 8.17 2.40 0.62 10.07 mar 0.007 0.03 2.67 2.22 3.26 5.70 apr 0.008 0.01 3.36 2.65 1.80 10.60 may 0.011 0.01 3.41 2.63 1.85 10.62 jun 0.009 0.01 3.27 2.46 2.41 8.23 jul 0.013 0.01 1.82 3.12 4.98 5.86 aug 0.014 0.01 2.28 2.83 2.86 8.09 sep 0.022 0.01 1.29 2.80 20.00 1.84 oct 0.023 0.02 1.74 2.23 3.21 6.54 nov 0.021 0.08 7.86 2.07 0.28 16.22 dec 0.009 0.03 13.64 1.63 0.66 6.18 station 5120025 jan 0.005 0.02 6.69 1.94 1.51 4.73 feb 0.004 0.02 5.53 2.11 2.18 4.46 mar 0.006 0.01 3.02 2.68 3.73 4.31 apr 0.008 0.03 2.57 2.21 1.59 12.04 may 0.016 0.09 1.16 2.48 10.82 3.14 jun 0.010 0.01 3.01 2.77 1.80 10.54 jul 0.011 0.01 1.88 3.79 3.58 9.91 aug 0.010 0.01 2.90 2.68 2.90 7.93 sep 0.014 0.02 1.83 2.32 5.37 5.17 oct 0.018 0.01 1.69 2.16 2.40 8.91 nov 0.007 0.03 17.87 1.70 0.18 19.36 dec 0.005 0.03 27.31 1.75 0.34 9.03 parameter estimates for λ and β denote the estimated storm origin arrival rate and waiting time for cell origin after the storm origin, respectively. there are no significant differences in λ and β at both stations. meanwhile, μc represents the mean number of cell per storm and η represents the mean duration of the cell. from the table, mean number of cells per storm, recorded higher values in november to february for both stations, indicating that rainfall activity is heavier during these months. it should be noted that this period is referred to as the northeast monsoon season which causes heavier rainfall in the eastern coast of the peninsular. kelantan which is located at the north eastern coast is exposed to the northeast monsoon wind during this period. however, the mean duration of the cell, η recorded relatively higher values in july for both stations. it should be noted that july corresponds to the southwest monsoon which takes place from may to august. hence, η does not give high contribution to the rainfall activity in kelantan. increase in shape parameter α implies higher probability occurrence of extreme and heavy rainfall [22]. the value of α for stations 4819027 and 5120025 is highest in september and may, respectively. in contrast, both stations have smaller value of α in november, implying the probability of the occurrence of rainfall extremes is small. however, the highest value for scale parameter θ is observed in november, with 16.22 mm/h for station 4819027 and 19.36 mm/h for station 5120025, implying higher rainfall extreme intensities during this month. according to [22], interannual variability in the extreme rainfall is driven by the leading mode of variability in the scale parameter. second order mode of the variability of rainfall extremes is associated with the leading mode of the variability of shape parameter. such results are consistent with the findings of this study where the scale parameter contributes more significant to the extreme rainfall activity in kelantan as compared to the shape parameter. awe-gen with gamma is used to generate 30 years of rainfall series at hourly scale in each station. the results in the form of graphical comparison are shown in figure 2. the mean, variance, lag-1 autocorrelation and skewness are well simulated for both stations. results also indicate that the frequency of non-precipitation as well as the transition probability are quite challenging for both stations to capture. due to its stations’ location at the eastern region of peninsular malaysia that receives higher amount of rainfall every year, the mean of dry interval is underestimated at both stations. for stations 4819027 and 5120025, it is underestimated by 0.8 and 0.7 days respectively as confirmed in figure 3. similarly, the mean of wet interval is also underestimated but to a lesser degree by 0.2 and 0.3 days, respectively. in tropical climate, the mean is usually preserved but the shape of the distribution can deviate from the observed. the simulated and observed extremes rainfall for time aggregation periods of 1 hour and 24 hours are illustrated in figure 4. for both stations, there is good match between simulated and observed values, especially for return periods up to 20-30 years. extreme values of dry intervals are poorly captured by the model. in contrast, extreme values of wet intervals are well captured by the model. engineering, technology & applied science research vol. 8, no. 1, 2018, 2537-2541 2540 www.etasr.com syafrina et al.: stochastic modeling of rainfall series in kelantan using an advanced weather generator (i) (ii) fig. 2. comparison between observed (red) and simulated (green) monthly statistics of rainfall of 1 hour scale for (i) station 2913001 and (ii) station 3411017 (i) (ii) fig. 3. comparison between observed (red) and simulated (green) of fraction of time, for dry interval length (a) consecutive days with precipitation depth lower than 1 [mm] and for wet interval length distribution (b) consecutive days with precipitation depth larger than 1 [mm] for (i) station 4819027 and (ii) station 5120025. eobs and σobs are the observed mean and standard deviation and esim and σsim are the simulated ones. (i) (ii) fig. 4. comparison between observed (red) and simulated (green) values of extreme precipitation (green crosses) at (a) 1-hour and (b) 24-hour aggregation periods, (c) extremes of dry and (d) wet interval durations for (i) station 4819027 and (ii) station 5120025 v. conclusions overall, the awe-gen model is capable of replicating the monthly rainfall series in kelantan through gamma distribution. although gamma is not a heavy-tailed distribution, it was found to be better in representing the rainfall intensity compared to the weibull distribution. the estimated parameter results indicate that there are no significant differences in λ and β at both stations. higher values of μc and θ suggest that there are heavy rainfall activities in kelantan, especially during the northeast monsoon season whereas η and α do not contribute significantly to the rainfall activity. results of this study are valuable, particularly to agricultural and storm water management planning. specifically, this model could be beneficial in terms of handling issues of insufficiency of hydrological data especially rainfall, at remote stations. acknowledgment the authors would like to thank the drainage and irrigation department for the rainfall data and iium and utm for supporting this research. also, the malaysian meteorological department (mmd) for the meteorological data. this research is funded by the research initiative grant scheme (project id: rigs16-079-0243) and utm vote 15h74. references [1] d. s. wilks, r. l. wilby, “the weather generation game: a review of stochastic weather models”, progress in physical geography, vol. 23, no. 3, pp. 329-357, 1999 engineering, technology & applied science research vol. 8, no. 1, 2018, 2537-2541 2541 www.etasr.com syafrina et al.: stochastic modeling of rainfall series in kelantan using an advanced weather generator [2] m. kevin, r. ramesh, o. john, a. imran, g. bahram, “evaluation of weather generator climgen for southern ontario”, canadian water resources journal, vol. 30, no. 4, pp. 315-330, 2005 [3] c. w. richardson, “stochastic simulation of daily precipitation, temperature, and solar radiation”, water resources research, vol. 17, no. 1, pp. 182–190, 1981 [4] c. w. richardson, d. a. wright, wgen: a model for generating daily weather variables, us department of agriculture, agricultural research service, ars-8, 1984 [5] a. d. nicks, l. j. lane, g. a. gander, “weather generator”, in: usda_water erosion prediction project: hillslope profile and watershed model documentation, nserl report no. 10, chapter 2, west lafayette, 1995 [6] m. a. semenov, e. m. barrow, “lars-wg, a stochastic weather generator for use in climate impact studies, user manual”, available at: http://resources.rothamsted.ac.uk/sites/default/files/groups/mas models/download/lars-wg-manual.pdf, 2002 [7] c. g. kilsby, p. jones, a. burton, a. ford, h. fowler, c. harpham, p. james, a. smith, r. l. wilby, “a daily weather generator for use in climate change studies”, environmental modelling and software, vol. 22, no. 12, pp. 1705–1719, 2007 [8] m. dubrovsky, j. buchteke, z. zalud, “high-frequency and lowfrequency variability in stochastic daily weather generator and its effect on agricultural and hydrologic modeling”, climatic change, vol. 63, no. 145-179, pp. 1123-1130, 2004 [9] q. j. wang, r. j. nathan, “a method for coupling daily and monthly time scales in stochastic generation of rainfall series”, journal of hydrology, vol. 346, no. 3-4, pp. 122–130, 2007 [10] d. e. keller, a weather generator for current and future climate conditions, phd thesis, eth-zurich 2015 [11] e. m. furrer, r. w. katz, “improving the simulation of extreme precipitation events by stochastic weather generators”, water resources research, vol. 44, no. 12, 2008 [12] j. chen, f. p. brissette, r. leconte, “uncertainty of downscaling method in quantifying the impact of climate change on hydrology”, journal of hydrology, vol. 401, no. 3-4, pp. 190-202, 2011 [13] m. a. semenov, “simulation of extreme weather events by a stochastic weather generator”, climate research, vol. 35, pp. 203-212, 2008 [14] s. mehan, t. guo, m. w. gitau, d. c. flanagan, “comparative study of different stochastic weather generators for long-term climate data simulation”, climate, vol. 5, no. 26, 2017 [15] s. fatichi, v. y. ivanov, e. caporali, “simulation of future climate scenarios with a weather generator”, advances in water resources, vol. 34, no. 4, pp. 448-467, 2011 [16] a. h. syafrina, m. d. zalina l. juneng, “historical trend of hourly extreme rainfall in peninsular malaysia”, theoretical & applied climatology, vol. 120, no. 1, pp. 259–285, 2015 [17] i. rodriguez-iturbe, p. s. eagleson, “mathematical models of rainstorm events in space and time”, water resources research, vol. 23 no.1, pp. 181-190, 1987 [18] s. dan'azumi, s. shamsudin, a. aris, “modeling the distribution of rainfall intensity using hourly data”, american journal of environmental sciences, vol. 6, no. 3, pp. 238-243, 2010 [19] y. fadhilah, m. d. zalina, v. t. v. nguyen, y. zulkifli, “performance of mixed exponential and exponential distribution representing rain cell intensity in neyman-scott rectangular pulse (nsrp) model”, malaysian journal of civil engineering, vol. 10, no. 1, pp. 55-72, 2007 [20] a. norzaida, m. d. zalina, y. fadhilah, “a comparative study of mixed exponential and weibull distributions in a stochastic model replicating a tropical rainfall process”, theoretical & applied climatology, vol. 118, pp. 597-607, 2014 [21] a. norzaida, m. d. zalina, y. fadhilah, “application of fourier series in managing the seasonality of convective and monsoon rainfall”, hydrological sciences journal, vol. 61, no. 10, pp. 1967-1980, 2016 [22] o. zolina, a. kapala, c. simmer, s. k. gulev, “analysis of extreme precipitation over europe from different reanalyses: a comparative assessment”, global and planetary change, vol. 44, no. 1-4, pp. 129– 161, 2004 engineering, technology & applied science research vol. 7, no. 4, 2017, 1870-1873 1870 www.etasr.com yousefian et al.: case study of effectiveness evaluation of staff training courses in refah bank case study of effectiveness evaluation of staff training courses in refah bank ebrahim yousefian department of humanities sciences faculty of public management khorasgan branch, islamic azad university, khorasgan, isfahan, iran ali chitsaz department of management university of isfahan isfahan, iran beheshteh karimpour department of english teaching khorasgan branch, islamic azad university khorasgan, isfahan, iran abstract—one of the newest and most well-known train patterns for evaluating the effectiveness of in-service staffs training is kircpatrick model. in this paper, the effectiveness of staff training courses of refah-bank is evaluated. a questionnaire consisted of five components which include: reaction, learning, of behavior, the results and the innovation in role of confounding factors is handed out. the survey results show that three factors (reactions, behavior and innovation) have a significant effect on the teachings effectiveness according to kircpatrick model. and that two factors (learning and results of the courses) have not a significant effect. keywords-kircpatrick model; mebbliav; training; staff i. introduction the fundamental problem in many training programs is that imparting training to work doesn't move well. the well known kirkpatrick model is the worldwide standard for evaluating the effectiveness of training [1]. the variables in this study consist of five cases. learning model components include response factor (satisfaction and organization of courses and facilities) and learning factors (learner readiness, self-efficacy and performance), behavioral factors (expectations of performance improvement and enhance one's knowledge and changes in behavior and attitudes improvement and enhance one's ability), results elements (results and efficiency training of colleagues, supervisor support, positive individual results, negative individual results, the administrator license, freedom to change and feedback) and innovation factors including (persistent, improvement in work, coordination of training methods and budget with innovation of staff). the main question in this research is that has in-service training courses held synonymous with innovation been effective based on the transition of the model? in this regard, the transition model is one of the newest and the most popular patterns in the evaluating literature of the effectiveness of staff's in-service training that can be used as a convenient and comprehensive tool to assess the effectiveness of in-service staff training. this model with four levels: 1) reaction 2) learning 3) behavior 4) results 5) innovation factors examine the effectiveness of the transition of education. eventually, the condition of persistence training staffs depends on the level of innovation. if in-service trainings are not properly, results will not be satisfactory. in [2], authors investigated the relationship between the transmitted training and performance of service organizations in case of saipa. the results show that all the factors studied on the halton transition model is desirable. in [3], authors investigated the transition of education in malaysia's national automotive company. results showed that halton model in the course of transmission is desirable this has facilitated a positive transition to work and education transfer occurred. in [4], authors evaluated the transition of education in the public administration of catalonia. results showed that the motivational elements are the most valuable one followed by work environment factors and transfer of control. the refah-kargaran bank is as an old and reputable bank in iran that intends to create major developments in staff education and improvement. the aim of the current study is to investigate the effect of in-service training on employee's performance with the interventionist role of innovation based on kirkpatrick model. ii. research methodology the study population included all employees of refah bank who have completed in-service training (165 people) and 113 are selected. a questionnaire was used as a measuring tool [4]. the first part of the questionnaire included demographic characteristics of respondents such as gender, education, and work experience and organizational position. the second part included 43 knowledge transfer questions. the learning model used includes components such as response factors (satisfaction organizing courses and facilities), learning factors (learner readiness, self-efficacy and performance), behavioral factors (expectations about behavior changes to improve the performance of one's knowledge, improve attitudes promotion and raising ability), results (results and efficiency training of colleagues, supervisor support, positive individual results, negative individual results, the administrator license, freedom to change and feedback) and innovation factors (persistence, work improvement, coordination of training methods and budget) (table i and figure 1). the learning component has earned the most points and this means that in-service training of employees has the greatest impact on learning. male respondents scored higher than female and they showed more confidence and more belief to engineering, technology & applied science research vol. 7, no. 4, 2017, 1870-1873 1871 www.etasr.com yousefian et al.: case study of effectiveness evaluation of staff training courses in refah bank the effectiveness of in-service training. younger participants scored higher that the older ones. interestingly, the innovative component allocated its maximum amount to the much younger group (under 25 years). graduates also scored higher compared to non-graduates. in fact, bachelor respondents' have shown more confidence and more belief to the effectiveness of in-service training. in terms of innovation, diploma holders scored higher. however, diploma holders and low literate people scored the lowest in terms of results for-service training. experienced respondents (over 21 years of experience) have shown more trust and belief in the effectiveness of in-service training. table i. categories of indicators associated with each variable for inventory studied variables index number cronbach's alpha questions reactive agents (satisfaction and organization of courses and facilities) 9 0.74 1-2-3-4-5-6-7-14-15 learning factors (learner readiness, self-efficacy and performance) 8 0.55 11-12-1322-23-2425-26 elements behavior (expectations about behavior changes to improve performance and enhance the ability of the individual) 12 0.71 8-9-10-3031-32-3334-35-3637-38 results (returns teaching fellow, supervisor support, positive individual results, negative personal consequences, administrator privileges, freedom to change and feedback) 9 0.78 16-17-1819-20-2127-28-29 innovation factors (survival, improvement in working and coordinating with innovative teaching methods and budget staff) 5 0.69 39-40-41-42-43 fig. 1. results of elements such as innovation agents, learning agents and reactive agents iii. the results of the survey the results show that there is a significant difference between the mean response element and the effectiveness of the training course. in other words there is a significant relationship between the independent variable (response elements) and the dependent variable (effect of the course). also, there is a significant relationship between the variables of innovation (as a confounding variable) and the dependent variable (effect of the course). (significant value=0.001 is less than 0.05=α). auxiliary variables as a moderating variable affect the reactive element to the variable relationship between the variables in the efficacy period (table ii). the results also showed that there is a significant difference between the mean element of learning and the effectiveness of the training course. in other words, there is a significant relationship between the independent variable (the learning element) and the dependent variable (effect of the course). there is a significant relationship between innovation auxiliary variables (as confounding variables) and the dependent variable (the effectiveness of the training course). (significant value=0.73 is greater than 0.05=α). auxiliary variables as a moderating variable influenced the effectiveness of the course and relationships between learning element to the variable (table iii). further, there is a significant difference between the behavior elements and the effectiveness of the training course. in other words there is a significant relationship between the independent variable (behavior elements) and the dependent variable (effect of the course). there is a significant relationship between the innovation auxiliary variables (as an intervening variable) and the dependent variable (effect of the course). auxiliary variables as a moderating variable affected the behavior element to the variable relationship (table iv). there is also a significant difference between the elements of the results and effectiveness of the training course. in other words there is a significant relationship between the independent variable (element results) and the dependent variable (effect of the course). (significant value=0.00 is smaller than the 0.05=α). there is a significant relationship between innovation auxiliary variables (as confounding variables) and the dependent variable (the effectiveness of training). auxiliary variables as a moderating variable does not affect result element to effectiveness of variable the efficacy period (table v). table vi focuses on the innovation relationship between refah bank's employees in isfahan province with the effectiveness of in-service training. the results show that, since the amount is significantly less than 5 percent h0, is rejected and as a result, the correlation between claims (h1) will be accepted. due to its meaningful value 0.03<0.05) the hypothesis is rejected. this means that there is a significant correlation between effectiveness and innovation. in fact, the innovation doesn't have linear relationship with effectiveness of educational. engineering, technology & applied science research vol. 7, no. 4, 2017, 1870-1873 1872 www.etasr.com yousefian et al.: case study of effectiveness evaluation of staff training courses in refah bank table ii. test of effect on the effectiveness of the mediation innovation variable by reactive element the dependent variable: the effectiveness of period a. r2 =. 687 (justified r2 =. 614) table iii. test the effect of learning on the effectiveness of the mediation innovation variable element the dependent variable: the effectiveness of period. factors sum of squares degrees of freedom average of squares f meaningful the corrected version 5.077 a 12 0.423 12.352 0.000 intercept 17.024 1 17.024 497.063 0.000 innovation 0.004 1 0.004 0.115 0.736 reaction 4.654 11 0.423 12.354 0.000 error 2.123 62 0.034 total 1053.415 75 the corrected total 7.200 74 a. r2 =. 705 (justified r2 =. 648) table iv. the test of the behavioral impact of on the effectiveness of the mediation innovation variable the dependent variable: the effectiveness of the period. factors sum of squares degrees of freedom average of squares f meaningful the corrected version 4.856 a 17 0.286 6.947 0.000 intercept 15.562 1 15.562 378.463 0.000 innovation 0.094 1 0.094 3.291 0.014 reaction 4.434 16 0.277 6.739 0.000 error 2.344 57 0.041 total 1053.415 75 the corrected total 7.200 74 a. r2 =. 674 (justified r2 =. 577) table v. test results on the effectiveness of the mediation innovation variable element effect the dependent variable: the effectiveness of the period factors sum of squares degrees of freedom average of squares f meaningful the corrected 5.991a 17 0.352 16.609 0.000 version 13.358 1 13.358 629.583 0.000 intercept 0.005 1 0.005 0.251 0.618 innovation 5.568 16 0.348 16.403 0.000 error 1.209 57 0.021 total 1053.415 75 the corrected total 7.200 74 a. r2 =. 832 (justifiedr2 =. 782) table vi. correlation coefficient between innovation and effectiveness effectiveness innovation pearson effectiveness significantly. (2-sided) number 1 0.242* 0.036 75 75 pearson effectiveness significantly .(2-sided) number 0.242* 1 0.036 75 75 a. variable relationship between gender and questionnaire components since a significant amount of the element behavior and efficacy is less than 5% h0 is rejected. this happens to behavior elements and component of effectiveness of training courses.it means that there is a significant relationship between gender and effectiveness and behavior. however, in reaction, learning, and result elements which are derived from the questionnaires significantly more than 5% h0 is not rejected. in fact, these elements don’t relate to gender (table vii). table vii. correlation coefficient of transfer models and gender reaction behavioral results innovation effectiveness pearson gender -.050 -.250* -.223 -.217 -.257* significantly. (2-sided) .669 .030 .054 .062 .026 number 75 75 75 75 75 b. relationships between age and questionnaire components since a significant amount of reactive, results and effectiveness of element is less than 5% h0 is rejected. this happens to behavior elements and component of effectiveness of training courses. it means that there is a significant correlation with age between effectiveness and behavior. in fact, these elements have a linear relationship with age. on the other hand in the behavioral elements and innovations which is derived from the questionnaires, there is significantly greater than 5% h0 and is not rejected. in fact, these elements are not correlated with age (table viii). table viii. correlation coefficient of transmission model and age reaction behavioral results innovation effectiveness pearson age 0.247* 0.153 0.349** 0.020 0.299** significantly. (2-sided) 0.033 0.191 0.002 0.862 0.009 number 75 75 75 75 75 c. the relationships between the education and the components of the questionnaire since a significant amount of all elements of the questionnaire is more than 5% h0 it is not rejected. it happens to the entire questionnaire. this means that there is no significant correlation between the components of the questionnaire and education (table ix). factors sum of squares degrees of freedom average of squares f meaningful the corrected version 4.948 a 14 0.353 9.418 0.000 intercept 10.827 1 10.827 288.490 0.000 innovation 0.498 1 0.498 13.268 0.001 reaction 4.526 13 0.348 9.277 0.000 error 2.252 60 0.038 total 1053.415 75 the corrected total 7.200 74 engineering, technology & applied science research vol. 7, no. 4, 2017, 1870-1873 1873 www.etasr.com yousefian et al.: case study of effectiveness evaluation of staff training courses in refah bank table ix. correlation coefficient of transfer model and education reaction behavioral results innovation effectiveness pearson education 0.065 0.023 0.101 0.173 0.069 significantly. (2-sided) 0.577 0.842 0.390 0.138 0.554 number 75 75 75 75 75 d. the relationships between the work experience and the components of the questionnaire since a significant amount of elements such reactions, results and effectiveness is less than 5% h0 is rejected and as a result, behavioral, result and effectiveness of the training components occurs. there is a relationship between effectiveness and behavior with significant work experience. on the other hand an innovative element derived from the questionnaire responses and significantly higher than the 5 percent h0 is not rejected. in fact, these elements don’t relate to work experience (table x). table x. correlation coefficient of work experience and components of the questionnaire reaction behavioral results innovation effectiveness work exp. pearson 0.170 0.229* 0.262* 0.067 0.299** significantly (2-sided) 0.144 0.048 0.023 0.569 0.009 number 75 75 75 75 75 e. the relationship between inventory positions and the components of the questionnaire since a significant amount more than 5% in all elements of the questionnaire h0 is not rejected. and there is no significant relationship among the components of the questionnaire and organizational posts (table xi). table xi. correlation coefficient transfer model elements and organizational post reaction behavioral results innovation effectiveness organiz. position pearson 0.125 0.096 0.166 0.024 0.140 significantly (2-sided) 0.284 0.414 0.155 0.835 0.230 number 75 75 75 75 75 iv. practical suggestions  training experts can put the metacognitive strategies training program as a part of the career points those employees using them to boost their capabilities in the study.  creativity and innovation are the basis of planning educational services so that the understanding of employees and director goes up in the expertise and competence of education. references [1] http://www.kirkpatrickpartners.com/our-philosophy/the-kirkpatrickmodel [2] f. rahimian, c. moller, “global erp implementations and harmonization of practices in multinational corporations: a conceptual framework”, nineteenth americas conference on information systems, chicago, illinois, august 15-17, 2013. [3] a. ahmad, effectiveness of learning transfer in national dual training system (ndts), phd thesis, universiti tun hussein onn malaysia, 2011 [4] c. quesada-pallares, “training transfer evaluation in the public administration of catalonia: the mevit factors model”, procediasocial and behavioral sciences, vol. 46, no. 1, pp. 1751-1755, 2012 [5] r. r. kazbour, h. m. mcgee, t. mooney, l. masica, r. o. brinkerhoff, “evaluating the impact of a performance-based methodology on transfer of training”, performance improvement quarterly, vol. 26, no. 1, pp. 5-33, 2013 engineering, technology & applied science research vol. 7, no. 3, 2017, 1582-1587 1582 www.etasr.com perisic and bojovic: application of time recursive processing for the development of a … application of time recursive processing for the development of a time/phase shifter djurdje m. perisic faculty of information technology slobomir p university, spu slobomir, bjeljina, republic of srpska, bih djurdje@beotel.rs miroslav bojovic faculty of electrical engineering university of belgrade belgrade, serbia mbojovic@etf.bg.ac.rs abstract—this paper describes a powerful digital time and/or phase shifter of pulse rates, based on time recursive processing. it can function either as a time shifter or as a phase shifter. the circuit can generate precise shifting for a pulse rate with a constant input period, but it is also capable to shift a pulse rate whose period is a ramp function. besides that, the shifter can be used in tracking and prediction applications. the shifter is described by recursive equations as a linear discrete system. all mathematical analyses are made using the z transform. computer simulations are employed to prove the correctness of the mathematical analysis. the realization of the shifter is described and, to demonstrate the shifter functioning, actual oscilloscope screenshots are presented. keywordstime shifter; phase shifter; digital circuit; pll i. introduction the field of time recursive processing (trp) has been described in detail in previous works such as [1-9]. the trp approach is based on the measurement and processing of the input and output periods and time differences between them. although the first idea was simply to discover a new kind of phase locked loop (pll) and frequency locked loop (fll), it turned out that trp is suitable for a much broader range of applications. namely, most of the circuits described in [1-9], possess some of the properties of either classic phase locked loop (pll) or classic frequency locked loop (fll). however, due to their properties, time recursive pll (tr pll) and time recursive fll (tr fll) exceed the applicability and functionality of classic pll and fll, improving the efficiency and expanding the scope and diversity of their applications. different applications include phase shifting in [1, 2], the development of digital frequency synthesizers [3], noise rejection applications [4-6] and a wide range of tracking and prediction [4, 5, 7]. all the algorithms described are very suitable for usage in a software form, like for example a software predictor [8]. although a very complex system, consisting of a lot of subsystems, it can also function as a fll, whose realization is based on the same technique [9]. tr pll and tr fll represent a completely new approach both in theory and in implementation and application. for example, the measurement of phase, frequency or amplitude, which are used in classic pll and fll, are changed by the measurement of time, which is much more convenient and more precise. let us remember that the classic pll tends to equalize both frequency and phase between the input and the output signals, reducing the phase difference to zero. unlike pll, classic fll tends to equalize the frequency, without taking care of the phase difference. when fll reaches the stable state, the phase difference between the input and output signals depends on the initial variable conditions and, possibly, it depends on the system parameters. in other words, the phase difference is the random variable. according to [1, 2] some of tr plls possess the ability to regulate the phase difference by either system parameters or by output control. this is an important feature of the tr pll, which can be utilized to generate phase differences of any value. note that the phase difference of any pll cannot depend on the initial conditions of the variables. in this paper, a new model of a time/phase shifter, based on trp, is described. it provides phase shifting in a band without limitations which is controlled by the clock frequency. under some system conditions, it can also provide time shifting linearly dependent on the value of an outside control. in comparison with the previous phase shifters of this type, described in [1, 2], this phase shifter can generate the proper shifting even in case the input period is a ramp function. ii. mathematical description of the shifter one general case of the time relation between an input signal sin and an output signal sop of the shifter, is shown in figure 1. the periods ti0, ti1,….tik, tik+1, and to0, to1,….tok, tok+1, as well as the time differences 0, 1, 2…..k, k+1, occur at discrete times respectively t0, t1, t2,…..tk, tk+1. the discrete times t0, t1, t2,….tk, tk+1 are defined by the falling edges of the pulses of sop in figure 1. note that, unlike the classic pll, all variables are distributed in time in figure 1. the natural recursive relation (1), between the variables, yields from figure 1. it was supposed that the time difference  is positive if the output signal leads the input signal. correspondingly, in case that the input signal leads, time difference  will take a negative value through the analysis. the main algorithm of the circuit is presented in (2), where "tk", as an outside control word, represents a step function and "a" and "m" are the system parameters. according to (1) and engineering, technology & applied science research vol. 7, no. 3, 2017, 1582-1587 1583 www.etasr.com perisic and bojovic: application of time recursive processing for the development of a … (2), the circuit has two output variables, which describe its behavior: 1k k k kto ti     (1) 1 1a kk k kti t mto       (2) fig. 1. time relations between all variables of the circuit. the output variables are (k+1) = f[ti(k)] and to(k+1) = f[ti(k)]. note that, because of simplicity, to(k), ti(k) and (k) are denoted in the article as tok, tik and k. it is now necessary to find the z transform of the output variables (k+1) and to(k+1) in order to analyze the properties of the shifter described. the z transform of (1) and (2) are given by respectively (3) and (4). time constants to0 and 0 are the initial values of the output variables to(k) and (k), which appear at discrete time t0 = 0. 0( ) ( ) ( ) ( )z z z z to z ti z        (3)  0 0a( ) ( ) ( ) ( )zto z zto ti z t z z z z m       (4) calculating (z) from (3) and using it into (4), gives: 0 0z mz zz z ( ) (z 1)z(a m) a ( ) ( ) z(z m 1) z(z m 1) t to to ti            (5) in the same way, changing to(z) from (5) to (3), gives: 0 0(z) (z )a( ) ( ) (z m 1) (z m 1) t z m to zz z ti z z z              (6) two transfer functions, presented by (7) and (8), describing the output variables of the shifter in dependence on the input period, can be defined from respectively (5) and (6). ( ) z(a m) a ( ) ( ) z(z m 1)to to z h z ti z       (7) ( ) a ( ) ( ) (z m 1) z z h z ti z z        (8) a. step analyzes of the circuit step analysis will discover under which conditions the circuit can possess the properties of a time/phase shifter. providing that the control time function t(k)=t=const., let us suppose that a step function, ti(k)=ti=const., is applied to the input. if we change the z transforms t(z) = t·z/(z-1) and ti(z) = ti·z/(z-1) into (5) and (6), we will get the z transform of the output variables for this input. changing t(z) and ti(z) into (5) and using the final value theorem, it is possible to find the final value of the output period in the time domain as to = lim to(k) if k, using to(z), as shown in (9). applying (9), to is calculated as shown in (10). to complete the information about the system properties, it is necessary to determine ∞, i.e. the final value of (k). if t(z) and ti(z) are changed into (6), using the final value theorem in the same way like for to, ∞ can be determined using (11). applying (11), ∞ is calculated and shown in (12). 1lim[( 1) ( )]zto z to z    (9) lim[ ( )]kto to k ti   (10) 1lim ( ) lim[( 1) ( )]k zk z z        (11) (1 ) / /ti a m t m    (12) the expressions (10) and (12) are valued only if the shifter is the stable system i.e. if |z1| < 1 and |z2| < 1, where z1 and z2 are the poles of the transfer function hto(z) or h(z), given by (7) and (8). since z1 = 0, and z2 = 1+m, it yields that the shifter is the stable system if (13) is satisfied. according to (10) and (12), it follows that the described shifter possesses the properties of a pll. this conclusion comes out from the facts that the output period to, for the stable system, equalizes the input period and that the time difference  does not depend on the initial conditions 0 and to0. 2 0m   (13) b. the time and/or phase shifting looking at (12), we can notice that total value of  consists of two parts. the first one is ti(1-a)/m. the term (1a)/m indicates the portion of a period ti, or the number of periods ti, for which the input pulse rate is phase shifted. according to its nature, the first part represents the phase shifting. the system stability does not depend on the parameter "a", so that the value of either positive or negative phase shifting is unlimited. the second part is equal to "-t/m". it represents the pure time shifting, which is controlled by "t". it can also be ether positive or negative. since control word "t" does not affect on the system stability, this kind of shifting can be also unlimited. so, two kinds of shifting can be generated simultaneously. but they can be also generated separately. if a=1, the first part in (12) does not take part in the shifting. at the same time, if control time function t=0, the second part in (12) has no effect on the shifting. to prove the correctness of the previous analysis, simulations of the shifter functioning are presented. at the same time, the simulations are employed to enable a further insight into the procedure and into the physical meaning of the variables described. the simulations are also used to discover additional properties and possible efficient applications of the shifter. all discrete values in simulations were merged to form continuous curves. note that all variables in the following diagrams were presented in time units. the time unit can be, sec, msec or any other, but assuming the same time units for ti, to,  and t. it was more suitable to use just “time unit” or abbreviated “t.u.” in the text. it was more convenient to omit the indication “t.u.” in diagrams. all simulations were made by matlab, using (1) and (2). engineering, technology & applied science research vol. 7, no. 3, 2017, 1582-1587 1584 www.etasr.com perisic and bojovic: application of time recursive processing for the development of a … let us first consider the time shifting, taking a=1. the locking procedure of the shifter is considered for three cases in figure 2. the input is a step function ti = 10 t.u. the parameter "m" and control word "t" are chosen carefully in order to demonstrate the different properties of the shifter. all values of "m" and "t", as well as the values of the initial conditions to0 and 0 are presented in figure 2. it can be seen in figure 2a, that for any value of "m" satisfying (13), the output period tends to the input period, but the transition time depends on the value of "m". for case nr. 2, (m=-1) the shifter is extremely fast. it reaches the stable state for only two steps. for case nr. 1, (m=-0.85), and case nr. 3 (m=-1.2), the shifter takes longer time to reach the stable state. the conclusion is that the greater deviation of parameter "m", with respect to m=-1, provides longer transition time of the shifter. note that for all three cases, the calculation of ∞=-t/m agrees with ∞ which can be seen on the simulated curves. for instance for case nr. 2, ∞=t/m=-(-3)/-1=-3. the same result can be seen in figure 2a. this agreement confirms the correctness of the simulation results and the correctness of the whole approach. fig. 2. time shifting (a=1 for all of three cases): a. the output period tends to the input period and the final value of time difference ∞ = -t/m, b. the case nr. 3, in figure 2a, is presented in the real time form. all periods of sin, sop and time differences k are calculated, showing the real time relation between them. for this case, t=0 (∞=0) and the shifter functions as a classic pll. the merged discrete values for case nr. 3, representing the output variables to3 and 3 in figure 2a, are shown in real time, in figure 2b. this presentation, in forms of pulse rates, exhibits the real time relations between all input and output variables. it also helps to better understand the physical mining of the simulated curves. the calculated values of all variables are shown for every step. all values are taken from the simulation results, but they can be calculated manually, step by step, using (1) and (2). according to the mathematical analyzes and simulation results obtained, the shifter functions as classic pll for t=0 and a=1. the negative values of the time differences k are shaded in figure 2b. let us now consider the properties of the circuit in case that it functions as the phase shifter. in this case, according to (12), t=0 and ∞= ti(1-a)/m. the locking procedure of the shifter is simulated for three cases in figure 3. the input is the step function ti = 10 t.u. all values of "m" and "a", as well as the values of the initial conditions to0 and 0 are presented in figure 3. it can be seen in figure 3a, that the role of parameter "m" is not changed. for any value of parameter "m" satisfying (13), the output period tends to the input period, but the transition time depends on the value of the parameter "m". for case nr. 2, (m=-1) the shifter reaches the stable state for only two steps. the conclusion is the same as in the case of the time shifter. the greater deviation of parameter "m", with respect to m=-1, provides longer transition time of the shifter. although the parameter "m" affects ∞, it is much more convenient to use "a" for the phase shifting. for case nr. 2, a=1 and 2∞=0, regardless of the values of "m". in this case phase shifter functions as a classic pll. for case nr. 1, a=1.16 (a> 1) and 1∞=ti(1-a)/m = 2 t.u. the same result for 1∞ can be seen in figure 3b. for case nr. 3, a=0.75 (a<1) and 3∞=ti(1-a)/m = 2 t.u. the same result can be also seen in figure 3b. fig. 3. phase shifting (t=0 for all of three cases) in the function of parameters "m" and "a": a. the output period tends to the input period, b. the final value of time difference ∞ = ti(1-a)/m, c. the final value of the phase shifting is ph∞ =2π·∞/to∞ [rad] = 2π·(1-a)/m [rad]. this agreement confirms the correctness of the simulation results and the correctness of the mathematical approach. we can now reach the general conclusion about the influence of parameter "a" to the phase shifting. if a>1, the phase shifting is positive. if however a<1, the phase shifting is negative. since the parameter "a" does not affect the stability of the system, both of them, the positive and the negative shifting can be unlimited. the only limitation is the capacity of the circuits which are built in the shifter. the general expression for the phase shifting, for both, the time and the phase shifter, can be engineering, technology & applied science research vol. 7, no. 3, 2017, 1582-1587 1585 www.etasr.com perisic and bojovic: application of time recursive processing for the development of a … expressed as ph∞ = 2π·∞/to∞ [rad]. changing ∞=ti(1-a)/m for the phase shifter, and taking in account that for the stable shifter ti=to∞, the expression turns into ph∞ = 2π·(1-a)/m [rad]. the transition state, as well the stable state, for all of three cases of the phase shifting are presented in figure 3c. according to the previous expression, ph1∞=2π·(1-1.16)/(0.8)=1.25 [rad], ph2∞=2π·(1-1)/(-1)=0 [rad] and ph3∞=2π·(10.75)/(-1.25)=-1.25 [rad]. all of calculated results agree with the simulated ones, shown in figure 3c. c. the shifting in case when the input is a ramp function besides the described shifting for the case when the input period is a step function, the time shifter (a=1) can be used for the shifting of an input pulse rate, whose period is a ramp function. to illustrate this ability, let us determine the well known velocity error, providing that the input period is the ramp function ti(k)=tiv(k)=p∙k, where “p” is a time constant. the definition of velocity error is kv=lim[tov(k)-tiv(k)] for k→∞. one more convenient expression for velocity error is kv = lim tiv(k)[hto(k)-1] for k→∞, where hto(k) is the transfer function given by (7). taking a=1 and using the previous expression and z transform of velocity function ti(z)=tiv(z)= z(p·k)=pz/(z-1)2, it can be found out that kv = 0. this means that the output of the shifter is capable to track the ramp input, without an error. in order to consider the shifting abilities of the circuit, let us now determine the behaviour of τv(k) for the velocity (ramp) input, if k→∞. using the final value theorem, τv∞=lim τv(k)k→∞ is calculated using τv(z) and shown in (14). the expression τv(z) is get out by the substitution of ti(z)=tiv(z) in (6) and taking a=1. according to (14), τv∞ is the time constant, which does not depend on the initial conditions. besides the parameters "m" and "t", τv∞ depends on the time constant "p", 1lim[( 1) ( )] ( ) /v v zz z p t m      (14) which is the slope of the ramp input function. it means the time shifting of the output pulses can be controlled by the control word "t". if t>p, τv∞>0 and the output pulse leads in time, just like in figure 1. if however t<p, τv∞ is negative and the output pulse is delayed in time, in comparison with the corresponding input pulse. it comes out that if t=p, τv∞ = 0, i.e. the shifter functions as classic pll, reducing the phase difference to zero, even for the ramp input function. to check the correctness of the obtained results, the simulations of to(k) and (k) for the velocity input tik=(10+4·k) t.u. are shown in figure 4. three cases for different parameters “m” and “t” are presented. all initial conditions and final values are shown in figure 4. for all of cases in figure 4a, the output periods track the input periods without an error. that means kv = 0, which agrees with the previous theoretical conclusion. note that the shifter takes only two steps to reach the stable state for m=-1, regardless of the fact that the input is the ramp function. for all cases in figure 4b, time differences tends to the time constant "(p-t)/m", given by (14), proving the correctness of the mathematical analyses. for case nr. 2, t=p=4 t.u. and according to (14), v2∞ = 0. that means the shifter predicts and generates the output period which is completely synchronized with the input pulses, even for the case when the input is a ramp function. for case nr. 1, v1∞=(p-t)/m=(4-7.75)/(-0.75)=5 t.u. for case nr. 3, v3∞=(pt)/m=[4-(-2)]/(-1.25)=-4.8 t.u. the calculated results agree with the simulated ones, shown in figure 4b. cases nr. 1 and nr. 3 prove that the shifter is able to generate both positive and negative shifting of the pulses of a ramp input, depending on the parameter "t". for case nr.1 t>p (v∞>0), the output pulses lead for v∞+ in comparison with the input pulses. for the case nr. 3, t<p (v∞ <0), the output pulses are delayed for v∞ in comparison with the input pulses. fig. 4. the time shifting of the ramp input function (a=1): a. the output periods, for all of three cases, track the input periods without an error, kv=0, b. the time shiftings tend to the time differences v∞, given by eq. (14). iii. realization of the shifter according to the results obtained, the optimum value of "m" for the shifting applications, is m=-1. firstly, the shifter is the fastest for m=-1 and secondly the realization of the shifter is much simpler if m=-1. for some other applications, where it is necessary to adapt the locking speed, different values of "m" can be required. taking m=-1, and changing a=fa/fc, where fa and fc are the clock frequencies, (2) turns into (15). according to (15), tk and k+1 are measured by the clock period tc=1/fc, tik is measured by the clock period ta = 1/fa and tok+1 is generated by the clock period tc=1/fc. the principal scheme of the realization, corresponding to (15) is shown in figure 5. 1 1c a c k ck k kf ti f t ff to        (15) fig. 5. the principal scheme of the phase shifter the shifter consists of a recursive calculation module (rcm) and a programmable period generator (ppg). rcm calculates tok+1 and ppg generates the output period at the next step. ppg was described in detail in [1-9]. the realization of rcm depends on the type of algorithm, but the realization of engineering, technology & applied science research vol. 7, no. 3, 2017, 1582-1587 1586 www.etasr.com perisic and bojovic: application of time recursive processing for the development of a … rcm according to (15), can be easily performed using the technique described in [1-9]. according to the previous conclusions, if fa=fc (a=1), the circuit functions as time shifter. if however fa is not equal to fc and tk=0, the circuit functions as the phase shifter. one eight bits shifter was realized by standard integrated circuits for a=1 (fa=fc), t=0 and m=-1. the input period, shown in figure 6, is the step function ti=1 [ms], corresponding to the frequency of 1[khz]. the clock frequency fc=6 [khz], so that the ratio ti/tc=6. the oscilloscope picture of the voltage waveforms, shown in figure 6, was taken when the shifter was in the stable state. in accordance with the chosen parameters, the shifter functions as a classic pll, striving to reduce the time difference to zero. however, that is not possible because the ratio ti/tc is very small. the ratio ti/tc is chosen intentionally small to enable the visibility of ∞+ and ∞ and to provide the evidence of the whole physical process. in accordance with the chosen parameters, the time difference ∞ is changing the sign at every step. if ti/tc increases, the widths of ∞+ and ∞would decrease and tend to zero. it can also be seen in figure 6 that whenever two pulses of sop occur during a period ti, it means that ti > to, and the coming “∞” is negative. if two pulses of sin comes during a period to, it means that to > ti, and the coming “∞” is positive. the previous explanations, at the same time, contribute to the understanding of the principles of the shifter functioning. fig. 6. the shifter is in the stable state. it functions as pll (a=1, m=1, t=0). the ratio ti/tc is only about six and the time differences ∞+ and ∞are visible. if ti/tc increases, the time differences tend to zero. iv. conclusion the description and illustration of the realized shifter represent one additional contribution to the shifters described in [1, 2]. the presented theoretical approach in whole, also represents the contribution to the field of trp. it was demonstrated that besides the processing of the input and output periods and the time differences between them, an additional control function can take part in the calculation of the output period. in dependence on the type of the control function, the shifter takes new properties. for instance, it was shown that if the additional control function is a step function, the shifter is able to provide the proper shifting even in case the input period is a ramp function. this example indicates that, using this approach, it is possible to develop new additional applications of the circuits and systems based on trp. in comparison with the shifters described in [1, 2], this shifter provide important advantages consisting of the better functionality and the wider applicability. firstly, unlike the mentioned shifters, this time shifter provides both the time shifting and the phase shifting. secondly, the time shifting does not depend on the input period, so that the desired value of either positive or negative shifting is directly proportional to the outside control word. this property significantly facilitates its practical realization and its practical usage. thirdly, this shifter can generate either a positive or negative shifting of the input pulse signal, even in case the input period is a ramp function. this feature provides a much wider field of application. it was shown that if t = 0, the shifter can function exactly as classic pll, which has already found a number of applications. the analysis and simulations showed that this phase shifter is extremely fast if m=-1. in this case, the shifter takes only two steps to reach the stable state. changing m in range of -2 to 0, it is possible to adapt a transient time of the shifter to the required application. the precision of the phase shifting can be extremely high. it is limited however by the speed of the used integrated circuits, since it depends on relation ti/tc. a higher ti/tc relation provides a higher shifting resolution. generally, the shifting band can be as large as necessary. however, the capacity of the built-in up-down counters must be large enough to satisfy the requirements for the shifting band and the shifter resolution. the identity of the analytical and simulation results, in every step, proves the correctness of the entire theoretical approach, as well as the validity of the obtained results. references [1] d. perisic, m. perisic, s. rankov, “phase shifter based on a recursive phase locked loop of the second order”, rev. roum. sci. techn.– electrotechn. et energ., vol. 59, no. 4, pp. 391–400, 2014 [2] d. perisic, a. zoric, d. babic, d. perisic, “recursive pll of the first order”, przegląd elektrotechniczny, vol. 89, no.7, pp. 50-53, 2013 [3] d. perisic, a. zoric, s. obradovic, d. perisic, “fll as digital period synthesizer based on binary rate multiplier control”, przegląd elektrotechniczny, vol. 89, no. 1a, pp. 145-148, 2013 [4] d. perisic, m. bojovic, “multipurpose time recursive pll ”, rev. roum. sci. techn.–electrotechn. et energ., vol. 61, no. 3, pp. 283–288, 2016 [5] d. perisic, a. zoric, m. perisic, d. mitic, “analysis and application of fll based on the processing of the input and output periods”, automatika, vol. 57, pp. 230–238, 2016 [6] d. perisic, m. perisic, d. mitic, m. vasic “time recursive frequency locked loop for the tracking applications”, rev. roum. sci. techn.– electrotechn. et energ., vol. 60, no. 2, pp. 195–203, 2015 [7] d. perisic, a. zoric, m. perisic, v. arsenovic, l. lazic “recursive pll based on the measurement and processing of time”, elektronika ir elektrotechnika, vol. 20, no. 5, pp. 33-36, 2014 [8] d. perisic, a. zoric, d. babic, d. perisic, “decoding and prediction of energy state in consumption control”, rev. roum. sci. techn.– electrotechn. et energ., vol. 58, no. 3, pp. 263–272, 2013 [9] d. perisic, a. zoric, s. obradovic, s. spalevic, “application of frequency locked loop in consumption peak load control”, przegląd elektrotechniczny, vol. 88, no. 1b, pp. 264-267, 2012 [10] r. n. dean, a. k. rane, “digital frequency-locked loop system for capacitance measurement”, ieee transactions on instrumentation and measurement, vol. 62, no. 4, pp. 777-784, 2013 [11] m. abdul-niby, m. alameen, h.baitie, "a simple phase shifting technique for an injection locked oscillator" engineering, technology & applied science research, vol. 6, no. 6, pp. 1303-1306, 2016 [12] d. jovcic, “phase locked loop system for facts”, ieee transactions on power systems, vol. 18, no. 3, pp. 2116-2124, 2003 engineering, technology & applied science research vol. 7, no. 3, 2017, 1582-1587 1587 www.etasr.com perisic and bojovic: application of time recursive processing for the development of a … [13] d. abramovich, “phase-locked loops: a control centric tutorial”, american control conference, vol 1, pp. 1-15, usa, november 07, 2002 [14] a. s. n. mokhtar, m. b. i. raez, m. marufuzzaman, m. a. m. ali, “hardware implementation of a high speed inverse park transformation using cordic and pll for foc brushless servo drive”, elektronika ir elektrotechnika, vol. 19, no. 3, pp. 23-26, 2013 [15] m. pastor, j. dudric, “grid-tied 15-level cascade inverter with predictive current control”, elektronika ir elektrotechnika, vol 18, no. 9, pp. 19-22, 2012 [16] g. bianchi, phase-locked loop synthesizer simulation, nc-hill, inc. new york, usa, 2005 [17] r. vich, z transform theory and application (mathematics and applications), springer, 1987 [18] d. b. tablot, frequency acquisition techniques for phase locked loops, wiley-ieee press, 2012 acknowledgement this article was supported by the ministry of science and technology of the republic of serbia within the project tr 32047. authors profile djurdje perisic was born in atenica near cacak, serbia in 1943. he graduated from the faculty of electrical engineering in belgrade in 1967. through an english government scholarship, he received an m.sc. from the cranfield institute of technology, england in 1976. he received a ph.d. at the technical academy in zagreb in 1983. after that he was awarded twice the fulbright and once the humboldt scholarship. he was awarded the "tesla’s award", the highest yugoslav recognition for contributions to the field of natural sciences, from the serbian academy of sciences in 1996. in 2003, as the dean of the faculty, he founded the first study programs for the faculty of information technology at spu. in 2013 he was elected a professor emeritus. his current research interests include the development of new approaches to electronic circuits and systems combining electronics, system theory and other fields. during last five years he has published fifteen papers in sci list journals and about 40 additional papers of international importance. miroslav bojovic was born in 1957. all his formal education, including the ph.d. (1989) are from the faculty of electrical engineering, university of belgrade, serbia. he realized the specialization at the faculty of computer science department, ucla, los angeles, usa, during 1988 and 1989. as a head of the computer science department at the faculty, he is currently engaged as a professor at the faculty of electrical engineering in belgrade in the field of database menagement system and software engineering and as a project leader of many projects in software engineering. one of his projects "mobilepdr" was awarded as the best software product in usa in the field of medical information systems in 2004. as a software product, it has been referenced in more than 100,000 different publications, all over the world. microsoft word etasr_v11_n6_pp7887-7891 engineering, technology & applied science research vol. 11, no. 6, 2021, 7887-7891 7887 www.etasr.com wong & danikas: functionally graded materials (fgm) for spacers in gas insulated systems … functionally graded materials (fgm) for spacers in gas insulated systems: a concise review and some comments k. l. wong rmit university school of engineering, high voltage laboratory melbourne, australia alan.wong@rmit.edu.au m. g. danikas democritus university of thrace department of electrical and computer engineering xanthi, greece mdanikas@ee.duth.gr abstract-functionally graded materials (fgms) present a solution to control electrical stresses in high voltage applications. in this paper, a concise review is presented on the fgms for spacers in gas-insulated systems. fgms offer the possibility of a more even electric field distribution and thus a viable solution for industrial applications. fgms are investigated here primarily as materials for permittivity control. some aspects of fgms are discussed as well as some thoughts on future challenges. keywords-functionally graded materials; gas insulated systems; dielectric constant; permittivity; triple junction point; dielectric strength; fillers; microfillers; nanofillers i. introduction electric stress control is a major challenge in high voltage engineering applications. excessive electric stress may lead to the breakdown of insulation and definite deterioration of high voltage equipment [1]. electric field stress control has been dealt with in some detail before, such as field distortions by conducting particles, field distortions by electrode asperities as well as field distortions due to multi-dielectric insulating arrangements [2]. sandwiched multi-layer insulating systems can cause problems if the layers are of different dielectric constant. however, such insulating systems – if made up from very thin layers – can be of advantage since they usually present fewer defects than thicker insulation slabs [2, 3]. as has been pointed out, sharp edges, small radius elements and needle points must be avoided in insulation design [4, 5]. elaborating further the question of multiple layer insulation, it was reported that the effect of multiple layers is particularly marked for materials where there is a wide spread in values of dielectric strength measured at different points on the surface. the main factor in this phenomenon is the loss of energy from the discharge at the interfaces. as has been mentioned some decades ago, a partial discharge having penetrated one layer cannot enter the next layer of the insulating material until the spot on the interface, which is centered on the discharge channel, has been charged to a potential which could produce a field comparable with that of the discharge channel at the level in question [6]. interfaces play a most important role in high voltage engineering applications. in traditional insulating materials, interfaces must be avoided or they must be treated in a way that they do not cause additional problems to the insulating system. as has been pointed out before, irrespectively of the theory put forward to explain pre-breakdown and breakdown phenomena, either electrode imperfections or mismatch of dielectric materials in a composite insulating system result in electric field intensifications that may lead to ultimate failure. it goes without saying that interfaces are the root of a variety of problems regarding the insulating systems [7]. a way out of such problems is the better matching between dielectric materials (in case of an insulating system), or an alleviation of the applied electric field in the case of an insulating material in direct contact with an electrode [8, 9]. another way is the use of functionally graded materials (fgms), which are materials characterized by gradual variation in composition and structure over volume, which may result in a more even distribution of the electric field. according to [10], fgms are novel materials, the properties of which change gradually with respect to their dimensions. it is the advanced development of hitherto used composite materials, consisting of two or more materials, in order to achieve the desired properties according to the application where an fgm can be used. expressed in a slightly different way, fgms are very advanced engineering materials designed for a specific property or function, in which spatial gradations in the structure (and possibly in the composition) provide them with the desired characteristics [11]. the present paper aims to offer a concise review of the aforementioned materials with an emphasis on spacers in gas insulated systems. ii. functionally graded materials in various high voltage applications, many electric field distortions may be observed. such distortions are caused by the shape of electrodes and/or spacers and to the mismatch of the insulating materials. distortions (or intensifications) of this kind may lower the electrical performance of insulating systems and of high voltage equipment. in other words, field intensifications may lead to partial discharges (pds) and electrical treeing. if not detected, these phenomena may lead to complete failure of the insulating systems [12-15]. thorough corresponding author: m. g. danikas engineering, technology & applied science research vol. 11, no. 6, 2021, 7887-7891 7888 www.etasr.com wong & danikas: functionally graded materials (fgm) for spacers in gas insulated systems … analyses of field distortions are described in [1, 2, 4, 16]. a possible remedy to field intensifications would be a smoothing out of problematic electrodes and the – as far as possible – better matching of the insulating materials in case of a composite insulating system. an alternative to the above approaches is the application of fgms, which with the well-controlled spatial distribution of dielectric constants inside would offer a more even electric field distribution [17, 18]. although such materials were studied regarding their homogenization, heat transfer, stress, stability, and dynamic analysis and fracture [19], what is of interest for us is the application of such materials in high voltage engineering [20]. fgms – as far as high voltage applications are concerned – consist of insulating materials with a certain filler concentration in order to vary one basic physical property, so that they can alleviate electric field intensifications [21]. in other words, fgms replace the sharp transition of properties with smooth and gradually changing properties of the materials such as physical, chemical, mechanical or electrical [11]. fgms do not encompass all possible high voltage applications. among them, fgms are applicable to spacers for gas-insulated power apparatus, cable joints, insulators and bushings, stator coils, and electrical insulation for power electronic modules [21, 22]. in the context of the present paper, a concise review will be given w.r.t. fgms regarding the spacers in gas insulated systems. in other words, the review will be confined in the aforementioned application. iii. fgms for spacers and gas-insulated equipment spacers are an indispensable part of gas-insulated switchgear [1, 23]. as was noted in [1], spacer flashover is the most probable breakdown mechanism in a compressed gas insulated system as any contamination of the space surface may produce flashover at a voltage (sometimes well) below the gas breakdown strength. epoxy resin is primarily the insulating material used for spacers [8]. as is noted in [24], triple junctions present an important problem for spacers since at those points high electric field intensifications may be observed. by building fgms with higher permittivities at both cathode and anode surfaces compared with other intermediate parts of the spacer, i.e. by having a u-distribution of permittivity, a relaxation of the electric field is obtained. according to [24], the maximum electric field was reduced by about 10% at the triple junction – in case of a foreign particle adhered to spacer with the application of a u-shape fgm (in this case epoxy resin). also in [24], it was reported that the electric field was relaxed by about 30% at both high voltage/spacer and ground/spacer interfaces by applying a ushape fgm. regarding the presence of foreign particles adhered to the spacer, an earlier study also indicated that their shape and location may influence the performance of fgm [25]. in [26], further discussions ensued w.r.t. the spacers with graded low fgm (gl-fgm), graded high fgm (gh-fgm), and graded u fgm (gu-fgm). this work was mainly a computer analysis of the various aforementioned fgms in reference to a three-phase insulated gas bus duct. one of the conclusions was that the gl-fgm results in rather high electric field stresses. such conclusions are not at variance with earlier research which showed that gl-fgm gives a field relaxation in a rather narrow range of permittivities whereas gh-fgm offers a field relaxation in a much wider range of permittivities [27]. authors in [28, 29] did not deviate from the main conclusions of [26], pointing out that the main problem in such structures is the triple point. in [26, 30], similar conclusions were reached regarding the gh-fgm, gu-fgm, and glfgm. the authors of [30] indicated that the highest percentage reduction of electric field stress is observed for gh-fgm and gu-fgm gradings. in the same paper, it was remarked that it is preferable to prepare fgms by applying centrifugal forces, incorporating thus fillers of different diameters in order to obtain permittivity distribution for uniform field distribution rather than three dimensional (3d) printing, since it is the first method that is more efficient. such views on the preparation method of fgms are also shared by other researchers [31, 32]. the authors of [11] take a more cautious approach w.r.t. the aforementioned preparation techniques by pointing out that the controllability of the centrifugation method is not always the desired one and that one of the obstacles of the 3d printing technology, among others, is the limitation of printing materials (another preparation method, namely the flexible mixture casting method, has as main drawback the forming of many interfaces of the composing resins). the centrifugation method seems to be also preferred in [33], although the authors remarked that a more flexible fabrication method is urgently required. however, a different view regarding the 3d printing technology was offered in [34], where satisfactory flashover characteristics were obtained for insulators at both sf6 and vacuum under dc voltages with the fused deposition modeling (fdm) manufacturing process. further criticism of the above preparation methods was also put forward in [35], where another method was proposed, besides the aforementioned approaches with fgms, namely to apply fgm to the spacer surface in order to form thickness (d) gradient surface layers of high permittivity (d-sfgm). this was done by the magnetron sputtering technique. the optimum layer thickness was found to be between 8 and 10 µm. the authors of [35], experimenting with d-sfgm, observed that electric field distribution is further homogenized, the maximum electric field strength at the hv triple junction is further reduced, and the ac flashover voltage was very satisfactory. relevant to [35] is the work by the same research group with fgms having spatial distribution of conductivity σ (σ-fgm) [36]. such materials were fabricated with the surface fluorination of the insulating material. such materials are more orientated to dc applications, where significant improvements were observed w.r.t. the flashover voltage as well as to the homogenization of electric field distribution. the authors of [37] approached the whole question of fgms from another point of view, namely that of the behavior of fgm spacers in the presence of spherical conducting particles in gas-insulated systems. they also noticed the beneficial effect of the fgms in this case, pointing out that the influence of the fgm spacer material may vary depending on the positioning and the size of the spherical particle w.r.t. the high voltage electrode and/or the ground electrode. fgm spacers seem to have a better overall engineering, technology & applied science research vol. 11, no. 6, 2021, 7887-7891 7889 www.etasr.com wong & danikas: functionally graded materials (fgm) for spacers in gas insulated systems … performance with adhering spherical particle than conventional materials. experimenting with ε-grading to the lower permittivity by fabricating fgms (glp-fgm), it was found that the maximum electric field strength of a fabricated coaxial disc-type glpfgm spacer at the hv-electrode/spacer interface can be reduced by 12% in comparison with the one of a conventional spacer with uniform permittivity [38]. in contradistinction to the centrifugation method, the flexible mixture casting (fmc) method [39], produced ε-fgms of a wide range of permittivities giving a relaxation of electric stress on the spacer surface by 64% in sf6 gas and an improvement of discharge inception voltage by 70% in sf6 gas at 0.4 mpa. a more unified approach to the question of spacers was dealt with in [40], where there was a simultaneous change of both electrode shape and insulating material for optimum electric field distribution. thus, the cathode shape was modified by rounding the cathode radius near the triple junction. the maximum electric field was efficiently reduced through the application of the fgm spacer. when compared to the uniform permittivity spacer model, a 26.5% decrease in the maximum electric field was obtained with the optimal fgm spacer configuration. fgms as solution for a more balanced distribution of electrical fields was also presented in [41], mentioning the research on post-type and truncated-cone-type solid insulators for gasinsulated switchgear, which were developed using the centrifugation technique to distribute the fillers and, therefore, permittivity. the authors of [41] present an example of a ushape permittivity grading, which reduces the electric field stress between 10 to 20 times. moreover, in the same paper, they propose the use of fgms as a viable solution of great importance (along, among others, with polymer nanocomposites, high temperature materials, charging control dielectrics and nonlinear dielectrics). emphasis on the centrifugal method was given in [42]. this method was successful in obtaining the fabrication of ε–fgm materials, for which both the packing fraction and size of the dispersed fillers were graded. according to the authors of [42], the fillers depending on their sizes play different roles in order to determine the profiles of the packing fraction and the resultant permittivity profiles in ε–fgm materials. among the small (with a diameter between 0.1 – 10 µm), medium (with a diameter between 10-100 µm), and larger fillers (with a diameter between 100 µm 1000 µm), the small and medium size fillers determine the gradient of permittivity in the dispersion layers whereas the larger fillers predominantly determine the permittivity in the fully packed area. the same group of researchers in an earlier paper rightly wrote that – w.r.t. the centrifugal method the proper choice of the process parameters such that of operational time, of the angular velocity and the statistical distribution of the filler size may lead to the desired profile of permittivities [43]. the authors in [44] proposed a multi-layer fgm approach, according to which different kinds of grading processes are applied and, by so doing, the non-homogeneous dispersion of nanoparticles is achieved between each layer, which in turn creates a smooth grading action and improves the electrical properties of the samples. an improvement in dielectric strength was noted. a comprehensive theoretical analysis of multi-layered fgms was offered in [45], where computational estimates of permittivity and conductivity gave results much closer to the experimental data than well-known models (maxwell-garnett’s model, bruggeman’s model, the coherent potential model, and lichtenecker’s model [46]). as was noted in [44], the theoretical estimates of permittivity and conductivity based on the models of [46] tend to deviate from the respective experimental values when filler loadings exceed the 10% of the volume, whereas this is not observed with the proposed computational model which is based on the representative volume element (rve) approach. iv. proposals for further research fgms contribute to the better distribution of electric fields in certain applications. a possibility for further research can be the exploration of these materials regarding their behavior in voltages at or just below the inception level. previous work with conventional insulating materials has shown that deteriorating phenomena can be observed at voltage levels below the inception level. past work compared the by-products emanating from deterioration above inception with the byproducts produced below inception. the by-products on both occasions were very similar [47-49]. moreover, charge injection and extraction may relate to a tree initiation mechanism that does not involve partial discharges [50, 51]. work done with polymer nanocomposites [52], also tends to confirm the conclusions of [47-49, 53, 54]. it would be interesting to see whether with the fgms one can get some experimental data at and below inception level, since charging phenomena below inception voltage seem to be important although not much attention has been paid to them. furthermore, with the advent of recent research, another possibility would be the use of fgms in high voltage applications having together micro-fillers as well as nanofillers [55]. another interesting possibility can be the application of such materials to high voltage applications requiring very thin layers. it is well known that considerable effort has been taken in order to improve the electrical performance of traditional high voltage insulators (glass/porcelain) with 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[57] m. dimitropoulou, d. pylarinos, k. siderakis, e. thalassinakis, and m. danikas, "comparative investigation of pollution accumulation and natural cleaning for different hv insulators," engineering, technology & applied science research, vol. 5, no. 2, pp. 764–774, apr. 2015, https://doi.org/10.48084/etasr.545. microsoft word etasr_v13_n4_pp11490-11496 engineering, technology & applied science research vol. 13, no. 4, 2023, 11490-11496 11490 www.etasr.com rajderkar & chandrakar: security enhancement through the allocation of a unified power flow … security enhancement through the allocation of a unified power flow controller (upfc) in a power network for congestion management vedashree p. rajderkar department of electrical engineering, g h raisoni college of engineering, india vedashree.rajderkar@raisoni.net (corresponding author) vinod k. chandrakar department of electrical engineering, g h raisoni college of engineering, india v12k5c63@gmail.com received: 31 may 2023 | revised: 22 june 2023 and 7 july 2023 | accepted: 8 july 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6075 abstract the electricity demand is continuously increasing, so a most efficient use of the current power system's capacity is desired. flexible ac transmission systems (factss), a recently developed transmission technology, are widely used to boost the power transfer ability of long-distance transmission line networks and to enhance the consistency of the transmission systems. the use of facts devices can lead to reduced flows on heavily loaded lines, targeted bus voltage levels, and better power network stability. in this study, an optimization method based on the optimal position of the unified power flow controller (upfc) is suggested to boost system security. it is decided that the real power flow is the best place for the upfc in this instance. the optimal placement during congestion has been determined using the genetic algorithm (ga) and the sensitivity to the useful power flow index. congestion is produced on the network and system performance is evaluated. the proposed solutions are evaluated in the ieee 30 bus network before being implemented in matlab. in the case of congestion, the security of the network is evaluated after connecting the upfc. the effectiveness of the proposed solution was verified with the help of the power world simulator 16.0. keywords-upfc; sensitivity to useful power flow index; genetic algorithm; location optimization; security i. introduction modern large and complex networks are delivering under stress as a result of the ongoing increase in demand. the utilities are forced to deal with continuous i 2 r loss, line overloads, and variations in bus voltage. power transmission systems require more capacity, flexibility, reliability, and security. electric utility companies search for various strategies to effectively use the existing transmission lines up to their working capacity. however, this has the side effect of raising the possibility of system instability while security issues emerge. on improving the network security, techniques that relieve stress have received much attention. line overloads have been addressed using load shedding and generation rescheduling methods. load shedding is frequently regarded as the last choice because it will interrupt the power supply of some customers. the operational costs associated with generation rescheduling are fairly substantial. the use of facts devices to redistribute power is preferred in order to solve line overload problems since it offers a financially appealing technique of resolving line overloads without switching off power. facts devices are frequently applied in networks to ensure steady state and secure operation. facts devices can alter system settings such as useful power, mvar power, and node voltage and are incorporated in the electrical networks to improve their flexibility, stability and security. upfc is considered to be a part of the most recent generation of facts. the upfc efficiently redistributes power within the power network. additionally, an existing transmission line can have a upfc built on it, something that requires less space than adding a new transmission corridor. due to the extremely high power flow control speeds of upfcs, overloads brought on by component failures or intermittent generation can potentially be immediately relieved. however, the number of upfc devices and the complexity of the power system enhance combinatorically the viable zone and the constraints to be taken into consideration in optimization approaches. authors in [1] explain that the line loading is tracked in real-time performance and can be kept under their thermal tolerance by a quick and effective dynamic response management of the upfc. in [2], the authors describe the scopf simulation used to decide the appropriate place for upfc in the standard network under higher load circumstances according to [3], the use of upfc may effectively decrease the n-1 congestion issue of engineering, technology & applied science research vol. 13, no. 4, 2023, 11490-11496 11491 www.etasr.com rajderkar & chandrakar: security enhancement through the allocation of a unified power flow … transmission channels running north to south and has a significant cost superiority over the old method. authors in [4] suggest incorporating a upfc into a newton-raphson load flow method. the created upfc model is based on a power injection strategy that considers four control modes to manage the voltage amplitude of a given node, the useful and mvar powers flow in a line concurrently or selectively. in [5], the best place of a dpfc in a network was suggested, followed by the optimum placement of two dpfcs in a system. the artificial algae method is used for the optimal placement of the dpfc in the electrical system. in [6], the authors present and execute a 161 kv upfc model on an 11-bus network. the weakest bus is located by using fvsi, and the most vital line was identified using mla. authors in [7] examine dynamic stability, proposing a method that uses a hybrid strategy to identify the best placement and size of the upfc. authors in [8] utilized the conventional strategy to place the tcsc and upfc in the best possible location for boosting system security under various operating situations and at the best facts parameter values. authors in [9] discuss various methods for reducing congestion, such as load shedding, ga, pso, minlp, sfla, and fuzzy logic systems. the best location for dg, nodal pricing, and cost-free methods are also discussed. in [10], the authors suggested a full-featured, reliable and adaptable model for ess and upfc together after briefly reviewing the models that are now in use, including the decoupled, power injection, and voltage source models. in order to reduce total grid losses, authors in [11], use the tabu search algorithm based on an improved hs method to represent an optimization challenge for an i grid. authors in [12], discuss how facts devices can enhance a transmission line's ability to handle power and maintain voltage. numerous researches have discussed the ideal location for upfc [13–16]. however, they are not concerned with the verification of the softwarebased congestion forecast. the location of upfc based on congestion management by using sensitivity based methods and ga in order to relive the congestion and to enhance the power system security and reliability is discussed in this paper. the results are validated by using power world simulator (pws). this investigation offers the ideal positioning for upfc based on the useful power flow performance index approach. the fact that the active power flow assessment index is a reliable indication of useful power security, a decrease in performance indicator (pi) caused by the placement of the facts controller will improve network security. the location of these devices in the network was determined using the sensitivity of pi with regard to the facts control variables which is comparable to upfc location determined by ga, for strengthening the security of system during congestion management. the decision on the placement of the upfc is made in accordance with the results, and verified was with the pws, ii. upfc design for steady state conditions, upfc static modeling was created. series and shunt converters were combined to create upfc. voltage (vs), insertion angle in a series with line (ϕs), and an element of shunt current (iq), which is in quadrature with voltage vi at the upfc's i th bus, are the three control parameters for upfc [8]. the equivalent circuit of the line incorporating the upfc is described in figure. 1. when a line includes upfc, its apparent powers are expressed as: ��� = −����� − 2�� �� �� cos�∅� − ��� + � �� ��� cos�∅� − � � + �� sin�∅� − � �� (1) ��� = �� �� + �� �� ��� sin�∅� − �� � + �� cos�∅� − �� �� (2) � � = � �� ��� cos�∅� − � � − �� sin�∅� − � �� (3) � � = −� �� ��� sin�∅� − � � + �� cos�∅� − � �� (4) �� = !� + "� #�$ # $ fig. 1. facts controller model. a. power world simulator software based upfc model a systematic approach is developed to simultaneously control real power, mvar power, and bus voltages [10]. the useful power, mvar power, or the voltage of each node can be used to secure the network. if the bus element is neutral to the bus parameters, the power flow solution is constant. upfc is connected in the line and always maintains the voltage (vet) in sending bus i and injects pbt-qbt at the receiving end to bus j as illustrated in figure 2. under loss-free upfc, the power values for bus i and bus j would be equal as indicated in figure 3. the upfc sending end's known values are pet and vet. when upfc is implemented at the sending, according to the design, an additional bus must be added to the network in the pws [10]. if a upfc is developed in the center of the line, the network will need to add two buses. fig. 2. upfc power flow model. fig. 3. upfc static model. engineering, technology & applied science research vol. 13, no. 4, 2023, 11490-11496 11492 www.etasr.com rajderkar & chandrakar: security enhancement through the allocation of a unified power flow … iii. upfc controller placement methodology the reserve capacity of the transmission system has a partial representation in load ratio. additionally, the reserve capacity increases as the load rate decreases. therefore, increasing the transmission capacity of overloaded lines could meet the needs of increasing load. regarding accident prevention, both the stability state and the typical power flow of the system are examined. after that, the system starts to use congestion management. here, the real power flow performance index and ga are used to calculate the maximum power flow and the most suitable position for placing the upfc is selected. the system returns to regular operation and security is enhanced after attaching the upfc. a. sensitivity-based method the performance of the line under routine and emergency circumstances affects the active power flow performance indicator (pi). the active power flow pi [8] technique can be used to describe the loadability of the system's functionality: �� = ∑ &'�( ) *+' *+'',. �(/+ 012 (5) where, wm =1, nl is the total number of lines in the system, wm is a real non-negative weighting coefficient, �30045 is the maximum load capacity of the line, �30 is the actual power flow in the line, and n = 2. the degree of severity is determined by the system's loading circumstances in both normal and emergency situations. the sensitivity technique is used to analyze the system's performance. low pi value means an operation within thermal limits under steady state conditions. the value of pi rises when an overloaded condition is reached. in this article, the active power flow performance indicator approach is used to decide where to allocate upfc in relation to series insertion angle (ϕs) as shown below: 6�7 = 8*9:;8∅< =∑ =0�30>/+012 ) 2*+'',-. ? 8*+':<8∅< (6) the real power injection in the line is taken into consideration when computing dc power flow equation [8] : �30 = @∑ #0( �( abc d e f, /(12(h�∑ #0( �(/(12(h� � � abc d = f (7) according to figure 1, the upfc is situated in line k, which connects buses i and j. pj is the additional electrical power that upfc in the system injects into the line. the network has n buses, and smn is the mn th part of the power flow matrix [s]. the following equation can be created by combining (6) and (7): 8*+':<8∅< = @ i#0� 8*j<:<8∅< � #0 8*k< :<8∅<l abc d e fi#0� 8*j<:<8∅< � #0 8*k< :<8∅<l � 8*k< :<8∅< abc d = f (8) where: 8*j<:<8∅<m∅� 1n = �2�� �� cos�∅� � �� � � � ��� cos�∅� �� � � �� sin�∅� � � �� o� $ �$ o∅$p∅$ =0 = � i�� rb$� � �� $�s� l due to its cost effectiveness, the useful power flow pi is derived using the aforementioned equation with regard to the series insertion angle as an installed upfc control variable in each line individually. it should be put in an ideal position. the optimum allocation for upfc placement is in the line with the most negative sensitivity index to improve system security, but other criteria may also be used to decide that upfc should not be situated close to a producing transformer, despite the most negative sensitivity index. b. genetic algorithm gas are methods for conducting a global search that are based on natural selection and genetics. they don't need any specialized knowledge or characteristics of the goal function and they can look for multiple potential solutions simultaneously. they are also excellent techniques for finding an effective answer to a complex problem since they consistently deliver high-quality solutions. furthermore, they are useful algorithms that are simple to apply to the analysis of power systems. the ratio of a line's actual power flow to its maximum power flow is known as the line's sensitivity factor. it is helpful in figuring out the severity of the line, where high severity indicates the line has a significant chance of collapsing soon. the fitness function to be maximized [16] is: ∑ ) *jk*jk',-./t� 12 (9) where �� is the flow of power on line ij, �� 045 is the maximum flow of power in line ij, and nl is the number of lines. for the best allocation of upfc, the line with the highest fitness value is taken into account. fig. 4. flowchart of the upfc device optimal allocation process. engineering, technology & applied science research vol. 13, no. 4, 2023, 11490-11496 11493 www.etasr.com rajderkar & chandrakar: security enhancement through the allocation of a unified power flow … the ga begins with the initial population being generated at random and continues with selection, crossover, and mutation before the maximum generation is attained. each string that relates to a location is used to construct the initial population, which is the transmission line's number where the facts is supposed to be placed. the position value differs for each string. every member of the population will then have its objective function (fitness) evaluated. gas have limitations to finding the objective function's largest positive value. in the process of reproduction, an individual is chosen to become part of a new generation based on its fitness. the primary goal of crossover is to combine the knowledge of two distinct individuals to create a new one. to prevent an early convergence to a local optimum, mutation is used to inject some type of artificial diversification into the population. figure 4 summarizes the suggested optimization method. the "arrangement of the facts locations" procedure is required to guarantee that each line has only one facts device. iv. simulation results on a modified ieee 30 bus network [11], the suggested technique for using upfc in the most effective way was employed using matlab. bus no. 1 was used as a reference. according to load flow analysis, line 4-6 has reached its maximum thermal limit. a. sensitivity approach the most suitable allocation of the upfc was computed based on active power flow. with regard to the insertion angle in series with line as a control variable, the upfc was put in each line for similar operational circumstances in order to decrease system's overloads without modifying the network's topology or without rescheduling generation. table i shows the pi sensitivity indicator in relation to upfc. according to table i, line 5-7 has the largest negative sensitivity index with respect to ϕs. therefore, it is appropriate to install the upfc in line 5-7 to prevent overloading and improve system security. table i. sensitivity based on pi on an ieee 30 bus network with overload at line 4-6 line no uvw = xyz[\x∅\ 1-3 -1.149867577 2-4 -1.378312267 2-5 -2.943605844 2-6 -4.151895176 3-4 -2.198711769 5-7 -7.896648528 b. genetic algorithm in this paper, we try to discover the optimal location for the upfc using ga. the best fitness function findings for upfc are displayed in table ii. table ii shows that the fitness values in lines 2-4 and 2-5 are the highest, however the installation for upfc location in lines 2-4 and 2-5 does not relieve the congestion. so, line 5-7 is the optimum location for the placement of upfc because it can control the useful power flow in line and enhance the security of the network. table ii. overload in line 4-6: ga based location for upfc on ieee 30 bus network line no best fitness value 1-3 0.933 2-4 1.0453 2-5 1.0443 2-6 0.9674 3-4 0.9304 5-7 0.9515 c. power world simulator despite having certain upfc properties that increase power system effectiveness, there is a limitation related to active power injection. this capability's implementation greatly improves upfc steady-state performance. the simple upfc parameters calculation and steady state upfc model simulation clearly demonstrate its superiority to other models. upfc parameters can be simply calculated without the need for initial values and their limits may be easily altered. the results would be more reliable if these investigations were conducted using the provided model in a real network rather than a simplified one as shown in table iii. figure 5 illustrates the system's congestion situation under steady state conditions. according to figure 6, adding a upfc to line 1-3 reduces overloading from 104% to 101% on line 4-6. figure 6 depicts the line loading limit of 101%. according to figure 7, even though overloading decreased after installing upfc in lines 2– 6, from 104% to 97%, according to pws, the situation is still dangerous because the power flow in lines 4-6 is indicated by a red arrow, indicating that the thermal limit has not yet been obeyed. the power flow illustrated by the green arrows in figure 8 shows that it runs within its thermal limit and decreases line 4-6 overloading from 104% to 97%. therefore, line 5-7 is an excellent location for upfc insertion according to the sensitivity indicator, ga, and the pws has verified this location for improving system security. table iii. location for upfc on the ieee 30 bus network using pws. line 4-6 is overloaded by 104% upfc placement in line no % loading reduces in line 4-6 after upfc placement 1-3 101 2-4 101 2-5 100 2-6 97 (congestion not relieved completely) 3-4 101 5-7 97 ( completely relieved) v. discussion on a large power network, congestion is the most frequently occurring problem. such problems can be avoided using upfc. simulation results indicate that the conventional sensitivity approach, based on coding methods, for determining the best location of upfc is line 5-7 in an ieee 30 bus network. the derived location is verified by the result of ga. the validation of the result is done by pws. the network security is significantly enhanced by upfc optimal location at line 5-7. engineering, technology & applied science research vol. 13, no. 4, 2023, 11490-11496 11494 www.etasr.com rajderkar & chandrakar: security enhancement through the allocation of a unified power flow … fig. 5. system overload on line 4-6 of a modified ieee 30 bus. fig. 6. upfc located in line 1-3. fig. 7. upfc located in line 2–6 (line 4-6 is shown in red despite 97% capacity). engineering, technology & applied science research vol. 13, no. 4, 2023, 11490-11496 11495 www.etasr.com rajderkar & chandrakar: security enhancement through the allocation of a unified power flow … fig. 8. upfc located in line 5-7 (green indicates the flow in line 4-6 displays 97% loading). vi. conclusion in this study, a sensitivity-based technique and ga have been developed for determining the most appropriate location for placing a upfc device. test results demonstrate that the sensitivity factor or ga can be utilized to successfully deploy upfcs in response to the desired objectives. the position of upfc can be chosen if there is congestion. with the use of pws, a comprehensive model of upfc must be taken into consideration after choosing the 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[26] p. jagtap and v. chandrakar, "comparative study of upfc controllers to improve transient and dynamic stabilty of power system," in 2021 ieee 4th international conference on computing, power and communication technologies (gucon), kuala lumpur, malaysia, sep. 2021, https://doi.org/10.1109/gucon50781.2021.9573804. engineering, technology & applied science research vol. 7, no. 6, 2017, 2156-2159 2156 www.etasr.com abdulla and abdulla: a comparative application for evaluating composite fabrics used … a comparative application for evaluating composite fabrics used in electromagnetic shielding f. gamze kizilcay abdulla electrical electronics engineering engineering faculty yuzuncu yil university van, turkey gamzekizilcay@yyu.edu.tr ruslan abdulla computer technologies t.o.b.b. t.s. vocational school karabuk university karabuk, turkey ruslanabdulla@karabuk.edu.tr abstract—composite fabrics containing metal filaments are used widely for preventing electromagnetic radiation. many experiments involving them are carried out continuously. results are simulated in order to analyze their performance. coding in matlab is a popular method to compare the electromagnetic shielding properties of composite fabrics but for different options matlab codes must be edited each time. scientists who are not experts in coding have difficulties on editing such codes. to overcome this, an application written in c# in visual studio with .net platform was developed. this application is integrated with bunifu, which allows the application to be well designed. the proposed interface is user friendly and lets the user choose the available fabric with its stitch length from panel section. by setting options one can get the electromagnetic parameters such as scattering (s) parameters, reflection, transmission and absorption coefficients and total shielding effectiveness (se) values with one click. as the application is integrated with matlab codes, output is given as a matlab graph with desired options. in this way the distinctions between the chosen fabrics can be analyzed easily. keywords-composite fabric; electromagnetic shielding; textile application; user interface i. introduction electronic devices cause electromagnetic pollution via irradiation. in such situations the body can not condemn its temperature and invites illnesses [1-3]. the most common devices that cause daily exposure at home are mobile phones and deck phones operating in rf and microwave frequencies, dsl and wifi modems, am signals and satellite broadcasts, microwave ovens, etc. [3-4]. many methods have been developed for obstructing electromagnetic radiation. one of them is shielding. shielding is defined as isolating the two media at circuit or device level in an electromagnetic sense. thus, a shielding material blocks completely or partially the passage of the signal. as shielding material, conductive or ferromagnetic materials are usually used. the conductance or magnetic permeability of these materials plays an active role in the reflection or absorption of the electromagnetic signal [5]. protective textile fabrics are commonly seen as shielding materials in electromagnetic shielding applications. these fabrics are known as conductive fabrics because the yarns that make up the fabric consist of fine metal filaments blended with the yarns. the main characteristic of conductive fabric is the ability to use conductive or ferromagnetic materials in its structure as a shield for electromagnetic fields. their main advantage is that they are flexible and therefore can cover any kind of gap and can prevent leaks from connection points. ease of mass production and low cost are also advantages of conductive fabrics [6-7]. the use area of conductive fabrics is quite wide. today this industrialized area can be seen in wearable technology, military and health [8]. a network analyzer is often used in electromagnetic shielding experiments. this device generates scattering parameter values which give clues about the shielding performance of the shielding material. it is possible to obtain reflection, transmission and absorption coefficient values as well as total electromagnetic shielding values by using appropriate conversion formulas from scattering parameters. with this application, scattering parameters and other electromagnetic units are displayed in options section. the scattering parameters obtained from electromagnetic shielding experiments of copper, silver and stainless steel cored cardigan, lacoste, milano, rib and weft knitted fabrics were used in this study. the application has an interface that allows comparison between the shielding materials displayed on main panel. the display of electromagnetic shielding results is usually done with matlab graphics. this requires the user to be familiar with matlab codes. however, it is still possible to develop an interface using the matlab gui features suitable for the user. but still, it is not aesthetic to make this interface with matlab and there are some deficiencies in reading the stored data from the computer as compared to the c# language. for this reason, in this work c# code is used on the visual studio .net platform. it is quite possible to develop better interface on the .net platform. this is even easier with a plugin named bunifu. by integrating bunifu it is much easier to get aesthetic designs, as interface objects can use the same c# code properties and methods. engineering, technology & applied science research vol. 7, no. 6, 2017, 2156-2159 2157 www.etasr.com abdulla and abdulla: a comparative application for evaluating composite fabrics used … ii. application this desktop application is made by using matlab and visual studio application programming interface (api). the functional part of the program is implemented with these two api's. with matlab, conversion formulas are executed according to user's preferences and results are displayed with graphs. with visual studio, easy interface is provided for the user and preferences are sent to matlab environment for processing. a bunifu plugin with its well designed objects was integrated with visual studio for a better interface. a. interface when the application is opened, two panels are displayed showing the fabric name and stitch length. this information is automatically retrieved from the application’s database (figure 1). these lists are automatically updated when different fabrics are added to or removed from the database. it is seen that the program page is widened by clicking on the stitch density of that fabric whichever fabric is desired to be compared (figure 2). in the expanding section, the selected fabric, stitch length and metal filament type are seen. in this example, copper cored lacoste, milano, cardigan, rib and weft knitted fabrics with a 4mm stitch density are selected. in the right part of the expanding section, there are options of electromagnetic parameters and graphical view. in the options section, one can select s parameters, and accordingly any of the options of reflection, transmission, absorption coefficients and total shielding effectiveness. preferences are configured so that only one electromagnetic parameter can be evaluated at a time. features other than electromagnetic parameters such as grid and markers relate to matlab graphical interface. it is recommended that these properties are set on for more precise analysis. b. working principle after running the application the user interface loads. during the loading process, required matlab packages and bunifu plugin load and are getting ready to execute. afterwards the data available are extracted into the interface. in the second stage, user chooses a fabric and stitch length. accordingly he decides which fabrics' electromagnetic properties are going to be compared. the user can select or deselect the fabric. after choosing the fabric user decides which graphics should be displayed. in the application presented electromagnetic shielding parameter options are scattering parameters, reflection, transmission and absorption parameters and the shielding effectiveness magnitudes. there are also minor properties about the viewing graphics. there are grids and markers which could be set on or off. the workflow is shown in figure 3. fig. 1. user interface fig. 2. expanding section fig. 3. an ordinary output (se) due user's preferences. engineering, technology & applied science research vol. 7, no. 6, 2017, 2156-2159 2158 www.etasr.com abdulla and abdulla: a comparative application for evaluating composite fabrics used … c. output electromagnetic parameters provided by the application are reachable on the options section. specific results are illustrated upon users' preferences (figure 4). this can be thought of as the best example of the compatibility of the interface with the graphical environment. it is also possible to obtain other electromagnetic parameters with the same shielding material. the relevant results are shown in graphics in appendix. fig. 4. working principle of application. iii. conclusion the application developed within the scope of this study has user friendly and functional features to meet the needs of researchers who are interested in the effects of electromagnetic shielding of textile fabrics but have difficulties in coding. automatic extraction of fabric information from the database makes the application dynamic and sustainable. when different fabrics are desired to be compared, entry of the relevant test results into the database is sufficient for the operation of the application. the results are shown graphically in matlab environment. in this way, the user can compare and analyze the electromagnetic shielding parameters of the desired fabrics, such as s, reflection, transmission, absorption parameters and total shielding effectiveness values. besides the introduction of new knitted fabrics to the proposed application, the addition and classification of woven conductive fabrics used in electromagnetic shielding, saving preferences, extracting statistics from graphs, adding visual themes can be considered as features for further studies. we think that the proposed study and application will have a positive impact on the literature. references [1] t. e. aldrich, c. e. easterly, “electromagnetic fields and public health”, environmental health perspectives, vol. 75, pp. 159-171,1987 [2] v. de santis, “ear temperature increase produced by cellular phones under extreme exposure conditions”, ieee transactions on microwave theory and techniques, vol. 60, no. 6, pp. 1728-1734, 2012 [3] l. cheng, t. zhang, m. guo, j. li, s. wang, h. tang, “electromagnetic shielding effectiveness and mathematical model of stainless steel composite fabric”, the journal of the textile institute. vol. 106, no. 6, pp. 577-586, 2014 [4] h. ozdemir, s. s. ugurlu, a. ozkurt, “the electromagnetic shielding of textured steel yarn based woven fabrics used for clothing”, journal of industrial textiles, vol. 45, no. 3, pp. 416-436, 2015 [5] l. sevgi, elektromanyetik uyumluluk elektromanyetik kirlilik, yapım matbaa, 2000 [6] b. s. dasaradan, “electromagnetic shielding effectiveness of copper core yarn knitted fabrics”, indian journal of fibre and textile research, vol. 34, pp. 149-154, 2009 [7] z. liu, x. c. wang, “influence of fabric weave type on the effectiveness of electromagnetic shielding woven fabric”, journal of electromagnetic waves and applications, vol. 26, no. 14-15, pp. 1848-1856, 2012 [8] j. banaszczyk, g. de mey, a. schwarz, l. van langenhove, “current distribution modelling in electrocundtive fabrics”, fibres & textiles in eastern europe, vol. 17, no. 2 (73), pp. 28-33, 2009 appendix 1.7 1.85 2 2.15 2.3 2.45 2.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 frequency (ghz) s 1 1 cardigan_4_copper lacoste_4_copper milano_4_copper rib_4_copper weft_4_copper 1.7 1.85 2 2.15 2.3 2.45 2.6 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 frequency (ghz) s 2 1 cardigan_4_copper lacoste_4_copper milano_4_copper rib_4_copper weft_4_copper (a) (b) fig. a1. scattering parameters a) s11 b) s21. engineering, technology & applied science research vol. 7, no. 6, 2017, 2156-2159 2159 www.etasr.com abdulla and abdulla: a comparative application for evaluating composite fabrics used … 1.7 1.85 2 2.15 2.3 2.45 2.6 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 frequency (ghz) r e fle ct io n c o e f. ( d b ) cardigan_4_copper lacoste_4_copper milano_4_copper rib_4_copper weft_4_copper 1.7 1.85 2 2.15 2.3 2.45 2.6 -20 -15 -10 -5 frequency (ghz) t ra n sm is si o n c o e f. (d b ) cardigan_4_copper lacoste_4_copper milano_4_copper rib_4_copper weft_4_copper (a) (b) 1.7 1.85 2 2.15 2.3 2.45 2.6 -15 -14 -13 -12 -11 -10 -9 -8 frequency (ghz) a b so rp ti o n c o e f. (d b ) cardigan_4_copper lacoste_4_copper milano_4_copper rib_4_copper weft_4_copper (c) fig. a2. coefficients a) reflection b) transmission c) absorption. engineering, technology & applied science research vol. 8, no. 1, 2018, 2572-2576 2572 www.etasr.com zaky et al.: sensorless induction motor drives using adaptive flux observer at low frequencies sensorless induction motor drives using adaptive flux observer at low frequencies mohamed s. zaky department of electrical engineering northern border university arar, saudi arabia mszaky78@yahoo.com hady abdel maksoud department of electrical engineering minoufiya university shebin el-kom, egypt hady_elgendy@yahoo.com haitham z. azazi department of electrical engineering minoufiya university shebin el-kom, egypt haitham_azazi@yahoo.com abstract—operation at low frequencies of sensorless drives using machine model-based estimation methods is a challenging issue. this paper proposes an adaptive flux observer (afo) method of speed estimation for sensorless induction motor (im) drives. the observer feedback gains are designed to guarantee accurate speed estimation, especially at low frequencies in the regenerating mode operation. a complete sensorless im drive with the proposed afo is executed in the laboratory. extensive experimental results under different operating conditions are provided to prove the effectiveness of the proposed afo, particularly under low stator frequencies in both motoring and regenerating modes of operation. keywords-sensorless control; induction motors; adaptive flux observer; low frequencies; observer feedback gain i. introduction precise speed information is very important for speed control of induction motor (im) drives. direct speed sensors or encoders are used for speed measurements. however, they have several disadvantages such as extra cost, extra space, extra wiring, careful mounting, and additional electronics. therefore, speed estimation methods of sensorless im drives were developed to replace the direct speed sensors. the sensorless drives are characterized by low cost, high reliability, decreased size, less maintenance, less wiring, and decreased complexity [1]. many speed estimation methods have been presented in the literature. they can be classified into two categories. the non-fundamental wave speed estimation methods are a good choice at zero and very low stator frequencies. they are independent of parameters variation. however, they increase the ripples and need special machine design. fundamental-wave-model-based approaches of speed estimation give good behavior during medium and high frequencies. however, they fail to guarantee the desired performance under very low and zero speeds [2]. they are highly dependent on the machine parameters, the back emf, inverter nonlinearity, and errors of the data acquisition converters. different speed estimation methods with and without parameters estimations were presented [3-8]. these methods can be classified as different estimation methods such as direct speed calculation method, model reference adaptive system method (mras) [1], kalman filter [2], adaptive flux observers (afo) [3, 6, 7], intelligent control based methods (ai) [5], and sliding mode observer (smo) [8]. nonfundamental wave speed estimation methods are a good choice at zero and very low stator frequencies [9]. they are independent of parameter variations. high frequency voltage injections are one class of these methods. numerous attempts and efforts were extensively proposed in [9-20]. in [9], a multiphase induction machine was utilized to obtain larger slotting harmonic magnitude compared to normal three phase induction machines. the machine slotting signal depends on the rotor slot type and bars. however, this method suffers from increasing the stator copper losses due to increasing the principle rotor slot losses. the transient voltage excitation using inform technique for sensorless speed estimation under very low and zero speed operation was addressed in [10]. high frequency injection (hfi) methods were used to energize the stator voltage with high frequency signal. the machine current components were utilized to estimate the rotor speed and angles using different separation algorithms as in [11-16]. to improve the performance of sensorless drive method based high sinusoidal voltage injection with high frequency, the square wave voltage injection schemes were utilized [17-19]. in [17-18], the conventional square voltage injection scheme needs high carrier signals with high frequency. a novel square wave carrier signal injection to overcome the disadvantages of the conventional ones was addressed in [19]. also, zero voltage vector injection scheme for online flux estimation was presented in [20]. however, these methods have torque ripples and need a special design of the machine. afo needs estimation of the machine parameters, especially at very low frequencies because the back emf is very low and the voltage drop on the stator resistance has a major effect. therefore, the sensorless control system with parameter estimation was designed as multiple-input-multiple output [3, 5, 6], or needs the designing of three estimators as independent single-input-single output systems as in [7]. therefore, this estimation complicated the sensorless drive systems. another problem is that the machine model-based methods of sensorless drives are incapable of operating stably during a long time under rated load at zero stator frequency. this instability is engineering, technology & applied science research vol. 8, no. 1, 2018, 2572-2576 2573 www.etasr.com zaky et al.: sensorless induction motor drives using adaptive flux observer at low frequencies maximized at regenerative mode of operation in the very low speed region [21-23]. this study’s key goals can be summarized as follow: 1) proposing afo for sensorless im drives. 2) designing of observer feedback gains for stable operation of afo at low frequencies based on lyapunov theory. 3) execution of the complete sensorless im using afo algorithm in the laboratory using dsp-ds1104 control board. 4) experimental results at low frequencies should verify the applicability of the proposed method. ii. im and observer models the dynamic d-q model of the im is described by stationary reference frame using (1).                                   s s s s s ds ds ds dr r qr s s s s s qs qs qs qr r dr s s s s dr ds r qr dr s s s s qr qs r dr qr pi bv ai c d pi bv ai c d p gi f p gi f   where,                         2 2 1 1 , , , g 1 1 , , 1 , , s m m s s r r r r s r m r r m s s r r r r l l a c d l ltl t t ll l l b t f l l ll r t and, t s s s s ds qsv v v     is dq stator voltage, t s s s s ds qsi i i     is dq stator current, t s s s r dr qri i i     is dq rotor current, t s s s s ds qs        is dq stator flux, t s s s r dr qr        is dq rotor flux, rs, rr are the stator and rotor resistances, lm, ls, lr are magnetizing inductance, stator inductance, and the rotor inductance, respectively, r is the rotor speed, j is the moment of inertia, and b is the viscous friction. the schematic diagram of ifoc for im with the afo is clarified in figure 1. fig. 1. the schematic diagram of ifoc for an im with the afo. iii. design of an adaptive flux observer a. structure of an adaptive flux observer an afo is described by a stationary reference frame based on (1) using (2):                                     1 2 ˆ ˆˆ ˆ ˆ ˆ ˆˆ ˆ ˆ ˆ ˆ ˆˆ ˆ ˆ ˆ ˆˆ ˆ s s s s s ds ds ds dr r qr id s s s s s qs qs qs qr r dr iq s s s s dr ds r qr dr s s s s qr qs r dr qr pi bv ai c d ke pi bv ai c d k e p gi f p gi f   where, k1 and k2 are the current and flux observer gains,  ŝ sid ds dse i i and   ŝ s iq qs qse i i . using (1) and (2), the current and flux errors are derived as follows.                                               1 2 ˆ ˆ ˆ ˆ s id id d r q qr r id s iq iq q r d dr r iq s d id r q qr r d s q iq r d dr r q pe ae ce d e d ke pe ae ce d e d k e pe ee e fe pe ee e fe   where, ˆ-   r r r ,     ˆ s s d dr dre ,     ˆ s s q qr qre . it is important to design the observer gains k1 and k2 of the current observer to ensure the system stability. proof 1: the lyapunov function can be selected as (4): engineering, technology & applied science research vol. 8, no. 1, 2018, 2572-2576 2574 www.etasr.com zaky et al.: sensorless induction motor drives using adaptive flux observer at low frequencies  2 2 1 1 2 2 id iqv e e   the first derivative is expressed as (5).                                  1 2 ˆ = ˆ id id iq iq s id id d r q qr r id s iq iq q r d dr r iq v e e e e e ae ce d e d ke e ae ce d e d k e   the sufficient conditions, to guarantee the stability of the current observer using lyapunov theory, are that a negative definite v is obtained. it is found that id ide ae and iq iqe ae are negative. consequently, the remaining terms of (5) should be negative to ensure the stability.                             1 2 ˆ 0 ˆ 0 s id d r q qr r id s iq q r d dr r iq e ce d e d ke e ce d e d k e   then, one can obtain,                              1 2 ˆ 0 ˆ 0 s d r q qr r id s q r d dr r iq ce d e d ke ce d e d ke   to satisfy the inequality of (7), k1 and k2 are designed as (8).                         1 2 ˆ ˆ s d r q qr r id s q r d dr r iq ce d e d k e ce d e d k e   the inequalities of (8) can be realized by selecting the values of k1 and k2 by (9).                        1 1 2 2 ˆ ˆ s d r q qr r id s q r d dr r iq ce d e d k k e ce d e d k k e    where, k1 and k2 are negative numbers. iv. experimental results the layout of the experimental system based on a dspds1104 is demonstrated in figure 2. it assembles from hardware and software components. the hardware components include a 1.1 kw im interfaced with dc generator for load torque applications, pwm inverter with six igbt's, gate drive and interface circuits, 3-phase full wave rectifier circuit, dspds1104 control board, incremental encoder, voltage and current sensors, and personal computer. an encoder to measure the speed is utilized for comparison purpose with estimated speed. the parameters of the im are shown in table i. the software components incorporate the matlab/simulink for model implementation and the dspace software. the effectiveness of the afo for speed estimation is proved and tested. the practical tests are demonstrated under different operating conditions to certify the sensorless im drive using the afo. v ol ta ge a nd c ur re nt s en so rs fig. 2. the layout of the experimental system based on a dsp-ds1104. table i. parameters of im rated power 1.1 kw stator resistance 7.4826 ohm supply voltage 380 volts rotor resistance 3.6840 ohm rated current 2.545 amp rotor leakage inductance 0.0221 h no. of poles 4 stator leakage inductance 0.0221 h supply frequency 50 hz mutual inductance 0.4114 h inertia 0.02 kg.m2 a. fast speed reversal figure 3 displays the practical tests of the reference and measured speeds. the figure shows the reference and measured speeds, the quadrature current, iqs, and the dq rotor fluxes. the sensorless im drive operates at reference speed of 6.28 rad/sec. the step torque of +7n.m is varied at t=1.5sec. then, the reference speed is changed to 6.28rad/sec at t=3.75sec. the torque is removed at t=7.5 sec. the im operates in the motoring mode (forward) during t=0 to 1.5sec at no-load and with loading of +7n.m at t=1.5sec to t=3.75sec. the im operates in the regenerating mode during t=3.75 to 7.5sec with negative speed and positive load. the im operates in the motoring mode (reverse) during t=7.5 to 12sec with no-load. it is seen that the measured speed and the estimated one are in a good convergence. b. slow speed reversal figure 4 displays the practical tests of the reference and measured speeds, the quadrature current, iqs, and the dq rotor fluxes under slow speed reversal. the speed reference of 10rad/sec is changed slowly to 10rad/sec with load torque change of +7n.m applied at t=1sec. as noted, the estimated speed is stable during the slow speed reversal, especially during the zero crossing point. engineering, technology & applied science research vol. 8, no. 1, 2018, 2572-2576 2575 www.etasr.com zaky et al.: sensorless induction motor drives using adaptive flux observer at low frequencies fig. 3. the practical tests of the reference and measured speeds, the quadrature current, iqs, and the dq rotor fluxes under fast speed reversal from 6.28rad/sec to 6.28rad/sec. positive torque of +7n.m applied at t=1.5sec and removed at 7.5sec. fig. 4. the practical tests of the reference and measured speeds, the quadrature current, iqs, and the dq rotor fluxes under slow speed reversal from 10rad/sec to 10rad/sec. positive torque of +7n.m applied at t=1sec. c. low speed during regenerating mode the practical tests of reference and measured speeds, quadrature current, iqs, and dq rotor fluxes in regenerating mode at low speed with the proposed gains are illustrated in figure 5. the speed reference is adjusted at 14rad/sec, then, a torque of 7n.m is applied at t=3.9sec. as noted, a stable sensorless drive is maintained. d. low speed during motoring mode the practical tests of the reference and measured speeds, the quadrature current, iqs, and the dq rotor fluxes during low speed in the motoring mode are presented with the proposed gains. figure 6 shows the speed reference of 14rad/sec with torque change of +7n.m applied at t=2.4 sec. practical tests reveal that the designed afo with the proposed feedback gains guarantees a stable operation in the low speed in both motoring and regenerating modes of operation. also, the estimated speed has a significant convergence with the measured speed during fast and slow speed reversal. fig. 5. the practical tests of the reference and measured speeds, the quadrature current, iqs, and the dq rotor fluxes under low speed regenerating mode of operation at 14 rad/sec. negative torque of 7 n.m applied at t=3.9 sec. v. conclusion the sensorless im drives using afo-based speed estimation method was successfully implemented in real-time for low frequency operation. the observer gains were calculated using lyapunov stability theory. the sensorless im drive were carried out using dsp-ds1104 platform, and it was examined under different operating conditions, especially at low frequencies in the motoring and regenerating modes of operation. it has been found that the estimated speed has a good convergence with the measured speed. moreover, the estimated speed tracks smoothly the measured speed during fast and slow speed change. this confirms that the designed feedback gains guarantees the efficacy of the designed afo, particularly at low frequencies. engineering, technology & applied science research vol. 8, no. 1, 2018, 2572-2576 2576 www.etasr.com zaky et al.: sensorless induction motor drives using adaptive flux observer at low frequencies fig. 6. the practical tests of the reference and measured speeds, the quadrature current, iqs, and the dq rotor fluxes under low speed motoring mode of operation at 14rad/sec. positive rated load torque of +7n.m applied at t=2.4sec. acknowledgement authors gratefully acknowledge the approval and the support of this research study by the grant no. eng-2017-1-7f-6930 from the deanship of scientific research at northern border university, arar, ksa. references [1] r. kumar, s. das, a. chattopadhyay, “comparative assessment of two different model reference adaptive system schemes for speed-sensorless 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full-order flux observers for sensorless induction motors”, ieee transactions on industrial electronics, vol. 51, no. 5, pp. 10331040, 2004 microsoft word zahedi-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 368-372 368 www.etasr.com zahedi and kahaei: frequency estimation of irregularly sampled data using a sparsity constrained… frequency estimation of irregularly sampled data using a sparsity constrained weighted least-squares approach adel zahedi school of electrical engineering iran university of science and technology tehran, iran azahedi@elec.iust.ac.ir mohammad hossein kahaei school of electrical engineering iran university of science and technology tehran, iran kahaei@iust.ac.ir abstract—in this paper, a new method for frequency estimation of irregularly sampled data is proposed. in comparison with the previous sparsity-based methods where the sparsity constraint is applied to a least-squares fitting problem, the proposed method is based on a sparsity constrained weighted least-squares problem. the resulting problem is solved in an iterative manner, allowing the usage of the solution obtained at each iteration to determine the weights of the least-squares fitting term at the next iteration. such an appropriate weighting of the least-squares fitting term enhances the performance of the proposed method. simulation results verify that the proposed method can detect the spectral peaks using a very short data record. compared to the previous one, the proposed method is less probable to miss the actual spectral peaks and exhibit spurious peaks. keywords-basis pursuit; sparse representation; overcomplete dictionaries; irregular sampling; spectrum estimation i. introduction spectral analysis of irregularly sampled data is ubiquitous in science and technology. the range of applications for this branch of signal processing includes, among others, the estimation of doppler frequency in radars [1], astronomical data analysis [2], the analysis of the heart rate variability in medical sciences [3] and turbulent velocity analysis in measurement systems [4]. let us denote by [ ] 1 2 t � y y y=y ⋯ the data-set taken at � sampling time instants [ ] 1 2 . t � t t t=t ⋯ the frequency grid on which the spectrum is to be computed is denoted by [ ]0 11 t m m f f f f f − − =f ⋯ ⋯ (1) with max , , , m m f f m m m m = = − … (2) for a predefined maximum frequency max f . also let us define an overcomplete dictionary of complex exponentials which is a � k× matrix defined as: ( ) 1 exp 2 t j � π=w tf (3) where 2 1k m= + , k �> , and ( )exp a for matrix a is defined as a matrix of the same size as a with elements computed as the exponential of the corresponding elements in a. from (3) it can be inferred that the m th column of w is a complex exponential function of frequency m f sampled at the sampling instants t. when the data set is known to be sinusoidal (which is the case for most applications), one of the most powerful techniques of spectrum estimation is to represent the dataset y as a linear combination of the columns of w ; i.e. to obtain a vector ŝ so that ˆ.=y ws . if so, the nonzero elements of ŝ demonstrate the amplitude of the spectral components at corresponding frequencies in .f redundancy of w gives rise to infinitely many solutions ŝ which opens the way to enforcing some more constraints to the solution. the simplest of them are the least-squares fitting methods; e.g. the lombscargle periodogram [5]. more sophisticated methods penalize the least-squares fitting term with a sparsity-enforcing term [68]. in [2, 9-10], the sparsity constraint is formulated as the 1 ℓ norm of the solution. this method is widely known in the literature as basis pursuit [11]. these methods are capable to estimate the spectral lines from very limited data records and allow super-resolution frequency estimation [9-10]. in [9], the dictionary w is defined as a collection of cisoids instead of complex exponentials. it is shown in [2, 10] that sparse approximation in the complex exponential dictionary outperforms the method of [9]. in this paper, we zoom in on the method of [10] which is the most recent amongst the above methods. the sparse approximation of y in w is the solution to the following optimization problem [12]: ( )2 1argˆ min k λ ∈ = − + s y wss s c (4) where λ is called the regularization parameter and 1 s is the norm of s defined as: etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 368-372 369 www.etasr.com zahedi and kahaei: frequency estimation of irregularly sampled data using a sparsity constrained… 1 1 k i i s = = ∑s (5) the cost function in (4) is the sum of two terms. the first one enforces the least squares fitting of the solution to the data set, and the second one guarantees the sparsity of the solution. this problem can be solved in polynomial time using a variety of methods [10]. it has been shown in [10] that if ŝ is a solution to (5) and 0 ˆ 2�<s (where 0 ŝ counts the number of nonzero elements in ˆ),s then it is the unique sparsest solution. roughly speaking, the minimizer of (4) is a sparse vector 0 11 ˆ ˆ ˆ ˆ ˆ ˆ t m m s s s s s− −=   s ⋯ ⋯ so that ˆws fits to the data-set in the least-squares sense. ˆ m s is thus an estimation of the amplitude of the signal component at frequency m f . problem (4) is known in the literature as basis pursuit denoising (bpdn) [10, 11]. in this paper, instead of the sparsity constrained leastsquares problem of (4), another cost function is proposed which can be interpreted as a sparsity constrained weighted leastsquares problem, and is solved iteratively. in order to refine the fitting to the data-set, in each iteration the obtained temporary solution is utilized to weight the least-squares term in the next iteration. since the proposed sparsity-based method solves a weighted least-squares problem in an iterative manner, it falls into the class of methods named iterative adaptive approach (iaa) [13-15]. this paper is organized as follows: in section ii, the proposed method is described in detail. in section iii, the proposed method is compared to the bpdn method of [10] formulated in (4) using simulation results. the paper is concluded in section iv. ii. proposed method a. problem formulation problem (4) can be rewritten in the following componentwise form: ( )2 1argmin , , ,ˆ m m s m m ms λ ∈ = − + = −y ws s … c (6) the iterative coordinate descent (icd) method described in [10] can be used to solve this scalar problem considering the following equivalence: ( ) ( )1 2 argmin ˆ ˆ m h m m m m s s s λλ φ ∈ = − + ⇔ =y s wws e c (7) where m w is the m th column of w, m e is defined as: m m m s= − +e y ws w (8) and for any complex number j x x e θ= the complex soft shrinkage function ( )xλφ is defined as [10]: ( ) ( ) , if 0, otherwise j x e x x θ λ λ λ φ  − > =   (9) it is necessary to mention again that the cost function in (6) is sum of two terms: a least-squares data-fitting term 2 −y ws and a sparsity enforcing 1 ℓ norm term 1 s . the value of the regularization parameter λ determines the relative emphasis on each one of these two terms. a large λ should be interpreted as a tendency to obtain a very sparse solution, while with a small λ the sparsity of the solution is sacrificed in favor of its fidelity to the data-set. the regularization parameter therefore makes a trade-off between the two important parameters of sparsity and fidelity to the data-set. the level of this trade-off is improved by increase of the number of data samples �. when � is large enough, the solution to (6) can be both sparse and fitted to the data set. the question is that if � is limited, is it possible to somehow improve the trade-off level? one possible answer is to be “parsimonious” in spending the recourses on minimization of the cost function by “wise” fitting to the data-set; i.e., by using a weighted least-squares fitting to the data-set instead of the simple least-squares. let us temporarily assume that for a specific m ( )m m m− ≤ ≤ , the solution ˆrs to the optimization problem is available for all ( ) .r m m r m≠ − ≤ ≤ inspired by [13], we define the covariance matrix for the m th component of ŝ as: 2 , ˆ m h m r r r r mr m s = ≠− ′ = ∑q a a (10) where r a is defined as: ( )exp 2r rj fπ=a t (11) for any nonzero vector �∈u ℂ we have: 2 , 2 2 , ˆ ˆ 0 h h m m h h r r rm r m r r r r m r mm s s =− =−≠ ≠ ′ = = ≥∑ ∑a a au q u u u u . thus m ′q is nonnegative definite. notice that according to (10), m ′q is the sum of 2m matrices h r r a a each of which of rank 1, and weighted by 2 ˆ . r s since the number of nonzero components of ŝ is 0 ŝ , m ′q is the sum of 0 ŝ or ( ) 0 ˆ 1−s rank 1 matrices (depending on the two different possibilities ˆ 0 m s = and ˆ 0 m s ≠ ). the matrix thus has the following rank: ( ) 0 0 0 0 0 0 ˆ, if 0 and 1 ˆ ˆ1, if 0 and 1 ˆ, if 0 and ˆ ˆ, if 0 and m m m m m � s � s � rnk � s � s � ′ ≠ − ≥  ′− ≠ − < =  ′ = ≥  ′ = < ′ s s s s s s q (12) therefore, it may or may not be of full-rank. specially, since ŝ is expected to be sparse, the 2 nd and 4 th cases of the etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 368-372 370 www.etasr.com zahedi and kahaei: frequency estimation of irregularly sampled data using a sparsity constrained… above relation are likely to happen. the following is a revised definition of the covariance matrix which has full-rank: 2 , ˆ m h m r r r m r m � � r m s ε ε ≠=− + +′= =∑q a qi ia (13) where ε is a small constant and � i is the � �× identity matrix. since m q is nonnegative definite and full-rank, it is positive definite (pd) and of course invertible. the optimization problem (6) is then replaced by the following 1 ℓ regularized weighted least-squares problem: ( ) ( ){ }11argm ,ˆ in , , m h m s m m s m m λ− ∈ = − − + = − y ws q y ws s … c (14) the problem (14) obviously cannot be solved directly, since one has to know its solution to compute m q using (13). b. how to solve it? as was shown in part ii.a, the matrix m q is pd, which means that 1 m − q is also pd. therefore, there is a unique cholesky factor m r for 1 m − q so that [16]: 1 h m m m − = r rq (15) substituting (15) in (14) yields: ( )2 1argmˆ in , , , m mm m s m m ms λ ∈ ′ ′= − + = −y w s s … c (16) where m ′y and m ′w are defined as: m m ′ =y r y (17) m m ′ =w r w (18) problem (16) can be solved using the icd method (7‒9) assuming that ˆ r s is known for all ,r m≠ so that , m q m r and therefore m ′y and m ′w can be computed. to cope with the problem of unavailability of ˆ , r s an iterative scheme can be used: starting from an initial guess (0) (0) (0)ˆ ˆ ˆ , t m m s s− =  s ⋯ at the i th iteration, ( )i m q can be computed using ( ) ( ) ( 1) ( 1) 1 1 ˆ ˆ ˆ ˆ, , , , . i i i i m m m m s s s s − − − − +… … the proposed algorithm is summarized in table i. it is noteworthy that an excellent initial guess to start the iterations is to use the solution of (4). c. computational complexity we compute the complexity order of one iteration of the proposed algorithm summarized in table i. here is the order of computations for the 5 steps of the algorithm: 1. in step 1, computation of h r r a a should be neglected, since it is performed only for one time at the beginning and will table i. proposed algorithm i,put: data-set y, dictionary w, regularization parameter λ, parameter ε , initial guess [ ]( 0 ) ( 0 ) ( 0 )ˆ ˆ ˆ t m m s s − =s ⋯ , number of iterations i. iteratio,s: for 1, 2, ,i i= … do the following: for , , 1, 0,1, ,m m m= − −… … perform the following steps: 1. compute ( )i m q from the following relation: 2 2 ( ) ( 1 1 1 ) ˆ ˆ m m � r m r i h i h m r r r r r m r s s ε − =− = − + += +∑ ∑q a a a a i 2. obtain ( )i m r from the cholesky decomposition of { } 1 ( )i m − q . 3. compute ( ) ( )i i m m ′ =y r y and ( ) ( )i i m m ′ =w r w . 4. compute: 1 ( ) ( ) ( ) ( 1) ( ) , ) , 1 ( ˆ ˆ m m i i i i i m r m r r m r r m i m r m s s − − =− = + ′ ′= −′ −∑ ∑e w wy where ( ) , i m r ′w is the rth column of ( )i m ′w . 5. compute ( ) ˆ i m s using the icd method as: { }( )( ) ( ) ( ),ˆ hi i im m m ms λφ ′= w e not vary during the whole process. also, we define the following matrix: 2( ) ˆ r m m i h r r r s =− = ∑q a a (19) computing ( )i q for only one time, all the matrices ( )i m q for ,...,m m m= − can be computed as: 2( ) ( ) ˆ m m m i i h m s= −q q a a (20) therefore, step 1 includes one single computation of ( )i q of order 2 � m and computation of ( )i m q from (20) for ,...,m m m= − each one of order 2 .� the overall process will be of order 2 .� m 2. this step includes the computation of the inverse of ( )i m q and then the cholesky decomposition (each of order 3 � ) for ,..., .m m m= − the overall computations will be of order 3 .� m 3. the complexity of this step is dominated by the computation of the matrix multiplication ( ) ( )i i m m ′ =w r w which is of order 2 � m for each m. the overall cost is thus 2 2 .� m etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 368-372 371 www.etasr.com zahedi and kahaei: frequency estimation of irregularly sampled data using a sparsity constrained… 4. computational cost of steps 4 and 5 is obviously negligible compared to steps 2 and 3. therefore, the dominant steps are step 2 of order 3 � m and step 3 of order 2 2 � m . since the dictionary is redundant, m is much larger than �, and therefore the overall computational complexity of the proposed method is of order 2 2 � m . complexity of the icd method to solve the bpdn problem (4) is of order �m which implies that the proposed method offers an improved performance in price of higher complexity. iii. simulation results in this section, the proposed method is compared with the bpdn method of [10] formulated in (4). to do so, we consider a signal with the following form: ( ) 1 ( ) cos 2 ( ) l k k k k y t a f t tπ ϕ ν = = + +∑ (21) where k ϕ are i.i.d. random variables in interval [0,2π) with uniform distribution and ( )tν is the additive noise. a data-set containing � samples is then formed by sampling this signal according to an irregular sampling pattern. the two methods are applied to the resulting data-set several times to be able to compare the frequency estimation methods accurately. the simulated signal consists of three sinusoidal terms with frequencies 1, 1.1 and 3 hz with amplitudes of 3, 4 and 1, respectively. the additive noise is assumed to be zero-mean white gaussian with standard deviation of 0.2.σ = the sampling pattern shown in figure 1 follows the poisson distribution with mean 1 1 s −λ = ; i.e. the difference between two adjacent sampling instants follows an exponential distribution with mean 1 s. number of data samples is assumed to be 24.� = the frequency grid f is limited to max 10f± = ± hz, therefore covers the interval of -10 to 10 hz with step-size of 0.05 hz. only 5i = iterations of the proposed algorithm were performed. fig. 1. sampling pattern. the value of the regularization parameter in (4) is selected as: max λ ρλ= (22) where max λ is defined as: max 1 max 2 hλ = w y (23) and ρ is a constant parameter [10]. for 1ρ ≥ the solution to (4) is identically zero [10], therefore ρ is assumed to be less than 1. in practice, 0.05ρ = seems to be a good choice [10]. in simulations, we use 0.05ρ = for both the proposed method and bpdn method. the value of ε is assumed to be 0.001. the result of 20 independent simulations altogether has been shown in figure 2. as can be seen from figure 2(a), the spectrum estimated by bpdn is full of spurious peaks. the amplitudes of many of these spurious peaks are higher than that of the actual peak at 3 hz. figure 2(b) shows that spurious peaks obtained by the proposed method are very rare with very small amplitudes. moreover, the proposed method is less likely to miss the small actual peak at 3 hz. to illustrate this, the area nearby the frequency 3 hz in figure 2 has been zoomed in and shown in figure 3. accurate counting of the number of circles (detected peaks) at 3 hz shows that the number of those peaks with nonzero amplitude in figure 3(a) is 15, while in figure 3(b) is 20. this means that bpdn has missed this peak in 5 experiments, while the proposed method has never missed it. figure 2(b) shows that the amplitude of the spectral peaks suggested by the proposed method is not exact. however, this should not be a serious problem. after the detection of the spectral peaks, their amplitude can be corrected by lest-squares fitting to the data-set y. the result of fitting the 3 spectral peaks detected by the proposed method to y is shown in figure 4. the actual values of the amplitudes are also shown in this figure with cross signs. as seen, the estimate values are very close to the actual ones. fig. 2. result of 20 independent simulations, (a) bpdn, (b) proposed method. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 368-372 372 www.etasr.com zahedi and kahaei: frequency estimation of irregularly sampled data using a sparsity constrained… fig. 3. zooming in the nearby of frequency 3 hz in figure 2, (a) bpdn, (b) proposed method. fig. 4. estimate amplitude of the spectral peaks detected by the proposed method after least-squares fitting to the data-set. the actual values are shown by cross signs. iv. conclusion an iterative sparsity-based method was proposed for the estimation of spectral lines of nonuniformly-sampled signals. the proposed method enforces the sparsity constraint to a weighted least-squares problem. it was shown via computer simulations that it is capable of estimating the spectral lines of the signal provided that a very limited number of data samples taken with arbitrary sampling pattern is available. the proposed method seems to be sensitive to the choice of a parameter named ε . therefore, the selection of an appropriate value for this parameter remains an open problem. 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[16] d. watkins, fundamentals of matrix comutations, john wiley and sons, 2002. engineering, technology & applied science research vol. 7, no. 2, 2017, 1504-1514 1504 www.etasr.com rastbood et al.: finite element based response surface methodology to optimize segmental tunnel… finite element based response surface methodology to optimize segmental tunnel lining armin rastbood school of mining engineering college of engineering, university of tehran tehran, iran arminrastbood88@gmail.com yaghoob gholipour school of civil engineering college of engineering, university of tehran tehran, iran ygholipour@ut.ac.ir abbas majdi school of mining engineering college of engineering, university of tehran tehran, iran amajdi@ut.ac.ir abstract—the main objective of this paper is to optimize the geometrical and engineering characteristics of concrete segments of tunnel lining using finite element (fe) based response surface methodology (rsm). input data for rsm statistical analysis were obtained using fem. in rsm analysis, thickness (t) and elasticity modulus of concrete segments (e), tunnel height (h), horizontal to vertical stress ratio (k) and position of key segment in tunnel lining ring (θ) were considered as input independent variables. maximum values of mises and tresca stresses and tunnel ring displacement (umax) were set as responses. analysis of variance (anova) was carried out to investigate the influence of each input variable on the responses. second-order polynomial equations in terms of influencing input variables were obtained for each response. it was found that elasticity modulus and key segment position variables were not included in yield stresses and ring displacement equations, and only tunnel height and stress ratio variables were included in ring displacement equation. finally optimization analysis of tunnel lining ring was performed. due to absence of elasticity modulus and key segment position variables in equations, their values were kept to average level and other variables were floated in related ranges. response parameters were set to minimum. it was concluded that to obtain optimum values for responses, ring thickness and tunnel height must be near to their maximum and minimum values, respectively and ground state must be similar to hydrostatic conditions. keywords-tunnel; segment; lining; response surface methodology; analysis of variance i. introduction nowadays, most number of the tunnels are excavated using shield tunneling method in soft ground conditions, because this type of tunneling is rapid, cost effectiveness and has minimum effect on surrounding environment. in general, this type of tunneling uses concrete segments as a tunnel support system. assembling concrete segments to each other in one excavation step forms a structure named ring [1, 2]. usually, the number of erected segments in a ring is more than four. successive rings compose a final support system of the tunnel, called lining. one of the segments in a ring is designed usually smaller than the other segments and is called the key segment. this causes the facility both in ring erection and excavation operation in curved alignments. key segment will be installed at the end of ring assembling operation. in figures 1 and 2 some nomenclatures of tunnel lining support system are illustrated. fig. 1. assembled ring in segment manufacturing factory, tabriz metroline 1 fig. 2. tunnel lining structure concrete segments have a complicated process from the design and construction points of view [3]. the final design of concrete segments must provide optimized ring bearing capacity against different types of loads both in ultimate limit state (uls) and serviceability limit state (sls) [4, 5]. in [6], an experimental equation to calculate the reduced effective moment of inertia of a ring with joints was proposed. the proposed equation includes segment number and joint stiffness parameter: 4ni,i.i n 4 ii e 2 je        (1) where ie is effective moment of inertia of jointed ring, ij is moment of inertia in the joints, i is the moment of inertia of a continuous ring without joints and n is the number of segments. engineering, technology & applied science research vol. 7, no. 2, 2017, 1504-1514 1505 www.etasr.com rastbood et al.: finite element based response surface methodology to optimize segmental tunnel… in [7], authors discussed about the main differences in the assumptions for three different models: the continuum ring model, the muir wood design model and the bedded beam model without bedding at the tunnel lining crown region. in [8], authors presented a comparative study between spatial (3d) computing static models and theoretical results of commonly used plain (2d) computing models for segmental tunnel lining. comprehensive methods for determination of structural forces in tunnel lining and segment design were presented in [9]. in [10], authors categorized all tunnel lining design methods into four major types: (a) empirical design methods; (b) experimental and laboratory modelling; (c) circular ring in elastic foundation model; and (d) continuum mechanics models including analytical methods and numerical methods. four most important models of tunnel lining structure by considering ring and segment joints are illustrated in [11]. in [12], authors discussed about the various load types imposed on shield machine and tunnel lining. in [13], authors performed a full scale test on three-rings of segmental lining structure of the shanghai changjiang tunnel with a diameter of 15m. in [14], author conducted a series of tests on small laboratory segmental tunnel lining were made from pvc to obtain their load bearing capacity. in this study authors focused on simple beam support tests to estimate joint stiffness. a comprehensive numerical model using 2d finite difference element model was proposed in [15]. in this paper many factors that influence tunnel lining behavior together with three different types of joint springs, i.e. rotational, axial and radial springs were modeled. some analytical solution are available for segmental tunnel lining design, as those proposed in [7, 16-19]. in [10], authors introduced an analytical equation for moment reduction factor based on the maximum horizontal displacement of a uniform ring. an analytical solution for analyzing tunnel lining in longitudinal direction was proposed in [20]. in [21], authors studied the elastic analysis of a circular lined tunnel by considering the delayed installation of the tunnel support. recently, many publications about numerical modelling of segmental tunnel lining both in 2d and 3d, considering more detailed aspects of shield tunneling were published [15, 22-25]. despite most comprehensive available attempts based on different approaches to analyze segmental tunnel lining in various point of view, there are no considerable publications in this field using statistical methods. in this paper, fem based response surface methodology (rsm) approach was organized to establish statistical equations between tunnel lining characteristics as input variables and generated stresses and displacements in tunnel lining structure as responses parameters using analysis of variance (anova). finally optimization analysis was performed for each response parameter in terms of input variables. ii. numerical modelling in this study, input data for statistical analysis, called experiments from now on, were obtained using the finite element method (abaqus [26]). in all fem models, one ring of tunnel lining support system composed from 5+1 segments. table i shows the engineering and geometrical characteristics of the concrete segments. the behavior of the tunnel lining is assumed to be elastic. in a ring, the shape of the five segments (a2-a6) are similar to each other except for the key segment (a1) which is smaller. in all numerical models, it is assumed that the ring is positioned far away from the tunnel face and is not influenced by shield machine loads and tunneling operation. beam-spring model introduced in [27] was used in numerical modeling. this type of segmental tunnel lining is proposed in several tunneling guidelines [9, 19]. interaction of ground on outer surface of tunnel lining was simulated using tangential and normal springs. stiffness of ground normal springs is evaluated using (2), [28, 29]:   ν1r.a.ek n  (2) where kn is the stiffness of radial spring, e and ν are the elasticity modulus and poison’s ratio of soil respectively, r is the tunnel radius, and a represents the effective area of tunnel lining that is subjected to implied force from the soil, and is calculated using (3): .bra  (3) where θ is radial angle between two successive radial springs applied on lining surface, and b represents effective area of each spring in tunnel longitudinal direction. the stiffness of tangential springs (kt) is assumed to be one-third of the normal spring stiffness (figure 3) [34]. the ring under the impact of interaction springs and surrounding ground load is shown in figures 4a and 4b respectively. 3d solid-stress elements with linear geometric order were used to model concrete segments (figure 5a). plane strain condition was considered in the models. also according to the literature, in transverse direction the segmental lining structure is usually designed in plane strain condition [9, 30-33]. in this study, it is assumed that origin of angle in transverse section of the model is positioned at tunnel crown (figure 5b). longitudinal joints of assembled segments in a ring and key segment position at θ=90° are shown in figure 5c. hard contact was assumed for interaction of six concrete to concrete contact surfaces in segment joints with frictional penalty coefficient of 0.4. fig. 3. constitutive relationship of the springs representing the ground reaction in the bedded-spring model. pn and pt represent the normal and tangential load, δn and δt are the normal and tangential displacement; kn and kt are the normal and tangential stiffness a. input data preparation for statistical rsm analysis the numerical model first was solved for t (concrete segment thickness) =30 cm, tunnel overburden h= 5m, k=0.5 (horizontal to vertical stress ratio), e(lining) =20 gpa and θ=0° engineering, technology & applied science research vol. 7, no. 2, 2017, 1504-1514 1506 www.etasr.com rastbood et al.: finite element based response surface methodology to optimize segmental tunnel… (key position at crown). then t, h, k and e values were kept constant and θ value changed 30°, 60°, 90°, 120°, 150° and 180° respectively. to prepare enough input data for statistical rsm, for each value of input variables, values of other input variables were changed according to the rule presented in table ii. these variables considered as input independent variables in statistical analysis. this table shows times of changes for each input variable and its value. due to the axisymmetric shape of the ring, key positions at 210°, 240°, 270°, 300° and 330° at lining periphery were neglected. finally 252 numerical models were analyzed. table i. engineering and geometrical properties of concrete segments engineering properties geometrical properties segment no. e* ν** ρ *** t **** central angle(°) a1(key segment) 30 a2-a6 20 0.15 2350 30 66 *elasticity modulus (gpa), **poisson ratio, *** density (kg/m3), **** thickness(cm) fig. 4. tunnel lining under ground springs and load: (a) ground radial and tangential springs, (b) surrounding ground load imposed on tunnel lining commonly, tresca and von mises yield criteria are used as failure criteria for materials. according to tresca yield criterion, material begins to yield when maximum absolute value of shear stress reaches to a critical value, and based on von mises yield criterion, material begins to yield when the second deviatoric stress invariant approaches to a critical value. so, due to importance of tresca and mises stresses, these both type of stresses together with ring displacement are considered for prediction analysis. figures 6a, 6b and 6c show extreme values resulted for von mises and tresca stresses, and ring displacements for t=30cm, h=15m, k=0.5, e=20 gpa and θ=0°. these output parameters considered as responses in statistical analysis. fig. 5. assembled ring of concrete segments: (a) meshed model, (b) origin of θ angle, (c) longitudinal joints and key position table ii. different values for input variables different values of 5 input variables t (cm) h(m) k e(gpa) key position(°) 30 40 5 15 25 0.5 1.0 1.5 20 35 0 30 60 90 120 150 180 fig. 6. extreme values and distribution of (a) von mises stresses (n/m2), (b) tresca stresses (n/m2) and (c) ring displacements (m) for t=30cm, h=15m, k=0.5, e=20 gpa and θ=0°. iii. response surface methodology response surface methodology (rsm) is a collection of statistical and mathematical techniques useful for developing, improving, and optimizing processes [35]. in most rsm problems, the form of the relationship between the response and the independent variables is unknown. thus, the first step in rsm is to find a suitable approximation for the true functional relationship between y and the set of independent variables [36]. linear or square polynomial functions are employed to explain the considered problem. if there is (a) (b) (a) (b) (c) engineering, technology & applied science research vol. 7, no. 2, 2017, 1504-1514 1507 www.etasr.com rastbood et al.: finite element based response surface methodology to optimize segmental tunnel… curvature in the system, then a polynomial of higher degree must be used, such as the second-order model in (4):    εxxβxβxββy jiij k 1i 2 iiii k 1i i0 (4) where y is the response, k is the number of variables, β0 is the constant term, βi represents the coefficients of the linear parameters, βii represents the coefficients of the quadratic parameter, βij represents the coefficients of the interaction parameters, xi represents the variables, and ε is the residual associated to the experiments [36]. rsm based statistical methodology is capable of optimizing the responses in terms of input variables. a flow chart of the rsm general procedure is shown in figure 7. quadratic regression equation was applied in rsm to establish equations between five input variables and three responses. in rsm, a series of analysis were conducted by historical data design (hdd) using design expert 10.0.1 (state ease, inc., minneapolis, mn, usa). historical data design enables the researcher to use data from a previous experiment or investigation. any set of numeric or categoric data can be analyzed via historical data design. as explained previously, 252 experiments conducted to provide data for statistical analysis. some sample values of five factors and three responses are shown in table iii. both for input variables and responses, their range, average value, ratio of maximum to minimum value, and standard deviation were as mentioned tables iv and v, respectively. table iii. prepared experiments from finite element modeling factor 1 factor 2 factor 3 factor 4 factor 5 response 1 response 2 response 3 run a:thickness (cm) b:height (m) c:k ratio (---) d:e modulous (gpa) e:theta (degree) misesmax (n/m 2 ) trescamax (n/m 2 ) umax (m) 1 30.00 5.00 0.50 20.00 0.00 3.003e+006 3.269e+006 0.005132 2 30.00 5.00 0.50 20.00 30.00 2.768e+006 3.019e+006 0.005211 3 30.00 5.00 0.50 20.00 60.00 3.099e+006 3.381e+006 0.005242 … … … … … … … … … 252 40.00 25.00 1.50 35.00 180.00 3.222e+007 3.465e+007 0.02388 table iv. input independent variables name units minimum maximum mean standard deviation. segment thickness (a) cm 30.00 40.00 35.00 5.01 height of tunnel (b) m 5.00 25.00 15.00 8.18 k (stress ratio) (c) --0.50 1.50 1.00 0.41 e (elasticity modulous) (d) gpa 20.00 35.00 27.50 7.51 θ (key position) (e) degree 0.00 180.00 90.00 60.12 table v. three responses of rsm analysis response name units analysis minimum maximum mean standard deviation. ratio mises max stress value n/m 2 polynomial 1.977e+006 6.05e+007 1.72815e+007 1.37813e+007 30.6019 tresca max stress value n/m 2 polynomial 2.115e+006 6.896e+007 1.91188e+007 1.55427e+007 32.6052 displacement max value m polynomial 0.004799 0.02973 0.0142558 0.00811969 6.19504 fig. 7. fem based rsm flow chart engineering, technology & applied science research vol. 7, no. 2, 2017, 1504-1514 1508 www.etasr.com rastbood et al.: finite element based response surface methodology to optimize segmental tunnel… a. analysis of variance (anova) the fitted mathematical equation to the data using rsm may not adequately explain the considered experiment. analysis of variance (anova) is a method to assess the reliability of fitted function. the significance of regression can be evaluated by the ratio between the mean of the square of regression (msreg) and the mean of the square of residuals (msres), considering their related degrees of freedom. the higher value of this ratio (f-value) represents that the statistical model is fitted properly to the experimental data. in this study, analysis of variance was used to evaluate the influence of each independent variable and their interactions on responses. statistical parameters of three proposed models for maximum misses stress, maximum tresca stress and maximum ring displacement are illustrated in table vi. the higher the fvalue, the better the significance of the model. “adequate precision” measures the signal to noise ratio. a ratio greater than 4 is desirable. for three responses, actual data against predicted ones are shown in figure 8. the evaluation of the fitted models is performed using the regression coefficient. presented models approximately show satisfactory regression values. also the predicted r-squared is in reasonable agreement with the adjusted r-squared. normal probability plot of the studied residuals for triple responses are illustrated in figure 9. these plots are to check the normality of residuals. table vi. statistical parameters of presented models for three responses statistical parameter maximum misses stress maximum tresca stress maximum ring displacement description f-value* 178.15 173.01 397.62 significant model adequate precision 46.953 46.546 49.470 adequate signal r-squared 0.8135 0.8090 0.8656 predicted r-squared 0.8021 0.7974 0.8597 adjusted r-squared 0.8090 0.8044 0.8634 the predicted r-squared is in reasonable agreement with the adjusted r-squared * there is only a 0.01% chance that an f-value this large could occur due to noise. fig. 8. actual and predicted values for maximum mises stress, maximum tresca stress and maximum ring displacement: (a) maximum mises stress (b) maximum tresca stress (c) maximum ring displacement fig. 9. plot of normal probability versus studentized residuals : (a) maximum mises stress (b) maximum tresca stress (c) maximum ring displacement (a) (b) (c) engineering, technology & applied science research vol. 7, no. 2, 2017, 1504-1514 1509 www.etasr.com rastbood et al.: finite element based response surface methodology to optimize segmental tunnel… if residual points follow a straight line, the normal probability plot indicates that the residuals are normally distributed. the more linear the shape of the normal probability plot, the better the quality of the model. b. second-order polynomial models in analysis of variance, values of "prob > f" less than 0.0500 indicate model terms are significant. for maximum mises stress case, a, b, c, ab, b2, c2 are significant model terms, table vii. values greater than 0.1000 indicate the model terms are not significant. so the included variables in the equation are tunnel lining thickness, tunnel height and k ratio. final equation in terms of actual factors for mises maximum stress is as follows (5): sqrt (misesmax) =7052-37.4*(thickness)+280.2*(height)11977.4*(k ratio)-2.16*(thickness * height)-3.03*(height)2 +6766*(k ratio)2 (5) for maximum tresca stress case, similar to maximum mises stress, a, b, c, ab, b2, c2 are significant model terms, table viii. final equation in terms of actual factors for tresca maximum stress is as follows (6): sqrt (trescamax) =7666.685-43.982*(thickness)+ 300.087*(height)-12816.724*(k ratio)-2.464*(thickness* height)-3.170*(height)2+7232.985*(k ratio)2 (6) for maximum ring displacement case, b, c, bc, c2 are significant model terms, table ix. so the included variables are tunnel height and k ratio. final equation in terms of actual factors for maximum ring displacement is: sqrt (umax) =0.189+4.215e-003*(height)-0.34*(k ratio)2.53e-00*(height * k ratio)+0.206*(k ratio)2 (7) c. response surface analysis of maximum mises stress, tresca stress and tunnel ring displacement the individual and interaction influence of included variables in equations (5) to (7) on responses are shown in figures 10 to 23. it must be noticed that in the analysis of the influence of each variable on the response, other input parameters are kept in their average values. table vii. anova for maximum mises stress analysis of variance table source sum of squares df mean square f value p-value prob > f model 5.157e+008 6 8.596e+007 178.15 < 0.0001 si g n if ic an t athickness 3.070e+007 1 3.070e+007 63.64 < 0.0001 b-height 2.162e+008 1 2.162e+008 448.10 < 0.0001 c-k ratio 1.015e+008 1 1.015e+008 210.33 < 0.0001 ab 1.962e+006 1 1.962e+006 4.07 0.0448 b2 5.169e+006 1 5.169e+006 10.71 0.0012 c2 1.602e+008 1 1.602e+008 332.08 < 0.0001 table viii. anova for maximum tresca stress analysis of variance source sum of squares df mean square f value p-value prob > f model 5.836e+008 6 9.727e+007 173.01 < 0.0001 si g n if ic an t a-thickness 4.128e+007 1 4.128e+007 73.42 < 0.0001 b-height 2.368e+008 1 2.368e+008 421.19 < 0.0001 c-k ratio 1.142e+008 1 1.142e+008 203.20 < 0.0001 ab 2.550e+006 1 2.550e+006 4.54 0.0342 b2 5.630e+006 1 5.630e+006 10.01 0.0018 c2 1.831e+008 1 1.831e+008 325.69 < 0.0001 table ix. anova for maximum lining ring displacement analysis of variance source sum of squares df mean square f value p-value prob > f model 0.26 4 0.065 397.62 < 0.0001 significant b-height 0.048 1 0.048 289.93 < 0.0001 c-k ratio 0.048 1 0.048 291.23 < 0.0001 bc 0.018 1 0.018 108.81 < 0.0001 c2 0.15 1 0.15 900.50 < 0.0001 according to figure 10, as tunnel lining thickness increases in its range, the maximum mises stress decreases slightly. maximum mises stress increases when tunnel height value increases from 5.0 m up to 25 m, figure 11. by increasing k ratio from 0.5 to unity (hydrostatic condition), maximum mises stress decreases, and consequently increases when k ratio increases from unity up to 1.5, figure 12. as can be seen from figure 13, simultaneously increasing both in lining thickness and tunnel height variables cause reduction in maximum mises stress, but tunnel height variable has more influence on maximum mises stress reduction than lining thickness variable. in a constant value of lining thickness, as k stress ratio increases up to unity, the maximum mises stress decreases, and then increase mutually with k ratio. this trend can be seen in all constant values of lining thickness. this effect is shown in figure 14 three dimensionally. analysis of variance showed that regression equations of maximum mises stress and maximum tresca stress, both include the same terms. as illustrated in figures 15-18, lining thickness, tunnel height, k ratio and thickness-height interaction have the same effect on maximum tresca stress as those effect on maximum mises stress. in a constant value of tunnel height, as lining thickness increases from 30 cm up to 40 cm, maximum tresca stress decreases slightly, but the rate of reduction in maximum tresca stress is greater in higher values of tunnel height (figure 19). for maximum displacement of a tunnel lining ring (umax), as tunnel height increases, maximum tunnel lining displacement increases (figure 20). by increasing k ratio from 0.5 to unity (hydrostatic condition), maximum ring displacement decreases and consequently, increase mutually when k ratio increases from unity to 1.5 (figure 21). engineering, technology & applied science research vol. 7, no. 2, 2017, 1504-1514 1510 www.etasr.com rastbood et al.: finite element based response surface methodology to optimize segmental tunnel… fig. 10. the effect of lining thickness on maximum mises thickness fig. 11. the effect of tunnel height on maximum mises stress fig. 12. the effect of k ratio on maximum mises stress fig. 13. the effect of thickness and height interaction in 2d plane on maximum mises stress fig. 14. the effect of thickness and height interaction in 3d space on maximum mises stress fig. 15. the effect of lining thickness on maximum tresca stress engineering, technology & applied science research vol. 7, no. 2, 2017, 1504-1514 1511 www.etasr.com rastbood et al.: finite element based response surface methodology to optimize segmental tunnel… fig. 16. the effect of tunnel height on maximum tresca stress fig. 17. the effect of k ratio on maximum tresca stress fig. 18. the effect of thickness and height interaction in 2d plane on maximum tresca stress fig. 19. the effect of thickness and height interaction in 3d space on maximum tresca stress fig. 20. the effect of tunnel height on maximum lining ring displacement fig. 21. the effect of tunnel height on maximum lining ring displacement engineering, technology & applied science research vol. 7, no. 2, 2017, 1504-1514 1512 www.etasr.com rastbood et al.: finite element based response surface methodology to optimize segmental tunnel… fig. 22. the effect of tunnel height and k ratio interaction in 2d plane on maximum lining ring displacement as it can be seen from figure 22, increasing simultaneously both in tunnel height and k ratio variables increases the maximum ring displacement, but tunnel height variable has more influence to increase the maximum ring displacement than k ratio variable. in all constant values of k ratio, as tunnel height increases, the maximum ring displacement increases slightly. this effect is shown dimensionally in figure 23. fig. 23. the effect of tunnel height and k ratio interaction in 3d space on maximum lining ring displacement d. optimization structural optimization based on fem requires special computational tools. this attempt has become a major part in this field of study, where optimization seems to be a mandatory process in design and economical points of view. optimization using numerical methods needs considerable computational cost and most likely is time consuming based on the complexity of the problem. application of fe based response surface methodology is an alternative solution to reduce computational cost and time of analysis considerably without deficiency in the models. therefore, to obtain an optimum structure for segmental tunnel lining both from geometrical and engineering point of view, at first constraints, goals and importance order of each input and response parameter were set according to table x. since the analysis of variance showed that elasticity modulus and key segment position variables are not involved in response equations, so their values were kept constant in average level during optimization process. domain of other input variables, i.e. tunnel lining thickness, tunnel height and k ratio were set into their ranges. to optimize the tunnel lining structure, response parameters, i.e. maximum mises and tresca stresses and maximum lining ring displacement were set to their minimum values. after optimization process, obtained results are presented in table xi. table x. goals and constraints of variables and responses constraints name goal lower limit upper limit importance a:thickness is in range 30 40 3 b:height is in range 5 25 3 c:k ratio is in range 0.5 1.5 3 d:e modulus average 20 35 3 e:theta average 0 180 3 misesmax minimize 1.977e+006 6.05e+007 3 trescamax minimize 2.115e+006 6.896e+007 3 umax minimize 0.004799 0.02973 5 one hundred solutions were proposed by the statistical analysis. although, desirability index was equal to unity in all proposed solutions, but the best solution is underlined in first row of table xi. plots of ramp display for best solution is shown in figure 24. optimum values of variables and responses are shown. table xi. proposed solutions to optimize tunnel lining characteristics solutions: no. thickness (cm) height (m) k ratio (--) e modulous* (gpa) theta* (°) misesmax (n/m2) trescamax (n/m2) umax (m) desirability index 1 38.595 5. 0.864 27.5 90 1972897.422 2104034.290 0.004 1 2 39.9 5.3 0.88 27.5 90 1960092.90 2069289.145 0.0037 1 3 39. 5.07 0.853 27.5 90 1958046.11 2082296.28 0.0036 1 4 39.7 5.08 0.94 27.5 90 1911454.36 2020534.00 0.0038 1 5 39.7 5.02 0.80 27.5 90 1951520.38 2068656.82 0.0037 1 6 39.5 5.10 0.84 27.5 90 1917118.97 2031757.06 0.0036 1 … … … … … … … … … … 100 34.4 5.0 0.852 27.5 90 2502924.69 2740456.29 0.0036 1 engineering, technology & applied science research vol. 7, no. 2, 2017, 1504-1514 1513 www.etasr.com rastbood et al.: finite element based response surface methodology to optimize segmental tunnel… desirability=1.0 fig. 24. optimized values: red and blue circles represent input variables and responses, respectively. from the optimization process it is concluded that to obtain minimum values for each three response parameters, ring thickness and tunnel height must be near to their maximum and minimum values, respectively and the tunnel lining must be embedded nearly in hydrostatic condition of the ground, i.e. a k ratio of 1. on the other hand, the higher values for tunnel lining thickness together with the lower values for tunnel height simultaneously, will induce both the minimum values for mises and tresca stress values and the displacement of tunnel lining ring in nearly hydrostatic ground conditions. iv. conclusions fem based response surface methodology was applied to prepare prediction models for segmental tunnel lining. quadratic regression equation was applied in rsm to establish equations between five input variables and three responses. obtained models were used to determine the maximum mises and tresca stresses and lining ring displacement generated in one ring of tunnel lining. analysis of variance was used to discuss about the influence of each independent input variable and their interactions on response parameters. for the three responses, the evaluation of the fitted models are performed by the regression coefficient. presented models approximately had acceptable values of regression. the terms in maximum mises and tresca stresse models were the same: concrete segment thickness (t), tunnel overburden (h) and stress ratio (k). the terms in maximum ring displacement model were tunnel overburden (h) and stress ration (k), i.e. concrete segment thickness and elasticity modulus of concrete segments and key position had no considerable effect on maximum ring displacement. it is found that tunnel height variable influenced the responses more than both segment thickness and k ratio variables in stress and displacement models, respectively. in the optimization process, it is concluded that to obtain minimum values for responses, ring thickness and tunnel height must be near to their maximum and minimum values, respectively and the tunnel must be embedded nearly in hydrostatic condition of the ground, i.e. a k ratio of 1. references [1] v. guglielmetti, p. grasso, a. mahtab, s. xu, mechanized tunnelling in urban areas: design methodology and construction control, crc press, 2008 [2] j. b. o'carroll, a guide to planning, constructing, and supervising earth pressure balance tbm tunneling, parsons brinckerhoff, 2005 [3] r. g. a. de waal, steel fibre reinforced tunnel segments-for the application in shield driven tunnel linings, tu delft, delft university of technology, 2000 [4] 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x. w. ge, y. tang, “an analytical solution for a jointed shield-driven tunnel lining”, international journal for numerical and analytical methods in geomechanics, vol. 25, no. 4, pp. 365-390, 2001 [11] y. koyama, “present status and technology of shield tunneling method in japan”, tunnelling and underground space technology, vol. 18, no. 2, pp. 145-159, 2003 [12] f. grübl, m. thewes, “recommendations of the german working group on design and calculation of shield machines”, tunnelling and underground space technology, vol. 21, no. 3, pp. 261-261, 2006 engineering, technology & applied science research vol. 7, no. 2, 2017, 1504-1514 1514 www.etasr.com rastbood et al.: finite element based response surface methodology to optimize segmental tunnel… [13] l. lu, x. lu, p. fan, “full-ring experimental study of the lining structure of shanghai changjiang tunnel”, 4th international conference on earthquake engineering, taipei, taiwan, 2006 [14] s. teachavorasinskun, t. chub-uppakarn, “experimental verification of joint effects on segmental tunnel lining”, electronic journal of geotechnical engineering, vol. 14, pp. 1-8, 2008 [15] n. do, d. dias, p. oreste, i. djeran-maigre, “2d numerical investigation of segmental tunnel lining behavior”, tunnelling and underground space technology, vol. 37, pp. 115-127, 2013 [16] h. morgan, “a contribution to the analysis of stress in a circular tunnel”, geotechnique, vol. 11, no. 1, pp. 37-46, 1961 [17] r. e. ranken, j. ghaboussi, a. hendron jr, analysis of ground-liner interaction for tunnels, department of transportation, office of the secretary , usa, 1978 [18] c. w. schwartz, h. h. einstein, “simplified analysis for groundstructurinet eraction in tunneling”, 21st us symposium on rock mechanics (usrms), american rock mechanics association, 1980 [19] japan society of civil engineers, japanese standard for shield tunnelling, tokyo,japan, jsce, 1996 [20] s. liao, f. peng, s. shen, “analysis of shearing effect on tunnel induced by load transfer along longitudinal direction”, tunnelling and underground space technology, vol. 23, no. 4, pp. 421-430, 2008 [21] c. carranza-torres, b. rysdahl, m. kasim, “on the elastic analysis of a circular lined tunnel considering the delayed installation of the support”, international journal of rock mechanics and mining sciences, vol. 61, pp. 57-85, 2013 [22] n. do, d. dias, p. oreste, “3d numerical investigation of mechanized twin tunnels in soft ground–influence of lagging distance between two tunnel faces”, engineering structures, vol.109, pp. 117-125, 2016 [23] n. do, d. dias, p. oreste, i. djeran-maigre, “behaviour of segmental tunnel linings under seismic loads studied with the hyperstatic reaction method”, soil dynamics and earthquake engineering, vol. 79, part a, pp. 108-117, 2015 [24] n. do, d. dias, p. oreste, “3d numerical investigation on the interaction between mechanized twin tunnels in soft ground”, environmental earth sciences, vol. 73, no. 5, pp. 2101-2113, 2015 [25] n. do, d. dias, p. oreste, i. djeran-maigre, “2d numerical investigation of segmental tunnel lining under seismic loading”, soil dynamics and earthquake engineering, vol. 72, pp. 66-76, 2015 [26] abaqus/cae user's manual, hibbitt, karlsson & sorensen, inc. 2014 [27] h. schulze, h. duddeck, “spannungen in schildvorgetriebenen tunneln”, beton-und stahlbetonbau, vol. 59, no. 8, pp. 169-175, 1964 [28] u. a. c. o. engineering, tunnels and shafts in rock engineer manual, em 1110-2-2901. dept. of the army, corps of engineers, washington, dc, 1997 [29] german committee for underground construction, recommendations for static analysis of shield tunnelling machines. tunnel. 7, pp. 44-58, 2005 [30] k. bakker, “structural design of linings for bored tunnels in soft ground”, heron, vol. 48, no. 1, pp. 33-63, 2003 [31] t. telford, tunnel lining design guide, british tunneling society and the institution of civil engineers. 2004 [32] x. huang, h. huang, j. zhang, “flattening of jointed shield-driven tunnel induced by longitudinal differential settlements”, tunnelling and underground space technology, vol. 31, pp. 20-32, 2012 [33] f. ye, c. gou, h. sun, y. liu, y. xia, z. zhou, “model test study on effective ratio of segment transverse bending rigidity of shield tunnel”, tunnelling and underground space technology, vol. 41, pp. 193-205, 2014 [34] f. barpi, m. barbero, d. peila, “numerical modelling of ground-tunnel support interaction using bedded-beam-spring model with fuzzy parameters”, gospodarka surowcami mineralnymi, vol. 27, pp. 71-87, 2011 [35] r. h. myers, d. c. montgomery, c. m. anderson-cook, response surface methodology: process and product optimization using designed experiments, john wiley & sons, 2016 [36] d. c. montgomery, design and analysis of experiments. john wiley & sons, 2008 microsoft word etasr_v12_n2_pp8467-8472 engineering, technology & applied science research vol. 12, no. 2, 2022, 8467-8472 8467 www.etasr.com hallil & redjem: assessment of urban vulnerability to flooding using multi-criteria analysis assessment of urban vulnerability to flooding using multi-criteria analysis the case study of el bayadh city, algeria abdelkader hallil city, environment, society and sustainable development laboratory department of urban engineering university of m’sila, algeria abdelkader.hallil@univ-msila.dz ali redjem city, environment, society and sustainable development laboratory department of urban engineering university of m’sila, algeria ali.redjem@univ-msila.dz received: 12 february 2022 | revised: 7 march 2022 | accepted: 13 march 2022 abstract-urban vulnerabilities must be studied and assessed to make cities more resilient to floods. this study aimed to assess the urban vulnerability of el bayadh city, located in the west of algeria, to floods and to identify flood-prone areas. using the hierarchical multi-criteria analysis (hma) method, a set of criteria was proposed such as population density, housing typology, type of equipment, and road network to measure the overall fragility of the study area. the geographic information system (gis) was used to translate the obtained results and develop the global vulnerability map. the most important results were: 5.6% of the study area had an extreme vulnerability, 7.97% high vulnerability, 8.5% medium vulnerability, and 77.87% low vulnerability. the results of this study can be used as a tool to assist local authorities during decision-making regarding flood danger assessment. keywords-flood; vulnerability; hierarchical multi-criteria analysis; geographic information system; el bayadh i. introduction over time, the world has confronted various natural disasters [1]. floods are among the most frequent and devastating natural hazards [2] and represent almost a quarter of all disasters due to their unpredictability. floods are caused by a random combination of severe weather factors and human actions [3] and dramatically affect human life, economy, and environment [4]. like other mediterranean countries, algeria is not immune to the risk of flooding due to the irregularity of rainfall, which has caused numerous disasters during the recent years [5]. floods in urban areas constitute a severe risk and have become more frequent and severe along with the rapid and unstoppable urban development [6]. given this situation, the present investigation aimed to assess the urban vulnerability to flooding risk of the city of el bayadh, located in the west of algeria. this area has suffered from numerous floods over time, as it happened in the city center in 2011 causing the death of 12 people and affecting 400 families. its fragility lies in its location, a sloping site, and the crossing by valleys. creating a global map of urban vulnerability to floods is very important in reducing effects since it is an element of development and risk management. according to the conceptual approach to vulnerability proposed in [7], vulnerability encompasses the potential damage of the exposed issues. therefore, the global analysis of vulnerability is a complex method that requires the superposition of numerous information on human, material, and environmental issues. for this reason, particular attention was paid in this study to the vulnerability assessment method. this research followed the hierarchical multi-criteria analysis (hma) method, one of the most famous methodologies for vulnerability assessments [8]. multi-criteria decision-making methods are increasingly used in various fields, such as natural resource management, environmental management, and spatial planning [6-9]. the principle of this approach is the division of a complex problem into small parts in a hierarchical structure of importance. this principle allows calculating the weight of all criteria and sub-criteria to determine the synthetic index of global vulnerability. the integration of the results of the multi-criteria analysis in the geographic information system (gis) allows the spatialization of the issues to elaborate the global map of vulnerability. hence, the combination of hma and gis provides a powerful spatial decision support system [10]. ii. materials and methods a. the study area the municipality of el bayadh is located in the west of algeria between latitude 33°40' north and longitude 01°00' east. according to the data from the communal office of statistics in 2020, the city is an integral part of the high plains region that covers an area of 46,350 hectares occupied by a population of 197,313. the case study represents the urban center of the municipality with an area of 4,024 hectares, as shown in figure 1. b. data collection the assessment of the overall vulnerability of the study area involves assessing the vulnerability of human, environmental, and material targets [11]. the factors used to corresponding author: abdelkader hallil engineering, technology & applied science research vol. 12, no. 2, 2022, 8467-8472 8468 www.etasr.com hallil & redjem: assessment of urban vulnerability to flooding using multi-criteria analysis estimate the vulnerability, according to feedback and data availability, are ranked in terms of their importance. the weight of these criteria was calculated using the hma method. the use of gis enables the spatialization of the elements presented and the production of a synthetic map. fig. 1. el bayadh city location. 1) population density by neighborhood population density is one of the factors that determine social vulnerability. according to the data from the directorate of programming and budgetary monitoring of the wilaya of el bayadh and the municipal statistics office, the urban population of the study area will reach 109,664 inhabitants in 2020. figure 2 illustrates the imbalance in the distribution of the population as the density reaches 299 per hectare in some districts. fig. 2. population density. 2) type of housing the type of housing (individual or collective) plays a role in the overall vulnerability of the city. the master plan of urban planning and development (mpud) shows that individual housing is dominant in the city with 75% of the total housing stock, as seen in figure 3. 3) the equipment the facilities are important components of the city, and their vulnerability to flooding influences the overall vulnerability. el bayadh city has several facilities that occupy approximately 194 hectares, as seen in figure 4. fig. 3. housing typology. fig. 4. type of equipment. 4) road network given the importance of this factor in terms of accessibility and transport, assessing its vulnerability to flooding is essential for the overall assessment. the road network of the city of el bayadh is divided into three sections, primary, secondary, and tertiary, as seen in figure 5. c. methods the assessment of urban vulnerability to flooding risk is a complex process, knowing that global analysis requires a lot of engineering, technology & applied science research vol. 12, no. 2, 2022, 8467-8472 8469 www.etasr.com hallil & redjem: assessment of urban vulnerability to flooding using multi-criteria analysis information on human, material, and environmental issues [11]. investigating the history of flood events and studying the statistics of previous experiences can build a repertoire of vulnerable issues. the hma method [12] was used to assess the global vulnerability of the city of el bayadh and to develop the vulnerability map. hma is a theory of relative measurement of intangible criteria [13]. this method is a framework for effective and rapid decision-making through simplification and the dissociation of the complex problem into parts [14]. the approach is usually based on three main elements: the decomposition of the complex problem into a hierarchy, measuring the priorities between the elements of each section, validating the consistency between the priorities, and the data of the judgments [12]. this method is used in business management or projects and deals with problems related to choices. several researchers have already used it to assess a territory's vulnerability to flooding [14-18]. the multicriteria analysis combined with gis allows the spatializing and mapping of the vulnerable elements, as seen in figure 6. fig. 5. road network. fig. 6. the analysis method followed in this study. 1) hierarchical multicriteria method (hma) hma is a systematic procedure for representing the elements of any problem [20]. this method provides an approach to calculate weights and evaluate criteria. it consists of three main steps: decomposition of the problem, comparison and synthesis of priorities, and the study of the consistency of judgments. a) decomposition of the problem the hma method breaks down the overall problem into smaller assessable criteria while maintaining their impact on the whole. the problem was broken down into three levels: objective, criteria, and possible alternatives [21]. b) the comparison this step involves the construction of a square matrix for the relative comparison of criteria of the same nature and level of the hierarchy. the appropriate numerical scale was proposed in 1980, as seen in table i, to assess the intensity of importance only for the upper part of the matrix, as the lower part contains reciprocal results [22]. table i. the appropriate numerical scale [22] levels of importance explanation 1 two features contribute equally to the objective. 3 personal experience and appreciation slightly favor one aspect over another. 5 experience and appreciation strongly favor one characteristic over another. 7 one characteristic is strongly favored, and its dominance is evidenced in practice 9 the evidence favoring one characteristic over another is as convincing as possible. 2,4,6,8 when a compromise is necessary. the matrix is filled according to the following equation: � � � �� � 1 �1.2 �1. 1/�1.2 1 �2. 1 1/�1. 1/�2. 1 � � (1) c) consistency of judgments to test for consistency and judge whether the data obtained are logically related to each other, thomas saaty proposed the following steps: �� � ��������� (2) where ci is the consistency index, λmax is the largest eigenvalue of the matrix, and n is the number of criteria. in (3), cr is the final consistency rate, cr controls whether the evaluations are sufficiently consistent, and ri is the random consistency index based on the number of criteria used in the matrix (table ii). �� � �� ⁄ �� (3) if cr is higher than 0.1, there is an inconsistency in the assessments. therefore, the matrix will have to be reassessed. engineering, technology & applied science research vol. 12, no. 2, 2022, 8467-8472 8470 www.etasr.com hallil & redjem: assessment of urban vulnerability to flooding using multi-criteria analysis table ii. random consistency indices n 1 2 3 4 5 6 7 8 9 10 ri 0 0 0.58 0.9 1.12 1.24 1.32 1.41 1.45 1.49 2) geographical information system (gis) after obtaining the results on the weight of each criterion by the hma, it was necessary to combine the multi-criteria analysis tools with gis to spatialize the vulnerable areas [23]. gis is an ideal tool because of its ability to manage large amounts of spatial data acquired from different sources [24, 26]. gis provides better results and interpretations in flood management [25]. integrating mcda methods into gis constitutes a powerful spatial decision support system [10]. iii. application, results, and discussion this study was based on the hma method, using sequential prioritization to assess the urban vulnerability of elbayadh to flooding. flood risk criteria were determined by consulting the available documents on the consequences of floods that had already hit the area and discussions with the city's local authorities [27]. the criteria used in the hma process, as in the comparison matrices, were population density (a), housing typology (b), facility typology (c), and road network (d). the damage levels of each criterion recorded in the previous flood events were applied in the saaty importance level when constructing the comparison matrices to be translated into weights. the same comparison and evaluation procedure was applied for the sub-criteria of the same level. table iii. criteria comparison results a b c d weight ranking a 1 2 3 5 0.468 1 b 1/2 1 3 3 0.291 2 c 1/3 1/3 1 5 0.172 3 d 1/5 1/3 1/5 1 0.067 4 table iv. results of consistency check on evaluations n λmax ci ri cr coherence 4 4.21 0.07 0.9 0.08 cr<0.1 table v. results of hma assessments of the sub-criteria criteria sub-criteria weight ranking density 0-27 00523 5 28-88 0.089 4 89-134 0.152 3 135-220 0.262 2 221-299 0.443 1 housing typology individual 0.75 1 collective 0.25 2 type of equipment security 0.205 2 education 0.176 3 health 0.261 1 administrative/service 0.168 4 commercial 0.037 7 religious 0.071 6 sport/cultural 0.081 5 road network main 0.637 1 secondary 0.258 2 tertiary 0.105 3 based on the results of the multi-criteria analysis, the weights of the criteria were aggregated into gis software qgis. using raster calculation practices, each raster was multiplied by the criteria weights according to (4) to produce the global urban vulnerability map shown in figure 7. global urban vulnerability � 0.468 , a . 0.291 , b .0.172 , c . 0.067 , d (4) fig. 7. global urban vulnerability map. table vi shows a numerical interpretation of the global vulnerability map. the surface area of the low vulnerability zones was estimated at 77.87% with a surface area of 3133ha, the medium vulnerability zones were estimated at 8.56% with a surface area of 344.27ha, the high vulnerability zones were estimated at 7.97% with a surface area of 320.60ha, and the remaining 5.6% represents the extreme vulnerability zones with a total surface area of 225.46ha. table vi. hma assessments of global vulnerability results degree of vulnerability area (ha) percentage (%) low vulnerability 3313.42 77.87 medium vulnerability 344.27 8.56 high vulnerability 320.60 7.97 extreme vulnerability 225.46 5.6 as shown in figure 7, the areas of high and extreme vulnerability are located in the city center, where the population density is very high, require adequate planning, and local authorities should investigate optimal solutions. iv. conclusions this study evaluated the urban vulnerability to flooding risks in el bayadh, algeria, using the hma method, which is based on the division of a complex problem into parts. for this purpose, the previous flood events were examined to bring out the criteria and sub-criteria of the same level that impact global vulnerability. the criteria obtained by consulting the engineering, technology & applied science research vol. 12, no. 2, 2022, 8467-8472 8471 www.etasr.com hallil & redjem: assessment of urban vulnerability to flooding using multi-criteria analysis documentation on the history of flooding in the study area and used in the hma process were: population density, typology of existing housing, classification of installed equipment, and road network. in the second stage, the importance of these criteria and sub-criteria was compared with the grading scale proposed by thomas saaty. the consistency of the evaluations was examined by constructing a binary matrix, and was 0.08, less than 0.1, so it was acceptable. after the prioritization and determination of the weights of each criterion and subcriterion, the results of hma were integrated into a gis tool to spatialize the exposed issues and map the vulnerable areas. based on the results and interpretations obtained through this evaluation, the following conclusions were drawn: • the development of a global flood risk vulnerability assessment model requires integrating a lot of detailed information on human, material, and environmental issues. • this research confirms that hma is a flexible and optimal process for evaluating the various factors and ranking them according to their importance. • the integration of gis tools allows the spatialization of vulnerable issues and the mapping of global vulnerability. • the final results of the general assessment show that the areas of high and extreme vulnerability are located in the city center, where there is a high population density, and represent a 13.57% rate with a surface area of 546ha. in comparison, lowand medium-vulnerability areas represent 86.3% of the study area with a surface of 3,658ha. the local authorities of el bayadh city should take appropriate preventive measures to reduce the risk of flooding by restructuring the most vulnerable areas. the originality of the analysis and assessment method was based on the use of a model appropriate to the context of el bayadh and the criteria used in the hma method. furthermore, more studies should be conducted in the future using other criteria that could reduce the risk of flooding. references [1] n. gendreau and g. oberlin, "modélisation de synthèse des crues : modèles hydrologiques en 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[27] n. harkat, s. chaouche, and m. bencherif, "flood hazard spatialization applied to the city of batna: a methodological approach," engineering, technology & applied science research, vol. 10, no. 3, pp. 5748–5758, jun. 2020, https://doi.org/10.48084/etasr. 3429. microsoft word etasr_v12_n1_pp8204-8209 engineering, technology & applied science research vol. 12, no. 1, 2022, 8204-8209 8204 www.etasr.com tuyet et al.: improving the curvelet saliency with deep convolutional neural networks for diabetic … improving the curvelet saliency and deep convolutional neural networks for diabetic retinopathy classification in fundus images vo thi hong tuyet department of information systems faculty of computer science and engineering ho chi minh city university of technology (hcmut) vietnam national university-ho chi minh city ho chi minh city, vietnam vthtuyet.sdh19@hcmut.edu.vn nguyen thanh binh department of information systems faculty of computer science and engineering ho chi minh city university of technology (hcmut) vietnam national university-ho chi minh city ho chi minh city, vietnam ntbinh@hcmut.edu.vn dang thanh tin information systems engineering laboratory faculty of electrical and electronics engineering ho chi minh city university of technology (hcmut) vietnam national university-ho chi minh city ho chi minh city, vietnam dttin@hcmut.edu.vn abstract-retinal vessel images give a wide range of the abnormal pixels of patients. therefore, classifying the diseases depending on fundus images is a popular approach. this paper proposes a new method to classify diabetic retinopathy in retinal blood vessel images based on curvelet saliency for segmentation. our approach includes three periods: pre-processing of the quality of input images, calculating the saliency map based on curvelet coefficients, and classifying vgg16. to evaluate the results of the proposed method stare and hrf datasets are used for testing with the jaccard index. the accuracy of the proposed method is about 98.42% and 97.96% with stare and hrf datasets respectively. keywords-saliency; vgg16; classification; diabetic retinopathy; retinal blood vessel i. introduction diabetes is a condition that occurs when the pancreas does not produce enough insulin or when the body loses its ability to metabolize insulin. manifestations of diabetic retinopathy include microaneurysms, intraretinal hemorrhage, hard exudates, macular edema, macular ischemia, neovascularization, vitreous hemorrhage, and traction retinal detachment. the fundus complication of diabetes is called diabetic retinopathy, which damages the small blood vessels in the retina. the retina is the light-sensitive area of the eyeball, where nerve cells receive images and send them to the brain for processing. the macula is most important for the most delicate images. diabetic retinopathy is the leading cause of vision loss or blindness in developed countries. therefore, the identification of diabetic retinopathy through retinal images is very important. recent advances in computer science, focused on machine learning to detect data patterns, can provide solutions for diabetic retinopathy disease detection through retinal imaging. the detection of bright lesions in the retinal blood vessels is hard work, but can help doctors in diagnosis and treatment. retinopathy is widely researched [1-5] and many different methods such as image saliency analysis [6, 7], machine learning techniques [8-10], wavelet and support vector machine [11], segmentation [12, 13], morphology [27], etc., are used. authors in [10] proposed a method to identify diabetes from retinal images using the dianet model with a multi-stage convolutional neural network (cnn). authors in [14] proposed a method for the detection of fundus image lesions by using a cnn to search with the shuffled frog leaping algorithm. authors in [15] used the discrete image clustering technique to separate the image foreground and background of the input image in order to classify the lesion results. authors in [16] proposed a method to segment premature infant retinal images to achieve an extracted retinal image with a map of blood vessels. authors in [17] suggested a contour detection method. they computed the image gradient value by applying type2 fuzzy rules to detect edges. authors in [18] used a cnn model to design a learning method for grading fundus images. however, the system was validated on a small dataset. authors in [19] proposed a method for diabetic retinopathy detection based on u-net and resnet-18. in their experiments, they assessed two segmentation images. this method gives corresponding author: nguyen thanh binh engineering, technology & applied science research vol. 12, no. 1, 2022, 8204-8209 8205 www.etasr.com tuyet et al.: improving the curvelet saliency with deep convolutional neural networks for diabetic … results with accuracy, but its complexity is high. authors in [20] proposed a method for retina image recognition. this method includes two phases: finding features for healthy retinal image recognition and using vascular and lesion-based features for diabetic retinopathy retinal image recognition. their experimental results were 100%, 96.67% and 97.78% for the considered databases. this paper proposes a method for diabetic retinopathy classification based on the improvement of the second general wavelet transform with the vgg-16 cnn. to evaluate the results of the proposed method and compare them with the results of other known methods, two (stare and hrf) open datasets were used for testing and the evaluation criterion of jaccard index (ji) was utilized. the accuracy of the proposed method is about 98.42% and 97.96% for stare and hrf datasets respectively. the main contributions of this study are: • the proposal of the deep vgg16 to classify diabetic retinopathy in fundus images. • increased accuracy of classification by curvelet saliency combined with vgg16. ii. classifying diabetic retinopathy with curvelet saliency and vgg16 the quality of retinal blood vessel images is affected by a wide range of reasons such as: noise, motion which creates blur images, and overlapping. the diabetic classification based on feature extraction is a popular state-of-the-art approach. this section presents the proposed method for diabetic retinopathy classification with curvelet saliency and vgg16 which is shown in figure 1. fig. 1. the proposed method for diabetes classification. the proposed method can be divided into 3 stages which depend on the characteristics of each step: pre-processing, curvelet saliency, and classification. the input data are the retinal blood vessel images of the system. green is the color channel chosen to be processed. the clahe redistributes the lightness values of the objects. the top-hat transform for mask making creates the morphology for the next stages. the 3 above steps are the preprocessing of the proposed method. the aim of preprocessing is to enhance the quality of the blood vessels in fundus images. secondly, the curvelet coefficients are calculated based on the curvelet transform with db4 in the decomposition steps. this value is applied in each level of the top-hat transform to form the threshold for saliency levels. the output is the curvelet saliency map for the final periods. finally, the vgg16 model classifies the images as diabetic or not. a. improving the features of retinal blood vessel images the aim of this step is to improve the features of fundus images. the thickness of blood vessels varies from 1 to 5 pixels. enhancing quality starts from the similar color and the approximation of the surrounding pixels. the color of fundus images includes three color channels, i.e. red-green-blue. among them, red is the saturated channel, green is the lighting, and blue is the contrast of vessels with the background. in our method, the green color is chosen because of the necessary lighting in blood detection. then, clahe is performed with the following steps: • not overlapping contextual areas and preserving 8×8 pixel blocks. • calculating the average number of pixels for preparing the division as in (1): ���� � ���� �� �/�� �� (1) where ���� is the average number of pixels, �� �� represents the gray levels of the divided areas, nrx and nry are the number of pixels for the xand y-dimension respectively. • from the average number of pixels, their product with the clipped pixels can be created with the i-th gray level. these values are the histogram of the clipped pixels. then, the conditions for histogram level setup are compared to the average to keep the better value. • applying the condition and probability density as in (2): ������� � ������ ������� ����� ������ ������ �� ! (2) where " = 0.04 is the scaling parameter of rayleigh distribution, y(i) is the rayleigh forward transform, and ymin is the lower bound of the pixel value. • updating the artifacts with the average histogram and probability density. • the final step in pre-processing is the top-hat transform. this transform creates the mask making and the subtraction process. the proposed method is divided into 2 levels (high and low) based on the number of distances between the gray levels of these pixels and the average histogram in the clahe step. the output of this step is the high-level and low-level curvelet coefficients. engineering, technology & applied science research vol. 12, no. 1, 2022, 8204-8209 8206 www.etasr.com tuyet et al.: improving the curvelet saliency with deep convolutional neural networks for diabetic … b. curvelet coefficients for choosing the saliency map the input of this step is the high and low level of the previous step. in each level, this approach uses the stages as in figure 2. the decomposition is done with db4 for division and subband creation. fig. 2. the curvelet coefficients for choosing saliency. the subband wj with a block size bj. in each level of fundus images f is noted as ∆�. an appropriate scale of sidelength ~2-s and q w is a collection of smooth windows localized around dyadic squares of fundus images as in (3): 1 1 2 2 [ /2 ,( 1) / 2 ] [ /2 ,( 1) / 2 ] s s s s q k k k k= + × + (3) then, the curvelet coefficients are calculated as follows: • renormalizing in each unit scale. • analyzing via the discrete ridgelet transform in each unit scale. • update the subbands of blocks based on the double value if their number is odd. however, if the block's number is even, the updates do not work. • in reversion, the curvelet domain with coefficients k depends on the number of scales in the list of subbands. the saliency level r(x) at pixel x is presented with level k. the curvelet saliency for final saliency prediction will be done with the algorithm described below: input: r(x) and k output: the saliency prediction function cal_curvletsaliency(r(x), k) the superpixel centers s = the average pixel i in grid while iteration t from 1 to v do: the association between pixel p and superpixel i is: ℚ%&' � e�)*+�,./0)� superpixel centers = ∑association in k end while return distance(pixel x with superpixel centers) end function the final output of this period is the saliency map of the areas of blood vessels in fundus images. the curvelet coefficient k is the condition for the association of superpixel centers in a map. c. vgg16 in the curvelet saliency map for diabetes classification the stage after the feature extraction of image segmentation from curvelet saliency is the classification by vgg16 with the architecture shown in figure 3. fig. 3. applying vgg16 for feature extraction in the curvelet saliency map. in this architecture, each level of the curvelet saliency will be submitted to the following procedures: • block 1: 2 convolution + 1 pooling • block 2: 2 convolution + 1 pooling • block 3: 3 convolution + 1 pooling • block 4: 3 convolution + 1 pooling • block 5: 3 convolution + 1 pooling • block 6: dense with 3 fully connected + relu • softmax at the end. at first, each input image is downsized with a 3×3 channel. the channel of the second block is 64×64 and the size is doubled for the below blocks. therefore, the channels of block 3, 4 and 5 are 128×128, 256×256, and 512×512. the padding is 2 pixels for 3×3 convolution layers. this size is the smallest size for the notion of left/right, up/down, and center. the stride of the convolution layer is also 2 pixels with the above padding. then, the pooling layer (max pooling) has a window size of 2×2 pixels and the stride has also 2 pixels. in block 6, the first and second fully connected layers have 1×1×4096 channels. however, the final fully connected layer is 1×1×1000 channels. the softmax (ranging from 0 to 1) gives the final classification as diabetes or non-diabetes in each level of the curvelet saliency. the differences between vgg16 in this paper with the traditional vgg16 are the stride and the multimodel applied in each level of the curvelet saliency. the synthesis of the multi-model (multi-results of softmax) is the max value. engineering, technology & applied science research vol. 12, no. 1, 2022, 8204-8209 8207 www.etasr.com tuyet et al.: improving the curvelet saliency with deep convolutional neural networks for diabetic … iii. experimentation and evaluation results a. datasets used the proposed method is actualized in the stare [21] and hrf (high-resolution fundus) [22] datasets. these datasets contain images of normal or diseased retinal blood vessels. these 2 datasets are public and free to be used in research and academic tasks. during the experiments 70% of the stare dataset was used for training and 30% for testing. the hrf dataset was used for testing (100%). the stare dataset [21] consists of 402 images (91 diabetes and 311 non-diabetes). their size is 605×700 pixels with 24 bits per pixel (standard rgb). in this dataset, a wide range of diseases are diagnosed based on retinal blood vessels. in this paper, the focused disease is diabetic retinopathy. the hrf dataset [22] includes 45 images (15 diabetes images of glaucomatous patients and 30 non-diabetes). the language used to develop the proposed method is python 3.9 and the configuration of the system is: 2.7ghz quad-core intel i7 processor and 16gb 2133mhz lpddr3 ram. b. evaluation metric and experimental results the main idea of the proposed method is based on the segmentation with curvelet saliency. therefore, the evaluation applies to the ji value. if a is the image segmentation and b is the ground truth image, the ji(a, b) is calculated by (4). the higher the ji value is, the better. ji�a,b� � |?∩a||?∪a| (4) to define the curvelet coefficients that adapt with the salient map more than others, table i shows the comparison of saliency segmentation by superpixels and other coefficients. it can be seen that the proposed curvelet coefficients give segmentation results near the ground truth of the retinal blood vessels in the hrf dataset. table ii exhibits the comparison results between the proposed method and matched filtering and fuzzy c-means clustering with integrated level set [23] and fully convolutional deep learning [24]. we can see that the average ji of the proposed method is better than the others. this experiment is practiced in hrf with 45 images for evaluation. the ground truth of each fundus image is given clearly in the dataset. therefore, the ji values are easy to compare. figure 4 presents some segmentation results of curvelet saliency in the hrf dataset and compares the proposed method with [23] and [24]. table i. average ji for saliency segmentation based on other coefficients method average ji saliency based on superpixels 85.1 saliency based on gaussian filter 90.42 saliency based on contourlet coefficients 91.37 proposed method (saliency based on curvelet coefficients) 98.25 fundus image from hrf dataset result of [23] result of [24] result of the proposed method ground truth diabetes image diabetes image non-diabetes image non-diabetes image ji = 91.7 ji = 90.55 ji = 92.72 ji = 93.7 ji = 95.34 ji = 95.84 ji = 94.15 ji = 96.81 ji = 98.62 ji = 98.37 ji = 97.89 ji = 99.04 fig. 4. segmentation result comparison in the hrf dataset. engineering, technology & applied science research vol. 12, no. 1, 2022, 8204-8209 8208 www.etasr.com tuyet et al.: improving the curvelet saliency with deep convolutional neural networks for diabetic … table ii. average ji of the proposed method and of other segmentation methods method average ji [23] 92.03 [24] 96.13 proposed 98.25 from tables i-ii and figure 4, the curvelet saliency adapts with segmentation in diabetic diseases. the next evaluation is the input of curvelet saliency for other deep learning models for diabetis classification. figure 5 shows the comparison chart of the results. in figure 5, we can see that vgg16 performs better than the other methods known, in terms of classification accuracy for classifying diabetic retinopathy in curvelet coefficients. the comparison was carried out between the proposed method with cnn, fully convolutional network (fcn), and u-net with vgg16. in the two datasets, the accuracy of vgg16 is higher for classifying diabetic retinopathy. table iii shows the classification results of vgg16 in detecting diabetes and non-diabetes images using deep cnn vgg-16 and googlenet [25], resnet50 and vgg-16 pretrained networks [26], and vgg16 in curvelet saliency. fig. 5. classification results of diabetic retinopathy of deep learning models based on curvelet saliency. table iii. diabetic retinopathy classification results results of vgg16 comparison dataset deep cnn vgg-16 and googlenet for diabetic retinopathy detection [25] diabetic retinopathy classification using resnet50 and vgg-16 pretrained networks [26] vgg16 in curvelet saliency stare 94.36 96.01 98.42 hrf 94.1 95.74 97.96 the curvelet coefficients are the main reason for the better results because they enhance the quality and divide the saliency levels. the curves adapt with the curvelet transform. these values make a condition for choosing saliency maps. therefore, the segmentation of fundus images is better. on the other hand, the multi-level curvelet coefficient for saliency consists of continuing the input of vgg16 with changing the stride and synthesis of multi-model vgg16. as a result, the classifying results are improved. the authors in the other works applied deep learning for classification based on the number of layers or by improving the parameters of the dataset. however, the input parameters are not easy to enhance. if we only focus on information on the surface, it is not enough. the proposed method offers multi-level processing with curvelet coefficients for salient map. the levels of fundus image quality are shown clearly. the deep vgg16 in each saliency level calculates a value for disease classification. iv. conclusion and future work diabetes can reduce the red blood cell rate, increase the ability of platelets to agglomerate, and increase blood viscosity. as a result, the capillaries become clogged, causing retinal ischemia. diagnosis in medicine is a vital task. any disease prediction or classification system must adapt to the medical images. the retinal vessel images give a wide range of abnormal pixels. therefore, classifying the diseases from fundus images is a popular research topic. this paper proposes a new method for classifying the diabetic retinopathy in retinal blood vessel images based on curvelet saliency for segmentation. our approach includes 3 steps: pre-processing of the input images, calculating the saliency map based on curvelet coefficients, and utilizing vgg16 for classification. the choice of the green color channel combined with enhancement and 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[27] s. xefteris, k. tserpes, and t. varvarigou, "a method for improving renogram production and detection of renal pelvis using mathematical morphology on scintigraphic images," engineering, technology & applied science research, vol. 2, no. 4, pp. 251–258, aug. 2012, https://doi.org/10.48084/etasr.206. microsoft word 5-777-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1133-1138 1133 www.etasr.com demirdelen et al.: a modular cascaded multilevel inverter based shunt hybrid active power filter… a modular cascaded multilevel inverter based shunt hybrid active power filter for selective harmonic and reactive power compensation under distorted/unbalanced grid voltage conditions t. demirdelen cukurova university, department of electrical and electronics engineering, balcali, adana, turkey tdemirdelen@cu.edu.tr r. i. kayaalp cukurova university, department of electrical and electronics engineering, balcali, adana, turkey ikayaalp@cu.edu.tr m. tumay cukurova university, department of electrical and electronics engineering, balcali, adana, turkey mtumay@cu.edu.tr abstract—in recent years, shunt hybrid active power filters are being increasingly considered as a viable alternative to both passive filters and active power filters for compensating harmonics. in literature, their applications are restricted to balanced systems and low voltage applications and therefore not for industrial applications. this paper investigates the performance of a modular cascaded multilevel inverter based shunt hybrid active power filter (shapf) for reactive power compensation and selective harmonics elimination under distorted/unbalanced grid voltage conditions in medium voltage levels. in the proposed control method, reactive power compensation is achieved successfully with a perceptible amount and the performance results of harmonic compensation are satisfactory. theoretical analysis and simulation results are obtained from an actual industrial network model in pscad. the simulation results are presented for a proposed system in order to demonstrate that the harmonic compensation performance meets the ieee-519 standard. keywords-harmonic compensation; medium voltage applications; modular cascaded multilevel inverter; reactive power compensation; shunt hybrid active power filter i. introduction in recent years, high power equipment has been employed in industrial applications due to the megawatt power level for many medium voltage applications. due to this condition, multilevel power converters are to be used as an alternative solution in medium and high voltage applications. multilevel converters have the ability to increase the output voltage without raising the voltage rating of switching components. thus, they are preferred to connect to medium voltage grids without using transformers. among the various multilevel converters topologies, cascaded inverters consist of several converters connected in series. thus, the high power and/or high voltage from the combination of the multiple modules would favor this topology in medium and high voltage applications. the modular multilevel inverter has been used as an alternative choice to conventional multilevel inverters. it has been designed to mitigate the drawbacks of conventional multilevel inverters such as the difficulty of balancing the capacitor voltage on higher order levels, the need for an output filter and interfacing transformer. also conventional multilevel inverters are not capable of fault management and fault ride through. the modular cascaded h-bridge multilevel inverter is one of the cascaded inverter topologies. the output multilevel voltage waveforms enable the reduction of harmonics in the synthesized current, reducing the size of the needed output filters. the cascaded multilevel inverter also has other advantages such as reduced voltage stresses on the semiconductor switches, as well as having higher efficiency when compared to other converter topologies [1]. using identical power cells leads to a modular structure, which is an effective means for cost reduction. the aforementioned reasons caused to compose the modular cascaded multilevel inverter based shapf investigated in this paper. the increase of nonlinear loads causes several power quality problems in power systems. the grid voltage and currents become non sinusoidal due to these types of loads. the traditional yet ineffective solution to reduce current harmonic distortion is passive filters. active power filters have become a new research emphasis on power electronics technology as a new and improved solution to the problem. hybrid active power filters effectively smooth the problems of passive filters and an active power filter solution may ensure a cost effective harmonic compensation. several hybrid apf (hapf) topologies are introduced in [2-10, 13] for reactive power and harmonic current filtering. the most common topologies are shunt hapf (shapf) [4-12] consisting of an apf and a passive filter connected in series with each other and series hapf [3] which is a combined system of the shunt passive filter and a series apf. an extensive overview of the topological structures is given in [2, engineering, technology & applied science research vol. 6, no. 5, 2016, 1133-1138 1134 www.etasr.com demirdelen et al.: a modular cascaded multilevel inverter based shunt hybrid active power filter… 13]. most articles describe research focused on low voltage levels. on the contrary, multilevel shapf (m-shapf) [6-7, 11-12] is the most often used in medium voltage levels in industrial applications. the controller design is the most important part due to its impact on the performance and stability of the overall system. for this reason, numerous control methods such as pq theory [4], dq theory [5-7, 12], fuzzy controller [8] etc… have been applied for the harmonic compensation in the literature. in literature, shunt hybrid active power filters [2-5, 8-10] are restricted to balanced systems and low voltage applications and thus cannot be employed for industrial applications. on account of the limitations between existing literatures, the purpose of this paper is the following: 1. to investigate the performance of the modular cascaded multilevel inverter based shunt hybrid active power filter for reactive power compensation and selective harmonics elimination under distorted/unbalanced grid voltage conditions. 2. to investigate the application of this control method in medium voltage levels. 3. to perform theoretical analysis and simulation results for an actual industrial network model in pscad. 4. to check the compliance of the results with the ieee519 standard. 5. to apply dynamic load changes and observe the system response. ii. proposed system and controller figure 1 shows the detailed circuit configuration of the proposed system. as shown, a modular cascaded multilevel inverter unit is connected to the grid through a lc filter tuned on the vicinity of the 5th harmonic. as shown in figure 2, the controller of the proposed system consists of six main parts: phase lock loop, harmonic reference generation, reactive current reference generation, selective harmonic reference generation, dc link voltage controller and final reference compensation currentpwm control block. a. differential phase lock loop the phase angle (θ) of the supply voltage is required which affects the performance of the control method. hence, an accurate phase tracking system is the key point of the control method to transform the measured current vectors into synchronously rotating d-q reference frame. thus, dif-pll is selected for extracting the phase angle (θ) [14] shown in figure 2 (a). b. harmonic reference generation the first step of harmonic current control is to isolate the harmonic components from the fundamental component of the grid currents. this is achieved through the dq transformation (2), synchronized with the pcc voltage vector, and a first order low pass filter (lpf) with cut off frequency of 10 hz. then the dq inverse transformation (4) produces the harmonic currents in the abc referential frame shown in figure 2 (b). the conversion matrix is: )1( 2 2 2 2 2 2 ) 3 2sin() 3 2sin(sin ) 3 2cos() 3 2cos(cos 3 2123                      ppp ppp dqt )2(123                      sc sb sa dq o q d i i i t i i i and the inverse conversion matrix is: )3( 2 2 ) 3 2sin() 3 2cos( 2 2 ) 3 2sin() 3 2cos( 2 2 sincos 3 2 123                          pp pp pp dqt )4( _ _ _ 123 __ __ __                      lpfo lpfq lpfd dq refharmonicc refharmonicb refharmonica i i i t i i i c. reactive current reference generation the reference current provided the essential reactive power is produced. in order to achieve the reactive power compensation of m-shapf, the reference current having 90o phase difference among the pcc point should be produced. to produce this reference current, the output voltage of m-shapf inverter should be generated in the phase with pcc voltage vector. the block diagram of reactive power control is shown in figure 2(c). )5(123                      sc sb sa dq o q d i i i t i i i )6( 0 0 _ 123 __ __ __                      fundq dq refreactivec refreactiveb refreactivea i t i i i for the realization of the reactive power compensation, the reference currents should be calculated. the reference currents are generated by the dq method. the first step is to isolate the fundamental components from the harmonic components of the grid currents. this is achieved through the dq transformation (5). the quadrature component of the source current which is taken from dq transformation is directly passed through the lpf. thus, the 50 hz component of the source current is generated. then this signal is applied to reproduce the reactive power compensation current by inversing the dq transformation (6). however, this reference current is in a quadrature axis. to achieve the reactive power compensation by the voltage controlled voltage source m-shapf, the reference current must be in the phase with the source voltage. thus, the reference current is transformed by using only the ˈdˈcomponent of the inverse dq transformation. engineering, technology & applied science research vol. 6, no. 5, 2016, 1133-1138 1135 www.etasr.com demirdelen et al.: a modular cascaded multilevel inverter based shunt hybrid active power filter… d. selective harmonic reference current generation selective harmonic elimination technique is generally based on the ideas of opposite harmonic injection (3rd, 5th, 7th, 9th,11th and 13th order) and it’s given to three phase voltage source inverter switches. in this paper, the passive filter part of the system is tuned on the 5th harmonic frequency. in addition, shapf compensates harmonics. however, 7th, 9th, 11th and 13th harmonics are still in the system with small amount. thus, fft methods is used for eliminating this harmonics. figure 2(d) represents the fft based selective harmonic elimination. firstly, 7th, 9th, 11th and 13th order harmonics are extracted by fft. then, three phase selective harmonic reference current is generated by using “sine” operator. fig. 1. proposed system e. dc link voltage controller * dcv is the dc link reference value for both harmonic and reactive power compensation selected 1.5 kv. by using the error signal generated by the conventional pi controller, the dq inverse transformation (7) produces the reference dc link control signals in the abc referential frame shown in figure 2 (e). a limiter is also applied to avoid the overflow problem of the controller. dc link is controlled by the reactive component of the error signal. thus, only the q component is used for dq inverse transformation. )7( 0 0 123 _ _ _                      errror dq cappic bcappi acappi vt v v v f. multilevel inverter control , final reference compensation current and pwm control block in this proposed system a seven level modular cascaded multilevel inverter is used. cascaded multilevel inverters include series h bridge inverters. cascaded inverters have structurally no problem of dc-link voltage unbalancing. thus, the cascaded inverter has been widely studied and used in fields of static var compensators (svcs), power line conditioners, voltage stabilizers and hybrid active power filters. to compare with the diode clamped or capacitor clamped inverter, the cascaded inverter does not need any voltage clamping diodes or voltage balancing capacitors. table i shows the switch combination of seven level cascaded multilevel inverter. table i. switch combination of seven level cascaded multilevel inverter for each phase switch state voltage vao s1 s2 s3 s4 s5 s6 s7 s8 s9 s10 s11 s12 3vdc 1 0 0 1 1 0 0 1 1 0 0 1 2vdc 1 0 0 1 1 0 0 1 0 0 1 1 vdc 1 0 0 1 0 0 1 1 0 0 1 1 0 0 0 1 1 0 0 1 1 0 0 1 1 -vdc 0 0 1 1 0 0 1 1 0 1 1 0 -2vdc 0 0 1 1 0 1 1 0 0 1 1 0 -3vdc 0 1 1 0 0 1 1 0 0 1 1 0 the final reference current consists of three phase harmonic reference current signals, three phase selective harmonic reference current signals, three phase reactive reference current signals and dc link control signals. the reference signal (in_harmonic_ref + in_fft_k_ref + in_reactive_ref + vcappi_n) is generated using these signals together. then, the reference signals are compared with carrier signals to generate switching signals shown in in figure 2(f). iii. simulation results the simulation studies are carried out using pscad/emtdc (three runs), aiming to evaluate the effectiveness and correctness of the control strategy used in the shapf under unbalanced/distorted grid voltage. the simulation parameters are given in table ii. the passive filters are tuned at 5th and the control signals of igbts are generated through the pulse width modulation generator whose amplitude and frequency of carrier wave are  1 and 10 khz, engineering, technology & applied science research vol. 6, no. 5, 2016, 1133-1138 1136 www.etasr.com demirdelen et al.: a modular cascaded multilevel inverter based shunt hybrid active power filter… respectively. ed + + + ++ ea eb ec eq ediff ia_harmonic_ref ic_harmonic_ref ib_harmonic_ref σ σ + +iq id d q id_lpf iq_lpf iq_fund σ +  ip kk vcappi_a limitter vcappi_b vcappi_c pwm gate signals switching signals s1n-12n reference vcappi_n in_harmonic_ref in_reactive_ref σ + + + harmonic current reference generation reactive current reference generation dc link voltage control final reference compensation current and pwm control block (b) (e) (f) isa isc isb abc d q abc ia_reactive_ref ic_reactive_ref ib_reactive_ref iq d q (c) isa isc isb abc d q abc0 d q abc 0 v*dc vdc verror carrier1 carrier2 carrier3 (n=a,b,c) differential phase lock loop (diff-pll) selective harmonic current reference generation fft ia_fft_k_ref sin (d) isa isc isb k x isn_fft_k (k=7,9,11,13 n=a,b,c) _ _ ib_fft_k_ref ic_fft_k_ref (a) σ + + in_fft_k_ref fig. 2. proposed controller table ii. simulation parameters parameters value line voltage 6.3 kv line frequency 50 hz supply inductance (ls) 1 mh rectifier inductance (ll) 0.6 mh filter (cf,lf) 16 µf, 25 mh load resistances(rload1 ) 100 ω load inductances(lload1) 600 mh load inductances(lac1) 13 mh switching frequency (fswitching) 10 khz simulation step time 20 µs inductive loads 1st load ( rload1 lload1) 360 kvar nonlinear load 60 kvar tuned freq. of series filter (ftuned) 250 hz first case is that three phase grid voltages are balanced. it is ideal condition and in literature most articles consider this condition. as shown in figure 3, the harmonic elements of the grid currents are almost eliminated. in the second case, one phase of grid voltages is distorted. 10% and 11th order harmonics is added to phase a voltage. as shown in figure 4, the reduced thd of the source current, while compensating harmonics, working distorted supply means, sinusoidal current is drawn from the source. last case is that the grid voltages are unbalanced as the case in industrial applications. phase c voltage has a lower value compared to other phase voltages. as shown in figure 5, the harmonic elements of the grid currents are almost eliminated. figure 6 represents that the source reactive power is nearly equal to zero for all cases. the passive filter supports a fixed reactive power which is equal to 220 kvar. the load reactive power capacity is nearly 320 kvar. thus, the inverter part of shapf supplies the remaining reactive power compensation which is nearly equal to 100 kvar. the shapf dc link voltage is stable for all cases shown as shown in figure 6. considering the simulation results, the proposed method can:  provide reactive power and harmonic compensation  reduce the thd of the source side current  apply for medium voltage applications  work not only with distorted but also with unbalance grid voltages. iv. conclusion a new control approach is investigated in order to ensure the ac current shaping, compensate the reactive power and regulate the dc voltage for a three phase modular cascaded multilevel inverter based shunt hybrid active power filter. the harmonic compensation is obtained by regulating the currents of the power systems. the reference reactive power compensation currents of the m-shapf are generated indirectly of the power systems. the dc link voltage control signals are based on the reactive power balance of system. the reactive power compensation is achieved successfully with a perceptible amount. the selective harmonic compensation engineering, technology & applied science research vol. 6, no. 5, 2016, 1133-1138 1137 www.etasr.com demirdelen et al.: a modular cascaded multilevel inverter based shunt hybrid active power filter… performance is satisfactory. the simulation results of the three phase three wire shapf are illustrated to verify all discussion and analysis and also show the effectiveness of the proposed controller. hence, the proposed m-shapf system can be considered an effective and economic solution for both harmonic and reactive power problems caused by the large capacity of linear and nonlinear loads under balanced, unbalanced and distorted grid voltages. 0.750 0.760 0.770 0.780 0.790 0.800 0.810 0.820 0.830 0.840 0.850 -8000 -6000 -4000 -2000 0 2000 4000 6000 8000 -100 -80 -60 -40 -20 0 20 40 60 80 100 -50 -40 -30 -20 -10 0 10 20 30 40 50 -100 -80 -60 -40 -20 0 20 40 60 80 a b c three phase source voltages(v) three phase load currents(a) three phase shapf currents(a) three phase source currents(a) fig. 3. three phase source voltages, load currents, shapf current and source currents under balanced grid voltage 0.750 0.760 0.770 0.780 0.790 0.800 0.810 0.820 0.830 0.840 0.850 -8000 -6000 -4000 -2000 0 2000 4000 6000 8000 a b c -100 -80 -60 -40 -20 0 20 40 60 80 100 -50 -40 -30 -20 -10 0 10 20 30 40 50 -100 -80 -60 -40 -20 0 20 40 60 80 three phase source voltages(v) three phase load currents(a) three phase shapf currents(a) three phase source currents(a) fig. 4. three phase source voltages, load currents, shapf current and source currents distorted grid voltage -8000 -6000 -4000 -2000 0 2000 4000 6000 8000 -100 -80 -60 -40 -20 0 20 40 60 80 100 -50 -40 -30 -20 -10 0 10 20 30 40 50 -100 -80 -60 -40 -20 0 20 40 60 80 0.750 0.760 0.770 0.780 0.790 0.800 0.810 0.820 0.830 0.840 0.850 a b c three phase source voltages(v) three phase load currents(a) three phase shapf currents(a) three phase source currents(a) fig. 5. three phase source voltages, load currents, shapf current and source currents under unbalanced grid voltage 0.750 0.760 0.770 0.780 0.790 0.800 0.810 0.820 0.830 0.840 0.850 0 100 200 300 400 500 600 700 800 900 0 100 200 300 400 500 600 700 800 900 -350 -250 -150 -50 50 150 250 350 1.5185 1.5188 1.5190 1.5193 1.5195 1.5198 1.5200 1.5203 1.5205 1.5208 0.00 0.50 1.00 1.50 2.00 2.50 3.00 -2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00 source reactive power (kvar) load reactive power (kvar) shapf reactive power (kvar) shapf dc link voltage (kv) shapf dc link voltage (kv) fig. 6. source, load, shapf reactive power and shapf dc link voltage engineering, technology & applied science research vol. 6, no. 5, 2016, 1133-1138 1138 www.etasr.com demirdelen et al.: a modular cascaded multilevel inverter based shunt hybrid active power filter… acknowledgment the authors would like to acknowledge the scientific and technological research council of turkey (tübi̇tak project number: 115r327) and the scientific project unit of cukurova university (fdk-2016-5828) for full financial support. references [1] x. bails, l.m. tolbert,“efficiency improved and current balanced threephase modular cascaded h bridge multilevel pv inverter for grid connected applications”, ieee energy conversion congress and exposition (ecce), pp. 4661–4669, 2014 [2] j. turunen, m. salo, h. tuusa, “comparison of three series hybrid active power filter topologies”, 11th international conference on. harmonics and quality of power, pp. 324–329, sept. 2004 [3] d. shaojun, l. jianben, t. kun, c. qiaofu, “modelling and industrial application of series hybrid active power filter”, iet power electronics, vol. 6, no. 8, pp. 1707–1714, 2013 [4] c. s. lam, w. h. choi, m. c. wong, y. d. han, “adaptive dc-link voltage-controlled hybrid active power filters for reactive power compensation”, ieee transactions on power electronics, vol. 27, no. 4, pp.1758–1772, 2012 [5] s. rahmani, a. hamadi, k. al-haddad, l. a. dessaint, “a combination of shunt hybrid power filter and thyristor-controlled reactor for power quality”, ieee transactions on industrial electronics, vol. 61, no. 5, pp. 2152–2164, 2014 [6] s. srianthumrong, h. akagi, “a medium voltage transformerless ac/dc power conversion system consisting of a diode rectifier and a shunt hybrid filter”, ieee transactions on industry applications, vol. 39, no. 3, pp. 874-882, 2003 [7] n. hatti, k. hasegawa, h. akagi, “a 6.6-kv transformerless motor drive using a five-level diode-clamped pwm inverter for energy savings of pumps and blowers”, ieee transactions on power electronics, vol. 24, no. 3, pp. 796–803, 2009 [8] j. wu, a. luo, s. peng, f. ma, z. zeng, m. t. chau, “system control of hybrid active power filter for reactive power compensation and harmonic suppression”, 6th ieee conference on industrial electronics and applications (iciea), pp. 862–866, beijing, china, 2011 [9] l. herman, i. papic, b. blazic, “a proportional-resonant current controller for selective harmonic compensation in a hybrid active power filter”, ieee transactions on power delivery, vol. 29, no. 5, pp. 2055–2065, 2014 [10] m. salehifar, a. shoulaie, “hybrid active filter for harmonic suppression and reactive power compensation”, 2009 international conference for technical postgraduates (techpos), pp. 1–4, 2009 [11] a. m. massoud, s. j. finney, a. j. cruden, b. w. williams, “threephase, three-wire, five-level cascaded shunt active filter for power conditioning, using two different space vector modulation techniques,” ieee transactions on power delivery, vol. 22, no. 4, pp. 2349–2361, 2007 [12] t. demirdelen, r. i. kayaalp, m. tumay, ”modeling and analysis of a multilevel parallel hybrid active power filter”, engineering, technology & applied science research, vol. 6, no. 3, pp. 976-981, 2016 [13] t. demirdelen, m. inci, k. cagatay bayindir, m. tumay, “review of hybrid active power filter topologies and controllers”, fourth international conference on power engineering, energy and electrical drives (powereng), pp. 587–592, may 13-17, 2013 [14] m. e. meral, “improved phase-locked loop for robust and fast tracking of three phases under unbalanced electric grid conditions”, iet generation, transmission & distribution, vol. 6, no. 2, pp. 152–160, 2012 microsoft word 02-725-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1217-1220 1217 www.etasr.com masomi zohrabad: application of hybrid hs and tabu search algorithm for optimal location… application of hybrid hs and tabu search algorithm for optimal location of facts devices to reduce power losses in power systems zynab masomi zohrabad department of electrical engineering, faculty of engineering mashhad branch, islamic azad university mashhad, iran zynab.masomizohrabad@chmail.ir abstract—power networks continue to grow following the annual growth of energy demand. as constructing new energy generation facilities bears a high cost, minimizing power grid losses becomes essential to permit low cost energy transmission in larger distances and additional areas. this study aims to model an optimization problem for an ieee 30-bus power grid using a tabu search algorithm based on an improved hybrid harmony search (hs) method to reduce overall grid losses. the proposed algorithm is applied to find the best location for the installation of a unified power flow controller (upfc). the results obtained from installation of the upfc in the grid are presented by displaying outputs. keywords-tabu search optimization algorithm; harmony search optimization algorithm; facts devices; upfc; ieee 30-bus grid; reduced losses i. introduction grid stability is an important topic in power systems as any delay or inability in stability control will affect quality and servicing loads. to provide a reliable and practical function, it is required to use precise control systems with high efficiency. flexible alternating current transmission systems (facts) allow a significant improvement in energy transmission with low investment cost and quick control [1]. the focus of this study is to find the optimal location of a unified power flow controller (upfc) in an ieee 30-bus grid for reducing losses in the power system. the method used is a hybrid harmony search (hs) and tabu search algorithm, the results of which are compared to that of standard hs. basically, upfc has two voltage source inverters (vsi) and a common dc link capacitor which is connected to the grid by two series-parallel transformers. potentially, upfc performs all series and parallel compensations simultaneously and can control phase angle, impedance and voltage range continuously. thus, it can control the real and reactive power of transmission line independently. upfc series and parallel elements work independently [2]. harmony search (hs) algorithm was first presented in [3]. hs algorithm has been inspired by music. the effort to find harmony in music resembles the effort to find the optimal conditions in an optimization process. in other words, the creativity of a musician to create an art piece could be compared with the search process in an optimization problem. in fact, there is a relative similarity between music and optimization as musical instruments correspond with decision variables in the optimization problem. in general, this algorithm is able to solve different optimization problems. moreover, the similarities between these two processes raise the idea of developing a new algorithm. in musical improvisation, the musician plays a musical scale at potential intervals, which together form a harmony vector. if all scales create an aesthetically good and acceptable harmony, this experience is stored in the memory of the musician and it will increase the likelihood of a better harmony. similarly, a decision variable in the engineering optimization problems is initially allocated a value within a permissible range, which can form a solution vector. if all decision variables generate a good and acceptable solution based on objective function, this experience is stored in the memory of the variable and increases the likelihood of better solutions. ii. harmony search in [4], an optimization process with three corresponding components was developed: 1: harmony memory (hm), 2: pitch adjustment, 3: random selection. harmony memory is very important, because it determines whether new solutions and harmonies can be accepted. to use hm effectively, a parameter is presented to indicate the likely consideration of hm harmony as hmcr (harmony memory considering rate) which is examined according to its rate and extent. for very low and close to zero hmcr, a small number of variables chosen for harmony are selected; for high and close to one hmcr, new values are randomly selected from the search space for the harmony variable. for a very high and close to one hmcr, it is more likely to select from hm and less likely to select from the search space randomly. in both cases, the algorithm does not converge to the optimal values or engineering, technology & applied science research vol. 6, no. 6, 2016, 1217-1220 1218 www.etasr.com masomi zohrabad: application of hybrid hs and tabu search algorithm for optimal location… optimization and convergence is very slow. to balance variables and higher quality solutions in hm (intensification) and random search in the search space and escape from local optimums (diversification), the value considered for hmcr is approximately 0.7 to 0.9. the second operator is pitch adjustment involving parameters such as bandwidth (bw, maximum value of the change in the selected variable) and pitch adjusting rate (par). these two parameters are used to create a new harmony (solution vector). hs algorithm is described below step by step: 1. define the objective function and algorithm parameters (hmcr, par and bw): to start solving the algorithm, fitness function and algorithm parameters are first determined. then, hmcr (representing likelihood of considering a variable of the memory) and par (representing likelihood of change in the selected variable of the matrix memory to a random size) which are two parameters ranging from zero to one are defined. usually, hmcr value is about 0.7 to 0.95, meaning that the likelihood of selection of hm is equal to 0.7 to 0.9. par value is about 0.1 to 0.5, meaning that the likelihood of minor changes in the selected value of hm is 0.1 to 0.5. to determine value of the change on the selected variable of matrix memory, another parameter (bw) is also defined, which is explained below. 2. form a matrix memory: a hm matrix is composed of several solutions or harmonies. the overall shape of this memory matrix is as follows:          hmc n hmc n xx xx hm .... . . . .......... 1 11 1 (1) 3. the number of rows in the memory matrix is equal to harmony memory size (hms); each row means a solution generated randomly. in this matrix, n is the number of variables. this matrix is the same popular music that a musician wants to play. each row is a harmony or piece of music. most likely, none of these harmonies or solutions is potentially the best harmony or solution. using a fitness function, fitness value or value of each solution is obtained. 4. produce a new solution or harmony: for a new harmony, several operators are required to generate the variables separately. to create value for the i-th variable, a random number is first generated between zero and one; this random number is compared with hmcr. if the random number is smaller than hmcr, a value will be selected for i-th variable of the memory matrix and i-th column. otherwise, a random value will be selected for i-th variable of search space. if a value of memory matrix is selected, another random number will be generated and compared with par. if the random number is smaller than par, the variable selected of the memory matrix will be changed to a smaller value by the following equation. to determine the change value on the variable selected of memory matrix, another parameter (bw) is defined. the new variable is obtained by the following variable: xnew = xold + bw + ε 5. update the memory matrix: similarly, all variables of a harmony are generated; then, its value is calculated by the fitness function and compared to the worst harmony in the memory matrix. if it surpasses the worst harmony in the memory matrix, a new harmony will replace the previous harmony. 6. stop condition: stop condition of the algorithm can be determined in different ways. usually, stop condition is to achieve the optimal value considered. other conditions are to keep the best harmony in the memory matrix intact or reach the specified number of repetitions [4]. iii. tabu search tabu search which was first presented by glover in 1986 [5] is a meta-heuristic optimization method for solving hybrid optimization problems based on local search algorithms to overcome their flaws. the overall structure of tabu search is described below: to achieve the optimal solution in an optimization problem, tabu search starts to move from an initial solution. then, the algorithm selects the best neighbor solution among neighbors of the current solution. if the solution is not on the tabu list, the algorithm will move to the neighbor solution. otherwise, the algorithm will check the aspiration criterion. based on the aspiration criterion, if the neighbor solution is better than the best solution found so far, the algorithm will move towards that solution, even if it is in the tabu list. after moving to neighbor solution, the tabu list is updated; that is, the previous move to the neighbor solution is placed on the tabu list to avoid return to that solution in a cycle. in fact, tabu list is an instrument in the tabu search algorithm by which the algorithm is prevented from falling into the local optimum. then, a number of moves previously put in the tabu list are removed from the list. the time when moves are placed in the tabu list is determined by a parameter called as tabu tenure. the move from the current solution to the neighbor solution continues until the stop criterion is met. different stop criteria can be considered for the algorithm. for example, limited number of moves to the neighbor solution can be a stop criterion [6]. iv. simulation results in this study, the objective function is to reduce losses in an ieee 30-bus grid, for which it is required to extract the y bus grid matrix. optimization concept suggests that those values of parameters are considered that minimize or maximize the function. all proper values for this are called possible solutions and the best value of these values is called optimal solution. optimization algorithms cover both maximization and minimization problems. the purpose of the defined problem is to reduce grid losses. by multiplying the loss function by -1, the algorithm can track the minimization of loss function [7]. in table i, ploss is total grid losses, i is the grid line current and q is the reactive power of the ieee 30-bus grid lines. engineering, technology & applied science research vol. 6, no. 6, 2016, 1217-1220 1219 www.etasr.com masomi zohrabad: application of hybrid hs and tabu search algorithm for optimal location… table i. output results of hs algorithm q i ploss -29.7154 64.9445 2.13e+07 37.7239 63.6607 2.13e+07 141.5347 65.4033 2.13e+07 -96.9429 68.7965 2.13e+07 6.6182 64.0102 2.13e+07 182.9972 55.4692 2.13e+07 136.3326 78.2278 2.13e+07 76.3367 46.6269 2.13e+07 99.7846 57.7902 2.13e+07 167.5033 62.7782 2.13e+07 -79.1372 63.7469 2.13e+07 -24.9722 70.3663 2.13e+07 142.7435 67.6466 2.13e+07 65.3306 56.0573 2.13e+07 15.1391 61.7173 2.13e+07 224.2357 68.983 2.13e+07 47.7569 68.0813 2.13e+07 -32.1558 65.1849 2.13e+07 -5.2751 68.9633 2.13e+07 143.7993 70.6929 2.13e+07 -123.3688 69.7048 2.13e+07 677.4 65.7603 2.13e+07 196.0636 58.19 2.13e+07 112.4595 57.1071 2.13e+07 187.7668 65.3285 2.13e+07 -314487 59.4643 2.13e+07 46.2256 61.8369 2.13e+07 143.9211 71.7156 2.13e+07 -73.5452 67.7943 2.13e+07 -15.941 66.1547 2.13e+07 an advantage of the hs algorithm is its rapid convergence due to its structure. its disadvantage is trapping in a local optimum because of less diversified search in final iterations. to overcome this problem tabu search is used in the final iterations of the algorithm. in this study, 50 hs iterations are selected. when the solution of this algorithm approached the optimal solution, the tabu search algorithm should start. figure 1 compares the hybrid algorithm presented by this study and hs algorithm. obviously, convergence speed in approaching the solution is greater in the hybrid algorithm. figure 2 depicts the difference clearer. if the number of iterations is changed to 3000, it will take the hs algorithm about 10 minutes (and more than ten minutes in some cases) to solve the problem whereas the hybrid algorithm suggested here will take about 4 minutes. through the search by the hybrid algorithm, upfc installation was located based on the lack of reactive power. this means that the buses with the most reactive power shortage are candidate for upfc installation. according to table ii, 5 buses are considered as candidates for a upfc installation. in this algorithm, candidates for upfc installations correspond to priorities of the buses 21, 4, 11, 29 and 18. both algorithms lead to a same solution. however, total loss is 2.0732*107 in hybrid algorithm and 2.1254*107 in hs algorithm, suggesting that the hybrid search algorithm is more able to minimize the loss than the hs algorithm. table ii. outputs of hybrid hsand tabu search algorithm upfc q i bus no ploss -29.715 64.9445 1 2.07e+02 37.7239 63.6607 2 2.07e+02 141.535 65.4033 3 2.07e+02 2 -96.943 68.7965 4 2.07e+02 6.6182 64.0102 5 2.07e+02 182.997 55.4692 6 2.07e+02 136.333 78.2278 7 2.07e+02 76.3367 46.6269 8 2.07e+02 99.7846 57.7902 9 2.07e+02 167.503 62.7782 10 2.07e+02 3 -79.137 63.7469 11 2.07e+02 -24.972 70.3663 12 2.07e+02 142.744 67.6466 13 2.07e+02 65.3306 56.0573 14 2.07e+02 15.1391 61.7173 15 2.07e+02 224.236 68.983 16 2.07e+02 47.7569 68.0813 17 2.07e+02 5 -32.156 65.1849 18 2.07e+02 -5.2751 68.9633 19 2.07e+02 143.799 70.6929 20 2.07e+02 1 -123.37 69.7048 21 2.07e+02 677.4 65.7603 22 2.07e+02 196.064 58.19 23 2.07e+02 112.46 57.1071 24 2.07e+02 187.767 65.3285 25 2.07e+02 -314487 59.4643 26 2.07e+02 46.2256 61.8369 27 2.07e+02 143.921 71.7156 28 2.07e+02 4 -73.545 67.7943 29 2.07e+02 -15.941 66.1547 30 2.07e+02 fig. 1. hs algorithm and hybrid algorithm (improved hs with tabu search) fig. 2. time versus the number of iterations v. conclusion considering the disadvantage of the hs optimization algorithm, a hybrid hs and tabu search algorithm was hs h-hs engineering, technology & applied science research vol. 6, no. 6, 2016, 1217-1220 1220 www.etasr.com masomi zohrabad: application of hybrid hs and tabu search algorithm for optimal location… suggested in this study. hs algorithm can be improved by another algorithm, such as tabu search, employed to find local optimums (in neighborhood to the global optimum). grid loss minimization and the best location for a upfc installation in a ieee 30-bus grid was considered as a focus of the comparison. this study showed that tabu search algorithm is very effective in improving hs algorithm. references [1] n. g. hingorani, l. gyugyi, understanding facts: concepts and technology of flexible ac transmission systems, wiley-ieee press, 1999 [2] a. kazemi, a. parizad, h. r. baghaee, “on the use of harmony search algorithm in placement of facts devices to improve power system security”, ieee eurocon '09, pp. 570-576, 2009 [3] x. wang, x. z. gao, k. zenger, an introduction to harmony search optimization method, springer cham heidelberg new york dordrecht london, 2014. [4] z. w. geem, j. h. kim, g. v. loganathan, “a new heuristic optimization algorithm: harmony search”, simulation, vol. 76, no. 2, pp. 60–68, 2001 [5] m. k. saka, “optimum design of steel skeleton structures”, in musicinspired harmony search algorithm, ed. by z.w. geem, springer, berlin, pp. 87–112, 2009 [6] c. h. guan, y. cao, j. shi, “tabu search algorithm for solving the vehicle routing problem”, iee third international symposium on information processing, pp. 74-77, october 15 17, 2010 [7] m. h. navidadham, “solving generalized vehicle routing problem by parallel universes and tabu search”, ieee 6th international conference on computing, communication and networking technologies (icccnt), dallas-fortworth, tx, usa, pp. 1-7, 2015 [8] d. shilane, j. s. martikainen, s. dudoit, s. j. ovaska, “a general framework for statistical performance comparison of evolutionary computation algorithms”, information sciences journal, no. 178, no. 14, pp. 2870-287, 2008 engineering, technology & applied science research vol. 7, no. 6, 2017, 2171-2176 2171 www.etasr.com samo et al.: temporal analysis of temperature and precipitation trends in shaheed benazir abad … temporal analysis of temperature and precipitation trends in shaheed benazir abad sindh, pakistan saleem raza samo energy & environment dpt, quaid-e-awam university of engineering, science & technology, nawabshah, pakistan sfaizsamo@yahoo.com nadeem-ul-karim bhatti civil engineering dpt, quaid-eawam university of engineering, science & technology, larkana, pakistan knadeem_b@quest.edu.pk abdullah saand civil engineering dpt, quaid-eawam university of engineering, science & technology, nawabshah, pakistan abdullah@quest.edu.pk manthar ali keerio civil engineering dpt, quaid-e-awam university of engineering, science & technology nawabshah, pakistan mantharali99@quest.edu.pk daddan khan bangwar civil engineering dpt, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan daddan@quest.edu.pk abstract—temperature and precipitation variations have a huge environmental, social and economic impact. this study aims to analyze the temporal variation of temperature and precipitation in shaheed benazir abad district by using the linear regression method, the trend magnitude, the mann-kendall test and the sen’s estimator of slope. the annual precipitation and monthly temperature data of shaheed benazir abad for the period of 1996-2014 are considered. the result shows that the diurnal temperature range of all months is decreasing due to the increasing of monthly minimum temperature at a faster rate than the monthly maximum temperature. however, the diurnal temperature range of extreme events is increasing. the results obtained by using mann-kendall test revealed that rainfall exhibits significant positive trend. the trends of rainfall and rainy days show that the amount of rainfall is increasing much more rapidly than that of rainy days which indicates the occurrence of heavy events. keywords-rainfall; diurnal temperature range; mann-kendall test; shaheed benazir abad i. introduction historical trends in surface climate components (like temperature and precipitation) have received significant concentration recently. to forecast climate shift loss of biodiversity, droughts, agricultural productivity, floods, precipitation and changes in temperature pattern need to be examined [1]. so the trends of precipitation and air temperature are very important to the analysis in the fields of climate sciences and hydrology [2]. but simultaneously, climate extremes are getting great attention [3]. these short duration episodes of extreme events of temperature and precipitation are responsible for huge environmental and socio-economic consequences [4-6]. various studies have been conducted to examine the trends in precipitation and temperature records. authors in [3] have found negative dtr trends in the south asia. authors in [7] showed that between 1965 and 2009 extreme events of both maximum and minimum temperature are increasing throughout pakistan. authors in [8] analyzed precipitation changeability across 15 locations of swat river basin, pakistan, over a 51-year study period (1961–2011) and showed a mix of positive (increasing) and negative (decreasing) patterns of monthly, seasonally, and annually precipitation. in iran, trends in extreme precipitation for the period 1951–2007 have been investigated by authors in [9] who found a strong upward trend. various studies all over the world concluded that the frequency and intensity of extreme climate events are rising. however the causes of such anomalies are not clearly known yet but the impacts of different factors like elnino/la-nina [10], different atmospheric oscillations [11], anthropogenic activities and intergalactic gravitational forces [12] have been analyzed. the relative to temperature, the longterm behavior of precipitation is characterized by larger spatial variability, demonstrating a proportionately higher dependence on local and regional variables. in this case, relatively smallscale analysis might be essential in practical applications [2]. the aim of this study is to examine the historical variability in temperature and precipitation trends of (1996–2014) over shaheed benazir abad district, sind, pakistan. ii. data and methodology a. study area description shaheed benazir abad is located at the center of sindh province of pakistan whose geographical coordinates are 26° 15' 0" north, 68° 25' 0" east. indus river is flowing at west border. the climate is tropical. the total projected population of the city was 1676000 in 2014. the area of the city is 4502 km2. the average rainfall in the district is 18.39 cm. the data engineering, technology & applied science research vol. 7, no. 6, 2017, 2171-2176 2172 www.etasr.com samo et al.: temporal analysis of temperature and precipitation trends in shaheed benazir abad … of pakistan meteorological department (pmd) station at the airport of nawabshah (opnh-417490) was used for this study [13]. b. methods monthly and annually minimum and maximum surface air temperatures, diurnal temperature range (dtr) and rainfall have been compiled for the years 1996 – 2014. the linear regression method is used to analyze the behavior of temperature and precipitation. the graphs of the temperature and rainfall for the 12 months of each year (228 months for the 19 year study period) were plotted. monthly graphs were then combined in a spreadsheet with the minimum, maximum dtr and rainfall of each month and then the trend line for every variable was plotted. various statistical procedures and techniques are used to detect and estimate trends in different climate parameters. these various statistical methods are broadly divided into parametric and non-parametric ones. parametric methods specially assume the normal distribution of concerned data while non-parametric methods are those which consider that the concerned data do not follow a specific distribution [2]. four statistical methods were used to detect and estimate the trends of temperature, humidity and precipitation. firstly, linear regression method was used to calculate the trend for each time series [14]. the trend magnitude was found by using the position of trend equation. the mann-kendall test was used to investigate the significance of all trends [15]. the sen's slope was used to determine the magnitude of all trends [16]. 1) the linear regression method the behavior of all parameters was computed and analyzed with following linear trend model by using linear regression method [17]. y x   (1) where α represents the slope of equation and β represents the yintercept and are calculated as: 2 2 2 y x x x y j j j j j n x x j j             (2)  22 j j j j j j n y x x y n x x          (3) where xj represents "years" and yj represents “parameters”. this method is frequently used to determine the trend. if the sign of α is positive then the trend is increasing and if the sign of α is negative then the trend is decreasing. when the value of α is equal to zero then there is no trend in time series. 2) the trend magnitude the second method was used to find out the trend magnitude. it was calculated by using:    δy=y initial point -y terminate point (4) where δy shows the total trend magnitude while y (initial point) and y (terminate point) represent the beginning and the end point of the trend equation respectively. the positive and negative sign of δy show the decreasing and increasing trend respectively. 3) the mann-kendal test the significance of trends of all time series of present study was assessed by using the mann-kendall test. it is a nonparametric test which is widely used in hydrological and climatological time series [18]. the world meteorological organization (wmo) has suggested the mann-kendall test for assessing the temporal trends in the time series of environmental data [19].this method was used to detect the statistically significant trends of long term data. there are two hypotheses to be tested in the mann-kendall test .one hypothesis is the null hypothesis h0 which means that there is no trend in concerned time series while the other one is the alternative hypothesis ha. this alternative hypothesis assumes that there is significant trend in the time series. the mannkendall statistic (s) is computed as follows:  1 1 1 n n i j i sign tj tis        (5) where,   1 if t 0 if t 1 if t j i j j t tsign tj ti t             (6) here tj and ti represent the data points at the time i and j respectively where j ˃ i and n is the last period in the time series. if n ˃ 10 then the statistic s approximately normally distributed with the mean of s is zero, the variance statistic var(s) is computed as   1( ) 1 2 5 18 var s n n n   (7) kendall's tau (τ) is obtained by applying mann-kendall test. it represents the correlation between two variables which means the value of tau describe the relationship between two variables [20]. mann-kendall τ is given by   21  nn s  (8) here, s represents the mann-kendall statistic and n shows the number of data pairs. the probability p is determined to know the confidence level in the hypothesis of mann-kendall test and it is computed as follows  1 100 p f z     (9) z is standard normal test statistics which is computed by using the following equation: 1 if 0 ( ) 0 if 0 1 if 0 ( ) s s var s z s s s var s                  (10) engineering, technology & applied science research vol. 7, no. 6, 2017, 2171-2176 2173 www.etasr.com samo et al.: temporal analysis of temperature and precipitation trends in shaheed benazir abad … in the equation (9), f(z) is a function of probability density and it is calculated by following equation: 2 2 1 ( ) 2 z f z e    (11) the value of p is very important for accepting and rejecting the hypothesis of mann-kendall test. the level of chosen significance is represented by alpha (α = 0.05). if the calculated value of p is greater than the value of α then ho cannot be rejected. if the value of p is less than the value of alpha then ha should be accepted [15]. 4) the sen’s estimator of slope this is a non-parametric method used to calculate the magnitude of linear trends which exist in time series data. the slope (mi) of all pairs of data is computed by (12). j k i x x m j k    (12) in the above equation, xj and xk represent data values at the time j and k respectively where j > k. the sen's estimator of slope is the median of these n values of mi. the sign of mmed indicates the reflection of trend of time series data. the positive sign of mmed represents the increasing trend while negative sign shows the decreasing trend [21]. addinsoft's xlstat 2015 was used for mann-kendall test and sen's estimator of slope. the hypothesis was tested at 95% confidence level for all variables. iii. results and analysis from the computed data, it was observed that the most critical section is, when tunnel face aligns the pile group center line (monitoring section). however, there are not any significant changes in surface settlement as tunnel face passes beyond the y/d3 from the monitoring section. therefore, it can be assumed that monitoring section attain the plane strain condition. a. trends in air temperature maximum, minimum air temperature and monthly diurnal air temperature range of shaheed benazir abad have been illustrated in figure 1 for the period of 1996–2014. figure 1(a) shows the fluctuations of dtr during study period due to various factors but the linear trend of dtr is decreasing steadily by a aslope of -0.05789°c per year during this 19 year period. specially, the decreasing trend of diurnal temperature range (dtr) is more significant during recent years. figure 1(b) shows the behavior of monthly maximum temperature which is slightly increasing with the rate of 0.000519°c/year, but the monthly minimum temperature is rising at a more faster rate, 0.06315°c/year as shown in figure 1(c). therefore, the significantly increasing trend of minimum temperature contributes to the decrease of diurnal temperature range. the investigation revealed that annual maximum temperature event during 1996-2014 has a rising trend and the rate of increase is 0.0736°c per year. this increase detected in maximum temperature events over the observed period, indicates that overall, days are getting warmer in shaheed benazir abad. on the contrary the annual minimum temperature event during the study period shows a decreasing trend at a rate of 0.014°c per year. this decrease detected in minimum temperature events over the observed period indicates that overall, nights are becoming cooler in shaheed benazir abad. these changes in temperature extremes ultimately contributed to the increase of the linear trend of dtr event which increases at the rate of 0.0357°c per year during 1996-2014 (figure 2). b. trends in rainfall the investigation of the variations in the precipitation patterns over the shaheed benazir abad indicates that there is a sharp increase in the linear trend of amount of rainfall during 1996-2014. the total amount of rainfall is increasing and the period of rainfall is also increasing. the average number of rainy days is 9.84. the trends of rainfall and its period indicate that the amount of rainfall is increasing much more rapidly than the number of rainy days, indicating the more frequent occurrence of heavy events (figure 3). the average annual precipitation in shaheed benazir abad is 18.39cm. however, several years may pass without significant rainfall while unprecedented rainfalls occurred in 2011 [22]. c. trend analysis by mann-kendall test the trends of temperature and rainfall in shaheed benazir abad were detected by using mann-kendall test. tables i and ii summarize the results obtained by applying mann-kendall test on time series of temperature and rainfall. the significance level was the same (α = 5%) for all parameters. the results revealed that four parameters have positive trends and remaining three parameters have negative trends as indicated in table ii. the p -values of six parameters are greater than alpha value (significance level) as indicated in table i which means that one can not reject the hypothesis ho. these values show that six parameters have insignificant trends. while the p-value of time series of rainfall is less than the value of alpha which is interpreted that the hypothesis ho should be rejected. it means that significant trend was detected for all month’s rainfall in shaheed benazir abad during study period. sen's estimator of slope was used to find out the magnitude of slopes of trends of temperature and rainfall in the study area. the result shows that precipitation exhibits significant increasing trend with slope of 22.07 and having 24.2105 mm/year magnitude. iv. discussion and conclusion there are five positive trends in time series and two negative trends according to the investigation of trend equation. but, the application of mann-kendall test revealed that there was only one positive trend which was statistically significant while there were no significant trends in the remaining time series. according to the trend equation investigation, the maximum and minimum temperature increased in the past 19 years by 0.000519°c per year and 0.06315°c per year respectively, while the diurnal temperature range (dtr) reduced by 0.05°c per year which is mostly because of the higher rate of increase for tmin relative to tmax. trends of engineering, technology & applied science research vol. 7, no. 6, 2017, 2171-2176 2174 www.etasr.com samo et al.: temporal analysis of temperature and precipitation trends in shaheed benazir abad … extreme temperature indicate that maximum temperature event is rising at the rate of 0.0736°c per year and minimum temperature event is decreasing at the rate of 0.014°c per year. the linear trend of dtr event is increasing at the rate of 0.0357°c per year. the investigation of the variations in the precipitation trends suggests that the total amount of rainfall is increasing and also the period of rainfall is increasing. however, the slope of linear trend of rainfall and its period show that the amount of rainfall is increasing much more rapidly than the number of rainy days which indicates the occurrence of heavy events. many years have passed without significant rainfall and unprecedented rainfall of about 650 mm occurred in 2011 which created havoc in the city. this extreme event of rainfall disturbed the whole ecosystem of the region. it can be concluded that extreme events are a driving force for climate change in sba. (a) monthly diurnal temperature range (b) monthly maximum temperature (c) monthly minimum temperature fig. 1. all months temperature variation in shaheed benazir abad table i. statistics by mann-kendall test of temperature and rainfall parameters mann-kendall statistic(s) kendall's tau p-value alpha test interpretation tmax -96.00 -0.004 0.533 0.05 accept ho tmin 571 0.022 0.309 0.05 accept ho dtr -1186 -0.047 0.850 0.05 accept ho tmax(event) 36 0.241 0.091 0.05 accept ho tmin(event) -19 -0.128 0.754 0.05 accept ho dtr(event) 36 0.238 0.092 0.05 accept ho rainfall 107 0.626 0.0001 0.05 reject ho table ii. nature of trends and their magnitutes parameters mann-kendall test nature trend significance sen's slope magnitude of trend tmax negative no 0.00 0.00052 (°c/year) tmin positive no 0.003 0.06315 (°c/year) dtr negative no -0.006 0.05789 (°c/year) tmax(event) positive no 0.083 0.07368 (°c/year) tmin(event) negative no -0.067 0.01421 (°c/year) dtr(event) positive no 0.154 0.03578 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pollution trend analysis using sen estimator method – a survey”, international journal of science and research, vol. 4, no. 3, 2015 [21] h. tabari, p. h. talaee, “analysis of trends in temperature data in arid and semi-arid regions of iran”, global and planetary change, vol. 79, no. 1-2, pp. 1-10, 2011 [22] a. mahmood, n. faisal, a. jameel, special report on pakistan’s monsoon 2011 rainfall, climate data processing centre, pakistan meteorological department, 2011 engineering, technology & applied science research vol. 8, no. 1, 2018, 2609-2615 2609 www.etasr.com gupta and swarnkar: intertied ac-dc hybrid system power sharing through intelligent droop … intertied ac-dc hybrid system power sharing through intelligent droop controller preeti gupta electrical engineering department maulana azad national institute of technology bhopal, india preeti.irig@gmail.com pankaj swarnkar electrical engineering department maulana azad national institute of technology bhopal, india p_swarnkar@yahoo.co.in abstract—the result of dg clustering is the hybrid power system while further clustering forms the intertied hybrid power system. interfacing of intertied hybrid power system requires an interlinking converter with a legitimate power administration and control system. in contrast to individual hybrid power system (hps), power administration of the intertied hybrid system is more complex. autonomous droop strategy is appropriate for the intertied hybrid system where communication links are not possible. this paper proposes a new topology for control in intertied hybrid system where two hybrid power systems are connected to each other through interlink power converter. evaluated frequencies in different hpss can diverse. in order to manage power flow a power management strategy with consideration characteristics of common bus, a pdcvdc 2 method is proposed, and compared with conventional droop, to realize power sharing among hps. the practicability of the proposed power sharing method is realized in matlab/simulink platform. keywords-intertied hybrid system; power sharing; intelligent controller i. introduction concerns about natural outflow from centralized power plants have extended excitement for dg establishment, despite the fact that dg infiltration in power structures is limited due to specific reasons like reliability necessities [1]. ηybrid power systems (hpss) are required to work both in grid connected power systems and standalone modes to fortify dependability and power quality [2]. grid accountability to maintain the system voltage and frequency with appropriate sharing of power in autonomous system is desirable [3-6]. the intertied hybrid system is a focus of research due to its high reliability and flexibility with integration of renewable energy sources. in this paper, the intertied hybrid system composed of different voltage and different frequency hps with either dc or ac source is considered. hence the intertied hybrid system can utilize the important characteristics of both dc and ac hps. in contrast to individual hps, power management of the intertied hps is more intricate because of interfacing ac and dc hps. hence the design of a power sharing controller for exploiting the features of intertied hps is a major challenge. for diverse applications, the configuration of intertied hps can be distinctive. the conventional intertied hps normally includes one ac hps and one dc hps. concentrating on this issue this paper proposes a new control method for intertied hps with two hpss of different frequency. some fast communication methods by using master-slave techniques is discussed in [7, 8], but due to requirement of communication links the system is not more reliable. while designing a controller for a vsc based hybrid system without communication link some issues have to be considered and conventional techniques mightbe inappropriate. in [9, 10], authors discussed conventional droop control, where enhanced dc current sharing is obtained with suppression of dc voltage deviations by low bandwidth communication signals but it excludes time delay effects. moreover, distributed secondary control in [11] overcomes the shortcoming of the conventional droop. different power management strategies of hybrid microgrids are discussed in [12]. from the perspective of power balance vdc 2-pdc droop control is developed in [13]. power sharing among intertied hps with artificial intelligence is proposed in [14] to enhance the operating battery lifetime. to overcome the limitations of previously mentioned methods an intertied hps with multiple hps is considered in this paper. proposed controller adopts decentralized controller which enhances the reliability of the system. the attractive feature of the control method is the linear relation between vdc2 and pdc. the proposed control assures power sharing in coordination with voltage and frequency support. also the control scheme is appropriate for different hps capacities. the effectiveness of the proposed power sharing control is verified by sps toolbox. ii. intertied hybrid system topology the proposed scheme for intertied hps is shown in figure 1. the intertied hps is composed of multiple ac hps of different rated frequencies and different rated dc hps. intertied hps are strictly free to have their own voltage and frequencies that better match with their sources and load. some countries have rated frequency of 50hz, others 60hz, 400hz frequency is found in aircraft supply networks. therefore different conditioned hps interlinking is necessary for appropriate power sharing and load adaptability. the higher system inertia of the intertied hps keeps the system stable under perturbation, while the feature of lower reserve requirement reduces the startup capital cost which includes the cost of inserting power converters. addition of power engineering, technology & applied science research vol. 8, no. 1, 2018, 2609-2615 2610 www.etasr.com gupta and swarnkar: intertied ac-dc hybrid system power sharing through intelligent droop … converters is therefore a universal approach more likely to draw researcher’s interest. some of already existing hpss include standalone power networks for electric ships, electric aircrafts and electric vehicles with their own preferred voltages and frequencies even though they are usually compactly small. the thought of clustering and interlinking has, in fact, been recently promoted by research, concentrating on the division of a local area network into subzones/ clusters of either the same or different voltage levels. the objective there is to enhance system reliability, security and efficiency by minimizing transmission and distribution losses. mppt can be applied for the dgs having intermittent nature. different ipcs are employed to interconnect different hpss according to rating. interlinking converters play an important role in providing bidirectional energy transfer between hpss. the intertied hpss can be connected to the ac utility mains through an intelligent switch. fig. 1. intertied hybrid system topology a standalone system should be capable of fulfilling the load demand. the sources will deliver the power depending upon the information received through explicit communication links without overstressing themselves. the problems of cost increase and single point failure can be resolved by droop control, where adjustment of voltage magnitude and frequency is to be sensed by each hps. the intertied hps considered in this paper is in standalone mode, however the controlling of standalone system is more complex when compared to grid connected system. iii. autonomous control for intertied hybrid system droop scheme has been extensively used for power sharing in conventional power generation which is now extended to intertied hps. the storage system satisfies the load demand under the power supply failure. the function of the storage system is to sustain the common dc link voltage with proper power sharing. the battery is connected to common bus through a dc-dc boost converter. since the intertied hps constitutes many hpss including storage system, they need to be connected to common bus with ipcs. the main role of ipc is to manage the power sharing and maintain constant voltage. when power failure occurs and storage system is providing the power to loads the relation between il and vdc is not linear: d l dv i dt  (1) due to nonlinear relation between current and voltage conventional droop control will not provide satisfactory performance. to look into power balance scenario the relation between pdc and vdc 2 is linear which motivatesthe application of a new droop strategy for improved performance. the control strategy involves inner and outer loops, where the controlling of vdc 2 is achieved by inner loop control by tracking the reference generation by outer loop. the power sharing is achieved by outer loop control by pdc-vdc2 droop. the inner loop static error elimination is done by pi controller followed by proportional controller to advance the system damping and reliability. the control law for pdc-vdc2 droop is expressed as 2 2* *( )refdc cb dc dcv v r p p   (2) wherer, vcb, vdc ref, pdc and pdc * are the droop coefficient, common bus voltage, reference output voltage, dc power and reference dc power respectively.figure 2 shows the simplified circuit of the proposed droop control where vcb is the common bus voltage and rline is the line resistance. dc power can be calculated as 2* * cb dc dc cb dc line v rp v v p r r     (3) fig. 2. circuit simplification for proposed droop control to simplify the equation assume **2 dccb rpvg  , and r>>rline then (3) can be rewritten as dc cb dc g v v p r   (4) engineering, technology & applied science research vol. 8, no. 1, 2018, 2609-2615 2611 www.etasr.com gupta and swarnkar: intertied ac-dc hybrid system power sharing through intelligent droop … dc dc cb rp g v v   (5) after solving the above equations pdc can be written as 2 cb dc g v p r   (6) the equation implies that pdc is inversely proportional to r and the matching of pdc and r is according to storage capacity. droop control method for hps1 and hps2 is based upon the conventional method. in (7)-(10) is dg unit number, is the frequency, is terminal voltage , is active power and is reactive power generation respectively. maxx x xf f m p  (7) max min ,max x x f f m p   (8) maxx x xv v p  (9) max min ,max x x v v q    (10) wheremx and nx are active and reactive droop coefficients.in this paper, four hpss are considered intertied by interlinking converters. droop control has the feature of active power flow from under-loaded to overloaded hps. droop control works under three conditions: under loading, over loading and heavy overloading.conventional droop control for the proposed system is shown in figure 3 where interlinking converters are implemented with two six switch converters. each interlinking converter’s power is equal and opposite tothe others’. outer loop consists of two pi controllers for active and reactive power errors. the two hpss of different frequencies are connected to the common dc bus. control strategy has two loops, inner and outer loop. the inner loop to tracks the reference to be generated by the outer loop. the reference value generated by the outer loop can be expressed as * *( ) ( )reff f f m p p    (11) * *( )refv v n q q   (12) here frefand vref, f*, v*, p*, q*, p, q, m and n are the reference output frequency and voltage, rated frequency, rated voltage, rated active power, rated reactive power, actual active and reactive power and droop coefficients respectively. δf is the change in the frequency due to change in load among different hpss. for interconnection of dc hpss, high voltage side is connected to common bus. the control procedure with two loops has idc-vdc characteristics to generate reference signal. the outer loop is used to track the reference signal. the control method follows the relation as *( )refdc dc dcv v v ri   (13) where vdc ref, vdc *, r, idc, δv are reference dc voltage, rated dc voltage, droop coefficient, actual output dc current and change in the voltage corresponding to change in the load among different hps. fig. 3. controller for intertied hybrid system engineering, technology & applied science research vol. 8, no. 1, 2018, 2609-2615 2612 www.etasr.com gupta and swarnkar: intertied ac-dc hybrid system power sharing through intelligent droop … fig. 4. interconnection of ipc in intertied hybrid system iv. powersharing among different hpss section iii focused on the control method for an individual hps. power interaction among different hpss in a intertied system is more complex and is analyzed in this section. the coordinated control among individual hpss ensures power fluctuations divided in all hpss whether dc or ac. enhanced performance can be achieved by supporting all hpss. all hpss are droop controlled, which implies changes in frequency and dc voltage according to change in load demand. the change in dc voltage for dc hps and frequency for ac hps represents power changes inside the dc or ac hps. ac and dc ipcs absorb power from or release power to the common bus, which represents changes in the whole intertied hybrid system. additionally frequency relates to power of ac loads and dc voltage relates to power of dc loads. above mentioned changes in frequency, dc voltage and common bus voltage require coordinated control for ac ipc and dc ipc. the control law can be expressed as  * *, , max min max min cb cbi m m m m p m m cb cb m m v vk f f f k s v v f f                 (14)  * *, , , , max min max min , , cb cbi n dc n dc n n p n n cb cb dc n dc n v vk v v v k s v v v v                 (15) whereδfm and δvk are the coordinated control signal for ipc of m-th ac hps and ipc of n-th dc hps respectively. proportional and integral constants for respective ac or dc hps are given by kp and ki. αm and αnare the correction coefficients in consideration to capacity of m-th and n-th ac and dc hps respectively.fm, fm *, fmmax, andfmmin, are actual frequency, rated frequency, maximum and minimum allowable range of frequency, vcb, vcb *, vcbmax and vcbmin are actual common bus voltage, rated common bus voltage, maximum and minimum allowable range of common bus voltage respectively. considering the capacity of the ac and dc hps, if one hps has high capacity compared to other hpss then the weak hps contribution to the system is less and strong hps should absorb or release power. in view of the above coordination the correction coefficient is proposed. the correction coefficient of p-th hps can be calculated as 1total c p p p total total p h h h h           (16) where hptotal and hpc and are total and critical load capacity of pth hps and htotal is the total capacity of intertied hps. it is clearly depicted from (16) that, for small capacity and high amount of critical loads, correction coefficient is large and subsequent changes in dc voltage and frequency are small. synchronization between change in voltage and change in frequency proves the efficacy of the proposed method. under steady state condition the relation between voltage and frequency considering capacity of the system is given by (17):  * * max min max min cb cb p p p cb cb p p v v f f v v f f       (17) figure 5 shows the corrected relative changes in ac frequency and dc voltage for the proposed control algorithm. the feedback variables are positioned at ipcs to share the coordinated power and can be realized to improve the reliability of the system. fig. 5. corrections for coordinated power control v. results and discussion the simulation was performed in matlab/simulink using building blocks from sps toolbox. the rated ac voltage of the hps1 and hps2 is 311v with frequency 60hz and 50hz respectively. the permissible variation range of the frequency is ±0.5hz and ±0.6hz respectively. the rated dc voltage of the hps3 and hps4 is 375 v and 380v respectively. the allowable variation range of the dc voltage is ±25v. the rated load power of hps1, hps2, hps3 and hps3 are 180kw, 130kw, 80kw and 70kw respectively. the storage hps maintains the dc voltage of the common bus, whose rated voltage is 1000v. the rated voltage of the battery is 370v. the engineering, technology & applied science research vol. 8, no. 1, 2018, 2609-2615 2613 www.etasr.com gupta and swarnkar: intertied ac-dc hybrid system power sharing through intelligent droop … allowable variation range of the common bus voltage is ±50v. the parameters of storages, ipc1, ipc2, ipc3 and ipc4 and are introduced in detail in table i. table i. controller parameters controller hps and ipc controller controlling parameter value battery battery voltage 600v common bus rated common bus voltage 1000v voltage controller storage kp 0.0007a/v 2 storage ki 0.07a/v 2-s ipc 3 & 4 kp 0.6a/v 2 ipc 3 & 4 ki 50a/v 2-s ipc 1 & 2 kp 0.8a/v ipc 1 & 2 ki 100a/v-s current controller storage kp 8v/a ipc 3 & 4 kp 3v/a coordinated power control coeffiecient α1=4, α2=0.75 kp 0.03hz ki 3hz/s frequency f1=60hz, f2=50hz to verify the proposed control, the dynamics of the intertied hybrid system operation states of the hps1 are changed while other hps states were kept stable. the system works in islanded mode under 2 states where statei and stateii represents the rated state and variable state respectively. in state-ii, load increases from 130kw to 180kw under the rated ac frequency and voltage. figure 6 shows the dynamics of the intertied hybrid system with the proposed control with changes in operation states of the hps1. figure 6(a) shows the load power where load at hps1 is suddenly increased from 180kw to 260kw. the ac frequencies are changed in coordination, which shows that ac and dc hpss support each other. in state ii, the load power of hps1 increases, consequently ac frequency decreases.due to hps2lower capacity relative changes of f1are smaller compared to the relative changes of f2. from figure 6(b), it is observed that the power coordination among hpss is well achieved. increase in the load power of hps1 is the overloading state of hps1. the other hps supports the power consumption by decreasing the dc voltages and ac frequencies. to match with electrical demand at hps1, all other hps supports and ipc are adjusting the power output according to correction coefficient α. since the correction coefficient α is different for different hpss so the relative changes in acfrequencies and dc voltages will be different as shown in figure 6(c). figure 7(a) shows the load power where load at hps1 is suddenly decreased from 240kw to 170kw but load on other hps remains constant. to cope up with the decrease in load all other ipcs will coordinate and decrease the source power according to total load demand (figure 7(b)). the incremental source power is based upon the correction coefficient. since the correction coefficient of all hpss is different and based upon hps capacity, each hps will change power accordingly.the decrease in load results in increase in frequency and due to coordinated control alone hps1 will not bear the major changes, the other hps will substantially increase the frequency in specified limit which reduces the overburden on hps1. (a) (b) (c) fig. 6. simulation results of intertied hybrid system with coordinated control (a) load power for increase in load on hps1 (b) source power for increase in load on hps1 (c) frequency for increase in load on hps1 to additionally verify the viability of the proposed power management method, the dynamics of the intertied hybrid system are tested with changes in operating conditions of the dc hps3. in figure 8 the outcomes are presented. as figure 8 shows, there are two states. the entire system operates in the stand alone mode with state i as rated state and state ii as variable state. in stateii, load on hps3 increases from 70kw to 130kw at 0.2 sec under the rated dc voltage. the operation states of the other hps in intertied hps are not changed. figure 8(a) demonstrates the change in load power of hps3.as shown in figure 8(b), due to changes in load power of hps3dc voltages of other hps changes in coordination, which implies that all hpss in intertied hybrid system can support each other. engineering, technology & applied science research vol. 8, no. 1, 2018, 2609-2615 2614 www.etasr.com gupta and swarnkar: intertied ac-dc hybrid system power sharing through intelligent droop … state i represents increase in load power of hps3, the coordination control will match the load demand with all the hps connected in intertied hybrid system as shown in figure 8(c). (a) (b) (c) fig. 7. simulation results of intertied hybrid system with coordinated control (a) load power for decrease in load on hps1 (b) source power for decrease in load on hps1 (c) frequency for decrease in load on hps1 to show further the viability of the proposed power management method, the dynamics of the intertied hybrid system are tested with decrease in load on hps3. figure 9 is the outcome with the proposed control. as evident from figure 9 the load on hps3 decreases from 70kw to 130kw at 0.2sec under the rated dc voltage. the operating conditions of all hps connected to intertied hybrid system are unchanged. figure 9(a) shows the change in load power of hps3 at 0.2sec. from 60kw to 30kw. decrease in load at hps3 will result in increase in dc voltage and cordinated control increases the dc voltage of other hps proportionate to the correction coefficient. in state i when the load power of hps decreases, due to the coordination control the source power of all hps will decrease accordingly as shown in figure 9(c). (a) (b) (c) fig. 8. simulation results of intertied hybrid system with coordinated control (a) load power for increase in load on hps3 (b) source power for increase in load on hps3 (c) frequency for increase in load on hps3 engineering, technology & applied science research vol. 8, no. 1, 2018, 2609-2615 2615 www.etasr.com gupta and swarnkar: intertied ac-dc hybrid system power sharing through intelligent droop … (a) (b) (c) fig. 9. simulation results of intertied hybrid system with coordinated control (a) load power for decrease in load on hps3 (b) source power for decrease in load on hps3 (c) frequency for decrease in load on hps3 the above mentioned results clearly show that the proposed power management method works well under different conditions and effective coordination among all hps is achieved. vi. conclusion a new control technique for an intertied hybrid ac/dc system with numerous hpss is proposed. the proposed decentralized power management method achieves good coordination among all hpss. in respect to common bus a pdcvdc 2 droop control strategy is proposed which maintains the common bus voltage and realizes power sharing in the storage hps. also the coordinated power control strategy ensures interaction among multiple hpss to look after the common bus voltage, ac frequency and dc voltage for the individual ipcs and to ensure proper power sharing. the results with coordinated control and without coordinated control are compared. the proposed control takes system capacities into consideration, which ensures the proper supply-demand and power quality of the intertied hps. references [1] m. reza, “stability analysis of transmission systems with high penetration of distributed generation”, phdthesis, delft technische universiteit, faculty of electrical engineering, mathematics and computer science, 2006 [2] p. piagi, r. h. lasseter, “autonomous control of microgrids”, ieee power engineering society general meeting,pp. 8-11, 2006 [3] m. c. chandorkar, d. m. divan, r. adapa, “control of parallel connected inverters in standalone ac supply systems”, ieee transactions on industry applications, vol. 29, no. 1, pp. 136–143, 1993 [4] n. pogaku, m. prodanovic, t. c. green, “modeling, analysis and testing of autonomous operation of an inverter-based microgrid”, ieee transactions on power electronics, vol. 22, no. 2, pp. 613–625, 2007 [5] d. de, v. ramanarayanan, “decentralized parallel operation of inverters sharing unbalanced and nonlinear loads”, ieee transactions on power electronics, vol. 25, no. 12, pp. 3015–3025, 2010 [6] m. prodanovic, t. c. green, h. mansir, “a survey of control methods for parallel three-phase inverters connection”,eighth international conference onpower electronics and variable speed drives, no. 475, pp. 472–477, 2000 [7] v. nasirian, s. moayedi, a. davoudi, f. l. lewis, “distributed cooperative control of dc microgrids,”ieee transactions on power electronics, vol. 30, no. 4, pp. 2288-2303, 2015 [8] p. wang, x. lu, x. yang, w. wang, d. xu, “an improved distributed secondary control method for dc microgrids with enhanced dynamic current sharing performance,”ieee transactions on power electronics, vol. 31, no. 9, pp. 6658-6673, 2016 [9] p. h. huang, p. c. liu, w. xiao, m. s. el moursi, “a novel droop-based average voltage sharing control strategy for dc microgrids,” ieee transactions on smart grid, vol. 6, no. 3, pp. 1096-1106, 2015 [10] x. lu, j. m. guerrero, k. sun, j. c. vasquez, “an improved droop control method for dc microgrids based on low bandwidth communication with dc bus voltage restoration and enhanced current sharing accuracy,”ieee transactions on power electronics, vol. 29, no. 4, pp. 1800-1812, 2014 [11] v. nasirian, s. moayedi, a. davoudi, f. l. lewis, “distributed cooperative control of dc microgrids,”ieee transactions on power electronics, vol. 30, no. 4, pp. 2288-2303, 2015 [12] f. nejabatkhah, y. w. li, “overview of power management strategies of hybrid ac/dc microgrid,”ieee transactions on power electronics, vol. 30, no. 12, pp. 7072-7089, 2015 [13] n. eghtedarpour, e. farjah, “power control and management in a hybrid ac/dc microgrid,” ieee transactions on smart grid, vol. 5, no. 3, pp. 1494-1505, 2014 [14] m. hosseinzadeh, f. rajaei salmasi, “power management of an isolated hybrid ac/dc micro-grid with fuzzy control of battery banks,”iet renewable power generation, vol. 9, no. 5, pp. 484-493, 2015 microsoft word etasr_v13_n4_pp11472-11483 engineering, technology & applied science research vol. 13, no. 4, 2023, 11472-11483 11472 www.etasr.com kassem et al.: prediction of solar irradiation in africa using linear-nonlinear hybrid models prediction of solar irradiation in africa using linear-nonlinear hybrid models youssef kassem department of mechanical engineering, engineering faculty, near east university, cyprus | energy, environment, and water research center, near east university, cyprus yousseuf.kassem@neu.edu..tr (corresponding author) huseyin camur department of mechanical engineering, engineering faculty, near east university, cyprus huseyin.camur@neu.edu.tr mustapha tanimu adamu department of mechanical engineering, engineering faculty, near east university, cyprus 20215363@std.neu.edu.tr takudzwa chikowero department of mechanical engineering, engineering faculty, near east university, cyprus 20215146@std.neu.edu.tr terry apreala department of mechanical engineering, engineering faculty, near east university, cyprus 20224420@std.neu.edu.tr received: 18 june 2023 | revised: 4 july 2023 | accepted: 5 july 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6131 abstract solar irradiation prediction including global horizontal irradiation (ghi) and direct normal irradiation (dni) is a useful technique for assessing the solar energy potential at specific locations. this study used five artificial neural network (ann) models and multiple linear regression (mlr) to predict ghi and dni in africa. additionally, a hybrid model combining mlr and anns was proposed to predict both ghi and dni and improve the accuracy of individual ann models. solar radiation (ghi and dni) and global meteorological data from 85 cities with different climatic conditions over africa during 2001-2020 were used to train and test the models developed. the pearson correlation coefficient was used to identify the most influential input variables to predict ghi and dni. two scenarios were proposed to achieve the goal, each with different input variables. the first scenario used influential input parameters, while the second incorporated geographical coordinates to assess their impact on solar radiation prediction accuracy. the results revealed that the suggested linear-nonlinear hybrid models outperformed all other models in terms of prediction accuracy. moreover, the investigation revealed that geographical coordinates have a minimal impact on the prediction of solar radiation. keywords-global horizontal irradiation; direct normal irradiation; multiple linear regression; artificial neural networks; hybrid model i. introduction the exploitation of fossil fuels faces increasing political and environmental challenges [1]. the use of renewable energy is one solution to address these issues and meet the growing global demand for electricity. renewable energy offers a solution to the pollution and environmental damage caused by fossil and nuclear energy [2]. the potential of renewable energy has inspired numerous researchers to explore clean technologies, intending to generate clean energy and minimize the effects of climate change [3-5]. among the various renewable resources, solar energy is particularly promising, with applications in electricity generation, as well as air and water heating/cooling [6]. solar photovoltaic (pv) energy generation uses solar modules that consist of multiple solar cells containing a pv material. engineering, technology & applied science research vol. 13, no. 4, 2023, 11472-11483 11473 www.etasr.com kassem et al.: prediction of solar irradiation in africa using linear-nonlinear hybrid models in general, assessing the energy generation potential for various solar technologies is based on two crucial parameters: global horizontal irradiation (ghi) and direct normal irradiation (dni) [7]. accurate measurement and prediction of ghi and dni are crucial in assessing the energy generation potential of various solar technologies. these parameters are key inputs for designing, operating, and optimizing the performance of solar power plants. according to [8], ghi is the total amount of solar radiation received on a horizontal surface, including both direct and diffuse radiation. on the other hand, dni is the amount of solar radiation received directly from the sun's rays, perpendicular to a surface. this type of radiation is particularly important for concentrated solar power (csp) plants that use mirrors or lenses to concentrate sunlight onto a receiver to produce high-temperature heat, which is then used to generate electricity [8]. therefore, accurate and reliable measurements of ghi and dni are essential for the effective operation and management of solar power plants in the future. recently, soft-computing approaches have emerged as particularly effective techniques for modeling global solar radiation in many regions around the world. soft-computing techniques enable efficient identification of relationships between dependent and independent variables, even for nonlinear natural processes. recently, various models have been developed, such as multilayer feed-forward neural networks, support vector machines, autoregressive integrated moving averages, etc., that use different meteorological and geographical elements to estimate the total amount of solar radiation in terms of ghi and dni [9-37]. based on previous scientific studies [9-37], the most relevant input parameters used to predict solar radiation are average temperature, pressure, relative humidity, wind speed, wind direction, sunshine hours, minimum and maximum temperatures, wetbulb temperature, atmospheric temperature, cloudiness, and evaporation. based on the above, various empirical models are used to estimate the annual amount of ghi and dni in africa, which is currently experiencing a major electricity crisis, with approximately 600 million people without access to electricity. rural areas are particularly affected, with electrification rates as low as 10%. this energy poverty has significant negative impacts on the economy, society, and health, as communities rely on unsafe and inefficient energy sources. however, the abundant sunshine in africa provides a unique opportunity for the development of solar energy systems, which have the potential to meet the energy needs of millions of people in the region. in this study, five ann models (feed-forward neural network, cascade forward neural network, elman neural network, layer recurrent neural network, and narx neural network) and multiple linear regression (mlr) were used to predict solar radiation data. moreover, this study proposed linear-nonlinear hybrid models that integrate anns and mlr for ghi and dni prediction. ghi, dni, and global meteorological data from 85 cities in africa with various climatic conditions were used to train and test the developed models. the pearson correlation coefficient was used to identify the most influential input variables for predicting ghi and dni. two scenarios were used for this purpose: the first one was created using the most influential input parameters, while the second incorporated geographical coordinates (latitude, longitude, and altitude) along with the influential input data to assess the impact of geographical coordinates on the accuracy of solar radiation prediction. data were obtained from the nasa power dataset for the period 2000-2021. ii. material and methods a. study area africa is a vast continent that spans the equator, and its climate varies greatly depending on the region. the continent includes several climatic zones, including tropical rainforest, savanna, and desert regions. the latitude and longitude of a region greatly influence its climate, which in turn affects weather patterns. the equator runs through the center of the continent, passing through countries. the weather in africa can also be affected by various natural phenomena, such as the el nino southern oscillation (enso), which is a climate cycle in the pacific ocean that affects global weather patterns. during el nino, the pacific ocean warms, leading to changes in atmospheric pressure and wind patterns that affect rainfall patterns in africa. b. data used the nasa power (prediction of worldwide energy resource) dataset is a comprehensive collection of solar and meteorological data that provides information on various crucial parameters crucial for studying and analyzing renewable energy resources and their potential. the dataset covers locations around the world, allowing researchers and analysts to access solar and meteorological data for virtually any location on earth. the nasa power dataset includes a wide range of parameters related to solar radiation and meteorological conditions. these data include solar radiation including ghi, dni, diffuse horizontal irradiance (dhi), and clear sky ghi, as well as meteorological data including temperature, relative humidity, wind speed, wind direction, precipitation, cloud cover, atmospheric pressure, and more. the dataset offers both hourly and daily temporal resolutions. hourly data are available for certain parameters, allowing for a more detailed analysis of solar and meteorological conditions throughout the day. daily data provide aggregated values for each parameter. the spatial resolution of the nasa power dataset varies depending on the specific parameter and the data source used. in general, the dataset provides information at a spatial resolution of approximately 1 km. the dataset integrates data from various sources, including satellite observations, ground measurements, and atmospheric models. nasa incorporates data from multiple sensors and instruments to provide accurate and reliable information. the nasa power dataset is freely accessible to the public through the nasa power web portal. therefore, data including ghi, dni, surface pressure, average, maximum, and minimum temperature, relative humidity, wind speed at 2 m height, average, maximum, and minimum wind speed at 10 m height, wind direction at 10 m height, frost point temperature, wet bulb temperature, cloud amount, and precipitation were collected for all the selected cities in africa shown in table i. engineering, technology & applied science research vol. 13, no. 4, 2023, 11472-11483 11474 www.etasr.com kassem et al.: prediction of solar irradiation in africa using linear-nonlinear hybrid models table i. information regarding the selected locations location latitude [n°] longitude [e°] altitude [m] location latitude [n°] longitude [e°] altitude [m] cairo 30.0 31.6 350.0 cabinda -5.1 12.3 103.0 kinshasa -4.3 15.3 277.0 fez 33.8 -4.9 971.0 vereeniging -26.6 27.9 1526.0 uyo 5.0 7.9 71.0 giza 30.0 31.2 19.0 mwanza -2.5 32.7 1134.0 luanda -9.5 13.5 201.0 lilongwe -14.0 33.7 1071.0 dar es salaam -6.8 39.3 15.0 kigali -1.9 30.1 1575.0 khartoum 15.6 32.5 387.0 bukavu -2.5 28.9 1533.0 johannesburg -26.2 28.1 1746.0 abomey 6.4 2.3 30.0 abidjan 5.4 -4.0 105.0 nnewi 6.0 7.0 163.0 alexandria 30.9 29.8 18.0 tripoli 32.8 13.3 31.0 addis ababa 9.0 38.8 2315.0 kaduna 10.4 7.9 661.0 nairobi -1.3 36.8 1657.0 aba 5.1 7.4 64.0 cape town -33.3 18.4 35.0 bujumbura -3.3 29.4 798.0 yaoundé 3.9 11.5 715.0 maputo -26.0 32.6 14.0 kano 12.0 8.5 454.0 hargeisa 9.6 44.1 1267.0 east rand -26.4 27.4 1590.0 bobodioulass 11.2 -4.3 420.0 umuahia 5.5 7.5 154.0 shubra el-kheima 30.1 31.2 28.0 douala 36.6 4.1 614.0 ikorodu 6.6 3.5 36.0 casablanca 33.3 -8.0 189.0 asmara 15.3 38.9 2342.0 ibadan 7.4 3.9 223.0 marrakesh 31.6 -8.0 468.0 antananarivo 19.0 46.7 1205.0 tshikapa -3.0 23.8 505.0 abuja 9.1 7.5 473.0 ilorin 8.5 4.5 318.0 kampala 0.3 32.6 1237.0 blantyre -15.8 35.0 698.0 kumasi 6.7 -1.6 260.0 agadir 30.7 -9.6 454.0 dakar 14.7 -17.3 6.0 misratah 32.4 15.1 9.0 port harcourt 4.8 7.0 18.0 lubumbashi -11.7 27.5 1262.0 durban -29.9 31.0 13.0 accra 5.8 0.1 39.0 ouagadougou 12.4 -1.5 299.0 brazzaville -3.0 23.8 505.0 lusaka -15.4 29.2 1149.0 monrovia 6.3 -10.8 6.0 algiers 36.8 3.1 31.0 tunis 33.8 9.4 43.0 bamako 12.6 -8.0 335.0 rabat 34.0 -6.8 87.0 omdurman 15.6 32.5 391.0 lomé 6.1 1.2 14.0 mbuji-mayi -6.1 23.6 678.0 benin city 6.3 5.6 90.0 pretoria -25.7 28.2 1338.0 owerri 5.5 7.0 74.0 kananga -5.9 22.4 636.0 warri 5.5 5.8 5.0 harare -17.9 31.1 1483.0 jos 9.9 8.9 1182.0 onitsha 6.1 6.8 51.0 bangui 4.4 18.6 355.0 n'djamena 12.1 15.1 297.0 nampula -15.1 39.3 430.0 nouakchott 18.1 -16.0 8.0 oran algeria 35.6 -0.7 162.0 mombasa -4.0 39.7 10.0 west rand -26.2 27.5 1589.0 niamey 13.5 2.1 207.0 lubango -14.9 13.5 1774.0 pointe-noire -4.8 11.9 16.0 gqeberha -34.0 25.6 52.0 c. artificial neural networks (anns) anns are a class of machine learning algorithms inspired by the structure and functioning of biological neural networks, such as the human brain [38]. an ann consists of interconnected nodes, called artificial neurons or "nodes," organized into layers. the three main types in an ann are the input, hidden, and output. the connections between neurons in an ann are represented by weights. during the training process, the weights are adjusted based on a mathematical optimization algorithm, such as gradient descent, to minimize the difference between the predicted and desired outputs. this adjustment is performed through a process called backpropagation, in which the error is propagated backward through the network to update the weights. activation functions play a crucial role in determining the output of a neuron based on the weighted inputs. the most common activation functions are logistic-sigmoid (logsig) and tangent-sigmoid (tansig) whose outputs lie between 0 and 1 and are defined as [38]: ������ = ��� � (1) � ���� = �� � �� � (2) in addition, a trial-and-error approach is typically employed to determine the optimal number of nodes in the hidden layer. this study used the trainlm training function, which updates the weights and biases of neuron connections based on the levenberg-marquardt (lm) optimization algorithm. the backpropagation algorithm, a type of gradient descent algorithm, serves as the learning algorithm for this purpose. the training process of an ann is crucial, involving the adjustment of weights and biases to minimize the disparity between the ann's output and the desired values. the mean squared error (mse) is used to optimize the performance of the trained ann model, which quantifies the average squared engineering, technology & applied science research vol. 13, no. 4, 2023, 11472-11483 11475 www.etasr.com kassem et al.: prediction of solar irradiation in africa using linear-nonlinear hybrid models difference between the predicted and actual values, serving as a measure to guide the training procedure toward better accuracy. figure 1 illustrates the schematic representation of the ann model developed to predict the ghi and dni. fig. 1. schematic representation of the ann model used. 1) feed-forward neural network (ffnn) ffnn is widely used in various domains to analyze different types of problems in different scenarios [38-40]. the levenberg-marquardt algorithm and the backpropagation method are commonly used techniques [40]. the trial and error method is used to determine the appropriate number of hidden layers and neurons, and mse is used to assess the performance of the training algorithm. it is important to note that the data were normalized within the range of 0-1. this study used the backpropagation algorithm for the training process. 2) cascade feed-forward neural network (cfnn) cfnn is conceptually similar to the ffnn [40-42] and consists of three types of layers: an input layer, one or more hidden layers, and an output layer. the input layer receives weights from the input data [38-40]. each subsequent layer receives weights from the input layer and all preceding layers [38-40]. biases are present in all layers, contributing to the network's functionality. the final layer corresponds to the output layer. the configuration of weights and biases is necessary for each layer. during the training phase, mse is computed to assess the model's performance. 3) elman neural network (enn) enn is a feedback neural network known for its exceptional computational capabilities [39-40], and consists of four layers, namely, the input, hidden, context, and output layers [39-40]. the input layer functions as the signal transmission component, while the output layer has a linear weight effect. the distinguishing feature of enn compared to backpropagation neural networks is the inclusion of the context layer [39-40]. 4) layer recurrent neural network (lrnn) lrnn incorporates recurrent connections at the layer level [41]. in traditional rnns, such as the elman or jordan architectures, the recurrent connections are typically at the neuron level. however, in lrnn, recurrent connections are established between entire layers of neurons, and each layer is associated with a recurrent connection that allows information to flow from the previous to the current time step within the same layer [41]. this enables the network to capture and utilize temporal dependencies in sequential data. recurrent connections in lrnn can improve the model's ability to process and analyze time series or sequential data, making it particularly suitable for tasks such as speech recognition, language modeling, and music generation, where capturing long-term dependencies is crucial. by incorporating layer-level recurrent connections, lrnn provides an alternative approach to modeling sequential data compared to traditional recurrent architectures. its unique structure allows the efficient processing of temporal information and can lead to improved performance in tasks that involve sequential data analysis. 5) nonlinear autoregressive retwork with exogenous input (narx) narx combines autoregressive elements with exogenous input to predict future values of a time series [42]. it is designed to capture nonlinear dependencies and patterns in time series data, incorporating both the past values of the target series (autoregressive component) and external factors or inputs that may influence the target series (exogenous component). narx typically consists of an input layer, one or more hidden layers, and an output layer. the input layer receives both the past values of the target series (autoregressive inputs) and any exogenous inputs that may be available. the hidden layers process the input information and learn to capture the nonlinear relationships and dynamics of the data. finally, the output layer generates the predicted values of the target series. an important aspect of the narx model is the use of time-delayed inputs, where past values of the target series and exogenous inputs are fed as input features with a time delay. the model can consider historical information and dependencies between past and future observations by including these time-delayed inputs. training the narx model typically involves using optimization algorithms, such as gradient descent, to adjust its weights and biases to minimize prediction errors. the performance of the narx model can be evaluated using mse or root mean squared error (rmse). narx has been used in various domains, including finance, economics, weather forecasting, and time series prediction tasks in general. its ability to capture nonlinear relationships and incorporate exogenous factors makes it a powerful tool for modeling and predicting complex time-series data. d. multiple linear regression (mlr) mlr is a statistical method to analyze the relationship between a dependent variable and multiple independent variables. it extends the concept of simple linear regression by considering multiple predictors simultaneously. in mlr, the goal is to create a linear equation that best fits the relationship between the dependent and independent variables. engineering, technology & applied science research vol. 13, no. 4, 2023, 11472-11483 11476 www.etasr.com kassem et al.: prediction of solar irradiation in africa using linear-nonlinear hybrid models e. hybrid modeling (hm) hm is a valuable technique for capturing different parts of the underlying patterns by combining several models [43]. in this study, an hm was developed by combining the predicted values of mlr and estimated residuals (error) by a nonlinear model (computational models). three steps were taken in the development of hm:  step 1: estimate the properties using the mathematical models and determine the residuals.  step 2: pass the residual through computational models to capture the nonlinearity of the data.  step 3: combine the obtained output from the mathematical and computational models to predict fuel properties. f. statistical indices the performance evaluation of the developed models involves the utilization of several statistical metrics. this study used the coefficient of determination (r2), rmse, and mean absolute error (mae). equations (3)-(5) present the mathematical expressions for these metrics. �� = 1 − ∑ ���,����,�� ����� ∑ ���,����,� !������ (3) �#$% = &�' ∑ � �,( − ),( � �'(*� (4) #+% = �' ∑ , �,( − ),( ,'(*� (5) table ii. descriptive statistics of the used data city dni (kwh/m 2 ) class ghi (kwh/m 2 ) class city dni (kwh/m 2 ) class ghi (kwh/m 2 ) class aba 929 1 (poor) 1650 4 (good) kigali 1142 2 (marginal) 1804 4 (good) abdijan 1004 2 (marginal) 1707 4 (good) kinshasa 1002 2 (marginal) 1640 4 (good) abomey calavi 1013 2 (marginal) 1692 4 (good) kumasi 1023 2 (marginal) 1713 4 (good) abuja 1321 3 (fair) 1918 5 (excellent) libreville 847 1 (poor) 1568 4 (good) accra 1254 2 (marginal) 1849 5 (excellent) lilongwe 1718 4 (good) 2010 5 (excellent) addis ababa 2111 5 (excellent) 2128 5 (excellent) lokoja 1080 2 (marginal) 1762 4 (good) agadir 2196 6 (outstanding) 2072 5 (excellent) lome 1091 2 (marginal) 1764 4 (good) alexandria 2111 5 (excellent) 2128 5 (excellent) luanda 1215 2 (marginal) 1752 4 (good) algiers 1756 4 (good) 1749 4 (good) lubango 2206 6 (outstanding) 2206 6 (outstanding) antananarivo 2086 5 (excellent) 2146 5 (excellent)) lubumbashi 1842 5 (excellent) 2082 5 (excellent) asmara 2027 5 (excellent) 2236 6 (outstanding) lusaka 2401 6 (outstanding) 2223 6 (outstanding) bamako 1754 4 (good) 2131 5 (excellent) maiduguri 1707 4 (good) 2153 6 (outstanding) bangui 1261 3 (fair) 1860 5 (excellent) maputo 1806 4 (good) 1833 4 (good) benguela 1866 5 (excellent) 2051 5 (excellent) marrakesh 2367 6 (outstanding) 2062 5 (excellent) benin city 914 1 (poor) 1625 4 (good) mbuji-mayi 1330 3 (fair) 1865 5 (excellent) blantyre 1716 4 (good) 1994 5 (excellent)) misratah 1777 4 (good) 1863 5 (excellent) bobo dioulasso 1658 4 (good) 2156 6 (outstanding) mombasa 1717 4 (good) 2067 5 (excellent) brazzaville 1023 2 (marginal) 1710 4 (good) monrovia 992 2 (marginal) 1665 4 (good) bujumbura 1184 2 (marginal) 1802 4 (good) mwanza 1577 4 (good) 1999 5 (excellent) bukavu 1075 2 (marginal) 1740 4 (good) nairobi 1761 4 (good) 2116 5 (excellent) cabinda 841 1 (poor) 1507 3 (fair) nampula 1745 4 (good) 2053 5 (excellent) cairo 2084 5 (excellent) 2083 5 (excellent) ndjamena 1849 5 (excellent) 2227 6 (outstanding) cape town 2516 6 (outstanding) 2025 5 (excellent) niamey 1806 4 (good) 2204 6 (outstanding) casablanca 1897 5 (excellent) 1891 5 (excellent) nnewi 899 1 (poor) 1613 4 (good) dakar 1589 4 (good) 2099 5 (excellent) nouakchott 1917 5 (excellent) 2289 6 (outstanding) dar es salam 1750 4 (good) 2062 5 (excellent) omdurman 2423 6 (outstanding) 2405 6 (outstanding) doula 852 1 (poor) 1554 4 (good) onitsha 955 2 (marginal) 1665 4 (good) durban 1679 4 (good) 1706 4 (good) oran 1813 4 (good) 1807 4 (good) east rand 992 2 (marginal) 1016 1 (poor) ouagadougou 1690 4 (good) 2119 5 (excellent) enugu 1019 2 (marginal) 1722 4 (good) owerri 929 1 (poor) 1650 4 (good) fez 2094 5 (excellent) 1956 5 (excellent) point-noire 902 1 (poor) 1555 4 (good) giza 1005 2 (marginal) 1676 4 (good) port harcourt 834 1 (poor) 1504 3 (fair) gqeberha 2124 5 (excellent) 1827 4 (good) pretoria 2323 6 (outstanding) 2070 5 (excellent) harare 2029 5 (excellent) 2117 5 (excellent) rabat 2197 6 (outstanding) 1965 5 (excellent) hargeisa 2460 6 (outstanding) 2442 6 (outstanding) shubra el-kheima 2084 5 (excellent) 2083 5 (excellent) ibadan 982 2 (marginal) 1676 4 (good) tangier 1935 5 (excellent) 1801 4 (good) ikorodu 1005 2 (marginal) 1676 4 (good) tripoli 1856 5 (excellent) 1970 5 (excellent) ilorin 1182 2 (marginal) 1824 4 (good) tshikapa 1022 2 (marginal) 1681 4 (good) johannesburg 2224 6 (outstanding) 2030 5 (excellent) tunis 2174 5 (excellent) 2038 5 (excellent) jos 1335 3 (fair) 1930 5 (excellent) umuahia 929 1 (poor) 1650 4 (good) kaduna 1510 3 (fair) 2038 5 (excellent) uyo 929 1 (poor) 1650 4 (good) kampala 1309 3 (fair) 1932 5 (excellent) vereeniging 2303 6 (outstanding) 2057 5 (excellent) kananga 1164 2 (marginal) 1779 4 (good) warri 809 1 (poor) 1555 4 (good) kano 1615 4 (good) 2126 5 (excellent)) west rand 2303 6 (outstanding) 2057 5 (excellent) khartoum 2423 6 (outstanding) 2405 6 (outstanding) yaounde 856 1 (poor) 1633 4 (good) engineering, technology & applied science research vol. 13, no. 4, 2023, 11472-11483 11477 www.etasr.com kassem et al.: prediction of solar irradiation in africa using linear-nonlinear hybrid models iii. results and discussion a. solar energy characteristics the classification of the solar energy potential was determined considering the annual ghi and dni values. the classification of solar resources can be found in [44]. table ii presents the classification of solar resources in a specific city based on ghi and dni values. based on the annual value of ghi, it is observed that most of the selected regions exhibit abundant solar resources and are classified into good, excellent, and outstanding categories. furthermore, solar resources in the east are classified as poor (class 1). moreover, it is noticed that the solar resources in cabinda and port harcourt are categorized as fair (class 3). consequently, these regions emerge as the most favorable locations for the future installation of pv systems, primarily due to their significantly high gsr values. based on the annual value of the dni, solar resources in 14% of the selected regions were classified as outstanding (class 6). these regions are agadir, rabat, lubango, johannesburg, vereeniging, west rand, pretoria, marrakesh, lusaka, khartoum, omdurman, hargeisa, and cape town. furthermore, solar resources in 14% of the selected regions (warri, port harcourt, cabinda, libreville, doula, yaounde, nnewi, point-noire, benin city, aba, owerri, umuahia, and uyo) were classified as poor (class 1). consequently, based on the high values of ghi and dni, it can be concluded that most of the selected locations are well-suited for the installation of both largeand small-scale pv systems. moreover, these regions are also highly suitable for implementing flat-plate pv systems and csp systems. b. selecting relevant parameters the evaluation of the solar potential of a specific location is a crucial initial step in the effective planning of solar energy systems. additionally, the prediction of solar radiation is influenced by various meteorological and geographical variables, making the identification of appropriate factors for accurate solar radiation prediction a significant area of research. according to [45], accurate information about the specific amount of solar energy available at a particular geographical location during a given period is essential and plays a vital role in the design process of pv systems. moreover, meteorological parameters play a pivotal role in influencing the amount of solar radiation [46-47]. furthermore, the orientation angles of a pv system have a significant impact on its performance [48-49]. table iii. pearson correlation matrix for input and output parameters ghi sl az sp tav rh ws-2 wd ws fpt wpt tmax tmin ca wsmax wsmin pc ghi sl 1 az -0.1 1 sp -0.13 0.49 1 tav -0.26 0.457 0.364 1 rh -0.27 0.076 0.315 -0.01 1 ws-2 0.161 -0.15 0.219 -0.29 -0.26 1 wd 0.023 0.24 0.312 -0.12 0.091 0.116 1 ws 0.185 -0.19 0.171 -0.33 -0.33 0.988 0.084 1 fpt -0.36 0.283 0.451 0.514 0.845 -0.36 0.018 -0.44 1 wpt -0.37 0.398 0.476 0.797 0.589 -0.38 -0.04 -0.45 0.928 1 tmax 0.225 0.244 0.062 0.218 -0.76 0.034 0.032 0.09 -0.53 -0.28 1 tmin -0.38 0.277 0.396 0.732 0.557 -0.23 -0.1 -0.32 0.869 0.93 -0.38 1 ca -0.24 0.089 0.014 0.278 0.677 -0.63 -0.19 -0.67 0.701 0.614 -0.56 0.587 1 wsmax 0.287 -0.22 0.038 -0.57 -0.37 0.822 0.079 0.852 -0.6 -0.67 0.178 -0.6 -0.67 1 wsmin -0.03 -0.09 0.158 0.011 -0.02 0.377 0.043 0.374 0 0.005 -0.04 0.069 -0.19 0.173 1 pc -0.27 0.104 0.03 0.266 0.642 -0.58 -0.15 -0.61 0.661 0.581 -0.48 0.502 0.732 -0.601 -0.159 1 ghi 0.162 -0.11 -0.36 0.013 -0.79 0.402 -0.08 0.444 -0.64 -0.45 0.557 -0.38 -0.76 0.385 0.123 -0.56 1 dni sl az sp tav rh ws-2 wd ws fpt wpt tmax tmin ca wsmax wsmin pc dni sl 1 az -0.1 1 sp -0.13 0.49 1 tav -0.26 0.457 0.364 1 rh -0.27 0.076 0.315 -0.01 1 ws-2 0.161 -0.15 0.219 -0.29 -0.26 1 wd 0.023 0.24 0.312 -0.12 0.091 0.116 1 ws 0.185 -0.19 0.171 -0.33 -0.33 0.988 0.084 1 fpt -0.36 0.283 0.451 0.514 0.845 -0.36 0.018 -0.44 1 wpt -0.37 0.398 0.476 0.797 0.589 -0.38 -0.04 -0.45 0.928 1 tmax 0.225 0.244 0.062 0.218 -0.76 0.034 0.032 0.09 -0.53 -0.28 1 tmin -0.38 0.277 0.396 0.732 0.557 -0.23 -0.1 -0.32 0.869 0.93 -0.38 1 ca -0.24 0.089 0.014 0.278 0.677 -0.63 -0.19 -0.67 0.701 0.614 -0.56 0.587 1 wsmax 0.287 -0.22 0.038 -0.57 -0.37 0.822 0.079 0.852 -0.6 -0.67 0.178 -0.6 -0.67 1 wsmin -0.03 -0.09 0.158 0.011 -0.02 0.377 0.043 0.374 0 0.005 -0.04 0.069 -0.19 0.173 1 pc -0.27 0.104 0.03 0.266 0.642 -0.58 -0.15 -0.61 0.661 0.581 -0.48 0.502 0.732 -0.601 -0.159 1 dni 0.289 -0.29 -0.27 -0.42 -0.72 0.586 0.083 0.637 -0.81 -0.76 0.477 -0.69 -0.92 0.7 0.129 -0.69 1 engineering, technology & applied science research vol. 13, no. 4, 2023, 11472-11483 11478 www.etasr.com kassem et al.: prediction of solar irradiation in africa using linear-nonlinear hybrid models this study used pearson’s correlation to identify the most influential input among potential variables. based on the pearson coefficient, the strength of the relationships can be categorized as follows [50]: 0.00–0.25 indicates a very weak relationship, 0.26–0.49 represents a weak relationship, 0.50– 0.69 corresponds to a moderate relationship, 0.70–0.89 signifies a strong relationship and 0.90–1.0 denotes a very strong relationship. table iii lists the pearson correlation matrix depicting the relationships between the potential input parameters and the failure modes. the matrix provides an overview of the correlation coefficients between these variables. this study investigated the influence of geographical coordinates on the accuracy of the prediction of ghi and dni. to achieve this objective, the proposed models were implemented and evaluated in two different scenarios, as shown in figure 2. different empirical models were used to predict the annual value of ghi and dni. in general, data partitioning can influence model performance [51]. moreover, in [51], it was concluded that empirical models achieve optimal performance when approximately 70-80% of the data are allocated for training and the remaining 20-30% are set aside for testing purposes. consequently, the data were divided into training and testing sets using an arbitrary approach, with 80% of the total data assigned to the training set and the remaining 20% designated for the testing set. table iv displays the descriptive statistics for the selected data. c. results of ann models an iterative algorithm was used to find the best neural network model and determine the optimal combination of input variables and hidden layer neurons. the study considered a range of 1-10 hidden layers and 10000-1000000 trial iterations. the levenberg-marquardt training algorithm was selected for its speed and reliability. each network was trained multiple times to prevent inaccurate estimates. the model with the lowest mse was chosen as the best-trained model. table v presents the optimal network structure and activation function. the performance evaluation of the developed models was performed using r2, rmse, and mae. table vi presents the values of these statistical indexes for all proposed ann models, and the following can be concluded:  for ghi prediction, it is noticed that the ffnn model had the highest r2 value compared to other models. on the other hand, the lrnn model had the lowest rmse and mae values, indicating superior performance compared to the other models. as shown in table vi, the accuracy of ghi prediction was reduced when the geographical coordinates lat, long, and alt were used as input variables for the models.  for dni prediction, it was found that the ffnn model exhibited the highest r2 value among all models, indicating its superiority. besides, the enn model demonstrated the lowest rmse and mae values, suggesting superior performance compared to the others. the results showed that the accuracy of the dni prediction increased when geographic coordinates were used as input variables. table iv. descriptive statistics of the used data data variable unit mean sd min. max. training lat. ° 3.6 17.0 -34.0 36.8 long ° 16.4 15.8 -17.3 46.7 alt. m 555.7 597.6 6.0 2342.0 sl. ° 17.7 15.7 -1.0 90.0 az. ° -54.4 81.8 -180.0 47.0 sp kpa 96.1 5.6 81.4 101.7 tav ℃ 23.6 3.6 8.4 30.1 rh % 68.8 15.2 23.8 89.2 ws-2m m/s 2.4 1.1 0.5 6.1 wd ° 195.2 94.2 0.4 359.5 ws m/s 3.4 1.2 1.0 7.2 fpt ℃ 16.0 5.6 4.1 24.3 wbt ℃ 19.8 3.9 7.2 25.7 tmax ℃ 36.5 4.9 25.3 46.9 tmin ℃ 11.9 5.9 -8.7 23.5 ca % 54.4 15.9 11.4 86.9 wsmax m/s 10.1 3.6 2.8 22.9 wsmin m/s 0.1 0.1 0.0 1.4 pc mm/day 2.8 1.9 0.0 20.3 dni kwh/m2/day 4.3 1.4 2.0 7.7 ghi kwh/m2/day 5.3 0.7 2.6 6.8 testing lat. ° 8.8 20.9 -26.6 35.6 long ° 11.4 11.6 -6.8 31.2 alt. m 403.9 528.1 5.0 1589.0 sl. ° 19.8 11.4 0.0 34.0 az. ° -27.2 67.2 -179.0 18.0 sp kpa 97.2 5.2 84.7 101.6 tav ℃ 22.4 3.4 15.8 28.6 rh % 70.8 15.6 39.3 90.3 ws-2m m/s 2.0 1.0 0.1 4.4 wd ° 228.7 101.0 0.9 360.0 wsav m/s 3.0 1.1 0.7 5.3 fpt ℃ 15.6 6.8 4.5 24.1 wpt ℃ 19.0 4.9 10.8 25.0 tmax ℃ 37.0 4.8 29.1 47.8 tmin ℃ 8.9 7.8 -6.2 21.2 ca % 54.3 18.9 22.8 84.6 wsmax m/s 9.9 4.4 1.7 20.9 wsmin m/s 0.1 0.1 0.0 0.5 pc mm/day 3.0 2.3 0.0 11.0 dni kwh/m2/day 4.2 1.7 1.8 7.1 ghi kwh/m2/day 5.0 0.6 4.0 6.0 sd: standard deviation; min. minimum; max.: maximum table v. best network structure based on the training set for horizontal solar radiation model scenario number of hidden layers number of neurons transfer function ffnn 1 2 5 tansig 2 1 15 tansig enn 1 2 10 logsig 2 2 10 tansig cfnn 1 1 15 logsig 2 1 5 tansig lrnn 1 2 5 tansig 2 2 15 tansig narx 1 2 15 logsig 2 1 5 tansig engineering, technology & applied science research vol. 13, no. 4, 2023, 11472-11483 11479 www.etasr.com kassem et al.: prediction of solar irradiation in africa using linear-nonlinear hybrid models fig. 2. model development for predicting ghi and dni considering the two scenarios. table vi. statistical indexes and scenario used for all proposed ann models in testing output scenario variable ffnn lrnn cfnn enn narx ghi sghi#1 r 2 0.8287 0.5404 0.8278 0.7986 0.7858 rmse 0.4386 0.3976 0.4125 0.4144 0.3537 mae 0.3826 0.3073 0.3438 0.3276 0.2472 sghi#2 r 2 0.8154 0.7657 0.5637 0.8263 0.6443 rmse 0.3226 0.4102 0.3920 0.6104 0.4080 mae 0.2711 0.3414 0.3283 0.5434 0.3029 dni sdni#1 r 2 0.9232 0.4533 0.9095 0.9047 0.9105 rmse 0.5975 1.5089 0.6266 0.5340 0.6725 mae 0.4354 1.0055 0.4458 0.3837 0.4945 sdni#2 r 2 0.8862 0.4739 0.9249 0.8987 0.8650 rmse 0.6694 1.4296 0.7061 0.5902 0.6720 mae 0.5243 0.9555 0.5563 0.4505 0.5075 rmse and mae are in kwh/m2 d. results of mlr mlr was used to predict the ghi and dni in africa. the training data were used to derive mathematical equations, represented by the following equations for the two scenarios: /01 = 8.562 − 0.035 ∙ �0 : 0.021 ∙ ;<= −0.018 ∙ => ? − 0.014 ∙ a+ : 0.012 ∙ <a (6) /01 = 9.172 − 0.049 ∙ �0 : 0.074 ∙ ;<= −0.034 ∙ => ? − 0.017 ∙ a+ : 0.018 ∙ <a :0.011 ∙ d � : 0.001 ∙ d��� (7) ef1 = 8.911 − 0.015 ∙ �0 : 1.533 ∙ g$�h − 1.46 ∙ g$ −0.188 ∙ ;<= − 0.016 ∙ =>�� : 0.061 ∙ g$ijk :0.034 ∙ <a (8) ef1 = 11.092 − 0.008 ∙ �0 : 2.113 ∙ g$�h − 2.078 ∙ g$ −0.268 ∙ ;<= − 0.022 ∙ =>�� : 0.038 ∙ g$ijk :0.06 ∙ <a − 0.011 ∙ � � − 0.014 ∙ d��� −0.001 ∙ +�� (9) figures 3 and 4 present the time series plots of the observed and predicted ghi and dni values for the two scenarios in the testing phase, using anns and mlr, respectively. fig. 3. time series and the scatter of observed and predicted ghi (a), (b) and dni (c), (d) for best scenario using ann models. engineering, technology & applied science research vol. 13, no. 4, 2023, 11472-11483 11480 www.etasr.com kassem et al.: prediction of solar irradiation in africa using linear-nonlinear hybrid models fig. 4. time series and the scatter of observed and predicted ghi (a), (b) and dni (c), (d) using mlr. the results demonstrate that incorporating latitude, longitude, and altitude as input variables in the models improved the predictive accuracy of ghi and dni by 1.67% and 0.78%, respectively. e. results of the hybrid models an hm refers to combining multiple types of techniques to improve the prediction accuracy of a single model (ffnn, enn, cfnn, lrnn, narx, and mlr). figures 5 and 6 show that the hms outperformed the others in terms of data fit. this implies that the hms provide a better fit to the observed data compared to the single ann models. figure 5 shows that the enn-mlr (sghi#2) model achieved a notably higher r2 value compared to other models. figure 6 shows that the cfnn-mlr (sdni#2) produced a high r2 value compared to the other models. figure 7 shows time series plots of the observed and predicted ghi and dni values for the testing phase. the enn-mlr (sghi#2) and cfnn-mlr (sdni#2) models demonstrated a stronger correlation and better overall fit to the data. fig. 5. rmse and mae for hm and single ann models for predicting ghi. fig. 6. rmse and mae for hm and single ann models for predicting dni. iv. discussion and conclusion accurate predictions of solar radiation, including ghi and dni, are vital for sizing, estimating energy production, monitoring performance, selecting optimal sites, and facilitating grid integration of solar systems. these predictions enable efficient planning, optimal utilization of solar resources, and the successful implementation of solar energy projects. according to [52], accurate solar radiation predictions help to determine the appropriate size and capacity of solar systems. furthermore, considering the ghi and dni values along with other factors such as panel efficiency and system losses, it is possible to forecast the expected energy output [9, 53]. furthermore, solar radiation measurements and predictions engineering, technology & applied science research vol. 13, no. 4, 2023, 11472-11483 11481 www.etasr.com kassem et al.: prediction of solar irradiation in africa using linear-nonlinear hybrid models allow for the continuous monitoring of the performance of a solar system [54]. additionally, accurate solar radiation predictions are essential for effectively integrating solar energy into the grid [55]. fig. 7. time series and the scatter of observed and predicted ghi and dni values using hms. the performance of 11 empirical models was evaluated for the prediction of ghi and dni. solar radiation data, including ghi and dni, from 85 cities having different climatic conditions all over africa during 2001-2020 were used for training and testing. based on the performance indexes, the proposed linear-nonlinear hybrid models exhibited superior performance in terms of predicting accuracy compared to all the other models considered. furthermore, the results showed that geographical coordinates have a minimal impact on the prediction of solar radiation, as also supported in other studies. in [46], it was found that latitude and longitude have minimal impact on the prediction of solar radiation. moreover, latitude and longitude are mainly used to determine the location of a specific site rather than directly influencing solar radiation levels [56-57]. future research should focus on employing advanced techniques such as knn, regression trees, boosting, and random forest models to improve the precision of predicting global solar radiation and the power output of pv systems. by 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[57] j. l. kafka and m. a. miller, "a climatology of solar irradiance and its controls across the united states: implications for solar panel orientation," renewable energy, vol. 135, pp. 897–907, may 2019, https://doi.org/10.1016/j.renene.2018.12.057. microsoft word 422-final-ed.doc engineering, technology & applied science research vol. 4, no. 2, 2014, 600-604 600 www.etasr.com djebli et al.: uniaxial fatigue of hdpe-100 pipe. experimental analysis uniaxial fatigue of hdpe-100 pipe experimental analysis a. djebli dept. of science and technology, lpq3m university of mascara mascara, algeria djebliabdelkader@yahoo.fr a. aid dept. of science and technology, lpq3m university of mascara mascara, algeria aid_abdelkrim@yahoo.com m. bendouba dept. of science and technology, lpq3m university of mascara mascara, algeria bendoubamos@yahoo.fr a. talha lml haute ecole d’ingénieur lille, france abderrahim.talha@hei.fr n. benseddiq lml université lille1 lille, france noureddine.benseddiq@univ-lille1.fr m. benguediab dept. of mechanics university djilali liabess sidi belabbess, algeria benguediab_m@yahoo.fr s. zengah dept. of science and technology, lpq3m university of mascara mascara, algeria zengahsahnoun@yahoo.fr abstract— in this paper, an experimental analysis for determining the fatigue strength of pe-100, one of the most used high density polyethylene (hdpe) materials for pipes, under cyclic axial loadings is presented. hdpe is a thermoplastic material used for piping systems, such as natural gas distribution systems, sewer systems and cold water systems, which provides a good alternative to metals such as cast iron or carbon steel. one of the causes for failures of hdpe pipes is fatigue which is the result of pipes being subjected to cyclic loading, such as internal pressure, weight loads or external loadings on buried pipes, which generate stress in different directions: circumferential, longitudinal and radial. hdpe pipes are fabricated using an extrusion process, which generates anisotropic properties. by testing in the laboratory a series of identical specimens obtained directly from pe-100 hdpe pipes in longitudinal directions, the relationships between amplitude stress and number of cycles (s-n curve) test frequency 2 hz and stress ratio r = 0.0 are established. keywordspolyethylen; pipe; semi-cristalline; fatigue; damage i. introduction the behavior of polymers gains more and more relevance in the study of materials, due to the growing utilization of polymers in complex applications, as a consequence of their technical advantages and lower cost [1]. the high density polyethylene (hdpe) is one of the most used polymers in the industry due to the diversity of its applications and to the multiple advantages that it has over more conventional materials. hdpe is extensively used in water and natural gas distribution system. however, a piping system is subjected to internal pressure or external loads varying in magnitude and frequency, generating different responses from the material [2]. such cyclic loads cause cumulative damage and cracking that could produce a piping system failure [3]. it is important to emphasize that this presents a problem that should be especially considered, since a stress value lower than yield strength can produce a pipe failure in a relative short period of operation if the pressure is cyclic [4]. in general, during their life, the materials can undergo a progressive damage under the effect of the mechanical, thermal or chemical stresses requests to which they are subjected. some aspects of fatigue crack propagation (fcp) and fracture are often discussed as they relate to specific cumulative damage theories and lifetime prediction methods. earlier reviews in polymer fatigue and fcp can be found in [5–11]. it is probable that the problems in materials subjected to cyclic pressure are generated by intrinsic defects during the manufacture process, which could generate failures in the pipe, causing great economic loss and operational damage in the piping systems [12]. at present, many companies test hdpe piping systems only hydrostatically, which allows the determination of pipe strength to monotonic loads but does not test the behavior of the material for alternating stresses, which are generally smaller than design stresses [13, 14]. life prediction and reliability evaluation is still a challenging problem despite the extensive progress made in the past decades. a comprehensive review of early developments can be found in [15]. the aim of this work is to obtain the fatigue strength and fatigue lifetime of hdpe pipes, specifically pe-100, one of the engineering, technology & applied science research vol. 4, no. 2, 2014, 600-604 601 www.etasr.com djebli et al.: uniaxial fatigue of hdpe-100 pipe. experimental analysis most widely used materials in the fabrication of polymers pipes. ii. material and experimental procedure in this work, pipes of 200 mm outside diameter, nominal wall thickness range between 11.4 and12.7 mm and 12 m length made of hdpe grade pe-100 are used. pipes were supplied by stpm chiali, an algerian company who produces pe-100 pipes for natural gas systems according to en 1555-1à 7 and iso 4437 [16]. the scope of this study includes tensile tests and axial fatigue tests. tensile testing is used for determining the monotonic mechanical properties of hdpe pipes, which are the bases for establishing several stress amplitude levels for fatigue testing. due to ground interaction and intern pressure, the axial stress can be relevant and even be greater than hoop stress. for this reason, it is necessary to evaluate the mechanical behavior of pipes in the axial direction. the specimens for both tensile tests and axial fatigue tests were cut directly from a hdpe grade pe-100 pipe, following the longitudinal direction, as shown in figure 1. cylinder sections were cut by a guillotine cutter used in the plastics pipes axially and transversally, to obtain curved plates, as shown in figure 2. a total of 160 specimens were fabricated in a cnc mechanized center model mill 55 with ge fanuc (emcoconcept mill), using the geometrical specifications shown in figure 3. fig. 1. longitudinal specimen direction for mechanical testing. fig. 2. cutting sections of cylinder fig. 3. tensile specimen according to astm d-638type i (dimensions in mm). a zwik, z 100 uni-axial tension testing machine (shown in figure 4), was used to monotonic tensile testing, according to astm-d638 standards [17]. tensile tests to 2 specimens for each strain rate of 0.1 and 0.01 s-1, were carried out. the uni-axial fatigue was conducted made on the multi-axial test platform of the mechanics laboratory of lille (lml), as shown in figure 5. fig. 4. zwik, z 100 uni-axial tension testing machine fig. 5. overview of the fatigue machine and its accessories engineering, technology & applied science research vol. 4, no. 2, 2014, 600-604 602 www.etasr.com djebli et al.: uniaxial fatigue of hdpe-100 pipe. experimental analysis the main experimental means were:  a platform made of a metal marble 3 m × 5 m in dimension, equipped with mesh rails, which allowed the alignment of cylinders, the fixing of the flanges and the adjustment of structure components.  a servo-hydraulic cylinder (of a set of four available) of total travel of ± 25 mm and maximum capacity of 100 kn, operable at high frequency (150 hz according to the amplitudes of the displacements of the actuator).  a control system to control the cylinder implemented by a console and an instron 8800 digital controller.  the rs software package labsite ist (instron structural testing systems) loaded onto a pc for the generation of instructions, data acquisition and processing the cylinder can be controlled by force, displacement or deformation, figure 5 shows an overview of the platform in biaxial and accessories. the fatigue experiments were carried out under uniaxiale constant amplitudes to determinate the wöhler curves. an equation for the s–n curve for the material was determined from a prior investigation according to astm standards [18]. the minimum number of specimens to obtain a reliable sample size in fatigue testing is determined using the astm e 739 standard [18], with a sample size of 3 for each value of stress amplitude level. table i shows the values of the test parameters considered in fatigue testing: load frequencies, stress ratios (r) and maximum stress levels. maximum stress levels are computed as a function of yield strength obtained from tensile tests. table i. fatigue testing parameters: load frequency (hz) stress ratio maximum stress levels (mpa) 2 0.0 15-16-17-18-19-2022-24-26 the typical scatter in the number of cycles obtained from fatigue tests makes it necessary to process the fatigue failure data using statistical techniques. due to the sample size, the mean square method is used to generate the stress–number of cycles diagrams (s-n) required for studying the fatigue behavior of the hdpe grade pe-100 pipe. each s-n diagram includes two sets of 50% constant probability and power law fitted from least squares) of survival data obtained by processing fatigue data using the normal distribution. then statistical data is adjusted using the least-squares method for obtaining three s-n-p curves (ps=50%). stress amplitude, sa, is computed by: 2 minmax sssa    stress ratio is computed as follow max min s s r   s-n data have usually power-law dependence [3]. for each set of statistical data (ps=50% and least-squares), the following power-law equation (basquin’s equation) is fitted to obtain a mathematical representation of each curve: bnas .max   where the maximum stress (smax) is obtained as a function of a, a coefficient that represents the value of smax at one cycle, and b, an exponent that depends of material and its characteristics. iii. results and discussion a. mechanical properties the mechanical properties for hdpe grade pe-100 pipes based on stress–strain diagrams (figure 6) obtained from tensional testing in longitudinal pipe direction, for 0.1 and 0.01 s-1 are shown in table ii. fig. 6. stress-strain curves for both strain rates, (a) global, (b) small deformation zoom. table ii. pe-100 pipe´s monotonic mechanical properties strain rate  (s-1) yield stress y (mpa) strain at yield y  (%) elastic modulus (mpa) 10-1 22.5 12.36 990 10-2 18.5 15.46 750 engineering, technology & applied science research vol. 4, no. 2, 2014, 600-604 603 www.etasr.com djebli et al.: uniaxial fatigue of hdpe-100 pipe. experimental analysis the curves are typical for semi-crystalline polymers. figure 6 shows the curves obtained for the two strain rates. the difference in the mechanical properties for both strain rates of testing is relevant; however the viscoelastic nature of our hdpe-100 is clearly manifested by the dependence of the strain rate. to examine the response of our hdpe, it is necessary to determine the contribution of viscosity in its behavior through the influence of strain rate on the mechanical properties. as seen in figure 5, the behavior of our hdpe for both strain rates is nonlinear and depends largely on strain rates. that said, it is of great interest for further study, to carefully consider such findings. constant maximum stress levels for fatigue testing were established using the yield strength reported in table 2, obtaining the following values: 24, 22, 20, 19, 18, 17, 16 and 15 mpa. b. elongation change during fatigue tests figure 7 shows the amplitude of specimen elongation measured during fatigue tests for, smax=16 mpa and smax=17 mpa. as shown, an increment of specimen elongation with increment of number of cycles can be observed. it is also shown that elongation changes are greater for 17 mpa than for 16 mpa. it is possible to correlate the elongation change with the cumulative damage phenomenon. these behaviors are expected due to the viscous nature of polymers and the magnitude of damage accumulation induced by cyclic loading, (so they depend widely on stress amplitude). fig. 7. elongation changes during fatigue testing longitudinal direction for two levels of maximum stress 16 an 17 mpa. c. s-n curves in figure 8, s-n-50 % curves obtained from pipe fatigue tests in longitudinal direction for a load frequency of 2 hz and r=0.0 are shown. in this case, stress level of 26 mpa was plotted in order to include the specimens’ low fatigue life time, and this to verify a consistence of basquin’s parameters, especially (a) which designates the maximum stress for one cycle. basquin’s equation for a survival probability of 50% data (ps=50%) is: 0.067 max 32.46s n   (4) in figure 9, experimental values curves obtained from pipe fatigue tests in longitudinal direction are plotted and the s-n curve is obtained directly by a least-squares method. basquin’s equation for a survival probability obtained from the scatter of data is: 0.068 max 32.24s n   (5) fig. 8. modeling the wöhler 50% failure probability. fig. 9. modeling the wöhler curve by the least-squares method. it is clear from the two figures above that the two methods give approximately the same results. table iii summarizes the parameters of basquin’s model for the two probabilistic methods used for establishing the wöhler curve. table iii. parameters for basquin model for the wöhler curve least squares method on the scatter points method of least squares on the midpoints (50%) a (mpa) c r2 a (mpa) c r2 32.24 0.068 0.866 32.46 0.067 0.9484 engineering, technology & applied science research vol. 4, no. 2, 2014, 600-604 604 www.etasr.com djebli et al.: uniaxial fatigue of hdpe-100 pipe. experimental analysis iv. conclusion in this work, an experimental fatigue study was carried out that showed that the fatigue strength of hdpe grade pe-100 pipes depends on the pipe stress. it is shown that the monotonic behavior of hdpe-100 is widely time dependent, because of the dependence on strain rate. subjected to cyclic loading, our hdpe exhibits a softening behavior detected by the increase of maximum elongation under maximum constant stress. fatigue lives of hdpe are widely stochastic and a scatter in the number of cycles to rupture is observed for the same stress level. the explanation of the difference could be related to factors related to the manufacturing process of hdpe grade pe-100 pipes; when a spider header is used for the pipe extrusion, weld lines are generated in the pipe which could cause weakening in circumferential specimens, if these zones are coincident to test zone. this behavior is not convenient for pipes subjected to internal pressure, which is the case for the majority of hdpe pipe applications, due to the greatest principal stress (hoop stress) which is coincident to the circumferential direction and its value can duplicate the longitudinal stress. the results obtained are in good agreement with literature results. acknowledgments authors would like to acknowledge to stpm chiali for the donation of pe-100 pipes and for allowing monotonic testing, and to lml (laboratory of mechanics of lille) for allowing fatigue testing and to mascara university for financial support. references [1] j. brewin, p. chapman, “recent developments in the design and manufacture of plastic pipes”, pipes wagga wagga '99 conference, australia, oct. 12-14, 1999 [2] s. h. joseph, “fatigue failure and service lifetimes in pvc pressure pipes”, plastics and rubber processing and applications, vol 4, 4, pp. 325-330, 1984. [3] n. e. dowling, mechanical behavior of materials. engineering methods for deformation, fracture and fatigue, prentice hall, usa, 1999 [4] a. k. gardner, k. b. king, j. r. cooper, “in-service care considerations of high pressure vessels in a commercial polyethylene process”, joint conference of the pressure vessels and piping, materials, nuclear engineering, solar energy divisions, denver, usa, vol. 48, pp. 151164, 1981 [5] j. a. manson, r. w. hertzberg, “fatigue failure in polymers”, critical review of macromolecular science, vol. 1, pp. 433-500, 1973 [6] r. w. hertzberg, j. a. manson, fatigue of engineering plastics, academic press, inc., orlando, 1980 [7] j. c. radon, “fatigue crack-growth in polymers” international journal of fracture, vol. 16, no. 6, pp. 533-552, 1980 [8] j. a. sauer, g. c. richardson, “fatigue of polymers”, international journal of fracture, vol. 16, no. 6, pp. 499-532, 1980 [9] m. t. takemori, “polymer fatigue”, annual review of materials science, vol. 14, pp. 171-204, 1984 [10] j. a. sauer, c. c. chen, “crazing and fatigue behavior in oneand twophase glassy polymers”, advances in polymer science, vol. 52/53, pp. 169-224, 1983 [11] j. m. schultz, in j. m. schultz, ed., treatise on materials science and technology, part b, academic press, inc., orlando, fla., 1977, p. 599. [12] e. oral, a. s. malhi arnaz, o. k. muratoglu, “mechanisms of decrease in fatigue crack propagation resistance in irradiated and melted uhmwpe”, biomaterials, vol 27, no. 6, pp. 917-925, 2006 [13] s. kannappan, introduction to pipe stress analysis, john wiley and sons, usa, 1986 [14] r. goncalves, introducción al análisis de esfuerzos, segunda edición, editado por r. goncalves, caracas, venezuela, 2002 [15] j. t. p. yao, f. kozin, y. k. wen, j. n. yang, g. i. schueller, o. ditlevsen, “stochastic fatigue, fracture and damage analysis”, structural safety, vol. 3, no. 3-4, pp. 231–267, 1986 [16] stpm chiali, “tubes, polyéthylène (pe) et accessoires”, catalogue technique. [17] astm d 638, american society for testing and material standard test method for tensile properties of plastics, 2002 [18] astme 739-91, standard practice for: statistical analysis of linearized stress-life (s–n) and strain-life (e–n) fatigue data, annual book of astm standards, vol. 03, no. 01, pp.614–260, philadelphia, 1999 microsoft word etasr_v12_n2_pp8328-8334 engineering, technology & applied science research vol. 12, no. 2, 2022, 8328-8334 8328 www.etasr.com zerroug et al.: robust adaptive fuzzy control of nonlinear systems robust adaptive fuzzy control of nonlinear systems nadjat zerroug department of electrical engineering quere laboratory ferhat abbas –sétif 1 university sétif, algeria nadjatzerroug@univ-setif.dz khalissa behih department of electrical engineering lsi laboratory ferhat abbas –sétif 1 university sétif, algeria khalissabehih@univ-setif.dz ziyad bouchama department of electromechanical engineering bachir el ibrahimi university arréridj, algeria ziad.bouchama@unniv-bba.dz khaled zehar department of electrical and electronics engineering university of bahrain al-manama, bahrain khaledzehar@uob.edu.bh received: 26 january 2022 | revised: 11 february 2022 | accepted: 12 february 2022 abstract-in this paper, an adaptive fuzzy fast terminal synergetic controller (ffsc) for a certain class of siso unknown nonlinear dynamic systems is proposed, that uses the concept of terminal attractor design, adaptive fuzzy synergetic control scheme, and lyapunov synthesis approach. in contrast to the existing adaptive fuzzy synergetic control design, where the fuzzy systems are used to approximate the unknown system functions while the synergetic control guarantees robustness and achieves the asymptotic stability of the closed-loop system, in our technique both the continuous synergetic control law and the fuzzy approximator are derived to ensure finite-time convergence. lyapunov conditions for finite-time stability and accuracy proofs in mathematics are presented to prove that the proposed adaptive scheme can achieve finite-time stable tracking of reference input and guarantee of the bonded system signals. simulation results illustrate the design procedures and demonstrate the performance of the proposed controller. keywords-nonlinear dynamic systems; synergetic control; robust control; fast time convergence; adaptive fuzzy systems i. introduction over the last few years, the development of nonlinear control techniques has been an active research topic and significant methods have been established, such as adaptive control [1], feedback control [2, 3], backstepping control [4], and sliding mode control (smc) [1, 5-8]. smc is often adopted due to its inherent advantages of fast dynamic response, guaranteed stability, robustness against matching external disturbances, and internal parameter variations [5-7], but it suffers from the drawback of chattering phenomena which limit the smc from being widely applied. therefore, another concept recently introduced, similar to the smc in the design, robustness, performance, and without discontinuous control law is the synergetic control (sc) theory [9-11]. the sc law, not causing chattering as in the smc approach, depends on a designer chosen macro-variable function imposing the desired dynamics to the system. in this process, system control design needs no model linearization but rather relies on the complete nonlinear system. its robustness and its ease in implementation have put forth this fairly new control approach. the sc has been successfully applied to nonlinear systems [12, 13], in the design of power system stabilizers [14, 15], and in many other electronic devices [10, 11]. in most of these applications, the sc law was designed based on the analytical description of the system dynamics, which is not available or is difficult to formulate. fuzzy systems [16, 17] have been presented to overcome the abovementioned problems in which the universal approximation theorem is used to prove that fuzzy systems can approximate any unknown dynamic system. the adaptive fuzzy sc concept has been proposed to address the control issue of unknown nonlinear dynamics systems [18-20]. the sc guarantees robustness and stability of the closed-loop system while the fuzzy systems are used in an adaptive scheme to approximate the nonlinear system functions. however, in this application, the sc law was designed based on asymptotic stability analysis and the system trajectories evolve to a specified attractor reaching the equilibrium in an infinite time. to address the issues of globally asymptotic stabilization, a terminal sc (tsc) scheme based on the concept of terminal attractor [4, 21-26] has recently been developed [22]. the scheme exhibits superior properties such as fast finite-time convergence to the origin, less steady-state errors, and highprecision performance in addition to disturbance attenuation. these features, however, have been achieved including requirement of prior knowledge about the dynamics of the process to be controlled. in this paper, a fast finite time algorithm combined with adaptive fuzzy systems (ffsc) is proposed to design a robust control system. this approach, inspired from adaptive fuzzy sc [18-20] aims to reinforce robustness and tracking. different nonlinear systems are used in a simulation study to assess the performances and the corresponding author: nadjat zerroug engineering, technology & applied science research vol. 12, no. 2, 2022, 8328-8334 8329 www.etasr.com zerroug et al.: robust adaptive fuzzy control of nonlinear systems effectiveness of the proposed ffsc approach. the obtained results are discussed and compared with the fsc. ii. fast terminal sc of a nonlinear system consider the nonlinear single input single output (siso) system, described by: 1 2 2 1 ( ) ( ) ( ) ( , ) ( , ) ( )) ( ) ( ) x t x t x t f x t g x t u t y t x t =  = +  = � � (1) where ( ) ( ) ( )1 2 x t x t x t=    is a vector of measurable states and ( ),f x t and ( ),g x t are nonlinear continuous functions. the control objective ( )u t is to force the system output ( )y t to track a given bounded desired reference trajectory in finite time and without chattering, i.e. the tracking error must converge to zero, under the constraint that all the signals must be bounded and the system be stable. the sc synthesis of the system (1) begins by defining a designer chosen macrovariable given as: e eψ λ= + � (2) where m e y y= − is the tracking error and 2 m ė x y= − its time derivative, m y is the desired trajectory, and λ is a positive constant. a. terminal synergetic control in this paper, we propose the following desired dynamic evolution of the macro-variable, aiming to reinforce robustness and better tracking in finite-time: p qk t ψ ψ= −� (3) where 0k > , 0t > are positive constants and p and q are positive odd constants with 0 / 1p q< < . taking the integral of both sides of (3) and evaluating the resulting equation in the closed interval ( )0ψ to ( )ftψ gives the following equation [23, 24, 26]: 1 (0) 1 p q f t t p k q ψ − =   −    (4) where f t is finite, indicating a finite-time convergence as opposed to the asymptotic infinite-time convergence to the attractor 0ψ = . this approach inspired from sliding mode techniques [23, 24] will be used to formulate the terminal synergetic control law: 1 ( , ) ( , ) p q m k u y f x t e g x t t λ ψ   = − − −    �� � (5) under the control law (5) with the macro variable (2), the trajectory of the closed-loop nonlinear system (1) can be driven onto the attractor 0ψ = in finite-time given by (4) ensuring rapid tracking. however, the tsc controller is only suitable when the error trajectory is nigh from attractor 0.ψ = to further improve convergence, we propose the fuzzy fast terminal synergetic controller given in the ensuing section. b. fast terminal synergetic control in this section, we will develop the fast terminal synergetic controller which will be robust to matched and mismatched uncertainties and the states system of (1) can converge to the equilibrium point in fast finite-time. therefore, the proposed desired dynamic evolution of the macro-variable is given as: 0 p q t kψ ψ βψ+ + =� (6) the dynamic (6) avoids the above-mentioned problem. it consists on a terminal attractor ( )p q k tψ ψ= −� when the error trajectory is close to 0ψ = and a fast convergence ( )tψ ψ β= −� when the error trajectory is far from 0.ψ = according to (6), we find the new convergence time determined by [23,24]: 1 * (0) ln 1 p q f t k t kp q βψ β − + =   −    (7) the fast synergetic control law u can then be obtained by (8): 1 ( ) ( ) p q m k u f x y e g x t t β λ ψ ψ   = − + − − −    �� � (8) under the control law (8) with macro-variable (2), the error trajectory of the closed-loop system (1) can be driven onto the manifold 0ψ = in finite time (7) ensuring rapid tracking. c. stability and robustness analysis the stability and robustness issue of the controller are addressed here by using the lyapunov stability theory. lemma 1 [24,26]: consider the nonlinear system described in (1). suppose there is a continuously differentiable function ( )v x defined in a neighborhood nd ⊂ ℜ of the origin, and there are real numbers , 0ρ σ > and 0 1γ< < such that ( ) 0v x > on d . the extended lyapunov function can be described as: ( ) ( ) ( ) 0v x v x v xγρ σ+ + ≤� (9) and the settling time can be given by: ( ) ( ) 1 0 0 1 1 f x t x ln γ ρ σ ρ γ σ − + ′ ≤ − (10) engineering, technology & applied science research vol. 12, no. 2, 2022, 8328-8334 8330 www.etasr.com zerroug et al.: robust adaptive fuzzy control of nonlinear systems proof: let’s consider the lyapunov function candidate 21 2 v ψ= . the time derivative of this function can be written as: [ ]( , ) ( , ) mv e f x t g x t u yλ ψ= + + −� � �� (11) by substituting (8) into (11), we obtain: 1 2 p qk v t t β ψ ψ   +   ≤ − −� (12) using ( ) 1 22vψ = , (12) can be rewritten as: 2 22 2 0 p q p qq qk v v v t t β  +    +     + + ≤� (13) we define the constants: 2 t β ρ = , 2 2 p q q k t σ  +     = and ( )1 2p qγ = + , such that ( )0 1 2 1p q< + < . in (13), the stability of the closed-loop system is guaranteed and the error trajectory can be driven onto the manifold 0ψ = in the finitetime ' f t given in (10). these performances with the control law given by (8), are easily designed if the dynamics of the system are known. however, nonlinear system parameters are not well known and imprecise, so it is difficult to implement the control law (8). therefore, an adaptive fuzzy finite time synergetic controller using a fuzzy logic system is proposed to circumvent these problems. iii. fuzzy fast terminal synergetic control of a nonlinear unknown system in a practical real case ( ),f x t and ( ),g x t are unknown and the external disturbance ( ) 0d t ≠ , so obtaining the control law of (8) is difficult. in this case, our proposal is to replace ( ) ( ),f x t d t+ , and ( ),g x t with their approximates using fuzzy logic systems and design an online updating law to estimate the system parameters by using lyapunov stability theory [25, 26]. using singleton fuzzification, product inference, and center-average defuzzification, the output of the fuzzy system is obtained as: ( ) ( ) ( ) 1 1 1 1 l i l i nm l if l i nm if l i y x y x x µ µ = = = =        =         ∑ ∏ ∑ ∏ (14) where ( ) i l f i xµ is the membership function of the linguistic variable i x and l y is the point in r at which l g µ achieves its maximum value (assuming ( ) 1l l g yµ = ). introducing the concept of fuzzy basis function vector ξ(x), (14) can be rewritten as: ( ) ( ) t y x xθ ξ= (15) where [ ]1... t l mθ θ θ= and 1 ( ) ( )... ( ) t m x x xξ ξ ξ =   are the fuzzy basis functions defined as: ( ) ( ) ( ) 1 1 1 l i l i n if i l nm if l i x x x µ ξ µ = = = =         ∏ ∑ ∏ (16) it should be noted that the approximation error issue has been addressed in detail in [16, 17], where the theorem is used to prove that the fuzzy systems can approximate any continuous real function on a compact set to any arbitrary accuracy while fuzzy rules are derived based on experts recommendations. therefore, the new control law is rewritten as: 1 ˆ( / ) ˆ( / ) p q f m g k u f x y e g x t t β θ λ ψ ψ θ = − + − − −   �� � (17) theorem [16, 17]: consider the control problem of the nonlinear system (1). if the control (17) is used and the parameter vectors f θ and g θ adjusted by the adaptive law are: ( ) f f f r xθ ψξ= −� (18) ( ) g g g r x uθ ψξ= −� (19) then the closed loop system signals will be bounded and the tracking error will converge to zero asymptotically. proof: the optimal parameters of fuzzy systems are defined as: ( ) ( )ˆˆ arg min sup / ( ( )) nf f f f z x r f x f x d t θ θ θ ∈ ∈   = − +    (20) ( ) ( )ˆ ˆarg min sup / ng g g g z x r g x g x θ θ θ ∈ ∈   = −   (21) where f z and g z are constraint sets for f θ and g θ respectively. the minimum approximation error is defined as: ( ) ( )ˆ ˆ( ) ( ) ( , ) ( ) ( , )f gw f x d t f x g x g x uθ θ = + − + −  (22) then, we have: ( ) ( ) t t f f g g m e x x u yψ λ θ ξ θ ξ= + + −� � �� (23) ˆ ˆ( ) ( ) ( ) ( ) t t t f f g g f f t g g m e x x u x x u w y ψ λ θ ξ θ ξ θ ξ θ ξ = + + + + + − �� � � �� (24) let: engineering, technology & applied science research vol. 12, no. 2, 2022, 8328-8334 8331 www.etasr.com zerroug et al.: robust adaptive fuzzy control of nonlinear systems ˆ ˆ f f f g g g θ θ θ θ θ θ  = −  = − � � (25) and let's consider the lyapunov function candidate: 21 1 1 2 2 2 t t f f g g f g v r r ψ θ θ θ θ= + +� � � � (26) where f r and g r are positive constants that will be used as learning rates in the adaptation procedure. the time derivative of v is obtained as: 1 1t t f f g g f g v r r ψψ θ θ θ θ= + +� �� � � � �� (27) ˆ ˆ( ) ( ) 1 1ˆ ˆ( ) ( ) t t f f g g m t t f f f g g g f g v e x x u w y x x u r r ψ λ θ ξ θ ξ θ ψξ θ θ ψξ θ  = + + + −      + + + +           � � �� � � � � (28) substituting the derivatives of f θ and g θ into (25), leads to: ( 1) 2 p q p q k v w t t k w t t β ψ ψ ψ β ψ ψ ψ +   = − − +   ≤ − − + � (29) based on the universal approximation theorem, the term wψ is very small, such that 0v ≤� . as a result, all closedloop system signals are bounded. iv. simulation results in order to investigate the proposed controller, simulations of the following examples were considered. a. example1: first order nonlinear system to illustrate the effectiveness of the proposed control algorithm, we design the ffsc controller for high-precision tracking of a nonlinear dynamic system given by (30), whose simulation results are compared with the fsc control scheme. ( ) ( ) ( ) ( )x t f x u t d t= + +� (30) where the nonlinear function ( ) ( ) ( ) 1 1 x t x t e f x e − − − = + is assumed to be unknown. the fuzzy set is defined over the discourse interval [-3, +3]. the membership functions are chosen as: ( )( )( ) 1 ( ) 1 exp 5 2 , nb x xµ − = + + ( )( )2( ) exp 1.5 ,nm x xµ = − + ( )( )2( ) exp 0.5 ,ns x xµ = − + ( )( )2( ) exp 0.5 ,ps x xµ = − − ( )( )2( ) exp 1.5 ,pm x xµ = − − ( )( )( ) 1 ( ) 1 exp 5 2 pb x xµ − = + − the simulation results with two different initial conditions are shown in figures 1-3. in both cases, the system outputs have good tracking, in the other hand the new controller has a faster convergence rate than fsc. the disturbance ( ) ( )0.3 1.1d t randn= has been taken into consideration in the simulation at 0.15s 1st≤ ≤ . as shown in figure 1, the control signals for both approaches are continuous and smooth despite the external perturbations, while the convergence of the signal of the proposed control to the equilibrium is faster. it can be seen from figure 1 that the macro-variable signal using ffsc reaches zero in a fast finite-time. fig. 1. the output trajectories with initial condition: (a) x(0) = 1, (b) x(0) = 1.5. fig. 2. control signals with initial condition: (a) x(0) = 1, (b) x(0) = 1.5. fig. 3. macro-variable evolution signals with initial condition: (a) x(0) = 1, (b) x(0) = 1.5. engineering, technology & applied science research vol. 12, no. 2, 2022, 8328-8334 8332 www.etasr.com zerroug et al.: robust adaptive fuzzy control of nonlinear systems b. example2: duffing forced-oscillation system the proposed approach will be furthermore used to control the duffing forced-oscillation system given by (31). 1 2 3 2 2 1 0.1 12 cos( ) ( ) ( ) x x x x x t u t d t =  = − − + + + � � (31) the control objective is to force the perturbed system to track a desired trajectory ( )sinmy t= and remove totally the effect of external disturbances. the disturbance is chosen as ( ) ( )1 5 sin .d t t= + the membership functions for system states , 1,2 i x i = are chosen as in example 1 and the 36 fuzzy rules are used to approximate the nonlinear function of the system ( )f x . the controller parameters are chosen as: 0.1,k = 1.5,β = 8,λ = 0.2,t = 5,q = 3.p = the simulation results are shown in figures 4-6. figure 4 describes the tracking performance of the proposed controllers, e.g. ffsc and fsc. the control signals and the macro-variables of two different schemes are depicted in figures 5 and 6 respectively. through the comparison, we can see that the proposed method can achieve better tracking performance than the fsc. fig. 4. the output trajectories with initial condition: (a) ( ) [ ]0 1,0 tx = and (b) ( ) [ ]0 2,0 tx = . fig. 5. control signals with initial condition: (a) ( ) [ ]0 1,0 tx = and (b) ( ) [ ]0 2,0 tx = . fig. 6. macro-variable evolution signals with initial condition: (a) ( ) [ ]0 1,0 tx = and (b) ( ) [ ]0 2,0 tx = . c. example3: inverted pendulum system in this example, the simulation has been carried out for an inverted pendulum system described by (32): 1 2 2 1 ( ) ( ) ( ) ( ) x x x f x g x u d t y t x =  = + +  = � � (32) the state-space variables are the position 1 x and the velocity 2 x . ( )u t and ( )y t are respectively the input and the output of the system. ( )f x and ( )g x are nonlinear continuous functions, such that: 2 2 1 1 1 2 1 ( ) cos( )sin( ) sin( ) ( ) ( ) ( ) cos ( )4 ( ) 3 ( ) c c m l x x x g x m m f x m x l m m − + = − + (33) 1 2 1 cos( ) ( ) ( ) ( )cos ( )4 ( ) 3 ( ) c c x m m g x m x l m m + = − + (34) where 1kg, c m = 0.1kg,m = 0.5m,l = and 29.8m/s .g = in order to approximate the functions ( )f x and ( )g x , we consider the following membership functions: ( )( )1 2 ( ) exp 6 / 24 i i if x xµ π π = − +   (35) ( )( )2 2 ( ) exp 12 / 24 i i if x xµ π π = − +   (36) ( )3 2 ( ) exp / 24 i i if x xµ π = −   (37) ( )( )4 2 ( ) exp 12 / 24 i i if x xµ π π = − −   (38) engineering, technology & applied science research vol. 12, no. 2, 2022, 8328-8334 8333 www.etasr.com zerroug et al.: robust adaptive fuzzy control of nonlinear systems ( )( )5 2 ( ) exp 6 / 24 i i if x xµ π π = − −   (39) the reference signal is given by: ( ) ( )( )sin 0.3sin 3 10 m y t t π = + (40) and the controller parameters are chosen as: 2.25,k = 5.5,β = 2,λ = 0.8,t = 13,q = 13.p = in the numerical simulation, we chose the disturbances and uncertainties as: ( ) ( )0.3 1.1d t randn= and 0.1kg,cm∆ = ± 0.01kg,m∆ = ± at 5st = . the reference tracking capability of the proposed ffsc controller is investigated and the results are compared with those given by the fsc controller for the same initial conditions. the system responses are given in figures 7-9. from these curves, the superior performance of faster and high-precision tracking of the proposed ffsc is clearly visible. unlike the conventional fsc control, the ffsc holds its robustness and stability in the presence of uncertainties and external disturbances, and can drive system states to a desired trajectory signal in a fast finite-time. fig. 7. the output trajectories with initial condition: (a) ( ) [ ]0 12,0x π= and (b) ( ) [ ]0 6,0x π= . fig. 8. control signals with initial condition: (a) ( ) [ ]0 12,0x π= and (b) ( ) [ ]0 6,0x π= . fig. 9. macro-variable evolution signals: (a) with initial condition ( ) [ ]0 12,0x π= and (b) with initial condition ( ) [ ]0 6,0x π= . v. conclusion a robust fuzzy fast finite-time synergetic control for the trajectory tracking of a class of nonlinear unknown systems has been proposed in this paper. the proposed ffsc can be used to design not only the continuous control law with fast and finitetime convergence to the equilibrium, but also the approximation of unknown dynamics of a nonlinear system with the use of fuzzy systems. based on the lyapunov stability theorem, it is rigorously proved that the stability of the closedloop system, in the presence of external disturbances, is ensured and the tracking performance is achieved in finitetime. references [1] p. swarnkar, s. jain, and r. k. nema, "effect of adaptation gain in model reference adaptive controlled second order system," engineering, technology & applied science research, vol. 1, no. 3, pp. 70–75, jun. 2011, https://doi.org/10.48084/etasr.11. 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[26] m. zak, "terminal attractors in neural networks," neural networks, vol. 2, no. 4, pp. 259–274, jan. 1989, https://doi.org/10.1016/0893-6080(89) 90036-1. microsoft word etasr_v11_n6_pp7892-7896 engineering, technology & applied science research vol. 11, no. 6, 2021, 7892-7896 7892 www.etasr.com ambati et al.: parametric analysis of the defected ground structure-based hairpin band pass filter … parametric analysis of the defected ground structure-based hairpin band pass filter for vsat system on chip applications navya ambati department of ece koneru lakshmaiah education foundation vaddeswaram, guntur, andhra pradesh, india govardhani immadi department of ece koneru lakshmaiah education foundation vaddeswaram, guntur, andhra pradesh, india m. venkata narayana department of ece koneru lakshmaiah education foundation vaddeswaram, guntur, andhra pradesh, india kalyan reddy bareddy department of ece koneru lakshmaiah education foundation vaddeswaram, guntur, andhra pradesh, india m. sri prapurna department of ece koneru lakshmaiah education foundation vaddeswaram, guntur, andhra pradesh, india jayadeep yanapu department of ece koneru lakshmaiah education foundation vaddeswaram, guntur, andhra pradesh, india abstract-in this study, a three-pole hairpin structure was fabricated on the top of the substrate material and an open loop microstrip structure at the ground to give a modified triple-band bpf with a unique design. a rogers (rt5880) material with εr = 2.2 and thickness of 1.27mm was used to fabricate the proposed structure. the space between two consecutive hairpin resonators has different distances d1 and d2 with values of 0.2mm and 0.4mm respectively. the proposed filter offers a compact size with low return loss. the equivalent lc circuit of the dgs and hairpin structure is obtained with the ansys electronic desktop and by using simple circuit analysis. the desired microstrip triple-band bpf operates at the ku band, resonates at 10.28ghz, 12ghz, and 14.62ghz, while the simulated and experimental results are almost identical. the proposed wideband bpf satisfies the international telecommunication union ((itu) region 3 spectrum requirements. direct broadcast service (dbs) and fixed satellite service (fss) in transmit mode respectively employ the frequency band 11.41-12.92ghz and 14-14.5ghz. keywords-hairpin line bpf; dgs; microstrip transmission line; group delay; return loss; insertion loss i. introduction international telecommunication union (itu) has divided the world into three zones for satellite applications in order to efficiently organize the spectrum. the frequency bands for fss in receive and transmit mode in region-3 are 12.2-12.7ghz and 14-14.5ghz respectively. the reception and transmit frequencies for dbs are 11.7-12.2ghz and 17.3-17.8ghz. in modern wireless communication systems, rf/microwave filter is one of its indispensable components. the development of transmission standards brought a fast-increasing growth of front-end rf devices and circuits [1, 2]. their multi-band operation ability, system requirements, small sized filter, low cost, simple fabrication, and higher performance have attracted abundant interest. to satisfy these demands, attention has been centered on the microstrip printed filters because of their advantages in cost, size, and weight. dgs with periodic or aperiodic arrays allows a rejection range in some frequency bands to increase the effective inductance of a microstrip transmission line. these rejection properties of the dgs are available to many circuits such as coplanar antennas, power dividers, filter, etc. [5-7]. bandpass filters (bpfs) play a very important role in wireless communication applications due to their superior performance, minute size, and low attenuation within the prescribed pass band and high attenuation within the stop band. ku-band is a part of the electromagnetic spectrum in the microwave frequency range. it ranges from 12 to 18ghz. the ku-band is mostly used for tv and vsat frameworks on boats. the band is split by the itu into segments, modified by nations. in this article, a new dgs is developed for the implementation of coupled line filter. an etched structure disrupts the shield current distribution in the ground plane. the properties of the transmission line, such as capacitance and inductance, can be affected by this disruption. as a result, the dgs is represented as an lc tank circuit [3, 4]. the circuit's sparameters are calculated with a 3d finite element method simulator. corresponding author: navya ambati (ambatinavya88@gmail.com) engineering, technology & applied science research vol. 11, no. 6, 2021, 7892-7896 7893 www.etasr.com ambati et al.: parametric analysis of the defected ground structure-based hairpin band pass filter … ii. filter geometry the proposed filter's design was simulated in the electromagnetic field simulator and is fabricated on a rogers (rt5880) substrate with permittivity �� = 2.2, loss tangent 0.0009, and thickness of 1.27mm. the suggested microstrip hairpin line bpf has a size limit of 14×16mm 2 . the distances d1 and d2 for two consecutive hairpin resonators are distinct, with values 0.2mm and 0.4mm respectively. the ground-based microstrip open loop resonators act as a band rejection resonator. here, we used 5 hairpin resonators to get an accurate range of frequency. the middle frequency corresponding to wavelength (λ) is affected by the length of the hairpin structure. we can observe that there is a change in ƒ0 while increasing the length of the microstrip resonators (l). a hairpin filter is designed at the ku band by keeping the length resonators fixed. to obtain wide band width, the hairpin line bpf is manufactured with 5 resonators in the top plane, a dual armed microstrip resonator in the ground plane, while the ends of these resonators are connected to a 50ω microstrip feed line. (a) (b) fig. 1. equivalent circuit diagram of the filter. (a) hairpin bpf, (b) dgs. fig. 2. geometry of the proposed filter. a. constructional details of the filter a hairpin line bpf with microstrip open loop resonators in the bottom of the substrate with dimensions is shown in figure 2. figure 3 shows the iteration-wise constructive design of a hairpin bpf with a defected ground structure. (a) (b) (c) (d) (e) (f) fig. 3. hairpin bpf with defected ground structure. (a) basic shape, (b) iteration 1, (c) iteration 2, (d) iteration 3, (e) iteration 4, (f) iteration 5. iteration 0 is the basic microstrip transmission line with a length and width of 15.45mm and 0.75mm. it is designed by using ansoft hfss. the length and width of the hairpin resonator are defined as l and w and are denoted by: l = �� � (1) where the guided wavelength is given as ��= ��� �� �� (2) ɛ���� � ɛ ��� � ɛ �� � �1 � � ��� � �� ��/� (3) where h, ɛ� are the thickness and relative permittivity of the substrate: � � = � п{(b-1)-ln(2b-1) � -1 �� !ln$b & 1' � 0.39 & $ ,.-� �� )]} (4) where: b = -,п. /0√ԑ (5) in iteration 1, a single hairpin structure is designed on the top of the substrate and is fed by a microstrip transmission line. in iteration 2, two hairpin structures are placed on the top of the substrate. in a similar manner, the hairpin structures are added one by one up to iteration 4, and in the final step a defected ground structure is added to the existing hairpin structure to design a tri band bpf. the proposed design is designed to operate at 12ghz. the three transmission zeros at the pass band frequency spectrum are obtained by the hairpin resonators and dual armed microstip open loop transmission resonators present in the filter. b. evolution the step by step procedure of the proposed hairpin line bpf is represented in figure 3. a 50ω microstrip transmission line with a certain length and width will transfer the entire frequencies from one port to another. the hairpin resonators in the structure will reject the respective frequencies from hitting the load. in the second example, the energy flow from the source to the load can be altered by a single resonator. the power is coupled via the resonators from the source to the load, which results in a narrow pass band. it is simple to understand this with the help of figure 4. engineering, technology & applied science research vol. 11, no. 6, 2021, 7892-7896 7894 www.etasr.com ambati et al.: parametric analysis of the defected ground structure-based hairpin band pass filter … fig. 4. parametric analysis of the return loss of the proposed filter by successively adding the hairpin resonators. c. filter analysis modeling and analysis of hairpin line bpf with dgs was performed using hfss. their equivalent circuits were drawn with the ansys electronic desktop. examination of each filter parameter provided an insight into optimizing the design. the ground plane's microstrip transmission lines contain two transmission zeros at the two ends of the pass band frequency spectrum. in tables i and ii, the measurements used to design the microstrip open loop resonator and hairpin filter are shown. table i. resonator measurements in the hairpin line microstrip bpf parameters values substrate length (l) 9mm substrate width (w) 15.45mm resonator length (l0-l4) 4.6mm resonator height (h0, h2) 2.12mm resonator height (h1, h3) 1.73mm resonator feed line length (f-f10) 0.75mm resonator feed line width (w1-w4) 2.25mm resonator width (w, w0) 1.5mm table i. measurements of the microstrip open loop resonators in the bottom plane parameters values resonator length (l0, l7) 0.75mm resonator length (l1) 5.37mm resonator length (l2) 2.88mm resonator length (l3, l6) 3.2mm resonator length (l4, l5) 1.7mm resonator width (w0) 8.903mm resonator width (w1, w2) 3.95mm resonator width (w3, w4) 3.2mm resonator width (w5, w6) 1.7mm resonator width (w7, w8) 3.275mm resonator width (w9) 4.403mm resonator width (w10, w11) 0.75mm resonator width (w12) 1.003mm (a) (b) (c) (d) fig. 5. (a) top view and (b) bottom view of the proposed bpf. (c) the fabricated bpf. (d) measuring the proposed bpf with a combinational analyzer. the design goals of the proposed filter are the acquisition of a well specified reflection coefficient with wide bandwidth and of a transmission coefficient that allows satellite communication applications. the top and bottom views of the proposed microstrip hairpin line bpf are shown in figure 5 and the dimensions used to design this filter are listed in tables i and ii. iii. results and discussion for real time validation, the built prototype was fabricated and tested. the plots show that the simulated and measured engineering, technology & applied science research vol. 11, no. 6, 2021, 7892-7896 7895 www.etasr.com ambati et al.: parametric analysis of the defected ground structure-based hairpin band pass filter … results are very close. the filter's return loss and insertion loss characteristics are detailed in figure 7 and the reflection coefficient is below 10db. the maximum possible filter’s bandwidth is found to be 0.6ghz, 1.6ghz, and 0.7ghz. the insertion loss is far below 3db in all states and the insertion loss obtained is 0.8db. table iii provides a summary of the performance parameters based on the literature, from which it is noted that the proposed filter offers better return loss, transmission coefficient, and a wider bandwidth. figure 5(d) represents the measurement of a transmission coefficient by using the anritsu combinational analyzer. the parameters that are measured with this combinational analyzer are the sparameter, group delay, and phase delay. fig. 6. return loss of the hairpin bpf without dgs. figure 4 indicates the parametric analysis of the return loss obtained by successively adding the hairpin structures. the proposed filter is the iteration 5 which is of the basic shape, where the return loss and insertion loss characteristics are better than in other iterations. figure 6 represents the return loss of the hairpin bpf without a dgs structure. only two resonant bands are achieved at 12ghz and 13.5ghz with a return loss of -16db and -17.2db. fig. 7. simulated vs measured results of return loss and insertion loss of the hairpin bpf with dgs. using the vector network analyzer, the reflection coefficient of the manufactured filter was calculated. the proposed filter resonates at 10.28ghz, 12ghz, and 14.62ghz. the relation between the measured and the computed group delay is shown in figure 9. for the designed frequency band, the variance of reflection coefficient across frequencies is less than 10db. the time domain characteristics of the microstrip hairpin line bpf are calculated by using group delay, as shown in figure 9. with a deviation of 0.2ns, the group delay of the suggested filter is maximally flat. the delay induced by the filter is therefore consistent across the operating range, resulting in minimal signal distortion. fig. 8. surface current distributions of the proposed bpf. fig. 9. simulated vs measured results of group delay of the proposed filter. the most important features for frequency and bandwidth of the proposed microstrip hairpin line bpf are: • the proposed filter is designed to operate at the frequency of 12ghz. we can easily control bandwidth and frequency. • the method is much simpler than the complicated standard methods such as coupling reducers and switched delay lines. • the filter's frequency and bandwidth tuning features are independent. • this filter is fabricated on a less valuable dielectric material, making many operations inexpensive and simple to replicate. without encroaching additional space, the two microstrip resonators are enclosed within the stepped loop structure. • by varying the size of the hairpin resonators and microstrip open loop structure accordingly, this prototype can be modelled to work at any desired frequency. engineering, technology & applied science research vol. 11, no. 6, 2021, 7892-7896 7896 www.etasr.com ambati et al.: parametric analysis of the defected ground structure-based hairpin band pass filter … table iii compares the proposed wideband bpf with various known wide band bpfs at the ku band. it is evident that the proposed wideband bpf has better bandwidth and insertion loss. filters at the ku band for satellite applications have been proposed in [8-11], but they all have narrower bandwidth and higher insertion loss. the proposed wideband bpf is compared with the bandpass filter proposed in [11] having high return loss, however the bpf has a bigger size and narrower bandwidth. also, chemical etching microstrip devices without dgss or vias also reduce process costs and improve manufacturing efficiency. table ii. comparison of the proposed with known bpfs ref. substrate reflection coefficient group delay area (mm 2 ) center frequency [8] rogers rt/duroid -14db 5×13 13.3ghz [9] gaas -15db 1.09×0.97 13.5ghz [10] fr4 -16db 0.5ns 11.12×8 14ghz [11] fr4 -11db 25×25 10ghz proposed rogers rt5880 -13.25db -12.8db -14.721db 0.2ns 14×16 10.28ghz 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[22] g. imamdi, m. v. narayan, a. navya, and a. roja, "reflector array antenna design at millimetric (mm) band for on the move applications," arpn journal of engineering and applied sciences, vol. 13, no. 1, pp. 352–359, 2018. microsoft word etasr_v12_n2_pp8236-8240 engineering, technology & applied science research vol. 12, no. 2, 2022, 8236-8240 8236 www.etasr.com kar & roy: probabilistic based reliability slope stability analysis using fosm, form, and mcs probabilistic based reliability slope stability analysis using fosm, form, and mcs saurav shekhar kar department of civil engineering national institute of technology, patna patna, india sauravk.phd17.ce@nitp.ac.in lal bahadur roy department of civil engineering national institute of technology, patna patna, india lbroy@nitp.ac.in received: 13 december 2021 | revised: 11 january 2022| accepted: 18 january 2022 abstract-soil uncertainties play an important part in the analysis and design of geotechnical structures. the effect of uncertainties on the geotechnical structures and their influence on the probability of failure or reliability of the structure is of great interest for geotechnical researchers. probabilistic-based slope stability analysis incorporates the uncertainties present in the soil, as expressed in terms of mean, variance, and autocorrelation. in this paper, reliability analysis of a finite cohesive soil slope based on the probabilistic approach is presented using the first order second moment (fosm) method, first order reliability method (form), and monte carlo simulation (mcs) method. stability analysis has been performed using the ordinary method of slices to calculate the factor of safety (fos) of the slope under undrained conditions. the reliability analysis has been implemented in the ms-excel spreadsheet environment and was mainly focused on the two models, namely the deterministic model for calculating the fos of the slope and the uncertainty model for generating the random variables of uncertain soil parameters. the reliability index (β) of the soil slope and its corresponding probability of failure (pf) was calculated using the above methods. the obtained result shows that the mcs method has significantly shown better performance than fosm and form because of its robustness and simple approach to calculate pf and β of the slope. keywords-reliability index; fosm; form; mcs; probability of failure i. introduction soil characteristics are influenced by various factors (e.g. characteristics of their origin rock, erosion and weathering actions, and sedimentation condition) and therefore, its properties vary spatially at different depths, something that is also referred to as inherent spatial variation of the soil. these inherent variations of the soil cannot be reduced as they are independent in nature, therefore, classified as aleatory uncertainty [1]. apart from the inherent variability of the soil, several other uncertainties such as measurement uncertainty, statistical uncertainty, and transformation model uncertainty affect the design and analysis work of geotechnical structures. the measurement uncertainties [2] arise due to system errors, sample mishandling, and testing errors which can be reduced by improving the knowledge on testing techniques and equipment, therefore, are classified as epistemic uncertainties [1]. the statistical uncertainty [2] is a part of the measurement uncertainty, which may arise due to the unavailability of the adequate number of sample data. the insufficiency of the model to represent the system's actual conditions, results into transformational model uncertainties [3]. these uncertainties can be reduced if proper correlations between the relevant parameters can be established. it has been shown that the epistemic uncertainties do not affect the geotechnical structures. the response of geotechnical structures is significantly affected by the inherent spatial variability of the soil [4-6]. these uncertainties affect the soil properties and ground stratification and subsequently influence the design of geotechnical structures. slope stability determination is based on fos. in the deterministic method of analysis, fos is expressed as the ratio of the resisting moment to the overturning moment. when fos > 1, the slope is considered as safe [7]. in the probabilistic approach of slope analysis, the uncertainty present in the soil is expressed in terms of its mean and standard deviation and is modeled using the autocorrelation function [8]. probabilistic slope stability analysis is used to address the various uncertainties present in the soil [9, 10] and calculate the �� and � of the slope. many probabilistic based reliability methods have been developed to estimate the values of � and �� for geotechnical structures specially for the slope problem, such as fosm [1, 11-13], form [1, 13-15], and mcs [13, 16-18]. in this study, probabilistic based reliability analysis of a finite cohesive soil slope is done using fosm, form, and mcs. the uncertainties present in the undrained shear strength of the soil at vertical depth have been considered. the spatial variations in undrained shear strength of the soil ���� are modeled by the one-dimensional random field theory and the autocorrelation function. the saturated unit weight �γ ��, ��, coordinates of the centre of slip surface �� ,� � and the radii of the slip surface �� � are used to prepare the sample data. the slope stability model has been prepared and analyzed in a msexcel spreadsheet which is divided into two parts, the deterministic and the uncertainty model. the obtained � and �� were compared. corresponding author: saurav shekhar kar engineering, technology & applied science research vol. 12, no. 2, 2022, 8236-8240 8237 www.etasr.com kar & roy: probabilistic based reliability slope stability analysis using fosm, form, and mcs ii. methodology a. deterministic model deterministic modeling is the process of estimating the ��� for a defined set of parameters using limit equilibrium methods. no concept of probability is used in the deterministic analysis. the ��� is calculated using the ordinary method of slices [19]: ��� � ∑ � ∆�� ∑�� � �� � � ∅� ∑ � �� � (1) where ′ is the effective cohesion, ∆" is the length of the arc, ∅′ is the effective frictional angle, # is the weight of the slice, $ is the inclination of the slice base. for cohesive soil under undrained condition, (1) can be further modified as: ��� � ∑ %& ∆� ∑ � �� � (2) where �� is the undrained shear strength of the soil. visual basic application (vba) codes have been written for determining the ��� values with respect to different center coordinates ��,��and radii of the slip surface ��� and the lowest value as ��� which corresponds to the critical slip surface having coordinates �� ,� � and radius �� � were identified. b. ucertainty model the uncertainty model is used to generate the uncertain parameters which are considered as random variables in reliability analysis. based on the distribution type, correlation details, and statistics of the random variables, the random samples of the uncertain parameters are obtained in the spreadsheet. in this study, the �� of the soil is taken as an uncertain parameter with respect to the depth '� . let �̅ �)���'*�,���'+�,…,���'��-. represent the vector of �� at different depths'� � '*,'+,…,'� . when �� is log-normally distributed, it can be represented as [9,20-21]: �̅ � /�0 �113 4 5" 676� (3) where 1 and 5 are the mean and standard deviation (sd) of 89)���'�, 13 is the 9 -column unit vector, 76 is the 9 dimensional standard normal vector, "3 is a 9 : 9 dimensional lower triangular matrix generated by the cholesky decomposition of ;3 � "3"3.. the correlation between 89)���'�� and 89<���'=�> at respective depth '� and '= is given as: ;3 � ;�= � /?@ a|cdecf| g h (4) where ;3 is the correlation matrix and i is the correlation length. i is defined as the length up to which the soil parameters are fully correlated. iii. reliability analysis a. fosm the fosm is a very simple method for calculating reliability based on the taylor’s first-order series expansion. the � is calculated using fosm [1,8,13,22-23] as: � � jklm@*nklm (5) where 1op% and 5op% are the mean and sd of fos. b. form in form, � is calculated in terms of length as the shortest distance measured from the origin of the failure surface and the design point. � is expressed in matrix formulation [22] as: � � qr9s t∈o vwxd@jdnd y . )r6-@* wxd@jdnd y , r � 1,2,…,9 (6) where � represents the failure domain, �� represents a set of random variables, 1� represents the mean of the random variable, 5� represents the sd of the random variable and )r6is the correlation matrix of uncertain parameters. c. mcs mcs is a mathematical procedure of continuously evaluating an empirical operator having a random variable of known probability distribution. for obtaining preferred accuracy level ��, the number of samples to be generated by mcs should be at least equal to 10/�� [18]. for example, for obtaining �� of 0.001 accuracy, the total number of samples to be generated by mcs should be at least equal to 10,000. figure 1 shows the flowchart of the slope stability analysis using mcs. the �� of the slope is calculated as the ratio of number of samples having ��� \ 1 to the total number of generated samples. the � corresponding to the �� is calculated as: � � ]@*�1 ^ ��� (7) where ] is the standard normal cumulative distribution function. fig. 1. systematic representation of mcs for slope stability analysis. iv. problem statement a finite cohesive slope [21], has been taken in this study to assess its reliability having uncertainty in undrained shear engineering, technology & applied science research vol. 12, no. 2, 2022, 8236-8240 8238 www.etasr.com kar & roy: probabilistic based reliability slope stability analysis using fosm, form, and mcs strength in vertical depth. the cross-section and soil properties of the slope are shown in figure 2. the slope stability analysis is carried out using the ordinary method of slices in undrained situation. hard stratum is assumed to be present at 15.0m below the soil. the total 15.0m soil layer is divided into 30 layers, each having thickness equal to 0.5m. the undrained shear strength with depth is log-normally distributed having an exponential correlation. the correlation length is taken as 2.0m. fig. 2. cross-section for the slope stability problem. v. results and discussion the critical slip circle is obtained by choosing different combination of center coordinates ��,�� and radius of the slip surface ��� to obtain minimum ���. table i shows the range of ��,�� and � taken in this study. table i. range of center coordinates and radius of the slip circle parameter minimum maximum range coordinate x (m) 1.0 4.0 3.0 coordinate y (m) 7.0 10.0 3.0 radius r (m) 11.0 16.0 5.0 fig. 3. deterministic model developed in ms-excel. based on this data, an area having the lowest ��� has been identified, and a grid of small intervals of 0.2m has been taken to further identify the critical slip surface. figure 3 shows the deterministic model worksheet of the example problem. table ii shows the ���, the center coordinates �� ,� �, and the radius ��� of the slip surface obtained with the deterministic model. table ii. critical slip circle and fos method _`a b (m) cd (m) ed (m) ordinary method (ms-excel) 1.248 16.0 2.6 8.8 after obtaining the ��� and critical slip surface, the uncertainty model is developed. figure 4 shows the uncertainty model worksheet. fig. 4. uncertainty model developed in ms-excel. fig. 5. ��� histogram showing the mean and the sd of the samples used in fosm. the �� values obtained in the uncertainty model are copied to the �� values in the deterministic model through linking of their input/output cell. by doing this task, the values of ��� generated in the deterministic model will become random and using the f9 key in ms-excel will produce random values of ���. by doing so, we could easily perform mcs, form, and fosm by continuously pressing f9 key, but instead, a vba engineering, technology & applied science research vol. 12, no. 2, 2022, 8236-8240 8239 www.etasr.com kar & roy: probabilistic based reliability slope stability analysis using fosm, form, and mcs macro code has been run in the ms-excel to calculate the random values of ���. for this study, a total of 1850 fos samples were generated and reliability analysis has been performed using fosm, form, and mcs. figure 5 shows the mean and sd obtained from the samples of fos in fosm. the value of � was calculated as 2.56 and the value of �� as 1 ^ ](2.56) = 0.52%. the � is estimated using (6). each term in (6) is computed using a code written in matlab. the correlation matrix )r6-, with dimensions of 31×31, was obtained using (4) and is shown in figure 6. the reliability is calculated for all the 1850 fos samples and the minimum value is reported as the reliability index. the � obtained using form is 2.62 which corresponds to a �� value of 0.44%. table iii summarizes the result of mcs obtained for i = 2m. all the 1850 samples were taken for mcs. for a specified target fos (say 1.2), out of the 1850 samples, 374 samples got values less than 1.2. in other words, it can be stated that these 374 samples failed. therefore, the �� is calculated as 374/1850 = 2.76%. this corresponds to a value of � equal to 1.92. fig. 6. correlation matrix )r6-. table iii. summary of mcs results f simulation technique samples target fos number of samples < target fos gh (%) i 2m mcs 1850 1.1 51 2.76 1.92 1850 1.2 374 20.22 0.83 1850 1.3 977 52.81 1850 1.4 1538 83.14 1850 1.5 1764 95.35 1850 1.6 1839 99.40 1850 1.7 1848 99.89 fig. 7. ��� histogram from mcs. the histogram of the ��� obtained from the 1850 mcs samples is illustrated in figure 7. it can be seen that out of the 1850 samples, 13 have fos values less than 1. the �� is calculated as 13/1850 = 0.7%. this corresponds to a value of � equal to 2.46. table iv summarizes the results of the obtained � and �� using the 3 different reliability methods. the value of �� varies from 0.44% to 0.70% having maximum relative difference among different methods of about 37%. there is a decrease of 26% in �� in fosm as compared to mcs. similarly, a difference of 37% in �� in form as compared to mcs is observed. the � of the slope varies from 2.46 to 2.62. table iv. tesults obtained from different reliability methods method samples β pf (%) relative difference in gh (%) fosm 1850 2.56 0.52 -26.0 form 1850 2.62 0.44 -37.0 mcs 1850 2.46 0.70 # # base value for calculating relative difference vi. result comparison authors in [22] assessed the reliability of a cohesive soil slope having spatial inherent variation in the undrained shear strength. the height of the slope is considered 10m having a slope angle of 26.6°. the hard stratum is present 20m below the top of the soil. they analyzed the slope and calculated the fos using the ordinary method of slices. further, they calculated the reliability index of the slope using fosm, form, and mcs. they concluded that various uncertainties can be taken into account rationally in probabilistic slope stability analysis through mcs. mcs method provides a robust and conceptually simple way to estimate the reliability index or slope failure probability. authors in [13] studied the reliability-based probabilistic method of analysis of a finite soil slope by considering the uncertainties in cohesion and angle of the internal friction of the soil. the height of the slope is considered to be 5m having a slope inclination of 1v:2h. the unit weight of the soil is taken as a constant and the hard stratum is present 15m below the top of the soil. they analyzed the slope using the ordinary method of slices and calculated the reliability index and its corresponding probability of failure of the slope using fosm, form, and mcs. they found that the mcs method performed significantly better than fosm and form. vii. conclusion and future work the current study mainly focuses on the reliability analysis of a finite cohesive soil slope in ms-excel spreadsheet environment based on the probabilistic approach. the effect of uncertainties arising due to the spatial variability of the soil was examined. a comparative study on the results of slope analysis using the fosm, form, and mcs reliability methods was presented. the obtained results show that mcs exhibited improved performance in comparison with the other methods due to its robustness and simple approach. when using the mcs method, it becomes very easy to generate any number of samples of the fos and calculate their failure probability and its corresponding reliability index. engineering, technology & applied science research vol. 12, no. 2, 2022, 8236-8240 8240 www.etasr.com kar & roy: probabilistic based reliability slope stability analysis using fosm, form, and mcs the study also presents the involvement of a large number of random variables modeled with the random field theory. the research also shows that the mcs method can assist in the understanding of the nature of complex problems and assessing the associated risk. this study will help in guiding the geotechnical practitioners dealing with slope stability analysis when various uncertainties are encountered in the soil and will help them in their decision-making process. in the future, the study will be further extended for a cohesive-frictional soil slope and layered soil slope using other sophisticated limit equilibrium methods, i.e. the bishop’s simplified method and the morgenstern-price method. references [1] g. b. baecher and j. t. christian, reliability and statistics in geotechnical engineering, 1st ed. hoboken, nj, usa: wiley, 2007. [2] f. h. kulhawy and c. h. trautmann, "estimation of in-situ test uncertainty," presented at the uncertainty in the geologic environment: from theory to practice, 1996, pp. 269–286. [3] k. k. phoon and f. h. kulhawy, "evaluation of geotechnical property variability," canadian geotechnical journal, vol. 36, no. 4, pp. 625– 639, 1999, https://doi.org/10.1139/t99-039. [4] k.-k. phoon and f. h. kulhawy, "characterization of geotechnical variability," canadian geotechnical journal, vol. 36, no. 4, pp. 612– 624, 1999, https://doi.org/10.1139/t99-038. [5] g. a. fenton and d. v. griffiths, "bearing-capacity prediction of spatially random c ϕ soils," canadian geotechnical journal, jan. 2011, https://doi.org/10.1139/t02-086. [6] g. a. fenton and d. v. griffiths, "probabilistic foundation settlement on spatially random soil," journal of geotechnical and geoenvironmental engineering, vol. 128, no. 5, pp. 381–390, may 2002, https://doi.org/10.1061/(asce)1090-0241(2002)128:5(381). [7] d. a. mangnejo, s. j. oad, s. a. kalhoro, s. ahmed, f. h. laghari, and z. a. siyal, "numerical analysis of soil slope stabilization by soil nailing technique," engineering, technology & applied science research, vol. 9, no. 4, pp. 4469–4473, aug. 2019, https://doi.org/ 10.48084/etasr.2859. [8] h. benzeguir, s. m. elachachi, d. nedjar, and m. bensafi, "reliability of buried pipes in heterogeneous soil subjected to seismic loads," engineering, technology & applied science research, vol. 11, no. 1, pp. 6708–6713, feb. 2021, https://doi.org/10.48084/etasr.4000. [9] a. h.-s. ang and w. h. tang, probability concepts in engineering planning and design, vol. 2: decision, risk, and reliability, 1st ed. new york, ny, usa: john wiley & sons inc, 1984. [10] k.-k. phoon, ed., reliability-based design in geotechnical engineering: computations and applications. london, uk: crc press, 2008. [11] w. h. tang, m. s. yucemen, and a. h.-s. ang, "probability-based short term design of soil slopes," canadian geotechnical journal, vol. 13, no. 3, aug. 1976, https://doi.org/10.1139/t76-024. [12] j. t. christian, c. c. ladd, and g. b. baecher, "reliability applied to slope stability analysis," journal of geotechnical engineering, vol. 120, no. 12, pp. 2180–2207, dec. 1994, https://doi.org/ 10.1061/(asce)0733-9410(1994)120:12(2180). [13] s. s. kar and l. b. roy, "reliability analysis of a finite slope considering the effects of soil uncertainty," international journal of performability engineering, vol. 17, no. 5, may 2021, art. no. 473, https://doi.org/10.23940/ijpe.21.05.p7.473483. [14] b. k. low and w. h. tang, "efficient spreadsheet algorithm for firstorder reliability method," journal of engineering mechanics, vol. 133, no. 12, pp. 1378–1387, dec. 2007, https://doi.org/10.1061/(asce)07339399(2007)133:12(1378). [15] b. k. low and w. h. tang, "probabilistic slope analysis using janbu’s generalized procedure of slices," computers and geotechnics, vol. 21, no. 2, pp. 121–142, jan. 1997, https://doi.org/10.1016/s0266-352x(97)0 0019-0. [16] r. y. rubinstein and d. p. kroese, simulation and the monte carlo method, 3rd ed. hoboken, nj, usa: wiley-interscience, 2016. [17] j. m. hammersley and d. c. handscomb, monte carlo methods. london, uk: methuen & co., 1965. [18] c. p. robert and g. casella, monte carlo statistical methods. new york, ny, usa: springer, 2010. [19] w. fellenius, "calculation of stability of earth dam," in transactions. 2nd congress large dams, washington dc, usa, 1936, vol. 4, pp. 445–462. [20] y. wang, z. cao, and s. k. au, "practical reliability analysis of slope stability by advanced monte carlo simulations in a spreadsheet," canadian geotechnical journal, vol. 48, no. 1, pp. 162–172, jan. 2011, https://doi.org/10.1139/t10-044. [21] s. k. au, z. j. cao, and y. wang, "implementing advanced monte carlo simulation under spreadsheet environment," structural safety, vol. 32, no. 5, pp. 281–292, sep. 2010, https://doi.org/10.1016/j.strusafe. 2010.03.004. [22] z. cao, y. wang, and d. li, probabilistic approaches for geotechnical site characterization and slope stability analysis, 1st ed. new york, ny, usa: springer, 2016. [23] n. m. okasha, "reliability-based design optimization of trusses with linked-discrete design variables using the improved firefly algorithm," engineering, technology & applied science research, vol. 6, no. 2, pp. 964–971, apr. 2016, https://doi.org/10.48084/etasr.675. authors profile saurav shekhar kar is a ph.d. scholar of the department of civil engineering, national institute of technology patna, patna, india. his research interests include probabilistic slope stability analysis and reliability analysis. lal bahadur roy is a professor at the department of civil engineering, national institute of technology patna, patna, india. his research interests include stability analysis of soil and rocks. microsoft word etasr_v11_n6_pp7950-7956 engineering, technology & applied science research vol. 11, no. 6, 2021, 7950-7956 7950 www.etasr.com alogla et al.: design and evaluation of transmitting antennas for solar power satellite systems design and evaluation of transmitting antennas for solar power satellite systems abdullah alogla department of electrical engineering college of engineering university of ha'il abdullahogla@gmail.com mohamed abdelaziz hassan eleiwa department of electrical engineering college of engineering university of ha'il ma.eleiwa@uoh.edu.sa hammad alshortan department of electrical engineering college of engineering university of ha'il en.hh2010@hotmail.com abstract-this study attempts to identify, design, and evaluate transmitting antennas for solar power satellite (sps) systems. the design approach aimed at meeting the sps operational requirements at ism bands, namely 2.4-2.5ghz for the nasa and 5.725-5.875ghz for the jaxa models. the primary attributes of sps antennas for transmitting beamed high-power microwaves (bhpms) are high power handling capability, efficiency, and directivity with narrow beamwidth and lower sidelobe levels. using a planar end-fed 20×20 swa module, the whole planar slotted waveguide antenna arrays (swaas) were designed for both the nasa and jaxa reference models having 1km diameter antenna aperture, peak power level over 1gw, directivity over 80dbi, side lobe level (sll) less than 20db, and pencil beam with hpbw less than 0.01°. the proposed slotted waveguide transmitting antenna arrays fulfilled the operational requirements for both the nasa and jaxa sps reference models. due to the higher operating frequency, the results showed that the proposed planar swa array performs better on the jaxa than on the nasa sps model. keywords-solar power satellites; microwave power transmission; slotted waveguide antenna arrays i. introductio n solar power satellites (spss), or space-based solar power (sbsp) systems are used to collect the solar power and convert it into microwave energy to be beamed to a ground station antenna on earth [1, 2]. several sps proposals have been introduced since the first sps concept, proposed by peter glaser in 1968. nasa with the us department of energy (doe) presented the first sps reference model in 1978. the second reference sps model was introduced by the japanese aerospace exploration agency (jaxa) in 2000, featuring electronic beam steering instead of mechanical antenna rotation. recently, nasa and jaxa introduced improved models, while other agencies in different countries became interested and proposed several sps models to be launched in different orbits. the latest sps concept is the smaller sps constellations, devised to overcome challenges such as weight, cost, and launching problems. overviews of the recent international sps models and research are presented in [3-5]. the specifications of nasa and jaxa reference models are presented in table i, as published in [6]. table i. reference sps models’ parameters model old jaxa jaxa_1 jaxa_2 nasa frequenc y 5.8ghz 5.8gh z 5.8ghz 2.45gh z transmitting antenna diameter 2.6km 1km 1.93km 1km transmitted power 1.3g w 1.3gw 1.3gw 6.72gw an sps system consists of the space and the ground stations. the space station consists of a solar energy collector, a microwave generator, and a transmitting antenna array, while the ground station mainly consists of the receiving antenna (rectenna). the major sps benefits are the permanent transfer of solar power from space to earth wirelessly, without cables, grids, towers, and carbon emissions. the main drawbacks of the sps technology are interferences and biological effects associated with the wireless transmission of electricity using high power microwave (hpm) signals [7-9]. efficiency improvement is one of the main challenges of sps systems, as it can reduce cost, interferences, and biological effects. the sps efficiency is a combination of dc-rf conversion efficiency, rf-dc conversion efficiency [10], and beam efficiency. beam efficiency depends on the transmitting and receiving antenna specifications, the wavelength, and the separation distance between the space and ground stations [11]. to improve beam efficiency, the transmitting antenna should be designed to radiate a narrow and controllable beam with suppressed sidelobes to concentrate the power on the receiving antenna aperture. therefore, a phased array antenna with retro-directive beam control is usually used for beaming high-power microwaves to the receiving antenna on earth [12corresponding author: abdullah alogla engineering, technology & applied science research vol. 11, no. 6, 2021, 7950-7956 7951 www.etasr.com alogla et al.: design and evaluation of transmitting antennas for solar power satellite systems 15]. tapered excitation is also commonly used to suppress the sidelobes, and thence more concentrated microwave power will be collected by the receiving antenna aperture area. the most famous excitation tapering techniques are chebyshev, taylor, villeneuve, gaussian, and binomial distributions. the radiating elements of the phased antenna system might be dipole, microstrip patch, reflector, horn, or slotted waveguide antenna (swa). due to their planar and rigid construction with low loss, high power handling capability, and high efficiency, swaas are more attractive candidates for application in microwave systems such as wireless communications, radars, and sps systems [16-21]. the general principles and components of microwave power transmission systems and their space applications are outlined in [16], while several swa arrays were designed in [17] with different tapered distributions for high power microwave applications. a slotted waveguide linear antenna array with 16 elements was designed at 9.4ghz for radar applications and simulated using hfss in [18]. subarraying techniques were applied in [19] with conventional longitudinal slot arrays to increase the relative bandwidth up to 15% at x-band for sar applications. a procedure based on elliott’s model was proposed in [20] to design shaped beam planar arrays. an analytical procedure was introduced in [21], based on babinet’s principle, to design and construct a slotted waveguide antenna array at 2.45ghz. recently, trapezoidal-shaped slots were used for increasing the bandwidth of swaas on 5g applications [22]. slots were cut on the surface of the circular waveguide wc69 and filled with teflon. a 4.54% of fractional bandwidth of the 24ghz center frequency was achieved with gains up to 14.71dbi over the operating bandwidth. a planar resonant swaa of 24×24 longitudinal slots on the broad surface of a rectangular waveguide was designed and simulated for satellite communications within the 29.5-31ghz frequency band in [23], using the sub arraying technique, but without achieving the required 5% fractional bandwidth. moreover, the simulated sll was found to be higher than the predicted 20db. the simulation results produced approximately the designed gain of 30dbi and 3 o beamwidth in both azimuth and elevation planes. an antenna with a metasurface placed inside at an optimized location was proposed in [24] for an efficient dc-rf sps module at 2.45ghz center frequency, without stating any further design details or parameters. the presented antenna patterns showed that the h-plane beamwidth was wider than the e-plane. simplified closed-form equations were used in [25] to calculate the slots’ lengths, widths, and their distribution along the length of the radiating and feeder swas. this method was applied to design an 8×8 planar swaa at 3.952ghz for maritime applications. the obtained hpbws were 9.6° and 11.4° with slrs of 22.3db and 28.1db for e and h planes, respectively. slots are ideal radiating elements that can be easily cut into the waveguide walls incorporating their waveguide feeding structures without the need for special matching networks. such integrated and robust antenna structures are conducive for the space stations of sps systems. the radiating slots may be cut on the waveguide walls in longitudinal (shunt), transversal (series), or inclined shapes. the slotted waveguide antenna arrays can be resonant (standing) or non-resonant (traveling) waves. the traveling wave array has larger bandwidth but lower efficiency due to the power absorbed by the terminating matched loads. also, the main beam direction of the traveling wave swaa depends on the operating frequency. on the other hand, resonant swaa has a narrower beamwidth with higher efficiency, its main beam direction is frequency independent, and it is always perpendicular to its array axis (broadside). due to these attractive features, this study adopted the resonant swaa for sps systems. to the best of our knowledge, no published papers have yet discussed an swaa design to meet the operational requirements of the reference sps models, apart from the scientific reports of nasa [26, 27] and jaxa [28, 29]. therefore, this study aims to analyze, design, and simulate operable swa arrays for the nasa and jaxa sps reference models using closed-form equation, babinet’s principle, and different software packages such as pcaad, antenna magus, and cst microwave studio. ii. swaa parameters and desig n procedures the main objective of this study was to design swa arrays as radiating elements for sps transmitting antenna systems. the designed swa arrays were simulated, and their performance was evaluated on the operational requirements of nasa and jaxa sps models shown in table ii. table ii. typical transmitting antenna parameters fo r nasa and jax a sps models parameter nasa model jaxa model frequenc y bandwidth [gh z] 2.4-2.5 5.8–5.9 operating frequenc y [gh z] 2.45 5.8 hpbw beamwidth [degrees] <4 o <4 o directivity [dbi] >30 >30 antenna diameter 1km 1km sidelobe level (sll) [db] <20 <20 output power (beamed to earth) >1.3gw >1.3gw the first step in designing an swa array is to choose the proper waveguide based on the frequency band. figure 1 shows the rectangular waveguide and its cross-section dimensions. fig. 1. rectangular w aveguide geometry and cross-sectional dimensions. assuming the dominant mode te10 is propagating, the waveguide parameters are: ��� � ���� ��� � � ; �� � ������ /���� (1) engineering, technology & applied science research vol. 11, no. 6, 2021, 7950-7956 7952 www.etasr.com alogla et al.: design and evaluation of transmitting antennas for solar power satellite systems ���� � ��� � � �� � , � � � � |��|� !�"#$% (2) &� � '(�' � � )*+, -�$% ./ 00�$%1 ��/�� 12 3�-/-�$% ��� 5 678 � 9, : � � � ��) , � � � � ; (3) where λc is the cutoff wavelength, λg is the guide wavelength, zgte is the guide impedance for te mode, and em and p are the electric field amplitude and power propagating into the waveguide, respectively. the attenuation constant due to power losses (pl) in the waveguide conducting walls is αc. based on the frequency bands of both nasa and jaxa sps models, the appropriate rectangular waveguides were chosen, their parameters were calculated using the above equations, and the results are presented in table iii. table iii. wave guides parameters for sps models parameter nasa model jaxa model sps frequency range [ghz] 2.4-2.5 5.8-5.9 operating frequenc y [ghz] 2.45 5.8 free space w avelength (λ) [mm] 122.45 51.72 proper rectangular waveguide wr340 wr159 waveguide frequency range [ghz] 2.2-3.3 4.9-7.05 waveguide dimensions [mm] a=86.36, b=43.18 a=40.39, b=20.19 cutoff wavelength (λc) for te10 [mm] 172.72 80.77 cutoff frequency (fc) for te10 [gh z] 1.737 3.714 guide wavelength (λg) [mm] 173.62 67.34 propagation constant (β) for te10 [rad/m] 36.206 93.323 attenuation coefficient (αc) [db/m] 0.01 0.04 waveguide impedance (zgte10) [ω] 534.5 490.8 figure 2 represents the sketch of a linear resonant swaa of n slots (a) and its equivalent circuit (b). the slots are cut longitudinally on the rectangular waveguide broad wall. the waveguide ends are terminated with short circuits, a quarter guide wavelength (λg/4) apart from the centers of last slots. the slot elements’ centers are placed half guide wavelength (ds= λg/2) apart and are offset on the opposite side of the waveguide centerline to ensure uniform phase excitation. the slot length was chosen to be resonant, approximately equal to half wavelength (ls=λ/2), and thus the longitudinal slot was equivalent to a shunt conductance g, as shown in figure 2(b). fig. 2. (a) reso nant shunt slotted waveguide array and (b) its equivalent circuit. an equation was developed in [30] for calculating the normalized slot conductance (gn=gn/gw) of the n-th narrow slot radiating into a half-space, which accounts for the actual slot length. this can be used to calculate each slot displacement xn, n=1, 2,…n: 2 20 0 0 464π 2 09 (cos( ) (0 464 )) ( ) g n n g a . x g . cos . sin b a λ λ π π λ λ = − (4) for perfect matching, the waveguide normalized input conductance should be equal to the total equivalent normalized conductance of the shunt slots for the end-fed linear swa array, i.e.: ∑ =>6>?� � 1 (5) the slot conductance is proportional to its radiated power, according to: => � ab>� (6) where an is the excitation coefficient of the n-th slot. the excitation coefficients are adjusted to yield the required pattern. equation (6) was substituted into (5) to get the constant c. then substituting c into (6) to get the normalized n-th slot’s conductance gn, and thence the n-th slot offset xn can be calculated from (4). for a center-fed linear swa array terminated b y short circuits at both ends, the matching condition provided b y (5) will be: ∑ =>6>?� � 2 (7) for the end-fed linear uniform array of n identical shunt slots, the normalized slot conductance is simply computed from (5) to be => � 1/d for all n. accordingly, the offset xn will be the same. alternatively, babinet’s principle could be used directly to design the swa array in terms of its dual dipole array, where the (thin) slot admittance ys is related to its complementary thin wire dipole impedance zw b y: ef � gf h ijf � 4�l/�� (8) where � � ��; � is the intrinsic impedance of the surrounding medium. substituting resonant conditions in free space (η=377, zw=73.2) into (8) gives the resonant slot conductance as: gf � ��mno.� onn� � 2.06st (9) the power radiated by a slot is �f � uf�gf . assuming a uniform electric field distribution across the slot aperture, es(x,z)=es, and slot voltage uf � vfwf, where ws is the slot width. the minimum slot width wf�x> is determined from the maximum power handling capability of the slot (p max ), which corresponds to applying the breakdown electric field ebd. substituting by the slot conductance gs from (9), and the free space breakdown electric field ebd=3mv/m=es, the minimum slot width will be equal to: wf�x> � y ���z√\] √� �^m _ � 0.00735√��^m (10) for a thin slot, the length to width slot ratio (ls/ws) should be kept larger than 10. the required number of slots n in the swa array can be estimated based on the maximum power handling capability, engineering, technology & applied science research vol. 11, no. 6, 2021, 7950-7956 7953 www.etasr.com alogla et al.: design and evaluation of transmitting antennas for solar power satellite systems specified voltage standing wave ratio vswr, bandwidth, and the required beamwidth and directivity. the required transmitting antenna diameter is approximately 1km for both nasa and jaxa models, as shown in table ii. the equivalent square aperture array shall have approximately equal x and y dimensions as lx=ly=886.41m. for a center-fed linear array, its waveguide length is c� � �df d 1 e h ��/4 h �� /4 , where d is the inter-element spacing from slots’ centers equal to g/2 for a resonant array. thus, the number of slot elements in x or y dimensions is ns=nx=ny=1772.82/λg, and the total number of slots nt required to a 1km diameter sps transmitting antenna area with a planar square array of slotted waveguides is calculated as: df � �df � � ��nn�.g��� � (11) iii. swa design and simulation based on the previous design procedures, several linear swa arrays having different numbers of slots with uniform and tapered distributions were designed and simulated using software packages such as pcaad, antenna magus, and cst microwave studio. linear uniform resonant swa arrays with 10 elements were designed for 2.45ghz and 5.8ghz frequencies. figure 3 shows the field pattern of its equivalent half-wave dipoles array for 2.45ghz, where 3db beamwidth was 7.05°, directivity was 11.6db, and sll was -13db. cheb yshev excitations were used for the same array to get its field pattern, where the 3db beamwidth was 7.790°, which was slightly wider than its uniform excitation counterpart, but the sll was largely suppressed to -20db. similar patterns with approximately the same pattern parameters were obtained for the arrays designed for 5.8ghz. fig. 3. the field patterns of a linear uniform array having10 uniform excitation half-wave dipoles at 2.45ghz. other linear swa arrays, having 20 elements, were designed for 2.45ghz and 5.8ghz, and figure 4 shows the field patterns for 5.8ghz. hpbw was narrower and decreased by more than a factor of half the 10-element arrays for both uniform and chebyshev excitations. similar patterns were obtained for the designed array at 2.45ghz. fig. 4. the field patterns of linear uniform array of 20 chebyshev excitation half wave dipoles at 5.8 ghz. planar arrays of 20×20 equivalent half-wave dipoles with the same dual-slot dimensions (ls=λ/2, dx=g/2, and dy=waveguide width a) were designed for 2.45ghz and 5.8ghz. the obtained patterns for both frequencies were quite similar. figures 5(a) and 5(b) show the array patterns with uniform and cheb yshev excitations at 2.45ghz, where a pencil beam was obtained with 3° hpbw in both planes. (a) (b) fig. 5. the field patterns for a planar uniform array of 20×20 half-wave dipoles at 2.45 ghz. (a) uniform and (b) chebyshev excitation. engineering, technology & applied science research vol. 11, no. 6, 2021, 7950-7956 7954 www.etasr.com alogla et al.: design and evaluation of transmitting antennas for solar power satellite systems linear and planar resonant swa arrays having 10 and 20 slots with uniform and villeneuve distributions were simulated for 2.45ghz and 5.8ghz. (a) (b) fig. 6. simulated reso nant swa arrays. (a) linear center-fed array, (b) end-fed planar array. the simulated swa arrays are shown in figures 6(a) and (b) for linear and planar structures respectively. the swa arrays’ parameters were obtained by plugging the data of table ii into (4)-(11). table iv shows the results for the 10-element linear swaas on 2.45ghz and 5.8ghz. table iv. design parameters of lin ear 10-element uniform resonant swa arrays for sps models parameter nasa model jaxa model no. of slot elements 10 10 slot length (ls) [mm] 61.22 25.86 slot spacing (ds) [mm] 86.81 33.67 slot width (ws) [mm] 6 2.8 slot offset (xs) [mm] 8.85 5.41 ratio (ls/ws) 10.2 9.24 short circuit end spacing 43.41 16.84 distance from feed slot to feed termination [mm] 79.36 33.52 feed waveguide length [mm] 158.7 67.05 feed slot length [mm] 57.9 24.46 feed slot width 6.118 2.584 feed slot angle [degrees] 45 45 swaa z-dimension [mm] 793.6 335.2 swaa x -dimension [mm] 158.7 67.05 swaa y -dimension [mm] 96.06 40.52 fig. 7. radiation patterns of linear resona nt center-fed 10-element uniform swa arrays at 2.45ghz (blue) and 5.8 gh z (red). the optimized array patterns for swa arrays with villeneuve distributions are shown in figure 7. the blue line refers to 2.45ghz and the red to 5.8ghz. their reflection coefficients (s11) are plotted versus frequency in figure 8. similarly, more linear resonant 10and 20-slot element swaas with uniform and villeneuve distributions were designed and simulated. such arrays were designed to be used as subarrays for the required planar swaa arrays b y nasa and jaxa sps models. the radiation patterns of a 20-slot linear uniform array with uniform and villeneuve distributions are shown in figure 9. fig. 8. reflection coefficients (s11) of linear resonant center-fed 10elements uniform swa arrays for nasa (blue) and jaxa (red) sps models. fig. 9. radiation patterns of linear reso nant 20-element uniform swa arrays for uniform (blue) and villeneuve (red) excitations. iv. swa performance evaluation the parameters of the previously described designs are summarized and presented in tables v-vii. tables v and vi show the pattern parameters for the slot complementary (dipole) linear and planar arrays of 10 and 20 element with uniform and chebyshev distributions for both models. table vii presents the antenna parameters of the linear swa arrays with uniform and villeneuve excitations. studying and comparing the antenna parameters for the uniform swa arrays concludes to: • the hpbw and sll of linear uniform arrays are approximately the same in tables v and vi, and are very engineering, technology & applied science research vol. 11, no. 6, 2021, 7950-7956 7955 www.etasr.com alogla et al.: design and evaluation of transmitting antennas for solar power satellite systems close to those produced b y the simulation of actual swa arrays (table vii). • the pattern parameters for linear uniform arrays in tables v and vii with tapered distributions are approximately the same for both cheb yshev (table v) and villeneuve (table vii). • the calculated pattern parameters, specifically the directivity do (maximum directive gain) and the 3db hpbw in table v, are compatible with the classical array theory, which states that for a linear uniform broadside array, if nd>>λ, then, do=2nd/λ, and hpbw=101.5λ/nd. • the obtained relative bandwidth, shown in table vii, is decreased to half when the number of elements is doubled from 10 to 20 for both uniform and villeneuve distributions, while the hpbw is getting narrower and halved when the number of elements is doubled. • the planar swa arrays presented in table vi are exhibiting narrow beams in both principal planes and thus the overall directivity was increased and found to be slightly larger than the summation of directivities of their constituting linear arrays in db scale, which is again compatible with the classical array theory. • the bandwidth of all designed arrays in table vii satisfied the bandwidth operational requirements for both sps models (bw=100mhz), except the 20 element arrays at 2.45ghz, where the bandwidth was found to be approximately equal to 50mhz for both uniform and villeneuve distributions. table v. lin ear slo t complem entary (d ipo le) array s’ specifications pattern parameters nasa model jaxa model n=10 n=20 n=10 n=20 uniform chebyshev uniform chebyshev uniform chebyshev uniform chebyshev half pow er beamwidth (hpbw) [deg] 7.05 7.79 3.42 3.68 7.76 8.40 3.8 4.05 sidelobelevel (sll) [db] -13.3 -20.00 -13.4 -20.00 -13.14 -20.00 -13.28 -20.00 directivity (do) [db] 11.6 11.4 14.6 14.4 11.3 11.1 14.2 14.1 table vi. planar slo t complem entary (d ipole) array s’ specifications parameters nasa model jaxa model 10x10 20x20 10x10 20x20 uniform chebyshev uniform chebyshev uniform chebyshev uniform chebyshev half pow er beamwidth (hpbw) [deg] 7.05×6.02 7.79×7.50 3.42×3.01 3.68×3.52 7.67×6.34 8.4×6.92 3.80×2.99 4.05×3.20 sidelobe level (sll) [db] -13.01 -20.30 -13.25 -20.31 -13.30 -20.40 -13.40 -20.33 directivity (do) [db] 24.8 24.6 31 30.8 24.70 24.5 30.90 30.7 table vii. swaa specifications specification nasa model jaxa model n=10 n=20 n=10 n=20 uniform villeneuve uniform villeneuve uniform villeneuve uniform villeneuve half pow er beamwidth (hpbw) [deg] 7.75 8.51 3.87 4.21 7.76 8.49 3.87 4.21 sidelobe level (sll) [db] -13.01 -20.61 -13.25 -20.51 -13.14 -20.40 -13.28 -20.37 directivity (d o) [db] 16.78 16.62 19.70 19.60 16.77 16.62 19.73 19.59 bandwidth (below the -10 db level) [mhz] 104.1 97.20 50.32 47.34 246.4 230.1 119.1 112.1 relative bandwidth (%) 4.25 3.97 2.05 1.93 4.25 3.97 2.05 1.93 practically, weight, dimensions, and gain are more critical than the bandwidth for sps operations. therefore, this study recommends the 20-element linear uniform swaa to be the subarray of the planar square array for sps transmitting antennas. equation (11) can be used to calculate the total number of slots nt on the proposed planar square arrays for both sps models and the total number of 20×20 planar array modules required to cover the whole transmitting antenna area, whose diameter is 1km for both sps models. these calculations show that the required number of 20×20 planar array modules is approximately 260,658 modules for the nasa and 1,732,699 modules for the jaxa models. accordingly, and due to the classical array theory calculations, the 3db beamwidth (hpbw) was found to be approximately 0.007° and 0.003° for the transmitting antennas of nasa and jaxa sps models, respectively, and the overall directivity (do) was found to be approximately equal to 83.22db and 90.7db for the nasa and jaxa sps models, respectively. v. conclusion based on the sps operational requirements, several linear and planar uniform swa arrays with uniform and tapered excitation distributions were designed and simulated using different software packages. the antenna patterns and parameters of the designed swa arrays obtained from the slot complementary (dipoles) elements, based on babinet’s principle, were found to be quite similar to those obtained by the simulation of actual swa arrays having the same parameters. based on extensive calculations, a planar array of 20×20 slot elements was proposed to be a module for the completely planar swa array to cover the 1km diameter area of the transmitting antennas for both nasa and jaxa sps models. the proposed transmitting antennas’ parameters were found to fulfill the operational requirements for both sps models. however, the antenna specifications of the proposed planar swa array for the jaxa are better than for the nasa sps model. such transmitting antennas achieve pencil beam with very narrow hpbw in the principle planes, which is engineering, technology & applied science research vol. 11, no. 6, 2021, 7950-7956 7956 www.etasr.com alogla et al.: design and evaluation of transmitting antennas for solar power satellite systems approximately 0.007 o and 0.003 o for nasa and jaxa sps models, respectively. moreover, the achieved overall directivity was found to be approximately 83.22db, and 90.7db for nasa and jaxa sps models, respectively. experimental verification is planned for the future. due to the higher operating frequency, the results confirmed that the antenna specifications of the proposed planar swa array for the jaxa were better than for the nasa sps model. several sps geometrical and technical challenges such as size, weight, cost, assembly, and launching are still under investigation. smaller satellite constellations are some latest proposals to overcome some of these challenges. references [1] j. o. mcspadden and j. c. mankins, "space solar power programs and microwave wireless power transmission technology," ieee microwave magazine, vol. 3, no. 4, pp. 46–57, dec. 2002, https://doi.org/10.1109/ mmw.2002.1145675. 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[28] h. matsumoto, "research on solar power station and microw ave pow er transmission in japan: technology and strategy (invited)," presented at the 2001 asia-pacific radio science conference (ap-rasc ’01), tokyo, japan, jan. 2001. [29] "outline of the basic plan on space policy (provisional translation)," national space policy secretariat, cabinet office, japan, jun. 2020. [30] r. elliott, "an improved design procedure for small arrays of shunt slots," ieee transactions on antennas and propagation, vol. 31, no. 1, pp. 48–53, jan. 1983, https://doi.org/10.1109/tap.1983.1143002. engineering, technology & applied science research vol. 8, no. 2, 2018, 2821-2826 2821 www.etasr.com sarosh et al: computational fluid dynamics (cfd) analysis of phthalic anhydride’s yield using lab … computational fluid dynamics (cfd) analysis of phthalic anhydride’s yield using lab synthesized and commercially available (v2o5/tio2) catalyst ali sarosh school of chemical and materials engineering national university of sciences and technology islamabad, pakistan ali-che-ms01@scme.nust.edu.pk erum pervaiz school of chemical and materials engineering national university of sciences and technology islamabad, pakistan erum.pervaiz@scme.nust.edu.pk arshad hussain school of chemical and materials engineering national university of sciences and technology islamabad, pakistan arshad.hussain@scme.nust.edu.pk muhammad ahsan school of chemical and materials engineering national university of sciences and technology islamabad, pakistan ahsan@scme.nust.edu.pk abstract—v2o5/tio2 is an important catalyst used in many industrial reactions like selective oxidation of o-xylene to phthalic anhydride, selective catalytic reduction of nox, selective oxidation of alkanes, etc. the partial oxidation of o-xylene to synthesize phthalic anhydride is an exothermic reaction and leaves hot spots on the catalyst’s surface. the yield of phthalic anhydride strongly depends on the activity and stability of the catalyst. in this work, a computational fluid dynamics (cfd) analysis has been conducted to compare the yield of lab prepared catalyst with the commercially used catalyst. this work is first attempt to simulate v2o5/tio2 catalyst for cracking heavy hydrocarbons in the petrochemical industry using kε turbulence and species transport models in cfd. the results obtained are in the form of scaled residuals, area-weighted average, and contours of pressure and temperature. simulation results of lab synthesized and commercially used catalysts, applying finite volume method (fvm) are compared, which emphasize the scope of cfd modeling in the catalytic cracking process of petrochemical industry. keywords-v2o5/tio2; computational fluid dynamics; cfd; hydrocarbon cracking; hydrodynamics; k-ε turbulence model; oxylene; phthalic anhydride i. introduction catalytic cracking is one of the fundamental processes in petrochemical industries. heavy hydrocarbons are cracked catalytically to give valuable products. for example, the partial oxidation of o-xylene with air is carried out in fixed bed reactor to produce phthalic anhydride. the reaction takes place in the gas phase in which the reactor is filled with catalyst v2o5/tio2. it is a selective oxidation process in which the ratio of o-xylene to air is set below the explosive limit [1]. as o-xylene reacts with air, the reaction becomes highly exothermic leaving hot spots on catalyst pellets which deactivate the catalyst. the industrial reactor is designed on low ratio of the tube to particle diameter to remove the heat of reaction instantly and to avoid catalyst hot spots and deactivation [1]. due to inefficient oxidation and rise in reaction temperature from (245oc to 480oc) the yield of phthalic anhydride decreases. consequently, series of byproducts like methyl maleic anhydride, benzoic acid, maleic anhydride, o-toluic acid, carbon dioxide, carbon monoxide and water are produced. phthalic anhydride is the intermediate product for the manufacturing of many chemicals. it acts as a plasticizer for the production of flexible polyvinyl chloride, polyester resins and is used as modifier for rubbers and polymers [1-7]. an attempt was made to develop v2o5/tio2 catalyst on lab scale with improved chemical and physical properties. through the sol-gel method, the nanosize catalyst was synthesized using vanadyl acetylacetonate and titanium isopropoxide. a controlled number of sulfates was introduced into the sample which provides acidic nature of the solid catalyst. the addition of sulfates enhanced the redox properties of the catalyst. the crystalline structure and morphological analysis of lab prepared catalyst have been done by using x-ray diffraction (xrd) and scanning electron microscopy (sem). computational fluid dynamics (cfd) analysis has been conducted to compare the activity of the commercially used catalyst and lab prepared catalyst. a three-dimensional reactor grid having triangular meshing and ceramics monolith substrate for catalyst support has been constructed in ansys fluent. the ceramics monolith substrate was made to control the heat transfer. the monolithic structures work more efficiently than random packing of catalyst [8]. in this research work, three-dimensional hydrodynamics and reaction study have been done using ansys fluent to compare the yield of phthalic anhydride and engineering, technology & applied science research vol. 8, no. 2, 2018, 2821-2826 2822 www.etasr.com sarosh et al: computational fluid dynamics (cfd) analysis of phthalic anhydride’s yield using lab … convergence of reactants. through reactor grids, comprehensive study of species transport, reaction mechanism, and hydrodynamics in term of scaled residuals, static pressure, static temperature, and area weighted average, has been conducted. the simulation results showed complete conversion of o-xylene to phthalic anhydride, without any byproduct formation. the temperature profile and hydrodynamics in the reactor are evaluated by applying industrial conditions. to our knowledge, this is the first attempt to model heavy hydrocarbon cracking in the presence of v2o5/tio2 using cfd with finite volume method (fvm) by implemented suitable governing equations and boundary conditions. ii. cfd modeling cfd helps to design, model, and analyze industrial applications. simulation of ceramics monolith substrate reactor has been conducted to study the partial oxidation of o-xylene with air to produce phthalic anhydride. this research may be considered as a meager contribution to better understanding of the interaction between gas phase reactants in the presence of a catalyst. the objectives of this cfd modeling are 1) to compare the yield of phthalic anhydride obtained from commercially used catalyst and lab prepared catalyst, 2) to understand reaction chemistry and heat transport in the reactor, 3) to optimize operating conditions of the reactor to maximize the yield of phthalic anhydride [9]. a. turbulance model the model equations for k and ε in realizable kε model have already been presented in [10-12] ( ) ( ) [( ) ] (1)tj k b m k j j k j k k ku g g y s t x x x                       and 2 1 2 1 3( ) ( ) [( ) ] (2) t j b j j j u cs c c c g s t x x x kk                                 where 1 max[0.43, ], , 2 (3)5 ij ij k c s s s s         as in other k-ε models, the eddy viscosity is computed from 2 (4)t k c    the difference between the realizable k-ε model and the standard rng k-ε models is that cµ is no longer a constant. it is computed from * 1 (5) o s c ku a a     where * (6)ij ij ij iju s s    and 2 (7)ij ij ijk k     (8)ij ij ijk k     here, ω is the mean rate-of-rotation tensor viewed in a rotating reference frame with the angular velocity ω . the model constants a and a are given by 4.04, 6 cos (9)o sa a   where 1 3 1 1 cos ( 6 ), , , ( ) (10) 3 2 ij jk ki j i ij ij ij i j s s s u u w w s s s s x xs              b. species transport model a particle undergoing an exothermic reaction in the gas phase is shown schematically in figure 1 where tp and t∞ are the temperatures while cd,b, cd,s, and ck are the concentrations [12-18]. ansys fluent uses the following equation to describe the rate of reaction r of a particle surface species j and the gas phase species ɳ. the reaction stoichiometry of reaction r, in this case, is described by particle species j(s) + gas phase species ɳ → products nr , , (11)j r p r j j rr a y r the effectiveness factor is related to the surface area and can be used in each reaction in the case of multiple reactions. , is given by 0.75 , 1, [ / 2] (12)po r r p t t d c d  the kinetic rate of reaction r is defined as ( / ) , (14)r r e rt kin r rr a t e   the rate of depletion of particle surface species for the reaction order nr = 1 is given as, , , , , , (15)kin r o tj r p r j n o r kin r r d r a y p d r   for reaction order nr = 0, equation (15) gives (11) fig. 1. a reacting particle in the multiple surface reactions model [12] the model equations required two important characteristics of the catalyst: 1) inertial resistance 2) viscous resistance. the inertial resistance of a catalyst is the built-in inertia which engineering, technology & applied science research vol. 8, no. 2, 2018, 2821-2826 2823 www.etasr.com sarosh et al: computational fluid dynamics (cfd) analysis of phthalic anhydride’s yield using lab … enables the catalyst to enhance the rate of reactants convergence into products but never gets consumed in a chemical reaction. it is observed that if a nanoscale catalyst is used in the reaction, the convergence of o-xylene to phthalic anhydride is increased. c. boundary conditions gambittm pre-processor is used to construct the 3d geometry of the system. the geometry of ceramic monolith substrate has been discretized using 125772 cells, 271496 faces, and 33608 nodes. grid size analysis has been carried out using three different mesh intervals. the simulation results from different geometries did not show any significant difference. triangular grids are used in the geometry of fixed bed reactor as shown in figures 2 and 3. the geometry dimensions are x=0.31m, y=0.128m, z=0.028m. o-xylene and air entered with a uniform velocity of 50m/s, pass through a ceramic monolith substrate of square-shaped channels and then exit through the outlet. the substrate is impermeable in y and z directions, which has been modeled by specifying loss coefficients three orders higher than in x direction. the properties of species, gases, and catalyst bed are mentioned in tables i and ii. fig. 2. schematic diagram of fixed bed reactor fig. 3. grids of fixed bed reactor table i. properties of species [19] reaction type surface of catalyst number of reactants 2 species c8h10, o2 stoichiometric coefficient 1, 3 rate exponent 1, 0.5 arrhenius rate 27000 j/kg mole pre-exponential factor 4.12 1011 number of products 2 species c8h4o3, h2o stoichiometric co-efficient 1, 3 rate exponent 0, 0 table ii. properties of reactants, products and catalysts [22] properties (units) o -x yl en e ph th al ic a nh yd ri de in du st ri al c at al ys t l ab sy nt he si ze d c at al ys t density (kg/m3) 880 1530 5067 5067 temp. (k) 298.15 367 630 780 cp (j/kg.k) 132.5 160 721.89 721.89 thermal conductivity (w/m.k) 0.131 kinetic theory 46.3 46.3 viscosity (kg/m.s) 0.760 0.00064 kinetic theory kinetic theory molecular weight (kg/kmole) 106.16 148 281.9 261.6 standard state enthalpy (j/mole) 19000 -3259.4 -880 -880 d. assumptions 1) the ideal gas law is assumed to hold while calculating the pressure-velocity variations on account of convergence and molar expansion due to heavy hydrocarbon cracking and gas phase temperature [20]. 2) catalyst particles are fixed as a cluster of a bed to account for the observed velocity of the gas [20]. 3) mass and heat resistance are assumed as negligible assuming plug flow conditions for both phases hence back mixing of multi-phases is neglected [20-21]. e. simulation setup ansys fluent worked for 100 iterations on an intel core i5 cpu with the 32-bit operating system and 4gb ram. the simulation steps are shown in figure 4. ansys fluent shows remarkable convergence while solving problems. there is no rule to predict convergence because scaled residue for one type of model doesn’t mean it’s same for another. therefore, it is important to examine and monitor the results through drag’s law and heat transfer coefficient. for all equations, the criteria of scaled residue must decrease to 10-3 except for radiations, energy and combustion reactions which are 10-6. for this work, scaled residuals decrease for both lab catalyst and commercial catalyst up to 10-6 [12]. iii. results and discussion simulations of lab prepared catalyst and commercial catalyst in the fixed bed reactor were run for 2 hours. constant catalytic performance was observed because of strong adhesion of lab v2o5/tio2 particles on monolith ceramics substrate. lab synthesized v2o5/tio2 (anatase) indicated the stability in catalytic behavior after the reaction. the lab catalyst showed significantly higher conversion of o-xylene to phthalic anhydride due to better catalyst activity as shown in figure 5. the comparison of the convergence of o-xylene for lab catalyst and commercially used catalyst is shown in figures 5-6. the lower selectivity of phthalic anhydride in the case of commercial catalyst is due to lower surface area of the catalyst which leads to the formation of intermediates and byproducts engineering, technology & applied science research vol. 8, no. 2, 2018, 2821-2826 2824 www.etasr.com sarosh et al: computational fluid dynamics (cfd) analysis of phthalic anhydride’s yield using lab … like cox. the percentage yield of commercial catalyst and labprepared catalyst has been calculated as 66.7% and 80% respectively. table iii shows the yield comparison among other models and the results obtained in this work. it is seen that maximum yield of phthalic anhydride can be achieved through lab synthesized catalyst. fig. 4. block diagram of simulation steps table iii. the yields of phthalic anhydride (pa) comparison calculated from this model with other models and industry data [1, 13]. comparison 1 yield of pa (this work) yield of pa [13] error commercial catalyst 66.7 % 67 % 0.44 % lab prepared catalyst 80 % 19.40 % comparison 2 yield of pa [1] commercial catalyst 66.7 % 79.5 % (with industrial values) 16.10 % lab prepared catalyst 80 % 0.62 % comparison 3 yield of pa [1] commercial catalyst 66.7 % 80.6 % (under optimum conditions) 17.24 % lab prepared catalyst 80 % 0.74 % this work also predicts the temperature and conversion profiles in case of lab prepared and commercially used catalysts. for combustion reactions, energy and heavy hydrocarbon cracking scaled residuals must reach to 10-6. figures 5 and 6 show the rate of conversion from o-xylene to phthalic anhydride, in which equation of continuity, species transport model, and turbulence model was applied. threedimensional velocity profile of catalysts, energy and thermal conductivity were calculated. both commercial and labprepared catalysts showed 10-6 convergence in 2hrs with 90 and 100 iterations respectively. the lab prepared catalyst showed a sudden drop when it reached 80 iterations in residuals which may be because of composition change [10]. the temperature and concentration were recorded at every point of the reactor. it helped in determining the optimum operating conditions to avoid deactivation of catalyst and side reactions. the temperature profile was obtained with time by solving the model equations. fig. 5. scaled residuals of commercial catalyst fig. 6. scaled residuals of lab prepared catalyst in figures 7-8, the contours show the temperature regimes of both commercially used and lab-prepared catalysts in radial and axial directions. due to the highly exothermic reaction, heat dispersion has been observed in the radial direction, which may be attributed to radiation from solid to solid, from gas to solids or to a combination of both mechanisms. unlike the commercially used catalyst, the lab prepared nanoscale v2o5/tio2 showed remarkably better temperature profiles. the temperature profile of lab prepared catalyst showed constant increment while the change in commercial catalyst varies. the results of lab synthesized nanocatalyst showed the best reaction temperature profile in order to get maximum yield of phthalic anhydride. due to low activity of the commercial catalyst, the reaction temperature reached the upper limit, as a result of which hot spots were formed on the catalyst surface which caused the deactivation of the commercial catalyst. furthermore, high catalytic temperature makes the small engineering, technology & applied science research vol. 8, no. 2, 2018, 2821-2826 2825 www.etasr.com sarosh et al: computational fluid dynamics (cfd) analysis of phthalic anhydride’s yield using lab … crystallites of active phase to agglomerate, generally termed as thermal sintering. the difference in the results of both catalysts may be linked to variations in size, catalyst shape and the bed porosity of. the porosity of bed effects the rate of turbulence which leads to variations in heat transport [2, 18, 23]. fig. 7. temperature contours of commercial catalyst (k) fig. 8. temperature contours of lab prepared catalyst (k) the cfd modeling done in this work provided point to point temperature and conversion by specifying the following conditions: a) inlet and outlet temperatures b) inlet composition of feed gas c) reactor surface temperature d) gas mass flow rate e) reactor size f) type of reaction g) size of catalyst [10, 11]. the study of this type of reactor and reaction system is highly sensitive to even a small variation in temperature, which can directly affect the concentrations of the reactants and inlet gas temperature. pressure-velocity coupling model was used to find the inlet pressure of gases for fixed bed reactor. two-phase flow regions require averaging of the fluid properties. these properties can lead to large errors due to the difference in magnitude order. an area-weighted average can lead to a significant improvement in the result quality and indicates suitable reaction mechanism and conditions. in the case of a micron-sized (commercially used) catalyst, high static pressure and high temperature are required to produce phthalic anhydride. an area-weighted average of the static pressure of commercially used and lab-prepared catalysts is shown in figures 9 and10 respectively. the results of commercial catalyst showed that it requires high pressure to achieve reaction condition. at 260kpa the reaction starts which requires high energy. the lab prepared catalyst having nano particle size (strong adhesion with ceramics monolith substrate) showed remarkably controlled pressure conditions. the difference in particle size has a noticeable influence on the convergence values in figures 9-10. fig. 9. convergence history of pressure of commercial catalyst fig. 10. convergence history of pressure of lab prepared catalyst iv. conclusion a cfd analysis has been done for nanoscale and commercially available v2o5/tio2 catalyst for the partial oxidation of o-xylene to phthalic anhydride. a threedimensional multiphase flow reaction model for fixed bed reactor was developed by using finite-volume method solver, ansys fluent. scaled residuals, temperature profile, contours of pressure and area weighted average are predicted by applying species transport and k-ε turbulence models. in this work, cfd simulations have been performed to predict the conversion of o-xylene to phthalic anhydride using v2o5/tio2 as a catalyst. the results of lab prepared catalyst showed better catalyst activity compared to the commercially used catalyst. fvm efficiently solved many model equations both for solid and gas phases. the nanoscale lab prepared catalyst showed better temperature profiles which favors the increase in catalyst’s life and phthalic anhydride’s yield. the proposed model is applicable for different simulation studies of fixed bed reactor. references [1] a.i. anastasov, “deactivation of an industrial v2o5–tio2 catalyst for oxidation of o-xylene into phthalic anhydride”, chemical engineering and processing: process intensification, vol. 42, no. 6, pp. 449-460, 2003 [2] h. zhao, s. bennici, j. shen, a. auroux, “the influence of the preparation method on the structural, acidic and redox properties of v2o5–tio2/so4 2− catalysts”, applied catalysis a: general, vol. 356, no. 2, pp. 121-128, 2009 [3] m. p. gimeno, j. gascon, c. tellez, j. herguido, m. menendez, “selective oxidation of o-xylene to phthalic anhydride over v2o5/tio2: kinetic study in a fluidized bed reactor”, chemical engineering and engineering, technology & applied science research vol. 8, no. 2, 2018, 2821-2826 2826 www.etasr.com sarosh et al: computational fluid dynamics (cfd) analysis of phthalic anhydride’s yield using lab … processing: process intensification, vol. 47, no. 9-10, pp. 1844-1852, 2008 [4] w. friedrichsen, o. goehre, process for the production of phthalic anhydride, u.s. patent no. 3,509,179, 1970 [5] d.j. hucknall, selective oxidation of hydrocarbons, academic press, 1974 [6] j.-j. shyue, m.r. de guire, “single-step preparation of mesoporous, anatase-based titanium-vanadium oxide and its application”, journal of the american chemical society, vol. 127, no. 36, pp. 12736-12742, 2005 [7] g. bond, “preparation and properties of vanadia/titania monolayer catalysts”, applied catalysis a: general, vol. 157, no. 1, pp. 91-103, 1997 [8] g. groppi, e. tronconi, c. cortelli, r. leanza, “conductive monolithic catalysts: development and industrial pilot tests for the oxidation of oxylene to phthalic anhydride”, industrial & engineering chemistry research, vol. 51, no. 22, pp. 7590-7596, 2011 [9] v.m. janardhanan, o. deutschmann, “computational fluid dynamics of catalytic reactors”, in: modeling and simulation of heterogeneous catalytic reactions: from the molecular process to the technical system, wiley-vch, 2011 [10] l. jiang, x. fang‐zhi, l. zheng‐hong, “a cfd modeling of the gas– solid two‐phase flow in an fcc riser under the electrostatic conditions”, asia‐pacific journal of chemical engineering, vol. 9, no. 5, pp. 645655, 2014 [11] j. chang, w. cai, k. zhang, f. meng, l. wang, y. yang, “computational investigation of the hydrodynamics, heat transfer and kinetic reaction in an fcc gasoline riser”, chemical engineering science, vol. 111, pp. 170-179, 2014 [12] i. fluent, “fluent 6.3 users guide”, fluent documentation, 2006 [13] p. mulheims, b. kraushaar-czarnetzki, “temperature profiles and process performances of sponge packings as compared to spherical catalysts in the oxidation of o-xylene to phthalic anhydride”, industrial & engineering chemistry research, vol. 50, no. 17, pp. 9925-9935, 2011 [14] m. hoj, t. kessler, p. beato, a. d. jensen, j. d. grunwaldt, “structure, activity and kinetics of supported molybdenum oxide and mixed molybdenum–vanadium oxide catalysts prepared by flame spray pyrolysis for propane ohd”, applied catalysis a: general, vol. 472, pp. 29-38, 2014 [15] b. p. muljadi, m. j. blunt, a. q. raeini, b. bijeljic, “the impact of porous media heterogeneity on non-darcy flow behaviour from porescale simulation”, advances in water resources, vol. 95, pp. 329-340, 2015 [16] a. w. lothongkum, p. sethapokin, p. ouraipryvan, “simulation of v2o5/tio2 catalyst activity by central composite design for optimal operating conditions and catalyst life in phthalic anhydride production”, journal of industrial and engineering chemistry, vol. 25, pp. 288-294, 2014 [17] y. m. ferng, k.-y. lin, “investigating effects of bcc and fcc arrangements on flow and heat transfer characteristics in pebbles through cfd methodology”, nuclear engineering and design, vol. 258, pp. 66-75, 2013 [18] d. e. cormack, g. i. beattie, “viscous flow effects in the periodic pressure cycling of gas-phase catalytic reactions”, chemical engineering science, vol. 34, no. 7, pp. 1001-1005, 1979 [19] p. frank, phthalic anhydride production, u.s. patent no. 2,117,359, 1938 [20] p. k. dasila, i. choudhury, d. saraf, s. chorpa, a. dalai, “parametric sensitivity studies in a commercial fcc unit”, advances in chemical engineering and science, vol. 2, no. 01, pp. 136-149, 2011 [21] h. ali, s. rohani, j. p. corriou, “modelling and control of a riser type fluid catalytic cracking (fcc) unit”, chemical engineering research and design, vol. 75, no. 4, pp. 401-412, 1997 [22] p. j. linstrom, w. mallard, nist chemistry webbook srd. 69, available at: https://webbook.nist.gov/chemistry/, 2001 [23] j. geertsma, “estimating the coefficient of inertial resistance in fluid flow through porous media”, society of petroleum engineers journal, vol. 14, no. 05, pp. 445-450, 1974 microsoft word etasr_v12_n3_pp8542-8547 engineering, technology & applied science research vol. 12, no. 3, 2022, 8542-8547 8542 www.etasr.com navarro: development of an alumni databank: the case of nueva ecija university of science and … development of an alumni databank: the case of nueva ecija university of science and technology emmanuel carlos navarro college of information and communications technology nueva ecija university of science and technology cabanatuan, philippines emmanuel.navarro@neust.edu.ph received: 6 january 2022 | revised: 19 february 2022 | accepted: 27 february 2022 abstractthe nueva ecija university of science and technology is the third oldest university in nueva ecija province. as the year progresses, the university keeps producing thousands of graduates during each academic year. an average of 4,737 individuals graduated from different programs during the past five years. the university is obligated by the commission on higher education to collect up-to-date data and information through the check system. unfortunately, the office of alumni affairs and placement, which is in charge to collect and manage the graduates' information, does not have an automated alumni database system. this paper presents the development of an alumni databank. the online database record management system for alumni considerably benefits the university's alumni affairs and placement office, particularly in tracing its graduates and managing graduates' profile information. it can manage alumni profiles, notify graduates of job advertisements, and is capable of generating statistical reports with data analytics. security measures were also employed to protect against any potential system breach and unauthorized use. keywords-alumni databank; electronic collection; analytics; higher education institution i. introduction the nueva ecija university of science and technology (neust) is the third oldest school in the province of nueva ecija. its academic mandate started in june 1908 in san isidro, nueva ecija. through the years, its name changed as more course offerings were introduced along with the increase of enrollees. it started providing vocational expertise as wright institute (1908-1928). in 1929, it was named nueva ecija trade school (1929-1953) offering secondary education, then central luzon school of arts and trades (1953-1964), in 1964, it was promulgated as central luzon polytechnic college (1964-1998) specializing in engineering courses, and in 1998 it started to be named nueva ecija university of science and technology [1]. the university produces thousands of graduates each academic year. a yearly average of 4,737 individuals graduated from different programs in the past five years [2]. the university's graduates are deployed in various industries, promoting the university and allowing it to attract more students and maintain its competitiveness. the commission on higher education (ched) mandates that higher education institutions, either private, local, or state universities, to submit data/information [3, 4]. with this development, the university regularly collects and manages records of its graduates. data collection is a fundamental step to take in each research study [5]. according to authors in [6], databases for alumni are vital to every learning institution. they emphasize the school's needs in collecting data and information to communicate, verify, archive, and research the alumni. many studies show that most colleges and universities, either private or public, must have a management tool to protect, maintain, and record their data. hence, graduate tracer studies (gts) are commonly becoming a regular practice worldwide [7]. doing this data/information collection helps the university monitor the graduates' placement, their specific skill sets, and the industry qualifications requirements. neust regularly conducts tracer studies to follow-up on its graduates. the ched per se has a knowledge management division which is composed of three sections: information management, knowledge resource, and system integration. each section's primary purpose is to formulate, coordinate, and implement policies and guidelines related to higher education data collection, processing, and data banking through the higher education management information system (hemis) in all ched offices and higher education institutions through the integration of ched electronic collection and knowledge system (checks) [8]. authors in [9], conducted a tracer study of bachelor of science in information technology (bsit) graduates. they extracted bsit graduates' data with personal information from the registrar's office of the campus using google forms [10]. after getting the list, the link https://tinyurl.com/bsit–tracer16–18 was disseminated to the cict neustsic closed group. the authors in [11] undertook a survey with the help of some students and other faculty members of the college of business administration and accountancy of their academic institution. various means of data gathering were utilized, such as email and facebook messaging. the same instruments were used in the tracer study conducted in neust atate campus with a total of 118 graduates, 65 of which were bsits (27 graduates of the year 2018 and 38 graduates of the year 2019), 24 were bsbas (batch 2018), and 29 were bsentres (batch 2019) [12]. corresponding author: emmanuel c. navarro engineering, technology & applied science research vol. 12, no. 3, 2022, 8542-8547 8543 www.etasr.com navarro: development of an alumni databank: the case of nueva ecija university of science and … in neust, the alumni affairs and placement office does not maintain an automated alumni database system to keep relevant data of the university graduates. instead, they still collect, process and file alumni data manually, which is tedious. the difficulty of alumni affairs and placement office starts when the graduates receive their diploma and other vital records from the university. obtaining data from them becomes more challenging due to the lack of communication, changes of personal information, and lack of pertinent linkage to them. thus, it takes some time to generate timely and reliable reports. to address these concerns, the development of an neust-sic alumni databank is timely and relevant to the needs of the university. the developed alumni databank intends to establish a network between the graduates and the alumni affairs and placement office. the provision of analytics allows the information to be processed quickly, enables clarity of communication, and focuses on further analysis [13]. the printable reports are inclusive of graduates' total number and employability and are filtered according to gender and course. the alumni databank is deemed necessary to know and assess the graduates' present status [14] and for the university to have an alumni record repository. ii. objectives the greatest assets of any academic institution are the product of its labor, the alumni. for this reason, the objective of this study is to develop the nuest-san isidro campus alumni databank, with the function to collect graduates' information that will help track their updated information as professionals and present a way to connect them to the university after graduation. furthermore, this study aims to design an online database record of alumni, that is able to notify graduates for job advertisements, post future university activities, and capable of report generation with data analytics. it also adheres to demand technology that provides various services for storage and data availability from any place and at any time [15]. iii. methodology this study used development research, a powerful method in the development of instructional technology. according to [16], the systematic review of designing, developing, and evaluating instructional programs, processes, and products must meet internal consistency and effectiveness criteria. the technology acceptance model (tam) was applied. authors in [17] define the tam as an information technology framework for understanding users' adoption and use of emerging technologies, particularly in the workplace environment. if a user perceives a technology as easy to use and perceives it as useful to his needs, chances are he will accept it [18]. fig. 1. tam. tam is an information system theory used to look at technology at work, which deals with user acceptability behavior. according to [19], the perceived usefulness defines the degree to which a person believes that the system's use will improve his performance. however, perceived ease of use refers to the degree to which a person believes that the system's service will be effortless. authors in [20] stated that perceived usefulness (pu) and perceived ease of use (peou) impact a person's state of mind toward utilizing a specific tool. the tam models' primary goal is to determine the dominant use to accept or not to accept new systems, technology, instruments, or devices. it intends to utilize by controlling the individual's personality toward using a specific means. iv. alumni databank design and limitations during the development process the neust san isidro campus alumni databank was developed for only the neust san isidro campus. the data were gathered through online interviews conducted with the campus alumni coordinator. further references were taken from the mandates of the ched relevant to the graduate tracer studies, which were taken online. system development life cycle (sdlc) was used in the development process. according to [21], a conceptual model includes policies and procedures for developing or altering systems throughout their cycle. authors in [22] determined that sdlc is a mechanism used to produce deliverable systems and a vital instrument that aids in effective and efficient information systems. authors in [23] explained that the lifecycle of an information system passes through various phases, starting with its conception down to the stage when it is no longer available for use. figure 2 depicts the typical development phases followed systematically with tasks such as planning, analysis, design, implementation, and maintenance required to accomplish new or modified information systems. fig. 2. information system life cycle. the development starts with the planning phase where the researcher understands the problem and identifies and lays down possible threats and project constraints that may hinder the integration. in addition to that, a gantt chart was created to monitor the progress of the project. the context diagram, drawn in figure 3, defines and identifies the extreme boundaries and course of information of the entire system. engineering, technology & applied science research vol. 12, no. 3, 2022, 8542-8547 8544 www.etasr.com navarro: development of an alumni databank: the case of nueva ecija university of science and … fig. 3. context diagram. fig. 4. level 1 representation of the dfd processes. the analysis phase included the detailed examination of collected data and user needs. in this way, processes can be tailored to fit any desired process [24]. this study dissected the collected data in multiple analyses to solve issues and come up with accurate and appropriate findings. authors in [25] stated that one of the prerequisites for each computer system is the assurance of data integrity. by this process, the system will make sure that no changes are made in the database while in operation. this study follows three comprehensive stages of data analysis motivated by [26] which breaks down that data analysis covers everything from reading the source method of data collection to the creation and visualization of the extracted data. the evaluation was first. this stage helps determine and characterize the information of collected data to provide an outcome to achieve a goal. secondly, the cleaning stages classified the information belonging to its entities. this eliminates duplications, irrelevant data, white spaces, and not valuable records. the output of this process is data integrity. lastly, the summarizing stage assures that the collected data are reliable and rich in information, which is the basis for formulating data-driven decisions. the design phase included designing the application, the database, and the user interface. this stage shows the way the system was conceptualized and ensures that the requirements have been met. several software engineering diagrams were made to recognize users' roles and the workflow processes of the developed system. figure 4 illustrates the technical drawing showing how the developed alumni databank system worked. the implementation phase started with coding and a series of tests to evaluate the system’s functionality and usability. lastly, the integration of the developed system into its new environment was conducted. features of the developed system are limited only to graduates' online registration, posting of job fairs, and neust alumni-related activities, and organization job hiring. the alumni coordinator of the said campus is the one who will maintain and manage the alumni databank system. the use-case diagram in figure 5 shows the distinct function and role of the user to the developed system. in this case, it describes the system's capability and how a particular user will utilize it. fig. 5. use-case diagram. a. database modeling the representation of database modeling in information systems is a conceptual way to describe the data structure, which is required in database management. in this way, the data collection will be easy to organize, manage, maintain, protect, and provide access to as a computerized database. there are a lot of structure diagrams in designing a database. one of the most frequently used and applied in this study in illustrating the relationships of different entities to each other within the system is the entity relationship diagram (erd) (figure 6). the presented database schema identifies the relationships and attributes in each entity, e.g. users related to alumni, works, and education belong to the same class. in this case, the values recorded to alumni, works, and education are also recorded to the users. the values from the users are all recorded to the alumni, works, and education. the primary purpose of the erd of the alumni databank is to visualize the physical database which is helpful in identifying mistakes and design flaws that allow necessary adjustments. data entries have to be performed by the end-users who are the alumni and the alumni personnel. b. security the developed alumni databank incorporates protective measures and protocols to protect the information and limit the engineering, technology & applied science research vol. 12, no. 3, 2022, 8542-8547 8545 www.etasr.com navarro: development of an alumni databank: the case of nueva ecija university of science and … possibility of data breach. to ensure the integrity and security of the system, the alumni databank has a user maintenance that allows two kinds of accounts that can be used to access the system. the "admin account," is the alumni coordinator, has complete control and responsibility for managing the system, and uses all the available functionalities, and the "end-user account" with limited access and designated for the university graduates. authentication features were used as the first line of protection. only users with authorized username and password can access it. also, the system administrator may check all the registered users which will serve as a countercheck for bogus accounts. fig. 6. an example erd used in the development of the alumni databank. v. results and discussion the alumni databank system was developed in order to help the alumni affairs and placement office of neust to collect data and locate the graduate's whereabouts and have updated information about them. figure 7 presents the system’s architecture design. an internet connection is required to facilitate communication between the alumni and the developed alumni databank [27]. the front-end of the system was developed using html5 for the web structures, css3 for design, and javascript for the system's functional behavior. jquery was also used for a more graphical representation of tables. bootstrap 4.1.3, an open-source front-end toolkit, was used to make the web application responsive [28] and fontawesome webfont icons provided the visual icons. using these front-end utilities, the alumni databank system was developed. back-end development refers to the server-side of an application [29], which means users cannot see how the back-end works. however, this code integrates the system between its database to the browser. to make this integration possible, php 7.3.4-2 [30] was used. mariadb ver 15.1 distrib 10.3.23 was used for defining the database structure along with mysql workbench and sublime text3 for coding. fig. 7. web application architecture of the alumni databank. tracking graduate whereabouts is significant for higher education institutions (heis). moreso, the integration of industry 4.0 in the education system impacts strategic leadership [31] and transforms data-driven operations. the alumni databank is designed to keep the graduate's records of neust san isidro campus and of the university as a whole. figures 8 and 9 show the reports through a bar chart, the graduates per year and per course. the assigned campus alumni coordinator will have access to maintain and manage the system, while only administrators and coordinators have full access to the alumni databank. the end-users' privileges include creating and updating their profiles and browsing posted job advertisements and announcements. figure 10 displays the announcement module wherein the administrators and coordinators can manage the creation of job advertisements and university-related activity announcements. only the administrator and the system developer can access the system database backup, access the graduate's lists and information, generate reports, and have the privilege to modify the system if there will be any change request. engineering, technology & applied science research vol. 12, no. 3, 2022, 8542-8547 8546 www.etasr.com navarro: development of an alumni databank: the case of nueva ecija university of science and … fig. 8. graduate reports per year. fig. 9. graduate reports per course. fig. 10. job advertisement, university related activity announcement page. the developed alumni databank establishes a network between the graduates and the alumni affairs and placement office. it considerably benefited the office, particularly in tracing its graduates and managing their profiled information. with the existing system of graduates tracing, the office staff in charge encounters difficulties in merely looking for them via social media platforms, not to mention the limited data available. some graduates who are not active in social media or whose profile is different from their actual names are not tracked at all. thus, the preparation of needed reports takes a lot of time and is prone for being incomplete, and is less reliable. this system would make it easier to prepare the documentation required by the ched by establishing a standard communication gateway with graduates to collect their information after graduation. compared to the manual system, obtaining data from them is no longer tedious since graduates themselves may update their personal information like contact numbers, address, and pertinent linkage to them can be acquired, tasks which were previously difficult to perform. the needed reports can easily be generated, printed or downloaded in pdf format by authorized system users. data analytics was also integrated for a visual presentation of reports which have been more useful as compared to traditional reports created with the manual system. vi. conclusion the repository of alumni record management for neust san isidro campus, was developed with the following functionalities: online registration, posting job opportunities offered by the university and other job advertisements from partner agencies. reports with analytics were provided inclusive of generation of graduates statistics, employability and graduates aggregated according to their gender. the developed system was able to produce printable reports of alumni records with some data analytics. for further improvement in the future, the following recommendations are hereby given: • integration of the alumni databank system to the university system for full utilization in the neust san isidro campus. • considering the said system implementation as a benchmark in aligning the inputs and processes of the neust, the said system can also be utilized in other colleges/campuses. • the university management of information system (mis) may integrate the alumni databank system to the university portal for deployment. • the alumni affairs and placement office director, the vice president for academic affairs, the vice president for research, extension and training office, and all alumni coordinator per colleges/campuses in cooperation of the deans and directors may provide a set of guidelines regarding the system use prior to implementation. references [1] "historical background," nueva ecija university of science and technology, jun. 07, 2020. https://neust.edu.ph/historical-background/ (accessed mar. 29, 2022). [2] "2020 higher education facts and figures," ched. https://ched.gov.ph/2020-higher-education-facts-and-figures/ (accessed mar. 29, 2022). [3] "2012 ched memorandum orders," ched. https://ched.gov.ph/2012ched-memorandum-orders/ (accessed mar. 29, 2022). [4] "2014 ched memorandum orders," ched. https://ched.gov.ph/2014ched-memorandum-orders/ (accessed mar. 29, 2022). engineering, technology & applied science research vol. 12, no. 3, 2022, 8542-8547 8547 www.etasr.com navarro: development of an alumni databank: the case of nueva ecija university of science and … [5] "how to collect data for research project," sep. 16, 2021. https://papersowl.com/blog/how-to-collect-data-for-research (accessed mar. 29, 2022). [6] j. etcuban and d. durano, "development of an alumni database for a university," iamure international journal of multidisciplinary research, vol. 12, pp. 109–128, jan. 2015, https://doi.org/10.7718/ iamure.v12i1.953. 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[31] m. f. mubarak, f. a. shaikh, m. mubarik, k. a. samo, and s. mastoi, "the impact of digital transformation on business performance: a study of pakistani smes," engineering technology & applied science research, vol. 9, no. 6, pp. 5056–5061, 2019, https://doi.org/10.48084/ etasr.3201. engineering, technology & applied science research vol. 7, no. 6, 2017, 2189-2193 2189 www.etasr.com saeed et al.: the impact of capability maturity model integration on return on investment in it … the impact of capability maturity model integration on return on investment in it industry: an exploratory case study anum saeed comsats institute of information technology islamabad, pakistan anum.saeed@comsats.edu.pk raja sher afgun usmani dcs&se international islamic university islamabad, pakistan sher.afgun@iiu.edu.pk hina akram comsats institute of information technology islamabad, pakistan hina.akram20@gmail.com syed m. saqlain dcs&se international islamic university islamabad, pakistan syed.saqlain@iiu.edu.pk anwar ghani dcs&se international islamic university islamabad, pakistan anwar.ghani@iiu.edu.pk abstract—capability maturity model integration (cmmi) is a framework known for improving the quality of processes on consistent basis. this paper makes an attempt to explore, analyze and describe the impact of cmmi in terms of return on investment (roi) for the it industry. an it organization who has acquired a maturity level of cmmi 2 is taken as case study. at first, in reference to the level of applied cmmi, a thorough study is completed. afterwards the luxuries and limitations are studied and explored with reference to organizations applying the monetary terms using roi framework. finally, the presented research highlights the key benefits and difficulties in switching to cmmi from conventional quality assurance. keywords-cmmi; return on investment; roi; it; quality assurance i. introduction it industry today has to deal with increased direct customer interaction as more services of an organization are exposed to the customer directly. this is one of the biggest factors driving it towards business goals such as customer satisfaction, performance, increasing security and decreasing time to market their products. in order to deliver such objectives, organizations are rapidly reviving themselves by spending more on quality assurance (qa) and testing. as of 2016-2017 organizations all over the world are spending 31% of their budget in addressing the quality problems [1]. in fact this year was proved to be different from the proceeding ones as the budget dropped from 35% to 31%. before that, the budget of qa and testing was raised from 18% to 35%. however despite this year’s reduction, there is an overall prediction that qa and testing budget will increase to 40% in 2019 [1]. to improve the quality of processes and control the cost of qa and testing, the organizations are adopting relative certifications and trainings. the capability maturity model integration (cmmi) is one the most popular training and certification programs adopted by more than 5,000 businesses from over 70 countries including united states, germany, china, italy, india, australia, pakistan etc. many international organizations and companies demand cmmi maturity to grant contracts as cmmi makes sure that organization processes are of international standard, hence cmmi helps an organization to compete on global scale. some of the salient advantages of cmmi are consistency, cost reduction, self-improvement and process improvement. the organizations that decide to improve the processes have to pay a significant investment of time and money. a variety of concerns are addressed by cmmi by ensuring process improvement through trustworthy manners. one of the better ways to present financial value is through return on investment (roi) [2, 3]. this research highlights how to improve and map efforts to the corporate objectives and expectations regarding the effects of cmmi adoption. the roi will be tracked on an ongoing basis. at the same time intermediate indicators like customer satisfaction, etc. will be tracked to determine the impact of improvement activities. roi calculation is used along with other approaches to develop a business case for a given proposal. the key objective of this research is to present a report containing results about the impact of cmmi and also to explain the continuity and future work in this spot. this study specifies and signifies that executing cmmi practices for quality over conventional quality practices is beneficial and the cost spent on obtaining/applying cmmi has break-even with benefits. furthermore, such information can be made part of quantitative management and be used as an input for improving processes and technologies. the training materials, appraisal methods and process improvement models used in this research are collected via product suite of cmmi. benchmark versions engineering, technology & applied science research vol. 7, no. 6, 2017, 2189-2193 2190 www.etasr.com saeed et al.: the impact of capability maturity model integration on return on investment in it … of the models and appraisal methods have been introduced. the use of cmm for scientific data management has been also proposed [5, 6]. ii. literature review several researches have shown numerous advantages of process maturity of an organization by using different assessment approaches [7-11]. an empirical study was carried out by authors in [12] to find out the effects of cmm on project performance and software quality in information systems (is). the authors claimed that is implementation strategies are related to cmm levels and higher cmm levels relate to higher software quality and project performance. authors in [13] explored benefits of cmm such as rework, schedule, productivity, defects, error defection effectiveness, and roi from the review of seventeen published articles. they concluded that investment in cmm programs leads to enhanced software development and maintenance. process quality can be improved by adopting cmmi models [14]. in [15], author isolated the effort of process maturity effects versus other factors effects through using 161-project samples. software development efforts can be reduced from 4% to 11% by raising organization to the next maturity level, but the percentage of reduction varies in each level of cmmi. return on investment [16], is an output observation when an organization implements some processes. the cost savings is realized by comparing it with the invested cost. the amount saved as a result of process improvement divided by the cost of process improvement is defined as improvement benefit index. the cost of improvement also caters the cost of personnel within a process improvement method such as consultant fees, purchasing tools, and the activities for improving management. the customer satisfaction is not easily quantified within the cost. with the similar procedure, the roi can be calculated against each key process area (kpa) of cmmi. according to authors in [17], business managers make their decisions on the basis of roi as it is a highly accepted metric representing adaptability and simplicity. roi can be calculated by using the following relation: roi= (gi-coi)/coi, where gi= gain from investment coi=cost of investment if an investment has a negative roi then usually it is not used. according to [18] in the it sector, the roi measures for evaluation are difficult to calculate by the management. only 20% of organizations have formal roi measures while 25% have plans to adopt it in the next 12 months. literature for cost reduction and impact on schedule using cmm is discussed below. according to boeing, australia [19] the average cost to fix defects was reduced to 33%. reduction in unit software cost was 20% according to lockheed martin [19]. 10% reduction in overall cost per maturity occurred according to northrop grumman [19]. boeing reported 50% reduction in the release, in rework following test up to 60% reduction. general motors reported a rise from 50% to 95% when number of milestones met. 25-30% productivity raised within three years [20]. lockheed martin reported 50% reduction of software defects and a 55% increase in award fees. implementing cmmi process improves schedule and budget predictability, cycle time, productivity, quality, customer satisfaction, and roi. cmmi process improvement may be established in various ways. for adopting cmmi product suite, several organizations have integrated, changed and updated the current processes with the cmmi processes, while some have established new processes. some organizations have expanded the scope of their improvement efforts by integrating software, hardware and related disciplines with the cmmi model to their existing models. in some cases, few organizations do not adopt cmmi. however, they have established a process which is emphasized differently than the software capability maturity model (swcmm), but the outcome shows the significance of the finest practices that are articulated in cmmi models. however, these organizations cannot be accredited as cmmi adopted. similarly, the impact of cmmi-based process improvement can be used to demonstrate many possible measures of performance. a highlevel description of the cmmi impact based process improvement is shown in figure 1. in the upper left, costs of process improvement are illustrated. in the center, box process capability and organizational maturity are depicted, and the benefits of process improvement are illustrated in the box on the right. as shown, in order to calculate roi or related measures the costs and benefits are combined [21]. iii. limitations consistently measuring roi is tough since organizations tend to refrain from sharing their financial data. the study concentrates on one specific software organization in pakistan, so the facts provided are specific to that organization. fig. 1. high-level model of cmmi impact iv. methodology cmmi is one of the ways to implement the quality plans and is generally used as a standard for software quality. the best way to plan quality is to implement cmmi. the quality is achieved by following and implementing cmmi’s defined rules and processes. based on cmmi standard, the center for advanced research in engineering (care) needs to create a quality plan that fulfills the requirement of cmmi. engineering, technology & applied science research vol. 7, no. 6, 2017, 2189-2193 2191 www.etasr.com saeed et al.: the impact of capability maturity model integration on return on investment in it … a. introduction of organization an engineering organization is taken as a case study. it has a history of good reputation by receiving acknowledgements in the form of international awards. it is a certified cmmi compliant organization with an engineering team of more than fifty employees and more than fifty employees as supporting staff. in the areas of emerging technologies, the organization offers an extensive list of products, expertise and design services. it stands at the forefront of the technology by focusing on research and development. the organization got flourished through a well-trained, creative, diverse and outstanding team responsible for outstanding products and system design portfolio. the organization achieved cmmi level 2 by implementing all 7 kpas of level 2 in two years. a brief summary of cmmi related implementations are:  process definition by quality engineering department.  training for managers and engineers regarding cmmi.  developed in-house software for configuration management, which also worked with concurrent versions system (cvs) and visual source safe (vss).  developed in-house software for reporting.  hired people for configuration management.  deployed special focus on documentation and task trackers. v. results a. cost this category covers the areas where organization reports reduction in the cost of the work product, process and general savings to model-based improvement at various stages, intermediate and final. the summary is shown in table i. table i. summary of benefits and impact: return on cost evaluation result average cost to fix defects 20% reduction unit testing process 7% reduction overhead rate 2% decrease average cost variance 15% reduction in expenses in first six months 2 million b. schedule the two important aspects i.e., schedule predictability improvement and reduction in time to complete tasks, are covered under this category. productivity is determined by the quantity of work done over a period of time. the summary is shown in table ii. c. quality the quality improvement is measured with reference to the reduction in the number of defects. pre-test rework is decreased throughout the duration of a project, which helps in satisfying the customer while improving the project quality. the main objective of the organization is to satisfy its customers by minimizing the defects through their identification at early stages. to achieve this goal, formal inspections of cmmi are quite helpful. the summary of benefits and impact of using cmmi standard with reference to quality is presented in table iii. table ii. summary of benefits and impact: schedule evaluation result reduction in the time required to turn around release 25% reduction in work due to pre and post test 60% increase in productivity 20% improvement in on-time delivery of project 15% improved and stabilized schedule yes table iii. summary of benefits and impact: quality evaluation result defects found in fielded systems 1% increase in focus on quality by developers yes reduction in severity of post-release defects yes improvement in quality of a code yes d. customer satisfaction quality improvement leads towards customer satisfaction. customer satisfaction can also be seen by measuring the process improvement benefits. the summary of customer satisfaction achieved through cmmi is given in table iv. table iv. summary of benefits and impact: customer satisfaction evaluation result increase in award fees: 20% received 58% customer award fees cmmi reduction in severity of post-release defects? yes improvement in quality of a code? yes e. return on investment (roi) return on investment (roi) may be calculated through a number of ways yet none of them is defined as official standard. some of these are as: • benefit cost ratio (bcr) • net present value (npv) • internal rate of return (irr) • payback period (pp), breakeven point (bep) ratio roi of an investment (capital) is the ratio of “total earnings before interest and taxes” and “average invested capital”. however, for calculating roi for a process improvement project, the computation used is: return on investment for a process improvement project = (benefits from process improvement – cost (investment) incurred towards undertaking process improvement). engineering, technology & applied science research vol. 7, no. 6, 2017, 2189-2193 2192 www.etasr.com saeed et al.: the impact of capability maturity model integration on return on investment in it … 1) past period initial investment: 285, 000,000, netprofit: 25,000,000. roi:10% 2) cmmi impact initial investment: 40,000,000, net profit: 75,000,000. roi:18% table v. summary of benefits and impact: roi results model 4:1 roi of quality activities cmmi 7:1 defects calculated per hour and time spent in preventing errors cmmi earlier defects detection and better project control implemented cmmi f. benefits and cost ratio roi can be calculated as simply the ratio of enjoyed benefits by a certain effort to the deserved cost. pros:  easy to compute  provides ways to compare the projects cons  time value of money (tvm) is not incorporated in roi  no approach to identify the dollar enormity of roi  cannot predict the time to achieve the desired results. fig. 2. impact of cmmi on roi table vi. summary of benefits and impact of cmmi before applying cmmi after applying cmmi (year 0) after applying cmmi (year 1) total cost 3 million 1 million 1 million 5 million benefits 0 5 million 5 million 10 million return 10% 18% 22% 15 million fig. 3. summary benefits and impact of cmmi figure 4 shows the rework have gone out of boundaries at periods 1, 3, 4, 5, and 6, while at other points everything is well managed. fig. 4. summary benefits and impact of cmmi (incorporating boundary conditions) vi. conclusion based on the discussion with project managers and team leaders, it was concluded that customer satisfaction can only be achieved by managing and incorporating their requirements into to the product. the following list summarizes the benefits of cmmi implementation.  the overall product cost along with finding and fixing the defects gets lowered.  there is considerable reduction in time to complete the desired projects.  the number of product defects is reduced, hence the quality gets improved.  rising of award fees demonstrates customer satisfaction through earlier and continuous delivery of valuable software  this case study claims a positive roi from cmmibased process improvement. this report validates that an organization benefits from cmmi, if it works hard at process improvement. it is hoped engineering, technology & applied science research vol. 7, no. 6, 2017, 2189-2193 2193 www.etasr.com saeed et al.: the impact of capability maturity model integration on return on investment in it … that from the current review, the organizations wishing to adopt cmmi can get useful information regarding its impact on roi. vii. recommendation for more improvement in the organizational processes and longtime success through customer satisfaction, organizations should take steps towards level 3, 4 and 5. opd an opf will provide a base to organization improving, better managing their processes and aligning their organizational vision with the work. upgrading their work to a higher level will be most helpful for them. references [1] capgemini. world quality report 2016-17, available at: https://www. capgemini.com/thought-leadership/world-quality-report-2016-17, 2017 [2] m. c. paulk, b. curtis, m. b. chrissis, c. v. weber, “capability maturity model, version 1.1”, ieee software, vol. 10, no. 4, pp. 18–27, 1993 [3] m. agrawal, k. chari, “software effort, quality, and cycle time: a study of cmmi level 5 projects”, ieee transactions on software engineering, vol. 33, no. 3, pp. 145–156, 2007 [4] m. diaz, j. king, “how cmm impacts quality, productivity, rework, and the bottom line”, the journal of defense software engineering, 2002 [5] k. crowston, j. qin, “a capability maturity model for scientific data management: evidence from the literature”, proceedings of the american society for information science and technology, vol. 48, no. 1, pp. 1–9, 2011 [6] r. bate, an integrated product development capability maturity model, cmu/sei-97-mm-001, software engineering institute, carnegie mellon university, 1997 [7] k. butler, “the economic benefits of software process improvement”, proceedings of crosstalk, hill afb, usa, pp. 14-17, 1995 [8] j. herbsleb, a. carleton, j. rozum, j. siegel, d. zubrow, benefits of cmm-based software process improvement: initial results, cmu/sei94-tr-13, software engineering institute, carnegie mellon university, pittsburgh, 1994 [9] s. humphrey, r. snyder, r. willis, “software process improvement at hughes aircraft”, ieee software, vol. 8, no. 4, pp. 11-23, 1991 [10] t. mcgibbon, a business case for software process improvement, final report, contract number f30602-92-c-0158, data and analysis center for software, kaman sciences corporation, new york, 1996 [11] h. wohlwend, s. rosenbaum, “schlumberger’s software improvement program”, ieee transactions on software engineering, vol. 20, no. 11, pp. 833-839, 1994 [12] h. girish, j. james, g. klein g., “software quality and is project performance improvements from software development process maturity and is implementation strategies”, journal of systems and software, vol. 80, no. 4, pp. 616-627, 2007 [13] d. galin, m. avrahami, “are cmm program investments beneficial? analyzing past studies”, software ieee, vol. 23, no. 6, pp. 81-87, 2006 [14] m. diaz, j. king, “how cmm impacts quality, productivity, rework, and the bottom line”, the journal of defense software engineering, vol. 15, no. 3, pp. 9-14, 2003 [15] b. clark, “quantifying the effects of process improvement on effort”, ieee software, vol. 17, no. 6, pp. 65-70, 2000 [16] d. j. paulish, a. d. carleton, “case studies of software-processimprovement measurement”, computer, vol. 27, no. 9, pp. 50–57, 1994 [17] k. el emam, d. r. goldenson, “an empirical review of software process assessments”, advances in computers, vol. 53, pp. 319–423, 2000 [18] b. violino, measurin return on investment, information week, pp. 36– 44, june 30, 1997 [19] d. goldenson, d. l. gibson, demonstrating the impact and benefits of cmmi: an update and preliminary results, software engineering institute, carnegie mellon university, 2003 [20] l. g. jones, a. l. soule, software process improvement and product line practice: cmmi and the framework for software product line practice, cmu/sei-2002-tn-012, software engineering institute, carnegie mellon university, 2002. [21] a. q. liu, “motorola software group’s china center: value added by cmmi”, software tech news, vol. 10, no. 1, pp. 18–23, 2007 engineering, technology & applied science research vol. 7, no. 3, 2017, 1732-1736 1732 www.etasr.com bharti et al.: controller design of dfig based wind turbine by using evolutionary soft computational … controller design of dfig based wind turbine by using evolutionary soft computational techniques om prakash bharti dpt of electrical engineering indian institute of technology banaras hindu university varanasi-221005, (u.p), india opiitbhu@gmail.com r. k. saket dpt of electrical engineering indian institute of technology banaras hindu university varanasi-221005, (u.p), india rksaket.eee@iitbhu.ac.in s. k. nagar dpt of electrical engineering indian institute of technology banaras hindu university varanasi-221005, (u.p), india sknagar.eee@iitbhu.ac.in abstract—this manuscript illustrates the controller design for a doubly fed induction generator based variable speed wind turbine by using a bioinspired scheme. this methodology is based on exploiting two proficient swarm intelligence based evolutionary soft computational procedures. the particle swarm optimization (pso) and bacterial foraging optimization (bfo) techniques are employed to design the controller intended for small damping plant of the dfig. wind energy overview and dfig operating principle along with the equivalent circuit model is adequately discussed in this paper. the controller design for dfig based wecs using pso and bfo are described comparatively in detail. the responses of the dfig system regarding terminal voltage, current, active-reactive power, and dc-link voltage have slightly improved with the evolutionary soft computational procedure. lastly, the obtained output is equated with a standard technique for performance improvement of dfig based wind energy conversion system. keywords-dfig; wind turbine; pid controller; matlab; simulink; model; pso; bfo; fitness; function abbreviations: dfig: doubly fed induction generator pid: proportional integral derivative pso: particle swarm optimization bfo: bacterial foraging optimization wecs: wind energy conversion systems wrsg: wound rotor synchronous generator pmsg: permanent magnet synchronous generator scig: singly excited induction generator. i. introduction wind power is considered probably the optimum available renewable energy sources and has widely developed in recent years due to its advantages such as low pollution, comparatively low capital cost involved and the short gestation period [1]. there have been several types of generators for wind energy conversion configuration. the older approach involved synchronous generators whereas the recent approach focuses more on induction generators of different types [2]. simple induction generators have a few weaknesses such as reactive power utilization and unregulated voltage profile during variable rotor speed. these problems can be solved by employing power electronic converter or regulators. the dfig is a wound rotor induction machine that can operate in supersynchronous and sub-synchronous manner. the benefits of the dfig as compared with fixed speed generators are that they improve power quality, reduce mechanical stress and fluctuations and exhibit excellent power imprisons [3]. the function of the dfig associated with the grid is facilitated through a rotor as well as a network side converter. however, an inverter related to the rotor side is used to provide give a fundamental frequency to sustain stator frequency at an invariable stage, despite the variations in mechanical power. the control of dfig presents a dual dilemma: to balance the velocity changes and reactive power. in reality, dfigs should be cut off from the network while the voltage inequity is more than 6% [3]. it has been described that the torque pulsation could be concentrated by using injected recompense current in the dfig rotor. in [4], authors presented a relevant study of a simplified model, in which the authors compare the fifth plus third order model of dfig followed using the investigation under faulted circumstances. however, in [5], authors offered magnitude along with frequency control of network associated dfig based on a coordinated model for wind power production [5]. the numerical differentiation based additive model approximately the nominal working position of dfig was used. the effectiveness of such type models can be validated from the outcomes offered. the ranking of wind turbines from 800kw to 3 mw but wind farm assortment is 2mw to 200mw [7]. in this paper, we provide an alternate technique to design a controller for the dfig system considered by [7, 8] using two bioinspired techniques. the obtained results are compared with existing solutions. the implementation of dfig for voltage regulation at a remote location has been described in a previous work [21]. the global trend toward clean energy is an inspiration for more integration of wind-based electrical energy in power systems [9]. vast and small wind turbines produce electrical energy for networks whereas they sustain stand-alone isolated areas like well [10]. however, the wind velocity changes radically depending on the environmental circumstances along with the time of operation. therefore, there is a huge margin of speed difference. such margins of speed alteration make the wound rotor induction machines appropriate for power engineering, technology & applied science research vol. 7, no. 3, 2017, 1732-1736 1733 www.etasr.com bharti et al.: controller design of dfig based wind turbine by using evolutionary soft computational … generation through wind energy [11]. wind turbines can run either at fixed speed (actually within a speed range about 1 %) or at varying speed [12]. for fixed speed wind turbines, induction generator is instantly coupled to the grid. hence, for a fixed-speed system, the turbulence of the wind will result in power fluctuations, which influence power quality. power electronic apparatus are used to control the dfig based variable-speed wind turbine. dfig based wind turbine aerodynamics has thoroughly been described in [13-16, 17]. ii. general idea and working principle of dfig a part of wound rotor induction generators, also known as dfig, is one of the most frequently used scheme in the wind energy industries [18]. currently, these types of generators are extensively accepted as one of the appropriate wind energy conversion systems. dfig is in nature a wound rotor induction generator, and the rotor circuit is usually controlled by electric power devices to allow variable speed operation. dfig stator winding associated directly to the grid by a power transformer and dfig’s power is usually ranged from a few kilowatts to several megawatts. the size for a rotor converter is about 30% of a full capacity converter. during low wind speed, more electrical energy could be acquired from a variable speed dfig, in distinguishing with a fixed speed wind generator [2]. the advantages of using dfig in wecs is described in [2]. whereas in [19] dfigs have two operating modes, in (i) mode nr>ns, s is –ve, then generator in super-synchronous mode and both stators, as well as rotor windings, deliver power to the grid. while in (ii) mode nr<ns, s is +ve the generator in subsynchronous mode and stator winding delivers power to both the grid and the rotor winding. the mathematical modeling of dfig is thoroughly explained in [20]. the machine data is available in per unit reactance form. a dfig equivalent circuit can be seen in [21]. the sixth order relations for unbalanced operations, is as follows [7, 8]: 0.000324 6 1.75 5 2366 4 7.9 6 3 7.5 9 2 5 12 2.18 14 6 2340 5 8.67 6 4 4.79 9 3 2.7 12 2 1.27 14 9.6 1 ( 4 ) s s s e s e s e s e s s e s e g s s e s e s e              iii. particle swarm optimization an overview and brief description for particle swarm optimization along with algorithm features is given in [22-28]. this approach is appropriate to solve nonlinear problems and is established on flock activities such as birds detect food using gathering. the first alternative of the pso algorithm brings using having the inhabitants (named the swarm) for the applicant result (known as particles). these particles are turned in the search space using a few straightforward formulas. the motions of the particles are guided to their best-known position in the search space in addition to the entire swarm's most prestigious situation. whenever an enhanced position is being detected, then it will move towards to guide the movement of the flock. the procedure is repetitive, furthermore using performing, so it is trusted, but not assured, that an adequate result will finally be detected. here in this procedure, a set of particles is introduced in the d-dimensional search space using at random selecting velocity as well as position. the first situation of the particle is considered as the best place to initiate, as well as the velocity of the particle is updated based on experience to the other particles from the swarming population. a. a minute representation for the algorithm we set the values of pso algorithm constants as inertia weight factor w = 0.3, along with acceleration constants c1, c2 = 1.5. as we have to optimize three parameters that are; kp, kd, ki to the controller, and search optimal value in the threedimensional search space. so we arbitrarily formatted a swarm of “100” population in three-dimensional search space using [xi,1 xi,2 xi,3] and [vi1 vi2 vi3] as preliminary situation as well as velocity. considered primary fitness function of each point along with the position with minimum fitness function is exhibited as gbest (initial value of global best optima) as well as the optimal fitness function as fbest1 (initial best fitness function). we ran the program by means of pso algorithm through thousands (or yet additional numbers) of iterations; in addition to program brought back the final optimal value of fitness function as “fbest” along with last global optimum point as “gbest.” b. the conception of fitness function to the controller design for best results we optimize all pid parameters ,of the and describe a three-dimensional search space in which all three dimensions present. every precise point in search space accounts for a particular arrangement of [kp, ki, and kd]. for which an appropriate answer has found, and a fitness function determines the performance of the position to the pid parameters. this fitness function comprises numerous essential features to the performance index for design. along with the best position in search space, the fitness function reaches an optimal value with four essential functions which defined fitness function. by this function; steady state errors, peak overshoot, rise time as well as settling time has been come out for the defined system. the contribution of these essential functions towards the innovative fitness function is determined by a scale factor. at best position fitness function has minimal value. the chosen fitness function is defined as follows: f = (1-exp (-β)) (mp +ess) + (exp (-β)) (ts tr) here f: fitness function, mp: peak overshoot, ts: settling time, tr: rise time, β: scaling factor (depends on upon the alternative of the designer), scaling factor β = 1. in the matlab library, we have to define a fitness function which has pid parameters as input values, as well as it returns fitness value of the pid based controller model as output and formatted as follows. the function [f] = fitness (kd kp ki) c. pso based controller gain the pso based controller gains for the 6th order transfer function reduced the model to the dfig system, at best fitness function (fbest=0.1967) by several iterations which are given in table i. table i. gains of the pso-based controller gbest parameters kp ki kd gains 39.9781 7.6902 0.0271 engineering, technology & applied science research vol. 7, no. 3, 2017, 1732-1736 1734 www.etasr.com bharti et al.: controller design of dfig based wind turbine by using evolutionary soft computational … iv. bacterial foraging optimization a. description a description for bacterial foraging optimization with algorithmic features is given [29-33]. the algorithm is heavily based on the behavior of e.colli bacteria. in the bacterial foraging optimization process four mobile behaviors are mimicked: 1) chemotaxis: a chemotactic step can be defined as a tumble followed by a tumble or a tumble a run lifetime. to represent a tumble a unit length random direction, x (j), is generated; this will be used to describe the direction of movement after a tumble. in particular : xi(j+1,k,l) =x i(j,k,l) + c(i)*x(j) , where xi(j,k,l) represents the ith bacterium at jth chemotactic, kth reproductive as well as lth elimination and dispersal step.c(i) is the size of the step taken in the random direction specified by a tumble( the run length unit). 2) swarming: e.colli cells can work cooperatively self-organize into highly structured colonies with high environmental adaptability using a complex communication means. overall, cells provide an attraction signal to each other, so they swarm together. the mathematical representation for swarming can be represented by: jcc(θ,p(j,k,l)) =ji cc(θ,θi(j,k,l)) =σ[dattract * exp(wattract *σ( θm –θi m)2)]+σ [hrepellant * exp (-wrepellant *σ (θm –θi m) 2)] where jcc(θ, p(j,k,l)) is the cost function value to be additional to the actual cost function, that is to be minimized to present a time-varying cost function. s is the total number of bacteria , p is the number of parameters to be optimized which are present in each bacterium and dattract, wattract,hrepellant, wrepellant are different coefficients that should be appropriately chosen. 3) reproduction: the least healthier bacteria die with the other each healthier bacteria split into two novel bacteria each placed in the similar position. 4) elimination and dispersal: it is probable that in the local surroundings, the lives of a population of bacteria changes either gradually (e.g., via utilization of nutrients) or abruptly due to some other influence. events can occur that all the bacteria in a region are killed, or a group is dispersed into a new part of the environment. they have the effect of possibly destroying the chemotactic progress. b. bfo based controller gain the bfo algorithm process as a flowchart is given in [33]. the bfo based controller gains for the 6th order transfer function reduced the model to the dfig system, at the fitness function (function f = fitness (kd kp ki)) by several iterations which are given in table ii. table ii. gains of the bfo-based controller v. simulation and results a. simulink response of the dfig system here wind farm dfig average model (matlab 13b) shows a 9 mw wind farm with the dfig driven by a variable speed wind turbine. it consisted of six 1.5 mw wind turbines and linked toward a 25 kv distribution system exports power to a 120 kv grid through a 30 km, 25 kv feeder. in this illustration, the wind velocity is preserved invariable at 15 m/s. the response of the dfig based wind turbine with the evolutionary soft computational procedure (pso-based controller) regarding voltage along with current at the terminals, active power generated; reactive power requirements and dc capacitor voltage in pu are shown in figures 1 and 2 respectively. as shown, the response of the dfig system regarding terminal voltage, current, active-reactive power and dc-link voltage has slightly improved with the pso based controller compared to the bfo based controller. fig. 1. (a) dfig based wind turbine average matlab simulink model diagram, (b) voltages at the dfig terminals in pu, (c) currents at the dfig terminals in pu parameters kp ki kd gains 0.1417 0.1472 0.1005 (a) (b) (c) engineering, technology & applied science research vol. 7, no. 3, 2017, 1732-1736 1735 www.etasr.com bharti et al.: controller design of dfig based wind turbine by using evolutionary soft computational … b. bfo based control response by pid controller the reaction of the bfo based pid controller is given in [7, 8]. as shown the system has zero undershot in the response of open loop system. the step response of the bfo based pidcontroller is shown in figure 3 and table iii. c. response of pid controller using pso method the step response of the pso based system is given in figure 4. it is observable by a comparison result of bfo based pid control along with one describe in this work which shows that; pso based pid controller has extended to sufficiently damped bfo based controller without compromising the speed of response to the control loop. now the step response of open as well as close loop reduced order system by pid controller with the pso technique is shown in figure 4 and table iv. d. comparison between bfo based pid controller and pidcontroller using pso method by comparing tables iii and iv the following observations can be made:  the designed pso based pid controller can reduce the steady state error to zero as the existing one.  the rise time, peak time and overshoot have been reduced to zero, and the response is no more underdamped.  the speed response is much better than that of the current controller. hence intended controller in this paper assists to eliminate reactive power variations in dfig system. fig. 2. (a) active power delivered of the dfig in pu (b) reactive power requirement of the dfig in pu (c) dc link voltage at the ordinary linkage capacitor fig. 3. step response of the bfo based pid controller table iii. step response of bfo based pid controller rise time settling time settling min settling max over shoot under shoot peak peak time 0.00 sec 62.3541 sec 0.0438 sec 0.4992 sec 0.0 % 0.0 % 0.500 0.0 sec fig. 4. step response of the pso-based pid controller table iv. step response of the pso-based pid controller rise time settling time settling min settling max over shoot under shoot peak peak time 0 sec 0.4061 sec -.0694 sec 0.4996 sec 0 % 13.8754% 0.50 0 sec vi. conclusion the bfo based pid controller improves system responses in comparison with an open loop system, while the pso based designed controller not only improves the system response but also reduces the percentage overshoot to zero. the obtained outcome demonstrates that the system using pso based controller settles down in less time compared to the bfo based pid controller scheme. the comparison between the pso based controller and the bfo based pid controller is discussed. it is accomplished that the settling time is condensed next to near about 62% along with the percentage overshoot; rise time and peak time are reduced to zero. finally, it is fulfilled that pso based control technique afford another alternative to (b) (c) (a) engineering, technology & applied science research vol. 7, no. 3, 2017, 1732-1736 1736 www.etasr.com bharti et al.: controller design of dfig based wind turbine by using evolutionary soft computational … propose a reliable and adequate controller to the dfig based wind energy conversion systems. acknowledgment the authors are highly thankful to the indian institute of technology, banaras hindu university, varanasi, uttar pradesh, india for partial funding this work. appendix: dfig simulation data base values: sb = 2 mva, vb = 690 v, ωb = 2пf (rad/s), f = 60 hz, zdc = vdc/idc, ib = 1900a, vdc = 1150 v, zb = (vb/ √ 3)/ib, lb = zb/ωb, ldc = zdc/ωb, , cb = 1/ (zb ωb), tb = sb/ωb, jb = sb/ (ωb 2), idc = sb/ydc, cdc = 1/ (zdc ωb) ,infinite bus voltage (pu): v dq, inf = [0.989 0.15] dfig (pu): rs = 0.023, rr = 0.016, ls = 0.180, lr = 0.16, lm = 2.9, dc link component: vdc ref = 1, cdc = 12.7227 references [1] f. yao, r. c. bansal, z. y. dong, r. k. saket, j. s. shakya, “wind energy resources: theory, design, and applications”, in: handbook of renewable energy technology, world scientific publishing house, singapore, 2011 [2] m. tazil, v. kumar, r. c. bansal, s. kong, z. y. dong, w. freitas, h. d. mathur, “three-phase doubly fed induction generators: an overview”. iet electric power applications, vol. 4, pp. 75–89, 2010 [3] t. brekken, n. mohan, “control of a doubly fed induction wind generator under unbalanced grid voltage conditions”, ieee trans. energy conv., vol. 22, no. 1, pp. 129–135, 2007 [4] j. b. ekanayake, l. holdsworth, n. jenkins, “comparison 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foundations of computational intelligence, lnee springer, vol. 3, pp23-55, 2009 [31] d. r. parhi, a. k. jha, “path planning of mobile robot using bacteria foraging optimization”, international journal of artificial intelligence and computational research, vol.4, no. 1, pp. 1-5, 2012 [32] p. siva subramanian, r. kayalvizhi, “an optimum setting of pid controller for boost converter using bacterial foraging optimization technique”, in: systems thinking approach for social problems, lecture notes in electrical engineering, vol. 327, springer, india, 2015 [33] c. yadav, m. singh, “bfo-pso optimized pid controller design using performance index parameter”, international journal of engineering development and research, vol. 3, no. 4, pp. 260-264, 2015 microsoft word etasr_v12_n1_pp8123-8128 engineering, technology & applied science research vol. 12, no. 1, 2022, 8123-8128 8123 www.etasr.com boualamallah et al.: evaluation of the effect of tightening torque on single-lap bolted joints evaluation of the effect of tightening torque on single-lap bolted joints djamal boualamallah laboratory of materials and reactive systems university of sidi bel abbes sidi bel abbes, algeria djamal.boualamallah@yahoo.com abdelkader ghazi laboratory of materials and reactive systems university of sidi bel abbes and university of mascara algeria ghaziaek@yahoo.fr abdelkader miloudi laboratory of materials and reactive systems university of sidi bel abbes sidi bel abbes, algeria miloudidz@yahoo.fr mohamed merzoug laboratory of materials and reactive systems university of sidi bel abbes sidi bel abbes, algeria m_merzoug01@yahoo.fr abstract-in this experimental research, a set of tests was conducted on single-lap bolted joints in terms of choosing between two types of bolts and exploiting the optimal solution for connecting samples. then the effect of the tightening torque on the mechanical behavior of single-lap joints was evaluated. six simple tensile tests were performed with different values of torque and the results are reported. keywords-bolted assembly; mechanical behavior; experimental approach; damage mechanisms i. introduction the construction of a structure generally involves the assembly of parts. different assembly technologies can be used: bolting, riveting, gluing, welding, or their combinations. it is natural to assume that increasing the number of the elements that contribute to the connection increases the complexity of the structure as a whole [1]. the advantage of bolted structures is their ease of installation [2-3]. this type of connection concerns both metal sheets (aluminum, steel, etc.) and composite sheets, with aluminum or steel bolt bodies. the use of this type of structure requires the mastery of their mechanical strength. several previous works have focused on the study of the mechanical characterization of bolted connections. these studies have focused on several aspects, including the following: • the flexibility of the fixation. • load transfer. • stress concentrations. • the effect of torque. • the effect of the clearance between the bore and the body of the bolt. • the different modes of rupture, etc. this type of assembly has the interesting advantage of its ease of realization (drilling of holes in the plates and mounting of the fastener with or without washers). moreover, the use of bolted assembly implies that the maintenance of a mechanical system is easier because we can repair or change the component that cannot function properly without separating all the parts of the structure. moreover, this type of assembly makes the transport and delivery of the components easier. the bolted assembly allows minimizing the volume of finished products. nevertheless, the presence of the bore hole is the weak point of this type of structure due to the concentration of stresses which is often the main cause of crack initiation. the dimensioning of this type of assembly must be based on numerical behavior models that allow choosing and optimizing the design parameters (dimensions), bolt and sheet (plate) properties, tightening torque, number of bolts, spacing between bolts, etc. that are optimal in terms of strength or stiffness. difficulty also lies in determining the load transfer rate between the bolt and the plates. it is important to note that in the case of complex three-dimensional structures containing a large number of fasteners, the importance of nonlinearities (behavior, contact) would quickly lead to excessive memory and calculation time requirements [1]. several research studies on bolted connections have addressed the influence of torque on their overall mechanical behavior under static and dynamic stresses [2]. authors in [4] have experimentally studied the mechanical strength of a bolted composite plate connection subjected to tensile-shear stress by analyzing the effects of the diameter of the washers and the value of the tightening torque. figure 1 shows that the increase in the tightening is accompanied by the breaking stress, but the configuration in terms of geometry of the sample is different in our research. authors in [5] carried out a numerical simulation corresponding author: djamal boualamallah engineering, technology & applied science research vol. 12, no. 1, 2022, 8123-8128 8124 www.etasr.com boualamallah et al.: evaluation of the effect of tightening torque on single-lap bolted joints of a bolted connection of aluminum plates of thickness e=2mm, with three values of the tightening torque cs= 1, 1.5, and 2kn. it was shown that the elastic load increases with the value of the tightening torque. authors in [6] studied the caulking around the fastener. the loss of preload and its influence on stress distribution was studied in [7]. authors in [8] studied the multi-line structure of fasteners under mechanical and thermal loading, taking into account several parameters such as clearance, friction between plates and transferred load. the analytical solution of this study is based on the principle of virtual powers. recently, authors in [9] studied the bolted joint in uni-axial tension, using two models, the first one based on latham and crockoft energy, and the second one based on gurson continuous damage. it was shown that the behavior of the structure is composed of 8 phases: linear elasticity of the material, sliding of the sheets corresponding to the bore/bolt clearance, matting phase, linear elasticity phase of the structure, plasticization phase around the substrate bores, stable and then unstable cracking phase which ends in rupture. it was found that if the tightening torque is low, the slippage appears earlier. in the work presented in this paper, we have studied the influence of the tightening torque and the bolt material (hardened and galvanized steel) on the strength of single-lap bolted connections through experimental tests. predicting failure mode in steel connection is a complicated task, requiring knowledge of stress distribution in the connection and understanding of different failure modes with different loading configurations. it is very difficult to model the complicated failure mechanism by analytical methods [10]. ii. material the material used is galvanized steel grade h300lad+z. figure 1 shows the elasto-plastic stress-strain curve behavior of the steel. such materials are characterized by increased mechanical strength and the ability to resist static and shock [11]. 0,0 0,5 1,0 1,5 2,0 2,5 0 100 200 300 400 500 600 c o n tr a in te [ m p a ] allongement [%] fig. 1. typical load-displacement curve of a specimen. the mechanical characteristics (table i) of the base metal such as yield strength σe, ultimate tensile strength σu, deformation ε, and young's modulus e were obtained from the curve in figure 1. table i. mechanical characteristics tensile test result characteristics �e [mpa] �u [mpa] e [mpa] ε [% ] value 410.12 580.22 210317.9 0.195 iii. bolts used the type of bolts used is hexagonal head steel (figure 2). for the bolts, the quality class is symbolized by two numbers. the first is one hundredth of the minimum tensile strength σr [mpa] of the material and the other is 10 times the ratio between the minimum yield strength (σe) and the breaking strength rr. the first series of bolts used are made of 4.8 galvanized steel with yield strength, σe = 320mpa and breaking strength σr = 400mpa. during the tightening operation with the minimum tightening torque (c=19nm) the wear of the bolt threads is obtained (figure 3). the second series of bolts used are made of hardened and tempered steel at 400°c of class 8.8 m5-20-10 (figure 2), whose dimensions are: nominal diameter 5.8mm, pitch: 0.8mm, σr ≈ 800mpa, and σe ≈ 640mpa. the hexagonal nut m5 10, is characterized by: minimum tensile stress ≈800mpa, yield strength σe ≈ 640mpa, pitch = 0.8mm, and thickness = 4.6mm. the flat washer is made of ordinary steel and has the following dimensions: minimum diameter = 6.5mm, maximum diameter = 12mm, and thickness = 1.6mm. fig. 2. bolt symbolization. fig. 3. wear of the zinc-plated steel bolt (4.8). fig. 4. oil-hardened steel bolt. engineering, technology & applied science research vol. 12, no. 1, 2022, 8123-8128 8125 www.etasr.com boualamallah et al.: evaluation of the effect of tightening torque on single-lap bolted joints iv. experimental procedure a. test specimens and machine when installing an assembly (bolt + washer + nut), it is essential to apply an appropriate tightening torque. this tightening torque is used to tension the bolt in order to keep the elements in contact. a torque wrench of eco budget brand 19-110 nm -1/2in was used (figure 5). the thickness of the sheet metal is 2mm. the types of specimens were tested as a single lap joint (figure 5). six values of tightening torque were used: 19, 25, 30, 33, 36, and 39n.m. in order to avoid the effects of friction with the nut of the bolt, a support washer was placed. the most frequently used single-bolt specimen is the tension-shear (tss) specimen (figure 6). the geometry of tensile-shear specimens is defined by [12, 13]. fig. 5. torque wrench eco budget. fig. 6. the studied configurations. in this case, the bolt is stressed mainly with shear, but this stress is not pure. a bending moment is induced that tends to cause the plates to bend and deflect (figure 7). it has been observed that the point of higher concentration of stress was in the first threads of the screw, near the screw head, whatever load was applied [14]. fig. 7. single lap joint loaded in tension-shear (sheet deformation spacing). b. influence of torque at the beginning of the tensile test of the assembly and the movement of the pieces on each other, the two influential parameters are the coefficient of friction and the torque. the first one is influenced by the surface condition and lubrication of the parts. the greater the clamping force, the greater the tensile force will be to obtain a relative displacement of the two substrates. in order to find the influence of the tightening torque, we performed tensile tests using 6 tightening torque values: 19, 25, 30, 33, 36, and 39nm, on a specimen with a bolt fastening. the substrates have a bore diameter of 6mm corresponding to a clearance of 0.2mm. the test results are presented by the load-displacement curves in figure 8. for the high torque m=40nm, the thread was damaged by rotation and the high torque power which produced heat and damaged the structure (figure 9). figure 10 shows the maximum load that the connection can support for different torque values. we notice that the optimal results are for the tightening torques of 25 and 30nm. this is because the tightening torque mainly influences the elastic phase before sliding and the maximum level of load [2-17]. the tightening torque has been correctly introduced by applying local compression to the substrate and by pulling the bolt, thus allowing the prestressing forces to be introduced into the substrates [17]. 0 2 4 6 8 10 12 14 16 18 20 22 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 m=19nm m=25nm m=30nm m=33nm m=36nm m=39nm l o a d [ n ] displacement [n] fig. 8. tensile curve load – displacement for 6 values of torque. engineering, technology & applied science research vol. 12, no. 1, 2022, 8123-8128 8126 www.etasr.com boualamallah et al.: evaluation of the effect of tightening torque on single-lap bolted joints fig. 9. thread breakage. fig. 10. variation of maximum load vs of torque. c. history of the damage mechanism of a bolted assembly the mechanical strength of bolted connections has been the subject of several studies. studies related to the mechanical strength in tension-shear, dynamics, fatigue, etc. can be found in the literature [2-9]. this work has been undertaken with the objective of identifying the chronology of fastener damage. figure 11 shows the evolution of the applied load as a function of the total displacement of the structure. fig. 11. load vs displacement of a bolted assembly. figure 11 highlights different phases of accommodation of the connection: (1) friction and sliding of the sheets, (2) elastic transfer, (3) plastic transfer phase of secondary bending, (4) pull-out of the element and breakage of the connection. from the knowledge of the different zones it is possible to deduce the stiffness of the bolted connection k, the elastic limit of the joint, and the breaking load. d. breaking mode and edge effect in these tensile experiments that produced a shear stress, the process was performed according to the standard and all recommended conditions for this type of test, so the results (figure 12) were in agreement with the literature used in the field of assemblies (shear stress and peel). figure 13 shows the failure modes for tightening torques of 19 and 39nm. we note that the failure occurred at the bolt, by shearing with a small displacement at the level of the structure of 5.6mm for m=39nm and 6.3mm for m=19nm. the maximum torque creates torsion in the bolt diameter, which means that the bolt is damaged before the tensile test. the low value of the torque m=19nm does not create the necessary adhesion for the structure [18]. fig. 12. mixed tensile-shear failure mode. fig. 13. mode of rupture for m=19nm and m=39nm. fig. 14. mode of rupture for m=33nm and m=36nm. for torques m=33nm and m=36nm, it can be seen from figure 14 that the strength is comparable with respect to the torque m=19nm, but the displacement is significant with engineering, technology & applied science research vol. 12, no. 1, 2022, 8123-8128 8127 www.etasr.com boualamallah et al.: evaluation of the effect of tightening torque on single-lap bolted joints respect to the latter; because the large value of the torque gives a clear adhesion between the substrates [15-19], so we have a mixed traction-shear failure mode. for torques m=25nm and m=30nm it can be seen from figure 15 that the resistance is high compared to the other torques. in this case, the mode of failure is acceptable [15-17], which means the deformation occurs at the bolt hole, and the bolt was not broken by the tensile operation. fig. 15. mode of rupture for m=25nm and m=30nm. it can be seen that the mode of failure is ductile because of the presence of the cups in the majority of the fracture surface. figure 16 shows the failure faces of the bolts. it is noted that the failure mode is ductile because of the presence of cups in the majority of the failure surface. the fracture face (which may also be located under the head of the bolt) has a grainy appearance which may be distributed at several levels of the threaded part. there is a generally localized break on the threaded part of the bolt. this rupture follows a plastic deformation of the material. fig. 16. faces of bolt failure. v. conclusion the indispensability of knowing the properties and mechanical characteristics of the components before any construction or assembly obliges us to always develop our instruments and means of calculation, testing and even control when it comes to the use of standardized components such as bolts. at the end of the work carried out within the framework of this article, which deals with the study of the rupture and damage of a bolted assembly made of thin sheets of thickness e=2mm in galvanized steel, we conclude to the following: • the nature of the material of the bolt has an overall influence on the behavior of the structure (type of steel). • the correct torque for the connection extends its service life, so it the value of the torque applied to the bolt must be carefully selected, because it has an obvious impact on the modification of the behavior of the structure and thus exceeds the danger from the point of view of fracture mechanics. references [1] o. omran, "développement d’un modèle de connecteur pour assemblage boulonné," ph.d. dissertation, université de picardie jules verne, amiens, france, 2015. [2] t. dang-hoang, "rupture et endommagement d’un assemblage boulonné : approche expérimentale et simulation numérique," ph.d. dissertation, l’université de lille, lille, france, 2009. [3] j. p. muzeau, "constructions métalliques," techniques de l’ingénieur, may 10, 2005. https://www.techniques-ingenieur.fr/base-documentaire/ archives-th12/archives-les-superstructures-du-batiment-tiacd/archive1/constructions-metalliques-c2521/ (accessed dec. 24, 2021). [4] u. a. khashaba, h. e. m. sallam, a. e. al-shorbagy, and m. a. seif, "effect of washer size and tightening torque on the performance of bolted joints in composite structures," composite structures, vol. 73, no. 3, pp. 310–317, jun. 2006, https://doi.org/10.1016/j.compstruct.2005. 02.004. [5] a. d. crocombe, r. wang, g. richardson, and c. i. underwood, "estimating the energy dissipated in a bolted spacecraft at resonance," computers and structures, vol. 84, no. 5–6, pp. 340–350, jan. 2006, https://doi.org/10.1016/j.compstruc.2005.09.024. [6] s. a. nassar, g. c. barber, and d. zuo, "bearing friction torque in bolted joints," tribology transactions, vol. 48, no. 1, pp. 69–75, jan. 2005, https://doi.org/10.1080/05698190590899967. [7] j. yang and f.-k. chang, "detection of bolt loosening in c–c composite thermal protection panels: i. diagnostic principle," smart materials and structures, vol. 15, no. 2, pp. 581–590, feb. 2006, https://doi.org/10.1088/0964-1726/15/2/041. [8] s.-w. yen, "multirow joint fastener load investigation," computers & structures, vol. 9, no. 5, pp. 483–488, nov. 1978, https://doi.org/ 10.1016/0045-7949(78)90045-7. [9] t. dang hoang, c. herbelot, a. imad, and n. benseddiq, "numerical modelling for prediction of ductile fracture of bolted structure under tension shear loading," finite elements in analysis and design, vol. 67, pp. 56–65, may 2013, https://doi.org/10.1016/j.finel.2012.12.003. [10] n. konkong, "an investigation on the ultimate strength of coldformed steel bolted connections," engineering, technology & applied science research, vol. 7, no. 4, pp. 1826–1832, aug. 2017, https://doi.org/10.48084/etasr.1243. [11] a. buketov, o. syzonenko, d. kruglyj, t. cherniavska, e. appazov, and k. klevtsov, "investigation of the influence of the synthesized ironcarbide mixture on the adhesive and mechanical properties of epoxy composites for parts of transport machines," engineering, technology & applied science research, vol. 10, no. 5, pp. 6214–6219, oct. 2020, https://doi.org/10.48084/etasr.3750. [12] iso 14324:2003. soudage par résistance — essais destructifs des soudures — méthode pour les essais de fatigue sur assemblages soudés par points. iso, 2003. engineering, technology & applied science research vol. 12, no. 1, 2022, 8123-8128 8128 www.etasr.com boualamallah et al.: evaluation of the effect of tightening torque on single-lap bolted joints [13] y. xiao and t. ishikawa, "bearing strength and failure behavior of bolted composite joints (part ii: modeling and simulation)," composites science and technology, vol. 65, no. 7, pp. 1032–1043, jun. 2005, https://doi.org/10.1016/j.compscitech.2004.12.049. [14] s. f. fakhouri, m. m. shimano, c. a. araujo, h. l. defino, and a. c. shimano, "photoelastic analysis of the vertebral fixation system using different screws," engineering, technology & applied science research, vol. 2, no. 2, pp. 190–195, apr. 2012, https://doi.org/10. 48084/etasr.144. [15] t. ireman, "three-dimensional stress analysis of bolted single-lap composite joints," composite structures, vol. 43, no. 3, pp. 195–216, nov. 1998, https://doi.org/10.1016/s0263-8223(98)00103-2. [16] f. c. campbell, structural composite materials. materials park, oh, usa: asm international, 2010. [17] c. t. mccarthy, m. a. mccarthy, and v. p. lawlor, "progressive damage analysis of multi-bolt composite joints with variable bolt–hole clearances," composites part b: engineering, vol. 36, no. 4, pp. 290– 305, jun. 2005, https://doi.org/10.1016/j.compositesb.2004.11.003. [18] g. kelly, "quasi-static strength and fatigue life of hybrid (bonded/bolted) composite single-lap joints," composite structures, vol. 72, no. 1, pp. 119–129, jan. 2006, https://doi.org/10.1016/j.compstruct. 2004.11.002. [19] k. aldas and f. sen, "stress analysis of hybrid joints of metal and composite plates via 3d-fem," indian journal of engineering and materials sciences, vol. 20, no. 2, pp. 92–100, may 2013. engineering, technology & applied science research vol. 7, no. 3, 2017, 1676-1680 1676 www.etasr.com abou taleb and al-jarrah: experimental study of an air lift pump experimental study of an air lift pump fawzy sh. abou taleb mechanical engineering department engineering college northern border university arar, saudi arabia fauzy1957@yahoo.com jawdat a. al-jarrah mechanical engineering department engineering college northern border university arar, saudi arabia jawdatj@yahoo.com abstract—in this investigation the effect of submergence ratio and air jacket on the performance of the air lift pump has been studied. three types of air jackets in addition to five levels of submergence ratios were used. each air jacket has a number of drilled holes distributed uniformly at the perimeter of the inside pipe, where the total area of drilled holes was kept constant. it has been found that the water flux increases as the submergence ratio increased. also it was found that the minimum air flux required to start discharging water from the pump decreases as the submergence ratio increases. air jacket with a hole of 4 mm diameter, resulted the highest performance for the air lift pump. keywords-airlift pump; air-jacket; performance; submergence ratio i. introduction an air lift pump is a device used to raise the liquid or slurries from a well or vessels through a vertical pipe, partially submerged in the liquid, by means of compressed air introduced into the pipe near the lower end [1]. the theory and principle of air lift pumps were described in detail in [2]. the main advantage of the air lift pump is that there are no mechanical below-ground components, so it is essentially simple and reliable and can easily handle sandy or gritty water [3, 4]. air lift pumps are used in a very wide range of applications, because of their simple construction, cost effective maintenance, easy performance and high reliability [5]. the two main disadvantages of the air lift pump are low water delivery height and low efficiency [6]. numerous theoretical as well as experimental studies have been published related to the interpretation and analysis of air lift pump performance. most of these studies were concerned with the analysis of design parameters and operational parameters on the performance of air lift pumps. in [7], authors studied design parameters such as riser diameter and air injector design. the operational parameters; such as submergence ratio, air injection conditions, and nature of solid phase, which required to be lifted were studied in [8]. in [9], authors studied the performance of the air lift pump for various values of submergence ratio. in [10], authors showed that the capacity and efficiency of the air lift pump are function of air mass flow rate, submergence ratio and the riser pipe length. the best efficiency ranges are found to be in slug and slug-churn flow regimes [11]. in this investigation the air lift pump performance was studied with different air jackets which are used to introduce the air to the pump. ii. experimental work the air lift pump is consisted of two main units, the first is the main body of the pump and the second is the air supply unit. figure 1 shows the main body of the air lift pump set-up which was used in this experiment. the body of the air lift pump consists mainly from a vertical pipe divided into static lift (submergence length) and static head (riser). in addition two tanks were used, one as a reservoir tank and the other as a collecting tank. compressed air with high pressure is injected through an air jacket. compressed air is supplied into the pump from the compressor tank through an air-supply line. the airflow rate is measured using a calibrated sharp-edged orifice meter connected to u-tube mercury manometer. the water flow rate is calculated by weighed the collected water for a specific time period. the length of suction pipe was chosen to prevent the injected air to bubble back into the water reservoir. fig. 1. schematic diagram of the main body of the airlift pump. the static lift (submergence length) is measured as the height of the free surface level water from the air injection system. submergence ratio is calculated as the submergence length divided by the length of the total length of the pipe (the sum of static lift and static head). the static head is the height engineering, technology & applied science research vol. 7, no. 3, 2017, 1676-1680 1677 www.etasr.com abou taleb and al-jarrah: experimental study of an air lift pump where the water is to be raised. the hydrostatic head in the water reservoir is also controlled by water control valve, so that submergence ratio is kept constant. five levels of submergence ratios were used in this investigation as 18, 25.8, 33.6, 41.4 and 49.2% . the air injection system is an air jacket type placed on the vertical pipe axis. the air jacket consists from a perforated internal pipe of 5.08 cm inside diameter surrounded by a large iron tube of 15.24 cm inside diameter. three types of air jackets were used in this analysis by varying the size of drilled holes, where the total air injection area is kept constant. figure 2 illustrates the used air-jacket in this analysis. each air jacket has a number of holes drilled uniformly through the perimeter of the pipe distributed into rows and columns. table i shows the hole size and the numbers of rows and columns of each air jackets that used in this analysis. the two pipes have a height of 20 cm and are flanged together forming the air injection system. according to this design, the air is uniformly distributed around the lifting pipe so that the radial momentum of the air is balanced with each other. fig. 2. schematic diagram of air injection jacket table i. types of air-iackets. air-jacket hole size, mm number of rows number of columns a1 2 12 8 a2 4 6 4 a3 6 5 2 iii. results and discussion the performance of the air lift pump is affected by many factors such as submergence ratio, air flow rate and the section area of riser pipe as suggested in [2]. in this investigation five levels of submergence ratio were used, 18, 25.8, 33.6, 41.4 and 49.2%. however, the terms of water flux jw, and air flux, ja, are used instead of water flow rate and air flow rate respectively. the flux of water and air are calculated by dividing the measured volumetric flow rate of water and air by the cross sectional area of the static head pipe. figure 3 shows the variations of the water flux, jw, with the variation of air flux, ja, at different submergence ratios. air flux, ja m/s 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 w at er f lu x, j w m /s 0.0 0.2 0.4 0.6 0.8 49.2% 41.4% 33.6% 25.8% 18% air jacket a1 (3a) air flux, ja, m/s 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 w at er f lu x, j w , m /s 0.0 0.2 0.4 0.6 0.8 1.0 49.2% 41.4% 33.6% 25.8% 18% air jacket a2 (3b) air flux, ja m/s 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 w at er f lu x, j w , m /s 0.0 0.2 0.4 0.6 0.8 49.2% 41.4% 33.6% 25.8% 18% air jacket a3 (3c) fig. 3. variation of water flux,jw, with air flux,ja, at different submergence ratio for air jackets (a) a1, (b) a2 and (c) a3 (a) (b) (c) engineering, technology & applied science research vol. 7, no. 3, 2017, 1676-1680 1678 www.etasr.com abou taleb and al-jarrah: experimental study of an air lift pump three types of air jackets a1, a2, and a3 were used in these experiments. it has been shown that the water flux is larger at submergence ratio of 49.2% than those of 41.4, 33.6, 25.8 and 18% for the same amount of air flux, where the same trend was obtained in [12]. figure 4 reveals the effect of air jacket types on the water flux. it has been found that the water flux is more in case of air jacket, a2, than that of other types of air jackets. however, the water flux increases as the air flux increases as shown in figures 3 and 4. but at higher air flux excess of air is introduced to the air jacket, which leads to decrease on the water flux. figure 3 shows that the amount of air flux that leads to decrease on the water flux increases as the submergence ratio increases. the scenario of air lift pump working, at low air flux, if small bubbles injected into the draft tube, the bubbles will remain distributed over the cross section of the tube and sustain flow regime known as bubble flow. while increasing the rate of the air flux, the small air bubbles begins to coalesce into larger bubble which in essence separate the water column into slug flow regime. the transition between these flow regimes is characterized as the bubbly-slug flow regime where small bubbles are found suspended within the liquid slugs between the larger air slugs [13]. increasing the size of air bubbles by using a larger hole size as in air jackets, a2, reduces the required air flux to has bubbly slug flow regime. however, it was reported that maximum water flux happened when the flow changed from bubbly-slug flow to slug-churn flow [11]. air flux, ja m/sec 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 w at er fl ux , j w m /s ec 0.0 0.2 0.4 0.6 0.8 1.0 air jacket a1 ( 2 mm) air jacket a2 ( 4 mm) air jacket a3 ( 6 mm) submergence ratio 49% (4a) air flux, ja m/sec 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 w at er fl ux , j w m /s ec 0.0 0.2 0.4 0.6 0.8 air jacket a1 ( 2 mm) air jacket a2 ( 4 mm) air jacket a3 ( 6 mm) submergence ratio 41.4% (4b) air flux, ja m/sec 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 w at er fl ux , j w m /s ec 0.0 0.1 0.2 0.3 0.4 0.5 0.6 air jacket a1 ( 2 mm) air jacket a2 ( 4 mm) air jacket a3 ( 6 mm) submergence ratio 33.6% (4c) air flux, ja m/sec 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 w at er fl ux , j w m /s ec 0.00 0.05 0.10 0.15 0.20 0.25 0.30 air jacket a1 ( 2 mm) air jacket a2 ( 4 mm) air jacket a3 ( 6 mm) submergence ratio 25.8% (4d) fig. 4. the effect of water jacket types on water flux at different submergence ratio of (a) 49%, (b) 41.4%, (c) 33.6% and (3d) 25.8% figure 5 shows the effect of drilled hole size of air jackets on water flux at different submergence ratio. the method of air injection has affected the airlift pump performance, different methods used before such as air stone, injector plates [14]. in this study the surface area of the air bubbles is changed by using three sizes of drilled holes 2, 4 and 6 mm for a1, a2 and a3 air jackets respectively. the total area of drilled holes was kept constant by varying the number of holes in each air jacket. it has been noticed that the air jacket, a2, has the best water flux for all submergence ratios, as shown in figure 5. at low submergence ratio of 33.6 and 25.8%, there is no difference in water flux resulted from a1 and a2 and its more clear at submergence ratio of 25.8% as shown in figure 3d, especially at low air flux. for a given depth of submergence, an airlift requires a minimum air inflow rate to start pumping water as noted in [15]. figure 6 shows the minimum air flux needed to start pumping of water, for each air jacket (c) (d) (a) (b) engineering, technology & applied science research vol. 7, no. 3, 2017, 1676-1680 1679 www.etasr.com abou taleb and al-jarrah: experimental study of an air lift pump with variation of submergence ratio. it has been shown that for higher submergence ratio less air flux is needed to start pumping. however, air jacket a2, needs minimum air flux especially at higher submergence ratio 49% compared by other air jackets a1 and a3. submergence ratio % 15 20 25 30 35 40 45 50 m in im um a ir flu x to s ta rt d is ch ar gi ng , j a m /s ec 0.0 0.5 1.0 1.5 2.0 air jacket a1 (2 mm) air jacket a2 (4 mm) air jacket a3 (6 mm) fig. 5. variation of minimum air flux to start discharging with submergence ratio air flux, ja m/sec 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 e ff ic ie nc ey % 0 5 10 15 20 air jacket a1 air jacket a2 airjacket a3 submergence ratio 49% (6a) air flux, ja m/sec 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 e ff ic ie nc ey % 0 5 10 15 20 air jacket a1 air jacket a2 airjacket a3 submergence ratio 41.4% (6b) air flux, ja m/sec 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 e ff ic ie nc ey % 0 2 4 6 8 10 12 14 air jacket a1 air jacket a2 airjacket a3 submergence ratio 33.6% (6c) air flux, ja m/sec 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 e ff ic ie nc ey % 0 2 4 6 8 10 air jacket a1 air jacket a2 airjacket a3 submergence ratio 25.8% (6d) fig. 6. variation of efficiency with air flux for submergence ratio of (a) 49%. (b) 41.4%, (c) 33.6% and (d)25.8% (a) (b) (c) (d) engineering, technology & applied science research vol. 7, no. 3, 2017, 1676-1680 1680 www.etasr.com abou taleb and al-jarrah: experimental study of an air lift pump the efficiency of the air-lift pump is calculated based on the definition in [16]. the efficiency is defined as the ratio of power required to lift the solid or the liquid phase to the point of discharge to the power required to compress the air isothermally through the compressor from atmospheric pressure to the air injection pressure. figure 7 shows the variation of the efficiency with air flux for three types of air jacket at different submergence ratios. the efficiency increased as the air flux increased to a certain level then for further increases of air flux the air-lift pump efficiency reduced. air jacket a2 has the best efficiency as compared to air jackets a1 and a3 at all submergence ratios. also, the efficiency increased as the submergence ratio increased as shown in figure 7. air jackets a1 and a3 have the same efficiency trend with the variation of submergence ratio. the ratio of air flux to water flux at the maximum efficiency was calculated using fig.5. it has been found that the air to water ratio at higher submergence ratio of 49.2% and 41.4, to be about 2. this agreed by which obtained in [17, 18] where it was stated that a gas to liquid ratio between 1 and 2 is ideal for optimum performance of an air lift for low head applications. air flux, ja m/s 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 e ff ic ie nc y % 0 5 10 15 20 49.2% 41.4% 33.6% 25.8% 18% air jacket a2 fig. 7. variation of efficiency with air flux at different submergence ratios. iv. conclusions the following concluded remarks can be deduced from the present study: 1) the maximum efficiency does not occur at the maximum water flux. 2) as the submergence ratio increases, the maximum water flux and maximum efficiency of the pump increase for the same air flux. 3) for the same air flux, air jacket, a2, has the maximum water flux and efficiency. 4) the minimum of air flux needed, to start water discharge from the pump, decreases as the submergence ratio increases. acknowledgment the authors wish to acknowledge the approval and support of this research study by grant 435-20 from deanship of scientific research in northern border university, arar, ksa. references [1] n. n. clark, r. j. dabolt, “a general equation of air lift pump operating in slug flow”, aiche. j., vol. 32, pp. 56-64, 1986 [2] d. j. nicklin “the airlift pump: theory and optimization”, trans. inst. chem. eng., vol. 41, pp. 29-39, 1963 [3] j. m. delhaye, “two-phase pipe flow”, int. chem. eng., vol. 23, pp. 385-410, 1983 [4] d. j. ryley, g. j. parker, “flowing geothermal wells: cerro priet wells m.91 and krafla well kj-9.1: computer analysis compared with experimental data”, int. conf. on geothermal energy, florence italy, pp 187-196, 1982 [5] a. mahrous, “experimental study of airlift pump 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a. kandil, h. a. warda, w. h. ahmed, “air-lift pump characteristics under two phase flow conditions”, int. j. of heat and flow, vol. 30, pp. 88-98, 2009 [12] v. c. samaras, d. p. margaris, “two-phase flow regime maps for air-lift pump vertical upward gas-liquid flow-part ii”, international journal of multiphase flow, vol. 31, no. 6, pp.757-766, 2005 [13] d. j. reinemann, m. b. timmons, “predicting oxygen transfer and total dissolved gas pressure in airlift pumping”, aquacultural engineering, vol. 8, pp. 29-46, 1989 [14] m. f. khalil, k. a. elshorbagy, s. z. kassab, r. i. fahmy, “effect of air injection method on the performance of an airlift pump”, int. j. heat and fluid flow, vol. 20, pp. 598-604, 1999 [15] g. l. morrison, t. i. zeineddine, m. henriksen, g. b. tatterson, “experimental analysis of the mechanics of reverse circulation air lift pump”, industrial engineering and chemical research, vol. 26, pp. 387391, 1987 [16] d. j. nicklin, “two phase bubble flow”, chemical eng. sci., vol. 17, pp. 693-702, 1962 [17] i. todoroki, y. sato, t. honda, “performance of airlift pump”, bulletin of the japan society of mechanical engineers, vol. 16, pp. 733-741, 1973 [18] c. j. loyless, a feasibility study of using airlift pumps for aeration, degasification, and water movement in recirculating aquaculture system, thesis, louisiana state university, 1995 engineering, technology & applied science research vol. 7, no. 3, 2017, 1629-1632 1629 www.etasr.com tashkandi et al.: spot welding of 6061 aluminum alloy by friction stir spot welding process spot welding of 6061 aluminum alloy by friction stir spot welding process mohammad a. tashkandi mechanical engineering department engineering college northern border university arar, saudi arabia tashkandi@gmail.com jawdat a. al-jarrah mechanical engineering department engineering college northern border university arar, saudi arabia jawdatj@yahoo.com masoud ibrahim chemical and material science engineering dpt, engineering college, northern border university arar, saudi arabia and industrial engineering department, faculty of engineering fayom university, egypt ibrahim_64@yahoo.com abstract—this study was focused on the effect of welding parameters on the lap-shear fracture load of the welded joints prepared by friction stir spot welding. four different weld parameters were analyzed: rotational speed, dwell time, pin length and shoulder size of the welding tool. it was found that the lap-shear fracture load increases with an increase of the welding parameters to a limited value and decreases with further increase. the strong welded joints failed under nugget-pull out fracture. keywords-friction stir spot welding; aluminum alloys; mechanical properties i. introduction friction stir spot welding (fssw) is a relatively new process that has recently received considerable attention from various industries including automotive [1, 2]. fssw was first developed by twi abington, uk in 1991 [3]. this new spot welding technique has been successfully applied in the automotive industry due to its high product quality, over 90% energy saving and 40% equipment cost saving versus the traditional electrical resistance spot welding (ersw) [4]. in the fssw process, a rotation tool is inserted into the overlapping work pieces to an established depth and then held for a certain time before being retracted [5, 6]. the development of reliable techniques for joining al to a steel sheet has become the subject of considerable interest [7]. electrical resistance spot welding is currently the dominant method used for joining steel car bodies, because it is fast, versatile, and easily automated [8]. unfortunately, when using ersw to weld al to steel, a thick intermetallic compound (imc) reaction layer is formed which can badly affect the joint performance [9]. friction stir spot welding is an alternative technology that has potential for joining multi-material structures [10–12]. there are many investigations in the literature about fssw. in [13], authors investigated the microstructures and failure mechanisms of fssw in aluminum 6111-t4 alloys. in [14], authors did some work on sheet aluminum joining. moreover, in [15] authors conducted experiments to investigate structureproperties relations in spot friction welded 6111-t4 aluminum. in [16], authors studied the fssw properties relating to microstructure and strain rates for aluminum 7075-t6 alloys. in [17], authors investigated fssw properties relating to local melting and tool slippage for aluminum 7075 alloys. furthermore, in [18] authors developed an empirical relationship using surface response methodology to predict the maximum strength for fssw joints [18]. in [19, 20], authors investigated fssw properties for aluminum 5754 and aa2014 alloys respectively. as for dissimilar material fssw, the fssw characteristics for al and mg alloys were investigated [21] and a feasibility study of fssw in advanced high-strength steels such as ahss has also been reported [22]. in [23], authors reported on the development of fssw robot system for the automobile industry. one needs to optimize the weld parameters for similar materials; in this case, al6061 and establish criteria for these optimum parameters. following this, one would consider joining dissimilar materials using fssw and find the perfect welding conditions for such applications. this paper investigated the effect of the friction spot stir welding on the lap-shear fracture load to establish an understanding of the optimum weld parameters. ii. experimental work 6061 aluminum alloy plates with a thickness of 3 mm were used to fabricate lap joints. the chemical composition of the studied material is given in table i. two rectangular aluminum plates of 100 x 30 mm were lap-welded by friction stir spot welding process. a conventional vertical milling machine was used for the welding process. the head of the milling machine was tilted 0.5 degrees and a special suitable fixture was designed to hold the plates during the welding process. the fixture was tightly secured on the milling machine table to prevent vibration occurring as a result of the frictional engineering, technology & applied science research vol. 7, no. 3, 2017, 1629-1632 1630 www.etasr.com tashkandi et al.: spot welding of 6061 aluminum alloy by friction stir spot welding process forces of the welding process. sample geometry for the welded plates is shown in figure 1. as indicated, the plates are 100 mm long by 30 mm wide and 3 mm thick. the overlap is 30 mm which is equal to the width of the samples. according to [24], the plate length is the most important factor affecting the test results. in addition, for the overlap to be sufficient, it should at least have the same length as the sample width. the welding parameters are discussed next; each of these welding parameters has five levels. table i. chemical composition of the alloy used (%wt). si mg cu fe mn ti zn cr al 0.75 0.9 0.5 0.5 0.15 0.05 0.03 0.03 rest fig. 1. sample geometry for the welding process the welding tool has a 4 mm square pin profile and was kept constant throughout the entire experiment. moreover, the welding tool has a constant shoulder height of 20 mm. the variable welding tool parameters were the shoulder diameter, pin length, tool rotational speed and dwell time. the welding tools have flat shoulders and were made from high-speed steel. five shoulder diameters were considered: 10, 12.5, 15, 17.5, and 20 mm. the second parameter was pin length which is the plunged length to produce the welded joint. pin lengths of 3.5, 4.0, 4.5, 5.0 and 5.5 mm were used. the third welding parameter was the tool rotational speed. tool rotational speeds of 350, 560, 900, 1120 and 1800 rpm were used. the last welding parameter was dwell time. dewll times of 20, 25, 30, 35 and 40 sec. were used. finally, shear load test on a universal tensile testing machine was carried out on all produced samples to measure the shear load of the welded plates. pure bending was achieved by proper alignment of the samples during the shear load test. this was done by using vice grips and adjusting the grip insert from side to side, so that the centerline of the upper and lower grips pass through the centerline of the welded part. finally, the focus of the study was to determine the max possible shear load and thus no stress calculations were carried out. iii. results and discussion joint strength prepared by the friction stir spot welding process was examined using universal testing machine. the lap-shear fracture load is recorded as the average of three readings of the tested specimens. the effect of rotational speed on lap-shear fracture load of the joints is given in figure 2. in these experiments the rotational speed changed as 350, 560, 900, 1120 and 1800 rpm, where the pin length, dwell time and shoulder diameter are kept constant at 4.5 mm, 35 sec, and 15 mm respectively. figure 2 shows that the lap-shear fracture load increased as the rotational speed increased from 350 up to 1120 rpm then the value of lap-shear fracture load drastically dropped at higher rotational speed of 1800 rpm. the same results were obtained previously in [25], where it was reported that when the rotational speed increased more than 750 rpm the tensile shear strength decreased. however, in [26] it was stated that high tool rotating speeds also give hot welds. hot welding parameters lead to low ultimate forces. in [27], authors stated that excessive heat input during fsw negatively affects the mechanical properties of joints. it has also been reported that the temperature goes up almost linearly with increase of rotation speed [28]. rotational speed, rpm 200 400 600 800 1000 1200 1400 1600 1800 2000 la ps he ar fr ac tu re lo ad , n 1000 1500 2000 2500 3000 3500 4000 pin length 4.5 mm dwell time 35 sec shoulder diameter 15 mm fig. 2. variation of lap-shear fracture load with rotational speed in [29], it was indicated that the rotation speed and plunge depth were the main influence factors for tensile-shear strength. the effect of tool pin length on the lap-shear fracture load is shown in figure 3. the pin length values changed from 3.5 mm to 5.5 mm with incremental 0.5 mm. the other welding parameters were kept constant. it has been shown that the joint strength increased as the pin length increased from 3.5 up to 4.5 mm, then the lap-shear fracture load fluctuate for further increases in pin length. the pin length of 4.5 mm resulted to have a higher joint strength. the welded aluminum sheets have 3 mm thickness in other words when the pin plunged to the mid depth of the lower sheet, the resulted joints have a maximum strength as shown in figure 3. however, further increasing in pin length has a moderate effect on welded spot joint shear strength, where the lap-shear fracture load dropped at pin length 5 mm, and slightly increased again at pin length of 5.5 mm. there is an optimum tool pin height which gives the highest tensile shear strength [30]. also, the same trend of lapshear fracture load with the pin length was obtained by previous researchers [31]. pin length, mm 3.0 3.5 4.0 4.5 5.0 5.5 6.0 la ps he ar fr ac tu re lo ad , n 1000 1500 2000 2500 3000 3500 4000 rotational speed 1120 rpm dwell time 35 sec shoulder diameter 15 mm fig. 3. variation of lap-shear fracture load with pin length engineering, technology & applied science research vol. 7, no. 3, 2017, 1629-1632 1631 www.etasr.com tashkandi et al.: spot welding of 6061 aluminum alloy by friction stir spot welding process figure 4 shows the effect of dwell time on the variation of lap-shear fracture load of the spot welded joints. in these sets of spot welding, the rotational speed, pin length and shoulder diameter were kept constant, while the dwell time was taken as 20, 25, 30, 35 and 40 sec. it was found that as the dwell time increased up to 35 sec, the lap-shear fracture load increased as well. excessive of frictional heat introduced to the welded parts due to longer thermal cycle reduces the lap-shear fracture load due to changes in microstructure [30]. figure 4 shows that the lap-shear fracture load decreases when the dwell time increased more than 35 sec. the amount of frictional heat introducing during the spot welding depends on the friction area between the welding parts and the welding tool [32]. dwell time, sec 15 20 25 30 35 40 45 la ps he ar fr ac tu re lo ad , n 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 pin length 4.5 mm shoulder diameter 15 mm rotional speed 1120 rpm fig. 4. variation of lap-shear fracture load with dwell time the shoulder diameter of the welding tool was taken as 10, 12.5, 15, 17.5 and 20 mm to study the effect of shoulder diameter on the lap-shear fracture load of welded joints produced by the friction spot stir welding process. figure 5 shows that joints welded by a welding tool that has a 15 mm shoulder diameter possess the optimum lap-shear strength compared by other joints produced by smaller or larger shoulder diameters. in lap-shear tensile tests, there are generally three different fracture modes: interfacial shear fracture, nugget pull-out fracture, and upper or lower sheet fracture [33]. figure 6 shows the typical fracture modes of the tensile-shear tests samples in this investigation. it was found that the joint with nugget pullout fracture had higher strength as also previously reported in [34]. for the nugget pull-out separation, two sheets tend to get separated at the partial bonding under loading. however, fracture modes mainly depended on the area of sz [35]. iv. conclusions in this study, aluminum sheets of 3 mm thickness were spot welded by friction spot stir welding process. we concluded the following:  the lap-shear fracture load is affected by fssw parameters like rotational speed, dwell time, pin length and shoulder diameter.  the lap-shear fracture load increased as the rotational speed increased up to 1120 rpm.  there is an optimum pin length that produces sound joints, in this study and for this type of material and size it was found to be 4.5 mm.  increasing the dwell time more than 35 sec. reduces the lapshear fracture load.  the nugget pull-out fracture mode happened at relatively higher lap-shear fracture load. shoulder diameter, mm 8 10 12 14 16 18 20 22 la ps he ar fr ac tu re lo ad , n 1000 1500 2000 2500 3000 3500 4000 pin length 4.5 mm dwell time 35 sec rotional speed 1120 rpm fig. 5. variation of lap-shear fracture load with shoulder diameter fig. 6. photographs of failure surfaces show the typical failure modes of test specimens. acknowledgment the authors wish to acknowledge the approval and support of this research study by grant 4-117-435 from deanship of scientific research in northern border university, arar, ksa. references [1] r. hancock, “friction welding of aluminum cuts energy cost by 99%”, welding journal, vol. 83, p. 40, 2004 [2] s. toshya, 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modes of dissimilar spot friction welds between aluminum 5754o and 7075-t6 sheets”, journal of materials processing technology, vol. 209, no. 8, pp. 3724–3739, 2009 engineering, technology & applied science research vol. 8, no. 1, 2018, 2367-2373 2367 www.etasr.com toz and erdogmus: a single sided edge marking method for detecting pectoral muscle in digital … a single sided edge marking method for detecting pectoral muscle in digital mammograms guliz toz electrical, electronic & computer engineering dpt duzce university institute of science and technology duzce, turkey glz.toz@gmail.com pakize erdogmus computer engineering dpt engineering faculty duzce university duzce,turkey pakizeerdogmus@duzce.edu.tr abstract—in the computer-assisted diagnosis of breast cancer, the removal of pectoral muscle from mammograms is very important. in this study, a new method, called single-sided edge marking (ssem) technique, is proposed for the identification of the pectoral muscle border from mammograms. 60 mammograms from the inbreast database were used to test the proposed method. the results obtained were compared for false positive rate, false negative rate, and sensitivity using the ground truth values pre-determined by radiologists for the same images. accordingly, it has been shown that the proposed method can detect the pectoral muscle border with an average of 95.6% sensitivity. keywords-inbreast database; pectoral muscle extraction; segmentation; mammogram i. introduction mammography is one of the basic and effective imaging techniques used for the detection and diagnosis of breast cancer. mammography is usually obtained in two forms, the mediolateral oblique view (mlo) and the craniocaudal (cc) view [1]. these two views are used to detect abnormal structures within the breast. however, because of the heterogeneity of the malignancies and overlapping of the intense fibro glandular tissue, it may be difficult to read and interpret mammograms in two-dimensional projection images [2]. human factors as fatigue, limitation of the human eye and others may also cause misinterpretations. in addition, mammography alone is not sufficient for a final diagnosis and a biopsy may also be needed. however, a small percentage of breast biopsies are shown to be cancerous (only 15-30% in case of [3]). therefore, a variety of computer aided diagnostic systems are employed as a second reader to radiologists. clinical trials indicate that the number of cancers detected by computer-aided diagnosis (cad) systems is increased by about 10%, which is comparable to double reading by two radiologists [4]. mlo-views mammograms often contain pectoral muscle. since pectoral muscle shows similar features with abnormal structures such as mass, it is confused with suspicious regions in cad studies and makes accurate diagnosis difficult [5]. for this reason, the removal of pectoral muscle from mammograms is important for accurate diagnosis. the automatic removal of pectoral muscle from mloviews mammograms is a necessary step. at the same time this procedure is quite difficult because values such as shape, size, and density in mammograms differ from mammogram to mammogram. the studies for detection of pectoral muscle from digital mammograms can be categorized in four main groups. these are density-based approaches [6, 7], line-based detection approaches [8, 9], wavelet-based segmentation [10, 11] and statistical [10, 12] methods. authors in [7] proposed a new adaptive method for the detection of pectoral muscle. in this method, the pectoral margin, position and orientation are estimated first with a suitable straight line. this line is then smoothed using the repeated "cliff detection" algorithm to draw the pectoral boundary more accurately. in [13], authors proposed an approach for the detection of segmentation at the pectoral muscle boundary based on the structure tensor. experimental results indicate that the proposed method distinguishes the pectoral muscle exactly with the segments [13]. in [14], authors conducted a study based on the positional characteristics of the pectoral muscle. they have combined iterative otsu thresholding and mathematical morphological processing to find the rough edge of the pectoral muscle. they applied multiple regression analysis to this rough border to obtain the correct segmentation of the pectoral muscle. in [15], authors combined median filtering, morphological erosion process, sobel edge detector and thresholding to find the breast rough limit, then use the gvf snake algorithm with gradient map setting to obtain the sensitivity breast border. authors in [16] used thresholding to identify pectoral muscles, connected component labeling to identify and remove the connected pixels outside the breast region and edge detection processes to identify the edge of the full breast. they used global thresholding for segmentation and removal of pectoral muscle. as a result, they noted that they have effectively removed the gauss and impulse noise and in general, they achieved 90.06% accuracy. in this study, the pectoral muscle border was first determined by a new method called by the authors as single sided edge marking (ssem), based on the geometrical properties of the pectoral muscle and neighborhood relations to extract the pectoral muscle from mammograms. later, the engineering, technology & applied science research vol. 8, no. 1, 2018, 2367-2373 2368 www.etasr.com toz and erdogmus: a single sided edge marking method for detecting pectoral muscle in digital … points found were reinforced with morphological operators and a rough pectoral muscle region was obtained. the boundary of the found candidate pectoral muscle area has been reconstructed and this boundary extracted by the linear interpolation method has been redefined so that the missing point does not exist. the results obtained by the radiology specialists with the ground-truth data for the same images were compared in terms of false positive rate, false negative rate and sensitivity. accordingly, it has been shown that the proposed method can detect the pectoral muscle border with a sensitivity of 95.6 percent. ii. material in this study, 60 mammogram received from the inbreast [17] database were used to test the methodology. the inbreast consists of 115 cases (410 images) of which 90 cases are from women with both breasts (4 images per case) and 25 cases are from mastectomy patients (2 images per case). several types of lesions (masses, calcifications, asymmetries, and distortions) are included. accurate contours made by specialists are also provided in xml format. iii. preprocessing before performing pectoral muscle area boundary detection, noise reduction and image enhancement [18-22] on the image are necessary. the flowchart for all followed in the current work is presented in figure 1. firstly, the image has been reduced to a size of 512x512 and the pixel intensity values have been reduced to 256 for decrease processing complexity. all images are then arranged in such a way that the pectoral muscle region is in their upper left corner. in order to achieve this, a mirror image of the mammogram is taken if the pectoral muscle region is located at the upper right corner of the mammogram. fig. 1. mammogram pre-processing flowchart no additional procedure has been performed in the mammograms that have the pectoral muscle region in their upper left corner (figure 2(b)). then, the mammogram image has been converted to a binary image by using an obtained experimentally threshold value σ = 0.09 (figure 2(c)). since, the largest region in the binary image is the breast region; a filter has been applied so that this area remains in the image. the resulting image was eroded using a two pixel structure element and then subtracted from the image obtained in the previous step. thus, the rough border of the breast region has been obtained as seen in figure 2(d). the resulting image has been multiplied by the original image and so the result is the image that contains only the breast region. then, the 3x3 median filter and biorthogonal wavelet transform have been used to remove noise and enhance the image. finally, the image has been enhanced with adaptive histogram equalization and the noise has been reduced by anisotropic diffusion method (figure 2(e)). the biorthogonal wavelet and anisotropic diffusion methods used for preprocessing are briefly described below.  biorthogonal wavelet transform wavelets are used in many areas including noise reduction in image processing. there are many wavelet families [23]. biorthogonal wavelet representation can be seen to have many advantages when compared to orthogonal wavelet representation [24]. for example, sub-band images do not change and have no overlap under translation. smoothing symmetric and asymmetric wavelet functions can be used to reduce the reflection of signal extensions and border effects [24]. because of these advantages, a biorthogonal wavelet (biorthogonal 3.1) has been used for noise reduction in this work.  anisotropic diffusion method anisotropic diffusion method is a technique aiming at reducing image noise. this method reduces the image noise while preserving important image details, such as lines, edges, etc. that are important for interpretation of the image. the diffusion equation can be formulated as follows [14].     , , . , , i div c x y t i c i c x y t i t          (1) where c(x,y,t) is the diffusion coefficient. c(x,y,t) is preserve edges in the image and usually chosen as a function of the image gradient which controls the rate of diffusion. the images related to the preprocessing operations are shown in figures 2 (a)-(e). iv. single sided edge marking (ssem) a. pectoral muscle characteristics for the method proposed in this study, some peculiar characteristics of the pectoral muscle were utilized:  the pectoral muscle region is a roughly triangular area.  the pectoral muscle border is approximately a straight line.  there is a certain density change between the pectoral muscle and the breast region.  pectoral muscle region is roughly homogeneous. the ssem method is based on the geometric characteristics of mammograms and the intensity difference between muscle and breast tissue. when we look at the geometrical properties of the mammograms, it is seen that it is a roughly triangular region that is narrowed from top to bottom. since the pectoral muscle region is brought to the upper left corner in the preprocessing, the edge detection process is performed at an engineering, technology & applied science research vol. 8, no. 1, 2018, 2367-2373 2369 www.etasr.com toz and erdogmus: a single sided edge marking method for detecting pectoral muscle in digital … angle of about 30° to 45° from right to left and from top to bottom. (a) (b) (c) (d) (e) fig. 2. (a) original mammogram. (b) mammography mirror image, reduced to 512x512 dimensions and 256 pixel intensity values. (c) segmented breast area. (d) extracted breast rough limit. (e) noise reduction and enhancement. b. ssem details first, three different threshold values have been defined for use in edge marking process. the first of these is the threshold value (φ) used to exclude non-mammogram regions in the images; this value is taken as 5. the second is the value (α) of how much the intensity values of the pixels are similar to each other and is taken as 1 in this study. the third threshold is the threshold value used for the density difference between the pectoral muscle and the breast region. this value is also set to 1 in this study. the fact that this value is kept small ensures that the pectoral muscle border is marked with as many points as possible. next the mammogram image (i) scanned pixel by pixel, ii,j = (i = 2,3,…m; j = 2,3,…,n-1), where, m defines the number of rows of the matrix i, and n is the number of columns. the selected pixel is evaluated together with its neighbors located at two pixel distances. the following conditions are used for this evaluation. , 1, 1 , 1, 1 , 1, , , 1 , , 1 , 1, 1 , 1, , 1, (i, j) or and _ 255 and _ i j i j i j i j i j i j i j i j i j i j i j i j i j i j i j i j i and i i or i i or i i i i if thenand i i i i and i i i new i new                                                           1 2, 2 , , 255 and ( 2) 0 then _ 255 _ i j i j i j if j i new else i new i               as a result of the evaluation made according to these conditions, the new mammogram image marked i_new is obtained on the border of the pectoral muscle. the reason for choosing pixel intensity values of 255 for marking the pectoral muscle margin, is that this is a value less common on the mammogram and easier to distinguish in binary images. a graphical representation of the ssem method and a sample application are presented in figure 3. (a) (b) (c) fig. 3. graphical representation of the ssem method and a sample application (a) graphical representation for border detection by ssem method. (b) a sample pixel intensity values of 6x18 muscle and breast area. (c) new mammographic image with marked pectoral muscle border as the result of ssem method. engineering, technology & applied science research vol. 8, no. 1, 2018, 2367-2373 2370 www.etasr.com toz and erdogmus: a single sided edge marking method for detecting pectoral muscle in digital … c. determination of candidate pectoral muscle and border area in order to find the candidate pectoral muscle region from the image of the new mammogram marked with the pectoral muscle boundaries as the result of the ssem method, two different variables, experimentally obtained and named as areamin and areamax were used in this study. areamin is the smallest possible pectoral muscle area and areamax is half of the largest possible mammogram region. in figure 4, there are sample mammogram images of areamax and areamin. (a) (b) (c) (d) fig. 4. (a), (b) original mammograms. (c) areamax example for the pectoral muscle region. (d) areamin example for the pectoral muscle region. when the ssem method is used, the pixel at the border of the candidate pectoral muscle is marked as 255. thus, the resulting image of ssem is converted a binary image with a threshold value of 0.99 (figure 5(b)) and the pectoral muscle border is strengthened by morphological operators (figure 5(c)). the image, which has been converted into a binary image with enhanced pectoral muscle strength, is cleaned from images smaller than the areamin. the cleaned image is added with the previously obtained rough breast region. then to create the pectoral muscle area, a line is drawn starting from the upper left corner and covering the pectoral muscle corner from top to bottom and left to right (figure 5(c)). the area between these lines and the border of the candidate pectoral muscle region is filled. two regions with the largest area are selected to detect the pectoral muscle region (figure 5(d)). the region located at the upper left of the other region and is bigger than the areamin and smaller than areamax is selected as the pectoral muscle region (figure 5(e)). there may be residual defects at the border of the candidate pectoral muscle region, sometimes after morphological processing (figure 6(b)). similar to the ssem method, while obtaining the boundaries of the pectoral muscle region to get rid of these disorders, the pectoral muscle location information was taken at an angle of about 30º-45º from the top down and left to right, and the muscle border was created. finally, a linear interpolation method was used to complete the missing points on the obtained boundaries, and the result obtained was regarded as the final muscle border (figure 6(c)). (a) (b) (c) (d) (e) fig. 5. (a) the original mammogram. (b) the binary image of the ssem result. (c) the mammogram after morphological processing. (d) mammogram with the selected two largest areas. (e) mammogram with the rough pectoral muscle area determined. the final muscle border obtained for a sample mammogram and the muscle margin plotted using ground truth values given by the experts for the same mammogram are presented in figure7. the flow chart of all the procedures used for boundary detection and for determining the candidate pectoral muscle region is presented in figure 8. v. experimental studies the proposed algorithm has been tested on 60 mammograms received from the inbreast database. the obtained results were evaluated in terms of false positive rate (fpr), false negative rate (fnr) and sensitivity with groundtruth data given by the radiologists. false positive (fp) is the engineering, technology & applied science research vol. 8, no. 1, 2018, 2367-2373 2371 www.etasr.com toz and erdogmus: a single sided edge marking method for detecting pectoral muscle in digital … pixel found by the algorithm as the region of the pectoral muscle but detected as a different tissue by the radiologist, false negative (fn) is the pixel shown by the radiologist as pectoral muscle but detected as a different tissue by the algorithm and true positive (tp) is the pixel determined by the radiologist as the pectoral muscle and is also found as the region of the pectoral muscle by the algorithm. fpr, tpr and sensitivity are defined by (2)-(4) and are presented in table i. fpr=fp/(tp+fp) (2) tpr=tp/(tp+fn), fnr=1-tpr (3) sensitivity=tp/(tp+fn) (4) (a) (b) (c) fig. 6. (a) original mammogram. (b) obtained mammogram image of rough pectoral muscle boundaries. (c) mammogram image of the final borders obtained by linear interpolation. fig. 7. muscle limit (red) plotted using ground truth values given by experts on a sample mammogram and muscle limit (green) found by the proposed method. fig. 8. flow chart of candidate pectoral muscle region and border determination as shown in table i, the proposed method was able to detect the pectoral muscle region with an average sensitivity of 95.6% for the 60 mammogram images. also, in order to show the performance of the proposed method on different mammogram images, images of pectoral muscle boundary detection applications for four different mammogram images are presented in figure 9. table i. performance measures performance measures parameters average fp rate average fn rate average sensitivity results 0,0274 0,04331 0,9566 vi. conclusions in this study, a new method has been proposed to determine the pectoral muscle and its borders on digital mammograms. in this method, the pectoral muscle border was determined using a technique based on geometric features of the pectoral muscle and neighborhood relations. the boundaries for the rough pectoral muscle region have been strengthened and adjusted and the linear interpolation method has been used to complete engineering, technology & applied science research vol. 8, no. 1, 2018, 2367-2373 2372 www.etasr.com toz and erdogmus: a single sided edge marking method for detecting pectoral muscle in digital … the missing points within this boundary and to establish border continuity. the recommended method was tested using 60 mammograms from the inbreast database. according to the results obtained, it has been shown that the proposed method can detect the pectoral muscle margin with an average of 95.6% sensitivity (a) (b) (c) (d) (e) (f) (g) (h) figure 9. (a, c, e, g) original mammograms. (b, d, f, h) muscle boundaries (red) drawn using ground truth values given by experts and muscle boundaries (green) found by the proposed method. acknowledgement the authors would like to thank the "breast research group, inesc porto, portugal" for allowing the use of the inbreast database of mammograms used in this study. conflicts of interest the authors declare that there is no conflict of interest regarding the publication of this article. references [1] s. radhika, s. sasikala, r. mariappan, “three-dimensional reconstruction of microcalcification clusters from cc and mlo views”, 2nd international conference on electronics and communication systems, pp. 607-611, 2015 [2] m. tan, b. zheng, “development of a new case based computer-aided detection scheme for screening mammography”, ieee embs conference on biomedical engineering and sciences, pp. 24-29, 2016 [3] i. christoyianni, a. koutras, e. dermatas, g. kokkinakis, “computer aided diagnosis of breast cancer in digitized mammograms”, computerized medical imaging and graphics, vol. 26, no. 5, pp. 309319, 2002 [4] k. doi, h. k. huang, “computer-aided diagnosis (cad) and imageguided decision support”, computerized medical imaging and graphics, vol. 31, no. 4-5, pp. 195-197, 2007 [5] r. j. ferrari, r. m. rangayyan, j. e. l. desautels, r. a. borges, a. f. frere, “automatic identification of the pectoral muscle in mammograms”, ieee transactions on medical imaging, vol. 23, no. 2, pp. 232–245, 2004 [6] a. sultana, m. ciuc, r. strungaru, “detection of pectoral muscle in mammograms using a mean-shift segmentation approach”, 8th international conference on communications, pp. 165–168, 2010 [7] s. m. kwok, r. chandrasekhar, y. attikiouzel, “automatic pectoral muscle segmentation on mammograms by straight line estimation and cliff detection”, the seventh australian and new zealand intelligent information systems conference, pp. 67–72, 2001 [8] m. yam, m. brady, r. highnam, c. behrenbruch, r. english, y.kita, 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[13] m. lee, y. chen, s. kim, j. kim, “segmentation of the pectoral muscle boundary in breast mr images”, ieee 11th international conference on bioinformatics and bioengineering, pp. 323-326, 2011 [14] c. c. liu, c. y. tsai, j. liu, c.-y. yu, s. s. yu, “a pectoral muscle segmentation algorithm for digital mammograms using otsu thresholding and multiple regression analysis”, computers & mathematics with applications, vol. 64, no. 5, pp. 1100-1107, 2012 [15] s. s. yu, c. y. tsai, c. c. liu, “a breast region extraction scheme for digital mammograms using gradient vector flow snake”, 4th international conference on new trends in information science and service science, pp. 715-720, 2010 [16] s. sreedevi, e. sherly, “a novel approach for removal of pectoral muscles in digital mammogram”, procedia computer science, vol. 46, pp. 1724-1731, 2015 [17] i. c. moreira, i. amaral, i. domingues, a. cardoso, m. j. cardoso, j. s. cardoso, “inbreast: toward a full-field digital mammographic database”, academic radiology, vol. 19, no. 2, pp. 236-248, 2012 engineering, technology & applied science research vol. 8, no. 1, 2018, 2367-2373 2373 www.etasr.com toz and erdogmus: a single sided edge marking method for detecting pectoral muscle in digital … [18] j. l. starck, f. murtagh, e. j. candes, d. l. donoho, “gray and color image contrast enhancement by the curvelet transform”, ieee transactions on image processing, vol. 12, no. 6, pp. 706-717, 2003 [19] j. s. lee, “digital image enhancement and noise filtering by use of local statistics”, ieee transactions on pattern analysis and machine intelligence, vol. pami-2, no. 2, pp. 165-168, 1980 [20] e. s. yelmanova, y. m. romanyshyn, “medical image contrast enhancement based on histogram”, ieee 37th international conference on electronics and nanotechnology, pp. 273-278, 2017 [21] m. a. abeed, a. k. biswas, m. m. al-rashid, j. atulasimha, s. bandyopadhyay, “image processing with dipole-coupled nanomagnets: noise suppression and edge enhancement detection”, ieee transactions on electron devices, vol. 64, no. 5, pp. 2417-2424, 2017 [22] m. regodic, l. gigovic, z. bajic, s. vasiljević “contrast enhancement of colour digital images”, tehnicki vjesnik, vol. 24 no. 3, pp. 935-941, 2017 [23] s. h. wang, t. m. zhan, y. chen, y. zhang, m. yang, h. m. lu, h. n. wang, b. liu, p. phillips, “multiple sclerosis detection based on biorthogonal wavelet transform, rbf kernel principal component analysis, and logistic regression”, ieee access, vol. 4, pp. 75677576, 2016 [24] m. vetterli, j. kovacevic, wavelets and subband coding, prentice hall ptr, 1995 engineering, technology & applied science research vol. 8, no. 1, 2018, 2585-2589 2585 www.etasr.com chakravorty and saraswat: modeling a distributed power flow controller with a pem fuel cell … modeling a distributed power flow controller with a pem fuel cell for power quality improvement jaydeep chakravorty electrical engineering department indus university ahmedabad, india jaydeepchak@yahoo.co.in jyoti saraswat electrical engineering department baddi university himachal pradesh, india jyotisara@gmail.com vinay bhatia hod electronics and communication engineering baddi university himachal pradesh, india abstract—electrical power demand is increasing at a relatively fast rate over the last years. because of this increasing demand the power system is becoming very complex. both electric utilities and end users of electric power are becoming increasingly concerned about power quality. this paper presents a new concept of distributed power flow controller (dpfc), which has been implemented with a proton exchange membrane (pem) fuel cell. in this paper, a pem fuel cell has been simulated in simulink/matlab and then has been used in the proposed dpfc model. the new proposed dpfc model has been tested on a ieee 30 bus system. keywords-dpfc; pem; power quality i. introduction power quality improvement is a major concern of the power industry [1]. to improve power quality, custom power devices are used [2]. facts devices, such as unified power flow controller (upfc) and synchronous static compensator (statcom), are used to alleviate the disturbance and improve the power system quality and reliability [3, 4]. the distributed power flow controller (dpfc) is a device in the facts family, derived from the upfc. compared with the upfc, dpfc has the same controlling capability to change all the parameters within the transmission system. in case of dpfc the commonly connected dc link between series and shunt converter is eliminated. fuel cells are electrochemical devices that convert chemical energy of a fuel directly to electric energy, without any moving parts [5, 6]. compared with the other fuel celltypes, pemfc show promising results with advantages such as low temperature, high power density, fast response, and zero emission if run with pure hydrogen [7]. in this paper, the dc source that is used in dpfc has been replaced by a pem fuel cell. the performance of the proposed new model of dpfc is then compared with some existing conventional dpfc models to check its performance. ii. proton exchange membrane fuel cell there are several models of fuel cells available in the literature. these range from stationary to dynamic models [810]. pem fuel cell consists of a solid polymerelectrolyte sandwiched between two electrodes (anode and cathode). in the electrolyte, only ions canexit and electrons are not allowed to pass through. so, the flow of electrons needs a path like anexternal circuit from the anode to the cathode to produce electricity because of a potential difference between the anode and cathode. the overall electrochemical reactions for a pem fuel cell fed witha hydrogen-containing anode and an oxygen containing cathode are: anode: 4h + 4e = 2h cathode: o + 4h + 4e = 2h o overall: 2h + o = 2h o + electricity + heat the output stack voltage v is given by the expression v = n e + rt2f lnp p .p − bln ci − ir (1) where ph2 is partial hydrogen pressure, po2 is partial oxygen pressure, ph2o is partial water pressure, rint is the internal resistance, i is the fuel cell current, b and c are constants, f is the faraday constant, r gases universal constant.the simulink block of pem fuel cell is shown in figure 1. fig. 1. pem fuel cell. iii. z source inverter in the proposed model of dpfc with pem fuel cell, a z source inverter (zsi) has been used. the zsi has the unique feature that it can boost/buck the output voltage by introducing shoot through operation mode, which is forbidden in traditional voltage source inverters [11]. with this feature, zsi provides a cheaper, simpler, buck-boost inversion by single power engineering, technology & applied science research vol. 8, no. 1, 2018, 2585-2589 2586 www.etasr.com chakravorty and saraswat: modeling a distributed power flow controller with a pem fuel cell … conversion stage, strong emi immunity and low harmonic distortion [12]. the model of z source inverter for fuel cell application is shown in figure 2. the dc link voltage of z source inverter is shown in figure 3. the alternate output voltage of the z source inverter without filter is shown in figure 4. the fft analysis of z source inverter is shown in figure 5. as shown, thd=287.23% and fundamental=36.35. to compensate this, an lc filter is employed. the filtered output is shown in figure 6. as shown, thd is now 0.66% and fundamental=1056. the fft analysis of z source inverter with filter is shown in figure 7. fig. 2. simulink model of zsi with pem fuel cell fig. 3. dc link voltage of zsi fig. 4. alternating output voltage on inverter. fig. 5. fft analysis of z source invereter. fig. 6. filtered output voltage of z source inverter. fig. 7. filtered output voltage of z source inverter. iv. proposed modelof dpfc the block diagram of dpfc is shown in figure 8. it mainly consists of five units namely, fundamental frequency model, 3rd harmonic model, series converter model, shunt converter model and control unit. in the figure, vs is the sending end voltage, vr is the receiving end voltage, i1 is the first harmonic current, i3 is the third harmonic current, vse,1 is the voltage at fundamental frequency injected by the series converter, vse,3 is the voltage at third frequency injected by the series converter, vse,ref is the modulated amplitude of the reference ac signal, generated by series control unit, vsh,ref is the modulated amplitude of the reference ac signal, generated by shunt control unit. vsh,1 and vsh,3 are the voltage magnitudes of the i th harmonic of the shunt converters [10]. fig. 8. dlock diagram of dpfc. the implementation of the five mentioned above blocks is presented below. the model of the fundamental frequency network has been modeled from (2): − − , = × (2) engineering, technology & applied science research vol. 8, no. 1, 2018, 2585-2589 2587 www.etasr.com chakravorty and saraswat: modeling a distributed power flow controller with a pem fuel cell … wherevs, vr,vse,1, z1 and i1 are the matrices of the three phase voltages, impedance at first harmonic and current respectively. the matlab/simulink model of the third harmonic network has been modeled from (3): , − , = × (3) where vsh,3,vse,3, z3 and i3 are the matrices of three phase third harmonic voltages, impedance and current respectively the series converter model has been modeled modeled from (4). = _ _ _ × _ + _ _ _ × _ +_ _ _ × _ + _ _ _ × _ (4) the shunt converter model is obtained from (5): c = v _ _ _ × i _ _ + v _ _ _ × i _ _ −v _ _ _ × i _ _ + v _ _ _ × i _ _ (5) the complete dpfc model with pem fuel cell and z inverteris shown in figure 9. the model is then used on a ieee 30 bus system. fig. 9. proposed dpfc model v. results the simulated results for the proposed circuit are shown in figures 10-15 whereas the performance of the proposed dpfc when used in the ieee 30 bus system is shown in figures 16 to 19. fig. 10. dpfc steady state line current fig. 11. dpfc steady state series converter voltage fig. 12. dpfc steady state bus voltage and current at delta side of the transformer. engineering, technology & applied science research vol. 8, no. 1, 2018, 2585-2589 2588 www.etasr.com chakravorty and saraswat: modeling a distributed power flow controller with a pem fuel cell … fig. 13. series converter voltage fig. 14. line current fig. 15. active and reactive power injected by series conveter at fundamental frequency. fig. 16. load voltage without dpfc fig. 17. load voltage with dpfc fig. 18. realand reactive without dpfc fig. 19. realand reactive with dpfc vi. conclusion in this paper, a new model of dpfc with a pem fuel cell and a z source inverter has been presented. the performance of z source inverter was tested and then it was used in the dpfc model with pem fuel cell. the proposed model was applied to an ieee 30 bus system. the performance of the system was checked with and without the proposed model. the simulations were performed in matlab/simulink. the result shows that the proposed dpfc gives an acceptable performance in regard of power quality improvement. to further improve the model, the optimal placement of the proposed dpfc model should be considered. references [1] s. masoud barakati, α. khoshkbar sadigh, ε. mokhtarpour, “voltage sag and swell compensation with dvr based on asymmetrical cascade multicell converter”, north american power symposium (naps), pp.1–7, 2011 engineering, technology & applied science research vol. 8, no. 1, 2018, 2585-2589 2589 www.etasr.com chakravorty and saraswat: modeling a distributed power flow controller with a pem fuel cell … [2] m. a. hannan, α. mohamed, “pscad/emtdc simulation of unified series-shunt compensator for power quality improvement”, ieee transactions on power delivery, vol. 20, no. 2, pp. 1650-1656, 2005 [3] a. l. olimpo, e. acha, “modeling and analysis of custom power systems by pscad/emtdc”, ieee transactions on power delivery, vol. 17, no. 1, pp. 266–272, 2002 [4] p. pohjanheimo, e. lakervi, “steady state modeling of custom power components in power distribution networks”, ieee power engineering society winter meeting, vol. 4, pp. 2949–2954, 2000 [5] c. spiegel, pem fuel cell modeling and simulation using matlab, elsevier, 2011 [6] g. bucci, e. fiorucci, f. ciancetta, f. veglio, “experimental characterization and modeling of pem fuel cells under dynamic load variations”, vol. 5, no. 2, pp. 75–84, 2010 [7] m. a. r. sadig al-baghdadi, “modelling of proton exchange membrane fuel cell performance based on semi-empirical equations”, renewable energy, vol. 30, no. 10, pp. 1587-1599, 2005 [8] m. uzunoglu, m. s. alam, “dynamic modelling, design and simulation of a combined pem fuel cell and ultra capacitor system for stand alone residential application”, ieee transactions on energy conversion, vol. 21, no. 3, pp. 767-775, 2006 [9] j. padulles, g. w. ault, j. r. mcdonald, “an approach to the dynamic modeling of fuel cellcharacteristics for distributed generation operation”, ieee-pes winter meeting, vol. 1, pp.134-138, 2000 [10] c. wang, m. h. nehrir, s. r. shaw, “dynamic model and model validation for pem fuel cells using electrical circuits”, ieee transactions on energy conversion, vol. 20, no. 2, pp. 442–451, 2005 [11] j. rabi, r. arumugam, “harmonics study and comparison of z-source inverter”, the american journal of applied sciences, vol. 2, no. 10, pp. 1418–1426, 2010 [12] a. ajam, b. soulat, a. safari, “a novel modelling and controlling of distributed power flow controller (dpfc) base on pso algorithm”, ecti transactions on electrical engineering, electronics and communications, vol. 11, no. 1, pp. 1-8, 2014 [13] a. jamshidi, s. masoud barakati, m. moradi ghahderijani, “impact of distributed power flow controller to improvepower quality based on synchronous reference frame method”, iacsit international journal of engineering and technology, vol. 4, no. 5, pp. 581-585, 2012 microsoft word etasr_v11_n6_pp7770-7775 engineering, technology & applied science research vol. 11, no. 6, 2021, 7770-7775 7770 www.etasr.com rajab: genetic algorithm-based multi-hop routing to improve the lifetime of wireless sensor networks genetic algorithm-based multi-hop routing to improve the lifetime of wireless sensor networks adel rajab college of computer science and information systems najran university najran, saudi arabia 77adel.rajab@gmail.com abstract-wireless sensor networks are known for their monitoring and tracking application-specific operations. these operations diversely demand improvement in existing strategies and their parameters. one key parameter is energy usage during operations. energy plays a vital role in each application, as the wireless sensor networks lack battery lifetime and energy resources. so, there is a need for an optimized and efficient routing method with regard to energy consumption in wireless sensor networks. for multi-hop routing, the genetic algorithm serves as a robust algorithm with diverse optimized routing plans to improve the lifespan for large-scale wireless sensor networks. in this paper, the genetic algorithm provides the optimized routes for data operations and improves the lifetime of wireless sensor networks by saving energy. the performance of the genetic algorithm is compared with the teen algorithm. keywords-wireless sensor networks; multi-hop; genetic algorithm; optimization; lifetime durability i. introduction wireless sensor networks (wsns) are constructed by many self-organized and multifunctional mobile or non-mobile sensor nodes operating wirelessly in an area [1-4]. these sensor nodes possess inherited abilities to sense and transmit the gathered data towards the sink or base station. therefore, the process of the data transmission towards the sink consumes more energy than the other processes such as data collection and data processing [5]. since the sensor nodes have smallsized batteries, the overall performance of the sensor network depends on their lifetime. additionally, the wsns are prone to failure and can be deployed randomly in hard-to-reach areas. to counter this problem, multi-hop communication plays an essential role in improving network lifetime [6-8]. in the multihop communication paradigm, the source node transmits the data through the intermediate sensor nodes. these intermediate sensor nodes relay the data towards the sink as depicted in figure 1. multi-hops minimize the energy consumption by consuming a tiny amount of energy to relay the data towards the neighbor and the nearest sensor nodes [9, 10], which are hard to find in the wsns if the optimal routing path is not determined. the optimal path towards the nearest sensor nodes is the key to save the extra consumption of the energy of the node. the genetic algorithm (ga) is used to save energy and determine all the possible paths in the wsns. the multi-hop communication paradigm with a focus on reduction of energy usage and optimal paths towards the nearest relay nodes is based on the distance among them. so, the distance among the sensor nodes from the source node towards the sink, all relay sensor nodes, and a possible number of multiple hops are determined by the ga in order to select the most optimal path for the data transmission. the results with the utilization of the ga prove that the multi-hop communication paradigm improves the wsns lifetime [11-15]. fig. 1. hop-to-hop communication. ii. related work there is abundant research literature in the field of wsns with regard to routing mechanisms and the improvement of energy utilization. multipath routing schemes have been proposed to replace the single path routing paradigms. replacing the single path or direct communication paradigms provides better performance of the network [8-11]. multipath routing provides the benefit to transmit the packets by more than two paths, thus the packet loss rate is minimized [11, 12]. on the other hand, the multipath technique reduces the chance corresponding author: adel rajab engineering, technology & applied science research vol. 11, no. 6, 2021, 7770-7775 7771 www.etasr.com rajab: genetic algorithm-based multi-hop routing to improve the lifetime of wireless sensor networks of malicious attacks and any kind of packet tempering [13]. multipath routing schemes for wsns based on the next hop have been proposed in [14-16]. the sensor nodes are deployed in a hierarchical form and the algorithms are set to send the message according to the pre-determined loop of the hierarchical form. the authors claimed that this resulted in better network performance and more saved energy. additionally, the routing schemes involving multiple paths reduced fault tolerance including error detection and error recovery. authors in [17] presents a solution to the problem of the unbalanced energy expenditure in wsns for multipath routing. the multiple-path routing scheme has been carried out in 3-d space and regional co-evolution. a protocol was designed to divide the one-hop path of the neighbor sensor node into many subspaces by partitions of the region. then the source node selects the optimal node and path to transmit the data. the co-evolution algorithm helps to find out the next hop. a multipath cost function model for the statistical estimation of the overall network, namely the total energy of the nodes and the energy used in relaying the data was proposed in [18-20]. multipath routing for the directional diffusion routing protocol from the source to the destination node with a certain probability of selecting one path among all possible paths was proposed in [19, 21-24]. authors in [25, 27] advocated loadbalancing energy schemes for wsns and energy harvesting for the overall network. they utilized aco (ant colony optimization) for multiple path finding and claimed satisfying results. the study used an electromagnetic antenna-based approach for energy harvesting to gain high performance of iot and wsns. numerous studies have been carried out on minimum energy consumption. the efficient usage of energy has been claimed as an important part to maximize the wsns lifetime through optimization [28-30]. the optimization also reduces the complexity of the overall network and provides many possible options for routing the data from source to destination. iii. genetic algorithm gas are meta-heuristic algorithms. the ga mimics the natural selection process [21] and has been used in various computer and ai applications. due to its robustness, many research scholars adopted ga for solving optimization problems. optimization finds the possible solutions to the problems and potential methods to tackle complications. as the ga mimics the natural selection process it follows the selection of healthy chromosomes. these chromosomes are selected by the fitness function, and are subjected to crossover and mutation [22-24]. the working mechanism of ga in this research is utilized with some modifications. all the operators of ga are used for selecting the best individuals from the population. the population comprises of all sensor nodes and sinks deployed in the area. after the selection of the best population, the ga finds fit individuals by applying the fitness function as shown in figure 2. each individual passes on the basis of their energy. then, other operators, namely crossover and mutation, are applied to select the best chromosome as shown in figure 3(a)-(b). for this research, the mutation probability is set to 0.8 [2, 24]. the process of mutation is depicted in figure 3(c). after the mutation operator, the best individual and the new fit individual are re-evaluated on the basis of their energy and only the fit individual can be obtained. fig. 2. operator utilization of ga. fig. 3. (a), (b) crossover and (c) mutation. iv. performance and simulation the experimental setup includes a dual-core intel processor with a cpu of 3.5ghz and 32gb ram. simulations have been carried out using matlab r2020b in windows 10. the sensor nodes are simulated as non-mobile but randomly deployed in a 100×100m 2 area with 4 sinks deployed at the corners. the multi-hop communication paradigm where the source node transmits the data through the relay nodes towards the nearest sink is shown in figure 4. all possible routing paths towards all sinks are determined by the ga. when a node gathers and transmits the data by the optimal path towards the (a) (b) (c) engineering, technology & applied science research vol. 11, no. 6, 2021, 7770-7775 7772 www.etasr.com rajab: genetic algorithm-based multi-hop routing to improve the lifetime of wireless sensor networks nearest sink, it follows the already optimized route from multiple possible routes determined by the ga. the multiple hop distance is evaluated and determined by the ga. all sinks broadcast their locations to all sensor nodes and the nodes only transmit the data towards the nearest sink as illustrated in figure 4. the simulation results comprise 40 and 50 sensor nodes deployed in a static manner along with static sinks [26]. the results of alive nodes, dead nodes, and overall packet transmission are compared with the standard teen algorithm's and they fairly outperform it in terms of energy expenditure and wsns lifetime maximization. a. simulation paramaters the studied wsn parameters are given in table i. each sink is responsible to collect the data from the nodes efficiently through optimized routes. route optimization and determination are done with the help of ga. the evaluation of the route is done in two manners, namely the direct distance evaluation and the multiple hop distance evaluation. the evaluation of the distance is based upon the energy consumption. it is observed that the nearest nodes have the least energy consumption in comparison with the more remote nodes. during the simulations, the most remote nodes died in a few rounds because of the long routes and direct distances. table i. simulation parameters parameters value size of the network 100×100m 2 number of nodes 40 and 50 initial energy 0.9 joules rounds 4000 dissipation of energy 50 nj/bit increase of energy �� � �� 10 pj/bit/m increase of energy �� � �� 0.0015 pj/bit/m b. simulation algorithm the proposed algorithm provides the routing mechanism among all sensor nodes and all sinks. it initially provides all the sensor nodes with a number of trial rounds. these trials are based on the energy levels of every sensor node and the distance among the sensor nodes and respective sinks. therefore, the distance and their selection of routes strictly depend upon their physical location, where they are deployed, and the nearest sink. pseudo code for the optimization. input: all nodes: ��� �� ��� total trials: ∅ battery life of each node: ∅����� network area: 100×100m 2 selected route and every route �: �� path optimization: � ���� for � from 0 until � do for � from 1until ∅ do ��� �� ��� produce random network ����� � sink locations are broadcasted. ����!"# $�%= 0 for every new network &# $�%� route determining from/to sink(s) end if '()��*�+%, # $�%� obtaining optimized routes -. �� ()��*�� # $�% reservation of optimal route do while � ∅�����> 0 operation of nodes until battery dies -. �� ()��*�� # $�% save the optimal route -. �� ()��*�� # $�% copy it for every iteration. end and return with -. �� ()��*�� # $�% v. simulation results the wsn is constructed with 40 and 50 sensor nodes and 4 sink stations located at the corners of the network area as illustrated in figures 5-6. the evaluation and simulation results of the randomly and static deployed sensor nodes and sinks show that the route distance is covered by multiple hop routing. that enhances the sensor node's battery lifetime and improves the network's lifetime. in other words, the network lifetime has, extensively, been increased by the use of the optimized multiple hop routes as depicted in figure 7. therefore, it has been experimentally proved that the network lifetime can be improved through optimum data transmission. although there are a number of routes in multiple hop routing mechanism the source sensor node only opts to transmit the data through the optimal one. fig. 4. deployment of 40 sensor nodes and sinks. fig. 5. deployment of 50 sensor nodes and sinks. engineering, technology & applied science research vol. 11, no. 6, 2021, 7770-7775 7773 www.etasr.com rajab: genetic algorithm-based multi-hop routing to improve the lifetime of wireless sensor networks fig. 6. data transmission to (a) sink 1 (b) sink 2, (c) sink 3, and (d) sink 4. the localization of 40 sensor and multi-hop relay sensor nodes is shown in figure 7. multiple paths are determined by the ga among all the sensor nodes and sinks. the sensor nodes in the nearest sensor node towards the sink receive the data and perform the execution. the source sends the data towards the nearest sink with the help of relay sensor nodes. the optimal distance towards sink 1 and sink 2 is 114.647ms and 107.225m respectively. sink 3 with 134.815m and sink 4 with 131.194m have optimal routes towards the farthest node. fig. 7. number of rounds vs. number of alive nodes for the proposed scheme and the teen algorithm. fig. 8. comparison of packets to sinks. the result comparison of this research with the standard teen algorithm [26] shows that the proposed scheme performs significantly better. the results show that the number of rounds vs. the number of alive nodes of the proposed scheme is bigger than the respective number of the teen standard algorithm as shown in figure 8. the data transmission towards the sinks and the comparison of the results with the standard teen algorithm are shown in figure 9. the packets with the proposed scheme at the rounds 1500, 2000, 2500, 3000, and 3700 have been received successfully at the end of engineering, technology & applied science research vol. 11, no. 6, 2021, 7770-7775 7774 www.etasr.com rajab: genetic algorithm-based multi-hop routing to improve the lifetime of wireless sensor networks the sink. also, the proposed scheme maximized the wsn's life durability and improved network performance. additionally, the comparison results show that the standard teen algorithm has significantly more dead nodes as the packet transmission increases, while the proposed algorithm performs better and increases network durability [26]. vi. discussion the proposed scheme improves the lifetime of the wsns. the ga determines all possible routes for data transmission and optimizes each route for efficient data delivery with minimum energy cost. the ga determines an optimized route for each sensor node. the simulation results are more compromising than the standard teen [26] algorithm's. the proposed work performed very well on 500, 1000, 2000, and 3700 rounds and enhanced network lifetime. vii. conclusions and future work in this study, a multi-hop routing scheme for wireless sensor networks, based on the energy optimization by ga for network lifetime maximization, has been proposed and examined. the ga provides the optimized routes for data operations and improves the lifetime of wsns by saving energy. the simulation results demonstrate the robust performance of the ga resulting in improved network lifetime. also, the proposed algorithm achieves a significant performance gain over the standard teen protocol. networks with a significant number of sensor nodes were simulated as non-mobile wsns. comparatively, the ga lost less nodes in 2000, 3000, and 4000 rounds, than the standard teen algorithm. in simulation results, the ga performed fairly better than the standard teen algorithm. regarding future work, the current study can be extended to mobile and hybrid optimization schemes. references [1] j. zhang, "wireless sensor networks: lecture 1," norrköping, sweden, jan. 17, 2014. 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college university hyderabad, pakistan kamranmk99@gmail.com muhammad mujtaba shaikh department of basic sciences and related studies mehran university of engineering and technology jamshoro, pakistan mujtaba.shaikh@faculty.muet.edu.pk abstract-in this paper, the radiation and slip effects are investigated on the boundary layer flow and heat transfer of fe2o3 and fe-water base nanofluids over a porous stretching/shrinking sheet. a similarity transformation is used to convert the system of governing partial differential equations into ordinary differential equations, which are then numerically solved in maple software with the help of the shooting technique. at different ranges of the applied parameters, dual solutions are found. the effects of the different physical factors such as radiation, nanoparticle volumetric fractions, suction, and slip parameters are determined and discussed. the skin-friction coefficient and local nusselt number are influenced significantly by the applied parameters. in the boundary layer regime, the increase in nanoparticle volume fractions and radiation parameters enhance the temperature and boundary-layer thicknesses, while increasing prandtl number, suction, and thermal slip parameters decrease the temperature and reduce thermal boundary-layer thicknesses. the suspension of iron nanoparticles shows more enhancement in skin friction and nusselt number than the iron oxide nanoparticles in base fluid water. keywords-boundary layer; dual solutions; shooting method; rediation; nanofluid i. introduction nanofluids are made up of solid nanoparticles and common base fluids such as water, oil, glycol, polymer fluids, and so on [1, 3-5]. the nanoparticles are made from metals, metal oxides, and carbides, and have far greater heat conductivity. their insertion considerably enhances thermo-physical properties such as thermal conductivity, viscosity, thermal diffusivity, and the convective heat transfer coefficient. nanofluids may be employed in many industrial and technological applications [2], including microelectronics, coolants, fuel cells, pharmaceutical operations, household freezers, chillers, and lubricants. several methods have been developed to improve the thermal conductivity of typical common liquids, including suspending macro/micro particles of solid materials in them. two types of nanofluid modelshave been created and effectively employed as a result of recent developments in nanotechnology. buongiorno [6] proposed the initial model, which incorporated 7 slip factors as critical components in generating a relative velocity between the nanoparticles and the base fluid. only thermophoresis and brownian motion were considered essential among the 7 slip components when creating a model for convective transport in nanofluids. the second nanofluid model was proposed by tiwari and das [7] to study the effect of nanoparticle volume fractions on thermal characteristics enhancement. researchers used and modified these two well-known nanofluid models by using different physical flow parameters [8-11]. many engineering and practical science applications, such as paper manufacturing, wire drawing, extrusion, metal spinning, and hot rolling, rely on the boundary layer flow through a stretching/shrinking sheet. crane [12] was the first to work on the stretched sheet. since then, a broad range of issues related to these topics was examined. authors in [13] examined the heat and mass transfer on a stretched sheet with suction and blowing. many researchers were also interested to study the flow over a stretching sheet. the study of viscous flow past on shrinking sheet along the suction action was pioneered in [14]. it is worth mentioning that mass suction is required to keep the flow inside boundary layer flowing. the analytic solution of the magnetohydrodynamic flow of a second grade fluid on a shrinking sheet was investigated in [15]. authors in [16] explored the mhd rotational flow of a viscous fluid over a corresponding author: muhammad mujtaba shaikh engineering, technology & applied science research vol. 12, no. 1, 2022, 8114-8122 8115 www.etasr.com lanjwani et al.: stability analysis of boundary layer flow and heat transfer of fe2o3 and fe-water … shrinking surface. authors in [17] were the first to investigate the nanofluid flow through the boundary layer of a stretching sheet. the boundary layer slip flow problem is quite relevant in practice. wang [18] analyzed the impact of the partial slip on flow of a viscous fluid through a stretching sheet using numerical simulations. authors in [19] examined the natural convection of magnetohydrodynamics nanofluid flow on a vertically flat plate. authors in [20] examined the impact of the particle sizes and volume fractions on the al2o3-water base nanofluid. authors in [21] studied the steady boundary-layer flow through a continuously moving plate with different nanoparticles immersed in water in a 2d (two-dimensional) flow. author in [22] considered 2d nanofluid flow past a moving plate in a continuous free-stream. authors in [23] examined 2d laminar stagnant-point fluid flow with heat absorption and generation. authors in [24] investigated the behavior of slip factors using single and multiphase nanomaterial models. authors in [25] inspected the inclination of the magnetic field in a convective radiative heat transfer micro-nanofluid using a porous medium. various scholars have studied the occurrence of multiple solutions to the boundary value problems. these solutions are caused by the non-linearity of the equations at various ranges of the physical parameters that can be seen in the literature. several academics assessed the stability of a range of solutions to find which is the stable and physically realizable. many scholars, including the authors in [26-28] have come up with different solutions and they proved that only one solution was found stable through stability analysis. the primary aim of this study is to determine how various flow parameters impact water-based nanofluids created by stretching and shrinking sheets. the tiwari and das model is used to investigate the heat radiation and slip effects of iron (fe) and iron oxide (fe2o3) nanoparticles. the similarity transformations are used to convert the partial differential equations into ordinary differential equations,. the shooting approach is applied for solution of the resulting system of equations. according to the findings of this study, dual solutions exist for certain ranges of the physical parameters that are illustrated in the graphs. due to the occurrence of dual solutions, the bvp4c matlab program is used to perform the stability analysis. the stability tests reveal that the first solution is the stable and the physically realizable, while the second is not stable. ii. problem formulation let's consider a two-dimensional boundary layer flow and heat transfer in a water-based nanofluid containing iron (fe) and iron oxide (fe2o3) nanoparticles over a stretching/ shrinking sheet. the sheet is considered to be parallel to the plane � = 0, and the flow is contained at � > 0. the sheet is stretched and shrunk with velocity �� = � , where � > 0 is the stretching rate, with two opposed and equal forces applied in the direction of the x-axis. the base fluid (water) and nanoparticles are considered to be in thermal equilibrium. table i lists the thermo physical properties of water as well as the nanoparticles that are used in the present study. table i. thermo physical values of base-fluid and solid nanoparticles [36] base fluid and kind of particles �� /��� ����/� �� ���/��� water (h2o) 997.1 4179 0.613 iron (fe) 7870 460 80 iron oxide (fe2o3) 5180 670 80.4 the governing equations of the problem by using the tiwari and das model [7] are written as: �� �� + ���� = 0 (1) � ���� + � ���� = �� !� �"� ��" (2) � �#�� + � �#�� = $%& � "# ��" − ()!*+,� �-. �� (3) the roseland approximation, /0 is defined as: /0 = −12∗45∗ �# 6 �� (4) where 7∗ is boltzmann's constant and k* is the absorption coefficient. it is assumed that the temperature difference is very small. as a result, when the taylor series is applied to the temperature of the free stream fluid flow which is indicated by 89 and ignoring higher order terms, the 81 can be defined as: 8 1 ≅ − 381 + 48894 (5) the specified boundary conditions are: � = ��; � = > �� + ? ���� ; 8 = 8� + @ �#�� ; at � = 0 � → 0; 8 → 89; as � → ∞ (6) where v, u are the velocity components in the x and y directions and f9 and �� are the velocities of free stream fluid and sheet respectively, a and b are slip factors, t, g%& ,$%& and i%& are the temperature, viscosity, thermal diffusivity and density of the nanofluid respectively, as defined in [32]: $%& = 5� )!*+,� , g%& = � �(jk�".m i%& = �1 −o�i& + oip 5� 5 = )q5 r5s,j)j5sr5 ,qk )q5 r5s,r)j5sr5 ,k )i�t,%& = �1 − o�)i�t,& + o)i�t,p (7) where ip and i& are the densities of solid nanoparticles volume fractions and fluid (water) respectively, u& and up are the thermal conductivities of the base fluid and solid nanoparticles volume fractions respectively. furthermore, the g%& (the viscosity of the nanofluid) was estimated in [33] and the similarity transformation is taken according to [34]: � = � vw�x�;� = −√� v�z�; z = �[ *\ ; ]�z� = #j#̂#_j#̂ (8) engineering, technology & applied science research vol. 12, no. 1, 2022, 8114-8122 8116 www.etasr.com lanjwani et al.: stability analysis of boundary layer flow and heat transfer of fe2o3 and fe-water … transformation (8) instantly fulfills the differentiation in terms of (1), however (2) and (3) are reduced to the following non-linear ordinary differential equations: ( �(jk�".m vwww + `�−o + 1� + o aip i&b cd )vvww − vwq, = 0 (9) ( e0 ( f�(jk�rka)!*+,s )!*+, b cg `5� 5 + 1 4 hid]ww + v]w = 0 (10) and the boundary conditions take the form: v�0� = j; vw�0� = > + kvww�0�; ]�0� = 1 + k#]′�0� at z = 0, vw�z� → 0; ]�z� → 0; as z → ∞� (11) where prime stands for the derivative with respect to z, hi)= 48947∗ u∗&u&b , is the radiative parameter, mn �= g& /u& � is the prandtl number, k = ?[� o&b is the velocity slip, k# = @[� o&b is the thermal slip parameter and > is the stretching/shrinking parameter. when 0 < > < 1, the fluid and the plate are moved in the similar direction. likewise, for > < 0 and > > 1, these are in opposite direction of the motion. when > < 0 shows that the flow of the ambient fluid is in the positive x-direction and the movement of sheet is in negative x-direction, > > 1 shows that the flow of ambient fluid is in the negative x-direction and the movement of the sheet in the positive x-direction. in the present paper, both cases are considered but main focus was given on > < 0. the local nusselt number q�� and the skin friction coefficient r& are key physical parameters that are described as: r& = s_! �_" , q�� = -_ 5 �#_j #̂ � (12) shear stress t� and surface heat diffusion /� are defined as: t� = g%& a����c�uv and /� = −` 5� 5 + 1 4 hida�#��c�uv (13) by the use of (8) and (13) in (12), we get: r&�hw��x" = (�(jk�".m vww�0� �hw��jx"q�� = −`5� 5 + 1 4 hid]w�0� (14) where hw� = ��_\ reports the reynolds number. iii. stability analysis as this problem has dual solutions, stability analysis is required to find a stable and physically reliable solution. to evaluate the stability of the solutions, at first the governing system of (2) and (3) will be written into an unsteady form like: �� �y + � ���� + � ���� = �� !� �"� ��" (15) �# �y + � �#�� + � �#�� = 5� )!z+,� a1 + 1{| 4 c � "# ��" (16) where t denotes the time. the transformation (8) will be modified by introducing new dimensionless time dependent variable t. � = � vw�x,s�;� = −√� v�z,t�; z = �[ *\ ; ]�z,t� = #j#̂ #_j#̂ and t = �� (17) by implementing (17) into the (15) and (16) we get: ��&�x,s� �x� + �−o + 1�q.� �`�−o + 1�+ oaip i&b cd�(q v�z,t� � "&�x,s� �x" − a�&�x,s��x c q − �"&�x,s��x�s �� = 0 (18) ( e0 ` 5� 5 + 1{| 4 d� "��x,s� �x" +f1− o + o )!*+,s)!*+, g� ���x,s� �x v�z,t� − ���x,s��s � = 0 (19) the boundary conditions are: v�0,t� = j ,�v�0,t��z = > + k �qv�0,t� �zq , ]�0,t� = 1 + k# �]�0,t��z , �&�x,s� �x → 0, ]�z,t� → 0 as z → ∞ (20) to obtain stability for the solutions v�z� = vv�z� and ]�z� = ]v�z� that satisfy the specified boundary value problem given in equations (2)-(3), we expressed: v�z,t� = ��z�wj�s + vv�z�, ]�z,t� = ��z�wj�s + ]v�z� �21� ��z� and ��z� are the related functions to ]v�z� and vv�z� respectively, and � is the unknown minimum eigenvalue. the following linear eigenvalue problem system is generated by using (19) into (18)-(21): ��� �x� + �−o + 1�q.� �`�−o + 1� + o aip i&b cd�� "� �x" vv + � �"&��x" − 2�&�x ���x + � ���x�� = 0 (22) ( e0 ` 5� 5 + 1{| 4 d� "� �x" + f1− o + o )!*+,s)!*+, g�vv �� �x + ����x � +��� = 0 (23) the set ��z� = �v�z� and ��z� = �v�z� is used in (22) and (23) to acquire the initial decay or growth of solutions of (21). therefore, the following system of eigenvalues has been solved: engineering, technology & applied science research vol. 12, no. 1, 2022, 8114-8122 8117 www.etasr.com lanjwani et al.: stability analysis of boundary layer flow and heat transfer of fe2o3 and fe-water … �vwww + �−o + 1�q.� �f�'o � 1� � o`!s! dg��vwwvv � ��vw ' 2vvw�vw � vvww�v�� � 0 (24) ( e0 ` 5� 5 � 1{| 4 d�vww � f1 ' o � o )!*+,s)!*+, g��v wvv � ]vw�v � ��v� � 0 (25) with boundary conditions: �v�0� � 0, �vw�0� � k�vww�0�, �v�0� � k#�vw�0� �vw�z� → 0, �v�z� → 0 as z → ∞ (26) to get the smallest eigenvalue, the linearized equations (24) and (25) with boundary conditions (26) are solved in matlab using the bvp4c solver techniques. as mentioned in [35], we must relax one boundary condition into the initial condition. in this case, �v′�z� → 0 as z → ∞ into �′vw �0� � 1. the smallest negative eigenvalues indicate the disturbance's initial growth. as a result, the solutions related to the fluid flow are said to be unstable. the fluid flow is said to be stable in case obtained smallest positive eigenvalues. iv. numerical method the boundary value problem given in (9) and (10) is solved using the shooting method in maple software, using the initial and boundary conditions (11). on the other hand, this method turns the boundary value problem into an initial value problem. therefore, we get: vw � �e,vww � �ee a1 � (�c�eew � �1 ' o�q.� �f1' o � o`!s! dg���ee ' ��e�q�� � 0 (27) ]w � ]e,ow � oe, ( e0 ( f�(jk�rka)!*+,s )!*+, b cg `5� 5 � 1 4 hid ]ew � �]e � 0 (28) the boundary conditions take the form: ��0� � j ,�e�0� � > � k�ee�0�,]�0� � 1 � k#]e�0� �ee�0� � $(,]e�0� � $q, (29) where $(, $q are taken as the unknown initial conditions. so, the shooting values for the missing initial values of $(, $q are important. the solution must satisfy the boundary conditions �e�z� → 0,]�z� → 0 as z → ∞ of the specified boundary value problem. the computation is done in maple by using the shootlib function and the shooting method. in this paper, the thickness of the boundary layer z9 is taken between 4 and 7, at which the convergence shown in the graphs is obtained. for fixed values of the used parameters, 2 velocity and temperature profiles are achieved, each totally satisfying the problem's required boundary conditions. as a result, the quantities vw′�0� and ']′�0�, have two distinct values. v. results and discussion the shooting method in maple is used to obtain the numerical solutions to the system of ordinary differential equations (9) and (10) that are subjects to the boundary conditions of (11). figures 2–17 show the results of the impact of the non-dimensional physical parameters on the velocity and temperatures profiles as well as the skin friction coefficient and nusselt numbers. table i shows the thermo physical properties of the base fluid and nanoparticles used in the present study. table ii shows the comparison result of the 2 numerical methods, the shooting method used in maple and the bvp4c used in matlab. the comparison shows much symmetry in the results that encourage us to consider that our obtained results are correct and trustworthy. in addition, in the case of dual solutions, stability analysis has been performed with bvp4c in matlab to determine which solution is reliable and stable by obtaining the smallest eigenvalue using (24)-(26). the solution which corresponds to a positive least eigenvalue is considered as a reliable and stable solution. the solution which corresponds to a negative least eigenvalue is considered as an unstable solution. table iii shows the numerical values of the stability of solutions for the different values of velocity slip and radiation. the eigenvalues ( � ) concerned to the second solutions are negative, while they are positive for the first solutions. the results of fe2o3-water base nanofluid and fewater base nanofluid are shown by different colors in plots. the solid lines are related to the study of the stable solution (first solution) and the dashed lines are used to denote the second, unstable solutions. table iv shows the critical points concerned to figures 2-5, where two solutions are merged. furthermore, the impact of the various used parameters of this study are presented and discussed below through graphs. fig. 1. physical illustration of the model. the variation in skin friction coefficient �v "�0�� and local nusselt number �' ]′�0�� along the change in stretching and shrinking parameter (>) under the impact of different values of the suction parameter �j� are shown in figures 2 and 3 respectively. for > � >* , there are dual solutions. both solutions merge at >*, and there is no solution for > p >* where >* denotes the critical point. figure 2 shows that when the suction rate is increased, the skin friction coefficient reduces for values > � 0 and rises for > p 0 in the first (stable) solution. furthermore, the rate of skin friction (drag force) is examined to be larger in fe2o3-water base nanofluid than in engineering, technology & applied science research vol. 12, no. 1, 2022, 8114-8122 8118 www.etasr.com lanjwani et al.: stability analysis of boundary layer flow and heat transfer of fe2o3 and fe-water … fe-water base nanofluid for > � 0 (for stretching case of the sheet) and vice versa for > < 0 (for shrinking case of the sheet) for the same values of the suction parameter �j�. the nusselt number (rate of heat transfer) rises as the suction parameter �j� is increased in both solutions (figure 3). in addition, the variations of skin friction coefficient �v ′′�0�� and local nusselt number �−] ′�0�� along the variation of the suction parameter at various values of nanoparticles volume fraction �o� are shown in figures 4-5. for j > j*, dual solutions also exist. at the critical point j*, both solutions merge, while no solution is observed for j < j*. in both fe2o3-water base and fe-water base nanofluids, the skin friction coefficient rises as the nanoparticle volume fraction increases, while it decreases in the second solution (figure 4). the rate of skin friction for the fe-water base nanofluid is observed to be greater than that of the fe2o3-water base nanofluid. it may be noted that the viscous fluid flow in figures 4 and 5 is shown by black colored lines. figure 5 shows that the nusselt number decreases with an increase in the rate of nanoparticles volume fraction in both solutions in both types of nanofluids. heat transfer rate is observed greater in fe-water base nanofluid than in fe2o3-water base nanofluid. the comparative results of the variations of the skin friction coefficient and local nusselt number with the variation of nanoparticles volume fraction regarding to fe2o3-water base nanofluid and fe-water base nanofluid are presented in figures 6 and 7. it is seen that the fe-nanoparticles show the greater resistance in flow, which means greater rate of skin friction coefficient is observed as compared to the fe2o3 in water base nanofluid. due to the greater resistance of suspending fe nanoparticles in water, the rate of heat transfer of fe-water base nanofluid remains greater than that of the fe2o3-water base nanofluid as shown in figure 7. furthermore, due to the repeated trend of the result, only graphs of fe-water base nanofluid are presented here for further study. furthermore, figures 8-17 show the velocity and temperature profiles for various values of the applied parameters. figures 8 and 9 show the velocity and the temperature profiles of the boundary layer flow of the fe-water base nanofluid at different values of nanoparticle volume fraction �o�. the influence of o shows that with any increment in the concentration of nanoparticles the velocity of the fluid decreases throughout the boundary layer region in the first (stable) solution. actually, the nanoparticles develop a friction in fluid molecules which retards the flow. the nanoparticles also increase the thermal conductivity of the base fluid, so the heat is transferred from the hot regime to the cold one in faster rate and in result, warms the thermal boundary layer regime. hence, the concentration of nanoparticles increases the temperature and the thermal boundary layer thickness of the base fluid as shown in figure 9. the effects of the suction parameter �j� on v ′�z� and ]�z� profiles are shown in figures 10 and 11. it can be clearly observed that any increment in s raises the suction rate of the fluid at sheet and in result, momentum boundary layer thickness and fluid velocity decrease in the first solution throughout the nanofluid flow. in the second solution, the opposite result can be observed. any increment in j decreases the thermal boundary layer thickness and the temperature of the nanofluid throughout the flow in both solutions. figures 12 and 13 show the impact of > (for shrinking case) on v ′�z� and ]�z� profiles respectively. both the profiles of velocity v ′�z� and temperature ]�z� are decreasing for increasing > (in the first solution) and increasing for increasing > (in the second solution) for the shrinking case. the influence of the prandtl number �mn� on the temperature profile ]�z� of the fe-water base nanofluid is shown in figure 14. when the parameter mn is raised, the temperature of the nanofluid decreases. because fluids with a high mn value have a low thermal diffusivity, the temperature of the moving fluid drops. the temperature and thickness of the boundary layer decrease as mn increases. the influence of radiation parameter �hi� on the temperature profile is drawn in figure 15. the temperature profile increases as the radiation parameter increases. as the value of hi increases, the divergence of radiating heat flux increases as u∗ decreases. as a consequence, the rate of radiating heat transfer to the fluid's boundary layer flow rises which increases the temperature of the fluid. the velocity profile v′�z� of the fe-water base nanofluid in the first solution decreases when the velocity slip parameter (k) increases, as can be seen in figure 16. basically, any increment in k shows more fluid particles slipping on sheet, so the fluid flow decelerates near the sheet. in the second solution, any change in parameter values causes the nanofluid velocity to rise. the influence of thermal slip parameter (k#) on the temperature profile ]�z� is shown in figure 17. when the thermal slip increases, the thickness of the thermal boundary layer and the temperature profile both decrease in both solutions. the fluid velocity is initially decreased when the thermal slip parameter is raised, resulting in a decrease in net molecular mobility. consequently, less molecular momentum decreases the thermal boundary layer thickness and the temperature profile. vi. conclusion the steady two-dimensional boundary layer flow and heat transfer of fe2o3 and fe-water base nanofluid over a flat stretching/shrinking sheet with radiation and slip effects were studied numerically in this paper. the nanofluid model in [7] is used with a porous medium. the similarity transformation is used to convert the system of partial differential equations into ordinary differential equations. the shooting method is used to solve these equations numerically. due to the existence of dual solutions, stability analysis is performed using bvp4c in matlab. the following conclusions are drawn based on the numerical investigations: • dual solutions are observed for certain ranges of stretching/shrinking and suction parameters. • stability analysis shows that one solution is stable and physically reliable while the other is unstable. • the skin friction coefficient decreases for > � 0 and increases for > < 0 as the rate of suction is increased. • the heat transfer rate and the skin friction coefficient are decreasing in the second solution when the velocity slip parameter k increases. engineering, technology & applied science research vol. 12, no. 1, 2022, 8114-8122 8119 www.etasr.com lanjwani et al.: stability analysis of boundary layer flow and heat transfer of fe2o3 and fe-water … • fe-water nanofluid shows a greater rate of skin friction and nusselt number as compared to fe2o3-water nanofluid. • an increase in nanoparticles' volume fraction decreases the skin friction coefficient and increases the nusselt number. • increase in velocity slip, suction, nanoparticles volume fraction, and shrinking parameters decreases the velocity profiles and the associated boundary layers thicknesses. • the rise in nanoparticle volumetric fraction and radiation increases the temperature profiles and the boundary layer thicknesses. table ii. comparison along the variation of vww�0�, and –]w�0� with > at � � 2, mn � 6.2, k � 0.1,o � 0.1 , k# � 0.7 and hi � 1.5 for fe-water base nanofluid parameter � shooting method bvp4c method  ww�¡� –¢w�¡�  ww�¡� –¢w�¡� -1 1.2976198 0.83568 1.297520 0.83667 -0.6 0.919529 0.59991 0.919595 0.598838 0 0.00000 0.88279 0.00000 0.883671 0.5 -0.92239 0.8969 -0.92356 0.89789 1 -1.69817 0.90856 -1.69773 0.90891 table iii. smallest eigenvalues against various k and hi values when k# � 0.7,o � 0.1, > � '1, j � 2 and mn � 6.2 for fewater base nanofluid parameters bvp4c method £ ¤¥ 1st solution 2nd solution 0.2 0.5 0.83568 -1.297520 0.2 1 0.59991 -0.919595 0.3 0.3 0.88279 -0.00000 0.4 0.6 0.8969 -0.92356 table iv. critical point values of the investigated nanofluids parameters numerical values critical point (fe) critical point (fe2o3) ¦ 2 -1.552 -1.1675 2.15 -1.811 -1.357 2.3 -2.092 -1.565 § 0 1.9096 1.9096 0.1 1.666 1.825 0.2 1.625 1.859 fig. 2. skin-friction v ′′�0� variation against various > and j values. fig. 3. nusselt number against various > and j values. fig. 4. skin-friction against various j and o values. fig. 5. nusselt number against various j and o values. fig. 6. skin-friction against o for the particular nanoparticles in water base nanofluid. engineering, technology & applied science research vol. 12, no. 1, 2022, 8114-8122 8120 www.etasr.com lanjwani et al.: stability analysis of boundary layer flow and heat transfer of fe2o3 and fe-water … fig. 7. nusselt number against o for particular nanoparticles in water base nanofluid. fig. 8. velocity v ′�z� against various o values. fig. 9. temperature ]�z� against various o values. fig. 10. velocity v ′�z� against various j values. fig. 11. temperature ] �z� against various j values. fig. 12. velocity v ′�z� against various > values. fig. 13. temperature ]�z� against various > values. fig. 14. temperature ]�z� against various mn values. engineering, technology & applied science research vol. 12, no. 1, 2022, 8114-8122 8121 www.etasr.com lanjwani et al.: stability analysis of boundary layer flow and heat transfer of fe2o3 and fe-water … fig. 15. temperature ]�z� against various hi values. fig. 16. velocity v′�z� against various k values. fig. 17. temperature ]�z� against various k# values. acknowledgment the authors are indebted to their institutes for facilitating this research. the authors declare no conflict of interest. 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[36] w. n. mutuku-njane, "analysis of hydromagnetic boundary layer flow and heat transfer of nanofluids," ph.d. dissertation, cape peninsula university of technology, cape town, south africa, 2014. microsoft word etasr_v11_n4_pp7495-7500 engineering, technology & applied science research vol. 11, no. 4, 2021, 7495-7500 7495 www.etasr.com al-marghilani: comprehensive analysis of iot malware evasion techniques comprehensive analysis of iot malware evasion techniques abdulsamad al-marghilani information technology department college of computer science & information technology northern border university rafha, saudi arabia a.marghilani@nbu.edu.sa abstract-malware detection in internet of things (iot) devices is a great challenge, as these devices lack certain characteristics such as homogeneity and security. malware is malicious software that affects a system as it can steal sensitive information, slow its speed, cause frequent hangs, and disrupt operations. the most common malware types are adware, computer viruses, spyware, trojans, worms, rootkits, key loggers, botnets, and ransomware. malware detection is critical for a system's security. many security researchers have studied the iot malware detection domain. many studies proposed the static or dynamic analysis on iot malware detection. this paper presents a survey of iot malware evasion techniques, reviewing and discussing various researches. malware uses a few common evasion techniques such as user interaction, environmental awareness, stegosploit, domain and ip identification, code obfuscation, code encryption, timing, and code compression. a comparative analysis was conducted pointing various advantages and disadvantages. this study provides guidelines on iot malware evasion techniques. keywords-iot; malware; evasion techniques; challenges; security i. introduction internet of things (iot) is a system where various interconnected objects transfer data over a wireless network without requiring any human intervention [1, 2]. various sensors, technologies, and software are embedded into these devices to connect and transfer data within the network [3]. iot has evolved by utilizing various technologies such as embedded systems, machine learning, real-time analytics, and commodity sensors [4-6]. many iot applications are considered consumer applications, e.g. home security and wearable technologies [7]. industrial applications of iot usually monitor industrial systems such as smart logistics management and smart robotics [8]. in commercial applications, iot devices work with each other to provide benefits such as smart offices and buildings, connected lighting, and so on [9]. moreover, iot is used in infrastructure to monitor and regulate areas, cities, or countries such as smart parking management and connected charging stations [10]. moreover, iot devices are connected to the internet and transfer large amounts of data [11]. as iot continues to grow, a critical issue is emerging regarding the privacy and the security of data transferred over the network. one such issue that affects data security in iot is malware [12]. iot devices lack security features and are more vulnerable to malware attacks as they are always connected to the internet. malware is software designed to gain unauthorized access to systems causing security threats [13]. the most common types of malware are worms ,viruses, spyware, adware, ransomware, and trojan horses [14]. worms duplicate themselves and spread from one system to another without requiring any human intervention [15]. viruses also duplicate themselves but differ from worms as they insert code in other programs [16]. spyware steals sensitive information without the user's knowledge [17], while adware is a type of software that displays unnecessary advertisements [18]. ransomware aims to lock a system and demand money to unlock it [19]. trojan horses aim to give unauthorized access to a system without the user’s knowledge [20]. various attacks can affect iot devices causing privacy and security issues. some attacks that infect iot devices are botnets, mirai, and prowli malware [21]. a botnet is a robot network controlled by a hacker who uses malware to hijack its devices [22]. mirai is a malware that is capable of propagating itself and infects unsecured devices including iot [23], while prowli is used to redirect users to fake websites. based on the type of strategy, approaches to detect malware can be categorized into two main domains: static and dynamic analysis [24]. malware detection can be performed on three bases: behavior-based, specification -based, and signature-based (figure 1). in behavior-based malware detection, the object is evaluated based on its actions [26] before executing actions to analyze suspicious activities and get rid of threats. this technique is further classified as static, dynamic, and hybrid. in specification-based malware detection, a policy or specification mediates events from any program [27], and this is also classified as static, dynamic, and hybrid. signature-based malware detection is working with known threats and detects them easily by establishing unique identifiers. it is also classified as static, dynamic, and hybrid [28]. this study aims to analyze the malware detection techniques in iot applications, compare the existing studies on iot malware evasion techniques highlighting their advantages and limitations, and identify the various malware evasion techniques. corresponding author: abdulsamad al-marghilani engineering, technology & applied science research vol. 11, no. 4, 2021, 7495-7500 7496 www.etasr.com al-marghilani: comprehensive analysis of iot malware evasion techniques fig. 1. malware detection techniques [25]. ii. security issues in iot applications securing network communications more effectively and efficiently is considered a very critical issue. mobile ad hoc networks are exposed to many packet-drop attacks because of their fundamental characteristics, such as vulnerabilities of the underlying typical routing protocols. the packet drop attacks include black-hole and grey-hole attacks. various types of black-hole attacks and their defects were examined in [29]. various schemes have been discovered for detecting black hole attacks, including learning, co-operative, and other schemes. several techniques, including their core functionality and performance, were examined. the trust-based is a learning scheme, better than other schemes, as it had higher prevention nature against the attacks. on the other hand, most trust-based schemes failed to balance past and existing trust values. moreover, as openness and flexibility made android a popular mobile platform, it is targeted by massive mobile malware highlighting the need for better detection and prevention [30]. this study utilized a lightweight framework to identify malware in android devices. data analysis and malware detection were carried out on the server-side, reducing the use of mobile devices' resources and not affecting user's experience. in this method, machine learning was combined with network traffic analysis resulting in more accurate detection rates. meanwhile, as this method is limited to existing malicious samples, more samples have to be collected and analyzed to improve it continuously. iot devices lack security and are highly heterogenous [31], so many challenges arise on the cross-architecture detection of iot malware. various studies utilize dynamic or static analysis. static analysis is more suitable for detecting malware in iot devices, as it is more effective on multi-architecture devices. in [31], non-graph and graph-based malware detection methods were used. graph-based methods were found to detect more accurately unseen and complicated malicious codes. the advantages and limitations were summarized based on processing time, detection analysis, and mechanism, while efficiency is required to be further enhanced. a graph-based lightweight detection method to deal with various malicious executable files in iot devices is yet to be designed and developed. a modern malware type that can evade system security is advanced persistent threats (apts), while its identification is a great challenge [32]. antimalware and antivirus systems are conventional security systems that fail in apts identification. this study used advanced evasive techniques and examined the evasion and sophisticated attack techniques. as such malware can bypass a firewall with ease, a security system has to be effective to identify and avert such cyber-attacks in the future. iii. challenges and associated techniques to enhance the security against malware iot devices have various security issues as malware increases. security researchers use machine learning techniques to deal with these security issues and enhance iot devices' efficiency. a malware detection framework, called malinsight, was proposed in [33]. in malinsight, malware is described from three aspects: basic structure, high-, and low-level behavior. malware was detected more effectively and accurately based on findings from file operations, structural features, network, and registry reflected from these three aspects. this framework can detect easily unseen malware. various features are yet to be added, including work on privileged management schemes, authentication to restrict malware execution and reduce potential harm. beaconing, another malware type difficult to detect, was studied in [34]. the collection and review of enough data to detect a beaconing malware's behavior is a challenging task. beaconing is one of the encryption -based attacks where hackers use encryption to hide their activities. two unsupervised learning agents were used to detect malicious beaconing, a real-time and a periodic agent. the proposed algorithm can detect three different malicious beaconing behaviors: distortion, skipped exchanges, and combined distortion and skipped exchanges. unsupervised machine learning algorithms can be used along with ai to check the accurate beaconing behaviors. botnet activities detection is critical for the availability, security, and reliability of internet services. existing systems find it difficult to detect novel botnets with high accuracy due to various reasons such as new botnets created to bypass current detection approaches, the similarity between normal and botnet traffic, and the high computational requirements of large amounts of data processing. a scalable and decentralized framework was utilized to address this problem in [35]. this framework discovered previously unseen botnet traffic, characterized the behavior of legitimate hosts, can detect novel botnets without any assumptions, and can be used in real-world scenarios. despite the advantages of adaptive training and low numbers of false alarms, it has some drawbacks as network traffic increases and attackers change their methods constantly to avoid detection. iv. various malware attacks in iot in [36], malware targeting mobile devices was explored as a considered serious threat. fraudulent mobile apps and injected malicious apps are two types of mobile malware attacks. three main phases were included in the analysis: preprocessing, extraction, and grouping. grouping strategy was used to choose valuable apis to identify android malware apps and it included the upcoming three strategies. an effective classification model was proposed that combined api calls and permission requests. three different strategies were proposed to choose the valuable api calls. empirical analysis showed that the proposed system was effective in detecting mobile engineering, technology & applied science research vol. 11, no. 4, 2021, 7495-7500 7497 www.etasr.com al-marghilani: comprehensive analysis of iot malware evasion techniques malware and helped the process of mobile application analysis and malware forensic investigation. cyber data breaches increase while investigating cyber-attacks manually is timeconsuming and error-prone. a novel machine-learning-based framework was proposed in [37] that identified cyber threats and investigated cyber security issues with incomplete or partial information. mitigations for the identified threat incidents are yet to be integrated and automated. reviews about malware android platform were examined in [38], including mobile malware attacks, detection techniques, vulnerabilities, and security solutions over a certain period. ransomware hijacks in files and resources were studied in [39], presenting a ransomware taxonomy, various factors and counteraction types, and threat success factors and techniques. existing and upcoming security threats in iot-enabled smart grids were studied in [40], discussing various data privacy concerns, attack motives, and data transfer techniques. threat vectors in smart grids were classified into attacks against privacy, integrity, availability, and authentication. this paper also discussed the cyber kill chain which is a seven-step attack procedure. time sensitive networking (tsn) was adopted for iot and smart grids to allow real-time communication, while six open directions were proposed for smart grid connectivity. the challenges to secure a smart manufacturing system were explored in [41]. smart manufacturing is an important component for industry and connects physical and digital environments through iot technologies. data analytics, machine learning, and cloud with industrial systems integration lead to potential benefits and new challenges. various factors were discussed which include existing vulnerabilities, weaknesses, security of existing manufacturing industrial systems, and preparing for future security challenges. v. various malware evasion techniques in iot in [42], four methods were proposed to detect malware using hamming distance. this approach helps discover similarities between various samples, and it included all nearest neighbours (ann), weighted all nearest neighbours (wann), first nearest neighbours (fnn), and k-medoid based nearest neighbours (kmnn). these machine learning methods were used to detect malicious software having high precision and recall rates. a software-defined visual analytic system was proposed in [43], which was preferred for large analysis. various classifications were performed by extracting image features using machine learning algorithms. the utilized classifiers were decision tree, svm, random forest, and logistic regression. decision tree and random-based classifiers were found to be the most accurate. in [44], machine learning techniques to detect malware were studied by examining unsolved issues, challenges, limitations, recent trends, and new research directions. the wide adoption of iot by industrial systems led to an increase in malware. a malware analysis system was proposed in [45], where malware evasive behavior was detected by measuring the deviation from a program's normal behavior. the analysis evasion malware sandbox (aems) was very effective in malware detection. this system automatically detected the evasion in malware samples and provided reasonable accuracy. the big data cybersecurity analytics (bdca) system, studied in [46], protects the organizational networks and data from cyber-attacks by analyzing data security. after conducting a systematic literature review, seventeen architectural tactics were identified to support twelve quality attributes such as scalability, performance, accuracy, security, and usability. various factors are yet to be included such as analysis among tactics, trade-offs, and big data processing frameworks. as hacking attacks on industrial control systems increase and many security vulnerabilities are detected on industrial iot, technical and regulatory perspectives were examined in [47] to solve the upcoming security threats. resource exploration and energy consumption were significant challenges in the context of smart energy infrastructure. two challenges arose from the legal perspective: balancing the obligations of network and information security (nis) with the desire for industrial iot, and the need for guidance from authorities on iot and computer emergency response teams (certs). handling temporal dimensions of security, the shift of infrastructure from offline to online, the way to engage critical systems and their infrastructural complexity, the best way to address implementation gaps are areas yet to be focussed in detail. in [48], a malware analysis system was examined to characterize the malware behavior and improve the defense mechanism. this system considered the entire analysis environment which included the sandbox and a few other components. a fully automated system was developed as a solution to improve the dynamic malware analysis process. integrating the malware analysis process with environment configuration made easy the deployment of a complex analysis environment. malware analysis architecture based on sdn (mars) provided useful analysis capabilities. dynamic configuration is yet to be enhanced and an extensive analysis of the malware ecosystem is needed. ensembles that comprise a set of classifiers were proposed as an effective approach to detect malware, but due to the high cost of data transfer, memory, and processing requirements, this approach failed to secure big data in the cloud. the hybrid consensus pruning (hcp) method was proposed in [49] to address this problem, by combining several classifier classes into one scheme. hcp was found to be more effective than ensemble pruning through directed hill climbing ensemble pruning (dhcep), k-means pruning, and ensemble pruning via individual contribution (epic) ordering. this hcp method provided better ensemble classifiers to detect malware than the other methods, as shown in table i. a classification of malware dynamic analysis evasion strategies was presented in [50]. conventionally, a sandbox was introduced to suffer unplanned impacts from unknown software [51]. thus, the term sandbox represents a segregated or highly managed environment for testing unverified programs. due to equivalence in nature, virtual machines (vms) and emulated environments are frequently viewed as sandboxes. however, in this study, the term sandbox is used to denote the isolated and contained environments that automatically examine the specific program without any human intervention. the isolating link, in this study, is the system’s autonomous nature. evasion comprises a sequence of methods engineering, technology & applied science research vol. 11, no. 4, 2021, 7495-7500 7498 www.etasr.com al-marghilani: comprehensive analysis of iot malware evasion techniques applied by malware to maintain stealth, hinder efforts or avoid detection. for example, a major evasion strategy is fingerprinting [52]. the malware attempts to identify its environment by using fingerprinting and confirm if it is an analysis or production system. on the other hand, the counter evasion mechanisms try to hide the clues and cues which may reveal the analysis system. when a system exposes minimum clues to malware, then this system is highly transparent. automated and manual analysis are the main terms that form the proposed classification. when an expert performs an analysis with the support of a debugger, then this is called manual analysis. on the other hand, if an expert utilizes the conventional sandboxing technology to execute a transparent debugger, it is considered as a manual dynamic analysis (mda). in contrast, automated analysis is performed by software or machine automatically. detection is simply a perceptive process that checks whether a specific file is malicious. in addition, analysis is an understanding process that defines how malware functions. however, this segregating line is unclear at present as the functions of automated analysis implemented like sandboxes are expanding. additionally, to report the behavior of malware, sandboxes are performing their functions as the primary automated detection techniques [53]. this study considers similar concepts, as the understanding of malware's behavior is regarded as manual and malware detection is regarded as automated. although the mda is efficient, it has serious drawbacks, e.g. it is time consuming. examining a huge count of malware samples requests an effective agile method. such requests led to an innovative pattern of analysis known as automated dynamic analysis (ada). table i. comparative analysis of iot malware detection using various evasion techniques paper techniques used description outcome advantages / disadvantages [29] learning, cooperative, and other schemes. fifteen techniques were involved and core functionalities were discussed. the performance of techniques to mitigate and detect a black hole attack was defined. trust-based scheme was better when compared with other schemes. the trust-based scheme had high prevention nature. nearly all trust-based methods failed to weigh balance accurately between past and existing trust values. [30] lightweight network traffic analysis and machine learning. machine learning algorithm was combined with network traffic analysis. this helped the detection of android malware. android malware was detected. the detection rate was found to have high accuracy but was limited to existing malicious samples. [31] non-graph and graph-based malware detection methods. two groups of malware detection methods were used: non-graph and graph-based methods. graph-based methods detected more accurately unseen and complicated malicious codes. this method can be used to improve efficiency in the future. a graph-based lightweight detection method is yet to be designed and developed. [32] advanced evasive techniques. this study explored evasion techniques and sophisticated attacks utilized by present-day malware. various malware analysis techniques were discussed. advanced evasive techniques can bypass a firewall easily. an efficient security system is required to identify and avert cyberattacks in the future. [33] malinsight. malware was summarized from three aspects: basic structure, low, and high-level behavior. malware was detected more effectively based on findings from operations on files, structural features, network, and registry which are reflected from the three aspects. the framework could easily detect unseen malware and help future researchers discover malware easily. work on privileged management schemes and authentication to restrict the malware execution and reduce the potential harm is yet to be done. [34] unsupervised machine learning algorithms. two unsupervised learning agents, a real-time and a periodic one, were used to detect malicious beaconing. three different malicious beaconing behaviors were detected: distortion, skipped exchanges, and combined. unsupervised machine learning could be used along with ai to check beaconing behaviors. [35] scalable and decentralized framework. scalable and decentralized frameworks were used. previously unseen botnet traffic was discovered and the behaviors of legitimate hosts were characterized. although the merits of adaptive training and the low number of false alarms, attackers changed their method constantly to avoid detection. the constant evolving of network traffic was also a drawback. [37] novel machine learning based framework. investigating cyber-attacks through manual processes is time-consuming and error-prone. a novel machine learning based framework was proposed. based on observed attack patterns, the proposed method identifies cyber threats. proposed a method for investigating cybersecurity issues with partial information. [42] ann, wann, fnn, kmnn. four methods were proposed to detect malware using hamming distance, helping to discover similarities between various samples. machine learning methods were used to detect malicious software. high precision and recall rates were obtained. other similarity measures with different features between two programs are yet to be defined. [49] hybrid consensus pruning (hcp). an advanced ensemble pruning method combined several classifier classes into one scheme. several analyses were made by comparing hcp with several pruning methods. hcp was the most effective. hcp provided better ensemble classifiers to detect malware. this work should be extended to internet traffic for security and mobile cloud computing. engineering, technology & applied science research vol. 11, no. 4, 2021, 7495-7500 7499 www.etasr.com al-marghilani: comprehensive analysis of iot malware evasion techniques vi. conclusion this paper reviewed iot malware detection and evasionbased techniques. the advantages and disadvantages of existing evasion-based iot malware detection techniques were discussed. trust-based schemes, hcp, and graph-based methods are the most effective malware detection techniques. malware evolves with high efficiency as attackers use advanced technologies to design malware that bypasses detection systems. as malware evolves, modern solutions are needed to detect and handle it. malware evasion methods were analyzed, while classifications for automated and manual analysis were presented. the summarized advantages and limitations can be used by researchers to improve the efficiency of iot malware detection systems [54-57]. the evasion attempts can be categorized as detection independent and detection dependent. effective generic schemes, namely path exploration techniques, are still needed for detection independent strategy. references [1] s. bhat, o. bhat, and p. gokhale, "applications of iot and iot: vision 2020," international advanced research journal in science, engineering and technology, vol. 5, no. 1, pp. 41–44, jan. 2018. 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[57] r. f. mansour and m. r. girgis, "steganography-based transmission of medical images over unsecure network for telemedicine applications," computers, materials & continua, vol. 68, no. 3, pp. 4069–4085, 2021, https://doi.org/10.32604/cmc.2021.017064. microsoft word etasr_v11_n5_pp7730-7737 engineering, technology & applied science research vol. 11, no. 5, 2021, 7730-7737 7730 www.etasr.com loyani & machuve: a deep learning-based mobile application for segmenting tuta absoluta’s … a deep learning-based mobile application for segmenting tuta absoluta’s damage on tomato plants loyani loyani school of computational and communication science and engineering the nelson mandela african institution of science and technology arusha, tanzania loyanil@nm-aist.ac.tz dina machuve school of computational and communication science and engineering the nelson mandela african institution of science and technology arusha, tanzania dina.machuve@nm-aist.ac.tz abstract-with the advances in technology, computer vision applications using deep learning methods like convolutional neural networks (cnns) have been extensively applied in agriculture. deploying these cnn models on mobile phones is beneficial in making them accessible to everyone, especially farmers and agricultural extension officers. this paper aims to automate the detection of damages caused by a devastating tomato pest known as tuta absoluta. to accomplish this objective, a cnn segmentation model trained on a tomato leaf image dataset is deployed on a smartphone application for early and real-time diagnosis of the pest and effective management at early tomato growth stages. the application can precisely detect and segment the shapes of tuta absoluta-infected areas on tomato leaves with a minimum confidence of 70% in 5 seconds only. keywords-mobile applications for agriculture; tuta absoluta; deep learning; convolutional neural networks; segmentation i. introduction agriculture is an important economic sector of the tanzanian economy, contributing about 29.1% of gross domestic product (gdp) and 67% of total employment [1]. tanzanian farmers grow a variety of crops for food and economic purposes. as one of the most widely grown crops in the world [2], the tomato plant is also grown in different parts of tanzania. in 2017, 247,135 tons of tomatoes were harvested in 54,520 hectares, which is equivalent to 64% of all fruits and vegetables in the country [1]. tomato (solanum lycopersicum l.) is considered a high-value crop and income resource for smallholder farmers in sub-saharan africa [3]. nevertheless, the invasive pest known as tuta absoluta is a major threat to tomato production [4]. it can greatly damage tomato yield to the extent that growers may give up production due to the costs and losses it causes. yield losses can reach percentages as high as 80-100% if no control measures are taken [5]. the pest is native to south america but has spread quickly, not only across the mediterranean basin but also across europe, middle east, asia, and africa, where it was first recorded in algeria in 2008 [6-8]. the first case of tuta absoluta in tanzania was recorded in august 2014 in arumeru district, arusha, and it has since spread to the other regions of the country [9]. the number of extension officers who are key facilitators in providing farmers with proper information on plant diseases and pest control is very limited to meet the farmers’ demands in tanzania [10]. although farmers and extension officers struggle with different methods to control the pest, there has not yet been an effective mechanism to exploit the tuta absoluta’s infestation on tomato leaves at early stages before causing great yield losses to farmers. the application of artificial intelligence (ai) plays an important role in precision agriculture due to its flexibility, high performance, accuracy, and cost efficiency [11-13]. computer vision techniques, such as deep convolutional neural networks (cnns) have shown promise to transform the agricultural field in plant disease diagnosis. several researchers developed cnn models using image datasets for pest and disease diagnosis in plants like tomato, banana, apple, cassava, cherry, alfalfa, wheat, and grapevine [14-21]. deploying these cnn models on mobile phones would be beneficial in making them accessible to everyone, especially farmers and agricultural extension officers. despite the widespread use of smartphones, cnn models are currently being deployed only on a few smartphone applications. the use of mobile applications to diagnose plant diseases has received little attention in the literature. for instance, petrellis [22] developed a windows smartphone application using image processing techniques for identifying vineyard diseases by extracting features from grape leaf images. it can be used as a standalone application or combined with a remote server, and it is also extensible to different plant diseases. accuracy higher than 90% was achieved in recognizing the vineyard diseases. as an extension of their previous works [22-24], the authors in [25] proposed a low complexity image processing and a classification method implemented on smartphones for disease diagnosis in grape, peach, and citrus plants with an extensible set of diseases. classification algorithms such as decision tree, random forest, naïve bayes, and neural networks were used in corresponding author: loyani loyani engineering, technology & applied science research vol. 11, no. 5, 2021, 7730-7737 7731 www.etasr.com loyani & machuve: a deep learning-based mobile application for segmenting tuta absoluta’s … their experiments. the experimental results show that the developed mobile application achieved accuracy between 80 to 98% for disease recognition. moreover, authors in [26] developed an image processing algorithm deployed in smartphones for detecting diseases in the wheat plant using a dataset of 3637 leaf images. the smartphone application was used to capture wheat leaf images that were then diagnosed online by comparison with stored previous algorithm results with accuracy higher than 80%. similarly, the authors in [27] developed a cnn model based on single shot multibox (ssd) architecture then deployed it on a mobile application for real-time detection of diseases in cassava plants. the model performed better with f1-scores of 79% and 54% on test data and real-world images respectively. authors in [28] proposed two deep cnns (resnet152 and inceptionv3) using a dataset of 3000 leaf images to detect fusarium wilt race 1 and black sigatoka banana diseases. the inceptionv3 model was deployed on an android mobile phone and achieved an accuracy of 99% in detecting the two diseases in real environment. authors in [29] proposed an automated irrigation and plant-leaf disease detection system using an android mobile application. the mobile application was used to take photos of the suspected plant leaves, which were then sent to a cloud server, where the image was processed by matching it to the plant leaf images with diseases stored in the cloud database. in this work, the classification was based on artificial neural networks (anns). in a recent study, researchers reported the performance of a deep learning object detection model for diagnosing plant diseases and pests [30]. the model was trained on 2756 images of cassava leaves exhibiting pest and disease symptoms. it was subsequently deployed as a mobile application in android smartphones, which was then tested in the field and proved to be 74-88% accurate in diagnosing cassava disease and pest symptoms. this diagnosis accuracy was higher than that of agricultural extension officers (40-58%) and farmers (18-31%). authors in [31] trained 5 cnn models using the plantvillage dataset [32] with 18,160 tomato leaf images to classify 10 labels. the cnn model resnet50, which had better prediction accuracy, was subsequently deployed in a mobile application to classify and identify tomato plant diseases successfully. early and real-time detection of tuta absoluta’s damages on tomato plants can play a vital role in managing the pest and enhancing farmers’ decisions. this study presents a mobile application called tutasegmenter [33] deployed with a deep cnn model to detect and segment the effects of a tomato leaf miner (tuta absoluta) on tomato plants. this intervention approach for early pest detection and effective management at primary tomato growth stages will help farmers avoid massive economic losses. ii. methods we used tensorflow framework to deploy the cnn semantic segmentation model in a smartphone to detect tuta absoluta’s damage on tomato plants. we employed transfer learning based on the u-net architecture which has shown best performance on the international symposium on biomedical imaging (isbi) dataset [34] for semantic segmentation. authors in [35] introduced this u-shaped cnn architecture, which has performed exceedingly well in the biomedical image segmentation and later in many other fields, outperforming earlier segmentation methods even after being trained with only a few images [36]. we fine-tuned the model parameters to our dataset, which comprised of 1212 tomato leaf images damaged with tuta absoluta at early growth stages. the tomato leaf image dataset was built with images collected from experimental fields in arusha and morogoro regions in tanzania. examples of leaf images in this dataset are shown in figure 1. fig. 1. sample images from the tomato leaf image dataset. fig. 2. conceptual framework. the experiments were conducted on a computer preinstalled with windows 10 equipped with one intel® core™ i7-8550u 3.6ghz cpu, intel® iris® plus graphics, 512gb ssd storage, and 16gb memory. google collaboratory with tesla p100-pcie gpu and 27gb memory was utilized. we implemented our proposed network using python v3.7.10 and the keras [37] module with tensorflow [38] as backend. the model’s performance was then evaluated using different evaluation metrics, and the model’s parameters were tuned to get an optimized model. the optimized cnn model was deployed on a samsung galaxy a02s android phone to enable farmers to automatically detect and segment engineering, technology & applied science research vol. 11, no. 5, 2021, 7730-7737 7732 www.etasr.com loyani & machuve: a deep learning-based mobile application for segmenting tuta absoluta’s … the affected areas on tomato plants. figure 2 shows the conceptual framework of this work. a. data preprocessing the dataset of healthy and tuta absoluta-infested tomato leaf images was collected from the fields in tanzania using canon eos kiss x7 and samsung sm-g570f cameras. the complete details of this dataset have been reported in [39] and are freely available to the research community at the open access repository in [40]. for this study, 1212 images of infested tomato plants were extracted from the dataset to develop the semantic segmentation model. each sample plant contained an average of 6 leaves which is equivalent to 7272 leaflets for the selected images in our dataset. labelme [41], an open-source graphical annotation tool (see figure 3), was then used to produce ground truth masks by manually drawing and labeling irregular polygons following the shape of the infested area. annotations were then saved in voc [42] format with their corresponding images. then, the dataset was split into training and test sets in 80:20 ratio as shown in table i. fig. 3. labelme annotation tool. table i. data distribution image set number of images training set 969 test set 243 total 1212 b. the cnn model the approach presented in this paper is an extension of the method described in [39] where a tuta absoluta semantic segmentation model based on u-net architecture was proposed. in this work, a u-net architecture was trained for 200 epochs using an annotated dataset of 1212 images resized to 512×512 pixels. the learning rate was set to 0.01 using the adam [42] optimization function and the sigmoid activation function. the cross-entropy loss, intersection over union (iou), and dice coefficient metrics were used to evaluate the model’s performance. then, an optimized tuta absoluta semantic segmentation model was deployed in an android smartphone. c. model deployment this refers to integrating a machine learning model into an existing production environment to make practical decisions. we deployed the proposed model into a mobile phone so that farmers and extension officers can use their smartphones to automatically detect affected areas on tomato plants. to deliver reliable, user-friendly, and efficient software in a short time, agile software development methodology was used in developing the tuta absoluta segmentation mobile application based on users’ feedback. we used the tensorflow lite (tflite) to convert our suggested model into a lighter format because cnn models are complex and heavy, requiring a lot of memory and storage space to run. converting the models into tflite format reduces their file size, increases execution speed, and introduces optimizations that do not affect accuracy. this enables us to execute cnn models efficiently and run inference on mobile devices with limited computing and memory resources. the cnn model was converted to a mobile-compatible format using the python programming language. the application’s interface and functionality were then defined using extensible markup language (xml) and kotlin programming language respectively. the mobile application software was implemented in android studio integrated development environment (ide) and tested in a samsung sm-a025f galaxy a02s smartphone. smartphone applications are becoming increasingly popular and necessary [44]. we developed an android application since android holds the bigger market share in africa of over 84% [45], where this research focuses. moreover, to achieve its purpose, the tuta absoluta segmentation mobile application was designed to capture and upload images, provide general information about tomatoes and the tuta absoluta pest, run inference using the cnn segmentation model, and display the segmentation results. since the application operates completely offline, it only takes 5s to run the inference on a captured tomato leaf image and accurately segment the tuta mines. the tuta absoluta segmentation mobile application is simple and easy to use, even without any guidance. d. software design in this paper, the design of the mobile application software is visualized using unified modelling language (uml) diagrams. this includes the use case, activity and sequence diagrams. a use case model outlines how different categories of users interact with the system, their expectations, and the actions that the system must take to meet these objectives. figure 4 depicts the use case diagram for the tuta absoluta segmentation mobile application. each of the use cases shown is described in table ii. moreover, the activity diagram describes the dynamic aspect of the application software. it graphically represents a series of actions or flow of control in a system with support for iteration and concurrency. the activity diagram for tuta absoluta segmentation mobile application is shown in figure 5. also, the sequence diagram depicts how objects interact with each other for a particular scenario. it details the way operations in the application software are carried out. figure 6 shows the sequence diagram for the tuta absoluta segmentation mobile application. engineering, technology & applied science research vol. 11, no. 5, 2021, 7730-7737 7733 www.etasr.com loyani & machuve: a deep learning-based mobile application for segmenting tuta absoluta’s … fig. 4. the use case diagram for tuta absoluta segmentation application. capture image disease diagnos is new image view tomato info view tuta info segment tuta upload image knowledge need existing image view segmentation results tomato tuta ab soluta run inf erence using cnn model • original image • p re dicted masks • mask overlay • execution time • labels found fig. 5. the activity diagram for tuta absoluta segmentation application. table ii. desciption of the use cases use case description actor (s) view tomato info the user(s) can display general information about tomatoes such as the scientific name, production statistics, and planting information. farmer or extension officer view tuta absoluta info the user(s) can display general information about tuta absoluta such as their common and scientific names, physiology, and life cycle. farmer or extension officer capture/take photo the user(s) can access their mobile phone’s camera to take a photo of a tomato plant. then the system will automatically run inference on the photo using the cnn model in the background to segment tuta mines. farmer or extension officer upload an image the user(s) can upload a tomato plant image from their mobile phone’s gallery. then the system will automatically run inference on the uploaded photo using the cnn model in the background to segment tuta mines. farmer or extension officer view image the user(s) can view the captured or uploaded image in the mobile application. farmer or extension officer display segmentation results the user(s) can display the original image, segmentation results, and overlay in the mobile application. farmer or extension officer us er app cnn model view tomato/tuta info displ ay tomato/tuta info upload/ca pture i mage segment /detect tut a mines segmentat ion results displ ay original ima ge displ ay segmentation re sults fig. 6. the sequence diagram for tuta absoluta segmentation application. iii. results and discussion the model’s performance was evaluated using the crossentropy loss, iou and dice coefficient evaluation metrics. the experimental results show that the u-net segmentation model achieved 78.60% and 82.86% of iou and dice coefficient, respectively. figure 7 shows the u-net training loss curve over 200 epochs. the losses dropped rapidly during early training iterations before stabilizing around 60 epochs, indicating that the model fits well on the characteristics of our dataset at both the early and late stages of the training process. fig. 7. training and validation loss for u-net. engineering, technology & applied science research vol. 11, no. 5, 2021, 7730-7737 7734 www.etasr.com loyani & machuve: a deep learning-based mobile application for segmenting tuta absoluta’s … figure 8 illustrates the confusion matrix for our segmenter. since our task is binary segmentation, we map 0 for the background class and 1 for tuta, the object of interest. as mentioned above, the u-net model was converted to tflite format and then embedded into a mobile application in android studio. deploying on mobile devices would help democratize model access while also protecting user privacy that runs inference offline. fig. 8. confusion matrix for the tuta absoluta segmentation model. fig. 9. tuta absoluta segmentation mobile application: (a) splash screen, (b) landing/home page. we developed a simple and user-friendly mobile application named tutasegmenter [33] to allow smooth interaction between the farmers/extension officers and the application. the application can be downloaded, free of charge, from the google playstore. the farmer/extension officer clicks on the application icon which welcomes them with a colorful splash screen that lasts only for 2s before landing on the scrollable home page. the home screen has two clickable cards with quick facts about the tomato plant and tuta absoluta, and a clickable floating button for tuta segmentation, as illustrated in figure 9. the user can read general information about tomatoes, such as their scientific name, production statistics, and cropping information such as the amount of water, soil, and fertilizer they require by clicking on the tomato plant card, as shown in figure 10(a). by selecting the tuta absoluta card from the main page, the user can view general information about the pest, including common and scientific names, physiology, and lifecycle (see figure 10(b)). this will assist the farmer in learning and comprehending the pest to adopt effective pest management and tomato plant care procedures. fig. 10. tuta absoluta segmentation mobile application: (a) description page for tomato cropping, (b) description page for tuta absoluta. additionally, on every page of the mobile application, we placed a clickable floating button for tuta segmentation so that the farmer can quickly navigate to the disease diagnostics page to detect and segment tuta mines in tomato leaf images. the disease diagnostics page allows the user to capture or upload images, then shows the results (predicted masks and masks overlay) displayed in a horizontally scrollable section along with the original image. the user can also view the input image size and detection details (labels found and the execution time) in the bottom sheet layout (see figure 11(c)). if the image is devoid of tuta mines, the application will display a text “no labels found” as shown in figure 11(a). engineering, technology & applied science research vol. 11, no. 5, 2021, 7730-7737 7735 www.etasr.com loyani & machuve: a deep learning-based mobile application for segmenting tuta absoluta’s … fig. 11. tuta absoluta segmentation mobile application. (a) a healthy plant. (b) original image and mask prediction. (c) segmentation results. iv. conclusion and future work this paper presents a cost-effective mobile application for real-time detection and segmentation of tuta absoluta’s damage on tomato plants at their early growth stages. we utilized a cnn model trained on a 1212 tomato leaf images dataset and optimized it for mobile deployment. we evaluated the performance of the deployed model on a mobile application that detects tuta mines in tomato leaf images with minimum detection confidence of 70%. the application was able to precisely detect and segment the shapes of tuta absolutainfected areas on tomato leaves in just 5s. since the deployed model operates offline, there are no running costs once installed. the application provides early and real-time diagnosis of the devastating pest, and effective management at early tomato growth stages to avoid huge economic losses. providing these services in the absence of a mobile network, makes the application ideal for use in remote areas, which is beneficial to smallholder farmers especially in developing countries. this study proves that the use of computer vision techniques is vital in revolutionizing disease and pest management in agriculture. in the future, we expect to continuously improve the diagnostic model in tuta absoluta segmentation application and add more knowledge as it becomes available to provide farmers with an ever-improving link to expert knowledge. also, we aim to make the application capable of determining the extent of damage and suggest appropriate actions to be taken to control the pest based on the severity status. the application will be translated to swahili, a widely spoken language in the eastern, central and southern parts of africa. acknowledgement the authors would like to thank the african development bank (afdb) for funding this work through project no. p-z1ia0-016 under grant no. 2100155032816. references [1] annual agriculture sample survey crop and livestock report. tanzania: ministry of agriculture, 2017. 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[45] "mobile operating system market share africa," statcounter global stats. https://gs.statcounter.com/os-market-share/mobile/africa (accessed sep. 30, 2021). microsoft word etasr_ahmad_s_r.doc etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 221-225 221 www.etasr.com ahmad and quegan: cloud masking for remotely sensed data using spectral and principal… cloud masking for remotely sensed data using spectral and principal components analysis asmala ahmad faculty of information and communication technology universiti teknikal malaysia melaka melaka, malaysia asmala@utem.edu.my shaun quegan school of mathematics and statistics university of sheffield sheffield, united kingdom s.quegan@shef.ac.uk abstract— two methods of cloud masking tuned to tropical conditions have been developed, based on spectral analysis and principal components analysis (pca) of moderate resolution imaging spectroradiometer (modis) data. in the spectral approach, thresholds were applied to four reflective bands (1, 2, 3, and 4), three thermal bands (29, 31 and 32), the band 2/band 1 ratio, and the difference between band 29 and 31 in order to detect clouds. the pca approach applied a threshold to the first principal component derived from the seven quantities used for spectral analysis. cloud detections were compared with the standard modis cloud mask, and their accuracy was assessed using reference images and geographical information on the study area. keywordscloud masking; spectral analysis; principal components analysis; reflectance; brightness temperature i. introduction typically, 50% of the earth’s surface is covered by clouds at any given time, where a cloud is defined as a visible mass of condensed water droplets or ice crystals suspended in the atmosphere above the earth's surface. in remote sensing, clouds are generally characterized by higher reflectance and lower temperature than the background. a thick opaque cloud blocks almost all information from the surface or near surface, while a thin cloud has some physical characteristics similar to other atmospheric constituents. misinterpretation of clouds may result in inaccuracy of various remote sensing applications, ranging from land cover classification to retrieval of atmospheric constituents (e.g. in air pollution studies). several cloud detection and masking studies have been reported in the literature. however, most of these algorithms were designed for a global scale [1-2], and little effort has been devoted to optimising regional methods. some regional cloud masking algorithms have been designed for high, low and mid latitude regions, and these customised cloud masking algorithms tend to work best for such regions [3-4]. little serious effort has been applied to the equatorial regions, especially south-east asia [5-6]. this study considers this issue for the particular case of malaysia. it uses modis terra data to examine the spectral behaviour of cloud, identify effective modis bands for cloud detection and determine suitable cloud detection and masking methods in this region. ii. materials and methods this study is based on the mod021km product from modis terra. a major advantage of modis is its wide range of spectral bands, with 36 spectral bands covering the visible, near infrared and thermal infrared wavelengths. in addition, modis, with its swath width of 2330 km, is capable of recording every point on the earth at least once every two days and has an equatorial crossing time of 10:30 a.m. local time. thus, it can cover the whole study area (peninsular malaysia) in a single day pass with a high frequency of revisit. mod021km contains data in the form of: (1) radiance (wm 2µm-1sr-1) for reflective bands; (2) radiances (wm-2µm-1sr-1) for emissive bands; and (3) reflectance (dimensionless) for reflective bands. peninsular malaysia is located within 6 o 47’ n, 88 o 25’ e (upper left), and 1 o 21’ n, 106 o 20’ e (lower right) as shown in figure 1. the haze-free data used in this study is within the south-east monsoon season dated 30 th january 2004. visual analysis was carried out on individual bands and on band combinations (i.e. three bands displayed simultaneously in the red, green and blue channels) prior to further processing. cloud appears brighter than the surrounding background in the visible spectral region, while it appears darker in the thermal spectral region because of its low cloud-top temperature. this guided the development of cloud detection methods based on spectral analysis; principal component analysis (pca) was also assessed. the results were then compared with the standard modis cloud mask. fig. 1. map of peninsular malaysia. etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 221-225 222 www.etasr.com ahmad and quegan: cloud masking for remotely sensed data using spectral and principal… a. spectral analysis cloud detection was carried out using tests based on reflective bands, ratios of reflective bands, thermal bands and differences of thermal bands. 1) cloud detection using reflective bands the selection of the reflective bands for cloud detection was based on their spectral response to cloud, their separability efficiency (the capability of discriminating cloud and other features based on means) and their data quality. the spectral response to cloud and separability efficiency are interrelated as they provide information on the contrast between clouds and other features [2, 7]. band data quality refers to the radiometric aspects of the data recorded by the bands. from these selection criteria, bands 1-4 were found to be the most useful for our purpose. an outcome from the separability analysis for the selected modis bands is shown in figure 2 cloud exhibits much higher reflectance than land for bands 1-4; therefore has a high capability of discriminating cloud and land compared to bands 5-7. fig. 2. plot of mean reflectance versus selected modis reflective bands dated 30 january 2004 for each band, visual discrimination of clouds allowed the histogram of their reflectance values to be determined. a preliminary threshold to separate cloud from land and ocean features was determined based on the minimum reflectance value of the cloud histogram. the cloud, land and ocean histograms for band 2 are shown in figure 3. in the corresponding image, pixels with reflectance larger than the threshold were labelled as cloud and masked in red; the cloud threshold is 0.36. this analysis was repeated for band 1 (0.31), band 3 (0.35) and band 4 (0.32). fig. 3. histogram of cloud, land and ocean reflectance values and the corresponding cloud mask (masked in red). for clouds, the band 1/band 2 ratio tends to be close to unity [2], and applying a pair of thresholds to this ratio is a widely used method of detecting clouds [7-8]. based on histograms of this ratio for cloud, land and ocean pixels, determination of a suitable threshold and generation of the cloud mask were carried out as in the previous section. it was found that cloud pixels have reflectance ratio values from 0.87 to 1.34. 2) cloud detection using thermal bands detection of clouds using satellite thermal infrared measurements has been used as a gross cloud check in the past [3, 8]. it has been shown to perform well at equatorial latitudes because of the low average variation of air temperature [5] and of the fact that there are few high altitude areas in these regions [6]. the cloud threshold and cloud mask were determined after converting the radiance data to brightness temperature for all 16 thermal bands (band 20 to 25 and band 27 to 36) using:         − = − 1e λhc2 l tλk hc 52 (1) where: l = radiance (wm-2µm-1sr-1) h = planck's constant (js) = 6.626 x 10 -34 js c = speed of light in vacuum (ms-1) = 3 x 10 8 ms-1 k = boltzmann gas constant (jk -1 ) = 1.381 × 10 -23 jk -1 λ = band or detector centre wavelength (µm) t = brightness temperature (k) b. principal component analysis pca is a technique that transforms an original set of correlated variables into a set of uncorrelated variables called principal components (pcs). it can simplify multivariate data by reducing its dimensionality and bringing out hidden features in the original datasets [9]. it makes use of statistical quantities known as eigenvectors which are derived from the covariance matrix of the original datasets. each pc is a linear combination of the original variables (typically in remote sensing, spectral bands). the pcs are ordered by the amount of variance they explain in the data, with successive pcs having progressively lower variation [10]. pca was carried out using the seven bands selected for spectral analysis, namely bands 1-4 from the reflective bands and 29, 31 and 32 from the thermal bands. for simplicity, these are kept as radiances [10]. seven pcs (pc1-7) were then generated from the covariance matrix. these pcs store information as transformed radiance or pca brightness (dimensionless) which can be either positive or negative. it was found that the difference between cloud and land was biggest in pc1 and very small in other pcs (figure 4); hence pc1 was preferred for cloud detection. the cloud thresholds and cloud masks were then determined by analysing the histograms of pc1. etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 221-225 223 www.etasr.com ahmad and quegan: cloud masking for remotely sensed data using spectral and principal… fig. 4. histogram of cloud, land and ocean reflectance values and the corresponding cloud mask (marked in red). iii. experiments and results the thresholds applied to bands 1-4, 29, 31, 32, the band 1/band 2 ratio, the brightness temperature difference band 29 – band 31 and the first principal component (pc1) are shown in table i. a pixel was labelled as cloudy if it was identified as cloud by at least one of these tests. iv. accuracy assessment the standard modis algorithms for detecting daytime cloud over land involves bands 1, 26, 27, 35, the ratio of band 2 and 1, the ratio of band 18 and 2, the difference of band 29 and 31, the difference of band 31 and 32, the difference of band 22 and 31 and the difference of band 20 and 22 [2]. table i. summary of cloud masking tests used group test cloud threshold rband2(r0.865) rband1(r0.659) rband4(r0.555) rband3(r0.470) rcloud ≥ 0.36 rcloud ≥ 0.31 rcloud ≥ 0.32 rcloud ≥ 0.35 rband2(r0.865)/rband1(r0.659) 0.87 ≤ btcloud < 1.34 btband31(bt11.030) btband32(bt12.020) btband29 (bt8.550) btcloud ≤ 259 btcloud ≤ 257 btcloud ≤ 260 s p e c tr a l a n a ly si s btband29(bt8.550) – btband31(bt11.030) btcloud ≥ 2.5 p c a pca applied to bands 14, 29, 31 and 32 to produce pc1 pca brightness ≥ -90 sea could be masked out by making use of the modis land-water mask [13], so the following analysis is for the land areas only. the results of the spectral analysis were compared with those from the standard modis algorithm by categorising pixels into four types: (1) detected as cloud by both approaches; (2) detected as cloud by the spectral analysis but noncloud by the modis standard cloud mask; (3) detected as cloud by the standard modis cloud mask but noncloud by the spectral analysis; and (4) not detected as cloud by both. the results are summarised in table ii. 20.8% of the pixels over land were detected as cloud and 69.1% as noncloud pixels by both the spectral analysis and the modis cloud mask. results are also depicted in figure 5. 9.5% of the pixels were detected as cloud by the spectral analysis but noncloud by the modis cloud mask, while 0.6% were detected as noncloud by the spectral analysis but cloud by the modis cloud mask. the outcomes of the pca were compared with those from the standard modis algorithm in a similar way, with results summarised in table iii. 19.8 % of the pixels over land were detected as cloud and 71.9 % as noncloud pixels by both the pca and the modis cloud mask, as shown in figure 6. by comparing both methods, more cloud pixels were detected by the spectral analysis than the pca. it was also found that the spectral analysis detected more cloud pixels than the modis cloud mask. objective methods for assessing the accuracy of the analyses are not available, so we have based our assessment of the different methods on visual inspection of reference images containing sparse cloud patches (an example is shown in figure 7a; bands 1, 2 and 3 displayed in channels red, green and blue respectively). it was found that in most places, the spectral analysis (shown in figure 7c) is capable of detecting more cloud than the standard modis cloud mask (shown in figure 7b) and yields a better match to the reference image. this is easily seen in the blue rectangle in figure 7, where the clearly visible cloud cover is detected by the spectral analysis but missed by the modis cloud mask. this area consists of a mountainous range known as the kledang range, where conditions are suitable for the development of stratus and lenticular cloud. when the mountain is warmer than the surrounding air, cumulonimbus and cumulus clouds also tend to form. subsequently, we compared our analysis with a cloud mask produced using a supervised classification algorithm (maximum likelihood). training pixels were obtained by manually delineating cloud and cloud free polygons within the scene [14]. undeniably, this cloud mask cannot be considered as a reference cloud mask per se, since it does not necessarily possess a better precision than our cloud mask and its accuracy is unknown. however the level of agreement of two cloud masks created with different approaches provides valuable information about the performance of both cloud masks. the agreement between both cloud masks was described by a confusion matrix (for cloud and non cloud), in which classification accuracy and kappa coefficient were used as performance indicator [15]. the spectral analysis produced classification accuracy of 98% with kappa coefficient 0.95, whereas the modis cloud mask yielded classification accuracy of 87% with kappa coefficient of 0.75. hence, the spectral analysis is seen to perform better than the modis cloud mask. v. discussion the high level of agreement (89.9%) between the spectral analysis and the standard modis cloud mask was expected, as both use similar spectral approaches and they share tests based on the band 2/band 1 ratio. band 1 provides good contrast between cloud and land, since land surfaces are less reflective below 0.72 µm; it has also proved effective in detecting low clouds [2]. the band 2/band 1 ratio is useful since cloud has similar reflectance properties in both bands and its presence can be indicated by a ratio close to unity. etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 221-225 224 www.etasr.com ahmad and quegan: cloud masking for remotely sensed data using spectral and principal… the spectral analysis and the modis cloud mask disagree on 10.1% of the pixels because of differences between the individual tests used in both methods and how they are combined. consequently, they tend to be sensitive to different types of clouds. unlike the spectral analysis, the modis cloud mask does not use band 2 to 4 (for low cloud) and band 29 to 32 (for high cloud), which has a high separability between cloud and noncloud features, thus tend to miss certain types of clouds. table ii. confusion matrix of modis cloud mask and spectral analysis spectral analysis (%) cloud non cloud total cloud 20.8 0.6 21.4 m o d is c lo u d m a sk (% ) non cloud 9.5 69.1 78.6 total 30.3 69.7 100 n o d ata w ater body d etected as cloud by both spectral/pca mask and m o d is cloud m ask d etected as cloud by spectral/p ca mask but not cloud b y m od is cloud m ask d etected as cloud by m od is clo ud m ask but not cloud b y spectral/p ca mask n ot detected as cloud in both spectral/p ca mask and m od is cloud m ask fig. 5. comparison between cloud cover detected by the standard modis cloud mask and by the spectral analysis. table iii. confusion matrix of modis cloud mask and pca pca (%) cloud non cloud total cloud 19.8 1.6 21.4 m o d is c lo u d m a sk (% ) non cloud 6.7 71.9 78.6 total 26.5 73.5 100 fig. 6. comparison between clouds detected by the standard modis cloud mask and the pca. (a) (b) (c) fig. 7. reference image (a), the modis cloud mask (b) and the mask derived from the spectral analysis (c). cloud is indicated by bright areas in (a) and red areas in (b) and (c). the modis cloud mask is designed for global applications, and hence contains features that are irrelevant in tropical latitudes (e.g., tests to distinguish cloud from snow cover). thus it may not be well suited to such regions, with their special geographical (location and topography), weather (atmospheric water vapor and aerosol concentrations) and radiative transfer conditions (variable path length, emissivity and reflectance) [11-12]. consequently, the optimal spectral thresholds for tropical areas do not necessarily serve for other latitudes [5]. despite the quite different approach used in the pca, surprisingly good agreement (91.7%) with the modis cloud mask was found. this indicates that cloud and noncloud have distinct signatures that emerge in the statistical data-based approach of pca, as well as in the rule-based approach of the spectral analysis. further work is needed to investigate the weightings of the channels in the pca analysis, and to compare them with how information is exploited in the spectral rulebased approach. the comparison of the spectral analysis and pca with the standard modis cloud mask shows that the spectral analysis is more reliable when assessed against reference images. the spectral analysis is simpler than the modis cloud mask because contains fewer tests, yet gives a higher agreement when compared against the mask produced using a supervised classification algorithm. vi. conclusion a spectral analysis based on histogram analysis to set thresholds for detection of clouds is found to be more suitable for tropical conditions than the global modis cloud mask, due its implicit allowance for local conditions. cloud detection by the use of the pca indicates that cloud regions have distinct statistical signatures, but the spectral analysis is more reliable. acknowledgment the authors would like to thank the malaysian ministry of higher education for funding this study. references [1] w. b. rossow, gardner, “cloud detection using satellite measurement of infrared and visible radiances for isccp”. journal of climate, vol. 6, pp. 2341 – 2369, 1993 [2] s. a. ackerman, k. i. strabala, w. p. menzel, r. a., frey, c. c. moeller, l. e. gumley, b. a. baum, c. schaaf, g. riggs, etasr engineering, technology & applied science research vol. 2, �o. 3, 2012, 221-225 225 www.etasr.com ahmad and quegan: cloud masking for remotely sensed data using spectral and principal… discriminating clear-sky from cloud with modis algorithm theoretical basis document. products: mod35. atbd reference number: atbd-mod-06, greenbelt: modis cloud mask team, 2002 [3] r. w. saunders, “an automated scheme for the removal of cloud contamination form avhrr radiances over western europe”, international journal of remote sensing, vol. 7, pp.867 – 886, 1986 [4] a. m. logar, d. e. lloyd, e. m. corwin, m. l. penaloza, r. e. feind, t. a. berendes, k. kuo, r. m. welch, “the aster polar cloud mask”, ieee transactions on geoscience and remote sensing, vol. 36, no. 4, pp. 1302 – 1312, 1998 [5] g. b. franya, a. p. cracknell, “a simple cloud masking approach using noaa avhrr daytime data for tropical areas”, international journal of remote sensing, vol. 16, no. 9, pp.1697–1705, 1995 [6] j. bendix, r. rollenbeck, w. e. palacios, “cloud detection in the tropics – a suitable tool for climate – ecological studies in the high mountains of equador”, international journal of remote sensing, vol. 25, no. 21, pp.4521 – 4540, 2004 [7] p. h. swain, s. m. davis, 1978. remote sensing: the quantitative approach. new york: mcgraw-hill. [8] r. w. saunders, k. t. kriebel, “an improved method for detecting clear sky and cloudy radiances from avhrr data”, international journal of remote sensing, vol. 9, no. 1, pp.123 –150, 1988 [9] w. p. loughlin, “principal component analysis for alteration mapping”, photogrammetry engineering and remote sensing, vol. 57, no. 9, pp.1163-1169, 1991 [10] d. w. hillger, j. d. clark, “principal component image analysis of modis for volcanic ash. part 1: most important bands and implications for future goes imagers”, journal of applied meteorology, vol. 41, no. 10, pp. 985-1001, 2002 [11] a. t. a jose, g. r. francisco, p. l. mercedes, m. canton, “an automatic cloud-masking system using backpro neural nets for avhrr scenes”, ieee transactions on geoscience and remote sensing, vol. 41, no. 4, pp. 826-831, 2003 [12] s. r. yhann, j. j. simpson, “application of neural networks to avhrr cloud segmentation”, ieee transactions on geoscience and remote sensing, vol. 33, no. 3, pp. 590-604, 1995 [13] c. o. justice, e. vermote, j. r. g. townshend, r. defries, d. p. roy, d. k. hall, v. v. salomonson, j. l. privette, g. riggs, a. strahler, w. lucht, r. b. myneni, y. knyazikhin, s. w. running, r. r nemani, w. zhengming, a. r. huete, w. van leeuwen, r. e. wolfe, l. giglio, muller, p. lewis, m. j. barnsley, “the moderate resolution imaging spectroradiometer (modis): land remote sensing for global change research”, ieee transactions on geoscience and remote sensing, vol. 36, no. 4, pp.1228-1249, 1998 [14] f. sedano, p. kempeneers, p. strobl, j. kucera, p. vogt, l. seebach, j. san-miguel-ayanz, “a cloud mask methodology for high resolution remote sensing data combining information from high and medium resolution optical sensors”, isprs journal of photogrammetry and remote sensing, vol. 66, pp. 588-596, 2011 [15] r. g. congalton, “a review of assessing the accuracy of classifications of remotely sensed data”, remote sensing of environment, vol. 37, no. 1, pp. 35-46, 1991 microsoft word 2-500-ce.doc engineering, technology & applied science research vol. 5, no. 1, 2015, 748-752 748 www.etasr.com tripathy and panigrahi: study of direct torque controlled 3-phase scim with two and three-level … study of direct torque controlled 3-phase scim with two and three-level inverters using st-dtc and fr-dtc scheme pradeep ranjan tripathy department of electrical engg, kiit polytechnic, kiit, 751024 bhubaneswar, india pradeeptripathy_10@yahoo.co.in bibhu prasad panigrahi department of electrical engg indira gandhi institute of technology, sarang. 759146 dhenkanal, india bibhu89@yahoo.com abstract— dtc control strategy helps to obtain fast and smooth control in 3–phase induction motors. it does not depend upon the machine parameters and transformation of reference frames. various control strategies on the direct torque control (dtc) scheme have been carried out in the present study. the suggested scheme is meant for designing the low cost control circuit for dtc implementation on 3-phase scim. three schemes with two types of inverters have been simulated in matlab (simulink) environment and the thd ratio in each case has been studied along with fast fourier transform (fft) tools to compare the advantages. keywords-foc; st-dtc; fr-dtc; 2li; 3li; six sectors; twelve sectors. i. introduction induction motors with conventional control schemes used in common industrial drives are not capable of providing fast and smooth torque variation, due to the inherent characteristics of the induction motor along with the complex, non linear and time varying dynamics. the inaccessibility of some states and outputs makes the input voltage prediction more difficult. though more effective control strategies in dc motors have been established, safety concerns related to flammability render these impracticable in many areas. the use of induction motor has thus become a popular practice, only after the invention of field oriented control (foc) in the 1970s. the foc scheme decouples the stator current into torque and flux producing components so as to control the induction motor like a dc motor. foc suffers from limitations arising from computationally intensive design procedures. the dependence of this scheme on most machine parameters and reference frame transformations contribute to these difficulties [1, 7]. the direct torque control (dtc) scheme postulated in 1980’s [2, 3] simplified the dynamic and steady state torque control. transformation of the reference frame is not required in this scheme. the stator resistance is enough to calculate the stator flux and torque. the torque control is performed keeping stator flux intact and changing the torque angle by acceleration or deceleration of the stator linked flux, by selecting the optimum voltage vector. the optimum voltage vector is derived from a switching table, based on the flux and torque errors and the angular position of the stator linked flux in space. implementation of this method is normally performed using high speed processors, [4-6, 8-10] which is a costly affair. low cost analog circuits can also be implemented for the dtc scheme, being economical for small industrial sectors [11, 12]. torque control is possible in two quadrant operation using low cost analog circuits [13-15]. the common drawback of this scheme is the ripple in current and torque. in present context, a descriptive study has been carried out for the comparative study of current, flux and torque response referred to a varying stepped torque command. the study is elaborated with the use of two level vsi and diode clamped three level inverter following a switching table based dtc (st-dtc) scheme and fuzzy rule based dtc (fr-dtc) scheme. all simulations have been carried out in matlab simulink environment. the switching look-up table and sector determination table have been realised using the state flow chart of the st-dtc scheme used for two and three level vsi. the fuzzy logic based lookup table uses twelve sectors to obtain better performance in torque and current. overall, the present study emphasizes on the use of the control scheme that can be implemented practically in various environments. an improvement of response is noticed through high level inverter use. ii. principle of dtc a. using two level inverter the stator terminal voltage and line currents are sensed and transformed to d-q stationary frame [14, 15]. two axis stator linked flux ψds and ψqs are estimated by integrating the emfs, which are obtained after compensating stator resistance voltage drop from two axes stator voltages. torque is calculated using d-q axis flux and current components. the instantaneous angular position of stator linked flux is determined digitally within six sectors in space [12, 14]. the absolute value of flux and the estimated torque are compared with their respective command values to obtain error signals. both error signals are inspected by two prefixed band limits to yield control signals. the torque control signal is of three levels (1, 0,-1) and the flux authors are thankful to ‘aicte, new delhi’, for support of research work. engineering, technology & applied science research vol. 5, no. 1, 2015, 748-752 749 www.etasr.com tripathy and panigrahi: study of direct torque controlled 3-phase scim with two and three-level … control signal is of two levels (1, 0). the look-up table (switching table) decides the switching pattern for 2-level vsi[14, 15]. it uses three inputs, torque and flux control signal along with the dwelling position of stator flux in sextant. the switching table decides the optimum switching voltage vector, based on acceleration or deceleration of torque and flux corresponding to command value. in the fr-dtc scheme, a fuzzy controller replaces the hysteresis bands used in st-dtc scheme [15]. the flux and torque errors obtained comparing the respective command values are used as input state variables for the fuzzy controller. the fuzzy controller uses the angular dwelling position of stator flux as the third input state variable (figure 1). fig. 1. (a) flux error membership function (b) torque error membership function (c) twelve angular dwelling position of stator flux the stator flux error variable is represented by three membership functions n, z and p. the three membership functions denote a decrease of the stator flux, no change of flux and an increase of the flux. the torque error is calculated by comparing the calculated electromagnetic torque with the desired command torque. the torque error variable is denoted by five membership functions: nl, ns, z, ps and pl [15]. corresponding functions represent a large or small decrease in torque, no change in torque and a small or large increase in torque. the angular position of the stator flux is defined in twelve sectors in the sextant. each sector of the st-dtc scheme is divided into two parts to facilitate the accurate judgement of call for voltage vector. considering the stator flux to dwell in the first 60o in the air gap space and assuming the torque and flux errors to be positive, the demanding voltage phasor will tend to increase the torque. the voltage demand can be satisfied with the voltage phasor in sector i or vi. if the flux is in the first 30o of sector i, then any one of the above voltage vectors can meet the purpose. when it is in the second 30o, the voltage phasor corresponding to sector vi of sextant provides the advancement of the flux vector. hence, 180 rules are defined to decide the optimum switching vector. mamdani method is used for defuzzification. the fuzzy controller gives three crisp outputs corresponding to the three legs of a 2-level vsi. b. using three level inverter the 3-level inverter needs a lower switching frequency, compared to the 2-level inverter, to achieve the desired sinusoidal voltage output. hence, current harmonic decreases and efficient utilisation of energy is obtained. in each phase there are two complementary switching pairs. while one of the switch pair is turned on, the other complementary switch pair remains turned off. in 3-level inverter a set of two switches turns on at any given time. in a 3-level inverter there are 3-evel output voltage and 5-level output line voltage. the possible switching state of any leg is s1-s2, s2-s1’ and s1’-s2’ providing output voltages 2vdc, vdc, 0 respectively. hence, the possible switching states in three phase 3-level inverter are 33 = 27. out of these 27 states, 24 states are active and 3 states are zero state vectors. the active vectors are of three types, such as 6 long vectors, 6 medium vectors and 12 short vectors. the long vectors are (002), (020), (022), (200), (220) and (202) having magnitude of √(vq 2+vd 2)=4vdc/3 . the medium vectors (012), (021), (120), (210), (102) and (201) have magnitude of 2vdc/√3 and the rest 12 short vectors have magnitude of 2vdc/3. the air gap space is divided into twelve sectors (figure 2), according to adjacent medium and long vectors each spreads with 300. instantaneous angular position of the stator flux is determined digitally as in table i. signal a1, a2 and a3 denote the angular position of stator flux. the signals are true if the absolute value of the ratio ψqs/ ψds is greater than or equal to tan (pi/2), tan(pi/4) and tan(5.pi/2) respectively. positive value of ψqs and ψds denote 1, otherwise 0. thus the dwelling position of stator linked flux is identified by the generating signal sθ. the absolute value of flux and the calculated torque are compared with their respective commands and generate the errors, which are further inspected by prefixed hysteresis bands to yield the flux control signal (sψ) and the torque control signal (st). fig. 2. twelve sectors with switching vectors (a) (b) (c) engineering, technology & applied science research vol. 5, no. 1, 2015, 748-752 750 www.etasr.com tripathy and panigrahi: study of direct torque controlled 3-phase scim with two and three-level … table i. dtc switching table for 3-level inverter sθ sψ st <1> <2> <3> <4> <5> <6> <7> <8> <9> <10> <11> <12> 1 1 v2(220) v8(210) v9(120) v2(220) v3(020) v9(120) v10(021) v3(020) v4(022) v10(021) v11(012) v4(022) v5(002) v11(012) v12(102) v5(002) v6(202) v12(102) v7(201) v6(202) v1(200) v7(201) v8(210) v1(200) 1 0 v26(111) v27(222) v25(000) v26(111) v27(222) v25(000) v26(111) v27(222) v25(000) v26(111) v27(222) v25(000) 1 -1 v6(202) v7(201) v7(201) v1(200) v1(200) v8(210) v8(210) v2(220) v2(220) v9(120) v9(120) v3(020) v3(020) v10(021) v10(021) v4(022) v4(022) v11(012) v11(012) v5(002) v5(002) v12(102) v12(102) v6(202) 0 1 v3(020) v10(021) v10(021) v4(022) v4(022) v11(012) v11(012) v5(002) v5(002) v12(102) v12(102) v6(202) v6(202) v7(201) v7(201) v1(200) v1(200) v8(210) v8(210) v2(220) v2(220) v9(120) v9(120) v3(020) 0 0 v25(000) v26(111) v27(222) v25(000) v26(111) v27(222) v25(000) v26(111) v27(222) v25(000) v26(111) v27(222) 0 -1 v5(002) v11(012) v12(102) v5(002) v6(202) v12(102) v7(201) v6(202) v1(200) v7(201) v8(210) v1(200) v2(220) v8(210) v9(120) v2(220) v3(020) v9(120) v10(021) v3(020) v4(022) v10(021) v11(012) v4(022) the switching table (table i) is formulated based on the angular position of the stator linked flux in space and the requirement of acceleration or deceleration of flux and torque, maintaining a constant magnitude of stator flux. hence, the lookup table decides the optimum switching vector for the three-level vsi with the help of the three inputs sψ, st, and sθ. based on the dwelling position of the stator flux in a particular sector the digital control signals of flux and torque indicate the required voltage state for switching. for example, while the stator flux dwells in sector <1> and both the flux and torque signal are 1, then four possible of switching states may be selected. those are long vector v2 (220), medium vector v8 (210), the short vector v15 (110) and its redundancies for increasing in both torque and flux. the switching vectors lie in sector <2> and sector <3>. similarly if flux and torque control signals are 0 and 1, voltage vectors v3 (020), v10 (021), v16 (010) and its redundancy may be selected. the redundant vectors are the switching states from v13 to v24 respectively. when the torque control signal is zero, no change in torque is needed and a zero vector, v25 (000), v26 (111) or v27 (222), is selected. the possible look up table is shown in table i. logic 2 stands for on condition of both upper arm switch, logic 1 for on condition of middle two switches and logic 0 for on condition of lower switches. the optimum switching vector for the corresponding inverter is decided by the switching table to achieve the required torque control. the switching states are depicted in figure 3. fig. 3. switching logic states in 3-level inverter iii. simulation study both st-dtc and fr-dtc schemes using two and three level inverters have been simulated in the matlab simulink environment. the machine parameters of the 3-phase, 0.75 kw, 50 hz, star connected induction motor are as follows: vll=415 v, ra=16.575 ω, rr=5.2183 ω, lls=llr=0.0404558 h, lm=0.5393595 h, p=4, j=0.0048742 kg-m 2, b=0.000001nm-s. the line value of stator voltage and current are sensed to transform into d-q component of voltage and current. using flux and torque estimator, flux and torque are calculated after compensating the stator resistance drop from the d-q stator voltage [13]. the absolute values of flux and torque are compared with their respective command values to obtain the corresponding errors. the flux command has been considered as the rated flux (1.00184 wb) and the rated torque as 5.0618 n-m. the simulation has been carried out with a variable two quadrant torque command with an equal time interval of 0.06 s. the initial step command is 30% for the first interval, which changes to 60% and then to 30% of rated torque in succeeding time intervals, and finally falls to zero. the negative torque command is set to 0.24 second. the errors obtained are compared in their respective hysteresis bands and control signals sψ and st are generated. both of these control signals along with the position of the stator linked flux sθ are judged by the distinguished lookup table meant for two-level and three-level inverters to obtain the optimum switching vectors. the flux and torque errors are directly used as the state variable inputs in the fuzzy controller of the fr-dtc scheme. the angular position of the stator linked flux is used as the third state variable. the scheme has been simulated for two and three level inverters. all the three state variables are processed by the fuzzy controller, using 180 fuzzy rules. the crisp outputs of the fuzzy controller are utilised for switching the inverters after generating its complement for lower switch of any inverter leg. the simulation has been performed for all three cases i.e. st-dtc for two and 3-level inverters and fr-dtc for 2-level inverter. the x-y plotting of the d-q flux (figure 4) is of circular shape for all schemes proving the spatial relation, and the magnitude versus time shows a constant magnitude of 1.00184629 wb, (figure 5a) at variable torque command in two quadrants. it is found that the flux ripple reduces with the use of high level inverter. the plot in figure 5c shows the dwelling position of the stator flux. it varies in the sextant within –π/2 to 3π/2 radians and its direction changes with a change in torque command. it is shown that the magnitude of stator flux remains intact with a variation of torque command either in forward or reverse direction. the two axis flux ψqs and ψds maintain π/2 radian phase difference as shown in figure 5. engineering, technology & applied science research vol. 5, no. 1, 2015, 748-752 751 www.etasr.com tripathy and panigrahi: study of direct torque controlled 3-phase scim with two and three-level … the variation of current in each scheme has been depicted in figures 7 and 8. the current settles to steady state comparatively quickly in the 3 level inverter based stdtc (3listdtc) scheme with least dynamic amplitude. the two axes current resemble the circular shape in x-y plotting and the frequency and magnitude changes along with the change of torque command. when motor changes its motion from forward to reverse the π/2 lagging property of the two axes current reverses. fig. 4. (a) xy plot of d-q flux (2li stdtc) (b) xy plot of d-q flux (2li frdtc) (c) xy plot of d-q flux in (3li stdtc)     fig. 5. (a) abs flux and angle vs time (2li stdtc) (b) abs flux and angle vs time (2li frdtc) (c) abs flux and angle vs time (3li stdtc) figure 9 shows the superimposed torque with its respective command value. the fast response of torque to the command value is noted in all three cases. rising torque in forward and reverse motoring during 30% to 60% rise mode has been considered as instance in figures 9 and 10. as seen in table ii, a faster response of change in torque has been observed in frdtc based 2-level inverter (0.12 milli-secs). in comparison, the fuzzy rule based dtc scheme provides faster response but ripples in torque increase. total harmonic distortion (thd) is measured using the fft tool. it is observed that thd in the stdtc scheme, applied with 3 level inverter, is lowest among the three schemes studied but torque response to command is quite slow. the air gap has been divided into six and twelve sectors for different approaches. figure 11 shows both postulations. the dwelling position of air gap flux in different sectors has been traced out in forward and reverse mode operation. accordingly the development of sectors has also been modified corresponding to the mode of motor operation.       fig. 6. (a) dq flux vs time (2li stdtc) (b) dq flux vs time (2li frdtc) (c) dq flux vs time (3li stdtc)     fig. 7. (a) xy plot of dq current in 2li stdtc (b) xy plot of dq current in 2li frdtc (c). xy plot of dq current in 3li stdtc fig. 8. (a) dq current vs time in 2li stdtc (b) dq current vs time in 2li frdtc (c) dq current vs time in 3li stdtc (a) (b) (c) (a) (b) (c) (b) (c) (a) (b) (c) (a) (a) (b) (c) engineering, technology & applied science research vol. 5, no. 1, 2015, 748-752 752 www.etasr.com tripathy and panigrahi: study of direct torque controlled 3-phase scim with two and three-level … fig. 9. (a) rising torque vs time at forward motoring (2listdtc) (b) rising torque vs time at forward motoring (2lifrdtc) (c) rising torque vs time at forward motoring (3listdtc) fig. 10. (a) rising torque vs time at reverse motoring (2listdtc ) (b) rising torque vs time at reverse motoring (2lifrdtc) (c) rising torque vs time at reverse motoring (3listdtc)     fig. 11. (a) six sector in two quadrant operation (b) twelve sector in two quadrant operation iv. conclusion the dtc scheme has been studied using three strategies in this paper. the classical st-dtc scheme has been implemented with the logical simulation of low cost analog circuits for 2-level and 3-level inverters. the same inverters have been simulated using fuzzy logic. the faster torque response is documented in the fr-dtc schemes (in comparison to the st-dtc scheme) but the thd values are also larger. in conclusion, to implement a low cost dtc scheme with the least harmonic distortion, the implementation with a diode clamped 3-level inverter seems preferable. table ii. torque performance & switching strategies 2 li stdtc 2li frdtc 3li stdtc 0.3t to 0.6t rise in forward motoring (m-s) 0.17 0.16 0.22 0.3t to 0.6t rise in reverse motoring (m-s) 0.15 0.12 0.15 % thd in torque 106.52 117.61 46.13 references [1] s f. blaschke, “the principle of field-orientation as applied to the trans vector 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switching table based direct torque control of induction motor drive”, iit conference, kharagpur, pp. 1–6, 2005 [12] b. p. panigrahi, d. prasad, s. sengupta, “a simple hardware realization of switching table based direct torque control of induction motor”, electric power systems research, vol. 77, no. 2, pp. 181–190, 2007 [13] d. prasad, b. p. panigrahi, s. sengupta, “digital simulation and hardware implementation of a simple scheme for direct torque control of induction motor”, energy conversion and management, vol. 49, no. 4, pp. 687-697, 2008 [14] p. r. tripathy, b. p. panigrahi, “simulation study on dtc based induction motor drives using matlab”, ieee proceedings of indicon, india, vol. 1, pp. 65-68, 2008 [15] p. r. tripathy, b. p. panigrahi, “simulation studies on switching table based dtc and fuzzy rule based dtc for three-phase squirrel cage induction motor”, engineering, technology & applied science research, vol. 2, no. 1, pp. 162-166, 2012 (c) (b) (a) (a) (b) (c) (a) (a) microsoft word final-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 201-208 201 www.etasr.com sahu et al: direct torque control for three-level �eutral point clamped inverter-fed induction motor… direct torque control for three-level neutral point clamped inverter-fed induction motor drive abstract—direct torque control (dtc) is a control technique in ac drive systems to obtain high performance torque control. the classical dtc drive contains a pair of hysteresis comparators and suffers from variable switching frequency and high torque ripple. these problems can be solved by using space vector depending on the reference torque and flux. in this paper the space vector modulation technique is applied to the three-level %eutral point clamped (%pc) inverter control in the proposed dtc-based induction motor drive system, resulting to a significant reduce of torque ripple. three-level neutral point clamped inverters have been widely used in medium voltage applications. this type of inverters have several advantages over standard two-level vsi, such as greater number of levels in the output voltage waveforms, less harmonic distortion in voltage and current waveforms and lower switching frequencies. this paper emphasizes the derivation of switching states using the space vector pulse width modulation (svpwm) technique. the control scheme is implemented using matlab/simulink. experimental results using dspace validate the steady-state and the dynamic performance of the proposed control strategy. keywordsdirect torque control; nutral point clamped(�pc); space vector pulse width modulation (svpwm); three-level inverter i. introduction the direct torque control (dtc) method has emerged as an alternative to field oriented control (foc) method for high performance ac drives since it was firstly proposed in the mid1980 [1-2]. the merits of dtc are fast torque response, simple structure (no need of complicated coordinate transformation, current regulation or modulation block), and robustness against motor parameter variation [3-7]. on the other hand, multi-level inverters have become a very attractive solution for high power application areas [8-11]. the three-level neutral point clamped (npc) inverter is one of the most commonly used multi-level inverter topologies in high power ac drives. by comparing to the standard two-level inverter, the three-level inverter presents its superiority in terms of lower stress across the semiconductors, lower voltage distortion, less harmonic content and lower switching frequency [12]. due to the above mentioned merits, the threelevel inverter fed dtc motor drive has become an important research topic in research and academic community over the past decade [13-21]. a variety of techniques have been proposed to overcome some of the drawbacks present in dtc [22]. some solution proposed are: dtc with the space vector pulse width modulation (svpwm)) [23]; the use of a duty-ratio controller to introduce a modulation between active vectors chosen from the look-up table and the zero vectors [24-25]; use of artificial intelligence techniques, such as neuro-fuzzy controller with svpwm [26-28]. however, the complexity of the control is considerably increased. among various modulation techniques for a multi-level inverter, svpwm is an attractive candidate due to the following merits. it directly uses the control variable given by the control system and identifies each switching vector as a point in complex space. it is suitable for digital signal processor (dsp) implementation and able to optimize switching sequences. in this paper, direct torque control-space vector modulation (dtc-svm) with three-level npc voltage source inverter is investigated. the proposed scheme is described clearly. simulation and experimental results are reported to demonstrate its effectiveness. the entire control scheme is implemented using matlab/simulink and hardware realization is done using dspace. the simulation and experimental results of the proposed scheme are found to be in close agreement, thereby indicating the feasibility of the proposed scheme in giving fast control of the induction motor torque. ii. induction motor model the dynamic model of an induction motor in the stationary reference frame can be written in d-q frame variables. stator voltage vector s v of the motor can be expressed as follows: dss ds ds ir dt d v += ψ (1) manoj kumar sahu associate professor, hod department of eee hi-tech college of engineering bput, odisha, india manojsahu.bls@gmail.com anup kumar panda professor department of ee nit rourkela, odisha, india, akpanda.ee@gmail.com bibhu prasad panigrahi professor , hod department of ee igit sarang, odisha, india bibhu89@yahoo.com etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 201-208 202 www.etasr.com sahu et al: direct torque control for three-level �eutral point clamped inverter-fed induction motor… qss qs qs ir dt d v += ψ (2) ss s s ir dt d v += ψ (3) τhe stator flux vector s ψ and components can be written as drmdssds ilil +=ψ (4) qrmqssqs ilil +=ψ (5) rmsss ilil +=ψ (6) the rotor flux vector r ψ and components in the stator reference frame is dsmdrrdr ilil +=ψ (7) qsmqrrqr ilil +=ψ (8) smrrr ilil +=ψ (9) where ds v and qs v are the stator voltages; ds i and qs i are the stator currents; dr i and qr i are the rotor currents; ds ψ and qs ψ are the stator fluxes; dr ψ and qr ψ are the rotor fluxes; si and ri are the stator and rotor currents vectors; sr is the stator winding resistance., and mrs lll ,, are stator, rotor self inductance and mutual inductance respectively. the electromagnetic torque e t developed by the induction motor in terms of stator and rotor flux vectors can be expressed as rs rs m e ll l pt ψψ σ ×= 2 3 rs rs m ll l p ψψ σ ×= 2 3 )sin( 2 3 rsrs rs m ll l p ρρψψ σ −×= )sin( 2 3 δψψ σ rs rs m ll l p= (10) where rs m ll l 2 1−=σ is the leakage factor ; p is the number of pole pairs; rs ρρ , are stator and rotor flux angles, respectively, and δ is the torque angle. from the above equation, clearly, the electromagnetic torque is cross vector product between the stator and rotor flux vectors. therefore, generally torque control can be performed by controlling torque angle δ with constant amplitude of the stator and rotor fluxes. an induction motor model is then used to predict the voltage required to drive the torque and flux to the reference values within a fixed time period. the required voltage is synthesized using space vector modulation. if the inverter is not capable of generating the required voltage, a voltage vector that will drive the torque and flux towards the reference values is used. these above fundamental equations with other equations and svpwm switching states are used for implementing dtc using svpwm in three-phase induction motor. a block diagram of this configuration is shown in figure 1. fig. 1. dtc using space vector modulation block diagram iii. generation of space vector pwm signals for dtcsvm three-level npc inverter fig. 2. three-level neutral point clamped inverter figure 2 shows the diagram of three-level neutral point clamped inverter. the operating status of the switches in the npc inverter can be represented by the switching states shown in table 1. in case of a two-level inverter there are a total of eight switching-states (six result into active vectors and two result into zero vector). the number of switching states for nlevel npc inverter is given by number of switching-states 3 n= (11) hence, in case of a three-level npc inverter, there are 27 switching-states and among them, three result in zero vector and 24 result in non-zero (active) vectors. each switching state (combination of phase/leg switches) produces a defined set of three-phase voltages (eventually, voltage space vector), which etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 201-208 203 www.etasr.com sahu et al: direct torque control for three-level �eutral point clamped inverter-fed induction motor… can be represented in a hexagon form. the svpwm method is an advanced, computation intensive pwm method and is possibly the best among all the known pwm techniques for variable-frequency drive applications. table i. switch states of a three-level npc inverter switch states s1 s2 s3 s4 output voltage on on off off +1/2 vs off on on off 0 off off on on -1/2vs the principle of the svpwm method is that the command voltage vector is approximately calculated by using three adjacent vectors. the duration of each voltage vectors obtained by vector calculations: * 332211 vtvtvtvt s =++ (12) s tttt =++ 321 (13) where 21 ,vv and 3 v are vectors that define the triangle region in which * v is located. 21 ,tt and 3 t are the corresponding vector durations and s t is the sampling time. in a three level inverter similar to a two-level inverter, each space vector diagram is divided into 6 sectors. for simplicity here only the switching patterns for sector a will be defined so that calculation procedure for the other sector will be similar. sector a is divided into 4 regions as shown in figure 3a, where all the possible switching states for each region are given as well. svpwm for three level inverter can be implemented by using the steps of sector determination, determination of the region in the sector, calculating the switching times ta, tb,tc and finding the switching states. iv. design steps for svpwm generation a. determining the sector α is calculated and then the sector, in which the command vector * v is located can be calculated as: if α is between 00 600 <≤ α , then * v will be in sector a, if α is between 00 12060 <≤ α , then * v will be in sector b, if α is between 00 180120 <≤ α , then * v will be in sector c, if α is between 00 240180 <≤ α , then * v will be in sector d, if α is between 00 300240 <≤ α , then * v will be in sector e, if α is between 00 360300 <≤ α , then * v will be in sector f. determining the region in the sector: for that: (a) (b) fig. 3. space vector diagram for m1 and m2 in sector a. from figure 3b 2 m and 1 m can be calculated as, α π sin.. 3 2 3 2 ) 3 sin( 2 n mb b ma ==== (14) ) 3 cos()sin.. 3 2 (cos. 1 π αα nn mmm −= (15) ) 3 sin (cos 1 α α −= n mm (16) from 1 m and 2 m we found, if 21 ,mm and 5.0)( 21 <+ mm , then * v is in region 1, if 5.0 1 >m , then * v is in region 2, if 5.0 2 >m , then * v is in region 3, if 1 m and 5.0 2 <m and 5.0)( 21 >+ mm , then * v is in region 4, calculating the switching times, ta, tb, tc: ta, tb, tc switching times for sector a is given in table 2. etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 201-208 204 www.etasr.com sahu et al: direct torque control for three-level �eutral point clamped inverter-fed induction motor… table ii. switching times for the sector region i region ii ta 1.1*m*ts*sin((π/3)-α) ts(1-1.1*m*sin(�+π/3)) tb ts/2(1-(2*1.1*sin(�+π/3)) 1.1*ts*m*sin� tc 1.1*ts*sin� ts/2((2*1.1*m*sin(π/3-�))-1) region iii region iv ta ts/2(1-2*1.1*m*sin�) ts/2(2*1.1*m*sin(�)-1) tb ts/2(2*1.1*m*sin((π/3) +�)-1) 1.1*m*ts*sin((π/3)-�) tc ts/2(1+2*1.1*m*sin(�-(π/3)) ts(1-(1.1*m*sin(�+π/3)) b. finding the switching states by considering the switching transition of only one device at any time, the switching orders given below are obtained for each region located in sector a if all switching states in each region are used. so, the switching signals for sector a are: region 1: -1-1-1,0-1-1,00-1,000,100,110,111 region 2: 0-1-1,1-1-1,10-1,100 region 3: 0-1-1,1-1-1,10-1,100,110 region 4: 00-1,10-1,11-1,110 1 represents for +vs / 2 and -1 for –vs / 2 and 0 represents for 0 state. fig. 4. switching signals of sector a in region 1 fig. 5. switching sequence for three-level svpwm inverter figure 4 represents the switching signals of sector a in region 1. in a similar method switching signals of other sectors can be calculated. the complete 27 switching sequence for three-level svpwm inverter is shown in figure 5. v. simulation and experimental result with discussion fig. 6. block diagram of the experimental set up. the experimental setup of the proposed control system is represented by the block diagram shown in figure 6. it consists of a dspace ds1104 controller board with tms320lf2407 slave processor, adc interface board cp1104, a four pole induction motor with its parameters listed in appendix. a three-phase vsi inverter is connected to the supply 300v dc bus voltage, with a switching frequency of 5khz .the ds1104 board is installed in pentium iv 1.5 ghz pc for software development and results visualization. the control program is written in matlab/simulink real time interface with sampling time of 100 µs. the experimental results are illustraed in figures 7, 8 and 9. etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 201-208 205 www.etasr.com sahu et al: direct torque control for three-level �eutral point clamped inverter-fed induction motor… fig. 7. experimental results: stator line voltage and current (three-level scheme). fig. 8. experimental results: reference and actual torques (three-level scheme). fig. 9. experimental results: steady-state stator flux (three-level scheme) 0 .1 .2 .3 .4 .5 -300 -200 -100 0 100 200 300 fig. 10. simulation results: stator line voltage (two-level scheme). 0 .1 .2 .3 .4 .5 -300 -200 -100 0 100 200 300 fig. 11. simulation results: stator line voltage (three-level scheme). 0 .1 .2 .3 .4 .5 -40 -20 0 20 40 fig. 12. simulation results: stator current (two-level scheme) 0 .1 .2 .3 .4 .5 -60 -40 -20 0 20 40 60 fig. 13. simulation results: stator current (three-level scheme). 0 .1 .2 .3 .4 .5 0 0.1 0.2 0.3 0.4 0.5 fig. 14. simulation results: stator flux (two-level scheme). etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 201-208 206 www.etasr.com sahu et al: direct torque control for three-level �eutral point clamped inverter-fed induction motor… 0 .1 .2 .3 .4 .5 0 0.2 0.4 0.6 fig. 15. simulation results: stator flux (three-level scheme). 0 .1 .2 .3 .4 .5 -5 0 5 10 15 20 developed torque reference torque fig. 16. simulation results: developed torque and reference torque (twolevelscheme). 0 .1 .2 .3 .4 .5 -20 0 20 40 60 80 developed torque reference torque fig. 17. simulation results: developed torque and reference torque (threelevelscheme). fig. 18. steady-state stator d-q axis flux locus (two-level scheme). fig. 19. steady-state stator d-q axis flux locus (three-level scheme). the dtc schemes were simulated using the matlab/simulink environment and the simulation results were found to be in agreement with the experimental results. figure 10 represents the stator line voltage of two-level classical dtc and figure 11 represents the line voltage of three-level svm-dtc. the percentage of thd of stator line voltage of two-level dtc is 106.12% and that of three-level dtc is 34.48%. figure 12 and figure 13 represent the stator current of two-level and three-level dtc respectively. the percentage of thd of stator current in two-level scheme is 58.12% and that of three-level is 28.09%. during transient study of stator current (two-level), current was zero up to 0.01 second. at 0.01 second, current suddenly rises to 35 a and then decreases to -30 a and come to steady-state at 0.05 seconds. in three-level dtc , there is no current zero state but initially stator transient current rises to 60 a then come to steady-state at 0.1 second and flows smoothly. figure 14 and figure 15 shows the stator flux of two-level and three-level schemes respectively. flux ripple of two-level is 0.03 wb and that of three-level is 0.02 wb under steady-state operation. figure 16 and figure 17 represent the torque response of two and threelevel schemes respectively. the reference torque is taken as 10 nm. the step rise in torque command is from 0% to 100% of rated torque (10 nm). the torque ripple for two-level schemes is found to be 13 nm and that of three-level scheme is 7.5 nm under steady-state operation. figure 18 represents the steadystate stator d-q axis flux locus for two-level inverter and figure 19 represents for three-level inverter. the stator d-q axis flux locus in the three-level scheme is more uniform compared to the two-level scheme. dtc-svm with three-level inverter gives lower thd of voltage and current and reduced ripple in flux and torque compared to the classical two-level dtc. therefore, it can be concluded that the dtc-svm with threelevel inverter gives better results than classical two-level dtc in all aspects. vi. conclusion this paper has reviewed different dtc strategies for pwm inverter-fed ac motor drives. the dtc represents a viable alternative to foc, another general philosophy for controlling etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 201-208 207 www.etasr.com sahu et al: direct torque control for three-level �eutral point clamped inverter-fed induction motor… ac drives. the main features of dtc can be summarized as follows: • according to adopted definition, dtc operates with closed torque and flux loops but without current controllers • dtc needs stator flux and torque estimation and therefore, is not sensitive to rotor parameters • dtc has fast dynamic response, • dtc has simple and robust control structure; however, the performance of dtc strongly depends on estimation accuracy of the stator flux and motor torque. dtc strategies using space vector modulation technique with detailed generation of space vector modulating signals have been discussed. constant switching frequency svpwm dtc schemes considerably improve the drive performance in terms of reduced torque and flux pulsations, reliable start up, well-defined harmonic spectrum and radiated noise. therefore, svpwm-dtc is an excellent solution for general purpose im drives in a very wide power range. the short sampling time required by the switching table dtc schemes makes them suited to very fast torque and flux controlled drives in spite of the simplicity of the control algorithm. in conclusion, it is believed that the dtc principle will continue to play a strategic role in the development of high performance drives. appendix induction motor rating and parameters (referred to stator) power 1.5 kw voltage(l-l) 415 v current 2.6 a frequency 50 hz rated torque 10 nm speed 1415 rpm stator resistance (rs) 0.55 ω rotor resistance (rr) 0.78 ω stator leakage inductance (lls) 0.00288h rotor leakage inductance (llr) 0.00286h mutual inductance between 0.0905h stator and rotor (lm) moment of inertia (j) 0.019kg-m 2 number of poles 4 front-end converter parameters input supply phase voltage 145 v(rms), 3 ph, 50 hz dc link voltage 300v synchronous link inductor 8.0 mh dc link capacitor c1 = c2 2200µf references [1] i. takahashi, t. noguchi, “a new quick-response and highefficiency control-strategy of an 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[18] y. zhang, j. zhu, z. zhao, w. xu, d. g. dorrell, “an improved direct torque control for three-level inverter-fed induction motor sensorless etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 201-208 208 www.etasr.com sahu et al: direct torque control for three-level �eutral point clamped inverter-fed induction motor… drive”, ieee transactions on power electronics, vol. 27, no. 3, pp. 1502-1513, 2012. [19] y. zhang, z. zhao, w. xu, d. g. dorrell, “speed sensorless direct torque control of 3-level inverter-fed induction motor drive based on optimized switching table”, in industrial electronics society, 2009. iecon’ 09. the 35 th annual conference of the ieee, pp. 1318-1323, 2009. [20] a. sapin, p. k. steamer, j. j. simond, “ modeling simulation and test of a three-level voltage-source-inverter with output lc filter and direct torque control”, ieee transactions on industry applications, vol. 43, no. 2, pp. 469-475, 2007. [21] y. zhang, z. jhao, t. lu, l. yuan, “ sensorless three-level inverter –fed induction motor drive based on indirect torque control”, in proc. ieee 6 th international power electronics and motion control conference ipemc’ 09, pp. 589-593, 2009. [22] g. buja, m. p. kazmierkowski, “direct torque control of pwm inverterfed ac motora survey”, ieee transactions on industrial electronics, vol. 51. no. 4, pp. 744-757, 2004. [23] t. g. habetler, f. profumo, m. pastorelli, l. tolbrt, “ direct torque control of induction machines using space vector modulation”, ieee transaction on industry applications, vol. 28, no. 5, pp. 1045-1053, 1992. [24] j. l. romeral, a. arias, e. aldabas, m. g. jayne, “novel direct torque control(dtc) scheme with fuzzy adaptive torque ripple reduction”, ieee transactions on industrial electronics, vol. 50, no. 3, pp. 487492, 2003. [25] i. g. bird, h. zelaya de la parra, “fuzzy logic torque ripple reduction for dtc based ac drives”, electronics letter, vol. 33, no. 17, pp. 1501-1502, 1997. [26] j. kang, s. sul, “new direct torque control of induction motor for minimum torque ripple and constant switching frequency”, ieee transactions on industrial electronics, vol. 35, no. 5, pp. 1076-1082, 1999. [27] suresh. mikkili, a. k. panda, “shaf for mitigation of current harmonics using p-q method with pi and fuzzy controllers”, engineering, technology & applied science research, vol. 1, no. 4, pp. 98-104, 2011. [28] a. gupta, a. m. khambadkone, “a space vector pwm scheme for multilevel inverters based on two-level space vector pwm”, ieee transactions on industrial electronics, vol. 53, no. 5, pp. 1631–1639, 2006. authors profile manoj kumar sahu was born in 1975, he received a b.e. degree in electrical engineering from university college of engineering (at present vssut university), burla, sambalpur university, india in 1997. he received the m.tech (power electronics and drives) from kiit university, bhubaneswar, india in 2007. at present, he is continuing his ph.d. in electrical engineering at utkal university, india, and holds the position of associate professor and hod at hi-tech college of engineering under biju pattnaik university and technology (bput), rourkela, india. he has fifteen years of experience in teaching and research. he has published over ten research papers in various journals and conferences proceedings. his research interests include electrical machines, power electronics, electrical drives and power systems. anup kumar panda was born in 1964, he received a bsc. degree in electrical engineering from the university college of engineering (at present vssut university), burla, sambalpur university, india in 1987. he received a m.tech (power electronics and drives) from the indian institute of technology, kharagpur, india in 1993 and a ph.d. in 2001 from utkal university. he has twenty five years of experience in teaching and research. he has published over forty five articles in journals and conferences. at present he is continuing as a professor in the department of electrical engineering at the national institute of technology, rourkela. his research interests include power electronics, power quality improvements in power system and electrical drives. bibhu prasad panigrahi was born in 1968, he received a b.sc. degree in electrical engineering from the university college of engineering (at present vssut university), burla, sambalpur university, india in 1989 and a m.tech. (power electronics and power systems) from the indian institute of technology, bombay, india in 1997. he obtained his ph.d. degree in electrical engineering from the indian institute of technology, kharagpur in 2007. he has twenty three years of experience in teaching and research. at present he is continuing as professor and hod in electrical engineering department at indira gandhi institute of technology, sarang, dhenkanal, india. he has published over thirty research papers in various journals and conferences proceedings. his research interest includes electrical machines, power electronics, electrical drives and power systems. microsoft word 10-727-ed.doc engineering, technology & applied science research vol. 6, no. 3, 2016, 1023-1028 1023 www.etasr.com elashmawy et al.: investigation of the effect of pipeline size on the cross flow injection process investigation of the effect of pipeline size on the cross flow injection process mohamed elashmawy dpt of mechanical engineering, university of hail, saudi arabia and dpt of engineering science, suez university, egypt arafat_696@yahoo.com abdulaziz alghamdi mechanical engineering engineering college university of hail saudi arabia a.alghamdi@uoh.edu.sa isam badawi mechanical engineering engineering college university of hail saudi arabia isam149@gmail.com abstract—injection pumps constitute an essential component for many industrial applications. the main focus of this study is to predict the effect of the size of the pipeline on the cross flow injection process. a test-rig was designed, built and equipped with three different pipelines, 1½", ¾" and ½" diameters. comparison was made under constant line pressure of 40-bar and line flow rate of 5 liter/min, with a fixed injection pump rotational speed of 100 rpm. the main parameter tested was the injection dose capacity at different pump displacements. cross flow mixing process is also theoretically studied using 3d-cfd analysis to show the injection cross flow behavior for the same geometry and parameters used for experimental test. results show that increasing the size of the pipeline increases injection pump doses ability. this effect is insignificant at lower injection pump displacements, while the effect of the size of the pipeline becomes dominant when increasing the displacement. by changing the size of the pipeline from ½" to 1½" diameter injection pump dose capacity increases by 3.24% at 100% pump displacement. selecting larger pipe sizes for injection ports is recommended whenever possible. keywordsinjection; mixing; cross-flow; cfd; receprocating i. introduction injection technology is essential for many industrial processes. the most widely used type is the diaphragm injection pump unit due to its simple and compact low cost design. diaphragm pumps have many problems related to their diaphragm material and electro-magnetic core. the membrane (diaphragm) is aggressively subjected to cyclic fatigue and high stresses at certain points which cause material failure within a relatively short time period. the different behavior in pumping speed and ultimate pressure of rotational speed controlled diaphragm pumps in comparison to constant-speed pumps is related to the mechanical properties of the valves and gas dynamics [1]. driving of the injection metering pumps could be hydraulically actuated, air/gas driven, electric/engine or power impelled. diaphragm pumps are normally operated by a heavy-duty gear reducer system for superior performance. hydraulically actuated diaphragm minimizes diaphragm fatigue. in case of a very low injection doses requirement micro injection pumps should be used. the parameters of the micro valveless pump were theoretically and experimentally investigated. results provide a useful reference for structure optimization of the micro valveless pump driving diaphragm [2]. the weak component of a pneumatic diaphragm pumps is its diaphragm material which govern the pump lifetime [3]. a developed inexpensive 6-bar flow system was introduced based on a low-cost diaphragm pump [4]. in order to satisfy high pressure injection applications, a piston pump unit should be used. piston pumps satisfy high volumetric efficiency due to a tight gap space between piston and cylinder [5]. another application concerning the mixing process is the t-junction used for cooling systems. in [6], authors studied the turbulent jet mechanics stating an optimum tee mixing condition. the study results show the importance of using the 90o bend after mixing pipe. the momentum ratio of the main and the branch velocities of the t-junction is also an important parameter. in [7], authors studied the mixing mechanism of the t-junction with the 90o bend. a visualization study was performed using a test rig having three sections, for separated visualization using particle image velocimetry. the three main mixing regions were clearly visualized. the strongest region having high cycle thermal fatigue was found near the downstream of wake region. in [8], authors studied the momentum ratio for general angled t-junctions using cfd simulation. the study shows the importance of cross flow angle parameter on increasing the velocity ratio which is an important parameter to enhance the design of pipeline systems. the main parameter in focus of the present study is the effect of the pipeline size on the performance of the injection process. an experimental test section was built of 3-different pipe sizes with a possibility to use each pipeline separately. a 3d-cfd study was also performed for the same three pipelines for comparison and evaluation of mixing process behavior based on velocity and pressure distribution within the mixing region. ii. experimental setup a high pressure water closed circuit test-rig is designed and schematically shown in figure 1. the test-rig is equipped with three different pipelines (½", ¾" and 1½") with possibility of engineering, technology & applied science research vol. 6, no. 3, 2016, 1023-1028 1024 www.etasr.com elashmawy et al.: investigation of the effect of pipeline size on the cross flow injection process operating each pipeline separately. injection pump used is the variable displacement reciprocating injection pump (vdrip), app. a steel pipelines according to ansi schedule 40 are used. fig. 1. schematic diagram of the test-rig. each pipeline is operated separately and engaged to the test-rig by means of combination of a high pressure valves. as shown in figure 1, there are three modes of valves: mode i: gv1 valve is closed; cv1 valve controls the flow in the ½" line. mode ii: gv1 valve is opened; gv2& cv1 are closed; cv2 controls the flow in the ¾" line. mode iii: gv1 and gv2 valves are opened while cv1 and cv2 are closed; cv3 controls the flow in the 1½" line. the injection port of the engaged line is connected to the injection pump (vdrip) and the other two injection ports are closed using a blind stop. vdrip is driven using a dc electric motor selected from the available automotive industry market "chp 12v 42w" [9]. an electronic regulator with an adjustable pulse width modulation (pwm) controller is used to control the speed of the vdrip which is measured using a laser rotational speed measuring instrument. an electric 3phase motor of 7.5 hp with a full speed of 3400 rpm at 60-hz is used. the motor speed is controlled using a 10 hp, 3-phase frequency inverter adjusted at 26.5 hz output (1505 rpm, 5 liter/min). iii. experimental results and discussion all experimental measurements were performed at a constant line flow rate (5 liter/min), constant line pressure (40bar), and constant vdrip rotational speed (100 rpm). figure 2 shows the effect of the size of the pipeline on the injection capacity for different pump displacements. the difference between ½" and ¾" pipelines show an insignificant effect with a slight enhancement of the injection quantity for the ¾" pipeline. increasing the pipe diameter up to 1½" enhances the injection capacity by a relatively significant percentage (3.24% relative to ½" pipeline size). the effect of the size of the pipeline becomes more significant when increasing the displacement of the injection pump. increasing the size of the pipeline enhances the injection percentage by very small quantities for low pump displacements and becomes negligible for very low injection displacement. significant enhancement occurs at higher displacements and maximizes at 100% pump displacement. figure 3 shows the effect of the size of the pipeline on the injection fluid power required to drive the injection process. increasing the size of the pipeline increases the demand of the injection fluid power at the same conditions of 40-bar pressure and 100 rpm rotational speed. this result indicates an enhancement of injection process volumetric efficiency due to increasing the size of the pipeline. figure 4 illustrates the effect of the size of the pipeline on the injection capacity and injection fluid power at the maximum pump displacement. the maximum increase of the injection capacity as well as injection fluid power (3.24%) is achieved when increasing the line size from ½" to 1½" (ainj/aline from 0.99 to 6.66) with 100% vdrip displacement, while this increase is limited to 0.71% when increasing the line size from ½" to ¾" (ainj/aline from 0.99 to 3.81) with 100% displacement. this result indicates a significant enhancement of the volumetric efficiency of the vdrip. figure 5 shows the effect of the size of the pipeline on the injection capacity and the injection fluid power at 50% of pump displacement. the injection capacity as well as the injection fluid power both are increased by 1.34% when increasing the size from ½" to 1½" (ainj/aline from 0.99 to 6.66), while this increase is limited to only 0.45% when increasing the size from ½" to ¾" (ainj/aline from 0.99 to 3.81). fig. 2. effect of the size of the pipeline on injection capacity for different vdrip displacements. fig. 3. effect of the size of the pipeline on injection fluid power for different vdrip displacements. engineering, technology & applied science research vol. 6, no. 3, 2016, 1023-1028 1025 www.etasr.com elashmawy et al.: investigation of the effect of pipeline size on the cross flow injection process fig. 4. effect of the size of the pipeline on the injection capacity and the injection fluid power at 100% vdrip displacement. fig. 5. effect of the size of the pipeline on the injection capacity and the injection fluid power at 50% vdrip displacement. iv. 3d-cfd simulation 3d-cfd ansys fluent simulation was performed using the same 3 different pipeline geometries (figure 6). because both line and injection streams are of water at the same initial temperatures, the mixing process is assumed to be isothermal. pipe wall roughness is typically taken as 40 μm for commercial steel pipe material. line flow is constant (5 liter/min) for all line pipes. turbulent flow regime is considered using k-ε model for the three pipelines (½", ¾", and 1½") where reynolds numbers are red=8600, 6500, and 3500 respectively. also, injection flow is turbulent (red=3570). the 3d-cfd analysis was performed for steady state taking the maximum instant injection flow as constant while in reality it was unsteady due to reciprocating single piston pump operation. the boundary conditions are: inlet mass flow rate = 0.08333 kg/s, injection mass flow rate = 0.008333 kg/s, isothermal temperature = 300k, mixture exit pressure = 40bar. the ansys fluent default meshing was used with inflation on the pipe and injection port surfaces, the mesh size was changed and results were compared until results reach stable and symmetry contours. the maximum number of nodes and elements was 124,670 and 386,467 respectively. figure 7 shows the effect of the cross flow injection on the velocity distribution within the mixing region along pipe centerline (x-axis) for the three pipe sizes. results show that increasing pipe diameter from ½" to ¾" slightly enhances velocity distribution and the velocity curve tends to be flatter after mixing region. whoever increasing pipe diameter to 1½" strongly enhances velocity distribution, the velocity curve is almost constant starting from short distance after mixing region. 1½" pipe size satisfies the lowest velocity fluctuations after injection port which indicates best mixing conditions due to lowest wake region compared to ½" and ¾" pipe sizes. figure 8 shows the effect of the cross flow injection on the static pressure difference distribution within the mixing region along pipe centerline (x-axis) for the three pipe sizes. increasing pipe diameter from ½" to ¾" slightly enhances pressure difference distribution. difference between maximum and minimum pressures was achieved at the injection zone and was 55 pa for ½" pipe while reduced to 32 pa for ¾" pipe. whoever using 1½" pipe strongly enhances and reduces the pressure difference to 9.5 pa. after the injection port (from x=0.03 to 0.2 m), the pressure difference was 50 pa, 17 pa, and 0.8 pa for ½", ¾" and 1½" pipes respectively. 1½" pipe size satisfies the lowest pressure difference required for flow at the lowest disturbance conditions. figure 9 shows the stream lines of the three pipe sizes. the lower part of the figure shows separated injection stream lines in order to focus on the behavior of the injection flow streams along the mixing region. the behavior of the stream lines show that the effect of pipe size for 1½" pipe injection stream lines is limited in narrow distance after injection port. while for ½" and ¾" pipes takes much longer distance to get fully mixed. figure 10 shows the velocity contours of the three pipe sizes. the upper contours show a velocity contours of the x-y plane at the centerline of the pipe (z=0) which certify the results achieved by stream lines insight. injection effect of ½" pipe is the strongest one and takes the longest distance before achieving complete mixing conditions. the ¾" pipe takes a slightly shorter distance, whoever 1½" pipe takes a very short distance to get fully mixed. the three lower contours show the velocity contours of the z-x plane at three different distances from centerline (y = r = 0, y ≈ ⅓ r , and y ≈ ⅔ r where r denotes the pipe radius). the z-x plane contours show clearly the wake region downstream the injection zone, the largest wake zone is achieved for the ½" pipe and then the ¾" pipe while the lowest wake zone is obtained for the 1½" pipe. the results obtained by cfd analysis are consistent with the results obtained by other researchers, [7-8]. fig. 6. schematic diagram of the 3d-cdf test-section x y engineering, technology & applied science research vol. 6, no. 3, 2016, 1023-1028 1026 www.etasr.com elashmawy et al.: investigation of the effect of pipeline size on the cross flow injection process fig. 7. effect of cross flow injection on the line velocity magnitude along x-axis, 3d-cfd ansys fluent analyses fig. 8. effect of cross flow injection on the line pressure difference distribution along x-axis, 3d-cfd ansys fluent analyses fig. 9. stream lines including cross flow injection, 3d-cfd ansys fluent analyses v. conclusions both experimental and theoretical operating conditions were the same. results are limited to 40 bar line pressure due to safety precautions (1½" pipeline was of welded steel with ansi schedule 40). the limitation of the pressure has no effect on the comparison results because all measurements and cfd ansys fluent analysis for all lines were operated under the same pressure (40 bar). moreover constant rotational speed (100 rpm) and constant line flow rate (5 lit/min) are fixed throughout the study. both experimental and theoretical results show that increasing the line size has positive impact on the performance of the cross flow injection process especially at higher pump displacements with significant increase of pipeline sizes. a maximum injection enhancement of 3.24% is achieved when increasing the injected pipeline size from ½" to 1½". the authors recommend designers to choose injection ports at maximum line sizes positions whenever possible. further research efforts are also recommended especially for the following parameters: • expanding the test for higher pressure ranges • studying the effect of line pressure on the performance of the injection process • studying the effect of vdrip displacement on pump volumetric efficiency especially at low displacements to give exact lower displacement limitation for vdrip. engineering, technology & applied science research vol. 6, no. 3, 2016, 1023-1028 1027 www.etasr.com elashmawy et al.: investigation of the effect of pipeline size on the cross flow injection process fig. 10. velocity contours of the cross flow mixing region for the three pipe sizes, 3d-cfd ansys fluent analyses appendix avdrip design aspects figure 11 shows a schematic diagram of the vdrip operating principal, the variable displacement is accomplished by means of a simple mechanical controlled stopper facility. the location of the stopper is driven and controlled by a threaded spindle having a hand-wheel attached to its upper end. controlling displacement is occurred during suction stroke. when the piston reaches the stopper liver it will stop leaving the cam to complete its journey without contacting the piston end. the position where the stopper located will control the suction dose and keep it until the cam hits the piston end again at the start of the delivery stroke and force the dose trapped inside cylinder to be injected to the line. this design requires low rotational speed (satisfied by nature) to avoid serious damages due to cam piston end collisions. figure 12 shows detailed 3d-cad design of the vdrip (a) and a photograph of the realized vdrip (b). fig. 11. schematic diagram of the vdrip principal. fig. 12. a:3d-cad of the vdrip, b: photograph of the realized vdrip. acknowledgment acknowledgments to deanship of scientific research, university of hail, ksa, for funding and supporting this project with code number of “e5-me, 2014” and making it feasible. references [1] r. lachenmann, j. dirscherl, “advanced performance of small diaphragm vacuum pumps through the use of mechatronics”, applied physics a-material science & processing, vol. 78, pp. 671-673, 2004 [2] x. hai-bo, f. xin, y. hua-yong, “effects of structural parameters and rigidity of driving diaphragm on flow characteristics of micro valveless pump”, journal of zhejiang university science, vol. 4 no. 1, pp. 5357, 2003 [3] a. kurteev, “diaphragms for pneumatic pumps, chemical and petroleum engineering”, vol. 47, no. 7-8, pp. 550-556, 2011 [4] a. ratka, h. berndt, “a novel analytical low-cost flow system based on a 0.6 mpa (84 psi) diaphragm pump applied to on-line trace prex y=r a b engineering, technology & applied science research vol. 6, no. 3, 2016, 1023-1028 1028 www.etasr.com elashmawy et al.: investigation of the effect of pipeline size on the cross flow injection process concentration in flame aas and icp-oes”, anal bioanal chem, vol. 375, no. 2, pp. 275-280, 2002 [5] h. murrenhoff, grundlagen der fluidtechnik teil 1: hyraulik. umdruck zur vorlesung, shaker verlag gmbh, germany, 2005 [6] s. m. hosseini, k. yuki, h. hashizume, “classification of turbulent jets in a t-junction area with a 90-deg bend upstream”, int. j. heat mass transfer, vol. 51, no. 9-10, pp. 2444–2454, 2008 [7] s. m. hosseini, k. yuki, h. hashizume, “experimental investigation of flow field structure in mixing tee”, asme j. fluids eng., vol. 131, no. 5, p. 051103, 2009 [8] s. qian, j. frith, n. kasahara, “classification of flow patterns in angled t-junctions for the evaluation of high cycle thermal fatigue”, asme j. pressure vessel technol., vol. 137, no. 2, p. 021301, 2014 [9] bosch, chp 12v 42w dc motor, data sheet, 2016, url:http://www.bosch-ibusiness.com/boaaelmoocs/category/chp/283/ product/681 microsoft word 104-312-2-ed-ed1.doc etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 177-181 177 www.etasr.com subrahmanyam et al: renewable energy systems:development and perspectives of a hybrid … perspectives renewable energy systems: development and perspectives of a hybrid solar-wind system j.b.v. subrahmanyam p. alluvada bandana k. bhanupriya c. shashidhar eee dept bharat institute of engineering &technology india jbvsjnm@gmail.com eee dept bharat institute of engineering &technology india allubiet@gmail.com bharat institute of engineering & technology india bandana.elec@ gmail.com bharat institute of engineering & technology india banukandasamy@ gmail.com bharat institute of engineering & technology india sasidhar_84@ yahoo.co.in abstract— considering the intermittent natural energy resources and the seasonal un-balance, a phtovoltaic-wind hybrid electrical power supply system was developed to accommodate remote locations where a conventional grid connection is inconvenient or expensive. however, the hybrid system can also be applied with grid connection and owners are allowed to sell excessive power back to the electric utility. the proposed set-up consists of a photo-voltaic solar-cell array, a mast mounted wind generator, lead-acid storage batteries, an inverter unit to convert dc to ac, electrical lighting loads, electrical heating loads, several fuse and junction boxes and associated wiring, and test instruments for measuring voltages, currents, power factors, and harmonic contamination data throughout the system. the proposed hybrid solar-wind power generating system can be extensively used to illustrate electrical concepts in hands-on laboratories and also for demonstrations in the industrial technology curriculum. this paper describes an analysis of local pv-wind hybrid systems for supplying electricity to a private house, farmhouse or small company with electrical power depending on the site needs. the major system components, work principle and specific working condition are presented. keywordssolar power; wind power; hybrid generation; renewable energy; grid i. introduction energy plays an important role in all types of development, including economic development. the world total energy annual consumption generally increases, with the vast majority of energy being produced by fossil fuels such as coal, oil and natural gas. in 2002 fossil fuels provided the three quarters of the total. with the current energy consumption rate, proven coal reserves should last for about 200 years, oil for approximately 40 years and natural gas for around 60 years. with constantly increasing development, diminishing fossil fuel resources and related environmental problems (e.g. emissions), sustainable development and the manner in which energy is produced and consumed is reconsidered. renewable energy [1], i.e., energy generated from solar, wind, biomass, geo-thermal, hydropower and ocean resources, could increase the diversity of energy supplies and offer “clean”-environmental friendly energy. although wind and solar energy sources are significantly less productive compared to fossil fuels, the use of photovoltaic (pv) cells and wind turbines [2] has increased rapidly during the last years, especially in developed countries. photovoltaic (pv) cells are electronic devices that are based on semiconductor technology and can produce an electric current directly from sunlight. the best silicon pv modules currently commercially available have an efficiency of over 18%, and it is expected that in about 10 years’ time module efficiencies may rise to 25%. wind power is basically electricity produced by a generator, which is driven by a turbine according to flowing air’s aerodynamics, and is one of the fastest growing renewable energy technologies around the world. pv modules and wind turbines [3] are now widely used in developed countries to produce electrical power in locations where it might be inconvenient or expensive to use conventional grid supplies, while other homeowners who choose the renewable energy sources prefer to connect their energy system to the grid as a huge ‘battery’ for some convenient grid-tied situation. however, when electricity grids are non-existent or rudimentary, all forms of energy can prove very expensive. in such cases, solar and wind energy can be highly competitive. the fact that natural energy resources are intermittent and storage batteries are expensive, has led to the utilization of so-called hybrid renewable energy systems. any power system that incorporates two or more of the following is referred to as a hybrid power system: pv panels, wind turbines, or diesel, propane, gasoline generators. for small loads, the most common combinations [4] are pv-wind hybrid system. etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 177-181 178 www.etasr.com subrahmanyam et al: renewable energy systems:development and perspectives of a hybrid … pv and wind is a good match, because inland wind speeds tend to be lower in summer, when solar energy can compensate, and higher in winter, when sunshine falls to very low levels. in this paper, a pv-wind hybrid system is presented able to supply electricity to a private house, farm house or a small company or an apartment, with electrical power depending on the site’s needs. the aim of this study is to introduce the local pv-wind hybrid system’s working principle by reviewing one case where the system is connected to the grid. a. special issues of wind turbines and pv cells as both wind and solar energy sources are inconsistent and non-stable. hybridizing solar and wind power sources together with storage batteries to cover the periods of time without sun or wind provides a stable form of power generation. however, the variable features, especially in the case of wind power, constitute a significant difference to the conventional fossil fuel, nuclear or hydro-based power generation. even so, wind energy is currently the least expensive renewable energy technology. photovoltaic or pv cells, known commonly as solar cells, convert the energy from sunlight into dc electricity. pvs offer added advantages over other renewable energy sources in that they give off no noise and require insignificant maintenance. although solar energy is well known to students (e.g. found on most calculators), their operating principles and governing relationships are unfortunately not as pedagogically simple as that of wind-turbines. however, they operate using the same semiconductor principles that govern diodes and transistors. the explanation of their functioning is straightforward and may even help many of the principles covered in semiconductor electronic classes to become more intuitive. wind-turbines and pv cells provide dc but most industrial uses of electricity require ac power. a semiconductor-based device known as a power inverter is used to convert the dc to ac. this device has a relatively simple operation and is a vivid illustration of many topics traditionally covered in power electronics classes. ii. system analysis a. specific site conditions for pv-wind hybrid system intermittent and seasonally unbalanced natural energy resources are the most important reason to install a hybrid energy system. the pv-wind hybrid system suits to conditions where sun light and wind has seasonal shifts i.e., in summer the daytime is long and sun light is strong enough, while in winter the days are shorter and there are more clouds, but there is usually an increased wind resource that can complement the solar resource. the pv-wind hybrid systems especially suit remote locations, where it is inconvenient or expensive to use conventional grid supplies. for the pv array, a direction without any obstacles facing the sun is needed. for the wind turbine, appropriate wind speed and wind direction are the key elements. the turbine should be subjected to non-turbulent wind and mounted higher than trees and other obstacles. b. system components in general, a local cost-efficient, safe, and durable pv-wind hybrid system is composed of the core part (pv modules and wind turbine), the pv modules mounting, the wind turbine tower, the dc-ac inverter, the safety equipment such as fuses, connectors and lighting arrestors, the measuring instruments, the batteries, the charge controller/regulator, the backup power resource for battery storage systems, the connection wires, switches and sockets. pv modules can be wired together to form a pv array. by wiring modules in series the available voltage is increased and by wiring in parallel, the available current is increased. either way, the power produced is the same. a typical pv module has a size of about 0.5 square meters (about 1.5 by 3.5 feet) and produces about 75 watts of dc electricity in full sun. wind turbine works the opposite of a fan. instead of using electricity to create wind, wind turbines use wind to create electricity. most turbines have either two or three blades. these three-bladed wind turbines are operated "upwind," with the blades facing the wind. the other common wind turbine type is the two-bladed, downwind turbine. the wind turns the blades, which spin a shaft, which is connected to a generator and produces electricity. utility-scale turbines range in size from 50 to 750 kilowatts. single small turbines, below 50 kilowatts, are used for homes, telecommunications dishes, or water pumping. dc-ac inverter changes low voltage direct current (dc) power, which is produced by the pv or wind turbine or is stored in the battery, to standard ac which is most commonly 120 or 240 vac, 50 or 60 hertz. the “modern sine wave” inverters supply uninterruptible power, i.e. there are no blackouts or brownouts. such inverters come in sizes from 250 watts to over 8,000 watts. there are also the "modified sine wave" inverters which are cheaper and can handle most household tasks. however, this type of inverters may create a buzz in some electronic equipment and telephones, which can be an annoyance. it should be noted that inverters have made great strides in performance and price in recent years. inverters can also provide a utility inter-tie between the renewable energy system and the utility grid, allowing the selling of excess energy to the utility. many inverters also have built-in battery chargers to keep the batteries topped off from either the grid or your generator. the pv modules mounting can be a ground mount that works either on rooftops or the ground, or pole mount for getting them up in the air. both are angle-adjustable so that pv array will face the sun as near to perpendicular as possible. many owners will adjust their mounting racks two to four times a year to get maximum exposure as the sun changes its angle during seasons. if the rooftop has a good angle to the sun, the modules could be mounted solidly to the roof without an adjustable rack. trackers are another pv mounting option, which are pole mounts that automatically adjust themselves so that the pv faces the sun throughout the day. because the wind turbine should be mounded into non-turbulent wind, a tall enough wind turbine tower is needed (9 m above anything within 120 m). and there should also be enough space to properly anchor the guy wires. etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 177-181 179 www.etasr.com subrahmanyam et al: renewable energy systems:development and perspectives of a hybrid … safety equipment includes over-current and lightning protection components. over-current protection components such as fuses and fused disconnectors protect the system's wiring and components in the event of short circuits. fusing protects from over-current situations, and disconnectors allow safe shutdown of system components for maintenance and repair. fuses and fused disconnectors are rated by the amount of current they can handle. they may be as small as a few amperes, in case of measuring instruments, to as large as 400 amperes, in case of the inverter. many renewable energy systems are in areas where thunderstorms and lightning are common. it should be considered that the wind turbine is always the highest building in the remote area. commercial lightning arrestors can be employed to boost protection of the system’s electronics against lightning. measuring instruments can keep track of the battery voltage, the amount of consumed power, the state of battery charge and the electricity traffic between the grid and the renewable energy system, if connected. some instruments have more than one channel to monitor two battery banks or a battery bank and a generating source for the hybrid systems. batteries store electrical energy produced by the renewable energy source in a reversible chemical reaction. most renewable energy systems use lead-acid batteries, typically encased in plastic, wired together in series and parallel strings. battery capacity is rated in amp-hours, with 1 amp-hour is the equivalent of drawing 1 amp steadily for one hour. a typical 12-volt system may have 800 amp-hours of battery capacity. this is the equivalent of 1,200 watts for eight hours if fully discharged and starting from a fully charged state. there are many brands and types of batteries available for renewable energy systems and the two most common batteries are the l16 and golf cart sizes. charge controller/regulator prevents the pv array and wind turbine from over-charging the battery. most modern controllers maintain system voltage regulation electronically by varying the width of dc pulses they send to the batteries (this is called pulse width modulation or pwm). this means the wider the pulse, the more power goes to the batteries. another category is the "shunt type" controllers which divert excess energy into a "shunt load." such controllers are more commonly used in wind or hydro systems, since these systems generally should not be run open circuit. unlike a pv module, most wind and hydro turbines cannot be switched on and off by the controller. a new generation of pv controllers employs "maximum power point tracking." they take advantage of the maximum power available in the module by adjusting both current and voltage. backup power resource can come either from a generator or from the utility grid when too much energy is consumed or when there has not been enough renewable energy coming into the system. however, in case of the hybrid system, the latter situation may be avoided, whereas a suitable energy consuming style might assist to solve the former problem. iii. process of establishing the system the process of establishing the energy supply system (figure 1) is an extremely important step. regardless the nature of the installed system, the calculation of the desired load and the site’s resources ought to be the first step. load analysis lists and adds up all energy consumed by the appliances powered by the system. resource measurement affects the system structure, efficiency, and cost. the design and installation of the system requires both knowledge and experience. fig. 1. steps for establishing a hybrid solar & wind plant a. methodology in order to address the shortcomings of existing instructional techniques for electrical power systems, the system is designed and implemented with the following goals: • to be completely different from systems traditionally employed in electricity labs (in other words, to be fresh and interesting). • to be intimately related to real world industrial power issues such as power quality. • to show a complex, interrelated system that is closer to the “real world” than the usual simple systems employed in educational labs. b. establishment of a wind/pv hybrid unit the hybrid unit contains two complete generating plants, a pv solar cell plant and a wind-turbine system. these sources are connected in parallel to a 120v ac line. the pv panel output is connected to a dc/ac inverter and is then supplied from the inverter’s output to a single-phase, 120 vac load. the overall project structure is presented in figure 2. the dc voltage measured across each pv unit (12 v dc) is shown in figure 3. the wind turbine is installed at the top of a steel tower that has a height of 18.3 meters and a diameter of 8.9 cm. the instrumentation panel depicted monitors the outputs of the generator using digital panel meters. one of the low maintenance features is the turbine’s brush-less alternator and an internal governor. the turbine’s blades are made of a carbon fiber reinforced composite that will intentionally deform as the turbine reaches its rated output. this deformation effect, changes the shape of the blade, causing it to go into a stall mode, thus limiting the rotation speed of the alternator and preventing damage in high kinds. another feature of the wind turbine is a sophisticated internal regulator that periodically checks the line voltage and corrects in case of low voltage conditions. etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 177-181 180 www.etasr.com subrahmanyam et al: renewable energy systems:development and perspectives of a hybrid … fig. 2. a simple hybrid solar & wind system fig. 3. the dc voltage measured across each pv unit (12 v dc) one of the largest problems in systems containing power inverters is power quality. this problem becomes serious if the inverter used in the system does not have a good sinusoidal waveform output and causes problems such as harmonic contamination and poor voltage regulation. according to ieee standards, a maximum of 3 to 4% total harmonic distortion may be allowed from inverter outputs. however, many inverter outputs have much larger harmonic distortion than allowed. to monitor and store the voltage, current, power, and harmonic contamination data, two power quality analyzers (types 39 and 41) are used in this system. in addition, permanently mounted ac/dc digital panel monitors form part of the system’s instrumentation. a laptop computer is interfaced to the system via the power quality analyzers to store data in real-time. voltage sags may cause a crucial damage to high precision measurement and protection devices, especially computer equipment present in many highly automated industrial plants. the ac filter is a circuit made up of a resistor (r), inductor (l), and a capacitor (c). such filters are commonly installed in industrial situations to remedy power quality problems. the inverter is of a six-pulse type and the inverter and the control circuit models are both standard models in the pscad/emtdc software package. iv. future study figure 4 illustrates the future direction of this project. a computer measurement and control bus will be added to the system. computer controlled relays will be added to allow all the major elements of the system to be switched in and out of the system through computer programs. the measurement bus will be connected to all the major signals in the system and will allow simultaneous data acquisition of all the major signals in the system. these improvements will allow the study of more complex issues such as power faults caused by sudden over voltages like lightning. these improvements will also provide similar benefits to electricity and electronics classes and will allow the course to be extended to control and instrumentation classes. fig. 4. block diagram of scope for future research v. conclusions the key element of the concept presented in this paper is that two or more renewable power sources can be connected to a power grid with complex electrical interactions. a complete hybrid power system such as the one described, may be too expensive and too labor intensive for many industrial technology departments. however, many of the mentioned benefits could be gleaned from having some subset of the system, for example a pv panel, batteries, and an inverter, or even just a pv panel and a dc motor. the enhancements to instruction, especially in making electrical power measurements more physical, intuitive, and real-world-like are substantial and the costs and labor involved in some adaptation of the ideas in this paper to a smaller scale setup are reasonable. the use of solar and wind hybrid power generation is an especially vivid and relevant choice for students of electrical technology as these are power sources of growing etasr engineering, technology & applied science research vol. 2, �o. 1, 2012, 177-181 181 www.etasr.com subrahmanyam et al: renewable energy systems:development and perspectives of a hybrid … technological, political, and economic importance. hybrid combinations of wind power, solar power, geothermal power, hydroelectric power, tidal power, biomass generated power, power from incineration of solid wastes, and many other technologies could also be considered depending on local interests and resources. references [1] g. boyle, renewable energy: power for a sustainable future, oxford university press, 2004 [2] y. dayu, local photovoltaic pv wind hybrid systems with battery storage or grid connection, master’s programme in renewable energy technology (physics), eee dept., bharat institute of engineering &technology, hyderabad,india, 2004 [3] g. pepermans, j. driesen, d. haeseldonckx, r. belmans, w. d’haeseleer, “distributed generation: definition, benefits and issues”, energy policy, vol. 33, no. 6, pp. 787–798, 2005 [4] a. m. azmy, i. erlich, “impact of distributed generation on the stability of electrical power systems”, ieee power engineering society general meeting, vol. 2, pp. 1056 – 1063, 2005 microsoft word etasr_v11_n4_pp7332-7335 engineering, technology & applied science research vol. 11, no. 4, 2021, 7332-7335 7332 www.etasr.com nguyen & phan: compressive strength studies on recycled binder concrete compressive strength studies on recycled binder concrete duy duan nguyen department of construction vinh city, vietnam duyduankxd@vinhuni.edu.vn van tien phan department of construction vinh city, vietnam vantienkxd@vinhuni.edu.vn abstract-recycled materials are gradually utilized in concrete. this paper examines the use of recycled binder in concrete. the compressive strength tests on concrete incorporating recycled binder instead of cement were carried out after 7, 14, and 28 days of curing. cement was replaced by the recycled binder in ratios of 10%, 20%, and 30% by weight. the results show that the compressive strength of concrete is strongly affected by the percentage of the recycled binder. it has been found that the compressive strength decreases linearly with the increasing content of recycled binder. the recycled binder does not affect the strength development of concrete. in order to apply recycled waste to concrete as a binder, it is necessary to perform supplement research with appropriate additives to compensate for the loss of the compressive strength. keywords-compressive strength; recycled concrete; fine aggregates i. introduction recycled aggregates can become a new source of material, replacing natural aggregates in concrete [1-3]. authors in [1] examined the use of crushed concrete produced from waste concrete as fine aggregates regarding the modulus of elasticity, pulse velocity, and long-term properties such as drying shrinkage and creep. they found that the detrimental effects of crushed concrete can be mitigated by a partial replacement of crushed concrete fines with pulverized fuel ash. another study replaced fine aggregates in concrete with recycled fine aggregates [2]. the authors found that fine recycled aggregates can be used to up to 10% ratio for producing c30 concrete and between 20-50% ratio for producing c25 concrete. thus, by using recycled fine concrete aggregates in concrete application, environmental impact and consumption of the natural resources can be significantly reduced. the replacement of fine recycled aggregates in concrete had also been investigated in [4-6]. the obtained results indicate that the recycled concretes have a suitable resistant and durable behavior, according to the limits indicated by different international codes for structural concrete [5]. the investigation on using recycled coarse aggregates instead of natural coarse aggregates in concrete has also been carried out by numerous authors [2, 6-10]. authors in [11] investigated the influence of the amount of recycled coarse aggregates on the properties of concrete, in which 4 different recycled aggregate concretes were produced with the same design compressive strength. the ratio of recycled coarse aggregates replacement had been used up to 100% [11]. authors in [12] conducted research on the influence of recycled aggregate types, including unbound stone, crushed concrete, crushed brick, to the properties of concrete [12]. the results showed that the performance of concrete containing each type of recycled aggregates was largely influenced by the aggregate nature and quality, in addition to the attached mortar content. the analysis above shows that using recycled aggregates from demolishing works as coarse and fine aggregates for concrete has been studied extensively. however, to the best of our knowledge, there is no research on the application of recycled aggregates as substitute for the binder, i.e. cement, in concrete. in this paper, an investigation on the compressive strength of concrete with partially replacement of cement with recycled fine aggregates is performed. the results will help understanding more about recycled concrete and may give recommendations for further studies. ii. composition of reycled concrete a. recycled concrete the concrete obtained after the demolition of a project was crushed. the crushed old concrete was then screened with a 0.14mm sieve. the resulting fine-grained mixture is shown in figure 1. fig. 1. recycled fine-grained mixture obtained from crushed old concrete. corresponding author: van tien phan engineering, technology & applied science research vol. 11, no. 4, 2021, 7332-7335 7333 www.etasr.com nguyen & phan: compressive strength studies on recycled binder concrete in order to investigate the influence of the replacement rate of the recycled fine-grained aggregates to the compressive strength of concrete, a reference mixture was selected. cement was then replaced by recycled fine-grained mixture, crushed and screened from old concrete, at various replacement rates, namely 10%, 20%, and 30% by weight. after casting, the samples were stored under normal conditions and were tested for compressive strength at 7, 14, and 28 days of curing. b. sand the sand used in the experiments has the following mechanical properties: • density 2.65g/cm3. • modulus of magnitude 2.50. • volumetric mass 1660kg/m3. c. cement commercial portland cement in vietnam, namely pcb40, with the following mechanical properties was used: • actual strength of cement 40mpa. • density 3.1g/cm3. d. coarse aggregates in this study, 20mm aggregates, the most common size of used in construction, have been used, with the following mechanical properties: • density 2.61g/cm3. • volumetric mass 1430kg/m3. iii. experimental set-up in this test, the push force was applied on both faces of the concrete specimens and the maximum compression that concrete bore without failure was noted (figure 2). cylindrical samples with size d150×h300 were cast and cured in normal conditions before being compressed to determine their compressive strength. the loading speed was set to 0.5kn/s. the replacement rates of cement were 0%, 10%, and 20% of the standard sample (reference sample) respectively. mix components for 1m3 of concrete are presented in table i. table i. mix components for 1m3 of concrete aggregate by mass cement (kg) sand (kg) aggregate (kg) water (kg) 292.5 648.3 1216.3 195.0 aggregate by volume cement (kg) sand (m 3 ) aggregate (m 3 ) water (lt) 292.5 0.391 0.851 195.0 table ii. experimental details of concrete samples no. notation description quantity 1 cp0 reference sample: mixture composition as describe in table i 3 samples for 7 days, 3 samples for 14 days, and 3 samples for 28 days. 2 cp10 cement replacement rate is 10% 3 cp20 cement replacement rate is 20% 4 cp30 cement replacement rate is 30% fig. 2. an in-process experiment (cp20-28 days) and the recorded destructive force. iv. results and discussion the obtained results of the compression tests (sample destructive force) are shown in table iii. from the value of the destructive force p (kn) of each sample, the compressive strength (mpa) is calculated as follows: bearing area: sample diameter is d = 15cm, so: s=π.r2= π. 7.52= 176.71cm2 (1) the compressive strength is then calculated by: r = α . p / s (2) where p is the destructive load of the sample, s is the compressive area (s=176.71cm2), α is the coefficient of converting the experimental results when compressing the samples with different sizes from the standard samples (150×150×150mm). with cylinder sample d150×h300, α = 1.2. table iii. recorded destructive forces no. replacement rate sample destructive force (kn) 7 days 14 days 28 days 1 0 % 171.21 239.11 295.2 2 176.1 225.99 293.5 3 173.51 229.39 294.1 4 10 % 167.09 213.19 288.1 5 163.13 226.09 286.2 6 154.71 219.41 281.3 7 20 % 152.01 199.19 262.1 8 153.04 199.73 259.4 9 151.50 215.29 265.8 10 30 % 153.23 200.96 251.2 11 151.44 196.87 252.4 12 145.46 190.60 250.8 the compressive strength of the experimental samples at 7, 14, and 28 days was calculated and is shown in table iv. it can be observed that the replacement of recycled binder significantly affected the compressive strength of concrete. the decrease is recorded as 3% at replacement rate of 10%, 10% at replacement rate of 20% and 14% at replacement rate of 30%.the results are presented graphically in figure 3. engineering, technology & applied science research vol. 11, no. 4, 2021, 7332-7335 7334 www.etasr.com nguyen & phan: compressive strength studies on recycled binder concrete table iv. calculated compressive strength of recycled concrete no. replacement rate compressive strength (mpa) 7 days mean value 14 days mean value 28 days mean value 1 0 % 11.62 11.79 16.23 15.72 20.04 19.98 2 11.95 15.34 19.93 3 11.78 15.57 19.97 4 10 % 11.34 10.98 14.47 14.91 19.56 19.36 5 11.07 15.35 19.43 6 10.50 14.89 19.10 7 20 % 10.32 10.33 13.52 13.90 17.79 17.82 8 10.39 13.56 17.61 9 10.28 14.62 18.04 10 30 % 10.40 10.19 13.64 13.32 17.05 17.07 11 10.28 13.36 17.13 12 9.87 12.94 17.03 fig. 3. compressive strength of concrete at various replacement rates of recycled binder. fig. 4. the development of the compressive strength of concrete. it can be seen that, basically, the strength development of concrete using recycled binder at a low rate (≤ 30%) is similar to the strength development of ordinary concrete, however the following points should be noted: • normal concrete (replacement rate 0%) grows up to 60% of its maximum design strength at the age of 7 days. this growth has slowed down to 56% by 10% replacement, 57% by 20% replacement, and 59% by 30% replacement of the recycled binder. that indicates that the replacement of recycled binder does not affect the strength development of concrete at an early age. • at 14 days of curing, the experimental concrete achieves about 78% of its maximum design strength. these rates are 77% by 10%, 78% by 20% and 78% by 30% replacement of recycled binder. this means that the replacement of recycled binder does not affect the strength development of concrete. the diminution of compressive strength of recycled concrete with partially replacement of recycled aggregates has been reported in [2, 3, 7 10, 12]. the present investigation on the influence of recycled binder on the compressive strength of concrete indicates that the compressive strength decreases linearly with the increasing percentage of the recycled binder. therefore, in order to apply recycled waste to concrete as a binder, it is necessary to perform supplement research with appropriate additives to compensate for the loss of the compressive strength. v. conclusion the current paper presented the results of a research on the compressive strength of concrete using recycled binder from demolition works. the rates of replacement were 0%, 10%, 20%, and 30%. the test samples were compressed to determine the values of compressive strength at different ages, namely 7 days, 14 days, and 28 days of curing. the results show that the compressive strength of concrete is strongly affected by the percentage of recycled binder replacement. it has been found that the compressive strength decreases linearly with the increase of the recycled binder content. the presence of recycled binder does not affect the strength development of concrete. in order to apply recycled waste to concrete as a binder, it is necessary to perform supplement research with appropriate additives to compensate for the loss of the compressive strength. references [1] r. sri ravindrarajah and c. t. tam, "recycling concrete as fine aggregate in concrete," international journal of cement composites and lightweight concrete, vol. 9, no. 4, pp. 235–241, nov. 1987, https://doi.org/10.1016/0262-5075(87)90007-8. [2] v. t. phan and t. h. nguyen, "the influence of fly ash on the compressive strength of recycled concrete utilizing coarse aggregates from demolition works," engineering, technology & applied science research, vol. 11, no. 3, pp. 7107–7110, jun. 2021, https://doi.org/10.48084/etasr.4145. [3] r. bolla, "influence of fly ash on the properties of recycled coarse aggregate concrete," international journal of emerging trends in engineering research, vol. 8, pp. 2097–2100, may 2020, https://doi.org/10.30534/ijeter/2020/101852020. [4] s. k. kirthika and s. k. singh, "durability studies on recycled fine aggregate concrete," construction and building materials, vol. 250, jul. 2020, art. no. 118850, https://doi.org/10.1016/j.conbuildmat.2020. 118850. [5] c. j. zega and á. a. di maio, "use of recycled fine aggregate in concretes with durable requirements," waste management, vol. 31, no. 11, pp. 2336–2340, nov. 2011, https://doi.org/10.1016/j.wasman. 2011.06.011. engineering, technology & applied science research vol. 11, no. 4, 2021, 7332-7335 7335 www.etasr.com nguyen & phan: compressive strength studies on recycled binder concrete [6] d. v. m. reddy and m. m. s. swaroop, "effect of recycled aggregates on strength and performance of recylced aggregate concrete," in 2nd international conference on design and manufacturing aspects for sustainable energy (icmed 2020), 2020, art. no. 01085, https://doi.org/10.1051/e3sconf/202018401085. [7] x. h. vu, t. c. vo, and v. t. phan, "study of the compressive strength of concrete with partial replacement of recycled coarse aggregates," engineering, technology & applied science research, vol. 11, no. 3, pp. 7191–7194, jun. 2021, https://doi.org/10.48084/etasr.4162. [8] m. oad, a. h. buller, b. a. memon, and n. a. memon, "impact of long-term loading on reinforced concrete beams made with partial replacement of coarse aggregates with recycled aggregates from old concrete," engineering, technology & applied science research, vol. 9, no. 1, pp. 3818–3821, feb. 2019, https://doi.org/10.48084/etasr.2498. [9] m. f. koondhar, b. a. memon, m. oad, f. a. chandio, and s. a. chandio, "water penetration of concrete made with coarse aggregates from demolishing waste," engineering, technology & applied science research, vol. 10, no. 6, pp. 6445–6449, dec. 2020, https://doi.org/ 10.48084/etasr.3891. [10] l. butler, j. s. west, and s. l. tighe, "effect of recycled concrete coarse aggregate from multiple sources on the hardened properties of concrete with equivalent compressive strength," construction and building materials, vol. 47, pp. 1292–1301, oct. 2013, https://doi.org/ 10.1016/j.conbuildmat.2013.05.074. [11] m. etxeberria, e. vázquez, a. marí, and m. barra, "influence of amount of recycled coarse aggregates and production process on properties of recycled aggregate concrete," cement and concrete research, vol. 37, no. 5, pp. 735–742, may 2007, https://doi.org/10.1016/j.cemconres. 2007.02.002. [12] n. a. abdulla, "effect of recycled coarse aggregate type on concrete," journal of materials in civil engineering, vol. 27, no. 10, oct. 2015, art. no. 04014273, https://doi.org/10.1061/(asce)mt.19435533.0001247. engineering, technology & applied science research vol. 8, no. 1, 2018, 2356-2360 2356 www.etasr.com bertoldo et al.: on the use of a 77 ghz automotive radar as a microwave rain gauge on the use of a 77 ghz automotive radar as a microwave rain gauge silvano bertoldo department of electronics and telecommunications politecnico di torino torino, italy silvano.bertoldo@polito.it claudio lucianaz department of electronics and telecommunications politecnico di torino torino, italy claudio.lucianaz@polito.it marco allegretti department of electronics and telecommunications politecnico di torino torino, italy marco.allegretti@polito.it abstract—the european telecommunications standards institute (etsi) defines the frequency band of 77 ghz (w-band) as the one dedicated to automatic cruise control long-range radars. a car can be thought as a moving integrated weather sensor since it can provide meteorological information exploiting the sensors installed on board. this work presents the preliminary analysis of how a 77 ghz mini radar can be used as a short range microwave rain gauge. after the discussion of the mie scattering formulation applied to a microwave rain gauge working in the w-band, the proposal of a new z-r equation to be used for correct rain estimation is given. atmospheric attenuation and absorption are estimated taking into account the itu-t recommendations. functional requirements in adapting automatic cruise control long-range radar to a microwave rain gauge are analyzed. the technical specifications are determined in order to meet the functional requirements. keywords-radar; microwave rain gauge; 77 ghz; w-band; mie scattering; z-r relation; weather radar; car as sensor i. introduction the advances of the automotive industry are highly dependent on the number of sensors installed on cars. in 2001 the number of sensors installed on a car was more than 100 [1] and this number keeps increasing. these sensors are considered essential components of any vehicle regardless of its luxury. car sensors are provided with a large set of systems and technologies that are commonly used to improve safety and comfort: antilock braking system (abs), electronic stability (esp), tire pressure control, accelerometers, thermometers, rain sensors that on newer cars are able to automatically turn on the windscreen wipers [2] etc. of course, as the demand for more automotive advances is increasing, the number of sensors in a vehicle is also increasing. for this reason, cars are also referred to with the innovative conception of “car as sensor”. cars as sensors can be used not only for purposes related to safety, monitoring and maintenance, but for a huge number of other applications that could be performed implicitly. some cars are equipped with radars. in particular, according etsi and its 20 published standards about automotive radars, two frequency bands are dedicated to specific automotive radar applications: the anti-collision shortrange radar operating at 24 ghz and 79 ghz and the automatic cruise control long-range radar operating at 77 ghz. a single car can also be thought as an integrated meteorological sensor providing real time weather monitoring. this work aims to show that, it is possible to use a 77 ghz radar as a microwave rain gauge for meteorological purposes and real time monitoring operations. this work is focused on this application and it also includes a theoretical analysis of mie scattering mechanism for raindrops at 77 ghz. the research group of remote sensing of the department of electronics and telecommunications (det) of politecnico di torino, has a strong background in environmental monitoring [3-5], active remote sensing [6, 7], and atmospheric studies. since 2010 it has also developed an x-band mini weather radar for rain measurements with high spatial and temporal resolution. it is capable of detecting rapid and extremely localized intense phenomena with very good accuracy [8] and it is particularly suited to be employed in complex orography environment and for local analysis of extreme events [9]. the idea presented in this work is the application of the acquired knowledge on radar meteorology in order to use a 77 ghz radar as a short-range microwave rain gauge, since many 77 ghz components are already on the market with relative low cost. ii. radar meteorology at 77 ghz in order to use a 77 ghz radar as a microwave rain gauge, the first step is to evaluate the atmospheric absorption and attenuation, since they can put some constraints on the operative range. according to [10, 11] the atmospheric absorption at the operative frequency of 77 ghz is about 1 db/km and it is sufficient low for a w-band microwave rain gauge. looking at the atmospheric absorption curve, the wband is located in correspondence of one of its relative minimums. the attenuation path can be evaluated according to [12]. for a distance equal to 1 km the free space attenuation is about 130 db. at the frequency of 77 ghz there is an atmospheric attenuation of 0.07 db/km caused by dry air and of 0.36 db/km caused by water vapor component. these values are computed considering the international standard atmosphere (isa) conditions, defined by the international civil aviation organization (icao) at the latitude of 45°. in engineering, technology & applied science research vol. 8, no. 1, 2018, 2356-2360 2357 www.etasr.com bertoldo et al.: on the use of a 77 ghz automotive radar as a microwave rain gauge calculations, the value of relative humidity was increased up to 100% since the radar is operative during a rain event. according to the itu recommendations, it is possible to evaluate the adjunctive attenuation due to the rain for different rain rates, both in horizontal and in vertical polarization. attenuation varies from 0.4 db/km for both polarizations and rain rate r=0.25 mm/h to 41.5 db/km for horizontal polarization and r=150 mm/h (an extremely high value). because of the raindrops’ shape (flattened on the bottom and with a curved dome on top) the attenuation on horizontal polarization is higher than the one on vertical polarization. summarizing all the partial values given by the recommendation, the adjunctive free space attenuation is less than 0.5 db/km and considering a standard rain rate of 20 mm/h, a realistic value of rain attenuation is 10–15 db/km. by combining all the values of absorption and attenuation, it is possible to conclude that a commercial 77 ghz automotive anti-collision radar can be used also for meteorological purposes since these values do not affect too much its propagation performance. however, since for a distance equal to 1 km the free space attenuation is about 130 db the operative range is quite short (maximum 100 m). this is why it can be used as a “short range” microwave rain gauge. the standard bands used for meteorological purposes are the s-band (frequencies equal to 2700-2900 mhz, with corresponding wavelength λ≈10-11 cm), the c-band (f=56005650 mhz, λ≈5 cm), the x-band (f=9300-9500 mhz, λ≈3 cm) and the ka-band (f=35 ghz, λ<1 cm). the rayleigh scattering model used in radar meteorology is valid for all of them. the model assumes that the physical size of the drops is much smaller than the used wavelengths. according to different studies about drop size distributions (dsd) (e.g. [13, 14]) raindrops have a diameter between 0.5 mm and 5 mm (figure 1). in the w-band (f=77 ghz, λ<4 mm), it is necessary to use the mie theory which gives a complete and mathematically rigorous solution to the scattering problem of an electromagnetic wave hitting a sphere, because raindrop size is comparable with the used wavelength. of course, the application of the mie theory implies the considering of raindrops as perfect spheres. although this is a rough approximation, it provides a first good estimate of raindrops shape that does not affect the results very much. assuming rayleigh scattering at a specific wavelength λ, the reflectivity η is given in (1): zkdddndk d o 2 4 5 62 4 5 max )(        (1) where k is the absorption coefficient of water, d is the spherical particle diameter, and n(d) is the dsd. the radar reflectivity factor z is proportional to the sixth moment of the dsd. assuming the mie scattering, the radar reflectivity factor z can be rewritten as in (2):  max )( 25 4 d o mie dddn k z    (2) where σmie is the backscattering cross section of a raindrop evaluated according to the mie theory. (a) (b) fig. 1. dsd according to marshal and palmer distribution [13] (a) and joss distribution for thunderstorm (b) for three different rain rates. it can be shown that according to both dsds, most of raindrops have a diameter lower than 5 mm. it is worth noticing that, according to the mie formulation, z is a function of the wavelength unlike the rayleigh scattering model in which it is frequency independent. therefore when using mie theory, for a microwave rain gauge operating at 77 ghz, a proper z-r relation must be specifically derived. most of z-r relationships determined in the scientific literature are obtained after the rayleigh hypothesis. the result of a relation obtained with mie scattering theory can be very different from the standard, analytically derived and empirical ones (e.g. [15]) and, since it is frequency dependent, it must be carefully evaluated. some examples of z-r relations obtained with mie theory can be found in [16, 17]. the dsd is related to the rain rate r defined as in (3):  max )()(106 34 d o dddvdndr  (3) where v(d) is the raindrop terminal velocity. assuming the validity of the common exponential relationship between z and r as in (4), and the definition of z in (2), a numerical simulation procedure has been set up to obtain the numerical values of the coefficients a and b of (4). the simulation procedure has been implemented in matlab exploiting the functions included in the maetzler toolbox [18, 19] which implements the numerical procedures of [20, 21] to solve the mie equations. barz  (4) engineering, technology & applied science research vol. 8, no. 1, 2018, 2356-2360 2358 www.etasr.com bertoldo et al.: on the use of a 77 ghz automotive radar as a microwave rain gauge the suitable z-r equation to be used for a weather radar operative at 77 ghz is reported in (5) and represented in figure 2 where it is also proposed a comparison with the most common equation based on rayleigh model [13]. equation (5) avoids the underestimation of the rainfall rate r caused by a wrong evaluation of the backscattering cross section, and hence the whole scattering raindrop mechanism [22]. 65.0130)77( rghzz  (5) fig. 2. example of underestimation of rain using a common z-r equation obtained with rayleigh scattering theory with respect to the one obtained with mie theory considering the marshall and palmer dsd the underestimation varies from 5 db to more than 20 db. in terms on rain rate it is an underestimation of some tenths of mm/h. iii. functional and techcnical specifications a. functional specifications according to the theoretical results mentioned above, it is possible to define the functional specifications for an automotive anti-collision radar used as a short microwave rain gauge. table i summarizes the functional specifications. the use of dual polarization is not strictly necessary for simple rain measurements. however, exploiting the polarimetry would improve the quantitative precipitation estimation (qpe) and would allow a classification of the hydrometeors [23]. moreover, the use of a frequency modulated continuous wave (fmcw) radar allows the transmitting of a very low power signal, with respect to the higher power values needed for alternative technologies. table i. summary of main functional specifications specification value max operative range 100 m range resolution 5-10 m sensitivity rain rate r=0.5 mm/h at 100 m operative frequency 77 ghz (w-band) polarization 2 orthogonal polarization (v – h) radar technology fmcw b. techcnical specifications the definition of technical specifications starts from the identification of the sensitivity required by the system to give the rain estimation with the desired level of accuracy. in radar meteorology, the sensitivity value is defined as the minimum detectable rain rate r at the maximum operating range of the radar. exploiting (5), the value of rainfall rate r [mm/h] is converted into the corresponding radar reflectivity factor z. a sensitivity value of r=0.5 mm/h is considered as a good value for a microwave rain gauge operating at 77 ghz at a maximum operative range of 100 m. it corresponds to z=20 dbz which will be used to obtain the radar constant. a noise figure fdb=15 db is assumed as a worst performance case, a value certainly high for a standard 77 ghz radar receiver. a receiver bandwidth b=20 mhz is also considered since it is sufficient to guarantee a spatial resolution of 10 m. according to fdb and b it is possible to obtain the equivalent noise power pn=– 85 dbm. considering that a minimum signal to noise ratio snr=3 db must be guaranteed for the proper working of the system, the transmitted power and the radar constant are determined. a good value of transmitted power is ptx=6 dbm, which is commonly used in commercial hardware for automotive radar. this value leads to an evaluation of radar constant kfmcw=66 db. it can be obtained using horn antennas with a gain g=30 dbm and half power beam width (hpbw) equal to 20° (0.35 rad). since 77 ghz commercial horn antennas usually have a maximum gain g=25 db, in order to realize a meteorological radar with the desired characteristics it is necessary to compensate the loss of 5 db with other techniques, such as amplification chains or even the use of different antenna types. since the system is probably an fmcw radar, it is necessary to evaluate its working parameters related to the maximum operative range (the sweep time t) and the spatial resolution (the chirp bandwidth bw). according to the functional specifications reported in table i, the spatial resolution must be at least 10 m. it means that the chirp bandwidth must be at least bw=15 mhz. this value can be easily obtained with commercial systems available in the automotive market and it is compatible with the previously considered noise bandwidth b. sweep time values in the range between 1 ms to 20 ms allow the reaching of a maximum range equal to 100 m. integrated chips already developed for the automotive field reduce greatly both costs and complexity, but the signal coherence cannot be usually guaranteed. therefore, in order to design a polarimetric system, while it is always possible to work with the magnitude of the polarimetric quantities of the scattering matrix to study the precipitations, the use of phases of polarimetric quantities depends on the type of the receiver and the used electronic components. a polarimetric microwave rain gauge must have two different hardware receiver chains, one for each orthogonal polarization. the processing unit follows the chains and computes all the required polarimetric quantities considering a single chain or both of them, if necessary. according to the specifications summarized in table ii, derived with the discussion about technical specifications, a brief sensitivity analysis has been carried out. figure 3 shows the variation of the radar reflectivity factor z and the received power prx as functions of the rainfall rate r. the system has a variation of about 15 db in terms of z and prx that corresponds to variation of r between 0 and 100 mm/h. it does not seem to be a large dynamic engineering, technology & applied science research vol. 8, no. 1, 2018, 2356-2360 2359 www.etasr.com bertoldo et al.: on the use of a 77 ghz automotive radar as a microwave rain gauge variation but it must be considered that most common values of rain rate are between 1 mm/h and 30 mm/h, corresponding to a variation of 12 db. a good acquisition software together with a good hardware system can be useful to measure the rain rate with the desired accuracy, confirming that a 77 ghz automotive anti collision radar can be used as a short range microwave rain gauge. table ii. summary of technical specifications specification value sensitivity 0.5 mm/h at 100 m (20 dbz at 100 m) noise figure 15 db receiver bandwidth < 20 mhz snr 3 db transmitted power 6 dbm radar constant 66 db antennas (gain and hpbw) 30 db – 20° chirp bandwidth < 15 mhz sweep time < 20 ms co r e fle ct iv ity fa ct o r z [d b z ] r e ce iv e d p o w e r p r x [d b m ] fig. 3. variation of radar reflectivity factor and received power with respect to rain rate. iv. conclusions this work presents how common automotive anti-collision radar operating at 77 ghz can be used as a microwave rain gauge. particular attention has been paid to numerically determine the proper z-r relationship for a radar operating in w-band using the mie scattering theory. at such frequencies, the z-r equations commonly determined with the rayleigh scattering model are not valid. the z-r relation obtained with mie scattering theory can be implemented on cars already equipped with the automatic cruise control “long-range radar” operating at 77 ghz. analyzing the functional and technical specification it has been shown that commercial anti-collision radar could, in principle, work well as a standalone microwave rain gauge providing a good qpe. in future, acquired and measured data can be elaborated with different parallel processing chains in order to allow cars to become “moving rain gauges” and build a network for precipitation monitoring and measurement, enhancing their conception of “car as sensor”. note that this kind of microwave rain gauges could be used on cars or standalone, and could be an integration of the common rain monitoring networks made by standard rain gauges and weather radars operating in different bands. a short-range microwave rain gauge could be very useful in complex orography environment where narrow valley and high mountains do not allow standard instrumentations to get detailed and localized information about precipitations. references [1] w. j. fleming, “overview of automotive sensors”, ieee sensors journal, vol. 1, no. 4, pp. 296-308, 2001 [2] u. haberlandt, m. sester, “areal rainfall estimation using moving cars as rain gauges – a modelling study”, hydrology and earth system sciences, vol. 14, pp. 1139-1151, 2010 [3] c. lucianaz, o. rorato, m. allegretti, m. mamino, m. roggero, f. diotri, “low cost dgps wireless network”, ieee-aps topical conference on antennas and propagation in wireless communications, pp. 792-795, 2011 [4] s. bertoldo, l. corgnati, a. losso, g. perona, “safety in forest fire fighting action: a new radiometric model to evaluate the safety distance for firemen working with hand-operated systems”, wit transactions on ecology and the environment, vol. 158, pp. 3-12, 2012 [5] a. a. khamukhin, s. bertoldo, “spectral analysis of forest fire noise for early detection using wireless sensor networks international siberian conference on control and communications, pp 1-4, 2016 [6] o. rorato, c. lucianaz, s. bertoldo, m. allegretti, g. perona, “a multipurpose node for low cost wireless sensor network”, ieee-aps topical conference on antennas and propagation in wireless communications, pp. 247-250, 2012 [7] g. greco, c. lucianaz, s. bertoldo, m. allegretti, “a solution for monitoring operations in harsh environment: a rfid reader for small uav”, international conference on electromagnetics in advanced applications, pp. 859-862, 2015 [8] s. shah, r. notarpietro, s. bertoldo, m. branca, c. lucianaz, o. rorato, m. allegretti, “automatic storm(s) identification in high resolution, short range, x-band radar images”, international conference on electromagnetics in advanced applications, pp. 945-948, 2013 [9] s. bertoldo, m. allegretti, g. greco, c. lucianaz, “extreme rain events analysis using x-band weather radar”, international conference on electromagnetics in advanced applications, pp. 157-160, 2015 [10] f. versluis, “millimetre wave radio technology”, microwave engineering europe, 2008 [11] the itu radiocommunication assembly, “recommendation itu-r p.676-6, attenuation by atmospheric gases”, available at: https://www.itu.int/rec/r-rec-p.676-6-200503-s/en, 2005 [12] the itu radiocommunication assembly, “recommendation itu-r p.838-3, specific attenuation model for rain for use in prediction methods”, available at https://www.itu.int/rec/r-rec-p.838-3-200503i/en, 2005 [13] j. marshall, w. palmer “the distribution of raindrops with size”, journal of meteorology, vol. 5, pp. 165-166, 1948 [14] r. gunn, g. d. kinzer, “the terminal velocity of fall for waterdrops in stagnant air”, journal of meteorology, vol. 6, pp. 243-248, 1949 [15] l. j. battan, radar observation of the atmosphere, university of chicago press, 1973 [16] u. n. rao, a. sarkar, m. mohan, “theoretical z-r relationship for precipitating systems using mie scattering approach”, indian journal of radio and space sciences, vol. 34, no. 3, pp. 191-196, 2005 [17] k. arai, x. m. liang, q. liu, “method for estimation of rain rate with rayleigh and mie scattering assumptions on the z–r relationship for different rainfall types”, advances in space research, vol. 36, no. 5, pp. 813–817, 2005 [18] c. matzler, “matlab functions for mie scattering and absorption”, research report no. 2002-08, june 2002, institute of applied physics, university of bern, 2002 [19] c. matzler, “effects of rain on propagation, absorption and scattering of microwave radiation based on the dielectric model of liebe, engineering, technology & applied science research vol. 8, no. 1, 2018, 2356-2360 2360 www.etasr.com bertoldo et al.: on the use of a 77 ghz automotive radar as a microwave rain gauge research report no. 2002-10, june 2002”, institute of applied physics, university of bern, 2002 [20] c. f. bohren, d. r. huffman, absorption and scattering of light by small particles, wiley, 1983 [21] h. j. liebe, g. a. hufford, t. manabe, “a model for the permittivity of water at frequencies below 1 thz”, international journal of infrared and millimeter waves, vol. 12, no. 7, pp. 659–675, 1991 [22] r. wexler, d. atlas, “radar reflectivity and attenuation of rain”. journal of applied meteorology, vol. 2, pp. 276-280, 1962 [23] v. n. bringi, v. chandrasekar, polarimetric doppler weather radar: principles and applications. cambridge university press, 2002 authors profile silvano bertoldo is a research assistant at the department of electronics and telecommunication (det) at politecnico di torino, torino, italy. he is alsoa member of the local research unit at det of the italian national interuniversity consortium for the physic od atmospheres and hydrospheres (cinfai). his research interests are manily focused on radar meteorology, other radar technologies and wireless sensor networks (wsns) for environmental monitoring. he received his msc in telecommunication engineering at politecnico di torino in 2008 and got his phd in communication engineering in 2014 with a thesis on x-band weather radar. keen of sports, in 2010 he attended an postgraduate improvement course in sport engineering at politecnico di torino. between may 2010 to december 2012 he was full member of the international sports engineering association (isea). since 2014 he is student member of siem (società italiana di elettromagnetismo), since 2016 is member of egu (european geosciences union) and since april 2017 is member of eufar (europoean facility for airborne research) as an expert of the working group "lidar and radar observation". claudio lucianaz is a research assistant at the department of electronic and telecommunication (det) at politecnico di torino, torino, italy. he is also a member of the local research unit at det of the italian national interuniversity consortium for the physic od atmospheres and hydrospheres (cinfai). his main research activities are wsns and global navigation satellite systems techniques for both precise positioning and environmental monitoring he received his msc in information technology engineering from politecnico di torino in 2006 and in 2010 he got his phd in electronic and communication engineering at politecnico di torino mainly working on electromagnetic wave propagation and synthetic aperture radars. since 2014 he is student member of siem (società italiana di elettromagnetismo). marco allegretti is a researcher at the department of electronic and telecommunication (det) at politecnico di torino, torino, italy. he is also a member of the local research unit at det of the italian national interuniversity consortium for the physic od atmospheres and hydrospheres (cinfai). he deals with his various research interests spacing from electromagnetic wave propagation to sensor electronic boards. he has been also the coordinator of large number of projects. he got his msc in electronic engineering from politecnico di torino, italy, in 2003. in 2005 he attended a master in safety engineering and risk analysis and in 2007 he got his phd in electronic and communication engineering at politecnico di torino. he was president of "ordine degli ingegneri della provincia di asti" in charge for the four years 2009-2017 and he is member of various italian engineering committees. engineering, technology & applied science research vol. 7, no. 5, 2017, 2047-2055 2047 www.etasr.com el-axir et al.: modeling and parameter optimization for surface roughness and residual stress in… modeling and parameter optimization for surface roughness and residual stress in dry turning process m. h. el-axir mechanical engineering dpt northern border university arar, saudi arabia ealaxir@yahoo.com m. m. elkhabeery mechanical engineering dpt northern border university arar, saudi arabia mmkhabeery@yahoo.com m. m. okasha mechanical engineering dpt northern border university saudi arabia (on leave from mechanical engineering dpt, faculty of industrial education, helwan university, egypt) abobanno@yahoo.com abstract—the influence of some turning variables and tool overhang on surface roughness parameters and residual stress induced due to machining 6061-t6 aluminum alloy is investigated in this paper. four input parameters (cutting speed, feed rate, depth of cut and tool overhang) are considered. tests are carried out by precision turning operation on a lathe. design of experiment techniques, i.e. response surface methodology (rsm) and taguchi's technique have been used to accomplish the objective of the experimental study. surface roughness parameters are measured using a portable surface roughness device while residual stresses are measured employing deflectionetching technique using electrochemical analysis. the results obtained reveal that feed and rotational speed play significant role in determining the average surface roughness. furthermore, the depth of cut and tool overhang are less significant parameters, whereas tool overhang interacts with feed rate. the best result of surface roughness was obtained using low or medium values of overhang with low speed and /or feed rate. minimum maximum tensile residual stress can be obtained with a combination of tool overhang of 37 mm with very low depth of cut, low rotational speed and feed rate of 0.188 mm/rev. keywords-al-6061-t; rs; surface roughness parameters; residual stress; turning parameters i. introduction aluminum alloys have high demand in many engineering applications because of their excellent mechanical properties. any production activity is performed with main objectives of good surface quality and higher production rate. metal machining process output is highly dependent on input variables, since small variations in one of the input variables results in a considerable change in the output variables. the integrity of the surface produced in machining (process output) is recognized to have a significant impact on product performance and life time. surface integrity represents the nature of the surface condition of a workpiece after manufacturing/machining. there are two aspects of surface integrity: surface topography characteristics and subsurface layer characteristics. the surface topography comprises of surface roughness, waviness, form errors, and flaws whereas the subsurface layer characteristics that can change due to processing include plastic deformation, residual stresses, cracks, hardness, phase changes, re-crystallization and intergranular attack [1-3]. in addition to the longitudinal feed, cutting speed and depth of cut, geometry of the tool and stability of machine tool also influences the all surface integrity elements. influence of cutting parameters on cutting force and surface finish was investigated in authors in [4]. feed rate was found to have significant influence on cutting force as well as surface roughness. depth of cut was found to have significant influence on cutting force, but has an insignificant influence on surface roughness. authors in [5] studied the effects of tool overhang on selection of machining parameters and surface finish. they found that too large and very small tool overhangs result in poor surface finish. further, optimum range of tool overhang with minimum tool vibrations was established. in [6], authors studied the effect of turning the aluminum with tools having different cutting edge materials and tool edges shapes on the surface roughness. authors in [7] investigated the effect of high speed turning of al 7075 which is a high strength aluminum alloy. authors in [8] used taguchi robust design principles to optimize the process parameters in turning al6061 alloy for mrr and surface roughness with single objective optimization. residual stress generation cannot be avoided after machining processes. residual stress is a major component of surface integrity and is identified as a key factor that influences fatigue life, dimension accuracy and corrosion resistance of machined components. thus, the residual stress in a machined layer has been studied by many researchers. the majority of research work on residual stresses in metal cutting has been limited to experimental study [9-13]. despite these efforts, the quantitative relationship between cutting conditions and residual stresses is still unknown due to the inherent complexity nature of the formation of residual stresses in metal cutting. a part of the recent research work in this field was engineering, technology & applied science research vol. 7, no. 5, 2017, 2047-2055 2048 www.etasr.com el-axir et al.: modeling and parameter optimization for surface roughness and residual stress in… based on the finite element models while others used different approaches to tackle the problem ranging from mathematical modeling to metallurgical investigations. the results presented in [14] show that material hardness has a direct and significant influence on the value of residual stress resulted by machining. it was reported that since the method of machining hardened steel differs from that of machining soft steel, the machined surface of soft steel does not show any stage of phase transformation. authors in [15] reported a case of deformation in machined surfaces of hardened steels and found that the residual stresses in soft steels are mostly tensile stresses while those remaining in hardened steels are mostly compressive stresses. another research which was conducted on two types of steel which have been machined by turning reported that residual stresses are influenced, to a great extent, by feed rate and nose radius and, to a certain extent, by the cutting speed and the rake angle. the results of the experiments conducted in [16, 17] show that the residual stresses of the tensile type is generated at the surface of many materials machined by milling in the presence of coolants. it was also showed that maximum residual stress increases with an increase in feed rate, depth of cut and the tensile stress of the workpiece material. authors in [18] investigated the effect of cutting variables (cutting speed, feed rate, depth of cut, geometry, and coating) on residual stresses in turning operations and reported that residual stresses on stainless steel components are due to plastic deformation and thermal effect on tool nose. the effect of high cutting speeds and feed rate on residual stresses on different hard steel materials has been investigated [19-21]. the residual stresses on the surface are of the compressive type and they increase downwards below the surface to the maximum at a certain depth, then decrease with further depth. taguchi method is widely used for optimizing industrial/production processes. the taguchi design optimization method can be divided into three stages: (a) system design, (b) parameter design and (c) tolerance design. among the three stages, the parameter design stage is considered to be the important stage. the steps followed in the taguchi parameter design are: selecting the proper orthogonal array (oa), running experiments based on the oa, analyzing data, identifying the optimum condition and conducting confirmation runs [22]. many researchers have used the taguchi method to optimize the various machining operations like turning, end milling, drilling, etc. in various alloys [23–28]. one approach to determine the relationship between various input parameters (independent variables) and responses (output variables) is response surface methodology (rsm), which also ascertains the significance of these parameters on the responses [29]. the main objective of the this work is to study the effects of tool overhang in addition to some turning parameters such as speed, feed rate and depth of cut on some surface integrity phases, namely surface roughness parameters and residual stress. the experiments were carried out on 6061-t6 aluminum alloy under dry conditions. turning operations are conducted on a cnc turning machine. the taguchi analysis is applied to obtain the optimal parameter combination using the experimental results. furthermore, analysis of variance (anova) was also carried out to examine the most significant factors for surface roughness parameters and residual stresses in the turning process. the rsm approach is applied to deduce mathematical models that relate the different input parameters to each response studied in this work. ii. experimental work a. workpiece material in this work, 6061-t6 aluminum alloy was used as workpieces material. this material was selected because of its importance and wide applications in industry. the chemical composition in weight percent and the mechanical properties are presented in tables i and ii. table i. the chemical composition of 6061-t6 aluminum alloy work material element mg si fe cu mn weight percent 0.8-1.2 0.80-0.40 0.70 0.15-0.40 0.15 element cr zi ti al weight percent 0.040.35 0.25 0.15 balance table ii. the mechanical properties of 6061-t6 aluminum alloy work material tensile strength, mpa yield stress, mpa elongation, % 428 355 10 b. workpiece preparation the materials were received in the form of bars with a diameter of 80 mm and were prepared into two groups. the first group (shown in figure 1) was used to study the effect of input parameters on the surface profile parameters where the second group (shown in figure 2) was used to study the input parameters on residual stresses. in the case of the first group, each workpiece was divided into five parts with four recesses for machining with different turning conditions whereas in the case of second group, the raw material was machined into ring shapes with the dimensions shown in figure 2. fig. 1. workpiece geometry of the first group fig. 2. workpiece geometry of the second group engineering, technology & applied science research vol. 7, no. 5, 2017, 2047-2055 2049 www.etasr.com el-axir et al.: modeling and parameter optimization for surface roughness and residual stress in… c. experimental procedure the experimental work was conducted on a cnc lathe (model edu vr1-lathe). the main advantage of using such a machine is its flexibility. it enables the turning operations to be accomplished easily in a sequential order. any change in the turning conditions can be easily adjusted. in order that the effect of each parameter on the surface characteristics of the workpiece can be well studied, only four turning parameters were chosen namely, turning speed n, feed rate f, depth of cut d and tool overhang t. the cutting tool overhang affects the surface quality, especially during the turning process, although this has not been reviewed much. based on application and theoretical approaches, it is known that cutting tools need to be clamped as short as possible to achieve the desired surface quality of the workpiece. in this work, the speed was selected in the range of 165: 2000 rpm, turning feed rate was selected in the range of 0.068: 0.468 mm/rev, depth of cut was selected in the range of 100: 500 µm. the turning process parameters and their ranges are given in table iii. dry machining is more popular in manufacturing as a means of reducing overhead costs and protecting the environment [30]. it has great significance for the factors of both economics and environment [31]. hence, the experiments were carried out under dry (unlubricated) conditions. table iii. turning parameters with range and values at five levels code 1 2 3 4 5 tool overhang t, mm 27 32 37 42 47 turning speed n, rpm 165 300 550 1100 2000 feed rate f, mm /rev 0.068 0.117 0.188 0.272 0.468 depth of cut d, µm 100 200 300 400 500 cutting conditions unlubricated (dry) the surface roughness parameters (ra, rp, rt, rz, and rsm) of each turning specimen was measured with a taylor hopson surface roughness tester. all the measurements were carried out with a cut off length of 0.8 mm and for each portion the average of three readings was used. the identification of residual stresses in the machined surface region was achieved by the deflection etching technique method using electrochemical analysis. this method depends on the fact that the machined parts containing residual stresses will undergo shape variation due to removal of layers from the machined surface. the removal of external layers by electrochemical analysis results in elimination of part of the residual stresses which, in turn, leads to redistribution of the residual stresses to the equilibrium position which results in shape variation. this shape variation will be measured, and by then the angle of deviation of the residual stresses can be calculated. when the machining on the ring is finished, the test specimen is prepared by drawing (marking) two parallel lines on the surface of the ring 5 mm apart and perpendicular to the periphery of the ring, then a third line perpendicular to the parallel lines is marked. the distance between the parallel lines along the perpendicular line is then measured. by then the rings are cut or sheared in a position between the two parallel lines, this will result in elimination of a part of the residual stresses causing a change in ring circularity. the distance between the two parallel lines is measured once more, the change in reading of the distance can be either positive or negative, depending on the type of net residual stresses either being tensile or compressive stresses respectively. the ring is then sectioned into two parts in such a way that one of them is extended 5 mm beyond the line presenting the diameter of the ring. the three unmachined surfaces of the ring are coated with an isolating and corrosion resistance coating. the small section of the ring will be used for the determination of material removal rates. this is done by electrolytic analysis. the part is immersed in the electrolyte, as shown in figure 3, which shows the set-up of the apparatus prepared for this purpose. the part will be electrolytically etched. etching is done in intervals of 5 minutes each. the decrease in the thickness is measured in each time, while the average thickness is found by weighing the specimen before and after etching. etching can be done in a wide range of voltage and current, but the satisfactory conditions are achieved when 75 mg sodium chloride is dissolved in 1 liter of water at current density of 3.3 ma/mm. the bigger section is used for determining the average residual stresses distribution. a magnification arm is attached to this part with a small mirror at the end and a laser pointer is used to measure angular deflection of the specimen while being etched (figure 3). fig. 3. experimental set-up of the electrolytic dissolution of workpiece material for measurement angular deviation it is worth mentioning that ring deflection consists of displacement and rotation components, but the application of this method enables measurement of rotation components only. the residual stresses relieved due to the removal of a certain layer consists of three components: stresses relieved due to removal of nth layer of metal, stresses relieved due to removal of previous layer, and stresses relieved due to initial cut of the ring. these stresses can be calculated as follows: 1) stresses relieved due to removal of present layer: , 2 / 3n c et prdt  (1) engineering, technology & applied science research vol. 7, no. 5, 2017, 2047-2055 2050 www.etasr.com el-axir et al.: modeling and parameter optimization for surface roughness and residual stress in… where e is modulus of elasticity, t is ring thickness, ε is angular rotation, r is ring radius. 2) stresses relieved due to removal of previous layers:     , 4 – 4 2 1 .... 1[ n p n o a t n t t n           (2) where a is ring deflection due to removal of n layers, to is initial ring thickness, δt is change in thickness due to etching 3) stresses relieved due to initial sectioning of the ring:  2, / 2 / 2n i ode r z t      (3) where δd is the change in ring diameter due to initial sectioning, z is the remaining ring thickness, to is the initial ring thickness. the total residual stresses relieved are then: σn, t = σn, c + σn, p + σn, i (4) it is worth to mention that the calculated residual stresses are the stresses towards the periphery of the circle; the axial and radial components of residual stresses are in fact small enough and can be ignored. more details about the deflection etching technique are given in [32]. iii. experimental design to evaluate the effects of turning parameters on some performance characteristics (surface roughness parameters and maximum residual stress) and to identify the performance characteristics under the optimal turning parameters, a specially designed experimental procedure is required. classical experimental design methods are complex and difficult to use. additionally, larger number of experiments has to be carried out when number of turning parameters increases. in this study, the main objective is to investigate the effect of the turning parameters (cutting conditions and tool overhang) on both surface roughness parameters and residual stresses generated in the work material. for the purpose of minimizing the experimental work, a simple and adequate experimental design named taguchi design is used. the taguchi method involves reducing the variation in a process through robust design of experiments. the overall objective of the method is to produce high quality product at a low cost. in this method, a loss function is used to calculate the deviation between the experimental value and the desired value. this loss function is further transformed into a signal-to-noise (s/n) ratio (η, db). there are several s/n ratios available depending on the type of characteristics; lower is better (lb), nominal is better (nb) and higher is better (hb) [22]. the experimental program was planned in accordance with the principles of experimental design suggested by taguchi technique with 4 input parameters each having 5 levels and involves 25 experimental observations. the scheme of experimentation adopted in the present study is given in table iv. table iv. experimental design orthogonal array observed values and s/n ratios exp. no input parameters surface profile parameters resid ual stress s/n ratios t, m m n , rp m f, m m / re v d , μ m ra, μm rp, μm rt, μm rz, μm rsm, μm rs, mpa ra rp rt rz rsm rs 1 27 165 0.068 100 1.41 3.800 10.45 8.300 67.50 130 -2.6 -11.1 -19.9 -17.8 -37.5 -41.4 2 27 300 0.117 200 2.27 5.650 13.65 11.75 121.5 170 -7.9 -15.4 -23.2 -21.9 -40.5 -45.0 3 27 550 0.188 300 4.49 10.84 28.42 14.00 180.4 160 -13.7 -21.5 -29.5 -24.6 -45.5 -44.4 4 27 1100 0.272 400 7.71 18.70 45.54 37.33 246.0 140 -17.6 -25.3 -33.4 -30.7 -48.4 -42.6 5 27 2000 0.498 500 11.6 26.20 57.90 51.10 395.0 110 -20.3 -27.8 -34.5 -33.3 -51.2 -41.3 6 32 165 0.117 300 2.09 5.400 16.35 12.35 98.00 150 -5.9 -13.9 -23.3 -20.4 -39.8 -44.3 7 32 300 0.188 400 4.04 8.700 21.70 18.35 153.5 170 -11.9 -19.1 -27.2 -25.6 -43.4 -44.2 8 32 550 0.272 500 6.50 14.75 30.75 26.20 217.0 150 -16.4 -23.5 -29.7 -28.9 -46.7 -42.6 9 32 1100 0.468 100 12.6 27.70 57.45 58.47 404.2 50 -22.5 -28.5 -35.3 -35.5 -51.6 -36.1 10 32 2000 0.068 200 2.39 5.700 15.40 12.45 52.50 135 -7.6 -15.8 -24.6 -22.4 -35.3 41.0 11 37 165 0.188 500 3.34 7.290 17.00 18.35 194.2 150 -10.4 -16.8 -30.3 24.1 -45.8 -43.8 12 37 300 0.272 100 8.50 14.60 35.95 37.00 277.5 100 -18.3 -23.3 -35.3 -31.2 -49.1 -39.5 13 37 550 0.468 200 13.4 27.10 55.70 52.60 400.0 110 -22.7 -28.7 -25.5 -34.1 -52.4 -40.7 14 37 1100 0.068 300 2.90 6.200 16.80 11.00 106.0 125 -9.5 -16.7 -28.2 -22.2 -39.3 -41.4 15 37 2000 0.11 400 3.94 10.15 27.00 19.90 99.00 120 -11.8 -19.6 -29.4 -26.2 -40.5 -42.4 16 42 165 0.272 200 5.10 10.36 27.76 22.23 264.0 130 -14.2 -20.5 -34.3 -28.0 -47.8 -43.5 17 42 300 0.468 300 11.2 22.00 55.00 45.00 360.0 160 -20.3 -26.2 -24.1 -32.0 -52.2 -42.9 18 42 550 0.068 400 2.24 6.800 18.45 12.35 75.00 140 -6.6 -15.6 -24.1 -20.0 -36.8 -44.3 19 42 1100 0.117 500 3.08 6.800 16.23 14.16 108.3 165 -10.2 -17.5 -24.8 -23.9 -41.4 -43 20 42 2000 0.188 100 5.88 12.70 30.45 25.90 187.0 90 -16.1 -22.8 -30.4 -29.1 -44.9 -38.9 21 47 165 0.468 400 5.60 13.00 40.65 25.65 390.0 200 -15.9 -23.8 -33.1 -30.2 -51.6 -44.6 22 47 300 0.068 500 1.45 3.850 9.150 7.600 74.50 170 -3.4 -11.7 -19.4 -18.1 -37.5 -46.2 23 47 550 0.117 100 3.28 7.650 17.65 14.70 117.5 140 -9.8 -17.7 -25.4 -23.2 -41.3 42.25 24 47 1100 0.188 200 6.08 13.33 37.65 28.73 192.6 145 -14.6 -21.2 -29.8 -27.5 -46.1 43.24 25 47 2000 0.272 300 8.03 19.33 54.20 37.50 264.3 140 -18.3 -25.5 -34.7 -30.8 -48.2 43.39 engineering, technology & applied science research vol. 7, no. 5, 2017, 2047-2055 2051 www.etasr.com el-axir et al.: modeling and parameter optimization for surface roughness and residual stress in… it should be pointed out here that the s/n ratio analysis is used to find out the optimum machining conditions. the anova analysis is used to find the percentage contribution of each of the input parameters on surface roughness and maximum residual stress. response surface methodology (rsm) quantifies the relationship between the controllable input parameters and the obtained response surfaces. also, rsm is a collection of mathematical and statistical techniques useful for analyzing problems in which several independent variables (parameters) influence a dependent variable (response-surface roughness and residual stress), and the goal is to optimize this response [33]. iv. results and discussion a. analysis of signal to noise (s/n) ratio taguchi uses s/n ratio to measure the quality characteristic deviating from the desired value. typically a smaller value of surface roughness and/or residual stress is desirable to obtain high surface quality and overcome the fracture of the material. thus, smaller-the-better for surface roughness and residual stress were selected during the present work. the mean s/n ratio for each level of the cutting parameters are computed and shown in table v. regardless of the lower-the-better or the higher-the better quality characteristic, the greater the s/n ratio corresponds to the smaller variance of the output characteristics around the desired value. therefore, from table v, it can be seen that the optimal turning performance for the average surface roughness (maximum signal to noise ratio value) was obtained at tool overhang 27 mm (level 1), rotational speed of 165 rpm (level 1), feed rate of 0.068 mm/rev (level 1) and 500 μm as a depth of cut (level 5) settings. the optimal turning performance for minimizing the maximum residual stress was obtained at tool overhang 37 mm (level 3), rotational speed of 1100 rpm (level 4), feed rate of 0.468 mm/rev (level 5) and 100 μm as a depth of cut (level 1) settings. b. analysis of variance analysis of variance (anova) [22] was carried out for a level of significance of 5%, i.e. for 95% level of confidence. the purpose of anova is to investigate which turning parameter significantly affects the performance characteristics [23]. table vi shows the results of anova for surface roughness ra and maximum residual stress. from the analysis of the average surface roughness data (table vi), it is observed that feed rate has the most significant effect on the surface roughness and its contribution is 82.21% followed by rotational speed (9.5% contribution), depth of cut (2.56% contribution) and tool overhang (1.97% contribution). from the analysis of the maximum residual stress data, it is observed that depth of cut (48.12% contribution) and tool overhang (25.2% contribution) play significant role in determining the maximum residual stress. furthermore, the rotational speed (8.99% contribution) and feed rate (11.68% contribution) are lesssignificant parameters. c. mathematical models table iv shows the arrangement and the results of the 25 experiments carried in this work based on the taguchi technique. these results are used to deduce the mathematical models, according response surface methodology (rsm), which is one of the main objectives of this work. this section presents a study of the development of response models for external turning in terms of tool overhang (x1), in addition to cutting conditions, namely; rotational speed (x2), feed rate (x3), and depth of cut (x4). three reading tests were made on the surface of each specimen and the mean value was calculated and presented in table iv. using these results, the response surface for five different profile parameters ra, rp, rt, rz, and rsm as functions of the four parameters used in this work are deduced as the following models: ra=-0.09556 + 1.3999x1 0.298x2 0.0736x3 + 0.1138x4 0.2317x1 2 + 0.0865x2 2 + 0.6218x3 2 – 0.1135x4 2 + 0.3753x1x2 0.426x1x3 + 0.0147x1x4 + 0.0518x2x4 rp= 2.003 + 0.4699x1 – 1.767x2 0.2159x3 + 1.923x4 0.096x1 2 + 0.041x2 2 + 1.383x3 2 – 0.410x4 2 + 0.924x1x2 – 1.057x1x3 + 0.036x1x4 0.011x2x4 rt= 5.999 – 3.293x1 – 6.342x2 + 1.086x3 + 9.0515x4 + 0.469x1 2 + 0.563x2 2 + 2.449x3 2 – 1.82x4 2 + 1.75x1x2 – 1.63x1x3 + 0.168x1x4 + 0.216x2x4 rz= 6.092 + 4.969x1 – 7.0534x2 + 2.696x3 – 0.345x4 – 0.762x1 2 + 0.588x2 2 + 2.44x3 2 – 0.481x4 2 + 1.737x1x2 – 2.424x1x3 + 0.407x1x4 + 0.101x2x4 rsm= 59.132 + 5.7456x1 – 12.836x2 + 9.229x3 – 1.647x4 + 0.552x1 2 + 2.231x2 2 + 13.95x3 2 – 1.293x4 2 + 0.475x1x2 – 4.77x1x3 + 1.98x1x4 0.865x2x4 mathematical model combining machining parameters with the maximum residual stress (mrs) was also generated as follows: mrs= 134.3 – 51.45x1 + 43.56x2 18.5x3 + 28.2x4 + 6.68x1 2 – 6.2x2 2 – 3.21x3 2 – 1.13x4 2– 3.38x1x2 + 10.22x1x3 – 1.81x1x4 0.52x2x4 table v. mean s/n response table for surface roughness and residual stress factor average surface roughness (ra) by factor level (db) rank maximum residual stress by factor level(db) rank 1 2 3 4 5 1 2 3 4 5 t -12.436* -12.87 -14.56 -13.46 -12.45 3 -42.94 -41.65 -41.57* -42.54 -43.94 2 n -9.79* -12.41 -13.84 -14.88 -14.85 2 -43.52 -43.58 -42.86 -41.28* -41.41 3 f -6.007* -9.104 -13.34 -16.97 -20.35 1 -42.87 -43.40 -42.91 -42.33 41.15* 4 d -13.86 -13.41 -13.55 -12.75 -12.20* 4 -39.65* -42.71 -43.31 -43.61 -43.37 1 engineering, technology & applied science research vol. 7, no. 5, 2017, 2047-2055 2052 www.etasr.com el-axir et al.: modeling and parameter optimization for surface roughness and residual stress in… table vi. analysis of surface roughness ra and maximum residual stress results surface roughness, ra maximum residual stress factor df seq ss adj ms f-ratio contribution % df seq ss adj ms f-ratio contribution % t 4 5.966 1.491 1.03 1.97 4 3980 995 2.29 17.46 n 4 29.4 7.352 5.06 9.5 4 4930 1232.5 2.84 21.62 f 4 252.7 63.186 43.48 82.14 4 1650 412.5 0.95 7.23 d 4 7.892 1.973 1.36 2.56 4 8770 2192.5 5.05 38.46 error 8 11.627 1.453 3.78 8 3470 433.7 15.21 total 24 307.64 24 22800 d. effect of turning parameters on surface roughness parameters in this investigation, the average surface roughness (ra) is considered as the main factor of surface roughness parameters and maximum residual stress that are obviously presented and discussed through rsm methodology. other surface roughness parameters can be discussed with the same manner followed in this investigation. figure 4 shows the effects of tool overhang on the average surface roughness at various speeds, feeds and depth of cut, respectively. it can be seen from these figures that tool overhang effect on surface roughness at different speeds is not the same as shown in figure 4a. at low speed, an increase in tool overhang leads to a slight increase in surface roughness. however, at high speed, an increase in tool overhang results in a considerable increase in the average surface roughness which means the quality of surface deteriorates. this may be due to instability (chatter) increases as the tool overhang length is increased specially at high turning speed. the second interaction is between tool overhang and feed, as shown in figure 4b. at low feed rate, an increase in tool overhang leads to a slightly increase in average surface roughness, whereas at high speed average surface roughness decreases gradually as the tool overhang is increased. the lowest average surface roughness was obtained with a combination of a very low tool overhang and a very low feed rate. from figure 4c, it can be realized that at any level of depth of cut the average surface roughness increases as the tool overhang is increased up to 33mm, whereas the average surface roughness starts to decrease gradually with a further increase in tool overhang. there is a relationship between chatter and tool overhang, and this relationship is not as well appreciated. changing the tool overhang length changes the overall system and therefore changes the signature frequencies. more experimental work should be carried out to investigate this relationship in detail and try to tune the system by selecting the precise tool overhang that causes a sweet spot to fall at the maximum speed of the spindle. fig. 4. effects of different turning parameters on average surface roughness fig. 5. residual stress distribution of some experiments carried out according to experimental design matrix (c) (b) (a) engineering, technology & applied science research vol. 7, no. 5, 2017, 2047-2055 2053 www.etasr.com el-axir et al.: modeling and parameter optimization for surface roughness and residual stress in… e. effect of turning parameters on maximum residual stress it is known that compressive residual stresses are more favorable for fatigue life than tensile residual stresses. furthermore, machining of most mechanical components, such as shafts, roller bearing and other mechanical components, is usually mad in a finishing operation and the residual stresses left behind by the machining process remain in the final product, which can be tensile or compressive depending on the used process parameters. figure 5 shows the results of residual stress distribution for machined specimens, as examples, which have been made according to the experimental design matrix represented in table iv. it should be pointed out here that the residual stress in most cases starts with very low tensile residual stress and increases to a maximum value at depth in the range from 15 to 45 μm. the residual stress then decreases gradually with a further increase in depth beneath the machined surface. figure 6a shows the relationship between maximum residual stress and two different input parameters, tool overhang and rotational speed. feed rate and depth of cut were kept constant at 0.188 mm/rev and 300 mm, respectively. it can be seen that an increase in tool overhang is associated with a decrease in the maximum tensile residual stresses, or a reversion into compressive stress till the compressive residual stresses reach the maximum. this can be attributed to the stability of tool overhang by increasing the tool overhang from 27 to 37 mm. further increase in tool overhang leads to a decrease in compressive residual stress or to reversion of compressive stresses to tensile stresses. therefore, higher tool overhangs are more likely to decrease tensile residual stresses. i.e. they are favorable in this concern, since high tensile residual stresses are not desirable as they can lead to cracking and fatigue. maximum residual stress is influenced by the change in feed rate coupled with changes in tool overhang. figure 6b shows the effect of tool overhang on maximum residual stress at different feed rates with constant rotational speed and depth of cut, 550 rpm and 300 µm, respectively. it can be seen that there is an interaction between tool overhang and feed rate. at low tool overhang the maximum tensile residual stress decreases with an increase in feed rate and may be reversed into compressive residual stress at high feed rate as a result of the dominant of mechanical effect due to increasing of cutting forces. however, the tensile residual stress considerably increases with an increase in feed rate at high tool overhang as result of gradually decreasing in the stability of cutting tool by increasing tool overhang more that 37 mm. it is often favorable to have compressive stresses in mechanical parts rather than tensile stresses as the compressive stresses play an important role in the function and service life of these parts. therefore, it is eminent to set up the cutting conditions in the range which tends to induce compressive stresses or very low tensile residual stress in the work material avoiding conditions inducing high tensile stresses as possible. the influence of tool overhang on the maximum residual stress at different depth of cut is shown in figure 6c. all results of this figure, for different combinations of tool overhang and depth of cut at constant speed and feed, tend to be tensile residual stress. it can be seen that the maximum tensile residual stress decreases gradually with an increase in tool overhang up to 37 mm reaching to a minimum value. further increase in tool overhang leads to a slightly increase in tensile residual stresses. the best result (low value of maximum tensile residual stress) is obtained at a combination of tool overhang of 37 mm with very low depth of cut used in this work. fig. 6. effect of turning parameters on maximum residual stress v. conclusions the influence of turning variables and tool overhang on surface roughness parameters and residual stress induced to a 6061-t6 aluminum alloy due to machining is discussed in this paper. cutting speed, feed rate, depth of cut and tool overhang are considered. surface roughness parameters and residual stresses are measured. based on the analysis of experimental results, the following conclusions can be drawn:  second-order surface roughness parameters and maximum residual stress prediction models have been developed. (a) (b) (c) engineering, technology & applied science research vol. 7, no. 5, 2017, 2047-2055 2054 www.etasr.com el-axir et al.: modeling and parameter optimization for surface roughness and residual stress in… analysis of variance has indicated that these models are adequate for the obtained experimental results.  process parameters are optimized using taguchi relation analysis and the optimum cutting conditions for minimizing surface roughness is t1n1f1d5 whereas for minimizing tensile residual stress is t3v4f5d1.  tool overhang interacts with feed rate. the best result of surface roughness was obtained using low or medium values of tool overhang with low speed and/or feed rate.  results of this study indicated that surface roughness parameters were most affected by feed rate. for different levels of tool overhang, speed and depth of cut, the average surface roughness considerably increases with an increase in feed rate.  in machining of 6061-t6 aluminum alloy, there is always a tendency of generation tensile residual stresses, depending on the cutting conditions.  minimum tensile residual stress can be obtained with a combination of tool overhang of 37 mm with very low depth of cut, low rotational speed, and feed rate of 0.188 mm/rev. vi. nomenclature anova analysis of variance d depth of cut, μm df degree of freedom f fisher’s number f feed rate, mm/rev ms mean sum of squares n rotational speed, rpm ra roughness average rp maximum profile peak height rsm mean spacing of profile irregularities rsm response surface methodology rt maximum height of the profile rz average maximum height of the profile s/n signal-to-noise ratio ss sum of squares t tool overhang, mm x1 code of tool overhang x2 code of rotational speed x3 code of feed rate x4 code of depth references [1] i. s. jawahir, e. brinksmeier, r. m’saubi, d. k. aspinwall, j. c. outeiro, d. meyer, d. umbrello, a. d. jayala, “surface integrity in material removal processes: recent advances”, cirp 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of titanium alloy ti-6242s”, journal of materials processing technology, vol. 185, no. 1-3, pp. 77-82, 2007 [31] m. nouari, a. ginting, “wear characteristics and performance of multilayer cvd-coated alloyed carbide tool in dry end milling of titanium alloy”, surface and coatings technology, vol. 200, no. 18-19, pp. 5663-5676, 2006 [32] o. belgasim, m. h. el-axir, “modeling of residual stresses induced in machining aluminum magnesium alloy (al-3mg)”, world congress on engineering 2010, vol ii, united kingdom, june 30-july 2, 2010 [33] m. n. das, n. c. giri, design and analysis of experiments, 2nd edition, john wiley, 1980 microsoft word etasr_v12_n2_pp8349-8353 engineering, technology & applied science research vol. 12, no. 2, 2022, 8349-8353 8349 www.etasr.com al-hilali et al.: static shear strength of a non-prismatic beam with transverse openings static shear strength of a non-prismatic beam with transverse openings amjad majeed al-hilali department of civil engineering university of baghdad baghdad, iraq amjadmajeedal@gmail.com amer farouk izzet department of civil engineering university of baghdad baghdad, iraq amer.f@coeng.uobaghdad.edu.iq nazar oukaili department of civil engineering university of baghdad baghdad, iraq nazar.oukaili@coeng.uobaghdad.edu.iq received: 29 january 2022 | revised: 10 february 2022 | accepted: 13 february 2022 abstract-in this study, a predicated formula is been proposed to find the shear strength of non-prismatic beams with or without openings. it depends on the contributions of concrete shear strength considering the beam depth variation and existing openings, shear steel reinforcements and defines the critical shear section, the effect of diagonal shear reinforcement, the effect of inclined tensile steel reinforcement, and the compression chord influence. the verification of the proposed formula has been conducted on the experimental test results of 26 non-prismatic beams with or without openings at the same loading conditions. the results reflect that the predicted formula finds the shear capacity of non-prismatic beams with openings, it is conservative and can be used for designing without the strength reduction factor. keywords-critical section; shear strength; opening; nonprismatic beam i. introduction the primary benefit of openings is that mechanical equipment may enter through the beams instead of below them. this decreases the building's floor-to-floor height and total cost. on the other hand, the load-carrying capacity of a reinforced concrete beam is diminished by the openings (i.e. deterioration of flexural and shear rigidities to the parts containing the opening) [1, 2]. to analyze and design beams with openings, various mechanical and numerical models have been presented for estimating their shear strength. most models adopt typical beams with a constant prismatic section along them. the reinforced concrete haunched beams (rchbs) are widely used. this type of beams has been extensively preferred in industrial and framed buildings, bridges, and structural portal frames, due to their advantages [3, 4]. the weight of the structure can be reduced and larger spans can be achieved by the use of rchbs instead of prismatic beams without clear deterioration in loading capacity [5]. only a few works have been conducted on the shear behavior of rchbs. it should be noted that since the effective depth of rchbs is variable along the length of the beams, their structural analysis and mechanical behavior differ from the analysis and behavior of prismatic beams. the aci-318-19 code gave only simple observations, while the aci 318-14 debates the variable depth members. these sections consider the effect of inclined flexural compression in calculating the shear strength of concrete where the internal shear forces at any cross-section are increased or decreased by the vertical component of inclined flexural forces. section 27.4.5.3 of the aci 318-14 discusses the inclined shear crack in the variable depth beams and recommends measuring the depth at the crack mid-length. according to the explanations stated above, the code did not provide any formulas to calculate the critical section or to consider the effect of the inclination on the shear force capacity of variable depth beams [6]. currently, only a few details are available for calculating the shear behavior of non-prismatic reinforced concrete beams with web openings. previous works dealt with solid prismatic reinforced concrete beams (with web openings). some of them considered the analysis of non-prismatic reinforced concrete beams without openings. the objective of the current paper includes introducing a new shear design model of rchbs with multiple transverse web openings. the proposed model depends on the experimental results. the proposed empirical expression considers the same conditions, adopting the total shear resistance of the rc beam with openings as the resistance provided by both concrete and the steel bars intersecting the failure plane by an angle of 45° pass through the center of the opening. corresponding author: amjad m. al-hilali engineering, technology & applied science research vol. 12, no. 2, 2022, 8349-8353 8350 www.etasr.com al-hilali et al.: static shear strength of a non-prismatic beam with transverse openings ii. previously proposed equations for shear resistance of rc beams with web openings a. shear design model for a prismatic beam with openings mansur [7] suggested that the beam may fail in two different modes. the first mode is similar to the failure seen in solid beams, where the failure plane passes through the opening's center. the second model includes the formation of two separate diagonal cracks, one in each member, linking the two solid beam segments, leading to failure. these kinds of failure were classified as beam-type failures and frame-type failures respectively. the developed equation for the beam-type failure depending on the failure mechanism is: �� = �� ��� �� � − ��� + �� ��� � �� − ��� + �� ��� ���� (1) where �� is the strength of concrete, �� is the web width, � is the effective depth, and �� is the diameter of the opening. �� is the area of vertical legs of stirrups per spacing, ��� is the yield of steel stirrups, � is the spacing between stirrups, �� is the cross-sectional area of the additional reinforcement within the failure section, and α is the angle of inclination of diagonal reinforcement. in the case of frame-type failure, mansur [7] considered the two chords to behave independently like a framed structure. therefore both chord members demand independent treatment. accordingly, a free-body diagram at the web opening was suggested. the applied shear, vu, may be distributed between the two chords in proportion to their cross-sectional areas. accordingly, the shear forces can be estimated by: ��� = �� �!�!"�# (2) ���� = �� − ��� (3) the architectural institute of japan (aij) (1988) [8] adopted the following expression to predict the shear capacity �� of beams that contain a small opening. �� = $%.%'()*.)+ �,-"�.../ 01"%.�( 21 − �.��456 7 + 0.846�< �. ���= �� (4) where >? = 0.82 (100as/ ��)0.23, �� is the diameter of the circular opening or, in the case of a square opening the diameter of the equivalent circle, which should be less than or equal to h/3, h is the total depth of the beam, and m vd is taken as less than or equal to 3. the term >� is a function of the effective depth d to account for size effects in shear and has a value from 0.72 to 1.0, ��� is the yield strength of stirrup reinforcement, dv is the distance between the top and bottom longitudinal bars, the term < � refers to the ratio of stirrup reinforcement with an area �� placed within a longitudinal distance dv/2 from the center of the opening and defined as: < � = �� @ab c"de@ c�#.4� )5( mansur [7] modified the maximum admissible shear force (vu)max formula of (aci 318) for rc beams with openings: ���f�g = 5 ∗ 0.85j0.17���′ . �. � − ���m (6) b. shear design models for rchbs without openings based on the aci 318 code’s equation intended for the evaluation of shear strength of prismatic concrete sections, authors in [9] proposed an expression for the shear strength which includes a modification factor that considers the depth variation along rchbs. this factor is presented by the term (1+1.7 �� n). the proposed expression considers also the effect of the inclined flexural reinforcement. it takes the following shape: o p.q@ = 20.16√fc + 17ρs wx.qyx 7 × 1 + 1.7 tan ∝� +ρv.fy + 0.25ρs. sin α (7) the german code din 1045-01 [10] addressed the shear resistance mechanism of rchbs in detail. it introduced (8) to design the shear resistance of rchbs: �d4 = �d45 − �,,4 − �!4 ≤ �dfc (8) �df c = 0.1. g. 100< . �,h�%.iii. �. �. g = 1 + j(%%4 ≤ �, < ≤ 0.02 (9) �,,4 = lm1%.'4 tan n (10) where �d4 is the concrete shear resistance, �d45 is the shear force, �,,4 is the shear resistance due to the inclination of the compression chord, �!4 is the shear resistance component of the inclined longitudinal tension reinforcements, and �df c is the design value of the shear bearing capacity of non-prismatic beams at design section. c. the critical effective section for rchbs the main challenge in predicting the shear strength of rchbs is the determination of the critical effective section due to the variation of depth along them. in this regard, some researchers aimed to give an appropriate formula for this topic. authors in [8] proposed an expression for estimating the effective depth at the critical section, defined in (11). �,n = �� + o6 − ��. tan n (11) o6 = �� + 45 �"pqb c�r� pqb c%.�srpqb c ≈ 2.7�� (12) equation (13) was proposed in [12] to predict the critical effective depth (�,n): �,n = �uvw = x1 + 1.35 tan nz ≤ j26{|}.6{~�r6{|}�(�� + ℎu�� 7 − �m (13) where ℎu�� is the maximum depth of the beam, ℎuvw is the minimum depth of the beam, � is the concrete cover, �uvw is the effective depth at maximum depth, and �6 is the nonprismatic length. authors in [13] formalized (14) to predict the effective depth at the critical section by the consideration of the effective depth of the rchbs on support. this equation was introduced in the experimental part of the study. the proposed range of the inclination angle lies between -14.62o and +14.62o. engineering, technology & applied science research vol. 12, no. 2, 2022, 8349-8353 8351 www.etasr.com al-hilali et al.: static shear strength of a non-prismatic beam with transverse openings ℎ, = λ × ℎ� (14) λ = 1 � 3.04 tan ∝�r%.�%s e 1.55 (15) where �� is the cross-sectional depth at support, �, is the critical depth, and α is the inclination angle. hassan [14] suggested the effective section at approximately a quarter of the length of rchbs for beams without openings. two mechanical models for failure were proposed in [13] depending on the position of the major diagonal shear crack. the proposed models differ from each other according to the contribution of the internal stresses. iii. the proposed formula the proposed equation consists of five discrete components as stated in (16). these components represent the contribution of the internal stresses to the proposed mechanical models as follows: �* � ∅x�� � �� � �4 � �� � ��z (16) where ∅ is the shear strength reduction factor, which equals to 0.75, �* is the ultimate shear strength resulting from the contributions of each concrete �� , �� is the shear reinforcement, �4is the diagonal reinforcement, ��the inclined flexural reinforcement, and �� is the compression chord contribution. a. contribution of concrete (��) the aci-318 approach predicts the shear strength of the reinforced concrete prismatic beams without shear reinforcement. this approach has been modified in [7] involving the subtraction of the depth of the opening from the effective depth. this information was modulated to (17), in which the effective depth d was replaced by the effective depth at a critical depth dc (from 14)) and �� is the diameter or depth of the opening: �� � �0.17��� � ��. �� � ��� (17) for prestressed rchbs with openings, the tension chord (lower chord) has been cracked at the ultimate stress, while the compression chord carried all the shear (upper chord). this is a safe approach because even after cracking, the lower chord will carry shear. the shear capacity of the compression chord can be found using the formula proposed in [15] for beams having prismatic sections, in which the balanced normal forces of lower chord tension and the compressive upper chord took into consideration the inclination of the upper chord ( ∝� in calculating the axial force. �� � 2 21 � �* de@∝(%%%�� 7 ��� ��. � � 0.17��� ��. � (18) where �=�� �� + �?� �?� (19) where ��, � , and �� are the width, depth, and the crosssectional area of the compression chord respectively, ��′ is the concrete strength, �� is the axial compression force in the upper chord, and �� is the nominal shear strength provided by concrete. b. contribution of shear reinforcement (��) shear reinforcement has a significant effect on the beam capacity. therefore, the corresponding equation of aci 318 was used to calculate the contribution of shear reinforcement (��). mansur [7] found that obtainable stirrups to support shear across the failure plane are those at the sides of the opening within a distance (�� � ��), where �� is the distance between the top and bottom longitudinal rebars, and �� is the opening's diameter (or depth). on the other hand, for non-prismatic beams, (19) has been adopted for rcbhs with openings. the dv is replaced by the ��� referring to the distance between the centroids of extreme tension and compression reinforcement layers at the critical section according to (14) and the parameters ��, � and, ��� represent the area, spacing, and yield strengths of the steel stirrups respectively (figure 1). �� � �� ��� � ��� � ��� (20) fig. 1. shear resistance components. c. contribution of diagonal reinforcement (�4) when diagonal reinforcement is used in an rc beam, energy absorption is improved and ensures that the beam with openings will reach its ultimate flexural capacity which is referred to as the flexural failure. mansur [7] converted the contribution of the additional diagonal steel reinforcement by adding the slope angle of reinforcement. the contribution of diagonal reinforcement may be calculated by: �4 � �� ��� sin ∝ (21) d. contribution of inclined flexural reinforcements (��) in the case of non-prismatic section with a horizontal upper chord and an inclined lower one, the nominal shear contribution of concrete and of the longitudinal reinforcement is affected by the non-prismatic inclination flexural reinforcements concerning each prestressing or mild steel due to the vertical component of forces and the truss action of the inclined steel bars, as shown in figure 2. equation (22) is developed to calculate the contribution of the inclined flexural reinforcements by adding the angle of inclined flexural strength which affects the ultimate shear strength. fig. 2. force actions of the varied-depth concrete members. engineering, technology & applied science research vol. 12, no. 2, 2022, 8349-8353 8352 www.etasr.com al-hilali et al.: static shear strength of a non-prismatic beam with transverse openings ��� � �� �� sin ∝ ��� � �?� �?� sin ∝ (21) �� � ��� � ��� where ���, ��� are the shear resistance due to prestressed and mild steel forces respectively, and, from equalizing the tensile and compressive forces, �� is the shear resistance due to the inclination of the compression chord of the beam. e. contribution of compression chord (��) all the previous design methods to define the nominal shear strength of rchbs neglect the compression chord influence. the new proposed formula includes the contribution of compression chord (�o ) which has been found from the flexural equilibrium. at a vertical section along the beam as shown in figure 3, the horizontal forces can be represented by two components: the horizontal component of the compressive force (�o�) equalized to the lower tensile force (� ). these components have the values (from equilibrium): ��� = � � �� ��+ �?� �?�� (22) the compression resultant �o acts at an angle α to the horizontal. the vertical component of the compressive resultant ��� has the value seen in (23). ��n � �,� �,6 , ��� � � ��n, �� � ���= �� ��+ �?� �?�� ��n (23) fig. 3. compression chord influence. iv. experimental database the experimental database, consisting of the test results of 26 rchbs, was compiled from [14, 16]. all tested beams were simply supported, had a rectangular cross-section with a width of 100mm, and varying height from 400mm at the center to 250mm at ends. all beams have a total length of 3000mm and a clear span of 2800mm. the one-point loading system was used. the experimental program conducted in [14] consisted of casting and testing 13 beams, including a reference beam without openings (solid). the details of reinforcement are the same for all the tested beams and consisted of 4-∅6mm coordinated in two layers in the compression chord and 2-∅6+2-∅12mm coordinated in two layers in the tension chord. closed shear stirrups, manufactured out of 4mm bars, were supplied over the entire span of the upper and lower chords of the tested specimens with openings at a constant spacing of 50mm. table i shows the parametric details of the tested beams. al-khafaji [16] progressed the study conducted by hassan [14] by using prestressing reinforcement, keeping the same experimental parameters. v. model verification a. statistical correlations the proposed formula has been verified with the experimental results [14, 16]. it should be mentioned that from the five shear strength contributions of the predicated formula in (16), only three of them have been verified because no diagonal steel reinforcement nor inclined tensile reinforcing were used. table ii shows the comparison of the experimental results and the predicted shear strength values resulting from the proposed formula. the correlations of the results are represented by the coefficient of variation (cov). the correlation factors for the experimental results of [14] to the proposed formula are: the average ���+ �+n� = 0.866, the standard deviation is 0.102 and the cov is 0.102. the correlation factors for the experimental results of [16] to the proposed formula are the average ���+ �+n� = 0.889, the standard deviation is 0.08, and the cov is 0.089. the statistical parameters stated above proved the good performance of (16) in [14, 16]. these results reflect that using the predicted formula to find the shear strength of non-prismatic beams with openings is conservative and can be used for design and analysis. b. analysis example we analyze the web openings for gt6 (3m) span, with ��′ of 35mpa, critical section from (14) λ = (1-3.04tan 5.906)–0.608 = 1.258 ≤ 1.55, and hc =315mm at a distance of 625mm from the support pass through the first opening near the support. contribution of concrete (��): �� � �0.17√35 � 100. 295 � 120� � 17.5 g� contribution of shear reinforcement (�s): �� � (�zi.% �% 275 � 120� � 28.5g� contribution of compression chord (��): �� � 226 z 600+ 56.5 z 550� ��5.9 � 17.25g�. so, we get: �� +n�4v,�!�4 . = 0.75(17.5+28.5+17.25)=47.43kn vi. conclusions • the common failure mode for non-prismatic beams with openings is diagonal shear failure which does not exceed beam-type failure or frame-type failure. • the shear strength contributions of the non-prismatic beam with openings consists of concrete (vc), shear reinforcement (��), diagonal reinforcement (�4 ), inclined flexural reinforcements (��), and compression chord (��). each has a different effect on the shear strength. • the results reflect that the predicted formula to find the shear capacity of non-prismatic beams with openings is conservative and can be used for design with the difference between the experimental results reaching 13% with 11.8% cov. engineering, technology & applied science research vol. 12, no. 2, 2022, 8349-8353 8353 www.etasr.com al-hilali et al.: static shear strength of a non-prismatic beam with transverse openings table i. details of the tested beams by [14] group beam mark shape of openings number of openings total area of openings (mm 2 ) width of openings (mm) height of upper chord (mm) height of lower chord (mm) a gb ----------0 --------------- gt6 trapezoidal 6 180000 200 100 100 gt8 8 174000 150 100 100 gt10 10 144000 100 100 100 b gth6 6 240000 200 75 75 gth8 8 234000 150 75 75 gth10 10 195000 100 75 75 c gp6 trapezoidal with inclined posts 6 154000 200 100 100 gp8 8 151000 150 100 100 gp10 10 138000 100 100 100 d gc1 circular 8 184200 d 75 75 gc2 8 128000 0.83d 100 100 gc3 8 82000 0.67d 120 120 table ii. analysis and experimental results of tested beams beam 's labeling ���� kn ���� kn ���� ���� beam 's labeling ���� kn ���� kn ���� ���� [14] [16] gb 45 57 0.789 pgb 74.2 82.5 0.89 gt6 38.9 47.43 0.82 pgt6 66.1 74.25 0.89 gt8 40.1 47.66 0.84 pgt8 70 74.77 0.936 gt10 41 47.77 0.85 pgt10 71 75.75 0.937 gth6 36.95 37.5 0.98 pgth6 47.45 67.5 0.702 gth8 38.4 38.25 1.00 pgth8 52.3 67.87 0.770 gth10 40.25 38.4 1.048 pgth10 56 68.25 0.820 gp6 41.25 49.57 0.83 pgp6 69 73.5 0.938 gp8 41.9 50.7 0.826 pgp8 70.85 74.25 0.954 gp10 42.2 58.2 0.725 pgp10 71.6 78.75 0.909 gc1 40.75 41.32 0.98 pgc1 68.7 71.25 0.964 gc2 43 51.45 0.835 pgc2 71.9 75 0.958 gc3 43.95 59.7 0.736 pgc3 72.35 80.25 0.901 average 0.866 average 0.889 standard deviation 0.102 standard deviation 0.08 cov 11.8% cov 8.9% references [1] m. a. j. hassan and a. f. izzet, "experimental and numerical comparison of reinforced concrete gable roof beams with openings of different configurations," engineering, technology & applied science research, vol. 9, no. 6, pp. 5066–5073, dec. 2019, https://doi.org/10.48084/etasr.3188. [2] f. j. alkhafaji and a. f. izzet, "prestress losses in concrete rafters with openings," engineering, technology & applied science research, vol. 10, no. 2, pp. 5512–5519, apr. 2020, https://doi.org/10.48084/ etasr.3390. [3] c. hou, k. matsumoto, and j. niwa, "shear failure mechanism of reinforced concrete haunched beams," journal of jsce, vol. 3, no. 1, pp. 230–245, may 2015, https://doi.org/10.2208/journalofjsce.3.1_230. [4] m. a. j. hassan and a. f. izzet, "serviceability of reinforced concrete gable roof beams with openings under static loads," engineering, technology & applied science research, vol. 9, no. 5, pp. 4813–4817, oct. 2019, https://doi.org/10.48084/etasr.3110. [5] p. k. naik and m. manjunath, "pushover analysis of multi-storey frame structure with haunched beam," international journal of trend in research and development, vol. 4, no. 3, pp. 333–336, jun. 2017. [6] aci committee 318, aci code-318-14: building code requirements for structural concrete and commentary. aci, 2014. [7] m. a. mansur, "effect of openings on the behaviour and strength of r/c beams in shear," cement and concrete composites, vol. 20, no. 6, pp. 477–486, jan. 1998, https://doi.org/10.1016/s0958-9465(98)00030-4. [8] standard for the structural calculation of reinforced concrete structures. tokyo, japan: architectural institute of japan, 1988. [9] s. y. debaiky and e. i. elniema, "behavior and strength of reinforced concrete haunched beams in shear," journal proceedings, vol. 79, no. 3, pp. 184–194, may 1982, https://doi.org/10.14359/10896. [10] din 1045-1:2001-07. concrete, reinforced and prestressed concrete structures part 1: design and construction. berlin, germany: beuth verlag, 2001. [11] i. a. macleod and a. houmsi, "shear strength of haunched beams without shear reinforcement," aci structural journal, vol. 91, no. 1, pp. 79–89, jan. 1994, https://doi.org/10.14359/4482. [12] a. tena-colunga, h. i. archundia-aranda, and ó. m. gonzález-cuevas, "behavior of reinforced concrete haunched beams subjected to static shear loading," engineering structures, vol. 30, no. 2, pp. 478–492, oct. 2008, https://doi.org/10.1016/j.engstruct.2007.04.017. [13] m. e. gulsan, h. m. albegmprli, and a. cevik, "finite element and design code assessment of reinforced concrete haunched beams," structural engineering and mechanics, vol. 66, no. 4, pp. 423–438, 2018, https://doi.org/10.12989/sem.2018.66.4.423. [14] m. a. hassan, "strength and serviceability of reinforced concrete gable roof beam with opening of different sizes," ph.d. dissertation, university of baghdad, baghdad, iraq, 2020. [15] j. m. savage, m. k. tadros, p. arumugasaamy, and l. g. fischer, "behavior and design of double tees with web openings," pci journal, vol. 41, no. 1, pp. 46–62, jan. 1996, https://doi.org/ 10.15554/pcij.01011996.46.62. [16] f. j. a. alkhafaji, "performance of perforated prestressed concrete gable rafters," ph.d. dissertation, university of baghdad, baghdad, iraq, 2020. microsoft word etasr_v12_n2_pp8278-8283 engineering, technology & applied science research vol. 12, no. 2, 2022, 8278-8283 8278 www.etasr.com abdelhamid et al.: lateral reliability assessment of eccentrically braced frames including horizontal … lateral reliability assessment of eccentrically braced frames including horizontal and vertical links under seismic loading fayçal abdelhamid lgc-roi, civil engineering laboratory risks and structures interactions, faculty of technology university of batna 2 batna, algeria f.abdelhamid@univ-batna2.dz mohamed saadi lgc-roi, civil engineering laboratory risks and structures interactions, faculty of technology university of batna 2 batna, algeria m.saadi@univ-batna2.dz djarir yahiaoui lgc-roi, civil engineering laboratory risks and structures interactions, faculty of technology university of batna 2 batna, algeria djarir.yahiaoui@univ-batna2.dz noureddine lahbari lgc-roi, civil engineering laboratory risks and structures interactions, faculty of technology university of batna 2 batna, algeria n.lahbari@univ-batna2.dz received: 20 january 2022 | accepted: 1 february 2022 abstract-eccentrically braced frames (ebfs) have been widely used in the last decades and proved their efficiency to resist strong earthquake intensities by providing suitable ductility and lateral stiffness. using the pbpd method for the design, ebfs can fulfill the target performance objectives under major earthquakes. the most commonly used configurations are the kshaped and the recent y-shaped ebfs, which have the advantage that the links are independent of the beam and can be easily replaced after an earthquake without serious damage to the beam and slab. this study focused on the lateral reliability of both systems under seismic loading. nonlinear static pushover and incremental dynamic analysis (ida) were performed on 5-story and 10-story kand y-shaped ebfs. a series of 14 nearand 7 far-field seismic records were considered to analyze and compare the inter-story drifts of both systems using the seismostruct software. moreover, peak ground accelerations (pga) and the different performance levels were also examined. keywords-eccentric braces; short links; incremental dynamic analysis; performance based design; interstory drift i. introduction during the last 50 years, many studies have been carried out through experimental and numerical research with the aim of better understanding the behavior of eccentrically braced frame (ebf) systems and developing adequate design methods to improve their performance against seismic and wind loads. this lateral load-resisting system, originated from japan, combines the advantages of both moment resisting frame (mrf) and concentrically braced frame (cbf) by ensuring high elastic stiffness and energy dissipation during severe earthquakes. one of the most important key parameters that controls the behavior of ebf systems is the segment e between braces or brace to the column. this segment, called the link, acts as a structural fuse to dissipate the energy induced by earthquakes in a building. the remaining parts of the structure are designed to remain essentially elastic when links yield. the link length ratio ρ is a function of e, plastic shear vp, and plastic moment mp capacities of the link [ρ=e/(mp/vp)]. depending on the length ratio (ρ), shear yielding controls the behavior of short links while flexural yielding is predominant in long links. the experimental research conducted in [1-4] showed that short links exhibit better performance under cyclic loadings in terms of ductility and strength. a link is classified as short if ρ<1.6, while links with ρ>2.6 are considered long. these practical limitations were proposed through experimental studies of various link specimens [3, 5-7] and were adopted by many design specifications, including aisc 341-10 [8]. the effect of adding stiffeners to improve the strength and energy dissipation capacity of links] to achieve a better performance of shear links and avoid web local buckling and strength degradation has been highlighted in [3, 9-10. unlike shear links, stiffeners in long links may not prevent flange buckling but could limit strength degradation [11]. intermediate stiffeners may be useful in flexural links if a significant axial force is acting on the link [12]. various numerical modeling techniques of links were developed in [10, 13-14] to demonstrate their accuracy with experimental results. more recently, a simplified approach was presented in [15] by modeling elements with concentrated hinges at the ends. this approach has been used in numerical studies [16, 17] corresponding author: fayçal abdelhamid engineering, technology & applied science research vol. 12, no. 2, 2022, 8278-8283 8279 www.etasr.com abdelhamid et al.: lateral reliability assessment of eccentrically braced frames including horizontal … highlighting some deficiencies in the cyclic response of links. in [18], the previous element model was improved using the uniaxial material model of zona and dall'asta to define the responses of the flexural and shear hinges. the efficiency of this approach was highlighted by comparing numerical and test results. more element models have been developed to model steel links and members in the ebfs. the model developed in [19, 20] was improved in [21] by combining axial, shear, and flexural hinges in the elements to demonstrate the accuracy of the proposed approach. alternative ebf systems were presented in [22] to improve the performance of structures by integrating a damping system to resist lateral loading. in [23], a linkage system was proposed that combined pall friction and rotational friction damper to improve energy dissipation capacity. in practical applications, systems with horizontal links (ktype) are the most commonly used because of their excellent performance during earthquakes. systems with vertical links (y-type) have also shown great cyclic performance in the experiments conducted in [24-26]. however, some deficiencies were observed at the conjunction of the vertical link and the braces due to significant out-of-plane deformations. the main goal of this study is to compare the lateral reliability of the ebf, including horizontal and vertical links, through nonlinear pushover and incremental dynamic analysis. for this purpose, 14 near-field and 7 far-field seismic records were selected to study the behavior of 5-story and 10-story ebf models. the parameter considered for the comparison of the two systems was the inter-story drift. ii. numerical modeling verification study as a first step, model validation was carried out to ensure that numerical results could represent the behavior of ebfs under real conditions. to achieve this purpose, the experimental test conducted in [27] was used to build a numerical model using the seismostruct 2021 software [28]. the specimen tested in [27] and compared with the numerical model was a single-story single-bay 1/2 scale y-ebf made with high-strength steel. the height and width of the specimen were 1.8m and 3.6m respectively, while a short link with a length of 0.5m was used. table i highlights the welded hshaped sections and the materials of the specimen elements. a vertical load of 400kn was applied to the top of the column to simulate the axial force transferred to it by the superstructure. monotonic loading and pseudostatic tests were performed at a loading speed of 0.05mm/s until structural failure [27]. table i. sections and materials of the specimen elements members sections material column h150××150×6×10 q460 beam h225×125×6×10 q460 link h225×125×6×10 q345 brace h125×120×6×10 q460 based on the experimental data, a numerical model was developed using seismostruct 2021 [28]. the element type defined in the numerical model for beam and column was the inelastic plastic-hinge force-based frame element "infrmfbph", where hinges were located at both ends of beam and column. an inelastic truss element was used for the braces, and an inelastic plastic hinge displacement-based frame element infrmdbph was assumed for the link, as shown in figure 1. the software automatically assigns the fibers of the section at the element’s end with a sufficient number to ensure an adequate reproduction of the stress-strain distribution across the cross-section of the member. fig. 1. the numerical model of the studied specimen. the modeling parameters used for the link were selected according to tables 9-7 of the asce 41-17 standard [29]. a bilinear stress-strain steel model with kinematic strain hardening was also defined for elements with their corresponding property values. pushover analysis was performed by imposing an incremental force at the top of the column until the model failed. the resulting capacity curve was compared with the experimental test results obtained in [27]. the comparison of the experimental and the numerical results is shown in figure 2. the ultimate base shear of the experimental test was approximately 680kn, while a value of 618kn was recorded in the simulation model. the results appear to agree with the experimental evaluation with a maximum relative error of 9%. therefore, it can be concluded that numerical modeling is capable of simulating the response of the specimen with sufficient accuracy and can be used to predict the dynamic behavior of ebfs. fig. 2. numerical model vs experimental test results. engineering, technology & applied science research vol. 12, no. 2, 2022, 8278-8283 8280 www.etasr.com abdelhamid et al.: lateral reliability assessment of eccentrically braced frames including horizontal … iii. pushover and incremental dynamic analysis in [27], four groups of y-type ebfs of 5, 10, 15, and 20 storeys were designed, using a performance-based seismic design method, according to the chinese seismic code for buildings [30]. ordinary and high-strength steel was used for each group to be compared in terms of bearing capacity, lateral stiffness, story drift, link rotation, and failure modes. the prototypes were characterized by a peak ground acceleration of 0.3g with a 10% probability of exceedance over 50 years. all frames had a typical story height of 3.6m, 3 bay spans of 7.2m, and a vertical link length of 0.8m. welded h-sections were used for all frame members except for the column where box sections were assigned. among the 8 designed y-type ebfs, frames with 5 and 10 storeys made with ordinary steel (q345) were investigated. additional ebf models were also studied in parallel, including horizontal (k-type) instead of vertical links, using the same cross-sections and geometrical dimensions as the selected models to ensure a fair comparison. pushover analysis was performed for all prototypes using the same member modeling parameters as for the verification model. connections were considered rigid for all models. the material yield strength used for all the element members was the nominal value of ordinary steel q345 (fy=345mpa), and the elastic modulus was equal to 2.06×105mpa. the dead and live loads applied on the floor were 5.0kn/m² and 2.0kn/m 2 , respectively. for the roof, the dead and live loads were 6.0kn/m² and 2.0kn/m². a snow load was also assigned to the roof with a value of 0.35kn/m² [27]. the fundamental periods obtained from the modal analysis of the investigated prototypes are shown in table ii, while the adopted sections for all members are presented in tables iii and iv. incremental dynamic analysis (ida) was also applied using a set of selected ground motion records from the peer nga database (14 near-field earthquakes and 7 far-field earthquakes), as recommended in fema695 [31]. each earthquake represents a particular seismic intensity and is used multiple times at different scales so that the structure is subjected to a wide range of elastic and inelastic behavior. tables v and vi highlight the ground motion records used in this analysis. the newmark integration method was used with β=0.25 and γ=0.5. the ida offers various advantages compared to the pushover analysis and has proved its accuracy by considering the effect of higher modes in the analysis [32-33]. fig. 3. 5-story y-type and k-type prototypes. fig. 4. 10-story y-type and k-type prototypes. table ii. fundamental periods models t1 (s) t2 (s) t3 (s) 5-story y-type 0.722 0.273 0.164 5-story k-type 0.610 0.225 0.137 10-story y-type 1.296 0.465 0.270 10-story k-type 1.191 0.415 0.231 table iii. 5-story ebf member sections story beam link column with brace column with no brace brace 5 h410×150×6×10 h330×150×4×10 400×400×16 300×300×12 h200×200×8×12 4 h440×150×10×16 h420×180×6×10 450×450×18 350×350×16 h200×200×10×16 3 h490×180×10×16 h410×180×8×12 500×500×18 350×350×16 h200×200×10×16 2 h520×200×10×16 h470×180×8×12 550×550×20 400×400×18 h220×220×10×16 1 h550×200×10×16 h500×180×8×12 550×550×20 450×450×18 h220×220×10×16 table iv. 10-story ebf member sections story beam link column with brace column with no brace brace 10 h440×160×6×10 h320×140×5×10 350×350×16 350×350×12 h200×200×10×16 9 h480×200×8×12 h310×150×8×14 400×400×16 350×350×12 h200×200×10×16 8 h490×200×10×16 h430×180×8×14 450×450×18 400×400×16 h220×220×10×16 7 h530×220×10×16 h420×200×10×16 450×450×20 400×400×16 h220×220×10×16 6 h560×240×10×16 h470×200×10×16 500×500×20 450×450×18 h220×220×10×16 5 h540×240×12×18 h510×200×10×16 500×500×20 450×450×18 h250×250×10×16 4 h570×240×12×18 h470×200×12×18 550×550×22 500×500×20 h250×250×10×16 3 h590×240×12×18 h490×200×12×18 550×550×22 500×500×20 h250×250×10×16 2 h610×240×12×18 h510×200×12×18 600×600×25 550×550×20 h250×250×10×16 1 h620×240×12×18 h520×200×12×18 600×600×25 550×550×20 h250×250×10×16 engineering, technology & applied science research vol. 12, no. 2, 2022, 8278-8283 8281 www.etasr.com abdelhamid et al.: lateral reliability assessment of eccentrically braced frames including horizontal … table v. near-field ground motion records earthquake name year station name magnitude rjb (km) cape mendocino 1992 petrolia 7.0 9.5 darfield_ new zealand 2010 tplc 7.0 6.11 duzce_ turkey 1999 lamont 1062 7.1 9.14 erzincan_ turkey 1992 erzincan 6.7 2.0 gazli_ ussr 1976 karakyr 6.8 3.92 imperial valley-06 1979 chihuahua 6.5 7.29 irpinia_ italy-01 1980 sturno (stn) 6.9 6.78 kobe_ japan 1995 port island 6.9 3.31 kocaeli_ turkey 1999 yarimca 7.5 1.38 loma prieta 1989 saratoga aloha ave 6.9 7.58 nahanni_ canada 1985 site 1 6.9 2.48 niigata_ japan 2004 nig017 6.8 4.22 northridge-01 1994 n hollywood coldwater can 6.7 7.89 superstition hills-02 1987 superstition mtn camera 6.5 5.61 table vi. far-field ground motion records. earthquake name year station name magnitude rjb (km) imperial valley-06 1979 delta 6.5 22.03 irpinia_ italy-01 1980 calitri 6.9 13.34 loma prieta 1989 gilroy array #4 7.0 13.81 san fernando 1971 la-hollywood stor ff 6.6 22.77 spitak_ armenia 1988 gukasian 6.7 23.99 superstition hills-02 1987 westmorland fire sta 6.5 13.03 tabas_ iran 1978 boshrooyeh 7.4 24.07 table vii. limit states of ebf according to fema 356 limit states recommended drifts (%) immediate occupancy (io) 0.5 life safety (ls) 1.5 collapse prevention (cp) 2.0 the demand parameter considered was the inter-story drift ratio (maximum inter-story drift of all storeys). the performance levels and their corresponding drift values for ebf are presented in table vii according to fema356 [34]. iv. results and discussion the seismic reliability of ebfs having k-type and y-type links was investigated using non-linear static pushover and incremental dynamic analysis on 5 and 10-story frames. a. pushover analysis the ebfs with vertical links exhibited higher inter-story drifts, especially in the intermediate storeys. the difference was about 20% between the drift of the k and y types for the 5-story model (maximum inter-story drift at the 3rd floor) and 53% for the 10-story model (maximum inter-story drift at the 5th floor). the inter-story drift is more significant as the height of the structure increases. the k-type system exhibited more important lateral stiffness than the y-type system in all cases. according to [30], the link deformation reaches the plastic limit state when the drift value of the story exceeds 2%. the results, shown in figure 5, indicate that the yielding of the links in the y-type models has already occurred for the intermediate stories, while in the k-type models the links reach the plastic limit state. b. incremental dynamic analysis (ida) a series of idas were performed on the selected ebf models to examine the performance of the k and y types at different earthquake intensities and to evaluate the peak ground accelerations corresponding to each specific limit state of the structures. the maximum inter-story drift recorded for the 5 and 10-story studied prototypes under the 21 selected earthquakes are shown in figures 6 and 7, where the peak ground acceleration (pga) was selected as the intensity measure, and the maximum inter-story drift ratio was selected as the response measure. the limit states io, ls, and cp at 0.5, 1.5, and 2% respectively, are shown in figures 6 and 7. the results in figure 7 show that the corresponding pga for the different damage levels is higher for models with horizontal links (k-type). in the 5-story ebfs, a pga of 0.73g was recorded for the k-type model against 0.4g for y-type at the collapse prevention level. for the 10-story ebfs, the ktype model reached the limit of 2% drift ratio at a pga of 0.5g while the y-type model reached the same limit at 0.31g. to attain the collapse prevention performance level, the k-type systems required 1.7 times higher average intensity than the ytype systems. it should be noted that as the height of the frame increases, the intensity that leads to the yielding of links decreases. this implies that shorter frames in general exhibit higher levels of reliability. the results in figure 7 also show that the links in both systems produced intensities above the intensity corresponding to the design hazard level, that is 0.3g. therefore, the performance-based seismic design method once again proved its efficiency in providing structures with good lateral stiffness to sustain subsequent earthquake intensities. (a) (b) fig. 5. inter-story drift ratio at 2% target (a) 5-story (b) 10-story models. engineering, technology & applied science research vol. 12, no. 2, 2022, 8278-8283 8282 www.etasr.com abdelhamid et al.: lateral reliability assessment of eccentrically braced frames including horizontal … (a) (b) fig. 6. ida curves of 5-story models (a) k-type (b) y-type. (a) (b) fig. 7. ida curves for 10-story models (a) k-type (b) y-type. a clear comparison between the median ida curves of 5 and 10-story prototypes is shown in figure 8. (a) (b) fig. 8. median ida curves (a) 5-story models (b) 10-story models. v. conclusions this study investigated the lateral performance of ebfs including horizontal and vertical links. modeling accuracy was examined using the seismostruct software by comparing the modeling results with the experimental test conducted in [27]. the selected 5and 10-story ebf models were analyzed using nonlinear pushover and incremental dynamic analysis over a series of 21 seismic records. the inter-story drifts obtained from the kand y-type ebf prototypes were compared under the same loading conditions. the following conclusions can be drawn: • the results indicate that both k-type and y-type systems can sustain major earthquake intensities and the links can meet the target performance objectives. however, the ktype system may absorb excessive seismic energy and provide better lateral stiffness by conferring smaller interstory drifts to the structure compared to the y-type system. the links in both systems start to yield in the intermediate floors but at different intensities (higher for the k-type models). low-rise ebfs exhibit higher levels of reliability in general, where links reach the plastic limit state at higher intensities than the intensity corresponding to the design hazard level. • with the same cross-sections, the k-type system exhibited better performance under the same loading conditions compared to the y-type system. to achieve the same performance as the y-type configuration, fewer crosssections are needed for the k-type reducing the construction cost. however, links in the y-type configuration can be engineering, technology & applied science research vol. 12, no. 2, 2022, 8278-8283 8283 www.etasr.com abdelhamid et al.: lateral reliability assessment of eccentrically braced frames including horizontal … easily replaced after being damaged by an earthquake as they are not integrated with beams. • the performance-based seismic design method (pbsd) demonstrated its efficiency in providing structures with sufficient lateral stiffness to resist major earthquake intensities. on the other hand, the numerical modeling with adequate parameters proved its ability to predict the dynamic behavior of ebfs with reasonable accuracy. references [1] c. w. roeder and e. p. popov, "inelastic behavior of eccentrically braced steel frames under cyclic loadings," american iron and steel institution, washington, dc, usa, ucb/eerc-77/18, dec. 1977. 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[34] "prestandard and commentary for the seismic rehabilitation of buildings," american society of civil engineers, nov. 2000. engineering, technology & applied science research vol. 7, no. 5, 2017, 2068-2072 2068 www.etasr.com fouad et al.: optimization of emulsion liquid membrane for lead separation from aqueous solutions optimization of emulsion liquid membrane for lead separation from aqueous solutions elsayed fouad chemical and materials engineering department northern border university arar, saudi arabia sayedfou700@gmail.com farooq ahmad chemical and materials engineering department northern border university arar, saudi arabia farooq_chem@yahoo.com khaled abdelrahman chemical and materials engineering department northern border university arar, saudi arabia km_abdelrahman@yahoo.com abstract—this study focuses on evaluating the process parameters and their effects on extraction of lead as well as emulsion breaking. the signal / noise ratios have been used to study the performance characteristics. six parameters affecting extraction by emulsion liquid membrane, namely, topo, span80, and internal phase concentration, feed/emulsion ratio, agitation time and feed ph have been optimized with considerations to lead extraction and emulsion breaking. the standardized effects of the independent variables and their interactions were tested by the analysis of variance (anova) with 95% confidence limits (α= 0.05) and pareto chart. the use of the optimal values of these parameters has been proved useful in maximizing the extraction efficiency and minimizing the emulsion breakage. topo concentration of 0.1498 m, span 80 concentration of 3.007 v%, internal phase concentration of 0.183 m, feed/emulsion volume ratio of 1.407, agitation time of 30 minutes, and feed ph of 5 are determined as the optimum parameters. keywords-lead; optimization; taguchi method; emulsion liquid membrane i. introduction lead contamination in an environment is a very important problem worldwide due to its highly toxic and nonbiodegradable nature[1]. the industrialized activities using lead such as batteries, photographic materials, pigments, fuels and explosives have contaminated the environment. various destructive effects have been found as a result of heavy metal pollution. therefore, a limit of 0.01 ppm for pb in the surface water was recognized by who and usepa [1]. there are several methods for treating pb discharges such as smelting [2], adsorption [3], ion exchange [4], and liquid-liquid extraction [5]. recently, liquid membranes [lm] have great attention to extract lead ions from wastewater streams [6–9]. emulsion liquid membrane (elm), combines an instantaneous extraction and stripping of the metal ion, is one of such methods. elm consists of an internal aqueous phase captured by a membrane phase. the membrane phase consists of the extractant dissolved in an organic diluent together with a surfactant to obtain stable emulsion droplets. so, elm process involves two steps (extraction and stripping) in one. the metal ions existing in waste solution form a complex with the extractant at the boundary of the emulsion globule and the aqueous feed phase. the complex formed is then transported through the organic phase to the organic stripping boundary from where it is stripped into the bulk of the internal aqueous phase [10, 11]. elm is an effective technique and used for zinc removal. commercialization for the removal of other heavy metals is limited due to emulsion breaking. the phenomenon of emulsion breaking has been attributed to the swelling of emulsion, i.e. water transport through the membrane causing in a decrease in the membrane / internal phase volume ratio. an increase in the internal phase volume will affect the dispersed droplets size distribution. moreover, the interfacial film of the surfactant molecules will expand over a higher number of water droplets causing a decrease in density. the interfacial film will be no longer resistant against collisions, and hence, increasing coalescence rate [1]. taguchi technique is a unique and powerful optimization tool that allows optimization with minimum number of experiments. this method can usefully optimize the emulsion liquid membrane [13-16]. the potential of this technique has not been utilized for the breaking of emulsion. in this paper taguchi method has been used to explore the potential of this technique for the optimization of breaking of emulsion. several other parameters affecting extraction of lead and emulsion breaking have been studied. these parameters include extractant and surfactant concentrations, stirring time, external phase acidity, internal phase concentration, and volume ratio of external phase to membrane phase. ii. experimental a. chemicals tri-octyl phosphine oxide (topo) was used as a diluent. sorbitan monooleate (span 80) was used as a surfactant. standard solution of 1000 ppm of pb++ stock was prepared by the dissolution of the proper amount of lead (ii) chloride, sigma into acidified double distilled water. external aqueous phase was prepared by diluting the required volume of 1000ppm solution to the desired concentration. b. emulsion preparation according to the experimental runs in table i, the organic solution was prepared in kerosene as a solvent by mixing with engineering, technology & applied science research vol. 7, no. 5, 2017, 2068-2072 2069 www.etasr.com fouad et al.: optimization of emulsion liquid membrane for lead separation from aqueous solutions the right amounts of span 80 and topo. the stripping aqueous solution of sulfuric acid as an internal phase was added to the organic solution under stirring at 10000 rpm using an ultraturax t25 homogenizer for 10 min, to produce the emulsion. the volume ratio of the internal phase to the membrane phase is 1. c. extraction procedure by elm the emulsion phase was spread into the external lean solution containing 300ppm of pb++ ions, and the solution was agitated at 400 rpm for an extraction time ranged from 1-30 min. the pb++-topo complex diffuses through the membrane to the interface of the internal phase droplets. thus, the reaction of back-extraction occurs, where the pb++ is preconcentrated in the internal phase and the extractant is regenerated. all extraction experiments were carried out in a batch system at room temperature of 25±1oc. aliquots of 10ml of raffinate aqueous solutions are taken for analysis. icp (perkin elmer, optima 7000 dv) is used for the analysis of pb++ ions. equation (1) is used for the calculation of extraction efficiency (e%):   100/)(%  oeo ccce (1) where c0: initial concentration of pb ++ in feed phase and ce: concentration of pb ++ in the lean solutions. the volume of an emulsion was also measured after the extraction experiment to calculate emulsion breakage (b%). the conductivity of the feed phase was estimated by a conductivity meter prior and after experiments. emulsion breakage (b %) was calculated by (2).      100/%  iiee cvcvb (2) where ve and ce are the volume and concentration (in terms of conductivity) of the feed aqueous phase at the end each run. vi and ci are the initial volume and concentration of the external aqueous phase. d. design of experiments using taguchi method the main objective of experimental design was to quantify the influence of the experimental aspects on extraction efficiency of lead, e% and emulsion breaking, b % using taguchi method. in taguchi method an orthogonal array for the design of experiments was used. in this study, six controllable factors were examined: concentration of topo and span80 in the organic phase, concentration of sulfuric acid in the internal phase, feed / emulsion volume ratio, agitating time, and feed phase ph. l25 orthogonal array was generated for five levels of each controllable factor (table i). only 25 tests, were conducted, rather than 7776 (i.e. 65) experimental runs, signifying a great saving in cost and time. in the taguchi method, signal to noise (s/n) ratio signifies quality features for the experimental data. s/n ratios were characterized into larger-the-better, nominal-the-best, and smaller the better. in the case of extraction efficiency (e %), quality characteristic was selected as the larger the better. for emulsion breakage (b %), smaller the better quality characteristic was selected. the s/n ratio is given for larger the better quality characteristic by (3) and smaller the better quality characteristic by (4) [13]. 2 1 1 / 10 log n i iys n n    (3) 2 1 1 / 10 log 1 n i i s n y n    (4) where n: number of trials under the identical experimental conditions, and yi: result of each repetitive measurement. from s/n ratio, the influence of the effective factors on process results can be seen and the optimum conditions of process factors can be determined. the statistical analysis of the results is applied using minitab 17 software. anova is used to attain the contribution % of each factor. iii. results and discussion a. statistical analysis table i mimics the results of the 25 runs. the s/n ratios were calculated by (3) and (4). the results showed that the e% of pb varied from 15 to 96.67% and s/n ratios ranged from 23.5218 to 39.7-058, dependent on the combination of the controllable factors. figure 1 presents the s/n ratio for each level of every controllable variable for extraction efficiency. by inspection of figure 1, topo concentration has the largest variance of s/n ratios, whereas feed phase ph has the smallest ones. therefore, topo concentration is the greatest significant controllable variable, while the non-significant factor is feed phase ph. further quantification of the significance of each controllable variable can be implies by the range of the s/n ratio (s/nmax s/nmin) given in table ii. a factor with a large range indicates that this factor is more significant and must be employed first. the range in descendent order was topo > int. phase > feed/emulsion ratio > span80 > stirring time > ext. ph. for the second response b% (figure 2), results shows that the b% varies from 4 to 72% and that the s/n ratios vary from -37.1466 to -12.0412. because the smaller-the-better characteristic, the highest s/n ratio is required to get the smallest breaking of emulsion (b %) (table iii). in the case of internal phase concentration when the lowest concentration (0.1m) is applied, the emulsion breaking can be diminished. high levels of span 80 concentration reduce the surface tension and then reduce the emulsion breaking to certain levels. the minimum emulsion breaking will be achieved at the lowest levels of topo and internal phase concentrations combined with the highest level of span 80 concentration and moderate levels of external phase ph and external/emulsion ratio. so, the optimum conditions for the maximum extraction efficiency and minimum emulsion breaking can be established at conditions tabulated in tables ii and iii. b. pareto charts the standardized effects of the distinct variables and their mutual interactive effects on the two responses are displayed in a pareto charts (figures 3 and 4). figures 4 and 5 show the pareto charts of standardized factor effects from which the size engineering, technology & applied science research vol. 7, no. 5, 2017, 2068-2072 2070 www.etasr.com fouad et al.: optimization of emulsion liquid membrane for lead separation from aqueous solutions and significance of each effect can be predicted. the vertical line showed on the graph with 95% confidence limits (α = 0.05) allows us to find out the most significant effects, such that some effect that extends past this vertical line is important [16]. the length of each block in the graph shows the standardized effect of that variable on the response [17, 18]. from this figure, it can be found that topo concentration is the most important parameter for lead extraction followed by span 80 and internal phase concentration. also the interaction of span 80 concentration and internal phase concentration plays an important role in emulsion liquid membrane system. increasing span 80 and internal phase concentration result in a more stable emulsion which improves the extraction % of lead. feed phase ph shows a least role in the recovery of lead by elm. table i. experimental design orthogonal array, results and their corresponding s/n ratios run input parameters levels observed values s/n ratio topo, m span80, v% int. phase, m ext/emulsion ratio stirring time, min. feed ph e% b% e% b% 1 0.05 3 0.1 1 1 0.5 30.00 30.00 29.5424 -29.5424 2 0.05 5 0.3 5 5 1.0 50.00 26.00 33.9794 -28.2995 3 0.05 7 0.5 10 10 2.0 55.00 18.00 34.8073 -25.1055 4 0.05 8 0.7 15 20 3.5 35.00 12.00 30.8814 -21.5836 5 0.05 10 1.0 20 30 5.0 15.00 9.00 23.5218 -19.0849 6 0.10 3 0.3 10 20 5.0 40.00 62.82 32.0412 -35.9620 7 0.10 5 0.5 15 30 0.5 42.57 54.00 32.5821 -34.6479 8 0.10 7 0.7 20 1 1.0 57.00 34.00 35.1175 -30.6296 9 0.10 8 1.0 1 5 2.0 24.50 20.00 27.7833 -26.0206 10 0.10 10 0.1 5 10 3.5 73.00 5.00 37.2665 -13.9794 11 0.15 3 0.5 20 5 3.5 50.00 60.00 33.9794 -35.5630 12 0.15 5 0.7 1 10 5.0 76.00 72.00 37.6163 -37.1466 13 0.15 7 1.0 5 20 0.5 65.00 56.00 36.2583 -34.9638 14 0.15 8 0.1 10 30 1.0 86.00 20.00 38.6900 -26.0206 15 0.15 10 0.3 15 1 2.0 94.42 14.50 39.5013 -23.2274 16 0.20 3 0.7 5 30 2.0 80.00 50.00 38.0618 -33.9794 17 0.20 5 1.0 10 1 3.5 96.67 40.00 39.7058 -32.0412 18 0.20 7 0.1 15 5 5.0 89.00 37.00 38.9878 -31.3640 19 0.20 8 0.3 20 10 0.5 91.00 30.00 39.1808 -29.5424 20 0.20 10 0.5 1 20 1.0 86.00 7.00 38.6900 -16.9020 21 0.25 3 1.0 15 10 1.0 70.00 50.00 36.9020 -33.9794 22 0.25 5 0.1 20 20 2.0 58.00 45.00 35.2686 -33.0643 23 0.25 7 0.3 1 30 3.5 92.00 37.00 39.2758 -31.3640 24 0.25 8 0.5 5 1 5.0 90.00 28.00 39.0849 -28.9432 25 0.25 10 0.7 10 5 0.5 85.00 4.00 38.5884 -12.0412 54321 39 38 37 36 35 34 33 32 31 30 54321 54321 54321 54321 54321 x1 m ea n of s n r at io s x2 x3 x4 x5 x6 data means signal-to-noise: larger is better 54321 -10 -15 -20 -25 -30 54321 54321 54321 54321 54321 x1 m ea n of s n r at io s x2 x3 x4 x5 x6 data means signal-to-noise: smaller is better fig. 1. main effects plot for s/n ratios for pb extraction (dashed line indicates mean value) fig. 2. main effects plot for s/n ratios for emulsion breaking (dashed line indicates mean value) on the other hand, figure 4 depicts the effects of the process variables and the interaction effect on, the most important phenomenon of elm, emulsion breaking. from pareto chart (figure 4), the great role of span 80 concentration is seemed followed by the interactive effects of feed/emulsion ratio and feed phase ph. the interaction between agitation time-feed phase ph, topo – span 80 concentration and span 80 – internal phase concentration affect to a reasonable degree the emulsion breaking. engineering, technology & applied science research vol. 7, no. 5, 2017, 2068-2072 2071 www.etasr.com fouad et al.: optimization of emulsion liquid membrane for lead separation from aqueous solutions term f d e c b a 6543210 a topo b span 80 c int. phase d ext./emulsion ratio e stirring time f feed ph factor name st an da r dized eff ect 2.101 pareto chart of the standardiz ed effects (response is e%; α = 0.05) term de bf acd bcd df be ad abd bd ae abf af ef cd ce abc ace cf ac abe ab bc 543210 a topo b span 80 c int. phase d ext./emulsion ratio e stirring time f feed ph factor name st an d a r dize d ef fe ct 4.303 pareto chart of the standardiz ed effec ts (response is e%; α = 0.05) fig. 3. pareto chart of a. independent parameters, b. interaction effects of elm parameters on extraction of lead. table ii. response table for signal / noise ratios of lead extraction efficiency (e%) (larger is better) l ev el t o p o , m s p a n 8 0 , v % in t. p h a se , m e x t. /e m u l. ra ti o s ti rr in g ti m e, m in . e x t. p h 1 30.55 34.11 35.95 34.58 36.59 35.23 2 32.96 35.83 36.80* 36.93* 34.66 36.68* 3 37.21 36.89* 35.83 36.77 37.15* 35.08 4 38.93* 35.12 36.05 35.77 34.63 36.22 5 37.82 35.51 32.83 33.41 34.43 34.25 delta s/n 8.38 2.78 3.96 3.52 2.73 2.43 rank 1 4 2 3 5 6 df 4 4 4 4 4 4 adjms 63.815 5.1571 11.752 11.14 8.1739 4.637 seqss 255.26 20.628 47.011 44.59 32.696 18.55 contrib. , % 60.96 4.93 11.22 10.65 7.8 4.43 *optimum level c. optimization in emulsion liquid membrane process, two responses (lead extraction, e % and emulsion breaking, b %) are existing and they are influenced by elm process factors. it is necessary to get high values of the e % response and low values of the b% to provide well elm performance. more responses influenced by more than one factors was predicted by the desirability approach [19]. considering the elm process, the extraction yield, e % is to be maximized to 100% and breaking, b% is to be reduced with the aim of 1%. the optimization was achieved with minitab response optimizer and the optimal factors were found to be topo concentration of 0.1498 m, span 80 concentration of 3.007 v%, internal phase concentration of 0.183 m, feed/emulsion volume ratio of 1.407, agitation time of 30 minutes, and feed ph of 5 (figure 5). as shown in figure 5, the predictable extraction, e % is 99% with an individual desirability of 1.0. the emulsion breaking, b% is expected as 1% with an individual desirability of 1.0. the composite desirability is estimated to be 1.0 and can be considered as reasonable for the response optimization. table iii. response table for signal / noise ratios of b% (smaller is better) l ev el t o p o , m s p a n 8 0 , v % in t. p h a se , m e x t. /e m u ls . ra ti o s ti rr in g ti m e, m in . e x t. p h 1 -24.72* -33.81 -26.79* -28.20 -28.88 -28.15 2 -28.25 -33.04 -29.68 -28.03 -26.66* -27.17 3 -31.38 -30.69 -28.23 -26.23* -27.95 -28.28 4 -28.77 -26.42 -27.08 -28.96 -28.50 -26.91* 5 -27.88 -17.05* -29.22 -29.58 -29.02 -30.50 delta 6.66 16.76 2.88 3.34 2.36 3.59 rank 2 1 5 4 6 3 df 4 4 4 4 4 4 adj ms 28.317 235.71 8.081 7.958 4.572 10.053 seq ss 113.27 942.86 32.32 31.83 18.29 40.21 contr ib., % 9.6 80 2.74 2.7 1.55 3.41 *optimum level iv. conclusions the optimization for the extraction % and emulsion breaking of the emulsion liquid membrane process with variations of the process parameters is necessary in order to get high extraction % and minimum emulsion breaking. in this study, the process parameters topo, span 80, internal phase concentrations, feed/emulsion ratio, agitation time, and feed phase ph have been optimized via taguchi method. some results get up from this study are shortened as follows:  the effect of emulsion liquid membrane on the pb extraction and emulsion breaking were evaluated with help of taguchi method. topo concentration was a dominant factor for extraction efficiency whereas the span 80 concentration was a dominant factor for emulsion breaking. optimal emulsion liquid membrane conditions to maximize the extraction efficiency and minimize breaking were determined.  the linear and quadratic topo and span80 concentrations were more significant founded by the anova and pareto chart analysis and the linear and quadratic feed phase ph terms were insignificant.  as a result of the optimization performed by response optimizer, for the maximum extraction % and minimum emulsion breaking, topo concentration of 0.1498 m, span b a engineering, technology & applied science research vol. 7, no. 5, 2017, 2068-2072 2072 www.etasr.com fouad et al.: optimization of emulsion liquid membrane for lead separation from aqueous solutions 80 concentration of 3.007v%, internal phase concentration of 0.183 m, feed/emulsion volume ratio of 1.407, agitation time of 30 minutes, and feed ph of 5 are determined as the optimum parameters. term d c e f a b 76543210 a topo b span 80 c int. phase d ext./emul sion ratio e stirri ng time f feed ph factor name stan d ar d ized effe ct 2.101 pareto chart of the st andar diz ed eff ec ts (response is b%; α = 0.05) term abd be de abc acd bcd abf abe ace ad cf bd af cd ac ae bf ce bc ab ef df 43210 a topo b span 80 c int. phase d ext./emul sion ratio e stirri ng time f feed ph factor name stan da r d ized effe ct 4.303 pareto chart of the st andar diz ed eff ec ts (response is b%; α = 0.05) fig. 4. pareto chart of a. independent parameters, b. interaction effects of elm parameters on emulsion breaking. optimal topo span 80 int. phase feed/e mul. ratio stirring time feed ph fig. 5. response optimizer of emulsion liquid membrane extraction of lead acknowledgment the authors wish to acknowledge the approval and the support of this research study by the deanship of scientific research grant no. 4/1/1436/5, northern border university, arar, ksa. references [1] a. b. lende, m. k. dinker, v. k. bhosale, s. p. kample, p. d. meshram, p. s. kulkarni, “emulsion ionic liquid membranes (eilms) for removal of pb(ii) from aqueous solutions”, rsc advances, vol. 4, no. 94, pp. 52316–52323, 2014 [2] j. lv, h. yang, z. jin, z. ma, y. song, 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[15] n. benyahia, n. belkhouche. j. a. jonsson, “a comparative study of experimental optimization and response surface methodology of bi (iii) extraction by emulsion organophosphorus liquid membrane”, journal of environmental chemical engineering, vol. 2, no. 3, pp. 1756-1766, 2014 [16] r. mohammadi, m. a. mohammadifar, a. m. mortazavian, m. rouhi, j. b. ghasemi, z. delshadian, “extraction optimization of pepsin-soluble collagen from eggshell membrane by response surface methodology (rsm)”, food chemistry, vol. 190, pp. 186 -193, 2016 [17] f. a. de bok, c. m. plugge, a. j. stams, “interspecies electron transfer in methanogenic propionate degrading consortia”, water research, vol. 38, no. 6, pp. 1368–1375, 2004 [18] h. y. yen, “taguchi optimization for cd(ii) removal from aqueous solutions using oyster shell powders”, desalination and water treatment, vol. 57, no. 43, pp. 20430–20438, 2016 [19] o. unal, “optimization of shot peening parameters by response surface methodology”, surface and coatings technology, vol. 305, pp. 99– 109, 2016 b a microsoft word etasr_v11_n6_pp7964-7967 engineering, technology & applied science research vol. 11, no. 6, 2021, 7964-7967 7964 www.etasr.com alshortan et al.: low cost high gain 8×8 planar array antenna for 5g applications at 28ghz low cost high gain 8×8 planar array antenna for 5g applications at 28ghz hammad h. alshortan department of electrical engineering university of hail hail, saudi arabia en.hail1411@gmail.com abdullah s. alogla department of electrical engineering university of hail hail, saudi arabia abdullahogla@gmail.com mohamed a. h. eleiwa department of electrical engineering university of hail hail, saudi arabia mohamed.eleiwa@yahoo.com muhammad i. khan department of electrical engineering university of hail hail, saudi arabia mu.khan@uoh.edu.sa abstractin next-generation mobile networks, hundreds of diverse devices aim to be interconnected, posing huge challenges in capacity, coverage, efficiency, reliability, and connectivity. these and other challenges are addressed at radio frequency (rf) parts such as several radiating unit antennas, with very fine beamforming capabilities along with the requirements of high gains and minimized size. this work presents an 8×8 aperture coupled microstrip patch antenna (ac-mpa) in the form of a planar array modeled for the 28ghz frequency band with high gain and compact size, making it suitable for 5g networks. the antenna is designed using a substrate with overall dimensions of 74.6×85.648×0.107mm 3 and relative permittivity of ε0 = 4.3. keywords-5g; microstrip patch antenna; planar array i. introduction moving towards 5g means increased data rate needs in order to meet the requirements of high quality applications such as video streaming, endless connectivity, and maximum capacity and coverage with reduced cost [1-3]. antenna arrays in next generation networks for mobile communication at higher frequency spectra, such as the mm-wave band, have received attention to meet and support the growing higher data rates with greater throughput and improved performance [4-6]. very precise and proper consideration is needed regarding the antenna design of future wireless devices due to increased operating frequency [7-10]. it is very challenging to put more antenna elements in a confined specific space. apart from design issues in terms of physical geometry, designing 5g broadband antennas, operating at multiple frequencies as candidates for 5g bands is a challenging issue. a number of array designs for 5g broadband communication have been proposed [11-13]. almost all these antennas occupy large space in mobile phone devices operating at very few 5g bands. in this work, a high gain, compact size, and wider band antenna has been proposed. the structure of the antenna contains 64 elements in an 8×8 array arrangement. at different scanning angles, it provides quite considerable radiation beams. the antenna has been modeled, simulated, and analyzed with the cst software [14]. geometry and structure of the antenna are discussed in detail below. the need of enhanced communication is essential due to the advancement and exponential growth of new technologies such as the massive internet of things (iot), which are less power demanding and low-cost. these technologies consist of connections among hundreds of small size sensors, with specific application such as agriculture, smart cities, smart home, etc.. services with specific purpose need very high throughput, lower latency, improved security, and reliability. therefore, communication needs wide coverage and faster service [15]. the proposed spectrum for 5g by 3gpp (3 rd generation partnership project) consists of two bands, one below 6ghz (also known as the sub-six band) and one above 6ghz, typically from 26ghz to 40ghz (also known as millimeter wave) [15-16]. ii. antenna design in order to fulfill the requirements of 5g networks in terms of flexibility, usefulness, proficiency, and integration, microstrip antennas are a considerable solution as they put together all the required characteristics. they are compacted and easy to develop on pcbs (printed circuit boards) costeffective solutions [17]. the primary structure of these antennas consists of a dielectric material both sides of which contain conducting sheets, one known as the radiating element (patch) and the other as the ground plane. an antenna array must be properly designed so that beam-forming and beamsteering abilities can be achieved. each element in the array must be separately fed. the proposed antenna is a planar array with 64 elements formed with single elements of dimensions 9.4×10.75×0.107mm 3 . figure 1 depicts the diagram of the proposed 5g array antenna. corresponding author: hammad alshortan engineering, technology & applied science research vol. 11, no. 6, 2021, 7964-7967 7965 www.etasr.com alshortan et al.: low cost high gain 8×8 planar array antenna for 5g applications at 28ghz (a) (b) fig. 1. single element patch antenna. (a) top view, (b) side view. iii. single element antenna figure 2 shows the schematic diagram of the single element of antenna and figure 3 shows its s11 result. these elements are further combined to form an antenna array. from the results it can be observed that return loss below -26db is achieved at 28ghz and a bandwidth around 4ghz is obtained. the values of the parameters affect the performance of the antenna in terms of its matching and band. the optimized antenna parameters are shown in table i. (a) (b) (c) (d) fig. 2. array antenna single element multiple views: (a) top, (b) bottom, (c) side, and (d) end. table i. antenna element parameter description name parameter value (mm) frequency 27.89 port_width 2.305 port_height 0.967 wavelength center 10.749 groundplane_width 10.749 groundplane_length 9.352 groundplane_feed_extension -1.702 la 2.799 wa 0.107 lf 2.973 wf 0.209 lp 3.978 wp 5.374 εb 4.3 εt 1 ls 0.478 hb 0.107 ht 0.859 tanδb 0 tanδt 0 iv. the proposed 5g antenna array the proposed design of the 5g antenna array with 64 elements formed using the discussed above single element is illustrated in figure 4. the design has overall dimensions of 74.6×85.648×0.107mm 3 . as can be seen, 64 compact antenna components with distance d are used to make an array in the top segment of the pcb. the antenna is constructed on the fr4 as bottom substrate and vacuum as the top part. fig. 3. s11 of the single element antenna. fig. 4. array arrangement of the 8×8 (64 elements) antenna. the antenna array was simulated in cst and the obtained values of s11 are shown in figure 5. it can be observed that the designed antenna provides wide bandwidth more than 4.5ghz with an acceptable value of return loss at 28ghz, i.e. -28.5db. similarly, after the simulation of the antenna, a gain of 10.34dbi is achieved. figure 6 gives the graphical representation of the 3d radiation pattern plot. fig. 5. s11 graph of the antenna array. lp wp engineering, technology & applied science research vol. 11, no. 6, 2021, 7964-7967 7966 www.etasr.com alshortan et al.: low cost high gain 8×8 planar array antenna for 5g applications at 28ghz fig. 6. 3d radiation pattern (gain) at 28ghz. the results obtained for the s-parameter of the 64-element antenna, simulated and analyzed in this work are shown in figure 7. it can be observed that a very consistent and directional response is obtained and radiation with a very acceptable s-parameter is attained. figures 8-9 show the eplane and h-plane patterns in polar and cartesian coordinates at 28ghz. fig. 7. s-parameter of the array arrangement in an 8×8 manner. (a) (b) fig. 8. e-plane pattern in (a) polar and (b) cartesian coordinates. (a) (b) fig. 9. h-plane pattern in (a) polar and (b) cartesian coordinates. the elements of the proposed array exhibit great performance. the efficiencies (radiation and total) of the proposed planar antenna array are exhibited in the related figures. it can be observed that adequate efficiency outcomes are achieved at 25-30ghz. higher than 97% radiation efficiency is gained. likewise, more than 70% total efficiency has been attained for the introduced array elements [18-19]. it can also be observed that the proposed 5g antenna design offers steady radiation (patterns/beams) with enough gain [20]. v. comparison with state of the art antennas a comparison with known related antennas is shown in table ii. it can be understood that the presented antenna is a low-cost antenna with much improved impedance bandwidth and acceptable peak gain in comparison with other known, state of the art antennas. the antenna has efficient planar structure, it is easy to implement and has a high directive gain. the presented antenna achieves an impedance bandwidth of 29% and a peak gain of 10.5dbi which outperforms the other antennas, and is adequate for millimeter-wave communication. it has a much wider bandwidth of 4.5ghz. table ii. comparison of the proposed antenna with previous works ref./year freq. band (ghz) bandwidth (ghz) peakg gain (dbi) type [21]/2021 24.25-29.5 6 0-5 phased array [22]/2018 39–49.3 2.0 5.5 reflector, omni [23]/2017 24–32 3.5 9 siw/tapered slot [24]/2016 57–67 2.2 micro-strip this work 25-30 4.5 10.5 planar array engineering, technology & applied science research vol. 11, no. 6, 2021, 7964-7967 7967 www.etasr.com alshortan et al.: low cost high gain 8×8 planar array antenna for 5g applications at 28ghz vi. conclusion the aim of this work was to present a new and compact array with wb function for 5g mobile communication. its arrangement includes 64 compact antennas in an 8×8 planar form, positioned at the top edge of the fr4-material mainboard. the fundamental properties of the proposed antenna were examined. the introduced array shows satisfactory features over its operation band, which can be appropriate for multi-mode communications in 5g systems. this antenna has a considerable bandwidth over 4.5ghz, a gain of about 10.5dbi and is offered as a solution for beamforming application scenarios. moreover, not only it has small dimensions but also it possesses a modular structure that can be simply scalable for a greater number of ports and elements. references [1] a. osseiran et al., "scenarios for 5g mobile and wireless communications: the vision of the metis project," ieee communications magazine, vol. 52, no. 5, pp. 26–35, may 2014, https://doi.org/10.1109/mcom.2014.6815890. 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[24] m. h. ghazizadeh and m. fakharzadeh, "60 ghz omni-directional segmented loop antenna," in 2016 ieee international symposium on antennas and propagation (apsursi), fajardo, pr, usa, jun. 2016, pp. 1653–1654, https://doi.org/10.1109/aps.2016.7696533. microsoft word 01-sifis_ed.doc etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 105-113 105 www.etasr.com tanovic et al: analysis of iptv channels watching preferences in bosnia and herzegovina analysis of iptv channels watching preferences in bosnia and herzegovina a. tanovic department for it development of multimedia services bh telecom d.d. sarajevo bosnia and herzegovina anel.tanovic@bhtelecom.ba i. androulidakis jožef stefan international postgraduate school jamova 39, ljubljana si-1000, slovenia sandro@noc.uoi.gr f. orucevic department of computer science and informatics university of sarajevo bosnia and herzegovina forucevic@etf.unsa.ba abstract – iptv service is a new service which is today offered from almost every telecom operator. one of the advantages of iptv service stemming from its architecture is certainly the fact that it is very easy to measure what tv channels are the ones mostly watched. this papers desribes this measurement and analysis results in one telecom operator in bosnia and herzegovina. they describe what tv channels are mostly watched in different time periods. we developed a simple weighting algorithm to order the channels by watching rate. based on it we are providing extensive tables. this paper forms an industrial contribution with results important for marketing but also is scientific contribution because it introduces one new method of scoring tv channels based on previous measurements in their audience. we also developed iptv statistics model and described results from this research for a new statistics model. this paper is the continuous of previously published contributions from this area. keywords – iptv; tv channel; telecom operator; channel rating; statistics model. i. introduction iptv service is a new ip service which is introduced in almost every telecom operator [2-4]. iptv system has several subsystems like: middleware system, video on demand system, encryption system, database system, monitoring system, statistics system and headend system [3-4]. middleware system and the statistics system are the important elements for the process of measurement of watched tv channels. the relationship between these 2 systems is shown in figure 1. figure 1. describes an iptv system in one telecom operator in bosnia and herzegovina where all measurements have been done. middleware system is responsible for the normal working of all iptv applications, video on demand system is responsible for all actions with video on demand contents, encyption system is responsible for the encoding and decoding of live tv channels and vod contents, database system is responsible for the storing of all data, monitoring system is responsible for the process of monitoring set top boxes in each geographical area in bosnia and herzegovina and headend system is responsible for the working of all satellite antennas, receivers and encoders [1, 3, 4]. statistics system is responsible for communication with every set top box and it has a mysql database where millions of records are placed about the watched tv channels. with red colour in figure 1 we are marking the statistics system and with blue colour the middleware system. figure 1. describes the position of statistics subsystem in the iptv system and its connections to other iptv subsystems, primarly to middleware subsystem which is responsible for communication with stb’s on which users are watching tv channels. fig. 1. the relationship between 2 iptv subsystems previous research of authors from this field is based on description of changing middleware system based on itil v3 recommendations [3] and the analysis of implementation of information security management in iptv system of telecom operator [4]. this research continues with researches in this telecom operator and the aim of all investigations is to improve business processes which are connected to iptv. this contribution builts upon [10] to further explore rating of iptv channels user’s preference [11]. section ii describes the methodology of the measurement which is done in telecom operator in bosnia and herzegovina and section iii has a detailed description of the results in graphs. section iv presents the conclusion of work in which is introduced one new method of scoring tv channels based on etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 105-113 106 www.etasr.com tanovic et al: analysis of iptv channels watching preferences in bosnia and herzegovina previous done measurements and new developed iptv statistics model. ii. methodology of the research statistics system is responsible for communication with every set top box [6, 7]. this system has internal scripts and a mysql database which is responsible for storing all data [5]. internal scripts communicate with every set top box and if user watches one tv channel more than 60 seconds, these scripts write the relevant new record in the mysql database. the value of 60 seconds is an approximate value stemming from previous research in the area, trying to answer the question of how many continuous seconds must elapse before we can say that the user is actually watching the given tv channel [8, 9]. the main table in this database is table stat which contains fields that are described in table i. table i. table stat in statistics database the name of field the meaning of field type of the variable event_id this field signs what type of iptv content is used for statistics – 1 is for tv, 2 is for vod, 3 is for radio integer channel_tag the name of tv channel varchar2 subscriber_id unique number for each subscriber integer device_id unique number for each set top box integer content_id unique number for each tv content integer timestamp the time when tv content starts datetime duration the duration of tv content integer rating the rating of tv content integer insert_date date and time when the record is inserted into mysql database datetime all measurements are done with a few sql queries which link all these fields: “select channel_tag, sum(duration)/3600 from stat s where s.event_id='1' and s.timestamp between '2011-05-01 00:00:00' and '2011-06-01 00:00:00' group by s.content_id” the measurements have been done on 30,000 of users and they included 16840649 records during may 2011. this month has been taken into account because the number of iptv users in telecom operator [4] was the biggest in this month. the number of tv channels is 75. the research has been done in 11 categories (each category corresponding to different time periods) and for each category we included the first 20 tv channels. for the rating algorithm, 20 points are given for the 1 st channel in order in each test category, 19 points are given for the 2 nd channel in order, 18 points are given for the 3 rd channel in order, 17 points are given for the 4 th channel in order etc. and for the last 20 th channel just 1 point. the summary results are given in table ii. table ii. the number of points for each tv channel the name of tv channel the number of points for each tv channel ftv 219 ntv hayat 200 obn 197 bht 189 nova tv 178 pink bih 171 minimax 141 otv valentino 139 hrt 1 123 fox life 122 tv 1 111 tvsa 97 fox crime 73 rtv slon 69 ntv jasmin 65 disney xd 58 arena sport 3 46 hrt 2 37 disc. travel & living 26 rtv tk 13 discovery 11 rtl + 6 arena sport 2 5 tv 1000 4 history channel 4 national geography 2 eurosport 2 arena sport 4 1 iii. results figure 2 presents the most watched tv channels during may 2011. figure 3 shows the most watched tv channels in the 1 st week of may 2011 from 1 st may to 8 th may. figure 4 presents the most watched tv channels in the 2 nd week of may 2011 from 8 th may to 15 th may. figure 5 shows the most watched tv channels in the 3 rd week of may 2011 from 15 th may to 22 th may. figure 6 shows the most watched tv channels in 4 th week of may 2011 from 22 nd may to 31 st may. figure 7 presents the most watched tv channels for working days through may 2011. as such, it includes every day except weekend days with total number of 24 days. figure 8 shows the most watched tv channels for weekend days through may 2011 with the total number of 7 days. figure 9 describes the most watched tv channels for morning hours which includes hours from 6 a.m. to 12 a.m. figure 10 presents the most watched tv channels for afternoon hours which includes hours from 12 a.m. to 8 p.m. figure 11 describes the most watched tv channels for evening hours which includes hours from 8 p.m. to 11 p.m. figure 12 presents the most watched tv channels for night hours which includes hours from 12 p.m. to 6 a.m. etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 105-113 107 www.etasr.com tanovic et al: analysis of iptv channels watching preferences in bosnia and herzegovina the column ‘the number of points for each tv channel’ in table ii is the summary of points for each tv channel in all measurements. in all measurements, we gave 20 points for the 1st tv channel, 19 points for the 2nd tv channel, 18 points for the 3rd tv channel and etc., and finally 2 points for the 19th tv channel and 1 point for the 20th tv channel. the total number of tv channels that have at least 1 point is 28. so even 47 tv channels, of the total number of tv channels which are 75, are not presented in this table. table ii shows that first 5 tv channels are local channels, and in first 10 channels is just 1 foreign tv channel. month report 0 200000 400000 600000 800000 1000000 1200000 1400000 1600000 ft v h a ya t t v o b n b h t 1 n o va t v p in k b h m in im ax o t v v al en tin o f o x l ife h r t 1 t v 1 t v s a f o x c rim e r t v s lo n n t v j as m in d is ne y x d a re n a s po rt 3 h r t 2 d is c. t ra ve l & l iv in g r t v t k tv channel n u m b e r o f w a tc h in g h o u rs fig. 2. the most watched tv channels in month (may 2011.) week 1 report 0 50000 100000 150000 200000 250000 300000 350000 400000 f t v o b n h a ya t t v b h t 1 n o va t v p in k b h m in im ax o t v v al en tin o f o x l ife h r t 1 t v 1 t v s a n t v j as m in r t v s lo n a re n a s po rt 3 f o x c rim e d is ne y x d d is c. t ra ve l & l iv in g d is co ve ry r t v t k tv channel n u m b e r o f w a tc h in g h o u rs fig. 3. the most watched tv channels in the 1 st week of month (may 2011.) etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 105-113 108 www.etasr.com tanovic et al: analysis of iptv channels watching preferences in bosnia and herzegovina week 2 report 0 50000 100000 150000 200000 250000 300000 ft v b h t 1 o b n h ay at t v n o va t v p in k b h m in im ax h r t 1 o t v v al en tin o f o x l ife t v s a t v 1 r tv s lo n n t v j as m in f o x c rim e d is ne y x d a re n a s po rt 3 h r t 2 d is c. t ra ve l & l iv in g d is co ve ry tv channel n u m b e r o f w a tc h in g h o u rs fig. 4. the most watched tv channels in the 2 nd week of month (may 2011.) week 3 report 0 50000 100000 150000 200000 250000 300000 350000 400000 ft v o b n h ay at t v p in k b h n o va t v b h t 1 m in im ax o t v v al en tin o f o x l ife t v 1 h r t 1 r tv s lo n t v s a f o x c rim e d is ne y x d n t v j as m in h r t 2 a re n a s po rt 3 d is c. t ra ve l & l iv in g d is co ve ry tv channel n u m b e r o f w a tc h in g h o u rs fig. 5. the most watched tv channels in the 3 rd week of month (may 2011.) etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 105-113 109 www.etasr.com tanovic et al: analysis of iptv channels watching preferences in bosnia and herzegovina week 4 report 0 50000 100000 150000 200000 250000 300000 350000 400000 450000 ft v h ay at t v o b n b h t 1 n o va t v p in k b h m in im ax o t v v al en tin o t v 1 f o x l ife h r t 1 t v s a f o x c rim e d is ne y x d n t v j as m in r tv s lo n h r t 2 r t v t k d is c. t ra ve l & l iv in g a re n a s po rt 3 tv channel n u m b e r o f w a tc h in g h o u rs fig. 6. the most watched tv channels in the 4 th week of month (may 2011.) working days report 0 200000 400000 600000 800000 1000000 1200000 ft v o b n h ay at t v b h t 1 n o va t v p in k b h m in im ax o t v v al en tin o f o x l ife h r t 1 t v s a t v 1 r tv s lo n f o x c rim e n t v j as m in d is ne y x d h r t 2 a re n a s po rt 3 d is c. t ra ve l & l iv in g d is co ve ry tv channel n u m b e r o f w a tc h in g h o u rs fig. 7. the most watched tv channels in working days of month (may 2011.) etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 105-113 110 www.etasr.com tanovic et al: analysis of iptv channels watching preferences in bosnia and herzegovina weekend days report 0 50000 100000 150000 200000 250000 300000 350000 ft v b h t 1 h ay at t v p in k b h n o va t v o b n m in im ax o t v v al en tin o t v 1 h r t 1 f o x l ife r tv s lo n n t v j as m in t v s a f o x c rim e a re n a s po rt 3 d is ne y x d r t v t k d is c. t ra ve l & l iv in g h r t 2 tv channel n u m b e r o f w a tc h in g h o u rs fig. 8. the most watched tv channels in weekend days of month (may 2011.) morning hours report 0 50000 100000 150000 200000 250000 300000 350000 h ay at t v ft v o b n p in k b h b h t 1 n o va t v m in im ax r tv s lo n h r t 1 t v s a n t v j as m in f o x l ife o t v v al en tin o d is ne y x d t v 1 f o x c rim e r t v t k h r t 2 d is c. t ra ve l & l iv in g d is co ve ry tv channel n u m b e r o f w a tc h in g h o u rs fig. 9. the most watched tv channels in morning hours of month (may 2011.) etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 105-113 111 www.etasr.com tanovic et al: analysis of iptv channels watching preferences in bosnia and herzegovina afternoon hours report 0 100000 200000 300000 400000 500000 600000 700000 ft v o b n h ay at t v b h t 1 n o va t v m in im ax p in k b h o t v v al en tin o f o x l ife d is ne y x d h r t 1 n t v j as m in t v 1 t v s a r tv s lo n f o x c rim e d is c. t ra ve l & l iv in g a re n a s po rt 3 d is co ve ry r t v t k tv channel n u m b e r o f w a tc h in g h o u rs fig. 10. the most watched tv channels in afternoon hours of month (may 2011.) evening hours report 0 50000 100000 150000 200000 250000 300000 350000 400000 f t v o b n h a ya t t v b h t 1 n o va t v p in k b h h r t 1 o t v v al en tin o t v 1 a re n a s po rt 3 f o x l ife t v s a h r t 2 f o x c rim e r t l + a re n a s po rt 2 t v 10 00 d is ne y x d e ur o sp o rt a re n a s po rt 4 tv channel n u m b e r o f w a tc h in g h o u rs fig. 11. the most watched tv channels in evening hours of month (may 2011.) etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 105-113 112 www.etasr.com tanovic et al: analysis of iptv channels watching preferences in bosnia and herzegovina night hours report 0 50000 100000 150000 200000 250000 300000 ft v n o va t v b h t 1 h ay at t v p in k b h o b n o t v v al en tin o t v 1 f o x l ife h r t 1 f o x c rim e t v s a h r t 2 a re n a s po rt 3 a re n a s po rt 2 d is c. t ra ve l & l iv in g h is to ry c h an ne l d is co ve ry n at g e o n t v j as m in tv channel n u m b e r o f w a tc h in g h o u rs fig. 12. the most watched tv channels in night hours of month (may 2011.) final results 219 200 197 189 178 171 141 139 123 122 111 97 73 69 65 58 46 37 26 13 11 6 5 4 4 2 2 1 0 50 100 150 200 250 f t v o b n n o v a t v m in im a x h r t 1 t v 1 f o x c r im e n t v j a s m in a r e n a s p o r t 3 d is c . t r a v e l & l iv in g d is c o v e r y a r e n a s p o r t 2 h is t o r y c h a n n e l e u r o s p o r t tv channel n u m b e r o f p o in ts fig. 13. final results after all 11 tests table iii. results for iptv statistics model for this research the name of category results for each category 1 st 42.5% 2 nd 30.1% 3 rd 25.7% 4 th 1.5% 5 th 0% etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 105-113 113 www.etasr.com tanovic et al: analysis of iptv channels watching preferences in bosnia and herzegovina iv. conclusion and future work comparison of results from figure 13 and other figures is giving these concluding remarks for telecom operator from bosnia and herzegovina: 1. final results are totally the same as the results from figure 2 which considers the most watched tv channels in a month for the first 20 channels except that in the final result tv channel hrt 1 is not on 10 th place but on 9 th place. 2. last seven tv channels on final figure 13 are obtained from figure 11 which represents the most watched tv channels in the evening hours. it means that for each analysis of the most watched tv channels, evening hours (from 8 p.m. to 11 p.m.) should be placed in the special category. 3. the analysis has shown that 28 tv channels are presented in the final table. the total number of tv channels are 75, so 47 tv channels are almost not watched. 4. 8 of 10 first tv channels are local tv channels and only minimax, which is on the 7 th place, and fox life, which is on the 10 th place, are foreign tv channels. simply conclusion is that local tv channels are more watched than foreign tv channels. 5. there are major differences in ratings between the first 6 tv channels and only minor differences in ratings between channels under the 6 th place. 6. first 12 tv channels are only important for the most users (the number of points is 100 and more). this is specific result for this telecom operator. this analysis can be used to predict user prefences about watching tv channels in bosnia and herzegovina. from previous research we can conclude what tv channels are most watched in: morning hours, afternoon hours, evening hours, night hours or during working days or weekends. in this way this investigation can be one important step for future sociology investigations about users’ preferences and wishes during different hours or different days. this research is important step for future not only technical studies but also sociological studies. because of future researches in this area and based on results that are produced in this investigation, we proposed a little iptv statistics model in which all tv channels are divided in 5 categories. in the first category are tv channels with a very high level of watching, in the second category are tv channels with a high level of watching, in the third category are tv channels with a medium level of watching, in the fourth category are tv channels with a low level of watching and in the fifth category are tv channels with a very low level of watching. for telecom operator with 100 tv channels in the 1 st category are first the most watched tv channels, in the 2 nd category are tv channels from 6 th to 10 th place, in the 3 rd category are tv channels from 11 th to 20 th place, in the 4 th category are tv channels from 21 st place to 50 th place and in the 5 th category are tv channels from 51 st place to 100 th place. the aim is to compare results from the same telecom operator in different months or from different telecom operators in the same month. future research in this area is based on these comparisons. table iii shows results for iptv statistics model which are produced in this research. this result shows that all 3 channel categories in this research are almost equally watched. references [1] a. tanovic, i. androulidakis, “improving the etom standard for telecom operators”, xxiii international symposium on information, communication and automation technologies, icat 2011, sarajevo, bosnia and herzegovina, 2011. [2] a. tanovic, f. orucevic, “implementation of the information system of the telecom operator using the itil v3 methodology for the service design phase”, 2 nd international conferences on advanced service computing, service computation 2010, pp. 82 91, lisbon, portugal, 2010. [3] a. tanovic, f. orucevic, “changing the middleware system for iptv services telecom operators based on the methodology of the change management process”, 3 rd international conferences on advances in multimedia, mmedia 2011, pp. 104 110, budapest, hungary, 2011. [4] a. tanovic, f. orucevic, “analysis of the implementation of the information security management in the iptvvoip system of the telecom operator”, 18 th international conference on systems, signals and image processing, iwssip 2011, pp. 1-5, sarajevo, bosnia and herzegovina, 2011, [5] j. huang, a.b. lee, d. mumford, “statistics of range images”, ieee conference on computer vision and pattern recognition, vol. 1, pp. 324-331, 2000. [6] p. gacs, j. t. tromp, p. m. b. vitanyi, “algorithmic statistics”, ieee transactions on information theory, vol. 47, no. 6, pp. 2443-2463, 2001. [7] y. j. won, mi-jung choi, byung-chul park, j. w. hong, hee-won lee, chan-kyu hwang, jae-hyoung yoo, “end-user iptv traffic measurement of residential broadband access networks”, ieee network operations and management symposium workshops, noms 2008, pp. 95-100, 2008. [8] t. zijian, r. c. cannizzaro, g. leus, p. banelli, “pilot-assisted time-varying channel estimation for ofdm systems”, ieee transactions on signal processing, vol. 55, no. 5, pp. 2226-2238, 2007. [9] m. k. tsatsanis, g.b. giannakis, “blind identification of timevarying channels using second-order statistics”, 29 th asilomar conference on signals, systems and computers, pp. 162-166, 1995. [10] m. -j. montpetit, h. calhoun, h. holtzman, d. grossman, “adding the community to channel surfing: a new approach to iptv channel change.” 6th ieee consumer communications and networking conference, ccnc 2009, pp. 1 – 5, las vegas, nevada, usa, 2009 [11] h. lin wang, j. gang wang, w. yun yau, “automated age regression for personalized iptv services”, ieee international conference on multimedia and expo (icme 2010), pp. 1333-1336, singapore, 2010. engineering, technology & applied science research vol. 7, no. 5, 2017, 2014-2016 2014 www.etasr.com madhukar and verma: hybrid semantic analysis of tweets: a case study of… hybrid semantic analysis of tweets: a case study of tweets on girl-child in india mani madhukar ibm india pvt ltd bangalore, india manimmadhukar@gmail.com seema verma banasthali university rajasthan, india seemaverma3@yahoo.com abstract—social networks have become one of the major and important parts of daily life. besides sharing ones views the social networking sites can also be very efficiently used to judge the behavior and attitude of individuals towards the posts. analysis of the mood of public on a particular social issue can be judged by several methods. analysis of the society mood towards any particular news in form of tweets is investigated in this paper. the key objective behind this research is to increase the accuracy and effectiveness of the classification by the process of natural language processing (nlp) techniques while focusing on semantics and world sense disambiguation. the process of classification includes the combination of the effect of various independent classifiers on one particular classification problem. the data that is available in the form of tweets on twitter can easily frame the insight of the public attitude towards the particular tweet. the proposed work implements a hybrid method that includes hybrid k, clustering and boosting. a comparison of this scheme versus a k-means/svm approach is provided. results are shown and discussed. keywords-natural language processing (nlp); sentiment analysis; social networking analysis; social networking sites (sns) i. introduction with the continuous increase in the use of social networking sites (sns), it has become quite possible to judge the sentiments and reactions of the public towards any news or tweet posted, a fact with interesting possibilities [1]. every conversation that occurs in the sns has several different reactions that depict the effectiveness of the post and help analyze the public sentiment towards it [2]. sentiment analysis is an interdisciplinary field that crosses natural language processing, artificial intelligence, and text mining. since most opinions are available in text format and its processing is easier than other formats, sentiment analysis has emerged as a subfield of text mining [3]. sentiment analysis appeared in the literature in 90’s for the first time and it became a major research topic in 00’s. classifying the polarity of a given text as positive or negative is the basic task of sentiment analysis. due to its many aspects it is often referred to with different names such as opinion mining, sentiment classification, sentiment analysis, and sentiment extraction. it is widely believed that sentiment analysis is needed and useful while it is also widely accepted that extracting sentiment from text is a hard semantic problem even for human beings. additionally, sentiment analysis is domain specific, therefore the polarity of some terms depends on the context in which they are used. for example, while “small” for “size” as a feature in the electronic products is positive, in agricultural products such as fruit it has a negative polarity. sentiment analysis is used in different domains such as shopping, entertainment, politics, education, marketing, and research and development. there are several sentiments of the public towards the sns posts that include: positive and negative along with the n-point scale that includes very good, good, satisfactory, bad and very bad [3]. text mining is the famous way to analyze and understand the sentiment of people integrated with the content posted and its methods are: machine learning, statistical/quantitative techniques or natural language processing [4]. the sentiment analysis is of two kinds, supervised or unsupervised. in [5] a method to apply an approach of mlt, based on maximal discrepancy concept, to the problem of svm model selection has been detailed. sentiment analysis approaches are reported in [6-8] and an overall review can be found in [9]. social media insights and especially twitter are also essential [10-13].this paper, following [14], focuses on sentiment classification in social issues, thus on determining the public’s reaction over a particular tweet in order to get the proper assistance to determine the public reaction towards the news and its effects. ii. implementig a hybrid approach social issues sentiment analysis automatically analyzes social issues. it identifies the positive, negative or neutral opinion. the conceptual framework comprises of four stages: data collection and cleaning; preprocessing; sentiment analysis and finally experiments and results. the architecture of the proposed framework for sentiment analysis is presented in figure 1. a. text collection and cleaning stage for the analysis of social issues tweets, data is collected. the input data will be raw text from tweets on social causes in india, in particular on ‘jnu agitation’, “intolerance in india”. the motivation for the topics has been derived from the a web interview of twitter india director in 2016, as the topics had the power to polarize the entire country and to shape opinion of common countrymen leading to a sharp divide in indian engineering, technology & applied science research vol. 7, no. 5, 2017, 2014-2016 2015 www.etasr.com madhukar and verma: hybrid semantic analysis of tweets: a case study of… society. for creating the corpus of tweets, the tweets are fetched from the twitter database based on hashtags (#), using twitter api for connecting and authenticating. the collected text is noisy and cleaning and parsing the data to form a corpus for further processing is required. b. preprocessing stage at this stage, the corpus is transformed into feature vectors. strings are converted into words using some filtration techniques. we adapted a simple feature selection as a preprocessing method to transform or tokenize the text stream to words. these methods constitute a sequence of the following asks: removing delimiters, removing numbers and stop words. for stop words removal, a list of stop words is provided in the filtration process. fig. 1. architecture of the proposed methodology c. sentiment analysis stage this stage of framework handles the polarity measurement and sentiments. we approach these tasks by employing the following hybrid machine learning methods. in this approach, we have combined clustering with classification. in clustering, hybrid clustering approach is used which combines the feature of k-modes and k-medoid algorithms. the functionality of the hybrid clustering is as follows:  the size of cluster is fixed and the output of the first phase forms initial clusters. here, the input array of elements is scanned and split up into sub-arrays, which represent the initial clusters.  the cluster sizes vary and the output of this phase are the finalized clusters. initial clusters are inputs for this phase. the centroids of these initial clusters are computed first, on the basis of which distance from other data elements are calculated. furthermore, the data elements having less or equal distance remains in the same cluster otherwise they are moved to appropriate clusters. the entire process continues until no changes in the clusters are detected.  for classification, improved bagging is used. classifying the clustered data is performed by using improved bagging technique which decreases the variance of the prediction using dataset using combinations with repetitions to produce multi-sets of same size of the dataset. for each multi set the boosting learning algorithm is applied to classify the instances and a model is created and a vote related to that model is generated. the average of all the predicted votes is considered to be the result of the classifier. iii. experimental results and discusions a. performance parameters  accuracy: accuracy is the percentage of testing set examples correctly classified by the classifier. it is the proportion of total number of predictions that are correctly classified in class. accuracy = (tp + tn) / (tp + fp + tn + fn) (1) where, tp is true positive, tn is true negative, fp is false positive, fn is false negative  precision: percentage of selected instances that are relevant and are correctly classified in class out of all documents in class. precision = (tp) / (tp + fp) (2)  recall: percentage of correct documents that are selected in class from the entire document actually belonging to class. recall = (tp) / (tp + fn) (3)  confusion matrix: also, known as contingency table or error matrix in supervised learning and in unsupervised learning is called matching matrix. in confusion matrix, roc is used to plot graph. various measures could be defined basing on values in a confusion matrix.  true positive (tp) and false positive (fp) rate: for multiple comparisons tp and fp is used and it is a type of error. tp is also called sensitivity as if a person has a disease how often will the test be positive is referred to as true positive rate. fp is an error in a test result indicates presence of a condition. tpr = (tp) / (tp + fn) (4) fpr = (fp) / (fp + tn) (5)  f-measure: a measure that combines precision and recall. f-measure = 2*(precision * recall) / precision + recall (6) so, considering every 6th frame leads to good enough results and speeds up the task. the output images of these are engineering, technology & applied science research vol. 7, no. 5, 2017, 2014-2016 2016 www.etasr.com madhukar and verma: hybrid semantic analysis of tweets: a case study of… then fused together for the final text detection. thus, fusion results obtained are more informative when every 6th frame is fused together. figures 2-4 shows the comparison graphs of tp rate and fp rate and precision recall and f measure of proposed technique with previous techniques. fig. 2. classification cccuracy comparison fig. 3. number of classified instances comparison. fig. 4. precision recall and f measure comparison. iv. conclusion and future scope sentiment analysis, as an interdisciplinary field that crosses natural language processing, artificial intelligence, and text mining, recognizes opinions of people regarding a product, service, object, or social issues expressed in a given text. up until recently most, if not all, research in sentiment analysis has been done on the products and services. determining public opinions regarding social issues is important for governance and decision making. this paper has focused on sentiment analysis of social issues. a new hybrid method for sentiment analysis of social issues is proposed. it extracts the opinions from each sentence, constructs correspondence opinion structures, and then determines their orientations regarding the social issue. this algorithm performs better in comparison with a previous k-means/svm approach. in the future, the work can be extended by containing a larger dataset and considering more instances which may cooperate in higher accurate prediction analysis. references [1] a. shaikh, t. pritam, p. ankita, w. shital, t. pooja, “stock exchange market prediction”, international journal of advances in computer science and technology, vol. 3, no. 5, pp. 349-351, 2014 [2] a. joshi, a. r. balamurali, p. bhattacharyya, r. mohanty, “c-feel-it: a sentiment analyzer for micro-blog”, hlt '11 proceedings of the 49th annual meeting of the association for computational linguistics: human language technologies: systems demonstrations, pp. 127-132, portland, oregon, june 21, 2011 [3] a. abbasi, “intelligent feature selection for opinion classification”, ieee intelligent systems, vol. 25, no. 4, pp. 75-79, 2010 [4] s. haykin, neural networks: a comprehensive foundation, prentice hall, 1998 [5] d. anguita, a. ghio, n. greco, l. oneto, s. ridella, “model selection for support vector machines: advantages and disadvantages of the machine learning theory”, proc. of the international joint conference on neural networks (ijcnn), barcelona, spain, 2010 [6] d. rajput, m. madhukar, s. verma, m. sharma, “sentiment analysis on big data using machine learning for holiday destinations”, 2015 ieee european modelling symposium , spain, october 6-8, 2015 [7] a. kumar, t. mary, “sentiment analysis: a perspective on its past, present and future”, international journal of intelligent systems and applications, vol. 10, pp.1-14, 2012 [8] a. somla, s. v. n. vishwanathan, introduction to machine learning, cambridge university press, 2009 [9] a. m. kaplan, m. haenlein, “users of the world, unite! the challenges and opportunities of social media”, business horizons, vol. 5, no. 1, pp. 59-68, 2010 [10] n. anitha, b. anitha, s. pradeepa, “sentiment classification approaches”, international journal of innovation engineering and technology, vol. 3, no. 1, pp. 22-31, 2013 [11] b. j. jansen, m. zhang, k. sobel, a. chowdury, “twitter power: tweets as electronic word of mouth”, journal of the american society for information science and technology, vol. 60, no. 11,pp. 2169–2188, 2009 [12] b. pang, l. lee, s. vaithyanathan, “thumbs up? sentiment classification using machine learning techniques”, proceedings of the conference on empirical methods in natural language processing, philadelphia, pp. 77-86, 2002 [13] c. vicient, a. moreno, “unsupervised topic discovery in microblogging networks”, expert systems with applications, vol. 42, pp. 6472–6485, 2015 [14] s. verma, m. sharma, d. rajput, m. madhukar, v. mittal, r. singh, “disclosing tweet polarity using feature representation factor”, international journal of latest trends in engineering and technology, vol. 5, no. 2, 2015 microsoft word etasr_v12_n2_pp8248-8252 engineering, technology & applied science research vol. 12, no. 2, 2022, 8248-8252 8248 www.etasr.com zisopol et al.: a statistical approach of the flexural strength of pla and abs 3d printed parts a statistical approach of the flexural strength of pla and abs 3d printed parts dragoș gabriel zisopol mechanical engineering petroleum – gas university ploiesti, romania zisopol@zisopol.ro ion nae mechanical engineering petroleum – gas university ploiesti, romania inae@upg-ploiesti.ro alexandra-ileana portoaca mechanical engineering petroleum – gas university ploiesti, romania alexandra.portoaca@upg-ploiesti.ro ibrahim ramadan mechanical engineering petroleum – gas university ploiesti, romania ing_ramadan@yahoo.com received: 7 january 2022 | accepted: 21 january 2022 abstract-the need for rapid obtaining parts has made researchers to widely study 3d common printing technologies like fdm (fused depositing modeling), sls (selective laser sintering), sla (stereolithography). although fdm can provide high geometrical complexity of parts at convenient costs and with efficient delivery logistics, a set of printing parameters of the raw materials used for manufacturing needs to be optimized accordingly. therefore, this study reveals the influence of printing parameters on the flexural strength of pla (polylactic acid) and abs (acrylonitrile butadiene styrene) printed samples, by applying the taguchi method and anova (analyisis of variance) of 3-point bending tests results. keywords-3d printing; experimental tests; 3-point bending; taguchi method i. introduction additive technologies can accomplish technical tasks like complex geometrical part manufacturing with minimum cost and less complex technology by using a single step fabrication process. fdm is the most common technique in additive manufacturing (am) that refers to the process in which successive layers of material are stored in a computercontrolled environment to create a three-dimensional object [1, 2]. however, in order to achieve the needed mechanical characteristics in industries such as bioengineering, aerospace, and automotive, several specific printing parameters must be adapted and optimized [2, 3]: • building orientation: usually testing specimens are flat, on edge, and upright oriented. • temperature conditions: environment, extrusion, bed and platform temperature. • slicing parameters: layer thickness, nozzle diameter/ bead/ road width, flow rate, deposition speed, infill percentage. the considaration of several printing parameters can ensure the quality of products, improving dimensional precision, avoiding the production of waste and large amount of scraps, and increasing productivity rates [3-7]. for the optimization of the process conditions of fdm rapid prototyping technology, several statistical optimization techniques have been successfully used. applying the taguchi method to determine the design of experiment, signal to noise (s/n) ratio and anova are commonly used to identify the influence of the determinant factors [3, 4, 8]. the novelty of this paper consists in the comparison of the flexural strength of the most common materials used within the fdm technology (pla and abs) and the behavior of printed parts related to process variables (layer thickness and infill percentage). this matter can be used to optimize the specific mechanical characteristics used for various technical applications. ii. materials, methods and procedures a. setting up process parameters beside process parameters, the materials used to manufacture the parts by the fdm process also significantly affect their mechanical properties. the most widely used raw materials are thermoplastics such as abs, pla, polyethylene, teflon, and polypropylene, high-impact polystyrene resin (hips), polyethylene terephthalate glycol (petg), and polyamide (pa). for pla and abs the specifications collected from filament producers are shown in table i. each 3d printed sample results from a combination of signal factors such as layer thickness and infill percentage as shown in table ii. b. sample preparation a total of 45 samples (5 samples of each combination of 3 layer thicknesses and 3 infill percentages) with standard corresponding author: alexandra-ileana portoaca engineering, technology & applied science research vol. 12, no. 2, 2022, 8248-8252 8249 www.etasr.com zisopol et al.: a statistical approach of the flexural strength of pla and abs 3d printed parts dimensions [9, 14, 15] (figure 1) were fabricated from pla and abs, with a raise e2 3d printer, with a volume capacity of 330×240×240mm and then were tested on a lloyd lrx force tester electro-mechanical testing machine (figure 2). autodesk inventor was used for designing the samples and the drawing was converted in stl format. process parameters were adjusted with the idea maker software, including internal structure pattern (figure 3), layer thickness, and infill percentage. table i. fdm flexural strength sample parameters parameters material specifications pla abs nozzle diameter 0.40 mm 0.40 mm build orientation flat flat layer thickness according to table ii according to table ii top solid layers 4 layers 4 layers bottom solid layers 4 layers 4 layers outline/perimeters shell 3 outlines 3 outlines internal fill pattern lines lines external fill pattern rectilinear rectilinear internal fill percentage according to table ii according to table ii internal infill angle offsets 180◦ 180◦ extruder temperature 210 ◦c 240 ◦c heated bed temperature 60 ◦c 110 ◦c default printing speed 70 mm/s 40 mm/s filament diameter 1.75 mm 1.75 mm filament density 1.24 g/cm3 1.05 g/cm table ii. fdm variance of signal factors signal factor selection levels layer thickness (a) infill percentage (b) 1 0.1 50% 2 0.2 75% 3 0.15 100% fig. 1. flexural specimen according to iso 178 [9]. c. flexural strength experimental tests the method is used to investigate the flexural behavior and to determine flexural strength. the deformation of the specimen gets to the point of maximum deflection, so, the maximum bending stress can be named flexural strength. the loading speed of the test was 1mm/min and the distance between the supports was calculated and measured at 64mm (l=16h, where h is the specimen’s height [9]). tests were performed at room temperature (20°c) and the samples were allowed to acclimatize for at least 24h. flexural strength was calculated with [9]: σ� � ����� (1) where σf is the flexural stress parameter in question, f is the maximum bending load (n), l is the span length (mm), b is the width of the specimen (mm), and h is the height of the specimen (mm). the results for each material are listed in tables iii and iv. fig. 2. electro-mechanical machine lloyd lrx force tester. fig. 3. internal and external infill pattern of the samples for the 3 point bending test. iii. results and discussion a. taguchi method and s/n ratio the actual results were analyzed with the minitab statistical software. with the taguchi method, parameter design converts the objective value to s/n ratio, which is known as the relation of s/n ratio in terms of the experimentally quality characteristic evaluation index [10-12]. s/n ratio represents a statistic reference that makes a comparison between the level of positive signal variables to the level of background noise parameters. in this study, the aim is to improve the mechanical properties of 3d printed parts and to transform signal parameters into system control factors. therefore, in minitab, the larger-the-better criterion is used, and s/n ration (η) is calculated with [4]: η � �10log���∑ � �� � ��� � (2) where η is the s/n ratio, wi is the i position result of the experiment, and p is the repeated times of a trial. the two experimental results in s/n ratio are shown in tables iii and iv. η1, η2 are the s/n ratio for flexural strength both for pla and abs samples. engineering, technology & applied science research vol. 12, no. 2, 2022, 8248-8252 8250 www.etasr.com zisopol et al.: a statistical approach of the flexural strength of pla and abs 3d printed parts table iii. means of flexural strength (pla) layer thickness (a) infill (b) maximum flexural strength (mpa) η1 1 1 106.9575 40.5842 1 2 110.9040 40.8989 1 3 107.9085 40.6611 2 1 95.4525 39.5957 2 2 110.9805 40.9049 2 3 113.5380 41.1028 3 1 101.1675 40.1008 3 2 109.1985 40.7643 table iv. means of flexural strength (abs) layer thickness (a) infill (b) maximum flexural strength (mpa) η2 1 1 71.9184 37.1368 1 2 75.3567 37.5424 1 3 77.7345 37.8123 2 1 52.5024 34.4036 2 2 56.1318 34.9842 2 3 78.4725 37.8943 3 1 50.2539 34.0234 3 2 55.4201 34.8733 by analyzing the s/n ratio, the significance of signal factor can be determined. the infill percentage ranks first (table v), so the layer thickness has a smaller significance, as shown in figure 4, in the pareto chart for pla samples. table v. response table for s/n ratios (pla and abs) level layer thickness (pla) infill (pla) level layer thickness (abs) infill (abs) 1 40.71 40.09 1 37.50 35.19 2 40.59 40.86 2 34.62 35.80 3 40.53 40.89 3 35.76 36.89 delta 0.18 0.80 delta 2.88 1.70 rank 2 1 rank 1 2 b. anova anova [13, 14, 16] was performed in order to identify the importance of factors and the influence on flexural strength. the results of the anova analysis applied to the pla test specimens are listed in table vi and express the total sum of square deviation (ss), total degrees of freedom (df), the variances or square means (ms), f-value ratio, and p-value. the level of confidence was considered 95% which relates to a p-value smaller or equal to 0.05 to accept or reject the initial hypothesis that all means are equal. consequently, a p-value of 0.838 confirms the level of significance of the signal factor layer thickness, but the f-value, which represents a ratio between the variance of the category groups related to the variance of the entire group suggest more pronounced influence of the infill percentage signal factor to the results of flexural strength of pla 3d printed test samples. in comparison, the relative influence of factors and interactions is determined by the applied anova to the flexural strength means of abs 3d printed samples. the results are listed in table vii. as it can be also seen in table v, in the case of using this raw material, the signal factor layer thickness is ranked first. the influence of the factor is also highlighted by the corresponding f-value (7.18) and can be observed in a graphical form in figure 5. however, a less significant difference, compared with the pla anova results, between the influences of the factors can be observed. table vi. anova for pla samples source df adj ss adj ms f-value p-value layer thickness 2 0.05082 0.02541 0.19 0.838 infill 2 1.22012 0.61006 4.45 0.096 residual error 4 0.54861 0.13715 total 8 1.81954 table vii. anova for abs samples source df adj ss adj ms f-value p-value layer thickness 2 677.7 338.86 7.18 0.047 infill 2 243.9 121.95 2.59 0.190 residual error 4 188.7 47.17 total 8 1110.3 fig. 4. pareto chart for pla samples with predictors: infill and layer thikness. fig. 5. pareto chart for abs samples with predictors: infill and layer thikness. finally, regarding the initial assumption, all p-values are greater than 0.05 (the initial hypothesis is confirmed and all means are equal), beside the one corresponding to the factor engineering, technology & applied science research vol. 12, no. 2, 2022, 8248-8252 8251 www.etasr.com zisopol et al.: a statistical approach of the flexural strength of pla and abs 3d printed parts layer thickness for abs samples which reveals that the initial hypothesis is rejected, so the means are not equal. c. graphical analysis the graphical representation of the significant factors layer thickness and infill percentage is displayed in the interaction plot for maximum flexural strength (figure 6). data means for pla 3d printed test samples reveal a correlation with the anova results and a similarity between the graphs concerning factor a is being observed. by comparison, the graphical representation of the interaction plot for maximum flexural strength for abs 3d printed test specimens reveals a higher level of significance in 0.10mm layer thickness, that can be distinguish in figure 7. as can be seen, for pla, the signal factor b (infill percentage) has a higher influence on the means of flexural strength, as for the abs, the layer thickness (signal factor b) is more significant. fig. 6. interaction plot between data means (pla). fig. 7. interaction plot between data means (abs). from the main effect plot for s/n ratio in figures 8 and for pla and abs 3d printed test specimens respectively, the optimum levels of the two main signal factors for each response of the part can be obtained intuitively. fig. 8. main effect plot for s/n ratio (pla). fig. 9. main effect plot for s/n ratio (abs). iv. conclusions in this study, the effect of layer thickness and infill percentage on the flexural strength of parts fabricated by fdm technology was conducted to compare pla and abs, the most commonly raw plastic materials used. the parts obtained with this technology have a different anisotropic behavior than those fabricated by injection [17]. in conclusion, the flexural strain results of the test specimens have been analyzed and processed with statistical software, performing s/n ratio and anova with the aim of obtaining the final significant factors and optimal printing parameters. thus, by processing the results it can be observed that layer thickness and infill parentage, as process variables, affect differently the performance of pla and abs printed parts in terms of flexural strength. infill percentage as a signal factor has a greater influence than layer thickness regarding the pla material while layer thickness is more significant for the abs material. pla has a better performance regarding the flexural strength (maximum value reached was 122.5125mpa and the average value was 107.4643mpa) in comparison with abs (maximum value reached 80.2350mpa and average value was engineering, technology & applied science research vol. 12, no. 2, 2022, 8248-8252 8252 www.etasr.com zisopol et al.: a statistical approach of the flexural strength of pla and abs 3d printed parts 63.7516mpa). for several applications and technical fields the use of pla is constrained by its low thermal resistance, low impact resistance, and glass transition temperature (55 and 60◦c) [1]. so, this study can be taken into consideration when choosing the appropriate material and adapting convenient printing parameters, but also considering other mechanical characteristics for the specific type of application. in [4], several different signal factors have been taken into account, so flexural strength has a range of values between 51.31 to 90.13mpa. the result of [1] reveals flexural strength with values ranging between 31.1 to 59.1mpa. the difference between the values obtained in this article and the values obtained in other studies can be explained by signal factors such as deposition orientation, deposition style, raster width, raster gap as well as using variations of plastic materials. in this regard, further studies will be conducted for a better understanding of the most significant factors and materials that can influence the main mechanical properties. references [1] j. c. camargo, á. r. machado, e. c. almeida, and e. f. m. s. silva, "mechanical properties of pla-graphene filament for fdm 3d printing," the international journal of advanced manufacturing technology, vol. 103, no. 5, pp. 2423–2443, dec. 2019, https://doi.org/ 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[13] g. s. peace, taguchi methods: a hands-on approach. reading, ms, usa: addison-wesley, 1992. [14] a. portoaca, i. nae, d. g. zisopol, and i. ramadan, "studies on the influence of fff parameters on the tensile properties of samples made of abs," iop conference series: materials science and engineering, vol. 1235, no. 1, nov. 2022, art. no. 012008, https://doi.org/10.1088/1757899x/1235/1/012008. [15] d. g. zisopol, i. nae, a. i. portoaca, and i. ramadan, "a theoretical and experimental research on the influence of fdm parameters on tensile strength and hardness of parts made of polylactic acid," engineering, technology & applied science research, vol. 11, no. 4, pp. 7458–7463, aug. 2021, https://doi.org/10.48084/etasr.4311. [16] c. f. j. wu and m. s. hamada, experiments: planning, analysis, and optimization, 2nd ed. hoboken, nj, usa: wiley, 2009. [17] n. n. antonescu, m. i. a. naboulsi, m. g. petrescu, and a. neacsa, " behaviour of metal-rubber couplings or any other plastic materials in translational motion under wear generating conditions ," journal of the balkan tribological association, vol. 12, no. 4, 2006. microsoft word 6-449-ed.doc engineering, technology & applied science research vol. 4, no. 3, 2014, 656-661 656 www.etasr.com sekrane and asroun: modelling the effects of aggregate size on alkali aggregate reaction expansion modelling the effects of aggregate size on alkali aggregate reaction expansion nawal zahira sekrane civil engineering and environment laboratory djillali liabes university of sidi bel abbes sidi bel abbés 22000, algeria n.sekrane@gmail.com aissa asroun civil engineering and environment laboratory djillali liabes university of sidi bel abbes sidi bel abbés 22000, algeria a_asroun@yahoo.fr abstract— this work aims at developing models to predict the potential expansion of concrete containing alkali-reactive aggregates. the paper gives measurements in order to provide experimental data concerning the effect of particle size of an alkali-reactive siliceous limestone on mortar expansion. results show that no expansion was measured on the mortars using small particles (0.5-1.0 mm) while the particles (1.0–2.0 mm) gave the largest expansions (0.217%). two models are proposed, the first one studies the correlations between the measured expansions and the size of aggregates, the second one calculates the thickness of the porous zone necessary to take again all the volume of the gel created. keywords-alkali aggregate reaction; expansion; particle size; model; porous zone. i. introduction alkali aggregate reaction (aar) affects numerous civil engineering structures and causes irreversible expansion and cracking. aar is a chemical reaction between the reactive siliceous phases of aggregates and alkalis of the cement. the product of the reaction (gel) leads to the apparition of a swelling pressure causing expansion and cracking. the consequences are a decrease in the functional capacities of civil engineering structures such as hydraulic dams. the gel volume formed by the chemical reaction can be used as input data to structural models [1]. one of the main difficulties is to assess the volume of this gel [2]. microscopic models [3–5] could be one method of doing this. such models should be able to predict the differences of expansions with the variation of all influential parameters such as the aggregate size and should be compared with experimental results. several papers deal with the effect of particle size of reactive aggregates on the expansion due to aar. experiments have been performed on different types of aggregates. it seems that the highest aar-expansion caused by the effect of the particle size of the reactive aggregate depends on the composition of the aggregate itself [6-10]. our work aims to study the effect of size for reactive siliceous limestone; this type of aggregate has been used in many structures. therefore, in order to test models to predict the potential expansion of concrete containing such alkali reactive aggregates, tests have been performed to provide experimental data on the effect of particle size on mortar expansion. this paper presents the experimental results and gives the data necessary for model development. three mixdesigns were studied containing one reactive size distribution (0.5-1.0 mm, 1.0-2.0 mm or 2.0-4.0 mm). first, the paper presents the experimental conditions of the tests; then, the measurements of aar-expansions are presented. finally, a model is proposed to analyze the experimental results by studying the correlations between the measured expansions and the size of aggregates. another model is presented, which calculates the thickness of the porous zone necessary to take again all the volume of the gel. ii. experimental conditions a. materials the cement used to carry out these tests was a cem i 42.5 portland cement which contains a rate of alkaline equivalent (na2oeq)≤0.6%, it has a blaine specific area of 3585 cm2/g and a density of 3.2. the chemical and mineralogical composition according to bogue formulas are given in tables i and ii respectively. a water to cement ratio of 0.45 was used. the aggregate used was the sand of the careers whose bed rock is a siliceous limestone which is an alkali-reactive rock. it is crushed and sieved to the following three size ranges: 0.5-1.0 mm, 1.0-2.0 mm and 2.0-4.0 mm with sand to cement ratio of 2.25. the chemical composition of the aggregate is given in tables iii. table i. chemical composition of the cement. oxide % sio2 22.07 cao 63.83 al2o3 6.41 fe2o3 4.16 mgo 0.21 so3 1.49 p.f 1.73 na2oeq 0.60 free cao 0.16 engineering, technology & applied science research vol. 4, no. 3, 2014, 656-661 657 www.etasr.com sekrane and asroun: modelling the effects of aggregate size on alkali aggregate reaction expansion table ii. mineralogical composition of the cement according to bogue. minerals % c3s 38.09 c2s 34.62 c3a 9.95 c4af 12.65 table iii. chemical composition of the aggregate.  oxide % sio2 5.92 cao 47.10 al2o3 3.32 fe2o3 0.99 mgo 0.85 so3 0.89 p.f 39.29 to prepare the soda solution, the pastilles of sodium hydroxide (naoh) were dissolved in distilled water. the mix designs are reported in the table iv. table iv. the quantities used for mortar. material mortar batch cement 800 g aggregate 1800 g water 360 ml sodium hydroxide 40 g/l b. mixing and moulding procedure for each test a mould of three prismatic samples of 40x40x160 mm was used. all samples were cast using the following protocol [11-12]: cement was mixed with water in the mixer at slow speed for 30 s; after, aggregate was added to the mix; mixing was continued for 30 s at high speed. molds were filled on two stages by carrying out 60 shocks after each stage using the table with shock. the bars were covered with plastic sheet and placed in a sealed container containing water. after 24 h, all samples were demolded and their initial length measurement were taken by the difrometer which is equipped with a comparator making it possible to carry out measurements with an exactitude less than or equal to 0.005 mm. each measurement was the mean of the values of the three samples. the bars were immersed in water in sealed containers which were then placed in an oven at 80°c for 24 h; then they were transferred in containers filled with a 1m naoh solution during 14 days in the oven at 80°c. the length changes of the bars were measured at 3, 5, 7, 10, 12 and 14 days, respectively. iii. experimental results and discussion the expansions for bars with a single fraction of reactive aggregate were obtained by subtracting the initial length of the samples taken at the time of the demolding from the final length at time (t). the relative variation length was given by the following formula: l ll ii i 01  (1) with i : relative deformation of sample i (i=1, 2, 3). il0 : the initial length of sample i (i = 1, 2, 3). il1 : the final length of sample i (i = 1, 2, 3). the expansion  was obtained by the mean of the i . expansion results for samples are reported in figure 1, a similar shape of expansion curve is observed and it is indicated that the expansion of bars basically increases with time. for the same content of reactive particles, the expansion was smaller for the 0.5-1.0 mm reactive particles than for the 1.0-2.0 mm and 2.0-4.0 mm reactive ones. using 0.10% as criteria for expansion, the bars with 0.5-1.0 mm aggregate particles showed aar-expansion lower than about (0.045%). it clearly indicates that, the bars with 1.0-2.0 mm size fraction gave the largest expansion (0.217%), for bars with 2.0-4.0 mm aggregate particles aar-expansion measured is (0.148%). figure 2 and figure 3 shows the kinetics of the aarexpansion measured for 14 days. for this reactive siliceous limestone, no aarexpansion was measured for small reactive particles (less than 1.0 mm). aar-expansion appeared for particles having diameters greater than 1.0 mm. the critical particle size that caused aar-expansion was around 1.25 mm and 1.75 mm. aar-expansion increased with the size of reactive particles between 0 and 1.75 mm. finally, the larger reactive particles (2.0-4.0 mm) showed lower expansions. iv. model and discussion the models presented in this section aim to improve the understanding of the experimental results obtained in the first part. the first model calculates the asymptotic expansion of mortars containing only one size [13], the second model calculates the distance in which the gel must diffuse in the paste to be completely adapted by the porosity [14]. finally, it should be noted that the fitted parameters supplied here are only applicable for the aggregate studied in this paper. the various assumptions constitutive of the models are (figure 4):  the siliceous aggregates are spherical of diameter di ;  a volume of silica produced “ n ” volume of gel ( n >1);  the small and coarse aggregates are attacked on an identical thickness “ x ”;  there exists a porous zone of thickness “ t ” surrounding the aggregates in which the products are formed;  the layer of the gel surrounding the aggregates is fine in comparison with the diameter of the aggregates and its thickness is uniform. the reactional mechanisms selected are inspired by those evoked in [15-17]. the ions (alkaline, ions hydroxyls and engineering, technology & applied science research vol. 4, no. 3, 2014, 656-661 658 www.etasr.com sekrane and asroun: modelling the effects of aggregate size on alkali aggregate reaction expansion calcium) penetrate in the reactive aggregates by diffusion. the siliceous system is attacked by the ions hydroxyls. the created negative charges are balanced by the alkaline ones and the ions calcium to form silico-alkaline products (gel) or silico-calcic. these products are formed in a zone of porosity surrounding the reactive aggregates. when the volume of the products becomes larger than porous volume available, the concrete starts to swell [18]. fig. 1. expansions of mortars with a single reactive fraction as a function of time. fig. 2. expansions of mortars containing reactive particles of size (0.5 1.0) mm, (1.0 2.0) mm, (2.0 4.0) mm measured at 14 days. fig. 3. relationship between expansion and reactive particles size. fig. 4. schematic of a reactive aggregate: (a) before the reaction and (b) after the reaction. a. asymptotic expansion model the expansion of the mortar is caused by the expansions of the aar-gels. it can be assumed that this expansion is caused by the volume variation of the aggregate (in the presence of gel). for the sake of simplicity, it is assumed that the mortar expansion due to aar ( aar ) is proportional to the aggregate expansion (2). for several sizes of reactive particles, the aggregate expansion is the sum of the expansions of all the reactive aggregates [13]. i n i iaar k     1 . (2) where: i : the expansion of one reactive aggregate of class i. i : the volume fraction of reactive aggregates of class i relative to the mortar volume (total volume of reactive aggregate of class i / total volume of the mortar). n : the number of classes of reactive aggregates. k : the fraction of expansion due to aar related to the expansion of reactive aggregates. during the reaction, at a given moment, the aggregate is attacked on a thickness “ x ” and it produces a volume of the gel equal to giv :             6 2 6 . 33 xdd nv iig i  (3) during the formation of the aar-gel, a part of the gel can migrate through the porosity close to the aggregate. therefore, the aggregate expansion for one aggregate i can be described by (4). i p i g i i v vv    (4) with: (a) (b) engineering, technology & applied science research vol. 4, no. 3, 2014, 656-661 659 www.etasr.com sekrane and asroun: modelling the effects of aggregate size on alkali aggregate reaction expansion p iv : the volume of the porosity close to the reactive aggregate in which the aar-gel can migrate without causing expansion. v i : the volume of one reactive particle, it is given by the following formula: 6 i i d v   (5) where: di : the diameter of the reactive particle. x  : the positive part of x , x < 0, x  = 0 if: x > 0, x  = x assuming that the gel can migrate along the same distance of the aggregate “ t ” whatever the size of the aggregate (simplifying hypothesis), the volume of the porosity is given by (6):   p dtd v iipi . 66 2 33             (6) where: p : is the porosity of the mortar. the combination of (2)–(6) for only one class of reactive particles leads to the (7).                                           1 3 32 . 3 32 1... id tidp id xidnikaar  (7) in order to carry out this calculation and in order to obtain a linear expansion (comparable to the measured expansion on mortars), the porosity of the mortar ( p ), the thickness of attack of the aggregates ( x ), the voluminal coefficient of the gel ( n ) and the distance ( t ) which gel must diffuse in the cement paste are fixed. these calculations are performed using maple 12. the calculated expansions are plotted in figure 5. these results are similar to the experiments results. it is shown that the bars with 0.5-1.0 mm size fraction showed aar-expansion equal to 0.031%, the bars with 1.0-2.0 mm size fraction gave the largest expansion (0.227%) and the bars with 2.0-4.0 mm size fraction gave expansion equal to 0.167%. figure 6 compares experiment results of aar-expansion of mortars containing one size of reactive particles with the results calculated by the asymptotic expansion model; they have a similar shape of expansion curve. it is observed that the model represents the experimental data well. to sum up, the model developed in this section assumes that the increase of aar-expansion with the size of reactive particles can be explained by the effect of the porosity connected to the reactive aggregate. the volume of gel was calculated according to (3) and the volume of porosity to be filled around each particle of diameter di before the expansion starts is given by (6). the expansion of mortar was then taken as the volumetric change of the aggregate due to the gel volume not contained in the porous zone (4). this simple relation allows the final expansion to be plotted against the reactive aggregate. the small reactive particles, because of their uniform distribution in the paste, could create gel distributed regularly in all the mortar. this gel would migrate in the matrix and to be easily adapted by the porosity of the cement paste, without creating expansion of the mortar. but, the gel produced around the coarse grains could generate considerable pressures leading to important macroscopic swellings if the thickness of porosity was little. fig. 5. expansion of the mortars against the diameter ( di ) of the reactive particles: calculated by the asymptotic expansion model (k=0.1, n=2.5, x=0.25, t=0.7, p=10%). fig. 6. expansion of the mortars against the diameter ( di ) of the reactive particles: comparison between the experiments and the asymptotic expansion model (k=0.1, n=2.5, x=0.25, t=0.7, p=10%). engineering, technology & applied science research vol. 4, no. 3, 2014, 656-661 660 www.etasr.com sekrane and asroun: modelling the effects of aggregate size on alkali aggregate reaction expansion b. model calculating the thickness “ t ” of the porous zone as cited in the first section, a porous zone of thickness “ t ” around the reactive aggregate exists, which is connected to the gel formation site. the volume of porosity to be filled around each particle of diameter di before the expansion starts was computed according to (6). if this thickness was little, the gel could not move without creating too important pressures on the matrix. our aim is to estimate this thickness according to the diameter of the reactive particles in order that gel created could be completely adapted by the porosity of the paste. the volume t iv for the gel created is equal to the sum of the volume of the gel produced by the aggregate during its reaction and of the volume of the porosity in which the gel can diffuse: tiv             6 2 6 33 xdd ii  +   p dtd ii . 66 2 33            (8) then it is necessary that: t i g i vv  (9) from (9), the distance “t” is calculated:    2 2. 1 3 3 33 ddxdd p n t iiii               (10) the results of calculations using maple 12 are plotted in figure 7. fig. 7. the distance “ t ” in which the gel must diffuse in the paste to be completely adapted by the porosity according to the diameter di of the aggregate ( n =2.5, x =0.25 mm, p =10%). figure 7 gives the evolution of “ t ” and shows that the gel produced in the small aggregates (0.5 mm) needs less distance to be adapted by the porosity of the paste ( t = 0.379 mm), however the thickness become important for aggregates greater than 1 mm. the figure shows also that an aggregate greater than 2 mm, for example, needs a thickness of porous zone higher than 1.13 mm for not generate pressures on the paste. then, the results of calculations by this model indicates that, if there is a lot of gel, “ t ” has to be large to prevent expansion for the reactive particles. v. conclusion in this paper a combination of experiments and modelling was used to study the size effects of the reactive siliceous limestone on aar-expansions. for this reason, three particle size fractions were studied in mortars and the experimental measurements were presented. the results indicate that, for the (40x40x160) mm specimen cured in the 1m naoh solution at 80°c, no aar-expansion was measured for the mortar bars containing (0.5-1.0 mm) size range while the mortar bars containing (1.0-2.0 mm) size range show the largest expansion, especially at early ages (0.217%) and for bars with (2.0-4.0 mm) aggregate particles, the aar-expansion measured is (0.148%). the first model sums up the main experimental observations; it allows some important phenomena related to the size of reactive aggregate to be interpreted easily. the smallest reactive particles did not cause expansion, but the largest ones expanded greatly. the second model aims to compute the thickness of the porous zone necessary to take back all the volume of the gel created by the reactive aggregates in the cement paste according to the diameter of the grains. the results indicate that the thickness increases with the diameter of the reactive aggregates. references [1] b. capra, a. sellier, “orthotropic modeling of alkali-aggregate reaction in concrete structures: numerical simulations”, mechanics of materials, vol. 35, no. 8, pp. 817–830, 2003 [2] a. sellier, e. bourdarot, s. multon, m. cyr, e. grimal, “assessment of the residual expansion for expertise of structures affected by aar”, 13th international conference on alkali-aggregate reaction in concrete, trondheim, norway, pp. 1004–1013, 2008 [3] z. p. bazant, a. steffens, “mathematical model for kinetics of alkali silica reaction in concrete”, cement and concrete research, vol. 30, no. 3, pp. 419–428, 2000 [4] a. sellier, j. p. bournazel, a. mébarki, “modelling the alkali aggregate reaction within a probabilistic frame-work”, 10th international conference on alkali-aggregate reaction in concrete, melbourne, australia, pp. 694–701, 1996 [5] s. poyet, a. sellier, b. capra, g. foray, j. m. torrenti, h. cognon, e. bourdarot, “chemical modelling of alkali silica reaction: influence of the reactive aggregate size distribution”, materials and structures, vol. 40, no. 2, pp. 229–239, 2007 [6] d. mcconnell, r. c. mielenz, w. y. holland, k. t. greene, “cementaggregate reaction in concrete”, journal of the american concrete institute, vol. 44, no. 2, pp. 93–128, 1947 [7] t. m. kelly, l. schuman, f. b. hornibrook, “a study of alkali-silica reactivity by means of mortar bar expansions”, journal of the american concrete institute, vol. 45, no. 1, pp. 57–80, 1948 [8] s. diamond, n. thaulow, “a study of expansion due to alkali-silica reaction as conditioned by the grain size of the reactive aggregate”, cement and concrete research, vol. 4, no. 4, pp. 591–607, 1974 [9] d. w. hobbs, w. a. gutteridge, “particle size of aggregate and its influence upon the expansion caused by the alkali-silica reaction”, magazine of concrete research, vol. 31, no. 109, pp. 235–242, 1979 engineering, technology & applied science research vol. 4, no. 3, 2014, 656-661 661 www.etasr.com sekrane and asroun: modelling the effects of aggregate size on alkali aggregate reaction expansion [10] m. kawamura, k. takemoto, s. hasaba, “application of quantitative edxa analyses and microhardness measurements to the study of alkalisilica reaction mechanisms”, 6th international conference of alkalis in concrete, copenhague, denmark, pp. 167–174, 1983 [11] r. e. oberholster, g. davies, “an accelerated method for testing the potential alkali reactivity of siliceous aggregates”, cement and concrete research, vol. 16, no. 2, pp.181-89, 1986 [12] d. lu, b. fournier, p. e. grattan-bellew, “evaluation of accelerated test methods for determining alkali-silica reactivity of concrete aggregates”, cement and concrete composites, vol. 28, no. 6, pp. 546–554, 2006 [13] s. multon, m. cyr, a. sellier, p. diederich, l. petit, “effects of aggregate size and alkali content on asr expansion”, cement and concrete research, vol. 40, no. 4, pp. 508–516, 2010 [14] m. moissan, “contribution to the mastery of alkali silica reaction by adding fine reactive aggregates in concrete”, doctoral thesis, toulouse, 2005 (“contribution à la maitrise de la réaction alcali silice par ajout de fines de granulats réactifs dans le béton”, thèse de doctorat, toulouse, 2005) [15] l. s. dent-glasser, n. kataoka, “the chemistry of alkali-aggregate reaction”, 5th international conference on alkali-aggregate reaction in concrete, cape town, south africa, 1981. [16] s. chatterji, n. thaulow, “some fundamentals of alkali-silica reaction”, 11th international conference on alkali-aggregate reaction in concrete, québec city, québec, pp. 21-29, 2000 [17] h. wang, j. e. gillott, “mechanism of alkali-silica reaction and the significance of calcium hydroxide”, cement and concrete research, vol. 21, no. 4, pp. 647-654, 1991 [18] s. poyet, “study of the degradation of concrete structures affected by alkali-silica reaction: experimental approach and multi-scale numerical modeling of damage in an environment variable hydro-chemomechanical”, doctoral thesis, university of marne-la-vallée, 2003. (“etude de la dégradation des ouvrages en béton atteints par la réaction alcali-silice : approche expérimentale et modélisation numérique multiéchelles des dégradations dans un environnement hydro-chemomécanique variable”, thèse de doctorat, université de marne-la-vallée, 2003) [19] c. f. dunant, k. l. scrivener, “effects of aggregate size on alkali– silica-reaction induced expansion”, cement and concrete research, vol. 42, no. 6, pp. 745-751, 2012 engineering, technology & applied science research vol. 7, no. 3, 2016, 1694-1698 1694 www.etasr.com farhat et al.: a compact quint-band bandpass filter based on stub-loaded resonators a compact quint-band bandpass filter based on stub-loaded resonators mohamad farhat school of engineering the australian college of kuwait, kuwait m.farhat@ack.edu.kw jagadissen munisami school of computing and engineering university of west london united kingdom kevin.munisami@uwl.ac.uk mohammed abdul-niby school of engineering the australian college of kuwait, kuwait m.nibi@ack.edu.kw michel nahas school of engineering the australian college of kuwait, kuwait m.nahas@ack.edu.kw abstract—this paper presents a planar quant-band bandpass filter with a high out-of-band rejection. the filter is based on inter-coupled stub-loaded resonators, where pairs of resonators are electromagnetically coupled to each other and the feed lines. this results in excitation of passbands, where the first and the third passbands are generated by λ/4 stub-loaded resonators. the second and the fifth passbands are excited by λ/2 stub-loaded resonators. and the fourth passband is generated by λ/2 resonators. the proposed technique provides sufficient degree of freedom to control the center frequency and bandwidth of the five passbands. in addition, the seven transmission zeros created around the passbands results in a quant-band filter with high selectivity, sharp 3db cut-off frequency, high isolation, and low passband insertion-loss. design methodology and simulation results of the filter are provided. keywords-quant-band; stub-loaded resonators; microstrip filter; planer filter i. introduction nowadays, there is a high need for high performance miniature microwave bandpass filters having a low production cost, compact size, low insertion losses and high passband selectivity for the rapidly evolving wireless communications market, such as satellite and mobile communication systems. in addition there is a high demand for multiband bandpass filters in wireless communication devices such as rf transceivers to operate in multiple but separated frequency bands so that users can access various services, such as wlan, ieee 802.16 (wimax) and rfid, with a single multimode handset or terminal. higher order bandpass filters are routinely modelled by cascading multiple single/dual-mode resonators. this straightforward approach results in an significant increase in the overall filter size and raises the fabrication cost. however, although many different methods [1-5] have been reported in generating multiband in a single configuration, the main problems still exist and it is due to difficulties in achieving good performance for all passbands, especially with more than three passbands. so far, most reported work with multiple band are limited to four or less [1-4] and only few methods have been reported on quint-band bandpass or more filters [5-7]. in [1], a multi-band filter using cpw-fed dual-mode doublesquare ring resonators was proposed. the resonant frequencies were controlled by tuning the perimeter ratio of the square rings. the bandwidth of the four passbands is different with high insertion loss. another design [2] implemented a multi-band filter by loading a transmission-line with either open or shortcircuited stubs in a parallel configuration. this technique requires an optimization method to control both the center frequency and the bandwidth of the filter. however, this technique occupies a high area with a dimension of 1.09λg×0.76λg. the multi-band filter in [3] is based on inserting two stepped-impedance resonators (sir). the filter’s passbands can be individually controlled by modifying the dimensions of the sirs. although the resulting filter is miniature in size, the 3db roll-off is skirt not sharp. in [4] a pair of squarering loaded resonators is used to excite quadruple-modes. the two resonators are connected to each other with a microstrip-line and are coupled to the input and output feedlines. this filter was fabricated on a 2-inch diameter 0.5mm thick mgo wafer of dielectric constant 9.8 with double-sided yba2cu3oy thin films. the size of the filter is 0.37λg×0.45λg. however this filter is very expensive as it needs to be cooled to a temperature of 77k. in [5], a quint-band bpf using tri-mode stub-loaded sirs was proposed. this filter cascaded five sets of tri-mode resonators along feeding lines. despite being a simple design, the insertion losses are around 3db and occupied a wide area. a compact double-layered quint-band bpf comprising three pairs of microstrip sirs and two pairs of slot resonators was reported in [6]. this type of filter is not only difficult to manufacture but also exhibits unacceptable insertion-loss resulting from multilayer properties. in [7] a quint-band bpf combining multimode resonator and λ/4 resonators was reported. however, this design occupies the relatively low 3db fractional bandwidths (fbws). in this paper, a novel quint-band bandpass filter structure is proposed and is based on inter-coupled λ/4, λ/2 stub-loaded and λ/2 resonators. the first and third passbands are determined by the λ/4 stub-loaded resonator, and the second, fifth passbands by the λ/2 stub-loaded resonator the fourth passband by the λ/2 engineering, technology & applied science research vol. 7, no. 3, 2016, 1694-1698 1695 www.etasr.com farhat et al.: a compact quint-band bandpass filter based on stub-loaded resonators resonator. the proposed quint-band filter generates seven transmission zeros located around the passbands to realize high selectivity, sharp 3db roll-off and high out-of-band rejection. the planar structure facilitates the design and reduces fabrication cost. with a size of 0.35λg×0.3λg, the filter is miniature compared to the aforementioned filters and this eases integration in wireless systems. the filter structure provides sufficient degree of freedom to control the center frequency and bandwidth of the five passband responses. the filter was designed and simulated at 2.4/3.5/4.9/5.8/6.7 ghz for different applications such as wlan and wimax amongst others. ii. filter configuration and analysis a. resonators configuration figure 1 shows the configuration of the proposed filter. it consists of six resonators. stub-loaded resonators 1 and 2 are λ/2 open-circuited at the coupling ends, and their other ends are parallel coupled to the 50 ω input/output feedlines of width w1 as shown in figure 2(a). resonators 3 and 4 are λ/2 resonators embedded inside resonators 1 and 2 for size reduction as shown in figure 2(b). the stub-loaded resonators 5 and 6 are λ/4 shortcircuited at the coupling ends, and are also parallel coupled with the feedlines as shown in figure 2(c). the λ/4 stub-loaded resonators (1 and 2) excite the first and third passbands in the filter response, resonators 3 and 4 excite the fourth passband and the λ/2 resonators (3 and 4) excite the second and fourth passbands. fig. 1. layout of the proposed quad-band bandpass filter structure. b. analysis of the quint-band bandpass filter the structure of the proposed λ/2 and λ/4 stub-loaded resonators are shown in figure 3(a) and figure 4(a), respectively. in figure 3(a), the λ/2 microstrip resonator is defined by parameters la, lb, z1 and z2 that denote the length and characteristic impedance of the microstrip-line and openstub, respectively. odd and even-mode analysis can be used to characterize the resonator. figure 3(b) and 3(c) show the odd and even-mode equivalent circuits, respectively. the odd and even frequencies are given by [8]: 2 (1)2odd a eff nc f f l     5 (2) 2even a b eff nc f f l l     where ε eff is the effective dielectric constant, n is the mode number (n = 1, 3, 5…,) and c is the speed of light in free space (3×108 m/s). fig. 2. structure of the proposed filter, (a) λ/2 stub-loaded resonator, (b) λ/2 resonators, and (c) λ/4 stub-loaded resonator. fig. 3. (a) structure of the proposed λ/2 stub-loaded resonator, (b) oddmode equivalent circuit, and (c) even-mode equivalent circuit. (a) (b) (c) (a) (b) (c) engineering, technology & applied science research vol. 7, no. 3, 2016, 1694-1698 1696 www.etasr.com farhat et al.: a compact quint-band bandpass filter based on stub-loaded resonators fig. 4. (a) structure of the proposed λ/4 stub-loaded resonator, (b) oddmode equivalent circuit, and (c) even-mode equivalent circuit. the λ/4 stub-loaded resonator in figure 4(a) is defined by lc, ld, z1 and z2, denoting the length and the characteristic impedance of the microstrip-line and open-stub, respectively. figure 4(b) and 4(c) show the odd and even-mode equivalent circuits, respectively, of the λ/4 stub-loaded resonator. the odd and even frequencies are given by: 2 (3)2odd a eff nc f f l     3 (4) 2even c b eff nc f f l l     on the other hand, resonators 3 and 4 are λ/4 resonators which excite the fourth passband, and its centre frequency is given by: 4 (5)2 e eff nc f l   where le = l7+ l8+ l9+ l12 c. feed and coupling scheme figure 5 shows the feed and coupling schemes employed in the filter, where the black and hollow circular nodes represent resonators and source/load respectively. figure 5(a) represents the feed and coupling scheme at the first (ƒ1) and the third (ƒ3) resonant frequencies. the corresponding insertion-loss responses are shown in figure 6. in contrast, the resonators 3, 4, 5 and 6 are non-resonating at ƒ1 and ƒ3, but are however excited at other passbands. similarly, figure 5(b) shows the feed and coupling scheme at the fourth (ƒ4) resonant frequency. figure 6 illustrates that resonators 1, 2, 5 and 6 are non-resonating at ƒ4. figure 5 (c) represents the feed and coupling scheme at the first (ƒ2) and the fifth (ƒ5) resonant frequencies. the corresponding insertion-loss response is shown in figure 6. in contrast, the resonators 1, 2, 3 and 4 are non-resonating at ƒ2 and ƒ5, but are excited at other passbands. source to load coupling is inherently realized as the non-resonating nodes are directly coupled with the resonating nodes. the passband bandwidth of the filter depends on the external q-factor and the coupling coefficient between the resonator pairs. in particular, this depends on the gaps (s3, s4, and s5), the width (w2) and the lengths (l5, l8 and l11). strong em coupling between the resonators is shown by the intensity of the current in figure 7. it is clear that only the desired resonator resonates at its associated frequency and form strong em coupling. fig. 5. feed and coupling scheme, (a) at the first and third resonant frequencies, (b) at the fourth resonant frequency, and (c) at the second and fifth resonant frequencies fig. 6. frequency response of the quad-band bandpass filter. (c) (b) (a) (a) (b) (c) engineering, technology & applied science research vol. 7, no. 3, 2016, 1694-1698 1697 www.etasr.com farhat et al.: a compact quint-band bandpass filter based on stub-loaded resonators (a) (b) (c) fig. 7. the surface current distribution of the proposed filter (a) at the fist (3 ghz), (b) the second (6.9 ghz) and (c) the third resonance frequency (8.6 ghz), respectively. iii. filter implementation the initial dimensions of the filter are determined based on the design specifications, in particular the desired passbands frequencies. fine-tuning is then necessary to achieve the desired response using an appropriate simulation tool. resonator pairs 5 and 6 determine the center frequency of the first and the third passbands and the lengths of the resonators can be calculated from (3) and (4). the length of the stub does not affect the fundamental resonant frequency ƒ1 but it can be used to control the frequency of the second harmonic of the resonator at ƒ3. this means that the length lc can be determined from ƒ1 and then the length of the open-stub (ld) is fine tuned to obtain the desired ƒ3. in this design technique the resonators have no loading effect over each other. thus, the λ/4 stub-loaded resonators have no affect on ƒ2 and ƒ5, as is evident from figure 6. on the other hand, resonators 1 and 2 determine ƒ2 and ƒ5 according to (1) and (2). similarly the length of the stub does not affect the fundamental resonant frequency ƒ2 but it can be used to control the frequency of the second harmonic ƒ5. therefore, ƒ2 can be determined by the length la, and the desired ƒ5 obtained through fine-tuning of the open-stub (lb). the resonant frequency ƒ4 is determined, characterized and controlled by resonators 3 and 4 according to (5). the second step is to determine the required bandwidth for each passband. as previously stated, the bandwidth of the filter’s passbands depends on the external q-factor and the coupling-coefficient between resonators. however, in this design the three pairs of resonators have no coupling effect over each other. thus, the bandwidth of the five passbands can be determined separately. the coupling-coefficient between the first and third passband depends on s3, w2 and l11, whereas the coupling-coefficient between the second and the fifth passbands depend on s5, w2 and l5, and the couplingcoefficient for the fourth passband depends on s4, w2 and l8. the external q-factor is determined by l2, w2 and s2 for the first and third passbands, l1, w2 and s1 for the second and the fifth passbands, and w1, w2, and l7 for the fourth passband. iv. simulation results to demonstrate the feasibility of the proposed concept, a quint-band filter was designed for fundamental resonant frequencies at 2.4/3.5/4.9/5.8/6.7 ghz. the filter was simulated on a substrate with a thickness of 0.76mm and relative dielectric constant of 2.17. following the design methodology in the preceding section, the filter’s dimensions were calculated to be (in millimeters): l1 = 5, l2 = 5, l3 = 13, l4 = 4.5, l5 = 5.8, l6 = 4.9, l7 = 6.24, l8 =5, l9 =4.65, l10 =6.3, l11 =2.8, l12 =3.5, l13 =4, l14 = 8, w1 = 0.5, s1 = 0.2, s2 = 0.2, s3 =0.9, s4 = 0.2, s5 = 1.09, and w2 = 2.42, which corresponds to a characteristic impedance of 50ω. simulations were performed using keysight technologies’ momentum 3d planar em simulator based on the method-of-moment (mom). figures 8-10 show the simulation results of the insertion-loss, return-loss and insertion/return losses respectively. the filter has five passband responses centered at 2.4/3.5/4.9/5.8/6.7 ghz with a high outof-band rejection. the insertion-losses at the five passbands are less than 1db, 1db, 1.5db, 1.3db and 2db, respectively. the corresponding return-losses are greater than 18db, 17db, 18db, 20db and 14db, respectively. the seven transmission zeros between the passbands result in the realization of a filter with high selectivity and high isolation between adjacent passbands. fig. 8. simulated insertion-loss response of the proposed filter. engineering, technology & applied science research vol. 7, no. 3, 2016, 1694-1698 1698 www.etasr.com farhat et al.: a compact quint-band bandpass filter based on stub-loaded resonators fig. 9. simulated return-loss response of the proposed filter. fig. 10. simulated insertion-loss and return-loss response of the proposed filter. v. conclusion a highly compact planar quant-band bandpass filter based on stub-loaded resonators is presented. three pairs of resonators are used to excite quant-mode resonances. the proposed technique provides a sufficient degree of freedom to alter the filter’s specifications in terms of centre frequency and bandwidth. source to load coupling and the resulting two transmission paths are inherently realized to create transmission zeros, resulting in high selectivity and high isolation between the five passbands. the design methodology has been verified through simulation results. the filter’s performance and compact size makes it attractive for application in multiband wireless communication systems. references [1] j. c. liu, j. w. wang, b. h. zeng, d. c. chang, “cpw-fed dual mode double-square-ring resonators for quad-band filters”, ieee microw. wireless compon. lett., vol. 20, no. 3, pp. 142–144, 2010 [2] c. cui, y. liu, “quad-band bandpass filter design by embedding dualband bandpass filter with dual-mode notch elements”, electronics letters, vol. 50, no. 23, pp. 1719–1720, 2014 [3] j. xiao, y. zhu, y. li, x. li, “miniature quad-band bandpass filter with passband individually controllable using folded sir”, electronics letters, vol. 50, no. 9, pp. 679–680, 2014 [4] h. liu, b. ren, x. guan, p. wen, y. wang, “quad-band hightemperature superconducting bandpass filter using quadruple-mode square ring loaded resonator”, ieee trans. on microwave theory and techniques, vol. 62, no. 12, pp. 2931–2941, 2014 [5] c. chen, “design of a compact microstrip quint-band filter based on the tri-mode stub-loaded stepped-impedance resonators”, ieee microw. wireless compon. lett., vol. 22, no. 7, pp. 357–359, 2012 [6] k. hsu, w. hung, w. tu, “compact quint-band microstrip bandpass filter using double-layered substrate”, proc. ieee mtt-s, int. dig., seattle, wa, usa, pp. 1–4, 2013 [7] j. ai, y. zhang, k. d. xu, d. li, y. fan, “miniaturized quint-band bandpass filter based on multi-mode resonator and λ/4 resonators with mixed electric and magnetic coupling”, microw. wirel. compon. lett., vol. 26, no. 5, pp. 343–345, 2016 [8] x. y. zhang, q. xue, “dual-band bandpass filter using stub-loaded resonators,” ieee microw. wireless. compon. lett., vol. 17, no. 8, pp. 583–585, 2007 microsoft word etasr_v11_n6_pp7809-7813 engineering, technology & applied science research vol. 11, no. 6, 2021, 7809-7813 7809 www.etasr.com basar et al.: investigation on the performance of a portable power generation system with a low-cost … investigation on the performance of a portable power generation system with a low-cost vertical axis wind turbine mohd farriz basar faculty of electrical & electronic engineering technology universiti teknikal malaysia melaka melaka, malaysia mfarriz@utem.edu.my aina musfirah norazizi faculty of electrical & electronic engineering technology universiti teknikal malaysia melaka melaka, malaysia ainamusfirah@utem.edu.my izadora mustaffa faculty of electrical & electronic engineering technology universiti teknikal malaysia melaka melaka, malaysia izadora@utem.edu.my carlos trenado colin leibniz research centre for working environment and human factors at tu dortmund university dortmund, germany trenado@ifado.de siti nor suhaila mirin faculty of electrical & electronic engineering technology universiti teknikal malaysia melaka melaka, malaysia suhaila@utem.edu.my zanariah jano institute of technogy management and entrepreneurship universiti teknikal malaysia melaka melaka, malaysia zanariahjano@utem.edu.my abstract—the purpose of this project was to develop an innovative, small-scale, and portable vertical axis wind turbine for power generation. the wind turbine was simple in design and economical. wind speeds ranging from 2.0ms -1 to 7.0ms -1 were tested on the proposed wind turbine. the experiments revealed that the turbine required a minimum wind speed of 3.9ms -1 to operate. according to the results, the proposed turbine achieved its maximum power output of 5.6w at a rotational speed of 65rpm when the wind speed was 7.0m/s. additionally, voltage and current increased proportionately with increasing wind speed. the proposed system showed an average coefficient factor between 0.10 and 0.12. this portable wind turbine potentially revolutionizes industry while raising public awareness about clean and renewable energy. keyword-power generation; vertical axis; wind turbine i. introduction between 2018 and 2050, global energy consumption is expected to grow by about 50%. most of this growth comes from non-organization for economic cooperation and development (non-oecd) countries, and it is concentrated in places with rapid economic growth, particularly in asia [1]. wind turbine power is one of the solutions to resolve these issues [2-4]. wind power was the fastest growing energy technology in the 1990s, in terms of installed capacity and annual growth rates [4-6]. prior to 1999, approximately 69% of all wind energy was installed in europe, 19% in north america, and 10% in asia and the pacific [7]. the innovative vertical axis wind turbine (vawt) to harness wind energy is proposed and implemented in this study. ii. concept of the wind turbine wind turbines are a type of power generation equipment that uses the kinetic energy of the wind to generate electricity [12]. wind turbines are typically classified into two types: horizontal axis wind turbines (hawts) and vawts [8-11]. hawt's main rotor shaft and generator are mounted on a tower [12-15]. vawtss have a fixed structure and are insensitive to wind direction [16-18]. typically, the vawt gearbox and electrical generator are located on the system's ground [19-21]. the basic difference between vawts and hawts is their blade orientation. to construct a wind turbine model, it is necessary to understand the fundamental computation for the wind turbine's generated kinetic energy. the schematic of a vawt is shown in figure 1. the arrows in figure 1 indicate the swept area for wind turbines [22]. the following equation expresses the potential power that can be harnessed from the kinetic energy of the wind [23]: �� = � � ��� (1) corresponding author: mohd farriz basar engineering, technology & applied science research vol. 11, no. 6, 2021, 7809-7813 7810 www.etasr.com basar et al.: investigation on the performance of a portable power generation system with a low-cost … where pw = power (w), ρ = density of the air (kgm -3 ), a = swept area (m 2 ), and v = velocity of wind (ms -1 ). fig. 1. schematic vertical axis wind turbine. the wind density of the air (ρ) at sea level is 1.2256kgm -3 [10]. theoretically, the kinetic energy generated by a wind turbine is proportional to the size of the swept area and the wind speed, as shown in (1). large wind turbines have a large swept area. the term "swept area" refers to the cross-sectional area through which wind flows [8]. the effective swept area of a vawt is shown in (2), as indicated by the arrows in figure 1. � = � (2) according to betz's law, the theoretical maximum efficiency of any wind turbine design is 0.59. a wind turbine can capture no more than 59% of the energy carried by the wind [11]. this is known as the "power coefficient," and is defined as follows: � = � � (3) where po is the power generated by the wind turbine and pw the available power in the wind. the power coefficient must account for all other components of a wind turbine system, such as the gearbox, bearings, and generator [11]. large wind turbines have a power coefficient of 0.45, but small wind turbines have a power coefficient of approximately 0.25 and can be placed in any location regardless of wind conditions [12]. iii. design and development the system proposed in this study was a modification of the savonius vawt currently in use. it was chosen because it is capable of harnessing more wind energy than other vawts. the wind proposed turbine is portable, user friendly and affordable, allowing its use by the public. a. design of a portable vawt the portable wind turbine depicted in figure 2 was created with the autodesk fusion 360 software. fusion 360 autodesk enabled the design of various wind turbines in 2d (twodimensional) or 3d (three-dimensional) and eased material selection for each part of the model. figure 3 shows the design of this project drawn with the fusion 360 autodesk. the proposed wind turbine had a simple geometrical design, consisting of three major components: the wind turbine, the generator, and a metal frame. fig. 2. vawt design with autodesk fusion 360 b. development of a low cost vawt this project was developed based on the design created by the fusion 360 autodesk. the system was simple to assemble and affordable in cost due to the use of basic materials available at local hardware stores. the materials used to construct the wind turbine were canvas for the blades of the turbine and round iron for the tower, pole, and blade frame. this turbine was supported by a modified stand hawking umbrella. additionally, a dc96-01218e permanent magnet motor was installed as the generator. this motor is frequently used in washing machines to rotate the tub. the wind turbine is light, easily transportable, and easy to store or assemble. the wind turbine consisted of 3 blades with 0.60m height and 0.46m radius. using (2), the effective swept area of each blade is a = 0.276m 2 . this wind turbine has a total height of 1.60m. figure 3 depicts a fully functional laboratory prototype. the cost of vawt is shown in table i. the entire cost was usd $129, and the vawt took approximately 6 hours to complete. the cost of the materials was only us $39, or 30.2% of the overall cost. us $90, or 69.7% of the entire cost, was spent on labor. the most expensive component of the turbine was the round iron used for the blade frame, tower, and pole, with the total cost of us $52 to develop. engineering, technology & applied science research vol. 11, no. 6, 2021, 7809-7813 7811 www.etasr.com basar et al.: investigation on the performance of a portable power generation system with a low-cost … fig. 3. a fully functional laboratory prototype. table i. vawt costs turbine parts costing material cost (usd) labour hours ($16/h) labour cost (usd) total (usd) canvas (qty: 3) *size : 0.46m (w) x 0.6m (h) 4 1 16 20 permanent magnet generator (qty: 1) 18 1 16 34 round iron for blade frame, tower & pole. (qty 1 set) 10 3 42 52 turbine stand (qty: 1) 5 0.5 8 13 coupling and seal. 2 n/a n/a 2 assembly and balancing. n/a 0.5 8 8 total 39 6 90 129 iv. experimental setup the proposed vawt's performance was evaluated with the use of an effective experimental setup that was simple to install and closely replicated the real conditions found in low wind areas. the wind turbine was tested by applying a modest wind speed to the blade in the horizontal direction. the artificial wind speed was produced using a 26-inch stand fan with a 160w motor and 3 different wind speed settings. figure 4 shows the experimental setup in the laboratory. the stand fan was positioned at various distances from the turbine in order to generate a variety of wind speed profiles. in figure 4, the "x" indicates the distance between the stand fan and the wind turbine. the wind speed profiles at a given distance "x" are shown in table ii. the results showed that the experimental setup produced artificial wind speeds ranging from 1m/s to 5m/s. a digital anemometer was used to determine the wind speed. meanwhile, a digital onosokki ht-4200 tachometer was utilized to determine the rotational speed of the wind turbine blade. the tachometer was able to detect speed without touching the moving item due to the addition of a reflector. the following are some aspects to consider when performing such experiments: • ensure there are no additional wind sources inside the laboratory. • experimental data are to be measured and recorded after the turbine has been spinning for 30s. • ensure the canvas used as a turbine blade is in a good condition before the experiment. fig. 4. experimental setup. table ii. wind speed profiles fan speed distance between the stand fan and the wind turbine (x) 1 m 2 m low (knob 1) 2.8ms -1 2.0ms -1 medium (knob 2) 4.8ms -1 3.9ms -1 high (knob 3) 7.0ms -1 5.1ms -1 v. performance analysis figures 5 and 6 and tables iii-v depict the proposed wind turbine's theoretical and measured performance curves. the results were shown for various wind speeds, with an emphasis on those less than 5m/s. a. minimum wind speed the section discusses the minimal wind speed required to rotate a wind turbine's blade. using the experiment setup discussed above, the speed was increased incrementally while simultaneously determining whether the blade rotated or not. once the blade rotated, the generator's output voltage was monitored. when the wind speed was 3.9ms -1 , the blades of vawt began rotating at 35rpm and concurrently created a voltage of 9.6v (figure 5, table iii). if the wind speed was less than 2.8ms -1 , the turbine did not run, and no output was generated. in order to move the turbine blade from its stationary position, wind with greater force and kinetic energy were required to push the turbine's mass and overcome the motor's torque. additionally, the experimental results indicated that the proposed system generated 15.1v at 65rpm with a wind speed of 7.0ms -1 . when the wind speed increased, the blade speed and the voltage output increased continually. the results demonstrated that the proposed vawt was able to produce significant power at low wind speeds. vawt stand fan x engineering, technology & applied science research vol. 11, no. 6, 2021, 7809-7813 7812 www.etasr.com basar et al.: investigation on the performance of a portable power generation system with a low-cost … table iii. blade speed for various wind speeds wind speed blade speed voltage (voc) 2.0ms -1 0 rpm 0.0v 2.8ms -1 0 rpm 0.0v 3.9ms -1 35 rpm 9.6v 4.8ms -1 43 rpm 11.1v 5.1ms -1 51 rpm 12.5v 7.0ms -1 65 rpm 15.1v fig. 5. blade speed and generated voltage. b. power output and efficiency this section examines the power generated by the wind turbine, the accessible power in the wind, and the system's efficiency. the voltage and current generated by the system should be determined. tables iv and v and figure 6 demonstrate the proposed wind turbine's overall performance. table iv. power output wind speed voltage (voc) current (isc) power output (po) 2.8ms -1 0.0v 0.0a 0.0w 3.9ms -1 9.6v 0.1a 1.0w 4.8ms -1 11.1v 0.16a 1.8w 5.1ms -1 12.5v 0.21a 2.6w 7.0ms -1 15.1v 0.37a 5.6w table v. efficiency of the proposed vawt wind speed power output (po) potential power (pw) coefficient factor (cp) 2.8ms -1 0.0w 3.9w 0.00 3.9ms -1 1.0w 9.7w 0.11 4.8ms -1 1.8w 18.1w 0.10 5.1ms -1 2.6w 21.7w 0.12 7.0ms -1 5.6w 56.1w 0.10 according to table iv, when the speed was less than 2.8ms -1 , no power was generated from the wind turbine, because it could not function when the blades were idle. additionally, the power generated increased continually as the wind speed increased. the highest output power was 5.6w when the wind speed was 7.0ms -1 . the voltage generated at that moment was 15.1v and the current was 0.37a. when the speed turbine was set to 3.9ms -1 , the power output and the generated current were 1.0w and 0.1a respectively. after measuring the proposed wind turbine's power output, the efficiency was determined. equation (1) was used to determine the wind's potential power. thus, using an effective swept area (a) of 0.276m 2 and an air density (ρ) of 1.22kgm -3 , the proposed wind turbine's efficiency was calculated, and the results are shown in table v. according to table v and figure 6, the coefficient factor (cp) ranged between 0.10 and 0.12. this is consistent with the discussion in section ii, where the maximum cp for a wind turbine was determined as 0.59. the experimental results demonstrated that the proposed system operated at an acceptable coefficient factor. as wind speed increased, the value of the power output and the potential power increased proportionately. however, the cp value remained between 0.10 and 0.12. the greatest potential power was generated when the wind speed was 8.3ms -1 . fig. 6. potential power and power output. in [10], the authors created a savonius vawt. they modified the typical savonius wind turbine model by adding single and multiple layer blades. wind rates of 6.46, 6.99, and 7.27m/s were used to test the system. the experimental results indicated that the redesigned wind turbine exhibits cp values ranging from 0.02 to 0.12. additionally, the actual power obtained was between 2.2w and 4.2w. the proposed turbine in the current study performs similarly to the one in [10]. both turbines perform similarly in terms of cp and output power when wind speeds are identical. this demonstrates that the proposed wind turbine's performance is acceptable and that it can contribute to the field of wind energy generation. vi. conclusion overall, the designed wind turbine works satisfactorily. despite its simplicity and low cost, the system is capable of producing a significant output power of up to 5.6w with an acceptable coefficient factor of 0.10 to 0.12. additionally, laboratory testing demonstrates that these wind turbines can generate power even when exposed to low-speed winds, less than 7.0ms -1 . this research also demonstrates that the proposed wind turbine will operate when a minimal wind speed 3.9ms -1 is available to move the turbine blades. the higher the wind speed, the higher the voltage, current, and the created power output. further research is needed to determine the impact of blade number and size on system performance. electric generators can also be diversified to produce more power. engineering, technology & applied science research vol. 11, no. 6, 2021, 7809-7813 7813 www.etasr.com basar et al.: investigation on the performance of a portable power generation system with a low-cost … acknowledgement the authors would like to express their appreciation to the universiti teknikal malaysia melaka (utem) for supplying the laboratory space and technical help. additionally, the authors would like to express their gratitude to mr. mohammad faisal zulfaqqar bin hasbullah for his technical assistance. references [1] "eia projects nearly 50% increase in world energy usage by 2050, led by 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[23] r. howell, n. qin, j. edwards, and n. durrani, "wind tunnel and numerical study of a small vertical axis wind turbine," renewable energy, vol. 35, no. 2, pp. 412–422, feb. 2010, https://doi.org/ 10.1016/j.renene.2009.07.025. microsoft word etasr_v12_n3_pp8506-8511 engineering, technology & applied science research vol. 12, no. 3, 2022, 8506-8511 8506 www.etasr.com soomro et al.: realistic determination of live loads on various reinforced concrete structures realistic determination of live loads on various reinforced concrete structures zuhairuddin soomro department of civil engineering quaid-e-awam university of engineering, science & technology larkano campus, pakistan zuhairuddin@quest.edu.pk salim khoso department of civil engineering quaid-e-awam university of engineering, science & technology larkano campus, pakistan engr.salimkhoso@gmail.com tariq ali department of civil engineering the islamia university of bahawalpur bahawalpur, pakistan tariqdehraj@gmail.com suhail ahmed abbasi department of civil engineering quaid-e-awam university of engineering, science & technology larkano campus, pakistan abbasi.suhail2009@gmail.com abdul aziz ansari department of civil engineering faculty of engineering, science, technology and management ziauddin university karachi, sindh, pakistan aziz.ansari@zu.edu.pk muhammad tayyab naqash department of civil engineering faculty of engineering islamic university of madinah saudi arabia engr.tayyabnaqash@gmail.com received: 27 january 2022 | revised: 8 february 2022 and 20 february 2022 | accepted: 21 february 2022 abstract-this paper presents various case studies of examined and calculated live loads on reinforced concrete structures. these case studies accumulated information and data of existing structures about their design live loads and acquired detailed drawings showing the reinforcement in their floor slab sections. the actual occupancy loads that act on the floor slabs were assessed, and the ultimate loads that an individual slab section should be able to support were calculated using the methods recommended by aci, cp-114, cp-110, and the yield line theory. a reinforced concrete slab panel was also tested to check the validity of the theoretically predicted ultimate loads. the results were compared to find a safety margin and, if necessary, recommend lower live load outlines for cost reduction. the case studies showed that there is sufficient margin to reduce design live loads on the floor slabs of residential buildings, especially in multistory apartment blocks. moreover, it was found that the live loads, especially on residential buildings, could be decreased to two-thirds of the code values without risking floor overloading. keywords-structures; loads; economy; case study; occupancy; slab; reinforcement i. introduction generally, loads are classified as dead loads, live loads, including people, supplies, and machines, environmental loads, including rains and snow loads, lateral loads, such as wind and blasts, dynamic loads due to earthquakes, upward loads, such as those due to water, earth pressure, waves, and ice, and loads induced by temperature and shrinkage [1]. among these, dead loads can be determined with a high degree of certainty. snow and rain loads are very rare in pakistan. the wind has a pronounced impact on tall buildings having more than 10-15 stories and has little significance in public or common residential buildings [2, 3]. using the maximum possible values given by the standards for the loads increases construction costs [4, 5]. for these reasons, probabilistic considerations are used to determine design loads. moreover, the design values of live loads are very rarely reached during the life spans of many structures [6, 7]. the load values are usually based on recommendations of foreign standards, which are very conservative compared to the actual live loads on floor slabs in pakistan. therefore, more realistic live loads should be determined for the design of the structures. assuming that a typical person weighs 68kg and occupies a space of 0.37m 2 , it has a live load of about 185kg/m 2 . people can be overloaded to produce a maximum load of 610kg/m 2 . however, such occupancy in a large area is very unlikely. another factor that also affects the decision regarding the intensity of live loads is that the probability of achieving the full design live loads on an entire floor decreases as its area increases. to incorporate this fact, building codes suggest live load reductions. one common way to achieve this is to reduce live load values for areas larger than 14m 2 at a rate of 0.08% per m 2 up to a reduction of 60% [8, 9], but this reduction does not apply to public assembly buildings. certain types of live loads may produce dynamic effects. however, more commonly, these are not considered explicitly, since a complete analysis would be excessively time-consuming [10, 11]. the live loads are conservative enough to account for increased stresses caused by the structure's vibration [12-15]. ii. present investigation a combined effect of both load enhancement and the safety factors of the materials allows a structure to withstand the imposed loads, which could vary even several times more than corresponding author: salim khoso engineering, technology & applied science research vol. 12, no. 3, 2022, 8506-8511 8507 www.etasr.com soomro et al.: realistic determination of live loads on various reinforced concrete structures the loads for which it was intended [16]. the safety factor ensures that a reasonable margin exists between the maximum operating load of the component and its load capacity. it has been common practice to introduce idealization, approximation, and larger bending moments based on conventional methods to design structures for a long time, increasing safety margins. although incidental overload can occur, the question arises of whether it can be possible to accommodate such massive loads to exhaust all the strength of the floor [17]. a reliability analysis exhibits an almost infinite load on a slab in monolithic connections with the structural members for its complete collapse. as an example, on the eve of the cricket world cup celebration, it was observed that a balcony of a house having dimensions of 1×5m was jampacked with almost 30 people. the people were weighing 2040kg approximately, which is equivalent to 458kg/m 2 . from the technical details of the slabs, the ultimate load-carrying capacity was calculated to be about 3,806kg/m 2 . nevertheless, this is one case of the overloadings that must be considered while proposing a realistic value of live loads. for this reason, the aci code recommended a live load of 488kg/m 2 for balconies and a minimum of 293kg/m 2 when the area of the balcony of a residential building does not exceed 9m 2 [18, 19]. this study examined a wide variety of existing reinforced cement concrete (rcc) buildings in different towns and cities of the sindh province in pakistan, including primary and secondary schools, urban and rural hospitals, mosques, residential villas, luxurious apartments, and multistory shopping centers and malls. technical data of buildings in terms of slab thickness, size, spacing, and arrangement of reinforcement bars were obtained, and the intensity of live loads acting on these slabs was assessed. the ultimate live loads were calculated by employing the methods recommended by aci [17], cp-114 [18], cp-110 [19], and yield line theory. a yield value of 275mpa was adopted for steel. wherever the principles of limit state design were applied, the partial safety factors for loads were presumed to be equal to unity. the bending moment factors for the calculations were selected from the respective design standards' tables wherever appropriate. a wide variety of chosen case studies are presented in the following sections [23-25]. a. multistory building this building was under construction during the investigation. the structural frame with floor slabs was already complete while dividing masonry walls were being erected. there was a large stack of bricks on the first-floor slab, soaked with water. the stack was approximately 1.5m in height and consisted of about 1000 bricks weighing about 3,450kg. the room's total area was 12.25m 2 (3.5×3.5m). adding the weight of 6 workers and 2 visitors, which is about 545kg, the total imposed load on the floor area was equal to 326kg/m 2 . this is much higher than the design live-load of 145kg/m 2 . however, from technical data, the slab was reinforced with main bars of 13mm diameter placed at 150mm c/c and distribution bars of 10mm diameter placed at 230mm c/c. the minimum standard load-carrying capacity, shown in table i, was 1,693kg/m 2 , which is 5.3 times more than the actual imposed load. thus, there is a possibility of reducing the design live-load without risking the stability and durability of the structure. it is expected that the actual occupancy loads of this flat, under normal circumstances, would not be more than the villa's [2627]. b. residential villa the residential villa was a double-story building that was assessed to have a total live load of 455kg, including all items of daily use, on a total floor area of 21m 2 . this can be compared with the lowest live load of 1450kg/m 2 calculated based on the elastic theory method and the recommendations of cp-114. this building had a considerable inherent margin of safety. even in occasional overload due to visitors on a festivity, the load will never touch the ultimate mark of 1665kg/m 2 calculated based on cp-110. therefore, there is enough margin to reduce the design live loads by reducing reinforcing steel and cost without sacrificing safety. c. vocational training center this building was a women's vocational training center with large halls occupied by professionals and trainees who sew, knit, embroider, and create patterns on clothing while many visitors were also wandering around. during peak hours, in the afternoon, the center was estimated to be jam-packed, and there would be approximately one person per 0.4m 2 of the corridor area. this would mean that the live loads of people would be about 183kg/m 2 , which is not constant but is probably the maximum that could be reached. allowing 4.5kgs per person as the weight of personal belongings, the average live load is approximately 195kg/m 2 . this may be compared with the minimum estimated live load of 757kg/m 2 from yield line theory. therefore, there is a lot of room for live load reduction. within the shops (3×9m), the occupancy loads of workers, sewing machines, and other items were estimated at 41.5kg/m 2 , which is much less than the design live load of 293kg/m 2 recommended by the british standard. d. community marriage hall this building was examined on a weekend night during a marriage. people were sitting on the floor, which was covered with a thick carpet. the number of persons sitting on the floor was counted and calculated approximately one per 0.3m 2 of the floor area. this load was too high and probably the maximum that could be accommodated within that space. therefore, the live load per m 2 of the persons was approximately 210kg/m 2 . adding the additional loads of moveable items, approximately at 24kg/m 2 , the total live load becomes 234kg/m 2 . this can be compared with the minimum standard estimated live load of 713kg/m 2 based on the yield line theory. it seems that there is also a substantial margin of safety in this case, and therefore, the live load could be reduced to some extent. e. primary school building this is a standard design adopted by the education works department for the construction of primary schools in various towns and villages of the sindh province. the original plan consists of only the ground floor with a provision of a first floor when it becomes essential. the classrooms were 5×6m wide, with a central beam that divided the floor slab into two panels of 3×5m. on the floor, the load would be that of engineering, technology & applied science research vol. 12, no. 3, 2022, 8506-8511 8508 www.etasr.com soomro et al.: realistic determination of live loads on various reinforced concrete structures children and benches. the benches and the average weight of the children were supposed to be around 32kg. the benches were arranged in two rows, each bench being 2m long. six children were sitting on each bench. however, 69 students were sitting in the classroom during the investigation. in front, there was a table weighing about 18kg and a chair for the instructor. it was estimated that the weight of each bench was approximately 27kg. therefore, the total live load on the floor was 2,817kg. the maximum live load using the recommendations of cp-114 was calculated to 1,400kg/m 2 , which can be compared with the actual live load of 98kg/m 2 . the highest ultimate standard load was 2,918kg/m 2 . so again, the margin of safety and, therefore, room for reduction in design live loads is sufficient. f. library building libraries are a common feature of cities and an integral part of almost all educational institutions, including high schools, colleges, and universities. this study examined the library building in moro city. the highest standard ultimate load was 3,270kg/m 2 for cp-110, while the minimum was found for cp114 and could be taken as a safe load that the slab was capable of carrying without the stresses exceeding their permitted values. the steel almirahs in the library were placed side by side beside the walls, almost touching the ceiling. books are heavy items and therefore their load is also considerable, but as they are placed beside the wall along the periphery of the room, their load induces a relatively small bending moment. the loads of furniture and persons divided by the floor area were estimated at less than 58kg/m 2 . however, considering a specific weight of books at 244kg/m 2 and the total number of books accommodated per panel of the slab, it was found that the uniformly distributed load due to books would be 234kg/m 2 . therefore, the total actual live load was 292kg/m 2 . g. boys hostel the work drawings of the quaid-e-awam university college of engineering, science & technology larkana hostel and the utilized steel during the construction of the slab were used to calculate the loads. although the hostel rooms were designed to accommodate three students each, four students were living in each room. there were 4 beds, 4 chairs, and 2 study tables. assuming 4 visitors and 45kg for each boy's personal belongings, including books, clothes, etc., the total live load on the floor slab would be equal to 980kg. this can be compared with the lowest standard ultimate live load of 2,152kg/m 2 calculated based on cp-114. the difference between actual and standard loads is so high that it can be undoubtedly deduced that the design live loads could have been reduced to decrease the cost of construction. during the games, a large number of students gather in the corridor to watch the match, standing along the periphery. the number of students was estimated to be one per 0.5m 2 of the corridor area. in that case, the live load would be in the range of 122kg/m 2 . this is much less than the load-carrying capacity of the slabs and reasonably less than the design live load. h. shopping center this shopping center is a double-story building in the heart of larkana city. as the number of visitors seems quite considerable, the live load should not be less than 150kg/m 2 on the corridor, taking into account one person per 0.5m 2 and 2.5kg of personal belongings, and 60kg/m 2 in the shops. thus, the live load prescribed for such public buildings is almost twice the design imposed. the standard live load carrying capacity of the floor slab was found to be between 483kg/m 2 and 1327kg/m 2 . i. shopping mall this building is located in hyderabad city. it consists of a basement, a ground floor, and five upper floors. it is a typical example of public buildings with a highly uncertain live load. the loads in stores and corridors were calculated separately, and depending on the heavier items placed in the stores and the extensive mobility of people in the corridors, it was inferred that the loads would not be less than in the previous case of the shopping center. however, as the 2 nd , 3 rd , and 4 th floors were residential apartments, their slabs were reinforced with the same diameter bars and spacing as those of the lower slabs. they were also reinforced with 13mm diameter bars at 150mm c/c with alternate bars bent up. the distribution bars had a 10mm diameter at 200mm c/c. for the residential floors, the margin is quite significant because the calculated live loads are as high as 2,098kg/m 2 . j. university corridor this corridor consists of closely spaced columns 2.7m c/c, a relatively smaller width of 3.5m as clear span as compared to the total corridor length of 22m. the corridor was designed for a total load of 975kg/m 2 , including the dead load and the live load of 490kg/m 2 . the design was accomplished following the elastic theory method. at any given time, it was observed that the number of persons passing never exceeds a single group of 5 or 6 people on a single panel. however, there is the possibility of large groups of students passing through the corridor occasionally. assuming that the corridor would be jam-packed with an average of one person per 0.4m 2 , the live load would be equal to 183kg/m 2 , which is only 15% of the ultimate strength of 1,170kg/m 2 given by cp-110. therefore, there is an enormous scope of reduction. k. community mosque a multistory mosque was visited on a friday when most of the people gather to pray. although many people were sitting closely, people were found sitting sparsely on the first floor. however, it was observed that during prayer, each person requires a strip of 0.5m width and 1.5m length on average, having an area of approximately 0.75m 2 . therefore, the average live load is equal to 102.5kg/m 2 . during the sermon, people do not sit in proper rows but gather together randomly, and the load in such a case was estimated at 234kg/m 2 , at the rate of one person per 0.3m 2 . this is approximately 12% of the maximum ultimate load of 1,908kg/m 2 imposed by cp-110. l. public hospital the uncertainty on the maximum intensity of live loads and the fluctuation of the occupancy load from point to point and time to time is large. however, in private rooms, the load intensity was not found to be much greater than in standard residential bedrooms. however, in casualty and general wards, engineering, technology & applied science research vol. 12, no. 3, 2022, 8506-8511 8509 www.etasr.com soomro et al.: realistic determination of live loads on various reinforced concrete structures the live loads due to visitors and other persons, including staff, other accompanied persons, and those waiting for their turn, are quite high. the maximum standard ultimate load, in this case, was specified as 2,465kg/m 2 by the yield line theory, while the minimum standard ultimate live load was 937kg/m 2 using cp114. the maximum intensity of the actual load was estimated at 145kg/m 2 for casualties and 39kg/m 2 for private rooms. therefore, a reduction of the design live load is possible. table i. ultimate live loads for the floor slabs of the studied buildings case study cp-114 cp-110 aci yield line assessed load code value code kg/m 2 kg/m 2 kg/m 2 kg/m 2 kg/m 2 kg/m 2 1 multistory building 1693 3748 3123 3016 364 147 b 2 residential villa 1450 1665 1498 1566 22 147 b 3 vocational training center 864 2157 1581 757 234 390 b 4 community marriage hall 1161 2435 2415 713 234 488 b 5 primary school building 1400 2206 2669 2918 98 292 b 6 library 1742 3270 3050 2723 292 60 reading room 150 stack room 80 corridor a a a 7 boys hostel 2152 3428 3953 3621 49 195 b 8 shopping center 483 1327 1161 1142 210 390 b 9 shopping mall 1020 2098 1801 1483 151 390 b 10 university corridor 3118 5719 5372 3240 183 390 a 11 community mosque 844 1908 1630 1327 337 0 b 12 public hospital 937 2128 1835 2465 185 195 b iii. experimental study a square rcc slab panel in a monolithic connection with an edge beam on all four sides with an effective span equal to 600mm and an overall thickness of 50mm was tested by applying a point load at its center. the slab was reinforced with a 3mm diameter wire, as shown in figure 1. fig. 1. the reinforcement cage. fig. 2. testing arrangement of the model. finite element software was used to analyze and design the model, employing a 4-nodded rectangular plate bending element with 3 degrees of freedom at each node. the design flexural load was maintained at 10kn. the punching shear strength of the slab and its ultimate flexural strength based on the actual material properties were determined in the laboratory. figure 2 shows the testing arrangement of the mode. the calculated live load carrying capacity based on flexure and punching shear was compared with the experimental ultimate load. the behavior of the model was studied in terms of load-displacement history, crack pattern, strain in concrete, mode of failure, and ultimate load [19, 20]. iv. result analysis and discussion from the case studies and the experimental results obtained, it can be deduced that the live loads adopted for the design of floor slabs are only a small amount of the total load-carrying capacity of the slab, computed based on the strength of concrete, the ratio of reinforcement steel, and boundary conditions. therefore, there is enough margin to reduce the design live loads and consequently the steel ratio and thus to reduce the cost of materials. however, it was also observed that there are not only live loads but standard requirements for a minimum ratio of reinforcing steel, including distribution steel and partial safety factors, that cause the increase in the moment of resistance of the floor slabs. thus there is not only the occupancy loads but there are several other aspects as well that must also be studied before concluding, such as creep of concrete, corrosion of steel, temperature stresses, occasional fires, probability of unforeseen drastic overloading, shock loading, lateral loading, redistribution of stresses between concrete and steel and consequently shifting of the neutral axis, quality of workmanship, use of standard materials, human errors during construction, and unexpected behavior of soil beneath the foundation. by examining only the load-carrying capacity and the live loads, it can be asserted that live loads, particularly on residential buildings, could be reduced to the 2/3 of standard values without risking floor overloading. during this investigation, it was observed that in all cases the engineering, technology & applied science research vol. 12, no. 3, 2022, 8506-8511 8510 www.etasr.com soomro et al.: realistic determination of live loads on various reinforced concrete structures slabs were designed and reinforcement was provided based on empirical values of bending moment coefficients, enhancing the load-carrying capacity of the slab un-proportionately. more economical sections could be reached if moment fields are predicted with the help of finite element analysis. this explains how the ultimate live loads in all case studies are far higher than the design code value of occupancy loads [20]. v. suggestions the scope of this study could be extended to a broader range of public buildings in metropolitan cities, such as karachi and lahore in pakistan or any other part of the world. a systematic investigation should be carried out on the floor areas where heavy concentrated loads of equipment and machinery are expected. it is also imperative to investigate the matter more objectively and study the long-term effects on the stability and durability of buildings if the reinforcement is reduced based on reduced design live loads. furthermore, no matter how rare, there is always a possibility of strong wind currents during a storm, which might cause over-stressing of the slab, which would then act as coupling media to resist the overturning effect of the lateral wind forces. this is where the additional moment of resistance due to higher design live loads would provide an extra margin of safety against failure. other sources of uncertainty, such as steel corrosion, concrete cover splitting, temperature stresses due to occasional exposure to fire, unexpected behavior of the soil beneath the foundation, and human errors during construction, should also be investigated. vi. conclusion the presented case studies showed that there is sufficient margin to reduce the design live loads on the floor slabs of residential buildings, particularly in multistory apartment blocks, reducing their construction cost. by considering the load-carrying capacity and occupancy loads, it can be affirmed that live loads, especially on residential buildings, could be decreased to two-thirds of the code values without risking floor overloading. experimentally, the actual strength of the rcc slabs was several times higher than the design loads and the ultimate loads proposed by the standards. therefore, there is enough margin to reduce construction cost by reducing the amount of reinforcement, providing that serviceability limits and code provisions regarding minimum reinforcing and distribution steel are not disregarded. acknowledgment this research was carried out in the structures laboratory of civil engineering department, quaid-e-awam university of engineering science & technology (quest), nawabshah, sindh, pakistan. the authors express their appreciation to the university authorities for providing the facilities and funds for this research. references [1] m. a. memon, a. a. ansari, and b. a. memon, "a review of intensity of live loads 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[21] "structural codes of practice. cp 114 : the structural use of reinforced concrete in buildings,", british standards institute, cp 114, 1965. [22] "structural codes of practice. cp 110:1:1972 for the structural use of concrete. part 1: design, materials and workmanship," britich standards institute, cp 110:1:1972, 1972. [23] m. t. naqash and a. alluqmani, "codal requirements using capacity design philosophy, and their applications in the design of steel structures in seismic zones," open journal of earthquake research, vol. 7, no. 2, pp. 88–107, mar. 2018, https://doi.org/10.4236/ ojer.2018.72006. [24] m. t. naqash, "codal comparisons for the seismic resistance of steel moment resisting frames (mrf). part a: codes approach," international journal of construction engineering and management, vol. 6, no. 6, pp. 254–263, 2017, https://doi.org/10.5923/j.ijcem. 20170606.04. 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[27] m. t. naqash, "pushover response of multi degree of freedom steel frames," civil engineering journal, vol. 6, pp. 86–97, dec. 2020, https://doi.org/10.28991/cej-2020-sp(emce)-08. microsoft word hayder_ed_modified.doc etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 241-245 241 www.etasr.com ahmed: �ew modeling and simulation platform for communications systems: (i) double sideband… new modeling and simulation platform for communications systems: (i) double sideband suppressed carrier am modulator dsb-sc hayder abdalrahem ahmed physics department, college of science basrah university basrah, iraq. dr.hayder73@yahoo.com abstract— the main goal of this paper is to introduce a new platform for the implementation and simulation of communication systems. scilab/scicos is an open source software for conducting communication system related experiments, aiming to provide an experimentation platform for research on communication theories. double sideband suppressed carrier (dsb-sc) modulator is modeled and simulated using this platform. keywordsdouble sideband modulator; filter design; scilab; scicos; modeling; simulation. i. introduction recent experiments of the communications theory are heavily relying on software for the purpose of simulating various communication systems. the widely used platforms are matlab/simulink [1-3] and systemview [4-6]. however, these simulation platforms are proprietary ones, thus imposing restrictions on scalability and flexibility. for these reasons, it has been decided to develop an open source simulation platform that is based on scilab/scicos [7] which can be used to model and simulate the communications theory systems. scilab is an open-source software that specializes in scientific computation. scicos provides a dynamic-model graphical simulator based on the scilab computing kernel. scilab is an interpreted language with dynamically typed objects. scilab runs, and is available in binary format, for the main available platforms: unix/linux workstations (the main software development is performed on linux workstations), windows, and macosx. macosx users can also install scilab using fink. compiling scilab from the source code is also possible and is fairly straightforward. scilab can be used as a scripting language to test algorithms or to perform numerical computations. but it is also a programming language, and the standard scilab library contains around 2000 scilab coded functions. scilab programs are thus quite compact and most of the time smaller than their equivalents in c, c++ or java. scicos contains a graphical editor that can be used to construct block diagram models of dynamical systems. the blocks can come from various palettes provided in scicos or can be user-defined. a tutorial for the use of scilab/scicos, with special emphasis on modeling and simulation tools divided into two parts, is provided [8]. the first part concerns scilab and includes a tutorial covering the language features, the data structures and specialized functions for creating graphics, importing and exporting data and interfacing external routines. the second part is dedicated to the modeling and simulation of dynamical systems in scicos. this type of modeling tools is widely used in the industry because of the modular and reusable mode features. ii. double sideband suppressed carrier am modulator dsb-sc many digital modulation techniques are dsb-sc with a digital message signal. therefore, it is appropriate to review this basic analog modulation. dsb-sc is the simplest form of amplitude modulation, generated by a mixer. this consists of an audio source combined with the frequency carrier, as shown in figurer 1. the message signal )(tm is multiplied with a high frequency carrier )2cos()( tfatc cc π= , where c a is the carrier amplitude and c f is the carrier frequency, to provide a dsbam signal modulated output s(t) as follows: ( ) ( ) ( ) ( ) cos(2 ) c c s t c t m t am t f tπ= ⋅ = (1) note that the amplitude of )(ts is )(tam , which varies according to the message signal )(tm , hence the name “amplitude modulation”. in other words, the message signal is now being carried in the amplitude of the dsb-am signal. the generation of )(ts is achieved by the modulator shown in figure 1. the voltage multiplier shown in figure 1, is commonly referred to as the mixer. etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 241-245 242 www.etasr.com ahmed: �ew modeling and simulation platform for communications systems: (i) double sideband… fig. 1. dsb-am modulator. if the message signal )2cos()( 0 tftm π= is a sinusoid at frequency f0<< fc, the dsb-am signal as given by (1) is: )2cos()()( tftamts c π= )2cos()2cos( 0 tftfa c ππ= (2) [ ] [ ]tff a tff a cc )(2cos 2 )(2cos 2 00 ++−= ππ since )cos()( tatm mm ω= and )cos()( tatc cc ω= , thus ( )[ ]( taatmtcts mcmc ωω −== cos 2 1 )().()( ( )[ ]t mc ωω ++ cos a plot of s(t) in (2) is shown in figure 2. note that a phase reversal occurs at the point where m(t) goes negative. the spectrum in the frequency domain region can be written as follows: ( ) ( )[ ] cc ffmffm a fs ++−= 2 )( (3) when the message signal m(t) is deterministic and has m(f) as its fourier transform, then the fourier transform s(f) of the dsb-am signal s(t) in (1) can be evaluated using the modulation properties [9]. in dsb-sc it is observed that there is a symmetry in the band structure. so, even if one half is transmitted, the other half can be recovered at the receiving end. by doing so, the bandwidth and power of transmission is reduced by half. fig. 2. dsb-am with a sinusoidal message signal. fig. 3. (a) message signal; (b) dsb-sc signal. iii. generate dsb signal using scilab/scicos before generating the dsb signal, it’s important to test the sinusoid generator block by connecting it directly to the scope (fft) as illustrated in the scicos block diagram shown in figure 4. fig. 4. test the sinusoid generator it is found that no results are obtained except when starting with the following values: clock_c period = sec101 7− × , clock_c ini time = sec101 7− × and sampling period (scope) = sec101 7− × . to simulate a diagram, it is sufficient to select the run operation from the simulate menu. simulation parameters can be set by the setup operation in the same menu. running the simulation for the system shown in figure 4 leads to the opening of a graphics window and the display of a sinusoidal signal. this window is opened and updated by the fft block. the simulation result is given in figure 5. in this case, the sinusoid generator frequency (rad/s) is 10 3 , 10 6 and 10 9 respectively. the simulation can be stopped using the stop button on the main scicos window, subsequent to which the user has the option of continuing the simulation, ending the simulation, or restarting it. figure 6 illustrates a scicos block diagram employed to generate a dsb signal. to get time-domain and frequencydomain responses, one can build the scicos block diagram shown in figure 7. figures 8 and 9 portray results obtained using scilab codes to describe the dsb signal. it should be noted that etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 241-245 243 www.etasr.com ahmed: �ew modeling and simulation platform for communications systems: (i) double sideband… although it is possible to modulate any signal over a sinusoid, it’s preferred to use a low frequency sinusoid to modulate a high frequency sinusoid without loss of generality. (a) (b) (c) fig. 5. results for different sinusoid generator frequency (rad/s), (a) 3 101× , (b) 6 101× and (c) 9 101× fig. 6. scicos block diagram to generate dsb signal (time-domain) fig. 7. scicos block diagram to generate dsb signal (time-domain and frequency-domain responses) fig. 8. time-domain and frequency-domain responses for dsb signal etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 241-245 244 www.etasr.com ahmed: �ew modeling and simulation platform for communications systems: (i) double sideband… 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 time (sec) a m p lit u d e 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -4 -3 -2 -1 0 1 2 3 4 time (sec) a m p lit u d e 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -4 -3 -2 -1 0 1 2 3 4 time (sec) a m p lit u d e fig. 9. db sinusoid signals for demodulation, the audio frequency and the carrier frequency must be exact, otherwise distortion is created. dsbsc can be demodulated if the modulation index is lower than one. this is best shown graphically. figure 11 illustrates the message signal that may modulate onto a carrier, the equation for this message signal is ( ) ( ) ( ) ( )ttts 12002cos218002cos21)( ππ −= . while figure 12 illustrates the carrier, in this case, ( )ttc 50002cos)( π= . finally, figure 13 represents the phase modulated signal with respect to time. fig. 10. run scilab codes, results the spectral analysis for double sideband with suppressed carrier fig. 11. the message signal, ( ) ( ) ( ) ( )ttts 12002cos218002cos21)( ππ −= . fig. 12. the carrier, ( )ttc 50002cos)( π= etasr engineering, technology & applied science research vol. 2, �o. 4, 2012, 241-245 245 www.etasr.com ahmed: �ew modeling and simulation platform for communications systems: (i) double sideband… 0 2000 4000 6000 8000 10000 12000 14000 16000 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 phase for signal vs time time p h a s e fig. 13. the phase for signal vs time iv. conclusion in scilab, objects are never declared or allocated explicitly; they have a dynamic type and their sizes can dynamically change according to the operators or functions applied. scicos provides a modular way to construct complex dynamical systems using a block diagram editor. scicos diagrams are compiled and simulated efficiently using a graphical editor/simulator based on the scilab computing kernel. scicos handles, in particular, the interaction between continuous-time dynamics and system events including events associated with the timing of a discrete-time clock. such events affect the way the numerical solver, which integrates the continuous-time dynamics, should be called. handling efficiently such matters by hand for complex dynamical systems can be extremely difficult. it is suggested that the dbs modulator can be simulated by this new platform. in amplitude modulation the amplitude of a high-frequency carrier is varied in direct proportion to the low-frequency (baseband) message signal. in this paper, the dsb was examined as a type of linear modulation schemes for both time and frequency domains, and emphasis was given to characteristics such as signal spectrum, power, bandwidth, demodulation methods, complexity and receivers. the scicos library of reusable modules (blocks) is used in the considered model, the scicos formalism, which must be respected in designing blocks and submodels, guarantees that modules constructed separately and interconnected can work harmoniously together as a large number of blocks are already available in scicos palettes. scicos is more than a modeling and simulation program. it contains many functionalities to help the designer optimize model parameters, validate models, generate c code, etc. the carrier frequency may be suppressed or transmitted at a relatively low level. this requires that the carrier frequency be generated, or otherwise derived, at the receiving site for demultiplexing. this type of transmission is known as double sideband suppressed carrier (dsb-sc). in a modulation process, a high frequency sinusoid is modified in accordance to the message signal to be transmitted. the high frequency sinusoid is the carrier and the message signal is the modulating signal. the modified carrier signal is the modulated signal. a consequence of modulation is a translation or shifting of the message spectrum to a higher frequency band. message signals, by nature, are low frequency or baseband signals. a baseband signal is a signal whose spectrum is positioned close to dc (ω=0). this type of modulation is double sideband suppressed carrier, or dsb-sc. the carrier must be reinserted at the receiver, however, to recover this modulation. in the time and frequency domains, dsb-sc modulation appears as shown in figures 8-10. the carrier is suppressed well below the level of the sidebands. references [1] m. rice, “teaching digital communications theory with simulink at brigham young university”, matlab digest, 2009 [2] y. zhan, j. a. clark, “a search-based framework for automatic testing of matlab/simulink models”, the journal of systems and software, vol. 81, pp. 262–285, 2008. [3] i. marsh, “the role of matlab and simulink in teaching communications”, available on: http://edusigcomm.info.ucl.ac.be/ pmwiki/uploads/workshop2011/20110504002/teach_wireless.pdf [4] m. chryssomallis, “simulation of mobile fading channels”, ieee antennas and propagation magazine, vol. 44, no. 6, pp. 172-183, 2002. [5] j. duan, y. yue, “on using systemview in the communication theory experiment teaching”, experiment science & technology, vol. tn911-4, 2007. [6] xu yanhong, “simulation experiment of communication theory based on systemview software”, journal of shijiazhuang institute of railway technology, vol. tn911, 2009 [7] http://www.scilab.org/ [8] s. l. campbell, j. p. chancelier, r. nikoukhah, modeling and simulation in scilab/scicos, springer, 2009. [9] t. t. ha, theory and design of digital communication systems, cambridge university press, 2011. engineering, technology & applied science research vol. 8, no. 2, 2018, 2758-2763 2758 www.etasr.com ngo et al.: assessing power system stability following load changes and considering uncertainty assessing power system stability following load changes and considering uncertainty van duong ngo university of danang danang, vietnam nvduong@ac.udn.vn van kien pham faculty of electrical engineering the university of danang—university of science and technology, vietnam pvkien@dut.udn.vn dinh duong le faculty of electrical engineering the university of danang—university of science and technology, vietnam ldduong@dut.udn.vn kim hung le faculty of electrical engineering the university of danang—university of science and technology, vietnam lekimhung@dut.udn.vn van ky huynh university of danang danang, vietnam hvky@ac.udn.vn abstract—an increase in load capacity during the operation of a power system usually causes voltage drop and leads to system instability, so it is necessary to monitor the effect of load changes. this article presents a method of assessing the power system stability according to the load node capacity considering uncertainty factors in the system. the proposed approach can be applied to large-scale power systems for voltage stability assessment in real-time. keywords-stability; power system; power plane; uncertainty; gaussian elimination i. introduction power system stability could be defined as “the ability of an electric power system, for a given initially operating condition, to regain a state of operating equilibrium after being subjected to a physical disturbance with most system variables bounded, so that practically the entire system remains intact” [1]. in [1], power system stability is broadly classified into three groups: frequency stability [2-4], rotor angle stability [5-7], and voltage stability [8-14]. voltage stability could be defined as the ability of the system to maintain steady voltages at all buses in the system after being subjected to a disturbance from a given initial operating condition [1, 8, 11]. voltage stability is divided into two subcategories: large and small disturbance stability. system faults, tripping transmission lines or dropping in generators are considered large disturbances whereas load changes are considered small disturbances. static voltage stability is considered in the present paper in particular. the system is assumed to be operated in an equilibrium state and static voltage stability analysis assesses the feasibility of the operating point to provide the system operators with a permissible region in which the system can operate normally. many techniques have been used in static voltage stability analysis in the literature. the well-known p-v and q-v curves are widely used [8, 15-20] to determine the maximum permissible loading of the system. in particular, a p-v curve provides the relationship between the real power load and bus voltage and it is depicted with a constant power factor [17]. contrariwise, a q-v curve, plotted for a constant power [17], gives the change of bus voltages with respect to reactive power injection or absorption. procedures for constructing both p-v and q-v curves are time-consuming because a large number of power flows is needed to be executed using conventional methods and models [21]. due to this drawback, they are not suitable to be used for online analysis. moreover, they could be used only for certain increasing modes and not for providing the whole view of the analysis. generally, they examine an individual bus by stressing the considered bus independently so they are not able to fully reflect the real stability condition of the system. in fact, voltage collapse occurs when the system load, i.e., real power and/or reactive power load, grows over a certain limit. hence, voltage stability boundary needs to be plotted on a power plane [17]. it will form a p-q curve [8, 22-26] that is very useful to determine boundary and operating regions for the system. once the boundary is determined, the distance from the operating point to the voltage collape of the system can be directly assessed. for this work, stability reserve ratios are widely used in practice. figure 1 shows, as an example, a p-q curve (stability boundary) that divides power plane into two regions: normal region and impossible operating region. from figure 1, stability reserve ratios pk and qk can be calculated as follows: lim 0 p 0 lim 0 q 0 p p k = 100% p q q k = 100% q where, p0 and q0 are real and reactive power of the considered load at the operating point; plim and qlim are the limitations of real and reactive power, recpectively. a p-q curve can be determined by various approaches. in [8, 22-24], the curve is characterized by a parabolic equation, while it is assumed to follow a circle in [25]. nevertheless, such assumptions on the shape of the curve make it unrealistic. in addition, those techniques usually require high computational time so they are not suitable for online voltage stability ass by cur acc loa out sta nu env sim ana cur pro po se sys sta cur loa gro nu rem adm (1) wh is t engineerin www.etasr sessment. in [2 -point without rve. however, counted for so ads, uncertain tages of branc fig. 1. in this pape ability conside mber of attrac vironment, w mplify a comp alytical techn rves. thanks ovide results q wer systems condly, in or stem, a large ability is asse rves built are ad is used to co ii. simpl considering ounding bus, mbered from maining buse mittance equa ). . . . 11 121 . . . 21 221 . . . f1 f21 y v y y v y ... .. y v y ... ..       . . . i1 i 21 . . . n1 n 21 y v y ... .. y v y                   here: . ii . 1 ij 1n i i j y z   the impedance ng, technology r.com 26], p-q curv t using any as , all of the abo ources of unce nties from re ches and gener p-q curve and er, we propose ering uncertai ctive features. we adopt gau plex diagram t nique develope to these techn quickly, hence for voltage s rder to take i number of pessed probabi realistic, since onstruct the cu lified power s a power netw denoted 0) 1 to f, loads a es are interm ations to presen . . . 2 1f2 f . . . 2 112 f . . . 2 ff2 f v ... y v v ... y v . ... ... v ... y v . ... ..    . . . 2 if2 f . . . 2 nf2 f . v ... y v . ... ... v ... y v   :y = ∑ e of branch bet y & applied sci ngo e e can be fastly ssumption abo ove mentioned ertainty in pow enewable sou rating units. operating region e an approach inties in pow firstly, for wo ussian elimina to a simple on ed in [26] fo niques, the pro e it can be ap stability assess into account -q curves is p ilistically. in e no assumptio urves. system diagr work with n+1 in which ge are represented mediate buse nt steady-state . . 1i i . . 2i i . . fi i ... y v ... ... y v ... ... ... ... ... y v ...       . . ii i . . ni i ... ... ... ... y v ... ... ... ... ... y v ...    self admittan tween i and j; ience research et al.: assessing y constructed out the shape d approaches a wer systems, su urces and ra s on power plane h to assess v wer systems w orking in a rea ation techniq ne, then we u or constructing oposed metho pplied to large sment in real randomness i plotted and v addition, the on on the chan ram algorith 1 buses (includ neration buse d by admittanc es, we can e of the system . . . 1n n 1 . . . 2 n n 2 . . . fn n f y v j y v j ... ... ... y v j       . . in n . . nn n ... ... ... y v 0 ... ... ... y v 0     nce ( . ij ijz = r + i = 1÷n; j = 1÷ h g power system pointof the are not uch as andom . oltage with a al-time que to use the g p-q od can e-scale l-time. in the oltage e p-q nge of hm ding a es are ces so form m as in (1) ij+ jx ÷n), j. mak foll . n . nn y y and wil i.e., adm last equ mak gen 2. gro ord load vol. 8, no. 2, 2 stability follo . ij . ij 1 z y : y from (1), ad ke a simplifi lows. first, devide b . .n1 1. nn y y v ...y y next, multiply . . .n1 nf in 1 . nn nn y y v ...y eventually, su d the nth comp l be eliminated after the abov , the last equa mittances for t bus. we rep uations from th ke an equivale neration buses fig. 2. equiv considered. in figure 2, ounding bus 0 der to assess th d, electromoti 2018, 2758-276 owing load cha = mutual a dopting gaussi ied equivalen both sides of t . . .nf ni f. . nn nn y y v ... y y y both sides o . . .f ni in f . n nn y y v ... y ubtract (3) from *   . . ifify y ponent in each d. ve steps, we c ation in (1). e the equivalen peat the abov he initial n eq ent network fo and a load bu . 1e . 2e . ie . fe . 1( f 1)z  . 10y . 2(f 1)z  . 20y . i ( f 1)z  . i0y . f( f 1)z  . f0y valent network w admittance y included admi he ability accor ive force εi (i 63 anges and cons admittance bet ian eliminatio nt diagram fo the last equatio . . i n n v ...+v = 0 f each equatio . . . in iniy v ...+y v m the ith equat . . nf in . nn y y y h equation in can eliminate o equation (4) i nt network aft ve process un quations in (1). or the consider us considered a . ( f 1)v  . ( f 1y  with f generation y(f+1)0 between ittance of the rding to chang i=1÷f) is con 2759 sidering uncer tween bus i an on method, we or the networ on in (1) by . y 0 (2) on in (2) with y . nv = 0 (3) tion in (2) yiel (4) (2) (i.e., iny . one equation in s used to calc fter eliminating ntill obtaining . therefore, w red network w as shown in f 1)0 n buses and a loa n bus f+1 and load at bus f+ ge at the consid nsiderd as con rtainty nd bus e can rk as nn . iny lds nv . . ) n (1), culate g the g f+1 we can with f figure ad bus d the +1. in dered nstant engineering, technology & applied science research vol. 8, no. 2, 2018, 2758-2763 2760 www.etasr.com ngo et al.: assessing power system stability following load changes and considering uncertainty (so yi0 can be eliminated) and the load is separated as in figure 3. . 1e . ( f 1)v  . 2e . ie . fe sl = pl+jql . 1( f 1)z  . 2( f 1)z  . i ( f 1)z  . f( f 1)z  . 0y fig. 3. simplified equivalent diagram. in figure 3, y = g + jb is parallel with the admittance of the load y = g + jb , where 0 ( f 1)0 lg g g  0 ( f 1)0 lb b b  2 l l f 1,ratedg p / v  2 l l f 1,ratedb q / v  and f 1,ratedv  is the rated voltage at bus f+1. equation (1) can be represented in a matrix form as in (5), in which the first matrix is denoted as y (called admittance matrix): . . . . . 11 12 1f 1i 1n . . . . . 21 22 2f 2i 2n . . . . . f1 f2 ff fi fn . . . . . i1 i2 if ii in +y y ... y ... -y ... y y +y ... +y ... y ... -y ... ... ... ... ... ... ... ... y y ... +y ... y ... y ... ... ... ... ... ... ... ... y y ... -y ... +y ... y ... ... ... ... ... . . . 1 1 . . 2 2 . . f f . . i i . . . . . . . n1 n2 nf ni nn n n v j v j ... ... v j= ... ... v j .. ... ... ... ... y y ... -y ... y ... +y v j (5) it is worth noting that when we need to assess voltage stability at a certain load bus, that bus is numbered f+1 before forming either (1) or (5). alternatively, at first, the equations are formed, then in order to consider any load bus i, rows i and f+1, and columns i and f+1 are exchanged. based on the above analysis, we developped an algorithm for making a simplified equivalent diagram for the considered network, as in figure 4. iii. representing uncertain factors in electrical power systems in a power system, random factors related to the load, failures of elements in the system, renewable energy sources can be represented by probability distribution functions [2729]. these functions describe the inherent nature of uncertainty factors and need to be integrated into the analysis of the system. in practice, such functions can be estimated based on historical data measured at loads, data on failures of lines, generating units, etc. in the literature load is usually expressed by a normal distribution function, while renewable power generation is usually represented by a generic function such as beta, gamma, weibull functions, etc [29]. random outage of an element such as transmission line, transformer, generating unit can be described by a 0-1 distribution function (0: outage state, 1: working state; an operating element can be failed with a certain probability) [29]. if all generating units in a power plant are the same, the combination of 0-1 distribution function for each unit could be represented by a binomial distribution function [29]. compute and form admittance matrix y of the system start power system components libraries calculate admittances of all branches of the system check information of power system (system parameters and operating parameters) s a ve m a tr ix y select the load bus i to calculate calculate admittances for simplifying the network diagram using (4) and k = n-1 exchange row i and row (f+1), column i and column (f+1) in matrix y k < (n f-1) set value k = n end true false true false calculate admittances of the simplified equivalent diagram with (f+1) buses in fig. 3 save result input data of the system (system parameters and operating parameters) fig. 4. algorithm for making a simplified equivalent diagram based on gaussian elimination method. iv. stability assessing algorithm development for an electrical power system with n buses (excluding a grounding bus, with f generation buses, bus 1 is considered as the slack bus), in order to examine the stability of the system according to the change at a certain load bus, first, we use the algorithm discussed in section ii to obtain the simplified equivalent diagram for the considered network. when the system is operating at a certain state with known network configuration, generating power, load, ect., we increase load at the considered bus and use the pragmatic criterion dq/dv presented in [26, 30] to construct the permissible operating region on a power plane under the conditions of a static stability limit as in figure 5. in figure 5, m1 is a certain operating point of the load considered belonging to stable region, while m2 belongs to unstable region of the system (see figure 1). suppose that the system is operating at m1, its stability and the dangerous level of increasing load can be evaluated according to the distance from m1 to the stability boundary. when random factors, as discussed in section iii, are considered, stability boundary is not represented by a single curve but by a set of curves as shown in figure 6. uncertainties in the system, related to load, renewable sources, random outages of lines, generating units, etc., can be represented by probability functions and set of random samples representing the sta sam are (se sys lin and sys loa and reg po wo if wit gre car avo ass con (fi nor (de be bra engineerin www.etasr ese functions c atistics [31, 32 mple. assume e plotted) and ee figure 6). stem in terms ne connecting d the probab stem can be ca therefore, b ad on power p d the system gions 1, 2, 3 o int m1, the orking at m2, it is working th probability eatter than a ce rry out approp oid instability sessing stabilit nsidering unce f fig. 6. set uncertainty in th we consider igure 8). in th rmal distribu eterministic va equal to 10% anch is assume ng, technology r.com can be genera 2]. in figure 6 e that n1 samp d the considere in order to of static volt the origin o a bility of unsta alculated as in 2 1 n 1 n p = ased on the o lane, the stabi falls into one on power plan system is cer the system is at m3, the sy y of instabilit ertain value, th priate remedi y for the syste ty of power sy ertainty is show 0 p [mw] q1 p1 m1 q p2 m fig. 5. operat 0 p [mw] q1 p1 m1 q p2 m p3 of p-q curves he system. v. model r the ieee 39 he system, loa ution charact alue [33]) and of its expecte ed to have pro y & applied sci ngo e ated using sam 6, each curve ples are genera ed load is ope evaluate dang tage stability, and m3 that i ability (dange (6):  100 % operating poin lity of the syst of three case ne): (1) if the rtainly stable certainly unst ystem may be ty p (0%<p<1 he operator of al actions to em. the prop ystems accord wn in detail in q [mva q2 m2 ting points on pow q [mva q2 m2 m3 q3 s on power pl ling and resu 9-bus system ad at each bu erized by it d standard dev ed value). ran obability of fai ience research et al.: assessing mpling techniqu is plotted for ated (i.e., n1 c erating at poin gerous level o we draw a st intersects n2 c erous level) o nt of the consi tem can be ass s (correspond load is work (p=0). 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stability li ght click on th the results of onditions. in ea se curves divid s 10, 11 and nstability of 0 00%) and inst vely. ult of voltage stab gion 1. ult of voltage stab gion 2. y & applied sci ngo e m is develope ding to load c gramming lan n as in figure mputer program d em according to lo luate the sys mit under unc he bus. figures bus 25 corres ach figure, a s de the power d 12 correspo 0%), unstable s tability with p bility assessment bility assessment ience research et al.: assessing ed to assess sta changes consid nguage. startin 9. developped for s oad changes. stem accordin certainty at a c s from 10 to 1 sponding to v set of 1000 cur plane into dif ond to stable state (probabil probability equ at bus 25 when t at bus 25 when t h g power system ability dering ng the stability ng to certain 12, for arious rves is fferent state lity of qual to the load the load und sys sys pro asse vol mak bas ana the app asse are use [1] [2] [3] [4] [5] [6] [7] [8] [9] vol. 8, no. 2, 2 stability follo fig. 12. resul is working at reg in this paper a der uncertaint tem related to tem, renewab obability distrib essment. the tage stability king a simplif sed on gaussia alytical techni ese techniques plied to large essment in rea realistic beca ed for their con p. kundur, j. canizares, n. h cutsem, v. v stability ieee/c ieee transacti 2004 j. hu, j. cao, stability based ieee transacti n. nguyen, j. penetration un on power syste n. hatziargyrio power systems power system 102, 1998 m. oluic, m. g transient stabi on power syste l. meegahapol angle and volt distributed wind no. 3, pp. 272-2 e. vittal, m. o penetrations o systems, vol. 2 c. w. taylor, p b. leonardi, v models for o transactions on 2018, 2758-276 owing load cha lt of voltage stabi gion 3. vi. co a methodology ty is proposed o loads, rand ble energy so bution functio proposed ap study thanks fied equivalen an elimination ique develope s allow us to p e-scale power al-time. moreo ause no assum nstruction. refe 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springer-verlag, 2003 [32] g. marsaglia, “random number generation”, in: a. ralston, e. d. reilly, eds, encyclopedia of computer science and engineering, van nostrand reinhold, pp. 1260-1264, 1983 [33] a. dissanayaka, risk based dynamic security assessment, msc thesis, university of manitoba, 2010 engineering, technology & applied science research vol. 7, no. 5, 2017, 1974-1979 1974 www.etasr.com nasir et al.: real time speed control of a dc motor based on its integer and non-integer … real time speed control of a dc motor based on its integer and non-integer models using pwm signal abdul wahid nasir electrical & electronics eng. dept. nit jamshedpur jamshedpur, india 2014rsee003@nitjsr.ac.in idamakanti kasireddy electrical & electronics eng. dept. nit jamshedpur jamshedpur, india 2015rsee002@nitjsr.ac.in arun kumar singh electrical & electronics eng. dept. nit jamshedpur jamshedpur, india aksingh.ee@nitjsr.ac.in abstract—this paper exploits the advantage of non-integer order modeling of a process over integer order, in those cases where the process model is required for control purpose. the present case deals with speed control of a dc motor. based on the real time open loop response, dc motor is being modeled as integer and non-integer order first order plus delay system. both these models are then separately used for determining two sets of proportional-integral-derivative (pid) controller parameters through ziegler nichols (zn) closed loop tuning method. in addition to this, a model based control technique i.e. internal model control (imc) is also implemented using both integer and non-integer model respectively. for carrying out the real time speed control of dc motor, labview platform has been used. after going through the results, it is observed that the controller performance considerably improves, if non-integer order model is used for controller design rather than integer order model. keywords-dc motor speed; fractional order system; pid; internal model control; labview i. introduction dc motor is having a prominent role in almost all industrial and robotic applications. its simplicity, reliability, economic feasibility and the ease with which such types of dc motor speed can be controlled, makes it omnipresent. with the recent advancements in power electronics, various switching control techniques emerged. pulse width modulation (pwm) technique is one of them, which has been used here for the speed control of dc motor by manipulating its duty cycle. here zn-pid & imc control technique is used to meet the control objective. since both these aforesaid control techniques require model of the process for controller design, therefore integer and non-integer (fractional) order model is determined from open loop step response of the dc motor. here, the concept of fractional calculus has been introduced in process modelling. the branch of calculus which is evolving due to the generalization of order of conventional integro-differential operator from integer to non-integer, is known as fractional calculus. due to increasing interest in this among researchers in recent decades [1-3], the solutions of various problems incorporating non-integer order integro-differential operator are now available making its application feasible in various fields of science and technology. these non-integer order fundamental operators, where ‘α’ is the operator order and ‘a’ & ‘t’ give the limits of the operator is defined as follows:   , 0 1 , 0 , 0 a t t a d dt d                      d (1) different definitions of this fractional integro-differential are given in [4]. the terms fractional order and non-integer order are used interchangeably. for carrying out all real time experimental work, labview platform has been used. for interfacing the dc motor dynamics with labview platform through computer, a labjack u3-hv data acquisition card (dac) was employed. for the rpm measurement of the motor, an infrared (ir) proximity sensor was used. in section ii step-wise outline of the work carried out is given. experimental setup is described in section iii. section iv gives the modelling of a dc motor based on its open loop data. the control schemes implemented for the speed control of dc motor is discussed briefly in section v. experimental results are presented and discussed in section vi. based on the various results obtained, conclusion are drawn and scope for future work is given in section vii. ii. experimental setup the experimental setup for the dc motor speed control system is shown in figure 1. it includes one 12 volts / 1-amp dc motor having maximum rpm of 2000. to the shaft of this motor is attached one circular disc, whose one half of the circular area is colored in silver and another half in black. an infrared (ir) proximity sensor having one ir transmitter and one ir receiver is engaged to sense the rpm of motor. the ir transmitter continuously transmits the ir ray on the rotating disc which is reflected back to the ir receiver to give positive output when falls on silver area and zero output when falls on black area, as the black area absorbs the ir ray rather than reflecting it. thus depending on the rotational speed of the motor a pulsating signal of specific frequency is generated at engineering, technology & applied science research vol. 7, no. 5, 2017, 1974-1979 1975 www.etasr.com nasir et al.: real time speed control of a dc motor based on its integer and non-integer … the output of ir transmitter. at the interval of every 0.1 second, the output frequency is measured and updated to the control algorithm employed in labview environment through a labjack make u3-uv, data acquisition card. based on current rpm information, the controller generates control signal in the form of pwm signal through the same data acquisition card. this signal is then fed to l298n dc motor driver circuit, through which the speed of motor is regulated to desired point. this is how a real time closed loop speed control system prototyping is implemented. dc motor computer labview environment ir proximity sensor l298n motor driver labjack u3-hv dac fig. 1. dc motor speed control system iii. integer & non-integer order modelling for the control system under study i.e. speed control of a dc motor, first of all different open loop step responses are noted to analyze the system behavior. since pwm is the input manipulating variable and rpm of the motor is output, controlled variable, therefore the duty cycle (in percentage) of pwm signal is varied to obtain the steady state rpm corresponding to each input signal. this input-output data is then plotted as shown in figure 2. 25 30 35 40 45 50 55 60 65 70 75 400 600 800 1000 1200 1400 1600 duty cycle of pwm signal (%) r o ta ti o n o f m o to r (r p m ) fig. 2. input output steady state characteristics from the nature of the plot, it can be concluded that within the specific input range of duty cycle i.e. 25% to 75%, dc motor speed response almost exhibits linear characteristic. so, the controller designed for any operating condition within this range should work well throughout the rpm range of 550 to 1600. the open loop transfer function relating input i.e. armature voltage and output i.e. rotational speed is given by (2) [5]:   _ ( ) ( ) t dc motor e t ks g v s ls r js b k k        (2) where θ : rotational speed of motor (rpm) v: armature voltage (v) j: moment of inertia of rotor (kg.m2) b: motor viscous friction constant (n.m.s) ke: electromotive force constant (v/rad/sec) kt: motor torque constant (n.m/amp) r: electric resistance (ohm) l: electric inductance (h) in many cases, where r>>l, the transfer function given by (2) reduces to first order system given by (3).  _ t dc motor e t k g r js b k k    (3) now the next step is to estimate the dc motor model parameter based on the step response. a step change in duty cycle of pwm signal is made from 50% to 75%, and rpm response data is obtained. since this response very much matches the characteristics of step response of first order plus delay system. therefore, it is deduced that the current system can be modelled as first order plus delay system. making use of the flexible feature [6-7] of fractional order calculus in modelling, the present system is not only modelled as integer but also as non-integer order system as given by (4) and (5) respectively. 1 ls integer k g e s   (4) 1 ls non integer k g e s     (5) here, genetic algorithm (ga) is used to estimate the values of parameters for integer model i.e. gain (k), time constant (τ) and delay (l) to minimize the value of integral of squared error (ise), the objective function considered [8-9]. similarly, the unknown parameters of non-integer model are obtained i.e. α, the order of the filter, along with k, τ & l. ga is stochastic search computational tool based on the theory of natural evolution, basically involving the process of selection, crossover and mutation. in 1975, holland [10], proposed the elementary principles of ga. based on this novel topic, later some literatures also surfaced [11]. to begin with, a random set of parameters is presumed, which mimics the genes of chromosomes, to be the possible solution of the search problem. an objective function is defined that reflects the fitness of these chromosomes, which when subjected to minimization or maximization under certain constraints yield the optimal result. the objective function considered for estimation of model parameters is integral of squared error (ise) subject to minimization is given by (6). different sets of engineering, technology & applied science research vol. 7, no. 5, 2017, 1974-1979 1976 www.etasr.com nasir et al.: real time speed control of a dc motor based on its integer and non-integer … model parameters are chosen from the search space based on ga at every simulation run, and the step response data of that particular model is obtained. this obtained model data is then compared to already existing system data to generate error which is ultimately used to calculate ise. this ise value is again passed to ga as feedback information, and this process continues until optimal minimum is reached. figure 3 represents the implementation of ga for model parameter estimation. 0 2 2 0 { ( ) ( )} { ( )} sp ise y t y t dt e t dt      (6) the discussed ga is implemented using matlab for current problem of finding model parameters. for carrying out all types of simulation work for model parameter estimation related to non-integer order plants, fomcon toolbox [12], has been used in matlab. table i shows the ga characteristics considered in the present case. table ii gives the integer and non-integer order transfer function model for dc motor speed with their corresponding ise values and figure 4 represents the step response for the dc motor speed system along with its integer and non-integer model. in the inset of figure 4, zoomed responses for specific time duration are given, so that the difference among all the three responses can be identified easily. ( )e s ise ga   model step input dc motor system system data model data fig. 3. model parameters estimation using ga fig. 4. open loop step responses table i. ga characteristics population size 50 fitness scaling function rank crossover function 0.8 crossover fraction scattered migration fraction 0.2 ending criterion function tolerance of 1e-4 table ii. model parameters nature of model transfer function ise integer order 0.34722.58 0.235 1 se s   440 noninteger order 0.364 0.91 23.358 0.25 1 se s  154 iv. controller design in spite of advancements in different schemes of controller in the recent past, pid still rules the application domain due to its simple architecture and its ability to control various types of linear and non-linear processes. most of the tuning of controller parameters for pid requires model of the process. another very simple control technique based on model of the process is internal model control (imc). both these control techniques i.e. pid & imc are implemented for the present pid & imc are implemented for the present case of dc motor speed control, and are discussed in nutshell under the following subsection respectively. a. pid control transfer function representation of pid controller relating error, e(s) and control signal, u(s) is given by (7). ( ) 1 1 ( ) d i u s kp t s e s t s          (7) where kp, ti & td are the controller tuning parameters. the transfer function of pi controller can be obtained by substituting td=0, in (7). similarly, for obtaining p-type controller transfer function, set ti=∞ and td=0. the basic pid controller tuning rules were proposed in [13], and were based on empirical data obtained from extensive experiments. authors in [14], further modified the tuning rules. since then various researchers are proposing several other methods for pid controller tuning. at present, ziegler nichols closed loop method/cycling method is used. although it is experimental based control design, but since the model of the process to be controlled is available, therefore, without disturbing the actual process, the controller parameters can be obtained. first of all, ultimate gain, ku and ultimate period, pu is determined by making td=0 and ti=∞ and varying proportional gain, kp such that the closed loop response becomes oscillatory having constant amplitude. the value of kp at which sustained oscillation occurs is the ultimate gain, ku and the period of the oscillation is the ultimate period, pu. after that the p, pi & pid parameter can be obtained using table iii. table iii. zn closed loop pid tuning controller type kp ti td p 0.5ku -- pi 0.45ku pu/1.2 - pid 0.6ku pu/2 pu/8 b. open loop imc internal model control (imc) is a model based control technique, where a process is “embedded” within the engineering, technology & applied science research vol. 7, no. 5, 2017, 1974-1979 1977 www.etasr.com nasir et al.: real time speed control of a dc motor based on its integer and non-integer … controller [15]. the open loop imc structure is given in figure 5, where q(s) is the model based controller and g(s) is the process. ( )u s( )q s ( )g s( )r s ( )y s model based controller proces s fig. 5. open loop internal model control consider a first order process g(s), given by (8), whose controller transfer function q(s) is given by (9). 1 k g s   (8) 1( ) ( ) ( )q s f s g s (9) where g-1(s) is the invertible part of g(s), with right hand side zeros and delay being factored out if they are present, to make q(s) stable. f(s) is the filter defined by (10). 1 ( ) ( 1) f s s   (10) the filter, f(s) is incorporated in the controller transfer function q(s) to make it proper i.e. physically realizable. the open loop control response y(s) is, ( ) ( ) ( ) ( ) ( ) ( )y s q s g s r s f s r s  (11) as seen from (11), the output response depends on filter time constant λ, hence it is considered as controller parameter. in the present case, imc technique will also use non-integer model, other than integer order model. therefore, before implementing non-integer model in real time control in labview platform, it is firstly converted to the equivalent higher integer order model using method described in [16], because the dynamics of non-integer order system can be well represented with the help of higher integer order model and vice-versa. v. results and discussions the pid controller parameters were tuned using ziegler nichol’s closed loop technique. as discussed in subsection iv.a, ultimate gain ku and ultimate period, pu is determined. since two types of model are available for the process. i.e. integer and non-integer order model, therefore for each nature of model, ku and pu are derived respectively as shown in table iv. table iv. ku and pu values parameter io model fo model ku 0.2125 0.2800 pu(sec) 1.8338 1.3035 based on these values of ku and pu, the controller parameters for p-type, pi-type and pid-type control are determined using zn formula as given in table iv for both the integer & non-integer model, which have been tabulated as follows in table v. table v. p, pi and pid controller parameters controller type kp ti(s) td(s) p io model 0.106 -- fo model 0.140 -- pi io model 0.095 1.528 - fo model 0.126 1.086 - pid io model 0.127 0.917 0.229 fo model 0.168 0.652 0.163 the p, pi & pid obtained from integer order model is tested against the step change in rpm. similarly, the controller performance is also evaluated for controllers obtained from non-integer order model. all the real time closed loop controlled response data is collected and plotted to have the comparative study. figures 6-8, represent the servo response for p, pi & pid control respectively. table vi gives the various performance indices for the different controllers under test. 0 1 2 3 4 5 6 7 8 9 10 0 500 1000 1500 time (s) s p e e d o f m o to r (r p m ) set-point controller parameter derived from io model controller parameter derived from fo model 0 1 2 3 4 5 6 7 8 9 10 0 20 40 60 80 100 time (s) d u ty c y c le o f p w m ( % ) p control output from fo model p control output from io model fig. 6. servo response of p controlled system 0 1 2 3 4 5 6 7 8 0 500 1000 1500 time (s) s p e e d o f m o to r (r p m ) set-point controller parameter derived from io model controller parameter derived from fo model 0 1 2 3 4 5 6 7 8 0 20 40 60 80 100 time (s) d u ty c y c le o f p w m ( % ) pi control output from fo model pi control output from io model fig. 7. servo response of pi controlled system engineering, technology & applied science research vol. 7, no. 5, 2017, 1974-1979 1978 www.etasr.com nasir et al.: real time speed control of a dc motor based on its integer and non-integer … after analyzing the closed loop step responses in figures 6– 8 and the data indicating various performance indices in table vi, it can be easily deduced that performance for the class of controllers obtained using non-integer order model is superior in every aspect than those obtained from integer order model for all p, pi & pid control schemes. there is one insignificant exception in p-type controller whose maximum overshoot is slightly more for the controller design using non-integer order model rather than integer order model. other performance index parameters such as rise time (tr) and peak time (tp) have not been included in table vi, as these parameters are almost identical for both cases, i.e. for controller obtained from integer and non-integer model. even, figures 6-8, the closed loop step response, conveys the same message. moving to other control technique employed for real time speed control of dc motor, i.e. imc, where the filter time constant, λ is controller parameter. the value of λ determines the nature of control performance. the aggressiveness of controller is inversely proportional to λ value, whereas robustness is directly proportional to value of λ. hence the value of λ is obtained through extensive simulations and is found to be λ=0.1. finally, imc open loop control is implemented in labview environment using the same value of λ here only open loop control has been implemented in order to just validate the fact that, since non-integer model captures the real time system dynamics better than integer order model, therefore the model based control technique incorporating non-integer model gives improved results rather than integer model. figure 9 shows the open loop control responses for imc obtained from both integer and non-integer order model for the step change made at t=0.4 second, from initial value of 0 to 600 rpm. table vii gives the transfer functions of different imc along with performance indices data. figure 9 and table vii data clearly depict the supremacy of imc based on non-integer order model over integer order model. table vi. performance indices for p, pi & pid controlled system performance indices p-type controller design using pi-type controller design using pid-type controller design using integer model non-integer model integer model non-integer model integer model non-integer model settling time, ±5% (s) 1.26 1.13 3.94 2.96 3.48 2.56 settling time, ±2% (s) 1.43 1.28 5.02 3.72 3.91 2.86 overshoot (%) 38 41 45 41 41 37.5 undershoot (%) --40 33 36.5 33.4 offset 340 274 nil nil nil nil ise 1.16e+7 8.12e+6 3.24e+6 2.52e+6 3.05e+6 2.35e+6 iae 3.29e+4 2.72e+4 9.49e+3 7.19e+3 8.71e+3 6.44e+3 vi. conclusion in this paper, two different control techniques, pid and imc have been implemented for the real time speed control of a dc motor. the aim of the present paper is to highlight the fact that non-integer order model is more efficient in capturing the dynamics of real time systems as compared to integer order model, and also the controllers based on non-integer models yield better performance rather than those based on the integer model. the conclusion is well validated by the results obtained from experimental setup. this work can be extended to control any system, wherever a model is required for controller design 0 1 2 3 4 5 6 7 8 9 10 0 500 1000 1500 time (s) s p e e d o f m o to r (r p m ) set-point controller parameter derived from io model controller parameter derived from fo model 0 1 2 3 4 5 6 7 8 9 10 0 20 40 60 80 100 time (s) d u ty c y c le o f p w m ( % ) pi control output from fo model pi control output from io model fig. 8. servo response of pid controlled system 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 200 400 600 800 time (s) s p e e d o f m o to r (r p m ) set-point imc based on io model imc based on fo model 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 10 20 30 time (s) d u ty c y c le o f p w m ( % ) control output for imc based fo model control output for imc based io model fig. 9. imc open loop control responses table vii. imc performance indices imc based on controller tf, q(s) offset ise iae integer order model 0 .2 3 5 1 2 2 .5 8 ( 0 .1 1) s s   30 3.22e+5 1.51e+3 non-integer order model 0.910.25 1 23.358(0.1 1) s s   negligi ble 2.79e+5 1.12e+3 . engineering, technology & applied science research vol. 7, no. 5, 2017, 1974-1979 1979 www.etasr.com nasir et al.: real time speed control of a dc motor based on its integer and non-integer … references [1] a. s. elwakil, “fractional order circuits and systems magazine: an emerging interdisciplinary research area”, ieee circuits and systems, vol. 10, no. 4, pp. 40-50, 2010 [2] m. o. efe, “fractional order systems in industrial automation – a survey”, ieee transaction of industrial informatics, vol. 7, no. 4, pp. 582-591, 2011 [3] s. kumar, “a new fractional modelling arising in engineering sciences and its analytical approximate solution”, alexandria engineering journal, vol. 52, no. 4, pp. 813-819, 2013 [4] c. a. monje, y. chen, b. m. vinagre, d. xue, v. feliu, fractional order systems and controls: fundamental and applications, springer-verlag, london, 2010 [5] “dc motor speed: system modeling”, http://ctms.engin.umich.edu/c tms/index.php?example=motorspeed&section=systemmodeling.html [6] a. vishwesh, p. s. v. natraj, “fractional order modeling of neutron transport in a nuclear reactor”, applied mathematical modelling, vol. 37, no. 23, pp. 9747-9767, 2013 [7] t. djamah, r. mansouri, s. dfennounce, m. bettayeb, “optimal low order model identification of fractional dynamic systems”, applied mathematics and computation, vol. 206, no. 2, pp. 543-554, 2008 [8] m. lankarany, a. rezazade, “parameter estimation optimization based on genetic algorithm applied to dc motor”, 2007 international conference on electrical engineering, lahore, pp. 1-6, april 11-12, 2007 [9] s. udomsuk, k. l. areerak, k. n. areerak, a. srikaew, “parameters identification of separately excited dc motor using adaptive tabu search technique”, international conference on advances in energy engineering, beijing, pp. 48-51, june 19-20, 2010 [10] j. h. holland, adaption in natural & artificial systems. cambridge ma: mit press, 1975 [11] d. e. goldberg, genetic algorithms in search optimization and machine learning. boston, ma: addison-wesley, 1989 [12] a. tepljakov, e. pettenkov, j. belikov, “fomcon: a matlab toolbox for fractional-order system identification and control”, international journal of microelectronics and computer science, vol. 2, no. 2, pp. 51-62, 2011 [13] j. g. ziegler, n. b. nichols, “optimum settings for automatic controllers”, transactions of asme, vol. 64, pp. 759-768, 1942 [14] g. h. cohen, g. a. coon, “theoretical considerations in retarded control”, transaction of asme, vol. 75, pp827, 1953 [15] b. wayne bequette, process control: modeling, design and simulation, 2nd ed., prentice hall, 2002 [16] d. xue, c. zhao, y. chen, “a modified approximation method of fractional order system”, international conference on mechatronics and automation, luoyang, henan, pp. 1043-1048, june 25-28, 2006 microsoft word 468-ce-r1.doc engineering, technology & applied science research vol. 4, no. 4, 2014, 662-668 662 www.etasr.com kioussis et al.: electrical trees in a composite insulating system consisted of epoxy resin and mica… electrical trees in a composite insulating system consisted of epoxy resin and mica: the case of multiple mica sheets for machine insulation v. a. kioussis m. g. danikas d. d. christantoni g. e. vardakis a. bairaktari department of electrical & computer engineering, democritus university of thrace, greece department of electrical & computer engineering, democritus university of thrace, greece department of electrical & computer engineering, democritus university of thrace, greece department of electrical & computer engineering, democritus university of thrace, greece department of electrical & computer engineering, democritus university of thrace, greece abstract— epoxy resin and mica sheets consist the essential insulation of rotating machine stator bars. such an insulation, although very resistant to partial discharges, is subjected to considerable electrical stresses and consequently electrical trees may ensue. in this paper, an effort is made to simulate electrical tree propagation in multiple epoxy resin/mica sheets with the aid of cellular automata (ca). an attempt to compare the simulation results with experimental results is also made. keywords-:electrical trees; composite insulation; dielectric strength; breakdown; mica sheets; epoxy resin; machine insulation i. introduction electrical trees constitute a network of channels full of either solid, gaseous or even liquid byproducts. electrical trees emanate either from sharp electrodes or from enclosed cavities or from other enclosed foreign particles in the insulation. they seem to come from partial discharge (pd) activity and/or local breakdowns of the insulating material. electrical trees can be of branch-type or of bush-type. propagation of electrical trees has as a consequence the total breakdown of the insulation. electrical tress are due mainly to electric field intensifications [1,2], but they depend also on the experimental (or service) conditions, i.e., among others, on the insulating material itself, the level of the applied voltage, the type of the applied voltage, the frequency, the inclusion of foreign particles, the humidity and the temperature [3]. for the creation of electrical trees, first of all there must be an injection of charges from the electrodes and/or from a foreign particle or cavity, then a propagation of small channels of diameter smaller than 10 μm in the insulation. the final stage is when the initial channels touch the opposite electrode and the channels acquire a larger diameter because of the pd inside them. during the final stage, the channels seem to be pipe-shaped channels. when the diameter of such channels acquires a critical value, the final breakdown ensues. such channels are characterized from diameter values between 10 μm and 150 μm [4]. rotating machines’ insulation consists of sheets of mica in epoxy resin. it is a good insulating system, resistant to pd. previous research indicated that the mica sheets elongate the treeing path and at the same time delays the time to total collapse [5]. in the context of the present paper, simulations of the growth of electrical trees are attempted in an epoxy resin/mica system with multiple mica sheets. a discussion follows as to whether such a system can withstand eventual breakdown. ii. the barrier effect in the case of rotating machine insulation the elongation of electrical tree paths and the deceleration of electrical tree growth have recently been experimentally studied. the mica sheet acts as a barrier and hinders the electrical tree growth. the longer the mica sheet, the more the time to breakdown. it was shown that electrical trees cannot penetrate the mica barriers and try to go around them, increasing thus the time to ultimate failure [6]. the mica sheets are influenced, among other factors, from mechanical stress and the space charges [7]. the number of mica sheets plays also a significant role in hindering the propagation of electrical trees in a composite insulation. electrical trees usually develop across the interfacial region between mica and epoxy resin or in overlapped areas [8]. the speed at which an electrical tree propagates across an interfacial region is defined from the chemical bonding between the mica sheets and epoxy resin. the mica sheet insertion affects the mechanical properties of the composite material. a decrease in tensile strength, modulus of elasticity and fracture roughness as a result of plasticization is mirrored in the decreased resistance of the material to electrical treeing growth [9]. the time to inception of electrical treeing is smaller in insulating systems which have internal mechanical stresses than in systems which are mechanical stress-free. important is the role of the bonding between mica sheet and epoxy resin [10]. the interfacial region between mica barrier and epoxy resin is affected by the temperature. electrical trees seem to acquire more pointed characteristics when the temperature rises, whereas they tend to be more spread out in lower temperatures. humidity plays also a role by affecting the internal mechanical stresses [11]. engineering, technology & applied science research vol. 4, no. 4, 2014, 662-668 663 www.etasr.com kioussis et al.: electrical trees in a composite insulating system consisted of epoxy resin and mica… in an ideal situation the mica sheets should be smooth but in practical conditions mica sheets may be deformed and, consequently, non-uniform electric field distributions may result. this in turn may give rise to partial discharges and the creation of electrical trees [12]. iii. simulation models of electrical trees various models on the simulation of electrical trees have been proposed, such as the npw model, based on the addition of a new branch or a new bond in the “lattice” according to a probabilistic approach [13, 14]. in another effort, it was considered that the local value of the damage/unit length had to be greater than a critical value wc. and the electric field value near the damaged area had to be greater than the critical dielectric strength of the material [15, 16]. in cases, where treeing is studied with the presence of a barrier, the phenomenon propagates through the weaker medium and not through the barriers. further, in another approach employing a non-uniform electrode arrangement, it was shown that treeing depends on the electric field intensity as well as on the presence of space charges [17]. iv. cellular automata simulation method cellular automata (ca) are used in the present paper for the simulation of the electrical tree propagation. in this model, the algorithm takes into account the variation of the dielectric constant of epoxy resin. the simulation of electrical tree propagation using cellular automata as a simulation method, has already been presented elsewhere [18, 19]. in the present paper a combination of two insulating materials is used (epoxy resin and mica sheet). the simulation method based on ca takes into account the fluctuations of permittivity, the local dielectric strength of the materials and the boundary conditions according to the electromagnetic theory at the interfaces between:  epoxy resin and mica sheet  epoxy resin and electrodes the simulation successfully reproduces electrical tree propagation with a point–plane electrode arrangement. moreover, it simulates conditions where homo and heterocharges are present [20, 21]. it also successfully reproduces tree formation in the presence of voids, conducting and nonconducting inclusions [22, 23]. time and space, according to ca, are discrete physical quantities and any physical system can be divided into a number of cells. every cell is defined by a number of parameters defining the internal state of the cell. a common rule for all cells is applied, determining the evolution of the phenomenon [24, 25]. the point that differentiates this geometry is applied to an epoxy resin sample and the electrical tree propagation is shown in two cases. in this paper, the electric field calculation is obtained with the aid of the partial differential equation toolbox (pde) of matlab. in the graphical user interface (gui) of pde, the suitable geometry for the electrical tree growth is chosen. the point electrode and the opposite plane electrode are placed between epoxy resin and more mica barriers. after the geometry construction, the boundary conditions between the interfaces of the materials are defined. the pde creates a mesh of nodes in the region of interest, according to the finite element method (fem). the potential distribution is calculated with the aid of laplace’s equation: 2v = 0 (1) according to ca, the insulating system is divided in a number of cells. in this paper, 60x60 and 100x100 cells are chosen to simulate the electrical tree propagation. the electrical field is calculated with the aid of: e = v/ x (2) the above equation, for the purposes of this simulation, is modified to: e  g va vb/ x (3) the dielectric inhomogeneity factor g takes values between 0.9 and 1.1. this factor is dimensionless and is created randomly corresponding to each cell through the appropriate matrix (60x60, 100x100). the above mentioned factor absorbs the fluctuations of the dielectric environment surrounding each cell, creating a variation in the electrical field strength calculated with the aid of cellular automata. this factor contributes to the notion of the internal state of the cell since it is used in the calculations of the electrical field for every cell separately [26]. the cells belonging to the physical insulating system are divided into five categories:  the cells belonging to the point electrode  the cells belonging to the plane electrode  the cells belonging to the electrical tree  the cells belonging to the main insulating material (epoxy resin)  the cells belonging to the second insulating material (mica sheets–mica volume). v. theoretical calculations the electric field is calculated with the aid of (3), for every cell separately, towards all directions. the algorithm compares each value with the local dielectric strength of the insulating material. this happens according to the ca rule for the evolution of the physical system. it is assumed that interactions are local. if the calculated electric field is larger than the local dielectric strength, then the algorithm converts the cell belonging to the insulating material into a cell of the treeing structure. when the algorithm checks each cell, a new geometry emerges with the addition of the new treeing cells. the boundary conditions are defined again and the process is repeated until the electrical tree finalizes its path. our initial assumption is that the field value at the tip of the upper needle electrode is almost equal to the dielectric strength of the insulating material. this helps the creation of the treeing engineering, technology & applied science research vol. 4, no. 4, 2014, 662-668 664 www.etasr.com kioussis et al.: electrical trees in a composite insulating system consisted of epoxy resin and mica… structure from the needle electrode and the further study of the propagation of the tree. the tree may finalize its path on the following cases: a) if the tree reaches the opposite electrode, b) if the calculated electric field is smaller than the local dielectric strength of the insulating material. for the tree propagation study in a system of parallel sheets of mica and of epoxy resin, the system was simulated with the aid of matlab. an electrode system of needle-plane was used and a positive voltage was applied to the needle upper electrode. the plane electrode was at zero voltage. the whole procedure followed the steps:  creation of the electrode arrangement via the partial differential equation toolbox (pde toolbox)  application of the potential values at the interfaces of the two materials as well as at the boundaries  creation of the necessary tables, one for the random fluctuation due to the dielectric environment, the other for the processing of the potential values  calculation of the electric field with the aid of laplace’s equation,  finding the places which are probable sources of treeing,  creation of a code with which each tree cell is controlled w.r.t. its five neighboring cells (this is obtained with a comparison of the electric field of each cell with the dielectric strength. if its value is larger than the dielectric strength, then the cell is already a cell of the tree) and  repetition of the whole procedure, i.e. the cells which came about from the above procedure are part of the treeing structure and the whole process is repeated in order to find new cells (it goes without saying that the values of the electric field are calculated again because of the changed new structure, which resulted from the propagation of the tree). the samples were constructed symmetrically (nxn) and the needle was put in the middle of the upper surface and in contact with the epoxy resin. the rest of the space between the needle and the earthed plane electrode was divided into sheets of epoxy resin and mica, so that all sheets to have the same thickness. the dielectric constants of epoxy resin were taken to be 4 and of mica 6. it is assumed that there are no space charges distributed inside the solid insulating material so the space charge density is equal to zero (ρ=0) and therefore laplace’s equation is solved for the potential distribution. the applied potential at the upper electrode is 28000 volts and 0 volts at the opposite plane electrode. it should be noted that for the calculation of the electric field between the two electrodes, the finite element method (fem) was used. as far as the boundaries of the sample and the air, the boundary conditions of von neumann were applied: e grad (v) + q v = g (4) where v is the potential (volt), g is the surface charge and q is a parameter defined on the interface. it was taken that q = 0 and g = 0, in order to avoid the generalized form of von neumann’s conditions. for the interfaces between epoxy resin and mica, dirichlet conditions were assumed, i.e.: h = v r (5) where r is the value of potential at the tip of the needle electrode. for the simulations presented, mixed boundary conditions of both types (neumanns’ and dirichlets’) are applied to the interfaces. the consecutive layers of epoxy resin and mica affect the potential distribution and therefore the resultant electric field inside the component dielectric. the potential values and the surface values applied to each interface between the materials are defined with the aid of the dielectric constants of mica and epoxy resin. the aforementioned values are also affected by the distance between the tip of the needle and the opposite plane electrode. the electrical tree propagation is a dynamical phenomenon where the potential at the tip of the tree is considered to be equal to the needle electrode potential so, as a consequence, no voltage drop appears along the electrical tree path. during the tree propagation, the graphical geometry alters so new values for boundary conditions of both types (potential values and surface charge values) are applied to the interfaces between the materials consisting the insulating system. electric fields develop in all regions of the composite insulating system. beginning from the plane electrode, the first electric field appears in epoxy resin between the plane earthed electrode and the first interface between the epoxy resin and the mica sheet. the second electric field appears inside the first mica sheet. inside the consecutive layers of mica and epoxy resin appear the respective electric fields which are homogeneous inside each layer due to the parallel interfaces between mica and epoxy resin. the following equation determines the potential distribution across the first interface between epoxy resin and mica: v (r) = c1 lnr + c2 (6) where r is the distance between the cell and the grounded opposite plane electrode and: v (r) = c3 lnr + c4 (7) defines the potential distribution across the second interface of mica and epoxy resin. the methodology that is followed for the definition of the potential at the interfaces between the consecutive layers of mica and epoxy resin is in agreement with the electromagnetic theory analysis where in two– dimensional geometries, such as it is studied in the present paper, the variable r which is the one-dimensional distance from the plane electrode is the appropriate variable for potential distribution and description because the resultant electric fields inside the layers are homogeneous. in such cases a one-dimensional variable (distance r) defines uniquely the engineering, technology & applied science research vol. 4, no. 4, 2014, 662-668 665 www.etasr.com kioussis et al.: electrical trees in a composite insulating system consisted of epoxy resin and mica… equipotential lines which are parallel to the interfaces without any need for a second variable. considering d1 the distance between the plane electrode and the first interface, d2 the distance between the plane electrode and the second interface and following with the same analysis, di the distance between the plane electrode and the i-th interface, there is a need, according to the electromagnetic theory, that (6) and (7) must be satisfied at the common surfaces (interfaces). for the first interface from the plane electrode the variable r=d1: c1 ln(d1) + c2 = c3 ln(d1) + c4 (8) the continuity of the vertical vectors of electric field results to: [c1 ln(d1)]/[ c3 ln(d1)]=ε2 /ε1 (9) where ε2=4 (epoxy resin) and ε1=6 (mica). the same procedure is followed for all interfaces and it is evident that it can be implemented also for the i-th interface between epoxy resin and mica sheet with a distance di from the plane electrode: c1 ln(di) + c2 = c3 ln(di) + c4 (10) the continuity of the vertical vectors of electric field results to: [c1 ln(di)]/[ c3 ln(di)]=ε2 /ε1 (11) figure 1 shows the distribution of the equipotential lines from the upper needle electrode down to the plane electrode. there are two mica sheets inside the main insulating material which is considered to be epoxy resin. it is obvious that there are five electric fields, i.e.  an electric field between the tip of the needle electrode and the first mica sheet  another one between the earthed plane electrode and the last mica sheet  another one between the mica sheets and  two electric fields inside the mica sheets. vi. simulation results simulation of a cell arrangement of 100x100 cells implies that the dimensions of each cell are 1x1 mm and the dimensions of the sample are 100x100 mm. three different voltages were applied at the point electrode, namely 35 kv, 28 kv and 27 kv. the critical strength was taken to be 26 kv/mm for epoxy resin and 35 kv/mm for the mica sheets (in all simulations the aforementioned dielectric strengths for epoxy resin and mica were kept the same for the sake of comparison). with 27 kv, treeing has a bushy form and its propagation is quasi-symmetric (figure 2), whereas with 28 kv treeing takes the form of a more pointed type (figure 3). it seems that in this case, the branches develop independently from each other. in figure 4, a voltage of 40 kv is applied. in contradistinction to the two previous cases, a voltage of 40 kv creates trees that penetrate the first mica sheet. fig. 1. potential lines distribution in a composite insulating system consisting from 60x60 cells engineering, technology & applied science research vol. 4, no. 4, 2014, 662-668 666 www.etasr.com kioussis et al.: electrical trees in a composite insulating system consisted of epoxy resin and mica… fig. 2. tree propagation for an applied voltage of 27 kv and a dielectric strength of 26 kv/mm (six mica sheets). fig. 3. tree propagation for an applied voltage of 28 kv and dielectric strength of 26 kv/mm (five mica sheets). fig. 4. tree propagation for an applied voltage of 35 kv and a dielectric strength of 26 kv/mm (five mica sheets). fig. 5. tree propagation for an applied voltage of 27 kv and dielectric strength of mica 35 kv/mm (three mica sheets). fig. 6. tree propagation for an applied voltage of 28 kv and dielectric strength of mica 35 kv/mm (three mica sheets). fig. 7. tree propagation for an applied voltage of 36 kv and dielectric strength of epoxy resin 26 kv/mm (five mica sheets). in a cell arrangement of 60x60 cells, the mica sheets as well as the epoxy resin have the same thicknesses as in the case of 100x100 cells. for voltages of 27 kv and 28 kv, the tree can only slightly penetrate the first mica sheet (figures 5 and 6), whereas with voltages of 36 kv and 37 kv (figures 7 and 8), there is a significant penetration of the sheets down to the earthed electrode. the dielectric strength of epoxy resin was taken to be 26 kv/mm and for the mica sheets 35 kv/mm. engineering, technology & applied science research vol. 4, no. 4, 2014, 662-668 667 www.etasr.com kioussis et al.: electrical trees in a composite insulating system consisted of epoxy resin and mica… fig. 8. tree propagation for an applied voltage of 37 kv and dielectric strength of epoxy resin 26 kv/mm (five mica sheets). it seems that mica sheets act as barriers to the tree propagation, hindering thus the ultimate failure of the whole system. the calculation of the electric field at each step and every point of the insulating system was accurate since with the aid of the pde toolbox the laplace’s equation is solved and the potential distribution is computed. particular attention should be paid to the factor g, which incorporates parameters such as the different dielectric environment and the existence of microcavities. generally speaking, the mica sheets hinder tree propagation and only when the electric field is too large, penetration occurs through the entire insulting system. comparison of the present simulation results with experimental data indicates that our method can simulate the reality of breakdown in complex machine insulating systems. experimental data have shown that treeing creates conducting paths, which in turn may be transformed into breakdown channels leading to total breakdown [27]. it seems from the above that the penetration of mica sheets depends on the local variation of the dielectric constant, on the applied voltage at the tip of the upper electrode and on the local breakdown strength of the insulating system. vii. discussion it is evident from the results that variations of the electric field produced by the factor g, influences the electrical tree propagation. such local variations of g contribute into the propagation of electrical trees [26]. in all simulations the mica sheet is considered to have a comparable thickness w.r.t. the sheets of epoxy resin. for the arrangement of 60x60 cells the sheets have the same thickness. for applied voltage of 27 kv and 28 kv, the treeing propagation cannot continue inside the mica sheets. on the contrary with 36 kv, the tree breaks down some mica sheets without penetrating through all of them. only with 37 kv there is a total breakdown of the whole insulating system. it is to be noted that in the first mica sheet, treeing is somehow of bushtype whereas –as the penetration continues– treeing has somehow a more pointed form. this can be explained by the fact that the dielectric constant and the dielectric strength of the mica sheets have higher values than those of the surrounding epoxy resin. it was noticed that with a higher applied voltage (28 kv), the tree presents a more pointed form. in other cases, with even higher applied voltages (37 kv and 38 kv), the treeing form starts as bushy to continue as more pointed. generally, the higher the applied voltage the more dense is the type of the tree. the above are in agreement with [10]. the applied voltage influences the shape and form of the tree in the material, as shown before [28]. although the sequence of events is not as simple as described in the present paper, we believe that the described above simulation method gives a reasonable insight as to the workings of machine insulation degradation. what was described before, it is not in disagreement with experimental data such as those presented in [29], where partial discharge activity and delamination are intimately linked and organic components (such as epoxy resin) degrade. the present work also somehow completes work done before [5], where it was also shown that mica sheets act as barriers hindering the propagation of electrical trees. in that case, however, only a limited number of mica sheets were used, whereas in the present paper a more or less full system of epoxy resin/mica sheets was investigated. in both papers the general conclusion is that mica sheets hinder the trees and the eventual breakdown. a last remark should be made: in all above simulations the dielectric strength was taken to be higher than that of the epoxy resin but much lower than the mica dielectric strength mentioned in textbooks [30]. we think that this assumption is thoroughly justified since values of 700 kv/mm (for phlogopite mica) and of 1000 kv/mm for muscovite mica (as mentioned in [30]) are obtained with small samples in laboratory conditions but are not realizable in actual industrial service conditions. viii. conclusions in this work, electrical treeing simulations were obtained under various voltages in a multi-mica sheet system surrounded by epoxy resin. the simulations were performed with a nonuniform electrode arrangement. trees appear and propagate and depending on the applied voltage, they reach the opposite electrode. the present simulations indicate that mica sheets act as barriers to the propagation of electrical trees. the present paper confirms previous simulation results and is in accordance with experimental data. references [1] d. kind, h. kaerner, high-voltage insulation technology, eds. vieweg & sohn, braunschweig, germany, 1985 [2] e. kuffel, w. s. zaengl, j. kuffel, high voltage engineering: fundamentals, 2nd edition, eds. newnes, oxford, england, 2000 [3] t. tanaka, a. greenwood, advanced power cable technology, vol. i, eds. crc press, boca raton, florida, usa, 1983. [4] r. vogelsang, t. farr, k. froehlich, “the effect of barriers on electrical tree propagation in composite insulation materials”, ieee transactions on dielectrics and electrical insulation, vol. 13, no. 1, pp. 373-382, 2006 [5] d. d. christantoni, m. g. danikas, g. e. vardakis, a. t. lekou, “simulation of electrical tree growth in a composite insulating system engineering, technology & applied science research vol. 4, no. 4, 2014, 662-668 668 www.etasr.com kioussis et al.: electrical trees in a composite insulating system consisted of epoxy resin and mica… consisted from epoxy resin and mica sheets”, international review on modelling and simulation, vol. 3, no. 2, pp. 241-249, 2010 [6] t. farr, r. vogelsang, k. froehlich, “a new deterministic model for tree in polymers with barriers”, annual report of conference on electrical insulation and dielectric phenomena (ceidp), kitchener, ontario, canada, pp. 673-676, october, 2001 [7] o. s. gefle, s. m. lebedev, v. ya. ushakov, “the mechanism of the barrier effect in solid dielectrics”, journal of physics d: applied physics, vol. 30, pp. 3267-3273, 1997 [8] r. vogelsang, t. farr, k. froehlich, “electrical tree propagation along barrier interfaces in epoxy resin”, annual report conference on electrical insulation and dielectric phenomena (ceidp), cancun, mexico, pp. 946-950, october, 2002 [9] b. r. varlow, g. j. malkin, “electrical treeing in mechanically prestressed insulation”, ieee transactions on dielectrics and electrical insulation, vol. 7, no. 6, pp. 721-724, 2000 [10] r. vogelsang, r. brutsch, k. froehlich, “the effect of tape overlappings in winding insulations on tree growth and breakdown time”, annual report conference on electrical insulation and dielectric phenomena (ceidp), boulder, new mexico, usa, pp. 294-297, october , 2004 [11] b. r. varlow, d. w. auckland, “the influence of mechanical factors on electrical treeing”, ieee transactions on dielectrics and electrical insulation, vol. 5, no. 5, pp. 761-766, 1998 [12] r. vogelsang, r. brutsch, k. froehlich, “how imperfections in mica tape barriers influence tree growth and breakdown time”, annual report conference on electrical insulation and dielectric phenomena (ceidp), albuquerque, usa, pp. 657-660, october, 2003 [13] l. niemeyer, l. pietronero, h. j. wiesmann, “fractal dimension of dielectric breakdown”, physical review letters, vol. 52, pp. 1033-1036, 1984 [14] h. j. wiesmann, h. r. zeller, “a fractal model of dielectric breakdown and prebrakdown in solid dielectrics”, journal of applied physics, vol. 60, pp. 1770-1773, 1986 [15] l. a. dissado, p. j. j. sweeny, “physical model for breakdown structures in solid dielectrics”, physical review, vol. b 48, pp. 1226112268, 1993 [16] j. c. fothrgill, l. a. dissado, p. j. j. sweeny, “a discharge avalanche theory for the propagation of electrical trees”, ieee transactions on dielectrics and electrical insulation, vol. 1, no. 3, pp. 474-486, 1994 [17] m. d. noskov, a. s. malinovski, m. sack, a. j. schwab, “selfconsistent modeling of electrical tree propagation and pd activity”, ieee transactions on dielectrics and electrical insulation, vol. 7, no. 6, pp. 725-733, 2000 [18] m. g. danikas, i. karafyllidis, a. thanailakis, a. m. bruning, “simulation of electrical tree growth in solid dielectrics containing voids of arbitrary shape”, modelling and simulation in materials science and engineering, vol. 4, pp. 535-552, 1996. [19] i. karafyllidis, m. g. danikas, a. thanailakis, a. m. bruning, “simulation of electrical tree growth in solid insulating materials”, archiv fuer elektrotechnik, vol. 81, pp. 183-192, 1998 [20] g. e. vardakis, m. g. danikas, i. karafyllidis, “simulation of space charge effects in electrical tree propagation using cellular automata”, materials letters, vol. 56, pp. 404-409, 2002 [21] g. e. vardakis, m. g. danikas, “simulation of tree propagation in polyethylene including air void by using cellular automata: the effect of space charges”, archiv fuer elektrotechnik, vol. 84, pp. 211-216, 2002 [22] g. e. vardakis, m. g. danikas, “simulation of electrical tree propagation using cellular automata: the case of conducting particle included in a dielectric in point-plane electrode arrangement”, journal of electrostatics, vol. 63, pp. 129-142, 2005 [23] g. e. vardakis, m. g. danikas, “simulation of electrical tree propagation in a solid insulating material containing spherical insulating particle of a different permittivity with the aid of cellular automata”, facta universitatis, vol. 17, pp. 377-389, 2004 [24] j. von neumann, theory of self-reproducing automata, university of illinois, urbana, 1966 [25] b. chopard, m. droz, cellular automata modeling of physical systems, cambridge university press, 1998 [26] g. e. vardakis, breakdown phenomena in solid insulating materials: a study of electrical tree propagation, ph. d. thesis, democritus university of thrace, department of electrical and computer engineering, xanthi, greece, 2006 (in greek) [27] m. g. danikas, a. d. karlis, “some observations on the dielectric breakdown and the importance of cavities in insulating materials used for cables and electrical machines”, advances in electrical and computer engineering, vol. 11, no. 2, pp. 123-126, 2011 [28] a. kelen, m. g. danikas, “evidence and presumption in pd diagnostics”, ieee transactions on dielectrics and electrical insulation, vol. 2, no. 5, pp. 780-795, 1995 [29] a. kelen, “studies on partial discharges on solid dielectrics: a contribution to the discharge resistance testing of insulating materials”, acta polytechnica scandinavica, no. ei 16, pp. 138, 1967 [30] m. s. naidu, v. kamaraju, high voltage engineering, 2nd edition, eds. tata mcgraw-hill publishing co. ltd., new delhi, india, 2000 engineering, technology & applied science research vol. 8, no. 4, 2018, 2919-2922 2919 www.etasr.com ahmad et al.: remediation of sulfidic wastewater by aeration in the presence of ultrasonic vibration remediation of sulfidic wastewater by aeration in the presence of ultrasonic vibration farooq ahmad department of chemical and material engineering college of engineering, northern border university arar, saudi arabia naveed ahmad department of chemical and material engineering college of engineering northern border university arar, saudi arabia abdulaal z. al-khazaal department of chemical and material engineering college of engineering northern border university arar, saudi arabia ibrahim alenezi department of chemical and material engineering, college of engineering northern border university arar, saudi arabia abstract—in the current study, the aerial oxidation of sodium sulfide in the presence of ultrasonic vibration is investigated. sulfide analysis was carried out by the methylene blue method. sodium sulfide is oxidized to elemental sulfur in the presence of ultrasonic vibration. the influence of air flow rate, initial sodium sulfide concentration and ultrasonic vibration intensity on the oxidation of sodium sulfide was investigated. the rate law equation regarding the oxidation of sulfide was determined from the experimental data. the order of reaction with respect to sulfide and oxygen was found to be 0.36 and 0.67 respectively. the overall reaction followed nearly first order kinetics. keywords-aeration; sulfide oxidation; ultrasonic vibration; kinetics; remediation; environment; air flow rate i. introduction different processes are followed for the removal of sulfides, including wet scrubbing, liquid redox technology, biofiltration, scavengers, carbon adsorption, iron salts, biocide process, anthraquinone and use of oxidizing agents [1-4]. as documented in [1-9], sulfide removal from wastewater is mainly achieved by oxidation. advanced oxidation is the latest among wastewater treatment techniques [1]. oxidation can be accomplished chemically or biologically [10]. chemical oxidation involves the removal of electrons and removal or addition of hydrogen [7]. in water and wastewater engineering, chemical oxidation serves the purpose of converting putrescible pollutant substances to innocuous or stabilized products [11]. reserachers in [9, 12-16] investigated the oxidation of sulfides in the presence of catalyst, however, catalytic oxidation suffers from certain drawbacks and it is not economically suitable for large continuous treatment processes. moreover, these catalysts are poisonous and hazardous and their complete recovery after treatment is essential. photo oxidation in both presence and absence of catalyst has also been studied [5, 6, 17, 18]. in the absence of catalyst, photo oxidation requires higher uv light intensity, which is not economically suitable for large continuous wastewater treatment processes [17, 18]. authors in [13] investigated the sulfide oxidation by atmospheric oxygen in presence of “sulfur black b” dye as a catalyst. the reaction was reported to be first order in sulfide concentration. authors in [11] made an exhaustive survey of the classical methods on sulfide oxidation. they carried out catalytic oxidation with dissolved oxygen using a number of catalysts including carbon black, ferric salts and a few organic compounds. authors in [16] reported the effect of fecl3 catalyst on the oxidation of na2s with dissolved oxygen. they analyzed the conversion data using a first order rate equation for sulfide removal. they found out that the rate constant is a function of fecl3 concentration. sulfide oxidation can be used for the synthesis of sulfones and sulfoxides. authors in [14] indicate that the reaction of sulfides with 30% hydrogen peroxide catalyzed by tantalum (v) chloride in acetonitrile, ipropanol, or t-butanol produces high yields of sulfoxides. authors in [19] developed the microbial fuel cell (mfc) for removal of sulfur-based pollutants. the fuel cell used activated carbon cloth and carbon fiber veil composite anode, air breathing dual cathodes and sulfate reducing species. in this system, most of the sulfide is electrochemically oxidized to sulfur. ii. experimental work a. analysis of sulfide we prepared the test solution using sodium sulfide of 60% purity. methylene blue method (mbm) [20] was used to analyze the sulfide, and estimated its concentration using dr 5000 hach uv-visible spectrophotometer. since elemental sulfur formation occurs during the oxidation process, carbon disulfide was added dropwise prior the analysis of sulfide for engineering, technology & applied science research vol. 8, no. 4, 2018, 2919-2922 2920 www.etasr.com ahmad et al.: remediation of sulfidic wastewater by aeration in the presence of ultrasonic vibration removing the elemental sulfur formed during the oxidation process. b. methodology a schematic diagram of the oxidation process is shown in figure 1. the reactor comprised of a glass reactor, ultrasonic vibrator, dissolved oxygen (do) probe and spurger for distributing the air in the solution taken in the reactor. the ultrasonic vibrator was connected to the power supply. the do probe was dipped into the liquid in the apparatus only to measure the dissolved oxygen concentration, and the ph probe monitored the solution’s ph. the glass reactor was dipped in the water inside the ultrasonic vibrator. the ultrasonic vibrator cannot be used as a reactor because in that case the temperature of the solution raises. the ultrasonic vibration is transferred into the solution inside the reactor through water present in the ultrasonic vibrator. before the sulfide analysis, carbon disulfide was added in order to dissolve the elemental sulfur formed during the oxidation. fig. 1. experimental set up for the sulfide oxidation in the presence of ultrasonic vibration. iii. results and discussion the aerial oxidation of sodium sulfide was investigated at different air flow rates, different initial sodium sulfide concentration and different ultrasonic vibration intensities. it was found that oxidation of sulfide produces elemental sulfur and sodium hydroxide. initial ph of the sulfide solution was found to be 12 or more depending upon on the initial sulfide concentration. the ph of the solution increased gradually with an ultimate value equal to 13 which is alkaline ph. the increase in the value of ph can be related to the liberation of caustic soda as a result of sulfide oxidation. the chemical reaction of sulfide and oxygen in the presence of ultrasonic vibration is the following: na s + o → 2naoh + s (1) a. effect of air flow rate the oxidation process was investigated at different air flow rates. it was found that the higher the atmospheric airflow rate at the opening of the spurger, the faster the sulfide oxidation. this is because higher atmospheric airflow rate at the opening of the spurger means larger concentration of oxygen in the liquid. the larger concentration of oxygen in the liquid will allow more reaction with the excited sulfide ions in the liquid. increased reaction will shorten the time to oxidize the sulfides in the liquid. it was observed that the amount of dissolved oxygen remained constant during the oxidation while the ph of the liquid increased over time. this happened because during air bubbling, the oxygen from the air gets dissolved in the solution and the dissolved oxygen reacts with sulfide ions. under a particular set of experimental conditions, the bubbling air supplied oxygen to the solution at a sufficiently high rate so that its concentration remained practically constant. the oxygen consumed by the sulfide ions was immediately replenished by absorption from the air bubbles. as sulfide was converted to elemental sulfur and sodium hydroxide, the ph increased up to 13. the effect of air flow rate on sulfide oxidation in the presence of ultrasonic vibration is shown in figure 2. b. effect of initial sulfide concentration the oxidation process was also investigated at different initial sulfide concentration. it was observed that oxidation of 800ppm of sulfide took 50 minutes. the rate of oxidation was found higher at higher initial sulfide concentration. increase in the initial sulfide concentration increased the time of sulfide oxidation. oxidation of 1000ppm of sulfide took nearly 60 minutes. the airflow rate and ultrasonic vibration intensity were fixed, at 4liter/minute and 100% respectively. from the experiment done using the experimental setup and process shown in figure 1, the concentration of sulfides was decreased over time while the concentration of sulfur was increased over time. oxidation of sulfide in the presence of ultrasonic vibration at different initial sulfide concentrations is shown in figure 3. from this experiment, it is apparent that the process of removing sulfide ions from synthetic wastewater by means of reaction between sulfide ions and dissolved oxygen in the presence of ultrasonic vibration in wastewater is quite effective. synthetic wastewater during treatment by aeration in the presence of ultrasonic vibration became turbid due to the formation of elemental sulfur. the turbidity of the solution was found higher at higher initial sulfide concentration indicating higher rate of formation of elemental sulfur at high sulfide concentration. c. effect of ultrasonic vibration intensity it was observed that at higher ultrasonic vibration intensity sulfide oxidation becomes faster. it may be related to the formation of larger amount of excited sulfide ions with the increase in the ultrasonic vibration intensity. the larger amount of excited sulfide ions in the liquid would allow more reaction with the oxygen and thus increased reaction that would shorten the time of the sulfides oxidation. the effect of ultrasonic vibration on sulfide oxidation is shown in figure 4. d. kinetics of sulfide oxidation in the presence of ultrasonic vibration a power law rate equation for sulfide oxidation is proposed in [21]: = (2) where k is the rate constant, m1 and m2 are orders of reaction with respect to oxygen partial pressure and sulfide respectively. a plot of the rate of sulfide oxidation against initial sulfide 900 ml na2s sol uti on 8 l di sti l led water fl ow diffuser ai r ultrasoni c bath u ltrasonic panel el ectroni c pl ug l/ mi n con vib rea rea by oxy log th res wa equ fro tw fig air fig diff fig diff engineerin www.etasr ncentrations o bration gives action with re action order w plotting the ygen partial garithmic scal he value of m1 spect to oxyge as calculated uation. the re om the slope o o concentratio g. 2. relations flow rates. g. 3. relations ferent initial sulfid g. 4. relations ferent sonication ng, technology r.com on a logarithm the order m espect to sul with respect to rate of sulfi pressure at le for constan is 0.67 which en partial pres at different eaction rate c of the plot of re on terms in (2) ship between time ship between time de concentrations ship between time intensities. y & applied sci ahmad et al. mic scale at a m2=0.36. thus fide concentr o oxygen was ide oxidation different air nt values of al h is the order ssure. partial air flow rate constant, k=0. eaction rate ag as shown in f e and sulfide duri e and oxidized su s. e and oxidized su ience research .: remediation constant ultra s the order o ration is 0.36 similarly foun against the flow rates ll other param of the reaction pressure of ox es using idea 55 was determ gainst the prod figure 5. ing oxidation at d ulfide during oxid ulfide during oxid v of sulfidic wa asonic of the 6. the nd out initial on a meters. n with xygen al gas mined duct of different dation at dation at fig. pres aera aera by con oxi pre con com ach the [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] vol. 8, no. 4, 20 astewater by aer 5. linear plo ssure of oxygen an sodium sulfi ation in the p ation in the pr air flow rate nclusions can dation: it was sence of ultras ncentration, u mplete remov hieved by aera e overall oxida m. ksibi, “ch wastewater trea 3, pp. 161–165, m. seredych, graphite derive materials chem f. ahmad, s. using iron salt no. 4, pp. 1455 c. e. ellis, environmental 30, 1998 w. spiller, d. stark, “photo-o in oxygen-satur journal of phot 2, pp. 161–173, c. a. linkous, aqueous sodium photochemistry 153–160, 2004 r. munter, “a prospects”, pr chemistry, vol j. g. bain, d. w sulfide oxidatio of contaminant n. ahmad, s. m wastewater by environmental ] [f. p. van der z removal by mo bioresource te 018, 2919-2922 ration in the pr ot between the pro nd rate of sulfide iv. co de is removed presence of u resence of ultra e and sulfide n be drawn found that the sonic vibration ultrasonic fre val of the su ation in the p ation followed refer emical oxidation atment”, chemica , 2006 t. j. bandosz, ed materials mo mistry and physics maitra, n. ahm s”, arabian journ 5–1462, 2017 “wet air oxi progress & susta wöhrle, g. schu oxidation of sodiu rated aqueous sol tochemistry and p , 1996 c. huang, j. r. f m sulfide to pro y and photobiolo advanced oxida roceedings of t . 50, pp. 59–80, 2 w. blowes, w. d on with reactive tr t hydrology, vol. maitra, b. k. du catalytic oxidatio sciences, vol. 21 zee, s. villaverde oderate oxygenati chnology, vol. 98 2 resence of ultra oduct of sulfide c oxidation on loga onclusion d from synthe ultrasonic vibr asonic vibratio e concentratio from the ul e rate of aerati n is faster at h equency and ulfide from t presence of ul d mostly first o rences n with hydrogen al engineering jou “adsorption of odified by incor s, vol. 113, no. 2 mad, “treatment o nal for science an idation of refm ainable energy, v ulz-ekloff, w. t. um sulfide by sulf lutions containing photobiology a: c fowler, “uv phot duce hydrogen a gy a: chemistry ation processes the estonian a 2011 d. robertson, e. o ransport at a mine . 41, no. 1–2, pp. utta, f. ahmad, “r on with hydrogen 1, no. 12, pp. 173 e, p. a. garcía, f. ion of anaerobic 8, no. 3, pp. 518– 2921 asonic vibratio oncentration and arithmic scale. etic wastewate ration. kineti on was investi on. the follo ltrasonic vibr ion of sulfide i higher initial su air flow the wastewat ltrasonic vibra order kinetics. peroxide for do urnal, vol. 119, n f hydrogen sulfi rporation of nitr 2–3, pp. 946–952, of sulfidic wast nd engineering, v mery spent ca vol. 17, no. 1, p ford, g. schnei fonated phthalocy g detergents or lat chemistry, vol. 9 tochemical oxida and sulfur”, jour y, vol. 168, no. current statu academy of sci o. frind, “model e drainage site”, j 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journal of photochemistry and photobiology a: chemistry, vol. 149, no. 1–3, pp. 23–30, 2002 [18] n. k. shammas, j. y. yang, p. c. yuan, y. t. hung, “photochemical treatment processes”, in: handbook of environmental engineering, 3rd edition, springer, pp. 229–270, 2007 [19] f. zhao, n. rahunen, j. r. varcoe, a. j. roberts, c. avignone-rossa, a. e. thumser, r. c. t. slade, “factors affecting the performance of microbial fuel cells for sulfur pollutants removal”, biosensors and bioelectronics, vol. 24, no. 7, pp. 1931–1936, 2009 [20] d. mallik, s. k. chaudhuri, “air oxidation of aqueous sodium sulfide”, water research, vol. 33, no. 2, pp. 585-590, 1999 [21] d. j. o’brien, f. b. birkner, “kinetics of oxygenation of reduced sulfur species in aqueous solution”, environmental science & technology, vol. 11, no. 12, pp. 1114–1120, 1977 microsoft word etasr_v13_n4_pp11263-11270 engineering, technology & applied science research vol. 13, no. 4, 2023, 11263-11270 11263 www.etasr.com chopparapu & seventline: an efficient multi-modal facial gesture-based ensemble classification and … an efficient multi-modal facial gesture-based ensemble classification and reaction to sound framework for large video sequences saiteja chopparapu department of eece, gitam (deemed to be university), india saiteja.chopparapu960@gmail.com (corresponding author) joseph beatrice seventline hod, department of eece, gitam (deemed to be university), india sjoesph@gitam.edu received: 3 june 2023 | revised: 11 june 2023 and 12 june 2023 | accepted: 13 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6087 abstract machine learning-based feature extraction and classification models play a vital role in evaluating and detecting patterns in multivariate facial expressions. most conventional feature extraction and multi-modal pattern detection models are independent of filters for multi-class classification problems. in traditional multi-modal facial feature extraction models, it is difficult to detect the dependent correlated feature sets and use ensemble classification processes. this study used advanced feature filtering, feature extraction measures, and ensemble multi-class expression prediction to optimize the efficiency of feature classification. a filter-based multi-feature ranking-based voting framework was implemented on different multiple-based classifiers. experimental results were evaluated on different multi-modal facial features for the automatic emotions listener using a speech synthesis library. the evaluation results showed that the proposed model had better feature classification, feature selection, prediction, and runtime than traditional approaches on heterogeneous facial databases. keywords-multi-modal facial features; feature ranking; multi-modal outlier component i. introduction automatic facial expression analysis in an image has two parts, extracting features and partitioning them into groups [1]. feature extraction is the process of getting information from an image or a series of images, and is usually performed in two steps: turning the input image into a feature vector and then reducing its number of dimensions. the need for real-time systems poses even more strict limits on how well these tasks can be performed. in general, the methods for feature extraction can be partitioned into two groups: model-based and pixel-based. model-based techniques, such as active appearance and active contour models, need some information and assumptions about the shape of facial features to model [24]. model-based methods are not affected by changes in lighting or head pose but take a long time to fit the model as they use iterative steps. pixel-based techniques usually work by mapping information about pixels to information about features without any modeling or iteration. pixel-based methods use pixels instead of making wrong assumptions about the shape of facial features, as model-based methods do. pixel-based methods get information about the face and take less time to process but have the drawback of being sensitive to changes in lighting and head position. facial expression analysis can be used to help with human-computer interaction, entertainment, medical applications (e.g. pain recognition), interactive videos, behavior monitoring, and figuring out when someone is lying. people's desire to interact with computers not only with their hands but also with their facial expressions is another important source of motivation. the progress in computer vision and social intelligence allows human-centered designs, instead of computer-centered ones, that only take into account the user's intentional input and ignore the majority of information communicated by affective states. deformable parts-models (dpms), also known as pictorial structure modeling, are one of the most common ways to make generic object detectors. recently, dpms have been used to find faces, and the results are state-of-the-art. estimating the dpm parameters is performed in two ways: weakly and strongly supervised [5-7]. generally, the svm classification scheme is based on the characteristics of the statistical learning mechanism [8]. minimizing structural risk is supported by the ability of the svm classifier to perform the entire classification process smoothly and effectively. additionally, the svm technique is quite effective in the case of small training data. engineering, technology & applied science research vol. 13, no. 4, 2023, 11263-11270 11264 www.etasr.com chopparapu & seventline: an efficient multi-modal facial gesture-based ensemble classification and … ii. literature review in a weakly supervised setting, the bounding boxes of the face and non-face images are used as examples of what to do and what not to do. the mixtures and the location of the part are known ahead of time but are kept secret in the training set. in this case, only facial bounding-box annotations are needed, so thousands of annotations can be made in just a few hours. in a strongly supervised setting, parts of the mixture are labeled in the training database, which also has facial images with facial landmarks that have been labeled. this method is not practical as marking important landmarks is time-consuming and takes hundreds of hours for a few thousand facial images. different arguments have been pointed out on how well weakly and strongly supervised annotations work. in [3], facial dpms trained with strongly supervised annotations performed better than those trained with weakly supervised annotations. in [4], the weakly supervised dpm with fixed a priori components performed better than the current best method. researchers are also concerned that dpms are hard to compute, making it hard to use them in real-time systems. recently, scientists have been trying to obtain real-time performance by simplifying computations. in [5], a branch-and-bound framework and a dual-tree data structure [6] were used to speed up star-shaped dpms. other approaches to speed up dpms are dpm fitting by computing filter correlations using the fourier transform [7], building a cascade of classifiers from dpms [9], and using a fast neighborhood-aware cascade strategy [10]. the dpms perform great in recognizing faces but cannot extract landmark points, which is a requirement for many facial expression analysis systems. an active appearance model (aam) and its variations [11] were used to get the best performance at the moment in landmark localization. aam variants work better because they use a fully connected matrix to model the shape, while dpms are partbased texture models. feature extraction turns an image into a feature vector so that classification can be done quickly. the need for real-time applications puts even more strict limits on how well this task can be performed. in [12], facial features, used to figure out how someone is feeling, were split into two main groups: primary and secondary features. primary features are the most basic and important ones that can be used to identify the six basic emotions [13]. secondary features are extra features that make emotion recognition more accurate and help distinguish features that are the same based on primary features. some secondary features are the length of the mouth, the side wrinkles on the nose, the presence of teeth, the angle of the eyebrows, and the thickness of the lips. geometric and appearance feature extraction methods are the two main types. researchers have created hybrid features by putting these two features together. face parts such as the nose, eyes, eyelids, and lips are used as landmarks to create geometric features. many different methods have been used to find landmarks by modeling facial features [14]. active contours are geometric models whose initial coordinates are set by the model's parameters. parametric shape models, on the other hand, are set by explicit shape equations. active contour models get closer to the truth more quickly, but they depend a lot on the initial parameters. active shape model (asm) was suggested as a way to solve this problem, as it is a shape-restricted iterative modeling method that uses a statistical model, called point distribution model (pdm), to get information about a shape that has already been used. a function that tries to save energy is used to fit the model to different images. the functions that try to minimize energy work either in the spatial [15] or the parametric domain [8]. in [16], a gabor filter bank was used with 8 orientations and 5 spatial frequencies to get gabor magnitudes from the whole face, and the adaboost method was then used to choose the subset of features. svm used the results of the filters chosen by adaboost to sort seven facial expressions based on how they make people feel. gabor features are used to extract features not only in the spatial but also in the temporal domain. in [17], gabor features were used to analyze the behavior of both faces at the same time. in [18], the use of spatiotemporal gabor filters was proposed to obtain information about space and time when recognizing subtle expressions. in [19], gabor features were used around landmark points to continuously estimate the intensity of facs data. a local binary pattern (lbp) was suggested for texture analysis in [20]. due to its small neighborhood, the basic lbp cannot find large-scale structures that are the most important. to solve this problem, a circular neighborhood was chosen that was centered on the pixel that needed to be labeled. several different versions of lbp have been suggested [21]. hog features were first used to find people, and they are made by counting how many times a gradient orientation shows up in certain parts of an image. the idea behind hog features is that the shape and look of facial features can be described by how intensity gradients are spread out. to find the hog features, the image is broken up into small, connected areas called cells, and a histogram is made for each cell. normalizing the histogram compensates for differences in light and dark. feature classification is used in several systems to help with recognition, verification, and identification. a facial expression analysis system needs to be able to recognize both static and changing patterns. dynamic patterns are the hardest to recognize because they change in space and time. this makes them the most difficult to classify. there are supervised and unsupervised methods to train facial expression analysis systems. in supervised learning, the event labels are already set in the training data, while in unsupervised learning, the training data are not labeled and event categories are figured out on their own [22]. there are two main types of facial expression recognition systems. in frame-based expression recognition, each video frame is examined on its own, while in sequencebased expression recognition, the movement between frames is examined, which depends on other frames in the video. in [23], a nearest neighbor classifier was used for the parameters that were calculated by fitting local parametric motion models to different parts of the face. facial expression recognition is another area where neural networks have been used [24]. in [25], fischer linear discriminant analysis was used to recognize expressions in the encrypted domain. in [26], a fuzzy relational approach was proposed to recognize human emotions from facial expressions, using three different fuzzy sets: high, low, and moderate. in [27], a genetic algorithm was used to adjust the engineering, technology & applied science research vol. 13, no. 4, 2023, 11263-11270 11265 www.etasr.com chopparapu & seventline: an efficient multi-modal facial gesture-based ensemble classification and … parameters of the membership function and make fuzzy inference systems work better. in [28], after the system was able to recognize faces at the frame level, facial features were modeled over time by adding the movement of facial expressions. a common way to divide expressions by time is to use hmms to find a match between the start, peak, and end of an action and an underlying latent state. in [29], hmm was used to recognize natural emotions. in [28], a dbn was used to model two types of temporal dependencies: how each au changes over time and how different aus change over time. in [31], a method was proposed and evaluated on several benchmark datasets, achieving high accuracy compared to previous methods, but had some potential drawbacks as the multi-region approach can increase computational cost and complexity. in [32], the proposed method leveraged the selfattention mechanism of the transformers to learn feature representations of facial images and improve the accuracy of facial expression recognition. the widely adopted vgg-face architecture was used for feature extraction, introducing a spatial and channel-wise attention mechanism to weigh feature maps. in [33], the first branch used a cnn with a local attention mechanism to extract local features, while the second used a cnn with a global attention mechanism to capture contextual global information. in [34], a method was proposed that extracted high-order statistical features, including the histogram of oriented gradients and local binary patterns, from the input facial images. iii. proposed framework this study designed a novel facial gesture-based sign detection method using multilevel facial features and an annotated sign database. this framework used sign text annotations, text audio library, and multi-model features to find and map the facial gestures to their corresponding sign annotation. each gesture and its pair of signs were fused for the training data. this model used different multi-modal feature ranking measures to classify the multi-modal features along with the sign annotations. finally, a hybrid ensemble heterogeneous multi-modal sign classification framework was implemented in the training data, using novel base classifiers such as linear feature extraction measures, non-linear feature extraction measures, and hybrid multidirectional local and global gradient descriptors, as shown in figure 1. the proposed framework included a novel metaheuristicbased feature ranking and classification approach on a real-time facial dataset. initially, facial data were taken as input for the feature extraction, ranking, and classification process using a 1sec interval video sequence. the video sequences with facial features were stored in a real-time cloud server for data analysis. the statistical feature anomaly detection approach was used to filter outliers in the input data. in the next step, the ensemble feature ranking approach was used to find the essential multi-modal features for the segmentation process. finally, an advanced ensemble learning model was used to optimize the prediction rate in the segmented classes. fig. 1. proposed multi-modal facial sign annotation and classification framework. the proposed model was implemented in 2 phases:  phase 1: multi-modal feature extraction measures and filtering.  phase 2: proposed feature segmentation-based ensemble classification. a. phase 1: feature extraction measures and filtering in this phase, different statistical measures such as log cosine and exponential inverse differential moment (lceidm), max-chi-correlation based inertia, facial curvatures, standard deviation, kurtosis, skewness, and rms were used to find the essential multi-modal features in each frame of the training dataset. filter-based feature ranking used the ant bee colony approach.  step 1: the missing values filling algorithm was: for each feature f in dataset d for each instance value i(j) in the f(i) do if (instance is null) then ������ = � { | ���� � − ���������� �|�/�� ��������� − � �����������} endif endfor endfor  step 2: initialization of ant parameters. �� = � { �. ��� �1 − ��� �, � !"#$ % & �' ()$�*+'* } ��, ∈ �0,1� engineering, technology & applied science research vol. 13, no. 4, 2023, 11263-11270 11266 www.etasr.com chopparapu & seventline: an efficient multi-modal facial gesture-based ensemble classification and …  step 3: employing bee phase: in this phase, new candidate solutions are generated for each employed bee. initially, each value of the employed bee was initialized to the new candidate solution c(i)=x(i).  step 4: the fitness value of the candidate solutions can be computed using: / 0� = ��123��345 ; if kerneli ≥ 0 / 0� =1+abs�6%7�%8� � ; otherwise b. phase 2: the proposed cluster-based ensemble classification framework this phase implemented a hybrid signal clustering approach to find the classes on the training data. here, cluster labels are used to predict the variation of the multi-modal gesture segmentation process. 1) feature segmentation framework two steps were implemented using the likelihood probability estimation functions. in the first step, referred to as the expectation step, model variables are estimated and the probability of each instance is predicted for the cluster assignment. let 9̂ represent the novel posterior estimation parameter used to predict the occurrence of each feature in the given large number of training samples. ;7 < =�9̂/>� is the occurrence of new patterns in the category of classes. in the expectation phase, the maximization of the probability estimation is performed on the training data as: ;7 < =�9̂/>?� = ?@a{ bc��� �5, bd�,e� �5. bd�}.∑ e�gd/ �5�h5ij|k|.e�gd/ �� in the maximization phase, model parameters are estimated using the signal features and their class patterns. in the maximization step, the probability of data occurrence in the given class is given as: ;7 < =�>/ l� , 9̂� = e� �5/ g5�.?@a{ e� gd�;?no..�}.4cp� e�q��^e� g/ r5 � these two phases are repeated until the number of maximum iterations or no change in the error rate. 2) proposed ensemble classification learning model a hybrid feature ranking-based decision tree model was constructed using the following equation: ;lstu�l, v? � = wx∑ � l� /| l� |y| z |�n� − [ �\g]�� �\y �!^y × � { ` �s 0 <al� , v?� , v<�b 0` �s 0 <� l� , v? �c where fi is the i-th cluster class and fj is the j-th cluster class. 3) mutual information-based feature ranking the ensemble feature ranking measure based on mutual information was given as: ��vℎ �ef 7%�t� , t� � = � {;7 < =�t�� × 8<h� t� /t�, ∑ ∑� |t� − tc | − o.i�*rj } ;7%�0 � 0 <� = − ;%�0 � 0 <�� t� �. 8<h� ;%�0 � 0 �<� t� �� k�0v<�b%�0� t� = ∑ ;7%�0 � 0 <�∑� the hybrid hellinger feature ranking measure is given as: math.cbrt(entropy(data)×total×ghdsplitcriterion.comput ehellinger(data)) ×pr/ ( chival(data)) 4) non-linear svm kernel function an advanced non-linear classification approach was used to find the essential multi-modal classification process. the proposed classification approach was used to detect the level of facial patterns based on the selected features. different filters were used in the framework to find the essential key features for the classification process. this approach was composed of the following steps:  step 1: feature space fs= f(filter(images))  step 2: for each feature map in the layer, compute the feature correlation among the different features space as: %, = �! ><77%8 0 <� alo�7�l. ∑ ���o�7� − mc�7��!?@ mc�7� = ∑ ��]c �7�n]oo, p]c �7� = ap]c �7�l. h�p�]�7� p�] �7� = ∑ q�] � �7� + ]?  step 3: apply the non-linear probabilistic optimization function as: � �{m�} = s. ∑ ∑ % & tuvwe5\w. t�h� , u7x�y�|zr|�n�,�n� where d is the euclidean distance. � � { = �! ∥ � h��q ∗~� �� + �� ∥ !. +� {m�} = s. ∑ ∑ % & tuvwe5\w. logw;�� w + �. �� ∑ ��� + �� ���n�|zr|�n�,�n� ;�� = e�c�� �5��x\y.3 (� $�5,��x\y���aw��w,|�$|l� ∑ 3 (� $�5,��x\yd∗��� ��dij where h� �`� , u7x y�st, and � is the number of segments. u�g = ∑ h� . u7x y/ ∑ h�|��|�n�|��|�n� �� = �! ln ��&���� � � = 7h�34,�� min �� q. ~� � + � − �� − �� ≤ � + ��∗ ��� − q. ~� � − � + �� ≤ � + �� �� , �� , �� ≥ 0, = 1,2, . . � �z = �� ef% v �t�;//�� ef% ><8f�� � 8f%� engineering, technology & applied science research vol. 13, no. 4, 2023, 11263-11270 11267 www.etasr.com chopparapu & seventline: an efficient multi-modal facial gesture-based ensemble classification and … ¡�z = ¡ �0<= ��x y = ℎ �0<h7 �= ��t� ` f�� �6%7�%8: `6��, 9� = % &q* /�2 ∗ �!� n = h�� = `6a∑ ¡�z , ∑ �z l 6%7�%8 ;7<= = 8 0� = 6;�t� = |¡�z /�∑ n ∗ ¡�z �| ` f�� �k�07<£�: `k�b� � = −`6�∑ b� . log�b� � , �¤ �� in the above equations, the probabilistic gaussian estimation function was used to find the ranked features on each multi-modal facial feature space. ;k = % &r* /�2 ∗ t�!� ∗ |¡�rj /�∑ n ∗ ¡�rj �| + % &r* / �2 ∗ t!!� ∗ ¡�r* /�∑ n ∗ ¡�r* � if (pe>0) then: ¥ = v8 �� /� ¦at� , t� l§ else continue let i be the input image and s be the input hyperplane with inter and intra-block regions intensities as m and n. then the objective function of the proposed model is given as: max {x∑ ��. min{qh0!��} + £� ¥�� ¥� �yk�&� &� x∑ e� ¥�� ¥� ys}k�&� �. min{qh0, ��} ≥ 0 e� ª 0 proof: in the following formulation, n(m, n) is used to find the multi-class objects in the given classification problem. the non-linear equation of the proposed model is solved using the following formulation, where wgt, s, m, and n are the input parameters, and the derivation of the proposed non-linear kernel equation is as follows: p��, p� = ∑ ⃦ �¥� − min{qh0, ��} ¥� �. p �k�n� ⃦�! + �. qh0 ⃦ p ⃦�! where s are the segmented regions, i is the block intensity, m and n are the block size, η is the scaling factor, and wgt is the weight of the block. = ∑ u7xa�¥� − min{qh0, ��} ¥� �. p � l� . a�¥� −k�n�min{qh0, ��} ¥� �. p � l + �. u7{�qh0 ∥ p ∥�� . �qh0 ∥ p ∥�} = ∑ u7xa�¥�� − p. �� . min{qh0, ��} ¥�� l. �k�n� a�¥� −min{qh0, ��} ¥� �. p � l + �. u7{�qh0 ∥ p ∥�� . �qh0 ∥ p ∥�} = ∑ u7{�¥�� . �¥� − p. �� . min{qh0, ��} ¥�� . �¥� −k�n��¥�� . min{qh0, ��} ¥� �. p � +p. �� . min{qh0, ��} ¥��. min{qh0, ��} ¥� �. p � } +�. u7{�qh0 ∥ p ∥��. �qh0 ∥ p ∥�} = ∑ u7­�¥�� . �¥� l − u7�p. �� . min {qh0, ��}¥��k�n� . �¥� � −u7a�¥��. min{qh0, ��} ¥� �. p � l +u7�p. �� . min{qh0, ��} ¥��. min{qh0, ��} ¥� �. p � �} + �. u7{�qh0 ∥ p ∥�� . �qh0 ∥ p ∥�} =�! ∑ u7a¥�� . ¥� l −k�n� � min {qh0, ��} ∑ u7ap. �� . ¥��. ¥� l −k�n� ∑ �. mink�n�∑ min{wgt, i±}! . tr�n. m¶.k�n� ¥�� . ¥� �. p ��} + �. qh0 !u7�∥p ∥�� . �∥ p ∥�} · ª �! ∑ a¥� l − � min {qh0, ��} ∑ ap. �� . ¥� l −k�n�k�n��. min{qh0, ��} . ∑ a¥� �. p � l +k�n�min qh0, ��}! . ∑ p. ¥� ��}k�n� + �. qh0 !�∥ p ∥�} + ¸ differentiating wgt, n we get: ·∗ =— � min {qh0, ��} ∑ a�� . ¥� l −k�n��. min{qh0, ��} . ∑ a¥� �. p � l +k�n�min{qh0, ��}! . ∑ ap. ¥� �l + � qh0 !k�n� �∥ p ∥�} + ¸ this z * estimates the feature class classification process. iv. experimental results the proposed framework was implemented in python with third-party audio annotation libraries. in the initial phase, all the facial features were extracted using multi-modal feature extraction and ranking measures. the extraction process used the apache math and weka libraries to improve the feature ranking process. these collected features were annotated using the training sign annotations. in this study, opencv was used to implement a novel ensemble multi-modal facial feature classification process. figures 2-5, represent the test data predictions for the neutral, happy, angry, and surprise classes using the different multimodal feature classes. in each figure, the respective class has a higher probability estimation compared to the other multi-modal feature classes using the ensemble classification process. fig. 2. experimental result of neutral facial class on the multi-modal different classes. fig. 3. experimental result of the happy facial class. engineering, technology & applied science research vol. 13, no. 4, 2023, 11263-11270 11268 www.etasr.com chopparapu & seventline: an efficient multi-modal facial gesture-based ensemble classification and … fig. 4. experimental result of the angry facial class. fig. 5. experimental result of the surprise facial class. table i displays the total count of features extracted using the proposed feature extraction measures for each multi-modal feature in the input data. this table provides information about the number of features extracted from different modalities or types of data. the multi-modal features undergo a filtering process to remove noisy features in each frame, ensuring that only relevant and meaningful features are retained for further analysis. noisy features, which may introduce errors or irrelevant variations, are eliminated to improve the quality and usefulness of the extracted features. the resulting filtered multi-modal features are then used for subsequent processing or analysis tasks. table i. performance analysis of the proposed multi-modal filtered features count and comparison to traditional models multi modal fer mi+cnn chisquare +cnn correlation +cnn kernelfs +cnn proposed fem #100 82 83 72 55 32 #200 86 79 64 64 34 #300 81 75 63 65 33 #400 89 86 72 59 30 #500 82 90 66 60 38 #600 88 92 71 63 31 #700 86 79 66 58 33 #800 82 92 68 66 30 #900 79 86 71 56 32 #1000 89 76 74 63 36 figure 6 represents the total feature count of the proposed feature extraction measures on each multi-modal feature on the input data. the results show that the proposed multi-modal features are filtered after removing the noisy features in each frame. table ii presents the test classification accuracy of the proposed multimodal facial features using an ensemble learning framework, presenting the accuracy scores obtained for different facial expression evaluations. the proposed filtered-based classification approach outperformed traditional models in terms of accuracy, indicating that the filtering process, which removed noisy features from the multimodal facial data, led to improved classification results. the ensemble learning framework combined with the filtered multimodal features contributed to higher accuracy in evaluating facial expressions. the results highlight the effectiveness of the proposed approach in achieving superior performance compared to traditional models. figure 7 shows the accuracy of the proposed multimodal facial feature ensemble learning framework. the results show that the proposed filtered-based classification had better accuracy than traditional models on different facial expression evaluations. fig. 6. performance analysis of the multi-modal filtered feature count of the proposed and traditional models. fig. 7. performance analysis of the proposed multi-modal class recall filter-based ensemble learning model with traditional models. table iii and figure 8 illustrate the test classification precision of the proposed multimodal facial feature model using an ensemble learning framework. the table shows the engineering, technology & applied science research vol. 13, no. 4, 2023, 11263-11270 11269 www.etasr.com chopparapu & seventline: an efficient multi-modal facial gesture-based ensemble classification and … precision scores achieved for various facial expression evaluations. the proposed model showed higher precision compared to traditional models. this suggests that the filtering process, which removes noisy features from multimodal facial data, improved precision in classifying facial expressions. the combination of the ensemble learning framework and the filtered multimodal features improved precision. these results emphasize the superiority of the proposed approach over the traditional models in accurately evaluating facial expressions. table ii. performance comparison of the proposed multi-modal filter-based ensemble learning model with traditional models multi modalfer chisqure+ cnn correlat+ cnn kernelfs+ cnn proposed fem #100 0.928 0.94 0.957 0.983 #200 0.93 0.924 0.966 0.981 #300 0.932 0.939 0.967 0.985 #400 0.924 0.925 0.962 0.989 #500 0.938 0.932 0.957 0.987 #600 0.924 0.929 0.967 0.985 #700 0.922 0.94 0.952 0.981 #800 0.931 0.927 0.97 0.988 #900 0.936 0.947 0.97 0.984 #1000 0.934 0.937 0.962 0.98 table iii. performance analysis of proposed multi-modal class precision filter-based ensemble learning and traditional models multi modal fer chisqure+ cnn correlat+ cnn kernelfs+ cnn proposed fem #100 0.92 0.937 0.955 0.983 #200 0.94 0.941 0.96 0.988 #300 0.926 0.925 0.964 0.985 #400 0.938 0.947 0.969 0.988 #500 0.937 0.923 0.963 0.981 #600 0.928 0.948 0.957 0.983 #700 0.938 0.927 0.957 0.984 #800 0.93 0.945 0.958 0.984 #900 0.923 0.933 0.962 0.985 #1000 0.924 0.944 0.958 0.98 fig. 8. performance comparison of the proposed multi-modal class filterbased ensemble learning model with traditional models. overall, the proposed approach offers superior precision in facial expression evaluation, showcasing its potential for more accurate and reliable results compared to traditional models. v. conclusion in this study, a hybrid approach combining multiple feature extraction and filtering techniques was designed and implemented for the ensemble classification of different multimodal classes. traditional models often suffer from high false positive rates and mean error rates when applied to various multi-modal facial classes. to address this issue, a filter-based multi-feature ranking system was integrated into a voting framework, which was implemented on different classifiers designed for multi-modal data. the experimental results were evaluated using various multi-modal facial features within an automatic emotion listener system utilizing a speech synthesis library. the proposed multi-modal facial gesture-based ensemble learner outperformed the traditional approaches on heterogeneous facial databases in terms of feature ranking, feature selection, prediction accuracy, and runtime performance. this paper showcased the effectiveness of the designed approach in improving the classification and prediction capabilities for multi-modal facial data, leading to improved performance compared to conventional methods. vi. declarations the facial images showing the output results were of the corresponding author, who has no objections to their use in this research paper. the authors declare that there is no conflict of interest associated with this study and they did not receive any financial support or funding that could influence the findings or conclusions of this study. data sharing does not apply to this article as no datasets were generated or analyzed during this study. references [1] b. zou, y. wang, x. zhang, x. lyu, and h. ma, "concordance between facial micro-expressions and physiological signals under emotion elicitation," pattern recognition letters, vol. 164, pp. 200–209, dec. 2022, https://doi.org/10.1016/j.patrec.2022.11.001. 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[34] d. mamieva, a. b. abdusalomov, m. mukhiddinov, and t. k. whangbo, "improved face detection method via learning small faces on hard images based on a deep learning approach," sensors, vol. 23, no. 1, jan. 2023, art. no. 502, https://doi.org/10.3390/s23010502. engineering, technology & applied science research vol. 7, no. 3, 2017, 1658-1663 1658 www.etasr.com younesi et al.: environmental risk assessment and management in oil platform construction phase … environmental risk assessment and management in oil platform construction phase activities: a case study azad younesi raouf rahmani jalil jaafari yousef mahdavi novo nordisk company iran urban water and waste water company baneh, iran dpt of environmental health engineering, school of public health, tehran university of medical sciences, tehran, iran dpt of environmental health engineering, health sciences research center, mazandaran university of medical sciences, iran abstract—the construction phase is one of the very risky stages engaged in oilfields, which usually involves minor to severe human, financial, and environmental damages. it includes a major part of lost working times, and in recent years, along with the development of oilfields and oil platform construction activities in iran, hazardous risks and events have occurred and have been recorded. therefore, this study aims to reduce the negative effects of the risks engaged in oil platform construction activities in the region under study, i.e. the abuzar oilfield. the indexing system method, along with determining the importance index, effect, and frequency of occurrence, was used in this study to evaluate the environmental risks of oil platform construction activities in abuzar oilfield. first, the project activities were identified and then, the effect of desired activities on environmental aspects (water, air, soil, human, waste production, and noise) was investigated. for quantitative estimation of risk values through interviewing the experts and using the tables of intensity, effect, and frequency of event occurrence, were calculated based on the formula governing the effect of different activities on the environment, and the risk value was determined. the research findings indicated that most of the environmental risks are in the range of average risks (72.9%) however 20.2% are in the range of low risks and 6.9% are in the range of high risks. finally, considering experts’ viewpoints, management solutions were proposed to reduce the risk of activities, and the risk priority numbers were calculated after performing the corrective actions. keywords-risk assessment and management; abuzar oilfield; oil; platform; environment i. introduction any engineering project encounters several risks during its life cycle. thus, in case of confronting any danger or risk, its consequences must be evaluated [1]. risk management refers to the systematic process of identifying, analyzing, and reacting to the risks involved in a project [2]. this management guarantees maximizing the probability and consequences of positive events, and minimizing the probability and consequences of negative events regarding the project objectives [3]. risk management acts as a prediction tool. it probes the uncertain future to identify the things that might cause serious risks and prevents them, or seeks for an important opportunity [4, 5]. oilfield exploration and production from oil reservoirs is one of the projects always associated with high risks [6, 7]. due to their unique features, the plans and projects related to oil industry are totally different to other plans and projects in terms of extent and type of the risk [8, 9]. the features and characteristics distinguishing oil industry plans and projects from other plans is the great volume of investment and long-term plans in this industry [9], so that the longer the plan implementation, the higher the associated uncertainties and risks [10, 11]. another unique feature in implementing the oilfield development plans is unknown and uncertain oil volume to be produced as the oil reservoir is located hundreds of meters under the ground, and it is not possible to certainly determine its volume, quality, and distribution [12, 13]. the construction phase is one of the very risky stages engaged in oilfields, which usually involves minor to severe human, financial, and environmental damages, and includes a major part of lost working times [14, 15], so that in recent years, along with the development of oilfields and oil platform construction activities in iran, hazardous risks and events have occurred and recorded [16-18] and several studies have addresses environmental risk management and evaluation in construction phases of oil projects in general and oilfields in particular [9, 19, 20]. this study aims to reduce the negative effects of the risks engaged in oil platform construction activities in the region under study, i.e., abuzar oilfield. abuzar oilfield, located 75 km from western khark island, includes three major production platforms of aa, ab, and ac. it has the greatest share of oil production in the persian gulf and iran. each oil platform in this field has the capacity of producing 80,000 barrels of oil per day. totally, 195,000220,000 barrels of oil is produced from this field on a daily basis. so far, 107 oil wells have been drilled in abuzar oilfield. according to the estimations, total reserve of this field is about engineering, technology & applied science research vol. 7, no. 3, 2017, 1658-1663 1659 www.etasr.com younesi et al.: environmental risk assessment and management in oil platform construction phase … 4 billion barrels of oil, 20% of which can be produced. the current production capacity of abuzar oilfield is 240,000 barrels per day. given the great oil volume of this field and the importance of oil platform construction risks due to the risky operations involved, risk assessment in abuzar oilfield is necessary. efforts have been made in this study to thoroughly investigate and identify the activities performed in the site and determine their potential damages in order to take the necessary measures for environmental risk management and reducing the risks prevailing in the site. ii. method the environmental risk assessment method used in this study has a general application in a wide range of risks [21]. according to this model, the primary focus is on identifying the plan activities. the plan activities were completely identified based on the field visits from abuzar oilfield platform construction plan. then, the effect of the desired activities on environmental aspects (water, air, soil, human, waste production, and noise) were investigated. in order to specify and classify the unexpected activities and events leasing to environmental risks in the projects, the unexpected activities and events in abuzar oilfield platform construction and their effects on environmental aspects were identified by investigating valid and scientific documents and expert survey, reported in table i. table i. unexpected activities and events in the operational site of constructing abuzar oilfield platforms and their effects on environmental aspects no. activities water pollution air pollution soil pollution noise waste effect on human health 1 pipe and equipment transportation * * * * 2 pipe and equipment lifting and displacing * * * * 3 gouging (preparing the welding point to complete the welding process) * * * * * 4 pulverizing and using stone grinding device * * * * * 5 pipe insulation * * * * 6 acetylene production and distribution * * * * * 7 hydrostatic pressure test * * * * 8 scaffolding * * 9 construction and repair of access roads * * * * * * 10 digging foundation, piling, flooring, and soil compression * * * * * * 11 storing the equipment, pipes, goods, and chemicals * * * * * 12 painting * * * * 13 tension removal * * * 14 sand blast * * * * * 15 secondary events, including fire and explosion caused by the adjacent projects * * * * * * 16 maritime transportation and unloading * * * * * 17 gasoline reservoir test * * * 18 running electricity networks * * 19 solid waste production * * * 20 wastewater production * * * 21 emergency evacuation under emergency situations * * * * 22 industrial radiography * * * * * 23 non-destructive tests * * * * 24 welding, electrode cutting, and electrode warming * * * * * 25 manual air and gas cutting, assembling * * * * * 26 working in closed environment * * * * * 27 de-rusting operations * * * * * 28 carpentry and wood cutting * * * * * 29 green space and gardening * * * * * 30 fiberglass pulp cutting * * * * * 31 repairing the machinery * * 32 cooking * * * * * 33 fire fighting * * * * * 34 waste incineration * * * * * 35 waste production and industrial waste storage * * * * 36 using heavy and light vehicles in the site and road * * * * 37 tour living, working in onshore and operational site * * * * 38 health care * * 39 manual transportation * 40 site visitors * 41 mt and pt destructive tests * * * 42 war, earthquake, and tsunami * * * * * * 43 ultrasonic tests and phase array * * * engineering, technology & applied science research vol. 7, no. 3, 2017, 1658-1663 1660 www.etasr.com younesi et al.: environmental risk assessment and management in oil platform construction phase … quantitative estimation of risk values was performed through interviewing the experts, including the professionals in the fields of environment and hse, who have a comprehensive knowledge about the site under study, and using the tables of intensity, effect, and frequency of event occurrence. environmental risk values were calculated based on the following formula [23] governing the effect of different activities on the environment: environmental risk = the effect of activity on environmental aspects × the importance of activity in environmental aspects × the frequency of event occurrence. and the risk value was quantitatively determined, and recorded in the rpn column of a prepared datasheet before performing the corrective actions [22]. after determining the activities and identifying the effects of air, soil, and water pollution, noise, waste, and the damage caused by these activities in order to quantify the risk associated with them, table ii of importance, effect, and frequency of event occurrence was created. the risk level based on importance, effect, and frequency of event occurrence is as the following [24, 25] (table iii): a. low risk: 1-14 b. moderate risk: 15-79 c. high risk: 80-125 table ii. risk classification matrix based on importance, effect, and frequency of event occurrence importance effect 1 2 3 4 5 frequency 1 1 2 3 4 5 1 2 4 8 12 16 29 2 3 9 19 27 36 45 3 4 16 32 48 64 80 4 5 35 50 75 100 125 5 after determining the type of risk, a complete list of actions to control and reduce the risk values were developed and discussed in an expert meeting. the best actions were selected by the experts and its list was confirmed by the risk assessment team, so that it could be announced to the project manager in order to reduce environmental risks. finally, the risk value was determined quantitatively after performing the corrective actions. iii. research findings the environmental risk values determined based on the results of field visits and related expert meetings for abuzar oilfield platforms are given in table iv. an example of calculating the environmental risks caused by project activities before/after performing the corrective actions is shown in this table. following, the analysis results of abuzar oilfield platform are explained. furthermore, according to table v, quantitative risk assessment during construction showed that 20.2% of risks had the numerical values in the range of 1-14 (low), 72.9% of the risks had numerical values in the range of 15-79 (moderate risk), and 6.9% of the risks had numerical values greater than 80 (figure 1). according to the management strategies proposed in this stage to remove, reduce, and control environmental risk, a re-evaluation was performed on the project risk values after performing corrective actions, and the number of project risks decreased according to table vi after performing corrective actions. according to table vi, quantitative evaluation of environmental risks involved in the project during construction after performing corrective actions showed that 80.3% environmental risks involved in construction phase are low risks, 19.7% of the risks are moderate risks (15-79), and 100% of the high risks were removed after performing corrective actions (figure 2). table iii. importance, effect, and frequency of event occurrence on environmental aspects numerical index importance effect frequency 1 an insignificant amount (if any) is distributed in the environment its effect is beyond the control of the unit never or less than once a year 2 a little amount is distributed in the environment has a little effect once in a 1-3 years 3 an average amount is distributed in the environment has an average effect once a month to once a year 4 a great amount is distributed in the environment has a great effect once a week to once a month 5 distribution completely depends on the environment has a direct effect once a day to once a week fig. 1. percentage of different environmental risks in the project before performing corrective actions fig. 2. percentage of different environmental risks involved in the project after performing corrective actions engineering, technology & applied science research vol. 7, no. 3, 2017, 1658-1663 1661 www.etasr.com younesi et al.: environmental risk assessment and management in oil platform construction phase … table iv. environmental risks caused by project activities before/after performing corrective actions no. activity risk estimation before performing the corrective actions risk estimation after performing the corrective actions decrease in risk value (%) 1 pipe and equipment transportation 112 46 58.9 2 pipe and equipment lifting and displacing 112 46 58.9 3 using heavy and light vehicles in the site and road 105 42 60.0 4 gouging 74 32 56.8 5 pulverizing and using stone grinding device 140 85 39.3 6 pipe insulation 95 35 63.2 7 acetylene production and distribution 160 80 50.0 8 pressure test 78 38 51.3 9 scaffolding 56 25 55.4 10 construction and repair of access roads 74 24 67.6 11 digging foundation, piling, flooring, and soil compression 112 68 39.3 12 storing the equipment, pipes, goods, and chemicals 160 64 60.0 13 painting 76 20 73.7 14 tension removal 145 60 58.6 15 sand blast 245 120 51.0 16 secondary events, including fire and explosion caused by the adjacent projects 188 160 14.9 17 war, earthquake, and tsunami 242 204 15.7 18 maritime transportation and unloading 74 40 45.9 19 gasoline reservoir test 70 32 54.3 20 running electricity networks 20 10 50.0 21 solid waste production 314 70 77.7 22 wastewater production 380 120 68.4 23 emergency evacuation 44 25 43.2 24 industrial radiography 314 112 64.3 25 working with cutting device, including cnc (muller) and handheld torches 124 44 64.5 26 gas welding and electrode cutting in open and closed environment 160 52 67.5 27 manual air and gas cutting, assembling 110 38 65.5 28 working in closed environment 276 124 55.1 29 de-rusting operations 78 32 59.0 30 carpentry and wood cutting 124 56 54.8 31 green space and gardening 98 44 55.1 32 fiberglass pulp cutting 120 52 56.7 33 repairing the machinery 262 84 67.9 34 cooking 244 82 66.4 35 fire fighting 110 56 49.1 36 waste incineration 136 64 52.9 37 waste production and industrial waste storage 202 88 56.4 38 working in onshore and working in site 286 72 74.8 39 health care 74 12 83.8 40 manual transportation 108 32 70.4 41 site visitors 36 12 66.7 42 mt and pt destructive tests 70 10 85.7 43 ultrasonic tests and phase array 64 22 65.5 table v. type and value of the environmental risks during construction risk classification the number of environmental risks in construction phase low risks (1-14) 38 moderate risks (15-79) 137 high risks (80-125) 13 total 188 according to table vii, the number of low environmental risks during construction phase after performing corrective actions increased from 38 to 151, which indicates 74.84% increase in low risks after performing corrective actions. moreover, the number of moderate environmental risks during construction phase after performing corrective actions decreased from 137 to 37, which indicates 72.98% decrease in moderate risks involved in construction phase. the number of environmental risks with values greater than 80 also reached zero, which indicates 100% decrease in high environmental risks after performing corrective actions. iv. discussion and conclusion among all oil companies and installations, the oil platforms and production facilities, especially compared to onshore and offshore facilities, are of great importance in terms of engineering, technology & applied science research vol. 7, no. 3, 2017, 1658-1663 1662 www.etasr.com younesi et al.: environmental risk assessment and management in oil platform construction phase … environmental damages due to their distance from the beach, great number of personnel, significant reserves of hydrocarbon and chemicals, unique operational conditions, and the potential to cause huge industrial accidents. therefore, knowing about their environmental aspects and consequences has an important and valuable role. final results in this study indicated that the construction phase is one of the very risky stages engaged in oilfields, which usually involves minor to severe environmental damages. most of the environmental damages are in the range of moderate risks (72.9%), 20.2% are in the range of low risks, and 6.9% are in the range of high risks. table vi. quantitative evaluation of environmental risks involved in the project during construction after performing corrective actions risk classification the number of environmental risks involved in construction phase low risks (1-14) 151 moderate risks (15-79) 37 high risks (80-125) total 188 table vii. estimating the values of risks invovlved in the project during construction phase after performing corrective actions risk classification the number of environmental risks involved in construction phase percentage of increase in low risks after performing corrective actions (114) 74.84% percentage of decrease in moderate risks after performing corrective actions (15-79) 72.97% percentage of decrease in high risks after performing corrective actions (>80) 100% the results of [26] on classification of different risks prevailing in the development of oil and gas fields showed that the exploration stage is considered as the riskiest stage in development of an oilfield. another previous research to evaluate the environmental risk using efmea method indicated that the greatest environmental risk is attributed to the construction phase, and 20% of its risk are in the range of low risks, 62% are in the range of medium risk and 18% are in the range of high risk [18]. in [27], authors addressed the evaluation and selection of risk responses of the projects during construction phase. their results showed that risk evaluation results in a significant improvement in time, cost, and quality of the project during construction phase. in a similar research [28], authors studied environmental risk management and evaluation in abadan. the purpose of their study was to remove, reduce, and control the existing environmental risks. 57 risk factors were determined during construction phase. except the 21 environmental risks that were within an acceptable range, all of them were in the range of high risks, and suitable control measures in accordance with the activity or the process had to be taken. in [29], authors investigated the factors associated with event occurrence in the construction phase of oil, gas, and petrochemical projects in assaluyeh and identifies four variables contributing in fatal occupational accidents during construction phase of the projects: unsafe conditions, unsafe operations, mismanagement factors, and using defective tools, materials, equipment and machinery, among which the unsafe conditions and mismanagement factors have a greater effect on occurrence of fatal accidents during construction phase. v. suggestions the following corrective actions are suggested to reduce the environmental risks identified and minimize them: 1) completing the environmental procedures and guidelines available in form of an integrated management system. 2) holding educational and training courses required for all employees at different levels to increase their level of knowledge and awareness regarding environmental issues. some of the important environmental educational courses identified during studies, which are necessary to be held for the employees are:  professional courses on risk assessment and evaluation for the experts in upper and middle levels  professional courses on combating oil pollution  managing emergency situation  managing the wastes at different levels 3) holding monthly meetings of hse committee, with presence of the authorities, hse experts, and contracting representatives in order to investigate the problems and propose a schedule to solve the problems and challenges. 4) integrating the preventive maintenance system in all operational sites under computerized maintenance management system. 5) performing environmental monitoring continuously and according to the integrated management system requirements and self-reported plan of environmental protection agencies. 6) removing the inconsistencies identified in the internal and external audits of the company and performing the corresponding corrective actions. 7) adopting preventive policies to control environmental risks, rather than the current reactive policies and procedures. 8) environmental risk assessment and analyzing the consequences before installing the new equipment or any changes in the process. 9) updating meteorological information (e.g., temperature, humidity, wind direction, wave height, predicting the storm and unfavorable weather conditions). engineering, technology & applied science research vol. 7, no. 3, 2017, 1658-1663 1663 www.etasr.com younesi et al.: environmental risk assessment and management in oil platform construction phase … 10) identifying certain regions and neighboring organizations and companies for mutual cooperation in emergency cases. 11) supplying the equipment required to prevent oil pollution, namely booms, skimmers, and oil separator elements (ose), in case of oil leakage and spilling into the sea. 12) using suitable inhibitors against internal and external corrosion of the equipment and pipes, and implementing corrosion management actions in offshore oil facilities. 13) conducting periodic and regular inspections of the facilities regarding hse, 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journal martyr yazd university of medical sciences, vol. 15, no. 4, pp. 75-83, 2007 engineering, technology & applied science research vol. 7, no. 6, 2017, 2210-2214 2210 www.etasr.com saand et al.: effect of soorh metakaolin on concrete compressive strength and durability effect of soorh metakaolin on concrete compressive strength and durability abdullah saand department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan abdullah@quest.edu.pk manthar ali keerio quaid-e-awam university of engineering, science & technology nawabshah, pakistan mantharali99@quest.edu.pk daddan khan bangwar department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan daddan@quest.edu.pk abstract—concrete durability is a key aspect for forecasting the expected life time of concrete structures. in this paper, the effect of compressive strength and durability of concrete containing metakaolin developed from a local natural material (soorh of thatta distict of sindh, pakistan) is investigated. soorh is calcined by an electric furnace at 8000c for 2 hours to produce metakaolin. one mix of ordinary concrete and five mixes of metakaolin concrete were prepared, where cement is replaced by developed metakaolin from 5% to 25% by weight, with 5% increment step. the concrete durability was tested for water penetration, carbonation depth and corrosion resistance. the obtained outcomes demonstrated that, 15% replacement level of local developed metakaolin presents considerable improvements in concrete properties. moreover, a considerable linear relationship was established between compressive strength and concrete durability indicators like water penetration, carbonation depth and corrosion resistance. keywords-compressive strength; durability; metakaolin; soorh; permeability; carbonation depth; corrosion i. introduction supplementary cementing materials (scms) are being utilized in concrete because of their economic and environmental advantages [1]. the usage of scms improves the properties of concrete, decreases the usage of cement and the construction cost [1]. metakaolin is a pozzolanic material, produced by the heating of kaolin clay (alumino-silicate material) at a temperature between 700–8500c [2-4]. metakaolin is produced by different researchers using different temperatures and durations. metakaolin was developed from calcined kaolin at 800 0c at 1 hour period in [5, 6]. kaolin was thermally treated at 800 0c for 2 hours to develop the metakaolin in [4, 7-11]. the kaolin was calcined at 800 0c for 3 hours to prepare metakaolin in [12, 13]. the durability properties of concrete with inclusion of local metakaolin of iran were investigated at 7, 28, 90 and 180 days by authors in [5]. the cement was replaced by local metakaolin as 0%, 10%, 12.5% and 15% by mass. it was found that metakaolin concrete has significant improvement in durability as compared to control concrete. it was observed that best substitution of cement by local metakaolin is 12.5% and 10 % at w/b ratio 0.4 and 0.35, correspondingly [5].the performance of metakaolin in high performance concrete were investigated in [14]. it was observed from test results that 15% replacement of cement with metakaolin had considerable improvement on durability properties of high performance concrete. authors in [15] showed that 10% to 15% replacement of cement with metakaolin has significant improvement in concrete durability properties. resistivity, upv and corrosion behavior of carbon steel using (5–20%) replacement of cement with metakaolin were studied in [16]. it was found that 15% replacement of cement with metakaolin improves resistivity, upv and corrosion of carbon steel. authors in [23] studied different specific surface areas of mk activated with sodium silicate and naoh they concluded that higher specific surface area of mk powders were characterized by quicker setting time, higher compressive strength and more homogeneous microstructure. approximately 0.8 tons of co2 is released in the environment while preparing one tone of cement, which is around 5–8% of global co2 emission [17]. the concrete structures are very common and cement is used to prepare the concrete. to decrease the cement manufacturing and therefore to decrease co2 release in atmosphere and the construction cost, an ecoefficient binder is very important for sustainability for possible cement replacement material. thus the objective of this research is to examine the durability related properties and compressive strength of concrete with inclusion of local metakaolin produced from soorh, which is abundantly available in district thatta, sindh, pakistan and is not yet explored and used as cement replacement material. ii. experimental work a. materials ordinary portland cement and the soorh raw material (local natural material) is used. in concrete specimen, clean natural hill sand retained from sieve ≠ 4 as fine aggregate and coarse aggregate retained from ¾ inch sieve was used. the specific gravity of fine and coarse aggregates was 2.72 and 2.84 respectively. soorh is a type of clay abundantly available in thatta district. physical properties, chemical composition and engineering, technology & applied science research vol. 7, no. 6, 2017, 2210-2214 2211 www.etasr.com saand et al.: effect of soorh metakaolin on concrete compressive strength and durability mineralogical composition of soorh clay and of metakaolin obtained by soorh thermal treatment are shown in tables i and ii. according to astm c 618, the minimum requirement for a pozzolanic material and metakaolin is sio2 + al2o3 + fe2o3 ≥ 70% and ≥ 85%, respectively. in metakaolin developed from soorh we see that sio2 +al2o3 + fe2o3 is found as 89.9 %, as shown in table i. therefore, the chemical composition of calcined soorh satisfies the requirements of natural pozzolanic material and metakaolin and that justifies its use in concrete as per astm c-618. the blaine fineness of developed metakaolin is less than the cement. from the data shown in table ii is obvious that after the calcination of soorh, the quantity of quartz (raw impurity) decreased from 47.1% to 36.3%. authors in [19] showed that the compressive strength of mortar can be equal or increased compared to control mortar by replacing the 30% of the cement in mortars with calcined clays having a high percentage of raw impurities (i.e. quartz more than 40%). table i. physical and chemical properties of cement, soorh and developed metakaolin constituent % by weight of cement % by weight of soorh % by weight of produced metakaolin sum of produced metakaolin: sio2+al2o3+fe2o3 sio2 20.78 55.89 62.18% al2o3 5.11 23.51 21.67 % cao 60.89 ------3.01% mgo 3 3.53 3.41% fe2o3 3.17 8.15 6.05% 89.9% k2o ----5.89 1.85% na2o3 ----1.89 1.03% tio2 ----1.14 1.03% in2o3 --------0.8% loi (%) 1.71 7.4 0.5 blaine fineness (cm2/g) 0.3008 0.2101 0.2339 specific gravity 3.15 2.64 2.60 table ii. mineral composition of soorh and developed metakaolin b. mix proportions of concrete plain concrete mix and metakaolin modified concrete mixes with w/c ratio of 0.55, slump range 25-50 mm were used. to prepare the metakaolin concrete mixes, the ordinary portland cement is replaced by metakaolin with 5%, 10%, 15%, 20% and 25% by weight of cement. therefore, six different mixes were prepared. for all mixes, 10 cylinders of 100 mm diameter and 200mm length were cast for investigation of compressive strength, carbonation and corrosion of concrete. five cubes of 100mm x 100 mm x 100 mm size cast for water penetration test. c. test methods the compression test was performed on the control specimens and metakaolin concretes using the universal testing machine astm c39. water penetration test and corrosion of concrete was conducted with bs en 12390-8:2009 and astm c876-80 respectively. carbonation depth of concrete was conducted by using phenolphthalein method. the compressive strength of concrete specimen were carried out at the age of 7 and 28 days, while permeability test (water penetration depth) of concrete was performed at 28 days and corrosion potential test and carbonation depth test of concrete were performed at 28 and 180 days. five specimens were used for each testing age. iii. results and discussion a. concrete compressive strength the compressive strength of 7 and 28 days ordinary and concrete prepared with (0 25%) substitution of cement by developed metakaolin is highlighted in figure 1. the compressive strength of metakaolin concrete is increased compared to plain concrete with the replacement of cement by metakaolin in the inclusion range from 5% to 15%. the maximum compressive strength, 31.65 mpa (i.e. 15.43% increase compared to control) at 28 days have been achieved at 15% substitution of cement with metakaolin. on further substitution of cement with developed metakaolin, the compressive strength of metakalin concretes is found smaller compared to ordinary concrete. authors in [16] found that 15% replacement of cement by metakaolin gave most favorable results compared to ordinary concrete and other replacement levels of cement with metakaolin. the reduction in compressive strength for mk20 and mk25 as compare to mk15 is due to the effect of the dilution of a clinker. the effect of dilution of clinker is an outcome of cement replacement with equal amount of metakaolin. b. permeability (water penetration depth) the comparison of water penetration depth at 28 days of ordinary and concrete prepared with (0 25%) substitution of cement by developed metakaolin is shown in figure 2. the results of water penetration test at figure 2 revealed that the water penetration depth of modified mixes is decreased compared to cm in the substitution range of 5 % to 15 %. the maximum reduction in water penetration depth is achieved at 15% replacement of (40% less from to control). on further substitution, water penetration depth. the 15% substitution provided 29% maximum reduction in permeability compared to plain concrete reported in [14]. permeability is the major factor of durability properties of concrete. the lower permeability of concrete proved more resistance against chemical attacks [20]. minerals soorh (%) developed metakaolin (%) quartz si2o5 47.1 36.3 illite k(al4si2o9(oh)3) 27.4 42.9 stevensite cao2mg2.9si4o10(oh)2.4h2o 12.1 16.5 kalonite al2si2o5(oh)4 11.9 - calcite magnesium mgo.06cao0.94(co3) 0.8 4.3 hematite fe2o3 0.7 - engineering, technology & applied science research vol. 7, no. 6, 2017, 2210-2214 2212 www.etasr.com saand et al.: effect of soorh metakaolin on concrete compressive strength and durability table iii. mix proportions of concrete concrete mix cement kg/m3 mk kg/m3 total binder kg/m3 w/b water kg/m3 fine aggregate kg/m3 coarse aggregate kg/m3 slump (mm) cm 346 -346 0.55 190 692 1038 25-50 mk5 328.7 17.3 346 0.55 190 692 1038 25-50 mk10 311.4 34.6 346 0.55 190 692 1038 25-50 mk15 294.1 51.9 346 0.55 190 692 1038 25-50 mk20 276.8 69.2 346 0.55 190 692 1038 25-50 mk25 259.5 86.5 346 0.55 190 692 1038 25-50 fig. 1. compressive strength of plain (c) and metakaolin concrete concrete corrosion potential the comparison of corrosion potential at 28 and 180 days of ordinary and concrete prepared with (0 25%) substitution of cement with metakaolin is shown in figure 3. the results of corrosion potential revealed that the corrosion potential of modified mixes is decreased compared to cm in the substitution range of 5% to 15%. the maximum decrease in corrosion potential is achieved at 15% substitution (5.7% decreased compared to control) and on further substitution, concrete corrosion potential is increased. it is that 15% replacement of cement with metakaolin is the optimum replacement level against steel corrosion [16]. c. concrete carbonation depth the comparison of carbonation depth at 28 and 180 days of ordinary and concrete prepared with (0 25%) substitution of cement by developed metakaolin is shown in figure 4. the results reveal that the carbonation depth of modified mixes is decreased compared to cm in the substitution range of 5 % to 20 %. the maximum decrease in carbonation depth is achieved at 15% substitution of cement with metakaolin (31% less compared to control) and on further substitution the concrete carbonation depth is increased. the decrease in carbonation depth in metakaolin concrete is due to pozzolanic activity of mineral admixtures [21]. d. correlation between compressive strength and durability of concrete test tesults the correlation between compressive strength and durability indicators of concrete i.e., water penetration depth, corrosion potential and carbonation depth was found and highlighted in figures 5 7. a significant linear relationship was established between compressive strength and durability related properties in the form of y = ax ± b and looks as the best fit for the figures with a good coefficient of correlation r2 ≥ 0.83. it is clear from figures 5-7 that as the compressive strength increases water penetration, corrosion potential and carbonation depth decrease consequently i.e. the durability of concrete increases. correlation among compressive strength and durability properties of metakaolin concrete was presented in [5, 22]. fig. 2. water penetration of ordinary and metakaolin concrete engineering, technology & applied science research vol. 7, no. 6, 2017, 2210-2214 2213 www.etasr.com saand et al.: effect of soorh metakaolin on concrete compressive strength and durability fig. 3. corrosion potential of ordinary and metakaolin concrete iv. conclusion the concrete durability and compressive strength have been significantly improved with the substitution of cement by metakaolin in the substitution range of 5% to 15%. the maximum compressive strength 31.65 mpa (i.e., 15.43% more as compared to plain concrete), the maximum reduction in water penetration depth (i.e. 40% less than control), the maximum decrease in corrosion potential (i.e. 5.7% less than that of control) and the maximum decrease in carbonation depth (i.e. 31% less than ordinary concrete) are achieved at 15% replacement of cement with developed local metakaolin. a significant linear relationship between test results of durability related tests and compressive strength of metakaolin concretes was found. it can be concluded on the basis of the results of compressive strength, water penetration, corrosion potential and carbonation depth, that 15% substitution of cement with the metakaolin in concrete is optimum. acknowledgement the authors would like to acknowledge the help of the department of civil engineering, quaid-e-awam university, engineering, science & technology, nawabshah for providing the testing facilities. fig. 4. carbonation depth of ordinary and metakaolin concrete fig. 5. relationship of compressive strength and corrosion of metakaolin concrete fig. 6. relationship of compressive strength and 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construction and building materials, vol. 35, pp. 752–760, 2012 [23] l. weng, k. sagoe-crentsil, t. brown, s. song, “effect of aluminates on the formations of geopolymers”, materials science and engineering: b, vol.117, no. 2, pp.163–168, 2005 engineering, technology & applied science research vol. 8, no. 1, 2018, 2604-2608 2604 www.etasr.com alameri et al.: manets and internet of things: the development of a data routing algorithm manets and internet of things: the development of a data routing algorithm i. a. alameri computer center jabir ibn hayyan medical university iraq ib.alameri@jmu.edu.iq abstract-internet of things (iot), is an innovative technology which allows the connection of physical things with the digital world through the use of heterogeneous networks and communication technologies. iot in smart environments interacts with wireless sensor network (wsn) and mobile ad ‐ hoc network (manet), becoming even more attractive and economically successful. interaction between wireless sensor and mobile ad‐hoc networks with the internet of things allows the creation of a new manet ‐ iot systems and it ‐ based networks. such systems give the user greater mobility and reduce costs. at the same time new challenging issues are opened in networking aspects. in this work, author proposed a routing solution for the iot system using a combination of manet protocols and wsn routing principles. the presented results of solution's investigation provide an effective approach to efficient energy consumption in the global manet‐iot system. that is a step forward to a reliable provision of services over global future internet infrastructure. keywords-iot; manet; dynamic routing; wireless sensor network i. introduction internet of things (iot) and cloud computing [1] represent a part of the future internet paradigm. the capability of objects (like physical or virtual things) to identify and communicate with each other at any time with evolving communication technologies gives the possibility to provide advanced services over global infrastructure in different areas of everyday life [2]. the interconnection of smart objects and its interoperability with global communications serve as a main incorporated idea in internet of things (iot) systems. in an iot system, a major role is played by the wireless sensor network (wsn) as its components comprise: sensing, data acquiring, heterogeneous connectivity and data processing. a wireless, self-configuring and multi-hop network is called mobile ad-hoc network (manet) [3]. each manet node operates as a router or as a network end system and is closely related to wsns. the interaction between manet and iot opens new ways for service provision in smart environments and challenging issues in its networking aspects. one of the important factors in manet‐iot systems is the energy balancing over nodes, since the iot system is based mostly on many different wireless sensors and selection from manet protocols focuses on the most efficient and shortest routes. a proper utilization of sensor's battery power is a significant key in maintaining network connectivity of a multihop wireless network. because of this, many researchers are focusing on designing energy efficient routing protocols that prolong network’s lifetime. wireless network protocols cannot be used directly due to resource constraints of sensors’ nodes, computational speed, and human interface with node's devices and network node density. therefore, there is a need of composite solution for routing over manet‐iot networks, which can use node residual energy efficiently and extend the network lifetime. in this paper, an algorithm of energy efficient and safe‐weighted clustering routing for the mobile iot system using a combination of manet and wsn routing principles is proposed. clustering is a method of making routing less complex, and for some sensor networks, more energy efficient. such combination of manet and wsn routing principles is able to increase the sensors lifetime in the overall mobile iot system. there is importance in deciding on how many cluster heads (chs) are needed and which sensor node shall act as the cluster head. manet network nodes were chosen as a cluster head and a proactive routing protocol was used in such a way that it is possible to control and update a table of information about the network state. nodes that lose their energy rapidly and are ended up with low energy were recognized and their workloads were limited for transactions. all investigations for the selection of a routing path over the manet‐iot system were performed using matlab. this research work provides important key insights into the combination of manet and wsn routing principles by increasing the sensors lifetime in the overall iot system. ii. literature review a. manet manets are independently self-organized networks without fixed topology. in such a network, each node acts both as a router and host at the same time. all network nodes are equivalent to each other and can join or move out freely in the network. mobile nodes present in the radio range of each other can communicate directly and transfer the necessary engineering, technology & applied science research vol. 8, no. 1, 2018, 2604-2608 2605 www.etasr.com alameri et al.: manets and internet of things: the development of a data routing algorithm information. all network nodes have a wireless interface to interact with each other. this kind of network can work anywhere and it is fully distributed without the assistance of any infrastructure as base stations or access points. there are two multiple ad-hoc network types: i) manet and ii) mobile ad-hoc sensor network. a mobile ad-hoc sensor network has much wider sequence of operations and requires less complicated setup steps in comparison with typical sensor networks which directly communicate with a centralized controller [5]. there are six main characteristics of manets [4]: dynamic topology, distributed operation, lightweight terminals, multi-hop routing, and shared physical medium and autonomous terminal. routing manet protocols can be categorized into three general categories: 1) topology‐based routing the routing types [5] are: (a) proactive routing protocols (routing table‐based), (b) reactive routing protocols (demand based) (c) hybrid routing protocols which consist of combinations of reactive and proactive protocols. one of them is zrp (zone routing protocol). 2) location‐based routing to make routing decision, the actual position of nodes is used by the location-based routing in any area. for example, by using global positioning system (gps), the information of location can be obtained. location‐aided routing (lar) protocol is an example of location‐based routing. 3) energy awareness based routing each network node supports multiple entries in routing tables. for choosing the optimal route, assessing power levels of network nodes is available. in this case, routing table corresponds to the nodes power level and is maintained by transferring relevant messages. the number of reachable nodes is determined by the number of entries in the routing table of nodes by using the power level. thus, the number of entries in routing tables gives the total number of network nodes [6]. b. internet of things (iot) the need to “recruit” all things that surrounds us was a great reason for the connection of electronics, devices, with digital communications, using internet as the main data transmission medium [7]. all communication, management and information exchange are processing among connected things and objects. the capability of real or virtual things and objects to be identifiable, to communicate and to interact allows us to build networks of interconnected objects, end users or other entities in the global internet network [9]. so the term “internet of things” mainly means the global infrastructure of interconnected things, devices, or objects, which can communicate, actuate, exchange their information over internet to the end users by using the interaction between communication technologies and networks. c. the interaction between internet of thing and manet possibilities of wide application of iot systems in different areas are directly dependent on the opportunities of interoperability between different communication technologies and networks in smart environments [8]. the growth of sensors quantity leads to the increasing human need for remote monitoring of different processes. and this became possible by the widespread deployment of wireless sensor networks (wsn). basically, wsn is a network, which consists of different sensors that are autonomously capable to read information from the measured object, to handle sensed data, temporarily store it and transfer them to another network node, which is also a sensor. as wsn is a normally centralized network [12], so the data, sensed and transferred from other sensors, are transmitted to the central node, which is usually called sink. in this manner, the wireless sensors are able to communicate with each other and thus open very wide usability opportunities of wireless sensor networks in iot systems. wireless sensor networks mainly are the basic element in the global iot system, as sensors have the ability to gather information from different things and transmit it over the network. however, the reliability of iot systems is highly dependent on the power consumption and scalability of wsn [13]. sensors should transmit measured data so efficiently to the sink, that their battery energy would be used at minimum level. because of this, wsn should easily accommodate network changes. this is related to the lifetime of wsn as well, as low or empty battery leads to the death of sensors. in this way, the routing principles and methods are very important and challenging issues of wsn as data should be transmitted by another sensor and the dead sensor should be eliminated from the routing path. these should be done with respect to quality of service (qos) over wsn [14]. wireless sensor network in general is similar to manet since both are multi-hoped and self-organized networks. however, the topology of manet is more changeable than wsn. manet protocols can allow it to act as a wsn backbone [15] and access wireless sensor network's nodes as well as exchange information with wsn about manet entry points [10]. these two networks can enable more effective and reliable cross‐network routing in the iot context. the intersection of manet, wsn and iot will be addressed as manet‐iot system, which is discussed in detail in section iii. networking in the manet‐iot system is based on manet routing protocols, wsn routing principles and data sensing, handling and processing using iot. in general, the networking of such a system is very challenging regarding routing aspects. also, it is related to system mobility and limited network sensor resources. most of manet protocols are designed with focus on qos [16, 17] and routing in wsns is focused on the efficient node energy consumption [18]. the connection of different things with limited features to the internet and the interaction with different wireless and mobile ad‐hoc networks must guarantee connectivity, accessibility and reliability of the manet‐iot system in smart environments. the solutions for the routing protocols of ad‐hoc network modification in order to fulfil the requirements of the iot were presented in [19]. routing principles were changed by integrating ipv6 [20]. however, the interaction of iot with manet and wsn requires new, optimized solutions for data routing in the manet‐iot system. author proposes an algorithm for data routing, which is mainly focused on energy engineering, technology & applied science research vol. 8, no. 1, 2018, 2604-2608 2606 www.etasr.com alameri et al.: manets and internet of things: the development of a data routing algorithm efficiency and safe weighted clustering in the manet‐iot system. the solution is described in sections iii and iv. iii. proposed manet-iot system data routing algorithm in order to describe complex networks like wsn, graphs are a suitable model. it can be assumed that wsn, in creating energy aware route selection schemes is a graph with edges representing communication links between vertices and vertices representing sensor nodes. a node’s residual energy is denoted by the weight on a vertex while the amount of energy that a node needs to transfer a unit of information along the edge is indicated by the weight on an edge [31]. the lowest energy level of any node on the route is called the residual energy. the sum of the weights on all the edges present on the route is the energy consumed along the route. the best and suitable energy aware route selection scheme for wsn is to use the nodes with higher energy levels in such a way that the total energy consumed along the data forwarding path is reduced. the proposed algorithm adopts dynamical monitoring, which controls the energy of the cluster heads, and a predefined threshold value. the purpose of this monitoring mechanism is the transferring of cluster head based on the comparison result between the threshold value and the cluster head’s energy. the algorithm presented in figure 1 has three phases: setup, steady and threshold. first step is a cluster head selection. all the chosen cluster heads send a message of advertisement to all the non-cluster head nodes after the selection of the cluster head. the non-cluster head nodes choose their cluster heads for the current round based on the received signal strength of the message advertised and send back a request message to the selected cluster heads informing their membership that leads to the formation of cluster. the message sent to the cluster heads includes the node's id and the location of the sender node. when all nodes are deployed, the network starts to select the cluster heads and carry out clustering and layering. then, the nodes begin to periodically start data collection and transmit them to the sink node. with the change of time, the network topology structure is also changing. if cluster head energy is lower than the predefined threshold value, the third loop is applied to replace cluster head by another node, which poses the largest energy within the cluster. the new cluster head continues to cooperate with cluster members. this way protects cluster heads with lower energy. this mechanism can protect cluster heads from quick death and prolong the network lifetime. when we have all the information about network and nodes, then we are choosing the routing method for transmission information. for the evaluation of network lifetime three route path selection methods are used: np (node place), bst (node battery state) and er (energy resource). the np aims to find the route with minimum hop count and for searching nodes, node location parameters or methods are used (rssi, aoa and toa). the cluster head evaluates all neighbor nodes in the cluster. if the information does not satisfy required criteria, cluster heads send message to the neighbor cluster head to help find a route to the sink. bst selects node with higher battery state. using the er method we calculate all network energy resources using the proposed algorithm. in the new algorithm, a threshold value is added in order to monitor the node’s energy. fig. 1. proposed common route choosing algorithm a. performance evaluation of routing algorithm simulation experiments are carried out using matlab. the principal goal of these simulations is to analyze our algorithm and compare it with others. for analyzing and comparing the performance of our proposed method we used two metrics: node energy and network lifetime (or number of rounds). network lifetime is one of the main characteristics to evaluate sensor network performance. such a parameter includes coverage, connectivity and node availability. network lifetime tn is defined as the time when sensor network loses connectivity. the route lifetime is defined by the first node failure: tnroute =min tγ, γ ε n where tγ is the lifetime of node γ in ij-route. we tested the proposed algorithm using an initial number of alive sensors n = 17, each with a range d = 8 m. we used a network of size m = 20 × 20 m, with a sink located at point coordinates [x = 7, y = 18]. according our proposed solution, the optimal number of cluster was first calculated. as shown in figure 2, in this case the optimal numbers of clusters are 3. the network at which we apply our tests is shown in figure 3. the engineering, technology & applied science research vol. 8, no. 1, 2018, 2604-2608 2607 www.etasr.com alameri et al.: manets and internet of things: the development of a data routing algorithm green round circle denotes the sink. the blue round circle denotes the cluster heads. the red and yellow round circles denote the sensors, but red can be the cluster head also. the connection line denotes the path of a single hop from the sensor nodes to the cluster head. in the first scenario, sensors are sending information to the sink over three cluster heads. figure 10 presents the simulation results (a) network lifetime, (b) each node battery energy and (c) dependency of node energy on the number of rounds. fig. 2. optimum number of clusters versus sensors and network size. fig. 3. the test network structure. as can been seen in figure 4, using such information to the routing method network lifetime (dimension is days) is 216, and the fastest losing power nodes 3 and 7. during the analysis of this data, we observe that the consumption of energy distribution is unbalanced in the network and observable the weakness network location. the next simulation step was to use routing change over the simulation period, when the node energy level is lower than the threshold value. figure 5 shows that after 90 rounds (a), the node 4 energy level is lower than the threshold value, therefore the sending information form node 7 we redirect from node 4 to node 3 and from nodes 11–7 to nodes 11–8. the next time (b) after 192 round we change other routes. using this algorithm, our simulation network lifetime was 368 (c). the energy parameters are shown in figure 6. for evaluation of the effectives of our proposed algorithm, further simulations were carried out. the simulation results are presented in figures 7 and 8. by comparing the results, we found that by using our proposed algorithm, the network lifetime is the longest than using simple or clustering without weight routing methods. the main objective of the dynamic cluster head rotation mechanism is to evenly distribute the energy load among all the sensor nodes so that there are no overly utilized sensor nodes that will run out of energy before the others. and we can see that the distribution of network nodes’ energy consumption becomes smoother (figure 8). the assumptions made for compare different routing are as follows: network nodes are homogeneous and not mobility; they are equipped with power control; have active and sleep mode; each sensor has a unique identifier and uniformly deployed over the target area to continuously monitor the environment. fig. 4. simulation results (a) network lifetime, (b) each node battery energy (c) dependency of node energy on the number of rounds. fig. 5. wsn lifetime using a node energy level threshold value for routing change. fig. 6. wsn energy parameters iv. conclusion in this paper, a proposed algorithm of energy efficient and safe‐weighted clustering routing for the mobile iot system using a combination of manet and wsn routing principles is presented. the clustering method is chosen because sensor nodes in a network organize themselves hierarchically. the simulation results show that if we use the combination method for information routing in the wireless sensor network, we increase sensor lifetime in the overall iot system. because we engineering, technology & applied science research vol. 8, no. 1, 2018, 2604-2608 2608 www.etasr.com alameri et al.: manets and internet of things: the development of a data routing algorithm used dynamical cluster head selection, the weighting factors are added for routing from the sensor to the sink. when the network is heterogeneous and mobile, using routing weight is very important mainly due to the network’s dynamic topology. weight function was used to calculate each sensor’s node value and thus the cost of all routes. fig. 7. wsn lifetime using the proposed algorithm fig. 8. wsn energy parameters using the proposed algorithm references [1] i. a. alameri, g. radchenko, “development of student information management system based on cloud computing platform” journal of applied computer science & mathematics, vol. 11, no. 2, pp. :4-19, 2017 [2] itu‐t/recommendation y.2060, overview of the internet of things, available at: 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received: 18 june 2023 | revised: 2 july 2023 | accepted: 3 july 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6132 abstract the adiabatic flame temperature (aft) in combustion represents the maximum attainable temperature at which the chemical energy in the reactant fuel is converted into sensible heat in combustion products without heat loss. aft depends on the fuel, oxidizer, and chemical composition of the products. computing aft requires solving either a nonlinear equation or a larger minimization problem. this study obtained the afts for oxy-methane (methane and oxygen), oxy-hydrogen (hydrogen and oxygen), airmethane (methane and air), and air-hydrogen (hydrogen and air) for stoichiometric conditions. the reactant temperature was 298.15 k (25°c), and the pressure was kept constant at 1 atm. two reaction mechanisms were attempted: a global single-step irreversible reaction for complete combustion and the gri-mech 3.0 elementary mechanism (53 species, 325 steps) for chemical equilibrium with its associated thermodynamic data. nasa cearun was the main modeling tool used. two other tools were used for benchmarking: an excel and a cantera-python implementation of gri-mech 3.0. the results showed that the afts for oxy-methane were 5,166.47 k (complete combustion) and 3,050.12 k (chemical equilibrium), and dropped to 2,326.35 k and 2,224.25 k for air-methane, respectively. the afts for oxy-hydrogen were 4,930.56 k (complete combustion) and 3,074.51 k (chemical equilibrium), and dropped to 2,520.33 k and 2,378.62 k for air-hydrogen, respectively. for eight combustion modeling cases, the relative deviation between the afts predicted by cearun and gri-mech 3.0 ranged from 0.064% to 3.503%. keywords-aft; adiabatic flame temperature; methane; hydrogen, chemical equilibrium with applications; cea; cearun; cantera; gri-mech 3.0 i. introduction combustion is a special case of an exothermic chemical reaction in which a fuel reacts with an oxidizer, and heat is released at a high rate. combustion is an important step in fuelfired thermal power plants [1], cars with internal combustion engines [2], fuel-fired heating systems, and even domestic devices such as cookers with burners or gas-fired water heaters. one of the characteristic features of combustion is the adiabatic flame temperature (aft), which is a theoretical upper limit for the combustion products under the assumption of no heat loss, such as loss due to convective heat transfer with the surroundings. the reaction is treated as occurring at a constant enthalpy and a constant pressure, which this study selected to be the common absolute reference value of 1 atm. the experimental measurement of aft is a very inconvenient and expensive process [3]. estimating aft using computational modeling is a powerful alternative, not just because of the eliminated physical setup and saved time, but also because it allows precise control of various combustion parameters, exploration of different combustion situations, and studying their effect on aft, as well as on the chemical composition of the mixture of combustion products. although the term calculated adiabatic flame temperature (caft) [4-5] can be used to specifically refer to aft estimated numerically rather than obtained experimentally, this study simply uses the term aft as a calculated value or as a concept in combustion science. there is a linear relationship between aft and nitrogen oxide (nox) emissions. nox refers to both nitric oxide (no) engineering, technology & applied science research vol. 13, no. 4, 2023, 11437-11444 11438 www.etasr.com marzouk: adiabatic flame temperatures for oxy-methane, oxy-hydrogen, air-methane, and air-… and nitrogen dioxide (no2) [6], which are air pollutants [7]. thus, a lower aft is desirable to limit the harmful air pollutant. this reduction in aft can be achieved by altering the fuel and blending it with oxygenated fuels, such as methanol or methyl tertiary-butyl ether [8]. high aft that leads to nox emissions can also be avoided by diluting combustion by introducing an excess oxidizer [9] or by exhaust gas recirculation (egr). combustion dilution with an egr rate of 1% (co2 and n2 gases) decreased aft and, thus, reduced nox emissions by approximately 4.98% [10]. the egr rate is the mass fraction of exhaust gas in the intake mixture of fresh air and exhaust gas that goes into the engine [11]. in [12], four different egr rates were investigated for combustion in an internal combustion engine with blended biodiesel fuel. analyzing several engine performance variables, such as engine cylinder temperature and nox, co, hydrocarbon (hc), and soot emissions, it was found that at 100% load, nox reduction was 49.9%, 64.3%, and 73.9% for egr rates of 5%, 10%, and 15%, respectively. in [13], it was shown that flame temperature is the essential cause of nox emissions in gas turbines or premixed-flame combustors because the production of thermal nox is directly related to temperature. in [14], aft and the lower explosion limit (lel) were used to estimate the limiting oxygen concentration (loc) of fuel-air-inert premixed systems, using nitrogen as an inert gas. if the combustion is made free from nitrogen, either in the fuel or in the oxidizer, the problem of nox formation at high temperatures is reduced [15]. there are some applications where an elevated combustion temperature and, thus, a high aft is desirable, such as oxy-acetylene gas welding [16] and magnetohydrodynamic (mhd) power extraction [17-18], where the fluid possesses electric conductivity [19] that is boosted at high temperatures due to partial ionization. the aim of low or high aft can be an important characteristic of a combustion process, which is modeled as a single or a few global chemical reactions, or a larger set of reactions through a detailed reaction mechanism. proper numerical prediction of aft requires a robust tool with sufficient information about the species involved in the reaction, as well as the reactions to be enabled during the modeled combustion process. this study focused on the combustion of two gaseous fuels: methane (ch4) and molecular hydrogen (h2), applying the free online tool cearun [20], which is a web-based version of the cea software. cea performs chemical equilibrium calculations as an optimization problem where the free energy is minimized to find the concentrations of the resultant species that correspond to an arbitrary set of reactant species [21-22]. cea has a long history that dates back to 1962 [23]. compared to the equilibrium constants approach to describe chemical equilibrium, the minimization of free energy approach, such as the gibbs free energy, with a constraint on mass balance [24], as used in cea, has the advantage of not requiring the set of reactions to be specified first. cearun has a large database of 166 species. for each of the two gaseous fuels considered, methane and hydrogen, aft is calculated for two combustion modes: oxyfuel combustion, where the oxidizer is pure molecular oxygen (o2), and air-combustion, where the oxidizer is air. air is conveniently made available in cearun as a single synthetic dry oxidizer species. however, internally it represents a mixture of four gaseous species with the following percentages by mole/volume [25]:  molecular nitrogen (n2): 78.0840%  molecular oxygen (o2): 20.9476%  argon (ar): 0.9365%  carbon dioxide (co2): 0.0319% this is a detailed four-component representation, accounting for even the marginal species of co2. there are studies with simpler three-component representations of air as an n2/o2/ar mixture with mole/volume percentages of 78/21/1% [26] or even just two-component representations as an n2/o2 mixture with mole/volume percentages of 78/22% [27]. for each of the four cases, two fuels and two oxidizers per fuel, two values were calculated for aft depending on the combustion mechanism of how the composition of the combustion product mixture is obtained. in the first type of combustion mechanism, the simplest reaction mechanism was assumed that had a single (one-step) global irreversible reaction, corresponding to complete combustion, where all of the fuel and oxygen react together and none of them appear in the products. in the second type of combustion mechanism, small amounts of reactants and new intermediate species, such as carbon monoxide (co), are allowed according to what a chemical equilibrium state allows, with reversible reactions enabled. the aft in this detailed combustion mechanism is more realistic and should be lower than its approximate value when assuming irreversible single-step combustion. calculating both afts and comparing them gives a measure of the impact of intermediate reaction steps and the level of error caused by the use of the simplest global reaction mechanism. this study calculated a total of eight afts using the cearun tool and eight additional afts as benchmarking values for equivalent conditions using the third version of the detailed reaction mechanism of the gas research institute, gri-mech 3.0. this reaction mechanism allows the inclusion of up to 53 species, with 325 reactions (reaction steps) [28]. therefore, this study presents a total of 16 afts, of which eight principal values were computed using cearun and eight benchmarking values using gri-mech 3.0. of the eight benchmarking cases, four correspond to a simple one-step reaction with complete combustion. in these cases, afts were estimated by solving a nonlinear equation using the microsoft excel goal seek solver [29-30], combined with tabulated data that incorporate several embedded formulas. the thermodynamic coefficients for a polynomial fitting function of the normalized molar enthalpy needed for this calculation were based on gri-mech 3.0, with a small change in the coefficient for n2 to enforce zero enthalpies at the reference temperature of 298.15 k. the low-temperature range coefficient a6l of n2 was changed here from the original value of -1,020.8999 to a new value of -1,021.07188. the air oxidizer engineering, technology & applied science research vol. 13, no. 4, 2023, 11437-11444 11439 www.etasr.com marzouk: adiabatic flame temperatures for oxy-methane, oxy-hydrogen, air-methane, and air-… was represented as a three-component mixture of n2/o2/ar with mole/volume percentages of 78/21/1%. for the other four benchmarking cases, gri-mech 3.0 was used through the open-source cantera library for chemical and thermal applications [31-32]. in this study, cantera was used with python to infer the chemical composition and simultaneously the aft. unlike cearun, gri-mech 3.0 does not have a customized species that acts as air. for the modeling cases where air was the oxidizer, the air was represented as a three-component mixture of n2/o2/ar with mole/volume percentages of 78/21/1%. the cantera version used was 2.6.0 and the version of the python programming environment, as a host for cantera, was 3.8.8. ii. mathematical formulas for gri-mech 3.0 (excel spreadsheet method) this section describes how aft is computed directly using the nonlinear solver tool goal seek in ms excel, using thermodynamic coefficients from gri-mech 3.0 for seven species included in modeling complete combustion. aft is the single unknown variable that satisfies the following condition as a balance of energy under constant overall molar enthalpy (h), during the chemical reaction(s) of the combustion process. the pressure was also kept constant as a second condition to allow reaching a unique solution. ∑ �� �� �����,� �� ������ = ∑ �� �� (��� )����� ��� (1) where ni is the number of moles of the i-th species in the reactants mixture, nj is the number of moles of the j-th species in the products mixture, hi(tini,i) is the molar enthalpy of the ith species evaluated at its initial temperature tini,i, and hj(tad) is the molar enthalpy of the j-th species evaluated at the common final aft (tad) for the product species. in this study, the initial temperature of all reactant species was 298.15 k, which is the reference temperature in cea, where 50 species, such as ar, h2, n2, and o2, have exactly zero enthalpy at that particular temperature [33]. in gri-mech 3.0, the molar enthalpy in a normalized (nondimensional) form is represented as a fifth-order (6-term) polynomial in the absolute temperature t in kelvins [34-35]. � ℜ � = ⎩⎪ ⎪⎨ ⎪⎪ ⎧ !"# + !%# �% + !&# � ' & + !(# � ) ( + !*# � + * + �,-� �.�� ≤ � ≤ �.�� !"� + !%� �% + !&� � ' & + !(� � ) ( + !*� � + * + �,0� �.�� ≤ � ≤ �.�1 (2) where symbol ℜ represents the universal (molar) gas constant, the polynomial coefficients a1l a6l correspond to a lowtemperature subrange for the polynomial from tmin to tmid, and the polynomial coefficients a1h a6h correspond to a hightemperature subrange for the polynomial from tmid to tmax. therefore, each species in gri-mech 3.0 is assigned 15 parameters, 12 polynomial coefficients, and 3 boundary temperatures to describe its molar enthalpy as a function of absolute temperature expressed in kelvins. for most species in gri-mech 3.0 (50 out of the total 53 species), the intermediate temperature tmid is 1,000 k. exceptionally, it is 1,382 k for hcno (fulminic acid), 1,368 k for hocn (cyanic acid), and 1,478 k for hnco (isocyanic acid). the polynomial in (2) was not introduced by ri-mech 3.0 itself but was developed earlier by nasa with two more coefficients, a7l and a7h for the entropy in the lowand the high-temperature subranges, respectively. therefore, this polynomial pattern is one part of three polynomials that are referred to as nasa 7-coefficient polynomials (one more polynomial is used for the molar specific heat capacity at constant pressure cp) regardless of whether the coefficients' values and corresponding temperature limits are provided by nasa itself or not. the gri-mech 3.0 coefficients and temperature subranges are generally different from those published by nasa, with a universal gas constant value of 8.314510 j/mol.k [36], although the variation with temperature is similar for both sets of parameters. the modeled simplified single-step reaction for oxy-fuel complete combustion of methane is: 2�( + 2 4% → 24% + 2 �%4 (3) the modeled simplified single-step reaction for oxy-fuel complete combustion of hydrogen is: 2 �% + 4% → 2 �%4 (4) the modeled simplified single-step reaction for air-fuel complete combustion of methane is: 2�( + 2 4% + 7.42857 ;% + 0.09524 >? → 24% + 2 �%4 + 7.42857 ;% + 0.09524 >? (5) the modeled simplified single-step reaction for air-fuel complete combustion of hydrogen is: 2 �% + 4% + 3.71429 ;% + 0.04762 >? → 2 �%4 + 3.71429 ;% + 0.04762 >? (6) the procedure of solving for aft requires solving a nonlinear equation in a single unknown. the pressure value is irrelevant in this procedure and does not impact the estimated aft. this corresponds to an ideal gas assumption, where the molar enthalpy of a gaseous species is a function of its temperature only and is independent of pressure [37]. iii. results figures 1-7 show the visual illustration of the normalized polynomial functions for the molar enthalpy for the seven species that appear in the complete combustion reactions of ar, ch4, co2, h2, h2o, n2, and o2, respectively. the profiles presented in these figures are for the non-dimensional quantity described by (2), with coefficients based on gri-mech 3.0 for one profile and based on nasa (1993 edition) values for the other. the total range of temperature associated with the polynomial coefficients from tmin to tmax is mentioned, for both the gri-mech 3.0 and the 1993 nasa coefficients. for these seven species, the intermediate temperature (tmid) separating the lowand high-temperature subranges is the same for both sets of polynomial coefficients, being 1,000 k. the figures show the smooth transition at tmid. engineering, technology & applied science research vol. 13, no. 4, 2023, 11437-11444 11440 www.etasr.com marzouk: adiabatic flame temperatures for oxy-methane, oxy-hydrogen, air-methane, and air-… fig. 1. normalized molar enthalpy of ar versus temperature as described by two 6-term polynomials. fig. 2. normalized molar enthalpy of ch4 versus temperature as described by two 6-term polynomials. fig. 3. normalized molar enthalpy of co2 versus temperature as described by two 6-term polynomials. fig. 4. normalized molar enthalpy of h2 versus temperature as described by two 6-term polynomials. fig. 5. normalized molar enthalpy of h2o versus temperature as described by two 6-term polynomials. fig. 6. normalized molar enthalpy of n2 versus temperature as described by two 6-term polynomials. fig. 7. normalized molar enthalpy of o2 versus temperature as described by two 6-term polynomials. the nasa coefficients for these seven species were designed for a wider temperature range with an uppertemperature limit of 6,000 k, while the upper-temperature limit for gri-mech 3.0 is 3,500 k for five species and 5,000 k for ar and n2. such a very hot temperature allowed by the nasa coefficients is not common in terrestrial combustion applications, and thus the gri-mech 3.0 narrower temperature range is generally reasonable. the two profiles are in good agreement for ar, co2, h2o, and n2. no noticeable deviation occurs for ch4, h2, and o2 before approximately 5,000 k. since the maximum aft predicted using gri-mech 3.0 for oxy-methane with assumed complete combustion was 5,153.6 k, which is not far from 5,000 k, the use of gri-mech 3.0 was engineering, technology & applied science research vol. 13, no. 4, 2023, 11437-11444 11441 www.etasr.com marzouk: adiabatic flame temperatures for oxy-methane, oxy-hydrogen, air-methane, and air-… considered acceptable despite being used outside the exact temperature range of its polynomial coefficients in some cases. figure 8 shows how the dimensional molar enthalpy for the seven selected species varied with the absolute temperature according to the polynomial coefficients of gri-mech 3.0. to convert from a non-dimensional version of the molar enthalpy to the dimensional version, the value of 8.314510 j/mol.k was used for the universal gas constant, ℜ. fig. 8. molar enthalpy (based on gri-mech 3.0 coefficients) of the 7 species that appear in the single-step complete combustion reaction of ch4 (in air or oxygen) or h2 (in air or oxygen). the used value of the universal gas constant was cited by nasa in its 1993 edition of the 7-coefficient fitting functions for thermodynamic properties and is the same value published later with an extended version (nasa 9-coefficient polynomial fitting functions) in 2002, where the non-dimensional molar enthalpy was also allowed to depend on 1/t 2 and ln(t)/t [38], and thus two terms were added to the fitting function. cea used this newer 9-coefficient fitting structure, but gri-mech 3.0 uses the original 7-coefficient polynomial structure. this is justifiable, because the increased complexity in the newer fitting function may not necessarily increase the fitting accuracy within the temperature range of interest for grimech 3.0 applications, while the newer fitting functions enabled very large temperatures up to 20,000 k. the cearun values were considered the principal, more accurate values, while the gri-mech 3.0 values were considered supplementary benchmarking values for comparison. table i lists the computed aft for oxy-methane complete combustion. the cearun value 5,166.47 k was very close to the gri-mech 3.0 prediction using the ms excel goal seek tool (5,153.68 k), and the relative deviation was only 0.248%. table ii shows that the oxy-hydrogen complete combustion aft from cearun was 4,930.56 k, which is 235.91 k lower than that of methane, and gri-mech 3.0 provided a lower prediction by 40.35 k. table i. aft for oxy-methane combustion single-step complete combustion cearun gri-mech 3.0 (excel) aft 5,166.47 k 5,153.68 k absolute difference 12.79 k absolute difference as a percentage of cearun value 0.248% table ii. aft for oxy-hydrogen combustion single-step complete combustion cearun gri-mech 3.0 (excel) aft 4,930.56 k 4,890.21 k absolute difference 40.35 k absolute difference as a percentage of cearun value 0.818% as shown in tables iii and iv, changing the oxidizer from pure oxygen to air significantly reduces aft for both fuels when assuming complete combustion. the reduction was 2,840.12 k for methane (55.0% aft in oxy-fuel complete combustion), and 2,410.23 k for hydrogen (48.9% aft in oxyfuel complete combustion). with air as the oxidizer, the complete combustion of hydrogen is hotter than that of methane. this is opposite to the situation of oxy-fuel complete combustion, with the difference in the estimated aft being 193.98 k. the relative deviation between gri-mech 3.0 and cearun is small, less than 0.2%, for either fuel. table iii. aft for air-methane combustion single-step complete combustion cearun gri-mech 3.0 (excel) aft 2,326.35 k 2,330.55 k absolute difference 4.20 k absolute difference as a percentage of cearun value 0.181% table iv. aft for air-hydrogen combustion single-step complete combustion cearun gri-mech 3.0 (excel) aft 2,520.33 k 2,524.36 k absolute difference 4.03 k absolute difference as a percentage of cearun value 0.160% investigating the afts in tables v-viii, when chemical equilibrium is used as the criterion to find the composition of the combustion products rather than enforcing a specific composition with a few species, reveals the impact of using a detailed realistic reaction mechanism or allowing for more species to appear through chemical equilibrium computation. the aft of oxy-fuel and air-fuel combustion of methane decreased by 2,116.35 k and 102.10 k, which is 41.1% and 4.39% of the respective complete combustion values, respectively. the aft of oxy-fuel and air-fuel combustion of hydrogen decreased by 1,856.05 k and 141.71 k, which is 37.6% and 5.62% of the respective complete combustion values, respectively. for both fuels, the effect of applying equilibrium computation is relaxed in air-fuel combustion, where the aft is already much lower than its higher value engineering, technology & applied science research vol. 13, no. 4, 2023, 11437-11444 11442 www.etasr.com marzouk: adiabatic flame temperatures for oxy-methane, oxy-hydrogen, air-methane, and air-… with oxy-fuel combustion. as an additional remark, the relative deviation between the aft predictions of cearun and the cantera implementation of gri-mech 3.0 for oxy-fuel combustion is much smaller, less than 0.08% for methane or hydrogen, than for air-fuel combustion (3.06% for methane and 3.50% for hydrogen). table v. aft for oxy-methane combustion chemical equilibrium combustion cearun gri-mech 3.0 (cantera) aft 3,050.12 k 3,052.06 k absolute difference 1.94 k absolute difference as a percentage of cearun value 0.064% a a. smallest magnitude of the relative deviation among all 8 cases. table vi. aft for oxy-hydrogen combustion chemical equilibrium combustion cearun gri-mech 3.0 (cantera) aft 3,074.51 k 3,076.92 k absolute difference 2.41 k absolute difference as a percentage of cearun value 0.078% table vii. aft for air-methane combustion chemical equilibrium combustion cearun gri-mech 3.0 (cantera) aft 2,224.25 k 2,156.25 k absolute difference 68.00 k absolute difference as a percentage of cearun value 3.057% table viii. aft for air-hydrogen combustion chemical equilibrium combustion cearun gri-mech 3.0 (cantera) aft 2,378.62 k 2,295.29 k absolute difference 83.33 absolute difference as a percentage of cearun value 3.503% a a. largest magnitude of the relative deviation among all 8 cases. iv. conclusions this study calculated 16 aft values for stoichiometric combustion for different methane and hydrogen combustion conditions. reactants were specified so that no excess fuel or oxidizer exists beyond what is theoretically needed for complete combustion. the initial temperature was 298.15 k as a common reference value and the absolute pressures were kept constant at a common reference value of 1 atm. half of the total cases, 8 out of 16, corresponded to methane gas, and the other half corresponded to molecular hydrogen gas. for each fuel, half of the cases, 4 out of 8 per fuel, corresponded to the use of pure oxygen as oxidizer, and the other half corresponded to the use of a mixture that mimicked dry air. for each oxidizer type, two ways were used to specify the final composition after combustion, namely, by enforcing a complete combustion, the simplest modeling method, or solving a chemical equilibrium problem that requires more computations. finally, for each way of specifying the final mixture, one case was modeled using the web-based tool cearun by nasa, while another supplementary case was modeled using the gri-mech 3.0 reaction mechanism either through ms excel or through the cantera python add-on package. the results show that oxycombustion is capable of reaching much higher temperatures than air-combustion, since the difference was 825.87 k in the case of methane and 695.89 k in the case of hydrogen. furthermore, simplified global reaction mechanisms can give a reasonable estimation of aft in air-fuel combustion when compared with detailed mechanisms, but they are largely inaccurate for oxy-fuel combustion. the study also showed that the cantera package with the embedded gri-mech 3.0 is relatively accurate for estimating aft, as it gave values similar to those obtained by the more comprehensive tool cearun. this study can be useful in the broad fields of combustion modeling, numerical simulation, and curve-fitting of thermodynamic properties through the following:  quantitatively identify the afts of two specific fuels with conventional air-combustion and non-conventional oxycombustion, under clearly described conditions. the modeled cases are reproducible for verification or use as test cases for an independent modeling tool, and for problems that need a good estimate of combustion peak temperatures.  provided examples that showed the impact of simplification in modeling aft calculations.  proposed a minor correction in one of the gri-mech 3.0 coefficients (for the nitrogen diatomic gaseous species) providing details and justification.  presented a validation analysis for cantera as a tool for computing aft through the reported relative deviation when compared to the more-detailed nasa-developed cearun tool for methane and hydrogen.  can be regarded as an overview of the valuable and free simulation tools of cearun and cantera, as well as the gri-mech 3.0 implementation of the nasa 7-coefficient polynomials, and the difference between this 7-coeffecient version of nasa fitting functions for thermodynamic properties and the newer 9-coefficient version.  the visual comparison between of the results after using the nasa 1993 and the gri-mech 3.0 coefficients to predict the normalized molar enthalpy for different species commonly used in combustion is also a useful component of the current study. in [39], the aft of hydrogen was mentioned as 2,382 k. the current study showed a much larger aft when oxygen was the oxidizer (3,074.51 k). the cited value was close to the value found here for airhydrogen combustion with chemical equilibrium (2,378.62 k). moreover, the cited value was not reproducible, given the lack of knowing the exact initial conditions (reactants temperatures), unless a guess of reasonable values is provided. in the current study, such details are provided. references engineering, technology & applied science research vol. 13, no. 4, 2023, 11437-11444 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[39] k. kikuchi, t. hori, and f. akamatsu, "fundamental study on hydrogen low-nox combustion using exhaust gas selfrecirculation," processes, vol. 10, no. 1, jan. 2022, art. no. 130, https://doi.org/10.3390/pr10010130. microsoft word 16-792-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1294-1296 1294 www.etasr.com soltani: a tunable low noise active bandpass filter using a noise canceling techniqu a tunable low noise active bandpass filter using a noise canceling technique n. soltani department of electrical engineering, malayer branch islamic azad university malayer, iran soltani.2000@yahoo.com abstract—a monolithic tunable low noise active bandpass filter is presented in this study. biasing voltages can control the center frequency and quality factor. by keeping the gain constant, the center frequency shift is 300 mhz. the quality factor can range from 90 to 290 at the center frequency. by using a noise cancelling circuit, noise is kept lower than 2.8 db. the proposed filter is designed using mmic technology with a center frequency of 2.4 ghz and a power consumption of 180 mw. ed02ah technology is used to simulate the circuit elements. keywords-microwave monolithic integrated circuit (mmic;, bandpass filter; quality factor; noise cancelling i. introduction a good noise figure (nf) performance in most circuit is necessary. for example, a good low noise amplifier (lna) design becomes very important because it is one of the key circuit blocks in a radio receiver system. since the lna can be directly added to the first stage in the receive path, it usually dominates the nf and the bandwidth in the receiver, and a variable gain lna can improve the dynamic range of the whole receiver [1]. especially in mobile communication or video electronic products, an lna with good nf performance wide bandwidth and larger dynamic range in its specification is needed. various applications of microwave frequencies have found special attention in different criteria. tunable filters in high frequency ranges have several advantages. they can reduce the complexity of a system avoiding the introduction of filter banks. multi band telecommunication systems, radiometers, and wideband radar systems are some of the applications of such filters. previous tuning methods include adjusting the cavity dimensions of the resonators or altering the resonant frequency of a ferromagnetic yttrium-iron-garnet element. new approaches are based on solid state varactor diodes [2, 3]. in this paper, a tunable low noise active bandpass filter using a noise canceling circuit is designed. we propose the design of a bandpass filter in which its nf is better than 2.8 db and its gain is more than 20 db. two dc voltages are used to bias varactor diode in such a way that the center frequency and quality factor would be controlled using these voltages [4]. ii. filter structure figure 1 shows the block diagram of the desired filter. this filter is consisted of six parts: an amplifier, the lc tank, the negative conductance and the noise canceling circuit. moreover, common gate and common drain structures are used to realize input and output impedance matching respectively. the resulted bandpass filter is shown in figure 2. in this filter, negative conductance is added to the lossy lc tank. as a result, quality factor increases. in the proposed circuit, the feedforward noise-canceling technique [5, 6] is used. the circuit of the feedforward noise canceling technique is composed of an input transistor, a resistance, feedforward voltage amplifier and one adder. by using common drain and common source structure, the noise of input transistor is effectively canceled, but again in this technique the noise of the feedforward voltage amplifier and the adder is not canceled. moreover, the noise of resistance is partly contributed in the signal. fig. 1. block diagram of desired filter iii. simulation results simulation results are shown in figure 3 to illustrate gain, input and output impedance matching and noise figure respectively. by inspections of these figures, one can see that the scattering parameters s11, s22 are in the desirable situation and by using the noise canceling circuit, the noise figure is kept under 2.8db. iv. frequency displacement we use the biasing voltage of varactor diodes to perform the frequency sweep. vf in figure 2 biased the varactor diode and the capacity would change due to the applied voltage. this engineering, technology & applied science research vol. 6, no. 6, 2016, 1294-1296 1295 www.etasr.com soltani: a tunable low noise active bandpass filter using a noise canceling techniqu voltage sweeps the frequency and shifts the center frequency. the frequency displacement is about 300 mhz. the simulation results and scattering parameters are illustrated in figure 4. by inspections of these figures, one can see that the scattering parameters are in desirable situation. the stability of this filter has been studied by rollett coefficient (k). this coefficient is always greater than one [7]. table i shows the magnitude of vf in each center frequency. also measured quality factors and gain are presented. fig. 2. the circuit of low noise active bandpass filter fig. 3. simulation results (a) gain parameter; (b) scattering parameters s11, s22 ;(c) noise figure fig. 4. frequency displacement, scattering parameter s11 and s22 and stability factor of the low noise bandpass filter (a) noise cancelling circuit (b) (c) engineering, technology & applied science research vol. 6, no. 6, 2016, 1294-1296 1296 www.etasr.com soltani: a tunable low noise active bandpass filter using a noise canceling techniqu table i. value of vf, ferecuency variation, gain and quality factor of the bandpass filter vf1(v) f0 (ghz) gain (db) q 4.2 2.219 10.02 43 4.4 2.475 16.23 58 5 2.413 13.05 53 5.2 2.477 10.00 48 5.5 2.515 8.76 19 v. increasing the quality factor by using va that is shown in figure 2, in a constant frequency, considerable improvement of gain and quality factor would be possible. this voltage is responsible to control the quality factor. as shown in figure 5 changing this voltage at 2.4 ghz gives considerable increment of quality factor from 90 to 290. we ignored the frequency shift of 50 mhz and the stability factor is also in desirable situation. va, gain, and quality factor of each filter are shown in table ii. fig. 5. quality factor increment and stability factor at 2.4 ghz table ii. value of va, gain and quality factor of bandpass filter va1 (v) gain (db) q 1 13.30 296 2 14.02 219 3 15.11 177 4 15.85 153 5 16.34 131 6 18.00 118 7 20.12 105 8 22.78 96 vi. statistical results in this section we simultaneously exerted 5% tolerance on the measure of 3 elements including resistor, capacitor, and transistor width in the low noise bandpass filter. these variations were completely random. figure 6 shows the simulation results of the combination of ten different situations. fig. 6. scattering parameters as a result of 5% tolerance vii. conclucion a tunable low noise active bandpass filter using feedforward noise canceling technique is presented. controlling the center frequency and quality factor is investigated using two biasing voltages. the center frequency shift is 300 mhz and considerable improvement of quality factors is achieved (from 90 to 290). future work should focus on the estimation of the desired biasing voltages of varactor diodes using a neural network to obtain the specific quality factor and center frequency. also, on using active inductor to decrease the chip area. other noise filters technologies such as bicmos or rfcmos should be evaluated in the same structure. references [1] i. mehr, s. rose, s. nesterenko, d. paterson, r. schreier, h. l’bahy, s. kidambi, m. elliott, s. puckett, “a dualconversion tuner for multistandard terrestrial and cable reception”, ieee vlsi circuits symp dig pp. 340-343, 2005 [2] c . musoll-anguiano, i . llamas-garro, z . brito-brito, l. pradelll, a. corona-chavez, “characterizing a tune all bandstop filter”, ieee mtt-s international microwave workshop series on signal integrity and high-speed interconnects, pp. 55-58, 2009. [3] a. r. brown, g. m. rebeiz, “a varactor tuned rf filter”, ieee transactions on microwave theory and techniques, vol. 46, no. 7, pp. 1157-1160, 2000 [4] a. alahyari, a. habibzadeh, m. dousti, “tunable active dual-band bandpass filter design using mmic technology”, international journal of engineering & technology, vol. 11, no. 1, pp. 11-16, 2011 [5] f. bruccoleri, e. a. m. klumperink, b. nauta, “wide-band cmos lownoise amplifier exploiting thermal noise canceling”, ieee journal of solid-state circuits, vol. 39, no. 2, pp. 275-282, 2004 [6] w. keping, w. zhigong, “a broadband noise-canceling cmos differential lna for 50–860mhz tv tuner”, international conference on microwave and millimeter wave technology, 20-22 dec. 2007 [7] m. dousti, p. langari, "a tunable active recursive filter for communication systems in sige bicmos”, aict 2009. international conference on application of information and communication technologies, 14-16 oct. 2009 microsoft word etasr_v11_n6_pp7763-7769 engineering, technology & applied science research vol. 11, no. 6, 2021, 7763-7769 7763 www.etasr.com abdulkareem et al.: post-fire behavior of non-prismatic beams with multiple rectangular openings … post-fire behavior of non-prismatic beams with multiple rectangular openings monotonically loaded bashar f. abdulkareem department of civil engineering university of baghdad baghdad, iraq bashar.faisal@muc.edu.iq amer f. izzet department of civil engineering university of baghdad baghdad, iraq amer.f@coeng.uobaghdad.edu.iq nazar oukaili department of civil engineering university of baghdad baghdad, iraq nazar.oukaili@coeng.uobaghdad.edu.iq abstract-the main objective of this paper is to study the behavior of non-prismatic reinforced concrete (nprc) beams with and without rectangular openings either when exposed to fire or not. the experimental program involves casting and testing 9 nprc beams divided into 3 main groups. these groups were categorized according to heating temperature (ambient temperature, 400°c, and 700°c), with each group containing 3 nprc beams (solid beams and beams with 6 and 8 trapezoidal openings). for beams with similar geometry, increasing the burning temperature results in their deterioration as reflected in their increasing mid-span deflection throughout the fire exposure period and their residual deflection after cooling. meanwhile, the existing openings situation was compounded. the burned nprc beams were left to gradually cool down under ambient laboratory conditions, and afterward, they were loaded until failure. the influence of temperature on the residual ultimate load-carrying capacity of each beam was studied by comparing these beams with unburned reference beams. increasing exposure temperature reduces the ultimate strength of solid nprc beams exposed to temperatures of 400°c and 700°c by about 5.7% and 10.84% respectively. meanwhile, nprc beams with trapezoidal openings showed ultimate strength reductions of 21.13% and 32.8% (for beams with 8 openings) and 28% and 34.4% (for beams with 6 openings) under the same burning conditions. the excessive mid-span deflections for these three types of beams were 2%–30.8%, 1.33%–21.8%, and 1.5%–17.4% under the same burning conditions. keywords-burning temperature; non-prismatic beams; openings number i. introduction reinforced concrete (rc) is often used in high-rise structures and other buildings. ensuring the fire safety of structural components is an important part of building design because fires are among the most dangerous environmental phenomena that may affect a structure during its life cycle. this requirement can be attributed to the fact that when other fire control measures fail, structural integrity becomes the last line of defense of a building. experimental investigations have been conducted in the past to highlight the effect of fires on the material characteristics of concrete with several mix proportions under different fire scenarios [1-4]. high temperature has been reported to reduce the material characteristics of concrete, including strength [5]. reinforcing steel is more sensitive than concrete at high temperatures [6]. while concrete and steel show a similar thermal expansion at temperatures up to 400°c, the latter significantly expands at higher temperatures. in addition, at 700°c, the steel bearing capacity of these materials reduces by about 20% [7]. structural failure mostly occurs when the reinforcement loses its effective strength via heating. therefore, researchers argue that a reinforcement with adequate cover has a sufficient fire resistance [8]. authors in [9] designed a numerical model in the form of a computer program to track the fire behavior of rc beams over the entire load range from pre-fire conditions to fire collapse. three stages were examined in their analysis, namely establishing the fire temperature–time development, calculating the heat transfer of fire through the structure, and interpreting the structural analysis results. authors in [10] studied the fire resistance of 6 rc beams and found that the fire resistance of hsc beams is lower than that of nsc beams. moreover, hsc beams exhibit a high level of spalling, which is largely affected by concrete permeability, fire exposure type, load level, and restraint conditions. similarly, the type of fire scenario, axial restraint, and load level significantly affect the overall fire resistance of rc beams. authors in [11] tested 9 rectangular beams to study the effect of multiple web openings along the span length of rc beams on their bending behavior. the plastic failure mechanism for beams having multiple openings is much longer than those for beams with a single opening. authors in [12] studied experimentally and theoretically the effect of strengthening on improving the flexural and shear strength of 12 simply supported, high-strength non-prismatic rc (nprc) beams with openings. experimental results show that when nprc beams are strengthened by a carbon fiber bar, the ultimate load for flexural and shear strengths increases by 16% and 15% respectively. authors in [13] investigated 4 rc beams with a rectangular cross-section under 3-point load until failure and found that perforating an rc beam with small web openings slightly reduces its ultimate load and increases its corresponding author: bashar f. abdulkareem engineering, technology & applied science research vol. 11, no. 6, 2021, 7763-7769 7764 www.etasr.com abdulkareem et al.: post-fire behavior of non-prismatic beams with multiple rectangular openings … ultimate deflection. authors in [14] studied the serviceability of reinforced concrete gable roof beams with openings under static loads obtaining good agreement between the analytical and the experimental results. authors in [15] investigated the structural behavior of rc beams with fiber-reinforced polymer (frp) bars and large rectangular openings and found that the presence of openings leads to the early formation of cracks at the locations of these openings. however, no study thus far has examined the high temperature resistance of nprc solid beams or beams with openings. ii. beam setup the experimental part was executed by manufacturing 9 scaled down (1/4) simply supported non-prismatic archetype roof beams. as shown in figure 1, these beams have a width of 10cm, an overall horizontal lower chord length of 300cm, and inclined upper chord heights of 40cm and 25cm at the midspan and ends respectively. all beams were reinforced identically with 4-∅6mm arranged by 2 layers in the top chord and 2-∅6+2-∅ 12mm arranged by 2 layers in the bottom chord (figures 2-4). transverse steel bars made of 6mm steel bars were provided at the solid ends of the solid beam gb and the other test specimens, and the openings were equally spaced at 10cm. closed shear stirrups made of 4mm ordinary steel bars were provided over the entire span of the upper and lower chords of the test sample with 5cm spacing. each beam was tested using a simple scheme with an effective span of 280cm. the tested beams were divided into 3 groups depending on the heating temperature (ambient, 400°c, and 700°c). each of these groups has 3 nprc beams (solid beam, and beams with 6 and 8 trapezoidal openings). (a) (b) (c) fig. 1. schematic layout of nprc beams (all dimensions are in mm). (a) solid nprc beams gb, gb-400, and gb-700, (b) nprc beams with trapezoid openings gt6, gt6-400, and gt6-700, (c) nprc beams with trapezoid openings gt8, gt8-400, and gt8-700. table i and figure 1 show the parametric details of the tested beams, where g denotes the nprc beams, b denotes the beams without openings, and t denotes the ones with trapezoidal openings. the number that follows each symbol represents the number of openings in each specimen. figures 24 show the configuration of the test beams and the reinforcement arrangement of the control and other nprc beams. in all beams with openings, the length of solid ends ranges from 40cm to 50cm to override shear or end bearing failure. meanwhile, a 20cm wide column was directly realized under mid-span load. fig. 2. steel reinforcement of gb, gb-400, and gb-700. section a-a (all dimensions are in mm). fig. 3. details of steel reinforcement of gt6, gt6-400, and gt6-700. sections b-b and c-c/ fig. 4. details of steel reinforcement of gt8, gt8-400, and gt8-700. normal concrete was used in the beams. the characteristics of concrete (e.g. modulus of elasticity, compressive and splitting tensile strength) were measured using steel cylindrical molds with 300mm height and 150mm diameter. the reinforcing steel bars had diameters of 4, 6, and 12mm, and the average yield, ultimate strength, and modulus of elasticity were determined by performing standard tests on the steel bars. the characteristics of the normal concrete and steel reinforcements used in this work are shown in tables ii and iii. engineering, technology & applied science research vol. 11, no. 6, 2021, 7763-7769 7765 www.etasr.com abdulkareem et al.: post-fire behavior of non-prismatic beams with multiple rectangular openings … table i. details of tested nprc beams group id beams id openings shape number of openings total area of openings (mm 2 ) width of openings (mm) ������� ��� �������� fire temperature ( o c) i gb 0 1.0 amb. gt6 trapezoid 6 180000 200 0.81 amb. gt8 trapezoid 8 174000 150 0.81 amb. ii gb-400 0 1.00 400 gt6-400 trapezoid 6 180000 200 0.81 400 gt8-400 trapezoid 8 174000 150 0.81 400 iii gb-700 0 1.00 700 gt6-700 trapezoid 6 180000 200 0.81 700 gt8-700 trapezoid 8 174000 150 0.81 700 table ii. material properties material ø (mm) yield stress (mpa) compressive strength (mpa) ultimate tensile strength (mpa) amb. 400 700 amb. 400 700 amb. 400 700 conc. ----32.6 25 12.6 --- steel 4 390 352 262 ---590 547 456 6 580 524 390 ---650 602 503 12 610 570 496 ---722 657 549 table iii. modulus of elasticity material ø (mm) modulus of elasticity (gpa) amb. 400 700 concrete -26.86 20.1 13.1 steel 4 200 200 194 6 200 200 194 12 200 200 194 iii. testing procedure the experimental program involved casting and testing of the nprc beams. they were monotonically loaded after exposure to high temperatures, as follows: a. burning stage the burning process was conducted in a furnace manufactured with a 4mm thick box-shaped steel plate to restrict heat and to burn one or more nprc beams simultaneously (figure 5). the furnace had an inner clear space of 0.8m height, 2m width, and 3.5m length and had the capability of maintaining 20 methane flames (nozzles). eight compressed air nozzles were positioned at the lower furnace level near the base to maintain enough space underneath the nprc beams, so the flames from the methane would be able to reach the nprc beams, simulating the burning of simply supported nprc beams. the upper level of the furnace had many small openings for thermocouple wires (k-type). the burning stage involved positioning each nprc beam above its idealized simply supported ends and reading the mid-span deflection from dial gauges. the nprc beams and control specimens were exposed to burning temperatures of 400°c or 700°c following the fire standard rate of astm e-119 [16]. the flame was supplied at the lower level of the furnace for an exposure period of 1h after reaching the target temperature. after this period, the flame was turned off, the furnace cover was removed, and the nprc beams were gradually cooled down under ambient air. fig. 5. furnace and burning process. b. load test stage figure 6 presents a schematic of the test setup. the nprc beams were simply supported by steel rollers with a solid steel plate. the left roller was welded to the bearing plate to simulate hinge support, whereas the right roller was not welded. to eliminate the difference in load due to the variations in the sizes and locations of the openings, the load was applied on a thick 10cm × 10cm steel plate positioned at the tapered crest end of a non-prismatic beam that was flatted horizontally. a hydraulic jack with a 50-ton capacity was used to apply load on the beams. the applied load was controlled using a load cell with a digital load reader. the load was applied with 2.5kn increments. a dial indicator was used to measure the vertical deflection at 150mm from the support, under each post, and at the mid-span. the beam was loaded until failure. deflection and the resulting strain were measured, the crack propagation engineering, technology & applied science research vol. 11, no. 6, 2021, 7763-7769 7766 www.etasr.com abdulkareem et al.: post-fire behavior of non-prismatic beams with multiple rectangular openings … was marked, and the crack width was measured at different load levels. fig. 6. test setup. iv. experimental results and discussion a. deflection at burning and cooling stages the target temperatures of 400°c and 700°c were reached after 7 and 10min respectively. they are approximately similar to those specified in astm e-119 [15] as shown in figure 7. after removing the furnace cover, the nprc beams were gradually cooled under ambient laboratory conditions. fig. 7. fire scenarios used in the burning test. fig. 8. history of mid span deflection group 400. figures 8 and 9 present the mid-span deflection versus time history of groups exposed to similar burning conditions. groups 400 and 700 correspond to the burning temperatures of 400°c and 700°c respectively. the mid-span deflection rate caused by heating increased through the burning periods of rising and target temperatures. thereafter, some of this deflection was restored during the cooling (third) period. meanwhile, the nprc beams with openings demonstrated a higher deflection increase rate after heat exposure. the recovery rate of gt6 was slightly greater than that of gt8. table iv presents the effect of openings, burning temperatures, and residual deflection of nprc beams at each exposure period. fig. 9. history of mid span deflection group 700. table iv. residual deflection at the end of the burning period and the cooling cycle. group beam id residual deflection at the third period (mm) nprc beams (with/ without) openings (%) nprc beams exposed to (700/400) o c (%) 400 gb-400 2.31 100 159 gt8-400 3.32 143 148 gt6-400 3.43 148 154 700 gb-700 3.67 100 gt8-700 4.92 134 gt6-700 5.27 143 b. monotonic load test post fire results 1) cracking and failure loads and modes of failure visible or not, most nprc beams cracked evenly during the fire exposure test stage. the first crack load is indicative of two things, the flexural crack load or the widening of post-fire cracks. all nprc beams cracked during the loading stage for loads varying between 17.5% and 23.5% of the corresponding load of failure. such disparity between cracking and the ultimate loads was clear for the unburned nprc beams (17.5%–20%) and decreased along with increasing temperature (20%–23.2% and 19.9%–23.5% at 400°c and 700°c respectively) as shown in table v. figure 12 shows the crack patterns of the tested beams. in all nprc beams, cracking occurred at loads below their respective service loads, although the ultimate load decreased with increasing temperature. therefore, the trustworthy design of these structural elements may be controlled by serviceability requirements. the average crack spacing was 60mm to 75mm for the nprc beams in the unburned group, 55mm to 70mm for the nprc beams exposed to 400°c, and 50mm to 65mm for the beams exposed to 700°c. engineering, technology & applied science research vol. 11, no. 6, 2021, 7763-7769 7767 www.etasr.com abdulkareem et al.: post-fire behavior of non-prismatic beams with multiple rectangular openings … table v. cracking and ultimate loads of the tested nprc beams group beam id no. of openings net area of the beam ��� (mm 2 ) first cracking load ��� (kn) ��� ���,�� ( % ) ��� ���,�� ( % ) failure load ���� ( kn ) ��� ���� ( % ) unburned gb -----982500 18 ----------90 20 gt6 6 802500 14 81.7 77.8 77.8 18 gt8 8 808500 14 82.3 77.8 80.2 17.5 400 gb-400 -----982500 17 ----------84.91 20 gt6-400 6 802500 13 81.7 76.5 56 23.2 gt8-400 8 808500 13 82.3 76.5 63.25 20.6 700 gb-700 -----982500 16 ----------80.24 19.9 gt6-700 6 802500 12 81.7 75 51.06 23.5 gt8-700 8 808500 12 82.3 75 53.9 22.3 relatively short surface hairline cracks began to form at 400°c and became very obvious at 700°c. apart from the effect of temperature, figures 10-11 show the correlation between the savings in concrete used in producing the tested nprc beams with openings and the percentage reduction in the load carrying capacity of these members. the maximum ratio of reduction in concrete consumption to the reduction in load-carrying capacity for nprc beams with openings was 1.72 for gt8 at ambient temperature, whereas the minimum ratio was 0.45 for gt6 exposed to 700°c. meanwhile, the ratio of reduction in concrete consumption to the reduction in loadcarrying capacity decreased along with increasing burning temperature. due to the exposure circumstance, the denominator (load-carrying capacity) showed a greater reduction than the numerator (concrete consumption). comparing the nprc beams with 8 openings with those having 6 openings reveals that the ultimate load-carrying capacity increased by 3.1%, 13%, and 5.5% at ambient temperature of 400°c, and 700°c respectively. fig. 10. effect of openings and the temperature on the ultimate capacity. fig. 11. failure load vs. exposure temperatures. (a) (b) (c) (d) (e) (f) (g) (h) (i) fig. 12. crack patterns. (a) gb, (b) gt6, (c) gt8, (d) gb-400, (e) gt6400, (f) gt8-400, (g) gb-700, (h) gt6-700, (i) gt8-700. engineering, technology & applied science research vol. 11, no. 6, 2021, 7763-7769 7768 www.etasr.com abdulkareem et al.: post-fire behavior of non-prismatic beams with multiple rectangular openings … 2) load-deflection relationship tables vi, vii and figures 13-15 show the mid-span deflection at different loading stages (20kn, 40kn, and ultimate load). at the ultimate load, the excessive mid-span deflection increased for the nprc beams with openings. the mid-span deflections of beams exposed to ambient temperature, 400°c, and 700°c ranged from 42.3% to 57.7%, 41.6% to 57%, and 32.4% to 41.5% respectively, depending on the number of posts between the openings and their total area. the stiffness of all nprc beams decreased with increasing burning temperature due to the deterioration of concrete during its exposure to fire, which in turn led to the increased deflection of these beams. a high rate of defects was observed at 700°c. table vi. load for tested nprc beams at ultimate stage group beam id openings number failure load ���� ( k n ) percentage of reduction (%) gb gb --90.0 --- gb-400 --84.9 5.7 gb-700 --80.24 10.8 gt8 gt8 8 80.2 --- gt8-400 8 63.25 21.13 gt8-700 8 53.9 32.8 gt6 gt6 6 77.8 --- gt6-400 6 56.0 28 gt6-700 6 51.1 34.3 table vii. load and corresponding deflection for the tested nprc beams at different loading stages and fire exposure conditions group beam id at 20 kn at 40 kn at ultimate load failure load ���� ( kn ) percentage of reduction (%) deflection (mm) percentage of increase (%) deflection (mm) percentage of increase (%) deflection (mm) percentage of increase (%) unburned gb 2.62 -----6.4 ---16.8 ---90.0 --- gt6 4.02 53.4 9.96 55.6 26.5 57.7 77.8 13.6 gt8 2.76 5.3 8.36 30.6 23.9 42.3 80.2 10.9 400 gb-400 4.43 ---8.32 ---17.1 ---84.9 --- gt6-400 6.28 41.8 13.76 65.4 26.9 57.0 56.0 34 gt8-400 5.11 15.3 11.61 39.5 24.2 41.6 63.25 25.5 700 gb-700 5.43 ---10.4 ---21.9 ---80.24 --- gt6-700 10.1 86.3 19.8 90 31.1 41.5 51.1 36.4 gt8-700 7.43 36.8 18.1 74 29.1 32.4 53.9 32.8 fig. 13. load-deflection curves, gb group. fig. 14. load-deflection curves, gt8 group. fig. 15. load-deflection curves, gt6 group. v. conclusions • increase in the burning temperature increased the mid-span deflection of nprc beams at all burning and cooling cycle periods. a similar increase was reported for residual deflection, which amounted to 143% and 148% for beams with 8 and 6 openings, respectively, at 400°c and to 134% and 143% at 700°c. • cracks began to form on the concrete surfaces of nprc beams after the burning and cooling processes. the number and width of cracks increased with burning temperature. • all nprc beams cracked during the loading stage at 17.5% to 23.5% of the corresponding failure load. the disparity between cracking and ultimate loads was obvious among the unburned nprc beams (17.5% to 20%) and decreased with increasing temperature (20%–23.2% and 19.9%– 23.5% at 400°c and 700°c burning temperatures). engineering, technology & applied science research vol. 11, no. 6, 2021, 7763-7769 7769 www.etasr.com abdulkareem et al.: post-fire behavior of non-prismatic beams with multiple rectangular openings … • increase in the exposure temperature reduced the ultimate strength of solid nprc beams by about 5.7% and 10.84% after exposure to 400°c and 700°c. the corresponding reductions for nprc beams with 8 and 6 trapezoidal openings were 21.13%–32.8% and 28%–34.4% respectively. under these same conditions, the excessive mid-span deflections for these beams were 2%–30.4%, 1.3%–21.8%, and 1.5%–17.4% for ambient temperature, 400°c, and 700°c respectively. • for the same length of extended beams, increasing the number of openings with a small area, which coincides with reducing the total area of openings by increasing the number of posts, improved the flexural behavior of nprc beams. relative to that of beams with 6 openings, the loadcarrying capacity of nprc beams with 8 openings increased by 3.1%, 13.0%, and 5.5% when exposed to ambient temperature, 400°c, and 700°c respectively. references [1] y. f. chang, y. h. chen, m. s. sheu, and g. c. yao, "residual stress– strain relationship for concrete after exposure to high temperatures," cement and concrete research, vol. 36, no. 10, pp. 1999–2005, oct. 2006, https://doi.org/10.1016/j.cemconres.2006.05.029. 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[17] a. h. buller, m. oad, and b. a. memon, "flexural strength of reinforced concrete rac beams exposed to 6-hour fire – part 2: rich mix," engineering, technology & applied science research, vol. 9, no. 1, pp. 3814–3817, feb. 2019, https://doi.org/10.48084/etasr.2494. microsoft word 15-729-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1195-1199 1195 www.etasr.com elsharkawi et al.: a novel image stream cipher based on dynamic substitution a novel image stream cipher based on dynamic substitution abdelfattah elsharkawi software engineering, communication engineering al-azhar university cairo, egypt sharkawi_eg@yahoo.com ragab m. el-sagheer software engineering, communication engineering al-azhar university cairo, egypt relbakar@gmail.com haitham akah space communication national authority for remote sensing and space science, cairo, egypt haitham_akah@narss.sci.eg hatem taha space communication national authority for remote sensing and space science, cairo, egypt hatem.taha@narss.sci.eg abstract—recently, many chaos-based stream cipher algorithms have been developed. traditional chaos stream cipher is based on xoring a generated secure random number sequence based on chaotic maps (e.g. logistic map, bernoulli map, tent map etc.) with the original image to get the encrypted image, this type of stream cipher seems to be vulnerable to chosen plaintext attacks. this paper introduces a new stream cipher algorithm based on dynamic substitution box. the new algorithm uses one substitution box (s-box) and a chaotic shuffling process. each byte in the plain image vector is substituted using a different sbox to get the cipher image vector. this algorithm is designed to be invulnerable to chosen plaintext attacks. in addition, this algorithm is more secured compared to conventional stream cipher. keywords-chaos; encryption; plain image; stream cipher; substitution box. i. introduction a huge amount of digital data (voices, images and video) is transferred from point to point on various global networks (internet, mobile networks, remote sensing satellites and others). it is necessary to protect such data from unauthorized interception or tampering on the open network. cryptography is the science that aims to hide (encrypt) the meaning of a message and splits into three main branches: symmetric cipher, asymmetric cipher and protocols [1]. cryptographic protocols are (roughly speaking), crypto protocols that deal with the application of cryptographic algorithms. symmetric and asymmetric algorithms can be viewed as building blocks with which applications such as secure internet communication can be realized. the transport layer security (tls) scheme, which is used in every web browser, is an example of a cryptographic protocol [2]. also, it can be defined as a series of steps, involving two or more parties, designed to accomplish a task [2]. asymmetric algorithms (also called public-key algorithms) are designed so that the key used for encryption is different from the key used for decryption. these algorithms are called “public-key” because the encryption key can be made public: a complete stranger can use the encryption key to encrypt a message, but only a specific person with the corresponding decryption key can decrypt the message. in these systems, the encryption key is often called the public key, and the decryption key is often called the private key. the private key is sometimes also called the secret key [2]. symmetric algorithms (sometimes called conventional algorithms) are used where the encryption key can be calculated from the decryption key and vice versa. in most symmetric algorithms, the encryption key and the decryption key are the same. these algorithms are also called secret-key algorithms, single-key algorithms, or one-key algorithms [2]. symmetric ciphers itself split into stream and block cipher. block ciphers encrypt an entire block of plaintext bits at a time with the same key. this means that the encryption of any plaintext bit in a given block depends on every other plaintext bit in the same block. in practice, the vast majority of block ciphers either has a block length of 128 bits (16 bytes) such as the advanced encryption standard (aes), or a block length of 64 bits (8 bytes) such as the data encryption standard (des) or triple des (3des) algorithm. stream ciphers encrypt bits or bytes individually. this is achieved by adding a bit or byte from a key stream to a plaintext stream. there are synchronous stream ciphers where the key stream depends only on the key and asynchronous ones where the key stream also depends on the cipher text. if the dotted line in figure 1 is present, the stream cipher is an asynchronous one. most practical stream ciphers are synchronous ones. when dealing with cryptographic applications, linear methods for generating pseudo-random sequences like linear feedback shift registers (lfsrs), linear conjugate gradient (lcgs) or their proper combinations are highly not recommended, since efficient algorithms are at disposal to predict the sequence on the basis of a relatively short sequence observation [3]. chaos is a fascinating phenomenon that has been observed in nature (weather and climate, dynamics of satellites in the solar system, time evolution of the magnetic field of celestial bodies, and population growth in ecology) and laboratory (electrical circuits, lasers, chemical reactions, fluid dynamics, mechanical systems, and magneto-mechanical devices and others). due to the inherent properties of chaotic systems such as statistical ergodicity, pseudo-randomness, and sensitivity to initial conditions and control parameters, the chaotic systems has been extensively applied in cryptography engineering, technology & applied science research vol. 6, no. 5, 2016, 1195-1199 1196 www.etasr.com elsharkawi et al.: a novel image stream cipher based on dynamic substitution [4]. s-boxes have been widely used as a base of new encryption strategies due to their properties such as nonlinearity, differential uniformity, and strict avalanche criterion. recently, the use of s-box became popular in image ciphers as a main approach to performing substitution. in this paper a new proposed stream cipher for the images is introduced based on chaotic substitution box which can be considered as a basic nonlinear component of symmetric key algorithms. fig. 1. synchronous and asynchronous stream ciphers ii. related work recently many chaotic key based image stream ciphers have been proposed. in [5] a chaotic key-based design for image encryption and decryption in which the gray level of each pixel is xored or xnored bit-by-bit to one of the two predetermined keys was introduced. this paper kept focus on three main factors i.e. high security, low computation and no distortion. in [6], an image algorithm that encodes digital images pixel by pixel was proposed. this algorithm then uses stream cipher that encrypts each pixel using a special mathematical set of functions known as the key. this algorithm uses the same key at both the sending and the receiving ends. some image encryption algorithms have been also recently proposed based on chaotic substitution. in [7], an image encryption algorithm based on the theory of s-box in advanced encryption standard (aes) was proposed. thirty different s-boxes structured by different irreducible polynomials were used. each element in the s-boxes is numbered from 0 to 255, and is one to one mapped. the algorithm uses logistic map which is based on a chaotic map as one s-box of the 30 s-boxes will be used in the byte substitution process until finishing the whole encrypting image. in [8], an image encryption algorithm in which an external 256-bit key is used while the last pixel of plain image is used to generate the parameters and the initial states of the chaotic systems for the first s-box was proposed. the plain image is divided into groups in which the pixels are substituted by s-boxes. the image pixels are divided to several groups according to rows and adjacent rows are collected in different groups. for each group, a new s-box is generated and used. by this way, the corrections between vertical adjacent pixels are smashed. and then the same method on columns in order to smash its corrections between horizontal adjacent pixels is used. in [9], an image encryption algorithm based on circular substitution box and key stream buffer was suggested. the s-box is considered as a circular sequence with a head pointer in this case, and each image pixel is replaced with an element of an s-box according to both the pixel value and the head pointer, the head pointer varies with the previous substituted pixel. it is found that some s-box-only ciphers are vulnerable to chosen plaintext attacks. in [10], the security issues for s-box-only image ciphers and presented a successful cryptanalysis was carefully studied. iii. proposed algorithm image data have special properties such as bulk capacity, high redundancy and high correlation among the pixels that imposes special requirements on any encryption technique [11]. the proposed algorithm was designed to match the image special properties and get a high speed processing on the hardware devices such as fpga or asic. the inter-pixel displacement or shifting of the image pixels, where pixels are completely moved from its position to a new position has been used in image encryption [12, 13]. in the proposed algorithm such displacement shall be applied to the s-box, where the positions of a dynamic substitution box contents will be used in displacement rather than using inter pixel displacement of images. a dynamic (16*16) s-box is used to substitute the input byte (image pixel) by another one, based on the input image byte and the logistic map output. this map is used to generate the chaotic keys which are used to shuffling the substitution box contents to get a dynamic substitution box. xn = r * xn-1 * ( 1 xn-1 ) (1) where r is the control parameter. the logistic map represents nothing more than an idealized population model. the proposed algorithm consists of four main blocks as shown in figure 2. the four blocks are the input (initial) substitution box, the shuffling keys generator block (e.g. two chaotic generators of logistic maps may be used to generate two keys, namely row key (rkey) and column key (ckey), the shuffling block and the substitution stage (output s-box). fig. 2. block diagram of proposed algorithm a. encryption steps • the plain image (indicated early or real stream) will be constructed as a stream vector of bytes, assuming a plain image p has n bytes, and then having engineering, technology & applied science research vol. 6, no. 5, 2016, 1195-1199 1197 www.etasr.com elsharkawi et al.: a novel image stream cipher based on dynamic substitution p = {p0, p1, …, pn-1} (2) • for each plain image byte, there are two 64 bit keys (rkey, ckey) which will be generated from logistic map generators, forming: rkey = {rkey0, rkey1, …, rkeyn-1} (3) ckey = {ckey0, ckey1, …., ckeyn-1} (4) • each generated key is divided into 4 bit sub rotation keys to get (16 row keys) + (16 column keys). • initial s-box matrix (16 * 16) is constructed as shown in figure 3. each element in the s-box is numbered from 0 to 255, and is one to one mapped. fig. 3. initial s-box • perform row shuffling (rotation) using rkey for the s-box (as indicated). • after finishing the row rotation, an intermediate s-box will be released. • perform column shuffling (rotation) using ckey for the intermediate s-box (after row shuffling). • after shuffling the initial s-box using row and column rotations, the newly constructed s-box will be used to get the encrypted value and will also be used as input s-box for the next generation samples (rotation keys). • the previous steps will be repeated until the end of the plain image. b. decryption steps the decryption steps are similar to the encryption steps. they use cipher image instead of plain image and inverse sbox instead of s-box but the same chaotic generators are used with the inverse of the initial s-box. due to random shuffling block, there are exhaustive number of s-boxes that can be constructed and used to substitute the plain image. additionally, the encrypted image is sensitive to the initial sbox which make the proposed algorithm robust to the chosen plaintext attacks and suitable for (huge images) such as remote sensing satellite images and video streams. hardware implementation can be used to increase the encryption speed, and hence realizing a real time algorithm. iv. results and discusion a good encryption algorithm should be robust against most kinds of known cryptanalytic, statistical and brute-force attacks. this section discusses the security analysis of the proposed algorithm such as statistical analysis, sensitivity analysis with respect to the key and key space analysis. to prove that the proposed cryptosystem is secure against most common attacks [4, 5], a simulation was carried out using national instruments software (ni lab view 2013) to encrypt a number of images using the proposed algorithm, and some calculations were performed as following. a. statistical analysis 1) entropy entropy is a cumulative measure of the frequency of the intensity levels in an image. due to the characteristics of the human eye, which is insensitive to high frequency components, an image of high entropy is not visually perceivable. entropy is given by 2 1logi i i h p p               (5) where pi is the frequency of intensity level i in the image, the maximum h for 8–bit image can attain is 8, and the average of our results is (h > 7.999). hence a statistical attack is very difficult to make. the entropies for different images are listed in table i. table i. entropy image sample original entropy entropy of [8] entropy of [14] proposed algorithm lena 7.44557 7.9971 7.9870 7.99937 baboon 7.35778 n.a. n.a. 7.99931 fixed value(125) 0.0 n.a. n.a. 7.99928 2) correlation coefficient analysis the correlation analysis is the most fundamental method used in determining the similarity between two images, especially in encryption applications. in order to evaluate the overall similarity between plain image and the encrypted image, the cross correlation between the two images will calculated. this is typically done at every step by subtracting the mean and dividing by the standard deviation. thus, the cross-correlation of an image f(x, y) with an image t(x,y) is      x,y σfσt tyxtfyxf n ),(),(1 (6) where n is the number of pixels in f and t , f and t are the averages of f(x, y) and t(x, y) respectively, σf is the standard deviation f(x ,y), and στ is the standard deviation of t(x, y) the correlation coefficient between the original image and the encrypted image is shown in table ii. engineering, technology & applied science research vol. 6, no. 5, 2016, 1195-1199 1198 www.etasr.com elsharkawi et al.: a novel image stream cipher based on dynamic substitution table ii. correlation coefficient image sample [14] proposed algorithm lena -0.0086 -0.00064 baboon n.a. -0.00271 peppers n.a. 0.00040 3) histogram referring to the plot of gray levels in an image against their frequencies of occurrence, the following figures show that the histogram is uniform and all gray levels have the same frequency of occurrence with the same probability. the histogram of the cipher image has no statistical relation to the plain image and hence does not provide any clue for a statistical attack on the proposed encryption scheme as shown in figures 4-6. b. sensitivity analysis 1) key space analysis in this algorithm, the key space depends on the chaotic map or maps which will be used in shuffling key generators. for example two logistic maps have been used for shuffling the substitution box. one for rows and the other for columns. logistic map equations are xn = r1 * xn-1 * ( 1 xn-1 ) (7) yn = r2 * yn-1 * ( 1 yn-1 ) (8) where r1, r2 are represented in 60 bits and the initial values xn, yn are represented in 64 bits value, while the least 4 bits were neglected to increase the key sensitivity. then the actual values are xn = 60 bits and yn = 60 bits. the number of key bits are = (kx + ky) = 60 + 60 + 60 + 60 = 240 bits which is an acceptable key space in symmetric key encryption in modern cryptography. 2) key sensitivity a perfect image encryption algorithm should be sensitive to small changes in the secret key. so the change of a single bit in the secret key should produce a completely different encrypted image. for testing the key sensitivity of the proposed algorithm, the following steps were performed: • two keys with only one bit difference have been chosen to encrypt the same plain baboon image (512 * 512) pixel. the two keys written in hexadecimal form the following code: k1=(kx+ky)=(123456789abcdef123456789abcdef+1 23456789abcdeff123456789abcde) and k2=(kx+ky)=(123456789abcdef123456789abcdef+1 23456789abcdeef123456789abcde) so, there are two encrypted images i1 with k1 and i2 with k2. • the encrypted images i1 and i2 were compared by calculation of the cross correlation between them. the above steps were repeated using different plain images with the same keys as shown in table iii. fig. 4. histograms: (a) baboon image, (b) histogram of plain baboon, (c) baboon encrypted image, (d) histogram of encrypted baboon. fig. 5. histograms: (a) peppers image, (b) histogram of plain peppers, (c) peppers encrypted image, (d) histogram of encrypted peppers. fig. 6. histograms: (a) fixed value image, (b) histogram of plain fixed value, (c) fixed value encrypted image, (d) histogram of encrypted fixed value. table iii. key sensitivity image sample cross correlation between encrypted images using (k1) and (k2) baboon -4.88697e-5 lena 0.000932412 fixed value(125) 0.000476637 engineering, technology & applied science research vol. 6, no. 5, 2016, 1195-1199 1199 www.etasr.com elsharkawi et al.: a novel image stream cipher based on dynamic substitution v. conclusion this paper proposed an image encryption algorithm based on a dynamic chaotic substitution box based on logistic maps. statistical results using entropy, correlations, and histogram show very good results for the proposed algorithm. simulation results show that it is also robust against most attacks due to the strong security, the key space, the initial s-box and the exhaustive number of s-boxes used in substitutions. the algorithm is so simple to be easily and efficiently implemented using hardware implementations such as fpga or asic chips. there is also no size limit to the input image because the algorithm works as an ergodic stream cipher. references [1] c. paar, ing. j. pelzl, understanding cryptography, springer, 2010 [2] b. schneier, applied cryptography, second edition, john wiley & sons, inc., 1996 [3] j. boyar, “inferring sequences produced by pseudo-random number generators”, j. acm, vol. 36, no. 1, pp. 129–141, 1989 [4] j. won, h. kim, “commun nonlinear sci numer simulat an image encryption scheme with a pseudorandom permutation based on chaotic maps”, commun. nonlinear sci. numer. simul., vol. 15, no. 12, pp. 3998-4006, 2010 [5] j. yen, j.guo, “a new chaotic key-based design for image encryption and decryption”, ieee international symposium on iscas 2000, geneva, pp. iv-49-iv-52, 2000 [6] a. kaushik, s. khanna, m. barnela, a. kumar, “stream encryption standard for digital images”, international journal of computer and electrical engineering, vol. 3, no. 2, pp. 240-243, 2011 [7] w. de, z. yuan-biao, “image encryption algorithm based on s-boxes substitution and chaos random sequence”, 2009 int. conf. comput. model. simulation, iccms 2009, pp. 110–113, 2009 [8] x. wang, q. wang, “a novel image encryption algorithm based on dynamic s-boxes constructed by chaos”, nonlinear dyn., vol. 75, no. 3, pp. 567–576, 2013 [9] x. zhang, z. zhao, j. wang, “chaotic image encryption based on circular substitution box and key stream buffer”, signal process. image commun., vol. 29, no. 8, pp. 902–913, 2014 [10] y. zhang, d. xiao, “cryptanalysis of s-box-only chaotic image ciphers against chosen plaintext attack”, nonlinear dyn., vol. 72, no. 4, pp. 751–756, 2013 [11] eduardo bayro corrochano, handbook of geometric computing, springer, 2005 [12] r. siwatch, v. kumar, “image encryption based on inter-pixel displacement”, international journal of scientific research engineering & technology, vol. 3, no. 3, pp. 673–676, 2014 [13] r. mathews, m. iaeng, a. goel, m. iaeng, p. saxena, v. p. mishra, “image encryption based on explosive inter-pixel displacement of the rgb attributes of a pixel”, proceedings of the world congress on engineering and computer science, vol. i, pp. 19–22, 2011 [14] b. aïssa, d. nadib, r. mohamedc, “image encryption using stream cipher based on nonlinear combination generator with enhanced security”, new trends math. sci., vol. 1, no. 1, pp. 10–19, 2013 engineering, technology & applied science research vol. 8, no. 2, 2018, 2699-2703 2699 www.etasr.com laghari et al.: quality analysis of urea plant wastewater and its impact on surface water bodies quality analysis of urea plant wastewater and its impact on surface water bodies abdul nasir laghari department of chemical engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan mashaalnasirlaghari@gmail.com zafar ali siyal department of energy and environment quaid-e-awam university of engineering, science & technology nawabshah, pakistan mohsinali soomro department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan daddan khan bangwar department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan abdul jabbar khokhar department of energy and environment quaid-e-awam university of engineering, science & technology nawabshah, pakistan hira lal soni department of chemical engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan abstract—this study was conducted on the canal water that flows besides an urea manufacturing facility. the study focused to evaluate the impact of facility’s effluents. the canal water quality is being affected drastically due to heavy load of pollutants discharged. samples were collected by grab sampling method, from various locations. these samples were analyzed regarding physiochemical parameters, i.e. temperature, ph, tds, tss, bod5, cod, heavy metals (fe, cu, cr, mn) and nh3 content. the canal water quality deteriorates after receiving a substantial load of effluents discharged from urea fertilizer plant. the results compared with who and neqs, showed that the effluent samples had alkaline nature with a high level of ammonia and bod5 and are not safe for aquatic life and environment. it is therefore recommended that discharge of untreated effluents should be stopped, or allowed within safe limits. keywords-wastewater; water quality; physiochemical analysis i. introduction water is used for numerous purposes such as food production, irrigation, manufacturing, drinking and waste disposal [1-2]. due to its unique structure, water has the ability to suspend, dissolve, and absorb a number of compounds that deteriorate the purity of drinking water, as it acquires contaminants from its surroundings [3]. ground and surface water can be polluted by industrial discharged effluents, sewage water and wastewater from contaminated sources [4]. a significant share of the industrial wastewater is being discharged into the water bodies without any proper treatment, subsequently reducing the quality of drinking water. the untreated water is sometimes also infiltrating aquifers, it causes damages on human health and mainly in the developing countries is the result of lack of safe and wholesome water supply [5]. many countries have incorporated wastewater reuse as an essential measurement of water resources planning. certain countries, like saudi arabia and jordan, have attempted to reuse the wastewater after proper treatment and have achieved significant success [6]. the quality of canal water is an issue of grave concern due to the rapid growth in industrial activities in mirpur mathelo, sindh. an urea fertilizer plant releases wastewater with toxic heavy metals and severe physiochemical parameters such as temperature, ph bod5, cod and ammonia, in the surroundings. heavy metal contamination of surface water has a potential toxic effect on the environment [7]. the polluted surface water thus threatens agriculture, aquatic life, and is raising both environmental and human health concerns [8]. the characteristics of fertilizer effluents vary depending on the type of fertilizer produced, operating conditions and control mechanism and they must be treated before disposal. although much work was done in this area of investigation, each industrial wastewater has its own chemical and mineralogical composition which implies that the treatment condition is different from one type of wastewater to another. this work aims to analyze the impact of liquid effluents of urea fertilizer plant on the quality of canal surface water, and on groundwater in nearby habitats of the fertilizer plant in mirpur mathelo, ghotki district, pakistan. it is found that the quality of surface water has been gradually deteriorating due to the continuous discarding of untreated effluents. the production capacity of ammonia by haber bosch process is 1250 mtd, and urea synthesized with the chemical reaction of ammonia and carbon dioxide, having a production capacity of 2175 mtd. wastewater generated in the fertilizer plant is about 5776 mtd. furthermore, heavy metals are major environmental contaminants, and their toxicity even at low concentration is a threat to ecology and water bodies. ‘heavy metals’ are metallic engineering, technology & applied science research vol. 8, no. 2, 2018, 2699-2703 2700 www.etasr.com laghari et al.: quality analysis of urea plant wastewater and its impact on surface water bodies elements of many types with relatively high density. heavy metals observed in ground samples including iron (fe), copper (cu), chromium (cr), and manganese (mn) [9]. water contamination affects the health of crops, livestock, and humans. wastewater irrigation, a common practice in pakistan, causes metal uptake by crops and therefore, risks the safety of food prepared from them and consequently brings potential hazards to the consumers. in addition to wastewater irrigation practice, agriculture industry in pakisatn heavily relies upon chemical fertilizers, such as, di-ammonium phosphate (dap) and urea are widely used fertilizers in the region. therefore, it also becomes important to assess the effect of such fertilizers on accumulated metals in soils, i.e., either deposited through wastewater irrigation or due to any other reasons. [10]. crops grown on contaminated soils bring hazards to both animals and humans. heavy metals are entered in an animal body, by their feeds, drinking water or through medication [11]. using wastewater, either from domestic or industrial effluents, may lead to depositing high concentrations of heavy metals on soils; which then concentrated in crop plant tissues and result in damaging the crop itself and the harvest and consequently bringing health hazards to the consumers [12]. ii. materials and methods a. study area the physiochemical study of the canal surface water was carried out at four different locations. water samples were analyzed by taking samples in clean polythene bottles without any air bubble from wastewater lagoon (location 1), 300m downstream from wastewater discharge point (location 2), 600m downstream from wastewater discharge point (location 3), 900m downstream from wastewater discharge point (location 4), covering thus 1km distance along the canal. surface water samples were then compared with national environment quality standard (neqs). samples were collected from each location at 15 day time intervals and were tagged as sample-1, sample-2, sample-3, and sample-4 respectively. plastic bottles were first rinsed with de-ionized water, sealed properly after collection and labeled accordingly. parameters were analyzed in the quest laboratory of energy and environment department, nawabshah. sampling locations of canal water and ground water are shown in figures 1 and 2 respectively. the industry which discharges effluents is fauji fertilizer company (ffc) limited’s urea fertilizer plant, situated in mirpur mathelo, ghotki district, pakistan. b. water sample analysis the samples collected were brought to quest environmental engineering department lab, for analysis of physiochemical parameters such as ph, total dissolved solids (tds), total suspended solids (tss), biochemical oxygen demand (bod5), chemical oxygen demand (cod), ammonia (nh3) and heavy metal content. the techniques used in characterizations are listed in table i. table ii shows the standard values of water quality parameters. fig. 1. surface water sampling locations (google earth screenshot) fig. 2. ground water sampling locations (google earth screenshot) table i. physiochemical parameter measurement [4] parameter technique instrument and model ph ph meter el430.020 tds tds meter con200, lovibond tss tss meter ph110, lovibond bod5 bod bottles with digital measurement cap and incubator 040552, lovibond cod reactor digestion method et108, lovibond ammonia nessler method using spectrophotometer spectrodirect, lovibond table ii. standard values of water quality parameters [8] parameters limit ph 6.5-8.5 bod5 0.2 mg/l cod 4 mg/l tds 1000 mg/l turbidity 10 ntu color 15 ptcu iii. results and discussion surface and ground water samples were analyzed to understand the impact of urea fertilizer plant to surface and ground water, impact that harms aquatic life, plants, animals and humans. a. temperature the water samples were taken in a beaker. the temperature was measured using an alcoholic thermometer and the results engineering, technology & applied science research vol. 8, no. 2, 2018, 2699-2703 2701 www.etasr.com laghari et al.: quality analysis of urea plant wastewater and its impact on surface water bodies are shown in figure 3. the temperature ranges between 52oc to 57oc at location-1, 39oc to 42oc at location-2, 34oc to 36oc at location-3 and 30oc to 32oc at location-4. the high values of water temperature observed could be attributed to the prevailing monthly summer conditions during the study period. b. ammonia (nh3) ammonia values are shown in figure 4,which ranges between 50mg/l to 55mg/l at location-1. at location-2, it was 20mg/l to 25mg/l. at location-3, it was 12mg/l to 17mg/l. at location-4, it was 3mg/l to 13mg/l. it is a fact that higher level (concentration) of ammonia causes direct toxic influence on aquatic life at high ph level. toxic level of ammonia for fish vary from 0.2-0.5 mg/l. ammonia toxicity is related to differences between species and ph rather than to the comparatively minor influences of salinity and temperature. in the marine environment the toxicity of ionized ammonia (nh4 +) should be considered [13]. c. ph ph is an important ecological factor, and water quality detector since aquatic organisms withstand normal ph and unable to tolerate variations. the surface effluent samples were taken in a beaker for ph measurements using and the results are shown in figure 5. it is seen that all samples collected for ph are alkaline in nature [5]. the highest ph value was observed at location-1, about ranging from 8.5 to 9.8. d. total dissolved solids (tds) the samples were taken in a beaker, and the multimeter probe was placed for few minutes. the tds levels (figure 6) vary from 2275mg/l to 2300mg/l (highest) at location-1 to 230mg/l to 252mg/l at location-4, when the limiting value of ecr 1997 is 1000mg/l [9]. e. total suspended solids (tss) the level of tss (figure 7) was 88mg/l to 97mg/l at location-1. at location-2, it was 72mg/l to 83mg/l. at location3, it was 68mg/l to 77mg/l. at location-4, it was 64mg/l to 66mg/l. all values were within standard limits. f. biochemical oxygen demand (bod5) biochemical oxygen demand (bod5) is the measure of the dissolved oxygen (do), required by the microorganisms to decay the organic matter present in a water sample. the sample taken in the beaker was first diluted with water. after inserting the probe, reading was taken, and finally, the beaker was placed inside the refrigerator at 200˚c for 5 days. afterwards, the data was retaken, and the result was obtained. the value of bod5 (figure 8) ranges from 150mg/l to 182mg/l at location-1. at location-2, it ranges between 115mg/l to 126mg/l. at location-3, it ranges between 110mg/l to 123mg/l. at location4, it ranges from 100mg/l to 105 mg/l. the high values at location-1, may cause severe hypoxia problem into streams, canal, and other enclosed water bodies [10]. fig. 3. variation in temperature fig. 4. variation in ammonia fig. 5. variation in ph fig. 6. variation in tds fig. 7. variation in tss engineering, technology & applied science research vol. 8, no. 2, 2018, 2699-2703 2702 www.etasr.com laghari et al.: quality analysis of urea plant wastewater and its impact on surface water bodies g. chemical oxygen demand (cod) chemical oxygen demand (cod) is a measure of oxygen required to decompose organic and inorganic waste equivalent to the amount of dichromate (oxidizing agent) consumed by dissolved and suspended matter under specific conditions [11]. the value of cod measured (figure 9) ranges between 105mg/l to 110mg/l at location-1. at the location-2, it ranges between 80mg/l to 88mg/l. at location-3, it ranges between 70mg/l to 77 mg/l. at location-4, it ranges from 18mg/l to 23mg/l. the permissible limit of cod for drinking water is 255mg/l [5, 12]. therefore, the observed values of cod for all locations are within allowable limits. cod is the total measurement of all chemicals (organics and in-organics) in the waste water, while bod5 is a measure of the amount of oxygen required for the bacteria to degrade the organic components present in waste water. h. iron (fe) the fe levels (figure 10) were 0.21mg/l to 0.27mg/l at groundwater location g-1. in groundwater location g-2, it was 0.15mg/l to 0.19mg/l. at g-3, it was 0.12mg/l to 0.18mg/l. at g-4, it was 0.11mg/l to 0.15mg/l. the safe limit for drinking water is 0.3mg/l. the abundance of species such as periphyton, benthic invertebrates and fish diversity are greatly affected by the direct and indirect effects of iron contamination. i. copper (cu) the level of cu (figure 11) was 0.051mg/l to 0.055mg/l at groundwater location g-1. in groundwater location g-2, it was 0.034mg/l to 0.038mg/l. in groundwater location g-3, it was 0.041mg/l to 0.045mg/l. in the groundwater location g-4, it was 0.035mg/l to 0.039 mg/l. toxicity from cu is rare, world health organization (who) suggest a safe consumsion upper limit 12mg/day for adults and 150µ/day for children [14]. j. chromium (cr) the level of cr (figure 12) was 0.018mg/l to 0.021mg/l at groundwater location g-1. at g-2, it was 0.011mg/l to 0.018mg/l. at g-3, was 0.02mg/l to 0.025mg/l. in g-4, it was 0.011mg/l to 0.018mg/l. a suggested upper limit in the united kingdom is 400mg/kg, and in the united states 1000mg/kg. due to the presence of excess oxygen in the environment, cr (iii) is oxidized to cr (vi), which is extremely toxic and highly soluble in water [19] . fig. 8. variation in bod5 fig. 9. variation in cod fig. 10. variation in fe fig. 11. variation in cu k. manganese (mn) the level of mn (figure 13) was 0.042mg/l to 0.047mg/l at the g-1. at g-2, it was 0.034mg/l to 0.038 mg/l. at g-3, it was 0.028mg/l to 0.029mg/l. at g-4, it was 0.021mg/l to 0.025mg/l. the standard for manganese is 0.05 mg/l. fig. 12. variation in cr fig. 13. variation in mn engineering, technology & applied science research vol. 8, no. 2, 2018, 2699-2703 2703 www.etasr.com laghari et al.: quality analysis of urea plant wastewater and its impact on surface water bodies iv. conclusions the study has shown that effluents discharged into surface canal water cause drastic impacts on the aquatic life, animals, plants and humans. the effluents discharged into the canal have increased temperature compared to given industrial limit. the results from samples taken from surface water represent that the effluents discharged from the plant contain adverse impacts on the quality of surface water. the continued discharge of the effluents in the canal may result in severe accumulation of the contaminants. sample analysis further showed that bod5 and ammonia levels are at alarming rates, which is hazardous for aquatic life, animals and humans. the open survey form the sample location revealed that the nearby residents suffer from several diseases that can be linked to the urea plant. the observed diseases include both common health issues (such as diarrhea, skin rash, indigestion, respiratory problems, hypertension) and complex and critical health diseases (i.e., gastric ulcer gout, rheumatism, conjunctivitis, pneumonia, malaria, tuberculosis and even cancer). heavy metals are too dangerous, even though they are found within safe limits, because they have the potentiality to accumulate in organisms over time. v. recommendations it is recommended that plant wastewater should not be discharged untreated. treatment process must be updated as a high level of ammonia, and bod5 are found in the test results. liquid effluents discharged from urea fertilizer plant through the sampling point-1 must be managed according to standard procedures. leakage from pipeline, valves or ammonia storage tank should be prevented through regular maintenance. the quality of surface canal water where plant effluents are discharged should be checked on a continuous basis to ensure its quality. the proper and effective implementation of national and international laws and regulations related to industrial effluents regarding wastewater. medical and financial assistance should be given to nearby residents who are continuously suffering from plant effluents and are also bearing the financial loss of their animals’ deaths. references [1] k. saeed-ur-rehman, a. wahid, r. b. tareen, s. a. kakar, m. tariq, s. a. kayani, “impact of municipal waste water of quetta city on biomass, physiology and yield of canola (brassica napus l.)”, pakistan journal of botany, vol. 42, no. 1, pp. 317–328, 2010 [2] d. balabanic, m. filipic, a. k. klemencic, b. zegura, “raw and biologically treated paper mill wastewater effluents and the recipient surface waters: cytotoxic and genotoxic activity and the presence of endocrine disrupting compounds”, the science of total environment, vol. 574, pp. 78–89, 2017 [3] m. a. khattak, n. ahmed, m. a. qazi, a. izhar, s. ilyas, m. n. chaudhary, m. s. a. khan, n. iqbal, t. waheed, “evaluation of ground water quality for irrigation and drinking purposes of the areas adjacent to hudiara industrial drain, lahore, pakistan”, pakistan journal of agricultural sciences, vol. 49, no. 4, pp. 549–556, 2012 [4] m. h. islam, m. rahman, f. u. ashraf, “assessment of water quality and impact of effluents from fertilizer factories to the lakhya river”, international journal of water resources and environmental engineering, vol. 2, no. 8, pp. 208–221, 2010 [5] r. shyamala, m. shanthi, p. lalitha, “physicochemical analysis of borewell water samples of telungupalayam area in coimbatore district, tamilnadu, india”, e-journal of chemistry, vol. 5, no. 4, pp. 924–929, 2008 [6] m. b. pescod, wastewater treatment and use in agriculture fao irrigation and drainage paper 47, fao, 1992 [7] a. m. abdel-satar, m. h. ali, m. e. goher, “indices of water quality and metal pollution of nile”, the egyptian journal of aquatic research, vol. 43, no. 1, pp. 21-29, 2017 [8] j. n. halder, m. n. islam, “water pollution and its impact on the human health”, journal of environment and human, vol. 2, no. 1, pp. 36–46, 2015 [9] ministry of environment and forest, the environment conservation rules, 1997, government of the people’s republic of bangladesh, ministry of environment and forest, 1997 [10] m. a. mallin, v. l. johnson, s. h. ensign, t. a. macpherson, “factors contributing to hypoxia in rivers, lakes, and streams”, limnology and oceanography, vol. 51, no. 1, part 2, pp. 690–701, 2006 [11] r. b. geerdink, r. s. van den hurk, o. j. epema, “chemical oxygen demand: historical perspectives and future challenges”, analytica chimica acta, vol. 961, pp. 1–11, 2017 [12] who, guidelines for drinking-water quality, who, 2011 [13] f. b. eddy, “ammonia in estuaries and effects on fish”, journal of fish biology, vol. 67, no. 6, pp. 1495–1513, 2005 [14] m. oliver, “soil, food security and human health: a review”, european journal of soil science, vol. 66, no. 2, pp. 257-276, 2015 engineering, technology & applied science research vol. 7, no. 6, 2017, 2308-2312 2308 www.etasr.com elashmawy: 3d-cfd simulation of confined cross-flow injection process using single piston pump 3d-cfd simulation of confined cross-flow injection process using single piston pump mohamed elashmawy mechanical engineering department university of hail, saudi arabia and engineering science department faculty of petroleum and mining engineering suez university, suez, egypt arafat_696@yahoo.com abstract—injection process into a confined cross flow is quite important for many applications including chemical engineering and water desalination technology. the aim of this study is to investigate the performance of the injection process into a confined cross-flow of a round pipe using a single piston injection pump. a computational fluid dynamics (cfd) analysis has been carried out to investigate the effect of the locations of the maximum velocity and minimum pressure on the confined crossflow process. the jet trajectory is analyzed and related to the injection pump shaft angle of rotation during the injection duty cycle by focusing on the maximum instant injection flow of the piston action. results indicate a low effect of the jet trajectory within the range related to the injection pump operational conditions. constant cross-flow was used and injection flow is altered to vary the jet to line flow ratio (qr). the maximum jet trajectory exhibits low penetration inside the cross-flow. the results showed three regions of the flow ratio effect zones with different behaviors. results also showed that getting closer to the injection port causes a significant decrease on the locations of the maximum velocity and minimum pressure. keywords3d-cfd; injection process; cross-flow; single piston i. introduction cross-flow injection is an important process for many applications. injection facility is essential plyer in this process. the most widely used type worldwide is the diaphragms pump type because of its simple and compact design with relatively low cost compared to other types. the disadvantage of this type is mainly due to its diaphragm material which subjected to intensive cyclic fatigue at certain points. many researches focused on the performance and design of the diaphragm pumps. to minimize diaphragm fatigue, hydraulically actuated diaphragm pumps are usually used. variable-speed drive is one of the controlling facilities used for such type. however using pneumatic diaphragm pumps is not sufficient to overcome the diaphragm material failure [1]. low cost is the main advantage of this pump type from long time ago and still the main motivation for its attractiveness. for high pressure injection application piston injection pumps are adequate device. some effort was done establishing a new injection concept based on line bleeding that is able to satisfy both high and low pressure requirements according to the pressure inside the line. the new concept requires no rotating parts having simple and compact design with very low cost [2, 3]. injection process into crossflow enhances flow characteristics. increasing the velocity of the cross-flow injection gradually reduces reynolds number and some other parameters. moreover the penetration of the jet in the cross-flow satisfies more than twice stronger and better mixing conditions than the jet in the co-flow case [4, 5]. the shear layer and vortices of the wake field near the wake region of the jet are very important to stabilize the chemical reaction and enhance the gas turbine performance [6]. using multilateral jets upstream from the exit of the nozzle helps to control the mixing field of the combustor [7]. when using two jets in cross-flow injection process, the two jets will merge into a single trajectory after mixed with the cross-flow. two tandem jets have more potential than one jet to penetrate deeper in the cross-flow. the rear jet penetrates deeper than the front jet because of the front jet simply shielded it [8, 9]. a research was performed concerning a classification of the turbulent jet mechanics of a t-junction for cooling systems in power plants. results provided optimum operating conditions of the tjunction in a real field of phoenix reactor showing the importance of a 90° bend component which enhances the mixing process mechanism. furthermore a visualization test-rig system with three separated sections to enable each section to be visualized separately with the particle image velocimetry (piv). three mixing regions appear accompanied by maximum velocity fluctuations: (1) close to the jet boundary, (2) above the jet (along the cross-flow), and (3) near the wake downstream area above the jet. region (3) is the strongest one which has a higher cycle thermal fatigue [10, 11]. a cfd simulation was performed based on the momentum ratio for tjunctions with different angles. the cross-flow angle with injection direction significantly affected the velocity ratio and it is important for improving the design of piping systems [12]. in cases when the mixing process has laminar flow, the mixing process becomes difficult. the pulsation and geometry effect on the mixing process within a microchannel was experimentally and numerically investigated. the results show that the geometry of the mixing region strongly affects the engineering, technology & applied science research vol. 7, no. 6, 2017, 2308-2312 2309 www.etasr.com elashmawy: 3d-cfd simulation of confined cross-flow injection process using single piston pump mixing quality. t and arrowed intersection geometries showed the best efficiency for the mixing process, while the singleright angle intersection showed the worst mixing behavior. a mixing enhancement of 71.9% could be reached for the singleright angle intersection when using flow pulsation while 153% mixing enhancement was reached by using a combination of flow pulsation and geometry effects [13]. recently a research work studied the effect of the size of the pipe lines (cross-flow pipe) on the cross-flow injection characteristics showing the importance of this parameter on enhancing the injection process and the design of the pipelines. results show that increasing pipeline size enhances injection pump dose by almost 3.24% at full pump displacement [14]. the aim of the current study is to predict the behavior of the locations of the maximum velocity and minimum static pressure within the injection process into a confined cross-flow. a computational fluid dynamics (cfd) analysis is performed and related to the instantaneous injection flow rates of a single piston pump driven by circular cam action. this study is a further research effort to continue the experimental work performed before in [14]. ii. cfd cross-flow injection simulation the cross-flow injection behavior is analyzed using 3dcfd (ansys-fluent). figure 1 shows a schematic diagram of the test section geometry. both line flow (cross-flow) and injection flow (jet-flow) are water (isothermal mixing process). water viscosity changes by 0.535% as the pressure change from 1 to 10 mpa [15]. it is convenient to use a constant viscosity and density of 1.003×10-3 pa.s and 998.2 kg/m3 respectively for both injection and cross-flow (injection) water streams. a constant line flow rate of 83.33×10-3 kg/s is used (similar to reference [14]). reynolds numbers are 6612, 7157 and 9918 for qr=0, 8.25% and 50% respectively. a standard kɛ turbulent flow model is included. table i shows the boundary conditions and the solution settings used for numerical solution operated by 3d-cfd (ansys-fluent). table ii shows the mesh independence of the cfd, 1.2 mesh size was selected with accuracy of 0.013% which is accepted to reduce time of calculations (70154 nodes and 182012 elements). figure 2 shows the convergence curves of the iteration parameters of the numerical calculations. the convergence attained after 259 iterations using hybrid initialization. figure 3 shows the duty cycle of the single piston injection pump. the maximum indicating injection flow is 6.875×10-6 m3/s (594 l/day) and occurred at α=113o shaft angle. the duty cycle is occurred from 0 to α=180o while from α=180o to α=360o injection duty stopped and suction duty started. fig. 1. schematic diagram of the cdf test-section. table i. boundary condition and solution method boundary conditions solution method (default) water density 998.2 (kg/m3) scheme simple water viscosity 1.003×10-3 kg/m.s gradient least square, cell based ainjection inlet water, (mass flow) 6.875×10-3 kg/s pressure second order line inlet water, (mass flow) 83.333×10-3 kg/s momentum second order upwind outlet (gauge pressure) 0 pa turbulent kinetic energy first order upwind wall no slip turbulent dissipation rate first order upwind a. injection inlet varies according to qr (here is the value according to qr=8.25%; at α=113o). iii. results and discussion results are based on steady flow in order to introduce an insight of the cross-flow injection process and look at the behavior of the injection in a confined cross-flow process, (jiccf) which is not experimentally performed in this work. figure 4 shows the cfd velocity contours related to pump shaft angle (α) of fig. 3. qr increased from zero to 8.25% with shaft angles from α=zero to α=113o then decreases to zero again from α=113o to α=180o. there are no injection occurred at α=zero and α=180o. figure 5 shows the jet trajectory for various shaft angles. increasing the flow ratio (jet velocity) increases the jet penetration ability (z-direction) and leads to a longer distance in the axial direction (x-direction) that is fully mixed with the cross-flow, causing a stronger wake behind the jet. in order to better understand the behavior of the jiccf, a 3d-cfd study is performed for the maximum jet action case (qr=8.25%) occurring at shaft angle α =113o to evaluate how the velocity and static pressure behave along the axial flow (cross-flow stream) at 3-different radial distances (centerline, z/d=1.3 and z/d=0.3). table ii. mesh independence element size (mm) nodes elements iterations maximum velocity (m/s) minimum pressure (pa) centerline z/d=0.3 centerline z/d=0.3 2.0 25493 61649 300 0.53 0.66 59.66 -74.37 1.8 30312 73711 350 0.53 0.78 60.37 -66.45 1.6 38928 96489 400 0.54 0.77 57.46 -65.29 1.4 49279 122914 500 0.53 0.76 57.42 -65.19 1.2 70154 182012 259 0.53 0.83 57.81 a-77.29 1.0 103511 270633 286 0.53 0.83 57.81 -77.30 0.8 163841 455125 325 0.53 0.83 57.81 -77.30 a. the error due to choosing 1.2 mm mesh size is 0.013%. engineering, technology & applied science research vol. 7, no. 6, 2017, 2308-2312 2310 www.etasr.com elashmawy: 3d-cfd simulation of confined cross-flow injection process using single piston pump fig. 2. convergence curves of the cfd iterations. fig. 3. injection duty cycle of the single piston action. fig. 4. cfd velocity contours related to pump shaft angle (α) of fig. 3. fig. 5. jet trajectory of the confined cross-flow injection for 6-shaft angles of the vdrip. fig. 6. velocity magnitude distribution in the axial direction of the cross-flow, qr=8.25%. fig. 7. position of the maximum velocity magnitude in the axial flow direction for a wide range of flow ratios (qr). figure 6 shows the velocity magnitude distribution in the x-direction. curves show a significant increase in the axial velocity directly after the injection port (x/d=0) followed by a significant decrease forming two peaks (maximum and minimum) at the pipe centerline. three peaks appeared when getting closer to the jet port minimum; before injection, a maximum occurred directly after injection, and then a minimum occurred again after that. figure 7 shows the effect of the flow ratio (qr) on the position of the maximum velocity magnitude along the x-direction where it is expected to have a wake region. a wider range of qr is studied in order to show the effect of qr on the position of the maximum velocity including the pump operational range (0-8.25%). the curves show three effect regions (similar to the three regions obtained qmax= 6.875×10-6 m3/s (594 l/day) @ α=113o engineering, technology & applied science research vol. 7, no. 6, 2017, 2308-2312 2311 www.etasr.com elashmawy: 3d-cfd simulation of confined cross-flow injection process using single piston pump by [11]). region (1) is a very narrow region with a range of qr from 0 to almost 5% as maximum, wherein increasing the qr sharply increases the location of the maximum velocity to x/d=3.08, 1.92 and 0.87 for centerline, z/d= 1.3 and z/d=0.3 respectively. in region (2), (qr=5%-30%) increasing the qr decreases the location of the maximum velocity to x/d=1.32, 0.75 and 0.81 for centerline, z/d= 1.3 and z/d=0.3 respectively. in region (3), (qr>30%) qr has no significant effect. moreover, getting closer to the jet port (z/d=1.3 and 0.3) decreases the location of the maximum velocity magnitude, indicating the strong effect of the jet action on the cross-flow stream. figure 8 shows the distribution of the static pressure along the x-direction for three different z-levels. the same general behavior of fig. 6 is obtained with slight differences in the location positions; the minimum static pressure is sharper and much closer to the jet portion. similar behavior as in fig. 7 is obtained in fig. 9, showing greater position ranges. in region (1), increasing the qr sharply increases the location of the minimum static pressures to x/d=7.9, 2 and 1.1 for centerline, z/d=1.3 and z/d=0.3 respectively. in region (2), increasing qr decreases the location of the minimum static pressures to x/d=1.32, 0.75 and 0.81 for centerline, z/d=1.3 and z/d=0.3 respectively. in region (3), qr has no effect on the location of the minimum static pressure. it is observed that the same locations were obtained for the maximum velocity and minimum static pressure (figs. 7 and 9) for z/d=1.3 and 0.3 while the location increased for the minimum static pressure at the centerline. figure 10 shows jiccf velocity contours and vectors. a: shows the velocity contours at the x-z plane followed by five sectional views at different levels parallel to the x-y plane at z/d =0.3, 0.7, 1.3, 1.9, and 2.3 (centerline). the wake region is very clear at z/d=0.3, 0.7 and 1.3 locations. b: shows velocity vectors similar to (a) focusing on the jet action region. c: shows the stream lines of the jet separated from the cross-flow focusing on the trajectory path of the jet action injected into the confined cross-flow; the performance of the jet trajectory shows low penetration inside the cross-flow (lower than the pipe centerline. d: shows the wake region and the two counter rotating vortex pairs occurring at x/d=1. e: shows a cross sectional view of the velocity contours. eleven equally spaced positions are introduced to show the jet mixing propagation behavior. the results obtained by fig. 10 (d) are consistence with the results obtained in [11,16,17]. also the results obtained by fig. 10 (b and c) are consistence with the results obtained in [12]. fig. 8. static pressure distribution along the cross-flow pipe, qr=8.25%. fig. 9. position of the minimum static pressure magnitude in the axial flow direction for a wide range of flow ratios (qr). fig. 10. cfd analysis at α = 113o (qr=8.25%); (a, b and c): velocity contours, vectors and streamlines along the pipeline flow direction, (d and e): velocity vectors and velocity contours across pipeline flow. engineering, technology & applied science research vol. 7, no. 6, 2017, 2308-2312 2312 www.etasr.com elashmawy: 3d-cfd simulation of confined cross-flow injection process using single piston pump iv. conclusions cfd analysis of the jet action into a confined cross-flow has been performed and related to instantaneous flow rates indicated by shaft angle variation of a single piston injection pump. the analysis also focused on the maximum indicated injection flow rate in the case when qr=8.25% at α=113o. the effect of the flow ratio (qr) on the position of the maximum velocity magnitude and minimum static pressure along the xdirection is also studied. a wider range of qr is considered. the results obtained by the 3d-cfd analysis showed a relatively small injection trajectory impact on the cross-flow within the injection flow range of the operational conditions of 83.33×10-6 m3/s line flow, 1.283×10-6 m3/s average injection flow and 6.875×10-6 m3/s maximum instant injection flow. all jet trajectory curves show low penetration inside the crossflow, and lay under the centerline of the pipeline. cdf results showed the 3-regions of the flow ratio effect on the maximum velocity locations along the x-direction (consistent with [11]). the first region is a very narrow region with a maximum 5% qr, the second region has qr = 5%-30%, and the third region has qr >30%. the same behave is obtained for the locations of the minimum static pressure. getting closer to the injection centerline significantly decreases the location positions of the maximum velocity and the minimum static pressure. increasing qr sharply increases the locations for the first region and decreases it for the second region while the third region indicates no significant effect. the results of the present study show that the locations of the maximum velocity and minimum static pressure are strongly related to qr. indicating that the location parameter could be the key point for designers beside the values of the maximum velocity and minimum static pressure. further research efforts are recommended including the following:  an experimental study of the same test section and parametric conditions is highly recommended validating the cfd results.  using a user defined boundary (udf) condition at the inlet would be more realistic. acknowledgment acknowledgments are due to the deanship of scientific research, university of hail, ksa for funding and supporting this project with code (e5-me 2014) and making it feasible. references [1] v. a. kurteev, “diaphragms for pneumatic pumps”, chemical and petroleum engineering, vol. 47, no. 78, pp. 550–556, 2011 [2] m. elashmawy, “novel injection concept: line bleeding injection pump (lbip)”, science innovation vol. 2, no. 4 pp. 37-42, 2014 [3] m. elashmawy, m. alnais, “developed design for line bleeding injection pump: double-act lbip”, international journal of mechanical engineering and applications, special issue: advanced fluid power sciences and technology ,vol. 3, no. 5, pp. 11-16, 2015 [4] s. majumder, d. sanyal, “relaminarization of axisymmetric turbulent flow with combined axial jet and side injection in a pipe”, journal of fluids engineering, vol. 132, no. 10, p. 101101, 2010 [5] c. cardenas, j. a. denev, r., suntz, h. bockhorn, “study of parameters and entrainment of a jet in cross-flow arrangement with transition at two low reynolds number”, experiments in fluids, 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k. yuki, h. hashizume, “experimental investigation of flow field structure in mixing tee”, journal of fluids engineering, vol. 131, no. 5, p. 051103, 2009 [12] s. qian, j. frith, n. kasahara, “classification of flow patterns in angled t-junctions for the evaluation of high cycle thermal fatigue”, journal of pressure vessel technology, vol. 137, no. 2, p. 021301, 2014 [13] h. ammar, a. ould el moctar, b. garnier, h, peerhossaini, “flow pulsation and geometry effects on mixing of two miscible fluids in microchannels”, journal of fluids engineering, vol. 136, no. 12, p. 121101, 2014 [14] m. elashmawy, a. alghamdi, i. badawi, “investigation of the effect of pipeline size on the cross-flow injection process”. engineering, technology & applied science research, vol. 6, no. 3, pp. 1023-1028, 2016 [15] j. w. schmelzer, e. d. zanotto, v. m fokin, “pressure dependence of viscosity”, journal of chemical physics, vol. 122, p. 074511, 2005 [16] p. k. selvam, r. kulenovic, e. laurien, “experimental and numerical analyses of turbulent mixing of coolant streams in a mixing tee”, fourth international conference on fatigue of nuclear reactor components, seville, spain, 2016 [17] b. krumbein, s. jakirlic, v. termini, a. mizobuchi, c. tropea, “flow and heat transfer in cross-stream type t-junctions: a computational study”, 10th international symposium on turbulence and shear flow phenomena (tsfp10), chicago, usa, july, 2017 microsoft word etasr_v12_n1_pp8013-8016 engineering, technology & applied science research vol. 12, no. 1, 2021, 8013-8016 8013 www.etasr.com el touati: deadline verification for web services using timed automata deadline verification for web services using timed automata yamen el touati faculty of computing and it northern border university kingdom of saudi arabia yamen.touati@nbu.edu.sa abstract-many computation tasks are made today on remote cloud platforms using web services. beyond the advantages provided by such services, many new challenges arise. one of the challenging problems is ensuring that web services respect critical deadlines. this is a critical issue, especially for real-time systems that use remote web services. this paper aims to propose a framework for deadline verification using timed automata (ta). keywords-web services; deadlines; timed automata; verification i. introduction in the last few years, most companies migrated to remote cloud-based services. in these systems, most of the communication is ensured via web services that offer quasiunlimited resources and computational power. however, companies face new challenges concerning security [1-4] and timing constraints [9-11, 19]. a web service is a software system designed to support interoperable machine-to-machine interaction over a network [6]. they provide flexible and efficient solutions to the sharing of information between people and businesses [6, 20]. by nature, a web service can face many random interferences that can cause delays in the required tasks [12-15, 18]. in many cases, it is not easy to check whether the specification deadlines are respected. in general, this is because some web services are composed of many correlated tasks, where delays and timing are propagated according to a dynamic schedule. in this particular context, timed automata [6-10] are suitable for modeling the evolution of a system focusing on time constraints. these are presented as an extension of finite-state automata with clocks into location. transitions can be executed when a linear constraint on clocks, called guard, is verified. this framework presents an interesting graphical interface combined with powerful computational power. moreover, it is more suitable to solve verification problems using a timed automata framework than performing algebraic calculus, which may be difficult to resolve if the size of the system increases. this paper proposes a new method based on timed automata reachability checking in order to resolve the problem of deadline verification. ii. background of timed automata and time transition systems ℝ� denotes nonnegative reals, x={x1,x2,…,xn} denotes the finite set of real-valued variables, and the circumflex (~) is used to denote an element of the set of operators {<,≤,=,≥,>,≠}. a simple inequality over x is an inequality of the form x~c, where x∈x and c∈ℝ� . a rectangular predicate over x is a conjunction of linear inequalities over x. c(x) denotes the set of linear predicates on x. a. timed automata a timed automaton [1,3] is a tuple a = (l, l0, x, σ, e, inv, f) where: • l is a finite set of locations (nodes) • l0 is the initial state • x is a finite set of non-negative real valued clocks • σ is a finite set of actions or events (labels) • e ⊂ l × c(x) × σ × 2x × l is a set of transitions. e ∈ e, and e=(l, δ, α, r, l i ) is defined, where l is the start location, δ is the guard, α is the action, r is the set of clocks to reset, and l i is the end location • inv ∈ c(x) l is a function that associates an invariant to each location • f ⊂ l is the set of final states b. semantic of timed automata the semantic of timed automata a=(l, l0, x, σ, e, inv) is given by a time transition system [2] sa= (q, q0, →), where: • q = l × ℝ� x • q0 = (l0, 0) is the initial state • →⊂ q × (σ ∪ ℝ�) × q is defined by: o (l,v) → a (l i ,v i ) (discrete transition) if ∃ (l, δ, a, r, ρ, l i ) ∈ e such that δ(v)=true, and vi=v[r ← 0][ρ] and inv(l i )(v i )=true o (l,v)→ t (l i ,v i ) (continuous transition) if l=li and vi=v+t and inv(li)(vi)=true corresponding author: yamen el touati engineering, technology & applied science research vol. 12, no. 1, 2021, 8013-8016 8014 www.etasr.com el touati: deadline verification for web services using timed automata it is noted that (l,v)→*(li,vi) in the case of a transition sequence of leading from (l,v) to (l i ,v i ). c. reachability in timed automata a run of a timed automaton a is a path in sa starting from . [[a]] denotes the set of all runs in the timed automaton a. it is noted that � , � →� � ′, ′� →� � ′′, ′′� is equivalent to � , � →� � � ′′, ′′�. a state � �, �� is considered as reachable, if: ∃� , � →�� �� � �, �� →�� �� � �, �� →�� �� … →�� �� � �, �� where � , � � � . a run: � , � →�� �� � �, �� →�� �� � �, �� →�� �� … →�� �� � �, ��… starting from � � � , � is a timed trace, denoted as: � � �� � � , � → ���, �� → ���, �� → ⋯ ���, ��… where � is a sequence of pairs ���, ��, �� ∈ e is a transition, and ��� ∈ �� is the delay between the two successive events �� and ���� where: � 0 and ∀# $ 1 : � � &� ' &�(�. iii. deadline verification in web services a web service can be modeled by a set of tasks with a timed automaton, where each location corresponds to a specific configuration in the web service’s lifecycle. transitions between locations correspond to a configuration change. thus, locations can be considered as elementary subtasks to fulfill the entire web service. some of these tasks may take a longer than expected time to be fulfilled. since the sequence of tasks and their exact duration is not easy to tackle in these systems, it would be interesting to investigate a way to check whether any critical deadline was broken. fig. 1. example of a timed automaton. a. checking deadline in timed automata consider the example shown in figure 1 and suppose that this timed automaton represents the behavior of a web service composed of 5 subtasks (those represented by locations l1 to l5). it can be assumed that the deadline of this web service is 16 time units (t.u). checking whether this deadline is respected is equivalent to checking if l3 is reached always before 16 t.u. in this case, l3 is always reached before 8 t.u, which means that the previous deadline is respected by the web service. to resolve this problem, a universal clock x0 (a clock that is never reset) can be added and check if the constraint x0≤15 is always verified. b. generalization this problem can be generalized for a timed automaton a=(l, l0, x, σ, e, inv) as: given a1 = (l, l0, x∪{x0}, σ∪{d}, e, inv) and deadline∈ ��, deadline is respected if: ∀ l∈ l, ∀ v∈ ℝ� such that (l0,0)→ * (l,v), v(x0)≤deadline (1) c. deadline verification steps to ensure that property (1) is respected, this problem is transformed into a reachability verification problem as follows. • a new derivative automaton is constructed a2=(l∪{ld}, l0, x∪{x0}, σ∪{d}, e∪ed, inv), such that: ed�{(l, x0>deadline, {d}, {}, ld), l∈l-f} • the reachability of ld should be checked. if ld is reachable, then the deadline is not guaranteed to be respected by the web service. the ld location has the behavior of a typical dead state. transitions are added from each nonfinal location to ld, with the guard x0>deadline, without any reset. fig. 2. updated timed automaton with dead state and universal clock – ld is not reachable in the example shown in figure 2, the suggested method is applied to proceed to deadline verification. location ld is reachable if the universal clock t0 reaches the limit defined by the deadline, here 16. in this particular case, the location ld is not reachable, which means that the web service satisfies the deadline constraint. however, if a more restrained deadline constraint is considered, e.g. x≤6, the transition guards leading engineering, technology & applied science research vol. 12, no. 1, 2021, 8013-8016 8015 www.etasr.com el touati: deadline verification for web services using timed automata to ld will have the form t0>6, as shown in figure 3. in this case, the location ld is reachable from any non-final location. in general, if the location ld is accessible from even a single location, then the deadline constraint becomes unsatisfied. fig. 3. updated timed automaton with dead state and universal clock – ld is reachable fig. 4. automata and computation of reachable space. fig. 5. reachable space. for any web service modeled by a timed automaton, the problem of checking deadlines is decidable. by construction, checking the deadline respect on automaton a is equivalent to checking the reachability of ld in automaton a2. if a transition is executed in ed, then the universal clock x0 exceeds the defined deadline, since the guard x0>deadline becomes true. furthermore, the reachability problem is known to be decidable for general timed automata [1], ensuring that the verification of the deadline is decidable. the proposed method to check a deadline is structural. it is sufficient to add a new ld location, a new universal clock, and as many transitions as the cardinality of the locations set. the proposed method was applied to the examples in figures 2 and 3 using the phaver tool [17]. phaver allows the computation of reachable space of timed automata. the automata and the computation of reachable space were defined, conforming to the phaver syntax, as shown in figure 4. the result reachable space is shown in figure 5. d. how to respect deadline constraints some web services may not meet some deadline requirements. when the number of clocks/locations increases, it is difficult to determine what are the possible updates on the behavior of the system to converge to the requirements. it is interesting to find a solution that describes the required values of the clocks with respect to the deadline constraints by following the following steps: • mark all locations where ld is reachable. this set is denoted as ld • ∀ l∈ ld, update inv(l) by adding the constraint t0 ≤ deadline • foreach l ∈ ld, perform a backward analysis considering the reverse automata and the new location environment [16] • merge all the reachable space. the result of these steps is a new automaton where the ld location is never reachable. the implementability of these new constraints on the web service can be checked by the developers or designers based on the new constraints obtained on locations and guards. moreover, it could be a starting point to enhance and upgrade the web service considering the new constraints. engineering, technology & applied science research vol. 12, no. 1, 2021, 8013-8016 8016 www.etasr.com el touati: deadline verification for web services using timed automata iv. conclusion this paper focused on the problem of deadline verification for web services that could be modeled by timed automata. this framework offers the possibility to model the internal behavior of a web service with explicit consideration of timing constraints. the contribution of this paper is to propose a way to transform this problem into a reachability verification problem of a derived automaton. this new automaton is obtained by a structural and linear transformation. future work consists of the generalization of this problem for a sequence of subtasks of a web service with multi-deadline constraints. moreover, it is possible to tackle the deadline verification in the context of web service composition [4, 8]. in this case, it is necessary to deal with the 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[20] f. h. khoso, a. lakhan, a. a. arain, m. a. soomro, s. z. nizamani, and k. kanwar, "a microservice-based system for industrial internet of things in fog-cloud assisted network," engineering, technology & applied science research, vol. 11, no. 2, pp. 7029–7032, apr. 2021, https://doi.org/10.48084/etasr.4077. microsoft word etasr_v11_n5_pp7598-7604 engineering, technology & applied science research vol. 11, no. 5, 2021, 7598-7604 7598 www.etasr.com chi et al.: english-vietnamese cross-lingual paraphrase identification using mt-dnn english-vietnamese cross-lingual paraphrase identification using mt-dnn hung vo tran chi faculty of information technology vnu-hcm university of science ho chi minh city, vietnam hung.votranchi@gmail.com duy lu anh faculty of information technology vnu-hcm university of science ho chi minh city, vietnam lu.duy.pro@gmail.com nguyen le thanh faculty of information technology vnu-hcm university of science ho chi minh city, vietnam lethanhnguyen.vn@gmail.com dien dinh faculty of information technology vnu-hcm university of science ho chi minh city, vietnam ddien@fit.hcmus.edu.vn abstract-paraphrase identification is a crucial task in natural language understanding, especially in cross-language information retrieval. nowadays, multi-task deep neural network (mtdnn) has become a state-of-the-art method that brings outstanding results in paraphrase identification [1]. in this paper, our proposed method based on mt-dnn [2] to detect similarities between english and vietnamese sentences, is proposed. we changed the shared layers of the original mt-dnn from original the bert [3] to other pre-trained multi-language models such as m-bert [3] or xlm-r [4] so that our model could work on cross-language (in our case, english and vietnamese) information retrieval. we also added some tasks as improvements to gain better results. as a result, we gained 2.3% and 2.5% increase in evaluated accuracy and f1. the proposed method was also implemented on other language pairs such as english – german and english – french. with those implementations, we got a 1.0%/0.7% improvement for english – german and a 0.7%/0.5% increase for english – french. keywords-mt-dnn; bert; xlm-r; english; vietnamese; cross-language; paraphrase identification i. introduction paraphrase identification (pi) is a task in natural language processing (nlp) that concerns detecting a pair of text fragments that has the same meaning at different textual levels [1]. pi has a relation with the way we would quantify the number of mutual semantics between two text fragments. measuring how two text fragments are semantically related is essential. the example in table i was taken from the mrpc (microsoft research paraphrase corpus) dataset and was translated to vietnamese. pi applications can be found in search engines, legal matters, or, especially, plagiarism check. a few solutions have been proposed for the mentioned problem such as the fuzzy-based method and the babelnet semantic network [5] or siamese lstm (long-short term memory) [6] but they are still limited. table i. an example of two english paraphrased sentences and their translation into vietnamese sentence a singapore is already the united states' 12th-largest trading partner, with two-way trade totaling more than $ 34 billion. singapore đã là đối tác thương mại lớn thứ 12 của hoa kỳ, với tổng kim ngạch thương mại hai chiều hơn 34 tỷ usd. sentence b although a small city-state, singapore is the 12th-largest trading partner of the united states, with trade volume of $ 33.4 billion last year. mặc dù là một thành phố nhỏ, singapore là đối tác thương mại lớn thứ 12 của hoa kỳ, với kim ngạch thương mại đạt 33,4 tỷ usd vào năm ngoái. with the use of transfer learning by applying the pre-trained model in machine learning models, nlp tasks in general or the pi task in particular had significant improvements in their results. among many pre-trained models, bidirectional encoder representation transformer (bert) [3], used to be considered as a state-of-the-art model, with impressive results in many nlp tasks. in this paper, the mt-dnn model was applied which is a combination of pre-trained models like bert [3], multilingual bert (m-bert) [3], or crosslanguage model roberta (xlm-r) [4] with multi-task learning (mtl). the objective of this study is to improve the pi task between pairs of multilingual documents (namely english and vietnamese) through applying transitional learning from a better pre-trained language model, with an mtl approach, including adding new improved tasks. ii. literature review a. pre-trained model and transfer learning transfer learning is a method of using pre-trained models and then optimize them for our purposes. a pre-trained model is a model that has been previously trained with a large dataset or with advanced methods to reduce the effort of training from scratch [8]. the model can then be further trained to fit the corresponding author: hung vo tran chi engineering, technology & applied science research vol. 11, no. 5, 2021, 7598-7604 7599 www.etasr.com chi et al.: english-vietnamese cross-lingual paraphrase identification using mt-dnn actual data set or used directly in a machine learning problem. between the pre-trained models, bert [3] which was a stateof-the-art model in 2019, is still a solution worth considering. specifically, bert was constructed based on transformer (or attention's mechanism), which is a deep learning model having combined inputs and outputs where the model calculates their weights. bert was trained on 2 main tasks: mlm (masked language modeling) and nsp (next sentence prediction). bert has been applied in many applications [9, 10]. m-bert is a single language model pre-trained from 104 languages (including english and vietnamese). it showed abilities to not only generalize cross-lingual but also to transform scripts between many languages without having lexical overlap [3]. xlm-r was trained with mlm only, but with much more data and was based on large-bert. the solution used in xlm-r to deal with the burden of multilinguality was to increase model capacity by learning much more data than before. authors in [4] showed that for the first time we can have a single large model for all languages without losing performance for any language. b. paraphrase identification methods before the rising of deep learning, the most common solutions were lexical, syntactic, semantic, or hybrid techniques. after that, some sophisticated approaches have been applied by supervised or unsupervised learning. fig. 1. the original architecture of the mt-dnn. by using supervised learning, many traditional techniques were applied [10-13] or more advanced, using pre-trained models, specifically bert and its improved models such as m-bert, xlm-r, etc. mtl is an approach that achieves the generalization of results by using the inductive transfer method [14]. with mtl, we assume that knowledge gained from previous tasks could help us achieve better results when learning a new task. the main benefits from mtl are: it helps us build a platform from the previous task in order to gain better results and it does not need a big dataset with labeled data (which is hard to get) as the deep neural networks (dnns) do [15]. furthermore, this approach creates a universal presentation without getting bias in any particular tasks. it could be achieved by regularized effects thus minimize overfitting error [15]. in the original mt-dnn architecture, we have two main layers: shared and task-specific. the first layer type takes the input and encodes them using lexicon encoder and transformer encoder (through the attention mechanism) to create embedding context vectors. these vectors are shared through all tasks. after that, the task-specific layer (depended on the tasks we use) will take these embedding vectors and process them to get the final results (e.g. with the pi problem, mt-dnn's task-specific layers will use the formula ������,�� � � � .� with ��,�� being the input pair and � � the weight matrix) iii. the proposed method a. schematic overview the overview of the proposed method can be seen in figure 2. fig. 2. the proposed solution. b. updating the pretrained model with the change of subject in our model from a single language to cross-language, we need to change the shared layers of the original mt-dnn in figure 1 due to two main reasons: • the original bert used in mt-dnn only can be used for english but for no other languages. • with many other multi-language pre-trained models, we can achieve not only better embedding but also have a positive effect on our results from the transfer learning method. we replaced bert with m-bert and xlm-r to be able to work on the english-vietnamese language pair. m-bert was not trained specifically for having shared presentations through languages. engineering, technology & applied science research vol. 11, no. 5, 2021, 7598-7604 7600 www.etasr.com chi et al.: english-vietnamese cross-lingual paraphrase identification using mt-dnn fig. 3. the proposed model. c. adding more tasks 1) cola-vie (corpus of linguistic acceptability in vietnamese) the existing cola [16] dataset was added to our model. translating the original dataset to vietnamese and training our model on this dataset could create a mapping in grammaticality between vietnamese and english. the cola dataset in the original language (english) helped the model to learn and get many unacceptable sentences for various reasons such as pragmatical anomalies, unavailable meanings, syntactic or semantic violations, etc. [16]. by translating the original cola dataset to vietnamese, we want our model to be able to learn when to accept a sentence in vietnamese with the same reasoning, which creates mappings in how we include and exclude sentences between vietnamese and english. with our evaluation task, which is mrpc, if two sentences in vietnamese and english are both acceptable, they will be more likely to be similar or paraphrased. 2) sst-vie (stanford sentiment treebank in vietnamese) contrary to the original sst, this dataset instead of using 5 classes (very negative, negative, neutral, positive, very positive), only uses 2 classes (positive and negative) which allows us to create easier and more accurate mapping. it does not only look for specific words such as love or hate (which can be wrong in cases of sarcasm or negative words being positive) but checks the whole sentence. with this, we can make use of pre-trained models presenting the context much better than only considering some words. the dataset was translated to vietnamese because: • it can help the model learn the presentation of context and vocabulary in vietnamese in order to improve accuracy when doing tasks that involved vietnamese. • to create class mapping in order to make our model able to differentiate negative or positive in vietnamese. thus, if two sentences in vietnamese and english are both in the same class, the chance they are paraphrased is higher. 3) ner-vie (named entity recognition in vietnamese) we used the datasets from conll (english) [17] and vlsp (vietnamese) [18] in order to recognize the named entities – which can help us extract information and get tags for words in a sentence in both languages and create the mapping between them. when the classes between conll and vlsp datasets were compared, it was found that they had the same labels. with that, we added this task to: • help our model to learn how to recognize the named entities in both vietnamese and english so it can extract information more efficiently (which is the original purpose of this task). • create mappings of the named entities between two languages. if two sentences in cross-language have several same-named entities, they are more likely to be relevant than those that do not. 4) pos-vie (part-of-speech tagging in vietnamese) with the same idea of ner, we tried to make our model recognize pos tags. when checking the dataset of conll and vlsp, we saw differences in quantity (49 to 35) and the engineering, technology & applied science research vol. 11, no. 5, 2021, 7598-7604 7601 www.etasr.com chi et al.: english-vietnamese cross-lingual paraphrase identification using mt-dnn number of similar tags (approximately 80%). the reasons behind this utilization are: • learning how to tag pos for sentences in both vietnamese and english could not only help our model to extract information but also to check the grammar in both languages. • if we have more identical part-of-speech tags in both sentences, the chance of being relevant will be higher. because the number of similar tags is little, we want our model to be able to create mappings between different tags in both languages. 5) wic (word in corpus) [19] the dataset of this task included 3,832 samples with 4 attributes. originally, this task is a binary classification problem that wants to define whether some words are the hypernyms of another word or not. we only used the labels combined with the hypernyms and the original words and removed the definitions of that word. as well as extending our vocabulary in english, we assume that if our model can learn the connection and the hierarchy between words, so it will not only be able to detect the link between a word in english and vietnamese but also to expand to its hypernyms in english as well. consequently, when we compare two sentences in vietnamese and english, not only words having the same meaning are checked but also any hypernyms, if they exist in english sentences, will influence the result. 6) semeval task 8 – 2010 [20] this dataset includes 8,000 samples with 3 attributes. by adding this dataset, we tried to expand mnli (multi-genre natural language inference) and snli (single natural language inference). while mnli only has some simple relationships (contradiction, neutral, and entailment), this task will specify the relationships with more details by increasing the number of relationships (19 classes in the dataset which includes 9 pairs of active or passive relationships and 1 class for others) and the positions of relationship’s subjects in the sentences. by using this task in the proposed model, we are able: • to use the benefit from ner and pos tasks if they improve our result, especially the specified pair of subjects in sentences so we can specify the relationship between them. • to expand the benefits from mnli and snli for a more specific classification of relationships. if two words belong to the same classification, they will be more likely to be paraphrased. table ii. the configuration of mt-dnn architecture of both xlm-r and m-bert num_embeddings embedding_dim padding_idx embeddings word_embeddings 250002 768 1 adding normlayer: size(768,) and dropout(p=0.1) position_embeddings 514 768 1 token_type_embeddings 1 768 1 in_features out_features bias encoder: include 11 linear bert layers bertselfattention 768 768 true 3 linear layers for query + key + value and dropout layers (p=0.1) bertselfoutput 768 768 true adding normlayer: size(768,) and dropout(p=0.1) bertintermediate 768 3072 true bertoutput 3072 768 true adding normlayer: size(768,) and dropout(p=0.1) pooler dense layer 768 768 true with activation function = tanh scoring list: number of layers = number of tasks linear 768 number of classes of this task true iv. implementation a. preparing the dataset we started with the original glue (general language understanding evaluation) dataset [21]. we used 9 out of 10 tasks in our dataset (excluding the ax dataset for format reasons). these 9 datasets represent 4 tasks that will be learned in our model. to make it more appropriate with our problems, we translated the dataset as follows: • single-sentence classification (cola and sst-2): we translated all to vietnamese and used both versions (vietnamese and english) to create single-vietnamesesentence classification (svsc). • pairwise text classification (mnli, rte, wnli, qqp, and mrpc dataset) and text similarity (sts-b questionanswering natural language inference): we kept the question in english and translated the answer to vietnamese. the ax (diagnostic in glue) dataset was excluded because we should create labels by using a model trained on mnli. • relevance ranking (qlni question-answering natural language inference): we kept the question in english and translated the answer to vietnamese. then, ner and pos from conll for english and from vlsp for vietnamese were added to make a mapping in entities from english to vietnamese and backwards. in the end, we added the wic-tsv and semeval-task8 2010 datasets to enhance the connection of words and relationships in english. we also translated semeval-task 8 2010 to vietnamese for learning relationships in this language. engineering, technology & applied science research vol. 11, no. 5, 2021, 7598-7604 7602 www.etasr.com chi et al.: english-vietnamese cross-lingual paraphrase identification using mt-dnn after translation, we used preprocessing scripts to encode our data with xlm-r (or m-bert) to make input for our model. so, our model inputs and outputs were: • inputs: a pair of sentences in english vietnamese • output: whether they are paraphrased or not example: inputs: there are 103 democrats in the assembly and 47 republicans đảng dân chủ chiếm ưu thế trong quốc hội trong khi đảng cộng hòa kiểm soát thượng viện. output: not paraphrased (true – in original methods they are marked as paraphrased) b. training for each time of traning, we selected the task we wanted to add to our original model and the hyperparameters. after many epochs, we got the checkpoint model which had best results on our mprc dataset c. fine-tuning in the fine-tuning stage, we striped the task-specific layers (included other tasks which are not mrpc) and trained our model (which has the best checkpoint from training) with the mrpc dataset again to achieve as best results as possible. the reason for our fine-tuning step is that it improves the result significantly with a little consumption of time and resources. as in the training step, we got the checkpoint model which had the best results on the mprc dataset after many epochs. d. configuration we used google colaboratory pro configuration with: intel xeon r (2 cores) 2.20 ghz cpu, nvidia v100-sxm2 (16gb vram hbm2) gpu, 12.72gb ram, and 150gb hard disk. table iii. results of vietnamese-english pairs task no finetuning with finetuning accuracy f1 score accuracy f1 score original architecture (xlm-r) – standard result 82.8 87.6 84.3 88.5 original architecture (xlm-r) + svsc 80.1 86.2 85.7 89.6 original architecture (xlm-r) + svsc, ner (english), pos (english) 79.1 85.2 84.8 88.8 original architecture (xlm-r) + svsc, ner (english) 77.9 84.3 81.6 86.3 original architecture (xlm-r) + svsc, pos (english) 80.6 86.4 83.8 88.3 original architecture (xlm-r) + svsc, ner (english, vietnamese), pos (english, vietnamese) 80.6 86.3 85.5 89.6 original architecture (xlm-r) + svsc, pos (english, vietnamese) 82.1 87.3 83.3 87.3 original architecture (xlm-r) + svsc, ner (english, vietnamese) 79.4 85.4 85.2 89.2 original architecture (xlm-r) + svsc, wic-tsv 83 88.1 87 91 original architecture (xlm-r) + svsc, wic-tsv, ner (english, vietnamese) 80.6 86.7 86 89.7 when configuring the pre-trained models, we used mbert and xlm-r with the following hyperparameter specifications: • batch-size: 8 • learning rate: 5×10-5 • gradient accumulation step: 4 (for making training more stable and faster) • while they have a different number of parameters, both xlm-r and m-bert have the same structure as presented in table ii. table iv. specifications of m-bert and xlm-r v. result and discussion the results from table v indicate that xlm-r shows an outstanding performance when compared to m-bert with a 9% and 6% increase in accuracy and f1 score respectively before the finetuning stage. after the finetuning stage, that gap expanded to 11% and 7%. that result could be explained by the way m-bert was trained, since it did not have shared presentations through languages specifically. table v. result of the original model with m-bert and xlm-r dataset pretrained model no finetuning with finetuning accuracy f1 score accuracy f1 score all dataset in glue m-bert 73.2 81.4 73.7 81.3 all dataset in glue xlm-r 82.8 87.6 84.3 88.5 on the other hand, xlm-r was trained with common crawl [4] which helps in gaining data from languages with low resources. with the result of 84.3% in accuracy and 88.5% in f1 score, we chose that result as our standard to compare when adding the improvement tasks. in table iii, when we look at the accuracy and f1 score in adding cola-vie and sst-vie, the results were all decreased by approximately 1-4% (accuracy) and 0.5-3% (f1 score). only the model with the additional wic task had a slightly higher result. after the finetuning stage, the results improved. the accuracy increased by 0.5-2.7% and the f1 score by 0.3-2.5% (with the highest result firmly belonging to the model which the wic task). in the final model, we had 83% and 88.1% before finetuning (accuracy and f1 score respectively). after the finetuning stage, those numbers increased to 87% and 91%. besides this increase, adding ner-en and pos-en tasks made our model's performance decrease. while the change of the evaluation's result after the finetuning stage was proved in the paper, adding pos-en and pos-vie did not improve the result. when looking at the data name number of layers detail name (in huggingface) m-bert 177865744 bert-base-multilingual-cased xlm-r 278060566 xlm-roberta-base engineering, technology & applied science research vol. 11, no. 5, 2021, 7598-7604 7603 www.etasr.com chi et al.: english-vietnamese cross-lingual paraphrase identification using mt-dnn from conll (english) and vlsp (vietnamese), they have differences in the number of total and identical tags. due to this, we must transfer those data to a universal pos tag. because of the differences in sentence structure, accurate mappings could not be created between the two languages and the context of learning was different, which incommodated our model. when we added ner-en and ner-vie, we also found that the result did not improved because the units in the vocabulary of english and vietnamese have differences. in english, a word is a single unit while in vietnamese, a word can be formed by many units (e.g in english we have "toothbrush" whereas in vietnamese will be "bàn-chải"). adding the wic task made the difference in terms of accuracy and f1 score. because this task did not care about the way words are built like ner or pos but concerned more about the meaning of the sentence or the connection between words, which improved our model significantly. in table vi, by applying the above improvements (svsc + wic-tsv) in german and french, we proved that adding this task not only worked for the original pair but also for other language pairs. more specifically, the result for english – german increased by 1.0% in terms of accuracy (from 86.2% to 87.2%) and 0.7% in f1 score (from 90.1% to 90.8%). in english – french, those numbers were 0.7% (from 85.5% to 86.2%) and 0.5% (from 89.7% to 90.2%). table vi. results of vietnamese-english pairs language pair no finetuning with finetuning accuracy f1 score accuracy f1 score english french 83.5 88.4 85.5 89.7 80.3 86.4 86.2 90.2 english german 81.8 87 86.2 90.1 82.1 87.3 87.2 90.8 for further improvements, many pre-trained models with better results could be applied to the model. another improvement is to standardize the dataset in the translation step so it could make the mappings more accurate. vi. conclusion in this paper, the application of mt-dnn with transfer learning (by using a pre-trained model improved from bert, m-bert, and xlm-r), combined with modified mtl for the cross-language english vietnamese pair to achieve competitive performance in paraphrase identification task, was studied and presented. the result evaluation stage confirmed the suitability of the proposed model which includes xlm-r, svsp, and tsv of wic which helped obtaining better results, such as 87% and 91% in accuracy and f1 score. besides the original language pair, our proposed method also had a good performance for english – german and english – french pairs with accuracy and f1 score of 86.2% and 90.2% and 87.2% and 90.8% respectively. our model can be improved by changing the pre-trained models with a state-of-the-art model in the future. acknowledgement this research is partially funded by the faculty of information technology, university of science, ho chi minh city, vietnam. references [1] a. amaral, "paraphrase identification and applications in finding answers in faq databases." 2013, [online]. available: https://fenix. tecnico.ulisboa.pt/downloadfile/395145918749/resumo.pdf. 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[21] a. wang, a. singh, j. michael, f. hill, o. levy, and s. bowman, "glue: a multi-task benchmark and analysis platform for natural language understanding," in proceedings of the 2018 emnlp workshop blackboxnlp: analyzing and interpreting neural networks for nlp, brussels, belgium, nov. 2018, pp. 353–355, https://doi.org/ 10.18653/v1/w18-5446. microsoft word etasr_v11_n5_pp7738-7744 engineering, technology & applied science research vol. 11, no. 5, 2021, 7738-7744 7738 www.etasr.com benaissa & khalfallah: industrial activity land suitability assessment using delphi and ahp … industrial activity land suitability assessment using delphi and ahp to control land consumption the case study of bordj bouarreridj, algeria fateh toufik benaissa department of urban engineering institute of urban techniques management university of msila msila, algeria fatehtoufik.benaissa@univ-msila.dz boudjemaa khalfallah department of urban engineering institute of urban techniques management university of msila msila, algeria boudjemaa.khalfalllah@univ-msila.dz abstract-studies and research on land suitability for the localization of economic and industrial activities in cities are attracting academics and local policies concerned with urban planning and organization in order to make urban areas more accommodating. the current paper aims to demonstrate the ability of visualization and simulation techniques to assist planners in preserving urban real estate by combining the delphi method with one of the multi-criteria hierarchical analysis decision-making techniques. the city of bordj bouarreridj in algeria was chosen as the case study and, with the participation of experts, a set of criteria were adopted to determine land suitability. three criteria were selected in the first phase with the use of the delphi method. in the second phase, we applied the analytical hierarchy process (ah, a hierarchical analysis method. during the third stage, the obtained results were translated into the gis program to derive the spatial suitability map. the following are among the most important achieved results: 13.38% (521.793 km 2 ) of the area was regarded to be of high suitability, 67.54% (2,634.758 km 2 ), achieved moderate suitability, 12.94% (504,794 km 2 ) attained low suitability, and 6.14% (239,685 km 2 ) were found to be not suitable at all. keywords-industrial activity; bordj bouarerridj; land suitability; control consumption; delphi method; ahp i. introduction both private and public sectors contribute to the increment of the area of cities. in algeria, we find that most of the construction of industrial zones is usually at the expense of agricultural lands, which affects the land uses of cities by covering the increasing housing demand [1]. the economic transformations of cities have created factors, represented in factories and workshops, that contribute to the emergence of management and organizational problems of the territory, especially about the allocation of lands and their suitability. the planners confront a dual problem in this situation. they must create initiatives and programs that maintain ecological balance while promoting economic growth, while they must act as mediators, attempting to prevent conflict and reduce objections. land use planning is a means of optimal allocation of land resources [2]. it is frequently utilized in the spatial allocation and characteristics of land size to scheme and arrange land usage of the studied areas. studying and identifying land-use needs for each land-use type is critical and fundamental for evaluating land use suitability for each land mapping unit [3]. land use suitability analyses are of considerable use in the planning of mega-cities [4]. as a result, it is critical to use a technique that allows weight estimation. one such strategy is the analytical hierarchy process (ahp), which is a multi-criteria decision-making method. the author in [5] used several variables that were related to the environmental aspect. he focused his studies on environmental indicators. in this study, the answers were obtained by experts and institutions, and the obtained data were analyzed with the ahp method, after which a map of spatial suitability was derived by the geographic information systems (gis). authors in [6] used ahp to determine the gis weights based on 12 variables. their study focused on social, economic, and environmental indicators. such methods have the largest number of variables but the participation of experts and sometimes residents is often necessary. authors in [7] used gis and ahp to select the best sites for urban growth in seremban, malaysia. many social, economic, and environmental factors were considered to create a final land suitability map, but the notable thing in this study is that the researchers relied on the selection of factors and variables on local literature and general observations only without relying on experts or residents. this paper presents the results obtained by integrating the delphi approach, ahp, and gis in analyzing the relevance of land use to economic activity to control the land consumption in urban areas. the case study area was the city of bordj bouarerridj. ii. materials and methods a. the study area bordj bouarerridj is an algerian city in the high eastern highlands. it is located in the algerian east in the middle of two atlas mountains series, the beban mountain range and the alhodna mountain range with a population density of 186.4 inhabitants/hectare in 2014, according to the nsb (national statistics bureau). its total area is estimated at 3901.02km2, i.e. corresponding author: fateh toufik benaissa engineering, technology & applied science research vol. 11, no. 5, 2021, 7738-7744 7739 www.etasr.com benaissa & khalfallah: industrial activity land suitability assessment using delphi and ahp … the 1/600 of the total area of algeria. the forms of land usage vary, the land appropriateness is broad, and the degree of use is high (figure 1). fig. 1. the study area. prepared by the researchers on the qgis program, 2021. b. data collection 1) suitability factors for land use for industrial activities the criteria defined by the delphi method to study the suitability of lands for economic and industrial activities, and their weights were appreciated by using the expert choice v11 program, which is an application for multi-criteria analysis through ahp. after collecting the geographical data, layers of determinant criteria, and sub-criteria were set in the opensource qgis program. the results are displayed graphically in figures 2-9. fig. 2. geological nature of the study area. prepared by the researchers on the qgis program. 2) nature and environment for this factor, forest areas, hydrographical networks, and watershed basins have been identified, through the bordj bouarerridj city reconstruction plan. the suitability subfactors were as follows (figure 2): forest areas: (0-5 km), (5-9 km), (9-13 km), and (> 13 km). hydrographical network: (0-5 km), (5-10 km), (10-15 km), and (> 15 km). watershed basins: (0-5 km), (5-10 km), (10-15 km), and (>15 km). fig. 3. railways of the study area. prepared by the researchers on qgis. fig. 4. principal roads of the study area. prepared by the researchers on qgis. 3) security and protection the relevant information was collected from the planning and reconstruction plans of the bordj bouarerridj state. layers were determined in the arc gis program in urban tissues, archaeological areas, slopes, and geological sites according to the opinion of experts and technicians. the range of suitability for the distance from residential areas was as follows: (< 4 km), (4-10 km), (10-15 km), and (> 15 km). for slope, the range of suitability was as follows: (< 4%), (4%-8%), (8%12%), and (> 12%). the geological nature was determined according to the permeability and type of soil. engineering, technology & applied science research vol. 11, no. 5, 2021, 7738-7744 7740 www.etasr.com benaissa & khalfallah: industrial activity land suitability assessment using delphi and ahp … fig. 5. watershed basins of the study area. prepared by the researchers on qgis. fig. 6. forests on the study area. prepared by the researchers on qgis. fig. 7. urban areas of the study area. prepared by the researchers on qgis. 4) economic determinant for this factor, we considered all the main roads and structured railway lines of the case study. the data were collected from the planning and reconstruction plans of bordj bouarerridj in 2018. the range of suitability was determined by the experts as follows: (0.5-4 km), (4-10 km), and (> 10 km) (figures 3, 4). fig. 8. water ways of the study area. prepared by the researchers on qgis. fig. 9. slopes of the study area. prepared by the researchers on qgis. c. methods industrial site selection is a spatial decision problem. such problems typically involve a large set of feasible alternatives [8]. land suitability for industrial activities is a somewhat complicated process considering the data and characteristics that distinguish them. therefore many possible alternatives must take as well as appropriate multi-faceted and often conflicting standards, such as economic, environmental, climate, social, etc. the delphi method is often applied to define the evaluation criteria as a way of structuring the method of collective communication to affect the complex problem of extracting and studying the influential factors to seek out the most appropriate sites. the suitability of lands for industrial activities in urban areas is determined by calculating the degree of importance of the percentage of significant value [9]. after, we used the ahp method which is used to solve complex decision problems [10]. that decision-making tool depends on reliable measurement and thorough evaluation to present suitable lands for economic activities [11]. it also serves as a helpful tool for capturing both subjective and objective assessment measures for checking the consistency of the evaluations and thus reducing bias in decision making [12]. this study is based on the ahp and through interactive computer programs (expert choice v11) [13]. the computer engineering, technology & applied science research vol. 11, no. 5, 2021, 7738-7744 7741 www.etasr.com benaissa & khalfallah: industrial activity land suitability assessment using delphi and ahp … uses a hierarchical framework of criteria and comparisons between them to establish the criterion weight. the additive transformation function of the weighted summation technique is applied to get a final score for each choice. expert choice network accepts no restriction on the size of the decision issued in this scenario. the dm's preferences on criteria are represented by cardinal weights [14]. fig. 10. the analysis used for this research. d. delphi method the delphi method is a consensus method that aims to find general agreement among an expert panel on a specific research topic [15]. it is considered a way for organizing the group communication process to facilitate group issue solving and model building. its principal area of application has remained that of technical forecasting [16]. in this research paper, we relied on 15 experts of various disciplines, namely geology, urbanization, economics, and law, who are familiar with the research topic and close to the decision-making authorities. our questions were presented to them in four stages. after the first stage, we sent an anonymous summary of the resume of the experts' outlook of each previous stage and its reasoning [17]. this gradually led to the convergence of viewpoints and after the questionnaire's results were obtained. through the questions posed to the experts and based on their opinions, criteria of approval for each standard set of subcriteria were set. after this, the ahp series pyramid was analyzed to determine the weights of the main indicators and the sub-criterions in expert choice v11 software. e. hierarchical analysis process ahp is a multiple-criteria decision-analysis (mcda) technique used in solving various decision-making problems [18-20]. it is suitable for the evaluation of complex multiattribute alternatives [21], because it is considered one of the most effective and easy procedures [22]. the ahp model has been applied to determine weights and ranks of all the subcategories [23]. the ahp methodology may tolerate inconsistency according to pair-wise comparison by given a measurement of evaluation inconsistency. this measurement is among the most essential parts of the priority determination process. the higher the consistency ratio, the assessment result becomes more inconsistent [24]. after the hierarchy creation, the relative importance of all resolution elements is captured and detected through binary comparisons. the expert choice is a decision-oriented program that provides support to decisionmakers by organizing information with regarding to the complexity of a multi-solution problem into a hierarchical model consisting of objective, potential scenarios, agents, and alternatives. the priorities are determined along with the comparison matrix. we begin with a matrix that is consistent and has known priority pi. pi/pj is used to compare alternatives i and j which is multiplied with the priority vector p results [25]: ��� ��⁄ �� ��⁄ ⋯ �� ��⁄�� ��⁄ �� ��⁄ ⋯ �� ��⁄⋮ ⋮ ⋱ ⋮�� ��⁄ �� ��⁄ ⋯ �� ��⁄ �����⋮�� � � � ����⋮�� (1) or grouped: �� � ��� (2) where �� is the prioritization vector, n the matrix dimension, and a the matrix of comparison. the author in [13] proposed a consistency index (ci) because priorities are only relevant if they are generated from coherent or close-to-consistent matrices, which is related to the eigenvalue method [26]: ci � ���� ���������� ����� (3) ��� !"#!�$�%&! � ∑ (".*" (4) the consistency ratio (cr) is calculated to measure the consistency of the solution [27], and it is obtained by (5). the random consistency index (ri) is shown in table i [28]. cr � ,-. (5) table i. random consistency index. n 1 2 3 4 5 6 7 8 9 10 ri 0 0 0.58 0.90 1.12 1.24 1.32 1.41 1.45 1.49 if cr ≥ 10% the data are considered inconsistent. if cr < 10% we have data consistency and the matrix is considered as having an acceptable consistency [25]. f. geographic information system (gis) gis is a process of mapping and integrating computerfounded information with the ability of data layer management to make appropriate decisions by combining geographical information layers [29]. data combined with an application of gis provide alternative, flexible and scalable means [30]. the availability of digital data archives since 1987 enables the quantitative and qualitative assessment of land use patterns [31]. accordingly, several studies have been conducted emphasizing the adoption of delphi, ahp, or a combination of these methods, with gis for modeling and analyzing spatial engineering, technology & applied science research vol. 11, no. 5, 2021, 7738-7744 7742 www.etasr.com benaissa & khalfallah: industrial activity land suitability assessment using delphi and ahp … suitability [32]. it assists decision-makers to assign priority weights to decision criteria, evaluate the suitable alternatives, and visualize the results [33]. iii. results and discussion this research relied on a mcda using the ahp analysis to study the suitability of land use for economic activity in order to control the consumption of urban land involving the opinions of experts in the field. eight criteria were used to quantify the suitability for economic and industrial land use, namely urban areas, slopes, forest areas, hydrographical network, watershed basins, geology, roads, and railways. a comparison matrix was implemented between the main factors and subfactors and paired-wise comparison was conducted between the sub-criteria of the same level [34]. afterwards, the weight of each determinant was extracted (figure 11). fig. 11. results of ahp among main and sub criteria. fig. 12. performance sensitivity for nodes. the proportion of consistency was less than 10%, which means that the distribution between the factors was acceptable. table ii. ahp key criteria rating criteria weight rating road 0.2265 2 railway 0.1531 3 geology 0.237 8 hydrographical network 0.571 6 watershed basins 0.0726 5 slope 0.1015 4 forest 0.0318 7 urban area 0.3338 1 fig. 13. priorities with respect to goal. based on the previous hierarchical analysis of the suitability of land use for economic and industrial activity, the role of gis comes in the form of a model that summarizes all stages of work in the arc gis. we compiled all the pre-defined standard maps in gis via raster calculators with each standard multiplied by the weight generated by the ahp and expert choice to produce a suitable land use map. (figure 14). fig. 14. the produced land suitability map for for economic and industrial activity regarding the bordj bouarerridj area. prepared by the researchers on the qgis program. the final map gross weight was calculated by raster calculation using (6): sl � 1row ∗ ror6 7 1rww ∗ rwr6 7 1gw ∗ gr6 71www ∗ wwr6 7 1waw ∗ war6 7 1sw ∗ sr6 7 1fw ∗ fr6 71uw ∗ ur6 (6) where sl is the suitability of land use for economic and industrial activity, w is the weight of each criterion, r is the classification of each criterion, ro stands for road, rw for railway, g for geology, ww for waterways, wa for water, s for slope, f for forest, and u for urban areas. through hierarchical analysis the proportion of land-use suitability for economic and industrial activity in the city of bordj bouarerridj was: • 13.38% of the total area with a total surface area of 521.793km2 achieved high suitability. • 67.54% of the total area with a total surface area of 504.794km2 achieved moderate suitability. • 12.94% of the total area with a total surface area of 2634.758km2 achieved low suitability. ,00 ,10 ,20 ,30 ,40 ,50 ,60 ,70 ,80 ,90 ,00 ,10 ,20 ,30 ,40 ,50 ,60 ,70 obj% alt% cl ha cl pt 5 km 9 km > 10 % 9 km 13 km lp li 0 km 5 km cl haye 8 % 10 % 5 km 10 km 2 km 4 km > 13 km > 12 km 4 % 8 % 7 km 12 km 4 km 10 km 0 % 4 % 3 km 7 km 10 km 15 km 0 km 3 km > 15 km watershed ba slope (l: ,1 urban area ( forest (l: , roads (l: ,2 railway (l: geologie (l: waterway (l: overall engineering, technology & applied science research vol. 11, no. 5, 2021, 7738-7744 7743 www.etasr.com benaissa & khalfallah: industrial activity land suitability assessment using delphi and ahp … • 6.14% of the total area with a total surface area of 239.685km2 was not suitable. the results are summarized in table iii. in the final map (figure 14) of the city of bordj bouarerridj' suitability of land usage for industrial activities, we note that the areas that achieved high suitability according to the ahp are the areas that are away from the urban tissues and near the road. table iii. percentage of ahp standard. classes area (km 2 ) % high suitability 521.793 13.38 % moderate suitability 2634.758 67.54 % low suitability 504.794 12.94 % no suitability 239.685 6.14 % total 3901.023 100 % iv. conclusions in this study, we utilized delphi methodology and ahp and gis technologies and a strategy was developed to assess the land use for economic activities and thus be able to manage the land consumption of metropolitan areas. the case study of this research was the state of bordj bouarerridj. a group of experts defined a set of criteria that helped determine the suitability of regions for economic activity. the ahp hierarchical analysis method was used to extract land-appropriate measures through the expert choice program. the consistency ratio was 0.03, which is less than 0.1, and therefore is considered favorable. after using the ahp method, spatial analysis of the study area was carried out, with the creation of a geographical database of the criteria specified by the experts in gis environment by creating a model using all accounted data to extract an appropriate map of land use for economic activity. we can conclude by saying that the combination of the delphi method and the hierarchical analysis using expert choice software in gis environment is a practical scientific method that gives accurate results in determining the land use suitability for economic activity, according to the defined criteria. however, these criteria remain variable factors because they depend on the specificities of each region. the produced map may be adapted to identify regions for future housing development, evaluate the worth of a property, and assist decision-makers in achieving balanced urban development. references [1] mohamed gherbi, "instruments of urban planning in algerian city: reality and challenges," journal of civil engineering and architecture, vol. 9, no. 7, pp. 807–812, jul. 2015, https://doi.org/10.17265/19347359/2015.07.007. 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[34] a. r. al-shabeeb, "the use of ahp within gis in selecting potential sites for water harvesting sites in the azraq basin—jordan," journal of geographic information system, vol. 8, no. 1, pp. 73–88, feb. 2016, https://doi.org/10.4236/jgis.2016.81008. microsoft word etasr_v12_n4_pp8831-8836 engineering, technology & applied science research vol. 12, no. 4, 2022, 8831-8836 8831 www.etasr.com duc et al.: an investigation of magnetic field influence in underground high voltage cable shields an investigation of magnetic field influence in underground high voltage cable shields hung bui duc school of electrical and electronic engineering hanoi university of science and technology hanoi, vietnam hung.buiduc@hust.edu.vn tu pham minh school of electrical and electronic engineering hanoi university of science and technology hanoi, vietnam tu.phamminh@hust.edu.vn dinh bui minh school of electrical and electronic engineering hanoi university of science and technology hanoi, vietnam dinh.buiminh@hust.edu.vn nam phan hoai school of electrical and electronic engineering hanoi university of science and technology hanoi, vietnam nam.ph211212m@sis.hust.edu.vn vuong dang quoc school of electrical and electronic engineering hanoi university of science and technology hanoi, vietnam vuong.dangquoc@hust.edu.vn received: 27 april 2022 | revised: 16 may 2022 and 21 may 2022 | accepted: 22 may 2022 abstract-magnetic fields and the shielding efficiency of the shields of underground high voltage cables are studied in this paper regarding several shielding configurations and materials. shielding efficiency and magnetic fields are computed for shields with the same mesh but from different shielding materials, such as aluminum, ferrite, metal, and steel. in order to get the best shield configuration depending on the source characteristics and the material, a conducting ferromagnetic region with various thickness values is considered as shielding. a finite element model is introduced to investigate the influence of the parameters of magnetic fields and the shielding efficiency of underground high voltage cables. furthermore, the reduction of the magnetic fields with or without shieldings is also presented. the developed method is performed with the magnetic vector potential formulations and validated on a practical problem. keywords-shielding efficiency; magnetic fields; eddy currents; underground power cables; finite element technique i. introduction magnetic fields cause a considerable disturbance of the operation and accuracy of sensitive electrical and electronic devices [1], while they pose an important issue to public health [2-5]. new regulations involving a drastic reduction of the allowable limits of exposure have been developed. unfortunately, the conclusion for that problem is not clear and, even if it is, it is still disputed. it cannot be concluded surely that there is no relation between magnetic fields and certain diseases. in addition, a lot of shield configurations can be used as magnetic shielding for underground high voltage cables such as open and closed shield structures. as proposed in [6], the use of thick and large flat sheets above underground high voltage cables gives a good shielding performance. this is also right for a minimal distance between shields and high voltage cables. in addition, good shielding efficiency is demonstrated for closed shield structures [7-9]. in [10], a unimoment method has been proposed to analyze the magnetic shielding of a source within a steel pipe made of ferromagnetic material. in [11], an analytic method has been developed for computing the losses in steel casting with an arbitrary cable arrangement. in [12], the power losses have been computed following the statistical theory. for the above reasons, remarkable efforts have been devoted to research activities aiming at studying suitable techniques to achieve the desired reduction of the magnetic fields generated by electrical systems. in many cases this can be done by simple and effective solutions that do not mean costly additional investments. magnetic fields (mfs) can be generated by high voltage transmission underground cables. several methods have been applied to compute the mfs. they are generally categorized as internal and external shielding methods [12-15]. although the obtained results from these methods are successful to a great degree in some cases, these techniques have also some drawbacks. corresponding author: vuong dang quoc engineering, technology & applied science research vol. 12, no. 4, 2022, 8831-8836 8832 www.etasr.com duc et al.: an investigation of magnetic field influence in underground high voltage cable shields in this paper, the influence of the parameters of the mfs on the shieldings covering underground high voltage cables with different cases of several configurations have been analyzed and simulated via finite element method. this will be presented with the magnetic vector potential formulations to compute and investigate the influence of the mfs and the reduction factor in the proximities due to the field sources. the developed method is validated on the practical problem. ii. magnetic shielding problems a. shielding problems of underground high voltage cables shielding is the most efficient solution to reduce the mfs generated by underground high voltage cables. two different shields can be considered: open shields and close shields. the open shield consists of a cover (flat) plate located above the high voltage cables (figure 1), and the close shield consists of a cable tray surrounding the cables (figure 1). the second case is more expensive than the first case, which is usually employed to reconfigure existing systems. the conductive materials for both cases can be made of aluminum, copper, or ferromagnetic materials. this selection is very important, because each material provides different shielding. there are two scenarios: if the shielding is a high conductive material, the reduction of the field is based on eddy current cancellation. this means that the eddy currents are induced in the conductive plate due to the mfs that partially cancel those of the source as pointed out in figure 2. if the shielding is a material with high permeability, the mechanism is known as flux shunting. this means that the magnetic flux density generated by the source is diverted into the magnetic material and away from the region to be shielded, as shown in figure 3. (a) (b) fig. 1. (a) open shield, (b) close shield. fig. 2. eddy current distributions in a cover plate. these two scenarios are characterized by different boundary conditions (bcs) which have to be analyzed in each configuration. from the above analysis, it is clear that it is not important to decide which shielding technique is the best to mitigate the field caused by an underground high voltage cable, because the shielding effectiveness depends on the configuration of the cables, with issues such as the distance between the cables and the shield, the thickness and width of the plate, etc. depending on the different properties of materials, the results obtained with magnetic materials differ from those obtained using conductive materials. the close shield usually gives a high field reduction near the source, whereas the open shield provides better results far from it. this is also strongly influenced by the arrangements (locations) of the cables. high conductive open shields are suitable for flat lines. however, for the vertical lines, the open shields made of ferromagnetic materials perform better [1]. moreover, it should be noted that magnetic materials are usually more expensive than conductive materials. for the above reasons, a full study/analysis of the parameters involved directly with the effectiveness of shields is presented in this paper to give a selection of suitable configurations for electrical systems. the considered shield parameters are: fig. 3. flux shunting shielding. • thickness and profile of the plate. • value of magnetic permeability and electric conductivity. • different types of materials used. • the distance from the source and the relationship with the dimensional characteristics of the source. b. canonical magnetodynamic problems a canonical magnetodynamic problem is defined in a domain ω, with boundary �ω = γ = γh ∪ γ e. the maxwell’s equations considered in the frequency domain and behavior laws are written in euclidean space ℝ� [16-18]: curl � �� , curl � ��� �, div � 0 (1a-b-c) � ��, � �� (2a-b) where � is the magnetic field (a/m), � is the magnetic flux density (t), � is the electric field (v/m), �� is the current density (a/m 2 ), � and � are the relative permeability and the electric conductivity (s/m). the bcs defined on γ are expressed as: � � �|� !" , � ∙ �|�$ %" (3a-b) where � is the unit normal exterior to ω, with ω ω& ∪ ω' & . the domains ω( and ω' & are respectively the conducting and non-conducting regions. equations (1a) and (1b) are solved engineering, technology & applied science research vol. 12, no. 4, 2022, 8831-8836 8833 www.etasr.com duc et al.: an investigation of magnetic field influence in underground high voltage cable shields with bcs taking the tangential component of � in (3a) and the normal component of � in (3 ) into account. the fields h, b, e, and j are defined to satisfy tonti’s diagram [9]. this means that � ∈ *+ ,curl; ω. , � ∈ */ ,curl; ω. , � ∈ � ,div; ω. , and � ∈ */ ,div; ω. , where *+ ,curl; ω. and */ ,div; ω. are function spaces containing the bcs and the fields defined on γ+ and γ/ of the studied domain ω. the fields !" and %" in (3) are generally equal to zero for classical homogeneous bcs. the field % in (1c) is derived from a vector potential 0 such that: % curl 0 (4) by combining (4) with (1b), we have curl (1 + ∂40. 0, which leads to the definition of an electric scalar potential 5 such that: 1 ��6 0 � grad 9 (5) c. magnetic vector potential weak formulations based on the weak form of ampere’s law (1a), the weak formulation of magnetic problems is written as [17-21]: ,�:;%, curl 0<.= � ,σ1, 0 <.=? + 〈� � a, 0 <〉 � ,!� , 0 <.=c , ∀ 0 < ∈ */ e,curl, ω. (6) by substituting the magnetic flux density % from (4) and the electrical field 1 from (5) into (6), we get: ,�:;curl 0, curl 0<.= + ,��6 0, 0 <.=? + ,� grad 5, 0 <.= +〈� � a, 0<〉� ,!� , 0 <.=c , ∀ 0 < ∈ */ e,curl, ω. (7) where */ e,curl, ω. is a function space defined on ω containing the basis functions for 0 as well as for the test function 0< . notations (· , · ) and < · , · > are respectively a volume integral and a surface integral of the product of their vector field arguments. the surface integral term 〈� � a, 0<〉� on �+ in (8) accounts for natural bcs that can be locally specified. this is the case for a homogeneous neumann bc, e.g. imposing a symmetry condition of "zero crossing current", i.e.: � � a|� 0 ⇒ � ∙ %|� 0 ⇔ � ∙ !|� 0 (9) iii. practical test the test problem considered for the 2d model is a shielding problem with different configurations. table i. properties of shielding materials [5, 8] material conductivity (h. i/k relative permeability (lm. aluminum 3.8×10 7 1 steel 10 7 500 metal 1.64×106 15,120 ferrite 2 10,000 three different cases of a flat arrangement of the underground high voltage cables were considered (figure 4): (a) a cover plate shield (horizontal plate shield) located above the three conductors, (b) a reverseu shield, and (c) close shield surrounding the three conductors. in all cases, the three conductors are supplied by balanced currents of 100a at a frequency of 50hz and voltage of 132kv. cable depth is fixed at 80cm, with a separation between cables of 25cm and conductor diameters of 20mm. (a) (b) (c) fig. 4. geometry of high voltage cables with different configurations: (a) no shield, (b) reverse u-shield, and (c) close shield. (a) (b) fig. 5. field lines in cover shield of (a) aluminum and (b) ferrite. engineering, technology & applied science research vol. 12, no. 4, 2022, 8831-8836 8834 www.etasr.com duc et al.: an investigation of magnetic field influence in underground high voltage cable shields the influence of geometrical parameters of the high voltage cables and the shield in the field generated at 1m height above the ground has been studied. the influence in the shielding factor (also called the reduction factor) can be defined as: no pq p (10) where b0 is the root mean square (rms) value of the field density without the shield, and b is the rms value of the field with the shield in place. by another way, sf can be considered as a position function of the shield. the biggest the sf is, the more significant the magnetic field reduction. the properties of shielding materials are given in table i [5, 8]. fig. 6. magnetic flux density distribution for different material shieldings (horizontal shield). fig. 7. reduction factor process with different thicknesses. two different cases are now considered for testing: without and with cover shield. the distribution of the field lines for the different material shields is presented in figure 5, where field lines can divert in the proximity of the cover shielding due to the different materials. the value of magnetic flux density along the shield at 1m above the ground is pointed in figure 6, for the cases without shield and with shields from different materials (aluminum, ferrite and steel). from the obtained results, it can be seen that the magnetic flux density distribution is very high for the cases without shield and with aluminum shield in comparison with the cases of the ferrite and steel shields, because the massive fields mostly focus on these materials with a little flux leakage to the surrounding air. this means that the magnetic inductions are almost refracted into these shields. the influence of magnetic flux density distribution in the final cost of the cover shield depends on its thickness. thus, there are several cases of thickness values from 1mm to 10mm for the considered materials which have to be examined. τhe relation of the rf with the shield thickness given in (10) is indicated in figure 7. it should be noted that the value increases when the thicknesses varies from 1 to 5mm for ferrite materials. from 6 to 10mm, the value of rf reduces noticeably. the influence of steel thickness increases noticeably from 1 to 10mm, while the thickness influence of aluminum material can be ignored. for the case of reverse-u shield, the field lines of aluminum and ferrite are illustrated in figure 8. the process of rf with different materials and thicknesses is presented in figure 9. the rf for steel, metal, and ferrite increases noticeably with thickness from 1 to 10mm as shown in figure 10. on the other hand, the influence of the aluminum shielding is weak and not worth considering. similarly with figure 6, the reluctances of ferrite and steel are smaller than the air’s (no shield case). due to this, massive fields mostly focus on these materials with a little leakage flux. (a) (b) fig. 8. field lines in reverse-u shield of (a) aluminum, (b) ferrite. fig. 9. magnetic flux density distributions with different material shieldings (reverseu shield). regarding the closed shield, the field lines on magnetic vector potentials are presented in figure 11. the magnetic flux density distribution with different material shieldings is shown in figure 12. it can be seen that the results of metal and ferrite materials are improved, getting similar to those obtained from the case of reverseu shield (figure 9). engineering, technology & applied science research vol. 12, no. 4, 2022, 8831-8836 8835 www.etasr.com duc et al.: an investigation of magnetic field influence in underground high voltage cable shields fig. 10. process of rf with different materials in reverse-u shield. (a) (b) fig. 11. field lines in closed shield of (a) alumimum, (b) ferrite. fig. 12. rf with different material shieldings (closed shield). iv. conclusion in this paper, the influence of magnetic flux density distribution on shielding efficiency for underground high voltage cables has been investigated with the magnetic vector potential formulations for several shielding configurations. regarding the shielding materials, the obtained results illustrated the influence of magnetic fields at 1m for the cases without shield and with shields from different materials, and the evolution of rf with thickness. high rf can be also obtained by increasing shield thickness when open shield made of high conductive materials is used. in the case of ferromagnetic materials, increasing shield thickness has a low effect. as a result, we can say that shield size has a relatively small effect on shielding: a larger shield decreases slightly the shielding efficiency of ferromagnetic shields, and increases it for shields made from aluminum. in fact, with increasing shield thickness, the shielding effectiveness improves without causing higher losses. in particular, it should be noted that if the best shielding effectiveness for a given thickness is required, a high permeability material is preferred. if a low cost per meter of shield is required, a ferromagnetic grade with lower permeability can be used. if low magnetic losses in the shield are important, aluminum is preferred. acknowledgement the authors wish to thank quy nhon university for their help and for providing the necessary equipment. references [1] b. banfai, g. g. karady, c. j. kim, and k. b. maracas, "magnetic field effects on crt computer monitors," ieee transactions on power delivery, vol. 15, no. 1, pp. 307–312, jan. 2000, https://doi.org/ 10.1109/61.847267. 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[11] w. moutassem and g. j. anders, "calculation of the eddy current and hysteresis losses in sheathed cables inside a steel pipe," ieee engineering, technology & applied science research vol. 12, no. 4, 2022, 8831-8836 8836 www.etasr.com duc et al.: an investigation of magnetic field influence in underground high voltage cable shields transactions on power delivery, vol. 25, no. 4, pp. 2054–2063, jul. 2010, https://doi.org/10.1109/tpwrd.2010.2049509. [12] g. bertotti, "general properties of power losses in soft ferromagnetic materials," ieee transactions on magnetics, vol. 24, no. 1, pp. 621– 630, jan. 1988, https://doi.org/10.1109/20.43994. [13] b. a. meyer, j. w. mitchell, and m. m. el-wakil, "convective heat transfer in vee-trough linear concentrators," solar energy, vol. 28, no. 1, pp. 33–40, jan. 1982, https://doi.org/10.1016/0038-092x(82)90221-3. [14] "advice on limiting exposure to electromagnetic fields (0-300 ghz)," smombie gate, jul. 06, 2004. https://smombiegate.org/advice-onlimiting-exposure-to-electromagnetic-fields-0-300-ghz/. [15] a. s. farag, m. m. dawoud, and i. o. habiballah, "implementation of shielding principles for magnetic field management of power cables," electric power systems research, vol. 48, no. 3, pp. 193–209, jan. 1999, https://doi.org/10.1016/s0378-7796(98)00108-4. [16] a. cipollone, a. fabbri, and e. zendri, "techniques for shielding underground power lines to minimize the exposure to elf magnetic field in residential areas," in international symposium on electromagnetic compatibility, sorrento, italy, sep. 2002. [17] v. d. quoc, "robust correction procedure for accurate thin shell models via a perturbation technique," engineering, technology & applied science research, vol. 10, no. 3, pp. 5832–5836, jun. 2020, https://doi.org/10.48084/etasr.3615. [18] v. d. quoc, "accurate magnetic shell approximations with magnetostatic finite element formulations by a subdomain approach," engineering, technology & applied science research, vol. 10, no. 4, pp. 5953–5957, aug. 2020, https://doi.org/10.48084/etasr.3678. [19] s. koroglu, p. sergeant, r. v. sabariego, v. q. dang, and m. d. wulf, "influence of contact resistance on shielding efficiency of shielding gutters for high-voltage cables," iet electric power applications, vol. 5, no. 9, pp. 715–720, nov. 2011, https://doi.org/10.1049/iet-epa. 2011.0081. [20] s. koroglu and p. sergeant, "electromagnetic losses in magnetic shields for buried high voltage cables," progress in electromagnetics research, vol. 115, pp. 441–460, 2011, https://doi.org/10.2528/ pier11022206. [21] t. p. minh et al., "finite element modeling of shunt reactors used in high voltage power systems," engineering, technology & applied science research, vol. 11, no. 4, pp. 7411–7416, aug. 2021, https://doi.org/10.48084/etasr.4271. engineering, technology & applied science research vol. 7, no. 4, 2017, 1838-1842 1838 www.etasr.com alghamdi: correlation between grain size distribution and silicon and oxygen contents at wadi arar … correlation between grain size distribution and silicon and oxygen contents at wadi arar sediments, kingdom of saudi arabia mohammed a. m. alghamdi engineering geology, earth science faculty king abdulaziz university jeddah, saudi arabia mmushrif@gmail.com abstract—quartz is the major mineral of wadi arar sediments. the top two elements contents are oxygen with 63.96 wt%, followed by silicon with 16.35 wt%. there is a positive, weak to medium correlation between grain size and silicon and oxygen contents. the correlation between oxygen and grain size is four times higher than that of silicon. at grain size ranges between 0.8 and 1.0 mm, both oxygen and silicon show the maximum correlation, which decrease gradually with finer and coarser grain sizes. for each element, the correlation between the element content and grain size is a fourth degree polynomial in the grain size. theoretically, the best two math models that represent the relation between the grain size distribution and each of individual oxygen and silicon content are y=8.84∙ln(x)+39.5 and y=2.26∙ln(x)+10.1 respectively, where y represents the element content percentage and x represents the corresponding grain size in mm. keywordsquartz; silicon; oxygen; grain size i. introduction wadi arar is located in the central part of the northern border region of the kingdom of saudi arabia (ksa). it penetrates arar city from the south west to the north east and divides arar city into two regions (figure 1). these regions and areas are characterized by a rocky layer of limestone and sandstone with a few of dolomite and silt. a few studies and boring reports about soil properties of wadi arar for foundations and projects construction were done [1]. analysis of grain size distribution has been widely used by engineering geologist and sedimentologists to classify sedimentary environments and investigate transport dynamics. grain size is also an important biotic component of the dune ecosystem. the grain size of sediments provides an indication of the shear stress that must be applied by the medium to initiate and sustain particle movement. grain size distribution is affected by other factors such as distance from the shoreline, distance from the recharge source area, source material, topography and transport mechanisms. the essential factors influencing the heavy metal contents in sediments include the physical and chemical properties (grain size, surface to volume ratio, heavy metal contents of the main geochemistry phase), in which grain size is a main control parameter. there is an indication that finer sediments contain more heavy metals than coarser ones. the main reason is that smaller grain size particles have a larger surface-to-volume ratio [2, 3]. however, some studies have indicated that coarser particles show a similar or even higher heavy metal concentration than finer ones and the presence of coarser particles are possibly responsible for higher metal content in the coarser size fractions [4, 5]. in [6], authors observed that the radon exhalation rate increases with an increase in grain size. in [7], authors found that the maximum concentrations of the platinum group and rare earth elements were observed at d50=1-2 and 1-4 µm respectively. in [8], the grain size distribution and heavy minerals at malindi bay coast, kenya were investigated. in [9], authors showed that the heavy metals concentrations increased with the decrease in particle size. in [10], it was found that most of elements have their highest concentrations in fine grain mud samples when compared with silt and silt-mud samples, with clay minerals possibly playing an important role. in [11], authors quantified mineral grain size distributions for process modelling using x-ray micro-tomography. in [1], it was found that deposits of wadi arar were silty sand (sm) according to unified soil classification system. in [12], authors concluded that if the grain size decreases, heavy metal content increases. in [13], authors showed the strong influence of grain size on sediment composition that is largely reflecting the greater grain size effect on mineralogy. in [14], authors found a distinct heterogeneity in particle size distribution and mineralogy throughout the boulder creek watershed in colorado, usa. there are not enough studies available to correlate grain size distribution with each of the two elements (silicon and oxygen) composing of quartz at wadi arar, kingdom of saudi arabia. accordingly, the present work is mainly focused on the quartz mineral. it is attempting to portray the grain size distribution of quartz mineral content on silicon and oxygen percentages at wadi arar. therefore, the study area is carefully engineering, technology & applied science research vol. 7, no. 4, 2017, 1838-1842 1839 www.etasr.com alghamdi: correlation between grain size distribution and silicon and oxygen contents at wadi arar … chosen to represent a key sector of quartz mineral content due to urban expansion in arar city. also, the present study is focuses on the part of wadi arar which will probably be developed for real estate (figure 1). figure 2 shows an explanation diagram of the scope and purpose of the present work. fig. 1. topographical plan of arar city and wadi arar (after alghamdi and hejazy, 2013) fig. 2. illustration diagram of the scope and purpose of the work. ii. geological setting the study area which located in the northwestern part of saudi arabia is underlain by late cretaceous sedimentary rocks of the aruma group and by paleogene and neogene sedimentary rocks, devonian, silurian, ordovician, and possible cambrian sedimentary units occurring in the subsurface. nonconsolidated gravel, sand and silt occupy most wadis and dissolution-subsidence depressions [15]. iii. methodology a. sampling for the purpose of measuring grain size distribution, thirty five disturbed samples were collected from seven locations in wadi arar, five from each location. the profiles of the locations were denoted by a, b, c, d, e, f and g profiles. profile a is located at the northeast point of the wadi facing arar city while profile g is located at the southeast point facing aljouf city. for the purpose of mineral and element analysis, three disturbed samples are taken from each location of each profile (figure 1). b. sieve analysis grain size distribution data are obtained using the sieve analysis test [1]. geometric means of percentages were calculated rather than arithmetic means because the geometric mean is more suitable when percentages are used. c. x-ray diffraction (xrd) the x-ray diffraction patterns of the selected soil samples under study were carried out using a phillips x, panalytical xray diffractometer at 40 kv and 40 ma with ni filter and cu kὰ radiation. the xrd runs were carried out up to 2θ 0f 69o. the traditional xrd patterns obtained from the current samples show more or less similar 2θ of the diffraction peaks. d. heavy liquid separation technique each of the investigated samples was subjected to heavy liquid separation technique using bromoform (sp. gr.=2.8) where most of quartz mineral is obtained in the light fraction while all of remaining mineral varieties were obtained in the heavy fraction. each of the individual light fraction was detected using scanning electron microscope. e. edx energy-dispersive x-ray spectroscopy (edx) analysis technique was used for the elemental analysis. edx spectroscopy depends on the principle that each element has a unique atomic structure resulting in a unique set of peaks on its electromagnetic emission spectrum, which allows for measuring the elemental composition of the specimen [16]. iv. results a. grain size distribution table i shows the geometric means of the percentage passing of grain size contents at all different locations. it is found that the maximum percentage passing occurs at locations e, while the minimum value occurs at location f (figure 3). b. mineralogy the xrd patterns of all samples clearly exhibit the typical phase of quartz mineral (figure 4). the quartz is the major engineering, technology & applied science research vol. 7, no. 4, 2017, 1838-1842 1840 www.etasr.com alghamdi: correlation between grain size distribution and silicon and oxygen contents at wadi arar … mineral with 58 % of the soil sample. in the xrd patterns, the highest peak of 2ɵ = 26.0o can be assigned to sio2 according to the standard pattern number 46-1045 (jcpds, 2000). xrd patterns for the other minerals show similar behavior and will be discussed in a future work. table i. geometric means of % passing at different locations sieve no diameter locations mean (%) (mm) a b c d e f g s4 4.75 80.77 89.43 83.8 86.87 90.23 68.38 88.78 83.71 s6 3.35 74.99 85.08 75.72 84.19 85.89 65.35 85.28 79.15 s10 2 66.95 74.8 68.31 73.77 79.25 60.81 78.88 71.54 s18 1 60.12 66.57 62.79 64.94 74.27 52.96 73.53 64.65 s20 0.85 51.76 55.65 53.1 57.67 67.49 45.4 65 56.14 s40 0.43 44.4 46.89 45.75 53.05 61.96 40.26 54.19 49.05 s60 0.25 37.32 40.25 38.29 44.2 53.75 30.56 44.91 40.78 s100 0.15 30.47 34.32 31.57 38.24 46.65 26.3 38.79 34.66 s200 0.08 24.77 27.91 27.74 33.18 41.4 19.8 30.99 28.73 fig. 3. grain size distribution curves of the studied soil samples of the different locations c. element concentrations figure 5 shows major and trace elements of the studied soil samples that were determined by energy dispersive x-ray analysis (edx). table ii shows the two major elements (si, o) contents of quartz at the different studied locations with an average percentage of 16.4% and 63.96 %, respectively. d. correlation to detect and compare the strength and direction of the linear relationships between grain size distributions and the content for each of silicon and oxygen concentrations, the correlation coefficients (r), were calculated using the values of table iii. the values of correlation coefficient (r) between grain size and both silicon and oxygen are plotted in figure 6. as shown in figure 6 the correlations increase with grain size for both elements (si, o) till around 1.0 mm, beyond which the correlations decrease gradually to 0.08 mm. at grain size 0.85 and 1.0 mm, which is the size of medium sand, the sample shows maximum correlation of 0.21% and 0.42 % for silicon and oxygen, respectively. on average, oxygen correlation is 39% higher than that of silicon. for o, the correlations increase from 0.18 at 0.075 mm to 0.42 at 1 mm. then it drops to 0.15 at 4.75 mm. for si it increases from 0.01 to 0.20 then drops down to 0.06 at the same grain sizes. the observed deviation is most probably due to the existence of composite quartz grains. some of quartz grains are stained, coated or locked with other mineral varieties; mainly carbonate. fig. 4. xrd patterns of the current sample fig. 5. edx spectrum of the current samples fig. 6. relation between correlation coefficient and grain size of si and o elements engineering, technology & applied science research vol. 7, no. 4, 2017, 1838-1842 1841 www.etasr.com alghamdi: correlation between grain size distribution and silicon and oxygen contents at wadi arar … table ii. geometric means of individual si and o element contents (%) elements locations mean % a b c d e f g silicon (si) 20.66 13.23 14.73 16.99 15.55 14.8 19.81 16.35 oxygen (o) 62.94 63.5 64.64 63.26 64.16 64 65.24 63.96 table iii. correlation between grain size and element (si, o) contents grain size (mm) 0.08 0.15 0.25 0.43 0.85 1 2 3.35 4.75 silicon (si) 0.18 0.22 0.21 0.27 0.4 0.42 0.31 0.12 0.15 oxygen (o) 0.01 0.07 0.1 0.12 0.21 0.15 0.11 0.07 0.06 e. polynomial regression the relation between grain size and its correlation with silicon and oxygen are fitted with polynomials of degree 2, as follows: y=-0.0263x2+0.0938x+0.2338 (1) for oxygen and by y=-0.0156x2+0.0648x+0.0742 (2) for silicon where y represents the correlation coefficient of the selected element and x represents the grain size in mm. the values of coefficient of determination (r2) are 0.40 for oxygen and 0.31 for silicon (i.e. 40% of oxygen and 31% of silicon of data are above the best fit curve). thus means that strength of the relations are medium. when the degree of the polynomial has increased to the fourth degree the r2 values are above 0.90 (figure 7). the fourth degree polynomial fitting is given by y=-0.0035x4+0.0652x3-0.3472x2+0.5612x+0.1211 (3) for oxygen and by y=-0.011x4+0.1168x3-0.4077x2+0.4933x-0.0124 (4) for silicon. the r2 values for the 4th degree fitting are 0.96 and 0.91 respectively (figure 8). fig. 7. second degree polynomial of correlation in grain size fig. 8. fourth degree polynomial of correlation in grain size v. element contents in each fraction to find the theoretical content of elements that corresponds to each grain size, the values in table i were multiplied by the values in table ii then divided by 100. tables iv and v show that content of oxygen and silicon respectively. the mean element content for each element (tables iv and v) is logarithmically modeled in term of grain size. the fitting for oxygen given by: y=8.8369ln(x)+39.5 (5) for silicon the fitting is given by y=2.2586ln(x)+10.096 (6) where y represents element content percentages and x the grain size (mm) table iv. oxygen in each fraction size (mm) locations mean (%) a b c d e f g 4.75 50.83 56.78 54.17 54.95 57.89 43.76 57.93 53.54 3.35 47.19 54.02 48.95 53.26 55.11 41.82 55.64 50.63 2 42.13 47.49 44.16 46.66 50.85 38.92 51.46 45.76 1 37.84 42.27 40.59 41.08 47.65 33.89 47.98 41.35 0.85 32.58 35.34 34.33 36.48 43.3 29.06 42.41 35.9 0.425 27.94 29.77 29.57 33.56 39.76 25.76 35.36 31.37 0.25 23.49 25.56 24.75 27.96 34.49 19.56 29.3 26.08 0.15 19.18 21.79 20.41 24.19 29.93 16.83 25.31 22.17 0.075 15.59 17.72 17.93 20.99 26.56 12.67 20.22 18.38 table v. silicon content in each fraction size (mm) locations mean (%) a b c d e f g 4.75 16.69 11.83 12.34 14.76 14.03 10.12 17.59 13.68 3.35 15.49 11.26 11.15 14.3 13.35 9.67 16.9 12.94 2 13.83 9.9 10.06 12.53 12.32 9 15.63 11.69 1 12.42 8.81 9.25 11.03 11.55 7.84 14.57 10.57 0.85 10.7 7.36 7.82 9.8 10.49 6.72 12.88 9.18 0.425 9.17 6.21 6.74 9.01 9.63 5.96 10.74 8.02 0.25 7.71 5.33 5.64 7.51 8.36 4.52 8.9 6.67 0.15 6.3 4.54 4.65 6.5 7.25 3.89 7.69 5.67 0.075 5.12 3.69 4.09 5.64 6.44 2.93 6.14 4.7 engineering, technology & applied science research vol. 7, no. 4, 2017, 1838-1842 1842 www.etasr.com alghamdi: correlation between grain size distribution and silicon and oxygen contents at wadi arar … both elements reflect a positive relation between their contents and grain size. the ratio of silicon content is a quarter of oxygen contents. with the increase of grain size content a diversion was observed between both elements (figure 9). fig. 9. relation between grain size and individual si and o element contents vi. conclusion the basic conclusions of this paper as as follows:  quartz represents the major mineral in wadi arar.  oxygen and silicon are the major elements in wadi arar.  the maximum correlation between grain size and element content appears at a grain size of 1.0 mm.  the max correlation between grain size and oxygen is double of that with silicon (0.42 and 0.21 respectively).  the strongest relation between grain size and its correlation with element content is a fourth degree polynomial.  the relation between element content (si, o) and grain size is a positive and logarithmic relation. references [1] m. alghamdi, a. hegazy, “physical properties of soil sediment in wadi 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microanalysis. springer, 2003 microsoft word etasr_v12_n4_pp9048-9055 engineering, technology & applied science research vol. 12, no. 4, 2022, 9048-9055 9048 www.etasr.com bouamra et al.: a low-profile wearable textile antenna using amc for wban applications at 5.8ghz a low-profile wearable textile antenna using amc for wban applications at 5.8ghz wahida bouamra department of physics faculty of sciences of tunis university of tunis el manar tunis, tunisia bouamra-wahida@hotmail.com imen sfar department of physics faculty of sciences of tunis university of tunis el manar tunis, tunisia imen.sfar.fst@gmail.com ameni mersani department of physics faculty of sciences of tunis university of tunis el manar tunis, tunisia mersani.ameni@gmail.com lotfi osman department of physics faculty of sciences of tunis university of tunis el manar tunis, tunisia lotfi.osman@supcom.tn jean-marc ribero department of electronics university nice-sophia antipolis sophia antipolis, france jean-marc.ribero@univ-cotedazur.fr received: 25 april 2022 | revised: 12 may 2022 | accepted: 7 june 2022 abstract-this paper presents a low-profile, wearable textile antenna, designed for wireless body area network (wban) applications operating in the 5.8ghz band for industrial, scientific, and medical (ism) applications. an artificial magnetic conductor (amc) structure was used to improve antenna performance and protect the human body from backradiation. the antenna with the integrated amc achieved a measured gain of 8.92dbi, an efficiency of 80%, a wide impedance bandwidth of 1.4ghz (24.1%), and sar values of 0.00103 and 0.00034w/kg for 10g and 1g tissues respectively. the proposed antenna was studied in a worn-on-body scenario using a multilayer numerical model of the human body. the influence of the thickness of each tissue layer of the human body was investigated. the results showed that the antenna maintained its performance, a stable gain was obtained, and the sar values were also below the ieee guidelines that guarantee the safety of the wearer. keywords-artificial magnetic conductor (amc); ism; specific absorption rate (sar); textile antenna; wban applications i. introduction wearable antennas have been intensively studied, as they are widely used in wban applications such as health monitoring, emergency services, identification systems, enterprise, space, military rescue activities, and physical training [1]. the use of body-worn electronic devices, such as smart glasses, watches, and textiles, has grown rapidly as a result of the increasing need for wireless communication. the main interests in the implementation of these systems are wellbeing, health, and lifestyle [2]. as a result, wireless body area networks (wbans) have attracted considerable attention [3]. antenna design for wban systems is challenging compared to conventional systems because the human body is a dispersive medium due to its high permittivity and conductivity [3]. many researchers studied different types of antennas to improve their performance near the human body. for example, in [3-5], monopoles with an artificial magnetic conductor (amc), a circular ring slot antenna with a siw cavity back, and a planar inverted f antenna (pifa) were presented as wearable textile antennas that provide stable performance near the human body. these antennas use rigid substrates, which can be uncomfortable for the human body, so different bending conditions must be considered [1]. body antennas are best made from flexible textiles and wearable materials that naturally conform to the body surface [6]. due to the recent rapid growth of electronic textile technology, several researchers focused on the application of flexible textile materials in antennas [7]. since the textile antenna is bent on the human body, the effects of deformation need to be studied. therefore, to obtain an optimal antenna design for wban systems, insensitivity to body effects and realization of practical wearable environments should be considered simultaneously [3]. in addition, a low-profile antenna is highly desirable to ensure comfort for the wearer. furthermore, the specific absorption ratio (sar) must be below the normal criteria and not exceed the critical values of 1.6w/kg for 1g of tissue or 2w/kg for 10g of tissue, according to the guidelines of ieee c95.1-1999 [8]. furthermore, one of the challenges of using a wearable antenna is the variation in tissue thickness, especially in the fat and muscle layers. this thickness is not the same for all individuals [9]. therefore, the effects of different thicknesses of body models on antenna performance need to be investigated. to overcome these problems, this study investigated a low-profile textile monopole antenna for wban applications at 5.8ghz. a 50ω coplanar waveguide (cpw) corresponding author: lotfi osman engineering, technology & applied science research vol. 12, no. 4, 2022, 9048-9055 9049 www.etasr.com bouamra et al.: a low-profile wearable textile antenna using amc for wban applications at 5.8ghz was used for the feed because it offers wider bandwidth and higher gain and needs to be metalized only on the one side. however, since the antenna must be placed near the human body, there is no ground plane to protect it from the generated back radiation. therefore, an amc is needed to improve antenna performance and protect the body from the effects of back radiation [6]. this study proposed a low-profile textile antenna loaded by an amc structure with high gain, high efficiency, and good isolation while achieving low sar level. moreover, the influence of the thickness of each tissue layer of a human body on the proposed antenna performance was studied for the first time to ensure that the antenna adapts to all individuals while maintaining performance stability. to ensure that the proposed antenna fits different human bodies, three different body models with different tissue thicknesses and compositions were considered to study the effect of human tissue thickness on antenna performance in terms of gain and sar. ii. antenna design and discussion a. antenna geometry the monopole antenna configuration was designed based on the design proposed in [5] and optimized for operation in the ism 5.8ghz band. figure 1 shows the dimensions and the fabricated prototype. the wearable antenna has a simple structure to avoid manufacturing complexities with overall dimensions of 14×22×0.58mm. the antenna was printed on a flexible polyester textile substrate with a dielectric constant ��=2.22, loss tangent tanδ=0.004, and a thin thickness of 0.5mm. the conductive layer was made of a 0.08mm thick pure electro-textile copper taffeta from less emf [5, 10] with a conductivity of 2.5×105s/m. it was smooth, soft, lightweight, pliable, and easy to cut and sew. a 50ω cpw was chosen to feed the antenna. design and simulations were carried out using cst microwave studio [11, 12]. the antenna was fabricated with the optimized dimensions listed in table i. (a) (b) fig. 1. geometry of the proposed antenna: (a) front view, (b) photograph of the manufactured prototype. table i. optimized dimensions of the proposed antenna parameter w l l1 a b c d e f value 32 22 11 5.1 5 3 0.2 4.5 5 b. parametric study figure 2(a) shows the evolution steps of the proposed antenna design. the design process was divided into three stages (ant 0, ant 1, and ant 2) to achieve the final design. the method used was to cut out both sides of the patch and insert a slot to achieve the desired resonant frequency by controlling the reflection coefficient parameters. figure 2(b) shows the reflection coefficients s11 of the three stages. the first antenna (ant 0) is a simple cpw antenna structure, which had a good impedance matching characteristic with a wide impedance bandwidth. the two sides of the patch were truncated in ant 1, resulting in better impedance matching, but caused a shift in the resonant frequency from 5.94ghz to 6.25ghz. in the final step, a slot was added to the patch to achieve the desired frequency. this variation also resulted in a good impedance match (s11= -58db) and a wide bandwidth of 2.18ghz (4.69-6.87ghz). (a) (b) fig. 2. (a) evolution steps of the design of the proposed antenna, (b) corresponding s11 reflection coefficients. the effect of parameter x and the width of slot c on the antenna’s impedance matching was examined. the antenna performance was examined for a variable length of x from 4 to 1.5mm, as shown in figure 3(a). as the length of x decreased, better impedance matching was achieved, and the center frequency of the reflection coefficient shifted to higher frequencies. figure 3(b) shows that varying c from 2 to 6mm resulted in a significant increase in impedance matching with an improvement in impedance bandwidth of about 600mhz. figure 4 shows the simulated and measured reflection coefficients of the antenna with optimal dimensions. good agreement was found in terms of bandwidth between simulation and measurement at the resonant frequency. the simulated -10db impedance bandwidth was 2.18ghz (4.6924,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 -60 -50 -40 -30 -20 -10 0 s 1 1 ( d b ) frequency (ghz) ant 2 ant 1 ant 0 engineering, technology & applied science research vol. 12, no. 4, 2022, 9048-9055 9050 www.etasr.com bouamra et al.: a low-profile wearable textile antenna using amc for wban applications at 5.8ghz 6.872ghz), while the measured bandwidth was 2.27ghz (4.55-6.82ghz), which largely covers the desired band. however, the measured s11 was 26 db lower than the simulated value due to imperfections during the manufacturing process. (a) (b) fig. 3. influence of parameters on the s11 performance of the proposed antenna: (a) effect of truncation width x, (b) slot width c. fig. 4. simulated and measured s11 of the antenna. iii. amc-backed antenna design and results a. amc unit cell design the amc structure is a good candidate for a reflective plane of the radiated wave in wearable antenna applications, as it reduces the radiation absorbed by the human body and improves performance [1, 4]. since the cpw antenna does not have a reflective plane and emits back-radiation, it should be isolated from the human body. several studies used various basic classical geometric shapes (square, triangle, circle, and cross) to form a wide and two-band amc surface [5, 8, 13-15]. this study focused on a hexagonal structure on textile because of its advantages in terms of size and bandwidth [13]. figure 5 shows the extended dimensions of the amc unit cell. the unit cell structure was developed on a felt substrate with a relative dielectric constant (εr) of 1.22, a loss tangent (tanδ) of 0.016, and a thickness of 2mm. the conductive material was copper taffeta. during the design of the amc structure and the simulation phase, the amc network was extended by one row and one column at a time until optimal performance in terms of gain and forward-to-backward ratio (fbr) was achieved. a good impedance match was achieved within 5.8ghz. the dimensions of the different structures were adjusted to achieve a 0° phase around 5.8ghz. the frequency bands were determined by variations of ±90° around the 0° phase values, as shown in figure 5. fig. 5. structure and simulated reflection coefficient phase of the amc unit cell. b. integration of the τextile antenna and amc surface figure 6(c) shows the manufactured prototype amc antenna. the monopole antenna was built on an amc layer with 2×2 units ανδ total dimensions of 34.8×39mm. a gap of 1mm thickness separated the antenna from the amc to minimize mismatch and electrical contact and avoid short circuits [8]. a foam-like rohacell substrate was placed in this space without changing the properties of the amc antenna structure. the expected impedance matching and radiation characteristics of the amc antenna at 5.8ghz wban applications were achieved by optimizing the geometric dimensions of the monopole antenna and the amc unit cell. c. measurement results and discussion figure 7 shows the measured reflection coefficient s11 of the amc antenna and the simulated results. it is noted that the simulated bandwidth is larger from 5.70 to 7.10ghz (24.1%) than the measured one, which ranges from 5.71 to 6.75ghz engineering, technology & applied science research vol. 12, no. 4, 2022, 9048-9055 9051 www.etasr.com bouamra et al.: a low-profile wearable textile antenna using amc for wban applications at 5.8ghz (17.9%). this small deviation may be due to uncertainty in the properties of the textile support and mechanical inaccuracies. note that all results can cover the ism band of 5.8ghz, which ensures that the proposed antenna can meet the requirements for 5.8ghz wban applications. (a) (b) (c) (d) fig. 6. amc antenna: (a) configuration of antenna on amc, (b) bottom view, (c) manufactured prototype, (d) measuring reflection coefficient s11. fig. 7. simulated and measured reflection coefficient of the amc antenna. figure 8 shows the radiation pattern measurements performed in the anechoic chamber of orange labs in the e and h planes at 5.8ghz of the antenna with and without amc. the results show that the amc antenna has stronger forward radiation, while the backward radiation was reduced by 20db by the amc reflector plane. thus, it was possible to reduce the backward scattering wave toward the human body. (a) (b) (c) fig. 8. measured radiation patterns of the antenna with and without amc at 5.8ghz: (a) measured performances of the amc antenna in the anechoic chamber, (b) e-plane, and (c) h-plane. figure 9 shows the measured gain and efficiency of the antenna with and without amc. the measured gains of the antenna with and without amc are 8.92 and 2.5dbi respectively. due to the hexagonal shape of the amc surface, the achieved gain is higher than the existing antennas'. the 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 -40 -35 -30 -25 -20 -15 -10 -5 0 s 1 1 ( d b ) frequency (ghz) meas. amc antenna sim. amc antenna 0 30 60 90 120 150 180 210 240 270 300 330 -4 0 -3 0 -2 0 -1 0 0 1 0 h-plane (θ=0) sim. antenna sim. amc antenna meas. antenna meas. amc antenna 0 30 60 90 120 150 180 210 240 270 300 330 -4 0 -3 0 -2 0 -1 0 0 1 0 sim. antenna meas. antenna sim. amc antenna e-plane (ꝕ=0) meas. amc antenna engineering, technology & applied science research vol. 12, no. 4, 2022, 9048-9055 9052 www.etasr.com bouamra et al.: a low-profile wearable textile antenna using amc for wban applications at 5.8ghz maximum measured efficiency of the antenna without amc was 60%, while the measured efficiency of the antenna with amc was almost 79.96% at 5.8ghz. these values show that the proposed amc textile antenna is very efficient. fig. 9. simulated and measured gain and efficiency of the textile antenna with and without amc. iv. antenna on the human body a. antenna performance in bending configuration in mobile systems, a wearable antenna is often bent as a result of the movement of the human body. to study the performance of the amc textile antenna in a dynamic body environment and under deformation, it was bent over a cylinder with a radius r of 60mm, representing the middle arm, in two planes (e and h). figure 10 shows the simulated s11 of the proposed amc antenna in flat and bent conditions in the e and h-plane. this figure shows that the bandwidth remained stable in both bending conditions and covered the 5.8ghz band. fig. 10. simulated reflection coefficient of the amc-antenna in bending conditions in both e and h planes. it is necessary to validate the performance and study the effects of human body loading on the proposed antenna. to reduce the simulation time, a 3d numerical model was studied. this model consisted of three layers representing skin, fat, and muscle tissue from the outside to the inside. the properties of the dispersive human tissue layers were taken from [16-18] and are shown in figure 11. fig. 11. modeling the 5.8ghz antenna with and without amc on the human body model. figure 12 shows that after removing the amc surface the resonant frequency shifted toward the lower band due to the high dielectric properties of human tissue [19]. this removal also affected the attenuation of the reflection coefficient and the detuning of the resonant frequency. on the other hand, the required operating bands of the amc antenna were achieved due to the high isolation provided by the amc. it can be noted that the reduction of the distance d between the antenna and the human body model leads to a mismatch of the reflection coefficient s11. therefore, protection from electromagnetic radiation was provided by a distance of 4mm between the amc antenna and the tissues of the multilayer models. fig. 12. reflection coefficient of the proposed antenna with and without amc, according to distance from the human body model (0-4mm). the antenna was placed directly on the skin of the arm, as shown in figure 13, and the reflection coefficient antenna was also plotted when placed on the body. the two results are close to each other. the differences compared to free space are negligible and cover the frequency band. 4,0 4,5 5,0 5,5 6,0 6,5 7,0 0 2 4 6 8 10 measured gain of the amc antenna measured gain of the antenna measured efficiency of the amc anenna measured efficiency of the antenna frequency (ghz) g a in ( d b i) 0 20 40 60 80 100 e ff ic ie n c y ( % ) 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 -35 -30 -25 -20 -15 -10 -5 0 s 1 1 ( d b ) frequency (ghz) amc antenna / body d=0mm amc antenna in free space antenna without amc / body d=0 mm antenna without amc / body d=2 mm antenna without amc / body d=4 mm amc antenna/ body d=2 mm amc antenna / body d= 4 mm engineering, technology & applied science research vol. 12, no. 4, 2022, 9048-9055 9053 www.etasr.com bouamra et al.: a low-profile wearable textile antenna using amc for wban applications at 5.8ghz fig. 13. measured reflection coefficient. b. sar validation sar was used to examine the health risks posed by portable antennas on the human body. according to the guidelines of the ieee standards c95.1-1999 [20] and c95.12005 [21], the rf energy absorbed by human tissue should not exceed the critical values of 1.6w/kg for 1g of tissue or 2w/kg for 10g of tissue. sar is given by a temporal derivative of the incremental energy (dw) scattered in an incremental mass (dm) contained in a volumetric element (dv) with a data density (ρ) [22], calculated by: ��� � ��� � ��� � � �� � ��� (w/kg) (1) ��� �� ���⁄ � �� � (2) where σ represents the conductivity in (s/m), ρ designates the mass density in (kg/m3), and e represents the electric field in (v/m). sar is related to the internal e-field by: � � �� ���� �/� (3) � � ��������/� (4) a numerical assessment of sar can be performed in case of a lack of equipment and the high cost of experimentally determined sar values. this work examined various numerical sar studies based on mass-averaged methods using the ieee c95.1 standard included in the cst mws software. the simulated 1g and 10g average sar at 5.8ghz for the antenna with and without amc on humans are shown in table ii. the obtained results show that the presence of the amc surface reduces sar and provides better protection to the human body. in both cases, the sar values of the amc antenna were lower than the sar limits, which guarantees its safe use. table ii. simulated sar of antenna with and without amc sar (w/kg) 1g tissue 10g tissue antenna without amc 0.038 0.14 antenna with amc 0.000103 0.000349 c. effects of tissue thickness on the amc antenna the thickness of the tissue layers, especially fat and muscle, varies from person to person. therefore, keeping the skin thickness constant at the average standard measurement of 3.6mm [5], different combinations of thickness values for fat and muscle layers can be studied for imaging multiple individuals [9]. table iii shows the parameters of three proposed models with different combinations, to examine how sar can be affected by the different thicknesses of human tissue layers. the thickness of the fat and muscle layers changed, while the thickness of the skin layer remained unchanged. in the first case, the thickness of the fat layer ranged from 7 to 27mm, whereas in the second, the thickness of the muscle layer varied from 23 to 63mm, while the third had simultaneous changes in the fat and muscle layers. furthermore, many thickness combinations of the fat and muscle layers with a total thickness of 60mm were considered. table iii. three examples of different human muscle and fat layers thickness case tissues thickness (mm) a b c d e 1 skin, s 3.6 3.6 3.6 3.6 3.6 fat, f 7 12 17 22 27 muscle, m 50 50 50 50 50 2 skin, s 3.6 3.6 3.6 3.6 3.6 fat, f 7 7 7 7 7 muscle, m 23 33 43 53 63 3 skin, s 3.6 3.6 3.6 3.6 3.6 fat, f 7 12 17 22 27 muscle, m 53 48 43 38 33 table iv shows the 1g and 10g sar, as well as the gain distribution for the amc antenna in different types of the human body at 5.8ghz. in the first case, where the fat layer increased while the size of the muscle and skin layers remained constant, a decrease in both sar values was observed. in model 2, where the muscle layer increased, the sar values were almost stable. in case 3, where the thickness of the fat and muscle layers was changed simultaneously, a small increase in sar values was observed, but it is noteworthy that all these values were below the normal sar criteria. in summary, the gain and sar values remained almost unchanged in all cases when the thickness of the different layers was varied, ensuring that the proposed amc antenna is a strong candidate for wban applications for different wearers. table iv. 1g and 10g sar for the amc antenna in various prototypes of the human body at 5.8ghz case a b c d e 1 sar (w/kg)/ 1g 0.46 0.45 0.43 0.42 0.42 sar (w/kg) /10 g 0.18 0.17 0.17 0.16 0.16 gain (dbi) 8.29 8.32 8.32 8.38 8.26 2 sar (w/kg) /1g 0.25 0.25 0.26 0.25 0.25 sar (w/kg) /10 g 0.09 0.10 0.09 0.10 0.10 gain (dbi) 8.24 8.23 8.24 8.24 8.23 3 sar (w/kg) /1g 0.41 0.47 0.42 0.43 0.45 sar (w/kg) /10g 0.16 0.181 0.164 0.169 0.17 gain (dbi) 8.29 8.29 8.29 8.29 8.29 engineering, technology & applied science research vol. 12, no. 4, 2022, 9048-9055 9054 www.etasr.com bouamra et al.: a low-profile wearable textile antenna using amc for wban applications at 5.8ghz table v. comparison of the proposed amc antenna to other studies ref freq. (ghz) dim (mm) /reflector type bw (ghz) gain (dbi) sar (w/kg) radiation efficiency (%) fs hbm fs hbm 1g 10g [3] 5.8 75×42×1 / ground plane 5.65-5.88 (3.96%) 5.62-5.97 (6.10) 3.12 37.7 [5] 5.8 102×68×3.6 / amc 4.30-5.90 (27.5%) 6.12 0.61 1.49 [23] 5.5 46x36x2 / ground plane 5.05-6.04 (18%) 5.13-5.93 (14.54) 5.9 5 0.9307 0.4016 74.1 [24] 5.5 42x28x4 / meta surface 4.96-5.90 (17%) 4.96-5.90 (17%) 6.7 0.3699 0.2170 77 this work 5.8 34.8×39×4.58/ amc 5.70-7.10 (24.1%) 5.8-7.23 (24.65%) 8.92 8.29 0.00103 0.000349 79.96 d. comparative study table v shows the performance comparison of the proposed wearable textile antenna with wban antennas proposed in other studies. it can be noted that the proposed antenna not only has the advantage of conformability and flexibility when worn on the human body due to the textile substrate but also has several advantages in terms of size and performance, such as high gain, low sar, bandwidth that is not affected when worn, and is still sufficient for the application. v. conclusion this study proposed a textile antenna for wearable applications operating in the 5.8ghz ism band. a flexible textile amc structure was used to protect the human body from back radiation and improve performance in terms of gain and efficiency. the antenna design had reduced dimensions of 34.8×39mm and 4.58mm thickness. the wearable amc antenna was examined in free space and on the human body. to ensure that the proposed antenna fits different human bodies, a study on the effects of the thickness of each tissue layer of a human body model on the antenna was conducted, which showed good and stable performance. these characteristics make the proposed wearable antenna a good candidate for wban applications. acknowledgment this study was conducted in collaboration with the lab of electronics, antennas, and telecommunications (leat) of the university of sophia antipolis, nice, france, and the measurements were performed in the anechoic chamber of orange labs. references [1] a. y. i. ashyap et al., "an overview of electromagnetic band-gap integrated wearable antennas," ieee access, vol. 8, pp. 7641–7658, 2020, https://doi.org/10.1109/access.2020.2963997. 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[24] l. wu, r. li, y. qin, and y. cui, "bandwidth-enhanced broadband dual-polarized antennas for 2g/3g/4g and imt services," ieee antennas and wireless propagation letters, vol. 17, no. 9, pp. 1702– 1706, sep. 2018, https://doi.org/10.1109/lawp.2018.2864185. microsoft word etasr_v11_n4_pp7343-7348 engineering, technology & applied science research vol. 11, no. 4, 2021, 7343-7348 7343 www.etasr.com chung: smoothing the power output of a wind turbine group with a compensation strategy of … smoothing the power output of a wind turbine group with a compensation strategy of power variation phan dinh chung faculty of electrical engineering the university of danang-university of science and technology danang, vietnam pdchung@dut.udn.vn abstract-this paper proposes a new scheme to reduce the output power variation range of a wind turbine group without an energy storage system. this proposal is based on the active power compensation principle for each wind turbine. in this research, the wind turbine operates in the active power control mode. the reference active power is calculated in such a way that it compensates for the difference between the average output power and the actual output power. to verify and evaluate the proposed method, we simulated a group of two 1.5mw-wind turbines in the simulink environment of matlab. simulation results were compared to the ones of a wind turbine group without any smoothing scheme and the ones of the same group with the exponential moving average method. from this comparison, we can conclude that with the proposed method, the actual output power of the wind turbine group becomes smoother than that of the wind turbine group without any smoothing scheme. moreover, the performance of the wind turbine group with the proposed method is better than that of the wind turbine group with the exponential moving average method. keywords-dfig; fluctuating compensation; power control; smoothing power; wind turbine i. introduction the energy demand has been increased rapidly in many developing countries whereas conventional energy resources are gradually exhausted [1]. this has boosted the exploiting of renewable energy resources such as wind, solar, geothermal, etc. to gradually replace fossil fuel-based resources like coal, oil, and natural gas. in many countries, wind energy has been practically accounted for a substantial rate in electricity demand [1]. however, the main drawback of wind turbines or wind farms is that they bring a negative impact on the connected grid because the output power fluctuates due to the natural variation of wind speed [2]. until now, many useful schemes were proposed to reduce the fluctuation in the output power of a wind turbine [2-19]. these schemes can be generally divided into two groups, energy storage system utilization [2-3, 8-13] and storage energy system misutilization [2,4-7]. by using an energy storage system as battery, super capacitor, etc. [8-13], we can adjust the amount of active power charging/discharging from the energy storage system to smooth the output power quite easily and hence, wind turbines can completely operate on their optimal power points to yield maximum available power. however, to obtain this benefit we must invest on the storage energy system installation and expect expensive operation cost. in contrast with the method of the energy storage system utilization, the controller utilization is hard to make the wind turbine operate completely on the maximum-power-point-tracking curve [2, 4]. moreover, by using the controller, the output power of the wind turbine is hardly as smooth as that using the energy storage system. the main reason is that it cannot store the redundant electrical power to release it as the output power is inadequate. however, the misutilization of an energy storage system does not require huge investments and maintenance cost. for the controller utilization of the wind turbine, some methods to smooth the power output of a wind turbine are inertia control [7], pitch control [14-17], dc link voltage control [18], etc. utilizing the inertia of the wind turbine can cause stress on its mechanical system whereas it is hard to respond quickly by using the pitch controller and a large amount of wind energy is wasted. in both pitch control and inertia methods, an anemometer must be used to provide the wind speed variation to the controller [2]. the dc voltage control method works on the principal of utilizing the dc link of the power converter, which is interfaced to the connected grid, as a small storage energy system to charge/discharge a small electrical energy amount during its operation interval, and hence the voltage on the dc-link is varied and this may bring a negative impact on the voltage at the point of common connection. moreover, this method is only applied in wind turbines that use a full-scale converter and is hard to implement in a doubly fed induction generator (dfig) wind turbine because of the converter’s small capacity. another way to smooth the output power is the use of the exponential moving average (ema) method to determine the average reference signal for the controller. depending on the smooth factor, this method can be either effective or ineffective. it is also noted that this method was not only used in the controller of a wind turbine but also in the controller of the energy storage system [4, 13, 19]. the objective of this research is the proposition of a new scheme for smoothing the output power of a wind turbine corresponding author: dinh chung phan engineering, technology & applied science research vol. 11, no. 4, 2021, 7343-7348 7344 www.etasr.com chung: smoothing the power output of a wind turbine group with a compensation strategy of … group without an energy storage system. the basis of the proposed scheme is to compensate the active power for the fluctuation in the output power. to obtain this objective, one must calculate the reference power, using it as an input signal of the rsc controller, such that it can compensate the variation in the actual output power. this scheme is evaluated via simulations in the simulink environment of matlab software. the simulation results of a wind turbine group with the proposed method will be compared to the ones without a smoothing method and with the ema method. it is noted that in order to evaluate the performance of the methods that smooth the output active power, we will use two indices, namely the smoothing function ∆������� and the electrical energy output of wind turbine group as (1)-(2) [3]: ∆������� ���� ��� � (1) � �� � (2) it is desired that the smoothing function ∆������� should be smaller in order for the output power to become smoother. moreover, the wind turbine group is always expected to withdraw as much electrical energy as possible and hence, a preferable method will provide a small value of the smoothing function and a high value of output electrical energy. ii. research configuration in this research, we consider a wind turbine group, as shown in figure 1, in which a dfig with 1.5mw capacity is employed. fig. 1. configuration of the wind turbine group. generally, a dfig wind turbine system consists of a 3blade system, a shaft system, and a dfig [20]. in the dfig wind turbine, the stator winding is connected directly to the grid whereas the rotor winding is interfaced to the grid via a back-to-back small capacity converter [21, 22]. this converter consists of a rotor side converter (rsc), a grid side converter (gsc) and a dc-link. via the rsc controller, we can adjust the output active power of the wind turbine. a. wind turbine the blade system converts wind energy to mechanical energy on its shaft. the efficiency of the conversion is represented by ����,��, namely power coefficient [8, 23]. this coefficient is reliant on both pitch angle � and tip speed ratio � [8, 24]: � � ���� (3) where r is the length of the blade, �� is the rotational velocity of the shaft, and �� the wind velocity at the wind turbine location. according to [8, 23], the coefficient ����,�� versus the tip speed ratio � at different values of � of a typical wind turbine is shown in figure 2(a) [8, 26]. it is easy to see that with a constant pitch angle, the power coefficient ����� reaches a maximum value at an optimal tip speed ratio. when we keep �=0, ����� will reach its maximum value ��� ! at ���� [25]. at a wind velocity �� and rotational velocity of shaft ��, the mechanical power on the wind turbine shaft is defined by [8, 24]: �� "# $%�#���λ,β���( (4) where $ is the density of air at the wind turbine location. (a) (b) fig. 2. (a) power coefficient versus tip speed ratio at different pitch angles and (b) mechanical power versus rotor velocity at different wind velocities. obviously, this mechanical power is reliant on the cubic of the wind velocity ��. when the wind velocity is over the rated value, the wind turbine should be remained at its rated power by adjusting the pitch angle � . by contrast, when the wind velocity is below the rated value, the pitch angle should be kept at a minimum value and the rotor speed should be adjusted so that the wind turbine operates at its optimal point (����,��� !�. from (3), (4), for �� ��� ! and � ����, we obtain [24]: �� "# $%�#��� !��( )��������( (5) where: engineering, technology & applied science research vol. 11, no. 4, 2021, 7343-7348 7345 www.etasr.com chung: smoothing the power output of a wind turbine group with a compensation strategy of … )��� "# $%�*��� !/λ���( (6) ����� ,-./��0 (7) when the wind velocity varies, the optimal rotor velocity ����� will be varied proportionally (7). hence, the locus of optimal operation point which is named maximum power point tracking (mppt) curve is computed as in (8). this locus is represented in figure 2(b). ����� "# $%�#��� !��( )�����( (8) b. doubly fed induction generator a dfig is principally an asynchronous generator and it consists of 2 windings, namely a stator winding and a rotor winding. in the 1 axis system, the rotor side voltage of a dfig is described as [24]: 2��3 ��4��3 5 67� �8�9:�� 5 ��6;7� < 0 >1 1 0 @4��3 5 �ab ac d0��e (9) where: 6 a�ab > ab ac (10) ; 1 > �� �c (11) �� is the resistance of rotor winding, 7� , 7�, and 7� represent the inductance of the rotor winding, the stator winding, and the magnetizing core respectively, 2��3 and 4��3 are the rotor voltage and rotor current in the 1 axis system, �� is the flux rotational velocity or angular frequency in the stator winding, ; is the slip factor, and �� the voltage magnitude in the stator winding terminal. the active power output of the dfig in total is calculated as [24, 25]: pg ph 5 pi (1 > s)ph (12) where �� is the active power exchanging to grid via the rotor side and �� the active power supplying to the connected grid via the stator side and in the 1 axis system. it is defined as [24]: �� # ( �� 4�3 > # ( ab ac �� 4�3 (13) in the 1 axis system, the electromechanical torque of the dfig can be calculated as: kl > # ( ab ac �c �� 4�3 (14) and the change of the rotational velocity of the rotor shaft in the dfig-wind turbine can be represented by [24]: m � �� �� k� > kl (15) where m is the inertia constant of the wind turbine system and k� the mechanical torque. iii. the scheme to smooth the output power to mitigate the fluctuation in the output power of the wind turbine, in this research the wind turbine must be operated in the power control mode. to adjust the output active power of the wind turbine, we should adjust the 4�3 component because by adjusting this component we can accommodate the torque (14) and hence the rotor velocity will be changed as in (15). as a result, the output active power will approach the desired value. in this research, we reuse the structure of rsc and gsc and utilize the controllers applied to rsc and gsc in [26]. the role of the rsc controller is to control the active power and the reactive power output of the wind turbine and the role of the gsc controller is to maintain a constant voltage on the dc-link and a zero reactive current output. however, the reference power of the rsc controller is modified. principally, it must compensate the fluctuation in its actual active power. the average output active power of each wind turbine is calculated as [8]: ��n o pq " q �� � q r (16) where k is the time interval, � �� �qr is the electrical energy output of each wind turbine in the period t, �� is the actual output power of each wind turbine, and ��n o the average active power of each wind turbine in the period t. the fluctuation in the output power can be calculated as: ∆�s� �� > ��n o (17) ∆�s� varies around zero, it can be either positive or negative. when ∆�s� is negative it means that the actual output power is lower than the average output power, and hence the reference power should be increased. on the contrary, with a positive ∆�s�, the actual output power is over the average value so the reference power should be reduced. hence, the power reference is defined by (18). equation (18) indicates that the reference power of each wind turbine compensates the variation of the actual output power. this is the main idea of the proposed method. ��lt ����� > ∆�s� (18) the reference power of the rsc controller is described in figure 3(a). figure 3(b) describes the reference power in the case of wind turbine using the ema method [4, 13, 19]. (a) (b) fig. 3. reference power for rsc controller: (a) proposed method and (b) ema method. iv. results and discussion the simulink environment in matlab software was used to simulate a group of two dfig-wind turbines using the engineering, technology & applied science research vol. 11, no. 4, 2021, 7343-7348 7346 www.etasr.com chung: smoothing the power output of a wind turbine group with a compensation strategy of … proposed scheme in order to verify it. the details of some models are shown in the appendix. the wind turbine capacity is 1.5mw and its power coefficient is described by (19) [23]: ����,�� 0.5176y""z[\ > 0.4� > 5^_ n`ab\ 5 0.0068� (19) where: 1 �8 1 � 5 0.008β > 0.035 �( 5 1 this wind turbine's characteristics are described in figure 2. to simulate the wind turbine system, we assume the wind speed data presented in figure 4. we use the dfig parameters described in detail in [27]. fig. 4. wind velocity data. here, we will compare the simulation results of the wind turbine group using the proposed method with the wind turbine group without any smoothing scheme (original) and with the wind turbine group using the ema method. the objective of the comparison to the original case is to verify the applicability of the proposed method to the wind turbines, whereas the comparison to the ema method is to indicate the benefits of the proposed method. a. comparison with the original case the main objective of this section is to verify and evaluate the efficiency of the proposed method. the simulation results will be compared to the original case, in which the wind turbines do not use any smoothing method or the ∆�s� in figure 3 is set at zero. the simulation results are shown in figure 5. as can be seen from figure 5, with the proposed method, the wind turbine group has a better performance than the original case. as can be seen from figure 5(a), the variation range of the power output is mitigated significantly in comparison to the original cage. clearly, from 50s to 150s, in the original case, the output power varies from around 1.5mw to 2.1mw whereas with the proposed method, it varies between 1.6mw and 2mw. at around 245s, the output power is 1.47mw and 1.55mw corresponding to the proposed method and the original case. to obtain this power output, the amount of compensation power of each wind turbine is calculated as shown in figure 5(b). with the proposed method, from 180s to 230s, the actual output power is higher than the average output power whereas from 230s to 310s, the actual output power is lower than the average output power. to compensate this difference, the reference power of each wind turbine, which is the input of the rsc controller, is shown in figure 5(c). we can see that, by comparing to the original case, the reference power is lower in the period from 180s to 210s and it is higher from 215s to 230s. clearly, the continuous curve in figure 5(c) is a little different to the summation of the broken curve in figure 5(c) and the curve in figure 5(b). the main reason is that the operation point of wind turbines is changed due to the reference output power. (a) (b) (c) (d) (e) fig. 5. simulation results with the proposed method and the original case: (a) power output, (b) compensation power, (c) reference power, (d) smoothing function, and (e) electrical energy. figure 5(d) indicates the smoothing function of two cases. obviously, with the proposed method, the smoothing function value is almost lower than that of the original case. at the end of the simulation period with the proposed method the smoothing function is around 3.58mw whereas with the original case it is around 5mw. therefore, the proposed method can be completely utilized to reduce the fluctuation in the output power of the wind turbine group. regarding the electrical energy output, figure 5(e) shows that the proposed method makes the electrical energy output of the wind turbine group a little lower than that of the original case. however, the amount of decrease is insignificant. at the end of the simulation interval, the electrical energy output is 0.2025mwh and 0.2035mwh for the proposed method and the original case engineering, technology & applied science research vol. 11, no. 4, 2021, 7343-7348 7347 www.etasr.com chung: smoothing the power output of a wind turbine group with a compensation strategy of … respectively. it means only 1kwh is lost due to the application of the proposed method. in conclusion, by using the proposed method, the reference power supplying the rsc controller compensated the variation of the output active power and hence the output active power of the group wind turbine varies with a smaller range of that of the original case. it means we can use the proposed method to mitigate the variation of the output power of the wind turbine group. b. comparison to the ema method the ema method was used to smooth the output power of the wind turbine [4, 13, 19]. in this research, the ema method is applied to wind turbines operating in the power control mode to determine the reference power (figure 3(b)). the reference power is described as: ��lt��� ��lt�� > k� 5 ey�������� > ��lt�� > k�^ (20) where k is the time period and e is the smoothing factor of ema, 0 f e f 1. in this research, we use e=0.5 and t=20s. the simulation results are shown in figure 6. (a) (b) (c) fig. 6. comparison between the proposed method and the ema method: (a) power output, (b) smoothing function, and (c) electrical energy. as can be seen from figure 6(a), the output power of the wind turbine group using the proposed method is obviously smoother than that of the ema method. around 250s, with the ema method, the output power is deeply reduced in comparison with that of the proposed method. by contrast, at the 330s, it becomes higher. hence, the performance of the wind turbine group with the ema method is not better than that with the proposed method. figure 6(b) indicates the smoothing function value of the wind turbine group. as can be seen from this figure, the smoothing function value with the proposed method is lower than that with the ema method. at the end of the simulation interval, they are around 3.58mw and 3.62mw for the proposed method and the ema method respectively. moreover, the electrical energy of the wind turbine group with the proposed method is a little higher than that with the ema method. from figure 6(c), the output electrical energy of the wind turbine group with the proposed method is 0.2025mwh whereas with the ema method is 0.2022mwh at the end of the simulation interval. therefore, the proposed method has a better performance than the ema method. v. conclusion this research proposed a new scheme to mitigate the fluctuation in the output power of a wind turbine group without an energy storage system. in this research, the active power control mode is used in wind turbines, and the reference active power is calculated to compensate the difference between the average output power and the actual output power. the proposed method is verified and evaluated by in the simulink environment of matlab. the simulation results of the proposed method, the ema method, and the original case were compared. the comparison indicated that when using the proposed method, the output power variation of the wind turbine group was mitigated significantly, and its performance is better than that of the ema method. appendix general model of the proposed method. refference power calculation. engineering, technology & applied science research vol. 11, no. 4, 2021, 7343-7348 7348 www.etasr.com chung: smoothing the power output of a wind turbine group with a compensation strategy of … simulation settings. references [1] "global renewables outlook: energy transformation 2050," international renewable energy agency, abu dhabi, united arab emirates, 2020. 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[24] p. d. chung, "voltage enhancement on dfig based wind farm terminal during grid faults," engineering, technology & applied science research, vol. 9, no. 5, pp. 4783–4788, oct. 2019, https://doi.org/10.48084/etasr.3117. [25] l. m. fernandez, c. a. garcia, and f. jurado, "comparative study on the performance of control systems for doubly fed induction generator (dfig) wind turbines operating with power regulation," energy, vol. 33, no. 9, pp. 1438–1452, sep. 2008, https://doi.org/10.1016/j.energy. 2008.05.006. [26] a. a. mohammed, "performance of control dynamics of wind turbine based on doubly fed induction generator under different modes of speed operation," conference papers in engineering, vol. 2013, aug. 2013, art. no. e125801, https://doi.org/10.1155/2013/125801. [27] g. s. kaloi, j. wang, and m. h. baloch, "active and reactive power control of the doubly fed induction generator based on wind energy conversion system," energy reports, vol. 2, pp. 194–200, nov. 2016, https://doi.org/10.1016/j.egyr.2016.08.001. engineering, technology & applied science research vol. 7, no. 4, 2017, 1786-1790 1786 www.etasr.com farhat et al.: a compact tri-band bandpass filter with high out-of-band rejection a compact tri-band bandpass filter with high out-of-band rejection mohamad farhat school of engineering the australian college of kuwait, kuwait m.farhat@ack.edu.kw mohammed abdul-niby school of engineering the australian college of kuwait, kuwait m.nibi@ack.edu.kw michel nahas school of engineering the australian college of kuwait, kuwait m.nahas@ack.edu.kw majdi alomari school of engineering the australian college of kuwait, kuwait m.alomari@ack.edu.kw abstract—this paper presents a planar tri-band bandpass filter with high out-of-band rejection over a wide band. the filter is based on two pairs of /4 resonators embedded inside an open loop ring resonator without any size increase, where each pair of resonators are electromagnetically coupled to each other and the feedlines. this results in the excitations of passbands, where the first passband is generated by the open loop resonators. the second and the third passbands are excited by /4 resonators. the proposed technique provides sufficient degrees of freedom to control the center frequency and bandwidth of the three passbands independently. in addition, the six transmission zeros created around the passbands results in a tri-band filter with high selectivity, sharp 3 db cut-off frequency, high isolation, low passband insertion-loss and high out-of-band harmonic rejection across an ultra-broadband frequency range up to 17 ghz. the proposed technique has the ability to switch from triple to dual band by removing one pair of the inner resonators. design methodology and simulation results of the filter are provided. keywords-tri-band; bandpass; filter; microstrip filter; planer i. introduction the growing demand of wireless communication applications necessitates rf transceivers to operate in multiple but separated frequency bands so that users can access various services, such as wlan, ieee 802.16 (wimax) and rfid, with a single multimode handset or terminal. higher order bandpass filters are routinely constituted by cascading multiple single-/dual-mode resonators. this straightforward approach unfortunately increases the overall filter size and raises the fabrication cost to a great extent. hence there is a demand for tri-band filters that are small enough to be easily integrated inside rf transceivers. other salient characteristics sought after in tri-band filters are low insertion-loss, excellent passband selectivity in order to efficiently utilize the em spectrum, and wide stopband or out-of-band rejection to minimize emi. these requirements present a challenge for the design engineers. various design approaches and structures have been used to develop tri-band bpfs. in [1], the tri-band filter was realized by cascaded multiband resonators. however, the design parameters were too complex and the circuit size is relatively high. to reduce the circuit size, many tri-band filters have been realized with a stepped impedance resonator (sir) because of their multiband behavior [2–5]. in [2], a tri-band bandpass filter was designed using a combined quarter-wavelength resonator. a trisection sir [3, 4] could be used to design the tri-band filter, and three passbands at any desired frequencies can be obtained by properly determining the impedance ratio. a multimode stepped-impedance resonator with a 0◦ tapped-feed structure was proposed to design a miniaturized tri-band bpf in [5]. in [3], to provide more freedom to control the filter harmonics responses, tri-section stepped-impedance resonators (tssirs) were proposed to build up tri-band bpfs. however, the resonant frequencies of the sir are dependent, complicating the filter design. modified stub-loaded resonator [6–8] have been utilized to design tri-band bpfs. in [6], the authors proposed a series of multi-stub loaded resonators to design tri-band bpfs. moreover, even and odd-mode analysis is utilized twice to analyze the resonance characteristics of multi-stub loaded resonator. in [7], a tri-band filter was designed by one set of stub-loaded shortended resonators. three embedded bending stub resonators were employed to achieve tri-band filter with compact size [8]. although the resulting filters are miniature in size, but have a high insertion-loss, the 3 db roll-off is skirt not sharp, and low out-of-band rejection. in this paper, a novel tri-band bandpass filter is presented that comprises of the main open loop resonators in which are embedded two pairs of λ/4 resonators. each pair of the embedded resonators, is designed to operate at a different frequency and generates three passbands without increasing the size of the main open loop resonators. the first passband is determined by the length of the open loop resonators, the second passband is determined by resonators 3 and 4, while the third passband is determined by resonators 5 and 6 as shown in figure 1. the proposed tri-band filter generates six transmission zeros located around the passbands to realize high selectivity, sharp 3 db roll-off and high out-of-band rejection. the planar structure facilitates the design and reduces fabrication cost. the filter is miniature compared to the aforementioned filters with a size of 0.25g×0.3g, which eases integration in wireless systems. the three pairs of resonators provide sufficient degree of freedom to control the center frequency and bandwidth of the three passband responses. based on the proposed concept, the filter was designed and simulated at 3/6.9/8.6 ghz. engineering, technology & applied science research vol. 7, no. 4, 2017, 1786-1790 1787 www.etasr.com farhat et al.: a compact tri-band bandpass filter with high out-of-band rejection ii. filter configuration and analysis a. resonators configuration figure 1 shows the topology of the microstrip bandpass filter. this is a second order filter having an asymmetric structure. the filter consists of two open loop resonators in a cshape configuration as shown in figure 1(a), which normally exhibits a single passband response with two transmission zeros to generate a quasi-elliptical response. in the example shown in figure 2, the passband of such a resonant structure has a centre frequency of 3.5 ghz. the lower transmission zero (ƒl) depends on the length l2 and its location can be calculated using (1); and the upper transmission zero (ƒu) depends on l1 and its location can be calculated using (2) [9]. therefore the centre frequency of the first passband (ƒ1) can be calculated using (3). two 50ω lines connected to the resonators acts as input/output ports with width w1. the main c-shape resonator structure was modified with the inclusion of four λ/4 resonators embedded inside the open loop resonators, as shown in figure 1(b). one end of these embedded resonators is shorted to ground. the resulting topology represents the proposed microstrip tri-band bandpass filter. the embedded resonators 3 and 4 generates the second passband with a centre frequency ƒ2 which is determined by the length l3 using eqn. (4); and resonators 5 and 6 generates the third passband with a centre frequency ƒ3 determined by length l4 using eqn.(5), the three passbands are shown in figure 2. 24 l eff nc f l   (1) 14 u eff nc f l   (2) 1 2 u lf ff   (3) 2 34 eff nc f l   (4) 4 44 eff nc f l   (5) where eff is the effective dielectric constant, n is the mode number (n = 1, 3, 5…,) and c is the speed of light in free space (3×108 m/s). the open loop c-shape resonators have a low out-of-band rejection. in order to increase the out-of-band rejection across a wide frequency spectrum, this is achieved with the assistance of triangular shaped capacitive loading at the open-end of the openloop resonators that incorporate “l” shaped slots [10]. the consequence of this is the realisation of harmonic suppression over a very wide frequency bandwidth extending up to 17 ghz as shown in figure 3. (a) (b) fig. 1. (a) the open-loop c-shape resonator and (b) the layout of the proposed filter with embedded resonators. fig. 2. frequency response of the tri-band bandpass filter. engineering, technology & applied science research vol. 7, no. 4, 2017, 1786-1790 1788 www.etasr.com farhat et al.: a compact tri-band bandpass filter with high out-of-band rejection fig. 3. simulated insertion-loss response of the proposed filter with and without embedded triangle. b. feed and coupling scheme figure 4 shows the feed and coupling schemes employed in the filter, where the black and hollow circular nodes represent resonators and source/load, respectively. figure 4(a) illustrates the feed and coupling scheme at the first resonant frequency (ƒ1), where resonators 1 and 2 resonate and form a strong electromagnetic coupling with each other and resonate at the first passband (ƒ1). the corresponding insertion-loss response is shown in figure 5. in contract, the resonators 3, 4, 5 and 6 are non-resonating at ƒ1 however are excited at the second and third passbands. similarly, figure 4(b) shows the feed and coupling scheme at the second resonant frequency (ƒ2), where resonators 3 and 4 resonate at second passband (ƒ2). the corresponding insertion-loss response is shown in figure 5. in contract, the resonators 1, 2, 5 and 6 are non-resonating at ƒ2. finally, figure 4(c) shows the feed and coupling scheme at the third resonant frequency (ƒ3), where resonators 5 and 6 resonate at third passband (ƒ3). the corresponding insertion-loss response is shown in fig. 5. in contract, the resonators 1, 2, 3 and 4 are nonresonating at ƒ3, however are excited at other passbands. source to load coupling is inherently realized as the non-resonating nodes are directly coupled with the resonating nodes. the intensity of the surface current distributions of the structure at different resonance frequencies are shown in figure 6. it is clear to see that only the desired resonators are resonating at its associated frequencies, and forming strong em coupling. the passband bandwidth of the filter depends on the external qfactor and the coupling coefficient between the resonator pairs. in particular, this depends on the gap (s1, s2, s3, s4 and s5) and the width (w2). iii. filter implementation the design procedure of the tri-band bandpass filter is now described. the initial dimensions of the filter are determined based on the design specifications, in particular the desired passbands frequencies. then, fine tuning is necessary to achieve the desired response using an appropriate simulation tool. (a) (b) (c) fig. 4. feed and coupling scheme, (a) at the first resonant frequencies, (b) at the second resonant frequencies, and (c) at the third resonant frequency. fig. 5. frequency response of the quad-band bandpass filter. resonator pair 1 and 2 determines the center frequency of the first passbands, the length of the resonators can be calculated from (1), (2) and (3). on the other hand, resonators 3 and 4 determine ƒ2 according to (4), and resonators 5 and 6 determine ƒ3 according to (5). in this design technique the inner resonators have no loading effect over the first passband and over each other, as is evident from figure 5. thus, the second and third passband can be controlled individually to any desired engineering, technology & applied science research vol. 7, no. 4, 2017, 1786-1790 1789 www.etasr.com farhat et al.: a compact tri-band bandpass filter with high out-of-band rejection frequencies, as is evident from figure 5. in additional, the proposed filter has the ability to be designed as a dual band by excluding any pairs of the inner resonators as shown in figure 5. (a) (b) (c) fig. 6. the surface current distribution of the proposed filter (a) at the fist (3 ghz), (b) the second (6.9 ghz) and (c) the third resonance frequency (8.6 ghz), respectively. the second step is to determine the required bandwidth for each passband. as mentioned earlier the bandwidth of the filter’s passbands depends on the external q-factor and the coupling-coefficient between resonators. also, in this design the three pairs of resonators have no coupling effect over each other. thus, the bandwidth of the three passbands can be determined separately. coupling-coefficient for the first passband depends on s1, w2 and l13, whereas the coupling-coefficient for the second passband depends on s2, w2, and s3, w2 for the third passband. the external q-factor is determined by l11, l12, w2, s4 and s3. by having a smaller gaps (s), a narrower width (w), a longer length (l) will result in a stronger coupling and hence a smaller external q-factor. on the contrary, the bigger gaps, wider width, a shorter length result in a weaker coupling and hence a higher external q-factor. iv. simulation results to demonstrate the feasibility of the proposed concept, a triband filter was designed for fundamental resonant frequencies at 3/6.9/8.6 ghz. the filter was simulated on a substrate with a 0.76 mm-thick and relative dielectric constant 2.17. following the design methodology in the preceding section the filter’s dimensions were determined to be (in millimeters): l1 = 19.5, l2 = 13, l3 = 8, l4 = 6, l5 = 1.6, l6 = 2.5, l7 = 1.4, l8 =1.3, l9 =1, l10 =0.5, l11 =2.4, l12 =1.2, l13 =5, w1 = 0.5, s1 = 0.23, s2 = 0.34, s3 = 0.74, s4 = 0.25, s5 = 0.23, and w2 = 2.42, which corresponds to a characteristic impedance of 50ω. simulation was performed using keysight technologies’ momentum 3d planar em simulator based on the method-of-moment (mom). fig. 7. simulated narrowband insertion-loss and return-loss response of the proposed filter. figures 7 and 8 show the simulation results narrow band and wideband, respectively. the filter has three passband responses centered at 3/6.9/8.6 ghz, with a high out-of-band rejection more than 12 db. the insertion-losses at the three passbands are less than 0.4 db, 1 db, and 1.4 db, respectively. the corresponding return-losses are greater than 24 db, 15db and 16 db, respectively. the six transmission zeros between the passbands result in the realization of a filter with high selectivity and high isolation between adjacent passbands. as shown in fig.8 the filter provides ultra-broadband spurii rejection greater than 15 db up to 17 ghz. v. conclusion a highly compact planar tri-band bandpass filter was presented based on two pairs of λ/4 resonators embedded inside the open loop resonators. the proposed technique provides a sufficient degree of freedom to alter the filter’s specifications in engineering, technology & applied science research vol. 7, no. 4, 2017, 1786-1790 1790 www.etasr.com farhat et al.: a compact tri-band bandpass filter with high out-of-band rejection terms of centre frequency and bandwidth. source to load coupling and the resulting three transmission paths are inherently realized to create transmission zeros, resulting in high selectivity and high isolation between the four passbands. the design methodology has been verified through simulation results. the filter’s performance and compact size makes it attractive for application in multiband wireless communication systems. fig. 8. simulated wideband insertion-loss and return-loss response of the proposed filter. references [1] c. f. chen, t. y. huang, r. b. wu, “design of dualand triple passband filters using alternately cascaded multiband resonators”, ieee trans. microw. theory tech., vol. 54, no. 9, pp. 3550–3558, 2006 [2] c. h. lee, c. i. g. hsu, h. k. jhuang, “design of a new tri-band microstrip bpf using combined quarter-wavelength sirs”, ieee microw. wire. compon. lett., vol. 16, no. 11, pp. 594–596, 2006 [3] c. i. g. hsu, c. h. lee, y. h. hsieh, “tri-band bandpass filter with sharp passband skirts designed using tri-section sirs”, ieee microw. wirel. compon. lett., vol. 18, no. 1, pp. 19–21, 2008 [4] q. x. chu, x. m. lin, “advanced triple-band bandpass filter using trisection sir”, electron. lett., vol. 44, no. 4, pp. 295–296, 2008 [5] h. w. liu, y. wang, x. m. wang, j. h. lei, w. y. xu, “compact and high selectivity tri-band bandpass filter using multimode steppedimpedance resonator”, ieee microw. wireless compon. lett., vol. 23, no. 10, pp. 536–538, 2013 [6] l. gao, j. xiang, q. xue, “novel compact tri-band bandpass filter using multi-stub-loaded resonator”, progress in electromagnetics research c, vol. 50, pp. 139–145, 2014 [7] x. y. zhang, l. gao, z. y. cai, x. l. zhao, “novel tri-band bandpass filter using stub-loaded short-ended resonator”, progress in electromagnetics research letters, vol. 40, pp. 81–92, 2013 [8] y. peng, l. zhang, y. leng, j. guan, “a compact tri-band passband filter based on three embedded bending stub resonators”, progress in electromagnetics research letters, vol. 37, pp. 189– 197, 2013 [9] m. farhat, b. s. virdee, "dual-band bandpass filter using open-loop resonators”, ieee proceedings of asia-pacific microwave conference, melbourne, pp. 1054 – 1057, december 5-8, 2011 [10] m. farhat, b. s. virdee, k. u. ahmed “novel microstrip bandpass filter with ultra-wide stopband”, german microwave conference, pp. 29-32, march 12-14, 2012 engineering, technology & applied science research vol. 7, no. 2, 2017, 1496-1503 1496 www.etasr.com boukerma and kadja: convective heat transfer of al2o3 and cuo nanofluids using various mixtures… convective heat transfer of al2o3 and cuo nanofluids using various mixtures of waterethylene glycol as base fluids karima boukerma department of physics faculty of science, university of 20 août 1955 skikda, algeria phy_karima@yahoo.fr mahfoud kadja department of mechanical engineering university of constantine 1 constantine, algeria kadja_mahfoud@yahoo.fr abstract—in this work, a numerical study has been performed on the convective heat transfer of al2o3/water-ethylene glycol (eg) and cuo/(w-eg) nanofluids flowing through a circular tube with circumferentially non-uniform heating (constant heat flux) under the laminar flow condition. we focus on the study of the effect of eg-water mixtures as base fluids with mass concentration ranging from 0% up to 100% ethylene glycol on forced convection. the effect on the flow and the convective heat transfer behavior of nanoparticle types, their volume fractions (φ=1-5%) and reynolds number are also investigated. the results obtained show that the highest values of the average heat transfer coefficient is observed between 40% and 50% of eg concentration. the average nusselt number increases with the increase in eg concentration in the base fluid, and the increase in the reynolds number and volume fraction. for concentrations of eg above 60%, and for all volume fractions, the increase of thermal performance of nanofluids became inversely proportional to the increase of reynolds number. in addition, cuo/(w-eg) nanofluids show the best thermal performance compared with al2o3/ (w-eg) nanofluids. keywords-enhanced heat transfer; nanofluids; numerical study; concentration; performance index nomenclature cp specific heat, j kg-1 k-1 d tube diameter, m d nanoparticle diameter, m h heat transfer coefficient, w m-2 k-1 k thermal conductivity, w·m-1·k-1 l length of the tube, m nu nusselt number p pressure, pa qw uniform heat flux, w m -2 re reynolds number (ρwind/μ) r radial direction t temperature, k u tangential velocity, m s-1 v radial velocity, m s-1 w axial velocity, m s-1 z axial direction greek symbols p pressure drop, pa θ angular coordinate μ viscosity, kg m-1 s-1 φ volume fraction ψ volume fraction of mixture  density, kgm-3 κ boltzmann constant, 1.38110-23, j k-1 subscripts ave average b bulk bf base fluid in inlet nf nanofluid p nanoparticle w wall i. introduction the efforts to enhance the heat exchangers performance in many industrial sectors (automotive, electronics, etc.) require the intensification of heat transfer by convection. improvements in exchange surfaces are a pathway already widely explored and reach their limits [1]. new optimization pathways must be considered. one of them is to use new fluids able to increase heat transfer such as the nanofluids. the nanofluids are nano-sized particle dispersions in a base fluid in order to improve certain properties. the diameter of such particles (called nanoparticles) is typically less than 100 nm [2]. in the case of a cooling liquid, one of the leading parameters to be taken into account to evaluate the potential for heat exchange is the thermal conductivity. however, the most widely used fluids, such as water, ethylene glycol (eg) or oil have only a low thermal conductivity relative to that of the solid. with nanofluids, the idea is to insert the nanoparticles in a base fluid in order to increase the effective thermal conductivity of the mixture. in [3], authors studied the nanofluids by preparing a mix of 100 nm of cu nanoparticles with water and oil. they found that engineering, technology & applied science research vol. 7, no. 2, 2017, 1496-1503 1497 www.etasr.com boukerma and kadja: convective heat transfer of al2o3 and cuo nanofluids using various mixtures… the thermal conductivity of nanofluids increases considerably with the concentration of nanoparticles. then they proposed a correlation to calculate the nusselt number as a function of peclet number for nanofluids. in [4], authors experimentally studied the forced convection laminar flow of cuo/water and al2o3/water nanofluids in a tube under constant temperature. they indicated that there is an increase in heat transfer with an increase in volume concentration for both nanofluids, but they found that al2o3 nanoparticles are more performant. in [5], authors studied a two dimensional laminar flow inside a triangular duct with the existence of a vortex generator. three types of nanofluids (al2o3/eg, cuo/eg and sio2/eg) with volume concentrations ranging from 1 to 6% were considered. their results show that sio2/eg has the highest value of nusselt number compared to other nanofluids. on the other hand, the value of the friction coefficient is the same for all nanofluids and nanoparticles concentrations considered. due to its relatively low molecular weight, ethylene glycol greatly lowers the water freezing point. therefore, the mixture of water–ethylene glycol was often used in cold countries [6-7]. several researchers measured experimentally the rheological properties of nanofluids with an eg-water mixture base fluid [8-10], and they proposed correlation equations for the thermophysical properties such as: viscosity, thermal conductivity and specific heat [11-12]. these properties were used to develop correlations for nusselt number and/or friction factor from experiments, as a function of these properties and the nanoparticle volume concentrations [13-15]. in [16], authors conducted an experimental study on the forced convective heat transfer of tio2 nanoparticles with mixture of eg-water (40:60 by volume) in a copper tube under laminar conditions. moreover, they studied the effect of mixtures of water and eg base fluid with different volume fractions (ranging from 0 % up to 50 % ethylene glycol) on local nusselt number. they found that there is 8.25 –20.52% increase in nusselt number when the eg fraction in water increases from 0 to 50%. in [17], authors measured the heat transfer coefficient of the secondary refrigerant based cnt (carbon nanotubes) nanofluid in a tubular heat exchanger at different operating temperatures. the base fluid was a mixture of eg -water (30:70 by volume). the obtained results showed that at 40 °c with a 0.45 vol. % cnt nanofluid the increase in thermal conductivity and average convective heat transfer coefficient was 19.73% and 159.3% respectively. they concluded that such increases occur because of the micro convection effects of the chaotic movement of the carbon nanotubes. in another study [18] with the same nanofluid cited above they investigated the convective heat transfer in various lengths of a tubular heat exchanger. they reported that contrary to what is customary for heat transfer, the nusselt number decreases with an increase in the reynolds number as the mwcnt (multiwalled carbon nanotubes) concentration increases in the base fluid. most of the articles, which dealt with the experimental or numerical research on heat transfer and nanofluid flow with an eg-water mixtures base fluid, are for fixed eg fractions in water and only a few considered different volume fractions, but in maximum up to 50%. this research focuses on the study of the effect of ethylene glycol based al2o3 and cuo nanofluids on forced convection in a circular tube with circumferentially non-uniform heating. the eg-water mixtures used in the computations have eg mass concentrations which vary in the interval from 0% up to 100 %. heat transfer with circumferentially non-uniform heating occurs in many applications such as evaporators, boilers and solar collectors [1]. ii. numerical simulation a. geometry in this study, we considered laminar forced convection flow of a nanofluid in a straight cylindrical pipe with a diameter d of 0.01m and the length l of 1m. the length was chosen so as to obtain hydrodynamically and thermally fully-developed flow at the outlet section. the tube was heated on one side (upper half) with a constant heat flux and insulated over the lower side. the problem treated is shown schematically in figure 1. fig. 1. geometry and boundary conditions b. governing equations our problem is modelled as laminar, steady flow and the three-dimensional one phase model for the nanofluid was used. pressure work and dissipation are neglected. the thermophysical properties of the nanofluid are assumed to be constant. under these assumptions the governing mass, momentum and energy equations for the nanofluid can be written as follows: continuity equation:   0 vnf (1) momentum equations:    vpvv nfnf   (2) energy equation:     tktvc nfnfp   (3) c. boundary conditions the nanofluid enters the channel at the inlet with a uniform axial velocity that is specified according to the flow reynolds number. the inlet temperature tin is taken as 300 k. the noslip boundary conditions at the walls are implemented in the present study, and a constant heat flux (5 kw/m2) is applied through the top half of the tube, while the bottom wall is considered adiabatic. for the channel outlet, the fully developed flow boundary condition is adopted. the boundary conditions can therefore be expressed as: • at the inlet of tube (z=0): inin ttandvuww  0, (4) engineering, technology & applied science research vol. 7, no. 2, 2017, 1496-1503 1498 www.etasr.com boukerma and kadja: convective heat transfer of al2o3 and cuo nanofluids using various mixtures… • at the fluid-wall interface (r=d/2): 0 wvu (5) w nf nf q r t k     :0  (6) 0:2     r t k nfnf (7) • at the tube outlet (z=l): the outflow boundary condition is applied, in which the flow velocity and temperature profiles are unchanging in the flow direction. c. thermophysical properties the base fluid is a mixture of water and eg in different mass concentrations, their thermophysical properties are calculated as follows [19]:   wateregm   1 (8) where m refers to “mixture”, ψ is the volume fraction of the mixture and ζ is the fluid physical property, for example: density, specific heat, thermal conductivity and viscosity. the thermophysical properties of the mixture are greatly modified by the addition of nanoparticles. many parameters characterizing these nanoparticles can have a significant effect on the values of the thermophysical parameters of the nanofluid obtained (the volume fraction φ, the size of the nanoparticles, the thermal conductivity of the base fluid and that of the nanoparticles, the temperature of the medium, etc.). the thermophysical properties of water, ethylene glycol (eg), al2o3 and cuo are summarized in table i. in this work, we assume that the nanoparticles are well dispersed in the base fluid. in order to calculate the thermophysical properties of the nanofluid, we use the equations given below which were found in the literature. in [9], author compared their density measurements of different nanoparticles in a base fluid of 60:40 ethylene glycol/water with predictions using equation (9) which was proposed in [20], and they found an excellent agreement between them.   pbfnf   1 (9) where nf , bf and p are the nanofluid, base fluid and nanoparticles densities, respectively, and φ is the volume fraction. the specific heat of nanofluids pnfc is computed using xuan and roetzel’s equation [21].   nf ppppbfbf pnf cc c     1 (10) where pbfc and ppc are specific heat at constant pressure of the base fluid and nanoparticles, respectively. the thermal conductivity formula proposed by vajjha and das [8] was used in this study. it incorporates the classical maxwell model and the brownian motion effect and is given by:           ,105 2 22 4 tf d t ck kkkk kkkk k pp pbfbfbf pbfbfp pbfbfp nf    (11) where the empirical function  ,tf for the nanofluids al2o3 and cuo is given by: ( ) ( )2 3 0 , 2.8217 10 3.917 10 t f t t f fæ ö÷ç ÷ç= ´ + ´ +÷ç ÷÷çè ø ( )2 33.0669 10 3.91123 10f-´ ´ (12) the factor  is presented in table ii. it is found using the experimental data of [8], and it represents the fraction of the liquid volume that travels with a particle. the viscosity of the nanofluid μnf is function of the volume fraction and viscosity of the base fluid μbf and is evaluated using the following equation [23]:   bf a nf ea  2 1 (13) where a1 and a2 are constants, their values are given in table iii. table i. thermophysical properties of nanoparticles and base fluids at t=300 k [22, 27] properties water eg al2o3 cuo density (kg/m3) 997 1,114.4 3,600 6,500 thermal conductivity (w/m k) 0.613 0.252 36 17.65 specific heat (j/kg k) 4179 2415 765 533 viscosity (n/m2 s) 0.000855 0.0157 table ii. the values of the factor b for al2o3 and cuo nanoparticles. type of particles β concentration temperature al2o3 8.4407(100φ) -1.07304 1%≤φ≤10% 298k≤t≤363k cuo 9.881(100 φ)-0.9446 1%≤φ≤6% 298k≤t≤363k table iii. viscosity coefficients for al2o3 and cuo nanoparticles. nanoparticles a1 a2 concentration al2o3 0.983 12.959 1%≤ φ ≤10% cuo 0.9197 22.8539 1%≤ φ ≤6% iii. numerical method and validation the simulation was carried out using fluent. the resolution of (1)-(3) is performed by discretizing the computational domain. in this way, all the discrete points constitute the computational domain mesh. at each discrete point of the domain, fluent uses the finite volume method for obtaining algebraic expressions which replace the nonlinear partial differential equations and which can be solved numerically. the resulting set of algebraic equations predicts the mass, momentum and energy in all the discrete points of the mesh. the finite volume method consists of integrating the conservation equations over each control volume in the mesh. the convective and viscous terms are discretized with a second order upwind scheme for more accuracy. the simple algorithm is used for pressure-velocity coupling. the convergence of the iterative process is determined by the concept of residues. in this study, the discretized equations are considered converged when all the equations have a residue less than 10-6. the gambit software was used to perform a 3d mesh. after several trials, we obtained the threshold of the engineering, technology & applied science research vol. 7, no. 2, 2017, 1496-1503 1499 www.etasr.com boukerma and kadja: convective heat transfer of al2o3 and cuo nanofluids using various mixtures… grids finesse above which the calculated solution becomes grid independent. the simulation was carried out on three types of grids (5  32  500, 7  40  500, 10  64  500) for pure water. figure 2 shows the independence test for the calculated local nusselt number along the tube on the grids used. according to the result of this test the mesh chosen is that with an average number of discretization points equal to (740500). we can also notice in figure 2 that our numerical results are in good agreement with the correlation developed in [28]. the validation of the cfd code has also been tested using the experimental results obtained by [24]. this result concerns the laminar flow in a circular tube heated by a constant flux where the heat flux (qw) equals to 9000 w/m 2 and the reynolds number (re) is about 799.53. the results for the local nusselt number (figure 3) agree well with our results. fig. 2. comparison of local nusselt number values for different grids fig. 3. comparison of numerical local nusselt number with the experimental values of [24] the local nusselt number and local heat transfer coefficient are calculated using the following equations: k dzh znu   )( )( (14)      bw w ztzt q zh   (15) where d and t(z)w are the tube diameter and wall temperature respectively, and t(z)b is the bulk fluid temperature calculated as follows:   a z a z b dav datv zt   )( (16) the average heat transfer coefficient (have) and nusselt number are expressed as [25]: bw ave tt q h   (17) k dh nu aveave   (18) where wt and bt are the wall and fluid average temperature respectively. iv. results and discussion the convective heat transfer was numerically investigated for flow of al2o3 and cuo nanofluids in a horizontal cylindrical tube which was heated on one side. mixtures of ethylene glycol/water as base fluid with mass concentration ranging from 0% to 100% ethylene glycol were used (so we get eleven base fluids). the computations were carried out with the reynolds numbers of 250, 500, 750 and 1000, and with different volume fractions of the nanoparticles which vary from 0% to 5%. figure 4 shows the average heat transfer coefficient (have) of base fluid mixtures of water/eg at different reynolds numbers. the highest values of the average heat transfer coefficient is observed between 40% and 50% of eg concentration, for instance at re=250 the values are 681.3 and 683.7 (w/m2k) respectively. as expected the heat transfer coefficient increases when the reynolds number increases. at a given reynolds number, the base fluid mixtures of water-eg (with different mass. % of eg) have highest average heat transfer coefficients, followed by ethylene glycol and pure water respectively. the effect of volume fraction (φ%) on average heat transfer coefficient for al2o3/w-eg nanofluids at re=1000 is depicted in figure 5. the average heat transfer coefficient increases as the volume fraction of al2o3 nanoparticles increases in the base fluid. also we can see that the highest values of have are between 40% and 50% of eg concentration. the influence of the reynolds number and the volume fraction on average nusselt number is illustrated in figures 6 and 7. figure 6 shows the effect of re on the average nusselt number (nuave) for a low volume fraction (1%) of al2o3 nanoparticles. nuave of al2o3/(water-eg) nanofluids is found to be higher than that of al2o3/water and lower than that of al2o3/eg. the reason being that the thermal conductivity of water is greater than that of water-eg mixtures and eg, respectively. figure 7 represents the variation of nuave with volume fraction of cuo/(water-eg) nanofluids at re=1000. the average nusselt number of the nanofluids is greater than that of base fluids. nuave increases as the concentration of ethylene glycol in the base fluid or the reynolds number or the volume fraction increase. the enhancement of thermal performance with cuo nanofluids is higher than that with al2o3 nanofluids especially at great values of reynolds number and volume fraction. figure 8 shows the thermal performance of nanofluids using different concentrations of ethylene glycol in the base fluid. the curves present the results of the average heat transfer coefficient ratio (hnf/hbf) between the nanofluid and the base fluid (it should be noted again that each concentration of eg represents a base fluid) at different volume fractions. as can be noticed there is an increase in heat transfer ratio as the engineering, technology & applied science research vol. 7, no. 2, 2017, 1496-1503 1500 www.etasr.com boukerma and kadja: convective heat transfer of al2o3 and cuo nanofluids using various mixtures… nanoparticle volume fraction increases. in the case of al2o3 nanoparticles and at re=250 the heat transfer coefficient ratio increases with the increase of the concentration of eg in the base fluid; but for other values of re the ratio hnf/hbf increases and then it decreases, for instance at re=500 and 1,000 the decrease in the ratio occurs at 80% and 40% of eg, respectively. consequently, it is observed that the increase in the ratio hnf/hbf is directly proportional, as expected, to the increase of the reynolds number for concentrations situated between 0% to 20% of eg. for concentrations between 30% and 40% of eg this ratio has approximately the same value. we find that from 50% of eg the ratio hnf/hbf decreases with increasing reynolds number and that this decrease appears more clearly from 80 % of eg in the base fluid. fig. 4. effect of reynolds number and water-eg mixture on average heat transfer coefficient fig. 5. variation of average heat transfer coefficient with volume fraction for al2o3/(w-eg) nanofluids concerning the cuo nanoparticles, we always get the same behavior as regards the influence of the concentration of eg on the heat exchange ratio for the different reynolds numbers. but we note that the decrease of the ratio hnf/hbf appears at a concentration of eg more advanced (about 30% of eg at re=1,000 and φ=4%) and in a faster manner than that of al2o3 nanofluids, and the inverse proportionality occurring between the heat transfer ratio and the reynolds number happens early at a concentration of 40% of eg in the base fluid. we can clearly observe from figure 8 that the cuo/(w-eg) nanofluids have the best average heat transfer coefficient ratio (heat transfer enhancement) compared with al2o3/(w-eg) nanofluids. the inverse relationship that occurs between the convective heat transfer ratio and the reynolds number and which increases with the volume fraction and the concentration of eg in base fluid, is probably caused by the increase in the viscosity upon the addition of nanoparticles and also because of the high viscosity of the eg compared to water, and may be at low reynolds numbers the increase of concentration of eg in the base fluid makes the nanoparticles more effective. fig. 6. variation of nusselt number with reynolds number for al2o3/(weg) nanofluids fig. 7. variation of nusselt number with volume fraction for cuo/(weg) nanofluids. from the above observations the nanofluids appear to be ideal when considering an increase in the thermal performance of heat transfer equipment. the addition of nanoparticles in a fluid allows an increase of the thermal conductivity but unfortunately also the viscosity which usually leads to an increase in pressure loss in the system. in the industrial applications of nanofluids, although an improvement of heat transfer is observed, the required pump power is increased compared with the case of the conventional fluid. a significant increase in the viscosity of the nanofluid could lead to an unfavorable energy performance of the industrial system. to illustrate this, we used a performance index "η" [26], where η represents the ratio between heat transfer enhancement and pressure drop in the system: , , ave nf nf ave bf bf h p h p h æ ö æ öd÷ç ÷ç÷ç ÷ç÷= ç ÷ç÷ ÷ç ÷ çd ÷çç ÷ç è øè ø (19) where bfaveh , and bfp are the average heat transfer coefficient and pressure drop of base fluids. to determine the effectiveness of each nanofluid, relative to its base fluid, figure 9 shows the variation of the performance index with al2o3/(w-eg) and cuo/(w-eg) nanofluids for various volume fractions at re=500. in this case have,bf and δρbf are the average heat transfer coefficient and pressure drop of the water-eg base fluid, respectively. as shown in this figure the performance index is below 1. so we can conclude that the base fluid (w-eg) is more effective, from the thermal point of engineering, technology & applied science research vol. 7, no. 2, 2017, 1496-1503 1501 www.etasr.com boukerma and kadja: convective heat transfer of al2o3 and cuo nanofluids using various mixtures… view, than the nanofluids. it is noted that the performance index decreases with the increase of the volume fraction of the nanoparticles, but it does not change with the concentration of eg (that is why we stopped at 50% of eg in this figure). we also see that the performance index of al2o3 nanofluids is higher compared to the one of cuo nanofluids. fig. 8. effect of different base fluids on heat transfer enhancement for various reynolds numbers and nanoparticles. figure 10 shows the evolution of the performance index as a function of the reynolds number in the case of water-eg based fluids. we can see that all the values corresponding to the base fluids (w-eg) are above those corresponding to the case of pure eg. this means that the performance index of base fluids, as it is defined, is favorable for the whole range of the concentration of eg. however, this performance index has significantly decreased with an increase of the concentration of eg in the base fluid. for example when the concentration of eg varies from 10% to 90%, η decreases from 49.36 to 1.36 for re=1,000. on the other hand, there is a small change in the value of the performance index with reynolds number. the evolution of the performance index with al2o3/(weg) nanofluids for different volume fractions at re=500 is depicted in figure 11. we note that the performance index decreases when the volume fraction of nanoparticles and the concentration of eg increase. for the concentration of eg varying from 10% to 70% in the base fluid we have a performance index greater than 1, which implies the use of nanofluids is favorable than pure eg. but from 80% of eg onwards the performance index becomes less than 1 for some volume fractions. for example η is less than 1 at φ= 4 % for the concentration of 80% of eg and at φ=2%, for the concentration of 90% of eg. fig. 9. variation of the performance index for different volume fractions.with al2o3/(w-eg) and cuo/(w-eg) nanofluids fig. 10. evolution of the performance index as a function of the reynolds number for different base fluids fig. 11. variation of the performance index with al2o3/(w-eg) nanofluids for different volume fractions. figure 12 shows the variation of the performance index with cuo/(w-eg) nanofluids for different volume fractions at re=500. it is observed that the performance index is greater than 1 up to 50% of eg, and then begins to decrease when the volume fraction and the concentration of eg increase. for instance, η is less than 1 at φ=5% for the concentration of 60% of eg and at φ=3% for the concentration of 80% of eg. engineering, technology & applied science research vol. 7, no. 2, 2017, 1496-1503 1502 www.etasr.com boukerma and kadja: convective heat transfer of al2o3 and cuo nanofluids using various mixtures… according to the two figures, we see that the performance index is always greater than 1 for φ=1%, and we also see that the al2o3/(w-eg) nanofluids have the highest performance index that the cuo/(w-eg) nanofluids. fig. 12. variation of the performance index with cuo/(w-eg) nanofluids for different volume fractions v. conclusion we investigated in the present research the effect of water eg based nanofluids with various compositions on convective heat transfer performance. heat transfer due to al2o3/(w-eg) and cuo/(w-eg) nanofluids flow inside a circular tube is studied numerically. the top half of the tube is heated with constant heat flux while the bottom is insulated. based on the presented results, the following conclusions can be drawn: • between 40% and 50% of concentration of eg, the average heat transfer coefficient has highest values. this coefficient increases when the nanoparticle volume fraction and reynolds number increase. • the average nusselt number of nanofluids with w-eg base fluids is found to be higher than that of water based nanofluids and lower than eg based nanofluids. • the average heat transfer coefficient ratio (hnf/hbf) increases when the volume fraction of nanoparticles increases. however, from 60% of concentration of eg, these ratios decrease with the increase of the reynolds number. • the use of the nanofluids al2o3/(w-eg) and cuo/(w-eg) is unfavorable compared to the use of pure water or watereg base fluids, but its use is favorable compared to the use of pure eg, except at higher concentration of eg and some volume fractions of nanoparticules. references [1] s. allahyari, a. behzadmehr, s. m. hosseini sarvari, “conjugate heat transfer of laminar mixed convection of a nanofluid through a horizontal tube with circumferentially non-uniform heating”, international journal of thermal sciences, vol. 50, pp. 1963-972, 2011 [2] s. u. s. choi, “enhancing thermal conductivity of fluids with nanoparticles”, international mechanical engineering congress and exposition, new york, 1995 [3] y. xuan, q. li, “heat transfer enhancement of nanofluids”, international journal of heat and fluid flow, vol. 21, pp. 58-64, 2000 [4] s. zeinali heris, s. g. etemad, m. nasr esfahany, “experimental investigation of oxide nanofluids laminar flow convective heat transfer”, international communications in heat and mass transfer, vol. 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theory”, petroleum science and technology, vol. 27, pp. 612–624, 2009 [10] v. kumaresan, r. velraj, “experimental investigation of the thermophysical properties of water-ethylene glycol mixture based cnt nanofluids”, thermochimica acta, vol.545, pp. 180– 186, 2012 [11] l. s. sundar, m. k. singh, e. v. ramana, b. singh, j. gracio, a. c. m. sousa, “enhanced thermal conductivity and viscosity of nanodiamond-nickel nanocomposite nanofluids”, scientific reports, vol. 4, art. no. 4039, 2014 [12] r. s. vajjha, d. k. das, “specific heat measurement of three nanofluids and development of new correlations”, journal of heat transfer, vol. 131, no. 7, art. no. 071601, 2009 [13] r. s. vajjha, d. k. das, d. p. kulkarni, “development of new correlations for convective heat transfer and friction factor in turbulent regime for nanofluids”, international journal of heat and mass transfer, vol. 53, pp. 4607–4618, 2010 [14] m. s. mojarrad, a. keshavarz, m. ziabasharhagh, m. mehdi, “experimental 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r. velraj, “convective heat transfer characteristics of cnt nanofluids in a tubular heat exchanger of various lengths for energy efficient cooling/heating system”, international journal of heat and mass transfer, vol. 60, pp. 413–421, 2013 [19] e. abu-nada, a. j. chamkha, “effect of nanofluid variable properties on natural convection in enclosures filled with a cuo-eg-water nanofluid”, international journal of thermal sciences, vol. 49, pp. 2339-2352, 2010 [20] b. c. pak, y. i. cho, “hydrodynamic and heat transfer study of dispersed fluids with submicron metallic oxide particles”, experimental heat transfer, vol. 11, pp. 151-170, 1998 engineering, technology & applied science research vol. 7, no. 2, 2017, 1496-1503 1503 www.etasr.com boukerma and kadja: convective heat transfer of al2o3 and cuo nanofluids using various mixtures… [21] y. xuana, w. roetzel, “conceptions for heat transfer correlation of nanofluids”, international journal of heat and mass transfer, vol. 43, pp. 3701-3707, 2000 [22] h. a. mohammed, a. n. al-shamani, j. m. sheriff, “thermal and hydraulic characteristics of turbulent nanofluids flow in a rib–groove channel”, international communications in heat and mass transfer, vol. 39, pp. 1584–1594, 2012 [23] r. s. vajjha, d. k. das, “a review and analysis on influence of temperature and concentration of nanofluids on thermophysical properties, heat transfer and pumping power”, international journal of heat and mass transfer, vol. 55, pp. 4063–4078, 2012 [24] e. esmaeilzadeh, h. almohammadi, s. nasiri vatan, a. n. omrani “experimental investigation of hydrodynamics and heat transfer characteristics of γ-al2o3/water under laminar flow inside a horizontal tube”, international journal of thermal sciences, vol. 63, pp. 361–37, 2013 [25] s. suresh, k. p. venkitaraj, p. selvakumar, m. chandrasekar, “effect of al2o3–cu/water hybrid nanofluid in heat transfer”, experimental thermal and fluid science, vol. 38, pp. 54–60, 2012 [26] p. razi, m. a. akhavan-behabadi, m. saeedinia, “pressure drop and thermal characteristics of cuo–base oil nanofluid laminar flow in flattened tubes under constant heat flux”, international communications in heat and mass transfer, vol. 38, pp. 964–971, 2011 [27] f. p. incropera, d. p. de witt, t. bergman, a. lavine, fundamentals of heat and mass transfer, wiley, 2006 [28] a. bejan, a. d. kraus, heat transfer handbook, john wiley & sons, 2003 microsoft word etasr_v12_n2_pp8388-8392 engineering, technology & applied science research vol. 12, no. 2, 2022, 8388-8392 8388 www.etasr.com ali hussain & aljalawi: effect of sustainable glass powder on the properties of reactive powder … effect of sustainable glass powder on the properties of reactive powder concrete with polypropylene fibers zainab ali hussain department of civil engineering college of engineering university of baghdad baghdad, iraq zainab.hussain2001m@coeng.uobaghdad.edu.iq nada mahdi fawzi aljalawi department of civil engineering college of engineering university of baghdad baghdad, iraq nada.aljalawi@coeng.uobaghdad.edu.iq received: 29 january 2022 | revised: 15 february 2022 | accepted: 19 february 2022 abstract-global warming and environmental damage have become major problems. the production of portland cement releases large quantities of gas, which cause pollution to the atmosphere. this problem can be solved via the use of sustainable materials, such as glass powder. this study investigates the effect of partial replacement of cement with sustainable glass powder at various percentages (0, 15, 20, and 25%) by weight of cement on some mechanical properties (compressive strength, flexural strength, absorption, and dry density) of reactive powder concrete (rpc) containing a percentage of polypropylene fibers (prpc) of 1% by weight. furthermore, steam curing was performed for 5 hours at 90 o c after hardening the sample directly. the rpc was designed using local cement, silica fume, and super plasticizer with a water/cement ratio of 0.2 to achieve a compressive strength of 96.3mpa at the age of 28 days, and it was tested at percentages of sustainable glass powder replacement of 0 and 20% by weight of cement. according to the study's findings, rpc's compressive strength rose up to 4.2% as a consequence of the use of sustainable glass powder replacement by 20%, flexural strength up to 15.3%, dry density up to 0.49%, and absorption reduction by 31.7% at the age of 28 days and in comparison with the reference mixture. keyword-reactive powder concrete; sustainable glass powder; polypropylene fiber; flexural strength; compressive strength i. introduction the requirements for high strength and high performance of concrete are the main reason for the production of reactive powder concrete (rpc) [1]. rpc is defined as a cementitious composite with very high strength and ductility [2]. the development of rpc is based on the idea that a material with a limited number of internal voids will have a larger loadcarrying capacity and will exhibit superior structural overall performance [3]. in order to manufacture cement, a large amount of natural resources and energy must be used in its production. the production of 1 ton of cement from start to finish requires about 1.5 tons of raw materials. it is vital to hunt for alternative binders because of the necessity to minimize co2 emissions. the need for more cost-effective and environmentally friendly cement ingredients has fueled the interest in alternative materials that may partly replace ordinary portland cement (opc), which is the most widely utilized [4]. the majority of the recent work in iraq's building sector has been devoted to determine the viability of local raw resources as substitutes for imported commodities that are required for certain practical uses [5]. additionally to traditional mineral admixtures, other materials, such as glass powder, can be used. when glass is utilized as an aggregate, its high alkali content facilitates the formation of the pozzolanic reaction that occurs when it is crushed into fine powder and used as a partial substitute for cement. it has been shown that the inclusion of glass powder has a positive effect on the expansion caused by alkali silica reaction. cracks in a concrete construction are unavoidable during the course of its life [6, 7]. structures exposed to the external environment are more prone to cracking because they are impacted via shrinkage or expansion in weight and drying, as well as other environmental variables. these cracks have an impact on the mechanical characteristics and the durability of the structures reduces. fibers may be used to solve this issue [8]. polypropylene fibers are regarded to be an excellent substitute for cotton, because of their excellent chemical stability and hydrophobic nature [9, 10]. it was found that using polypropylene fibers to volume percentages up to 0.45% produced results that were comparable to those achieved with steel fibers [11]. authors in [12] checked the mechanical and fresh properties of rpc. they produced rpc with a compressive strength of 130mpa under standard processing conditions at the age of 28 days. the strength obtained at 28 days of curing is equivalent to approximately 70% of the strength achieved at 7 days. the results show that the addition of fibers led to a significant improvement in compressive strength and bending compared to concrete without fibers [13]. corresponding author: zainab ali hussain engineering, technology & applied science research vol. 12, no. 2, 2022, 8388-8392 8389 www.etasr.com ali hussain & aljalawi: effect of sustainable glass powder on the properties of reactive powder … ii. materials a. cement opc (cem i 42.5r) was used in this study. the physical and chemical requirements comply with [14]. b. silica fume (sf) silica fume was employed to improve rheological properties via the lubrication effect caused by the spherical shape of the material. the chemical and physical properties as well as the strength activity index are in accordance with the [15] standard. c. fine aggregates the utilized fine aggregates had a good gradation, were free from harmful substances that have an impact on the results of the examination, and passed through the 0.6mm sieve, and complied with the requirements of [16]. d. polypropylene fibers belgian fibers polypropylenes fibers were used for reinforcement. the specifications and properties of the fibers used throughout the experimental work are illustrated in table i and figure 1. table i. polypropylene fiber properties* fig. 1. polypropylene fibers used in this work. e. glass powder in this study, sustainable glass powder (figure 2) resulting from shops selling window glasses was used. because it was difficult to be disposed of, it was recycled and grounded to the required finesse according to the requirements of [17]. at first the grinding process was carried out with the use of an iron hammer that crushed the waste glass into small pieces. then an industrial grinder was used. the chemical and physical properties and strength activity index comply with [18], as show in table ii. fig. 2. glass powder used in this work. table ii. chemical and physical properties of glass powder oxide composition test result % limit of astm c618-15 class n specification requirements silicon oxide (sio2) 64.22 min(70) aluminum oxide(al2o3) 9.6 (79.02) iron oxide(fe2o3) 5.2 sulfur trioxide (so3) 2.1 max(4) calcium oxide (cao) 4.26 ---- magnesium oxide (mgo) 1.65 ---- loss of ignition 3.21 max(10) percent retained on 45µm (no.325) 32% 34% strength activity index % with opc at 7 days. 101.4 min (75) f. water the water used in this study was clean and free from harmful substances, complying with [19]. g. chemical admixtures given that adding fibers to the mixture reduces mixture workability, therefore a superplasticizer was added to the mixture. this type g product, conforms to [20] and the manufacturer's suggested dose varied from 0.5 to 2.5lt per 100kg of cement. iii. reactive powder concrete design for the purpose of obtaining rpc with the desirable properties, strength design of 95mpa was adopted [12]. table iii summarizes the mix design rpc containing polypropylene fibers by 1% vol. of concrete. the used dosage of superplasticizer was 1.8lt/100kg of cement. table iii. details of rpc mix proportions for (kg/m 3 ) mix type opc fine aggregates silica fume glass powder water weight w/cm m.0% 950 1045 238 ---208 0.175 m.15% 807.5 1045 238 142.5 208 0.175 m.20% 760 1045 238 190 208 0.175 m.25% 712.5 1045 238 237.5 208 0.175 iv. curing samples after the samples were removed from the molds, they were placed in the steam curing device for 5 hours at a temperature of 90 o c as shown in figure 3. after that, the samples were description specifications length 6mm diameter 34µm aspect ratio 0.176 density 0.91g/cm 3 young modulus 3750mpa *data sheet engineering, technology & applied science research vol. 12, no. 2, 2022, 8388-8392 8390 www.etasr.com ali hussain & aljalawi: effect of sustainable glass powder on the properties of reactive powder … outed from the steam curing device and were placed in the normal treatment tank for the age of test. fig. 3. the cycle of steam curing. v. results and discussion a. flow test regarding the flow for prpc samples, a minor increase was achieved with increased replacement percentage as shown in figure 4. this occurred due to the small size of the glass powder particles in addition to the glassy texture and the spherical shape that makes them work as spherical bearings that lubricate the mix. thus the glass powder acts as a superior plasticizer that increases workability and reduces the friction that occurs between the particles. this result agrees with the results of [21]. fig. 4. relationship between flow and flass powder percentage for prpc. b. compressive strength the sustainable glass powder was utilized in 4 percentages (0, 15, 20, 25%) by weight of cement. we notice through the values shown in figures 5-6 that the glass powder affects the chemical reactions in the cement. the highest value of compressive strength was obtained when the replacement ratio was 20%, due to the pozzolanic reaction caused by the glass powder in the rpc mixture being energetically triggered via the high temperature used for steam curing leading to the formation of a denser microstructure and a quicker development of strength. finely dispersed glass powder acts as a supplementary cementitious material micro filler within the concrete matrix, causing the strength to increase. this result agrees with the results of [22, 24]. fig. 5. testing a prismatic concrete sample. fig. 6. relationship between the compressive strength and age for prpc. c. flexural strength the flexural strength values of the mixture with 20% replacement with glass powder were greater than the reference mixture's values as shown in figure 7. this increase was caused by the great pozzolanic properties of the glass powder that play a micro filler function in the concrete matrix rpc mix. the flexural strength of prpc was improved via extending the curing age due to the continued cement hydration as the curing age progressed. this result agrees with [25, 26]. fig. 7. relationship between the flexural strength and age for prpc. d. dry bulk density the results of the oven-dry density of hardened test for replacement ratio of 20% sustainable glass powder at the age of engineering, technology & applied science research vol. 12, no. 2, 2022, 8388-8392 8391 www.etasr.com ali hussain & aljalawi: effect of sustainable glass powder on the properties of reactive powder … 7, 28, and 90 days was higher than the reference mixtures (figure 9). this increase was caused by the fact that the glass powder has the potential to react with the cao generated from the cement hydration leading to the formation of additional binder material, which is a calcium silicate hydrate gel, which contributes to the increase in the density of the mortar by filling the spaces between the cement paste and fine aggregates. this result agrees [27, 28]. fig. 8. testing a cubic concrete sample. fig. 9. relationship between dry bulk density and age for prpc. fig. 10. relationship between absorption (%) and age for prpc. e. water absorption the findings of the absorption test revealed that the amount of sustainable glass powder present is inversely proportional to the amount of absorption (figure 10). the sustainable glass powder can act as a supplementary cementitious material and form larger amounts of c-s-h gel that can fill the spaces in the concrete matrix that would be filled with water. this result agrees with the findings in [24]. vi. conclusion after experimenting in the laboratory and comparing the values of the reference rpc mixture with the mixtures of replacement ratios of 15, 20, and 25% by weight of cement, it is concluded that: • the compressive strength at 15% replacement increased by about 1.39% at the age of 7 days, 2.39% at the age of 28 days, and by 3% at 90 days. at 20% replacement, the increase was about 2.39, 4.2, and 6.1% at 7, 28, and 90 days respectively. at 25% replacement ratio, the opposite occurred. the compressive strength was less than that of the reference mixture by about 3% at 7 days, but in later ages (28, 90 days) there was a decline in the decrease to 2.8 and 2.5%. • the highest flexural strength of 9.53mpa was achieved at 28 days at 20% replacement. • the water absorption of the 20% replacement mixture was less than the reference mixture's by 31.7% at the age of 28 days. • the dry density of prpc showed slight increases when the cement was replaced by 20% by sustainable glass powder at all ages. the prpc density achieved by this replacement rate was 2436, 2448, and 2457kg/m 3 at 7, 28, and 90 days. • the utilized in this study sustainable glass powder is very good in improving the mechanical 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[28] m. c. g. juenger and r. siddique, "recent advances in understanding the role of supplementary cementitious materials in concrete," cement and concrete research, vol. 78, pp. 71–80, sep. 2015, https://doi.org/10.1016/j.cemconres.2015.03.018. engineering, technology & applied science research vol. 8, no. 1, 2018, 2532-2536 2532 www.etasr.com jahanbakhsh gudakahriz et al.: a stable tora based for routing in mobile ad ηoc networks a stable tora based for routing in mobile ad ηoc networks sajjad jahanbakhsh gudakahriz department of computer engineering germi branch islamic azad university germi, iran sa_jahanbakhsh@iaugermi.ac.ir shahram jamali computer engineering department university of mohaghegh ardabili ardabil, iran jamali@iust.ac.ir mina vajed khiavi department of computer engineering germi branch islamic azad university germi, iran m_vajed@yahoo.com alireza soleimani department of computer engineering meshkin shahr branch islamic azad university meshkin shahr, iran alireza.soleimany@yahoo.com abstract—a mobile ad hoc network (manet) is defined as a set of mobile nodes which communicate through wireless links with no central infrastructure. in these networks nodes are always moving and could enter to or exit from the network at any time. therefore, network topology is completely dynamic. another characteristic of these networks is the low node energy level, resulting from inherent node limitations. stable routing is one method to face routing challenges in mobile ad hoc networks. the objective of this study is to stabilize tora protocol which is a distributed routing protocol, with high adaptation, efficiency, and suitability for large and dense mobile ad hoc networks and thus to provide a new high efficiency protocol. the proposed protocol introduced as stable-tora has been compared with base protocol tora in different scenarios via ns-2 simulator environment and its efficiency is evaluated. keywords-mobile ad hoc networks; routing; stable routing; tora protocol i. introduction ad hoc networks are possible to implement when connecting one or more computers equipped with wireless network cards [1, 2]. a mobile ad hoc network (manet) can configure its self on the fly. infrastructure access points are not used in the wireless ad hoc topology in which, each computer can act either as a node or as a wireless access point / routing agent. ad hoc networks are not usually used for long-term applications because they have relatively low stability and that is why they are used temporarily. routing in manets is always considered as a challenging issue. in manets, nodes have not previous knowledge of network topology. therefore, they have to discover the destination’s location in order to communicate with other nodes. the general idea is that a new node optionally broadcasts its presence to the network and listens to its neighbors. so the node partially gets informed about its close nodes and as this happens throughout the network, a node ends up learning all other nodes or at least knows a way to reach them [3-5]. one group of manets routing protocols is the table driven protocols. in this routing method, each node acquires routing information via saving other nodes’ local information and this information is used to data transfer through different nodes [6]. another group of manets routing protocols is the on demand protocols. in this group, the route between two nodes is formed when there is a necessity for communication between two nodes and they are short lived. when there is need for a route by a source node, if it does not have a valid route for the destination node, it will start the process of discovering the path to reach the destination. it is possible for a mid-node to have a route to the destination [6]. due to the dynamic topology of manets, discovered routes may vanish anytime and then there would be a need for re-routing. quick changes in topology would lead to increased need of re-routing and this would decrease the network efficiency. one of the methods to overcome this problem is stable routing. the objective of stable routing is that during route discovery the established routes would have high stability with longer durability. this will cause reduction in need for rerouting and increase the network efficiency [7, 8]. stable routing protocols provided for manets are a rather recent research field. according to recent analytic results, lifetime of a route, reflecting the route stability depends on route length and lifetime of each link in the route. in [9-12] a few stable routing protocols are presented. the research objective in the current paper is to provide a stable routing protocol for ad hoc networks. ii. tora and stable-tora tora protocol [13] is a distributed routing protocol for mobile ad hoc networks. this protocol has high adaptation, is efficient and scalable. tora is run in three major phases: route forming, route maintaining and route deleting. forming a route from one node to another needs publishing some directed link from the source node to the destination node. this is only done when a node with direction-less links needs a route to destination. therefore route forming is a process of giving direction to links in a partially or fully direction-less network. engineering, technology & applied science research vol. 8, no. 1, 2018, 2532-2536 2533 www.etasr.com jahanbakhsh gudakahriz et al.: a stable tora based for routing in mobile ad ηoc networks the method used for this goal is done via the query/reply process defined in [14], which makes a directed acyclic graph (dag) with root at destination. such a dag is known as a destination rooted dag. route maintenance is the reaction against topology changes in the network, in a way that in limited time routes should be established again. tora is efficient in responding to topology changes and is able to recognize network splitting. this leads to the third phase which is route deleting. during the recognition of network splitting, in order to clear invalid routes, their links should change to nondirected links. protocol run these three phases using three distinct control packets including: query packet (qry), update packet (upd), and clear packet (clr). routing in mobile ad hoc networks suffers major challenges including node mobility, dynamic topology, and limited node battery capacity. mobility of the nodes causes rapid changes in network topology and designed routing algorithms should adapt the routing based on this dynamic topology. limited node battery capacity is another challenge, based on which routing algorithms should send via different routes in a balanced manner, so the node batteries discharge with a similar rate. that way network lifetime increases. increase in network lifetime would lead to increase in network efficiency [15]. one of the efficient methods to improve routing in mobile ad hoc networks is to select routes with high stability [16]. this would result in decrease in packet reduction, routing delay, and routing overhead, since the need for rerouting is reduced. in this part the objective is to improve tora routing protocol via discovering and using stable routes. the introduced protocol is called stable-tora where route stability, in terms of route links lifetime and nodes energy level, is considered during route discovery. in fact the most important criteria to evaluate stability of a route are route links’ lifetime and nodes’ energy level [16]. link lifetime parameter indicates how long the link between two nodes will be available and energy parameter also shows how long the node will be online. therefore, we consider these two parameters as the main factors in route stability and by applying them the stable-tora protocol is produced. a. stable-tora protocol tora protocol is a multipath routing protocol for manets. this protocol discovers all routes available between the source node and the destination node, and among discovered routes it uses the shortest route to send and receive data. the problem of this protocol is that during discovery of all possible routes between the source and destination it is possible some routes to vanish in near future and the discovery of these routes leads only to overhead and efficiency reduction. in order to solve this problem, it is planned that during routing the discovered and established routes would be those that are high in terms of stability and have low probability of vanishing in the near future. in order to find routes with high stability in tora protocol it is necessary to add these parameters to the record of each node:  parameter of minimum lifetime of a link between two nodes: this parameter would be added to the record of each node as min_ttl and shows the minimum lifetime of link in the route.  parameter of minimum energy of route nodes: would be added to the record of each node as min_energy and shows minimum energy of the nodes in the route.  parameter of route suitability would be added to the record of each node as rs. it will show the amount of suitability and quality of the route. routing procedure in stable-tora protocol would ignore repeated packets during sending route query packets to discover distinct node routes. also each node calculates its remaining energy percentage and also the lifetime of the link between it and the previous node when it receives a route query packet. if remaining energy percentage of this node is less than minimum energy of route query packet, it will put this amount in min_energy field, otherwise it will put the amount of route query packet in min_energy field. it also compares link lifetime with amount in received route query packet and repeats the above mentioned task to initialize minimum lifetime of the link. when route query packet arrives to the destination neighborhood, the suitability of the route is calculated according to (1) and if the route has the desired suitability, the packet suitability will be added to the demand of route reply and a route reply packet will be sent towards source. if the route query packet has not the desired suitability, it will not be answered and the route will not be discovered. rs= (e×t)/h (1) where e=min_energy, t=min_ttl/maximum ttl, h=hopcount/n. in (1), energy and link stability are put in numerator since these parameters have direct relationship with route quality and suitability, while route length goes to denominator since route quality and suitability have converse relationship with route length. also, min_energy is the percentage of remaining energy of each node, so it is a number between zero and one. on the other hand, in order to change the amount of link lifetime and route length to zero-one interval, we divide these two parameters to their maximum possible amount resulting for these parameters to have a similar to min_energy effect on calculating route suitability. designed stable-tora protocol includes these stages: 1) sending route query packets from source to destination in distributed way. 2) removing repeated route query packets in nodes. 3) adding minimum energy of route nodes and minimum lifetime of route links to route query packet. 4) wherever there is a possibility for sending route reply packet, route suitability is calculated via (1) and if rs is higher than a threshold, it means that this route has the desired suitability, a route reply packet is sent back to the source and route is discovered. if route suitability calculated via (1) is lower than the threshold, this route is considered not to have the desired suitability and no route reply packet is sent. engineering, technology & applied science research vol. 8, no. 1, 2018, 2532-2536 2534 www.etasr.com jahanbakhsh gudakahriz et al.: a stable tora based for routing in mobile ad ηoc networks 5) after calculating the route suitability and in case of having one, rs value obtained by (1) is added to the route reply packet and is sent to the source. if there are different routes, the source uses the route with the highest suitability. iii. efficiency evaluation in order to investigate the effects of the provided idea, we run some simulations in ns-2 simulator [17]. in order to implement stable-tora protocol, we applied the mentioned changes on tora protocol. in order to evaluate, we simulated stable-tora protocol alongside with tora protocol in terms of different scenarios and compared the efficiency of these two protocols based on these criteria:  packet delivery ratio: is the ratio of data packets delivered to destination to data packets sent from the source [18].  end to end delay: this criterion equals to the mean time required for each data packet to travel from the source node to the destination node [18].  routing overhead: this equals to the total number of routing packets in the network [19].  network lifetime: the time the first node runs out of energy [20]. a. first simulation scenario: efficiency criteria against the number of nodes in this scenario, the number of nodes has been considered variable and equal to 30, 40, 50, and 60. simulation parameters have been presented in table i and the simulation results are shown in figures 1 to 4. based on the simulation results, we conclude that stable-tora protocol has better performance than tora regarding the number of nodes. it has increased performance in the parameters of quality of packet delivery ratio and network lifetime, and has better end to end delay and routing overhead. b. second simulation scenario: efficiency criteria based on different pause times in this scenario, the pause time has been considered variable. we simulated the produced different pause time scenario for 500 seconds with tora and stable-tora protocols. adjusted parameters have been presented in table ii and simulation results have been shown in figures 5 to 8. table i. first simulation scenario parameters parameters parameter values environment 1000 m × 1000 m nodes number 30, 40, 50, 60 routing protocol tora and stable-tora transmission range 250m simulation time 500 second mac layer standard 802.11 traffic type cbr (udp) buffer size 50 packets nodes pause time 0 seconds node moving speed 20 m/s nodes position random fig. 1. packet delivery ratio versus node number. fig. 2. end-to-end delay versus node number. fig. 3. routing overhead versus nodes number. fig. 4. network life time versus node number. different pause times have been suggested as a researched parameter in order for the protocols to be evaluated in different statuses in terms of topological dynamicity. in figures 5-8 we see that stable-tora has better packet delivery ratio, smaller engineering, technology & applied science research vol. 8, no. 1, 2018, 2532-2536 2535 www.etasr.com jahanbakhsh gudakahriz et al.: a stable tora based for routing in mobile ad ηoc networks end-to-end delay, smaller overhead and greater network life time. based on these, we conclude that changes applied on tora protocol in order to provide a new protocol, have caused better results and the new protocol shows suitable and better performance. we can summarize by saying that the stable-tora provided protocol, performs better in different situations compared with tora in terms of packet delivery ratio, end to end delay, routing overhead and network lifetime. better stable-tora performance is due to that the routes discovered, which have better quality in terms of route nodes energy, route links lifetime, and route length, are proved to be more efficient and to have higher stability and lifetime. therefore packets are delivered through more reliable routes and have higher possibility of reaching destination. also, the long route lifetime reduces the need for re-routing. table ii. second simulation scenario parameters parameters parameters values environment 1000 m × 1000 m nodes number 50 routing protocol tora and stable-tora transmission range 250m simulation time 500 second mac layer standard 802.11 traffic type cbr (udp) buffer size 50 packets nodes pause time 0, 100, 200, 500 seconds node moving speed 20 m/s nodes position random fig. 5. packet delivery ratio versus pause time. fig. 6. end-to-end delay versus pause time fig. 7. routing overhead versus pause time. fig. 8. network life time versus pause time. iv. conclusion in this paper we introduced the stable-tora protocol, which is a routing protocol for mobile ad hoc networks. this protocol is based on the tora routing protocol and has been provided in order to make this protocol more stable by discovery and use of high quality routes. simulation results showed that the stable-tora protocol acts better in terms of packet delivery ratio, end to end delay, routing overhead, and network lifetime compared to tora protocol, which is due to discovery and use of high quality routes. research in this field should implement the same idea in other routing protocols in mobile ad hoc networks that do not consider 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“neighborhood-based interference minimization for stable position-based routing in mobile ad hoc networks”, future generation computer systems, vol. 64, pp. 88–97, 2016 [17] ns-2, the network simulator, http://nsnam.sourceforge.net/wiki/ index.php [18] j. g. sajjad, j. shahram, v. k. mina, “energy efficient routing in mobile ad hoc networks by using honey bee mating optimization”, journal of advances in computer research, vol. 3, no. 4, pp. 77-87, 2012 [19] m. k. marina, s. r. das, “on-demand multipath distance vector routing in ad hoc networks”, ninth international conference on network protocols, pp. 14-23, 2011 [20] s. jamali, s. jahanbakhsh, “ba-tora: a multipath routing protocol for manets by inspiration from bee and ant colonies”, przeglad elektrotechniczny (electrical review), vol. 2011, no. 7, pp. 183-187, 2011 engineering, technology & applied science research vol. 8, no. 2, 2018, 2750-2754 2750 www.etasr.com ben khedher: experimental evaluation of a flat plate solar collector under hail city climate experimental evaluation of a flat plate solar collector under hail city climate nidhal ben khedher mechanical engineering department college of engineering, hail university hail, saudi arabia n.khedher@uoh.edu.sa laboratoire d'études des systèmes thermiques et énergétiques ecole nationale d'ingénieurs de monastir university of monastir monastir, tunisia abstract—flat plate solar water heaters are widely used for water heating in low-temperature residential applications. in this paper the thermal performance of a solar flat plate water heater under hail weather conditions (latitude 27°52΄n longitude 41°69΄e) was experimentally investigated. fluid was circulated through the imbedded copper tubes in the flat plate collector and inlet and outlet temperatures of the fluid were noted at five minute intervals. the experimental-time was between 9:00am-15:00pm. a study was carried out experimentally to present the efficiency curves of a flat plate solar collector at different flow rates. ashrae standard 93-2003 was followed for calculation of instantaneous efficiency of solar collector. result shows that the flow rate of the circulating fluid highly influence the thermal efficiency of the solar collector. optimum flow rate of 2.5l/min leads to maximum collector efficiency. keywords-flat plate solar collector; low rate; thermal efficiency; ashrae standard 93-2003 i. introduction solar energy is becoming an alternative for the limited fossil fuel resources. the recent increased interest in renewable energy has created a need for research in the area of solar technology. one of the simplest and most direct applications of this energy is the conversion of solar radiation into heat. solar radiation can be widely used for water heating in hot water systems, as well as a supporting energy source for central heating installations. the energy of the solar radiation is in this case converted to heat with the use of solar panels. using the sun's energy to heat water is not a new idea. more than one hundred years ago, black painted water tanks were used as simple solar water heaters in a number of countries. however, the solar water heating technology has greatly improved during the past century. today there are more than 30 million square meters of solar collectors installed around the globe. most solar water heating systems for buildings have two main parts: a solar collector and a storage tank. a flat plate solar collector [13] is the most popular solar energy based device which absorbs the heat of sun rays through its body (usually with black color for maximum absorption) and then transfers the absorbed heat to the working fluid for raising its temperature. the efficiency of flat plate solar collectors as a group of water heaters depends on many factors such as climate conditions (especially solar radiation intensity), materials and design of collector as well as the working fluid type and mass flux rate. authors in [4] reviewed applications of nanofluid in evacuated tube and flat plate solar collectors from efficiency, economic and environmental considerations and concluded that nanofluids offer a better alternative to conventional fluid. authors in [5] presented theoretically and experimentally the enhancement of heat transfer to the working fluid with a metal porous medium placed inside pipes. the metallic mesh inserted in the collector, provided a higher water temperature compared to the conventional collector and it is the presence of the aluminum mesh inside the channels that distributes heat more evenly. author in [6] investigated experimentally the design of flatplate solar collector system. in [7], authors presented an experimental analysis and a thermal and hydrodynamic modelling of a newly designed flat-plate solar collector characterized by its corrugated channel and by the high surface area directly in contact with the heat transport fluid. authors in [8] studied the effect of nanofluids on the performance of solar collector and solar water heater from efficiency, economy and environmental points of view. authors in [2] reviewed advancements made in the field of solar thermal technology with emphasis on techniques employed for performance augmentation. for a sunny country like saudi arabia it is very important to use the sun as main source of energy in many ways such as heating applications and generating electricity. in our study we will evaluate the thermal efficiency of a flat plate solar collector during winter season at four flow rates. the collector is working in closed loop where the water is stored in a tank and it is controlled to evaluate the stored heat. ii. experimentation and methodological approach a. experiments on solar collector the experiments on the flat plate solar collector were carried out in hail city (latitude 27°52’n longitude 41°69’e). engineering, technology & applied science research vol. 8, no. 2, 2018, 2750-2754 2751 www.etasr.com ben khedher: experimental evaluation of a flat plate solar collector under hail city climate the collector type is te39 collector provided by tecquipment. figures 1 and 2 illustrate a schematic of the experimental setup, and a photograph of the flat plate solar collector, respectively. the collector specifications are given in table i. the main part of the te39 flat plate solar energy collector is a modern solar collector panel, it is two sheets of preformed stainless steel welded together to form integral parallel water channels. an airtight box with a clear acrylic cover encloses the surface of the panel. a thick layer of insulating material on the back of the panel reduces heat loss to the rear. fig. 1. schematic of the experimental set-up. table i. experimental setup description item details type single pass flat plate solar energy heat absorber overall size maximum 1500mm height x 2400mm length x 110mm depth collector cover acrylic -1 overall dimensions 1.8m2 effective surface area 1.6m2 maximum water inlet pressure 3bar pump type mains powered, centrifugal energy input to water 55w in order to determine the performance of the prototype under various conditions, the apparatus was equipped with the necessary instrumentation. a schematic diagram of the apparatus is shown in figure 1, demonstrating the positioning of the instrumentation within the prototype. an electrical pump circulates the working fluid. a heat exchanger transfers heat energy from the solar collector to the tank which has a capacity of 30l. a flow sensor measures the fluid flow rate. a simple valve was installed to control the flow rate. a series of thermocouples type k were fitted on the collector (with accuracy of ±0.1°c), measuring the temperature of the working fluid in the collector at the inlet ti and outlet to, the ambient temperature ta and the stored water temperature th. the solar radiation g was measured by a solar meter with accuracy of ±2%. the solar collector was set to angle of inclination equal to that of hail. fig. 2. picture of the set-up. in the current study, the instruction given in ashrae standard 93-2003 [9] has been implemented to evaluate the thermal performance of the solar collector. the purpose of this standard is to test the thermal performance of solar collectors that use single-phase fluids. the experiments were performed from 9am to 3pm (local time) on several days in january 2018. the best data satisfying conditions of ashrae standard have been taken. experimental results are expressed in the form of graphs that indicate the collector efficiency against a reduced temperature parameter [(ti–ta)/g]. the efficiency of solar collector was examined at various flow rates of 1.5, 2, 2.5 engineering, technology & applied science research vol. 8, no. 2, 2018, 2750-2754 2752 www.etasr.com ben khedher: experimental evaluation of a flat plate solar collector under hail city climate and 3l/min. all the tested runs were collected using acquisition card system (figure 3). moreover, we designed the coil tank to store the hot water and to evaluate the solar collector working in a closed loop (figure 4). the coil heat exchanger is made from copper. fig. 3. data acquisition of the experimental setup. fig. 4. the designed coil tank. b. testing method based on the ashrae standard 93-2003 [9], the thermal performance of the solar collector is evaluated. if g is the intensity of solar radiation, in w/m2, incident on the aperture plane of the solar collector having a collector surface area of am2, then the amount of solar radiation received by the collector is: qiga (1) however, a part of this radiation is reflected back to the sky, another component is absorbed by the glazing and the rest is transmitted through the glazing and reaches the absorber plate as short wave radiation. therefore the conversion factor indicates the percentage of the solar rays penetrating the transparent cover of the collector (transmission) and the percentage being absorbed. basically, it is the product of the rate of transmission τ of the cover and the absorption rate α of the absorber. thus, qiga (2) as the collector absorbs heat its temperature is getting higher than that of the surrounding and heat is lost to the atmosphere by convection and radiation. the rate of heat loss (qo) depends on the collector overall heat transfer coefficient (ul) and the collector temperature. = − (3) thus, the rate of useful energy extracted by the collector (qu), expressed as a rate of extraction under steady state conditions, is proportional to the rate of useful energy absorbed by the collector, minus the amount lost by the collector to its surroundings. this is expressed as follows: 0 ( )u i l c aq q q g a u t t     (4) it is also known that the rate of extraction of heat from the collector may be measured by means of the amount of heat carried away in the fluid passed through it, that is: = − (5) equation (4) proves to be somewhat inconvenient because of the difficulty in defining the collector average temperature. it is convenient to define a quantity that relates the actual useful energy gain of a collector to the useful gain if the whole collector surface were at the fluid inlet temperature. this quantity is known as “the collector heat removal factor (fr)” and is expressed as: = (6) the maximum possible useful energy gain in a solar collector occurs when the whole collector is at the inlet fluid temperature. the actual useful energy gain qu, is found by multiplying the collector heat removal factor fr by the maximum possible useful energy gain. this allows the rewriting of (4): = − − (7) equation (7) is a widely used relationship for measuring collector energy gain and is generally known as the “hottelwhillier-bliss equation”. the collector efficiency η is defined as the ratio of the useful energy gain qu to the incident solar energy over a particular time period: the thermal performance of the solar collector is checked by determining the values of instantaneous efficiency for different combinations of incident radiation, ambient temperature, and inlet fluid temperature. the instantaneous efficiency is defined as the ratio of useful energy gain to the solar energy received by absorber plate of the collector. the instantaneous thermal efficiency of the collector is: = (8) η = (9) = − (10) if it is assumed that fr, τ, α, ul are constants for a given collector and flow rate, then the efficiency is a linear function of the three parameters defining the operating condition: solar irradiance (g), fluid inlet temperature (ti) and ambient air temperature (ta). thus, the performance of a flat-plate collector can be approximated by measuring these three parameters in experiments. engineering, technology & applied science research vol. 8, no. 2, 2018, 2750-2754 2753 www.etasr.com ben khedher: experimental evaluation of a flat plate solar collector under hail city climate iii. results and discussion experiments were carried out at the roof top of mechanical engineering department of the college of engineering of hail. from figure 5 it is not so easy to judge which flow rate ensuring the highest outlet temperature, because outlet temperature is highly influenced by the outdoor conditions (solar radiation, air temperature, wind speed). moreover, a solar collector working in a closed loop it is dependent to the initial hot water tank temperature. as shown in figure 6 the initial outlet temperatures (at 9:00am) are different. for example for the case of 1.5l/min flow rate the outlet temperature starts from 34°c. however, it starts from 18°c for the case of 2.5l/min. this behavior is justified by the variability of weather conditions which leads to different initial hot water tank temperatures. the temperature of the hot water in the thermal storage tank depends on the effectiveness of the heat exchanger and the temperature difference between the outlet and inlet fluid. the flow rate equals to 2.5l/min produced the highest storage tank temperature of 82.5°c as shown in figure 6. figure 7 shows the variation of collector efficiency versus the reduced temperature parameter for water and different mass flux rates. the experimental data are fitted with linear equations to obtain the characteristic parameters of the collector and having better judgment about the effect of flow rate on the thermal efficiency. as it can be seen, at a given value of reduced temperature parameter, with increasing flow rate, the efficiency increases till reaching an optimum value corresponding to the flow rate 2.5l/min. based on (5) and (6), the useful heat energy rate increases with an increase in mass flux, on the other hand, useful heat energy rate is directly proportional to efficiency. therefore, the efficiency increases with increasing mass flux. with increasing vol. flow rate from 1.5l/min to 2.5l/min the maximum enhancement in efficiency was found to be about 15%. table ii provides more details regarding figure 5 and the solar collector performance when the working fluid is water. this table shows the values of the removed energy parameter frul and the absorbed energy parameter fr (τα) for the four flow rates (1.5l/min, 2l/min, 2.5l/min, 3l/min). it is seen that both removed energy and absorbed energy parameters have an optimum value corresponding to vol. flow rate of 2.5l/min. the collector efficiency η is plotted against (ti–ta )/g. the slope of this line (-fr ul) represents the rate of heat loss from the collector. for example, collectors with cover sheets will have less of a slope than those without cover sheets. table ii. values of f u and f ( ) for different flow rates vol. flow rate (l/min) ( ) ‒ 1.5 0.779228 -7.7476 2 0.666701 -3.2787 2.5 0.952 -13.6875 3 0.921 -12.2477 there are two interesting operating points on figure 7. the first is the maximum collection efficiency, called the optical efficiency. this occurs when the fluid inlet temperature equals ambient temperature (ti=ta). for this condition, the δt/g value is zero and the intercept is fr(τ α). the other point of interest is the intercept with the δt/g axis. this point of operation can be reached when useful energy is no longer removed from the collector, a condition that can happen if fluid flow through the collector stops (power failure). in this case, the optical energy coming in must be equal to the heat loss, requiring that the temperature of the absorber increase until this balance occurs. this maximum temperature difference or “stagnation temperature” is defined by this point. for wellinsulated collectors the stagnation temperature can reach very high levels causing fluid boiling. fig. 5. outlet temperature at different flow rates. fig. 6. hot stored water at different flow rates. fig. 7. solar collector efficiency curve at four flow rates for water. engineering, technology & applied science research vol. 8, no. 2, 2018, 2750-2754 2754 www.etasr.com ben khedher: experimental evaluation of a flat plate solar collector under hail city climate from the optimum flow rate (2.5l/min) corresponding to the highest efficiency we presented in figure 8 the solar radiation, ambient temperature, hot water temperature, the inlet and the outlet temperatures. from this figure we can notice that the stagnation of outlet and hot water temperatures is reached at 1:30 pm. fig. 8. hot solar intensity and various temperatures of solar collector at flow rate 2.5l/min. iv. conclusion ashrae standard 93-2003 was detailed, then followed for calculation of the efficiency of a flat plate solar collector. a more precise and detailed analysis should include the fact, that the overall heat loss coefficient (ul) and other factors as the heat removal factor (fr) are not constant values and they are tightly dependent on fluid flow rate. the present experiment focused on a comparative analysis of a four different flow rates (1.5 l/min, 2l/min, 2.5l/min, 3l/min) and their effect on the performance of flat plate solar collector. the experiment findings established that maximum efficiency, when reduced temperature parameter [(ti–ta)/g] equals to zero, was 95% for flow rate 2.5l/min. references [1] y. tian, c. y. zhao, “a review of solar collectors and thermal energy storage in solar thermal applications”, applied energy, vol. 104, pp. 538-553, 2013 [2] s. suman, m. k. khan, m. pathak, “performance enhancement of solar collectors—a review”, renewable and sustainable energy reviews, vol. 49, pp. 192-210, 2015 [3] x. xu, y. lei, z. xiaosong, p. donggen, “review on the development of flat-plate solar collector and its building-integrated designing”, ises world congress 2007 (vol. i – vol. v), pp. 623-626, springer, berlin, heidelberg, 2008 [4] m. j. muhammad, i. a. muhammad, n. a. che sidik, m. n. a. w. muhammad yazid, “thermal performance enhancement of flat-plate and evacuated tube solar collectors using nanofluid: a review”, international communications in heat and mass transfer, vol. 76, pp. 6–15, 2016 [5] g. iordanou, “experimental investigations using partial porous medium inside the channels of flat plate solar water collectors”, journal of engineering science and technology review, vol. 5, no. 1, pp. 30-33, 2012 [6] m. sahib ali, “experimental study of solar hot water system design”, thiqar university journal for engineering sciences, vol. 3, no. 1, pp. 1–14, 2012 [7] a. alvarez, o. cabeza, m. c. muniz, l. m. varela, “experimental and numerical investigation of a flat-plate solar collector”, energy, vol. 35, no. 9, pp. 3707-3716, 2010 [8] o. mahian, a. kianifar, s. a. kalogirou, i. pop, s. wongwises, “a review of the applications of nanofluids in solar energy”, international journal of heat and mass transfer, vol. 57, no. 2, pp. 582–94, 2013 [9] american society of heating, refrigerating & air conditioning engineers, standard 93-2003, methods of testing to determine the thermal performance of solar collectors, ashrae, 2003 microsoft word etasr_v12_n2_pp8289-8295 engineering, technology & applied science research vol. 12, no. 2, 2022, 8289-8295 8289 www.etasr.com hussein & abbas: a semi-empirical equation based on the strut-and-tie model for the shear strength … a semi-empirical equation based on the strut-andtie model for the shear strength prediction of deep beams with multiple large web openings lara t. hussein department of civil engineering college of engineering university of baghdad baghdad, iraq l.hussein1001@coeng.uobaghdad.edu.iq rafaa m. abbas department of civil engineering college of engineering university of baghdad baghdad, iraq dr.rafaa@coeng.uobaghdad.edu.iq received: 9 january 2022 | revised: 25 january 2022 | accepted: 27 january 2022 abstract-the behavior and shear strength of full-scale (t-section) reinforced concrete deep beams, designed according to the strutand-tie approach of aci code-19 specifications, with various large web openings were investigated in this paper. a total of 7 deep beam specimens with identical shear span-to-depth ratios have been tested under mid-span concentrated load applied monotonically until beam failure. the main variables studied were the effects of width and depth of the web openings on deep beam performance. experimental data results were calibrated with the strut-and-tie approach, adopted by aci 318-19 code for the design of deep beams. the provided strut-and-tie design model in aci 318-19 code provision was assessed and found to be unsatisfactory for deep beams with large web openings. a simplified empirical equation to estimate the shear strength for deep t-beams with large web openings based on the strut-and-tie model was proposed and verified with numerical analysis. the numerical study considered three-dimensional finite element models, in abaqus software, that have been developed to simulate and predict the performance of deep beams. the results of numerical simulations were in good agreement and exhibited close correlation with the experimental data. the test results showed that the enlargement in the size of web openings substantially reduces the elements' shear capacity. the experiments revealed that increasing the width of the openings has more effect than the depth at reducing the load-carrying capacity. keywords-deep beams; reinforced concrete; t-beams, web opening; strut-and-tie model; finite element analysis; shear strength i. introduction shear behavior of reinforced concrete members (slender members that have span-to-depth ratios greater than 2.5) is a complex phenomenon which is influenced by a large number of parameters [1, 2]. this complexity is more pronounced in deep beams (members that have small, less than 2.5, span-to-depth ratios) because the applied load is transferred mainly through the formation of arching which causes a highly nonlinear strain distribution in the cross section so that the shear strain is dominant [3, 4]. in deep beams, the strain distribution is nonlinear and the load is transferred to the support by a compression strut joining the loading point and the support [2, 5-9]. the creation of web openings is often required for the accommodation of electrical and mechanical conduits. enlargement of openings due to architectural/mechanical requirements may reduce the element’s shear capacity [9, 10]. design code provisions typically use sectional models to determine the shear and flexure capacities of slender members [11-13]. in deep beams, traditional sectional design approaches based on plane sectional theory are not applicable, a nonlinear distribution of strains dominates the response and arch action becomes the primary force-transfer mechanism following diagonal cracking [5, 13]. most codes of practice rely on empirical or semi-empirical equations for the design of deep beams, however, these equations are limited by the extent of the experimental results used for their calibration [2]. modern design codes such as ec2 and aci 318-19 have adopted design approaches based on the implementation of strut-and-tie mechanistic models (stms) because they appear more rational and relatively simple to apply. the design of deep beams based on the strut-and-tie model relies on the lower bound theory of plasticity and assumes that both concrete and steel are perfectly plastic materials [3]. the stm idealizes the complex flow of stresses using a pin-jointed truss consisting of compression struts and tension ties, which allows easier monitoring of the force flow [14]. there is no provision for the designing of deep beams with openings in current design codes. in the current study, 7 deep beams were tested until failure and a comparison was made with the strut-and-tie design approach adopted by the aci 318-19 code. the effects of the openings were also considered. from the experimental results, it can be noticed that increasing the width of the openings has more effects than increasing the depth in reducing the load carrying capacity. this agrees with the statement that as the opening's distance from what can be called the loaded quadrant to the unloaded quadrant, the strength of the beam increases [15]. the experimental results were compared with the corresponding author: lara t. hussein engineering, technology & applied science research vol. 12, no. 2, 2022, 8289-8295 8290 www.etasr.com hussein & abbas: a semi-empirical equation based on the strut-and-tie model for the shear strength … numerical finite element analysis results of [16]. opening’s configuration was investigated in [17, 18] and an increase in ultimate load capacity compared with that of quadrilateral openings when circular openings were used was reported in [19]. finite element modeling (fem) is one of the most powerful tools in simulating structural elements in a variety of fields. the successful simulation of specific elements relies upon the realistic representation of the material properties in fem. however, due to the complexity of the constitutive material properties concrete, modeling the behavior of reinforced concrete, in particular shear, has been, and still is, a challenging issue [16, 20]. ii. strut-and-tie model the stm is based on the fact that within a distance from a source of disturbance such as a concentrated load or support, the distribution of strain in the member is nonlinear (st. venant’s principle) [10, 21]. plain sections do not remain plain. nonlinear strain distributions in concrete members, caused by changes in geometry or loading conditions, are referred to as a disturbed regions or d-regions [14] (d-for discontinuity or disturbed), while, the linear strain distribution regions are called b-regions (b-for bernoulli or beam). the stm is an approach to design discontinuous d-regions in reinforced concrete structures to reduce the complex states of stress into a truss comprised of simple, uniaxial stress paths [21] (figure 1). fig. 1. strut-and-tie formation in deep beam, truss model (strut, tie, and nodes). these truss models represent all internal force effects and do not require separate flexure and shear models, as in the slender member case. strut-and tie modeling is based on the lowerbound theory of plasticity and the model capacity is always less than the actual capacity [14]. struts are used to represent the assumed compressive stress fields in the concrete. ties represent the primary tension reinforcement with the tie location made to correspond to the centroid of the reinforcement. while the tie also consists of the concrete surrounding the reinforcement, this concrete is not directly considered in the design but will reduce the tie elongation [22]. the struts and ties intersect at nodes. most design specifications recognize 3 major node types: ccc-nodes bounded by struts only, cct-nodes bounded by one tie and two or more struts, and ctt-nodes bounded by one strut and two or more ties. the aci design provision allows the use of any truss configuration according to the designer provisions [2, 21]. iii. experimental work seven full scale reinforced concrete deep beams with large web openings were casted and tested until failure in order to study their shear strength. the objectives of this study were to investigate experimentally the main parameters of the laboratory testing which include: • the width of the opening e, considering e/l as the ratio of the width of the opening to the shear span of the beam as: 0.4, 0.53, 0.67. • the depth of opening d, adopting d/h as the ratio of depth of the opening to the height of the beam section as: 0.48, 0.6. the constants were: • concrete compressive strength. • type of loading. • span length to height of the section ratio (l/h). • the two openings were symmetrically located relative to the center-line of the beam and the center of each opening was located at 0.45h from the soffit of the beam. the experimental specimens were designed according to aci 318-19 and were fabricated with dimensions of 1950mm length, 1000mm height, 750mm flange width, 125mm flange thickness, and 250mm web thickness. the testing program of this study tried to investigate deep beams with large web openings, with varying e/l ratio (0.4, 0.53, 0.67), and d/h ratio (0.48, 0.6), designated by [dp-de], where dp stands for deep beam, d for the opening depth, and e for the opening width. the symbols for the reinforced deep beams with large web openings and for the solid beam were dp_48x36, dp_48x48, dp_48x60, dp_60x36, dp_60x48, dp_60x60, and dp_solid that was subjected to static loading. a. concrete materials for concrete production, the cement, sand, coarse aggregate mixing ratio was 1: 1.7: 2.6 in weight. the water-cement ratio was 0.5 for the production of ordinary concrete with compressive strength of 25mpa. b. steel reinforcement for all specimens, the longitudinal deformed steel bars that have been used in this study had nominal diameter of 16mm and 10mm for the main reinforcement and the compression reinforcement respectively. for shear reinforcements and skin reinforcements, steel bars of 8mm diameter were used. reinforcement diameters and spacing where chosen according to the aci318-19 requirements. according to astm a615, tensile tests for the steel bars were carried out using the testing machine available in the laboratory of construction materials at the college of engineering, university of baghdad. all deep engineering, technology & applied science research vol. 12, no. 2, 2022, 8289-8295 8291 www.etasr.com hussein & abbas: a semi-empirical equation based on the strut-and-tie model for the shear strength … beams had the same distribution-ratio of interior steel reinforcement. the main (longitudinal flexural tensile) reinforcement is 3∅16mm deformed steel bars, while the longitudinal compression reinforcement is 4∅10mm deformed steel bars. the proposed flexural tension reinforcement aspect has been checked with articles 9.9.3.2 and 9.6.1 of the aci 318m, 2019. skin reinforcement and vertical shear reinforcement (stirrups) were designed and distributed with ∅ 8mm@150mm) along the 2-sides. proposed stirrups reinforcement aspects have been checked with articles 9.9.3.1 and 9.9.4.3 of the aci 318m, 2019 (figure 2). (a) (b) fig. 2. (a) steel reinforcement in the experimental work of dp-60x60. (b) steel reinforcement in the experimental work of dp-solid. c. test setup upon the completion of the preparation, installation, and calibration of all devices and equipment required for the tests (figure 3), the beams were subjected to monotonically increasing static loading up to failure. fig. 3. equipment and test setup. the experimental investigation was carried out using a 500kn capacity hydraulic actuator that exposed the structural member to a concentrated load that was applied in 5kn increments. the tested specimens were simply supported and bearing plates under the load and above the supports have been used to better distribute the stress and to avoid any local crushing. iv. experimental test results a. load-deflection relations at each load step of the static test program, the vertical deflection of the specimens was recorded and the following conclusions were drawn: • for an increase of the opening width from 360mm to 600mm, and of the e/l from 0.4 to 0.67, the load carrying capacity of the beams was reduced by about 66%, for group60 and group48 [10] (figure 4). • increase in the opening depth from 480mm to 600mm, and in d/h from 0.48 to 0.6, led to a reduction in the load carrying capacity of about 25% (figure 4). • for group48 and group60, the load-deflection relations behave more as a linear relation because of the reduced engineering, technology & applied science research vol. 12, no. 2, 2022, 8289-8295 8292 www.etasr.com hussein & abbas: a semi-empirical equation based on the strut-and-tie model for the shear strength … beam rigidity, ei, as a result of introducing large web openings [23]. • group60 has less load carrying capacity than group-48 as a result on increasing opening depth that led to beam stiffness reduction [15]. • increased deflection was noticed at increasing opening width as a result of reduced rigidity, ei, and hence, increased displacements [9]. • figure 4(c) shows the significant effect of opening presence in reducing load carrying capacity, introducing web openings of e-600mm x d-600mm which can reduce the load carrying capacity by about 300% as compared with the solid beam, resulting to reduced rigidity and increased displacement. • as the opening enlarged, the deep beams were exposed to higher stresses as a result of opposing the web opening to the compression struts and intersecting the load path propagation which in turn reduced the deep beam capacity [3]. • increasing the opening width has more effect in decreasing the load carrying capacity of the deep beams than increasing its depth. the more opposed the opening sites in the inner quarter of the shear span to the load path that propagates from the support to the applied load region, the more reduction in the load carrying capacity. b. crack pattern, load capacity, and failure mode during each test, cracks were marked at each discrete load increment. figure 5 shows typical crack patterns of the 7 specimens. specimens with web openings were having the same response and behavior up to failure. a summary of first crack load, flexure cracks, ultimate load, and failure mode is presented in figure 5(a) which shows the crack pattern for dp_48x48. a crack pattern comparison of the experimental and the finite element analysis results can be seen in figure 5(b). the crack pattern at each load increment was marked. the first inclined crack was propagating from the support regions toward the lower opening corner at load 20-30% of the ultimate load as shown in figure 5(a) with the crack designated with number (1) being the first crack. at load 25-35% of the ultimate load, a diagonal tension crack number (2) propagated at the upper opening corner toward the applied load region. flexural number (3) cracks appeared at 35-44% of the ultimate load. a typical cracking pattern (beam-column) conjunction, horizontal crack, appeared at loading stage 44-50% of the ultimate load as indicated by crack numbering (4). at loading stage 40-60% of the ultimate load, the tension cracks designated with number (2) propagated in the flange with additional inclined crack approaching near the applied load region appeared (crack number (5)). the serviceability load, i.e. a diagonal crack reaching width of 0.3mm appeared at 60% of the ultimate load. at increasing load until failure, cracks that start at the support regions extend toward the opening corner cracks and fuse with them forming long cracks that got wider until the beam failed. the shear failure is indicated with number (6). the crack patterns shown in figure 5(a) present the strut-and-tie formation as expected for the load-path. the stress path and strut-and-tie configurations are shown clearly in figures 5(a)-(b) [10]. (a) (b) (c) fig. 4. comparison of load-deflection curves for dp_48 group and dp_60 group with solid case. (a) load-deflection curve of group_48, (b) loaddeflection curve of dp_60 group, (c) load-deflection curve of dp-48x48, dp60x60, and dp-solid. introducing large web openings in the deep beam transforms it into an ordinary connected beam-column (crack number (4)) [10]. the load-deflection curve behaves semi-linearly, which proves that the deep beams act as ordinary beams more than as deep beams, as a result of the larger web openings at the shear zone which change their geometry (figure 6) [23]. introducing web openings intersects the stress path and leads to changed deep beam geometry which affects the deep beam behavior and shear capacity [23]. the tested specimen dp_48x48 as obtained from abaqus program is shown in figure 5(b). the crack patterns were selected at the failure stage. the initial cracks were generated at the support regions and propagated engineering, technology & applied science research vol. 12, no. 2, 2022, 8289-8295 8293 www.etasr.com hussein & abbas: a semi-empirical equation based on the strut-and-tie model for the shear strength … toward the lower corner of the openings. cracks at the upper corner of the opening extended toward the applied load region, which is compatible with the experimental tests. this comparison showed complete matching with the experimental results. (a) (b) fig. 5. (a) designated experimental crack pattern of dp_48x48, and tfor ton, (b) designated crack pattern of the numerical finite element model for specimen dp_48x48. fig. 6. comparison of experimental and finite element load-deflection relations of specimen dp_48x48. v. the proposed empirical equation in aci design code there is no provision for designing deep beams with web openings. the stm provided by aci code overestimates the actual strength of the deep beams with web openings, while it is based on the lower bound theorem, adding a numerous error in the design based on aci approach. for this reason, in this study, 7 deep beams were tested and the results were compared with the numerical finite element results implemented in abaqus in order to investigate the opening effects on the load carrying capacity of the deep beams. the specimens shear strength is specimen-size dependent, it increases when size increase: ������� � � ���� ����� �� (1) where v������� is the load-carrying capacity, ultimate shear strength in deep beam without web opening, v��������� is the opening imaginary shear capacity, h is the depth of the beam, l it’s the shear span, e the opening width, and d the opening depth. from (1), we get: v��������� � �� � .v������� (2) the shear strength for deep beam with opening v�� �!: v�� �!"������� #���� ����� v�� �! � $1& �� � ' . v������� (3) then, by comparing the tests results of 66 specimens modeled with abaqus, with a wide range variety of opening depths and widths from 100mm to 800mm, and by trial and error procedure, the empirical equation was created. the results showed that the opening width has more effect than the opening depth on decreasing the ultimate capacity. also, the load carrying capacity of the deep beam decreases as the ratio of the web opening size to shear span-to-depth of deep beam increases accordingly to the proposed equation. the inclusion of web opening width to the shear span ratio, which is the most influential factor on the shear behavior of the deep beam, into the proposed equation gives us: v�� �! � $(1& �� �� (1) � �* �' . v������� (4) v��!�+, � $(1& �� � � (1) � � * �' . v���+, where: v������� � v���+, and v�� �! � v��!�+,. the applicability of this equation is limited to deep beams with shear span to depth ratio of 0.95. the center of the openings is located at 0.45h from the soffit of the beam and the opening location at the inner quarter of the shear span. regression analysis was conducted for the theoretical results and the effects of depth, width, and opening size to shear span to beam depth ratio on the shear strength of the beam and the results are shown in figure 7. vi. failure load the calibration of the failure load obtained from the finite element analysis, the experimental work, and the proposed equation for deep beams with web openings in strut-and-time approach for each static tested specimen is shown in table i. in the finite element analysis, the failure load is defined as the solution for a minimum increment of load that does not converge due to numerous cracks. abaqus overestimates the failure load of the specimens since the finite element method engineering, technology & applied science research vol. 12, no. 2, 2022, 8289-8295 8294 www.etasr.com hussein & abbas: a semi-empirical equation based on the strut-and-tie model for the shear strength … considers the modeled member as rigid bodies which show stiffer and stringer behavior than the real ones. the higher stiffness in the finite element models come from several factors adopted in the finite element analysis. a perfect bond is assumed between the steel bars and the concrete. in reality, there is a slip percentage that reduces the composite action between the steel bars and concrete [24]. also, the finite element analysis ignores the micro crack effects that exist due to the drying shrinkage of the concrete that reduces the stiffness of the actual specimens. thus, the overall stiffness of the finite element models is higher than that of the experimental ones. (a) (b) (c) fig. 7. opening (a) depth, (b) width, and (c) size to shear span to depth ratio effect on deep beams. table i. comparison of the failure load for the experimental, stm, and fem beams specimen failure load, kn -./01 -234. -2536 -234. -234. -2./01 -2536 dp-48x36 260 226 280 0.86 1.07 dp-48x48 200 189 210 0.94 1.05 dp-48x60 156 157 170 1.00 1.08 dp-60x36 210 201 230 0.95 1.09 dp-60x48 172 150 180 0.87 1.04 dp-60x60 135 120 150 0.89 1.11 dp-solid 495 400 546 0.80 1.10 vii. conclusion in this paper, seven full scale deep beams with different web openings were examined. the main variables studied were the effects of width and depth of the web openings on the performance of the deep beams. the following conclusions can be drawn from the findings of this study: • from the experimental results it can be noticed that increasing the width of the opening has more pronounced effect than the opening depth at reducing the load carrying capacity. • increasing the opening width (i.e. increasing the e/l ratio from 0.4 to 0.67) reduces the load carrying capacity by about 50%, while increasing the opening depth (i.e. increasing d/h ratio from 0.48 to 0.6) led to a reduction in the load carrying capacity by about 28%. • the first visible inclined cracks normally appeared in the support bearing regions and formed toward the opening corner at load levels of about 20-30% of the ultimate load. • the calibrated numerical models indicated that load deflection response was stiffer than the experimental one and there was a good agreement in both trend and amplitude with variation in the load capacity by about 5% to 10%. • the strut-and-tie approach for the design based on aci 318-19 code provisions may over predict the shear strength of the deep t-beam with large opening up to about 125% of the actual capacity because it ignores the web opening effects. • the proposed empirical equation, based on the stm of the aci code, showed good agreement with the experimental and numerical results of about 90%. the study recommends investigating the limits of the critical web opening size that turn the nonlinear behavior of deep beams into linear. acknowledgment the authors would like to express their gratitude to the staff of the civil engineering department at the university of baghdad. engineering, technology & applied science research vol. 12, no. 2, 2022, 8289-8295 8295 www.etasr.com hussein & abbas: a semi-empirical equation based on the strut-and-tie model for the shear strength … references [1] k. h. tan and h. y. lu, "shear behavior of large reinforced concrete deep beams and code comparisons," structural journal, vol. 96, no. 5, pp. 836–846, sep. 1999, https://doi.org/10.14359/738. 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[24] "abaqus analysis user’s guide (6.14)." http://130.149.89.49:2080/ v6.14/books/usb/default.htm (accessed feb. 08, 2022). microsoft word etasr_v12_n1_pp8223-8227 engineering, technology & applied science research vol. 12, no. 1, 2022, 8223-8227 8223 www.etasr.com minh et al.: a novel approach for the modeling of electromagnetic forces in air-gap shunt reactors a novel approach for the modeling of electromagnetic forces in air-gap shunt reactors hung bui duc school of electrical engineering hanoi university of science and technology vietnam hung.buiduc@hust.edu.vn tu pham minh school of electrical engineering hanoi university of science and technology vietnam tu.phaminh@hust.edu.vn tuan phung anh school of electrical engineering hanoi university of science and technology vietnam tuanphunganh1@hust.edu.vn vuong dang quoc school of electrical engineering hanoi university of science and technology hanoi, vietnam vuong.dangquoc@hust.edu.vn abstract-shunt reactors are usually used in electrical systems to imbibe reactive powers created by capacitive powers on the lines when the system is operating on low or no loads. moreover, they are also used to balance reactive powers and maintain the stability of a specified voltage. in general, the air gaps of a magnetic circuit shunt reactor are arranged along the iron core to reduce the influence of fringing and leakage fluxes. therefore, non-magnetic materials made of ceramics or marbles are often used in air gaps to separate the iron core packets. the direction of the fringing flux is perpendicular to the laminations, so the core packets of the shunt reactor are generally made from radially laminated silicon steels. due to the alternating electromagnetic field through the core, a periodically altered electromagnetic force is produced between the core packets, tending to compress the ceramic spacers. this electromagnetic force causes vibration and noise in the core. in this research, a finite element approach based on the maxwell stress tensor was developed to compute the magnetic flux density and the electromagnetic forces appearing in a shunt reactor. keywords-shunt reactor; air gaps; magnetic flux density; electromagnetic force; maxwell stress tensor i. introduction a shunt reactor (sr) is an important component widely used in power transmission systems to improve stability and efficiency. parasitic capacitance occurs in a line when the system is working under low or no load. especially for a long line, its value is very large and leads to a voltage increase, causing an overvoltage at its end. hence, to maintain voltage stability according to the regulations and balance the reactive power in electrical systems, the sr is proposed to absorb the excess reactive power created by the line capacitance [1-4]. in addition, in order to reduce the magnetic flux and to avoid the saturation of the magnetic circuit, air gaps are added in the iron core of the sr to increase the reluctance values. on the other hand, fringing fluxes appear around the air gaps [6-9], increasing the winding inductance and causing nonuniform magnetic fields in the iron core packets of the sr. nonmagnetic materials such as ceramic or marble are often used in air gaps to separate the iron core packets. the fringing flux departs and reenters the lamination perpendicularly, so the core packets of the sr are generally made from radially laminated silicon steels. because of the alternating electromagnetic field through the core, a periodically altering electromagnetic force is produced between the core packets, tending to compress the ceramic spacers. the force on the core packets is a maxwell force that causes vibration and noise. maxwell forces are acting at twice the power frequency due to the sinusoidal flux passing through the windings at the power frequency. many researchers have investigated transient situations and magnetic fields in sr or calculated the air-gap reluctance and inductance of winding for magnetic circuits [6-12]. in [13], a method was introduced to calculate the leakage fields in aircore reactors using a 3d reluctance network. testing problems of gapped-core reactors were presented in [14, 15]. some researchers investigated the temperature field distribution [16, 17]. in this research, a finite element method (fem) based on maxwell stress tensor theory [18] was developed for an iron core gapped sr to compute the magnetic flux density and the electromagnetic force on the core packets. these fields are the inherent reason for the vibration and noise and tend to compress the ceramic spacers. ii. methodology a. the structure of a gapped-core shunt reactor the structure of an sr is illustrated in figure 1. the mid limb with the non-magnetic gaps is enclosed by the winding. the winding is also enclosed by a frame of core steel providing the return path for the magnetic field. three single-phase srs are connected to provide a three-phase transmission line. a corresponding author: hung bui duc engineering, technology & applied science research vol. 12, no. 1, 2022, 8223-8227 8224 www.etasr.com minh et al.: a novel approach for the modeling of electromagnetic forces in air-gap shunt reactors three-phase sr can also be used, having 3 or 5 limbed cores. figure 1(b) shows a three-limbed core sr having a strong magnetic coupling between the 3 phases. a 5-limbed core is shown in figure 1(c), where the phases are magnetically independent due to the enclosing magnetic frame formed by the two yokes and the two unwound side-limbs. the gapped core limbs are built of core packets. the core packet type is further classified into parallel and radially laminated core types by the core packet laminating methods. the parallel laminated core type has steel plates in parallel in the same direction as the power transformer core, and the radially laminated core type is constructed as a cylindrical core packet by laminating steel plates in the radial direction arranged in a wedge-shaped pattern [14]. the core packet is filled with epoxy resin and molded into one solid unit. fig. 1. modeling of the shunt reactor: (a) single-phase, (b) 3-phase 3limbed core, (c) 3-phase 5-limbed core [6]. the vibration in the srs is usually higher than in transformers as a result of the magnetic forces between the consecutive core packets. therefore, the core is designed to eliminate excessive vibrations. the non-magnetic gaps are established by using cylindrical spacers to take the large magnetic forces appearing between the discs in a gapped core sr. the height of the distance spacer is equal to the height of the air gap. the core packets are stacked and cemented together to form a core limb column. dimensional stability and core tightness can be fixed by an epoxy impregnated polyester material and a fiberglass cloth of a few millimeters between the last limb packet and the top/bottom yoke. the yokes and side limbs, normally with a rectangular cross-section, make up the magnetic circuit. b. parameters of the shunt reactor a single-phase sr of 35mvar (500/√3kv and 50hz) was considered to calculate the electromagnetic force in the core packets. a simple model of this single-phase sr is shown in figure 2. the volume of the air gaps was determined by the equations describing the magnetic circuit model. it should be noted that this volume depends on the main parameters of the shunt reactor, i.e. reactive power, magnetic inductance, winding inductance, frequency, and energy storage in the winding space air gap. iron materials have usually a high magnetic permeability (µ=µr.µ0) compared to the air gap permeability (µ0). therefore, the reluctance of the magnetic core is very small, compared to the reluctance of the air gaps, and can be neglected in the equivalent magnetic circuit. in addition, the winding resistance is normally very small compared to the inductance and can be neglected when defining the parameters of the electric circuits. from the relationship between the magnetomotive force (mmf), magnetic flux, and reluctances of the magnetic circuit, the magnetic flux density on the core can be determined via the reactive power and the volume of the air gap as: �� � � �� .�. � (1) where bm, vg, and µ0 are the maximum flux density, the air gap volume, and air permeability respectively. the obtained results of the sr of 35mvar are shown in table i [10] fig. 2. model of the shunt reactor. table i. sr results by the analytic method parameters notation results reactive power q (mvar) 35 rated voltage u (kv) 500/√3 rated current i (a) 121,24 totalinductance l (h) 7.5788 core dimension dc (mm) 673 height of core hc (mm) 1758 total air gap length lg (mm) 363 turn number n (turn) 2166 width of winding ww (mm) 248 height of winding hw (mm) 1488 c. calculation of the electromagnetic force in the gapped core of the sr, vibrations can be very high due to the magnetic forces between the consecutive core packets. thus, the ceramic spacers and any other gap materials should tolerate these forces without any significant shrinkage. the electromagnetic force acting on the core packets can be computed by either the maxwell stress tensor approach or the virtual work method [20]. this force is given by: � � ∆�∆� � �� ��� ��, (2) where ac is the cross-sectional area, and ∆x is the translation of a body. the surface force density is therefore given by: f� � ��� � �� ��� (n/m2) (3) the higher the operating flux density, the higher the attractive force is. therefore, the operation flux density is typically lower than the value used sometimes in power transformers. according to (2), it is necessary to increase the total volumic air gap to reduce the magnetic flux density. the force between the core packets can be calculated by (3) if the flux distribution is uniform. however, as the flux distribution in the sr is non-uniform, the finite element approach is generally applied with the virtual work principles. the magnetic flux density can be determined through the mmf and the air gap parameters as: hc dc hw ww hy dy wy engineering, technology & applied science research vol. 12, no. 1, 2022, 8223-8227 8225 www.etasr.com minh et al.: a novel approach for the modeling of electromagnetic forces in air-gap shunt reactors � � ��� � � !."#� (4) the surface force density can also be calculated by: f� = � � � ! �"� #� (n/m 2 ) (5) the maxwell stress tensor approach is widely used for computing electromagnetic forces. when ignoring the magnetostriction, the distribution of the magnetic forces in the core packets can be defined as: �$ = − � � h.h ∇� (6) on the material surface, fv can be written in terms of normal and tangential components as: �$ � − ��)h*� + h,�∇� � − �� .h*� + �/���0∇� � − �� )h*� ∇� − b,� ∇2 (7) since 3��� � −42, where reluctivity is 2 � ��. the force density at the surface can be defined as: �5 � − �� )h*� )� − �− b,� )2 − 2--6 (8) where n is the unit normal vector to the surface. in the gappedcore sr, the force density between two packets can be determined by (8), which when the fringing effect is negligible (ht=0) becomes: �5 � �� )b,� )2 − 2--6 (9) the reluctivity 2 of the core material in (9) is negligible. thus, the magnitude of the force per unit area perpendicular to the surface can be expressed as: �7 � �� ��� (n/m2) (10) this force is a function of the square of the flux density. the higher the operating flux density, the higher the forces of attraction are. d. modeling of the shunt reactor via a finite element approach maxwell's equations and the constitutive laws of the problem are written as [10-13]: ∇ × 9 � − :�:* (11) ∇ • b � 0 (12) ∇ × < � = + :>:* (13) b � ∇ × a (14) the value of the magnetic flux density b corresponding to the magnetic field intensity h is: � � �< (15) the magnetization forces were calculated by applying the maxwell stress tensor locally. the maxwell stress tensor for magnetic fields is a 3×3 matrix and has a unit of n/m 2 : @ � a�b<b − �� �<�c<b�d<b �b<c�c<c − ���<�d<c �b<d�c<d�d<d − ���<ef 6b6c6dg (16) this is also a suitable approach for computing the force distributions. the divergence of the stress tensor h$ is defined by the volume force density in (16a), while the volume force is defined in (16b): f$ � ∇ ∙ @ (16a) �$ � k ∇ ∙ @lm$ (16b) the force on the surface of the core packets can be obtained by: �7 � k @ln7 (17) the tangential ft and the normal fn components of the force f per unit area on an elemental surface can be expressed in terms of the tangential and normal field components as: �* � �,<* (18a) �, � �� . �� �,� − � <*�0 (18b) both the normal component of b and the tangential component of h should be determined. in this part, the fem was used to determine the modeled sr parameters, utilizing the ansys maxwell software [20]. the accuracy and the validity of fem have been proven in recent studies [10, 12, 19]. due to the anisotropy of the magnetic properties, a set of 3d laminated coordinate systems was defined considering the anisotropy of magnetic properties for laminated silicon steel in the rolling direction (rd), the transverse direction (td), and the lamination direction (ld). the models of all parts (yokes, core packets, windings) in the 3d coordinate system were created, and core packets are shown in figure 3(a). then, the lamination direction of the yokes and all core packets was chosen in the 3d laminated coordinate systems. the core packet of the sr was generally made from radially laminated silicon steels, as shown in figure 3(c). the mapping between the laminated and the rectangular spatial coordinate systems is presented in table ii. iii. results and discussion the mapping distributions of the magnetic flux density in the sr core are presented in figure 4. the magnetic flux density in the sr model is shown in figure 4(a)-(b). the distribution of the magnetic flux density on a core packet, generally made from radially laminated silicon steels as figure 3(c), is presented in figure 4(c). the magnetic flux density is unevenly distributed, especially in the core packets. the magnetic flux density around the core’s corner is larger than in its interior due to the characteristics of the sr, which has air gaps between the core packets to increase the reluctance of the magnetic circuit. however, the fringing flux around the air gaps engineering, technology & applied science research vol. 12, no. 1, 2022, 8223-8227 8226 www.etasr.com minh et al.: a novel approach for the modeling of electromagnetic forces in air-gap shunt reactors increases the magnetic flux around the iron core packets. together with the fringing flux, it is directed to the laminated silicon steel in the transverse direction, which has worse magnetic properties than the rolling direction. the magnetic flux density along the lines y1-y2 and y3-y4 is shown in figure 5. fig. 3. 3d model of the single-phase sr and the radially laminated silicon steels. table ii. mapping between the two coordinate systems part rd td ld core packets z-axis perpendicular z-axis radial as a fan-shaped top and bottom yokes x-axis z-axis y-axis side yokes z-axis x-axis y-axis fig. 4. the magnetic flux density on the magnetic circuit and iron core packets. fig. 5. magnetic flux density along the lines y1-y2 and y3-y4 on the surface of a core packet. in the same way, the magnetic flux density around the outermost edge is highlighted in figure 5. it is significantly larger than the rest, while this magnetic flux density is directly related to the electromagnetic force acting on the core packets. this electromagnetic force component will act on the ceramic plates that separate the core packets. the distribution of the force density on the surface of the core packets is shown in figure 6. in the gapped-core sr, the magnetic force acts between the core packets like close electromagnets and can be interpreted as attractive forces that try to minimize the gap length. due to the very high magnetic attraction forces between the core packets, the ceramic spacers and any other air gap material should tolerate these forces without any significant shrinking. as shown in (14), these forces are a function of the square of the flux density, and thus the higher the operating flux density, the higher the forces of attraction are. the operating flux density is typically lower than the value usually used in power transformers. the cut values of the electromagnetic force density on the lines y1-y2 and y3-y4 on the core’s surface are shown in figure 7. it can be observed that these forces have the same value but in the opposite direction. fig. 6. distribution of the force density on the surface of the core packets. fig. 7. distribution of force density along the lines y1-y2 and y3-y4 on the core surface. figures 5 and 7 show that the electromagnetic force results are similar to the magnetic field results. the electromagnetic force around the outermost edge is also significantly larger than in the rest. figure 8 shows the post-processing normal forces acting on the top and bottom surfaces of the core packets. the positive normal forces are linked to the top surfaces of the core packets, whereas the negative normal forces are linked to the bottom surfaces. as shown in figures 6 and 8, the forces acting on the top and bottom surfaces of each core packet are in the opposite directions and have approximately the same magnitude, resulting in a net force acting close to zero on each core packet. the ceramic spacers are in contact with the bottom surfaces of the upper core and the top surfaces of the lower core packets. due to the two surface forces acting on the ceramic spacer in the opposite directions, these spacers suffer huge compression forces and should withstand approximately 257.5kn/m 2 or 26.3ton/m 2 . if the flux density on the iron cores is doubled, these forces will increase 4 times to over engineering, technology & applied science research vol. 12, no. 1, 2022, 8223-8227 8227 www.etasr.com minh et al.: a novel approach for the modeling of electromagnetic forces in air-gap shunt reactors 100ton/m 2 . to withstand the very high forces acting on the ceramic spacers, their height has to be precisely uniform to ensure a uniform force distribution on all the ceramic spacers. usually, the spacers are first glued to the core packet and then grinded to be equal. this result explains why during the design of shunt reactors, the flux density of their core should be smaller than the core of the power transformer, even using the same magnetic material. fig. 8. force density distribution along the lines y1-y2 and y3-y4 on the surface of the core packets. iv. conclusion this study investigated the electromagnetic forces on the core packets of a shunt reactor by both the virtual work method and the maxwell stress tensor approach. in both methods, the normal forces are a function of the square of the flux density. finite element approach, using ansys maxwell software, was applied to compute the magnetic flux density distribution and the normal surface forces density on the core packets. the forces acting on the top and bottom surfaces of each core packet are in opposite directions and have approximately the same magnitude, resulting in a near-to-zero net force acting on each core packet. however, as the surface forces act on the ceramic spacers in opposite directions, they become huge compression forces. therefore, these results will be useful to researchers, design engineers, and manufacturers when choosing the appropriate magnetic flux density on the core in order to control the electromagnetic forces acting on the spacers between the core packets. acknowledgment this study was funded by the hanoi university of science and technology (hust) under grant number t2021-pc-006. references [1] g. deb, "ferranti effect in transmission line," international journal of electrical and computer engineering (ijece), vol. 2, no. 4, 2012. [2] a. d. s. sri, k. t. devi, k. d. raju, and b. tanya, "depiction and compensation of ferranti effect in transmission line," international journal for research in applied science and engineering technology, vol. 6, no. 3, pp. 1522–1526, mar. 2018, https://doi.org/10.22214/ ijraset.2018.3234. [3] z. lubosny, "the issues of reactive power compensation in highvoltage transmission lines," acta energetica, vol. 23, no. 2, pp. 102– 108, 2015, https://doi.org/10.12736/issn.2300-3022.2015210. [4] "shunt reactors for medium and high voltage networks: from development to use," siemens, nurnberg, germany, 2018. [5] h. amreiz, a. janbey, and m. darwish, "emulation of series and shunt reactor compensation," in 2020 55th international universities power engineering conference (upec), sep. 2020, pp. 1–6, https://doi.org/ 10.1109/upec49904.2020.9209786. [6] l. m. escribano, r. prieto, j. a. oliver, j. a. cobos, and j. uceda, "new modeling strategy for the fringing energy in magnetic components with air gap," in apec. seventeenth annual ieee applied power electronics conference and exposition (cat. no.02ch37335), mar. 2002, vol. 1, pp. 144–150, vol. 1, https://doi.org/10.1109/apec. 2002.989240. [7] s. grebovic, n. oprasic, and a. balota, "influence of shunt reactor switching on overvoltages in 400 kv substation," in 2020 9th mediterranean conference on embedded computing (meco), jun. 2020, pp. 1–4, https://doi.org/10.1109/meco49872.2020.9134116. [8] r. p. hutahaean and g. sianipar, "transient analysis of 150 kv shunt reactor at bulukumba substation," in proceedings of the 2011 international conference on electrical engineering and informatics, jul. 2011, pp. 1–6, https://doi.org/10.1109/iceei.2011.6021818. [9] e. kurt, a. arabul, i. senol, and f. k. arabul, " an investigation on flux density of three phase distributed air-gap 3-5 legged shunt reactor ," in proceedings of the ires 21st international conference, amsterdam, netherlands, dec. 2015. [10] t. p. minh et al., "finite element modeling of shunt reactors used in high voltage power systems," engineering, technology & applied science research, vol. 11, no. 4, pp. 7411–7416, aug. 2021, https://doi.org/10.48084/etasr.4271. [11] v. d. quoc, "robust correction procedure for accurate thin shell models via a perturbation technique," engineering, technology & applied science research, vol. 10, no. 3, pp. 5832–5836, jun. 2020, https://doi.org/10.48084/etasr.3615. [12] v. d. quoc, "accurate magnetic shell approximations with magnetostatic finite element formulations by a subdomain approach," engineering, technology & applied science research, vol. 10, no. 4, pp. 5953–5957, aug. 2020, https://doi.org/10.48084/etasr.3678. [13] a. s. nunes, p. kuo-peng, and m. g. vanti, "air core reactor analysis based on rnm method," presented at the compumag 2013, budapest, hungary, jul. 2013. [14] g. w. alexander, r. h. hopkinson, and a. u. welch, "design and application of ehv shunt reactors," ieee transactions on power apparatus and systems, vol. pas-85, no. 12, pp. 1247–1258, sep. 1966, https://doi.org/10.1109/tpas.1966.291643. [15] j. p. vora, b. l. johnson, and h. c. barnes, "a new shunt reactor principle proved: designed data and factory test results for units built on the insulated core principle," ieee transactions on power apparatus and systems, vol. pas-92, no. 3, pp. 900–906, feb. 1973, https://doi.org/10.1109/tpas.1973.293655. [16] f. yuan et al., "thermal optimization for dry type air core reactor base on fem," in 2018 21st international conference on electrical machines and systems (icems), jul. 2018, pp. 1726–1730, https://doi.org/10.23919/icems.2018.8549257. [17] s. magdaleno-adame, r. escarela-perez, j. c. olivares-galvan, e. campero-littlewood, and r. ocon-valdez, "temperature reduction in the clamping bolt zone of shunt reactors: design enhancements," ieee transactions on power delivery, vol. 29, no. 6, pp. 2648–2655, sep. 2014, https://doi.org/10.1109/tpwrd.2014.2322994. [18] s. v. kulkarni and s. a. khaparde, transformer engineering : design, technology, and diagnostics, 2nd ed. boca raton, fl, usa: crc press, 2017. [19] k. dawood, g. komurgoz, and f. isik, "modeling of distribution transformer for analysis of core losses of different core materials using fem," in 2019 8th international conference on modeling simulation and applied optimization (icmsao), apr. 2019, pp. 1–5, https://doi.org/10.1109/icmsao.2019.8880392. [20] "customer support and help desk | ansys." https://www.ansys.com/ support (accessed jan. 15, 2022). microsoft word etasr_v12_n3_pp8694-8700 engineering, technology & applied science research vol. 12, no. 3, 2022, 8694-8700 8694 www.etasr.com lamjad & khalfallah: the inclusion of the environmental dimension of sustainability in studying … the inclusion of the environmental dimension of sustainability in studying informal settlements using the indi system the case study of bousaada city, algeria imane lamdjad laboratory of urban and environmental techniques university of m'sila m'sila ,algeria imane.lamdjad@univ-msila.dz boudjemaa khalfallah laboratory of urban and environmental techniques university of m'sila m'sila ,algeria boudjemaa.khalfalllah@univ-msila.dz received: 28 january 2022 | revised: 7 march 2022 | accepted: 15 march 2022 abstract-the phenomenon of informal settlements is considered one of the most common global issues that have negative effects on several life aspects. all algerian cities face this problem, including the city of bousaada and the neighborhood of sidi slimane, which is considered one of the largest informal settlements in the city. although the neighborhood has benefited from the vulnerable housing absorption program funded by the international bank for reconstruction and development, the latter did not achieve the set goals. therefore, it has become necessary to think about the use of modern and effective criteria for assessing the environmental dimension of sustainability, such as the indi system of impact indicators built into ecoquartiergrid2011 in order to contribute to the development of these neighborhoods, to ensure a better quality of life for the residents, and achieve sustainable development in light of the environmental dimension. on this basis, the present study aims to use the indi system to integrate the environmental dimension of sustainability in informal settlements and to investigate the environmental shortcomings that the neighborhood sidi slimane suffers from in order to suggest possible solutions to develop it and improve the quality of life for the residents. in pursuance of this aim, the approach of the current research is descriptiveanalytical in order to design an approach that deals with the criteria of the indi system in environmental studies. the research concludes that both indi and ecoquatiergrid 2011 will help improve the quality of life of the population for millions of individuals and residents in algeria and in developing countries that suffer from the problem of informal housing. a guideline based on indi and ecoquatiergrid 2011 indicators is recommended and incorporated into environmental studies as a reference. the novelty of the current research lies in finding practical and technical solutions to the problem of squatter housing through the use of the indi indicator system and its integration with ecoquartiergrid2011 based on 40 topics and 318 indicators covering the economic, social, and environmental dimensions. keywords-environmental dimension; quality of life; indicator impact system indi; informal settlements; bousaada city i. introduction the phenomenon of informal settlement growth is considered one of the biggest issues that threaten cities in general [1] and bousaada in particular. the latter is attributed to the high population density [2], rapid urban growth, and the inability of regulatory authorities to address this phenomenon. the number of individuals living in informal settlements reached 725 million in 2000, and 860 million in 2013 [2]. the inclusion of the environmental dimension of sustainability has become necessary in informal settlements as it directly affects the quality of human life and society [3]. this effect is manifested in inadequate housing, the absence of generally accepted building standards, the high occupancy rate of housing, the deterioration of basic infrastructure [4-5], the spread of pollution and epidemics, unsanitary living conditions [6], in addition to the deterioration of living conditions such as the lack of necessary public facilities and equipment, the deterioration of the road network and the sewage network [7], the lack of green and public spaces, and poverty and social exclusion [8]. informal settlements are characterized by the deterioration of their physical conditions. they are usually built with reinforced concrete, which is economical [9] and the impact of associated risks [10] is neglected, along with the risks regarding the quality of housing [11] and the construction of public projects [12]. these poor conditions clearly and directly impede the achievement of sustainable development in its environmental dimension. the environmental dimension of sustainability aims to improve the management of natural resources, protect biodiversity, and provide a healthy and livable human environment [13], while consuming renewable resources [14, 15]. ii. research methodology and tools a. research tools the current research paper follows the descriptive analytical approach and the indi evaluation system in order to corresponding author: imane lamjad engineering, technology & applied science research vol. 12, no. 3, 2022, 8694-8700 8695 www.etasr.com lamjad & khalfallah: the inclusion of the environmental dimension of sustainability in studying … assess the sidi slimane informal settlement. the study’s aim is to help achieve the environmental dimension of sustainability and improve the quality of life of the residents. in addition to that, field investigation has been conducted. b. procedures of the case study this study revolves around bousaada, an algerian city. it is located at a distance of 250km from the capital, with an estimated population density of 614 inhabitants/km2 in 2014. furthermore, it is characterized by its strategic location and its natural, cultural and historical characteristics [18-19]. the district of sidi slimane was chosen as a case study, as it is one of the largest informal settlements in the city. the latter has grown in the '80's due to the absence of the concerned authorities and the increase in population growth and rural migration towards the center of bousaada. sidi slimane is estimated to be 115 hectares, with a population of 45,000 people. [20]. the sidi slimane informal settlement is evaluated by merging the evaluation program indi with ecoquartiergrid2011 that consists of 40 topics and 318 indicators that include economic, social and environmental dimensions [16-17], see table i. 1) indi and ecoquartiergrid2011 indi is a program that aims to evaluate and develop all existing residential neighborhoods, and is used in projects that include rehabilitation, urban renewal, and urban expansion and works to achieve sustainable development and improve participation between urban actors and residents. ecoquartiergrid2011 has been incorporated into this system as an important part of the development of the indi index database. the indi rating system helps stakeholders, architects and urban planners improve the quality of life of residents and users. it is also the only tool among the global assessment systems that aims to assess the neighborhood before and after its improvement [16], moreover, ecoquartiergrid2011 focuses on assessing the environmental dimension more and helps old and new neighborhoods integrate the environmental dimension of sustainability [17]. 2) stepwise methods executed to achieve the objectives three gradual methods have been followed in order to achieve the goal of the study, which is to integrate the environmental dimension of sustainability in the sidi slimane neighborhood in order to improve the quality of life of the residents: • the stage of data collection: it is represented in collecting the initial information (documents, urban plans, site visits). • evaluation stage: by entering data into the integrated indi program database and evaluating it, it contributes to identifying deficiencies and how to enhance them. • data review stage: it is the output of the evaluation process and is represented in two parts: a section for the outputs of the indi program and a section for the outputs of ecoquartier 2011 grid, both in the form of graphs and tables. table i. topics of indi and ecoquartier 2011 indicators topics of ecoquartier grid2011 topics of the indi indicator impact system d im e n s io n s o f s u s ta in a b il it y good location and familiarity with the project energy management in project design e n v ir o n m e n ta l comfortable and healthy living environment energy management in buildings preserving biodiversity and enhancing nature in the city optical comfort use of non-renewable resources and waste mobility management water saving department field consumption rationalization of energy needs biodiversity reduced greenhouse gas emissions sustainable water management valuing the agricultural environment and forests managing sustainable and natural resources quality of housing, population and private spaces regulating transportation and reducing car use quality of public spaces and green spaces alternative and sustainable transport security and health risks and pollution reduction dense neighborhood and/or context adapted fighting poverty and social exclusion (work and housing) e c o n o m ic dynamics of local development new ways of thinking and acting financial and legal feasibility maintaining continuity of approach access to high-quality public facilities and utilities s o c ia l monitoring and consultation solidarity and the responsibility to live sharing the collective effort and integrating the neighborhood into the city coexistence promotion solidarity and the politics of social cohesion learning management and evaluation culture, education and training evaluation and value as a method of education promoting heritage and identity participation involvement of residents and users 3) rating values of the indi system the evaluation results are classified according to the evaluation field (0,1,2,3,4,5) according to five classifications, see table ii. table ii. indi rating evaluation values evaluation 0 absence of evaluation 1 very insufficient 2 somewhat insufficient 3 average 4 somewhat satisfying 5 very satisfying engineering, technology & applied science research vol. 12, no. 3, 2022, 8694-8700 8696 www.etasr.com lamjad & khalfallah: the inclusion of the environmental dimension of sustainability in studying … 4) the evaluation process the evaluation process is carried out according to the explanatory scheme of figure 1. fig. 1. the evaluation process. iii. results and discussion sidi slimane informal settlement was evaluated with the use of the indi and with ecoquartiergrid2011, see tables iiiiv and figures 2-3. the aim of this study is to explore the shortcomings and insufficiencies in order to address the problem of substandard housing and to improve the quality of life for the population in the studied area. table iii. assessment results of sidi slimane according to the indi system assessment results of sidi slimane using the indi indicator impact system initial evaluation energy management in project design 0.3 energy management in buildings 0.3 optical comfort 1 mobility management 0.3 field consumption 3 biodiversity 0.5 sustainable water management 0.5 managing sustainable and natural resources 0.5 fighting poverty and social exclusion (work and housing) 0.8 access to high-quality services and facilities 1.8 quality of residential buildings, residences, and private spaces 0.6 quality of public spaces and green spaces 0.4 security and health risks and noise reduction 0.3 contribute to the collective effort and the integration of neighborhoods in the city 0.9 solidarity and politics of social cohesion 0.2 culture, education and training 0.2 a new way of thinking and acting 0.3 evaluation and capitalization as a pathway to learning and improvement 0.7 partnership 0.5 involvement of residents and users 0.2 fig. 2. circuit diagram of the results of the assessment of the sidi slimane neighborhood according to the indi assessment program. engineering, technology & applied science research vol. 12, no. 3, 2022, 8694-8700 8697 www.etasr.com lamjad & khalfallah: the inclusion of the environmental dimension of sustainability in studying … fig. 3. circuit diagram of the results of the assessment of the sidi slimane neighborhood according to ecoquartiergrid2011. it is shown in figure 2 that the field consumption index obtained the highest value (3), which is an average rating, explaining the increase of the informal settlement at the expense of natural areas and trees, the absence of oversight by the concerned authorities, and the weak application of laws aimed at reducing squatter housing. most indicators of the environmental dimension of sustainability obtained a rating value around 0, which shows that the study area was randomly built without taking into account the appropriate orientation of the neighborhood to benefit as much as possible from the sunrays, and not taking into account climatic factors (such as wind direction, air currents, and shade) in addition to the lack of a network electricity and gas in the studied area, and failure to preserve natural areas, local trees, and plants when building. furthermore, figure 2 shows that the light comfort index obtained a value of 1, a very insufficient rating, and this explains the absence of public lighting in most of the streets of the study field. finally, the indicator of obtaining high-quality public facilities and utilities obtained a value of 1.8, a very insufficient rating, and this explains the lack of the necessary equipment and facilities and their distance from housing, and that these facilities do not consider persons with disabilities. it is displayed in figure 3 that the dense and/or contextadapted living indicator has the highest value (2.3), corresponding to a somewhat insufficient rating and this explains the consumption of the urban area in the field of study. the figure also shows that the functional blending index obtained a very insufficient rating (1.7), due to the absence of diversification in urban functions at the level of neighborhoods, residential islands, and housing units. as a conclusion, most of the indicators of the environmental dimension of sustainability got a value of 0 rating. this is explained by the absence of energy-saving buildings, the absence of a culture of preserving the environment and biodiversity, and the absence of a culture of reducing the volume and quantity of solid and household waste. table iv. assessment results of sidi slimane according to ecoquartier2011 assessment results of sidi slimane using ecoquartier 2011 initial evaluation good location and familiarity with the project 0.3 monitoring and consultation 0.6 financial and legal feasibility 0.5 learn how to manage and evaluate 0.6 maintain continuity of approach 0.1 promote coexistence 0.6 solidarity and responsibility to live 0.5 comfortable and healthy living environment 0.7 valuing heritage and identity 0.5 dense neighborhood / or context adapted 2.3 functional blending 1.7 regulating transportation and reducing car use 0.3 alternative and sustainable transport 0.2 dynamism and local development 0.6 valorization of the agricultural and forestry field 0.7 reduce greenhouse gas emissions 0 rationalization of energy needs 0.2 water saving department 0.2 use of non-renewable resources and waste 0.1 preserving biodiversity and enhancing nature in the city 0.5 the research gap appears by referring to previous studies, the author in [21] believes that the absence of the principle of participation and the absence of negotiation to limit the informal settlement of the studied area (the hanna nassif community managed settlement upgrading pilot project) with the authorities and government agencies negatively affect the quality of life of the residents. a two-pronged approach was used: forward-looking proactive strategies to contain new urban populations and slum upgrading to address the needs of the people currently living in slums. authors in [22] believe that improving the quality of life of their case study (slumimprovement projects in india) dwellers in india is linked to the development of a comprehensive legal framework that enables governmental and non-governmental agencies to deal quickly engineering, technology & applied science research vol. 12, no. 3, 2022, 8694-8700 8698 www.etasr.com lamjad & khalfallah: the inclusion of the environmental dimension of sustainability in studying … with the structuring and implementation of slum improvement projects, promoting participation, transparency, and cooperation between governmental and non-governmental entities to support financial governance and facilitating land tenure. there is no method or evaluation program that was followed in this study, but direct suggestions were made. authors in [23] argue that improving the quality of life of individuals of their case study, which includes providing basic needs such as adequate housing, sanitation, and waste management, especially with the covid-19 pandemic, requires improving medical care for slum dwellers and working to improve the economic situation. the proposed actions are the establishment of emergency planning committees in the informal settlements, the application of the strategy of solid waste management and collection, and the provision of food aid. no method or evaluation program were followed in this study, but direct suggestions were made. the research contribution of the current study lies in finding practical and technical solutions to the problem of informal settlement through the use of the indi indicator impact system and its integration with ecoquartiergrid 2011with the aim of achieving the environmental dimension of sustainability and improving the quality of life in the sidi slimane informal settlement. iv. conclusion this research aims to use the indicator impact system indi to integrate the environmental dimension of sustainability and the environmental shortcomings that the neighborhood sidi slimane suffers from in order to suggest possible solutions to improve the quality of life of the residents. the results showed strong absence of the indicators of the environmental dimension of sustainability, stronger than the economic and social ones. this study has many advantages over the previous ones since it differs in the methods and the results. while there is no method or evaluation program that was followed in previous studies, and directly suggestions and recommendations were made, the current study focuses on the process of evaluation which is based on 40 topics and 318 indicators covering the economic, social, and environmental dimensions. this is what enables us to provide comprehensive, accurate, and practical solutions according to the study's results. in addition, the utilized techniques were used for the first time to address the problem of informal settlement. the previous studies took into account only 9 indicators at most to investigate the quality of life of the residents in informal settlements, which is insufficient and not comprehensive to address the problem, which faces several environmental, economic, and social challenges, which were studied without the utilization of programs or evaluation systems. the current study provides a starting point to understand and address the problem of informal settlement using the indi technology integrated into ecoquartiergrid 2011 in developing countries, specifically in algeria. these techniques are very useful in extracting deficiencies at the level of social and economic dimensions, especially environmental dimensions, and thus addressing the problem of informal settlement. the implication of these findings is that these new technologies will be available to decision-makers and urban planners and will increase profitability, enhance the economy of the cities and improve environmental sustainability in informal settlements. the indi and ecoquartiergrid 2011 may become a form of sustainable urban development that requires coordination, cooperation and realization of the principle of participation between the different urban actors, i.e. local and governmental authorities, the private sector, civil society, and the population. both the evaluation systems, indi and ecoquatiergird 2011 will help improve the quality of life of the population for millions of residents in algeria and in developing countries that suffer from the problem of informal housing, and help in rationalizing energy consumption, protecting the environment, reducing pollution, and promoting development as a conclusion, a guideline to improve the quality of life in an informal settlement in the city of bousaada, based on indi and ecoquatiergrid 2011 criteria and indicators should be developed, and it should be integrated into environmental studies as a reference, taking into account the recommendations shown in table v. table v. a guideline for improving the quality of life in sidi slimane based on indi and ecoquartier2011 criteria and indicators recommendations indicators -it is necessary to provide all housing in the slum of sidi slimane with electricity, gas, and sewage facilities. -there is a need to take into account the appropriate orientation of the building to benefit as much as possible from sunlight and climatic factors (such as wind direction, air currents, shade) when designing the building. -the establishment of housing units within the field of study that achieves self-sufficiency in energy needs so as to produce and use clean energy efficiently and effectively is proposed. energy management in project design -energy efficiency can be achieved by reducing the use of electricity and gas, heating, ventilation, cooling, artificial lighting, and making use of natural lighting as much as possible. -local and sustainable building materials that enhance heat gain must be utilized. energy management in the building -all primary and secondary roads in the field of study must be equiped with public lighting. optical comfort -the development of an integrated and sustainable transportation system that takes into account quality, pricing, security and safety, and provides common public transportation such as buses is suggested. -the use of bicycles and allocating areas for pedestrians must be encouraged. -the necessity of providing car parking, taking into account the distance of less than 300m between the dwelling and the stopping station is underlined. -the provision of public transportation at all times and at the end of the week must be taken into account. -lanes for bicycles must be allocated. -the necessity of enabling persons with disabilities to have easy access to public transportation is underlined. mobility management engineering, technology & applied science research vol. 12, no. 3, 2022, 8694-8700 8699 www.etasr.com lamjad & khalfallah: the inclusion of the environmental dimension of sustainability in studying … -there is a need to protect and preserve agricultural areas, forests, and trees. -tightening of supervision by the concerned authorities and the application of laws that limit random housing that consumes the urban space excessively is suggested. field consumption -the preservation of natural areas when initiating the processes of preparing the neighborhood must be taken into account. -the continuity of natural areas should be preserved. -there is a need to take proactive measures aimed at preserving trees when constructing buildings. -different types of native plants must be cultivated. biodiversity -there is a necessity of providing all housing units in the study area with potable water, rationalizing the consumption of domestic drinking water. -the quality of potable water must be ensured (taking into account sanitary, physical and chemical conditions and compliance with water quality standards). -water leakage can be reduced by repairing and renovating old channels. -work has to be done in order to establish separate rainwater and greywater treatment centers. sustainable water management -there is a necessity of using local building materials and energy-saving conservation techniques. sustainable management of natural resources and materials -there is a necessity of providing equitable employment and housing positions for all segments of society. -there is a necessity of reducing squatter housing because it negatively affects the economy. fighting poverty and social exclusion (work and housing) -there is a necessity of increasing the number of health, security, and educational equipment in the studied neighborhood, as it is insufficient. -there is a necessity of taking into account the proximity of the housing in the case of the area to public facilities (shops, school, mail, health centers, etc.) within a range of 300m. -public facilities and facilities must provide access to persons with disabilities. access to high-quality services and facilities -the quality of housing must be improved. -work has to be done in order to achieve quality in public roads, common spaces between residences, private spaces, and stairs, and secure access. -the privacy of the dwellings and the interfaces between private and public spaces must be taken into account. -there is a necessity of furnishing the streets and general lighting at the level of the studied neighborhood in order to serve the residents. quality of residential buildings, residences, and private spaces -there is a necessity of providing public spaces and green spaces within the field of study. abandoned and unbuilt spaces can be exploited. -the population has to be informed and sensitized to the preservation of green spaces and natural areas. -there is a need to take into account the hierarchy of spaces and ease of reading in the design of green and public spaces. quality of public and green spaces -there is a necessity of preparing a preventive plan for the natural disasters that the studied area suffers from (the danger of falling stones and floods). -strict instructions must be established to reduce the risk of accidents in construction workshops. -the construction waste must be disposed of immediately after the completion of the construction process. security and health risks and noise reduction -there is a necessity of diversification in urban functions at the neighborhood level, residential islands, and housing units to achieve functional blending. contribute to the collective effort and the integration of neighborhoods in the city -the studied area contains only individual housing, so it is necessary to diversify the housing style through the establishment of social housing to enhance interaction between residents and achieve social diversity. solidarity and politics of social cohesion -there is a necessity of valuing heritage and local identity is underlined. -awareness-raising and media campaigns at the level of the studied neighborhood on protecting the environment and preserving green spaces and natural areas must be carried out. culture, education, and training -programs of training and educating workers and engineers of governmental and non-governmental agencies, private sector, associations, civil society, and the population can be carried out. -there is a necessity of calculating the project budget and the total cost of the initialization operations. a new way of thinking and acting: approaches, methods, and tools -there is a need for continuous adaptation and improvement of the project. evaluation and capitalization as a path to action and improvement -the preparation of a charter for the project of environmentally sustainable residential neighborhoods that include the various actors and partners in the project, is proposed. partners -consultation and involving residents and users in evaluating the project's stages and planning for the establishment of public facilities, public spaces and green spaces is suggested. involvement of residents and users references [1] m. j. maghsoodi tilaki, r. a. mustafa, m. hedayati 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[14] s. e. bibri, "the eco-city and its core environmental dimension of sustainability: green energy technologies and their integration with datadriven smart solutions," energy informatics, vol. 3, no. 1, jun. 2020, art. no. 4, https://doi.org/10.1186/s42162-020-00107-7. [15] m. l. banda and s. fulton, "litigating climate change in national courts: recent trends and developments in global climate law," environmental law reporter, vol. 47, no. 2, jan. 2017. [16] c. charlot -valdieu and p. outrequin, designing and evaluating an ecodistrict project with the indi reference system. paris, france: éditions du moniteur, 2012. [17] call for e’coquartier projects 2011, explanatory notice of the e’ecoquartier grid. paris, france: ministry of ecology, sustainable development, transport and housing, 2011. [18] review of the master plan for the preparation and reconstruction of the municipality of bousaada. batna, algeria: office of studies and achievements in reconstruction in batna, 2014. 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[23] j. corburn et al., "slum health: arresting covid-19 and improving well-being in urban informal settlements," journal of urban health, vol. 97, no. 3, pp. 348–357, jun. 2020, https://doi.org/10.1007/s11524020-00438-6. microsoft word etasr_v13_n4_pp11412-11418 engineering, technology & applied science research vol. 13, no. 4, 2023, 11412-11419 11412 www.etasr.com abedi et al.: the effect of interior stiffeners on the flexural behavior of concrete-filled steel tube … the effect of interior stiffeners on the flexural behavior of concrete-filled steel tube composite box girders hussam aldin o. abedi civil engineering department, mustansiriayh university, iraq hussamalsodany86@gmail.com mohammed m. rasheed civil engineering department, mustansiriayh university, iraq mmrk72@uomustansiriyah.edu.iq rusul abed a. alwaili civil engineering department, mustansiriayh university, iraq rusulalwaili88@gmail.com received: 3 june 2023 | revised: 19 june 2023 and 23 june 2023 | accepted: 29 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6088 abstract the composite box girder is a structural element with high torsional stiffness and resistance against flexural loads. a new form of bridge construction is the concrete-filled steel tubes (cfsts) linked to composite slabs by steel trusses. in this study, four different kinds of composite box girders linked to steel tubes filled with concrete were analyzed experimentally and numerically while being subjected to flexural loads. the specimens were evaluated when subjected to a focused load at the mid-span. the first model is a concrete-filled tube without stiffeners and was considered the control specimen, the second model is a concrete-filled tube with internal i–shaped stiffeners welded inside the steel tube, the third was filled with t-shaped stiffeners, and the fourth with v-shaped stiffeners. the test results showed that the cfst sections with interior stiffeners gave higher strength capacity and less deflection than the control specimen. the best shape of the stiffeners was the t-shape. the numerical analysis results were in accordance with the test results. keywords-composite box girder; concrete filled tubes; truss; flexural strength capacity; bridge analysis; finite element modeling; abaqus i. introduction composite bridges made from steel (girder) and concrete (slab) are the best way to reduce dead loads, such as the selfweight of the bridge. during the recent years, the composite bridges are constructed with top concrete slabs with steel trusses and bottom concrete-filled steel tubes (cfsts). this type of bridge contains a large number of truss joints so there is stress concentration at these joints’ location that reduces flexural capacity and may lead to failure [1]. the load-bearing structural system is served by the cfst composite trusses. while the shear force is converted into the axial force of the webs, the applied moment by the external load is converted into the axial forces of the upper and lower chords of the truss. the composite truss's chords are susceptible to axial force, thus the ideal approach is to fill the compressive chords with concrete due to its greater axial strength. in addition, the concrete core within the steel tube improves the buckling behavior of the steel tubes. additionally, the steel tube further encloses the concrete core [2]. the compressive strength of the slab and of the filled steel section (bottom chord), along with the geometry of the steel tube, have a significant impact on the behavior and strength capacity, crack propagation in the slab, deflection, and slip at the interface between the steel section and concrete, according to the experimental results of composite sections under the effect of concentrated load at the mid span of the top slab. while the load capacity and deflection are somewhat affected by the shear connections, the slip is more significantly affected [3]. the cfst section enhances the tensile strength by about 11% more than the steel section alone (hollow) [4]. cfst trusses with bracings for connections and a bottom chord filled with concrete are commonly used. the cfst enhances the flexural stiffness and joint strength of the truss as well as the compressive and tensile strength of the chords to prevent them from bowing inward and squeezing the lower chord's steel tube engineering, technology & applied science research vol. 13, no. 4, 2023, 11412-11419 11413 www.etasr.com abedi et al.: the effect of interior stiffeners on the flexural behavior of concrete-filled steel tube … (whole). the hollow steel section reduces the cost as it acts as a formwork for concrete casting [5-8]. in [9], a comparison was made between two kinds of trusses. the first truss was filled with concrete and the second truss was hollow. the strength capacity of the first member was 17.5% higher. in [10], six samples were tested with various girder trusses to examine the effects of the hollow upper and lower chords of the truss on the welded joints. according to the test findings, the inclusion of cfst chords boosted the joint's stiffness and load capacity, preventing the plastic failure of the chord's surface. in [11], eight specimens, including two hollow chord curved truss girders, four curved, and two straight cfst truss girders, were tested. the specimens' flexural behavior was examined without taking into account the height/span ratio and the presence of concrete infill. according to the test findings, curved cfst truss girders delivered greater stiffness and ultimate loads than straight cfst truss girders and curved hollow truss girders. in [12], four specimens were tested to explore the effect of the member’s truss layout (diagonal and vertical) connected to lower and upper cfst members. different modes of failure appeared, such as surface plasticity, local buckling, shear in the lower chord, and support failure. authors in [13] investigated the flexural performance of cfst tube composite trusses considering different web configurations, such as transverse braces. according to the test findings, local buckling and surface plasticity at the bottom or the upper chord were the diagonal braces' failure modes. in comparison to the other specimens, the specimen with diagonal bracing exhibited better load capacity, stiffness, and ductility. the flexural strength of concrete girder enhanced by external structural materials due to prior damaged was studied in [14]. a bridge may fail due to the action of terrorist attacks such as explosives, so it is needed to make the bridge gliders strong enough [15], which damages the concrete girders [16]. according to the studies mentioned above, the research is limited in this area and more studies are needed to understand the behavior of such structures. the present study focuses on the influence of cfsts on the flexural performance of composite box girders under static load. the effect of the presences stiffeners inside of cfst is also studied. ii. experimental work four models of cfsts which support concrete deck slabs are presented in this study. the model specimens include a control specimen and three specimens with different stiffener shapes welded along inside the cfst beam, as shown in table i. table i. specimen marks and descriptions specimen description stiffener shape b g composite tubular box girder filled with truss and concrete not applicable b g w i composite tubular box girder filled with truss and concrete with i shaped stiffeners i b g w t composite tubular box girder filled with truss and concrete with t-shaped stiffeners t b g w v composite tubular box girder filled with truss and concrete with v-shaped stiffeners v the geometry of the composite slabs, the connected truss, and cfsts of all the tested specimens was the same except the shape of the interior stiffeners inside the cfst beam. the width of the specimens was 450 mm, the depth was 400 mm, and the total length was 2000 mm, in which the span from center to center between the supports was 1800 mm. the thickness of the concrete deck slabs was 100 mm. the trusses with 6 mm thickness were connected with the top concrete slabs by 8 mm thickness plates in which stud shear connectors were welded in above. the diameter of the stud shear connector was 12 mm distributed with center to center spacing of 100 mm. a steel tube with a thickness of 1.27 mm was used to fabricate the square tube cross-sections with outside depth and width of 150 mm. based on selected dimensions, the width/thickness ratio is 118.11 so tube section was a slender section [17]. the steel tubes and the trusses were connected by weld connections. the three tested specimens had the same dimensions with the control specimen and differed only by the presence of the internal stiffeners with different shapes provided along the full length of each specimen. the steel stiffeners (i, t and v shaped) were separately fabricated and welded at their designed locations on a flat steel plate, after which, the plate was carefully folded by a press machine to achieve the suggested square shape of a cold-formed square steel tube. the square-shaped tube was fabricated by folding the flat steel plate into three folded sides. to complete the tube, the remaining face was formed by fully welding a flat steel plate onto the open edges along the already folded plate using a welding machine. the single stiffeners (along the span) were welded inside the steel tube as shown in figure 1. ordinary portland cement-type i was cast in the concrete deck slabs and infill steel tubes. its mechanical properties can be seen in table ii. fig. 1. specimens details. (a) no stiffeners (bg), (b) i stiffeners (bgwi), (c) t stiffeners (bgwt), and (d) v stiffeners (bgwv). table ii. mechanical properties of concrete (slab and filled concrete) compressive strength fc (mpa) modulus of rupture fr (mpa) splitting tensile strength ft (mpa) modulus of elasticity ec (mpa) poisson ratio ν 30 3.337 4.244 25743 0.2 the above steel plates were connected with concrete deck slabs by shear connector studs. the geometry and specifications are listed in tables iii and iv, respectively. the concrete deck slab reinforcement and geometry are listed in table v. the dimensions of the steel tubes and the filling concrete are listed in table vi. the mechanical properties of engineering, technology & applied science research vol. 13, no. 4, 2023, 11412-11419 11414 www.etasr.com abedi et al.: the effect of interior stiffeners on the flexural behavior of concrete-filled steel tube … the main reinforcement of the slabs are listed in table vii. truss member properties and dimensions are listed in table viii. table iii. shear stud connectors diameter (mm) height (mm) spacing (mm) 10 63.5 100 table iv. mechanical properties of shear stud connectors fy (mpa) es (mpa) ν 412 200000 0.3 table v. concrete slab details slab depth (mm) slab width (mm) main bottom reinforcement 100 450 ø10@100 in both directions table vi. steel tube and filling concrete dimensions concrete steel tube (mm) depth (mm) width (mm) depth and width-square section thickness 150 150 150 1.27 table vii. mechanical properties of the reinforcement bar diameter (mm) fy (mpa) ultimate strength fu (mpa) es (mpa) v 10 487.67 660 200000 0.30 table viii. truss member dimensions type depth (mm) width (mm) thickness (mm) channel 25.4 50.8 6 figure 2 shows the stud shear connector distribution along the deck slab welded to the upper steel plate, figure 3 shows the deck slab reinforcement layout, figure 4 shows the specimen setup and the strain gauges, in which two of them are located at the shear zone as st1 and st2 at each support's end while st3 is located at the bottom center of each specimen. central point load was applied up to failure in each specimen. the concentrated load was applied at the mid-span on the top surface of the deck slab. strains and deflections were recorded for each load step and were then plotted. fig. 2. stud shear connector distribution. fig. 3. main reinforcements of the slab layout. fig. 4. location of the strain gauges. iii. test results in the current investigation, four specimens, including the control composite girder connected by steel truss to cfst without interior stiffeners and three specimens with different stiffeners were tested under concentrated load. the test results of are shown in table ix. table ix. test results model load capacity (kn) deflection at maximum load (mm) deflection at failure (mm) maximum strain st1 x10 -3 st2 x10 -3 st3 x10 -3 bg 168.70 15.53 16.88 1.3 1.06 0.071 bgwi 196.24 16.40 18.60 0.59 0.59 0.314 bgwt 220.53 24.00 28.51 0.57 0.54 0.560 bgwv 212.93 13.14 13.97 1.34 1.39 1.08 table x. stiffness and ductility of the tested specimens model increase of strength load capacity (%) deflection at the load of bg (mm) deflection decrease (%) stiffness (kn/mm) ductility bg --15.53 --10.86 1.09 bgwi 16.32 10.87 30.01 11.96 1.13 bgwt 30.72 10.51 32.32 9.19 1.19 bgwv 26.22 8.03 48.29 16.20 1.06 the recorded strain values listed in table ix for st1 and st2 are the same, but differ from st3 which is located at the bottom center of the cfst beam. all strains were measured engineering, technology & applied science research vol. 13, no. 4, 2023, 11412-11419 11415 www.etasr.com abedi et al.: the effect of interior stiffeners on the flexural behavior of concrete-filled steel tube … with the limiting value recommended by aci-318-2019 [18] which is less than 0.005. the stiffness and ductility of the tested specimens are listed in table x. the stiffness was found by dividing the maximum strength capacity with the corresponding deflection and the ductility was the result of the division of the deflection at failure by the deflection at maximum load capacity. specimen bgwv exhibits the highest stiffness while specimen bgwt the lowest. specimen bgwt gave the highest ductility of 1.19 and specimen bgwv the lowest of 1.06 in. the behavior and strength of the tested specimens are represented by the recorded load-deflection and load-strain relations for each applied load step. figure 5 shows the loaddeflection variations for the tested specimens. in general, the variation started as linear up to the inflection point. thereafter, the specimens behave as nonlinear and their stiffness reduces. the inflection points differ in magnitude due to the differences in the connection of the unfilled concrete with the steel tube to form the cfst section. specimen bgwv has the highest strength capacity with lowest deflection followed by bgwt, bgwi, and bg. fig. 5. load-deflection relation of the tested specimens. figures 6 to 8 represent the load-strain variations of the tested specimens. st1 and st2 are the strains at the left and the right diagonal tension at the supports and st3 represents the strain at the middle in the bottom of each specimen. the recorded strains st1 and st2 are almost equal. the strain of specimen bgwv was the lowest at the supports due to the connection stiffeners, followed by bgwi, bgwt, and bg. the strain st3 of the control specimen bg was the lowest. fig. 6. load-strain st1 of the tested specimens. fig. 7. load-strain st2 of the tested specimens. fig. 8. load-strain sts of the tested specimens. iv. finite element analysis element types were used to simulate the performance of cfsts of composite box girders. the concrete element had 8 nodes. the truss element model had 2 nodes and the steel tube model shell element had 4. the contact between the concrete and bottom steel plate, concrete and with inner surface of the steel tube involved finite sliding with surface-to-surface formulation, which is the default method in abaqus for contact enforcement. fig. 9. finite element model of the whole box girder. the t3d2 with 2-node linear 3-d truss element was used to simulate reinforcements, stud shear connectors, and stiffeners. the shear stud connectors were simulated in such a manner that there would be no uplift failure so they can only be deformed horizontally due. the 4-node s4r doubly curved shell element was used to simulate the steel tube [19]. figure 9 shows the finite element model simulation in abaqus. engineering, technology & applied science research vol. 13, no. 4, 2023, 11412-11419 11416 www.etasr.com abedi et al.: the effect of interior stiffeners on the flexural behavior of concrete-filled steel tube … mainly, there are two material modeling approaches for concrete in abaqus, which are concrete smeared cracking and concrete damaged plasticity (cdp) which is adopted in the present study. for the cdp model, in order to solve the drucker-prager plastic flow function and yield function, these parameters must be defined: dilation angle, form factor, eccentricity, bi-axial compressive stress ratio, dilation angle, and viscosity. the factors used to model the concrete are listed in table xi. table xi. damage plasticity data damage plasticity data dilation angle ϕ e fb0/fc0 k v 31 0.1 1.16 0.667 0 the stress-strain variation of concrete and steel are presented in figures 10 and 11 respectively. (a) (b) fig. 10. stress-strain variation of concrete: (a) compression, (b) tension [20]. fig. 11. stress-strain variation of steel. figures 12-15 show the experimental and fem analysis results of the load-mid span deflection for all specimens. the comparison shows a closeness in the results. table xii lists the comparison analysis results. the finite element performance for all simulated models gave lower deflection than the experimental tests due to the rigid body of the model and the compatibility between the connected nodes of the elements. figures 16-19 show the deflection of all models. fig. 12. load-deflection relation of the experimental and fem results for the bg specimen. fig. 13. load-deflection relation of the experimental and fem results for the bgwi specimen. fig. 14. load-deflection relation of the experimental and fem results for the bgwt specimen. table i. comparison between the experimental and fem analysis results model load capacity (kn) maximum deflection (mm) fem/ experimental experimental fem experimental fem load deflection bg 168.70 179.12 15.53 25.00 1.06 1.06 bgwi 196.24 200.00 16.4 15.00 1.01 0.90 bgwt 212.93 210.70 24 15.36 0.99 1.16 bgwv 220.53 210.50 13.14 19.20 0.95 0.80 engineering, technology & applied science research vol. 13, no. 4, 2023, 11412-11419 11417 www.etasr.com abedi et al.: the effect of interior stiffeners on the flexural behavior of concrete-filled steel tube … fig. 15. load-deflection relation of the experimental and fem results for the bgwv specimen. fig. 16. deflection of model bg at failure. fig. 17. deflection of model bgwi at failure. fig. 18. deflection of model bgwt at failure. fig. 19. deflection of model bgwv at failure. v. von mises stresses the von mises stress were used to check out whether the adopted ductile material, i.e. steel, will yield or fracture. figures 20-23 show the von mises stress distributions of all simulated models. the stress concentration occurs at the bottom of the cfst beam. model bgwv exhibits the minimum stress concentration and model bgwi the maximum. the von mises stress contours that represent the stress distributions show uniformity. the von mises maximum values ranged between 463 and 496 mpa, so the mean of the maximum value is more than the yield strength of the steel tube (383 mpa), so there is a fracture for all models at the failure stage. fig. 20. von mises stresses of model bg at the final loading stage-fe results. fig. 21. von mises stresses of model bgwi at the final loading stage-fe results. fig. 22. von mises stresses of model bgwt at the final loading stage-fe results. fig. 23. von mises stresses of model bgwv at the final loading stage-fe results. vi. discussion the control specimen without interior stiffeners inside the cfst beam gave the lower strength capacity due to the absence of stiffeners, leading to a lack of interaction and a slip development between the steel tube and the filled concrete. in this case, the resistance force was only the frictional force (adhesive) between the concrete and the steel section. maximum strength capacity occurs in the case of t-shaped engineering, technology & applied science research vol. 13, no. 4, 2023, 11412-11419 11418 www.etasr.com abedi et al.: the effect of interior stiffeners on the flexural behavior of concrete-filled steel tube … stiffeners due to their resistance to the shear flow developed at the interface between the concrete and the steel tube. the other specimens, with i and v stiffeners, gave higher strength capacity than the control bg but less than bgwt. the deflection of specimen bgwt was less than control's and the specimens that used different stiffener shapes acquired more composite action while the flange of the stiffeners gave higher resistance to the composite bottom chord. the results of the finite element analysis were close with the experimental ones, giving less deflection due to the rigid body between the connected nodes of the elements. the number of shear stud connectors with full interaction between the steel plate and the deck reinforced concrete slab that lead the slip at the interface becomes very small or vanishes. no uplift failure occurred between the steel plate and the concrete deck slab in the experiments and finite element modeling. vii. conclusions based on the test and finite element analysis results of the four considered concrete filled steel tube box girders under flexural loads, the following conclusions can be reported:  the strength capacity of the composite girders connected by trusses to the filled steel tubes at the bottom chord depends on the presence of interior stiffeners. the presence of interior stiffeners increases the bond between the concrete and the interior face of the cfsts, making the concrete and the steel tube to work as a unity (full interaction) so that there is no slip, therefore the deflection become less and the strength capacity becomes higher and the developed flexural stress (bending stress) is reduced.  the strength capacity of composite girders depends on the shape of the stiffeners. the t-shaped stiffeners gave higher strength capacity than the other types.  deflection and strain become less in the presence of stiffeners because there is no slip between the inside concrete and the hollow steel tube.  the interior stiffeners increase the strength capacity and ductility, so they delay the occurrence of failure and prevent large deformations.  interior stiffeners improved the strength capacity of the tubes, meaning that the stiffeners improve the concrete confinement effects. references [1] y. chen, j. dong, and t. xu, "composite box girder with corrugated steel webs and trusses – a new type of bridge structure," engineering structures, vol. 166, pp. 354–362, jul. 2018, https://doi.org/10.1016/ j.engstruct.2018.03.047. 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[18] aci committee 318, 318-19 building code requirements for structural concrete and commentary. farmington hills, mi, usa: american concrete institute, 2019. [19] "abaqus 6.14 documentation." http://130.149.89.49:2080/v6.14/. [20] j. b. mander, m. j. n. priestley, and r. park, "theoretical stress‐strain model for confined concrete," journal of structural engineering, vol. 114, no. 8, pp. 1804–1826, sep. 1988, https://doi.org/10.1061/(asce) 0733-9445(1988)114:8(1804). engineering, technology & applied science research vol. 7, no. 6, 2017, 2177-2183 2177 www.etasr.com khodabakhshi-javinani and askarian-abyaneh: evaluation of moving average window technique … evaluation of moving average window technique as low-pass filter in microprocessor-based protecting relays naser khodabakhshi-javinani electrical engineering department amirkabir university of technology tehran, iran naser@aut.ac.ir hossein askarian-abyaneh electrical engineering department amirkabir university of technology tehran, iran askarian@aut.ac.ir abstract—over the last decades, with the increase in the use of harmonic source devices, the filtering process has received more attention than ever before. digital relays operate according to accurate thresholds and precise setting values. in signal flow graphs of relays, the low-pass filter plays a crucial role in prefiltering and purifying waveforms performance estimating techniques to estimate the expected impedances, currents, voltage etc. the main process is conducted in the cpu through methods such as man and morrison, fourier, walsh-based techniques, least-square methods etc. to purify waveforms polluted with loworder harmonics, it is necessary to design and embed cutting frequency in a narrow band which would be costly. in this article, a technique is presented which is able to eliminate specified harmonics, noise and dc offset, attenuate whole harmonic order and hand low-pass filtered signals to cpu. the proposed method is evaluated by eight case studies and compared with first and second order low-pass filter. keywords-low-pass filter; power system protection; harmonics and noisy waveforms; moving average window (maw); central processing unit (cpu) i. introduction disturbances are a main power quality issue in power systems. voltage and current waveform distortions such as harmonics and noises are the main disturbances. distorted waveform might be originated by sources, appliances, and loads [1-4]. most of the harmonic sources such as power electronic converters, inject different levels of harmonics to the power grid. the harmonic sources can be divided into the following categories in a power grid [5-7]:  electrical machines (in point of physically distortion creation) and non-linear loads are defined as nonsemiconductor based harmonic sources.  motor control devices, hvdc power transmission system, facts systems, electrical vehicle and cyclo-converters in low-speed and high torque machines are called semiconductor based harmonic sources. as introduced in [8], adjustable speed driver (asd), capacitors, circuit breakers, fuses, conductors, lighting, meters, transformers, rotating machines, telephone interference and protective relaying are affected by harmonics distortion. international standards for power quality such as ieee519, iec 61000, and en 50160 established admissible harmonic levels and their emission limits [9-11]. a prior research on power system harmonics has been done in 1983 by an ieee working group [12]. along with 50 years of operational reports, the effect of harmonics has been categorized in some clauses. the 8th clause of this report points to relay malfunction by harmonics [5]. this topic is notable when the decision-making process depends on the rate of waveform distortion. this distortion affects the operating point of relays and consequently the decision-making system [13]. in protective relays, most of the measurement units determine the peak value and the zero crossing of the voltage and current waveforms. therefore, the harmonics can cause mis-operation of the microprocessorbased relays [14]. this issue has notably been investigated in case of power distribution system protection conducted on static under-frequency and over-current relays [15]. authors in [7, 16] presented analytical approaches based on relay characteristics and performed theoretical and experimental analysis to derive phase angles of low-order harmonics on the tripping time of overcurrent relays. harmonic order and amplitudes are determinant. authors in [17] indicated the effects of noisy electrical signals on digital relays and they proposed a filter capable of filtering selective harmonic components. a low-pass filter is a well known yet primitive approach to deal with power system harmonics. to eliminate low-order harmonics, low-pass filter with sharp cut-off frequency is required and that frequency should be set among the fundamental and the next order harmonics [1]. setting the cut-off frequency in a narrow frequency band makes the design complex. although the process of low-pass filter design is theoretically effortless, it is practically not economical in order to filter low order harmonics. any distortion may lead to unexpected relay operation. this fact is apparent especially in overcurrent relays [17, 19]. the fast operation of the relays is influenced by harmonic current which is less or more than nominal [20, 21]. this deviation is limited to 15%. in over current relays and with the presence of low-order harmonics, they can operate up to 60% faster than engineering, technology & applied science research vol. 7, no. 6, 2017, 2177-2183 2178 www.etasr.com khodabakhshi-javinani and askarian-abyaneh: evaluation of moving average window technique … normal and standard condition [22]. harmonics also have undeniable effects on frequency protection relays. in under frequency relays, the 10% thd, increases operating time twice. therefore, it is recommended to limit the harmonic pollution to 5% [23]. also, harmonics have a severe impact on differential relays. figure 1shows the basic components of the typical digital relay which lp filter situates after surge protective circuits although the prevalent low-pass filtering might be suitable for high-frequency harmonics, the performance and cost are considerable especially in filtering low-order harmonics [24]. there are many detection and calculation algorithms and techniques operated on filtereddiscrete waveforms to estimate operation territory such: mann & morrison method [25], rockefeller & udren technique [26], fourier and walsh-based technique [27, 28], least-square methods [29], differential equation technique and travellingwave-based methods but they are applied in central processing units (cpu) [30]. the moving average window (maw) technique is a numeric-mathematical based transform function to simulate the waveform with selective resolution. also, the averaging technique used to model discrete spaces to continuous one such as switches in converters [18]. in low pass filter design, setting sharp cutting frequency makes the design process complex and costly. the proposed method is an efficient technique to estimate signals with variable resolution. in this article, the maw technique in two schemes is compared with the common first and second order low-pass filters which are applied in protective relays. figure 1 describes maw embedded in the protective relay as a low-pass filter. the maw has the sampling frequency as the only tuning parameter and its response is comparable with the second order filter design with two tuning parameters. the design simplicity and the low computational burden is the two main advantages of the proposed method.  mann & morrison method,  rockefeller & udren technique,  fourier and walsh-based technique,  least-square methods,  differential equation technique  travelling-wave-based methods  first order  second order  moving averaging window (the proposed method) fig. 1. basic components of a digital relay and the situation of moving averaging window in filtering process. engineering, technology & applied science research vol. 7, no. 6, 2017, 2177-2183 2179 www.etasr.com khodabakhshi-javinani and askarian-abyaneh: evaluation of moving average window technique … ii. proposed method in order to design a conventional low-pass filter, the optimal tuning of a sharp and accurate cutoff frequency is required, something complicated and cost-effective in implementation. the moving averaged window (maw) technique can estimate the fundamental only through selecting a proper sampling frequency. a. moving average window many studies have been published on maw applications in signal processing and modeling scope. maw applications are summarized in the estimation of waveforms with various degree of resolution and rate of processing power [18]. the maw technique is capable of fault detection, direction estimation, and faulty phase identification [31-33]. this technique is less sensitive to noise for sampling frequency around the noise frequency. the proposed technique defines a transfer function in continuous time-domain mode. equation (1) shows maw transfer function wherein x(t) is under process waveform. ( )x t is averaged waveform along window length of ts. 1 ( ) ( ) s t t t s x t x d t      (1) the frequency response of (1) is shown in (2) which is the fourier transform of impulse response of (1) and is called lowpass filter frequently [31]. 2( ) sinc( ) 2 stj stx j e      (2) where sinc( )=sin( )/   , ts, and fs are sampling time and frequency respectively and fs defines the sampling/window length. the moving window is demonstrated in figure 2. figure 3 shows the maw‘s frequency response. in figure 3(a), ω frequency (nominal frequency) is rejected by the filter in π radian phase and other frequencies are attenuated except dc. selecting ts, the filter output can be zero at fs. as shown in figure 3(b), the filter’s phase response lags. the shown characteristic in amplitude and phase could lead up to article’s main purpose of the usage of maw as a low-pass filter. b. filter response to harmonic polluted signal by applying polluted waveform in (1) as the input variable, (3) is obtained, which shows mathematical-time domain of harmonically distorted signals with odd-order frequencies. 0 2 1 2 1 2 1 1 ( ) sin(2 ) n k k k k x t x x f t        (3) where, x1 is the fundamental frequency, x2k+1 and f2k+1 are oddharmonic order amplitude and frequencies, respectively and φ2k+1 is corresponded phase angle. applying (1) to (3), the averaged equation is derived as (4): 0 2 1 2 1 2 1 2 1 1 ( ) sin(2 ) n k k k k s k x t x a f t f t           (4) 2 1 2 1 2 1sinc( )k k k sa x f t   (5) where πf2k+1ts is phase lagging in filtered signal. in figure 4, the amplitudes of 13 harmonic orders are illustrated by different averaging window frequencies. in figure 4 we see that the amplitude of harmonics varies by sampling frequency. the main idea lies there. since high sampling frequency leads to the amplifying of harmonics order, in some frequencies, harmonic orders tend to be zero. the zero crossing frequencies are an integer multiple of each harmonic frequency. table i shows the amplitude of each zero-crossing frequency which plays an important role in maw philosophy. moving window 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-2 -1.5 -1 -0.5 0 0.5 1 1.5 2 ts time, sec a m pl itu de , p .u fig. 2. moving window applied to distorted input waveform containing harmonics and gaussian noise with variance 0.01 m ag ni tu de ph as e, d eg frequency, hz (a) (b) frequency, hz fig. 3. the proposed filter characteristics based on maw. (a) magnitude response. (b) phase response 0 200 400 600 800 1000 1200 1400 1600 1800 2000 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 sampling frequency, fs, hz amplitude p.u. fig. 4. the amplitude of response of maw by varying sampling frequency up to 13th harmonic order engineering, technology & applied science research vol. 7, no. 6, 2017, 2177-2183 2180 www.etasr.com khodabakhshi-javinani and askarian-abyaneh: evaluation of moving average window technique … in fact, averaging theory waived harmonic order which is swept with the corresponding frequency. in table i, by selecting 150 hz as maw sampling frequency, weakening the related harmonic order (3rd and 9th) is achieved. this fact is carried out on other harmonic orders. table ii shows the phase lagging of each selected sample frequency. as it can be derived from tables i and ii, by applying fs=150 hz, 300-degree phase lagging in fundamental and 17.32% decaying in magnitude are achieved. in section iv, two filtering strategies are discussed and the ability of maw would be evaluated in comparison with first and second order low-pass filter. table i. the amplitude of harmonic order in zero-crossing frequency harmonic order fs (hz) 1st 3rd 5th 7th 9th 11th 13th 150 0.827 0 0.1654 0.1181 0 0.0752 0.0636 250 0.9355 0.5045 0 0.2162 0.1039 0.085 0.1164 350 0.9667 0.7241 0.3484 0 0.1935 0.1974 0.0744 450 0.9798 0.827 0.5642 0.263 0 0.1674 0.217 550 0.9864 0.882 0.6931 0.455 0.2103 0 0.1456 650 0.9903 0.9146 0.7738 0.5868 0.3784 0.1748 0 table ii. phase lagging degree in applying maw with variable sampling frequency harmonic order fs (hz) 1st 3rd 5th 7th 9th 11th 13th 150 300 180 60 300 180 60 300 250 324 252 180 108 36 324 252 350 334.28 282.85 231.43 180 128.57 77.14 25.71 450 340 300 260 220 180 140 100 550 343.64 310.91 278.18 245.45 212.73 180 147.27 650 346.15 318.46 290.77 263.07 235.38 207.69 180 iii. simulation and result a. dc offset elimination according to figure 3 and to the frequency response of maw, the dc component is amplified to 100%. the maw technique is capable of eliminating dc offset of input waveforms easily through surviving maw in fundamental frequency. figure 5 shows the process of dc offset elimination which is proposed by maw with a fundamental frequency sweep, e.g. fs=50 hz, dc offset totally removed. maw fs=50 hz + _ inputs dc offset dc eliminated inputs fig. 5. proposed method for eliminating of dc offset on input waveforms before the main filtering b. sampling frequency, fs sampling frequency has a crucial role in estimating fundamental waveform and harmonic’s content. the sampling frequency is obtained by inherent characteristics of local harmonic properties. in order to filter the harmonic polluted waveforms, two harmonic elimination strategies are defined. figure 6 shows the flowchart in explanation of these strategies. as it shows, the fs has a key role in this filtering process. 1) selective harmonic elimination due to selective harmonic order elimination, it is enough to select corresponding harmonic frequency as the sampling frequency. table i illustrates selective harmonic scheme. 2) general harmonic attenuation as it can be derived from table i, by selecting fs=150 hz, the harmonic reduction is started with the aim of maximum elimination of 3rd harmonic order. this strategy is defined as selective harmonic weakening by concentration on 3rd harmonic order elimination. in general harmonic attenuation strategy, the objective function sets on achieving minimum thd. in this strategy, fs tunes to minimize output thd by applying maw. 3) maw technique evaluation in order to prove maw sufficiency, the simulation is performed by comparing two conventional low-pass filters and maw. table iii shows 8 case studies of polluted waveforms. the first two cases of table iii present the most common harmonic existence with notable amplitude in the power system. the thd would be considered as a criterion pollution rate [32, 33]. the simulation was performed on first order low-pass filter (lpf-1), second order low-pass filter (lpf-2), maw-general, and maw-selective. table iv presents the result of filtered case studies which have been introduced in table iii. the first two columns are the result of the first and second order traditional low-pass filter. these filter characteristics are given in appendix. the last two columns result applied general and selective maw to these case studies. methodologies have been discussed in section iv. according to first order filtering results in case 1, the thd decreases from 60.21% to 23.99% and fundamental weakens from 100% to 71%. the second order low-pass filter is set on high-quality factors and the full amount of fundamental amplitude. two parameters (ωc, ξ) should be set and therefore, two poles add to system transfer function order level. the result shows that by applying second order lpf, fundamental is kept to 100% and thd factor decreased to 5.98%. filtering with maw-general strategy has been done by setting fs=144 hz to achieve minimum thd. in the case of presence of various harmonic orders, the general maw suggested for general decreasing harmonic content. in addition, table iv shows the ability of maw technique in both general and selective harmonic decaying. the result is that maw has the best performance in comparison to traditional low-pass filtering methods. as for the various order of harmonics, the maw-general scheme results better than maw -selective. similarly, in the polluted waveform with specific harmonic order, the maw-selective has the best performance. figure 7 illustrates the effect of lpf1, lpf2, maw-general and maw-selective on case 1. fft analysis is calculated with transient-free waveforms through thd, tihd and tshd. engineering, technology & applied science research vol. 7, no. 6, 2017, 2177-2183 2181 www.etasr.com khodabakhshi-javinani and askarian-abyaneh: evaluation of moving average window technique … strategies and fs determination maw fs filtered waveform amplitude dc offset elimination + _ maw 50 hz is strategy selective? fs fs=144hz yes no phase-shifting calculation start input waveform output decision symbol output symbol process symbol manual input symbol merge symbol merging amplitude and phase fig. 6. proposed technique flowchart table iii. 8 case studies evaluating by may technique fundamental 3rd 5th 7th 9th 11th 13th thd c as es 1 100% 50% 30% 10% 8% 6% 5% 60.21% 2 100% 50% 50% 10% 0 0 0 71.41% 3 100% 50% 0 0 0 0 0 50% 4 100% 0 30% 0 0 0 0 30% 5 100% 0 0 30% 0 0 0 30% 6 100% 0 0 0 30% 0 0 30% 7 100% 0 0 0 0 30% 0 30% 8 100% 0 0 0 0 0 30% 30% iv. conclusion the signal processing of digital relays has mainly focused on algorithms to find out and estimate the operation criteria. many techniques and methods have been proposed. it is clear that pre-filtering produces better results when using a low-pass filter. the design of sharp cutting frequency among fundamental and first harmonic order, causes complexity and cost. therefore the moving average window was proposed to eliminate dc offset, noise and attenuate harmonic content. the proposed technique could satisfyingly substitute the traditional first and second order low-pass filter. the evaluation test was done in 8 case studies and the results are tabulated and illustrated. the maw has the ability to eliminate specified harmonic order or attenuate whole harmonic order. thus, two filtering strategies are defined and verified with the 8 case studies. low computational burden and only one tuning parameter (fs) are two main advantages of maw. table iv. result of 8 case studies filtering by 4 strategies: lpf-1, lpf-2, maw-general and maw selective lpf-1 (%) lpf-2 (%) maw-general (%) maw-selective (%) fund. 3rd 5th thd fund. 3rd 5th thd fund. 3rd 5th thd fund. 3rd 5th thd c as es 1 71 16 6 23.99 100 5.85 1.22 5.98 fs=144 hz fs=150 hz 82.7 0 4.97 6.2 81.315 1.994 4.05 5.81 fs=250 hz 93.55 25.23 0 27.09 2 71 16 10 26.39 100 5.85 2.04 6.20 fs=136 hz fs=150 hz 82.7 0 8.27 10.1 79.20 4.58 4.21 8 fs=250 hz 93.54 25.22 0 27.06 3 71 16 0 22.36 100 5.85 0 5.85 82.7 0 0 0 82.7 0 0 0 4 71 0 6 8.32 100 0 1.22 1.22 93.55 0 0 0 93.55 0 0 0 5 71 0 0 6 100 0 0 0.62 96.67 0 0 0 96.67 0 0 0 6 71 0 0 4.69 100 0 0 0.37 97.98 0 0 0 97.98 0 0 0 7 71 0 0 3.84 100 0 0 0.25 98.64 0 0 0 98.64 0 0 0 8 71 0 0 3.25 100 0 0 0.18 99.03 0 0 0 99.03 0 0 0 engineering, technology & applied science research vol. 7, no. 6, 2017, 2177-2183 2182 www.etasr.com khodabakhshi-javinani and askarian-abyaneh: evaluation of moving average window technique … a 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0 5 10 15 20 25 30 0 0.2 0.4 0.6 0.8 1 thd% = 60.2084 tihd% = 0.046798 tshd% = 0.011681 -1.5 -1 -0.5 0 0.5 1 1.5 b -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 0 5 10 15 20 25 30 0 0.2 0.4 0.6 0.8 thd% = 23.9932 tihd% = 0.023194 tshd% = 0.023993 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 c -2 -1 0 1 2 -2 -1 0 1 2 0 5 10 15 20 25 30 0 0.5 1 thd% = 5.9823 tihd% = 0.42009 tshd% = 0.77405 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 d -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 0 5 10 15 20 25 300 0.5 1 thd% = 5.814 tihd% = 1.5935e-13 tshd% = 3.1673e-13 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 f -1 -0.5 0 0.5 1 -1 -0.5 0 0.5 1 0 5 10 15 20 25 30 0 0.5 1 thd% = 27.0933 tihd% = 2.272e-13 tshd% = 2.7745e-13 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 fig. 7. simulation result of case 1: (a) original waveform (b) lpf1 waveform both original and without transient-free waveform (c) lpf2 waveform both original and transient-free waveform (d) maw-general with fs=144 hz both original and transient-free waveform (e) maw-selective with fs=150 hz both original and transient-free waveform (f) maw-selective with fs=250 hz both original and transient-free wavefor appendix first order low-pass filter 1 ( ) 1 c h s 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“transmission-line protection: a directional comparison scheme using the average of superimposed components”, ieee transactions on power delivery, vol. 28, no. 2, pp. 955-964, 2013 [33] a. k. pradhan, a. routray, s. r. mohanty, “a moving sum approach for fault detection of power systems”, electric power components and systems, vol. 34, no. 4, pp. 385-399, 2006 engineering, technology & applied science research vol. 7, no. 3, 2017, 1708-1712 1708 www.etasr.com soni and shah: qos frameworks for multimedia traffic in mobile adhoc networks: a comparative review qos frameworks for multimedia traffic in mobile adhoc networks: a comparative review sunil soni computer engineering dpt marwadi education foundation, india and faculty of technology, r.k. university, india profsjsoni@gmail.com j. s. shah government engineering college gujarat, india jssld@yahoo.com abstract—manets (mobile adhoc networks) has gained an increased interest by the research community. regular intelligent exchanges of multimedia will be typical in manet, though the extended motivation on qos (quality of service). however, various properties of the discussed qos framework are provisioned for qos as a challenging concern. providing qos provisioning is, to a great degree, challenging in manets in view of bouncing correspondences, center point movability and nonattendance of central coordination. thus, most of the research has focused on giving qos guarantees in manets coordinating traditions. though huge numbers of qos coordinating procedures have been proposed in composing, focusing on different qos estimations yet none of the prescribed or discussed frameworks achieves a universal course of action. there exist several genuine necessary research areas of focus such as qos metric assurance and cost limit layout, source level scheduling framework and qos coordinating. in this paper, working and connecting of various qos frameworks for manets is investigated throughout several veritable focus areas of research. after a comparative review, it is concluded that there is still a good scope of research for proposing a qos framework for manets which could have cross-layer advantages, resource reservation, connection admission control, multi-constrained qos parameters, hard qos assurance, proactive routing advantages etc. keywords-manet; qos; framework; olsr; routing protocols; multimedia traffic; admission control; resource reservation i. introduction the major focus area of research in the field of mobile adhoc networks (manets) has been to solve the issues surrounding data exchanges. in recent times, extraordinary extension of two major areas namely manet routing protocol and qos have been thoroughly investigated. various routing methodologies for remote systems, namely dsr (dynamic source routing) and aodv (adhoc on-demand distance vector) uses best effort routing. in this technique all the nodes under certain given degree compete for the common medium. no protections or figures can be given here on when a node is allowed to send, this is sufficient to simply find a course from a source to one or different goals of qos routing, these routes furthermore need to satisfy at least one qos impediments. to guarantee these restrictions after a course was found, resource reservations on the taking intrigue hubs are made. initially, when manet change started, qos was not the first priority. that was the reason for best effort routing models became apparent. gradually, with the development of huge numbers of time-sensitive applications, qos has become more basic and then ever, prompting to a development of various research excitements from best effort routing to qos based routing. other than the quality parameter in manet, it also assures a testing mechanism. this mechanism is a direct result of the dynamic topology, limited information exchange limit and essentialness basic. manets are of need of a gigantic change in the structure; the frameworks which are used for wired networks cannot be mapped completely to manet framework. the way has to be found by the routing mechanism which satisfies the qos parameter at the beginning of a session. and this parameter is required to act according to desired output. however, a universally accepted course of action is yet to be described. for comparisons sake, the best metric would be using cross-layer arranges, multi-restrictions routing metric whereas multicast routing based on qos can be also explored for further future research directions. though manet has been making various multimedia exchanges, there exists a vast amount of qos (quality of service) parameters to be considered. regardless, various characteristics of manet make qos provisioning a troublesome issue. as compared to conventional wired networks giving qos accreditations is incredibly troublesome and testing in manet, because of multi-hop interchanges, dispute for channel access and several issues such as node portability. in any case, in the latest several recent years, more research thought has focused on giving qos guarantees in manet directing traditions. ii. review of qos routing proposals major and eminent routing algorithms e.g. olsr (optimized link state routing) [1] and aodv (adhoc ondemand distance vector) protocols have been discussed for qos provisioning in [4]. this protocol has chief advantages that it detects the accessible situation of the connection. feasibility to extend the qos data in protocol form in such a way that the each different hosts thinks about it ahead of time about the nature of the recommended route. due to the reactive engineering, technology & applied science research vol. 7, no. 3, 2017, 1708-1712 1709 www.etasr.com soni and shah: qos frameworks for multimedia traffic in mobile adhoc networks: a comparative review nature of aodv, it lacks the functionality mentioned above. the olsr protocol performs the best in high density traffic. regardless, the best situation is the time when we have a significant number of hosts. quality metric can be also extended in olsr protocol. as stated in [5 – 7], novel olsr (optimized link state routing) is outperformed by olsr-md (minimum delay) and olsr-etx (estimated transmission time). olsr-md [5] and olsr-etx [5] can be used to overcome drawbacks connected to olsr (novel) namely low bandwidth and throughput. the above mentioned protocols have the advantages that they have extended packet size to go with minimum delay that perform better under any given scenario. apart from default mpr (multipoint relay), many similar modifications can be made in olsr [1]. qos optimization can be introduced in olsr routing protocols. components like grouping might be converged with olsr compared to preferring mpr. in [9], authors presented an adept metric than the hop distance which states olsr (optimized link state routing) in terms of qos. there exist various measurements which are discussed for including qos parameters in olsr protocol [2] and exclusively considered metric for manet, delay and bandwidth criteria as compared to hop distance count algorithm. in like manner, admission control is associated in each mpr. in [10], authors suggested the cac (connection admission control) – olsr to ensure all action streams with necessities of qos. this seems to work especially well for video and voice tjat are just yielded in the mesh system. it has shown that the affirmation control instrument for multi-hop remote work frameworks considering the endorsed standard and the olsr coordinates tradition. requirements of qos which cannot be disregarded such already conceded activity streams. as part of future work, cac-olsr will be completed in work switches remembering the true objective to be evaluated in a bona fide framework. also, adaptability ought to be explored in a circumstance with incalculable hubs and streams, and the segments direct with hub portability. the future work approach may include the channel occupancy metric and estimation criteria. in [13], authors proposed a cross-layer design (cld) approach in olsr protocol with a specific end goal. proposed here is a strategy in perspective where a cross layer plan is implemented. this is done in order to revamp the whole execution of olsr [8] by using ber (bit error rate) which is a mix between the association accessibility and breaking point. in the proposed heuristic estimation, the technique is to find the propelled route similarly mostly vital subjective ci (cumulative index) and slightest ber with a particular true objective to upgrade working of mpr (multipoint relay) assurance count and course computation. a system which is given is directly inbound to olsr protocol. here it is not considering reservation signaling, connection admission control, stream classifier considerations that are very basics of trade of essential information. any current qos structure can be used with the proposed architecture to give outstandingly strict qos provisioning. in [14], authors presented the strategy which is suggested majorly reflects on upon significance of two differing need levels for development streams: best effort level and other are being high effort level. the suggested framework in which a center point can isolate among action streams with different need levels by dispensing them assorted ways towards a similar goal. the approach which is presented, suggests a procedure works with two tables: drt (dedicated routing table) and srt (standard routing table) which will redirect the data movement streams. qolsr (quality optimized link state routing) which means qos development of olsr protocol [2] is considered for alter as opposed to basic olsr protocol. proposed arrangement found simply constrained to the qolsr convention, it’s additionally not countering cac (connection admission control), reservation signaling, stream classifier ideas that are extremely vital for the qos information exchange. the observations are not contrasted. in [15], authors found that a perfect way might not always be the shortest or quickest way and considering the system outline, diverse decisions, for instance, a highly dynamic path of huge data transmission might be prevalent intrigue. to get such decisions and upgrade the relative quality between ending customers, makers suggested to execute at each center point an evaluation of the transfer speed tender among each adjacent center point and tends to ensure the decision of a route with the help of each multi point relays which give a greater transmission capacity en route. the transfer speed offer estimation on each association relies on upon the examination of dispute outlines to induce the course of action of maximal cadres. after transmission capacity estimated instead of choosing the congest among the given route, makers endeavor to find the way that ensures the most imperative transfer speed. the discussed arrangement concentrates on data transfer capacity estimation at every hub for discovering high transmission capacity ways, however defer limitation is not considered. also reservation signaling, cac (connection admission control), flow classifier which are really important in the given perspective. in [16], authors discussed about coordinating qos using olsr (optimized link state routing) by enhancing the mpr (multipoint relay) decision criteria. also qos focused on end to end delay and effective transmission speed, another figuring has been proposed. considering the qos requirements, the proposed figuring picks the perfect route from source to goal. not under any condition like selecting the mpr considering singular qos estimations, the figuring considers both effective transmission capacity and ending points postpone through the technique to map them on lone estimations. different criteria are used to make a lone estimation. the given course of action does not involve cac (connection admission control), stream separation and reservation signaling thoughts that are uncommonly fundamental for the qos data trade. in [17], authors proposed qos with cross-layering in terms of the clq-olsr (cross layer quality optimized link state routing) which increases the profitably abusing multi-radio and multi-channel strategy by reinforcing sound correspondence mechanism and steady sight. authors have arranged two game plans of coordinating segments: physically changed m-olsr (physical modified optimized link state routing) [17] and predictable controlling, to suit organize development. none of the above recommendations oversee stipulation of advantages, channel resources and cross layering outline for engineering, technology & applied science research vol. 7, no. 3, 2017, 1708-1712 1710 www.etasr.com soni and shah: qos frameworks for multimedia traffic in mobile adhoc networks: a comparative review manets. so it is indeed requirement of qos structure that can be effectively relevant to whichever convention and additionally gives qos parts like cross layering, stream classifier, reservation signaling, and connection admission control and so on. iii. review of qos framework proposals the versatility associated with manet also increases the viabilities such as continually hinting at a topology level, stumpy medium nature. contradictory to this, the target applications where manets are desired to acknowledge will have high relevance (e.g. military applications, emergency networks, several commercial applications, academics applications etc.). all of these have an incredibly strict need of quality media. it is this need and requirement which lets the qos parameters and frameworks as the most desired in manet. complexities are truly subject to unremitting changes and assortments in order to oversee qos as per following:  in customary wired systems, wired connection limit is constant. while if there should arise an occurrence of manet remote connection limit not at all steady among hubs. it is fluctuating along time in view of incessant alter in physical layer (e.g. because of versatility, updates in neighborhood situations). presently as qos related real world applications requires some amount of guaranteed data transfer capacity for transferring data (e.g. to get postpone or transfer speed imperatives), that can bring about brief administration interference for qos applications.  in manets, remote mobile nodes go after assets with their neighbor hubs. so multi-hop correspondence which is regularly utilized for broadcasting as a part of manets will expend a great deal more accessible system limit that in the customary wired system.  in manets, the portability of nodes likewise includes and facilitate many-sided quality at the directing layer. here alongside the issue of varieties in the accessible transmission capacity, there are different issues also like if there should arise an occurrence of connection breakages information ought to be rerouted through different ways. qos applications running on the system is needed at a specific qos level (e.g. distinct postponement or transfer speed imperatives), information ought to be rerouted in a very much coordinated way and additionally it ought to take after same transmission capacity prerequisites concurred at the beginning application time. it is possible that qos in manets needs data transfer capacity accessible at one moment, while a moment later it may be unrealistic for the system to offer the required measure of transmission capacity. accordingly, congestion may happen effortlessly which can bring about additional bundle misfortune due to end to end delays. any arrangement characterized will by one means or another requirement to think these challenges into the record. in [18], authors proposed the insignia (in-band signaling with admission control) framework which is an ip-based behavior of central structure which sponsorships adaptable administration ways in manet have been talked about by creators which shown the blueprint, use, and evaluation of insignia [18]. a framework relies on upon an in-band hailing and sensitive state resource organization way which is suitable for supporting adaptability and ending point nature of organization in significantly active circumstances where a system topology, center point accessibility, and ending points qos is time variant. creators in like manner gave organize layer game plan which is free of the mac (medium access control) layer. the hailing information related to the qos framework is typified in data groups, making this technique basic and "lightweight". in any case, the key drawback of suggestion is it’s created explicitly for static adhoc networks with no flexibility and it is not oversee reservation of advantages. in [19], authors have suggested the instigated approach swan (service differentiation in stateless wireless adhoc networks) where a stateless system demonstrate that involves disseminated control computations to pass on organization division in flexible remote exceptionally selected systems in a direct, versatile and lively way. they have used rate regulation for tcp (transmission control protocol) and udp (user datagram protocol) best-effort movement, and source based confirmation control of udp steady action. swan [19] uses unambiguous stop up the notice to dynamically coordinate surrendered continuous action despite system stream brought on by adaptability or development overweight conditions. a novel piece of swan is that it needn't bother with the assistance of a qos-skilled mac. then again perhaps, sensitive steady organizations are built using obtainable best effort distant mac development. swan uses cross layering arrangement that utilizes system and connection layers data and it depends on diffserv thought of conventional wired systems. the fundamental issue of swan is that it is not managing reservation of assets that is really a pivotal part of qos related steering. in [20], authors proposed to keep qos a logically developing in manets. as the huge amount of data is transferred and progressing through various applications during the transmission. a manet is a connection-less system in which the parameters like limited amount of resources, flexibility which impacts qos. as a reply, prtmac (proactive real time medium access control) was presented [20] tradition which somehow assures to provide qos to the extent delay, throughput. it also does support qos with benefit reservation instrument. once the advantages are spared, center points get tip top access on the benefit. proposed strategy concentrates on extremely specific mac conventions. so it would require significant changes if there should be an occurrence of applying it on other directing conventions. in [11] another qos structure was proposed named brawn (bandwidth reservation over adhoc network). the discussed idea is to permit end to end reservation of data transfer capacity in a specially appointed remote system. reservation of resources is on demand, at any given point of time an end node begins an application with particular need of qos, this application should team up with the reservation flagging module. also the prescribed inward design of the given system known as brawn [11] has connections between the diverse engineering, technology & applied science research vol. 7, no. 3, 2017, 1708-1712 1711 www.etasr.com soni and shah: qos frameworks for multimedia traffic in mobile adhoc networks: a comparative review modules for setting up a qos parameter. as seen with several applications qos requests know about the operation of the convention and demand the assets through the reservation signaling module. basic constraints faced in brawn (bandwidth reservation over adhoc network):  due to the primary nature of brawn design, it focuses only on adhoc networks. mobility and versatility challenges are not covered. so portability should be tended to. but as we go along, “mobility” will present a few new difficulties for brawn that we should manage fittingly. it is because of the fact that the always showing signs of change system topology may bring about varieties of the accessible transfer speed or surprisingly more terrible there is the likelihood that a connection breaks influences at least one qos routes.  brawn works absolutely on the network layer, with the goal that we could not have the capacity to exploit the data from the lower layers. so cross-layer configuration could be proposed for in any event data trade between mac (medium access control) layer and network layers.  up gradations of internal working of resource reservation and admission control can be performed.  compared to mac (medium access control) using rts (request to send) / cts (clear to send), pure csma (carrier sense multiple access) protocol is used which eases the various computations and bandwidth estimations.  also, in-band signaling protocol as an alternative can be used for the explicitly signal out-bands reservation. iv. a comparative review of qos frameworks table i shows the most popular qos design frameworks and their comparative review for qos in manets. table i shows the details, review points and scope of improvement for each respective qos framework. from table i, it is easy to understand that no particular qos framework is capable of fully assuring today’s real/non real time multimedia traffic flows in manet. so as a future work, a qos framework for manet should be proposed by considering factors like crosslayer advantages, resource reservation, connection admission control (cac), multi-constrained qos parameters, hard qos assurance and proactive routing advantages. the following observations are made after careful review of each framework. authors also believe that following observations are important for further research to design a new qos framework specifically for multimedia traffic in manet.  insignia can be extended for mobility issue in manet. in order to tackle multimedia traffic handsomely some features e.g resource reservation, cac could be added further in future work.  swan is basically a cross layer design which can be extended further by incorporating it with proactive routing protocol (e.g. olsr) to get maximum benefit of crosslayered information and to support multi-constrained qos parameters. also resource reservation, cac could be added further.  prtmac can be improved further by incorporating it with network layer. it can also been incorporated with proactive routing protocol.  brawn can be worked on in future for dynamic mobile network (mobility) as it is just proposed and fitted for the static networks. there is no arrangement for checking delay estimation. it is single constraint architecture; not a multiconstraint one. it can be likewise improved for versatility perspective too. so there is a decent extent of research for amplifying its segments for offering almost hard qos ensures in manet where nodes are widespread or versatile. table i. a comparative review of qos frameworks qos framework features review points scope of improveme nt in-band signaling support for qos in mobile adhoc networks (insignia) [18] network layer arrangement or independent of the mac layer with the qos component is embodied in information parcels, making it easy, simple and also lightweight 1. designed explicitly for adhoc wireless networks 2. reservation of resources or mobility issues are not considered it can be extended for mobility and resource reservation stateless wireless ad hoc networks (swan) [19] cross-layer solution (network and link layers). it is based on the diffserv idea reservation of resources is not considered it can be extended for mobility and resource reservation proactive realtime mac (prtmac) [20] focused on very particular mac protocols reservation of resources is not considered it can be extended for any routing based (network layer) protocol bandwidth reservation for ad-hoc wireless networks (brawn) [11] reservation signaling module/ connection admission control/ endto-end reservation of bandwidth/ cac prevents congestion in the network 1. best suited for multimedia traffic where qos is very important criteria 2. best suited for olsr integration 3. it does not support multiconstraint qos parameters mobility and scalability can be also analyzed. cross layering can be added further. it can be also extended for multiconstraint qos parameters v. conclusion the objective of this paper is to review the currently wellknown qos routing mechanisms/architectures and qos engineering, technology & applied science research vol. 7, no. 3, 2017, 1708-1712 1712 www.etasr.com soni and shah: qos frameworks for multimedia traffic in mobile adhoc networks: a comparative review frameworks specifically for multimedia traffic in manets. two broad categories of qos solutions are reviewed. first the qos solutions which are specifically depended on routing protocol in terms of new hop selection based on the qos parameters. then, qos solutions provided by some specific design frameworks with integration of various modules and applicable on any routing protocol with minor changes. after a comparative review of various qos frameworks, it is concluded that there is still a good scope of research for proposing a qos framework for manets (specifically for multimedia traffic) which could have cross-layer advantages, resource reservation, connection admission control, multiconstrained qos parameters, hard qos assurance, proactive routing advantages etc. as a future work, one should focuse on designing a qos framework for multimedia traffic in manets by exploiting cross-layering (network and data-link layer information exchange) and use of proactive routing protocol (e.g. olsr) with resource reservation and connection admission as a separate modules. along with this, flow classifier can be also added to classify non-multimedia and multimedia data from application layer itself. references [1] t. clausen, p. jacquet, rfc 3626: optimized link state routing protocol (olsr), 2003 [2] a. tonnesen, implementing and extending the optimized link state routing protocol, msc thesis, university of oslo, 2004 [3] y. ge, quality-of-service routing in ad-hoc networks using olsr, msc thesis, carleton university, 2002 [4] a. huhtonen, “comparing aodv and olsr routing protocols”, hut t-110.551 seminar on internetworking, sjökulla, 2004 [5] a. pandey, m. baliyan, “performance analysis of olsr and modified version of olsr-etx/md/ml in mesh networks”, international journal of computer science & communication networks, vol. 2, no. 2, pp. 268-271, 2012 [6] d. passos, d. teixeira, “mesh network performance measurements”, 5th international information and telecommunication technologies symposium, 2006 [7] d. de couto, d. aguayo, “a high throughput path metric for multihop wireless routing”, mobicom ’03, usa, 2003 [8] p. jacquet, t. clausen, a. laouiti, a. quyyum, l. viennot, “optimized link state routing protocol for ad hoc networks”, ieee inmic 2001, international multi topic conference, pakistan, 30-30 dec. 2001 [9] a. munaretto, h. badis, a. agha, “a link-state qos routing protocol for ad hoc networks”, 4th international workshop on mobile and wireless communications network, sweden, 9-11 sept. 2002 [10] e. mineiro, d. muchaluat-saade, “admission control for qos provision in wireless mesh networks”, 2012 ieee symposium on computers and communications (iscc), turkey, 1-4 july 2012 [11] r. guimaraes, quality of service on ad-hoc wireless networks, phd thesis, universitat politècnica de catalunya, spain, 2008 [12] b. a. mohan, h. sarojadevi, “study of scalability issue in optimized link state routing (olsr) protocol”, international journal of advanced technology & engineering research, vol. 2, no. 4, pp. 4044, 2012 [13] t. sanguankotchakorn, s. k. wijayasekara, n. sugino, “a cross-layer design approach in olsr manet using ber and weighted connectivity index”, 19th ieee international conference on networks (icon), singapore, 11-13 dec. 2013 [14] g. rigazzi, v. palma, g.tamea, f. santucci, a. neri, “a cross-layer routing protocol with quality of service support for flexible deployment in manets”, 2012 ieee globecom workshops (gc wkshps), pp. 508-512, usa, 3-7 dec. 2012 [15] d. moad, s. djahel, f. n. abdesselam, “improving the quality of service routing in olsr protocol”, 2012 international conference on communications and information technology (iccit), tunisia, 26-28 june 2012 [16] s. banik, b. roy, b. saha, n. chaki, “design of qos routing framework based on olsr protocol”, 2010 international conference on advances in recent technologies in communication and computing (artcom), india, 16-17 oct. 2010 [17] y. peng, l. guo, q. gai, “cross-layer qos-aware routing protocol for multi-radio multi-channel wireless mesh networks”, ieee 14th international conference on communication technology (icct), china, 9-11 nov. 2012 [18] s. b. lee, g. s. ahn, x. zhang, a. t. campbell, “insignia: an ipbased quality of service framework for mobile ad hoc networks”, journal of parallel and distributed computing, vol. 60, pp. 374-406, 2000 [19] g. s. ahn, a. t. campbell, a. veres, l. h. sun, “swan: service differentiation in stateless wireless ad hoc networks”, twenty-first annual joint conference of the ieee computer and communications societies infocom 2002, usa, 23-27 june 2002 [20] g. u. devi, g. kavitha, “resource reservation using prtmac protocol in manet”, international journal of computer networks and wireless communications, vol. 2, no. 3, pp. 328-334, 2012 engineering, technology & applied science research vol. 7, no. 6, 2017, 2104-2108 2104 www.etasr.com perisic et al.: a frequency multiplier based on time recursive processing a frequency multiplier based on time recursive processing djurdje m. perisic faculty of information technology slobomir p university (spu) slobomir, republic of srpska, bih djurdje@beotel.rs aleksandar zoric faculty of technical science university of kosovska mitrovica kosovska mitrovica, serbia acazoric@yahoo.com zeljko gavric faculty of information technology slobomir p university (spu) slobomir, republic of srpska, bih zeljko.gavric@spu.ba abstract—this paper describes a digital frequency multiplier for a pulse rate. the multiplier is based on the recursive processing of the input and output periods and their time differences. special emphasis is devoted to the techniques which provide the development of multipliers based on this principle. the circuit is defined by two system parameters. one is the ratio of two clock frequencies and the other is a division factor of a binary counter. the realization of the circuit is described. the region of the system parameters for the stable circuit is presented. the different aspects of applications and limitations in realization of the circuit are considered. all mathematical analyses are made using a z transform approach. it is shown that the circuit can be also used in tracking and prediction applications. computer simulations are performed to prove the correctness of the math and the whole approach. keywords-frequency multiplier; digital circuit; pll; fll i. introduction the time recursive processing (trp) approach is based on the measurement and processing of the input and output periods and the time differences between them. as stated in [110], this approach is suitable for the development of different kinds of trp phase locked loops (trp pll) and trp frequency locked loops (trp fll), which possess some new additional properties in comparison to the classic pll and fll. due to these new properties, the development of new kinds of circuits and applications is provided. the classic pll and fll might be roughly divided into analog, hybrid and digital ones. all of them are frequency based systems, their frequency and phase are physically interconnected with time. due to this close interdependence, new kind of trp circuits can be described using the period instead of the frequency and changing the phase by the time difference between the input and output signals. in order to describe trp circuits, recursive equations, in form of linear discrete system, are used, providing a new approach to description, analysis, realization and applications. unlike the classic pll, which generates the output signal always in phase with the input signal, trp pll is able to provide very precise control time and phase shifting [1]. power time shifters are further described in [2, 3]. the technique used for the realization of trp pll and trp fll is applied for the realization of frequency synthesizers in [4]. the applications of trp pll and trp fll for noise rejection are described in [5-7]. a wide range of tracking and prediction applications is described in [5, 6, 8]. most of the algorithms described in [1-10] are suitable for usage in a software form. all electronics trp applications can be realized in a software form that can be applied anywhere. all that is necessary is to determine the corresponding analogy between trp electronics variables and the corresponding ones, relating to another field. such a software predictor is described in [9]. very complex systems, consisting of a lot of subsystems, can also function as a fll, whose realization is based on the same trp technique [10]. it is well known that a frequency multiplier can be realized by classic pll or fll, just by using a counter in a feedback connection. the factor of frequency multiplication, in such solutions, is equal to the division factor of the counter. in this article the mentioned principle of the frequency multiplication is applied to one suitable trp pll model. the analysis specifics in the realization and application of this approach are presented. the results obtained can be applied to any type of trp pll or trp fll. ii. mathematical description of the circuit one general case of the time relation between an input signal sin and an output signal sop of the circuit is shown in figure 1. the periods ti0, ti1,….tik, tik+1, and to0, to1,….tok, tok+1, as well as the time differences 0, 1, 2…..k, k+1, occur at discrete times respectively t0, t1, t2,…..tk, tk+1. the discrete times t0, t1, t2,….tk, tk+1 are defined by the falling edges of the pulses of sop in figure 1. note that, unlike the classic pll, all variables are distributed in time in figure 1. the natural recursive relation (1), between the variables, yields from figure 1. it was supposed that the time difference  is positive if the input signal leads the output signal. correspondingly, in case that the output signal leads, time difference  will take the negative value through the analysis. let us start analyzing the main algorithm of the circuit which is presented by (2), where m and q are the system parameters. we will see later on that the part tok+1=tik+mk+1 of (2) represents trp pll for its self. if trp pll is in the stable state, the output to is equal to the input ti. the parameter q in (2) represents the division factor, which can be, generally, less or greater than one. the idea is to generate the output engineering, technology & applied science research vol. 7, no. 6, 2017, 2104-2108 2105 www.etasr.com perisic et al.: a frequency multiplier based on time recursive processing period/frequency which is q times less/greater, so that after division by q, the circuit generates the output period which is equal to the input period. it is expected, guided by the known principles in the realization of the frequency multipliers by the conventional pll, that the period/frequency before the division should be q times less/greater than the input period/frequency. however, the circuit does not behave according to the expectations. the following analysis will discover the proper functioning way of the circuit, described by (2), as well as the techniques which will enable the circuit to function as a frequency multiplier. 1k k k kti to     (1) 1 1 k k k ti m to q       (2) fig. 1. time relations between all variables of the circuit according to (1) and (2), the circuit has two output variables, which depend on tik. the output variables are (k+1)=f[ti(k)] and to(k+1)=f[ti(k)]. note that, because of simplicity, to(k), ti(k) and (k) are denoted in the article as tok, tik and k. it is now necessary to find out the z transform of the output variables (k+1) and to(k+1) in order to analyze the properties of the circuit described. the z transform of (1) and (2) are given by (3) and (4) respectively. time constants to0 and 0 are the initial values of the output variables to(k) and (k), which appear at discrete time t0 = 0. 0( ) ( ) ( ) ( )z z z z ti z to z        (3)  0 0 ( ) ( ) ( ) ti z z z z m zto z zto q       (4) calculating (z) from (3) and changing it into (4), it can be found out: 0 0 m z z 1 1 z( ) (z 1) z ( ) ( ) z(z 1 / ) z(z 1 / ) m to z q q q q to ti m q m q           (5) in the same way, changing to(z) from (5) to (3), can be calculated: 0 0 ( / )1 / ( ) ( ) z(z 1 / ) z(z 1 / ) to z z m qz q z ti z m q m q             (6) two transfer functions, presented by (7) and (8), describe the output variables of the circuit in dependence on the input period. they are defined from (5) and (6) respectively. ( ) z( / 1 / ) 1 / ( ) ( ) z(z 1 / ) to to z m q q q h z ti z m q       (7) ( ) 1 / ( ) ( ) z(z 1 / ) z z q h z ti z m q        (8) step analysis will discover the properties of the circuit described. let us suppose that the step function, ti(k)=ti=const., is applied to the input. if we change the z transforms ti(z)=ti·z/(z-1) into (5) and (6), we will get the z transform of the output variables for this input. changing ti(z) into (5) and using the final value theorem, it is possible to find the final value of the output period in the time domain as to=lim[to(k)] if k, using to(z), as shown in (9). applying (9), to is calculated and shown in (10). to complete the information about the system properties, it is necessary to determine ∞, i.e. the final value of (k). if ti(z) are substituted into (6), using the final value theorem in the same way like for to, ∞ can be determined using (11). applying (11), ∞ is calculated and shown in (12). 1lim[( 1) ( )]zto z to z    (9) lim[ ( )]kto to k ti   (10) 1lim ( ) lim[( 1) ( )]k zk z z        (11) ( 1) /ti q m    (12) the expressions (10) and (12) are valued only if the circuit is the stable system i.e. if |z1|<1 and |z2|<1, where z1 and z2 are the poles of the transfer function hto(z) or h(z), given by (7) and (8). since z1=0, and z2 =1-m/q, it yields that the circuit is the stable system if (13) is satisfied. according to (10) and (12), it follows that the described circuit possesses the properties of a pll. this conclusion comes out from the facts that the output period to, for the stable system, equalizes the input period and that the time difference  does not depend on the initial conditions 0 and to0. 0 2m q  (13) iii. realization of the multiplier looking at (10), we can notice that regardless of the counter in feedback connection, the output period to is equal to the input period ti if the circuit reaches the stable state. the expected frequency multiplication is not performed, because the main algorithm, given by (2), compensated the influence of the division factor q to the output period to. however, the influence of q is made on the final value of time difference ∞, see (12), and on the region of the parameter m in (13). due to this influence, the region of m, for the stable system is enlarged. the region of the parameter for the stable system, according to (13), is presented in figure 2. fig. 2. the circuit is stable for the shaded region of parameters m and q. the circuit functions as a classic pll for q=1. engineering, technology & applied science research vol. 7, no. 6, 2017, 2104-2108 2106 www.etasr.com perisic et al.: a frequency multiplier based on time recursive processing note that, according to (12), if q=1 then ∞ = 0. the circuit functions as classic pll. if q=1, it means that there is no counter in feedback connection. let us first consider the realization of the circuit for q=1. changing q=1 and m=fm/fc into (2), where fm and fc are the clock frequencies of clock signals sm and sc, (2) turns into (14). according to (14), k+1 is measured by the clock period tm=1/fm, tik is measured by the clock period tc=1/fc and tok+1 is generated by the clock period tc=1/fc. the principal scheme of the circuit, corresponding to (14), is shown in figure 3. the circuit consists of recursive calculation module (rcm) and programmable period generator (ppg). rcm calculates tok+1 and ppg generates the output period at the next step. the realization of rcm, according to (14), can be easily performed using the technique described in [1-10]. 1 1mk k kc c f f ti fto      (14) fig. 3. the principal scheme of the circuit for q=1 ppg was described in details through [1-10], but in order to explain the development of the multiplier, it is now necessary to remember the general principles of its functioning. when the calculated tok+1 is entered as a binary word tobk+1 from rcm to ppg, ppg will count down pulses of clock signal sc as long as an up-down counter, incorporated in ppg, reaches zero. in that moment ppg generates the output pulse of sop which is, at the same time, used to enter the new binary word tobk+1, representing the next output period tok+1. after that, the described counting down, restarts and the process is continuously repeated. the result of this processing is the constant generation of pulses of sop. the period of sop is to=todˑtc, where tod is the decimal value of tob. let us now suppose that the frequency of clock sc is qc times greater. according to the previous explanation of the way of ppg functioning, it is obvious that the counting down would be qc times faster and the output period will be qc times decreased, because the new to=todˑtc/qc. in other words, we would get the output frequency, which is qc times greater than the input frequency. on the other hand, this would disrupt and destabilize an established mode of circuit functioning, because the expected output period which is fed into rcm, would be qc times decreased. to escape this disturbance at the input of rcm, it is necessary only to incorporate a counter in feedback connection whose division factor is qc. at the output of the counter, the output period would be the expected one, just like in case of the circuit, shown in figure 3, which corresponds to the case q=1. in other words, the influence of the increased clock frequency and the affect of the counter in feedback connection would compensate each other. in this way, the additional part of the circuit, outside of rcm, increases the output frequency qc times and immediately decreases it also qc times, providing the frequency multiplication of the input frequency by qc, at the output of ppg. due to fact that the additional part of circuit is outside of rcm, it does not obstruct the calculation in accordance with the main algorithm. it is now necessary to explain how it is possible to realize the described solution practically. the necessary additions, in comparison to the circuit presented in figure 3, can be seen at the principle scheme of multiplier, shown in figure 4. to realize the described principle of the frequency multiplication it is necessary to memorize the binary form of the current output period tobk in a register "reg". binary form tobk will be taken by ppg qc times during the calculation of the next output period tobk+1. whenever ppg generates an output pulse of sopq, its trailing edge is differentiated. new generated pulse is fed to input "load" of ppg over or gate and it is used for the reentering of tobk into ppg, providing the continuously generation of pulse rate sopq, whose frequency is qc times greater than an input frequency of sin. after qc pulses of sopq are generated, a trailing edge of sopc will appear at the output of the counter. this trailing edge is differentiated and new generated pulse is used to preset the next binary form of the output period tobk+1 into register and into ppg, simultaneously. the binary word tobk+1 will be used to generate next qc pulses of sopq. finally, in order to adapt sopc to rcm, the pulses of sopc are narrowed by monostable multivibrator mm. after the modification shown in figure 4 is made, in comparison with the principal scheme shown in figure 3, a new model of the principal scheme of the multiplier is shown in figure 5. the modifications are made inside the ppg to compensate the effects of the counter in the feedback connection. note that rcm modules in figure 3 and in figure 5 function completely in the same way, providing that the same input signal sin is fed into them, so that most of the additional parts in figure 4, together with the existing ppg, can be considered as a new expanded ppg (ex-ppg), shown in figure 5. accordingly, signal sop shown in figure 3, is identical to signal sop, shown in figure 5. fig. 4. the principal scheme of the multiplier. the multiplication factor is qc. fig. 5. the simplified principal scheme of the multiplier with ex-ppg and a counter in the feedback connection. the multiplication factor is qc. one eight bit multiplier was realized with the standard integrated circuits for q=1 and m=1 (fm=fc). the multiplication factor, related to ex-ppg, is qc=10. the input period is the step function ti=1ms, corresponding to the frequency of 1khz. the clock frequencies fc=fm=30 khz, qc·fc=300 khz so that the ratio will be ti/tc=30. the oscilloscope picture of the voltage waveforms, shown in figure 6, was taken when the multiplier engineering, technology & applied science research vol. 7, no. 6, 2017, 2104-2108 2107 www.etasr.com perisic et al.: a frequency multiplier based on time recursive processing was in the stable state. the chosen waveforms correspond to the signals sin, sopq, sopc and sop, shown in figure 5. in accordance with the chosen parameters, the multiplier functions as classic pll, striving to reduce the time difference to zero. due to the fact that ti/tc=30, the reduction is rather successful. the input and output periods are equaled and the time difference between the signals sin and sop is zero in figure 6. however, at the output of ex-ppg, signal sopq is generated, whose frequency is 10khz, i.e. it is ten times greater than the input frequency of 1khz. the function of monostable multivibrator mm is also shown by signal sop in figure 6. although the generation of the multiplied frequency was performed inside ex-ppg, the generation of sopq was controlled by the closed loop system and the multiplier possesses all properties of described trp-pll. fig. 6. the oscilloscope picture of the multiplier voltage waveforms for q=1, m=1 (fc=fm=30 khz), qc=10 and ti=1ms (frequency of 1khz). iv. other properties of the circuit other circuit’s properties are equally important either for the frequency multipliers or for other applications. to analyze them, it is necessary to simulate the functioning of the circuit for different practical situations. besides the study of the new properties, the simulations are to enable better insight into the procedure and into the physical meaning of the variables described. at last, they are to prove the correctness of the previous analysis. all discrete values in simulations were merged to form continuous curves. all variables in the following diagrams were presented in time units, which can be, sec, msec or any other, providing that the same time units are used for all time variables (ti, to, and ). it was more suitable to use just “time unit” or abbreviated “t.u.” in the text and to omit the indication “t.u.” in diagrams. all simulations were conducted in matlab, using (1) and (2). let us first simulate the functioning of the circuit for the step input. the locking procedure of the circuit, for the step input, is considered for three cases in figure 7. the step input is ti = 10 t.u. the parameters m and q are chosen carefully in order to demonstrate the properties of the circuit. all values of m and q, as well as the values of the initial conditions to0 and 0 are presented in figure 7. in figure 7a can be seen that for any value of parameter m satisfying (13), the output period tends to the input period, but the transition time depends on the values of m and q. note that if m=q (cases nr. 1 and nr. 2), the stable state is reached in two steps only. for all of three cases, the calculation of ∞ agrees with ∞ which can be seen on the simulated curves. according to (12), for case nr. 1: 1∞=tiˑ(q1)/m=10ˑ(1-1)/1=0 t.u., for case nr. 2: 2∞=tiˑ(q-1)/m=10ˑ(21)/2=5 t.u. and for case nr. 3: 3∞=tiˑ(q-1)/m=10ˑ(61)/4.7=10.63 t.u. the same simulated results can be seen in figure 7a. the agreement between the simulated and calculated values, confirms the correctness of the simulation results and the correctness of the whole approach. the merged discrete values for the case nr. 1, representing the output variables to1 and 1 in figure 7a, are shown in the real time, in figure 7b. this presentation is given in form of the pulse rates. it reveals the real time relations between all input and output variables and helps the better understanding of the physical mining of the simulated curves. all values, shown in figure 7b, are taken from the simulation results, but they can be also calculated manually, step by step, using (1) and (2). according to the mathematical analysis and simulation results obtained, the circuit functions as classic pll for m=1 and q=1. these parameter values were used for the development of the realized multiplier. however, the parameters can take any values satisfying (13). it is of interest to investigate the ability of the circuit to track a ramp function (velocity function). to illustrate this ability, let us determine well known velocity error, providing that the input period is the ramp function ti(k)=tiv(k)=p·k, where p is a time constant. the definition of velocity error is kv=lim[tov(k)-tiv(k)]k→∞. the previous expression can be transform into kv=lim {tiv(k)[ hto(k)-1]}k→∞, where hto(k) is the inverse z transform of the transfer function hto(z), given by (7). due to the final value theorem, it is possible to find kv using another expression, given in z transform form kv = lim{(z-1)·tiv(z)·[hto(z)-1]}z→1. using the previous expression and z transform of velocity function tiv(z)=z(p·k)=pz/(z-1) 2, kv is calculated and presented by (15) according to which, the output of the circuit will track the velocity input without an error only if q=1. otherwise the output will track the velocity input with the constant error kv. (1 ) /kv p q m   (15) fig. 7. (a). the output period tends to the input period and the final value of time difference ∞ = ti(q-1)/m. (b). all periods of sin, sop and time differences k, for the case nr. 1, are calculated and presented to show the real time relation between variables. for this case, m=1 and q=1 (∞=0) and the circuit functions as a classic pll. engineering, technology & applied science research vol. 7, no. 6, 2017, 2104-2108 2108 www.etasr.com perisic et al.: a frequency multiplier based on time recursive processing to complete the information about the system properties, it is necessary to determine ∞, i.e. the final value of (k) for q=1. if ti(z)=tiv(z) and q=1 are substituted into (6), we will get v(z). using the final value theorem, v∞ is determined and shown by (16). 1lim[( 1) ( )] /v v zz z p m     (16) to prove the correctness of the previous analysis, three cases of the locking procedure are simulated and presented in figure 8 for the velocity input tik=(10+2·k) t.u., (p=2 t.u.). according to case nr. 1 in figure 8a, the circuit is able to track the velocity input without an error if q=1. for cases nr. 2 and nr. 3, q is not equal to one and the circuit tracks the velocity input with constant velocity errors. according to (15) the velocity errors could be calculated as kv1=pˑ(1-q)/m=2·(11)/1=0 t.u., kv2=2·(1-2)/2=-1 t.u. and kv3=2·(1-6)/4.7=-2.127 t.u. the same values of kv1, kv2, and kv3 were reached by simulation, which are presented in figure 8c. the time differences for these three cases are shown in figure 8b. for the case nr. 1, q=1 and the final value v1∞ can be calculated using (16). according to (16), v1∞=p/m=2/1=2 t.u. the same value of v1∞ was calculated by simulation in figure 8b. for the cases nr. 2 and nr. 3, q is not equal to one and the time differences v2∞ and v3∞ tend to infinity. regarding the obtained results, it is more suitable to choose q=1 for the realization of the multiplier. firstly, the circuit possesses the better tracking properties. secondly, in case that q is not equal to one, the requirements for the circuit capacity are stronger in the tracking applications, since the variable  can reach undesirable large value. another important conclusion is that the circuit is extremely fast if m=q. according to figures 7 and 8, if q=m, the circuit takes only two steps to reach the stable state (cases nr. 1 and nr. 2). fig. 8. the transition and stable state of the circuit for the velocity input: (a). the output periods track the input periods for three cases. (b). the corresponding time differences are presented. for the case nr. 1 (q=1), according to (16), v1∞=p/m=2. (c). the simulated velocity errors are in accordance with (15). for the case nr. 1 (q=1), according to (15), kv1∞=0. v. conclusion the description, simulation and presentation of the realized multiplier demonstrate a new technique for a practical application of trp circuits. this technique can be applied for the realization of frequency multipliers, as a type of upgrade, to any type of trp pll or trp fll. however, the described technique can also be used for frequency multiplication, independently of trp circuits, even as an open loop system. the presented theoretical approach also provides a contribution to the field of the phase shifting based on trp pll. some trp pll are able to provide different types of controlled phase shifting, either by using an outside control word or by using the system parameters. it was demonstrated in this paper that a division factor of a counter, positioned in a feedback connection in a trp pll, can also be used for phase shifting. as shown, the described circuit is suitable for tracking and prediction applications. the proposed circuit provides the capability to regulate the transition speed so that it can be adapted to specific application. the precision of the multiplication is limited by the capacity of the built-in updown counters. higher precision requires greater circuit capacity. the maximum factor of the frequency multiplication is limited by the speed of the used integrated circuits and by the required precision of the multiplication. references [1] d. m. perisic, m. bojovic, “application of time recursive processing for the development of the time/phase shifter”, engineering, technology & applied science research, vol. 7, no. 3, pp. 1582-1587, 2017 [2] d. m. perisic, m. perisic, s. rankov, “phase shifter based on a recursive phase locked loop of the second order”, revue roumaine des sciences techniques, serie electrotechnique et energetique, vol. 59, no. 4, pp. 391–400, 2014 [3] d. m. perisic, a. zoric, d. babic, d. d. perisic, “recursive pll of the first order”, przeglad elektrotechniczny, vol. 89, no. 7, pp. 50-53, 2013 [4] d. m. perisic, a. zoric, s. obradovic, d. d. perisic, “fll as digital period synthesizer based on binary rate multiplier control”, przeglad elektrotechniczny, vol. 89, no. 1, pp. 145-148, 2013 [5] d. m. perisic, m. bojovic, “multipurpose time recursive pll”, revue roumaine des sciences techniques, serie electrotechnique et energetique, vol. 61, no. 3, pp. 283–288, 2016 [6] d. m. perisic, a. zoric, m. perisic, d. mitic, “analysis and application of fll based on the processing of the input and output periods”, automatika, vol. 57, no. 1, pp. 230–238, 2016 [7] d. m. perisic, m. perisic, d. mitic, m. vasic “time recursive frequency locked loop for the tracking applications”, revue roumaine des sciences techniques, serie electrotechnique et energetique, vol. 60, no. 2, pp. 195–203, 2015 [8] d. m. perisic, a. zoric, m. perisic, v. arsenovic, lj. lazic “recursive pll based on the measurement and processing of time”, elektronika ir elektrotechnika, vol. 20, no. 5, pp. 33-36, 2014 [9] d. m. perisic, a. zoric, d. babic, d. d. perisic, “decoding and prediction of energy state in consumption control”, revue roumaine des sciences techniques, serie electrotechnique et energetique, vol. 58, no. 3, pp. 263–272, 2013 [10] d. m. perisic, a. zoric, s. obradovic, s. spalevic, “application of frequency locked loop in consumption peak load control”, przeglad elektrotechniczny, electrical review, vol. 88, no. 1b, pp. 264-267, 2012 acknowledgement this article was supported by the ministry of science and technology of the republic of serbia within the project iii 47016. microsoft word etasr_v12_n2_pp8435-8443 engineering, technology & applied science research vol. 12, no. 2, 2022, 8435-8443 8435 www.etasr.com kassem et al.: groundwater quality assessment based on water quality index in northern cyprus groundwater quality assessment based on water quality index in northern cyprus youssef kassem department of mechanical engineering engineering faculty near east university nicosia, cyprus yousseuf.kassem@neu.edu.tr hüseyin gökçekuş department of civil engineering civil and environmental engineering faculty near east university nicosia, cyprus huseyin.gokcekus@neu.edu.tr temel rizza department of civil engineering civil and environmental engineering faculty near east university nicosia, cyprus temel.rizza@neu.edu.tr received: 30 january 2022 | revised: 28 february 2022 | accepted: 4 march 2022 abstract—the largest coastal aquifer in northwestern cyprus is the morphou aquifer. the objective of the current study was to evaluate the quality of the groundwater and its suitability for drinking purposes in the morphou (güzelyurt) region, cyprus. to realize this aim, 118 groundwater samples were collected during wet and dry seasons over a period of 11 years. major physicochemical characteristics (electrical conductivity, ph, bicarbonate, calcium, magnesium, chloride, and total and carbonate hardness) were measured and analyzed. the assessment of groundwater quality was evaluated with the help of the water quality index (wqi). the results demonstrated that 56% and 50% of the groundwater samples during dry and wet seasons respectively were unsatisfactory according to the cl limits of the who standard. in addition, approximately 10% of the groundwater samples come under class 2 (good water), 30% of the samples come under class 3 (fairwater), 13% come under classes 4 and 5, and the rest under class 6 (unsuitable for drinking). keywords-morphou; water quality; groundwater level changes; groundwater; physicochemical parameters; water quality index i. introduction groundwater is the main source of water used for multiple purposes in arid and semi-arid regions [1-4]. additionally, due to the pollution of surface water bodies, groundwater has become an important source to secure the safety of water supply [5]. the growth of populations and increasing climate variations reduced the groundwater level due to the imbalance between groundwater recharge and extraction. this is especially true for cyprus. the island suffers from periodic drought due to the general decrease in precipitation [6-8]. since they represent the main source for drinking and irrigation water supplies, groundwater resources in cyprus are of major concern about the quality and water supplier’s sustainability. in northern cyprus, the water resources are categorized into groundwater, surface water (dam), and the turkey-north cyprus water pipeline project [9, 10]. furthermore, river basins and dams are the main surface water resources [11]. as mentioned above, groundwater is the main water source in the island. due to the over-pumping rate, the level of the groundwater declined and reached 45-50m below sea level [1215] and its quality has been reduced due to the saltwater intrusion and bedrock contamination [14]. according to [1618], the chloride concentration has reached 7000ppm in several coastal locations. the kyrenia mountain aquifer, morphou (güzelyurt) aquifer, and gazimağusa aquifer are considered the main aquifers of northern cyprus. morphou aquifer is the largest coastal aquifer, which provides water for irrigation and municipal purposes. additionally, according to [9, 19-21], overexploitation is the main drive for the decline in the groundwater level below sea level in some sites in the region [9, 19]. in general, the agriculture sector is important in the selected region [22-24]. in northern cyprus, the total agricultural area and the total irrigated area are about 187069 ha and 9714 ha respectively [9]. moreover, agricultural production has decreased and crop yield has been reduced due to the poor water quality and changes in rainfalls. thus, the study area is currently facing significant water challenges. determining the status of groundwater for drinking purposes using the water quality index (wqi) in morphou aquifer is the main aim of the current paper. in this study, 118 groundwater samples were collected and their physicochemical characteristics were analyzed. the results are compared with the who water quality standard. figure 1 illustrates the flowchart of the current study. corresponding author youssef kassem engineering, technology & applied science research vol. 12, no. 2, 2022, 8435-8443 8436 www.etasr.com kassem et al.: groundwater quality assessment based on water quality index in northern cyprus fig. 1. flowchart of the procedure followed in the current study. ii. materials and methods a. study area and sample collection figure 2 shows the location of the morphou region, which covers an area of 381km 2 and has average altitude of 45m above sea level. fig. 2. cyprus map and location of the morphou region. in the present study, the data of 118 wells, distributed over the selected region, have been used to analyze the static groundwater level and quality in the region (figure 3). the data were measured during two seasons (recharge season, april, may, and june, and charge season, november, december, and january). the study data cover a period from 2006 to 2016. the physicochemical properties (electrical conductivity, ph, bicarbonate, calcium, magnesium, chloride, and hardness in terms of total hardness and carbonate hardness) were analyzed and evaluated. the collected water samples were examined by following the standard methods. generally, the groundwater samples were collected with 1l polythene bottles and their physicochemical characteristics were analyzed. the sample bottles were washed with distilled water before sample collection. the instrumental and volumetric methods utilized to measure the physicochemical properties are listed in table i. the temperature of each sample was measured using a common mercury thermometer. fig. 3. map sample locations, prepared with arcgis 10. table i. instrumental and volumetric methods used in the chemical analysis of groundwater samples parameter unit method/ instrument reagents ph ph meter ph 4, 7, and 9.2 (buffer solutions) ec �s/cm ec meter potassium chloride hco3 mg/l volumetric hydrosulfuric acid, phenolphthalein, and methyl orange ca 2+ mg/l volumetric edta, sodium hydroxide, and murexide mg +2 mg/l calculation (th-ca 2+ ) cl mg/l argentometric silver nitrate, potassium chromate b. correlations between the physicochemical parameters the interrelationships between physicochemical variables were examined using pearson product-moment correlation followed by a parametric method for normal distribution. according to [25], pearson's correlation coefficient (r) can be estimated using (1). moreover, the data are standardized with (2). � � ∑ ��� � � �� ��� � � � � 1 ⁄ ���� (1) � � ���̅� (2) where � , � , �� , �� are the sample means and standard deviations of ��, ��, � � 1,… , , � is the initial data value, and �̅ and � are the average and standard deviation of data respectively. correlation coefficients and p-values were calculated with minitab 17 software. c. water quality index (wqi) several studies have classified groundwater with the help of wqi [26, 27] as shown in table ii. the wqi calculation was engineering, technology & applied science research vol. 12, no. 2, 2022, 8435-8443 8437 www.etasr.com kassem et al.: groundwater quality assessment based on water quality index in northern cyprus carried out using a weighted arithmetic index as shown below [29]. water quality rating is calculated as: �� � � ����� ����� ! 100 (3) where �� is the water quality rating for the nth parameter, #� is the observed value of the n th parameter, �� is the standard permissible value of the n th parameter, and #� is its ideal value. the unit weight ($�) for each water quality parameter is determined by: $� � % '� (4) where $� is the unit weight of the nth parameter, (� is its standard value, and ) is constant proportionality, which is calculated using the below equation: ) � *∑* '�⁄ (5) the overall wqi is estimated by: wqi � ∑ .�/�∑ /� (6) table ii. classes proposed for wqi for drinking (wqid) [28] class range type of groundwater 1 <25 excellent water 2 25-50 good water 3 50-75 fairwater 4 75-100 poor water 5 100-150 very poor water 6 >150 unsuitable for drinking/irrigation iii. results a. physicochemical parameters of the selected wells table iii summarizes the descriptive statistics of the analyzed variables of the collected samples. the groundwater temperature is within the range of 20-250 for both wet and dry seasons. 1) ph generally, ph is an essential indicator that can be utilized for evaluating water quality and contamination degree in water bodies [30]. as shown in table iii, the ph value of most groundwater samples varied from 6.4 to 8.3 with an average value of 7.7 for the dry season. regarding the wet season, the ph value of groundwater samples ranged from 7.1 to 8.3 with an average value of 7.7. based on the findings, the groundwater in the selected region is slightly acidic to alkaline in nature. 2) electrical conductivity (ec) ec is another important property that measures the ions present in the water. there is a strong relationship between ec and total dissolved solids (tds) [30, 31] and a relationship with salinity [32]. in the present study, ec ranges from 604.0 to 8690.0μs/cm for both seasons (see table iii). table iv presents the classification of ec ranges and types. thus, for the dry season, 55% of the total groundwater samples come under type i, 24% under type ii, and 21% under type iii, as shown in figure 4. during the wet season, 54% of the groundwater samples come under type i, 23% under type ii, and 23% under type iii. table iii. physicochemical parameter statistics results variable dry season who standard mean sd minimum maximum ec [μs/cm] 2132.0 1769.0 606.0 8690.0 500 ph [-] 7.7 0.2 7.1 8.3 6.5-8.5 temperature [0 ] 24.6 0.4 22.5 25.0 co3 [mg/l] 5.8 21.6 0.0 233.0 hco3 [mg/l] 281.2 95.5 137.3 621.5 500 th [mg/l] 685.0 1089.0 84.0 9371.0 ch [mg/l] 240.9 92.5 126.7 761.4 ca 2+ [mg/l] 131.3 204.1 15.5 1620.0 75 mg +2 [mg/l] 86.7 139.2 10.8 1252.7 50 cl [mg/l] 593.9 940.8 65.9 8317.1 250 variable wet season who standard mean sd minimum maximum ec [μs/cm] 2088.0 1650.0 604.0 7873.0 500 ph [-] 7.7 0.2 7.1 8.3 6.5-8.5 temperature [0 ] 25.0 0.1 24.2 25.7 co3 [mg/l] 4.0 4.9 0.0 39.1 hco3 [mg/l] 270.0 83.9 127.0 562.8 500 th [mg/l] 654.0 1089.0 74.0 9650.0 ch [mg/l] 228.5 78.1 132.5 632.1 ca 2+ [mg/l] 133.3 207.7 15.5 1622.8 75 mg +2 [mg/l] 84.2 150.4 6.4 1317.9 50 cl [mg/l] 579.3 912.9 64.4 8200.6 250 table iv. ec classification [33] range type <1500μs/cm type i (the enrichments of salt are low) 1500-3000μs/cm type ii (the enrichments of salt are medium) > 3000μs/cm type iii (the enrichments of salt are high) fig. 4. ec values of the groundwater samples during wet and dry season. 3) chloride (23�) it is commonly found in nature as sodium, potassium, and calcium salts. both natural and human factors contribute to the engineering, technology & applied science research vol. 12, no. 2, 2022, 8435-8443 8438 www.etasr.com kassem et al.: groundwater quality assessment based on water quality index in northern cyprus presence of chloride in groundwater [34]. the results show that the cl�concentration in the collected samples varied from 64.4 to 8317.1mg/l as shown in table iii. in general, cl� concentrations above about 250mg/l can give a detectable taste in water. cl� is mainly derived from non-lithological sources and its solubility is generally high. 4) calcium (ca 2+ ) and magnesium (mg +2 ) they are important parameters for evaluating water quality. ca 2+ and mg +2 have a direct relationship with hardness [35]. the results showed that the ca 2+ and mg +2 in groundwater samples are within the range of 15.5-1622.8mg/l and 6.41317.9mg/l respectively. additionally, it was found that the majority of the samples have a higher concentration of ca 2+ and mg +2 compared to the safety limits of the who standard. 5) total hardness and carbonate hardness ca 2+ and mg +2 are the principal ions responsible for total hardness (th). the observed value of th in the samples lies between 84.0 and 9371.0mg/l as shown in table iii. table v shows the classification of th values. according to this, during the dry season, approximately 52% of the groundwater samples come under the very hard category, 34% fall in the hard category, and 14% fall under the moderate category, with no samples belonging to the soft category (figure 5). similarly, for the wet season, 49% of the samples come under the very hard category, 36% under the hard category, 15% under the moderate category, and 1% under the soft category. carbonate hardness (ch) is a measure of the water hardness caused by the presence of carbonate (co7�8) and bicarbonate (hco7� ) anions. the observed value of ch ranges from 10 to 3120mg/l. 6) standard deviations in the geochemistry of groundwater the standard deviations (sds) of the chemical parameters are shown in table iii. ec and th have the highest sds, followed by cl . b. interrelations of physicochemical parameters to show the relationship between the physicochemical parameters, the correlation coefficient (r) model was used (table vi). for the dry season, it was found that ec shows strong positive correlation with ph (-0.551), hco3 (0.708), th (0.847), ch (0.728), ca 2+ (0.866), mg +2 (0.814), and cl (0.847). for the wet season, ec has a strong positive correlation with ph, co3, hco3, th, ch, ca 2+ , mg +2 , and cl . this indicates that the groundwater is mainly controlled by ca 2+ , mg +2 , and cl , which depend on anthropogenic activities and mineral solubility, water flow path conditions, and topographical features. the t (sample temperature) has a good correlation with co3 (-0.335) and hco3 (0.259) for the dry season. it is noticed that there is no relationship between the chemical parameters and temperature samples for the wet season. in addition, it is found that the th is in good positive correlation with ch, ca 2+ , mg +2 , and cl . also, the ca 2+ has a good positive correlation with cl and mg +2 , while mg +2 has a significant positive correlation with cl , reflecting the influences of ca 2+ and mg +2 bearing minerals, in addition to the sources of anthropogenic and marine origin. fig. 5. th values of the groundwater samples. table v. th classification [36] range type <75mg/l soft 75-150 mg/l moderate 150-300 mg/l hard < 300 mg/l very hard c. suitability of groundwater quality for drinking in general, it is observed that the groundwater is free of color, odor and turbidity in the field. the physicochemical characteristics of the collected samples regarding its drinking suitability are shown in table vii. based on the previous sections, the ph value, which ranges between 6.4 and 8.3 with an average of 7.7 for both seasons, indicates that all the collected samples are within the safe limit specified by the who standard. as shown in table viii, 78% and 68% of the samples are above the th specification during dry and wet seasons respectively. according to [37], hardness is an essential factor for estimating the water usability for drinking and other domestic purposes. moreover, the ca 2+ concentrations indicate that about 40% of the samples are above the ca 2+ specification of the who standard. the concentration of mg +2 indicated that 60% of the samples were below the safe water limit of 30mg/l. mortality rates for cardiovascular diseases are associated with a deficit of ca 2+ and mg +2 in drinking water [37-39]. furthermore, bicarbonate is a major element in groundwater chemistry and the human body and may result from the weathering of silicate minerals [40]. it is observed that the hco3 concentration of about 32% of the samples was more than 300mg/l. generally, the high concentration of hco3 can lead to the emergence of kidney stones in the presence of a higher concentration of ca 2+ [33]. the results demonstrated that 56% and 50% of the groundwater samples during dry and wet seasons were unsatisfactory according to the cl specifications of who. engineering, technology & applied science research vol. 12, no. 2, 2022, 8435-8443 8439 www.etasr.com kassem et al.: groundwater quality assessment based on water quality index in northern cyprus table vi. the correlation coefficient of the analyzed physicochemical groundwater parameters for both seasons d r y s e a s o n ec ph t co3 hco3 th ch ca 2+ mg +2 cl ec pearson correlation 1 -0.551** 0.082 0.03 0.708** 0.847** 0.728** 0.866** 0.814** 0.847** sig. (2-tailed) 0 0.379 0.75 0 0 0 0 0 0 ph pearson correlation 1 -0.222* -0.05 -0.618** -0.436** -0.584** -0.448** -0.424** -0.449** sig. (2-tailed) 0.017 0.611 0 0 0 0 0 0 t pearson correlation 1 -0.335** .0259** 0.021 0.167 0.072 0.001 0.01 sig. (2-tailed) 0.005 0.825 0.074 0.44 0.993 0.916 co3 pearson correlation 0.011 0.004 -0.01 -0.01 0.016 0.023 sig. (2-tailed) 0.908 0.963 0.954 0.955 0.865 0.805 hco3 pearson correlation 1 0.504** 0.866** 0.523** 0.473** 0.511** sig. (2-tailed) 0 0 0 0 0 th pearson correlation 1 0.733** 0.982** 0.990** 0.983** sig. (2-tailed) 0 0 0 0 ch pearson correlation 1 0.719** 0.724** 0.750** sig. (2-tailed) 0 0 0 ca 2+ pearson correlation 1 0.954** 0.968** sig. (2-tailed) 0 0 mg +2 pearson correlation 1 0.976** sig. (2-tailed) 0 cl pearson correlation 1 sig. (2-tailed) w e t s e a s o n ec pearson correlation 1.0 -0.673** 0.0 -0.321** 0.717** 0.788** 0.747** 0.844** 0.765** 0.805** sig. (2-tailed) 0 1.0 0.001 0.0 0 0 0 0 0 ph pearson correlation 1 -0.1 0.523** -0.637** -0.503** -0.625** -0.539** -0.471** -0.527** sig. (2-tailed) 0.5 0 0.0 0 0 0 0 0 t pearson correlation 1 -0.133 0.0 -0.145 -0.13 -0.105 -0.149 -0.138 sig. (2-tailed) 0.164 0.6 0.129 0.175 0.271 0.118 0.148 co3 pearson correlation 1 -0.206* -0.249** -0.138 -0.274** -0.236* -0.258** sig. (2-tailed) 0.0 0.008 0.147 0.004 0.013 0.006 hco3 pearson correlation 1. 0.548** 0.939** 0.566** 0.529** 0.598** sig. (2-tailed) 0 0 0 0 0 th pearson correlation 1 0.709** 0.982** 0.985** 0.982** sig. (2-tailed) 0 0 0 0 ch pearson correlation 1 0.703** 0.689** 0.752** sig. (2-tailed) 0 0 0 ca 2+ pearson correlation 1 0.966** 0.956** sig. (2-tailed) 0 0 mg +2 pearson correlation 1 0.962** sig. (2-tailed) 0 clpearson correlation 1 sig. (2-tailed) **. correlation is significant at the 0.01 level (2-tailed). *. correlation is significant at the 0.05 level (2-tailed). table vii. groundwater quality criteria for drinking variable who (2011) % of samples exceeding the safe limit dry season wet season ec [μs/cm] 1000 68% 66% ph [-] 6.5-8.5 0% 0% hco3 [mg/l] 120 100% 100% th [mg/l] 200 78% 68% ca 2+ [mg/l] 75 41% 40% mg +2 [mg/l] 50 42% 41% cl [mg/l] 250 56% 50% d. water quality index groundwater quality and its suitability for drinking were assessed with the wqi method. five parameters (ph, th, ca 2+ , mg +2 , and cl ) were taken into account for the calculation of the wqi and the who drinking water standards were considered. table viii. relative weights of chemical parameters parameters who standard (2011) weight relative weight ec [μs/cm] 1000 4.00 0.235 hco3 [mg/l] 120 1.00 0.059 th [mg/l] 200 3.00 0.176 ca 2+ [mg/l] 75 3.00 0.176 mg +2 [mg/l] 50 3.00 0.176 cl[mg/l] 250 3.00 0.176 sum 24.00 1.000 weighted values were set according to the relative importance of groundwater parameters in drinking water quality. chloride was given the maximum weight of 5, as it plays the most significant role in water quality assessment. the other parameters were assigned weights between 1 and 5 engineering, technology & applied science research vol. 12, no. 2, 2022, 8435-8443 8440 www.etasr.com kassem et al.: groundwater quality assessment based on water quality index in northern cyprus depending on their importance in water quality determination. the computed $� values for groundwater parameters are presented in table viii. wqi values were computed and the water quality types for each sample location are given in table ix. it is found that approximately 10% of the groundwater samples come under class 2 (good water), 30% of the samples come under class 3 (fairwater), 13% of groundwater samples come under class 4 and 5, and the rest of the groundwater samples under the class 6 (unsuitable for drinking). table ix. groundwater quality index classification of the samples based on wqi for both seasons site name wqi water quality category site name wqi water quality category 4043 morphou 42.69 good 555 bostanci 80.16 poor 2318 akçay 44.76 good 2472 morphou 83.94 poor 4030 morphou 44.90 good 5011 aydinköy 85.52 poor 345 morphou 45.65 good 2434 aydinköy 85.67 poor 2328 morphou 47.70 good 2404 aydinköy 86.81 poor 1790 morphou 47.82 good 588 bostanci 89.79 poor 349 morphou 48.05 good 2424 aydinköy 92.13 poor 350 morphou 48.43 good 578 günesköy 93.19 poor 5043 akçay 48.79 good 4550 doganci 93.40 poor 2356 bostanci 49.14 good 415 morphou 94.82 poor 593 morphou 49.38 good 1004 sahinler 94.87 poor 2407 morphou 49.71 good 2321 bostanci 98.94 poor 1741 akçay 50.74 fair 532 morphou 100.84 very poor 2326 bostanci 50.76 fair 1780 bostanci 102.77 very poor 2490 zümrütköy 50.98 fair 4548 doganci 106.48 very poor 1742 akçay 51.14 fair 4517 doganci 106.64 very poor 2336 morphou 51.37 fair 4520 doganci 110.05 very poor 372 morphou 52.52 fair 4516 doganci 110.12 very poor 4310 morphou 52.81 fair 586 bostanci 111.35 very poor 594 bostanci 53.04 fair 529 morphou 120.26 very poor 367 morphou 53.52 fair 4288 cengizköy 130.44 very poor 2400 morphou 53.99 fair 525 morphou 133.71 very poor 369 morphou 54.32 fair 1836 morphou 134.23 very poor 5042 morphou 55.33 fair 615 aydinköy 135.80 very poor 411 morphou 55.98 fair 2343 bostanci 137.36 very poor 2398 morphou 56.77 fair 533 günesköy 138.53 very poor 558/b bostanci 57.03 fair 4547 doganci 141.69 very poor 4270 günesköy 57.22 fair 4026 kalkanli 158.11 unsuitable for drinking 390 morphou 59.09 fair 287 morphou 159.05 unsuitable for drinking 1005 sahinler 59.16 fair 1763 kalkanli 160.97 unsuitable for drinking 577 günesköy 60.85 fair 295 morphou 162.89 unsuitable for drinking 5018 sahinler 61.55 fair 115 aydinköy 168.81 unsuitable for drinking 2473 morphou 61.56 fair 2345 morphou 172.51 unsuitable for drinking 2294 bostanci 62.80 fair 1793 morphou 178.14 unsuitable for drinking 589 bostanci 62.97 fair 1694 kalkanli 183.99 unsuitable for drinking 418 morphou 63.47 fair 292 kalkanli 189.83 unsuitable for drinking 339 morphou 63.72 fair 2346 morphou 195.88 unsuitable for drinking 2429 bostanci 64.08 fair 318 morphou 201.06 unsuitable for drinking 2453 morphou 66.78 fair 5041 morphou 201.79 unsuitable for drinking 2338 morphou 67.84 fair 2392 kalkanli 202.35 unsuitable for drinking 517 morphou 68.26 fair 311 morphou 207.47 unsuitable for drinking 2412 bostanci 69.79 fair 319 morphou 207.47 unsuitable for drinking 4029 morphou 70.21 fair 300 kalkanli 211.82 unsuitable for drinking 2399 bostanci 70.32 fair 4002 aydinköy 221.72 unsuitable for drinking 385 morphou 70.45 fair 288 kalkanli 230.76 unsuitable for drinking 4521 doganci 71.14 fair 1764 morphou 241.35 unsuitable for drinking 2317 akçay 73.48 fair 2391 kalkanli 267.67 unsuitable for drinking 524 morphou 75.96 poor 645 aydinköy 269.11 unsuitable for drinking 2320 günesköy 77.90 poor 120 aydinköy 271.97 unsuitable for drinking 5012 aydinköy 79.20 poor 617 aydinköy 282.65 unsuitable for drinking 633 aydinköy 286.50 unsuitable for drinking 542 morphou 454.55 unsuitable for drinking 806 morphou 296.12 unsuitable for drinking 548 morphou 471.40 unsuitable for drinking 646 aydinköy 305.99 unsuitable for drinking 1676 morphou 495.66 unsuitable for drinking 5081 kalkanli 314.14 unsuitable for drinking 466 morphou 509.60 unsuitable for drinking 107 günesköy 316.60 unsuitable for drinking 2450 morphou 532.79 unsuitable for drinking 2172 kumköy 329.49 unsuitable for drinking 5 kumköy 672.73 unsuitable for drinking 644 aydinköy 370.90 unsuitable for drinking 423 morphou 708.33 unsuitable for drinking 536 günesköy 409.99 unsuitable for drinking 8 kumköy 1828.98 unsuitable for drinking engineering, technology & applied science research vol. 12, no. 2, 2022, 8435-8443 8441 www.etasr.com kassem et al.: groundwater quality assessment based on water quality index in northern cyprus iv. discussion groundwater is the main water source for drinking and agricultural and domestic purposes in the selected region. the quality of water was evaluated using wqi. to the best of our knowledge, no study has been conducted on the groundwater of the region with the use of wqi. based on the groundwater analysis, it has been possible to understand the geochemical groundwater quality in morphou and to evaluate its suitability for drinking purposes. the groundwater quality was evaluated along with the coastal aquifers of the morphou region. agricultural activities in northern cyprus are carried out mainly in the selected area. the results indicated that the groundwater in the selected region is slightly acidic to alkaline in nature. similar results have been reported in previous studies [41, 42]. additionally, the results demonstrated that the concentration of cl in groundwater is above the minimum limit of the who standard, due to the agricultural activities that take place in the area [43]. based on this finding, the majority of groundwater samples demonstrated that the concentration of ca 2+ and mg +2 above the chloride indicated seawater intrusion into coastal aquifers [44]. according to [9, 16, 21], the groundwater level reached the mean level of the sea in some sites due to over-pumping. in addition, the amount of salt contamination is within the range of 1000-5000mg/g [9]. moreover, the concentration of ca 2+ and mg +2 in the majority of the groundwater samples did not meet the acceptable limits for drinking water. according to [45-47], the high amount of ca 2+ in the groundwater is attributed to cation exchange between minerals. besides, the higher amount of mg +2 than that of ca 2+ is attributable to the effects of ferromagnesium minerals present in the rocks of the region [48]. moreover, it is found that the values of th and ch are within the range of 84.0-9371.0mg/l and 10-3120 mg/l respectively. according to [49], the groundwater’s suitability is dependent on the result of an increase in the concentration of carbonate and bicarbonate more than the sum of the calcium and magnesium content of the water. in the end, the results demonstrated that the majority of the groundwater samples are not suitable for drinking. v. conclusions periodic assessment of the quality of drinking water sources is necessary to ensure the quality and security of the water supply. consequently, the present study evaluated the groundwater quality for drinking water supply in the morphou region based on the wqi. to achieve this, 118 samples of groundwater were collected seasonally during the period from 2006 to 2016 and the main physical and chemical properties were analyzed. it was found that the ph value of most of the groundwater samples varied from 6.4 to 8.3 and from 7.1 to 8.3 during dry and wet seasons respectively. additionally, based on ec classification, the results indicate that 55% of the majority of groundwater samples come under type i, 24% under type ii, and 22% under type iii during both seasons. moreover, the results indicated that the th values varied from 84.0 to 9371.0mg/l and approximately 50% of the groundwater samples come under the very hard category. thus, the groundwater is characterized by higher concentrations of th, hco3, and cl − and is not safe. furthermore, it is found that approximately 10% of the groundwater samples come under class 2 (good water), 30% of the samples come under class 3 (fairwater), 13% of groundwater samples come under class 4 and 5 and the rest of the groundwater samples are unsuitable for drinking. in the current study, there was no consideration of groundwater level and climate parameters, particularly rainfall. thus future research should focus on the investigation of the relationship between groundwater level, groundwater quality, and climate parameters using machine learning models and gis. acknowledgment the authors would like to acknowledge the faculty of civil and 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techniques with support vector machine (svm). the developed models were based on the vgg16 architecture and early or late fusion techniques were applied to concatenate the output from a fully connected layer. the results showed that the developed models based on early fusion performed better than the developed models on either late fusion or vgg16 alone. in addition, it was found that the models using the svm classifier had better efficiency in classifying the diseases appearing on rose leaves than the models using the softmax function classifier. in particular, a hybrid deep learning model based on early fusion and svm, which applied the categorical hinge loss function, yielded a validation accuracy of 88.33% and a validation loss of 0.0679, which were higher than the ones of the other models. moreover, this model was evaluated by 10-fold cross-validation with 90.26% accuracy, 90.59% precision, 92.44% recall, and 91.50% f1-score for disease classification on rose leaves. keywords-hybrid deep learning; neural networks; rose leaf diseases; support vector machine i. introduction roses are widely produced and exported globally. in 2019, the export value of roses was more than 175 million us dollars. the top five countries with the highest export rankings are netherlands, denmark, uganda, germany, and canada [1]. in cultivating roses, pest problems such as insect infestations are often encountered along with pathogens caused by fungi, viruses, and bacteria [2]. there are also diseases caused by nutritional deficiencies such as in nitrogen, iron, zinc, and magnesium. disease symptoms can be detected in roots, stems, branches, leaves, and buds or flowers. especially the leaves are a source of various infectious disease symptoms. however, classifying an infected disease requires skill and experience. for example, rose mosaic disease is a common disease worldwide and can sometimes be caused by more than one pathogen [3]. image processing methods for plant disease classification are currently being studied [4] combined with machine learning such as support vector machine (svm) [5] or k-nearest neighbors (knn) [6]. for example, the authors in [7] classified 4 rose leaf diseases using machine learning with with at least 94% accuracy. in addition to machine learning, other methods such as deep learning and neural networks are applied to recognize and classify plant diseases. the author in [8] developed a convolutional neural network (cnn) model, which applied mobilenet and transfer learning for rose disease classification. over 30 and at least 15 rose diseases can be observed on the leaves [2]. most of the research used a single perspective or a single set of images as the dataset for model training. however, in the deep learning model training, it is necessary to use images with multiple perspectives, such as image augmentation, and include image segmentation to highlight features that appear on the image. this approach usually increases the accuracy of the model. moreover, there are currently very few studies that have applied hybrid deep learning models to classify plant diseases. therefore, this research aims to develop rose leaf disease classification models using hybrid deep learning. besides, this work also compares the performance of models using different classifiers, namely softmax function and svm. ii. research methodology a. image data collection this study classifies rose diseases by identifying the symptoms on leaves based on image processing and cnn. a program was developed using the google search engine and chromedriver utility to search and download rose leaf images with dimensions of at least 224 pixels. all downloaded images were rechecked and labeled. moreover, the author took photos of rose leaves with and without diseases with an android mobile phone. therefore, a dataset of 4,032 downloaded and taken pictures was formed. the imagres were categorized to 16 different classes with regard to the shown rose disease (15 diseases + 1 normal/control) as shown in table i. finally, all images were resized and cropped to the dimension of 224×224 pixels. corresponding author: sumitra nuanmeesri engineering, technology & applied science research vol. 11, no. 5, 2021, 7678-7683 7679 www.etasr.com nuanmeesri: a hybrid deep learning and optimized machine learning approach for rose leaf … table i. rose leaf images classification no. label disease caused by amount (images) 1 bs black spot fungi 295 2 dm downy mildew fungi 272 3 pm powdery mildew fungi 281 4 bm black mold fungi 245 5 bb botrytis blight fungi 234 6 vw verticillium wilt fungi 220 7 cls cercospora leaf spot fungi 279 8 atn anthracnose fungi 276 9 rt rust fungi 280 10 rm rose mosaic virus 270 11 rr rose rosette virus 236 12 rsd rose spring dwarf virus 281 13 slr strawberry latent ringspot virus 183 14 ib insect bites insect 192 15 nd nutrient deficiencies 238 16 nm normal (disease-free) 250 b. image augmentation during the deep learning training mstage many images are needed to increase the performance of the model. if a particular class has a small number of images, it can affect classification accuracy. thus, the author increased the number of training images by using the image augmentation technique, including vertical and horizontal flips, rotation (45, -45, 90, -90 degrees), shearing (45 and -45 degrees), and random zoom-in up to 200%. thus, the number of the images increased from 4,032 to 40,320 images. the example of image augmentation is shown in figure 1. fig. 1. example of image augmentation. c. image processing image processing was applied to emphasize the physical appearance of the rose leaves. the preliminary step is that the rose leaf was separated from the background pixels with the grabcut [9] method based on the graph-cut technique. such an output image is illustrated in figure 2. fig. 2. the background pixels are removed by the grabcut method. the images obtained after the removal of the background pixels were subjected to image color-spacing and image thresholding processing. 1) hue, saturation, value color space hue, saturation, value (hsv) is a color space model which includes ranges of color type between 0 to 360 degrees, vibrancy, and color brightness. this work focused on color ranges around 120 degrees, which are related to the green color of a rose leaf. all green areas were desaturated with the lower saturation as grayness. as a result, any color not related to green was accelerated to become more emphatic. 2) truncated adaptive gaussian thresholding truncated adaptive gaussian thresholding (tagt) is a combination technique between truncate and adaptive gaussian thresholding. for truncate thresholding, an image without background pixels is processed. pixels greater than the threshold value ����� = 127, were assigned that value [10]: ���� , �� �threshold, if ��� ,�� � �������� ,��, otherwise (1) where ��� ,�� refers to the input pixel coordination, and ���� , �� refers to the output pixel coordination. next, the threshold was adjusted from the weighted sum of the block size of the pixel neighborhood at 7×7 using adaptive gaussian and binary thresholding, as in (2) [10]. ���� ,�� ��� ���, if ��� , �� � ��� ,��0, otherwise (2) where �� ��� refers to the maximum value assigned to the pixels and ��� ,�� refers to the individual threshold calculation of each pixel. 3) double inverse-binary thresholding double inverse-binary thresholding (dibt) is a thresholding method with twice applied inverse-binary thresholding. first, the image without background pixels is taken through a thresholding process between inverse-binary and binary, where the threshold values are set to 100 and 0 respectively. the resulting image from the first step was adjusted to the threshold value of 127 by inverse-binary thresholding, calculated in (3) [10]. ���� ,�� �0, if ��� ,�� � ��� ,���� ���, otherwise (3) this results in an image emphasizing the expected coordinates of the suspected position of disease infection or wilt on the rose leaf. each original image will result to 3 more images, namely hsv, tagt, and dibt, as shown in figure 3. fig. 3. example of each image processing. engineering, technology & applied science research vol. 11, no. 5, 2021, 7678-7683 7680 www.etasr.com nuanmeesri: a hybrid deep learning and optimized machine learning approach for rose leaf … d. hybrid deep learning modeling in this step the cnn models for the classification of diseases on a rose leaf were developed. twelve models were developed as follows. 1) visual geometry group16-based cnn model visual geometry group16 (vgg16) model is a cnn architecture presented in [11]. the input images of the vgg16based cnn model were set to 224×224 pixels for processing through 16 weight layers, including 13 convolution layers and 3 fully connected layers. all convolution layers have a 3×3 kernel size, 1 pixel of padding size, and the rectified linear unit (relu) activation function. spatial pooling followed with 5 max-pooling layers with a 2×2 pixel filter and stride 2. further, 1 flatten layer was included before feeding the output to the fully connected layers. furthermore, the softmax activation function was applied with 1,000 output classes in the last fully connected layer. thus, the total trainable parameters of this model were 138,357,544 as shown in figure 4. fig. 4. vgg16-based cnn model architecture. according to figure 4, the "process: a" refers to feature extraction layers, "process: b" refers to the flatten layer, and "process: c" refers to the fully connected layers. this research used the original image dataset with 16 labeled output classes (see table i) to develop the vgg16-based cnn model. therefore, the softmax layer (in process: c) was set to 16 instead of 1000 classes. the overall trainable parameters of this model were 134,326,096. 2) early fusion model the early fusion (ef) model was developed based on the vgg16-based cnn model. it starts with the images that have undergone each image thresholding processing separately (original, hsv, tagt, and dibt images) to each channel of cnn for extracting features (see process: a in figure 4) with the vgg16 architecture. the outputs obtained for each dataset were fused and flattened before being classified with the fully connected layers, as shown in figure 5. the sum of the trainable parameters was 484,041,973. 3) late fusion model the vgg16-based cnn model was extended to the late fusion (lf) model in this work. the lf model starts with each processed image as input (as the ef model) for each cnn channel, then fused each output obtained after classification by the softmax activation function. after the fusion of the results obtained from the 4 image types, they were classified by 2 dense layers of size 4,096 and were finalized with the softmax function to 16 output classes (figure 6). the total trainable parameters were 586,665,136. 7 fig. 5. vgg16-based early fusion model. fig. 6. vgg16-based late fusion model. 4) vgg16-based svm models according to the vgg16-based cnn model, the softmax activation function was used to classify the final output at the last layer. in contrast, this vgg16-based svm model applied the svm classifier instead of the softmax activation function, as shown in figure 7. fig. 7. vgg16-based svm model. svm is a popular classifier for supervised learning algorithms, especially for binary classification. in this work, multi-class svm is required to classify 16 classes of rose leaf disease images. there are several classifiers for multi-class svm. in this work various multi-class svm classifiers were applied including l2-svm, categorical hinge loss svm (chl-svm), and weston-watkins svm (ww-svm), to the vgg16-based cnn models as follows. the l2-svm is based on the optimization of l2 norm and squared hinge loss (shl) which is calculated in (4) and (5). engineering, technology & applied science research vol. 11, no. 5, 2021, 7678-7683 7681 www.etasr.com nuanmeesri: a hybrid deep learning and optimized machine learning approach for rose leaf … � � ! + # (4) $ ∑ max�0,1− �+!��,-!./ (5) where � refers to the weight of dataset 0, ! refers to the augmentation of sample data vectors, # refers to the bias, 1 refers to the number of samples in a dataset, �+ refers to the actual class, and � refers to the predicted class. then, the shl was optimized with a minimum of euclidean norm and a large error penalty. thus, the l2-svm was formulated in (6). min / , ‖�‖, , + 4 ∑ max(0,1 − �+!(� ! + #�� ,!./ (6) where ‖�‖, refers to the euclidean norm (l2 norm regularization), and 4 refers to the large error penalty for misclassification in which 4 > 0. the chl-svm or multi-class hinge loss function was implemented with tensorflow 2 based keras and is calculated in (7) [12]. $ = max50,1 + max5(1 − �+��6 − ∑ �+!�! !./ 6 (7) regarding the ww-svm or weston-watkins hinge loss [13], the linear classifier was calculated in (8), and the optimization was formulated in (9). $ = ∑ ∑ max(0,1 + �! − �7�789: � !./ (8) min / , ∑ ‖�7‖ ,; 7./ + 4 ∑ ∑ max(0,1 + �! − �7�789: � !./ (9) where � refers to the weight, < refers to the number of classes, = refers to the number of samples in the dataset, � refers to the predicted class, and 4 refers to the large error penalty for misclassification in which 4 > 0. finally, the last fully connected layer with the softmax function was replaced with the multi-class svm to classify the final output. therefore, 3 vgg16-based svm models, namely vgg16 & l2-svm, vgg16 & chl-svm, and vgg16 & ww-svm, were developed with different multi-class svm classifiers. 5) early fusion-based svm models the early fusion-based svm model applied the 3 different multi-class svm classifiers to the last fully connected layer with softmax of the ef model. thus, 3 ef models were developed, namely ef & l2-svm, ef & chl-svm, and ef & ww-svm. 6) late fusion-based svm models the lf model included two softmax functions at two layers: before fusion and at the last layer of the model. thus, the softmax classifier of the last layer was bypassed and replaced with the multi-class svm classifiers. therefore, 3 late fusion-based svm models were developed: lf & l2-svm, lf & chl-svm, and lf & ww-svm. by default, all models are based on vgg16 and cnn architecture. the image dataset was randomly split into 70%, 15%, and 15% for training, validating, and testing respectively. the hyperparameters were set as follows: the batch size was 64, the learning rate was 0.001, and training took 200 epochs. the models were compiled with the adam optimizer. e. model evaluation all models were evaluated and validated by the accuracy and loss value during the training processing. in addition, the vgg16-based cnn, ef, and lf models that applied the softmax function at the fully connected layer were evaluated using the categorical cross-entropy loss [14]: cross-entropy = −∑ ∑ �!,b log5e!,b6 f b./ 7 !./ (10) where � refers to the total of input, � refers to the number of classes, �!,b refers to the input � of class g, e!,b refers to the probability of the predicted class g by input �. further, the k-fold cross-validation was used to estimate the learning skill of the model based on an unseen dataset. the kfold cross-validation is mainly used to measure performance for machine learning models but can also be applied to deep learning models. thus, all 12 models were evaluated by 10-fold cross-validation in this work. the performance of the models was validated on accuracy (acc) [15], precision (prec) [16], recall (rec) [17], and f1-score. iii. results all 12 models were trained, validated, and tested and their performances were compared. a. model training and validation performance the results showed that the models developed with the early fusion technique performed better than late fusion and vgg16 models. especially, the model developed with the early fusion method and categorical hinge loss for the svm (ef & chl-svm) gave the best accuracy among the models as shown in table ii. table ii. accuracy and loss values results between training and validation of the models models training validation acc loss acc loss vgg16 (softmax) 94.71 0.1847 83.28 0.4063 vgg16 & l2-svm 95.09 0.1656 83.79 0.3643 vgg16 & chl-svm 96.03 0.1185 84.32 0.2607 vgg16 & ww-svm 95.59 0.1404 84.25 0.3090 ef (softmax) 97.09 0.0654 87.31 0.1438 ef & l2-svm 97.37 0.0514 87.62 0.1130 ef & chl-svm 98.28 0.0309 88.33 0.0679 ef & ww-svm 97.91 0.0443 88.07 0.0974 lf (softmax) 96.44 0.0981 84.19 0.2159 lf & l2-svm 96.86 0.0770 84.87 0.1695 lf & chl-svm 97.21 0.0597 85.44 0.1313 lf & ww-svm 96.97 0.0714 85.02 0.1570 according to table ii, the ef & chl-svm model yielded a training accuracy of 98.28% and a training loss of 0.0309. in addition, it gave a validation accuracy of 88.33% and a validation loss of 0.0679. the accuracy and loss error between training and validation of the ef & chl-svm are shown in figure 8. the validation accuracy of the ef & chl-svm model for rose leaf disease classification can be normalized and displayed as a confusion matrix, as shown in figure 9. the ef engineering, technology & applied science research vol. 11, no. 5, 2021, 7678-7683 7682 www.etasr.com nuanmeesri: a hybrid deep learning and optimized machine learning approach for rose leaf … & chi-svm model was able to classify the disease-free (nm) rose leaves with 98.95% accuracy. the most accurate classifications of rose leaf diseases were vw, ib, and dm, with 98.48%, 94.08%, and 92.68% accuracy respectively. for most of the other diseases the accuracy was higher than 87%, except for bb, atn, cls, and slr which had less than 83%. especially, the slr disease had the lowest accuracy of 74.44%. fig. 8. the performance of training and validation of the ef & chl-svm model. fig. 9. the validation accuracy of the ef & chl-svm model in a confusion matrix. b. model evaluation all developed models were tested and evaluated by 10-fold cross-validation with a test dataset. the result showed that the performances of the ef-based models were higher than the lfbased and vgg16-based models'. regarding the ef-based models, the ef & chl-svm had the highest performance with 90.26% accuracy, 90.59% precision, 92.44% recall, and 91.50% f1-score as shown in table iii. table iii. cross-validation performance models acc prec rec f1-score vgg16 (softmax) 86.16 87.03 89.05 88.03 vgg16 & l2-svm 86.37 87.27 89.16 88.20 vgg16 & chl-svm 86.90 87.81 89.47 88.63 vgg16 & ww-svm 86.62 87.53 89.30 88.41 ef (softmax) 89.54 90.20 91.90 91.04 ef & l2-svm 89.85 90.51 92.14 91.32 ef & chl-svm 90.26 90.59 92.44 91.50 ef & ww-svm 90.08 90.63 92.42 91.51 lf (softmax) 87.62 88.56 90.04 89.30 lf & l2-svm 87.83 88.78 90.19 89.48 lf & chl-svm 88.31 89.13 90.68 89.90 lf & ww-svm 88.05 88.88 90.43 89.65 iv. conclusion this research developed 12 models for classifying rose diseases from the symptoms that appear on the rose leaves using a cnn model based on vgg16 architecture and image processing. the classification of rose diseases consists of 16 classes (9 classes for diseases caused by fungi, 4 for virus diseases, 1 for insect bit, 1 for nutrient deficiencies, and 1 disease-free class). the 12 developed cnn models were divided into three groups: vgg16, ef, and lf. in addition, each group was divided into two classifier types: softmax and svm. the softmax function was used in 3 models, namely the vgg16-based cnn, ef, and lf models. the utilized multiclass svm classifiers were l2-svm, chl-svm, and wwsvm. there were 4,032 rose leaf images for model training. the images were resized to 224×224 pixels and underwent image augmentation, resulting in a dataset of 40,320 images. these images were subjected to image processing, including removal of background pixels, hsv color space, tagt, and dibt, to emphasize their features. both tagt and dibt are based on image thresholding processing. ultimately, the dataset was split to 70% for training, 15% for validation, and 15% for model testing by 10-fold cross-validation. the results showed that the ef-based models gave the highest training, validation, and testing performance values, followed by the lf-based and the vgg16-based models. in addition, the models developed with the svm classifier performed higher than the models using the softmax function. the model using chl-svm showed the highest performance, followed by the models using ww-svm, l2-svm, and softmax function. thus, the ef & chl-svm, a developed model based on the early fusion method and employing the svm categorical hinge loss function was the most suitable model for classifying diseases on rose leaves with an accuracy of at least 88.33%. the models developed in [7, 8] had accuracy not less than 94%, which is higher than the accuracy of the chl-svm model in this work. however, these two studies only classified 4 rose leaf diseases, unlike this study which classified 15. moreover, it is evident that image processing can improve rose leaf disease classification accuracy, especially when the features are fused. besides, it was found that svm gave better engineering, technology & applied science research vol. 11, no. 5, 2021, 7678-7683 7683 www.etasr.com nuanmeesri: a hybrid deep learning and optimized machine learning approach for rose leaf … results as a classifier than the softmax activation function, which is consistent with the findings in [18]. regarding further work, the author plans to develop a model based on u-net deep learning and a transfer learning approach to detect and classify diseases on plants and then integrate it to the internet of things. acknowledgment the author wishes to thank the institute for research and development, suan sunandha rajabhat university, for supporting this research. references [1] "top countries for export of roses," nationmaster. https://www.nationmaster.com/nmx/ranking/export-of-roses (accessed sep. 21, 2021). [2] r. k. horst and r. a. cloyd, compendium of rose diseases and pests. second edition, 2nd ed. st. paul, mi, usa: the american phytopathological society, 2007. [3] i. vazquez-iglesias et al., "high throughput sequencing and rt-qpcr assay reveal the presence of rose cryptic virus-1 in the united kingdom," journal of plant pathology, vol. 101, no. 4, pp. 1171–1175, nov. 2019, https://doi.org/10.1007/s42161-019-00307-5. [4] s. minaee, m. jafari, and n. safaie, "design and development of a rose plant disease-detection and site-specific spraying system based on a combination of infrared and visible images," journal of agricultural science and technology, vol. 20, no. 1, pp. 23–36, jan. 2018. [5] d. das, m. singh, s. s. mohanty, and s. chakravarty, "leaf disease detection using support vector machine," in 2020 international conference on communication and signal processing (iccsp), chennai, india, jul. 2020, pp. 1036–1040, https://doi.org/ 10.1109/iccsp48568.2020.9182128. [6] a. a. bharate and m. s. shirdhonkar, "a review on plant disease detection using image processing," in 2017 international conference on intelligent sustainable systems (iciss), palladam, india, dec. 2017, pp. 103–109, https://doi.org/10.1109/iss1.2017.8389326. [7] k. swetharani and v. prasad, "design and implementation of an efficient rose leaf disease detection using k-nearest neighbours," international journal of recent technology and engineering, vol. 9, no. 3, pp. 21–27, sep. 2020, https://doi.org/10.35940/ijrte.c4213.099320. [8] a. rajbongshi, t. sarker, md. m. ahamad, and md. m. rahman, "rose diseases recognition using mobilenet," in 2020 4th international symposium on multidisciplinary studies and innovative technologies (ismsit), istanbul, turkey, oct. 2020, https://doi.org/10.1109/ ismsit50672.2020.9254420. [9] c. rother, v. kolmogorov, and a. blake, "‘grabcut’: interactive foreground extraction using iterated graph cuts," acm transactions on graphics, vol. 23, no. 3, pp. 309–314, aug. 2004, https://doi.org/ 10.1145/1015706.1015720. [10] "opencv: miscellaneous image transformations," opencv. https://docs.opencv.org/master/d7/d1b/group__imgproc__misc.html (accessed sep. 21, 2021). [11] k. simonyan and a. zisserman, "very deep convolutional networks for large-scale image recognition," arxiv:1409.1556 [cs], apr. 2015, accessed: sep. 21, 2021. [online]. available: http://arxiv.org/ abs/1409.1556. [12] "tf.keras.losses.categoricalhinge," tensorflow. https://www.tensorflow .org/api_docs/python/tf/keras/losses/categoricalhinge (accessed sep. 21, 2021). [13] j. weston and c. watkins, "support vector machines for multi-class pattern recognition," presented at the 7th european symposium on artificial neural networks, bruges, belgium, jan. 1999. [14] l. poomhiran, p. meesad, and s. nuanmeesri, "improving the recognition performance of lip reading using the concatenated three sequence keyframe image technique," engineering, technology & applied science research, vol. 11, no. 2, pp. 6986–6992, apr. 2021, https://doi.org/10.48084/etasr.4102. [15] s. nuanmeesri, "development of community tourism enhancement in emerging cities using gamification and adaptive tourism recommendation," journal of king saud university computer and information sciences, apr. 2021, https://doi.org/10.1016/ j.jksuci.2021.04.007. [16] s. nuanmeesri and w. sriurai, "thai water buffalo disease analysis with the application of feature selection technique and multi-layer perceptron neural network," engineering, technology & applied science research, vol. 11, no. 2, pp. 6907–6911, apr. 2021, https://doi.org/10.48084/etasr.4049. [17] a. n. saeed, "a machine learning based approach for segmenting retinal nerve images using artificial neural networks," engineering, technology & applied science research, vol. 10, no. 4, pp. 5986–5991, aug. 2020, https://doi.org/10.48084/etasr.3666. [18] h. hasan, h. z. m. shafri, and m. habshi, "a comparison between support vector machine (svm) and convolutional neural network (cnn) models for hyperspectral image classification," iop conference series: earth and environmental science, vol. 357, nov. 2019, art. no. 012035, https://doi.org/10.1088/1755-1315/357/1/012035. author's profile sumitra nuanmeesri received her ph.d. in information technology at the king mongkut’s university of technology north bangkok, thailand. she is an assistant professor in the information technology department, faculty of science and technology at suan sunandha rajabhat university, thailand. her research interests include speech recognition, data mining, deep learning, image processing, mobile application, supply chain management system, internet of things, robotics, augmented reality, and virtual reality microsoft word 3-mavr-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1124-1129 1124 www.etasr.com mavrikakιs et al.: laboratory investigation of the hydrophobicity transfer mechanism… laboratory investigation of the hydrophobicity transfer mechanism on composite insulators aged in coastal service n. mavrikakιs electrical engineering dpt, tei of crete, greece mavrikakisnikos@ gmail.com k. siderakis electrical engineering dpt, tei of crete, greece ksiderakis@ staff.teicrete.gr e. koudoumas electrical engineering dpt, tei of crete, greece koudoumas@ staff.teicrete.gr e.drakakis electrical engineering dpt, tei of crete, greece edrakakis@ staff.teicrete.gr e. kymakis electrical engineering dpt, tei of crete, greece kymakis@ staff.teicrete.gr abstract—silicone rubber (sir) insulators are known to maintain their surface hydrophobicity even under severe pollution conditions in contrast to the other composite insulator materials used at the last decades. this critical advantage of silicone rubber insulators has made them dominant in high voltage power systems despite the fact that there are other composite materials with better static hydrophobicity. in service conditions, priority is given to the dynamic performance of hydrophobicity due to the unpredictable environmental pollution conditions. this dynamic performance of silicone rubber insulators is also known as hydrophobicity transfer mechanism. in literature, the hydrophobicity transfer mechanism of silicone rubber is related to the reorientation of methyl-groups and the existence of low molecular weight components. however there are many parameters which can change the effectiveness of this mechanism. some of them referred to the ageing effects on the material structure. thus it is of great importance to investigate the hydrophobicity transfer mechanism of field aged composite insulators. for this reason a new experimental procedure is introduced based on cigre tb 442. the results of field aged insulators are compared to that of a new sir insulator revealing the superiority of silicone rubber even after 17 years of field ageing. keywords-hydrophobicity; recovery; transfer; field; ageing; silicone rubber; lmw components, sio2 i. introduction environmental pollution is one of the most significant factors which can affect the reliability of high voltage power systems [14]. in literature, many network failures have been recorded relating to the environmental pollution of insulators, especially for traditional ceramic insulators [2-6]. the problem of environmental pollution was commonly dealt with by washing traditional ceramic insulators, usually using water in high pressure with the aid of helicopters [2, 4]. this method has a lot of disadvantages that includes cost, risks, need for frequent cleaning, defining the optimum schedule and the breakdown of electricity along the transmission line under cleaning. during the last twenty years, a large percentage of power network operators decided to switch to hydrophobic insulators and coatings [7]. thus, the faults relating to environmental pollution have been worldwide reduced [8, 9]. however, the lifetime of composite coatings and insulators is questionable due to their structure vulnerability to ageing factors [10]. during the insulators exposure in service, there are time periods when their hydrophobicity is lost. then, their behavior is similar to ceramic ones. however, some hydrophobic materials, mainly silicone rubber, are able to recover their original hydrophobicity after a finite time. this advantage of silicone rubber over other composite materials is known as the hydrophobicity transfer mechanism [11]. this feature of silicone rubbers is closely related to the material elemental structure, namely to the reorientation of the side methyl-groups of the polymer molecules and the existence of low molecular weight components. due to the fact that the hydrophobicity transfer is strongly related to the ageing condition of the material, it is of major importance to investigate the mechanism for field aged insulators, considering that in service conditions the environmental pollution is not predictable and can not be postponed. thus, the time of hydrophobicity recovery is a critical parameter related to the environmental pollution accumulation rate. ii. hydrophobicity transfer the ability of surface hydrophobicity recovery following a possible deterioration caused by field stress factors is one of the most significant advantages of silicone rubber. this property is strongly related to the polymer elemental structure. specifically, two mechanisms are suggested in the literature as dominant for the hydrophobicity transfer:  reorientation of methyl-groups  diffusion of low molecular components engineering, technology & applied science research vol. 6, no. 5, 2016, 1124-1129 1125 www.etasr.com mavrikakιs et al.: laboratory investigation of the hydrophobicity transfer mechanism… a. reorientation of methyl-groups as it is well known, the low surface energy of silicone rubber is a result of the existence of side methyl groups, which tend to spread out at the interface (figure 1). fig. 1. structure of silicone rubber. however the material ageing limits the beneficial hydrophobicity effect of methyl-groups either by imposing the last reorientation towards the inside of the structure or by the scission and replacement of the last with hydroxyl groups. therefore these reactions contribute to the increase of surface energy and finally to the hydrophobicity loss. in many cases, the recovery of hydrophobicity can be observed after the end of the stress. this is possible, due to the exceptional flexibility of the polymer chains of silicone rubber. thus the hydroxyl groups redirect inwardly to the material, restoring finally the methyl groups to the surface. this behavior has been confirmed in the laboratory by implementing salt-fog tests [12-16]. it must be noted that the referred mechanism requires a clean surface, which is not possible in real conditions. in the most of cases the insulator surface is covered with a hydrophilic layer of pollution, which determines the behavior. furthermore, the insulator surface in service conditions is stressed by electrical activity, thus the requirement of withdrawal of stress is not possible. therefore, the reorientation of side methyl groups should be considered a secondary recovery mechanism. b. diffusion of low molecular weight components the main recovery mechanism of hydrophobicity is the diffusion of low molecular weight components of the material. these molecules are already formed in the volume (bulk) of the material during the polymerization procedure [17, 18]. considering that the lmw consist of 4 to 14 monomers [19] in comparison to thousands monomers comprised in an average polymer chain, the lmw are quite mobile. these short length backbone chains resulting from curing procedure of polymer move in the volume of the material and tend to migrate from the bulk to the surface when the total surface energy of the material tends to increase. thereby lmw components penetrate into the surface pollution layer, varying the initial hydrophilic behavior to hydrophobic [20]. this feature is illustrated in figure 2. figure 2(a) shows an rtv sir coated porcelain insulator, which is covered by a layer of environmental pollution. however the insulator presents hydrophobic behavior which is related to the existence of lmw components as illustrated in figure 2(b). in an attempt to remove the environmental pollution from the insulator surface, a transient loss of hydrophobicity is observed as evident in figures 2(c) and 2(d). fig. 2. sir coated ceramic insulator the deposition of hydrophilic environmental pollution on the insulator surface may suspend the advantage of a hydrophobic surface. thus, the presence of low molecular weight components and their ability to diffuse from the volume to surface are of major importance for material efficiency. iii. hydrophobicity transfer parameters a. type and quantity of lmw components τhe hydrophobicity transfer mechanism is mainly based on the diffusion of lmw components from the bulk material to the surface. therefore the speed and the recovery time depend on the concentration difference between the volume and the surface of the material. initially the quantity of lmw components is related to the polymerization process followed and the thickness of the material. the initial amount may be changed during the material lifetime mainly due to ageing procedure. specifically the natural cleaning [21], the increase of surface heat (evaporation) and procedure relating to crosslinking reactions may result in reduced amounts of lmw molecules. on the other hand, scission of long length backbone chains of polymer can form lwm components. depending on the conditions and the balance developed, the lmw components exhaustion time is determined [22, 23]. it must be noted that the quantity of molecules is of great importance, namely the type of chain (linear of circular). in (a) (b) (c) (d) engineering, technology & applied science research vol. 6, no. 5, 2016, 1124-1129 1126 www.etasr.com mavrikakιs et al.: laboratory investigation of the hydrophobicity transfer mechanism… [24], it was shown that that the presence of cyclic chains is related to the faster recovery time. the latter was confirmed in [25]. b. relative position of lmw components in the bulk material the relative position of lmw components in the bulk material is of great importance for hydrophobicity transfer time. as it is well known, the lmw components move with a finite speed towards the surface. thus, the closer to the surface the lmw components are, the faster the material recovers. it must be noted that in aged material the amount of lmw components close to the surface is exhausted, thus they emerge from large depth, which requires more time [19, 26]. c. material composition due to the low intermolecular forces developed in pdms molecules, the lmw components present high mobility. however, the existence of fillers, particularly inorganic, can limit the mobility of lmw components due to the friction phenomenon [23, 27]. it must be noted that ath which is commonly used as filler in sir insulators, can contribute to a slower mobility of lmw molecules to the surface [28]. moreover, higher amount of filler means lower amount of polymer and thus lower quantity of lmw components [22, 27]. furthermore, the crosslinking reactions during the vulcanization process of the material can create a solid matrix close to the surface of the material preventing the migration of lmw component from the bulk to the surface. the additional crosslinking reactions and the byproducts such as sio2 come from the surface electrical activity in service conditions can suppress any possibility of hydrophobicity recovery. d. temperature as referred, the hydrophobicity transfer mechanism is based on the diffusion of lmw molecules. thus, in addition to the quantity, the high ambient temperature can accelerate too the mobility of these molecules, achieving faster hydrophobicity recovery [22, 29, 30]. e. type of pollutants the pollutants’ type may affect the possibility of the hydrophobicity recovery through the diffusion of lmw components. as previously referred, the lmw components penetrate into the surface pollution layer, changing its behavior from hydrophilic to hydrophobic. in fact, the lmw components are absorbed by the surface layer of soil, characterized by the higher surface energy than that of the material [31]. specifically, the higher the energy difference between the pollution layer and the material, the stronger the lmw molecules absorption from the pollutants. thus the pollutants’ structure [31-34] and their concentration can essentially determine the hydrophobicity transfer speed. table i is referred to the mobility of lmw components depending on the pollutants’ type. it must be noted that in the case of the material hydrophobicity transfer loss, its original hydrophobicity can be recovered by cleaning the material surface. various methods were tried in [35] in field conditions. the most acceptable method is the insulator cleaning with high pressure water as well as in the case of the uncoated insulators [36]. table i. pollution effect on the mobility of lmw type of pollutants mobility of lmw components inert kieselguhr, caolin, clay in the case of kieselguhr and clay the diffusion is very easy. the same is for caolin clay (longer hydrophobicity transfer time [33, 34] ). metal oxides sio2, zno, fe2o3, al2o3. hydrophobicity transfer is achieved between a time interval of 12 h and 24 h [32, 33]. inorgani c salts baso4, caso4, znso4, nh4cl, cacl2, nacl, kcl limited mobility, longer hydrophobicity transfer time is required [33, 34]. mixtures clay+ nacl, clay + caso4 the behavior depends on the content, according to the above behavior [33, 34]. iv. experimental procedure in order to investigate the effect of field ageing factors on the hydrophobicity transfer mechanism of composite insulators in service the following procedure was adopted. two fieldaged 150 kv sir insulators operating in the transmission system of crete were removed from the lines. the insulators were operating for a period of 17 years in different locations, characterized by different pollution severity, of the coastal high voltage network of crete (figure 3) [37-40]. table ii summarizes the main details for the field aged insulators examined and the pollution severity of their locations. the insulators were from different manufacturers, thus they were differing in material composition. the results of fieldaged insulators are compared to these of a new one sir insulator, used as reference. the fact that the insulators did not present failures during their 17 years of operation indicates the effective condition of the hydrophobicity. the experimental procedure, implemented in this study, has been introduced in cigre tb 442 of wg d1.14. an artificial pollution slurry made of 70% silica powder sio2 and 30% of water by weight was applied on the sample’s surface as illustrated in figure 5. the total thickness of the pollution layer on the sample’s surface was less than 0.5 mm. fig. 3. location of field-aged composite insulators table ii. insulators’ details insulator polymeric material years in service pollution severity a sir new b epdm & ath 17 heavy c sir& ath 17 medium engineering, technology & applied science research vol. 6, no. 5, 2016, 1124-1129 1127 www.etasr.com mavrikakιs et al.: laboratory investigation of the hydrophobicity transfer mechanism… a b c fig. 4. the three composite insulators prior to the deposition of the artificial pollution slurry on the sample’s surface, the upper shed of the polymeric housing of the field aged insulator was removed. samples about 10 mm x 10 mm x 5 mm were created from these sheds. the samples were cleaned with deionized water and stored in dry conditions for 24 hours. after that the initial contact angle was measured for each sample, which was used as reference point for each sample. fig. 5. deposition of artificial pollution slurry on sample’s surface after that, the artificial pollution slurry was applied on the samples’ surfaces as illustrated in figure 5. following the contact angle, indicator of hydrophobicity condition, of each sample was measured in certain time intervals. during the contact angle measurements, the conditions were constant, namely the ambient temperature was 23oc, the relative humidity was 50% and the barometric pressure was 755 mm hg. v. results water droplets, 10 μl in volume, were applied on the artificial polluted samples’ surfaces. the angle formed between the water droplet and the surface of the sample was measured with the ksv-cam 101 instrument according to method a of iec 62073. the measurements were taken in certain time intervals within 24 hours. the evaluation of hydrophobicity transfer mechanism is achieved by analyzing the recorded contact angle measurements. the contact angle measurements after the deposition of the artificial pollution slurry were compared to the initial contact angle in order to evaluate the hydrophobicity transfer speed. fig. 6. measure of contact angle changes of hydrophobicity for the field-aged and the new one composite insulators during the experimental procedure are presented in figure 7 . 0 20 40 60 80 100 120 140 0 4 8 12 16 20 24 co nt ac t a ng le (o ) time (h ) ins a (new sir) ins b (17 years epdm & ath) ins c (17 years sir & ath) fig. 7. hydrophobicity transfer speed of insulators sio2 h2o slurry soft brush sample deposition engineering, technology & applied science research vol. 6, no. 5, 2016, 1124-1129 1128 www.etasr.com mavrikakιs et al.: laboratory investigation of the hydrophobicity transfer mechanism… as previously referred, hydrophobicity transfer is a feature of silicone rubbers. both the field aged and the new sir (figure 7) insulators were found to be able to recover their origin surface hydrophobicity within 24 hours in contrast to field-aged epdm insulator. the surface hydrophobicity of the latter is strongly related to the hydrophobicity behavior of the artificial pollution slurry deposited on its surface. in this study the initial hydrophobic epdm insulator was changed to hydrophilic after its pollution deposition. that means that in service conditions epdm insulators are hydrophobic only immediately after their cleaning, thus they may effectively operate for long time in areas with light pollution severity. the hydrophobicity transfer mechanism was detected for both sir insulators. the results showed that the hydrophobicity transfer speed of the field aged insulator is comparable to that of the new sir insulator without presenting significant differences. the results are in good agreement with that presented in table i. according to that, the hydrophobicity transfer time of sir insulators in the case of sio2 pollutants is estimated from 12 to 24 hours. in this study the surface hydrophobicity of sir insulators changed from hydrophilic (contract angle < 90o) to hydrophobic (contact angle > 90o) after 12 h from the artificial pollution slurry deposition and they finally recovered they initial hydrophobicity within 24 hours. vi. conclusions surface hydrophobicity is of the most significant advantages of composite insulators compared to traditional ceramic insulators. some materials such as sir have the feature to gradually recover their lost hydrophobicity in the case of their deposition with hydrophilic environmental pollution. this property is known as the hydrophobicity transfer mechanism and it is closely related to the condition of the material and the conditions exposed. in this study, a short review to the hydrophobicity transfer mechanism was performed and following results for two field aged and a new composite insulator, used as reference, were presented by introducing an experimental procedure based on cigre tb 442. as expected, a hydrophobicity transfer mechanism was not found for the epdm insulator. on the other hand, both sir insulators were able to recover their surface hydrophobicity within 24 hours. the non-significant differences between the field-aged and the new insulator are mainly related to the different material composition of insulators and the field ageing effects. considering that the sir insulator was removed from service after 17 years, its hydrophobicity performance can be considered excellent. acknowledgment this work was partly supported by the polydiagno research project (project code 11syn-7-1503) which is implemented through the operational program “competitiveness and enterpreneurship”. action “cooperation 2011” and is cofinanced by the european union and greek national funds (national strategic reference framework 20072013). references [1] j. s. t. looms, insulators for high voltages, iee power engineering series, ed.7, 1987 [2] cigre wg 33-04-01, polluted insulators: a review of 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[37] d. pylarinos, k. siderakis, e. thalassinakis, n. mavrikakis, e. koudoumas, e. drakakis, e. kymakis, "a new approach for open air insulator test stations: experience from talos and the polydiagno project", journal of electrical engineering, vol. 16, no. 2, art. no. 16.2.32, pp. 269-273, 2016 [38] m. dimitropoulou, d. pylarinos, k. siderakis, e. thalassinakis, m. danikas, "comparative investigation of pollution accumulation and natural cleaning for different hv insulators", engineering, technology & applied science research, vol. 5, no. 2, pp. 764-774, 2015 [39] m. dimitropoulou, d. pylarinos, k. siderakis, e. thalassinakis, m. danikas, "insulation coordination and pollution measurements in the island of crete", icpadm international conference on the properties and applications of dielectric materials, sydney, australia, july 19-22, 2015 [40] d. pylarinos, k. siderakis, e. thalassinakis,"comparative investigation of silicone rubber composite and room temperature vulcanized coated glass insulators installed in coastal overhead transmission lines", ieee electrical insulation magazine, vol. 31, no. 2, pp. 23-29, 2015 microsoft word 04-suresh-ed.doc etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 98-104 98 www.etasr.com suresh and panda: shaf for mitigation of current harmonics using p-q method with … shaf for mitigation of current harmonics using p-q method with pi and fuzzy controllers suresh mikkili ph.d scholar nit rourkela, india msuresh.ee@gmail.com anup kumar panda professor nit rourkela, india akpanda.ee@gmail.com abstract— commencing with incandescent light bulb, every load today creates harmonics. unfortunately, these loads vary with respect to their amount of harmonic content and response to problems caused by harmonics. the issue of harmonics is of great concern to engineers, building designers and also in industrial applications because they do not just distort voltage waveforms, but they can also overheat the building wiring, cause nuisance tripping, overheat transformer units, and cause random end-user equipment failures. thus, power quality has become more and more serious with each passing day. as a result active power filters (apf) gain attention due to their excellent harmonic compensation. but still the performance of the active filter seems to be in contradiction with different control techniques. the main objective of this paper is to analyze shunt active filters employing fuzzy and pi controllers. the active and reactive power method (p-q) is used for the analysis. extensive simulations were carried out; simulations were performed with balance, unbalanced and non sinusoidal conditions. simulation results validate the dynamic behaviour of fuzzy logic controller over pi controller. keywordsharmonic compensation, shunt active power filters (shaf), p-q control strategy, pi controller, fuzzy controller i. introduction instantaneous active and reactive theory (p-q theory) was introduced in 1984 [1]. since then, many scientists and engineers [2-5] made significant contributions to its modifications in three-phase four-wire circuits and its applications to power electronic equipment. the p-q theory is based on a set of instantaneous powers defined in the time domain. no restrictions are imposed on the voltage and current waveforms, and it can be applied to three phase systems with or without neutral wire for three phase generic voltage and current waveforms. thus, it is valid not only in the steady state but also in the transient state. the p-q theory needs an additional phase locked loop (pll) circuit for synchronization and therefore p-q method is frequency variant. eminent issues always arise in three-phase four-wire systems. it is well-known that zero line may be overheated or cause fire disaster as a result of excessive harmonic current that is going through the zero line (even three times that of normal current). thus, a perfect compensator is necessary to avoid the consequences due to harmonics. though several control strategies and controllers have been developed, still the performance of filters is not equivalent under distorted conditions. present paper focuses on two controllers (fuzzy and pi) and a filter, employing the instantaneous active and reactive power (p-q) method [6] under different main voltages. ii. shunt active filter configuration to employ apfs in three-phase four-wire systems, two types of configurations are possible; one is a three-leg structure with the neutral conductor being connected to midpoint of dclink capacitor (figure 1) and the other one is a four-leg structure, where a fourth leg is provided exclusively for neutral current compensation (figure 2). fig. 1. three-leg shunt apf with non-linear load. the four-leg eight-switch apf topology is usually preferred as many researchers have pointed out this configuration as the most proficient alternative to be used in shunt apf [7] (figure 2). the three-leg six-switch split-capacitor configuration of shunt apf suffers from several shortcomings such as: (a) control circuit is somewhat complex (b) voltages of the two capacitors of split-capacitor need to be properly balanced (c) large dc-link capacitors are required. etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 98-104 99 www.etasr.com suresh and panda: shaf for mitigation of current harmonics using p-q method with … however, this topology is sometimes preferred due to less switching devices and lower switching losses compared to the eight-switch topology [8]. the higher order harmonics generated in the eight switch configuration due to frequent switching of semiconductor devices can be eliminated by the use of rc high-pass filter and switching losses occurring in the vsi can also be minimized by the use of dc-link voltage regulator. moreover, the four-leg apf has simple dc-link voltage controller, requires small dc-link capacitor, and the control scheme is also quite simple to implement. fig. 2. four-leg shunt apf with non-linear load iii. instantaneous active and reactive power control strategy the control algorithm block diagram for p–q method [1] is shown in figure 3. the three-phase source voltages (vsa, vsb, vsc) and load currents (ila, ilb, ilc) in the a–b–c coordinates are algebraically transformed to the α–β–0 coordinates using clarke’s transformation as shown in (1) and (2), followed by the calculation of the instantaneous active power (p), reactive power (q) and zero-sequence power (p0) as shown in (3). v v v v v 1 1 1 2 2 2 0 a 2 1 1 = 1 vα b3 2 2 β c3 3 0 2 2                              (1) 1 1 1 2 2 2i i 0 la 2 1 1 i = 1 iα lb3 2 2 i iβ 3 3 lc 0 2 2                                   (2) p v 0 0 i 0 0 0 p = 0 v v iα αβ q i 0 v -v βαβ                              (3) � ɶ p p p q q q = + = + (4) for reactive and harmonic compensation, the entire reactive power and ac component of active power are utilized as the reference power. the reference currents in α-β coordinates are calculated by using (5). �v vi * α βcα p + ∆ p1 = i * 2 2 v -v -qv + vcβ αβα β                   (5) the additional average power required to compensate for the losses in vsi due to the switching of semi-conductor devices is such that, 0 loss p p p∆ = + , where loss p is the average value of losses occurring in the inverter and is obtained from the voltage regulator. dc-link voltage regulator is designed to give both good compensation and an excellent transient response. the actual dc-link capacitor voltage (vdc) is compared by a reference value (vdc*) and the error is processed in a pi controller. * * 1 1 0 2 -ii * 0ca 2 1 1 3 i * = icαcb 3 2 22 ii * cβcc 1 1 3 2 22                                   (6) appropriate design of pll allows proper operation under distorted and unbalanced voltage conditions. controller includes small changes in positive sequence detector as harmonic compensation is mainly concentrated on three phase four wire [9]. in threephase three wire, va′, vb′, vc′ are used in transformations given by (7). in three phase four wire are modified as vα′, vβ′ and given by (8). 1 0 v 'a v 'α2 1 3 v ' = v 'b 3 2 2 β v 'c 1 3 2 2                                (7) etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 98-104 100 www.etasr.com suresh and panda: shaf for mitigation of current harmonics using p-q method with … loss p �p 0 p fig. 3. reference current extraction with conventional p-q method α β α ββ α v v ip iq v v      =            a α b β c 1 1 v 1 v 2 2 3 3v 0 v2 2 2 v 3                  =         la α lb lc 1 1 1 2 2 3 3 0 2 2 i i 2 i i 3 i β      =                      * cα α β c * cβ β α c α β i * v v -p1 = 2 2i * v -v qv + v           −      cα c 1 0 i *ca i *1 32 i * = cb i *3 2 2 i *cc 1 3 2 2 β             −              −   fig. 4. control method for shunt current compensation based on p-q theory etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 98-104 101 www.etasr.com suresh and panda: shaf for mitigation of current harmonics using p-q method with … i ' -i 'v ' α βα p'1 = v ' 2 2 i ' i ' q'i ' + i 'β αβα β                 (8) iv. construction of pi controller figure 5 shows the internal structure of the control circuit. the control scheme consists of a pi controller, a limiter, and a three phase sine wave generator for reference current generation and generation of switching signals. the peak value of reference currents is estimated by regulating the dc link voltage. the actual capacitor voltage is compared with a set reference value [10]. fig. 5. conventional pi controller the error signal is then processed through a pi controller, which contributes to zero steady error in tracking the reference current signal. the output of the pi controller is considered as peak value of the supply current (imax), which is composed of two components: (a) fundamental active power component of load current, and (b) loss component of apf to maintain the average capacitor voltage to a constant value. the peak value of the current (imax) is multiplied by the unit sine vectors in phase with the respective source voltages to obtain the reference compensating currents. these estimated reference currents (isa*, isb*, isc*) and sensed actual currents (isa, isb, isc ) are compared at a hysteresis band, which gives the error signal for the modulation technique. this error signal decides the operation of the converter switches. in this current control circuit configuration, the source/supply currents isabc are made to follow the sinusoidal reference current iabc, within a fixed hysteretic band. the width of hysteresis window determines the source current pattern, its harmonic spectrum and the switching frequency of the devices [11]. the dc link capacitor voltage is kept constant throughout the operating range of the converter. each phase of the converter is controlled independently. to increase the current of a particular phase, the lower switch of the converter associated with that particular phase is turned on. to decrease the current the upper switch of the respective converter phase is turned on. v. construction of fuzzy controller figure 6 shows the internal structure of the control circuit. the control scheme consists of a fuzzy controller, a limiter, and three phase sine wave generator for reference current generation and generation of switching signals. the peak value of reference currents is estimated by regulating the dc link voltage. the actual capacitor voltage is compared with a set reference value. the error signal is then processed through a fuzzy controller, which contributes to zero steady error in tracking the reference current signal. fig. 6. conventional fuzzy controller a fuzzy controller converts a linguistic control strategy into an automatic control strategy, and fuzzy rules are constructed by expert experience or knowledge database. firstly, input voltage vdc and the input reference voltage vdc-ref have been placed of the angular velocity to be the input variables of the fuzzy logic controller. then the output variable of the fuzzy logic controller is presented by the control current imax. to convert these numerical variables into linguistic variables, the following seven fuzzy levels or sets are chosen [12]: nb (negative big), nm (negative medium), ns (negative small), ze (zero), ps (positive small), pm (positive medium), and pb (positive big) as shown in figure 7. the fuzzy controller is characterized as follows: (i) seven fuzzy sets for each input and output. (ii) fuzzification using continuous universe of discourse. (iii) implication using mamdani's 'min' operator. (iv) de-fuzzification using the 'centroid' method. fuzzification: the process of converting a numerical variable (real number) convert to a linguistic variable (fuzzy number) is called fuzzification. de-fuzzification:the rules of flc generate required output in a linguistic variable (fuzzy number), according to real world requirements, linguistic variables have to be transformed to crisp output (real number). database: the database stores the definition of the membership function required by fuzzifier and defuzzifier. vi. simulation results figure 8 and figure 9 illustrates the performance of shunt active power filter under different main voltages. as load is highly inductive, the current is integrated with rich harmonics. initially, system performance is analyzed with balanced sinusoidal conditions. pi and fuzzy are good enough in etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 98-104 102 www.etasr.com suresh and panda: shaf for mitigation of current harmonics using p-q method with … suppressing harmonics and thd is about 2.85% and 1.27%, but under un-balanced and non-sinusoidal conditions fuzzy shows superior performance over pi controller and thd at this instant with pi are 4.36% and 5.31 %, where as in fuzzy it is about 2.98% and 3.85%. (figure 10). vii. conclusion in the present paper two controllers are developed and verified with three phase four wire system. even though both controllers are capable to compensate the current harmonics in the 3 phase 4-wire system, it is observed that the fuzzy controller shows more dynamic performance over conventional pi controller. with fuzzy logic and p-q approach a novel shunt active filter can be developed. table i. system parameters fig. 7. input vdc normalized membership function. table ii. rule base 3p h 4w non-sin p -q with fuzzy controller 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -400 -300 -200 -100 0 100 200 300 400 time (sec) s o u rc e v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) s o u rc e c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) f il te r c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 0 200 400 600 800 1000 time (sec) d c l in k v o lt a g e ( v o lt s ) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -40 -30 -20 -10 0 10 20 30 40 time (sec) l o a d c u rr e n t ( a m p s) 0 10 20 30 40 50 0 1 2 3 4 5 harmonic order thd= 3.85% m a g ( % o f f u n d a m e n ta l) 3p h 4w non-sin p -q with pi controller 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -400 -300 -200 -100 0 100 200 300 400 time (sec) s o u rc e v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) s o u rc e c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) f il te r c u rr e n t ( a m p s ) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 0 200 400 600 800 1000 time (sec) d c l in k v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -40 -30 -20 -10 0 10 20 30 40 time (sec) l o a d c u rr e n t ( a m p s) 0 10 20 30 40 50 0 2 4 6 8 10 harmonic order thd= 5.31% m a g ( % o f f u n d a m e n ta l) (a) (b) fig. 8. p-q control strategy response under bal non-sin with (a) pi controller (b) fuzzy controller etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 98-104 103 www.etasr.com suresh and panda: shaf for mitigation of current harmonics using p-q method with … 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -400 -300 -200 -100 0 100 200 300 400 time (sec) s o u rc e v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) s o u rc e c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (amps) f il te r c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 0 200 400 600 800 1000 time (sec) d c l in k v o lt a g e (v o lt s) 3ph 4w bal sin p-q with pi controller 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -40 -30 -20 -10 0 10 20 30 40 time (sec) l o a d c u rr e n t ( a m p s) 0 10 20 30 40 50 0 0.2 0.4 0.6 0.8 1 harmonic order thd= 2.15% m a g ( % o f f u n d a m e n ta l) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -400 -300 -200 -100 0 100 200 300 400 time (sec) s o u rc e v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) s o u rc e c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) f il te r c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 0 200 400 600 800 1000 d c l in k v o lt a g e (v o lt s) time (sec) 3ph 4w bal sin p-q with fuzzy controller 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -40 -30 -20 -10 0 10 20 30 40 time (sec) l o a d c u rr e n t ( a m p s) 0 10 20 30 40 50 0 0.2 0.4 0.6 0.8 1 harmonic order thd= 1.27% m a g ( % o f f u n d a m e n ta l) 3ph 4w un-bal p -q with pi controller 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -400 -300 -200 -100 0 100 200 300 400 time (sec) s o u rc e v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) s o u rc e c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) f il te r c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 0 200 400 600 800 1000 time (sec) d c l in k v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -40 -30 -20 -10 0 10 20 30 40 time (sec) l o a d c u rr e n t ( a m p s) 0 10 20 30 40 50 0 1 2 3 4 5 harmonic order thd= 4.16% m a g ( % o f f u n d a m e n ta l) 3p h 4w un-bal p -q with fuzzy controller 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -400 -300 -200 -100 0 100 200 300 400 time (sec) s o u rc e v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) s o u rc e c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -150 -100 -50 0 50 100 150 time (sec) f il te r c u rr e n t ( a m p s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 0 200 400 600 800 1000 time (sec) d c l in k v o lt a g e (v o lt s) 0.352 0.354 0.356 0.358 0.36 0.362 0.364 0.366 0.368 0.37 0.372 -40 -30 -20 -10 0 10 20 30 40 time (sec) l o a d c u rr e n t ( a m p s) 0 10 20 30 40 50 0 0.2 0.4 0.6 0.8 1 harmonic order thd= 2.98% m a g ( % o f f u n d a m e n ta l) (a) (b) (c) (d) fig. 9. 3ph 4wire shunt ative filter using p-q control strategy response under (a)bal sin with pi (b) bal sin with fuzzy (c) un-bal sin with pi (d) un-bal sin with fuzzy controller etasr engineering, technology & applied science research vol. 1, �o. 4, 2011, 98-104 104 www.etasr.com suresh and panda: shaf for mitigation of current harmonics using p-q method with … fig. 10. thd for p-q method with pi and fuzzy controllers references [1] h akagi, h. kanazawa, y. nabae “instantaneous reactive power compensators comprising switching devices without energy storage components” ieee transactions on industry applications, vol. ia20, no. 3, pp 625-630, 1984 [2] l. gyugyi, e. c. strycula, “active ac power filters”, ieee iias annual meeting, pp. 529-535, 1996 [3] f. z. peng, g. w. ott jr, d. j adams, “harmonic and reactive power compensation based on the generalized instantaneous reactive power theory for three-phase four-wire systems”, ieee transactions on power electronics, vol. 13, no. 5, pp. 1174-1181, 1998 [4] m. i. m. montero, e. r. cadaval, f. b. gonzalez, “comparison of control strategies for shunt active power filters in three-phase fourwire systems”, ieee transactions on power electronics, vol. 22, no. 1, pp. 229-236, 2007. [5] m. suresh, a. k. panda, s. yellasiri, “fuzzy controller based 3phase 4wire shunt active filter for mitigation of current harmonics with combined p-q and id-iq control strategies”, journal of energy and power engineering, vol. 3, no. 1, pp. 43-52, 2011 [6] h. akagi, e. h. watanabe, “instantaneous power theory and applications to power conditioning”, new jersey. ieee press/wileyinter-science isbn: 978-0-470-10761-4, 2007 [7] v. soares, p. verdelho, g. marques, “active power filter control circuit based on the instantaneous active and reactive current id –iq method”, ieee power electronics specialists conference, vol. 2, pp. 1096-1101, 1997 [8] m. aredes, j. hafner, k. heumann, “three-phase four-wire shunt active filter control strategies”, ieee transactions on power electronics, vol. 12, no. 2, pp. 311–318, 1997 [9] p. rodriguez, j. i. candela, a. luna, l. asiminoaei, “current harmonics cancellation in three-phase four-wire systems by using a four-branch star filtering topology”, ieee transactions on power electronics, vol. 24, no. 8, pp. 1939-1950, 2009 [10] p. salmeron, r. s. herrera, “distorted and unbalanced systems compensation within instantaneous reactive power framework”, ieee transactions on power delivery, vol. 21, no. 3, pp. 1655-1662, 2006 [11] s. mikkili, a. k. panda, "simulation and rtds hardware implementation of shaf for mitigation of current harmonics with pq and id-iq control strategies using pi controller", engineering, technology & applied science research, vol. 1, no. 3, pp. 54-62, 2011 [12] s. k. jain, p. agrawal, h. o. gupta, “fuzzy logic controlled shunt active power filter for power quality improvement” ieee proceedings electric power applications, vol. 149, no. 5, pp. 317–328, 2002 authors profile suresh mikkili was born in bapatla, andhra pradesh, india on 5 th aug 1985. he received b.tech degree in electrical and electronics engineering from jntu university hyderabad in may 2006 and masters (m.tech) in electrical engineering from n.i.t rourkela, india in may 2008. he has worked as a asst.prof in electrical engineering, s.i.t.e, t.p.gudem from june 2008 to dec-2009 and in v.k.r & v.n.b engineering college from dec2009 to july 2010. he is currently pursuing the ph.d degree in electrical engineering at n.i.t rourkela, india from july 2010. his main area of research includes power quality improvement issues, active filters, and soft computing techniques. . anup kumar panda: born in 1964. he received the b.tech in electrical engineering from sambalpur university, india in 1987. he received the m.tech in power electronics and drives from indian institute of technology, kharagpur, india in 1993 and ph.d. in 2001 from utkal university. join as a faculty in igit, sarang in 1990. served there for eleven years and then join national institute of technology, rourkela in january 2001 as an assistant professor and currently continuing as a professor in the department of electrical engineering. he has published over forty articles in journals and conferences. he has completed two mhrd projects and one nampet project. guided two ph.d. scholars and currently guiding four scholars in the area of power electronics & drives. his research interest include analysis and design of high frequency power conversion circuits, power factor correction circuits, power quality improvement in power system and electric drives. engineering, technology & applied science research vol. 8, no. 1, 2018, 2616-2620 2616 www.etasr.com laghari et al.: groundwater quality analysis for human consumption: a case study of sukkur city… groundwater quality analysis for human consumption a case study of sukkur city, pakistan abdul nasir laghari department of chemical engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan mashaalnasirlaghari@gmail.com zafar ali siyal department of energy and environment quaid-e-awam university of engineering, science & technology nawabshah, pakistan daddan k. bangwar department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan mohsin ali soomro department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan gordhan walasai department of mechanical engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan faheem akhter shaikh department of chemical engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan abstract—drinking water quantity and quality is of the utmost importance. if the drinking water gets contaminated, it can result in severe health problems. for example, the continuous consumption of drinking water containing more than permissible amounts of fluoride can lead to bone deterioration and increased risk of bone fracture [1]. the present study was carried out to check the quality of underground water of sukkur city. the analyzed parameters were fluoride, sodium, magnesium, calcium, potassium, iron, arsenic, tds, ph, conductivity, odor, color and taste. world health organization (who) standards were followed in present study. underground water samples were collected from 20 different populated locations of sukkur city. only arsenic, ph, iron and potassium were found to be within health safe limits while the rest of the parameters exceeded the permissible standards set out by who. the tds, sodium, fluoride and magnesium were over the limits at some locations. keywords-groundwater; water quality; physiochemical analysis i. introduction safe drinking water is the one of the core factors for a healthy life. our two main water sources are underground and surface water. only 3% of the underground water is fresh water and approximately 1.5 billion people use this water for drinking purpose [2]. in pakistan, the average consumption of water is 1 gallon per day for drinking and 188 gallons for other purposes [3]. it is estimated that 17% of the world population is drinking water which is unsafe to drink, 32% consume from safe sources and the remaining 51% from centralized pipe supply systems [4]. in pakistan, the unsafe quality of drinking water results in 30% of all diseases, 40% of all deaths and the majority of infant deaths. many waterborne diseases are a direct result of polluted water consumption, like diarrhea, malaria, intestinal worms, anemia, cholera etc. [5]. many of the leading causes of ground water contamination are industrial liquid waste, agrochemical disposal and untreated discharge of effluents [6]. there is unfortunately a lack of surveillance and monitoring programs to check the drinking water quality in pakistan, a situations that gets worse considering the pathetic institutional and government arrangements, insufficiency of well-equipped laboratories, non-compliance of who standards and absence of a legal framework for drinking water quality problems [7]. present study’s purpose is to analyze the underground water quality of sukkur city, compare the obtained results with who standards and put forward the measures need to be taken. ii. material and methods a. study area and sampling locations sukkur city is situated on west bank of indus river at latitudes 27°05' to 28°02'n and longitudes 68°47' to 69°43'e, altitude of 67m in sindh province. it is the 3rd largest city of sindh and 14thof pakistan. in this city, 60-80% of drinking water is taken from surface water. figure 1 shows the map of sukkur city, on which the sample locations are circled with red color and sample number, while the table i shows location names. b. water sample collection around 20 water samples are taken from different sites of sukkur city, particularly places from where people collect their drinking water. the standard method of sample collectionis that sample bottles are sterilized and collected in clean polyethylene bottles [8]. engineering, technology & applied science research vol. 8, no. 1, 2018, 2616-2620 2617 www.etasr.com laghari et al.: groundwater quality analysis for human consumption: a case study of sukkur city… fig. 1. sampling locations table i. sampling locations sample no. detail of locations spl1 shahi bazar thalla chowk spl2 bandar wall road spl3 old sabzi mandi, ghanta ghar spl4 teer chowk spl5 barrage college spl6 city point military road spl7 bihar colony spl8 sheikh muhala ayoob gate spl9 old sukkur spl10 garibabad beri chowk spl11 maki masjid new pind spl12 adam shah colony spl13 bachal shah colony spl14 new goth sukkur spl15 makka goth shikarpur road spl16 food storage near lu biscuit factory spl17 main sabzimandi shikarpur road spl18 sorath society spl19 society near kheer thar canal spl20 jaferia society c. parameters tested in present study, 12 water quality parameters were tested. they were as ph, tds, fluoride, sodium, magnesium, calcium, potassium, iron, arsenic, conductivity, odor, color andtaste. all experimental work and tests were conducted according to standards and conducted at energy & environment engineering department, quest nawabshah [9]. table ii lists the equipment used for this study. iii. results and discussion table iii shows the world health organization (who) standards for potable water suitable for human consumption. the study results are benchmarked against these standards. a. ph phis the degree of acidity or basicity of an aqueous solution. the ph value ranges from 0 to 14 and 7 being neutral.ph less than 7 indicates acidity and greater than 7 indicates basicity [10]. the recommended ph value by the who for drinking water is from 6.5 to 8.5. figure2 shows the acquired ph values of water samples at all locations. location spl13 has ph=7,8 which is the highest. this may be caused by the presence of toxic metals even at low concentration like copper and lead that are usually responsible for making the water alkaline. the use of agrochemicals, i.e., mostly plant nutrients and fertilizers, in the locality is responsible for the high concentration of heavy metals, which is definitely a major health risk. such contaminations are possible to reach and retain in soil layers and may even percolate to the groundwater aquifers, thus inducing a greater human health risk [19]. moreover, the geological structure of the catchment and buffering capacity also tends to influence the ph value of the water. the measured ph values of all the locations are within the who limits. table i. list of equipment used apparatus name model number titration apparatus calorimeter dr 2800 flame photometer 420 arsenic kit econo quick 481298 ph meter model 215 tds meter model 651 ec conductivity meter gmh 3430 table ii. who standards for potable water parameter standard value ph 6.5-8.5 tds 1000 mg/l sodium 200 mg/l fluoride 1.5 mg/l potassium 12 mg/l iron 0.3 mg/l magnesium 150 mg/l arsenic 50 mg/l calcium 200 mg/l b. total dissolved solids (tds) the measured values of tds for samples of all the locations are presented in figure3. the satisfactory value proposed by who is 1000 mg/l, while the measured values of tds at 9 locations: spl3, spl7, spl9, spl10, spl11, spl14, spl15, spl17, spl20 exceed the desired limit. the highest values are recorded at spl14 and spl15 and it is 6 engineering, technology & applied science research vol. 8, no. 1, 2018, 2616-2620 2618 www.etasr.com laghari et al.: groundwater quality analysis for human consumption: a case study of sukkur city… times higher than the desired limit. uncontrolled wastewater outflows both from domestic and industrial domains are the most possible reasons for high tds values in the region, as certain portions of such flows are then percolate to the aquifers and polluting the groundwater. the tds values exceeding the limits may affect the aesthetic water quality [11]. fig. 2. ph results of 20 groundwater locations of sukkur city fig. 3. tds resultsof 20 groundwater locations of sukkur city c. sodium measured values of sodium for samples of all the locations are presented in figure 4.sodium is found higher than who standards in samples spl10, spl14, spl15, spl17 and spl20. the excessive dose of sodium intake may cause nausea, dehydration, muscle twitching and vomiting. effects of sodium overdose in infant may be different with gastrointestinal infection fluid loss, dehydration, neurological damage and hypernatremia [12]. fig. 4. sodium results of 20 groundwater locations of sukkur city d. fluoride the measured fluoride values for all locations are presented in figure 5. fluoride higher than the desired limit was found in sites spl9, spl14, spl17, spl18 and spl20. this may be because of the abundance of phosphorite rocks in those areas as the fluoride in the water mostly comes from these rocks. the ground water at particular areas is not suitable for drinking purposes.dental and skeletal fluorosis are health hazards relevant towater consumptionof higher fluoride concentration [13]. fig. 5. groundwater fluorideconcentration results of various sampling locations of sukkur city e. potassium all samples measured results for potassium are under the permissible limit regarding who guidelines and are presented in figure 6. such concentration of potassium in ground water could not have adverse effects for human health [14]. fig. 6. potassium results at various sampling locations f. iron measured iron values for all locations are presented in figure 7 and they are found within the permissible limits of who standards, thus the consumption of underground water of sukkur city is safe regarding this aspect [15]. fig. 7. iron results at various sampling locations of sukkur city g. magnesium measured values of magnesium are presented in figure 8at three locations i.e. sample numbers spl14, spl15 and spl20 magnesium is found higher than the desired limit. the excessive intake of magnesium may cause vomiting and diarrhea. high dose of magnesium in water may cause nerve problems, muscle slackening and depressions [16]. engineering, technology & applied science research vol. 8, no. 1, 2018, 2616-2620 2619 www.etasr.com laghari et al.: groundwater quality analysis for human consumption: a case study of sukkur city… h. arsenic measured results of arsenic are presented in figure 9 and were found to be within permissible limits of who guidelines [17]. furthermore, no reports of lung bladder and skin cancer were found in the sampling premises, confirming that water is free from as. fig. 8. groundwater magnesium results of at various sampling locations fig. 9. groundwaterarsenic results at various sampling locations i. calcium the measured values of calcium for all locations are presented in figure 10. the location majority has values within the desired limit but few locations exceeded it i.e. spl2, spl14, spl15 and spl20. calcium determineswater hardness, inadequate calcium intake may cause increased risks of nephrolithiasis (kidney stones), osteoporosis, hypertension, coronary artery disease, and obesity [18]. fig. 10. calcium results at various sampling locations of sukkur city j. electrical conductivity (ec) measured ec results are presented in figure 11. it was observed that most of the ec values were beyond the permissible limit. only five locations out of 20 showed satisfactory results. the exceeding values of ec indicate the sum of the cation (or anions), or in other terms, the total concentration of salts. high temperature may also be another possible reason for increased ec values, as the ec of solutions approximately increases 2 percent with increase in each °c of temperature.the unit of electrical conductivity is deci-siemen per meter (ds/m). the higher ec may cause a gastrointestinal irritation in human beings. fig. 11. ec of groundwater at various sampling locations of sukkur city iv. conclusions it was concluded that overall quality of underground water at most of the locations was quite satisfactory, since the results of many parameters of various locations were under permissible limits. arsenic, ph, iron, potassium were within limits throughout all the locations while some parameters were exceeding the limits at various locations. tds was higher at locations spl3, spl7, spl9, spl10, spl14, spl15, spl17 and spl20. sodium was higher at locations spl10, spl14, spl15, spl17, and spl20. fluoride was higher at locations spl9, spl14, spl17, spl18 and spl20. magnesium was higher at locations spl14, spl15 and spl20. calcium was higher at locations spl2, spl14, spl15 and spl20. ec was higher at all locations except spl2, spl6, spl13 and spl16. based on the results of this study, it is recommended that locations number spl14 (new goth sukkur), spl15 (makka goth shikarpur road) and spl20 (jaferia society) must be examined thoroughly and possibly remedial measures must be taken into action. acknowledgment authors are thankful to the faculty of energy & environment engineering department for their assistance and support. references [1] r. buamah, c. a. oduro, m. h. sadik,“fluoride removal from drinking water using regenerated aluminum oxide coated media”, journal of environmental chemical engineering, vol. 4, no. 1, pp. 250-258, 2016 [2] m. m. mekonnen, a. y. hoekstra,“four billion people facing severe water scarcity”, science advances, vol. 2, no. 2, e1500323, 2016 [3] m. t. shah, j. ara, s. muhammad, s. khan, s. tariq, “health risk assessment via surface water and sub-surface water consumption in the mafic and ultramafic terrain, mohmand agency, northern pakistan”, journal of geochemical exploration, vol. 118, pp. 60-67, 2012 [4] m. l. susko, m. s. bloom, i. a. neamtiu, a. a. appleton, s. surdu, c. pop, e. f. fitzgerald, d. anastasiu, e. s. gurzau,“low-level arsenic exposure via drinking water consumption and female fecundity-a preliminary investigation”, environmental research, vol. 154, pp. 120125, 2017 [5] s. khan, m. shahnaz, n. jehan, s. rehman, m. tahirshah, i. din, “drinking water quality and human health risk in charsadda district, pakistan”, journal of cleaner production, vol. 60, pp. 93-101, 2013 [6] united states environmental protection agency, seminar publication wellhead protection guide for small communities, 1993 [7] a. rasool, a. farooqi, t. xiao, s. masood, m. aqeelkamran, s. bibi, “elevated levels of arsenic and trace metals in drinking water of tehsil engineering, technology & applied science research vol. 8, no. 1, 2018, 2616-2620 2620 www.etasr.com laghari et al.: groundwater quality analysis for human consumption: a case study of sukkur city… mailsi, punjab, pakistan”, journal of geochemical exploration, vol. 169, pp. 89-99, 2016 [8] united states environmental protection agency,quick guide to drinking water sample collection, available at https://www.epa.gov/region8-waterops/quick-guide-drinking-water-ampl e-collection. [9] pakistan environmental protection agency, national standards for drinking water quality, 2008 [10] s. l. gora, s. a. andrews, “adsorption of natural organic matter and disinfection byproduct precursors from surface water on tio 2 nanoparticles: ph effects, isotherm modelling and implications for using tio 2 for drinking water treatment”, chemosphere, vol. 174, pp. 363370, 2017 [11] h. y. hu, y. du,q. y. wu, x. zhao, x. tang, z. chen, “differences in dissolved organic matter between reclaimed water source and drinking water source”, science of the total environment, vol. 551-552, pp. 133142, 2016 [12] w. h. hallenbeck, g. r. brenniman, r. j. anderson, “high sodium in drinking water and its effect on blood pressure. (n.d.)”, american journal of epidemiology, vol. 114, no. 6, pp. 817-826, 1981 [13] l. xu, g. chen, c. peng, h. qiao, f. ke, r. hou, d. li, h. cai, x. wan, “adsorptive removal of fluoride from drinking water using porous starch loaded with common metal ions”, carbohydrate polymers, vol. 160, pp. 82-89, 2017 [14] world health organization, potassium in drinking-water, available at: http://www.who.int/water_sanitation_health/water-quality/guidelines/ch emicals/potassium-background.pdf, 2009 [15] world health organization, iron in drinking-water, available at: http://www.who.int/water_sanitation_health/dwq/chemicals/iron.pdf, 2003 [16] world health organization, calcium and magnesiumin drinking-water, available at: http://www.who.int/water_sanitation_health/publications/ publication_9789241563550/en/, 2009 [17] p. wongsasuluk, s. chotpantarat, w. siriwong, m. robson,“heavy metal contamination and human health risk assessment in drinking water from shallow groundwater wells in an agricultural area in ubon ratchathani province, thailand”, environmental geochemistry and health, vol. 36, no. 1, pp. 169-182, 2014 microsoft word etasr_v11_n4_pp7536-7541 engineering, technology & applied science research vol. 11, no. 5, 2021, 7536-7541 7536 www.etasr.com mohguen & bouguezel: denoising the ecg signal using ensemble empirical mode decomposition denoising the ecg signal using ensemble empirical mode decomposition wahiba mohguen ccns laboratory department of electronics faculty of technology university of ferhat abbas setif 1 setif, algeria wasotel@yahoo.fr saad bouguezel ccns laboratory department of electronics faculty of technology university of ferhat abbas setif 1 setif, algeria bouguezel_saad@yahoo.com abstract-in this paper, a novel electrocardiogram (ecg) denoising method based on the ensemble empirical mode decomposition (eemd) is proposed by introducing a modified customized thresholding function. the basic principle of this method is to decompose the noisy ecg signal into a series of intrinsic mode functions (imfs) using the eemd algorithm. moreover, a modified customized thresholding function was adopted for reducing the noise from the ecg signal and preserve the qrs complexes. the denoised signal was reconstructed using all thresholded imfs. real ecg signals having different additive white gaussian noise (awgn) levels were employed from the mit-bih database to evaluate the performance of the proposed method. for this purpose, output snr (snrout), mean square error (mse), and percentage root mean square difference (prd) parameters were used at different input snrs (snrin). the simulation results showed that the proposed method provided significant improvements over existing denoising methods. keywords-denoising; ecg; emd; eemd; customized thresholding i. introduction empirical mode decomposition (emd) is a powerful algorithm for splitting non-stationary signals [1]. the goal of emd is to represent the signals as sums of zero-mean oscillating components, named intrinsic mode functions (imfs) via a sifting process [1]. signal reconstruction is achieved by summing all imfs and the residual. emd techniques have been used for signal denoising, and specifically, those based on thresholding were developed in [210]. a denoising technique can be based on signal estimation using all the previously thresholded imfs [3-13]. since the useful information of the signal is often concentrated on lowfrequency imfs (last imfs) and the noise is primarily located in high-frequency imfs (first imfs), another approach is to perform denoising by partial construction of the signal with the imfs that contain useful information [2, 14]. authors in [2] proposed a method for estimating the energy of noisy imfs from a theoretical model and imfs' energies of the test signal, and the signal was reconstructed partially by using only the imfs that contained useful information, eliminating those that essentially maintained noise. in [14], an emd consecutive mean square error (emd-cmse) method was developed for imf selection. since electrocardiogram (ecg) signals are nonstationary and nonlinear methods, a wavelet thresholding technique was proposed in [15, 16] without preserving ecg components such as qrs complexes [17]. a customized thresholding function was proposed in [18] to overcome the disadvantages of hard and soft thresholding functions [15, 16]. emd combined with a customized thresholding function (emd-custom) can be useful for reducing noise and significantly improve the results of emd soft and hard thresholding [3, 4, 8]. to overcome the drawbacks of emd such as mode mixing (presence of oscillations of different amplitudes in one mode) [1], a variant of the emd algorithm called ensemble empirical mode decomposition (eemd) was proposed in [19]. eemd was based on averaging the modes obtained from emd applied to several trials of additive gaussian white moise (awgn) added to the signal. the eemd decomposition resolved efficiently the mode mixing and has been widely used in noise reduction. moreover, eemd achieved better denoising performance than emd with a reduced number of trials. the main objective of this paper is to propose a denoising method for ecg signals using eemd and a modified custom thresholding function. the basic principle of the proposed method is to decompose the noisy signal into a series of imfs using the eemd algorithm and then use the modified custom thresholding function. the denoised signal is reconstructed using all the thresholded imfs. denoising experiments were used on mit-bih ecg signals to assess the performance of the proposed method [20] with different awgn levels. three standard parameters were used at different input snr (snrin): output snr (snrout), mean square error (mse), and percentage root mean square difference (prd). the proposed method is compared to emd-cmse [14], emd-custom [8], and wavelet [15,16] denoising methods. ii. wavelet denoising wavelet denoising is a powerful tool for removing the noisy component of a corrupted data sequence [15, 16]. its corresponding author: wahiba mohguen engineering, technology & applied science research vol. 11, no. 5, 2021, 7536-7541 7537 www.etasr.com mohguen & bouguezel: denoising the ecg signal using ensemble empirical mode decomposition basic steps are: • decompose: choose a wavelet and a level n. compute the wavelet decomposition of the signal at level n. • threshold detail coefficients: for each level from 1 to n, select a threshold and apply soft thresholding to the detail coefficients. • reconstruct: compute wavelet reconstruction using the original approximation coefficients of level n and the modified detail coefficients of levels 1 to n. this work used the symlet wavelet (sym8), while thresholding can be performed by using the soft or hard thresholding of the input signal. wavelet soft thresholdingbased denoising technique was applied, the signal was divided into a set of approximations, and detail coefficients were thresholded using soft thresholding. the universal threshold estimator proposed in [15, 16] was used. iii. emd-custom thresholding emd-custom suggests the decomposition of a noisy signal to noisy imfs via the emd algorithm [1]. after that, the noisy denoted imfs were thresholded using a customized thresholding function [18]. finally, the denoised signal was reconstructed using all thresholded imfs. the outline of the emd-custom [8] method is demonstrated in figure 1. fig. 1. outline of the emd-custom. iv. eemd algorithm the eemd method [19] overcomes the "mode mixing" problem of the emd method and consists of: • adding a white noise ����� to the original signal ����: ����� � ���� �����, 1 � � �� (1) where ne is the ensemble number. • decomposing the noisy signal ����� into imfs by the emd method to obtain the corresponding imf of each order denoted ������, where i is the imf order, j is the trial index, n is the number of imfs, and 1 � � � �. • calculating the mean of the corresponding imfs as the final signal imf, by: ��������� � ��� ∑ �� ����, 1 � � � � ����� (2) v. proposed denoising method the proposed method suggests the decomposition of the noisy signal to noisy imfs via the eemd algorithm [19]. afterward, the noisy imfs denoted as ����� are thresholded using a modified custom thresholding function. let ���� be a noisy signal given as: ���� � ���� ���� (3) where ���� is the noiseless signal and ���� is an independent noise of finite amplitude. the proposed eemd-custom method consists of the following steps: • decompose the noisy signal ���� by the eemd algorithm to extract the noisy imfs �����. • apply a modified custom thresholding function on the noisy imfs ����� . a modification of the customized thresholding function [18] is introduced to define a new one as: �̂���� � ������ �!"#�����$%1 &'(�,�� |�����| * (�0, �� |�����| � , (4) where 0 , (�, 0 � & � 1 and (� is the universal threshold reported in [15, 16] defined as: (� � ./0�2ln �"� (5) where c is a constant depending on the type of the signal, n is the length of the signal, and ie is given by: 0� � �456 78�, � � 2,3,4,…,� (6) where 0�< is the energy of the first imf, obtained as: 0�< � =>�?�@a�|b4�c�|d.fghi j < (7) where k � 0.719 and 7 � 2.01 are empirically calculated constants [2]. • reconstruct the signal using: �n��� � ∑ �̂����� ��� o��� (8) where o��� is the residual signal. vi. results and discussion in this section, the results of the proposed denoising method are assessed compared to three denoising methods: wavelet denoising [15, 16], emd-cmse [14], and emd-custom [8]. the proposed eemd-custom algorithm was applied to 8 real biomedical ecg signals using the mit-bih database [20], labeled 111m, 112m, 113m, 114m, 115m, 116m, 121m, and 122m. an awgn was added to each clean ecg signal at different snrin levels: -4db, 0 db, 4 db, 8 db, and 12 db. the data length was 2048. at first, each noisy ecg signal was decomposed into a series of imfs via the eemd algorithm, and subsequently, the modified customized thresholding function (4) was utilized to threshold all imfs for reducing noise and preserve qrs complexes. thresholding can be used to detect qrs complexes [21]. so, the combination between eemd and the modified customized thresholding function can be considered as an r peak preservation technique, as the imfs containing high-frequency signal information (qrs complex) were thresholded by the modified customized thresholding function to preserve the qrs complexes. finally, the denoised signal was reconstructed using all thresholded imfs. three standard parameters, snrout, mse, and prd, were used to evaluate the capabilities of the proposed method at different snrin, which were respectively given as: engineering, technology & applied science research vol. 11, no. 5, 2021, 7536-7541 7538 www.etasr.com mohguen & bouguezel: denoising the ecg signal using ensemble empirical mode decomposition p�qrsc � 10log�d ∑ �v�c��5wxy4∑ �vn�c�8v�c�wxy4 �5 (9) zp0 � �a∑ ��n��� ����ac�� (10) [q\ � 100∗ ^∑ �vn�c�8v�c��5wxy4∑ �v�c��5wxy4 (11) the performance of the proposed eemd-custom method was evaluated for different values of ensemble number ne (10, 20, 30, 40, 50, 100, 150, 200, 250, 300). figure 2 depicts the snrout for different values of ne at snrin=4db on ecg record 112m. figure 3 displays the plot of snrout for different values of ne at snrin=4db on ecg records 114m, 116m, and 122m. as it can be observed, the snrout increases as ne increases. moreover, the proposed method achieved a significant improvement when ne was high. based on the results, an ensemble number of 200 was selected as the best eemd parameter. furthermore, as the results of the proposed eemd-custom method were influenced by the α value in (4), an appropriate value of α should be determined. fig. 2. snrout of the proposed eemd-custom in terms of ne, snrin=4db, for the ecg 112m signal. fig. 3. snrout of the proposed eemd-custom in terms of ne, snrin=4db, for the ecg records 114m, 116m, and 122 m. figures 4 and 5 show the snrout of the proposed eemdcustom method as a function of α for different ecg signals. the value of the ensemble number was ne=200, the snrin was 8db, and the value of α was determined by trials between 0.1 and 1, with a fixed step of 0.1. the values of a where the snrout was maximum, were 0.7, 0.3, 0.5, 0.5, 0.5, 0.5, 0.3, and 0.5 for ecg records 111m, 112m, 113m, 114m, 115m, 116m, 121m, and 122m respectively. the α parameter depended on snrin and the type of ecg signal. fig. 4. snrout of the proposed eemd-custom in terms of α, snrin=8db, for different ecg signals. fig. 5. snrout of the proposed eemd-custom in terms of α, snrin=8db, for the ecg records 111m, 113m, and 115 m. the snrout of five ecg signals at various snrin values is presented in table i to provide quantitative analysis. the proposed eemd-custom denoising method on the ecg record 112m reached an improvement of snr equal to 6.95db at snrin=-4db compared to the wavelet denoising method. an improvement of 3.89db was obtained at snrin=0db compared to emd-cmse, while an improvement of 4.46db was obtained at snrin=-4db compared to the emd-custom. the proposed eemd-custom denoising method improved snr by 6.36db, 4.34db, and 3.87db on the ecg 121m at snrin=-4db compared to wavelet denoising [2], emd-cmse [5,6] and emd-custom [8], respectively. as it can be noted, the proposed method worked better for high and low values of snrin. moreover, the values of mse and prd of ecg signals for different snrin values are presented in tables ii and iii, respectively. the quality of the reconstructed ecg signal was evaluated in terms of prd, snrout, and mse. the mse and prd values should be small for better denoising and preserving ecg signal details. lower prd and mse values indicate better preservation of physiological information in ecg signal processing [17]. as it can be noted, the proposed eemdcustom method provided less mse and prd than the other methods. engineering, technology & applied science research vol. 11, no. 5, 2021, 7536-7541 7539 www.etasr.com mohguen & bouguezel: denoising the ecg signal using ensemble empirical mode decomposition table i. snrout obtained by different methods signals methods snrin (db) wavelet (sym 8) emd cmse emd custom proposed eemd custom ecg 111.m -4 1.44 2.33 2.83 4.48 0 5.38 5.87 6.51 7.79 4 9.24 9.75 10.41 11.24 8 12.90 12.79 14.26 14.69 12 16.16 14.82 17.56 17.69 ecg 112.m -4 4.61 7.89 7.10 11.56 0 8.58 10.27 10.94 14.16 4 12.44 13.78 14.31 15,95 8 16.10 16.36 17.54 18.03 12 19.36 18.71 20.77 20.99 ecg 113.m -4 1.43 2.96 3.95 5.86 0 5.35 6.12 7.55 9.20 4 9.17 9.41 11.12 12.54 8 12.75 12.75 14.89 15.77 12 15.85 16.04 18.48 18.84 ecg 114.m -4 4.21 6.37 6.13 8.44 0 7.57 7.38 9.65 10.43 4 10.30 10.54 12.00 12.48 8 12.16 12.56 15.56 15.75 12 13.20 13.64 18.00 18.33 ecg 115.m -4 1.43 3.61 4.12 6.46 0 5.36 5.87 7.72 10.16 4 9.18 9.64 11.51 13.30 8 12.77 12.87 15.02 16.54 12 15.88 14.79 18.61 19.25 ecg 116. m -4 4.26 5.64 5.96 7.54 0 8.06 7.94 9.28 9.98 4 11.23 10.30 12.10 12.60 8 13.68 13.81 15.71 16.27 12 15.24 16.88 19.02 19.32 ecg 121.m -4 4.66 6.68 7.15 11.02 0 8.64 8.52 10.36 12.98 4 12.58 12.49 13.57 15.44 8 16.42 16.66 17.56 18.37 12 20.07 18.75 20.93 21.14 ecg 122.m -4 4.57 6.95 6.45 8.60 0 8.45 8.14 9.85 10.62 4 12.14 11.81 13.02 12.99 8 15.42 15.03 16.05 16.47 12 18.03 18.32 19.17 19.68 fig. 6. snrout versus snrin for different denoising methods. figures 6, 7, and 8 present snrout, mse, and prd versus snrin of the denoised real ecg record 121m for wavelet denoising [2], emd-cmse [5, 6], emd-custom [8], and the proposed eemd-custom method. the proposed eemdcustom method gave better results in all cases. fig. 7. mse versus snrin for different denoising methods. fig. 8. prd versus snrin for different denoising methods. the clean ecg records 112m and 122m, their noisy versions, and denoised ecg records using the proposed eemd-custom at snrin=8db with ne=200 are depicted in figures 9 and 10 respectively. it can be noted that the proposed method removes noise successfully. figure 11 depicts the denoised ecg record 122m using the wavelet method at snrin=8db. a careful comparison of the denoised signals in figures 10 and 11 shows that the proposed method preserves morphological information of ecg better than the wavelet denoising method. the results also indicate that the proposed method can remove noise from real ecg signals and provide significant improvements in denoising performance. the computational complexity of eemd can be expressed as: _���� � �� ∗_��� (12) demonstrating that eemd takes more time than emd. fig. 9. ecg 112m signal denoised by the proposed eemd-custom method. engineering, technology & applied science research vol. 11, no. 5, 2021, 7536-7541 7540 www.etasr.com mohguen & bouguezel: denoising the ecg signal using ensemble empirical mode decomposition fig. 10. ecg 122m signal denoised by the proposed eemd-custom method. table ii. mse obtained by different methods. signals methods snrin (db) wavelet (sym 8) emdcmse emdcustom proposed eemd custom ecg 111.m -4 0.0405 0.0330 0.0293 0.0201 0 0.0163 0.0146 0.0125 0.0093 4 0.0067 0.0059 0.0051 0.0042 8 0.0028 0.0029 0.0021 0.0019 12 0.0013 0.0018 0.0009 0.0009 ecg 112.m -4 0.3053 0.1432 0.1719 0.0615 0 0.1221 0.0828 0.0710 0.0338 4 0.0502 0.0368 0.0327 0.0229 8 0.0216 0.0203 0.0155 0.0138 12 0.0102 0.0118 0.0073 0.0070 ecg 113.m -4 0.1819 0.1278 0.1017 0.0655 0 0.0736 0.0618 0.0443 0.0303 4 0.0305 0.0289 0.0195 0.0140 8 0.0134 0.0134 0.0081 0.0066 12 0.0065 0.0062 0.0035 0.0033 ecg 114.m -4 0.0201 0.0122 0.0129 0.0076 0 0.0092 0.0097 0.0057 0.0048 4 0.0049 0.0046 0.0030 0.0030 8 0.0032 0.0029 0.0014 0.0014 12 0.0025 0.0022 0.0007 0.0007 ecg 115.m -4 0.2492 0.1506 0.1342 0.0782 0 0.1008 0.0896 0.0585 0.0334 4 0.0418 0.0376 0.0244 0.0161 8 0.0183 0.0178 0.0109 0.0076 12 0.0089 0.0114 0.0047 0.0041 ecg 116.m -4 0.5085 0.3698 0.3437 0.2389 0 0.2116 0.2176 0.1600 0.1361 4 0.1019 0.1263 0.0835 0.0743 8 0.0580 0.0564 0.0364 0.0319 12 0.0405 0.0278 0.0169 0.0158 ecg 121.m -4 0.2197 0.1381 0.1238 0.0507 0 0.0878 0.090 0.0591 0.0323 4 0.0354 0.0361 0.0282 0.0183 8 0.0146 0.0138 0.0112 0.0093 12 0.0063 0.0085 0.0051 0.0049 ecg 122.m -4 0.2767 0.3997 0.1793 0.1092 0 0.1131 0.1214 0.0819 0.0687 4 0.0484 0.0522 0.0395 0.0398 8 0.0227 0.0248 0.0196 0.0178 12 0.0124 0.0116 0.0096 0.0085 fig. 11. ecg 122m signal denoised by the wavelet (sym8) method. table iii. prd obtained by different methods. signals methods snrin (db) wavelet (sym 8) emd cmse emd custom proposed eemd custom ecg 111.m -4 84.60 76.43 72.13 59.66 0 53.79 50.86 47.21 40.77 4 34.49 32.53 30.16 27.41 8 22.62 22.91 19.34 18.41 12 15.55 18.13 13.23 13.03 ecg 112.m -4 58.81 40.28 44.13 26.41 0 37.20 30.64 28.36 19.58 4 23.86 20.44 19.24 16.12 8 15.65 15.20 13.27 12.53 12 10.76 20.63 9.14 8.92 ecg 113.m -4 84.79 71.08 63.41 50.89 0 53.95 66.91 41.88 34.65 4 34.75 33.82 27.77 23.59 8 23.02 23.02 17.99 16.26 12 16.12 15.76 11.90 11.42 ecg 114.m -4 61.58 47.99 49.35 37.81 0 41.78 42.74 32.92 30.07 4 30.52 29.69 23.74 23.75 8 24.64 23.53 16.67 16.29 12 21.86 20.78 12.10 12.10 ecg 115.m -4 84.78 65.92 62.22 47.50 0 53.94 50.85 41.07 31.03 4 34.73 32.94 26.56 21.61 8 22.98 22.70 17.73 14.89 12 16.06 18.20 11.73 10.89 ecg 116.m -4 61.22 52.21 50.34 41.97 0 39.50 40.05 34.35 31.68 4 27.41 30.52 24.81 23.41 8 20.67 20.39 16.38 15.35 12 17.27 14.31 11.18 10.80 ecg 121.m -4 58.45 46.34 43.88 28.08 0 36.96 37.49 30.32 22.43 4 23.49 23.72 20.96 16.90 8 15.08 14.68 13.23 12.05 12 9.91 11.54 8.98 8.76 ecg 122.m -4 59.05 44.87 47.54 37.11 0 37.75 39.12 32.14 29.43 4 24.71 25.66 22.32 22.40 8 16.92 22.60 15.75 15.00 12 12.54 12.12 11.00 10.36 engineering, technology & applied science research vol. 11, no. 5, 2021, 7536-7541 7541 www.etasr.com mohguen & bouguezel: denoising the ecg signal using ensemble empirical mode decomposition vii. conclusion this paper presented a 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[21] m. elgendi, m. jonkman, and f. d. boer, "improved qrs detection algorithm using dynamic thresholds," international journal of hybrid information technology, vol. 2, no. 1, pp. 65–80, jan. 2009. microsoft word 9-731-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1158-1161 1158 www.etasr.com abrar et al.:. recovery of nickel from reformer catalysts of direct reduction, using the pressurized… recovery of nickel from reformer catalysts of direct reduction, using the pressurized dissolving method in nitric acid behdad abrar department of materials science and technology sharif university of technology tehran, iran mohammad halali department of materials science and technology sharif university of technology tehran, iran ali pourfathi department of materials science and technology sharif university of technology tehran, iran abstract—in the process of direct reduction of iron pellet and production of sponge iron, nio/al2o3 act as a catalyst for the generation of carbon monoxide and hydrogen by vapor and natural gas. as an expensive material used in midrex method for steel units, this type of catalyst has major environmental problems after accumulation. the steel industry in iran hopes to employ the midrex technique for the 80 percent of the 50 million tons of steel. thus, the problem of spent catalysts will become a serious environmental challenge. through the hydrometallurgy method, the present study investigates a possible solution to the problem of catalyst depot (due to heavy metals such as nickel) via nickel recovery, which may increase the possibility of selling or re-using the precious and expensive metal. the present research studied the nickel recovery from spent catalysts of nio/al2o3 used in reduction gas reliefs of the production of sponge iron unit. in this study, the parameters of temperature, concentration, time and rpm were studied using pressurized dissolving method. 100% efficiency was achieved at 140 °c for 120 minutes, nitric acid concentration of 1.5 mm, rpm of 600 and 40 s/l 40 grams per liter. keywords-catalyst; high-pressure hydrogenation; nitric acid; nickel i. introduction hydrometallurgical methods and processes are considered as environmental-friendly by the metal recycling industry of various sources. the benefits of such techniques includes low energy consumption, production of less gas pollutants and products, production of less waste and maximum recovery compared to other methods [1]. catalyst consumption and thus production of spent catalysts is increasing with a tremendous rate, and the global growth is estimated to be about 4.4%. [2]. it is estimated that the current worldwide value of these wastes is between 150,000 to 170,000 tons per year [3]. spent catalysts are considered as secondary sources of some valuable elements. in recent years, many studies have been conducted to recover various metals from the waste. catalysts discussed here were mainly used in the steel industry and oil and petrochemical processes such as desulphurization hydrocracking, synthesis of methane and ammonia, hydrogenation etc. the catalyst are usually alumina or silicabased with some elements added to them which includes: molybdenum, nickel, tungsten, platinum, rhenium, vanadium, zinc, copper, cobalt and chromium or their oxides. the catalyst examined in this study is al2o3/nio and the focus of interest is the recovery of nickel from the waste. nickel oxide containing catalysts are often used as a catalyst in the process of reforming and hydrocracking [4]. ii. midrex process the process of reforming is defined as the hydrocarbons reaction with oxidants such as water vapor and carbon dioxide to produce a mixture of hydrogen and carbon monoxide. usually, nickel is taken as catalyst in such process. the number of reactions that occur in the methane reforming condition is high and the most important types are as the following: 224 3hcoohch  222 hcoohco  2224 42 hcoohch  224 22 hcococh  steam reforming of natural gas is the most important and most economical process for production of synthesis gas in petrochemical and steel plants. the synthesis gas is consumed in production units of methanol, ammonia, and in refining and production of sponge iron. in the production units of sponge iron, iron ore is reduced under atmospheric pressure by synthesis gas. the processes for producing synthesis gas used in these units are used in or near atmospheric pressure. in the midrex process, natural gas at a temperature of about 1200 k in plug tube fixed bed reformers reacts with steam and as a result the synthesis gas is produced. engineering, technology & applied science research vol. 6, no. 5, 2016, 1158-1161 1159 www.etasr.com abrar et al.:. recovery of nickel from reformer catalysts of direct reduction, using the pressurized… iii. methodology in order to achieve the research objectives, first in the study investigation and study of the domestic and foreign research activities conducted on spent catalysts used in midrex process were considered. but since midrex method and in general a method for production of sponge iron (dri) by using natural gas is specialized to the countries with huge gas reserves (first of all iran), considerable researches have not been conducted on this matter and recovery of the precious metals contained in it (including nickel). as a result, in the study phase, we focused on the similar catalysts of this method (al2o3/nio) in other industries such as petrochemical, oil and gas, and production of chemical fertilizer and vegetable oil. similar studies have been conducted by various researchers. in [5], the acidic recovery of nickel from spent catalysts used in the industry of production of palm oil in malaysia was studied. in [6], optimizing the parameters for extraction of nickel, molybdenum, vanadium and aluminum from spent catalyst using oxalic acid catalyst in the presence of hydrogen peroxide was investigated. in [7], the two-step dissolving first by ammonia and then by 10% sulfuric acid was investigated. in [8], the authors used two-step dissolving to recover metals present in the catalyst. in [9], the recovery of molybdenum, nickel, cobalt and aluminum from spent catalysts using the alkaline and acidic two-stage dissolving approach was studied. in [10], the authors investigated the catalyst dissolving using acidized bacteria. in [11], the recovery of nickel from hydrogenation catalyst using thiobacillus thiuoxidane as a solver agent and the desulfosuccinatesvibrio5 bacteria as dissolving agent was investigated [11] iv. experimental methods a. materials precursor materials used in the study consisted of catalyst (nio/al2o3) spent in the direct reduction gas reliefs (midrex method) of khuzestan steel company, nitric acid 65% merck, distilled water processed in the extraction of metals laboratory of sharif university of technology, iran. the catalyst used in this study approximately consisted of 12.5% nickel in the form of nickel oxide based on alpha alumina phase (insoluble in nitric acid), form the major part of the catalyst (approximately 85%). fig. 1. the powder used b. catalyst preparation the catalysts used in this study require preparation before dissolving, because of the special working conditions under which they have been spent. normally gas relief catalysts act as the reaction catalyst at a temperature of about 1000 °c and produce the hydrogen and carbon monoxide gases in order to reduce the iron pellets. but part of the sulfur in the natural gas together with sulfur and carbon in the gas recycled from the midrex furnace that again put under the reaction, have deposited on the surface of the catalyst and after an hour lead to poisoning of the catalyst which is then dumped into the drain. this is done in order to remove carbon and specially sulfur from the surface of catalyst, which disrupt the nickel dissolving process. in this study, before the crushing operations, roasting operation was performed to remove sulfur and carbon, so that the catalysts were put in the furnace at 700 °c and under laminar flow of air, they were heat treated for 4 hours. the results of xrf analysis of catalysts showed that the most important elements in the catalyst was aluminum (43%) in the form of aluminum oxide and nickel (12.15%) in the form of nickel oxide. fig. 2. spent catalysts fig. 3. the reactor used c. experimental method since pressurized dissolving method was less used, we decided to use this method for tests, considering its advantages (according to the clausius-clapeyron relationship, increase of pressure also increases the evaporation temperature). as a result tests can be carried out at higher temperatures. by increasing the temperature, dissolving time can be reduced and also lower concentrations of acid may be used. engineering, technology & applied science research vol. 6, no. 5, 2016, 1158-1161 1160 www.etasr.com abrar et al.:. recovery of nickel from reformer catalysts of direct reduction, using the pressurized… also, argon gas was used for the implementation of pressurized environment, which was less risky than hydrogen, despite oxygen does not react with solution. in addition, an argon gas capsule was available in the laboratory. besides the nitric acid was used which was stronger compared to sulfuric acid. variables of temperature, time, concentration and effectiveness of the rpm on dissolution efficiency were studied. however, although at first seeds of different sizes were available in the laboratory, the aim of the study was not to study the effect of particle size, so the grain size was selected to be +1. in addition, pressure was constant at 10 bar and solid to liquid ratio was 40 grams per liter. in order to study the effect of temperature, 4 tests were conducted where temperature varies whereas other factors are kept constant (table i). a similar approach was followed to investigate the effects of concentration (table ii) and time (table iii). five runs were conducted in the latter case to increase the accuracy. to investigate the effect of rpm, a comparison mode was taken between 300 and 600 while other parameters were fixed as just the effectiveness of efficiency on it was examined (table iv). vi. results and discussion a comparison of dissolving results vs temperature is shown in table v. as shown, an increase of temperature led to an increase of the dissolution efficiency. the results of table v show that the increase of temperature has an optimization effect. the reason may be because of the increase of acid evaporation rate. after raising the temperature, two factors compete each other. one of them is the increase of temperature which enhances the efficiency and another is the excess reduction of acid concentration after the optimum temperature. of course the optimum temperature can be improved by raising the system pressure. also we should point out that after a while increase of temperature is not effective, which is probably because of dissolution of whole nickel in the solution and so increase of time would not affect the efficiency. results of tests conducted to check the effects of acid concentration are given in table vi. as shown, by doubling the concentration, the dissolving efficiency was also approximately doubled. this can due to an increase to the molarity of acid solution which may help more nickel to move to the solution from the dust. the results from the investigation of the effect or rpm changes are shown in table vii. table i. temperature effect i. n o . o f e x pe r im e n t t (° c ) c on ce nt ra tio n (m ) t im e (m in ) s/ l ) gr am /li te r ( r pm p (b ar ) g ra in s iz e 1 110 1.5 120 40 600 10 +1 2 120 1.5 120 40 600 10 +1 3 130 1.5 120 40 600 10 +1 4 140 1.5 120 40 600 10 +1 table ii. concentration effect n o. o f ex pe ri m en t t (° c ) c on ce nt ra t io n (m ) t im e (m in ) s/ l gr am /li te r ( r pm p (b ar ) g ra in s iz e 1 120 0.25 120 40 600 10 +1 2 120 0.50 120 40 600 10 +1 3 120 1 120 40 600 10 +1 4 120 1.5 120 40 600 10 +1 table iii. time effect n o. o f ex pe ri m en t t (° c ) c on ce nt ra ti on (m ) t im e (m in ) s/ l gr am /li te r ( r pm p (b ar ) g ra in s iz e 1 120 1.5 15 40 600 10 +1 2 120 1.5 30 40 600 10 +1 3 120 1.5 60 40 600 10 +1 4 120 1.5 90 40 600 10 +1 5 120 1.5 120 40 600 10 +1 table iv. rpm effect n o. o f ex pe rim en t t (° c ) c on ce nt ra tio n (m ) t im e (m in ) s/ l ) gr am /li te r ( r pm p (b ar ) g ra in s iz e 1 120 1.5 120 40 600 10 +1 2 120 1.5 120 40 300 10 +1 table v. comparison of dissolving results at different temperatures n o. o f ex pe ri m en t t (° c ) c on ce nt ra tio n (m ) t im e (m in ) r pm p (b ar ) g ra in s iz e ef fi ci en cy (% ) 1 110 1.5 120 600 10 +1 34 2 120 1.5 120 600 10 +1 66 3 130 1.5 120 600 10 +1 85 4 140 1.5 120 600 10 +1 98 table vi. comparison of dissolving results at different acid concentrations n o. o f ex pe ri m en t t (° c ) c on ce nt ra tio n (m ) t im e (m in ) s/ l (g ra m /li te r) r pm p (b ar ) g ra in s iz e e ff ic ie nc y (% ) 1 120 0.25 120 40 600 10 +1 15 2 120 0.50 120 40 600 10 +1 30 3 120 1 120 40 600 10 +1 52 4 120 1.5 120 40 600 10 +1 66 engineering, technology & applied science research vol. 6, no. 5, 2016, 1158-1161 1161 www.etasr.com abrar et al.:. recovery of nickel from reformer catalysts of direct reduction, using the pressurized… table vii. comparison of dissolving results at various rpms ii. conclusion the present study dealt with the recovery of nickel form direct reduction reformer catalyst using the pressurized dissolution in nitric method. the nio/al2o3 spent catalyst considered in this study was used in the direct reduction relief gases catalysts for production of sponge iron. the parameters of temperature, concentration of acid, time and rpm were investigated via pressurized dissolution method. results showed that at 140 °c maximum dissolution can be obtained but over this optimum temperature a reverse effect is noticed. another important factor is the rpm change effect, as a change from 600 to 300 caused a decrease of 10% of dissolution efficiency. finally, it is shown that efficiency was improved when dissolution time increased. references [1] j. y. lee, s. v. rao, b. n. kumar, d. j. kang, b. r. reddy.,”nickel recovery from spent raneynickel catalyst through dilute sulfuric acid leaching and soda ash precipitation”, journal of hazardous materials, vol. 176, pp. 1122-1125, 2009 [2] r. p. silvy, “future trends in refining catalyst market”, appl. catal., vol. 261, pp. 247–252, 2004 [3] p. dufresne, “hydroprocessing catalysts regeneration and recycling”, appl. catal. a: gen., vol. 322, pp. 67–75, 2007 [4] m. marafi, a. stanislaus, “spent catalyst waste management: a review: part i-developments in hydroprocessing catalyst waste reduction and use”, resources, conservation and recycling, vol. 52, no. 6, pp. 859873, 2008 [5] j. idris, m. musa, c. y. yin, k. h. hamid, “recovery of nickel from spent catalyst from palm oil hydrogenation process using acidic solutions”, journal of industrial and engineering chemistry, vol. 25, no. 16, pp. 251-5, 2010 [6] w. mulak, a. szymczycha, a. lesniewicz, w. zyrnicki, “preliminary results of metals leaching from a spent hydrodesulphurization (hds) catalyst”, physicochemical problems of mineral processing, vol. 40, pp. 69–76, 2006 [7] d. d. sun, j. h. tay, c. easton, “recovery and encapsulation of heavy metals on refinery spent hydrotreating catalyst”, water science and technology, vol. 42, pp.71–7, 2000 [8] m. marafi, a. stanislaus., “spent hydroprocessing catalyst management: a review, part ii-advances in metal recovery and safe disposal methods”, resources, conservation and recycling, vol. 53, pp. 1–26, 2008 [9] k. h. park, d. mohapatra, c. nam.,”two stage leaching of activated spent hds catalyst and solvent extraction of aluminium using organophosphinic extractant, cyanex 272”, journal of hazardous materials, vol. 148, pp. 287–295, 2007 [10] d. mishra, d. j. kim, d. e. ralph, j. g. ann, y. h. rhee, “bioleaching of spent catalysts using cidophilic bacteria and its kinetic aspect”, journal of hazardous materials, vol.152, pp. 1082–91, 2008 [11] v. bosio, m. viera, e. donati, “integrated bacterial process for the treatment of a spent nickel catalyst”, journal of hazardous materials, vol. 154, pp. 804-810, 2008 n o. o f ex pe ri m en t t (° c ) c on ce nt ra tio n (m ) t im e (m in ) s/ l (g ra m /li te r) r pm p (b ar ) g ra in s iz e ef fi ci en cy (% ) 1 120 1.5 120 40 600 10 +1 80 2 120 1.5 30 40 300 10 +1 73 microsoft word etasr_7-1_1363-1368.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1363-1368 1363 www.etasr.com ateekh-ur-rehman and alkahtani: automobile tire assessment: a multi-criteria approach automobile tire assessment: a multi-criteria approach ateekh-ur-rehman industrial engineering department, college of engineering, king saud university, riyadh, ksa arehman@ksu.edu.sa mohammed alkahtani industrial engineering department, college of engineering, king saud university, riyadh, ksa moalkahtani@ksu.edu.sa abstract—in response to the present dynamic market, automobile manufacturing industries are constantly evaluating and improving their manufacturing strategies to stay competitive. it is also evident that they evaluate those strategies considering multiple criteria. in one such case, an automobile project manager has to ensure that the selected tire (among the available alternatives) complies with the prospective automobile’s performance. this paper presents an approach for the assessment of alternative automobile tires taking into account multiple criteria, such as tire sustainability, tire road performance, environmental issues, tire purchase cost and tire road grip. the presented approach is quite helpful to any decision maker who is interested not only in ranking alternatives but also in establishing the superiority of an alternative over others. the approach also helps to specify the position of each alternative with respect to ideal solution. a case illustration is used to demonstrate an application of the approach. keywords-automobile tire; multi-criteria; decision making i. introduction in the tire market, there is a wide variety of tires for light & heavy automobiles. therefore, the justification of tire choice is an important and a crucial issue. thus, in response to the present dynamic market and green ecofriendly need, automobile manufacturing industries are constantly evaluating and improving their vendor selection strategies to stay competitive. nowadays, the automobile sector is receiving much attention from the research community. as tires plays an important role in an automobile’s performance, an automobile manufacturer has to select tires that are correctly sized and rated for its automobile to fulfill a fundamental set of criteria, such as load-carrying capacity, cushioning, dampening, braking torque, cornering force, dimensional stability, steering response, rolling resistance, and expected life span [1-3]. researchers also highlighted that elongation and tensile strength of the tire are important as quality control criteria in evaluating automobile road performance [4, 5]. from the open source database, it is clear that there is an enormous increase in major road accidents. a significant contributing factor to these accidents is tire failure. a field investigation of eight different brands of tires to understand the reasons for tire failure was reported in [4]. for example, catastrophic separation and tire blowouts are common events directed to serious road accidents [6]. tire blowouts are extremely a safety issue concern. close to 13% of road accidents reported are attributed to tire failure [7]. hence, one of the issues faced by the automobile research and development department is to test the alternative tires on multiple measures. the present paper attempts to present an approach to assess alternative automobile tires taking into account multiple criteria, such as tire sustainability, tire road performance, environmental issues, tire purchase cost and tire road grip. a case study is presented to show an application of the approach. ii. multi-criteria decision making: a review multi-criteria decision-making approaches are widely used in service and manufacturing industries. any decision-making approach concerned with the task of ranking a set of finite alternatives. researchers [8-9] have reviewed common multicriteria decision making approaches and examined the advantages and disadvantages and also explained the relative strengths and weaknesses. some of the multi-criteria decisionmaking approaches use additive formulas to classify the alternatives on hand. the summary of the most commonly used multi-criteria decision-making methods presented below:  analytic hierarchy process (ahp): a multi-criteria decision making approach introduced in [10]. the approach needs the decision tree with the goal at the top-level, criteria and sub-criteria in middle levels, and the alternatives at the bottom. in ahp, the experts and decision makers do pairwise comparison and select the best alternative according to the highest rank between alternatives. the drawback of the approach is that its unidirectional relationship characteristic cannot handle the complexity of many problems.  analytic network process (anp): the anp method is a general form of the ahp, anp introduced in [9]. anp partly overcomes the drawback of ahp and deals with the problem as a network of complex relationships between alternatives and criteria where all elements are connected [11].  preference ranking organization method for enrichment evaluation (promethee): this method uses the positive and negative outranking flows to rank the alternatives. these outranking flows do not usually induce the same rankings. subsequently, the approach considers the net outranking flow to do a pair-wise comparison of engineering, technology & applied science research vol. 7, no. 1, 2017, 1363-1368 1364 www.etasr.com ateekh-ur-rehman and alkahtani: automobile tire assessment: a multi-criteria approach alternatives to rank them with respect to multiple criteria [12].  the elimination and choice translating reality (electre): the electre approach focused on the dominance relations between alternatives. it is based on outranking relationships, and uses thresholds of indifference & preference to do pair-wise comparison between alternatives [13]. as the approach incorporates the fuzzy nature of decision-making, decision makers prefer the electre approach over the other approaches.  the technique for order preference by similarity to ideal solutions (topsis): this approach is based on the concept that the selected alternative should have the shortest distance from the positive ideal solution and the farthest distance from the negative ideal solution. the approach demarcates the positive ideal and negative ideal solutions. in this approach, the euclidean distance approach is used to check the relative closeness of the alternatives to the ideal solution [14-15]. in general, multi-criteria decision-making approaches have the following basic steps [15]: (a) formulate of the decision tree using alternatives, criteria and sub-criteria (b) determine the relative importance of the criteria and the impacts of the alternatives on these criteria. (c) process the numerical values to find a ranking of each alternative. apply value judgment on acceptable tradeoffs and evaluation, and (d) calculate final ranking and make decision. researchers and practitioners have adopted multi-criteria decision analysis in some industrial applications, such as in manufacturing technology investment decisions [16], for evaluation of energy plans [6] and for manufacturing nonfinancial justification [17]. in particular, automobile researchers adopted multi-criteria decision approach to select suitable tires for two-wheel drive tractors operating in sandy clay loam soils [18]. an intelligent tire model derived that can show the relationships between driving conditions and tire strain [19]. similarly, a qualitative formula developed to estimate the tire wear [20]. iii. comparative assessment : an approach an integrated multi criteria approach for an automobile tire assessment presented here in this section. the approach evaluates the decision hierarchy and derives weights for each criteria and sub-criteria using ahp [9-10] (refer steps 1 to 3). these weights are further used to do comparative assessment using topsis approach [14-15] (refer steps 4 to 9). the details about each step and calculations involved are presented here below. step 1: develop the decision hierarchy the approach needs a decision hierarchy, with the goal at the top-level, the criteria and the sub-criteria (attributes) in middle levels, and the alternatives at the bottom. figure 1 illustrates the decision hierarchy. fig. 1. the decision hierarchy step 2: do pairwise comparisons of criteria and attributes in is recommends that these pairwise comparisons be carried out using verbal responses and or non-verbal responses [10]. for example, the decision maker asked to answer whether criterion1 and criterion2 are of equal importance or whether one is more important than the other. if he/she indicates that criterion1 is more important, later he/she has to specify is criterion1: weakly more important, strongly more important, very strongly more important or extremely more important? resulted set of comparisons expressed in the form of criteria comparative matrix (ccm) as given below.   1 2 k l 1 2 k l criteria c c . c . . c c 1 x . . . . . c 1/x 1 . . . . . . . . . . . . . ccm= 1 c . . . 1 . . . . . . . . . . . . . . . . . 1 1/y c . . . . . y 1                                 in the above matrix, the criterion c1 is x times more important than criterion c2. similarly, do pairwise comparison for group of attributes for a given criterion. resulted set of comparisons expressed in the form of attribute comparative matrix (acm) as below.   1 2 j n 1 2 j n attrb a a . a . a a 1 z . . . . a 1/z 1 . . . . acm= 2. . . . . . . a . . . 1 . . . . . . . . . a . . . . . 1                             in the above matrix, the attribute a1 is z times more important than attribute a2. engineering, technology & applied science research vol. 7, no. 1, 2017, 1363-1368 1365 www.etasr.com ateekh-ur-rehman and alkahtani: automobile tire assessment: a multi-criteria approach step 3: transform the pairwise comparisons of attributes into attributes weight: after each comparison done, the obtained values converted by ahp process into a set of weights, which are then normalized. an approach based on eigenvalues is recommended [10]. since this involves a relative complex mathematical procedure, software such as super decision is used. these weights are subsequently used to get weighted normalized matrix. the normalized weights for attribute (wj) expressed as (3).  j 1 2 n-1 nw = w w . . w w for attributes (3) step 4: establish decision matrix and calculate normalized decision matrix: qualitative and quantitative data for given alternatives expressed as decision matrix (dm) as given below. 1 j n 1 11 1n i1 ij in m m1 mn a . a . a alter x . . . x . . . . . . dm= (4) alter x . x . x . . . . . . alter x . . . x i                        in the above matrix (4) 1 to m are alternatives and 1 to n are the attributes. x11 represents data entry for an alternative (alter1) with respect to an attribute (a1). this information is further treated as a decision matrix and transformed into the normalized decision matrix (ndm). the ndm represents relative performance of existing alternatives and represented in matrix form as. 1 j n 1 11 1n i i1 ij in m m1 mn i j a . a . a alter r . . . r . . . . . . ndm= (5) alter r . . r . r . . . . . . alter r . . . r                         the ndm data obtained using dm and (6). x ij r = (6) ij 2x iji  in (6), xij is measured value of alternative i with respect to attribute j and rij is the normalized score for alternative i w.r.t attribute j. step 5: construct the weighted normalized decision matrix: this step uses of set of criteria and attributes weight obtained at step 3. thus the normalized decision matrix value rij is converted into the weighted normalized. the wdm data is obtained using (8). step 6: establish the ideal and negative ideal solution: let jmax be the set of attributes (where preference is ‘maximum value’) and jmin be the set of negative attributes (where preference is ‘minimum value’). the positive ideal solution set expressed as (9). 1 j n 1 11 1n i i1 ij in m m1 mn i j a . a . a alter v . . . v . . . . . . wdm= (7) alter v . v . v . . . . . . alter v . . . v                         ij j ijv =w ×r (8)  * * * * *1 2 j nv = v ,v ,…v ……v (9) in (9), v*j = {maxvij if (j ϵ jmax) or minvij if ( j ϵ jmin)} the negative ideal solution set expressed as below.  ' ' ' '1 2 j nv = v ,v ,…v ……v (10) where v'j = {minvij if (j ϵ jmax) or maxvij if ( j ϵ jmin)} step 7: establish the separation measures for each alternative: the separation measure for an alternative from the ideal alternative s*i is established using (11).   1 22* * i j ij j s = v -v (11)         similarly, the separation measure for an alternative from the worst alternative s'i is established using (12).   1/2 2' ' i j ij j s = v -v 1( 2)         in above (11) and (12), the number of alternatives varies from 1 to m, vij is weighted normalized data for an alternative i with respect to an attribute j. step 8: establish the relative closeness of an alternative with respect to the ideal solution: the closeness measure c*i for an alternative with respect to the ideal alternative established using (13).   ' * i i * ' i i s c = (13) s +s where, s*i is the separation measure for an alternative from the ideal alternative, and s'i is the separation measure for an alternative from the worst alternative and while, c*i is the closeness measure. note c*i satisfies 0 < c * i < 1. the obtained values of vij, v * j, v ' j, s * i, s ' i and c * i in matrix form as closeness matrix (cm) (refer to (14)). step 9: select the best alternative: finally the alternatives ranked in descending order based on closeness value c*i. engineering, technology & applied science research vol. 7, no. 1, 2017, 1363-1368 1366 www.etasr.com ateekh-ur-rehman and alkahtani: automobile tire assessment: a multi-criteria approach * ' * 1 2 n i i i * ' * 1 11 12 1n 1 1 1 * ' * 2 21 22 2n 2 2 2 * ' * m m1 m2 mn m m m * j ' j i j a a . a s s c alter v v . v s s c alter v v . v s s c cm= (14). . . . . . . . alter v v . v s s c v . . . . . v . . . . .                              iv. application of the approach at the start the general goal was stated as ‘to rank the available alternative tires’. there were five criteria considered such as tire sustainability (tsu), tire performance (tp), tire grip (tg), tire environmental hazard (teh) and tire cost (tc). as shown in figure 2, these criteria were further fragmented down into attributes at next level. for example, criterion tire sustainability, the attributes tire carrying load capacity (tlc), tire cushioning, and tire long lasting (tll) quantified. similarly, for criterion tire performance, the attributes tire thread depth (ttd) and tire maximum speed (ts) measured. whereas, for criterion tire environmental hazard, the attributes tire noise pollution (tnp) and tire rolling resistance (trr) measured. and, for criterion tire grip, the attributes such as tire dry grip (tdg) and tire wet grip (twg) scores obtained. finally, the alternatives added in the lower level to the hierarchy. fig. 2. automobile tire decision hierarchy pairwise comparisons carried out using quantitative and qualitative responses. for example, in order to assess whether tsu and tp criteria had equal importance or whether one was more important than the other. if the professional indicated that tp was more important, then he was later asked if the tp was weakly more important, strongly more important, very strongly more important, or extremely more important. likewise, pairwise comparisons were carried out. the obtained pairwise comparative data expressed (refer to (1)) as in the form of criteria comparative matrix (ccm). in the following ccm matrix, the tsu quantified 3 times more important than criterion tp. subsequently, decision makers asked to do pairwise comparison of attributes for each criterion. the outcome of experts’ opinion expressed (refer to (2)) as acm matrix. criteria tsu tp teh tg tc tsu* 1 3 4 2 2 tp 0.33 1 2 0.5 0.33 ccm= teh 0.25 0.5 1 0.5 0.33 tg 0.5 2 2 1 2 tc 0.5 3 3 0.5 1                    for tsu* tlc tcu tll for teh tnp trr tlc 1 3 0.5 tnp 1 0.5 tcu 0.33 1 0.33 trr 2 1 tll 2 3 1 acm= for tg tdg twg for tp ttd ts tdg 1 3 ttd 1 2 twg 0.33 1 ts 0.5 1                                      *refer to figure 2 the cell values in the above set of matrices represent pairwise comparison of attributes for the given criterion. as presented, decision makers stated that for the given criterion tsu, the attribute tlc was three-time more important than tcu, and while tll was three times more important than tcu and two times more important than tlc. after pairwise comparison of attribute, the obtained scores converted into normalized weights (refer to (3)). the obtained normalized weights were as: j tlc tcu tll tnp trr ttd ts tdg twg tc w = 0.0807 0.0337 0.1228 0.0809 0.1619 0.1619 0.0809 0.1823 0.0607 0.0288       table i presents the list of the alternative tires. it highlights the performance of alternative tires aligned with multiple criteria and their attributes. as presented in table i, qualitative and quantitative data for given alternatives expressed (refer to (4)) as decision matrix (dm). it is clear that each attributes have different dimensions to measure. there is a need to transform various attribute dimensions into non-dimensional attributes, and to do neutral comparisons across criteria and attributes. the obtained outcome is presented in table ii. taking into account each of these normalize decision matrix and attribute weights for each alternative, weighted normalized decision matrix derived using (9), the derived outcome is as presented in table iii. subsequently, attributes categorized into two sets as vj* and v'j, the set of maximization attributes and minimization attributes. in table iii, wj is weight for attribute j, vj* is ideal solution for attribute j, and vj is negative ideal solution for attribute j. subsequently, to perform the sensitivity analysis, in the presented approach different set of weights used (table iv). the separation measure for all alternative tires and their closeness value with respect to the best and worst solution obtained and corresponding closeness score ci* for each alternative presented in table v. subsequently, these alternative tires are ranked based on closeness score ci*. in engineering, technology & applied science research vol. 7, no. 1, 2017, 1363-1368 1367 www.etasr.com ateekh-ur-rehman and alkahtani: automobile tire assessment: a multi-criteria approach table v, si* is separation measure for given alternative i from ideal alternative, sj is separation measure for given alternative i from negative ideal alternative and ci* is closeness measure for alternative i. table i. input data for assessment of alternative tires tsu* tp teh tc tg tlc tcu tll ttd ts tnp trr tc tdg twg max# max max max max min min min max max tire codes kg scale months mm km/hr ratio ratio $ % % t01 1060 3 12 8.2 180 5.5 18 5 91.8 54 t02 1090 5 30 9 200 2 12 3 95.2 58 t03 1120 4 24 9 200 4 14 5 94.5 57.5 t04 1060 2 18 8.4 190 6 16 5 92 53 t05 1090 3 20 8.6 200 5.5 18 3 91.5 55 t06 1090 4 20 8.6 210 3 14 2 92.7 58.8 t07 1000 4 24 8.6 200 3 13 2 93 56.5 t08 1060 3 18 8.4 170 5 17 3 90 53.2 t09 1090 5 30 8.6 190 3.5 15 5 95.8 56 t10 1060 4 20 8.8 210 2.5 13 1 95 57 t11 925 3 18 8.4 210 6 18 4 89 53 t12 1120 4 18 8.8 210 4.5 12 3 93 55.7 t13 1120 5 24 9 180 3.5 16 2 94.5 56.7 very good good satisfactory average below averagetcu score 5 4 3 2 1 above $500 $ 400 to 500 $ 250 to 400 $150 to 250 below $150 tc score 5 4 3 2 1 note: *refer figure 2, max: objective maximize, min: objective minimize table ii. normalized scores for each attribute & alternative codes↓ tlc tcu tll ttd ts tnp trr tc tdg twg t01 0.27 0.21 0.15 0.26 0.25 0.35 0.33 0.39 0.27 0.27 t02 0.28 0.36 0.38 0.29 0.28 0.13 0.22 0.23 0.28 0.29 t03 0.29 0.29 0.31 0.29 0.28 0.25 0.25 0.39 0.28 0.29 t04 0.27 0.14 0.23 0.27 0.27 0.38 0.29 0.39 0.27 0.26 t05 0.28 0.21 0.25 0.28 0.28 0.35 0.33 0.23 0.27 0.27 t06 0.28 0.29 0.25 0.28 0.30 0.19 0.25 0.16 0.28 0.29 t07 0.26 0.29 0.31 0.28 0.28 0.19 0.24 0.16 0.28 0.28 t08 0.27 0.21 0.23 0.27 0.24 0.32 0.31 0.23 0.27 0.26 t09 0.28 0.36 0.38 0.28 0.27 0.22 0.27 0.39 0.29 0.28 t10 0.27 0.29 0.25 0.28 0.30 0.16 0.24 0.08 0.28 0.28 t11 0.24 0.21 0.23 0.27 0.30 0.38 0.33 0.31 0.27 0.26 t12 0.29 0.29 0.23 0.28 0.30 0.29 0.22 0.23 0.28 0.28 t13 0.29 0.36 0.31 0.29 0.25 0.22 0.29 0.16 0.28 0.28 table iii. weighted normalized scores for each attribute & alternative codes↓ tlc tcu tll ttd ts tnp trr tc tdg twg wj→ 0.08070.0337 0.1282 0.1619 0.0809 0.0809 0.1619 0.0288 0.1823 0.0607 t01 0.022 0.007 0.020 0.043 0.021 0.028 0.053 0.011 0.050 0.016 t02 0.023 0.012 0.049 0.047 0.023 0.010 0.035 0.007 0.052 0.018 t03 0.023 0.010 0.039 0.047 0.023 0.021 0.041 0.011 0.051 0.017 t04 0.022 0.005 0.029 0.044 0.022 0.031 0.047 0.011 0.050 0.016 t05 0.023 0.007 0.033 0.045 0.023 0.028 0.053 0.007 0.050 0.017 t06 0.023 0.010 0.033 0.045 0.024 0.015 0.041 0.004 0.050 0.018 t07 0.021 0.010 0.039 0.045 0.023 0.015 0.038 0.004 0.051 0.017 t08 0.022 0.007 0.029 0.044 0.019 0.026 0.050 0.007 0.049 0.016 t09 0.023 0.012 0.049 0.045 0.022 0.018 0.044 0.011 0.052 0.017 t10 0.022 0.010 0.033 0.046 0.024 0.013 0.038 0.002 0.052 0.017 t11 0.019 0.007 0.029 0.044 0.024 0.031 0.053 0.009 0.048 0.016 t12 0.023 0.010 0.029 0.046 0.024 0.023 0.035 0.007 0.051 0.017 t13 0.023 0.012 0.039 0.047 0.021 0.018 0.047 0.004 0.051 0.017 v*j 0.023 0.012 0.049 0.047 0.024 0.010 0.035 0.002 0.052 0.018 v'j 0.019 0.005 0.020 0.043 0.019 0.031 0.053 0.011 0.048 0.016 table iv. set of weights used for sensitivity analysis attribute weight used tlc tcu tll ttd ts tnp trr tc tdg twg ahp 0.08070.03370.12820.16190.08090.08090.16190.02880.18230.0607 equal 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 unequal 0.05 0.05 0.05 0.05 0.1 0.05 0.1 0.01 0.5 0.04 table v. separation measures and relative closeness for each alternative tire from ideal solution and rank of alternative tire if ahp weights were given to all attribute if equal weights were given to all attribute if unequal random weights were given to attributes tire codes si * si ' ci * r a n k si * si ' ci * r a n k si * si ' ci * r a n k t01 0.041 0.005 0.108 13 0.049 0.009 0.153 13 0.022 0.006 0.105 13 t02 0.005 0.042 0.899 1 0.016 0.045 0.743 1 0.002 0.025 0.856 1 t03 0.018 0.027 0.596 6 0.036 0.027 0.429 8 0.010 0.017 0.561 5 t04 0.033 0.012 0.268 11 0.049 0.010 0.165 12 0.021 0.008 0.259 10 t05 0.031 0.015 0.330 9 0.035 0.021 0.376 9 0.020 0.009 0.339 9 t06 0.019 0.026 0.580 7 0.018 0.037 0.668 5 0.010 0.017 0.589 6 t07 0.013 0.031 0.709 2 0.015 0.038 0.716 3 0.008 0.019 0.711 4 t08 0.030 0.013 0.298 10 0.034 0.020 0.371 10 0.020 0.007 0.311 11 t09 0.015 0.035 0.696 3 0.033 0.036 0.521 6 0.008 0.021 0.653 3 t10 0.017 0.029 0.633 4 0.015 0.044 0.742 2 0.008 0.020 0.647 2 t11 0.035 0.011 0.244 12 0.042 0.014 0.252 11 0.023 0.008 0.245 12 t12 0.024 0.024 0.497 8 0.028 0.028 0.500 7 0.012 0.017 0.497 8 t13 0.018 0.027 0.604 5 0.017 0.039 0.701 4 0.011 0.018 0.611 7 v. discussion for an automobile project in saudi arabia, the goal set was to use a scientific multi criteria approach to make sure that the selected tire (among available alternatives) complies with prospective automobile performance. for the assessment of alternative automobile tires multiple criteria, such as tire sustainability, tire road performance, environmental issues, tire purchase cost and tire road grip are taken into account by the decision makers. the decision makers were interested not only in ranking alternatives but also in establishing the superiority of an alternative over others. there are varieties of attributes which may either support or oppose a particular alternative. by employing a single attribute analysis, as presented in table iii, it is evident that each given attribute produced significantly different preference choices. for example, if one chooses to maximize tcu (tire cushioning) of the automobile the first three preferences are tire t02, t09 and t13. whereas to minimize tire noise pollution (tnp) the first three preferences are t02, t10 and t06. so it is observed that a multiple criteria analysis approach is more suitable than a single criterion analysis. when considering multiple criteria and attributes, the presented approach used ten attributes to assess alternative tires. similarly, using expert opinion and pairwise comparison of attributes, weighted normalized weights for each attributes obtained. further considering multiple attributes, their corresponding weights and objective function; thirteen alternative tires evaluated. from table v it is clear that alternative tire t02 is the first, and t01 is the last preferred choice, if ahp weights are assigned to each attributes. in case, engineering, technology & applied science research vol. 7, no. 1, 2017, 1363-1368 1368 www.etasr.com ateekh-ur-rehman and alkahtani: automobile tire assessment: a multi-criteria approach persons involved in decision-making are of the opinion that equal or unequal random weights given to all tire attributes, it is evident that the present model exhibits sensitively. the sensitivity analysis shows variation in the ranking of alternative tires (table v). after the sensitivity analysis, tire t02 with load carrying capacity of 1090 kg, having very good tire cushioning while driving, having 2.5 years of life, the best thread depth, and very excellent tire grip in dry weather is the ideal first preference choice. in case, if the inclination towards an ideal preference is not satisfactory, then this approach is quite helpful to an analyst who is interested not only in ranking alternatives but also in establishing the superiority of an alternative over others. vi. conclusion the paper presents a multi criteria approach for practical decision-making. here the approach evaluates the decision hierarchy and derives weights for multiple criteria and their attributes. the approach also incorporates these weights and does multi criteria decision analysis. the model synthesizes the preference relationships for each alternative tire to produce the desired outranking relationship between the entire alternatives. the evaluation criteria for alternative tires were broadly related to tire sustainability, tire road performance, environmental issues, and tire purchase cost and tire road grip. in the presented model, limiting factor is five criteria and ten attributes, to assess the thirteen tires. considering the expected growth of automobile manufacturing sector, in future, one could extend the present work with other criteria and attributes, and also he/she incorporates the fuzzy characteristics. in the auto industry, the approach is quite helpful to any decision maker who is interested not only in ranking alternatives but also in establishing the superiority of an alternative over others if it exists. acknowledgment authors are thankful to the research center of college of engineering, deanship of scientific research, king saud university for the support. references [1] b. rodgers, w. waddell, “tire engineering science and technology of rubber”, science and technology of rubber, elsevier, 2005 [2] m. j. l. boada, b. l. boada, d. garcia-pozuelo, v. diazet, “neuralempirical tire model based on recursive lazy learning under combined longitudinal and lateral slip 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s. j. kim, k. s. kim, y. s. yoon. “development of a tire model based on an analysis of tire strain obtained by an intelligent tire system”, international journal of automotive technology, vol. 16, no. 5, pp. 865-875, 2015 [20] m. m. da silva, r. h. cunha, a. c. neto, “a simplified model for evaluating tire wear during conceptual design”, international journal of automotive technology, vol. 13, no. 6, pp. 915-922, 2012 microsoft word etasr_v12_n4_pp8872-8877 engineering, technology & applied science research vol. 12, no. 4, 2022, 8872-8877 8872 www.etasr.com ozturk & cayiroglu: a real-time application of singular spectrum analysis to object tracking with … a real-time application of singular spectrum analysis to object tracking with sift ali ozturk department of mechatronics vocational school of technical sciences mus alparslan university mus, turkey a.ozturk@alparslan.edu.tr ibrahim cayiroglu department of mechatronics faculty of engineering karabuk university karabuk, turkey icayiroglu@karabuk.edu.tr received: 27 april 2022 | revised: 31 may 2022 | accepted: 1 june 2022 abstractthis study combined sift and ssa to propose a novel algorithm for real-time object tracking. the proposed algorithm utilizes an intermediate fixed-size buffer and a modified ssa algorithm. since the complete reconstruction step of the ssa algorithm was unnecessary, it was considerably simplified. in addition, the execution time of a matlab implementation of the ssa algorithm was compared with a respective c++ implementation. moreover, the performance of the two different matching algorithms in the detection, the flannbasedmatcher and brute-force matcher algorithms of the opencv library, was compared. keywords-object tracking; object detection; computer vision; sift; ssa i. introduction object tracking or visual tracking has been employed, studied, and commercialized in a broad spectrum of applications such as simultaneous localization and mapping (slam), traffic surveillance, pedestrian counting, hand gesture recognition, tracking the path of protein stress granules in cells, and video compression [1]. object tracking can be defined as dynamic object detection [2]. the main problems of object tracking are common with object detection, such as occlusion, clutter in the background, viewpoint changes due to affine transformation such as translation and rotation, scale changes (zoom in and out), and photometric deformation such as distortion, blur, and illumination changes. the most important challenge is still the speed or real-time performance of the online tracker, such as the tracker used in visual servoing in robotics [3]. on the other hand, object tracking has some problems of its own. an optimal algorithm for visual tracking can vary depending on the camera’s position, the number of cameras, and the number of moving objects. in the case of a stationary camera, background removal can simplify the task by eliminating the stationary pixels [4]. if the number of moving objects and the target object increase, then the task becomes complicated. object tracking consists of two important steps: detecting the object of interest and tracking it in the following frames [5]. object detection can be defined as template matching in which a template or a model is detected within a scene. typically, a template is the picture of an object of interest. detection can be defined as enclosing a given template in the scene in a rectangle. in object tracking, the basic task is to track the object as long as it exists in the scene. scale invariant feature transform (sift) is one of the most robust local descriptors which can be used in object tracking [6-8]. it has been utilized in a broad spectrum of applications, such as face recognition, gender recognition [9], and smoke detection [10]. it is a good candidate to tackle the problems of tracking, such as translation, rotation, occlusion, and scale. a method was proposed in [11] to track objects by combining sift with mean shift. in [12], sift was utilized with kanadelucas-tomasi tracker (klt) [13] for uav-based applications. in this approach, the object was detected with sift, and its location was computed with klt. since the algorithms are not perfectly robust to all image transformations and deformations, the object of interest can be lost or detected with low accuracy during any object tracking task. in such cases, the pose can be recovered or improved by using filters or smoothing. singular spectrum analysis (ssa) is a method of time series analysis based on multivariate statistics. it is also known as the principal component analysis of time series [14]. ssa is considered to be a non-parametric (model-free) filtering technique. however, it can also be used for modeling [15]. it has been mainly used in applications that require postprocessing [16, 17]. ssa was combined with the kalman filter to smooth real-time positioning data obtained from the global navigation satellite system (gnss) in [18]. however, there is no description of how ssa was implemented in real-time. a rank-one eigenvector update was proposed in a recursive framework in [19] for the identification of structural damage detection in real-time by utilizing first-order perturbation (fop) for the henkel matrix. this paper proposes an object-tracking algorithm utilizing sift and ssa. to the best of our knowledge, this is the first study that employs sift and ssa in object tracking. as ssa always requires a batch of data, its real-time implementation was carried out using a fixed-sized buffer. since the real-time implementation of saa does not require a full reconstruction step by diagonal averaging, the reconstruction algorithm was considerably simplified. corresponding author: ali ozturk engineering, technology & applied science research vol. 12, no. 4, 2022, 8872-8877 8873 www.etasr.com ozturk & cayiroglu: a real-time application of singular spectrum analysis to object tracking with … ii. method this section investigates the ssa algorithm, provides the real-time implementation, describes object tracking with a template matching algorithm, and provides the details of the experiments. a. singular spectrum analysis the ssa algorithm can be summarized in four steps: embedding, singular value decomposition (svd), grouping, and finally, reconstruction. in the embedding step, a henkel matrix was constructed from the input signal. each column of the henkel matrix is a portion of the signal obtained by windowing with a selected window length. this process is also called a caterpillar since it behaves as such. if the length of the raw signal is n and the window length is l, the size of the henkel matrix is l×k, where l is the rows, � is the columns, and k=n-l+1. figure 1 shows an example of the embedding step. in this example, a henkel matrix is created from an input signal. the size of the signal is 10, and the window length is 4. therefore, the size of the resulting matrix is 7×4. fig. 1. an example of the embedding step. in the svd step, the singular value decomposition of the trajectory matrix is computed. if x is the henkel matrix, then the trajectory matrix is xx t , where x t is the transpose of x. the henkel matrix can be written as a sum of different and independent matrices with the aid of svd. this decomposition can be stated as follows: � � �� � �� � ⋯ � �� (1) where each xi is called an elementary matrix. each elementary matrix xi is calculated as follows: � � � � � , � � 1, ⋯ , � (2) where ui denotes the eigenvectors of svd, and each vector vi is calculated as follows: � �� �� �� , � � 1, ⋯ � (3) each elementary matrix � corresponds to one of the eigenvalues of svd. it should be noted that: ‖� ‖� � � , � � 1, ⋯ , � (4) the contribution of each elementary matrix to x is proportional to its corresponding eigenvalue λi. the eigenvalues are sorted in decreasing order. in ssa, elementary matrices corresponding to small eigenvalues are considered to be the noise portion of the signal. this portion is excluded in the grouping step: �� � ∑ � � �� (5) where r<m. the value of r is decided by looking at the ratio of the sum of the first r eigenvalues to the sum of all eigenvalues. if the value of this ratio is greater than a certain threshold, the sum of the first r elementary matrices (5) is considered to be an optimal approximation of the henkel matrix x. finally, in reconstruction, the optimal approximation of the henkel matrix, �� is converted to a time series. the reconstruction operation should be considered to be the inverse operation of the construction of the henkel matrix from the raw signal. this inverse operation is performed by diagonal averaging on the approximated henkel matrix (figure 1). the diagonal averaging is realized in three steps: top diagonalization, center, diagonalization, and tail diagonalization on the approximated henkel matrix as follows: �� � ⎩⎪ ⎨ ⎪⎧ � �"� ∑ # ,�$ "��"� �� , �% 0 ' ( ) *∗ , 1� -∗ ∑ # ,�$ "�∗ �� , �% *∗ , 1 ' ( ) . ∗ � /$� ∑ # ,�$ "�/$0 ∗"� ��$0∗"� , �% . ∗ ' ( ) 1 (6) where # ,2 , 1 ' � ' * , 1 ' 3 ' . denote entries of the approximated henkel matrix and, �� , 0 ' ( ) 1, are entries of the reconstructed time series. two parameters affect the result of ssa: the window length l and the reconstruction parameter r. the last one is determined by the eigenvalues as explained above. in general, the first or at least the sum of two eigenvalues constitutes the largest portion of the sum of all eigenvalues. however, there is no rule on how to select l. the choice of l affects the result of the filter. if l increases, the smoothing effect of the filter increases. this value can be determined by test and trial. b. real-time implementation of ssa the real-time implementation of ssa was conducted by using a fixed-size buffer (figure 2). at first, this buffer is filled with data. the size of the buffer is determined beforehand. so, this method requires a time delay to start filtering. once the buffer is full, the filtering operation starts. as new frames arrive, the buffer is updated. however, for the real-time implementation of ssa, there is no need for full reconstruction by diagonal averaging. since the last frame is written on the last element of the buffer, it is sufficient to recover only the last element of the approximated trajectory matrix, as follows: % � ��45 , 1, � , 16 (7) where f is the data filtered and the size of the approximated henkel matrix �� is 5 7 � . it is assumed that the first index starts from zero. thus, using (7), the reconstruction algorithm is significantly simplified by omitting diagonal averaging, compared to (6). this method is called real-time ssa (rtssa). engineering, technology & applied science research vol. 12, no. 4, 2022, 8872-8877 8874 www.etasr.com ozturk & cayiroglu: a real-time application of singular spectrum analysis to object tracking with … fig. 2. fixed-size buffer used for real-time implementation of ssa. c. object tracking with template matching template matching is the task of detecting a given template within a given scene. typically, a template is the picture of an object of interest. detection can be defined as enclosing a given template in the scene in a rectangle. figures 3 and 4 show the template used in this study and the detection task respectively. fig. 3. a matched sample frame from the video. fig. 4. a detection example from the video. this study used sift for object detection. sift is a local descriptor, typically invariant to local occlusion [20]. sift has two main parts: keypoint detection and feature description. keypoints (or salient points) are detected on the gaussian scale-space pyramid [21, 22]. this kind of keypoint detection makes the algorithm scale (zoom in and out) invariant. a dominant orientation of each keypoint is computed using the histogram of oriented gradients (hog). this computation makes the algorithm orientation invariant. finally, a feature vector for each keypoint is calculated using hog [23]. the normalization of the feature vector makes it invariant to changes in illumination. in summary, sift is invariant to translation, rotation, scale change (zoom in and out), partial occlusion, and illumination change. the runtime performance of sift mainly depends on the size of the image and the number of the extracted keypoints. in this study, sift was implemented using opencv 4.5.5. once the keypoints and features are computed both on the template and scene, the following task is matching. for the matching algorithm, the flannbasedmatcher of opencv can be utilized. the fast library for approximated nearest neighbor (flann) speeds up the matching task by using the k-nearest neighbor [24]. if the number of the extracted keypoints is low, the brute-force matcher of opencv can alternatively be utilized. figure 3 shows the sift keypoints on both the template and the scene, as well as the matched keypoints. once the matching pairs between the template and the scene are detected, the template’s corners should be projected on the scene. a homography matrix is needed for this projection. the opencv findhomography function was used to obtain the homography matrix using the ransac algorithm. finally, the opencv perspetivetransform function provides four corners of the rectangular polygon that encloses the template in the scene. d. experimental setup an everest sc-hd03 webcam was used to capture the video. in the video, the template (a penholder) was moved by hand. it was mobilized, moved away from the camera, zoomed in, rotated, and twisted in different directions. during this process, the pixel coordinates of the center point of the detected four corners of the template in the scene were considered to be the pose of the object. this center point is shown by a blue circle in figure 4. the video consists of 1439 frames. the size of each frame was 640×480. a c/c++ code was written for ssa and rt-ssa, using the eigen library [25], with floating-point arithmetic.the c/c++ code is available in [26]. on the other hand, matlab utilizes double-point arithmetic by default. the c/c++ code was compiled with gcc 9.4.0 on ubuntu 20.04 lts and run on an intel i9-10850k cpu @3.60ghz with 16gb ram. the parameters, notations, and abbreviations used in the results are shown in table i. as was observed, the first eigenvalue always constituted more than 90% of all. so, the reconstruction parameter r of ssa was taken as 1 for all tests. table i. notations and abbreviations used in results notation/ abbreviation explanation pose position of the object (x and y coordinates) flann flannbasedmatcher of opencv brute-force brute-force matcher of opencv filter-30-3 rt-ssa with a buffer of size 30, and window length of 3 filter-30-9 rt-ssa with a buffer of size 30, and window length of 9 iii. results this section, initially, presents the results of template matching according to two different matching methodologies, flann and brute-force. then, the results of the execution time of saa are provided. finally, the results of the application of real-time saa to object tracking are summarized. a. template matching figure 5 shows the results of flann and brute-force matching. as shown, flann lost the pose of the object in frame 562. however, the brute-force graph shows no loss at engineering, technology & applied science research vol. 12, no. 4, 2022, 8872-8877 8875 www.etasr.com ozturk & cayiroglu: a real-time application of singular spectrum analysis to object tracking with … any frame. the average number of keypoints on the scene is 67, which is considered low. therefore, it is more feasible to use the brute-force matcher. flann should be preferred when the number of keypoints is high. the average matching time with the brute-force matcher was about 3ms, while the average detection time of sift was about 33ms. fig. 5. results of the flannbasedmatcher and brute-force matching algorithms. b. execution time of ssa figure 6 shows the speed of the c++ and matlab ssa implementations. as shown, when the data length is 1k, the c++ implementation of ssa reaches 1000fps. this speed meets the requirements of many real-time applications. fig. 6. speed of c++ and matlab implementations of ssa algorithm for data length (1k=1024). execution time is expressed in fps. fig. 7. speed-up ratio of a c++ over a matlab implementation of ssa. figure 7 shows the speed-up ratio of a c++ over the matlab implementation of ssa. the c++ implementation of ssa is up to 18 times faster than matlab. however, matlab code can still meet the speed requirements of many applications. c. application of ssa to real-time object tracking figures 8 and 9 show the x and y coordinates of the pose of the object when it is filtered with the real-time ssa. figures 10-12 show the scaled points a, b, and c marked in figure 8. these figures show that as the window length increases, the filter smoothing effect increases, and fluctuations smooth out. however, when the object changes its directions (figure 10), the filter may considerably move away from the actual pose because of over smoothing. therefore, the extensive parameters of the filter can be avoided. fig. 8. application of real-time ssa to object’s x coordinate obtained with brute force matcher. fig. 9. application of real-time ssa to object’s y coordinate obtained with brute force matcher. fig. 10. zoom in point a of figure 8. fig. 11. zoom in point b of figure 8. engineering, technology & applied science research vol. 12, no. 4, 2022, 8872-8877 8876 www.etasr.com ozturk & cayiroglu: a real-time application of singular spectrum analysis to object tracking with … fig. 12. zoom in point c of figure 8. iv. conclusion sift and ssa are two different methods that have become popular in the last two decades. sift is a local object detection algorithm. on the other hand, ssa is a filtering technique that utilizes some methods of multivariate statics, such as pca. this study combined sift with ssa for real-time object tracking. the main contributions of this paper can be summarized as follows: • the results of two different feature matching methods, flannbasedmatcher and brute-force matcher, were compared. • sift and ssa were used in a real-time object tracking application for the first time. • a c++ implementation of ssa was coded using the eigen library. • the performance (execution time) of c++ and matlab implementations of ssa were compared. • a novel method for the real-time implementation of ssa was presented, simplifying the reconstruction step. performance comparison showed that the classic ssa algorithm has enough speed for many real-time implementations and that the c/c++ code was faster than matlab. as the proposed real-time method did not require full reconstruction, it simplifies the ssa reconstruction step. moreover, instead of updating the raw data buffer, the henkel matrix can be updated by omitting the embedding step of ssa, which could be future work. on the other hand, it was also observed that the performance of the object detection algorithm heavily depends on the matching algorithm. it was concluded that if the number of keypoints is low, then the brute-force matcher should be preferred instead of the flannbasedmatcher. references [1] m. y. abbass, k.-c. kwon, n. kim, s. a. abdelwahab, f. e. a. elsamie, and a. a. m. khalaf, "a survey on online learning for visual tracking," the visual computer, vol. 37, no. 5, pp. 993–1014, may 2021, https://doi.org/10.1007/s00371-020-01848-y. 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[22] i. r. otero and m. delbracio, "computing an exact gaussian scalespace," image processing on line, vol. 6, pp. 8–26, feb. 2016, https://doi.org/10.5201/ipol.2016.117. [23] n. dalal and b. triggs, "histograms of oriented gradients for human detection," in 2005 ieee computer society conference on computer vision and pattern recognition (cvpr’05), san diego, ca, usa, jun. 2005, vol. 1, pp. 886–893 vol. 1, https://doi.org/10.1109/cvpr.2005. 177. [24] m. muja and d. g. lowe, "fast approximate nearest neighbors with automatic algorithm configuration," presented at the international conference on computer vision theory and applications, feb. 2009, vol. 1, pp. 331–340, https://doi.org/10.5220/0001787803310340. [25] "eigen library," eigen. https://eigen.tuxfamily.org. [26] a. ozturk, "ozturk-ali/ssa," may 30, 2022. https://github.com/ozturkali/ssa. engineering, technology & applied science research vol. 7, no. 6, 2017, 2236-2239 2236 www.etasr.com mehr and saba: ductility evaluation of steel structures with reduced beam sections and post-tensioned … ductility evaluation of steel structures with reduced beam sections and post-tensioned cables using the finite element method esmaeil hashemi mehr civil engineering (structural engineering) dpt, faculty of engineering, islamic azad university of arak, arak, iran hamid reza saba amirkabir university of technology tehran, iran abstract—given the importance of structure strengthening, this research introduces a particular type of steel structure in which the reduced beam section and post-tensioned cables were used for creating centralized property and preventing the formation of plastic hinges in the beam and columns. after introducing the system, abaqus modeling results are compared with a reliable laboratory sample to check its accuracy. good convergence was seen which shows the modeling accuracy. the results of the model’s nonlinear static analysis revealed that the above steel structure has higher ductility when compared to conventional steel structures. also, the results showed that with the rising of height, span length and early post-tensioned power of the cables we can increase the ductility of the structure. keywords-post-tensioned cables; reduced beam section; ductility. i. introduction the importance of designing resistant structures against the lateral forces is a crucial matter in iran. in recent years, according to urban development and construction progress in the country, the attention to the issue of earthquakes and the importance of wind power in high-rise buildings has been a serious issue. the clamped connections of steel structures in northridge earthquake (1994) and kobe earthquake (1995) showed poor performance and generally sustained the brittle fracture of the weld flange of the beam to the column. looking for a solution to avoid similar cases in the future, the researchers presented the connections of reduced beam section (rbs). in 1996 the direct connection was invented, and then its shape according to bending moment diagrams was modified under lateral load effects. afterwards, the linear reduced beam section was created. another type of this connection was introduced as a linear radial connection in late 1998. finally, the radial cutting connection was proposed [1].the results of the comparison experiments of steel moment frames to conventional bending and reduced section show that the moment frames with rbs connections are better than conventional bending frames. the behavior factor is one of the most important design parameters and in fact, it is the impact of ductility in the elastic design of the structure. therefore, recognition of such criterion is very important for the lateral systems. one of the main objectives in the design of steel structures is failure of the connecting place as the last stage of structural collapse, after the failure of beams and columns. but in recent earthquakes, failure of connections occurred before the one of beams and columns. in fact, while rigid connections have high resistance and hardness, the performed studies indicate that their low ductility causes the premature rupture [2]. after the northridge earthquake, extensive studies in the field of steel moment connections for increasing the ductility and reducing damage to the main members were performed. the result is the introduction of rigid connections with higher ductility due to the receding of the plastic hinge from junction place [3] and various screw connections [4]. in this direction, a new type of steel connection inspired by the idea of posttensioned precast concrete connections was introduced in [5]. in the proposed connection, the cable was used to create bending, shearing resistance, and restoring force. in a system with post-tensioned connections, instead of conventional reinforcements, a series of cables (tendons) with high tensile strength are used. these cables are placed under great tension at the two ends of the beam. thus, post-tensioned cables after releasing tend to shrink and achieve the primary mode. today, the moment frames with new connections are expected to tolerate the large inelastic deformations in beams and columns that occur in great earthquakes, though the disadvantages of new procedures designed steel frames are the formation of the plastic hinge and local buckling in the structural elements in large earthquakes. permanent non-elastic deformations in beams and columns create large drifts which lead to loss of structural function. in contrast, in the centralist structures, the significant non-elastic deformations and residual drift in beams and columns can be deleted by the opening of the connection distance. therefore, it seems that the centralist structures can, without damage to the main structural members, return to their original position after the earthquake. unlike the conventional steel frames which are based on the ductility and endurance of structural materials, ductility behavior of the centralist structures is constant because of the behavior of posttensioned cables or high quality fittings. in these connections before the cyclic loading, the strong cables or fittings become post-tensioned. due to post-tensioned force at the cables during engineering, technology & applied science research vol. 7, no. 6, 2017, 2236-2239 2237 www.etasr.com mehr and saba: ductility evaluation of steel structures with reduced beam sections and post-tensioned … an earthquake, these cables tend to turn back the structure to its original position (before the earthquake). it should be noted that in order to the structure to be able to maintain its centralization property, the post-tensioned cables and the main connection parts should remain in the elastic form [6]. what this study seeks, is evaluating nonlinear behavior of steel structures in which, the type of connection being used is a combination of reduced beam section and post-tensioned cables. also, we are trying to investigate the effect of important seismic parameters such as height, span and primary posttensioned power of cables. ii. model validation in this study, the presented model in [7] was used. the analyzed connection type in the laboratory by authors of [7] was in the cross-shaped form and it was made by two beams in two sides of a column, cable, corner and amplifier, forehead, double and continuity plates. the beams at the free end have a rollers support and the column at the law part has a joint support and it is free at the top. these conditions are based on the intersection points of the beams and columns in frames under lateral load. the height of the used column in connection sample is 3962 mm and its total length, including two beams and column section height, is equal to 8992 mm. the made connection sample that is ready for loading in the laboratory is indicated in figure 1. the analytical model and its geometric characteristics are similar to vitro model modeled by finite element software abaqus. the cable modeling faces many problems, because of the happening of numerous buckling and the entrance of the plate to the area after buckling. analysis type can have a significant impact on the results thus the theory of large deformations is used. in figure 2 results of the modeling in abaqus software are compared with the laboratory sample results. a. introduction of the case study model the case study model is a onefloor and onespan type of frame. the explanation of its properties explained in [8]. the beams are ipe40 and the axis to axis length is 4 meters. the columns are ipb34 and the axis to axis is length 2 meters. the post-tensioned cables have 20 mm inner diameter, and the holder diameter of 30 mm. the length of each cable is 4.33 meters. the primary post-tensioned force of each cable is 40 kn. fastener screws of the corners to beam and column are the a490 type and their body diameter is 30 mm and holder diameters are 40mm. the region soil is type iii. the mechanical properties of the materials used in modeling are expressed in table i. the connection of the corners to beam flange and the column flange, was made with 2 and 4 high strength screws respectively. for connecting the hardeners to beam flange the weld has been used. figure 3 indicates the way of the beam connection to a column. as you see in this system for connecting the beam to the column, the corner on the top and bottom of the beam is used as well as steel cables with high resistance. these cables are placed along with the beams and pass through the column flanges and finally they hold outside of the connection area. as an effect of cable controlling, a primary tensile force is created, the connection members go under pressure and an initial bending moment is created in the connection. it should be said that the beams and columns are not directly connected to each other and there is 2 cm distance by the column flange hardener [9]. fig. 1. the laboratory sample used to measure model validation fig. 2. the load chart_ lateral displacement of the laboratory samples and finite element model table i. mechanical properties of the case study steel frame materials material type e (gpa) fy (mpa) fu (mpa) υ beam, column and hardener 210 345 520 0.3 cable 210 1120 1400 0.3 screw 210 854 913 0.3 b. element and the brigade networking the used element in the structural parts modeling is the solid type. this element is three-dimensional. it is in two forms of wedge and square. it loads any general form under any loading. this element can tolerate the tension, pressure, bending and turning. it is used for modeling solid objects. the continuum brigade networking is used in the modeling. this kind of element is considered as standard volumetric elements in abaqus. engineering, technology & applied science research vol. 7, no. 6, 2017, 2236-2239 2238 www.etasr.com mehr and saba: ductility evaluation of steel structures with reduced beam sections and post-tensioned … fig. 3. the way of connecting the beam to column in the steel frame system that has post-tensioned cables c. way of loading loading type is nonlinear static. in this kind of loading after moving in the form of cycling during 13 cycles to the top of the columns, the hysteresis chart is drawn and through it, the pushover chart of the structure. after that, the ductility of the structure is determined by converting the pushover chart to a two-line chart by using the related relationships. d. ductility factor (μ) ductility factor of the structure is the maximum lateral shift ratio to the lateral movement like yielding (1). the ductility factor of a structure indicates the entrance rate of the structure to the non-linear zone. / max y    (1) δmax is the maximum lateral displacement and δy is the lateral displacement like the structural yield limit. in order to determine the ductility value and ductility factor firstly we should convert the pushover chart of the structure into two linear charts using a simple two-line method [6]. afterwards we can estimate the values of ductility and ductility factor. iii. results a. evaluation of ductility factor for the evaluation of ductility factor of a steel frame that has reduced beam section and post-tensioned cables in comparison with the normal frame, we consider a steel frame with cable and a normal frame without cable and the manner of connecting all of its parts by welding. they are similar to the steel frame with cable in the aspect of materials kind and size, loading circumstance and modeling. both of the model’s length from axis to axis is 4 meters and primary post-tensioned force is 40 kn. after the modeling, both models go under non-linear static analysis. table ii indicates the movement of yielding, resistance and ductility in both of the models. table ii. comparison of the movement of yielding, resistance and ductility of the normal steel frame and steel frame with cable type of the steel frame δy(m) ω μ normal 0.0067 1.52 13.53 with cable 0.0063 1.53 14.66 according to table ii, the steel frame with cable has higher ductility factor in comparison with the normal steel frame. therefore, we can increase the rate of ductility factor and consequently the seismic function of structures by using the post-tensioned cables in steel frames. b. investigation of the effects of height on the ductility factor for the investigation of the height effect on the ductility factor of the structure, we consider three models of the steel frame with cables with heights of 2.7, 3.7, 4.7m consecutively. the length of the span from axis to axis is 4 meters and posttensioned force is 40 kn. the results of non-linear statistical analysis of the models are expressed in table iii. table iii. effect of height on the ductility factor of steel frame with cable type of the steel frame δy(m) ω μ steel frame with cable with the height of 2.7m 0.0063 1.53 14.66 steel frame with cable with the height of 3.7m 0.0052 1.26 17.75 steel frame with cable with the height of 4.7m 0.0051 1.24 17.97 according to the results of the table iii, the larger value of ductility factor is related to the model with the height of 4.7m and the smaller value of ductility is for the model with the height of 2.7m. therefore, the height affects the rate of ductility factor of steel frame with cable. we can increase the structure’s rate of ductility factor by raising the height. c. evaluation of the effect of the length of the span on the ductility factor in order to evaluate the effect of the length of the span on the ductility factor, we consider three models of steel frames with 2.7m cable height, length of spans from axis to axis is 3, 4, and 5 meters consecutively and post-tensioned force of 40 kn. the results of the models non-linear statistical analysis are indicated in table iv. based on the results of the table iv, the larger value of ductility factor is related to the 5m length of span model and the smaller value of the ductility factor is for the model with 3mlength span. therefore, the length of the span effects the rate of the ductility factor of the steel frame with cable. we can increase the rate of the ductility factor by raising the length of the span (between 3 to 5 meters). d. effect of the primary post-tensioned force for checking the effect of the primary post-tensioned force on the ductility of the structure, we consider three models of steel frames with cables with 2.7m height, the length span from axis to axis of 4 meters and post-tensioned force of 20, 40 and engineering, technology & applied science research vol. 7, no. 6, 2017, 2236-2239 2239 www.etasr.com mehr and saba: ductility evaluation of steel structures with reduced beam sections and post-tensioned … 60 kn consecutively. the results of non-linear statistical analysis of the models are shown in table v. according to the results of table v, the larger value of ductility factor is related to the model with the primary post-tensioned force of 60 kn and the smaller value is for the model with the primary posttensioned force of 20 kn. therefore, the primary posttensioned force of the cables has an effect on the rate of ductility factor of the steel frame with cable. we can increase the rate of the ductility factor and consequently the seismic function of the structure by raising the primary post-tensioned force (between 20 to 60 kn). table iv. effect of the length of the span on the rate of ductility factor type of the steel frame δy(m) ω μ steel frame with cable with length span of 3m 0.0065 1.53 14.22 steel frame with cable with length span of 4m 0.0063 1.53 14.66 steel frame with cable with length span of 5m 0.0055 1.37 16.79 table v. effect of the primary post-tensioned force of the cables on the rate of the ductility factor type of the steel frame δy (m) ω μ steel frame with cable with post-tensioned force of 20 kn 0.0064 1.52 14.42 steel frame with cable with post-tensioned force of 40 kn 0.0063 1.53 14.66 steel frame with cable with post-tensioned force of 60 kn 0.0056 1.40 16.50 iv. conclusion in this study, we introduce the steel frame with reduced beam section and post-tensioned cables. based on the results, the steel frame with cable has more ductility when compared to the normal steel frame. the findings of the current study indicate that the increased height, length of the span and primary cable post-tensioned force cause increase in the ductility factor of the structure and consequently improve its seismic behavior. references [1] s. j. chen, c. h. yeh, j. m. chu, “ductile steel beam-to-column connections for seismic resistance”, journal of structural engineering, vol. 122, no. 11, pp. 1292-1299, 1996 [2] n. f. youssef, d. bonowitz, j. l. gross, a survey of steel momentresisting frame buildings affected by the 1994 northridge earthquake, us national institute of standards and technology, 1995 [3] m. d. engelhardt, t. winneberger, a. j. zekany, t. j. potyraj, “the dogbone connection: part ii”, modern steel construction, vol. 36, no. 8, pp. 46-55, 1996 [4] c. w. roeder, sac program to assure ductile connection performance, mazzolani and tremblay, 2000 [5] j. m. ricles, r. sause, m. m. garlock, c. zhao, “posttensioned seismicresistant connections for steel frames”, journal of structural engineering, vol. 127, no. 2, pp. 113-121, 2001 [6] a. niknam, e. sanaee, behavior and seismic design of steel buildings based on the regulation ubc , hormozgan university press, 2002 [7] m. m. garlock, j. m., ricles, r. sause, “experimental studies of fullscale posttensioned steel connections”, journal of structural engineering, vol. 131, no. 3, pp. 438-448, 2005 [8] m. khan babaei, investigating seismic behavior of knee bracing system in steel structure, university of zanjan press, 2004 [9] t. vidic, p. fajfar, m. fischinger, “consistent inelastic design spectra: strength and displacement”, earthquake engineering & structural dynamics, vol. 23, no. 5, pp. 507-521, 1994 engineering, technology & applied science research vol. 8, no. 2, 2018, 2775-2784 2775 www.etasr.com khan et al.: blindsense: an accessibility-inclusive universal user interface for blind people blindsense: an accessibility-inclusive universal user interface for blind people akif khan department of computer science university of peshawar peshawar, pakistan akif@uop.edu.pk shah khusro department of computer science university of peshawar peshawar, pakistan khusro@uop.edu.pk iftikhar alam department of computer science university of peshawar peshawar, pakistan iftikharalam@uop.edu.pk abstract—a large number of blind people use smartphone-based assistive technology to perform their common activities. in order to provide a better user experience the existing user interface paradigm needs to be revisited. a simplified, semantically consistent, and blind-friendly adaptive user interface model is proposed. the proposed solution is evaluated through an empirical study on 63 blind people leveraging an improved user experience in performing common activities on a smartphone. keywords-adaptive ui; blind people; smartphone; blindfriendly i. introduction a large number of blind people are using state-of-the-art assistive technologies for performing their daily life activities [1-3]. smartphone-based assistive technologies are an emerging trend for the blind people due to the inbuilt features such as accessibility, usability, and enhanced interactions [4, 5]. the accessibility services such as talking back, gesture controls, haptic feedback, screen magnifier, large text, color contrast, inverted colors, screen brightness, shortcuts, and virtual assistants are facilitating blind and visually impaired people in performing several operations on the smartphones. however, existing smartphone-based interfaces are posed to several issues in delivering a unified, usable and adaptive solution to the blind people. the navigational complexity in the interface design, lack of consistency in the button, icons, layout screens, identifying, selecting non-visual items on the screen, and traditional input mechanism is contributing in an increased cognitive overload [6]. in addition, every mobile application has its specific flow of interaction, placement of non-visual items, layout preferences, and distinct functionality. notably, it is difficult to establish a balance between accessibility and usability of a mobile application. in most of the cases, the mobile apps are either accessible but barely usable or usable but barely accessible [7]. nowadays, the available mobile apps are mostly inaccessible to the blind people. this is because these apps are either having limited usability or do not adhere to the web/mobile accessibility guidelines [8]. the usability of the smartphone-based user interface can be improved by using adaptive user interface paradigms. adaptive user interfaces support context-awareness and can generate a new instance of the interface by changes in the environment, user preferences, and device usage [9]. this can help blind people in the personalization of their smartphone-based user interface (ui) layouts, widgets, and ui controls of a particular application, irrespective of their technical ability, skillset, and device handling capabilities. to gain a considerably improved blindfriendly interface design requires an extensive revision, in order to meet the requirements and needs of the blind people. this may require a technical framework supported by an adaptation mechanism to address the diverse user capabilities, needs, and context-of-use to ensure a high degree of usability and acceptability [10]. this paper aims to devise a universal ui design for blind people, to customize the interface components of the commonly available mobile applications into a blind-friendly simplified ui. this will provide a simplified, semantically consistent, easy to use interface for operating commonly available mobile apps on the smartphone. in addition, the blind people will be having better control over the interface customization, and re-organization of interface elements as per their requirements. the vital contribution of this paper is to improve the user experience of the blind people. the upcoming section provides an overview of related work pertains to accessibility-inclusive user interfaces design. ii. related work through a series of studies, researchers have analyzed and identified recommendations for the accessibility-inclusive uis for blind people [11, 12]. the emergence of smartphone-based uis has opened new vistas for visually impaired and blind people. however, the cost of usability, accessibility, and the challenge of how to make this device more usable to the blind people emerges [13]. the pre-touchscreen era witnessed that the mobile device possessed physical controls for navigation and operational usage. however, existing touchscreen interfaces are vibrant to a number of issues due to the non existence of physical buttons, and user interface controls making it insufficient to drive these devices [14, 15]. some common usability issues are demonstrated in table i. engineering, technology & applied science research vol. 8, no. 2, 2018, 2775-2784 2776 www.etasr.com khan et al.: blindsense: an accessibility-inclusive universal user interface for blind people table i. common usability issues in touchscreen user interfaces for blind people parameter description hci model coverage [26] limitation [14, 16-19] cognitive overload [21, 22] limited organizational and operational capabilities of existing accessibility services are resulting in increased cognitive overload. complex ui design, processing inadequate labels of ui components, missing links, accessing non-visual items on screen, task performance, and inconsistency are some of the factors contributing in the cognitive overload for blind people task,domain, dialog, presentation, platform, user semantic lost, navigational complexity, task adequacy, dimensional trade-off, device independence placement and selecting non-visual items, layouts, search [12, 23-27] placing non-visual items on the screen, locating and identifying a particular item of interest are key issues. remembering user action status, and following a pattern of activities is a challenge. searching and retrieval of particular information is difficult activity to perform as well. task, dialog, presentation, user semantic lost, navigational complexity, task adequacy keys with multiple functions [28] lack of physical keys on soft keypad resulting in higher chances of wrong touches. besides, many actions are associated with one key, which creates confusion for these people. usually they are unaware of the type of functionality is associated with a particular key task, presentation, user semantic lost, task adequacy automated assistance [29] automated assistance tools receive information proactively without a user request. extensive utilization of such assistance systems may burden the blind people. user, platform semantic lost, task adequacy, cognitive overload haptic feedback [30] the utilization of haptic feedbacks and gesture controls are an emerging issue for blind people, e.g., consistent and appropriate feedback at the right time is inadequate in the existing interfaces. task, dialog, presentation, user task adequacy, dimensional trade-off user control over interface components (ui adaptation) [31] inadequate ui flexibility and limited control over ui personalization is a key issue. besides, every mobile application provides a meaningful entry and exit paths/points and should accommodate users requirements, and allow the user to customize interface layouts, and manipulate non-visual objects directly. task, dialog, presentation, user semantic lost, navigational complexity, task adequacy, dimensional trade-off device incompatibility [32] the final user interface generated on different devices acts inversely. this final generated outcome does not offer interoperability with different operating systems, and devices. certain applications require pre-installed libraries, and utilities to operate rationally. cross-mobile and cross-platform support is a primary aspect lacking in the currently available interfaces. task, domain, dialog, presentation, platform, user semantic lost, dimensional trade-off, device independence context of use [12, 27] lack of non-usage of the context of use and subsequent adaptation support results in loss of precise and accurate information of device, environment and users. task, domain, dialog, presentation, platform ,user semantic lost, navigational complexity, task adequacy, dimensional trade-off, device independence lack of logical order, navigational items, and menu hierarchy [24, 32] logical order of non-visual items, contents, and ui elements is a challenging opportunity. complex menu hierarchy creates difficulties in accessing the right menu selection at the right time task, dialog, presentation, user semantic lost, navigational complexity, task adequacy, dimensional trade-off limited consistency and persistency [31]. existing interfaces have limited persistency and consistency due to which it is difficult for the blind people to remember every action on the screen. task, presentation semantic lost, navigational complexity, task adequacy learnability and discoverability of the uis [12] learnability and discoverability are the key challenges in currently available applications. discoverability is the time factor and ease by which the user can begin an effective interaction with the system. task, presentation, user semantic lost, navigational complexity,task adequacy inadequate mapping of feedbacks [10] though, the first generation of haptic feedbacks is available in the form of vibratory motors, but still, this can provide a limited sensation in operating smartphones for blind people task, dialog, presentation, user semantic lost, task adequacy, dimensional trade-off exhaustive textentry [12] typical keypad, inadequate labels, smaller ui elements and text-to-speech responses in text-entry reduces the efficiency of the blind people. the error rate and a number of missed-touches in using traditional keypads are usually high. task, presentation semantic lost, task adequacy screen orientation, size, resolution [17] the usability of the touchscreen interfaces is affected by the screen elements such as the size of screen and change of orientation. the small size of button and ui elements have to divest effect on the performance. screen orientation also leads to increase the difficulty level of these people in learnability and discoverability. task, dialog, presentation, user semantic lost, navigational complexity, task adequacy, dimensional trade-off, device independence user model fragmentation [13, 17] every application has preserved several models locally. each application store and retrieve model information from the local repository ensuring the reuse of application models. however, heterogeneous application models may reflect a partial view of the user behavior and application usage in a particular scenario. task, domain, dialog, presentation platform, user semantic lost, navigational complexity, task adequacy, dimensional trade-off, device independence engineering, technology & applied science research vol. 8, no. 2, 2018, 2775-2784 2777 www.etasr.com khan et al.: blindsense: an accessibility-inclusive universal user interface for blind people the inclusion of accessibility in performing daily tasks through different applications and systems is highlighted in [14, 16-19]. screen readers and built-in accessibility services have considerably improved the usability of device footprints for blind people [20]. the preliminary focus was the ability to interact with the smartphones in performing common tasks such as reading a text message, identifying objects of interest and colors [4]. the advent of touchscreen technology has replaced the physical controls, elements, and directional anchors, resulting in creating difficulties in several operations. however, the tactical feedback, haptics, and multimodal interaction triggered a better basis for visual/auditory interactions [17, 21]. besides, the touchscreen offers a number of challenging opportunities such as haptic feedback, gesture control systems [22], text-to-speech system, and screen reading accessibility services (e.g., talkback for android, voice over for apple) enables blind people to read out the contents of the screen and operate smartphone interfaces [23]. blind people usually avoid contents that develop accessibility problems for them [24]. even sighted people consume 66% of their time in editing and correcting text in an automatic speech recognizer output on the desktop system [25]. besides the above reported issues, table i is depicting usability issues faced by blind people in performing various activities on smartphones. these problems are identified and analyzed in the specific context of hci model [26] including task, domain, dialog, presentation, platform, and user model. in summary, the usability of touchscreen uis merits further investigation. this requires the revamping of existing uis based on the needs and expectations of the blind people. many researchers have now emphasized on the development of a user-adaptive paradigm of designing simple to use, accessible, and user-friendly interfaces based on the guidelines of hci [14, 27-29]. in addition, few studies proposed usable and accessibility-inclusive uis. however, the results need further improvement. researchers should consider the improvement in the accessibility, usability, technical, and operational effectiveness of the smartphone-based uis for blind people. from the findings of literature review in the area of humancomputer interaction, usability, accessibility and diversified requirements of the blind people, we come up with a universal accessibility framework on smartphone uis for blind people. the proposed framework is designed keeping in view the related work mentioned in table i. the proposed blindsense, a universal ui design is discussed in the next section. iii. blind-friendly universal user interface design the technical abilities and tasks involved in the design of smartphone-based blind-friendly ui have been analyzed in the above section. we have analyzed common mobile applications by capturing the details of the nature of the app, category, total number of activities, number of inputs, number of outputs, number of ui controls used in the application, context of use, and minimal feature set. these common applications include sms, call, contacts, email, skype, whatsapp, facebook, twitter, calendar, location, clock, reminders, reading books, reading documents, identifying products, reading news, weather, instagram, and chrome. however, these applications have been designed for sighted people thus, a number of activities and sub-activities are either redundant, repetitive or having complex navigational structure, or need a long route to follow. the minimal feature sets were extracted through manual usability heuristics. the information is reported in table ii. thus, suggesting a minimal set of activities, input, outputs and contents in performing common applications have been outlined prior to the design of our proposed architecture. the proposed blindsense, a simplified, consistent, usable, adaptive universal ui model is based on user preferences, device logging, and context of use. the novel contribution is to customize/generate an optimal interface extracted from the existing common applications user interface controls, layouts, user interfaces, and widgets. this automatic transformation will be relying on semantic web technologies to model, and transform user interfaces resulting in transforming the complicated design of the existing mobile applications into blind-friendly and simplified ui. the blindsense is a pluggable layer-based architecture promoting openness and flexibility in the technical design of the system. the designers or users can define their screen layouts, text-entry plug-ins, adaptation rules, templates, themes, and mode/pattern of interactions. the proposed architecture is illustrated in figure 1. the architecture details are provided below. table ii. smartphone applications for performing common activities applicat ion category activi ties input ui cont rols minimal set feature call communication 13 43 12 6 sms communication 11 35 5 5 contacts communication 15 44 4 5 emails communication 25 67 12 8 calendar productivity 7 32 8 3 clock productivity 13 35 5 4 location navigation 14 32 6 4 facebook communication 26 58 7 5 twitter communication 18 40 4 4 skype communication 30 45 9 4 whatsapp communication 24 35 9 4 chrome suring internet 19 26 8 3 instagram picture sharing 11 30 8 5 news information access 14 40 5 4 weather information access 5 14 4 3 reading books text reader 14 25 6 2 reading document text reader 16 28 8 3 a. user interface layer the ui layer serves as an interaction point between the smartphone and blind people. the blindsense application presents a wizard to the blind people to customize their ui. the user inputs are captured through text-entry, gesture controls and voice commands for personalization and other operations. the application transforms the features extracted from common element set (ces) to minimal feature set (mfs) through the process of abstraction and adaptation. ces describes features of the ui, layouts, themes, widgets etc. the system automatically extracts mes from the user preferences, device engineering, technology & applied science research vol. 8, no. 2, 2018, 2775-2784 2778 www.etasr.com khan et al.: blindsense: an accessibility-inclusive universal user interface for blind people logging history, the context of use and the environment. these feature-sets are deployed at the activity or application level depending on a number of i/o of ui elements. for instance, a number of elements, input/outputs in a activity or an application level as reported in table ii. fig. 1. universal user interface architecture b. transformation layer this layer ensures the delivery of a simplified and personalized ui representing user, impairment, accessibility, devices, ui components, and adaptation models. adaptation knowledge base contains a set of personalization and adaptation rules. the input from user information model (uim) and the context model are processed on this layer which results in the generation of the simplified ui. a user model may contain static (such as screen partitions) or dynamic (such as level of abstraction) information. the uim consists of the following profiles: user capability, interest (interest level: high, low, and medium, interest category: computer, sports, entertainment, food, reading etc.), education, health, impairment profiles (visually impaired, blind, deaf-blind, and motor-impaired etc.), emergency, and social profiles. adaptation manager is consisting of classes representing information related to several models for ui adaptation. adaptation manager retrieves abstraction levels, and adaptation rules related to a specific disability from the adaptation repository. abstraction mechanism can be applied to elements, group elements, presentation, and application level. for instance, adaptation rule related to the sequence generation of action and activities would be performed at the task and domain level. the final ui will be generated using android xml layouts. in case of changes in the user preferences, adaptation components are updated with the latest information retrieved from user profile ontology and a new instance of the ui is generated c. context layer this layer captures, and stores information pertain to device, environment, user, and context through context extractor. the context model is composed of the user, platform, and environment models. the user model describes the needs and preferences while the platform model provides information related to device and platform, including screen resolution size, screen divisions, button size, keypads, aspect ratio, etc. the environment model represents information specific to the location of the user point of interaction, the level of ambient light etc. however, selective context sensing is performed in our case. similarly, the light and noise sensing are not required all the time for continuous updating in the ui. this can be setup once, be stored and retrieved anytime. the smartphone sensors store data in the form of key-value pairs, nested structure and in the formal ontology. a user context model containing information about context provider, context property, and context status is generated at the end. context data extractor filters the context data in relevance to ui adaptation. d. semantic layer the insight into the deeper aspect of ui adaptation involves the handling of model information, context-awareness, and their associated semantics. this layer encapsulates access to a comprehensive ui adaptation ontology used for user profiling and preferences, adaptation, context, devices and accessibility ontologies. it provides technology-independent access to metadata encoded in the ontology. additional contents may also be associated with the activities and tasks related to ui modeling, e.g. multimedia captions, audio descriptions, and interpretation of several other patterns. the architecture is developed using re-configurable modular approach for realizing the inclusion of semantic web technologies. e. storage layer the storage layer is responsible for managing several storage sources including ontologies, data store etc. information about user profiling, preferences, contextual data, adaptation rules, and layouts details is stored and retrieved from this layer, once all required data has articulated from the relevant models. blindsense uses semantic reasoning capabilities of the ontological modeling to present a final ui to blind people. the user may change his/her preferences related to layout, theme, and interaction’s type in the runtime. the structural model of universal ui model is represented in state transition diagram (std) in figure 2. fig. 2. std for system initialization engineering, technology & applied science research vol. 8, no. 2, 2018, 2775-2784 2779 www.etasr.com khan et al.: blindsense: an accessibility-inclusive universal user interface for blind people all these states are stored in the system and are executed in a specific order. the diagram begins with start, where it waits for input. once the user provides a particular input, other processes are initiated by switching several states to complete an activity or perform a particular action. in case of error, the system is returned to the initial state, and the error is recorded in the system memory accordingly. f. perspective workflow blindsense can be used as accessibility service or as an individual application. by enabling accessibility service for the first time, the system loads specific installed applications of common use and extracts common element features. user starts personalizing the layout by selecting a few preferences about screen divisions, mode of interactions, etc. also, the device logging, context of use, and user profiling are automatically articulated. the rules used for the generation of simplified ui are checked in the adaptation repository where specific rules for adaptation are applied. in case of non-availability of specific rules for given transformation, the transformation is set to be default or baseline specification. the complete application simplification process is illustrated in figure 3. the prototype is developed using android sdk. fig. 3. blindsense proof-of-concept iv. aims and hypotheses we studied the user experience by analyzing user satisfaction in performing several activities on the proposed universal ui design. each participant has demonstrated his perceived usefulness, ease of use, system usability scale, and user experience. to the best of our knowledge, a similar universal ui design for blind people has not presented before. thus, the aim was to investigate the effect of user experience in using common applications on a smartphone using universal ui design to gain a systematic understanding of user experience in overall operations. we aimed at formulating an assumption of which variables are the most central to user's experience. following hypotheses were made:  h1: the perception of perceived usefulness in performing common activities through a universal ui for blind people in terms of the success of solving tasks/activities on smartphone influences a positive user satisfaction.  h2: the ease of use in personalizing a universal ui for blind people in term of task completion, personalization, and a number of accurate touches will improve the user experience.  h3: consistency will lead to a more positive attitude towards an improved user experience in accessing nonvisual items, and skipping irrelevant items on a universal ui for blind people  h4: improved system usability scale will lead to a more positive attitude towards the use of universal ui for blind people.  h5: consistency in the interface elements will lead to a more positive attitude towards the ease of use in accessing and operating a universal ui for blind people on a smartphone. besides we will analyze whether a specific usability parameter was most influential in the particular case or otherwise. the key variables include user satisfaction, perceived usefulness, ease of use. system usability scale will be predicated on having a positive/negative influence on blind people’s user experience. v. evaluation and results the evaluation of the proposed solution was conducted through an empirical study. the usability of the proposed ui design and the individual components of the architecture were evaluated using already established methods, metrics, and usability parameters related to hci. we were interested to find the user experience of blind people by performing a number of tasks associated with user interface customization and operating smartphone applications with the ease of use. a. participation sixty three (4 females, 59 male) participants took part in this study. the median age of participants was 39 years, within range of 22-56 years. in the pre-application assessment, participants experience was rated on a four-item scale: beginner, intermediate, advanced and expert. the participant level of smartphone usage experience varied from beginner to advanced. usability experts observed the navigational and orientation skills the blind people have in performing common tasks/activities. the experts mainly judged the confidence and frustration level of the participants. table iii summarizes general information about the participants along with other indicators, i.e. information related to their background, age, gender and smartphone usage experience. the participants reported their level of experience in the initial trials. b. procedure the participants were introduced to the blindsense framework and a demonstration of the required steps to perform one-by-one was provided. the study spanned for eleven weeks and consisted of the following components: (1) pre-application usage assessment and collection of background data, (2) introductory session with our universal ui framework and initial trials, (3) in-the-wild device usage, (4) interviews and observations. a practice trial session on the general tasks and operational usage of several scenarios was performed. participants were allowed to practice in a trial session on general tasks and activities such as unlocking the phone, placing a call, sending a message, etc. the participants were engineering, technology & applied science research vol. 8, no. 2, 2018, 2775-2784 2780 www.etasr.com khan et al.: blindsense: an accessibility-inclusive universal user interface for blind people asked to perform 121 predefined tasks. average time exercised on each participant was about 66 minutes. the researchers were directly involved in observing the execution of the tasks performed. besides, we acquired the services of nine professional facilitators who assisted the participants during the entire study. we continued the sequence of grouping and interviewing up to finishing all participants in the same pattern. in addition, all participants were provided with a samsung s6 and an htc one smartphone running on android. the talkback screen reading application and data collection service, and the blindsense application were pre-installed on the devices. for each task we recorded the time of completion, the degree of accuracy in performing common activities like placing a call, sending messages, etc. the result section presents the responses collected through a structured questionnaire, interview, and observations. the university ethics committee/irb has approved the consent procedure for this study. written consent was obtained from the caretakers of the participants. the participants were informed about the study objective, study procedure, potential risks etc. the study checklist was verbally communicated to all blind people, with their verbal approval while the caretakers issued the written consent. table iii. participants information details variable group number of participants percent age sd gender female 4 6.35 38.89087 male 59 93.65 age (years) 22 to 35 36 57.14 16.97056 36 to 45 12 19.05 45 to 56 15 23.81 background educated 45 71.43 19.09188 literate 18 28.57 smartphone usage experience 1 month 14 38.10 3.535534 3 months 19 30.16 6 months 9 14.29 9 months 17 11.11 12 months 4 6.35 observed expertise beginner 17 26.98 7.67 intermediate 19 11.97 advance 21 33.33 experts 4 6.34 c. analysis and validation procedures/data analysis we run statistical correlation analysis of observations to define the relationship between ux attributes of the universal ui on attitude, intention to use, perceived usefulness, understandability and learnability, operability, ease of use, system usability scale, minimal memory load, consistency, and user satisfaction. the statistical software spss 21 using amos 21 was used for analysis and structuring modeling. the first step was to define a measurement model and test the relationship among several dependent and independent variables. the assessment of measurement model validity was conducted by checking goodness-of-fit indices (gfi). we used confirmatory factor analysis (cfa) using maximum likelihood to verify the reliability, convergent validity, composite reliability and average variance of each construct. the measurement model had 60 variables for 10 latent variables. in order to confirm the fitness of proposed model, the chi-square, chi-square/d.f., gfi, incremental fit index (ifi), normed fit index (nfi), comparative fit index (cfi), tucker-lewis index (tli), parsimony goodness of fit index (pgfi) and root mean square error of approximation (rmsea) were assessed. the measures mentioned above indicated that the estimated covariance metrics of the proposed measurement and observed model were found satisfactory. the reliability test was accessed through cronbach’s alpha. the cfa model indicates that the overall fit index measurement model found a satisfactory ratio of chi-square to the degree of freedom (x2/df)=1.577, rmsea=0.076, cfi=0.727, nfi=0.939, ifi=0.949, tli=0.696, pgfi=0.539. in addition, the measurement model was found to have strong internal reliability and convergent validity. the cronbach’s alpha values, item-total correlation, factor loading, composite reliability, and average variance extracted from the analysis report a robust fitness. tables iv-vi show confirmatory factor loadings of each item with their respective reliability scores. the factor loadings having value above 0.05 are considered as acceptable in general practice, whereas the reported factor loadings exceeded 0.06. similarly, the value of cronbach’s alpha reliability score 0.70 is considered an acceptable reliability score. in the reported data, the scores are above 0.70. in addition, to verify the internal consistency of each latent variable, we have measured the construct reliability too. it is acceptable when the composite reliability is higher than 0.07 and ave is higher than 0.05. the reported score is mostly above the acceptable range of construct reliability. figure 4 shows the diagram of the final structural model generated from the relationship of latent variables. the results are depicted in a standardized regression weights in different paths. all the paths were found significant at the level of p<0.001. as depicted, the perceived usefulness has an impact on the user satisfaction with high impact path weight (path coefficient=0.22). research model overall had satisfactory variance in the user experience in operating adaptive user interfaces. in tables vii a summary is presented. table iv. measurement and structural model fit indexes fit index recommended values structural model x2/df ≤ 3.00 2.877 cfi ≤ 3.00 0.898 gfi ≥ 0.90 0.937 nfi ≥ 0.90 0.954 ifi ≥ 0.90 0.900 tli ≥ 0.50 0.879 pcfi ≥ 0.50 0.754 rfi ≤ 1.00 0.825 pnfi ≥ 0.50 0.716 rmsea < 0.08 0.070 engineering, technology & applied science research vol. 8, no. 2, 2018, 2775-2784 2781 www.etasr.com khan et al.: blindsense: an accessibility-inclusive universal user interface for blind people table v. internal reliability and convergent validity – part i internal reliability convergent average latent constructs measurement items mean (sd) cronbach’s alpha item-total correlation factor loading composite reliability average variance extracted attitude att1 2.75 0.011 0.825 0.652 0.802 0.511 0.721 att2 3.18 0.904 0.641 0.838 att3 2.61 1.005 0.693 0.822 att4 2.74 1.079 0.625 0.929 intention to use iu1 3.89 0.635 0.860 0.711 0.796 0.525 0.736 iu2 3.82 0.619 0.760 0.850 iu3 3.97 0.730 0.727 0.808 iu4 3.84 0.734 0.668 0.967 perceived usefulness pu1 2.79 0.864 0.959 0.662 0.692 0.816 0.711 pu2 2.78 0.870 0.919 0.922 pu3 2.73 0.865 0.894 0.917 pu4 2.98 0.889 0.793 0.794 pu5 2.97 0.915 0.803 0.831 pu6 2.78 0.870 0.868 0.894 pu7 2.86 0.913 0.872 0.890 pu8 2.89 0.969 0.751 0.805 pu9 2.90 0.928 0.848 0.867 understandability and learnability ul1 2.84 0.884 0.528 0.361 0.787 0.088 0.701 ul2 3.13 0.975 0.361 0.885 operability op1 2.89 0.863 0.879 0.541 0.758 0.832 0.706 op2 2.70 0.994 0.515 0.890 op3 3.06 0.914 0.575 0.902 op4 2.56 0.980 0.578 0.819 op5 2.70 1.087 0.556 0.907 op6 2.54 1.045 0.680 0.769 op7 2.43 1.011 0.803 0.869 op8 2.33 0.803 0.766 0.838 op09 2.44 0.947 0.706 0.797 op10 2.44 0.963 0.587 0.798 op11 3.13 0.975 0.240 0.885 fig. 4. structural model for improving user satisfaction engineering, technology & applied science research vol. 8, no. 2, 2018, 2775-2784 2782 www.etasr.com khan et al.: blindsense: an accessibility-inclusive universal user interface for blind people table vi. internal reliability and convergent validity – part ii ease of use eu1 4.08 0.666 0.889 0.725 0.771 0.746 0.770 eu2 4.03 0.682 0.772 0.854 eu3 4.05 0.644 0.802 0.881 eu4 4.07 0.629 0.847 0.916 eu5 4.03 0.632 0.733 0.794 eu6 4.13 0.645 0.692 0.742 eu7 2.33 0.961 0.215 0.791 eu8 4.16 0.835 0.816 0.806 system usability scale (sus) sus1 3.58 0.897 0.926 0.717 0.989 0.763 0.705 sus2 3.40 0.931 0.751 0.763 sus3 3.60 0.877 0.783 0.722 sus4 3.69 0.801 0.845 0.845 sus5 3.45 0.862 0.782 0.798 sus6 3.65 0.812 0.732 0.879 sus7 3.69 0.861 0.825 0.899 sus8 3.74 0.700 0.559 0.795 minimal memory load mml1 3.71 0.705 0.894 0.611 0.689 0.761 0.702 mml2 3.97 0.647 0.710 0.904 mml3 3.87 0.772 0.711 0.785 mml4 3.62 0.851 0.730 0.804 mml5 3.67 0.783 0.804 0.892 mml6 3.78 0.888 0.685 0.866 mml7 3.75 0.761 0.693 0.771 mml8 3.13 0.942 0.507 0.769 user satisfaction us1 2.56 1.028 0.940 0.745 0.820 0.676 0.813 us2 2.40 1.040 0.897 0.933 us3 2.30 0.835 0.909 0.939 us4 2.38 0.958 0.881 0.932 us5 2.33 0.916 0.794 0.880 consistency co1 2.71 0.974 0.807 0.604 0.889 0.769 0.716 co2 2.92 0.955 0.555 0.887 co3 2.94 1.014 0.577 0.900 co4 3.89 0.743 0.489 0.966 co5 3.68 0.820 0.535 0.847 co6 3.79 0.626 0.567 0.859 co7 3.89 0.675 0.368 0.734 c08 3.11 1.002 0.452 0.650 table vii. summary of hypothesis tests hypothesis uc sc t se p h1 : pu→us 0.138 0.303 2.483 0.056 0.016 h2 : eu→us 0.777 0.469 4.153 0.18 0.000 h3: co→us 0.442 0.287 2.336 0.189 0.023 h4 : sus→us 0.506 0.400 3.407 0.148 0.001 h5: co→eu 0.298 0.320 2.635 0.113 0.011 uc: unstandardized coefficient, sc: standardized coefficient, se: standard error, p: significance in respect of hypothesis: perceived usefulness was positively associated with user satisfaction (h1, β=0.3030, p=0.016), ease of use (h2, β=0.469, p<0.000). consistency (h3, β =0.287, p<0.023), system usability scale (h4, β=0.400, p<0.001) and consistency concerning ease of use (h5, β=0.320, p<0.011) had a positive effect on the user experience of blind people in using adaptive ui. the significance of all hypotheses was <005 thus each hypothesis is accepted. vi. discussion understanding the need for developing an accessibilityinclusive ui for blind people, our research articulates usability, ease of use, consistency, usefulness, and accessibility for generating a simplified, consistent and universal ui design for blind people. the study proposed, developed and validated a blind-friendly universal ui design for operating common applications on smartphone resulting in enriched user experience. as hypothesized, the parameters used, i.e. ease of use, consistency, operability, perceived usefulness, minimal memory load, system usability scale were found to have a positive effect to user satisfaction and user experience. ultimately, a consensus was reached on the acceptance of using universal user interface model. the user’s attitude towards the use of the suggested application was reported as effective, pleasant and enjoyable. for statistical validation, this study measured ease of use, consistency, operability, perceived usefulness, minimal memory load, system usability scale, understandability and learnability (i.e., the fundamental determinants of user acceptance of any technology acceptance model (tam)) through a survey questionnaire. the results resulted in a satisfactory response. through a series of interventions of model evaluations and validations, the hypothesis that user satisfaction is positively affected by the adaptation of the universal ui design for blind people is accepted. the study also verified the relationship between the usability of ui and user satisfaction. user satisfaction is an important factor in the design of smartphone-based uis. in addition, the study results are consistent with earlier studies on engineering, technology & applied science research vol. 8, no. 2, 2018, 2775-2784 2783 www.etasr.com khan et al.: blindsense: an accessibility-inclusive universal user interface for blind people the usability and accessibility of smartphone applications. the findings collectively investigate that various features of the smartphone-based uis and layouts such as screen size, user controls, navigational complexity, user interaction, and feedbacks convey positive psychological effects in a particular user context [30]. methodologically, a potential threat to the investigation is to undertake this approach on visually-dense interfaces such as game and entertainment applications. besides, the potential of smartphone capabilities can be used for hedonic and utilitarian purposes [31]. as depicted in the results, some users find the universal interface design to be a convenient and efficient one for completing their tasks, while others perceived this as a bit uncomfortable and annoying. therefore, the including of more visually complex tasks may be further investigated. vii. conclusion a large number of smartphone applications does not comply with the mobile accessibility guidelines. these applications do not specifically meet the requirements of blind people. thus, these people are facing numerous challenges in accessing and operating smartphone interface components such as finding a button, understanding layouts, interface navigation etc. besides, a blind person has to learn every new application, and their features resulting in penetrating learnability and discoverability. they have to learn and apply their previous experience and this may result in varying user experience. the findings of this study illustrated that a simplified, semantically consistent, and context-sensitive universal ui design contributes to having a satisfactory positive evaluation. the main contribution of this proposed research study was an attempt to improve the user experience of blind people in operating smartphones through a universal interface design by using adaptive ui paradigm for personalization. we have adopted measurement items from existing web/mobile usability and revamped a number of parameters for this study. the proposed solution addressed the problems of simplicity, reduction, organization, and prioritization [32] by providing a semantically consistent, simplified, task-oriented, and contextsensitive ui design. during the study, the proposed intervention has significantly reduced the cognitive user overload. the consistency in the division of smartphone screen enables blind people to memorize the flow of activities and actions with ease. thus there is a slim chance of getting lost in a given navigation workflow. our results illustrate that our proposed solution is more robust, easy to use and adaptable than other solutions operated through the accessibility services. our future work will focus on extending this framework for visually complex/navigationally-dense applications. emotion-based uis design may also be investigated further. moreover, the optimization of gui layouts and elements will be considered in the particular focus with gesture control systems, and eyetracking systems. acknowledgment the authors would like to acknowledge the support of the higher education commission (hec) of pakistan. references [1] j. a. kientz, s. n. patel, a. z. tyebkhan, b. gane, j. wiley, g. d. abowd, “where's my stuff?: design and evaluation of a mobile system for locating lost items for the visually impaired”, 8th international acm sigaccess conference on computers and accessibility, portland, usa, pp. 103-110, october 23-25, 2006 [2] j. r. fruchterman, “in the palm of your hand: a vision of the future of technology for people with visual impairments”, journal of visual impairment and blindness, vol. 97, no. 10, pp. 585-591, 2003 [3] j. mccarthy, p. wright, “technology as experience”, interactions, vol. 11, no. 5, pp. 42-43, 2004 [4] l. hakobyan, j. lumsden, d. o’sullivan, h. bartlett, “mobile assistive technologies for the visually impaired”, survey of ophthalmology, vol. 58, no. 6, pp. 513-528, 2013 [5] f. f.-h. nah, d. zhang, j. krogstie, s. zhao, “editorial of the special issue on mobile human-computer interaction”, international journal of human–computer interaction, vol. 33, no. 6, pp. 429-430, 2017 [6] b. adipat, d. zhang, “interface design for mobile applications”, amcis 2005 proceedings, ais electronic library, p. 494, 2005 [7] b. leporini, f. paterno, “applying web usability criteria for visionimpaired users: does it really improve task performance?”, international journal of human–computer interaction, vol. 24, no. 1, pp. 17-47, 2008 [8] w3c, web accessibility initiative, available at: http://www.w3.org/ wai/ [9] p. a. akiki, a. k. bandara, y. yu, “adaptive model-driven user interface development systems”, acm computing surveys, vol. 47, no. 1, 2015 [10] d. weld, c. anderson, p. domingos, o. etzioni, k. gajos, t. lau, s. wolfman, “automatically personalizing user interfaces”, ijcai' 03 18th international joint conference on artificial intelligence, acapulco, mexico, pp. 1613-1619, 2003 [11] a. bhowmick, s. m. hazarika, “an insight into assistive technology for the visually impaired and blind people: state-of-the-art and future trends”, journal on multimodal user interfaces, vol. 11, no. 2, pp. 149172, 2017 [12] w. grussenmeyer, e. folmer, “accessible touchscreen technology for people with visual impairments: a survey”, acm transactions on accessible computing, vol. 9, no. 2, article no. 6, 2017 [13] h. sieverthson, m. lund, usability challenges for the mobile web: an enterprise perspective, bsc thesis, university of bora, 2017 [14] s. k. kane, c. jayant, j. o. wobbrock, r. e. ladner, “freedom to roam: a study of mobile device adoption and accessibility for people with visual and motor disabilities”, in: proceedings of the 11th international acm sigaccess conference on computers and accessibility, pp. 115-122, acm, 2009 [15] p. strumillo, p. skulimowski, m. polanczyk, “programming symbian smartphones for the blind and visually impaired”, in: computers in medical activity, advances in intelligent and soft computing, vol 65. pp. 129-136, springer, 2009 [16] m. l. dorigo, b. harriehausen-mühlbauer, i. stengel, p. s. haskelldowland, “nonvisual presentation and navigation within the structure of digital text-documents on mobile devices”, lecture notes in computer science, vol. 8011, pp. 311-320, 2013 [17] r. j. p. damaceno, j. c. braga, j. p. mena-chalco, “mobile device accessibility for the visually impaired: problems mapping and recommendations”, in: universal access in the information society, pp. 1-15, springer-verlag, berlin, heidelber, 2017 [18] g. e. legge, p. j. beckmann, b. s. tjan, g. havey, k. kramer, d. rolkosky, r. cage, m. chen, s. puchakayala, a. rangarajan, “indoor navigation by people with visual impairment using a digital sign system”, plos one, vol. 8, no. 10, p. e76783, 2013 [19] m. rodriguez-sanchez, m. moreno-alvarez, e. martin, s. borromeo, j. hernandez-tamames, “accessible smartphones for blind users: a case study for a wayfinding system”, expert systems with applications, vol. 41, no. 16, pp. 7210-7222, 2014 engineering, technology & applied science research vol. 8, no. 2, 2018, 2775-2784 2784 www.etasr.com khan et al.: blindsense: an accessibility-inclusive universal user interface for blind people [20] e. brady, m. r. morris, y. zhong, s. white, j. p. bigham, “visual challenges in the everyday lives of blind people”, sigchi conference on human factors in computing systems, paris, france, pp. 2117-2126, 2013 [21] n. mi, l. a. cavuoto, k. benson, t. smith-jackson, m. a. nussbaum, “a heuristic checklist for an accessible smartphone interface design”, universal access in the information society, vol. 13, no. 4, pp. 351365, 2014 [22] m. c. buzzi, m. buzzi, b. leporini, a. trujillo, “analyzing visually impaired people’s touch gestures on smartphones”, multimedia tools and applications, vol. 76, no. 4, pp. 5141-5169, 2017 [23] t. paek, d. m. chickering, “improving command and control speech recognition on mobile devices: using predictive user models for language modeling”, user modeling and user-adapted interaction, vol. 17, no. 1-2, pp. 93-117, 2007 [24] j. p. bigham, a. c. cavender, j. t. brudvik, j. o. wobbrock, r. e. lander, “webinsitu: a comparative analysis of blind and sighted browsing behavior”, 9th international acm sigaccess conference on computers and accessibility, tempe, usa, pp. 51-58, 2007 [25] s. k. kane, j. o. wobbrock, r. e. ladner, “usable gestures for blind people: understanding preference and performance”, proceedings of the acm chi conference on human factors in computing systems, vancouver, canada, pp. 413-422, may 7-12, 2011 [26] p. szekely, p. luo, r. neches, “beyond interface builders: model-based interface tools”, in : proceedings of the interact '93 and chi '93 conference on human factors in computing systems, acm, pp. 383390, 1993 [27] j. abascal, c. nicolle, “moving towards inclusive design guidelines for socially and ethically aware hci”, interacting with computers, vol. 17, no. 5, pp. 484-505, 2005 [28] u. persad, p. langdon, j. clarkson, “characterising user capabilities to support inclusive design evaluation”, universal access in the information society, vol. 6, no. 2, pp. 119-135, 2007 [29] o. plos, s. buisine, a. aoussat, f. mantelet, c. dumas, “a universalist strategy for the design of assistive technology”, international journal of industrial ergonomics, vol. 42, no. 6, pp. 533-541, 2012 [30] j. p. forgas, “mood and judgment: the affect infusion model (aim)”, psychological bulletin, vol. 117, no. 1, pp. 39-66, 1995 [31] k. j. kim, s. s. sundar, “does screen size matter for smartphones? utilitarian and hedonic effects of screen size on smartphone adoption”, cyberpsychology, behavior, and social networking, vol. 17, no. 7, pp. 466-473, 2014 [32] j. maeda, the laws of simplicity (simplicity: design, technology, business, life), mit press, 2006 microsoft word etasr_v11_n5_pp7615-7618 engineering, technology & applied science research vol. 11, no. 5, 2021, 7615-7618 7615 www.etasr.com minh et al.: efficiency improvement of permanent magnet bldc motors for electric vehicles efficiency improvement of permanent magnet bldc motors for electric vehicles dinh bui minh school of electrical engineering hanoi university of science and technology vietnam dinh.buiminh@hust.edu.vn vuong dang quoc school of electrical engineering hanoi university of science and technology vietnam vuong.dangquoc@hust.edu.vn phuong nguyen huy school of electrical engineering hanoi university of science and technology vietnam phuong.nguyenhuy@hust.edu.vn abstract-a permanent magnet brushless dc (bldc) motor has been designed with different rotor configurations based on the arrangement of the permanent magnets. rotor configurations strongly affect the torque and efficiency performance of permanent magnet electric motors. in this paper, different rotor configurations of the permanent magnet bldc motor with parallel the halbach array permanent magnet were compared and evaluated. many applications of electric drives or air-crafts have recently preferred the surface-mounted permanent magnet design due to its ease of construction and maintenance. the finite element technique has been used for the analysis and comparison of different geometry parameters and rotor magnet configurations to improve efficiency and torque performance. a comprehensive design of a three-phase permanent magnet bldc 35kw motor is presented and simulations were conducted to evaluate its design. the skewing rotor and halbach magnet array are applied to the permanent surface-mounted magnet on the bldc motor for eliminating torque ripples. in order to observe the skewing rotor effect, the rotor lamination layers were skewed with different angles and halbach sinusoidal arrays. the determined skewing angle, the eliminated theoretically cogging torque, and the back electromotive force harmonics were also analyzed. keywords-bldc; permanent magnet; finite element method; ansys maxwell; speed; magnetic flux density i. introduction permanent magnet (pm) brushless dc (bldc) motors are widely used due to features such as compactness, low weight, high efficiency, and easy assembly [1, 2]. the reliability of bldc motor is high since it is easy to mount the pm and has a robust structure. different rotor configurations are available for the pm bldc motor, e.g. the surface mounted pm design with the interior/exterior rotor, the interior pm design with buried magnets due to specific strengths and weaknesses [3-5]. among these, there are the radial-flux motors, the surface mounted types with different magnet arrangement that have been used for electrical drives. this paper introduces a novel design of the bldc35kw-z36p12 rotor with high efficiency and low torque ripple. the electromagnetic performance of the pm bldc with 36 stator slots and 12 rotor poles is discussed in this paper. ii. electromagnetic torque analysis the aim is to lower the cost with high overload efficiency and reliability. high efficiency and torque density for electric vehicle applications are the first priorities of this design program. the calculation process of the proposed bldc motor conducted with the speed software is presented in figure 1. the geometry specifications of the motor used for the analysis are given in table i. fig. 1. design calculation process. table i. geometry specifications of the pm bldc motor no parameters unit 1 outer diameter 218 mm 2 rotor diameter 142 mm 3 slot length 112 mm 4 normal torque 200 nm 5 maximum torque 350 nm 6 speed 3600 rpm corresponding author: vuong dang quoc engineering, technology & applied science research vol. 11, no. 5, 2021, 7615-7618 7616 www.etasr.com minh et al.: efficiency improvement of permanent magnet bldc motors for electric vehicles the geometry dimensions of the pm bldc motor are saved in a database in matrix form. when the export command is generated, the drawing process will be executed. the program is developed with the matlab dxf library shown in figure 2. for the drawing circle line, rotating object of stator slots, 2d modeling is implemented to get geometrical formulas of the circle lines. the algorithm needs to satisfy two requirements: the shape of these lines must be similar to the desired curves and the least possible points must be used. using the minimum number of lines will help the system because it will not have to store a lot of data, which will slow down speed and present difficulties at exporting the drawings. on the other hand, rotation and mirroring are difficult tasks in programming. the strategy is to use a loop function to redraw several times and trigonometric function with angle steps was applied returning good results. fig. 2. matlab dxf drawing. the system will export separate drawings of the motor, the rotor, and the stator. these drawings can be used in several simulation programs and in the design and manufacturing progress. the detail parameters are shown in table ii. table ii. design parameters of pm bldc motor parameters values unit stator bore 142 mm tooth width 7 mm slot depth 29 mm tooth tip depth 1 slot opening 3 tooth tip angle 30 degrees pole number 12 magnet thickness 4 mm housing dia 228 mm stator lam dia 218 mm stator bore 142 mm airgap 1 mm programs can support the material weight and volume calculation because the power and torque density are also important factors in each motor design. from the geometry parameters, the material weights of two pm bldc motors were obtained and are shown in table iii. the two pm bldc motors with the parallel magnet and the halbach magnet array are presented in figure 3. the magnet thickness of the conventional design is 4 mm and the electric angle is 150 0 while the halbach magnet array has a thickness of 3.5 mm and 175 electric embraces. the total weight of a novel design of the halbach magnet is lower with the same magnet weight. table iii. weight details of the pm bldc motors parameters material parallel halbach stator lam (back iron) m350-50a 3.947 3.947 s tator lam (yooth) m350-50a 4.967 4.317 stator lamination [total] 8.913 8.263 armature winding [active] copper (pure) 3.23 3.621 armature ewdg [front] copper (pure) 1.273 0.4767 armature ewdg [rear] copper (pure) 1.273 0.4767 armature winding [total] 5.777 4.575 rotor lam (back iron) m350-50a 8.811 8.811 rot inter lam (back iron) 4.02e-05 4.02e-05 rotor lamination [total] 8.812 8.812 magnet n30uh 0.9613 0.9613 total 25.42 23.57 fig. 3. bldc motor p=12, z=36 parrallel magnet (left) and halbach magnet (right). electro magnetic force (emf) and torque, calculated by a matlab analytical coupling program with the finite element method (fem) are expressed as [11, 12]: �� � �� � ��� � � (1) � � �� � ������� (2) �� � √� � ������������ (3) where tph is the turn per phase term, te is the electromagnetic torque and ea is the back emf. the electromagnetic performances based on this design are shown in table iv. the most important parameter is the efficiency of 93.792%. the efficiency of halbach magnet and skewed rotor with 5 slices is optimized by the control current of 250a with 200vdc. table iv. electromagnetic performance comparison parameters parallel magnet halbach magnet unit average torque 226.42 243.41 nm torque ripple 24.635 13.081 nm torque ripple [%] 10.815 5.3608 % cogging torque ripple 20.709 4.4287 nm input power 38555 96326 w output power 35389 90347 w total losses 3165.9 5979.7 w system efficiency 91.789 93.792 % shaft torque 225.3 239.65 nm engineering, technology & applied science research vol. 11, no. 5, 2021, 7615-7618 7617 www.etasr.com minh et al.: efficiency improvement of permanent magnet bldc motors for electric vehicles in order to evaluate the maximum torque of the motor, a maximum current is applied to determine when the permanent magnetic is irrecoverable. the maximum torque is 350 nm at the speed of 1500 rpm with a current of 500 a. efficiency is calculated based on copper and iron losses. those losses depend on the stator and rotor teeth dimensions. an efficiency map of the halbach magnet array with rotor skewed slices is shown in figure 4. (a) (b) fig. 4. efficiency map of (a) power and (b) torque. the torque and speed operation areas have been plotted with different efficiency values. the maximum torque acquired is 350 nm at the speed of 1000 rpm with low efficiency of 79%. a 2d bldc motor model is solved and simulated by fem [13-15]. after meshing the geometry model including the magnetic, the silicon steel, and the insolation materials, the flux density distribution of rotor and stator, is shown in figure 5. fig. 5. flux density results. the flux density of the air gaps is investigated in one pole. many steps of rotor position, currents, torque, and flux density were recorded and saved in matlab files to plot those characteristics. the leakage flux lines are enclosed to air gap areas, which also helps to increase the flux density and reduce the rotor yoke iron loss. iii. torque ripple analysis of rotor skewed slices skewing slices of rotor are frequently used in pm bldc motors for eliminating the cogging torque. for the optimum skew angle of those slices, the cogging torque can be eliminated theoretically. the skewed slots for the rotor slices are illustrated in figure 6. fig. 6. rotor skewing slices. the torque ripple results are shown in figure 7. the cogging torque can be calculated by the stored energy in the air gap. the variation of the co-energy given the cogging torque is expressed as [6-8]: �� � �� �� (4) where tc is the cogging torque, ∂θ is the displacement with mechanical degree, and ∂w is the stored co-energy in the air gap. fig. 7. torque ripple analysis. the cogging torque is periodic along the air gap. by using this periodicity feature, the fourier series of the cogging torque can be obtained [6, 7]: � ���!"# � ∑ % � & '() . �'. sin !�/�"� 0 "'# (5) where ksk is the skew factor that is 1 for non-skewed motor laminations, cp is the least common multiple of the number of poles and number of stator slots, ti is the absolute value of the harmonic i, θm is the mechanical angle between the stator and the rotor axis while the motor is rotating, and "' represents the phase angle. the skew factor ksk is defined by: % � � 1'2! 3456 � 7 # '8�9 �/; (6) where αsk is the skew angle and ns is the number of the slide. the average values of load torques are nearly the same values for even one slot pitch skewed motor result in terms of average engineering, technology & applied science research vol. 11, no. 5, 2021, 7615-7618 7618 www.etasr.com minh et al.: efficiency improvement of permanent magnet bldc motors for electric vehicles load torque that are coherent with the non-skewed motor model. the relative torque ripples can be defined as: �<'��=� � !>?@ab>?3c# >@de (7) if the skew angle is increased, the torque ripple is reduced along with the average torque, so for optimal torque performance the ratio of magnetic pole/stator slots needs to be increased. iv. conclusion in this paper, a comprehensive design of the pm bldc motor for electric vehicles has been presented. the design was computed by the analytical method, it was optimized by the speed software and the electromagnetic characteristics were evaluated by fem. in particular, the parallel and halbach pm array rotor with skewed slides have been compared in terms of efficiency, torque, and cogging torque. the torque ripple is minimum with a skew angle of 8 degrees. the best skewing angle is determined by a stator slot angle of 10 degrees. for the electrical drive, the pm surface mounted motor is easy to arrange halbach and skewing structures. acknowledgement the authors wish to thank the technical university of berlin for providing the means and conditions needed to carry out this work. references [1] y. park, h. kim, h. jang, s.-h. ham, j. lee, and d.-h. jung, "efficiency improvement of permanent magnet bldc with halbach magnet array for drone," ieee transactions on applied superconductivity, vol. 30, no. 4, pp. 1–5, jun. 2020, https://doi.org/ 10.1109/tasc.2020.2971672. [2] p. ji, w. song, and y. yang, "overview on application of permanent magnet brushless dc motor," electrical machinery technology, vol. 40, pp. 32–36, 2003. [3] b. v. r. kumar and k. s. kumar, "design of a new dual rotor radial flux bldc motor with halbach array magnets for an electric vehicle," in 2016 ieee international conference on power electronics, drives and energy systems (pedes), trivandrum, india, dec. 2016, https://doi.org/10.1109/pedes.2016.7914552. [4] a. vadde and s. sachin, "influence of rotor design in bldc motor for two -wheeler electric vehicle," in 2021 1st international conference on power electronics and energy (icpee), bhubaneswar, india, jan. 2021, https://doi.org/10.1109/icpee50452.2021.9358520. [5] v. r. bommadevara, "design of a high power density halbach bldc motor for electric vehicle propulsion.," in 2018 ieee international magnetics conference (intermag), singapore, apr. 2018, https://doi.org/10.1109/intmag.2018.8508741. [6] l. dosiek and p. pillay, "cogging torque reduction in permanent magnet machines," ieee transactions on industry applications, vol. 43, no. 6, pp. 1565–1571, nov. 2007, https://doi.org/10.1109/ tia.2007.908160. [7] r. krishnan, switched reluctance motor drives: modeling, simulation, analysis, design, and applications, 1st ed. boca raton, fl, usa: crc press, 2001. [8] v. d. quoc, "robust correction procedure for accurate thin shell models via a perturbation technique," engineering, technology & applied science research, vol. 10, no. 3, pp. 5832–5836, jun. 2020, https://doi.org/10.48084/etasr.3615. [9] v. d. quoc, "accurate magnetic shell approximations with magnetostatic finite element formulations by a subdomain approach," engineering, technology & applied science research, vol. 10, no. 4, pp. 5953–5957, aug. 2020, https://doi.org/10.48084/etasr.3678. [10] r. islam, i. husain, a. fardoun, and k. mclaughlin, "permanentmagnet synchronous motor magnet designs with skewing for torque ripple and cogging torque reduction," ieee transactions on industry applications, vol. 45, no. 1, pp. 152–160, jan. 2009, https://doi.org/ 10.1109/tia.2008.2009653. [11] m. d. bui, s. schneider, s. arnaout, and u. schaefer, "torque maximization of a high-speed switched reluctance starter in acceleration test," in 2013 15th european conference on power electronics and applications (epe), lille, france, sep. 2013, https://doi.org/10.1109/ epe.2013.6631908. [12] d. b. minh, l. d. hai, t. l. anh, and v. d. quoc, "electromagnetic torque analysis of srm 12/8 by rotor/stator pole angle," engineering, technology & applied science research, vol. 11, no. 3, pp. 7187–7190, jun. 2021, https://doi.org/10.48084/etasr.4168. [13] m. yildirim and h. kurum, "influence of poles embrace on in-wheel switched reluctance motor design," in 2018 ieee 18th international power electronics and motion control conference (pemc), budapest, hungary, aug. 2018, pp. 562–567, https://doi.org/10.1109/epepemc. 2018.8521859. [14] a. tap, l. xheladini, t. asan, m. imeryuz, m. yilmaz, and l. t. ergene, "effects of the rotor design parameters on the torque production of a pmasynrm for washing machine applications," in 2017 international conference on optimization of electrical and electronic equipment (optim) 2017 intl aegean conference on electrical machines and power electronics (acemp), brasov, romania, may 2017, pp. 370–375, https://doi.org/10.1109/optim.2017.7974998. [15] v. q. dang and c. geuzaine, "two-way coupling of thin shell finite element magnetic models via an iterative subproblem method," compel the international journal for computation and mathematics in electrical and electronic engineering, vol. 39, no. 5, pp. 1085–1097, jan. 2020, https://doi.org/10.1108/compel-01-2020-0035. microsoft word etasr_v11_n6_pp7793-7799 engineering, technology & applied science research vol. 11, no. 6, 2021, 7793-7799 7793 www.etasr.com lachumanan et al.: analysis of a multilevel voltage-based coordinating controller for solar-wind … analysis of a multilevel voltage-based coordinating controller for solar-wind energy generator: a simulation, development and validation approach thilagawathy lachumanan faculty of electronics and computer engineering universiti teknikal malaysia melaka melaka, malaysia thilagaa1@hotmail.com ranjit singh sarban singh advanced sensors and embedded controls centre for telecommunication research and innovation faculty of electronics and computer engineering universiti teknikal malaysia melaka melaka, malaysia ranjit.singh@utem.edu.my mohd ibrahim shapiai centre of artificial intelligence and robotic ikohza malaysia – japan international institute of technology universiti teknologi malaysia kuala lumpur, malaysia md_ibrahim83@utm.my t. joseph sahaya anand faculty of mechanical and manufacturing engineering technology universiti teknikal malaysia melaka melaka, malaysia anand@utem.edu.my abstract-this paper presents the development and the performance analysis of the developed model of a voltage-based coordinating controller. this model is developed to perform activities such as sensing, measuring, switching, coordinating, and effectively managing the output voltages produced by the solar-wind renewable energy sources in order to supply the connected load or/and charge the battery storage system. the developed model has different tasks to perform when solar-wind energy sources both produce output voltages simultaneously, also contributing to solving the requirements of different synchronization algorithms for a multi-agent renewable energy system. the sensed and measured output voltages of the solarwind energy sources are used as directive information to allow the developed model’s controller to supply the available power to the connected load or/and charge the battery storage system. also, the produced information at the model’s controller input is used to individually control the other sub-system, which directly assists in achieving the aim of simultaneous operation when both solar and wind energy sources produce output voltages. the model is developed and simulated in matlab/simulink. the simulation results are used to validate the developed methodology and the aims of the developed model. keywords-voltage-based; coordinating controller; renewable energy sources; matlab/simulink; solar-wind i. introduction irregularity of energy production and generation by renewable energy sources (ress) [1] makes it necessary for the microgrid system to integrate an energy storage system to stabilize the overall performance of the dc-based microgrid systems [2-5]. reviewing the evolution of dc-based microgrid systems [6] and their complexity, energy management systems (emss) [7-12] have been introduced. the ems technology for microgrid-based systems is divided into two categories: (i) centralized ems (cems) [8] and (ii) decentralized ems (dems) [12]. a cems is also known as the ac-based system, a microgrid connected to a transmission grid while the dems is a dc-based system where the microgrid is a standalone system. systems that have employed the emss into the distributed generation (dg) sources such as solar photovoltaic (pv) panels [13], wind turbine systems [14], hydropower systems [15], etc., into dc-based microgrid systems provide a reliable solution able to supply electrical power to rural communities where the national grid is not reachable [16]. systems proposed in [8, 17, 18] deploy a centralized agent which transfers and shares information and electricity with the other agents' controllers. the other agents are ress, the grid network, load consumption, and the battery storage system. the centralized agent acts as the master, and it is responsible for managing the data and sending the action to agents based on the real-time information. in [9], the decentralized multi agent was introduced. each agent in the proposed system works by receiving information through sensors. the disadvantage of this method is that each agent has its own algorithm and needs to be synchronized with complicated coding. authors in [19] suggested a voltage divider switching technique as the sensing and measuring of output voltages of ress. the voltage divider switching configuration is proposed for self-intervention of a hybrid renewable energy system. corresponding author: ranjit singh sarban singh engineering, technology & applied science research vol. 11, no. 6, 2021, 7793-7799 7794 www.etasr.com lachumanan et al.: analysis of a multilevel voltage-based coordinating controller for solar-wind … the disadvantage found in [9] and the advantage of having ems dc-based microgrid systems for the rural communities encouraged the development of the vbcc (voltage-based coordinating controller) model for the dc-based solar-wind res microgrid system. with the development of vbcc, a single mechanism was used instead of different algorithms for each agent. in terms of contribution, the developed vbcc can strategically contribute, control, and manage the connected sources via its multilevel voltage sensing and measurement mechanism. besides that, the integration of multilevel voltage sensing reduces the impact on the system, when the voltage is low. the voltage is used to charge the battery energy storage and at the same time discharge the battery to the connected load. the proposed vbcc senses, measures, coordinates, controls, and effectively manages the output voltages from the distributed generators for the connected load and charge battery energy system. ii. system components the developed vbcc consists of: • electronic stateflow condition circuit (escc) • electronic logic "and" gate circuit (elgc) • electronic conditions switching circuit (ecsc) • dc boost converter (dc-bc) • current conversion circuit (ccc) the vbcc is responsible for sensing, measuring, coordinating, switching, and effectively managing the generated energies from solar-wind ress which generate output simultaneously while performing different roles when the vbcc is operating. figure 1 shows the modeled block diagram of the integrated vbcc. solar energy is produced from solar pv panels and wind energy is produced from a wind turbine generator as shown in figure 1. fig. 1. the vbcc developed model. table i. solar-wind grouped conditions no. grouped conditions 1 0v≤vsolar<10v and 0v≤ vwind <10v 2 0v≤ vsolar <10v and 10v≥vwind>12v 3 0v≤ vsolar <10v and 12v≥ vwind ≥15v 4 10v≥ vsolar >12v and 0v≤ vwind <10v 5 10v≥ vsolar >12v and 10v≥ vwind >12v 6 10v≥ vsolar >12v and 12v≥ vwind ≥15v 7 12v≥ vsolar ≥15v and 0v≤ vwind <10v 8 12v≥ vsolar ≥15v and 10v≥ vwind >12v 9 12v≥ vsolar ≥15v and 12v≥ vwind ≥15v the solar and wind stateflow condition charts are categorized into 3 divisions which are: • 0 volt ≤ vr < 10 volt • 10 volt ≤ vr < 12 volt • 12 volt ≤ vr ≤ 15 volt where r is the solar or wind ress shown in figure 1. the ranges of output voltages for the solar – wind ress are summarized in table i. engineering, technology & applied science research vol. 11, no. 6, 2021, 7793-7799 7795 www.etasr.com lachumanan et al.: analysis of a multilevel voltage-based coordinating controller for solar-wind … iii. working principle of the components of the vbcc system a. electronic stateflow condition circuit (escc) the escc senses the total output analogue voltage amount of the individual solar wind res based on the primary division voltage ranges shown in figure 2. for example, if the solar source produces voltage 9v and the wind produces 9v, then solar10 and wind10 in figure 2 will produce a logic 1. this logic 1 then will be sent into the electronic logic "and" gate circuit. (a) (b) fig. 2. solar – wind primary voltage division ranges. b. electronic logic "and" gate circuit (elgc) the elgc is combinational of 9 and gates and is shown in figure 3. each of the 9 and gates takes an individual logic from each primary division range from the escc shown in figure 2. the 2 inputs of the and gate produce a single logic output which is used to switch on any respective switching circuit in the electronic conditions switching circuits shown in figure 1. when solar0 and wind0 are equal to logic 1, the s0w0 outputs a logic 1 too. the s10w10 logic 1 is sent to switch on s10w10 of electronic conditions switching circuits. the other combinational and gate circuits also have their decision-making roles based on the combinational input logics from the stateflow condition charts of solar – wind primary voltage division ranges. fig. 3. the 9 and gate combinational circuit. c. electronic conditions switching circuit (ecsc) the ecsc of 9 conditional switching circuits is shown in figure 4(a). figure 4(b) shows the s10w10 condition switching circuit which is integrated as one conditional switching circuit in figure 4(a). the s10w10 output logic 1 mentioned in section b is sent into s10w10 of the conditional switching circuit of electronic conditions switching circuit in figure 4(a). the s10w10 logic 1 then turns on the relays shown in figure 4(b). when the relays are turned on, the output from the switches is sent to the spdt relays to turn on the spdt relays from normally open (no) to normally closed (nc). when the spdt relays are at nc, the solar and wind input voltages are connected to s10w10/s and s10w10/w as shown in figure 1. the s10w10/s and s10w10/w will output voltages in the range of 10v to 12v to next respective system component. d. dc boost converter the direct current (dc) boost converter (bc) is shown in figure 5. in an explained example, the s10w10/s and s10w10/w will output voltage of 10v to 12v. then the output voltage of s10w10/w is connected to s10w10/w. the 10v to 12v from s10w10/w is sent into the dc-bc input as shown in figure 6. the dc_bc output will output an increased voltage compared to the input voltage at the dc_bc input. the increased voltage output at the dc_bc output is used to perform the battery energy system charging process as shown in figure 5. engineering, technology & applied science research vol. 11, no. 6, 2021, 7793-7799 7796 www.etasr.com lachumanan et al.: analysis of a multilevel voltage-based coordinating controller for solar-wind … (a) (b) fig. 4. (a) 9 conditional switching circuits, (b) s10w10 condition switching circuit. the s10w10/s will output voltage between 10v and 12v which is sent into s10w10/s as shown in figure 1. the input 10v-12v at s10w10/s is sent into the s10w10/s input shown in figure 7. from there, it is sent to the dc bc at both voltage inputs as shown in figure 8. but only one dc bc is activated which is the volt10 dc bc. logic 1 of s10w10/s is sent into volt10 port to switch the spdt relay from no to nc and allow the 10v to 12v incoming voltage to be increased. fig. 5. dc – dc boost converters. fig. 6. the dc boost converter circuit. fig. 7. dc to ac voltage output. solar_input_s10 wind_input_w10 engineering, technology & applied science research vol. 11, no. 6, 2021, 7793-7799 7797 www.etasr.com lachumanan et al.: analysis of a multilevel voltage-based coordinating controller for solar-wind … fig. 8. dc boost converter and dc to ac inverter system. the increased output voltage from the dc bc is supplied into converter volt10 which is a dc to ac inverter. the inverter will invert the dc input voltage to an ac voltage which is used to supply to any connected load. iv. results and discussion the proposed vbcc model was fully developed in matlab/simulink. voltage sensing and measuring method was used to assist the controller in coordinating, switching, and effectively managing the respective tasks such as supplying the inverted dc voltage into ac for connected load or boosting the dc voltage to perform charging on the battery energy system. at in the beginning of this paper, we used the condition s10w10 to depict the developed vbcc’s system methodology. thus, the condition s10w10 will also be used to present the results of each stage of the developed vbcc to validate the developed system’s overall performance and to analyze the respective required generated signals. a. solar – wind renewable energy sources figure 9 shows the solar wind ress input voltages captured based on the preset value shown in figure 1. hence, the 11v voltage captured is an amount of the voltage that the connected solar – wind ress are producing. these voltages are then sent into the escc as shown in figure 1. in the escc, these voltages are captured by the individual solar and wind stateflow chart shown in figure 10. hence, when the solar and wind stateflow condition charts capture the output voltages of the solar – wind ress, a logic 1 is produced by each stateflow condition chart. referring to figure 10, solar and wind stateflow condition charts give a logic 1 for 11v sensed and measured voltage. fig. 9. solar – wind ress input voltages. (a) (b) fig. 10. 11v of solar – wind stateflow condition chart. both logics are sent into the electronic logic "and" gate circuit through the ports solar10 and wind10 as shown in figure 1. figure 11 shows the solar10 and wind10 logic output based on the sensed and measured output voltage shown in figure 10. the solar10 and wind10 logic 1 is sent into the and gate lo6 shown in figure 3 for an output of logic 1. table ii. and gates combinational output – s10w10 and gates combinations output s0w0 0 s0w10 0 s0w12 0 s10w0 0 s10w10 1 s10w12 0 s12w0 0 s12w10 0 s12w12 0 engineering, technology & applied science research vol. 11, no. 6, 2021, 7793-7799 7798 www.etasr.com lachumanan et al.: analysis of a multilevel voltage-based coordinating controller for solar-wind … based on table ii, the combinational output of the s10w10 and gates shown in figure 3 is the logic 1. this s10w10 logic 1 is sent to the s10w10 port of electronic condition switching circuit as shown in figure 1. the s10w10 logic 1 connects the port 7 s10w10 of the 9 conditional switching circuits shown in figure 4(a) to activate the s10w10 condition switching circuit shown in figure 4(b). the s10w10 logic 1 will switch the relays from no to nc to allow the solar input 11v and wind input 11v to flow into port 1 (s10w10/s) and 2 (s10w10/w) as shown in figure 4. figure 12 shows the 11v voltage output captured at ports s10w10/s and s10w10/w as shown in figure 4(a). (a) (b) fig. 11. solar stateflow condition chart – (a) solar10 logic output and (b) wind10 logic output. referring to figure 1, the 11v voltage at s10w10/s is connected to the current conversion circuit, while the 11v voltage at s10w10/w is connected to the dc bc. figure 13 shows the input 11v voltage at s10w10/w – dc-bc input and the approximately 16v voltage output at the dc_bc output as shown in figure 6. the 16v voltage output at the dc_bc output is connected to the battery energy system as shown in figure 5 to charge the batteries used as an energy storage system. figure 14 shows the results captured when the 16v voltage output at the dc_bc output is connected as input to the dc to ac inverter. the 16v voltage is inverted into 240v ac voltage output at the dc to ac inverter, which is then used to supply the connected load. fig. 12. voltage output at s10w10/s and s10w10/w. fig. 13. input and output voltage – dc boost converter. fig. 14. 16v voltage input and 240v ac output at the dc to ac inverter. the presented results are for condition s10w10, while the results for all the other conditions were compiled and are presented in tables iii and iv. v. conclusion based on the presented literature review, a vbcc for solar – wind res was proposed, modeled, and developed in this paper. the modeling and development of the vbcc was conducted in order to sense and measure the incoming voltages from the solar and wind res. the other aims of vbcc are to coordinate, switch, and effectively manage the produced energy from the available voltages. the presented research engineering, technology & applied science research vol. 11, no. 6, 2021, 7793-7799 7799 www.etasr.com lachumanan et al.: analysis of a multilevel voltage-based coordinating controller for solar-wind … methodology has successfully developed the vbcc. the obtained results show that the developed vbcc can coordinate, switch, and effectively manage the available energy for connected load and battery energy system charging. table iii. escc output logic conditions escc output logic conditions s0 s10 s12 w0 w10 w12 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 table iv. elgc combinational output logics elgc combinational output logics c9 c8 c7 c6 c5 c4 c3 c2 c12 s0w0 s0w10 s0w12 s10w0 s10w10 s10w12 s12w0 s12w10 s12w12 1 1 1 1 1 1 1 1 1 acknowledgment the authors gratefully acknowledge the support by the centre of telecommunication research & innovation (cetri), fakulti kejuruteraan elektronik dan kejuruteraan komputer (fkekk), and faculty of mechanical and manufacturing engineering technology (ftkmp), universiti teknikal malaysia melaka, and the ministry of higher education, malaysia. also, the authors thank the centre of artificial intelligence and robotic ikohza malaysia-japan international institute of technology, universiti teknologi malaysia (utm). references [1] md. s. alam, f. s. al-ismail, a. salem, and m. a. abido, "high-level penetration of renewable energy sources into grid utility: challenges and solutions," ieee access, vol. 8, pp. 190277–190299, 2020, https://doi.org/10.1109/access.2020.3031481. 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[19] r. s. s. singh, m. abbod, and w. balachandran, "renewable energy resource self-intervention control technique using simulink/stateflow modeling," in proceedings of the 50th universities power engineering conference (upec 2015), trent, uk, 2015, vol. 2015, https://doi.org/ 10.1109/upec.2015.7339803. engineering, technology & applied science research vol. 7, no. 5, 2017, 2030-2040 2030 www.etasr.com soomro et al: 3d centrifuge modeling of the effect of twin tunneling to an existing pile group 3d centrifuge modeling of the effect of twin tunneling to an existing pile group mukhtiar ali soomro dpt. of civil engineering quaid-e-awam university of engineering, science & technolgy nawabshah, pakistan eng.soomro@gmail.com manthar ali keerio dpt. of civil engineering quaid-e-awam university of engineering, science & technolgy larkana, pakistan mantharali99@quest.edu.pk mohsin ali soomro dpt. of civil engineering quaid-e-awam university of engineering, science & technolgy nawabshah, pakistan drmohsin@quest.edu.pk daddan khan bangwar dpt. of civil engineering quaid-e-awam university of engineering, science & technolgy nawabshah, pakistan daddan@quest.edu.pk abstract—in densely built urban areas, it is inevitable that tunnels will be constructed near existing pile groups. the bearing capacity of a pile group depends on shear stress along the soil-pile interface and normal stress underneath the pile toe while the two would be adversely affected by the unloading process of tunneling. although extensive studies have been conducted to investigate the effects of tunnel construction on existing single piles, the influence of twin tunnel advancement on an existing pile group is merely reported in the literature. in this study, a series of three-dimensional centrifuge tests were carried out to investigate the response of an existing pile group under working load subjected to twin tunneling at various locations in dry toyoura sand. in each twin tunneling test, the first tunnel is constructed near the mid-depth of the pile shaft, while the second tunnel is subsequently constructed either next to, below or right underneath the pile toe (tests g_st, g_sb and g_su, respectively). among the three tests, the 2nd tunnel excavated near the pile toe (test g_st) results in the smallest settlement but the largest transverse tilting (0.2%) of pile group. significant bending moment was induced at the pile head (1.4 times of its bending moment capacity) due to the 2nd tunnel t. on the contrary, tunneling right underneath the toe of pile (i.e., test g_su) results in the smallest tilting but largest settlement of the pile group (4.6% of pile diameter) and incremental mobilisation of shaft resistance (13%). due to stress release by the twin tunneling, the axial force taken by the front piles close to tunnels was reduced and partially transferred to the rear piles. this load transfer can increase the axial force in rear piles by 24%. keywords-twin tunneling; pile group; three-dimensional; soilstructure interaction; centrifuge modeling i. introduction due to land shortage, high-rise buildings are preferred to meet the development and economical growth in major cities. the construction of high rise buildings often requires deep foundations such as pile group when the underlying soil and rock strata do not have sufficient bearing capacity. in densely built urban cities, tunnels are likely to be constructed adjacent to existing deep foundations. one recent example is mrt north east line c704 project in singapore, in which twin tunnels were carried out near the shaft of an existing pile group [1]. it is well recognized that the capacity of a pile group depends on mobilized stresses in the ground while tunneling is essentially a stress release process. therefore, it is vital to investigate the adverse effects of tunneling on existing pile foundations. there have been a number of studies addressing this problem. among previous studies, numerical analyses, analytical solutions and centrifuge modeling are most frequently adopted [2-16]. generally speaking, tunneling adjacent to existing pile foundations, results in substantial changes in the axial load of piles and in pile settlement. both are found to heavily depend on tunnel location in relation to the pile. however, these studies focused on pile response to single tunneling. however, twin tunneling has been increasingly constructed while developing underground metro lines [17]. excavation of twin tunnels adjacent to existing pile foundations would result in more complicated load transfer mechanisms within a single pile or between piles in a group. accordingly, settlement or tilting of pile foundations would be more concerned. as far as field monitoring is concerned, very few researchers have investigated the effects of twin tunneling on piles. in [1], authors reported a case history of twin shield tunneling adjacent to an existing pile group in singapore. however, instrumentation only includes strain gauges along a limited portion of piles near tunnels. settlement and tilting of the pile group were not reported. regarding model tests, authors in [18] carried out two centrifuge tests to investigate influence of construction sequences of twin tunneling on an existing single pile in medium dense dry sand. the two construction sequences considered are: (i) tunneling near the middle of the pile shaft followed by tunneling near the pile toe (test st); (ii) tunneling near the pile toe followed by tunneling near the middle of the pile shaft (test ts). it is concluded that the measured pile settlement caused by tunneling sequence st is 33% larger for than by tunneling sequence ts. a larger reduction in the end bearing resistance and shaft resistance at the lower part of the pile is resulted from tunneling near the pile toe in test st than in test ts. on other hand, construction sequences have limited effect on ground surface settlement and bending moment of pile. location of tunnels relative to the pile, which were shown to significantly affect pile response by engineering, technology & applied science research vol. 7, no. 5, 2017, 2030-2040 2031 www.etasr.com soomro et al: 3d centrifuge modeling of the effect of twin tunneling to an existing pile group previous study, was not considered in this study. to investigate responses of pile group subjected to twin tunneling at various locations, a series of centrifuge were carried out in this study. the test series consists of one pile load test in “greenfield” and three other tests with tunnels constructed at various locations relative to an existing pile group. measurements in the centrifuge tests include settlement and tilting of the pile group, axial load and bending moment of each pile at various tunneling stage. ii. experimental program and setup it is well recognized that soil behavior is stress-dependent. by using a geotechnical centrifuge, a proper stress field can be recreated in a soil model by applying centrifugal acceleration n times greater than earth’s gravitational acceleration (g). table i. summarizes scale factors relevant to this study. physical quantity scaling factor (model /prototype) gravitational acceleration n length 1/n area 1/n2 volume 1/n3 settlement n stress 1 strain 1 force 1/n2 density 1 mass 1/n3 flexural rigidity 1/n4 bending moment 1/n3 in this study, four centrifuge model tests were carried out at the geotechnical centrifuge facility of the hong kong university of science and technology [19, 20]. the 400 g-ton centrifuge has an arm radius of 4.2 m and is equipped with a two-dimensional hydraulic shaking table and a four-axis robotic manipulator. all of centrifuge tests reported herein were carried out at a centrifugal acceleration of 40 g. figure 1a shows elevation view of test g_st, which is intended to investigate responses of a pile group due to tunneling near the mid-depth of pile shaft and subsequently near the pile toe. the shallow tunnel was simulated prior to the deep one, since this construction sequence was shown to affect pile settlement more severely, than the reversed sequence [18]. the horizontal distance from the centerline of the tunnel to the nearest pile is 0.75d. diameter and length of each pile are 20 mm (0.88 m in prototype) and 600 mm (24.0 m in prototype), respectively. the pile cap was elevated by 110 mm (above the ground surface) and hence the embedded depth of each pile is 490 mm (19.6 m in prototype). diameter of each tunnel (d) is 152 mm (6.08 m in prototype). cover-to-diameter ratios (c/d) of the tunnels located near the pile shaft and pile toe are 1.5 and 2.7, respectively. figures 1b and 1c show elevation view of tests g_sb and g_su, respectively. in these two tests, the first tunneling is carried out at the same location as that in test g_st (c/d=1.5), while the second tunnel in both tests g_sb and g_su is constructed below and right underneath the toe of the pile group (c/d ratios in both tests are equal to 3.7), respectively. 152 152 184 850 (2x2) pile group 1245 114 toyoura sand (medium dense) 490 1st tunnel (s) 28 224 38 110 374 2nd tunnel (t) dead weight 8.6 kg (a) pile cap 190 152 152 850 (2x2) pile group 1245 114 toyoura sand (medium dense) 490 28 224 110 374 32 1st tunnel (s) 2nd tunnel (b) (b) dead weight 8.6 kgpile cap 190 152 152 850 (2x2) pile group 1245 114 toyoura sand (medium dense) 490 28 224 110 374 32 1st tunnel (s) 2nd tunnel (u) (c) dead weight 8.6 kgpile cap fig. 1. elevation view of centrifuge tests: (a) g_st; (b) g_sb and (c) g_su. all dimensions are in mm in model scale figure 2a illustrates plan view of a typical test (i.e., test g_st). it can be seen that length of each model tunnel (along (a) (b) (c) engineering, technology & applied science research vol. 7, no. 5, 2017, 2030-2040 2032 www.etasr.com soomro et al: 3d centrifuge modeling of the effect of twin tunneling to an existing pile group its longitudinal direction) is 380 mm, which is equivalent to 2.5d. each tunnel consists of five construction stages, with the tunnel face advancing by a distance of 0.5d in each stage. in addition to the three tests described above, in-flight pile load test (test g_l) is carried out to obtain the load settlement curve of the pile group in “greenfield” (i.e., with absence of tunnels). table ii summarizes centrifuge test program in this study. 7 6 622.5 4 9 5 4 9 5 1st tunnel (s) 2nd tunnel (u) d ir ec ti o n o f tu n n el a d v a n ce m en t y/d=-1.0 y/d=-0.5 y/d=0.0 y/d=0.5 y/d=1.0 y/d=1.5 y/d=-1.0 y/d=-0.5 y/d=0.0 y/d=0.5 y/d=1.0 y/d=1.5 x y monitoring section 149473.5 7 6 7 6 7 6 7 6 dead weight (8.6 kg)piles y xl1 dead weight (8.6 kg) l2 l3 fig. 2. (a) plan view of a typical centrifuge test (test g_su) (all dimensions are in mm in model scale); (b) instrumentation at the pile cap table ii. centrifuge test program test id c/d remark dr: % g_l n/a pile load test 65 g_st 1.5, 2.7 twin tunneling near pile shaft and pile toe, respectively 65 g_sb 1.5, 3.7 twin tunneling near pile shaft and below pile toe, respectively 64 g_su 1.5, 3.7 twin tunneling near pile shaft and right underneath pile toe, respectively 65 a. in-flight simulation ofttunnel excavation in each twin tunneling test (except the pile load test), each model tunnel consists of five independent cylindrical rubber bags (see figure 2a). each rubber bag was filled with de-aired water. three-dimensional tunnel excavation was simulated inflight by draining away a controlled amount of water from each rubber bag one by one. the amount of water drained away from each rubber bag was equivalent to a volume loss of 1.0%. draining water from the rubber bag at 40g caused deformation mostly at the top of the rubber bag but small at the bottom because of the weight of the bag/water. this is similar to the characteristics of ground deformation caused by a shield tunnel, near which ground mainly deforms at the tunnel crown and sides [21, 22] while very small ground displacement takes place at the tunnel invert [23, 24]. b. model pile group and instrumentation a 2×2 model pile group was used to replicate 0.88 m diameter of concrete piles at prototype scale in this study as shown in figure 3. the four piles were connected to a relatively rigid pile cap, which corresponds to a 1 m thick reinforced concrete cap in prototype with a flexural rigidity of 15 gnm2. each model pile was made of an aluminum tube with a young’s modulus of 70 gpa. the aluminum tube was 600 mm long and it had outer and inner diameters of 19 and 15 mm (i.e., wall thickness=2 mm), respectively. each pile was instrumented with semiconductor strain gauges (sgs) bonded on external surface of the piles at ten levels at spacing of 60 mm (2.4 m in prototype scale) to measure axial load and bending due to tunneling. full wheatstone bridge strain gauges were arranged for temperature compensation for axial and bending. these sgs have a guage factor (gf) 150 which is higher than conventional foil gauges (gf=2). it implies that these strain gauges are able to measure strain as low as ±1.5 µ strains. each pile was calibrated for the axial and bending measurement prior to each test. for axial calibration, each pile was applied force gradually on the top of pile using actuator. the corresponding outputs were then related to axial forces. for bending calibration, each pile was placed on two knife edges supports at each end of pile, making pile as simply supported beam. then different weights were hanged not only at centre but also at distance of one-third and two-third from left support. strain gauge outputs were then related to calculated bending moments. the sgs were protected by a 1.5 mm thick epoxy coating uniformly applied to the shaft of each pile. the epoxy was not coated with sand. to measure the interface property between toyoura sand and epoxy-coated pile shaft, two direct shear tests were carried out. the measured average friction angle of the toyoura sand-expoxy interface was 18o. in addition, the surface roughness was measured using an optical profiler. the measured absolute interface roughness rmax is approximately 15 µm. the normalised roughness rn, which is defined in [25] as a ratio of rmax to the mean particle size of sand (d50) is 0.09. author in [26] classified interfaces with rn smaller than 0.02 as smooth interfaces and interfaces with rn larger than 0.10 as completely rough interfaces. based on this criterion, the pilesoil interface in this study may be described as relatively rough. by taking stiffness of the epoxy coating (young’s modulus=2 gpa) into account, axial rigidity (emam) and bending rigidity (emim) of each model pile are 7670 kn and 284 nm 2, respectively. according to scaling factors summarized in table i, the corresponding emam and emim of each pile in prototype scale are 12,272 mn and 727 mnm2 in prototype, respectively. linear variable differential transformers (lvdts) were installed at various places of the pile cap (see figure 2b) to measure settlement of the pile group (“l2”), transverse tilting (a) (b) engineering, technology & applied science research vol. 7, no. 5, 2017, 2030-2040 2033 www.etasr.com soomro et al: 3d centrifuge modeling of the effect of twin tunneling to an existing pile group of the pile group (deduced from measurement of “l1” and “l3”). 600 mm a typical level of strain gauges 120 mm 120 mm 22 mm fig. 3. model pile group and instrumentation (all dimensions are in mm in model scale) c. pile loading system in the pile load test (test g_l), a vertical load was applied to the pile cap incrementally using a hydraulic jack. each load increment is controlled by a load cell attached to the piston of the hydraulic jack. while settlement of the pile group is measured by a lvdt located at the centre of the pile cap. based on the pile load test, working load of the pile group can be determined according to a displacement controlled criterion (discussed later). the obtained working load is then applied to the three tests with tunneling simulated (tests g_st, g_sb, g_su), by mounting a dead weight on top of the pile cap before centrifuge testing (at 1g). d. testing material and model preparation according to author of [27], toyoura sand consists of subangular particles and has a mean diameter (d50) of 0.17 mm and a uniformity coefficient (uc) of 1.7. the maximum and minimum void ratios of the sand are 0.977 and 0.597, respectively. regarding grain size effects, authors in [28] suggested that the grain size of soil only becomes significant when it exceeds 1/30th of an important model dimension such as pile diameter. in this study, the grain size of toyoura sand (0.17 mm) is only 1/118th of the pile diameter (20 mm), suggesting that the scale effects on load carried by the pile toe are likely to be negligible. in each test, the model sandy ground was prepared by pluvial deposition method (i.e., raining dry toyoura sand into the model box) at 1g. during the sand raining process, a constant falling height of sand (i.e., 500 mm) was maintained to result in medium-dense sand (with relative density of about 65%, based on previous calibrations). when the sand bed reached the elevation where the invert of the tunnel should be located, the model tunnel was placed on the sand bed at its designed position. then the pluvial deposition of sand was continued. similarly, the pile group (including the pile cap) was temporarily fixed at its design location (with the cap pinned to a temporary supporting beam) as the sand bed reached the toe level of the pile group. this was then followed by pluvial deposition of sand around the piles. when the sand hopper approached the pile cap during the subsequent sand raining, a guiding plate (inclined with an angle of 30o relative to the vertical plane) was mounted under the opening of the sand hopper to guide the sand to fall into the gap within piles. under this circumstance, the falling height of sand was changed to 300 mm to result in a relative density of about 65%. by using the pluvial deposition method to form sand bed around the pile at 1g, the initial stress around the model pile is small. subsequently, as the g-level increased during a test, the initial stress around the pile also increased under the ko conditions, which could be regarded as similar to that adjacent to a nondisplacement pile. in each test, the 750 mm thick sand bed was formed layer by layer (i.e., 50 mm thick for each layer). after the preparation of each layer, the average density of the layer was deduced by measuring the weight and volume of sand used. figure 4 shows the measured distributions of sand density with depth in all four centrifuge tests at 1g. it can be seen that the maximum difference in density is less than 0.6%. take test st for an example, the minimum density at the location of tunnel s is 1527 kg/m3, which is 0.5% smaller than the maximum density of 1534 kg/m3 obtained at about 725 mm below the surface of the sand bed. the measured average relative density (i.e., dr) in each test is summarized in table ii. it can be seen that the percentage difference of dr between each tests is less than 2%. this suggests that the soil samples prepared in these four tests are likely to be comparable. 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 1510 1520 1530 1540 1550 density (ρ): kg/m3 d ep th : m m g_l g_st g_sb g_su tunnel axis (s) tunnel axis (t) pile group 1525 1527 tunnel axis (b/u) 1534 fig. 4. distributions of initial density of sand bed with depth in all four tests engineering, technology & applied science research vol. 7, no. 5, 2017, 2030-2040 2034 www.etasr.com soomro et al: 3d centrifuge modeling of the effect of twin tunneling to an existing pile group e. test procedure after assembling the centrifuge model package, a dead weight was fixed on top of the pile cap to serve as working load (determined from the pile load test g_l). then the whole package was mounted onto the swinging platform and spun up to 40 g. upon reaching 40 g, in-flight twin tunnel excavations were simulated one after the other. each tunnel was simulated in five stages, by draining away water from five rubber bags (with a 1.0% volume loss for each), respectively. during the entire testing process, transverse tilting of the pile group, settlement of the pile group (in the center of the pile cap), axial load and bending movement along each pile were recorded. in the pile load test (test g_l), no dead weight was placed on top of the pile cap at 1g. instead, a hydraulic actuator was mounted onto the model box. after reaching 40g, in-flight pile load test was carried out by loading the pile cap incrementally with the hydraulic jack. axial load acting on the pile cap and pile group settlement were measured during the pile load test. iii. interpretation of tests results all tests results are presented in this paper are in prototype scale, unless stated otherwise. a. determination of axial load bearing capacity of the pile group the principal objective of this study is to investigate the behaviour of existing 2×2 pile group (under working load) during advancement of twin (piggyback) tunneling. therefore, it was mandatory to determine working load to be applied on pile group before commencement of tunnels. to achieve this objective an in-flight pile group load test (i.e. test g_l) was carried out with absence of tunnels. the load was applied with an increment of 640 kn (i.e. 400 n in model scale) to 12160 kn (i.e. 7600 n in model scale). figure 5 shows load settlement relationship obtained from test g_l. the settlement is normalized by the pile diameter (dp). based on the load settlement curve, ultimate capacity of the pile was deduced by a settlement acceptance failure criterion proposed by authors in [29] for single pile. the failure criterion is given by following expression: ,max 1 0.045 2 h p ph p p p p l d a e    (1) where δph,max is the maximum pile head movement which defines the ultimate load, ph is the pile head load, lp is the pile length, ep is the pile shaft elastic modulus, ap is the crosssectional area of the pile, and dp is the pile diameter. the reason for adopting [29]’s failure criterion is because it takes the effects of pile length into consideration. it can be seen from the figure that the ultimate load (i.e., 8.3 kn) deduced from the failure criterion is sufficiently large to reveal a “yield” point (see “estimated yield point” in the figure) of the loaddisplacement curve for the pile group. the “yield” point is estimated as a point from which the load-displacement curve starts to deviate from the tangent line passing through the origin. with a factor of safety (fos) of 1.5, the working load was determined as 5.55 mn. a dead weight of 8.6 kg (equivalent to 5.55 mn at prototype scale) was mounted on pile cap at 1g-level to serve as a working load on the pile group. settlement of 3.0%dp (i.e. 24 mm) of the pile group due to application working load can be predicted from load settlement curve (shown in figure 5) 0 2 4 6 8 10 12 14 16 18 20 0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 load: mn n o rm a li se d p il e g o ru p s et tl em en t (s p /d p ): % failure criterion (ng et al., 2001a) tangent line estimated yield point working load fig. 5. load settlement curve obtained from in-flight pile group load test (i.e. test g_l) b. settlement of pile group figures 6a and 6b show incremental settlement (sp) of pile group during advancement of the first tunnel (i.e., tunnel s) and the second tunnel (i.e., tunnels t, b and u) in all the three tests (i.e. g_st, g_sb and g_su). construction stages of the tunnels are indicated by distance (i.e., y) between tunnel face to centerline of pile group (defined as monitoring section in figure 6). the sp and y are normalized by pile diameter (dp) and tunnel diameter (d), respectively. measured incremental settlement of a single pile due to twin tunneling in a centrifuge [18], is also included in the figure for comparison. centrifuge model package (including dimension of each component and volume loss due to tunneling) of the test reported by [18] are the same as that of test g_st in this study, except adopting single pile in their test. in addition, relative density of sand model in their test (i.e., 62%) is slightly lower than that in this study (i.e., 65%). figure 6a shows that in all the three tests, sp of pile group due to advancement of the first tunnel (s) is very similar. this suggests repeatability of the three tests. furthermore, it can be seen that sp of pile group increased almost linearly with tunneling stages (i.e., y/d). a similar trend can be observed from the reported centrifuge test of single pile subjected to tunneling near its pile shaft [18] in terms of magnitude, tunneling induced settlement of the single pile is much larger (about 300% larger) than that of the pile group, as expected. engineering, technology & applied science research vol. 7, no. 5, 2017, 2030-2040 2035 www.etasr.com soomro et al: 3d centrifuge modeling of the effect of twin tunneling to an existing pile group 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 -1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00 1.25 1.50 y/d s p/ d p (% ) g_st g_sb g_su this study 1st tunnel 2nd tunnel s t b u sectional view y/d=-1.0 y/d=-0.5 y/d= 0.0 y/d= 0.5 y/d= 1.0 y/d= 1.5 y/d=-1.0 y/d=-0.5 y/d =1.0 y/d =1.5 p2 p3 p4 p1 -y +y plan view st single pile (ng et al.,2012) reported centrifuge data monitoring se ction 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 -1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00 1.25 1.50 y/d s p/ d p (% ) g_st g_sb g_su this study st single pile (ng et al.,2012) reported centrifuge data fig. 6. induced settlement of pile group due to advancement of: (a) 1st tunnel (i.e., tunnel s); (b) 2nd tunnel (i.e., tunnel t, b and u) different from tunneling near the mid-depth of the pile shaft, the subsequent tunneling adjacent to the pile toe (i.e., tunnels s, t and u) resulted in a non-linear increase of sp with construction stages (see figure 6b). in all the three tests, settlement rate of sp of pile group increased as tunnel face approached the monitoring section (ms) and decreased as it moved away from ms. this trend is similar to that observed from a single pile subjected to tunneling near the pile toe [18]. while second tunnels (i.e., tunnels t, b and u) were constructed adjacent to the pile toe, the smallest sp was induced in test where tunnel is closest to the pile toe. the largest sp is caused by tunneling right underneath the pile (i.e., tunnel u). this is because tunneling right underneath the pile group resulted in the largest reduction of toe resistance of all four piles (discussed later). the reduction of toe resistance is compensated by mobilizing shaft resistance of all four piles, causing larger sp of pile group than that in the other two tests. these test results suggest that sp of pile group does not depend only on offset of tunnel from the pile toe, but also location of tunnel relative to the pile toe. author in [30] carried out field measurement of axially loaded single piles subjected to tunneling either right underneath the pile, or underneath but with an offset of the pile. the measurements also show the largest sp of pile was caused by the tunneling right underneath the pile. the measured results shown in figures 6a and 6b imply that the tunnel driving distance simulated (2.5 times of tunnel diameter) is still insufficient to establish maximum pile settlement, although this should not affect the comparative nature and findings of this study significantly. by comparing figures 6a and 6b, it can be seen that tunneling adjacent to the pile toe (in all three tests) caused much larger settlement than that near pile shaft. total settlements of pile group (due to working load and twin tunneling) in tests g_st, g_sb and g_su are 32, 34 and 37 mm (i.e., 4.0, 4.3 and 4.6% of pile diameter), respectively. these three values satisfy a reliabilitybased serviceability criteria (i.e., 56 mm), which was developed based on 95 buildings experiencing settlement [31]. c. tilting of pile cap figure 7a compares transverse tilting of the pile cap due to the first tunneling in all the three tests. each tilting was deduced as a ratio of differential settlement at two edges of the pile cap (measured by l1 and l3, see figure 2b) to the distance between them. positive value means the pile cap tilts towards the first tunnel, and vice versa. in all the three tests, tilting of pile group due to the first tunneling (i.e., tunnel s) is very similar. repeatability of the three tests is further confirmed. during the tunneling process, tilting of pile group increased almost linearly with excavation stages (i.e., y/d). after the first tunneling, incremental tilting in all three tests was about 0.05%. during the second tunneling (see figure 7b), pile cap tilts nonlinearly with excavation stages in tests g_t and g_b. in both tests, increasing ratio of titling increased as tunnel face approached the monitoring section then decreased as it passed by. larger tilting was always resulted in test g_t than that in test g_b, as the former induced larger difference between stress release near front (p1) and rear pile (p2) (discussed later). while tunnel was excavated right underneath the pile toe (i.e., tunnel u), little tilting was induced. this is because front pile row (p1 and p3) and rear pile row (p2 and p4) are subjected to same amount of stress release in the test. centrifuge test results reported by [18] show that that a single pile affected by the construction of a shallow tunnel and then followed by a deep tunnel would settle more than a pile response to a reversed tunneling sequence. based on their test results, it may be deduced that a shallow tunnel constructed near a pile group and then followed by a deep tunnel would result in larger settlement of the front pile (closet to the tunnel being excavated) and hence larger differential settlement (i.e., tilting) between the front pile and the rear pile (furthest from the tunnel being excavated). after twin tunneling, the maximum tilting of pile group (occurred in test g_st) was about 0.2%. this is exactly equal to allowable tilt limit (i.e. 0.2%) suggested by eurocode 7 [32] for building. it seems the “building” would be safe while subjected to construction of twin tunnels with configurations defined in this study (figure 1). (a) (b) engineering, technology & applied science research vol. 7, no. 5, 2017, 2030-2040 2036 www.etasr.com soomro et al: 3d centrifuge modeling of the effect of twin tunneling to an existing pile group 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 -1.0 -0.5 0.0 0.5 1.0 1.5 y/d t il ti n g ( % ) g_st g_sb g_su y/d=-1.0 y/d=-0.5 y/d= 0.0 y/d= 0.5 y/d= 1.0 y/d= 1.5 y/d=-1.0 y/d=-0.5 y/d =1.0 y/d =1.5 p2 p3 p4 p1 -y +y plan view 1st tunnel 2nd tunnel s t b u sectional view monitoring s e ction +ve -ve 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 -1.0 -0.5 0.0 0.5 1.0 1.5 y/d t il ti n g ( % ) g_st g_sb g_su (b) fig. 7. induced transverse tilting of the pile cap tilting due to advancement of: (a) 1st tunnel (i.e., tunnel s); (b) 2nd tunnel (i.e., tunnel t, b and u) d. bending moment profile the tilting at the pile cap caused by twin tunneling (figure 7) should have induced bending moment in piles. figures 8a, 8b and 8c compare the measured incremental bending moment along the front pile (p1) and rear pile (p2) due to the twin tunneling in the three tests. a positive bending moments means that tensile stress was induced along pile shaft facing the first tunnel. due to the first tunneling, the induced bending moment in each test is very similar. therefore, bending moment caused by the first tunneling is only illustrated in figure 9a. it can be seen that the maximum positive bending moment was induced near the location of the first tunnel, which caused stress release and hence soil displacement towards it. this positive bending moment was counter-balanced by negative bending moment near the pile cap. due to the second tunneling, bending moment in tests g_st and g_sb increased significantly while it remains almost the same in test g_su. these observations are consistent with measured tilting, shown in figure 8. the most significant bending moment (i.e., 1120 knm) was developed in both front and rear piles near pile cap in test g_t. based on [4], yield moment of the pile used in this study is about 800 knm, which is less than the maximum bending moment developed in test g_t. authors in [4] carried out a series of centrifuge tests to investigate pile group responses due to tunneling in stiff clay. they also reported measured maximum induced bending moment at the head of front and rear piles when tunnel was constructed near and below the pile toes. however, the magnitudes of maximum bending moment are much smaller than bending moment capacity. much larger bending moment measured in this study may be due to the reason that stiffness of medium dense sand (this study) is larger than that of stiff clay [4]. e. axial load distribution in this section, measured axial load of two typical piles in each row (front pile (p1) and rear pile (p2) (see insets in figure 9) are selected for discussions. figure 9a shows axial load distribution along the selected piles when the first and the second tunneling (i.e., tunnels s and t) reaches the monitoring section (i.e. y/d=0.0) in test g_st. before tunnel excavations (at working load condition), axial load distributions along both piles are similar. therefore, only load distribution along the pile p1 is included for reference. it can be seen that about 45 and 46% of load carried by pile p1 (i.e. 1367 kn) at working load is carried by toe and lower half of shaft (i.e., 0.5≤z/lp≤1.0) of the pile, respectively. when the first tunnel (i.e., tunnel s) was constructed at c/d=1.5, the pile p1 experienced stress release which caused reduction of shaft resistances above the spring line of tunnel (s). consequently, axial load acting on the pile group not only transferred to the lower half of front pile p1 shaft but also to its adjacent rear pile p2 to maintain equilibrium. toe and shaft resistance at lower half of shaft of pile p1 increased by 8 and 10%, respectively. this load transfer is similar to that observed from a single pile subjected to tunneling near the pile shaft [18]. however, in pile group load also transfer to rear pile as all pile are rigidly connected with pile cap. as second tunnel (i.e., tunnel t) was constructed near pile toe, stress release occurred near lower portion of shaft and toe of pile p1. consequently, shaft resistance at lower shaft of pile p1 reduces by 66% and toe resistance was increased by 24% to carry the load. if the tunneling sequence were reversed (i.e., constructing the deep tunnel prior to the shallow one), a smaller reduction in the end bearing resistance and shaft resistance at the lower part of the pile is expected as revealed by authors in [18] from their investigation of the effects of tunneling sequence. some of the load transferred to pile p2 and increased its head load by 24%. to carry the load transferred from front pile p1, pile p2 mobilized its shaft capacity and toe resistance. the shaft and toe resistance increases by 30 and 35%, respectively. the significant load re-distribution (24%) between piles p1 and p2 in test g_st is likely to be associated with the differential settlement between the two piles (i.e., transverse tilting), which is the maximum among the three tests. if the tunneling sequences were reversed, smaller titling of the pile cap is expected (as discussed in the section “tilting of pile cap”), resulting smaller load re-distribution among piles. (a) (b) engineering, technology & applied science research vol. 7, no. 5, 2017, 2030-2040 2037 www.etasr.com soomro et al: 3d centrifuge modeling of the effect of twin tunneling to an existing pile group figure 9b shows the axial load distribution after the 1st tunneling and when the 2nd tunnel face reached the monitoring section in test g_sb. when the second tunnel (i.e., tunnel b) was constructed below pile toe (c/d=3.7) and at an offset from pile group, front pile (p1) experiences largest stress release than the rear pile toe (p2). as a result, the toe resistance of pile p1 decreases by 32%. the pile has to settle to mobilize its shaft capacity to carry the load. consequently, 20% of the load has been transferred to rear pile p2 to maintain equilibrium. figure 9c shows the axial load distribution after the 1st tunneling and when the 2nd tunnel face reached the monitoring section in test g_sb shows the axial load distribution along the pile p1 and pile p2 in test g_su. since the second tunnel (i.e., tunnel u) is located right underneath of the pile group, the stress release due to tunnel u causes reduction in toe resistance of both the piles. the toe resistance of both the piles was reduced by 48%. to maintain equilibrium, pile group has to settle to mobilize more shaft resistance as a block. the most significant increase (58%) took place at a depth ranging from 0.2 to 0.87 time of lp. consequently, pile group settlement in test g_su is the largest of all the three tests. however, no tilting of pile cap induced during construction of second tunnel (u).based on the horizontal stress acting on this portion of the pile shaft and frictional coefficient of the toyoura sand-epoxy interface (i.e., 0.3), this incremental mobilized shaft resistance due to tunneling u is equivalent to 13% of its ultimate value. among all the three tests, the maximum mobilized shaft resistance (equal to 70% of the ultimate value) took place along the upper part of the piles (0.2<z/lp<0.87) in test g_su. in this test, the application of working load resulted in a mobilization of 57% while the remaining 13% was caused by twin tunneling su. iv. summary and conclusions a series of centrifuge model tests were carried out to investigate the effects of twin tunnel advancement on an existing pile group under working load in dry sand. in each centrifuge model test, twin tunneling was simulated threedimensionally one after the other in-flight. the conclusions drawn are based on four centrifuge tests in dry sand only. any extrapolation from these results should be treated with caution. based on the test results, the following conclusions may be drawn:  when the first tunnel was excavated near mid depth of pile group shaft in each test, axial load acting on the pile group not only transferred to the lower half of front pile (nearest to tunnel) but also to the rear pile (furthest to tunnel). load transfers between piles can increase the axial load of the rear pile by up to 24%.  compared to the 1st tunneling near pile shaft (i.e., tunnel s), the construction of the 2nd tunnel adjacent to pile toe (i.e., tunnels t, b and u) induces much larger settlement of the pile group. among the three different scenarios (or tunnels t, b and u), tunneling right underneath the pile due to tunnel u induced the largest pile settlement (4.6% of pile diameter) and incremental mobilization of shaft resistance (13%). this is because stress release right underneath the pile group resulted in the largest reduction of toe resistance of the pile group. the reduction of toe resistance is compensated mainly by mobilizing shaft resistance of all four piles. in spite of the relatively large settlement, little tilting of pile cap was induced by the 2nd tunnel underneath the pile group, as stress release below each pile toe was symmetrical.  measured total settlements of pile group (due to working pile load and effects of twin tunneling) in tests g_st, g_sb and g_su are 32, 34 and 37 mm, respectively. based on pile acceptance criterion, these induced extra settlements due to twin tunneling correspond to an apparent loss of pile group capacity of 18, 23 and 30%, respectively.  compared to the construction of the 2nd tunnels b and u, the advancement of the 2nd tunnel, t, near the toe of the pile group caused a larger difference of stress release in soil around the front pile and the rear pile, leading to the largest 0.2% transverse tilting of pile cap. correspondingly, a significant bending moment (being 1.4 times of its ultimate bending capacity) was developed near the pile head. this implies that 2nd tunnel construction using a volume loss (1%) near the toe of a pile group may potentially cause structural failure of piles, even though the induced tilting does not exceed the allowable limit suggested by [32]. references [1] c. h. pang, k. y. yong, y. k. chow, “three dimensional numerical simulation of tunnel advancement on adjacent pile foundation” underground space use: analysis of the past and lessons for the future, pp. 1141–1147. london: taylor and francis, 2005 [2] a. bezuijen, j. s. van der schrier, “the influence of a bored tunnel on pile foundations”, centrifuge’94, rotterdam, netherlands. pp. 681-686, 1994 [3] l. t. chen, h. g. poulos, n. loganathan, “pile responses caused by tunneling”, journal of geotechnical and geoenvironmental engineering, vol. 125, no. 3, pp. 207-215, 1999 [4] n. loganathan, h .g. poulos, d. p. stewart, “centrifuge model testing of tunneling-induced ground and pile deformations”, geotechnique, vol. 50, no.3, pp. 283-294, 2000 [5] h. mroueh, i. shahrour, “three-dimensional finite element analysis of the interaction between tunneling and pile foundations”, international journal for numerical and analytical methods in geomechanics, vol. 26, no. 3, pp. 217-230, 2002 [6] s. w. jacobsz, j. r. standing, r. j. mair, t. hahiwara, t. suiyama, “centrifuge modeling of tunneling near driven piles”, soil and 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geoenvironmental engineering, vol. 131, no. 2, pp. 193–201, 2005 engineering, technology & applied science research vol. 7, no. 5, 2017, 2030-2040 2038 www.etasr.com soomro et al: 3d centrifuge modeling of the effect of twin tunneling to an existing pile group -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 -1200 -1000 -800 -600 -400 -200 0 200 400 600 induced bending moment (knm) z/ l p front pile (p1) after 1st tunnel (s) after 2nd tunnel(t) rear pile (p2) after 1st tunnel(s) after 2nd tunnel(t) 1st tunnel 2nd tunnel s t springline (t) springline (s) (a) y/d=-1.0 y/d=-0.5 y/d= 0.0 y/d= 0.5 y/d= 1.0 y/d= 1.5 p2 p3 p4 p1 -y +y plan view monitoring s e ction -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 -1200 -1000 -800 -600 -400 -200 0 200 400 600 induced bending moment (knm) z/ l p front pile (p1) after 1st tunnel (s) after 2nd tunnel (b) rear pile (p2) after first tunnel (s) after 2nd tunnel (b) 1st tunnel 2nd tunnel b s springline (s) (b) y/d=-1.0 y/d=-0.5 y/d= 0.0 y/d= 0.5 y/d= 1.0 y/d= 1.5 p2 p3 p4 p1 -y +y plan view monitoring se ction -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 -1200 -1000 -800 -600 -400 -200 0 200 400 600 induced bending moment (knm) z/ l p front pile (p1) after 1st tunnel (s) after 2nd tunnel (u) rear pile (p2) after 1st tunnel (s) after 2nd tunnel (u) springline (s) 1st tunnel 2nd tunnel u s (c) y/d=-1.0 y/d=-0.5 y/d= 0.0 y/d= 0.5 y/d= 1.0 y/d= 1.5 y/d=-1.0 y/d=-0.5 y/d =1.0 y/d =1.5 p2 p3 p4 p1 -y +y plan view monitoring se ction fig. 8. bending moment in front pile (p1) and rear pile (p2) due to advancement of both tunnels in: (a) test g_st (b) test g_sb (c) test g_s (b) (c) (a) engineering, technology & applied science research vol. 7, no. 5, 2017, 2030-2040 2039 www.etasr.com soomro et al: 3d centrifuge modeling of the effect of twin tunneling to an existing pile group fig. 9. axial force distribution in front pile (p1) and rear pile (p2) due to advancement of: (a) twin tunnels in test g_st (i.e., tunnels s and t); (b) 2nd tunnel in test g_sb (i.e., tunnel b); (c) 2nd tunnel in test g_su (i.e., tunnel u) -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.2 0.4 0.6 0.8 1.0 1.2 1.4 normalised axial load (p/pw) z/ l p after 1st front pile (p1) rear pile (p2) 2nd tunnel (u) front pile (p1) rear pile (p2) 1st tunnel 2nd tunnel u s springline (s) after 1st tunnel (s) y/d=-1.0 y/d=-0.5 y/d= 0.0 y/d= 0.5 y/d= 1.0 y/d= 1.5 p2 p3 p4 p1 -y +y plan view monitoring se ction (c) -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.2 0.4 0.6 0.8 1.0 1.2 1.4 normalised axial load (p/pw) z/ l p after 1st tunnel front pile (p1) rear pile (p2) 2nd tunnel (b) front pile (p1) rear pile (p2) springline (s) 1st tunnel 2nd tunnel b s2nd tunnel (b) after 1st tunnel (s) y/d=-1.0 y/d=-0.5 y/d= 0.0 y/d= 0.5 y/d= 1.0 y/d= 1.5 p2 p3 p4 p1 -y +y plan view monitoring se ction (b) -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.2 0.4 0.6 0.8 1.0 1.2 1.4 normalised axial load (p/pw) z/ l p before tunnelling 1st tunnel (s) front pile (p1) rear pile (p2) 2nd tunnel(t) front pile (p1) rear pile (p2) 1st tunnel 2nd tunnel s t 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standardization (cen), 2001 engineering, technology & applied science research vol. 8, no. 1, 2018, 2590-2594 2590 www.etasr.com shaikh : keyword detection techniques: a comprehensive study keyword detection techniques a comprehensive study zaffar ahmed shaikh faculty of computer science & information technology benazir bhutto shaheed university lyari, karachi, pakistan zashaikh@bbsul.edu.pk abstract—automatic identification of influential segments from a large amount of data is an important part of topic detection and tracking (tdt). this can be done using keyword identification via collocation techniques, word co-occurrence networks, topic modeling and other machine learning techniques. this paper reviews existing traditional keyword extraction techniques and analyzes them to make useful insights and to give future directions for better automatic, unsupervised and language independent research. the paper reviews extant literature on existing traditional tdt approaches for automatic identification of influential segments from a large amount of data in keyword detection task. the current keyword detection techniques used by researchers have been discussed. inferences have been drawn from current keyword detection techniques used by researchers, their advantages and disadvantages over the previous studies and the analysis results have been provided in tabular form. although keyword detection has been widely explored, there is still a large scope and need for identifying topics from the uncertain usergenerated data. keywords-keyword detection; information retrieval; topic detection; machine learning; comprehensive study i. introduction keyword extraction using manual methods is slow, expensive and bristling with mistakes [1]. in recent years, many automatic bursty keyword extraction techniques have been proposed to extract keywords from large amounts of data. these keywords are helpful in identifying themes and influential segments and framing semantic web and other applications of natural language processing [2, 3]. automatic keyword detection research area is related to topic detection and tracking (tdt) domain which was proposed in [4]. various applications use keyword extraction techniques for web search, report generation and cataloguing [5]. this area is intended to identify the most useful terms which include many sub-processes. documents are introduced in ms word, html, or pdf formats. initially, the documents are pre-processed to remove redundant and unimportant information [6, 7]. the data is then processed through different keyword extraction approaches including statistical approach, linguistic approach, machine learning approach, network based approach and topic modelling approach [8, 9]. in statistical approach, term frequency–inverse document frequency (tf-idf) is the most widely used technique for keyword extraction. the researchers use tf-idf to give a document a score based upon some query. a change in score occurs when a query is changed or updated. without a query, there is no score [10]. recently many new techniques have been developed for statistical keyword extraction [11]. these include pagerank, lexrank, etc. in pagerank, the researchers assign a score to a document based upon the documents it links to, and the documents which link to it. it is a global ranking scheme [10]. therefore, in pagerank, the score does not change (like in tf-idf) depending on the query used. as observed, pagerank and lexrank algorithms perform better than tf-idf. in linguistic approach, automatically identifying keywords is similar to semantic resemblance [12]. in machine learning approach, the keyword extraction technique is considered as classification technique [13]. different dictionaries including wordnet, sentinet and conceptnet are used for keyword extraction techniques. in network based algorithms, the nature and semantics of word co-occurrence networks is studied to identify important terms. in this, nodes are considered as words and edges are considered as co-occurrence frequency [14]. many useful insights have been obtained from these algorithms for identifying influential segments and keywords. topic modelling techniques have been popularized in [15]. authors introduced latent dirichlet allocation technique which is used to identify which document is related to which topic and to what extent [16]. this has been further improved by hierarchical dirichlet process, pachinko allocation model, relational topic modeling, conditional topic random fields and recently by hierarchical pitman– yor–dirichlet language model and graph topic model [17]. although keyword extraction is an important area of research and many researchers and practitioners gave a lot of attention to it, state of the art keyword extraction method is still not observed as compared to many other core natural language processing tasks [18]. this paper reviews existing traditional keyword extraction techniques and analyzes them to make useful insights to give future directions for better automatic, unsupervised and language independent research. engineering, technology & applied science research vol. 8, no. 1, 2018, 2590-2594 2591 www.etasr.com shaikh : keyword detection techniques: a comprehensive study ii. related work authors in [19] developed a so-called tool ‘keyword extractor’ for automatic extraction of most likely terms that closely match experts’ preferences. their study was related to brain research which involved worldwide collaborations and exchange of information among neuroinformatics centers and portal sites. the main objective of their study was the efficient use of resources and the improvement in the quality of brain research. each center and site developed their own set of keywords for classification of the main text and the resources. the researchers tested their tool over the abstract database of two science journals. authors in [20] extracted keywords from a chinese microblog. to extract keywords, they performed five steps and used three features (i.e., graph model, semantic space, and location of words). in the first step, researchers downloaded microblog api of a user. secondly, they preprocessed the data by applying data cleaning, word segment, pos tagging, and stop word removal techniques. to extract keywords, researchers in the third step created a graph model that was based on the co-occurrence between words. they assigned sequence numbers to the words according to their location and developed weight of the words by using the score formula. in the fourth step, researchers first created a semantic space that was based on topic extraction and then computed statistical weight of the words by using tf-idf. in the fifth and last step, researchers first identified location of words, and then, based on the location of those words, computed the rank value of each word. authors in [21] focused on the structure approach and graph generation. the approach used in this paper is structure based in which researchers created graph model and identified bursty topics and events. in topic clustering, twitter tweets were separated to produce homogeneous graphs and heterogeneous graphs. for homogeneous graphs, researchers used oslom algorithm to find interaction among users. for heterogeneous graphs, rankclus algorithm was used to construct a set of tweets ranked with number. finally, from both graph results, the concept, theme or event of a tweet was measured by joining tweets with the same name. researchers planned ahead to develop graph models to be used for different types of events and to construct a method that can define events. authors in [22] developed a keyword extraction technique for tweets with high variance and lexical variant problems. lexical variants are examples of free variation in language. they are characterized by similarity in phonetical or spelling form and identity of both meaning and distribution. the authors used brown clustering and continuous word vector methods. in brown clustering method, they clustered words having same meaning (such as no, noo, etc.) and then found out the features for the individual cluster. in continuous word vector method, the authors defined a layer by finding its probability and then the word is changed into continuous word vector. next, they predicted the length of the keyword by calculating the ratio between the number of keywords and the total number of words in the tweets. in the end, linear regression method was used to predict the number of keywords. authors in [23] developed a system to detect popular keyword trend and bursty keywords. their system detects keyword abbreviations and any typing and spacing errors. the first step they took is to collect the candidate keywords (i.e., the first word starting with the capital letter or the word enclosed in quotation mark is considered as candidate keyword). the second step was to merge keywords. to do so, they considered acronyms and typo and spacing errors, and then, found out the tf accordingly. finally, they detected popular keywords from the candidate keywords which were merged, and then, selected bursty keywords using the burst ratio technique. authors in [24] gave the idea of topol (a topic detection method based on topology data analysis) which identifies the irrelevant noisy data from the useful data. the first step of the authors was the preprocessing step in which the elimination of the hashtags, the urls, and the non-textual symbols from a tweet was done. their second step was mapping, in which a matrix was generated by applying the svd technique. in the third step, which the authors called the topic extraction step, the topics were selected based on the interest. finally, the results were computed based on topic recall, keyword precision, and keyword recall parameters. authors in [25] presented and discussed different methods and approaches used in the keyword extraction task. they also proposed a graph based keyword extraction method for the croatian language which is based on extraction of nodes. the authors used selectivity-based keyword extraction method in which text is represented in the form of vertex and edges. the result is computed on the in-degree, out-degree, closeness and selectivity. authors in [26] developed a keyword extraction method that represents text with a graph, applies the centrality measure and finds the relevant vertices. authors proposed a three-step based technique called tkg (twitter keyword graph). the first step was the pre-processing in which stop words were removed. in the second step, a graph was developed in which nearest neighbor and all neighbors were considered. finally, the results were computed based on the precision, recall, f-measure test scores and graph scalability. authors in [27] proposed an information summarization method for the large quantum of information which is disseminated everyday through tweets. their method collects tweets using a specific keyword and then, summarizes them to find out the topics. the authors provide two algorithms: topic extraction using agf (tda) and topic clustering and tweet retrieval (tctr). the methodology first extracts tweets from twitter and then applies the tf-idf technique to find out weights and word frequency. the agf is evaluated using keyword rating. finally, the results are calculated based on the class entropy, purity, and cluster entropy. authors in [28] proposed a technique in which a user can search using a search engine but without entering any keywords. the google similarity distance technique is used to find the keywords. a log is maintained in which user behavior and repository is saved. so, the need for the repository is abolished and everything is done online and in real time. keyword expansion and extraction methods are used to extract relevant and accurate information. in keyword expansion, help is provided to user to enter the exact keyword and to get the exact information. in keyword extraction, the word is analyzed based on the occurrence on the length and frequency. keyword extraction method relies on statistical approaches and machine learning approaches. the proposed methodology of the authors is composed of three parts: 1-g engineering, technology & applied science research vol. 8, no. 1, 2018, 2590-2594 2592 www.etasr.com shaikh : keyword detection techniques: a comprehensive study filtering, google similarity distance calculation, and search results filtering. finally, the results are calculated based on the parameters of precision and recall. the relationship between top k results is evaluated. thus, the authors proposed a system in which user just needs to browse the web page and the relevant keywords are generated. the system suits well for the science stream as the words are clear but may not be accurate for the social science. authors in [29] produced a facility based on bayesian text classification approach called high relevance keyword extraction (hrke) to extract the keywords at the stage of classification without the use of pre-classification process. the facility uses a posterior probability value to extract keywords. the hrke first extracts the words from the text. next, the posterior probability is calculated. finally, the tf-idf method is used to assign weights to words. authors claim that the hrke facility improves the performance and accuracy of the bayesian classifier and reduces time consumption. the experiment was conducted on three dataset-featured article datasets. in the end, the corresponding threshold and accuracy graph is plotted. authors in [30] address the problem of part-of-speech (pos) tagging from the richer text of twitter. authors developed a pos tagset first. secondly, they performed manual tagging on the dataset. afterwards, the features for the pos tagger were developed. finally, the experiments were conducted to develop the annotated dataset for the research community. the hashtags, urls, and emotions were considered. the results were obtained with 90 percent accuracy. authors concluded claiming that the approach can be applied to linguistic analysis of social media, and the annotated data can be used in semi supervised learning. authors in [31] gave a solution to the problem of statistical keyword extraction from the text by adapting entropic and clustering approaches. authors made changes in these approaches and proposed a new technique which detects keywords as per user’s needs. the main objective of the authors was to find and rank important words in the text. the two approaches were applied on short texts (such as web pages, articles, glossary terms, generic short text etc.) and long texts (such as books, periodicals etc.). results were evaluated and the clustering approach proved to be better for both cases, while the entropic approach suited well for the long text and did not perform well for the partitioned text. authors in [32] proposed a metric called entropy difference (ed) for the ranking of the words on a chinese dataset. authors used shannon’s entropy method which is the difference between intrinsic and extrinsic modes. the idea of intrinsic and extrinsic modes is that meaningful words are grouped together. therefore, the words are extracted and ranked according to the entropy difference. authors calculated mean, mode and median on entropy differences. their ed metric proved to be a good choice in word ranking. the method differentiates between the words that define authors’ purpose and the irrelevant words which are present randomly in the text. this method is well suited for single document of which no information is known in advance. authors in [33] provided a solution to the inherent noisy and short nature tweet problem of twitter streams called hybridseg. authors incorporated local context knowledge of the tweets with global knowledge bases for better tweet segmentation. the tweet segmentation process was performed on two tweet datasets. the tweets were split into segments to extract meaning of the information conveyed through the tweet. results show that hybridseg significantly improved tweet segmentation quality compared with other traditional approaches. authors claim that the segment based entity is better than word based entity. author in [34] provided a unique solution to the keyword extraction problem called conceptextractor. the conceptextractor do not decide on the relevance of a term during the extraction phase, instead, it only extracts generic concepts from texts and postpones the decision about relevant terms based on the needs of the downstream applications. authors claim that unlike other statistical extractors, conceptextractor can identify single-word and multi-word expressions using the same methodology. results were evaluated based on three languages. precision and recall were used for the result evaluation. authors also defined a metric to specificity both single and multi-word expressions usable in other languages. authors in [35] considered various chinese keyword extraction methods. in this paper, extended tf approach has been defined which considers chinese characteristics with tf method. authors also developed a classification model based on support vector machine (svm) algorithm. many improvement strategies were defined and four experiments were performed to evaluate the results. results showed that svm optimized the keywords. precision and recall rate improved much better. authors concluded that the improved tf method is much better than the traditional tf method in terms of accuracy and precision. authors in [36] discovered and classified terms that are either document title or ‘title-like’. their idea was that the terms that are title or title like should behave in the same way in a document. the classifier was trained using distributional and linguistic features to find the behavior of the terms. different features were considered such as location, frequency, document size etc. the rating was calculated on the basis of topical, thematic and title terms. after this the evaluation was performed based on recall and precision. the recall rate of finding the title terms was high but the precision rate was low because some of the words which were not titles were also identified in title terms. authors in [37] developed a sensitive text analysis for extracting taskoriented information from unstructured biological text sources using a combination of natural language, dynamic programming techniques and text classification methods. using computable functions, the model finds out matching sequences, identifies effects of various factors and handles complex information sequences. authors pre-processed the text contents and applied them with entity tagging component to find out the causes of diseases related to low-quality food. results show that the bottom-up scanning of key-value pairs improves content finding which can be used to generate relevant sequences to the testing task. the method improves information retrieval accuracy in biological text analysis and reporting applications. iii. analysis of keyword extraction approaches table i provides inferences drawn from modern keyword detection techniques, their advantages and disadvantages over previous studies, and result analysis. engineering, technology & applied science research vol. 8, no. 1, 2018, 2590-2594 2593 www.etasr.com shaikh : keyword detection techniques: a comprehensive study table i. analysis of existing keyword detection techniques paper techniques used advantages disadvantages results / analysis [20] a) graph model b) semantic space a) can detect the words which are wrongly segmented. b) extracts keywords from a micro blog. a) not suitable for large texts. b) some terms will not be distinguished. best performance obtained is 0.6972 [21] a) oslom algorithm b) page rank algorithm a) able to identify the topics of twitter event. b) less expensive. not able to identify the events based on graph clusters. best result obtained from structured based approach. [22] a) brown clustering b) continuous word vector a) improved state of the art for keyword extraction. b) automatically keyword extraction. not suitable for facebook text keyword extraction. accuracy for precision obtained is 72.05, recall 75.16. [24] topol a) suitable for noisy data. b) reduces computation time and improves topic extraction result. suffers from data fragmentation. the result obtained is 0.5380 for recall,0.7500 for precision. [26] a) tf-idf b) kea c) proposed tkg a) tkg proved to be robust and superior compared to other approaches b) tkg is simpler to use than kea the best configuration of tkg was not found tkg results better compared to kea and tf-idf. [28] a) statistics approach b) machine learning approach a) search engine which can automatically extract important keywords b) system works well not suitable for business management domain high recall rate [29] bayesian approach a) low cost, simple and efficient method. b) handles raw data without text preprocessing. a) presence of noisy data may degrade the performance. b) feature selection method degrades the efficiency of classification task. improved accuracy [31] a) entropic b) clustering approach a) suitable for both long and short texts. b) reliable obtained results. median and mode did not give the correct result. good clustering results for both short and long texts. [32] shannon entropy a) suitable for text with no information known in advance. b) easy to numerically implement. median and mode did not give the correct result. better results for single document. [33] hybrid segmentation high quality tweet segmentation. manual segmentation is expensive. improved precision. [34] statistical language independent good for extracting single and multiword expressions. not suitable for long text improved precision and recall. [36] a) decision tree classifier b) pattern recognition easy title determination a) not easy to determine the best document size. b) precision was not significant than recall. recall 85% was achieved for title like terms. [37] a) sensitive text analysis b) context-based extraction method a) category-oriented approach for extraction of task-specific information b) investigations into recall and precision were carried out. not tested on generic data. a) food safety is analyzed to prevent future consequences. b) improved classification accuracy by utilizing optimization constraints. c) causes of diseases related to low-quality food were identified. iv. conclusions this paper extends understanding of widely used `existing approaches to keyword detection in the identification of influential segments from a large amount of textual data or documents. therefore, extant literature on existing traditional tdt approaches to automatic identification of important words was reviewed and discussed. techniques reviewed include collocation, word co-occurrence networks, topic modelling and other machine learning approaches. results show that the majority of these techniques is domain dependent and language dependent. it 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journal, vol. 58, no. 4, pp. 644-655, 2014 [33] c. li, a. sun, j. weng, q. he, “exploiting hybrid contexts for tweet segmentation”, 36th international acm sigir conference on research and development in information retrieval, pp. 523–532, 2013 [34] j. m. j. ventura, automatic extraction of concepts from texts and applications, diss. universidade nova de lisboa, 2014 [35] b. hong, d. zhen, “an extended keyword extraction method”, physics procedia, vol. 24b, pp. 1120-1127, 2012 [36] c. w. wong, r. w. luk, e. k. ho, “discovering ‘title-like2 terms”, information processing & management, vol. 41, no. 4, pp. 789–800, 2005 [37] d. kuttiyapillai, r. rajeswari, “a method for extracting task-oriented information from biological text sources”, international journal of data mining and bioinformatics, vol. 12, no. 4, pp. 387-399, 2015 author profile dr. zaffar ahmed shaikh received his phd in computer science from the institute of business administration, karachi (iba-karachi) in 2017. he is currently working as an assistant professor at benazir bhutto shaheed university, lyari, karachi, pakistan. he has twenty-three research publications to his credit and has received several research grants from epfl (switzerland), higher education commission (pakistan), ministry of higher education (ksa) and iba-karachi. his research interests include data sciences, knowledge management, language & technology, learning environments, moocs, social software, technology enhanced learning etc. dr. shaikh is a professional member of acm and ieee. microsoft word etasr_v12_n4_pp8843-8849 engineering, technology & applied science research vol. 12, no. 4, 2022, 8843-8849 8843 www.etasr.com hassooni & al zaidee: behavior and strength of composite columns under the impact of uniaxial … behavior and strength of composite columns under the impact of uniaxial compression loading anas nahidh hassooni civil engineering department college of engineering university of baghdad and uruk university baghdad, iraq anasnahidh@gmail.com salah r. al zaidee civil engineering department college of engineering university of baghdad baghdad, iraq salahalzaidee2004@googlemail.com received: 12 january 2022 | revised: 3 february 2022 | accepted: 10 february 2022 abstract-the concrete filled steel tube column (cfst) is classified as a composite structural element. this type of column was adopted as the main loaded member in many buildings due to its excellent mechanical properties. cfst columns have high strength and ductility behavior, and they can sustain heavy loads with high performance. these led to their adoption in many countries. in the current study, the behavior and strength of cfst columns under the effect of axial compression load with parameters such as the diameter to thickness ratio and the height to diameter ratio were investigated. strength carrying capacity and axial and lateral deformations with axial and lateral strains were explored. the test results showed that smaller heights within the same material gave higher strength capacity. the stiffness of the cfst is more than concrete and hollow steel section specimens' due to its capability of high strength capacity with low displacement. also, the composite action of cfst gave more stiffness. keywords-composite column; cfst; compression load; strength column capacity; column deformation i. introduction concrete filled steel tube columns (cfstcs) are classified as main structural elements that can carry different types of loading when used as structural members in buildings. this type of structural element has high stability and stiffness due to its superior mechanical properties due to the composite action [1]. concrete column jacketing is done by steel tubes or fiber reinforced polymer (frp) sheets with the fibers oriented around the concrete column in order to work like stirrups so that they provide confinement to prevent the formation of plastic hinges, splitting, and buckling [2]. the main purpose of concrete column condiment by steel tubes is to form a composite structural member. the benefits of confinement of a concrete column by steel tubes are increased stiffness, stability, increased strength capacity, and reduced buckling. the presence of steel tubes increases the concrete compressive strength and the column becomes more resistant, not only against gravity loads, but also against lateral loads such as wind or seismic. authors in [3] studied the influence of confinement by rings around the steel tubes of cfst columns subjected to axial load. the main objective of the proposed methodology is to restrict the elastic lateral dilation of concrete casted inside the steel tube. the test results showed that the suggested ring configuration enhanced the axial load-capacity of cfst columns, improved stiffness, and decreased the strength degradation rate. the presence of steel rings reduced the lateral deformation of cfst columns. authors in [4] reviewed the applications and development of cfst members. it was shown that this structural member type enhanced stiffness, increased strength, and improved ductility due to the composite action between concrete and steel. authors in [5] studied the performance of cfst columns under the effect of axial load. variables like steel tube thickness and reinforcing bars and columns with and without foundations were considered. the experimental tests showed that the presence of reinforcing bars made the composite columns stronger. bending failure occurred when the weld strength of the casing was greater than the limit of the axial compression load, whereas when the weld strength was less than the limit of the applied load, the failure became open splitting of the steel casing. authors in [6] studied the mechanism of cfst failure with circular and square cross sections. the full scale of cfst columns under the effect of uniaxial compression load was considered. finite element analysis was utilized to check out the test results. it was found that the contact pressure at the interface between the concrete core and the surrounding steel tube was uniform. as was pointed out in the experimental tests, the failure mode of the cfst column circular cross section was drum but local buckling occurred in the case of square cfst column. the simulation results showed that the confinement of the steel tube that surrounded the concrete core affected the ultimate load carrying capacity and the ductility of square and circle cfst columns. authors in [7] studied the effects of steel rings around the external steel tube of the cfst column. the larger poisson’s ratio of steel led to the delamination at the interface between the concrete core and the surrounding steel tube. theoretical models that predicate and estimate the load-strain as lateral and longitudinal curves were simulated and experimentally tested. the theoretical model results were close to the experimental test results. authors in [8] studied the corresponding author: anas nahidh hassooni engineering, technology & applied science research vol. 12, no. 4, 2022, 8843-8849 8844 www.etasr.com hassooni & al zaidee: behavior and strength of composite columns under the impact of uniaxial … influence of concrete grade of cfst confinement column under axial load. the considered parameters were concrete compressive strength (infill) and diameter/thickness ratio of the steel tube in a total of six specimens. the conducted tests were focused on the strength capacity of the cfst column, stresses in concrete and steel tube, and confinement of column specimens. the test results showed that concrete with low compressive strength had more ductility and confinement. the presence of steel tubes surrounding the concrete core gave passive confinement to the concrete column. authors in [9] reviewed the stiffening of cfst columns experimentally and theoretically. authors in [10] studied the performance of cfsts with high-strength concrete core subjected to axial compression load. authors in [11] investigated the behavior of cfst columns subjected to axial compression load. concrete core size, steel tube shape, and diameter/thickness ratio were considered. the experimental tests showed that the most significant parameter affecting the strength capacity of the cfst column was the thickness of steel tube which also had more impact on the degree of confinement of the concrete core. in addition, the load-deformation of circular specimens showed strain-hardening or perfectly plastic behavior after yielding. authors in [12] proposed a finite element model to predict the performance and strength of cfst columns under the effect of axial load. the predicted behavior of the modified model was verified with experimental data. authors in [13], studied the behavior of slender columns under the effect of combined loading by simulating the performance of different slender columns under the impact of eccentric axial force. they concluded that concrete strength, level of axial load, and column slender ratio were the most important factors affecting the reduction coefficients and the effective bending stiffness. authors in [14] estimated the column capacity by testing 9 sandwich column specimens under axial compression load. the columns were made of normal strength concrete, whereas column portions were made from comparatively higher strength concrete. the test results showed that the aspect ratio affects the strength of such columns. summarizing the literature review, composite columns have higher strength capacity, stability, and stiffness than reinforced concrete columns or plain steel columns. ii. aim of the current study the aim of the present study is to investigate the behavior and strength of concrete-filled steel tubes subjected to uniaxial loading and to compare them with control samples of concrete and steel tube columns. the mechanical properties of the studied concrete and steel tubes, such as compressive, flexural, splitting, and tensile strength and the modulus of elasticity by the stress-strain curve of the tested samples were explored. for the steel section, yielding and stress-strain behavior were studied to obtain the steel modulus of elasticity. the investigation focused into the behavior of the tested specimens and recorded the experimental data that represent column capacity strength, buckling, and longitudinal and lateral displacements. different specimens were prepared and tested considering different parameters such as slenderness ratio and confinement steel tube sections. iii. experimental part a. material preparation three columns with different heights (400, 800, and 1200wmm) were designed with steel tube thicknesses of 1.35mm and concrete core diameter of 76mm. the specimens were tested under the effect of uniaxial compression load. the concrete and steel tube's mechanical properties are listed in table i, in which the concrete mechanical properties are based on [15] for compressive strength, [16] for splitting tensile strength, [17] for modulus of rupture, and [18] for modulus of elasticity. the mechanical steel tube by tensile test was based on [19]. water cement ratio for concrete core was 0.38 and the average of 3 specimens for each tested concrete was adopted. table i. mechanical properties concrete steel tube fc ’ (mpa) ec (mpa) fr (mpa) fy (mpa) es (mpa) 48 41500 7.55 295 205000 table ii. model marks mark description specimen geometry concrete core diameter (mm) steel tube (mm) do t di h (×10 2 ) ht/do do/t cc concrete 73.3 4 5.46 8 10.91 12 16.37 hsc steel 76 1.35 73.3 4 5.26 56.3 8 10.53 12 15.79 cfst composite 73.3 76 1.35 73.3 4 5.26 56.3 8 10.53 12 15.79 in table ii, do is the outer diameter, t is the steel tube thickness, di is the inner diameter, and h is the specimen height. figure 1shows the specimens of hollow steel section, concrete and composite respectively, while figure 2 present the specimen setup under the machine test. b. preparation of specimens each hollow steel tube specimen was prepped carefully by cutting the required specimen height (400, 800 or 1200mm) and then making the end smooth and level to ensure that the applied load was distributed symmetrically. concrete was inserted in the mold after it was oiled to prevent the adhesion between the concrete surface and the inner mold. for cfst specimens, the steel tubes were cleaned from unrequired materials such as dust to ensure there is suitable interaction between them and concrete. the bottoms of the steel tubes were closed with silicone and thick steel plates that were removed before testing the specimen and after the concrete was poured. the top of each specimen (rounded 5mm) was left empty to level the concrete by epoxy. each specimen was placed at the center of the testing machine to avoid eccentric loading. then, compressive load was applied at a constant rate. axial and lateral displacement and strain were recorded for each applied load step up to failure for each column type (hsc, cc, and cfst). engineering, technology & applied science research vol. 12, no. 4, 2022, 8843-8849 8845 www.etasr.com hassooni & al zaidee: behavior and strength of composite columns under the impact of uniaxial … (a) (b) (c) fig. 1. (a) steel specimens (hsc), (b) concrete specimens (cc), and (c) composite specimens (cfst). fig. 2. specimen setup. iv. test results figures 3-14 show the axial and lateral load-displacement and longitudinal and lateral load-strain for all tested specimens. all tested specimens behaved nonlinearly up to the inflection point that depends on the parameters and specifications of each specimen. this inflection point relies on many parameters such as slenderness ratio, column type, and applied load. each specimen reached maximum load capacity and after that the applied load dropped down, but they gave displacement at failure greater than the displacement at maximum load. fig. 3. applied load-axial displacement variation for h= 400mm. fig. 4. applied load-axial displacement variation for h=800mm. fig. 5. applied load-axial displacement variation for h=1200mm. fig. 6. applied load-lateral displacement variation for h=400mm. fig. 7. applied load-lateral displacement variation for h=800mm. engineering, technology & applied science research vol. 12, no. 4, 2022, 8843-8849 8846 www.etasr.com hassooni & al zaidee: behavior and strength of composite columns under the impact of uniaxial … fig. 8. applied load-lateral displacement variation for h=1200mm. fig. 9. applied load-axial strain variation for h=400mm. fig. 10. applied load-axial strain variation for h=800mm. fig. 11. applied load-axial strain variation for h=1200mm. fig. 12. applied load-lateral strain variation for h=400mm. fig. 13. applied load-lateral strain variation for h=800mm. fig. 14. applied load-lateral strain variation for h=1200mm. the ductility of a structural member is the ability to bear or endure considerable deflection before failure. the ductility of a structural element is a very important quality indicator because it provides signs of collapse or failure, so the total collapse of a structural member may be prevented while the member can undergo more deformations (large deformations) without fail. concrete is a brittle material, so the presence of steel tubes that surrounds the concrete core enhances its properties. the ductility u for all tested specimens is calculated by dividing the deflection at ultimate load δu by the deflection at yield δy: u y u ∆ ∆ = (1) the stiffness of the tested specimens is the resistance of an elastic body to deflection or deformation by an applied force. the stiffness μ is defined as the ratio of the ultimate load p� to ultimate load deflection δ�: u u p µ ∆ = (2) figures 15 to 18 show the axial and lateral ductility and stiffness of all tested specimens. concrete specimens have a constant ductility because concrete is a brittle material so that there is a plastic zone so the displacement at failure is approximately the same with the one at maximum load. the ductility of hsc specimens is more than concrete specimens' with the same height because steel is a ductile material. the cfst specimen with 1200mm height has longitudinal (axial) ductility more than the other specimens. regarding the lateral displacement, the ductility of concrete was about the same, the hsc specimen with 800mm height had more than the other specimens, and the cfst with 1200mm height was the highest among the cfst specimens. engineering, technology & applied science research vol. 12, no. 4, 2022, 8843-8849 8847 www.etasr.com hassooni & al zaidee: behavior and strength of composite columns under the impact of uniaxial … table iii. test results-axial displacement and strain based on maximum and failure load mark height (mm) test results max. load (kn) failure load (kn) max. axial displace ment (mm) axial displace ment at failure (mm) max. strain strain at failure load cc 400 224.00 225.00 3.00 3.02 2019 2053 800 196.64 197.00 2.66 2.68 2025 2050 1200 171.30 171.60 3.65 3.68 2575 2595 hsc 400 104.66 91.78 2.47 3.04 1876 1900 800 99.40 69.56 2.27 3.63 1672 1700 1200 96.08 78.04 3.15 3.75 1844 1875 cfst 400 415.08 402.98 3.76 4.55 4159 4300 800 358.86 338.06 5.59 7.94 11832 11880 1200 327.81 275.51 6.99 10.19 3296 3330 table iv. test results-lateral displacement and lateral strain based on maximum and failure load mark height (mm) test results max. load (kn) failure load (kn) max. lateral displace ment (mm) lateral displace ment at failure (mm) max. strain strain at failure load cc 400 224.00 225.00 1.16 1.17 700 755 800 196.64 197.00 0.90 0.91 307 365 1200 171.30 171.60 4.03 4.05 408 470 hsc 400 104.66 91.78 0.8 1.15 585 625 800 99.40 69.56 4.05 5.28 785 920 1200 96.08 78.04 1.17 1.22 380 420 cfst 400 415.08 402.98 2.08 2.21 2913 3784 800 358.86 338.06 8.44 10.08 5936 9986 1200 327.81 275.51 11.87 28.06 2190 3125 table v. axial and lateral ductility and stiffness mark height (mm) ductility (axial) stiffness (axial) (kn/mm) ductility (lateral) stiffness (lateral) (kn/mm) cc 400 1.01 74.67 1.01 193.10 800 1.01 73.92 1.01 218.49 1200 1.01 46.93 1.00 42.51 hsc 400 1.23 42.37 1.44 130.83 800 1.60 43.79 1.30 24.54 1200 1.19 30.50 1.04 82.12 cfst 400 1.21 110.39 1.06 199.56 800 1.42 64.20 1.19 42.52 1200 1.46 46.90 2.36 27.62 fig. 15. axial ductility variation of all specimens. fig. 16. lateral ductility variation of all specimens. fig. 17. axial stiffness variation of all specimens. fig. 18. latertal stiffness variation of all specimens. the axial stiffness of the concrete specimen was higher when its height was 800mm, while regarding the hsc and cfst specimens maximum axial stiffness was measured at 400mm. maximum lateral stiffness of cc, hsc, and cfst was measured for specimen height of 400mm, 800mm, and 400mm respectively. v. modes of failure the failure modes of all specimens are illustrated in figure 19. the concrete specimens exhibited shear failure that caused cuts in plain concrete. the hsc specimens exhibited local buckling due to the end effect. the cfst specimens exhibited steel yielding and global buckling. when the applied load is increased, large axial strain is developed and the steel tubes fracture. in the cfst specimens, the presence of steel tubes provides confinement to the concrete core and worked as a composite that led to buckled failure mode. engineering, technology & applied science research vol. 12, no. 4, 2022, 8843-8849 8848 www.etasr.com hassooni & al zaidee: behavior and strength of composite columns under the impact of uniaxial … cfst-400 hsc-400 cc-400 cfst-800 hsc-800 cc-800 cfst-1200 hsc-1200 cc-1200 fig. 19. failure modes of the tested specimens. vi. discussion based on the experimental results, the strength capacity of each specimen is compared with the others of its group (table vi) and with the other groups for specimens of the same height (table vii). the smallest height within the same material gave the highest strength capacity because short specimens have low slenderness ratio. the cfst specimen gave higher strength than the others because they have higher stiffness due to the higher moment of inertia and equivalent modulus of elasticity due to the composite action between the concrete core and the surrounding steel tube. hsc exhibited the smallest strength carrying capacity because it has solid cross section. table vi. strength carrying capacity within the same material mark height (mm) maximum load (kn) % decrease in load capacity cc 400 224.00 -- 800 196.64 12.21 1200 171.30 23.53 hsc 400 104.66 -- 800 99.40 5.03 1200 96.08 8.20 cfst 400 415.08 -- 800 358.86 13.54 1200 327.81 21.02 table vii. strength carrying capacity for same specimen height height (mm) mark maximum load (kn) % increase in load capacity 400 hsc 104.66 -- cc 224.00 114.03 cfst 415.08 296.60 800 hsc 99.40 -- cc 196.64 97.83 cfst 358.86 261.03 1200 hsc 96.08 -- cc 171.30 78.29 cfst 327.81 281.18 axial (longitudinal) displacement for long specimens (800 and 1200mm) increased as the height increased because axial displacement relies on the load and on the height (pl/ae), so for the same rigidity (ae) the displacement increased. figure 3 shows that for the same load, the axial displacement developed in the hsc specimen was more than the other specimens' and the displacement of cfst was less. the same phenomena were observed and plotted for lateral displacement. axial strain and lateral strain for cfst specimens were less than the other specimens' (cc and hsc) for the same reasons. the ductility of cfst specimens was more than the hsc and cc (brittle material-less ductility) specimens because the steel tubes surrounding the concrete core gave more strength without sudden failure and the displacement at failure load became more (large deformation). the stiffness of the cfst is more than the cc and hsc specimens' due to its capability of high strength capacity with low displacement. also the composite action of cfst gave more stiffness (ei) due to its increased equivalent modulus of elasticity and transformed moment of inertia. vii. conclusion the test results of the strength of composite columns under the effect of uniaxial compression loading, indicated that the shorter columns of the same material had higher strength capacity. the stiffness of composite specimens was higher than the concrete and hollow steel specimens'. the behavior and strength of composite column differed from steel and hollow steel due to the composite action between concrete and steel that gave higher strength and more realistic behavior. more study is required in order to investigate steel fiber concrete confined by steel tubes. engineering, technology & applied science research vol. 12, no. 4, 2022, 8843-8849 8849 www.etasr.com hassooni & al zaidee: behavior and strength of composite columns under the impact of uniaxial … references [1] c. wu, j. li, and y. su, "5 ultra-high performance concrete-filled steel tubular columns," in development of ultra-high performance concrete against blasts, c. wu, j. li, and y. su, eds. woodhead publishing, 2018, pp. 283–395. 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[19] astm a370-21: standard test methods and definitions for mechanical testing of steel products. astm. engineering, technology & applied science research vol. 8, no. 1, 2018, 2389-2392 2389 www.etasr.com assis and romao: numerical simulation of 1d unsteady heat conduction-convection in spherical … numerical simulation of 1d unsteady heat conduction-convection in spherical and cylindrical coordinates by fourth-order fdm leticia helena paulino de assis basic and environmental sciences department university of sao paulo lorena, sao paulo, brazil leticia.hpa@alunos.eel.usp.br estaner claro romao basic and environmental sciences department university of sao paulo lorena, sao paulo, brazil estaner23@usp.br abstract—this paper aims to apply the fourth order finite difference method (fdm) to solve the one-dimensional unsteady conduction-convection equation with energy generation (or sink) in cylindrical and spherical coordinates. two applications were compared through exact solutions to demonstrate the accuracy of the proposed formulation. keywords-central difference method; cylindrical and spherical coordinates; numerical simulation; numerical efficiency i. introduction according to [1], conduction refers to the transport of energy in a medium due to the temperature gradient. the onedimensional convection-diffusion equations with transient heat generation were solved by the fourth-order fdm. the transient regime arises with the change of boundary conditions. if the surface temperature of a system is changed, the temperature of each point of that system will change until it reaches a stationary temperature distribution. it is important to emphasize that the idea of using the fourth order finite difference method has already been successfully implemented in [2-6] for problems set in cartesian coordinates, and thus, the same idea in cylindrical and spherical coordinates is now proposed. this paper will investigate numerically the onedimensional unsteady convection-diffusion equations with heat generation in cylindrical and spherical coordinates. from [1, 7], we have the equations, respectively, q r t r rr k r t v t t c rp                            1  (1) q r t r rr k r t v t t c rp                            2 2 1  (2) where t(r,t) is the temperature (k), r is the cylindrical or spherical coordinates (m), is the thermal conductivity (w/m.k), ρ is the specific mass (kg/m3 ), cp is the specific heat at constant pressure (j/kg.k) and ̇ is the energy generation (k/s). ii. numerical formulation before starting the numerical formulation of (1)-(2), we rearrange these equations as follows, p r c q r t r t v rt t                    2 2 (3) p r c q r t r t v rt t                    2 22 (4) where  (m2/s) is the thermal diffusivity with α=k/cp. a. temporal discretization for temporal discretization of the (3) and (4) will be used the crank-nicolson method [8], as follows,                                           1 1 2 12 1 5.0 n p n r n n c q r t v rr t tt     n n p n r n t c q r t v rr t                                             2 2 (5) and                                           1 1 2 12 1 25.0 n p n r n n c q r t v rr t tt     n n p n r n t c q r t v rr t                                            2 2 2 (6) b. spatial discretization following the formulation, the spatial discretization using high-order finite difference method for internal nodes will be engineering, technology & applied science research vol. 8, no. 1, 2018, 2389-2392 2390 www.etasr.com assis and romao: numerical simulation of 1d unsteady heat conduction-convection in spherical … realized according to the following (i.e. the same principle used in [8]). 1) internal nodes in the internal nodes of the computational mesh, the following fourth-order central finite differences were used to discretize the first and second order partial derivatives, respectively [7-9], r tttt r t iiii       12 88 2112 (7) 2 2112 2 2 12 163016 r ttttt r t iiiii       (8) which when replaced in (5) and (6), obtain the expressions, for cylindrical and spherical coordinates, respectively, 1 12 1 22 333 2 242424                                 n i rn i r t r tv rr t r t t r tv rr t r t  1 12 1 2 333 2 4 5 1                          ni rn i t r tv rr t r t t r t  p n n i r c qt t r tv rr t r t   11 22 5.0 242424                     n i rn i r t r tv rr t r t t r tv rr t r t 1222 333 2 242424                                n i rn i t r tv rr t r t t r t 122 333 2 4 5 1                         p n n i r c qt t r tv rr t r t                    5.0 242424 22 (9) and 1 12 1 22 33 2 3 2 241224                                 n i rn i r t r tv rr t r t t r tv rr t r t  1 12 1 2 33 2 3 2 4 5 1                          ni rn i t r tv rr t r t t r t  p n n i r c qt t r tv rr t r t   11 22 5.0 241224                     n i rn i r t r tv rr t r t t r tv rr t r t 1222 33 2 3 2 241224                                n i rn i t r tv rr t r t t r t 122 33 2 3 2 4 5 1                         p n n i r c qt t r tv rr t r t                    5.0 241224 22 (10) 2) nodes distant δr of the boundary for discretization of nodes near the boundary it is not possible to use (7) and (8), for example, a node at a distance δr from the boundary will not have two nodes to its left. thus, for these nodes (5) and (6) will be used to discretize the following second order central finite difference, r tt r t ii       2 11 (11) 2 11 2 2 2 r ttt r t iii       (12) and thus when applying (11) and (12) in (5) and (6), we result in, 1 2 1 12 1 442                         n i n i r t r t t r tv rr t r t  p n n i r c qt t r tv rr t r t   11 12 5.0 442                     n i n i r t r t t r tv rr t r t                         212 1442  p n n i r c qt t r tv rr t r t                    5.0 442 12 (13) 1 2 1 12 1 422                         n i n i r t r t t r tv rr t r t  p n n i r c qt t r tv rr t r t   11 12 5.0 422                     n i n i r t r t t r tv rr t r t                         212 1422  p n n i r c qt t r tv rr t r t                    5.0 422 12 (14) in summary, (9) and (13) construct the linear system that solves the problem governed by (5) (cylindrical coordinates) and (10) and (14) solve the problem governed by (6) (spherical coordinates). iii. numerical applications linear systems are set, using (9) and (13) for cylindrical coordinates and (10) and (14) for spherical coordinates, and solved using fortran. the values of temperature in all nodes of the computational mesh were constructed in predetermined domains. in both applications it was considered that 0.5r 1, 0t1,  =cp=α=1 and vr=1. 1) application 1. the exact solution proposed is given by t(r,t)=er+t. from (3) and (4) we obtain, in cylindrical and spherical coordinates, respectively, engineering, technology & applied science research vol. 8, no. 1, 2018, 2389-2392 2391 www.etasr.com assis and romao: numerical simulation of 1d unsteady heat conduction-convection in spherical …            r vecq r tr p 1            r vecq r tr p 2 1 by the variation of δr and δt, the influence of the temporal and spatial refinements was studied, by comparing the results of the numerical solutions and the exact solution, as shown in tables i and ii. what can be noticed in tables i and ii is that with the refinement in space and time, the numerical precision improves with each greater refinement, as expected. in order to show the numerical efficiency of the proposed formulation, and remembering that in many cases numerical formulations are not very efficient in cases of highly convective problems, table iii presents, the numerical precision for some values of vr for the two types of refinements. it is clear that for the vr values adopted, the formulation continues to have excellent numerical precision. table i. errors for different values of variation in space and time in cylindrical coordinates, application 1 t r 10-1 510-2 210-2 10-2 10-3 510-2 1.56e-04 4.33e-05 1.19e-05 7.77e-06 6.85e-06 2.510-2 1.50e-04 3.78e-05 6.36e-06 1.87e-06 4.68e-07 10-2 1.50e-04 3.75e-05 6.00e-06 1.51e-06 2.46e-08 510-3 1.50e-04 3.75e-05 6.00e-06 1.49e-06 1.56e-08 table ii. errors for different values of variation in space and time in spherical coordinates, application 1 t r 10-1 510-2 210-2 10-2 10-3 510-2 1.67e-04 5.28e-05 2.15e-05 1.80e-05 1.70e-05 2.510-2 1.53e-04 3.88e-05 7.00e-06 2.47e-06 1.12e-06 10-2 1.52e-04 3.79e-05 6.09e-06 1.54e-06 3.97e-08 510-3 1.52e-04 3.79e-05 6.07e-06 1.52e-06 1.67e-08 table iii. errors for different values of vr, application 1 vr r=510-2 and t=10-1 r=510-3 and t=10-3 cylindrical spherical cylindrical spherical 0.1 1.62e-04 1.71e-04 1.62e-08 1.71e-08 0.5 1.55e-04 1.69e-04 1.59e-08 1.69e-08 1 1.56e-04 1.67e-04 1.56e-08 1.67e-08 2 1.48e-04 1.61e-04 1.49e-08 1.61e-08 5 1.22e-04 1.36e-04 1.23e-08 1.39e-08 10 7.32e-05 8.90e-05 7.40e-09 9.10e-09 20 5.49e-05 4.56e-05 1.43e-08 1.34e-08 2) application 2. the exact solution proposed is given by t(r,t) = sin(2(r + t)). from (3) and (4) we obtain, in cylindrical and spherical coordinates, respectively, p r c q trtr r v            ))(2sin(4))(2cos(12 p r c q trtr r v            ))(2sin(4))(2cos( 2 12 by the variation of δr and δt, the influence of the temporal and spatial refinements was studied, by comparing the results of the numerical solutions and the exact solution, as shown in tables iv and v. it is observed from tables iv and v that the numerical precision obtained in application 2 is extremely similar to that presented in application 1, meaning that the formulation proposed in this work behaved well for two types of exact solutions, exponential and sine. table vi presents, for the two types of refinements the precision for various values of vr. the method’s efficiency is clearly shown as in application 1. table iv. errors for different values of variation in space and time in cylindrical coordinates, application 2 t r 10-1 510-2 210-2 10-2 10-3 510-2 2.02e-04 5.11e-05 1.11e-05 7.22e-06 6.46e-06 2.510-2 1.99e-04 4.96e-05 8.06e-06 2.13e-06 5.17e-07 10-2 1.99e-04 4.96e-05 7.93e-06 1.99e-06 2.56e-08 510-3 1.99e-04 4.96e-05 7.93e-06 1.98e-06 2.01e-08 table v. errors for different values of variation in space and time in spherical coordinates, application 2 t r 10-1 510-2 210-2 10-2 10-3 510-2 2.14e-04 6.46e-05 2.65e-05 2.30e-05 2.22e-05 2.510-2 2.02e-04 5.09e-05 8.87e-06 2.96e-06 1.56e-06 10-2 2.01e-04 5.00e-05 8.02e-06 2.02e-06 4.94e-08 510-3 2.01e-04 5.00e-05 8.00e-06 2.00e-06 2.14e-08 table vi. errors for different values of vr, application 2 vr r=510-2 and t=10-1 r=510-3 and t=10-3 cylindrical spherical cylindrical spherical 0.1 2.05e-04 2.19e-04 2.06e-08 2.17e-08 0.5 2.03e-04 2.17e-04 2.04e-08 2.16e-08 1 2.00e-04 2.14e-04 2.01e-08 2.14e-08 2 1.92e-04 2.07e-04 1.93e-08 2.09e-08 5 1.57e-04 1.80e-04 1.60e-08 1.83e-08 10 9.01e-05 1.13e-04 8.74e-09 1.14e-08 20 1.10e-04 9.82e-05 1.60e-08 1.42e-08 iv. conclusion the fourth order finite difference method (fdm) was employed to solve the one-dimensional unsteady conductionconvection equation with energy generation in cylindrical and spherical coordinates. two applications were compared to demonstrate the accuracy of the proposed formulation. an improvement in result-terms was documented. it was observed that both spatial and time refinements were effective, but time was found to be more effective. the errors obtained in cylindrical and spherical coordinates were low and satisfactory, in both applications tested. acknowledgements the fapesp (procs. 2014/06679-8 and 2016/16867-1) and cnpq (proc. 400898/2016-0) supported the present work. engineering, technology & applied science research vol. 8, no. 1, 2018, 2389-2392 2392 www.etasr.com assis and romao: numerical simulation of 1d unsteady heat conduction-convection in spherical … references [1] t. l. bergman, a. s. lavine, f. p. incropera, d. de witt, fundamentals of heat and mass transfer, fifth edition, john wiley & sons, 2003 [2] 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[7] j. r. welty, c. e. wilson, g. l. rorrer, fundamental of heat and mass transfer, 4th ed., wiley, 2001 [8] m .d. campos, e. c. romao, “a high-order finite-difference scheme with a linearization technique for solving of three-dimensional burgers equation”, computer modeling in engineering & sciences, vol. 103, pp. 139-154, 2014 [9] t. j. chung, computational fluid dynamics, cambridge university press, 2002 engineering, technology & applied science research vol. 8, no. 2, 2018, 2814-2817 2814 www.etasr.com alghamdi: synthesis and mechanical characterization of high density polyethylene/graphene … synthesis and mechanical characterization of high density polyethylene/graphene nanocomposites abdulaziz s. alghamdi mechanical engineering department college of engineering, university of hail hail, saudi arabia asbg945@hotmail.com abstract—the purpose of this work is to investigate the effects of graphene nanosheets (gnss) addition on the mechanical and thermal properties of high density polyethylene (hdpe). the hdpe/graphene nanocomposites were synthesized using solution blending approach. hdpe was incorporated with graphene nanosheets in a solvent at various weights of fractions (0.1, 0.2, 0.4 and 0.5 wt%), and then the micro-hardness, elastic modulus, tensile strength, strain at break and thermal properties of the nanocomposites were measured and compared. the results showed that the use of xylene solvent at high temperature combined with mechanical stirring can fully dissolve hdpe pellets. scanning electron microscope (sem) showed that gnss were homogenously dispersed in the polyethylene matrix at low weights of fractions. the addition of just 0.2 wt% gnss resulted in 100% increase in the micro-hardness value. the elastic modulus and tensile strength properties are proportionally increased with increasing gnss content up to 0.4 wt%. however, at higher weight of fraction, a reduction in these properties is observed. the crystallinity and strain at break properties are reduced with the addition of gnss. keywords-hdpe; polymer; graphene; nanocomposite; thermal; mechanical i. introduction polymer-based nanocomposites of current academic interest are finding an increasing range of industrial applications, making them the most widely commercialised class of nanocomposites [1]. the incorporation of low weight of fraction of nanoparticles or nanosheets can lead to a significant improvement in the polymer properties like tensile strength, elastic modulus, wear and scratch resistance, electrical and thermal conductivity, thermal and flammability resistance and impact strength [2-5]. in addition, many polymer nanocomposites can be fabricated and processed by the use of methods similar to those used for standard polymers, which is important from an economic point of view. in recent years, researchers have focussed on the synthesis of new nanocomposites, starting from careful material selection and process control either by the direct use of an existing technique or by modified and adapted techniques. various types of nanofillers have been used in polymer-based nanocomposite fabrication, such as exfoliated clay, modified carbon nanotubes and graphene [6-15]. however, achieving the uniform dispersion of the nanofillers is still an important scientific and technological challenge in nanocomposite fabrication. graphene nanosheets, with their outstanding thermal, electrical, optical, and mechanical properties as well as their low cost compared to carbon nanotubes can be a cost-effective alternative to carbon nanotubes and can be widely used for the fabrication of polymeric nanocomposites [16-18]. graphene nanosheets are relatively easier to disperse homogeneously in the neat polymer matrix compared to carbon nanotubes and possess a higher surface area to volume ratio that improves bonding and load transfer properties, and consequently increases the strength [19-21]. high-density polyethylene (hdpe) is a thermoplastic polymer that can be blended with different reinforcement materials to further enhance its overall properties like strength and thermal properties [16, 21, 22]. the mechanical, thermal, electrical and surface hydrophobic properties of hdpe can be improved with the addition of 1 to 8 wt% graphene nanoflakes to the matrix using solution blending [16]. however, using large quantities of graphene nanosheets can increase the production cost. therefore, in this research, small quantities of graphene nanosheets (0.1-0.5 wt%) were incorporated with hdpe in a proper solvent, and then the mechanical and thermal properties of the resultant nanocomposites were determined using various techniques. ii. experimental work a. materials the polymer-based nanocomposite presented in this work is high density polyethylene (hdpe) with the addition of graphene nanosheets (gnss) at various weight percentages (0.1, 0.2, 0.4 and 0.5 wt% gnss). hdpe pellets were purchased from sabic company, saudi arabia in 2016. graphene nanosheets were purchased from graphene laboratories inc., usa, with average thickness<3nm (between 3-8 graphene monolayers) and lateral dimensions 2-8 microns. b. processing an in-house solution blending technique was used to perform a well dispersed gnss into the hdpe matrix. graphene nanosheets were dispersed in alcohol using sonicator for 30 minutes. then, the mixture was dried for 24 hours. gnss were dispersed again in xylene for 30 min using son dis and hot app dri pla usi pre wa tes c. usi mi co (u ana of hea ma the the car ins tem 1m tem +1 ex per ind and a. cal see po add wit add nan b. com of po roo ho fas sho nan hom ho agg engineer www.etasr nication, and spersions. in o d the dispersio t plate at 130 plied simultan ied for 24 hou aced in a squ ing furnace t essed using h ater was used st specimens w mechanical t the morpho ing a philip icroscope-fiel ompany (eindh usa). dsc, (t alyze the effe hdpe. the s ated from 35 ass fraction of e heat of fusio e equilibrium rried out using stron corpor mperature (22± mm/s. flir ca mperature distr 50c and acc xcel to study th rformed using denter (vicker d average was i thermal ana figure 2 an lorimetry resu en that the ad ints. however dition of 0.1 th the increa dition of gn nocomposites. graphene na the use of x mbined with m hdpe in a lyethylene ma om temperatu owever, the ap ster dissolving ows the sem nocomposites. mogenously in owever, at 0.5 gregations of ring, technolog r.com then hdpe order to improv on of gnss, a 0c and mec neously for 2 h urs at 150c. uare steel mou o 220°c for hydraulic pres d to cool the m were cut to the testing and c ology of the n ps xl30 env ld emission hoven, the n ta instrument ct of gnss ad specimens we to 200°c at f crystallinity on with that fo melting point g an instron 5 ration (norw ±2ºc). the sp amera was use ribution, with curacy of ±1c he material be g force of 1 rs test), the in s taken. iii. result alysis nd table i p ults for hdpe ddition of gn r the crystallin wt% graphen ase of graphe nss has no ef . anosheets disp xylene as chem mechanical sti short period aterials, large ure combine pplication of g as well as le images for the . it can be n the hdpe m 5 wt% graphe graphene nan gy & applied sc algh e pellets wer ve the dissolvi and also reduc hanical stirrer hours. then, th the nanocom uld (100×100 30 min. the ss machine at mould to room dimensions sh characterizatio nanocomposite vironmental gun (esem netherlands) an ts, shimadzu d ddition on the re sealed in a a rate of 10° is then determ or fully crystal t (290kj/kg). 5969 tensile te wood, ma, peed rate used d to measure t temperature r c. all results ehavior. micro 100g for 5 s ndentation wa ts and discus present the di and its nanoco nss has no eff nity is reduce ne. further red ene percentag ffect on the persion mical solvent rring resulted d of time. u quantities of s d with high specific temp ess quantity of e microstructu seen that gn matrix up to 0. ene, some ca nosheets can cience researc hamdi: synthesi re added int ing of hdpe p ce the time ne r at 100r.p.m he dispersions mposite materia ×1mm) and h en, the mould t 7mpa for 1 m temperature hown in figure on. es was invest scanning ele m-feg) from nd fei quant dsc60) was u e thermal prop aluminium pan °c per minute mined by comp line polyethyl tensile tests esting machine usa) at d in this work the sample's su range from -20 were plotted ohardness tests econds with as repeated 5 sion ifferential sca omposites. it c ffect on the m ed by 14% wi duction is occ ge. however, crystallinity o at high tempe in 100% disso usually, to dis solvents are u h speed agit perature can le f solvents. fig ure of hdpe a nss are disp 4 wt% of grap avitations and be observed ch v is and mechani to the pellets eeded, m were s were al was heated d was 10min. e. the e 1. tigated ectron m fei ta 250 sed to perties ns and e. the paring lene at s were e from room k was urface 0c to using s were sharp times anning can be melting ith the curred more of the erature olving ssolve used at tation. ead to gure 3 and its persed phene. large in the mic volu cap fig. wt% hdp nano vol. 8, no. 2, 20 ical characteri crostructure. t ume ratio an pacity between table i. the materials hdpe hdpe-0.1 wt g hdpe-0.2 wt g hdpe-0.4 wt g hdpe-0.5 wt g f fig. 2. 3. sem imag % graphene (c) hd pe-0.5 wt% gra osheets or agglom 18, 2814-2817 ization of high this can lead nd consequen n graphene and ermal propertie s cry e graphene graphene graphene graphene ig. 1. dimens dsc results for h ges for the micros dpe-0.2 wt% gra aphene (the arrow meration) density polyet to reduction ntly reduction d hdpe matrix es of hdpe based ystallinity % 59.22 50.97 43.02 43.67 44.54 sions of the specim hdpe and its nan structure of (a) h aphene (d) hdpe ws indicate the 2815 thylene/graphe in surface ar of load car x. d nanocomposit melting point ( 136.76 134.78 136.52 136.39 133.57 men nocomposites hdpe and (b) hdp e-0.4 wt% graphe presence of gra ene … rea to rrying tes c) pe-0.1 ene (e) aphene c. 0.2 val ma nan attr ma ho res we the red d. gen me res nan gen me ma rea pro pla the it sig 0.2 red occ the inc 0.4 ela th wh con the engineer www.etasr microhardne it can be see 2 wt% resulted lues. the emb atrix almost nocomposites ributed to the atrix and the g sting material sulted in a red ere almost sim e existence o duction in the fig. 4. eff tensile test during the neration durin echanical pro searches [6, 7 nofillers in th neration durin easured to av aximum tempe ached 35˚c, w operties. ther astic deformat e effect of gn can be seen gnificant reduc 2 wt% of gn duction in the curs with the e elastic mod creased with in 4 wt%. at 0.5 astic modulus his is probably hich affected nsequently the e tensile load. ring, technolog r.com ess results en from figur d in a significa bedding of jus doubled the comparing e well dispers good interactio l. increasing t duction in the milar the neat m of nanoplatele surface to volu ffect of gnss add results tensile test ng plastic defo operties of 7, 10] provide he polyethylen ng plastic def void such in erature generat which has no s refore, the ef tion is neglect ss addition on that the prese ction in the st nss into the e strain at bra addition of 0.5 dulus and ten ncrease of the 5 wt% gnss, and tensile str y due to the pr the surface e stress distri gy & applied sc algh re 4 that the a ant increase in st 0.2 wt% gn micro-hardne to pure hd sion of gnss on between the the weight of e micro-hardne material. this ts aggregates ume ratio. dition on the micro ting, the ph ormation can p polymeric d evidence th ne matrix can formation. th nfluences. it ted during the significant effe ffect of heat ted in this wo n the percentag ence of these train at break. hdpe matri ake. more red 5 wt% gnss. nsile strength weight percen a reduction i rength values resence of gn e area to v ibution during cience researc hamdi: synthesi addition of gn n the micro-har nss into the h ess values o dpe. this ca s into the po e nanosheets an f fraction of ess values and s is probably d and therefor o-hardness values henomena of potentially affe materials. s hat the existen n increase the herefore the h is found tha plastic deform fects on the ma generation d ork. figure 5 s ge of strain at b nanofillers c the embeddi ix resulted in duction up to on the other of the hdp ntage of gnss is observed in as seen in fig nss agglomera volume ration g the applicati ch v is and mechani nss to rdness hdpe of the an be olymer nd the gnss d they due to re the s. f heat ect the everal nce of e heat heat is at the mation aterial during shows break. caused ing of n 30% o 60% hand, e are s up to n both gure 5. ations, n and ion of fig. stren 1) 2) 3) 4) 5) [1] [2] [3] [4] [5] [6] vol. 8, no. 2, 20 ical characteri 5. effect of ngth, (c) on the el the main find the use o temperature in fully hd compared to the addition a remarkabl which reache only 0.2 wt% the heat g measured an the addition percentage o elastic modu the addition fraction (0.5 observed. r. bogue, “nan assembly auto m. alexandre “polyethylene techniques: syn 8, pp. 2123-213 s. s. ray, m. review from pr vol. 28, no. 11 k. yusoh, j. polyurethane/or nanoindentation 224, 2010 z. z. wang, p nano-sio2/poly wear, vol. 269 a. s. alghamd strain rate effec polyethylene/ca no. 6, pp. 1105 18, 2814-2817 ization of high gnss addition lastic modulus iv. co dings in this w of solution combined wi dpe pellets the use of thi n of low weigh le increase i ed double that % gnss. generation dur nd the effect w n of gnss cau of strain at bre ulus and tensi of reinforcem 5 wt%), a red refer nocomposites: a r omation, vol. 31, , p. dubois, t layered silicate nthesis and mecha 32, 2002 okamoto, “poly reparation to pro , pp. 1539–1641, jin, m. song, rganoclay nano n”, progress in or p. gua, z. zhang ycarbonate comp , no. 1-2, pp. 21– di, i. a. ashcrof cts on heat gener arbon black nano –1113, 2013 density polyet (a) on strain at nclusion work are summ blending ap ith mechanica dissolving in s method at ro ht fraction of in the micro t of hdpe wi ring plastic d was ignored. used significan ak. ile strength ar ments, however duction in th rences review of techno no. 2, pp. 106-11 t. sun, j. m. e prepared by anical properties” ymer/layered silic cessing”, progres 2003 “subsurface me ocomposite thin rganic coatings, v g, “indentation an osite coating at –25, 2010 ft, m. song, d. ration during the composites”, pol 2816 thylene/graphe t brake, (b) on marised as: proach at h l stirring resu n a short per oom temperatu gnss resulte ohardness valu ith the addition deformation nt reduction in re increased w r at higher we hese propertie ology and applica 12, 2011 garces, r. je polymerisation, polymer, vol. 4 cate nanocompos ss in polymer sc echanical propert n films studie vol. 67, no. 2, pp nd scratch behav the micro/nanocai, “morpholog plastic deformat lymer testing, v ene … tensile high ulted riod ure. d in ues, n of was n the with ight s 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management in organizations: a case study azin mesbah dpt of information technology management, college of management and economics, science and research branch, islamic azad university, tehran, iran. mohammadreza babaei dpt of industrial management college of management and accounting, yadegar-e-imam khomeini (rah), shahre rey branch, islamic azad university tehran, iran alireza shabanali faculty of management department of management university of tehran tehran, iran abstract—knowledge management is a systematic approach to improve organizational ability to mobilize knowledge and facilitate decision-making in setting business strategy. this study identifies the outcomes of an effectively implemented knowledge management in one of the departments of ‘iran khodro’ as an empirical case study. effective factors on effectiveness of knowledge management and effective outcomes of knowledge management were extracted by a semi-structured interview in three questions with 20 experts. then, results of interviews and the factors extracted from literature were integrated; by removing similar factors, 52 factors were identified and organized in three groups. using exploratory delphi analysis in two stages (by expert’s judgments), 30 out of 52 factors extracted from literature and interview were identified as outcomes of knowledge management implemented in the organizations; these factors were evaluated through a second questionnaire in 32 questions for prioritization of their significance in the studied organization by experts and managers. based on the coefficient calculated for the confirmed factors in three groups of outcomes, the top priority was knowledge, followed by human resource organization and performance, respectively. ranking of the rest is explained below. keywords-knowledge management; outcomes of effective knowledge management; performance outcomes of knowledge management; knowledge outcomes of knowledge management; model development. i. introduction currently, any organization needs to acquire, create, store and use knowledge as one of the most important determinants of growth and development [1]. effective knowledge strategy promotes the organization [2]. according to [3], intellectual capitals account for 60-70% of the real value of companies. empirical evidence suggests that this could be the basis for economic growth and development, because competitiveness of companies is not for physical and financial resources, but for quality of human capitals and intellectual capitals as well as quantity and quality of knowledge, innovation, creativity etc. [4]. in [5], authors addressed knowledge management from the perspective of information technology with two cognitive and social strategies. many scholars claim that any knowledge management strategy emphasizes two main aspects, i.e. system and human. according to [6], knowledge management refers to optimization of organizational knowledge by using a variety of techniques to achieve greater productivity. knowledge management is a systematic process for managing knowledge in organizations. in other words, knowledge management can be defined as creation, collection, transfer and employment of knowledge to promote organizational efficiency [7]. because knowledge plays an important and strategic role in research organizations, it is essential to develop a model to measure effectiveness of knowledge management in these organizations by professionals and experts [8]. different scholars have suggested different models with a variety of indicators for measuring effectiveness of knowledge management in organizations. for example, a model was presented in [9] with 5 criteria (employees, data, information, knowledge and wisdom) and 30 sub-criteria for measuring effectiveness of organizational knowledge management. it was claimed that the most important problems with development of this model included multiplicity of goals, difficulty evaluation and fuzzy nature of knowledge management which must be overcome. models to evaluate the performance of knowledge management based on financial and non-financial criteria and critical factors in order to improve quality of knowledge management systems have also been presented [10]. therefore, the development of a model in which all effective factors on effectiveness and success of knowledge can be considered as ranked by experts of this industry can help a large industrialmanufacturing organization to take advantage of knowledge management and its processes for developing new products, eliminating defects of products to achieve global quality standards, taking advantage of market opportunities, identifying strengths and advantages of rivals, improving and promoting research and development continuously [1]. engineering, technology & applied science research vol. 7, no. 2, 2017, 1575-1581 1576 www.etasr.com mesbah et al.: measuring the success level and effectiveness of knowledge management in... in order to fill the research gap in the field of effective factors on success and effectiveness of knowledge management and their ranking in government industrial organizations such as iran khodro, it is essential to develop models which consider all effective factors on effectiveness and knowledge management in organizations. by these models, managers and planners can implement knowledge management in the organization by a full knowledge of factors which guarantee their success in implementing knowledge management in research and operational departments. they can also improve knowledge management processes in departments in which these processes have been already implemented by a full knowledge of these factors and their significance in success of knowledge management. the present study tends to identify components and variables of effectiveness of knowledge management implemented in the organization. ii. literature review  knowledge: knowledge refers to argument on information and data to achieve efficiency, problem solving, decisionmaking, learning and teaching. according to [11], there are two types of knowledge: explicit and implicit. implicit knowledge involves high levels of expertise and skills; implicit knowledge lacks a distributable structure and a specific form. it is difficult to classify and document implicit knowledge. explicit knowledge refers to a more realistic and logical form of technical knowledge which can be documented in a distributable form without any need for interpersonal relationships and can be transported with a single process and strategy.  knowledge management: knowledge management refers to any process or acts of producing, acquiring, capturing, promoting, socializing and employing knowledge which can increase learning and performance of the organization. knowledge management is a process through which organizations generate capital from members' ideas and knowledge-based assets. according to [12], knowledge management is a mechanism to create a work environment in which knowledge and expertise are easily distributed and to provide opportunities to distribute knowledge and information at the right time so that people can act effectively and efficiently. in this study, knowledge management operationally refers to creation, searching, sharing and employment of knowledge in one of the departments of iran khodro for operational and managerial processes.  effectiveness: theoretically, effectiveness of measures taken to achieve goals is predetermined. in simpler words, an effectiveness study measures realization of goals. in other words, effectiveness shows the extent of efforts made to achieve the considered results, while utilization of resources to achieve the results is related to efficiency. in [13] it was stated that effectiveness means doing things right. according to [13] effectiveness is the key to the success of organizations. operationally, this study uses effectiveness as properly implemented knowledge management in the studied organization in terms of creation, search, employment and sharing of knowledge.  key success factors: theoretically, key success factors include a limited number of activities which are followed by successfully competitive performance. in other words, these factors include characteristics, conditions or variables which can have a significant effect on success of competitive position, if properly managed [14]. studying the role of key success factors in effectiveness of knowledge management in project and temporary organizations, authors in [15] presented four types of factors including knowledge culture (developed networks of knowledge, flexibility in solving problems, senior management commitment), structural factors (inter-department structure), process factors (knowledge control processes and maturity of knowledge processes) and technological factors (communication systems and knowledge storage systems). through an exploratory analysis of the factors creating success and effectiveness of knowledge management in insurance organizations. in [16], authors identified environmental factors, personal factors in managers and employees, knowledge characteristics in the organization, organizational factors, technological and cultural infrastructures. in [17], authors examined the effectiveness of knowledge management in knowledge-based organizations and concluded that organizational factors, knowledge resources, type of communications, knowledge holding and organization of knowledge repositories and a long-term approach to knowledge management are effective factors on effectiveness of knowledge management. iii. materials and methods this was an extended qualitative research and a field study. data was collected by surveying through a valid questionnaire. semi-structured interview and delphi analysis were used to identify the most important outcomes of knowledge management in the organization among 20 experts (top managers and experts of iran khodro in tehran who were familiar with the concept of knowledge management as well as university professors who were experts in scientific and practical implementation of knowledge management in organizations). for ranking outcomes of knowledge management identified by experts, topsis analysis was done on responses of experts and 150 managers and experts of a department of iran khdro in which the author tended to measure outcomes of knowledge management implemented in that department. using cochran’s formula, the sample size was reduced to 108: 2 2 2 2 (1 ) 1 1 1 z p q dn z p q n d = æ ö÷ç ÷+ -ç ÷ç ÷çè ø where, n is the size of population; n is the size of sample; z=1.96; q=50 and p=50; d=0.05. this was a test and hypothesis study in which hypotheses were tested by using relevant data. to measure and analyze the data obtained, descriptive statistics were used to obtain means and standard deviations of questions and frequency distribution of responses given to each question and histogram in a 5-point likert scale in both questionnaires engineering, technology & applied science research vol. 7, no. 2, 2017, 1575-1581 1577 www.etasr.com mesbah et al.: measuring the success level and effectiveness of knowledge management in... by using excel 2010 and spss 19. for inferential statistics, weight of factors listed in the first questionnaire was determined by delphi; multi-criteria decision-making topsis was used to rank the confirmed factors using t-test. to measure reliability of the first questionnaire, cronbach’s alpha was calculated by using spss; table i presents output of this process: table i. reliability of the variables related to the second questionnaire variable cronbach's alpha number of questions performance 0.875 12 knowledge 0.909 11 human resource 0.902 9 total reliability 0.937 32 as shown in the table i, α>0.7 confirmed reliability of the questionnaire; that is, the questions were internally consistent and the responses were given carefully. thus, the results could be used for statistical analysis. formal and content validity were used to measure validity of the first and second questionnaires. before the questionnaires were distributed among the samples, the advisor and supervisor professors were asked to review the questionnaires in terms of the number of questions and their relevance to the subject and content validity. moreover, they were asked to see whether the measured elements could formally measure the considered concept. the objections to the questions were determined and resolved in the questionnaire; then, formal and content validity of the questions were confirmed by the professors. iv. results a. delphi analysis to identify the most important outcomes of knowledge management the first questionnaire was used to identify the most important outcomes of knowledge management through delphi analysis. according to the analysis, 52 factors identified and given to 20 experts were reduced to 30 factors through two delphi stages. 1) first delphi stage the questionnaire with 52 questions (effective factors on effectiveness and outcomes of knowledge management) was distributed among 20 experts and managers. they were asked to express their agreement or disagreement to all 25 questions based on their experiences and knowledge in 5 states of optimality (from very low optimality to very high optimality). then, the scores were determined by calculating standard deviation of responses (table ii). according to the results of first delphi stage, 13 out of 52 factors (sd>1.7) were discarded:  improved emergency management.  improved operational procedures.  increased efficiency.  change management.  reengineering processes.  flexible and standard knowledge structure.  security and protection of knowledge.  developed knowledge networks.  updated information systems. table ii. results of first delphi stage component factor sd 1 continuous learning culture 0.47 2 improved emergency management 1.89 3 improved specialized marketing processes 0.11 4 quality management 0.77 5 improved customer service 0.82 6 organizational learning 0.74 7 improved operational procedures 1.78 8 organizational integration 0.89 9 innovative products 0.61 10 leadership in innovation 0.30 11 increased competitive advantage 0.74 12 increased efficiency 1.78 13 increased effectiveness 0.049 14 efficient innovation 0.81 15 optimal customer relationship 0.96 16 increased creativity 0.04 17 developed technological infrastructures 0.92 18 change management 1.87 19 improved financial and non-financial performance (organizational performance) 0.41 20 reengineering processes 1.89 21 flexible problem solving 0.11 22 r&d and its success 0.77 23 organizational research 0.89 24 knowledge creation 1.42 25 knowledge conversion 1.39 26 flexible and standard knowledge structure 1.85 27 knowledge localization 0.49 28 facilitated knowledge acquisition (discussion and interaction) 0.63 29 formulated knowledge strategies 0.49 30 modeling strategy and effective knowledge structure 0.83 31 knowledge classification 1.10 32 security and protection of knowledge 1.91 33 developed knowledge networks 1.80 34 organized knowledge repositories 0.45 35 organizational learning 0.49 36 new knowledge production 0.53 37 updated information systems 1.71 38 standardized procedures 1.5 39 employee participation and learning 1.12 40 new ideas of employees 1.79 41 team work and participation 0.63 42 knowledge empowerment of managers 0.45 43 human resource development 1.65 44 focus on organizational needs 1.42 45 expert knowledge and motivation 0.99 46 non-resistance to technology 1.84 47 knowledge-based vision and mission 1.31 48 improved organizational structure and reduced concentration (flexible structure) 1.90 49 evaluation of readiness and current level of knowledge management in organizations 1.63 50 incentive measures for staff particularly creative and innovative staff 0.79 51 spiral and flexible career paths within the organization, especially for knowledge forces 1.90 52 open and flexible communication with environment and competitors 1.16 engineering, technology & applied science research vol. 7, no. 2, 2017, 1575-1581 1578 www.etasr.com mesbah et al.: measuring the success level and effectiveness of knowledge management in...  new ideas of employees.  non-resistance to technology.  improved organizational structure and reduced concentration (flexible structure).  spiral and flexible career paths within the organization, especially for knowledge forces. 2) second delphi stage the rest 39 factors were evaluated by experts more strictly (sd=1); thus, 9 other factors were discarded. finally, 30 factors remained for further analysis. the discarded factors included:  improved organizational structure and reduced concentration (flexible structure).  flexible problem solving.  knowledge localization.  facilitated knowledge acquisition (discussion and interaction).  organized knowledge repositories.  organizational learning.  optimal customer relationship.  increased creativity.  developed technological infrastructures. finally, 30 out of 52 factors extracted from literature and interviews were identified as outcomes of knowledge management implemented in the organization. these 30 factors were ranked through the second questionnaire by the experts using topsis. 3) t-test for presence or absence of the determined factors by delphi analysis two hypotheses h1 and h0 were considered for each of 32 factors determined in the second questionnaire. h0 assumed that the factor was not effective on effective outcomes of knowledge management and h1 assumed that the factor was effective on effective outcomes of knowledge management. since h0 was accepted (sig<0.05), the factors 2, 3, 4, 5, 7, 8, 9, 10, 12, 13, 14, 15, 16, 20, 22, 23, 24, 25, 26, 28, 29 and 31 were effective. therefore, following factors were considered as effective outcomes of knowledge management implemented in the studied organization.  growth of market processes.  in this organization, management is concerned with quality management processes in the field of quality of products and manufacturing processes.  management commitment to implementation of quality standards and monitoring of implementation.  management considers customer needs and gathers information about them.  integration exists in processes (production and support).  management considers product innovation in terms of quality and design.  innovations are used to improve market performance.  mechanisms are defined for sharing information between different departments.  value creation is improved for customer relying on knowledge gained from customers and the market.  financial performance is improved in terms of sales and net profit.  management considers increase in research in the organization to improve performance.  adequate budget is allocated for research for improving products and services.  the organization considers knowledge creation through discussion and teamwork.  classification of knowledge related to customer needs and their availability.  management emphasizes staff training and research encouragement.  procedures and guidelines of various processes are standardized.  employee participation in decision-making  management facilitates teamwork and participation among employees.  empowerment of operational management and training  awareness of organizational needs regarding customers, suppliers, employees and processes.  this organization considers knowledge of workers and motivates them to apply their knowledge in their jobs.  encouragement of creative and innovative staff. since sig>0.05 for the factors 1, 6, 11, 17, 18, 19, 21, 27, 30 and 32, the hypothesis on equal lower and upper bounds of the considered strict effectiveness (3.5) was not rejected; moreover, h0 was accepted because the upper bound was smaller. therefore, the following factors were not considered as effective outcomes of knowledge management implemented in the studied organization.  lack of concern for organizational learning and turn it into a strategy for management.  not using external environment to learn more information about production processes and performance improvement.  sharing information of processes among departments which have failed to increase effectiveness of production and products.  lack of attention to conversion of implicit experience of experienced staff to information available to all employees, particularly new employees.  lack of attention to redeployment of activities of competitors to improve processes.  lack of attention to acquiring knowledge of customers by their feedback and inclusion of their feedback in production processes.  unavailability of knowledge related to competitors and their products and their movements in the automotive market.  lack of attention to empowerment of employees for challenging jobs.  lack of emphasis on learning in mission and vision.  lack of good and effective communication with rival firms and external environment. b. ranking of effective outcomes of knowledge management by topsis out of 32 factors identified as effective outcomes of knowledge management, 22 factors were extracted from t-test as the most important outcomes of knowledge management. engineering, technology & applied science research vol. 7, no. 2, 2017, 1575-1581 1579 www.etasr.com mesbah et al.: measuring the success level and effectiveness of knowledge management in... this section ranks these 22 factors by using topsis, as follows: 1) normalization of decision matrix to compare the scores given based on a 5-point likert scale from very low optimality (1) to very high optimality (5), the decision matrix of given scores was normalized to a weighted unscaled matrix by using the euclidean norm. each number in the column was divided by the root square sum of the numbers in that column. mathematically, this can be written as: 2 1 ( 2 )i ji j m i j i a n a = = å thus, judgments of 108 experts were extracted in three groups (performance, knowledge, and human resource organization) and then normalized. { } { } * * * * * 1 2 ( m a x ) , ( m i n , , , i j i j ii n a j j j j a n n n n n ¢= î î =  (3) { } { }1 2 ( m i n ) , ( m a x , , , i j i j i i n a j j j j a n n n n n ¢= î î =  (4) 2) calculation of distance of any alternative from pis and nis this section determines the distance of any factors from positive ideal solution (pis) and negative ideal solution (nis) by using following formula: * * 2 1 ( ) ( 5 ) n i i j j j s n n = = -å 2 1 ( ) ( 6 ) n i i j j j s n n= = -å table iii lists the results related to distance of factors from pis and nis. table iii. the results related to distance of factors from positive and negative ideals factor distance from pis distance from nis 1 performance 1.948709 0.274707 2 knowledge 0.526325 1.768677 3 human resource organization 0.724977 1.691601 3) calculation of closeness of any factor to pis and nis this section determines closeness (cl) which is equal to minimum alternative distance divided by sum of minimum alternative distance and ideal alternative distance. cl was calculated by following formula. the results are listed in table iv. * ( 7 )ii i i d c l d d + = + table iv. closeness of factors to pis and nis and final ranking factor cl rank performance 0.123552 3 knowledge 0.770665 1 human resource -organization 0.699999 2 based on cl calculated for factors of each class of outcomes, the outcomes can be ranked in a descending form. in this regard, the top ranked outcome is knowledge, followed by human resource -organization and performance. note that, the above stages were performed for all factors separately. c. ranking of performance outcomes using topsis following steps were taken to rank performance outcomes by using topsis:  normalization of decision matrix.  calculation of pis and nis.  calculation of distance of any alternative from pis and nis.  calculation of closeness of any factor to pis and nis. based on cl calculated for 10 performance outcomes, the top ranked factor was considerable improvement of financial performance and the last factor was improvement of performance by innovation (table v and table vi). table v. distance of factors from pis and nis performance outcomes distance from pis distance from nis 1 growth of marketing processes 1.687797 1.633763 2 attention to quality management 2.260535 1.104352 3 management commitment to quality standards 2.221774 1.179989 4 attention to customer needs 2.307012 0.974596 5 integration of processes (production and support) 2.451424 0.779589 6 innovation in quality and design 2.445249 0.800397 7 improvement of performance by innovation 2.480419 0.697787 8 correct information sharing mechanism 0.623792 2.529572 9 superiority over competitors by value creation for customers 0.60855 2.543649 10 considerable improvement of financial performance 0.595425 2.532824 table vi. closeness of factors to pis and nis and final ranking of performance outcomes performance outcome cl rank 1 growth of marketing processes 0.491866 4 2 attention to quality management 0.328199 6 management commitment to quality standards 0.346876 5 4 attention to customer needs 0.296987 7 5 integration of processes (production and support) 0.241283 9 6 innovation in quality and design 0.246606 8 7 improvement of performance by innovation 0.219554 10 8 correct information sharing mechanism 0.802182 3 9 superiority over competitors by value creation for customers 0.806944 2 10 considerable improvement of financial performance 0.809662 1 d. ranking of knowledge outcomes using topsis based on cl calculated for 7 knowledge outcomes, the top ranked factor was teamwork in most layers and the last factor engineering, technology & applied science research vol. 7, no. 2, 2017, 1575-1581 1580 www.etasr.com mesbah et al.: measuring the success level and effectiveness of knowledge management in... was management encouragement for r&d (table vii and table viii). table vii. distance of factors from pis and nis knowledge outcome distance from pis distance from nis 1 special attention to r&d 0.640068 1.22891 2 allocation of budget to r&d 0.617216 1.250669 3 teamwork in most layers 0.543496 1.300591 4 classification of the knowledge obtained from customer 1.071552 0.827225 5 management encouragement for r&d 1.184694 0.755773 6 standardization of processing procedures 1.131584 0.817202 7 employee participation in decision making 0.866669 0.996876 table viii. closeness of factors to pis and nis and final ranking of knowledge outcomes knowledge outcome cl rank 1 special attention to r&d 0.65753 3 2 allocation of budget to r&d 0.669564 2 3 teamwork in most layers 0.705276 1 4 classification of the knowledge obtained from customer 0.435662 5 5 management encouragement for r&d 0.38948 7 6 standardization of processing procedures 0.419339 6 7 employee participation in decision making 0.534935 4 e. ranking of human resource -organization outcomes using topsis based on cl calculated for 5 human resource -organization outcomes, the top ranked factor was operational management training and the last factor was encouragement of creative and innovative employees (table ix and table x). table ix. distance of factors from pis and nis human resource -organization outcomes distance from pis distance from nis 1 facilitation of teamwork and participation 0.8540399 1.055667 2 operational management training 0.7263504 1.1967989 3 encouragement of creative and innovative employees 1.1407226 0.8260286 4 management awareness of requirements and processes 1.066389 0.8378727 5 employee encouragement for job motivation 0.8272775 1.1752109 table x. closeness of factors to pis and nis and final ranking of human resource -organization outcomes human resource -organization outcome cl rank 1 facilitation of teamwork and participation 0.55279 3 2 operational management training 0.622312 1 3 encouragement of creative and innovative employees 0.419997 5 4 management awareness of requirements and processes 0.439999 4 5 employee encouragement for job motivation 0.586875 2 v. discussion one of the most important effects of knowledge management is its effect on organizational performance. knowledge management can influence organizational performance directly or indirectly; its effect is direct because knowledge is used for profitable products and indirect because knowledge management can be used for virtual leadership of the industry which can increase customer loyalty and acquire competitive advantage. the factors extracted from literature and semi-structured interviews with experts were reduced to 30 factors through 2 delphi stages and confirmed as the most important outcomes of knowledge management in three groups of performance, knowledge and human resource -organization. those 30 factors were included in a second questionnaire (32 questions) for running t-test. results of t-test showed that 22 outcomes were more influenced than other 10 factors. these 22 outcomes include: a. human resource -organization  educational planning for operational managers.  continuous attention to knowledge workers.  facilitation of knowledge participation.  updated database of customer needs.  encouragement of creative personal for knowledge activities. b. knowledge  facilitation of organizational interactions for knowledge creation.  allocation of research budget.  development of r&d based on market needs.  effective participation of employees in organizational decision making.  easy access to customer demands.  standardization of procedures.  motivational facilities for personnel to enrich knowledge resources. c. performance  increased financial performance.  competitive advantage in knowledge creation.  facilitated knowledge sharing within the organization.  growth of marketing processes.  management commitment to standards.  attention to quality management processes.  identification of customer needs.  growth of innovation and quality.  customer satisfaction.  integration of organizational processes. vi. conclusion according to the results, it can be concluded that the top ranked outcome of knowledge management implemented in the studied organization is knowledge, followed by human resource-organization and performance. based on cl calculated for 10 performance outcomes, the top ranked factor was considerable improvement of financial performance and the last factor was improvement of performance by innovation. based on cl calculated for 7 knowledge outcomes, the top ranked factor was teamwork in most layers and the last factor was management encouragement for r&d. based on cl calculated for 5 human resource-organization outcomes, the top engineering, technology & applied science research vol. 7, no. 2, 2017, 1575-1581 1581 www.etasr.com mesbah et al.: measuring the success level and effectiveness of knowledge management in... ranked factor was operational management training and the last factor was encouragement of creative and innovative employees. references [1] p. j. hsieh, b. lin, c. lin, “the construction and application of knowledge navigator model (knm™): an evaluation of knowledge management maturity”, expert systems with applications, vol. 36, no. 2, pp. 4087-4100, 2009 [2] n. åkerman, “knowledge-acquisition strategies and the effects on market knowledge–profiling the internationalizing firm”, european management journal, vol. 33, no. 2, pp. 79-88, 2015 [3] r. l. priem, j. f. butler, “is the resource-based “view” a useful perspective for strategic management research?”, academy of management review, vol. 26, no.1, pp. 22-40, 2001 [4] p. wolf, “balanced evaluation: monioring the "success" of a knowledge management project”, forum: qualitative social research, vol. 11, no. 3, pp. 148-161, 2016 [5] j. swan, s. newell, h. scarbrough, d. hislop, “knowledge management and innovation:networks and networking”, journal of 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firms”, academy of management journal, vol. 48, no. 2, pp. 346-357, 2005 microsoft word etasr_v11_n6_pp7750-7756 engineering, technology & applied science research vol. 11, no. 6, 2021, 7750-7756 7750 www.etasr.com serradj et al.: a contribution to the thermal field evaluation at the tool-part interface for the … a contribution to the thermal field evaluation at the tool-part interface for the optimization of machining conditions nasreddine benhadji serradj department of mechanical engineering university of tlemcen tlemcen, algeria kawther4499@yahoo.fr abdelillah djamal kara ali department of mechanical engineering university of tlemcen tlemcen, algeria dj_kara_ali@yahoo.fr mohamed el amine ghernaout department of mechanical engineering university of tlemcen tlemcen, algeria e_amine2001@yahoo.fr abstract-in this study, an experimental measurement methodology is implemented that allows obtaining consistent temperature data during the turning operation of semi-hard c20 steel using snmg carbide insert, allowing us to have better control at the tool-part interface. the interactions of the phenomena influencing the cut led our choices on the development of a correlation model for the analysis and prediction of the relationships between the machining parameters by measurement of the temperature. the measurement procedure implemented for the temperature estimate is based on the use of an flir a325sc type infrared camera mounted and protected by a device on the machine tool. the taguchi method was chosen to find the relationships between the input factors (cutting speed (vc), feed rate (a), depth of cut (p)), and the output factor (temperature (t)). in the future, we will develop a numerical validation model to simulate the machining process in order to predict temperatures. keywords-machining conditions; temperature measurement; infrared camera; thermal transfer; taguchi plan; emissivity i. introduction during machining, maximum heat occurs at the tool-part interface. it affects, among others, tool life, surface finish, and cutting forces. at the heart of the process, two main phenomena interact: a very strong plastic deformation in the shear zones and the friction of the chip on the cutting face of the tool. we can also add the friction of the draft face on the newly generated surface (figure 1). since the first experimental work of taylor (1905-1907) on the influence of temperature in machining, significant progress has been made in improving knowledge about metal cutting. the bibliographic research carried out in [1] on the different thermal aspects during machining shows the difficulties of direct measurement. authors in [2] showed that several methods are possible for measuring temperatures during the cutting process: • measurement by metallurgical analysis of the cutting insert after machining. authors in [3] showed that it is possible to determine the temperature map in the cutting tool as a function of the phase transformations detected during a metallographic analysis of a high speed steel tool. this is an a posteriori measurement method. • measurement by thermocouples implanted in the cutting insert. in [4], it was shown that for this type of thermal measurement, the temperature mapping is carried out from point readings obtained by thermocouples implanted in the insert of the cutting tool. • temperature evaluation by thermocouples directly in contact with the tool-part pair. in this particular case, only an average value of the temperature can be obtained. authors in [5] proposed the use of the tool-part contact as a hot junction for the thermocouple. the two preceding methods present major hazards relating to the installation of thermocouples. fig. 1. sources of heat generation in machining. corresponding author: mohamed el amine ghernaout engineering, technology & applied science research vol. 11, no. 6, 2021, 7750-7756 7751 www.etasr.com serradj et al.: a contribution to the thermal field evaluation at the tool-part interface for the … our job focused on taking the temperature with an infrared camera without contact. the response time is fast, thus allowing the capture of the intermittent heat generation. this capture can allow us to regulate the cutting parameters if there is a sudden increase in temperature. the camera is mounted and protected by a device on the machine tool. ii. thermal flows almost all of the chip formation work is degraded in the form of heat. this results in a high temperature rise in the chip formation zone. the correlation between cutting conditions and temperature is shown in figure 2, with regard particular to the primary influence of the cutting speed factor. fig. 2. correlation between cutting conditions and temperature. in this section, we will recall the modes of heat transfer and the influence factors expressed in this method of measurement. surface temperature measurements implement three heat transfer modes that we briefly recall below along with the relationships of the listed laws. • conduction: corresponds to the transfer of heat within an opaque medium, without displacement of matter, under the influence of a temperature difference. fourier’s law (1) describes this transfer mechanism [9-10]: ɸ � λ.s.���� � (1) • convection: corresponds to the transfer of heat between a solid and a moving fluid (liquid or gas). newton’s law (2) describes this transfer mechanism [9-10]: ɸ � h.s t� �t�� (2) • radiation: corresponds to the transfer of heat in the form of an electromagnetic wave, emitted by a surface. stefan’s law (3) describes this transfer mechanism [9-10]: ɸ � σ.s.��. t�� �t��� (3) to obtain consistent temperature data at the tool-part interface, an experimental measurement methodology is proposed using acquisition instrumentation, equipped with an infrared camera and a unit for processing the measured values. iii. measurement by infrared radiation the large amount of heat released in the chip formation zone and the difficulties of evacuation of this generated energy, result in very high and localized temperatures. these in turn have a significant impact on the dimensional and geometric precision of the produced surfaces and the lifetime of the cutting tools. the knowledge of the thermal field is therefore an essential element in the analysis and control of these phenomena. a. infrared thermography thermal imaging is a contactless technology that converts infrared waves into a temperature image. figure 3 shows schematically the overall principle of this method. fig. 3. radiometric chain of the camera. b. theoretical elements increase in temperature due to machining causes electromagnetic radiation described by planck's law. this law, for a black body, is the basis of temperature measurement by radiation analysis. it has a spectral distribution, which depends on the material. its intensity or its luminance can be measured and its analysis allows finding the temperature [6]. l� � �� � ������ �! (4) where c1 and c2 are constants: c1 = 1.191×10 -16 w.m 2 .sr -1 and c2 = 1.438×10 -2 m.k, h is the planck constant, k the boltzmann constant, c the speed of light, t the absolute temperature in kelvin degrees, and λ the wavelength in m [9-10]. emissivity ε is a property of surfaces depending on the nature of the material, its surface quality, the wavelength and the angle of observation. its prior evaluation is essential to determine the absolute value of the temperature from the light flux signal [7]. ε � #α #β (5) where lα is the luminance of the measured object and lβ the luminance of the black body [9-10]. iv. experimental procedure although the undertaken studies so far in the area of cutting (mechanism of chip formation, behavior of tools, thermal appearance, and damage of the cutting edges) have made significant progress in the understanding of the process, it is necessary to update and continue them, in order to meet the engineering, technology & applied science research vol. 11, no. 6, 2021, 7750-7756 7752 www.etasr.com serradj et al.: a contribution to the thermal field evaluation at the tool-part interface for the … new conditions of the industrial context. the complexity and interactions of the many factors involved in the cutting phenomena require specific experiments for each material, in order to define the best choice of tools and corresponding optimal cutting conditions, based on the analysis of their wear behaviors. a. means of realization in order to take into account the dominant elements of machining, the current analysis was restricted to steel and conventional machining processes. • machine tool used: the machining was carried out on a conventional parallel lathe made by tos trencin (figure 4). it is a rigid, powerful, precise and well-sealed machine. the main motor of the machine is asynchronous type. • machined material: the material used for these tests is the c20 non-alloy steel for heat treatments frequently used in industry. the chemical composition and physic properties are presented in tables i and ii. fig. 4. radiometric chain of the camera. table i. chemical composition element c fe mn p s % 0.138 98.11 1.062 0.013 0.011 table ii. physical properties property value units elastic modulus 2.049999984e+011 n/m 2 mass density 7850 kg/m 3 thermal conductivity 52 w/(m*k) specific heat 486 j/(kg*k) • insert and tool holders: the insert used in our tests were chosen according to the machining conditions and a small beak radius (r = 0,8 mm). the reference selected is snmg 12-04-08 (figure 5). the choice of the tool holder was oriented on a pcln r 20-20 k12. the properties of the insert are shown in table iii. • measurement process used: the objective of this contribution is to measure temperatures in the chip formation zone in order to collect thermal data from the cutting mechanism. the quality of the information sought requires that it be captured as close as possible to the chip creation area. temperatures were recorded using the flir a325sc thermal camera (figure 6). the camera is coupled with flir research ir max measuring software for maximum intuitiveness in display, recording and advanced thermal data processing (figure 7) [8]. table iii. insert properties wafer shape snmg insert size 120408 matter carbide insert thickness (mm) 4.76 edge length (mm) 12 insert radius (mm) 0.8 draft angle (°) 0 number of cutting edges 8 fig. 5. pad and its diagram of the range of applications. (a) (b) fig. 6. (a) thermal camera flir a325sc, (b) the experimental device. fig. 7. chain of acquisition and processing of the thermal data. • calibration of the camera: the camera is calibrated in the factory to make accurate measurements and thermal images. however, knowledge of the calibration curve (figure 8) is essential for advanced control of radiometric measurement. engineering, technology & applied science research vol. 11, no. 6, 2021, 7750-7756 7753 www.etasr.com serradj et al.: a contribution to the thermal field evaluation at the tool-part interface for the … fig. 8. calibration curves for the flir a325sc. • influence of emissivity: when making an infrared measurement, we record the energy ɸ emitted by the studied body and refer to stefan’s law of radiation of the black body: ɸ � σt� (6) where σ is the boltzmann constant and t the temperature of the studied body, identified with an ideal black body [9-10]. in addition, the measurement requires knowledge of the emissivity coefficient of the studied body. for this, we put the tool (insert) in an oven whose temperature is known thanks to a standard thermometer. after reaching thermal equilibrium, in situ measurements were taken with the camera. knowing the temperature in the oven, the temperature measured during machining, and the emissivity coefficient displayed on the camera, the actual coefficient of emissivity of the tool is deduced during machining using (6) [9]. we have taken the same approach to determine the emissivity of the machined material. b. preliminary tests in order to verify the possibility of recording the influence and the variability of the thermal fluctuations during the machining, a first series of tests was conducted to control the sensitivity and the capacity of our measuring system to capture and analyze the thermograms (figure 9). these preliminary tests were carried out under the variability conditions summarized in table iv, in which the results of the experiment for the qualification and validation of the measurement method are grouped. over the length of the machining, we chose 10 positions for the temperature reading, using the camera software. these points are taken during the machining stabilization period. the experimental results illustrated in figure 10 allow us to conclude that the temperature variations are very small in the steady state for invariant cutting parameters. on the other hand, the heat flux generated during machining is largely evacuated by the chip. in figure 11, the curves represent the temperatures of the chip, the machined surface and the cutting edge of the tool. two curves (tool-part) have practically the same shape and very close temperature thresholds (near 100°c). on the other hand, the chip temperature curve shows a marked increase in temperature (around 300°c), which confirms the theoretical results which state that the chip evacuates the most important temperature flow. fig. 9. thermograms: tool-part. table iv. experimental results position part tool chip 1 114.6 79.2 300.7 2 117.6 89.02 298.7 3 117.5 93.3 299.5 4 114.9 95.5 302 5 117.6 96.2 295.5 6 122 96.3 288.3 7 118 97 299.3 8 120.1 97.3 288 9 113.3 99.9 291.3 10 113.4 98.6 289.2 average 116.90 94.23 295.25 fig. 10. temperature variations (quickplot). fig. 11. temperature variations. engineering, technology & applied science research vol. 11, no. 6, 2021, 7750-7756 7754 www.etasr.com serradj et al.: a contribution to the thermal field evaluation at the tool-part interface for the … v. reference tests the large number of variables controlling the manufacturing process requires mathematical models to represent this process. these models should be developed using only the most significant parameters. tests are used to build first and second order models by multiple regression methods. the aim of developing mathematical models is to understand the combined effect of the parameters involved and to facilitate the optimization of the machining process. during the carried out tests, various machining parameters such as cutting speed, feed rate, and depth of cut, vary according to the design of experiments as independent variables in order to be linked to the response, namely the cutting temperature [t = f (v, f, p)], by prediction equations of the type: t � b% &b'x' & b)x) &b*x* (7) the choice of cutting conditions was conditioned by the range of rotational speeds of the machine and the temperature measurement range of the infrared camera. table v summarizes the results of the experiments. figure 12 shows the effect of cutting conditions on temperature variation. changing the depth of cut has a very high effect on the cutting temperature while the cutting speed and feed rate have a moderate effect on the cutting temperature. table v. cutting parameters parameter code levels 1 2 3 4 cutting speed vc (m/min) x1 78 112 157 220 feed rate a (mm/rev) x2 0.08 0.11 0.14 0.20 depth of cut p (mm) x3 0.25 0.5 0.75 1 turning conditions machining without lubrication fig. 12. the effects of cutting conditions on temperature. after treatment and elimination upstream of the insignificant terms of the model, we obtain the following prediction equation that relates the input and output parameters: t tool= 9.7 + 0.0877 vc + 139.7 a + 74.96 p (8) a. effects of cutting speed on temperature we can see the different levels of the temperature curves according to the cutting speed in figure 13. they increase with the evolution of the depth of cut. at 112m/min cutting speed (point a) a temperature peak can be observed which can be explained by unfavorable cutting conditions, generating entanglement of the chip around the cutting edge, as shown by the thermogram of figure 14. at high cutting speed (point b), the chip flow is restored, the cutting temperature drops shown by the thermogram (figure 15). fig. 13. temperature according to cutting speed. fig. 14. thermogram at point a. fig. 15. thermogram at point b. fig. 16. temperature according to the feed rate. engineering, technology & applied science research vol. 11, no. 6, 2021, 7750-7756 7755 www.etasr.com serradj et al.: a contribution to the thermal field evaluation at the tool-part interface for the … b. effects of feed rate on temperature figure 16 shows the different levels of the temperature curves depending on the feed rate. they increase with increasing depth of cut. at the feed rate of 0.11tr/min (point c) a lower temperature can be observed which can be explained by cutting conditions which favor the flow of the chip around the cutting edge, as shown in the thermogram in figure 18. at high cutting speed (point d), the chip remains at the cutting edge, which generates an increase in temperature shown by the thermograms in figures 17 and 18. fig. 17. thermogram at point c. fig. 18. thermogram at point d. c. effects of depth of cut on temperature the different levels of the temperature curves according to the depth of cut are exhibited in figure 19. they increase with the evolution of the cutting speed. fig. 19. temperature as a function of depth of cut. at the 0.5mm depth of cut (point e) a temperature peak can be observed which can be explained by cutting conditions favoring the flow of the chip around the cutting edge, as shown by the thermogram of figure 20. with a depth of 0.75mm (point f), the chip is evacuated more easily, which generates a decrease in temperature (thermogram figure 21). fig. 20. thermogram at point e. fig. 21. thermogram at point f. vi. conclusions knowledge of the distribution of the temperature flow between the cutting tool, the chip and the workpiece provides useful information for optimizing manufacturing conditions. therefore, it is essential to determine the relationship between the cutting parameters and the temperature distribution. the current paper focuses on the infrared thermography procedure for establishing an experimental methodology, which allows the evaluation of the cutting temperature during the machining operations for different cutting parameters. the experimentation allowed us to evaluate the distribution of the temperature flow on the machined surface of the part, the chip, and the cutting edge. for a large cutting penetration, the friction increases for both the tool and the chip and generates an increase in temperature, so we took (from thermograms) the maximum temperatures of the tool and the chip which were 112.63°c and 275.1°c. the optimal conditions for the good quality of the part are moderate temperatures for high cutting speeds and small depths of cut. the chosen infrared camera used in the experiments has many advantages such as the ability to take measurements without contact with a very little disturbance between the surface of the studied object and its surrounding environment, its measurement capacity in real time, a wide range of operating temperatures, and the ability to adapt to all types of materials. the obtained results during our tests allowed concluding on one hand that the temperature variations are very weak in permanent regimes for invariant cutting parameters and on the other that the heat flux generated during machining is largely evacuated by the chip. the major difficulty in taking the machining sequence by the camera is the winding of the chip, hence the need to choose good cutting engineering, technology & applied science research vol. 11, no. 6, 2021, 7750-7756 7756 www.etasr.com serradj et al.: a contribution to the thermal field evaluation at the tool-part interface for the … conditions and to have good protection and fixation of the camera. in the future, our work will be extended to other materials. we will also try to define a correlation between the cutting temperature and the wear of the tool during machining. we are encouraged by the results of this work to extend to higher speeds (ugv) and to use a more efficient infrared camera for larger measurement range. references [1] r. f. brito, s. r. carvalho, and s. m. m. lima e 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[2] o. pantalé, r. rakotomalala, and m. touratier, “an ale threedimensional model of orthogonal, oblique metal cutting processes,” international journal of forming processes, vol. vol.1, pp. 371–388, sep. 1998. [3] p. k. wright and e. m. trent, “metallographic methods of determining temperatures gradients in cutting tools,” 1973. [4] w. bouzid, “etude experimentale et numerique de la coupe orthogonale,” ph.d. dissertation, arts et métiers paristech, paris, france, 1993. [5] d. a. stephenson, “tool-work thermocouple temperature measurements—theory and implementation issues,” journal of engineering for industry, vol. 115, no. 4, pp. 432–437, nov. 1993, https://doi.org/10.1115/1.2901786. [6] i. bonnet and j. gabelli, “probing planck’s law at home,” european journal of physics, vol. 31, no. 6, pp. 1463–1471, 2010, https://doi.org/ 10.1088/0143-0807/31/6/012. 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[14] g. sidebotham, “heat transfer modes: conduction, convection, and radiation,” in heat transfer modeling: an inductive approach, g. sidebotham, ed. cham, switzerland: springer international publishing, 2015, pp. 61–93, https://doi.org/10.1007/978-3-319-14514-3_3. [15] d. pajani and l. audaire, “thermographie technologies et applications : thermographie et utilisation des caméras thermiques,” techniques de l’ingénieur, mar. 2013, accessed: oct. 06, 2021. [online]. available: https://www.techniques-ingenieur.fr/basedocumentaire/genie-industriel-th6/mise-en-uvre-de-la-maintenance42136210/thermographie-r2741/thermographie-et-utilisation-descameras-thermiques-r2741v2niv10002.html. [16] o. riou, p.-o. logerais, and j.-f. durastanti, “quantitative study of the temperature dependence of normal lwir apparent emissivity,” infrared physics & technology, vol. 60, pp. 244–250, sep. 2013, https://doi.org/ 10.1016/j.infrared.2013.05.012. [17] j. goupy and l. creighton, introduction aux plans d’expériences, 3rd ed. paris, france: dunod, 2006. [18] s. atlati, “développement d’une nouvelle approche hybride pour la modélisation des échanges thermiques à l’interface outil-copeau : application à l’usinage de l’alliage d’aluminium aéronautique aa2024t351,” ph.d. dissertation, université de lorraine, lorraine, france, 2012. engineering, technology & applied science research vol. 7, no. 4, 2017, 1753-1758 1753 www.etasr.com shariatmadar and jafarian: application of minimum-time optimal control system in buck-boost … application of minimum-time optimal control system in buck-boost bi-linear converters seyed mohammad shariatmadar electrical engineering department naragh branch, islamic azad university naragh, iran shariatmadar@iau-naragh.ac.ir seyed mohammad javad jafarian electrical engineering department shahed university tehran, iran mohammad.jafarian@gmail.com abstract—in this study, the theory of minimum-time optimal control system in buck-boost bi-linear converters is described, so that output voltage regulation is carried out within minimum time. for this purpose, the pontryagin's minimum principle is applied to find optimal switching level applying minimum-time optimal control rules. the results revealed that by utilizing an optimal switching level instead of classical switching patterns, output voltage regulation will be carried out within minimum time. however, transient energy index of increased overvoltage significantly reduces in order to attain minimum time optimal control in reduced output load. the laboratory results were used in order to verify numerical simulations. keywords-buck-boost converter; sliding mode control; minimum-time control; bi-linear converter i. introduction several methods have been introduced to control dc-to-dc switching converters [1-7]. common controllers employed in these converters include the pwm traditional controller based on current control or voltage control [1-2]. design based on the averaging method from the state space based on the small signal method in these controllers will not bring about a proper dynamic performance in large-signal disturbances. due to the non-linear nature of these converters, nonlinear control methods have been recommended to improve the stability and resistance properties of controller in these systems [4-6]. the sliding mode control technique is one of the modern non-linear methods utilized in variable structure systems such as dc-todc switching converters [7-8]. ease of implementation, proper dynamic performance and stability are achieved by the application of this type of nonlinear control technique. nevertheless, non-fixed and high switching frequency, regulation error of steady state and complicated design are among the difficulties of implementing the sliding mode controller in dc-to-dc switching converters [9]. non-minimum phase systems encounter certain limitations. this feature in voltage control method leads to complex design and inadequate dynamic response to identify frequency traversing via resonance frequency [1]. despite the failure to maintain system stability and large signal disturbances, the current control method has faster transient response when compared to voltage control in a similar system. several methods have been proposed to control boost converter in sliding mode, and especially in the latter years in an effort to enhance their performance [9-16], including pwm constant frequency based on voltage or current control, adaptive sliding mode controller and dual integral sliding level [12-16]. looking back on these methods, we can conclude that in the majority of these systems, system stability and performance have targeted steady state while static behavior of system have been considered by researchers. nevertheless, several studies have selected non-linear switching level to enhance system transient performance under sliding mode controllers [17]. in these systems, despite an improvement in system behavior, in contrast to linear switching level, transient response of system in large-signal disturbances do not exhibit proper behavior. in this study, the pontryagin's minimum principle in buckboost bilinear converters is investigated and regulations of minimum-time optimal control are derived. the optimized closed-loop controller works on output voltage regulation in each output disturbance. simulation results reveal that the performance of buck-boost time optimal converters exhibited a better transient performance when compared to the sliding mode controller. ii. introduction to sliding mode controller variable nonlinear dynamic system with the timeline below is assumed as follows: 1 2( ) ( ) ( ) ( ) ( )inx t a x t b x t u t b v u t   (1) where x(t),v u(t), vin are mode vector, disturbance input and input voltage of system respectively. a, b1, b2 are also fixed matrices with appropriate dimensions. the initial conditions and balance points in system in tf are assumed as follows: 0(0) ( )f f x x x t x   (2) in addition, restrictions of control input are as follows: ( )n pu u t u  (3) engineering, technology & applied science research vol. 7, no. 4, 2017, 1753-1758 1754 www.etasr.com shariatmadar and jafarian: application of minimum-time optimal control system in buck-boost … where up>0 and un≤0 are upper and lower limits of control inputs. in classical systems design of switching level, ssm(x) is a linear combination of system status: ( ) ( ( ) ( ))tsm fs x x t x t  (4) where β is the sliding coefficient vector of system. the provisions to reach switching level and sliding on switching level are two sufficient conditions for the implementation of sliding mode controller in one of the customized systems. the first provision is to examine the reaching of system trajectory to switching level which is achieved by one of the following conditions: 0 0 0 0 p sm n sm p sm n sm if x s then x s if x s then x s         (5) where xp and xn are steady state values of state vector with up and un control inputs. the second condition (sliding) will be provided using the following relationship: 1 2 1 2 0 lim ( , ) ( , ) 0 sm sm sm s s x x s x x   (6) where 1 2( ( , ))sms x x  are time function of switching level function. the sliding coefficients of β is selected in (4) in such a way that the condition of (6) will be established. according to (5) and (6), control rule of infinite switching frequency in sliding mode regime is as follows: ( ) 0 ( ) ( ) 0 p sm n sm u s x u t u s x     (7) the stability of the ystem in second grade systems is provided by trajectory guidance of system towards a stable equilibrium point in sliding mode regime [7]. iii. optimal control of non-oscillatory dynamic systems. in minimum time problem, we focus on minimizing function as follows: 0 ( ) ft j u dt  (8) we suppose that in (1), the values of a, b1, b2 are as follows: 1 1 2 2 0 0 0 , , 0 0 1 a b b                       (9) where a1 and a2 are real eigenvalues of system. the hamiltonian function of systems (1) with constant values (9) in minimum-time optimal control system is as follows:               1 1 1 2 2 2 2 , , 1 ( ) ( ) in h x t t u t t x t t x t v t u t           (10) where λ(t) is auxiliary variable of system status which is obtained as follows:      11 2 2 ( ) 0 0 0 1 int t u t v t                        (11) the optimal condition to apply pontryagin's minimum principle as well as hamiltonian’s minimum function (10) when compared to u(t) limited control input could be obtained as follows:       * max 2 min 2 0 0 u u t t u t       (12) due to lack of freedom of primary values in status auxiliary variables, minimum-time optimal control command is impossible by this method. on the contrary, according to (1), (3) and (9), system status variables will be obtained as follows:     11 1 0 txx t e  (13)         2 * * 2 2 2 0t x u t x t e u t      (14) where * u could be one and /or zero. because of the nature of the bang-bang, u(t) command and constant control input, the fastest way to damped fluctuations of system is to place trajectory system on the trajectory leading to equilibrium point. so, the optimal switching level could be obtained by (12)-(13) as reverse time dynamic so that the dynamics of the system could be utilized to move towards the equilibrium point [17]. so, as a result of independent variables’ dynamics in the above equations, the optimal switching level could be obtained by eliminating time from (12)-(13) and expressing parameter changes in terms of each other as follows:              12 1 1 * ln * 2 2 2 fx t x t fx u t x t e u t t         (15) iv. optimal control of fluctuating dynamic systems it is assumed that a, b1, b2 values in (1) are as follows: 1 2 0 0 , , 0 1 a b b                          (16) where a and ω are real and imaginary eigenvalues of system. the hamiltonian’s function in system (1) with constant values (15) in minimum-time optimal control system are as follows:                    1 1 1 2 2 2 2 1 2 , , 1 ( ) ( ) ( ) ( ) in h x t t u t t x t t x t t x t t x t v t u t                  (17) where λ(t) is the auxiliary variable of system status which is obtained as follows:      1 2 ( ) 0 1 int t u t v t                         (18) according to (16) and application of pontryagin's minimum principle as well as hamiltonian’s minimum engineering, technology & applied science research vol. 7, no. 4, 2017, 1753-1758 1755 www.etasr.com shariatmadar and jafarian: application of minimum-time optimal control system in buck-boost … function (10) compared to limited control input, (11) will be repeated. due to the nature of the bang-bang,  *u t command, constant control input and unlimited number of input control status changes, the minimum-time control trajectory for every control input status will be obtained separately:      1 1 2 * * 2 ( ) (0) cos (0) sin( ) sin( ) t n n x t e x t x t u t t u t                  (19)      2 2 1 * * 2 ( ) (0) cos( ) (0) sin( ) cos( ) ( ) t n n x t e x t x t u t t u t                  (20) while: 2 2 n    (21) as earlier mentioned, minimum-time optimal control is obtained by positioning system variables on trajectory resulting from system dynamics and leading them to the point. in fluctuating dynamic systems, with regard to bang-bang property of u(t) control input, hamiltonian’s minimum function (16) for λ2(t) changes as well as dependence of λ2(t) status auxiliary function signal on ω frequency, in minimumtime optimal function, u(t) control input for π/ω maximum time unit will be constant. so, minimum-time switching function to reach ultimate time or equilibrium point of system for lower π/ω time unit (as reverse time) related to moving on trajectory will result from system dynamics. thereafter, using the generalized results, minimum-time optimal control will be proved in bilinear systems. v. optimal control of bilinear systems hamiltonian’s function (1) with limited control input in minimum-time optimal control is as follows:          1 2 , , 1 ( ) ( ) ( )t in h x t t u t t a x t b x t u t b v       (22) where λ(t) is the auxiliary variable of system status which is defined as follows: 1 1 ( , , , , ) ( ) ( ) ( ) ( ) h x u v t t x a t b t u t              (23) the optimal condition to apply pontryagin's minimum principle and hamiltonian’s minimum function when compared to limited control input could be obtained (17). in bilinear systems with bang-bang input, depending on the type of control subsystems in each control input (dynamic, fluctuating or dynamic fluctuating), the switching optimum level will be determined. figure 1 illustrates the schematic of a buck-boost multiple area converter in nonlinear control of sliding mode. r1, r2 and rl are leakage resistance of the inductor, capacitor and output load respectively, vi represents the input voltage, t1 and t2 which are defined as u(t) in equations which are open and close at zero value respectively. in this converter, the status variables are defined as follows: rl il(t) 1 -1 + vout(t) vout(t)vref iref r2 t2 c switching surface k2k1 + _ + _ classical smc: k1=β1 k2=β2 optimal smc: k1=vout /vp k2=1 r3= r1/(r1-1) vi r1 r3 l r1 t2 + fig. 1. buck-boost multiple area converter schematic vi. minimum-time optimal control in buck-boost multiple area converter 1 2 1 0 ( )( ) ( )( ) 1 0 o li i l i tx t v c v tx t v                      (24) where v0(t) and il(t) are capacitor voltage and inductor current, vi is fixed nonregulated input voltage. with normalization of state-space model of buck-boost converter (figure 1), new equations could be expressed as follows: ( ) ( ) 2 1 1 1 2 ( ) 1 ( ) ( ) ( ) ( ) 1 ( ) ( ( ) )x u x u x x u q x t t t t t t t t += =  (25) where lq r c l and t lct = are quality coefficient and normalized time variable in buck-boost converter respectively. by comparing (1) and (34), normalized matrix of state space system is displayed as follows: 1 1 0 1 0 1 0 1 1 0 q                     1 1 2a b b (26) in this model, u(τ) is controllable input with two 0 and 1 variables. for u(τ)=1 value, system equations will be transformed into non-fluctuating dynamic form (9) and 1 21 , 0q   will be resulted. so, in this case, based on (12) and (13), x1(τ) and x2(τ) status variables could be defined as follows: engineering, technology & applied science research vol. 7, no. 4, 2017, 1753-1758 1756 www.etasr.com shariatmadar and jafarian: application of minimum-time optimal control system in buck-boost …    1 1 0 qxx e     (27)    2 2. 0iv xx    (28) therefore, minimum-time optimal switching level for ( ) 1u   command will be equal to:         1 1 ln 2 2 f x q x f ixx v e       (29) for u(τ)=0, the system equations (25) will be transformed into fluctuating dynamic form (15). accordingly, a and ω, by calculating eigen values of a matrix will be obtained as 21 41 , 2 2 q q q      . in this condition, based on (18) and (19) , x1new(τ) and x2new(τ) status variables could be defined as follows:         1 1 20 cos (0) sin ] new new new x e x x      (30)       2 2 1(0) cos (0) sin ] new new new x e x x      (31) and: 1 1 2 2 ( ) ( )0 ( ) ( )1 new new x t x t x t x t                 (32) figure 2 illustrates the minimum-time optimal switching level function in buck-boost system. fig. 2. optimal switchinglevel function in buck-boost converter vii. implementation and comparison of minimumtime optimal controller and classical sliding mode in buck-boost multiple area converter the switching level for sliding mode converter based on (4), is defined as follows: 1 2 1 1 2 2 ( , ) ( ) ( ) 0 sm ref ref s x x x v x i      (33) while β1=0, β2=1. closed loop under reduced output load of increased transient energy index is introduced to compare the transient operation of the two systems as follows: 2 0 ( ) ( ( ) ) t out refj t v t v dt  (34) the simulation results of output voltage and inductor current in buck-boost converter under reduction of load from rl=5ω to rl=15ω in classical and minimum-time optimal systems are illustrated in figures 3-4. the buck-boost parameters are shown in τable i. 0 50 100 150 200 0 1 2 3 4 5 time��s � i l �a� optimal smc classical smc 0 50 100 150 200 10 12 14 16 18 20 22 tim e��s � v o u t�v� classical smc optimal smc fig. 3. fig. 3. buck-boost multi area converter to reduce output load from 5 to 15ω. a) output voltage b) inductor current fig. 4. increased energy index of classical multi area converter and optimal buck-boost minimum-time systems under reduction of load from 5 to 15ω. the results indicated that despite the equality of maximum voltage amplitude of current in minimum-time optimal and classical sliding mode systems, the disturbance in minimumtime optimal systems was omitted within time less than similar classical systems. the increased energy index induced from output voltage (33) in minimum-time optimal systems is lower a b engineering, technology & applied science research vol. 7, no. 4, 2017, 1753-1758 1757 www.etasr.com shariatmadar and jafarian: application of minimum-time optimal control system in buck-boost … than classical systems (figure 4). figure 5 shows the experimental setup that provided for the test. figure 6 illustrates the applied results of reduced load which confirms the findings of analytical simulation analysis. in second condition, system performance under increased load from rl=15ω to rl=5ω in classical as well as minimum-time optimal systems has been compared and analyzed. the output voltage simulation results and inductor current with vp=7 v, vn=0 and vref=10 under increased load from rl=5ω to rl=15ω are illustrated in figure 7. according to this figure, we could say that inductor current needs to save more energy so as to achieve output voltage regulation within minimum time. fig. 5. experimental setup fig. 6. buck-boost multi area converter in reduced load from 5 to 15ω. a) schematic, b) optimal controller. despite the access to minimum regulation of output voltage in increased output load, voltage drop amplitude in minimumtime optimal systems is larger than similar classical sliding mode systems. so, application of minimum-time optimal control in buck-boost multi area converter enables us to remove disturbances in the least possible time and energy. in this situation, converter switching is a function of status variables (output voltage and inductor current) as though it will reach the maximum value simultaneously in output phase voltage phase and inductor current. so, the minimum-time optimal controller enhances the system dynamic performance and decreases the transient parameter of output overvoltage. vn table i. buckboost parameters nominal value parameter description 7 v vp positive voltage {0 or -7} vn negative voltage 3.4 μf c capacitance 96 μη l inductance {11 ω, 15 ω} r load resistance 10 v vref desired output voltage 0.2 ω r1 leakage resistance inductor 10-8 ω r2 leakage resistance capacitor 0 50 100 150 200 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 time��s � i l �a� optimal smc classical smc 0 50 100 150 200 2 4 6 8 10 time��s � v o ut �v� classicalsmc optimal smc fig. 7. classical converter and buck-boost minimum-time optimal systems in increased output load from 15 to 5ω. a) output voltage, b) inductor current viii. conclusion the present study examined the modeling and designing of minimum-time optimal controller of sliding mode in buckboost multi area converter systems. findings were also examined and analyzed. the results show that the application of switching level instead of classic model causes the output voltage regulation to be implemented within minimum time. b a a b engineering, technology & applied science research vol. 7, no. 4, 2017, 1753-1758 1758 www.etasr.com shariatmadar and jafarian: application of minimum-time optimal control system in buck-boost … however, the transient energy index of increased voltage in minimum-time optimal controller significantly decreases. by substituting optimal instead of classical switching surface, the output voltage could be regulated in minimum time. in addition, transient over voltage energy index in optimal buckboost smc for load step decreased was effectively reduced. references [1] h. p. nabi, p. dadashi, a. shoulaie, “a novel structure for vector control of symmetrical six-phase induction machines with three current sensors”, engineering, technology & applied science research,vol. 1, no. 2, pp. 23-29, 2011 [2] r. jadeja, a. ved, s. chauhan, “an investigation on the performance of random pwm controlled converters”, 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control for multi-quadrant buck converters”, iet power electronics, vol. 4, no. 1, pp. 143-146, 2011 microsoft word etasr_v12_n1_pp7998-8006 engineering, technology & applied science research vol. 12, no. 1, 2022, 7998-8006 7998 www.etasr.com alrfaay et al.: r-sor: ranked social-based routing protocol in opportunistic mobile social networks r-sor: ranked social-based routing protocol in opportunistic mobile social networks mohamad alrfaay common first year deanship jouf university sakaka, saudi arabia mhrifai@ju.edu.sa slim chaoui college of computer and information sciences jouf university sakaka, saudi arabia schaoui@ju.edu.sa aref kurd ali faculty of computer science and information technology universiti malaysia sarawak (unimas) sarawak, malaysia abhznk@gmail.com halikul lenando faculty of computer science and information technology universiti malaysia sarawak (unimas) sarawak, malaysia cool@unimas.my saad alanazi college of computer and information sciences jouf university sakaka, saudi arabia sanazi@ju.edu.sa abstract-exploiting social information to improve routing performance is an increasing trend in opportunistic mobile social networks (omsns). selecting the next message’s relay node based on the user’s social behavior is a critical factor in attaining a high delivery rate. so, to ascertain the most efficient selection of the next relay, the correlation between daily social activities and the social characteristics in the user profiles can be exploited. in this paper, we consider the impact of the social characteristics on mobile user activities during certain periods of the day and then rank these characteristics based on their relative importance in order to be included in the routing protocol. these processes consolidate the proposed ranked social-based routing (r-sor) protocol to provide an effective way for data dissemination in omsn. we use the real data set infocom06 to evaluate the proposed protocol. the experimental results show that the proposed protocol has higher routing efficiency than flooding-based protocols such as epsoc and epidemic, prediction-based protocols such as prophet, and social-based protocols such as msm and bubble rap. keywords-opportunistic networks; mobile social networks; data dissemination; social-based routing i. introduction nowadays, smart mobile devices are present in all areas of human activity. they transform the ways of sharing data into a new paradigm of mobile social networks (msns) [1-4]. msns combine the social features of users carrying mobile devices in the strategy for data delivery. in an opportunistic mobile social network (omsn), the mobile nodes communicate opportunistically and data forwarding occurs when they encounter each other. in other words, routes from the sender to the destination of a message are created dynamically, and any possible node can opportunistically be used for the next hop. for these reasons, data routing in such networks is a crucial challenge. the store-carry-forward (scf) method was developed as a data forwarding mechanism in opportunistic networks. with the scf mechanism, each node stores data packets in the buffer. when the node encounters another node, it forwards the duplicated data packets. as a result, network resources such as bandwidth and node packet buffers are consumed in large amounts. for this reason, selecting the appropriate relay is a major challenge and key issue in omsns. in [5], the performance of different routing protocols in opportunistic networks is analyzed. for instance, epidemic routing protocols [6, 7] use a flooding-based principle for spreading copies of messages to newly discovered contacts. prediction-based routing protocols, such as prophet [8, 9], use contact history between users to estimate nodes’ delivery probability which characterizes the probability of successfully delivering a message to the destination from a local node. social-based routing is an emerging research trend where researchers look for ways to use social information of individuals to assist routing as it has been found that people follow almost stable patterns in their social behavior [10]. routing in mobile networks is a challenging issue [11], networks such as the vehicular ad-hoc network (vanet) and corresponding author: mohamad alrfaay engineering, technology & applied science research vol. 12, no. 1, 2022, 7998-8006 7999 www.etasr.com alrfaay et al.: r-sor: ranked social-based routing protocol in opportunistic mobile social networks the wireless sensor network (wsn) require efficient routing protocols due to their dynamic topology [12, 13]. exploiting long-term social features in a disruptive and varied network environment for routing is a fruitful approach [14-16]. several social aware routing protocols have been proposed [17-19]. social aware schemes exploit different social metrics such as centrality [20, 21], similarity [22], betweenness [23], and social ties and friendship [24]. a user’s social profile contains a vector of several social features such as nationality, language, and topics of interest. these social features influence the social behavior and activity of the mobile user. for examples, persons of the same nationality contact each other more often, people having common interests and contacts do similar actions, individuals with common language tend to meet and talk with each other longer, etc. in addition, most people follow a stable pattern or routine in their daily life. generally, humans have different social activities at different periods of the day. the influence of social features changes according to the day period. for example, most people who meet in the evening share the same nationality or similar affiliations. the main objective of this work is to design an efficient forwarding scheme in order to achieve high delivery ratio and to decrease the network overhead. this is carried out by involving the ranking of social features with regard to a specific day slicing mechanism in the routing process. our contribution is focused on designing a ranked social-based routing protocol which is referred to as r-sor protocol that seeks to improve the performance of omsns by considering the regularity of users’ social behavior and by exploiting the relative impact of the social features during each day period. the contributions made under the proposed scheme are: • we define a set of social profiles which can be involved in the routing process of omsn. • we estimate the probabilistic behavior of social activities according to the dynamic changes over time with regard to the defined day periods. an algorithm for updating the nodes' periods is proposed for this purpose. • an algorithm for ranking social features according to their estimated probabilities is proposed. • we developed the proposed r-sor algorithm by selecting the best relay node having the highest rank of social feature similar to that of the destination in the current day period. in order to investigate the proposed r-sor approach, we carried out experiments using the real data set infocom06 [25] to explore the impact of different social features in different time periods. the result of the simulation experiments exhibits the efficiency of the r-sor protocol, in comparison to 5 benchmark routing protocols, namely flooding-based protocols such as epsoc and epidemic, prediction-based protocols such as prophet, and social-based protocols such as msm and bubble rap. ii. related works generally, routing schemes in omsns can be classified into different categories such as flooding-based, mobility prediction-based, context aware, and social aware protocols. the stability of human social preferences and the regular patterns that social behavior follows give the opportunity to develop information provision. several social features have been exploited by the research community [24]. for example, the simbet routing protocol utilizes two social features, similarity and betweenness, for the forwarding process [26]. the values of betweenness centrality and similarity for each node are estimated with the ego network analysis technique. only local available information is considered. messages are forwarded towards the node with higher betweenness centrality to increase the possibility of finding the potential carrier to the final destination. concentrating load on centralized nodes in simbet results in network congestion in theses nodes. in [27], the authors propose the bubble rap protocol which exploits two social and structural metrics, centrality and community. in this scheme, nodes belong to different sized communities and have different levels of centrality which was denoted as rank. there are two ranking types for each node, the local ranking inside the node’s community and the global ranking for the entire network. both levels of ranking are used for forwarding data. messages are forwarded to nodes having higher global ranking until a node in the destination’s community is encountered. then, the messages are forwarded to nodes having a higher local ranking within the destination’s community. however, employing the community detection methods require network information collecting and results to exchanges which lead to an overhead increase in the networks. the research in the utilization of multiple social features to develop effective social aware routing is gaining interest. the authors in [28], introduced the intelligent tree (int-tree) routing protocol which exploits social ties, community density, and similarity of interests to improve routing performance. intercommunity and intra-community communications were considered. for intra-community communications, the social ties between nodes are utilized to select the next forwarders. authors in [29] exploited both offline and online user’s social network information to propose a social-based forwarding strategy for opportunistic networks. they combined the dynamic online centrality and the detected centrality based on the contact history. thereupon, the delivery ratio was increased and the message replication number was reduced. authors in [30] proposed the multi-layer social network based opportunistic routing (ml-sor) protocol that considered the dynamics in social structure and user behavior by exploiting 3 social features, namely node centrality, community structure, and the social ties. offline temporal social information gained from nodes’ encountering and online static social information acquired from social networks were utilized for the better selection of the next carrier. authors in [31] proposed the proximity-interest-social (pis) routing protocol that considered 3 social factors, physical proximity, user interests, and user social relationships. these factors were used along with the slot time management mechanism and a copy control way to develop an effective forwarding scheme. authors in [32] proposed a multiple social metrics-based routing protocol where 3 social metrics were exploited, centrality, social similarity, and social activeness. forwarding decisions were made based on combinations of the impact of these three metrics and the correlation among them. engineering, technology & applied science research vol. 12, no. 1, 2022, 7998-8006 8000 www.etasr.com alrfaay et al.: r-sor: ranked social-based routing protocol in opportunistic mobile social networks authors in [33] proposed a social aware routing scheme which depends on the features of the opportunistic network. in this scheme, dependability ratio, usability ratio, and weight factor are calculated as weights of human activities to obtain the optimal cooperation nodes in the network. authors in [34] proposed the fuzzy routing-forwarding algorithm (fcns) which exploits comprehensive node similarity (social and mobile similarities) in opportunistic social networks. information about the state of the network is collected and updated to evaluate the social and mobile similarities of the nodes in the network, and then the transmission preference for each node is calculated through the fuzzy evaluation. the forwarding strategy depends on comparing the transmission preference of the nodes where the node with higher transmission preference will be selected as a message relay. in addition, fcns uses a feedback mechanism for more stable forwarding of the message in the network. the results showed good achievement in terms of delivery ratio and routing overhead. authors in [35] considered the context of social importance when exploiting social similarity to improve routing performance in mobile opportunistic networks. context information are recorded in nodes’ buffer and a relay node is selected if it has the most similar social behavior to the destination. authors in [19] proposed a hybrid routing scheme to enhance the routing efficiency of the epidemic protocol by exploiting social properties. degree centrality metric was used to adjust the time to live (ttl) value of the forwarded messages in the seeking of decrease the redundancy of epidemic protocol. thereupon, epsoc forwards messages towards the nodes that have higher degree centrality values. in contrast to these works where a limited number of social features and social activity patterns were considered in the implementation of the routing protocols, the proposed approach allows us to exploit all social characteristics available in a user’s social profile. the proposed approach considers the mutual correlation between the importance of a social feature and the node's interactions in the network. as long as the impact of different social features and social activity patterns over time is an important issue we also rank them according to user's social activity during different periods of the day. for each time period, we recorded and updated node contacts and ranked the social features based on their impact. the details of the proposed protocol and the related algorithms are presented below. iii. the r-sor protocol the r-sor protocol is a social-based routing protocol that ranks social characteristics and exploits them for efficient message forwarding in omsns. several social characteristics such as nationality, language, interest topics, membership, and hobbies can be stored in a user’s social profile. social behavior and activities of the people are a reflection of their social characteristics during their daily routine. for example, researchers with similar interesting research topics encounter each other and make a discussion for a long time during meeting activities, students with common hobbies tend to form groups and interconnect regularly in the campus, etc. these simple examples indicate that social features have an impact on the individuals' social behavior during their daily routine. in table i, the notations and definitions that will be use throughout the r-sor protocol algorithms are summarized. table i. used notations and definitions notation definition �� social feature. �� number of social features. f set of social features. p day time period. �� set of day time periods where the node i encounters other nodes in the network. �� � set of the encountered nodes by the node i at the day time period p. � � number of contacts between node i and node j in the day time period p. �,� � number of contacts of node i with other nodes that share same social feature �� at the day time period p. ��,� � social feature contact weight of a given social feature �� in the node i at the day period p. �� , � set of values of a social feature �� ∈ � in the node j at the day time period p. ���� highest ranked social feature of destination in the current day time period. a. updating nodes’ contacts per day time period people have daily routines, they follow almost stable patterns of social behavior in their everyday life. to consider the development of the people’s social behavior during the different time periods of their everyday life, we propose the slicing of the day into 6 time periods, each one 4 hours long, as depicted in figure 1. this division in different time periods has been reported in [33, 36] and evolves social structures that reflect the different interactions that users have over different daytime periods. each node records and updates the history of the nodes it encounters per time period, while roaming on the network. these contacts’ information set will be exploited to rank the social features. let � be the set of contact events during the day time period p, p=1,…, 6. a contact event c within a time period is characterized by the couple of contact nodes i and j and is denoted by �����,�,��. the number of contacts of a node i with a node j during a time period p is calculated based on the following equation: � � = ∑ �����,�,���∈�� (1) where �����, �, �� = 1 if there is a direct connection between i and j at the contact event c, otherwise �����, �,�� = 0. hence, the total number of contacts of node i in the time period p is calculated as: � � = ∑ � � ∈!" � (2) where �� � denotes the set of nodes encountering the node i within the time period p. algorithm 1, shown in figure 2 is used to update node contacts for each day time period. engineering, technology & applied science research vol. 12, no. 1, 2022, 7998-8006 8001 www.etasr.com alrfaay et al.: r-sor: ranked social-based routing protocol in opportunistic mobile social networks fig. 1. sor social feature for a node over day periods. fig. 2. algorithm 1: pseudo-code of update node’s periods. b. ranking social features mobile nodes have several social features stored in the user's profile. each social feature available in the user’s profile may have a single value, like the country feature, or multiple values such as the nationality and interesting topics. for every time period, the contacts with other nodes are recorded in the period contacts profile. accordingly, the social features of each node are ranked according to the number of contacts with other nodes that are associated with the same social features. let � = $�%, . . . ,�'() be the set of social features which can be associated to the nodes in the network, where �� is the number of social features included in the ranking process, and let �� ,� be the set of values that a social feature�� can take at the node i, * � 1,. . . ,��. for a given node i and a time period p, the number of contacts with other nodes that share the same social feature �� is counted and is denoted by �,� � . this is calculated using: �,� � � ∑ +� ��,�� ∈!" � (4) where +� ��, �� � 1 if �� ,� ∩ �� , ∅ . in other words, the number of contacts of the node i with regard to the social feature �� is incremented by 1 when a node j encounters the node i if and only if at least 1 value of the concerned social feature is similar in both nodes. accordingly, the weight of contacts associated with the social feature �� of node i at time period p is calculated by: ��,� � � �",/ � �" � (5) it is worth noting that ��,� � is a measure of significance of a given social feature ��and is referred to as social feature contact (sfc) weight. the main idea behind this work is to involve the values of the sfc weights in the ranking process of the social features which is ultimately used as input in the forwarding decision. to this end, the sfc weights of each node in the network are calculated and stored in ascending order in the node's profile. the social feature that has the highest sfc weight value is the top-ranked social feature and is considered as the most impactful on the message forwarding process. algorithm 2 (figure 3) is used to record and update the ranked vector of the social features. fig. 3. algorithm 2: pseudo-code of ranking social features. engineering, technology & applied science research vol. 12, no. 1, 2022, 7998-8006 8002 www.etasr.com alrfaay et al.: r-sor: ranked social-based routing protocol in opportunistic mobile social networks c. r-sor forwarding strategy the r-sor protocol includes two steps before starting the message forwarding process. the first step is devoted to reap the patterns of the mobile user’s social behavior in the corresponding day time period while the second step is to rank the sfc weights that will be involved in the forwarding decision. based on the aforementioned description, every node ranks its social features per time period using the algorithm 2. algorithm 3 describes the proposed r-sor algorithm for message forwarding. let node i be the current node. if a node j encounters the node i, then at first, node j will be checked for the availability of the destination’s top-ranked social feature in its social profile. if available, then the number of contacts regarding this feature in node j will be compared to that in node i. if the number of concerned contacts of node j is greater than that of node i, then the message will be forward to node j else node i will still carrying the message. a message forwarding will also occur if the destination’s top-ranked social feature is available in node j but not available in node i. fig. 4. forwarding process in sor. figure 4 shows an example of the message forwarding process. let s and d be the sender and destination pair nodes respectively, and let n1, n2, and n3 be the intermediate nodes which are candidates for the next forwarding process. assume that in the current day time period, the top-ranked social feature for node d is the "language". node s will select from the intermediate nodes (n1, n2, and n3) that have common languages, in this case nodes n1 and n3, will be selected. node s will further choose the node that has the highest rank for language feature, in this example n3. the forwarding algorithm is shown in figure 5 (algorithm 3). iv. performance evaluation a. data set the dataset infocom06 [25] was used for the simulations. this dataset is suitable for this study because of the viability of social characteristics of the mobile users. the participants were asked for filling answers in a questionnaire about different social features. we obtained this social information and attached it as social profiles for the mobile users in our experiments. we exploited the 10 available social characteristics, namely nationality, studies, languages, affiliation position, city, country, stay, member and topics. in this dataset, 78 mobile imotes have a wireless range of around 30 meters using bluetooth technology for communication. the encountering nodes within the short range of the 78 nodes are saved and tracked. fig. 5. algorithm 3: pseudo-code of r-sor forwarding algorithm. b. simulation setup the opportunistic network environment (one) [37] was used to conduct the experiments and to evaluate the proposed protocol. one is a java-based simulation program which is designed primarily for opportunistic networks. the performance of the proposed r-sor protocol is compared with that of 5 benchmark routing protocols, namely epidemic and epsoc which are flooding-based routing protocols, prophet which is a prediction-based routing protocol and bubble rap and msm which are social-based routing protocols. the simulation settings are summarized in table ii. engineering, technology & applied science research vol. 12, no. 1, 2022, 7998-8006 8003 www.etasr.com alrfaay et al.: r-sor: ranked social-based routing protocol in opportunistic mobile social networks table ii. simulation settings parameter value interface bluetooth number of nodes 78 short range devices transmission speed 2 mbps mobility real trace data (infocom06) buffer size 1, 2, 5, 15, 25, 35, 45, 55 mb routing protocols r-sor, epidemic, prophet, bubblerap, epsoc, and msm message size 128 kb message frequency 1 message every 30 to 40s in each experiment, we evaluate the performance of considered protocols based on the following metrics: • successful delivery ratio: it is the ratio between the number of delivered messages and the total number of created messages. the ideal value of the successful delivery ratio is 1.0. this is attained when all created messages are delivered to their destinations. • overhead ratio: it reflects how many redundant messages are transmitted to deliver one message. it simply reflects the transmission cost in a network. • average latency: it is the average of the time elapsed between message creation and delivery. • average hop count: it is the average number of hops that messages traverse to reach the destination. c. experiments and results to evaluate the performance of the r-sor protocol and provide a comparison against the performances of the other protocols, message ttl and buffer size values are varied in the carried experiments. it is worth noting that ttl and buffer size have a crucial impact on the routing performance in omsns because of the opportunistic behavior of the mobile node communication and the use of the scf mechanism for message passing. figures 6-9 show the performance of the proposed rsor protocol compared to that of the other routing protocols in terms of delivery ratio, overhead ratio, average latency, and average hop count. the experiments were carried out for different ttl values around the values given in table ii (from 10m until 1.6 days). figure 6 shows the delivery ratio performances of the different protocols with varying ttl. the figure shows that for low-range ttl values (10m-1h), the delivery ratio performance of all the routing protocols are low, due to the fact that the ttl value of a dropped message is set to 0. increasing the ttl value causes rising up the delivery ratio (from ttl value of 8h, we observe a certain saturation), due to the delivering of quite a lot of messages to the destinations. for higher ttl values (over 16h), the delivery ratio decreases slightly with further ttl increase. this is the result of the increased number of carried and ultimately dropped messages in the networks which affects negatively the delivery ratio. the figure reveals that the r-sor protocol outperforms all other protocols for ttl values higher than 8h. hence, messages with high ttl value are more probably carried by nodes that have strong social relations enabling rsor to achieve higher delivery ratio. the r-sor protocol considers the regular patterns of the users' social activity during their everyday life and carries out a ranking of the social characteristics based on the encountering rate in each day time period. this finding strongly implies that the adopted raking strategy leads to the selection of the relay node that has higher probability to encounter the destination. fig. 6. delivery ratio over ttl change. fig. 7. overhead ratio over ttl change. figure 7 presents the relationship between the overhead ratio and ttl value. it can be seen that the r-sor protocol outperforms the epidemic, prophet and bubble rap protocols and its superiority is obviously manifested at high ttl values (higher than 1h). in these scenarios, messages do not expire quickly, which enables the r-sor protocol to update the contact profiles of the nodes and ultimately to rank the social characteristics in each day time period. the r-sor protocol considers all social characteristics in the user’s profile and ranks them according to the social activities of the mobile nodes for each period. as a result, nodes with strong social relationships with the destination node are chosen as relays. this reduces the number of intermediate nodes involved in the forwarding process and increases the likelihood of delivering the message, and consequently, the overhead ratio is decreased substantially. in addition, figure 7 shows that the overhead ratio of the epsoc and msm protocols is lower than that of the r-sor protocol. this can be explained by the fact that these protocols apply rigorously defined rules for selecting the next forwarder. nonetheless, negative impact on the delivery ratio is pronounced as outlined in figure 6. 0 500 1000 1500 2000 2500 0 0.1 0.2 0.3 0.4 0.5 ttl (minutes) d e li v e ry r a ti o r-sor msm epsoc bubblerap prophet epidemic 0 500 1000 1500 2000 2500 0 200 400 600 800 1000 1200 1400 ttl (minutes) o v e rh e a d r a ti o r-sor msm epsoc bubblerap prophet epidemic engineering, technology & applied science research vol. 12, no. 1, 2022, 7998-8006 8004 www.etasr.com alrfaay et al.: r-sor: ranked social-based routing protocol in opportunistic mobile social networks fig. 8. average latency over ttl change. figure 8 shows that the higher the ttl-value, the higher the average latency for all protocols. it is worth noting that raising the ttl gives the messages the opportunity to traverse longer paths to reach their destinations. hence, the higher the ttl value, the higher the average end-to-end delay. we see that the r-sor protocol outperforms the others in terms of average latency, with the exceptions of epidemic and epsoc which are the most prominent protocols regarding this evaluation metric because of their flooding-based forwarding strategy. the figure reveals that choosing the appropriate relay based on the social feature ranking increases the likelihood to encounter the destination, so messages are delivered in less time, and thus the effectiveness of the r-sor protocol in terms of the average latency metric is confirmed. the performance evaluation of the protocols regarding the average hop count is shown in figure 9. as the ttl increases, the hop counts increase for all protocols until they reach stable levels. the epidemic protocol performance is affected by the ttl variation more than the other protocols because of its floodingbased forwarding strategy. the figure shows that the r-sor protocol outperforms the non-social-based protocols (epidemic and prophet). the hop counts are reduced in r-sor because exploiting social features limit the number of candidate relay nodes, as a relay node is only chosen if it has a similar value to the destination's top-ranked social feature. comparing to social-based protocols (bubble rap, epsoc, and msm) the rsor protocol has a similar-to-slightly better performance fig. 9. average hop count over ttl change. in the following experiments the performance metrics are evaluated by varying the buffer size while the ttl value is set to a constant value (10 hours). this value is selected based on the evaluation of the previous experiments. all protocols have good performance for this ttl value. the message size is set to 128kb. three levels of buffer size will be considered in this study, namely low level (1, 2, and 5mb), middle level (15, 25, and 35mb), and high level (45 and 55mb). it is worth noting that increasing the buffer size means increasing the capacity of messages a mobile node can carry. figure 10 shows the performance of the protocols in terms of delivery ratio with varying buffer size. it is obvious that increasing the buffer size leads to increased delivery ratios for all routing protocols. a higher buffer size enables the mobile nodes to store and carry more messages and ultimately to deliver them to the destinations. the figure illustrates that the r-sor protocol outperforms the other protocols with respect to the delivery ratio for all buffer size levels. moreover, the figure shows that the superiority of the r-sor protocol over the others is better exhibited at low and middle buffer size levels. this can be explained by the fact that the r-sor protocol manages the buffer size more efficiently than the other protocols. the r-sor involves all the social characteristics of the mobile users and adopts the ranking algorithm to select the next relay node. this leads to forwarding messages only to nodes that provide higher likelihood to encounter the destination. consequently, the r-sor protocol will be an effective forwarding mechanism especially in resourceconstrained opportunistic networks. fig. 10. delivery ratio over buffer size change. figure 11 outlines the overhead ratio with varying buffer size value for all protocols. it is obvious that increasing the buffer size results in decreasing the overhead ratio in the omsn as intermediate nodes are enabled to carry more messages for later delivery. the r-sor protocol shows a low overhead ratio in the omsn. it outperforms epidemic, prophet, and bubble rap protocols, especially for low buffer size levels. moreover, the figure shows that the r-sor protocol slightly outperforms the epsoc and msm protocols due to the fact that they apply strict social-based forwarding decision rules. nonetheless, the delivery ratio for these protocols is lower than that of the proposed r-sor protocol as shown in figure 10. 0 500 1000 1500 2000 2500 0 0.5 1 1.5 2 x 10 4 ttl (minutes) a v e ra g e l a te n c y r-sor msm epsoc bubblerap prophet epidemic 0 500 1000 1500 2000 2500 0 2 4 6 8 10 12 14 ttl (minutes) a v e ra g e h o p c o u n t r-sor msm epsoc bubblerap prophet epidemic 0 10 20 30 40 50 60 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 buffer size (mb) d e li v e ry r a ti o r-sor msm epsoc bubblerap prophet epidemic engineering, technology & applied science research vol. 12, no. 1, 2022, 7998-8006 8005 www.etasr.com alrfaay et al.: r-sor: ranked social-based routing protocol in opportunistic mobile social networks fig. 11. overhead ratio over buffer size change. figure 12 shows the performance of the routing protocols in terms of average latency with varying buffer size. it can be seen that increasing the buffer size results to an increase in the average latency. consequently, the messages will have a larger end-to-end delay to reach the destinations. for low buffer size levels, it is observed that the r-sor protocol has lower average latency than prophet, bubble rap, and msm protocols while the epidemic and epsoc protocols outperform all protocols due to their flooding-based forwarding strategy. fig. 12. average latency over buffer size change. fig. 13. average hop count over buffer size change. exploiting users' social characteristics and ranking them based on the encountering rate in each time period enable the r-sor to select the forwarder node that has the higher likelihood to deliver the message in a lower end-to-end delay. increasing the buffer size above 25mb, r-sor, prophet, and bubble rap protocols achieve almost similar performance. they benefit from the ability to store more messages in the mobile nodes and they outperform epidemic, epsoc, and msm. the average hop count evaluation results are shown in figure 13. the figure reveals that the r-sor protocol achieves low hop count and outperforms the epidemic and prophet protocols due to the fact that only nodes that have similarity with the top ranked social feature of the destination will be selected for message forwarding. hence, a low number of nodes will corporate in delivering the messages in the omsn and hence a low average hop count is attained. the achievement of the r-sor protocol in terms of average hop count is close to that of the bubble rap and epsoc protocols and is slightly higher than that of the msm protocol. this is because the msm protocol applies stricter rules in forwarding messages than the r-sor protocol as it exploits multiple social metrics for relay selection which leads to the decrease of the intermediate nodes. however, as we mentioned before and as shown in figure 10, this impacts negatively the performance in terms of delivery ratio, where the r-sor protocol outperforms the msm protocol. v. conclusion in this paper, the r-sor protocol is proposed, which aims to enhance the routing efficiency in omsns. the r-sor protocol ranks the social properties of the mobile users in an omsn during day time periods, and exploits the impact of social features in order to develop a more efficient forwarding scheme. the empirical results using real data show that the rsor outperforms other benchmark protocols, namely floodingbased protocols such as epsoc and epidemic, prediction-based protocols such as prophet, 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[37] a. keränen, j. ott, and t. kärkkäinen, "the one simulator for dtn protocol evaluation," presented at the 2nd international icst conference on simulation tools and techniques, rome, italy, may 2010, https://doi.org/10.4108/icst.simutools2009.5674. microsoft word etasr_v12_n6_pp9536-9545 engineering, technology & applied science research vol. 12, no. 6, 2022, 9536-9545 9536 www.etasr.com nasir: determination of the harmonic losses in an induction motor fed by an inverter determination of the harmonic losses in an induction motor fed by an inverter bilal abdullah nasir department of electrical techniques northern technical university mosul, iraq bilalalnasir@ntu.edu.iq received: 24 april 2022 | revised: 16 may 2022 | accepted: 19 may 2022 abstract-the advancement, development, improvement, and increased use of power electronic converters led to the efficient speed control of electrical drives. the most famous three-phase induction motor-related control to pulse-width modulation (pwm) technique is used to operate multilevel inverters such as variable-frequency or six-step voltage source inverter (vsi). switching devices of the inverter are used in the drive systems and act as the main source of harmonics. when the induction motor is fed from the pwm inverter, it will be supplied by low order (5th, 7th, 11th) time harmonic voltage. the motor performance is affected by the presence of these time harmonic components because the additional losses generated in the motor defect its performance, generate pulsating torque, and reduce efficiency. in this work, the analysis of a dynamic model of an induction motor in transient and steady-state operation is developed, considering the effect of time-harmonic voltages generated by the inverter, skin effect, skew effect, temperature rise effect, iron core loss, stray load loss, and magnetic saturation on the motor performance. the performance of the motor is studied by the time-harmonic equivalent circuit and by the fundamental equivalent circuit. the motor performance in terms of efficiency and power factor is compared with the experimental results for both sinusoidal and vsi motor feeds in order to validate the model accuracy. keywords-dynamic modeling; additional losses; 3-phase bridge inverter; 3-phase diode rectifier; harmonic equivalent circuit; switching functions i. introduction it has been observed that the electrical machine losses increase if the supply voltage has harmonics. this gained attention at the early '70s, as the machines were supplied with static six-step inverters. the additional ohmic losses were produced in the machine windings due to the flowing of harmonic currents. the ohmic losses in the rotor windings of the induction machines can increase considerably due to the skin effect. there is also an increase in the machine iron losses due to the flowing of harmonic currents [1-5]. at low harmonic frequency (< 2.5khz), the harmonic losses are also increased with the machine load due to the slight reduction of the machine inductances caused by the saturation effect [6-7]. measuring the harmonic losses in electrical machines is a very complex task, and its determination by subtracting the output power from the input power is very sensitive to errors of measurement [8]. at the beginning of this century, the calculation of harmonic losses was extended by numerical methods with computer analysis based on the finite element method (fem) [9-11]. in numerical methods, the computational process is a heavy burden and the complete structure of the machine has to be known [12]. the early adopted six-step inverters showed a defect in machine performance due to the pulsating torques and increasing harmonic losses [13-14]. in modern semiconducting techniques, the switching frequency and modulation index of pwm variable speed drives can be allowed to be further increased and eliminate all harmonics below the switching frequency. although this technique can increase the machine performance and reduce noise emissions, the machine harmonic losses cannot be reduced considerably by increasing the switching frequency above 10khz [15-24]. to model the harmonic losses of the induction machines with different power ratings, a complete equivalent circuit including all harmonic loss components was first presented in [5]. in this circuit, the resistances are connected in parallel to the leakage inductances accounting for the harmonic stray load losses in the machine windings. the harmonic losses due to the skew-effect and skineffect are not included in this equivalent circuit model. all the equivalent circuit impedances must be frequency-dependent to take effect on the skin [25-28]. variable speed drives are commonly used in many industrial applications. to supply the motor with variable frequency, the induction motor is fed from the six-step uncontrolled rectifier and the rectifier output is connected to the six-step voltage source inverter (vsi). two capacitors are connected across the rectifier output to remove the ripple. due to the motor being fed from the switching inverter, the dynamic model developed to study the motor performance must be valid for any voltage and current waveform. a complete dynamic model is required for harmonics analysis. the model must include the main parameters of the machine for transient and steady-state operation. in this paper, an accurate dynamic model of the induction motor fed from a six-step vsi is presented using the switching functions for inverter modeling and the d-q axes synchronously rotating reference frame corresponding author: bilal abdullah nasir engineering, technology & applied science research vol. 12, no. 6, 2022, 9536-9545 9537 www.etasr.com nasir: determination of the harmonic losses in an induction motor fed by an inverter model for induction motor modeling. in this comprehensive modeling, the harmonics, as additional losses, are calculated and analyzed easily. the accuracy of the model has been verified through matlab simulations and the harmonic equivalent circuit of the machine, which is presented in this work as a powerful tool for motor performance calculation. ii. modeling of the induction motor an accurate estimation parameter of the induction motorequivalent circuit is required to implement these parameters for high-performance determination. the stator and rotor winding temperatures can be determined according to the ieee standard 112-b by measuring the stator no-load and load currents, and the rotor current is determined at different load conditions. the skin effect on the stator parameters can be determined from the stator geometry. the iron core resistances are determined from the no-load test considering the effect of slip and core temperature. the magnetizing reactance is calculated from the no-load test at different supply voltages and rated frequencies to consider the saturation effect. the stator and rotor winding resistances �� and �� � depend on temperature variation and skin effect. the stator and rotor leakage reactances �ℓ� and �� ℓ� depend on skin effect and saturation. the magnetizing inductance �� depends on the magnetic saturation. the iron core resistance �� depends on motor slip and iron core temperature. fig. 1. the proposed fundamental circuit of induction motor. the proposed equivalent circuit in figure 1 contains the additional resistances ����ℓ and ����ℓ that model the stray losses in the stator and rotor circuits. the stray losses depend on the voltage drops due to the leakage reactance, the iron core resistances, and stator and rotor resistance. also, the proposed equivalent circuit can deal with the effect of rotor skewing on the parameters of the rotor circuit. the iron core resistance is varied with the temperature and air-gap voltage and is calculated from the no-load test of the motor as [25]: �� = �� ∕ ��� ∗ (��ℓ − �� ∗ �� )� (1) �� = �� ∗ �� = �� ∗ �� ∗ sin (ϕ�) (2) �� = !"ℓ#$%&∗'ℓ(') * +& (3) where �� is the magnetizing voltage per phase and is calculated in terms of magnetizing reactance �� , magnetizing current �� , no-load current �� , and no-load sine of power factor angle sinφο. the iron core resistance was obtained in terms of air-gap voltage from the no-load test and curve-fitting technique [25]. ��= (1-d) is the temperature coefficient of the iron core loss, and d is the iron core power loss varying rate per , � determined as [25]: = .�� (�/) − �� (�)0 �� (�/)1 (4) where �� (�/) and �� (�) represent the iron core power losses at ambient temperature and at any temperature. these iron core power losses are measured from the no-load test. ��ℓ is the active no-load power loss per phase, ��� is the stator resistance per phase at ambient temperature, 2�ℓ is the reactive no-load power loss per phase, and �ℓ� is the stator leakage reactance per phase. the rotor load resistance ��� �(1 − 4)/4 is derived in terms of rotor phase resistance �� � and rotor series stray loss resistance ����ℓ as: ��� �(1 − 4) 4⁄ = 1 1 78� 9(:#�)� − ����ℓ; − 1 �<=⁄1 *1 (5) where �<= is the mechanical loss resistance. the nonlinearity of the machine iron core and mechanical resistances due to the saturation of the magnetic core is considered by the dynamic model to improve the accuracy of simulation results. the resistances �� and �<= are determined practically from the noload test at zero slip to be modeled by polynomial-curve fitting as: �� = −0.0001985 ∗ ��c + 0.111 ∗ �� − 23.11 ∗ �� + 840 (6) �<h = −6.167 ∗ ��k + 0.00419 ∗ ��c − 1.074 ∗ �� +127.4 ∗ �� + 560 (7) the resistance of the iron core �� can be referred to on the stator and rotor circuits as a voltage drop to keep the dynamic 4 th order model fixed while the effect of the iron core loss in the dynamic model of figure 2 is considered. the reflecting resistances on the stator circuit ���� and on the rotor circuit ���� are calculated as [26]: ���� = (�� ∗ l� ∗ mn ) ∕ ��� + (l� + mn ) � (8) ���� = 4 ∗ ���� (9) where 4 is the motor slip and mn is the magnetizing inductance per phase obtained from the no-load test as: engineering, technology & applied science research vol. 12, no. 6, 2022, 9536-9545 9538 www.etasr.com nasir: determination of the harmonic losses in an induction motor fed by an inverter mn = �� ∕ l� (10) where l� = (2 ∗ o ∗ p) is the angular frequency in rad/s. the modified magnetizing inductance m� of the dynamic model (figure 2) is calculated as: m� = mn ∗ �� ∕ ��� + (l� ∗ mn ) � (11) the stray load loss resistances vary with the variation of stator and rotor resistances due to the temperature variation. these resistances are derived and introduced in the dynamic model as series resistances in the stator and rotor circuits [27]: ����ℓ = (l� ∗ mℓ� ) ∗ �� ∕ ��� + (l� ∗ mℓ� ) � (12) ����ℓ = q ∗ (l� ∗ m´ℓ� ) ∕ �´� (13) where ����ℓ and ����ℓ are the series stator and rotor winding stray-load loss resistances respectively, q is the motor slip, and mℓ� is the rotor leakage inductance per phase. all induction motors and generators operate in the saturation region and their characteristics are non-linear. the variation of magnetizing reactance �� is the main factor in producing the magnetizing voltage ��, which is the main factor that produces the iron-core losses, rotor current, mechanical losses, and output power. the saturation reduces �� and tends to increase. the saturation effect is taken by the relation �� = p(��). this function is obtained practically from the noload test by varying the supply voltage from 125% to 25% of the rated value. then the measurements of �� and �� can be interpolated by the curve fitting technique. (a) (b) fig. 2. (a) d-axis and (b) q-axis equivalent circuit models of the induction motor in the synchronously rotating frame. the rotor phase leakage reactance ��� ℓ� is corrected by the skew factor ��s [25]: ��� ℓ� = ')t(u& v1 − ��s w + ' � ℓ9 t(u& (14) ��s = 4xy z[∗\]!9 ^ ∕ vo ∗ �_ ∕ 2� w (15) where �_ is the machine magnetic pole-pair, and 2� is the number of rotor slots (bars). the rotor phase resistance is corrected by the skew factor as: ��� � = �� � ∕ ��s (16) the rotor phase resistance and leakage reactance are corrected by the skin effect as [25]: ���� � = ��� � ∗ . 0.5 + 0.5 ∗ `q� q�⁄ 0 (17) ���� ℓ� = ��� ℓ� ∗ . 0.4 + 0.6 ∗ `q� q�⁄ 0 (18) where q� is the rated machine slip and q� is the machine slip at maximum torque which can be given as [27]: q� = (�� � + ����ℓ) ∕ .(�� + ����ℓ) + (�ℓ� + �� ℓ� ) 0½ (19) also, the machine slip can be corrected due to the temperature effect as [25]: engineering, technology & applied science research vol. 12, no. 6, 2022, 9536-9545 9539 www.etasr.com nasir: determination of the harmonic losses in an induction motor fed by an inverter q��,� = q�,� ∗ (c� + �d ) ∕ (c�e< + �d ) (20) where c� is the rotor bar temperature at any load, c�e< is the temperature of insulation class level, which can be obtained from the insulation class table, and �d is a constant equal to 225 for aluminum rotor bar type. the dynamic electrical equations of the induction motor are derived from the proposed equivalent circuit in figure 2 as: f�g = (�� + ����ℓ + ���� ) x�g + ���� ∗ h́�g − l� ∗ m� ∗ h́�s (21) f�s = l� ∗ (mℓ� + m�) ∗ x�g + l� ∗ m� ∗ h́�g (22) j = ���� ∗ x�g + z���� � + ����ℓ + ���� ^ ∗ h́�g + l�ℓ ∗ zm��� ℓ� + m�^ h́�s (23) j = l�ℓ ∗ m� ∗ x�g + l�ℓ ∗ zm��� ℓ� + m�^ ∗ h́�g + z���� � + ����ℓ + ���� ^ ∗ h́�s (24) where l�ℓ = l� − l� = 4 ∗ l� is the slip speed in rad/s, l� = �_ ∗ l� is the electrical angular speed of the motor in rad/s, and k�g , k�s , k� �g and k� �s are the stator and rotor flux linkages in the d-q axes of figure 2 respectively, defined as : k�g = mℓ� ∗ x�g + m� ∗ x�g (25) k�s = mℓ� ∗ x�s + m� ∗ x�s (26) k� �g = m��� ℓ� ∗ h́�g + m� ∗ x�g (27) k� �s = m��� ℓ� ∗ h́�s + m� ∗ x�s (28) where x�g , h́�g , x�s, and h́�s are stator and rotor currents in the d and q axes respectively. the rotor mechanical speed l� is calculated from the dynamic mechanical model as: g=) gl = :m vce − cℓ − �< ∗ l�w (29) where ce is the electromagnetic torque of the motor, calculated as [27]: ce = zc ^ ∗ �_ ∗ m� ∗ (x�g ∗ h́�s − x�s ∗ h́�g ) (30) where cℓ is the motor load torque (n.m), n is the moment of inertia (��. o ), �_ is the magnetic pole-pair number, and �< is the viscosity resistance factor (n.m/(rad/s)). iii. modeling of the six-step voltage source inverter the matlab simulation tool was utilized for the design and analysis of the power inverter system. the switching function method can be used to represent the inverter itself. inverter harmonics and switching losses can be calculated through simulations. the switching function method is used when the exact physical forms of the power electronic switches such as transistors and thyristors are not of concern. using the concept of the switching function, inverters can be modeled for performance calculation. the transfer function model has several advantages in modeling vsis. the power circuit of the inverter can be simplified into input and output variables and calculated easily, the inverter topologies can be derived easily, and the implementation of gating control pulses are simpler. based on the theory of the transfer function of the vsi, the dc input voltage �g to the inverter and the output currents (xd, xp, x ) are independent variables, while the input current �g and the output line voltages (qdp , qp , q d ) are dependent variables. these variables are related as [20]: [qdp , qp , q d ] = [tf] [�g ] (31) [�g ] = [tf] [ xd , xp , x ] (32) where [tf] is the transfer function of the vsi, expressed in the form of switching functions of the three-phase bridge vsi. figure 3 shows the schematic diagram of the whole system containing the vsi fed 3-phase induction motor system. the sinusoidal 3-phase supply feeds the 3-phase uncontrolled diode bridge rectifier. a dc link with two capacitances is connected across the output diode rectifier to remove the ripple. the vsi behaves as a 3-phase voltage source to the induction motor. fig. 3. rectifier-inverter-induction motor system. let q:, q , qc, qk, qr, and qs be the switching functions for the three legs (a, b, c). q: and qk for pole (a), qc and qs for pole (b), and qr and q for pole (c). the switching function is defined as 1 when the switch is on and 0 when the switch is off. by applying kirchhoff's voltage law to the closed-loop in the circuit in figure 3, taking the conditions corresponding to the switching functions for each leg and after series manipulation, the motor (load) phase voltages become [29]: qd/ = tuvs (2q: + q − qc − 2qk − qr + qs) (33) engineering, technology & applied science research vol. 12, no. 6, 2022, 9536-9545 9540 www.etasr.com nasir: determination of the harmonic losses in an induction motor fed by an inverter qp/ = tuvs (2qc + q − q − 2qs − qr + qk) (34) q / = tuvs (2qr + qk − qk − 2q − qc + qs) (35) the input dc (�g ) to the 3-phase inverter is expressed in terms of switching functions ( q: ⟶ qs) and inverter output currents (xd , xp , x ) as : �g = (q: − qk). xd + (qc − qs). xp + (qr − q ). x (36) iv. modeling of the 3-phase bridge rectifier by using the 3-phase bridge diode rectifier, the 3-phase ag input power supply ( qd , qp , q ) is converted into the dc voltage (�g ) output power supply to the inverter. the input supply voltages are given as: qd = �� . sin (lx) (37) qp = �� . sin (lx − 2π/3) (38) q = �� . sin (lx + 2π/3) (39) where �� is the maximum supply voltage. the switching functions ( q: − qs ) of the diode bridge rectifier have the same expression as the voltage source inverter. the input and output variables of the 3-phase diode bridge rectifier are related as: zxdxpx { = zq:qcqr − qkqsq { . ��g � (40) ��g � = �(q: − qk). (qc − qs). (qr − q )�. z qdqpq { (41) the three-phase supply voltages are converted to d-q axis components using the transformation matrix as: |�g�s } = | cos(lx) cos(lx + 2π/3) ��4(lx − 2π/3)− sin(lx) −sin(lx + 2π/3) − 4xy(lx − 2π/3)} . z qdqpq { (42) where �g and �s are the components of the synchronously rotating d-q axes of the supply voltages. the output dc voltage of the bridge rectifier is expressed as: �g = c.√c[ . .�g + �s 0 +& (43) v. harmonic equivalent circuit and performance calculation the proposed fundamental equivalent circuit of the induction motor is shown in figure 1, where �� , �ℓ�, and ����ℓ are the stator winding resistance, leakage reactance, and stray load loss resistance respectively, while �� � , ����ℓ, and �� ℓ� are rotor winding resistance, stray loss resistance, and leakage reactance respectively, �� is the magnetizing reactance, �� is the iron core loss resistance, �<= is the friction and windage (mechanical) loss resistance, and ��� � (1 − 4) 4⁄ is the motor load resistance, considering the effect of rotor stray load resistance ����ℓ and mechanical resistance �<= into account, as calculated by (5). there are two types of harmonics generated in the induction motor. the first type is the space harmonic generated in the air gap as pulsating torques due to the magnetic interaction between different phases to produce the revolving magnetic field in the air gap. space harmonics are reduced by improved design procedures and optimization [30]. these harmonics affect the motor starting and generate noise and vibration. the second type is the time-harmonics, which are generated due to the applications of variable frequency drives in modern power systems using six-step vsis. time harmonics increase the motor heat by increasing the motor temperature. the timeharmonic losses are generated due to the inverter switching and are impressed in the machine as additional losses. the additional time-harmonic losses are not load-dependent. for a balanced 3-phase inverter output voltage supply, only the odd harmonics should be taken into account. the third and its multiple harmonics are in the same phase and should also not be considered. considering only the non-triple odd harmonics (5 th , 7 th , 11 th , etc.), the fourier series of the phase voltages are given as [27]: qd = �:� . sin(l� x) + �r� . sin(5l� x) + ��� . sin(7l� x) + ... (44) qp/ = �:� . sin(l�x − 120°) + �r� . sin(5l� x − 120° ) +��� . sin(7l�x − 120°) + …. (45) q / = �:� . sin(l�x + 120°) + �r� . sin(5l�x + 120° ) +��� . sin(7l�x + 120°) + …. (46) where �:� , �r� , ��� are the maximum values of the fundamental, 5 th , and 7 th harmonic components and l� is the angular frequency of the supply voltage. for each harmonic component, the motor equivalent circuit components are approximately represented by multiplying these components by a constant factor k, which represents the order of the harmonic. the fundamental circuit of figure 1 is converted to a time-harmonic equivalent circuit as shown in figure 4, taking the effect of core loss resistance �� as a voltage drop in the stator and rotor circuits. resistances ���� � and ���� � are reflected series resistances of the iron core harmonic resistance �� � at the stator and rotor windings [25]. fig. 4. proposed equivalent circuit for time-harmonic calculation. equations (44)-(46) of the output inverter phase voltage indicate that the 5 th harmonic voltage component has a negative phase sequence, whereas the 7 th harmonic has a positive phase engineering, technology & applied science research vol. 12, no. 6, 2022, 9536-9545 9541 www.etasr.com nasir: determination of the harmonic losses in an induction motor fed by an inverter sequence like the fundamental component. the magnetic flux generated in the air gap due to the 5 th harmonics opposes that due to the 7 th harmonics. the rotor speed is related to the fundamental frequency, and it appears practically constant concerning the harmonic field is given as [31]: q� = (�#:)��� for forwarding rotating fields (47) q� = (��:)#�� for backward rotating fields (48) from figure 4, if �. �� is assumed to approach infinity and �. (�ℓ� + �� ℓ� ) is greater than ��� , ����ℓ , ��� , and ����ℓ , then the current of the k-th harmonic component is: �� = �� .� . (�ℓ� + �� ℓ� )0 = t]��&.('ℓ(�'� ℓ9) 1 (49) the corresponding expression of the rms harmonic ripple current �� is obtained by the superposition principle as [18]: �� = ��r + �� + �:: + �:c + �:� + ⋯ �+& (50) the total stator and rotor windings copper losses and stray load losses due to the fundamental and harmonic ripple currents are obtained as: ρ ��� = 3. v�_�� + �� w. (�� + ����ℓ ) (51) ρ ��� = 3. v��_�� + �� w. v�� � + ����ℓw (52) the stray load losses are generated in the machine essentially due to hysteresis and eddy currents induced by the stator and rotor windings leakage fluxes. if �_�� is the fundamental stator phase current of the motor and �� is the total harmonic ripple of the phase current, and by applying the superposition theorem, the stator input phase current �� when the motor is fed from the six-step vsi is obtained as : �� = .�_�� + �� 0+& (53) the total input power to the motor is: ρ�� = 3. �_� . �� . ��4ϕ (54) the friction and windage (mechanical) power loss due to the harmonic mechanical resistance �<=� depends on the airgap magnetizing voltage v� and is obtained as: p<=� = 3. �� (� . r<=� ) 1 (55) the iron core loss of the k-th harmonic is obtained as: ρ� � = 3. �� �� �⁄ (56) then, the superposition principle is applied to find the total harmonic core losses as: ρ� � = ∑ ρ� ���r ,�,… (57) the fundamental iron core losses are obtained as: ρ� = 3. �� �� ⁄ (58) then, the total iron core loss is obtained as: ρ� l = ρ� + ρ� � (59) the simplified formula for the k-th time-harmonic electromagnetic torque ce� is derived by [32]: t�� = c.$�9�& .8� 9�� .=(� = c.$�� & .8� 9 �� .=(� (60) where l�� = �. l� is the angular speed of the k-th harmonic. the k-th rotor harmonic current is equal to the k-th stator timeharmonic current because �. �� is very large. the harmonic torque is generated by the interaction between the harmonic flux of the stator and the rotor flux. the harmonic torque is smaller than the fundamental motor torque because the harmonic current and fluxes are comparable to the normal and the torque generated by the harmonic components is partially canceled by the harmonic torque that moves in the negative direction. the 5 th harmonic torque opposes the 7 th harmonic torque, and a similar opposition happens between the 11 th and 13 th harmonics [18]. the k-th time-harmonic mechanical output power from the motor is derived as: p�� = c.$�9�& .8�� 9 .(:#��)�� (61) the total harmonic mechanical output power is obtained by the superposition theorem as: ρ�� = ∑ ρ����r ,�,::,… (62) then, the net mechanical output power is determined as: �� = c.$�9& .8�� 9 .(:#�)� − p�� (63) the efficiency of the motor fed from the six-step vsi is: �% = �)��" . 100 (64) the efficiency of the motor will drop when the machine is operated with vsi due to increasing losses and heat. the losses are dissipated as heat. the harmonic currents increase the copper and iron-core losses. this leads to a higher temperature in the stator winding, iron core, and rotor bars. the power factor cos(�) is defined as the ratio of the output mechanical power to the apparent input power �d as: �. � = cos(�) = \)\�" = �)√c.tℓ.$ℓ (65) where �ℓ and �ℓ are the line supply voltage and the current of the motor. the lagging power factor can be corrected by introducing capacitors. since vsi has capacitors on the dc bus, this provides isolation of the induction motor as the load from the network, to improve the overall power factor of the system. when the vsi starts the induction motor, low frequency applies to the motor and high starting currents will be avoided. after that, the applied voltage and frequency are increased to accelerate the motor to the steady-state speed without drawing excessive current [33]. vi. results and discussion to examine the validity of the dynamic model of the whole system and the harmonic equivalent circuit of the motor when engineering, technology & applied science research vol. 12, no. 6, 2022, 9536-9545 9542 www.etasr.com nasir: determination of the harmonic losses in an induction motor fed by an inverter fed from the six-step vsi, the motor performance is simulated in transient and steady-state operation in matlab and the results are compared with the ones measured when the motor is fed from the sinusoidal power supply. the parameters of the fundamental equivalent circuit at 50hz supply are given in table i. table i. fundamental equivalent circuit parameters machine power (kw) �  (¡) ¢� £ (¡) ¤¥¦ (¡) ¤� ¥£ (¡) ¤§ (¡) moment of inertia (kg.m 2 ) 2.0 5.1 3.5 5.0 7.5 88.0 0.03 the iron-core and the mechanical loss resistances �� and �<= are varied with air-gap voltage �� and their relations are generated by the curve-fitting technique as given in (6)-(7). the iron core resistance �� is reflected on the stator and rotor circuits to stay in the dynamic model of the 4 th order, although the iron core is considered in the model. the reflecting resistances ���� and ���� are derived by (8)-(9). the stator and rotor stray load resistances are varied with stator and rotor phase resistances and are derived by (12)-(13). a. results of the dynamic model figures (5)-(8) show the starting-up motor speed, electromagnetic torque, stator phase current, and rotor phase current when the motor is fed from a 50hz six-step vsi supply. the results show that there are harmful harmonic currents in the stator and rotor. these harmonic currents affect the motor performance by introducing pulsating torques, overheating, and noise. fig. 5. start-up motor speed with inverter supply. fig. 6. start-up motor torque with inverter supply. fig. 7. start-up motor-stator phase current with inverter supply. fig. 8. start-up motor-rotor phase current with inverter supply. fig. 9. start-up motor speed with sinusoidal supply. fig. 10. start-up motor torque with sinusoidal supply. engineering, technology & applied science research vol. 12, no. 6, 2022, 9536-9545 9543 www.etasr.com nasir: determination of the harmonic losses in an induction motor fed by an inverter fig. 11. start-up motor-stator phase current with sinusoidal supply. fig. 12. start-up motor-rotor phase current with sinusoidal supply. figures (9)-(12) show the starting-up motor speed, torque, stator phase current, and rotor phase current when the motor is fed from a 50hz sinusoidal supply using the parameters of the fundamental equivalent circuit of the motor. the results show there are no harmonic currents in the stator and the rotor of the motor. b. results of the harmonic equivalent circuit figure 13 compares the measured efficiency of the motor fed from the sinusoidal and vsi supplies with that produced from the simulations in matlab. the supply current of the vsi contains high harmonics, which contribute to additional motor losses and cause the motor efficiency to decrease by 3% compared to that of the sinusoidal supply voltage at full load operation. similarly, figure 14 compares the measured power factor from the vsi supply with that measured from the sinusoidal supply. due to the harmonic currents in the vsi supply, the power factor is reduced by 0.08 compared to that of the sinusoidal supply, while the power factor in matlab simulation is higher than that of the sinusoidal supply operation by 0.05 at full load, because the harmonic currents are not considered in the fundamental equivalent circuit of the motor. figure 15 compares the measured total motor losses fed from the sinusoidal and vsi supplies with that of matlab simulations predicted from the harmonic equivalent circuit and the fundamental equivalent circuit. due to the vsi supply which contains high harmonic currents, the measured losses from the vsi fed motor are higher than those measured from the sinusoidal supply. the generated additional losses decrease the motor's efficiency. the predicted total losses from the harmonic equivalent circuit are 13% higher than that of the fundamental equivalent circuit. figure 16 shows the detailed losses of the induction motor fed from the vsi supply predicted by the matlab simulation of the harmonic equivalent circuit. fig. 13. measured motor efficiency. fig. 14. measured motor power factor. since the iron core loss is a function of air-gap voltage and frequency, the harmonic currents add extra losses to the iron core loss. the iron core loss reached 50% of the total losses at full load operation. also, the presence of harmonic currents causes a rise in the losses of stator and rotor windings, according to (51)-(52). the stray load losses in the stator and rotor windings are also increased due to the harmonic currents. the friction and windage losses are assumed to be fixed and not affected by the harmonic currents. vii. conclusion the recent developments in power electronics and semiconductor material technologies improved power electronic ac engineering, technology & applied science research vol. 12, no. 6, 2022, 9536-9545 9544 www.etasr.com nasir: determination of the harmonic losses in an induction motor fed by an inverter drive systems. different circuit topologies of inverters, such as the six-step vsi have been used. in the six-step vsi fed induction motor, low order time harmonics (5 th , 7 th , 11 th ) that lead to additional motor losses are generated. these additional losses are not load-depended and are estimated as the difference between the no-load losses with vsi and the sinusoidal supply. the increase of total losses in the vsi supply by nearly 20% is caused by the time-harmonic currents generated by the vsi and the conduction and switching losses of the inverter. as expected, the motor efficiency with pwmvsi supply is lower than that with the sinusoidal supply by about 3%. fig. 15. measured total motor losses. fig. 16. details of motor losses with vsi supply. the stray load loss is increased by 30% with the vsi supply in comparison with the sinusoidal supply. the core losses at rated power are increased by 50% with the vsi supply, because these losses depend on the air-gap voltage and supply frequency. when the motor is operated with a vsi supply instead of a sinusoidal supply, the motor power factor is reduced by 0.08 and the stator and rotor copper losses are increased by 30% due to the harmonic current and the skin effect. the additional losses generated with the vsi supply lead to a higher temperature in the stator and rotor windings. the harmonic currents lead to extra reactive currents resulting to a decrease of the motor power factor. when the motor operates by a vsi supply, it applies low frequency and voltage to the motor in order to avoid the high inrush current. the motor supply voltage must be kept in the same proportion with the supply frequency for all motor speeds to maintain the rated torque constant and to avoid magnetic saturation. by good design of the motor structure and the output passive filter, and increasing the inverter switching frequency, the harmonics can be mitigated. references [1] e. a. klingshirn and h. e. jordan, "polyphase induction motor performance and losses on nonsinusoidal voltage sources," ieee transactions on power apparatus and systems, vol. pas-87, no. 3, pp. 624–631, mar. 1968, https://doi.org/10.1109/tpas.1968.292172. 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[33] n. h. mugheri and m. u. keerio, "an optimal fuzzy logic-based pi controller for the speed control of an induction motor using the v/f method," engineering, technology & applied science research, vol. 11, no. 4, pp. 7399–7404, aug. 2021, https://doi.org/10.48084/ etasr.4255. engineering, technology & applied science research vol. 7, no. 6, 2017, 2215-2221 2215 www.etasr.com nikseresht and ziarati: a demand estimation algorithm for inventory management systems using … a demand estimation algorithm for inventory management systems using censored data alireza nikseresht computer science and engineering department shiraz university shiraz, iran anikseresht@cse.shirazu.ac.ir koorush ziarati computer science and engineering department shiraz university shiraz, iran ziarati@shirazu.ac.ir abstract—during the selling time horizon of a product category, a number of products may become unavailable sooner than others and the customers may substitute their desired product with another or leave the system without purchase. so, the recorded sales do not show the actual demand of each product. in this paper, a nonparametric algorithm to estimate true demand using censored data is proposed. a customer choice model is employed to model the demand and then a nonlinear least square method is used to estimate the demand model parameters without assuming any distribution on customer’s arrival. a simple heuristic approach is applied to make the objective function convex, making the algorithm perform much faster and guaranteeing the convergence. simulated dataset of different sizes are used to evaluate the proposed method. the results show a 23% improvement in root mean square error between estimated and simulated true demand, in contrast to alternate methods usually used in practice. keywords-demand; estimation; inventory; revenue; inventory; management; control; unconstraining; uncensoring i. introduction modeling demand and estimating the true demand is crucial in every inventory management system. inventory management systems rely on accurate demand estimating methods [1]. in inventory management systems the demands are usually observed in several periods during a selling horizon. due to inventory constraints the demand is truncated in some periods, so only censored sales data are recorded. using this kind of data as true demand causes underestimation or overestimation of true demands. if the companies overestimate the true demand, then they may stock more than the needs (overstock), so they eventually are forced to mark down the prices to sell those merchandises, especially when the goods are perishable or seasonal. if they underestimate the true demand, they may stock less than the needs (understock), in this situation they not only missing out on sales but also loosing discount from their suppliers and customer loyalty, as product availability is an important factor of customer satisfaction [2]. in both situations the companies loose revenue. ignoring the correlation of demand between related products leads to inefficient estimates of the true demand [3, 4]. empirical studies show that an amount between 45% and 84% of demand can be substituted [5, 6]. in [7], it is showed that the cost of ignoring demand dependency is 1% higher than ignoring censorship. to illustrate this problem, suppose that an online library offers 2 types of books for each isbn: 1-new book, 2-used books and their quantities are 30 for new books and 15 for used books. in this context, assume that 20 customers arrive and want to buy used books. however, due to limited stock, just 15 customers will buy their preferable product, and the other 5 customers should do something else. in such a situation, the current information systems just registers the successful sales and does not record any information about unsuccessful requests, so the observed sales are a censored view of true demand. therefore, in such cases, the sales data could not show the true demands. for example, here the sales data show 15 requests (the observed demand), but the true demand was 20 which is not visible. the observed sales of new books are 20, again this observed sales could not show the true demand because some customers bought new books as a substitute for used books, so the observed sales of new books are a mixture of true and substitute demand. as foregoing example shows, the substitution will increase sales in substitute products which are available. in the rest of the paper this phenomenon is referred as recaptured demand. nevertheless, measuring true demands by using the available sales data is not an easy task [8]. if the accuracy of forecasting grows about 20%, the resulting revenue will improve about 1% [9]. in [10], it was found that if we have a negative bias in forecast, up to 3% of the potential profit may be lost. if the data remain censored and we use them as the true demands, the true demands will be underestimated, causing a spiral down effect over time [11-13]. as a result, it is rational to look forward to methods measuring the true demands from the available data and use these data for forecasting and managing inventory [14]. the process of finding true demand, which in literature is called unconstraining, fills the gap between the true and the observed demands, and its goal is to provide accurate data required for the forecasting module [15]. in this paper, we propose a method in order to unconstrain censored data or in other word estimate true demand using sales transaction data in a fast, accurate, and very simple manner. the proposed algorithm is an extension of rdfso algorithm which is an iterative demand estimation algorithm considering stockout [16]. as rdfso, our method just needs transactional sales engineering, technology & applied science research vol. 7, no. 6, 2017, 2215-2221 2216 www.etasr.com nikseresht and ziarati: a demand estimation algorithm for inventory management systems using … data and product availability, and does not assume any special distribution for customer arrival, thus, it is non-parametric and makes use of the advantages of not requiring any assumption on the form of the distribution function. the proposed method uses a simple heuristic approach to convexify the objective function, thus the algorithm is fast and always converge. by estimating substitute demand as well as true demand, the problem of demand double counting is avoided. the multinomial logit choice model is employed to model the demands, and the choice model parameters are estimated by applying an algorithm which tries to reduce the error between the observed and the estimated sales data in each iteration. two types of datasets are used for evaluation: 1. a dataset with full observation of demand occurrences and 2. a dataset with censored observation of demands. dataset 1 which contains unconstrained observation is served as a benchmark to evaluate our work. ii. literature review one of the most popular approaches to estimate substituted demands is the multinomial logit model (mnl) and expectation maximization (em) is often employed to find the customer choice model parameters. authors in [17] applied a discrete choice model to model customer behavior and found the related parameters using em method. in their proposed method, they assumed a distribution function for demand and then tried to find its parameters from the observed data, indicating that their methods perform well. authors in [18, 19] utilized the idea of customer choice set to model the buying behavior of customers. they applied em algorithm to unconstrain the censored data, not assuming a fixed arrival rate for customers as is regularly done. instead, they estimated a demand function for each group of customers by analyzing observed data. they tested their method on real data, demonstrating that their proposed method just overestimates 5% and takes 10 to 15 iterations to converge, which makes it suitable for real-world application. authors in [20] proposed an em-based method estimating spilled and substitute demands. their method only needs the observed sales data, product availability, and company market share. their main idea is to consider the problem as primary demand or customer first choice. they supposed that each customer has a set of choices with a primary or first choice. each customer could buy his/her first choice, and if the first choice is not available, the next choice is substituted or leaves the system without purchasing anything. then they tried to estimate primary demands, substitute demands, and no purchase count, using em. in revenue management setting, authors in [21] employed a double exponential smoothing or holt winter-based method to find true demand using the observed sales. they compared their method with naïve methods, pd, and em and showed that their method outperforms the others. modeling customer choice is a high dimensional problem and it is difficult to dealing with, so to deal with its difficulty, many researchers prefer to assume a priori distribution and parametric model which they think is able to adequately capture choice model behavior [22]. the side effects of all parametric approaches are misspecification of the model and overestimation or underestimation of true demand. authors in [23] studied an assortment planning model with substitutable products. they considered three types of substitution: 1-stockout based 2assortment-based 3-the customers select their favorite item to buy from what they see on shelves. it is also assumed that if a customer could not buy his/her favorite item, he/she will buy a substitute product or leave the store. by this assumption, the number of substitutions is limited and the problem is made tractable. then, a procedure for estimating substitution parameters is proposed with a heuristic approach for solving the assortment planning problem. authors in [24] applied a stochastic newsvendor model for perishable and non-perishable items that jointly optimizes assortment and associated order volumes considering storage constraints. their method is able to find the efficient solution for ordinary problem sizes in retail using an optimal procedure and in case of large problem instances a heuristic is applied to find near optimal solutions in reasonable time. using numerical tests, they showed that their heuristic produces near optimal solutions and outperforms heuristic of authors in [23]. they also revealed that considering substitution effects has a significant impact on the total revenue and solution structure. authors in [25] proposed a method able to learn demand using continuous observation of sale occurrences in a bayesian fashion. they have considered 3 types of observations: 1. sales along with a binary variable which shows the product availability status. 2. continuous observation of sales until the stockout happens. 3. full observation of the demand. they showed that in case of continuous observation, a firm optimal ordering quantity is greater than observation type 1, then with numerical results they found that in continuous observation 76.1% of loss in expected profit eliminates in contrast to type 1 of observation. they assumed that the demand is independent, so they do not consider product substitution in their work. our paper brings two main contributions to the literature. first, our work contributes to the literature by introducing an easy-toimplement non-parametric estimation algorithm for estimating multinomial logit choice model parameters in a reasonable computation time and accuracy. second, we also have devised a heuristic to convexify the objective function which shortens the execution time and guarantees the convergence. iii. problem description demand estimation under the customer-driven substitution scheme is studied in this paper. in the customer-driven substitution scheme, when the first-choice product of the customer is not available on the shelf, the customer may purchase, with a certain probability, another product in the same category in lieu of his/her first-choice product. for example, market a offers a category which contains 4 items. now suppose that a customer comes to buy a product in that category, and with respect to features such as price, weight, production date etc he/she prioritizes the items and chooses an item. in other words, each customer faces a set of choices, and then he/she arranges these choice sets based on their benefits and chooses to buy the first item of that sorted choice set. suppose that customer b wants to buy a bottle of milk, then faces the choice offered by retailer a (table i). he arranges the items as c1-c2-c3-c4, meaning that the highest priority is buying the product c1, then c2, and so on. if a customer could not buy product c1, two conditions occur: the customer buys the other product (substitute), c2, or leaves the system without engineering, technology & applied science research vol. 7, no. 6, 2017, 2215-2221 2217 www.etasr.com nikseresht and ziarati: a demand estimation algorithm for inventory management systems using … purchase (denial). it is obvious that the number of sales of products c1 and c2 could not show the real demand. if these data are used as true demands and are fed into the forecasting module, a spiral down effect will occur in estimation, and the total revenue begins to decrease [11]. retailers are interested in recognizing how customers prioritize the products offered and select an item to buy. table i. products and their features offered by retailer a in a category price $ fat production date weight(liter) items 1.2 1% 2016-06-01 1.5 c1 1 1% 2016-06-01 1 c2 1 2% 2016-05-30 1 c3 0.75 3% 2016-06-01 0.85 c4 iv. demand model we consider a firm that presents n products. selling time horizon is discretized and, indexed by t = 1. . . t, where t is the number of periods or time frames between the time when a product is presented for sale and the time it expires. the periods could be different in length, for example period 1 may be a day, but period 2 may be 12 hours. a set of products (ct) is offered in period t: ct= (c1t, c2t, …, cnt). ojt is the number of observed sales of product j in the interval t, and ot is the observed sale vector in interval t: ot= (o1t, o2t, …, ont). in our model each product ci has a fixed preference weight vi which customers sort the products based on the product preference weight, then choose the first one from the list if it was available. the preference weight of no purchase is v0 =1. we assumed that the preference vector is constant in each period for all customers. using these preference weights we rewrite the mnl choice probability as in [26]: 0 ( , ) t j ii c v p j t v v    (1) the probability of choosing product j which is not available in period t is: p(j,t)=0. based on no purchase preference weight or v0 =1 the no purchase probability is defined as: 0 0 1 (0, ) 1 t t i ii c i c v p t v v v        (2) we are able to calculate the number of purchases in each period using the number of customers arriving in period t or at. the probable number of sales of product j in period t if all products are available (true demand) is as follows: 01 ( , ). j jt t tn ii v d p j t a a v v     (3) using the estimated number of sales, we could calculate total sale in each period t as: 0 t j t jt tj c j v e d a v v      (4) by using (4), we can estimate the number of arrivals: 0 0 n j t t t jt tj j v q e q d a v v         0j t t j v v a q v     (5) the number of customers who could not buy their first choice in period t is estimated by using: t t jtj c s d    (6) the number of requests which choose class k as a substitute in period t, could be estimated by the means of multiplying st (the number of customers who could not buy their first choice) by the probability of choosing class k: 0 . ( , ) . , k c t k kt t t t jj c v r s p k t s v v      (7) the number of sales of product j in period t or ojt consists of three components: 1the number of customers interested in product j as their first choice (true demand or djt), 2the number of customers buying j because their first choice was not available (recapture or rjt), and 3the number of customers unable to buy product j as their preferred product (spill or sjt) [27, 28]. thus, the demand mass balance equation is as follows: ojt = djt + rjt -sjt (8) equation (6) is used to compute spill and recapture. it is also used to estimate the observed sales. it should not be forgotten that at first we need the preference vector v to be able to compute spill and recapture. therefore, at first we try to estimate the preference vector, and by using it along with foregoing formulas the number of true demands, recaptures, and spills is estimated. v. nptdea algorithm the nonparametric true demand estimation algorithm or nptdea is an iterative algorithm which starts with an initial value for preference vector and tries to make a better estimate for preference vector in each iteration by minimizing an error function which is the gap between estimated and observed sales in each period: e = ojt – ( djt + rjt sjt) (9) the objective function which should be minimized is: 21min( . ) 2vj e  (10) a. analysis of objective function to show the objective function is non-convex, assume a firm offer two products a and b in ten periods. at the first 6 periods both of the products were available, but later only product b was available. based on foregoing equations the engineering, technology & applied science research vol. 7, no. 6, 2017, 2215-2221 2218 www.etasr.com nikseresht and ziarati: a demand estimation algorithm for inventory management systems using … error function in the first 6 periods which all products were available (so no spill and recapture exist) becomes: 22 1 1 1 2 22 1 2 1 2 [ , ] [ ,1] * [ , ] [ , 2] * i i x t i x t v v v x t i x t v v v                        (11) also the hessian matrix is not positive definite. the 3d plot of (11) is shown in figure 1. in the last 4 periods which product a is not available, because of recapturing spilled demands, the error function is like: 2 1 2 1 2 2 21 1 2 1 2 [ , ] ( [ , 2] ( 1) * [ , ] * ( 1) * ) 1 i i x t i x t v v v x t i v v v v              (12) the value of v1 is not updated as product a is not available, so we assume the value of v1 is set to its optimal value, then we plot the error function by fixing v1 at its optimal value. the plot is shown in figure 2 and obviously is not convex and it is ill structured. b. convexification process because of the fractional terms in the demand equation (3) the objective function is not convex. we made a simple heuristic to make that function convex. as we said before, the nonconvexity is because of the existence of the fractional term in the demand function, so if we replace the denominator (σvj+v0) with a fixed value, the objective function becomes convex. this value could be extracted from market share. we have considered the market share the same as that in [29]: 0 1 0 / (1 ) v j j j v m v v v          (13) figure 3 shows the error function after convexification. the initial value of preference weight for product j could be found as: / number of products 1 j m v m       (14) c. pseudo code of nptdea: 1. ct: set of available products in period t. 2. v: preference weight vector. 3. u: utility of products vector. 4. at: the number of arrival in period t. 5. ot: the vector of purchases in period t. 6. m: the market share (if it is available) 7. initialize : estimating vj for each product j in [1..n] / (1 ) /jv n    8. for each period t in [1..t] compute at based on vjs: 0j t t j v v a q v     compute no purchase: dot=at-qt for each product j in [1..n] 0 j jt t i v d a v v   if ( cjt not available) vj_new=vj_old s = s + dj else 0 . t j j jj c v r s v v    _ ( ( / ) ( / ) t jt j new t j j c j o o v mean a v s v v     fig. 1. the 3d plot of equation 11 (error function befor convexification) fig. 2. plot of (12) by fixing the v1 at its optimal level. engineering, technology & applied science research vol. 7, no. 6, 2017, 2215-2221 2219 www.etasr.com nikseresht and ziarati: a demand estimation algorithm for inventory management systems using … fig. 3. 3d plot of error function after convexification. vi. simulation and results a. simulation process and data in this section the simulation process is described and the data used for the evaluating of the proposed algorithm. the simulation process is as follows: i. select a customer choice model. this is a predefined model which some products and their preference weights. the market share and customer arrival pattern is also defined. this model may pick from real-world data or synthetic datasets. for example, we have a model with products c1 to c5 and the preference vector of v = (0.299, 0.199, 0.122, 0.092, 0.057). the market share is 43% and the customer arrival in each period is simulated with a poisson process with the mean of 80. the no purchase preference weight is v0 = 1 and the number of periods is 15. ii. use the selected model to simulate the purchase of products in each period. by having the simulated number of arrivals in each period, we are able to simulate the number of sales for each product and the number of no purchase using (3). iii. apply product availability matrix on simulated sales from step ii. the product availability info is in matrix format, with the number of columns equal to the number of periods and the number of rows equal to the number of products. for example avli,j = 1 means that the product i is available in period j and vice versa. this information could be available exogenously or filled randomly. by applying the product availability on simulated data, if the product i was not available on period j (ie. avli,j=0) the simulated sales of that product on foregoing period reset to zero (ie. di,j = 0). iv. by executing nptdea algorithm on the generated dataset the preference vector is estimated. v. using estimated preference vector we are able to find the true demand and to show the accuracy of proposed algorithm when the estimated true demand and simulated true demand are compared. a sample of the simulated dataset is shown in table ii. it is shown that in the periods 1 to 3, all products are available and in the period 1 the number of sales for products c1 and c2 is 26 and 17, and so on. in the period 1, the number of arrivals to the system is 84, which is generated by a poisson distribution function with mean=80. during that period, 58 customers out of 84 customers buy the products, while the other 26 leave the system without purchase. the number of arrivals and no purchase is not visible in real-world application. thus, we separated these values in two lines entitled hidden data. each dataset contains 100 instances of selling horizons, which each instance contains a category of items and the number of sales of each product in that category on every period. for example, in our 5x10 dataset which contains a category of 5 products and 10 intervals, we have 100 instances of sales. this means 100*10*5 intervals or 5000 sales data records. table ii. a sample of simulated data for a specific category. pro ducts c1 c2 c3 c4 c5 h id d en d a ta no purchases # a rr iv a ls 1 13 11 1 4 5 42 76 2 15 6 8 9 0 42 80 3 13 7 3 4 3 43 73 4 na 9 5 7 5 67 93 5 na 10 8 7 2 56 83 6 na na 4 3 2 74 83 7 na na 9 9 4 71 93 8 na na na 6 1 67 74 9 na na na 7 9 74 90 10 na na na na 3 81 84 na means the product is not available in that period b. results as a result of applying the nptdea algorithm on simulated dataset, preference vector v is estimated. table iii shows a sample of estimated preference vector in contrast to the true value of preference vector which is used to generate the simulated dataset. there are two favorable attributes for an estimator: accuracy and precision. accuracy is lack of bias and precision is small variance. if an estimator is unbiased, then we just look at its variance. if it is biased we sometimes look at the mean squared error. as the table iii shows, our estimator has a negative bias on estimated values and this is because of changing the objective function to a convex form and the new convex function is always below the true values. table iii shows the mean square error and variance of proposed algorithm for estimating the values of preference vector. as table iii shows the values of mse and variance are almost equal and this is because of the mean of the estimated preference vector is almost equal to the true value of preference vector. figure 4 exhibits the box plot of estimated preference values for 100 algorithm executions over simulated datasets. the line in the middle of the box is the median. the box itself represents the middle 50% of the data. the box edges are the 25th and 75th percentiles. there is some disk visible below or above of some boxes which shows that in some cases the engineering, technology & applied science research vol. 7, no. 6, 2017, 2215-2221 2220 www.etasr.com nikseresht and ziarati: a demand estimation algorithm for inventory management systems using … simulated sales were far from the regular values, so as a result the estimated preference of that simulated dataset is far from the median. figure 5 shows the cumulative sum of simulated demand, estimated demand, observed sales and estimated sales over 15 periods for products c1 to c4. table iii. mean, variance and mean square error of difference between estimated and true values of preferences. products c1 c2 c3 c4 c5 preferences v1 v2 v3 v4 v5 true value 0.299 0.199 0.122 0.092 0.057 estimated value 0.286 0.197 0.121 0.091 0.056 mean -0.0136 -0.0029 -0.0004 -0.0015 -0.0003 variance 0.0012 0.0007 0.0004 0.0002 0.0001 mse 0.0014 0.0007 0.0004 0.0002 0.0001 fig. 4. the boxplot of preference values. fig. 5. the cummulative sum of simulated and estimated demand, observed sales and estimated sales over 15 periods for products c1(a), c2(b), c3(c) and c4(d) it is obvious that estimated sales are always close, but a bit upper than observed sales. one of the important aspects of the simulation is that even hidden data not observable in the real world are generated and thus the accuracy of the estimation process can be evaluated better. to gain a better insight of the results and of the accuracy of the proposed method we have compared the results against two other methods which are usually applied in practice: 1-expectation maximization or em and 2-projection detruncation or pd methods [15, 30, 31]. to compare the results we have applied the three above methods on a dataset for 1000 times, then the mean of root mean square error for each method was calculated. the result of the comparison is depicted in table iv. the results show that our proposed method outperforms em and pd and has about 21% to 23% improvement in root mean square error compared to the other two methods. table iv. root mean square error between estimated true demand and simulated true demand in contrast to em and pd. c4 c3 c2 c1 methods 0.68 1.53 4.05 3.19 nptdea rmse 2.5 2.35 4.15 3.28 em rmse 2.46 2.14 4.21 3.28 pd rmse table v. execution time for different datasets. execution time for 100 instance(sec) dataset 2.01 5x15 3.72 5x30 4.70 10x30 9.12 10x60 12.77 20x60 different size datasets are used to show the efficiency and speed of the proposed algorithm. at first we evaluated it with a rather small dataset of 5 products and 15 periods. in this case the algorithm lasts 2.01 seconds to estimate 100 instances. the second dataset is composed of observed sales from a category with 5 products and 30 time intervals. the third data set is in a category having 10 products sold in 30 intervals. our last and bigger dataset consisted of 20 products and 60 time intervals. for the last dataset the algorithm takes about 12.77 seconds to solve 100 instances, which is very good for this size of dataset in contrast to current demand estimation methods. table v shows the execution time for all five datasets. r revision 3.2.2 was used to implement the algorithm on a computer with an intel core2 quad q8300 and 4 gb of internal memory. code execution time is measured by proc.time() in r. engineering, technology & applied science research vol. 7, no. 6, 2017, 2215-2221 2221 www.etasr.com nikseresht and ziarati: a demand estimation algorithm for inventory management systems using … vii. conclusion this paper presented a new approach for the estimation of true demand. the demand is modeled using the customer choice model. transactional sales data, product availability and market share are the only data used to estimate the choice model parameters, which are customer preferences in a set of substitutable products. spilled and recaptured demands are estimated alongside with true demand. the problem of double counting demands in available products is resolved by considering spill and recapture. most current methods assume an a priori distribution to estimate customer arrival in each period, so they suffer from misspecification of the distribution function and its parameters. unlike these methods, the proposed method is nonparametric and estimates customer arrival in a simple manner. numerical experiments confirm that proposed method performs well in terms of speed and estimation accuracy. based on the simulation results, our method improved root mean square error between simulated and estimated demands by 23%, in contrast to other methods such as pd and em. for a rather large dataset, it estimates the true demand, spill and recapture rather fast. we believe that the proposed method could be a good replacement for current demand estimation methods in practice. references [1] n. agrawal, s. a. 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tathagata, “revenue impacts of demand unconstraining and accounting for dependency”, journal of revenue and pricing management, vol. 10, no. 4, pp. 367–381, 2011 [8] r. r. wickham, evaluation of forecasting techniques for short-term demand of air transportation, msc thesis, massachusetts institute technology, 1995 [9] k. t. talluri, g. j. van ryzin, i. z. karaesmen, g. j. vulcano, “revenue management: models and methods”, 2008 winter simulation conference, pp. 145–156, 2008 [10] l. r. weatherford, “a review of optimization modeling assumptions in revenue management situations”, agifors reservations and yield management study group, 1997 [11] w. l. cooper, t. homem-de-mello, a. j. kleywegt, “models of the spiral-down effect in revenue management”, operations research, vol. 54, no. 5, pp. 968–987, 2006 [12] r. saleh, “estimating lost demand with imperfect availability indicators”, agifors reservations and yield management study group, 1997 [13] r. j. a. little, d. b. rubin, statistical 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management by unconstraining demand estimates from censored data, universal-publishers, 2001 [31] tarek abdallah, g. vulcano, “demand estimation under the multinomial logit model from sales transaction”, working paper, available at: https://www.researchgate.net/profile/gustavo_vulcano, 2016 microsoft word etasr_v11_n5_pp7684-7688 engineering, technology & applied science research vol. 11, no. 5, 2021, 7684-7688 7684 www.etasr.com katireddy et al.: innovative design and analysis of an electrically small reconfigurable antenna for … innovative design and analysis of an electrically small reconfigurable antenna for gps and blue tooth applications harshitha reddy katireddy department of ece koneru lakshmaiah education foundation vaddeswaram, guntur, andhra pradesh, india govardhanee_ec@kluniversity.in m. venkata narayana department of ece koneru lakshmaiah education foundation vaddeswaram, guntur, andhra pradesh, india mvn@kluniversity.in govardhani immadi department of ece koneru lakshmaiah education foundation vaddeswaram, guntur, andhra pradesh, india govardhanee_ec@kluniversity.in abstract-in this paper, an electrically small, planar antenna with broad side radiation pattern is presented. the design contains a dipole and a segmented circular loop which works equivalent to that of a magnetic dipole. a circular patch with slots is used to provide impedance matching. in general, electrically small antennas suffer from narrow bandwidth. in this paper, the reconfigurability of the small antenna for two different applications, 1.5ghz and 2.4ghz, is discussed. this reconfigurability was achieved by using a bar 64-03w pin diode to adjust the resonant frequency. two reconfigurable frequency bands were achieved at 1.5ghz and 2.4ghz with broad side radiation patterns. keywords-electrically small antenna; pin diode; end fire radiation pattern; nfrp elements i. introduction the components used in wireless communication systems such as antennas, filters, multiplexers, modulators, etc. are continuously miniaturized and intelligentized [1-3]. frequency reconfigurable electrically small antennas are often suitable and are used for compact, wearable devices [4, 5]. an antenna with a broad front-to-back ratio and an equivalent pattern of e and h plane radiation is shown in [6]. the research groups in [7-10] and [11-15] have extensively researched antennas with the combination of electric and magnetic dipoles. the quarter wavelength patch with vertical orientation is commonly used in [7] as a magnetic dipole, which is coupled with the electric dipole to design complementary antennas with a wavelength of 0.25λ0 [8-12]. nfrp elements were used in [13] to design electric and magnetic dipoles, contributing to the design of dual band electrically small antennas. most of the tiny electrically small antennas are not reconfigurable except from [4] and [5]. three magnetic nfrp elements were paired with two electric nfrp elements in [5] to achieve the reconfigurability of their radiation pattern. a planar, reconfigurable complementary antenna with a single layer pattern was indicated in [16]. in addition to the reconfigurability of polarization and radiation reconfigurability patterns, due to its powerful spectrum use, frequency reconfigurability has gained a lot of attention [1720]. utilizing appropriate antenna size, different frequency reconfigurable monopole antennas [17-19], patch antennas [2022] and quasi-yagi uda antennas [23-24] have been created. in order to obtain a unidirectional radiation pattern which increases the antenna size, a broad ground plane is required. by eliminating the ground plane, the complementary huygens source antenna is used to achieve high front-to-back ratios with less distance. this paper introduces an electrically small reconfigurable antenna. to produce the magnetic dipole that is combined with the rectangular bar electric dipole to obtain the end fire radiation pattern, a segmented circular loop is used. this antenna is 35mm×35mm×1.6mm in size and has a single coating. in addition, the design is expanded by inserting a pin diode in the electric dipole to achieve frequency reconfigurability. two resonant bands were obtained at 1.5 and 2.4ghz and the end fire radiation pattern was maintained. this antenna was fabricated in order to obtain a practical realization of the results. a good agreement between the simulated and the experimental results was obtained. ii. antenna mechanism the magnetic dipole is considered to be a loop with a uniform current distribution. due to its low radiation resistance and high reactance, its impedance matching is poor. the diameter of the outer loop is 16.8mm at the resonant frequency and the current distribution is uniform and flows along the y-axis (figure 1). the electrical and magnetic dipoles are excited in a perpendicular manner in order to design this planar, electrically small antenna. the strip line and the corresponding author: govardhani. immadi engineering, technology & applied science research vol. 11, no. 5, 2021, 7684-7688 7685 www.etasr.com katireddy et al.: innovative design and analysis of an electrically small reconfigurable antenna for … circular loop on the top and bottom layers of the substrate are mounted at this end. the length and width of the patch are calculated by (1)-(3). � � ����� √ � ɛ �� (1) where v0 is the velocity of light in free space. � ����√ɛ���� � 2�� (2) �� � 0.412� �ɛ������.�������.�� ��ɛ����!�.�"#�����.# � (3) where ∆l is the extension in length due to fringing effects. the effective dielectric constant is given by: ɛ$%&& � ɛ���� ' ɛ�!� � (1 ' ) �� � *+ !�/� (4) the actual length and width of the ground plane can be calculated by (5) and (6): lg=6h+l (5) wg=6h+w (6) where l is the length of the patch, w its width, and h is the thickness of the substrate. length and width of the feed line are calculated by: b= ��-. √ɛ�/0 (7) where zc is the characteristic impedance and ɛr the relative permittivity of the substrate. lf= 12 3√ɛ��� (8) the radius of the patch is calculated by: a= � √�� .45ɛ�6789 5� .4:��.;;��< (9) small antennas are those in which the largest dimension is less than the one-tenth of the wave length (λ /10). small antennas are those having k.a<1, where k=wave number= �п 1 =0.0314. for the proposed antenna the obtained k.a value is: k.a=0.0314×16.8=0.527<1. iii. antenna design consideration figure 1 represents the configuration of the electrically small planar antenna. it mainly consists of a segmented loop and strip line fabricated on a fr4 substrate with 4.4 relative permittivity, 1.6mm thickness, 35mm length, and 35mm width. the top layer of the antenna is fabricated with a strip line and it is fed by an edge feed acting as an electric dipole. the bottom layer of the antenna, i.e. in the ground plane, contains an outer circle with radius r4 and an inner circle with radius r3 (see table i). the proposed antenna was designed and analyzed experimentally. the prototype of the antenna was fabricated and the result was verified by a vector network analyzer (figure 2). figure 3 shows the fabricated antenna. fig. 1. the designed planar electrically small antenna. fig. 2. antenna parameter testing using vna. table i. dimensions of the designed planar electrically small antenna parameter l w l1 w1 r1 r2 r3 r4 value (mm) 35 35 35 1.5 10 12.2 15 16.8 (a) (b) fig. 3. images showing the prototype of the proposed planar electrically small antenna: (a) top view, (b) bottom view. iv. results and discussion return loss is the most preferred parameter to test an antenna. instead of using 2 different antennas at different frequencies, a single antenna can switch between 2 frequencies. in the proposed model, the antenna can switch between 1.5ghz and 2.4ghz. figure 4 shows the return loss of the antenna when the diode is in the off state. during the off state, the antenna resonates at 2.4ghz, with a return loss value of -15.8dbm for the simulated and -13.01dbm for the actual antenna. figure 5 represents the equivalent circuit diagram of a pin diode in on and off state. during the on state, the antenna resonates at 1.5ghz and only the resistor and inductor values are used. during the off state, the antenna resonates at engineering, technology & applied science research vol. 11, no. 5, 2021, 7684-7688 7686 www.etasr.com katireddy et al.: innovative design and analysis of an electrically small reconfigurable antenna for … 2.4ghz and the resistor, capacitor, and inductor values are used. figure 6 shows the return loss of the antenna when the diode is at the on state. the proposed antenna resonates at 1.5ghz with a return loss value of -15.07db for the simulated model and -13.08db for the fabricated model. voltage standing wave ratio (vswr) is a significant parameter for estimating the behavior of the rf components at high frequencies. the proposed antenna resonates at 2.4ghz with circular polarization when the diode is in the off state. figure 8 shows the 3d radiation pattern of the antenna with broad side radiation. maximum radiation exists in the xy plane. the maximum possible gain is about 1db at θ=0 o . figures 9-10 represent the patterns of the antenna at various azimuthal and elevation planes. fig. 4. return loss of the antenna when the diode is in the off state. (a) (b) fig. 5. equivalent circuit diagram of a pin diode. (a) on, (b) off. fig. 6. return loss when the diode is in the on state. fig. 7. vswr of the antenna. fig. 8. 3d radiation pattern of the antenna. (a) (b) (c) (d) (e) (f) fig. 9. azimuth pattern at θ = (a) 0 o , (b) 30 o , (c) 60 o , (d) 90 o , (e) 120 o , (f) 180 o . purple line: simulated results, red line: measured results. . engineering, technology & applied science research vol. 11, no. 5, 2021, 7684-7688 7687 www.etasr.com katireddy et al.: innovative design and analysis of an electrically small reconfigurable antenna for … (a) (b) (c) (d) (e) (f) fig. 10. elevation pattern at φ= (a) 0 o , (b) 30 o , (c) 60 o , (d) 90 o , (e) 120 o , (f) 180 o . purple line: simulated results, red line: measured results. the comparison with other proposed designs in table ii shows that that the proposed antenna offers better results in terms of return loss and gain. table ii. performance comparison of the proposed antenna with other, known antennas ref substrate reconfigurable area (mm 3 ) center frequency gain (db) [1] fr-4 epoxy frequency 45×40×1.6 1.28ghz 1.62ghz ------ [6] rt duroid 5880 frequency 45×38×0.254 2.4ghz ------ [7] polyimide frequency 45×35×3.2 1.6ghz 0.9db [8] fr4 frequency 95×100×14 1.71ghz ------- proposed fr4 frequency 35×35×1.6 1.5ghz 2.4ghz 1.86db v. conclusion based on the complementary concept, an electrically small, coplanar antenna was realized by combing the equivalent magnetic dipole of a segmented loop and the electric dipole of a strip line. the antenna is designed on a fr4 epoxy substrate, having a small area of 35×35×1.6mm 3 . the antenna showed satisfying broadside radiation performance, exhibiting a gain of 1.86db. it has been found that the resonance frequencies of both the electric dipole and the magnetic dipole (segmented loop) can be easily tuned with pin diodes. therefore, a frequency-reconfigurable complementary antenna was further developed. two reconfigurable broadside radiation bands have been achieved at 1.5 and 2.4ghz. references [1] w. b. hong, k.-h. back, and s. ko, "millimeterwave 5g antennas for smartphones: overview and experimental demonstration," ieee transactions on antennas and propagation, vol. 65, no. 12, pp. 62506261, december 2017, https://doi.org/10.110 9/tap.2017.2740963. 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[24] g. imamdi, m. v. narayan, a. navya, and a. roja, "reflector array antenna design at millimetric (mm) band for on the move applications," vol. 13, no. 1, pp. 352–359, jan. 2018. microsoft word etasr_v12_n2_pp8306-8310 engineering, technology & applied science research vol. 12, no. 2, 2022, 8306-8310 8306 www.etasr.com xue et al.: beneficial reuse of municipal solid waste incineration bottom slag in civil engineering beneficial reuse of municipal solid waste incineration bottom slag in civil engineering minghua xue ji'nan institute of geotechnical investigation and surveying ji'nan, shandong, china minhrac@163.com wenkui hu ji'nan institute of geotechnical investigation and surveying ji'nan, shandong, china noahhwk@126.com liu huanyu ji'nan institute of geotechnical investigation and surveying ji'nan, shandong, china lhy1787@126.com yao fu ji'nan institute of geotechnical investigation and surveying ji'nan, shandong, china 358245449@qq.com received: 15 december 2021 | revised: 29 january 2022 | accepted: 1 february 2022 abstract-rapid economic development has caused many disturbing problems in many countries. waste disposal is a prominent one of those problems. waste incineration has gradually become the most popular treatment method. waste incineration has many advantages, such as processing capacity, short period, recycling and utilization of resources, etc., but it also produces a lot of incineration bottom slag. landfilling is one of the methods for waste incineration bottom slag treatment. however, many domestic waste landfill sites no longer accept incineration bottom slag. therefore, finding sufficient ways to deal with the incineration bottom slag has become an urgent problem. with the increase of environmental pressure and the development of technology, the beneficial use of incineration bottom slag has been gradually considered. municipal solid waste incineration bottom slag is an atypical particulate material, similar to some construction materials of civil engineering. for a construction material, basic physical properties and engineering properties are important factors in its performance. however, there is limited research about the engineering performance of incineration bottom slag. the purpose of this paper is to investigate the basic physical and mechanical properties of the incineration bottom slag from one incineration plant in wuhan and provide a theoretical basis for its application in civil engineering. through laboratory tests, we found that the incineration slag completely meets the engineering requirements and is harmless to the environment. the incineration bottom slag can be used for road embankment filling, sludge dewatering treatment improvement, landfill site covering, it can substitute aggregates in concrete, etc. keywords-municipal solid waste incineration bottom slag; beneficial reuse; civil engineering; engineering properties; laboratory test i. introduction with the rapid economic development, people's living standards have improved significantly while the population density has increased along with the output of domestic waste. approximately 2 billion tons of domestic waste are produced globally each year [1]. in 2016, the production of waste was about 200 million tons in china, as shown in figure 1, with a yearly increase of 5.99%. traditional domestic waste treatment methods mainly include composting and centralized sanitary landfills. however, composting treatment has problems such as long cycles, sanitary conditions, and secondary pollution. sanitary landfill is often limited by the landfill site resources. however, compared with compost treatment and sanitary landfills, the waste incineration treatment technology has the advantages of short treatment cycle, high treatment efficiency, small footprint, and high degree of harmlessness [2-6]. with its unique technical advantages, waste incineration treatment has gradually become a popular waste treatment technology. during the recent years the proportion of domestic waste treated by incineration has increased. the residue produced by the incinerator is called incineration ash. china generally divides garbage ash into two categories: incineration bottom slag and fly ash. the incineration bottom slag content is about 80% of the ash slag, and the fly ash is accounted for the 20%. the research on the incineration bottom slag of domestic waste incineration has a long history, and the domestic research on the bottom slag of waste incineration started relatively late. authors in [8] comprehensively introduced the main components of waste incineration ash and did related research on basic inorganic chemical properties, organic chemical properties, and heavy metal leaching toxicity. authors in [9] studied the compaction properties of cohesive soil coarsegrained soil through experiments. the test results showed that the coarse-grain content greatly affects the compaction properties of the soil. when the coarse-grain content is 50%70%, the compaction effect is ideal. authors in [10] conducted an experimental study on the improvement of the bottom slag and clay mixed soil and found that when the content of coarse particles in the coarse-grained soil is small, the maximum dry density changes little with the increase of its content. when the content of coarse particles further increases, the density corresponding author: xue minghua engineering, technology & applied science research vol. 12, no. 2, 2022, 8306-8310 8307 www.etasr.com xue et al.: beneficial reuse of municipal solid waste incineration bottom slag in civil engineering gradually increases, and the dry density reaches its maximum at 60%. authors in [11, 12] conducted compaction tests on a mixture of bottom slag and clay of a certain incineration power plant and found that the waste incineration bottom slag belongs to coarse-grained soil, it is poorly graded, but its particle gradation is easy to modify, and the bottom slag soil mixed with a certain amount of clay shows good compaction characteristics. in addition, the tests also showed that the claybottom slag mixed soil has good shear resistance. fig. 1. harmless treatment of domestic garbage in china during 20062016. authors in [13] analyzed the material properties of the incineration bottom slag and explored the influence of water content on the strength of the incineration bottom slag through ultrasonic tests, saturated triaxial tests, and unconfined compressive strength tests. authors in [14] studied the strength of the incineration bottom slag through triaxial tests and reported that the organic matter content greatly affects its elastic deformability. authors in [15] analyzed the element composition and microstructure of the incineration bottom slag. authors in [16] conducted a solidification experiment on the bottom slag-sludge mixture. authors in [17] analyzed the potential thoroughfare of incineration bottom slag in road construction through direct shear tests and three-axis analysis. regarding the resource utilization of incineration bottom slag, foreign research started earlier and is relatively systematic. at present, the resource utilization of incineration bottom slag has not been systematically analyzed in china. this paper aims to conduct a systematic study on the basic physical properties and engineering characteristics of incineration bottom slag and provide a theoretical basis for its utilization in civil engineering. the article will mainly analyze the basic physical property tests (screening test, density test, water content test, limit water content test, and specific gravity test), mechanical properties (compaction test, direct shear test, and load-bearing ratio test), and the environmental impact. based on the research findings, further analysis of the direction in which the incineration bottom slag can be used as a resource is conducted. ii. basic physical properties of incineration bottom slag due to the regional differences in waste classification and waste composition, the composition of waste incineration bottom slag varies greatly. the composition of the incineration bottom slag largely determines its performance and affects its engineering applications. first, the basic physical properties of the incineration bottom slag were analyzed. the sample was taken from a garbage incineration plant in wuhan, china. the bottom slag was off-white and light brown when the water content was high. the incineration bottom slag contained a lot of ceramic and glass fragments. the basic physical properties of the measured incineration bottom slag include specific gravity, water content, particle gradation, and limited water content. the measured parameters were compared with natural gravel and other building materials. the test operation rules and procedures were carried out following the standard soil test method (gb/t 50123-2019) [18] and highway soil test regulation (jtge40-2007) [19]. a. specific gravity test the specific gravity of a solid refers to the ratio of the density of the substance in a fully compacted state to the density of pure water at 4°c under standard atmospheric pressure. it is a dimensionless value and is generally affected by temperature and pressure. the specific gravity can represent the relative density of the soil, which is often used in engineering to calculate its compactness. table i. specific gravity of incineration bottom slag temperature ( o c) specific gravity of water mass of solid (g) mass of equal volume of water (g) gs average gs 22.2 0.997724 30.12 11.02 2.72 2.71 22.2 0.997724 30.06 11.04 2.71 22.0 0.997769 29.89 11.00 2.71 the results show that the average specific gravity of the waste incineration bottom slag is 2.71. the detailed results are shown in table i. in general, the specific gravity of sandy soil lies in the range of 2.65-2.69, the specific gravity of silt is in the range of 2.70-2.71, the specific gravity of silty clay is in the range of 2.72-2.73, and the specific gravity of clay is in the range of 2.74-2.76. it can be seen that the specific gravity of the bottom dross is close to that of the silty clay. b. particle analysis test particle gradation refers to the relative content of each particle group. the particle size gradation of the soil affects its strength, permeability, and frost resistance. a well-graded soil can achieve a higher degree of compaction and has better mechanical properties. poorly graded soil has many larger pores and good permeability. it can be used in drainage structures and filter layers in engineering. the particle gradation analysis result of the bottom slag is shown in figure 2. the average particle size of the bottom slag (i.e. d50) is 2.0mm, and the particles in the sample with a particle size in the range of 1-60mm account for 52.97% of the total mass of the incineration bottom slag sample. the content of particles with a particle size of less than 0.1mm is 3.47%. it can be seen that the bottom slag is sandy soil, so it belongs to coarsegrained soil. engineering, technology & applied science research vol. 12, no. 2, 2022, 8306-8310 8308 www.etasr.com xue et al.: beneficial reuse of municipal solid waste incineration bottom slag in civil engineering fig. 2. gradation curve of bottom slag particles. the uneven coefficient of the bottom slag was calculated as cu > 5 and belongs to the inhomogeneous category. the curvature coefficient was cc < 1, the bottom slag particle size is discontinuous, and it also can be seen from figure 2 that two-particle groups, i.e. 0.075-0.1mm and 1-2mm are missing. in summary, the incineration bottom slag belongs to poor gradation. c. water content test water content refers to the ratio of the mass of solids to the mass of water in the sample. it can be seen from the test results that the natural air-dried water content of the incineration bottom slag is 6.3%. considering that the water content of the incineration bottom slag is greatly affected by the stacking time and location, the impact of the water content in engineering applications is negligible. d. atterberg limits test the water content between the two consistencies of cohesive soil is called the atterberg limit content of the soil. the atterberg limit water content from the plastic state to the liquid state of the soil is called the liquid limit, and the atterberg limit water content between the plastic state and the semi-solid state is the plasticity limit. through the atterberg limits water content test, the liquid limit and plastic limit of the soil can be determined, the state of the soil can be evaluated, and the classification of the soil can be clarified. the test results show that the liquid limit of the incineration bottom slag is 26.5%, and the plastic limit is 3.6%. the plasticity index is 22.9%, and the liquid limit index is 0.11. the incineration bottom slag is in a hard plastic state under the sampling state, and its plasticity is not strong. iii. engineering characteristics of the incineration bottom slag a. proctor compaction test seven different sets of compaction tests were carried out to analyze the compaction characteristics of the incineration bottom slag. by applying different compaction works to soil samples with different water content, they can reach different degrees of compaction. the corresponding dry density was determined, in order to obtain the optimal moisture content and maximum dry density through analysis, which can be used for the design and construction of backfill projects. fig. 3. curves of water content and maximum dry density. the relationship between the water content of the incineration bottom slag and the maximum dry density curve is shown in figure 3. the best water content of the incineration bottom slag under heavy compaction test conditions is 11%, and the maximum dry density is 2.05g/cm 3 . it can be seen that when the water content of the incineration bottom slag is lower than 11%, the soil quality is relatively uniform, the strength is high, so it is not suitable for compaction, and additional settlement is likely to occur when the soil samples are immersed in water. when the incineration bottom slag is in a state where the water content is greater than 11%, the soil structure is dispersed, has strong plasticity, and a strong ability to adapt to deformation, but it has low strength and strong anisotropy. in summary, when the incineration bottom slag is at a suitable water content, it can show good compaction, strong plasticity, and high strength. b. direct shear test the direct shear test is a simple and effective method to determine the shear strength of the soil. the maximum shear stress of the soil under different vertical loads and pressures was determined, and finally two important shear strength indexes of soil were obtained, cohesion c and friction angle φ, which can be used as an important theoretical basis for evaluating soil bearing capacity. the relationship curve between the shear strength of the bottom slag and the vertical pressure is shown in figure 4. according to the analytical test results, the friction angle of the bottom slag is 31.8°, and the cohesion is 41.2kpa. fig. 4. relationship between shear strength and vertical pressure. engineering, technology & applied science research vol. 12, no. 2, 2022, 8306-8310 8309 www.etasr.com xue et al.: beneficial reuse of municipal solid waste incineration bottom slag in civil engineering c. cbr test the california bearing ratio (cbr) test evaluates the loadbearing capacity of the soil material through the use of a probe of a specific size to penetrate the soil sample. the bearing ratio is a value that characterizes the ability of a material to resist local deformation. it refers to the ratio of the unit pressure when the penetration amount reaches 2.5mm or 5mm to the load strength when the standard crushed stone sample is pressed into the same penetration amount. fig. 5. relationship between water content and penetration. the relationship between water content and penetration is shown in figure 5. from the relationship between water content and the cbr value, it can be seen that the cbr value changes parabolically with the change of water content. the parabola reaches the highest point at the optimal water content, and the maximum cbr value is obtained. for bottom slag samples with the same water content, the higher the compaction times, the greater the cbr value. when the water content is the same, the more compaction times, the greater the unit compaction work received by the sample, the higher the degree of compaction, and the stronger the bearing capacity, which is manifested by the gradual increase in the cbr value. iv. engineering application analysis a. embankment backfill in highway construction, a large amount of earthwork is needed to fill the roadbed and the pavement. from the aforementioned screening and compaction tests, it can be seen that the bottom slag has good framework and compaction performance. according to the relevant standards of highway quality acceptance, the maximum compaction degree of the first-class expressway is required to reach 96% under heavy compaction conditions, and 95% for the second-class highway. it can be seen from the compaction test that the compaction of the incineration bottom slag can reach 97% under the conditions of the heavy compaction test, which means it meets the highway quality acceptance standard. b. binder admixture in many silt treatment projects, due to the characteristics of high water content, weak permeability, and low strength of silt, its processing efficiency is greatly hindered. the bottom slag of waste incineration is different from sludge. it has a porous surface, strong water absorption, high strength, and a certain amount of pozzolanic activity. if the aggregate properties of the incineration bottom slag, higher water absorption, and pozzolanic activity are considered, the waste incineration bottom slag can be mixed into the sludge and improve its mechanical properties and increase its volume. therefore, the treatment efficiency can be improved significantly. from the results of particle size analysis, it can be seen that the content in particles larger than 5mm in the bottom slag is 70.15%, while the content of particles smaller than 5mm is only 29.85%. therefore, the size of the incineration bottom slag is above 4.75mm, which meets the requirements of gb/t14685-2011 [23]. it can be used as a gravel-like aggregate in the solidification of sludge, playing a good skeleton function. in the mixed soil material, the bottom slag plays the role of the coarse-grained framework, and the fine particles in the sludge fill the pores between the particles. c. use in concrete and asphalt instead of aggregates through the analysis of the bearing ratio and the test results, the incineration bottom slag has good local compressive strength. the content of particles within the range of 2-60mm in the bottom slag is 52.97%, and the content of particles smaller than 0.1mm is 3.47%. high content of large particles can play a very good skeleton effect. according to gb/t14684-2001 [24], the thickness and particle gradation are evaluated, and the fine-grain modulus is calculated to be 2.5, and the particle gradation is within a reasonable range, indicating that the bottom slag can be used as gravel aggregates in concrete. v. discussion in most developed countries, the comprehensive utilization rate of incineration bottom slag is very high, and in some reaches 100% [20, 21]. however, the characteristics of the solid waste incineration bottom slag are significantly affected by the region, and its economic development level. this paper studies the physical and mechanical properties of the solid waste incineration bottom slag in central china, represented by wuhan, and analyzes the feasibility of recycling the incineration bottom slag in civil engineering. for example, the cu and cc of incineration bottom slag in suzhou area reported in [22] are 0.05 and 44, respectively, and the optimal moisture content is around 17%, which diverge greatly from the values obtained in this paper. therefore, the comprehensive reuse of incineration bottom slag needs to consider many factors, and it is necessary to take measures according to local conditions, and take the optimal resource recycling method according to the characteristics of incineration bottom slag in different regions. vi. conclusions this paper conducted a series of experimental studies on the bottom slag of waste incineration, analyzed its basic physical and mechanical properties, and conducted a feasibility analysis of its resource utilization in civil engineering. the following conclusions were drawn: • the incineration bottom slag has similar properties to sandy soil. the content of coarse particles is relatively high, the surface is loose and porous, and the water absorption rate is relatively high. the specific gravity is about 2.71. under engineering, technology & applied science research vol. 12, no. 2, 2022, 8306-8310 8310 www.etasr.com xue et al.: beneficial reuse of municipal solid waste incineration bottom slag in civil engineering heavy compaction conditions, it can reach a compaction degree more than 95%, and the effective cbr is not less than 72.96% at the optimal water content. • the specific gravity of the incineration bottom slag is close to that of sand, with good compaction performance, high compressive strength and low shear strength. the incineration bottom slag has good framework supportability, strong water absorption, and easy to improve gradation. • when the incineration bottom slag is matched with different materials, it can show better engineering properties. the incineration bottom slag can be combined with fine-grained soil and be used to road embankment filling. due to the good compatibility of the incineration bottom slag, the improved particle size gradation is better, and the compaction effect is significantly improved. in addition, the bottom slag can be used as sludge solidified aggregates to replace aggregates of cement concrete and asphalt materials. references [1] m. bekhiti, h. trouzine, and a. asroun, "properties of waste tire rubber powder," engineering, technology & applied science research, vol. 4, no. 4, pp. 669–672, aug. 2014, https://doi.org/10.48084/ etasr.439. 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[24] gb/t 14684-2011. sand for construction. beijing, china: china planning press, 2011. engineering, technology & applied science research vol. 7, no. 6, 2017, 2273-2276 2273 www.etasr.com narimani and farhoudi: design of a self-phased quadrifilar helix antenna for satellite communication design of a self-phased quadrifilar helix antenna for satellite communication razieh narimani satellite research institute iranian space research center tehran, iran r.narimani@isrc.ac.ir leila farhoudi satellite research institute iranian space research center tehran, iran l.farhoudi@isrc.ac.ir abstract—the objective of this study is the design and implementation of a quadrifilar helix antenna (qha) for telemetry, tracking and control of a low earth orbit (leo) satellite. because of its cardioid-shaped circularly polarized beam, qha can satisfy requirements of satellite communications completely. in this paper, a variation of qha referred to as “selfphased qha” with a single feeding circuit, has been proposed to reduce implementation complexity. the designed antenna has been analyzed and the experimental results show that the radiation pattern provides good wide-beam in the desired frequency while the antenna’s bandwidth is around 200mhz when vswr is less than 2. keywords-quadrifilar helix antenna; circular polarization; satellite communication i. introduction there are many applications for the quadrifilar helix antenna (qha), because of its cardioid-shaped circularly polarized beam [1], such as global positioning systems [2, 3], mobile handsets and terminals [4-6] and space applications [7, 8] such as satellite payloads [9]. in the literature, there are several designs for dual-band qhas [10-15]. the aim of this study is to design and implement a qha for telemetry, tracking and control (tt&c) subsystem, which can be used as both receiver and transmitter. the designed antenna has a simple feeding circuit that makes the implementation easier. tt&c subsystem is one of the major parts of a low earth orbit (leo) satellite which is responsible for the communication between the satellite and the ground. the link between ground station and tt&c must always be fully operational. a connection loss would result in control loss of the satellite. for this reason the pattern of the antenna is a vital issue. in a leo satellite with attitude determination and control subsystem, tt&c antenna radiation should be from both sides of the satellite because in both nadir and anti-nadir pointing situation the communication link should be stable. the desired radiation pattern can be achieved by using a single antenna or a combination of multiple antennas. here, the antenna pattern has been achieved by using two separate s-band self-phased qhas described below. ii. antenna design and implementation a. self-phased qha the qha was first introduced in [1] and further designed in [16, 17]. in order to reduce complexity of the feeding circuit, a variation of qha referred to as “self-phased qha” has been proposed. the self-phased qha is composed of two bifilar loops, fed in parallel, designed with different resonant lengths, resulting 90° current phase shift with respect to one another. optimizing the dimension of the bifilars, will improve the performance of the antenna. since the input impedance of r+jr for longer loop and r-jr of shorter one is achieved, input impedance of r is obtained for the antenna when the two elements are excited by a single source [18]. we utilize the self-phased qha in s-band as both transmitter and receiver antenna for a leo satellite. b. simulation of the designed antenna firstly, a self-phased qha has been designed and simulated in s-band frequency by cst software. figure 1 shows the simulated antenna. the geometrical configuration of a helix consists usually of n turns, diameter d and spacing s between each turn. the total length of the antenna is l=ns, while the total length of the wire is ln=nl0, where l0 is the length of the wire between each turn and c=πd is the circumference of the helix. another important parameter is the pitch angle α which is the angle formed by a line tangent to the helix wire and a plane perpendicular to the helix axis. the pitch angle is defined by [19]: -1 sα=tan πd       (1) based on the proposed design, dimensions of the antenna are computed as follows. the larger loop is specified by: n=0.25, d = 24.2 mm, s=0.36λ, l=ns=0.25*0.36λ=0.09λ, f=2.25ghz→λ=0.133m and α = 32.2°. the smaller one is characterized as follows: n=0.25, d = 22.9 mm, s=0.34λ, l=ns=0.25*0.36λ=0.085λ, f=2.25ghz→ λ=0.133m and α = 32.16°. a semi-rigid coaxial cable can be used as balun and engineering, technology & applied science research vol. 7, no. 6, 2017, 2273-2276 2274 www.etasr.com narimani and farhoudi: design of a self-phased quadrifilar helix antenna for satellite communication base of the antenna. the length of the cable used as balun is λ/4 of the minimum operating frequency. as such, it covers the highest frequency as well. this structure is a simple 1:1 current balun which causes 180◦ phase shift in the antenna’s feed. fig. 1. simulated antenna in cst. fig. 2. helix geometry. fig. 3. feeding circuit. we assume the following case study to use the designed antenna as tt&c antenna of a leo satellite, in which, the ground station communicates with a the satellite in 500 km orbit beginning from 10° elevation angles. antenna pattern should be measured in a corresponding boresight angle which is computed by the following formula: -1 e e r boresight=2sin ( cose) r +h (2) where re is earth radius, h denotes the orbit of the satellite, and e is the elevation angle. based on above assumptions, boresight angle is calculated as 120 which corresponds to θ=60°. as shown in figure 4 antenna gain is always higher than 1.5dbi. thickness of the wire used to simulate the antenna, will put the vswr of the antenna in its proper range, making the antenna applicable in both uplink and downlink frequencies. vswr is shown in figure 5. fig. 4. simulated antenna pattern. fig. 5. vswr of the simulated antenna. c. implementation and using as tt&c antenna based on antenna simulation described in the previous session, a self-phased antenna has been implemented in laboratory (figure 6). figure 7 illustrate antenna pattern and vswr for the implemented antenna which is measured in a far field antenna chamber. the measurement results are in close agreement with simulation. as mentioned earlier, the implemented antenna has been designed to be used as transmitter and receiver antenna individually in tt&c subsystem. in order to make this antenna applicable to this usage, it is required to position two separate antennas, each in one side of the satellite (in nadir and anti-nadir side) in order to have acceptable radiation coverage. because of the size of the satellite, shown in figure 9 we run the simulation using the mlfmm solver method in cst software. the result of impedance simulation within frequency range is shown in figure 10. for a satellite with attitude determination and control subsystem, in nadir pointing situation, antenna radiation should be calculated in θ=120°. for this θ the antenna pattern is shown in figure 10. in anti-nadir satellite pointing, antenna radiation should be calculated in θ=60° and the antenna pattern is shown in figure 11. since there is not considerable engineering, technology & applied science research vol. 7, no. 6, 2017, 2273-2276 2275 www.etasr.com narimani and farhoudi: design of a self-phased quadrifilar helix antenna for satellite communication difference between the simulated antenna and the one built in laboratory, it can be induced that in a similar way the simulation of the antennas and a real situation would produce the similar results with negligible error. based on the numerical results, the antenna designed in this paper, can be used as tt&c antenna. fig. 6. implemented antenna. fig. 7. implemented antenna pattern (phi=0). fig. 8. vswr of the implemented antenna. fig. 9. satellite model with two antennas. fig. 10. radiation pattern in nadir. fig. 11. radiation pattern in zenith. iii. conclusion in this paper, a comparison of the vswr and radiation pattern properties of a self-phased quadrifilar helix antenna is presented. the simulated and measured results show that the bandwidth of the antenna is around 200mhz when vswr ≤ 2. using single feeding circuit reduces the complexity of fabrication and the weight of the antenna. as reliability is a main concern in satellite communication, lower complexity leads to reducing the number of failures of the system. references [1] c. c. kilgus, “multi-element fractional turn helices”, ieee transactions on antennas and propagation, vol. 16, no. 4, pp. 499–500, 1968 [2] j. m. tranquilla, s. r. best, “a study of the quadrifilar helix antenna for global positioning system (gps) applications”, ieee transactions on antennas and propagation, vol. 38, no. 10, pp. 1545–1550, 1990 [3] y.-s. wang, s.-j. chung, “a miniature quadrifilar helix antenna for global positioning satellite reception”, ieee transactions on antennas and propagation, vol. 57, no.12, pp. 3746-3651, 2009 [4] g. nicolaidis, o. leisten, j. c. vardaxoglou, “tlm investigation of dielectric loaded bifilar personal telephone antennas”, iee national conference on antennas and propagation, pp. 16-19, 1999 [5] a. kumar, fixed and mobile terminal antennas, artech house, 1991 [6] b. fan , l. xu , h. zhang , y. wang, “design of a dual(uhf/s) bands antenna handset”, 11th international symposium on antennas, propagation and em theory, pp. 118-120, 2016 [7] a. takacs, t. idda, h. aubert, h. diez, “miniaturization of quadrifilar helix antennas for space applications”, 15th international symposium on antenna technology and applied electromagnetics, pp. 1-3, 2012 engineering, technology & applied science research vol. 7, no. 6, 2017, 2273-2276 2276 www.etasr.com narimani and farhoudi: design of a self-phased quadrifilar helix antenna for satellite communication [8] j. costantine, y. tawk, i. maqueda, m. sakovsky, g. olson, s. pellegrino, c. g. christodoulou, “uhf deployable helical antennas for cubesats”, ieee transactions on antennas and propagation, vol. 64, no. 9, pp. 3752-3759, 2016 [9] r. cahill, i. cartmell, g. van dooren, k. clibbon, c. sillence, “performance of shaped beam quadrifilar antennas on the metop spacecraft”, iee proceedings microwaves, antennas and propagation vol. 145, no. 1, pp. 19-24, 1998 [10] d. lamensdorf, m. a. smolinski, “dual-band quadrifilar helix antenna”, ieee antennas and propagation society international symposium, pp. 488–491, 2002 [11] r. sainati, j. groppelli, r. olesen, a. stanland, “a band-switched resonant quadrifilar helix”, eee transactions on antennas and propagation, vol. 30, no. 5, pp. 1010–1013, 1982 [12] a. a. agius, s. r. saunders, b. g. evans, “antenna design for the ico handheld terminal”, 10th conference on antennas and propagation, pp. 1385–1389, 1997 [13] m. hosseini, m. hakkak, p. rezaei, “design of a dual-band quadrifilar helix antenna”, ieee antennas and wireless propagation letters, vol. 4, no.1, pp. 39-42, 2005 [14] k. chen, h. wang, y. huang, j. wang, “a compact dual-band assembled printed quadrifilar helix antenna for cnss application”, international symposium on antennas & propagation, pp. 1233-1236, 2013 [15] b. ning, j. lei, y. cao, l. dong, “a conical quadrifilar helix antenna for gnss applications”, international symposium on antennas & propagation, pp. 543-546, 2013 [16] c. c. kilgus, “resonant quadrifilar helix design”, microwave journal, vol 13, pp. 49–54, 1970 [17] c. c. kilgus, “shaped-conical radiation pattern performance of the backfire quadrifilar helix”, ieee transactions of antennas and propagation, vol. 23,pp. 392–397, 1975 [18] m. amin, r. cahill, “bandwidth limitation of two-port fed and selfphased quadrifilar helix antennas”, microwave and optical technology letters, vol. 46, no. 1, pp. 11-15, 2005 [19] c. a. balanis, antenna theory, analysis and design, 2nd edition, john willey and sons inc, 2002 microsoft word 4-616-ed.doc engineering, technology & applied science research vol. 6, no. 1, 2016, 917-922 917 www.etasr.com karkush: impacts of soil contamination on the response of piles foundation under a combination… impacts of soil contamination on the response of piles foundation under a combination of loading mahdi o. karkush civil engineering department university of baghdad baghdad, iraq mahdi_karkush@coeng.uobaghdad.edu.iq abstract—  the behavior of single piles driven into contaminated clayey soil samples subjected to a combination of static axial and cyclic lateral loadings have been studied in this research. a laboratory model was manufactured especially for studying such behavior. a solid circular cross sectional area pile of diameter 19 mm and made from aluminum, the pile was embedded into the soil with an eccentricity to embedded length (e/l) ratio of 0.334. the intact soil samples and industrial wastewater were obtained from the center of iraq. the industrial wastewater is a byproduct disposed from musayib thermal electric power plant. the intact clayey soil samples were synthetically contaminated with four percentages of 10, 20, 40 and 100% from the weight of water used in the soaking process which continued for a period of 30 days. the different percentages of contaminant concentrations have significant effects on the lateral load-displacement relation of the piles subjected to a combination of axial and lateral loadings. the vertical displacement under the same vertical load increased by 5–95%, the axial strength of piles decreased by 10–34% and the lateral-bearing capacity of the piles decreased by 10–34% with increasing the percentage of contamination from 10 to 100%. the ratio of permanent lateral displacement to the total lateral displacement was increased by 23–27% when the concentration of contaminant increased by 10-100%. generally, the application of axial loading increases the lateral-bearing capacity of piles, and reduces the total lateral displacement. keywords-industrial wastewater; soil contamination; clayey soil; axial loading; cyclic lateral loading; pile foundation; almusayib city i. introduction soil contamination can be defined as the sum of all factors that deteriorate the quality, texture and mineral content of the soil [1]. soil contamination becomes a contentious issue due to the large-scale development of industries, raising the standard of living, and the urbanization of small towns. the main sources of soil contamination are agricultural activities, urban activities, industrial effluents, and solid waste [2]. the major generators of industrial solid wastes are the thermal power plants producing coal ash, the integrated iron and steel mills, processing industries generating press mud, pulp and paper. manassero and shackleford [3] classified the industrial wastes as residue from incineration processes (fly ash), residues from metallurgical industrial processes, residues from construction, oil industries, electric power stations, subsoil treatment and investigation, and residues from waste liquid, and gas treatment plants. piles are columnar elements in a foundation which have the function of transferring load from the superstructure through weak compressible strata or through water, onto stiffer or more compact and less compressible soils or onto rocks [4]. pile foundations are extensively used in onshore, offshore, wind turbine, and marine structures. the piles that are supporting these structures are inevitably subjected to lateral static and cyclical loading generated by wave, current, wind and others. combinations of vertical and horizontal loads are carried out where piles are used to support retaining walls, bridge piers and abutments, and machinery foundations. the response of piles subjected to lateral cyclic loading had been studied by many researchers [5-10], the main observations on the response of a pile subjected to quasistatic cyclical lateral loading are summarized as follows:  both lateral displacement and moment increase with increasing the number of cyclic loading level  the ultimate lateral load capacity decreases when increasing the number of cyclic loading level  the cyclical behavior of the pile is similar in homogenous and heterogeneous soils  the lateral displacement and the bending moments developed near the piles of a group are greater than that of a single pile  for cohesionless soils, no gap is observed at the end of the cyclic loading  effects of cyclical degradation are more severe for stiff soils than in soft clay  the loading rate has a significant effect on the displacement action of the pile  one-way cyclic lateral loading produces higher permanent displacement and greater cumulative deflection of the piles than the two-way cyclic lateral loading. poulos and davis [11] referred two phenomena that contribute to an increase in the displacement of laterally loaded piles with a growing number of cycles: the structural phenomenon known as "shakedown" of the pile in soil, and the engineering, technology & applied science research vol. 6, no. 1, 2016, 917-922 918 www.etasr.com karkush: impacts of soil contamination on the response of piles foundation under a combination… phenomenon of cyclical soil degradation. dewaikar et al. [8] studied the ultimate lateral load of flexible free-headed piles in a soft clayey soil under cyclical loading. the initial degradation is very high at about 8% for the first five cycles, while the degradation was only 3% of cycles from 100 to 200. haigh and bolton [10] studied the response of a large-diameter single-pile under one-way force of cyclical lateral loads. also, they discussed the accumulated pile shaft horizontal displacement caused by the permanent cyclical lateral displacement, and the effects of lateral loads on the pile cyclical lateral secant stiffness. basack [9] studied the response of 2×2 piles group subjected to horizontal cyclical load in soft clay. the experimental setup was designed in such a manner that the cyclical loading test could be performed under both the displacement-controlled and the load-controlled modes. following investigation, it has been observed that under the effect of lateral cyclic loading on a pile group in soft clay, the pile capacity decreases. karkush and abdul kareem in [12] studied the effects of soil contamination on the behavior of a single pile subjected to lateral cyclic loading, and in [13] studied the effects of contamination on the behavior of a group of piles subjected to lateral cyclic loading. in both cases of a single pile and a group of piles, increasing the concentration of contamination causes a decrease in the lateral-bearing capacity of piles, and an increase in the total and permanent lateral displacements. in this research, the impacts of industrial wastewater on the performance of single pile foundation driven in contaminated clayey soil under a combination of static axial load and lateral cyclical loads has been investigated experimentally, where several ratios of contaminant mixed with soil synthetically. ii. experimental work the intact soil samples were obtained from al-musayib city which is located at the center of iraq (utm: 33n515276, 44e28102), from a depth of 4 m below the natural ground level. the contaminant is an industrial wastewater discharged of the thermal electrical power plant as byproduct. the soil samples were soaked by industrial wastewater for 30 days in plastic covered containers. the industrial wastewater was added in four ratios of 10, 20, 40 and 100% from the weight of the distilled water used in the soaking process, where these soil samples are designated as c0, c1, c2, c3 and c4 for intact and contaminated soil samples, respectively. the properties and dimensions of the used pile models are listed in table i. table i. material properties and dimensions of pile model property symbol value length e+l 500 mm diameter d 19 mm tensile strength fy 95 mpa ultimate tensile strength fu 110 mpa young modulus e 69 gpa moment of inertia i 6.397×10-9 m4 bending stiffness ei 4.41×10-4 mn.m2 the pile used in the present work with l/d≥20 is considered long, flexible and a free-head pile [4]. the pileloading model consisted of a steel container, pile-fixing tool, dial gauge-fixing tool, and load application system, as shown in figures 1 and 2. the details and specifications of this model, pile material and geotechnical properties of soils were well explained in [12]. fig. 1. pile loading model-vertical displacement. fig. 2. pile loading model-lateral displacement. iii. pile model loading test the basic scheme for the test follows the below steps:  preparing the pile model, soil sample, and the necessary prescribed instruments and equipment.  add the soil in six layers (each 80 mm thick) with tamping to reach the field unit weight and moisture content.  insert the pile into the soil up to the required embedded depth with (e/l) equal to 0.334  install the loading system (hydraulic pressure jack, pressure gauge, load cell, and digital weighing indicator) and dial gauge at the free head of the pile  soak the soil sample in distilled water to cover the soil sample in the box. for intact soil, only distilled water was used, whereas a chemical solution (distilled water mixed with industrial wastewater in four concentrations 10, 20, 40 and 100% by weight of water) was used for soaking the contaminated soil samples. then, the soil sample was soaked for 6 hours before starting the loading process engineering, technology & applied science research vol. 6, no. 1, 2016, 917-922 919 www.etasr.com karkush: impacts of soil contamination on the response of piles foundation under a combination…  start the axial loading process by adding incremental loads of 0, 10, 20, 40, 60, 80, 100, 120, 140 and 160 n  record the readings of the dial gauge during axial loading to calculate the vertical displacement of the piles cap  start the lateral loading process by adding incremental loads of 10, 20, 40, 80, 120, 160, 200, 250, 300, 350, 400, 450 and 500 n. the rate of loading cycle was 1 cycle/min for each load increment in both the loading and unloading stages.  the rate of cyclical loading should be at a uniform rate, the best rate is one loading cycle in each minute. when the rate is rapid, the lateral displacement records the largest or less than a displacement of the previous cycle. when the loading rate is one cycle in five minutes, the next displacement becomes less than a displacement in a previous cycle due to the recovery of soil deformation.  record the readings of the dial gauge during loading (total lateral displacement) and when unloading (permanent lateral displacement).  stop the test when the total lateral displacement reach 14 mm, so the number of increments may change according to the ultimate lateral-bearing capacity of the pile and soil. iv. results and discussions the contamination has significant effects on the behavior of piles subjected to a combination of axial loading and lateral cyclical loading. the main relations obtained from this research are: axial static load–vertical displacement and lateral cyclic load–total and permanent lateral displacements. the variation of vertical displacement with axial load and time are shown in figures 3 and 4 respectively. at the same level of axial loading of 300 n, the vertical displacement was decreased by 5, 10, 26 and 95% for soil samples c1, c2, c3 and c4, respectively, compared to the pile inserted in intact soil. the variation of total lateral displacements with lateral cyclic loading are given in figures 5 to 8, while the variation of permanent lateral displacement with lateral cyclic loading are given in figures 9 to 12. the lateral load capacity of the piles decreased with increasing the concentration of contaminat in soil due to increasing the ultimate moment on the pile head, which causes an increase in the lateral displacement and a decrease in the soil strength around the pile shaft. the lateral-bearing capacity after 100 cycles of loading decreased by 10, 10, 24 and 34% for soil samples c1, c2, c3 and c4, respectively. it is noticed that there is no difference in the ultimate bearing capacity of c1 and c2, but there is a noticible difference in the total lateral displacement. the soil degradation caused by contamination led to weakening of the soil strength, where the degradation rate of lateral displacement increases with increasing the number of loading cycles. based on the results, the degradation of displacement is high for the first 10 cycles. the results obtained from this study for e/l = 0.334 were compared with those obtained by karkush and abdul kareem [12] for e/l equals 0.25 and 0.5 as shown in table ii. based on the results, the application of axial load causes an increase in the lateralbearing capacity and a decrease in the total lateral displacement of pile. also, the lateral-bearing capacity of pile decreased with increasing the ratio of contamination and e/l, while an adverse effects was observed in lateral displacement of pile. fig. 3. vertical displacements versus vertical load. fig. 4. vertical displacements versus time. fig. 5. total lateral displacement versus lateral load at n = 1 cycle. engineering, technology & applied science research vol. 6, no. 1, 2016, 917-922 920 www.etasr.com karkush: impacts of soil contamination on the response of piles foundation under a combination… fig. 6. total lateral displacements versus lateral load at n = 25 cycles. fig. 7. total lateral displacements versus lateral load at n = 50 cycles. fig. 8. total lateral displacements versus lateral load at n = 100 cycles. fig. 9. permanent lateral displacements versus lateral load at n = 1 cycle. fig. 10. permanent lateral displacements versus lateral load at n = 25 cycles. fig. 11. permanent lateral displacements versus lateral load at n = 50 cycles. engineering, technology & applied science research vol. 6, no. 1, 2016, 917-922 921 www.etasr.com karkush: impacts of soil contamination on the response of piles foundation under a combination… fig. 12. permanent lateral displacements versus lateral load at n = 100 cycles. table ii. lateral displacements and load capacity soil sample total lateral displacement (mm) lateral load capacity (n) e/l e/l 0.25 0. 5 0.334 0.25 0. 5 0.334 c0 13.25 13.10 13.20 440 320 500 c1 13.39 13.42 11.17 420 300 450 c2 13.46 12.88 13.29 400 280 450 c3 13.28 13.45 13.40 360 270 380 c4 13.36 13.46 13.23 280 220 330 the ultimate single pile lateral capacity is calculated using the model proposed in [14]. the proposed degradation model is a function of number of load cycles, the ratio of the elasticity modulus of soil to the undrained shear strength, and the degradation factor (df). the degradation factor is the ratio of total lateral displacement at first cycle to the total lateral displacement of cycle 100. the proposed equation is: , (1 log( ) ln( ) 0.031) (1)u p f f u e p p n d c      where, pu,p is the proposed ultimate lateral load, pf is the maximum lateral load lead to failure of pile, e is young modulus of pile material, cu is the undrained shear strength of soil and n is the number of loading cycles. the results obtained from the proposed equation are compared with those obtained experimentally as shown in table iii. table iii. variation of lateral capacities of piles with loading cycles soil sample df e/cu pf (n) pu,p (n) n=1 n=10 n=25 n=50 n=100 c0 0.897 106 500 500 435 409 390 370 c1 0.892 102 450 450 392 369 352 335 c2 0.876 100 450 450 394 371 354 337 c3 0.845 108 380 380 333 315 301 287 c4 0.829 98 330 330 291 276 264 252 the ratio of proposed pu,p to pf from the first loading cycles to one hundred ranges (0.74~1), (0.744~1), (0.749~1), (0.755~1) and (0.764~1) for soil samples c0, c1, c2, c3 and c4, respectively. these ratios offers to the validity of the proposed model, as the proposed model shows well agreement between the estimated value of lateral bearing capacity and that measured experimentally when compared at the first cycle of loading, but the difference between estimated and measured lateral bearing capacity increases with increasing the number of loading cycles. v. conclusions industrial wastewater has diverse effects on the lateral carrying capacity of piles subjected to lateral cyclical loading. also, it has diverse impacts on the vertical and total and permanent lateral displacements. the conclusions can be summarized as follows:  at the same level of axial loading (300 n) on the piles, the vertical displacement increased by 5, 10, 26 and 95% in soil samples c0, c1, c2, c3 and c4, respectively, in comparison with the vertical displacement of the piles driven into intact soil  the axial loading resistance of piles decreased with an increase of the percentage of contamination, where the axial loads decreased by 10, 10, 24 and 34% in soil samples c0, c1, c2, c3 and c4, respectively. it is important to note that samples c2 and c3 failed at different magnitudes of vertical displacement  the lateral-bearing capacity of the piles decreased by 10, 10, 24 and 34% in soil samples c0, c1, c2, c3 and c4, respectively, in comparison with the lateral-bearing capacity of the piles in intact soil  the ratios of permanent lateral displacement to the total lateral displacement are 28, 27, 23, 26 and 27% in soil samples c0, c1, c2, c3 and c4, respectively. these ratios are approximately constant because they depend on pile material properties, not on the soil properties  the presence of axial loading increased the lateral-bearing capacity of piles, and reduced the lateral displacement of piles  more studies required about the effects of drainage from the soil when pile foundation subjected to axial and lateral loading simultaneously. references [1] l. n. reddi, h. i. inyang, geoenvironmental engineering principles and applications, marcel dekker inc. new york, 2000 [2] h. d. sharma, k. r. reddi, geoenvironmental engineering site remediation, waste containment, and emerging waste management technologies, john wiley and sons, inc, 2004 [3] m. manassero, c. d. shackelford, “classification of industrial wastes for re-use and landfilling”, proc., 1st iceg, edmonton, bitech publishers, richmond b.c, 1994 [4] m. j. tomlinson, pile design and construction practice, 4th edition. london, view point publication, 1994 [5] b. b. broms, “lateral resistance of piles in cohesionlesssoils'”, proceeding of asce, vol. 90, pp. 123-156, 1964 engineering, technology & applied science research vol. 6, no. 1, 2016, 917-922 922 www.etasr.com karkush: impacts of soil contamination on the response of piles foundation under a combination… [6] l. c. reese, w. r. cox, f. d. koop, “analysis of laterally loaded piles in sand”, 6th off shore technology conference, houston, vol. 2, pp. 473-483, 1974 [7] s. basack, “effect of lateral cyclic load on axial capacity of pile group in sand”, int. seminar on civil and infrastructural engineering, university of technology, mara, malaysia, 2006 [8] d. m. dewaikar, s. v. padmavathi, r. s. salimath, “ultimate lateral load of a pile in soft clay under cyclic loading”, 12th international conference of international association for computer methods and advances in geomechanics, pp. 3498 – 3507, 2008 [9] s. basack, “response of vertical pile group subjected to horizontal cyclic load in soft clay”, latin american journal of solids and structures, vol. 7, pp. 91–103, 2009 [10] s. k. haigh, m. d. bolton, “centrifuge modeling of mono pile under cyclic lateral loads”, 7th international conference on physical modeling in geotechnics, zurich, vol. 2, pp. 965-970, 2012 [11] h. g. poulos, e. h. davis, pile foundation analysis and design, john wiley and sons, new york, 1980 [12] m. o. karkush, m. s. abdul kareem, “behavior of pile foundation subjected to lateral cyclic loading in contaminated soils”, journal of civil engineering research, vol. 5, no. 6, pp.144-150, 2015 [13] m. o. karkush, m. s. abdul kareem, “behavior of piles group subjected to lateral cyclic loading in contaminated soils”, international journal of geomate, vol. 10, no. 21, 2016 [14] m. o. karkush, m. s. abdul kareem, “lateral load-carrying capacity of a pile foundation in contaminated soils” (unpublished) engineering, technology & applied science research vol. 7, no. 5, 2017, 2005-2009 2005 www.etasr.com catana et al.: gas turbine engine starting applicated on tv2-117 turboshaft gas turbine engine starting applicated on tv2-117 turboshaft razvan marius catana gas turbine experimentation complex, rr&di for gas turbines comoti bucharest, romania razvan.catana@comoti.ro grigore cican aerospace sciences “elie carafoli” department politehnica university of bucharest bucharest, romania grigore.cican@upb.ro gabriel dediu gas turbine experimentation complex, rr&di for gas turbines comoti bucharest, romania gabriel.dediu@comoti.ro abstract—the paper presents the examination of two different types of engine starting configurations, applicated on tv2-117a turboshaft, running into the test bench. the first type of starting configuration is a normal starting, with the engine connected to the dynamometer which controls the free turbine speed by the dynamometer load. the second type of starting is a different one, the engine is not connected with the dynamometer, therefore it results that there is no control of the free turbine speed from the dynamometer, only from the engine but in particular conditions. to achieve the starting phase an instrumentation scheme is created, to control and monitor the engine, and a starting sequence with all the parameters, confirmations and commands that are involved into the starting phase. the engine starting is performed by the test bench operating system, composed of an acquisition system and a programmable controller, wherewith is running the starting sequence. keywordturboshaf; starting; instrumentation scheme; graphic interface; monitoring parameters i. introduction the starting and the testing of gas turbine engines will be performed each time the engine is overhauled [6], taken out of preservation, or each time the engine encounters a problem which affects its working parameters. there are some references about starting and testing procedures of turboshaft engines but only for the new generation of this type of engine [1, 2]. the testing of gas turbine engines implies an automatic system in order to monitor the main parameters and to control the engine in time of running. for starting and testing older generation of turboshaft engines which are not equipped with electronic control units, it is necessary to create the instrumentation and the graphic interface in order to monitor and record the main and secondary parameters, confirmations and warnings which describe the engine operation. in this paper, a logical scheme for starting sequence of tv2-11a turboshaft engine, which will be run into a test bench will be realized. in one case the engine will be started in connection with the dynamometer at different loads, and in the other case the engine is not connected with the dynamometer which means the engine will start without any brake and any load. the tv2-117a [3], is a turboshaft engine with a free-turbine composed of two rotors, the rotor of the gas generator and the rotor of the free power turbine. the gas generator consists of nine stage axial compressor, of which four stator stages are with variable geometry, an annular combustion chamber and two stage axial turbines. the power turbine is also an axial turbine, consisting of two stages, which is controlled by a speed regulator. the free power turbine speed regulator maintains constant the free power turbine speed, by fuel control, in connection with the engine main fuel pump. in the starting phase the free power turbine speed regulator is a hydro mechanical speed controller that ensures the free power turbine not to over speed. in flight configuration, (figure 1), the engine transfers power from the free turbine rotor through a drive train assembly to the main rotor blade 1 and to the tail rotor blade 6, in the following way: the engine delivers power to the main gear box, by the main drive shaft 2, to the main rotor blade 1, also from the main gear box 2, by tail drive shaft 3 through an intermediate gear box 4, and by a secondary tail drive shaft 5, a part of power is delivered to the tail rotor blade 6. all the drive gear assemblies develop a resistive torque who defines the idle speed of the free power turbine at the idle engine mode. so in this case, on starting phase the engine starts with a mechanical load which is the resistive torque of the helicopter drive train assembly. in the idle mode [1], the engine develops maximum power around p ≈ 60 kw, at ntp = 45±10% free power turbine speed and gas generator speed around ngg = 65±1%. the rotor of the gas generator works at a maximum speed of ngg = 21200 rpm, delivers an air flow rate around of da ≈ 7.5 kg/s, and makes an overall pressure ratio ≈ 6.5:1, at the maximum free power turbine speed of ntp = 12000 rpm. fig. 1. helicopter drive train assembly ii. starting configuration to execute a normal starting, into the test bench, the engine is connected to the dynamometer,(figure 2), which is a brake for the free power turbine. to start the engine in the same engineering, technology & applied science research vol. 7, no. 5, 2017, 2005-2009 2006 www.etasr.com catana et al.: gas turbine engine starting applicated on tv2-117 turboshaft conditions as on helicopter, from dynamometer it is demanded the resistive torque value of the drive train assembly. the dynamometer has the capability to demand any load to start the engine. if you demand a lower load, the engine will start with a higher speed of free turbine, or if you demand a higher load the engine will start with a lower speed of free power turbine. in this case the value of load, modifies the starting value of the free turbine speed. fig. 2. turboshaft starting configuration to make an engine run into a normal starting configuration it is necessary to calculate the resistive torque, which is the value of demanded dynamometer load. to calculate the resistive starting torque the next equation is used [4]. ]nm[100 ntp p30 c      to execute the second type of starting, the engine is not connected with the dynamometer, so there is no brake for the free power turbine rotor, which means that the free turbine will produce a higher idle speed. in this case the control of the free turbine speed is made by free turbine speed regulator. if the free turbine speed exceeds 12000 rpm then the free turbine regulator reduces the fuel flow to the combustion chamber, through the main fuel pump, which means a low idle of a gas generator. if the free turbine speed not exceeds more than 90% of 12000rpm, then the gas generator has a normal idle and the free turbine speed can be higher with 20% or 50% than the normal idle free turbine speed. iii. engine startup procedure tv2-117a is a turboshaft engine which is not equipped with an engine control unit, and to perform an automatic start, into a test bench, it is required to have a control and acquisition system, which contain a programmable logic controller capable to execute the starting sequence inserted into the logic controller under a programming code. to achieve the starting sequence the main parameters and commands that will be instrumented to monitor the engine working are established [5]. tv2-117a engine has a standard instrumentation, (figure 3), formed of main parameters as gas generator shaft speed ngg, inlet turbine temperature t3m, fuel flow dc, oil pressure pumi, outlet oil temperature tume, vibrations vbm, and main commands of engine as starter, cmd3, ignition unit ign, cmd4, starting fuel valves se1-2, cmd5, start lever em_stop, cmd2, and an external commands as fuel pump p_pc, cmd1. for a detailed monitoring it is instrumented the engine with additional parameters as air flow da, free power turbine shaft speed ntp, compressor outlet static pressure p2s, and inlet fuel pressure ppc. for execution of the engine starting general diagram of the operating system is presented, consisting of general engine instrumentation and an acquisition system, that are used for engine operation from a control panel located in the test bench control room. from the control panel the signal of commands is transmitted to the actual commands, which are the engine starting system components, and which are involved into the starting phase. the engine run starting procedure [7] contains the steps of the starting sequence, (figure 4), which involves commands, confirmations and conditions that participate to the starting phase. there are a series of confirmations and warning lights reported to the engine parameters. the running program can execute a dry motoring, a wet motoring and an engine run. in this case only the engine run mode is showed. fig. 3. tv2-117a instrumentations and acquisition system to perform an engine run starting, select the button dedicated to the engine run and the sequence will start automatically, in function of time or speed ngg parameter, or manual controlled. so the logical starting sequence of engine run begins with the initialisation of the commands in-cmd, warning lights in-lh, and a starting condition spc of a series of parameters which confirms the engine is ready for starting. engine run sequence starts with: select engine run sl3 in on position then turn on the fuel pump, by acting the cmd1 command in on position, check if fuel pressure increases and wait the fuel pressure to be above the minimum value. if the condition is satisfied, the warning light goes off and it opens the engine fuel shut off valve by moving the start lever and acting the cmd2 command in on position, to allow the fuel to enter into the engine. if the start lever is in open position then a time t0r will start to be counted. at time t1r, it turns on the starter by acting the cmd3 command in on position. at time t2r the ignition is energized by acting the cmd4 command in on position. with the starter in on position the speed ngg begins to increase and when exceeds 17% it opens the starting fuel supply valves by acting the cmd5 command in on position, to allow the fuel to enter into the engine fuel system and to be ignited into the combustion chamber. at the same time the speed ngg and oil pressure pum have to increase until they exceed minimum values of the operations, the speed ngg must be higher than 60%, pum must be higher than 2bar, engineering, technology & applied science research vol. 7, no. 5, 2017, 2005-2009 2007 www.etasr.com catana et al.: gas turbine engine starting applicated on tv2-117 turboshaft and the inlet turbine temperature must be lower than 600°c. if ngg speed, oil pressure pum and inlet turbine temperature t3m, respect the condition then the engine continues to run and when the engine is on the stable idle speed, then it stops the starter, ignition and starting fuel supply valve by acting the cmd5, cmd4, cmd3 commands in off position, so in this way the engine is on idle mode. in idle mode the engine works for maximum five minutes, monitoring and recording the main parameters and then it stops the engine by acting the cmd2 command in off position. for the starting examinations an interface display was made to monitor in real time the engine parameters, confirmations and commands, to be viewed by the engine operator. the interface can be designed in different programs but in this case the interface it was designed into a dedicated engine running programming (figures 4-5). fig. 4. the logical starting scheme iv. sensors and mesuring devices to monitor the main parameters of the tv2-117 turboshaft, a series of sensors and transducers was mounted on the engine, as presented in figure 6. for measuring the engine speed ngg, free turbine speed ntp, compressor discharge static pressure pics, outlet engine oil temperature tum, fuel flow dc, vibrations vbm, a tachogenerator is used, an inductive speed transducer, pressure transducers, pt100 sensor, a fuel flow meter and accelerometers. for measuring of inlet turbine temperature t3m, the engine is equipped with 34 thermocouples. v. results from tv2-117 turboshaft starting on the test bench was obtained a series of variation curves between some engine main parameters (figures 9-16). the engine starting is performed and showed until idle mode. the engine runs are made in two configurations, normal starting, with minimum load (figure 5), helicopter starting load (figure 7), unusable starting, with no load and no connection with the dynamometer (figure 8). in figure 5 is showed a normal starting with 5nm torque value of dynamometer load. in all the cases the engine has a normal starting, the main parameters have small differences between them and only the major differences are in the values of the free turbine speed. for the unusable starting (figure 8), the free turbine has no brake, so the free turbine speed exceeds 90% without limiting the engine idle. fig. 5. engine monitoring interface fig. 6. sensors and measuring devices for tv2-117 turboshaft engine fig. 7. normal starting with the same helicopter starting load≈ 100 nm fig. 8. unusable starting with no load and no connection with the dynamometer engineering, technology & applied science research vol. 7, no. 5, 2017, 2005-2009 2008 www.etasr.com catana et al.: gas turbine engine starting applicated on tv2-117 turboshaft fig. 9. inlet turbine temperature variation with engine speed fig. 10. static overall pressure ratio variation with engine speed fig. 11. air flow variation with engine speed fig. 12. fuel flow variation with engine speed fig. 13. free turbine speed variation with engine speed fig. 14. vibration variation with engine speed fig. 15. free turbine speed variation with starting time fig. 16. engine speed variation with starting time engineering, technology & applied science research vol. 7, no. 5, 2017, 2005-2009 2009 www.etasr.com catana et al.: gas turbine engine starting applicated on tv2-117 turboshaft vi. conclusions this paper presented a logic sequence procedure of engine starting, represented by a sequence diagram based on a general engine instrumentation scheme, in order to start up an engine which is not equipped with an electronic engine control. to perform a starting, into the test bench, the engine has an operating system composed of an acquisition system and a programmable logic controller connected with the engine and with the control panel. the paper examines two different types of starting and for that it was made a series of engine runs with different dynamometers loads, 5nm and 100nm torque values, and an engine run without load and dynamometer. in case of starting with the minimum load of 5nm torque value, the free turbine speed is around 67% and the engine has a normal idle around 64%. the engine obtained a power of 51kw. in case of normal starting with the helicopter load ≈100nm torque value, the free turbine speed is around 45%, the same as is specified in the engine book, the engine has a normal idle around 65% and obtained power of 61kw. in case of unusable starting with no load, the free turbine speed is around 93%, and the engine has a normal idle around 65%. the inlet turbine speed is higher for the higher load and lower for the unload starting. the static overall pressure ratio and air flow, has almost the same values and the same variation curves. the fuel flow is similar for load starting but for unload starting the fuel flow is lower than normal starting between 20÷30% of gas generator speed. the free turbine speed in higher for the unload starting and lower for the higher load. the difference between free turbine speeds is 20% higher for minimum load and 47% for the unload starting, than the normal starting. in case of vibrations the unload starting has somewhat higher values than the normal starting. the starting time is somehow similar, the unload starting and the minimum load starting has the starting time little bigger than normal starting. in conclusion the engine can be started load or unload, and results do not affect the gas generator idle but obtain different values of free turbine speed in function of load values. references [1] w. liou, c. hoong leong, “gas turbine engine testing education, western michigan university”, collection of technical papers, 45th aiaa aerospace sciences meeting, vol. 13, pp. 8716-8724, 2007 [2] c. h. leong, j., jacob, w. w. liou, “development of a turbojet engine lab for propulsion education”, 40th aiaa/asme/sae/asme joint propulsion conference and exhibit, aiaa paper 2004-4085, 2004 [3] tv2-117a base maintenance and training manual, bucharest, 1973 [4] h dumitrescu, propeller calculation, publishing house romanian academy, bucharest, 1990 [5] federal aviation administration, aviation maintenance technician hand book, vol.1, faa-h-8083-32 [6] federal aviation administration, aviation maintenance technician hand book, vol.2, faa-h-8083-32 [7] g. cican, v. stanciu, v. silvestru, r. m. catana, fundamentals of gas turbine engine starting, processes and experiments, printech, bucharest, 2016 microsoft word etasr_v12_n3_pp8520-8524 engineering, technology & applied science research vol. 12, no. 3, 2022, 8520-8524 8520 www.etasr.com khoso et al.: the effect of water-binder ratio and rha on the mechanical performance of … the effect of water-binder ratio and rha on the mechanical performance of sustainable concrete salim khoso department of civil engineering quaid-e-awam university of engineering, science & technology larkano campus, pakistan engr.salimkhoso@gmail.com suhail ahmed abbasi department of civil engineering quaid-e-awam university of engineering, science & technology larkano campus, pakistan abbasi.suhail2009@gmail.com tariq ali department of civil engineering the islamia university of bahawalpur pakistan tariqdehraj@gmail.com zuhairuddin soomro department of civil engineering quaid-e-awam university of engineering, science & technology larkano campus, pakistan zuhairuddin@quest.edu.pk muhammad tayyab naqash department of civil engineering faculty of engineering islamic university in madinah saudi arabia engr.tayyabnaqash@gmail.com abdul aziz ansari department of civil engineering, faculty of engineering, science, technology and management ziauddin university karachi, sindh, pakistan aziz.ansari@zu.edu.pk received: 30 january 2022 | revised: 16 february 2022 | accepted: 22 february 2022 abstract-nowadays, the utilization of industrial energy, as well as construction waste, is of high concern. the current paper describes a study of the mechanical properties of cement concrete mixes utilizing rice husk ash (rha) as a cement substitute. the use of such industrial and agricultural by-products has been the focus of waste reduction for economic, environmental, and technical reasons. in this research, the compressive and split tensile strength of concrete was studied through a 15% substitution of cement with rha with 0.40, 0.45, and 0.50 waterbinder ratios. it has been found that the addition of rha significantly improves the mechanical properties of concrete for the used water-binder ratios. the ultimate strength in both compressive and tensile strength was observed at a water-binder ratio of 0.50. it has also been observed that as the water to cement ratio increased, higher gains in concrete's compressive and tensile strength were obtained for all curing periods keywords-rice husk ash; water-binder ratio; slump; compressive strength; tensile ttrength i. introduction cement concrete is considered one of the most important building materials and is extensively used in a variety of structures. this material however, also has a significant carbon footprint, as its production accounts for nearly 7% of total greenhouse gas emissions [1]. efforts have been made to use industrial waste materials in concrete as cement replacements in order to reduce carbon emissions. utilizing waste in the construction industry helps reducing the disposal problem. during the last few years, many researchers have recognized that the use of pozzolanic materials like sugarcane bagasse ash (scba), silica fume, fly ash (fa), and rha, not only improves the characteristics of concrete, but also it provides low-cost construction options [2, 28]. global production of rice equals nearly 700 million tons per year, and this value is increasing as the consumption of rice is increasing. table i gives the list of the countries leading the rice growth around the world and the potential production of husk and ash. the use of rha as a partial cement substitute will provide cheaper materials for low-cost construction. rha is very rich in silica, however, the silica content depends on the type of rice husk, the burning method, and the combustion period [3]. the utilization of global rice between 2014 and 2015 was estimated to hit 700 million tons [4, 5]. in pakistan, rice husk is being used as a food additive, and sometimes the by-product of rice husk is used in kilns as fuel. the rice husk used as fuel in kilns and other places generates huge amounts of rha with no useful application. it is commonly discarded and dumped in open areas taking up a lot of space and causing environmental pollution. this waste has been used as cement replacement to minimize its impact on the environment [6, 7]. rha can produce pozzolanic activity at temperatures around 400 0 c, and, due to the contained water, the amorphous silica present in rha can also take part in the reaction with ca(oh)2 to produce c-s-h gel [8, 9, 29]. the addition of rha in concrete has reached significant importance as it is considered environmentally safe and more durable for infrastructural development [10, 11, 30]. it has been found that using rha in concrete increases compressive and tensile strength [12, 13, 31], reduces permeability [14] and chemical attacks [15], has minimal effects of alkali-silica reactivity (asr) [16], reduces the shrinkage due to particle packing, leads to the formation of denser concrete with improved workability [17], reduces heat transfer to the walls of various structures [18], and diminishes the need of superplasticizers [19, 20]. corresponding author: salim khoso engineering, technology & applied science research vol. 12, no. 3, 2022, 8520-8524 8521 www.etasr.com khoso et al.: the effect of water-binder ratio and rha on the mechanical performance of … the aim of this study is to use rha in concrete and observe its impact on the water-binder ratio, while minimizing its effect on the environment by using it as a cement replacement material. table i. rha in the top 20 countries regarding rice production [4-5] country rice production (tons) % of total rice production produced husk (20% of total) (tons) potential ash production (18% of husk) (tons) china 204,350,000 29.26 40,870,000 7,356,600 india 152,660,000 21.86 30,532,000 5,495,760 indonesia 69,554,048 9.96 13,910,810 2,503,946 bangladesh 39,000,000 5.59 7,800,000 1,404,000 viet-nam 43,709,000 6.26 8,741,800 1,573,524 thailand 37,080,000 5.31 7,416,000 1,334,880 burma 33,200,000 4.75 6,640,000 1,195,200 philippines 18,500,000 2.65 3,700,000 666,000 brazil 11,500,000 1.65 2,300,000 414,000 japan 10,700,400 1.53 2,140,080 385,214 usa 10,606,000 1.52 2,121,200 381,816 korea 7,509,000 1.08 1,501,800 270,324 pakistan 5,800,000 0.83 1,160,000 208,800 egypt 5,700,000 0.82 1,140,000 205,200 nepal 4,750,000 0.68 950,000 171,000 cambodia 4,099,016 0.59 819,803 147,565 nigeria 3,000,000 0.43 600,000 108,000 sri lanka 2,710,000 0.39 542,000 97,560 colombia 2,400,440 0.34 480,088 86,416 laos 2,350,000 0.34 470,000 84,600 rest of the world 29,118,000 4.17 5,823,600 1,048,248 total (world) 698,295,904 100 139,659,181 25,138,653 ii. materials and methods a. materials the materials utilized in this study consist of cement, fine aggregates, coarse aggregates, and potable water. elephant brand cement was purchased from a local distributor of materials and was used as a binder in all samples. the cement was purchased after checking the date of manufacture, and no cement older than 20 days was used. the fine aggregates used was clean natural hill sand, free from clay and other impurities, having passed through a 4.75mm sieve. the coarse aggregates, with a maximum size of 19mm, were washed and dried before use. rha was collected from locally available brick kilns in the vicinity of larkana, sindh, pakistan. it is generally the waste material left over after the baking of bricks in kilns. the rha used in this experimental work was free from other ingredients and passed through a 325-sieve. drinking water with a ph value of 7.3 was used [21, 22]. b. methodology concrete samples with rha as supplementary cementitious material with a mix proportion of 1:2:4 were prepared. three different water to cement (w/c) ratios of 0.40, 0.45, 0.50 were used in the samples. for the rha-modified concrete mixtures, the cement was substituted with 15% rha (by weight). three mixtures of plain concrete and three mixtures of rha concrete were prepared. for each mixture 30 cubes, and for each age 5 cubes (90 cubes in total), each measuring 150mm×150mm× 150mm were fabricated. three different curing ages, namely 7, 14, and 28 days were considered. similarly, for each mixture (30 cylinders) and for each age (5 cylinders), cylinders of 150mm diameter and 300mm height were fabricated in order to check the tensile strength of both concretes with regard to the same curing ages. the concrete samples were fabricated and removed from the molds after one day and were placed in a water tank for the curing periods [23-25]. iii. results and discsussion a. workability slump cone test was carried out for all the prepared concrete mixes to check their workability. the results are presented in table ii. it can be observed that using rha in concrete causes minimal changes and has a minor effect on workability. however, a reduction in workability was observed due to the higher water absorption due to the presence of rha in concrete [26, 27]. b. compression test 1) results of plain and rha concrete at 0.40 w/c ratio the results of the compressive strength test of the cubes for both plain and the rha concrete with 15% cement substituted with rha at 7, 14, and 28 days using 0.40 w/c ratio are given in table iii and figure 1. table ii. slump cone test results batch w/c ratio mix proportion slump of plain cement concrete (mm) slump of rha concrete (mm) 1 0.40 1:2:4 85 81 2 0.45 1:2:4 92 87 3 0.50 1:2:4 96 91 fig. 1. comparison of the compression test results of plain and rha mixed concrete at 0.40 w/c ratio. table iii. compression test results, 0.40 w/c ratio curing days compression test results of plain concrete (mpa) compression test results of rha concrete (mpa) increase in compressive strength of rha over plain concrete (%) 7 22.57 23.09 2.30 14 28.08 28.76 2.42 28 33.99 34.61 1.82 engineering, technology & applied science research vol. 12, no. 3, 2022, 8520-8524 8522 www.etasr.com khoso et al.: the effect of water-binder ratio and rha on the mechanical performance of … it can be observed that the compressive strength of the specimens made with rha concrete is higher than the strength of plain concrete at all ages (7, 14, and 28 days) when using the 0.40 w/c ratio. the maximum compressive strength of the rha concrete at the age of 14 days is 2.42% higher than the plain cement concrete. 2) results of plain and rha concrete at 0.45 w/c ratio the results of the compressive strength test of the cubes of plain concrete using 15% replacement of cement with rha at 7, 14, and 28 days when using 0.45 w/c ratio are given in table iv and in figure 2. table iv. compression test results, 0.45w/c ratio curing days compression test results of plain concrete (mpa) compression test results of rha concrete (mpa) increase in compressive strength of rha over plain concrete (%) 7 20.33 21.55 6.00 14 25.88 27.19 5.06 28 30.62 32.05 4.67 fig. 2. comparison of the compression test results of plain and rha mixed concrete at 0.45 w/c ratio. it can be seen that the specimens made with rha have more compressive strength when compared to the control concrete samples at all curing ages. the maximum compression test of rha concrete at 7 days curing period is 6% more than the control concrete specimens'. 3) results of plain and rha concrete at 0.50 w/c ratio the results of the compression test of the plain concrete and the rha concrete using 15% replacement of cement with rha at 7, 14, and 28 days using 0.50 w/c ratio are given in table v and figure 3. table v. compression test results, 0.50 w/c ratio curing days compression test results of plain concrete (mpa) compression test results of rha concrete (mpa) increase in compressive strength of rha over plain concrete (%) 7 days 17.41 19.25 10.57 14 days 21.99 23.96 8.96 28 days 27.22 30.75 12.97 fig. 3. comparison of the compression test results of plain and rha mixed concrete at 0.50 w/c ratio. the results of the compression test of plain concrete cubes and those with 15% replacement of cement with rha at 7, 14, and 28 days using 0.50 w/c ratio show a gain in strength for the mixed samples. the maximum compression test result of rha concrete was achieved at 28 days, and is 12.97% more than the plain cement concrete. c. tensile strength test 1) results of plain and rha concrete at 0.40 w/c ratio table vi and figure 4 show the results of the tensile strength test of the cylinders for control concrete and for rha concrete using 15% replacement of cement with rha at 7, 14, and 28 days using 0.40 w/c ratio. it can be observed that rha concrete has more tensile strength than the control concrete. the maximum tensile strength of rha mixed concrete is observed at 7 days and is 8.07% more than the plain concrete's. table vi. tensile test results, 0.40 w/c ratio curing days tensile strength of plain concrete (mpa) tensile strength of rha concrete (mpa) increase in tensile strength of rha over plain concrete (%) 7 2.23 2.41 8.072 14 2.79 2.99 7.168 28 3.38 3.59 6.213 fig. 4. comparison of the tensile test results of plain and rha mixed concrete at 0.40 w/c ratio. engineering, technology & applied science research vol. 12, no. 3, 2022, 8520-8524 8523 www.etasr.com khoso et al.: the effect of water-binder ratio and rha on the mechanical performance of … 2) results of plain and rha concrete at 0.45 w/c ratio the results of the tensile strength test of the cylinders made from plain concrete using 15% replacement of cement with rha at 7, 14, and 28 days and 0.45 w/c ratio are given in table vii and figure 5. the results at 7, 14, and 28 days show that rha possesses more strength than the control concrete. higher tensile strength results were obtained at all curing periods for the rha concrete specimens. the maximum tensile strength of the rha concrete at 14 days is 11.88% more than the plain concrete's. table vii. tensile test results, 0.45 w/c ratio curing days tensile strength of plain concrete (mpa) tensile strength of rha concrete (mpa) increase in tensile strength of rha over plain concrete (%) 7 2.09 2.33 11.48 14 2.61 2.92 11.88 28 3.03 3.32 9.57 fig. 5. comparison of the tensile test results of plain and rha mixed concrete at 0.45 w/c ratio. 3) results of plain and rha concrete at 0.50 w/c ratio the results of the tensile strength test of the cylinders of plain concrete and those made of rha concrete using 15% replacement of cement with rha at 7, 14, and 28 days with 0.50 w/c ratio are given in table viii and figure 6. fig. 6. comparison of the tensile test results of plain and rha mixed concrete at 0.50 w/c ratio. the results show that the tensile strength of rha concrete is higher than that of control concrete for all curing periods. the maximum tensile strength of rha concrete was obtained at 28 days curing period, and is 14.87% more than the control concrete specimens'. table viii. tensile test results, 0.50 w/c ratio curing days tensile strength of plain concrete (mpa) tensile strength of rha concrete (mpa) increase in tensile strength of rha over plain concrete (%) 7 1.75 1.99 13.71 14 2.21 2.51 13.57 28 2.69 3.09 14.87 iv. conclusions this study has mainly focused on the inherent mechanical properties, which include compressive and tensile strength, of rha concrete at different curing periods and various w/c ratios. the results revealed that replacing cement with 15% of rha improved the mechanical properties for curing periods of 7, 14, and 28 days. from the findings, it could be concluded that: • the maximum compression test results of concrete specimens made with rha and with 0.40, 0.45, and 0.50 w/c ratios resulted to 2.42%, 6%, and 12.97% more strength than those obtained using control concrete specimens respectively. • the maximum increase in compressive strength was achieved when cement was replaced with 15% rha for 0.50 w/c ratio at 28 days curing period and was 14.87%. • the increase in the tensile strength of concrete specimens fabricated with rha concrete with 0.40, 0.45, and 0.50 w/c ratios was 8.07%, 11.88%, and 14.87% respectively. • the maximum increase in tensile strength when using 15% rha cement was observed at 0.50 w/c ratio at 28 days, which was 12.97% more than that of plain concrete. • cement concrete made with rha has the property to not only enhance the strength of cement concretebut also to save construction material cost, ultimately making these new structures more economical than the traditional ones. furthermore, the use of rha shown an increase in the strength of concrete at 15% rha replacement. it has also been observed that as the w/c ratio is increased, higher gains in compressive and tensile strength of concrete were obtained at all curing periods. acknowledgment the authors are grateful to the quaid-e-awam university of engineering, science and technology, campus larkano for providing the required 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[31] a. s. buller, z. a. tunio, f. u. r. abro, t. ali, and k. a. jamali, "influence of coarse aggregate gradation on the mechnical properties of concrete, part ii: no-fines vs. ordinary concrete," engineering, technology & applied science research, vol. 9, no. 5, pp. 4623–4626, oct. 2019, https://doi.org/10.48084/etasr.3021. engineering, technology & applied science research vol. 8, no. 1, 2018, 2598-2603 2598 www.etasr.com spruogis et al.: further research on an anti-swing control system for overhead cranes further research on an anti-swing control system for overhead cranes bronislovas spruogis dpt of mobile machinery and railway transport vilnius gediminas technical university vilnius, lithuania bronislovas.spruogis@vgtu.lt arunas jakstas dpt of mechanical and material engineering vilnius gediminas technical university vilnius, lithuania arunas.jakstas@vgtu.lt vladimir gican dpt of mechatronics, robotics and digital manufacturing vilnius gediminas technical university vilnius, lithuania vladimir.gican@vgtu.lt vytautas turla dpt of mechatronics, robotics and digital manufacturing vilnius gediminas technical university vilnius, lithuania vytautas.turla@vgtu.lt vadim moksin dpt of mechanical and material engineering vilnius gediminas technical university vilnius, lithuania vadim.moksin@vgtu.lt abstract—a method of reducing load oscillations that occur when overhead crane reaches destination position is presented in the article. the use of control drive scheme of crane bridge and trolley that ensures a smooth phase trajectory transition of the load to the optimum trajectory in accordance with pontryagin's maximum principle is proposed. mentioned control system changes the magnitude or direction of the traction force at the moment when the load is located above the destination. it is found that the degree of change of the traction force depends on the hoisting rope deviation angle from vertical. this study was conducted in order to provide more accurate and fast handling of loads by overhead crane. keywords-anti-swing control system; load; oscillations; overhead crane; pontryagin’s maximum principle i. introduction overhead cranes are widely used in industrial environments to transport loads from one place to another. due to high safety standards and requirements of small swing angle, high positioning accuracy and short transportation time, crane operation is complicated work that should be automated. however, in industrial practice, most of these machines are manually operated by long-time trained operators. this situation results in low labor productivity, low work safety etc [1]. for this reason, some researchers have started to address the control problem for overhead cranes [2]. a new fuzzy controller for anti-swing and position control of an overhead travelling crane was proposed based on the single input rule modules (sirms) dynamically connected fuzzy inference model [3]. velocity and position of the trolley as well as an angular velocity and swing angle of the rope were selected as inputs while the acceleration of the trolley was selected as an output [3]. if the initial conditions aren’t zeroed or disturbances appear during the movement, then closed control systems should be used [4, 5]. in cases when it is necessary to control the slewing motion in cranes, the systems controlling the angular velocity of the jib can be used. the angular acceleration profile of the jib is considered as an output of these systems [6]. a nonlinear controller was proposed in [7] for the trolley cranes using lyapunov method. a modified version of slidingsurface control was then utilized to achieve position control of the trolley [7]. a fuzzy logic control system with sliding mode control concept was developed for an overhead crane system in [8]. authors in [9] suggested nonlinear coupling control law to stabilize overhead crane with three degree of freedom using lasalle’s invariance theorem. in [10] a nonlinear tracking controller for controlling the load velocity and position was designed with two loops: an outer loop was intended for position tracking, and an inner loop was intended for stabilizing the oscillations using a singular perturbation design. however, the desired result was obtained only for the case when the swing angle dynamics is much faster than the trolley motion dynamics. in [11] a nonlinear control scheme incorporating parameter adaptive mechanism was proposed to ensure the overall closed-loop system stability. by applying the designed controller, the position error is driven to zero while the swing angle is rapidly damped to achieve swing stabilization. it is known that certain types of load lifting mechanisms result in double-pendulum dynamics [12]. many researchers have worked to provide solutions to the problems posed by the double-pendulum dynamics [13]. their works can roughly be divided into two categories: feedback control and input shaping. feedback control strategy uses measurements and estimation of system state to suppress oscillations [12, 14, 15]. in [13] a command-smoothing scheme was presented to suppress the complex oscillations of the load. simulations of a large range of motions were used to analyze the dynamic engineering, technology & applied science research vol. 8, no. 1, 2018, 2598-2603 2599 www.etasr.com spruogis et al.: further research on an anti-swing control system for overhead cranes behavior of the cranes and the robustness of this method. in order to meet the demand for faster load handling, crane motion must be controlled so that its dynamic performance is optimized. specifically, the control of overhead crane systems aims to achieve both position and anti-swing control [16]. as the swing of the load depends on the acceleration of the trolley, minimizing both operation time and load swing can be defined as partially contradictory requirements. the anti-swing control problem involves reducing the load swing while moving it to the desired position as fast as possible [17]. one particular and effective feedforward approach to reduce vibrations in machines is input shaping [18]. in order to control mechanical systems, a novel fast control strategy was proposed in [19]. the controller includes proportional derivative (pd) regulator and fuzzy cerebellar model articulation controller. for an overhead crane, this control system can realize both position tracking and anti-swing control [19]. in [20], evolutionary-based algorithm for fuzzy logic-based data-driven predictive model of time between failures and adaptive crane control system design were proposed. in the present paper, possibilities of the optimization of overhead crane control to increase the load positioning accuracy and reduce the transportation time are discussed. ii. model and simulation simulation model of the overhead crane was developed using matlab/simulink software [21]. previous research works [22] showed that significant load swing occurs during transportation by the overhead crane. the swing has negative effect on the performance of the equipment and usually it is required to reduce the load swing amplitude to the admissible level. in order to reduce the load swing amplitude, following measures can be applied:  equipment that applies a force to the load at certain moments of time. the direction of such a force is opposite to the direction of deviation of the load.  a stabilizing force can be also applied to the load attachment point by means of special control of the crane’s motors. it is interesting to compare both control approaches. the dynamic model of the overhead crane is presented in figure 1. the crane consists of three parts: a load lifting mechanism, a trolley and a bridge. the position of the mass mθ (figure 1) can be described by the following formulas: ,cossin yxm lx    ,sin ym ly    where l is the length of the rope: ,0 lll    where l0 is the length of the rope without a load attached which is determined by angular position of the rope drum, l is the elongation of the rope caused by the load. the deviation angle of the rope (figure 1) is: . 22 l yx mm    vertical displacement of the load (figure 1) caused by swing:  .coscos1 yxm lz    fig. 1. the dynamic model of the overhead crane equations (1-5) are used to determine kinetic and potential energy of the mechanical system of load lifting mechanism as well as its dissipative function in lagrange equations of second kind. during the creation of the mathematical model, experience of industrial enterprise vilniaus kranai ab was evaluated claiming that rope angular deviation from the vertical does not exceed 5 degrees. obtained after appropriate processing in accordance with techniques presented in [23] equations and used coordinates are presented in [21]. modeling of the mechanical system was carried out with the following parameters (data obtained from the experiments carried out at vilniaus kranai ab): standard gravity g=9.81m/s2, load mass m=1000kg, trolley mass mx=5000kg, mass of the trolley and the bridge my=10000kg, damping coefficient at the rope attachment point h2=1nms/rad, rope damping coefficient h1=1000ns/m, initial rope tension stiffness c1=1716000n/m, damping coefficient of the trolley along axis x hx=1000ns/m, damping of the crane along axis y hy=2000ns/m. nonlinearity of the rope elongation-load relationship is taken into consideration in the mathematical model. for description simplicity, two additional coordinates and their derivatives were introduced: ,, 00 xlxl lxlx     , , 0 0 lm lm xxx xxx      ,, 00 ylyl lyly     engineering, technology & applied science research vol. 8, no. 1, 2018, 2598-2603 2600 www.etasr.com spruogis et al.: further research on an anti-swing control system for overhead cranes ., 00 lmlm yyyyyy    obtained model describes the mechanical system of the overhead crane and the load position changes caused by the rope attachment point position changes in directions x and y and by inclination of the load on the rope by angles θx and θy (figure 1). forces fx and fy are generated by the motors of the trolley and the bridge and determine the rope movement attachment point. motors are controlled by controllers. the algorithm of the controllers can be based on pontryagin’s maximum principle [24]. if the trolley moves with low energy dissipation and in absence of restoring force (which cannot exceed the value predetermined by the motor power), the optimum phase trajectory consists of two parabolas. in the first segment (the acceleration) the control parameter u1 and the phase trajectory is described by the following equation:   , 2 1 2 sdxx    where s is the arbitrary constant. in the second segment (deceleration) the control parameter u–1 (i.e. the motor is reversed) and the phase point moves to the parabola that crosses the zero point of coordinates:   , 2 1 2 sdxx    the optimum phase trajectory under absence of restoring force and energy dissipation conditions is presented in figure 2. fig. 2. optimum phase trajectory in accordance with pontryagin’s maximum principle in order to investigate the dynamic behavior of mechanical system of the crane, a simulink diagram was developed. the control subsystem is described in [21]. the model operates as follows. traction force is applied from the motor of the bridge (entry fx) to the model and movement of the trolley along the x axis towards the point of coordinate start. during the periods of acceleration and deceleration, the phase trajectories are described by (10) and (11) for the case of negligible dissipative forces. if energy dissipation is significant, acceleration and deceleration curves are different from parabolas. during the simulink model creation it was assumed that in the case of motor power disconnection, corresponding wheels are braked and then disengaged when the motor is turned on. figure 3(a) shows the traction force fx versus time relationship for the case of simple drive braking. load oscillation amplitude versus time plot obtained during vertical hoisting of the load is presented in figure 3(b). the traction force was considered to change at the moment when the point of winding of the rope on the drum is located over the place of destination of the load. phase trajectory of the load is presented in figure 3(c). an increase of oscillation amplitude is observed during of the braking of the drive (figure 3(b)). in the case of application of the proposed anti-swing control system, phase trajectory of the load should coincide with the optimum trajectory in accordance with pontryagin's maximum principle (figure 2). it is established that the decrease of traction force from 1300 to 1200 n eliminates an increase of load oscillation amplitude that occurs due to the change of the traction force (figures 4(a), 4(b)). however, the oscillations excited by the load movement remain for considerable time (figure 4(c)).a more detailed study of the load dynamics showed the influence of oscillation phase at the moment of change of traction force. it can be stated that in the case of slight deviation of the rope from vertical position, smooth transition to the optimum phase trajectory is carried out with a significant reduction of traction force while its application direction is maintained (figure 5). effective oscillat ion damping can be achieved also by reversing the traction force (figures 6(a), 6(b)). in this case, the amount of force that is necessary to apply in the opposite direction is only part of the initial value (figure 6(a)). a smooth transition to the optimum phase trajectory is achieved as well (figure 6(c)). in the case of a significant deviation of the rope from vertical position at the moment of change of the traction force (figure 7) timely transition of the phase trajectory to optimum trajectory is provided by the increase of the traction force while its application direction is maintained. iii. conclusions studies have shown that the application of pontryagin’s maximum principle allows the developing of overhead crane drive control system capable of providing effective rope oscillation damping. in order to simplify the control system, magnitude and direction of the traction force should be changed at the moment when the point of winding of the rope on the drum is located over the place of destination of the load. the change degree of magnitude and direction of the traction force depends on the rope deviation angle from vertical. in the case of slight rope deviation from the vertical position at the moment of change of the traction force, load oscillations are reduced by decreasing the traction force while its application direction is maintained. however, if it is necessary to reduce engineering, technology & applied science research vol. 8, no. 1, 2018, 2598-2603 2601 www.etasr.com spruogis et al.: further research on an anti-swing control system for overhead cranes the damping time to a minimum, direction of the traction force should be changed while at the same time its magnitude should be reduced. if at the moment of change of the traction force rope deviation is close to the amplitude of the oscillations, the effective oscillation damping is provided by increasing the traction force while its application direction is maintained. the proposed control system is capable to control both trolley and bridge drives. fig. 3. traction force (a) and load oscillation amplitude (b) vs. time plots and phase trajectory plot (c) obtained for the case of absence of anti-swing system fig. 4. traction force (a) and load oscillation amplitude (b) vs. time plots and phase trajectory plot (c) obtained for the case of the reduction of traction force from 1300 to 1200n fig. 5. traction force (a) and load oscillation amplitude (b) vs. time plots and phase trajectory plot (c) obtained for the case of the slight deviation of the rope from vertical position at the moment of change of the traction force engineering, technology & applied science research vol. 8, no. 1, 2018, 2598-2603 2602 www.etasr.com spruogis et al.: further research on an anti-swing control system for overhead cranes fig. 6. traction force (a) and load oscillation amplitude (b) vs. time plots and phase trajectory plot (c) obtained for the case of the reversing of the traction force fig. 7. traction force (a) and load oscillation amplitude (b) vs. time plots and phase trajectory plot (c) obtained for the case of the significant deviation of the rope from vertical position at the moment of change of the traction force references [1] n. sun, y. fang, “new energy analytical results for the regulation of underactuated overhead cranes: an end-effector motion-based approach”, ieee transactions on industrial electronics, vol. 59, no. 12, pp. 47234734, 2012 [2] k. c. c. peng, w. singhose, d. h. frakes, “hand motion crane 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abstract—a number of methods have been used in partial discharge (pd) detection and recognition. among these methods, ultra-high frequency (uhf) detection and recognition based on a single signal have attracted much attention. in this paper, a uhf pd detection system is built, and samples are acquired through experiments on a real power transformer. the received signal is decomposed into different frequency ranges through wavelet packet decomposition (wpd). in each frequency range, a pattern recognition neural network is built, and then the relationship between the information in that frequency range and pd type is described. by comparing the recognition accuracy of these networks, frequency range selection is optimized. in this specific case (the specific transformer, pd sources, and uhf sensors), results show that low frequency (156.25 mhz to 312.5 mhz) and high frequency ranges (1093.75 mhz to 1250 mhz) contain the most information for recognition. if a pd detection recognition system is to be designed, then the performance around these frequency ranges should be given attention. keywordspartial discharge; wavelet transform; neural network i. introduction a power transformer is one of the most important equipment in electric power systems. the use of partial discharge (pd) measurement can help in the evaluation of the dielectric condition of high-voltage equipment. the electrical detection of pd can be regarded as an important tool for both, quality tests on hv equipment in the laboratory and diagnosis tests on site [1]. recognition of pd types, as a part of pd measurement, contributes to pd source location and early fault diagnosis. for power transformers, pd is a symptom of insulation defect or degradation. furthermore, different types of defects usually produce different pd waveforms, so it is possible to recognize the sources of the pd from its measured signal [2]. using ultra-high frequency (uhf) sensor is an effective method to detect pd signals [3-7]. after receiving uhf pd signals, signal processing and analysis are supposed to reveal the type of potential insulation faults or defects, which helps to locate the pd source and determine needed follow-up maintenance. the traditional uhf pd recognition methods, represented by n-q-φ pattern are based on statistical properties of pd phase distribution. several algorithms for uhf pd recognition have been introduced. in 1991, neural network was introduced into this pattern [8]. to remove disturbance and improve recognition accuracy, many researchers have developed modified and novel methods. among these new ideas, the two most attractive ones are the following: one idea is to introduce a filter as pretreatment, and the representative method is wavelet analysis. this improvement was first adopted in gis [9], and then in power transformers [10-12]. the other idea is to extract information not from phase distribution but from a single pd signal. in [13], three features (skewness, kurtosis, and energy) were extracted. in [14], frequency characteristics of typical pd in gis are studied, and their results serve as substantial criteria for optimal band width selection for high frequency detection. the aforementioned methods are flexible, but more experiments are needed for validation, especially experiments in real power transformers rather than in tanks. in addition, in the use of wavelets, signals are decomposed into different frequency ranges, and a basic issue arises as to which frequency range contains more information. in this paper, a real power transformer with multiple pd sources is constructed. uhf method is employed to receive pd signals. wavelet packet decomposition (wpd), being one of the most flexible methods that use wavelets is adopted to decompose pd signals into different frequency ranges. in each frequency range, a pattern recognition neural network is built, and then the relationship between information in a particular frequency range and pd type is described. by comparing the recognition accuracy of these networks, frequency range selection is optimized. based on experimental results, frequency characteristics of uhf pd signals in power transformer are studied. ii. algorithm pd signal is a broadband signal, and its frequency range is generally between 300 mhz and 1500 mhz or even more. engineering, technology & applied science research vol. 6, no. 1, 2016, 906-912 907 www.etasr.com fan et al.: uhf pd experiments on real power transformer and its frequency characteristics results furthermore, signals received by uhf sensors are usually polluted by different types of noise, which include continuous noise from communication systems, thermal noise from detection systems and periodic pulse-shaped noise from thyristor operations, among others. in this section, with the use of wpd, the received signal (composed of pd signal and noise) is decomposed into different frequency ranges. in each frequency range, a pattern recognition neural network is built. obviously, a more accurate recognition means more useful information and less noise in that frequency range. then, quantitative comparison is feasible. a. wavelet packet decomposition periodic signals are decomposed into different frequency ranges by fourier transform, whereas nonperiodic signals are decomposed by wpd. wpd, which comes from discrete wavelet transform, is more flexible because it has more filters. previously, discrete wavelet transform has been applied to uhf pd denoising [15, 16]. in discrete wavelet transform, original signal s is decomposed into a1 and d1. a1 is the approximation component and contains a low-frequency component, whereas d1 is a detail component containing the high-frequency component. subsequently, a1 is decomposed into aa2 and da2 and is followed by aa2, aaa3 etc. after an nlevel discrete wavelet transform, n+1 signals, containing components from different frequency ranges, are obtained. in wpd, after s is decomposed into a1 and d1, a1 is decomposed into aa2 and da2, while d1 is also decomposed. highfrequency components are decomposed in wpd, but not in discrete wavelet transform. for example, when decomposition level n is set to 3, signal s is represented as s = d1 + da2 + daa3 + aaa3 in discrete wavelet transform, whereas its expansion is more flexible in wpd. for example, we can write s = d1 + dda3 + ada3 + aa2, and we can use other decomposition techniques depending on the situation. in this paper, the pd signal is detected by a uhf sensor, and the sensor is linked to amplifier, and then oscilloscope. the sampling frequency of the original signal is 5 ghz, which is determined by the oscilloscope. however the working frequency range of the amplifier is 0 ghz to 1.5 ghz, and that means the high frequency part is meaningless. to answer which frequency range contains more information, the original signal is decomposed into some different frequency ranges with the same width. the structure of the wpd used in this paper is shown in figure 1. d1 and da2 are high frequency part and are removed. s1 to s8 are 8 components of different ranges, and consequently, signal s is represented as s = s1 + s2 + s3 + s4 + s5 + s6 + s7 + s8. the frequency range of each component is shown in table i. in figure 2, two signals, a point-to-plate type and a suspended-particle type (different pd types will be discussed in section 3), are decomposed. roughly, the two signals have different s6 and s8 components, which suggest that the frequency ranges of these two components are more important in pd recognition for this specific case. however, to be strict and precise, quantitative measures (discussed in section 2.2) and numerous experiments (discussed in section 3) are needed. fig. 1. structure of wpd used in this paper table i. frequency range of each component component frequency range (mhz) s1 0 to 156.25 s2 156.25 to 312.5 s3 312.5 to 468.75 s4 468.75 to 625 s5 625 to 781.25 s6 781.25 to 937.5 s7 937.5 to 1093.75 b. pattern recognition neural networks the earliest neural networks probably date back to 1990 [17]. with the developments in computing science, neural networks are able to solve complex problems in the field of science. in this section, a neural network is used in pd recognition, and then the relationship between the information in a particular frequency range and pd type is described. furthermore, to remove the effect of starting time (discussed in this section later), a pretreatment based on fast fourier transform (fft) is adopted. these two parts, neural networks and pretreatment, make up the special pattern recognition neural network in this paper. 1) neural networks essentially, neural networks are special functions designed to solve the problem of curve fitting. to neural networks, a pd signal is viewed as an input, whereas pd type is the output. given enough samples, proper parameter settings, and training, the neural networks attempt to recognize pd type. if no neural network obtains high accuracy, then the recognition is an illposed problem, which suggests that the inputs do not have sufficient information. in other words, signals in that frequency range are less important. a typical and basic neural network is shown in figure 3; this is a two-layer feed-forward network with sigmoid hidden and softmax output neurons. in figure 3, w is weight, b is threshold, and f and r are activation functions. in this recognition neural network case, f is sigmoid and r is softmax. outputs, namely, target vectors, have n elements (n is the number of pd types); for each target vector, one element is 1, and the others are 0. in this network, inputs are to be classified into n different pd types. the number of neurons in the hidden layer is an important parameter, as it affects the balance between precision and computational complexity. the number of neurons has been tried and determined by experience. engineering, technology & applied science research vol. 6, no. 1, 2016, 906-912 908 www.etasr.com fan et al.: uhf pd experiments on real power transformer and its frequency characteristics results fig. 2. example of signal decomposition results fig. 3. structure of a neural network. 2) pretreatment for neural networks, the input is a pd signal, which is a vector, namely, a time series, [s(−inf), . . . , s(−1), s(0), s(1), . . . , s(inf)], where, s(0) is around the start of pd. however, the input for a neural network is supposed to be a vector with a limited length, ss = [s(0), s(1), . . . , s(l − 1)], where, l is the length. obviously, l should be large enough to contain sufficient information, but a more considerable length means a larger amount of calculation in recognition later. the length is drawn from experience and is suited to the exact conditions of measurement and the study purpose. in [18] and [19], some statistics suggest that pd duration may be several hundreds of nanoseconds. furthermore, the precise location of s(0) affects recognition accuracy to a great extent. then, pretreatment is needed to remove the effect of starting time. the current mature approach is the use of energy criterion [20]. the energy criterion is based on the observation that sound emission signals, in particular when of middle to bad quality, are predominantly characterised by a variation of their energy content, rather than a fluctuation of their frequency composition [21]. suppose s = [s(−n1), . . . , s(−1), s(0), s(1), . . . , s(n2)] is a section of what we generate from the detection equipment. the energy curve e(i) of the sampled signal s(i) is defined here as the cumulative sum of amplitude values. the separation of the signal from the noise part and the realization of the criterion are managed with      1 2 1 2 ( ) , , ..., i k n ee i e i i s k i i n n         where, a negative trend δ is introduced. the trend is dependent on the total energy e(n2) of the signal and the signal length. it is determined by   2 1 2 1 e n n n     the calculated partial energy curve ee(i) features a global minimum, which is assumed to correspond with the signal arrival time or onset. letting s(0) be between s(−n1) and s(n2) is not difficult, given n1 and n2 are large enough. then, we locate s(0) after the minimum ee is found. considering the sampling pd signal is discrete, when pd starting point is between two sampling points, an error is inevitable. although the error is small and even smaller than the sampling period, it may be amplified in the subsequent steps. in the pretreatment, fft is used to solve such a problem. engineering, technology & applied science research vol. 6, no. 1, 2016, 906-912 909 www.etasr.com fan et al.: uhf pd experiments on real power transformer and its frequency characteristics results fft is widely applied in engineering, science, and mathematics [22]. fft causes no information loss and requires only small computational cost. another characteristic of fft is that a change in amplitude characteristics in the frequency domain does not occur when a delay or advance occurs in the time domain. this characteristic means that the amplitude characteristics of pd signals do not change even when the precise location of s(0) fails. furthermore, experimental results (discussed in section 4) suggest that amplitude characteristics contain sufficient information in pd recognition. the fft is defined as       1 1 0 , 1, 2,..., l i k i f k ss i k l       2 /j le   where, i is the loop variable, j is the imaginary unit, and | | is the modulus of the complex number. thus, f is the amplitude characteristics of ss and with the same length. from the above neural networks and pretreatment, the algorithm, a special pattern recognition neural network is proposed, whose structure is shown in figure 4. s is the pd signal received by the uhf detection system. after applying the energy criterion, the pd starting time is roughly located. when the length l is set, we have ss, a vector with a limited length. f is the amplitude characteristics in the frequency domain, which are from the fft of ss and have the same length. at last, a neural network is trained. in the neural network, f is the input, and pd type is the output. the effect of starting time is completely removed. thus, the highest accuracy that the algorithm achieves is closely related to the information of the inputs. in addition, when si takes the place of s, the relationship between information in each frequency range and pd type is measured. fig. 4. structure of the algorithm. iii. experiments to acquire sufficient examples for the neural network training, full-scale experiments are conducted in a real power transformer with multiple pd sources. a uhf pd detection system is employed to receive pd signals. the system consists of the uhf sensor (uhf antenna), amplifier, oscilloscope, and computer. the power transformer is shown in figure 5. its rated power is 6300/6300 kva, and its rated voltage is 110/35/10.5 kv. pd sources are placed inside the transformer and can be viewed through the windows. there are 9 measurement points on the transformer. dismountable antenna can be installed on these points. the distance between source and antenna is 0.5~1.5 m. the pd sources have five types, namely, point to plate (a sharp protrusion on an electrode), surface (slender) discharge (surface contamination on an insulating support), surface (flat) discharge (surface contamination on another insulating support), suspended particle (a loose metallic particle in transformer oil), and cavity discharge (a cavity within solid insulation). when we apply a voltage on these pd sources, pd signals are generated, and the signals vary with the voltage. the media between pd source and measurement point is oil. the transformer and pd sources have been used in similar experiments [11, 23]. in the uhf pd detection system, the uhf sensor is the most important part. three types of uhf sensor, namely, goubau antenna, monopole antenna, and discone antenna (figure 6), have been tested. the design requirements of all three types are the same. for each uhf sensor type and each pd type, some samples are acquired through experiments under different voltages. ac voltage is applied to the pd source. with the voltage increasing stepwise, the detection system begins to receive pd signals. when the voltage is too high such that the noise suddenly increases or the waveform is obviously polluted and meaningless, the voltage is removed. the pd sources are different. thus, the numbers of samples across groups are not the same. details are shown in table ii. a total of 9970 examples are obtained. each sample has a single pd signal. these samples are divided into three groups by uhf sensor type. in each group, the pd signals are decomposed by wpd into eight components with different frequency ranges. furthermore, five wavelets, namely, haar, db2, db8, sym2, and sym8, are tested. “haar” is the most basic wavelet. “db” refers to daubechies wavelets, and “sym” refers to symlets. in each component, the special pattern recognition neural network is trained. three sensor types, eight frequency ranges, and five wavelet types result in 120 (3×8×5) neural networks in all. by comparing the recognition accuracy of these networks, sensor type, frequency range, and wavelet type selection is optimized.during pretreatment, length l is 1000. as the sampling frequency is 5 ghz, the first 200 ns of pd signals from the starting point, which is enough for recognition based on our experience, are saved. the number of neurons in the hidden layer is set to 50 in neural networks. as results show, such complexity is enough to solve this problem. these neural networks are trained with scaled conjugate gradient backpropagation. sample division during training is 70% training, 15% validation, and 15% testing. fig. 5. power transformer used in the experiments. engineering, technology & applied science research vol. 6, no. 1, 2016, 906-912 910 www.etasr.com fan et al.: uhf pd experiments on real power transformer and its frequency characteristics results fig. 6. uhf sensors used in experiments. table ii. sample details sample number goubau monopole discone point to plate 281 859 1718 surface (slender) 360 360 720 surface (flat) 551 551 1102 suspended particle 566 566 1132 cavity 301 301 602 iv. results a. single component in the case of haar wavelet and goubau antenna, for example, samples in the goubau group are decomposed into s1 to s8. in each si, a special pattern recognition neural network is trained. the recognition accuracies of the different components are listed in table iii. the best accuracy is s2 and the worst is s5. that means, s2 contains the highest amount of useful information, whereas s5 contains the least amount of useful information. in addition, recognition accuracy is quite high, which suggests that amplitude characteristics contain enough information for pd recognition in this specific case, as mentioned in the previous section. results from other wavelets and other antenna types are shown in figure 7. comparison of the results by wavelet shows that in the goubau and monopole groups, wavelet types only slightly influence recognition accuracy, which does not hold true in the discone group. a comparison between the results by antenna type shows that the first two groups are better than the last one. thus, the use of discone antenna is not recommended for this specific case. more notably, when the 15 subfigures in figure 7 are added together, we have the distribution characteristic of a single component, as shown in figure 8. a histogram bar is used to plot the quantitative distribution. elements of recognition accuracy in all the settings (wavelets and antenna types) are sorted into five equally spaced bins along the x-axis between the minimum and maximum values. bins are displayed as rectangles such that the height of each rectangle indicates the number of elements in the bin. the recognition accuracy of s5 is clearly located mainly around 0.65, whereas that of s2 is located around 0.9. thus, the s5 frequency component (from 625 mhz to 781.25 mhz) contains less information for pd recognition. it should be noted that the distribution characteristic reflects the overall performance of different frequency ranges. b. multi-adjacent components in a similar way, recognition accuracies of s1+s2 and s1+s2+s3 are compared. results are shown in figure 9. bars in warm color are more likely to be in low accuracy ranges. an obvious trend is that the low-frequency range contains the most information, whereas the mid-frequency range contains the least information. fig. 7. results with different wavelets and antenna types. fig. 8. distribution of single component. table iii. recognition accuracies in haar and goubau case component recognition accuracy s1 0.956289461 s2 0.972316659 s3 0.869354055 s4 0.954346770 s5 0.796017484 s6 0.895094706 s7 0.856726566 s8 0.907236523 c. quantitative results although a figure is an intuitional representation of results, a quantitative study is necessary to generate precise results. mean value and variance are basic statistics. the statistical properties of figures 8 and 9 are listed in table iv. a high mean value means good performance, and a low variance engineering, technology & applied science research vol. 6, no. 1, 2016, 906-912 911 www.etasr.com fan et al.: uhf pd experiments on real power transformer and its frequency characteristics results indicates stability. compared with the single-component group, the multi-adjacent-component groups have a better performance (higher average and lower deviation). the results suggest that even if some components, s5 for example, contain the least useful information, they still facilitate recognition. the low components contain the most information, especially s2 (from 156.25 mhz to 312.5 mhz); the mid-components contain the least information, especially s5 (from 625 mhz to 781.25 mhz). in addition, components in the high-frequency range, s8 (1093.75 mhz to 1250 mhz) for example, are also important in recognition. however, we need to stress that the results pertain to a specific case. to verify the universality of the results, additional experiments and analysis are required. fig. 9. distribution of multi-adjacent components. v. discussion one of the most fundamental and important mission for the uhf pd detection is to tell the pd type. to improve the recognition accuracy, a number of advanced algorithms and after-treatments are introduced. however, a basic question is whether we obtain enough information by the detection system. in this paper, quantitative results for this specific case (the specific transformer, pd sources, and uhf sensors) show that the low-frequency range (156.25 mhz to 312.5 mhz) and high-frequency range (1093.75 mhz to 1250 mhz) contain the most information for recognition. table iv. quantitative results component(s) average standard deviation s1 0.8803 0.0068 s2 0.9215 0.0060 s3 0.7929 0.0183 s4 0.8827 0.0087 s5 0.6689 0.0035 s6 0.7531 0.0056 s7 0.7724 0.0207 s8 0.7976 0.0073 s1+s2 0.9591 0.0011 s2+s3 0.9548 0.0018 s3+s4 0.9439 0.0025 s4+s5 0.9223 0.0035 s5+s6 0.8430 0.0025 s6+s7 0.8511 0.0188 s7+s8 0.9093 0.0052 s1+s2+s3 0.9702 0.0004 s2+s3+s4 0.9726 0.0007 s3+s4+s5 0.9586 0.0014 s4+s5+s6 0.9504 0.0014 s5+s6+s7 0.9191 0.0018 s6+s7+s8 0.9362 0.0029 the basic key conclusions for different frequency ranges are listed as follows: • regarding the very low frequency range (lower than 156.25 mhz), it has to be pointed out that it is not the best range for pd recognition. this may be partly because the signal pollution by radio broadcasting, whose frequency in china is about 100 mhz. • regarding the low frequency range (156.25 mhz to 312.5 mhz) it has to be pointed out that it is the best range for recognition. however, if the sensor involves such range only, it may be a severe problem to distinguish between pd and corona. the middle low range is effective but not practical. • regarding the middle frequency range (312.5 mhz to 1093.75 mhz) it has to be pointed out that it is shown to be the worst range. that suggest the main pollution is in this range, especially the mobile phone signal whose range is about 1000 mhz in china. this pollution is strong and is impossible to be shielded. • regarding the high frequency range (1093.75 mhz to 1250 mhz) it has to be pointed out that it found to be near the best and common uhf system emphasizes it. also, it is the key to distinguish between pd and corona. • regarding the very high frequency range (higher than 1250 mhz) it has to be pointed out that it almost exceeds the effective range of the detecting system. it is really hard engineering, technology & applied science research vol. 6, no. 1, 2016, 906-912 912 www.etasr.com fan et al.: uhf pd experiments on real power transformer and its frequency characteristics results to increase the working frequency range of the system, on e.g. antenna design and amplifier bandwidth design. furthermore, comparisons of the method proposed in the present paper should be made with recent work [24], where four classic pd patterns, including floating pd, needle pd, oil learance pd and void pd in press-board were studied. moreover, it would be useful if the proposed technique here can be tried and studied in pd detection with different detection methods [25]. vi. conclusions and prospects in this paper, the uhf method is employed to receive pd signals. the received signal is decomposed into different frequency ranges by using wpd. in each frequency range, a pattern recognition neural network is built, and then the relationship between the information in a specific frequency range and pd type is described. by comparing the recognition accuracy of these networks and through experiments, information in different frequency ranges is studied. quantitative results for this specific case (the specific transformer, pd sources, and uhf sensors) show that the lowfrequency range (156.25 mhz to 312.5 mhz) and highfrequency range (1093.75 mhz to 1250 mhz) contain the most information for recognition. if a pd detection system is to be designed, then the performance around these frequency ranges should be given special attention. furthermore, we can recognize pd type based on a single signal, and several frequency ranges are important. however, we stress again that all these results are applicable to a specific case only. additional experiments are necessary. moreover, a theoretical explanation may be provided in future studies. references [1] e. lemke, p. schmiegel, introduction to fundamentals of pd diagnostics, lemke diagnostics gmbh, germany, 2000 [2] r. bartnikas, “partial discharges. their mechanism, detection and measurement”, ieee transactions on dielectrics and electrical insulation, vol. 9, no. 5, pp. 763-808, 2002 [3] b. f. hampton, r. j. meats, 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detection and localization in the power transformers in the factory tests”, ieee transactions on dielectrics and electrical insulation, vol. 22, no. 1, pp. 448-455, 2015 [8] h. suzuki, t. endoh, “pattern recognition of partial discharge in xlpe cables using a neural network”, proceedings of the 3rd international conference on properties and applications of dielectric materials, tokyo, japan, pp. 43-48, 8-12 july, 1991 [9] z. m. li, y. p. feng, j. q. chen, x. z. zhang, “uhf partial discharge monitoring in gis and signal processing”, proceedings of 1998 international symposium on.electrical insulating materials, toyohashi, japan, pp. 67-70, 27-30 september, 1998 [10] l. yang, m. d. judd, “recognising multiple partial discharge sources in power transformers by wavelet analysis of uhf signals”, iee proceedings-science, measurement and technology, vol. 150, no. 3 pp. 119-127, 2003 [11] y. wang, j. wu, z. li, y. yin, “research on a practical de-noising method and the characterization of partial discharge uhf signals”, ieee transactions on dielectrics and electrical insulation, vol. 21, no. 5, pp. 2206-2216, 2014 [12] k. wang, j. li, s. zhang, r. liao, “a hybrid algorithm based on s transform and affinity propagation clustering for separation of two simultaneously artificial partial discharge sources”, ieee transactions on dielectrics and electrical insulation, vol. 22, no. 2, pp. 1042-1060, 2015 [13] h. h. sinaga, b. t. phung, t. r. blackburn, “recognition of single and multiple partial discharge sources in transformers based on ultra-high frequency signals”, iet generation, transmission & distribution vol. 8, no. 1, pp. 160-169, 2014 [14] w. gao, d. zhao, d. ding, s. yao, “investigation of frequency characteristics of typical pd and the propagation properties in gis”, ieee transactions on dielectrics and electrical insulation, vol. 22, no. 3, pp. 1654-1662, 2015 [15] l. yang, m. d. judd, c. j. bennoch, “denoising uhf signal for pd detection in transformers based on 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phenomena, usa, 14-17 october, 2001 [20] s. markalous, s. tenbohlen, k. feser, “detection and location of partial discharges in power transformers using acoustic and electromagnetic signals”, ieee transactions on dielectrics and electrical insulation, vol. 15, no. 6, pp. 1576-1583, 2008 [21] c. u. grosse, h. reinhardt, “schallemissionsquellen automatisch lokalisieren: entwicklung eines algorithmus”, materialprüfung, vol. 41, no. 9, pp. 342-347, 1999 [22] j. w. cooley, j. w. tukey, “an algorithm for the machine calculation of complex fourier series”, mathematics of computation, vol. 19, no. 90, pp. 297-301, 1965 [23] y. wang, c. zhu, q. wang, z. wang, y. yin, “processing of partial discharge ultra-high frequency signals from a true size transformer”, 2013 ieee international conference on solid dielectrics (icsd), bologna, italy, pp. 1012-1015, 30 june – 4 july 2013 [24] x. zhao, y. h. cheng, y. -p. meng, m. g. danikas, “applying wpd and svd to classification of em wave induced by partial discharge in power transformer”, journal of electrical engineering, vol. 64, no. 4, pp. 222-229, 2013 [25] r. sarathi, p. d. singh, m. g. danikas, “characterization of partial discharges in transformer oil insulation under ac and dc voltage using acoustic emission technique”, journal of electrical engineering, vol. 58, no. 2, pp. 91-97, 2007 microsoft word etasr_v11_n5_pp7689-7694 engineering, technology & applied science research vol. 11, no. 5, 2021, 7689-7694 7689 www.etasr.com abd & ahmed: the effect of low velocity impact loading on self-compacting concrete reinforced … the effect of low velocity impact loading on selfcompacting concrete reinforced with carbon fiber reinforced polymers julnar muhsin abd civil engineering department college of engineering university of baghdad j.abd1901m@coeng.uobaghdad.edu.iq ikram faraoun ahmed civil engineering department college of engineering university of baghdad ikram.faroun@coeng.uobaghdad.edu.iq abstract-self-compacting concrete (scc) reduces environmental noise and has more workability. this research presents an investigation of the behavior of scc under mechanical loading (impact loading). two types of cement have been used to produce scc mixtures, ordinary portland cement (opc) and portland limestone cement (plc), which reduces the emission of carbon dioxide during the manufacturing process. the mixes were reinforced with carbon fiber reinforced polymer (cfrp) which is usually used to improve the seismic performance of masonry walls, to replace lost steel reinforcements, or to increase column strength and ductility. workability tests were carried out for fresh scc. prepared concrete slabs of 500×500×50mm were tested for low-velocity impact loading at ages of 28, 56, and 90 days after water curing. the results were compared with the ones of non-reinforced scc mixes and show a significant effect on the impact resistance after the scc was reinforced with cfrp. the strongest impact resistance was recorded for reinforcing slabs made from opc scc, while for the reinforced concrete slabs produced from plc the results were less, but at a close rate. keywords-self-compacted concrete;carbon fiber reinforced polymer; impact loading test; portland limestone cement i. introduction self-compacted concrete (scc) is a kind of concrete that is cast without being compacted and fills the formwork with its own weight. scc provides some advantages in comparison with traditional concrete, including enhanced building quality, quicker construction activity, lower costs, increased in-situ concrete quality under challenging casting loads, decreased accidents, noise and vibrations, while it assists in the attainment of higher surface quality [1]. one of the drawbacks of scc is its large cost, which is due to the usage of large amounts of portland cement (pc) and chemical additives. the scc cost will be lowered if the mineral additions replace a portion of the pc, particularly if the mineral additives are industrial waste or by-products. furthermore, the use of mineral additives in the manufacturing of scc has not only economical but also environmental benefits [2]. cement manufacturing emits a large quantity of carbon dioxide and necessitates a large amount of energy [3]. blending limestone with conventional opc or intergrading limestone and cement clinker produces portland limestone cement (plc). the increased use of plc in the concrete industry is mostly owed to its lower raw material usage and energy savings in clinker production [4]. components made of fiber reinforced polymer (frp) have been utilized extensively and effectively in seismic enhancement projects [5]. traditional metal and ceramic materials are being displaced in a wide range of high-performance implant applications due to their high specific strength, superior corrosion resistance, low weight, and design flexibility. the fiber-matrix interface is essential to the performance of fiber-reinforced composites. a visible interface can guarantee that stress is effectively transmitted from the weaker matrix to the stronger fiber, reducing stress concentrations and improving the overall mechanical characteristics [6]. throughout their functioning lives, many structures or structural parts are likely to be subjected to impact forces or even repeated impacts. impact forces can occur by a variety of causes. one example is the impact of moving automobiles on columns and walls of structures in accidents. other instances include the effect of dropped items from high elevations, the effects of projectiles in wars or terror acts and the effects of water on hydraulic infrastructure, offshore structures, or bridge piers. impact forces apply short-term dynamic loads to the material, subjecting it to unusual and unwanted stresses, particularly in brittle materials such as concrete. this type of loading necessitates improved microstructural performance in order to be efficiently absorbed. additive fibers can improve concrete responsiveness under static and dynamic loads. several testing techniques have been developed in order to get a satisfactory measurement of frc impact resistance. the drop-weight, projectile impact charpy pendulum, and the explosive and repeated blows drop-weight impact (rbdwi) tests are among them [7]. ii. material characterization a. cement in this study, two types of cement were employed, plc and opc. the plc was manufactured in karbala city in iraq by the corresponding author: julnar muhsin abd engineering, technology & applied science research vol. 11, no. 5, 2021, 7689-7694 7690 www.etasr.com abd & ahmed: the effect of low velocity impact loading on self-compacting concrete reinforced … lafarge company, it is commercially known as karasta, and it was purchased at a local market. to minimize exposure, it was stored in a dry area. tables i and ii show the chemical composition and the physical properties of the karasta cement. this cement complied with the en 197-1:2011 [8]. opc commercially known as mass was also utilized. its physical and chemical properties conform to the iraqi standard no. 5 of 2019 [9] and are given in tables iii and iv. table i. chemical composition of karasta cement compound percentage by weight limit of en 197-1:2011 magnesia (mgo) 1.83 ≤ 5% sulfate (so3) 2.35 ≤ 2.5 cao 62.11 l.o.i 7.44 ≤ 4 sio2 18.39 al2o3 4.63 fe2o3 2.77 total 99.52 c3a 7.58 chloride content 0.01 ≤ 0.10 % i.r 1.38 ≤ 1.5 table ii. physical properties of karasta cement physical properties test result limits of en 197-1:2011 specific surface area (blaine method) cm2/g 4875 ≥ 2500 initial setting (min) 90 ≥ 45 compressive strength (mpa) at: 2 days 8 ≥ 10 20 28 days 34 ≥ 42.5 table iii. chemical composition of mass cement oxides test results limits of the iraqi standard no.5/2019 for opc cao 62.32 sio2 21.34 al2o3 4.93 fe2o3 5.43 mgo 2.12 max 5% so3 2.35 max2.8% l.o.i. 1.72 max 4% lsf 0.86 0.66-1.02 saturation coefficient 0.83 max 1.5% constituent% according to bogue equations c3s 76.28 c2s 3.73 c3a 6.72 c4af 16.5 table iv. physical properties of mass cement physical properties test results limits of the iraqi standard no.5/2019 for opc specific surface area (blaine method) m2/kg 376 min 250 setting time (vicat's apparatus) initial setting (min) 2:5 ≥ 45 final setting (hr) 4:00 ≤ 10 soundness using autoclave method (mm) 0.12 ≤ 0.8 compressive strength (mpa) at: 2 days 26 ≥ 20 28 days 47 ≥ 42.5 b. fine aggregates as fine aggregates, natural sand from the al-ukhaider area was used. table v shows the physical and chemical properties and table vi shows the sieve analysis of the sand used, which conforms to the limits of iraq specification no. 45/1984 zone 2 [10]. table v. chemical and physical properties of fine aggregates property test result i.q.s.45: 1984 limits specific gravity 2.6 absorption (%) 0.72 density (kg/m3) 1580 sulphate content (so3) 0.2 0.50% (max) table vi. sieve analysis sieve no. passing % limits of iraqi specification no.45/1984 10 mm 100 100 4.75 mm 93.3 100-90 2.36 mm 77.7 100-75 1.18 mm 66.6 90-55 600 µm 54.4 59-35 300 µm 26.3 30-8 150 µm 3.1 100 c. coarse aggregates (gravel) the maximum size of the crushed gravel used was 10mm. the gravel was obtained from the al-nabaie area in iraq. its physical properties were examined in the laboratory of the ministry of construction and housing, building research department, and it satisfies the iraqi standard iqs no. 45/1984 as shown in table vii. table vii. grading of natural coarse aggregates sieve size (mm) cumulative passing (%) limits of is no.45/1984 for 14-15mm 20 100 100 14 98 100-90 10 75 85-50 5 4 10-0 sulphate cotent (so3) 0.6 maximum 1% d. limestone powder limestone powder was used as an inert mineral filler in order to maintain and improve the segregation resistance, to increase the amount of powder (cement and filler), and to increase the workability and density of concrete. its chemical composition is shown in table viii. table viii. chemical composition of limestone powder oxides % cao 48.28 mgo 3.97 l.o.i 42.48 ir 2.00 e. high range water reducing admixture (hrwra) betonac-1030 is a highly efficient polycarboxylate polymer based superplasticizer that is intended to preserve workability engineering, technology & applied science research vol. 11, no. 5, 2021, 7689-7694 7691 www.etasr.com abd & ahmed: the effect of low velocity impact loading on self-compacting concrete reinforced … and improve slump-flow life and thus it provides concrete of extremely high workability without segregation, achieving high initial compressive strength. it permits the constant production of self-compacting concrete and complies with the criteria of astm c494 type f and din en 934-2 [11]. typically, 0.6% to 1.5% of cement weight is used, although this can be modified to fulfill a broader range of concrete specifications. the technical description of betonac-1030 is presented in table ix. table ix. technical description of betonac-1030 calcium chloride nail solid contents 40% ph 7.5 at 20oc packaging available in 220kg drums or 1100kg ibcs storage/shelf life at least 1 year if stored in originally sealed packaging and protected from direct sunbeam, extreme heat, and frost. *manufacturer properties f. water in concrete mixes and specimen treatment, tap water from the university campus was employed. the temperature of the mixing water was kept constant at 25.2°c g. carbon fiber reinforced polymer the carbon fiber used is a mid-strength unidirectional woven carbon fiber fabric commercially known as sikawrap300 c, intended for either dry or wet use. it is a fabric that may be used in a variety of strengthening purposes. it is flexible and adaptable to various surface planes and geometries (columns, beams, piles, walls, silos, etc). also, it has a low density and contributes as little weight as possible. in comparison with conventional strengthening, it is highly cost effective. table x indicates the technical properties of the carbon fibers used according to the manufacturer company. table x. carbon fiber properties laminate nominal thickness 0.167mm laminate nominal cross section 167mm2 per m width dry fiber density 1.82g/cm3 dry fiber thickness 0.167mm based on fibre content area density 304g/m2 ±10g/m2 (carbon fibres only) dry fiber tensile strength 4000n/mm2 iso 10618 dry fiber modulus of elasticity in tension 230000n/mm2 dry fiber elongation at break 1.7 % *manufacturer properties h. epoxy impregnation resin sikadur-330 is an anisotropic epoxy-based impregnating resin and adhesive in two components. it can be utilized in dry and wet applications. the wet application technique requires a primer resin for bonding. it is produced for manual immersion procedures and is simple to mix and apply with a trowel and an insemination roller. it has excellent adhesion to vertical and overhanging surfaces and excellent adherence to a wide range of substrates. its mechanical characteristics are exceptional and there is no need for a different primer. table xi indicates the technical properties of sikadur-330 table xi. properties of sikadur-330 composition epoxy resin color component a: white paste b: grey paste a + b mixed: light grey paste density 1.30 ± 0.1kg/l (component a+b mixed) at 23°c modulus of elasticity in flexure ~ 3 800 n/mm2 (7 days at 23°c) (din en 1465) tensile strength ~ 30 n/mm2 (7 days at +23°c) (iso 527) modulus of elasticity in tension ~ 4 500 n/mm2 (7 days at +23°c) (iso 527) tensile adhesion strength concrete fracture (> 4n/mm2) on sandblasted substrate (en iso 4624) i. concrete mixes to achieve the research objectives, two types of mixes were prepared according to aci-211 [12]. the details of the mixes used throughout this investigation are given in table xii. table xii. details of the prepared mixes mix symbol description of the mix p1 reference mix with opc r1p mix with opc reinforced with carbon fibers p2 mix with karasta lpc r2p mix with karasta lpc reinforced with carbon fibers table xiii. main details of the used mixes mix cement kg/m3 fa kg/m 3 ca kg/m 3 ld kg/m 3 w kg/m 3 sp kg/m 3 w/p opc plc p1 400 684 760 80 168 6 0.42 p2 400 684 760 80 168 6 0.42 j. mixing procedure the mixing process was carried out in accordance with the astmc-192/02 standard [13] and cohesive concrete mixtures were obtained. the mixing steps are: 1. fine saturated surface dry (ssd) aggregates were mixed with the one-third of water. 2. the cement and the mineral additives were added along with another one-third of water, and then the ingredients were mixed for one minute. 3. the ssd coarse aggregates were added with the last third of the water and one third of the superior plasticizer. the mixture was mixed for a minute and a half, and then it was left for half a minute to rest. 4. then, two thirds of the remaining superior plasticizer were added and the mixture was mixed well for a minute and a half. 5. the mixture was discharged for testing and pouring. the total mixing time is about 5 minutes. iii. results and discussion a. fresh properties 1) slump flow engineering, technology & applied science research vol. 11, no. 5, 2021, 7689-7694 7692 www.etasr.com abd & ahmed: the effect of low velocity impact loading on self-compacting concrete reinforced … stagnant flow results are shown in table xv. all results are within the acceptance criteria of efnarc, 2005 [14] (table xiv). table xiv. acceptance criteria [14] method unit typical range of values minimum maximum slump flow by abrams cone mm 650 800 t50 cm slump flow sec 2 5 v-funnel sec 6 12 time increase, v-funnel at t=5min sec 0 3 u-box h1-h2 (mm) 0 30 l-box h2/h1 0.8 1.0 fig. 1. slump test. table xv. scc rheological properties results mix slump flow (mm) t500 (sec) v-funnel time (sec) l-box height ratio (h2/h1) opc 667 5 11 0.825 plc 7 44 3 8 0.941 2) t500mm slump flow times (t500) were in the range of 3-5s. all results are within the acceptance criteria of [14]. 3) v-funnel time the results are consistent with the reported scc accepted standards [14]. the stagnation values for binary and ternary mixtures that include opc and plc are shown in table xiv. leveling results range from 667 to 744mm. therefore, all mixtures are assumed to have good consistency and workability from the packaging point of view. 4) l-box the l-box height ratios varied from 0.843 to 0.948 (table xv). from the obtained results it was found that the fluidity was good for all the mixtures since it was greater than 0.8, which is considered the minimum critical value [14]. b. mechanical properties (impact resistance) the device used to measure impact resistance contains three parts: • the main support part: it consists of an iron bracket that is strong enough to support the examination device during the examination and withstand the impact. it also contains another support for which the examination form is placed. it is made of angle iron and is well fixed to prevent the movement of the form during the examination. • the iron structure for dropping the block: it is a cylindrical tube with an inner diameter of 10.5cm which is fixed with supports that prevent it from moving during the examination. this tube contains openings of different heights (0.5, 1.0, 1.7m). the height of 1m was used to examine the reinforced slabs for this research. • the falling block: it is an iron ball, weighing 3kg with a diameter of 9.5cm. this mass is thrown several times from a height of 1m on the model. fig. 2. l-box test. c. examination method each model was placed on the supporting iron structure, and then the iron block was dropped from the specified height of 1m on the model. the number of blows that were required for the first crack to occur and the number of strikes that caused failure are shown in table xvi. the average of 3 slabs was taken for each variable at ages of 28, 56, and 90 days according to [15]. the failure pattern was observed in the unreinforced slab, which is divided into several pieces. the typical failure behavior of unreinforced concrete specimens under impact resistance is shown in figure 4. the stages of failure in the reinforced slab were categorized as: in the first stage the first crack occurs, during the second stage fragmentation occurs, and at the third stage failure occurs with cracks in the corners of the slab and the occurrence of a full hole so that the reinforcement appears. the typical failure behavior of reinforced concrete specimens under impact resistance is shown in figure 5. reinforcement of scc improves the impact resistance because the carbon fiber reinforced with polymer used in this research has good mechanical properties to curb cracking and absorb high energy when withdrawn from the concrete, which makes the reinforced slabs to have high strength and flexibility engineering, technology & applied science research vol. 11, no. 5, 2021, 7689-7694 7693 www.etasr.com abd & ahmed: the effect of low velocity impact loading on self-compacting concrete reinforced … and makes them capable of withstanding external shocks better than scc without reinforcement. the impact resistance (number of blows) increases with the curing age, as can be seen in figure 3. this is consistent with the findings in previous studies that examined the reaction of low impact velocity carbon fiber reinforced polymer (cfrp) epoxy laminates. table xvi. slab under the impact resistance test average impact resistance mix 28 days 56 days 90 days number of blows required for first crack failure first crack failure first crack failure p1 1 2 1 3 1 3 p1r 2 40 2 54 2 70 p2 1 2 1 2 1 3 p2r 2 37 2 49 2 65 fig. 3. impact resistance with different ages of curing. fig. 4. typical failure behavior of unreiforced concrete slabs. fig. 5. typical failure behavior of reiforced concrete slabs. it is known that damage caused by low impact velocity (where there is no hole) in cfrp laminates rises with the impact energy when submitted to impact loads. as a result, the design of fibers and the sequence of stacking play a crucial part in the compliance under these temperature and loading circumstances with cfrp composites. thermal variation does not produce interlaminar strains in the plain-woven laminate employed, where the fibers were oriented parallel in each ply, and damage extension after impact does not rise significantly at low temperatures [16]. based on the extensive experimental data, reinforcing of scc with the use of recycled cfrp fibers increases the mechanical characteristics and impact resistance of specimens [17]. iv. conclusion the following conclusions can be drawn from the results of the experimental work: • the use of limestone powder as filler for scc and the replacement percentage do not affect the properties of solid concrete. • carbon fibers can be used for reinforcement and consolidation and they show high impact resistance. • impact resistance was more powerful and reached 70 blows in slabs containing opc at the age of 90 days. • the results between scc with opc slabs and scc with plc slabs are not so paradoxical. this research contributes to the understanding of the impact behavior of concrete slabs made with carbon fibers. in practice, concrete slabs reinforced with cfrp and produced from plc can be used in many different applications. the scc made with locally available materials could be widely used instead of conventional concrete at complex construction sites. this reinforcing system is used to increase the strength and ductility of columns and the loading capacity of structural elements, enabling changes in use, alterations and refurbishment, and structural design and construction defect corrections. the use of lime dust and plc to produce sustainable scc is environmentally beneficial since the carbon dioxide emissions and energy consumption are reduced by reducing the amount of cement being manufactured and used. references [1] n. a. memon, m. a. memon, n. a. lakho, f. a. memon, m. a. keerio, and a. n. memon, "a review on self compacting concrete with cementitious materials and fibers," engineering, technology & applied science research, vol. 8, no. 3, pp. 2969–2974, jun. 2018, https://doi.org/10.48084/etasr.2006. [2] m. uysal and m. sumer, "performance of self-compacting concrete containing different mineral admixtures," construction and building materials, vol. 25, no. 11, pp. 4112–4120, nov. 2011, https://doi.org/ 10.1016/j.conbuildmat.2011.04.032. [3] n. bheel, a. s. memon, i. a. khaskheli, n. m. talpur, s. m. talpur, and m. a. khanzada, "effect of sugarcane bagasse ash and lime stone fines on the mechanical properties of concrete," engineering, technology & applied science research, vol. 10, no. 2, pp. 5534–5537, apr. 2020, https://doi.org/10.48084/etasr.3434. [4] f. shaker, a. rashad, and m. allam, "properties of concrete incorporating locally produced portland limestone cement," ain shams engineering journal, vol. 9, no. 4, pp. 2301–2309, dec. 2018, https://doi.org/10.1016/j.asej.2017.04.005. 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[6] s. r. abid, m. l. abdul-hussein, n. s. ayoob, s. h. ali, and a. l. kadhum, "repeated drop-weight impact tests on self-compacting concrete reinforced with micro-steel fiber," heliyon, vol. 6, no. 1, jan. art. no. e03198, 2020, https://doi.org/10.1016/j.heliyon.2020.e03198. engineering, technology & applied science research vol. 11, no. 5, 2021, 7689-7694 7694 www.etasr.com abd & ahmed: the effect of low velocity impact loading on self-compacting concrete reinforced … [7] m. a. sanjuán and c. argiz, "the new european standard on common cements specifications en 197-1:2011," materiales de construcción, vol. 62, no. 307, pp. 425–430, sep. 2012, https://doi.org/10.3989/ mc.2012.07711. [8] iraqi specification no. 5 : portland cement. baghdad, iraq: central agency for standardization and quality control, 2019. [9] iraqi specification no. 45: aggregates. baghdad, iraq: central agency for standardization and quality control, 1984. [10] c09 committee, "specification for chemical admixtures for concrete," astm international, west conshohocken, pa, usa. https://doi.org/ 10.1520/c0494_c0494m-12. [11] aci committee 211, aci prc-211.1-91: standard practice for selecting proportions for normal, heavyweight, and mass concrete (reapproved 2009). aci, 2002. [12] "standard practice for making and curing concrete test specimens in the laboratory," astm international, west conshohocken, pa, usa, astm c192/c192m-07. [13] bibm, cembureau, ermco, efca, and efnarc, the european guidelines for self-compacting concrete: specification, production and use. 2005. [14] aci committee 544, "design considerations for steel fiber reinforced concrete," aci, west conshohocken, pa, usa, aci 544.4r-88, 1988. [15] t. gómez-del rı́o, r. zaera, e. barbero, and c. navarro, "damage in cfrps due to low velocity impact at low temperature," composites part b: engineering, vol. 36, no. 1, pp. 41–50, jan. 2005, https://doi.org/ 10.1016/j.compositesb.2004.04.003. [16] m. mastali and a. dalvand, "the impact resistance and mechanical properties of self-compacting concrete reinforced with recycled cfrp pieces," composites part b: engineering, vol. 92, pp. 360–376, may 2016, https://doi.org/10.1016/j.compositesb.2016.01.046. microsoft word 1-azizi.doc etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 49-53 49 www.etasr.com azizi and gholami: optimum scheme for insulation system in hv generator… optimum scheme for insulation system in hv generator based on electromagnetic analysis d. azizi dept of ee iust tehran, iran azizi@iust.ac.ir a. gholami dept of ee iust tehran, iran abstract— electrical insulations are one of the basic parts of electrical machinery in any sizes and characteristics. focusing on insulating, studies on the operation of industrial-electrical machinery came to the fact that the most important part of a machine is the stator. this fact reveals the requirement for inspection of the electrical machine insulation along with the electromagnetic tensions. therefore with respect to insulation system improvement of stator, the hv generator can be optimized. dielectric parameters such as insulation thickness, spacing, material types, geometry of winding and slot are major design consideration. a very powerful method available to analyze electromagnetic performance is finite element method (fem) which is used in this paper. the analysis of various stator coil and slot configurations are used to design the better dielectric system to reduce electrical stresses in order to increase the power of generator in the same volume of core. these processes of optimization have been done according the proposed algorithm. in this algorithm the technical constraints have been considered. this paper describes the process used to perform classical design and improvement analysis of stator slot’s insulation with respect to objective function and constraints. keywordsinsulation; fem; machine; magnetic; thermal i. introduction safe operation of electrical machine, particularly high power generators strongly depends upon the health of stator coil insulation. industrial researches show that troubles initiated in the stator winding insulation are one of the primary root causes of electric machine failures [1, 2 and 3]. it is shown in [4, 5] that 30-40 % of ac machine failures are stator related and also shown in [6] that 60-70 % high voltage machine failures result from stator insulation troubles. the winding and core of stator integrity plays essential role in the reliability of the alternator [7-11]. thus, performing the optimal design consist of electromagnetic study with respect to thermal limits in core, winding and insulation of stator slots is necessary. to attain an improved design electromagnetic analysis with observe to real condition is performed which completes pervious researches. the reason of applying the method is investigating the effects of electrical, magnetically and thermal stresses on insulation parts. the main idea involves finding the optimum scheme of stator slot’s insulation with respect to possible stresses and constraints. fem analysis is used to simulate the electric, magnetic and thermal field simultaneously. the main supremacies of the simulations in comparison with other researchers are: • simulating ordinary rotation of rotor. • considering magnetic saturation of core. • considering of technical constraints. according to this method, various configurations of stator (winding, core, slot, insulation) for operation conditions are proposed to investigate the possibility of improvement high voltage generator characteristics with respect to proposed optimization algorithm. ii. classical design m phase machine classical design has definite steps which are considered in this section. the induced kva by armature can be obtained from: 3 ph 10)tφf2( −⋅⋅⋅⋅⋅⋅⋅= phw ikmq π (1) where: φ: total flux, iph: phase current, kw: winding factor, f: frequency, tph: winding turn in phase the equation (1) can be rewritten as (regarding to 2 s pn f = , phz ii = and ph mtz 2= ) 3 z 10)i)(φ( 22 −⋅⋅⋅⋅= ws knzpq π (2) total magnetic flux in air gape is called magnetic loading which is used to calculate especial magnetic loading (bav) as bellow: total magnetic loading = φp ⋅ (3) πdl φp b a =ν (4) where: d: diameter, l: length. etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 49-53 50 www.etasr.com azizi and gholami: optimum scheme for insulation system in hv generator… total current loading and especial current loading introduced by the following equations: total current loading = zi z ⋅ (5) dπ zi ac z= (6) by replacement and from equations (4) and (6) in equation (2), it can be shown that: =⋅= −3 sαν 10dαc)n)((πdlb 22 w kq π π s lnd 23 w 2 )10ck11.1( −⋅β απ αν (7) where: 3 w 2 0 10ck11.1 −⋅β= απ ανc (8) kw is winding factor which is calculated by multiplying kc and kd. kc is assumed one and kd is obtained from equation (9). 2 sin 2 sin a q qa k d = (9) iii. case study according to section 2, a generator with different insulation is designed as the case study. the selected generator is synchronous, three phase and two poles. rated frequency, voltage and power are respectively 50hz, 20 kv and 1 mva. wiring is form-wound multi-turn type and has many insulation layers with different specifications. in this study the turn insulation and the strand insulation are the same, i.e. nylon type. ground wall insulation type is ptef and semi conductive coating is si(c) with characters identified in table 1. table i. electrical and thermal specifications of used insulations quantities symbols & dimensions 2ylon insulation ptef insulation si(c) insulation heat capacity c [j/(kg*k)] 1700 1420 700 young’s modulus e [pa] 2e9 3e9 170e9 thermal expansion coeff. α [1/k] 280e-6 70e-6 2.6e-6 relative permittivity ε 4 2 11.7 thermal conductivity k [w/(m*k)] 0.26 0.19 130 density rho [kg/m^3] 1150 1190 2329 iv. electromagnetic models [12] ampere’s law is the main part to derive electromagnetic system equation. t d jbve t d jh e ∂ ∂ ++×+= ∂ ∂ +=×∇ σσ (10) where: • e is the electric field intensity • d is the electric displacement or electric flux density • h is the magnetic field intensity • b is the magnetic flux density • j is the current density • je is the externally generated current • σ is the electrical conductivity • v is the velocity time variant-harmonic field’s effect can be introduced by equations (11) and (12): ab ×∇= (11) t a ve ∂ ∂ −−∇= (12) ampere’s law is rewritten by equations (11) and (12) combining with constitutive relationships b=µ0(h+m) and d=ε0e+p , as: ( ) ( ) ( ) ( ) pjjvjav maaj e ωωεσσ µεωωσ +=∇++×∇×− −×∇×∇+− − 0 1 00 2 (13) in which ω, ε0, µ0, m and p respectively refer to angular frequency, relative permittivity, relative permeability, magnetization vector and electric polarization vector. in the case of 2-dimensional-plane, there are no variations in z-direction, so the electric field is parallel to z-axis. , therefore v∇ is written as −∆v/l, where ∆v is the potential difference over the distance l. now these equations are simplified to: ( ) z e z zz x y z pjj l v ajav m m a ωσ εωωσσµ ++ ∆ =         −+∇+     − −∇∇− − 0 21 0 .. (14) in the ax-symmetric case, another form of the electric potential gradient has been used ( r2π loop v v − =∇ ) as the electric field is only present in the azimuthally direction. the above equation, in cylindrical coordinates, becomes: etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 49-53 51 www.etasr.com azizi and gholami: optimum scheme for insulation system in hv generator… [ ] ( ) pjj r v uvujr z u r u vr m m u z z u r u r zr eloop r r z ω π σ σεωωσσ µµ ϕ ++= +−+                 ∂ ∂ ∂ ∂ +                         − −      +         ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂− −− 2 2. 0 . 0 2 1 0 1 0 (15) the dependent variable u is the nonzero component of the magnetic potential divided by the radial coordinate r, so that: r a u ϕ= (16) the application mode performs this transformation to avoid singularities on the symmetry axis. v. optimization algorithm the optimization procedure is presented in the optimization algorithm (figure 1). fig. 3. flow chart of the optimization procedure vi. simulation and results following the development of the study, magnetic field distribution for cylindrical windings with two layers is simulated (figure 2). coupling the equations makes the capability of simulating electrical field and potential distribution as shown in (figures 3, 4). varying configuration can include winding’s geometry, slot depth, slot width, winding layers and material types of insulation. to study the effects of each varying on operation conditions some configurations are proposed. it should be mentioned that these changes of configuration are done according to optimization algorithm (figure 1). in first step, cubic windings in the same cross section are used as figure 5. the results of simulations show that electric field distribution has changed but the maximum electric field value is constant. the electric field distribution between winding layers has reduced intensively which allows adding a more layer (figure 6). this means that the operation power can be enhanced 50 %. the length and depth of slots are two other options which impress design parameters. for this purpose, in the final step, the width of slot is increased. this is required the reduction of core volume which causes relatively core saturation (figure 7). fig. 4. magnetic field distribution and flux lines fig. 5. potential distribution in a sample slot etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 49-53 52 www.etasr.com azizi and gholami: optimum scheme for insulation system in hv generator… fig. 6. electrical field in a sample slot (mode 1) fig. 7. electrical field distribution for cubic winding (mode 2) fig. 8. electrical field distribution for cubic windings with three layers (mode 3) fig. 9. flux lines and magnetic distribution in generator with larger slot (mode 4) table ii. maximum values of electrical, magnetical and thermal fields in all modes electrical field (kv/mm) magnetic flux density (t) temperature (˚̊̊̊c) mode 1 2.77 1.5 78 mode 2 2.77 1.5 79 mode 3 2.97 1.5 87 mode 4 1.86 1.73 112 comparing between varied configurations indicates that changing in the shape of winding geometry and insulation class are more effective. thus, it can be claimed that the model of figure 6 (mode 3) is the optimum configuration. vii. conclusion the majority of high voltage machine failures result from stator insulation problems. on the other hand electrical and magnetic stresses are the important factors of exhaustion in generators. therefore selection of proper wiring scheme can decrease these stresses. different schemes with regard to different construction have different characters and specification. the finite element electromagnetic and thermal analyses are useful to improve the configuration of stator which conquests the previous problems in classical design. in this paper, some proposed configurations presented and compared. it can be extracted from results that the configuration of figure 6 is the optimum case with respect to mentioned algorithm. references [1] f. t. emery, d. pavlik, “electrostatic field analysis of high voltage generator stator insulation systems”, ieee annual report conference on electrical insulation and dielectric phenomena, vol. 2, pp. 510 – 513, 2000 [2] m. arshad, a. khaliq, s. m. islam, “turbo generator stator winding condition assessment”, powercon international conference on power system technology, vol. 2, pp. 1399 1403, 2004. etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 49-53 53 www.etasr.com azizi and gholami: optimum scheme for insulation system in hv generator… [3] s. b. lee, j. yang, k. younsi, r. m. bharadwaj, “an on-line groundwall and phase to phase insulation quality assessment technique for ac-machine stator winding”, ieee transactions on industry application, vol. 42, no. 4, pp. 946 – 957, 2006. [4] p. o’donnell, “report of large motor reliability survey of industrial and commercial installations: part i”, ieee transactions on industry application, vol. ia-21, no. 4, pp. 853–864, 1985. [5] “report of large motor reliability survey of industrial and commercial installations: part ii”, ieee transactions on industry application, vol. ia-21, no. 4, pp. 865–872, 1985. [6] p. f. albrecht, j. c. appiarius, d. k. sharma, “assessment of the reliability of motors in utility applications—updated”, ieee transactions on energy conversion, vol. ec-1, no. 1, pp. 39–46, 1986. [7] g. c. montanari, m. cacciari, “a probabilistic insulation life model for combined thermal-electrical stresses”, ieee transactions on electrical insulation vol. ei-20 no. 3, 1985. [8] g. j. anders, j. endrenyi, g. l. ford, g. c. stone, “a probabilistic model for evaluating the remaining life of electrical insulation in rotating machines”, leee transactions on energy conversion, vol. 5, no. 4, pp. 761 – 767, 1990. [9] s. b. pandey, “estimation for a life model of transformer insulation under combined electrical and thermal stress”, ieee transactions on reliability, vol. 41, no. 3, pp. 466 – 468, 1992. [10] h. s. endicott, b. d. hatch, r. g. sohmer, “application of the eyring model to capacitor aging data”, ieee transactions component parts, vol. 12, no. 1, pp. 34-41, 1965 [11] t. s. ramu, ‘‘on the estimation of life power apparatus insulation under combined electrical and thermal stress,’’ ieee transactions on electrical insulation, vol. ei-20, pp. 70-78, 1985. [12] d. azizi, a. gholami, a. vahedi, “analysis of the deterioration effects of stator insulation on the its electro-thermal property”, international journal of electrical and electronics engineering, vol. 3, no. 11, pp. 697701, 2009. authors profile diako azizi was born in 1985. he has received b.sc. degree in electrical engineering from tabriz university, tabriz, iran in 2007. and he received the master degree in electrical power engineering from the university of science and technology, tehran, iran in 2009. he is presently pursuing the ph.d. degree in electrical power engineering, iran university of science and technology. his research interests are aging of insulations in electrical machines. ahmad gholami has received his b.sc. degree in electrical engineering from iust, tehran, iran, in 1975, the m.sc. and phd degrees in electrical engineering from umist, manchester, england, in 1986 and 1989 respectively. he is currently an associate professor in the electrical engineering department of iran university of science and technology. his main research activities are high voltage engineering, electrical insulation, insulation coordination, transmission lines and substations planning. microsoft word etasr_v11_n4_pp7501-7507 engineering, technology & applied science research vol. 11, no. 4, 2021, 7501-7507 7501 www.etasr.com saad: enhancement of solar cell modeling with mppt command practice with an electronic edge filter enhancement of solar cell modeling with mppt command practice with an electronic edge filter said saad faculty of sciences of monastir university of monastir monastir, tunisia said.saad@fst.rnu.tn abstracta new photovoltaic cell modeling based on an electronically tunable edge filter is presented in this paper. the new model is subjected to temperature, illumination, and resistance variations. in addition, an mppt (maximum power point tracker) command was exposed with a calculation algorithm based on a microcontroller card that used the behavior of an electronically tunable edge filter. the results confirm those published in the literature, showing the influence of the position of the leakage variation in our model, which can give more power. the simulation results show that the proposed command is efficient to determine the mpp point. keywords-photovoltaic cell; illumination; mppt; calculation algorithm; electronic tunable efge filter i. introduction today, renewable energies, such as photovoltaic, wind, or hydraulic energy appear to be inexhaustible and easily exploitable. if we take the example of solar energy, an area of 145000km 2 (4% of the arid deserts surface) of photovoltaic (pv) panels would be sufficient to cover the global energy needs [1]. moreover, the enhancement of the efficiency of the pvs and the design and the implementation of pv systems pose challenges to builders, scientists, and researchers [2]. for a pv installation, the variations of illumination, temperature, and in load charge cause a degradation of the power supplied by the pv generator. in addition, the design of a pv cell may also have a negative effect on the performance and the results delivered to the load charge [3], that’s why a new model of pv cell is proposed in this paper where a leakage resistance is inserted in series with the diode of the cell. the purpose is to demonstrate that when we minimize the leakage effect in construction we can improve the current delivered to the charge. a solar cell presents nonlinear characteristics [4]. in order to extract the maximum power at each instant from the solar cell terminals and transfer it to the load, an adaptation stage is used between the solar cell and the load [5]. however, in order to find the maximum power point (mpp) point we use algorithms and commands. several mpp tracking techniques have been developed. these approaches can be divided into smart and classical schemes. in the first scheme category, we find ripple-based extremum seeking control [6], neural networks [7], dissimilation particle swarm optimization [8], and the takagi-sugeno fuzzy model [9]. in the second category, we have the perturb & observe (p&o) [10], the effect of the dc/dc circuit voltage converter [12], and the incremental conductance perturbation [13] methods. the method of ripple-based extremum seeking is fast, but the current control is less stable than the voltage control [6]. the approach of neural networks has proved to be very efficient and accurate, but complex [7]. the method of particle swarm optimization gives good results, however it is complex because it is based on neural networks. the fuzzy method can directly drive the system to the mpp without searching the mpp and measuring illumination [9], but it is more complicated and uses feedback in the calculations. for the approaches of p&o and the incremental conductance perturbation, the reasoning is the same and it is simple, also the results are the same with a difference of 0.13% in dynamic conditions and as low as 0.02% in static conditions [10]. also the methods that use the p&o suffer from oscillations which we always want to minimize. the method of effect of the dc/dc circuit voltage converter is practical [11], and may be unstable [12, 14]. all the presented approaches and methods aim to advance the pv system efficiency. however, they suffer from certain stability problems, especially in rapid climate changes. in this paper, we researched a pv generator cell that works longer under the optimum conditions. furthermore, the implementation of the calculation algorithm that finds the mppt is presented and investigated. this method is based on an electronic card, and to the best of our knowledge, has not been presented before. the digital controller in the card is realized by a microcontroller-based system where the pv cell and the card are simulated in matlab simulink and proteus isis. the obtained results are clearly shown and discussed. ii. solar cell modeling pv solar energy comes from the direct transformation of a part of solar radiation to electrical energy. the responsible element of this transformation is the pv cell which gives a dc current. the generated voltage can vary between 0.3v and 0.7v depending on the material used and its arrangement as well as the temperature of the cell and its age [15]. furthermore, the energy efficiency performance achieved industrially is 13 to 14% for cells based on monocrystalline silicon, 11 to 12% for polycrystalline silicon, and 7 to 8% for amorphous silicon in thin films [16]. the general model of a corresponding author: said saad engineering, technology & applied science research vol. 11, no. 4, 2021, 7501-7507 7502 www.etasr.com saad: enhancement of solar cell modeling with mppt command practice with an electronic edge filter pv cell behaves equivalently to a current source shunted by a diode. the model is completed by a series resistor rs due to the contribution of the base resistors and the junction front and back with front contacts and a shunt parallel resistor, rp, which comes from the metal contacts and the leakage resistors on the periphery of the pv cell [17]. figure 1 shows this behavior and table i gives the parameters of our resistance components. fig. 1. model of the pv cell. table i. resistance component values of the pv cell model component value rs 0.01ω rp 10ω the mathematical model for the current-voltage characteristic of a pv cell is given by [17]: i�� � i�� � i� �e �� ���.�� �.� � 1� � �������.���� (1) where i�� represents the current supplied by the cell when it operates as a generator, i�� represents the photocurrent of the cell depending on illumination and temperature, i� represents the saturation current, v�� represents the voltage across the cell, and v� � �.��� represents the thermodynamic potential with k being the boltzmann’s constant, t# the effective temperature of the cells in kelvin, q is the electron charge, n represents the ideality factor of the junction, r� represents the shunt resistance that characterizes the leakage currents, and r� represents the serial resistance of various contact and connection resistances on the other hand, we can characterize the pv cell by a current i## that represents the highest current that a cell can deliver. it is a function of temperature, illumination wavelength, the area of active zone of the pv cell, and the mobility of the electrons. also, we can characterize the cell by the voltage between the cell electrodes in the case of no charge in the output of the cell, v#'. it is a function of cell type, illumination wavelength, the material of active zone of the cell, and the type of contact between the active layer and the electrodes. in addition, the efficiency ratio of power, (, can also characterize the pv cell. it is defined by [18,19]: ( � )*+,)-� (2) where p/01 represents the maximum power delivered by the cell and p23 represents the incident power to the area of the cell. our proposed model is based on various electric characterizations of each element that are presented in figure 1. figure 2 illustrates the proposed model. the leakage current, presented by the resistance r�, is in series with the diode of connection. it is clear that the current delivered by the cell is augmented by the ip term that represents the leakage current. the leakage r� can be carefully varied in the phase of construction. thus, if his value is augmented, the current delivered to the charge is augmented and so the power. fig. 2. the proposed model. the current delivered by the proposed cell is: i�� � i�� � i� �e �� ���.�� �.� � 1� 4 �������.���� (3) the photonic current of the pv cell depends directly on the solar illumination and on the variation of the temperature. the following expression gives the photonic current [18]: i�� � 55678 9i��678 � k2;t# � t#678<= (4) where i��_?@a is the photonic current under reference condition, k2 is the current sensitivity coefficient for the temperature, g is the real illumination, g?@a is the illumination under the reference condition, t# is the real cell temperature, and t#_?@a is the cell temperature under the reference condition. fig. 3. currentoutput voltage characteristic of the proposed model. figure 3 represents the current-output voltage characteristic and figure 4 represents the power-output voltage characteristic of the proposed model under standard conditions: 1000w/m 2 illumination and 20°c temperature. the presented curves are similar with the results published engineering, technology & applied science research vol. 11, no. 4, 2021, 7501-7507 7503 www.etasr.com saad: enhancement of solar cell modeling with mppt command practice with an electronic edge filter previously in this field [5, 8, 10]. the characteristics of our model are summarized in table ii. the obtained results are similar with the results in [10, 13, 16]. fig. 4. power – output voltage characteristic of the proposed model. table ii. characteristics of the proposed model characteristic value open circuit voltage (v) 0.575 short circuit current (a) 3.8 voltage at maximum power (v) 0.5 current at maximum power (a) 3.6 cells 1 iii. characteristics of the pv cell under variations of temperature and illumination temperature is a very important characteristic in the pv cell behavior. figures 5 and 6 present the influence of the temperature in the current output voltage and power output voltage characteristics under fixed illumination of 1000w/m 2 . the curves show that the temperature negatively influences the open circuit voltage where the more the temperature increases the more the open circuit voltage decreases while the circuit current increases slightly. thus, the maximum power of the pv cell undergoes a decrease when the temperature increases, which is confirmed in the curves of figure 6. fig. 5. influence of the temperature on the current – output voltage characteristics. fig. 6. influence of the temperature on the power – output voltage characteristics. figures 7 and 8 present the influence of the illumination in the current output voltage and power output voltage characteristics under a fixed temperature of 25°c. from the curves, when the illumination varies for a given temperature, the current of the circuit varies in proportion to the illumination, and at the same time, the voltage varies very little. in addition, power increases when the illumination increases due to the rise in the current. thus the results show that the mpp varies clearly with illumination. fig. 7. influence of the illumination on the current – output voltage characteristics. fig. 8. influence of the illumination on the power – output voltage characteristics of the proposed model. iv. characteristics of the photovoltaic cell under variations of model resistances figures 9 and 10 present the influence of the serial resistance rs in the current output voltage and power – output voltage characteristics. this resistance acts on the slope engineering, technology & applied science research vol. 11, no. 4, 2021, 7501-7507 7504 www.etasr.com saad: enhancement of solar cell modeling with mppt command practice with an electronic edge filter of the current – output voltage characteristic but does not modify the output open circuit voltage and slightly decreases the circuit current value. however, the increase in the resistance value results in a decrease in the slope of the power curve and the values of the mpp. fig. 9. influence of the serial resistance rs on the current – output voltage characteristics of the proposed model. fig. 10. influence of the serial resistance rs on the power – output voltage characteristics of the proposed model. the resistance rp takes into account the inevitable leaks of the current which occur between the terminals of the solar cell. this resistance has a high value, andits effect is mainly in the current generation part. it is for this reason that we put this resistance in series with the diode instead of putting it in parallel in our proposed model. fig. 11. influence of the current leakage resistance rp on the current output voltage characteristics of the proposed model. figures 11 and 12 present the influence of the leakage current resistance rp in the characteristics current – output voltage and power – output voltage. in the normal case, the influence of the parallel resistance on the current – output voltage characteristic results in a slight decrease in the open circuit voltage and a decrease in the slope. in addition, the power supplied by the solar cell varies with this parallel resistance, the more this high resistance, the more important the supplied power. for our model, the simulation results confirm those mentioned above for a normal model. however, it is very clear from figure 12 that we have increased the mpp, which is very important for a solar cell generator and is a clear advantage of the proposed model. fig. 12. influence of the current leakage resistance rp on the power – output voltage characteristics of the proposed model. v. the mppt algorithm this part demonstrates the algorithm that provides in each instance the maximum power delivered from the pv cell. maximum power means finding the mpp of the proposed model. this method is named mppt (maximum power point tracking). in this part, a command that can find this mpp is demonstrated. figure 13 represents the mpp position delivered by the pv cell under variations of illumination and fixed temperature of 25°c. in addition, in order to assure that the solar cell operates at its mpp, controllers are utilized to minimize the error between the operating power and the maximum variable reference power based on optimal methods and depending on climatic conditions. figure 14 presents the principal of our mppt command. the used circuit is that of a tunable edge filter based on a microcontroller system. the purpose is to give maximum power without fluctuations. the organigram algorithm of the command mpp is given in figure 15. fig. 13. mpp position in the characteristics of the pv cell under illumination variation and 25°c. engineering, technology & applied science research vol. 11, no. 4, 2021, 7501-7507 7505 www.etasr.com saad: enhancement of solar cell modeling with mppt command practice with an electronic edge filter fig. 14. command mpp, tunable edge filter, in the pv generator: cell and charge. fig. 15. organigram algorithm of the mpp command using a tunable edge filter. for our mpp command and tunable edge filter, the evolution of the power is analyzed after each voltage or current fluctuation. thus, we measure the voltage and we calculate the current. after that, we calculate the power delivered by the solar cell at each tunable time interval according to the variation of lighting and the temperature. the basis of our electronic tunable edge filter is a pic16f877a microcontroller, an optocoupler, a nand logic component, a high and low side driver for external n-channel mosfet, and an n-channel mosfet. the last component is used to control the adaptation stage in order to reach the mpp, see figure 17. the reasoning is that we have a power value and we measure the new value. the difference between the two values must lie between the maximum edge and the minimum edge of the tunable filter represented by pref(i) and vref(i). this edge is defined in the microcontroller program each time. once the value is determined and meets the criteria of the tunable filter, the mosfet becomes busy in the adaptation stage and thus we have a maximum of power which is delivered to the load according to the duty cycle d. the simulation of our mpp command and the adaptation stage for different values of illumination under a constant temperature of 25°c is given in figure 16. this figure shows that the power is stable for a determined period for a constant value of illumination. table iii resumes the characteristic of our mppt and shows the comparison with other methods that are presented in [20]. from the result, we can say that our proposed mppt is practical and efficient in acquiring the mpp and controlling the dc/dc converter to the load. as an example of the usefulness of the proposed scheme and its encouraging results, it may be used to improve the use of the pv technology in hybrid vehicles [21]. fig. 16. illustration of the power delivered to the charge after the determination of the mpp with the tunable edge filter. table iii. comparison of mppt techniq ues mppt technique tunable edge filter p & o incremental conductance perturbation neural network type of sensor used voltage voltage and current voltage and current voltage and current identification of pv panel parameters no no no yes complexity low low average high precision 96% 95% 98% 99% vi. conclusion a new pv cell model was presented in this paper. the obtained results confirm the results of published previous works. the new model was subjected to temperature, illumination, and serial and leakage resistance variations. the influence of the position of the leakage variation in our model shows that our model can give more power. in addition, a mppt command was presented. the command is an electronic tunable filter using a microcontroller system. the simulation results show that the proposed command is efficient in determining the mpp. engineering, technology & applied science research vol. 11, no. 4, 2021, 7501-7507 7506 www.etasr.com saad: enhancement of solar cell modeling with mppt command practice with an electronic edge filter fig. 17. the electronic tunable edge filter for the mpp command. references [1] k. kassmi, m. hamdaoui, and f. olivié, "conception et modélisation d’un système photovoltaïque adapté par une commande mppt analogique," revue des energies renouvelables, vol. 10, no. 4, pp. 451– 462, 2007. 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[21] m. e. bendib and a. mekias, "solar panel and wireless power transmission system as a smart grid for electric vehicles," engineering, technology & applied science research, vol. 10, no. 3, pp. 5683–5688, jun. 2020, https://doi.org/10.48084/etasr.3473. microsoft word etasr_v12_n3_pp8592-8596 engineering, technology & applied science research vol. 12, no. 3, 2022, 8592-8596 8592 www.etasr.com le et al.: a power line lightning protection method for television and radio stations a power line lightning protection method for television and radio stations quang trung le engineering and technology department lilama 2 international technology college dong nai, vietnam qtrungttc2@gmail.com trong nghia le electrical and electronics department hcmc university of technology and education ho chi minh city, vietnam trongnghia@hcmute.edu.vn huy anh quyen electrical and electronics department hcmc university of technology and education ho chi minh city, vietnam anhqh@hcmute.edu.vn trieu tan phung electrical and electronics department cao thang technical college ho chi minh city, vietnam phungtrieutan@caothang.edu.vn hong hau pham engineering and technology department lilama 2 international technology college dong nai, vietnam hauph.ute@gmail.com received: 13 january 2022 | revised: 25 march 2022 | accepted: 1 april 2022 abstract-the existing research on lightning protection focuses on risk assessment or equipment selection. there has not been any thorough research about lightning protection including risk assessment for a building in order to identify the risks when selecting lightning protection equipment according to technical requirements and cost optimization. the objective of the current paper is to propose a new risk computational method of damages by lightning for a television and radio station (trs). the new computational method consists of nine steps for identifying two risk indices, human life loss (r1) and service loss (r2). if the value of r1 is higher than the regulatory limit value rt1 and the value of r2 is higher than the regulatory limit value rt2, the damage risks due to lightning are very serious. therefore, the trs is necessary to select lightning protection solutions to reduce these risks. in addition, the paper proposes a six-step procedure for selecting and testing surge protective devices. the proposed calculations are then applied to a real trs in vietnam, and some testing results are simulated in matlab-simulink. keywords-risk of damage by lightning; lightning protection system (lps); surge protection measures (spm); television and radio station (trs) i. introduction power system development can cause many problems. the issue of maintaining and stabilizing the power system when there is a problem is always a topic of interest [1, 2]. there have been many studies regarding the assessment of the risk of damages by lightning to buildings [3, 5-7] and the guidelines for selecting and installing lightning protection equipment [4, 8, 9]. based on the above, we propose an overall protection method for surge protective devices on power lines connected to the trs including risk assessment, equipment selection, and installation for reducing the risks of damages caused by lightning. this overall method is proposed for applying surge protective devices (spds) on power lines for a trs in vietnam. based on the computation of the damage values of the trs, the paper provides a solution for selecting spds suitable to the characteristics of the trs. this research focuses on the risk values about the human life loss (r1) and service loss (r2). when these two indices are higher than the regulatory limit values, trs must be installed with spds to reduce the risk of damage by lightning. besides, the estimation of lightning protection level is performed by simulations in matlab/simulink. with the simulation results, it is possible to select the spds that satisfy with the real requirements of the trs with a reasonable investment funding. ii. a new computation method for selecting lightning surge protective devices on power lines a. the procedure for assessing risk values for the trs this section proposes a new computational method for identifying risk values r1 and r2 for a trs. the method includes nine steps as shown in figure 1. corresponding author: trieu tan phung engineering, technology & applied science research vol. 12, no. 3, 2022, 8592-8596 8593 www.etasr.com le et al.: a power line lightning protection method for television and radio stations fig. 1. procedure for assessing the risk values for the trs. • step 1: determine the parameters of the trs encompassing height, length, width; height of antenna tower, degree of shielding by the structures around, density of lightning, measures of fire protection, installation method, and length of the power and service lines directly connected to the trs, and the current lightning protection equipment. • step 2: compute the risk components by the lightning strikes direct and indirect to the trs. then, identify risk values r1 and r2. • step 3: collate risk values of the r1 and r2 with the rt1 and rt2 (regulatory limit values rt1 and rt2 are referenced to iec 62305-2 [5]). if these risk values are bigger than rt1 and rt2, move to the step 4. • step 4: check if the trs has been installed with lightning protection system (lps) or not. if the trs has not been installed with lps, transfer to step 6. if the trs has been installed with lps, transfer to step 5. • step 5: check if the trs has been installed with surge protection measures (spm) on the power lines or not. if the trs has been installed with lps and spm but the risk values of the r1 and r2 are still higher than rt1 and rt2 risk values, go to step 8. if the trs has not been installed with spm, go to step 7. • step 6: select a suitable lps for installation and go to step 9. • step 7: select a suitable spm equipment on the power line for reducing the risk values and go to step 9. • step 8: select additional spm equipment and go to step 9. • step 9: recompute r1 and r2 and go back to step 3. table i. recommend maximum lightning current exposure level low medium high environment of building the building is located in an urban/ suburban area. the building is located in plain. the building is located in areas where there is high lightning risk by the surrounding environment (pylons or mountainous regions, trees, wet areas, ponds, etc.) recommended maximum lightning current (ka) 20 40 65 b. the procedure for testing and installing spds based the calculated values of r1 and r2, the procedure for selecting and testing spds is implemented in 6 steps, shown in figure 2. fig. 2. procedure for testing and installing spds. • step 1: relying on the single-line diagram of power lines connected to the trs, build a model of the electrical network in matlab/simulink including surge currents. • step 2: choose the spds for installing on the power lines. • step 3: identify the locations for installing the spds on the power lines for essential main switchboard (emsb) and main switchboard (msb). engineering, technology & applied science research vol. 12, no. 3, 2022, 8592-8596 8594 www.etasr.com le et al.: a power line lightning protection method for television and radio stations • step 4: simulate for checking the withstanding of the spds on the power lines with wave impulse 8/20µs. • step 5: check the protection voltage value (up). the up has to satisfy the requirements in (1) for electrical equipment [9] and in (2) for electronic devices [6]. if these requirements are not satisfied, the procedure goes back to step 2. if these requirements are satisfied, go to step 6. up ≤ (1200+un) (1) up ≤ 1.5un (2) • step 6: the trs is protected. iii. computation for a real trs a. characteristics of the real trs the studied trs was built by reinforced concrete in an area with the lightning flash density of 13.7 strikes/km 2 /year without nearby higher buildings. the distance from the antenna tower to the station is 4m, and the height of the antenna tower is 55m. the length of the power lines connected to the station is 550m, and the telecom line is 960m. lps is already installed, and the telecom lines are designed with spm. however, the power lines are not protected by spm. the trs needs to calculate the r1 and r2 and then select for the spd to be installed on the power lines b. assessing the damage risk due to lightning for the studied trs the followed steps of the proposed method are: • step 1: define the parameters of the trs. • step 2: compute the risk values of r1 and r2. the results are shown in table iii. • step 3: the risk value r2 is higher than the regulatory limit rt2 [5]. • step 4: class i lps is installed in the trs. • step 5: the trs is not yet installed with spm on power lines. • step 7: select spd with lps class ii. • step 9: recomputation of the risk values after installing the spd. the results are shown in table iv. after the spd installation, the r1 and r2 risk values were less than the regulatory limit values [5]. therefore, the trs is protected and the risk of damages by lightning is limited. in addition, the effective protection of spd on the power lines is implemented below. c. implementing the selection and testing the protection level of spd on the power lines the followed steps of the proposed method are: • step 1: based on the single-line diagram of the power lines connected to the trs and the electric devices used in the trs, the distribution network model is built in the matlab as shown in figure 3. table ii. trs parameters parameter notation value density of ground flash (flashes/km 2 /year) ng 13.7 structure dimensions (m) l×w×h 12×8×10 heigher of antenna tower t (m) hanten 55 location factor cd 1 measures for protection pb 0.02 coordinated spds peb 0.01 shield at external structure boundary ks1 1 type of floor rt 10 -3 probability of a dangerous discharge based on structure type ps 0.2 probability that lightning will cause a shock to animal or human being outside the structure due to touch and step voltage ph 0.01 measures of protection pta 10 -2 protection against touch voltages ptu 10 -2 risk of fire rf 10 -3 fire protection rp 0.2 shield at internal structure boundary ks2 1 hazard hz 2 loss of human life due to touch and step voltage lt 10 -2 due to physical damage lf 10 -2 due to failure of the internal system lo loss of service due to physical damage lf 10 -2 due to failure of the internal system lo 10 -2 table iii. risk values before spd installing computed risk values regulatory limit risk values comparison r1=4.69×10 -6 rt1=10 -5 r1< rt1 r2=0.034 rt2=10 -3 r2> rt2 table iv. risk values after spd installation computed risk values regulatory limit risk values comparison r1=7.753×10 -8 rt1=10 -5 r1< rt1 r2=0.00022 rt2=10 -3 r2<rt2 • step 2: the spd class i is selected to be installed at the essential main switchboard (emsb) with 275v rated voltage and 40ka rated current. besides, spd class ii is chosen to be installed at the ac main switch board (msb) with 275v rated voltage and 25ka rated current. • step 3: define the location for installing spd on the power lines at emsb and msb. • step 4: simulate and test the withstanding capacity of the spd on power lines and the protection voltage of the load. the location of trs has a lightning density of 13.7 strikes/km 2 /year, a surge current of 8/20µs and 40ka which is considered before installing the spd. the protection voltages at the loads are presented in table v, and their waveforms are presented in figures 4-5. • step 5: from the results (table v), there are some critical points. the protection voltage value across the ac load is 385.000v and across the dc load is 458v. these voltage values are higher than the tolerable voltage values of 1430v and 72v respectively. these tolerable voltage values are calculated using (1) and (2) with the nominal voltage of the system being 230v for ac load and 48v for dc load. therefore, trs needs to install spd for protecting the electronic devices against the surges on the power lines. engineering, technology & applied science research vol. 12, no. 3, 2022, 8592-8596 8595 www.etasr.com le et al.: a power line lightning protection method for television and radio stations • step 2: select the spd of class i with rated voltage of 275v and rated current of 40ka for installation at the emsb, the spd of class ii with rated voltage of 275v and rated current of 25ka for installation at the msb. • step 3: the selected spds are installed on the power lines at the emsb and msb, and their models are added in the simulation network. • step 4: simulate for spd class i with waveform of 8/20µs, surge current of 40ka and spd class ii with waveform of 8/20µs, surge current of 25ka. the simulation result with ac load is shown in table vi and with dc load in table vii. fig. 3. model of the distribution network in matlab-simulink. table v. simulation results of the protection voltage at loads without spd installed amplitude of rated current 8/20µs (ka) peak of protection voltage across the ac load (v) peak of protection voltage across the dc load (v) 40 386.000 459 table vi. protection voltage values at the ac load after spd installation at the emsb and msb surge current 8/20µs (ka) voltage tolerance (%) spd class i spd class ii rated voltage (v) rated current (ka) protection voltage across the load (v) rated voltage (v) rated current (ka) protection voltage across the load (v) 40 10 275 40 1779 275 25 1118 fig. 4. waveform of protection voltage across the ac load when spd is not installed. fig. 5. waveform protection voltage across dc load after spd installation. the conclusion after the simulation results with ac load about the protection capacity of spds is that the trs needs to select and install spd class i with surge current 40ka and spd class ii with surge current 25ka. after installing the spd class i, the protection voltage across the dc load is 64v. this voltage value is lower than the limit of 72v. therefore, the trs needs to select and install spd class i with surge current of 40ka. engineering, technology & applied science research vol. 12, no. 3, 2022, 8592-8596 8596 www.etasr.com le et al.: a power line lightning protection method for television and radio stations • step 5: the final solution is installed with spd class i with rated voltage of 275v and rated current of 40ka and spd class ii with rated voltage of 275v and rated current of 25ka. • step 6: the structure is fully protected from surges on the power line. fig. 6. waveform of the protection voltage across the ac load after the installation of class i and ii spds. table vii. protection voltage values at the dc load after installing spds at the emsb rated voltage of spd class i rated current (ka) voltage tolerance (%) surge current 8/20µs (ka) protection voltage across the load (v) 275 40 10 40 64 fig. 7. waveform of protection voltage across the dc load after the spd installation. iv. conclusion this paper proposes a new computation method for protecting from lightning propagation on the power lines of a trs. it involves nine steps for calculating the risk values of human life loss (r1) and service loss (r2) and six steps for selecting and testing the protection level of spd on the power lines. the effectiveness of this method is tested on a real trs in vietnam. references [1] g. shahgholian and a. fattollahi, "improving power system stability using transfer function: a comparative analysis," engineering, technology & applied science research, vol. 7, no. 5, pp. 1946–1952, oct. 2017, https://doi.org/10.48084/etasr.1341. [2] d. v. ngo, k. v. pham, d. d. le, k. h. le, and k. v. huynh, "assessing power system stability following load changes and considering uncertainty," engineering, technology & applied science research, vol. 8, no. 2, pp. 2758–2763, apr. 2018, https://doi.org/ 10.48084/etasr.1892. [3] z. janklovics, "the place and role of power supply in the overvoltage protection and risk assessment of damages to telecommunication sites due to lightning discharges," in the second international telecommunications energy special conference, budapest, hungary, apr. 1997, pp. 439–446, https://doi.org/10.1109/ telesc.1997.655748. [4] en 62305-2:2012 protection against lightning part 2: risk management. sist, 2012. [5] as / nzs 1768:2007 lightning protection western australia. western australia: department of mines, industry regulation and safety, 2017. [6] risk assessment of damages to television and radio station due to lightning discharges. itu, 1997. [7] nfpa 780: standard for the installation of lightning protection systems. quincy, ma, usa: nfpa, 2020. [8] iec 61643-21-2012 performance requirements and testing methods, 1.1. iec, 2018. [9] a. khodadadi, m. h. nazari, and s. h. hosseinian, "designing an optimal lightning protection scheme for substations using shielding wires," engineering, technology & applied science research, vol. 7, no. 3, pp. 1595–1599, jun. 2017, https://doi.org/10.48084/etasr.1175. microsoft word etasr_v12_n4_pp8785-8790 engineering, technology & applied science research vol. 12, no. 4, 2022, 8785-8790 8785 www.etasr.com kayabasi et al.: functionally graded material production and characterization using the vertical … functionally graded material production and characterization using the vertical separator molding technique and the powder metallurgy method i. kayabasi motor vehicles and transportation technology department küre vocational school of higher education kastamonu university kastamonu, turkey ikayabasi@kastamonu.edu.tr g. sur mechanical engineering department engineering faculty karabuk university karabuk, turkey gokhansur@karabuk.edu.tr h. gokkaya mechanical engineering department engineering faculty karabuk university karabuk, turkey hgokkaya@karabuk.edu.tr y. sun metallurgy and materials engineering department engineering faculty karabuk university karabuk, turkey ysun@karabuk.edu.tr received: 28 april 2022 | revised: 12 may 2022 | accepted: 15 may 2022 abstract-functionally graded materials (fgms) are advanced customized engineering materials that gradually and continuously change their composition. the current study investigated the production feasibility and some post-production mechanical/physical properties of b4c particle-reinforced (avg. 40µm) aa7075 matrix (avg. 60µm) fgm composites with the vertical separator molding technique using the high-temperature isostatic pressing powder metallurgy method. fgms produced consist of three (0 – 30 – 60 wt. % b4c) and four (0 – 20 – 40 – 60 wt. % b4c) layers. the powders were mixed in a power blender mixer for 2h and were placed in the mold sections with a vertical separator. the lid was closed, and a pre-pressure of 10mpa was applied. the fgm green sheet was transferred from the vertical separator mold to the hot work tool steel with a press. in this mold, fgms were sintered at 560°c for 30 min under a pressure of 325mpa. microstructural examinations did not reveal any separation or crack formation in the layer transition regions of the fgms. in addition, a relatively homogeneous b4c reinforcing distribution was observed in the layers with a low reinforcement ratio (wt. 20% and 30%) compared to the other layers. the highest hardness was 170 hbn in one layer of the four-layer fgm containing 40% by weight b4c reinforcement. the highest transverse rupture strength was measured in the test performed from the region with the most reinforcement of the four-layer fgm at 482mpa. keywords-functionally graded material; powder metallurgy; hot pressing; transverse rupture strength i. introduction fgms are widely used in various fields such as aerospace, automotive, electronics, defense industry, gas turbine engines, and engineering applications. they have emerged as a relatively new material class [1, 2]. the fgms are materials that change their composition and structure and seriously alter their material properties gradually along with their height [3, 4]. functionally graded metal matrix composites (fgmmcs) with metal and ceramic content have great potential and importance for the fabrication and design of components and structures. fgmmcs have superior features to bring advanced engineering components to a better level along with material design. specific properties such as high-temperature surface wear resistance, thermal mismatch correction, reduction of interfacial stresses, minimization of thermal stresses, increased metal-ceramic interfacial adhesion, delayed crack formation, and increased fracture toughness can be obtained by utilizing fgmmcs [1]. aluminum matrix composite (amc) is considered one of the most promising materials due to its lightweight and high specific strength values [5-7]. among the existing amcs, aa7075 is a matrix material with high strength, sufficient toughness, and corrosion resistance [8]. the vast-majority of reinforcing materials of amcs are non-metallic ceramic materials. al2o3, sic, and b4c are the most commonly used ceramic reinforcements in amcs [9]. b4c reinforcement material stands out among ceramics due to its good chemical inertness, high hardness, high elastic modulus, and high melting properties [10]. one of the most important areas in fgm research is the production method [1]. many different fabrication methods have been developed to fabricate fgms, such as gas-based corresponding author: i.kayabasi engineering, technology & applied science research vol. 12, no. 4, 2022, 8785-8790 8786 www.etasr.com kayabasi et al.: functionally graded material production and characterization using the vertical … methods, liquid-phase methods, solid-phase methods, and biopolymeric-based functionally graded structures. powder metallurgy, one of the solid phase methods, is a good method for obtaining a homogeneous and graded structure in fgm production [11, 12]. the powder metallurgy method offers advantages such as low processing temperature, ease of obtaining the final product, continuity in product quality, and low cost with its suitability for mass production compared to melting methods [13, 14]. in fgm production by powder metallurgy method, powders are gradually laid into the mold according to the reinforcement ratio [15]. this process is mostly carried out based on one's dexterity. it is difficult to obtain a smooth transition surface between layers in such manual procedures. in fgm production with another powder metallurgy method, the powder is laid in the mold for each stage and subjected to pre-pressing [16, 17]. this adversely affects the formation of the desired bond structure on the layer transition surfaces during the sintering phase. vertical separator molding technique has been developed in order to obtain a smoother transition zone, to create the desired bond structure in the layer transition zones, and to provide the layer transition zones in the desired two-dimensional geometric structures. in this study, a two-stage mold consisting of a vertical separator, a filling chamber, and a hot-pressing mold was designed and manufactured for fgm production under the high temperature isostatic pressing technique of the powder metallurgy method. the availability of planeness of transition surfaces of the b4c reinforced aa7075 matrix fgms with 3 (0-30-60% wt.) and 4 (0-20-40-60% wt.) layers of the same thickness as the manufactured mold was examined, along with the post-production metallurgical and mechanical properties. ii. materials and methods this study was carried out for fgm production. the chemical composition of aa7075 matrix (avg. 60μm) is presented in table i. reinforcement material b4c (avg. 40μm) powder was used. table i. chemical composition of aa7075 element zn mg cr cu fe si mn ti al %avg. 5.5 2.5 2.5 1.6 0.5 0.4 0.3 0.2 bal. the scanning electron microscopy (sem) images of matrix and reinforcement are shown in figure 1. sem investigations showed that aa7075 powder was relatively spherical in shape and variable in grain size. it has been observed that the reinforcement b4c powder was composed of particles with complex geometry and sharp edges, whose aspect ratio is relatively close to each other. in determining the percent weight ratio of the reinforcement of the fgm layers, one side is designed in a brittle structure with a high reinforcement ratio (high hardness, high wear resistance, high compressive strength), and the other side is designed in a tensile structure without reinforcement (high toughness, high % elongation). information about the number of layers and reinforcement content of the produced fgms are presented in table ii. (a) (b) fig. 1. sem images of the powders used in fgm production: (a) aa7075, (b) b4c. table ii. layer and reinforcement ratios of the produced fgms number of layers 3 4 layer reinforcement rates (% wt.) 0 – 30 – 60 0 – 20 – 40 – 60 under the ratios in table ii, matrix and reinforcement powders were weighed on a precision balance at suitable values for the mixing ratio of each layer. in order to obtain a homogeneous powder mixture, it was mixed in a power mix blender for 2 hours. the mixed powders were filled into mold chambers (3 layers 60×60×8mm, 4 layers 60×60×6mm), whose layer areas were separated in equal volume by vertical steel separators. after the powder filling process, the steel separators were removed, the upper surface of the mold was closed, and a pre-compression force of 10mpa was applied under uniaxial hydraulic press. the pre-compression force was applied from the surface of the layer with the highest reinforcement ratio (60% wt. b4c). pre-compressed green sheet fgm was transferred into a separate mold made of hot work tool steel using a hydraulic press to carry out high-temperature isostatic pressing and sintering processes. green sheet fgm samples were heated up to 560°c in a hot work tool steel mold and waited for 30min. then, sintering was carried out at this temperature for 30min under a pressure of 325mpa and the samples were left to cool in the mold at room temperature. at engineering, technology & applied science research vol. 12, no. 4, 2022, 8785-8790 8787 www.etasr.com kayabasi et al.: functionally graded material production and characterization using the vertical … least two fgm samples were produced from each layer number. the samples were 60×60×12.7 ±0.13mm in size. the produced fgm samples and the cross-sectional macro views of the 3 and 4 layered samples are shown in figure 2. the microstructure characterization of the produced fgm samples was investigated using the fei quanta feg 250 sem located in kastamonu university central research laboratories and research center. the hardness values of the layers of the fgms were determined by the brinell hardness measurement method using the qness q250m type hardness measuring device at karabuk university’s iron and steel institute. fig. 2. fgm sample images: (a) after sintering, (b) 3-layer cross-sectional view, (c) 4-layer cross-sectional view. fgm hardness measurements were carried out using 2.5mm diameter steel balls under a 62.5kg load. at least 5 measurements were made for each layer of the fgm, and the average determined the hardness value for the general layer. the produced fgms were cut according to the astm b528-05 standard (31.9×12.7×12.7±0.13mm) and turned into transverse rupture strength test specimens. transverse rupture strength tests were performed on the cut samples in a 50kn capacity instron 3369 tension/compression device. transverse rupture strength tests were performed at a deformation rate of 2mm/min. transverse rupture strength load was applied separately to the layer surface of the fgm with the highest reinforcement and to the layer surface without reinforcement. the transverse rupture strength test results were determined by the average of the measurements after at least 4 measurements in each direction. iii. results and discussion a. microstructure results sem images of each layer and the interlayer transition zones were taken to determine the microstructure properties of the produced fgms. sem images are given in figure 3 for the 3-layer fgm and figure 4 for the 4-layer fgm. (a) (b) fig. 3. sem microstructure images of 3-layer fgms: (a) 0% to 30% wt. b4c transition surface image, (b) 30% to 60% wt. b4c transition surface image. (a) (b) (c) engineering, technology & applied science research vol. 12, no. 4, 2022, 8785-8790 8788 www.etasr.com kayabasi et al.: functionally graded material production and characterization using the vertical … it was determined that b4c reinforcement in fgms settled at grain boundaries and showed a relatively homogeneous distribution in low-rate layers. it was observed that b4c reinforcement accumulated at the grain boundary with increasing reinforcement ratios. it is not easy to obtain a homogeneous distribution while producing composite materials with the powder metallurgy technique because the reinforcement can settle at the grain boundaries. (a) (b) (c) fig. 4. sem microstructure images of 4-layer fgms: (a) 0% to 20% wt. b4c transition surface image, (b) 20% to 40% wt. b4c transition surface image, (c) 40% to 60% wt. b4c transition surface image. in addition, it has been reported that the porosity increases due to the increasing reinforcement ratio [1, 18]. it was determined that agglomeration and micropores increased as the amount of reinforcement increased in the layers of the produced fgms. when the transition zones between the layers of the produced fgms were examined, no delamination was observed. it has been observed that the transition of fgm between layers is continuous and has structural integrity. b. hardness results it has been reported that the hardness value increases with the increase of the ratio in the reinforcement structure in composite materials up to certain values [19-22]. the hardness measurements performed on the layers of the produced fgm samples showed that the hardness value increased up to 40% wt. b4c, and after this value, it decreased depending on the decreasing matrix amount and increasing porosity. similarly, in [15], the measured hardness value was 40% wt. graphs of change in the hardness (brinell; hbn) values of each layer depending on the number of layers of fgms are presented in figure 5. (a) (b) fig. 5. layer hardness of fgms: (a) 3-layer, (b) 4-layer. it can be seen in figure 5 that the hardness increases to a certain extent (30% wt. b4c in 3 layers and 40% wt. b4c in 4 layers) depending on the increase of layer reinforcement. suppose a composite is produced with success within the desired limits (homogeneous distribution property, porosity amount, etc.) of composite materials. in that case, it is expected engineering, technology & applied science research vol. 12, no. 4, 2022, 8785-8790 8789 www.etasr.com kayabasi et al.: functionally graded material production and characterization using the vertical … that the mechanical properties and hardness values will increase according to the mixture theory as the reinforcement ratio increases up to a certain value. equation (1) presents the mathematical expression used to theoretically calculate the hardness of the composites according to the mixture theory. �� � ���� � ���� (1) where hk is the hardness of the composite, hm is the hardness of the matrix, fm is the weight ratio of the matrix, ht is the reinforcement hardness, and ft is the reinforcement by weight ratio. it was determined that the layer with the highest hardness value of the produced fgms was the third layer of the 4-layer fgm reinforced with 40%wt. b4c. the hardness of this layer was measured as 170hbn. the lowest hardness value was 94hbn in the layer with the highest reinforcement ratio (60% wt.) of the 3-layer composite. when the sem images of the 3and 4-layer fgms in figure 3 and figure 4 are examined, it was seen that the 60% wt. b4c reinforced layer had the highest porosity. therefore, brinell's hardness decreased in layers containing 60% wt. b4c reinforcement. c. transverse rupture strength tests result in order to determine the breaking strength of fgms, transverse rupture strength test was performed on reinforced and non-reinforced layer surfaces under test conditions prepared under the astm b528-05 standard. the flexure stress-strain graphs obtained as a result of the experiments are presented in figure 6. it can be seen in figure 6 that the transverse rupture strength of fgms differs according to the region where the load is applied. the measured transverse rupture strength of the fgm was higher (~153% in the 3-layer, ~65% in the 4-layer composite) with the application of the fracture load from the dense region of the reinforcement, because composites are more resistant to compressive stresses [23]. the highest obtained transverse rupture strength was 482mpa, from a 4-layer fgm applied to the load region with the highest number of reinforcement. in figure 6(b), 4-layer fgm transverse ruptured from the region with less reinforcement showed brittle fracture than the 3-layer fgm due to the decreased amount of matrix due to the layer increase. the increase in strength in composites can be explained according to the law of mixtures. equation (2) shows the strength increase in composite materials according to the law of mixtures [24, 25]. �� � ���� � ���� (2) where σk refers to the mechanical strength of the composite, σm refers to the mechanical strength of the matrix, fm refers to the weight ratio of the matrix, σt refers to the mechanical strength of the reinforcement, and ft refers to the weight ratio of the reinforcement. this equation predicts the strength values when the composite is produced within the desired limits without exceeding the ideal production conditions. as the ratio of the side with a higher strength value compared to others increases, the strength of the composite also increases. it was observed that the porosity increased as the amount of reinforcement increased, in accordance with [1, 15]. the highest brinell hardness in fgm was obtained in the 40% wt. b4c layer. as the reinforcement ratio increased, the hardness of the composite decreased. similar results were found in [1]. the best results in the transverse rupture strength test were obtained on the reinforced layer surface. similar results were obtained in [15]. (a) (b) fig. 6. fgm transverse rupture strength graphics: (a) 3-layer, (b) 4-layer. iv. conclusions this study produced 3 (0-30-60% wt.) and 4 (0-20-40-60 wt.%) layers of b4c reinforced aa7075 matrix fgm with the vertical separator moulding technique. the following results were obtained in this study, in which the microstructure characterization, hardness and transverse rupture strength of the produced fgms were examined. • with the vertical separator moulding technique, fgms with smooth surface transition were successfully produced without any delamination in the transition areas. • it was determined that the distribution of b4c reinforcement in the layers of fgms with a low reinforcement ratio (wt. 20% and 30%) was relatively homogeneous compared to the other layers. • no delamination was observed between the layers of fgm. engineering, technology & applied science research vol. 12, no. 4, 2022, 8785-8790 8790 www.etasr.com kayabasi et al.: functionally graded material production and characterization using the vertical … • the highest porosity was observed in the layer containing 60 wt.% b4c. the lowest measured brinell hardness was 92hbn in the 3-layer fgm containing 60% wt. b4c reinforcement. • the highest measured brinell hardness was 170hbn in the 4-layer fgm containing 40% wt. b4c reinforcement. • in terms of transverse rupture strength, the tests applied to the reinforcement layer surface gave better results than the tests applied to the non-reinforcement layer surface (~153% in three layers, ~65% in four layers). • the greatest measured transverse rupture strength was 482mpa due to the application of the load from the region of the 4-layer fgm with the highest reinforcement. references [1] f. erdemir, a. canakci, and t. varol, "microstructural characterization and mechanical properties of functionally graded al2024/sic composites prepared by powder metallurgy techniques," transactions of nonferrous metals society of china, vol. 25, no. 11, pp. 3569–3577, nov. 2015, https://doi.org/10.1016/s1003-6326(15)63996-6. 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[25] w. d. callister jr and d. g. rethwisch, materials science and engineering: an introduction, 9th edition. hoboken, nj, usa: wiley, 2013. microsoft word etasr_v11_n6_pp7927-7931 engineering, technology & applied science research vol. 11, no. 6, 2021, 7927-7931 7927 www.etasr.com malkanthi et al.: enhancement of the properties of compressed stabilized earth blocks through the … enhancement of the properties of compressed stabilized earth blocks through the replacement of clay and silt with fly ash s. n. malkanthi department of civil and environmental engineering university of ruhuna sri lanka snmalkanthi@cee.ruh.ac.lk harsha galabada department of civil engineering university of moratuwa sri lanka hyasasiri@yahoo.com a. a. d. a. j. perera department of civil engineering university of moratuwa sri lanka asoka@uom.lk p. dhammika dharmaratne department of civil engineering university of moratuwa sri lanka makway.cons@gmail.com abstract—the use of earth as a building material, in different forms, such as unburnt and burnt bricks, rammed earth, mud blocks, and soil blocks, is a common practice globally. this study is focused on soil blocks stabilized with cement which are referred to as cement stabilized earth blocks (csebs). the strength and durability of csebs are primarily governed by the amount of silt and clay content (finer) in the soil. many researchers have shown that low finer content improves the properties of cseb and they have altered the finer content by adding different additives. the current study used a washing method to reduce the finer content and fly ash was utilized as finer to re-fill the soil to the required finer content amount. also, soil grading was modified by adding larger particles that were separated from the same soil to fit the soil grading to the optimization curves mentioned in the literature. the finer content was changed to 5%, 7.5%, and 10%. blocks were made by stabilizing the soil with 6%, 8%, and 10% cement and with the size of 150mm×150mm×150mm. the results revealed that fly ash addition up to 10% improves the properties of csebs and compressive strength changes from 4.28n/mm 2 to 13.43n/mm 2 . keywords-cement stabilized earth blocks; fly ash; reduced silt and clay; improved properties i. introduction earth is one of the oldest and most widespread construction materials [1]. raw earth as a building material has many advantages [2–5]. soils in their natural state lack in strength, durability, and dimension stability. authors in [6] showed the mechanical weakness and the absence of standard procedures to measure strength and stiffness as some demerits of earthbased constructions. these deficiencies can be overcome by stabilizing the soil to produce building materials [7]. compressed stabilized earth blocks (csebs) are one such building material. authors in [8] used soil to produce mud concrete blocks. authors in [9], on their extensive literature survey, have shown the advantages and disadvantages of using earth-based building materials. they have the inherent advantages of being eco-friendly, having low thermal conductivity, while they are abundantly available in nature. however, the loss of strength and dimensional stability when in contact with water for a long time, is a serious disadvantage. due to these disadvantages, the use of csebs as a common building material is not as expected. the use of burnt bricks and cement blocks is popular in si lankan housing construction also. as per statistics, the construction industry consumes a huge cost for burnt bricks and soil blocks usage is not even mentioned in the statistics [10]. the two main challenges of csebs are durability and compressive strength. the main variable for both these critical parameters is related to the amount of silt and clay (finer) in csebs. past research work established the optimum finer in the region ranging from 5% to 20% related to compressive strength but no firm indication of the range was associated with the durability of csebs. lateritic soil is used for the production of csebs and the content of silt and clay in lateritic soils is generally around the range from 20 to 35% [11]. csebs can be used to overcome the problems associated with burnt bricks such as material availability and the economic viability. generally, many researchers have shown the effect of finer content to the properties of csebs. the effect of soil grading to enhance the cseb properties was examined in [12]. the authors showed that the particle size distribution of soil can be modified to fit into the theoretical distribution suggested by particle packing theories. based on that, particle packing concepts suggested in [13–15] are valid for cseb production. crushed construction waste also can be used to modify the particle size distribution of the soil [16]. for corresponding author: s.n. malkanthi engineering, technology & applied science research vol. 11, no. 6, 2021, 7927-7931 7928 www.etasr.com malkanthi et al.: enhancement of the properties of compressed stabilized earth blocks through the … other soil-based products like mud concrete also, particle percentages in the different ranges need to be controlled [8]. the current research examined the reduction of finer content by washing the soil for the production of csebs. removing finer content to a certain extent may improve durability. production practicability is another concern. with high clay content, the production process may face problems. therefore, removing finer may help the production process and lower its cost. with this finer reduction, there can be more voids in the soil mix. therefore, the study suggests the addition of fly ash to act as finer. with this background, the objective of the study is to check the suitability of using fly ash as a replacement for finer content in the soil to produce csebs. ii. use of fly ash for cseb production fly ash is a fine, glass-like powder recovered from gases created by coal-fired electric power generation and its particles are generally spherical in shape and range in size from 0.5µm to 100µm [17]. sio2, al2o3, fe2o3, and occasionally cao are the main chemical components present in fly ash [18]. it has a long history of use as an engineering material and has been successfully employed in geotechnical applications [19]. additionally, the use of fly ash to enhance the properties of concrete is not rare. authors in [20] have used fly ash/rice husk ash mixture to enhance the properties of concrete. authors in [21] showed the effect of using fly ash on the compressive strength of green concrete. most of the times, fly ash is classified as secondary binder and cannot induce the desired effect by itself. however, with the presence of activators can form a cementitious compound which can improve the strength of the soil [22]. highest compressive strength of csebs can be achieved when they were incorporated with 10% fly ash. the lowest water absorption was experienced by csebs when the fly ash percentage was 15% [23]. authors in [24] have used high carbon fly ash for compressed earth blocks. as per their studies, they have varied the fly ash content from 0% to 50% in 10% intervals keeping the cement content constant. blocks with 0% fly ash have shown the maximum compressive strength and the lowest water absorption. they concluded that 25% fly ash content gives the optimum compressive strength. authors in [25] used lime and fly ash for soil blocks. their study showed that the unconfined compression strength of the laterite soil with 5% fly ash and 15% lime was found to be around 2.5 times more than the strength of natural laterite soil. also, they have shown that the average compressive strength of the blocks tested after 28 days of curing was more than the minimum compressive strength of fired bricks as per is: 1077 (1992). the water absorption value obtained for 28 days of curing was below the minimum value as specified in is: 1077(1992). iii. research methodology soil is the dominant part of csebs. geotechnical analysis was carried out to analyze the characteristics of the soil. wet sieve analysis as per [26] was conducted to identify the silt and clay content accurately. atterberg test was conducted as per [27]. specific gravity test also was performed to identify the physical properties of the soil. wet sieve analysis showed that the soil contains 28% silt and clay. therefore, to reduce the silt and clay content, the soil was washed. the washed soil consisted of nearly 5% slit and clay content. this particle size distribution of the soil revealed that modification is needed to get its particle distribution to fit into the optimization curves as described by the particle packing theories. also, finer content was changed to 5%, 7.5%, and 10% by adding fly ash. this fly ash was taken from norechcholai lakvijaya power plant, sri lanka. fly ash was tested for its particle size distribution and chemical composition. table i shows the chemical composition of the fly ash. earlier separated larger particles in the range of 2.0-6.0mm and 6.0-12.0mm as in figure 1(a) and 1(b) were also added to get the soil particle size distribution as per optimization curves. as per the objective of the study, cement was used as stabilizer in 6%, 8%, and 10% proportions. table i. chemical an alysis of fly ash constituents determined content % test method calcium as cao 5.63 acid digestion and atomic absorption spectrometry magnesium as mgo 1.59 iron as fe2o3 3.35 aluminum as al2o3 19.74 potassium as k2o 0.47 sodium as na2o 0.95 manganese as mno 0.05 phosphorus as p2o5 1.89 acid digestion and uv/vis titanium as tio2 1.98 silicon as sio2 47.48 gravimetry loss on ignition 16.79 fig. 1. (a) gravel 2.0-6.0mm, (b) gravel 6.0-12.0mm. since the mixure of soil has more gravel parts and the casting was carried out using a cement sand block-making machine, the water requirement was comparatively less. for the practical easiness of casting 8-10% water (by soil weight) was sufficient. for each combination, 10 blocks were cast resulting to a total of 90 blocks. the 150mm×150mm×150mm blocks were prepared using the cement sand block-making machine shown in figure 2. both vibration and compaction were applied to block casting. vibration time was regulated based on the preliminary conducted test. casted blocks were cured using wet gunny bags and water for 7 and 28 days. cast blocks were tested to determine their dry and wet compressive strengths, dry density, and water absorption, as per sls 1382 (part 2) [28] as strength-related tests. each block was placed carefully in the testing machine below the center of the upper bearing block and load was added until failure. the compressive strength was determined using the load at failure. figure 3 shows the testing procedure and the cast blocks. engineering, technology & applied science research vol. 11, no. 6, 2021, 7927-7931 7929 www.etasr.com malkanthi et al.: enhancement of the properties of compressed stabilized earth blocks through the … fig. 2. use of block making machine for cseb production. fig. 3. cast blocks and compressive test procedure. the dry density of the blocks was determined after keeping the blocks in the oven for more than 24 hours at 105 0 c. each specimen was oven-dried to a constant mass, weighed and measured to determine its dry density which was calculated by: �� � ����� �� ������ �� � 10� (1) to determine the water absorption of the blocks, oven-dried test specimens were immersed in water for 24 hours, and the increase in the mass of each specimen was calculated and expressed as a percentage of the specimen’s initial dry mass. � � ��������� ������ ��� �� � �� �! ��� �� � � �! ��� �� � � 100 (2) iv. results and discussion the used original soil consists of 5% finer and its grading shows it as a fine-grained soil. so, gravel had to be added to fit the grading into the optimization curve. then, finer content got to be reduced, hence separated finer should be added. fly ash was added to the mix as finer, and the prepared csebs were tested. the fly ash used for the blocks was sieved through a 0.425mm sieve. in this study, the purpose of using fly ash is to replace finer particles. other than that, its binding properties were not considered. the specific gravity of fly ash is 2.2 and it is less than that of original soil (2.7) resulting in reduced specific gravity for the soil-fly ash mix. when mixing the soil and fly ash, the expected final particle size distribution was determined as per the power line. a maximum density line has been proposed in [29]. it gives a direction to select a correct proportion of aggregates to get the maximum density. so, to match with the power line, other than the fly ash, different size larger particles were also added to the mixture. these larger particles were earlier extracted from the same soil. figure 4 shows the particle size distribution for fly ash, used soil, reconstitute soil and its comparison to the power line. fig. 4. comparison of particle size distribution. a. properties of csebs with fly ash replacement finer content was changed to 5%, 7.5%, and 10% by adding fly ash. blocks were made with 6%, 8%, and 10% cement stabilizer. the dry compressive strength (at 7 and 28 days) and the wet compressive strength (at 28 days) of blocks made with fly ash as finer are shown in figures 5-7. considering the compressive strength results of blocks with fly ash replacement, when the cement content is 10%, high compressive strength can be achieved, irrespective of the finer content. among the tested samples, 7.5% finer with fly ash replacement has given the highest compressive strength. the test results were compared with sls 1382 specification for csebs and sls 855 specification for cement blocks. according to the test results shown in table ii, when the cement content is 10% for all the selected finer contents, compressive strength values are above the limiting value for grade 1 cseb (6.0n/mm 2 and 2.4n/mm 2 for dry and wet compressive strength respectively). for 5% and 7.5% finer and 8% cement, compressive strength values reached grade 2 cseb (4.0 6.0n/mm 2 for dry compressive strength and 1.6 2.4n/mm 2 for wet compressive strength). even with 6% cement, 7.5% finer can produce grade 3 cseb (2.8 4.0n/mm 2 for dry compressive strength and 1.2 1.6n/mm 2 for wet compressive strength). engineering, technology & applied science research vol. 11, no. 6, 2021, 7927-7931 7930 www.etasr.com malkanthi et al.: enhancement of the properties of compressed stabilized earth blocks through the … fig. 5. 7-day dry compressive strength results of soil blocks with fly ash. fig. 6. 28-day dry compressive strength results of soil blocks with fly ash. cement & 5 6 7 8 9 10 11 c o m p re s s iv e s tr e n g th ( m p a ) 1 2 3 4 5 6 7 8 5% finer with fly ash 7.5% finer with fly ash 10% finer with fly ash fig. 7. 28-day wet compressive strength results of soil blocks with fly ash. also, the density and water absorption values (table iii) are satisfied with the specified value (1750kg/m 3 and 15% respectively) in sls 1382 part 1. out of all the finer contents, 7.5% finer replacement has the highest density and lowest water absorption when the cement replacement is 10%. table ii. compressiv e stren gth results cement % 6 8 10 5% finer with fly ash dry 2.72 4.57 9.8 wet 1.85 2.6 5.25 dry/wet 0.680 0.569 0.536 7.5% finer with fly ash dry 2.79 4.76 13.43 wet 1.67 3.16 7.35 dry/wet 0.599 0.664 0.546 10% finer with fly ash dry 2.43 3.76 8.75 wet 1.45 2.85 4.28 dry/wet 0.597 0.758 0.489 table iii. density and water absorption results cement % 6 8 10 5% finer with fly ash density (kg/m 3 ) 1968 1903 1943 water absorption % 10.33 11.28 9.34 7.5% finer with fly ash density (kg/m 3 ) 1865 1833 2074 water absorption % 11.40 12.40 6.32 10% finer with fly ash density (kg/m 3 ) 1761 1778 1912 water absorption % 13.89 13.77 11.54 v. conclusions the current study used the abundantly available soil with high silt and clay (finer) content. the reduction of excessive finer was done by washing the soil. then, the study focused on replacing the silt and clay content in the soil with fly ash for cseb production. also, soil grading was modified to fit into the optimization curves as explained in particle packing theories. the use of the washing method for finer reduction and the use of traditional cement sand block making machines for block production do not require highly technical skills. hence, the local construction industry can use this method easily. the most notable findings of the present study are: • with 10% cement stabilization, csebs with all fly ash addition achieved high values of dry and wet compressive strengths, satisfying the grade 1 requirements. • 8% cement stabilization gives compressive strength values of grade 2 blocks for all fly ash addition percentages. • even with 6% cement stabilization, 7.5% fly ash addition gives compressive strength in the grade 3 range. • all the blocks, irrespective of the cement and fly ash content, have densities and water absorption values that satisfy the sls 1382 requirements. the studies [12, 16] showed similar behavior of blocks’ compressive strengths. both studies showed that 10% cement usage for block production leads to high compressive strength. authors in [7] also recommended 10% as the highest cement percentage considering the financial aspect. further, 7.5% finer contained soil contributes to improved properties compared to engineering, technology & applied science research vol. 11, no. 6, 2021, 7927-7931 7931 www.etasr.com malkanthi et al.: enhancement of the properties of compressed stabilized earth blocks through the … 5% and 10% finer contributions. based on the obtained results, this study suggests the washing of soil as a novel method to reduce its finer content for soil block production. finally, it can be concluded that the addition of fly ash as finer results to the improvement of the properties of csebs. acknowledgment this research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. the authors would like to acknowledge the support given by mr. d. m. n. l. dissanayaka, technical officer of the structural testing laboratory, mr. h. t. r. m. thanthirige, technical officer of the building materials laboratory, and ms. w. u. b. rukma, technical officer of the construction engineering and management division, university of moratuwa, sri lanka. references [1] d. silveira, h. varum, a. costa, t. martins, h. pereira, and j. almeida, "mechanical properties of adobe bricks in ancient constructions," construction and building materials, vol. 28, no. 1, pp. 36–44, mar. 2012, https://doi.org/10.1016/j.conbuildmat.2011.08.046. [2] j. c. morel, a. mesbah, m. oggero, and p. walker, "building houses with local materials: means to drastically reduce the environmental impact of construction," building and environment, vol. 36, no. 10, pp. 1119–1126, dec. 2001, https://doi.org/10.1016/s0360-1323(00)00054-8. [3] d. allinson and m. hall, "hygrothermal analysis of a stabilised rammed earth test building in the uk," energy and buildings, vol. 42, no. 6, pp. 845–852, jun. 2010, https://doi.org/10.1016/j.enbuild.2009.12.005. [4] f. pacheco-torgal and s. jalali, "earth construction: lessons from the past for future eco-efficient construction," construction and building materials, vol. 29, pp. 512–519, apr. 2012, https://doi.org/10.1016/ j.conbuildmat.2011.10.054. [5] f. mcgregor, a. heath, e. fodde, and a. shea, "conditions affecting the moisture buffering measurement performed on compressed earth blocks," building and environment, vol. 75, pp. 11–18, may 2014, https://doi.org/10.1016/j.buildenv.2014.01.009. [6] j. e. aubert, p. maillard, j. c. morel, and m. al rafii, "towards a simple compressive strength test for earth bricks?," materials and structures, vol. 49, no. 5, pp. 1641–1654, may 2016, https://doi.org/ 10.1617/s11527-015-0601-y. [7] p. j. walker, "strength, durability and shrinkage characteristics of cement stabilised soil blocks," cement and concrete composites, vol. 17, no. 4, pp. 301–310, jan. 1995, https://doi.org/10.1016/0958-9465(95) 00019-9. [8] g. h. galabada, m. rajapaksha, f. r. arooz, and r. halwatura, "identifying the impact of concrete specimens size and shape on compressive strength: a case study of mud concrete," engineering, technology & applied science research, vol. 9, no. 5, pp. 4667–4672, oct. 2019, https://doi.org/10.48084/etasr.3020. [9] a. l. murmu and a. patel, "towards sustainable bricks production: an overview," construction and building materials, vol. 165, pp. 112–125, mar. 2018, https://doi.org/10.1016/j.conbuildmat.2018.01.038. [10] annual survey of construction industries. battaramulla, sri lanka: department of census and statistics, 2015. [11] s. n. malkanthi and a. perera, "durability of compressed stabilized earth blocks with reduced clay and silt," iop conference series: materials science and engineering, vol. 431, nov. 2018, art. no. 082010, https://doi.org/10.1088/1757-899x/431/8/082010. [12] s. n. malkanthi and a. a. d. a. j. perera, "particle packing application for improvement in the properties of compressed stabilized earth blocks with reduced clay and silt," engineering, technology & applied science research, vol. 9, no. 4, pp. 4538–4542, aug. 2019, https://doi.org/10.48084/etasr.3002. [13] s. a. a. m. fennis and j. c. walraven, "using particle packing technology for sustainable concrete mixture design," heron, vol. 57, no. 2, pp. 73–102, 2012. [14] m. n. mangulkar and s. s. jamkar, "review of particle packing theories used for concrete mix proportioning," international journal of scientific & engineering research, vol. 4, no. 5, pp. 143–148, 2013. [15] s. v. kumar and m. santhanam, "particle packing theories and their application in concrete mixture proportioning: a review," indian concrete journal, vol. 77, pp. 1324–1331, sep. 2003.. [16] s. n. malkanthi, w. g. s. wickramasinghe, and a. a. d. a. j. perera, "use of construction waste to modify soil grading for compressed stabilized earth blocks (cseb) production," case studies in construction materials, vol. 15, dec. 2021, art. no. e00717, https://doi.org/10.1016/j.cscm.2021.e00717. [17] techno economic feasibility report on flyash bricks. new delhi, india: building materials & technology promotion council. [18] "fly ash suppliers in india | fly ash manufacturers & exporters in india cementation." https://cementationindia.com/fly-ash.html (accessed nov. 20, 2021). [19] a. a. landman, "aspects of solid-state chemistry of fly ash and ultramarine pigments," ph.d. dissertation, university of pretoria, pretoria, south africa, 2005. [20] n. bheel, m. a. jokhio, j. a. abbasi, h. b. lashari, m. i. qureshi, and a. s. qureshi, "rice husk ash and fly ash effects on the mechanical properties of concrete," engineering, technology & applied science research, vol. 10, no. 2, pp. 5402–5405, apr. 2020, https://doi.org/ 10.48084/etasr.3363. [21] s. a. chandio, b. a. memon, m. oad, f. a. chandio, and m. u. memon, "effect of fly ash on the compressive strength of green concrete," engineering, technology & applied science research, vol. 10, no. 3, pp. 5728–5731, jun. 2020, https://doi.org/10.48084/etasr.3499. [22] g. p. makusa, state of the art review: soil stabilization methods and materials in engineering practice. luleå, sweden: luleå university of technology, 2012. [23] a. a. sofi, t. a. sheikh, r. a. wani, and a. manzoor, "cement stabilized earth blocks (cseb): an economic and eco-friendly building material," iosr journal of mechanical and civil engineering, vol. 13, no. 6, pp. 6–11, 2016. [24] c. egenti, j. khatib, and d. oloke, "high carbon fly ash and soil in shelled compressed earth masonry units," international journal of interdisciplinary research and innovations, vol. 3, no. 4, pp. 61–65, dec. 2015. [25] t. shetty, b. k. rao, and j. b. pai, "a feasibility study on the compressive strength of flyash and lime stabilized laterite soil blocks," international journal of innovative research in science, engineering and technology, vol. 5, no. 9, pp. 73–80, 2016, https://doi.org/10.15680/ijirset.2016.0505512. [26] astm c117 (2003), standard test method for materials finer than 75 µ m ( no . 200 ) sieve in mineral. west conshohocken, pa, usa: astm international, 2003. [27] astm d4318-10, standard test methods for liquid limit, plastic limit and plasticity index of soils. west conshohocken, pa, usa: astm international, 2010. [28] specification for compressed stabilized earth blocks: part 2 test methods. colombo, sri lanka: sri lanka standard institution. [29] t. c. powers, the properties of fresh concrete, first edition. new york, ny, usa: wiley, 1968. microsoft word hairik-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 338-344 338 www.etasr.com thejel et al: simulation and experimental verification of a hb-type vernier motor simulation and experimental verification of a hb-type vernier motor rabee' hashim thejel department of electrical engineering university of basrah basrah, iraq rabee_alabbasi@yahoo.com haroutuon a. hairik department of electrical engineering university of basrah basrah, iraq haroutuonhairik@ymail.com mazin abdulelah alwan department of electrical engineering university of basrah basrah, iraq mazin_alwan@yahoo.com abstract— direct drive motors are used as actuators in numerous applications in which they must rotate at low speeds with high torque and low torque ripple. various types of vernier motors have been studied recently. the hb type vernier motor is one of them. its rotor structure is the same as in a hb type stepping motor but has a field winding at the rotor and has multiphase windings in the stator. in the present work, a matlab simulation of a hb type vernier motor is presented. to validate the motor results and response, the authors fabricated the motor and implemented its drive circuit. the motor was tested for different load conditions. experimental results are found identical to simulation results and it is also shown that the motor has low torque ripple. keywords-direct drive; actuator; hb-type; vernier; matlab list of symbols eo electromotive force (v). f frequency (hz). if field current (a). �1 number of turns of phase “a”. �2 number of rotor single coil turns. �sp synchronous speed (r.p.m). p differential operator (d/dt). r1 stator winding resistance per phase (ω). rf rotor winding resistance (ω). te electric torque (nm). tl load torque (nm). xs synchronous reactance (ω). α phase shift for three phase or in general = m 2π . δl power angle (rad). ω1 supply angular frequency (rad/sec). ωm rotor angular speed (rad/sec). 2θ1 stator coil pitch = sn 2π . 2θ2 rotor coil pitch = rn2 2π . θ′ angle between the rotor adjacent n-silent pole and s-silent pole. i. introduction application of direct drive systems in robot and factory automation is constantly increasing, due to their controllability and high accuracy, requiring motors with high torque at low speed. stepping motors and dc brushless motors are used as direct drive motors. a stepping motor has a concentrated stator winding and is driven by a pulse-shaped exaction voltage. therefore, in principle, torque pulsation exists during rotation. meanwhile, various types of vernier motors have been developed, such as variable reluctance vernier motors and permanent magnet vernier motors. the latest is probably the hb type vernier motor which has the advantage of low torque ripple. the construction of the hb type vernier motor requires a field winding in the rotor and multiphase distributed winding in the stator. as a result, the hb type vernier motor is identical to a general synchronous machine in regards of voltage equation and torque formula [1, 2]. in this paper, the mathematical model of the hb type vernier motor is described and the matlab/simulink software package is used to study the dynamic motor responses due to normal and sudden load torque. to validate the simulation, the authors fabricated a motor and implemented a drive circuit. a sudden load torque was applied to the motor shaft by using a loading device and motor torque response was recorded. results are presented and discussed. ii. structure of hb-type vernier motor and experimental design the motor is a vernier-synchronous type and is not selfstarting in the speed range of 50 to 150 rpm. it is started with a special starting circuit at reduced frequency and then gradually increased to the actual speed [3]. the stator of the hb-type vernier motor has �s slots. these slots have ordinary three-phase windings [4] with �p number of etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 338-344 339 www.etasr.com thejel et al: simulation and experimental verification of a hb-type vernier motor poles. the rotor consists of two parts which pinches the field windings that axially penetrate the flux in the rotor as shown in figure 1. each rotor part consists of a number of salient poles (�r). the first part contains the n-magnetized salient poles and the second part contains the s-magnetized salient poles which are deviated by half a slot in the circumferential direction. thus, these poles are appears alternately. the rotating magnetic fields in the gap are the basic wave fields generated by the three winding of the stator and the (�s ± �p/2) degree harmonic (slot harmonic) field by pulsation of the gap permeance distribution attributable to the stator slots. the rotor rotates in synchronization with the slot harmonic rotating magnetic field. the main relationship to design the hb-type vernier motor which is similar to the hb-type stepper motor is given by [4]: r p s � 2 � � =± (1) the synchronous speed of the hb-type vernier motor is expressed as shown below: r�2 f120 r�2 p� p� f120 sp� == (2) for the present motor, which has �s=36, �r=30, and �p=12, if f=50 hz, the synchronous speed is 100 rpm. iii. voltage equation and torque formula the motor has three phase windings in the stator and a field winding in the rotor. thus, the inductance matrix of the present hb-type vernier motor has 4×4 size and can be written as given in (3) [5, 6]: where, l1 is the self inductance of the stator winding per phase, lm is the mutual inductance between stator phases, mr is the mutual inductance between the stator phase winding and the rotor winding, and lf is the self inductance of the rotor winding, θ′ is the angle between the rotor adjacent n-silent pole and the s-silent pole, α is the stator winding phase shift for three phase equal to ( 3 2π ). fig. 1. rotor of hb-type vernier motor the voltage equation of the hb-type vernier motor is similar to those for a general synchronous machine and is given by [1, 2]: [ ] [ ] [ ]{ } [ ]i.lpr v += (4) where p=d/dt. substituting for the inductance matrix [l] from (3) into (4) gives: ( )         −′′ −− ++− −++ =             αθθ r�cosrmpr�cosrmp 2 mlp 2 mlp )ml1l(p1r 2 mlp 2 mlp)ml1l(p1r fv cv bv av ( ) ( ) ( )                     +−′ −′++ −′− ′− fi ci bi ai . fplfr2r�cosrpm 2r�cosrpm)ml1l(p1r r�cosrmp 2 mlp r�cosrmp 2 mlp αθ αθ αθ θ (5) on the condition that a balanced three-phase voltage is applied and a balanced three-phase current flows through the motor. the synchronous torque of the hb-type vernier motor is expressed as follows: 1 3 . . . sin( ) o r r l s ve t � � x δ ω = (6) where eo is the induced electromotive force and xs is the synchronous reactance, expressed as follows: 1 3 o f f e m i ω = (7) 1 1 3 ( ) 2 s m x l l aω= + (8) where, 3 2 f r m m=          −′′ −− +− −+ = )(r�cosrmr�cosrm 2 ml 2 ml ml1l 2 ml 2 ml ml1l ]l[ αθθ         −′ −′+ −′− ′− fl)2(r�cosrm )2(r�cosrmml1l )(r�cosrm 2 ml r�cosrm 2 ml αθ αθ αθ θ (3) etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 338-344 340 www.etasr.com thejel et al: simulation and experimental verification of a hb-type vernier motor the usefulness of transforming an abc-reference frame to a dq-reference frame stems from the fact that although each of the stator phases sees a time-varying inductance due to the saliency of the rotor, the transformed quantities rotate with the rotor and hence see constant magnetic paths [6]. the relationship between a set of dq variables and the corresponding set of three-phase abc variables is provided by the transformation matrix tdq. since the three-phase systems studied in this research are balanced, no 0-axis components are present, which allows using a simplified version of dqtransformation [5]: a d dq b q c v v t v v v =               (9) where 2 2 cos cos( ) cos( ) 2 3 3 2 23 sin sin( ) sin( ) 3 3 m m m dq m m m t t t t t t t π π ω ω ω π π ω ω ω − + = − +            (10) and m ω is the speed (rad/sec) of the rotating frame. the inverse transformation from dq to abc currents is defined as: 1 a d b q c dq i i i t i i − =              (11) by applying (9) on the stator part of (5), simplifying and then adding the rotor part, the dq-model of hb-type vernier motor can be obtained as shown in (12): 1 1 1 1 1 1 3 3 3 ( ) ( ) 2 2 2 3 3 3 ( ) ( ) . 2 2 2 3 0 2 m r m m r d d q r m m m r m r q f f r f f r p l l � l l p m v i v � l l r p l l � m i v i p m r p l ω ω ω + + − + = + + + − +                                  (12) the electromagnetic torque is approximately given by: e r f f q t � m i i= − (13) the dynamic equation of the mechanical torque is given by: m e f m l d j t b t dt ω ω= − − (14) where, j is the motor moment of inertia (kg.m2), f b is the motor viscous fraction factor (nm/rad/sec), and tl is the mechanical load torque in nm. iv. matlab simulation the first row of (12) can be rearranged as follows: 1 1 [ ] d d d s r m q f f s pi v r i l � i m pi l ω= − + − (15) where, 1 3 ( ) 2 s m l l l= + the matlab simulink representation of (15) is given in figure 2. the second row of (12) is rewritten as: 1 1 [ ] q q q s r m d r m f f s pi v r i l � i � m i l ω ω= − − + (16) this equation is simulated as shown in figure 3. the third row of (12) is rearranged in (17) and simulated as shown in figure 4. 1 [ ] f f f d f f f p i v m p i r i l = − + (17) the overall mathematical model of the hb-type vernier motor given in (13)-(17) is simulated using matlab. simulation can be very useful in many scientific studies to formulate a hypothesis or a mathematical model, to explain the observations and to predict the behavior of a system from solutions or properties of the model. the model used is shown in figure 5, where the “abc to dq” block is given by (9) and the “dq to abc” block is given by (11). the parameters of the present hb-type vernier motor are listed in table i. v. simulation results the motor drive circuit in this paper consists of a space vector pulse width modulation (svpwm) and a three phase voltage source inverter (vsi). svpwm is a more sophisticated technique for generating a sine wave that provides a higher voltage to the motor with lower total harmonic distortion [7]. the rotor dc voltage is vf=28 v. the matlab simulation results of 'a' phase voltages of the svpwm vsi at f=50 hz, e=220 v, and * sv =0.55 pu. are shown in figure 6. the motor model shows that the steady state speed changes linearly with frequency as shown in figure 7. the motor behavior due to sudden change of the shaft load is also tested. the motor is first driven at no load, and then the load is suddenly changed to 5 n.m at t = 2 sec. the test results of the motor speed and torque are shown in figures 8-9. the motor three-phase currents are shown in figure 10. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 338-344 341 www.etasr.com thejel et al: simulation and experimental verification of a hb-type vernier motor fig. 2. implemented simulink model of (15) table i. parameters of the motor used in this paper. r1 0.9 ω rf 2.8 ω l1 0.055 h lm 0.0557 h mr 0.0196 h lf 0.0178 h j 0.01 kg.m2 b 0.05 nm/rad/sec fig. 3. implemented simulink model of (16) fig. 4. implemented simulink model of (17) fig. 5. implemented simulink model of the complete motor dq-model etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 338-344 342 www.etasr.com thejel et al: simulation and experimental verification of a hb-type vernier motor fig. 6. inverter phases ‘a’ voltage when f=50 hz, * sv =0.55 pu fig. 7. steady state speed-frequency curve of hb type vernier motor fig. 8. speed response of the hb type vernier motor fig. 9. torque response of the hb type vernier motor fig. 10. three phase currents of the hb type vernier motor. vi. expernimtal implementation the motor was fabricated in order to validate the motor mathematical model simulation. the motor specifications are given in table ii: table ii. specification of test motor. outside diameter of rotor 110 mm inside diameter of stator 111 mm core length 89 mm 1umber of stator turns per phase 336 1umber of field turns 305 the stator of the motor has 36 slots and is wounded with three phase windings with 12 poles as shown in figure 11. the rotor of the motor has 30 silent poles in each side. the field winding is supplied with dc current through two slip rings as shown in figure 12. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 338-344 343 www.etasr.com thejel et al: simulation and experimental verification of a hb-type vernier motor fig. 11. stator of test vernier motor fig. 12. rotor of test vernier motor the experimental motor drive circuit is based on the space vector technique and is consisted of two main parts, three phase inverters and a pc computer interface with an inverter to generate six gates pluses based on svpwm as shown in figure 13. fig. 13. motor drive circuit vii. experimental results the motor is not self-starting for a frequency range greater than 20 hz. it is started with low frequency increasing step by step until it reaches 50 hz. the speed of the motor is measured by using a shaft encoder connected on the motor shaft. the experimental motor speed profiles at starting and steady state are shown in figure 14. the motor phase voltage and current are shown in figure 15. the motor is tested for sudden load changes by using a loading device as shown in figure 16. the motor is tested for two cases. at first, the motor operates with no load and then a sudden load of 5 nm is applied. in the second case, the load is suddenly removed from the motor. the results show that the motor has a short period of torque oscillation as shown in figures 17 and 18. fig. 14. experimental speed profile of the motor fig. 15. motor phase voltage and current etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 338-344 344 www.etasr.com thejel et al: simulation and experimental verification of a hb-type vernier motor fig. 16. motor set for loading test fig. 17. motor torque response for 5 nm sudden load torque fig. 18. motor torque response for no load viii. conclusions in this paper, the mathematical model of a hb-type vernier motor was simulated using the matlab/simulink software package. to validate the simulation, a test motor was fabricated. results showed that: • the motor steady state speed changes linearly with frequency. • the motor phase voltage and current simulation results are identical with the experimental results. • the motor speed and torque profiles exhibit small amounts of oscillation due to sudden changes in the shaft load. references: [1] h. suda, y. matsushima, l. xu, and y. anazawa , “analysis of hb-type vernier motor”, ieej transactions on industry applications, vol. 125, no. 3, pp. 270-276, 2005. [2] h. suda, y. anazawa, “torque analysis of hb-type vernier motor”, the ieee international electric machines and drives conference, iemdc '07, pp. 709-714, turkey, 2007. [3] l blaisdell, r rubin, o mahr, “ats mechanically despun communications satellite antenna”, ieee transaction on antennas and propagation, vol. 17, no. 4, pp. 415-528, 1969. [4] c. h. lee, “vernier motor and its design”, ieee transactions on power apparatus and systems, vol. 82, no. 66, pp. 343-349, 1963. [5] a. e. fitzgerald, c. kingsley jr., s. umans, electric machinery, sixth edition, mcgraw-hill companies, inc., 2003. [6] c. m. ong, dynamic simulation of electric machinery: using matlab/simulink, prentice hall ptr, 1998. [7] a. bonnet, t. alukaiday, p. c. k. luk, “a high performance space vector motor drive controller”, iee colloquium on dsp chips in real time measurement and control (digest no: 1997/301), united kingdom, 1997. microsoft word 05-741-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1235-1240 1235 www.etasr.com alizadeh and minaei-bidgoli: introducing a hybrid data mining model to evaluate customer loyalty introducing a hybrid data mining model to evaluate customer loyalty hossein alizadeh department of computer engineering, buinzahra branch, islamic azad university, buinzahra, iran hossein7alizadeh@gmail.com behrouz minaei-bidgoli school of computer engineering, iran university of science & technology, tehran, iran fhm1390@yahoo.com abstract—the main aim of this study was introducing a comprehensive model of bank customers᾽ loyalty evaluation based on the assessment and comparison of different clustering methods᾽ performance. this study also pursues the following specific objectives: a) using different clustering methods and comparing them for customer classification, b) finding the effective variables in determining the customer loyalty, and c) using different collective classification methods to increase the modeling accuracy and comparing the results with the basic methods. since loyal customers generate more profit, this study aims at introducing a two-step model for classification of customers and their loyalty. for this purpose, various methods of clustering such as k-medoids, x-means and k-means were used, the last of which outperformed the other two through comparing with davis-bouldin index. customers were clustered by using kmeans and members of these four clusters were analyzed and labeled. then, a predictive model was run based on demographic variables of customers using various classification methods such as dt (decision tree), ann (artificial neural networks), nb (naive bayes), knn (k-nearest neighbors) and svm (support vector machine), as well as their bagging and boosting to predict the class of loyal customers. the results showed that the baggingann was the most accurate method in predicting loyal customers. this two-stage model can be used in banks and financial institutions with similar data to identify the type of future customers. keywords-loyalty; data mining; clustering; classification; evaluation i. introduction customer relationship management (crm) is one of the most important areas in which data mining techniques has been widely used [1]. crm is a set of processes and systems which support business strategies in order to create beneficial relationships between current customers and future customers [1-3]. with the increasing importance of crm in all domains of industry, researchers need a standardized framework to achieve satisfactory results by using effective data mining processes. there are many companies which could retain their customers and increase their potential profit by evaluating customer value (potential participation) and loyalty [5]. database management systems, data mining techniques and classification methods have changed the entire process of marketing [6]. research conducted in this context noted unbalanced classes in customer dataset [7]. this means that customers who are loyal have formed a smaller proportion of total customers. in general, management of unbalanced classes is a key factor for success in direct marketing and loyal customer analysis [8]. customer retention and customer development may prove more attractive and less expensive for many organizations compared to finding new customers [9, 10]. the main challenge in customer segmentation is the presence of different customer related variables and the high degree of heterogeneity in customer behavior [11]. customer variables are generally divided into two categories: behavioral variables and characteristic variables [12]. characteristic variables included demographic, geographic and psychological variables, while behavioral variables encompassed reaction and tendency of customers to products and brands [12]. a large number of studies in the field of customer value analysis and value based customer segmentation through data mining techniques have used rfm variables [13]. using three parameters, r (recency: how recently did the customer purchase?), f (frequency: how often do they purchase?) and m (monetary value: how much do they spend?), these studies have attempted to value and segment customers in terms of their loyalty [11, 14]. there are other influential variables for customer segmentation. it has been claimed that rfm model does not differentiate customers who have long-term relationships with the organization and those with short-term relationships. that is why the variable duration of the first purchase to the last purchase of the customer (l) is added to the model. the combination of demographic variables such as year of birth and gender, as well as behavioral variables of customers, may be used to analyze customer value and loyalty. in [15] authors used customer clustering for categorization of different industries for exploring the consumption patterns of electronic services. after successful modeling, they were able to designate the clusters correctly and extract the relevant patterns. in [16], authors used the k-means, rfm variables and rfm weighted variables for clustering of the customers. finally they employed the multi-objective genetic algorithm to determine the score of each group of customers that showed greater accuracy in comparison to other methods. however, there is no comprehensive study on the factors influencing the engineering, technology & applied science research vol. 6, no. 6, 2016, 1235-1240 1236 www.etasr.com alizadeh and minaei-bidgoli: introducing a hybrid data mining model to evaluate customer loyalty customer loyalty in banking. on the other hand, most researches in this area have only used clustering methods rather than other data mining methods such as classification. hence, one of the main challenges in this study is to use group classification methods (ensemble learning) in order to deal with this problem in dataset. this study presents a model for customer value analysis based on customer segmentation, using data mining techniques such as clustering and classification, to find loyal customers. the main objective of this study is customer segmentation using different clustering methods such as k-means as well as their existing four classes of variables to identify the variables effective in customer segmentation in respect with loyalty. in the second step, this study is aimed at presenting a classification model based on mass classification methods to predict the loyalty of new customers. ii. materials and methods there are two standard methods of data mining projects [15]. the first method is cross-industry standard process for data mining (crisp-dm) and the second method is semma (sample, explore, modify, model and assess). the former was developed by a consortium of the companies spss, daimlerchrysler and ncr (national cash register). the latter was also suggested by the institute of sas [17]. semma is a five-step method consisting of sampling, data exploration, data modification, modeling and model assessment. in addition to these steps, crisp-dm involves a two-step business understanding in the first phase and deployment in the last phase. crisp-dm compared with semma, is closer to knowledge discovery method in databases proposed by fayyad et al. (1996) [18]. moreover, crisp-dm has been widely used in customer segmentation projects by using rfm [19, 11, and 7]. thus, this project also uses crisp-dm. futher, the rapiminer data mining software, the featured software of the year 2013 for data mining was used. the crisp-dm phases include: 1. business understanding: understanding the aims, investigating the situation, understanding the data mining goals and creating the plan project; 2. data understanding: collecting primary data, describing data, data exploration, data quality review; 3. data preparation: data selection, data cleaning and replacement (if necessary), and ultimately producing new variable data integration; 4. modeling: choosing modeling method, building the model prototype, building the final model, and initial evaluation of the model. 5. evaluation: evaluation of results and process review. 6. deployment: a specific plan for application of the model in real world is be prepared. iii. results initially the data is derived from the tourism bank of iran’s database. the stored transactional data contained information related to 2124 customers. then the customer data is integrated; that is the primary dataset containing transactional customer variables is incorporated into a table. thus, every customer should have a data record. three variables, r (time of the last transaction), m (total monetary volume of transactions for both creditor and debtor) and f (the number of transactions) are extracted for each customer. in this new generated dataset, only one record exists per customer. a. descriptive statistics in order to explain data as well as basic knowledge extraction from data collection in this section, some univariate statistics such as mean, standard deviation and bivariate statistics such as correlation are used. table i summarizes the univariate statistics pertaining to some of the variables in the dataset. according to this table, the average age of customers is about 39 years and sd=10 indicate that the customers are mostly young. majority of customers have a bachelor’s degree and most of them are male. given that sd=125 for f (the number of transactions) ranging from 1 to 3150, obviously the customers᾽ behavior is highly diverse. table i. statistics related to variables variable type mean and sd. min. /max. iteration of discrete variables age continuous avg=39.131 +/10.967 [4 ; 87] education discrete mode=-9999 (1470), least=19046 (2) 19043 (112), 19040 (284), 19052 (158), 19037 (40), 19055 (31), 19049 (27), 19046 (2) gender discrete mode=1180 (1888), least=1181 (236) 1180 (1888), 1181 (236) marriage discrete mode=1184 (1230), least=1185 (894) 1185 (894), 1184 (1230) m (bedehkar) continuous avg=7077957513.45 +/53016182057.36 [-619938.000 ; 1223605648286.000] m (bestankar) continuous avg=5543003252.14 +/41457587768.67 [-389961.000 ; 935889627450.000] r continuous avg=16307.65 +/83.24 [16011.000 ; 16372.000] f continuous avg=33.18 +/125.25 [1.000 ; 3150.000] engineering, technology & applied science research vol. 6, no. 6, 2016, 1235-1240 1237 www.etasr.com alizadeh and minaei-bidgoli: introducing a hybrid data mining model to evaluate customer loyalty iv. correlation analysis of variables table ii shows the results of correlation analysis between different variables. this correlation is presented by the wellknown pearson coefficient. the pearson correlation ranges from -1 to +1; closer values to +1 indicate direct linear correlation between the two variables and closer values to -1 indicate indirect correlation between the two variables. the closer values to zero mean no correlation between the two variables. according to this table, there is highly positive correlation or highly negative correlation between some variables. for example, it is clear that m creditor (m bedehkar) and m debtor (m bestankar) representing the total credit and debt have a highly positive correlation with f, as expected. interestingly, there is a correlation between m debtor (m bedehkar) and marital status. table ii. pearson correlation test on variables age education gender marriage m (bedehkar) m (bestankar) r f age 1.000 0.186 0.001 -0.537 0.098 0.085 -0.022 0.108 education 0.186 1.000 0.200 -0.340 0.034 0.046 -0.001 0.103 gender 0.001 0.200 1.000 -0.123 -0.001 0.004 0.033 0.024 marriage -0.537 -0.340 -0.123 1.000 -0.130 -0.126 0.026 -0.181 m (bedehkar) 0.098 0.034 -0.001 -0.130 1.000 0.899 0.095 0.761 m (bestankar) 0.085 0.046 0.004 -0.126 0.899 1.000 0.096 0.704 r -0.022 -0.001 0.033 0.026 0.095 0.096 1.000 0.171 f 0.108 0.103 0.024 -0.181 0.761 0.704 0.171 1.000 a. extraction of new variables using banking expert opinions, we decided to generate more variables from the current dataset. since the customers deposit (credit) and withdraw (debit) their accounts, it was decided to calculate f and r twice per customer. that is, they are calculated once for debit accounts of each customer and once for credit accounts of the same customer. given the significance of account balance, it is decided to subtract m creditor (m bestankar) of each customer including total deposits from m debtor (m bedehkar) including total withdrawal; the result is recorded as a variable. thus, behavioral dataset includes the following variables: • r debtor (rbedehkar): time span from the last withdrawal day relative to a certain date (01.01.1970) in days. • r creditor (rbestankar): time span from the last deposit relative to a certain date (01.01.1970) in days. • f debtor (fbedehkar): number of withdrawals of a customer from his/her bank account. • f creditor (fbestankar): number of deposits of a customer to his/her bank account. • m debtor (mbedehkar): number of withdrawals of a customer from bank accounts in general. • m creditor (mbestankar): number of deposits of a customer to bank accounts in general. • mtotal: total amount of credit minus total amount of debit. these variables are incorporated in the next clustering. v. discretization of variables in this section, data is discretized. the reason for this is that the variables have different ranges. for example, f ranges from 1 to 3150, while m has a relatively broader range. thus, m will have a greater effect on clustering if the dataset is incorporated unchanged in the clustering. at this point, frequency-based discretization is used. in this way, each of fbestankar, rbestankar, rbedehkar and mtotal is divided into five ranges, provided that equal number of records is set in each range. fbedehkar is divided into four ranges, because it includes many equal values. accordingly, all variables are normalized prior to clustering. a. modeling a two-stage modeling is performed in this study. in the first stage, the behavioral data including fbestankar, fbedehkar, rbestankar, rbedehkar and mtotal are incorporated in clustering and customers are labeled in accordance with their value. based on demographic and geographic variables, such as age, education, gender, marriage and place of birth (birth_city), the labels are modeled through classification, and the top model is identified and selected in each stage. b. clustering k-means, c-means and k-medoids are used for clustering of variables generated previously which in fact represent customer behavior. in using k-means and k-medoids which are unable to identify the optimal number of clusters, clustering was performed in a range from 2 to 9 clusters and davies-bouldin index was calculated in each stage. davies-bouldin index (vdb) which has many applications uses similarity measure of two clusters. this index calculates the average similarity of each cluster to the most similar cluster. the higher the index, the better clusters are generated. many other indices have been designed in recent years to overcome shortcomings of previous indices. however we refrain from mentioning them here due to their lengthy calculations. cn db i i=1c 1 v = r n å four clusters are generated in k-means and seven clusters are generated in k-medoids. on the other hand, x-means is able to identify the number of clusters; thus, the dataset is divided into four clusters. table iii shows the value of davies-bouldin engineering, technology & applied science research vol. 6, no. 6, 2016, 1235-1240 1238 www.etasr.com alizadeh and minaei-bidgoli: introducing a hybrid data mining model to evaluate customer loyalty index for optimal number of clusters for the three clustering methods. table iii. results of clustering method optimal number of clusters davis-bouldin index k-means 4 0.92 x-means 4 0.94 k-medoids 7 1.208 four clusters are selected as optimal clusters for grouping customers in both k-means and x-means, while seven clusters are selected as optimal clusters in k-medoids. however, the davies-bouldin index is equal to 0.92 in k-means and 0.94 in x-means for 4 clusters and 1.121 in k-medoids for 7 clusters. as a result, k-means is chosen as a better method for clustering. in order to label the clusters, the table pertinent to the information of cluster centers is analyzed. the results are as follows: given that creditor refers to the customer who deposits in his account, obviously, rbestankar and fbestankar are higher in cluster_2 than other clusters (mean=4.39 and 4.34, respectively). moreover, customers of cluster_2 gain higher scores in terms of mtotal than other clusters. fbedehkar and rbedehkar are relatively lower than members of other clusters. for this reason, the members of this cluster are labeled as loyal customers. customers of the cluster_0 are the second highest following cluster_2 in terms of rbestankar and fbestankar, while mtotal is equal to 1.18, on average, which is the lowest compared to members of other clusters. in cluster_0, fbedehkar and rbedehkar are lower than other clusters. thus, customers can be labeled as active, but with little capital. certainly, cluster_1 includes the customer class with weak loyalty, because rbestankar and fbestankar are lower than other clusters. moreover, mtotal is slightly higher than cluster_0. fbedehkar and rbedehkar are higher in the cluster_1. fbedehkar and rbedehkar are evidently higher in cluster_3. mtotal is equal to 3.92, on average. moreover, rbestankar and fbestankar are medium to other clusters. thus, members of cluster_3 can be potentially labeled. in order to calculate the scores of customers in each cluster, the mtotal, fbestankar and rbestankar values are summed up and subtracted from fbedehkar and rbedehkar variables᾽ values. the following table shows scores of members of each cluster. for clarity, the obtained values are normalized. table iv. scores of each cluster cluster_0 cluster_1 cluster_2 cluster_3 total score 5.47 -2.69 8.81 0.59 normalized score 0.71 0.00 1.00 0.28 apparently, customers of cluster_1 belong to class of customers with weak loyalty (total score=-2.69 and normalized score=0) and customers of cluster_2 are very loyal customers (total score=8.81 and normalized score=1). two other clusters include medium customers. c. classification in order to develop a predictive model at this stage, customers who are in loyal cluster are labeled as good and other customers are labeled as bad. using demographic variables including age, education, marital status, gender and birth city, modelling is performed by classification methods. at this stage, the decision-tree (dt), k-nearest neighbors (knn), naive bayes (nb), support vector machine (svm) and artificial neural networks (ann) as well as their bagging and boosting are used. thus, 15 classifications are made on the dataset. it should be noted that the methods employed in this section are those that have achieved better results in most studies compared with other methods. such methods and the relevant parameters are summarized below: • naive bayes: this method has no parameters to set. in bagging and boosting models of this method, the bag number parameter for bagging and the number of repetitions for boosting was set to 10. • k-nearest neighbors: in this method, there is only one adjustable parameter: k. this value was changed in the range from 5 to 15. the best parameter combination was obtained here with the value 13 for the parameter k. in bagging and boosting models of this method, the number of bag parameter for bagging and the number of repetitions for boosting was set to 10. • artificial neural networks: in this method, using the hidden layers of algorithm, a non-linear input-output mapping is performed. the main objective of this method is finding the appropriate weights for the network so that all the initial training data are accurately classified or predicted. the parameters set for this method in rapidminer software are the learning rate of 3.0, momentum of 2.0, the number of training cycles equal to 500; the number of hidden layers was set by the software itself. in bagging and boosting models of this method also the number of bag parameter for bagging and the number of repetitions for boosting was to 10. • decision tree: the c.5 algorithm is used for building a decision tree or set of rules. this algorithm works through sample analysis based on the feature that receives the maximum information. the parameters set in this model are gini index of branching, the tree depth equal to 15 and the minimum size of branching equal to 30. at this stage, also the decision tree bagging and boosting methods were used. the number of bags parameter in bagging method and the number of iterations in boosting method was set to 10. • support vector machine: another intelligent model having acceptable performance in predicting the complex and nonlinear features is the support vector machine (svm) for which the number of bags parameter in bagging method and the number of iterations in boosting method was set to 10. accuracy and f-measure are used to evaluate the methods used. in the diagram below, vertical axis shows accuracy and the horizontal axis shows f-measure for the models used. obviously, bagging-ann outperforms other methods in terms of f-measure. it is followed by bagging-dt, boostingdt and dt in terms of accuracy and f-measure. moreover, ann and boosting-ann never recognize minority class in this dataset. knn-based methods have also unsatisfactory performance. one of the objectives of this study is to determine effectiveness of mass classification. therefore, the methods engineering, technology & applied science research vol. 6, no. 6, 2016, 1235-1240 1239 www.etasr.com alizadeh and minaei-bidgoli: introducing a hybrid data mining model to evaluate customer loyalty with the higher accuracy, on average, are determined. thus, the following table calculates the mean of accuracy and f-measure for all the methods used as well as the used bagging and boosting methods. according totable v, bagging techniques have the lowest accuracy (mean=78.42%) and highest fmeasure (mean=15.49%). clearly, the boosting techniques have failed in increasing the accuracy of modeling. it should be noted that the f-measure value is very low due to the serious imbalances in the relevant category. table v. mean of accuracy and f-measure for the models used method mean accuracy f-measure basic methods 81.00 8.55 bagging methods 78.42 15.49 boosting methods 81.00 8.55 d. classification by changing the balance of classes considering the imbalance of the classes in the under study problem, and because about 17% of the customers were loyal customers which was much less than other customers with weak loyalty, we decided the next phase that the two upper clusters having more loyal customers than other clusters, to adopt a class of loyal customers (instead of just one cluster) and thus, about 36% of customers were considered as loyal customers, and modeling was performed on this more balanced dataset. finally after modeling, the mean of different indices for the base models, the bagging and boosting models are listed table vi. table vi. the mean accuracy and f-measure indeces in all models for more balanced dataset method used accuracy f-measure ann 82.57% 0 bagging – ann 71.9 21.83% boosting – ann 82.57% 0 as can be seen, the best f-measure obtained (21.83%) is related to bagging-ann; obviously, ann and boosting-ann are unable to predict loyal (good) customers; despite their accuracy (82.5%), these models are excluded from further analyses. bagging-ann is selected as the best model (71.9% accuracy). as indicated in table vii, the f-measure value has decreased considerably which is due to the intense imbalance in the related classes. to solve the serious imbalance problem in the classes it was decided that the two no 2 and no 0 clusters which had more loyal customers compared to other clusters be rated as good class customers and the existing customers in the other two clusters are considered as belong to the bad class or class of customers with weak loyalty. thus, about 36% of customers are loyal. this leads to better balance between loyal customers and customers with weak loyalty. finally, the modelling is done by all the listed modeling techniques used previously. table viii presents the results of evaluation on this new dataset. obviously, the fmeasure of neural networks has considerably improved with change in the class balance compared to pre-classification stage; accordingly in this stage considering better balance in the classes compared with the previous stage, nb has the best recognition in the modelling (70% accuracy). moreover, bagging-ann is the best method in terms of f-measure (78.97%). table vii. customer classification using ann the method used accuracy f-measure ann 82.57% 0 bagging – ann 71.9 21.83% boosting – ann 82.57% 0 table viii. classification of customers using new dataset model accuracy f-measure dt 66.88% 75.66% bagging-dt 68.45% 76.66% boosting-dt 67.82% 76.36% ann 65.15% 78.90% bagging-ann 65.31% 78.97% boosting ann 65.15% 78.90% knn 64.36% 72.22% bagging-knn 61.54% 68.63% boosting knn 66.41% 74.82% nb 70.96% 77.52% bagging nb 69.07% 76.24% boosting nb 70.17% 77.70% svm 61.15% 71.65% bagging svm 64.42% 70.35% boosting nb 63.34% 73.35% vi. discussion & future work considering the study results, it is clear that the customers᾽ available demographic variables were not sufficient enough due to the lack of some very influential variables of customer loyalty such as the income variable, etc. also, because the bagging and boosting collective classification methods in this study achieved better accuracy than the basic methods in detecting the loyal customers, it can be stated that it would be preferable to use other collective classification methods of predicting the customer loyalty class in the future studies. among the methods used in this study, the k-nearest neighbors in all three basic, bagging and boosting methods in the first dataset has achieved better accuracy, although given the nature of modeling in which the f-measure index constitutes a more important indicator, using the bagging method in artificial neural networks would be more appropriate. on the other hand, given that in the second modeling attempt was made to label two clusters of customers as “loyal”, the modeling results on this dataset indicates that the f-measure index in this state can be brought up to 78.97%, which is much better than the previous state. for the purpose of development of the results of this study the following propositions can be made: • using other computational methods such as fuzzy logic and other methods to enhance the accuracy of modeling. • it must be noted that in the present study the data pertaining to one of the banks which were more suitable than the data of other banks were used, although it suffers engineering, technology & applied science research vol. 6, no. 6, 2016, 1235-1240 1240 www.etasr.com alizadeh and minaei-bidgoli: introducing a hybrid data mining model to evaluate customer loyalty from many shortcomings in terms of the lack of demographical variables like the employment, place of residence, etc., which is hoped to get better results in the future through data restoration. • implementation of the proposed model of the study on other datasets and reporting the results. • using more variables for modeling on such datasets. vii. conclusion a comprehensive model of bank customers᾽ loyalty evaluation based on the assessment and comparison of different clustering methods᾽ performance was proposed and the different approaches were evaluated with significant accuracy being achieved. results are shown in detail and further discussed whereas future work perspectives and improvements are proposed. the two-stage model proposed can be used in banks and financial institutions with similar data to identify the type of future customers. references [1] e. w. t. ngai, l. xiu, d. c. k. chau, “application of data mining techniques in customer relationship management: a literature review and classification”, expert systems with applications, vol. 36, no. 2, pp. 2592-2602, 2009 [2] r. ling, d. c. yen, “customer relationship management: an analysis framework and implementation strategies”, the journal of computer information systems, vol. 41, no. 3, pp. 82-97, 2001 [3] d. k. tiwary, “application of data mining in customer relationship management (crm)”, advances in computational sciences and technology, vol. 3, no. 4, pp. 527-540, 2010 [4] s. rosset, e. neumann, u. eick, n. vatnik, “customer lifetime value models for decision support”, data mining and knowledge discovery. vol. 7, no. 3, pp. 321-339, 2003 [5] y. h. liang, “integration of data mining technologies to analyze customer value for the automotive maintenance industry”, expert systems with applications. vol. 37, no. 12, pp. 7489-7496, 2010 [6] m. re, g. valentini, “ensemble methods: a review” in advances in machine learning and data mining for astronomy, chapman & hall, 2012 [7] m. alvandi, s. fazli, f. s. abdoli, “k-mean clustering method for analysis 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procedia computer science, vol. 3, pp. 1327-1332, 2011 [12] p. kolter, marketing management, 11th edition, pearson education, new jerse,. 2003 [13] j. t. wei, s. y. lin, c. c. weng, h. h. wu, “a case study of applying lrfm model in market segmentation of a children’s dental clinic”, expert systems with applications, vol. 39, no. 5, pp. 5529-5533, 2012 [14] c. h. cheng, y. s. chen, “classifying the segmentation of customer value via rfm model and rs theory”, expert systems with applications, vol. 36, no. 3, pp. 4176-4184, 2009 [15] h. khodzi, e. akhondzadeh-noughabi, b. minaei-bidgoli, “a new application of rfm clustering for guild segmentation to mine the pattern of using banks’ e-payment services”, journal of global marketing, vol. 27, no. 3, pp. 178-190, 2014 [16] z. zalaghi, y. a. varzi, “measuring customer loyalty using an extended rfm and clustering technique”, management science letters, vol. 4, no. 5, pp. 905-912, 2014 [17] a. azevedo, m. f. santos, “kdd, semma and crisp-dm: a parallel overview”, iadis european conference on data mining, amsterdam, the netherlands, july 24-26, 2008 [18] s. s. rohanizadeh, m. b. moghadam, “a proposed data mining methodology and its application to industrial procedures”, journal of industrial engineering, vol. 4, pp. 37-50, 2009 [19] m. bizhani, m. j. tarokh, “behavioral rules of bank’s point-of-sale for segments description and scoring prediction”, international journal of industrial engineering computations, vol. 2, no. 2, pp. 337-350, 2011 microsoft word 13-799-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1182-1186 1182 www.etasr.com krishna and srinivas kumar: hybridizing differential evolution with a genetic algorithm for color… hybridizing differential evolution with a genetic algorithm for color image segmentation r. v. v. krishna aditya college of engineering & technology kakinada, india rvvkrishnaece@gmail.com s. srinivas kumar jawaharlal nehru technological university kakinada, india samay_ssk2@yahoo.com abstract-this paper proposes a hybrid of differential evolution and genetic algorithms to solve the color image segmentation problem. clustering based color image segmentation algorithms segment an image by clustering the features of color and texture, thereby obtaining accurate prototype cluster centers. in the proposed algorithm, the color features are obtained using the homogeneity model. a new texture feature named power law descriptor (pld) which is a modification of weber local descriptor (wld) is proposed and further used as a texture feature for clustering. genetic algorithms are competent in handling binary variables, while differential evolution on the other hand is more efficient in handling real parameters. the obtained texture feature is binary in nature and the color feature is a real value, which suits very well the hybrid cluster center optimization problem in image segmentation. thus in the proposed algorithm, the optimum texture feature centers are evolved using genetic algorithms, whereas the optimum color feature centers are evolved using differential evolution. keywords-differential evolution; genetic algorithm; clustering; segmentation; hybrid algorithms; rough sets; fuzzy sets; soft sets i. introduction color image segmentation is to divide a chromatic image into different homogeneous and connected regions based on color, texture and their combination [10]. it is an essential part of image analysis and decides the final output of any image analysis task. segmentation methods can be categorized based on the technique used (edge based, region based, fuzzy and neural networks based, feature clustering based etc). in this paper, the color image segmentation performed is based on feature clustering. the consistency of clustering based segmentation methods such as k-means, fuzzy-c-means, etc are limited by the initially chosen cluster centers, and also on the cardinality of chosen cluster centers. this problem is solved by using evolutionary computing in this paper. the population of initial cluster centers is formed by the repeated application of the soft rough fuzzy-c-means (srfcm) clustering algorithm. the optimal cluster centers are evolved by applying a hybrid of two exemplary evolutionary algorithms, differential evolution (de) and genetic algorithms (gas). genetic algorithms are heuristic global search methods that mimic the process of natural selection and uses fixed-length strings to represent possible solutions. gas are driven by a fitness function defined to evaluate a solution’s ability to deal with a given task, ending up in bringing out an optimum solution [17]. de is a simple yet powerful algorithm for real parameter optimization proposed in [21]. de is different from traditional algorithms in the sense that it perturbs the current generation population members with the scaled differences [22]. de has been applied to a number of real world problems due to its simple and robust nature. similar hybrid approaches have been reported in the literature for a variety of applications. an improved differential evolution method has been proposed in to optimize the multi-objective parameters in fuzzy clustering [14] as well as gas [4]. in [11] a recurrent network design by hybridizing ga and particle swarm optimization (pso) was proposed. hybridization of de and quantum pso (qpso), named deqpso, was proposed in [7]. in [23], a hybrid of ga and de for solving the unit commitment scheduling problem in power systems was proposed. in [25], the multi objective optimization proposed employed gas, pso, and adaptive metropolis search (ans). in general, it can be considered that gas very ably handle binary variables and de is more capable in handling continuous variables. motivated by this, a composite feature of both color and texture is formed to solve the color image segmentation problem. texture consists the binary part of the solution and color the real part. ga operates on the texture part and de operates on the color part, so that the hybrid optimizer effectively explores both the binary and real search domain. ii. color and texture feature extraction a. color feature extraction the color image consists of multiple bands, with each band containing a range of intensity values. the color image is represented in different color spaces rgb, lab, his, hsv etc. it is very important to extract the effective pixel-level image features [26]. here, the lab color model is used for color feature extraction because it is very convenient to measure small color difference. the pixel level color feature of a color component can be computed as follows: (1) prepare a window engineering, technology & applied science research vol. 6, no. 5, 2016, 1182-1186 1183 www.etasr.com krishna and srinivas kumar: hybridizing differential evolution with a genetic algorithm for color… of size 3˟3 for the construction of pixel-level color feature, (2) calculate pixel wise color feature related to the color component using pixel homogeneity, extracted from the image, so that it reflects the uniformity of an image object. pixel variance in terms of standard deviation and discontinuity in terms of edge detection, of color component are calculated. the product of normalized standard deviation and normalized edge discontinuity information is deducted from unity to obtain pixel homogeneity of the objects in the image. b. texture feature extraction: power law descriptor: the weber’s law states that the ratio of incremental threshold to the background intensity is a constant [2]. in short, weber’s law says that the size of a just noticeable difference is a constant proportion of the original stimulus value. in [5], it was proposed that this could be employed as a texture descriptor. but in [1], it was stated that empirical data such as an image does not always fit well into weber’s law and a modification was suggested (guilford power law) that could model the perception of human beings better. iii. soft rough fuzzy c-means algorithm (srfcm) srfcm has its roots in the k-means algorithm. this basic algorithm was evolved to the rough k-means (rkm) that was proposed in [12] borrowing some of the concepts of rough set theory [19] and rough fuzzy c-means algorithm which was applied to medical image segmentation problem [15]. in a segmentation problem, the task is to know whether two objects are similar, and a measure of their similarity is needed for clustering different objects in an image [13] the fundamental steps of srfcm are as follows: (1) assume m random initial cluster prototypes (2) find membership uik between m cluster centers and k data points (3) allocate each data point to the lower or upper approximation and (4) make the final assignment based on the difference between the highest and next highest membership of a data point in all clusters (5) compute the similarity of sample points soft set to the cluster centre soft set, calculate the maximum similarity and assign a pixel to a cluster to which it has maximum similarity after fuzzification (6) compute the updated cluster prototype for each cluster (7) iterate and run steps 2–6 until there are no further changes in cluster centroids. iv. degah algorithm the proposed algorithm is named degah due to it being a de and gas hybrid. its basic flowchart is shown in figure 1. a. chromosome formation & population initialization in this image segmentation problem based on clustering, every pixel in the image is represented by a concatenation of color and texture features to form an integrated feature of size  21*1 nn where 1n and 2n are the lengths of binary texture feature and real color features respectively. the individual chromosome in the degah algorithm is formed by first running the srfcm clustering algorithm, to obtain k cluster centers, each of size  21*1 nn . the resulting, k cluster centers or prototypes are arranged in line to form a chromosome of size  21*1 nnk . this process of srfcm clustering is repeated n times to form an initial population of size  21* nnkn .the typical value of n=20 is used in this experimentation. b. fitness evaluation in evolutionary algorithms, the right of way of the genetic strings is ordered according to the fitness values calculated based on a cost function. by maximizing or minimizing the fitness values at each generation, the genetic string with the global optimum could be identified to be the terminal clustering result. currently, many indices, such as k-means index (kmi), separation index (si), partition separation index (pasi), davies-bouldin index (dbi), and fuzzy c-means index (fcmi), are used as the fitness functions of evolutionary algorithms. in all the referred indices, the intra-cluster distance is minimized and inter-cluster distance is maximized. in our experimental work the davies-bouldin index (dbi) is chosen as the fitness function owing to its optimal computational complexity [8]. c. elitism elitism entails upon copying a small proportion of the fittest solutions, unaltered into the future generation. this ensures that ea’s does not waste re-discovering previously discarded partial solutions. candidate solutions that are preserved unchanged through elitism remain eligible for selection as parents when breeding the remainder of the next generation. in our proposed algorithm, the top (n/5) ranked chromosomes are preserved and named as elite and are directly eligible for crossover in the next generation. d. chromosome variation the hybridization of the ga and de takes place in the variation step at each generation. in the variation step, the optimum binary texture feature centers are obtained with ga operators and the optimum real color feature centers are obtained using de operators as discussed below. all the initial population of the combined color and texture centers are evaluated by dbi. if the termination criteria are not satisfied, the texture portion of the solution is speckled by a genetic algorithm and the color portion is scrambled by differential evolution. the ge variation operation involves two operations viz crossover and mutation. in crossover, two parent chromosomes are mixed, based on two point crossover and crossover probability to yield two offspring chromosomes. the color component is varied by using differential evolution. de also performs the two operations, mutation and crossover. e. termination criteria two termination conditions as shown below are employed. the algorithm is terminated if any of the termination conditions is met. condition 1: if for 200 consecutive generations, the objective function of the best solution (found so far) does not improve by 0.01 and condition 2: if the maximum allowed generations is reached. engineering, technology & applied science research vol. 6, no. 5, 2016, 1182-1186 1184 www.etasr.com krishna and srinivas kumar: hybridizing differential evolution with a genetic algorithm for color… fig. 1. the degah flowchart v. performance measures there exists many segmentation evaluation measures [6] such as sensitivity, specificity, precision, recall, roc, f-measure, local consistency error, global consistency error etc. the performance measures proposed in [16] which are rand index (ri), variation of information (voi), global consistency error (gce), and boundary displacement error (bde) are used in evaluating and comparing our segmentation results with benchmark algorithms. a. rand index the rand index indicates the proportion of pixels which are in agreement between the computed segmentation (cs) and the ground truth (gt). [16]. b. variation of information the variation of information (voi) is a measure that specifies the variation between computed segmentation and ground truth. the difference between average conditional entropy of computed segmentation (cs) and ground truth (gt) is used to measure the vagueness in cs which cannot be expressed by gt. c. global consistency error global consistency error is a measure of the limits to which the computed segmentation can be seen as transformation of ground truth towards computed segmentation. similar segmentations match, as both have genesis in the same image, but undergo segmentation at different scales. if one segment is proper subset of the other, then the pixel lies in an area of refinement, and the error should be zero. if there is no subset relationship, then the two regions overlap. d. boundary displacement error the boundary displacement error is a measure of the displacement error averaged between boundary pixels in computed segmentation and the nearest boundary pixels in the ground truth. bde should be low for good segmentation. vi. results and discussion in [8], the well-known j-segmentation (jseg) algorithm, which combines both quantization process and clustering techniques for extraction of color-texture cues in images was proposed. mean shift clustering in sync with edge information was employed for edge detection and image segmentation [5]. the proposed algorithm is applied on five natural color images (bear, boat, church, horse, tiger) obtained from berkeley segmentation data base. results are compared with the ga without hybridization, and the works in [5] and [8] which are known to be bench mark algorithms in the field of color image segmentation. results are summarized in tables i-ii and depicted in figure 2. table i. ri & voi ri voi image degah ga jseg [8] edision [5] degah ga jseg [8] edision [5] 1 0.69 0.39 0.61 0.68 1.81 4.52 2.09 2.55 2 0.62 0.57 0.45 0.46 3.01 3.60 3.64 5.61 3 0.73 0.72 0.45 0.67 2.52 2.66 3.03 3.06 4 0.65 0.62 0.45 0.46 2.98 3.33 3.34 5.33 5 0.82 0.71 0.47 0.54 2.53 2.62 2.63 4.15 table ii. gce & bde gce bde image degah ga jseg [8] edision [5] degah ga jseg [8] edision [5] bear 0.14 0.19 0.19 0.19 5.01 5.99 6.12 6.00 boat 0.31 0.31 0.32 0.31 3.45 4.21 4.22 3.45 church 0.17 0.19 0.21 0.19 3.85 4.95 10.24 8.74 horse 0.24 0.24 0.25 0.24 3.01 3.06 7.29 5.86 tiger 0.16 0.18 0.20 0.19 4.36 4.11 13.05 9.49 engineering, technology & applied science research vol. 6, no. 5, 2016, 1182-1186 1185 www.etasr.com krishna and srinivas kumar: hybridizing differential evolution with a genetic algorithm for color… fig. 2. a sum of the results vii. conclusion and future work the approach proposed in this paper is a robust and novel technique which hybridizes two exemplary evolutionary algorithms (differential evolution and genetic algorithms) for solving the color image segmentation problem. extensive experimentation was conducted on images from berkeley segmentation database. the effectiveness of the proposed algorithm is demonstrated through the comparison with other state of the art algorithms. the results shows that, in the proposed algorithm, inter cluster distance has been maximized and intra clustering distance has been minimized. various performance metrics have been compared and the proposed algorithm shows better results compared with other existing benchmark algorithms. the proposed algorithm can also be extended by hybridizing with other evolutionary algorithms like simulated annealing and pso, which further increases the clustering accuracy. references [1] t. augustin, “the problem of meaningfulness: weber’s law, guilford’s power law, and the near-miss-to-weber’s law”, mathematical social sciences, vol. 57, no. 1, pp. 117-130, 2009 [2] a. k. jain, fundamentals of digital signal processing, englewood cliffs, nj: prentice-hall, 1989 [3] s. bandyopadhyay, u. maulik, “nonparametric genetic clustering: comparison of validity indices”, in ieee trans. systems, man, and 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bandyopadhyay, “genetic algorithm-based clustering technique”, pattern recognition, vol. 33, no. 9, pp. 1455–1465, 2000 [25] j. vrugt, b. robinson, “improved evolutionary optimization from genetically adaptive multi method search”, proceedings of the national academy of sciences, vol. 104, no. 3, pp. 708711, 2007 [26] x. y. wang, wang. t, juan b“color image segmentation using pixel wise support vector machine cklassification”, pattern recognition, vol. 44, no. 4, pp. 777–787, 2011 microsoft word etasr_v11_n6_pp7875-7880 engineering, technology & applied science research vol. 11, no. 6, 2021, 7875-7880 7875 www.etasr.com uwamahoro et al.: a battery voltage level monitoring system for telecommunication towers a battery voltage level monitoring system for telecommunication towers rahab uwamahoro school of computational and communication sciences and engineering the nelson mandela african institution of science and technology arusha, tanzania neema mduma school of computational and communication sciences and engineering the nelson mandela african institution of science and technology arusha, tanzania dina machuve school of computational and communication sciences and engineering the nelson mandela african institution of science and technology arusha, tanzania abstract-voltage fluctuations in batteries form a major challenge the telecommunication towers face. these fluctuations mostly occur due to poor management and the lack of a battery voltage level monitoring system. the current paper presents a battery voltage-level monitoring system to be used in telecommunication towers. the proposed solution is incorporated with a centralized mobile application dashboard for accessing the live data of the installed battery, integrated with voltage-level, current, temperature, fire, and gas sensors. an arduino uno microcontroller board is used to process and analyze the collected data from the sensors. the global service message (gsm) module is used to monitor and store data to the cloud. users are alerted in the case of low voltage, fire, and increase in harmful gases in the tower through short message service (sms). the experiment was conducted at ngorongoro and manyara telecommunication towers. the developed system can be used in accessing battery information remotely while allowing real-time continuous monitoring of battery usage. the proposed battery voltage-level monitoring system contributes to the elimination of battery hazards in towers. therefore, the proposed battery voltage level monitoring system can be adopted by telecommunication tower engineers for the reduction of voltage fluctuation risks. keywords-battery voltage level monitoring; telecommunication towers; renewable energy; gsm sim 800l module; dashboard i. introduction rapidly growing population, technological advancements, and climate change, raise the demand for more energy [1], which is expected to increase the greenhouse gas (ghg) emissions in the atmosphere. global population, for instance, is expected to increase from 7.7 to 9 billion by 2050 [2], whereas, in sub-saharan africa, where tanzania is located, the population is predicted to double by 2050 [3]. also, 80% of the 1.4 billion of the global population living in rural areas have inadequate access to electricity [4, 5]. these people not only have a low life quality but also lack access to technology, which means that they fall under the energy poverty deception category. the instability of the national grid and the low proportion of the population accessing it, makes renewable energy a priority for electrification, especially in africa, since it is low-cost, user-friendly, and can reduce carbon footprint [6]. telecom tower companies in tanzania have found significant reliable use of renewable energy by using solar panels to power their services during power outages and hence enabling a costefficient evolution to a low-carbon power system [7]. the advancements in solar energy are increasing in tanzania [8]. however, solar energy offers efficient production only during the day. this necessitates energy storage in batteries to ensure the continuation of services [9-12]. telecom towers connect people with their business remotely by accessing the internet and other services. powering the towers requires a stable energy source for versatile operations. to guarantee their uninterrupted operation, the towers need to depend on renewable energy sources, like solar panels, to eliminate the inconveniences caused by unpredictable power cuts on the national grid [13, 14]. the most serious challenge encountered by telecom towers is the unexpected voltage drops followed by cutoffs that occur without alerting users to act accordingly. this makes the tower services unavailable, thus lowering productivity while putting sensitive electrical equipment at risk. additionally, the hydrogen gas from batteries affects human health and the environment [15-17]. so, there is a need to monitor and eliminate battery voltage-level changes and other parameters that may pose a threat to public health and safety. among the factors that have been identified as the primary contributors to voltage fluctuations are the lack of battery data visualization and the big number of devices allocated to be powered by a battery [18]. they, therefore, lack information with regard to when the voltage battery is expected to be low for timely actions. with the technological advancements through the corresponding author: rahab uwamahoro (uwamahoror@nm-aist.ac.tz) engineering, technology & applied science research vol. 11, no. 6, 2021, 7875-7880 7876 www.etasr.com uwamahoro et al.: a battery voltage level monitoring system for telecommunication towers internet of things (iot), accessing data remotely has been a routine for many companies and individuals. iot is proved to be fundamental in receiving, controlling, and accessing data remotely and acting accordingly. the technology is also userfriendly and grants real-time data access [19, 20]. taking advantage of this technological advancement, some studies have been carried out to review, analyze, monitor, and compute data for real-time sensing in different areas [21, 22]. however, most of these studies have only concentrated on monitoring geographical areas and excluded monitoring batteries installed in towers. several measuring components have been used to monitor voltage fluctuations in batteries. voltage changes in batteries have been reviewed to identify battery parameters that can be at risk due to voltage changes in order to improve the economic and sustainable use of their energy [23]. one recent approach included the integration of an arduino microcontroller board with thermometer, voltmeter, and ammeter sensors through a correlation and regression algorithm to measure the battery’s state of charge and estimate its useful remaining life [24]. the study showed that battery estimation on the state of charge, state of health, and discharge rate with its remaining useful life can be derived in real-time. however, this system failed to estimate the remaining voltage of the battery and presented a low real-time data acquisition due to the usage of an sd-card which lacks efficiency in data security. so, there is a need to develop a low-cost, efficient battery voltage-level monitoring system to increase the sustainable utilization of the voltage stored in the battery remotely. authors in [25] conducted a simulation work on discharging and charging of battery banks for telecom sites in india. similar work was conducted in [26], again in india, aimed to control the voltage drop of the battery bank. however, these works were limited only on the simulation approach without being tested to real life applications. authors in [27] presented a review on the methods of monitoring the charging and discharging of batteries connected to renewable energy sources through a centralized controller. however, they took into consideration only the energy supplied to the load without alerting the user on battery discharge and charge. changes in current, temperature, and the state of health of the battery are considered as the factors affecting the most voltage fluctuation in batteries installed in electric vehicles, which is only beneficial to only a section of battery users [28]. besides, some studies use high technological methods which turn away most users from adopting them due to their high costs and requirements of high technical skills to operate [29]. sustainable development goal (sdg) number 7 is to ensure access to modern, affordable, clean, and reliable energy for all by 2030 [30]. however, the previous works have failed to contribute to the accomplishment of this goal. to eliminate these challenges, the present study proposes a low battery voltage level monitoring system that can be beneficial to all battery users in accessing battery information remotely by allowing them to continuously monitor the battery usage in real-time and contribute to the elimination of battery hazards. with this, attention needs to be drawn to a cost-effective and user-friendly battery voltage-level monitoring system. this will contribute to real-time access of information about faults in batteries and consumption, through a dashboard for the sustainability of usage. ii. materials and methods this study was carried out at 2 towers of habari node public limited company which is an internet service provider (isp) in arusha, tanzania. firstly, coordinates of the towers were measured with gprs devices, as shown in table i. the two towers were selected due to their ability to store energy in batteries. also, they are most affected by voltage fluctuations due to the huge number of users residing far from company offices. the coordinate measurements helped in sending data to the towers accurately without any data loss. furthermore, the measured coordinates assisted system installation and the testing process in the field. table i. tower locations location coordinates latitude (lat) longitude (long) ngorongoro -3.27544 35.438886 manyara -3.37764 35.81857 the voltage levels of the installed batteries and solar panels in the tower were measured. the currents through the batteries and the solar panels were measured manually with a digital ac/dc uni-t ut890d multimeter. the measurements were conducted on two batteries located in ngorongoro tower and manyara tower as shown in table ii. the results present a mix of used and full batteries with different values. furthermore, their cutoff times were observed based on the voltage stored in the batteries. the measurements helped in the development and real application of the proposed system. table ii. manual measurement results battery location voltage results battery solar load low voltage time (hrs) ngorongoro 14.8v 20v 0.05 11.88v 6 manyara 14.5v 20v 0.07 11.8v 4 a. hardware integration after data collection, verification of the hardware part was done using the proteus simulation software. figure 1 shows the system overview design in the circuit, which consists of voltage sensor, current sensor, gas sensor, frame sensor, an arduino uno microcontroller board, the sim808 gsm/gprs/gps module, a 14.8v to 14.5 v battery for power supply, and a 20v solar panel. simulations were conducted before the real application of the integrated circuit components to ensure they behaved efficiently. the components were integrated into the proteus software. arduino uno, was selected due to its efficiency to help the development of the proposed low-cost system. it consists of 14 digital input and output pins and 6 analog pins. the voltage sensor which acts as a voltage divider was connected to measure the voltage level of the batteries and solar panels. the gsm module transmitter (tx) and receiver (rx) pins were connected to pins 0 and 1 respectively. the fire sensor was connected to pin 2 of the arduino and the gas sensor was connected to pin 10. furthermore, two relays were connected, one to allow the voltage from the solar panel to go engineering, technology & applied science research vol. 11, no. 6, 2021, 7875-7880 7877 www.etasr.com uwamahoro et al.: a battery voltage level monitoring system for telecommunication towers to the battery and the other to allow the load to function. the load used was a bubble light, tested at 5v at ngorongoro and 3v at manyara. four light-emitting diode (led) indicators were used to alert the user if any hazard was happening near the batteries. the red leds represent hazard, the blue network connection, the yellow represent the relay, and the green was for power. a long leg pin was connected to pin 10 of the arduino and set to the output of the gsm module. in real life system application, a short message notification was used as an alert to the user with the help of the gsm module. the gsm was powered by 12v and the other components were supplied with 5v voltage from the arduino. after system simulation, the hardware components were integrated for real-life application and their interactions proved the system functionality and its compliance with the requirements. figure 2 shows the prototype integration of the gsm and the sensors. fig. 1. circuit diagram of the developed system. fig. 2. prototype integration. b. calculations the calculations shown below helped in producing reliable and accurate voltages to the batteries and the solar panels. the values read by the analog pin of the arduino were converted and the voltage stored in the battery was considered to be the battery voltage. let the value to be read by the analog pin be the adc-value as shown in (1): ��� ���� � � ��� � ���� (1) where adc represents the analog to digital converter, 5 is the reference voltage of the arduino, and 1024 is the adc resolution. the formula for calculating the voltage divider is: �� ����� � � ��� (2) the resistances r3 and r4 are presented in figure 3. r4 in this work was 30kω and r3 was 7.5κω. therefore, the voltage divider is 37.5κω. the adc voltage is calculated as shown in (3), (4), and figure 3. ��� ���� � � �� ����� � ����� ���� � (3) therefore: ��� ���� � � �.� � !"#"$% ��.� � !"#"$% � ����� ���� � (4) engineering, technology & applied science research vol. 11, no. 6, 2021, 7875-7880 7878 www.etasr.com uwamahoro et al.: a battery voltage level monitoring system for telecommunication towers from (1), the adc-voltage is calculated as: ��� voltage � ��� � ��� 0.00489 (5) substitution of adc-voltage in (3) gives (6): adc value x 0.0049= 7.5 kho 37.5 kho x battery voltage (6) for 0.02444 adc-value, the solar–volt is shown in (7). 1�� � 2 ���� � 0.2445 ��� � ��� (7) therefore, the voltage constant used in the code battery was 0.02499999 and for the solar constant, it was 0.02499989. fig. 3. voltage divider. iii. results and discussion this section contains the results of the system's tests and analysis. the voltage sensor experiment was recorded to ensure that the circuit was in good working order followed by recording experiments and results used to verify battery voltage fluctuations as shown in table iii. analysis was conducted for the proposed system and the two batteries located in the respectice towers as shown in figure 4. their voltage levels and the current from solar panels and the load were successfully measured by the developed system as shown in table iii. furthermore, the system could measure the humidity of the battery and detect gas and fire near the battery. a 14.8v fully-charged battery which reached 11.86v after usage was used for the ngorongoro tower and an 11.85v used rechargeable solar battery for the manyara tower. a voltmeter was used to compare the voltage measured manually with the voltage measured by the system as shown in table iii. the two voltages were found to be the same. this helped to know the voltage level of the batteries before they reached low voltage. the gsm could send sms notifications to the intended users to act accordingly. the other parameters were monitored similarly. the measurements taken manually with a multimeter showed that the voltage level was different due to the usage of different batteries. figure 4(a) shows the solar battery used in the experiment, figure 4(b) shows the prototype testing with a voltmeter, and figure 4(c) shows the complete prototype with 5v solar lamp as the load and solar panel. table iii. results from the developed system battery voltage results current humidity gas fire multimeter (v) voltage sensor solar load detected not detected detected not detected 1 11.86v 11.87v 20v 0.00 good no yes no yes 2 11.85v 11.86v 20v 0.03 good no yes no yes fig. 4. system testing. from the multimeter measurements, the value was accurately similar to the one measured using the system as shown in table iii. it can, therefore, be concluded that the voltage sensor provides valid measurement values of the batteries. the other battery parameters were measured to determine whether they could be risky to humans and the environment. using current as an example, the current sensor load and the dc for which a solar panel was used to charge the batteries were respectively measured. the solar panel was able to charge the battery, the lamp was used as a load, and its current was measured and monitored respectively as shown in figure 4. battery voltage data were sent to one centralized mobile application dashboard. a. the dashboard data figure 5 shows the final prototype of both systems tested for ngorongoro and manyara towers. data from the sensors were collected and sent to a mobile app dashboard as shown in figure 6. the battery parameters were updated every 5s, they were stored in the cloud using the thingsweb server, and were displayed on the arduino ide serial monitor. the actual voltage and current comparison were used to control the voltage level of the battery installed in each tower. the comparison was done based on measuring the actual battery voltage to the remainder, and the current coming from the solar panel to the battery to the actual current. furthermore, temperature, humidity, fire, and gas were continuously monitored to assess whether they were detected or not. as shown in figure 6, the screenshot of the app developed for monitoring the batteries shows that the approach was effectively evaluated and met the requirements in instances of live data every 5s. figure 7 shows the screenshot of a message received as an alert to the user about the low voltage of the battery installed at ngorongoro tower which enabled the user to turn on the relay. data were uploaded onto the dashboard and stored on a server. when the load was connected and the solar panel begun to power the battery, the current was efficiently measured by the system as shown in figure 7. the load charging current was 0.32 since the 5v solar lamp was engineering, technology & applied science research vol. 11, no. 6, 2021, 7875-7880 7879 www.etasr.com uwamahoro et al.: a battery voltage level monitoring system for telecommunication towers connected as the load and the solar panel current was 0.32 as it was charging the low battery. fire and gas were not detected at the ngorongoro tower. furthermore, the system was able to alert the user of the low battery voltage 11.8v at the ngorongoro tower using a message sent by the gsm project (figure 7). fig. 5. final prototypes for manyara and ngorongoro towers. fig. 6. the developed mobile application dashboard. fig. 7. short message alert received from the system installed at ngorongoro. b. discussion the conducted experiments proved the validity of the status information from batteries located in the telecommunication towers: their voltage and current levels, temperatures, and presence of fire or gas were monitored while the risks of voltage fluctuation were reduced. figures 6 and 7 show the monitoring and access through the mobile dashboard of the voltage level and other battery status parameters from the battery located at the ngorongoro tower. data processed from the sensor were sent in real-time to the cloud and battery voltage level, current, temperature, fire warning, and gas status were visualized through the mobile app dashboard as shown in figures 5 and 6. iv. conclusion and future work the current work lays the foundation for the development of a battery voltage level monitoring system for communication towers to ensure suitable battery performance and real-time monitoring. the development of the system consisted of the integration of sensors for battery monitoring devices and a dashboard as a user interface which ensures central monitoring. the system can send information to the administrator dashboard via a cloud server from the related towers using its coordinate locations via the gprs internet module. an sms notification is sent to the user as an alert when the battery voltage becomes low. the dashboard allows real-time access and monitoring of the 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[30] "1.1 billion people still lack electricity. this could be the solution," world economic forum. https://www.weforum.org/agenda/2018/06/1billion-people-lack-electricity-solution-mini-grid-iea/ (accessed nov. 06, 2021). authors profile rahab uwamahoro received her bachelor in computer science from the kigali independent university (ulk), rwanda. currently, she is taking her masters in embedded and mobile system (emos) program, specialty in embedded systems at the nelson mandela african institution of science and technology (nm-aist) in tanzania. her research interest lies in digital solutions, renewable energy, smart home automation, and smart agriculture. neema mduma is a lecturer at the nelson mandela african institution of science and technology (nmaist) in tanzania. she got her phd and msc degrees in information, communication sciences and engineering from nm-aist in 2020 and 2016 respectively. during her phd, she developed a machine learning model called bakishule which aimed at preventing students from dropping out of school. neema’s efforts towards women in science have been recognized through an award from l’oréal unesco in 2020. her research interests are artificial intelligence, machine learning, and data science. dina machuve is a senior lecturer and researcher at the nelson mandela african institution of science and technology (nm-aist) in tanzania. she holds a phd in information, communication science and engineering from nm-aist (2016), an msc in electrical engineering from tennessee technological university, (2008), and a bsc in electrical engineering from the university of dar es salaam (2001). her research interests are data science and agriculture informatics in schools. engineering, technology & applied science research vol. 8, no. 2, 2018, 2827-2833 2827 www.etasr.com mashwani and khusro: the design and development of a semantic file system ontology the design and development of a semantic file system ontology syed rahman mashwani department of computer science university of peshawar peshawar, pakistan syed.rahman@uop.edu.pk shah khusro department of computer science university of peshawar peshawar, pakistan khusro@uop.edu.pk abstract—semantic file system (sfs) is the vision for the future of file systems where information is given with explicit meaning to be processed by machines automatically and consumed by the users easily. sfss extend traditional file systems to organize and retrieve information according to their semantics, intent and relationships with other resources rather than their physical locations. ontology-based file system is a step to dissolve the borders between semantic web and semantic desktop to make the desktop part of a single giant web. unfortunately, to the best of the authors’ current knowledge, so far, no effort has been exercised to develop an ontology for sfss. this work contributes a sfs ontology, which extends nepomuk information element ontology framework into the domain of sfss. the proposed sfs ontology is freely available with full technical definitions of terms and complete class hierarchy to be used for any purpose in information technology (it). in addition, as a proof-of-concept implementation, we deploy the proposed ontology in the 360ᵒ sfs. finally, to get most of the benefits of the ontology, this paper also presents a semantics-aware file manager. keywords-file systems; information management; information retrieval, semantic desktop i. introduction traditional file systems organize files in hierarchy of folders which have certain limitations. in addition, information contained in files varies in structure. semantics of the information is restricted to the boundaries of their applications, and therefore, are difficult to mine and retrieve. for efficient and precise retrieval of information, machines must be able to understand it, which needs semantics. semantic web (sw) [1] deals with information overload on the web. efforts have been put in binging this semantics-awareness to the desktop [2], which has resulted in improvements especially in file retrieval [3]. however, for file systems to be effective and accurate, semantic desktop needs semantic file system (sfs) immensely [4]. ontology-based sfs has the potential to dissolve the borders between sw and semantic desktop (sd) to make the desktop part of a single giant web. however, to the best of our knowledge, we found no file system ontology published according to linked data principles [5]. therefore, the main contribution of this paper is the development of an sfs ontology and its publishing on the web to be freely accessible and reusable by other researchers. we deploy the sfs ontology on our developed sfs called 360ᵒ-sfs. in addition, this paper presents a semantic-aware file manager (fm) called 360ᵒ-fm that is based on the same ontology. ii. motivation and need this section elaborates the potential role of sfs ontology with the help of motivating scenarios. these scenarios have been used in the evaluation of sfs ontology in section v. a. scenario 1: single centralized machine friendly metadata repository for all agents traditional file systems are limited to the basic metadata about files. the information is preserved by the operating system and application software using different structures, which are not machine friendly. in addition, the application must be aware of the structure of the file in order to use it. moreover, it became difficult for each application to understand the structure of all possible file types. therefore, it is necessary to make available the file metadata in a single, sharable repository with easy to understand structure so that any application can easily use it. b. scenario 2: advanced search queries traditional file systems maintain basic file metadata including file name, date created, modified and time accessed etc., which is exploited by search engines. a semantically enhanced file system could maintain an adequate amount of metadata in a single shared repository with rules enough to perform reasoning by sfss. c. scenario 3: generating file recommendations a user often faces difficulties while organizing files. to handle this issue, machines must be aware of the semantics of directories. this knowledge could be exploited in recommending directories to the users while they organize files. in addition, a directory having name tim berners-lee can be linked e.g., using owl:sameas to his uri or any other resource having matching labels or a music album directory in the file system can be linked to the uri of that album in an linked open data (lod) set. linking local directories and files to lod enables the user to explore additional related information. in a similar way, files could also be recommended engineering, technology & applied science research vol. 8, no. 2, 2018, 2827-2833 2828 www.etasr.com mashwani and khusro: the design and development of a semantic file system ontology to be interlinked with other files or simply deleted if user intends to do so. e.g.,  if a user deletes some songs of an album in directory a then songs of the same album that are stored in directory b can be recommended for deletion.  a file that was created together or frequently accessed with the deleted file can also be recommended.  similarly, duplicated, near duplicated or earlier versions of deleted files can be recommended for deletion. d. scenario 4: static contents in directories traditional file systems organize files in native structures (directories), which are taxonomy-oriented. one of the shortcomings of native structure is that a directory always shows the same contents no matter in what context a user is accessing information. a file importance changes according to different factors, such as file access frequency, time, user’s geographical location, or a user obligations (a user may have many appointments, meetings, presentations, etc. in a day). but a directory shows fragments of multiple contexts rather than a single context. a semantically enhanced system could present task specific files to a user. files could be dynamically organized in such a way that a user can access important files easily. iii. semantic file system ontology development ontology can either be developed from scratch or by reusing existing ontologies and vocabularies. building ontology from the scratch may result in multiple disparate vocabularies for similar entities making the data integration task difficult [2]. ontology reuse exploits the existing ontological knowledge to create new ontologies [6]. several existing ontologies describing portions of large domain can be integrated while developing a large ontology [7] to address new or emerging problems. in addition, this reuse reduces the cost and improves the quality of resulting ontology. moreover, the interoperability among applications gets increased as it provides a deeper, machine-processable and commonly agreed upon understanding of the underlying domain of interest. without reuse, the lack of integration will treat ontology like traditional static knowledge bases and therefore, will not be able to contribute to the realization of the sw [6, 8]. it is always encouraged not to reinvent the wheel but to use or extend terms from existing widely used vocabularies[7, 9-11]. we follow the same practice of reusing terms from existing popular vocabularies. based on [11], we performed the following steps for reusing existing ontologies in developing an sfs ontology. a. step 1. discovery of ontologies for reuse finding ontological resources is an important step for reuse. in sw, ontologies as well as their concepts and properties are identified via uris, which makes ontologies and ontological entities accessible on the web and discoverable by crawlers [6]. in searching relevant ontologies, we used traditional web search engines like google, sw search engines including swogle [12], watson [13], ontosearch [14], ontology repositories including daml ontology library, protégé owl library, etc., and linked open vocabularies. b. step 2. selecting relevant reuse candidates table i depicts vocabularies that we have manually selected for possible reuse after carefully proofreading. nepomuk intends to bring solution to annotate and interlink arbitrary information on the local desktop making it machine processable. in addition, it enables interconnection and information exchange among desktops [15]. nepomuk ontologies are carefully crafted by a large team of experts over many years. its aim is to provide a unified vocabulary for describing desktop resources. w3c basic geo is a widely used vocabulary for representing latitude, longitude and altitude information about spatially-located things. c. step 3. customization, extending and integrating relevant ontologies the identified reusable ontologies were integrated into the final application ontology. we mostly reused terms of nepomuk ontologies. nepomuk ontologies provide basic terms to describe desktop resources. to capture more semantics and to best fit in the domain of sfss we extend them by defining new properties. table ii presents the competency questions to be answered by an sfs ontology. iv. terms description of sfs ontology we follow linked data best practices [5] while designing our sfs ontology. the namespace of the ontology is defined as “https://w3id.org/sfs-ontology#”. each term in the ontology is accessible via persistent http uris with content negotiation capability. if a uri is accessed by a human, then humanreadable information is provided and if it is accessed by a machine then machine-understandable information is provided to client. the web server is configured to do this redirection by exploiting 303 see other http status code. to maximize interoperability, almost all classes and most of the properties are reused from nie ontology framework (see table i). where applicable, we defined new terms to extend them into the domain of sfss. in the following, we describe the newly defined/extended terms. a. classes description fileaccess fileaccess is uniquely identified by time, latitude, longitude and altitude. an object of fileaccess is created upon each file access. the fileaccesslocation property relates objects of nfo:filedataobject and fileaccess classes. this enables a user to track accessed time and location of a file. super class: rdfs:resource in domain of: fileaccessedlocation in range of: nfo:filedataobject restrictions: sfs:fileaccessedtime some(existential) datetime, sfs:fileaccessedtime maximum cardinality 1, geo:location some (existential) geo:point, geo:location maximum cardinality 1, engineering, technology & applied science research vol. 8, no. 2, 2018, 2827-2833 2829 www.etasr.com mashwani and khusro: the design and development of a semantic file system ontology table i. reuse candidates. the percentage refers to the total number of reused (r)/newly defined (n) terms in sfs ontology vocabulary name category concepts properties total terms % of terms object data sfs ontology https://w3id.org/sfs-ontology/ sfs 1 15 7 23 (n) 10.8 nepomuk information element core ontology (nie) http://www.semanticdesktop.org/ontologies/2007/01/19/nie/ general/ documents 10 14 28 33 (r) 15.6 nepomuk file ontology (nfo) http://www.semanticdesktop.org/ontologies/2007/03/22/nfo general/ documents 58 17 57 63 (r) 29.7 nepomuk exif ontology (nexif) http://www.semanticdesktop.org/ontologies/2007/05/10/nexif/ multimedia 5 8 148 47 (r) 22.2 nepomuk id3 ontology (nid3) http://www.semanticdesktop.org/ontologies/2007/05/10/nid3 multimedia 10 28 29 29 (r) 13.7 basic geo vocabulary (geo) http://www.w3.org/2003/01/geo/ location 2 1 4 6 (r) 2.8 nepomuk annotation ontology (nao) http://www.semanticdesktop.org/ontologies/2007/08/15/nao/ annotations 9 17 15 3 (r) 1.4 nepomuk contact ontology (nco) http://www.semanticdesktop.org/ontologies/2007/03/22/nco contact 41 33 34 2 (r) 0.9 nepomuk multimedia ontology (nmm) http://www.semanticdesktop.org/ontologies/2009/02/19/nmm multimedia 12 16 21 6 (r) 2.8 total number of terms in sfs ontology 212 100% table ii. competency questions which files are temporally related to user’s current context? which files are related to the user’s current geographical context? get me those files which are frequently accessed by the user at a specific geographical location get me those files which are frequently accessed by the user at specific temporal duration show me all those files which are frequently accessed with the file a show me all related files which are in the child directories of the path xyz show me all related files which are in the parent directories of the path xyz get me those files which are tagged with (w or x) and y but not z get me all files created by xyz application get me all files created by xyz hardware (digital camera etc.) get me those files accessed at a specific geographic point, city or country etc. get me all those pictures taken with camera xyz at geographical location xyz and having resolution higher than xyz. show me duplicate and near duplicate files of file xyz show all those files which are recently created or modified by application xyz show me files which are created together with file xyz get me those files which are frequently accessed on sunday b. properties description: fileaccessedlocation_time it relates objects of nfo:filedataobject and fileaccess classes, which enables a user to track the accessed time and location of a file so that frequently accessed timings and locations can be calculated. domains: nfo:filedataobject ranges: fileaccess belongedtocontainer it is the previous container of a file, which models the containment relations between normal or compressed files and folders at their previously stored locations. a user groups semantically related files in a folder. if a user places a file in one folder and then after some time he/she moves it to another folder then it indicates that files in both folders are somehow related to each other. tracking previous containers/folders of a file enables relating files based on these semantics. domains: nie:dataobject ranges: nfo:datacontainer disjoint with: nfo:belongstocontainer filecreatedbyapplication this property relates a file to the application with which it was created. it helps in maintaining provenance of a file. domains: nfo:filedataobject ranges: nfo:application characteristics: functional filemodifiedbyapplication this property tracks applications that make changes to a file. this property helps in maintaining provenance of a file. domains: nfo:filedataobject ranges: nfo:application filecreatedbyuser it is the user who creates the file. this property helps in maintaining provenance of a file. domains: nfo:filedataobject ranges: nco:contact characteristics: functional filecreatedfrom a file created from (the contents of) another file. if file b is created from file a and file c is created from file b then it can be inferred that file c is created from file a. engineering, technology & applied science research vol. 8, no. 2, 2018, 2827-2833 2830 www.etasr.com mashwani and khusro: the design and development of a semantic file system ontology domains: nfo:filedataobject ranges: nfo:filedataobject characteristics: transitive filecreatedtogather it relates two files that are created together within a predefined threshold time. domains: nfo:filedataobject ranges: nfo:filedataobject characteristics: symmetric fileduplicateof it relates a file to its exact match. files are duplicates of each other if they are content-wise 100 % identical. domains: nfo:filedataobject ranges: nfo:filedataobject characteristics: symmetric filefrequentlyaccessedwith it represents a file which is frequently accessed with another file. domains: nfo:filedataobject ranges: nfo:filedataobject characteristics: symmetric filemodifiedbyuser it tracks users who modify the file. this property helps in preserving provenance information of a file. domains: nfo:filedataobject ranges: nco:contact filecreatedondevice it represents the computer or device on which a file is created. this property helps in maintaining provenance of a file. domains: nfo:filedataobject ranges: characteristics: functional filemodifiedondevice it tracks devices/computers on which a file is modified. a file is annotated each time if it is modified on a different device. this property helps in preserving the provenance information of the file. domains: nfo:filedataobject ranges: filemanualpeaklocation manual location based annotation. the difference between filepeaklocation and filemanualpeaklocation is that in the former annotation is done automatically as a user interacts with files and in the later the annotation is done manually by a user. domains: nfo:filedataobject ranges: geo:point filemodifiedbyapplication this property relates a file to an application that makes changes to a file. it helps in maintaining provenance information of a file. domains: nfo:filedataobject ranges: nfo:application filenearduplicateof this property relates two files that are identical to some extent (e.g. older versions of the same file). it uses a similarity threshold to detect near-duplicates. e.g. if similarity between two files is greater than 80%, then both files are "near duplicates". domains: nfo:filedataobject ranges: nfo:filedataobject characteristics: symmetric filepeaklocation this property represents the geographical location where a file is frequently accessed. domains: nfo:filedataobject ranges: geo:point fileaccessedcounter this property means the number of times a file is accessed. domains: nfo:filedataobject ranges: xsd:integer maximal cardinality: 1 fileaccessedtime file accessed time. domains: nfo:filedataobject, sfs:fileaccessedtime range: xsd:datetime fileaccessedhistory the date and time is recorded each time a file is accessed to maintain a file’s accessed history. domains: nfo:filedataobject ranges: xsd:datetime filemodifiedhistory the date and time is recorded each time a file is modified to maintain a file’s history. domains: nfo:filedataobject ranges: xsd:datetime filepeakday this property represents a file's peak day, the day on which a file is frequently accessed. its value ranges from 0-6, with 0 being sunday. domains: nfo:filedataobject ranges: xsd:integer filepeakhour this property represents hour of the file. the value ranges from 0 to 23. engineering, technology & applied science research vol. 8, no. 2, 2018, 2827-2833 2831 www.etasr.com mashwani and khusro: the design and development of a semantic file system ontology domains: nfo:filedataobject ranges: xsd:integer contenttype this property represents the minimum age restriction of the user to access a file or folder. if its value is set to 18 then the contents will not be accessible to non-adults. domains: nfo:filedataobject, nfo:datacontainer ranges: xsd:integer maximal cardinality: 1 v. deploying ontology the ontology was developed using protégé and is freely available under a creative commons attribution license from https://w3id.org/sfs-ontology/. sfs ontology was deployed on our developed file system called 360ᵒ-sfs, which is freely available from https://w3id.org/360-sfs/. the 360ᵒ-sfs automatically creates objects of classes and annotates them while the user interacts with file system resources. we also developed a file manager which enables the user to browse files semantically by exploiting the same centralized knowledgebase. a. 360ᵒ semantic file system for proof-of-concept implementation, we deployed the proposed ontology on 360ᵒ-sfs. the 360ᵒ-sfs enables a user to semantically retrieve files in less time and with less human effort. this is done via now and tags special folders. the contents of these special folders change dynamically according to the user’s current context, as discussed in scenario 5. the system creates instances of the classes and annotates them according to user’s interaction with file system resources. this is done with the help of file system events. for instance, if a user creates a file or a folder in the file system then an instance of the nfo:localfiledataobject or nfo:folder is created respectively and annotated with the required information. if a user deletes a file then upon file delete event that particular object of nfo: localfiledataobject is deleted from knowledge base along with its all references. b. 360ᵒ file manager 360ᵒ-sfs is backward compatible with traditional file managers as well as all other software applications. however, access to full semantics is not possible through traditional file managers. to make the most from the file system ontology, file managers need to be ontology aware to manipulate file system resources accordingly. therefore, to further facilitate user’s interaction with 360ᵒ-sfs, we propose 360ᵒ-file manager (fm), (figure 1). the 360ᵒ-fm extends traditional hierarchical file organization by overcoming some of its limitations. in the following, we explain the interface and functionality of 360ᵒfm: 1. “traditional pane” provides access to the stored files in a way like that of traditional file managers. 2. “semantic pane” enables a user to access files semantically. it shows the contents of now and tags directories, eliminating the need of going into now and tags directories. 2.1. “semantic sub-pane-1” this pane has two tabs: now and tags. now tab recommends files only on the basis of temporal and user’s geographical location while tags tab facilitates file management based on tags. now tab shows only those files that are accessed frequently at current time and geographical location. the items in subpane-1 (contents of now and tags tabs) are computed on the basis of currently selected directory (territory) in traditional pane. only those links are shown in subpane-1, which are stored within a selected directory. all files stored in the parent directories of the selected directory are ignored. each time the user selects another directory in traditional pane, the contents of sub-pane-1 are refreshed to show contextually relevant files accordingly. 2.2. “semantic sub-pane-2” shows files which are semantically related to the currently selected file in the details view of traditional pane. each time a user selects a file in details-view of traditional pane, contents of subpane-2 are refreshed to show contextually relevant files accordingly. the internal tab shows links to the file system internal files while linked cloud tab relates the selected files to linked cloud. the linked cloud could be private linked cloud or linked open data cloud. the show inferences check box enables or disables inferences in sub-pane-2. the semantic pane is the only difference between 360ᵒ-fm and a traditional file manager. in addition, plugins can be developed for traditional file managers to show the semantic contents in a way similar to semantic pane. a file manager may allow a user to sort files based on context relevancy. furthermore, file icon size can increase or decrease as per its relevance to the current context and color gradient of the file’s icon can also be modified to make the important files prominent in a directory. as stated in scenario 1, 360ᵒ-sfs maintains a single centralized machine friendly metadata repository. the repository is accessible to all agents and advanced queries can be performed, as discussed in scenario 2. the 360ᵒ-fm exploits the repository and enables file retrieval semantically. in addition, different applications can exploit the repository for recommendations within their respective interfaces and also semantically related files can be recommended along with recently opened files. vi. related work the term semantic file system was first in [16]. file type specific transducers mine and index attributes from files. they used virtual directories for file navigation based on the extracted attributes. authors in [17] further extended the idea and proposed the sfs that also considers users to define arbitrary metadata for files in the form of key-value pairs. the work of [18-22] are based on tags semantics that enable users to retrieve files based on tags assigned to them. gfs [23] is also a tag-based file system but its advantage over other file systems is that it provides associative access to tags based navigation and does not replace traditional hierarchical folder navigation. authors in [24] proposed the changing of folder and file icons according to their popularity to assist the user to engineering, technology & applied science research vol. 8, no. 2, 2018, 2827-2833 2832 www.etasr.com mashwani and khusro: the design and development of a semantic file system ontology locate important files easily. files are uploaded to a webserver. the popularity of files is calculated based on the users’ annotations. in lifs [25], authors propose linking files internally in a file system and offer support for arbitrary annotations. authors in [26, 27] propose linking of desktop and web resources. the proposed system enables a user to browse web resources as if they are stored on desktop. in [28], authors describe different benefits of ontology based file systems. although, many sfss have been proposed, to the best of our knowledge, no effort has been exercised till date to develop ontology for sfss and make it available for public use by publishing it according to linked data principles. fig. 1. 360ᵒ file manager – an interface for interacting with file system resources vii. conclusion the main contribution of this paper lies in the shape of sfs ontology. sfs ontology intends to provide vocabulary upon which sfss could be built. we designed and published sfs ontology by following linked data best practices. for interoperability, we reused or extended terms from existing popular vocabularies. the terms of the proposed sfs ontology are provided with persistent uris with content negotiation capability. for the proof-of-concept implementation, we have deployed our developed 360ᵒ-sfs and 360ᵒ file manager using the proposed ontology, which enables the retrieval of files on the basis of semantics, intent and relationships with other files rather than their physical locations as with traditional file systems. the proposed sfs ontology is by no means complete, more terms may appear in future. the sfs ontology is freely available with full technical term definitions and complete class hierarchy for any purpose in information technology. sfs ontology remains open for additions and corrections upon feedback. references [1] t. berners-lee, j. hendler, o. lassila, “the semantic web”, scientific american, vol. 284, no. 5, pp. 28-37, 2001 [2] a. mylka, l. sauermann, m. sintek, l. van elst, nepomuk information element ontology, available at: http://oscaf.sourceforge.net/ nie.html, 2013. [3] b. schandl, b. haslhofer, “the sile model: a semantic file system infrastructure for the desktop”, the semantic web: research and applications. eswc 2009. lecture notes in computer science, vol. 5554, pp. 51-65, springer, berlin, heidelberg, 2009 [4] l. sauermann, a. bernardi, a. dengel, “overview and outlook on the semantic desktop”, proceedings of the 2005 international conference on semantic desktop workshop: next generation information management d collaboration infrastructure, vol. 175 pp. 74-91, 2005 [5] t. berners-lee, “linked data”, available at: http://www.w3.org/ designissues/linkeddata.html, 2006 [6] e. simperl, “reusing ontologies on the semantic web: a feasibility study”, data & knowledge engineering, vol. 68, no. 10, pp. 905-925, 2009 [7] n. f. noy, d. l. mcguinness, ontology development 101: a guide to creating your first ontology, available at: https://protege.stanford.edu /publications/ontology_development/ontology101.pdf, 2001 [8] r. stecher, c. niederée, w. nejdl, p. bouquet, “adaptive ontology reuse: finding and re-using sub-ontologies”, international journal of web information systems, vol. 4, no. 2, pp. 198-214, 2008 [9] b. schandl, b. haslhofer, “files are siles: extending file systems with semantic annotations”, international journal on semantic web and information systems, vol. 6, no. 3, pp. 1-21, 2010 [10] m. poveda villalón, m. c. suárez-figueroa, a. gómez-pérez, “the landscape of ontology reuse in linked data”, in 1st ontology engineering in a data-driven world (oedw 2012) workshop at the 18th international conference on knowledge engineering and knowledge management (ekaw2012), galway, irlanda, october 8-12, 2012 [11] m. c. pattuelli, a. provo, h. thorsen, “ontology building for linked open data: a pragmatic perspective”, journal of library metadata, vol. 15, no. 3-4, pp. 265-294, 2015 [12] t. finin, y. peng, r. s. cost, j. sachs, a. joshi, p. reddivari, r. pan, v. doshi, l. ding et al., “swoogle: a search and metadata engine for the semantic web”, 13th acm international conference on information and knowledge management, pp. 652-659, acm, 2004 [13] m. d’ aquin, m. sabou, m. dzbor, c. baldassarre, s. angeletou, e. motta, “watson: a gateway for the semantic web”, in poster session of the european semantic web conference, eswc, innsbruck, austria, june 3-7, 2007 [14] y. zhang, w. vasconcelos, d. sleeman, “ontosearch: an ontology search engine”, research and development in intelligent systems xxi, pp. 58-69, springer-verlag london, 2005 engineering, technology & applied science research vol. 8, no. 2, 2018, 2827-2833 2833 www.etasr.com mashwani and khusro: the design and development of a semantic file system ontology [15] t. groza, z. handschuh, k. möller, g. grimnes, l. sauermann, e. minack, c. mesnage, m. jazayeri, g. reif, r. gudjónsdottir, “the nepomuk project-on the way to the social semantic desktop”, proceedings of i-semantics 07, graz, austria, pp. 201-211, 2007 [16] d. k. gifford, p. jouvelot, m. a. sheldon, j. w. o'toole jr, “semantic file systems”, proceedings of the thirteenth acm symposium on operating systems principles, pacific grove, california, united states, pp. 16-25, october 13-16, 1991 [17] d. garg, v. mehta, s. pandit, m. de rosa, “a writable semantic file system”, in: selected project reports, fall 2005 advanced os & distributed systems (15-712), pp. 56-65, carnegie mellon university, pittsburgh, 2005 [18] y. padioleau, b. sigonneau, o. ridoux, “lisfs: a logical information system as a file system”, proceedings of the 28th international conference on software engineering, pp. 803-806, 2006 [19] tx0, “tagsistant: semantic file system”, available at: http://www.tagsistant.net, 2007 [20] s. schenk, o. görlitz, s. staab, “tagfs: bringing semantic metadata to the filesystem”, in: poster at the 3rd european semantic web conference (eswc), budva, montenegro, june 11-14, 2006 [21] s. bloehdorn, o. görlitz, s. schenk, m. völkel, “tagfs tag semantics for hierarchical file systems”, proceedings of the 6th international conference on knowledge management (i-know 06), graz, austria. vol. 8, pp. 6-8, 2006 [22] s. bloehdorn, “semfs semantic file system”, available at: http://semanticweb.org/wiki/semfs, 2009 [23] d. di sarli, f. geraci, “gfs: a graph-based file system enhanced with semantic features”, proceedings of the 2017 international conference on information system and data mining, pp. 51-55, april 1-3, 2017 [24] b. mizrachi, l. s. deluca, file folder display, us patent 20170109010, 2017 [25] s. ames, n. bobb, k. m. greenan, o. s. hofmann, m. w. storer, c. maltzahn, e. l. miller, s. a. brandt, “lifs: an attribute-rich file system for storage class memories”, 23rd ieee/14th nasa goddard conference on mass storage systems and technologies, may 15-18, 2006 [26] b. schandl, “tripfs: exposing file systems as linked data”, linked open data triplification challenge, graz, austria, september 2-4, 2009 [27] b. schandl, “representing linked data as virtual file systems”, 2nd international workshop on linked data on the web madrid, spain, april 20, 2009 [28] h. b. ngo, c. bac, f. silber-chaussumier, t. q. le, “towards ontology-based semantic file systems”, 2007 ieee international conference on research, innovation and vision for the future, hanoi, vietnam, pp. 8-13, march 5-9, 2007 engineering, technology & applied science research vol. 8, no. 2, 2018, 2656-2662 2656 www.etasr.com yildirim et al.: influence of material and geometrical properties of permanent magnets on … influence of material and geometrical properties of permanent magnets on cogging torque of bldc merve yildirim department of electrical and electronics engineering university of firat elazıg, turkey merveyildirim@firat.edu.tr hasan kurum department of electrical and electronics engineering university of firat elazıg, turkey hkurum@firat.edu.tr damijan miljavec department of electrical engineering university of ljubljana ljubljana, slovenia damijan.miljavec@fe.uni-lj.si selma corovic department of electrical engineering university of ljubljana ljubljana, slovenia selma.corovic@fe.uni-lj.si abstract—aim of this study is to investigate the influence of both material and geometrical properties of surface mounted permanent magnets (pm) on cogging torque of a brushless dc motor (bldc) by means of numerical modeling based on finite element method (fem). to this end, a 2d numerical model of the bldc motor is built by using the software package ansys maxwell. in this study, we analyze the machine properties in no excitation mode (i.e. no stator current is applied) and calculate the distribution of magnetic flux density within the entire motor, the magnetic flux density in the air gap, the cogging torque and the back electromotor force (emf). firstly, analysis is performed for four different magnets. it is seen that while cogging torque, back emf, and magnetic flux density in the air gap for the strongest magnet material have the highest values, the lowest values of these are obtained for the weakest magnet. in the second part of the study, the effect of variation of magnet geometry on the cogging torque, magnetic field density and back emf of bldc is examined. three magnet embrace values are handled in this study. when the magnet embrace increases, the value of the cogging torque reduces. besides, the maximum values of the back emf are approximately the same for different magnet embraces, while shapes of the back emf only change based on the magnet embrace. according to the results, the cogging torque strongly depends on the material and geometrical properties of the magnets. keywords-bldc; cogging torque; ansys maxwell; finite element method i. introduction permanent magnet brushless dc (pm bldc) motors are widely used in different industrial applications such as automotive industry, robots, air conditioners etc. [1, 2]. bldc motors have important advantages such as small size, high reliability, high efficiency and power density because of not having rotor winding and rotor copper losses, faster response, and low maintenance cost due to not having brushes [3-8]. on the other hand, they have some drawbacks such as complex control technique, torque pulsation, vibration, and noise. the torque pulsation occurs due to the cogging torque [1, 9]. namely, when the rotor rotates, cogging torque is observed because of the different reluctances created by interaction of the rotor magnets and the stator configuration [10]. this may cause undesirable noise and vibration in pm bldc motors. it is therefore of outmost importance to reduce or minimize the cogging torque. design strategies for cogging torque reduction include magnet shape optimization, fractional slot/pole design, control techniques of the excitation currents etc. [1]. numerous studies have approached the problem of the cogging torque by using numerical modeling in combination with different optimization methods. for example, in [1] optimum bldc motor was designed for minimum torque pulsation using finite element modeling and particle swarm optimization methods. the effect of convenient number of magnet poles and stator slots was examined and it was observed that the obtained structure minimized the cogging torque and torque pulsation. in [11], the dynamic behavior of bldc motor and the effect of magnet embrace on the resulting torque characteristic were investigated by using particle swarm optimization and imperialist competitive algorithm. a detailed study of optimal rotor designs by optimization of magnet embrace and thickness values was performed in [12]. authors in [13] investigated the effects of different magnet embraces on motor efficiency and cogging torque of pm bldc motor by using genetic algorithm based optimization. in [14], new design models were examined for reducing the cogging torque of pm bldc motor. it was observed that the cogging torque obtained from parallel magnetization was smaller than that of radial magnetization. authors in [15] explained the analysis of interior-type pm bldc motor with 24-slot for reduction of the cogging torque causing torque ripple. by changing some physical parameters including magnet arc, slot openings, bifurcated slot teeth, and hole types, pm bldc motor was analyzed. the results showed that the cogging torque and torque ripple reduced and the average torque remained in 1% range. in [16], analysis of bldc motor design was realized to be used in unmanned aerial vehicle hybrid drive. by selecting permanent magnets optimum pole arcs, the effect on the cogging torque, electromagnetic torque, induced voltage and circulating currents occurred by the result of the assumed configuration of stator windings. the current waveforms, voltages, and the electromagnetic torque were given for a selected motor working point. the effect of rotor magnet pole arc on the engineering, technology & applied science research vol. 8, no. 2, 2018, 2656-2662 2657 www.etasr.com yildirim et al.: influence of material and geometrical properties of permanent magnets on … cogging torque of pmsm was examined in [17]. the parameters and material properties of external rotor pmsm having three-phase, 12 slot and 8 poles were analyzed in 2d fem using opera. the influence on the phase back emf produced by the pmsm was also explained. a lower cogging torque means more sinusoidal phase back emf waveform. it was seen that the magnet pole arc had an important role in the reduction of the cogging torque and lower torque ripple was obtained by decreasing the magnet pole arc. design and analysis of an axial flux pm motors were explained in [18]. firstly, the cogging torque was calculated without fe analysis. then, it was minimized by skew angle and this value was validated by fe analysis and experimental studies. authors in [19] explained rotor shape optimization of interior pm bldc motor based on the magnetization direction to maximize back emf. fem analyses for four different models of general magnet shapes were realized for four magnetization directions. as an initial model, the best magnet shape and magnetization direction were chosen for optimization. then, optimization of the motor was carried out to obtain maximum back-emf and minimum cogging torque. the optimized design was validated by the experimental studies on a manufactured motor. the influence of pole embrace on the cogging torque and unbalanced magnetic forces of bldc motors with 14 poles and 12 slots used in the submarines was examined in [20]. the cogging torque and unbalanced magnetic forces in bldc motors cause acoustic noise. hence, the cogging torque should be minimized. cogging torque was calculated for different pole embraces by using fem. the optimal pole embrace to reduce the cogging torque and unbalanced magnetic forces was obtained. as observed in the literature, the studies on reducing the cogging torque have been commonly realized by using different optimization methods. in this study, the influence of both material and geometrical properties of the surface mounted pms on the cogging torque, back emf and distribution of magnetic flux density b of bldc motor are separately examined. besides, while stator windings have been generally supplied with excitation current in the other studies, the difference in this work is that no current has been applied to the windings and only the excitation from the magnets is taken into account. 2d finite element based numerical model of surface mounted pm bldc motor is built and analyzed in ansys maxwell software. firstly, the analysis for four different magnet types, namely alnico5, ceramic5, smco28, and ndfe35 is performed for the same rotor and stator geometry. in the second part of the study, the influence of magnet geometry on the cogging torque, back emf and distribution of b is examined by investigating three different magnet embraces (i.e. 0.833, 0.625, and 0.416). in this case, the stator geometry and material properties of magnets are kept constant. finally, the results of the study are compared to the literature. ii. definition of motor geometry and methods in this study, a bldc motor with 4 poles, 3 phases and 24 slots with surface mounted permanent magnets on the rotor was studied. we analyzed the motor properties in two dimensions. bldc motor geometry and assignment of the excitations to the coils are shown in figure 1. following output physical quantities were calculated and analyzed: cogging torque, back emf in stator windings and magnetic flux density. distribution of magnetic flux density within the entire motor was firstly calculated and visualized. absolute value and normal and radial components of the magnetic flux density in the center of the air gap were also calculated. motor parameters used in design are given in table i. table i. motor design parameters npole total number of poles 4 rsh radius of shaft 9.003 mm rr radius of rotor 25.154 mm wg width of airgap 0.503 mm lmag length of magnet 6.987 mm rso outer radius of stator 48 mm nslot number of stator slots 24 wst width of stator tooth 2.76 mm sd depth of stator slot 12.07 mm a. b. fig. 1. a. bldc motor geometry, b. assignment of the excitations to the coils in the bldc motor model, back emf and torque are given as functions of rotor position [2]. armature winding and torque equations are used in the motor model. the voltage equations within the armature windings can be defined by (1), (2) and (3): a a a a di v ri l e dt    (1) b b b b di v ri l e dt    (2) c c c c di v ri l e dt    (3) where va, vb and vc are the supplied voltages to each phase (a, b, c), r is armature winding resistance, i is phase current, l is inductance and e is back emf. as the rotor position changes, variable magnetic field is obtained and this causes induced emf [15]. thus, the magnetic field affects the produced back emf. back emf e can be explained from faraday’s law: d e n dt    (4) where n is the number of the turns, φ is the flux linkage, and t is time. there is a 120 angle between the first harmonics of back emf of each phase as described with (5), (6) and (7) engineering, technology & applied science research vol. 8, no. 2, 2018, 2656-2662 2658 www.etasr.com yildirim et al.: influence of material and geometrical properties of permanent magnets on …     sin ia e e t k t (5)   2 3i b ee t k sin t        (6)   2 3i c ee t k sin t        (7) where keı is back emf first harmonic amplitude [2]. when the rotor rotates, the change of the reluctance in the air gap due to the slots causes the cogging torque. the cogging torque can be calculated from the stored energy in the air gap as follows [19]: cog dw t d   (8) where w is the stored energy, θ is the angular rotor position and tcog is the cogging torque produced by magnet excitation. the tcog is expressed in detail by (9):  2 0.5 g mcog drt d    (9) where φg is the flux of the air gap and rm is the magnetic reluctance [1]. since in this study the current i was 0a, only the back emf and cogging torque were calculated and analyzed. the back emf was calculated by applying the constant speed and the number of turns per coil as 500 rpm and 20 turns respectively. the calculation of the cogging torque was performed by applying one mechanical degree angular rotation. automatic finite element mesh is generated in all models. iii. definition of material properties in this work, stainless steel is used as bldc shaft material and cooper is selected for the windings. the material properties of magnets, shaft and windings are taken from the ansys maxwell library. the b-h curve of the ferromagnetic is manually imported into the software. the b-h curve of the ferromagnetic material used for the rotor and stator core is given in figure 2. the saturation point for this material is set at b=1.7t. the b-h curves for four different magnets used in this study, namely alnico5, ceramic5, smco28, and ndfe35 are given in figure 3. as shown in figure 3, the permanent magnetic flux density br values for alnico5, ceramic5, smco28, and ndfe35 are 1.26t, 0.395t, 1.07t, 1.23t, respectively. the values of coercitive force hc for these magnets are -50.9295, -190.986, -820.000, -890.000 ka/m, respectively. fig. 2. the b-h curve of the ferromagnetic material used for the stator and rotor core fig. 3. b-h curves of permanent magnet materials iv. definition of magnet embrace magnet embrace is defined as the ratio of rotor pole pitch to the pole arc in pm machines, which can be expressed by embrace    (10) where γ and β are rotor pole pitch and pole arc of the pm, respectively [11]. magnet embrace is shown in figure 4. it has already been shown that the cogging torque can be successfully reduced by the optimum selection of the magnet embrace [12]. in this study, three different magnet embrace values namely 0.416, 0.625, and 0.833 are investigated as ilustrated in figure 5. fig. 4. magnet embrace illustration a. b. c. fig. 5. the bldc geometries of different magnet embraces investigated in this study: a. the reference magnet embrace 0.833, b. magnet embrace 0.625, and c. magnet embrace 0.416. engineering, technology & applied science research vol. 8, no. 2, 2018, 2656-2662 2659 www.etasr.com yildirim et al.: influence of material and geometrical properties of permanent magnets on … v. results and discussions a. influence of magnet type on the bldc properties by using the reference geometry of the motor which is magnet embrace 0.833 as shown in figure 5a, the results for different magnet types are given in this subsection. firstly, the distributions of magnetic flux density b [t] in the bldc calculated for alnico5, ceramic5, smco28, and ndfe35 are compared in figures 6a, 6b, 6c, 6d respectively. the highest b is obtained in figure 6d, due to the fact that the strongest magnet ndfe35 is used (b-h curve in figure 3). the lowest b is obtained with the weakest magnet ceramic5 as shown in figure 6b. figure 6b also shows that the saturation within the stator is not exceeded and the b is somewhat low, while the saturation point is exceeded in figures 6a, 6c and 6d and the b is too high. this means that that the magnets should be properly selected and adjusted to the stator and rotor machine geometry and to the material properties of the machine. the calculated absolute values of |b| in the airgap are compared for different magnet materials using the reference magnet embrace 0.833 in figure 7. the normal and tangential components btan and bnormal are also shown in figure 8 separately for each magnet. the highest value of |b| in the air gap is found for ndfe35 magnet, while the weakest one is obtained for ceramic5. comparison of the cogging torque and the back emf for different magnet materials using the reference magnet is shown in figures 9 and 10 respectively. fig. 6. the distribution of b in the machine for different magnet materials using the reference magnet embrace 0.833 fig. 7. comparison of |b| in the airgap for different magnet materials using the reference magnet embrace 0.833 a. b. c. d. fig. 8. comparison of b components in the air gap for different magnet materials using the reference magnet embrace 0.833 fig. 9. comparison of the cogging torque for different magnet materials using the reference magnet embrace 0.833 the normal and tangential components btan and bnormal are also shown in figure 8 separately for each magnet. results in figures 9 and 10 show that cogging torque and back emf for the strongest magnet material (ndfe35) have the highest peak to peak values which are 33.332mnm and 23.948v, respectively. on the contrary, the lowest peak to peak values are obtained for the weakest magnet, ceramic5, as 17.752mnm and 7.702v, respectively. the curves for alnico5 differ from the ones for the other materials due to different b-h characteristic shown in the figure 3. the nonsymetries present in the curves of tcogg in figure 9 are related to the finite element mesh quality. it can also be observed that while b in the airgap is high, the cogging torque and back emf will also be high. therefore, the highest value of the cogging torque and the back emf are for ndfe35 magnet, while the lowest values of the cogging torque and the back emf are obtained for engineering, technology & applied science research vol. 8, no. 2, 2018, 2656-2662 2660 www.etasr.com yildirim et al.: influence of material and geometrical properties of permanent magnets on … ceramic5 using the same magnet embrace as shown in figures 7, 8, 9 and 10. a. b. c. d. fig. 10. comparison of back emf for different magnet materials using the reference magnet embrace 0.833 b. influence of magnet embrace on the cogging torque, b in the airgap, and back emf of bldc in this subsection, the results of numerical analysis for three different magnet embraces such as 0.833, 0.625, and 0.416 are shown and discussed. ceramic5 magnet is used for all examined magnet embraces. |b| in the airgap are compared for different magnet embraces using ceramic5 magnet in figure 11. as seen in figure 11, maximum values of |b| remain the same, while the width of the curves increases as the magnet embraces increase. the btan and bnormal components are given in figure 12a, 12b, 12c separately for each magnet embrace. the maximum values of btan and bnormal components in the airgap are the same for different magnet dimensions, however, the width of the curve only changes. calculated cogging torque and back emf are compared for different magnet embraces in figures 13 and 14 respectively. figure 13 shows that the cogging torque value is the highest for the smallest magnet embrace (0.416) due to the highest reluctance change. as the magnet embrace increases, the value of the cogging torque decreases, which is in agreement with the literature data [13]. as shown in figure 14, the maximum values of the back emf are almost the same for different magnet embraces, while the shapes of the back emf are significantly different. fig. 11. comparison of |b| in the air gap for ceramic5 magnet material using three different magnet embraces a. b. c. fig. 12. comparison of b components in the air gap for magnet embraces a. 0.833, b. 0.625 c. 0.416 of ceramic5 magnet fig. 13. comparison of tcogg for different magnet embraces engineering, technology & applied science research vol. 8, no. 2, 2018, 2656-2662 2661 www.etasr.com yildirim et al.: influence of material and geometrical properties of permanent magnets on … a. b. c. fig. 14. comparison of back emf for different magnet embraces vi. conclusions in this paper, the effects of material and geometrical properties of magnets on the cogging torque, back emf, and distribution of the magnetic flux density of the modeled pm bldc motor are examined and the motor is successfully analyzed by using ansys maxwell software without applying any current to the stator windings. firstly, the influence of four magnet materials on the cogging torque, back emf, and b in the air gap is examined by using the reference magnet embrace 0.833. it is seen that the highest cogging torque is obtained with the strongest magnet, while the lowest cogging torque is obtained with the least stronger magnet (ceramic5). besides, b is somewhat low when using ceramic5 magnets, while the ndfe35 magnet results in an excessively high b. the effect of magnet embrace on the cogging torque is handled. it is observed that while magnet embrace increases, cogging torque decreases. however, maximum values of the back emf are almost the same for different magnet embraces, while the shapes of the back emf vary. furthermore, maximum value of |b| in the air gap remains the same, when the curve width increases as the magnet embrace increases. as seen from the results, to obtain the optimum properties of bldc such as b below the saturation point, minimum cogging torque and adequate shape of back emf, the rotor and stator geometry have to be properly designed and adequate materials selected according to the motor geometry and its material properties. references [1] m. pourjafari, e. f. choolabi, m. j. bolan, “optimum design of brushless dc motor with minimum torque pulsation using fem and pso”, aut journal of electrical engineering, vol. 44, no. 2, pp. 59-70, 2012 [2] y. s. jeon, h. s. mok, g. h. choe, d. k. kim, j. s. ryu, “a new simulation model of bldc motor with real back emf waveform”, 7th workshop on computers in power electronics, blacksburg, usa pp. 217-220, july 16-18, 2000 [3] m. yildirim, m. polat, h. kurum, “a survey on comparison of electric motor types and drives used for electric vehicles”, 16th international power electronics and motion control conference and exposition, antalya, turkey, pp. 218-223, september 21-24, 2014 [4] s. m. jang, h. w. cho, s. k. choi, “design and analysis of a high-speed brushless dc motor for centrifugal compressor”, ieee transactions on magnetics, vol. 43, no. 6, pp. 2573-2575, 2007 [5] p. bajec, b. pevec, d. miljavec, “optimal control of brushless pm motor in parallel hybrid propulsion system”, mechatronics, vol. 20, no. 4, pp. 464-473, 2010 [6] r. n. nanekaran, e. f. chulabi, “shape optimization of the permanent magnet pole of the brushless dc motor by fem”, electrical power engineering frontier, vol. 3, no. 3, pp. 16-24, 2014 [7] a. saygın, c. ocak, a. dalcali, e. celik, “optimum rotor design of small pm bldc motor based on high efficiency criteria”, arpn journal of engineering and applied sciences, vol. 10, no. 19, pp. 91279132, 2015 [8] c. ocak, i. tarımer, a. dalcali, d. uygun, “investigation effects of narrowing rotor pole embrace to efficiency and cogging torque at pm bldc motor”, tem journal, vol. 5, no. 1, pp. 25-31, 2016 [9] j. g. kim, h. g. kim, i. d. kim, “program architecture for realizing design optimization of a bldc motor”, 7th international conference on power electronics and drive systems, bangkok, thailand, pp. 893-896, november 27-30, 2007 [10] k. j. kang, g. h. jang, s. j. sung, “frequency characteristics of bemf, cogging torque and umf in a hdd spindle motor due to unevenly magnetized pm”, ieee transactions on magnetics, vol. 49, no. 6, pp. 2578-2581, 2013 [11] l. ferraris, f. franchini, e. poskovic, “design optimization of bonded pm bldc motors with reference to the cogging torque amplitude”, 41st annual conference of the ieee industrial electronics society, yokohama, japan, pp. 001264-001269, november 9-12, 2015 [12] m. p. anjana, k. s. shinoy, j. joy, “comparative analysis of surface mounted and tangentially magnetized permanent magnet bldc motor using finite element method”, annual international conference on emerging research areas: magnetics, machines and drives, kottayam, india, pp. 1-5, july 24-26, 2014 [13] c. carunaiselvane, s. jeevananthan, “generalized procedure for bldc motor design and substantiation in magnet 7.1.1software”, international conference on computing, electronics and electrical technologies, pp. 18-25, kumaracoil, india, march 21-22, 2012 [14] v. keloth, m. mijas, p. a. manu, p. thomas, v. m. menon, r. p. praveen, “analysis of cogging torque reduction techniques of a slotless pmbldc motor”, annual international conference on emerging research areas: magnetics, machines and drives, kottayam, india, july 24-26, 2014 [15] y. donmezer, l. t. ergene, “cogging torque analysis of interior-type permanent-magnet brushless dc motor used in washers”, 8th international symposium on advanced electromechanical motion systems and electric drives joint symposium, lille, france, july 1-3, 2009 [16] p. bogusz, m. korkosz, a. powrozek, j. prokop, p wygonik, “an analysis of properties of the bldc motor for unmanned aerial vehicle hybrid drive”, international conference on electrical drives and power electronics, tatranska lomnica, slovakia, pp. 458-464, september 2123, 2015 [17] p. ling, d. ishak, t. l. tiang, “influence of magnet pole arc variation on the performance of external rotor permanent magnet synchronous machine based on finite element analysis”, ieee international conference on power and energy (pecon), melaka, malaysia, pp. 552557, november 28-29, 2016 [18] j. h. choi, j. h. kim, d. h. kim, y. s. baek, “design and parametric analysis of axial flux pm motors with minimized cogging torque”, ieee transactions on magnetics, vol. 45, no. 6, pp. 2855-2858, 2009 [19] h. s. kim, y. m. you, b. i. kwon, “rotor shape optimization of interior permanent magnet bldc motor according to magnetization direction”, ieee transactions on magnetics, vol. 49, no. 5, pp. 2193-2196, 2013 engineering, technology & applied science research vol. 8, no. 2, 2018, 2656-2662 2662 www.etasr.com yildirim et al.: influence of material and geometrical properties of permanent magnets on … [20] m. sargazi, m. esmaili, m. jafarboland, m. khajavi, “effect of pole embrace on the cogging torque and unbalanced magnetic forces of bldc motors”, 22nd iranian conference on electrical engineering, tehran, iran, pp. 826-830, may 20-22, 2014 microsoft word etasr_v12_n2_pp8374-8381 engineering, technology & applied science research vol. 12, no. 2, 2022, 8374-8381 8374 www.etasr.com filipova-petrakieva & dochev: short-term forecasting of hourly electricity power demand short-term forecasting of hourly electricity power demand reggresion and cluster methods for short-term prognosis simona filipova-petrakieva department of theory of electrical engineering faculty of automation technical university of sofia sofia, bulgaria petrakievas-te@tu-sofia.bg vencislav dochev department of computer systems faculty of computer systems and technologies technical university of sofia sofia, bulgaria ventsidochev@abv.bg received: 28 january 2022 | accepted: 10 february 2022 abstract-the optimal use of electric power consumption is a fundamental indicator of the normal use of energy resources. its quantity depends on the loads connected to the electric power grid, which are measured on an hourly basis. this paper examines forecasting methods for hourly electrical power demands for 7 days. data for the period of 1 january 2015 and 24 december 2020 were processed, while the models' forecasts were tested on actual power load data between 25 and 31 december 2020, obtained from the energy system operator of the republic of bulgaria. two groups of methods were used for the prognosis: classical regression methods and clustering algorithms. the first group included "moving window" and arima, while the second examined k-means, time series k-means, mini batch k-means, agglomerative clustering, and optics. the results showed high accuracy of the forecasts for the prognosis period. keywords-short-term prognosis; hourly electricity power demand; regression analysis; clustering methods i. introduction electric power consumption is a key to the normal function of any economy. in recent years, the consumption of electrical power has increased along with the human population and the development of technology. proper use of the available energy resources is a necessity since solid fuels are finite, they will run out in the future, and, their extraction and processing pollute the environment. for these reasons, various types of renewable energy sources have emerged. unfortunately, for some of them, the generation of electricity depends on the season, geographical location, type of energy extraction technology, certain economic and political factors, etc. also, the storage of this type of energy is difficult and costly. on the other hand, the production of electric power should neither exceed nor fall short of the amount of electric power required by the end-users. for this reason, algorithms have been developed for power generation in hydraulic power plants, guaranteeing the optimal parameters of the produced energy under the dynamic change of requirements from the electric supply companies and the market [1, 2]. despite the physical nature of the predicted subject, the forecasts are long-term, medium-term, and shortterm. the requirements that any reliable forecast must satisfy were given in [3]. there are various models for determining forecast assessments using different mathematical approaches to obtain the prognoses. for the operational control of power plants, it would be desirable to obtain precise short-term load forecasting assessments to guarantee power supply and load dispatch. the empirical mode decomposition (emd) method and the particle swarm optimization (pso) algorithm were successfully hybridized with the support vector regression (svr) to produce a satisfactory forecast performance in [4]. decomposed intrinsic mode functions (imfs) are defined as three items: 1) containing the random and the middle term, 2) containing the middle and the trend (residual) term, and 3) containing the middle terms only, where the random term represents the high-frequency part of the electric power load data, the middle term represents the multiple-frequency part, and the trend term represents the low-frequency part. based on these assumptions, the svr-pso was created, and the forecast results were calculated as (1) + (2) – (3). the suggested model improved the forecast accuracy, while the data for the model synthesis were taken from the australian electricity market. short-term power demand forecasts contribute significantly to the synthesis of the smart grid. in [5], a deep model based on convolutional neural networks (cnns), long short-term memory (lstm), and discrete wavelet transform (dwt) was proposed. this model was divided into two parts. the first part corresponded to the time-domain feature extraction, while dwt was responsible for the frequency domain. the model extracted both time and frequency-domain features separately using the neural network. subsequently, they merged as timefrequency features. the latter was fed into lstm to mine the features, which had a long-time dependency. in [6], a daily power consumption forecast was created for the hightemperature period. the model was based on a portrait-based multivariate regression model. the portrait of each substation area was derived using the clustering method based on the label system. then, the regression model was applied to forecast each cluster. the synthesized model was validated using electricity consumption data from shanghai. a hybrid deep learning neural network framework, which combined cnn corresponding author: simona filipova-petrakieva engineering, technology & applied science research vol. 12, no. 2, 2022, 8374-8381 8375 www.etasr.com filipova-petrakieva & dochev: short-term forecasting of hourly electricity power demand with lstm for making power consumption forecasts, was proposed in [7]. the original short-term forecasting strategy was extended to a multi-step forecasting strategy to introduce more response time for electricity market bidding. the following forecasting approaches were built: auto-regressive integrated moving average (arima), persistent model, svr, and lstm. in addition, a k-step power consumption forecasting strategy was used to promote the proposed framework for use in real-world applications. power production of photovoltaic (pv) plants is an important way of producing green energy, and different models exist to predict their self-consumption. two hybrid models were suggested in [8] to forecast power consumption (cnnlstm and convlstm) were suggested in [8]. these models were found to be more accurate than the standard lstm. in [9], a deep model named tl-mclstm was proposed as a multiple-output strategy to predict multi-step short-term power consumption. the model contained three channels: power consumption, time location, and customer behavior. the first channel reflects the change and the general trend of use. the second channel reflects the hidden pattern of customer habits, recording information about time, day of the week, and holidays. the third channel combines a convolution autoencoder and k-means to identify customer behavior. the first two channels were individually trained through the lstm, as it had an excellent memory function. the extracted features from the lstm in these channels were combined with customer behavior as comprehensive features to forecast. other mathematical approaches for creating short-term forecasting models are imperialist competitive algorithms, support vector machines (svm), and hierarchical cluster analysis svm. these approaches were used in [10] for the prognosis of the hourly electricity load. in [11], a new modeling approach was proposed for medium-term probabilistic power consumption using neural networks and incorporating trend, seasonality, and weather conditions as explicative variables in a neural network with an autoregressive feature. in [12], fuzzy logic was incorporated into a neural network. in this study, a model was divided into two subsystems: a network with backpropagation making the forecast and using data from previous months, and an autocorrelation module using temperature and production load differences for air conditioning and consumption between the previous and the forecast months. this model is appropriate for two types of industrial consumers: consumers for climate control and consumers for production activities. a mid-long term load structure forecasting model was developed in [13], based on grey theory, where the system state equations and the grey dynamic model group on various types of electrical load were established. the model provided a midlong-term forecast, in terms of the system dominant and associated factors determined by the grey correlative degree analysis method, using the gm(1, n, x ((0))) model derived from the gm(1, n). the power consumption of the considered grid was predicted in the medium and long term in a case study utilizing the proposed model. long-term forecasting of electricity consumption is quite difficult as its reliability depends on many different factors. during daytime, there may be several peaks in consumption which lead to a complete discharge of the battery to one of the peaks. as a result, the total peak power consumption does not decrease. to optimize the operation of storage devices, a dayahead forecast is often used, which allows determining the total number of peaks. in this sense, a long-term forecast of power consumption based on the use of exogenous parameters in the decision tree model was used in [14]. this forecast was based on the idea of determining the optimal storage capacity for a specific consumer, which optimizes the costs of leveling the load schedule. in [15], a detailed overview of current forecasting methods for power consumption was presented. some forecast approaches were summarized as grey and artificial neural network theory, among which the forecasting principle of the grey model gm(1,1) was developed. the econometric model method was also discussed. in addition, comprehensive analysis, analysis prediction, and other methods, which could be applied in short-term, medium-term, and long-term electricity demand forecasting were also discussed. the accuracy of the methods mentioned above improved by applying newly developed machine learning smart algorithms, such as deep learning, q-learning, extreme learning, etc. the processed data described the power consumption of guangzhou city between 2000-2008, and the forecasts were made for 2009. this study examines a short-term 7-day forecast of the hourly demand for electric power in the republic of bulgaria. these prognoses can be used to analyze the energy system models used for planning the bulgarian energy market, as described in [16]. a similar prognosis was presented in 2002 [17], but these models are obsolete today and do not guarantee high forecast accuracy. the increasing price of natural gas during the recent months has led to the rising prices of the entire production, supplies, and services. the sharp increase in the price of european natural gas prices [18] leads to lifetime evaluation and the urgent need to use the available gas resources economically and appropriately, by finding ways to make the production of other types of energy resources cheaper (nuclear plants, photovoltaics, wind turbines, etc.) as well as to forecast the quantities needed as accurately as possible. ii. the essence of forecasting methods the models created by all forecasting approaches for electric power demand predict the consumption for a given period, based on data for power consumption in previous periods. the forecast value is either a point or an interval, where the actual electrical load is most likely wrong. various methods use a variety of mathematical frameworks to make such forecasts, such as regression analysis [19-24], regression analysis, neural networks, and least square svms [25], regression analysis, decision tree, and neural networks [26], cluster analysis [27], fractional brownian motion [28], etc. a. classical regression analysis methods regression analysis is a time series approximation of points by a specific function, usually in the form of a polynomial. the accuracy of the approximation depends on the amount of input data and the order of the approximating function. therefore, a compromise must always be searched between the amount of engineering, technology & applied science research vol. 12, no. 2, 2022, 8374-8381 8376 www.etasr.com filipova-petrakieva & dochev: short-term forecasting of hourly electricity power demand input data and the order of the approximating polynomial. this study used the following two methods to perform short-term hourly electrical power demand forecasts based on regression models using the moving window and autoregressive integrated moving average (arima) methods. • moving window [22]: this method takes samples from the input data and applies a formula to calculate the forecast value. the moving window method is commonly used for solving practical problems. when working with averaged data, the resulting value is used as the predicted value. the accuracy of the method increases as the processed data increase. but this fact, on the other hand, increases the time to process the data until the final forecast is obtained. • arima [23, 24]: this method consists of introducing a distance between the data in the form of an error. this distance can be computed using the euclidean or another type of norm. the predicted quantity at a given moment is computed as a function of that quantity at previous moments and/or error values. b. cluster analysis methods for each studied time interval, the measured data of the hourly electrical power demand are obtained and form an acceptable range of variation. the accuracy of the synthesized model is tested by checking whether the actual electrical power load during the hour is between the predicted interval. if so, the method determines to which part of it falls into. • k-means [29, 30]: this is a very simple method, for simple applications, which converges relatively quickly. its main weakness is that it is not stable to statistical errors. on the other hand, there is a different result for each execution. some improvements of classic k-means were suggested in [31], by defining a hypercube of constraints for each centroid that acquires weights for each attribute of each class to use a weighted euclidean distance as a similarity criterion in the clustering procedure and thus reduce the limitation effects. • time series (ts) k-means [32]: this method uses dynamic time distortion and soft dynamic time distortion algorithms for distance calculation between the data, instead of the euclidean formula. this ensures higher forecast accuracy of the ts k-means algorithm but increases significantly the data processing time. • mini batch k-means [33]: this method was designed to process large data partitioned into clusters. its main advantage over k-means is the reduced time to partition the data into clusters, which is proportional to the size of the clusters formed. this is very important when processing the data from hourly electrical power demand measurements for a day. thus, 24 new values are processed each day. • agglomerative clustering [34, 35]: this method belongs to methods that use a hierarchical structure and is based on the so-called bottom-up approach. the algorithm supports an "active set" of clusters and decides which two clusters to merge at each stage. when two clusters are merged, the latter disappears from the set while the newly formed is added. this is repeated until all clusters are finally merged into a single. during the execution of the algorithm, a binary tree that accounts for the union of pairs of clusters is formed and called a dendrogram. in this method, the problem of defining the number of clusters is solved by design. there is no need to change the algorithm as new data come in, as in time series k-means and mini batch k-means. a basic problem in k-means forecasting is the problem of defining the number of clusters. this is not a problem when working with fixed data ranges, but when working with time series, updating the value for the number of clusters is required, and this is not an automatic process. agglomerative clustering solves this problem at the core of its design. • ordering points to identify the clustering structure (optics) [36, 37]: like mini batch k-means, this method is designed to process large data which can be fast changed and temporally ordered. this method is based on the density principle. the implemented algorithm (dbscan) searches for the point with the highest local density and forms a cluster around it. when the radius of a neighborhood change, the algorithm keeps the hierarchy of the clusters formed so far. optics has high classification accuracy and smaller error than the above-mentioned clustering methods. its main disadvantage is the slow performance due to large data processing. iii. analysis of the forecasts’ results this study examines the forecast models using data for electricity power demand (in mwh) on the territory of the republic of bulgaria. data were acquired from the bulgarian electricity system operator (eso) [38]. the analyzed period was from 1 january 2015 to 24 december 2020. the load was averaged for each hour of the investigated day. the forecast assessments were also performed hourly for each day in the period between 25 and 31 december 2020. the forecasts were compared with the actual hourly electrical power demand for this period. for simplicity, without losing generality, only the forecast results for the 21st (8-9 p.m.) hour of the prognosis days are provided. this interval was chosen as the electrical power load is at its highest, and its prediction is the most important. the application for making forecasts was written in python 3. two regression forecasting methods were used: regression with moving window and arima. the accuracy of the arima model is determined by the extended dickeyfuller rooting test [39] implemented using the statsmodels.tsa.stattools function [40]. this study used five cluster forecasting methods: k-means, time series k-means, mini batch k-means, agglomerative clustering, and optics. the quality of the clusters obtained by each method was evaluated by applying the silhouette method [41]. this method calculates the distances between individual points in a cluster, as well as the distances to points belonging to other clusters. this gives an idea of the density of the cluster and the fitting of each point to the others in the cluster. the forecasted electrical power demand results for the 21st hour of the day (8-9 p.m.) for the period 25th 31st december 2020 from each method used is shown in figures 2-8 in blue, while the actual electrical power load is marked in red. engineering, technology & applied science research vol. 12, no. 2, 2022, 8374-8381 8377 www.etasr.com filipova-petrakieva & dochev: short-term forecasting of hourly electricity power demand fig. 1. forecasts from moving window compared with real power load. fig. 2. forecasts from arima compared with real power load. fig. 3. forecasts from k-means compared with real power load. fig. 4. forecasts from ts k-means compared with real power load. fig. 5. forecasts from mini batch k-means compared with real power load. fig. 6. forecasts from agglomerative clustering compared with real power load. fig. 7. forecasts from optics compared with real power load. in both regression methods, moving window and arima, the actual electrical power consumption data are dispersed around the predicted ones determined by the corresponding approximating polynomial. therefore, the classical regression algorithms are quite inaccurate and do not follow the trend of the actual values as the cluster methods. this is because they provide point estimates of the forecasted values, while cluster algorithms provide ranges, defined by minimum, average, and maximum values. for the cluster methods, except for optics, the actual hourly electrical power demands are always less than the lower bound of the respective forecast variation ranges of the load. on the one hand, this is preferable because it introduces conservatism to the resulting estimates. on the other engineering, technology & applied science research vol. 12, no. 2, 2022, 8374-8381 8378 www.etasr.com filipova-petrakieva & dochev: short-term forecasting of hourly electricity power demand hand, it shows that the estimates given by the optics cluster method are the most accurate. mini batch k-means ranks right behind optics. its minimum forecasting assessments are the closest, mostly at the top and sometimes at the bottom, to the actual hourly power load. the ts k-means graphs are similar to the mini batch k-means, i.e. the actual hourly electrical power demands are quite close to the lower bound of the calculated range. these differences are slightly larger compared to those obtained with mini batch k-means. otherwise, they are all smaller than the corresponding differences estimated with the other clustering methods. the forecast ranges, determined by agglomerative clustering, are the most compact (short) in comparison to the other clustering methods. however, the actual hourly power load for the study period is much smaller than the minimum forecast value for each time zone considered. perhaps, with a larger input sample, the actual hourly electrical power demand would fall in those areas that are almost point-wise. then the forecast assessments in the agglomerative clustering method will be more accurate. the graphs in figures 2-8 show that the most inaccurate estimates were obtained by k-means and agglomerative clustering. they contained the greatest degree of conservatism on actual electrical power loads. this is not dangerous, as it leads to a surplus of produced electric power and the users' needs will always be met. the accuracy of each method, shown in figures 9-15, was calculated for each hour of the day based on the resulting 7-day forecast period. the most accurate forecasts were obtained by the optics method, closely followed by the mini batch kmeans. k-means and agglomerative clustering methods gave the most inaccurate prediction results. the largest error was seen in the estimate given by each method for the 7th hour of the day. the two methods using regression analysis gave similar accuracy results. for both methods, the most inaccurate estimate was for the 7th hour (0.22%), followed by about 0.5% for the 17th and 18th hours. the regression estimates were more accurate than k-means and agglomerative clustering, and they are comparable to ts k-means, and mini batch kmeans, but contain a larger degree of dispersion around the average value of 0.2%. last but not least, they are much less accurate than optics. fig. 8. accuracy of the moving window method. fig. 9. accuracy of the assessments obtained by the arima method. fig. 10. accuracy of the assessments obtained by the k-means method. fig. 11. accuracy of the assessments obtained by the ts k-means method. fig. 12. accuracy of the mini batch k-means method. engineering, technology & applied science research vol. 12, no. 2, 2022, 8374-8381 8379 www.etasr.com filipova-petrakieva & dochev: short-term forecasting of hourly electricity power demand fig. 13. accuracy of the assessments obtained by agglomerative clustering. fig. 14. accuracy of the assessments obtained by the optics method. the most accurate and compact was the optics method, varying in the interval [0%, 0.02%] coincident with the mean of the exact interval 0.01%. it was followed by the ts kmeans, whose range of variation of estimates was very narrow [0.18%, 0.2%] and the dominant error values were 0.19%. mini batch k-means was third in terms of compactness of the forecasting error. it also provided estimates with small variance (0.18%) around the average value, and the range of variation of the estimates was [0.9%, 1.3%]. the error graphs of k-means and agglomerative clustering were quite similar. in both cases, the largest error was observed in the prediction for the 7th (0.4% and 0.38%) and the 15th hour of the day (0.3% and 0.28%) for k-means and agglomerative clustering respectively. the execution time of ts k-means was worse by far in comparison to the other algorithms, although its performance is good enough for algorithms to be implemented and executed daily without compromising the process of forecasting. regression methods were less accurate than the cluster ones, except k-means and agglomerative clustering. another disadvantage is that they require a long time to train the models and a large amount of data to guarantee an adequate forecast, which is not typical for clustering methods. k-means and agglomerative clustering are in the last place in terms of forecasting accuracy, but their largest error is 0.38% and occurs only for one hour of the day, which is not fatal for short-term forecasts. in principle, the accuracy of the forecast results can be increased by increasing the amount of input data used to train each algorithm. however, data older than 10 years should not be utilized, as the influence of many economic, political, geographic, and other factors change the trend of the forecasts and cannot be reliable. iv. conclusion and future research although the delta between the minimum and maximum forecast cluster values is smaller for insufficient data input, the results showed a decrease in accuracy with the quantity of input data. as a greater number of input points was fed to the algorithms, the predicted outcome was not as precise but much more accurate. this study trained each method with data for 4 years, 1 year, and 4 months. one conclusion is that there is no real impact from feeding the algorithms with data larger than 1 year since the accuracy remains roughly the same, but the precision is harmed. using additional functions and methods to adjust the needs to the strengths of the algorithms may be a great advantage, as the clustering algorithms are not very well suited to forecast time-series data. however, using the right toolset could advantage the system to be applied to an environment that does not provide enough input data, where other algorithms may suffer from data scarcity. cluster methods' forecast results are much more accurate than those obtained by regression analysis methods. moreover, they require fewer time resources to process the input data to train the models and obtain the final predictions. the data used in the models synthesized in this paper to persform short-term forecasts of hourly electricity power demand on the territory of the republic of bulgaria are universal. they can be used to perform any kind of short-term hourly forecasts of arbitrary quantities. they were applied to this case because the authors had this kind of data to process. and they are only illustrative of their applicability. one 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[39] w. a. fuller, introduction to statistical time series. new york, ny, usa: john wiliey & sons, ltd, 1996. engineering, technology & applied science research vol. 12, no. 2, 2022, 8374-8381 8381 www.etasr.com filipova-petrakieva & dochev: short-term forecasting of hourly electricity power demand [40] statsmodels library api reference: statsmodels.tsa.stattools https://www.statsmodels.org/stable/generated/statsmodels.tsa.stattools.a dfuller.html [41] scikit-learn api reference: silhouette, scikit-learn. https://scikitlearn/stable/auto_examples/cluster/plot_kmeans_silhouette_analysis.htm l (accessed feb. 24, 2022). authors profile simona filipova-petrakieva was born in 1971 in sofia, bulgaria. she finished the secondary school of mathematics in sofia, bulgaria (1989). she received b.s. and m.s. in electronics and automatics from the technical university of sofia, bulgaria (1994), and acquired her ph.d. degree in electrical engineering, electronics and automatics, theory of electrical engineering in 2005. since 2009 she teaches as an associate professor in the department of theory of electrical engineering, faculty of automation, tu sofia, bulgaria. her research interests include theory of electrical engineering, cluster analysis, graph theory, interval methods for analysis and synthesis of linear circuits and systems, discrete event systems, discrete structures in mathematics, electrical power consumption, electric and hybrid vehicles. her teaching activities include courses of the theory of electrical engineering and discrete structures in mathematics. she is a regular member of ieee and in december 2021 she was invited to become a senior member. ventsislav dochev was born in pleven, bulgaria, (1999). he finished the vasil levski high school in troyan, bulgaria (2017). he received a b.s. in computer science from the technical university of sofia, bulgaria, (2021). he is currently studying for a m.s. degree in information retrieval and knowledge discovery at kliment ohridski sofia university. since 2018 he is working as a quality assurance team leader in a company developing camera software. his research interests include artificial inteligence, cluster analysis, knowlege extraction, applied mathematics and statistics. 1180-3817-1-pb.pdf engineering, technology & applied science research� vol. 7, no. 4, 2017, 1820-1825� ������ �� www.etasr.com azhari and mesbahi: safety index evaluation and calibration of load and resistance factors for … � ������� ���� �������� �� ������������ ���������� �� ������� ����������������� ������������� �������� ������� ����� ������������ �� � �������� ��!����� � � "����"#������ $�%����� ����������� �� ���� � �������������� �� � ������� "#���� �������� ���������� � �� � "&�#����'()*+�����&����� ,����������#��,�������� $�%����� ����������� �� ���� � �������������� �� � ������� "#���� �������� ���������� � �� �� ,��������#�+�����&���� � � abstract-�� � �� �������������� ������� ��������� ����� �� �� � � �� �� ��������� ��������������� ������ ��� ������������� � ����� ��� ���������� ����������� ������ ������ � ����� �������� ������ ��� �������� ��� �� �� � � ������ �� ��� �� �� ������� �� � � ������ ��� ��� � �������� �� � � �� ����� ��� ���������� ����� ������� � �� ����������� ������� ����� ���� �������!�� �� ������ ������� ��� ��� "��� ��� ����������� �� ����������������� � ��� ���� �� ��� �� ������� ��� ������� � � � � �� �� � � ����� ���� �� � �� �� � � ����� ����� � ��� ���� ���� ���� ���#$��� �� � ����� � ��������� ������������ ������������ ������� �� �������� $��� �� � ��������� ����� � ��� �� � � �� ������� ���� ��������� ���� �� ��� ��� � ������� �� ��� ���� ��������� %��� ����� ������ �� �� ����� �������������� ��� ��������� ������������� �������� � � � � �� ���� ���� ����� & ��������� � ������ ����� � ������ � ����� '����� � � ����� �(�� � ��������� � ������ ����� � ������ ���� ���� ������� �����'����� �� ����� �(������$���� �� �������� � � ���� ����� ����������������� �� �������)������������ ���������� � �������� � �� ������������� � � ����� ������� ���������� ������� ���� � ���� �������* ���������������������� ������ ��� ��������� ����� ����� ��� ������� ���� � ����� ��� ������ ����� ���� ��� � ��� � �� ����� �� � ���� ���� � ����� ����������� � ����� � �������� ������������� �� �������� �� � � �� ������������� ���� � keywords-reinforced concrete beam; reliability-based design; monte-carlo simulation; safety factor; load and resistance factors &� )&� .!�/$��! 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������������ �a��&�'( � .�&�)x' �%%&�;*6)(= �);;:� re tr ac te d microsoft word kute-ed.doc etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 359-362 359 www.etasr.com kute and kharat: analysis of quality of service for the aomdv routing protocol analysis of quality of service for the aomdv routing protocol vivek b. kute. comp. engg. deptt st. vincent pallotti college of engg & tech, nagpur, india vivek_kute@rediffmail.com m. u. kharat comp. engg deptt. met’s institute of engg, nashik, india mukharat@rediffmail.com abstract—due to the dynamic nature of mobile ad-hoc �etworks (ma�ets), the provision of quality of service (qos) guarantees is challenging. the route failure probability in a ma�et is increased due to the mobility of nodes, which increases routing overhead. multi-path routing protocols have relatively greater ability to reduce the routing overheads. this paper discuses the performance analysis of the ad-hoc on-demand multi-path distance vector (aomdv) routing protocol. aomdv is a multipath extension of a very well known single path routing protocol, (aodv). extensive simulations were carried out using ns-2.34 and the study concluded that for cbr traffic aomdv performance degrades as the data packet generation rate increases. keywords-ad-hoc; mobile; network; ma�et; aomdv; qos; i. introduction a mobile ad-hoc network is a self configuring network of mobile devices. the provision of quality of service (qos) guarantees is much more challenging in mobile ad-hoc networks (manets) than that of wire-line networks. this is mainly due to the mobile nature of manets’ nodes, and other characteristics of manets such as multi hop communication and lack of central coordination. therefore, designing a manet routing protocol that guarantees the desired qos is challenging. many routing protocols for manets have been proposed. depending on the time of route discovery manet routing protocols are divided into two categories; table-driven (proactive) routing protocol and on-demand (reactive) routing protocol. in table-driven routing protocols the routes are discovered and refreshed periodically. all routing related information is stored in routing tables at each node. whenever a traffic source needs a route, it uses the route available in the routing table. in contrast to this, the traffic source initiates route discovery process when it needs route in case of on-demand routing protocols. manet nodes are mobile and, hence, route failure probability is greater. the route discovery process has to start whenever a route fails. each route discovery flood is associated with significant latency and overhead. among the on-demand routing protocols, manet multipath routing protocols have relatively greater ability to reduce the route discovery frequency than manet single path routing protocols. on-demand multi-path routing protocols discover multiple paths between a source-destination pair, in a single route discovery. so a new discovery is needed only when all these paths fail. in contrast, a single path routing protocol has to invoke a new route discovery whenever the only path from source to destination fails. [1] the ad-hoc on-demand multi-path distance vector (aomdv) routing protocol is a multi-path extension of the ad-hoc on-demand distance vector (aodv) routing protocol. aomdv has three novel aspects compared to other on-demand multi-path routing protocols. firstly, it does not have internodal coordination overheads like some other protocols. secondly, it ensures disjoint ness of alternate routes via distributed computation without the use of source routing. thirdly, aomdv computes alternate paths with minimal additional overhead over aodv. it does this by exploiting as much as possible already available alternate path routing information [1]. in this paper we analyze the performance of the aomdv routing protocol with two different traffic types, cbr and tcp. the rest of this paper is organized as follows. in section 2 we discuss different qos issues for manets. we review the aomdv routing protocol in section 3. in section 4 we present performance evaluation of aomdv’s cbr and tcp traffic using network simulator-2. finally in section 5 we present the conclusion. ii. qos issues for manets multimedia applications often have stringent time and reliability-sensitive service requirements, which the network must cater to. networks are expected to provide guaranteed qos. the traditional best effort delivery network can not guarantee today’s requirements. the majority of the solutions proposed in manet have focused on the two metrics, throughput and delay. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 359-362 360 www.etasr.com kute and kharat: analysis of quality of service for the aomdv routing protocol providing better qos in manet is challenging due to the following issues: • node mobility: manet nodes move at will. this makes the topology dynamic. this means that topology information has a limited lifetime and must be updated frequently to allow data packets to be routed to their destinations. this updating means more routing overheads. also, due to the node mobility packet losses increase, the end to end delay gets also affected. • lack of central control: the principal advantage of manet is that it is deployed without planning in unknown terrains, hazardous conditions and its members can change dynamically. this makes it difficult to have any centralized control. hence the controlling activities will be distributed among the nodes, which require lot of information exchange. this also adds up to the routing overheads. [2, 3]. designing a routing protocol to meet these qos demands is challenging. in [4, 5] aodv routing protocol is analyzed for performance in the view of meeting different qos demands. in [2], it was shown that multi-path routing performs better than single path routing. it was also shown that aomdv offers a significant reduction in delay and routing load. the impact of traffic flow on energy consumption of aomdv compared with aodv is analyzed in [6]. the authors proposed load spreading on different paths, so that the load will be balanced in more paths resulting in energy preservation of nodes in the network. aodv and aomdv were compared in presence of selfish behaviors of nodes in [7]. it was shown that multi-path routing is better than single path routing in presence of selfish behavior. iii. aomdv routing protocol the basic idea behind multi-path routing is of finding multiple paths between a source and a destination. on-demand routing protocols for manets discover a route when a source needs to communicate with a destination. the multi-path routing protocol discovers multiple paths during the single route discovery process. these multiple paths can be used for load spreading or as backup routes when the primary route fails [2]. aomdv is a multi-path extension of aodv. in aodv when a source wants to communicate to a destination it initiates a route discovery process by flooding a route request (rreq) packet for destination through the network. duplicate rreqs are recognized, and discarded, using unique sequence numbers. an intermediate node, receiving a non-duplicate rreq packet, first sets up a reverse path to the source using the previous hop of the rreq as the next hop on the reverse path. if a valid route to the destination is available in its routing table, then the intermediate node generates a route reply (rrep) packet, otherwise the rreq is rebroadcast. when the destination receives a non-duplicate rreq, it also generates rrep. the rrep is routed back to the source via the reverse path. a node updates its routing information and propagates the rrep upon receiving further rreps only if a rrep contains either a larger destination sequence number (fresh) or a shorter route is found. like aodv, aomdv is based on distance vector concept and uses hop by hop routing approach. moreover, aomdv also finds routes on demand using a route discovery procedure. unlike aodv, aomdv finds multiple routes in a single route discovery procedure. in aodv all duplicate rreqs are discarded whereas aomdv look for an opportunity of getting an alternate route with each duplicate rreq. in aomdv, rreq propagation from the source towards the destination establishes multiple reverse paths both at intermediate nodes as well as the destination. multiple rreps traverse these reverse paths back, to form multiple forward paths to the destination at the source and intermediate nodes. aomdv also provides intermediate nodes with alternate paths as they are found to be useful in reducing route discovery frequency. the core of the aomdv protocol lies in ensuring that multiple paths discovered are loop free and disjoint; and in efficiently finding such paths using a flood-based route discovery. aomdv route update rules, applied locally at each node, play a key role in maintaining loop-freedom and disjoint-ness properties. [1, 811]. aomdv is usually compared with aodv. in this paper, aomdv performance is investigated with respect to cbr and tcp traffic. iv. simulation environment we used network simulator-2 (ns-2) version 2.34 [12] for the simulation and the 802.11 mac protocol for shared access to wireless channels. aomdv protocol is simulated with cbr and tcp traffic. the simulation parameters used are shown in table i. the size of the topology was set in a 1000x1000 grid. multiple sources and destinations were used. the traffic types analyzed are cbr and tcp. random waypoint mobility model is used for node mobility. packet transmission rate is modified. we have analyzed the performance of aomdv with cbr and tcp traffic types at different rate of packet transmission. also different numbers of sources and destinations are used. we used 100 nodes having 50 connections for both cbr and tcp traffic. the simulation run time was set to 200 s. data packet size was set to 512 bytes. we have measured the following: throughput, drop packet ratio (dpr), average delay (avg delay), route discovery frequency and routing overhead. v. result and analysis here we study the effect of data rate on the performance of aomdv. the mean node speed is kept to 5 and the number of connections to 50. the data packet generation rate is increased at each connection from 1 to 5 packets/s. for each packet rate the simulation is run for 200 s. figures 1 to 5 show the analysis of aomdv with respect to the packet rate. figures 6 to 8 give the analysis of aomdv traffic with respect to average delay. it is evident from the following graphs that aomdv performance degrades with the increase in packet rate. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 359-362 361 www.etasr.com kute and kharat: analysis of quality of service for the aomdv routing protocol throughput (kbps) 0 100 200 300 400 500 600 1 2 3 4 5 packet send rate (packets/s) t h ro u g h p u t (k b p s ) cbr tcp fig. 1. throughput vs. packet send rate dpr 0 10 20 30 40 50 60 70 1 2 3 4 5 packet send rate (packets/s) d p r cbr tcp fig. 2. dpr vs. packet send rate avg delay 0 500 1000 1500 2000 2500 1 2 3 4 5 packet send rate (packets/s) a v g d e la y ( m s ) cbr tcp fig. 3. avg delay vs. packet send rate route discovery frequency 0 1 2 3 4 5 1 2 3 4 5 packet send rate (packets/s) r td is f rq (/ s ) cbr tcp fig. 4. route discovery frequency vs. packet send rate routing overhead 0 200 400 600 800 1000 1 2 3 4 5 packet send rate (packes/s) r to v e rh d (p a c k e ts /s ) cbr tcp fig. 5. routing overhead vs. packet send rate thrput (kbps) vs avg delay (ms) 0 10 20 30 40 50 60 70 80 90 67.2 1010.13 1331.18 1240.61 2360.2 avg delay (ms) t h rp u t (k b p s ) fig. 6. throughput vs. avg delay dpr vs avg delay (ms) 0 10 20 30 40 50 60 70 67.2 1010.13 1331.18 1240.61 2360.2 avg delay (ms) d p r fig. 7. dpr vs. avg delay rt overhead (packets/s) vs avg delay (ms) 0 100 200 300 400 500 600 700 800 900 1000 67.2 1010.13 1331.18 1240.61 2360.2 avg delay (ms) r t o v e rh e a d ( p a c k e ts /s ) fig. 8. routing overhead vs avg delay etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 359-362 362 www.etasr.com kute and kharat: analysis of quality of service for the aomdv routing protocol table i. mulation parameters parameters values topology size 1000x1000 no. of nodes 100 no. of sources multiple no. of destinations multiple packet size 512 bytes mac protocol ieee 802.11 simulation time 200 s traffic types cbr/tcp simulation run 200 s for each packet rate vi. conclusion and future work in this paper we discus aomdv routing protocol, a multipath extension to aodv. we also discuss different qos issues for mobile ad hoc networks. we have analyzed different qos issues of aomdv with varying data packet generation rate. from the simulation results we concluded that with increase in packet rate aomdv performance degrades for cbr traffic whereas for tcp traffic it is consistent. in future work, aomdv will be analyzed with respect to the mean node speed, which is kept constant in this paper, and to the number of connections. references [1] m. k. marina, s. r. das, “ad hoc on-demand multipath distance vector routing”, wirel. commun. mob. comput., vol. 6, pp. 969-988, 2006 [2] v. c. patil, r. v. biradar, r. r. mudholkar, s. r. sawant, “on-demand multipath routing protocols for mobile ad hoc networks issues and comparison”, international journal of wireless communication and simulation, vol. 2, no 1, pp. 21-38, 2010 [3] l. hanzo ii, r. tafazolli, “a survey of qos routing solutions for mobile ad hoc networks”, ieee communications surveys & tutorials, vol. 9, no. 2, pp. 50-70, 2007 [4] y. lu, y. zhong, b. bhargava, “packet loss in mobile ad hoc networks”, technical report, dept. of comp. sci, purdue uni., tr 03009, 2003. [5] j. liu, f. li, “an improvement of aodv protocol based on reliable delivery in mobile ad hoc networks”, 5th international conference on information assurance and security, vol. 1, pp. 507-510, 2009 [6] s. malini, e. kannan, a. valarmathi, c. daniel sundar rajan, “traffic based energy consumption analysis of aomdv protocol in a mobile ad hoc network”, international journal of computer applications, vol. 14, no. 6, pp. 43-46, 2011 [7] a. r. sangi, j. liu, z. liu, “performance comparison of single and multi-path routing protocol in manet with selfish behaviours”, world academy of science, engineering and technology, vol. 41, pp. 828832, 2010 [8] m. k. marina, s. r. das, “on-demand multipath distance vector routing in ad hoc networks”, ieee 9th international conference on network protocols (icnp), vol. 1, pp. 14-23, 2001 [9] m. t. toussaint, “multipath routing in mobile ad hoc networks”, report, dtc. 5966 freeband/cactus project, 2003 [10] c. e. perkins, e. m. royer, “ad hoc on-demand distance vector routing”, ieee 2nd workshop on mobile computing systems and applications (wmcsa), vol. 1, pp. 90-100, 1999. [11] v. b. kute, m. u. kharat, “survey on qos for multi-path routing protocols in mobile ad-hoc networks”, 3rd international conference on machine learning and computing (icmlc 2011), vol. 4, pp. 524-528, 2011 [12] k. fall, k. varadhan, the ns manual, http://www.isi.edu/nsnam/ns/nsdocumentation.html, last accessed: jan 6, 2009 microsoft word etasr_v12_n3_pp8532-8541 engineering, technology & applied science research vol. 12, no. 3, 2022, 8532-8541 8532 www.etasr.com omari & bousnina: the iconic language in reading and interpretation of the cognitive map the iconic language in reading and interpretation of the cognitive map the case study of individual rural housing lemzara, setif assia omari mediterranean architecture research laboratory department of architecture ferhat abbas setif university 1 setif, algeria assia.omari@univ-setif.dz monia bousnina mediterranean architecture research laboratory department of architecture ferhat abbas setif university 1 setif, algeria mounia.bousnina@univ-setif.dz received: 26 february 2022 | revised: 20 march 2022 | accepted: 22 march 2022 abstractthe graphic representation of the "vision" of the land planner in identifying rural communities entails several cognitive mechanisms. this first step of establishing a basic degree of environmental awareness is critical. the assignment requires the capacity to embody a complex visual world and convey it graphically in a simple and illustrated manner. this article examines an intervention in a rural agglomeration's space. it is a set of ordered functions endowed with meaning. the article aims to scientifically explain the process of creating a participatory habitat and investigate the experience of the occupants by developing a scientific language with graphomotor capabilities around the concepts of vision, space, and representations. the method used is the collection and interpretation of twelve cognitive maps created by the designer and residents of douar lemzara, setif, algeria. the concepts and models of cognitive mapping point to the conclusion that the cognitive map is an effective method for reading the environment's actual information. cognitive map analysis enables a better understanding of the most prominent physical characteristics of urban areas. based on the analysis of respondents' cognitive maps, it is recommended to prioritize the treatment of algeria's urban environment and engage residents in land use and planning. this opportunity to investigate and approach cognitive representations of space represents a novel mode of investigation and enrichment of the toolkits of various stakeholders in space, as well as an opportunity to improve inhabitants' experience. keywords-vision; rural; mind map; inhabitant experience; cognitive mechanism; representation i. introduction the cognitive map has been defined as a collection of mental representations and ideas that are constructed in order to visualize and process data. mental maps and mind maps are used interchangeably. they are tools that enable strategists to transcend the limitations of short-term memory and analyze information over extended periods of time [1]. authors in [2] elaborated the explanation of cognitive maps: cognitive maps are mental representations of the world in which we live. human cognitive maps examine how individuals define their personal experiences and views, which determines their decision to live in and continue to live in certain locations [3]. in the same vein, authors in [4] have elaborated that the role of images in a metropolis's environment is meditative. a global image language establishes connections between the residents of new types of cities, as well as between words and physical elements. authors in [5] have advocated for the use of mental maps by architects and planners to gain a better understanding of the considerations that must be made before beginning to visualize a successful public space. they have further elaborated that the effectiveness of cognitive mapping will be determined by the users' involuntary association with the space. the positioning of blocks, the structure's significance, the degree to which it is used, the user interface, and natural factors all contribute to cognitive mapping. authors in [6] conducted a study in cognitive maps as correspondence associated with specific locations or spatial images that people have of their physical environment and that primarily influence spatial behavior. people's cognitive maps of a location form as a result of regular interactions with the neighborhood [3]. the experiences will result in the formation of memories and the development of conscious representations. each representation, experience, and memory is unique and specific to each individual in a variety of settings and circumstances [7]. the investigation of the encoded mental maps focuses on the cognitive representations of the rural agglomeration space. the cognitive representations of space are examined in their functional and social dimensions [8]. the experience of the constructor of the mental map of the physical location lends the map a metaphorical significance. thus, the mental map transforms into a cognitive map [9]. this step is critical for architects since it establishes the site's identity where environmental data are gathered, and post-sketch analysis is conducted. this is a challenging phase to analyze throughout the project design process, which the current study attempts to clarify via the development of an analytical grid. authors in [10] proposed to begin by reexamining the urban framework of the algerian cities and their evolution in response to the changing trade circumstances imposed by globalization, rather than just the metropolitan area. similarly, studies have been conducted to illustrate how visualization and simulation approaches might aid planners in maintaining urban areas [11]. corresponding author: assia omari engineering, technology & applied science research vol. 12, no. 3, 2022, 8532-8541 8533 www.etasr.com omari & bousnina: the iconic language in reading and interpretation of the cognitive map in this regard, the current study examines the methodology of using cognitive maps as an effective planning tool. the current research attempts to uncover information about the users' relationships with their surroundings via iconic language. specifically, it investigates the effect of affectivity and memory on the identification and orientation of locations and the mobility and imageability of belonging contexts. ii. methodology a. context of the study algerian public authorities sought to bring constructions into compliance, striking a balance between the interests of the residents and their demands for housing and the public interest in urban planning on economic, social, cultural, environmental, and aesthetic aspects [12]. accordingly, in 2000, the ministry of housing and spatial planning launched a program of "500 aided rural housing units" in the wilaya of setif, as a part of a process of "aid to the stone" recommended by algeria's housing policy (1 million aided social housing units). this initiative was designed for residents of rural agglomerations on the upper plateaus. one of these regions is the state of setif, which concretized a significant portion of the program by analyzing a sample of 150/500 rural housing units. the mental maps developed collaboratively by the operational actors, i.e. the urban subdivision's technical service, prospective buyers, and the architect in charge of the operation all contribute to making the position of each land base geographically recognizable and fully apparent. one hundred and fifty mental maps have replaced many site designs in the construction permit files. the corpus of the research was utilized to create a unique (personalized) scenario plan for each construction permit graphic file. the replacement of the project's scenario plan for the term and subsequently for the mental map legitimized the application for a construction permit and enabled the commencement of the complex process of "dwelling" as an existential position. this resulted in the automatic acquisition of a slew of rights, including financial assistance, access to the property, development of premises via various connections (gas, water, electricity, sanitation), and structuring of neighborhood facilities (schools, health care rooms, mosques, and administrative offices), among others, depending on the size and scope of the actions established. in situ, the real-size operation ensures new information in an environment, resulting in modifications in environmental knowledge [13]. this quantifiable knowledge is concerned with the collective memory of incidental information encountered along simulated routes and represented by cognitive maps [14]. the measures of knowledge are concerned with the accuracy of the route maps, the memory of scene displacement encountered along the simulated routes, the frames of reference or spatial references, and the coherences of these representations [15]. this operation aims to create innovative hypotheses about suburban and rural agglomerations on the outskirts of setif. by providing access to everyday requirements, public transportation contributes significantly to maintaining and boosting urban wellbeing [16]. hence, the bus shelters were examined more closely: their visibility, their usage, their usefulness, and their environmental importance were determined through the decoding and deciphering of a representation of the area in question [9]. additionally, this inquiry conjures the growth of individualism and the disintegration of a social framework as a result of the territory's expanding urbanization. the whole process is formalized and agreed upon in advance within the same group via the introduction of new forms of employment based on allocation in place of the family domain as a symbol of progress and modernity. this research opportunity necessitates a close examination of its substratum's social morphology and way of thinking via observation of its development and a realtime survey of its active region [17]. b. mental maps as a planning tool the use of field experiences in the professions responsible for urban morphology has nowadays become more than necessary. the focus is on maximizing the project's effect, not only of the project itself but also of the actions and procedures that resulted in it. consequently, tracing a collection of buildings is straightforward: all that is required is field surveys, rights-of-way mapping, or a topographic survey. however, comprehending the synergy of these buildings in terms of neighborhood unity, socio-spatial organization, or any behavior is quite different. this means that the architect or planner uses the location map or site plan to demonstrate the apparent spatial phenomena of location and the unseen features that underpin these visible spatial phenomena in structure and process. thus, cognitive mapping develops into a field for identifying the unseen mental map, which serves as a decisionsupport tool [15]. this analytical technique is based on a detailed understanding of the visual components of the mental maps that are the simpler to read, perceive, learn, and comprehend. it is primarily concerned with the shape and logic of the connections between its components. second, it delves into the logic and organizational mechanisms of the habitat in rural agglomerations by examining the residential space's physical configurations and social representations. c. purpose of the study the purpose of this study is to re-examine the questioning of orientation, followed by the taking of position and reconstruction of the inhabitant's reference markers in space, specifically, to understand how its cognitive representations are constructed through the query. as a result, the paper discusses how these sites were physically represented and how the urban subdivision's technician identified the establishment plates for rural residences. d. the sample of the study the following criteria were used to choose representative samples: the peri-urban region was chosen because the eastern portion of setif is experiencing significant changes in terms of expansion and urban growth. these changes entailed the assistance for housing development programs, the new city of ouled saber, and rural housing. the density of the mental maps located in the same place is another factor for selecting this setting. moreover, the location of the study has a unique geographical position in respect to the pairs setif constantine and setif batna. this is reflected in the mobility and growth polarity of the region in regard to road networks and mobility. engineering, technology & applied science research vol. 12, no. 3, 2022, 8532-8541 8534 www.etasr.com omari & bousnina: the iconic language in reading and interpretation of the cognitive map table i. encoding of 12 mental maps of lamzara city (office of architecture "carré d'art", 2002) code 01/c3 02/c3 03/c3 04/c3 m e n ta l m a p code 05/c3 06/c3 07/c3 08/c3 m e n ta l m a p code 09/c3 10/c3 11/c3 12/c3 m e n ta l m a p to develop the 150 files for rural housing purchase, building licenses were required. the project owners in many administrative districts (daira of guedjel, ouled saber, and setif) requested that the engineering offices (project managers) create requests in both graphic and textual form in order to generate the administrative file required to get the building permit. the decree of the building permit is critical in releasing the first tranche of financial assistance for the realization of the projects. this study opportunity was critical for the researchers since it allowed them to create meaningful syntheses of such operational experiences. the designers and residents collaborated to create scenario plans, which revealed previously unnoticed spatial features. these constructions disclose living areas that are unique to natural surroundings, as opposed to urban ones, while current urban planning tools such as the regional spatial planning scheme and the master plan of land use and urbanism analyze the situation of these rural agglomerations solely in terms of excess land reserves for city production or flows and economic exchanges. twelve mental maps are used in this context to address how the people of these rural agglomerations' living spaces are socio-spatially organized, and how the projection and localization of their future habitat facilitate access to their territory's "mental map" in terms of representation and social organization [6]. e. objectives the purpose of this strategy is to elicit common qualities among the mental maps gathered, as well as those that are unique to each person and those that form groupings. additionally, the following questions are tackled: engineering, technology & applied science research vol. 12, no. 3, 2022, 8532-8541 8535 www.etasr.com omari & bousnina: the iconic language in reading and interpretation of the cognitive map • is it required to build cognitive maps of a certain social group before developing development plans for the rural agglomerations in question? • can the mind map be used as a planning tool at the metadesign phase of development plans? the collection of 150 location graphics depicts skewed spatial maps of numerous rural villages. the fundamental objective is to determine the approximate location of evolving housing cells and to provide information about the spatial distribution of localized content [15]. this stage pertains to the research's mechanical component. it elucidates the fundamental properties of the spatialized experience by providing an explanation for phenomenological cognitive mapping study. for architects and urban planners, the map as an exploration and communication tool facilitates a better understanding of the space under consideration, "the agglomeration," and its conceptual meaning. as a result, it is necessary to assume responsibility for future expectations of occupants about the design and spatial development of their living surroundings. f. data collection the data collection phase has undergone several stages: the temporal encoding of the pre-project phase between 2000 and 2001 entailed the establishment of the cognitive maps. afterwards, from 2002 to 2003, the phase of submitting requests for building permits was formed of textual components and traditional documents, which include the scenario plan, the mass plan, numerous section plans, the elevations, and the details of execution. the data were collected from the architecture company "carré d'art's" written and digital archives between 2000-2005, the cadastre of setif, the regional spatial planning scheme and the master plan of land use. then, 35 mechta and douar locations were selected as representative samples of rural villages. twelve mental maps were collected and used as the primary tool for analysis and classification (table i). iii. methods of analysis a. classification of mental maps according to rob kitchin before analyzing the corpus of the study, it was necessary to conduct a classification of the corpus by relevance to the research issue: the geographical location of the agglomeration according to common or particular criteria. this categorization follows the logic of exploration and decoding, rather than just validating the accuracy of localization. in accordance, the current research deployed the approach of typological categorization of rob kitchin [18]. this method enabled the treatment and categorization of the corpus's numerous spatial representations according to their appearance and functional aspects. this classification technique analyzes and categorizes the various spatial representations found in the research corpus based on their apparent shapes. kitchin suggested the following classification of mental maps: • the fundamental method (free drawings without constraints). • the conventional method (focusing on specific aspects of an environment and the representation of certain elements). • the framed method (by proposing a background map or imposing a scale). • the transverse method (representing the evolution of the stages of successive representations). • the method of visual language. • the overlapping technique: verbal and pictorial information. b. rob kitchin technique using kitchin's technique, the mental maps were grouped according to the most effective and direct manner of easily locating intervention spots [18]. the traditional approach is focused on the unique characteristics of an area, and the depiction of certain features since the mind map incorporates both verbal and pictorial information (the cross technique). by combining the sensory input from the surroundings, the creator of each mind map created an ideal course of travel-oriented toward a goal or objective from a starting point. these data are filtered, consolidated, and sometimes forecasted. this structure is, in reality, a spatial encoding [14]. therefore, the identified and evaluated mental maps are functional representations of the geographical space. they are constructed by geographical experiences on two levels, one functional and one social [8]. it appears that these mental maps are primarily envisioned as information constructs. each map is a unique and single creation [19], created immediately in response to the specific location of the displacement and indirectly via a tailored translation of ambient spatial information. c. study of the shape of the mental maps 1) classification of the cognitive maps and the encoding of space various strategies have been deployed to read the mental maps to uncover cognitive representations of space, to decipher the hand drawings (mental maps of situations) in their iconographic forms and to arrive at a recognizable and collective level of scientific reading and interpretation through the analysis of shared and disparate features and the iconic message created by each of the analyzed maps. a) the technique of rothwell this approach allows the competency of the map designer to articulate his or her depiction of the place inside the metropolitan region to be evaluated [20]. the purpose is to orient oneself in sparse space using a spatial reference and to find and position the plot of the project land in respect to property boundaries and permanent landmarks to optimize the itinerary. this approach infuses the drawing with the dimension of mastery of spatial size and proportions. b) the technique of canter this is a technique that provides information about the shape and nature of spatial structures when selecting the land for the realization of a project by moving to the site with the future buyer and establishing the exact location of the project and determining the parcel's metric dimensions. by incorporating four cognitive tasks, this technique explains and engineering, technology & applied science research vol. 12, no. 3, 2022, 8532-8541 8536 www.etasr.com omari & bousnina: the iconic language in reading and interpretation of the cognitive map categorizes the phases of elaboration and generation of spatial mental maps [21]: • spatial orientation by the designation of geographic north. • the reduction of a large-scale extended space to the size of a white a4 sheet of paper. • the implementation of geometrical projections according to their organizational logic and the identification of components according to their perceptual appearance rank. • the portrayal of the mental picture's constituents symbolically and customarily. c) the technique of byrne this approach is founded on the premise that the outcome of the graphic output is contingent upon the designer's starting point for completing the work at hand and the desired outcome. additionally, the skills of the designer to project himself into geographical space and his mastery of measurement, scale, and plane geometry were considered. d) downs and stea technique as an analytical tool, it entails creating a correlation between the drawing (the freehand sketch) and the spatial representation: the result of the internalization of environmental information, its codifications, and externalizations [16]. this operation aims to communicate information about the project's location and status to the responder and interviewer by presenting technical expertise via standard visual language. e) cross reading through the different techniques the application and intersection of all of these methodologies resulted in cross-reading of the various maps of the lamzara area. this reading was carried out in order to extract as much useful information as possible from the majority of the representations to determine the common characteristics of this rural agglomeration. it is an activity for the expectations of a population while predicting its living environment. the purpose is to create an analytical grid that enables the maps to be classified and sub-groups using common criteria derived from the various research approaches outlined above and to determine the iconic message included within each mind map (table ii). iv. results and analysis a. the structure and the nature of the link between the mental maps according to table iii, about 80% of mental maps are on a territorial scale: (between batna, setif, and ras -el -maa) (n°01c3/03c3/04c3/05c3/06c3/07c3/08c3/09c3/09c3/10c 3/11c3), while 20% are on a more local scale: (guedjel centre, r'mada, and ras -el-ma (02c3 and 12c3). this demonstrates the critical nature of the regional size of the agglomeration. this territorial inscription is explained by the gravitational and boundary location of the agglomeration concerning the very active vehicle flow along the national road (nr) 75. this road axis becomes a structuring axis and a major reference for the entire population of lamzara, especially if the dwellings are located near this flow, implying the significance of the shape of the building, distance, course geometry, orientation, morphology, and time of exposure concerning the mobility and displacements in this environment [7]. this latter is constructed according to a perceptual logic, which results in the perception mechanism along a route. the quality of the connection is determined by this logic [14]. it is characterized by the existence or absence of relationships between closed and open geometric shapes and the rest of the natural world. thus, the legibility of the environment contributes to the accessibility and location of goals through a clear view and route across a loosely constructed framework. this clarity results from the inherent simplicity of interactions and the nature of the connections between the built and unbuilt areas. b. spatial and social representations the examined mental maps exhibit several typologies. they are classified according to the routes and geometrical structure of spatial representations and the functional quality of the connections that constitute social representations. the aim of the cognitive maps is to represent beliefs about the relationship between concepts [13]. in contrast, the analysis of the mental maps (table ii) reveals the presence of an iconic message that facilitates the location of intervention sites and provides information about the degree of mastery of knowledge about the perceived physical environment and its associated social behavioral practices. the resultant picture of the lamzara agglomeration is a fluid region with a high level of daily mobility inside the territorial geographical unit. the latter is traversed by nr 75, which facilitates heavy road traffic which, due to its regularity, divides the area into two entities: lamzara east and lamzara west. the repeated appearance of schools, mosques, and bus stops in all mental maps indicates the presence of a cognitivebehavioral routine [22], which is detected using an indirect technique that calculates the frequency of appearance of elements associated with the target (the housing project) in the study corpus. the social practice of neighborhood equipment contributes to the intelligibility of the agglomeration. it has been observed that the route diagram evolves in response to "directed navigation" [16], with the ultimate objective of sketching a clear ideal path for the location of the project. the examination of the graphic criteria found in a sample of lamzara's rural settlements, namely orientation, lines, surfaces, shapes and symbols and their linkages has revealed the significance of each graphic criterion category to its analogical spatial counterpart. each mental map is composed of graphic elements that form the basis for the construction of meaning by their configuration and disposition. the presence of similar meanings in the bulk of the lamzara sample is due to the environment itself but to the representations of the social group that developed them just by encompassing a shared culture and environment over a certain period [23]. engineering, technology & applied science research vol. 12, no. 3, 2022, 8532-8541 8537 www.etasr.com omari & bousnina: the iconic language in reading and interpretation of the cognitive map table ii. structuring of the iconic message of the mental maps of the lamzara agglomeration reading the shape of the mental maps using the cross method spatial unit: lemzara agglomeration c3 category of graphic criteria iconic message, downs and stea index: environment not known. known environment, but not mastered known and mastered environment orientation, rothwell and canter index: geographic north in the direction of the sheet a4 and the writing. spatial scale ratio by rothwell and byrne index: local /territorial/ communal /interwilaya in relation to the a4 sheet symbols and transcriptions, canter's index: line, curve, polygon, surface, signs, words, toponyms, the path. byrne's index : (the link or junction) perceptual logic according to the target: focal, direct, indirect, hierarchical. map 01c3 arrow to the right from batna to setif centre /a4 inter-wilaya 6 lines 7 polygons 9 words indirect hierarchical known environment, but not mastered map 02c3 arrow to the right center of guedjel and r'mada/a4 inter -communale 2 lines 15 polygons 6 curves 16 words direct known environment, but not mastered map 03c3 arrow to the left from setif centre to batna/a4 inter-wilaya 6 lines 6 curves 9 polygons 1 ovoid surfaces indirect hierarchical known environment, but not mastered map 04c3 arrow to the right from setif centre to batna/a4 inter-wilaya 2 lines 1 curve 6 polygons 1 cross direct known environment, but not mastered map 05c3 arrow to the right from batna to setif centre /a4 inter-wilaya 8 lines 5 polygons 1 circle direct known environment, but not mastered map 06c3 arrow to the right from batna to setif centre /a4 inter-wilaya 8 lines 2 curves 9 polygons 1 cross indirect known and mastered environment map 07c3 arrow to the right from setif centre to batna/a4 inter-wilaya 2 lines 1 surface 6 polygons no junction registered known and mastered environment map 08c3 arrow to the left from setif centre to batna/a4 inter-wilaya 7 lines multi curve 4 polygons indirect hierarchical known environment, but not mastered map 09c3 arrow to the right from setif centre to batna/a4 inter-wilaya 7 lines multi curve 4 polygons indirect hierarchical known environment, but not mastered map 10c3 arrow upwards from setif centre to batna/a4 inter-wilaya 2 lines 5 polygons no junction registered known environment, but not mastered map 11c3 arrow to the right from batna to setif centre /a4 inter-wilaya bipolar 19 lines 2 curves 9 polygons direct known and mastered environment map 12c3 arrow to the left multipolar : batna /setif /ras el maa 8 lines 1 cross 5 polygons direct known and mastered environment significance nr 75 is an axis of geographical orientation and divides the agglomeration into right and left parts, and gives importance to residential mobility the importance of territorial registration of the agglomeration is due to its gravitational position in relation to the nr 75. the morphology of the urban fabric is easily apprehended due to the clarity of the visibility of the spatial referents of the perceived environment. the legibility and intelligibility of the space participates in the accessibility and the location of the targets following the clarity of vision and path through the loose built framework. this clarity is due to the simplicity of the relations and the nature of the legible links between the built and the unbuilt environment. the representation of the lamzara agglomeration is strongly known and mildly mastered due to the presence of a simple and explicit structural logic. this controlled environmental knowledge is reflected in the majority of the cognitive maps. engineering, technology & applied science research vol. 12, no. 3, 2022, 8532-8541 8538 www.etasr.com omari & bousnina: the iconic language in reading and interpretation of the cognitive map table iii. synthesis of the reading of the mental maps rothwell and canter index rothwell and byrne index symbols and transcriptions, canter's index byrne's index iconic message, downs and stea index l e ft r ig h t u p w a r d local territorial closed built open, not built direct link indirect link no junction known and mastered known and not mastered not known and not mastered synthesis of the 12 mental maps of lamzara 2 9 1 02 10 25% 75% 06 04 02 04 08 00 table iv. information construction and production of meaning maps iconic message spatial representation social representation 01c3/02c3/03c3/ 04c3//05c3/08c3/ 09c3/10c3 known and mastered environment -the legibility of the paths is materialized by the presence of geometric links between the closed structures (polygons and spots) and the open structures (points and lines). -the links in the majority of the maps are direct, indirect or combined (hierarchical, in the form of loops, branches, ramified). -the maps in this case become illustrated maps thus rich in information. they become cognitive maps. -the existence of several levels of construction in the same map reflects the graphic ability of the constructor or draftsman to elucidate a complex environmental reality in a simple and understandable iconic message. the representation of the lamzara agglomeration is strongly mastered as a result of the presence of a simple and explicit structural logic. this mastered environmental knowledge is reflected in the majority of the cognitive maps (85%). the inhabitants of lamzara consider the nr 75 as a major spatial reference and give it socio-economic importance because this axis raises the rank of this small village to that of a structured and compact village agglomeration by the introduction of the semidetached along the nr 75 axis. this situation introduces the notion of street in a rural environment with sparse morphology. -the proximity of the nr 75 is for the agglomeration of lamzara a lever and gives potentiality for future development. 11c3/12c3/07c3 known and not mastered environment -ambiguity of pathways: absence of links between closed and open structures. -they are deduced maps or simple constructions by linking to one or two spatial referents at most, making a total abstraction of the rest of the environment. -they are generally maps of clear and recognizable geographical location. the consideration of a smaller scale and the disparity with the rest of the agglomeration is mainly due to the clarity of the situation and its location by the majority of residents and visitors of lamzara. c. examination of the morphic structure of the mental map 1) techniques used to study the morphic structure the morphic structure analysis approach was utilized in the context of a ph.d. dissertation and offered the identification of a typology of place morphic structures via the reading of developing representative cognitive maps [24]. this analytical method is a necessary basis to comprehend the logic and structure of the complete system portrayed and examined. 2) morphic structures of mental maps this categorization aims to denote the various morphic structures inside the researched agglomeration using lamzara's 12 maps. the cognitive maps are provided as typological structures. table v identifies two prominent morphological structures: structure resembling an itinerary and structure resembling axiality. this demonstrates the focus of the designers on mobility and spatial navigation inside the lamzara agglomeration region. throughout the diagram's creation and examination, the 12 mental maps interact with their environment. the findings indicate the presence of two prominent morphological patterns in the form of routes and axiality. as observed, 80% of the analyzed maps are sequential, indicating the agglomeration's importance for mobility. they establish causation between the nr 75 and the project by using the locative verbs find oneself, locate oneself, and position oneself in connection to the nr 75. the quality and quantity of features in the mental maps are also very informative in terms of transferring information on the morphic arrangement and structure of the various paths. consider the following behavioral routine [21]: the map 06c3 informs of an alternate route for the target's localization in order to minimize the error factor and accessibility time. the map implicitly implies the person who constructed it and the person who transmitted the information in the route to be borrowed, which is a matter of behavioral routines. as a result, it may be concluded that each diagram or mind map formed linkages between the designer's memories, the environment's facts, and the conducted interviews with the occupants. d. coherence measures for spatial representations the correspondence approach entails retracing the routes, finding reference points, assessing the physical legibility of space (the quality of the forms), and presenting them with a novel experience. this may be accomplished in situ via the researchers' comments or photos or through the use of an aerial engineering, technology & applied science research vol. 12, no. 3, 2022, 8532-8541 8539 www.etasr.com omari & bousnina: the iconic language in reading and interpretation of the cognitive map snapshot of the location (as is the case in this study). the purpose of this approach is to highlight the distinction between perception and representation of measurable geometric space and assess the degree of similarity between the mental map and geographic reality. the approach enabled the assertion of the constructor of the cognitive map's degree of expertise and his capacity to embody and visually portray the experienced world at a reduced size. this approach allows the precise assessment of the degree of similarity between the picture viewed and perceived with the associated mental map. table v. typologies of the structures of the spatial representation and configuration of cognitive morphic structures of lemzara [24] configuration of morphic structures [24] s1 s2 s3 s4 s5 s6 s7 s8 s9 structure in the form of a route structure in the form of axiality structure in the form of a cross structure in the form of a double crossing structure in the combined form of centrality and axiality structure as a sequential plan structure in the form of topological centrality structure in the form of a spot structure as a fragment sequential maps spatiale maps typology of spatial categories 1 2 3 4 5 6 7 8 9 map name 05c3 12c3 07c3 xxx xxx 03c3 02c3 09c3 xx x 11c3 04c3 08c3 xxx xxx 01c3 06c3 10c3 x xx 12 9 6 / / / 2 / 1 / (a) (b) (c) (d) fig. 1. application of the technique of [25] in the calculation of spatial regression-map 02/c3: (a) digital mind map: superimposition of the digitized mental map on a grid representing a spatial unit, (b) aerial view (google maps): overlay of the geographic image g on a grid representing a spatial unit, (c) the superposition of a on b perception by correspondences, (d) the spatial regression percentage rate of accuracy: by triangulation, the degree of similarity between the geographical reality and the mental representation is close to 70% of the general criteria. the approach in [25] entails superimposing the scaled planar representations on the same reference frame, with a minimum of 3 reference points. this approach was applied on a small sample (1 map), since most of the assessed maps are sequential maps showing the agglomeration's relevance for movement (figure 1). this map will be used as a starting point for analysis to simulate constructing a cognitive location model in rural areas. the purpose of this analysis is to develop a cognitive reading tool for spatial regressions and to calculate the rates of accuracy for correspondences in terms of closeness or distance between cognitive distances. the processing of the cognitive picture enabled the quantification of the variations between the two locations for each constituent while also emphasizing the individual variances. consequently, it is possible to differentiate between distortion and coherence in the cognitive image, which is unavoidably wrong beforehand. spatial distortion, therefore, indicates abnormalities in the cognitive representations of space that are inaccurate. this is why freehand sketching techniques and concurrent consideration of the direction and distance between parts are of paramount importance. v. discussion various evaluations of cognitive maps using different techniques reveal that their schematic consistency is saturated with particular knowledge and data. the analysis and collection of mental representations through schematic data connected with items and their physical reality counterparts provides a valuable tool to access valuable information. these data cannot function independently of their socio-spatial environments because each of them emits one or more iconic messages. the purpose of the iconic messages in this study is to develop a grid for deciphering and analyzing spatial representations by starting with the individuals' graphic productions or mental maps. consequently, the data creation process enables the establishment of a conductive environment for initiating the design process. this relates to the conceptual idea phase for architects and to the stage of gathering and organizing data that enables the development of a scenario, including the stretching engineering, technology & applied science research vol. 12, no. 3, 2022, 8532-8541 8540 www.etasr.com omari & bousnina: the iconic language in reading and interpretation of the cognitive map or tightening of urbanistic logic for urban planners. the phase of data creation is critical for interpreting and comprehending the underlying structures of mental maps. this stage entails drawing paths for the tool's successful engagement in architecture, urbanism, and territorial planning at the appropriate scale. the purpose is to create new methods to search for design tools at various architectural, urban, and even territorial sizes that are vision-based and allow for the establishment of linkages between environmental data, the designer's memory, and the client's needs. vi. conclusion the purpose of this research is to examine the mental map as a tool for efficient urban planning. individuals design their own maps using this approach, based on a series of questions on orientation, lines, surfaces, forms, and symbols. the cognitive representations of space are examined in their functional and social dimensions. in accordance, the current research deployed the approach of typological categorization of [18]. this strategy allowed for the treatment and classification of the various spatial representations of the corpus on the basis of their appearance and function. four different methods for examining and classifying mental maps were utilized to analyze and interpret these maps. additionally, the morphic structure of the mental representations was deployed to comprehend the logic and structure of the complete portrayed and examined system. additionally, the coherence structure of the mental maps was examined to emphasize the distinction between perception and representation of quantifiable geometric space and allowed the assessment of the degree of resemblance between the mental map and the geographic reality. to increase the collective representation of space, the most frequently used technique is freehand drawing or graphic production of a vision of a physical environment saturated with social significance synthesized on external support, typically a white a4 sheet of paper. the advantage of this technique is that it is adaptable and usable in a variety of contexts. the mental map transmits a structured message and is necessary for architectural projection and urban planning. however, the accuracy of the physical information is secondary to its cognitive capacity, which reflects other structures in the interpretation of socio-spatial representations beyond physical reality. this study attempted to elevate the image and its associated iconic language. the cognitive picture of space representation in rural and sparse settings is primarily a decision support tool for spatial concerns, such as housing programming and planning. as a result, it is greatly influenced by the interaction of the individual with the environment, and it serves as a valuable indication of this relationship throughout the inhabitant's experiences with the rural housing program's implementation. throughout the research, various strategies were used to elicit patterns of cognition and orientation in the geographical environment of the individual in connection to his group of belonging and his residential trajectory. this has allowed for an understanding of the integration process of the individual (beneficiary) and his role in establishing his own space within his constrained social group and geographical and territorial surroundings. this is true from the procedural step of site selection through the reconfiguration of wthat was originally offered as an evolving template for rural-dwelling units. this experience allowed a deeper understanding of the environmental knowledge and its configurations by collecting a diverse range of data that allows the simultaneous collection of physical components and social representations. it was discovered that the names and rankings assigned to this information throughout the map's development and their spatial relationships affect the overall spatial structure that creates them. environmental information has been supported, including physical visibility of the environment, subjective accessibility to locations, cognitive hurdles, activity and daily mobility, location choices, residential strategies, and perceived suburban polarity. at the same time, it externalizes social representations, allowing the social legibility of the studied environment, the affective appropriation of places and physical elements, and social relationships within the space. in this situation, the map takes on the role of an exploratory research tool. it can be used to assess the impact of integrating the same rural housing prototype through a variety of different configurations of interior and exterior land bases within preexisting urbanisable perimeters on its current and future morphological evolution and within its anchorage location and immediate environment. acknowledgment the authors are grateful to the mediterranean architecture research laboratory for their contribution in the current research. references [1] t. sammut-bonnici and j. mcgee, "cognitive map," in wiley encyclopedia of management, new york, ny, usa: john wiley & sons, 2015, pp. 1–3. 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[26] a. byrne, perception and conceptual content. cambridge, ma, usa: mit press, 2005. microsoft word etasr_v13_n2_pp10501-10504 engineering, technology & applied science research vol. 13, no. 2, 2023, 10501-10504 10501 www.etasr.com ramdani et al.: the effects of resistance spot welding parameters on the mechanical behavior of … the effects of resistance spot welding parameters on the mechanical behavior of stainless steel mohammed ramdani ingeniery of mechanical systems and materials laboratory (is2m), university of tlemcen, algeria r2006amdani@yahoo.fr mustapha benachour ingeniery of mechanical systems and materials laboratory (is2m), university of tlemcen, algeria bmf_12002@yahoo.fr (corresponding author) mohammed rahou higher school of applied sciences of tlemcen, algeria | ingeniery of mechanical systems and materials laboratory (is2m), university of tlemcen, algeria am_rahou@yahoo.fr received: 18 january 2023 | revised: 6 february 2023 | accepted: 16 february 2023 abstract the resistance spot welding process is a promising method for welding thin sheets of similar and dissimilar materials, principally stainless steel. resistance spot welding is ensured using the combined effect of mechanical pressure and electric current through the thin sheets. in this experimental study, 304l stainless steel sheets were welded by resistance spot welding at various welding parameters. the welding parameters were welding effort, welding time, and welding current. welding current varied from 10ka to 16ka, welding time varied from 10 to 13 cycles, and welding effort was fixed to 8 bars. the results showed that welding time had little effect on the mechanical properties compared to the welding current. the experimental results also showed that welding current is an important parameter for joining sheets and their mechanical strength. the external aspects of the spots were examined to determine the influence of welding parameters on the welded joints. keywords-rsw; welding parameters; welding current; mechanical strength; stainless steel 304l i. introduction the resistance spot welding (rsw) process is widely used in the manufacturing industry for joining metal sheets. spot welding is the predominant joining process in several industries, especially in assembling automobile components. however, other products such as aerospace, furniture, and domestic equipment are joined using rsw [1]. rsw is one of the primary methods to join sheet metals on automotive components [2]. stainless steel sheets are increasingly used in several applications due to their high corrosion resistance and good weldability [3]. the rsw process can be described by many parameters, such as time, current, and welding effort. welding current is the most effective and common parameter to influence the welding result of a given material configuration. welding time is important when calculating heat generation and resulting welds formation. additionally, the force magnitude is another variable that affects the outcome of the weld. many rsw studies showed that the formation of nuggets in any welded material depends on the optimized combination of parameters [4-7]. weld quality is affected by several welding parameters: current intensity, welding time, force applied by the electrodes, contact resistance, and electrode size [8]. in [7], the effect of current and weld time with constant force on nugget growth was investigated in 304 austenitic stainless steel rsw. in [9], an attempt was made to optimize the welding parameters, namely welding current and time, in the rsw of aisi 316l austenitic stainless steel sheets. the static tensile shear test is the most common laboratory test used in the determination of weld strength due to its simplicity [10]. in [11-12], the most important factor affecting the tensile shear load-bearing capacity was the size of the weld nugget, as it depended mostly on the weldin engineering, technology & applied science research vol. 13, no. 2, 2023, 10501-10504 10502 www.etasr.com ramdani et al.: the effects of resistance spot welding parameters on the mechanical behavior of … g current. the effect of welding current at constant welding time is considered in the evaluation of nugget size and tensileshear load-bearing capacity of jointed materials. the influence of the rsw process parameters on 316 stainless steel was studied in [13]. the effects of welding parameters on the tensile shear strength of the joints were investigated in [14]. the effect of 3-9ka welding current on the structure and mechanical properties of welded joints was investigated in [5] for stainless and low-carbon steel. an increase in the tensile strength of the weld coupon was noticed when the welding current increased. otherwise, the variation in welding current had no significant effect on the hardness value, as it mainly affected the size of the fusion zone and the heat-affected zone. in [15], the resistance of 304 stainless steel plates assembled by rsw was studied, along with the formation of nuggets under the effect of welding parameters in a dp600 dual-phase steel. in [16], the relations between nugget diameter and welding current and hardness along the welding zone of austenitic stainless steel 304 were studied. the results showed that the weld nugget increased with increasing welding current. in [17], assembled aisi-1008 steel sheets were welded by rsw, showing that the welding current was the most effective parameter controlling the weld tensile strength and the nugget diameter. in [18], weld current was the major governing factor affecting the tensile shear strength of resistance spot welded specimens in dissimilar joints formed by stainless steel 304 and galvanized steel, as it presented a high percentage compared to welding time and force. in [19-20], it was shown that using a high welding current, the material can exhibit high mechanical properties, and the tensile shear load-bearing capacity increased as the welding current increased. this paper presents an experimental study to determine the effect of rsw parameters on tensile-shear strength of homogeneous lap joints in stainless steel 304l with a thickness of 2mm and the geometric aspect of the welded points under the variation of welding current and time. ii. experimental procedure this study used 304l stainless steel sheets with a thickness of 2.0mm. tables i and ii show its chemical composition and mechanical properties, respectively. table i. chemical composition of 304l c si mn p s cr ni < 0.03 < 1.00 < 2.00 < 0.045 < 0.015 17.5-19.5 8-10 table ii. mechanical characteristics of 304l e (gpa) e (mpa) uts (mpa) a% hrb provider data 200 310 520-670 45 80 max tested specimens 190 336 655 43.2 60 figure 1 shows the stress-strain curve of 304l stainless steel, and figure 2 shows the shape of the specimens, which were prepared with a size of 115×20×2mm. the overlap dimension a was equal to 20mm. the spot welding machine aro fix type mc was used to join the overlapped samples. the settings of the rsw parameters directly depend on the application and are usually determined by testing. the welding parameters used in this study were the recommended for 304l stainless steel; welding current varied from 10 to 16ka, welding time varied from 11 to 13 cycles, and the applied electrode force was equal to 8 bars with a diameter equal to 6mm. fig. 1. stress-strain curve of 304l stainlees steel. fig. 2. welding specimen by rsw. iii. results and discussion based on tensile shear tests, this study evaluated the maximum tensile shear force value for the joint that allows a fracture to occur [21]. moreover, the diameter’s dimension and the depth of spot welded points were determined under varying welding parameters. figure 3 shows the load versus displacement curves obtained from the tensile-shear test performed on specimens with acceptable rsw joints under varying welding currents and time. figure 3 shows the variation of the load versus the displacement until the fracture of the welded assembly by rsw for 8 bar welding force at t=11 cycles. the increase in current intensity increased the area of plastic deformation. this figure highlights several points by type. points a present little distorted points. at points b, rotation occurred to align the sheets in the direction of loading and necking starts. points c show the maximum breaking loads. points d show the maximum effort achieved when the fracture propagated across the thickness in the neck region of one of the sheets, the propagation of the fracture in the base metal, and the tear around the point of the specimen to the final fracture. figure 4 shows the effect of welding current and welding time on the maximum breaking load (points c) for 8 bar welding force. welding current varied from 11 to 16ka, and the time ranged from 11 to 13 cycles. the appearance shows an engineering, technology & applied science research vol. 13, no. 2, 2023, 10501-10504 10503 www.etasr.com ramdani et al.: the effects of resistance spot welding parameters on the mechanical behavior of … increase in maximum tensile shear load bearing when increasing the welding current. statistical tests are necessary on the fracture surfaces to better understand some interactions of welding parameters and random phenomena. in addition, the medium effect of welding time was noticed and the differences in the maximum tensile shear load-bearing for all welding currents varied from 0.18 to 2kn. fig. 3. effect of welding current on the mechanical behavior of the welded assembly by rsw at 8 bar welding force and 10 cycles welding time. fig. 4. effect of welding current and welding time on maximum tensile shear load bearing for welding force f=8 bar. figure 5 shows the effect of the welding current on the external diameter of the rsw point. an increase in weld current increases the external diameter of rsw for all welding times. for all welding currents and times, the maximum difference of the external diameter was 0.4mm, observed at welding current i=11ka, while the minimum was observed at i=16ka. this result shows that the effect of welding time is very small. figure 6 shows the effect of welding current and welding time. a minimum depth, equal to 0.6mm, was produced at i=10kn and t=12 cycles, and the maximum depth of 1.12mm was produced at 13 cycles. this graph shows a random effect. statistical analysis is required to investigate the effect of welding parameters on the geometric parameters of rsw. figure 7 shows the fracture of welded 304l steel sheets plate by rsw under tension/shear loads. the fracture was initiated in the heated affected zone and propagated in the base metal. this propagation was made according to the mode i of fracture. fig. 5. effect of welding current and welding time on the external diameter of rsw for welding force f=8 bar. fig. 6. effect of welding current on maximum tensile shear load bearing for welding force f=8 bar. (a) (b) (c) fig. 7. effect of welding parameters on the fracture modes in rsw for applied load f= 8 bar: (a) i=10ka, t=10 cycles, (b) i=10ka, t=11 cycles, and (c) i=10ka, t=13 cycles. iv. conclusion an rsw process was applied on 304l stainless steel to experimentally investigate the external parameters of the rsw joints and the maximum tensile shear load bearing of the joints. furthermore, the influence of welding parameters, including welding current and welding time at fixed welding force, on the engineering, technology & applied science research vol. 13, no. 2, 2023, 10501-10504 10504 www.etasr.com ramdani et al.: the effects of resistance spot welding parameters on the mechanical behavior of … maximum tensile shear load bearing of the joints was studied using a factorial test. the conclusions deduced from this study are summarized as follows:  the diameters of the rsw joints increased with increasing welding current and time.  welding time has a medium effect on the external diameter and the depth of rsw.  an increase in welding current allows the increasing the depth of rsw.  tensile/shear tests show that the welding current is the dominant parameter in the evolution of the load/displacement curves.  increasing welding intensity increases the plastic deformation zone and the maximum tensile shear load bearing of joints. references [1] d. tanmoy, "resistance spot welding: principles and its applications," in engineering principles, k. o. cooke and r. c. cozza, eds. london, uk: intechopen, 2022. 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[18] f. ternane, m. benachour, f. sebaa, and n. benachour, "regression modeling and process analysis of resistance spot welding on dissimilar steel sheets," engineering, technology & applied science research, vol. 12, no. 4, pp. 8896–8900, aug. 2022, https://doi.org/10.48084/etasr.5059. [19] a. alzahougi, m. elitas, and b. demir, "rsw junctions of advanced automotive sheet steel by using different electrode pressures," engineering, technology & applied science research, vol. 8, no. 5, pp. 3492–3495, oct. 2018, https://doi.org/10.48084/etasr.2342. [20] m. elitas and b. demir, "the effects of the welding parameters on tensile properties of rsw junctions of dp1000 sheet steel," engineering, technology & applied science research, vol. 8, no. 4, pp. 3116–3120, aug. 2018, https://doi.org/10.48084/etasr.2115. [21] s. kim, i. hwang, m. kang, j. park, and j. yu, "prediction of indentation depth of resistance spot welding using electrode displacement signal," journal of welding and joining, vol. 39, no. 3, pp. 314–322, jun. 2021, https://doi.org/10.5781/jwj.2021.39.3.10. engineering, technology & applied science research vol. 8, no. 1, 2017, 2621-2626 2621 www.etasr.com behrens et al.: developing an algorithm to consider mutliple demand response objectives: applying … perspectives developing an algorithm to consider mutliple demand response objectives applying an algorithm engineering-oriented approach for the residential context dennis behrens dpt of information systems and enterprise modelling university of hildesheim hildesheim, germany dennis.behrens@uni-hildesheim.de thorsten schoormann dpt of information systems and enterprise modelling university of hildesheim hildesheim, germany thorsten.schoormann@unihildesheim.de ralf knackstedt dpt of information systems and enterprise modelling university of hildesheim hildesheim, germany ralf.knackstedt@uni-hildesheim.de abstract—due to technological improvement and changing environment, energy grids face various challenges, which, for example, deal with integrating new appliances such as electric vehicles and photovoltaic. managing such grids has become increasingly important for research and practice, since, for example, grid reliability and cost benefits are endangered. demand response (dr) is one possibility to contribute to this crucial task by shifting and managing energy loads in particular. realizing dr thereby can address multiple objectives (such as cost savings, peak load reduction and flattening the load profile) to obtain various goals. however, current research lacks algorithms that address multiple dr objectives sufficiently. this paper aims to design a multi-objective dr optimization algorithm and to purpose a solution strategy. we therefore first investigate the research field and existing solutions, and then design an algorithm suitable for taking multiple objectives into account. the algorithm has a predictable runtime and guarantees termination. keywords-optimization; demand response; demand side management; algorithm engineering; greedy heuristic i. motivation nowadays, because of technological improvements and changing environment, energy grids are facing various challenges, such as growing energy demand, new consumption patterns through new living behaviors and emerging economies and therefore rising pollution (e.g., carbon emissions) [1]. as a result, sustainable concepts such as renewable energy (e.g., photovoltaic (pv), wind and water) that is moreover often used in a decentralized way and new appliances, especially electric vehicles (evs) are implemented [2]. these concepts thereby result in a more volatile energy generation and consummation that affects both supplier and consumer. effects of these might be critical peaks, contingencies, a volatile load profile, and disadvantages in the market performance as well as an insufficient infrastructure usage. these can result in blackouts, brownouts, shortages, a high spinning reserve and can endanger energy grid reliability. especially residential context management faces major transformation—for example, increasing implementation of evs and decentralized energy generation as well as new storages—and can contribute to this problem, as the energy consumed in this sector is about 38% of the total consumption and therefore worthy enough to be in our scope [3]. however, to support these situations, a management of new appliances in energy grids is necessary. one possibility to manage appliances in such grids is given by demand response (dr). dr focuses on optimizing consumption patterns, for example, according to external signals (e.g., pricing signals). therefore, dr uses algorithms which can be heterogeneous regarding addressed objective, optimization methods or communication structure [4]. optimization in dr is carried out by shifting or managing loads which is provoked by incentive-based programs [5] such as different types of dynamic pricing (e.g., time-of-use pricing (toup), critical-peak pricing (cpp), and real-time pricing (rtp) [6, 7]). in order to allow using dynamic pricing, different infrastructure (smart metering, controlling and communication mechanisms) is required. due to the fact that the existing infrastructure is not widespread, a popular dynamic pricing scheme is toup with two different pricing intervals: a low pricing interval in the off-peak hours (usually in the night and the early morning) and a high pricing interval during the peak hours. this approach has the advantage that the pricing signal is known and predictable, and the communicational effort is low. however, this mostly generic and simple approach may result in misleading incentives—for example: a user, switching on all deferrable devices at the time the lower pricing interval starts. thus, a new peak is created and the load profile is fluctuating. consequently, we need a pricing that does (i) not need further infrastructure and (ii) addresses the engineering, technology & applied science research vol. 8, no. 1, 2017, 2621-2626 2622 www.etasr.com behrens et al.: developing an algorithm to consider mutliple demand response objectives: applying … misleading incentive from toup. a possible solution is, based on the toup, to provide a pricing function that extra charges the additional peaks and a fluctuating load profile or benefit if additional peaks are avoided and a flattened load profile is achieved. similar types of pricing signals/tariffs already exist [8], for example, pricings that (a) try to deliver a load depended pricing function, (b) deliver a critical peak pricing signal or (c) combine three different pricing intervals and a fourth, optional, pricing phase during peak hours. in order to achieve costsavings with the new pricings, consumers need to respect not only the time-of-use of appliances, but also peak load reduction and load profile flattening. however, current dr algorithms usually take a single factor or objective into account (e.g., costs or peak-load reduction [9, 10]). thus, we currently lack the considering of multiple relevant factors. particular algorithms try to combine different goals, for example, to minimize costs and maximize the comfort level of users [10–12]. authors in [13] identified four objectives, addressing major dr goals: lower energy consumption, peak load reduction, load profile flattening and cost reduction. authors in [14] address multiple goals, however, the resulting optimization problem gets complex and challenging to solve. they therefore propose a greedy algorithm to find a solution. nevertheless, to use this algorithm, an extensive amount of data is needed, and thus, the optimization is slow, and the communication and computational costs are high. hence, a possible solution to optimize the usage with dr in the stated pricing scheme, is to address multiple objectives simultaneously. however, we currently lack the research that contributes to the achievement of multiple goals at the same time while requiring less information, due to reduced communication and calculation costs [10], and is also easy to implement. this study reports on the design, implementation and analysis of a particular algorithm which is capable of considering multiple drobjectives. with this new algorithm several stakeholders can benefit such as (a) users as they can reach several goals (e.g. realize cost savings and maximize welfare), (b) energy providers as they can give more incentives to the users and thereby achieve more efficient generation or predictability, (c) energy grids can get more stable and can react more flexible on contingencies, (d) appliances (e.g. evs) and infrastructure (e.g. storages and pvs) will be embedded in a more fertile way, (e) emissions will be reduced, and (f) acceptance of dr may increase. ii. related work a. methods and algorithms in the dr field in order to identify solution concepts for an algorithm suitable for realizing multiple goals and to ensure that no research exists which already answers our research question sufficiently, we conducted an extensive literature search. moreover, [15–17] conducted literature reviews in the field and were consequently considered as well. one finding is, that especially the supplier side has been in the focus in this research field (e.g., the trading-agent-competition deals with the question, how energy suppliers can give an optimal pricing signal to the consumers, according to a given set of energy demand and predicted consumption [18]). focusing on the consumer side, to the best of our knowledge, we could not identify any appropriate solution. addressed goals thereby are heterogeneous such as cost reduction [19–21] or peak load reduction [22–24]. some algorithms try to achieve two goals simultaneously, for example, reducing costs while maximizing users’ comfort (or at least retain a certain comfort level) [25– 28]. these goals are often realized on the basis of a cost function which is externally given by an energy supplier and the comfort level is considered as an additional condition to the objective function. authors in [14] considered multiple goals, however, these are not suitable for answering our research question sufficiently, as multiple and difficult to solve optimization functions are used. moreover, authors in [13] identified multiple-objectives that can be achieved when implementing dr in the residential context. the optimization problem is constructed with multiple objective functions, each optimizing towards one goal (load profile flattening, cost reduction, comfort maximization, peak load reduction). however, multiple objective functions mostly return in a complex problem and the solution therefore is more difficult. hence, we could not identify any research, answering our research question sufficiently. however, we get an idea, how a possible algorithm could be arranged. b. model from the dr field the main goal of our study is to consider several objectives. a constrained multi-objective optimization problem (cmop) is defined as follows [10, 29] ( x =vector of inputs): )](),...,(),([)( 21 xfxfxfxf k   under the additional conditions ( ()g and ()h =conditional functions): 0)( xg i  mi ,...,1    0)( xh j  nj ,...,1    under certain assumptions, a pareto-optimal solving strategy can be found, however, often this is not given because the optimization model is too complex. some dr models can be traced back to this generalized model [13]. because we want to derive a single optimization function model and we have to consider several constraints regarding the appliances [30] to meet the application area, we choose the optimization model of [31], based on [30], which aims at reducing the costs of the overall system with the help of a toup, which can be exchanged to several other dp alternatives. our model uses the following variables: let n be all considered living units and an be all the appliances of living unit nn  and ω be the sample rate of the discrete model (number of time periods) over one day. moreover, let    nn aa h an h n hx , with },...,1,0{  zh be the sum of all appliances naa  of all living unit nn  in the timeslot h . engineering, technology & applied science research vol. 8, no. 1, 2017, 2621-2626 2623 www.etasr.com behrens et al.: developing an algorithm to consider mutliple demand response objectives: applying … let k anl , be the load profile in a local time interval },...,1,0{ ,anltk  ,   ltk k anan ll ,, the load sum and an , the length of load naa  . in doing so, we can transform a given horizontal and inseparable load profile from its local time interval tl to the global one t through shifting the whole tl by an appropriate constant mn,a, i.e., ank mkh , with ananm ,,0   . furthermore, let min, , h an be the min and max, , h an be the max borders for a load h anx , with th  , naa  so we can specify, in which borders the intensity of load a can be shifted, i.e., max, ,, min, , h an h an h an x   . we note that the given load profiles have to satisfy max, ,, min, , h an h an h an kl   for all ltk  to get a feasible solution. let αn,α be the starting and βn,α be the ending time slot of a load for an appliance α, then we can restrict time interval τ to [αn,α, βn,α ]. we note that the interval length between αn,α and βn,α has to be at least the length of the load profile δn,α. to get a feasible solution, i.e., βn,α−αn,α≥δn,α. turning a constraint i on and off for each appliance a individually let }1,0{iac be a binary variable that shows if a constraint is turned on or not for the appliance α. the objective function describes the costs of the given load profiles, while the cost in a timeslot h is a function depending on h and the total load hx i.e., hhh xxhcc *),( . hh h h h xxhccch anx *),(min 00,    (4) an h anh lx ,,0    naann  , (5) 1 ,, *)( a k an h an clx k   n an aann k   , ,,...,0 , (6) 0*)( 0*)( 2 , min, , 2max, ,,   a h an h an a h an h an cx cx    naann  ,  (7) 0*)( , , 3 ,,   an anh aan h an clx    naann  ,  (8) }1,0{,0,  i a h an cx  3,2,1, ,,   iaa nnth n (9) iii. research μethodology due to the fact that we want to create a new artifact, our research methodology follows the design-science-research (dsr) paradigm [32]. moreover, for designing an algorithm, we found two different approaches: (a) “algorithm theory” (at) and (b) “algorithm engineering” (ae) [33]. at focuses on the formulation of the mathematical model and afterwards proofs that it finds an (optimal) solution in a guaranteed time. ae addresses the application area, which gets more important nowadays, as data volume, real time computing, etc. is getting more complex. this approach does not aim at proofing a guaranteed time and optimization for all possible inputs but rather to guarantee a good performance and result for common inputs of the application area. the evaluation is carried out with an experiment, which is an inductive reasoning approach. the ae approach consists of five different (main) steps: modeling the application area as basis for the design phase, followed by the analysis of the designed algorithm, implementation of the algorithm and finally the evaluation. τhese steps have a strong relationship to the application, receiving application depending information (e.g. input data or the mathematical model) or contributing to the application (e.g. delivering a library to use or giving a performance guarantee). because the dr context, as our application area, is a complex field [34], we assume the ae approach as more suitable. moreover, the evaluation in the dsr field should focus the real world problem, respectively the application area [35]. iv. design a. adapted optimization model the stated model (section ii.b) aims at cost reduction. for expanding this, we need to identify suitable objectives in the field in order to design an optimization model. authors in [13] identified several objectives that need to be integrated in the optimization model. these indicators match with most of the dr objectives, such as peak load minimization, load profile flattening, reliability ensuring, market performance maximization or utility and welfare maximization. as these are additional objectives, they need to be included in the optimization function (done in [13] in a generalized form for a single home). nevertheless, authors use multiple optimization functions, which result in an even more complex problem and the algorithm gets inefficient, for example, regarding the calculation time [31]. we therefore need less objective functions [33]. our main goal is to design an optimization model with only one objective function, thus, we need to consider all goals there. one approach, as the cost function is already integrated in the stated model, could be realized with the help of ‘penalty costs’. the basic idea is that all three objectives influence a cost factor, which then, based on a kwh price, gives the costs a certain timestamp for placing the load. the objective function is formulated in the following way, over the optimization horizon: h hh anx xcc *)(min 0 ,   , where  is the vector of additionally needed information to calculate the penalty costs. first of all, the timeslot is needed to consider time dependent costs (e.g. toup or cpp). in order to achieve a flattening of the load profile, measured for example by the mean-squared-error (mse), the fluctuation needs to be minimized. therefore, we implement rising penalty costs for deviations from the arithmetic mean of the last x timestamps. this means, if the placement of a certain load in timeslot y rises or lowers the consumption in that timeslot more than a certain percentage compared to the arithmetic mean of the last engineering, technology & applied science research vol. 8, no. 1, 2017, 2621-2626 2624 www.etasr.com behrens et al.: developing an algorithm to consider mutliple demand response objectives: applying … x timeslots, the cost factor is raised and penalty costs are added. the same procedure is chosen to integrate a more effective peak load reduction. if the placement in timeslot y will create a new peak, the cost factor should be raised by a certain percentage. at this point, two upcoming questions must be answered: first, how can the additional information be gathered and, second, how do the penalty costs look like. the penalty costs need certain parameters, which need to be instantiated (filled with concrete values). for example, how much are the penalty costs increasing when creating a new peak? however, because the selection of the concrete values does not influence the performance of the algorithm according to its runtime, we do this in the following analyzation phase. the objective function now looks the following: h h h hx xccch an *)(min 00 ,    (10) both function c() and vector θ still need to be defined. θ needs to involve information about the timestamp h, the load in this timestamp hx , the arithmetic mean of the last j timestamps mean(h-j) and the actual peak load peak. moreover, parameters for (a) the cost function (a toup with two different intervals for low price (lp) and high price (hp) is chosen) with additional information, such as costs in different intervals and interval lengths, (b) increasing cost rate ρ for σ% of deviation from the mean, and (c) increasing cost rate τ for a new peak are needed.  )),(,,()( peakjhmeanxhcc h (11)       ωhba;h0: lpc bha:hpc c 1 1 1              σ1 σ2 σ3 ... σ0: 0c σ1: 1ρcc σ2: 2ρcc ... c h h 2 12 12 2 x |j)mean(hx|       peakx:τ*cc sonst: 0c c h 13 3 3 b. needs for additional information the initial optimization model requires a cost function, depending on the timeslot and the amount of energy consumption in this timeslot. this information is suitable for most pricing schemes such as toup and rtp. by using the new objective function, we now need further information about the arithmetic mean of the last j timeslots and the highest peak so far in the overall load profile. depending on the control scheme (e.g. [4]), this information can be given on different ways:  autonomous control: this control scheme has no communication and a local decision making. therefore, the local controller can only access local information and the optimization is done based on this information. however, this local information should be easily accessible because the local controller has not to deal with security and privacy concerns [36].  direct control: in this case (one or two way communication) the centralized controller has all the needed information and the decision making about the load shifting is made directly. however, we have to deal with privacy concerns etc.  indirect control and transactional control: in both cases the decision making is done locally. however, because of the one or two way communication infrastructure, the information needed can be send either from the central controller or the other users. besides privacy concerns, it has to be argued, which information is used: only each user’s local information of or the overall information from the grid. c. possible solving strategies in order to solve the stated optimization problem, we need a suitable method. eas have proven to be effective in finding good approximations of cmops’ optimal solutions, as stated in [10]. other possibilities are greedy, hill-climbing or branchand-bound algorithms [37, 38]. the greedy heuristic is a method relatively easy to implement with a guaranteed runtime and already known in the dr field. especially the runtime needs special attention here. hence, we choose the greedy heuristic. however other heuristics are possible too. solving the optimization problem with the greedy heuristic can be done in two different ways. the classic greedy algorithm—in the dr field—sorts all shiftable loads either downward or upward according to their (summarized) consumption. this means, the biggest or lowest load is picked first. afterwards, the load is placed in the “best” timeslot. no matter which sorting strategy is chosen, we need to identify the best timeslot to place the picked load afterwards. in former greedy applications, this is, for example, the place with the lowest energy consumption or the timeslot with the biggest energy generation. in our algorithm, the best placement is threefold: (a) cheapest place according the cost-function, (b) place with the lowest resulting fluctuation of the load profile and (c) no new peak is created. an advantage of our approach is that the functionality remains more or less the same compared to the classic greedy, only the identification of the best placement changes. the greedy pseudocode for solving our algorithm is shown in table i. table i. greedy pseudocode start take maximum/minimum load 02 search the cheapest place for the load 03 calculate consumption – generation 04 find lowest result 05 place the load at this place end take the next load and start again v. analysis the analysis should provide two outcomes: first, the algorithm’s success in finding a solution and its runtime. because we have a solution strategy—here a greedy heuristic—and an algorithm that places the load, we need to look at both parts of our solving strategy. we can state, that the engineering, technology & applied science research vol. 8, no. 1, 2017, 2621-2626 2625 www.etasr.com behrens et al.: developing an algorithm to consider mutliple demand response objectives: applying … greedy heuristic will achieve a result, as we just have to sort the amount of shiftable loads and place them afterwards till they are all set. next, our algorithm focuses each possible timeslot and calculates the costs. afterwards, the time with the lowest costs is selected. accordingly, we argue that the termination is guaranteed, as a timeslot can be identified. the runtime is a little more complex. we need to sort n loads— thus, we have an average runtime of o(n·log(n)) and o(n²) in the worst case, for example, with quicksort. moreover, our placement algorithm needs to look at m timeslots and calculate the costs for each the runtime therefore is o(n·m). the overall runtime is then o(m+n·log (n)) for the average case and o (n·m+n²) for the worst case. as we can expect the average case most likely or we can obligate the users to deliver the loads pre-sorted, we can be relatively sure to get an average case. as we are in the ae setting, which means the application area is more important than the worst case, we can guarantee a performance of o(n·m+n·log(n))=o(n·(m+log(n))). following our research methodology, the analysis is an evaluation of the first step according to the functionality and runtime. we can now state, that both can be guaranteed. vi. conclusion a. contribution in this article we discuss, that in the dr field a multiple objective optimization is valuable and useful. hence, a new multi-objective optimization problem and a possible solving strategy for the non-linear problem (cmop) is formulated and suitable factors for consideration in the cmop are derived. the overall runtime is o(n·(m+log(n))). b. limitations first, we cannot be sure, that we found all relevant factors to answer the question sufficiently. however, even if a new factor has to be taken into account, the optimization problem and the cost function can be enhanced. second, we cannot assure that neither the formulated optimization problem nor the solving strategy with a greedy heuristic is the best or optimal solution. as we did not state to formulate or find the best performing solution, but a first iteration towards this, we assume the research question answered (to this point). c. further research in further steps of our research, we particularly (1) implement the proposed algorithm and (2) carry out various experiments for evaluation. for creating an easy to use library for different strategies, we plan to program the algorithm in java and deploy an api. the implementation phase includes that the following parameters need to be filled with values:  how much should the cost factor raised, when the actual placement deviates too much from the mean?  how much deviation from the mean is too much?  if a new peak is created, how much should the cost factor increase? as a follow up step, we plan to evaluate the algorithm with an experiment. therefore, appropriate data has to be selected and prepared. recorded data from naturalistic living units (analyzed for example in [39, 40]) or artificial data, which has a sufficient quality [41, 42] is possible. in the naturalistic data case, we have to add additional information to the data, for example, the time of usage. for generating artificial data, the loadprofilegenerator (lpg) [43] can be used, since it has predefined load profiles and uses a behavior model for each user in a living unit to simulate the data. we already conducted first simulations with single households as well as with different combinations in a microgrid. the runtime was as expected. moreover, the received results indicated, that we achieved the same or nearly the same cost-savings compared to a cost-only-objective algorithm. however, we achieved a better load flattening and peak load reduction compared the status quo (no dr) on the one side and the cost-only algorithm on the other side, but, neither the load profile flattening nor the peak load reduction was as good as that of a convex cost algorithm which was our aim in the first place. nevertheless we reached (nearly) the same amount of cost savings while the load profile flattening and peak load reduction were achieved as well in these early 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performance analysis and comparison of symmetrical and asymmetrical dual stator induction generators for wind energy conversion systems ramesh singh department of electrical engineering delhi technological university delhi, india vishal verma department of electrical engineering delhi technological university delhi, india abstract—the emergence of micro/nano level wind generation has opened the research on induction generator (ig) topologies having easier and finer control available in multiphase generators. to establish the suitability of multiphase generators for wind generators the analysis of their performance based on the developed model for the same rating of six phase symmetrical (60˚) and asymmetrical (30˚) igs is presented. a comparative performance evaluation of grid-excited six phase symmetrical and asymmetrical igs also known as dual stator induction generators (dsigs) is presented through simulation results in matlab/simulink environment amidst load perturbations, limited variation of wind speed and perturbations in voltage and frequency of the non stiff micro-grid to which they are connected. based on the performance indices like flux of direct and quadrature axis, speed variations, terminal voltage drop/rise, range of operational speed variation etc., a comparative analysis with the help of the results is drawn to establish the suitability of asymmetrical multiphase igs for grid connected wind generators. keywords-dual stator induction generator; wind energy conversion system i. introduction recent advances and research in the field of power electronics has changed the scenario of power generation from large scale generation to distributed micro, nano and pico generation. due to their suitability for power generating at variable speed and having rugged brushless structure with maintenance, free operation squirrel cage induction generators (scigs) are fast finding place for wind generation. the specific requirements for grid connected generator coupled with wind turbines include better regulation of terminal voltage, better stability, uniform distribution of flux, higher electrical inertia to meet the transients, higher efficiency and cost effectiveness and better low voltage ride through (lvrt) capability. normally multistage gear train/single stage plenary gear train is employed for coupling scig to enable its working in a wide range of speed variation, but larger gear ratio and multistage gear train reduces efficiency to a great extent by incurring losses [1]. reported literature reveals that full rated back to back voltage source converter (btb-vsc) may be employed to harvest energy in higher speed range by vector or scalar control of ig side vsc [2]. such topologies increase the cost of the system as full power passes through the dc link. to overcome such issues dfigs were introduced where direct grid connection of stator winding was possible for operation amidst large variation of wind speed [2]. such configuration removes the dependency on gear train thus becomes more efficient and cost effective for large power range [3]. employing wound rotor induction machine increases the machine cost and requires regular maintenance [3]. moreover the lvrt capability of dfig is also very poor [4]. to offset the increased cost and lvrt capability such machines are well suited for coupling with big wind turbines [4]. to make the suitability of dfig regarding free structure maintenance i.e. getting rid of slip-rings and ig with better lvrt brushless doubly fed induction generator (bdfig) which has two stator windings with one nested loops rotor winding is reported in literature [5]. bdfigs have demonstrated better lvrt capability and have shown their suitability to work with variable speed operation [5]. the increased cost of bdfigs like dfig leaves the scope for furthering in research with multi stator igs for wind energy applications. other reported topology included split phase induction generators (spigs) where there are two stator windings with squirrel cage rotor but the poles of both stators are different. sharing of power between them is made via rotor, making transient response slower and incurring considerable losses [5-7]. dual stator induction generators (dsigs) have emerged as suitable alternative to both dfigs and bdfigs where the two stator windings are used with squirrel cage rotor, and both stators have the same number of poles and are excited with power frequency, thus establishing transaction of power through both stator windings independently and via rotor. in addition they establish flux coupling between both stators enhancing transient characteristics and efficiency [6, 8, 9]. a narrow speed operation without multi-gear systems remains the only limiting factor of dsig [8]. the demerit is offset as the power density is high in such machines and rotor is cheaper with normal stator construction. the reliability of power generation is also increased as now two three phase sets deliver power to the connected three phase loads [6, 9, 10]. normally engineering, technology & applied science research vol. 8, no. 1, 2018, 2464-2470 2465 www.etasr.com singh and verma: performance analysis and comparison of symmetrical and asymmetrical dual stator … the dsig has been proposed with both symmetrical and asymmetrical winding structures for isolated application and with different kinds of load. therefore, a need to critically evaluate the performance of both kinds of generators under real life conditions emerges. dsigs in case of low wind speed can act as two winding transformers to transect power between two stator windings connecting two power circuits and in case of adequate wind speed, generate power from wind and supply to the two networks connected across the two windings, thereby reducing the effective loading on either or both feeders. an assembly / cluster of such small rated dsigs connected in parallel may support additional benefits. in this paper, the performance of dsigs with symmetrical and asymmetrical stator winding coupled with weak grid is evaluated on the basis of voltage regulation and lvrt capability which in turn is based on establishment of air gap flux. since the saturation of flux poses an impediment in operation of igs, a careful study of flux in air gap is also carried out. the connected load is perturbed intentionally to observe and compare the performance of the mentioned above two types of dsigs with respect to direct and quadrature axis flux and terminal voltage. the fault ride through capability is also evaluated by creating a lg fault. the stability during fault and the voltage recovery performance is also compared. the simulated results under matlab environment are presented and evaluated for different operating conditions. ii. system configuration in the proposed scheme a 5 hp, 4 pole dsig is connected directly to two different sets of three phase distribution feeders (dfs), df 1 and df 2 with appropriate relative phase shifts in respective set of phases. figure 1 shows the test bench configuration used for comparative evaluation of symmetrical and asymmetrical dsig. according to the connected ig appropriate relative phase shifts in respective set of phases is provide on the df1. reactive power demand of dsig is supported by the distribution feeders to which the winding sets are connected respectively. two separate capacitor banks (c= 9 µf) are provided at each stator winding terminal to partially support reactive power requirement and filter the currents for range of current harmonics and restraining them to enter the terminals of dsig. different types of passive loads are connected to both set of three phase windings of dsig to study the effect of load dynamics seen by the proposed configurations. iii. mathematical modeling two balanced three phase windings displaced to each other by 30˚(asymmetrical) and 60˚(symmetrical) are considered for modeling of dsig under the following assumptions: air-gap is uniform and the windings are sinusoidally distributed around the air-gap and the magnetic saturation and core-losses are neglected. the voltage equations are written in d-q axis for dsig in synchronous reference frame as: )()(. 11111 dsqsqssqs pirv   (1a) )()(. 11111 qsdsdssds pirv   (1b) )()(. 22222 dsqsqssqs pirv   (2a) fig. 1. block diagram of the considered system. )()(. 22222 qsdsdssds pirv   (2b) ))(()(. drrqrqrrqr wpirv   (3a) ))(()(. qrrdrdrrdr wpirv   (3b) )()(. 212111 qrqsqsmqsqslmqslsqs iiiliilil  (4a) )()(. 212111 drdsdsmdsdslmdslsds iiiliilil  (4b) )()(. 212122 qrqsqsmqsqslmqslsqs iiiliilil  (5a) )()(. 212122 drdsdsmdsdslmdslsds iiiliilil  (5b) )(. 21 qrqsqsmqrlrqr iiilil  (6a) )(. 21 drdsdsmdrlrdr iiilil  (6b) since the model is designed for squirrel cage induction generator, therefore, qrv =0 and drv =0. thus the real and reactive power flowing in the two circuits can be represented as in equations (7a-d). 11111 .. qsqsdsds ivivp  (7a) 11111 .. dsqsqsds ivivq  (7b) 22222 .. qsqsdsds ivivp  (7c) 22222 .. dsqsqsds ivivq  (7d) where χqs1, χqs2 are stator q-axis flux linkage components, χds1, χds2 are stator d-axis flux linkage components, χ'qr, χ'dr are rotor q-axis and d-axis flux linkage components, iqs1, iqs2 are engineering, technology & applied science research vol. 8, no. 1, 2018, 2464-2470 2466 www.etasr.com singh and verma: performance analysis and comparison of symmetrical and asymmetrical dual stator … stator q-axis current components, ids1, ids2 are stator d-axis current components, i'qr, i'dr are rotor q-axis and d-axis current components, lls is stator leakage inductance, lm is air gap inductance, llm is stator mutual leakage inductance, l'lr is rotor leakage inductance, þ is (d/dt), ω and ωr are synchronous flux and rotor speed, rs and rr are stator and rotor resistances, vqs1, vds1, vqs2, vds2, v'qr and v'dr are the stator and rotor q-axis and daxis voltages respectively. the equivalent circuit of dsig generator in d-q reference frame is shown in figure 2(a) and 2(b) respectively. the developed modeling equations do not differentiate between the symmetrical and asymmetrical machines since the instantaneous parameters represent the waveforms, therefore more clarity on the subject would be visible through its depiction on phasor diagrams. (a) (b) fig. 2. (a) equivalent circuit of dsig in d-axis (b) equivalent circuit of dsig in q-axis iv. comparative phasor based analysis it is important to analyze both types of dsig’s from the flux distribution point of view, which can be depicted separately by analysing the effect of loading on both leading and lagging windings and their contribution on direct and quadrature axes. the differences in operating characteristics are visible and strongly influence the results shown with both dsigs. figure 3 shows the phasor diagram showing leading and lagging winding currents of asymmetrical and symmetrical dsig in terms of direct axis and quadrature axis. to study the effect of leading and lagging winding current on one another the projection of one current is taken on the other current and the resultant leading and lagging current phasor is drawn. for simplification and ease of understanding the resultant phasors for both dsigs are calculated taking leading winding as a reference. the projections of a current phasor are represented by dotted lines with the same color to that of the current phasor. superscripts ‘*’ and ‘**’ are used to represent the direct axis and quadrature axis projections of lagging winding on leading winding axis and superscripts ‘#’ and ‘##’ are used to represent the direct axis and quadrature axis projections of leading winding on lagging winding axis. thick solid hashed lines represent the net leading and lagging winding current after incorporating the projections of their respective direct and quadrature current components. figures 3(a), 3(d) for instance represent the direct and quadrature components for current phasor of leading and lagging winding asymmetrical dsig. figure 3(b) represents the projection of lagging winding currents upon leading winding currents of asymmetrical dsig. figure 3(c) represents the resultant leading winding current of asymmetrical dsig incorporating the projections shown in figure 3(b). similarly figures 3(e), 3(f) represent the projections of leading winding currents on the lagging winding currents and the resultant lagging winding currents after incorporating the projections respectively for asymmetrical dsig. figures 3(g-l) represent the current phasor for symmetrical dsig for projection on leading and lagging winding currents. the quadrature and direct axis components of current phasors depicted in figures 3(c), 3(f), 3(i) and 3(l) are also represented mathematically in equations (8)-(9), (11)(12), (14)-(15) and (17)-(18) respectively. the net current phasors are given by (10), (13), (16) and (19).  for asymmetrical dsig for projection of lagging winding side to leading winding side: 37.20,1 ji asq  (8) 037.1,1 ji asd  (9) 37.237.1,1 ji asnet  (10) for projection of leading winding side to lagging winding side: 19.169.0,2 ji asq  (11) 18.105.2,2 ji asd  (12) 37.236.1,2 ji asnet  (13)  for symmetrical dsig for projection of lagging winding side to leading winding side: 37.20,1 ji sq  (14) 063.0,1 ji sd  (15) 37.263.0,1 ji snet  (16) for projection of leading winding side to lagging winding side: 31.055.0,2 ji sq  (17) 31.233.1,2 ji sd  (18) 62.278.0,2 ji snet  (19) engineering, technology & applied science research vol. 8, no. 1, 2018, 2464-2470 2467 www.etasr.com singh and verma: performance analysis and comparison of symmetrical and asymmetrical dual stator … comparing (10) with (16), when projection of lagging winding current component is added with current component of leading winding, it is observed that even for more real power generation the asymmetrical dsig demands nearly the same reactive power demanded by the symmetrical dsig, for lesser active power generation. the same is evident from comparison of figures 3(c) and 3(i) and collaborated by comparing (13) with (19). asymmetrical dsig (a) phasor of id and iq for both leading (i1) and lagging (i2)winding currents (b) projection of id and iq of lagging (i2) winding current on leading winding current (i1) (c) resultant id and iq of leading (i1) winding current (d) phasor of id and iq for both leading (i1) and lagging (i2)winding currents (e) projection of id and iq of leading (i1) winding current on lagging winding current (i2) (f) resultant id and iq of lagging (i2) winding current symmetrical dsig (g) phasor of id and iq for both leading (i1) and lagging (i2)winding currents (h) projection of id and iq of lagging (i2) winding current on leading winding current (i1) (i) resultant id and iq of leading (i1) winding current (j) phasor of id and iq for both leading (i1) and lagging (i2)winding currents (k) projection of id and iq of leading (i2) winding current on lagging winding current (i1) (l) resultant id and iq of leading (i1) winding current fig. 3. dsig phasor diagram: (a)-(f) asymmetrical dsig: projection of lagging to leading, (g)-(l) symmetrical dsig: projection of lagging to leading winding engineering, technology & applied science research vol. 8, no. 1, 2018, 2464-2470 2468 www.etasr.com singh and verma: performance analysis and comparison of symmetrical and asymmetrical dual stator … v. matlab simulation the type of dsig under consideration is 5 hp, 4 pole, 50 hz, 415 v. leading winding side of dsig is connected to grid with respective phase shift of 30˚ for asymmetrical and 60˚ for symmetrical winding type dsig. similarly lagging winding side of dsig is connected to grid without any phase shift. both the grid connections are identical except the difference in their phase for connection to leading side. two distinct equal value three phase capacitor banks are connected to both the winding sets (leading and lagging) of dsig to partially support the excitation and to filter out any harmonics arriving from load towards generators. different types of passive loadings (resistive and resistive-inductive loads) are considered connected to both sides with details given in table i. table i. rating of different loads type of load value of load resistive r= 180 ω resistive inductive z= 180 ω (0.8 pf) vi. performance evaluation the performance of weak grid coupled dsigs with symmetrical and asymmetrical stator windings is evaluated comparatively on the basis of voltage regulation and operation under low voltage which in turn is based on establishment of air gap flux. since the saturation of flux poses as an impediment in operation of ig a careful study of flux in air gap is requisite. the simulated results under matlab environment are evaluated for different operating conditions. the connected load is perturbed intentionally to observe and compare the performance of the afore said two types of dsigs in respect of direct and quadrature axis flux and terminal voltage on the point of common coupling. the utilization of the core and transient characteristic is also been compared by analyzing the direct and quadrature axis flux under steady state and transient conditions during the occurrence of single phase lg fault. perturbing loads are applied to the terminals of both winding sets of dsig and their relative effect on their voltage profile and flux are observed and evaluated. to study the effect of cross-coupling, the igs are loaded in three steps. initially from t = 0 to t = 0.2s both dsigs are at no-load. it may be observed from figure 5 that equal terminal voltages of 340 v are present. at t = 0.2s when both winding sets of the dsigs are equally loaded with 1.75 kw upf load on each winding set it resulted in the voltage fall from 340 v to 330 v for both symmetrical and asymmetrical dsigs. further at t = 0.3s when the loading on leading winding side of both the igs is increased by 750w each, whereas on lagging side load is kept as it is, a fall in voltage on the leading winding side of the igs is observed, which varied from 330v to 322v. but as the cross coupling effect which is more prominent for the asymmetrical dsig the voltage at the lagging winding side increases to 335v, whereas, in the symmetrical dsig where the effect is not prominent the terminal voltage remain almost same at 330v. again at t = 0.4s, a load is applied at the lagging winding of both symmetrical as well as asymmetrical dsig the additional load applied is the preceding perturbation on leading side withdrawn. the terminal voltage of lagging winding side is decreased from 331v to 322v for symmetrical dsig and from 335v to 328v for asymmetrical dsig. the effect of cross-coupling in asymmetrical dsig is once again clearly visible with rise of terminal voltage on the leading winding side i.e. from 322v to 335v. on the other hand, the terminal voltage of leading winding for symmetrical dsig shows small effect of cross-coupling with a rise of terminal voltage (from 322v to 330v). fig. 4. matlab / simulink model of the proposed system detailed comparison between symmetrical and asymmetrical dsig is also carried out by analysis of the flux distribution. it may be observed in figure 6(a), that the core utilization is very well justified in asymmetrical dsig where both direct and quadrature axis flux are nearly equal giving a circular shape of d-q flux graph. whereas, in figure 6(b) it is evident that the d axis and q axis flux is highly skewed in symmetrical dsig and the fluxes are not equal, giving it an elliptical shape on the d-q axis indicating its vulnerability to core saturation. prior to loading the quadrature axis flux values of symmetrical dsig ranges from -1 to 1 p.u. and -0.75 to 0.75 p.u. for asymmetrical dsig and, the direct axis flux value ranges from -0.25 to 0.25 p.u. and 0.75 to 0.75 p.u. for symmetrical and asymmetrical dsig respectively. it may be observed from figure 6 that after resistive loading on lagging winding side the d-q plot of flux gets slightly compressed vertically and slightly bulges horizontally for both symmetrical and asymmetrical dsig in the same proportion. the similar effect is observed for both igs for the loading changes on winding side. to examine the fault ride through capability of dsig a line to ground fault is created for ten (10) cycles and d-q axis fluxes are plotted in figure 7 before fault, during fault and during recovery period. figure 7 shows the plot for direct and quadrature axis flux during pre-fault period for both symmetrical and asymmetrical dsig. it may be observed from figure 7 that asymmetrical dsig shows better stability during fault, which helps during recovery period after fault is removed, compared to symmetrical dsig. during pre fault conditions the direct and quadrature axis flux values for symmetrical dsig are observed as (-0.35 to 0.35) and (-0.95 to 0.95) respectively, whereas, for asymmetrical dsig they vary engineering, technology & applied science research vol. 8, no. 1, 2018, 2464-2470 2469 www.etasr.com singh and verma: performance analysis and comparison of symmetrical and asymmetrical dual stator … between (-0.8 to 0.8) and (-0.6 to 0.6) respectively. quadrature flux of symmetrical dsig shows more drastic changes when compared with asymmetrical dsig, whereas, the direct axis flux show relatively lesser decrementing tendency than for the quadrature axis. the symmetrical dsig witness a decrease from 0.35 to 0.15 p.u. (55% drop) and asymmetrical dsig witness the decrease from 0.8 to 0.45 p.u. (43% drop) in the direct axis flux, whereas, quadrature axis see a decrease from 0.9 to 0.75 p.u. (15% drop) for symmetrical dsig and almost no change in quadrature axis flux for asymmetrical dsig. during recovery period also the tendency of asymmetrical dsig to get back to normal position is fast as the growth in quadrature axis flux is more rapid than in case of symmetrical dsig. the symmetrical dsig shows a slower response compared to asymmetrical dsig during recovery. the results of the comprehensive analysis are presented in table ii, which depicts the relative merits of asymmetrical dsig over the symmetrical dsig for different operating conditions including lvrt and fault conditions. 320 v 320 v 320 v 0.15 0.2 0.25 0.3 0.35 0.4 0.45 320 v time (s) loading on both windings loading on leading winding loading on lagging winding fig. 5. terminal voltages of symmetrical and asymmetrical dsig fig. 6. effect of loading on air gap flux table ii. comparative chart of symmetrical and asymmetrical dsig under different loading and fault conditions property voltage (cross-coupling) current thd fault ride through d-q flux graph symmetrical dsig less pronounced higher poor asymmetrical asymmetrical dsig more pronounced lower good symmetrical engineering, technology & applied science research vol. 8, no. 1, 2018, 2464-2470 2470 www.etasr.com singh and verma: performance analysis and comparison of symmetrical and asymmetrical dual stator … fig. 7. effect of lg fault(10cycles) on air gap flux vii. conclusion in this paper, we presented a comparative evaluation of operating characteristics of symmetrical and asymmetrical dsig. the mathematical model of both dsigs has been developed for comparative analysis. a phasor analysis was also drawn in terms of winding currents for symmetrical and asymmetrical type dsigs. the comparative performance of the igs was observed on the basis of demonstrated results for perturbing loads through direct and quadrature axis flux of the air gap and dynamics during recovery of voltage. demonstrated result also revealed the asymmetrical generator harvests, the advantage of cross coupling which enables the regulation of voltage by magnetizing the effect of reduction in flux. results demonstrated the superiority of asymmetrical dsig for wind energy applications. practically provision of a phase shift of 30˚ is easily attained with the help of star delta transformer thus adds to the merits of asymmetrical generator over the symmetrical one. references [1] h. polinder, f. f. a. van der pijl, g.-j. de vilder, p. j. tavner, “comparison of direct-drive and geared generator concepts for wind turbines”, ieee transactions on energy conversion, vol. 21, no. 3, pp. 725-73, 2006 [2] k. protsenko, d. xu, “modeling and control of brushless doubly-fed induction generators in wind energy applications”, ieee transactions on power electronics, vol. 23, no. 3, pp. 1191-1197, 2008 [3] f. bu, y. hu, w. huang, s. zhuang, k. shi, “control strategy and dynamic performance of dual stator-winding induction generator variable frequency ac generating system with inductive and capacitive loads”, ieee transactions on power electronics, vol. 29, no. 4, pp. 16811692, 2014 [4] t. long, s. shao, p. malliband, e. abdi, r. a. mcmahon, “crowbarless fault ride-through of the brushless doubly fed induction generator in a wind turbine under symmetrical voltage dips”, ieee transactions on industrial electronics, vol. 60, no. 7, pp. 2833-2841, 2013 [5] s. tohidi, h. oraee, m. r. zolghadri, s. shao, p. tavner, “analysis and enhancement of low-voltage ride-through capability of brushless doubly fed induction generator”, ieee transactions on industrial electronics, vol. 60, no. 3, pp. 1146-1155, 2013 [6] r. boraci, m. babescu, n. budisan, a. r. boraci, “mathematical model of the two orthogonal three-phase windings stator generator”, 5th international symposium on applied computational intelligence and informatics, romania, may 2829, 2009 [7] s. shao, t. long, e. abdi, richard a. mcmahon, “dynamic control of the brushless doubly fed induction generator under unbalanced operation”, ieee transactions on industrial electronics, vol. 60, no. 6, pp. 2465-2476, 2013 [8] n. budisan, o. prostean, r. boraci, i. szeidert, v. muller, “the dual induction generator for renewable energy conversion systems. experimental results, problems and solutions”, ieee international joint conferences on computational cybernetics and technical informatics, romania, may 27-29, 2010 [9] r. singh, v. verma, “dual stator induction generator for rural electrification”, international journal of applied engineering research, vol. 12, no. 16, pp. 5865-587, 2017 [10] f. bu, l. zhu, w. huang, h. xu, h. liu, y. gao, "control strategy of ac&dc hybrid generating system based on dual stator-winding induction generator for micro-grid application”, ieee transportation electrification conference and expo, pp. 013-017, 2016 engineering, technology & applied science research vol. 7, no. 4, 2017, 1765-1770 1765 www.etasr.com anjum et al.: machining and surface characteristics of aisi 304l after electric discharge machining … machining and surface characteristics of aisi 304l after electric discharge machining for copper and graphite electrodes in different dielectric liquids saba anjum masood shah n. a. anjum shahid mehmood waqas anwar mechanical engineering department, university of engineering and technology taxila, pakistan sabaanjum_2k9@ yahoo.com mechanical engineering department, university of engineering and technology taxila, pakistan masood.shah@ uettaxila.edu.pk mechanical engineering department, university of engineering and technology taxila, pakistan nazeer.anjum@ uettaxila.edu.pk mechanical engineering department, university of engineering and technology taxila, pakistan shahid.mehmood@ uettaxila.edu.pk institute of space technology, engineering research and development sector, islamabad, pakistan waqasanwar_16@ yahoo.com abstract—in electric discharge machining (edm), the thermal energy used for material erosion depends on the intensity of electric sparks, the thermal conductivities of electrode material and the dielectric liquid. in this paper, the effect of edm on aisi 304l steel is studied using copper and graphite electrodes and distilled water and kerosene oil as dielectric liquids. material removal rates (mrr), tool wear rates (twr) and surface conditions are calculated for four different combinations with the two electrode materials and the two dielectric liquids. these investigations are carried out at different pulse currents. machined surfaces are evaluated by morphological studies, energy dispersive spectrographs (eds) and white layer thickness using scanning electron microscopy (sem). it is found that a transfer of carbon takes place from the kerosene oil and the graphite electrodes into the machined surface which alters the metallurgical characteristics, depending on the electrical and thermal conductivities of the electrode material and the dielectric liquid. keywords-electric discharge machine; material removal rate; electrode wear rate; white layer i. introduction electric discharge machining (edm) is a non-conventional machining process, which is used for machining of complex and intricate shapes with high precision. this is a non-contact machining process in which material is removed by the thermal energy produced by electric sparks in a dielectric medium. a part of molten material is removed only by solidifying residue on the surface and a surface layer is produced which is known as white layer [1-3]. electrodes used in electric discharge machining are generally made of copper, graphite, tungsten, aluminum, brass etc. based on the electrical and thermal conductivities. tool wear rate is the biggest problem in edm which causes inaccurate machining [4]. proper selection of electrode material is necessary for attaining desired surface conditions [5]. a number of researches are carried out to evaluate the effect of different type of materials, sizes and geometries for electrode [6,7]. the selection of electrode material as well as the proper dielectric liquid is very important since these parameters determine the material removal rate (mrr), the electrode wear rate (ewr), and surface finish [8]. the increase in pulse current causes higher electrode wear. tool wear rate (twr), mrr, diametric over cut on tool steel have been investigated and it was found that aluminum and copper electrodes offer best machining rates [9]. in [10], authors studied mrr and ew of aluminum and mild steel for copper and brass electrodes and found that electrode wear was higher for machining of mild steel compared to aluminum. in [11], authors investigated the effect of copper and graphite electrode on aisi p20 tool steel for different polarities and determined that copper electrode provides best surface roughness for negative polarity. in [12], authors presented a detailed review for the effect of different types of dielectric liquids on edm characteristics and concluded that with distilled water machining accuracy is superior as compared to hydrocarbon oil. in [13], authors determined the effect of using deionized water, kerosene oil and water in oil emulsion as dielectric liquid on c35 carbon steel and found that microcracks formed with water as a dielectric liquid had little penetrations as compared to the kerosene oil. the consequent residual stresses increase below the surface reaching maximum value [14, 15]. in [16], authors studied the effect of oil based, de-ionized water, gracious and commercial water based dielectric liquids and found that water and gracious based dielectric liquids offer good mrr and are health friendly. in [17], authors compared the influence of kerosene and distilled water for electric discharge machining of ti-6al-4v and found that carbon from kerosene oil stuck with electrode surface and retards machining process. experimental investigations which are limited to the determination of the effect different electrode materials on engineering, technology & applied science research vol. 7, no. 4, 2017, 1765-1770 1766 www.etasr.com anjum et al.: machining and surface characteristics of aisi 304l after electric discharge machining … material removal rate and electrode wear rate are available [4, 18]. the effect of electrode materials in combination with different types of dielectric liquids is rarely investigated. the present study is unique in such a way that surface morphology, its composition and white layer thickness are studied along with mrr and twr for different combinations of electrode material and dielectric liquid. the effects of copper and graphite electrodes in both dielectric liquids (distilled water and kerosene oil) are investigated for edm of carbon steel aisi 304l. ii. experimentation the material investigated is low carbon steel aisi 304l and chemical composition of the material is presented in table 1. the experimental work is conducted by using die sinking electrical discharge machine neuer m 50. the effect of two types of electrode material i.e graphite and copper for two types of dielectric liquids i.e kerosene and de-ionized water are evaluated. as different kinds of dielectric liquids are used in this study, machining is carried out in such a way that one dielectric liquid could not be contaminated by the other. for this purpose, a workpiece fixture is used that contains two separate chambers as shown in figure 1. machining is performed in one chamber and other chamber is used as reservoir. an external pump is used to deliver dielectric liquid from reservoir to the machining chamber. the experimental conditions used for the current investigation are presented in table ii. discharge current is the only electric parameter which is varied whereas other electric parameters such as pulse-on time, pulse-off time, voltage, and gap are kept constant. physical properties of the electrode materials are given in table iii. fig. 1. experimental setup. table i. chemical composition of stainless steel grade 304l chemical c mn p s si cr ni n percentage 0.030 max 2.00 max 0.045 max 0.030 max 0.75 max 1820 812 0.10 max table ii. experimental conditions working parameters description work piece material ss 304l electrode material copper and graphite dielectric water and kerosene peak current 4.5, 6, 9, 12a plus duration 90(µs) plus off time 5(µs) working time 30 minutes table iii. physical properties of copper and graphite electrodes [ 4] physical properties copper graphite melting point (◦c) 1083 455 thermal conductivity (w/mk) 380.7 160.0 electrical conductivity compared with silver (%) 92 0.11 electrical resistivity (µ/cm) 1.96 0.12 coefficient of thermal expansion (×10−6×c−1) 6.6 7.8 specific gravity at 20 ◦c (g/cm3) 8.9 1.75 specific heat (cal/g ◦c) 0.092 0.17 four different combinations of electrode material and dielectric liquid during edm which are evaluated in this study are given in table iv. the material removal rate (mrr) and the electrode wear rate (ewr) are obtained by measuring the masses of the work-piece and the electrode before and after machining and corresponding formulas are given below, mrr= (m1-m2)/ ρw. t (1) ewr= (m1-m2)/ ρe. t (2) where m1 and m2 are masses of workpiece before and after machining respectively. m1 and m2 are masses of electrode before and after machining respectively. ρw is the density of workpiece material and ρe is the density of electrode material. t is machining time. after edm machining, the samples are cut perpendicular to machined surface, embedded in epoxy and then polished. then etched with diluted solution of hf with nitric acid for 15 seconds. surface morphology and white layer thickness are determined by scanning electron microscope (sem). table iv. combinations of electrode material and dielectric liquids conditions electrode material dielectric liquid symbol 1 copper distilled water cw 2 copper kerosene oil ck 3 graphite distilled water gw 4 graphite kerosene oil gk iii. results and discussions a. material removal rate (mrr) initially material removal rate (mrr) is determined for four different discharge current levels. results of mrr are given in table v and are shown in figure 2. it is observed that distilled water when used as dielectric liquid gives higher mrr as compared to kerosene oil for both of the electrode materials. the behavior of mrr with respect to electrode material is engineering, technology & applied science research vol. 7, no. 4, 2017, 1765-1770 1767 www.etasr.com anjum et al.: machining and surface characteristics of aisi 304l after electric discharge machining … different on lower and higher side of discharge current. at lower side mrr is higher for graphite, whereas at higher side copper material gives higher values. for high discharge current (roughing conditions), copper electrode is giving higher mrr whereas for lower discharge current (finishing conditions) graphite electrode is suitable. this is due to lower ionization energy is required for dielectric break-down in case of water as compared to kerosene oil. also it can be seen that mrr is proportional to pulse current for all combination. fig. 2. material removal rate with respect to pulse current. table v. mrr at different experimental conditions. current (a) copper (mm3/min) graphite (mm3/min) distilled water kerosene distilled water kerosene 4.5 7.76 3.08 15.6 7.12 6 16.9 7.43 18.6 7.70 9 26.2 15.8 20.7 17.4 12 31.4 19.5 23.8 27.0 b. electrode wear rate (ewr) since machining occurs at very high temperature that increase probability of chemical reaction between the elements of electrode material and dielectric liquid, due to which erosion of electrode material can take place. tool wear rate is usually determined for identification of dimensional accuracy of the machined geometry, also the machining cost is suffered by electrode wear. dielectric liquids act as coolant for both workpiece and electrode after each discharge. the cooling rate depends essentially on the thermal conductivity of dielectric liquid. the results of twr are given in table vi and shown in figure 3. distilled water has lower de-ionization level relative to kerosene oil which results intense sparks comparative to kerosene oil. also copper material produces more intensive sparks due to high electric conductivity as compared to graphite material. however relative lower thermal conductively of graphite generate more heat and hence melting. therefore, the wear rate of graphite in combination with water is higher. however, the combination of water and copper has an abnormal behavior where electrode wear rate is decreasing with increasing discharge current. this shows that spark generation is becoming unstable with increasing discharge current. also negative wear ratio is observed in case of kerosene oil only as carbon layer stuck at the bottom surface of electrode. the carbon is produced due to disintegration of hydrocarbon kerosene oil. table vi. twr at different experimental conditions. current (a) copper (mm3/min) graphite (mm3/min) dis. water kerosene dis. water kerosene 4.5 0.749 -0.3.00 2.80 -0.369 6 0.787 -0.150 3.98 -0.723 9 0.337 0.337 4.57 -0.560 12 0.0749 1.650 5.31 0.737 fig. 3. tool wear ratio with respect to pulse current c. microscopy after each spark, a decrease in pressure occurs resulting a tiny localized explosion, due to which, molten material is splashed away forming surface crater. only a portion of material could be removed and the remaining material resolidified forming a layer. this layer has different characteristics compared to the base material. it is also well noted by different studies that this layer is known as white layer and its thickness depends on the discharge energy [1]. the amount of discharge energy per unit area depends on pulse current and pulse-on time. presence of white layer is undesirable due to its poor characteristics. this layer is harder and brittle due to rapid cooling. due to rapid cooling residual stresses are developed, which are tensile in nature. surface cracking occur if magnitude of residual stresses exceed material strength. in [19], these cracks were classified into three types. the first type of surface cracks initiates from the surface and penetrates into white layer up to the interface of white layer and base material. the second type of surface cracks is those which penetrate into the base material. the third type of surface cracks is found near boundaries of craters and globules. these cracks have very low penetration and do not affect the surface properties. surface morphology of the machined surface using kerosene oil as dielectric is shown for both electrodes in figure 4. it is clearly shown that surface cracks are uniformly distributed on the whole surface however these cracks are more pronounced when graphite electrode is used. the crosssectional images are indicating that these cracks are of the first type that penetrate until the interface. globules and surface pits are seen in case of copper electrode whereas blackish contents are collected in crater like cavities for graphite electrode, which are definitely carbon particles. [20] reported high increase in carbon contents on the machined surface by more cracking of kerosene oil for graphite electrode and also due to the decomposition of graphite into carbon contents in vigorous condition. engineering, technology & applied science research vol. 7, no. 4, 2017, 1765-1770 1768 www.etasr.com anjum et al.: machining and surface characteristics of aisi 304l after electric discharge machining … fig. 4. influence of copper and graphite electrode on surface morphology using kerosene oil at 6 a pulse current fig. 5. influence of copper and graphite electrodes using distilled water at 6 a pulse current. engineering, technology & applied science research vol. 7, no. 4, 2017, 1765-1770 1769 www.etasr.com anjum et al.: machining and surface characteristics of aisi 304l after electric discharge machining … for the distilled water as the dielectric liquid, the effect of electrode materials on electric discharge machined surface is shown in figure 5. it is observed that the use of copper electrodes is resulting to a relatively smooth surface with less amount of cavities and globules. none of the cracks are visible on the surface. the surface obtained by graphite electrode is uneven containing globules and appendages of resolidified material on crater rims. surface seems to have cracks of the third type having very low penetration into the white layer. this might be because of relatively higher cooling rate of the molten material in distilled water. white layer displays less micro cracks for the work-piece using kerosene, compared to that using distilled water. this is due to the increase of carbon contents in the white layer that make material hard and brittle. surface is cracked when residual stresses overcome the ultimate strength of the material. energy dispersive spectrographs (eds) of machined surface using kerosene oil and distilled water along with graphite electrode are shown in figure 6. it is observed that the white layer is contaminated by carbon contents that are transferred by decomposition of kerosene oil and graphite electrode during machining. therefore the white layer formed by combination of kerosene oil as dielectric liquid and graphite electrode has highest contamination of carbon. fig. 6. eds spectrographs for graphite electrode in kerosene oil and distilled water table vii. white layer thickness at different conditions current (a) copper graphite dis. water kerosene dis. water kerosene 6 7.90 15.80 4.58 17.67 9 10.16 6.08 5.51 21.31 12 12.94 21.65 7.95 13.56 fig. 7. awlt for different combinations. the average values of white layer thickness for four different conditions are given in table vii and their behavior with pulse current are shown in figure 7. a comparison of the white layer thickness of the two dielectric shows that the average thickness of white layer using kerosene is higher than distilled water for both electrode materials. this is because of the difference in thermal conductivities of water and kerosene. the thermal conductivity of water is more than kerosene, due to which, the generated thermal energy dissipates quickly resulting less amount of material melting. results also show that thickness of white layer depends on pulse current directly. intensive electric sparks are generated at high pulse current that produce more thermal energy during electric discharge machining. iv. conclusions the influence of two electrode materials and two dielectric liquids on low carbon steel 304l is studied for different pulse currents. their effect is investigated in terms of surface conditions like surface morphology, chemical composition and white layer thickness. generally it was observed that surface cracking is proportional to the amount of carbon contents present in white layer formed after electric discharge machining. the white layer is most enriched with carbon contents when graphite electrode is used in combination with kerosene oil as dielectric liquid, therefore, the surface cracking is highest in this case followed by combination of copper electrode with kerosene than graphite electrode with distilled water. surface cracking is not seen for the combination of copper electrode with distilled water. graphite electrode has extreme wear rates, which is highest when used in distilled water and lowest for kerosene oil. an interesting effect of discharge current on ewr of copper electrode in distilled water is seen where contrary to other combinations ewr is decreasing with increasing pulse current. distilled water offers higher mrr as compared to kerosene where graphite and copper should be respectively preferred for finish and rough machining conditions. the thickness of the white layer is higher in kerosene as compared to distilled water, however, the response of electrode material is different for dielectric liquids. graphite results higher thickness than copper when machining in kerosene whereas this order is reversed when machining in distilled water. the combination of copper electrode with distilled water for machining at a pulse current higher than 6 a is suggested for best machining outcome in the form of surface condition, high mrr and decreased twr. kerosene oil distilled water engineering, technology & applied science research vol. 7, no. 4, 2017, 1765-1770 1770 www.etasr.com anjum et al.: machining and surface characteristics of aisi 304l after electric discharge machining … references [1] k. h. ho, s. t. newman, "state of the art electrical discharge machining (edm)", international journal of machine tools and manufacture, vol. 43, no. 13, pp. 1287-1300, 2003 [2] s. mehmood, m. shah, r. a. pasha, s. khushnood, a. sultan, "influence of electric discharge machining on fatigue limit of high strength aluminum alloy under finish machining", journal of the chinese institute of engineers, vol. 40, no. 2, pp. 118-125, 2017 [3] s. mehmood, r. a. pasha, a. sultan, "effect of electric discharge machining on material removal rate and white 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applied science research vol. 7, no. 2, 2017, 1567-1574 1567 www.etasr.com bolhari et al.: perceived possibility of disclosure and ethical decision making in an … perceived possibility of disclosure and ethical decision making in an information technology context alireza bolhari reza radfar mahmood alborzi alireza poorebrahimi mahmood dehghani dpt of information technology management, science and research branch, islamic azad university, tehran, iran alireza@bolhari.com dpt of industrial management, science and research branch, islamic azad university, tehran, iran radfar@gmail.com dpt of information technology management, science and research branch, islamic azad university, tehran, iran mahmood_alborzi@ yahoo.com dpt of management and accounting, islamic azad university karaj, iran poorebrahimi@ gmail.com school of behavioral sciences and mental health, iran university of medical sciences, tehran, iran mdehghani2004@ gmail.com abstract—to date, substantial research studies have been conducted in the field of ethical decision making in many disciplines. however, ethical efforts in the context of information technology have been limited. in this research, a focus has been put on modeling ethical decision making in cyberspace with emphasis on business intelligence scenarios. the model is comprised of six exogenous and two endogenous constructs, among them seven were delicately selected from valid and empirically tested ethical models and the eighth one is developed by the authors. after pre-testing the model by experts, reliability, convergent and discriminant validities were approved. data were collected from 188 it personnel in the banking industry of iran. results revealed that the perceived importance of an it ethical issue, ethical judgment, ethical obligation, perceived possibility of disclosure, ego strength, and locus of control directly impact ethical intention. however, no impact from law on ethical obligation and codes of ethics on ethical intention was observed. as shown, a higher possibility on acting unethically occurs when the person feels confident that his/her actions will go unnoticed. keywords-information technology; business intelligence; ethical decision making; perceived possibility of disclosure; it ethics i. introduction ethics, as in its simple definition delivered in [1], is the values and principles leading to a right or wrong behavior. the perception of ethics in the digital world slightly varies from brick and mortar organizations and in most cases, recognition of a right or wrong behavior gets complicated. organizations, which typically live in uncertain and vague atmosphere [2], have faced noteworthy ethical issues. in order to decrease these unethical actions, managers should lead employees toward a more organizational ethical environment [3]. this concern about ethical decision making in information technology (it) has always been an interest point for researchers [4]. in [5], it was noted that ethical issues in business management have long-term and wide-spread adverse effects. furthermore, results were identified that may lead to challenges for managers. in [6], authors have identified ethical decision making as a fundamental factor that influences information systems’ success including business intelligence systems. others have noted that ethical issues in the context of businesses bring decreased productivity, increased uncertainty [4], elimination of work opportunities, environmental pollution [5], higher work absence and customer dissatisfaction [1]. in [7], the author urged business managers on the subject of ethical decision making and its potential adverse influences. in [8], authors stated that studying the way an individual makes ethical decisions improves ethical decision making in organizations. in [9], it was proposed that when dealing with computers, the theory of reasoned action fails and does not satisfactorily model ethical decisions. in [10], an investigation about ethical decision making methods in knowledge management systems was conducted and a number of policies was suggested to maintain an ethical-based climate organization-wide. in [11], authors called the importance of ethical issues in computer and internet usage as a concept that is "lost in cyberspace". they conducted their study around ethical judgment and ethical intention and mainly considered gender differences. in [12], the chance of being caught as influencing ethical behavior was discussed but it was also implied that individuals with greater technical knowledge may be more aware of the ways they may get caught, and may be more cautious than others. a very early approach on it ethical decision making was presented in [13] where an it model with two new factors: ego strength and locus of control was proposed [13]. this model engineering, technology & applied science research vol. 7, no. 2, 2017, 1567-1574 1568 www.etasr.com bolhari et al.: perceived possibility of disclosure and ethical decision making in an… was retested in [14] with about 1990 observations. although some contradictions were found, the overall model was reapproved. in [15], authors modeled it ethical decision making based on reasoned actions, perceived importance, planned behaviors, and individual characteristics. they also included age and sex in their models. in [16], authors proposed a process for it ethical decision making by investigating information system students. they mainly focused on age, sex and religion as the influencing factors. ii. it ethical decision making model a. perceived importance of an ethical issue in the ethical decision making literature, scholars have referred to the perceived importance of an ethical issue in different names such as ethical perception [17], perceived ethical problem [18] and ethical issue [19]. in [20], it was stated that perceived importance of an ethical issue corresponds to the importance, significance, and fundamentality of an issue. an instrument was proposed to measure the perceived importance that later became a dominant instrument in this area. in [21], authors tested the impact of perceived importance of an ethical issue on ethical intention among 235 business managers who were randomly selected and found a positive impact. in a study among higher education students and with deployment of three ethical scenarios, it was reported that perceived importance is an indicator of ethical judgment [22]. in information technology, equivalent findings show that perceived importance affects ethical intention and judgment [15, 23]. accordingly, hypothesis 1a and 1b are as follows: • h1a: perceived importance of an ethical issue positively influences ethical intention. • h1b: perceived importance of an ethical issue positively influences ethical judgment. b. ethical judgment and ethical obligation according to [24], ethical judgment refers to a judgment made ethically according to the correctness, acceptability and appropriateness of an issue. this is in accordance with the definition of ethical judgment in [25]: decision makers’ assessment of correct behavior in an ethical decision making situation. in a simplified definition, ethical judgment is one’s evaluation of his/her action to be good or bad [26]. previous research studies have shown a meaningful relationship between ethical judgment and ethical intention. in an early research about software piracy, in [27], authors revealed that ethical judgment positively predicts ethical intention in copying and distributing software packages illegally. the same finding is approved in [28] between peer groups. this was achieved by conducting a research to investigate the relationship between ethical judgment and ethical intention in scenarios about unethical cases. another research has shown a positive and influential impact on ethical intention between automobile salespeople [17]. the same findings are presented by others [29-33]. as a result, the second hypothesis is as follows: • h2: ethical judgment positively influences ethical intention. ethical obligation or normative belief [14] is the alignment of the decision maker’s behavior by personal and social pressures [34]. for the first time, in [35] a scale was developed with one question about organ donation to measure ethical obligation. this question further became popular among other research studies. for instance, in [15] and [36] authors investigated the impact of demographic characteristics on ethical decision making among computer college students and used the construct from [35] to measure ethical obligation. they showed that ethical obligation is an indicator of ethical intention. besides, ethical judgment is found to predict ethical obligation [27]. this relationship is further investigated by other scholars and the same finding is found [29, 31]. therefore, we theorized hypotheses three and four as follows: • h3: ethical judgment positively influences ethical obligation. • h4: ethical obligation positively influences ethical intention. c. law and codes of ethics law is the “rule and measure of actions directing them to proper ends” [37] and forces individuals to conform their actions to norms. additionally, law reveals preferences of a community or society [38, 39, 17]. according to these definitions, it seems apparent that law and codes of ethics must -to some degreeconfine decision makers’ behaviors toward proper ends. in this regard, dunfee [39] believed that ethics is deeply tangled with law and they cannot be realized without another one. in an early research in this domain, the role of codes of ethics on computer misuse is investigated and results showed that company’s codes of ethics slightly limits behavior of information system personnel [40]. besides, hunt and vitell [41] mentioned legal environment as an influential factor in ethics. they argued that law and codes of ethics potentially limit decision makers’ intention to commit more ethical actions. this happens when law influences ethical obligation and codes of ethics influences ethical intention. accordingly, hypotheses 5 and 6 are as follows: • h5: law has a significant impact on ethical obligation. • h6: codes of ethics has a significant impact on ethical intention. d. ego strength and locus of control one of the most important factors that influence human behavior is ego strength [42]. this relates to the ability to bear stress and tension in various occasions [43]. accordingly, in [44] ego strength was defined as one’s proficiency to control his/her instinct and social needs. in other ethical research studies, ego strength has also been called “self-identity” [45, 46, 47]. ego strength has been introduced to the field of ethical decision making since 1986 [48] and research studies have approved that it impacts ethical intention [23, 15]. locus of control, on the other hand, refers to one’s tendency to relate his/her success or failure to internal or external factors. in another word, one’s belief about their engineering, technology & applied science research vol. 7, no. 2, 2017, 1567-1574 1569 www.etasr.com bolhari et al.: perceived possibility of disclosure and ethical decision making in an… behavior and its outcomes is called locus of control [49]. in [50], authors reported no significant relation between locus of control and ethical intention. they concluded that locus of control does not relate to ethical intention in sales managers. the same finding was observed in [51] in workplace environments. this however, is against the findings of an early study that reported a positive relationship between locus of control and ethical intention [52]. even though, one year later, authors [53] reported a contradicting finding stating that no relation was observed among management students. in [54], it was stated that locus of control is an indicator of ethical behavior among the united states managers and executives. the higher locus of control determined more ethical decisions. for the first time in the field of information technology, ego strength and locus of control was applied to assess ethical behavior in [13]. it was found that ego strength and locus of control influence ethical intention. moreover, in [14] authors testified ego strength as an indicator of ethical intention among it students. thus, the corresponding hypotheses are: • h7: ego strength has a significant impact on ethical intention. • h8: locus of control has a significant impact on ethical intention. e. perceived possibility of disclosure through the extensive review of the decision making literature, we found that the perceived possibility of disclosure of decision results (we named it perceived possibility of disclosure or its short form perceived disclosure) has not been investigated before and may have direct or indirect effect on ethical decision making. the following scenarios clarify the core meaning of our construct: • in a company, payrolls are sent to personnel’s email addresses. sarah, by chance, has found her colleague’s (sam) email password. in one instance, consider the situation that sarah is upmost confident that if she checks sam’s payroll, he will not notice it. in another instance, she is almost assured that sam would notice that she has checked his payroll. in the two mentioned instances, what are the possibilities of checking the payroll? are they the same? • adam works for a company that develops software packages. for personal reasons, he needs a system restore application to repair his own laptop. in his company’s products’ list, there is a 120$ system restore application. consider two cases. in one case, he certainly knows that no one would notice if he takes home a copy of the software. in another case, he that feels the possibility of disclosure is high. this means that his boss, for example, will notice his action and this would have adverse consequences for him. will adam perform the same actions in either case? does his intention vary? accordingly, hypothesis 9 is as follows: • h9: perceived possibility of disclosure has significant impact on ethical intention. to encapsulate, our model of ethical decision making in the context of information technology and above mentioned hypotheses are shown in figure 1. fig. 1. conceptual model iii. methods a. samples the test population was comprised of business intelligence experts, managers, supervisors and end-users that had professional experience in banking industry. they were all experts or familiar with business intelligence concepts and techniques such as data mining, recommender systems, data warehouse, performance dashboards and scorecards, reality mining, etc. pls states that the minimum sample size must be at least 10 times of the number of structural paths to a specific construct [31]. in our model, there are seven paths to ethical intention; as a result, 70 samples provides a sufficient sample. of the 364 it personnel of a bank in iran, 188 (male=107 and female=81) participated in this research. the average age was 39 and it varied from 18 to 69. of the respondents, 87 (46.3%) had less than 5 years of related experiences and 65 (34.6%) had 5 to 10 years. b. constructs the basis of data collection was a questionnaire employed in preceding research studies. constructs were selected from the valid ones in the literature (table i). of the constructs, we developed the perceived possibility of disclosure. our questionnaire started with three sample ethical decision making scenarios to align respondents with the context of it ethical decision making. following the scenarios, we presented 33 questions for eight constructs and face-validated our questionnaire by pre-testing among several experts and university professors [57]. c. confirmatory factor analysis smartpls 2.0.m3 was used for confirmatory factor analysis (cfa), which is a path modeling software based on partial least-squares. in [58], it was stated that smartpls requires less engineering, technology & applied science research vol. 7, no. 2, 2017, 1567-1574 1570 www.etasr.com bolhari et al.: perceived possibility of disclosure and ethical decision making in an… demands and samples in comparison with other approaches like structural equation modeling. this leading point makes partial least-square method a valid and commonly referenced in data analysis and surveys [59, 58, 60]. prior to data analysis, reliability and validity of the constructs must be measured [61]. convergent and divergent (discriminant) validity are parts of construct validity which indicate the measurements within our constructs. as a result, we explored these three parameters for our constructs as follows. reliability measures the overall consistency of a measure. confirmatory factor analysis in partial least squares presents composite reliability for every construct and the overall cronbach’s alpha. the internal consistency is considered acceptable if cronbach’s alpha is exceeded from 0.70 [62, 61]. table ii demonstrates the reliability of our constructs. table i. constructs of the questionnaire construct questions reference perceived importance of ethical issue (pi) 1-4 [20] ethical judgment (ej) 5-7 [24] ethical obligation (eo) 8-10 [36] perceived possibility of disclosure (pd) 11-12 [55] locus of control (loc) 13-24 current study ego strength (es) 25-31 [13] law 32 [13] codes of ethics 33 [2] table ii. reliabilities of the constructs no. of items t-values factor loadings (fl) cronbach’s alpha (ca) composite reliability (cr) criteria t-value>1.96 fl>0.707 ca>0.70 cr>0.70 pi 4 50.3 0.89 0.79 0.90 ej 3 9.4 0.79 0.83 0.88 eo 3 16.7 0.81 0.72 0.79 pd 2 83.6 0.95 0.81 0.87 loc 12 14.3 0.82 0.89 0.95 es 7 50.9 0.92 0.88 0.91 lc 2 61.2 0.91 0.78 0.88 we examined convergent validity by the criteria proposed in [63]. firstly, each factor loadings must exceed 0.70 (to be precise: 0.707) and be significant. this ensures that more than ½ of the variance is covered by latent construct [58]. secondly, all the constructs must have at least 0.70 of reliability and 0.50 of average variance extracted (ave). in our research, all the factor loadings are more than 0.70 and they are significant at 0.001 level. moreover, composite reliabilities exceed 0.70 with a minimum of 0.79 (table ii). table iii shows the average variance extracted. all the numbers are over 0.50 with a minimum of 0.68. so, convergent validity is satisfied. to test the discriminant validity of the scales, we used square root of average variance extracted and construct item loadings. for square roots, it has been advised that each construct must have higher inter-construct coefficients [59]. table iii shows that all square toots of aves are the highest numbers in coefficients (the highest is 0.89 for ethical obligation and the lowest is 0.68 for ego strength). moreover, for construct item loadings they recommend that loadings of within-constructs must be at least 0.10 higher than the cross loadings of inter-constructs. our research satisfies this criterion. thus, the discriminant validity of the scales is approved. table iii. average variance extracted pi ej eo pd loc es lc pi 0.81 ej 0.49 0.76 eo 0.49 0.44 0.89 pd 0.47 0.42 0.39 0.88 loc 0.33 0.38 0.36 0.43 0.77 es 0.32 0.30 0.26 0.40 0.41 0.68 lc 0.29 0.28 0.18 0.35 0.29 0.39 0.73 iv. results having a valid and reliable model for ethical decision making in the context of information technology, we tested our hypotheses. as depicted in figure 2, results showed that at the significance level of p<0.05, all hypothesized paths are confirmed except for the direct paths from law to ethical obligation (b=0.02 and t-value=0.13) and codes of ethics to ethical intention (b=0.01 and t-value=0.11). figure 2 also shows r2 values for dependent variables of ethical judgment (0.16), ethical obligation (0.48), and ethical intention (0.32). moreover, two paths for indirect effects are as follows: • perceived importance on ethical intention through ethical judgment; • ethical judgment on ethical intention through ethical obligation. the indirect effect of law on ethical intention is not significant since the direct path from law to ethical obligation is not significant (b=0.02 and t-value=0.13). considering direct and indirect effects, the total effects on ethical intention are 0.62 for perceived possibility of disclosure, 0.80 for perceived importance, 0.51 for ethical judgment, 0.24 for ethical obligation, 0.43 for ego strength, and 0.44 for locus of control. in addition, 32% of the variance of ethical intention is explained by perceived possibility of disclosure, perceived importance, ethical judgment, ego strength and locus of control. furthermore, 29% of the variance of ethical judgment is explained by perceived importance and 48% of the variance of ethical obligation is met by ethical judgment. no unexpected path is revealed. v. discussion perceived importance has a significant direct effect on ethical intention; therefore hypothesis h1a is confirmed. perceived importance has been a valid and widely used construct in ethical decision making models. in [64], authors declared that if perceived importance of an ethical issue in an individual is high, the intention to commit an unethical action is low. this is in accordance with the findings of the present study. this is due to the perception of the decision makers that implies the degree of criticalness of the situation [65]. it was also found that perceived importance positively affects ethical judgment (h1b) and ethical judgment affects ethical intention (h2). thus h1b and h2 are confirmed. engineering, technology & applied science research vol. 7, no. 2, 2017, 1567-1574 1571 www.etasr.com bolhari et al.: perceived possibility of disclosure and ethical decision making in an… concerning the impact of ethical judgment on ethical intention, our finding supports previous endeavors [27, 28, 31]. this happens regardless of the context of decision making; either it or non-it. in [66], authors stated that when a person is higher in ethical judgment, he/she tends to commit a higher ethical decision. in [67], authors redefined ethical judgment as the way a person evaluates which actions fit which occasions. since ethical judgment is commonly met by immediate and routine mental process [26], this reveals the logic behind the impact of ethical judgment on intention. an indirect effect of perceived importance on ethical intention through ethical judgment was observed. the same finding were reported in [64]. this is in accordance with [14, 65] that uncovered the role of perceived importance on ethical intention in an it context. to interpret this relation, we may justify that if someone perceives a high-important issue, their ethical judgment strengthens and this lowers their intention level. in the third hypothesis, we investigated the impact of ethical judgment on ethical obligation and found that ethical judgment is an indicator of ethical obligation. although there are no evidences about this hypothesis in it, a significant impact among u.s. business students has been reported in [65]. the impact of ethical obligation on ethical intention was tested in the fourth hypothesis and we observed a direct impact. similarly, in [36], authors found a positive relation between ethical obligation and intention among computer college students. earlier, this relation was put into test between 423 united states’ students of computing classes with the same findings [15]. likewise, in [23] authors presented similar results with it-based scenarios. fig. 2. structural model in our research, we did not find any meaningful impact from law on ethical obligation and codes of ethics on ethical intention. so, h5 and h6 are not confirmed. there have been contradictory findings concerning law and codes of ethics. for instance, in [17] authors found that law (legal perception) has a positive impact on ethical obligation only in two of their five scenarios. they concluded that among automobile sales people, law is not an indicator of ethical obligation. on the other hand, in [68], authors showed that codes of ethics are a substantial indicator in predicting ethical intention among hong king’s companies. in [2], it was argued that although individuals may be aware of laws in their society or organizational norms, but they prefer not to adhere to them. he then adds that this might be due to their understandings of law and codes of ethics as a behavior-limiting factor in ethical decision making [69]. instead, law and codes of ethics must be an integral part of the behavior of every individual. we may refer to three reasons why the impact of law on ethical obligation is not supported. first, the enactment of cyber-space laws in iran goes back to 2000s. for instance, computer crimes law (enacted in 2009), electronic commerce law (enacted in 2004), and supporting software developers’ rights law or namely copyright law (enacted in 2000) are only a decade old and contain a number of problems that affect their applicability and efficiency [70]. moreover, the majority of people in iran, even it professionals, are not familiar with laws [71]. furthermore, designated punishments in the above mentioned laws are not preventive measures. almost the same reasons may apply to codes of ethics. in [2], it was propsoed that law and codes of ethics may be proper mechanisms to prevent unethical actions through organizations. however, regarding our findings in it ethics, this domain requires further investigations. considering hypotheses 7 and 8, like other researchers, we found that ego strength and locus of control each have direct impact on ethical intention. in [54], the same finding among managers in the united states was reported. it was affirmed that locus of control is an indicator of ethical decision making, but functions differently for people with internal or external locus of control. the one who looks at others and takes his/her decisions based on their actions, has more powerful external locus of control and the one who takes decisions individually, possesses more influential internal locus of control. a crosscountry research between u.s. and taiwan business managers revealed that locus of control was an indicator of ethical intention, but it was more significant in taiwan [71]. however, findings in another it study between university students in malaysia revealed that locus of control and ego strength do not affect intention [23]. in an it context, in [14] it was found that ego strength has a direct effect on ethical intention, but they did not report the same for locus of control. this contradiction may be referred to different scenarios and samples. further investigations may clarify the role of locus of control and ego strength. in the ninth hypothesis, we noted a direct impact from perceived possibility of disclosure on ethical intention. thus, h9 is confirmed. as we stated earlier, we developed perceived possibility of disclosure as a new construct in the decision making context. to further investigate the impact of perceived disclosure on ethical decision making, we conducted a simple survey based on six unethical scenarios originally derived from [6]. each scenario is followed by a single question: “if you were 100% sure that nobody will understand that you have had committed this action, how likely would you do it?” respondents were to choose from six answers: impossible (scored 0); very unlikely (scored 1); unlikely (scored 2); maybe (scored 3); likely (scored 4); and very likely (scored 5). they engineering, technology & applied science research vol. 7, no. 2, 2017, 1567-1574 1572 www.etasr.com bolhari et al.: perceived possibility of disclosure and ethical decision making in an… were assured that their responses will be confidentially saved solely for research purposes. the results of analyzing 166 returned questionnaires revealed astounding facts (table iv). regardless of the scenarios, by average, more than 82 percent of the respondents claimed to “likely” or “very likely” would do the unethical action. it is notable that only 16 persons of the respondents (about 10%) reported “impossible” or “very unlikely” to the scenarios. table iv. results of analyzing scenarios scenario ave.* (%) stdev. no. of responses scored 4 or 5 % of responses scored 4 or 5 no. 1 3.99 (79.76) 1.34 124 77.01 no. 2 4.01 (80.12) 1.29 117 72.67 no. 3 3.99 (79.76) 1.23 120 74.53 no. 4 4.13 (82.65) 1.16 130 80.74 no. 5 4.34 (86.75) 1.03 142 88.19 no. 6 4.23 (84.70) 1.18 134 83.22 total 4.12 (82.31) 0.50 82.31 *average varies from 0 to 5. vi. conclusions in this study we tried to model how an ethical decision is made in an information technology context. our findings approved previous endeavors that perceived importance of an issue, ethical judgment, ethical obligation, ego strength and locus of control affect one’s ethical intention. further, the possibility of disclosure surfaces as a significant factor. moreover, it was found that law and codes of ethics do not affect ethical intention. this is in alignment and also contradiction with previous research studies. to mention this research’s limitations, we might refer to the possible impact of religion on ethical intention. however, it has been proposed that this factor has a low impact on the it field [73] and even the core logic behind this argument has been challenged [23]. the same argument can be supported for culture [74]. finally gender and demographic factors have not been considered, and this should be a field for future studies. appendix all the names (persons and companies) in the following scenarios are imaginary. any similarity is unintentional. scenario 1: target marketing in banks alfa bank, as the biggest public bank of the country, owns a business intelligence system to validate customers and offer marketing plans for each accredited customer individually. mason, an information technology expert who was involved in the development of the business intelligence system, has authorized access to its data warehouse. he has a friend, james, in one of the branches of the alfa bank. mason extracts a list of customers who are recommended to be offered with ease-loan (a loan that is easily payable to a customer due to his/her credits) and gives it to james. he calls each customer and offers an ease-loan with a commission of 2 percents. mason and james share the commission. after that, mason permanently deletes the records of the customers from the data warehouse. scenario 2: health information system the ministry of health affairs employs a health information system (his) with a module named "fraud detection". this module helps find forged medical documents and expenses. all the public and private hospitals and institutes have controlled and authorized access to the information system. dr. brooks, a general practitioner employed in the ministry of health affairs, has been engaged in the process of his development to clarify business requirements. accidentally, he has an admin access to his since the information system is published country-wide. dr. brooks, as a user of the system, frequently uses admin features to ease and facilitate working processes and to avoid bureaucracy. scenario 3: insurance database milton, a graduate student in software engineering, works for marion insurance company. he has an authorized access to the database with more than 100 million records. as a part of his job, milton extracts rules (rule extraction) by data mining techniques and reports to his supervisor. for instance, he finds that those customers who are younger than 24, are single and have a record of more than one accident, are classified as high risk customers. milton decides to document the data mining process and hand-in a collection of the rules to his data mining course in university. scenario 4: widget development felix is a software developer and works in a company that sells and supports software packages. the company has numerous projects. felix is a member of a team that works on developing a financial management system (fms). he has developed a reporting widget which delivers customized and drill-down features. since felix has developed the widget by himself, he also uses its source code in a software package that he is developing for himself at weekends at home. scenario 5: stockbroker dalton stockbroker corporation has a decision support system (dss) which analyzes stock exchange transactions and generates short-term buy-orsell quotes using a neural network engine. this company offers a monthly membership plan for 25 usd and presents at least 15 quotes. sheridan, an it specialist in the company, has an authorized access to dss and she is responsible for database maintenance. she extracts quotes daily and sends a few of them to her husband to buy or sell stocks and earn profits. scenario 6: 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comparison", issues in information systems, vol. 12, no. 1, pp. 78-87, 2011 engineering, technology & applied science research vol. 8, no. 1, 2018, 2562-2567 2562 www.etasr.com bewoor and patil: empirical analysis of single and multi document summarization using clustering … empirical analysis of single and multi document summarization using clustering algorithms mrunal s. bewoor department of computer engineering bharati vidyapeeth (deemed to be) university college of engineering pune, india msbewoor@bvucoep.edu.in suhas h. patil department of computer engineering bharati vidyapeeth (deemed to be) university college of engineering pune, india shpatil@bvucoep.edu.in abstract—the availability of various digital sources has created a demand for text mining mechanisms. effective summary generation mechanisms are needed in order to utilize relevant information from often overwhelming digital data sources. in this view, this paper conducts a survey of various single as well as multi-document text summarization techniques. it also provides analysis of treating a query sentence as a common one, segmented from documents for text summarization. experimental results show the degree of effectiveness in text summarization over different clustering algorithms. keywords-text mining; text summarization; clustering i. introduction the extensive use of internet has caused a vast growth in the usage of digital information. people use online information services, like social media, every day resulting to the availability of a huge amount of unstructured digital information. this information is directly accessible to a large number of end-users [1-2]. the user accesses this information through queries, but the improvement of precision and speed is always an issue. the information retrieval (ir) systems have resolved this to some extent. this information overload problem is more sensitive when there is a need of taking a decision or of deep understanding of a problem the ir systems solve this through user issued queries the obtained result most of the times overwhelms users with too many answers, and provided documents that may not be relevant to the topic asked. the multi document summarization has an ability to summarize a complete document set. ideally it is a process of query shared information extraction through a set of multiple text documents. the techniques used in single-document summarization can also be used in multi-document summarization [3]. the comparison of single and multidocument summarization is presented in table i. web information retrieval relevant to the issued query is a tedious task. information retrieval tools can be used for retrieval relevant to the topic specified by the query. the results obtained sometimes may not preserve the required content. summary generation or automatic text summarization is the creation of abstracts or summaries, with the help of a computer program, from one or more documents. there are specifically two types of text summarization techniques, generic and query specific [4]. it becomes a difficult task for the user to go through a large number of retrieved documents [5]. this difficulty can be resolved with the use of query specific document summary generation. the generated summary or abstract must preserve the semantics and central idea of an input text [6]. below we present the main existing approaches to multi document summarization: a. feature based method the extractive type summarization approach identifies the most related sentences from the original text and place them together to generate a concise summary. the process identifies relevant sentences based on features like sentence length, word frequency title word, sentence position, cue word, proper noun etc. b. cluster based method the initiative of clustering is to group similar objects into classes. in case of multidocument summarization, these objects refer to the sentences and the classes represent the cluster each sentence belongs to. considering the type of documents that concentrate on different subjects or topics, some of the researchers try to integrate the clustering concept based on the sentence similarity. the most common similarity measure is cosine similarity. the sentence selection is performed by selecting sentences from each cluster on the basis of ranking tfidf in that cluster. c. graph based method this method uses the basic concept behind the graph to represent the relationship elements. related elements in the graph are linked. in case of text, the element relationship is the similarity between the sentences. it is represented as an ordered pair graph g=(v, e), where v is set of elements representing sentences and e is set of edges representing the association among the sentences. the strongly connected sentences are considered in the summary. many graph based approaches use cosine similarity to identify the association. engineering, technology & applied science research vol. 8, no. 1, 2018, 2562-2567 2563 www.etasr.com bewoor and patil: empirical analysis of single and multi document summarization using clustering … d. knowledge based method the documents are organized with the text content related to a specific topic belonging to a particular domain. every domain has a common knowledge structure. the researchers have common background knowledge structure (i.e. ontology) to improve the summary results. there have been efforts to utilize the background knowledge. many applications have tailored their model to be ontology-driven [4]. ontology can be useful for domain specific documents where key concepts corresponding to the domain can be identified. the technique is implemented as query specific related to the respective domain by identifying keywords. e. our approach this paper presents a combined approach by using topic queries or important keywords corresponding to the document set and the fundamental concept of clustering as well as language features to extract the relevant sentences from the original document set. the features of clustering algorithms and nlp based retrieval can be useful in preserving the context of the information in the retrieval process [7]. table i. comparison of single and multiple document summarization process comparison features single document summarization multi-document summarization degree of coherence change in sequence of sentence selection do not affect the degree of coherence. the order of sentence selection may affect the degree of coherence. redundancy topics in a single document are related. the degree of redundancy is high. some information that may be seen as redundant might be important and vice versa. compression ratio usually much smaller usually higher. crossreference cross reference resolution can be easily resolved cross reference resolution is a greater challenge ii. system architexture the process of automatic text summarization consists of mainly two tasks. the first one is to recognize the most significant text portions and the second is to obtain the coherent summaries. information retrieval (ir) process is used to search documents on web. since massive amount of vague data is available on the web [8], the use of ir tools has given rise to the necessity of query dependent document summarization. the ir system has demoralized the natural language processing techniques to support a range of natural language queries. the type of query processing for text summarization without nlp support may result in imprecise summary and user may not view correct or reliable results [9]. the system considers original document or document set in txt form. documents are preprocessed using basic steps of natural language processing (nlp), like sentence detection, tokenization, part-of-speech tagging, chunking and parsing. the nlp is implemented using the open nlp tool. the nlp steps help to identify the correct word match with respect to the context within the document by removing the ambiguity if any [10]. the result obtained after pre-processing is further given to clustering algorithms along with the keywords used for summarization process. the clustering algorithms such as em, graph based method, fuzzy c-means, dbscan, and hierarchical clustering algorithms are used to obtain the summary. the summary is also computed with a simple query specific approach [11]. the result obtained as a summary can be evaluated on the basis of qualitative and quantitative metrics. the precision, recall and f-measure are quality measuring metrics and compression retention ratio are quantity measuring metrics [12]. fig. 1. system architecture. iii. impact of clustering in auto text summarization the concept of clustering is very helpful in the text domain as document objects as words, sentences, paragraphs to be clustered are of varying granularities. clustering is particularly useful to put together documents to get better retrieval and support browsing. in [13], authors recognized and selected clustering algorithms for obtaining document summary. the main motive of the research was to extract in the summary those sentences that are more relevant to the original input text by using clustering algorithm features which can group the objects based on the relevancy [14]. the approach tries to combine two major approaches of summary generation: extractive and is abstractive. results obtained with different methods are then evaluated for the summary quality. iv. experimentation and result discussion results are tested for the inputs from existing datasets like reuter. reuter dataset is a popular dataset for text mining experiments. different splits into training test and unused data have been considered. in the case of abstractive type of engineering, technology & applied science research vol. 8, no. 1, 2018, 2562-2567 2564 www.etasr.com bewoor and patil: empirical analysis of single and multi document summarization using clustering … summarization, the quality of the summary obtained is more important. this quality is judged on the basis of qualitative evaluation parameters. the length or the size of the summarized text is evaluated on the basis of quantitative measures compression ratio and retention ratio. results obtained are compared on the basis of these evaluation measures. the summaries generated are also compared with existing query summarizers, copernic summarizer and web summarizer. these two tools are query based summarizers[15]. the values for these parameters for the corresponding document are calculated as shown below. precision indicates the probability at which the retrieved document is relevant in the search: precision=no. of different terms in summary/no. of different terms in query. recall is the probability that relevant document is retrieved in the search: recall=no. of correct matching sentences in the summary/no. of all relevant sentences in the original document f-measure is the harmonic mean of precision and recall: f-measure= 2*((precision*recall)/(precision+ recall) compression ratio= no. of sentences in summary/total no. of sentences in original document. retention ratio=no. of relevant query words in summary/no. of query terms in original data. precision, recall and f-measure measure the quality of the summary, and so they, along with execution time, are called qualitative parameters [16]. compression ratio and retention ratio measure the length or quantity of the sentences in the summary and therefore are called quantitative parameters. results are shown in tables ii-iv and figures 2-7 for various methodologies in data obtained from wikiart (data set a, single document summarization), reuter (data set b, multi document summarization) and wiki internet (data set c, multi document summarization) data sets. table ii. performance evaluation for data set a methodology precision recall f-measure compression ratio retention ratio execution time expectation maximization clustering 1 0.1 0.18182 0.04776 0.70394 5,516 fuzzy c-means 1 0.07627 0.14173 0.03582 0.86227 78 db-scan clustering 1 0.03383 0.06545 0.08955 0.93577 123 graph theorotic clustering 1 0.0604 0.11392 0.06567 0.94715 76892 hierarchical agglomerative clustering 1 0.03435 0.06642 0.08955 0.93577 496 query specific 1 0.03383 0.06545 0.08955 0.93577 41 copernic 1 0.5263 0.1 0.0806 0.63737 1,451 web summarizer 1 0.5263 0.1 0.0806 0.5708 786 table iii. performance evaluation for data set b methodology precision recall f-measure compression ratio retention ratio execution time expectation maximization clustering 0.77778 0.10588 0.18639 0.02738 0.91125 20,206 fuzzy c-means 1 0.01415 0.02791 0.0306 0.95639 995 db-scan clustering 1 0.00904 0.01791 0.0306 0.98448 46 graph theorotic clustering 0.55556 0.02206 0.04243 0.01852 0.98742 6,788 hierarchical agglomerative clustering 1 0.00907 0.01798 0.0306 0.98448 8,809 query specific 1 0.00904 0.01791 0.8306 0.98448 20 copernic 0.22222 0.01305 0.02466 0.00725 0.8198 3,593 web summarizer 0.22222 0.01004 0.01921 0.00725 0.74515 1,601 table iv. performance evaluation for data set c methodology precision recall f-measure compression ratio retention ratio execution time expectation maximization clustering 1 0.15254 0.26471 0.07595 0.73022 3,419 fuzzy c-means 1 0.07627 0.14173 0.10127 0.85801 60 db-scan clustering 1 0.03125 0.06061 0.10127 0.94967 20 graph theorotic clustering 1 0.07563 0.14062 0.10127 0.95827 705 hierarchical agglomerative clustering 1 0.03169 0.06143 0.10127 0.94967 662 query specific 1 0.03125 0.06061 0.10127 0.94967 43 copernic 1 0.02083 0.04082 0.06329 0.6572 380 web summarizer 1 0.02778 0.05405 0.08228 0.69023 842 engineering, technology & applied science research vol. 8, no. 1, 2018, 2562-2567 2565 www.etasr.com bewoor and patil: empirical analysis of single and multi document summarization using clustering … fig. 2. comparison graph of all summaries for data set a fig. 3. comparison graph of execution time for various summarization methods in data set a fig. 4. comparison graph of all summaries for data set b fig. 5. comparison graph of execution time for various summarization methods in data set b engineering, technology & applied science research vol. 8, no. 1, 2018, 2562-2567 2566 www.etasr.com bewoor and patil: empirical analysis of single and multi document summarization using clustering … fig. 6. comparison graph of all summaries for data set c . fig. 7. comparison graph of execution time for various summarization methods in data set c v. conclusion results generated by all summarization methods are evaluated considering result quality with respect to the context within the input text and the length of the input text. document summarization should focus on the context, length being the secondary aspect. fuzzy c means generates better summary. considering both quantity and quality parameters, clustering is an unsupervised text summarization technique, which can be used as supervised by integrating it with a supervised approach. this may give an optimal solution for this problem. the research work should focus on improving the quality of clusters which directly relates with the gist of the original input document. references [1] a. kaushik, s. naithani, “a comprehensive study of text mining approach”, international journal of computer science and network security, vol. 16, no. 2, pp. 69–76, 2016 [2] r. varadarajan, v. hristidis, “a system for query-specific document summarization”, 15th acm international conference on information and knowledge management, pp. 622-631, 2006 [3] j. goldstein, v. mittal, j. carbonell, m. kantrowitz, “multi-document summarization by sentence extraction”, naacl-anlpworkshop on automatic summarization, vol. 4, pp. 40–48, 2000 [4] y. j. kumar, n. salim, “automatic multi document summarization approaches”, journal of computer science, vol. 8, no. 1, pp. 133–140, 2012 [5] s. gholamrezazadeh, m. a. salehi, b. gholamzadeh, “a comprehensive survey on text 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[16] m. hassel, evaluation of automatic text summarization, licentiate thesis, 2004 engineering, technology & applied science research vol. 7, no. 5, 2017, 1922-1929 1922 www.etasr.com hamdi et al.: rectangular strain-rosette method for measuring the mode i stress … rectangular strain-rosette method for measuring the mode i stress-intensity factor ki and t-stress adel hamdi el manar preparatory institute for engineering studies, tunis, tunisia ahamdi.tu@gmail.com noureddine benseddiq lille laboratory of mechanics university of lille villeneuve d’ascq, france noureddine.benseddiq@univ-lille1.fr fatah mejni lille laboratory of mechanics university of lille villeneuve d’ascq, france fatah.mejni@gmail.com abstract—in this paper, a new experimental technique for measuring stress intensity factor (sif) and t-stress under mode i loading is developed. the expressions of the normal and tangential strains close to the crack tip are given using the first five terms of the generalized westergaard formulation. in order to accurately determine the sif and t-stress, the method exploits the optimal positioning of a rectangular strain gage rosette near a crack tip in mode i. thus, errors due to the higher order terms of the asymptotic expansion are eliminated. finally, a comparison of the analytical results with finite element calculations, for different specimen dimensions, is carried out. keywords-fracture toughness; stress intensity factor; t-stress; strain gage; finite element method i. introduction in linear elastic fracture mechanics (lefm), the primary focus is generally based upon the stress intensity factor (sif), as a critical parameter, that defines whether an existing crack in a specimen grows or not. it is proportional to the first singular term of the williams [1] series expansion. accurate values of sif are necessary to predict and prevent fracture in components. the approach, based on a single parameter, is not able to fully interpreting some circumstances that occur. nevertheless, there is experimental evidence [2, 3] showing that the constant stress may affect fracture mechanics properties. a second parameter, introduced in [4], also plays an important role in fracture processes and commonly referred to as the t-stress, which is the second non-singular term in the williams [1] series expansion. it represents the stress acting parallel to the crack plane and it is independent of the distance from the crack tip and proportional to the applied stresses. tstress plays a key role in stability of the crack paths and it has a significant influence on the shape and the size of the plastic zone around the crack tip in ductile materials [5-8]. to determine the sif in cracked specimens, three methods have been developed over the last years [9], analytical, numerical and experimental. due to the complexity of the mathematical developments, analytical methods are limited to simple configurations and therefore one must resort to numerical or experimental methods [9]. experimental techniques, such as the compliance [10, 11], photo-elasticity [12-14], caustics [15, 16] and strain gage [17, 18] methods were developed. strain gage technique is the most common method used to analyse stress field. it is relatively simple because it can measure surface strains accurately directly within strain gradient zones. the use of strain gages to determine the sif near the crack tip has been suggested [19]. other experimental methods like compliance measurements and photo-elasticity were developed [20, 21], however, they have some limitations in the case of opaque materials. authors in [17] were the first to develop a simple strain gage technique allowing to measure the static mode i sif of isotropic bodies. they identified the region, around the crack tip, for accurate measurement of the strains. to describe the strain field, the authors used a truncated strain series, based upon the generalized westergaard approach [22]. the main advantage of the dally and sanford method is that only one strain gage is sufficient to determine the mode i sif, which can be placed far away from the crack tip. however, this technique requires prior knowledge of the strain representation which is a function of the specimen’s geometry and the applied loading. on one hand, authors in [23] and [24] extended the technique described in [17] to mixed mode sif and dynamic sif, respectively. on the other hand, authors in [25] and [26] used the technique from [17] with static and dynamic cracks, respectively. note that no procedure for selection of radial location of strain gage was reported in their works. authors in [27] determined, for some cracked samples, the dynamic sif in isotropic materials by placing strain gages within the singularity dominated zone. in [31], authors determined, using strain gage technique, mode i sif by solving large number of deterministic equations. other strain gage methods specifically designed for measuring static mode i sif have been proposed in [28] and [29]. authors in [28] used two strain gages for measuring the mode i sif. however, the locations (radial distances) of the strain gages necessitate, beforehand, the knowledge of the plastic zone size. authors in [29] developed a single strain gage technique based on the asymptotic strain expressions. they suggested that strain gages could be placed at distances, from the crack tip, greater than half the specimen thickness measured. their results showed that the measured normalized sif is a function of the applied loads, the thickness of the specimen and the angular position from the crack. recently, another technique was proposed [30], using a three strain gage rosette to determine the mixed mode sif. placing the rosette engineering, technology & applied science research vol. 7, no. 5, 2017, 1922-1929 1923 www.etasr.com hamdi et al.: rectangular strain-rosette method for measuring the mode i stress … near the crack tip but outside the plastic zone was suggested. one can conclude from the literature investigation that the single strain gage method [17] is widely used compared to other strain gage techniques. while some recommendations available for radial locations of strain gage were developed in [26, 28, 30]. note that, in their works, also, no procedures were mentioned for determination of valid radial locations. the only attempts have been made by authors in [32-34] to determine the optimal radial locations using single and double strain gage cracked configurations. in fact, in their works, they [32, 33] presented a new methodology based upon the finite element analysis (fea), supported by theoretical foundations. experimental validation of the methodology for determination of maximum permissible strain gage radial location is presented in [34]. to numerically and analytically determine the t-stress, different methods have been proposed in the literature for different types of specimens. authors in [35, 36] showed that the sign and the magnitude of the t-stress substantially change the size and shape of the crack tip plastic zone. in [37, 38] authors showed that t-stress can be evaluated using a modified j-integral based on fea. in [39] authors have studied the stress field around the crack front for a single edge specimen subjected to bending and tension to determine the tstress in a three-dimensional model. similar investigation was conducted in [40] for center cracked plates. in [41] authors have evaluated elasto-dynamic t-stress by using the interaction integral from the boundary element solution. in [42] authors have developed a stress difference method to evaluate the tstress with a crack problem. authors in [43] determined, using fea, the t-stress and obtained stabilised t-stress distribution along ligament. despite the importance of the t-stress, the experimental techniques, dealing with accurate measurement of t-stress are very limited in the literature. inspired by the fact that thermoelastic stress analysis (tsa) is an ideal technique for the determination of mode i, ii and mixed sif [44, 45], authors in [46] have developed a technique to determine the tstress and mixed-mode sif from tsa images. also, the same authors [47] developed a technique to determine the t-stress and mode i sif from digital image correlation (dic). fe simulation was undertaken and good agreement between experimental and numerical results was found. they concluded that the technique is applicable for fatigue crack studies and tstress determinations. an extension was made [48] to the method described in [17] to calculate the mode i sif and tstress. they used rectangular rosettes to evaluate the t-stress. this work deals with the development of a new method for sif and t-stress determination by using one or two rectangular rosettes. as a first step, the formulation of the normal strains, close to the crack tip, are given using the first five terms of the generalized westergaard formulation [22]. then, in a second step, these formulations are applied to analytically determine the optimum locations for the rectangular rosette to eliminate the errors due to higher order terms of the asymptotic expansion. ii. problem formulation in [17] was showed that the region around a crack tip (traction free crack faces) can be divided into three zones: very near field (zone i), near field (zone ii) and far field (zone iii) as shown in figure 1. zone i is closed to the crack tip and the first singular term of the strain series is sufficient to represent the strain field. however, it is not a valid zone for accurate measurement of strains because the stress state is threedimensional [49] and the strain field is severely affected by the plasticity. also, errors in measuring the position of the strain gage are excessive if they are located very close to the crack tip. zone iii is not either suitable for strain calculation because a large number of terms in the strain series is required to obtain accurate results. therefore, it was identified [17] that the intermediate region (zone ii) is favourable and optimum for accurate measurement of the strains. in this zone, a singular term and a small number of higher order terms correctly describe the strain field. fig. 1. different regions around the crack tip. a. multi-term representation of the strain field the equations of the near strain field are calculated using the generalized westergaard approach [22]. thus, the modified airy stress function is given by:      ( ) ( ) ( ) (1)z z y z z y y z       where , , d z d z dy z z y dz dz dz    (2) and the complex analytic functions z(z) and y(z) are defined as: 1 1 2 2 0 1 ( ) (3) 2 n nn n i n n n n k z z a z a z z         0 0 1 ( ) (4) 2 m m m mx m m m m y z b z b z        for a given problem, these series, in terms of the complex variable z = x + iy, contain an infinite number of coefficients (a0, a1, a2,….., a∞ ; b0, b1, b2,….., b∞) that can be determined using the boundary conditions. the stress components for the entire domain are represented in [17] as:       ( ) ( ') ( ') 2 ( ) ( ) ( ') ( ') ( ') ( ') ( ) xx yy xy z y z y y z y z y y z y y                         (5) engineering, technology & applied science research vol. 7, no. 5, 2017, 1922-1929 1924 www.etasr.com hamdi et al.: rectangular strain-rosette method for measuring the mode i stress … by substituting (5) into the plane stress-strain relations:     1 1 1 xx xx yy yy yy xx xy xy e e               (6) one can obtain the following generalized equations of the strain field:       1 2 1 2 ( ) ( ') ( ') 2 ( ) ( ) ( ') ( ') 2 ( ) ( ') ( ') ( ) xx yy xy e f z f y z y y e f z f y z y y y z y y                            (7) where f1 =1-, f2 =1+. the substitution of the complex functions z(z) and y(z), from (3) and (4), gives an exact representation of the strain field, in the domain, with an infinite number of coefficients an and bm. it is assumed that the strain field in the zone ii is sufficiently represented, by the five terms series, n =0, 1, 2 and m =0, 1, with the unknown coefficients a0, a1, a2, b0 and b1. in this zone, the five terms representation of the strain field is expressed as:                   1 2 1 2 0 1 0 2 2 0 1 2 1 1 3 22 1 2 2 cos 2 sin 2 sin 3 2 2 cos 2 sin 2 2 cos( ) (8) 3 cos 3 2 sin sin 2 2 xxe f f a r b r f f a r b f f a r o r                                               1 02 1 2 0 0 1 2 2 1 2 1 1 3 22 1 2 2 cos 2 sin 2 sin 3 2 2 cos 2 sin 2 2 cos( ) (9) 3 cos 3 2 sin sin 2 2 yye f f a r b r f f a r b r f f a r o r                                       1 1 2 2 2 0 1 3 22 1 2 sin( ) cos 3 2 cos 2 (10) ¨ 4 3 cos 2 xye f a r a r b r a r o r               in these equations, a0, a1, a2, b0 and b1 are determined using the specimen geometry and the boundary conditions. the coefficients a0 and b0 are proportional, under a mode i loading, to the sif ki and the t-stress, respectively: 0 0 2 (11) 2 (12) ik a t b   b. five-term strain field relative to a rotated coordinate system the strains relative to a rotated coordinate system (α, β), with its origin at an arbitrary point p(r,) as defined in figure 2, are determined from the first strain invariant as: xx yy       (13) fig. 2. strain gage location and orientation [17]. the complex form of the strain transformation equations is expressed as the following form:   2iyy xx xyi i e             (14) for an angle  that coincides with , substituting (7) into (14) leads to:         1 2 2 ( ) ( ) ( ') ( ') ( ) cos(2 ) ( ') ( ') ( ) sin(2 ) rre f z y f y z y y f y z y y                 (15)         1 2 2 ( ) ( ) ( ') ( ') ( ) cos(2 ) ( ') ( ') ( ) sin(2 ) e f z y f y z y y f y z y y                 (16) replacing n = 0, 1, 2 and m = 0, 1 in (3) and (4) and substituting the results for the truncated series into (15) and (16) gives:     1 2 1 2 0 0 1 2 0 1 2 1 2 1 1 2 1 3 cos cos cos 2 4 2 2 cos(2 ) 1 5 + cos cos cos (17) 2 4 2 2 1 + cos( ) cos( ) 3 cos(3 ) 2 rre f f a r f f b r f f a r f f                                                                       1 3 2 1 2 2 2 3 3 3 7 + cos cos cos 2 4 2 2 b r f f a r o r                                 engineering, technology & applied science research vol. 7, no. 5, 2017, 1922-1929 1925 www.etasr.com hamdi et al.: rectangular strain-rosette method for measuring the mode i stress …     1 2 1 2 0 0 1 2 0 1 2 1 2 1 1 2 1 3 cos cos cos 2 4 2 2 cos(2 ) 1 5 cos cos cos (18) 2 4 2 2 1 cos( ) cos( ) 3cos(3 ) 2 e f f a r f f b r f f a r f f                                                                         1 3 2 1 2 2 2 3 3 3 7 cos cos cos 2 4 2 2 b r f f a r o r                                   c. rectangular strain-rosette location and orientation note that it is possible to obtain the data necessary to determine ki and t-stress by using single or two rectangular rosettes placed in zone ii. equations (17) and (18) are used to determine an optimal location of the rosette capable to eliminate some higher order terms. indeed, two approaches will be described herein to illustrate the procedure: 1) the single rosette is used to provide the data necessary to evaluate ki with a three term solution and t-stress with a two term solution; 2) the two rosettes are used to provide the data necessary to evaluate ki and t-stress with a four term solution. each of these two approaches will be developed below as an individual case. c.1. case i: single rectangular rosette  ki determination with three term solution the singular term a0 can be calculated along any direction , where the constant term b0 vanishes or can be set to zero by superposing rr with an appropriate fraction of . using (17) and (18), it is evident that the constant b0 will vanish if:                    1 2 1 2 1 2 1 3 2 2 0 1 3 2 2 1 1 3 3 2 2 22 2 cos(2 ) cos(2 ) 2 cos / 2 1 8 sin / 2 2 cos / 2 1 4 sin / 2 4 sin( ) sin(2 ) (19) 2 cos / 2 4 sin ( ) 12 sin / 2 1 rr e f f f f f f a r a r b r a r o r                                  considering (19), note that the term a1 can be eliminated if: 3     (20) when substituting (20) into (19), one can obtain the following relation:   2 1 1 3 22 2 0 1 2 2 3 3 3 3 3 4 4 rr rre f f a r b r a r o r                  (21) this result indicates that a single two element rectangular rosette can provide the necessary data to calculate the ki, with a three term solution, if  is selected as (20). substituting (11) into (21), the expression of ki can be written as:     1 2 2 2 1 2 1 3 3 rr i r e k f          (22) where 1 2 1 1 f f        whatever the type of used material, (22) represents the relation between ki and the normal strains rr and . it can be measured using two elements of a rectangular rosette, placed in zone ii, along a radial line drawn from the crack tip  = ±60°. for example, when considering an aluminium specimen with =1/3, the substitution of f1 =2/3 and =1/2 into (22) gives: 2 2 3 rr i r e k    (23) one can notice from (23) that, for an aluminium material, a single strain gage is sufficient to provide the data necessary to evaluate ki value. note that (23) is the first formula proposed by authors in [17].  t-stress determination with two term solution generally, the advantage to use a two strain gage rosettes is to providing the first two terms of the asymptotic expansion. therefore, it is possible to obtain the necessary data to determine the t-stress, from a two-term representation, by using the same rectangular rosette placed in zone ii along = ± /3. it is clear that (17) and (18) subjected to the restriction of (20), respectively, lead to:           1 02 1 2 0 1 2 0 1 2 1 2 1 1 2 1 3 22 1 3 1 4 2 8 2 3 1 2 2 7 4 4 3 3 8 rre f f a r f f b r f f a r f f b r a r o r             (24)           1 02 1 2 0 1 2 0 1 2 1 2 1 1 2 1 3 22 1 3 1 4 2 8 2 3 1 2 2 7 4 4 3 3 8 e f f a r f f b r f f a r f f b r a r o r             (25) if (24) and (25) are truncated after the first two terms, their resolutions directly provide the expressions of ki and t-stress. in this context, it is important to mention that ki is determined from a three term representation because the coefficients associated to b0 and a1 are proportional with a same factor of proportionality. therefore, the elimination of one of these two terms leads necessarily to the elimination of the other one. if engineering, technology & applied science research vol. 7, no. 5, 2017, 1922-1929 1926 www.etasr.com hamdi et al.: rectangular strain-rosette method for measuring the mode i stress … we use a two term description of the strain field around the crack tip, the natural elimination of a0 along the considered direction can be exploited to determine the t-stress. now, considering (24) and (25), it is evident that the dominant term a0 vanishes if:       1 2 1 2 1 2 1 0 2 0 1 3 22 1 2 4 4 6 3 3 15 3 3 rr e f f f f f f b r a r b r a r o r             (26) this result indicates that the same rectangular rosette, used to calculate ki, can be employed also to provide the data necessary to determine the t-stress from a two term representation. substituting (12) into (26), the expression of the t-stress becomes:     1 4 1 4 1 3 rre t f          (27) for example, when considering again the aluminium material with = 1/3, the substitution of f1 = 2/3 and = 1/2 into (27) gives:  3 2 rret      (28) the expressions (22) and (27) indicate that, when a rectangular rosette is placed in zone ii along  = ±60°, the measured strains rr and  allow to get the data necessary to evaluate ki and t-stress from a representation with three and two terms, respectively. c.2. case ii: two rectangular rosettes  ki determination with four term solution it is possible to obtain the data necessary to determine the ki value, from a four term representation, using two rectangular strain rosettes placed in two discrete locations in zone ii with the same value of  = ±60°. the four strain gage measurements, rra, , rrb, , and their respective positions ra, rb and a = b are used to solve (21) for a0 and b1. thus, when solving (21), for a0 (or ki) and b1, using data obtained from rosettes ra and rb, one can write:       3 2 1 2 2 2 1 2 1 (29) 3 3 1 a b a ba rr rr i e r q q k f q                         1 1 2 2 1 3 2 1 2 1 2 1 (30) 6 1 a b a brr rr b e q q b f r q                                  where ra = qrb. equations (29) and (30) can be rewritten as the following form: 3 2 3 21 a bi i i k q k k q    (31) 1 2 1 3 3 2 2 3 4 2 1 a bi i b q k k b q q r             (32) where kia and kib are calculated from (22). these are the sif evaluated, by the data of ra and rb, respectively, using a three term approach. to bring out the simplicity of our approach, consider again the aluminium specimen (= 1/3, f1 = 2/3 and =1/2). equations (31) and (32) become:   3 2 2 2 3 1 a ba rr rr i e r q k q           (33) 1 2 1 3 22 1 a brr rr b e q b r q               (34) it is clearly shown from (33) and (34) that, in this case, two strain gages are sufficient to evaluate ki and b1 values. note that (33) is the second formula proposed in [17], the authors of which used two strain gages, to determine the ki value for an aluminium specimen.  t-stress determination with four-term solution using the same data obtained with the rosettes ra and rb and solving (26), for b0 or t-stress, gives:         1 1 2 2 1 2 1 2 1 1 4 1 4 1 3 1 5 a b a brr rr b e q q t f q q r b                  (35) where the expression of b1 is given in(30) and (32). note that for b1 = 0, the expression in (35) leads to the t-stress expression for a three term representation. equation (37) can be rewritten as follows: 1 21 2 1 3 2 2 5 3 1 4 2 1 a bi i a b b q k k t q t t q r q                (36) where ta and tb are obtained from (27). these are the tstresses evaluated by the data, provided by ra and rb, respectively, with a two term approach. engineering, technology & applied science research vol. 7, no. 5, 2017, 1922-1929 1927 www.etasr.com hamdi et al.: rectangular strain-rosette method for measuring the mode i stress … again, when considering the aluminium material (= 1/3, f1 = 2/3 and = 1/2), (36) can be expressed as:    1 1 1 12 2 2 2 1 3 2 2 3 5 (37) 2 1 1 a b a b a brr rr rr rr q q q qe t q q                    finite element analysis based upon the stress and rectangular strain rosette methods described above, we used the fea with ansys software to determine the sif ki and the t-stress under mode i loading. d. finite element model the standard test using a central cracked plate (ccp) specimen is shown in figure 3. also, we have reported in the same figure the dimensions of the sample. the thickness is 6 mm in a plane strain state. the width of all samples is maintained at w = 50 mm, while, the length of the crack is variable. for the calculations, the values of a/w are taken equal to 0.2, 0.3 and 0.4. due to the symmetry, only one half of the ccp specimen is considered. in the crack tip region, 24 rows of elements were used. each row consists of iso-parametric quadratic triangular mesh with 0.05 mm size. a square root singularity in the stress/strain field was produced at the crack tip by considering quarter point scaling between the circumferential rows of nodes surrounding this region (figure 4). the specimen’s material is the aluminum t66082 with the mechanical properties: e = 75000 mpa, υ = 0.33 and kic = 29 mpa.m1/2. fig. 3. plate specimen with central crack under uniaxial tension. fig. 4. singular elements around the crack tip. e. results and discussion we calculated the sif obtained by placing the gages at different radii from 2 mm to 42 mm. the obtained results of the sif ki are shown in figure 5. however, when using two rosettes, ki is very stable regardless of the gage position in zone ii [17]; i.e. for a/w = 0.2 the distance is less than 16 mm and for important ratios of a/w, the distance is up to 30 mm. this result is in good agreement with the theory findings because the order of the asymptotic expansion in the case of two gages is higher. these results are compared to those obtained with the displacement method implemented in the fe software that we used. figure 6 shows the variation of the tstress as a function of the rectangular rosettes position with respect to the crack tip. the results are compared to those obtained by the stress method proposed in [43], t = xx yy for  = 0, for the three ratios a/w (0.2, 0.3 and 0.4). one can observe that the use of a single rosette requires a position close to the crack tip, where the stress field is very unstable. however, when the order of the asymptotic expansion is equal to 2 (case of two rectangular rosettes), the results become in good agreement with those of the stress method. otherwise, singular elements in the fe calculations allow to a better approximation of the stress field near the crack tip. thereby our results in terms of t-stress, obtained with the stress method, are very stable compared to those of the literature. fig. 5. sif for (a) a/w = 0.2, (b) a/w = 0.3 and (c) a/w = 0.4. engineering, technology & applied science research vol. 7, no. 5, 2017, 1922-1929 1928 www.etasr.com hamdi et al.: rectangular strain-rosette method for measuring the mode i stress … iii. conclusion in this paper we have proposed a simple method for determining the mode i sif (ki) and t-stress using one or two strain gage rosettes. a five term solution was derived from the generalized westergaard stress functions in order to give an experimental approach for measuring ki and t-stress. in fact, the use of one or two strain gage rosettes, placed in an only one orientation, is an important property of this method. two specific cases were considered in reducing the five term theory to a simple and practical approach. we have shown, on the one hand, that a single rectangular rosette with suitable placement and orientation can be used to provide measurement of ki and t-stress while accounting for the effect of some higher order terms. on the other hand, two strain gage rosettes placed in two discrete positions with the same orientation are capable to provide the information necessary to evaluate ki and t-stress from a four term representation. fig. 6. t-stress for (a) a/w = 0.2, (b) a/w = 0.3 and (c) a/w = 0.4. references [1] m. l. williams, “on the stress distribution at the base of a stationary crack”, journal of applied mechanics, no. 24, pp. 109-114, 1957 [2] d. e. richardson, j. g. goree, “experimental veri_cation of a new two-parameter fracture mode”, fracture mechanics: twenty-third symposium, astm stp 1189, pp. 738-750, 1993 [3] y. j chao, s. liu, b. j. broviak, “brittle fracture: variation of fracture toughness with constraint and crack curving under mode i conditions”, experimental mechanics, vol 41, no. 3, pp. 232-241, 2001 [4] g. r. irwin, “discussion of the dynamic stress distribution surrounding a running crack – a photoelastic analysis”, proceedings of the society for experimental 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2008 [47] m. zanganeh, r. a. tomlinson, j. r. yates, “t-stress determination using digital image correlation”, society for experimental mechanics 11th international congress and exhibition on experimental and applied mechanics, pp. 511-517, 2008 [48] m. j. maleski, m. s. kirugulige, h. v. tippur, “a method for measuring mode i crack tip constraint under static and dynamic loading conditions”, experimental mechanics 44, no. 5, pp. 522-532, 2004 [49] j. rosakis, k. ravi-chandar, “on crack-tip stress state: an experimental evaluation of three-dimensional effects”, international journal of solids and structures, vol. 22, no. 2, pp. 121-134, 1986 microsoft word etasr_v12_n1_pp8193-8198 engineering, technology & applied science research vol. 12, no. 1, 2022, 8193-8198 8193 www.etasr.com abbas & hussein: prestressing effects on full scale deep beams with large web openings prestressing effects on full scale deep beams with large web openings an experimental and numerical study rafaa m. abbas department of civil engineering college of engineering university of baghdad baghdad, iraq dr.rafaa@coeng.uobaghdad.edu.iq lara t. hussein department of civil engineering college of engineering university of baghdad baghdad, iraq l.hussein1001@coeng.uobaghdad.edu.iq abstract-most studies on deep beams have been made with reinforced concrete deep beams, only a few studies investigate the response of prestressed deep beams, while, to the best of our knowledge, there is not a study that investigates the response of full scale (t-section) prestressed deep beams with large web openings. an experimental and numerical study was conducted in order to investigate the shear strength of ordinary reinforced and partially prestressed full scale (t-section) deep beams that contain large web openings in order to investigate the prestressing existence effects on the deep beam responses and to better understand the effects of prestressing locations and opening depth to beam depth ratio on the deep beam performance and behavior. a total of seven deep beam specimens with identical shear span-to-depth ratio, compressive strength of concrete, and amount of horizontal and vertical web reinforcement ratios have been tested under mid-span concentrated load applied monotonically until failure. the main variables studied were the effects of depth of the web openings and the prestressing location on deep beam performance. the test results showed that the enlargement in the size of web openings substantially reduces the element’s shear capacities, while prestressing strands location above the web openings have more effect at increasing the element’s shear capacities. the numerical study considered three-dimensional finite element models that has been developed in abaqus software to simulate and predict the performance of prestressed deep beams. the results of numerical simulations were in good agreement with the experimental ones. keywords-deep beam; large web openings; pre-stressing; finite element; shear strength; static loading i. introduction shear behavior of reinforced concrete members (slender members that have span-to-depth ratios greater than 2.5) is a complex phenomenon influenced by a large number of parameters [1, 2]. this complexity is more pronounced in deep beams (members that have small span-to-depth ratios, less than 2.5) because the applied load is transferred mainly through the formation of arching which causes a highly nonlinear strain distribution in the cross section so that the shear strain is dominant [3]. in deep beams, the strain distribution is nonlinear and the load is transferred to the support by a compression strut joining the loading point and the support [1, 4-7]. the creation of web openings is often required for the accommodation of electrical and mechanical conduits. enlargement of openings due to architectural/mechanical requirements reduces the element’s shear capacity [8]. openings' configuration was investigated in [9] and an increase in ultimate load capacity when circular openings were used was reported. many studies investigated the pre-stressing effects [10]. pre-stressing a deep beam can increase significantly its load carrying capacity [11]. finite element modeling (fem) is a powerful tool in simulating structural elements in a variety of fields. in fem, the successful simulation of specific elements relies upon the realistic representation of the material properties. however, due to the complexity of the constitutive material properties, modeling the behavior of reinforced concrete, shear in particular, has been, and still is, a challenging issue [12]. in the current study, 7 deep beams were tested and a comparison was made with the results of the numerical analysis (fem) that was implemented with the aid of abaqus/cae program in order to investigate the effect of openings and pre-stressing locations. the comparison included load-deflection relation, load-strain relation at specific locations, crack pattern, and failure stage load. from the experimental results a significant decrease in load carrying capacity can be noticed when large web openings are introduced, and that agrees with the statement that the further the opening is located from what can be called the loaded quadrant and the nearer to the unloaded quadrant, the strength of the beam increases [13] and the deep beam acts as an ordinary beam. also, pre-stressing location above the openings has more effect above the soffit in increasing load carrying capacity of the deep beam. the experimental results showed a good agreement with the numerical ones and can predict the pre-stressed deep beam strength accurately. ii. fem description a. geometry and element types in order to investigate the pre-stress effects on the response and performances of full scale t-section deep beams with large web openings under monotonic loading, three-dimensional (3d) fe models of simple supports that have been partially precorresponding author: lara t. hussein engineering, technology & applied science research vol. 12, no. 1, 2022, 8193-8198 8194 www.etasr.com abbas & hussein: prestressing effects on full scale deep beams with large web openings stressed and reinforced were constructed as a reference. the geometry, dimensions, and configuration of the fe beams were identical to the actual tested specimens. four partially prestressed concrete deep beams with web openings, two reinforced deep beams with web openings, and one-solid beam were designed according to the strut-and-tie approach [14]. the full scale (t-section) deep beam specimens had the same geometry with dimensions of 1950mm length, 1000mm height, 750mm flange width, 125mm flange thickness, and 250mm web thickness, having 900mm span, 25mpa concrete compressive strength, and the same main reinforcement with the shear reinforcement. the specimens were tested and analyzed under monotonic loading at mid-span. the main variable was the size of web openings, and pre-stressing location (above the openings or above the soffit). the adopted pre-stress level was selected so that it satisfied the limit of 0.62��� [15]. the objective of this study is to investigate experimentally and numerically the: • location of pre-stressed strand across the height of the section: case (1) – pre-stressed strand above the soffit of the beam at 0.07h, where h is the height of the section case (2) – pre-stressing strand above the top surface of openings at 0.07h. • height of opening d, adopting ratios of the height of the opening to the height of section d/h equal to 0.48 and 0.6. the constants were: • concrete's compressive strength. • span length to height of the section ratio (l/h). • two openings symmetrically located relative to the centerline of the beam. • the width of the opening d. • the center of each opening was located at 0.45h from the soffit of the beam. the practical program of this study was to investigate four deep beams with large web openings that were partially prestressed at various locations (0.07h mm) above the openings and above the soffit. the beams were designated with the dpde-op symbols for partially pre-stressed deep beams with large web openings (480mm×480mm, 600mm×480mm) and different pre-stressing locations (opfor above opening and spfor above soffit). for more details of specimens and reinforcements properties, see table i. table i. properties of the reinforcements of the post tensioned deep beams beam main reinf. �� (mm 2 ) compression reinf. �� �(mm 2 ) pre-stressed �� (mm 2 ) skin reinf. ��� (mm 2 ) � %� � (mpa) pre-stressing force ��� (kn) dp-48×48 3016 4010 --50 0.2 430 286 dp-48×48-op 3016 4010 2012.7 50 0.2 430 286 dp-48×48-sp 3016 4010 2012.7 50 0.2 430 286 dp-60×48 3016 4010 --50 0.2 430 286 dp-60×48-op 3016 4010 2012.7 50 0.2 430 286 dp-60×48-sp 3016 4010 2012.7 50 0.2 430 286 dp-solid 3016 4010 2012.7 50 0.2 430 -- b. numerical modeling the numerical investigations were carried out using the commercial fe tool abaqus/explicit finite element code. the concrete and the pre-stressed bars were modeled as three dimensional deformable bodies and the reinforcement as three dimensional truss. the interaction between concrete and steel was modeled using the constraint option available in abaqus/cae wherein the concrete was taken as the host region and the steel as the embedded region (figure 1(a)). the element types that were used in the fe model for concrete were 8-noded linear bricks and 2-noded linear three dimensional trusses. the beam boundaries of the two ends were restrained with respect to all the degrees of freedom. the stresses for posttensioned strands were added in predefined fields as shown in figure 1(b) and the loading applied was linearly varied to maximum, until failure occurred. concrete damaged plasticity (cdp) modeling was used and the johnson-cook elastoviscoplastic material model available in abaqus finite element code was employed for modeling the steel reinforcing bar material. the mesh sensitivity in concrete and steel was studied and the size of the elements was chosen based on the mesh convergence studied for concrete and reinforcements. the meshing of the elements of deep beams and reinforcement is shown in figure 1(c)-(d). (a) (b) (c) (d) fig. 1. (a) embedded regions, (b) applying prestress, (c) meshing of the model dp-48×48-op, (d) meshing of the model dp-48×48-sp. engineering, technology & applied science research vol. 12, no. 1, 2022, 8193-8198 8195 www.etasr.com abbas & hussein: prestressing effects on full scale deep beams with large web openings iii. results and discussion • the first crack appeared at the support regions toward the lower opening corner for the 48×48 and 60×48 specimens at 31% and 28% of the ultimate load respectively. the loadcarrying capacity decreased as a result of the increasing opening depth [11]. • for the prestressed specimens 48×48-op and 60×48-op, the first crack was initiated at around 25%-26% of the ultimate load. the prestressing strands above the opening applied more compression stress and hence initial cracks above the openings appeared before the initiation of the first crack of the ordinary reinforced deep beams. • at 48×48-sp and 60×48-sp specimens, the initial crack propagated at the upper corner of the openings toward the applied load region at 33%-34% of the ultimate load, as a result of the prestressing strand location at the tension zone [16]. • flexure cracks appeared in all specimens, except specimens with prestressing above the soffit. there were no early flexure cracks as a result of tie action. they appeared at 3444% whereas the flange shear cracks appeared at 33-52% of the ultimate load. • as a result of large web openings, a typical crack pattern (column-beam) conjunction occurred. horizontal cracks appeared at 32-47% of the ultimate load (figure 2(a)-(b), crack number 3). • the existence of web openings (480mm×480mm) can reduce the load carrying capacity by about 156kn (figure 3). (a) (b) fig. 2. specimen dp-48×48-sp: (a) experimental and (b) simulated crack patterns. (a) (b) (c) fig. 3. comparison of reinforced and pre-stressed deep beams with the solid deep beam. • the stresses paths and strut-and-tie configurations are shown clearly in figure 2(a)-(b) [17]. • the comparison of the ultimate load according to the prestress location shows that the prestressing strands above the web openings increase the load carrying capacity by about 14% in the case of 480mm depth and by 22% in the case of 600mm depth (figure 3). when the pre-stressing strands are above the soffit the load carrying capacity increases by about 2.38% and 17% for 480mm depth and 600mm depth respectively (figure 3). • introducing web openings reduces the solid deep beam strength by about 136-209kn for 48×48 and 60×48 respectively (figure 3). increasing the web opening depth, from 480mm to 600mm, decreases the load carrying capacity by about 31% for reinforced deep beams and 15% for pre-stressed deep beams (figure 3), as a result of intersecting the load path [8]. • introducing large web openings in the deep beam transforms it into an ordinary beam-column (figure 2(a)(b), crack number 3) [17]. engineering, technology & applied science research vol. 12, no. 1, 2022, 8193-8198 8196 www.etasr.com abbas & hussein: prestressing effects on full scale deep beams with large web openings (a) (b) (c) (d) fig. 4. comparison of load versus deflection between experiments and simulations. • the load-deflection curve behaves semi-linearly, which shows that the deep beams act as ordinary beams more than as deep beams, as a result of the large web openings at the shear zone which change their geometry (figure 3) [17]. • the comparison of the load-deflection relation results of the tested specimens with the fem results is shown in figure 4. it is noted that the numerical load deflection responses are stiffer than the experimental ones and there is a good agreement in both trend and amplitude which varies from 5 to 10%. • the deflection reaches 8mm-10mm and stresses at the failure stage (figure 5). (a) (b) fig. 5. specimen dp-48×48-op: (a) deflection counter, (b) stresses at the failure stage. iv. calibration with the prestressed solid model based on the fem results, a calibration of solid deep beams with a pre-stressed solid deep (pre-stress location at ��=930mm) beam in finite element analysis using abaqus was done. the obtained crack patterns of the pre-stressed solid deep beam are presented in figure 6. the comparison with the simulated model shows that the existence of pre-stressing in the case of the solid deep beam increased the ultimate strength by about 37% than ordinary reinforced solid deep [16] (figure 7). fig. 6. showing the crack patterns of the solid deep beam. the load-deflection curve for prestressed and ordinary reinforced solid deep beams is linear. as a result of the underreinforcement, the steel reaches its yield strain before the concrete reaches the failure strain which is 0.0035. figure 7 shows the significant crack patterns in tension. the engineering, technology & applied science research vol. 12, no. 1, 2022, 8193-8198 8197 www.etasr.com abbas & hussein: prestressing effects on full scale deep beams with large web openings compression zone does not show any kind of failure which can lead to a ductile failure. the influence of the longitudinal reinforcement on ductility is defined by the relative neutral axis position along the cross section of the element. for lower values of neutral axis position, the beams have higher cross section heights and, consequently, lower longitudinal reinforcement rates, which grant more ductility to these beams at the ultimate limit state. when the concrete resistance increases, the amount of longitudinal reinforcement required to maintain the same ductility also increases. therefore, a direct dependence between the ductility factor and the longitudinal reinforcement rate was observed [18]. fig. 7. load-deflection relations of simulated and experimentally examined pre-stressed solid deep beams. v. comparison of numerical and experimental results the numerical models which simulate the actual tested specimens were able to predict the accurate shear capacity of each specimen with error varying around 10% (table ii). the highest shear capacity was observed with the solid deep beam (figure 8). fig. 8. experimental and numerical shear capacity results. as the opening depth increased, the shear capacity will decrease simultaneously. the dp-60×48 deep beam has the lesser shear capacity. the enlargement of the opening size reduces the shear capacity [11]. introducing prestressing strands can increase the load-carrying capacity by about 35% [16]. it is observed that a prestressed solid deep beam has grater load carrying capacity than ordinary reinforced solid deep beams by around 37%. when the prestressing location is above the web opening, it provides greater shear capacity than when it is above the soffit. adding prestressing strands above the openings increased the compression struts and hence increased the shear capacity [14]. introducing web openings intersects the stresses paths and changes the geometry of the deep beam affecting its behavior and shear capacity [17]. the existence of web openings (480mm×480mm and 600mm×480mm) can reduce the load carrying capacity (by about 135 and 209kn respectively). more details about each specimen’s simulated and experimentally tested shear capacity can be seen in figure 8 and table ii. table ii. experimental and numerical results specimens shear strength (kn ) experimental numerical num/exp ratio dp-48×48 210 228 1.08 dp-48×48-op 280 308 1.1 dp-48×48-sp 220 232 1.05 dp-60×48 160 176 1.32 dp-60×48-op 260 267 1.02 dp-60×48-sp 200 227 1.13 dp-solid 495 546 1.1 dp-solid-sp --550 -- vi. conclusion in this paper, seven beam specimens with large web openings and different pre-stressing locations were examined. the numerical model predictions were compared with the experimental results and the following conclusions can be drawn: • introducing pre-stress at a location above the opening can increase the load carrying capacity by 14% and 22%, whereas when the pre-stressing location is above the soffit, the load carrying capacity is increased by 2.3% and 17% for dp-48×48 and dp-60×48 respectively. • pre-stressing on beams with larger opening depth increases more the ultimate load capacity. • introducing web openings can reduce significantly the load carrying capacity by at least 136kn (480mm×480mm web openings), in comparison with the solid beam. • the solid deep beam has bigger strength than the prestressed deep beam with openings. • the numerical results comparison showed that, in the case of pre-stressed solid deep beam, as the location of the prestressing �� decreases, its effects on increasing the beam strength decrease. in the case of pre-stressed deep beams with openings, the load carrying capacity of deep beam increased when the pre-stressing location �� decreased. • from the fem result analysis, it can be seen that the models are stiffer than the experimental specimens. acknowledgments the authors would like to express their gratitude to the staff of the civil engineering department at the university of baghdad. engineering, technology & applied science research vol. 12, no. 1, 2022, 8193-8198 8198 www.etasr.com abbas & hussein: prestressing effects on full scale deep beams with large web openings references [1] m. p. collins, e. c. bentz, and e. g. sherwood, "where is shear reinforcement required? review of research results and design procedures," aci structural journal, vol. 105, no. 4, pp. 590–600, sep. 2008. 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[18] c. nogueira and i. rodrigues, "ductility analysis of rc beams considering the concrete confinement effect produced by the shear reinforcement: a numerical approach," latin american journal of solids and structures, vol. 14, no. 13, pp. 2342–2372, jan. 2017, https://doi.org/10.1590/1679-78253904. microsoft word etasr_v11_n6_pp7861-7866 engineering, technology & applied science research vol. 11, no. 6, 2021, 7861-7866 7861 www.etasr.com mugheri et al.: robust speed control of a three phase induction motor using support vector regression robust speed control of a three phase induction motor using support vector regression noor hussain mugheri department of electrical engineering quaid-e-awam university of engineering science and technology nawabshah, sindh, pakistan noorhussain@quest.edu.pk muhammad usman keerio department of electrical engineering quaid-e-awam university of engineering science and technology nawabshah, sindh, pakistan usmankeerio@quest.edu saadullah chandio department of electrical engineering quaid-e-awam university of engineering science and technology nawabshah, sindh, pakistan sadchandio@quest.edu.pk riaz hussain memon department of electrical engineering quaid-e-awam university of engineering science and technology nawabshah, sindh, pakistan r.hmemon@quest.edu.pk abstract-the three phase induction motor (tim) is one of the most widely used motors due to its low price, robustness, low maintenance cost, and high efficiency. in this paper, a support vector regression (svr) based controller for tim speed control using indirect vector control (ivc) is presented. the ivc method is more frequently used because it enables better speed control of the tim with higher dynamic performance. artificial neural network (ann) controllers have been widely used for tim speed control for several reasons such as their ability to successfully train without prior knowledge of the mathematical model, their learning ability, and their fast implementation speed. the svr-based controller overcomes the drawbacks of the annbased controller, i.e. its low accuracy, overfitting, and poor generalization ability. the speed response under the proposed controller is faster in terms of rising and settling time. the dynamic speed response of the proposed controller is also superior to that of the ann-pi controller. the performance of the proposed controller was compared for tim speed control with an ann-pi controller via simulations in simulink. keywordsthree-phase induction motor; indirect vector control; ann controller; svr controller i. introduction its simple structure, inexpensive, and good robustness have made the three-phase induction motor (tim) a most attractive choice [1, 2] for industrial applications. in high performance speed control of the tim, the indirect vector control (ivc) method is extensively used. the ivc method of speed control has been preferred due to its good dynamic performance [3, 4]. ann research has been increasing fast since the '80s [5]. annbased controllers are widely used for the speed control of the tim. the anns have the capability to map non-linear dependencies in the data without using any preconceptions. their ability to successfully train without prior knowledge of the mathematical model and load variations are their main advantages [6, 7]. however, ann controllers have some drawbacks such as: low accuracy, poor generalization ability, and overfitting [8]. a support vector regression (svr) -based controller can overcome the drawbacks of the ann controller with superior generalization ability. it has high accuracy and good performance despite the small training samples [9, 10]. recently, the svr technique has been applied in the field of electrical engineering. m. pellegrini proposed a technique based on svr for short-term load forecasting in smart grids and concluded that the svr can predict load demand more accurately than the ann [11]. authors in [12] proposed an svr model for predicting the electricity consumption and concluded that the proposed model predicts the electricity consumption with higher accuracy than the ann model. authors in [13] proposed an svr based dynamic behavioral model for rf power amplifiers. the obtained results show that the svr model gives an improved performance and predicts the behavior of power amplifier more accurately than the ann model. authors in [14] presented solar power forecasting using svr and ann and concluded that the best solar power forecast is obtained with the svr model. authors in [15] developed an svr model for the prediction of light energy consumption. the obtained results showed that the proposed model outperformed the ann model [15]. authors in [16] presented an svr-based behavioral model for rf power transistors. the obtained results suggested that the svr based approach is more efficient and overcomes the overfitting issue of the ann-based approach. the reason for choosing svr over anns is that it is based on the structural risk minimization principle that minimizes the generalization errors, rather than minimizing the errors on the training data as is the case of the anns [17]. corresponding author: noor hussain mugheri engineering, technology & applied science research vol. 11, no. 6, 2021, 7861-7866 7862 www.etasr.com mugheri et al.: robust speed control of a three phase induction motor using support vector regression ii. the proposed framework different controllers have been developed to control the speed of tim as pi [18, 19], fuzzy-pi [20-22], anns [23-25], ann-pi [26], fuzzy-neuro [27, 28] and support vector machine (svm) [29]. this paper presents a new pi-svr controller technique for speed tracking of tim based on ivc. for the first time, the svr-pi controller is successfully developed and implemented for tim speed control using the ivc. here, the radial basis function (rbf) is used as the kernel function. the proposed controller approach has the advantages of having very fast response, superior dynamic performance, and higher stability. figure 1 depicts the block diagram of the suggested framework. an insulated-gate bipolar transistor (igbt) inverter converts the dc voltage to ac voltage and variable frequency. the tim is fed by the pwm inverter. the tim provides feedback signals to the svrpi controller. the speed control approach employed here is ivc, which is a dynamic and reliable control method. fig. 1. block diagram of the proposed framework. iii. the artificial neural network controller an ann-pi controller was developed for tim speed control. figure 2 depicts the simulink model of the ann-pi controller. fig. 2. the ann-pi tim controller. figure 3 depicts the construction of the developed ann controller. the hidden layer uses a logarithmic sigmoid activation function and the output uses a linear activation function. (a) (b) (c) fig. 3. the ann controller developed in simulink. (a) internal layers, (b) weight and bias of the first layer, (c) weight and bias of the second layer. iv. support vector machine for regression svm is a machine learning technique that can be used for classification and regression analysis. when svm is used for regression analysis, it is termed as svr [30-32]. svr is considered as a non-parametric technique because it depends on kernel functions. in linear epsilon-intensive svr (ɛ-svr), the training data set comprises of the observed response values and the predictor variables. the aim is to determine a function f(x) that deviates from yn by no more than ɛ for each training point x and simultaneously is as even as possible [33]. here, the rbf used as the kernel function. this paper for the first time presents a modern performing svr-pi controller. the trained svr calculates the output according to the reference constant speed. then the output of the trained svr is added to the pi output. it makes the tim speed response faster and stable. table i shows the epsilon, sigma and c parameters for svr. epsilon denotes the epsilon-insensitive loss function, sigma is the rbf kernel, and c is the upper limit of double problem variable alpha. figure 4 depicts the simulation in simulink of the svr-pi controller. table i. svr parameters parameters ɛ σ c values 10 -6 0.6 10 4 v. results and discussion the tim was built using the asynchronous machine block in simulink. the complete simulation in simulink of the tim speed control using ivc is shown in figure 5. the threephase induction motor is fed by the three-phase inverter that is built using a universal bridge block. the tim drives a mechanical load characterized by inertia, friction coefficient, engineering, technology & applied science research vol. 11, no. 6, 2021, 7861-7866 7863 www.etasr.com mugheri et al.: robust speed control of a three phase induction motor using support vector regression and load torque. the speed control loop produces the quadrature-axis current reference that controls the tim speed using the svr based controller. originally, the three phase induction motor is at standstill without load. then the load is increased from 0 to 200nm. simulations were carried out on both controllers. the simulated results of the svr controller were compared with the results of the ann controller. table ii summarizes the simulation results of the ann-pi and svr-pi controllers. fig. 4. the three-phase induction motor controller using svr-pi. fig. 5. the complete simulation in simulink of the ivc based tim speed controller. engineering, technology & applied science research vol. 11, no. 6, 2021, 7861-7866 7864 www.etasr.com mugheri et al.: robust speed control of a three phase induction motor using support vector regression table ii. performance analysis load (nm) controller settling time (s) overshoot (%) rise time (s) 0 ann-pi 0.567 0 0.508 svr-pi 0.408 0 0.367 50 ann-pi 0.684 0 0.613 svr-pi 0.475 0 0.417 100 ann-pi 0.861 0 0.772 svr-pi 0.541 0 0.487 150 ann-pi 1.161 0 1.041 svr-pi 0.647 0 0.581 200 ann-pi 1.782 0 1.596 svr-pi 0.810 0 0.718 figure 6 shows that the svr-pi controller has better performance than the ann-pi controller. the settling time and rise time of svr-pi controller are smaller than the ann-pi controller's. fig. 6. no load response of the tim. fig. 7. speed response of the tim at 50nm load. figure 7 shows that the svr controller gives better settling time and faster response than the ann-pi controller. as shown in figure 8, the motor reaches the reference speed faster when using the svr-pi controller. when we use the ann controller for a load of 150nm, it will increase rise time and settling time. on the other hand, as illustrated in figure 9, the proposed controller performs better with less settling and rise time. fig. 8. speed response of the tim at 100nm load. fig. 9. speed response of the tim at 150nm load. fig. 10. speed response of the tim at 200nm load. we used the ann controller for a large load of 200nm as shown in figure 10. we see that the system suffers from high settling time of 1.782s and high rise time of 1.596s, while the svr controller takes only 0.810s to stabilize and has a rise time of 0.718s. to study the tim dynamic performance, a step change in load torque and a step change in reference speed are employed. figures 11 and 12 show the dynamic response of the tim. due to the huge increase in load, the ann controller 0 0.5 1 1.5 2 2.5 3 0 20 40 60 80 100 120 time (sec) s p e e d ( ra d /s e c ) svr ann 0 0.5 1 1.5 2 2.5 3 -20 0 20 40 60 80 100 120 time (sec) s p e e d ( ra d /s e c ) svr ann 0 0.5 1 1.5 2 2.5 3 -20 0 20 40 60 80 100 120 time (sec) s p e e d ( ra d /s e c ) svr ann 0 0.5 1 1.5 2 2.5 3 -20 0 20 40 60 80 100 120 time (sec) s p e e d ( ra d /s e c ) svr ann 0 0.5 1 1.5 2 2.5 3 -20 0 20 40 60 80 100 120 time (sec) s p e e d ( ra d /s e c ) svr ann engineering, technology & applied science research vol. 11, no. 6, 2021, 7861-7866 7865 www.etasr.com mugheri et al.: robust speed control of a three phase induction motor using support vector regression does not settle down at a required initial and final speed steps. the svr controller settles down at the initial and final reference speed step of 100rad/s and 160rad/s without undershoot and with small settling and rise times. these results indicate that the svr controller gives a robust and superior dynamic performance. fig. 11. dynamic speed response of the tim with the final speed reference at 160rad/s at t=0.4s and a 300nm load at t=1.6s with svr and ann controllers. fig. 12. dynamic speed response of the tim with the initial speed reference at 100rad/s at t=0.4s and a 300nm load at t=1.6s with svr and ann controllers. vi. conclusion this paper presents for the first time the use of svr with pi controller for tim speed control using ivc. this method combines the advantages of the svr technique and the conventional pi controller to further improve the tim speed response. the ivc is widely used for speed control due to its simple configuration. the controller was successfully developed and simulated in matlab/simulink. the ann controller offer no % os due to its self-learning ability. the proposed controller was tested at different load torque values and had less rise time and faster settling time than the ann controller. the simulation results suggested that the svr controller is generally more effective and performs faster. the proposed controller improves greatly the dynamic performance. on the other hand, the dynamic performance of the ann controller is poor. appendix tim electrical parameters 3 phases, poles = 4, p = 50hp, ns=1800rpm voltage = 460v, f = 60hz rs = 0.087ω, rr = 0.227ω ls = 0.8mh, lr = 0.8mh lm = 34.7mh j = 1.662kg-m 2 references [1] a. abdel menaem, m. elgamal, a.-h. abdel-aty, e. e. mahmoud, z. chen, and m. a. hassan, "a proposed ann-based acceleration control scheme for soft starting induction motor," ieee access, vol. 9, pp. 4253–4265, 2021, 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[33] s. kavitha, s. varuna, and r. ramya, "a comparative analysis on linear regression and support vector regression," in 2016 online international conference on green engineering and technologies (ic-get), coimbatore, india, nov. 2016, pp. 1–5, https://doi.org/10.1109/ get.2016.7916627. etasr paper format engineering, technology & applied science research vol. 8, no. 2, 2018, 2627-2632 2627 www.etasr.com melisinos and danikas: on polymers nanocomposites: electrical treeing, breakdown models and … on polymers nanocomposites: electrical treeing, breakdown models and related simulations g. melissinos democritus university of thrace department of electrical and computer engineering power systems laboratory, xanthi, greece melissinosgeorg@gmail.com m. g. danikas democritus university of thrace department of electrical and computer engineering power systems laboratory, xanthi, greece mdanikas@ee.duth.gr abstract—this paper deals with polymer nanocomposites and their related breakdown mechanisms. polymer nanocomposites seem to be a very promising alternative to conventional polymers regarding high voltage applications. some developed breakdown models are discussed as well as the mechanism of treeing in such materials. treeing simulation results are presented. keywords-polymer; nanocomposites; insulation; treeeing; breakdown. i. introduction polymeric materials have been used for a long time in high voltage engineering [1]. polymer nanocomposites were proposed more than twenty years ago as a plausible alternative to traditional polymeric materials [2] but their full potential was realized more recently [3]. it was realized that the unique properties of polymer nanocomposites were due to the interfaces formed between the nanoparticles and the surrounding polymer matrix. for this reason, it was emphasized that it was mandatory that the coupling of the interfacial region and the base polymer was crucial for the development of new insulating materials [4-6]. in polymer nanocomposites the nanoparticles are homogenously dispersed in the matrix in concentrations <10 wt%, the size of particles being smaller than 100 nm. the interfacial region in the nanocomposites is significantly increased in comparison to microcomposites, due to the nanometric scale of the particles, which means that the augmentation of the interfacial region gives to nanocomposites different and unique properties compared to microcomposites. nanoparticles can improve or adjust significantly different properties, such as electrical, mechanical, thermal, and optical but with the condition to be homogenously dispersed in the polymer matrix. a very good dispersion of the nanoparticles into the polymer matrix can be achieved by using different methods and preparation techniques among them mechanical dispersion methods, including ultrasonic vibration or special sol-gel techniques, high shear energy dispersion mixing and/or through a tailored surface modification of the nanoparticles [7]. lack of compatibility between the polymer matrix and the nanoparticles may cause the formation of agglomerations [8]. for applications in high voltage engineering, it is imperative that such polymer nanocomposite materials have high breakdown strength and a high resistance to electrical treeing. it is the purpose of this paper to review some of the published breakdown and treeing models as well as to give some simulation results regarding treeing in nanocomposites. ii. breakdown and degradation in polymer nanocomposites at breakdown, the electric field frees bound electrons. if the applied electric field is sufficiently high, free electrons from background radiation may become accelerated to velocities that can liberate additional electrons during collisions with neutral atoms or molecules in a process called avalanche breakdown. breakdown occurs quite abruptly, resulting in the formation of an electrically conductive path, thus destroying the insulating capability of the material. the first approach, an effort made so that the breakdown strength be explained on quantum mechanics level, was proposed in [9] that suggested the low energy criterion, which says that fast avalanche breakdown can only occur if the average energy gained of electrons are larger than the average energy losses of electrons. von hippel‟ s theory was the basis for the density functional perturbation theory (dfpt), for estimating the breakdown of new insulating materials [10] and also for the determination of the depths of impurity states created by common chemical impurities [11]. depths of traps/hopping sites were between 0.1 ev and 2.4 ev and were classified into shallow traps/hopping sites, deep traps, and deeper traps. such depths suggest that chemical impurities can play major roles in trapping and hopping processes, can explain the observed activation energy of conduction, and shape the barriers to charge injection. the type of impurity bonds and their lengths are correlated with the depth of impurities they create. such correlation is linear [11]. in 2005, ma and others showed in experiments with ldpe/tio2 nanocomposite, that the breakdown strength improved after the treatment of nanoparticles surface with silanes, which promoted deep trapping of charges [12]. han and others, in their experiments with ldpe/nay nanocomposite with 3 wt% zeolite nanoparticles, concluded that deep traps that create homo space charges can suppress the injection of charges from the electrodes, decrease the mobility mailto:melissinosgeorg@gmail.com engineering, technology & applied science research vol. 8, no. 2, 2018, 2627-2632 2628 www.etasr.com melisinos and danikas: on polymers nanocomposites: electrical treeing, breakdown models and … of charge carriers resulting in improved breakdown strength [13]. classical theories of breakdown may apply to polymer nanocomposites, such as the electrical avalanche breakdown [14], the water treeing breakdown theory [15], the electrical treeing breakdown theory [16], the thermal breakdown theory [17] and the electromechanical breakdown theory [18]. it happens, however, that in certain cases, the above mentioned models can be intermingled, as is the case of [19], where it was pointed out that, for pe and eva polymer samples, thermal breakdown happens along with dominating fast avalanche mechanism at low temperatures and a dominating electromechanical mechanism at higher temperatures, depending on the temperature level. it is to be remembered that besides such classical models of breakdown, in the case of polymer nanocomposites, a crucial role plays the interface between the polymer matrix and the nanoparticles. the improved nanodielectric properties seem to stem from the immensely enlarged interface region around the nanoparticles, in usually low concentrations (1-10 wt%) in comparison of the interface regions of microcomposites with the same concentrations. in a simple example, kickelbick [20] demonstrated the importance of the interface in nanoscale level, as almost every nanoparticle in the nanocomposite, has surface that interacts with the polymer matrix. generally speaking, nanocomposites seem to have higher breakdown strength than their conventional counterparts. in the following chapter, interface models and related problems and interpretations will be studied. iii. interfaces in nanocomposites apparently the degrading mechanisms of the polymers, such as partial discharges (pd) and electrical and/or water treeing, can also lead polymer nanocomposites to destructive failure [21]. in [22], authors suggested that the advantageous nanocomposite properties have their origins in the behavior of the interfacial interaction zone surrounding the nanoparticles. in this regard, two main features would appear to be dominant a) the mobility ascribed to the physical and chemical bonding occurring at the interface, and b) the formation of a double layer in the interfacial region which can influence local conductivity. the mobility and the type and degree of crystallinity changes with nanoparticle addition in the polymers [23]. moreover the polymeric chain mobility in the interface zone is affected by many factors, such as the polymeric chain length [21], the morphology of the nanoparticle surface and the polymer-particle interactions (repulsive or attractive) [24], the kind of polymer-particle chemical bonds [25] and the wt% nanoparticle concentrations [26, 27]. in [28], authros observed in nanocomposite with silica nanoparticles, two glass transition temperatures (gtt), and they proposed for the explanation of these morphological and structural anomalies a model according to which the lower gtt was attributed to the usual polymeric regions, while the higher to the interface zone with the reduced mobility. for concentrations of nanoparticles more than 10 wt% the mobility is considerably decreased, while for above 20 wt% the polymeric chains are almost immobilized. in [29], authors suggested that in order for the voltage endurance to be increased in a nanocomposite, internal charges should be decreased through interfacial effects and if the interaction zone is the primary agency in determining the electrical behavior, then clearly the engineering of nanodielectrics should he centered on chemical modifications of the interface. in [12], the authors presented the results of the influence of surface modification of tio2 nanoparticles on the short breakdown strength and space charge distribution of ldpe. they concluded that the improved dielectric breakdown strength was directly due to beneficial effects related to the variation of the electrical features at the particle surface due to introduction of polar groups. for the same reason, with the use of surface modified nanoparticles, the formation of space charge was suppressed. in [30], it was reported that the deep traps for electron carriers which are formed by additives in polymers, reduced the energy of space charges, while the created homocharges hindered further charge injection from the electrodes, which improved the breakdown strength. in a later work [31], the authors presented a hypothesis for the mechanisms that lead to the improved ac, dc and impulse breakdown strength of composite xlpe with nanoparticles sio2. they suggested that „the inclusion of nanoparticles provides myriad scattering obstacles and trap sites in the charge carriers‟ paths, effectively reducing carrier mobility and thus carrier energy. the result is homocharge buildup at the electrodes, which increases the voltage required for further charge injection due to blocking by the homocharge‟. scattering, caused by both particle/polymer interfaces and possibly disrupted crystalline structure, contributes to the better electrical behavior of nanocomposites besides the defect reduction via chemical linkage between nanoparticles and polymer or the introduction of deep trap sites in the polymer due to the surface modifier groups [32]. from all the above reports it is clear that there are many factors that influence the breakdown strength of nanocomposites, but the involved dominant breakdown mechanism is partly dependent on the temperature conditions, as for example a temperature increase will reduce the polymer mechanical strength. regarding water tree retardation in nanocomposites, the addition of mgo nanoparticles in ldpe and xlpe in different concentrations managed to improve the nanocomposite strength in water tree growth as well as to observe the temperature effect on its development [33]. in [34, 35] the influence of the interface mechanical strength in barium titanate-polyvinydene fluoride nanocomposite breakdown strength was investigated. in the interface area the titanate covered bariun nanoparticles were cross linked to the polyvinydene fluoride matrix forming an organically integrated body, which posed a potential barrier which prevented charge carriers to cross through the interface area. the charge carriers are confined in the polymer area only, which promotes energy storage, while, with the tetrafluorophthalic acid nanoparticle treatment, a passivation layer around the interfacial area is formed, thus reducing the generation of charge carriers which may results in ionic or dc conduction and the decrease of the breakdown strength. yet in other publications, it was proved that nanoparticle treatment which resulted in covalently-bonded interface polymer-particle nanocomposites exhibit improved breakdown strength [36, 37]. it is quite clear from the above engineering, technology & applied science research vol. 8, no. 2, 2018, 2627-2632 2629 www.etasr.com melisinos and danikas: on polymers nanocomposites: electrical treeing, breakdown models and … that interfaces and their treatment are dominant factors in defining the breakdown strength of polymer nanocomposites. interface models were proposed in the past that tried –at least partially– to interpret the behavior of polymer nanocomposites. this subject was already partly treated [38, 39] and it will be treated in more detail separately in a future publication, consequently interface models only briefly will be mentioned here. interface models are extremely useful for better understanding the interfacial properties of nanocomposites and they basically treat the areas around the nanoparticles, offering thus interpretations as to why polymer nanocomposites have improved electrical behavior compared to their conventional counterparts. main interface models – referring to nanocomposites – are the lewis model, the wilkes model, the tanaka multi-core model, tsagaropoulos‟ model, the potential barrier model, the interphase model, the polymer chain alignment model, the water shell model, the dual layer model, the physical model for the explanation of surface degradation mechanism, the physical model for tree growth, chen‟s model and the percolation model. all the above mentioned models –as said to be discussed in a future paper represent a significant effort towards the understanding of the properties that emerge in polymer nanocomposites. there is not, however, a universal model so far, that will cover all the experimental facets that are simulated by all these models. iv. breakdown and related mechanisms various models have been proposed for the breakdown of polymers. partial discharges (pd) is a major source of electrical degradation and occur in voids, de-laminations and other defects in an insulation system. pd may cause electrical treeing. electrical treeing is the main indication of aging and ultimately leads to insulation breakdown and eventual failure of the electrical equipment. various models have been proposed for the breakdown of polymers. niemeyer, pietronero and wiesmann (npw) [40, 41] introduced a stochastic model in which the evolution of the tree-like patterns are explicitly depend on local electric field strength and a factor which modulates the randomization of the process. the fractal dimensions of the experimentally obtained tree-like patterns, are in general, in accordance with the patterns obtained from the breakdown simulations, which advocates in favor of the fractal characteristic of the electrical trees. an improved model was proposed in [42], where there was a generalization by introducing a breakdown criterion for tree formation, so that the branches could only be added if the local field at a branch tip exceeded a critical threshold field for growth, and by introducing an internal field within the tree channels that would add to the electrode potential at the tip of the tree, implying thus that the tree channel could not be considered without resistance. more recently, dodd [43] presented his deterministic model which s successful in simulating electric trees in dielectric without the need of a random variable, a requirement of previous stochastic models. instability in the spatial development of partial discharges within the tree structure takes the role of the stochastic element as used in previous models to produce branched tree structures. in yet another model, electric treeing is simulated with the use of von neumann cellular automata (ca) theory. more specifically, it is presumed that electric charges in the electrode tip create electric field that surpasses the dielectric strength of the polymer insulator and a gradual tree-like channel formation is spread in it. on every step the local potential on every point is being recalculated, due to local dielectric permittivity fluctuations caused by the tree channel propagations [44, 45]. dissado and sweeney [46] proposed a deterministic quantitative physical model for the breakdown of solids by discharges originating from voids or channel tips. it is found that fractal tree-like structures are formed only when the local electric fields at the tree tips are allowed to fluctuate about their laplace values. by considering the local-field enhancement factor as a white noise, which is produced by the breakdown mechanism itself, it is shown that the amount of branching depends only on the range of fluctuations allowed. noskov‟ s model took into account pd erosion or the real distribution of the electric field due to space charges, and also that the electric trees had to emanate always from matrix defects . the model could estimate electrical tree propagation and pd activity within growing tree channels. the local electric field and the damage accumulation in the dielectric material were constituent into the tree growth, while the increase of the damage was proportional to the pd energy release in the channels. the electric field distribution was determined by the charge deposition within the tree structure and the electrode geometry, while charge distribution changes within the channels during pd. pd starts when the electric field along the channels exceeds a threshold inception value and stops when the field falls below the threshold quenching value [47]. although the above mentioned publications refer mainly to conventional polymers, their ideas could also apply to nanocomposites. the ca model, for example, was applied to simulate electrical treeing in nanocomposites [48]. however, a drawback of the ca model is that it does not consider in detail the interface region around the nanoparticles. on the other hand, this is understandable since there is no generally accepted model for the interfaces as yet. generally speaking, in the various models, in order an electrical tree simulation to take place in nanocomposites, local fluctuations are used, flactuations of factors that simultaneously comprise variables of functions that determine the conditional representation of the discrete cells of the polymer matrix and of the nanoparticles of the nanocomposite. factors that can be used as variables, are the electric field or the released energy due to pd activity, with the first to be greatly preferred because it can be easily calculated. the ca model considers as decisive factor the local change –even slightly– of the dielectric constant that in turn affects the local electric field [48]. v. treeing simulations treeing simulations in nanocomposites were based on the model developed in [48]. as nanocomposites consist of different materials, it is only logical to try to develop the simulations on previous treeing models of conventional polymers [44, 45]. more specifically, the initial ca model for nanodielectrics, had analysis 5000x5000 cells, a point-plane electrode arrangement and every nanoparticle was presented in just one cell. generally the design concepts of a previous model [44, 45] are applied to nanocomposite treeing simulation engineering, technology & applied science research vol. 8, no. 2, 2018, 2627-2632 2630 www.etasr.com melisinos and danikas: on polymers nanocomposites: electrical treeing, breakdown models and … model, with in addition, the presence of some nanoparticles around the tip of high voltage electrode. cell‟s condition is given by ci,j={efi,j, tfi,j, gi,j, vi,j} where efi,j denotes whether the cell belongs to the nanocomposite or electrode, tfi,j denotes tree cells, gi,j cell‟s inhomogeneity factor and vi,j cell‟s potential. the electric field is calculated by e=g γv/d , where g the inhomogeneity factor taking random values between 0,91,1, d the distance between neighbor cells and γv the potential between them. for electric tree propagation an algorithm is executed first to the cells at the electrode tip and when the electric field exceeds the nanocomposite breakdown strength, the cells are converted to tree cells and this procedure is repeated to all cells until the tree propagation stops. the cell potential is calculated solving laplace or poisson equations as well as the boundary conditions determined as described in [44, 45].the potential distribution is also affected by interactions between the nanoparticles due to their proximity. cox in his work [49] in a model with two spheres calculated accurately enough sphere potentials φα, φβ, with e the external electric field, d the distance between sphere centers, a sphere radius, k the sphere permittivity ratio to that of the polymer, λ=cosθ, λ=cosθ and pn a legendre n grade polyonym. when in the nanocomposite there is a defect or microparticle the potential is φ=-(3/((ε2/ε1) +2))δ r cosθ , where ε1 the polymer permittivity and ε2 that of the microparticle while r is it‟s radius and θ the angle between the electric field vector and radius. 1 1 2 1 [( ) (1) ( )] 2 ( 1) n nd a n n n δ a n φ a p d n k           1 1 2 1 [( ) ( 1) ( )] 2 ( 1) n nd b n n n δ a n φ a p λ d n k            simulations -regarding the influence of space charges on the development of electrical treeingwith the model described briefly above as well as in [48] gave results qualitatively not different from those reported in [50, 51]. specifically, it was shown that space homocharges around the high voltage tip electrode, hinder further charge diffusion from the electrode into the matrix, as well as electric tree growth and breakdown of the nanodielectric. it was shown also that electrical tree deployment through the nanocomposite, was taking place only through the polymer matrix deviating from the nanoparticles, which increased significantly the lengths of electrical tree paths to the opposite electrode, resulting in increased breakdown strength and delayed breakdown. furthermore, the effect of the size of nanoparticles included in a nanocomposite was simulated (figures 1 and 2). it is evident that smaller size nanoparticles (which means more nanoparticles per volume) have a beneficial effect on hindering electrical treeing, in accordance with experimental results published in [52]. in other words, an increase in wt% nanoparticle content, offers a longer treeing path and thus a higher breakdown strength. it must, however, kept in mind that not only the size of nanoparticles in important but also, among other factors, the coupling agents. coupling agents in nanocomposites are more effective in small sizes of nanoparticles and increase tree breakdown time [52]. an interesting parameter which was investigated was the presence of air voids in a nanocomposite (figures 3 and 4). fig. 1. electrical tree propagation in epoxy/tio2 nanocomposite with 100 nm nanoparticles diameter fig. 2. electrical tree propagation in epoxy/tio2 nanocomposite with 200 nm nanoparticles diameter fig. 3. tree propagation in a nanocomposite (epoxy resin with tio2 nanoparticles) in the presence of one air-filled void fig. 4. tree propagation in a nanocomposite (epoxy resin with tio2 nanoparticles) in the presence of two air-filled voids engineering, technology & applied science research vol. 8, no. 2, 2018, 2627-2632 2631 www.etasr.com melisinos and danikas: on polymers nanocomposites: electrical treeing, breakdown models and … simulations with the model described above [48], indicated that voids cause –as in conventional polymers– problems. as shown in figures 3 and 4, in the presence of an air void, electrical treeing is encouraged despite the existing nanoparticles. with two air-filled voids, treeing propagation becomes even worse. the outcome of all the above simulations and cited technical literature converge to a general conclusion, that the increase of the nanoparticle content -up to a certain percentage– may impede electric tree propagation and pd activity and erosion in nanocomposites. however, even nanocomposites must avoid defects, such as air-filled voids, that are detrimental to all kinds of insulation systems. vi. conclusions in this paper, a background as to the some aspects of polymer nanocomposites was given. some advantages of these materials as well as some of their problem areas were commented upon. simulations of electrical tree propagation, based on a ca model, were presented. it was shown that the size of the nanoparticles plays a crucial role in determining 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silica filler size on treeing breakdown lifetimeof epoxy nanocomposites”, proceedings of international conference on properties and applications of dielectric materials (icpadm), pp. 733-736, 2009 microsoft word 146-472-1-sm-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 196-200 196 www.etasr.com antic et al:anti-swing fuzzy controller applied in 3d crane system anti-swing fuzzy controller applied in a 3d crane system dragan antić dpt of con. sys. fac. of electronic engineering niš, serbia dragan.antic@ elfak.ni.ac.rs zoran jovanović dpt of con. sys. fac. of electronic engineering niš, serbia zoran.jovanovic@ elfak.ni.ac.rs staniša perić dpt of con. sys. fac. of electronic engineering niš, serbia stanisa.peric@ elfak.ni.ac.rs saša nikolić dpt of con. sys. fac. of electronic engineering niš, serbia sasa.s.nikolic@ elfak.ni.ac.rs marko milojković dpt of con. sys. fac. of electronic engineering niš, serbia marko.milojkovic@e lfak.ni.ac.rs miloš milošević r&d center alfatec niš, serbia milos.milosevic @alfatec.rs abstract—it is well known that fuzzy logic can be used in the control of complex systems described by highly nonlinear mathematical models. however, the main difficulty in the design of a fuzzy controller comes with the adjustment of the controller’s parameters that are usually determined by human experts’ knowledge or trial and error methods. in this paper, we describe an implementation of fuzzy logic in order to reduce oscillations during the positioning of a 3d crane system. the fuzzy controller’s structure is quite simple, requiring only two input variables. the proposed fuzzy controller has been applied to an experimental laboratory framework and results show that oscillations are significantly reduced. keywordsfuzzy controller; anti-swing control; 3d crane system i. introduction the crane system is an electromechanical system, which is used to lift and lower some materials and to move them from one place to another. it is mainly used for lifting heavy things and moving loads beyond the normal capability of a man. there are several types of crane systems, but in our interest is in the 3d crane system, where the payload attached to the end of the lift-line can move freely in three dimensions. the 3d crane mathematical model is rather complicated, and it is often simplified in some way. the exact mathematical models for crane systems are very important for controller design. many attempts were made to introduce simplified models or to use some control techniques to cope with system uncertainness. in [1], several 3d crane mathematical models, depending on the number of variables, are described. the authors gave (i) a complete nonlinear model with constant pendulum length and two control forces, (ii) a complete nonlinear model with varying pendulum length and three control forces, and (iii) a simplified model with tree control forces. on the other hand, when the friction and gravity are unknown, neural networks (nns) can be used [2]. nns are used for approximation of the whole nonlinearity of robot dynamics, but they can be adjusted for 3d crane system. moreover, the authors in [3] propose an adaptive pd control with gravity compensation for the case where parameters in gravitational torque vector are unknown. it is well-known that some control techniques do not require an exactly known mathematical model of the controlled plant. having in mind this, the robust methods are seemed to be the right choice in the control of 3d crane system. the main objective in the control of 3d crane system is to position the payload in the desired location without oscillations. there are many papers dealing with this control problem. in [4], boundary conditions are used in the time optimal control. in [5], the authors improve the previous paper and the optimal control is calculated so that the corresponding trajectory satisfies the specified boundary conditions and the oscillations during the transfer are minimized. however, some requirements of time optimization must be neglected if we want to increase robustness. in [6], it is proposed to use zero angular velocity at the target point. gain scheduling, in order to increase tracking accuracy, is proposed in [7]. authors in [8], interpreted the crane as a large workspace serving robot, and developed several observers. intelligent control algorithms, such as fuzzy, sliding mode, neural, genetics etc., have a lot of advantages related to the interpolative reasoning approach, but also have some restrictions due to their complexity. in [9], authors investigate the intelligent control algorithms (pid, fuzzy) applied in 3d crane model control. in [10], a network-based self-tuning controller is presented, based on using a multilayer perceptron, as a self-tuner for the controller. the given method is verified by simulations in different conditions. the implementation of genetic algorithms in determining parameters of a 3d crane system model is given in [11]. the validation of the model and parameters are performed by digital simulation and comparison with the experimental results. the method proposed had satisfactory control performance under a wide range of operating conditions and reduced oscillations during the positioning of payload cart. a sliding mode anti-swing control for overhead cranes is proposed in [12]. the proposed control realizes a typical anti-swing trajectory control, allowing highspeed load hoisting motion and sufficient damping of load swing. in [13], a new fuzzy anti-swing control scheme for a three-dimensional overhead crane is proposed. the proposed control consists of a position servo control and a fuzzy logic control. the validation of the proposed control is done by etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 196-200 197 www.etasr.com antic et al:anti-swing fuzzy controller applied in 3d crane system experiments with a three-dimensional prototype overhead crane. as we mentioned before the main control goal is to reduce the swing of the payload while moving it to the desired position as fast as possible. however, the swing of the payload depends on the acceleration of the trolley, so minimizing the operation time and minimizing the payload swing are partially conflicting requirements. having this in mind, one particular method for limiting vibration in flexible systems by shaping the input to the system is presented in [14]. as difference to the most previous input shaping strategies, this method does not require a precise system model or lengthy numerical computation. in [15], the author proposes one method for a high performance anti-swing control of overhead cranes, where the motion planning problem is solved as a kinematic problem. in [16], the authors developed a nonlinear model for an overhead crane and then that model is used for anti-swing control development. the feedback control is used to specify the crane speed at every moment. in [17], a nonlinear tracking controller with two loops (outer and inner), is designed. loops are used to stabilize the internal oscillatory dynamics. similar to the most of the previously described papers, in this paper we developed an anti-swing control method in order to reduce the oscillations during the positioning of a 3d crane system. the difference between the desired and actual position and the derivative of that difference are used as the input variables for the fuzzy controller. the main advantage of this controller is that its structure is quite simple in comparison to some other structures mentioned above. the paper is organized as follows. section ii starts with the description of the 3d crane experimental framework used for the validation of the proposed control algorithm, and continues with the mathematical model of the 3d crane system. the controller design is presented in section iii. in section iv, the proposed control method is applied to the crane system and experimental results are discussed. concluding remarks are given in section v. ii. 3d crane system a. laboratory experimental framework description practical 3d crane framework, used in experiments performed in this paper, is presented in figure 1 [1]. this framework, made by inteco, is placed in the laboratory of control systems in faculty of electronic engineering, nis, serbia. 3d crane represents a nonlinear electromechanical system having a complex dynamic behavior and creating challenging control problems. the 3d crane system consists of a payload hanging on a pendulum-like lift-line wound by a motor mounted on a cart. the payload attached to the end of the lift-line can move freely in three dimensions: in x direction (both the rail and the cart can move horizontal), in y direction (the cart can move horizontal along the rail) and in z direction (the payload is lifted and lowered in this direction). fig. 1. 3d crane system made by inteco. there is one dc motor, at the end of each axis. furthermore, there are five identical measuring encoders measuring five state variables: the cart coordinates on the horizontal plane (used for controller design), the lift-line length (in our case used as constant), and two deviation angles of the payload. the encoders measure movements with a high resolution equal to 4096 pulses per rotation. the deviation of the load is measured with a high accuracy equal to 0.0015 rad. the power interface amplifies the control signals which are transmitted from the pc to the dc motors. it also converts the encoders pulse signals to the digital 16-bit number. the pc equipped with the rt-dac/pci multipurpose digital i/o board communicates with the power interface board. the whole logic necessary to activate and read the encoder signals and to generate the appropriate sequence of pulses of pulse width modulation (pwm) to control the dc motors is configured in the xilinx chip of the rt-dac/pci board. all functions of the board are accessed from the 3d crane toolbox which operates directly in the matlab® /simulink® environment. the user has rapid access to all basic functions of the 3d crane control system from the main control window in matlab. it includes tests, drivers, models and application examples. the main driver is located in the rtwt device driver column. the driver is a software go-between for the real crane matlab environment and the rt-dac/pci acquisition board. the driver has three pwm inputs (dc motor controls) for the x, y and z axes. there are eight outputs of the driver: x position, y position, z position, two angles and additionally three safety switches. according to a preprogrammed logic the internal xilinx program of the rtdac/pci board can use the switches to stop the dc motors. b. 3d crane mathematical model graphical representation of the 3d crane system is depicted in figure 2. despite the model simplification, it preserves the fundamental characteristics of the real system. the forces acting on this system and relevant variables, needed for the model development, are presented. an important element in the construction of the mathematical model is the appropriate choice of the system of coordinates. despite the fact that the etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 196-200 198 www.etasr.com antic et al:anti-swing fuzzy controller applied in 3d crane system cartesian system is simple in interpretation, it is not convenient for the description of the rotational motion dynamics, so we choose the spherical system. as we can see from figure 2, the position of the payload is described by two angles α and β . the shortcoming of the spherical system of coordinates is that for every point on the y-axis, the corresponding value of β is not uniquely determined. however, this is not valid in the case of the real crane systems, so it can be neglected. the position of the payload is described by the following equations: cos c w x x r α= + , (1) sin sin c w y y r α β= + , (2) sin cos c z r α β= − , (3) where w x represents the distance of the rail with the cart from the center of the construction frame, and w y is the distance of the cart from the center of the rail. the parameters of the 3d crane model are given in the table i. in similar manner, the dynamics of the crane can be obtained as: c c x m x s= −ɺɺ , (4) c c y m x s= −ɺɺ , (5) c c z c m x s m g= − −ɺɺ , (6) w w x x x m x f t s= − +ɺɺ , (7) ( )w s w y y ym m x f t s+ = − +ɺɺ , (8) where sx, sy and sz are the components of the vector s. fig. 2. 3d crane system: coordinates and forces. table i. parameters of 3d crane model symbol description r length of the lift-line α angle between the y-axis and the lift line β angle between the negative direction on the z-axis and the projection of the lift line onto the xz plane mc mass of the payload mw mass of the cart ms mass of the moving rail xc, yc, zc coordinates of the payload s reaction force in the lift-line acting on the cart fx force driving the rail with cart fy force driving the cart along the rail tx, ty friction forces cos x s s α= , (9) sin sin y s s α β= , (10) sin cos z s s α β= − . (11) the mathematical model of 3d crane system is completely determined by these equations. this model is used as the controlled plant for the controller design, presented in the next section. iii. controler design in [18], we considered the implementation of genetic algorithms in the determination of the parameters of pi controllers. in this section we propose an anti swing fuzzy controller, which gives better results compared to [18]. a control structure, based on fuzzy controllers, is developed for the previously described experimental framework. the main fuzzy controller’s structure is shown in figure 3. as it can be seen, it consists of three processes: fuzzification, fuzzy concluding, based on fuzzy rules, and deffuzification. let us define the error for x position of the payload as: x cdes c e x x= −= −= −= − (12) where the xcdes represents desired and the xc is actual, x position of the payload, respectively. differentiating (12) results in: ( ) ( )x x cdes c d d e e x x dt dt = = −ɺ (13) in a similar manner, the error y e and the error first derivative y eɺ for the y position of the payload can be defined. these four etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 196-200 199 www.etasr.com antic et al:anti-swing fuzzy controller applied in 3d crane system variables are used as inputs for the two anti-swing controllers, one for the x position and one for the y position of the payload, as shown in figure 4. the coordinate zc of the payload is considered to be a constant. the controller outputs are named ux and uy, and they represent the pwm inputs (dc motor controls) for the xand yaxis, respectively. each of the associated fuzzy variables for e, eɺ and u has seven linguistic terms. this terms are described by equally distributed gaussian membership functions for e and eɺ and triangular ones for u. we choose a qualitative category for each of them as nl (negative large), nm (negative medium), ns (negative small), ze (zero), ps (positive small), pm (positive medium) and pl (positive large). the rule base for the antiswing controller is presented in table ii, and it has the same form for xand y-axis, so we give only one. as a defuzzification method according to the control problem specificity, the center of gravity (cog) method was chosen. fig. 3. standard structure of fuzzy controller. fig. 4. simulation block diagram of the 3d crane control. fig. 5. experimental results for x and y positions. table ii. anti-swing fuzzy controller rule base eɺ e *l *m *s ze ps pm pl pl ze ns nm nl nl nl nl pm ps ze ns nm nl nl nl ps pm ps ze ns nm nl nl ze pl pm ps ze ns nm nl *s pl pl pm ps ze ns nm *m pl pl pl pm ps ze ns *l pl pl pl pl pm ps ze iv. experimental results practical verification of the proposed anti-swing fuzzy controller is performed on the experimental 3d crane setup presented in figure 1. as mentioned earlier, this is the experimental environment in which the users verify their 3d control algorithms in real time using matlab and simulink toolboxes. the experimental results of the 3d crane with the proposed anti-swing fuzzy controller are compared with the results obtained by the implementation of a pi controller [18]. the square wave is used as a reference signal. this type of signal matches the real situation, where the cart with payload is driven from the home position to the desired position and back to the home position. the square signal has amplitude of 0.8m and frequency of 0.1hz. it is assumed that the crane starts from home position (xc, yc)=(0, 0). experimental time was set to 25s. the results of the payload positions after using anti-swing fuzzy controllers are shown in figure 5. it is shown that the proposed control algorithm gives quite better results in comparison to those in [18]. however, due to oscillations, actual y position slightly exceeds the desired position. on the other hand, it tracks desired position quite well. v. conclusion this paper deals with the problem of reducing oscillations during the positioning of the payload. the 3d crane system is described by a nonlinear model, so using some robust methods in the control seems to be the right choice. in this paper, we present an anti-swing fuzzy controller for 3d crane positioning. the difference between desired and actual position and the first derivative of that difference are used as inputs for the controller. the short description of experimental framework and its mathematical model are given first, and then, experimental setup is employed for the practical verification of the proposed control algorithm. results show that the method described in the paper shows good system accuracy. acknowledgment this paper was realized as a part of the projects tr 35005 and iii 44006, financed by the ministry of education and science of the republic of serbia for the period 2011-2014. etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 196-200 200 www.etasr.com antic et 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[18] z. jovanović, d. antić, z. stajić, m. milošević, s. nikolić, s. perić, “genetic algorithms applied in parameters determination of the 3d crane model”, facta universitatis series: automatic control and robotics, vol. 10, no. 1, pp. 19-27, 2011. microsoft word etasr_v12_n1_pp8199-8203 engineering, technology & applied science research vol. 12, no. 1, 2022, 8199-8203 8199 www.etasr.com pravenn & roy: assessment of groundwater quality using water quality indices: a case study of … assessment of groundwater quality using water quality indices: a case study of paliganj distributary, bihar, india k. praveen civil engineering department national institute of technology patna patna, india praveen.ce17@nitp.ac.in l. b. roy civil engineering department national institute of technology patna patna, india lbroy@nitp.ac.in abstract-groundwater quality evaluation in the command area of paliganj distributary of the sone irrigation scheme in india was carried out during two different seasons in the year 2020, namely pre-monsoon, i.e. during march, and post-monsoon, i.e. during october. forty groundwater samples were obtained from hand pumps and dug wells in the study area during the preand post-monsoon seasons. the chemical characteristics of groundwater samples were determined according to american public health association approved process. twelve parameters, namely, ph, ec, tds, ca, mg, na, f, so4, k, cl, and hco3 were used to compute the water quality based on the weighted arithmetic water quality index method. in the study area, ca 2+ mg + -hco3 − , and ca 2+ -mg + -na + -hco3 were the dominant hydro-chemical facies. all the samples were found to belong to excellent to good category for drinking purposes during premonsoon period. however, during the post-monsoon season, only 75% of the samples fell into the excellent to good group, while the remaining 25% fell into the poor for drinking purposes category. by analyzing through the irrigation quality index, 80% of the samples are considered highly suitable for irrigation and the remaining 20% come under the medium category. thus, it was seen that the majority of groundwater samples are suitable for drinking and irrigation purposes, although groundwater in some portions of the area had high salinity and the sodium adsorption ratio (sar), showing that it is unsuitable for irrigation and requires adequate drainage. keywords-chemical parameters; water quality index; weighted arithmetic index; irrigation water quality index i. introduction the pressure on all natural resources to provide enough food and raw materials to meet the demand has increased as a result of the large increase in human population [1]. drinking and irrigation water supplies will be further stressed. increased demand may result in substantial changes in the hydrologic cycle, such as a decrease in the groundwater level or a reduction in groundwater quality [2, 3]. water in sufficient quantity and of acceptable quality is a fundamental need, yet preserving that quality is difficult. the chemical, physical, and biological characteristics of water are referred to as water quality. if the values of these parameters exceed the stated limitations, they are harmful to human health [4]. water quality index (wqi) is a statistic for expressing the level of water quality in a single numerical statement. it summarizes numerous water quality criteria to determine the acceptability of a water source for drinking purposes. wqi is one of the most effective techniques to quantify water quality. it is commonly used to assess the acceptability of water sources for human consumption. individual water quality factors have been shown to be difficult to understand when they are used to explain water quality for the general public [5-10]. the weighted arithmetic wqi was first proposed in [11] and further modified in [12]. in general, wqi is a technique for determining water quality conditions, and they, like any other tool, necessitate the understanding of water principles and basic ideas. wqi is a single, dimensionless number that is calculated by combining the major parameters that influence water quality. in general, wqi can avoid the challenges of drawing conclusions from vast amounts of water quality study data. the irrigation water quality (iwq) concept was implemented by using a model established in [13] to assess the appropriateness of groundwater for irrigation purpose. authors in [14] investigated uranium and other water quality parameters in drinking water sources in 5 districts of kerala, southern india, using the wqi method. groundwater in some cities on the right bank of the river ganges and in the vicinity of the study area, suffers from tds, nitrate concentration and fluoride contamination. the result and analysis of the present study shows the current status of groundwater in the study area. ii. materials and methods a total of 40 groundwater samples were collected from the paliganj block during march, 2020 (pre-monsoon) and again at the same locations during october 2020 (post-monsoon) to analyze seasonal variation. new, clean 1000ml polyethylene bottles were used to collect the groundwater samples. at the time of collection, the bottles were thoroughly rinsed 3 times with the same collection of samples. all groundwater samples were taken from hand pumps and dug wells. the groundwater samples were collected from the hand pumps after 5min of pumping. this method removes the stored groundwater in the corresponding author: k praveen engineering, technology & applied science research vol. 12, no. 1, 2022, 8199-8203 8200 www.etasr.com pravenn & roy: assessment of groundwater quality using water quality indices: a case study of … well. at the time of sample collection, ph, ec, and tds readings were measured by a mobile field kit. these factors fluctuate with storage time [15]. the laboratory tests were conducted in the central groundwater board (cgwb), patna. by using a flame photometer, major cations like sodium and potassium were determined. thermo-orion bench top ion electrode was used to determine fluoride and chloride. the total hardness and total alkalinity were determined by titration. the methods and techniques used to analyze all water quality parameters are shown in table i. the standard procedure given by apha [16] was used. table i. methods and techniques used chemical parameter method ph mobile ph meter electrical conductivity (ec) mobile ec meter total dissolved solids (tds) mobile tds meter chloride (cl ) ion chromatography sulphate (so4) spectro photometer nitrate (no3 ) ion chromatography calcium (ca +2 ) titration method by using edta solution magnesium (mg +2 ) titration method by using edta solution sodium (na + ) flame photometer 128 potassium (k + ) flame photometer 128 fluoride (f ) ion chromatography bicarbonate (hco3 ) titration method by using h2so4 solution a. the study area the sone command area aggregate catchment zone of the waterway is 71,259km 2 , of which 17,651km 2 lie in bihar. the remaining 53,608km 2 lie in chhattisgarh, madhya pradesh, uttar pradesh, and jharkhand states of india. the paliganj distributary is a part of the sone canal system in south bihar. the sone river flows north-eastward from the deccan plateau before joining the ganges not far from the city of patna. the sone canal system diverts water from the river to irrigate a design command area of over 700,000ha. fig. 1. index map of paliganj distributary, sone canal system. (source: bihar state second irrigation commission). b. water quality index methodology the weighted arithmetic wqi was used, considering 12 different chemical parameters. the world health organization (who) and the bureau of indian standards (bis) established standard values for several water quality indicators as shown in table ii. table ii. chemical parameters considered fo r wqi, their standard values, and recommend in g o rgan ization s chemical parameters (ec-µs/cm, all other parameters in mg/l) standard value recommending organization ph 6.5-8.5 who ec 400 who tds 500 who f 1 bis hco3 244 bis ca 2+ 75 bis mg 2+ 30 bis total hardness (th) 300 bis no3 45 bis so4 400 bis cl 200 bis total alkalinity (ta) 200 bis the weighted arithmetic index approach [12] was used to calculate the wqi: wqi � �∑�� �∑ � � (1) where wn is the unit weight of the nth water quality parameter and qn is its quality rating. based on the wqi value, the status of water quality is divided into 5 categories, i.e. wqi value between 0 and 25 is excellent, a value between 26 and 50 comes under good, a value between 51 to 75 comes under poor, a value between 76 and 100 comes under very poor, and a value above 100 is unsuitable for drinking purposes. the equation used to compute the quality rating qn is: � � ������������ 100 (2) where vn is the observed parameter's actual value and vi denotes the parameter's ideal value. except for ph (vi = 7), vs is the maximum permitted value for the nth water quality parameter. the formula for calculating wn is: �� � ��� (3) where k is the proportionality constant, which is derived by: � � � �∑ ������ ….�# (4) c. irrigation water quality index methodology iwq [17, 19] is based on a linear combination of 5 sets of irrigation water quality indicators that have the ability to affect soil quality and crop output significantly. throughout this method, the 5 groups were analyzed at the same time and then merged to provide a single index value, which is subsequently reviewed to find the suitability of irrigation water. authors in [18] proposed the guidelines for the selection of water quality parameters given in tables iii and iv. these water quality parameters not only reflect best the related risk, but they also interact with others to form the resource's basic water quality pattern. moreover, these parameters are set up in such a way that a non-technical policy maker could understand the tool's results and use the procedure without difficulty. engineering, technology & applied science research vol. 12, no. 1, 2022, 8199-8203 8201 www.etasr.com pravenn & roy: assessment of groundwater quality using water quality indices: a case study of … table iii. iwq index parameter classification [19] hazard unit weight chemical parameter range rating suitability salinity 5 ec > 3,000 1 low 700 ≤ ec ≤ 3,000 2 medium ec < 700 3 high infiltration and permeability 4 details are given in table iv specific ion toxicity 3 sar > 9 1 low 3.0 ≤ sar ≤ 9.0 2 medium sar < 3 3 high b < 0.7 3 high 0.7 ≤ b ≤ 3.0 2 medium b > 3.0 1 low ci < 140 3 high 140 ≤ ci ≤ 350 2 medium ci > 350 1 low trace element toxicity 2 details are given in table v effects on sensitive crops 1 no3< 5.0 3 high 5.0 ≤ no3≤ 30.0 2 medium no3> 30.0 1 low hco3< 90 3 high 90 ≤ hco3≤ 500 2 medium hco3> 500 1 low ph <6.5 or ph > 8.5 1 low 6.5 ≤ ph < 7.0 and 8.0 < ph ≤ 8.5 2 medium 7 ≤ph≤ 8 3 high iwq index =∑ $%&%'� (5) where g represents the contribution of each of the five risk factors that are important in determining the irrigation system's quality and i represents the incremental index. the salinity is the first considered parameter: $�=(� )� (6) where w is the hazard group's weight value and r represent the parameter's rating value, as shown in table iii. the permeability hazard and infiltration, which is represented by the ec – sar combination and is formulated as: $*= (* )* (7) where w is the weight value, and r represents the parameter's rating value as shown in table iv. the third category is specific ion toxicity, which is defined as a weighted average of the three ions in water (sar, chloride, and boron ions): $+= , + ∑ )-+-'� (8) where j represents an incremental index, w is the group's weight value as shown in table iv, and r represents each parameter's rating value as shown in table iv. the trace element toxicity category is calculated as the weighted average of all the ions available for analysis: $.= ,/0 ∑ )�0�'� (9) where w is the group's weight and n is the total number of trace elements that can be analyzed. as shown in table v, k is the incremental index, and r represents the rating value of each parameter. the 5th and final category is the weighted average of several influences on sensitive crops, which are represented by no3 and hco3 ions, and the ph of water. $&= ,1+ ∑ )2+2'� (10) where l represents the incremental index, w represents the group's weight value, and r is each parameter's rating value, as shown in table iii. table iv. in filtration and permeability h azard classification [19] sar rating suitability ec <3 3–6 6–12 12–20 > 20 <200 <300 <500 <1300 <2900 3 low 700–200 1200– 300 1900– 500 2900– 1300 5000– 2900 2 medium >700 >1200 >1900 >2900 >5000 1 high table v. toxicity classification factor range rating suitability fluoride (mg/l) f > 15 1 low 1.0 ≤ f ≤ 15.0 2 medium f < 1 3 high table vi. iwq index classification iwq index water suitability for irrigation < 22 low 22–37 medium > 37 high for the computation of the index's total value, suitability analysis has been performed using the 3 categories listed in table vi. the values in the table were derived by providing different rating factors (i.e. 1, 2, and 3) to each parameter while keeping the weighted coefficient constant, resulting in 3 different index values. the upper and lower limits for each category in table vi are determined by the medians of these values. iii. results and discussion the current study involves the estimation of wqi for water samples obtained from 20 sampling locations during preand post-monsoon season. a total of 40 groundwater samples of wqi were considered and the weighted arithmetic index method was used. the results are shown in figure 2. the methods that were employed in the analysis of various water chemical parameters are given in table i. table vii shows the calculated sar values of the study area. it should be noted that the sar value of four locations is more than 10, which indicates salinity hazard, requiring adequate drainage. the different water quality parameters were compared to the international standards recommended by who [15, 20] and bis-2012 [21] (table viii). after analyzing the water quality index during the premonsoon season, 35% of the samples came under the excellent engineering, technology & applied science research vol. 12, no. 1, 2022, 8199-8203 8202 www.etasr.com pravenn & roy: assessment of groundwater quality using water quality indices: a case study of … category and the remaining 65% under the good category for drinking purposes. during the post-monsoon season, 15% of the samples come under the excellent category, 60% under the good category, and the remaining 25% are poor to very poor. table vii. calculated sar values of the study area location pre-monsoon post-monsoon sar sar paipura 5.4 2.5 fathepur 5 2.6 kurkuri 3.1 2.6 sarsi 2.7 3.1 shiyarampur 2.8 5.6 bara 3 2.4 satpura 3.2 2.6 pipardah 2.7 8.8 lalganj 10.5 4.4 gulitar 11 7.8 makmilpur 10.2 4.1 baratpura 3.4 11.2 achhua 17.4 12.3 dulhin bazar 2.8 11.1 ular pond 8.4 6.1 bhimnichak 3.2 6.4 harpura 3.2 4.3 nabi nagar 4.6 2.7 aktiyarpur 2 6.6 khapura 3.5 5 table viii. internation al standard s used to compare vario us water quality parameters parameter who/bis -limit pre-monsoon post-monsoon no. of samples % of samples exceeded no. of samples % of samples exceeded ph 6.5-8.5 20 0 20 0 ec 400 20 65 20 60 tds 500 20 20 20 15 f 1 20 0 20 0 cl 250 20 0 20 0 hco3 244 20 50 20 45 so4 400 20 0 20 0 no3 45 20 10 20 0 ca +2 75 20 5 20 5 mg +2 30 20 20 20 10 ta 200 20 70 20 55 th 200 20 35 20 25 fig. 2. preand postmonsoon wqis. iwq index [13] was used for groundwater assessment for irrigation purposes in the command area of paliganj distributary of the sone irrigation scheme in india. by analyzing the groundwater samples showed in table ix with the iwq index, 80% of the samples came under the highly suitable for irrigation purposes category and the remaining 20% under the medium suitable category. therefore, overall, all groundwater samples in the study area are considered suitable for irrigation purposes, but some areas have high sodium percentage and sar value, indicating irrigation unsuitability. therefore, adequate drainage is required to overcome this problem. table ix. iwq index with irrigation water status in the study area location g-1 g-2 g-3 g-4 g-5 iwq status of water for irrigation paipura 15 4 18 6 1.98 44.98 high fathepur 15 4 12 6 2.31 39.31 high kurkuri 15 8 18 6 2.31 49.31 high sarsi 15 4 18 6 2.31 45.31 high shiyarampur 15 8 18 6 2.31 49.31 high bara 15 8 18 6 1.98 48.98 high satpura 15 8 18 6 1.98 48.98 high pipardah 15 8 27 6 2.64 58.64 high lalganj 10 8 9 6 2.31 35.31 medium gulitar 10 8 9 6 1.65 34.65 medium makmilpur 10 8 9 6 1.65 34.65 medium baratpura 15 8 12 6 2.31 43.31 high achhua 15 4 6 6 2.64 33.64 medium dulhin bazar 10 12 27 6 1.98 56.98 high ular pond 15 8 12 6 2.31 43.31 high bhimnichak 15 8 12 6 2.31 43.31 high harpura 15 8 12 6 2.31 43.31 high nabi nagar 15 8 12 6 2.31 43.31 high aktiyarpur 15 8 18 6 2.31 49.31 high khapura 15 4 18 6 2.64 45.64 high iv. result comparison authors in [22] analyzed groundwater samples from 14 different stations of patna city based on wqi and the results placed the water in the good category. however, none of their samples was found suitable for drinking purposes as they were all found to have high concentration of total and fecal coliform. also, they found that tds and nitrate concentration at some locations were above the standards' limits for drinking water. authors in [23] studied groundwater quality for samples collected from different locations of sabour block in bhagalpur district, bihar using wqi. they found that around 7% of the samples had wqi score greater than 100, the limit for drinking water. based on this, they suggested water safety and remediation measures. v. conclusions the wqi is a single value calculated from a set of water quality parameters that can be used to determine the quality and drinkability of a water sample. wqi estimation can help us save time and effort while dealing with groundwater data. it can also facilitate to communicate the data-driven decision with only one value. by analyzing wqi through the weighted arithmetic index method, during the pre-monsoon season, all engineering, technology & applied science research vol. 12, no. 1, 2022, 8199-8203 8203 www.etasr.com pravenn & roy: assessment of groundwater quality using water quality indices: a case study of … samples were either excellent or good for drinking purposes. however, during the post-monsoon season, only 75% of the samples fell into the excellent to good range, while the remaining 25% fell were poor to extremely poor. by analyzing the samples through the iwq index, 80% of them fell in the highly recommended for irrigation category and 20% were medium suitable for irrigation purposes. therefore, the overall groundwater quality is considered satisfying with respect to the standard values given by who and bis, but in some parts of the study area the groundwater has high salinity and sar, indicating that it is unsuitable for irrigation and requires adequate drainage. a collaborative multi-agency approach is recommended in order to ensure that agencies responsible for the study area are involved in the management of water quality. the outcome of this study may be used for the effective monitoring of water quality for drinking and irrigation purposes in the study area 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[23] d. verma, j. mandal, r. padbhushan, s. kumar, and m. lal, "water quality index for the assessment of groundwater quality in the sabour block of bhagalpur district, bihar," international journal of agriculture, environment and biotechnology, vol. 9, no. 4, pp. 467–472, may 2016, https://doi.org/10.5958/2230-732x.2016.00061.9. microsoft word etasr_v12_n1_pp7993-7997 engineering, technology & applied science research vol. 12, no. 1, 2022, 7993-7997 7993 www.etasr.com kumar et al.: automatic diagnosis of covid-19 related pneumonia from cxr and ct-scan images automatic diagnosis of covid-19 related pneumonia from cxr and ct-scan images naresh kumar department of computer science & engineering maharaja surajmal institute of technology new delhi, india narsumsaini@gmail.com manish gupta department of computer science & engineering moradabad institute of technology moradabad, india manishymca2007@gmail.com adeel hashmi department of computer science & engineering maharaja surajmal institute of technology new delhi, india ashashmi10@gmail.com ankit kundu department of computer science & engineering maharaja surajmal institute of technology new delhi, india ankitkundu93@gmail.com abstract-covid-19 is a highly infectious disease that spreads extremely fast and is transmitted through indirect or direct contact. the scientists have categorized the covid-19 cases into five different types: severe, critical, asymptomatic, moderate, and mild. up to may 2021 more than 133.2 million peoples have been infected and almost 2.9 million people have lost their lives from covid-19. to diagnose covid-19, practitioners use rt-pcr tests that suffer from many false positive (fp) and false negative (fn) results while they take a long time. one solution to this is the conduction of a greater number of tests simultaneously to improve the true positive (tp) ratio. however, ct-scan and xray images can also be used for early detection of covid-19 related pneumonia. by the use of modern deep learning techniques, accuracy of more than 95% can be achieved. we used eight cnn (covnet)-based deep learning models, namely resnet 152 v2, inceptionresnet v2, xception, inception v3, resnet 50, nasnetlarge, densenet 201, and vgg 16 for both x-rays and ct-scans to diagnose pneumonia. the achieved comparative results show that the proposed models are able to differentiate the covid-19 positive cases. keywords-artificial intelligence; covid-19 detection; convolutional neural networks; deep learning i. introduction covid-19 epidemic has caused millions of deaths worldwide [1-4]. the detection of corona virus positive cases is done through rt-pcr tests which take approximately 2 days to give results [5-7]. it is very crucial to diagnose the positive cases at early stages and quarantine them instantly. the infection can also be identified by pneumonia in chest x-ray (cxr) or ct-scan (cts) images of the patients, which is a much faster process [8-10]. these images are analyzed by the experts to locate the infection, which may take time due to the large number of patients. an automated and accurate artificial intelligence-based system to locate the infection in the images can considerably speed up the process. this work aims to help identify the covid-19 pneumonia from cxr and cts images. a deep learning approach has been used to build the models, i.e. convolutional neural networks (covnets) including resnet152v2, xception, inceptionresnetv2, resnet50, inceptionv3, nasnetlarge, densenet 201, and vgg-16 for the classification of the images as corona virus positive or not. the models were trained with a dataset containing cxr and cts images of covid and noncovid patients. comparative analysis of all the models is performed using various metrics to determine the best approach. in the recent studies, researchers have observed the bilateral relation of cxr and cts images with covid-19. they have observed the imaging patterns on the cxr and cts of the lungs for the diagnosis of ncov (novel coronavirus) infection [11]. also, it was found that with the help of deep learning techniques it is possible to achieve much higher image classification accuracy from cxr and cts images in the diagnostic process of corona virus. it has been observed that 4% of the patients had false negative (fn) corona result when tested with the rt-pcr kit. the study in [12] was related to the sensitivity of the real time polymerase chain reaction and ctss during diagnosis of ncov were acquired. the authors observed that the rt-pcr is less accurate and also its sensitivity is much lower than that of the cts. deep learning techniques provide much better results in the diagnosis process of acute pneumonia in csrs [13] or ctss [14, 15]. in [14], strong deep learning-based models have been used for the classification of cts images. the authors have used the imaging patterns of the cts images of lungs to differentiate the covid positive from the covid negative cases. however, their model achieved sensitivity under 90% and was unable to reach much accurate results. the authors in [15] built an automated system for the diagnosis and quantification of sars-cov-2 based on artificial intelligence. their automated system generates an output giving the quantitative opacity and 3corresponding author: adeel hashmi engineering, technology & applied science research vol. 12, no. 1, 2022, 7993-7997 7994 www.etasr.com kumar et al.: automatic diagnosis of covid-19 related pneumonia from cxr and ct-scan images dimensional output for opacities. their model is more efficient against pixel spacing. in [16], a transfer learning-based system was developed for the diagnosis of covid-19 from cxrs. from the above discussion and from [17, 18], it has been concluded that cxr and cts images can be utilized for the early diagnosis of ncov positive cases. in [19], the authors designed an automated ensemble system for the initial stage diagnosis of ncov from cxrs. they used two popular open-source datasets of cxr images for their research work. the first dataset was used for binary classification (i.e. covid-healthy and covid-positive) and the second dataset was used for multi-class classification (i.e. covid-healthy, covid-positive, pneumonia-positive, and tuberculosis-positive respectively). they used the pre-trained covnet combination of efficientnet, googlenet, and xception in their model. the results were summated and an absolute or relative voting was carried out to obtain the final decision. comparative analysis of their proposed model was done with some other covnets such as resnet-152v2, densenet-201, inceptionresnetv2, and vgg-16 to assess the capabilities of the model. their model outshined all the abovementioned covnets in both binary and multi-class classification and achieved decent accuracy rates of 99.21% and 98.95% for multi-class classification and binary classification respectively. the authors of [20] proposed a metaheuristic-based automated system for the early diagnosis of ncov positive patients from cxr images. they have used cnn for their experiments along with spea-2 for the proper tuning of the model’s parameters. they resized the dimensions of the images in the datasets to 259×259×3, which is the optimal size of the input image for the model. they computed the probability score of each class and the one with the maximum value was taken as the final. the performance of the proposed model was compared to vgg19, vgg16, resnet50, alexnet, resnet-34, inceptionnet, xception, densenet 201, and googlenet in terms of accuracy, f1 score, sensitivity, recall, and area under the roc curve. their proposed metaheuristic-based model performed well in multi-class classification and achieved accuracy of 99.97% and 99.13% on training and testing sets respectively. in [21] the authors used a multi-class dataset and deep covnet and xception model for their image classification model. the performance was evaluated with svm, random forest, back propagation network, adaptive neuro-fuzzy inference systems, covnet, vggnet, resnet50, alexnet, etc. they achieved accuracy of 97.40%. the authors in [22] proposed an automated system for pre-screening of covid, heart illness, and diabetes using machine learning models. for portability, they built an android application for early prediction or severity diagnosis at home without having to travel to clinics. they used three binary datasets, one for each considered disease. for the covid dataset they arranged the data in two groups, one group containing the data points regarding the countries having less than 10,000 cases and the other one for countries with more than 10,000 cases and marked them as 0 and 1 respectively. they applied the logistic regression on the training set in all the datasets. they also applied the cross validation technique to get the most optimized result from the model. they claimed that real-time diagnosis could be possible with the usage of an android application, also it would help in tweaking or dropping updates in the future. the proposed model was compare with other ml models such as lr, j48, knn, svm, ann, rf, and gb. their model achieved an accuracy rate of 95%, 94.20%, and 87% on diabetes, covid, and heart disease datasets respectively. the authors in [23] developed an automated system named dark covidnet for the early screening of covid-19 from cxr images. their model gave a decent accuracy of 98%, but it was trained on a small dataset of 125 cxr images. ii. methodology a. dataset open source datasets from github repository and kaggle, were used to train the above-mentioned models. the dataset in [24] is a 740mb dataset source containing 7252 cxr images (3612 cxr images of covid-19 patients and more than 3600 non-covid cxr images), whereas [25] is a dataset containing 1000 cxr images of covid-19 and healthy people (495 covid19 positive and 505 covid-19 negative images), as shown in figures 1-2. fig. 1. visualization of a few non-covid cxr images. fig. 2. visualization of a few ovid cxr images. regarding cts images, [26] is a 231mb dataset consisting of 2481 cts images (out of which 1252 images are of covid19 patients and 1229 are from healthy people), whereas [27] is a dataset used to train the models on chest cts images. it consists of 750 images of covid-19 patients and healthy people (353 images of covid-positive patients and 397 of healthy people). the utilization ratio of the complete dataset is 80:20, i.e. 80% of the complete dataset is used to train the model and the rest 20% is used for testing. figure 3 depicts a few computed tomography (ct) images from the dataset of the people infected from ncov 2019, while figure 4 illustrates the visualization of a few ct images of healthy people present in the dataset used to train the models. b. covnet (cnn) overview covnet has very good performance in diagnostics, agriculture, and industry [28-33]. figure 5 illustrates a general engineering, technology & applied science research vol. 12, no. 1, 2022, 7993-7997 7995 www.etasr.com kumar et al.: automatic diagnosis of covid-19 related pneumonia from cxr and ct-scan images architecture of a cnn having an input layer, two convolution layers, each followed by a pooling layer, followed by two consecutive fully-connected layers, and at the end there is a softmax activation function [34, 35]. fig. 3. ct scan images of covid patients. fig. 4. ct scan images of normal patients. fig. 5. general architecture of the covnet. c. the proposed architecture table i. covnet architecture utilized for covid-19 detection layer (type) output shape param # input_1 (inputlayer) [(none, 224, 224, 3)] 0 conv2d (conv2d) (none, 224, 224, 32) 896 dropout (dropout) (none, 224, 224, 32) 0 activation (activation) (none, 224, 224, 32) 0 max_pooling2d (maxpooling2d) (none, 112, 112, 32) 0 conv2d_1 (conv2d) (none, 112, 112, 64) 18496 dropout_1 (dropout) (none, 112, 112, 64) 0 activation_1 (activation) (none, 112, 112, 64) 0 max_pooling2d_1 (maxpooling2d) (none, 56, 56, 64) 0 conv2d_2 (conv2d) (none, 56, 56, 128) 73856 dropout_2 (dropout) (none, 56, 56, 128) 0 activation_2 (activation) (none, 56, 56, 128) max_pooling2d_2 (maxpooling2d) (none, 28, 28, 128) 0 conv2d_3 (conv2d) (none, 28, 28, 256) 295168 dropout_3 (dropout) (none, 28, 28, 256) 0 activation_3 (activation) (none, 28, 28, 256) 0 max_pooling2d_3 (maxpooling2d) (none, 14, 14, 256) 0 flatten (flatten) (none, 50176) 0 dense (dense) (none, 64) 3211328 dropout_4 (dropout) (none, 64) 0 dense_1 (dense) (none, 1) 65 the utilized architecture is depicted in table i. the model consists of convolution layers that extract possible characteristics from medical scans and feed them to the input layer, which is then followed by the pooling layer. the average pooling strategy of 2×2 is being used in this study, which minimizes or divides the feature mapping by 2 and transmits the output to the hidden or middle layer, which is masked behind the softmax activation function and comprises of pooling and convolution layers. the activation function aids the middle layer in selecting the best input based on the weights. the data processed by the middle layer are sent as input for prediction to the dense or fully-connected layer. because it delivers the final classification or predictions, the dense layer is also known as the output layer. iii. results the proposed models were implemented using keras. all the tests were run on a google colaboratory console with 12gb ram and a tesla k80 gpu. the validity of the covnets has been examined in two stages. in the first stage, classification reports of the 8 covnet models were produced for 500 epochs for both cxr and cts images. after that, confusion matrices were constructed. after a comparison analysis of the models, the best method was identified. table ii compares the results of the proposed model with 8 standard covnet models on the cxr test dataset. the inception v3 outperformed the other covnets in terms of accuracy, peaking at 9%. the xception model, on the other hand, yields nearly identical prediction figures to the inception v3 network and scores 2% lower in terms of accuracy, while it also gives 97%, 87%, and 89% specificity, sensitivity, and f1-score respectively. in terms of accuracy, precision, recall, and f1score, the resnet 50 network has the lowest prediction figures of 83%, 76%, 92%, and 81% respectively. the vgg16 model produces some incredible results, with accuracy, precision, sensitivity, and f1-score values of 92%, 86%, 98%, and 92%. the rest of the models produced similar findings, with the exceptions of densenet 201 and resnet 152 v2, which produce significantly better results than the other two models (inceptionresnet v2, nasnetlarge covnet model) in all metrics. in terms of overall statistics, the proposed model produced the best end prediction values when all of the measures were taken into consideration. table ii. cxr results model metric precision recall f1-score accuracy nasnetlarge 0.89 0.83 0.86 0.86 densenet 201 0.94 0.82 0.88 0.89 resnet 152 v2 0.91 0.85 0.88 0.88 inception resnet v2 0.86 0.80 0.83 0.84 resnet 50 0.76 0.92 0.81 0.83 xception 0.97 0.87 0.89 0.93 inception v3 0.87 0.98 0.91 0.95 vgg 16 0.86 0.98 0.92 0.92 proposed model 0.96 0.95 0.96 0.98 the statistics of the models in diagnosing ncov illness from ctss are shown in table iii. all of the models were developed using a binary classification data sample. with accuracy, specificity, sensitivity, and f1-score values of 93%, 98%, 92%, engineering, technology & applied science research vol. 12, no. 1, 2022, 7993-7997 7996 www.etasr.com kumar et al.: automatic diagnosis of covid-19 related pneumonia from cxr and ct-scan images and 96% on the ct testing data sample, the xception model performed exceptionally well and delivered highly competitive figures. the vgg 16 and inception v3 both provide 92% accuracy, however the rest of the metrics for both neural networks are 92%, 92%, 92%, and 93%, 97%, and 95% respectively, while nasnetlarge and resnet produced the lowest prediction figures. the accuracy rates of densenet 201, inceptionresnet v2, and resnet 152 v2, are all in the range of 80-90%. in terms of overall statistics, the proposed model produced the best possible end prediction values when all the measures were taken into consideration. table iii. cts results model metric precision recall f1-score accuracy nasnetlarge 0.75 0.79 0.77 0.77 densenet 201 0.89 0.79 0.79 0.81 resnet 152 v2 0.88 0.83 0.86 0.86 inception resnet v2 0.75 0.99 0.84 0.83 resnet 50 0.83 0.74 0.76 0.79 xception 0.93 0.98 0.92 0.96 inception v3 0.93 0.97 0.95 0.92 vgg 16 0.92 0.92 0.92 0.92 proposed model 0.97 1.00 0.96 0.97 iv. conclusion and future work cxr and cts images were employed in this study to overcome the lack of precision with real-time polymerase chain reaction tests for ncov illness diagnosis. cxr and cts reports were employed as medical imaging procedures. cxr and cts reports suggest certain prospective patterns (pneumonia) and have bilateral effects with ncov, according to a large number of research publications and detailed reviews [36, 37]. manual testing of these medical photos on the other hand takes a long time and may culminate in diagnostic inaccuracy. image categorization, speech recognition, and other applications benefit greatly from covnets. all the covnet models listed above have been correctly trained, and the parameters have been fine-tuned. the models were trained using a dataset with a substantial number of images. to assess the capabilities of all the aforementioned models, a thorough comparison was carried out using a variety of popular benchmarks such as accuracy, precision, recall, and f1-score. inception v3 and xception showed the highest accuracy of 95% and 93% respectively whereas in ctss, xception inception v3 exhibited the highest scores (96% and 92% respectively). both the covnet models, i.e. 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[37] d. n. n. das, d. n. kumar, d. sharma, and s. rao, “covid19 – transmission of corona virus and it’s mathematical model to analyze,” journal of critical reviews, vol. 7, no. 19, pp. 4779–4784, 2020, https://doi.org/10.31838/jcr.07.19.559. engineering, technology & applied science research vol. 7, no. 6, 2017, 2260-2265 2260 www.etasr.com jafarzadeh et al.: an enhanced genetic algorithm for the generalized traveling … an enhanced genetic algorithm for the generalized traveling salesman problem hassan jafarzadeh department of systems and information engineering university of virginia charlottesville, virginia, usa hj2bh@virginia.edu nazanin moradinasab department of industrial engineering tarbiat modares university tehran, iran nmn2ie@gmail.com milad elyasi department of industrial engineering ozyegin university istanbul, turkey milad.elyasi@ozu.edu.tr abstract—the generalized traveling salesman problem (gtsp) deals with finding the minimum-cost tour in a clustered set of cities. in this problem, the traveler is interested in finding the best path that goes through all clusters. as this problem is nphard, implementing a metaheuristic algorithm to solve the large scale problems is inevitable. the performance of these algorithms can be intensively promoted by other heuristic algorithms. in this study, a search method is developed that improves the quality of the solutions and competition time considerably in comparison with genetic algorithm. in the proposed algorithm, the genetic algorithms with the nearest neighbor search (nns) are combined and a heuristic mutation operator is applied. according to the experimental results on a set of standard test problems with symmetric distances, the proposed algorithm finds the best solutions in most cases with the least computational time. the proposed algorithm is highly competitive with the published until now algorithms in both solution quality and running time. keywords-genetic algorithms; traveling salesman; generalized; nearest neighbor i. introduction genetic algorithm (ga) is a search heuristic that mimics the process of natural evolution [1]. this heuristic algorithm (also sometimes called a metaheuristic) is routinely used to generate useful solutions to optimization and search problems. gas belong to the larger class of evolutionary algorithms (ea), which generate solutions to optimization problems using techniques inspired by natural evolution, such as inheritance, mutation, selection, and crossover. in a genetic algorithm, a population of candidate solutions (called individuals, creatures, or phenotypes) to an optimization problem is evolved toward better solutions. each candidate solution has a set of properties (its chromosomes or genotype) which can be mutated and altered [2]. the evolution usually starts from a population of randomly generated individuals and is an iterative process, with each iteration’s population called a generation. in each generation, the fitness of every individual in the population is evaluated. the fitness is usually the value of the objective function in the optimization problem being solved. the more fit individuals are stochastically selected from the current population, and each individual’s genome is modified (recombined and possibly randomly mutated) to form a new generation. the new generation of candidate solutions is then used in the next iteration of the algorithm. the algorithm continues to run until one of the following criteria is met:  a pre-defined fitness score is reached  a specified number of iterations are completed or alternatively, a set time limit is reached  no improvement is achieved in a specified number of iterations the generalized traveling salesman problem (gtsp) is a generalized version of the traveling salesman problem (tsp). in this problem, the cities are divided into a number of clusters and the traveling salesman has to find the minimum-cost tour which passes through exactly one city from each cluster. consider r which is formed by a set of nodes that has been separated to m non-empty incompatible proper subsets: 1 m ii r v r n    (1) each node has been connected by one or more arcs from e, so that each arc connects two nodes from different clusters. ( , ) i v , j v , i j i ji j e     in which r and e compose  ,g r e , that represents the gtsp’s net. the shortest tour that starts from one node of a cluster and passes through only one node of every other clusters and finishes at the starting point is desired. ii. literature review the generalized form of tsp is called gtsp, and this problem’s aim is optimizing the path between polygons instead of the single nodes. authors in [3, 4] studied precision algorithms and theoretical approaches to solve this problem. an integer linear program and also, exact and heuristic separation procedure for some classes of facet-defining inequalities, which are used within a branch-and-cut algorithm for the exact solution of gtsp was proposed in [5]. in this study the best objective values of the aforementioned paper were used, in order to test the results of proposed algorithm. engineering, technology & applied science research vol. 7, no. 6, 2017, 2260-2265 2261 www.etasr.com jafarzadeh et al.: an enhanced genetic algorithm for the generalized traveling … authors in [6] developed an innovative algorithm for minimizing airtime of a cutting tool. 3ρ/2 approximation algorithm has been presented in [7], where ρ is the number of cities in the largest cluster while the worst-case bound may be weak, as ρ may be quite large. another approximation algorithm for the group steiner tree problem has been proposed in [8]. in both [7, 8], the triangle inequality must be satisfied. authors in [9] proposed an efficient innovative approach for solving gtsp. in their method, random-key ga is combined with a local tour improvement heuristic to improve the quality of solutions and the time required for obtaining them. a particle swarm optimization based algorithm was recently developed as well by authors in [10]. also, an ant colony optimization (aco) is used to solve gtsp in [11]. authors in [12] proposed a ga with several new features, including isolated initial populations and a new reproduction mechanism based on the tsp ordered crossover operator. this new mechanism was called mrox, for modified rotational ordered crossover. another way to solve the gtsp is to turn it into the tsp [13]. the procedure of adaptation of a tsp neighborhood for the gtsp has been formalized in [14]. authors in [15] proposed memetic algorithm to solve the gtsp where the crossover operator relies on large neighborhood search. their main contribution was the originality of their crossover procedure. the lin–kernighan heuristic is known to be a very successful tsp one. a number of adaptations of lin– kernighan for the gtsp are presented by authors in [14]. they have discussed several approaches to adapt tsp local search for the gtsp. authors in [16] have extended the ant colony optimization method from tsp to gtsp and based on the basic extended aco method, they have developed an improved method by considering the group influence, besides a mutation process and a local search technique, namely 2-opt search has been applied. applications of the gtsp are also discussed in [17]. a local-global approach for the generalized traveling salesman problem and also an efficient algorithm for solving the problem based on genetic algorithms is proposed in [18, 19]. a new memetic algorithm to solve the symmetric and asymmetric instances of gtsp which is called gk is presented by authors in [20]. their new memetic algorithm due to powerful local search, well-fitted genetic operators and new efficient termination condition improved the older versions and the given experimental results show its capability. local-global approach for the gtsp is presented in [19]. a novel hybrid metaheuristic algorithm approach using genetic algorithms is described based on this approach. computational results are reported and compared for euclidean tsp-lib instances. results show that the proposed hybrid algorithm leads to good solutions in a reasonable amount of time. also, the consultantguided search technique with a local-global approach is combined by authors in [21] in order to solve efficiently the gtsp. they use candidate lists in order to reduce the search space and they introduce efficient variants of 2-opt and 3-opt local search in order to improve the solutions. different local search implementations e.g. 2-opt, 3-opt, k-op and swap have been compared empirically by authors in [14]. an ensemble of discrete differential evolution algorithms with parallel populations is presented in [22]. in a single populated discrete differential evolution (dde) algorithm, the destruction and construction (dc) procedure is employed to generate the mutant population whereas the trial population is obtained through a crossover operator. iii. mathematical formulation mathematical formulation will provide us the other aspect of the problem which will be an instrumental tool for pondering. also the ip formulation can help us towards finding other powerful algorithms in future researches. by considering these facts, researchers try to present the exhaustive and easy to understand ip formulation. six distinct formulations of the gtsp as an integer programming are described in [23]. these ip formulations are “compact” in the sense that the number of constraints and variables is a polynomial function of the number of nodes in the problem. in this paper, a new ip formulation is described. symbols used in the presented mathematical model are as follows: m : number of clusters in : number of nodes in thi cluster 1, ,i m  m : set of clusters  1, ,m m  n : number of nodes 1 m i i n n    1 if node from cluster is chosen 0 o.w. th th ij j i y     1 if there is an arc from node from cluster to node from cluster 0 o.w. th th th th ijkl j x i l k      the cost of traveling from node from cluster to node from cluste r : th th th th ijkl j i l k c 1 if there is an arc from cluster to cluster 0 o.w. th th ik i k z     by considering the cited symbols above, the mathematical model of the problem will be composed of one objective function and some constraints. after introducing the mathematical model, the descriptions about the objective function and constraints will be given. 1 1 1 1 min i kn nm m jkl jkl i k j i z ci xi       1 1 {1, 2,..., } in ij j y i m     1 1 , {1, 2,..., }, {1, 2,..., } knm ijkl ij i k l x y k i i m j n         1 1 , {1, 2,..., }, {1, 2,..., } inm ijkl kl k i j x y k i k m l n         1 1 , , {1, 2,..., } i kn n ijkl ik j l x z k i i k m        1 , ik i s k s z s m s        engineering, technology & applied science research vol. 7, no. 6, 2017, 2260-2265 2262 www.etasr.com jafarzadeh et al.: an enhanced genetic algorithm for the generalized traveling … {0,1}ijy  {0,1}ijklx  {0,1}ikz  objective function shows the total cost of traveling that should be minimized. the first constraint emphasizes that exactly one node from each cluster should be chosen. the second and third constraints state that the maximum number of output and input arcs is one. the fourth and the fifth constraints ensure that there is not any sub-tour in travelled rout. and finally, last three definitions show that the used variables are boolean. iv. genetic algorithm approach for gtsp in this section, the constructive sections of genetic algorithm and the quantity of the parameters for solving the gtsp are presented. the most suitable amount for these parameters has been found by trial and error. a. chromosome representation figure 1 illustrates the bipartite chromosome that has been used. assume that m, is the number of clusters and n1, n2, ….., nm represent the number of nodes in each cluster respectively. let m=8, n1=3, n2=8, n3=3, n4=5, n5=6, n6=4, n7=6, n8=7. a possible solution is shown in figure 1. the first row contains integers 1 to 8 that represents the sequence of clusters that have been visited by the traveling salesman. numbers in the second row represent the city chosen from each cluster. 5 7 3 2 4 8 1 6 4 5 3 6 1 7 3 3 fig. 1. chromosome representation so this chromosome suggests that the traveling salesman should start his trip by visiting the fourth city from the fifth cluster and after finishing his job should go to the fifth city from the seventh cluster. by using this type of chromosome, there will be m! ways to arrange numbers on the first row and there are also ni possible arrangements for the i th cluster. so, for a problem with m clusters and , {1, 2,..., }in i m  nodes in each cluster, the bipartite chromosome has 1 ! ! m ii m n  possible forms which are the size of the solution space. after computing the fitness of each chromosome, the algorithm directly passes chromosome of highest fitness value to the next generation. therefore, the best solution is never lost. the fitness function plotted by the algorithm is always ascending type. b. reproduction when a new population is created, the algorithm replaces 10% of the worst solutions with a random population. this way, the diversity would be preserved and a larger area of the solution space would be covered. c. crossover in this algorithm, a simplified greedy selection crossover (gsx) operator is used. this operator is adapted for the bipartite. the major merits of this operator would be revealed in problems of a larger size. in this kind of cross over, a similar city is selected arbitrarily in both chromosomes. this city is put in the first gen of offspring. in these parents, we have two cities right next to the selected first gen. their distance from the first gen is considered and the nearest one is selected as the second gen. we will do the described step for the third city etc. the function of this operator for tsp with per mutative chromosome coding is described thoroughly by [24]. d. mutation an improving mutation operator is utilized in this algorithm. we know that an optimal path in this problem does not have any crossing segments, and mutation operator applies this theorem to promote the quality of the existing solutions. a random chromosome is picked, and each consecutive pair of its genes that makes a connecting line between two centers is analyzed for possible crossing with other pairs. if the algorithm finds such couple of pairs it exchanges those genes. 3 2 4 7 1 5 6 4 5 3 6 1 7 3 3 5 1 7 4 2 6 4 7 1 6 3 5 3 fig. 2. mutation e. nearest neighbor search nearest neighbor search (nns) is an optimization problem for finding the closest points in metric spaces. the problem is: pseudocode: nearest neighbor search algorithm 1. required c% a random chromosome 2. 2 11 ( 1).[ ] 1m rand              3. γ←[c(min(α,β):max(α,β))] 4. l←zeros(β-α+1) % size of matrix zeros is (β-α+1) 5. for i=1:β-α 6. μ←∞ 7. for j=i+1:β-α+1 8. 2 2( ) ( ) ( ) ( )( ) ( )i j i jx x y y        9. if (δ<μ) 10 μ←δ 11. η←ξ 12. endif engineering, technology & applied science research vol. 7, no. 6, 2017, 2260-2265 2263 www.etasr.com jafarzadeh et al.: an enhanced genetic algorithm for the generalized traveling … 13. endfor 14. λ(i)←γ(η) 15. endfor 16. return λ given a set of points in a metric space m and a query point q m , find the closest point in s to q. in this paper, nns algorithm is used for promoting efficiency of ga for solving the gtsp. in the given pseudocode, c shows a sample chromosome from ga that is related randomly from the population. the algorithm generates two integer and random numbers (i.e. line 2) to pick a string of genes between them and then apply nns on the extracted string. this string is showed by  in the third line. the improved string will be returned by  at the end of algorithm which has been pre-allocated in line 4. in the provided loop, algorithm finds the closest point to the point that already exists in the  . then, it searches within the remaining points that have not been assigned yet, and it repeats these steps till reordering all the selected points as string  . the algorithm stops when (i) the best solution that has been obtained by algorithm, appears repeatedly in a specific number of iterations or (ii) when a specific number of iterations is performed. v. computational results the number of iterations to meet the first termination criterion was set to 250 and the second criterion will differ from problem to problem, the population size iteration was set to 60, the crossover rate was set to 85% and the mutation rate was set to 5%. in every case, the best solution was obtained in less than 0.4 seconds. for investigating the efficiency of the proposed algorithm, standard test problems that are generated in [20] were solved and the results of them were collected in tables i and ii. table i, presents the computational results in both terms of quality of solutions and cpu time. in table ii, the results of comparison between ga, nearest neighbor search, ga+nns and gk have been illustrated. gk is a state-of-the-art algorithm for solving the gtsp which is presented by [20]. “problem” shows the standard test problem. “best” presents the best known objective function value for each problem. “best obtained value” is the objective value that proposed algorithm reached. “opt” represents the number of trials that algorithm obtained the best known objective function value in 10 time runs. “average” illustrates the mean of obtained tour length in 10 time runs. “err (%)” represents the relative error, where the relative error is calculated as: 100 a verage opt err opt    . table i. computational results: quality of solutions and time problem best best obtained value opt average err (%) cpu time 10att48 5394 5394 10 5394 0.00 0.00 11eil51 174 174 10 174 0.00 0.01 12brazil53 15332 15332 10 15332 0.00 0.01 14st70 316 316 10 316 0.00 0.01 16eil76 209 209 10 209 0.00 0.01 16pr76 64925 64925 10 64925 0.00 0.01 20kroa100 9711 9711 10 9711 0.00 0.02 20rat99 497 497 10 497 0.00 0.03 20rd100 3650 3650 10 3650 0.00 0.03 21eil101 249 249 10 249 0.00 0.02 21lin105 8213 8213 10 8213 0.00 0.03 22pr107 27898 27898 10 27898 0.00 0.04 24gr120 2769 2769 10 2769 0.00 0.06 25pr124 36605 36605 10 36605 0.00 0.07 26bier127 74118 74118 10 74118 0.00 0.09 28pr136 42570 42570 10 42570 0.00 0.09 29pr144 45886 45886 10 45886 0.00 0.11 30kroa150 11018 11018 9 11018 0.01 0.08 31pr152 51576 51576 9 51576 0.01 0.16 32u159 22664 22664 9 22671 0.02 0.19 39rat195 854 854 10 854 0.00 0.24 40d198 10557 10557 10 10557 0.00 0.24 40kroa200 13406 13406 9 13406 0.01 0.36 40krob200 13111 13111 10 13111 0.00 0.30 45ts225 68340 68340 8 68340 0.03 0.32 46pr226 64007 64007 8 64012 0.04 0.51 53gil262 1013 1013 9 1013 0.02 0.53 53pr264 29549 29549 8 29549 0.04 0.49 60pr299 22615 22615 7 22615 0.06 0.43 64lin318 20765 20765 5 20774 0.09 0.88 80rd400 6361 6361 8 6361 0.05 1.00 84fl417 9651 9651 9 9651 0.02 1.22 88pr439 60099 60099 6 60107 0.07 1.04 89pcb442 21657 21657 3 21663 0.09 1.41 engineering, technology & applied science research vol. 7, no. 6, 2017, 2260-2265 2264 www.etasr.com jafarzadeh et al.: an enhanced genetic algorithm for the generalized traveling … table ii. comparing the result between the proposed algorithm and ga and nn problem best ga nns gk ga+nns err (%) cpu time err (%) cpu time err (%) cpu time err (%) cpu time 10att48 5394 0.00 0 0.00 0.00 11eil51 174 0.00 0.1 0.00 0.4 0.00 0.01 12brazil53 15332 0.00 0.3 0.00 0.01 14st70 316 0.00 0.2 0.00 0.8 0.00 0.01 16eil76 209 0.00 0.2 0.00 1.1 0.00 0.01 16pr76 64925 0.00 0.2 0.00 1.9 0.00 0.01 20kroa100 9711 0.00 0.7 0.00 7.3 0.00 0.02 20rat99 497 0.00 0.8 0.00 2.8 0.00 0.03 20rd100 3650 0.00 0.3 0.80 8.3 0.00 0.03 21eil101 249 0.00 0.2 0.40 3 0.00 0.02 21lin105 8213 0.00 0.3 0.00 3.7 0.00 0.03 22pr107 27898 0.00 0.4 0.00 5.2 0.00 0.04 24gr120 2769 0.00 0.5 0.00 0.06 25pr124 36605 0.00 0.6 0.00 12 0.00 0.07 26bier127 74118 0.00 0.5 9.68 7.8 0.00 0.09 28pr136 42570 0.00 0.5 5.54 9.6 0.00 0.09 29pr144 45886 0.00 0.3 0.00 11.8 0.00 0.11 30kroa150 11018 0.00 1.3 0.00 22.9 0.01 0.08 31pr152 51576 0.00 1.5 1.80 10.3 0.01 0.16 32u159 22664 0.00 0.6 2.79 26.5 0.02 0.19 39rat195 854 0.00 0.7 1.29 86 0.00 0.24 40d198 10557 0.00 1.2 0.60 118.8 0.00 0.14 0.00 0.24 40kroa200 13406 0.00 2.7 5.25 53 0.00 0.14 0.01 0.36 40krob200 13111 0.00 1.4 0.00 135.2 0.00 0.16 0.00 0.30 45ts225 68340 0.00 2.4 0.00 117.8 0.00 0.24 0.03 0.32 46pr226 64007 0.00 1 2.17 67.6 0.00 0.1 0.04 0.51 53gil262 1013 0.79 1.9 1.88 122.7 0.00 0.31 0.02 0.53 53pr264 29549 0.00 1.3 5.73 147.2 0.00 0.24 0.04 0.49 60pr299 22615 0.02 6.1 2.01 281.8 0.00 0.42 0.06 0.43 64lin318 20765 0.00 3.5 4.92 317 0.00 0.45 0.09 0.88 80rd400 6361 1.37 3.5 3.98 1137.1 0.00 1.07 0.05 1.00 84fl417 9651 0.07 2.4 1.07 1341 0.00 0.73 0.02 1.22 88pr439 60099 0.23 9.1 4.02 1238.9 0.00 1.48 0.07 1.04 89pcb442 21657 1.31 10.1 0.22 838.4 0.00 1.72 0.09 1.41 finally, “cpu time” shows the elapsed time for obtaining the best solution. which are the times until the termination criteria are satisfied. by considering the provided results for ga and nns algorithm in table ii, it is inferable that the combination of these two algorithms has better performance in comparison with ga and nns alone. based on the results of table i, the stability of presented algorithm is visible. in the “err (%)” column the percentage of error for most instances is zero, and in the other ones this amount is nominal. also, the “opt” column clarifies that the algorithm reaches the best solution in most cases. vi. conclusion in this paper, the formulation of the gtsp has been expanded, and a ga was combined with nns for solving it. the proposed algorithm was tested on standard test problems and the results were collected in two tables. in most runs, the best solution was obtained at a minimum time. the proposed algorithm is proven to be efficient for solving gtsp, in terms of both the quality of obtained solutions and the least running time. to evaluate the performance of the presented algorithm, its results are compared with a state-of-the-art algorithm (gk) and the quality of results is satisfactory, and also its running time is better. references [1] m. mitchell, an introduction to genetic algorithms, mit press, 1998 [2] d. whitley, “a genetic algorithm tutorial”, statistics and computing, vol. 4, no. 2, pp. 65–85, 1994 [3] g. laporte, y.nobert, “generalized traveling salesman problem through n-sets of nodes–an integer programming approach”, information systems and operational research, vol. 21, no. 1, pp. 61-75, 1983 [4] g. laporte, h. mercure, y. nobert, “finding the shortest hamiltonian circuit through n clusters: a lagrangean relaxation approach”, gongressus numerantium, vol. 48, pp. 277-290, 1985 [5] m. fischetti, j. j. s. gonzalez, p. toth, “a branch-and-cut algorithm for the symmetric generalized traveling salesman problem”, operations research, vol. 45, no. 3, pp. 378-394, 1997 [6] k. castelino, r. d'souza, p. k. wright, “tool-path optimization for minimizing airtime during machining”, journal of manufacturing 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salesman problem”, gecco, association for computing machinery, pp.481-488, 2011 [22] m. fatih tasgetiren, p. n. suganthan, q. k. pan, “an ensemble of discrete differential evolution algorithms for solving the generalized traveling salesman problem”, applied mathematics and computation, vol. 215, no.9, pp. 3356–3368, 2010 [23] p. c. pop, “new integer programming formulations of the generalized traveling salesman problem”, american journal of applied sciences, vol. 4, no. 11, pp. 932-937, 2007 [24] l. qu, r, sun, a” synergetic approach to genetic algorithm for solving traveling salesman problem”, information sciences, vol. 117, no. 3-4, pp. 267-283, 1999 microsoft word etasr_v11_n4_pp7531-7535 engineering, technology & applied science research vol. 11, no. 5, 2021, 7531-7535 7531 www.etasr.com dwairi: increasing gain evaluation of 2×1 and 2×2 mimo microstrip antennas increasing gain evaluation of 2×1 and 2×2 mimo microstrip antennas majed omar dwairi al-balqa applied university faculty of engineering technology department of communication technology jordan, amman majeddw@bau.edu.jo abstract-in this paper, a semi-circular ultra-wideband antenna has been modified according to the 2×1 and 2×2 mimo scenarios. the proposed antennas were designed based on the fr-4 substrate material with dimensions of 36×50mm and 60×60mm for 2×1 and 2×2 scenarios respectively. simulation results show that a gain improvement of the proposed mimo antennas from 1 to 2.5db has been achieved in comparison with the single patch antenna. the radiation pattern for the original and the proposed 2×2 mimo antennas are exhibited. the main advantage of the proposed antennas is that the gain improves without the need to increase the operating power. this makes the proposed mimo antennas suitable to be used for uwb antenna applications. keywords-microstrip antenna; ultra-wideband; multi-input multi-output; released gain i. introduction the microstrip antenna has received the attention of microwave antenna designers in ultra-wideband (uwb) applications. this can be clearly seen after the adaption of the uwb range of 3.1-10.6ghz from the federal communication community 2002 [1]. microstrip antennas received much attention due to their advantages, when compared with other microwave antennas, such as low profile, light weight, low cost, capability of many frequency operations, and easy integration with the microwave integrated circuit. many investigated directions in microstrip antenna design have been proposed. also, many researchers analyzed and experimented with different microstrip antenna simulation tools [2]. the effect of inserting different slots in order to enhance the operating bandwidth has also been studied [3-8]. in [9-12], different patch and ground slots were inserted to eliminate unwanted narrow frequency bands, known as filters. muliinput multi-output (mimo) microstrip antenna technology received more attention in microwave wireless communications, due to its ability to increase operating data throughput and its range without the need for additional transmitted power or bandwidth. mimo technology received more attention as it does not need any additional spectrum while transmitting and receiving information from its multiple channels at the same time. by a proper design and layout of mimo antenna, multipath characteristics of the wireless communications can be controlled. in [13], a high gain mimo antenna was introduced for a mm-wave planar antenna by choosing the proper size of the feeding line and loading shorted vias on the particular location of the microstrip line. the mutual coupling effect is one of the most challenging in designing mimo antennas. the authors minimized the mutual coupling for the designed mimo by inserting ground slots orthogonally, receiving a triple band resonance frequency: 2.11ghz-2.23ghz, 3.24ghz-3.32ghz, and 3.92ghz4.42ghz [13]. in [14-16], the authors produced insulation between the patch and the feeding element using aperture coupling and dgs for isolating the ground. to achieve high isolation mimo microstrip for wlan applications, aperturecoupling was used to isolate the t-shaped and orthogonal microstrip around the squared patch. in [17], four pair conformal microstrip mimo antennas of 35ghz have been investigated, resulting in increased bandwidth with reduced side lobes at the same time. authors in [18, 19] experimented with a 2×2 mimo microstrip antenna, suitable for new wireless communication demands. the investigated antenna was designed for 5g mobile handset. in [20], the authors designed a four-element mimo patch antenna for the 5g mobile handset that increases the signal-to-noise ratio and reduces bit error rate (ber). in [21], a high gain pentagonal microstrip antenna compatible for 5g applications, with a received gain of 6.17db was proposed. in this paper, an uwb antenna [7] has been modified to 2×1 and 2×2 mimo scenarios. the modified antennas are compared in terms of increased released gain without any additional power. the expected gain increased from 1 to 2.5db which shows the effectiveness of the proposed antennas. ii. mimo antenna design figures 1(b) and 2(b) show the front and back views of the investigated antenna respectively. this antenna was modified to the case of 2×1 structure by extending the width of the substrate to the double of its original value and adding p = 2mm to separate the ground of two antennas. the added patch antenna chased the same dimensions with inverting 180 degrees. the modified 2×2 microstrip antenna was designed by extending the dimension of the substrate width and length to the substrate width plus substrate length (ws + ls) as shown in corresponding author: majed omar dwairi engineering, technology & applied science research vol. 11, no. 5, 2021, 7531-7535 7532 www.etasr.com dwairi: increasing gain evaluation of 2×1 and 2×2 mimo microstrip antennas figures 1(c) and 2(c). all the investigated antenna materials are built on fr-4 with the substrate with dielectric tangent loss = tan δ= 0.02 and relative permittivity εr =4.4. the dimensions of the investigated antennas are listed in table i. the microstrip patch antenna in [7] was investigated to enhance the bandwidth by adding different slots on the ground. in our work, the chosen slot is the dinking cup-shaped. the bandwidth of the investigated 2×1 and 2×2 antennas was limited to the maximum frequency of 15ghz in order to increase the released gain. in our work, the cst-2019 simulation tool was used. fig. 1. front view of (a) the single antenna, (b) the mimo 2×1 antenna, (c) the mimo2×2 antenna. fig. 2. back view of (a) the single antenna, (b) the mimo 2×1 antenna, (c) the mimo2×2 antenna. iii. results and discussion all simulations were performed with the cst mw studio 2019 simulation tool. a. return loss results to investigate the return loss s11, the bandwidth was limited to the frequency band from 2 to 15ghz. the results of s11, s22 for the 2×1 antenna are shown in figure 3 and the results of s11, s22, s33, and s44 for the 2×2 antenna are presented in figure 4. it is evident that all the parameter values are within the investigated uwb. the received return loss for each of the antennas and the coupling of the other antennas are presented in figures 5-8. in these figures, it can be seen that the reflection parameters have many resonant frequencies, from -17 to -32db, while the coupling of the antenna reaches -50db. the received return loss s11 for the original, 2×1, and 2×2 antennas at the operating band of frequencies is shown in figure 9. figure 3 shows the return loss versus frequencies for the original, 2×1, and 2×2 antennas. it can be noted that the two investigated antennas are still operating within the uwb range. moreover, both of them start before the original antenna for return loss s11 < -10 db, and the upper frequency ends after the original antenna for return loss s11< -10 db. table i. investigated antenna parameters antenna elements dimensions [mm] patch rp=8.5, rr=5.36, tp=0.009 feed line lf = 16.82, wf = 2 substrate [mm] ls = 36, ws= 24 , ts= 1.6 ,p=2 partial ground plane [mm] lg = 15, wg = ws drinking cup shape ground slots dimensions [mm] 2 3 4 5 6 7 8 9 10 11 12 13 14 15 -25 -20 -15 -10 -5 0 r e tu rn l o s s [ d b ] frequency [ghz] s21 s12 s22 s11 fig. 3. reflection and transmssion coefficients for the 2×1 mimo antenna. table ii lists the comparison between the original and the two investigated antennas in terms of bandwidth and relative bandwidth. the relative bandwidth for the 2×1 and 2×2 antennas are more than the original antenna by 7.5% and 11.4%, respectively. the relative bandwidth is given by: ��� � 2 ���� �� � (1) engineering, technology & applied science research vol. 11, no. 5, 2021, 7531-7535 7533 www.etasr.com dwairi: increasing gain evaluation of 2×1 and 2×2 mimo microstrip antennas 2 3 4 5 6 7 8 9 10 11 12 13 14 15 -35 -30 -25 -20 -15 -10 -5 0 r e tu rn l o s s [ d b ] frequency [ghz] s44 s33 s22 s11 fig. 4. return loss for 2×2 mimo antenna. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 -50 -40 -30 -20 -10 0 r e tu rn l o s s [ d b ] frequency [ghz] s14 s13 s12 s11 fig. 5. the return loss for the first antenna and the coupling antenna for 2×2 mimo. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 -50 -40 -30 -20 -10 0 r e tu rn l o s s [ d b ] frequency [ghz] s24 s23 s22 s21 fig. 6. the return loss for the second antenna and the coupling antenna for 2×2 mimo. table ii. relative bandwidth antenna bandwidth [ghz] relative bandwidth % original 3.02-13.9 128.6 mimo 2×1 2.85-15 136.1 mimo 2×2 2.65-15 140 2 3 4 5 6 7 8 9 10 11 12 13 14 15 -50 -40 -30 -20 -10 0 r e tu rn l o s s [ d b ] frequency [ghz] s34 s33 s32 s31 fig. 7. the return loss for the third antenna and the coupling antenna for 2×2 mimo. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 -50 -40 -30 -20 -10 0 r e tu rn l o s s [ d b ] frequency [ghz] s44 s43 s42 s41 fig. 8. the return loss for the fourth antenna and the coupling antenna for 2×2 mimo. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 -35 -30 -25 -20 -15 -10 -5 0 s 1 1 [ d b ] frequency [ghz] mimo2by2 mimo2by1 single ant. fig. 9. return loss versus frequencies for the original, 2×1, and 2×2 antennas. b. voltage standing wave ratio (vswr) results figure 10 shows the results of the investigated antennas in terms of vswr versus the operating uwb frequencies. as shown, the whole operating bandwidth lies below vswr equal to 2, which is expected based on the return loss results. engineering, technology & applied science research vol. 11, no. 5, 2021, 7531-7535 7534 www.etasr.com dwairi: increasing gain evaluation of 2×1 and 2×2 mimo microstrip antennas fig. 10. vswr versus operating frequencies for the original, 2×1, and 2×2 antennas. c. released gain investigation the main purpose of this work was to evaluate the released gain for the original and the proposed 2×1 and 2×2 uwb microstrip antennas. figure 11 represents the released gain for the original antenna and the proposed mimo antennas. it can be seen from the figure that the maximum gain for a single antenna was 5.2db at 8.4ghz. for the 2×1 antenna, the maximum gain was 5.76db at 9ghz and for the 2×2 antenna it was 6.03db at 8.4ghz. table iii lists the gain for the three antennas at different frequencies. fig. 11. the released gain for the original, 2×1, and 2×2 antennas. table iii. comparison of the gain vs frequency of the original and the proposed antennas antenna gain (db) frequency (hz) original mimo 2×1 mimo 2×2 3.2 1.52 3.42 4.01 5 3.42 4.66 4.55 7.6 3.26 4.98 4.68 8.6 5 5.72 5.94 9.6 2.47 4.47 4.6 11 3.2 4.1 4,4 12 3.25 4.93 4.4 14.6 3.73 3.26 4.65 figure 12 gives a fast view of the comparison between the original and the two proposed mimo antennas with different gain. the proposed antennas' gain exceed 2.5db for some frequencies. fig. 12. comparison between the gain and the frequency for the original, 2×1, and 2×2 antennas. d. radiation pattern figure 13 shows the radiation pattern in the far-field for different selected resonance frequencies related to the original antenna and the proposed 2×2 antenna. it is evident that the radiation pattern for both antennas is omnidirectional for the lower resonant frequencies and directional for the higher ones. fig. 13. radiation pattern (far-field pattern) for the original antenna and the mimo 2×2 antenna. e. a comparison beween the proposed 2×2 mimo antenna and other reported works in order to evaluate the proposed antenna, it is worth to compare it with the results of other reported works. the comparisons were conducted in terms of antenna dimensions, number of antennas in mimo, operating frequencies, and peak gain. as shown in table iv, it is clear that some of the reported works have peak gain more than that of the proposed antenna, but, in general, our peak gain is quite satisfying and similar or bigger than that of the other reported gains. the importance of engineering, technology & applied science research vol. 11, no. 5, 2021, 7531-7535 7535 www.etasr.com dwairi: increasing gain evaluation of 2×1 and 2×2 mimo microstrip antennas the investigated antenna is that it operates in uwb frequencies which allows it to be implemented in different narrow bands. table iv. comparison of the proposed antennas and other reported works ref. dimensions [mm] mimo antenna operating frequency [ghz] peak gain for mimo antenna [db] [12] 20×24 2×1 42.0-49.0 >8 [14] 70×70 2×2 2-4.5 1.84-3.49 [18] 20×45 2×2 2.97-19.82 3.3-8.12 [19] 15×10.3 2×2 27-28.95 6.14 [20] 66×66 2×2 2.2-2.7 6.17 proposed 60×60 2×2 2.65-15 >6 iv. conclusion two uwb 2×2 and 2×1 microstrip patch antennas have been introduced in this paper. the released gain improvement, compared to the original one, for the two proposed mimo antennas varied from 1 to 2.5db without increasing the radiated power so, it is evident that the proposed mimo antennas' release gain is bigger than that of the used uwb antenna for the same operating frequencies, which 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[20] r. s. bhadade and s. p. mahajan, "high gain circularly polarized pentagonal microstrip for massive mimo base station," advanced electromagnetics, vol. 8, no. 3, pp. 83–91, sep. 2019, https://doi.org/ 10.7716/aem.v8i3.764. microsoft word etasr_v11_n6_pp7922-7926 engineering, technology & applied science research vol. 11, no. 6, 2021, 7922-7926 7922 www.etasr.com bakria et al.: chaos control and stabilization of a pid controlled buck converter using the … chaos control and stabilization of a pid controlled buck converter using the spotted hyena optimizer derradji bakria laadi laboratory department of sciences and technology ziane achour university of djelfa djelfa, algeria bakriaderradji@gmail.com messaouda azzouzi department of sciences and technology ziane achour university of djelfa djelfa, algeria dr.azzouzi@yahoo.fr djamal gozim department of sciences and technology ziane achour university of djelfa djelfa, algeria gozimansour@gmail.com abstract-the voltage controlled buck converter by constantfrequency pulse-width modulation in continuous conduction mode gives rise to a variety of nonlinear behaviors depending on the circuit parameters values, which complicate their analysis and control. in this paper, a description of the dc/dc buck converter and an overview of some of its chaotic dynamics is presented. a solution based on the optimized pid controller is suggested to eliminate the observed nonlinear phenomena and to enhance the dynamics of the converter. the parameters of the controller are optimized with the spotted hyena optimizer (sho) which uses the sum of the error between the reference voltage and the output voltage as well as the error between the values of the inductor current in every switch opening instant to determine the fitness of each solution. the simulations results in matlab proved the efficiency of the proposed solution. keywords-buck converter; nonlinear behavior; optimized pid controller; spotted hyena optimizer i. introduction dc-dc switched mode power converters have been widely used in many industrial and domestic applications such as hybrid cars, photovoltaic solar energy applications, cell phones chargers, etc. due to their high efficiency compared to the conventional linear regulators. to achieve the desired performance, the dc-dc converters can be either current controlled or voltage controlled. controllers based on linear theory can be used due to their easy and low implementation cost and the good performance around the operating point [1, 2]. however, they do not take into consideration the nonlinear phenomena that can occur in the converter in high frequencies or when one of the parameters of the converter changes [3-6]. recent research has proposed numerous solutions to address the above-mentioned problems. for instance, in [7], boost converter discrete-time models were used as an example to present an analytical solution that allows the prediction of nonlinear phenomena in digital current mode controlled power converters. meanwhile, in [8] the authors proposed a new method for the design of a stable and robust feedback control using the bifurcation analysis of the bilinear averaged model of boost converter and constrained stabilization principles. another approach for designing a controller that guarantees the system's global stability was introduced in [9]. the approach is based on the principles of the contraction theory of switched systems. nonetheless, the aforementioned works are based on analytical solutions and are a bit complex, and hard to implement in real plants. fuzzy logic-based controllers have been used to control chaos in many studies [10-18]. however, the use of fuzzy logic complicates the control system and requires considerable computation time and a large memory space, while the use of the controllers based on metaheuristic algorithms ensure, at least, the same performance as the fuzzy controllers with less complexity and implementation cost [1921]. nonetheless, most of previous works that use this type of controller are using the integral absolute error (iae) as an adaptation coefficient which is insufficient to estimate the fitness of each solution during the search. nonlinear phenomena elimination in power converters is still an open research subject, although good results have been achieved in the literature. in this paper, we propose a method of shifting the nonlinear phenomena and expand the stability range of the converters without the need of complicated analysis methods or additional circuits. using the powerful tools of matlab and the state-space model of the buck converter as an example, we designed a pid regulator that guarantees both global stability of the system and parameter disturbance rejection (load, input voltage, reference voltage). this design is based on the spotted hyena optimizer (sho) to determine the optimum gains of the controller using appropriate adaptation coefficients. corresponding author: derradji bakria engineering, technology & applied science research vol. 11, no. 6, 2021, 7922-7926 7923 www.etasr.com bakria et al.: chaos control and stabilization of a pid controlled buck converter using the … ii. system description a. buck converter a buck converter is a switch mode power supply (smps) that converts a dc voltage into a lower dc voltage through the commutation between different configurations [22, 23]. buck converters are generally controlled via voltage mode control. in this control mode, the error (ℇ(t)) between the output voltage (�����) and the reference voltage (��� ) is used to obtain the control signal ( ���� ). the latter is compared with the sawtooth signal to generate the pwm signal needed to derive the switch. the proposed study circuit is illustrated in figure 1. fig. 1. voltage controlled buck converter. the state of the system is expressed by the vector � ���,����with: x�� ��x� ��� (1) where the state matrices �� and �� for each configuration are: �� �� �� !"#$%"&%' ()(()*(+, � -" ��"%")�" .�"%")� -� .�"%")�/ 00 1 ,�� 2 34 �06 (2) �7 �� �� !"8%"&%' ()(()*(+, � -" ��"%")�" .�"%")� -� .�"%")�/ 00 1 ,�7 900: (3) �; 2 0 0 0 -�.�"%")�6 ,�; 9 0 0: (4) equation (5) represents the solution of (1): x���� <=>�?-?@��x���a����-���� ��-��� (5) the behavior of the system is described in each configuration using (5) where the final state of the system in the current configuration is considered as the initial state x���a� for the next one. b. spotted hyena optimizer sho imitates the natural hunting behavior of the spotted hyenas to find the optimum solution for an optimization problem [24, 25]. a pack of spotted hyenas follow an organized group hunting technique that can be divided into three main behaviors: 1) searching and encircling prey when the hunt begins, the pack of the spotted hyenas has no information about the position of the prey, therefore the current fittest search agent will decide the possible location of the prey in the search space. then, the rest of the pack will surround this position. 2) hunting the group hunting behavior of the spotted hyenas is based on a cluster of trusted friends that guide the members of the pack during the hunt. 3) attacking all search agents will be forced to move towards the position of the prey. more details on the mathematical model of the sho algorithm can be found in [24, 25]. c. sho application in this study, the sho algorithm was applied to determine the optimal parameters of a pid controller that would improve the dynamics of the converter. it is based on the minimization of the steady state error between the reference and the measured voltage, and the error between the successive values of the inductor current (measured in each switch opening instant) which are the peaks of the inductor current. equation (6) represents the proposed objective function. b��� c�b� � c7b7 (6) b� d∑ �f>-g�h i> j (7) b7 k |m���|?n?@ o� (8) where b� is the standard deviation of inductor current values measured in each switch opening instant, and b7 represents the integral absolute error (iae). fig. 2. closed loop system with sho. figure 2 presents the control block diagram of the system, where pq , p� and pr are respectively the proportional, the integral, and the derivative gains obtained by the sho. iii. results and discussion the mathematical model of the proposed circuit presented in figure 1 was simulated in matlab using (2)-(5). the converter and controller parameters are presented in table i. engineering, technology & applied science research vol. 11, no. 6, 2021, 7922-7926 7924 www.etasr.com bakria et al.: chaos control and stabilization of a pid controlled buck converter using the … table i. parameters of the proposed circuit converter �s 24 ω b 2500 tu vwx vy 0.0177 � z 0.02 t v� 2 ω 47 [b v. 0.2 ω v 22 ω optimizer c� 100 c7 1 iterations 100 search agents 20 controller pq 8 p� 800 pr 0.0001 a. original behavior in this study, the input voltage was chosen for study and observation while the other parameters had fixed values. as shown in figure 3, the converter dynamics clearly changed from period 1, to period 2, to period 4, and then to chaotic dynamic behavior. (a) (b) (c) (d) (e) fig. 3. (a) bifurcation diagram varying �s. (b) phase plan diagram �� �� and the inductor current ����� of period 1 when �s 24� . (c) phase plan diagram �� �� and the inductor current ����� of period 2 when �s 30�. (d) phase plan diagram �� �� and the inductor current ����� of period 4 when �s 34�. (e) phase plan diagram �� �� and the inductor current ����� of chaos when �s 40�. the input voltage �s was set to start from 20v, and then it increased gradually to 80v. the converter exhibits the stable period 1 behavior when �s _ 26� followed by the unstable period 2 behavior when 26 a �s _ 33.25�.�fterwards, the converter exhibits the unstable period 4 when 33.25 a �s _34.75� . finally, the converter shows irregular behavior (chaos) when �s e 34.75�. figures 3(b), 3(c), 3(d) and 3(e) show the phase plan diagram �� �� and the inductor current ����� of the aforementioned behaviors respectively. b. optimized behavior as shown in the convergence curve in figure 4, the sho algorithm finds the optimal gains of the controller after a few iterations. figure 5 is the voltage wave diagram obtained before and after the optimized pid controller was implemented, where the latter begins after 0.06s. it is clear from the wave form of the output voltage and the phase plan diagram �� �� that the converter returns to the stable period 1 behavior at 0.067s. fig. 4. convergence curve. fig. 5. v� after applying the optimized parameters. the bifurcation diagram in figure 6 proves that the optimized controller is able to extend the stability range of the converter up to 80v of �s. for more efficiency evaluation, the robustness of the control to the sudden changes in the parameters of the converter has been tested. the response of the output voltage �� to a sudden change in the input voltage, the reference voltage and load are presented in figure 7. engineering, technology & applied science research vol. 11, no. 6, 2021, 7922-7926 7925 www.etasr.com bakria et al.: chaos control and stabilization of a pid controlled buck converter using the … fig. 6. bifurcation diagram varying �s using the optimized pid. (a) (b) (c) fig. 7. system response to changes in: (a) input voltage, (b) reference voltage, (c) load. in the first 40ms, the system is subject to the parameters given in table i, as shown in figure 7(a). steady state is reached in 6ms with no overshoot. at t=40ms, the input voltage is increased to 30v, as it is remarked, and the controller was able to stabilize the system. at the same instant as before, we repeated the same scenario by inducing a sudden change in the reference voltage. at t=40ms, the reference voltage changed to 5v, and the controller adapts with the change and stabilizes the system to the new operating point. the results are shown in figure 7(b). the same scenario is repeated again to test the response of the system to the change in load. at t=40ms we changed the load to 35ω. from figure 7(c), it can be seen that the system remains stable and tracks the reference voltage. iv. conclusion in this paper, pi d controller gain tuning for a voltage controlled dc-dc buck converter is formulated as an optimization problem. this optimization is aimed to produce gains for the controller that would guarantee a robust closed loop. in addition, the objective function used to evaluate the fitness of the gains during the optimization is based on the sum of the error between the reference voltage and the output voltage as well as the error between the values of the inductor current in every switch opining instant. the sho was used to solve this problem. to evaluate the efficiency of the designed controller to shift nonlinear phenomena, the bifurcation diagram obtained using the optimized controller is compared to that presented in the literature. we also tested the capability of the controller to reject the disturbance in the parameters of the converter (load, input voltage, and reference voltage). the obtained results prove the efficiency of the proposed solution to shift the nonlinear phenomena and to expand the range of the desired period 1 behavior. in addition to its high efficiency, this solution offers a simple control circuit and low implementation cost without the need of additional circuits. references [1] a. g. perry, g. feng, y.-f. liu, and p. c. sen, "a design method for pi-like fuzzy logic controllers for dc–dc converter," ieee transactions on industrial electronics, vol. 54, no. 5, pp. 2688–2696, oct. 2007, https://doi.org/10.1109/tie.2007.899858. 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[25] g. dhiman and a. kaur, "spotted hyena optimizer for solving engineering design problems," in international conference on machine learning and data science, noida, india, dec. 2017, pp. 114–119, https://doi.org/10.1109/mlds.2017.5. microsoft word etasr_v12_n2_pp8311-8315 engineering, technology & applied science research vol. 12, no. 2, 2022, 8311-8315 8311 www.etasr.com truong: a ternary neural network with compressed quantized weight matrix for low power … a ternary neural network with compressed quantized weight matrix for low power embedded systems son ngoc truong faculty of electrical and electronics engineering ho chi minh city university of technology and education hcm city, vietnam sontn@hcmute.edu.vn received: 14 january 2022 | revised: 2 february 2022 | accepted: 11 february 2022 abstract—in this paper, we propose a method of transforming a real-valued matrix to a ternary matrix with controllable sparsity. the sparsity of quantized weight matrices can be controlled by adjusting the threshold during the training and quantizing process. a 3-layer ternary neural network was trained with the mnist dataset using the proposed adjustable dynamic threshold. the sparsity of the quantized weight matrices varied from 0.1 to 0.6 and the obtained recognition rate reduced from 91% to 88%. the sparse weight matrices were compressed by the compressed sparse row format to speed up the ternary neural network, which can be deployed on low-power embedded systems, such as the raspberry pi 3 board. the ternary neural network with the sparsity of quantized weight matrices of 0.1 is 4.24 times faster than the ternary neural network without compressing weight matrices. the ternary neural network is faster as the sparsity of quantized weight matrices increases. when the sparsity of the quantized weight matrices is as high as 0.6, the recognition rate degrades by 3%, however, the speed is 9.35 times the ternary neural network's without compressing quantized weight matrices. ternary neural network work with compressed sparse matrices is feasible for low-cost, low-power embedded systems. keywords—ternary neural network; deep learning; image recognition; quantized neural network. i. introduction deep neural networks (dnns) have achieved impressive success in the field of computer vision [1-4]. modelling the human brain using dnns requires a massive number of computation tasks including addition and multiplication. therefore, it is often challenging to implement dnns on lowpower edge devices such as mobile embedded systems [5]. edge computing has been attracted much attention recently because it has a lot of advantages in terms of cost and security. to run dnns on low-power edge devices, many optimized dnn architectures have been proposed. to increase the accuracy, dnns can be trained on a gpu and then the trained models are loaded to low-cost embedded systems, such as the raspberry pi board [6-8]. another method is to add the external accelerating neural computer stick (ncs) to the raspberry pi when deploying the dnns on it [9]. these deployments of dnns on the low-cost raspberry pi board are based on the full-precision weight, which dramatically consumes power and processing time. the memory usage and inference speed of such models have not been considered. an alternative technique to enhance the performance of dnns deployed on low-cost computers is to quantize the parameters to speed up the dnns' run-time and reduce memory consumption [10-17]. traditionally, 32-bit floating-point is used for numerical formats in dnns, which has a big impact on speed and memory usage. reducing the number of bits representing dnn parameters is considered for low-power edge devices. in particular, using numerical formats with lower precision than 32-bit floating point yields numerous benefits. 16-bit floating-point and 8-bit floating-point are commonly used for lightweight dnns without sacrificing accuracy [5]. substantial research efforts to use lower precision such as ternary and binary representation of parameters (synaptic weights) have been invested to make possible the implement of dnns on low-power edge devices [10-17]. a binary neural network constrains synaptic weights to the binary space of {-1,1}. in a binary neural network, the conventional 32-bit floating-point multipliers are replaced by the logical xnor operations to speed up running time and reduce memory consumption. however, the accuracy of binary neural networks is lower than full-precision neural networks because only one bit is used to represent the synaptic weight and the activation function. to increase the accuracy, ternary neural networks that constraint the synaptic weights to the ternary space {-1, 0, 1} have been proposed [14-16]. when training a ternary neural network, the weights are updated using real-valued variables and are then constrained to -1, 0, or +1 using the ternarization function [14-16]. the ternazization with dynamic threshold yields faster convergence in the training phase and higher accuracy in the inference phase [18]. however, the dynamic threshold, which is based on the mean and standard deviation of real-valued variables, produces an unpredicted number of -1, 0, and +1 bits in the synaptic weight matrices. in this work, we adjust the threshold during the quantization process to obtain sparse weight matrices with corresponding author: son ngoc truong engineering, technology & applied science research vol. 12, no. 2, 2022, 8311-8315 8312 www.etasr.com truong: a ternary neural network with compressed quantized weight matrix for low power … different sparsity (number of zero values), and measure the accuracy of the ternary neural network with different sparsity of quantized weight matrices. it turned out that we can increase the sparsity quantized weight matrices with small loss in accuracy. the sparse weight matrices are then compressed to reduce the size and speed up the matrix multiplication, which consumes most time in the forward pass of dnns. ii. ternary neural network with compressed weight matrices for low-power embedded systems figure 1 shows the concept of a ternary neural network in which the weights are constrained to -1, 0, and 1 [18, 19]. x1 xn are binary inputs and h1 hm are the neuron outputs of the hidden layer, which are also quantized to binary. y1 yk are the neuron outputs for k classes. in figure 1, wh is the inputto-hidden layer weight matrix and wo is the hidden-to-output layer weight matrix. here, the weight matrices are composed of -1, 0, and 1 representing the inhibitory, contactless, and excitatory synapses. fig. 1. the conceptual diagram of a ternary neural network, where the synaptic weights are -1, 0, or +1 representing inhibitory, contactless, and excitatory synapses. ternary neural network represents weights using fewer bits than a full-precision neural network. the ternary weights can be represented by lower bit signed integer values or complementary binary arrays [19]. the amount of required memory for the model’s parameters of ternary neural networks is substantially less than that of the full-precision neural networks. the ternary neural network is trained using the traditional gradient descent method that updates the weights in the direction of the maximum decrease of the loss function. the weights are updated with real values and transformed to the binary values using the following quantization function [18]: r threshold t threshold r threshold r threshold -1, if w <=-w w = 0, if -w <w <w +1, if w >=w      (1) where wthreshold is the threshold weight, wr is the real-valued weight, and wt is the ternary weight of -1, 0, or +1. by using (1), the ternary weights are obtained by comparing the realvalued weights with a positive threshold value. it can be observed that for every training iteration, the distributions of synaptic weights are different. therefore, a dynamic threshold is selected using the gaussian distribution proposed in our previous work [18]. the proposed method attempts to equalize the number of negative weights, zero weights, and positive weights. the quantization function with dynamic threshold is presented in (2) [18]: r t r r -1, if w <=µ-0.44σ w = 0, if µ-0.44σ<w <µ+0.44σ +1, if w >=µ+0.44σ      (2) where µ and σ are respectively the mean and standard deviation of real valued synaptic weights. according to the gaussian distribution, if the threshold is selected to be µ-0.44σ and µ+0.44σ, we obtain 33%, 34%, and 33% as the number of negative synaptic weights, zero-value synaptic weights, and positive synaptic weights respectively [18]. the percentages of negative, zero, and positive synaptic weights are maintained constantly every epoch of the training process because the threshold is adapted to the distribution of synaptic weights. increasing the number of zero values in quantized weight matrices leads to higher sparsity. the sparse matrix can be compressed to reduce the memory consumption and the matrix multiplication time. in this work, we control the percentage of zeros by modifying the quantization function as follows: r t r r -1, if w <=µ-λσ w = 0, if µ-λσ<w <µ+λσ +1, if w >=µ+λσ      (3) where λ is a variable that controls the threshold. in (3), if we increase λ, the number of zeros will increase. the higher the value of λ, the higher the sparseness of the quantized weight matrices. the sparse weight matrices can be compressed to reduce the memory usage and speed up the forward pass. the sparse weight matrices are compressed using the compressed sparse row (csr) format, which potentially leads to a substantial decrease in computational time and speeds-up the neural networks [20-23]. fig. 2. an example of csr. (a) sparse matrix with high sparsity and (b) csr representation of the sparse matrix x1 xi xn h1 h2 +1 -1 -1 hj hm y1 yk+1 +1 0 0 -1 +1 +1 -1 wh= +1 -1 +1 +1 0 +1 0 -1 0 +1 0 -1 0 -1 0 +1 0 -1 wo= 1000 0-100 10-10 -101-1(a) 0 3 4 6(b) 71 1 -1 -1 -1 row pointer column indices1 -10 2 3 1 2 3 3 data values00000 0 1 0 0 12 engineering, technology & applied science research vol. 12, no. 2, 2022, 8311-8315 8313 www.etasr.com truong: a ternary neural network with compressed quantized weight matrix for low power … figure 2 shows an example of the csr format when representing a sparse matrix. figure 2(a) shows a sparse matrix and its csr representation is shown in figure 2(b). csr is a popular and general-purpose sparse matrix representation. the matrix is stored using three arrays, which are the row pointer array, the column indices array, and the data values array [23]. the pointer array stores the pointers to the beginning of every row, the column indices stores the corresponding column indices, and the data value array stores the nonzero values, as illustrated in figure 2. the row pointer array begins with the value of 0, for the first row, the first, the 2 nd , and the 3 rd column of the sparse matrix have the values of respectively 1, 1, and -1, presented in the column indices array and data values in figure 2(b). the second row of the sparse matrix is represented by the second element in the row pointer array, which has the value of 3. the value of -1 in the second row is represented by the column indices of 1 and the data value of -1, as shown in figure 2(b). the sparse matrix in figure 2(a) can be compressed by using the arrays in figure 2(b). by doing this, the memory and time consumption for matrix multiplication are significantly reduced. during the forward-pass propagation, the neuron’s output is calculated by using matrix multiplication. assume that x = [x1, x2, ..., xn] is the 1×n input vector, wh is the m×n inputto-hidden layer weight matrix, h = [h1, h2, ..., hm] is the output vector of the hidden layer, the forward-pass propagation performs the below computational task: h = σ(xw� � ) (4) equation (4) consumes more power and time as we increase the size of the input vector and the weight matrix. if the weight matrix is sparse and represented by csr, we can replace the matrix multiplication in (4) with the sparse matrix-vector multiplication, which is faster than traditional matrix multiplication [20]. in this work, we represent weight matrices using sparse matrices and compress them with csr. the sparse matrix multiplication is performed by using the scientific python (scipy) library to save computational time [24]. iii. experimental results a three-layer ternary neural network was deployed on a lowpower raspberry pi board for the application of image recognition. the network was trained and tested on the mnist dataset for recognizing images of handwritten digits [25]. the input layer has 784 units corresponding to 784 image pixels. the inputs are binary. the hidden layer has 512 neurons and the output layer has 10 neurons for recognizing 10 digits. the network is trained using stochastic gradient descent with the momentum method. the real-valued weights are transformed to binary weights using the proposed adjustable dynamic threshold. by adjusting the variable in (3), we achieved the recognition rate with varied sparsity of quantized weight matrices, as presented in figure 3. in figure 3, the sparsity of the quantized weight matrix is varied from 0.1 to 0.6 by adjusting λ, as explained above. the recognition rate slightly degraded as the sparsity of the quantized weight matrix increased. when the sparsity of the quantized weight matrices was as small as 0.1, the ternary neural network produced a recognition rate of 91%. when the sparsity of the quantized weight matrix increased to 0.6, the recognition rate was reduced by 3%. the results indicated that increasing the sparsity of the quantized weight matrix led to a small decrease in accuracy. in this work, the training is performed on edge device, raspberry pi board, and the network is simply constituted of an input layer, a hidden layer, and an output layer with the weights quantized to -1, 0, and +1. the ternary weights are obtained by the proposed dynamic threshold quantization with controllable output sparsity. the accuracy of the ternary neural network is slightly lower than the fullprecision neural network, however it has the advantages of less memory usage and faster inference time. more importantly, the proposed ternary neural network is promising for low-cost edge devices. sparse quantized weight matrices were represented using the csr format, which significantly enhances the inference processing. with a fixed-size sparse quantized weight matrix, the higher sparsity results in the smaller size csr representation and faster csr matrix multiplication. fig. 3. recognition rate with varied sparsity of quantized weight matrices. fig. 4. inference time with varied sparsity of quantized weight matrices. figure 4 shows the inference time of the 3-layer ternary neural network deployed on a low-power embedded system, raspberry pi 3, for an input image with varied sparsity of quantized weight matrices. the inference time is the forward0.1 0.2 0.3 0.4 0.5 0.6 80 82 84 86 88 90 92 94 96 98 100 r e c o g n it io n r a te ( % ) sparsity recognition rate 0.1 0.2 0.3 0.4 0.5 0.6 0 5 10 15 20 25 30 in fe re n c e t im e ( m s ) sparsity inference time engineering, technology & applied science research vol. 12, no. 2, 2022, 8311-8315 8314 www.etasr.com truong: a ternary neural network with compressed quantized weight matrix for low power … pass propagation time required to propagate one image from the input layer to the output layer, which is also the time for predicting one image. for the uncompressed quantized weight matrices, the forward pass propagation takes 87.28ms, and such inference time does not depend on the sparsity of quantized weight matrices. figure 4 shows the inference time with varied sparsity of quantized weight matrices when the quantized weight matrices were compressed with csr. the matrix multiplication is performed using the scientific python library for the input vector and csr arrays. for a sparsity of 0.1, the forward-pass propagation takes 20.606ms, which 4.24 times faster than the ternary neural network with uncompressed quantized weight matrices. more interestingly, when the sparsity increases, the array size of csr representation for sparse matrices is more reduced, resulting in faster multiplication. for a sparsity of 0.6, the inference time of the compressed-weight-matrix ternary neural network is 9.335ms, which is 9.35 times faster than the original ternary neural network. quantizing the weight matrix is one of the techniques that are suitable for deploying dnns on low-cost computers. quantized neural networks can save the required memory for storing the model’s parameters and internal parameters, and implementing faster than full-precision neural networks for speech and image recognition, as presented in [19]. in this work, we propose a method to control the sparsity of quantized weight matrices during the training process and compress the weight matrices using csr representation. the high sparsity of quantized weight matrices sacrifices little accuracy, but speeds up the ternary neural network by a factor that reaches 9.35. the proposed idea is deployed on a simple 3-layer neural network for hand-written character recognition. utilizing high sparsity quantized weight matrices and csr makes the ternary neural network possible to implement on low-cost, low-power embedded systems such as general-purpose raspberry pi 3 board. iv. conclusion in this paper, we proposed a quantization function that can control the sparsity of quantized weight matrices for ternary neural networks. the sparsity of quantized weight matrices of the ternary network varied from 0.1 to 0.6 when the ternary neural network was trained with the mnist dataset. the obtained recognition rate varied from 91% to 88%. the sparse weight matrices were compressed using the csr format. the ternary neural network with compressed weight matrices was 4.24 times and 9.35 times faster than the original ternary neural network, when the sparsity of the quantized weight matrices was 0.1 and 0.6 respectively. ternary neural networks with compressed quantized weight matrices are suitable for implementation on low-power embedded systems for the application of image recognition. acknowledgment this research is supported by the ho chi minh city university of technology and education (hcmute), vietnam. references [1] k. l. masita, a. n. hasan, and t. shongwe, "deep learning in object detection: a review," in international conference on artificial intelligence, big data, computing and data communication systems, durban, south africa, aug. 2020, pp. 1–11, https://doi.org/10.1109/ 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[20] j. l. greathouse and m. daga, "efficient sparse matrix-vector multiplication on gpus using the csr storage format," in sc ’14: proceedings of the international conference for high performance computing, networking, storage and analysis, new orleans, la, usa, nov. 2014, pp. 769–780, https://doi.org/10.1109/sc.2014.68. [21] x. feng, h. jin, r. zheng, k. hu, j. zeng, and z. shao, "optimization of sparse matrix-vector multiplication with variant csr on gpus," in 17th international conference on parallel and distributed systems, tainan, taiwan, dec. 2011, pp. 165–172, https://doi.org/10.1109/ icpads.2011.91. [22] h. kabir, j. d. booth, and p. raghavan, "a multilevel compressed sparse row format for efficient sparse computations on multicore processors," in 21st international conference on high performance computing, goa, india, dec. 2014, pp. 1–10, https://doi.org/ 10.1109/hipc.2014.7116882. 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[25] l. deng, "the mnist database of handwritten digit images for machine learning research [best of the web]," ieee signal processing magazine, vol. 29, no. 6, pp. 141–142, aug. 2012, https://doi.org/ 10.1109/msp.2012.2211477. microsoft word etasr_v12_n2_pp8359-8365 engineering, technology & applied science research vol. 12, no. 2, 2022, 8359-8365 8359 www.etasr.com mydin: influence of sticky rice and jaggery sugar addition on lime mortar influence of sticky rice and jaggery sugar addition on lime mortar m. a. othuman mydin school of housing, building and planning universiti sains malaysia penang, malaysia azree@usm.my received: 1 february 2022 | revised: 17 february 2022 and 19 february 2022 | accepted: 21 february 2022 abstract-lime mortar has many advantages, yet its durability properties are the most remarkable, making it very useful in building preservation. traditional mortar for conservation and restoration work contains lime, which guarantees that the fresh mortar is applied to the underlying layer, increases its setting time, and gives adequate workability. this research aims to determine the durability performance, mechanical properties, and optimum percentage of organic admixtures to be used in lime mortar. five mix proportions and one control lime mortar mix were prepared. mixes with jaggery sugar and sticky rice with weight proportions of 3%, 6%, 9%, 12%, and 15% were compared with the control lime mortar mix. the results show that 9% sticky rice lime mortar achieved the highest performance in terms of mechanical and durability properties. keywords-lime mortar; conservation; jaggery sugar; sticky rice; water absorption i. introduction lime mortar is being replaced by modern materials in the renovation of old buildings, since the development of cement in the 19th century [1], because of the problems encountered with the use of lime mortar, including prolonged setting and hardening periods, especially at high relative humidity, low internal cohesion, poor mechanical properties, and high porosity [2]. such properties make lime mortar susceptible to damage by salt contamination after being saturated with water [3]. however, issues also arise when modern materials and techniques are adopted in the renovation and reconstruction of existing ancient buildings. moisture and salt gradually accumulate behind the impervious finishes and cannot evaporate, thereby accelerating timber decay, which allows the growth of beetles [4]. consequently, high humidity causes the plastering to blister, makes the layers of paint fail and the joists rot, and, in time, the building may collapse. when lime is adopted as plaster in a building, the problems of condensation and blistering can be reduced. a building can withstand humid conditions by evaporating its excess moisture [5]. nowadays, the utilization of lime mortar for the restoration of historic buildings is being revitalized because of the detrimental characteristics of portland cement, such as its high thermal expansion coefficient and its brittleness [6]. the small pores of portland cement that produce its low porosity can delay the movement of water within the masonry and cause deterioration to occur due to the presence of water in the cement matrix, while the salts are evaporated into the adjacent bricks [7]. besides, lime is a standard universal binding medium for work including plastering and is used with mortars for building houses with historic masonry. one of the main reasons for its wide-ranging functions is that it allows buildings to breathe [8]. hence, this study focuses on the potential utilization of sticky rice and jaggery sugar as additives in lime-based mortar. ii. material constituents, mix proportions, and tests a. materials and tools the materials involved in this research were lime putty, glutinous rice flour, jaggery sugar, and fine sand which were obtained from local suppliers. in addition, some tools were required in order to prepare, measure, and determine the mechanical properties and the performance of the samples. for instance, the researchers used an electronic balance, a mortar mixer, a mold (figure 1), a vibrating table, an oven, a gotech universal testing machine, a desiccator, a flow table, and a rice cooker. b. mix design a mortar mix design is defined as the procedure of identifying the appropriate proportions of lime: sand: water for the lime mortar to achieve effective levels of mechanical strength and good performance of the structures. the lime mortar mix design included some steps, calculations, and laboratory testing to identify the correct proportions of the mix. a group using the design mix of lime: sand: water with a ratio of 1: 2.5: 0.45, and another 10 groups of the design mix with the addition of additives in 3% increments of weight fraction, were prepared. the mix proportions and mortar designation ratios are illustrated in table i. c. experimental setup 1) workability test the flow table test consisted of a table with a diameter of 300mm and a mould manufactured in the shape of a conical frustum. firstly, the conical frustum was filled with mortar in corresponding author: m. a. othuman mydin engineering, technology & applied science research vol. 12, no. 2, 2022, 8359-8365 8360 www.etasr.com mydin: influence of sticky rice and jaggery sugar addition on lime mortar two layers, and each layer was compacted by 10 blows with a tamping rod. the excess mortar was removed from the top of the conical frustum and flattened. after 15s, the conical frustum was removed slowly from the mortar with a steady upward pull, before immediately being lifted and dropped on the table by turning the wheel at a specified height and repeating this 15 times in 15s. lastly, the final diameter of the spread sample was measured using vernier callipers. fig. 1. a mortar mixer was used to prepare the lime mortar. table i. mix proportions and mortar designation ratios mortar group weight fraction (%) ratio lime: sand: water: admixture lime putty fine sand water sticky rice jaggery sugar control 0 1 2.5 0.45 sticky rice lime mortar 3 1 2.5 0.45 0.03 6 1 2.5 0.45 0.06 9 1 2.5 0.45 0.09 12 1 2.5 0.45 0.12 15 1 2.5 0.45 0.15 jaggery sugar lime mortar 3 1 2.5 0.45 0.03 6 1 2.5 0.45 0.06 9 1 2.5 0.45 0.09 12 1 2.5 0.45 0.12 15 1 2.5 0.45 0.15 2) water absorption test the water absorption test was conducted in compliance with bs en 1881-122 [9]. nine cylinder specimens with dimensions ø75mm×100mm high were used. the samples were removed from the curing tank 3 days before the test and were oven-dried at 105±5°c for 72±2h. then, the samples were taken from the oven and were allowed to cool to room temperature. immediately after cooling, the samples were weighed under standard conditions. then, the samples were immersed in water for 30±0.5min. then, the samples were removed from the bucket and the water on the surface was removed using a dry cloth. 3) porosity test the porosity test was conducted in compliance with bs en 993-1 [10], as shown in figure 2. cylinders measuring ø45mm×50mm were withdrawn from the curing tank 3 days in advance. then, the samples were dried in the oven at a temperature of 105±5°c for at least 72±2h to remove all the moisture and the dry samples were weighed after the heat had radiated. the dry samples were immersed in a vacuum watersaturated machine and were covered with the lid by slipping off the lid carefully to maintain airtight conditions in the desiccator. then, the vacuum pump was turned on and the samples were soaked in water for 48±2h. afterwards, a dry cloth was used to wipe the liquid from the surface of the samples before the saturated samples were weighed with an electronic balance. the readings were recorded, and the difference was measured. fig. 2. porosity test was carried out with the vacuum saturation method. 4) compression test the compression test was carried out in accordance with bs en 1881-116 [11]. three specimen cubes measuring 150mm×150mm×150mm were obtained before the test. one day before the test, the specimens were taken from the curing tank and were dried for 24h in the oven. once the specimens had cooled to room temperature, the test was conducted with the gotech universal testing machine. figure 3 illustrates the setup of the axial compression test. fig. 3. compression test setup. 5) flexural test according to bs en 1521 [12], the flexural test was conducted on 40mm×40mm×160mm lime mortar prisms, as shown in figure 4. the specimens were removed from the curing tank and oven-dried for 24h before the test. the specimens were then placed on two supporting rollers, with a third roller situated above the specimen and midway between the supporting rollers. next, the samples were slowly moved down the roller to ensure that the top surface of the prism was in contact with the loading roller. the load was applied to the prism at a constant rate until failure. engineering, technology & applied science research vol. 12, no. 2, 2022, 8359-8365 8361 www.etasr.com mydin: influence of sticky rice and jaggery sugar addition on lime mortar fig. 4. flexural test setup. iii. results and discussion a. workability figure 5 illustrates the results of the fresh lime mortar workability with different percentages of sticky rice and jaggery sugar. the workability of the control group (lime mortar without sticky rice or jaggery sugar) was 16.1mm, which was the lowest workability of all the fresh lime mortars. the consistency increased to 16.5mm, 16.9mm, and 17.6mm with the addition of 3%, 6%, and 9% sticky rice respectively. however, the workability of the mortar mix decreased to 16.7mm and 16.3mm when 12% and 15% of sticky rice were added. moreover, the addition of 3% and 6% of jaggery sugar increased the workability to 16.8mm and 17.9mm respectively, while the workability of the mortar mix started to decrease when 9%, 12%, and 15% of the jaggery sugar were added. when the concentration of sticky rice reached 9%, the lime and sand particles slid against each other easily. fig. 5. workability of lime mortar with different percentages of sticky rice and jaggery sugar. sticky rice functions as a viscosity modifier that improves the consistency of lime mortar. on the other hand, when the concentration reached 12%, the workability decreased due to the high adhesive strength of the sticky rice which caused the lime and sand particles to bind together easily, thus preventing the particles from sliding against each other [13]. sticky rice acted as a lubricant, making the mortar easier to spread. apart from that, the addition of jaggery sugar extended the setting time of the lime mortar due to the formation of a thin layer on the mortar particles and the delay in the process of hydration. the calcium ions improved the solubility and prevented the formation of calcium hydroxide. this improved the setting properties of the lime mortar. b. water absorption figure 6 shows the result of the water absorption of lime mortar with different percentages of sticky rice and jaggery sugar. the control group achieved the highest water absorption, which was 14.4%. the water absorption of the mortar mixture dropped drastically to 13.7%, 13.1%, and 12.5% with the addition of 3%, 6%, and 9% sticky rice solution respectively. however, it increased to 13.3% and 13.6% when 12% and 15% of sticky rice solution were added. on the other hand, the water absorption was 14.1% when 3% of jaggery sugar were added, and this decreased dramatically to 13.2% when 6% of jaggery sugar were added. however, the water absorption of the mortar mixture increased again with the addition of 9%, 12%, and 15% jaggery sugar. fig. 6. water absorption of lime mortar with different percentages of sticky rice and jaggery sugar. the control group of lime mortar had the highest water absorption due to the presence of capillaries that enabled the water to access the mortar easily [14]. the presence of sticky rice produced a more compact mortar structure. the interaction between the sticky rice polysaccharides and calcium carbonate was also one of the factors that caused the lowest absorption of lime mortar. during the curing of the sticky rice lime mortar, the amylopectin controlled the growth of calcium carbonate and produced a compact structure with less calcium carbonate, which reduced the penetration of water and increased durability [15]. moreover, the addition of jaggery sugar provided a thin layer of coverage on the mortar surface, which led to reduced contact between the pores and restricted the transport of water. the addition of sticky rice and jaggery sugar into lime mortar lessened both fresh and hardened bulk density values under both dry and humid curing [16]. as stated above, sticky rice can be considered an aqua gel. when evenly integrated into fresh mortar mixes, it becomes encased within the mortar. as mortar dried, the aqua gel shrank, and void spaces were developed. moisture from within the aqua gel particles slowly diffused to the surface of the mortar and evaporated, further reducing the water absorption capacity. c. porosity the porosity of lime mortar with different percentages of sticky rice and jaggery sugar is shown in figure 7. based on the data collected, the porosity of the control group (58.9%) engineering, technology & applied science research vol. 12, no. 2, 2022, 8359-8365 8362 www.etasr.com mydin: influence of sticky rice and jaggery sugar addition on lime mortar was the highest among the lime mortar mixtures. the porosity of the lime mortar mix dropped to 56.7%, 56.1%, and 55.4% when 3%, 6%, and 9% of sticky rice solution were added into the lime mortar respectively. when the concentration of sticky rice reached 12% and 15%, the porosity increased again to 55.9% and 56.6%. when the jaggery sugar solution was added at 3%, the porosity was 57.3%. the porosity dropped to 56.8% after the addition of 6% jaggery sugar and rose to 57.1%, 57.7%, and 58.2% for 9%, 12%, and 15% of jaggery sugar addition. the control group had the highest porosity since the addition of the admixture influenced the microstructure of the lime mortar. changing the pore size distribution increased the volume of air voids and led to the highest porosity among the lime mortar mixtures. according to [17], reduced porosity with the increase in weight fraction of sticky rice (up to an optimum of 9%) and jaggery sugar (up to an optimum of 6%) could indicate diminished pore size, volume, and capillary interconnections, which should be due to the continuous formation of hydration products, taking up more space in mortar pores, making mortar denser and more compact with a reduction in porosity. when the mortar is first mixed, it is a dense slurry, with the sand and sticky rice/jaggery sugar uniformly distributed and surrounded by water. primary porosity is developed through the movement of water due to either absorption into the surrounding masonry unit or evaporation to the air. authors in [18] stated that these pores are highly interconnected and fluid transport through these pores is by capillary transport. the total porosity is further influenced by the carbonation of ca(oh)2 to caco3. accommodation of the volume change is taken up by a reduction of total porosity but no significant shift in pore size distribution with the addition of jaggery sugar/sticky rice. fig. 7. the porosity of lime mortar with different percentages of sticky rice and jaggery sugar. d. compressive strength the results of the compressive strength of lime mortar after 7, 28, and 56 days with different percentages of sticky rice and jaggery sugar are illustrated in figure 8. compared with the control group of lime mortar, the compressive strength of the mortar mixes surged when 3%, 6%, and 9% of sticky rice solution were added and declined when 12% and 15% of sticky rice were added. moreover, the addition of 3% and 6% of jaggery sugar enhanced the compressive strength, which dropped steadily for 9%, 12%, and 15% addition. the 9% sticky rice lime mortar showed the highest compressive strength as the sticky rice was able to accelerate the process of setting and hardening, which improved the bonding ability. furthermore, the addition of sticky rice helped to refine the size of portlandite and calcite crystals to produce a more compact microstructure [19]. however, it was found that 6% of jaggery sugar had the second-highest compressive strength. according to [20], this is because the existence of sucrose in the jaggery sugar improved the initial and final setting times, but it did not affect the compressive strength. authors in [21] found that sticky rice could significantly improve mechanical strengths and compatibility of air lime mortars and control the growth of caco3 crystals. authors in [22] reported that the addition of 5% of sticky rice in air lime mortars could accelerate mortar setting and hardening, increase compressive and bonding strength, while, at the same time slightly reducing mortar density and water resistance. fig. 8. compressive strength of lime mortar with different percentages of sticky rice and jaggery sugar on days 7, 28 and 56. e. flexural strength figure 9 presents the flexural strength of lime mortar with different percentages of sticky rice and jaggery sugar after 7, 28, and 56 days. the flexural strength rose when 3%, 6%, and 9% of sticky rice were added to the lime mortar, but this fell with the addition of 12% and 15% sticky rice. therefore, the sticky rice in a proportion of more than 6% limited the improvement in the lime mortar strength. the addition of jaggery sugar in proportions of 3% and 6% increased the flexural strength of the mortar. however, the flexural strength fell when 9%, 12%, and 15% of jaggery sugar were added. authors in [23] reported that the mechanical strengths of limesticky rice mortar can be considerably boosted by cyclic wetting–drying and dilute sulfate acid actions, causing more porous matrices and coarser particles. authors in [25] concluded that sticky rice inclusion could stimulate noticeable conglomeration in mortar, leading to inhomogeneous strain field and creating micro-cracks during wetting–drying cycles. the results in [25] showed that biomineralization may occur in lime-sticky rice mortars, where sticky rice functioned as a template to control the growth of caco3 crystals. the addition of an appropriate amount of sticky rice can improve the strength of lime mortar due to its water retention, which is engineering, technology & applied science research vol. 12, no. 2, 2022, 8359-8365 8363 www.etasr.com mydin: influence of sticky rice and jaggery sugar addition on lime mortar beneficial to the carbonation process of the lime, increasing mechanical strength. however, excessive organic matter will act as a retarder and limit the carbonation of lime mortar [26]. therefore, the addition of sticky rice exceeding 9% reduced performance in terms of flexural strength. meanwhile, the addition of jaggery sugar resulted in the reduced performance of lime mortar in terms of flexural strength compared to the addition of sticky rice. fig. 9. flexural strength of lime mortar with different percentages of sticky rice and jaggery sugar on days 7, 28 and 56. f. porosity-water absorption relationship figure 10 shows the water absorption versus porosity using different percentages of additives with lime mortar. the relationship between the water absorption and porosity increased exponentially with a correlation coefficient (r2) of 0.8234. fig. 10. relationship between water absorption and porosity of the lime mortar. the results show that the control group of lime mortar had the highest porosity-water absorption relationship. normally, lime mortar mixtures with higher water absorption and porosity are less durable. the porosity influences the water absorption of lime mortar. as the porosity decreases, the pore sizes decrease, leading to a reduction in water absorption. the presence of additives makes the structure of lime mortar denser and harder. in this research, different percentages of sticky rice and jaggery sugar were used to improve the durability properties of lime mortar. the sticky rice addition of 9% was considered the best solution to be used with regard to the improvement of the durability performance of the mortar. the sticky rice influenced the microstructure of the lime mortar causing the pore sizes to reduce and thereby decrease the volume of air voids. this led to the lowest porosity levels among the lime mortar mixtures. hence, the water absorption reduced as the water could flow through the porous gaps, and the water had been removed from the mortar through the capillary forces. g. compressive-flexural strength relationship figures 11-13 show the compressive strength against the flexural strength of lime mortar mix on days 7, 28, and 56 respectively. these figures show that the relationship between the compressive strength and flexural strength increases with a very high correlation coefficient (r2) of 0.9627 (day-7), 0.9509 (day-28), and 0.9917 (day-56). fig. 11. compressive-flexural strengths relationship on day 7. fig. 12. compressive-flexural strengths relationship on day 28. compressive and flexural strength are important as they reveal the behavior of each mixture. the results show that the highest compressive-flexural strength relationship was found in 9% sticky rice lime mortar. the hardened properties of lime mortar enable the delivery of compressive and flexural stress within the units of the structure. in this study, it was discovered engineering, technology & applied science research vol. 12, no. 2, 2022, 8359-8365 8364 www.etasr.com mydin: influence of sticky rice and jaggery sugar addition on lime mortar that the addition of admixtures, especially sticky rice, enabled the mortar to withstand a higher amount of movement, under compressive or flexural loads. different percentages (3%, 6%, 9%, 12%, and 15%) of sticky rice and jaggery sugar were applied to improve the mechanical properties of lime mortar. however, 9% sticky rice was considered as the best additive in improving the durability and mechanical properties. this happens because the sticky rice can accelerate the process of setting and hardening, and results in good adhesion properties between the sand and lime. fig. 13. compressive-flexural strengths relationship on day 56. h. discussion replacing or repairing masonry buildings is usually necessary for the restoration of historical constructions, but the selection of a proper lime-based mortar is often challenging. an improper selection can lead to failure of the restoration work, and perhaps even further damage. therefore, thorough understanding of the original lime-based mortar technology and the production of suitable replacement materials is important. many kinds of materials have been used over the years in masonry mortars, and the technology has gradually evolved from the single-component mortar of ancient times to hybrid versions containing several ingredients. this study was performed to systematically examine the potential use of sticky rice and jaggery sugar in lime mortar to help determine the proper courses of action in restoring ancient buildings. lime mortars with varying sticky rice and jaggery sugar content were prepared and tested. the durability and mechanical properties of lime mortar were found to be significantly improved by the introduction of sticky rice and jaggery sugar, suggesting that sticky rice-lime mortar is a suitable material for repairing mortar in ancient masonry. moreover, the amylopectin in the lime mortar was found to act as an inhibitor. the growth of the calcium carbonate crystals is controlled by its presence, and compact structure results, which may explain the enhanced performance of this organic-inorganic composite compared to single-component lime mortar. iv. conclusion overall, 9% of sticky rice is determined to be the best proportion of additive to use in lime mortar. more specifically, the presence of sticky rice can quicken the setting and hardening times and improve the bonding between the sand and lime particles. the inclusion of 9% sticky rice and 6% jaggery sugar in lime mortar also resulted in lower porosity. the presence of polysaccharides in sticky rice produced a compact microstructure of the lime mortar. the water retention properties of the sticky rice were beneficial, in terms of carbonation process, in improving the flexural strength of the lime mortar. to summarize, 9% sticky rice and 6% jaggery sugar were the optimum percentages of additives to be used in lime mortar. the sticky rice was discovered to be a better additive than jaggery sugar. the sticky rice not only improved the setting and hardening times but also increased the compressive and flexural strengths. the test results show that the inclusion of 9% of sticky rice and 6% jaggery sugar in lime mortar has more stable durability properties, greater mechanical strength, and is more compatible, which makes it a suitable restoration mortar for ancient masonry buildings. the possible practical application of the mortar with sticky rice and jaggery sugar upon the results of the performed study includes foundation settlement and plant growth, and cracks between building blocks. sticky rice and jaggery sugar lime mortar can be used as joint mortar. references [1] r. hanley and s. pavia, "a study of the workability of natural hydraulic lime mortars and its influence on strength," materials and structures, vol. 41, no. 2, pp. 373–381, nov. 2008, https://doi.org/10.1617/s11527007-9250-0. 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[22] p. zhao, m. d. jackson, y. zhang, g. li, p. j. m. monteiro, and l. yang, "material characteristics of ancient chinese lime binder and experimental reproductions with organic admixtures," construction and building materials, vol. 84, pp. 477–488, mar. 2015, https://doi.org/ 10.1016/j.conbuildmat.2015.03.065. [23] q. zhang, b. li, q. zeng, j. deng, j. wang, and d. yan, "erosion of aerial lime and sticky rice mortars by cyclic wetting–drying and dilute sulfate acid actions," advances in cement research, vol. 32, no. 8, pp. 343–357, dec. 2020, https://doi.org/10.1680/jadcr.18.00103. [24] r. yang, k. li, l. wang, m. bornert, z. zhang, and t. hu, "a microexperimental insight into the mechanical behavior of sticky rice slurrylime mortar subject to wetting-drying cycles," journal of materials science, vol. 51, no. 18, pp. 8422–8433, jun. 2016, https://doi.org/ 10.1007/s10853-016-0099-x. [25] y. zeng, b. zhang, and x. liang, "a case study and mechanism investigation of typical mortars used on ancient architecture in china," thermochimica acta, vol. 473, no. 1, pp. 1–6, apr. 2008, https://doi.org/ 10.1016/j.tca.2008.03.019. [26] m. a. o. mydin, "preliminary studies on the development of limebased mortar with added egg white," international journal of technology, vol. 8, no. 5, pp. 800–810, oct. 2017, https://doi.org/ 10.14716/ijtech.v8i5.442. authors profile md azree othuman mydin attained his ph.d. degree in civil engineering from the university of manchester, uk in 2010. this followed a b.sc (building technology) and a m.sc. (building technology) that were earned in 2004 & 2005 respectively from universiti sains malaysia. before joining universiti sains malaysia as a lecturer, he worked with the penang development corporation consultancy (pdcc) as a civil and structural engineer. his specializations lie in the areas of lightweight foamed concrete technology, concrete structure assessment, building construction, building pathology, and industrialized building systems. up to date, he has secured 4 frgs grants, 5 rui grants, 3 short-term grants, and 1 incentive grant. the total amount of grants is approximately rm1.08million. in terms of publication, many of his papers have been published in international journals. since 2010, he has published more than 200 research papers indexed in isi and scopus. moreover, he has presented more than 120 papers at local and international conferences. through publications, he has been able to generate a wider network and frequently discusses topics with fellow researchers from other countries. his current h-index is 15 and he has achieved 505 citations out of 905 total since 2010. microsoft word etasr_v12_n3_pp8772-8776 engineering, technology & applied science research vol. 12, no. 3, 2022, 8772-8776 8772 www.etasr.com ray et al.: implementation of a hybrid technique for the predictive control of the residential heating … implementation of a hybrid technique for the predictive control of the residential heating ventilation and air conditioning systems mitali ray school of electrical engineering kiit deemed to be university bhubaneswar, odisha, india mitaliray87@gmail.com padarbinda samal school of electrical engineering kiit deemed to be university bhubaneswar, odisha, india padarbindasamal87@gmail.com chinmoy kumar panigrahi school of electrical engineering kiit deemed to be university bhubaneswar, odisha, india panigrahichinmoy@gmail.com received: 29 april 2022 | accepted: 15 may 2022 abstract-since daily energy needs are increasing, it is imperative to find ways to save energy, such as improving the energy consumption of buildings. heating ventilating and airconditioning (hvac) loads account for the majority of a building's energy use. the accurate estimation of energy consumption and the examination of various ways to improve the energy efficiency of buildings are very important. this paper presents an analysis of hvac loads in a residential building by examining three neural networks (nns): feed-forward (ff), cascaded forward backpropagation (cfbp), and elman backpropagation (ebp) networks, based on mean absolute error (mae), mean square error (mse), and mean relative error (mre). furthermore, these networks were combined in hybrid nns to obtain more optimized results. these results were also compared with other approaches and showed better prediction performance. keywords-hvac loads; neural networks; energy management; hybrid networks i. introduction the building sector, which includes both residential and commercial structures, is responsible for up to 36% of global energy use, according to the energy information administration (eia) [1]. since 2015, worldwide energy consumption in the residential sector and transportation has climbed at a pace of 1.1% per year according to the international energy agency. according to eia, global energy consumption in the commercial sector is predicted to grow at a pace of 1.2% per year from 2015 to 2040. the rise in energy consumption due to buildings is predicted to be bigger in developing than in developed countries. to reduce energy consumption in buildings, a nation's main objective in terms of the policy is to make them more energy-efficient. factors that influence energy efficiency management in a building include occupancy levels, heating and cooling loads, the climatic zone, and the exterior envelope of the building. the prediction and study of energy consumption in buildings are carried out using energy simulation tools, which are frequently used in the construction industry and assist in the design of buildings and efficient management of their energy use [2]. these tools have limitations such as long computational times and the requirement of programming expertise [3]. there are also applications using machine learning tools that are comparatively faster and more convenient [3]. once a model is properly trained, obtaining answers by modifying a few parameters of the building's design becomes quite simple. the use of support vector machine (svm) to predict the energy consumption of buildings in a tropical environment was examined in [4]. an svm was used to forecast the cooling demand of a building on an hourly basis in [5]. several regression models were created and validated to anticipate the heating demand of residential buildings in [3]. the use of artificial neural networks (anns) has been explored in different diversified areas [6-8]. in residential buildings, anns are used to forecast heating load (hl) and cooling load (cl) based on various characteristics of the buildings [6, 10-12]. although it is a substantial characteristic, the glazing area does not appear to be connected to hl or cl, which is an important limitation of [6]. this paper presents a comparative analysis and hybridization of nns for forecasting the heating and cooling loads of an hvac system. mae, mse, and mre were taken as performance indicators, considering eight input variables. corresponding author: mitali ray engineering, technology & applied science research vol. 12, no. 3, 2022, 8772-8776 8773 www.etasr.com ray et al.: implementation of a hybrid technique for the predictive control of the residential heating … ii. neural networks an ann is a series of algorithms that aspires to establish a correlation among a set of data through a certain procedure that replicates the human brain operation. an ann refers to a system of neurons, either organic or artificial. anns are used as problem-solving methods, with the capability of developing solutions to extremely difficult problems and uncovering hidden patterns in large datasets. this results in a collection of approaches that can be employed to provide a fast and costeffective solution to a complex real-world challenge. moreover, anns have self-learning abilities to produce the output, which is not limited to the inputs provided to them. anns were used in [8, 9] to predict thermal loads and in [10] to analyze the energy consumption of a building. in this work, the implementation of hybrid anns was performed by considering the sequential combination of any two anns among feedforward (ff), cascaded forward backpropagation (cfbp), and elman back-propagation (ebp) to estimate the thermal loads of a residential building. furthermore, a comparative analysis was conducted with other approaches to validate the results. a. feedforward network ff anns are used to learn the mapping between the independent (inputs) and dependent (outputs) variables and predict the outputs. ff networks consist of a series of connected layers. the first layer is connected to the network input. each subsequent layer is connected to the layer above it via the previous layer's connection. the output of the network is produced by the final layer, as shown in figure 1. the network is simpler than other recurrent networks and can be used efficiently in pattern recognition. the network does not have feedback, so the output of each layer does not affect the same layer. in this study, a 3-hidden layer network with 20–20– 20 neurons was considered with tansig as the transfer function and purelin as the output layer activation function. fig. 1. feedforward network. b. cascaded forward backpropagation network the cfbp network model includes a connection from the input and every previous layer to the following layers, as shown in figure 2. this network can accommodate the nonlinear relationship between input and output without eliminating their linear relationship. a 3-hidden layer network with 20–20–20 neurons was considered, where tansig was considered as the transfer and the output layer activation function, as it provided better results than other combinations. c. elman backpropagation network the ebp network is a two-layer backpropagation network where a recurrent connection exists from the output of the hidden layer to its input with a tap delay. the recurrent connection allows the network to both detect and generate time-varying patterns, as shown in figure 3. in this study, a 3hidden layer network with 20–20–20 neurons per layer was considered, where tansig is considered as both the transfer and the output layer activation function, as it provided better results than other combinations. fig. 2. cascaded forward backpropagation network. fig. 3. elman backpropagation network. iii. proposed model and input-output dataset a. the proposed model performance analysis was based on the prediction of heating and cooling loads in a residential building using hybrid neural networks. initially, three different anns were trained, tested, and validated by considering 10-fold cross-validation. then, a sequential combination of anns was performed to model hybrid networks. the output generated by an input from the input training pattern was then compared with the targeted output, aiming to minimize the error function, as shown in (1): ������ � � ∑ ||� � � || � �� (1) where u is the number of sets of the training ordered pairs, which depends on the number of samples being taken, bi is the network output, ti is the target output, and e is the error function. b. input-output database the proposed method was experimentally validated using a dataset collected from the uci machine learning repository [6, 11]. the ecotect software was used to simulate 12 distinct building shapes and generate 768 possible building shapes. relative compactness, surface area, wall area, roof area, overall height, orientation, glazing area, and glazing area distribution (x1,…,x8) were the input variables of the dataset, and heating and cooling loads (y1 and y2) were the output variables. more information on the simulation experiments can be found in [6]. the output variables have a substantial correlation with the first five input variables in the examined dataset. as the volumes of the buildings are assumed to be constant, the values of x1 (relative compactness) and x2 (surface area) are inversely proportional. the input variables x4 (roof area) and x5 (height) are highly correlated. the correlation coefficient (-0.937) shows that these two variables are roughly inversely proportional. engineering, technology & applied science research vol. 12, no. 3, 2022, 8772-8776 8774 www.etasr.com ray et al.: implementation of a hybrid technique for the predictive control of the residential heating … iv. performance analysis of the ann model the trainlm algorithm was used for training. tansig was considered as the output layer activation function for the cfbp and the ebp networks, as it provided smaller errors for these two networks. similarly, purelin was considered as the output layer activation function for the ff network. the comparative analysis was obtained by changing the performance goal and learning rate in a step-by-step manner. the weight initialization with arbitrary values and bias updates was performed. the accuracy of these models was measured by the mae, mse, and mre performance indicators: ��� � ∑ |�����| � ��� � (2) ��� � ∑ |�����| �� ��� � (3) ��� � ∑ |�����| � ��� ��� (4) where yi is the predicted value, xi is the true value, and n is the number of samples. performance analysis was conducted on these three networks. three hidden layers were used in all networks, with 20 neurons in each layer. the trainlm function updates weights and biases as per levenberg-marquardt optimization and is the fastest backpropagation algorithm. therefore, the trainlm was used as a common training algorithm for all networks. the performance goal was set to 10e-5, and the learning rate was taken as 0.01 for all three networks. analysis was conducted based on mae, mse, and mre performance evaluators. as purelin is a linear transfer function that gave an accurate result in the ff network, it was used as an output layer activation function in ff. similarly, as tansig is a hyperbolic tangent sigmoid transfer function, and is preferable to be used where speed is important, it was used as the output layer activation function for both cfbp and ebp. the behaviors of all three networks are shown in table i. then among all cfbp networks with 20-20-20-2 neurons, the tansig-tansig-tansig-tansig transfer function was chosen as the optimal network with fewer errors. table i. performance by varying neural networks ann heating load cooling load mae mse mre mae mse mre ff 0.1248 0.033 0.0075 0.1686 0.0611 0.0087 cfbp 0.1023 0.0326 0.0058 0.1406 0.0473 0.0072 ebp 0.2023 0.0819 0.0106 0.2471 0.1193 0.0117 v. hybrid model performance calculation a hybrid ann is a valuable learning tool where numerous anns are collaboratively used to solve a problem and improve the predicted output of a sequential data set. mae, mse, and mre were used as the performance indicators for each model in order to calculate the best hybrid configuration. performance indicators were used to select the best algorithm. in this study, a hybrid intelligent model was designed by combining two of the proposed models, which were efficient for network analysis. two of the mentioned algorithms were considered for each combination. as in the performance analysis of the anns, the best results were obtained with 20-20-20-2 neurons, tansig-tansig-tansig-purelin transfer function, trainlm training algorithm, 10e-7 performance goal, and learning rate of 0.01 for the ff network. the best result for the cfbp network was achieved by using 20-20-20-2 neurons, tansig-tansig-tansigtansig transfer function, trainlm training algorithm, 10e-7 performance goal, and learning rate of 0.01. similarly, the best result for the ebp network was achieved using 20-20-20-2 neurons, tansig-tansig-tansig-tansig transfer function, trainlm training algorithm, 10e-7 performance goal, and learning rate of 0.01. the block diagram of the hybrid network is shown in figure 4, and the flow chart of the hybridization is shown in figure 5. fig. 4. block diagram of the hybrid network. fig. 5. flowchart of the hybridization of the neural network. six different combinations were considered as hybrid networks: ff and cfbp, ff and ebp, ebp and ff, ebp and cfbp, cfbp and ff, and cfbp and ebp. engineering, technology & applied science research vol. 12, no. 3, 2022, 8772-8776 8775 www.etasr.com ray et al.: implementation of a hybrid technique for the predictive control of the residential heating … vi. results and analysis the performance analysis of these hybrid networks is shown in table ii. it can be observed that the best results were achieved in the ff and cfbp hybrid network, with 0.0466 and 0.0797 for mae in hl and cl, 0.0071 and 0.0166 for mse in hl and cl, and 0.0031 and 0.0039 mre in hl and cl respectively. in this network, the computational time was also very smaller (28s). its error plot is shown in figure 6 and the variation between target and actual values is shown in figure 7. the variation between the target and the actual output of the ff and cfbp hybrid network for 768 sample numbers was very low. this signifies achievements of least error by this hybrid network compared to the others. table ii. performance analysis of hybrid models hybrid neural network heating load cooling load time mae mse mre mae mse mre (s) ff and cfbp 0.0466 0.0071 0.0031 0.0797 0.0166 0.0039 28 ff and ebp 0.1097 0.0281 0.0067 0.0775 0.0153 0.0040 100 ebp and ff 0.1002 0.0287 0.0051 0.0932 0.0229 0.0038 172 ebp and cfbp 0.0834 0.0227 0.0046 0.0757 0.0184 0.0035 186 cfbp and ff 0.0202 0.0009 0.0010 0.1368 0.0277 0.0048 146 cfbp and ebp 0.1052 0.0244 0.0076 0.0663 0.0102 0.0032 196 (a) (b) fig. 6. error plots for: (a) heating load, (b) cooling load. (a) (b) fig. 7. target vs actual outputs: (a) heating load, (b) cooling load. vii. comparison with other methods the proposed method was also compared with other methods. different performance evaluators like mae, mse, and mre were considered for error analysis. in [6], iteratively reweighted least squares (irls) and random forests (rf) were used for the prediction of heating and cooling loads. it was found that mae, mse, and mre for the hl using irls were 2.14, 9.87, 10.09, and using rf were 0.51, 1.03, and 9.41 respectively, while the mae, mse, and mre for cl using irls were 2.21, 11.46, 2.18, and using rf were 1.42, 6.59, 4.62. svr and mlp were implemented with the same data in [14] to predict the heating and cooling loads, using mae and mse as performance evaluators. the results were found to be 0.778, 0.7838 in svr and 0.4118, 0.2335 in mlp for hl, and 1.4762, 3.024 in svr and 2.0973, 6.896 in mlp for cl. in [15], the backpropagation method achieved mae, mse, and mre of 0.1000, 0.0335, and 0.0053 for hl, and 0.1254, 0.763, and 0.0062 for cl. the error analysis is shown in table iii. it can be observed that the proposed hybrid ff and cfbp method improved mae, mse, and mre for both heating and cooling loads, compared to the above-mentioned methods. table iii. comparison with other methods proposed methods mae mse mre hl cl hl cl hl cl irls [6] 2.14 2.21 9.87 11.46 10.09 2.18 rf [6] 0.51 1.42 1.03 6.59 9.41 4.62 svr [14] 0.778 1.4762 0.7838 3.024 mlp [14] 0.4118 2.0973 0.2335 6.896 backpropagation [15] 0.1000 0.1254 0.0335 0.763 0.0053 0.0062 ff and cfbp 0.0466 0.0797 0.0071 0.0166 0.0031 0.0039 0 100 200 300 400 500 600 700 800 sample number -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 e rr o r fo r f ee d f o rw ar d a n d c as ca d e d fe e d f o rw ar d b ac k p ro p ag at io n sample number actual output target output 0 100 200 300 400 500 600 700 800 5 10 15 20 25 30 35 40 45 h e at in g lo ad in kw (f e ed fo rw ar d a n d c a s c ad ed fo rw ar d b a c k p ro p a g a ti o n ) sample number actual output target output 0 100 200 300 400 500 600 700 800 10 15 20 25 30 35 40 45 50 c oo lin g lo ad in kw (f ee d fo rw ar d a n d c as c ad ed fo rw ar d b ac k p ro p ag at io n) engineering, technology & applied science research vol. 12, no. 3, 2022, 8772-8776 8776 www.etasr.com ray et al.: implementation of a hybrid technique for the predictive control of the residential heating … viii. conclusion in this study, a hybrid ann was proposed to estimate the consumption of hvac loads in a residential building for an eight-input dataset with 768 building samples. the hybrid model of feed-forward and cascaded forward back propagation (ff and cfbp) gave mean absolute errors of 0.0466 and 0.0797, mean square errors of 0.0071 and 0.0166, mean relative errors of 0.0031 and 0.0039 for heating and cooling loads respectively. the results showed that the suggested hybrid neural network had the lowest statistical errors and the best prediction performance. the difficulty of collecting actual building energy datasets is a drawback in this field of building efficiency enhancement. the use of real-world data by considering weather parameters like temperature, global solar radiation, etc, can give better results in future studies. references [1] "iea – international energy agency," iea. https://www.iea.org. 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more sabotaging attacks occur including phishing attacks which jeopardize users' security and critical information like their passwords and credentials. several solutions have been proposed for existing dangers. one of which is the use of one-time passwords. this issue has remained as a main challenge and requires more extensive research. in this research, we have focused on one-time password combinations and we also have proposed solutions based on behavioral patterns which lead to significant optimizations while tending the simplicity for users. efficiency of the proposed method has been measured through defining scenarios, modeling and simulations based on a prevention rate index. in addition, complexity coefficient of the proposed method showing the probability of unpredictability of passwords for attackers has been calculated. ultimately, a descriptive comparison has shown that the proposed method is superior to some of the existing methods. keywords-phishing; one-time password; cyber attacks i. introduction electronic banking continuously requires new methods aimed at improvement of security, with respect to the extensiveness of bank, commercial and personal transactions and that most of them are conducted on the internet. one proposed method for this purpose is the use of one-time passwords (otps). otps are considered as suitable alternatives for secondary passwords and are proposed for securing the access of users to various electronic systems. in otps, encryption technics are used for production of one-time random passwords. using one-time passwords for functions including authentication, not only improves the security of transactions, but also can be used for prevention of attacks aimed at stealing users' information. these types of attacks are known as phishing attacks. these have various forms and constantly impose a threat on users' security in virtual spaces. phishing attacks are considered as a serious threat for classified information. usually, an attacker sends out fake messages to fool people in order to steal their personal information. unaware users who follow the instructions of these messages are directed to fake pages and then are asked to enter their credentials. any sabotaging attack using a fake webpage for persuasion of users towards entering their security details is described as a phishing attack. according to observations in [1], more than 70 percent of phishing activities are aimed at stealing usernames and passwords of users' accounts. by making use of these information and user accounts, an attacker can even have access to more valuable information. otps can protect authentication mechanisms against different types of attacks. authors in [1] proposed a method based on production of a unique random password at each login time. this method employs timestamps and number sequences for calculations. a test version of a two-factor authentication has been developed for cellphones based on this method and it has been practically used for one year. authors in [2] proposed a method for prevention of phishing attacks. this method uses keywords to validate the originality of webpages. by this means direction of users' towards fake pages is prevented. authors in [3] proposed a handy authentication system which eliminates the need for entering password during the process of authentication. authors in [4] investigated different phishing methods along with methods of prevention. they proposed a method that makes use of a combination of otps and voice recognition for the prevention of phishing attacks. authors in [5] proposed a design that makes use of development and integration of two famous protocols, pjp and amp with otps. the pjp protocol uses passwords' security key. on the other hand, amp protocol is an optimized account management system which considers user’s previous activities in order to decide whether to lock the account or not. in addition, the proposed method uses the md5 standard hash technic before transfer and saving in order to protect passwords. ultimately, the security has been analyzed through making use of several simulated public attacks aiming for passwords. authors in [6] proposed a method for prevention of phishing threats in websites. this method benefits from a visual encryption by making use of images and otp. in this method, the main image is divided into two blocks and also a one-time password is generated as well. in [7], author elaborated on cons of typed passwords and proposed a method that makes use of picture combinations for passwords. this method can be a suitable alternative for typed passwords. sms based authentication methods send a one-time password to the cellphone of users. afterwards, users may engineering, technology & applied science research vol. 7, no. 6, 2017, 2328-2333 2329 www.etasr.com nasiri et al.: using combined one-time password for prevention of phishing attacks enter the received code in order to verify their login. although that this method is well capable of preventing unauthorized use of passwords, still an attacker may guess a set of passwords which lead to either a successful attack or blockage of user's account. authors in [8] proposed a system that enables the service device to validate the correctness of the one-time password. in this method, the password will only be sent to the system if its correctness is validated. this method not only reduces the risk of successful attacks, but also warns the system so that required defensive mechanisms are applied in time. as smart phones have become more and more prevalent, different otp generators have also been developed as smartphone applications. however there is no guaranty for classification of generated passwords. authors in [9] proposed a solution which not only has a suitable flexibility, but also makes use of hardware based security as well. by this means, smartphones are transformed into a suitable apparatus for generation of onetime passwords. in fact the former is done without taking any effects from the device's security glitches or imposing any impacts on the operating system. although otps are widely used for prevention of phishing and replay attacks, supplying the security of otps is also a main challenge. in [10], authors proposed a model for optimization of security of otps. this method uses elliptic curve and iris biometrics encryptions. among the advantages of this method, it can be referred to shorted key lengths compared to rsa and dynamic production of private keys when necessary. in this research, authors have investigated different phishing methods along with methods of using otps. the aforementioned methods are combined in order to obtain a general solution and ultimately, a method for preventing phishing attacks and promoting users’ information confidentiality, will be proposed. ii. proposed method a. general description benefitting from the idea of otps, this paper presents a new method that combines text and image encryption methods with innovative solutions based on behavioral parameters. this method increases the complexity of the generated otp and makes it hard for attackers to reveal them through their, usually automatically, tools. in other words, a set of behaviors would be specified for the user and the user should enter the received otp with respect to the determined behavioral pattern. on the user's side, the aforementioned pattern is transformed into a code and later, it is compared with the determined behavioral pattern by the service provider side. after validation, the rest of the combined otp will be evaluated. the proposed method is a combined solution that includes image passwords, typed text messages and behavioral patterns. in the proposed method, a profile is created during registering phase. at this point, in addition to entering required information including name, surname, personal information, a unique username and the password; the user must also select a category of images which would be used for the generation of the visual password. typed password would also be generated based on the user's account information. nonetheless, the user must also determine a special behavioral pattern for entering the password. specific typed, visual and behavioral pattern passwords are generated during each phase of the process of authentication based on the unique username of each individual user. the visual password would be shown to the user on the login page. the typed password will be sent to the user along with an instruction determining the behavioral pattern. afterwards, a time window would appear on the service provider side which is aimed for controlling the time length of validity of the generated otp. the user observes the visual password on the login page and receives the sms code including the typed password and the determined behavioral pattern. he/she should enter his/her password along with typed, visual and behavioral pattern passwords received. on the user's side, the entire activities of the user including his/her behavioral patterns would be saved and encrypted. these behavioral patterns would be used for the generation of the otp sent towards the service provider. the validation sector on the service provider side will first investigate the time window and then, will extract the behavioral pattern and decrypt it. in case of a match, the system will proceed towards investigating the visual and typed passwords. if the values match with predetermined values, the entered username and password would be authenticated. the aforementioned procedure means that user authentication mechanism is executed in a multilevel process. different aspects of the proposed method would be explained with more details in the following. b. registration and creation of user profile in this phase, the user must enter the following information which would shape his/her user account. this user account or profile will be used during the generation phases of visual, typed and behavioral pattern (bp) passwords.  name  surname  father's name  id number  national code  birth place  birth date  residence place  occupation  academic degree  username  password  a category of images  behavioral pattern for entering the information c. generation of visual password the proposed method includes ten categories of different images for the visual password generation. each of these engineering, technology & applied science research vol. 7, no. 6, 2017, 2328-2333 2330 www.etasr.com nasiri et al.: using combined one-time password for prevention of phishing attacks categories includes 100 images. the user must select one of these categories while signing up. at this phase, the selected category will be used for the generation of visual passwords. based on the visual password generation method, a 5·2 matrix of existing images would be created with one image in each slot of the matrix. the user observes the matrix and selects the image related to his/her selected category. by doing so a number would be generated according to the position of selected image. this number would also be a part of the generated otp. by making use of this mechanism, the possibility of guessing the otp by human attackers will be reduced up to ten times. since category image detection is very difficult for a program, then even automatic applications do not have a better chance compared to human attackers. d. generation of typed password the process of typed password generation is also based on the existing information on the user's profile. for this purpose, a text field existing on the user's profile will be sent to the user along with a four digit random number. by observing the specific field, the user makes sure that the sent otp is original. afterwards, he/she will select the title of the field number sent to him/her and then enter the four digit random number. afterwards, a two digit number is generated based on the position of the selected field on the matrix. this number is used in generation of the otp in conjunction with a random number. the reason for using a two digit number is that here it is possible to have repeated fields. for example national codes and id numbers of users may be similar in some cases. therefore the user must be able to select two matrix slots and a number will be generated based on the priority of his/her choices. for example, if based on image 2, the user first selects his/her id number and then his/her national code; the generated number will be 45. in case the user has done the reverse, then the generated number would be 54. for cases with no repetitions, digit 0 is selected as the last digit of the code. for example if a user's name was hassan and the same field was sent to him, by selecting the name option, number of 10 would be used as a part of otp. e. generation of behavioral pattern password a highly important point taken note of in the previous section is that user's behavioral pattern can be used as a highly suitable criterion for the generation of one-time passwords. in previous example it was observed that priority of conduction of activities by a user can result in generation of various different codes. inspired from this, we are introducing the idea of the use of behavioral patterns. in other words, the text message sent to the user includes an order for his/her activities. for example the user would be told to first enter the random number, then the typed password and finally the visual password. by this simple scenario and without needing to add a mechanism that is observable by the attacker, we have been able to reduce the possibility of guessing the combined password up to 6 times. in fact if the number of behaviors used in this type of encryption were equal to n, then the possibility of guessing the otp will be reduced for n times. combination of this method with previously mentioned methods results in a significant deal of reduction in possibility of guessing the otp. this in turn shows the superior efficiency of the proposed method. f. sending an sms to the user since mobile phones are commonly used throughout the world, using the mechanism of sending a text message is considered as a suitable solution for sending the user the visual code and the instructions related to behavioral pattern. this issue significantly improves the security of proposed method. g. activation of time window since the time length of validity of otps must be limited, therefore for each time of sending a user an otp, a time window is activated on the service provider side. in case the process of authentication does not complete during this time window, the sent otp will lose its validity and expire. in this case, the user must resend a request for receiving the otp. the point worth mentioning in this phase is that the time length specified for the timer should be logical based on existing and used mechanisms. based on the following scenario, we have specified a time length of 3 minutes for the time window. h. validation the process of validation starts when the user receives the otp. after decryption, the validity must be determined in shortest time possible in order to reduce the server side's computation overhead. in this research, we propose the following order: 1. time window 2. behavioral pattern 3. visual password 4. typed password in case the process of authentication fails in any of the above mentioned phases, the whole process will terminate and the user will receive a message of authentication failure. i. saving and encrypting users' activities since the proposed method makes use of users' behavioral patterns, therefore it requires solutions for saving the activities of the user in order to be able to determine their and conduct the behavioral encryption. for this purpose, it is recommended to make use of two separate services on the client side. the first service saves the activities of the user and the second service encrypts them. by doing so, the principles of service oriented architecture are considered for as well. j. receiving typed and visual passwords another service used on the client side will receive the visual and typed passwords and prepares them for production of the otp. k. generating and sending the otp in this phase, a unique number will be produced as a part of otp based on behavioral patterns, typed passwords and visual passwords. the otp will be sent to the service provider for engineering, technology & applied science research vol. 7, no. 6, 2017, 2328-2333 2331 www.etasr.com nasiri et al.: using combined one-time password for prevention of phishing attacks validation. since the used password includes no information regarding user's profile, therefore it will have a high security against phishing attacks. iii. simulation results in order to evaluate the proposed method, it was simulated in matlab and its performance has been studied under different scenarios. additionally, rates of prevention of different attacks have been investigated. afterwards, complexity coefficient of the proposed method has been analytically measured. finally, a descriptive comparison has been made between the proposed method and previous ones. a. simulation the required data for evaluation have been collected through the modeling of different types of attacks. two possible outcomes are considered for each attack. either the proposed method is able to resist the attack or not. in order to make this simulation as simple as possible, we assumed that the phishing attack was partially successful and the attacker has been able to hypothesize a primary combination for the otp. these hypotheses are used for evaluation as special data. each of the scenarios mentioned in table i requires consideration for different sets of conditions in order to be realized. we have simulated this by assuming that the attacker has obtained access to parts of information existing on the user's profile. we have ultimately designed a suitable set of data for investigation of results of attacks of interest. we have created a hypothetical user profile for our simulations (table ii). table i. scenarios used for simulation of phishing attacks title details scenario 1 the attacker directs the user towards a fake website and tries to steal his/her password. in this case the user must notice the fakeness of the webpage and act reluctantly scenario 2 the attacker fakes the user's identity and obtains access to the website and tries to guess the password. in this case the website must identify the attacker based on behavioral patterns scenario 3 the attacker saves the previous otps sent to the user and tries to complete its knowledge about the user's profile. in this case the complexity coefficient of the otp must be able to challenge the activities of the attacker table ii. profile of the hypothetic user title value name 'ali' surname 'reazaie' father's name 'mohammad' id number '8' national code '3040488254' birth date '11/1370/11' birth place 'karaj' residence 'tehran' occupation 'student' academic degree 'm.a .' username 'ali123' password '789ali425r' image category 'flower' behavioral pattern 'pic-text-num' b. test results figure 1 shows the prevention rate of the proposed method based on performed experiments in aforementioned scenarios. the rate of prevention of phishing has been yielded as 100% for the proposed method. this shows the superior efficiency and functionality of the proposed method in terms of prevention of phishing attacks. fig. 1. comparison of prevention rates of the proposed method c. analysis of complexity coefficient complexity coefficient of a password shows the power of that password in prevention of being guessed by attackers. in cases in which an attacker has obtained partial of full access to user's information, still an otp must show a suitable preventive nature in this regard. while keeping the simplicity of our method, we have elaborated on its complexity at different levels. 1) behavior at this level, using behavioral patterns plays a significant role. we have defined behavioral patterns as a series of activities by users. based on these activities, we have considered different orders for entering different parts of the otp. at this level, the coefficient of complexity increases according to number of different parts of an otp and based on the factorial relationship of number of parts of otp. in other words, if there are n numbers of parts of otp, then the complexity coefficient will be relative to the factorial of this value. complexity_factor  n! (1) 2) comprehension at this level we have made use of human comprehension of images. a human user can easily distinguish different image categories. however this would be a very hard task for an automated program. therefore by making use of this method, a new level of complexity is introduced. this issue also holds for identification of categories related to text information. therefore if k numbers of image categories are used, and each category includes m numbers of pictures, then the complexity coefficient of otp will increase relative to the following relation: complexity_factor  mk (2) the upper content also holds for text categories as well. in case there are t numbers of text categories, the complexity engineering, technology & applied science research vol. 7, no. 6, 2017, 2328-2333 2332 www.etasr.com nasiri et al.: using combined one-time password for prevention of phishing attacks coefficient of the proposed otp increases relatively to the following relation. complexity_factor  c × t2 (3) in (3), c is a constant value and is relative to attacker's identification of text categories. 3) diversity in this level, the number of digits produced for the otp is highly important. if the number of used digits is equal to d digits, then the complexity coefficient will increase relative to the following relationship. complexity_factor  10d (4) 4) overall therefore, the overall complexity of the proposed method can be estimated easily: complexity_factor = n! × mk × c × t2 × 10d (5) putting used values in the variables we have: complexity_factor = 3! × 10010 × c × 102 × 104 => complexity_factor = 6c1026 (6) even assuming that the attacker has complete knowledge regarding text categories of the used language, still the obtained value is large and significant. this is definitely a suitable security for the used password. with respect to simplicity and user-friendly state of the passwords created, this issue is considered highly important. d. descriptive comparison table iii represents a descriptive comparison between the proposed method and other combined or simple methods. it has been assumed that simple methods merely use numbers for generation of otps and that combined methods do not use bps. table iii. descriptive comparison of proposed method criterion simple method combined method proposed method complexity less average more prevention rate less average more simplicity more less less attractiveness less more more e. final evaluation according to the results, the proposed method is evidently highly efficient against phishing attacks and imposes several improvements on complexity coefficient of the generated otp along with preventing different types of phishing attacks. the proposed method has high overall efficiency and has introduced several optimizations. based on simulation results, on analytic investigation of complexity coefficients and on descriptive comparisons it can be expected that the present research will become a starting point for future researches regarding growth and development of otps aimed at prevention of phishing attacks. main breakthrough of this project is paying attention to users' behavioral patterns. separation of coding of the otp in calculations on the server and client sides is another advantage of the proposed method. in fact even if attacks such as eavesdropping are present, the security of the protocol may still be maintained. figure 2 shows this issue based on a series of sample generated codes in proposed method. fig. 2. a sample of generated codes in proposed method iv. conclusions and discussion in this research we proposed a combined method for prevention of phishing attacks based on visual, text and behavioral patterns which is also relative to the number of selected factors for behavioral patterns and therefore can reduce significantly the rate of phishing attacks success. in addition, the proposed solution is based on selection of images and texts and input of numerical texts with special patterns that may seem attractive to users. in this article, we have proposed the idea of using users' behavioral patterns. by behavioral patterns it is referred to a series of activities performed by a user which can be considered as a special and specific profile for the user and based on it, different passwords could be generated. this idea can open a new door in the domain of encryption. experiments, analysis and comparisons have shown a suitable efficiency for our proposed method and therefore this method can be selected as a suitable solution for different internet based activities including internet banking and e-commerce. the research domains related to security against phishing attacks require a more extensive and comprehensive data set for the evaluation of new methods. therefore, our first recommendation is the conduction of more researches for production of a suitable data set with data belonging to different cyber-attack types. this recommendation can also play a significant role in standardization of future researches. since attackers' behavioral pattern plays a significant role in this domain, it is required to conduct specific activities in terms of creating a behavioral profile for attackers. as a future research suggestion, attention could be paid to even more complicated behavioral patterns. if it was possible to hide the engineering, technology & applied science research vol. 7, no. 6, 2017, 2328-2333 2333 www.etasr.com nasiri et al.: using combined one-time password for prevention of phishing attacks behavioral pattern within the otp, increased security could be yielded in the otp combination. even though the proposed method has shown a good performance in experimental conditions, it is still required to be tested in real applications. so, as one last suggestion, attention should be paid to the point that academic studies must have a suitable relation with the related industry. the feedbacks and ideas of real users should be available and used for descriptive evaluations by the academic community. doing so can have a crucial role in promotion of academic studies and optimization of the relation between the former and related industries. references [1] c. huang, s. ma, k. chen, “using one-time passwords to prevent password phishing attacks”, journal of network and computer applications, vol. 34, no. 4, pp. 1292-1301, 2011 [2] m. mishra, a. j. gaurav, a. jain, “preventive anti-phishing technique using code word”, international journal of computer science and information technologies, vol. 3, no. 3, pp. 4248-4250, 2012 [3] y. huang, z. huang, h. zhao, x. lai, “a new one-time password method”, ieri procedia,vol. 4, pp. 32-37, 2013 [4] k. marimuthu, d. ganesh gopal, h. mehta, a. r. p. boominathan, “a novel way of integrating voice recognition and one time passwords to prevent password phishing attacks”, international journal of distributed and parallel systems, vol. 5, no. 4, pp. 11-20, 2014 [5] a. onashoga, a. sodiya, a. afolorunso, “one-time server-specific password authentication scheme”, journal of computing and information technology, vol. 20, no. 2, pp. 85-93, 2012 [6] p. p. n. g. phani kumar, r. john mathew, “an advanced anti phishing approach based on two-tier validation”, international journal of research in computer and communication technology, vol. 3, no. 9, pp. 1015-1017, 2014 [7] b. k. kushwaha, “an approach for user authentication one time password (numeric and graphical) scheme”, journal of global research in computer science, vol. 3, no. 11, pp. 54-57, 2012 [8] j. hwang, y. hsu, g. liao, “an sms-based one-time-password scheme with client-side validation”, journal of digital information management, vol. 13, no. 2, pp. 69-75, 2015 [9] h. sun, k. sun, y. wang, j. jing, “trust otp: transforming smartphones into secure one-time password tokens”, 22nd acm sigsac conference on computer and communications security, pp. 976-988, 2015 [10] d. mahto, d. k. yadav, “security improvement of one-time password using crypto-biometric model”, 3rd international conference on advanced computing, networking and informatics, vol. 2, pp. 347-353, india, 2015 microsoft word etasr_v12_n6_pp9715-9719 engineering, technology & applied science research vol. 6, no. 12, 2022, 9715-9719 9715 www.etasr.com gatcha et al.: an anisotropic diffusion adaptive filter for image denoising and restoration applied on … an anisotropic diffusion adaptive filter for image denoising and restoration applied on satellite remote sensing images a case study messaouda gatcha aaid laboratory faculty of exact sciences and computers ziane achour university djelfa, algeria messaoudamath2017@gmail.com farid messelmi dmm laboratory faculty of exact sciences and computers ziane achour university djelfa, algeria foudimath@yahoo.fr slami saadi aaid laboratory faculty of exact sciences and computers ziane achour university djelfa, algeria saadisdz@gmail.com received: 22 september 2022 | revised: 1 october 2022 | accepted: 2 october 2022 abstract-this paper proposes an operating approach based on the anisotropic diffusion method to restore and denoise satellite remote sensing images (srsis). the contents of the approach are the motion by mean curvature to detect the noise direction for each degraded pixel and preserve the original edges of the image, and the gradient in the gaussian kernel which restores the degraded pixel locally, assuring the estimation of its original value and saving the contrast of the image. the algorithm, concluded by our proposed system, treats noised srsis regardless of noise type, so better restoration is achieved. experiments of the proposed system and of other approaches were conducted in matlab in order to demonstrate the efficiency of the proposed approach and its performance was confirmed through evaluation with psnr and ssim. keywords-image restoration; anisotropic diffusion; regularization; satellite remote sensing images i. introduction satellite remote sensing images (srsis) are known for their fussy response or tendency to be corrupted due to multiple aspects of noise that might occur, such as time, feedbacks, accuracy, lighting, landforms, surface reflections, and reflection angles. mathematically, image denoising is an illposed problem due to the fact that the added noise has divergent characteristics. partial differential equations (pde) in the anisotropic diffusion method provide a safe executive solution for image restoration, as a consequence of the multidirectional gradient through the noised (corrupted) pixel neighborhoods, and assist an easy transpass from a system to another when we change the noise type. the earlier works in the image denoising field, start with the marr-hildreth edge detector [1] by finding the zerocrossing of the second derivative d2 of intensity. author in [2] considers the image structure using the divergence of the image, focusing on blurred ones. perona-malik equation [3] has been applied many times. in [4], motion by mean curvature appears in the degenerate diffusion term, which diffuses the image in the orthogonal direction to its gradient and does not diffuse at all in the direction of the gradient. more recently, authors in [5], proposed an improved empirical mode decomposition and adaptive center-weighted average (emd-acwa) denoising scheme by estimating the noise energies of all intrinsic mode functions, using an energy model, called noise-only model. it turns out that the empirical mode decomposition acts on fractional gaussian noise as a dyadic filter bank. authors in [6] worked on speckle noise elimination. the denoising research was applied to color images in [7]. there are many studies regarding srsis [8] using different techniques, such as as curvelet transform [9], wavelet packet transform [10], multifractral analysis[11], undecimated discrete wavelet transform [12], etc. ii. recent works about satellite remote sensing image denoising authors in [13] extended the existing learning-based methods in several aspects. their work combines a realistic corresponding author: messaouda gatcha engineering, technology & applied science research vol. 6, no. 12, 2022, 9715-9719 9716 www.etasr.com gatcha et al.: an anisotropic diffusion adaptive filter for image denoising and restoration applied on … physical noise model of the camera with real noise samples from dark frames to generate realistic training data. they formulated a physical noise model for a charge coupled device (ccd) sensor and presented a novel application of learning-based lowlight image denoising suitable for lunar surface images. they combined a physical noise model with real noise samples and scene selection based on three dimension (3d) ray tracing to generate training data and by conditioning the model on the camera’s environmental metadata at the time of image capture. authors in [14] resort to the plug-and-play (pnp) framework to address the hyperspectral image (hsi) denoising task by proposing a pnphsi (plug-and-playhyperspectral images) denoising model with low-rank representation and a prior cnn (convolutional neural network) denoiser. in the proposed pnp framework, the eigen-images are denoised by a drunet (dilated-residual u-net) submodel. in [15], the enhanced adaptive generalized gaussian distribution (aggd) and the improved aggd threshold function enhanced the qualitative and quantitative results of tnn and optimization-based noise removal. the improved aggd consists of two main parts. in the interval [-t, t], the function is adaptive ggd (generalized gaussian distribution), and behind the interval, it is a non-linear function. iii. the proposed method for satellite remote sensing images denoising in this paper, we propose an anisotropic diffusion approach on the basis of pde, containινγ motion by mean curvature, convolution product, gaussian kernel, and time of processing term: 0 ( ). * . . (0, , ) ( , ) t i i c t g i i div i i x y i x y              (1) where it is the enhanced image from the noised image i and 1 ( ) 1 4 ² c t t    is the diffusion problem coefficient term that helps to enhance the image contrast and keeps it from turning darker during the execution process. the motion by the mean curvature term is the degenerated diffusion term . i i div i          which precises the noised pixel and noise direction in its multidirectional neighboring, and * ig is the gaussian kernel mask with � standard deviation. for noised pixel restoration we used a � � � mask to redefine the value of the noised pixel from its neighboring pixels. the numerical solution of the pde in the earlier system, is found by the finite differences (fd) method [16], simpsons improved method [16], and the convolution product [17, 18], where the image pixel is the step for the mesh required in the numerical treatment of the image, that means we will work locally for each pixel in the digital image. for the image clarification sought during the image acquisition process, the time step is calculated as: ' t n   (2) where t is the time range, n′ the number of iterations, and k=1..t the time index. fig. 1. the image regularization process. iv. problem stability in this section, the following theorem is used to prove the stability of the proposed method [19]. theorem: let �. � � � be the problem and �. � � � � � its perturbed version. the euler explicit schema of the problem �. � � � is stable if ∃ � 0: ∃ℎ� � 0 ∀ℎ � ℎ� , ∀ � � ∈ � such that �. � � � � � � � � accepts a unique solution � � ∈ � . furthermore: �� � � � � � �� � ��� � � � , where a is a constant, � � the approximated solution, � the approximated solution space, � � the approximated function, and � the approximated function space. we apply the previous theorem on our problem, when the subset ω is associated with the norm sup. in !" � #$ %& the operator #. %. is linear, so we prove that �! � � ω� � ��� � � ω� , where !" � $ "(),*,+�,$ ",*,+� , i is the image, and !" � � ., /, 0� , so we have $ 1(),2,3�,$ 1,2,3� � � ., /, 0�. then we have: ( 1, , ) ( , , ) . ( , , )i k i j i k i j f k i j   1 . k k k ij ij ij i i f   -1 , , , max max . max k k k ij ij ij i j i j i j i i f  1 0 , , , max max . max k ij ij ij i j i j i j i i f  engineering, technology & applied science research vol. 6, no. 12, 2022, 9715-9719 9717 www.etasr.com gatcha et al.: an anisotropic diffusion adaptive filter for image denoising and restoration applied on … by adding side by side, we get: 0 , , , max max . . max k k ij ij ij i j i j i j i i n f  ( ) ( ) h h h h i f  where the schema is stable for α = 1+t. v. results and discussion in order to estimate the efficiency of the proposed image restoration model, we applied it on different types of noise (salt and pepper, gaussian, speckle). we carried out the algorithm simulations using a windows 32 bit pc powered by an intel 2.6ghz processor with 2gb ram. the experiments were performed in matlab r2017 [20, 21] due to its image processing toolbox, with time intervals took between τ=01s and τ=60s according to the image size and the number for iterations, noting that :  psnr: peak signal to noise ratio. it gives a noise free 4 � 5 monochrome for image ! and its noisy approximation.  ssim: structure similarity index metric. it is a method for predicting the perceived quality of measuring the similarity between two images, usually an original and a restored image. the euler explicit schema extracted from the discretization of the system (1) concludes the algorithm programmed in matlab and gives the process to the noised image restoration. the manipulation gets into the following steps:  step 1: program the convolution product based on the gaussian kernel as a σ×σ mask with σ standard deviation and scale parameter.  step 2: verify the image dimension that should be dim(i)=2. then convert the image grayscale with single values for pixels.  step 3: filter the image by motion by mean curvature to detect degraded pixels.  step 4: determine time step τ, number of iterations k, and standard deviation σ.  step 5: start a loop from k=1 to k=k restoring the degraded pixels and enhancing the image, calculating psnr and ssim to measure the improvement from the achieved results. tables ii-iv demonstrate the manipulation results for different types of noise applied on the images (figures 1-5) in table i. the iteration number of the denoising process is between 10 and 20 for remarkabale enhancement with high psnr, whilst table v describes a comparison with the results obtained by the works mentioned above (see section ⅱ) and the obtained results by the proposed anisotropic diffusion method where there is a round-trip in psnr and the clarity of images. table i. image description image size image name figure 1 1.28 mega map of brussels view satellite-belgium figure 2 520 ko band8 crop chip figure 3 812 ko shannon airplane irlande figure 4 925 ko algerian sahara figure 5 1.02 mega irlande table ii. reduced salt and pepper noise for d = 0.1 k = 10 original image noised image restored image psnr ssim 29.3953 0.5774 27.4245 0.8199 30.2833 0.7961 27.6886 0.8725 26.3484 0.8521 table iii. reduced gaussian noise � = 0.1, k = 10 original image noised image restored image psnr ssim 31.7707 0.5347 28.9869 0.6346 28.7726 0.5922 27.8323 0.7509 29.4133 0.6985 engineering, technology & applied science research vol. 6, no. 12, 2022, 9715-9719 9718 www.etasr.com gatcha et al.: an anisotropic diffusion adaptive filter for image denoising and restoration applied on … table iv. reduced speckle noise σ = 0.1, k = 20 original image noised image restored image psnr ssim 30.2091 0.5137 24.1765 0.6187 25.2453 0.5092 27.8884 0.4084 25.4414 0.6341 the algorithm outperforms the other approaches regarding the regularization of the noised image for gaussian and speckle noise. it also did not turn the image darker due to the gradient, as can be also seen in the comparison part. vi. conclusion image denoising and enhancement in order to improve image quality for more exact information extracting is a trending research topic. especially the capturing of satellite remote sensing images has the obstacle of the long distance barrier between objects and sensors, so captured images are more liable for noise like environment effects, light concentration and camera sharpness. the partial differential equation systems give a reliable point of view that helps this development, based on the multidirectional gradient that allows noise detection in several directions independently and locally for better regularization, unlike the total variation method which treats the noised image globally. table v. comparison results with recent works other works proposed original image noised image restored image psnr restored image psnr [13] 43.33 38.58 [14] 42.14 40.76 [15] 34.27 35.79 references [1] d. marr and e. hildreth, "theory of edge detection," proceedings of the royal society of london, series b. biological sciences, vol. 207, no. 1167, https://doi.org/10.1098/rspb.1980.0020. 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[21] "mathworks makers of matlab and simulink matlab & simulink," mathworks. https://www.mathworks.com/. microsoft word 17-800-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1207-1211 1207 www.etasr.com s. vairamuthu and s. margret anouncia: reconnoitering students' satisfaction of an online based… reconnoitering students' satisfaction of an online based assessment system to improve usability using pso: an examination into a problem solving and programming course s. vairamuthu school of computing science and engineering vit university vellore, india svairamuthu@vit.ac.in s. margret anouncia school of computing science and engineering vit university vellore, india smargretanouncia@vit.ac.in abstract—end users’ computing environment has been consistently changing in recent years due to the major advancements of information technology. this work aimed to measure the level of users’ satisfaction and provide feedbacks for continuous improvement of a course offered in an academic institution. end users here were the students enrolled for the course and the faculty members who offered the same and also acted as an assessor for the assessments. all assessments were scheduled and conducted online. this study was conducted to focus on two different aspects: measuring user satisfaction and investigating information systems measures to improve usability using nature inspired computing. for user satisfaction analysis, the study employed the multicriteria satisfaction analysis. the course considered was a problem solving and programming course offered to the fresh students enrolled in the first year of the undergraduate degree program in the academic institution during 2015-2016. to identify the factors for improved usability, pso was employed in this work. keywords-user satisfaction; multi-criteria user satisfaction analysis; web portal; information systems i. introduction academic and traditional portals, also termed as web portals, play a nominal role in recent technological innovations, as a gateway for services and information from various sources in a united way with the help of a single user interface [2]. these portals facilitate search capabilities, database access, registration for new users and personalization, etc. when employed in academic institutions their role slightly differs. many universities are making an attempt to introduce their services through academic portals, third party ones or institution based. such portals may be used for education, notification and even examination purposes. as these kinds of services are offered by third parties sometimes, it becomes mandatory that the investment and the efforts made for this purpose should satisfy the expectations of all the stake holders. this can be measured based on the level of satisfaction of all end users. it should be noted that an individual’s attitude to use of computers and the related actions to accomplish a task in an organization can be considered as end user satisfaction [3]. evaluation of online based assessment systems based on usability factors would be more interesting and difficult when compared with normal applications for two major reasons: locality of access and access environment. this kind of usability testing of assessment systems would normally have a greater impact on various kinds of users on a day-to-day basis otherwise the difficulties encountered will cause the users not to choose the same category for these kinds of assessment purposes. ii. literature survey usability has been evolving since 1980’s with its roots in hci (human computer interaction). it examines the interaction between users and the computers so as to make it more meaningful and effective. hci investigates the way developing and using interactive applications affect users, societies and organizations, and in [4] the impact of not proper designed was investigated. in [5], it was stated that hci deals with user tasks, actions or behaviors and goals with computerized systems and interfaces. in [6], it was claimed that evaluating usability contains methods to measure usability characteristics and to identify specific problems. in [7], it was claimed that there was not unique agreement on a single definition of usability. in [8], usability was defined as an effort to calculate friendliness to yield some measurable attributes of end users like users skill, time to learn, productivity from using the system and evaluation of users approach with the system. the financial aspect is also important. for example, in [9], it was shown that poorly designed websites yielded negative impacts financially. organizations may move to alternatives if any website fails to meet the end users’ needs and expectations [10]. in [11], it was observed that web services to implement business processes had low usability even though there were significant advances and investments made. in [12], it was stated that easy navigation was one of the critical components engineering, technology & applied science research vol. 6, no. 5, 2016, 1207-1211 1208 www.etasr.com s. vairamuthu and s. margret anouncia: reconnoitering students' satisfaction of an online based… of usability, and an attempt to specify the term was made in [7]. in [13], a methodology to evaluate the usability of web portals that encompassed task-based testing, questionnaire based on satisfaction and semi-structured interviews was proposed. in [14], several usability criteria were mentioned, broadly categorized as organization of contents and readability, links and navigation, design of user interface, effectiveness and performance and information on education. in [15], a model for web usability evaluation was designed to evaluate higher educational websites that involved students of the concerned institutions with a similar categorization (five major elements). in [16], website analysis & measurement inventory (wammi) was used for assessing a university’s website. the multicriteria satisfaction analysis (musa) method has been proposed as a mean to measure customer’s satisfaction [17]. the underlying principle in [17] was to aggregate the individual’s collective value function claiming that the global satisfaction of any customers depend on a group of criteria that represents various dimensions of their service characteristics. in [18], authors performed a study based on questionnaire to measure the usability of six universities of lebanon. the questionnaire measured various usability attributes among various users. in [19], it was demonstrated that usability would be a paired act–insufficient functionality that would reduce the application’s use when clutter and complexity made any interface very difficult to be used. in [20, 21], authors claimed that knowledge-intensive workers and organizations relied more on the available services at web portals which can incorporate business processes playing a vital role in organization’s functionality. in [22], six categories to measure usability along with the methods to collect analyze and present the data related to usability were proposed. in [23], it was debated that information sources together with users’ activity in web portal accounted towards appropriate observation and modeling. further, techniques to determining model parameters and presented models based on mathematics towards portal operation were also proposed. in [24], it was stated that usability improvement in organization portals require effective management work in several stages and suggested to approach any information systems through several levels. in [25], the use of analytics was recommended as it provide timely intelligence for business that would best be suitable for maintaining and gaining competitive advantage. in [26], it was claimed that analytics enabled the evidence-based management. in [27], it was argued that the influences of it were often influenced by human and indirect, environmental and organizational factors and so measuring information systems success was complex and illusive. in [28-30], it was proclaimed that system quality was strongly related to satisfaction of the user in any knowledge management system. iii. objectives the objective of this study was to evaluate the usability of a web based assessment system for one of the courses offered inan academic institution. the study focused insight into the following: • analyzing the various usability attributes. • getting students’ subjective opinion. • checking individual’s ability for completion of tasks. • checking accessibility compliance. • identifying the factors to improve usability of the system using pso iv. overview of course structure and organization the course taken for this work is problem solving and programming which was offered in an academic institution in the first year of students enrolled in 2015-16. the institution makes use of the skillrack portal for this course only for assessment process. the course is offered as a lab based course for a period of six months. the major stake holders of this course are students and faculty members offering the course. the maximum enrollment is 65 per class. three lab sessions per week for a period of 15 weeks is planned for this course. the maximum duration for the course is 90 hours which is scheduled as 45 sessions of 2 hours each. based on the regulations of the institution, the students are eligible to earn 3 credits upon successful completion. this course aims to make students familiarize themselves in the core idea of fundamentals in problem solving. python is chosen as our platform programming language to exercise the learned concepts in this course. as part of this course, students are expected to complete a small set of problems termed as practice problem set. this series of problem solving by students contribute 40% towards their final grading. also, a series of assessments are planned for evaluating the students’ competency level obtained via this course. usually, multiple choice questions, debugging questions and problems with coding will be the part of individual assessment. every assessment will be evaluated for 10 marks for mcqs, 10 marks for debugging and 30 marks for coding thus 50 marks in total. apart from this practice problems and assessments, to test the students’ higher order thinking level, two challenging tasks will be given for the students each contributing to 10% in their final grading. put together, the assessments contribute 40% and the practice problem set contribute 40% and the challenging tasks contribute 20% for the final grading. a. stakeholders of this course the course as stated uses the portal for several purposes. various stake holders of this course are: • core management team • dean • facilitator • faculty members • technical personnel for portal • students the core management team includes the management authorities who initiated this process to introduce the change in delivery mode of course viz. online. dean is the person who is responsible for the entire process as he monitors the entire engineering, technology & applied science research vol. 6, no. 5, 2016, 1207-1211 1209 www.etasr.com s. vairamuthu and s. margret anouncia: reconnoitering students' satisfaction of an online based… process and keeps things updated with the top management. one of the faculty members is designated as the facilitator who holds all the rights similar to an administrator. the facilitator may be assisted by another team of faculty and technical staff. facilitator responsibilities include: preparing and uploading questions for practice sessions and assessments, scheduling/rescheduling of assessments. faculty members play the role of assessor of this course apart from the traditional teaching. the technical staff from the company assists the moderator in managing the users, preparing the system for practice problems and assessments like question uploading, time management, etc. students use this portal for solving their practice problem sets and taking up the assessments online. they can idealize their own progress after individual assessments. figure 1 depicts the interaction. fig. 1. use case diagram of the course evaluation for the entire course was based on several rubrics which were decided by a team of experts. there are 6 rubrics finalized for grading the students. figure 1 captures the various users of this portal related to the course apart from the traditional stake holders i.e. the management team. the course was offered in two different sessions with combination of many lab slots in morning and evening. in all sessions, there were a minimum of two persons responsible for the course delivery and monitoring. one of them must be the faculty member, who was in charge of the entire course assisted by a person who helped in monitoring. in some cases, the lab may contain two faculty members. v. research materials and method as part of this study, many tasks were identified from the entire stake holder’s perspective. students started using the portal for their daily activities. after successful implementation of this system, we decided to study the level of fulfillment of users and their expectations satisfied out of this course. a traditional questionnaire was formulated focusing on aspects of usability and users’ responses were gathered through a google form. musa (multi-criteria user satisfaction analysis) was employed for result interpretation. it was focused on two different perspectives: global satisfaction and partial satisfaction analysis, based on a 5-point scale. major classification included: • system quality • information quality • technical quality • service quality the questionnaire focused on the acquired competency level of individual students along with the facility to mark whether or not the course met their objective. also, students were given provisions to express their suggestions to make improvements in the portal. as we concentrated in two different satisfactions measurement levels (global satisfaction and partial satisfaction), we finally gave the students a choice to rank the overall satisfaction level they experienced from this portal. around 2000 students recorded their feedback on the usability of the portal. many students didn’t want to reveal their identity. vi. results to interpret the results using the musa method, the segregation of data collected from the students were carried out as the first step. to facilitate this process, the collected 8 parameters were organized into 4 factors viz. system quality, information quality, technical quality and service quality as shown in figure 2. results are shown in table i. fig. 2. usability factors in order to find out the factors to improve by musa method, it was decided to follow the procedure given below: • identify the desired level of satisfaction measure. • determine how usability factors plays in deciding the overall satisfaction score. • apply regression with four factors. • interpret the values arrived in regression. engineering, technology & applied science research vol. 6, no. 5, 2016, 1207-1211 1210 www.etasr.com s. vairamuthu and s. margret anouncia: reconnoitering students' satisfaction of an online based… • following were the desired procedure: • desired level of satisfaction: 60% usability factors and their individual contributions are shown in table ii. table i. summary of data collected factors(fi) and attributes (ai) mean standard deviation f1. system quality a1. ease-of-use 3.40 1.11 a2. efficiency 3.31 1.25 f2. information quality a1. interaction 2.42 1.08 a2. navigation 3.38 1.08 f3. technical quality a1. memorability 2.94 0.96 a2. learnability 1.63 0.73 f4. service quality a1. response time 3.86 1.03 a2. users satisfaction 3.24 1.02 table ii. usability attributes factors attributes % measure a1. ease-of-use 15 system quality (30%) a2. efficiency 15 a1. interaction 14 information quality (20%) a2. navigation 6 a1. memorability 7.5 technical quality (30%) a2. learnability 22.5 a1. response time 8 service quality (20%) a2. users satisfaction 12 considering the above four factors, regression analysis was carried out as follows: let y be the overall quality (dependent variable) that would be determined by four independent variables x1, x2, x3 and x4. modeling the relationship between the above mentioned dependent and independent variables, the results obtained were: one-on-one regression [y=mx+c], where y refers overall quality and x refers factors is given below: (0.508) (0.002)total sq= + (1) (0.544) ( 0.001)total iq= + (2) (0.515) ( 0.001)total tq= + (3) (0.503) (0.009)total seq= + (4) where total denotes overall quality while sq, iq, tq and seq represents individual quality factors viz., system quality, information quality, technical quality and service quality respectively. combining all the four independent variables sq, iq, tq and seq and results of multiple regressions carried out and the result is given below in equation 6 which take the general form: 1 2 3 4y c x sq x iq x tq x seq= + + + + (5) where, y is overall quality and x1 to x4 represents 4 factors viz system quality, information quality, technical quality and service quality and c is constant. seqtqiqsqy )002.0()009.0()008.0()002.0()52.0(  (6) to achieve the desired results of regression, the nature inspired computation pso was used. pso optimizes a problem using iterations to improve the measure of desired quality. it uses simple formulae to move particles around search space using the given formulae. individual iteration influences the move from local best toward the best known position in search space thus by optimizing the measure. to obtain the desired level of satisfaction which we had fixed at 60%, by applying pso, the system quality at 0.07 with information quality at 0.24 whereastechnical quality was at 0.07 and the service quality took the value 0.24. only for the above mentioned values for the chosen factors, it was found to be optimized using pso. but observing the results from the data gathered, it was evident that both system quality and technical quality needs improvement. the attributes ease-of-use and efficiency of system quality along with memorability and learnability of technical quality were influencing the overall quality. vii. discussion analyzing the individual components in partial satisfaction measure, student’s previous knowledge about computers contributed less in deciding the overall satisfaction level. if we take a closer look into this interpretation, the global satisfaction level of the portal is entirely different from the partial satisfaction level criteria. the factors contributed for the partial satisfaction level when measured individually differs drastically from the overall satisfaction measure. several suggestions were recorded as their feedback to improve the usability of the portal that included improvements in user interface, competency levels of questions etc. some of the major findings were as follows: • almost 50% of the students that participated insisted that the interface needs more changes in ui. • the questions for assessments should consider the competency level of all the students that depends on memorability and learnability factors. • the infrastructure in terms of connectivity needs improvement for efficient utilization. • the time bound assessments can be changed so as to make portal easy to use at any time. the achieved usability was yet to be improved. the usability of the portal can be improved by incorporating multimodal hci features with the existing features of the portal. mmhci features include speech synthesis, gesture recognition, eye tracking, etc. the fundamental aim of incorporating multi modal aspect into the existing system was to enhance the users’ experience. the satisfaction may be improved when the portal fulfill the users requirements. so, incorporating any of the multimodal concepts would lead towards improved usability. possible modality may be integrating speech synthesizer would lead to reduce the number of key strokes for all the users. minimal number of key strokes engineering, technology & applied science research vol. 6, no. 5, 2016, 1207-1211 1211 www.etasr.com s. vairamuthu and s. margret anouncia: reconnoitering students' satisfaction of an online based… may help users achieving more interactivity and improve speed during their interaction. viii. conclusion user interface design plays a vital role in usability of any online portal. the usability evaluation of an online assessment system was studied here in depth considering all factors that contribute in usability. the object of the study was a course offered in an academic institution. faculty members and students were considered as end users. a questionnaire was filled and multi-criteria user satisfaction analysis was employed for result 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security framework to mitigate and avoid unexpected security threats in … a novel security framework to mitigate and avoid unexpected security threats in saudi arabia ahmad alshammari department of computer sciences, faculty of computing and information technology, northern border university, saudi arabia ahmad.almkhaidsh@nbu.edu.sa (corresponding author) received: 5 june 2023 | revised: 20 june 2023 | accepted: 26 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6091 abstract many organizations around the world suffer large losses due to unexpected risks which can have a profound impact on their survival. this paper presents a novel security framework to address the security needs of saudi organizations. there are four stages in the security framework: risk assessment and management, security intelligence and analytics, security policies and procedures, and security monitoring. a comprehensive security solution was provided by combining common security frameworks, e.g. iso/iec 27001:2013, nist cybersecurity framework, and cobit. the developed framework was designed to help saudi organizations identify, assess, and control risks and respond to unexpected events in a timely and effective manner. it is expected to help organizations develop and implement effective security measures to protect their critical assets and operations from security threats. the proposed framework is comprehensive and can cover most organizations' requirements. keywords-security frameworks; security models; iso/iec 27001:2013; nist cybersecurity framework; cobit i. introduction many organizations experience a global revolution in governance that could affect how they manage their information. organizations must ensure that their information is adequately protected and in compliance with information security laws [1]. a company's chief information officer should not only be responsible for securing data but also handle them as part of its governance practices. it is critical to note that corporate information security governance includes accountability to shareholders, compliance with legal requirements, setting well-planned security policies, spearheading security awareness and education, defining roles and responsibilities within an organization, establishing contingency plans, and implementing best practices [2]. the security of saudi arabian organizations is becoming increasingly important. the current challenges include a lack of emergency response plans that can lead to confusion and chaos during a crisis, poor risk management practices that can cause a company to be unprepared for a potential disaster, inadequate investment in cyber security infrastructure that can leave organizations vulnerable to cyberattacks, weak internal control systems that can leave organizations open to fraud and corruption, poor data protection and backup measures that can cause a company to lose important data in the event of a disaster, poor communication and collaboration between departments that can lead to delays in responding to an incident or event, insufficient training and awareness on emergency response procedures that can lead to mismanagement and errors, and inadequate insurance coverage that can leave a company exposed to financial losses due to an incident or event. this study aims to develop a novel security framework using the design science method (dsm) for saudi organizations to avoid or mitigate expected incidents and risks. the proposed security framework embeds four stages, derived from existing security frameworks, such as iso/iec 27001:2013, nist cybersecurity framework, and cobit: risk assessment and management, security intelligence, security policies, and security monitoring. iso/iec 27001:2013 specifies the requirements for establishing, implementing, maintaining, and continuously improving information security management systems (isms) [3]. the nist cybersecurity framework embeds 5 steps and translates the meaning of documents, such as iso/iec27001, into understandable information [4]. cobit is an internal control structure of policies, procedures, and practices to provide organizational results and prevent, detect, and improve undesirable actions [5]. the proposed framework could enable saudi organizations to better protect their data and systems and manage their security posture. ii. related works many studies addressed the security concerns of saudi arabian organizations and companies. in [6], various engineering, technology & applied science research vol. 13, no. 4, 2023, 11445-11450 11446 www.etasr.com alshammari: a novel security framework to mitigate and avoid unexpected security threats in … cyberattacks in saudi arabia were examined, along with their effects, and solutions for a permanent solution to the problem were proposed. cyberattacks were analyzed based on the type, source, extent, and type of information or service that was compromised. in [7], a model was presented to evaluate security risks. essentially, it was a concept to understand and manage it security risks comprehensively based on risk-based security management that incorporates organizational culture, knowledge, and security management. in [8], an information security policy compliance model was proposed that included variables such as resource weakness, self-efficiency, and awareness. according to the proposed model, security policy compliance is determined by three factors: self-efficiency, resource weakness, and awareness. the model suggested that when these three variables are high, compliance with security policies is more likely. organizations should focus on increasing self-efficiency, reducing resource weakness, and increasing awareness to increase the likelihood of successful security policy compliance. in [9], a consistent framework was presented to measure the condition and suitability of the information security management frameworks of small and medium-sized organizations. however, small and mediumsized companies might not find it flexible enough to use it. in [10], the role of secondary education in promoting information security among saudi arabian students was studied, as well as its realities, difficulties, and the necessary conditions for activation. the study discovered considerable discrepancies between men and women in what was needed to improve their culture. secondary education was found to play a weak role in improving students' attitudes toward information security, but first, the necessary prerequisites must be met. in [11], cloud attacks were studied among graduate students, discovering that most attacks were related to cloud storage security concerns. it was also noted that social networking security helps and creates awareness of the necessity of social awareness programs in higher education institutions. in [12], the perspectives of it personnel in saudi companies were investigated. most of the companies studied had implemented information security policies and used ethical technology, but many of these policies were not properly and efficiently enforced or made public. the study encouraged the saudi communications and information technology commission to create a national framework for instructing companies on ethical information security procedures. in [13], a model was developed to analyze the is success model and cybersecurity elements that affect the efficiency and use of e-gov services in saudi arabia. the findings showed that the basic is constructs had a significant impact on the satisfaction of users and the degree of danger they perceived. in [14], cybersecurity was investigated from the saudi arabian e-gov projects' point of view, presenting a comprehensive approach that incorporated scientific principles. the study considered the operating environment of the project, focused on security, and claimed that cybersecurity must be developed and customized to meet the needs of citizens served by an e-gov system. in [15], a cybersecurity maturity assessment framework (scmaf) was proposed for heis in saudi arabia, which was a comprehensive and customized security maturity assessment framework that can be used as a self-assessment method to establish security levels and highlight weaknesses and mitigation plans. scmaf was implemented as a lightweight assessment tool that can be provided online or offline to ensure data privacy. in [16], the amount of data lost or stolen during data breaches was determined and the effectiveness of cybersecurity policies was investigated in companies. multiple regression tests were used to evaluate the effectiveness of 12 cybersecurity practices in three areas for small businesses: financial loss, loss of sensitive data, and restoration time. in [17], the applicability of a theory-based model and the determinants of information security compliance behaviors (iscb) among healthcare professionals in saudi arabian government hospitals were identified. the findings implied that while demographic traits have little effect on iscb, moderating and uncommon factors, such as religion and morality, do. in [18], difficulties and impediments in security, privacy, reliability, integration, and data portability were examined in the health and patient care industries. privacy and security issues with cloud computing and electronic health were discussed, as well as potential methods for dealing with them [19]. in [20], the security of different web applications was evaluated using a hybrid fuzzy analytical hierarchy processtechnique for order of preference by similarity to ideal solution (fuzzy ahp-topsis) method. the study suggested integrating security in-between web application development. in [21], the present methods of the gcc countries for managing e-waste were reviewed, projecting the output until 2040 and covering the potential long-term effects on the economy, security, and ecology, suggesting steps to protect private data contained in discarded electronic components. the study recommended a thorough review of current legislation to address potential security and environmental challenges and emphasize economic opportunities. additionally, several studies aimed at discovering the risks for organizations. organizations can use these studies to classify and respond to security events, mitigate risks, and expand their overall security attitude with the help of digital forensics. numerous studies investigated and discovered incidents, data breaches, and other digital attacks on organizations [22-61]. as a result, the above review shows that saudi arabian organizations lack a comprehensive security framework to mitigate and avert possible risks, leading to a difficult situation in terms of monitoring, managing, and protecting all assets and resources of the organization. iii. methodology this study used dsm to develop a new security framework for saudi organizations to mitigate and avoid unexpected events. dsm uses a combination of research methods to develop and test design solutions [62-63]. according to design science, research can solve design problems and improve products, services, and systems. the development process involves five steps:  identifying the problem  creating research questions  conducting an e-literature review  developing a novel security framework engineering, technology & applied science research vol. 13, no. 4, 2023, 11445-11450 11447 www.etasr.com alshammari: a novel security framework to mitigate and avoid unexpected security threats in …  investigating and validating the framework a. identifying the problem the purpose of this step is to identify the current problems that saudi organizations face in the event of unexpected events or incidents. assets may be destroyed or compromised due to such incidents. several saudi organizations are currently experiencing problems that may be affected by unexpected events, including the absence of disaster response plans, insufficient investment in cybersecurity, weak interior controls, lack of communication between sectors, and inadequate training and understanding of emergency response procedures. b. creating research questions this step determines the research questions to identify the limitations and drawbacks of traditional security models for saudi organizations. the research questions were "what security measures should saudi organizations implement to protect confidential data and reduce the risk of data breaches?", "how do saudi organizations protect their data?", and "what are their limitations with the existing security models?" c. e-literature review this step involved research on current security models and frameworks used by saudi organizations. the search results included only articles published in journals and conferences between 2015 and 2023 in english. this period was selected because it ensured the availability of sufficient data. table i summarizes the search results. the articles were filtered according to the research objectives. for this purpose, inclusion/exclusion criteria were selected. based on the analysis of the security models and frameworks discovered, the development of a novel security framework was required to mitigate and avoid unexpected events. the proposed security framework should provide an integrated approach to security risk management, be comprehensive, and include components such as threat analysis, risk assessment, incident response, and security monitoring. table i. research results summary search engines keywords results ieee explorer security frameworks, security models, and saudi organizations 89 scopus 108 springer 1010 web of science 95 google scholar 1503 d. developing a novel security framework the proposed security framework for saudi organizations consists of five steps, as shown in figure 1: risk assessment and management, security intelligence and analysis, security policies and procedures, and security monitoring. the developed framework was based on iso/iec 27001:2013, nist cybersecurity framework, cobit, and the sans top 20 critical security controls. 1) risk assessment and management stage a process that threatens a company's earnings and capital should be identified, assessed, and controlled. this stage involves identifying potential risks, assessing their likelihood and impact, and implementing measures to reduce risks to an acceptable level. an organization's operations would not be complete without it. this minimizes the risk of unexpected losses and maximizes the success potential of the organization. in addition, it helps to comply with applicable laws. processes, operations, and products are analyzed for potential weaknesses or vulnerabilities. assessing risk involves determining the likelihood of an event occurring and its impact on the organization. in addition to quantitative methods, qualitative methods, such as interviews and surveys, can also be used. as a third step, develop strategies that can involve changing processes and procedures, implementing new technologies, or insurance policies. lastly, the organization should monitor and review its strategies over time to ensure their effectiveness. fig. 1. the proposed security framework for saudi organizations. engineering, technology & applied science research vol. 13, no. 4, 2023, 11445-11450 11448 www.etasr.com alshammari: a novel security framework to mitigate and avoid unexpected security threats in … 2) security intelligence and analytics stage in this stage, information is collected, analyzed, and interpreted. organizations can detect and respond to potential threats with a detailed understanding of their security posture. this stage consists of several steps. first, collect and analyze data from a variety of sources, such as networks, endpoints, applications, databases, and cloud services. second, automated threat detection using advanced algorithms and machine learning techniques. it is necessary to develop and implement a threat response and restoration plan to resolve the issue. third, incident response and forensics, in which evidence is collected and analyzed to determine the cause and scope of a security incident. fourth, risk and compliance management helps organizations identify, assess, mitigate, and comply with applicable laws and regulations. the final step is to protect information assets through security operations. 3) security policies and procedures organizations can develop and implement security policies and procedures tailored to their specific needs and objectives to protect information systems, networks, and other assets from risks. four components make up this stage: first, the development of security policies helps organizations protect their assets, data, and systems, as they provide guidelines to define acceptable use of technology. the second step is to implement security procedures to ensure compliance with security policies. authentication systems, access control systems, and encryption techniques are examples of technical controls. in the third step, security logs, reports, and user activities are reviewed and audited regularly to ensure that policies and procedures are followed and that security incidents are handled appropriately. in the final step, employees must be trained and made aware of security policies and procedures, as well as provided with resources to make them aware of risks and vulnerabilities. security-related training and awareness campaigns should be provided regularly. 4) security monitoring stage this step aims to regularly evaluate an organization's networks, systems, and applications to ensure that there are no vulnerabilities or malicious activity present. monitoring an organization's it environment continuously for suspicious or harmful behavior involves continuously observing and analyzing its activities. there are eight components in this stage. first, security event logging and analysis collects and analyzes logs from various sources, such as network traffic, applications, and systems, to detect anomalies or suspicious behaviors. the second step is intrusion prevention and detection which detects and blocks malicious traffic. third, vulnerability scanning identifies and mitigates any potential threats by regularly scanning the network for known vulnerabilities. in the fourth step, it is ensured that all assets are secure, including hardware and software. in the fifth step, network monitoring is used to detect suspicious or malicious activity. in the sixth step, endpoint security is installed and monitored on all devices to protect them from malware or malware-like attacks. the seventh step involves user access controls, which establish policies to control access to resources by ensuring that they have the necessary permissions. finally, security auditing is performed to identify any security vulnerabilities in systems and networks. 5) testing and validating the framework the developed framework must be tested and validated to ensure its capacity and effectiveness before using it in a simulated environment. security experts and the organization should also evaluate and validate the framework's effectiveness. future work will implement this step. iv. discussion the proposed framework includes four stages: risk assessment and management, security intelligence and analytics, security policies and procedures, and security monitoring. organizations must identify, assess, and mitigate potential risks during the risk assessment and management stage. this stage identifies potential vulnerabilities and threats, assesses their likelihood, and develops and implements security measures to mitigate them. data must be collected and analyzed to determine potential vulnerabilities and threats. machine learning and artificial intelligence technologies can be used to detect anomalies by monitoring network activity and analyzing user behaviors. developing and implementing security policies and procedures that protect the organization from potential threats and vulnerabilities is the goal of the policy and procedures stage. this stage also includes policies for access control, user authentication, and encryption. lastly, security monitoring involves monitoring any suspicious activity within the organization's systems. monitoring user behavior and reviewing access control policies are some of the steps involved in this stage. the proposed security framework provides a comprehensive approach to protect the organization from potential threats and vulnerabilities. as part of the security process, the organization's systems are monitored for suspicious activity and identified, assessed, and mitigated risks. this security framework was developed using iso/iec 27001:2013, the nist cybersecurity framework, and cobit, which are three common security frameworks. the proposed model may also work with organizations in other countries than saudi arabia, as it is built based on these common security frameworks. for instance, risk assessment and management are provided by the nist framework, security intelligence and analytics are provided by the cobit framework, and iso / iec 27001:2013 was used for developing security policies and procedures. v. conclusion this study proposed a security framework for saudi organizations to mitigate and avoid unexpected security events. the proposed framework was based on iso/iec 27001:2013, the nist cybersecurity framework, and cobit, and included four stages: risk assessment and management, security intelligence and analysis, security policies and procedures, and security monitoring. the proposed framework can also be applied in organizations of other countries, as it is based on three common security frameworks. references [1] r. saint-germain, "information security management best practice based on iso/iec 17799; the international information security standard engineering, technology 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science engineering department bhagwan parshuram institute of technology delhi, india surbhimittal19970@gmail.com abstract—in this study, an approach is being proposed which will predict the output of an observation based on several parameters which employ the weighted score classification method. we will use the weighted scores concept for classification by representing data points on graph with respect to a threshold value found through the proposed algorithm. secondly, cluster analysis method is employed to group the observational parameters to verify our approach. the algorithm is simple in terms of calculations required to arrive at a conclusion and provides greater accuracy for large datasets. the use of the weighted score method along with the curve fitting and cluster analysis will improve its performance. the algorithm is made in such a way that the intermediate values can be processed for clustering at the same time. the proposed algorithm excels due to its simplistic approach and provides an accuracy of 97.72%. keywords-weighted score; classification; clustering; deviation; threshold; svm; decision tree i. introduction classification is a data mining technique in which a collection of data is categorized into classes in which the training dataset may or may not have class labels. a dataset may have two or more class labels. in this work we are focusing on binary classification using clustering technique based on curve analysis and weighted score method followed by verification. to illustrate with an example, let us suppose that we have a dataset containing data about spam from a repository. we want to identify the data points above and below the threshold level which are classified as spam and not spam respectively. the threshold level can be obtained through sorting and processing of the dataset. the proposed algorithm preprocesses the dataset to find the weighted score as well as to predict the threshold value, which is then represented graphically. after this step, verification is done using cluster analysis. observations on various datasets were found to be accurate to a high degree. deviations of various data points from the threshold values were obtained and various inferences were found. we have also calculated the individual effect of an attribute with respect to its effect on classification. data provided by datasets contain hidden information that might not be known to the user. an effort has been made to develop a new algorithm to facilitate mining techniques. the simplistic approach of the algorithm is easy to understand and implement. the proposed algorithm is based on clustering which acts as a stable preprocessing method for binary classification. weighted score method assigns different importance degrees to the instances of a dataset. the proposed classifier calculates the mean of each sample which is multiplied with each attribute’s value summed up to assign a weight to that sample. a threshold value is taken and plotted data points fall below or above it. the minimum and maximum values among the weighted sample sums are subtracted from the threshold value which is halved to obtain the centers of two clusters. clustering is performed using these centers and by taking maximum distance into consideration which will be the same with the distance between a center and the threshold value. the clusters obtained correspond to the binary class labels which classify the dataset. observations are cross verified using the clustering method. weighted score is a simple technique and also incorporates the individual contribution of an attribute consisting of its weighted score in its contribution to the deviation of the data point from the threshold. engineering, technology & applied science research vol. 8, no. 2, 2018, 2853-2858 2854 www.etasr.com jain et al: an enhanced binary classifier incorporating weighted scores ii. literature review various studies have been proposed for classifying datasets into two categories. previous researchers utilized different classification approaches. svm (support vector machines), is basically used for classification and regression analysis and employs supervised learning techniques. in svm algorithm, new examples are assigned or classified into categories and therefore it is regarded as a non-probabilistic classifier. svm can be thought of as a clustering algorithm in space in which points belonging to a cluster are distant from points of other clusters. in that space a hyper-plane divides the points in groups. a particular hyper-plane with the characterization of minimizing the total distance of the data points on either of its sides is selected. this is also called a linear classifier. there are various variations to the basic approach of the svm namely linear kernel svm, polynomial kernel svm and radial kernel svm. the most efficient method for fitting svm is the sequential minimal optimization (smo) method. it breaks the problem down into sub-problems that can be solved analytically rather than numerically. there are various svm applications like the recognition of standing people in a picture. authors in [1] used svm along with k nearest neighbor (knn) for visual category recognition. authors in [2] used variations of svm to predict the future popularity of social media messages. the disadvantages of svm are that the theory only covers the determination of the parameters for a given value of the regularization and kernel parameters and is dependent on the kernel choice. as a result, svm comes up with the problem of overfitting from optimizing the parameters to model selection. kernel models can be quite sensitive to overfitting the model selection criterion [3]. in [4], local space time features were used for recognizing complex motion patterns using svm. a decision tree is a predictive model to go from observations and related choices about an item to possible outcomes about the item's target value. it has various applications in statistics, data mining and machine learning. in this structure, each node denotes a test on an attribute, leaves represent class labels and branches represent conjunctions of features that denote the test outcome. besides being simple to interpret and understand, decision trees are able to handle both categorical and numerical data [5]. to solve the problem of fragmentation and replication, a notion of decision graphs has been introduced which allows disjunctions or joins. there are assumptions taken into consideration regarding decision tree algorithm. at the beginning, the whole training set is considered as the root. feature values are preferred to be categorical. if the values are continuous then they are discretized prior to building the model. records are distributed recursively on the basis of attribute values. the decision tree algorithm is sensitive to root selection. if the dataset consists of n attributes then the decision of which attribute to place at the root or at different tree levels as internal nodes is a complicated step. any random node cannot be placed at the root. if the random approach is followed, it may give bad results with low accuracy. placing attributes is done by statistical approach. a variation of this weighted class based decision tree [6] has been proposed in which weights are easy assigned according to the importance of class labels which are further classified using a decision tree. the dataset is split in this approach which might potentially introduce bias where small changes in the dataset can introduce big impact. decision-tree can lead to overcomplex trees that do not generalize well the training data. studies have shown that classification issues are often more precise when using a combination of classifiers which outperform a highly specific classifier [7]. using a combination of classifiers noisy data can be handled in a better way with augmented accuracy and speed even though complexity issues may emerge [8]. weighted score method assigns different importance degrees to instances of a dataset and is often used as a pre-processing method. automated weighted sum (awsum) uses a weighted sum approach where feature values are assigned weights that are summed and compared to a threshold in order to classify an example. it provides insight into the data [9]. authors in [10] dealt with the weighted score fusion method which involves the classification of a fruit based on the diverse and complementary features that can be used to describe it. the algorithm has various steps which involve preprocessing, multiple feature selection, optimal feature selection and svm. however, the approach requires improvements in the real world environment. a quadratic classifier is used in statistical classification to separate measurements of two or more classes of objects or events using a quadric surface. it is a more general version of the linear classifier. statistical classification considers a set of vectors of observations x of an object or event, each of which has a known type y referred to as the training set. the problem is then to determine the class of a new observation vector. the correct solution is quadratic in nature. in the special case where each observation consists of two measurements, this means that the surfaces separating the classes will be conic sections, thus the quadratic model is the generalization of the linear approach developed to incorporate the conic separating surfaces for classification. quadratic discriminant analysis (qda) is closely related to linear discriminant analysis (lda), where it is assumed that the measurements from each class are normally distributed. unlike lda however, in qda there is no assumption that the covariance of each of the classes is identical. classification error rate ranges around 20%-30%. an artificial neural network consists of units (neurons), arranged in layers, which convert an input vector into some output. each unit takes an input, applies a (most probably a nonlinear) function to it and then passes the output on to the next layer. the networks are defined to be feed-forward, which means that a unit feeds its output to all the units on the next layer, but there is no feedback to the previous layer. weightings are applied to the signals passing from one unit to another. these weightings are tuned in the training phase (learning phase) to adopt the neural network to the particular problem. the network processes records one at a time, and learns by comparing their classification with the known actual classification. the errors from the initial classification are fed back into the network and used to modify the network's algorithm for further iterations. neurons are organized into layers: input, hidden and output. the input layer is composed not of full neurons but rather consists simply of the record's values that are inputted to the next layer of neurons. next there are one or more hidden layers. 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data point int was found re each data old level. h v jain et al: ime s s s s s r he data m the were of data gives served tances e was ts had d to be point algo ave data clus data that oth fou lead clus ver k m clus sca sign poi rep and the the bot the util clas som wei get effi use the of sup nec [1] [2] [3] [4] [5] vol. 8, no. 2, 20 : an enhanced on the resu orithm, it was erage accuracy a and its weig stering and c aset can be s t are above or her cluster divi und that fixing d to effectiv stering we can rification to ac means. it is im ster centers sh ale to obtain u nificance, it g nts of the resentations: o d the other pe accuracy of th threshold valu th cases theref e algorithm is lizes the weigh ssification at th the proposed me other effic ighted score su a higher leve icient in handl ed to function threshold leve the authors w the bhagwan pport and enco cessary facilitie h. zhang, a. c nearest neighbo ieee compute recognition, ne b. yu, c. mia marketing me modeling and science, vol. 6 c. j. c. burge recognition”, d c. schuldt, i. l svm approach (icpr ) 2004, c p. j. tan, d. l way joins”, in: notes in comp heidelberg, 200 018, 2853-2858 d binary classif vi. co ults obtained s found that t y. the algorith ghted represen cluster produc imply calcula r below the th ided by the tot g of initial cen ve clustering. n also involve hieve higher d mportant that th hould be done useful results. gives a center dataset. t one was with r ertained to the he classificatio ue. it was obse fore the obtain different from hted score of he same time. vii. fu d classifier ca ient clustering uch as fuzzy k el of accuracy ling initial cen as a neural cl el and perform acknow would like to t n parshuram i ouragement du es at institute. refer c. berg, m. maire or classification er society confer ew york, usa, p ao, l. kwok, “t ssages”, in: so prediction. sbp 589, pp. 317-324 s, “a tutorial on data min. knowl. laptev, b. caput h”, 17th internatio cambridge, uk, v . dowe, “mml i : advances in a puter science, vo 03 8 fier incorporat onclusion by the imple the algorithm hm allowed pr ntation allowe ction. the pre ated using the hreshold value tal number of ntroids and ma apart from e other cluster degree of prec he plotting of t e on the same the threshold r point for cl there were respect to the p e clustering al on depending erved that the ned threshold v m traditional w data point for uture work an be enhance g algorithm ca k means, proba y in clustering ntroids. the alg lassifier to aut m the classifica wledgment thank dr. paya institute of t uring the resea rences e, j. malik, “svm for visual catego rence on compu pp. 2126-2136, jun toward predictin ocial computing p 2011. lecture , springer, berlin n support vecto . disc., vol. 2, no to, “recognizing onal conference o vol. 3, pp. 32-36, inference of decis artificial intellige ol. 2903, pp. 269 2857 ting weighted s ementation o is having 97 e-processing o d the simultan ecision rates e number of p e and belong t the clusters. i aximum value m using k m ring algorithm ision such as f the data point graph with p d point is of lassifying the two data proposed algor lgorithm empl on the selecti center coincid value was accu weighted score r the clustering d in various w an be applied t abilistic k mea g as they are gorithm can al tomatically ide ation. al pahwa, prin technology fo arch and prov m-knn: discrimi ory recognition”, uter vision and p ne 17-22, 2006 ng popularity of g, behavioral-c e notes in com n, heidelberg, 201 r machines for p o. 2, pp. 121–167 human actions: a on pattern recog , 2004 sion graphs with ence. ai 2003. l 9-281, springer, b scores f the 7.72% of the neous for a points to the it was es can means ms for fuzzy ts and proper great data point rithm loyed ion of ded in urate. e as it g and ways. to the ans to more lso be entify ncipal or her viding inative , 2006 pattern social cultural mputer 11 pattern 7, 1998 a local gnition, multilecture berlin, engineering, technology & applied science research vol. 8, no. 2, 2018, 2853-2858 2858 www.etasr.com jain et al: an enhanced binary classifier incorporating weighted scores [6] j. l. polo, f. berzal, j. c. cubero, “weighted classification using decision trees for binary classification problems”, ii congreso español de informática, pp. 333-341, zaragoza, spain, september 11-14, 2007 [7] c. chiu, y. ku, t. lie, y. chen, “internet auction fraud detection using social network analysis and classification tree approaches”, international journal of electronic commerce, vol. 15, no. 3, pp. 123-147, 2011 [8] h. neven, v. s. denchev, g. rose, w. g. macready, “training a binary classifier with the quantum adiabatic algorithm”, arxiv preprint arxiv:0811.0416, 2008 [9] a. quinn, a. stranieri, j. yearwood, “classification for accuracy and insight: a weighted sum approach”, proceedings of the sixth australasian conference on data mining and analytics, vol. 70, pp. 203208, australian computer society inc., 2007 [10] l. kuncheva, j. bezdek, r. duin. “decision templates for multiple classifier fusion: an experimental comparison”, pattern recognition, vol. 24, no. 2, pp. 299–314, 2001 [11] d. virmani, s. taneja, g. malhotra, “normalization based k means clustering algorithm”, arxiv preprint arxiv:1503.00900, 2015 [12] m. a. mazurowski, p. a. habas, j. m. zurada, j. y. lo, j. a. baker, g. d. tourassi, “training neural network classifiers for medical decision making: the effects of imbalanced datasets on classification performance”, neural networks, vol. 21, no. 2-3, pp. 427-436, 2008 [13] j. s. bridle, “probabilistic interpretation of feedforward classification network outputs, with relationships to statistical pattern recognition”, in: neurocomputing. nato asi series (series f: computer and systems sciences), vol. 68, pp. 227-236, springer, berlin, heidelberg, 1990 [14] machine learning depository, wholesale customers data set, https://archive.ics.uci.edu/ml/datasets/wholesale+customers [15] usarrests, http://stat.ethz.ch/r-manual/r-devel/library/datasets/html/ usarrests.html [16] “datasets distributed with r git source tree”, https://forge.scilab.org/ index.php/p/rdataset/source/tree/master/csv/datasets/attenu.csv [17] https://raw.githubusercontent.com/vincentarelbundock/rdatasets/master/ csv/datasets/quakes.csv [18] https://raw.githubusercontent.com/vincentarelbundock/rdatasets/master/ csv/datasets/volcano.csv [19] https://raw.githubusercontent.com/vincentarelbundock/rdatasets/master/ csv/boot/channing.csv [20] https://raw.githubusercontent.com/vincentarelbundock/rdatasets/master/ csv/boot/neuro.csv engineering, technology & applied science research vol. 8, no. 2, 2018, 2663-2667 2663 www.etasr.com ben khedher: numerical study of the thermal behavior of a composite phase change material … numerical study of the thermal behavior of a composite phase change material (pcm) room nidhal ben khedher mechanical engineering department college of engineering hail university hail, saudi arabia laboratoire d'études des systèmes thermiques et énergétiques ecole nationale d'ingénieurs de monastir university of monastir monastir, tunisia n.khedher@uoh.edu.sa abstract—in this study, thermal performance of building walls integrated with phase change materials (pcm) was evaluated in terms of indoor temperature reduction and heat transfer time delay. pcm was incorporated as thin layer placed longitudinally within walls. the thermal performance of a room with and without pcm was evaluated numerically. the developed model is based on the enthalpy formulation for pcm melting and solidification, which is solved by an implicit finite difference method. the effect of pcm type on heat gain indoors was studied. three phase change materials (n-octadecane, n-eicosane and calcium chloride hexahydrate) were tested in hot weather. results showed that octadecane is the best in ensuring an indoor temperature close to 27 °c for the test room. moreover, optimal thickness of the pcm layer within the walls is critical for heat transfer reduction and management and should be carefully chosen. keywords-pcm; passive cooling; energy storage; building i. introduction currently, research is focusing on the optimization of energy systems. one of the ways to save energy is the passive climate control. consequently, passive air conditioning systems, in which phase change materials (pcms) are used, have received particular attention in recent years [1-4]. the major reason for using these systems is the high energy capacity of some pcms during melting or solidification, compared to sensible heat systems. since, sensible heat storage requires large temperature differences. to raise these temperature differences consumes large amounts of energy. the advantage of some pcms, which is the large heat capacity during phase change, is that the latent heat-cooling of pcm is more economical while allowing the storage and release of energy at a constant temperature. integration of pcms in buildings is an interesting way to reduce energy consumption or to improve comfort [5-7]. for pcms, several criteria may be applied in order to select the appropriate one. various pcm types have been explored for passive air conditioning, including hydrides, salts and their mixtures, acids, paraffin and non-paraffin. pcms should have melting/freezing temperature in the practical range of application and they must have a high latent heat of fusion and a high thermal conductivity [8]. several researches were conducted to study the thermal behavior of the pcm room in summer. authors in [9] produced micro-encapsulated pcms which were used in the room walls while another room without pcm was built as reference. the pcm room can decrease the maximum temperature by 4oc in summer. authors in [10] experimentally investigated a new pcm wallboard, the experiments were carried out in a fullscale test room which was completely controlled. it was found that the indoor air temperature for the case without pcm fluctuated from 36.6 to 18.9 °c, whereas for the pcm case it is varying from 32.8 to 19.8 °c. authors in [11] tested pcms with two typical construction materials for mediterranean construction in real conditions. several cubicles were built and their thermal performance was analyzed. for each construction material, macro-encapsulated pcm was added in one cubicle (rt-27 and sp-25 a8). results showed that the pcm can reduce the peak temperatures up to 1 °c and reduce the daily fluctuations. moreover, it can reduce the electrical energy consumption by about 15%. authors in [12] studied the effects of the encapsulated pcm on the thermal performance of a brick masonry wall. the influences of the phase change process of the pcm over the attenuation of temperature fluctuations and time constant were essentially evaluated. this work deals with a numerical study of the thermal behavior of walls built with construction materials used in southern city in tunisia (gafsa) and in which pcms were added. the model, based on the enthalpy formulation, is described by an equation of heat transfer which is solved by an implicit method of finite differences. we analyzed the influence of wall thickness and its composition as well as the effect of pcm materials on the evolution of the indoor temperature. engineering, technology & applied science research vol. 8, no. 2, 2018, 2663-2667 2664 www.etasr.com ben khedher: numerical study of the thermal behavior of a composite phase change material … ii. physical model and mathematical formulation indoor temperature is an important parameter for the notion of comfort. in order to study the efficiency of wall/pcm without ventilation, thermal behavior was simulated by determining the evolution of the interior temperature of a room. a. physical model in order to predict the evolution of the indoor temperature of a room built by walls containing the pcm, a composite pcm room is considered. the dimensions of this room are shown in figure 1. the indoor temperature is calculated numerically by solving the equation of energy conservation of the air inside the room. the pcm wall is composed of two layers (figure 1): an ordinary wall that contains brick and cement mortar 0.25 m thick and a layer of microencapsulated pcm inside the room with 0.01 m thickness. fig. 1. pcm composite wall. b. mathematical formulation the heat transfer process is managed by the conduction phenomenon. the following assumptions were made when establishing the numerical model of the phase change process: 1) the heat transfer of the pcm envelop was one-dimensional, 2) the pcm was homogeneous and isotropic, 3) the convection effect in the molten pcm was neglected, 4) the thermophysical properties of the pcm are constant except the specific heat capacity during the melting and freezing process. the computational domain to be studied is composed of two sub domains (ordinary wall and pcm layer):  for ordinary wall (brick + mortar) the energy equation: 2 2 c . b b b p b b t t t x        (1)  for the pcm layer the numerical model was established by the sensible heat capacity method, the governing equation is:   2 ,, 2 pcm pcm pcm effpcm eff t t c t x        (2) the expression of   ,pcm eff c for the pcm is defined as below:         2 2 solid fusion h pcmsolid liquid solid liquid fusion fusionliquid c t t c c l t t t t t c t t t                               knowing that δt is the is the melting temperature range. 1) external conditions the outdoor side of the wall is subjected to a time dependent radiation and forced convection boundary conditions, with ho=20 w/m°c. the indoor surface is a free convection boundary condition with hi=10 w/m°c. the heat flow into the outdoor wall can be expressed as (3) or (4): os conv s correcq q q q   (3)    4 4os o o os s o surrq h a t t aq a t t       (4) where to is the outdoor air temperature, tos the outdoor surface temperature, α the solar absorptivity of the wall surface, and qs is the solar flux radiation. the last term in (4) represents the correction for the radiation heat transfer when the surrounding and the ambient temperatures are not equal. it is assumed that these two temperatures are equal in this study. the heat flow into the outdoor surface can be expressed as:  os o s osq h a t t  (5) where ts is the solar-air temperature, which is defined as: s s o o q t t h   (6) the boundary conditions were:  interface wall/pcm: , 1 1 pcm b pcm eff b x x x x t t x x           (7)  interface outdoor/wall:   0 b b out b out x t h t t x        (8) 2) model of the indoor air: the energy conservation equation for the indoor air is: r ,in , 1 v l n a p w s in win i dt c q q q q dt       (9) where vr represents room cubage, qw,in the convection heat transfer rate between air and inner surfaces of the room, qs,c the convection heat transfer rate from the indoor heat source, ql the heat transfer rate by air leakage and qwin the engineering, technology & applied science research vol. 8, no. 2, 2018, 2663-2667 2665 www.etasr.com ben khedher: numerical study of the thermal behavior of a composite phase change material … heat transfer rate through the window. qw,in, ql and qwin are calculated by the following equations:  ,in , ,w i w i i w iq h t t a    (10)  win win o i winq a t t u    (11)  rvleakage a p o iq c ach t t    (12) , 1, s in i i nbt q p    (13) where tw,i is the inner surface temperature of a wall, ceiling and floor while aw,i is its area. uwin and awin are overall heat transfer coefficient and the window area the respectively. pi is the heat generation rate by the equipment. iii. numerical treatment the equations set, with initial and boundary conditions have been solved numerically using the finite difference method. 2 1 1 2 2 2i i it t tt x x            (14) the energy equation after discretization: 2 0 1 12 p i i i i it t t t tc t x             (15) after factorization the energy equation becomes: 0 2 2 2 1 12p i p i i i ct t t t c x t x x t                        (16) the resulting algebraic system from assembling the contributions of all sub-volumes has the following general form 1 1i i ii i i i a t b t c t d        (17) with 0 2 2 2 2 , , , p p i i i i i c c t a b c d x x t x t                 the discretization of the heat equation over the entire domain allows us to obtain a tri diagonal matrix system. the resolution of this system was made by thomas's algorithm known by tdma (tri diagonal matrix algorithm). iv. results and discussion the effectiveness of the pcm_brick is evaluated by representing the indoor temperature evolution during three days of summer (july 2017) of a typical room situated in a tunisian southern city (gafsa). the room dimension are 5.0 m (length)×3.0 m (width)×3.0 m (height). the room walls are built from pcm brick (brick impregnated with pcm). total indoor heat generation rate by equipment, light and occupants etc. is assumed to be 100 w. the typical day weather of july in gafsa, is chosen as the outdoor climate data. hourly variation of outdoor air temperature and solar radiation are shown in figure 2. table i lists the main parameters of the studied room. 0 5 10 15 20 time (h) 20 24 28 32 36 40 t e m p e ra tu re ( °c ) 0 200 400 600 800 1000 r a d ia ti o n ( w /m 2 ) temperature (°c) radiation (w/m2) fig. 2. hourly variation of solar radiation and ambient temperature for a typical day of the month of july 2017 for tunisian southern city gafsa a. effect of pcm type the effectiveness of the pcm/wall system is evaluated by comparing the heat flux at its internal surface with that of a regular wall without pcm. the melting temperature of the three pcms chosen is close to the ambient temperature of a summer day. thermo-physical properties of these pcms are summarized in table i table i. thermal properties of wall and pcms material melting temprature (°c) λ (w/m°c) cp (kj/kgc°) ρ (kg/m3) lh mcp (kj/c°) brick wall 1.15 0.84 1600 noctadecane 27 0.385 (solid), 0.148 (liquid) 1.934 (solid), 2.196 (liquid) 865 (solid) 780 (liquid) 243.5 n-eicosane 37 0.15 (solid), 0.15 (liquid) 2.01 (solid), 2.04 (liquid) 778 (solid) 856 (liquid) 241 calcium chloride hexahydrate cacl26h2o 29 1.09 (solid), 0.54 (liquid) 2.4 (solid), 2.04 (liquid) 1710 (solid), 1500 (liquid) 164 figure 3 shows the variation of the indoor temperature for different pcms with layer thickness equal to 1 cm. it is clearly noticed that the addition of pcm to a wall results in the stabilization of the indoor temperature to a much lower temperature than that of an ordinary wall. in addition, it is noticed that octodecane stabilizes the internal temperature to a temperature close to its melting temperature. this result shows that octodecane stores heat in latent form by fusion at a constant temperature equal to its melting temperature. from figure 4, it is clear that octadecane is the more effective when compared to other tested pcms. since it has the most suitable melting temperature for the operating conditions (external engineering, technology & applied science research vol. 8, no. 2, 2018, 2663-2667 2666 www.etasr.com ben khedher: numerical study of the thermal behavior of a composite phase change material … temperature varies between 45 °c and 20 °c). moreover, the resulting indoor temperature lies in the comfort zone. for this reason we will choose the octadecane for the remaining tests. fig. 3. simulated hourly indoor air temperature for various types of pcm fig. 4. evolution of the pcm temperature at the node in the interior b. effect of pcm layer thickness the study of the influence of the pcm layer thickness on the variation of the internal temperature is very important for the optimization of wall/pcm performance. from figure 5 it is noted that the internal temperature for thickness equal to 0.5 cm has a peak and an overheating of 4 degrees after three days of operation. this behaviour is justified by the fact that the mass of octadecane for this thickness (0.5 cm) is not sufficient to store all the heat coming from the outside during three hot days of operation. consequently, extra heat is stored in the sensible form. hence the sudden increase in the internal temperature is noticed. however, for thickness greater than or equal to 1 cm, there is practically the same change in the indoor temperature. so, the thickness of pcm layer should be carefully optimized because of the high pcm cost. since, with 2cm thickness we have the same indoor temperature as with 1cm, it can be concluded that there is an optimum thickness allowing maximum efficiency and minimal economic cost. v. conclusion pcms used in buildings can enhance indoor thermal comfort and reduce energy consumption for space cooling and heating. in present research, a detailed study of three pcm layers combined in the building envelopes has been carried out to analyze the thermal performance in a typical city in tunisia during summer. generally, the efficiency of pcm application depends on the pcm selection of suitable melting/freezing point and latent heat. to enhance the applicability of walls fitted with a thin layer of pcm, a theoretical investigation of mathematical model has been explored in detail. current research finds that the octadecane layer with 1cm thickness performs well for the test room. pcm layer thickness is a critical parameter which should be carefully optimized. fig. 5. hourly variation of solar radiation and ambient temperature for a typical day of july 2017 for gafsa references [1] n. soares, j. j. costa, a. r. gaspar, p. santos, “review of passive pcm latent heat thermal energy storage systems towards buildings’ energy efficiency”, energy and buildings, vol. 59, pp. 82–103, 2013 [2] f. kuznik, d. david, k. johannes, j. j. roux, “a review on phase change materials integrated in building walls”, renewable and sustainable energy reviews, vol. 15, no. 1, pp. 379-391, 2011 [3] e. oro, a. de gracia, a. castell, m. m. farid, l. f. cabeza, “review on phase change materials (pcms) for cold thermal energy storage applications”, applied energy, vol. 99, pp. 513-533, 2012 [4] c. wani, p. k. loharkar, “a review of phase change materials as an alternative for solar thermal energy storage”, materials today: proceedings, vol. 4, no. 9, pp. 10264-10267, 2017 [5] y. cui, j. xie, j. liu, s. pan, “review of phase change materials integrated in building walls for energy saving”, procedia engineering, vol. 121, pp. 763-770, 2015 [6] c. amaral, r. vicente, p. a. a. p. marques, a. barros-timmons, “phase change materials and carbon nanostructures for thermal energy storage: a literature review”, renewable and sustainable energy reviews, vol. 79, pp. 1212-1228, 2017 [7] a. m. khudhair, m. m. farid, “a review on energy conservation in building applications with thermal storage by latent heat using phase change materials”, energy conversion and management, vol. 45, no. 2, pp. 263-275, 2004 [8] y. zhang, g. zhou, k. lin, q. zhang, h. di, “application of latent heat thermal energy storage in buildings: state-of-the-art and outlook”, building and environment, vol. 42, no. 6, pp. 2197–2209, 2007 [9] v. v. tyagi, d. buddhi, “pcm thermal storage in buildings: a state of art”, renewable and sustainable energy reviews, vol. 11, no. 6, pp. 1146-1166, 2007 engineering, technology & applied science research vol. 8, no. 2, 2018, 2663-2667 2667 www.etasr.com ben khedher: numerical study of the thermal behavior of a composite phase change material … [10] f. kuznik, j. virgone, j. j. roux, “energetic efficiency of room wall containing pcm wallboard: a fullscale experimental investigation”, energy and buildings, vol. 40, no. 2, pp. 148-156, 2008 [11] a. castell, i. martorell, m. medrano, g. perez, l. f. cabeza, “experimental study of using pcm in brick constructive solutions for passive cooling”, energy and buildings, vol. 42, no. 4, pp. 534-540, 2010 [12] r. vicente, t. silva, “brick masonry walls with pcm macrocapsules: an experimental approach”, applied thermal engineering, vol. 67, no. 12, pp. 24–34, 2014 engineering, technology & applied science research vol. 7, no. 3, 2017, 1664-1669 1664 www.etasr.com sabeti et al.: simulation of thermal stratification and salinity using the ce-qual-w2 model … simulation of thermal stratification and salinity using the ce-qual-w2 model (case study: mamloo dam) ramtin sabeti dpt of water resources engineering and management, islamic azad university, central tehran branch tehran, iran saeed jamali group of water engineering and hydraulic structure, faculty of civil engineering, islamic azad university, central tehran branch tehran, iran houman hajikandi jamali group of water engineering and hydraulic structure, faculty of civil engineering, islamic azad university, central tehran branch tehran, iran abstract—due to the shortage of fresh water, the quality of stored water in reservoirs has become increasingly important. thermal regime and salinity are factors that affect the quality of water reservoirs. these two parameters were studied in mamloo dam in tehran province. this dam has recently started to be uses as a source of drinking water for tehran and thus its water quality is of increased importance. in this regard, the hydrodynamic model for 2014 to 2015 was built and calibrated by the ce-qual-w2 model and the model was used to simulate the thermal regime and salinity up to 2020. two main scenarios were studied in this period, the continuation of the current situation or a 2.5% increase in water requirements and 5% decrease in discharge. the results show that the reservoir will experience thermal stratification in the summer and vertical mixing in the winter. dased on these results mamloo reservoir is in branch of warm monomictic lake. also results showed that thermal stratification and ssalinity stratification dominates simultaneity. besides this issue with 2.5% increase in water requirements and 5% decrease in discharge, duration of summer thermal stratification will decrease although intensity of thermal stratification will increase. keywords-thermal stratification; salinity; ce-qual-w2 model; mamloo reservoir i. introduction lakes and reservoirs are among the important resources of surface water. laminar flow in these resources leads to their stratification and slow movement. thermal regime in water quality models is important in two senses. firstly, temperature has a direct effect on the chemical reaction rate. secondly, thermal equilibrium has a great effect on mixing in fresh water systems [1]. thermal regime of the lakes is mainly the result of interaction between two processes of heat transfer at the lake surface and the effect of gravity on density difference. depending on the season, heat exchange at the interface of surface lake and the atmosphere leads to an increase or decrease in the temperature of water surface, which is caused by factors such as the amount of energy of the sun, air temperature, relative humidity, wind velocity, and percentage of sky cloud [2]. the wind blowing on the lake surface results in mixing of the surface part of the water and transfer of heat and momentum to the lower part. a buoyancy force exists against mixing, which prevents further mixing. this force is created by the density difference at different temperatures and causes the denser part of the water to be positioned at lower parts [3]. in the reservoirs and lakes of high length, using the averaged 2d model in the width is inevitable for accurate prediction of thermal stratification and water quality. a suitable and accurate method in 2d modeling is simultaneous modeling of the flow and qualitative parameters. fluid flow modeling is performed using the mass, momentum, and energy conservation equations. in many turbulent flows, the reynolds equations modeling the averaged 3d turbulent fluid flow in time can be used. furthermore, mathematical models are developed depending on the spatial and temporal changes, the factors influencing the conditions of aquatic ecosystems, especially dam reservoirs [4]. selecting a model consistent with the conditions and effective factors, as well as the available information and data, is one of the fundamental steps in mathematical simulation of aquatic ecosystems, namely dam reservoirs. ce-qual-w2 software is a 2d model (horizontal and vertical) for water quality and hydrodynamic, which can model structures such as deep rivers, dam reservoir, lakes, and estuaries. this model was developed in 1995 by water estuary studies (wes) of the engineers of us army, and works based on solving non-permanent, 2d, hydrodynamic, and dispersion equations [5]. in this study, the thermal stratification and salinity of mamloo dam reservoir is modeled using the 3.7 version of this software introduced in 2012. ii. the studied region mamloo dam reservoir is located on jajrood river, about 45 km from east of tehran. the studied region is located between 32-35 northern latitude and 38-52 eastern longitude of the equator, which is a part of tehran province regarding the divisions of the country [6]. the purpose of building this dam was to take advantage of the capacity of catchment area of jajrood river and supply the agricultural water of varamin and pakdasht and part of the need for drinking water in tehran. engineering, technology & applied science research vol. 7, no. 3, 2017, 1664-1669 1665 www.etasr.com sabeti et al.: simulation of thermal stratification and salinity using the ce-qual-w2 model … dam operations started in august 2002 and ended in 2010. the type of dam is soiled with clay core and ogee spillway, 89 m height from foundation, 27 m width in the foundation, and 10 m width in the dam crest. reservoir volume is 250 m3, the lake area is 620 acres, and the lake length is 8500 m [7]. the concentration of different qualitative parameters in the reservoir changes with the input concentration and thermal stratification in depth. the tds (total dissolved solid) concentration is usually higher in the lower layers than the upper layers. the project of water supply from mamloo dam to tehran city for drinking and domestic usage has been implemented during recent years, and has added to the importance of the water quality of this reservoir. given the issues discussed above, studying the salinity and thermal regime of mamloo dam reservoir is an important step in controlling its water quality. iii. model development the input information required for simulating temperature and salinity in the software are: simplified dimensions of the reservoir, meteorological information (air temperature, dew point, wind direction and velocity, cloud cover), input and output flow rates, temperature of input flows, water temperature in depth, tds at different times and depth intervals, hydraulic conductivity of lateral branches, and boundary conditions [8]. the geometrical shape of mamloo dam reservoir was divided into a primary branch with 21 longitudinal elements, each having 200 m length, by 1:10,000 maps provided by tehran regional water organization. reservoir depth was also divided into 37 elements of 1, 2, and 3 m depth. figure 1 shows a view of the geometrical model of mamloo sam reservoir. fig. 1. a view of the geometry of mamloo dam reservoir in ce-qual-w2 software the output spillway level of this reservoir is 1,224 m from sea level, and the minimum production level is 1,169 m from the sea level. this data was also fed to the model. to develop the model, the water year data from 2014 to 2015, taken from tehran regional water organization, were used, and the hydrodynamic model was developed. calibration of the hydrodynamic model was done in two steps: the first step was done by matching the volume/height plots obtained by simulation results and the real data of mamloo dam. in the second step, the water height obtained by simulation was matched with the real height by controlling the input and output flows of the reservoir. qualitative calibration also consists of two steps: thermal and salinity calibration. in thermal calibration, first, the most important parameters were specified by performing a sensitivity analysis on the parameters involved in thermal modeling of the reservoir; then, integration of simulation results with observations was done by changing the parameters. table i shows the results of sensitivity analysis with respect to the temperature in mamloo dam reservoir. the closer the coefficient of sensitivity of the parameters to 1, the higher the effect of that parameter. coefficients less than 0.5 usually have no effect and don’t require investigation. this way, the wind impact factor was selected as the most effective parameter in thermal calibration of mamloo dam reservoir. table i. temperature sinsitivity coefficient in the reservoir with respect to the changes in that parameter coefficient the value of impact factor longitudinal viscosity of eddy 0.17 longitudinal dispersion of eddy 0.21 chezy or manning coefficient 0.05 wind impact (wind power) 0.85 absorption of solar radiation at the surface 0.13 light reduction in clean water 0.17 light reduction in non-organic solid material 0.11 light reduction in organic solid material 0.07 simulation of thermal conditions and tds for future years was performed assuming a continuation of the current situation or a 2.5% increase in water demand and a 5% reduction in the amount of water discharge. according to the information of tehran regional water organization and meteorological department, the weather of the region studied was relatively unstable, and its wind impact factor for correcting the effect of wind velocity measurement was far from the dam reservoir, varied from 0.5 to 0.9 for mountain areas and foothills, and equal to 1 for open and flat land. given the topography of the region, this coefficient was selected to be 0.86 at the beginning of calibration. the above procedure was also used for salinity engineering, technology & applied science research vol. 7, no. 3, 2017, 1664-1669 1666 www.etasr.com sabeti et al.: simulation of thermal stratification and salinity using the ce-qual-w2 model … calibration, except that the amount of input tds, input layer, and overpass and underpass at time of entering the reservoir were evaluated in this stage. qualitative information of 20142015 water years was used for calibration and validation of the model. the calibrated model was validated land application; thereupon the two qualitative scenarios above were selected for modeling. iv. discussion and conclusion in most parts of the world, the surface of lakes and reservoirs passes through a specific temperature cycle during the year. temperature trend of mamloo dam in the reservoir depth, based on the assumptions made regarding continuation of the current situation, 2.5% increase in water demand, and 5% decrease in the amount of water discharge, in 2020 is shown in figure 2 and figure 3. the main reasons for temperature variation in water depth are thermal contact with the atmosphere and changes in the amount of solar radiation. heat transfer from the surface to depth is often affected by solar radiation, long wave radiation of the atmosphere, thermal flows associated with evaporation and precipitation, surface and sub-surface inflow and outflow, and thermal contact with the lake bed [9]. fig. 2. temperature variation in mamloo dam reservoir depth, assuming continuation of the current situation until 2020 fig. 3. temperature variation in mamloo dam reservoir depth, assuming a 2.5% increase in water demand and a 5% reduction in water discharge until 2020 it is clear from figure 2 that assuming continuation of the current situation until 2020, temperature difference between superficial and deep layers increases in the time interval from october to april and a thermal stratification forms. the maximum temperature gradient and stratification peak is also observed in summer. after the hot season, the layers at different depths experience thermal mixing and the thermal stratification in the reservoir breaks down. stratification intensity decreases by cooling the air, and the thermal mixing conditions in the reservoir will be re-achieved in autumn. in case of a 2.5% increase in water demand and a 5% reduction in water discharge, as shown in figure 3, the thermal regime in the reservoir doesn’t change, but it increases when the reservoir experiences thermal mixing, following which a reduction in stratification time of the reservoir is observed. given the numbers of the sluice located at the level close to the bottom of the reservoir, further water exploitation reduces the retention time of deep layers and helps vertical mixing in the reservoir. in other words, further water exploitation brings the reservoir closer to optima; production level in terms of temperature. tds variation in reservoir depth up to 2020 water is shown in figure 4 and figure 5. fig. 4. tds variation in reservoir depth, assuming continuation of the current situation until 2020 fig. 5. tds variation in reservoir depth, assuming a 2.5% increase in water demand and a 5% reduction in water discharge until 2020 engineering, technology & applied science research vol. 7, no. 3, 2017, 1664-1669 1667 www.etasr.com sabeti et al.: simulation of thermal stratification and salinity using the ce-qual-w2 model … comparing these two figures with figures 2 and figure 3 indicates that tds follows the trend of temperature variation, and a change in tds is observed whenever there is any temperature change. however, given the dependency of tds to the elements dissolved in it, other reactions and the amount of tds input cannot be evaluated only by temperature profile. therefore, it can be argued that tds changes with changing temperature, so that whenever there is a temperature change in the reservoir, changes in tcs concentration will be observed as well. more importantly, an increase in tds concentration is observed in any part with intensive thermal gradient. studying the surface temperature variation of different lakes at similar weather conditions, it was found that the average daily temperature of different lakes are similar; there is only a little difference between them in spring. in hot seasons and during summer, smaller lakes tend to absorb heat more quickly [10]. it is the mixing properties of the lake that determines how effectively and to what extent does the temperature transfers vertically to depth. if the surface temperature of dam reservoir exceeds 4˚c, it warms up and becomes less dense, so there is the possibility of mixing up to a more limited depth. this depth depends on the limited energy provided by the wind. in most reservoirs, like mamloo dam reservoir, thermal stratification in the summer period starts by starting the density difference. in deep lakes, the thermal stratifications remains until the cold weather of autumn and winter creates a circulation in deep waters. the warmer surface layer of water is called epilimnion, while the lower cooler layers not mixing with the epilimnion during stratification is called hypolimnion. a clear temperature gradient is formed at the interface of these two layers, called thermocline or thermo-layer. in summer stratification conditions, a metalimnion forms between epilimnion and hypolimnion, which connects to these two layers by thermocline. figure 6 shows these layers in thermal profile of mamloo dam reservoir at 50 m distance from dam crest. the profile of temperature variation in mamloo dam reservoir depth for different seasons of the year is shown in figures 7 and figure 8. to plot the results, the first day of the last month in each season was taken as indicator of each season. the profiles obtained for autumn and winter show complete thermal mixing at reservoir depth. the surface layer gets warm in autumn and winter by solar radiation and contact with the atmosphere, bit the deeper layers are preserved from the main source of heat. fig. 6. thermal stratification formed in summer 2020 in mamloo dam reservoir fig. 7. temperature profile of mamloo dam reservoir in a 100 m distance from the dam crest during 2020, assuming continuation of the current situation engineering, technology & applied science research vol. 7, no. 3, 2017, 1664-1669 1668 www.etasr.com sabeti et al.: simulation of thermal stratification and salinity using the ce-qual-w2 model … fig. 8. temperature profile of mamloo dam reservoir in a 100 m distance from the dam crest during 2020, assuming a 2.5% increase in water demand and a 5% reduction in water discharge figure 7 and figure 8 show that thermal stratification in mamloo dam reservoir starts to form at the beginning of spring, and reaches its peak in summer. epilimnion and atmosphere exchange heat and volatile components such as different gases. this layer randomly rotates and mixes under the influence of wind and climate changes during stratification period. in contrast, the hypolimnion has no interaction with the atmosphere and transfer of the dissolved materials is partially done by the metalimnion and thermo-layer, which have high temperature gradient. in many lakes, only chemical deposition transfers a great deal of materials from the metalimnion. wind is a decisive factor in the thickness of epilimnion in most of the lakes. in lakes with very low wind velocity, other factors may have the primary role, one example of which is a very clean and transparent lake, in which the light can diffuse to the depth greater than the depth of wind mixing [11]. there are also situations in which gas molecular diffusion is the main factor determining the ice layer thickness at surface of the lake. in mamloo dam reservoir, the thickness of epilimnion is not constant during stratification period. a thin layers forms in spring, which gradually thickens in summer due to the light flow of wind. this situation continues until autumn, when the stratification gradually disappears by the surface cold water. therefore, identifying simple method for measurement or determination of epilimnion thickness is very useful in the study of water resources. all results proved that mamloo dam reservoir is in the category of warm monomictic lakes. warm monomictic lakes are located in low levels and low latitudes, in which the temperature of the lake doesn't exceed 4ᵒc. in this kind of lakes and reservoirs, thermal stratification is once done in summer and complete mixing is once done in winter. given the position of our country in terms of altitude and geographical location, most of the dams in the country are located in this region, and most of the reservoirs, especially deep reservoirs, namely mamloo dam reservoir, are located in the warm monomictic region. figure 9 and figure 10 show tds in mamloo dam reservoir depth during 2019-2020 water years. according to tds profile, assuming continuation of the current situation, tds variation hasn't significantly changed with respect to the changes in the input, and it preserves the prevailing regime. assuming a 2.5% increase in water demand and a 5% reduction in water discharge, the results indicate that no changes has occurred in this parameter by increasing mixing power of the reservoir. therefore, the results imply higher dependence of tds to the input. mamloo dam reservoir experiences one stratification and one complete mixing during a year and fits into the category of warm monomictic lakes. this type of lakes is located in low levels and low latitudes, in which the average temperature of the lake never exceeds 4ᵒc [12]. in this summer, stratification forms in summer and complete mixing occurs in winter. given the position of our country in terms of altitude and geographical location, most of the dams in the country are locates in this region, and most of the reservoirs, especially deep ones, such as mamloo dam reservoir, are located in warm monomictic region. in hot seasons when there is thermal stratification, tds also experiences stratification according to similar studies, and it decreases with increasing depth. thereupon, the necessity of documenting this parameter and investigating the conditions prevailing at the bottom of mamloo reservoir is of great importance. assuming continuation of the current situation or a 2.5% increase in water demand and a 5% decrease in the amount of water discharge until 2020, this lake will still remain in the category of warm monomictic lakes. v. suggestions exploiting water from lower lakes of the reservoir helps its vertical mixing and reduces the thickness of hypolimnion and the time required for creation of thermal stratification conditions. discharging the depositions from the reservoir helps to reduce retention time and thickness of the hypolimnion. regular qualitative measurements in reservoir surface and depth are an important step in formulating a management pattern suitable for this reservoir. increasing field studies provides the possibility of long-term prediction of the reservoir conditions prevailing in mamloo dam reservoir, and increases the confidence interval of the decisions. it is suggested to use ce-qual-w2 model in 2d modeling of other reservoirs in tehran province, so that an integrated management pattern could be formulated using the results of these studies. engineering, technology & applied science research vol. 7, no. 3, 2017, 1664-1669 1669 www.etasr.com sabeti et al.: simulation of thermal stratification and salinity using the ce-qual-w2 model … fig. 9. tds profile of mamloo dam reservoir in a 100 m distance from the dam crest during 2020, assuming continuation of the current situation fig. 10. tds profile of mamloo dam reservoir in a 100 m distance from the dam crest during 2020, assuming a 2.5% increase in water demand and a 5% reduction in water discharge references [1] j. soltani, m. r. alavi moghadam, “the effect of thermal stratification on water quality in iran's dams-an overview”, proceedings of 8th national conference of environmental health, tehran, iran, vol. 1, no. 1, pp. 8-10, 2005 [2] e. g. chung, s. g. schladow, j. perez-losada, d. m. robertson, “a linked hydrodynamic and water quality model for the salton sea”, hydrobiologia, vol. 604, no. 1, pp. 57-75, 2008 [3] b. klein, w. roether, b. b. manca, d. bregant, v. beitzel, v. kovacevic, a. luchetta, “the large deep water transient in the eastern mediterranean”, deep sea research part i: oceanographic research papers, vol. 46, no. 3, pp. 371-414, 1999 [4] h. hekmatifar, m. nazariha, s. givehchy, “the assessment of agriculture damages due to flood by using modeling in arc view & hec-ras”, journal of environmental science and technology, vol. 11, no. 4, pp. 15-20, 2009 [5] t. m. cole, s. a. wells, ce-qual-w2: a two-dimensional, laterally averaged, hydrodynamic and water quality model, version 3.7, user manual, washington, dc, 2011. [6] a. g. behbahani, k. khoshbakht, a. davari, l. tabrizi, h. veisi, a. alipour, “assessing the effect of socio-economic factors on agrobiodiversity in homegardens of jajrood and jamabrood in tehran province (iran)”, advances in environmental biology, vol. 2, no. 1, pp.1708-1716, 2012 [7] tehran regional water organization, water supply project to tehran, 2010. [8] ministry of power, guidelines for water quality studies of large reservoirs, tehran publication, 2010 [9] d. m. imboden, a. wüest, “mixing mechanisms in lakes” in: physics and chemistry of lakes, springer berlin heidelberg, 1995 [10] b. boehrer, m. schultze, “stratification of lakes”, reviews of geophysics, vol. 46, no. 2, pp. 10-15, 2008 [11] m. sicard, c. pérez, f. rocadenbosch, j. m. baldasano, d. garcíavizcaino, “mixed-layer depth determination in the barcelona coastal area from regular lidar measurements: methods, results and limitations”, boundary-layer meteorology, vol. 119, no. 1, pp. 135-157, 2006 [12] p. r. kannel, s. r. kanel, s. lee, y. s. lee, t. y. gan, “a review of public domain water quality models for simulating dissolved oxygen in rivers and streams”, environmental modeling & assessment, vol. 16, no. 2, pp.183-204, 2011 microsoft word 11-743-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1167-1174 1167 www.etasr.com sangrody and shariatmadar: a lyapunov function for vector control drives in induction machines a lyapunov function for vector control drives in induction machines reza sangrody department of electrical engineering firoozkooh branch, islamic azad university firoozkooh, iran rezaa_sangrody@yahoo.com seyed mohammad shariatmadar department of electrical engineering naragh branch, islamic azad university naragh, iran shariatmadar@iau-naragh.ac.ir abstract—in this paper a useful lyapunov function for vector control of induction machines is introduced. to do this, some beneficial theorems are reviewed and by applying these theorems and state equations to a vector control drive, its candidate lyapunov function is achieved. range of set points such as reference speed, reference flux linkage values and speed controller gain is obtained for such a drive and therefore these values can be set offline to avoid unstable behavior. the simulated and experimental results are given in the last section of the paper to show the efficacy of the given lyapunov function. keywords-lyapunov function; stable area; vector control drives i. introduction a linear system shows stable, unstable, or oscillated responses; however, in a nonlinear system other kinds of behaviors such as bifurcated, chaotic and sub harmonic may occur. electric machines are highly nonlinear systems because they have mutual dynamics. in addition, electric drives, or other controller types, are implemented in electric machines to control their speed, torque and thus also result to a nonlinear behavior. these time responses are not acceptable except the stable cases from an application point of view. it is obvious that these nonlinear behaviors cause fluctuation in electromagnetic torque, speed of the rotor, current and voltage components, flux linkages, etc. strange time responses in electric machines drives such as induction machines, synchronous reluctance machines, permanent magnet synchronous machines, dc machines, brushless dc machines , etc. has been reported in several paper [1-7]. nowadays vector control drives of induction machines are more suitable for a variety of applications such as trains, conveyer belts because of their dynamical behavior as well as for having a tough structure and cheap price. as mentioned, these drives may represent stable, unstable and chaotic responses. there are some researches that show the bifurcated and chaotic response of these drives caused by different reasons like inverter malfunction [8, 9], error in parameters' values like rotor and stator resistances [10-13] or even because of an inherent nonlinearity of the system [14]. some researchers used poincare map to study these behaviors. the poincare map is a powerful method to investigate the strange behaviors such as chaotic and bifurcated ones [14, 15]. this map is useful for power electronic systems such as dc-dc choppers. however, it is not useful and applicable enough to analyze the stability of other systems such as induction machine drives which are the case study of this paper. one of the most powerful methods to study the global stability of nonlinear systems is the lyapunov method. using a lyapunov function is the main core of the method. finding these functions for nonlinear systems is difficult. suitable theorems to evaluate the stability of nonlinear systems are needed [14]. in this paper these theorems are used to achieve a useful lyapunov function for vector control drives in induction machines. ii. candidate lyapunov function for transformed dynamics finding the lyapunov function for a nonlinear system is very important, because stability analysis or controller design such as sliding mode controller, adaptive control, etc. are based on this function. according to the lyapunov theory there is a nonlinear system such as:   nrxxfx  (1) if a function such as rrv n : with the following conditions exists then the origin ( 0x ) is a stable equilibrium state for this system: 0)0(,0)0( ∞→)(;∞→ 0)( 0)(    vv xvx xv xv   (2) the shortcoming of this theorem is that there is not a unique method to obtain a lyapunov function. sometimes this theorem is named lyapunov direct method. there is another theorem based on linearized dynamical equations of a nonlinear system. it talks about local stability conditions for the equilibrium states of a system. this method is called indirect lyapunov method in nonlinear system theory. engineering, technology & applied science research vol. 6, no. 5, 2016, 1167-1174 1168 www.etasr.com sangrody and shariatmadar: a lyapunov function for vector control drives in induction machines in [14], it was shown that if there exists a lyapunov function like )( xv for nonlinear system such as (1), then what can be concluded about the stability of a system such as: )(1 xfhx  (3) this system is a transformed system and two theories are introduced in [16] to achieve its lyapunov function. the origin will be stable equilibrium point for this system if there exists a positive function )( xg that satisfies the following conditions. 0)))(()(( 2  hdxxvxg t (4) and )( xg will exist if the following matrix be symmetric:                            h xv x xg x xv xv x xg x xv xv x xg x xv t nn t t                                                                    2 2 2 22 2 2 11 2 ln ln ln  (5) one of the most applicable lyapunov functions is quadratic function. its global form is:   pxxxv t (6) in this equation p is a positive matrix. by using the above method, if system (1) has a quadratic lyapunov function and ph is positive and symmetric, its transformed system such as (2) has a quadratic lyapunov function. its lyapunov function is :    phdxxxw t (7) it can be shown that dynamical equation of almost all rotational electric machines is:                               xnx xnx xnx axhx n t t t   2 1 1 (8) x , 1h and a are originated from current components, inductance, moment of inertia, and resistance of machine. also the other states ( xnx i t ) are originated from rotational voltages. this dynamic system is a transformed system therefore the above mentioned method can be used to study its stability. if a quadratic function such as (5) is found in a way that ph is positive and symmetric and the following condition is satisfied: 02 1                xnx xnx xnx px n t t t t  (9) then (6) shows its lyapunov function. iii. rotor field oriented vector control system to investigate the stability of a system, first its model must be decided. the electrical model of squirrel cage induction machine in the synchronous reference oriented to the arbitrary g  flux linkage vector frame is shown in (10) [17].                      gg ggg g g rrgrs sgsss r s jir jiru dt d             (10) in these equations, gs i   , gr i   , gs   and gr   are current and flux linkage vectors of stator and rotor, respectively which can be expressed according to direct and quadrature components of stator current ( sxi , syi ) and direct and quadrature components of rotor current ( rxi , ryi ). ryrxr sysxs smrrr rmsss jiii jiii ilil ilil ggg ggg               (11) also gs u   is voltage vector of stator, g and r are angular speed of the frame and rotor respectively, which can be achieved by mechanical equation.   lrsrmr tbiipl dt d j gg      5.1 (12) in this equation  shows the vector product. using this model, rotor field oriented vector control of induction machines can be achieved. suppose the frame is oriented tor the rotor flux linkage so: grrx     (13) sy r m ryry i l l i  0 (14) the electrical equation of the rotor can be decoupled to the real and imaginary parts.   0 rxryrgrxr dt d ir  (15)   0 ryrxrgryr dt d ir  (16) using (13), (14), (15), and (16) it can be written as: engineering, technology & applied science research vol. 6, no. 5, 2016, 1167-1174 1169 www.etasr.com sangrody and shariatmadar: a lyapunov function for vector control drives in induction machines 0 rxrxr dt d ir  (17)   ryr rx rg ir    (18) the first equation shows rxi is affected by direct component of rotor flux linkage, therefore when its variation is slow or even it is constant in the steady state, rxi becomes zero. as a result the motor torque can be written as:  rsme iiplt   5.1 (19) sxmrrx ilr    (20) equation (20) shows that rotor flux can be controlled by direct component of stator current and therefore from (19) the torque can be controlled by quadrature component of stator current. as a result the goal of the vector control is satisfied. to implement this control two problems remain. the first one is that the rotor flux linkage vector must be tracked. to do this, (18) can be used to produce: dt i i dt syr sx rgr             (21) the second one is that the direct and quadrature current components must be produced. if the voltage source inverter is used to produce these components, a control strategy will be needed to produce them. to do this, each component of stator voltages such as sxu is divided into two components ( dxxsx uuu  ). one of these components ( xu ) is used to control the same current component ( sxi ) and the other is supplied to control the other component ( syi ): sygsxsxsdxxsx dt d iruuu   (22) sxgsysysdyysy dt d iruuu   (23) sysgsygdx ilu   (24) sxsgsxgdy ilu   (25) in these equations          r m ss l l ll 2 is the stator transient inductance. by using reference values of current instead of their actual values, the voltage references for inverter are achieved. flux linkage is controlled by reference direct current component, but reference quadrature current component is adjusted to control the speed because this component controls torque. therefore reference current components are defined as: m ref sxref l i   (26)    dtkki rrefirrefpsyref     (27) a rotor flux oriented vector control model can be written according to the above discussion.                      1d i i i i dt d i r ry rx sy sx                                               rref lrrysxrxsym rxrsxm sxrefr syref ryr ryrsym sxrefr syref rxr rxmsxssyssxrefssyrefs rymsyssxssyrefssxrefs tbiiiipl j ilil i i ir ilil i i ir ililmirimlir ililmirimlir     5.1 1 (28) in these equations          sxrefr syref r i i m   and 1d is :                          l l sm sm mr mr l l l ll ll ll ll l d 00000 00000 0000 0000 0000 0000 11 (29) 2 mrsl llll  figure (1) depicts a rotor field oriented vector control drive. fig. 1. rotor field oriented vector control drive. engineering, technology & applied science research vol. 6, no. 5, 2016, 1167-1174 1170 www.etasr.com sangrody and shariatmadar: a lyapunov function for vector control drives in induction machines iv. stability analysis of the system to study the stability analysis of a rotor field oriented vector control at first the equilibrium point of (28) must be obtained. the zero state of the dynamical equation of the system must be transformed to the origin. when the speed controller is only proportional controller, the equilibrium point of this system is [14]: r psxrefm lref r psxrefm r sxrefm rl ryry m r syrxsxrefsx l kipl b t l kipl ipl bt ii l l iiii      2 2 * * ***** 5.1 5.1 5.1 ,,0,              (30) but when the speed controller is proportional-integral, the equilibrium is [14]:    i sy irefr sxrefm rl ryry m r syrxsxrefsx k i ipl bt ii l l iiii * ** * ***** , 5.1 ,,0,    (31) for simplicity the proportional speed controller is considered. the new variables for the new system are chosen as: * 5 * 4 * 3 * 2 * 1 , ,, rrryry rxrxsysysxsx xiix iixiixiix    (32) therefore dynamical equations of the new system are:                      sxrefr rrefp r sxrefr rrefp sxrefrysymte te mrr r mp mrr mssps mssps i xk t x i xk s ixixxxixxplt bxt jdt dx xlxltxr x lk xlxltxr xlxlsxrxkr xlxlsxrxksl l x x x x dt d            * 5 * 5 * 5 4 * 141 * 23 5 5 134 5243 3125 4215 1 4 3 2 1 5.1 1                                            (33) l is machine inductances given bellow:                rm rm ms ms ll ll ll ll l 00 00 00 00 (34) this system's equation is similar to equation (7). in this equation h and in are given below:          j l h 1 0 0                      0 2 0 2 0 2 0000 00000 2 0000 00000 1 ms m s mlml ml ml n                         0 2 0 2 0 2 0000 00000 2 0000 00000 2 ms m s mlml ml ml n (35)                         0 2 0 2 0 2 0000 00000 2 0000 00000 3 ms m s mlml ml ml n                      0 2 0 2 0 2 0000 00000 2 0000 00000 4 ms m s mlml ml ml n                              00000 0000 2 3 000 2 3 0 00 2 3 00 0 2 3 000 5 j pl j pl j pl j pl n m m m m engineering, technology & applied science research vol. 6, no. 5, 2016, 1167-1174 1171 www.etasr.com sangrody and shariatmadar: a lyapunov function for vector control drives in induction machines          sxrefr p i k m   1 sxrefr p i k n   according to (7) matrix p can be:                    p j p 3 2 0000 01000 00100 00010 00001 (36) this matrix satisfies the conditions mentioned in section2.the lyapunov function of the system is obtained according to (7):   2 53131 2 4 2 3 2 2 2 1 2 3 2 22 x p j xxlxxl xlxlxlxlxw mm rrss   (37) boundary of different parameters such as speed controllers values, the reference speed, or flux values to have stable response can be achieved using this lyapunov function. to do this time derivation of this function must be negative. v. experimental approach an experimental prototype was prepared by the authors to verify the analysis. a laboratory 175 w and four pole three phase induction motor whose parameters and characteristics are shown in table i is used. at91sam7s64 microcontroller is used to implement the rotor speed calculation and filtering, speed controller, and processing operation including the calculation of reference voltage values for inverter, pulsewidth-modulation (pwm), dc bus voltage control, reference values setting such as reference speed and reference flux linkage, etc. table i. induction motor parameters parameter description value rs stator resistor 43.1 ω rr rotor resistor 72 ω ls stator inductance 1.995 h lr rotor inductance 1.995 h lm mag. inductance 1.96 h j moment of inertia 0.0024 kgm b friction coefficient 0.001 kgm/s tl no-load torque 0.1 nm this microcontroller can work with 55 mhz clock signal but it was used with 48 mhz clock and has arm core therefore it can be used for this drive which needs high speed processing operation. to measure the speed of the rotor a 2000pulse/revolution speed encoder is connected to the shaft of rotor. its pulses after a voltage level adjusting are used for counter of the microcontroller. microcontroller gives the actual speed by calculating the speed and filtering it by an fir filtering and a low-pass filter to neutralize the quantization error and noise. a logic operation board is designed to operate on pwm pulses produced by microcontroller. these pulses after high-speed optocouplers are delivered to the power section. an inverter with igbt switches, rc snubber circuit, and high-speed anti-parallel power diodes is designed to supply the motor. fig. 2. experimental set-up diagram. fig. 3. vector control response: (a) flux linkage response, (b) torque response pwm pulses are delivered to igbt driver circuits to turn the igbt switches on or off. also a 530-volt dc bus voltage is designed using three phase voltages, rectifiers, ntc resistors, relay, capacitors, discharge circuit, etc. the output current is (a) (b) engineering, technology & applied science research vol. 6, no. 5, 2016, 1167-1174 1172 www.etasr.com sangrody and shariatmadar: a lyapunov function for vector control drives in induction machines monitored using a shunt resistor and a digital oscilloscope. figure (2) shows the block diagram of experimental setup. figure (3) shows dynamical response of the system depicted in figure (1). as illustrated in figure (3a) when the value of flux reference is changed, electromagnetic torque of the motor does not affected. also, as seen in figure (3b) when the load torque is changed, the value of flux fluctuates negligibly. table ii. equilibrium points for three set points case ref ref pk *syi * rxi * ryi * r * i 1 230 0.95 2 0.48 0.11 -0.11 230 1.18 2 230 0.1 5 0.05 1.12 -1.12 230 1.12 3 130 0.95 2 0.48 0.08 -0.08 130 0.82 table ii shows three set point and speed controller values for rotor field oriented vector control drive and also their equilibrium states calculated by (30). figures (4a) and (4b) illustrates dynamical responses of the system by changing the set points from case 1 to case 2 at t=6.98 sec. as shown in these figures, the system response is stable in case 1 and is unstable in case 2. these results are shown in [14] that the case 2 has a chaotic response. figure (5) portrays the lyapunov time derivative for two cases. as shown in case 1, time derivation of the lyapunov function becomes negative and remains until zero which shows that this set point is stable. when the set point changes to case 2, time derivative of lyapunov function becomes positive and negative alternatively which shows that the system response converges to the equilibrium point and then diverges from it. fig. 4. current responses of cases 1 and 2: (a) simulation, (b) experimental fig. 5. derivation value of lyapunov function for cases 1 and 2. it is clear that there is a stable region in the phase plane. it is obtained numerically for both cases.  xw for sradref /230 , wbref 95.0 , 2pk and 1.0ik is:   6154151 411656462 53232522 2 554535 2 4 2 3 2 2 2 1 007.0048.009.0 8.12495.906.209.2 48.0804.12459.4141.63 000067.063.4004.006.0 93.2093.2093.2093.20 xxxxxxx xxxxxxxxx xxxxxxxx xxxxxx xxxxxw      (38) figures (6) shows the area in which the  xw is negative for case 1 and 2, respectively. for these cases the other three states vary between -0.1 and 0.1. according to the lyapunov theorem the case 1 is stable and the case 2 is not stable because in case 1 there is an area around the origin in which  xw is negative. but in case 2 there is not such an area around the origin, so it is not stable. the phase plane trajectories for these cases are also shown in these figures. note that these trajectories do not intersect with each other in the space. fig. 6. area of negative lyapunov time derivative. (a) stable area for case 1. (b) stable area for case 2. (c) stable area for case 1 (magnified). (d) stable area for case 2 (magnified). as discussed above, the trajectories of the system cannot settle down to the origin in case 2 because the derivation of lyapunov function is not negative even in a small area around (a) (b) (a) (b) (c) (d) engineering, technology & applied science research vol. 6, no. 5, 2016, 1167-1174 1173 www.etasr.com sangrody and shariatmadar: a lyapunov function for vector control drives in induction machines the origin. generally speaking, this fact can be used to determine whether or not a case has a stable condition. as an example, consider the following case (case 3). figure (7) shows the area in which time derivative of lyapunov function is negative. as it is obvious there is an area around the origin in which the time derivative of lyapunov function is negative. therefore this case is a stable case. figures (8a) and (8b) illustrate the simulated and experimental response of the drive for case 3, respectively. the state space trajectory is given in figure (7). fig. 7. stable areas for case 3: (a) stable area for case 3, (b) stable area for case 3 (magnified). fig. 8. current responses for case 3: (a) simulation (b) experimental this method can be used to find the range of speed controller's gain values, reference flux, reference speed, etc. for stable responses. the figure (9a) and (9c) illustrate the area in which time derivative of the lyapunov function is negative for different speed proportional controller gains. as shown, there is a range of this parameter which makes the system to be stable. also figure (9b) and (9d) show the areas for different reference flux linkages. also in these cases there is a range of flux linkages which makes the system stable. fig. 9. area of negative lyapunov derivation for different parameters. (a) different kpω (b) different ψref (c) different kpω (magnified) (d) different ψref (magnified). vi. conclusion in this paper a useful lyapunov function is achieved for vector control drives of induction machines. stable range of set points such as reference flux linkage, speed or other parameters of the system can be investigated using this function. by obtaining this stable condition for each drive, they can be set offline to avoid unstable response or chaotic behavior. acknowledgment this paper is result of a research sponsored by firoozkooh branch, islamic azad university, firoozkooh, iran. references [1] z. park, j. b. park, y. h. joo, b. zhang, g. chen, “bifurcation and chaos in a permanent magnet synchronous motor”, ieee transaction on circuits-i, vol. 49, pp. 383-387, 2002 [2] d. q. wei, x. s. luo, b. h. wang, j. q. fang, “robust adaptive dynamic surface control of chaos in permanent magnet synchronous motor”, phys. letter a, vol. 363, pp. 71-77, 2007 [3] m. babaei, j. nazarzadeh, j. faiz, “nonlinear feedback control of chaos in synchronous reluctance motor drive systems”, ieee international conference on industrial technology (icit 2008), pp. 1-5, china, 2008 [4] y. gao, k. t. chau, “hopf bifurcation and chaos in synchronous reluctance motor drives”, ieee trnsaction on energy conver, vol. 19, pp. 296-302, 2004 [5] j h chen, k t chau, c c chan, q jiang, “subharmonics and chaos in switched reluctance motor drives”, ieee transaction on energy convertion, vol. 17, pp. 73-78, 2002 [6] h. ren, d. liu, “nonlinear feedback control of chaos in permanent magnet synchronous motor”, ieee transaction on circuits-ii vol. 53, pp. 45-50, 2006 [7] t tang, m yang, h li, d shen, “a new discovery and analysis on chaos and bifurcation in dc motor drive system with full-bridge converter”, 1st ieee conference on industrial electronics and applications, pp. 1-6, singapore, 2006 [8] i. nagy, “tolerance band based current control of induction machines highlighted with the theory of chaos”, 3rd ieee international power electronics congress, ciep '94, pp. 155-160, mexico, 1994 [9] z. suto, i. nagy, e. masada, “avoiding chaotic processes in current control of ac drive”, 29th annual ieee power electronics specialists conference, pesc 98, pp. 255-261, japan,1998 (a) (b) (b) (a) (a) (b) (c) (d) engineering, technology & applied science research vol. 6, no. 5, 2016, 1167-1174 1174 www.etasr.com sangrody and shariatmadar: a lyapunov function for vector control drives in induction machines [10] t. asakura, k. yoneda, y. saito, m. shioya, “chaos detection in velocity control of induction motor and its control by using neural network”, 5th ieee international conference on signal processing proceedings; pp. 1633-1638, china, 2000 [11] t. asakura, y. saito, m. shioya, “chaos detection and neuro-control in vector control system”, ieee region 10 conference on computers, communications, control and power engineering, pp. 1347-1350, china, 2002 [12] f. salas, r. ortega, j. aracil, “hopf bifurcation in indirect field-oriented control of induction motors”, automatica, vol. 38, pp. 829-835, 2002 [13] a. b. ozer, e. akin, “chaos control in vector-controlled induction motor drive”, electric power components and systems, vol. 36, pp. 733-740, 2008 [14] r. a. sangrody, j. nazarzadeh, k. y. nikravesh, “inherent chaotic behavior in vector control drives of induction machines”, electric power components and systems, vol. 40, pp.1-20, 2012 [15] h. zhang, x. ma, b. xue, w. liu, “study of intermittent bifurcations and chaos in boost pfc converters by nonlinear discrete models”, chaos soliton fractal, vol. 23, pp. 431-444, 2005 [16] k. y. nikranesh, nonlinear system stability analysis lyapunov-based approach, usa: crc press, pp. 106-111, 2013 [17] p. vas, sensorless vector and direct torque control, uk: oxford university press, 1998 authors profile reza sangrody was born in babol, iran in 1981. he received his bsc and msc degree in power electrical engineering from mazandaran university in 2003 and 2005, respectively. he received his phd degree in power electrical engineering from islamic azad university, science and research branch in 2012. at present his interest areas include nonlinear dynamical systems, power electronic applications and control of electrical drives. mr. sangrody joined islamic azad university, firoozkooh branch in 2006 as faculty member. seyed mohammad shariatmadar was born in qom, iran, in august 1973. he received the b.sc. degree from tehran university, tehran, iran, in 1996, the m.sc. degree from the south tehran branch, azad university, in 2003 and the ph.d. degree in electrical engineering at the science and research branch, islamic azad university tehran, iran in 2011. his current research interests include modeling, analysis, and control of electrical machines, power electronic drives and nonlinear phenomena in power electronics systems engineering, technology & applied science research vol. 7, no. 4, 2017, 1737-1740 1737 www.etasr.com sykaras et al.: a study of sir/epdm mixtures for outdoor insulators a study of sir/epdm mixtures for outdoor insulators a. sykaras democritus university of thrace, department of electrical and computer engineering, xanthi, greece v. rajini ssn college of engineering, department of electrical and electronics engineering, chennai, india m. g. danikas democritus university of thrace, department of electrical and computer engineering, xanthi, greece r. sarathi indian institute of technology madras, department of electrical engineering, chennai, tamil nadu, india abstract—this paper deals with the flashover voltages on samples of silicone rubber/ethylene propylene diene monomer (sir/epdm) mixtures under the influence of a uniform electric field. five different mixtures of sir/epdm were investigated. various sir/epdm mixtures (100% epdm, 10% sir + 90% epdm, 30% sir + 70% epdm, 50% sir + 50% epdm, 70% sir + 30% epdm, 90% sir + 10% epdm, 100% sir) were tested for different water droplet arrangements, different water conductivities, different droplet volumes as well as different droplet positioning w.r.t. the electrodes. the 50% sir + 50% epdm mixture proved to be the best mixture regarding the flashover voltage. keywords-sir; epdm; insulators; high voltage; polymeric i. introduction polymeric outdoor insulators are in use in the past few decades [1]. one of the most popular insulating materials for this application is silicone rubber [2]. lately, efforts have been undertaken in order to combine mixtures of silicone rubber (sir) with ethylene propylene diene monomer (epdm), which is also a good insulating material. sir has excellent hydrophobicity [2] and it performs very well in polluted areas, whereas it lacks in mechanical strength. epdm has high mechanical strength but its resistance to uv radiation is not that good and it seems to loose, as time passes by, its hydrophobicity [3]. an admixture of the two aforementioned materials may be a good way of having a new polymer with improved properties, both electrical and mechanical. mixtures of the two materials in various proportions have been studied in [4]. hydrophobic surfaces are characterized by a low surface energy. on hydrophobic surfaces, water forms discrete droplets and, consequently, leakage currents are minimized and the formation of dry zones becomes more difficult [3]. as a result, the probability of flashover is reduced. the main characteristic of hydrophobicity is the contact angle. the lower the surface energy of the insulating surface, the larger the contact angle θ [5]. needless to say that, a hydrophobic surface presents a contact angle of more than 900 whereas a hydrophilic surface has a contact angle of less than 900. on polymeric surfaces, the shape of water droplets depends on the surface material, the surface pollution, the surface deterioration, the droplet conductivity, the surface roughness, the charging of the droplet as well as the angle of the insulator sheds [6]. it has been reported elsewhere that the larger the droplet volume, the smaller the contact angle becomes, and consequently, the probability of a flashover increases [6]. the electric field distribution is greatly affected by the presence of a droplet on an insulating surface. it is already noted that the field lines inside the droplet are less dense because of the high dielectric constant of water. an intensification of electric field is observed at the triple junctions (where the three materials, air/droplet/silicone rubber, meet) [6, 7]. when a uniform electric field is applied, a water droplet (not charged) begins to oscillate at a certain field value. the oscillation frequency may be twice as much of that of the applied voltage. as the voltage increases, the oscillation becomes even more pronounced until a flashover ensues. with a charged droplet, the shape of the droplet –as the voltage increase– becomes asymmetrical and the oscillation frequency is the same with that of the applied voltage [6]. in the context of the present paper, various mixtures of sir/epdm (100% epdm, 10% sir + 90% epdm, 30% sir + 70% epdm, 50% sir + 50% epdm, 70% sir + 30% epdm, 90% sir + 10% epdm, 100% sir) were investigated, with the purpose to see which of them presented the highest flashover voltage. in order to observe this, a uniform electrode arrangement was used. since the flashover voltage is affected by the presence of humidity (water droplets) on the surface of an insulator, water droplets of various conductivities and volumes were placed on the surface of the samples. ii. sir/epdm mixtures silicone rubber is widely used for outdoor insulation because of its excellent hydrophobicity, good resistance to oxidation and ozone as well its perseverance in higher temperatures. moreover, it is thermally stable and it functions well under polluted conditions. it is, however, more expensive than other insulating materials and it has a smaller mechanical strength. epdm performs well under high temperatures and humidity, it presents small dielectric losses and very good dielectric strength, it is resistant to corona discharges and it is engineering, technology & applied science research vol. 7, no. 4, 2017, 1737-1740 1738 www.etasr.com sykaras et al.: a study of sir/epdm mixtures for outdoor insulators less expensive compared to silicone rubber. it is, however, sensitive to uv radiation and to pollution and it is less thermally stable in comparison to sir. it is intended that a combination of the two aforementioned materials may give improvements regarding the mechanical strength, the resistance to uv radiation and to oxidation and ozone, the thermal stability, the hydrophobicity and the cost [6, 8, 9]. it has been observed that, generally speaking, the electrical properties improve with the increase of sir in the mixture. regarding the mechanical properties, the tensile strength decreases with the percentage increase of sir, in other words, a percentage increase of sir implies a reduction of mechanical strength. data published elsewhere, regarding the relation between the various percentages of sir/epdm mixtures with important quantities, such as tracking resistance, tensile strength, dielectric strength, surface resistivity, volume resistivity, arc resistance and dielectric constant, indicated that there is an interplay between the percentages of the two materials w.r.t. the above properties [4]. referring to the experimental data of [4], it is understandable that the mechanical strength of sir can be considerably increased with the addition of epdm. a sir/epdm mixture renders somehow worse electrical properties – in comparison to a 100% sir – but such a decrease is not that big when the addition of epdm is not more than 50%. mixtures having equal quantities of sir and of epdm present good electrical and mechanical properties. an addition of more than 50% epdm is not to be recommended because of a significant degradation of the electrical properties. mixtures with more than 70% sir present excellent electrical properties but their mechanical strength is not that satisfying. furthermore, mixtures of 50% sir + 50% epdm are less expensive than “pure” sir. iii. experimental equipment for the experiments, a dry transformer was used giving voltages up to 24 kv. a horizontal wooden surface was used for putting the samples. two copper electrodes were used. in the photographs shown in figure 1 the power supply, the electrodes and the horizontal wooden surface, on which the experiments were performed, can be seen. the insulating materials used in the context of the present paper are given in table i. fig. 1. experimental set-up table i. mixture composition blend percentage in sir percentage in epdm a 90% 10% b 70% 30% c 50% 50% d 30% 70% e 10% 90% iv. conductivities, droplet arrangements and experimental procedure water droplets of various conductivities were used, from almost distilled water (1.4 μs/cm) up to 10000 μs/cm (conductivities used were: 1.4 μs/cm, 100 μs/cm, 200 μs/cm, 500 μs/cm, 1000 μs/cm, 2000 μs/cm, 5000 μs/cm and 10000 μs/cm). the droplets arrangements are shown in figure 2. in the top arrangement (with one droplet) has a volume of 0.1 ml, at a distance of 1.25 cm from the electrodes. in the bottom arrangement, the two droplets have each volume of 0.05 ml, and their distance from the respective electrodes is 0.8 cm. the electrodes in all experiments were at a distance of 2.5 cm from each other. fig. 2. water droplet arrangements after positioning the droplets on the polymer surface, the voltage was slowly raised until flashover occurred. after that and after cleaning the surface and positioning new droplets on it, the voltage was raised up to the previous flashover value minus 1.2 kv, so that no new flashover would occur. at this voltage value, the arrangements could stay for 5 min. if no flashover occurred, the voltage was raised by 0.4 kv and the procedure was repeated until flashover occurred. the new flashover value was recorded. the reason for allowing the voltage for 5 min at each voltage level was because a ceratin time was required for the droplets to deform and for the pd to start. the deformation of a single droplet can be seen in figure 3. in figure 4, the successive phases of formation of an arc are given for a single droplet of 1000 μs/cm on sample c. the oscillations of droplets on samples rich in sir (mixtures a and b) are more intense because of their better hydrophobicity, i.e. for a constant droplet volume, in hydrophobic materials, the contact angle is large and the engineering, technology & applied science research vol. 7, no. 4, 2017, 1737-1740 1739 www.etasr.com sykaras et al.: a study of sir/epdm mixtures for outdoor insulators contact surface small and, consequently, the droplet oscillates more. the flashovers on samples rich in sir are more intense, thus forming bigger arcs. an increase in droplet volume, in droplet number as well as in water conductivity, leads to a flashover in lower voltages. increase of conductivity, and especially at values of 5000 μs/cm and 10000 μs/cm, causes deterioration of the sample surface. samples rich in epdm show more intensive deterioration (especially in the higher water conductivities), as is shown in figure 5. rich in epdm samples showed a reduction of flashover voltage because of the deterioration of their surface. fig. 3. deformation of a single droplet on sample a (droplet conductivity 1.4 μs/cm) fig. 4. arcing of a single droplet on sample c fig. 5. the state of the samples after the experiments. v. experimental results and discussion figure 6 refers to flashover voltages for samples a, b, c, d, and e (table i) and for a droplet volume of 0.1 ml at a distance of 1.25 cm from the electrodes. figure 7 shows flashover voltages for samples a, b, c, d, and e for an arrangement of two droplets, each of 0.05 ml at a distance of 0.8 cm from the electrodes and also between them. from the above mentioned figures, it is evident that the influence of water conductivity on flashover voltage is prominent. no matter the droplet arrangement, the droplet volume or the droplet number, or even the sample composition, an increase in water conductivity leads to a decrease of flashover voltage. droplet volume as well as droplet number effect was noted previously [10-13]. larger droplet volume and/or droplet number leads to a lower flashover voltage [14-15. the beneficial effect of silicone rubber on epdm was also noted recently [16]. fig. 6. flashover voltage in terms of droplet conductivity with a 0.1 ml water droplet for the various mixtures fig. 7. flashover voltage in terms of droplet conductivity with two droplets each of 0.05 ml for the various mixtures it seems that mixture c (50% sir 50% epdm) presents a satisfying flashover behavior. this is in accordance with [4], where it was shown that this mixture presented the best combination of electrical and mechanical properties. mixtures d and b (table 1) follow regarding the flashover behavior. mixtures a (90% sir – 10% epdm) and e (10% sir – 90% epdm) present the worst behavior regarding the flashover engineering, technology & applied science research vol. 7, no. 4, 2017, 1737-1740 1740 www.etasr.com sykaras et al.: a study of sir/epdm mixtures for outdoor insulators voltage. from the measurements performed in the context of this work, mixture c seems to electrically behave the best in comparison with the rest of the mixtures. this is perhaps due to the fact that the percentage 50% sir – 50% epdm preserves somehow in the best way the electric and mechanical properties of the constituent materials. for future work, it is recommended a further series of experiments regarding surface discharges and flashover voltages, taking into account the surface roughness of the samples, the more detailed study of the contact angle for the various blends as well as the use of other electrode arrangements and larger samples. the latter will allow the probable use of larger water droplets, which in turn will give a more ample variety of results. vi. conclusion in the context of this paper, an investigation was performed for various mixtures of sir and epdm, regarding the flashover voltage. experiments with water droplets of various conductivities under the influence of a uniform electric field indicated that the mixture having 50% sir – 50% epdm gives the most satisfactory data. this renders the aforementioned mixture a reliable candidate for industrial outdoor high voltage applications. acknowledgments the samples were prepared at ssn college of engineering, department of electrical and electronics engineering, chennai, tamil nadu, india. references [1] r. gorur, “high voltage outdoor insulation technology”, cont. a. dyn. syst., vol. 44, pp. 131-191, 1994 [2] m. g. danikas, "ageing properties of silicone rubber materials used in high voltage composite insulators", j. elec. electron. engg., austr., vol.15, no. 2, pp. 193-202, 1995 [3] s. m. gubanski, a. e. vlastos, “wettability of naturally aged silicone and epdm composite insulators”, ieee transactions on power delivery, vol. 5,no. 3, pp. 1527 – 1535, 1990 [4] r. r. prabu, s. usa, k. udayakumar, m. a. khan, s. s. m. abdul majeed, “electrical insulation characteristics of silicone and epdm polymeric blends – part i”, ieee trans. diel. electr. insul., vol. 14, no. 5, pp. 1207-1214, 2007 [5] j. k. kim, in-hwan kim, “characteristics of surface wettability and hydrophobicity and recovery ability of epdm rubber and silicone rubber for polymer insulators”, j. appl. polymer sci., vol. 79, pp. 2251-2257, 2001 [6] o. fujii, k. honsali, y. mizuno, k. naito, “a basic study on the effect of voltage stress on a water droplet on a silicone rubber surface”, ieee trans. diel. electr. insul., vol. 16, no. 1, pp. 116-122, 2009 [7] e. kuffel, w. s. zaengl, j. kuffel, high voltage engineering: fundamentals, eds. newness, oxford, uk, 2000 [8] m. mohseni, m. geramian, h. mirzadeh, “manufacturing and evaluation of epdm-silicone blends used in housing of high voltage composite insulators”, proc. 17th int. conf. electricity distribution, paper no. 44, session 1, barcelona, spain, 2003 [9] r. deepalaxmi, v. rajini, “performance evaluation of gamma irradiated sir-epdm blends”, nuclear engineering and design, vol. 273, pp. 602-614, 2014 [10] α. bairaktari, m. danikas, x. zhao, y. cheng, y. zhang, “behaviour of water droplets under the influence of a uniform electric field in nanocomposite samples of epoxy resin/tio2”, engineering, technology & applied science research, vol. 3, no. 5, pp. 511-515, 2015 [11] c. charalambous, m. danikas, y. yin, n. vordos, j. w. nolan, a. mitropoulos, “study of the behavior of water droplets under the influence of a uniform electric field on conventional polyethylene and on crosslinked polyethylene (xlpe) with mgo nanoparticles samples”, engineering, technology & applied science research, vol. 7, no. 1, pp. 1323-1328, 2017 [12] m. g. danikas, p. rakitzis, k. karakoulidis, “study of parameters related to deterioration phenomena due to water droplets on polymeric surfaces”, j. electr. eng., vol. 57, no. 3, pp. 130-137, 2006 [13] m. g. danikas, p. ramnalis, r. sarathi, “experimental results on the behavior of water droplets on polymeric surfaces under the influence of electric fields: the case of an inclined test arrangement for pvc, rubber and silicone rubber”, funktechnikplus journal, vol. 1, no.2, pp. 19-39, 2013 [14] k. karakoulidis, m. g. danikas, p. rakitzis, “deterioration phenomena on polymeric insulating surfaces due to water droplets”, j. electr. eng., vol. 56, no. 7-8, pp. 169-175, 2005 [15] s. c. kechagia, m. g. danikas, r. sarathi, “water droplets and breakdown phenomena on polymer nanocomposite surfaces under the influence of uniform electric fields”, malaysian polym. j., vol. 8, no. 2, pp. 41-47, 2013 [16] a. ragab, l. s. nasrat, s. m. el-khodary, s. el-debeiky, “performance of epdm cable terminations under various polluted conditions”, international journal of innovative research in electrical, electronics, instrumentation and control engineering, vol. 2, no. 8, pp. 1780-1783, 2014 microsoft word 1-nabi.doc etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 23-29 23 www.etasr.com �abi et al: a �ovel structure for vector control of symmetrical six-phase induction machines… a novel structure for vector control of symmetrical six-phase induction machines with three current sensors hamidreza pairodin nabi departement of electrical engineering iran university of science and technology (iust) tehran,iran h_pairo@ elec.iust.ac.ir pooya dadashi departement of electrical engineering iran university of science and technology (iust) tehran,iran pooyadadashi@yahoo.com abbas shoulaie departement of electrical engineering iran university of science and technology (iust) tehran,iran shoulaie@ iust.ac.ir abstract— vector control is one of the most popular multiphase induction machine drive methods due to its dynamic performance. since all phase currents are needed in vector control drive, by increasing phase numbers, the number of required current sensors increases which is one of the disadvantages of vector control in multiphase machine drives. in this paper vector control of a symmetrical six-phase induction machine with a novel configuration is presented. the aforementioned configuration is designed in a simple way that only three current sensors will be needed. analytical equations are extracted in this paper to show that some of current components which do not contribute in torque production will be eliminated due to the proposed scheme. simulation and experimental results are provided to verify the benefits of the proposed configuration. keywordssymmetrical six-phase induction machine; vector control; current sensor; multiphase drives. i. introduction in early 1990s, study on multiphase machines accelerated; until the beginning of recent century, it became practical in industries. multiphase induction machines are predominantly used in electric ship propulsion, traction and generally in high power applications [1-3]. multiphase induction machines have some advantages over three phase induction machines. employing multi-phase induction machines would reduce the pulsating torque and would increase the efficiency of the machine. six-phase induction machines have 6.7% reduction in stator copper loss compared to the same machine wound with an equivalent three-phase winding of the same pitch [4-5]. also, multiphase induction machines have less noise pollution compared to three-phase ones [6]. among several benefits, high phase numbers provide better motor performance following loss of one or more phases; in addition using multiphase induction machines obtain the capability to start and run even with some phases open circuited [7-9]. the other advantage is the improvement of torque in multiphase machines with concentrated winding. lyra et al. [10] showed that additional torque production can be obtained by injecting third harmonic current. also, increasing phase number to at least five (or more) enables completely independent vector control of two (or more) multiphase machines that are supplied from a single current-controlled voltage source inverter [11-12]. further, the switched voltage profile in the motors’ windings and their behaviour is evaluated in [13] to achieve independent feed forward voltage control of two series connected six-phase and three-phase induction machines. recently, several control techniques are considered about induction machines which application of each method depends on desired specific condition [14-15]. one of these methods is called scalar and it is more suitable for low power applications [16]. in contrast, vector control of induction machines was introduced by blaschke [17] and hasse [18] which has better dynamic response. despite of the higher phase number in multiphase induction machines, they have more degrees of freedom. nevertheless, all these techniques are applicable for multiphase induction machines with little differences [19]. a specific problem encountered in multiphase drive systems is that generation of certain low-order voltage harmonics in the voltage source inverter output. low-order stator voltage harmonics maps into yx − components using ordinary reference frame technique. according to the possibility of flowing yx − current components, the tendency is to create sinusoidal voltage at the output of the inverter. the existence of low order harmonics in input supply leads to large stator current harmonics which only restricted by stator leakage impedance [20]; whereas machines with sinusoidal mmf distribution have very small impedance for yx − voltage components [2]. although with non-sinusoidal voltage source, multiphase machines generally have more stator copper loss, but they always have less rotor copper loss versus three phase machines [21]. the asymmetrical six-phase induction machines (two threephase with 30 o displacement) are the most frequently etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 23-29 24 www.etasr.com �abi et al: a �ovel structure for vector control of symmetrical six-phase induction machines… considered multiphase machines in industrial applications. the choice of asymmetrical six-phase machine rather than symmetrical (two three-phase with 60 o displacement) is for existence of sixth harmonic of torque caused by the fifth and seventh harmonics of the stator current in symmetrical ones. however, implementation of proper pwm strategy, with sufficiently high switching frequency, leads to the same performance of symmetrical and asymmetrical six-phase machines for a six-phase vsi [19]. in this context, excellent high performance quality of rotor flux oriented control of a symmetrical six-phase induction machine has been demonstrated in [22]. with advances in power semiconductor technology and improvement in control methods, the trend to low cost drive systems is increased. by reducing the number of equipments used in these systems, the final cost will be reduced too. reduction in the number of current sensors will result in lower cost of these drive systems. in [23] a rotor field-oriented control of dual-three-phase induction machine, employing only two current sensors, has been presented. a novel torque and speed control structure for low-cost induction machine drive with a single dc-link current sensor presented in [24]. in vector control of symmetrical six-phase machines, in regular manner, we need at least five current sensors. in this paper, proposed configuration of symmetrical six-phase induction machine leads to minimizing the number of current sensors which only three current sensors will be needed. ii. indirect vector control of multiphase induction machines the main objective of vector control of induction machines is to control them like separately excited dc machines. in this section, the model of a symmetrical six-phase induction machine and its vector control algorithm will be presented. a. six-phase machine model an induction machine can be modelled with state-space equations. in these equations, voltage and frequency are as inputs and the outputs of the state-space equations are speed, position, torque, flux, current or a combination of them. the stator equations in arbitrary common reference frame are shown in equation (1) [12]: and rotor equations are as follows: dsmdrmlrdr dr qrrsdrrdr ilill dt d irv ++=+−−== )(,)(0 λ λ λωω qsmqrmlrqr qr drrsqrsqr ilill dt d irv ++=+−+== )(,)(0 λ λ λωω rxlrrx rx rxrrx il dt d irv 11 1 11 ,0 =+== λ λ rylrry ry ryrry il dt d irv 11 1 11 ,0 =+== λ λ rlrrx r rrr il dt d irv + + ++ =+== 01 0 00 ,0 λ λ rlrr r rrr il dt d irv −− − −− =+== 00 0 00 ,0 λ λ (2) in these equations, the various symbols denote the following: rs, the stator resistance per phase; rr, the referred rotor resistance per phase; m l , the mutual inductance per phase; lls, the stator leakage inductance per phase; llr, the stator referred rotor leakage inductance per phase; s ω and r ω are synchronous speed and electrical rotor speed both in rad/sec. it should be noted that m l is equal to m3 which m is the maximum mutual inductance value between stator and rotor. the torque equation is as follows: ][ qrdsqsdrme iiiilpt −= (3) b. six-phase induction machine vector control algorithm since the considered induction machine is symmetrical with sinusoidally stator winding, then the only difference between vector control scheme of a three-phase and six-phase induction machine is due to the decoupling transformation matrix [19]. in vector control of induction machines, the direct axis should be aligned with rotor flux vector, and then the quadrature component of rotor flux will be equal to zero: drr λλ = 0)( =++= qrmlrqsmqr illilλ qs mlr m qr i ll l i + −= 0= qr λ 0= qr dt d λ (4) by substituting the equation (4) in equation (2), the followings are obtained: rr m ds dt d t l i λ]1[ 1 += ds qs r rs i i t . 1 =−ωω (5) it should be noted that, in these equations, rotor time constant, tr, is equal to )/)(( rmlr rll + . under these conditions, with using equations (3) and (4), the torque equation will become as: drmdsmlsds ds qssdssds ilill dt d irv ++=+−= )(, λ λ λω qrmqsmlsqs qs dssqssqs ilill dt d irv ++=++= )(, λ λ λω sxlssx sx sxsx il dt d irv 11 1 11 , =+= λ λ sylssy sy sysy il dt d irv 11 1 11 , =+= λ λ slss s sss il dt d irv ++ + ++ =+= 00 0 00 , λ λ slss s sss il dt d irv −− − −− =+= 00 0 00 , λ λ (1) etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 23-29 25 www.etasr.com �abi et al: a �ovel structure for vector control of symmetrical six-phase induction machines… qsdre ikt λ= (6) where k is torque constant. this equation shows that if rotor flux will not be distorted, then the quadrature component of the stator current, iqs, can control the torque and the rotor flux can be controlled with direct component of stator current [25]. proper performance of control system and using correct estimated parameters ensure that rotor flux will not be distorted. ∫ ω *ω * ds i θ * qsi 62 → * 1 i * 6 i * 3 i * 4i * 5 i * * . 1 ds qs r i i t s 1 * 2i fig. 1. indirect vector control diagram of six-phase induction machine iii. proposed structure for minimizing the independent currents in six-phase induction machines in this section, the proposed structure for reducing current sensors is considered. the current references in the block diagram of figure 1 are as follows: )sincos( 6 2 *** 1 θθ qsds iii −= )) 6 2 sin() 6 2 cos(( 6 2 *** 2 π θ π θ −−−= qsds iii m )) 6 10 sin() 6 10 cos(( 6 2 *** 6 π θ π θ −−−= qsds iii (7) the proposed structure is based on the connection diagram of six-phase induction machines. figure 2 shows two different connection diagram of six-phase induction machine. figure 2(a) shows the star-connected six-phase induction machine and figure 2(b) illustrates the proposed structure. if the current references of equation (7) will be applied to a machine with configuration of figure 2(a), then the relation between motor currents would be as: 6321621 ...0... iiiiiii −−−−=→=+++ (8) this equation shows that there are five independent currents for a six-phase machine. respectively, according to the structure of figure 2(a), just a single current sensor can be eliminated. in symmetrical six-phase induction machines, under symmetrical and balanced source, the current of mth phase is equal to the negative of the ( 3+m )th phase current ( )3( +−= mm ii ). so in six-phase induction machines, there is the possibility of using the structure of figure 2(b). as shown in figure 2(b), the second end of mth phase is directly connected the second end of ( 3+m )th phase (m=1, 2, and 3). hence, it is clear that the current of mth phase is instantaneously equal to the current of ( 3+m )th phase. so the relation between phase currents will be as follows: 41 ii −= 52 ii −= 63 ii −= (9) this equation shows that with using the structure of figure 2(b), the number of independent currents will be equal to three and consequently the number of current sensors can be reduced to three sensors. iv. analysis of the proposed structure in this section, the effect of this structure on the different current components of six-phase induction machines is considered. for this purpose, the currents of six-phase induction machines are transformed using decoupling transformation matrix of equation (10) [26].                     −−−− + = 2/12/12/12/12/12/1 2/12/12/12/12/12/1 10sin8sin6sin4sin2sin0 10cos8cos6cos4cos2cos1 5sin4sin3sin2sinsin0 5cos4cos3cos2coscos1 0 0 1 1 6 2 ααααα ααααα ααααα ααααα β α y x c (10) where in this equation 6 2πα = . by applying the matrix of equation (10), the βα − current components will be as: )5cos(...)cos( 621 ααα iiii +++= )5sin(...)sin(0 62 ααβ iii +++= (11) with substituting equation (9) in equation (11), the followings are obtained: )]5cos()2[cos( )]4cos()[cos()]3cos(1[ 3 21 αα αααα −+ −+−= i iii )]5sin()2[sin( )]4sin()[sin()]3sin(0[ 3 21 αα αααβ −+ −+−= i iii (12) it is clear that ))2cos(())1cos(( αα +−=− mm and ))2sin(())1sin(( αα +−=− mm which m=1, 2, and 3. so, it would be concluded that: )2cos(2)cos(22 321 ααα iiii ++= )2sin(2)sin(20 32 ααβ iii ++= (13) for considering the effect of this structure on the x1-y1 current components, the x1-y1 current component equations etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 23-29 26 www.etasr.com �abi et al: a �ovel structure for vector control of symmetrical six-phase induction machines… are considered. the general form of x1-y1 current components will be as follows: )10cos(...)2cos( 6211 αα iiii x +++= )10sin(...)2sin(0 621 αα iii y +++= (14) by substituting equation (9) in equation (13), it would be concluded that: )]10cos()4[cos( )]8cos()2[cos()]6cos(1[ 3 211 αα ααα −+ −+−= i iii x )]10sin()4[sin( )]8sin()2[sin()]6sin(0[ 3 211 αα ααα −+ −+−= i iii y (15) and simply, the followings are obtained: ))2(2cos())1(2cos( αα +=− mm ))2(2sin())1(2sin( αα +=− mm (16) where in this equation m=1, 2, 3. then: 0,0 11 == yx ii (17) these equations show that 1x i and 1y i are equal to zero. it should be noted that 1x i and 1y i don't contribute in torque production. by applying the transformation matrix of equation (10) to six-phase currents, the zero sequence currents are as: ]...[ 2 1 63210 iiiii ++++=+ ]...[ 2 1 63210 iiiii −++−=− (18) by substituting the equation (9) in equation (18), the followings are obtained: 0 0 =+i ][ 2 2 3210 iiii +−=− (19) equations (10) to (19) show that x1-y1 current components and positive zero sequence current component will be eliminated due to the structure of figure 2(b). v. hystsresis modulation the reference currents for hysteresis control are obtained from vector control block diagram of figure 1. the injected currents from phase 1 to phase 3 are measured and fed back to hysteresis control block. so the switching status of each switch is characterized by the difference between reference current and actual current ( i∆ ). 3, * ≤−=∆ miii real mmm (20) the following equation is used for characterizing the status of the switches of each branch: 3 0 1 ≤ −<∆ >∆    = m bi bi s m m m (21) where, m s is the status of the switches in mth branch which m=1, 2 and 3, and b is the hysteresis band. hence, 1= m s represent that the upper switch in mth branch is on and the lower switch is off. similarly, 0= m s represent that upper switch is off and lower switch is on. determination of the switching status of the switches in the branches with number greater than 3 is derived from the structure of figure 2(b). as it would be concluded from figure 2(b), the switching status of the switches in ( 3+m )th branch is opposite of the switches in mth branch. so, just the first three phase currents are measured and fed back to the hysteresis block and the switching status of all twelve switches of six-phase inverter would be determined from theses three currents. 3 0 1 1 0 3 ≤ = =    =+ m s s s m m m (22) (a) (b) fig. 2. connection diagram of six-phase induction machine: (a) star connected, (b) proposed structure * 1 i * 3 i * 2 i real i 1 real i 2 real i 3 1 s 2 s 3 s 4 s 5 s 6 s fig. 3. hysteresis block diagram ( m s determines the switching status of the mth branch switches) etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 23-29 27 www.etasr.com �abi et al: a �ovel structure for vector control of symmetrical six-phase induction machines… vi. simulation results to verify the proposed structure, the vector control of a symmetrical six-phase induction machine is simulated in matlab/simulink. the parameters of six-phase machine are represented in appendix i. first in this section, the performance of the vector control of six-phase induction machine with proposed structure is investigated under load variations which the results are shown in figures 4-6. for this purpose, the six-phase machine connections are similar to figure 2(b) and just currents of phase 1, phase 2 and phase 3 are fed back to hysteresis block and the switching status of all switches is specified from section v; so the exact control on the current of the other phases is easily achievable. in simulation of this system, the speed command is set to 550rpm; the motor runs under no-load condition and an 11n.m torque is applied to the motor as load at t=10s. figure 4 and figure5 show the electromagnetic torque and the speed response of the six-phase induction machine. the current of phase 1, as sample, is illustrated in figure 6. as shown in these figures, results verify the performance of vector control with proposed structure under load variation. the simulation results for investigating the performance of vector control under speed command variation are shown in figures 7-9. in this simulation, the motor works under no-load condition; and the speed command is 550rpm which increases to the 700rpm at t=5.5s. the electromagnetic torque and speed response are illustrated in figure 7 and figure 8. as depicted in figure 8, the motor speed follows the speed command. as the vector control is in speed control mode, the motor speed should follow the speed command and should be kept constant under load changes. so, these results verify the vector control of sixphase induction machine using three current sensors with proposed. fig. 4. electromagnetic torque of symmetrical six-phase induction machine (a load of 11n.m is applied at t=10s) fig. 5. speed response of symmetrical six-phase induction machine (the speed command is 550 rpm) fig. 6. phase 1 current (speed command is set to 550 rpm and a 11n.m load is applied at t=10s) fig. 7. electromagnetic torque of symmetrical six-phase induction machine (the motor is working under no-load condition) fig. 8. speed response of symmetrical six-phase induction machine (the speed command varies from 550rpm to 700rpm at t=5.5s) fig. 9. phase 1 current (the motor is under no-load condition and the speed command varies from 550rpm to 700rpm at t=5.5s) etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 23-29 28 www.etasr.com �abi et al: a �ovel structure for vector control of symmetrical six-phase induction machines… vii. experimental results an experimental setup is constructed for verifying the application of the proposed structure. in this section, the experimental results of a symmetrical six-phase induction machine are presented. the microcontroller used in controller board is dspic30f4011. only the first three phase currents, i.e. i1, i2, and i3, are measured using lem sensors. the experimental tests have been performed on a six-phase induction machine with 48 slots on stator, 4-pole and 50hz. this machine is coupled with a dc generator as load. the perphase parameters of the six-phase induction machine are represented in appendix i. the experimental setup is shown in figure 10. motor phase currents are sampled via a data acquisition apparatus (usb-4711a) and the motor speed is measured using digital tachometer rm-1501. speed and current samples are plotted with matlab. for implementing the proposed structure, the connections of the motor is similar to figure 2(b) and the current sensors are placed only on the phase 1, phase 2 and phase 3. similar to simulation results, first, the vector control with proposed structure is tested under load variations. for being comparable, the simulation and experimental tests are under same conditions. so, in the first test, the speed command is set to 550rpm and the load increases from zero to 11n.m at t=10s. the speed is shown in figure 11. because of low sampling rate of digital tachometer, the transients in the speed response are not observable. as depicted in figure 11, the speed is set to 550rpm before and after applying the load. the phase 1 current is illustrated in figure 12. the test results verify the performance of indirect vector control of symmetrical sixphase induction machine with proposed structure under variations of load and speed command. fig. 10. experimental setup fig. 11. speed response of symmetrical six-phase induction machine (the speed command is 550 rpm) fig. 12. measured phase 1 current (speed command is set to 550rpm and a 11n.m load is applied at t=10s) fig. 13. speed response of symmetrical six-phase induction machine (the speed command varies from 550rpm to 700rpm at t=5.5s) fig. 14. measured phase 1 current (the motor is under no-load condition and the speed command varies from 550rpm to 700rpm at t=5.5s) etasr engineering, technology & applied science research vol. 1, �o. 2, 2011, 23-29 29 www.etasr.com �abi et al: a �ovel structure for vector control of symmetrical six-phase induction machines… viii. conclusion this paper presents a new structure for vector control of six-phase induction machines with minimum independent currents. the independent currents are minimized as a result of increasing the neutral points. it should be mentioned that the drawback of this scheme is a little reduction in reliability compared to conventional symmetrical six-phase drive systems while its reliability is still better than three-phase ones. furthermore, all advantages of six-phase induction machines are retained due to the proposed structure. the analytical equations verify that not only this structure reduces the current sensors, but also yields in eliminating some current components which do not contribute in torque production. with proposed structure, 1x i , 1y i and +0i are equal to zero. simulation and experimental results verified the performance of vector control of symmetrical six-phase induction machines with proposed structure. appendix the motor parameters are as follows: rpmn s 1500= , hpp n 3= , ω= 33.0rr , ω= 87.0sr , hl m 079.= , mhll lslr 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[20] a. iqbal, e. levi, “space vector pwm techniques for sinusoidal output voltage generation with a fve-phase voltage source inverter”, electric power components & systems, vol. 34, no. 2, pp. 119–140, 2006 [21] e.a. klingshirn, “high phase order induction motors part idescription and theoretical considerations”, ieee transactions on power apparatus and systems, vol. pas-102, no. 1, pp. 47 – 53, 1983. [22] s.n. vukosavic, m. jones, e. levi, j. varga, “rotor fux oriented control of a symmetrical six-phase induction machine”, electric power systems research, vol. 75, no. 2–3, pp. 142–152, 2005. [23] r. bojoi, a. tenconi, g. griva, f. profumo, “vector control of dual three-phase induction motor drives using two current sensors”, ieee transactions on industry applications, vol. 42, no. 5, pp. 1284 – 1292, 2006. [24] s. n. vukosavic, a. m. stankovic, “sensorless induction motor drive with a single dc-link current sensor and instantaneous active and reactive power feedback”, ieee transactions on industry applications, vol. 48, no. 1, pp. 195 – 204, 2001. [25] a. m. trzynadlowski, control of induction motor, san diego, usa: academic press, 2001. [26] m. jones, s. n. vukosavic, e. levi, a. iqbal, “a six-phase seriesconnected two-motor drive with decoupled dynamic control”, ieee transactions on industry applications, vol. 41, no. 4, pp. 1056–1066, 2005. engineering, technology & applied science research vol. 7, no. 5, 2017, 2094-2097 2094 www.etasr.com galarpe and leopoldo: potential recovery of silver (ag) from x-ray fixer waste by alkaline treatment potential recovery of silver (ag) from x-ray fixer waste by alkaline treatment van ryan kristopher r. galarpe environmental science & technology/physics dpt university of science and technology of southern philippines (ustp) philippines vanryankristoher.galarpe@ustp.edu.ph girlie d. leopoldo chemistry department university of science and technology of southern philippines (ustp) philippines girlie_leopoldo@yahoo.com abstract—the study aims to establish a chemical method of silver recovery from x-ray processing fixer waste by alkaline treatment using sodium hydroxide (naoh). the samples used in the study were collected from selected hospitals and radiology centers in cagayan de oro city, philippines. the naoh precipitation method was employed by varying the amount of naoh from 8.00 g to 15.00 g per 600 ml of the fixer waste sample. the recovered crude silver for the two sampling periods ranged from 0.88 g to 2.46 g. the method resulted to optimum recovery at ph 9. the one way anova indicates that there are significant differences on the amount of silver recovered when varying the amount of naoh in “sampling a”. the tukey test further reveals that there exists an evident rise in the recovered silver using 10.00 g to 15.00 g of naoh. in “sampling b” the amount of silver recovered does not significantly differ when varying the amount of naoh used on average basis. the raw data, however, also revealed a significant rise in the amount of silver recovered using 10.00 g to 15.00 g of naoh where ph was approximately 9. keywords-xray; fixer waste; naoh; recovery ; silver (ag) i. introduction in the advent of modernization, several researches have been established to gaze on alternative means of collecting metals with a goal of reducing the dependence on traditional ore mining and at the same time decreasing the metal content of waste materials. silver is of no exemption with its focal demand in the market and wide consumption both in industrial and technological applications. the increasing use for silver is significant in the industry of x-ray processing and photography. this metal is often used as component of film emulsion containing silver halide grain, commonly silver bromide (agbr). the silver grains in the emulsion acts as a light sensitive material responsible for image formation. during xray film processing the unreacted silver halide remaining on the film reacts with the fixer solution (thiosulfate compounds) resulting to the formation of silver thiosulfate complex [ag(s2o3)23-] in a process known as fixing. the complex produced goes with the fixer back into a tank which is subject for disposal upon several usages. the produced waste contains high concentration of silver complexes. thus, the release of such to any body of water promotes prolonged exposure of the environment to water-soluble inorganic chemicals and pollutants. levels of these waste chemicals can make water unfit to drink, harm fish and other aquatic life, depress crop yields, and accelerates corrosion to equipment that uses such water. having known of the potential hazard brought by x-ray processing fixer waste, and the valued metal present, it is therefore sensible to recover the precious silver metal it contain. several studies elsewhere recovered silver from spent x-ray fixer waste and films through the use of enzymes and alkaline solutions [1-8] but none focused directly using low cost sodium hydroxide recovery (naoh) method to to x-ray fixer waste. studies in the past similarly employed other methods like electrochemistry [9-12]. this study dealt on the recovery of silver by employing the sodium hydroxide precipitation method. several conditions were carried out for the purpose of establishing a good system of silver recovery. these conditions include varying the amount of naoh, and determining the ph of the mixture in every amount of the precipitating agent added. the study tried to recover silver from x-ray processing fixer wastes by naoh precipitation and examine the effect of varying the naoh amount on the silver recovery. specifically, the study sought to answer the following questions: 1. what amount of naoh and ph is most suitable to recover crude silver from a certain amount of x-ray fixer waste by naoh precipitation method? 2. are there significant differences on the amount of crude silver recovered by varying the amount of naoh? 3. what is the optimum condition to recover silver from x-ray fixer waste by naoh precipitation? ii. materials and methods a. study setting the fixer waste samples were collected from selected hospitals and radiology centers in cagayan de oro city. these include northern mindanao medical center, capitol university medical city, madonna and children’s hospital, maria reyna hospital, and microstar diagnostic center. the choices of the said sampling sites were based on the abundance of x-ray processing fixer wastes. the experimentations and analyses were conducted in the chemistry laboratory and automotive engineering, technology & applied science research vol. 7, no. 5, 2017, 2094-2097 2095 www.etasr.com galarpe and leopoldo: potential recovery of silver (ag) from x-ray fixer waste by alkaline treatment laboratory of the university of science and technology of southern philippines (ustp). other analysis was conducted in the department of agriculture 10-regional soil testing laboratory. b. sampling scheme the study constitutes two sampling periods. samples (4 to 6l) were taken per sampling period from the selected sites. figures 1-4 show x-ray film processors and fixer waste collection from one specific site. equal volumes of fixer wastes collected were mixed and homogenized as a composite sample prior to analysis. the composite sample was analyzed for silver recovery at three (3) trials per amount of naoh. the ph of the resulting mixture was also determined. the dried residue produced was smelted for silver extraction. c. sample preparation equal volumes of x-ray processing fixer wastes from selected sampling sites were mixed. the produced composite sample was stored in a 20 l capacity polyethylene container. fig. 1. x-ray machine generating spent fixer waste in northern mindanao medical center (nmmc) fig. 2. collection of spent fixer waste in northern mindanao medical center (nmmc) fig. 3. collection of spent fixer waste in a private hospital fig. 4. collection of spent fixer waste in a medical clinic d. recovery of ag by naoh precipitation a 600-ml volume of fixer waste from the composite sample was placed into a 1000-ml beaker. with the use of a 5 sitter cole parmer magnetic stirrer, the sample was stirred for 10 mins. a weighed amount of naoh was added into the stirred sample. another 30 minutes of stirring was applied to complete the precipitation. the ph of the resulting mixture was also determined using a metler toledo mp220 ph meter. the amounts of naoh used and tried were 8.00, 9.00, 10.00, 11.00, 12.00, 13.00, 14.00, and 15.00 g. the precipitate of the produced mixture (turbid yellow to black) was allowed to settle or separate (for 24 h or more) from the mother liquor. the mother liquor of the resulting mixture was then collected using a measuring pipet. the remaining slurry (precipitate) was placed into a pre-weighed drying vessel covered by a watch glass and dried for three hours under low heat to prevent loss of the analyte by bumping or splattering. the dried sample was then placed in a desiccator for 30 minutes and weighed using a top-loading balance. the dried sample was scraped from the vessel using a metal spatula and transferred into a ceramic vessel and added with 2.00 g borax. the pulverized sampleborax mixture was then smelted using oxy-acetylene. the isolated crude silver was picked using forceps and then weighed. e. statistical analysis descriptive statistic was employed in order to get the average amount of silver recovered at different amount of naoh added. one way-analysis of variance (one wayanova) was also employed to statistically evaluate he difference on the silver recovered by varying the amount of naoh. further test by the tukey method was used to determine specific factor(s) that significantly differ statistically. statistical tests were conducted at 0.05 level fo significance. iii. results and discussions a. summary of results as can be seen in tables i and ii, the amount of silver recovered is dependent on the amount of naoh. although the result shows inconsistencies, an increase in the mass of naoh generally results to an increase in silver recovery. similarly, an increase in the ph of the resulting mixture generally results to an increase in silver recovery. the result of the two sampling periods indicate that a minimum of 10.00 g naoh was necessary to recover a significant amount of silver from 600 ml volume of x-ray fixer waste. the use of 10.00 g naoh results to a ph approximately near to 9 which was within the 8engineering, technology & applied science research vol. 7, no. 5, 2017, 2094-2097 2096 www.etasr.com galarpe and leopoldo: potential recovery of silver (ag) from x-ray fixer waste by alkaline treatment 10 ph range necessary for silver hydroxide precipitation to occur as stated in the literature [1, 2]. the decrease in ph after adding 12.00 g naoh as compared to ph of the mixture when adding 11.00 g naoh was true to both sampling periods. these may be due to processes/reactions occurring in the mixture itself. the fixer waste was primarily a mixture of the silver thiosulfate complex, acetic acid, ammonium bisulfite, and sodium bisulfite. thus these other chemical components of the fixer other than the silver complexes perhaps have interfered in the precipitation process. the inconsistencies in the silver recovered, on the other hand, may be because the silver was still crude thus resulting to the variations in the masses of the silver recovered. confirmatory trials were actually made in order to assess if usage of increased amount (the ones employed in the study) of naoh was sufficient to recover silver from the fixer waste sample. this was done by conducting two trials of the recovery study in sampling 1 using approximately 25.00 g of naoh. the results revealed that the amount of silver recovered differs only by 0.07 g from the average silver recovered using 14.00 g. thus, the use of 10.0015.00 g of naoh can be considered appropriate amount to recover silver from 600 ml of x-ray fixer waste. figure 5 shows an example of the recovered crude silver. fig. 5. crude silver recoverd table i. summary of results (sampling period 1) analysis no. amount of naoh (g) ph amount of ag recovered (g) 1 8.01 ±0.00 8.80 ± 0.08 0.88 ± 0.34 2 9.07 ±0.01 8.77 ± 0.04 1.34 ± 0.04 3 10.00 ± 0.00 8.97 ± 0.08 1.70 ± 0.21 4 11.03 ± 0.02 9.08 ± 0.02 1.28 ± 0.18 5 12.08 ± 0.06 8.88 ± 0.10 1.71 ± 0.07 6 13.03 ± 0.01 9.14 ± 0.02 1.92 ± 0.19 7 14.01 ± 0.01 9.20 ± 0.05 2.26 ± 0.12 8 15.02 ± 0.01 9.33 ± 0.02 1.96 ± 0.20 9 (confirmatory test) 25.24 ± 0.01 9.44 ± 0.30 2.33 ± 0.28 table ii. summary of results (sampling period 2) analysis no amount of naoh (g) ph amount of ag recovered (g) 1 8.05 ±0.01 8.82 ± 0.00 1.29 ± 0.39 2 9.01 ±0.11 8.96 ± 0.01 1.67 ± 0.32 3 10.04 ± 0.02 9.04 ± 0.02 2.46 ± 0.47 4 11.03 ± 0.02 9.09 ± 0.01 1.92 ± 0.32 5 12.04 ± 0.02 9.02 ± 0.11 1.66 ± 0.38 6 13.03 ± 0.01 9.13 ± 0.15 1.67 ± 0.48 7 14.01 ± 0.01 9.29 ± 0.03 1.82 ± 0.35 8 15.01 ± 0.01 9.35 ± 0.02 1.95 ± 0.23 b. statisical analyses the anova result shows that the amount of silver recovered by varying the amount of naoh was significant with p-value = 0.000 (sampling a). this implied that there were significant differences on the average amount of recovered crude silver between varying amounts of naoh used (table iii). further analysis using tukey test (“figure 6) was done in order to determine at which specific means of silver recovered with varying amount of naoh exhibited significant difference. table iii. summary of anova analyses sampling f value p value decision a 16.12 0.000 significant difference b 2.45 0.066 no significant difference fig. 6. tukey test on the average amount of silver recovered with varying amount of naoh in sampling a it can be extrapolated from figure 4 that their was a significant difference between the means/averages of silver recovered using naoh at 8.01 g-10.00 g, 8.01 g-12.08 g, 8.01 g13.03 g, 8.01 g-14.01 g, 8.01 g-15.02 g, 9.07 g-13.03 g, 9.07 g-14.01 g, 9.07 g-15.02 g, 10.00 g14.01 g, 11.03 g13.03 g, 11.03 g-14.01 g, 11.03 g-15.02 g, 12.08 g-14.01g respectively. the result in sampling a only showed that the amount of naoh that can produce more crude silver was within the range of 10.00 g to 15.00 g. for sampling b, statically the results showed that the amount of silver recovered in sampling b do not differ significantly with p-value = 0.066. although the pvalue confirms no significant difference since it exceeds the critical value at 0.05, the raw data obtained in sampling b have shown a significant rise on the amount of silver recovered by using approximately 10.00 g to 15.00 g of naoh. notably, data used for one way -anova were those averages amount of the three trials done and thus if lower or higher values were present of recovered crude silver the resulting averages considerably may be pulled. engineering, technology & applied science research vol. 7, no. 5, 2017, 2094-2097 2097 www.etasr.com galarpe and leopoldo: potential recovery of silver (ag) from x-ray fixer waste by alkaline treatment c. optimum condition figures 7 and 8 present the graph showing amount of naoh and ph against the amount of silver recovered. it can be extrapolated in the present findings that optimum amount of crude silver can be recovered at ph approximately 9 (figure 7) and naoh approximately 10 g (figure 8). the method used in this study for fixer waste was not established in literature, considering that alkaline treatment was commonly used in waste x-ray films analysis [5]. however, the use of other alkali like potassium boro-hydride (kbh4) at ph 8~9 showed 98.0% and 95.8% silver recovery [2]. the same ph in this study similarly showed optimum condition for recovery. fig. 7. relationship between ph and amount of crude silver recovered fig. 8. relationship between amount of alkaline reagent used and the amount of crude silver recovered iv. conclusions the study investigates a chemical method of silver recovery from x-ray processing fixer waste by alkaline treatment using sodium hydroxide (naoh). the samples considered were taken from selected hospitals and radiology centers in philippines. overall, approximately 10.00-15.00 g naoh is found to be the optimal practical amount of precipitating agent for the recovery of crude silver from a specified volume of x-ray fixer waste. recovery improvement below and above the above range was insignificant as far as the amount of crude silver produced is concerned. the naoh precipitation method works under basic condition with ph of 9 to 12. references: [1] s. shankar, s. v. more, r. s. laxman, “recovery of silver from waste x-ray film by alkaline protease from conidiobolus coronatus” , kathmandu university journal of science, engineering and technology, vol. 6, no. 1, pp. 60-69, 2011 [2] h. zhouxiang, w. jianying, z. ma, h. jifan, “a method to recover silver from waste x-ray films with spent fixing bath”, hydrometallurgy, vol. 92, no. 3, pp. 148-151, 2008 [3] v. i. e. ajiwe, i. e. anyadiegwu, “recovery of silver from industrial wastes, cassava solution effects”, separation and purification technology, vol. 18, no. 2, pp. 89-92, 2000 [4] n. nakiboglu, d. toscali, i. yasa, “silver recovery from waste photographic films by using enzymatic method”, turkish journal of chemistry, vol. 25, no. 3, pp. 349-353, 2001 [5] n. nakiboglu, d. toscali, g. a. nisli, “a novel silver recovery method from waste photographic films with naoh stripping”, turkish journal of chemistry, vol. 27, no. 1, pp. 127-133, 2003 [6] a. d. bas, e. y. yazici, h. deveci, “recovery of silver from x-ray film processing effluents by hydrogen peroxide treatment”, hydrometallurgy, vol. 121, pp. 22-27, 2012 [7] v. choudhary, “recovery of silver from used x-ray films by aspergillus versicolor protease”, journal of academia and industrial research, vol. 2, no. 1, pp. 39-41, 2003 [8] j. marinkovic, m. korac, z. kamberovic, i. matic, “recycling of silver from exposed x-ray films”, acta metallurgica slovaca, vol. 12, pp. 262-268, 2006 [9] p. a. ramirez, v. e. reyes, m. a. veloz, “silver recovery from radiographic films using an electrochemical reactor”, international journal of electrochemical science, vol. 6, pp. 6151-6164, 2011 [10] j. p. chen, l. l. lim, “recovery of precious metals by an electrochemical deposition method”, chemosphere, vol. 60, no. 10, pp. 1384-1392, 2005 [11] j. bentley, u.s. patent no. 3,715,291. washington, dc: u.s. patent and trademark office. 1973 [12] r. scheidegger, a. zurrer, u.s. patent no. 4,139,431. washington, dc: u.s. patent and trademark office, 1979 authors profile van ryan kristopher r. galarpe is presently purusing a phd in science education-chemistry in the university of science and technology of southern philippines. she is a graduate of msc environmental science in the university of san carlos, cebu philippines on 2013 under the department of science and technology (dost) scholarship grant. she also earned her bsc in applied physical sciences (major chemistry and physics) in the university of science and technology of southern philippines (ustp) as academic scholar. her research work experience focused on solid waste management, environmental chemistry and toxicology, science education, and environmental science. girlie d. leopoldo is presently working as an assistant professor in the university of science and technology of southern philippines (ustp) under the department of chemistry. she earned her bsc in chemistry and msc in chemistry from the mindanao state university-iligan institute of technology (msu-iit) in the philippines. her present work is focused mainly on environmental analytical chemistry which include water quality analysis. engineering, technology & applied science research vol. 8, no. 1, 2018, 2374-2378 2374 www.etasr.com gegechkori et al.: using fast hot shock wave consolidation technology to produce superconducting mgb2 using fast hot shock wave consolidation technology to produce superconducting mgb2 t. gegechkori g. mamniashvili a. peikrishvili condensed matter physics department andronikashvili institute of physics ivane javakhishvili tbilisi state university tbilisi, georgia tatagegechkori@yahoo.com condensed matter physics department andronikashvili institute of physics ivane javakhishvili tbilisi state university tbilisi, georgia mgrigor@rocketmail.com materials science department f. tavadze institute of metallurgy and materials science tbilisi, georgia akaki.peikrishvili@yahoo.com v. peikrishvili b. godibadze materials science department f. tavadze institute of metallurgy and materials science tbilisi, georgia vaxoo3@gmail.com blasting technologies department g. tsulukidze mining institute tbilisi, georgia bgodibadze@gmail.com abstract—the original hot shock wave assisted consolidation method combining high temperature was applied with the twostage explosive process without any further sintering to produce superconducting materials with high density and integrity. the consolidation of mgb2 billets was performed at temperatures above the mg melting point and up to 1000oc in partially liquid condition of mg-2b blend powders. the influence of the type of boron (b) isotope in the composition on critical temperature and superconductive properties was evaluated. an example of a hybrid cu-mgb2–cu superconducting tube, possibly useable in hybrid energy transmission lines, is demonstrated and conclusions are discussed. keywords-superconductivity; mgb2; fast fabrication; explosive consolidation; hybrid energy lines; magnetization; isotopic effect i. introduction the superconductive properties of mgb2 with c32 structure and critical transformation temperature of tc=39k was discovered in 2001 [1]. since then, intensive investigation and development of different types of mgb2 superconductive materials in various forms and efforts to increase their tc above 39k takes place worldwide [2-5]. the technology of developing superconductive materials belongs to traditional powder metallurgy: preparing and densification of mg and b powder blends in static conditions with their further sintering processes [6, 7]. results described in [8], where mg-2b blend powders were first compacted in cylindrical pellets and were after loaded in hot conditions with 2 gpa pressure, seem also interesting. the observation of clear correlation between the synthesis condition and crystal structure of the formed two phases mgb2-mgo composites as well as between their superconductive properties allowed the conclusion that redistribution of oxygen in the mgb2 matrix structure and formation of mgo phase may be considered as positive effects. existing data of the application of shock wave consolidation technology for the fabrication of high dense mgb2 billets with higher tc temperature practically gave the same results and the limit of tc=40k is still considered maximal. additional sintering processes after the shock wave compression are highly recommended for providing full transformation of consolidating blend phases into the mgb2 composites. the goals of the current investigation are: • the development of high dense hybrid mgb2 billets using the hot shock wave fabrication technology without any further sintering processes • the development of cylindrical combined cu-mgb2-cu composites using copper substrate materials • the investigation of the role of temperature in the process of consolidation and sintering of mgb2 • the consolidation of mgb2 billets above the melting point of mg up to 1000oc in partially liquid matrix of mg-2b blend powders • the evaluation and investigation of structure property relationship ii. experimental procedures the novelty of the proposed nonconventional approach relies on the fact that the consolidation of the samples from coarse (under 10-15 µ) mg-2b blend powders was performed in two stages [9]. the explosive pre-densification of the powders was made at room temperatures. in some cases before dynamic pre densification the loading of precursors into the engineering, technology & applied science research vol. 8, no. 1, 2018, 2374-2378 2375 www.etasr.com gegechkori et al.: using fast hot shock wave consolidation technology to produce superconducting mgb2 containers were performed by static means. in all cases, the second stage was done by the hot explosive compaction (hec) but at temperatures under 1000oc with loading intensity around 5 gpa. cylindrical compaction geometry was used in all of the hec experiments. at first stage the mg-2b powders were placed inside a copper-tube container. the container was sealed at both ends with threaded steel plugs. a concentric cardboard box was filled with the powdered explosive materials and was placed around the cylindrical sample container (figure 1). fig. 1. the procedure of preliminary densification of mg-2b blend powders: 1. bottom plug of copper tube. 2. precursor powders. 3. explosive powder. 4. upper plug of steel tube. 5. electric detonator. 6. products of detonation. 7. consolidated powders. the key operational component of the hec experiments with vertical configuration of explosive charge that allows the consolidation of all type of powders at elevated temperatures is presented in figure 2. the application of vertical configuration of charge allows the increasing of the size of explosive charges without limitation. as a result, the pulse duration during the shock wave loading will increase resulting in obtaining samples with higher densities. on the other hand the increasing of pulse duration in some cases will allow the decrease of consolidating temperature and the compressing of samples at lower temperatures and as a result the cost reduction of obtained billets too. the hec device (figure 2) consists of 3 main parts: the heating system (a cylindrical heating furnace), the cylindrical feeding system and the explosive charge set-up. the preliminary pre-densified cylindrical billets (1) are located in the central hole of the heating furnace (4). the heating billet is fixed in the furnace by an opening and closing mechanism (6). after reaching the necessary temperature the opening (6) sheet opens the furnace and the billet moves through the feeding system (9-11) to the explosive charge set-up (17). after receiving the signal that the billet passed through the feeding system and is located in final position (13), the detonation takes place and explosive compression of heated billets occurs. determined by the volume, type, and density of the sample composition, the heating lasts about 60 min. the temperature is measured using a chromel-alumel thermocouple whose tip is situated inside the heating furnace. at the reaching of the desired temperature the furnace is switched off remotely and the feeding mechanism opens. billets pass through the feeding tube inside the cylindrical charge. as soon as the billet reaches the bottom of explosive charge in requested position, the detonation circuit switches on automatically and the explosive is detonated (figure 3). the corresponding pressure at the wall of the steel container is around 5 gpa. figure 3 represents the explosive charge construction in detail. the hec sample consisting of preliminary compacted powder (1) in cylindrical container (2), closed by plug (3), after its movement is located in the explosive charge set up consisting of feeding tube (5), explosive charge (6) and detonator/detonation cord (7). the additional steel tablets at the end of the container were used for avoiding the cutting of the container end and the securing of billets during the hec experiments. figure 4 represents the billets after the first stage of pre-densification and the secondary consolidation at 1000°c. fig. 2. set-up of hec device. 1. consolidating powder material. 2. cylindrical steel container. 3. steel container plugs. 4. furnace heating wires. 5. furnace ppening and closing. 6. furnace opening sheet. 7. furnace closing sheet. 8. basic construction of hec device. 9. feeding steel tube for samples. 10. movement tube for heated container. 11. connecting tube from rub. 12. accessory for the fixing of explosive charge. 13. circle fixing passing of steel container. 14. detonator. 15. detonating cord. 16. flying tube for hec. 17. explosive charge. 18. lowest level of steel container. 19.bottom fixing and stopping steel container. 20. sand. fig. 3. experimental set up for hec of cylindrical billets explosive charge at the bottom according to the general view of hec device (figure 1). fig. 4. the billets from mg-2b blend powders after consolidation with intensity of loading under 10 gpa: a) first stage pre-densification by shock waves at room temperatures, b) consolidation of the same billets at 1000°c with intensity of loading under 5 gpa. (a) (b) engineering, technology & applied science research vol. 8, no. 1, 2018, 2374-2378 2376 www.etasr.com gegechkori et al.: using fast hot shock wave consolidation technology to produce superconducting mgb2 iii. results cylindrical tubes from steel and copper were used in order to consolidate high dense superconductive mgb2 billets. as further investigation showed, the high temperature consolidation of mg-2b precursors in steel containers had positive effect and allows the fabrication of two phase mgb2mgo near to theoretical density with critical temperatures around tc= 38k. in contrast to steel containers, the shock wave fabrication of mg-2b powder blends in cu containers leads to the formation of undesirable phases such as mgcu2. this occurs because of the diffusion of copper atoms under the shock wave front towards the container center causing further chemical reactions with mg and the formation of mgcu2. the reaction was so intense and exothermic that the surface between the container’s wall and mg-2b precursors fully melted. the effect connected with the formation of mgcu2 behind the shock wave front is described in [3]. in order to prevent the movement of cu atoms by the shock wave front towards the container center, tantalum foils with thickness of 100µm were used as intermediate layers between the copper container’s wall and the blend powders. as a result no mgcu2 inside the consolidated mg-2b composites were observed. figure 5 represents microstructure of hec mg-2b precursors obtained at 940oc in copper container. the central part and the edges of hec precursors differ and traces of high temperature and melting/crystallization processes can be observed. the existence of micro cracks on the edge of hec precursors (figure 5b) may be explained as a result of thermal stresses during the rapid cooling process. figure 6 represents the macrostructure of consolidated mg2b composition with the application of an intermediate layer from ta foil at different magnifications. the application of ta intermediate layer between the cu container’s wall and composites provides full protection of consolidated powders from the transportation of cu atoms and as a result the formation of mgcu2 does not occur. this was confirmed by xray analysis where there was demonstrated that the application of thin ta intermediate layer fully prevents the diffusion of cu atoms towards consolidated compositions. figures 7 and 8 represent the diffraction pictures of hec mg-2b composites showing the phase formation and confirming the efficiency of the application of ta intermediate layer. as mentioned, the application of thin ta layer prevents the diffusion of copper and no traces of cu or mgcu2 can be observed (figure 8). in contrast to this, the existence of copper inside the samples may be easily observed in the case of copper container without the tantalum layer (figure 7). the identification of phase lines from the diffraction picture (figure 8) shows that after hec of mg-2b precursors only two phase compositions (mgb2 and mgo) were formed. this was confirmed by sem investigations where the advantages of hec technology for the fabrication of two phase mgb2-mgo composites near the theoretical density without porous and any other visible structure defects, were demonstrated (figure 9). figure 10 represents the microstructures of hec mg-2b precursors obtained at 940oc with correspondent spectral analysis with element identification. we see that the diffusion of copper atoms into the hec mg-2b precursors is not occurring. the element identification shows that we may only consider the existence of two phases. the light (bright) phase of spectrum-1 on the microstructure (figure 10) belongs to mg when dark region on the spectrum-2 shows only elements of mg and b. fig. 5. the microstructure of hec mg-2b blend powders after two stage shock wave loading in copper container at 940 o c with loading intensity of 5gp: a) central part b) edge. fig. 6. the macrostructure of hec mg-2b precursors at 940°c in copper container with application of intermediate tantalum layer. fig. 7. the diffraction picture of hec mg-2b composite powders after consolidation at 940 o c in copper container. fig. 8. the diffraction picture of hec mg-2b composite powders obtained at 9400c in copper container with application of protecting intermediate tantalum layer. (b) (a) engineering, technology & applied science research vol. 8, no. 1, 2018, 2374-2378 2377 www.etasr.com gegechkori et al.: using fast hot shock wave consolidation technology to produce superconducting mgb2 fig. 9. the macrostructure of hec mg-2b precursors near to the edge obtained at 940⁰c using intermediate ta layer. as it’s seen from spectral analysis and atom distribution there diffusion of copper atoms into the hec mg-2b precursors is fully prevented. fig. 10. the microstructures of hec mg-2b composites and their correspondent spectral analyses with element identification obtained at 940oc with application of intermediate ta layer. the intensity of loading onto the container’s wall was around 5 gpa. after that we can be sure that after the chemical reactions under the shock wave front full transformation of starting elements into the two phase composition from mgb2 and mgo occurs. the observation of eutectic colonies on the microstructure confirms the fact of melting/crystallization processes behind the shock wave front. in order to evaluate the superconductive characteristics of obtained billets the magnetic moment temperature dependence in zero-field-cooled (zfc) and field-cooled (fc) modes depending on experimental conditions and type of boron precursors were investigated. as reported in [9, 12] the application of low temperatures up to 9000c and hec of mg-2b precursors in steel containers did not give results. in spite of high density and uniform distribution of phases they did not obtain superconductive characteristics. the investigation of hec processes for mg-2b precursors in copper container gave same results and no superconductive characteristics below 900oc. figure 11 presents the data of measurements for hec mg-2b composition powders consolidated under 1000oc temperatures in copper container with loading intensity under 5 gpa. the investigation on the type of b isotope influence onto the final superconductive characteristics of mgb2 after the hec at 940oc shows that in contrast to the 11b isotope, the application of 10b isotopes in mg-b precursors provides increased tc by 1k. such difference may be explained by the lower mass of 10b nucleus compared to 11b. this confirms the important role of temperature in the formation of superconductive mgb2 phase in the whole volume of the sample and corresponds with literature data, where only after sintering processes above 900oc the formation of mgb2 phase with tc =40 k took place. the difference of tc between the hec and sintered mgb2 composites may be explained due to a rest of non-reacted mg and b phases or due to the existence of some oxides in precursors. this could be checked by increasing hec temperature or by the application of further sintering processes. the careful selection of initial mg and b phases is important too and in case of consolidation mg-2b precursors with the abovementioned corrections the chance to increase tc in the hec samples increases essentially. (a) (b) (c) fig. 11. magnetic moment temperature dependence measurements in zerofield-cooled (zfc) and field-cooled (fc) modes, showing the superconducting transition depending on container material and type of boron precursors. a) hec in steel container at 1000⁰c. b) hec in cu container with 10b isotope at 940⁰c. c) hec in cu container with 11b isotope at 940⁰c. the experiments for hec of mg-2b composition powders in copper container were performed below and above the mg melting point. the consolidation was carried out at 500, 700, 950, and 1000˚c with loading intensity around 5gpa. it was experimentally established that the comparatively lowtemperature consolidations at 500˚c and 700˚c give no results and obtained compacts have no superconducting properties. the hec technology allows also the production of multilayer cylindrical tubes (pipes) with the cu/mgb2/cu structure which could find important applications for the production of superconducting cables for simultaneous transport of hydrogen and electrical power in hybrid mgb2-based electric power transmission lines filled with liquid hydrogen [11]. an example of practical realization of hybrid cu-mgb2–cu superconductive cylindrical tubes for hybrid power transmission lines is demonstrated in figure 12. fig. 12. view of cross-section of hybrid cu-mgb2–cu superconductiving tube. engineering, technology & applied science research vol. 8, no. 1, 2018, 2374-2378 2378 www.etasr.com gegechkori et al.: using fast hot shock wave consolidation technology to produce superconducting mgb2 iv. discussion hec of mg-2b composite powders were performed in copper containers below and above the mg melting point. in order to determine the role of temperature, the consolidations were carried out at 500, 700 and 940 ˚c. at 500˚c and 700˚c the consolidation gives no results and the obtained compacts have no superconductive characteristics. the application of higher temperatures provides the formation of mgb2 composition in the whole volume of hec billets with maximal value of tc=38.5k without any post sintering process. this confirms the important role of temperature in the formation of superconductive mgb2 and corresponds with the literature data where only after sintering processes above 900˚c the formation of mgb2 phase with tc=40k takes place. the difference of tc between the hec and sintered mgb2 composites may be explained due to unreacted mg and b phases or due to the existence of oxides in the starting materials. this could be checked by increasing hec temperature or by the application of further sintering processes. the careful selection of initial mg and b phases is important too and in case of consolidation mg-2b precursors with corrections mentioned above the chance to increase tc of hec samples increases essentially. next experimental stage is the fabrication of mgb2 superconductive materials. v. conclusion the liquid phase shock wave consolidation of mg-2b precursors in copper container at 940˚c temperature provides the formation of mgb2 phase in the whole billet volume with maximal tc=38.5k. the application of an intermediate layer is an important technological solution which prevents the penetration of cu atoms to the consolidated mg-2b composites having as result the formation of mgcu2 phases. the type of applied b powder has influence on the final result of superconductive characteristics mgb2 and in case of isotopic 10b precursors better results are achieved (38.5k against 37.5 for 11b). the purity of materials is important factor and the existence of oxygen in the form of oxides in starting powders leads to reducing tc and to nonuniformity in fabricated billets. acknowledgment this research was supported by shota rustaveli national science foundation (srnsf) [grant number 217004]. references [1] j. nagamatsu, n. nakagawa, t. muranaka, y. zenitani, j. akimitsu, “superconductivity at 39 k in magnesium diboride”, nature, vol. 410, no. 6824, pp. 63-64, 2001 [2] c. h. jiang, t. nakane, h. hatakeyama, h. kumakura, “enhanced jc property in nano-sic doped thin mgb2/fe wires by a modified in situ pit process”, physica c, vol. 422, no. 3-4, pp. 127-131, 2005 [3] v. i. mali, v. a. neronov, v. p. perminov, m. a. korchagin, t. s. teslenko, “explosive incited magnesium diboride synthesis”, chemistry for sustainable development, vol. 13, no. 3, pp. 449–451, 2005 [4] n. orlinska, a. zaleski, z. wokulski, g. dercz, “characterization of heat treatment mgb2 rods obtained by pit technique with explosive consolidation method”, archives of metallurgy and materials, vol. 33, no. 3, pp. 927-932, 2008 [5] m. j. holcomb, “supercurrents in magnesium diboride/metal composite wire”, physica c: superconductivity and its applications, vol. 423, no. 3-4, pp. 103-108, 2005 [6] t. a. priknha, w. gawalek, ya. m. savchuk, v. e. moshchil, n. v. sergienko, a. b. surzhenko, m. wendt, s. n. dub, v. s. melnikov, ch. schmidt, o. a. nagorny, “high-pressure synthesis of a bulk superconductive mgb2-based material”, physica c: superconductivity, vol. 386, pp. 565-568, 2003 [7] a. g. mamalis, i. n. vottea, d. e. manolakos, “explosive compaction/cladding of metal sheathed/superconducting grooved plates: fe modeling and validation”, physica c: superconductivity, vol. 410, pp. 881-883, 2004 [8] a. p. shapovalov, “high pressure syntheses of nanostructured superconducting materials based on magnesium diboride”, high pressure physics and engineering, vol, 23, no. 4, pp. 35-45, 2013 [9] g. маmniashvili, d. daraselia, d. japaridze, a. peikrishvili, b. godibadze, “liquid-phase shock-assisted consolidation of superconducting mgb2 composites”, journal of superconductivity and novel magnetism, vol. 28, no. 7, pp. 1926-1929, 2015 [10] d. daraselia, d. japaridze, a. jibuti, a. shengelaya, k. a. muller, “rapid solid-state synthesis of oxides by means of irradiation with light”, journal of superconductivity and novel magnetism, vol. 26, no. 10, pp. 2987-2991, 2013 [11] v. v. kostyuk, i. v. antyukhov, e. v. blagov, v. s. vysotsky, b. i. katorgin, a. a. nosov, s. s. fetisov, v. p. firsov, “experimental hybrid power transmission line with liquid hydrogen and mgb2 based superconducting cable”, technical physics letters, vol. 38, no. 3, pp. 279-282, 2012 [12] t. gegechkori, b. godibadze, v. peikrishvili, g. mamniashvili, a. peikrishvili, “one stage production of superconducting mgb2 and hybrid power transmission lines by the hot shock wave consolidation technology, international journal of applied engineering research, vol. 12, no. 14, pp. 4729-4734, 2017 microsoft word etasr_v12_n3_pp8634-8639 engineering, technology & applied science research vol. 12, no. 3, 2022, 8634-8639 8634 www.etasr.com khlifi et al.: performance analysis of a hybrid microgrid with energy management performance analysis of a hybrid microgrid with energy management mohamed arbi khlifi department of electrical engineering, faculty of engineering, islamic university of madinah, saudi arabia and sime laboratory, ensit, university of tunis, tunisia mohamedarbi.khlifi@issatm.rnu.tn abdulrahman alkassem department of electrical engineering, faculty of engineering, islamic university of madinah saudi arabia rahman.alkasem@gmail.com azzedine draou department of electrical engineering, faculty of engineering, islamic university of madinah, saudi arabia adraou@yahoo.com received: 28 february 2022 | revised: 28 march 2022 | accepted: 4 april 2022 abstract-in a hybrid microgrid system, various renewable energy resources may be integrated and modeled on-site, in such a way as to provide an optimal, consistent, and sustainable energy production at a cost-effective rate throughout the year. in this paper, a microgrid prototype consisting of a wind turbine and a photovoltaic (pv) panel is modeled and thoroughly investigated through various changes in inputs. the long-term goal of this work in ium is to develop a concise and complete microgrid system model that can be used to simulate and fully understand its behavior and operation. the proposed model including power sources, power electronic converters, and load has been modeled in matlab/simulink. keywords-pv microgrid; grid modeling; microgrid; wind turbine; battery i. introduction during the recent years, there was a huge demand of energy from vital sectors such as the manufacturing industry, the transportation system, and general construction industry which indicated a steady growth in economic development. however, this energy is related to environment concerns because the use of fossil fuel and coal for the generation of electricity generation emits greenhouse gases (ghg). thus, numerous stake holders aim the developing countries to use clean and green energy with financial support [1-2]. with the steady increase in global population, the demand for energy has increased dramatically and this has led to a high pressure on actual energy infrastructures to generate power above their nominal capacity. the development of electric power generation methods to make the kingdom of saudi arabia a logistical center connecting three continents and thus enhance sustainable economic growth and competitiveness, while achieving convergence between all services to meet the kingdom’s needs by raising the level of protection, rationalizing energy, and improving the quality of operations and performance for providing effective services to all beneficiaries, is in line with saudi vision 2030 [3-5]. power generation projects are among the most important projects that the governments seek to present to their citizens to develop cities, provide basic services to the society and raise the state’s economy by owning an integrated power generation system [68]. to extend the national grid for rural areas and remote places, a high price has to be spent for building such large power networks. this has prompted decision makers to look for alternatives energy resources such as renewable energy in local levels [9-12]. to address the challenge of this global developmental crisis, numerous meetings have been conducted between government and private stakeholders without much success bearing in mind that the population will be without any access to electricity [13-14]. the use of the alternative renewable sources such as hybrid microgrid systems is a way of achieving this objective. this will allow the generation of eco-friendly electricity in remote areas by suppressing the effect of climate change. recently, and as a short term solution to this energy crisis, hybrid microgrids have been thoroughly used as an alternative for the generation and distribution of renewable energy in remote locations [15-18]. a microgrid system is usually composed of distributed energy resources like photovoltaic panels, wind turbines, fuel cells, or micro turbines that may be connected to the distribution network at a medium voltage. microgrids can also work off the main grid to meet customer needs, improve reliability, lower emissions, and improve power quality at a reduces price. the optimal use of hybrid microgrids assets as an alternative to the main grid extension has allowed for electricity generation at a reduced overall price [19-20]. in this paper, energy management with specific aspects related to remote localities is proposed, powered solely by corresponding author: mohamed arbi khlifi engineering, technology & applied science research vol. 12, no. 3, 2022, 8634-8639 8635 www.etasr.com khlifi et al.: performance analysis of a hybrid microgrid with energy management renewable resources where the grid extension is not plausible. these solutions can be applied for isolated water pumping, irrigation, household applications, etc. in the future, with the development of more efficient technologies, the proposed solutions will be of great interest for telecommunications applications and hydrogen storage. recently many research works have been published on the field of modeling and simulation of isolated hybrid systems [21-24]. in this paper, we mainly focus on the study of strategies for the energy management in a hybrid microgrid. three different energy management strategies are considered: photovoltaic system, wind turbine, and batteries. the major contribution of this paper is the presentation of a simulation model of a hybrid microgrid energy system made up of pv panels, wind turbine, and battery for storage. this paper provides the overall description of the proposed methodology of the management strategy of the system. the effectiveness of the proposed hybrid microgrid energy system is confirmed through the simulation under several situations such as variation in power demand. ii. hybrid ac/dc microgrid microgrids are effective systems for managing dispersed resources like small-scale distributed generators and renewable energy resources. the microgrid structure allows for more efficient operation which could lead to lower emissions and fewer power outages. microgrids can be made up of a complicated mix of ac and dc sources, as well as ac and dc loads, and power electronic interfaces. the benefits of both ac and dc microgrids are combined in a single network architecture with hybrid ac/dc microgrids. by permitting seamless connection to numerous ac and dc sources and loads, it decreases the losses associated with multiple conversions from dc to ac and vice versa. it may also be linked to the national grid or used as a stand-alone power source. when connected to the utility grid, the ac and dc microgrids receive energy from it to balance between load demand and supply, resulting in a acceptable power balance with the grid. when there is an excess of power in the ac and dc microgrids, the power will flow to the utility grid. on the contrary, when there is a shortage of power in the ac and dc microgrids, power is returned back to the ac and dc microgrids by the utility grid. usually, the energy storage systems (esss) are used primarily to compensate any shortage of energy since the generating units are supposed to provide the majority of the energy consumed in the system. thus, the ac and dc microgrids will deliver energy with a steady bus voltage and reduced harmonics to the utility grid. the main converter in the microgrid will minimize any unbalance occurring from the loads and when the output of the dc sources exceeds the output of the dc loads, the converter acts as an inverter, transferring power from dc to ac. iii. modeling of the microrgid a. pv array with mppt usually, the sun is considered as a potential source of energy as it is consistent and clean, as opposed to other types of energy that contaminate the atmosphere and the environment, such as coal, oil, and oil derivatives. a pv cell is usually considered as a current source in parallel with a diode as shown in figure 1. with the increase of intensity of sun light, current is produced by the pv cell [18]. fig. 1. electrical model of a solar cell. ideal case: ( ) exp 1pvpv cc isc r s r r t ve e i i k t t i e e v    = + − − −       (1) real case: ( ) exp 1 pv cc isc r r r pv s pv pv s pv s t sh e e i i k t t e e v r i v r i i v r = + − −  +  +   − −           (2) we use the model of (1) and (2) [18], due to the difficulty of estimating the pv system's behavior. we may be able to determine the panel's i-u and p-u properties using this approach. it may also allow us to adjust the voltage, current, and power while changing the number of cells in series and parallel in the panels. the modeling of a panel composed of ns modules in series and np modules in parallel is given. the diode current ip is obtained by [18]: 0 exp 1 p s p s p p p ph t p p s p s sh sh v r i n n i n i i v n v r i n r r     +       = − −               − − (3) figure 2 shows the i-v characteristics of the panel as defined for this application at various ambient temperatures and a constant irradiation of 1000w/m2. it can be seen that when the temperature rises, the power produced by the pv panel decreases. temperature fluctuations have little effect on the short circuit current. figure 3 depicts the pv panel's i-v characteristics at constant temperature of 25°c and various irradiation values. the higher the degree of solar irradiation, the more power the pv generates. as a result, any change in the irradiance level will alter the short circuit current value proportionately. engineering, technology & applied science research vol. 12, no. 3, 2022, 8634-8639 8636 www.etasr.com khlifi et al.: performance analysis of a hybrid microgrid with energy management fig. 2. i-v characteristics at different temperature and constant irradiance of 1000w/m2. fig. 3. i-v characteristics of pv at constant temperature of 250c and different irradiances. b. wind turbine modeling wind energy conversion is the world's fastest-growing source of new electric generation, and it is likely to stay that way for a long time in future. it is more appealing than other sources because of its extended lifespan, emission-free operation, and low cost. these turbines supplement the use of other electric power sources by delivering the most costeffective solution in a variety of situations. figure 4 shows the steady state features of the wind turbine as modeled by its variable pitch. in the first input, the per unit of the generator base speed is taken and the synchronous speed is modeled as the base speed of a synchronous or asynchronous generator. the second and third inputs are the blade pitch angle and the wind speed in m/s. the base speed of the permanent-magnet generator may be considered as the speed for nominal voltage generation and no load application. the rest parameters, such as the drive train's stiffness, will be taken as infinite whereas the turbine's friction factor and inertia will be combined with those of the generator. the following equation calculates the turbine's output power [16]: 3( , ) 2 m p wind a p c v ρ λ β= (4) we can use numerical integration using the trapezoidal rule to determine the total amount of electrical energy produced by the panel [16]: 1 1 1 1 ( ) ~ ( ) 2 sunset n i i isunrise e p t dt p p t − + = = + ∆∑∫ (5) for a constant step size we can calculate the energy production as [16]: 1 1 2 1 1 ( ) ~ 2 2 sunset n n i isunrise e p t dt p p p t − =   = + + ∆      ∑∫ (6) figure 4 depicts the simulink mathematical model of a wind turbine. the generator speed of the nominal generator speed, the pitch angle in degrees, and the wind speed in m/s are used as the three inputs. the output is the torque applied to the generator shaft which can be obtained by dividing the rotational speed by the wind speed to get the tip speed ratio in pu value. fig. 4. simulink mathematical model of the wind turbine. fig. 5. turbine power characteristics with wind as parameter. engineering, technology & applied science research vol. 12, no. 3, 2022, 8634-8639 8637 www.etasr.com khlifi et al.: performance analysis of a hybrid microgrid with energy management figure 5 shows a series of mechanical power curves versus wind speed changes. it can be seen that average wind speed of 3.81m/s is obtained as the base wind speed. moreover, we have obtained the maximum power as 0.73 pu (kp = 0.73) at base wind speed, and the maximum rotational speed is 1.2 pu at base rotational speed. c. battery operating to support the pv system storage energy is used in this simulation to help the pv system fulfill the load power requirements. because the battery active power reference (pa) will be led by (7), it might be considered the foundation of a stand-alone system. the battery will not only be used to supply its energy to help the pv system (ppv) meet the needs of the load's demand (p). it will also store the energy generated by the pv system when it exceeds the power demand of the load [17]. a pv lp p p= − (7) figure 6 illustrates the simulink model of the battery and in figure 7 we can notice the presence of three regions related to the flow characteristics of the battery. in the first region and during the charging of the battery, an exponential drop in voltage occurs. the area corresponding to the available charge in the battery before the drop of the voltage below its nominal voltage is depicted in the second region. the third region corresponds to the discharge cycle of the battery as the voltage drops. this drop depends on the type of the battery. moreover, the battery will recharge if the current becomes negative. fig. 6. battery model. fig. 7. charge and discharge characteristics of the battery. as can be seen in figure 7, the value is not always zero because of the existence of power losses (inductors and equivalent resistances) which are not supported by the battery. iv. the proposed power management system (pms) in this paper three different management strategies are compared. the main objective of this current study presented in this paper is to propose three different energy management strategies that can satisfy the following criteria: • guarantee the electrical energy required by the user, • manage efficiently the resources, and • minimize the excess energy. the management strategy will define the autonomous control of the power sharing scheme with the local load demand. it will also guarantee the reliability operation of the generating units' production. the pms aims to ensure power balancing among generating units as well as load management during power outages, with vital and critical loads being prioritized. this is important to prevent the dc bus voltage from collapsing due to the microgrid being overloaded and to keep the circulating currents to a minimum. the sub-units are related to the dc bus at which the output is reversed. moreover, the pms is designed to provide power that has a larger renewable fraction, and can adjust all of the electric parameters supplied by the inverters based on the energy demand. however, the pms will not rely on communication protocols of the producing units to increase the network's overall efficiency. the pms algorithm, which is used to determine the best network configuration for the pvwind-battery category, employs a cycle charging and load following dispatch strategy. the network's operational cycle is described below. a. energy management a (ppv + pw < pload) due to the changing nature of the renewable sources caused by seasonal climate variations, the energy produced by these sources is either insufficient or unavailable in this stage. the energy stored in the battery will be used to supply power to the local community, provided that the battery storage is within the operation's minimal soc. the system will remain in this condition until the restoration of power or until the battery' capacity falls under 25%. b. energy management b (ppv+ pw > pload) the required load demand energy to the local community will rely mainly on the renewable sources and any excess of power will automatically be stored in the battery bank. the battery is in a charging state at this point. c. energy management c (pload < socmin ) when the battery's soc falls below the minimum permitted limit of 25% and renewable energy is unavailable, the system's operation is taken over by the diesel generator. the generator is offered as a backup to avoid the system from completely collapsing if the renewable energy sources are unavailable for an extended period of time. no discharge from the battery will engineering, technology & applied science research vol. 12, no. 3, 2022, 8634-8639 8638 www.etasr.com khlifi et al.: performance analysis of a hybrid microgrid with energy management occur in this case since any extra power will be stored in the battery bank. d. discussion when the combined power of the pv panel and the wind turbine exceeds the load requirements, the excess electricity will be stored in the battery. if, on the contrary, this power is insufficient to satisfy the load requirement, the battery will begin to discharge its stored energy to service the load. if the battery runs out of the stored energy, and electricity from the pv and wind turbine system is not available, the generator kicks in, providing the needed power to service the load with an excess as charge in the battery system. v. conclusion a thorough evaluation of the mostly often utilized techniques in the literature for ac and dc microgrids was conducted in this paper in order to discover strategies that can be applied in hybrid microgrids. the main functions that a management plan should provide have been gathered, and a classification of the mostly studied hierarchical controls has been developed. the effectiveness of a hybrid microgrid for utilizing distributed renewable energy while meeting local load demand has also been discussed. microgrid modeling and operation modes were also analyzed and presented. the microgrid serves as a vital link between dispersed generation and renewable energy. the approaches for power management are depicted. when opposed to a standard grid, the nature of the microgrid is irregular and intermittent. acknowledgment the authors extend their appreciation to the deputyship for research & innovation, ministry of education, saudi arabia for funding this research work through the project number (20/10). references [1] s. muchande and s. thale, "hierarchical control of a low voltage dc microgrid with coordinated power management strategies," engineering, technology & applied science research, vol. 12, no. 1, pp. 8045–8052, feb. 2022, https://doi.org/10.48084/etasr.4625. [2] l. t. h. nhung, t. t. phung, h. m. v. nguyen, t. n. le, t. a. nguyen, and t. d. vo, "load shedding in microgrids with dual neural networks and ahp algorithm," engineering, technology & applied science research, vol. 12, no. 1, pp. 8090–8095, feb. 2022, https://doi.org/ 10.48084/etasr.4652. [3] a. a. bakar et al., "decentralized virtual impedance-based circulating current suppression control for islanded microgrids," engineering, technology & applied science research, vol. 11, no. 1, pp. 6734–6739, feb. 2021, https://doi.org/10.48084/etasr.3895. [4] t. le and b. l. n. phung, "load shedding in microgrids with consideration of voltage quality improvement," engineering, technology & applied science research, vol. 11, no. 1, pp. 6680–6686, feb. 2021, https://doi.org/10.48084/etasr.3931. 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[12] s. bracco and f. delfino, "a mathematical model for the dynamic simulation of low size cogeneration gas turbines within smart microgrids," energy, vol. 119, pp. 710–723, jan. 2017, https://doi.org/10.1016/j.energy.2016.11.033. [13] y. du, x. lu, j. wang, and s. lukic, "distributed secondary control strategy for microgrid operation with dynamic boundaries," ieee transactions on smart grid, vol. 10, no. 5, pp. 5269–5282, sep. 2019, https://doi.org/10.1109/tsg.2018.2879793. [14] p. ferraro, e. crisostomi, r. shorten, and f. milano, "stochastic frequency control of grid-connected microgrids," ieee transactions on power systems, vol. 33, no. 5, pp. 5704–5713, sep. 2018, https://doi.org/10.1109/tpwrs.2018.2821370. [15] m. a. hassan, "dynamic stability of an autonomous microgrid considering active load impact with a new dedicated synchronization scheme," ieee transactions on power systems, vol. 33, no. 5, pp. 4994–5005, sep. 2018, https://doi.org/10.1109/tpwrs. 2018.2798160. 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[23] e. pathan, a. a. bakar, s. a. zulkifi, m. h. khan, h. arshad, and m. asad, "a robust frequency controller based on linear matrix inequality for a parallel islanded microgrid," engineering, technology & applied science research, vol. 10, no. 5, pp. 6264–6269, oct. 2020, https://doi.org/10.48084/etasr.3769. engineering, technology & applied science research vol. 12, no. 3, 2022, 8634-8639 8639 www.etasr.com khlifi et al.: performance analysis of a hybrid microgrid with energy management [24] q. n. u. islam, s. m. abdullah, and m. a. hossain, "optimized controller design for an islanded microgrid using non-dominated sorting sine cosine algorithm (nssca)," engineering, technology & applied science research, vol. 10, no. 4, pp. 6052–6056, aug. 2020, https://doi.org/10.48084/etasr.3468. microsoft word etasr_v11_n6_pp7800-7804 engineering, technology & applied science research vol. 11, no. 6, 2021, 7800-7804 7800 www.etasr.com najeeb & fawzi: the effect of using plastic strips and sheets on the properties of slurry infiltrated … the effect of using plastic strips and sheets on the properties of slurry infiltrated fiber concrete adraa m. najeeb department of civil engineering university of baghdad baghdad, iraq a.najib1101@coeng.uobaghdad.edu.iq nada mahdi fawzi department of civil engineering university of baghdad baghdad, iraq nada.aljalawi@coeng.uobaghdad.edu.iq abstract-slurry infiltrated fiber concrete (sifcon) is a highstrong material that is regarded as a unique type of high fiber content concrete. this paper aims to study the influence of the use of plastic strips and plastic sheets in the sifcon slurry. three sets (normal sifcon as control, sifcon with plastic strips, and sifcon with plastic sheet), in a 1:1.08 cement-sand ratio by weight has been used with water to cement ratio (w/c) by weight equal to 0.3, and superplasticizer equal to 1% by weight. in addition, 6% by volume crimped steel fibers with an aspect ratio of 60 were applied and 1.34% by volume plastic was used, in strips of 5×1cm for both prism and cube samples and in sheets of 25×5cm and 7×7cm for prism and cube samples respectively. the compressive and flexural strength tests studies were conducted on typical cubes of 10×10×10cm and prisms of 40×7×7cm respectively to find out the way the plastic affects the sifcon properties. the results indicate that the models with plastic sheets placed in sifcon slurry give the highest compressive and flexural strength whereas the models with plastic strips gave the lowest. the difference percentages in compressive and flexural strength were -27.3, 8, -3.8 and 66.6% for all sets respectively when compared to the control set (using no plastic). keywords-sifcon; plastic strips; plastic sheet; crimped fibers; aspect ratio i. introduction there is a need to develop new forms of concrete that utilize fieldwork at reduced cost and in less time, therefore theoretical studies have been conducted utilizing building materials, additives, and sustainable materials of variopus types to create and discover types of concrete other than the conventional concrete, one of which is the slurry infiltrated fiber concrete (sifcon). sifcon is developed by increasing the percentage of steel fibers in the cement slurry. it has exceptionally high strength as compared to steel fibers reinforced concrete. sifcon is an extra strong material that incorporates fibers in a high percentage volume [1]. sifcon's matrix has no coarse particles but a high concentration of cementitious component. it may, however, incorporate fine (or coarse) sand as well as additives such as fly ash, micro silica, and latex emulsions. the ratios of cement and sand used to make sifcon are typically 1:1, 1:1.5, or 1:2. the water cement ratio ranges from 0.3 to 0.4. the percentage of superplasticizers in cement ranges from 2 to 5% by weight. the proportion of fibers by volume can vary from 4 to 20%, while the present practical range is between 4 and 12% [2]. sifcon is being frequently used, particularly in seismic modification design and in constructions subjected to impact forces. it also exhibits novel behavioral phenomena such as the fiber lock [3]. sifcon is used within applications where large ductility and energy absorbing are required, such as seismic-resistant reinforced concrete members and structures subjected to unusual or exploding forces. pavement toppings, pre-stressed beams repairs, and structural reinforced concrete element restoration are some of its other successful uses. in addition, it is used in military structures against blasts, industrial sites, runways, and bridge foundations [3, 4]. an investigation about the effectiveness of combining steel and polypropylene fibers in various combinations in the sifcon had been studied using fibers to cover 1/1, 1/3, and 2/3 of the molds in [5]. the mechanical and physical characteristics of sifcon were investigated in this study. the usage of fibers in different combinations resulted in raising the fiber volume. the greatest flexural strength rates were obtained using specimens entirely filled with fibers, which were 44.02mpa and 41.23mpa with steel fiber at lengths of 6cm and 3.5cm respectively, and with a composite of 6cm steel and 5cm polypropylene fiber. the usage of polypropylene fibers in conjunction with steel fibers enhanced fracture toughness and flexural strength. as a result, it had been discovered that polypropylene fibers offer great benefits over the use of sifcon in terms of cost and unit weight due to their reduced cost and density. the effect of adding steel fibers on the mechanical properties of concrete had been examined in [6] using fraction volumes of 0.5, 0.75, and 1 of concrete and an aspect ratio of 100. the study was conducted on ordinary concrete specimens (cubes and prisms) and on concrete reinforced with steel fibers that had been water cured. all the mixtures had the same volumetric percentage of coarse and fine aggregates, and the same amount of water, resulting in a constant w/c ratio of 0.54. the largest increase percentage in compressive strength for specimens of concrete reinforced with steel fibers cured in water for 90 days was 8, 11.1, and 17.1%. the flexural strength of prisms cured in water increased with curing time. the corresponding author: adraa m. najeeb engineering, technology & applied science research vol. 11, no. 6, 2021, 7800-7804 7801 www.etasr.com najeeb & fawzi: the effect of using plastic strips and sheets on the properties of slurry infiltrated … maximum improvements at 90 days of curing for plain concrete and concrete reinforced with fiber for all sets were 30.4, 36.8, and 44.3% respectively. regarding the curing temperature of high performance concrete, the influence of curing temperatures of 30, 40, and 50˚c on the compressive strength growth of high performance concrete was studied in [7]. the results were compared to concrete cured under standard circumstances at the usual curing temperature of 21˚c. the study findings revealed that at early ages, the rate of strength growth is larger at high than at reduced curing temperatures, with the greatest rising percentage in compressive strength at 50˚c. yet, at older ages, the strength produced at elevated curing temperatures was lower than that produced at normal temperatures, and the greatest percentage of loss was 5.7% percent at the curing temperature of 50˚c in 91 days curing age . self-compacted concrete (scc) is considered to have advantages similar to sifcon's, such as improved construction quality and faster construction activity. various fibers were utilized in [8] as fiber reinforcement in scc. they were proved to have a significant impact on the fresh and hardened characteristics of scc. in most situations, the inclusion of fibers reduces the fresh characteristics of concrete (e.g. flow ability, passing ability, and segregation resistance), but increases the mechanical properties substantially. the kind and shape of fiber, aspect ratio, and volumetric fraction were found to be important parameters regarding the performance of scc. the aim of adding and promoting the usage of plastic waste in concrete was studied in [9]. the flexural strength and the workability of concrete were examined using different percentages of plastic fibers. m15 grade concrete beams were casted and cured for 7 and 28 days. the results showed that the use of plastic fibers reduced workability marginally while they increased flexural strength by 16.5% at 0.6% addition of plastic fibers in concrete [9]. ii. materials used the investigation work has been carried out in the civil engineering department's laboratory at the university of baghdad. the used materials were: • ordinary portland cement type 42.5r complying to [10]. • zone 4 sand complying to [11]. • crimped steel fibers with a circular cross-section, with a length of 6cm, diameter of 0.1cm, and aspect ratio of 60 were utilized. table i explains the characteristics of steel fibers, and figure 1 depicts their form. • tap water complying with [12] was utilized. • sika viscocrete – 1316 hi-tech high range water reduction superplasticizer was utilized. the superplasticizer meets the type d and g criteria of [13]. • the plastic strips used were 5cm long and 1cm wide and were cut from plastic water bottles (figure 2). • plastic sheets, 25×5cm for prisms and 7×7cm for cubes having openings of 1×1.5cm, were used (figure 2). table i. steel fiber properties fiber type crosssection lengthl (mm) diameter (mm) aspect ratio density (kg/m 3 ) tensile strength (mpa) crimped circular 60 1 60 7870 >800 note: the values are according to the importing company fig. 1. crimped steel fibers. fig. 2. plastic strips and sheets. iii. mixing design and procedure the cement-to-sand ratio was set at 1:1.08 by weight, the w/c ratio was set at 0.3 by weight, and the superplasticizer percentage was set at 1% by cement weight. crimped steel fibers were utilized at a rate of 6% by volume. cement and sand were mixed in their dry form. the superplasticizer was added to the water in a bowl and they were stirred until a homogeneous solution was produced. then, the water with the superplasticizer were gradually added to the dried materials and blend until a homogeneous slurry mixture was obtained. before casting, all the molds (10×10×10cm cubes and 40×7×7cm prisms) were cleaned and lubricated. for the first sifcon set (control set), a thin layer of the slurry was placed in the molds and then the entire fiber quantity was placed at once. another layer of slurry was placed over the fibers and it was let to be penetrated by them. for the second set of sifcon with plastic strips, a thin layer of the slurry was put into the molds first, followed by the fibers with plastic strips all at once, and then another layer of the slurry was poured over the fibers. for the last set, a layer of slurry was first placed in the molds, followed by a layer of fibers and slurry, then the plastic sheet was placed in the middle. afterward, again one layer of fibers and one of slurry were placed and let to penetrated. to ensure that there are no honeycombs inside the specimens, the molds were lightly knocked on the outer face. the top surface of the specimens does not need to be level because the mixture is slurry and claims a level face on its own. regarding demolding, all specimens were submerged in a basin with tap water at room temperature in accordance with [14], until testing time. engineering, technology & applied science research vol. 11, no. 6, 2021, 7800-7804 7802 www.etasr.com najeeb & fawzi: the effect of using plastic strips and sheets on the properties of slurry infiltrated … iv. test procedures a. compressive strength test the compressive strength test was performed on the 10×10×10cm cubes in accordance with [15]. this test was carried out using a compressive strength hydraulic machine with 2000kn capacity at fixed load (figure 3). the outcomes are the average of cubes for each set at ages of 7 and 28 days. fig. 3. compressive strength measuring equipment. b. flexural strength test the flexural strength test was carried out in accordance with [16] employing the 40×7×7cm prisms. this test was performed with the use of a flexural strength test machine with capacity up to 400kn (figure 4). the average of each batch at ages of 7 and 28 days was used as the final result. fig. 4. flexural strength measuring equipment. v. results and discussion a. compressive strength test results the cubes prepared for compressive strength test were inspected at the age of 7 and 28 days for all sets. the outcomes show that adding plastic sheet in the sifcon mixture gives higher results than the mixture with the plastic strips and the control, while the results of plastic strip sifcon are lower than the other two sets. the reason for the enhanced results when the plastic sheets are present is the contribution of the sheets in keeping the steel fibers distributed over the entire model without falling to the bottom due to their higher density. the reason for the presence of holes in the plastic sheets is that they allow the slurry to penetrate the entire form without accumulating on the top of the sheets. the reason for the reduction in the outcomes when the plastic strips are present is the relatively large cross section of the plastic strip, which leads to the heterogeneity of the specimens, which in turn leads to the reduction in the outcome. table ii and figures 5-7 show the outcomes of the compressive strength tests. the outcomes of this study are higher than the ones in [17, 18]. fig. 5. compressive strength change with age. fig. 6. compressive strength change with age when using 6% steel fibers. fig. 7. sample for tested for compressive strength after failure. engineering, technology & applied science research vol. 11, no. 6, 2021, 7800-7804 7803 www.etasr.com najeeb & fawzi: the effect of using plastic strips and sheets on the properties of slurry infiltrated … b. flexural strength test results the specimens showed no deformation during the flexural strength testing. the fibers have been removed from the hardened slurry, in contrast to the plastic that remained conjoined, indicating that the adhesion between the fibers and the hardened slurry has been overcome. despite this, the adhesion between the hardened slurry and the fibers is excellent, agreeing with the findings in [5]. the prisms were tested for flexural strength at 7 and 28 days. the outcomes demonstrate that, the set using plastic sheets between the sifcon slurry layers performed better than the set using plastic strips and the control mix, while the set using plastic strips produced the worst results. the enhanced results of the set containing plastic sheets were caused by the homogeneity of the respective samples which kept the fibers distributed over the entire sample. the negative outcomes of the set containing plastic strips must be attributed to the nonhomogeneity of the samples due to the relatively large cross section of the plastic strips. the outcomes of this paper are higher than the ones in [9, 19]. table ii and figures 8-10 show the outcomes of the flexural strength tests. fig. 8. flexural strength change with age. fig. 9. flexural strength change with age when using 6% steel fibers. as a result summary, incorporating plastic sheets between the sifcon's slurry layers gives an enhanced result regarding compressive and flexural strength since the specimens are having good distribution of fibers over the entire model. incorporating plastic strips along with steel fibers inside the sifcon slurry reduces the outcomes of compressive and flexural strength tests due to the cross section of the plastic strips used which leads to uneven steel fiber distribution in the samples. fig. 10. a sample for flexural strength test after failure. table ii. results of compressive and flexural strength tests set control set sifcon with plastic strips set sifcon with plastic sheet set compressive strength (mpa) age (day) 7 28 7 28 7 28 34.72 53.74 25.23 39.04 37.50 57.84 % change 0 -27.3 8 flexural strength (mpa) age (day) 7 28 7 28 7 28 7.52 8.89 7.23 8.55 12.53 14.83 % change 0 -3.8 66.6 vi. conclusions in this study, used plastic was re-used as a sustainable material in sifcon mixes. the outcomes of this investigation obtained from using 10×10×10cm cubes and 40×7×7cm prisms with 6% steel fibers and plastic strips or sheets. the samples were cured for 7 and 28 days and then their compressive and flexural strength was tested. as a conclusion of this investigation the following points should be noted: • the results of compressive strength tests demonstrate that the use of plastic sheets within the sifcon enhanced the results by about 8%. the combination of plastic strips with steel fibers in sifcon gives a reduction in the results of about 27.3%. • the flexural strength test outcomes clarify that the plastic sheets used within the sifcon improve the result by about 66.6%, while using plastic strips with steel fibers in sifcon reduces the result by about 3.8%. references [1] k. dagar, "slurry infiltrated fibrous concrete (sifcon)," international journal of applied engineering and technology, vol. 2, no. 2, pp. 99– 100, 2012. [2] r. giridhar and p. r. m. rao, "determination of mechanical properties of slurry infiltrated concrete (sifcon)," international journal for technological research in engineering, vol. 2, no. 7, pp. 1366–1368, mar. 2015. [3] s. a salih, q. j. frayyeh, and m. a. al-wahab ali, "flexural behavior of slurry infiltrated fiber concrete (sifcon) containing supplementary cementitiouse materials," journal of engineering and sustainable development, vol. 22, no. 2, pp. 35–48, 2018, https://doi.org/10.31272/jeasd.2018.2.32. engineering, technology & applied science research vol. 11, no. 6, 2021, 7800-7804 7804 www.etasr.com najeeb & fawzi: the effect of using plastic strips and sheets on the properties of slurry infiltrated … [4] n. soylu and a. f. bingöl, "research on effect of the quantity and aspect ratio of steel fibers on compressive and flexural strength of sifcon," challenge journal of structural mechanics, vol. 5, no. 1, p. 29, mar. 2019, https://doi.org/10.20528/cjsmec.2019.01.004. 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[14] "standard practice for making and curing concrete test specimens in the laboratory," astm international, west conshohocken, pa, usa, astm c192/c192m-07. [15] bs en 12390-4:2019: testing hardened concrete compressive strength. specification for testing machines. london, uk: british standards institution, 2019. [16] bs en 12390-5:2019: testing hardened concrete flexural strength of test specimens. london, uk: british standards institution, 2019. [17] a. a. thomas and j. mathews, "strength and behaviour of sifcon with different types of fibers," international journal of civil engineering and technology, vol. 5, no. 12, pp. 25–30, dec. 2014. [18] s. a. khan and g. selvaraju, "characteristic of slurry infiltrated fibrous concrete (sifcon) produced by partially replacing cement by mineral admixtures and steel fibers by waste plastic fibers," journal of advanced research in engineering knowledge, vol. 7, no. 1, pp. 1– 15, 2019. [19] b. h. a. bakar, a. t. noaman, and h. m. akil, "cumulative effect of crumb rubber and steel fiber on the flexural toughness of concrete," engineering, technology & applied science research, vol. 7, no. 1, pp. 1345–1352, feb. 2017, https://doi.org/10.48084/etasr.854. engineering, technology & applied science research vol. 7, no. 4, 2017, 1883-1887 1883 www.etasr.com arabloo: auditor tenure and accounting conservatism: testing moderating effect of owner’s … auditor tenure and accounting conservatism: testing moderating effect of owner’s importance mehrdad dadgar arabloo department of management and accounting central tehran branch, islamic azad university tehran, iran abstract—conservatism is one of the salient features of financial reporting that has attracted more attention in recent years because of financial scandals. several recent studies have focused specifically on conservatism. this research tries to investigate the effect of auditor tenure and the importance of the client's accounting conservatism by using panel data model, multivariate regression, and data of 114 companies listed in tehran stock exchange during the years 2011 to 2015. the results showed that there is an inverse relationship between auditor tenure and conservatism of auditees; moreover, the client’s importance has an additive effect on the inverse relationship between auditor tenure and conservatism of client. keywords-auditor tenure; accounting conservatism; importance; client i. introduction observing the principle of conservatism is a component of reliability of the information. in [1], it was stated that conservatism is a different verifiability to identify revenues and costs that leads to understatement of profits and assets. conditional conservatism, which will be considered in this study, is also called post-event conservatism or conservatism affiliated with news. it signifies timely recognition of bad news from good news in the event of profit (loss). therefore, conservative policies by providing a negative picture of the financial situation and profitability of the business unit reduces pressures and the threat of competition on the one hand and moderates shareholders and investors' expectations of future performance of the business unit on the other hand. by assessing the benefits and costs of adopting a conservative or aggressive approach, managers do seek to maximize wealth of their stakeholders. it seems that conservatism increases with increasing competitive pressures. conservatism is one of the salient features of financial reporting that has attracted more attention in recent years because of financial scandals. although many accountants agree on the presence of conservatism in the regulation of the financial statements, no comprehensive definition has been provided for conservatism. however, two major features of conservatism been examined in accounting texts. first, downward siding of the book value of capital relative to market value; second, tendency to accelerate the identification of costs and delay in the recognition of revenue. it is stated in paragraph 95 of statement of financial accounting concepts no. 2, “if two amounts are not equally likely, conservatism does not necessarily dictate using the more pessimistic amount rather than the more likely one”. from the perspective of financial statement preparers, conservatism is as an attempt to choose a method of accepted accounting methods that result in one of the following items: slower revenue recognition, rapid diagnosis cost, lower valuation of assets, or higher evaluation of debts. in statement of financial accounting concepts no. 2, financial accounting standards board has reduced to some extent from the importance of conservatism because there is no sign of it in the hierarchy of features. the statement does not confirm presentation of undercounting value of the assets or profits (or offering more value than actually). however, researchers have presented some explanations for conservative financial reporting. all explanations show that conservatism is useful to users of accounting reports. the explanations include (1) contractual explanation, (2) legal proceedings explanation, (3) income tax explanation, and (4) legal explanation [2]. experts, researchers, and official bodies setting accounting and auditing standards as well as professional conduct rituals try to classify factors that can affect the quality of audit. most of them have adopted a normative view and they emphasize on factors such as independence, professional competence, professional skepticism, planning and proper supervision of audit work and so on. some other experts adopted a descriptive approach and they have considered auditor reputation, his membership in professional associations and organizations, auditor size, auditor expertise in a particular industry [3], audit fees [4], and results of coworkers [5] as factors affecting audit quality. this research emphasizes on the issue of auditor tenure and the relative importance of the client. the results of previous empirical studies [6] indicate the relationship between auditor tenure and audit quality. the company management has the primary responsibility for preparing the financial statements; but the accusing finger has pointed towards auditors in recent financial scandals in the world so that these events are generally called “failure of auditing”. it is believed generally that lack of independence and poor quality of the audit has led to such incidents. following these events, regulators and accounting standard developers have tried to formulate regulations for improving auditor independence and audit quality [7]. for example, ratification of sarbanes–oxley engineering, technology & applied science research vol. 7, no. 4, 2017, 1883-1887 1884 www.etasr.com arabloo: auditor tenure and accounting conservatism: testing moderating effect of owner’s … act of 2002 is an effort in this regard. section 203 of the act obliges the audit firms that change their associates and managers after 5 consecutive years of working on a client [8]. in addition, as stated in [9], auditors show more leniencies to the clients who are more important in terms of remuneration and credit. accordingly, they try more to maintain the client. with these lines, this study investigates the effect of auditor tenure and the importance of the client on the auditees’ conservatism in the companies listed in tehran stock exchange. ii. research background and literature review according to [3], conservatism means that the accountant must report the lowest value for assets and highest value for its liabilities among the possible values. revenue should be recognized later, not sooner; costs should be recognized sooner rather than later. accounting conservatism can be defined as the tendency of accounting in application of higher degree of verifiability for recognition of good news versus bad news [2]. conservatism is a different verifiability to identify revenues and costs that leads to understatement of profits and assets. recent studies have divided conservatism into conditional and unconditional conservatism [1]. numerous studies suggest adopting a conservative approach in normal conditions because interests of conservative approach outweigh its costs [1]. the effects of conservatism can be attributed to two issues. first, financial reporting standards that obligates conservative reporting; second, accounting practices selected by management to prepare financial statements. the second aspect is usually regarded as the image of conservatism in related literature. for example, conservative financial reporting by a company could imply the existence of higher uncertainty, higher risk, and eventually more conservatism; hence, it is obligated in the related standards. it may also indicate that the company has selected conservative accounting procedures for financial reporting. in the real world, both of them may be important and their relative importance differs. thus, companies aiming to provide conservative financial reports may not represent significant level of conservatism if the level of uncertainty and ambiguity is low. on the contrary, company with an aggressive policy of financial reporting may represent a significant level of conservatism if the level of uncertainty and ambiguity is high [10]. moreover, according to [11], long-term relationship between the auditor and the auditee creates a friendship between them; thus, it may reduce the reliability of financial statements. in 1996, the government accounting office in the united states announced that major frauds in the country had caused by most long-term relationships between auditor and auditee. it is not clear whether the mandatory auditor rotation is real solution to the problems related to poor quality of financial reporting. previous studies have shown that in the early years of interaction with the client auditor's motives may be different from other years. in general, auditor incentives relates to the balance between the tendency of auditors to maintain and benefit from the relationship between the auditor and the auditee [12]. auditing quality is a function of education, training, and knowledge of professional standards with the independence and impartiality, auditors’ awareness of the client's industry and business operations, and the relationship between active auditing team and management of the client’s company. there are two schools of thought about long-term audit tenure of auditory institutions. the first school of thought believes that auditory institutions with long-term audit tenure have relatively more knowledge of industry and business of a company and they can present higher quality and more auditing performance [11, 13-15]. another school of thought claims that in auditory institutions with long-term audit tenure, there is the possibility of familiarity (or even friendship) between the audit team members and client’s staff that increases the probability of destruction of auditing program. it reduces the likelihood of making decisions contrary to past years; hence, they may present and less efficient and lower quality auditing [16-20]. this school of thought has attracted the attention of many countries. in this regard, the results of [21] show that percent increase in the auditing quality of small companies is higher than large companies. in other words, audit quality improves when the audited units are smaller. in [22], authors concluded that changing audit institutions is generally useful the costs associated with changing audit institutions is less than its advantages. in [23], it was concluded that egyptian auditors are fully aware of the concept of audit quality and they agree with benefits of long-term relationship with the client in order to increase audit quality. the results of his study showed that mandatory rotation of audit institutions is a good strategy to increase independence of auditing institutions in egypt. in [24], authors concluded that increasing audit tenure leads to increasing audit quality. the results of [9] showed that the amount of clients’ accounting conservatism reduce with increasing auditor tenure. however, the relative importance of client in relation to auditor tenure and accounting conservatism has been evaluated insignificant. in iran, the findings in [25] represent that auditor rotation is directly related to the change in auditor’s opinion. the results of [26] indicate the direct and significant relationship between changing audit institutions and conservative earnings reporting of companies listed on the tehran stock exchange. overall, findings suggest that changing audit institution increases conservatism in profits reported by companies listed on the tehran stock exchange [27] concluded that there is a significant relationship between independent auditor rotation and audit report. in terms of auditor rotation type, the result of hypothesis testing indicates that there is no significant relationship between auditor rotation type and audit report in the surveyed firms. iii. research hypotheses according to the explanations provided in theoretical foundations and literature review, hypotheses are put forward as follows:  there is an inverse relationship between auditor tenure and accounting conservatism of clients.  client importance has additive effect on the inverse relationship between auditor tenure and conservatism of clients. engineering, technology & applied science research vol. 7, no. 4, 2017, 1883-1887 1885 www.etasr.com arabloo: auditor tenure and accounting conservatism: testing moderating effect of owner’s … iv. research methodology since results of this study can be used in decisions of managers, investors, analysts, capital market participants, the securities and exchange, and auditors, this is a practical research in terms of objectives. besides, this is a descriptivecorrelational research with respect to the way to deduce the hypotheses because it employs regression and correlation techniques to uncover the relationships among variables. accordingly, it uses inductive reasoning for its purposes. in addition, this is a positive research because the researcher makes their conclusion based on testing the available data. v. research models and variables the following models are used to test the research hypotheses: i,t 0 1 i,t 2 i,t 3 i,t i,t 4 i,t 5 i,t i,t 6 i,t net income = α + α stock return + α dummy negative stock return + α stock return * dummy negative stock return + α auditor tenure + α auditor tenure *stock return +α auditor tenure *dum i,t 7 i,t i,t i,t 8 i,t 9 i,t i,t 10 i,t my negative stock return + α auditor tenure *dummy negative stock return *stock return +α client importance + α client importance *stock return + α client importance * dummy negative st i,t 11 i,t i,t i,t 12 i,t i,t i,t i,t 13 i,t 14 ock return + α client importance * stock return * dummy negative stock return + α clientimportance *auditor tenure * stock return *dummy negative stock return + α firm size + α leve i,t i,trage + ε where 1) dependent variable:  net incomei, t: net income of company i in year t, which is the ratio of net income to total assets. 2) independent variables:  stock returni, t: stock returns of the company that is equal to the sum of dividend per share and difference of the share market prices at the end of the year and the beginning of the year divided by share market price at the beginning of the year;  dummy negative stock returni, t: negative stock returns that is marked by one if it is negative; otherwise it is marked by zero;  auditor tenurei, t: company auditor tenure that is equal to the number of continuous cooperation between audit firm and client.  client importancei, t: the importance of client of audit firm. it is marked by one if proportion of sales revenue for the client to sales revenue for all clients of the audit firm is greater than 0.2; otherwise, it is marked by zero. 3) control variables:  firm sizei, t = company size, which is equal to natural logarithm of total assets.  leveragei, t = financial leverage is the ratio of total debt to total company assets. vi. statistical population and statistical sample research statistical population includes companies listed on tehran stock exchange during the years 2011 to 2015. the sample will be selected through a systematic elimination from the statistical population. in this manner, sample contains all available companies in the population with the following criteria:  it should have no change in financial period during the intended period.  it should be regarded as active companies in the area of financial activities and it should not be from investment companies, banks, insurance companies, and financial institutions.  data for the variables should be available during the period 2011 to 2015.  their financial year ended in 21 march (last day of persian calendar) to enable researcher to used panel data in=f it is necessary. the process leads to selection of 114 companies. vii. research findings a. descriptive statistics the required descriptive indicators of variables including mean, median (central criteria), standard deviation, maximum, and minimum (scattering parameters) have been calculated. the results are represented in table i. table i. descriptive indicators of the studied variables standard deviationminimum maximum median mean research variables 0.125 -0.289 0.631 0.09 0.112 net income 0.937 -0.783 4.7 0.037 0.329 stock returns 0.498 0.000 1.000 0.000 0.456 negative stock returns 3.936 1.000 15.000 3.000 4.026 auditor tenure 0.405 0.000 1.000 0.000 0.207 importance of audit firm client 1.441 10.166 19.106 13.741 13.835 company size 0.188 0.065 0.986 0.584 0.579 financial leverage mean is considered as the main and most important central index. mean indicates equilibrium and center of distribution; median is the point dividing a sample into two equal parts. as it can be seen in the above table, the mean value of the variable stock returns is 0.329 and its median is 0.037. in general, distribution measures evaluate the dispersion of samples around the mean. standard deviation is one of the most important distribution measures. according to the table above, this measure for the variable stock returns is equal to 4.7 and its minimum is -0.783. characteristics of all variables are evident in the table i. engineering, technology & applied science research vol. 7, no. 4, 2017, 1883-1887 1886 www.etasr.com arabloo: auditor tenure and accounting conservatism: testing moderating effect of owner’s … b. inferential statistics results of testing the research hypotheses through fixed effects model and generalized least squares estimation method are mentioned in table ii. table ii. results of testing hypotheses significance level tstatistics standard deviation coefficients variables 0.000 12.332 0.042 0.526 fixed value 0.000 7.751 0.002 0.015 stock returns 0.63 0.481 0.005 0.002 negative stock returns 0.000 -5.003 0.019 -0.096 negative stock returns* stock returns 0.205 -1.267 0.0006 -0.0008 auditor tenure 0.075 1.783 0.006 0.01 stock returns *auditor tenure 0.561 0.58 0.001 0.0009 auditor tenure * negative stock returns 0.000 8.332 0.004 0.036 auditor tenure * stock returns * negative stock returns 0.007 2.708 0.009 0.025 client importance 0.637 0.471 0.005 0.002 client importance * stock returns 0.701 -0.384 0.016 -0.006 client importance * negative stock returns 0.305 1.025 0.35 0.037 client importance * stock returns * negative stock returns 0.002 3.117 0.005 0.015 client importance * auditor tenure * stock returns * negative stock returns 0.000 -4.865 0.003 -0.015 company size 0.000 -14.048 0.025 -0.351 financial leverage 0.537 adjusted coefficient of determination 64.803 f-statistic 2.019 durbin-watson coefficient 0.000 significance level of f-statistics 0.004 hausman test significance level 0.000 significance level chow test according to the results of table ii, since t-statistic for the variable negative stock returns* stock returns is greater than 1.965 and its significance level is less than 0.05, there is significant inverse relationship between negative stock returns* stock returns and net income of listed companies in tehran stock exchange. therefore, existence of conservatism is confirmed in the studied sample. moreover, since t-statistic for the variable auditor tenure* stock returns * negative stock returns is greater than +1.965 and its significance level is less than 0.05, there is a significant direct relationship between auditor tenure * stock returns * negative stock returns and net income of listed companies in tehran stock exchange. accordingly, increasing auditor tenure reduces company-wide accounting conservatism. in this way, the first hypothesis of this study is confirmed. in addition, since t-statistic for the variable client importance*auditor tenure * stock returns *negative stock returns is greater than +1.965 and its significance level is less than 0.05, there is a significant direct relationship between client importance*auditor tenure * stock returns * negative stock returns and net income of listed companies in tehran stock exchange. thus, increasing client’s importance strengthens destructive effect of auditor tenure on accounting conservatism in a company. viii. conclusion according to available theoretical and empirical evidence, conservative financial reporting by a company could imply the existence of higher uncertainty, higher risk, and eventually more conservatism; hence, it is obligated in the related standards. it may also indicate that the company has selected conservative accounting procedures for financial reporting. in the real world, both of them may be important and their relative importance differs. with emphasis on the concept of accounting conservatism, this study has tried to investigate the effect of auditor tenure on accounting conservatism companies using data from 114 companies listed on tehran stock exchange during the five-year period ending in 2015. the results of testing the first hypothesis of research indicated that increasing auditor tenure reduces accounting conservatism. it should be noted in this regard that conservative policies by providing a negative picture of the financial situation and profitability of the business unit reduces pressures and the threat of competition on the one hand and moderates shareholders and investors' expectations of future performance of the business unit on the other hand. numerous studies suggest adopting a conservative approach in normal conditions because interests of conservative approach outweigh its costs. there is the possibility of familiarity (or even friendship) between the audit team members and client’s staff in auditory institutions with long-term audit tenure; it increases the probability of destruction of auditing program. then, it reduces the likelihood of making decisions contrary to past years; hence, they may present and less efficient and lower quality auditing. in this manner, increasing auditor tenure will be accompanied by reduction in accounting conservatism. this conclusion is in line with the findings in [9]. the results of testing second hypothesis (client importance has additive effect on the inverse relationship between auditor tenure and conservatism of clients) is consistent with the findings in [9]. in this regard, it should be explained that auditors show more leniencies to the clients who are more important in terms of remuneration and credit. accordingly, they try more to maintain the client. in this way, increasing client importance adds the effect of auditor tenure on conservatism. references [1] s. basu, “the conservatism principle and the asymmetric timeliness of earnings”, journal of accounting and economics, vol. 24, no. 1, pp. 337, 1997 engineering, technology & applied science research vol. 7, no. 4, 2017, 1883-1887 1887 www.etasr.com arabloo: auditor tenure and accounting conservatism: testing moderating effect of owner’s … [2] r. l. watts, “conservatism in accounting part i: explanations and implications”, accounting horizons, vol. 17, no. 3, pp. 207-221, 2003 [3] r. watts, j. zimmerman, positive accounting theory. prentice-hall, englewood cliffs, nj, 1986 [4] p. a. copley, “the association between municipal disclosure practices and audit quality”, journal of accounting and public policy, vol. 10, no. 4, pp. 245-266, 1992 [5] g. colbert, d. murray, “the association between audit quality and auditor size: an analysis of small cpa firms”, journal of accounting, auditing and finance, vol. 13, no. 2, pp. 135-150, 1998 [6] m. dao, t. pham, “audit tenure, auditor specialization and audit report lag”, managerial auditing journal, vol. 29, no. 6, pp. 490-512, 2014 [7] h. y. lee, v. mande, m. son, “do lengthy auditor tenure and the provision of non-audit services by the external auditor reduce audit report lags?”, international journal of auditing, vol. 13, no. 2, pp. 87104, 2009 [8] u. s. congress, the sarbanes-oxley act of 2002, 107th congress of the united states of america, h. r. 3763, washington, d.c., government printing office, 2009 [9] l. k. rickett, a. maggina, p. alam, “auditor tenure and accounting conservatism: evidence from greece”, managerial auditing journal, vol. 31, no. 6, pp. 10-25, 2016 [10] r. a. price, accounting conservatism and the asymmetry in the earnings response to current and lagged returns, stanford university, 2005. [11] v. e. johnson, i. k. khurana, j. k. reynolds, “audit-firm tenure and the quality of financial reports”, contemporary accounting research, vol. 19, no. 4, pp. 637-660, 2002 [12] d. citron, r. taffler, “the audit report under going concern uncertainties: an empirical analysis”, accounting and business research, vol. 22, no. 88, pp. 337-346, 1992 [13] m. a. geiger, k. raghunandan, “auditor tenure and audit reporting failures”, auditing, vol. 21, no. 1, pp. 67-78, 2002 [14] j. n. myers, l. a. myers, t. c. omer, “exploring the term of the auditor-client relationship and the quality of earnings: a case for mandatory auditor rotation?”, the accounting review, vol. 78, no. 3, pp. 779-799, 2003 [15] j. v. carcello, a. l. nagy, “audit firm tenure and fraudulent financial reporting”, auditing: a journal of practice & theory, vol. 23, no. 2, pp. 55-70, 2004 [16] m. l. defond, k. r. subramanyam, “auditor changes and discretionary accruals”, journal of accounting & economics, vol. 25, no. 1, pp. 3568, 1998 [17] b. arel, r. g. brody, k. pany, “audit firm rotation and audit quality”, the cpa journal, vol. 75, no. 1, pp. 36-39, 2005 [18] s. k. gates, d. j. lowe, p. m. j. reckers, “restoring public confidence in capital markets through auditor rotation”, managerial auditing journal, vol. 22, no. 1, pp. 5-17, 2007 [19] m. dao, s. mishra, k. raghunandan, “auditor tenure and shareholder ratification of the auditor”, accounting horizons, vol. 22, no. 3, pp. 297-314, 2008 [20] b. w. daniels, q. booker, “loan officers' reactions to audit rotation”, journal of behavioral studies in business, vol. 1, no. 1, pp. 1-13, 2009 [21] a. nagy, “mandatory audit firm turnover, financial reporting quality and client bargaining power: the case of arthur andersen”, accounting horizons, vol. 19, no. 2, pp. 51-68, 2005 [22] a. b. jackson, m. moldrich, p. roebuck, “mandatory audit firm rotation and audit quality”, managerial auditing journal, vol. 23, no. 5, pp. 420 – 437, 2008 [23] d. mostafa, the impact of the auditor rotation on the audit quality: a field study from egypt, ssrn, 2010 [24] m. cameran, p. annalisa, m. trombetta, mandatory audit firm rotation and audit quality, european accounting review forthcoming, ssrn, 2014 [25] m. bani mahd, m. morade zade fard, m. zeinali, “the relationship between changing independent auditor and the auditor's report”, journal of accounting knowledge, vol. 4, no. 14, pp. 91-108, 2013 [26] e. malekian, f. abdi poor, “the relationship between changes of audit firm and conservative reporting profits of companies listed on the tehran stock exchange”, journal of accounting knowledge, vol. 11, no. 41, pp. 173-157, 2014 [27] h. vakili fard, s. muhammadi, “audit firm rotation and type of audit report”, research of financial accounting and auditing, vol. 7, no. 25, pp. 33-48, 2015 microsoft word etasr_v12_n1_pp8058-8062 engineering, technology & applied science research vol. 12, no. 1, 2022, 8058-8062 8058 www.etasr.com berrouche: a non-parametric empirical method for nonlinear and non-stationary signal analysis a non-parametric empirical method for nonlinear and non-stationary signal analysis yaakoub berrouche lis laboratory, department of electronics faculty of technology ferhat abbes sétif 1 university sétif, algeria berrouchey@gmail.com abstract-a non-parametric ensemble empirical mode decomposition (nceemd) method is a novel technique for nonlinear and non-stationary signal analysis to detect a gearbox fault. the nceemd method was based on the ceemd, but the gaussian white noise was replaced by the fractional gaussian noise. the nceemd method does not need to choose the appropriate snr and the number of ensemble trials before signal processing, which makes it a non-parametric method. this new approach was evaluated using a simulated malfunction signal representing two typical faults in gearbox systems: modulation and rub-impact. its performance was evaluated in terms of mse and computation time. a comparative study between the emd, eemd, ceemd, and nceemd methods showed that the latter performed better by improving the computation time and accuracy of ceemd. the proposed method is a non-parametric method that provides a powerful tool in extracting the modulation and the rub-impact features from a vibration signal. the nceemd method helps to track down the gearbox faults and resolve this crucial problem in mechanical machines. keywords-complementary ensemble empirical mode decomposition; fractional gaussian noise; gearbox fault detection; nonlinear signal analysis i. introduction gears are common and vital components in rotating machines, having a typical nonlinear and non-stationary signal. monitoring the condition of a gear can help in the early detection of potential failures and avoidance of damages [1]. the predictions are based on the analysis of vibration signals generated by mechanical equipment. many conventional methods of signal processing, such as statistical methods and fourier analysis, have been applied to the analysis of vibration signals to diagnose gearbox faults. however, these methods are based on the assumption that the signals are stationary and linear, while gear defects have the nature of non-stationary processes [1]. several methods have been proposed to deal with nonstationary signals. among these techniques, the wavelet transform has good localization properties in the time and frequency domains, and it has been applied to the detection of damage in gear systems [2, 3]. however, the main drawback of the wavelet transform is the definitive choice of the wavelet base function before it is used [1, 4], making it non-adaptive. the empirical mode decomposition (emd) was developed as a powerful tool to analyze nonlinear and non-stationary signals [5], and it has been applied in machine fault diagnosis [1, 610]. emd decomposes a signal into a finite number of intrinsic mode functions (imfs) by taking advantage of the signal’s local properties. however, the main drawback of emd is the mode mixing problem, where oscillations of different time scales can appear in one imf, or oscillations with the same time scale can appear in different imfs. to overcome the mode mixing problem, the ensemble empirical mode decomposition (eemd) was proposed as an improved method of emd [11]. eemd is a noise-assisted data analysis method where the true imfs are defined as the mean of an ensemble of trials, each consisting of the original signal plus a finite white noise. eemd has been applied to the diagnosis of rotating machinery faults [12-14]. however, the resulting imfs can be corrupted by additive white noise. the residue noise can be decreased by using a large number of ensemble trials (ne), resulting in high computation times. the complementary eemd method (ceemd) was proposed to reduce computational times [15]. for this purpose, the white noise is added and subtracted separately from the original signal to generate two sets of imfs. the average of imfs of the same order could effectively reduce the final white noise residue. this study proposes a new method named nceemd to enhance the performance of ceemd by reducing the number of ensemble trials and therefore the amount of calculation and computation time. the nceemd method is based on the principles of the ceemd, but the gaussian white noise is replaced by fractional gaussian noise [16, 17]. the proposed method was evaluated using a simulated malfunction signal caused by modulation and rub-impact that represent two typical faults in gearbox systems. its performance was evaluated in terms of fault diagnosis and computation time, and it was compared with the performance of emd, eemd, and ceemd methods. ii. mathematical theory a. emd algorithm the emd method decomposes any non-linear and nonstationary signal into a finite number of imf components by corresponding author: yaakoub berrouche engineering, technology & applied science research vol. 12, no. 1, 2022, 8058-8062 8059 www.etasr.com berrouche: a non-parametric empirical method for nonlinear and non-stationary signal analysis taking advantage of the local properties of the signal. this process is applied without requiring an a priori basis as the wavelet method by using a sifting algorithm. so, the original signal can be obtained by superposing the obtained m-1 imfs and one residual r(t) as [5]: ���� � ∑ �� �� � ��� � ���� (1) a more detailed description is provided in [5]. however, the main disadvantage of emd is the problem of mode mixing, which affects the decomposition accuracy and the interpretation of the results. b. eemd algorithm the eemd was proposed in [11] to overcome the mode mixing problem of emd. the eemd method defines the true imf as the mean of an ensemble of trials, each consisting of the investigated signal corrupted by an additive white noise [11]. for a given number of ensemble trials ne, a finite white noise is added to the signal in each trial, and then this noisy signal is decomposed into imfs by using the emd method [11]. eventually, the true imfs are obtained by averaging the imfs of the same order. a complete description can be found in [11]. the eemd method removes the problem of mode mixing. however, the resulting imfs will be contaminated by the added noise. the added noise in the decomposed results can be reduced by using a large number of ensemble trials, increasing computation time. c. ceemd algorithm the ceemd method was proposed to reduce the computational time of eemd and the white noise residue. in this approach, white noise is added and subtracted separately from the original signal to generate two sets of imfs with positive and negative noises [15]. the average of imfs of the same order could eliminate the noise residue in the final imfs. a drawback of ceemd is the selection of the right level of added white noise and the number of adequate trials before each signal processing. d. nceemd algorithm this study proposes the nceemd method to further reduce the number of ensemble trials. this method is based on the ceemd method, but the gaussian white noise was replaced by the fractional gaussian noise (fgn). the fgn is a stationary process obtained by periodically sampling the fractional brownian motion process bh(t) and by computing the first difference, defined by [17]: ���� � ����� � ���� � 1� (2) the autocorrelation of fgn is given by: ����� � �� � �|� � 1|�� � 2|�|�� � |� � 1|��� (3) the fgn is characterized by the hurst exponent h, where 0 < h < 1, and its variance σ 2 . for � � ½ the fgn process is a white noise process, while other values produce nonzero correlations. for 0 < h < ½ the correlation is negative, the autocorrelation decays very rapidly, and the frequency response looks like a high-pass filter. for ½ < h < 1 the correlation is positive and the autocorrelation decays very slowly. the frequency response is similar to a low-pass filter. e. hurst exponent selection the fgn is characterized by a hurst exponent h which is defined in two intervals. two criteria were used in a systematic approach to select an appropriate h and ensure a successful nceemd decomposition. the first criterion was to determine the values of h that provide decomposition without mode mixing and no redundant imf components. figure 1(a) represents the different results of nceemd decomposition for the simulated malfunction signal described in section iii, according to the hurst exponent where a value of 0 represents no redundant imf component and the value of -1 represents the mode mixing [18]. therefore, h within the range of [0, 1/2] is a good value for a successful nceemd decomposition. furthermore, it has been shown that the bandwidth of each imf in the emd method was much narrower for h lower than ½, and it increased with h greater than ½ [16]. then, to ensure that the nceemd method behaves like an effective filter without mode mixing, the range 0 ! � ! ½ must be chosen. the second criterion was used to determine the exact value of h in the selected range. to reach this aim, the accuracy of the decomposition using rmse between the imf1 and the rubimpact component of the simulated malfunction signal was evaluated according to the hurst exponent, as shown in figure 1(b). as it can be noted, the method has fewer errors in the range of 0.16 < h < 0.20, while rmse has a minimum at h=0.185. therefore, the appropriate value of the hurst exponent is h=0.185. (a) (b) fig. 1. hurst exponent selection: (a) relationship between the hurst exponent and decomposition results obtained from nceemd, (b) relationship between the hurst exponent and rmse (nceemd method). iii. simulation experiments simulation experiments were conducted on a gearbox signal model, as an example of a non-linear and non-stationary engineering, technology & applied science research vol. 12, no. 1, 2022, 8058-8062 8060 www.etasr.com berrouche: a non-parametric empirical method for nonlinear and non-stationary signal analysis signal, to analyze the performance of the proposed method and compare it with the conventional empirical method. a. gearbox signal model the vibration signal, acquired from a normal gearbox, composed of a pair of gears and meshing under a constant load and speed, is represented by [19]: ���� � ∑ "# � #�$ %&��2'()*+� + ,#� (4) where m is the number of tooth-meshing harmonics, xm and φm are the amplitude and the phase modulation function of the m th meshing harmonic, respectively, n is the teeth number of the gear, fs is the rotating frequency, and nfs is the meshing frequency. when gears with faults are meshing, the amplitude and the phase of the vibration signal would be modulated. the gear fault vibration signal can be expressed by [19]: -��� � ∑ "#.1 + /#���0 � #�$ %&�.2'()*+� + ,# + 1#���0 (5) where am(t) and bm(t) are periodic functions whose frequencies are the rotating frequency and its multiples that include the fault information of the gear vibration signal. in this study, the normal gear vibration signal was used with one periodic function of the m th meshing harmonic of the amplitude and phase. when gears with a fault are meshing, both the amplitude and phase of this signal are modulated by the same periodic functions ((am(t)=bm(t)). in addition to the modulation, the gear fault vibration signal can also include a rub-impact fault. therefore, all the decomposition methods mentioned in section ii were tested and compared on a simulation signal that included modulation and rub-impact components. b. application of nceemd on the gearbox signal the nceemd and two conventional methods were tested on a simulated gearbox signal as an example of a nonlinear and non-stationary signal. two typical faults exist in a fault diagnosis of a gearbox: modulation and rub-impact. when the local rub-impact occurs in the gear, it produces an impact signal characterized by pulses of very short duration whose amplitude decreases exponentially. in addition, the normal gear vibration signal, with one periodic function of the m th meshing harmonic, was modulated by amplitude and phase modulation. the rub-impact signal, the amplitude, the phase-modulating signal, and the simulated malfunction signal that combines them are shown in figure 2. the simulated malfunction signal was decomposed by nceemd and the conventional methods emd and eemd to extract the rub-impact component and detect a fault, as shown in figures 3-5. by comparing the decomposed components, nceemd successfully extracted the various components embedded in the simulated malfunction signal without mode mixing. this best performance in terms of rmse was obtained with one trial and a low level of added fgn (snr=25db). on the other hand, emd failed to extract the rub-impact component due to mode mixing between different imfs. likewise, eemd extracted the rub-impact component but with a high computation time (number of ensembles ne=200) and high error rate. these results suggest that nceemd is a sufficient method to diagnose a gearbox signal. (a) (b) fig. 2. gearbox signal: (a) the rub-impact signal, (b) the simulated malfunction signal. (a) (b) fig. 3. the decomposed two components obtained by nceemd. (a) imf1, (b) imf2. in conventional empirical methods, the level of noise added and the number of ensemble trials are the two primordial parameters needed to ensure a successful decomposition. therefore, to measure the performance of nceemd and show that it can solve the problem of choosing the level of white noise added and determine the number of ensemble trials before processing, the appropriate number of ensemble trials is calculated by evaluating the correlation between the imf1 and the high-frequency component in the simulated malfunction signal. 0,00 0,05 0,10 0,15 0,20 0,25 0,30 -0,30 -0,15 0,00 0,15 0,30 a m p l i t u d e time (s) 0,00 0,05 0,10 0,15 0,20 0,25 0,30 -1,50 -0,75 0,00 0,75 1,50 a m p l i t u d e time (s) 0,00 0,05 0,10 0,15 0,20 0,25 0,30 -0,30 -0,15 0,00 0,15 0,30 a m p l i t u d e time (s) 0,00 0,05 0,10 0,15 0,20 0,25 0,30 -1,50 -0,75 0,00 0,75 1,50 a m p l i t u d e time (s) engineering, technology & applied science research vol. 12, no. 1, 2022, 8058-8062 8061 www.etasr.com berrouche: a non-parametric empirical method for nonlinear and non-stationary signal analysis (a) (b) fig. 4. the decomposed two components obtained by emd. (a) imf1, (b) imf2. (a) (b) fig. 5. the decomposed two components obtained by eemd. (a) imf1, (b) imf2. the relationship between the number of ensemble trials and the decomposition results obtained by eemd (snr=20db), ceemd (snr=10db), and nceemd are shown in figure 6. these results show that nceemd requires a high snr and one trial to reach a 95% of correlation. this means that the proposed method needs a low level of noise added with one trial to ensure successful decomposition. on the other hand, conventional methods need low snr and a large number of ensemble trials before signal processing. furthermore, the proposed method is non-parametric and decomposes any nonlinear and non-stationary signal in low computation time and high accuracy, compared to the classical methods. (a) (b) (c) fig. 6. relationship between the correlation coefficient and the number of ensemble trials: (a) eemd, (b) ceemd, (c) nceemd. iv. conclusion gearbox fault detection is a crucial task in mechanical machines. this paper proposed an efficient fault detection technique by introducing a new method named nceemd. three techniques were compared, namely eemd, ceemd, and nceemd. simulation experiments showed that eemd, ceemd, and nceemd managed to extract the gear meshing and the rub-impact fault components from a gearbox signal. however, the eemd and ceemd methods used a large number of ensemble trials and a high level of added noise that caused large computational time and more contamination with noise. however, the proposed nceemd method achieved better performance in terms of accuracy and computational time, without choosing any parameters before signal processing. therefore, the proposed method is non-parametric and more adequate to deal with a nonlinear and non-stationary signal. 0,00 0,05 0,10 0,15 0,20 0,25 0,30 -1,50 -0,75 0,00 0,75 1,50 a m p l i t u d e time (s) 0,00 0,05 0,10 0,15 0,20 0,25 0,30 -1,0 -0,5 0,0 0,5 1,0 a m p l i t u d e time (s) 0,00 0,05 0,10 0,15 0,20 0,25 0,30 -0,30 -0,15 0,00 0,15 0,30 a m p l i t u d e time (s) 0,00 0,05 0,10 0,15 0,20 0,25 0,30 -1,50 -0,75 0,00 0,75 1,50 a m p l i t u d e time (s) 0 100 200 300 400 500 600 700 0,70 0,75 0,80 0,85 0,90 0,95 1,00 c o rr e la ti v e c o e ff ic ie n t ne 0 1 2 3 4 5 6 7 8 9 10 0,93 0,94 0,95 0,96 0,97 c o rr e la ti v e c o e ff ic ie n t ne 0 1 2 3 4 5 6 7 8 9 10 0,950 0,952 0,954 0,956 0,958 0,960 0,962 0,964 0,966 c o rr e la ti v e c o e ff ic ie n t ne engineering, technology & applied science research vol. 12, no. 1, 2022, 8058-8062 8062 www.etasr.com berrouche: a non-parametric empirical method for nonlinear and non-stationary signal analysis references [1] s. j. loutridis, "damage detection in gear systems using empirical mode decomposition," engineering structures, vol. 26, no. 12, pp. 1833–1841, oct. 2004, https://doi.org/10.1016/j.engstruct.2004.07.007. 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[23] a. y. al-rawashdeh, "investigation of an induction wound rotor motor to work as a synchronous generator," engineering, technology & applied science research, vol. 9, no. 2, pp. 4071–4074, apr. 2019, https://doi.org/10.48084/etasr.2606. microsoft word etasr_7-1_1316-1322.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1316-1322 1316 www.etasr.com pylarinos and pellas: incorporating open/free gis and gps software in power transmission line… incorporating open/free gis and gps software in power transmission line routine work: the case of crete and rhodes d. pylarinos islands network operation department hellenic electricity distribution network operator s.a. greece d.pylarinos@deddie.gr i. pellas islands network operation department hellenic electricity distribution network operator s.a. greece i.pellas@deddie.gr abstract—geographical information system (gis) and global positioning system (gps) software are widely gaining attention in power system planning and operation. although commercial systems are increasingly being incorporated in power systems applications, they are yet to be fully incorporated in the routine work of utilities (and especially in the work of crews), due to several reasons such as cost, portability, connectivity, performance/speed, infrastructure etc. this paper focuses on incorporating certain open/free gis and gps software in routine transmission line work. the case study is the 150kv transmission systems of the greek islands of crete and rhodes which show increased complexity due to certain localized factors such as greek legislation, the diverse terrain/routes, the segmented design due to the network’s growth over the years (regarding both voltage levels and routes) and the use of different coordinate reference systems (or geodetic systems) from the greek state. the main goals of this work was to incorporate open/free software that provided limitless online access points, offline navigation and a user friendly design that wouldn’t require any additional training, programming etc. the basic scheme described in this paper can be followed to provide similar results in other applications. keywords-power transmission system; gis; gps; offline navigation; free; open; software; geodetic systems; coordinate reference system. i. introduction a power system can roughly be described as a network with three major discrete parts: generation, transmission and distribution, although further categorizing may be employed depending on the voltage level (e.g. subtransmission, ultra high voltage transmission etc), the type of current (ac/dc) and other characteristics [1]. the “transmission” term includes the long distance routes connecting high voltage substations, usually through overhead transmission lines (underground power cables may also be used). the basic structures of an overhead transmission line are the high voltage conductors and the towers (of various designs) used to support these conductors [1-2]. line route design traditionally considers a variety of factors such as potential urban growth, location of cities, perpetual or actual location of substations, terrain, weather, legislation, costs etc (e.g. [2-4]) whereas recent developments include the use of advanced geographical representation systems (e.g. [5-7]). a geographical information system (gis) [8] is used to present and manipulate spatial or geographical data whereas a global positioning system (gps) [9] is used to provide geolocations taken from satellite(s) to earth receivers (independently of telephonic/network connection). such capabilities may be used in a variety of applications in power systems (e.g. [5-7, 10-15]) and various commercial software can be found that utilize gis capabilities for power systems (e.g. [16-17]). the most familiar gis system outside the power industry is undoubtedly google earth [18] which is provided free of charge by google. in fact, google has recently made its business version (google earth pro [19]) also free [20]. several other gis software are also available (a slightly outdated list can be found in [21]) but google earth’s popularity, user friendly design, speed and additional capabilities offered through other cooperating software, have made it difficult to ignore even in the electric power commercial software industry. thus, commercial suites incorporate google earth (e.g. [22]) whereas the service of entering/depicting the data in google earth is also commercially available (e.g. [23]). this paper focuses on the work done in 2016 to incorporate open/free gis and gps software in the routine work of the transmission lines subsection of the islands network operation department of the hellenic electricity distribution network operator (hedno), responsible for the operation and maintenance of the high voltage networks of the islands of crete and rhodes. three were the major goals set: the first was to depict the transmission network in a free gis software that could be used by all interested personnel with no limitations. the second was to migrate the data to a low cost portable device equipped with gps that could offer free offline navigation. the third was that the scheme followed should require no programming of any kind and that it should be easy to use by all personnel including technicians. these goals were achieved with the use of additional (besides google earth) engineering, technology & applied science research vol. 7, no. 1, 2017, 1316-1322 1317 www.etasr.com pylarinos and pellas: incorporating open/free gis and gps software in power transmission line… open/free software such as ge-path [24] and maps.me (formerly known as mapswithme) [25]. the latter works with free mapping data from openstreetmap [26] and accepts the import of keyhole markup language (kml) [27] files acquired through google earth. a low-cost android tablet was used as a gps navigation device. in case of ios devices, similar software (such as galileo offline maps [28]) may be used. the offline capability of google maps [29] was also investigated. it should be noted that additional aid was needed to move through the different coordinate reference systems and although such a software is freely available [30] and widely used in greece, the simpler approach of online bulk convention through a website [31] was followed in this case. the overall scheme is described step by step in the following sections. ii. the case of crete and rhodes: background the greek power system was constructed, owned, operated and maintained by the public power corporation (ppc) [32] until 2011. following eu directives, ppc broke up and the new scheme was (roughly) that the distribution department formed the hellenic electricity distribution network operator (hedno) [33] whereas the transmission department formed the independent power transmission operator (ipto) [34]. however, the isolated high voltage transmission systems of the greek islands of crete and rhodes remained under the responsibility of hedno after the break up and are operated and maintained by hedno’s islands network operation department. the voltage level for both systems is 150kv today, but this is a result of a gradual upgrade from 66kv. in fact, rhodes moved to 150kv in the current decade whereas although most of the cretan network had been upgraded since the 70s, a small part was still functioning at 66kv in the 00s. as power demands grew, the system kept expanding through the years with new substations and line routes being added and single-circuit lines being upgraded to double-circuit lines. at the moment there are three major upgrade projects in progress: upgrading a single circuit part of the cretan power system to double circuit, adding a stepdown substation in crete and adding a power plant in rhodes. the current and near future situations are depicted in figures 1-2 and table i. fig. 1. the power system of rhodes. left: current scheme, right: near future scheme. squares denote power plants and triangles denote step down substations. red line denotes a double circuit and yellow line denotes a single circuit. (screenshots from google earth pro, map data: google, image landsat, data sio, noaa, u.s. navy, nga, gebco) fig. 2. the power system of crete in 2016. up: current scheme, down: near future scheme. squares denote power plants and triangles denote step down substations. red line denotes a double circuit and yellow line denotes a single circuit. (screenshots from google earth pro, map data: google, image landsat, data sio, noaa, u.s. navy, nga, gebco) table i. transmission system data power plants & substations (s/s) transmission line circuits (s/s to s/s) appr. line axes length (tower to tower) number of towers today crete 19 22 581.5 km 1629rhodes 5 8 120.2 km 361 near future crete 20 24 581.5 km 1629 rhodes 6 9 146.5 km 435 as shown, it is not easy to get a clear image of the system from figures 1-2 and table i. this is largely because of the segmented design and gradual upgrade of the system. in an effort to minimize costs, new substation have been connected to the system using existing routes by upgrading single circuit lines to double circuit lines and adding some new towers when necessary. it should be noted that when a transmission line is to be constructed, private property (the area needed for each tower) needs to be expropriated. further, under greek law, an area of certain width to the left and the right of the line needs to be partially expropriated in order to enforce building regulations/prohibitions. therefore, whenever a new route is decided an announcement is posted in the official government gazette (ogg) [35] which is published and maintained by the national printing house [36]. for every route addition/change a new announcement in the ogg has to be posted. today, there are announcements in over 60 different issues of the ogg regarding just the transmission lines of crete currently in service with the first announcement dating back in the 60s. and since expropriation takes place, each tower has to be named in order to be legally referred to. the initial naming usually consists of numbers that increment throughout the line’s route. however, during the various stages of studying and construction, towers may be added or removed. this creates a problem as old towers cannot be renamed (in legal terms) and the problem becomes more intense as new routes and towers engineering, technology & applied science research vol. 7, no. 1, 2017, 1316-1322 1318 www.etasr.com pylarinos and pellas: incorporating open/free gis and gps software in power transmission line… are added. further, it is rather often that lines are constructed next to each other (in an attempt to follow the optimal route in the area). thus, towers standing next to each other may have the same number in their respective ogg issues. this means that an additional notation is needed to safely discriminate them in the field. this notation usually comes from the first letters of the (initial) two ending points/substations. however, as single circuits are upgraded to double circuits and as parts of older lines are used for new ones, following a coherent and safe to interpret naming scheme throughout the network becomes impossible. additionally, it is important to note that only one double circuit line (in rhodes) connects the same two substations with its both circuits. this means that there are several “junctions” along the network (figure 3). further, there are also cases that single circuit lines coming from different directions meet at a certain tower and from there on continue their route together in a double circuit line (upper right image in figure 3). fig. 3. images from the power transmission system of crete and rhodes. (screenshots from google earth pro, map data: google, upper right image: (c) 2016 digital globe) at this point one should add the additional difficulty of the terrain. the usual line route design tries to make the most of mountains in an effort to minimize costs and keep the lines away from urban areas. this means that getting to a certain tower or from one tower to the next may prove tricky as different mountain roads/paths need to be followed. in fact, a significant part of the training of new linemen has to focus in familiarizing with the different routes needed to be followed to reach each tower. iii. coordinate reference systems geodetic systems (or coordinate reference systems) are coordinate systems used to map the location of places on earth [37]. however, moving from a three dimensional object (of imperfect shape) to two dimensional maps becomes tricky. each geodetic system refers to a base point (or “anchor”). as the distance of mapping from the base point decreases, the accuracy increases. therefore, although there is a universal geodetic system (the world geodetic system usually referred to as wgs84) [38], countries also maintain their own geodetic systems for a variety of reasons (historical, accuracy, independence from the us provided wgs84 etc). in the case of greece, things are slightly more complicated as historically there have been various different geodetic systems used by various public services (with different base points and representation/calculation forms) [39]. thus, the transmission line construction files may include coordinates in various reference systems (although detailed coordinates for each tower may not be documented in case of older lines, which are not few). further, queries from state services (or citizens) may also refer to different coordinates systems. today, the hellenic geodetic reference system 1987 (hgrs87) (or greek geodetic reference system 1987–ggrs87 or egsa87 using the greek acronym) [40] has been accepted by most involved parties as a common reference. however, the official goal is to migrate to the hellenic terrestrial reference system 2007 (htrs07) [41]. it should be noted that moving from one coordinate system to another is bound to insert some deviance, for example moving from ggrs87 to htrs07 will insert a difference of 8 cm or less throughout the country whereas moving from htrs07 to wgs84 inserts an average difference of less than 1 m [41]. there are several websites that offer an online transformation capability, but most of them offer just a single point transformation capability (e.g. [42]). however, since a list of some coordinates in ggrs87 was available, a bulk transformation service was needed. a freeware software [30] that conducts most transformations (from one system to the next) is widely used in greece (especially in the private sector), however a simpler approach through the website of a private company [31] that offers free bulk transformation between four systems (wgs84, egsa87, hrts07 and hatt) was followed in this case. it should be noted that several sites of public agencies may be used for random cross-checking (e.g. the national cadastral agency offers the ability to put points on the greek map using aerial photos taken in 2007-2009 [43]). iv. working with bulk data the next step would be to import the data in google earth. this can be done easily via two ways: the first is to use a website that offer free conversion of the coordinates data file to a keyhole markup language (kml) file that can be simply drugged and dropped in google earth. for example such a service (that accepts both xls and cvs file types) is available at [44]. the second way is to switch to the free business version of google earth (google earth pro [19]) and use the provided import function. however, google earth pro accepts only csv files and this inserts an additional issue for the greek user. in greece, the comma is used as a decimal separator and the point (fullstop) is used as the thousand separator. this inserts an obvious problem when working with comma separated values (csv) files that use the comma as a delimiter symbol and the point as a decimal symbol. although, ms office offers the ability to use custom symbols (independently from system settings) this ability seems to be rather buggy when working with csv files and other software. to avoid any issues, system settings should be set in the manner followed by csv files. these settings should be maintained also when exporting kml engineering, technology & applied science research vol. 7, no. 1, 2017, 1316-1322 1319 www.etasr.com pylarinos and pellas: incorporating open/free gis and gps software in power transmission line… data to a csv format. it should be noted that in order to maintain the name of each point (placemark) through the import process, the user has to use a template for all placemarks, or else all names will be set to null [45]. keeping the description is slightly more complicated. in this particular case, the online transformation from csv to kml through [46] has been employed, which also provides additional capabilities. v. working with google earth pro and gepath some fine adjustment may be needed for placemark location for an optimal viewing result, which should be fairly easy as most towers are clearly visible in google earth (figure 4). this deviation could be generated through transformation accuracy errors (from ggrs87 to wgs84) or through the inaccuracy inhibited when low cost gps devices have been used by the line crew to note the coordinates of placmearks in cases that official coordinates do not exist. the next stage is to add a placemark to each side of double circuit towers (on the end of the longest visible cross arm) in order to later depict circuit routes (figure 4). then, gepath [24] can be used to automatically connect the cross arms placemarks and also calculate distances (e.g. from both ends and/or the previous and next placemark in each group) (figure 4). it should be noted that if a tower is not visible in google earth (e.g. due to a cloud) the user may refer to older satellite images. however, a previously undocumented bug should be reported here: if the user moves back in time and then returns to the current date, an overall displacement of the satellite images seems to take place which may throw the whole project off track. fig. 4. upper pictures: working in google earth: left: tower placemarks may need fine adjustments, middle: adding cross arms placemarks, right: adding circuits using gepath. bottom pictures: screenshots from the final result (line axes have been deselected for viewing in this case). a click on each placemark (square or dot) will show its name/info. an example is shown in the bottom right picture (for the yellow cross arm placemark). the actual info have been removed to portary the generic scheme. (screenshots from google earth pro, map data: google) it is also important to note that the desired formatting of lines (width, color) can be set in gepath but also in google earth. additional placemarks may be used for substations (figures 1 and 2) and gepath can also be used to draw the area limits of each substation. finally, the user can now organize the data in google earth in the way that makes most sense to him. the tree-like organization of data in google earth allows for the user to have branches (and sub-branches) so that the needed information at a given time can easily be selected for viewing. however, as explained in the following section, data may have to be tighter organized in order to be ported to other software/devices. vi. offline navigation the next step is to use the data to facilitate offline navigation. on-line navigation was not considered as this would require a certain cost and would also mean a dependency on connectivity (which could be a major issue when following line routes through mountainous areas). it should be noted that usual low-cost gps navigation devices are insufficient for this purpose as most of them do not offer a bulk import function and those that do, usually have a limit on the number of placemarks that may be imported (2,000 placemarks is the usual limit, which is rather lower than the needed in this case). thus, it was decided to purchase a low-cost tablet that could be equipped with free software that offers off-line navigation. the maps.me software (previously named mapswithme) [25] was chosen as it provided offline mapping, navigation, map editing, kml import function and worked on low cost anroid tablets. the software gets the map data from openstreetmap (osm) [26]. it should be noted that galileo [28] seems to be a software of similar function for ios. it should be stressed that each individual segment of data has to be imported as an individual kml file in maps.me in order to be selectable for viewing as maps.me does not support treelike schemes for kml data. by “clicking” each placemark, its name and attributes/information appear. thus, the cross arms placemarks have to be maintained (circuit line routes are not clickable) in order for the user to be able to get each circuit’s name (usually referring to the two ending points) and info. different colors may be used for each circuit route. the data can be organized in various ways to provide better usability, keeping in mind that the maps.me software does not provide a tree-like organization of kml files. the approach followed in this case was to have people working with a small number of kml data files so that selecting and deselecting items for viewing would be easy. one kml file is used for tower placemarks, one for line axes (a line connecting tower placemarks), one for cross arms placemarks, one for the actual circuit lines and one for the placemarks and area limits related to substations. the followed scheme is shown in figure 5. however, other approaches can also be followed (individual files for each line/circuit, a file for phase position, a file for insulator types, a file for tower design etc). in the approach followed in this paper, the crossarms placemarks’ names include the name of the tower and the two connecting ends (stating both substations and the name of the isolators/disconnectors/switches). each placemark’s info may refer to distance (from ends or from next/previous placemark), tower design/type, insulators, position of phases etc. screenshots from the final result (maps.me software equipped with all data and used in our low cost tablet) are shown in figures 6-11. engineering, technology & applied science research vol. 7, no. 1, 2017, 1316-1322 1320 www.etasr.com pylarinos and pellas: incorporating open/free gis and gps software in power transmission line… fig. 5. the tree-like scheme followed for the organization of data.. during this work, two software versions were used: one available through slideme (version 4.4.3, figures 6-8) and one available through google play (version 6.5.2, figures 9-11). a multiple placemarks representation with no line axes is shown in detail in figure 7 whereas the tower and line axes representation (with no circuit lines and cross arms placemarks) along with the navigation interface is shown in figure 8 (from the 4.4.3 version). it should be noted that, in general, different colors should be assigned to axes and circuit lines to avoid confusion. a significant advantage of this software is its steady zooming function during navigation, which suits better this particular task since it can provide a wider view of the area which allows the crew team to identify distant towers during navigation (figure 9). further, newer software versions (such as the 6.5.2 version) provide additional/improved functions (easy-to-use map editing, calculating routes from starting points different to the user’s location, calculating hiking and bike routes, improved searching etc), increased map detail and significantly more preset placemarks with some of them, strangely enough, corresponding to towers (marked as “power towers”). however, increased zoom is needed to make these preset placemarks visible (as dots) and their positioning should not be considered as accurate since the placemark data are probably offered by other users through the map editing capabilities provided (figure 10). in general, the latest version should be used but older versions (such as the 4.4.3 tested in this case) are also sufficient for the task. fig. 6. the transmission system of crete (left) and rhodes (right) ready for offline navigation (screenshots from mapswithme/maps.me version 4.4.3, map data from openstreetmap) fig. 7. multiple placemark representation with the line axes deselected for viewing. left: a single circuit line (up) and a double circuit line (down). middle: the “junction” depicted in the lower left image of figure 3. right: entering a substation (an extra placemark is used for the substation and the area limits are drawn in black) (screenshots from mapswithme/maps.me version 4.4.3, map data from openstreetmap) fig. 8. offline navigation using the mapswithme software and following a single placemark represenation (only tower placemarks and line axes selected for viewing): zooming out (left) and in (right) (screenshots from mapswithme/maps.me version 4.4.3, map data from openstreetmap) fig. 9. upper image: navigation with tower and axes placemarks on (screenshot from mapswithme/maps.me version 6.5.2, map data from openstreetmap). lower image: the same area as shown in google earth pro (screenshot from google earth pro, map data: data sio, noaa, u.s. navy, nga, gebco) fig. 10. several preset placemarks are provided by maps.me for “power towers”. increased zoom is needed to make these preset placemarks visible (as dots) and their location is not always accurate. in this image two screenshots have been merged: the background screenshot shows a dot placemark selected and its description to the left reads “power tower” (the last four coordinate digits have been deliberately blackened). the exact position of the tower migrated through the scheme described in this paper is noted with the red star placemark. the foreground screenshot shows a zoomin of the area. (screenshot from mapswithme/maps.me version 6.5.2, map data from openstreetmap) engineering, technology & applied science research vol. 7, no. 1, 2017, 1316-1322 1321 www.etasr.com pylarinos and pellas: incorporating open/free gis and gps software in power transmission line… it should be stressed that the representation in google earth is made from a certain angle whereas maps.me uses a fully vertical representation, so it is obvious that data files that look perfect in one software will not look that perfect in the other (e.g. both cross arms placemarks may appear on the same side of a tower or the tower placemark may appear closer to one of the two cross arms placemarks). this is a minor issue and the user can either ignore it or create different files specially designed for viewing in each software. the approach followed in this case is to aim for a perfect visual result in google earth as this representation is using actual photographs instead of maps. the navigation on the other hand, is usually conducted using only the towers/axes kml files whereas cross arms and circuit line data are used only in special cases (e.g. to discriminate between the two circuits after reaching a certain tower) and thus such issues were considered as minor problems that could be ignored (figure 11). it should be mentioned that an offline function is also provided through google maps [29] however the map data should be periodically downloaded and both google maps and google earth seem to hang up in our low-cost tablet. however, these are interesting alternatives as they would provide actual satellite images instead of maps and some mountain roads may not be visible in maps. there is a possible workaround for that issue however when using maps.me and openstreetmap as they provide a map editing function and also custom routes may be drawn in google earth and then be ported as kml files. finally, it should be noted that other devices (e.g. private smartphones of employees) may also be equipped with the software and data and be used for navigation. vii. additional potential uses the main objective of this work was to provide the capability of free mapping and navigation of the transmission systems of crete and rhodes, mainly to aid the work of the transmission lines subsection of the transmission system operation section of the islands network operations department of the hedno s.a. besides the basic uses described previously in this paper, there are other potential uses that could be mentioned. for example, the kml files may also be given to employees working on other sections in order to help them get a more representative image of the system and possibly help them in their work (e.g. dispatching centers may use it to assess potential hazards such as ongoing fires). an additional use is related to greek legislation that, as explained earlier, enforces restriction on construction/building activities in proximity of high voltage lines. the restriction may be e.g. a full prohibition of any building construction. however, the exact restriction is not the same for each line nor throughout each line’s length, and field inspections and topographical measurements may be required. therefore, placing a certain property on the same navigation device with the transmission system can be of use. further, as line crews are equipped with this low cost system and use it as a navigation device, it is easy for them to note placemarks of interest during inspections or other regular work throughout the system (e.g. a tree that needs to be cut). the cumulative distance calculation function provided through gepath may also be used to assist fault location. the data can also be used for public display. the easiest way to do this is to use the google maps embedding function [47]. an example for crete is shown at [48]. in this case, certain data (names, exact position of towers etc) have been removed (a similar policy has been followed throughout this paper) and only tower placemarks and line axes are depicted. fig. 11. upper image: navigating to a certain tower (only tower and axes shown). middle image: reaching the tower (turning on all placemarks). (screenshots from mapswithme/maps.me version 6.5.2, map data from openstreetmap). lower image: view of the tower in google earth pro (screesnshot for google earth pro, map data: google). viii. conclusion incorporating gis and gps technology may significantly assist the work of any geographically spread out engineering, technology & applied science research vol. 7, no. 1, 2017, 1316-1322 1322 www.etasr.com pylarinos and pellas: incorporating open/free gis and gps software in power transmission line… organization/service and, obviously, power transmission systems. the focus of this paper is on incorporating open/free gis and gps software to assist the routine work of the creterhodes transmission system operation section and especially of the transmission lines subsection. the isolated transmission systems of these two greek islands demonstrate several peculiarities that strengthen the need and increase the positive effect of such tools. the characteristics of these systems are discussed and a detailed step by step guide throughout the overall project is provided. the basic goal accomplished was to provide a free and user friendly scheme that would provide unlimited online access and offline navigation. the scheme described in this paper is currently used by the transmission lines subsection of the islands network operation department of the hellenic electricity distribution network operator. however, the basic scheme can also be used as a low cost alternative for other tasks inside or outside the power sector. references [1] l. l. grigsby (editor), the electric power engineering handbook: electric power generation, transmission and distribution, crcpress taylor and francis group, 2012 [2] t. gonen, electric power transmission system engineering analysis and design, 2nd edition, john wiley & sons, 1988 [3] h. h. farr, transmission line design manual, united states department of the interior, 1980 [4] supplemental municipal consultation filing, transmission line route/configuration alternatives, 2011 [5] y. wang, w. huang, y. li, q. b. tu, x. tain, “optimal design of transmission line route based on gis”, applied mechanics and materials, vols. 644-650, pp. 3522-3527, 2014 [6] y. yang, y. liu, y. cao, “study on a method of design for rural power distribution lines based on 3d gis technology”, mathematical and computer modelling, vol. 51, pp. 1293-1298, 2010 [7] b. meehan, gis for enhanced electrical utility performance, artech house, 2013 [8] wikipedia, “geographic information system”, https://en.wikipedia.org/ wiki/geographic_information_system [9] wikipedia, “global positioning system”, https://en.wikipedia.org/ wiki/global_positioning_system [10] s. saxena, m. ali, k. gandhi, n. ranjan, “protection of transmission system using global positioning system”, mit international journal of electrical and instrumentation engineering, vol. 3, no. 1, pp. 33–39, 2013 [11] s. kamboj, r. dahiya, “application of gps for sag measurement of overhead power transmission line”, international journal on electrical engineering and informatics, vol. 3, no. 3, pp. 268-277, 2011 [12] z. hu, y. chen, “new method of live line measuring the inductance parameters of transmission lines based on gps technology”, ieee transactions on power delivery, vol. 23, no. 3, pp. 1288-1295, 2008 [13] n. g. boulaxis, m. p. papadopoulos, “optimal feeder routing in distribution system planning using dynamic programming technique and gis facilities”, ieee transactions on power delivery, vol. 17, no. 1, pp. 242-247, jan 2002 [14] y. liu, d. liu, y. xie, “research on auxiliary design system for rural power grids based on 3d gis”, journal of software, vol. 8, no. 3, pp. 652-658, 2013 [15] n. parkpoom, “gis-based model for implementation on power transformer planning within thailand power network”, asia-oceania regional council of cigre, china, september 3-5, 2013 [16] esri, arcgis, http://www.esri.com/industries/electric [17] general electric, ge smallworld, https://www.gegridsolutions.com/ geospatial/catalog/smallworld_core.htm [18] google earth, https://www.google.com/earth/ [19] google earth pro, https://www.google.co.uk/earth/download/gep/ agree.html [20] r. broida, “get google earth pro for free”, https://www.cnet.com/news/ get-google-earth-pro-for-free/ [21] geocommunity, “gis viewing tools you shouldn't be without!”, http://spatialnews.geocomm.com/features/viewers2002/ [22] n. patwardhan, “power system visualization with google earth”, siemens power technology, no. 100, 2007 [23] ampirical solutions – engineering and epc services for transmission systems, http://www.power-technology.com/contractors/business/ampiri cal-solutions/ampirical-solutions2.html [24] gepath, http://www.sgrillo.net/googleearth/gepath.htm [25] maps.me, http://maps.me/en/home [26] openstreetmap, https://www.openstreetmap.org [27] google developers, “keyhole markup language, kml documentation introduction”, https://developers.google.com/kml/documentation/ [28] galileo offline maps, https://galileo-app.com/ [29] google maps help, “download areas and navigate offline”, https://support.google.com/maps/answer/6291838?co=genie.platform %3dandroid&hl=en [30] coord gr, http://users.auth.gr/kvek/coords_gr.zip [31] the.mos s.a., http://www.themos-sa.gr/proj/index.php [32] public power corporation s.a., https://www.dei.gr/en [33] hellenic electricity distribution network operator s. a., http://www. deddie.gr/en/i-etaireia/profil [34] independent power transmission operator s. a., http://www.admie. gr/nc/en/home/ [35] official government gazette, http://www.hellenicparliament.gr/en/ vouli-ton-ellinon/i-bibliothiki/koinovouleftiki-syllogi/efimeris-tiskyverniseos-fek/ [36] national printing house, http://www.et.gr/ [37] wikipedia, “geodetic datum”, https://en.wikipedia.org/wiki/geodetic_ datum [38] wikipedia, “world geodetic system”, https://en.wikipedia.org/wiki/ world_geodetic_system [39] mapref.org, map projections gr, http://mapref.org/mapprojectionsgr .html [40] wikipedia, “hellenic geodetic reference system 1987”, https://en. wikipedia.org/wiki/hellenic_geodetic_reference_system_1987 [41] national cadastral agency, “user guide for hepos”, http://www. hepos.gr/hepos/hepos_gen_guidelines_v1_1_gr.pdf (in greek) [42] the world coordinate converter, http://twcc.fr/# [43] national cadastral agency, http://gis.ktimanet.gr/wms/ktbasemap/ default.aspx [44] mapsdata online converters, http://www.mapsdata.co.uk/online-fileconverter/#latlon-instructions [45] google earth help forum, “how do i fill the name for each placemark automatically while importing from a csv file in google earth pro”, https://productforums.google.com/forum/#!topic/earth/ied75ocntmi [46] earth point, “excel to kml-display excel files on google earth”, https://www.earthpoint.us/exceltokml.aspx [47] google maps help, “embed a map or share a location”, https://support. google.com/maps/answer/144361?co=genie.platform%3ddesktop&hl =en [48] talos high voltage test station, the transmission system of crete, http://talos-ts.com/index.php/the-station/transmission-system-of-crete microsoft word 3-441.doc engineering, technology & applied science research vol. 4, no. 3, 2014, 636-643 636 www.etasr.com danikas et al.: a review of two nanocomposite insulating materials models … a review of two nanocomposite insulating materials models: lewis’ contribution in the development of the models, their differences, their similarities and future challenges m. g. danikas democritus university of thrace, department of electrical and computer engineering, xanthi, greece mdanikas@ee.duth.gr a. bairaktari democritus university of thrace, department of electrical and computer engineering, xanthi, greece agbairaktari@gmail.com r. sarathi indian institute of technology madras, department of electrical engineering, chennai, india rsarathi@gmail.com a. basri bin abd ghani tnb research sdn. bhd., high voltage cable diagnostics, distribution unit, selangor, malaysia abasri.aghani@tnbr.com.my abstract— nanocomposite polymers are nowadays a major field of research. this paper investigates the interpretational possibilities of two models developed, namely, tsagaropoulos’ model and tanaka’s model. particular emphasis is given to lewis’ model, which was the first one to be proposed and whose contribution to the aforementioned models was significant. the two models were developed separately and independently from each other. they both consider various layers around the nanoparticles. they both consider well bonded and more loosen layers. similarities and differences between the two models are pointed out and discussed as well as possibilities for further research in order to shed light on some aspects of electrical phenomena in these materials. particular emphasis is given to the interfaces between the nanoparticles and the surrounding base material. comments are offered regarding the challenges facing the two models w.r.t. the interpretation of discharges on nanocomposite surfaces. possible new areas of research are suggested and new challenges for the aforementioned models are pointed out. keywords – nanocomposites; nanoparticles; glass transition temperature; electrical trees; dielectric breakdown; breakdown strength; discharge path; surface discharge i. introduction more than twenty years now researchers try to improve conventional polymers by adding minute particles (nanoparticles) into the polymer matrix, thus changing their electrical, mechanical and thermal properties [1-4]. there are by now practically hundreds (if not thousands) of publications regarding nanocomposites and their related properties [5, 6]. as was remarked elsewhere among other things, “the emergence of a new class of dielectrics, ca. 2001 and first experimental data evidencing nanocomposites as dielectrics in 2002 stirred things up for the last decade” and “[although] nanodielectrics are not a panacea … [they] have definitely a future” [7]. of considerable interest is the subject as to why nanoparticles inserted into conventional polymers improve so dramatically the various properties of nanocomposites. the improvement may be due to the interfaces present because of the numerous nanoparticles. it is most certain that what is valid in conventional physics, is not necessarily valid for nanocomposites. three of the most interesting models that have been developed w.r.t. the interpretation of some of the electrical properties and/or electrical phenomena in nanocomposites are the following: lewis’ model [1], tsagaropoulos’ model [8] (it was proposed especially as a possible explanation as to why nanocomposites show the behavior they do, regarding the glass transition temperature) and tanaka’s model, as a possibility to explain various phenomena, such as electrical treeing and dielectric breakdown in nanocomposites [9, 10]. it is to be pointed out that lewis’ model was chronologically the first proposed. a first approach of nanocomposites models developed was made in [11], where two of the models were analyzed. parts of [11] are incorporated in the present paper, especially those that have to do with the description of tsagaropoulos’ and tanaka’s models. it is the aim of the present paper to analyze aspects of the two aforementioned models (tsagaropoulos’ and tanaka’s) as well as to compare them regarding their interpretational possibilities. ii. the role of nanoparticle interfaces interfaces play a critical role in classical insulating systems [12, 13]. their function is paramount to the good functioning of such systems, in such a way that some researchers claim that the problems of insulating materials are not but problems of interfaces. in the case, however, of the nanocomposites, their role, although it is extremely important, is not the same with that of classical interfaces. engineering, technology & applied science research vol. 4, no. 3, 2014, 636-643 637 www.etasr.com danikas et al.: a review of two nanocomposite insulating materials models … the role of interfaces has been pointed out in [1]. the improved properties of nanocomposites are due to the behavior of the interfacial interaction zone which surrounds the nanoparticles. the characteristics of the interfacial interaction zone are the following: 1) mobility, which depends on the physico-chemical bonds created on the common surface, and 2) formation at the interface of a double layer, which may affect the local conductivity. the effect of these two mechanisms is due to the considerable increase of the interfacial surface area [14]. in fact, the surface area formed by nanoparticles (and consequently the interfacial surface area) is three orders of magnitude larger than that of the microparticles [15]. moreover, the maxwell-wagner polarization is not so evident in the case of the nanocomposites, as it is with conventional polymers. this is because of the size of the nanoparticles, which as they become too small, they do not present the maxwell-wagner polarization. maxwell-wagner polarization changes significantly as the dimensions of inserted particles approach the length of polymer chain [16]. with the addition of nanoparticles in a base polymer, the aforementioned mobility and the structure of the surrounding polymer change considerably. the nanoparticles have a large surface area and this is the reason as to why the interaction zones in a nanocomposite are much larger than in a conventional polymer or in a polymer containing microparticles. in [1], it is proposed that around the nanoparticles a stern layer and a diffuse double layer (layer gouy-chapman) are formed, which have a high conductivity in opposition to the low conductivity of the surrounding material. charge movement through these layers is relatively easy [17]. in this way, a current flow is possible between the nanoparticles. in another paper [18], it was noted that the significant interfacial polarization in conventional polymers is mitigated in nanocomposites, where a short-range highly immobilized layer develops near the surface of the nanoparticle. this layer affects a much larger region surrounding the nanoparticle in which conformational behavior and chain kinetics are greatly altered. it is that this interaction zone is important for the material property modifications, especially if the curvature of the nanoparticles approaches the chain conformation length of the polymer. lewis based his approach on o’ konski’s model and on the consideration of the double layer. lewis’ model differed from that of tanaka, in that lewis proposed just two layers whereas tanaka proposed in fact four (multi-core model based on bonded layer, bound layer, loose layer and double layer overlapping with the other three layers). tanaka ’s model is similar to that of lewis only in that last double layer. tanaka postulated that defects and impurities are likely to be present on the outer layer in his proposed multi-core model [9]. such defects and impurities may act as traps, which will be distributed in shallower energy levels than traps originally present in base materials. deep traps are likely to be formed in the second layer of the multi-core model. this may mean the increase in space charge because the deeper traps will trap carriers only after all shallow trap levels have been filled up [19]. tanaka elaborated this approach in a further paper, where he remarked that treeing is affected by such deep traps. according to his approach, treeing is attributed to accelerated electrons passing between neighboring nanoparticles colliding with interfaces between the polymer and the nanofillers [20]. nanoparticles – because of their extended surface area change the very nature of the polymer altering the depth and density of trap sites, reducing in this way charge carrier mobility and energy [7]. it is true that as the particles become smaller and smaller, the role of interfaces becomes more important. a very important point mentioned in [21], is the following: that an improvement in breakdown strength of nanocomposites in comparison with conventional polymers is more evident in mediumor long-term degradation properties. the aspect ratios of nanoparticles and the interfacial properties are crucial for the electrical behavior of a nanocomposite. the role of interfaces (and consequently of interphase, which consists of polymer chains having different morphology from that of the surrounding uninfluenced polymer) was also emphasized in [22, 23], where it was shown that nanocomposites with higher interphase content have a higher resistance to tracking and erosion than nanocomposites with lower interphase content. in [24], the role of interfaces is also emphasized. interfacial strengthening between silica nanoparticles and the organic polymer (epoxy resin) through the silane coupling help reduce the mobility of charge carriers and thus increase the partial discharge resistance. the authors give also another interesting approach of the improvement of the electrical behavior, namely that the nanoparticles fill the space thus decreasing the volume of epoxy resin. a different approach is mentioned in [25], where photos of nanocomposite samples were taken showing in detail the dispersion of nanoparticles and their concentration. the techniques used were the tem (transmission electron microscopy), afm (atomic force microscopy) and xdc (xray disc centrifuge). nanoparticles were clearly shown and agglomerations of particles were also spotted. the role of interfaces is also emphasized in [26], where is pointed out that nanofillers provide large interface density but low trapping efficiency due to the better quality of polymernanograin interfaces. in this same paper, it is also stated that “… nanofiller dispersed in the microcomposite material forms plaques between the micro-sized particles providing an additional barrier to pd propagation”, in agreement with previous results [27]. in [28], a highly exciting aspect is reported, namely, that there is an optimum value of filler concentration for each particle size of mica. in other words, the electrical behavior is determined not only by the percentage of contained nanoparticles. iii. tsagaropoulos’ nanocomposite model tsagaropoulos’ model is analyzed in [8]. it assumes two basic layers around a nanoparticle, an inner tightly bound layer in which polymer motion is severely restricted, and another intermediate layer which is more loosely bound. at the first layer, at a distance of 1 to 20 angstrom from the nanoparticle surface, the polymer is physically (if not chemically) adsorbed and its dynamics is slowed down as a consequence of this – therefore, it is generally thought to be tightly bound. at larger engineering, technology & applied science research vol. 4, no. 3, 2014, 636-643 638 www.etasr.com danikas et al.: a review of two nanocomposite insulating materials models … distances of about 25 to 90 angstrom from the nanoparticle surface, the polymer is believed to be less tight and perform an intermediate dynamics; this layer is more loosely bound [29]. in [30], a third layer is also assumed, that of the unrestricted bulk polymer. the gist of tsagaropoulos’ model is the morphology of the polymer around the filler particles. it is, in other words, the sequence of events accompanying the incorporation of increasing amounts of silica particles in the polymer. this results in a decrease of the average interparticle distance d. layers of polymer are tightly bound to nanoparticles. the model deals in principle with the two glass transition temperatures in nanofilled polymers. the polymer chains capable of participating in the second glass transition will be called polymer of reduced mobility or loosely bound polymer. in [8], the critical percentage of nanoparticles is put up to 10%, in all probability because it is at this percentage where the average interparticle distance has a ‘critical’ value dcr. as the average interparticle distance decreases further, with the incorporation of more filler particles, the mobility restrictions become so severe that the loosely bound polymer is gradually transformed to tightly bound. the volume fraction of loosely bound polymer decreases, resulting in a decrease in the area of the second tan δ peak. on the contrary, the volume fraction of tightly bound polymer increases. as the interparticle distance decreases, it is the most restricted regions of loosely bound polymer which are transformed first into tightly bound polymer. the regions with the highest tg will be eliminated earliest as filler content increases, resulting in an actual decrease of the second tg. at lower filler content, the amount of the immobilized polymer around the particles is small, allowing for sufficiently strong interactions between the loosely bound polymer and the particles. as the amount of immobile polymer increases at higher nanoparticle contents, such interactions will become weaker. consequently, as the immobile polymer does not restrict the chain mobility as efficiently as the nanoparticles, the second tg decreases. eventually, with a very high nanoparticle content (in [8], the authors mention contents of more than 50 wt%), the average interparticle distance will be much smaller than dcr, with the result that nearly all polymer chains are immobilized. explaining tsagaropoulos’ model in other words, one can note that the loosely bound polymer exhibits its own glass transition, whereas the tightly bound does not participate in the glass transition. at lower concentrations of nanoparticles, the interparticle distances are large and the mobility of the polymer next to the tightly bound layers is not influenced. such regions cannot form a second glass transition, despite the fact that the temperature of the first glass transition decreases. by the nanoparticle concentration, the interparticle distances are reduced. when the loosely bound layers start to overlap – and a critical interparticle distance is reached – they can exhibit their own glass transition. when the nanoparticle concentration increases further, the polymer regions with reduced mobility decrease but the immobilized regions increase. consequently, the loosely bound layers are converted into tightly bound layers and thus, there is a reduction of the second glass transition temperature. higher filler loading implies smaller interparticle distances, the volume fraction of the loose polymer layer is reduced and the nanoparticles themselves start acting as barriers to the flow of current between the electrodes [31]. the focus of tsagaropoulos’ model is on the influence of filler particles on the mobility of polymer chains [32]. tsagaropoulos’ model claims that the discrete bound layer can result in a second glass transition temperature but work on thin films did not point to a discrete layer of affected material but to a far field effect [33]. to emphasize this point, in yet another publication, it was remarked that the two-layer model by tsagaropoulos does not embody the physics of the whole situation [34]. in the latter publication, it was claimed that the mere presence of regions of modified mobility in the proximity of nanoparticles cannot explain the glass transition temperature results. the smallest interparticle spacings, which would percolate first, would dominate the behavior. such interaction effects apply also in the case of functionalized nanoparticles, the only difference being that in close vicinity to the nanoparticles, the regions have reduced mobility. the glass transition process in restricted geometries requires the interaction of near surface regions of altered mobility. although the authors of [34] differentiate from tsagaropoulos’ model, they also use terms such as ‘regions of reduced mobility’, which remind us well of tsagaropoulos’ model. justification to a certain extent of tsagaropoulos’ model is mentioned in [30], where nmr data support it, since as was mentioned in a previous paper, ‘… the adsorption layer differing in mobility from bulk pdms could be detected just above the glass transition temperature in systems filled with hydrophobic aerosil’ [35]. further support for this model was given in [29], where faster processes correspond to bulk polymer whereas slower processes are interpreted in terms of tightly bound polymer chains, whose segmental dynamics are slowed down w.r.t. bulk dynamics as a consequence of the interaction with the silica nanoparticle surface. further support is offered in [36], where dynamic mechanical thermal analysis suggests that polymer chain motion in polymer electrolytes is affected by the presence of nanoparticle surfaces, i.e. glass transition temperature increases by increasing the percentage of nanoparticles. additional support of tsagaropoulos’ model came relatively recently in [37], where the authors investigating polymer blends (pp/epr)/w/pep and (pp/epr)/s/pep, observed a second peak of relaxation at -38 and -36 c in the presence of pep copolymer. the authors of [37] explained the observation by using tsagaropoulos’ model, i.e. that the strongly bound layer, immediately surrounding the nanoparticle does not participate in the glass transition, the second loosely bound interfacial layer is responsible for the second glass transition and the quasi-bulk polymer remains unaffected by the nanoparticle. echoes of support of tsagaropoulos’ model can also be found in [38], where the authors, by investigating nanocomposites consisting of mixtures of peek (poly(ether-ether-ketone))and nanoparticles, contributed the increase in microhardness to the dominant role of increased crystallinity and peek morphology in the vicinity of the nanoparticles. tsagaropoulos’ model is commented favorably in [39], where it is pointed out that shifts in tg to either higher or lower temperatures are observed with nanocomposites by appropriately tuning the interactions between polymer and nanoparticles. the magnitude of the engineering, technology & applied science research vol. 4, no. 3, 2014, 636-643 639 www.etasr.com danikas et al.: a review of two nanocomposite insulating materials models … shifts is dependent on the relative quantities of the polymer and the nanoparticles; a greater nanoparticle concentration results in a more dramatic effect. moreover, the viscoelastic response of the polymer matrix composite is altered significantly by the presence of silica nanoparticles in comparison to that of the bulk polymer, as was pointed out in [40]. the authors explain this with the aid of tsagaropoulos’ model. in studying the role of various nanoparticles on the electrical properties of epoxy resin, other researchers explained the decrease of permittivity of nanocomposites by considering that the interaction between nanoparticles and polymer matrix reduces the mobility of epoxy chain in the bulk material, which results in a reduction of the effective permittivity of epoxy nanocomposites. the thin immobile nano-layers, which are formed, restrict the mobility of the epoxy chain. as the loading concentration increases, more immobile layers are formed and the mobility of the epoxy chain decreases continuously, resulting thus in a reduction of the permittivity of the nanocomposite [41]. further support for tsagaropoulos’ model can also be traced in [42], where the broadening of the tan δ peak to higher temperatures as well as the decrease of the magnitude of tan δ peak are attributed, by the authors, to the variation in interaction between pan (polyacrylnitrile) and ato (antimony-doped tin oxide). the motion of pan molecules closer to the nano-ato particles would be more constrained than those farther away from it. echoes of tsagaropoulos’ model can also be found in [43], where with a high fraction of nanoparticles offers a lower degree of crystallization might occur, since the mobility of the polymer matrix chain segments will decrease during the period of crystallization. in [44], the authors seem to accept tsagaropoulos’ model claiming that “for the pc/mwnt composite, the higher tan δ peak becomes broader, which may be considered that the mobility of the polymer chain becomes more restricted by the mwnt … [possible explanation is that] … the phase separation morphology model according [to which] the lower tanδ peak of the polymer composites corresponded to the tg of the polymer matrix, and the higher tanδ peak of the polymer composites corresponded to the tg of the confined polymer chain by the filler”. also in [45], a second thermal transition above the glass transition which was noted for samples in excess of 20 wt% fumed silica, was attributed to the polymer closely interacting with the silica filler, i.e. what is termed bound polymer. relatively recently, it was pointed out that nanofillers can constrain the mobility of polymer chains as well as their relaxation spectra, which can change the glass transition temperature and modulus of the matrix [46]. concluding, one may say that tsagaropoulos’ model indicates the presence of two tanδ peaks, one related to the base polymer and the other – which occurs at higher temperatures – is due to polymer regions of reduced mobility because of the nanoparticles. as a general comment, one may say that tsagaropoulos’ model, despite some weaknesses, is generally accepted as a nanocomposite model explaining various aspects of nanocomposite behavior, especially those having to do with the glass transition temperature. iv. tanaka’s nanocomposite model tanaka’s model consists of a multicore description for nanoparticles [9, 10]. it bears also the name ‘multi-core’ model since it considers more than two layers. tanaka working independently of tsagropoulos, proposed another model. there is a bonded layer around the nanoparticle (first or innermost layer), a bound layer (second layer), a loose layer (third layer) and an electric double layer overlapping the above three layers. the first layer corresponds to a transition layer tightly bonded to both inorganic and organic substances by coupling agents, such as silane. its thickness is postulated to be of about 1 nm. the first layer is tied by ionic, covalent, hydrogen and van der waals bondings. the second layer is an interfacial region consisting of a layer of polymer chains strongly bound and/or interacted to be first layer and the surface of the inorganic particle. the thickness of this layer is between 2 and 9 nm. these values depend on the strength of the polymer-particle interaction. obviously, the stronger the interaction, the larger the polymer fraction. chain mobility and crystallinity are deeply involved. the former is directly related to glass transition temperatures. the average chain conformation can be altered and/or the type and degree of crystallinity can change. the third layer is a region of loosely coupling and interacting to the second layer. the loose layer has different chain conformation, chain mobility and even free volume or crystallinity from the polymer matrix. this layer is of several tens of nm thick. the fourth layer, the electric double layer, forms a long distance dipole. this will affect electrical conduction and dielectric properties in the low frequency region. as is indicated in [10], a nanoparticle is charged positively or negatively when a polymer has mobile charge carriers, which are distributed in the interface so that the counter charges with the opposite polarity are diffused outward from the contact surface to the debye shielding length corresponding to the couy-chapman diffuse layer in which charge decays exponentially according to the born approximation. in other words, tanaka’s model considers that nanoparticles are positively or negatively charged, taking into account that are inserted into polymeric materials which end to be either positively or negatively charged. such charging may in some ways have an effect on discharge treeing paths. simulation results until now give some good grounds to tanaka’s model. as was indicated previously, electrical tree paths in a nanocomposite go through the polymer and not through the nanoparticles [47, 48]. treeing paths may propagate through the polymer and/or they may touch nanoparticles and circumvent them. simulation data show that in no case treeing paths go through the nanoparticles. although one may say that these are just simulation results, i.e. they do not take into account all possible involved parameters, it is undeniable that they at least – partially simulate realistic conditions. also in [49], it was indicated that in absence and/or in presence of homocharges/heterocharges, nanoparticles act as elementary barriers to the propagation of electrical trees. moreover, simulations with homocharge presence show that the tree propagation stops at a certain stage. this although it may not explain the gist of tanaka’s model, it shows, however, that with charges of the same polarity the tree growth stops. homocharges and scattering mechanism (due to nanoparticles engineering, technology & applied science research vol. 4, no. 3, 2014, 636-643 640 www.etasr.com danikas et al.: a review of two nanocomposite insulating materials models … and the interfacial regions) contribute to the enhancement of the dielectric properties of nanocomposites [50]. evidence, that converges with the simulation results presented in [47, 48], was published recently, where was remarked that layered montmorillonite particles have the strongest effect on slowing down the propagation of electrical treeing in ldpe [21]. in the latter paper, it is also pointed out that the strongest benefit from nanostructuration is gained in the mid-term performance of the material. furthermore, other researchers observed that nanofillers relate to the excellent resistance to partial discharges and electrical treeing in the cases of epoxy with alumina and of epoxy with silica nanocomposites [51], whereas others still claim that because the distances between nanoparticles are very small, they hinder the movement of charge carriers and thus the dielectric strength increases [52]. in another paper [53], the authors present photographic evidence indicating that tree channels extend between nanoparticles and expand in a direction perpendicular to tree length to contact nanoparticles. this means that trees interact with nanoparticles when they become thicker. this presumably suggests that trees are modified through the applied field and in turn they modify the nanocomposite structure. tanaka’s model was extensively discussed in [54], where it was remarked that the third layer will have a dominant effect on the overall performance of the nanocomposite, as being much larger than the first two layers. with high nanoparticle percentage, about 50% of the total volume will be affected and one may assume that it is possible that also the shell layer interfaces will overlap. this point is somehow shown, albeit with all reservations of the simulation parameters, in [47-49], where treeing paths penetrate through the polymer. in the aforementioned publications, the tree propagation is shown in a nanocomposite with well defined nanoparticles and a space charge density of 40 c/m3. homocharge was considered. the tree propagation stopped with homocharges present. tanaka’s model was discussed in [55-57], where the authors used an analogy of the model to explain the percolation of charge carriers through overlapping water shells. in [55-57], it was claimed that the inner layer of water may surround the nanoparticle and the second water layer to be dispersed but sufficiently concentrated to be conductive. it was considered that the inner and outer layers are likely to provide a channel for charges and carriers. once the water shell around a nanoparticle can overlap with the others, charges and carriers may move with through the interaction zone between neighboring particles. tanaka’s model in fact, in the above publications, helped to study the electrical properties of epoxy resin nanocomposites as a function of hydration. in another publication, the authors tend to agree with tanaka’s model and with tanaka’s estimate of the interaction zone as a fraction of a nm when the coupling of inorganic surface with the polymer matrix increases by using silane [58]. the authors of [58], however, put more emphasis on the intensity and specificity of the chemical activity – which will affect the polymerization of the interface – and not so much on the thickness of this zone. another researcher, in [59], seems to accept tanaka’s model when he discusses overlapping zones between the nanoparticles and complete percolation through interaction zones and volumetric concentration. in the same publication, he carries on to ask pertinent questions regarding the nature of interaction zone around the nanoparticles, the layers which comprise the interaction zones and their thicknesses. tanaka’s model is much more recent than tsagaropoulos’ model. it was positively received by the scientific community since it offers plausible explanations as to the some aspects of the electrical behavior of nanocomposites. it must, however, be noted that more experimental results, and particularly photographic evidence, are needed in order to fully verify it. optical microscopy as well as sem are needed to exactly trace the discharge and/or treeing paths in nanocomposites. this point is also stressed below. good reliable photographs should be obtained by cutting the nanocomposite in very thin slices. this is a most daunting task and by no means an easy one. a further point to be mentioned is the crossover phenomenon, observed under certain conditions, i.e. the fact that tree propagation is different between base epoxy resin and its nanocomposite counterpart under different voltage conditions. it was observed that at lower voltages, the tree propagation speed for nanocomposites is lower than that for base epoxy resin. on the contrary, at higher voltages, the tree propagation speed is higher in nanocomposite epoxy resin than in base epoxy resin [6]. although an explanation was offered, namely that an erosion type of degradation takes place under lower voltages whereas a progressive type of degradation takes place at higher voltages, further work is needed, bearing in mind tanaka’s model, regarding the explanation of the above mentioned crossover phenomenon. v. the two models: similarities and differences regarding interpretational possibilities, tanaka’s model is not different from tsagaropoulos’ model. needless to say that both models are indebted to the original lewis’ publication [1]. both models tend to assume an inner bonding layer, strongly attached to the nanoparticle, they differ, however, somehow (but not radically) in the way they perceive the reaction to other nanoparticles and/or to the rest of the polymer. their major difference is in the number of assumed layers, and not so much as to what these layers may do. tanaka’s model seems to be more complete in that it considers in some detail the workings of the polymer matrix/nanoparticle interface. both models try to explain the second glass transition temperature. both models assume that the interparticle region is the weak link in the polymer – nanoparticle system. tsagaropoulos’ model tends to explain rather well the glass transition temperature variation when nanoparticles are added to a conventional polymer. tanaka’s model also tries to explain the glass transition temperature variations by claiming that “… improvement in glass transition temperature must originate from the formation of the second and third layers of the multi-core model. it indicates that fillers and matrices are rather tightly bonded through these layers” [9]. tsagaropoulos’ model refers more to glass transition temperature data without any elaboration regarding the electrical treeing and breakdown strength of nanocomposites. tanaka’s model tackles precisely these issues. although the two aforementioned models differ in their number of layers, engineering, technology & applied science research vol. 4, no. 3, 2014, 636-643 641 www.etasr.com danikas et al.: a review of two nanocomposite insulating materials models … their respective thicknesses and their possibility of interpretation of various phenomena, they both refer to layers surrounding a nanoparticle and they both explain why with the addition of nanoparticles there is a marked improvement in the properties of conventional polymers. recent simulation results [47-49] indicate that electrical treeing goes through the polymer matrix, avoiding thus the nanoparticles. this is an indication of validity of both models but not yet a proof. the indication seems to be stronger in tanaka’s model (which assumes charged nanoparticles), since the simulations show that – in the presence of homocharges – trees propagate through the polymer matrix. one may well argue that homocharges are not the same and they are not perceived as the same as the charged nanoparticles in tanaka’s model. tanaka’s model assumes an electric double layer for each nanoparticle, and it also assumes that this is the result of triboelectricity. the answer to such claims is that, although homocharges are something different, they also assume the same polarity charges around the nanoparticles and in this respect, their end result will be the same. these simulation data, however, do not go against tsagaropoulos’ model since this model is also based on tightly bound layers hindering breakdown events and thus strengthening the nanocomposite. it has to be clear that the above two models are not by any means exhausted in the references cited here. recent research indicated that, with the aforementioned models justified to a certain extent, higher stresses and a reduction in insulation thickness would be possible [60, 61]. in the context of the present work, we tried to approach both models, their respective merits and to point out some aspects in need of further research. vi. proposals for further research what is missing for the time being, is not so much experimental data regarding the improvement of the electrical properties of nanocomposites w.r.t. the conventional composites, but more photographic evidence. in this respect, sem photographs (or tem photographs), among others, may indeed give information as to the directions followed by treeing and/or discharge paths in nanocomposites. they may indicate whether such paths avoid the nanoparticles. sem evidence for the time being confirms that nanoparticles act as a sort of barriers opposed to the advancement of electrical treeing. sem evidence confirms that discharge and treeing paths go round the nanoparticles. more evidence, however, is needed. this task is by no means simple, since it is difficult to obtain clear treeing paths round nanoparticles. physical models regarding the treeing path have been proposed [62]. such models propose that trees will dwell at the nanoparticle surface and try to propagate through the nanoparticle-polymer interface. the nanoparticles would create a hindrance to growth, and they will prevent trees to grow in rather straightforward directions. trees will propagate from nanoparticle to nanoparticle through the polymer. consequently, the tree structure will be dense and zigzag. reference [62] implies that trees propagate through the weaker insulating material and not through the nanoparticles. such models, however, no matter how plausible explanations they may offer, have to be supported by evidence and this evidence can be given by sophisticated photographic techniques. photographic techniques can be either sem or tem, which may shed light to the inner workings of pre-breakdown and breakdown phenomena in nanocomposites. one cannot enough overstress that such photographs are very difficult to obtain since, in order to get such photographs a cutting of the samples with more than surgical precision is required. needless to say that, the two aforementioned models have to be tried in various kinds of nanocomposites. it is only through the variety of nanoparticle-polymer combinations that more insight as to the workings of the improvement of the nanocomposite properties may be gained. moreover, the aforementioned models should also be tried with various nanoparticles concentrations as well as with various nanoparticle dimensions in order to check their validity. generally speaking, there is an optimum percentage (wt%), depending on the base polymer matrix and the nanoparticles, beyond which the electrical properties of the nanocomposite cannot be improved (not to say, they worsen). what are the interpretational possibilities of the two aforementioned models regarding the optimum percentage of nanoparticles? are the so-called agglomerations of nanoparticles – as the nanoparticle percentage goes up a reasonable and adequate explanation for the optimum percentage of nanoparticles? on the other hand, from the side of simulations, more refined simulations have to be performed which should closely resemble to the real trees. in that, a better evaluation of the various parameters has to be taken into account, i.e. a better evaluation of the electric field distribution inside a nanocomposite. in other words, a better evaluation has to be made regarding the influence of the nanoparticles on the very existence of the electric field in the nanocomposite. how the nanoparticles affect the electric field? what is the effect of their proximity on the electric field distribution? regarding some more general questions, how a proposed model may interpret not only electrical trees inside the main insulation volume but also the influence of surface discharges on a nanocomposite? the case of surface discharges is most interesting since according to previous work, nanoparticles play a dominant role in determining the surface flashover of nanocomposites and their agglomerations on the surface of the nanocomposite tend to hinder further surface degradation. consequently the role of nanoparticle agglomerations (which in the bulk of the nanocomposite may have a rather negative effect), has to be clarified in the light of relatively recent work [63]. further recent research on water droplets on nanocomposite surfaces points out to the importance of surface phenomena on nanocomposite surfaces [64, 65]. it would be scientifically highly interesting if the models proposed by tsagaropoulos and tanaka can be tested also against surface discharge phenomena, which doubtless cause significant degradation. a step even further would be to test these models w.r.t. the thermal and mechanical properties of polymer nanocomposites [66, 67]. a further point to be researched and discussed in the future is the following: given that nanocomposite polymers may be used also for outdoor applications, what are the interpretational engineering, technology & applied science research vol. 4, no. 3, 2014, 636-643 642 www.etasr.com danikas et al.: a review of two nanocomposite insulating materials models … possibilities of the aforementioned models as to the effect of water and/or water diffusion in nanocomposites? how functionalization (i.e. the chemical adjustment of nanoparticles to the better bonding with the base polymer matrix) of the nanoparticles can hinder water diffusion? can the nanocomposite models described in the present paper – take into account such phenomena? vii. conclusions in this paper, a comparison between two well known models is being made. both models have their own merit, both were influenced by the original contribution by lewis, both are supported by some experimental evidence and recent simulation data. the models, tsagaropoulos’ model and tanaka’ s model, have their own explanatory power and they are based on the idea of more and less well bonded layers around nanoparticles in the polymer matrix. more research has to be carried out, however, regarding the photographic evidence of the treeing and/or discharge paths in nanocomposite polymers. such photographs have to be either sem or tem. the validity of the models should also be tested regarding the thermal and mechanical properties of the said materials, since in high voltage applications it is very often the case of combined electrical, thermal and mechanical stresses. acknowledgments one of the authors (mgd) wishes to express his gratitude to professor toshikatsu tanaka of waseda university, graduate school of information, production and systems, for having invited him as visiting scholar in his laboratory during the academic year 2008-09 and having introduced him to the subject of nanocomposites. references [1] t. j. lewis, “nanometric dielectrics”, ieee trans. diel. electr. insul, vol. 1, pp. 812-825, 1994 [2] m. takala, h. ranta, j. pelto, s. virtanen, 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[66] r. k. sahu, “understanding the electrical, thermal and mechanical properties of epoxy nanocomposites”, ph.d. thesis, indian institute of technology madras, department of electrical engineering, chennai, india, 2007 [67] r. sarathi, m. g. danikas, “understanding the mechanical properties of epoxy nanocomposite insulating materials”, j. electr. eng., vol. 60, no. 6, pp. 358-361, 2009. microsoft word etasr_v11_n6_pp7814-7823 engineering, technology & applied science research vol. 11, no. 6, 2021, 7814-7823 7814 www.etasr.com huu & ngoc: a two-level desired load profile tracking algorithm for electric two-wheeler … a two-level desired load profile tracking algorithm for electric two-wheeler charging stations duc nguyen huu faculty of energy technology electric power university hanoi, vietnam ducnh@epu.edu.vn van nguyen ngoc faculty of electrical engineering electric power university hanoi, vietnam vannn@epu.edu.vn abstract-in vietnam and in other developing countries, twowheeled electric vehicles are potential alternatives to gasolinepowered motorbikes. the growth in the number of electric twowheelers (e2ws) requires a large power demand of charging load. in addition, the increasing spread in the appearance and penetration of rooftop photovoltaic (pv) power systems, with their intermittence and uncertain nature, poses technical challenges that need to be addressed. the coordination of pv rooftop operation and ev charging may be an effective solution to meet the emerging load demand from evs, increasing solar power penetration while minimizing the cost of grid reinforcement or possible upgrades. in this paper, a two-level desired load profile tracking algorithm for pv integrated electric bicycles/electric motorcycle charging stations is proposed with the purposes of load leveling, valley filling, and peak shaving. the simulation results show that the proposed algorithm is an effective solution, significantly improving the load profile, especially when compared with uncontrolled charging and constant charging power scheme. keywords-electric two-wheelers; charging stations; load leveling; charging algorithm; solar power i. introduction the transport sector currently accounts for about 20% of co2 emissions and more than 50% of fossil fuel consumption. recently, transport electrification has been considered as an effective measure to reduce greenhouse gas (ghg) emissions. however, basically, the ghg reduction purpose is only obtainable if the energy used for transport electrification is from renewable sources, instead of fossil fuel power plants [1]. therefore, ev charging combined with renewable energy offers the potential for eco-friendly and sustainable development in both transportation and energy sectors. in vietnam, the transition to electric mobility has notable characteristics. instead of electric cars, electric bikes and motorcycles (hereafter referred to as electric two-wheelers or e2ws) have been more attractive [2, 3]. a continuous growing in the number of affordable e2ws in urban traffic initiates necessities like charging points at homes and workplaces. more charging load leads to a higher demand for electrical energy. with modest battery capacity and charging power compared to electric cars, e2ws charging at home might utilize portable chargers (which came with evs) plugging in standard socket outlets. because of modest power rating, these chargers, often of one direction type, are designed to optimally supply electricity to the ev’s battery without caring of the electricity price scheme and the impacts to the grid or to other loads. however, in locations like offices, supermarkets, campuses, apartment buildings, transport terminals, or public parkings, a high number of e2ws charging simultaneously would introduce a very high charging demand which might impact the grid or the provided power quality. in such cases, dedicated charging facilities are required, which could regulate and coordinate charging loads in the station, decide each ev’s charging pattern based on ev owners’ settings, technical constraints and/or economic/technical objectives. in other business models, such as battery swapping stations, coordination charging of batteries in the station might be more imperative since it can help both station operators/service providers and ev users to maximize their benefits. regarding to the electrical energy sector, vietnam has a great potential of solar power [4] exploitation. according to the draft national power development plan for the period 20212030, with a vision to 2045 (draft master plan viii or pdp8), the total installed capacity in 2020 was about 69,094mw, with hydropower accounting for 30%, coal-fired power for 30%, gas natural/diesel power for 13%, and renewable energy for 26% [5] of total production. total solar power generation in 2020 was 10.6×10 9 kwh, of which rooftop solar power was 1.16×10 9 kwh. in comparison with other power sources, renewable energy, especially solar power, is developed very quickly in vietnam. however, because of its intermittent and uncertain nature, the continuing growth in the share of pv power leads to grid issues such as power, voltage and frequency fluctuations. this requires expensive spinning reserves, directly affecting the economic efficiency. in addition, transmission/distribution system infrastructure investment does not keep up with pv development, which results in cut-downs in the solar output. corresponding author: duc nguyen huu engineering, technology & applied science research vol. 11, no. 6, 2021, 7814-7823 7815 www.etasr.com huu & ngoc: a two-level desired load profile tracking algorithm for electric two-wheeler … by the end of december 31, 2020, there were 101,029 rooftop pv projects (nearly 9,296mwp installed capacity) connected to the national power system [5]. the development in the distributed rooftop solar power sources, along with the increasing popularity of e2ws, poses technical challenges that need to be addressed. uncontrolled ev charging may increase the peak load demand and energy losses in residential buildings and distribution power grids [6-8], which result in inefficient operation of the system. noteworthily, the higher amount of solar pv output usually corresponds to low load time (about from 10 am to 2 pm), resulting in needs of load shifting or energy storage systems. if the ev charging and discharging processes are properly controlled, ev batteries can also act as both loads and as energy storage devices or power regulating components. the involvement of evs might contribute to increase renewable energy penetration without impact on grid stability because solar power is locally generated and consumed. the participation of ev batteries and pv systems contributes to smart grids with lots of potential such as load shifting, valley filling, peak clipping (peak shaving), regulation and spinning reserve. several researches on optimal allocation of evs are mentioned in [9], combined pv and ev charging in [10] and efficiency improvement of ev’s motors in [11]. a. related work it is shown that, the uncoordinated ev charging can trigger power loss and voltage deviation significantly [7]. with regard to load shifting and valley filling, studies focused on shifting the charging load to off-peak hours rather than uncontrolled charging. in [12], the authors proposed a decentralized valley filling strategy to build a day-ahead pricing scheme by solving the overall generation cost optimization problem (including base load and evs). the pricing scheme is then broadcasted to vehicle owners to indirectly regulate charging behavior. changing the charging pattern of each ev leads to valley filling at the system level. authors in [13] proposed a decentralized charging algorithm for a large number of evs by applying the nash equilibrium principle. the authors found out that if the evs are uniformly distributed, charging based on the nash equilibrium principle would fill the overnight valley optimally. linear programming was used in [14] to minimize the total electricity cost and reduce the power peak in a time of use (tou) price market while quadratic programming (qp) is utilized to minimize the overall load variance in a regional micro-grid in [15]. a decentralized charging protocol based on qp is also adopted to achieve the valley filling for the grid operators in [16]. in [17], a heuristic charging strategy for commercial buildings containing pv systems and evs is proposed, where the ev charging rate is adjusted according to the variation of pv generation and the charging priority of each ev. similarly, in [18], a centralized heuristic charging strategy is proposed to achieve the valley-filling for large scale evs. there are a very few studies relating e2ws charging. authors in [19] developed a pv-powered electric bicycle charging station providing ac/dc and wireless charging. the charging station had a built-in energy storage device that allows both grid-connected and standalone operations. authors in [20] introduced a charging station powered by the grid, fuel cells, and pv to unburden the grid from charging. the station can provide service when power outages occur. however, the aforementioned studies were restricted to only developing a pv integrated charging station for e2ws. they did not focus on e2ws optimal charging especially when a large number of vehicles are charging simultaneously. in general, researchers mainly focus on charging algorithms for electric cars with large battery capacity and significant charging/discharging power. there are very few studies aimed at developing control algorithms and operation schemes for electric bicycles/electric motorbikes charging stations, although the potential of this vehicle type is undeniable in urban traffic. besides, due to the great number of vehicles in the station, the application of multitarget optimal charging algorithms for electric cars may not be computationally feasible for e2ws. a higher vehicle number in the station means a higher number of variables, which requires a higher computational capability. b. the proposed algorithm in this study, we propose a two-level desired load profile tracking algorithm to allocate charging power to electric bicycles/electric motorcycles. the algorithm has a small number of iterations and does not require high computational capability. the contributions of the proposed algorithm are summarized as follows: the study proposes and develops an algorithm (level 1) to find out the total charging power scheme for e2ws in the charging station. the total charging scheme and the netload compose the desired total load profile. based on the total charging scheme, a power allocation algorithm (level 2) is proposed and utilized to decide the charging pattern of each e2w or group of e2ws having similar parameters. these charging patterns satisfy the charging requirements of e2ws and the aggregated charging powers approximate to the total charging power attained after level the implementation. the proposed algorithm is applied for load leveling, peak clipping, and valley filling. by utilizing the algorithm, rooftop pv penetration rate can be increased with lesser impact on microgrids. the algorithm helps to increase the penetration of e2ws without requiring grid upgradation or reinforcement. ii. system modelling a. ev charging infrastructure model in this study, the charging station is controlled and managed by a centralized controller that optimizes the coordination of e2w loads with other loads and with the rooftop pv generation in order to improve load profile and perform valley filling and peak clipping. based on the existing load, the controller estimates the total charging power pattern supplied to all e2ws in the station. the estimation process is planed considering the total required energy of e2ws and other technical constraints. the controller then allocates the total charging power to each e2w or a group of e2ws at each period, which results in a specific charging pattern for each e2w or group. assuming that the charging station accommodates n electric bikes/electric motorcycles, evi is the i th e2w in the n-vehicle parking at the charging station. let ����� be the total amount of energy stored in the batteries at time t, ����� is the non-ev load demand minus the power generated by solar panels at time t, also known as the netload, engineering, technology & applied science research vol. 11, no. 6, 2021, 7814-7823 7816 www.etasr.com huu & ngoc: a two-level desired load profile tracking algorithm for electric two-wheeler … ����� is the total load demand (charging load plus netload); � is the discretization in time, and ���� is the total charging power of all e2ws at time t. we assume that the charging station is connected to the grid, to the load of the building, and to a rooftop pv system, and all chargers have a vehicle to grid (v2g) feature. thus, the charging station can be described by the following discrete-time linear equations: ���� +1� = �����+ ����.� (1) ����� = ����� + ���� (2) in this study, � = 0.5h = 30min. since the chargers at the station include the v2g feature, the power exchange between the grid and e2ws can be implemented in two directions. the charging behavior of all evs can be determined by the sign of ����� where ����� > 0 ( ���� > 0) if the aggregated batteries receive energy from the microgrid and ����� < 0 ( ���� < 0) if the aggregated batteries discharge energy to the grid. the power constraints of charging and discharging processes (assuming all the evs in the station are connected to the chargers) can be described as: �ℎ������: ���� ≤ ����∑ ����� !"# ,∑ %���� !"# & (3) ��'(ℎ������: ���� ≥ ��*�∑ ��!+� !"# ,∑ %�!+� !"# & (4) where ����� and ��!+� are the maximum charging and discharging power of charger i respectively and %����, %�!+� are the maximum permitted charging and discharging powers of evi. it is assumed that all e2ws have the same %���, %�!+ and ���� , ��!+ of all chargers are uniform. then, the constraints in equations (3) and (4) become: �ℎ������: ���� ≤ ���,-. ����,-. %���. (5) ��'(ℎ������: ���� ≥ ��*,-. ��!+,-. %�!+. (6) where ��!+ (discharge) and ���� (charge) are respectively the maximum permitted discharging/charging powers of the chargers. %�!+ (discharge), %��� (charge) are the maximum allowable discharging/charging powers of the battery, depending on the battery status. in this study, it is assumed that the charging power of an e2w has a positive sign and has a highest value of 400w. discharging power is negative and the maximum value is -400w. in addition, the total charging and discharging power must not exceed the feeder capacity: �ℎ������: ���� ≤ /00102��� − ����� = ���� (7) ��'(ℎ������: ���� ≥ − /00102��� +����� = − ���� (8) where ���� is the maximum power that the grid can exchange with the ev loads, which is equivalent to the maximum gridmicrogrid exchange power ( /00102���) minus the net load. it is assumed that the non-ev load demand is uncontrolled. the charging station needs to control the total charging demand of the evs so as to do not violate the constrains (7) and (8). the constraint on energy requirement of e2ws is: 4� = ∑ 4567��58 ��5��9 :; �<� !"# = ∑ =!�>�'�?@�ab! −c���?@�ab!� !"# (9) =∑ de !��� fg fh i !"# = 1 − j where 4� is the total amount of the energy required by all the vehicles in the station, =! is �<� ’s battery capacity, >�'�?@�ab! is the soc of �<� at the end of the working day, c���?@�ab! is the initial soc of �<�, �k is the beginning time of the charging process, �� is the departure time, and !��� is the charging/discharging power of �<� at time t. if a working day from time �k to the �� is divided into l periods with duration � , the above constraint becomes: 4� = ∑ =!�>�'�?@�ab! − c���?@�ab!� !"# = ∑ m∑ !n.� on"# p !"# (10) where !n is the charging power of �<� at period (4). individually, each ev must satisfy the following constraints: the amount of required energy constraint: 4ab! = =!�>�'�?@�ab! −c���?@�ab!� = e !��� fg fh = ∑ !n.� on"# �11� the constraint on charging/discharging power: �ℎ������: !��� ≤ ���, ����, %���. = abqrrrrr ��'(ℎ������: !��� ≥ ��*, ��!+, %�!+. = ab! (13) in this study, it is assumed that a charging station is built on the campus of epu, servicing 160 electric bicycles/electric motorbikes during working hours from 7 am to 17 pm. the e2w’s battery has a capacity of 1200wh. maximum charging/discharging powers are 400/-400w, respectively. batteries are not allowed to discharge if the soc is less than 10%. at the end of the working day, the e2ws’ batteries are full. b. rooftop pv simulation we conduct this study using data from our previous work on the feasibility of pv-integrated charging station for e2ws [3]. accordingly, the rooftop pv system is designed and simulated as follows: • capacity: 150kwp. • location: electric power university (epu), 21°02'49", 105°47'07"; hoang quoc viet street, cau giay district, vietnam. • scale: most of electric bicycles / motorbikes currently adopt battery capacity of about 0.57-1.2kwh. the charging station is assumed to serve about 160 e2ws staying at the station from 7h00 am to 17h00 pm. • sunshine hours, solar irradiation, temperature at the site are shown in table i. engineering, technology & applied science research vol. 11, no. 6, 2021, 7814-7823 7817 www.etasr.com huu & ngoc: a two-level desired load profile tracking algorithm for electric two-wheeler … table i. solar irradiation parameters parameter daily average value yearly average value direct normal irradiation (dni) 1.688 kwh/m 2 /day 616 kwh/m 2 /year global horizontal irradiation (ghi) 3.584 kwh/m 2 /day 1308 kwh/m 2 /year diffuse horizontal irradiation (dif) 2.320 kwh/m 2 /day 847 kwh/m 2 /year global tilted irradiation at optimum angle 3.652 kwh/m 2 /day 1333 kwh/m 2 /year air temperature 24.1 o c terrain elevation 12 m after conducting the simulation, the power output of the pv system in a typical day of each month was obtained and is shown in table ii. c. non-ev load profile in order to meet the charging demands of e2ws, the charging station at the epu is interconnected with the grid and the rooftop pv system. it is also connected to building’s loads, forming a microgrid. the load profile of non-ev loads in a typical day is shown in figure 1. for the purpose of testing the algorithm effectiveness, we did not investigate non-ev load profiles in a typical working day/weekend and we did not account for load demand variation in different seasons. we assumed that the daily profile of non-ev loads is homogeneous. it is realized that a working day consists of two peaks: the first peak occurs at about 10 am and the second at around 14 pm. the difference between the highest and the lowest load demand is quite large with the highest load being more than 3.6 times higher than the lowest. when considering rooftop pv power, the net load profiles in january and july are shown in figures 2 and 3. the integration of the 150kwp rooftop pv system significantly reduces electricity consumption, but the unmatched figures of solar power profile and non-ev load profile result in more serious variations in the netload. off-peak periods of netload usually occur around 12 am due to high solar power and low non-ev load. in january, the netload reaches the peak of nearly 40kw at 8 am. this figure is 5.7 times greater than the lowest value of 7kw at 12 am. in july, the netload is even negative from 10:305 am to 14 pm, meaning that if there is no charging load participation, the rooftop pv power, after meeting load demand, can be injected into the grid. iii. the proposed algorithm to implement load leveling we propose a two-level desired load profile tracking algorithm. a. level 1: total charging pattern finding this level includes the following steps: • at the beginning of the process, collect the data of e2ws in the charging station. • collect the data of non-ev load and solar power output forecast. • calculate the total load demand and the total energy demand of e2ws. table ii. solar power output (w) jan feb mar apr may jun jul aug sep oct nov dec 0-5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 5-5.5 0.0 0.0 0.0 0.0 307.7 307.7 333.3 0.0 0.0 0.0 0.0 0.0 5.5-6 0.0 0.0 0.0 0.0 1692.3 1692.3 1666.7 0.0 0.0 0.0 0.0 0.0 6-6.5 0.0 0.0 285.7 3125.0 7407.4 7407.4 6352.9 5446.8 3600.0 2777.8 695.7 307.7 6.5-7 0.0 0.0 1714.3 6875.0 12592.6 12592.6 11647.1 10553.2 8400.0 7222.2 3304.3 1692.3 7-7.5 4235.3 5953.5 8800.0 14450.0 20756.8 20571.4 20756.8 19592.6 18438.1 17465.3 13927.7 7692.3 7.5-8 7764.7 10046.5 13200.0 19550.0 27243.2 27428.6 27243.2 26407.4 25561.9 24534.7 20072.3 12307.7 8-8.5 14222.2 16790.7 19555.6 26488.2 36000.0 36571.4 35788.2 35788.2 36000.0 34795.2 29257.1 19168.3 8.5-9 17777.8 21209.3 24444.4 31511.8 42000.0 43428.6 42211.8 42211.8 42000.0 41204.8 34742.9 24831.7 9-9.5 21942.9 26698.4 30461.5 37426.9 49614.7 52608.7 50841.6 50612.6 49843.3 49843.3 41634.4 32885.9 9.5-10 26057.1 31301.6 35538.5 42573.1 54385.3 57391.3 55158.4 55387.4 54156.7 54156.7 46365.6 37114.1 10-10.5 31565.2 37097.6 42316.9 49308.1 60298.0 63533.8 61015.9 62015.6 59775.1 60259.1 52778.3 42549.5 10.5-11 34434.8 40902.4 45683.1 52691.9 63702.0 66466.2 62984.1 63984.4 62224.9 61740.9 55221.7 45450.5 11-11.5 37788.8 45782.4 50260.9 57016.9 68258.1 70750.9 65503.8 67000.0 65750.9 63751.0 58504.2 49261.1 11.5-12 40211.2 48217.6 51739.1 58983.1 69741.9 71249.1 66496.2 67000.0 66249.1 64249.0 59495.8 50738.9 12-12.5 44251.4 52504.9 55018.9 63275.7 73014.1 73793.6 69014.9 68796.9 68534.4 67063.5 62276.2 54019.2 12.5-13 43748.6 51495.1 52981.1 60724.3 70985.9 70206.4 66985.1 65203.1 65465.6 62936.5 59723.8 51980.8 13-13.5 45097.6 52083.3 52356.0 59342.5 70595.4 67871.5 66601.6 62608.7 64155.2 60729.0 59450.2 51634.4 13.5-14 40902.4 47916.7 47644.0 54657.5 65404.6 62128.5 61398.4 57391.3 57844.8 53271.0 52549.8 46365.6 14-14.5 38281.3 45522.6 45127.5 52067.8 62296.3 57742.6 57742.6 53763.4 53355.6 47410.3 47716.1 43457.1 14.5-15 31718.8 38477.4 36872.5 43932.2 53703.7 50257.4 50257.4 46236.6 44644.4 38589.7 38283.9 34542.9 15-15.5 26784.8 33306.9 29714.3 37551.7 47040.0 44444.4 44137.9 39876.9 37551.7 32044.0 31441.9 27842.1 15.5-16 19215.2 24693.1 22285.7 28448.3 36960.0 35555.6 35862.1 32123.1 28448.3 21956.0 20558.1 18157.9 16-16.5 12903.2 17818.2 16095.2 21018.2 28800.0 28444.4 29411.8 26520.5 21407.4 12945.0 10364.4 9074.1 16.5-17 7096.8 10181.8 9904.8 12981.8 19200.0 19555.6 20588.2 17479.5 12592.6 7055.0 5635.6 4925.9 17-17.5 1333.3 2666.7 4000.0 5333.3 10666.7 11571.4 12903.2 9333.3 4000.0 1200.0 933.3 800.0 17.5-18 666.7 1333.3 2000.0 2666.7 5333.3 6428.6 7096.8 4666.7 2000.0 600.0 466.7 400.0 18-18.5 0.0 0.0 0.0 0.0 0.0 2000.0 2000.0 0.0 0.0 0.0 0.0 0.0 18.5-24 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 engineering, technology & applied science research vol. 11, no. 6, 2021, 7814-7823 7818 www.etasr.com huu & ngoc: a two-level desired load profile tracking algorithm for electric two-wheeler … fig. 1. non-ev load profile. fig. 2. netload in january. fig. 3. netload in june. • define the desired total load profile (including charging load and netload) which satisfies the total load demand as well as the charging energy requirement. • at each period, preliminary total charging power can be obtained by subtracting the netload from the desired total load. • browse all periods, implement correction if at a certain period the total charging power of e2ws violates the constraints. reallocate the power at the unsatisfactory period for the remaining periods in order to ensure that at the end of the working day, the total amount of energy supplied to the e2ws meets the requirements. at the end of this step, we obtain an improved total charging power profile. • calculate the battery capacity of the representative. browse all periods, check the depth of discharge (dod) and the maximum battery capacity constraints. reallocate charging power at the unsatisfactory period for the remaining time steps. at the end of this reallocation, we find the final total charging pattern. b. level 2 based on the total charging pattern obtained at level 1, allocating the total charging power for each ev or groups of similar parameter evs is conducted. level 2 includes the following steps: • browse the ev groups. • repeat the steps of level 1 in order to identify the preliminary charging power pattern for the considered group. • check the charging/discharging power constraints at each period. • browse all periods, conduct corrections and reallocate if there is any charging/discharging power constraint violation. • calculate battery capacity. check whether there is any dod or maximum battery capacity violation. if the constraints are violated, reallocate the charging/discharging power of the unsatisfactory period for the remaining periods. • after the two corrections above, conduct the third reallocation, so as to the sum of ev groups’ charging power at each period reaches the total charging demand (after level 1) with predefined error. the pseudocode of the proposed algorithm is shown below. c. algorithm: desired totallload profile tracking – load leveling 1: input: at the beginning, the controller acquires data of e2ws in the charging station. the data includes: • the battery capacity of evi: =! • the initial soc and the required soc at the departure time of the evi: c���?@�ab!; >�'�?@�ab! • the maximum charging and discharging power of evi: abqrrrrr (charging); ab! (discharging) • the permitted depth of discharge of evi: �@�ab! • besides, non-ev load forecast and pv power output forecast are also collected. 2: output: at each time step t = 1, 2, 3, …, m, output the total desired charging power. 3: procedure: engineering, technology & applied science research vol. 11, no. 6, 2021, 7814-7823 7819 www.etasr.com huu & ngoc: a two-level desired load profile tracking algorithm for electric two-wheeler … 4: total required energy assignment: 4� ← 0 5: for � = 1 to do 6: calculate the required energy of evi: 4ab! ← =!�>�'�?@�ab! −c���?@�ab!� 7: 4� ∶=4� +4ab! 8: end for 9: calculate the initial soc of an ev which can be a representative of e2ws in the station. 10: preliminary allocation of 4� for m periods. calculate the preliminary total charging power at each time step: v20_� ← 4� l.� 11: for � = 1 to l do 12:calculate netload at each time step: �! = +x+yab_! − zx[�2_! 13: calculate the total load: ��_! = ��_! + v20_� 14: end for 15: average ��_! in m time periods. from the desired load profile, get the total load demand at each time step ��\_! 16: for � = 1 to l do 17: calculate the preliminary total charging power at each time step: �! = ��\_! −�! 18: check charging/discharging power constrains at period i � �!� 19: if �! violates power constraints 20: reallocate �! for the remaining periods in order to ensure that at the end of the working day, the total amount of the energy supplied to the e2ws meets the requirements and the allocation does not make charging powers at the remaining periods violate the power constraints. 21:end if 22: end for 23: for � = 1 to l do 24: calculate battery capacity of the representative at period i. 25: if the battery capacity at period i violates dod or maximum battery capacity constraints 26: reallocate the charging power at the period (which violates the constraints) for the remaining periods. the allocation does not make charging powers at the remaining periods violate the power constraints. 27: end if 28: end for iv. simulation and analysis the current study assumes that the accurate day-ahead forecast of non-ev load and generation capacity forecast of the solar power system are available. for the purpose of verifying the effectiveness of the proposed algorithm, we did not consider the variations in the accuracy of the forecasts. with 160 e2ws in the charging station, we relied on the research data of [21] about the charging behavior. accordingly, the initial soc distribution is shown in table iii. table iii. initial soc distribution percentage initial soc group 11.6 % 90 – 100% soc g1 14.8 % 80 – 90% soc g2 14.9 % 70 – 80% soc g3 14.9 % 60 – 70% soc g4 13.7 % 50 – 60% soc g5 10.8 % 40 – 50% soc g6 8.4 % 30 – 40% soc g7 6.1 % 20 – 30% soc g8 3.5 % 10 – 20% soc g9 1.3 % 0 – 10% soc g10 the average initial state of charge of the evs is 62%. in more than two thirds of all charges, the initial state of charge was above 50% soc and 11.6% of all charges were even initiated with a nearly full battery with more than 90% soc. the required amount of energy �4�� of the 160 e2ws is determined by (9). the battery capacity of an e2w is 1200w and the maximum allowable charging/discharging power is 400/-400w respectively. in this study, we divided the 160 evs into 10 groups as shown in table iii. in order to investigate the efficiency of the algorithm, simulations were conducted considering three cases: • case 1: max speed charging: e2ws are charged at maximum charging rate from 7 am until reaching the required amount of energy. • case 2: constant charging power: e2ws are charged at a constant rate during working time so that the required amount of energy is attainable at 17 pm. • case 3: smart charging: e2ws follow the proposed algorithm. the simulation results of the three cases during january, which is the month having the lowest solar power generation, are shown in figure 4. it was found that, in case 1, when the e2ws are charged at the maximum rate, the peak load occurred at 7:30 am. this is 14.7 times higher than lowest load at 12 am and 2.5 times higher than the netload peak value. when the vehicles are charged at constant power, the difference between peak and base load does not improve compared to the netload profile. the peak load, which occurs at 8 am, is 46.25kw and the base load is 14kw at 12 am. with the proposed algorithm, the charging and discharging powers of the vehicles are controlled to reduce peak load and perform valley filling and load leveling. the load power from 7 am to 17 pm ranges from 32.27kw to 33.53kw. at the last time steps, although the netload is higher than the average load, the e2ws’ battery does not discharge to ensure that it is full at the engineering, technology & applied science research vol. 11, no. 6, 2021, 7814-7823 7820 www.etasr.com huu & ngoc: a two-level desired load profile tracking algorithm for electric two-wheeler … departure time. in case 3, the profile of total charging load and charging profiles of typical e2ws in 10 groups are shown in figures 5 and 6. fig. 4. load profile in january. fig. 5. total charging load profile in case 3. fig. 6. charging profiles of the 10 e2w groups in case 3. generally, it is found that, from 7:30 am to 10 am, the total charging power of e2ws in the station is negative, meaning that the batteries discharge energy, partly powering non-ev loads so as to reduce the peak load. at the hours of large solar power and low netload, the total charging power increases in order to absorb electricity from the solar panels and perform valley filling. considering the typical charging patterns of the 10 e2w groups, group 1 which has the biggest initial soc, performs energy discharge during the first hours, whereas group 10 has the lowest initial soc. so, in general, this group is mainly charged from 7 am to 17 pm. the change in the battery capacity representing the 160 e2ws in the station is shown in figure 7. the battery capacity increases rapidly from 10:30 am and 15 pm, corresponding to the periods of highest solar power and charging rate. figure 8 illustrates the typical battery capacity variation of the 10 e2w groups. fig. 7. battery capacity profile of the representative in january. fig. 8. typical battery capacity variation of 10 e2w groups in january. fig. 9. load profile in june. engineering, technology & applied science research vol. 11, no. 6, 2021, 7814-7823 7821 www.etasr.com huu & ngoc: a two-level desired load profile tracking algorithm for electric two-wheeler … the load profile for the three different charging schemes during june (the month with the largest solar power generation) is shown in figure 9. compared to january, the netload in june is much lower because this is the month with the largest solar power output. if there is no charging load or even there is a charging load following scheme 1 or 2, at high solar power output duration, pv generation does not only meet the load demand but also it can inject the surplus power into the grid. however, in case 1, the simultaneous charging of e2ws as soon as they are connected to the chargers makes the total load reach a very high peak, up to 78.67kw at 7:30 am. in case 2, the peak load reaches 26.9kw at 16:30 pm, which is significantly lower than the peak load in case 1. in the case of charging following the proposed algorithm, the peak load decrease does not improve compared to case 2, but the load fluctuation is significantly reduced. the valley filling effect is clearly observable from 10:30 am to 13:30 pm and peak shaving occurs from 7 am to 9:30 am. the total charging power profile during june and the charging profiles of the 10 e2w groups are shown in figures 10 and 11. generally, with the high solar power in june, e2ws’ batteries only discharge energy to reduce peak load in the early morning. from 9 am onwards, when the solar power output is high, the battery will be in the charging process. in comparison to january, the charging ends earlier as the excess solar power allows the vehicles to be charged at a higher power. fig. 10. total charging power in june. fig. 11. charging patterns of the 10 e2w groups. fig. 12. battery capacity profile of the representative during june. fig. 13. typical battery capacity variation of the 10 e2w groups during june. the battery capacity change of the representative is shown in figure 12. figure 13 shows the battery capacity variation of the 10 e2w groups. by about 14 pm, most e2ws were fully charged. at the end of the working day, the batteries were not discharged to ensure that the vehicles are fully charged at 17 pm. v. conclusions in case of a given electricity tariff, optimizing ev charging cost may result in a large number of vehicles charging simultaneously during low-cost price periods. this can lead to unwanted peak load and an adversely impact on the grid stability and power quality. if the utilities adjust electricity tariff according to real-time load demand variations (indirectly adjusting to the charging behavior of ev owners), the algorithm that identifies real-time tariff may not converge. unlike the case of electric cars, the decentralized approaches through adjusting the electricity tariff do not make much sense in changing the behavior of individual e2w owner because the charging power and battery capacity of e2ws are much lower. however, when a large number of electric bicycles and electric scooters are present in buildings, offices, campuses, public parking, etc., the uncontrolled charging of that large number of e2ws at the same time might trigger many unwanted technical problems. engineering, technology & applied science research vol. 11, no. 6, 2021, 7814-7823 7822 www.etasr.com huu & ngoc: a two-level desired load profile tracking algorithm for electric two-wheeler … compared to other studies on load leveling using centralized approach, the proposed algorithm does not focus on forming and solving optimal objective functions. instead, we derive from the estimated total amount of energy required by evs and non-ev loads to establish the desired total load profile. charging power is then allocated to the e2ws on the basis of that desired profile and relevant constraints. therefore, when compared to prior studies [15, 16, 22-24] our algorithm does not require high computational capability or computational time of the controller for solving optimization problems. it also ensures the finding each e2w's or group of e2ws’ charging schedule. this is especially meaningful because the number of e2ws in the charging station can be very higher than the number of electric cars, leading to a higher number of variables in the optimization problems. in this study, we propose a power distribution algorithm for e2ws in an integrated pv charging station. the controller implements a two-level algorithm tracking the desired load profile in order to perform load leveling, valley filling, and peak clipping. the study offers a novel approach to control 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[28] k. strunz, e. abbasi, and d. n. huu, "dc microgrid for wind and solar power integration," ieee journal of emerging and selected topics in power electronics, vol. 2, no. 1, pp. 115–126, mar. 2014, https://doi.org/ 10.1109/jestpe.2013.2294738. microsoft word etasr_v12_n2_pp8253-8258 engineering, technology & applied science research vol. 12, no. 2, 2022, 8253-8258 8253 www.etasr.com boukhalfa et al.: performance enhancement of the dpc control based on a vgpi controller applied … performance enhancement of the dpc control based on a vgpi controller applied to a grid connected pv system mohamed boukhalfa laadi laboratory faculty of science and technology university of djelfa djelfa, algeria med.boukhalfa18@gmail.com amar benaissa laadi laboratory faculty of science and technology university of djelfa djelfa, algeria benaissa_am@yahoo.fr mohamed r. bengourina centre de développement des energies renouvelables algiers, algeria bengourina.rida@yahoo.fr a. khoudiri laadi laboratory faculty of science and technology university of djelfa djelfa, algeria a.khoudiri@yahoo.fr mohamed boudiaf laadi laboratory faculty of science and technology university of djelfa djelfa, algeria m.boudiaf@univ-djelfa.dz received: 17 december 2021 | revised: 16 january 2022 | accepted: 21 january 2022 abstract-even though the pi controller is among the most widespread controllers in photovoltaic (pv) systems, it presents overshoots and undershoots in the tracking trajectory mode. this major disadvantage remains an open problem. in the current paper, a direct power control (dpc) of a three-phase gridconnected pv system based on a variable gain pi (vgpi) controller is developed to remove the overshoots and undershoots in the classical pi controller. the proposed control system has been tested in the matlab/simulink environment. the simulation results demonstrate the feasibility and robustness of the proposed method in terms of overshoots, undershoots, and current quality. keywords-photovolatic system; direct power control; vgpi controller; overshoots; undershoots i. introduction the high growth rate of photovoltaic (pv) systems over the last several years allows them to play a more important role in the future mixed power grid [1]. however, the cost of pv systems must be reduced further in order to increase the level of their penetration and to make the pv power plant eligible as compared to conventional energy [2]. most pv systems are connected to the distribution grid, where the inverter is receiving increased interest in order to generate power [3]. many control structures for grid associated pv systems have been developed thanks to the advanced development of power electronics technology and the digitization of pv systems. these control structures have the same goals, but with different principles of operation. they can generally be divided into two categories, the control loops of powers and currents. direct power control (dpc) is a kind of high-performance control structure for grid connected pv systems based on active and reactive power similar to the conventional direct torque control (dtc) strategy for electrical machines [4]. in the classical structure of dpc, a pi controller is used for controlling the dc bus voltage. these organs are of general use in many applications because they have simple design and easy tuning parameters [5]. however, the pi controllers have problems in removing the overshoots and undershoot in the tracking trajectory of continuous power as it is affected by solar radiation. this problem is due to the controller parameters which are constant. this is why the idea of designing a variable gain regulator has been proposed to overcome this trade off. a vgpi controller can be seen as a generalization of a classical pi controller with the proportional and integrator gains varying corresponding author: boukhalfa mohamed engineering, technology & applied science research vol. 12, no. 2, 2022, 8253-8258 8254 www.etasr.com boukhalfa et al.: performance enhancement of the dpc control based on a vgpi controller applied … along a tuning curve [6]. several authors have chosen to solve the problem with other methods such as: non-linear approaches [7, 8], fuzzy logic controllers [9, 10], artificial neural networks (anns) [11], and metaheuristic optimization [12, 13]. however, these solutions are complex and not appreciated by the industry. in this paper, a vgpi regulator is proposed to replace the pi regulator to control the dc bus voltage of the grid connected pv inverter. a detailed study of the coordinated control between the dpc control and the vgpi controller is given. simulations on a 3.7kw two-stage pv system are performed in order to check the effectiveness of the dpc based on the proposed topology under several test conditions. ii. control structure of two-stage three-phase grid-connected pv systems a. system overview the proposed conversion system is shown in figure 1. it consists of two stage grid associated pv systems. two main tasks should be achieved by the grid associated pv inverters: (1) maximum power point tracking (mppt) control to extract the maximum power provided by the pv panels and (2) the injection of grid current with high power quality. fig. 1. three-phase grid associated pv system with p&o mppt and dpc control based on a vgpi controller. fig. 2. flowchart of the p&o mppt algorithm. b. boost converter controller the boost converter controls the maximum power output using mppt control. the mppt algorithm is implemented in the boost converter. hill-climbing and fractional methods are widely adopted in pv systems. perturb and observe (p&o) is a type of hill-climbing method consisting of a continuous reference voltage search process to reach the maximum power point (mpp) [14]. the principle of p&o is depicted in the flowchart in figure 2. c. lookup table based direct power control dpc for grid associated inverters was developed to have control on the instantaneous active and reactive power directly by selecting the optimum switching state of the converter, which was first proposed in [15] and more clearly presented in [16]. the main principle of dpc is similar to dtc in motor drives [17]. it directly selects the desired voltage vector from a predefined switching table, according to the grid voltage position (or virtual flux position) and the errors between the reference active/reactive power and feedback value. the control structure of a typical dpc is represented in figure 1. the switch table is shown in table i. the power calculation block reads as: s s s s p jq= + (1) 3 3 ( . ) ( . . ) 2 2 s s s s s s s v ip v i v iαβ αβ α α β β= = + (2) 3 3 ( ) ( . . ) 2 2 ss s s s s s q v i v i v iαβ αβ β α α β= × = − (3) where: s s s v v jvαβ α β= + and s s si i jiαβ α β= + . in order to obtain the position of grid voltage vector, the angle of grid voltage can be calculated based on vsα and vsβ as: � � ������ �� � � (4) the switch table is based on the position of the grid voltage vector. in order to optimize the performance of the converter, the grid voltage can be divided into 12 sectors. the angle of the 12 sectors can be obtained as: ( ) ( )2 1 , 1,2,....,12. 6 6 n n n n π π θ− ≤ =≤ − (5) fig. 3. plant (α, β) divided in 12 sectors. yes yes no yes no no yes start measure vpv(k), ipv(k) ppv(k)= vpv(k). ipv(k) ppv (k)ppv (k-1)=0 ppv (k) ppv (k-1)>0 decrease vref vref= vref-∆d vpv (k) vpv (k-1)>0 vpv (k) vpv (k-1)>0 increase vref vref= vref+∆d decrease vref vref= vref-∆d increase vref vref= vref+∆d engineering, technology & applied science research vol. 12, no. 2, 2022, 8253-8258 8255 www.etasr.com boukhalfa et al.: performance enhancement of the dpc control based on a vgpi controller applied … the power hysteresis controller consists of active power and reactive power hysteresis controllers. the input is the error between the reference and the real power. the output reflects the status of power deviation, which can be expressed as sp and sq. sp and sq only have two statuses, which can be expressed as: �� � � 0 � ����� ���1 � ����� ��� (6) �� � �0 � ����� ���1 � ����� ��� (7) where hp and hq are the hysteresis bands. dpc has been known as a powerful and robust control scheme for grid connected inverters, but high-power ripples and variable switching frequency are two of the most notable drawbacks of the conventional dpc. furthermore, the required sampling frequency is usually very high in order to achieve relative satisfactory performance which increases the hardware burden and might limit the application of this method. the proposed switching table for all sectors is represented in the table i. table i. sector switching table sp sq θ1 θ2 θ3 θ4 θ5 θ6 θ7 θ8 θ9 θ10 θ11 θ12 1 1 v6 v7 v1 v0 v2 v7 v3 v0 v4 v7 v5 v0 1 0 v7 v7 v0 v0 v7 v7 v6 v0 v5 v7 v0 v0 0 1 v6 v1 v1 v2 v2 v3 v3 v4 v4 v5 v5 v6 0 0 v1 v2 v2 v3 v3 v4 v4 v3 v3 v6 v6 v1 iii. vgpi controller to reduce variations and instability in the dc link voltage a vgpi controller is proposed for the dc link voltage regulation. the error between the voltage of the capacitor vdc and the reference voltage vdcref are used as an input to the vgpi controller and the output is the reference active power pref. a vgpi controller is a most generalized classical pi controller [18] with varying gain in time along a polynomial curve. this gain attains its final value as the steady state is reached [6]. this controller with continually adapted parameters can limit overshoot during startups with a rapid load disturbance rejection. figure 4 shows the block diagram of the vg-pi controller. fig. 4. block diagram of the vgpi controller. the speed vgpi controller delivers at its output the inverter current: .( ) . ( ). sm p dcref dc i dcref dc i k v v k v v dtω ω= − + −∫ (8) kpω, kiω are given by: �� � !"��� ���#$ % &�� ' ���# () � � *+ ��� () � , *+ (9) �# � !�#� % &�� ' () � � *+ �#� () � , *+ (10) where kpi and kpf are the initial and final values of the proportional gain, and kif is the integrator gain final value. *+ and n are the saturation time and the polynomial degree. consequently, the reference power quantity is deduced as: ���� � -+./01 (11) a. vgpi controller parameter setting the parameters are obtained by the test-error method as follows [6,18]: • choose a value �#� to obtain a rapid load disturbance rejection. • set the degree n and the saturation time *+. • derive the values ��# and ��� so as the smallest overshoot and undershoot are obtained. • to eliminate completely the overshoot and undershoot, increase*+. if the excess is not eliminated, increase n. b. performance verification of the vg-pi control the effectiveness of the proposed control has been verified on matlab/simulink. the system configuration is shown in figure 1 and the system parameters are given in table ii. table ii. parameters of the two-stage three-phase gridconnected pv pv rated power 3 kw boost converter inductor l = 6 mh pv-side capacitor cpv = 200 µf l-filter lf = 2.5 mh switching frequency boost converter: fb = 16 khz, dc-link voltage vdc = 450 v grid nominal voltage (rms) vg = 230 v grid nominal frequency ω = 2π×50 rad/s first, a variable solar irradiance profile as plotted in figure 5 has been utilized in the simulation. the solar irradiance level starts from 1000w/m 2 , then it decreases to 400w/m 2 and after that it increases to 800w/m 2 , and finally decreases to 200w/m 2 . the pv power amounts attain their optimum theoretical values, which are respectively 3.6kw, 1.39kw, and 0.67kw, within milliseconds despite solar irradiance variations. the temperature is kept constant all time and equal to 25°c. engineering, technology & applied science research vol. 12, no. 2, 2022, 8253-8258 8256 www.etasr.com boukhalfa et al.: performance enhancement of the dpc control based on a vgpi controller applied … (a) (b) (c) fig. 5. (a) solar radiation, (b) current of the pv array, and (c) pv power. (a) (b) (c) fig. 6. simulation results of the proposed dpc with pi controller. (a) grid current and voltage, (b) active power reference and response, (c) reactive power reference and response. figures 6 and 7 show the simulation results for systems with pi and vgpi controllers. grid current (is), grid voltage (vs), reactive power (qs), and active power (ps) are depicted. the results show that the current is sinusoidal after the control application but with opposition in phase with the corresponding voltages. the negative sign of the utility active power (ps) means current injection to the grid or load. the reactive power is always zero. note that the wave chatring of active and reactive power is generally acceptable for both regulation approaches. furthermore, a perfect decoupling is observed between active and reactive powers. by inspecting figure 8, one can clearly see that the dc voltage perturbations at the instants of the power variation are very weak as compared to those of the pi regulator. this indicates the robustness of the vgpi approach. (a) (b) (c) fig. 7. simulation results of the proposed dpc with vgpi controller. (a) grid current and voltage, (b) active power reference and response, (c) reactive power reference and response. figure 9 shows the behavior of an ac current phase as a function of the solar irradiance (1000, 400, 800, 200w/m 2 ). it is worth noting that the dc-bus voltage and the instantaneous powers present good tracking to their reference values with low overshoot, undershoot and total harmonic distortion (thd). this is consistent with the information reported in [19-21]. table iii summarizes the obtained values of the overshoot and undershoot stabilization time along with the thd. from this table, one can see that for each considered irradiation, the overshoot and undershoot recorded with the use of the vgpi regulator are superior than their counterparts if the pi regulator is used. besides, the thd is less than 5% for all irradiation values being considered here. hence, our derived thd is in accordance with the iec 61727 and ieee 1547 recommendations respectively. 0 0.2 0.4 0.6 0.8 1 time (s) 0 10 20 ipv (a) engineering, technology & applied science research vol. 12, no. 2, 2022, 8253-8258 8257 www.etasr.com boukhalfa et al.: performance enhancement of the dpc control based on a vgpi controller applied … fig. 8. dc converter voltage. fig. 9. grid current and harmonic spectrum with pi and vgpi controllers. table iii. comparative study irradiation parameters dpc-pi dpc-vgpi 1000 w/m 2 overshoot % 4.22 3.4 undershoot % 0.82 0.155 ts (s) 0.172 0.087 thd % 1.23 0.84 400 w/m 2 overshoot % 0.71 0.06 undershoot % 2.866 1.142 ts (s) 0.138 0.044 thd % 2.29 2.07 800 w/m 2 overshoot % 0.8 0.066 undershoot % 0.2 0 ts (s) 0.146 0.07 thd % 1.34 1.09 200 w/m 2 overshoot % 0.55 0 undershoot % 2.577 0.9 ts (s) 0.136 0.059 thd % 4.45 4.28 iv. conclusion dpc control based on vgpi controller applied to a grid connected pv system has been proposed and discussed in this paper. the analysis of the obtained results shows the robustness, the effectiveness, and the good performance of the proposed vgpi controller based on the dpc strategy. this regulator outperforms the pi controller, from the point of view of the response time and follow-up of the reference values. finally, as perspectives of this study, further efforts are to be carried out to optimize the control system with consideration of the shading effect and deep voltages grids. references [1] a. sangwongwanich, y. yang, f. blaabjerg, and h. wang, "benchmarking of constant power generation strategies for singlephase grid-connected photovoltaic systems," ieee transactions on industry applications, vol. 54, no. 1, pp. 447–457, jan. 2018, https://doi.org/10.1109/tia.2017.2740380. 0.2 0.205 0.21 0.215 0.22 time (s) -10 0 10 (a) 0.4 0.405 0.41 0.415 0.42 time (s) -5 0 5 (b) 0.7 0.705 0.71 0.715 0.72 time (s) -10 0 10 (c) 0.9 0.905 0.91 0.915 0.92 time (s) -2 0 2 (d) 0 10 20 30 40 harmonic order 0 0.5 1 1.5 2 fundamental (50hz) = 1.923 , thd= 4.45%, pi 0 10 20 30 40 harmonic order 0 5 10 fundamental (50hz) = 8.303 , thd= 1.34%, pi 0 10 20 30 40 harmonic order 0 1 2 3 4 5 fundamental (50hz) = 4.008 , thd= 2.29%, pi 0 10 20 30 40 harmonic order 0 5 10 15 fundamental (50hz) = 10.42 , thd= 1.23%, pi 0 10 20 30 40 harmonic order 0 5 10 15 fundamental (50hz) = 10.42 , thd= 0.84%, vgpi 0 10 20 30 40 harmonic order 0 1 2 3 4 5 fundamental (50hz) = 4.003 , thd= 2.07%, vgpi 0 10 20 30 40 harmonic order 0 5 10 fundamental (50hz) = 8.282 , thd= 1.09%, vgpi 0 10 20 30 40 harmonic order 0 0.5 1 1.5 2 fundamental (50hz) = 1.92 , thd= 4.28%, vgpi engineering, technology & applied science research vol. 12, no. 2, 2022, 8253-8258 8258 www.etasr.com boukhalfa et al.: performance enhancement of the dpc control based on a vgpi controller applied … [2] a. sangwongwanich, y. yang, f. blaabjerg, and d. sera, "delta power control strategy for multistring grid-connected pv inverters," ieee transactions on industry applications, vol. 53, no. 4, pp. 3862–3870, jul. 2017, https://doi.org/10.1109/tia.2017.2681044. 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[21] b. korich, a. benaissa, b. rabhi, and d. bakria, "a novel mppt design for a partially shaded pv system using spotted hyena optimization algorithm," engineering, technology & applied science research, vol. 11, no. 6, pp. 7776–7781, dec. 2021, https://doi.org/ 10.48084/etasr.4490. microsoft word etasr_v12_n1_pp8007-8012 engineering, technology & applied science research vol. 12, no. 1, 2022, 8007-8012 8007 www.etasr.com saidani & ghodhbani: hardware acceleration of video edge detection with hight level synthesis on … hardware acceleration of video edge detection with hight level synthesis on the xilinx zynq platform taoufik saidani department of computer science faculty of computing and information technology northern border university rafha, saudi arabia and laboratory of electronics and microelectronics faculty of sciences of monastir university of monastir monastir, tunisia taoufik.saidan@nbu.edu.sa refka ghodhbani department of computer science faculty of computing and information technology northern border university rafha, saudi arabia and laboratory of electronics and microelectronics faculty of sciences of monastir university of monastir monastir, tunisia refka.ghodhbani@nbu.edu.sa abstract-the study conducted in the current paper consists of validating an original design flow for the rapid prototyping of real-time image and video processing applications on fpgas. a video application for edge detection with simulink hdl coder and vivado high-level synthesis (hls) has been designed as if the code was going to be executed on a conventional processor. the developed tools will automatically translate the code into vhdl hardware language using an advanced compilation technique. this amounts to embedding processors on xilinx zynq-7000 system on-chip (soc) device in an optimal manner. this automated hardware design flow reduces the time to create a prototype since only the high-level description is required. the design of the video edge detection system is implemented on xilinx zynq-7000 platform. the result of the implementation gave effective resource utilization and a good frame rate (95 fps) under 170mhz frequency. keywords-high-level synthesis; automated hardware design; codesign; xilinx zynq-7000 i. introduction over the past ten years, several architectures combining reconfigurable processors and/or circuits (field programmable gate arrays-fpgas) have been proposed for the acceleration of the execution of increasingly complex applications [1]. dedicated signal and image processing systems currently use either processors with general or dedicated use, wired solutions configured for specific circuits of the asic type, or a combination of these two. however, the conjugation of the increasing algorithm complexity and the large volume of data to process, usually with strong real-time constraints, requires performance that processors cannot provide [2]. parallel processing can provide speed and programming flexibility, but at the expense of cost and complexity of implementation. in addition, the use of asics which offer more processing speed suffers from rigidity and expensive development. indeed, adding a new functionality to a wired system will surely require a redesign of one or more asics and will increase cost [3]. the reconfigurable architectures represent an appropriate response, they offer better performance than programmable architectures and more flexibility than wired solutions. they use reconfigurable logic components that allow the user to modify the architecture after manufacturing it in a software way, unlike the asic whose algorithms are wired in silicon [2, 3]. video and image processing are now booming and playing an increasingly important role in our everyday life [4, 6]. the integration of embedded systems in the field of modern wireless communications allows us to respond quickly to its ever-increasing demands. the invention of the fpga made possible the concept of reconfigurable material hardware for video and image processing systems. the traditional design of video and image system architecture around the fpga does not allow high productivity [3, 4]. the latter can be improved by using a new design technique based on the model based design (mbd) model [5]. tools based on this technique are intended for embedded systems, the development of signal processing algorithms, the rapid integration of systems, and the analysis of the behavior of complex digital systems for a wide variety of cases. to resolve this constraint, many high level synthesis tools have been developed to take advantage of this technique to achieve fpga rapid prototyping [3]. the fpga with its great integration capabilities and reconfiguration is a key component in rapidly developing prototypes. in the objective of encouraging the wide distribution of this type of circuits, it is necessary to improve the development environments to make them more accessible to non-electronics experts[8, 9]. the current study consists in proposing and validating a design flow for the rapid prototyping of real-time image processing applications on fpgas. it programs a model with hdl coder library as if the code was going to be executed on a zynq 7000 [8, 14]. the developed tools will automatically generate the code into hardware language (vhdl) using an advanced compilation technique. this amounts to embedding processors in the fpga in an optimal way. corresponding author: taoufik saidani engineering, technology & applied science research vol. 12, no. 1, 2022, 8007-8012 8008 www.etasr.com saidani & ghodhbani: hardware acceleration of video edge detection with hight level synthesis on … ii. acceleration of the proposed architecture figure 1 shows the functional diagram of the proposed system architecture. the design is applicable to both video and image processing since the input pixels are processed successively. for embedded video processing, the process requires mega pixels. it is built by a video block that can be programmed by adapted algorithms and thus accelerate complex and heavy (in terms of resources and execution time) algorithms on the integrated blocks of the xilinx soc platform. the output of the video and image systems is passed directly to a video processing block and a display component [10]. the various video and image processing accelerators in fpga are implemented in platform systems of the xilinx zynq 7000 [5, 8]. fig. 1. the proposed global diagram for video and image system architecture. in the architecture shown in figure 1, the advanced extensible interface (axi) interconnects the processor that transmits the input video to the video processing pipeline system. the usb camera shares the interfaces and communicates with the arm processor. the frame data are stored in the memory controller. once the video ip core finalizes the process on the frame, it is displayed via the hdmi display. the pipeline is continued for the next iterations [14]. iii. mbd model based design for video and image processing the mbd technique for fpgas results from the need to design complex dsp systems which require specific arithmetic units such as the addition-compare-select unit for the viterbi decoder. these specific computing units require a finer level of fpga-based circuit optimization [11]. this level of optimization is generally associated with traditional digital design video and image processing system. model-based design is essentially a way of describing how a system will interact with the analog world in real time. this fpga prototyping technique consists of converting the model of the system in question from its mathematical formulation to an executable specification [12]. the mbd technique provides a common framework that involves different phases of the development process. this reduces the time to market needed to create a complete model. the associated design phases to this technique allow the designer to locate and correct errors before prototyping the system [13]. there are many tools available for designing fpga systems using the mbd technique. most of these tools take advantage of the standardized unified modeling language (uml). these tools differ in the way they describe a system and define its characteristics. some implementation techniques used by these tools may be less effective than others. however, they guarantee rapid prototyping of the system ensuring time efficiency. the choice of a tool depends on many factors such as the level of flexibility, the availability of pre-built libraries/blocks, and the overall understanding of these blocks. some uml-based tools are the arti-real time studio, the ilogix's rhapsody, matlab and simulink realtime workshop [9]. these tools are used for the design of an embedded multiprocessor environment. the tools that allow the generation of hdl code for the fpga can be classified into two categories, the block-based tools and those based on the c language of blocks that generate hdl code from the block diagram, which is then used by the synthesis tool hardware to implement the system design on fpga. most of these tools, such as synplify dsp, xilinx system generator, dsp builder altera , and simulink hdl coder [5], are based on simulink and matlab environment. these tools guarantee a high level modeling environment of signal processing algorithms. blocks from the simulink library are used with ip cores from fpga suppliers to create hdl code specific to the platform in question. tools such as the simulink hdl coder allow more flexibility to the designer, as they integrate matlab functions and m-block files. with these tools, the designer develops a simulink model, then translates it to the fpga environment. the second category of mbd tools uses c programming language to create an abstraction for the design of systems. among these tools are the mentor graphics catapult c and the celoxica’s handelc. the main motivation behind these tools is the simulink hdl coder, which is commonly used for the implementation of embedded systems on fpga [13]. fig. 2. a complete solution for embedded vision. simulink hdl coder is an mbd tool that enables modeling, analysis, and simulation of systems. it gives a wellstructured graphical environment for the designer that allows him/her to create system designs of a high level of complexity. in addition, this tool allows the user to create flexible custom blocks from matlab functions. the simulink hdl coder allows the designer to create hdl code bit-precise and synthesizable from the model developed using simulink blocks. the obtained hdl code can be synthesized and mapped to the target fpga board using tools such as altera quartus ii, synplify, and xilinx vivado. the simulink hdl coder has many built libraries [15]. some of these predefined libraries include adders, multipliers, accumulators, integrators, multi-port switches, lookup tables, etc. engineering, technology & applied science research vol. 12, no. 1, 2022, 8007-8012 8009 www.etasr.com saidani & ghodhbani: hardware acceleration of video edge detection with hight level synthesis on … iv. model based mdb design for fpga prototyping a typical mbd design flow for implementing fpga-based video and image processing system is shown in figure 3. a. system specifications the design of any dsp block always begins with defining the design specifications. this definition represents an abstract way to describe the main function of the block. at the end of this step, different parameters are obtained, such as the type of input/output and the basic mathematical function of the block. we can always determine whether the design of the block can be reused or not [12]. b. analysis of design needs as mentioned above, the basic mathematical function of the block is determined in the specification phase. the next step in the design process is to identify the algorithm required for the implementation practice. this algorithm is chosen based on many factors such as complexity, duration of the calculation, and the resources used. the algorithm is then subdivided into functions [12]. fig. 3. model-based design for embedded vision. c. simulation and modeling in this step we convert the design specifications into a highlevel model using mbd tools such as the simulink hdl coder and xsg. this step consists in representing the mathematic equations in the form of models. libraries and blocks provided by the tool facilitate this representation. the resulting model is then tested by observing the output for the various test input signals. despite the wide variety of features and blocks provided by simulink, only certain blocks can be converted using its hdl conversion environment which means that the other blocks must be replaced or built using the primitive libraries of the hdl converter tools such as vhdl [12]. d. system implementation this is the most important step. it consists of an automatic generation mechanism which is provided by the mbd tools. the flow advisor tool provided by simulink hdl coder, helps checking the model compatibility for code generation, converting the floating point model to a fixed point model, setting the clock, types of input/output data into the fixed point model, and data scaling. when the hdl code is generated, it can be synthesized using the simulink hdl coder tool. the latter supports simulation tools. it also supports the synthesis tools of xilinx and altera [14]. v. experimental applications a. sobel edge detector the sobel operator allows to locally evaluate the norm of the two-dimensional spatial gradient of a grayscale image. the regions of strong local variations in intensity corresponding to the contours are amplified. along the ox and oy axes, the sobel operator approximates the directional derivatives using a convolution of the image f(x,y) with 3×3 masks. we notice that the mask of the sobel operator corresponds in fact to the application of a smoothing operation by the (1 0 1) operator followed by the application of a derivation operation by the (1 0 -1) operator in the orthogonal direction. the 3×3 matrix is convolved with the image to calculate the approximated horizontal and vertical gradients gx and gy as follows: ��� � �1 0 �12 0 �21 0 �1 (1) ��y � � 1 2 10 0 0�1 �2 �1 (2) the approximate absolute gradient magnitude and the gradient angle of each pixel are shown by: |��| � �′�� � �′�� (3) � � arctan ��� ����) (4) b. edge detection hardware design using simulink the proposed video edge detection hardware prototyping uses the sobel filter algorithm, and it has been designed with the simulink hdl coder toolbox, so this design can be inserted as an fpga ip core within any video processing pipeline flexibly. this is followed by a detailed description of the proposed hardware architecture. figure 4 presents the top-level module for video edge detection based on the sobel filter. the "video from file" block obtains the input video for the video edge detection system from the directory. this input video is converted to frames. the frames are serialized to pixels. since the pixel values are of double type, the "convert" block is used. pixel-streaming processing is performed by hdl implementations of image and video processing algorithms. therefore, a pixel stream is created with the simulink "serialize" blocks [12]. the inverse process at the output of video processing system is performed by a "deserialize" block to verify the output processed in image format. these two blocks are depicted in figures 6 and figure 7 respectively. c. synthesis and fpga implementation finally, in the third step (figure 8), the simulink hdl coder converts the video edge detection software-hardware model into axi4 streaming bus compliant ip core in the form of hdl (vhdl) source code. to verify in real time the engineering, technology & applied science research vol. 12, no. 1, 2022, 8007-8012 8010 www.etasr.com saidani & ghodhbani: hardware acceleration of video edge detection with hight level synthesis on … functionality of this ip core in a practical environment, a hardware–software co-design (hw-sw) has been implemented directly on a xilinx zynq-7000 ap soc xc7z020-clg484 fpga running at 170mhz. simulink hdl coder generates a full vivado project for the hw-sw. this project can be implemented in the xilinx vivado tool (version 2019.1), with all the software and hardware peripherals. also, the color transform ip core and the sobel core are connected across a single bus. fig. 4. simulink hdl coder model for video edge detection. fig. 5. simulink hdl coder model for video edge detection core. fig. 6. frame pixel serialization. fig. 7. frame pixel deserialization. fig. 8. hdl workflow for the video edge detection system. the hls tool allows the generation of stream interfaces incorporating the hardware accelerator (ip). once the high level synthesis is completed, a compressed file (.zip) containing all hardware components is generated. this file is exported to the media vivado packages to generate our sw/hw design. at this level, the vivado tool constitutes a complete environment for the design of the finalized sw/hw architecture. the latter allows the installation of an on-board processor connected to one or several hardware accelerators through axi interconnection buses specific to the selected platform. for example, in order to reset the ip core, one has to write 0x1 to the bit 0 of the ipcore_reset register. to enable or disable the ip core, 0x1 or 0x0 must be written to the ipcore_enable register. engineering, technology & applied science research vol. 12, no. 1, 2022, 8007-8012 8011 www.etasr.com saidani & ghodhbani: hardware acceleration of video edge detection with hight level synthesis on … fig. 9. software-hardware interface via axi4-lite. to access the data ports of the matlab/simulink algorithm, read or write to the associated data registers. the axi4 slave port to pipeline register ratio is selected as 35 in task 3.2 for this model. the default delay to read the axi4 register is one clock cycle. depending on the selected ratio and the io connected to the axi4 interface, register pipelining is introduced in the read logic of the axi4 registers. for this model the axi4 pipeline register ratio setting 35 is larger than all the readable axi4 slave registers. the total readable axi4 slave registers are 1, so no pipelining is added to the axi4 register read back logic. figure 11 shows the design created using the xilinx's vivado cad tool. fig. 10. the axi zynq interface. fig. 11. hw/sw video edge detection architecture. in figure 11, the blue rectangle encircles the ip zynq7 processing system which represents the processor part of the xilinx zynq-7000 soc. this ip is used to make the system configurations, such as configuring clocks and enabling the propagation of security status from arm cores (the security state of the processor part) to the reconfigurable part. the rest of the blocks constitute the elements that are implemented in the reconfigurable part of the soc. the black rectangle encircles the axi interconnect which allows the ips to be connected to each other. the green rectangle surrounds the edge detection ips with sobel filters. the red rectangle surrounds the direct and reverse color transformation ip. d. resource utilization at the next step, we implemented our video processing system cores on zynq-7020 soc. the resources used are presented in table i. data values, instruction memories, and the firmware are stored in bram. the consumed luts and dffs define the architecture of the processor including control signals, internal registers, and microcode. the optimum frequency for our proposed system core is approximately 170mhz and 95fps for throughput. the complexity of the implemented design affects the resources of the utilized zynq7000 soc. the proposed design is performed for input resolution of 1080-1920 frames. the reconfigurable soc platform using vivado is approved by these results. table i. resource utilization and maximum frequency for the video sobel edge detection module maximum frequency 170 mhz lut-ff pairs 3816.667 7.38% luts as logic 2727.667 5.12% luts as memory 648.6667 3.73% slice registers 2465 2.32% ram 36/18 0 0 dsp48 0 0 vi. conclusion in this paper, a high level model-based hardware design flow using mbd tools was presented. the proposed design flow was put by a video edge detection prototyping into a zynq 7000 soc board. each step of the adopted high level synthesis engineering, technology & applied science research vol. 12, no. 1, 2022, 8007-8012 8012 www.etasr.com saidani & ghodhbani: hardware acceleration of video edge detection with hight level synthesis on … prototyping design, from the top level description to the hardware implementation, was described. the global design process can reduce the time of processing by 65%. the experimental results of the proposed video design based on sobel edge detection reimburse the hardware constraints reducing the complexity for embedded video processing in fpgas. references [1] h. m. abdelgawad, m. safar, and a. m. wahba, "high level synthesis of canny edge detection algorithm on zynq platform," international journal of computer and information engineering, vol. 9, no. 1, pp. 148–152, jan. 2015. [2] t. t. duong, j. h. seo, t. d. tran, b. j. young, and j. w. jeon, "evaluation of embedded systems for automotive image processing," in 2018 19th ieee/acis international conference on software engineering, artificial intelligence, networking and parallel/distributed computing (snpd), busan, korea (south), jun. 2018, pp. 123–128, https://doi.org/10.1109/snpd.2018.8441073. [3] c. li, y. bi, f. marzani, and f. yang, "fast fpga prototyping for realtime image processing with very high-level synthesis," journal of realtime image processing, vol. 16, no. 5, pp. 1795–1812, oct. 2019, https://doi.org/10.1007/s11554-017-0688-1. [4] m. b. ayed, s. elkosantini, and m. abid, "an automated surveillance system based on multi-processor and gpu architecture," engineering, technology & applied science research, vol. 7, no. 6, pp. 2319–2323, dec. 2017, https://doi.org/10.48084/etasr.1645. [5] arjona, r., baturone, i., 2020. using simulink hdl coder to implement a fingerprint recognition algorithm into an fpga, in: 2020 xiv technologies applied to electronics teaching conference (taee). presented at the 2020 xiv technologies applied to electronics teaching conference (taee), porto, portugal, https://doi.org/ 10.1109/taee46915.2020.9163790. [6] h. mestiri, i. barraj, and m. machhout, "aes high-level systemc modeling using aspect oriented programming approach," engineering, technology & applied science research, vol. 11, no. 1, pp. 6719–6723, feb. 2021, https://doi.org/10.48084/etasr.3971. [7] l. zouari, s. chtourou, m. b. ayed, and s. a. alshaya, "a comparative study of computer-aided engineering techniques for robot arm applications," engineering, technology & applied science research, vol. 10, no. 6, pp. 6526–6532, dec. 2020, https://doi.org/10.48084/ etasr.3885. [8] t. han, g. w. liu, h. cai, and b. wang, "the face detection and location system based on zynq," in 2014 11th international conference on fuzzy systems and knowledge discovery (fskd), xiamen, china, aug. 2014, pp. 835–839, https://doi.org/10.1109/fskd.2014.6980946. [9] a. alsheikhy and y. f. said, "design of embedded vision system based on fpga-soc," international journal of advanced computer science and applications, vol. 10, no. 10, 2019, https://doi.org/ 10.14569/ijacsa.2019.0101013. [10] j. jiang, c. liu, and s. ling, "an fpga implementation for real-time edge detection," journal of real-time image processing, vol. 15, no. 4, pp. 787–797, dec. 2018, https://doi.org/10.1007/s11554-015-0521-7. [11] r. ghodhbani, l. horrigue, t. saidani, and m. atri, "fast fpga prototyping based real-time image and video processing with highlevel synthesis," international journal of advanced computer science and applications, vol. 11, no. 2, 2020, https://doi.org/10.14569/ijacsa. 2020.0110215. [12] "hdl coder evaluation reference guide," mathworks. https://nl.mathworks.com/matlabcentral/fileexchange/58941-hdl-coderevaluation-reference-guide (accessed dec. 08, 2021). [13] "accelerate design space exploration using hdl coder optimizations video," mathworks. https://nl.mathworks.com/videos/acceleratedesign-space-exploration-using-hdl-coder-optimizations-81998.html (accessed dec. 08, 2021). [14] l. h. crockett, r. a. elliot, m. a. enderwitz, and r. w. stewart, the zynq book: embedded processing with the arm cortex-a9 on the xilinx zynq-7000 all programmable soc. glasgow, uk: strathclyde academic media, 2014. [15] introduction to fpga design with vivado high-level synthesis (ug998). xilinx, 2019. microsoft word etasr_v13_n4_pp11366-11374 engineering, technology & applied science research vol. 13, no. 4, 2023, 11366-11374 11366 www.etasr.com otieno et al.: an evaluation of the performance of lateritic soil stabilized with cement and biochars … an evaluation of the performance of lateritic soil stabilized with cement and biochars to be used in road bases of low-volume sealed roads meshack otieno department of civil, construction and environmental engineering, jomo kenyatta university of agriculture and technology, kenya otimeshacko@gmail.com (corresponding author) charles kabubo department of civil, construction and environmental engineering, jomo kenyatta university of agriculture and technology, kenya kabcha@jkuat.ac.ke zachary gariy department of civil, construction and environmental engineering, jomo kenyatta university of agriculture and technology, kenya zagariy@eng.jkuat.ac.ke received: 13 may 2023 | revised: 2 june 2023 | accepted: 17 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6040 abstract the study investigated the effects of adding saw dust ash (sda) and sugar cane bagasse ash (scba) on the strength of cement with stabilized lateritic soil. the experiments carried out in both the lateritic soil and stabilized lateritic soil considered atterberg limits, sieve/hydrometer analysis, compaction, soaked california bearing ratio (cbr), and unconfined compressive strength (ucs) at various curing periods. ordinary portland cement (opc) was introduced into the soil with varying content (0%, 3%, 5%, 7%, and 9%) by weight of the soil sample. the results showed that cbr and ucs increased to 175.7% and 1.999 mpa, respectively, as the opc content increased to 7%. the optimal opc content to meet the 1.5mpa ucs requirement for road bases on low-volume sealed roads in kenya was 7%. the next treatment involved partially replacing the opc content with sda and scba in different doses (7-0-0%, 51-1%, 3-2-2%, 1-3-3%, and 0-3.5-3.5%, respectively) for various curing periods. the results showed that cbr and ucs decreased as the opc content decreased and scba and sda increased. at a content of 5% opc, 1% sda, and 1% scba, ucs and cbr were 1.877 mpa and 149%, respectively, suggesting that it was the optimal dosage to meet the 1.5mpa ucs requirement for road bases on low-volume sealed roads in kenya. the durability test indicated that the specimens treated with 5% opc, 1% sda, and 1% scba met the 80% durability index mark, as recommended for cement-stabilized soils. previous studies used sda and scba separately with cement or lime to stabilize the subgrade or subbase of roads, but this study focused on using these materials together as a partial opc replacement to stabilize lateritic road bases for use in low-volume sealed roads. the goal was to use local agricultural and industrial waste materials in road construction and improve the strength characteristics of road bases while preserving the environment through waste utilization. keywords-low volume sealed roads; saw dust ash; sugarcane bagasse ash i. introduction cement has a considerably high carbon dioxide (co2) footprint that contributes significantly to global anthropogenic emissions. climate change is considered a cumulative phenomenon that can increase global temperatures due to the presence of co2 in the atmosphere. the burning of fossil fuels for the production of cement contributes to the greenhouse effect, which is a major cause of climate change [1]. therefore, it is important to explore alternatives to reduce the overreliance engineering, technology & applied science research vol. 13, no. 4, 2023, 11366-11374 11367 www.etasr.com otieno et al.: an evaluation of the performance of lateritic soil stabilized with cement and biochars … on conventional materials in concrete production, such as using agricultural and industrial waste such as sugar cane bagasse ash (scba) and saw dust ash (sda). transport infrastructure is a key point in long-term economic development. developing countries face challenges related to their fragile transportation system, which does not facilitate transport. in these countries, the growing trade exchange, the increase in the number of vehicles, and the concentration of administrative services in county centers increase the deterioration of roads. therefore, sustainable road construction materials with superior mechanical properties are needed [2]. the increase in population in urban areas in most developing countries has resulted in the need to expand the transportation infrastructure to enable upcountry communities to travel and carry their goods conveniently [3-4]. roads and railway embankments and beds become vulnerable when the soil has a considerable proportion of clay minerals, as this type of soil has low engineering properties. the high proportion of fine-grained soil particles in the majority of residual tropical lateritic soils contributes to their low engineering characteristics [4-5]. however, the construction of gravel roads has become more expensive due to the increasing demand, variations in land use, high rate of gravel loss, environmental degradation, and considerable high frequency of re-graveling. lateritic soil, which is widespread in tropical countries, including kenya, could replace gravel in low-volume roads. low-volume roads have an average daily traffic (adt) below 250 vehicles per day [6]. materials in their natural state are sometimes not strong enough to meet the demands of modern-day road infrastructure. in civil engineering, for projects such as roads, building foundations, and dams, among others, soil stabilization is essential, as most lateritic soils typically have low bearing capacity and low strength due to the high clay content [7]. most lateritic gravels are not suitable for road bases, due to their poor nodule hardness (incomplete lateralization) and high plasticity [8]. as roads use aggregates, the contribution of the aggregate cost to the total cost of road construction is significant. in india, the use of recycled building waste aggregates was explored to reduce material costs [9]. there are many reasons for using lateritic soil cement, such as the lack of crushed rock, the reduction in the use of crushed rock for environmental reasons, the difficulty to access and the depletion of quarry sites, transportation costs, and the considerable amount of energy demands in mining, transportation, and burning, which also contribute to the total co2 emissions. cost reduction and environmentally friendly characteristics are the added benefit of stabilizing locally available soils for road construction [4, 11-13]. kenya's road network is 161,451 km and is valued at over ksh 3.5 trillion. this constitutes one of the country's largest public investments. the government has invested in lowvolume sealed roads (lvsr) across the country to open up rural areas, and so far about 4,500 km of lvsr projects have been completed with a further 3,800 km under construction. in total, there is over 5,900 km of ongoing national road development programs across the country approximated at ksh 658 billion [14]. in [15], optimal results were achieved by adding 6% sda by weight to lateritic soils, showing that sda acts satisfactorily as a cheap stabilizing agent for subgrade and subbase purposes in lateritic soils. in [16], the maximum compressive strength of stabilized soil was obtained using 5% lime and 8% sda, while in [17] it was concluded that sda can be considered a cheap and acceptable stabilizing agent in road construction to improve most geotechnical properties of soft clay soils. in [18], the maximum unconfined compressive strength (ucs) and california bearing ratio (cbr) values of 698 kn/m 2 and 43% were recorded for soil treated with 8% lime and 6% bagasse ash, but although the properties of the natural soil improved, it did not meet the criterion of 1710 kn/m 2 specified by the transport and road research laboratory (trrl) (1977) for adequate stabilization using ordinary portland cement (opc). the use of a hydrated lime-bagasse ash mixture to stabilize expansive soil could meet cbr requirements for most specifications for subgrade or even subbase course materials for road and highway construction purposes [19]. in [4, 20], mdd and omc of treated soil generally showed decrease and increase trends, respectively, with a higher bagasse ash content. soil samples stabilized with bagasse ash recorded some gain in ucs but did not meet the 7-day 1,700 kn/m 2 strength criterion recommended by trrl (1977) for base course materials. in [21], the maximum cbr value was 16% for soil treated with 2% bagasse ash and did not meet the requirement of the nigerian general specifications (1997) of 180% for the laboratory-tested cement-stabilized material mixin-place method, concluding that bagasse ash cannot be used as a standalone stabilizer in road construction. ii. research gap previous studies used sda and scba separately with cement or lime to stabilize the subgrade or subbase. this study focuses on the use of these two materials together as partial replacements of cement to stabilize lateritic road bases for possible use in low-volume sealed roads. this study aims to use local agricultural and industrial waste materials in road construction to improve the strength characteristics of road bases while at the same time preserving the environment through waste utilization. the results of this study promote rural mobility, enhance trade activities with a reduction in travel time, can provide beneficial income to woodworkers and sugar industries through the utilization of waste, and finally protect the environment. iii. materials and methods this study used lateritic soil (ls), opc 42.5n, sda, and scba. the ls used was collected from kiambu county, kenya. the opc used was cem i 42.5 n, produced by bamburi cement company in kenya. opc cem i was chosen because it had 95-100% clinker compared to 65-94% for cem ii, which means that cem i had higher strength [4, 22]. in addition, using a higher percentage of clinker, the targeted strength could be achieved faster [3]. the sda was obtained from the kiambu town timber factory in kenya. scba was obtained from sony sugar company in awendo, migori county, kenya. figures 1, 2, and 3 show the respective materials. engineering, technology & applied science research vol. 13, no. 4, 2023, 11366-11374 11368 www.etasr.com otieno et al.: an evaluation of the performance of lateritic soil stabilized with cement and biochars … fig. 1. lateritic soil. fig. 2. sugar cane bagasse ash. fig. 3. saw dust ash. the physical and mechanical properties of the soil were determined according to [23], including liquid limit (ll), plastic limit (pl), plastic index (pi), shrinkage limit (sl), specific gravity (sg), particle size distribution (psd), optimum moisture content (omc), maximum dry density (mdd), cbr, and ucs, followed by classification. the elemental properties of ls, cement, sda, and scba were investigated according to [23], using x-ray fluorescence (xrf) through a shimadzu edx-800hs energy dispersive xray spectrometer in the materials testing and research division (mtrd) of the ministry of roads and transport (mort) in kenya. the soil was first stabilized by adding varying proportions of cement, ranging from 0, 3, 5, 7, and 9% by weight of the soil. the soil component was 100, 97, 95, 93, and 91%, respectively. previous studies adopted comparable proportions for soil stabilization for possible use in road construction [3-4, 25-29]. significant tests were carried out on the soil-cement samples to obtain the optimal cement content (m%). the tests included atterberg limits, omc, mdd, and cbr according to [23], and ucs according to [24]. ucs tests were carried out on samples compacted at their omc in a standard proctor mold with internal diameter and height of 100 and 115 mm, respectively. samples were cured for 7, 14, and 28 days under controlled conditions. then, they were subjected to a uniaxial compression test at a rate of 0.2 m/s, using a compression machine. it is worth noting that trial speeds above 0.2 m/s produced lower values than expected [4, 26]. the maximum load and compressive strength were recorded at the time of failure. the second study involved the partial replacement of opc with equal amounts of sda and scba, as shown in table i, to produce soil-cement-sdascba samples [20]. figures 4, 5, and 6 show some tested samples, the soaking process of the cbr samples, and the ucs samples testing setup, respectively. fig. 4. ucs samples to be tested fig. 5. cbr sample soaking. fig. 6. ucs sample testing. soil-cement-sda-scba samples were subjected to durability tests according to [23]. durability was expressed in terms of the resistance of the samples to loss of strength. this was achieved by dividing the ucs value obtained from stabilized samples cured for 7 days and soaked in water for another 7 days by the ucs value obtained from another set of stabilized samples cured for 14 days under controlled conditions. this test method was preferred to the wet and dry and freeze-thaw tests specified in the astm standard because it better represents field conditions in the study area. the same testing method was adopted in [30] to assess the durability of ls stabilized with eggshell and cement, and in [31] to assess the durability of cement-stabilized ls for use as a flexible pavement construction material. after establishing the optimal opc content, the other tests were performed to determine the optimal opc, sda, and scba content, as shown in table i, according to [23-24]. m represents the optimal opc content obtained in the initial experimental investigation and replaced by equal proportions of sda and scba in the second study. engineering, technology & applied science research vol. 13, no. 4, 2023, 11366-11374 11369 www.etasr.com otieno et al.: an evaluation of the performance of lateritic soil stabilized with cement and biochars … table i. experimental design s/n soil (%) cement (%) scba(%) sda (%) b1 100-m m-0.0-0.0 0.0 0.0 b2 100-m m-1.0-1.0 1.0 1.0 b3 100-m m-2.0-2.0 2.0 2.0 b4 100-m m-3.0-3.0 3.0 3.0 b5 100-m m-3.5-3.5 3.5 3.5 iv. results and discussion a. characterization of ls, sda, and scba 1) particle size distribution figure 7 shows the particle size distribution curve of ls with contents of 17.8% clay, 24.7% sand, 52.6% gravel, and 4.9% silt. the soil was classified as a-2-7: silty, clay gravel sand, according to the aashto classification, and gc with uscs, which is clay gravel with sand. this implies that it cannot be used as a road base construction material, therefore, it must be stabilized [2, 4, 26]. fig. 7. psd curve of the ls-scba-sda. 2) chemical composition of ls, sda, and scba the prominent oxides found in ls were silica, iron, and aluminum oxides, which accounted for 42.94% sio2, 28.47% fe2o3, and 18.29% al2o3, respectively. the silica to sesquioxide ratio (sio2)/(al2o3+fe2o3) was used as an indication of the extent of laterization. the ratio was found to be 0.92, which is less than 1.33, indicating that the ls used was true laterite [2, 32]. the sum of the silica and sesquioxide content in scba was 78.59% (59.92% sio2, 11.58% fe2o3, and 7.09% al2o3,), which is greater than the required 70% minimum [33], showing that the sample is a pozzolanic material (table ii). the sda did not exhibit pozzolanic characteristics given the sum of 3.54% silica and sesquioxide content (0% sio2, 2.58% fe2o3, and 0.96% al2o3,). the results obtained for ls were consistent with those of [5, 34-35]. table ii. element properties of ls, opc, scba, sda elements sda opc scba ls fe % 2.580 4.080 11.580 28.470 mgo % 4.030 0.490 al2o3, % 0.960 6.020 7.090 18.290 sio2, % 25.300 59.920 42.940 k2o, % 15.710 5.130 1.280 cao, % 66.070 59.500 10.390 0.460 tio2, % 0.410 1.930 2.360 p2o5, % 3.690 1.500 0.210 s, % 3.750 2.630 1.110 0.140 cl, % 1.150 0.0010 0.210 0.040 insoluble residue, % 4.410 loss on ignition @750 0 c 4.390 b. stabilization of laterite soil with cement 1) effects of cement on atterberg limits and compaction figure 8 shows that pi was reduced, which implies that the soil plasticity improved as the higher the pi, the more clayey the soil [4, 20, 36]. figures 9 and 10 show the influence of cement on the compaction properties of ls. mdd and omc for untreated soil were obtained at 1.72 g/cm 3 and 18.0%, respectively. after adding cement to 3, 5, 7, and 9%, mdd increased to 1.76, 1.76, 1.77, and 1.79 g/cm 3 , respectively. similarly, the omc increased to 18.0, 21.5, 21.5, 24.5, and 24.7% by adding 3, 5, 7, and 9% cement, respectively. the increase in omc may be due to the flocculation and agglomeration of clay-sized particles resulting from cat-ion exchange, which also causes an increase in volume. when the cement content increases, the increase in omc may be due to the increase in fine content and the greater amounts of water required for cement hydration [4, 20, 37-38]. the increase in omc may be due to the stabilizing binder that requires more moisture for the dissociation of calcium ions and the subsequent hydration process [4, 20, 30, 39]. the increase in mdd may be due to the greater affinity of water for the hydration process. fig. 8. atterberg limits with cement content. fig. 9. omc with cement content. engineering, technology & applied science research vol. 13, no. 4, 2023, 11366-11374 11370 www.etasr.com otieno et al.: an evaluation of the performance of lateritic soil stabilized with cement and biochars … fig. 10. mdd with cement content. 2) effect of cement on california bearing ratio figure 11 shows the summary of cbr for varying cement content of 0, 3, 5, 7, and 9% in ls. cbr increased from 30.9 to 175.7% with increasing cement content, where the maximum value was achieved with 7% cement and then decreased to 102.6% with 9% cement content. the increase in cbr agrees with [4, 20, 29, 39-41]. the increase in cbr with cement addition may be due to the availability of large quantities of calcium necessary for the formation of calcium silicate hydrate (csh) and calcium aluminate hydrate (cah), which are the main compounds responsible for strength gain [42]. the decrease in cbr at 9% may be due to large amounts of cement that were not mobilized in the reaction, thus reducing the bond in the cement-soil matrix [4, 20, 39, 43-44]. fig. 11. variation of soaked cbr with cement content. 3) effect of cement on unconfined compressive strength figure 12 shows that ucs increased with cement content. at 7 days of curing, the ucs of ls of 0.226 mpa improved to 0.483, 0.775, 1.99, and 2.769 mpa for cement content of 3, 5, 7, and 9%, respectively. this increase is consistent with [29, 45]. strength gain due to cement was attributed to decreased soil porosity when cement is added, as well as to the compaction and hydration of cement [25, 46]. the ucs at 7 days of curing is the most important strength criterion used for cement-stabilized materials for road purposes. in [47], it was concluded that the ucs test should be used to determine the strength of the cement-stabilized soil base. since ucs at 7 days of curing increased with cement content and all soil-cement mixes above 7% cement content meet the requirements of the kenya pavement design guideline for lvsr [48], which recommends a minimum of 1.5 mpa for road bases, the 7% cement content was identified as optimal. this is nearly in agreement with [49], where 2 and 6% cement were proposed to stabilize colombian ls for use in the construction of lowto medium-volume roads. in [50], the use of 9.23% opc was recommended to meet the requirement of 80% cbr, which can achieve a strength of 1428.09 kpa. there was no significant change in ucs with curing periods of 14 and 28 days, respectively. the slightly higher values obtained at 14 days could be due to swelling as a result of comparably longer curing periods [4, 20]. fig. 12. variation of ucs with cement content. c. stabilization of ls with opc, sda, and scba 1) effect on atterberg limits and compaction fig. 13. atterberg limits with cement, scba, and sda. ls was stabilized with sda and scba as a replacement for cement for the optimal content of 7%. figure 13 shows that pi increased from 12.3 to 22.42%. the increase in pi may be attributed to the addition of sda and scba, which have engineering, technology & applied science research vol. 13, no. 4, 2023, 11366-11374 11371 www.etasr.com otieno et al.: an evaluation of the performance of lateritic soil stabilized with cement and biochars … higher water absorption affinity [2, 7, 51]. according to [36], the higher the pi, the more clayey the soil. figure 14 shows that an increase in sda-scba content from 0 to 3.5% along with a decrease in cement content from 7 to 0% showed a slight increase in omc from 24.5% (b1) to 26.4% (b5). fig. 14. omc with cement, scba, and sda. figure 15 shows that mdd had a slight decrease from 1.77 g/cm 3 to 1.74 g/cm 3 at b5. this is consistent with [2, 31]. the minimal changes can be attributed to the addition of small amounts of sda-scba in the soil-cement mixture [26, 39]. fig. 15. mdd with cement, scba, and sda. 2) effect of opc-sda-scba on california bearing ratio figure 16 shows that cbr decreased from 175.7% (b1) to 32.3% (b5) [2, 7]. the gradual decrease in cbr may be due to the high amount of sda-scba that was not mobilized in the reaction, which therefore occupied more space in the sample and thus reduced bonding in soil-cement-sda-scba mixtures [39, 52]. the chemical reaction induced by stabilizers and soil and catalyzed by compaction may be responsible for the decrease in cbr, but in [47] it was stated that the ucs test should be used to determine the strength of cement-stabilized soil base. as stabilized materials are rigid or semi-rigid, cbr is meaningless, and the most convenient strength criterion for such materials is ucs [8]. fig. 16. cbr with cement-scba-sda content. 3) effect of opc-sda-scba on unconfined compressive strength figure 17 shows that ucs decreased from 1.999 to 0.305 mpa, from 2.184 to 0.246 mpa, and 2.258 to 0.287 mpa for 7, 14, and 28 days of curing, respectively, with an increase in sda, scba content from 0 to 3.5% and a decrease in cement content from 7% to 0 [2, 7]. the lower specific gravity of sda and scba replacing those of the soil and cement may contribute to the decrease of ucs. the ucs value at 7 days curing for 5% opc, 1% sda, and 1% scba was 1.877 mpa, which is within the range specified in the kenya pavement design guideline for lvsr of above 1.5 mpa for road bases. according to [8], cbr is meaningless for rigid or semi-rigid stabilized materials, the most convenient strength criterion for such materials is ucs, and a minimum ucs of 1800 kn/m 2 is required on the laboratory mix compacted at 95% mdd after 7 days cure plus 7 days soak, which is economically justified for traffic classes t1 to t3. in this study, the results for 7 days cure and 7 days soak were 1.539 mpa (b2), which was the optimal combination. fig. 17. ucs with cement-scba-sda content. 4) effect of opc-sda-scba on durability figure 18 shows the durability results of the optimal soilcement-sda-scba admixtures under simulated tropical engineering, technology & applied science research vol. 13, no. 4, 2023, 11366-11374 11372 www.etasr.com otieno et al.: an evaluation of the performance of lateritic soil stabilized with cement and biochars … conditions, determined from the resistance of the samples to strength loss. ucs decreased to 94.71% (b1), 82.03% (b2), 75.61% (b3), 61.35% (b4), and 47.64% (b5). the durability of the soil-cement-sda-scba content in b2 was found to be satisfactory, as the values were above the recommended minimum of 80% [31]. the decreasing trend of ucs against wetting-drying cycles was ascribed to the degradation of cement bonding [53]. furthermore, in [54], it was stated that strength reduction against wetting-drying is due to the back pressure caused by the absorbed pore water and the softening of the specimens due to water immersion. fig. 18. durability with opc-scba-sda content. v. conclusions this study evaluated the effects of adding sda and scba on cement-stabilized ls by selecting five different cement proportions to determine the optimal cement content. this optimal cement content was partially replaced by sda and scba to determine the optimal cement-sda-scba content for the stabilization of ls road bases in lvsr. the results of this study shed light on the following issues:  the grain size distribution curve of ls indicates the high content of gravel (52.6%), sand (24.7%), silt (4.9%), and clay (17.8%). the soil was classified as a-2-7 silty, clay gravel sand according to aashto classification and gc according to uscs, which is clayey gravel with sand. the sum of the silica and sesquioxide contents in scba was 78.59%, which was greater than the minimum 70% required by astm c 618-05 (2005) [33], indicating that it was pozzolanic, while the sda sample did not exhibit pozzolanic characteristics.  there was a strength gain from 0 to 9% with cement addition in ls at a curing period of 7 days, but the corresponding strength gain at curing periods of 14 and 28 days was minimal. the optimal dose for the stabilization of ls was 7%, with a ucs of 1.999 mpa at 7 days of curing. this meets the kenya pavement design guideline for lvsr, which recommends a ucs of 1.5 mpa.  there was a significant decrease in strength with the addition of sda and scba to cement-stabilized ls. the optimal cement-sda-scba content was 5, 1, and 1%, respectively, which had a strength of 1.877 mpa. this strength was found sufficient to obtain a ucs of more than 1.5 mpa for lvsr, as specified in the kenya pavement design guideline.  there was a decrease in durability with the addition of sda and scba to cement-stabilized ls. the durability of the cement-sda-scba content at 5% cement, 1% sda, and 1% scba was 82.03%, which was satisfactory as the values were above the recommended minimum of 80%. conflicts of interest the authors declare that there are no conflicts of interest regarding this study. funding statement this study was funded by the jomo kenyatta university of agriculture and technology, the african development bank, and the national construction authority. acknowledgement the authors are grateful to the jomo kenyatta university of agriculture and technology, the materials testing & research centre in the ministry of transport & infrastructure, the national construction authority, and the african development bank for providing support to complete this study. references [1] y. sadek, t. rikioui, t. abdoun, and a. dadi, "influence of compaction energy on 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[54] a. bhurtel and a. eisazadeh, "strength and durability of bottom ash and lime stabilized bangkok clay," ksce journal of civil engineering, vol. 24, no. 2, pp. 404–411, feb. 2020, https://doi.org/ 10.1007/s12205-019-0850-3. engineering, technology & applied science research vol. 7, no. 4, 2017, 1746-1752 1746 www.etasr.com gope et al.: transmission congestion management using a wind integrated compressed air energy … transmission congestion management using a wind integrated compressed air energy storage system sadhan gope electrical engineering department mizoram university, tanhril aizawl, mizoram, india sadhan.nit@gmail.com arup kumar goswami electrical engineering department national institute of technology silchar, assam, india gosarup@gmail.com prashant kumar tiwari electrical engineering department national institute of technology silchar, assam, india prashant081.in@gmail.com abstract—transmission congestion is a vital problem in the power system security and reliability sector. to ensure the stable operation of the system, a congestion free power network is desirable. in this paper, a new congestion management (cm) technique, the wind integrated compressed air energy storage (wcaes) system is used to alleviate transmission congestion and to minimize congestion mitigation cost. the cm problem has been solved by using the generator sensitivity factor (gsf) and the bus sensitivity factor (bsf). bsf is used for finding the optimal location of wcaes in the system. gsf with a moth flame optimization (mfo) algorithm is used for rescheduling the generators to alleviate congestion and to minimize congestion cost by improving security margin. the impact of the wcaes system is tested with a 39 bus system. to validate this approach, the same problem has been solved with a particle swarm optimization (pso) algorithm and the obtained results are compared with the ones from the mfo algorithm. keywords-wind farm; compressed air energy storage; bus sensitivity factor; generator sensitivity factor; moth flame optimization algorithm i. introduction line congestion, especially in a deregulated environment, is one of the most important issues for system operators. a permissible range of power security margin to maintain the system’s security network is the necessity. within fixed thermal limits of transmission lines, thermal generators are rescheduled for congestion alleviation [1]. recently, requisite amount of works are in process to minimize the congestion in deregulated power market. in [2-4], congestion mitigation techniques are discussed with the integration of flexible ac transmission system (facts) devices. for diminution of congestion, series facts devices are used for enhancement of voltage and transient stability of the system. the generator rescheduling approach is one of the most important techniques in cm problem. active power rescheduling is done for congestion mitigation by using the relative electrical distance (red) approach [5]. reactive power is also important for congestion mitigation. real and reactive power rescheduling approach has been used for cm in [6]. in deregulated electricity market, market flow strategy concepts are often used for congestion management [7-9]. utilization of wind sources is one of the fastest growing renewable energy sectors in the world. so, it is a priori requirement to analyze the impact of wind energy sources in power system security enhancement. a wind integrated congestion management approach is discussed in [10-11]. due to the unpredictable nature of wind power, storage devices are essential in the power system security field. the optimal placement of energy storage units to maximize the hourly social welfare in deregulated power system is investigated in [12]. compressed air energy storage (caes) system is an important storage technology for storing electricity in modern power system. caes provides the flexibility of the unpredictable power suppliers by reducing their energy deviations penalties over the entire scheduling period in a deregulated power market [13-14]. in this paper, wind power with caes has been implemented to mitigate congestion and optimize generator rescheduling cost. caes is mainly used to deal with the uncertainty of the wind power. the sensitivity of the busses towards congestion is calculated using bsf. optimal location for wcaes is based on bsf only. implantation of wcaes checks system violation and reduces system active power rescheduling cost. mfo algorithm and gsf is used to reschedule the generator for mitigating congestion. a 39 bus new england test system is used for validating the proposed method. ii. wind integrated compressed air energy storage (wcaes) the main purpose of using caes with wind farms (wf) is to supply constant power to the grid. surplus wind power generated (more than contract wind power generation) is stored in the caes. on the other side, when there is a deficit of contract wind power, the caes generates the required amount of power of the contract power. natural gas is used in caes. excess wf power generation is used to compress natural air and accumulate in storage device. when there is a shortage of wind power as per the contractual agreement, compressed air is expanded in a gas turbine, mixed with natural gas and generates the electricity. it is assumed that compression and expansion process takes place at steady state condition. air pressure, flow of air, potential and kinetic energy engineering, technology & applied science research vol. 7, no. 4, 2017, 1746-1752 1747 www.etasr.com gope et al.: transmission congestion management using a wind integrated compressed air energy … effects and nuclear or chemical reaction are neglected here. the detailed construction and its operation are given in [15]. figure 1 shows the caes implementation flow chart in the proposed congestion mitigation approach. fig. 1 implementation flow chart of caes iii. bsf and gsf calculation the active power flow in a congested transmission line at time interval t can be written as [11]: 2| || || | cos( ) ( ) cost t t t t t t t t tij i j ij ij i j i ij ijp v v y v y       (1) a. bus sensitivity factor (bsf) the change in active power flow in the congested line to the change in nth bus power is called bus sensitivity factor and expressed by [11]: t ijk n n p bsf p    (2) the detail bsf derivations are given in [11]. b. generator sensitivity factor (gsf) the change in active power flow in the congested line to the change in generator active power supply is called generator sensitivity factor and expressed by [11]: ( )t tij ggsf p p   (3) the detail gsf derivations are given in [11]. c. problem formulation the main objective of this paper is to minimize the congestion cost of thermal generating units and can be expressed by the following mathematical equation: 1 * n g t g i g i i m in c p t t     (4) the solution of above equation will be obtained when following constraints are satisfied. 0 max 1 (( ) ) 1, 2, 3, 4........... , ng t i gi k k i gsf p mva mva k n t t        (5) min min max max 1, 2, 3, 4...... t t t gi gi gi gi gi gi gip p p p p p p i ng t t             (6) min max 1, 2, 3, 4...... t t gi gi gi gip p p p i ng t t        (7) 1 0 ng t t t t t gi wind cg cc dl i p p p p p t t          (8) 1t t tcc cd cg t t       (9) max0 t t cc cc ccp p t t    (10) exp max0 t t cg cgp p t t    (11) exp max0 t t cd cdp p t t    (12) min maxte e e t t    (13) 1 * ( * ) t t cd t t cc cc cd p e e t p f t t f      (14) *cc cdf f  (15) (0) inte e (16) iv. implementation of moth flame optimization (mfo) algorithm moth flame optimization (mfo) algorithm is a nature inspired meta-heuristic population based algorithm proposed in [16]. with the help of transverse orientation method, moth travels in night and maintains a specified angle with respect to moon. single dimensional or two dimensional or three dimensional or hyper dimensional space vectors is utilized by moth for flying in nature [16]. the set of moths is represented by the following matrix: 1,1 1,2 1, 2,1 2,2 2, ,1 ,2 , ....... ....... .. .. .. .. .. .. .. .. ....... n n m m m n                           (17) the fitness value of all moths is stored in following matrix: 1 2 .. .. fm fm fm fm m                      (18) engineering, technology & applied science research vol. 7, no. 4, 2017, 1746-1752 1748 www.etasr.com gope et al.: transmission congestion management using a wind integrated compressed air energy … the fitness value of all flames is stored in following matrix: 1,1 1,2 1, 2,1 2,2 2, ,,1 ,2 ....... ....... .. .. .. .. .. .. .. .. ....... fl fl fl n fl fl fl n fl fl fl fl m nm m                              (19) as shown in (17) and (19), the moths dimension and flames arrays are equal. the following matrix is utilized for storing the fitness value of flames: 1 2 .. .. flm flm flm flm m                      (20) the actual search agents are moths and flames are the best position of them. moths travel around the search space to obtain the best position. with this technique, moths do not lose their best fitness solution in any circumstance [16]. a flow chart of the algorithm is shown in figure 2. to obtain an optimal performance, parameters are set as such: moths number=30, flames number=30 and iterations number=300. fig. 2. implementing flow chart of mfo algorithm v. results and discussion the proposed cm concept has been investigated on the 39 bus new england system. the 39 bus new england test system data has been taken from [11]. the actual and forecasts wind speed data are taken from [17]. based on the wind speed data, wind power is calculated and shown in figure 3. it is assumed, that a total 50 number of wind turbine generators are connected in the wind farm. it is also assumed that all the wind generation units are operating at the same speed. the investment cost of wind power generation is 3.75 $/hr [18]. fig. 3 actual, forecasted and contracted wind power the contracted wf power is shown in figure 3, which is decided based on the forecasted wf power and the load pattern of the system. if there is any deficit on contracted wind power, then caes storage will fill up that deficit and if there is any surplus of wind power, caes will compensate that power. if caes storage is unable to compensate the excess power, then dump load consumes that extra power to stabilize the system. the caes minimum and maximum energy storage level is considered as 20 mwhr and 100 mwhr respectively. initial energy level of caes is assumed as 80 percent of its maximum energy level capaciy. the overall electrical conversion factor of caes is considered as 70%. the conversion factor of compressor and conversion factor of turbine is assumed as 0.81% and 0.86% respectively. the load connected to each bus is assumed time varying and this is implemented by multiplying a load scaling factor (lsf) at each interval. table i shows the lsf for a 24 hour scheduling period. table i. load scaling factor (lsf) for 24 hour hour lsf hour lsf hour lsf 1 1 9 1.082 17 1.042 2 0.964 10 1.089 18 1.01 3 0.932 11 1.094 19 1 4 0.905 12 1.0965 20 1.042 5 0.865 13 1.0976 21 1.012 6 0.852 14 1.101 22 1.065 7 0.896 15 1.098 23 1.031 8 1 16 1.082 24 1 . the proposed congestion management technique is applied to minimize congestion cost, mitigate transmission congestion and improve the security margin. as per proposed approach, the contract wind power has changed in every hour as per the contractual agreement of the wind farm. generator rescheduling takes the key role in congestion management problem. in the proposed congestion mitigation technique, line (14-34) outage is done for creating line violation in the system. the (15-16) line is congested due to the (14-34) line outage. so, generators need to be rescheduled based on the gsf to mitigate this congestion. figure 4 shows the gsf without considering the wcaes system. before connecting the wcaes system in the system, bsf is calculated and shown in engineering, technology & applied science research vol. 7, no. 4, 2017, 1746-1752 1749 www.etasr.com gope et al.: transmission congestion management using a wind integrated compressed air energy … figure 5. based on the bsf, wcaes system is connected most sensitive bus i.e. bus number 14 in the test system. for connecting wcaes in the test system, bsf is calculated for a total scheduling period i.e. 24 hour in one hour interval and it is seen that each interval bsf is high in bus number 14. practically it is not always correct that wcaes system has to be connected in the most sensitive bus. for practical implementation, we have to see the suitable location and sufficient space for wcaes system. if this condition is not satisfied in the most sensitive bus, then we can go for second highest sensitive bus and so on. after connecting the wcaes system, security limit is checked by system operator in the power system. it is seen that the 15-16 line is violated due to the 14-34 line outage. so, the violation has to be mitigated by using generator rescheduling approach. fig. 4. generator sensitivity factor without wcaes. fig. 5. bus sensitivity factor without wcaes for rescheduling the generators, gsf is calculated with integration of wcaes system and shown in figure 6. figure 7 shows the congested line (15-16) power flow with and without presence of wcaes system before rescheduling the generators. from figure 4 and figure 6, it is seen that the gsf value is less for each scheduling interval with the presence of wcaes system. less gsf means, less amount power need to be rescheduled for minimizing the congestion. table iii and table iv represent the amount of active power rescheduling in each interval for mitigating congestion without and with presence of wcaes system respectively. in each case, generators are rescheduled by using mfo algorithm with help of gsf. in the proposed method, the wcaes system plays a very important role for mitigating congestion and minimizing rescheduling cost. from table iii it is seen that total rescheduling amount using mfo algorithm for a 24 hour scheduling period without the presence of the wcaes system is 14567.59 mw, whereas from table iv it is seen that total rescheduling amount using the mfo algorithm for the same period with the presence of wcaes system is 14125.34 mw. to show the effectiveness of the wcaes system, it is connected in the most sensitive bus and line violation has been calculated with and without the presence of the wcaes system (table ii). table ii shows the mva flow (before and after rescheduling) for a 24 hour scheduling period with and without the presence of the wcaes system. from a technical point of view, less generation of a wcaes has been chosen in spite of the fact that a higher rating wcaes may produce a huge impact in the rescheduling process for congestion management. from table ii, it is seen that for most of the scheduling time the mva flow is less with the wcaes system. to show the impact of the wcaes system, rescheduling cost is also calculated (table v). in table v, it is observed that 2nd to 7th hour intervals, congestion mitigation cost is zero because in that period there is no line violation. it is seen from table i that load scaling factor is less in 2nd to 7th hour interval i.e. system load is less as compared to other interval in the scheduling period. from table v, it is seen that rescheduling cost using mfo with line outage and without presence of the wcaes system is 13579.76 $/24hr, whereas rescheduling cost with line outage and with the presence of the wcaes system is 13248.43 $/24hr. table ii. mva flow with and without wcaes for 24 hour hr mva flow before rescheduling mva flow after rescheduling without wcaes with wcaes without wcaes with wcaes pso mfo pso mfo 1 581 569 497 497 496 496 2 474 474 474* 474* 474* 474* 3 378 378 378* 378* 378* 378* 4 298 298 298* 298* 298* 298* 5 180 180 180* 180* 180* 180* 6 142 142 142* 142* 142* 142* 7 272 272 272* 272* 272* 272* 8 581 557 497 497 496 496 9 827 807 499 499 499 498 10 848 832 499 499 499 499 11 863 847 499 499 499 499 12 871 855 499 499 499 499 13 874 862 499 499 498 498 14 885 873 498 498 497 496 15 875 874 496 497 496 494 16 827 826 498 499 496 496 17 707 704 499 498 496 493 18 611 607 497 497 489 486 19 581 577 497 497 496 496 20 707 704 495 496 483 482 21 617 609 498 498 494 492 22 776 770 499 499 499 498 23 674 667 498 499 498 498 24 581 577 497 497 496 496 *rescheduling is not required engineering, technology & applied science research vol. 7, no. 4, 2017, 1746-1752 1750 www.etasr.com gope et al.: transmission congestion management using a wind integrated compressed air energy … table iii. generator rescheduling amount without wcaes using mfo algorithm for 24 hour scheduling period time g1(mw) g2(mw) g3(mw) g4(mw) g5(mw) g6(mw) g7(mw) g8(mw) g9(mw) g10(mw) total (mw) 1 -75.34 -33.61 -45.45 nr nr nr nr 18.33 -105.03 250 527.77 2 nr nr nr nr nr nr nr nr nr nr 0 3 nr nr nr nr nr nr nr nr nr nr 0 4 nr nr nr nr nr nr nr nr nr nr 0 5 nr nr nr nr nr nr nr nr nr nr 0 6 nr nr nr nr nr nr nr nr nr nr 0 7 nr nr nr nr nr nr nr nr nr nr 0 8 -75.34 -33.61 -45.45 nr nr nr nr 18.33 -105.03 250 527.77 9 -130.24 126.75 36.6 68.72 88.92 56.54 78.3 110.67 -101.05 248.2 1045.99 10 -143.87 134.56 32.65 86.11 76.87 51.82 80.12 115.07 -99.81 250 1070.88 11 -148.24 134.76 27.89 56.67 90.45 60.87 76.34 130.49 -106.68 250 1082.39 12 -152.88 140.21 30.12 68.56 86.8 42.12 79.21 136.65 -102.9 249.67 1089.12 13 -137.87 154.66 20.9 90.28 100.01 46.23 75.98 130.08 -100.21 240.22 1096.44 14 -160.07 144.21 24.6 81.22 92.82 48.54 81.53 124.04 -89.21 253.59 1099.83 15 -136.87 154.63 20.92 89.88 99.89 46.23 75.37 130.24 -100.24 243.25 1097.52 16 -130.24 126.75 36.6 68.72 88.92 56.54 78.3 110.67 -101.05 248.2 1045.99 17 -87.8 37.93 -18.69 2.03 84.02 nr nr 97.44 -81.01 232.32 641.24 18 -78.43 35.33 -20.62 nr 76.76 nr nr 99.23 -83.66 204.65 598.68 19 -75.34 -33.61 -45.45 nr nr nr nr 18.33 -105.03 250 527.77 20 -86.8 38.93 -17.69 nr 88.02 nr nr 100 -80.01 250 662.49 21 -86.34 -102.61 -45.67 nr nr nr nr 25.33 -96.36 248.23 604.54 22 -95.2 45.93 -27.69 14.67 98.45 nr nr 99.45 -68.9 252.6 702.89 23 -78.43 45.33 -28.62 nr 80.23 nr nr 83.56 -95.67 206.67 618.51 24 -75.34 -33.61 -45.45 nr nr nr nr 18.33 -105.03 250 527.77 total 14567.59 table iv. generator rescheduling amount with wcaes using mfo algorithm for 24 hour scheduling period time g1(mw) g2(mw) g3(mw) g4(mw) g5(mw) g6(mw) g7(mw) g8(mw) g9(mw) g10(mw) total (mw) 1 -72.34 -35.61 -43.45 nr nr nr nr 15.12 -97.65 239.8 503.97 2 nr nr nr nr nr nr nr nr nr nr 0 3 nr nr nr nr nr nr nr nr nr nr 0 4 nr nr nr nr nr nr nr nr nr nr 0 5 nr nr nr nr nr nr nr nr nr nr 0 6 nr nr nr nr nr nr nr nr nr nr 0 7 nr nr nr nr nr nr nr nr nr nr 0 8 -68.36 -35.48 -37.65 nr nr nr nr 22.46 -93.03 235.89 492.87 9 -122.24 117.75 38.62 65.23 82.92 57.34 72.3 112.63 -96.05 242.2 1007.28 10 -127.44 122.85 38.6 67.72 86.92 58.54 74.3 113.67 -101.05 246.2 1037.29 11 -134.87 128.56 32.65 76.11 84.87 51.82 80.12 115.07 -99.81 248.5 1052.38 12 -143.87 132.56 34.75 75.21 86.87 50.82 80.12 115.17 -100.21 247.2 1066.78 13 -145.24 134.76 27.89 56.67 88.45 55.87 76.34 130.49 -105.68 249.1 1070.49 14 -147.88 136.21 33.12 71.66 85.8 46.12 79.21 132.65 -102.9 248.3 1083.85 15 -139.87 141.63 20.92 89.88 95.89 46.23 75.37 130.24 -100.24 245.25 1085.52 16 -122.24 120.75 36.6 68.72 88.92 56.54 78.3 107.67 -101.05 248.2 1028.99 17 -84.8 37.93 -19.69 nr 81.02 nr nr 95.44 -79.01 230.32 628.21 18 -81.44 35.33 -20.62 nr 76.76 nr nr 94.22 -73.66 204.65 586.68 19 -68.36 -35.48 -37.65 nr nr nr nr 22.46 -93.03 235.89 492.87 20 -84.8 37.93 -19.69 nr 81.02 nr nr 95.44 -79.01 230.32 628.21 21 -80.44 35.33 -20.62 nr 74.76 nr nr 95.22 -78.66 203.65 588.68 22 -89.2 45.93 -27.69 14.67 92.45 nr nr 98.45 -68.9 245.6 682.89 23 -75.43 45.33 -25.62 nr 78.23 nr nr 83.56 -80.67 206.67 595.51 24 -68.36 -35.48 -37.65 nr nr nr nr 22.46 -93.03 235.89 492.87 total 14125.34 *nr= not rescheduled for calculating rescheduling cost with the presence of the wcaes system, wind power investment cost is also considered. for analyzing this study, we are considering wcaes system supplies power mainly from wind farm. from table v, it is seen that by using mfo, congestion cost reduced by 331.33$/24hr with the presence of the wcaes system compared to without the presence of the wcaes system in the scheduling period. from table v, it is also seen that rescheduling cost using pso with line outage and without presence of wcaes system is 13584.43 $/24hr, where as rescheduling cost with line outage and with the presence of the wcaes system is 13252.97 $/24hr, which is slightly higher than the mfo algorithm results. table vi shows the losses and minimum voltage of the system. from table vi, it is observed that system voltage is better and losses are less in presence of the wcaes system. improved voltage profile indicates the better stability of the system after congestion management. figure 8 shows the caes operation for a 24 hour scheduling period. it shows the power and energy exchange for the entire scheduling period. engineering, technology & applied science research vol. 7, no. 4, 2017, 1746-1752 1751 www.etasr.com gope et al.: transmission congestion management using a wind integrated compressed air energy … table v. rescheduling cost ($/h) for 24 hour scheduling period hour congestion cost ($/h) using pso congestion cost ($/h)using mfo without wcaes with wcaes without wcaes with wcaes 1 231.54 215.12 231.45 214.76 2 0 0 0 0 3 0 0 0 0 4 0 0 0 0 5 0 0 0 0 6 0 0 0 0 7 0 0 0 0 8 231.54 215.12 231.45 214.76 9 1175.67 1108.24 1175.39 1108.53 10 1190.21 1183.94 1189.76 1183.6 11 1202.84 1189.65 1202.89 1189.28 12 1216.06 1198.16 1215.65 1197.65 13 1227.76 1202.57 1227.73 1202.13 14 1243.59 1225.26 1242.94 1224.87 15 1228.64 1225.68 1228.12 1225.62 16 1176.33 1173.18 1175.39 1172.74 17 575.98 567.48 576.25 567.57 18 324.17 313.08 323.77 312.86 19 231.54 215.12 231.45 214.74 20 594.45 567.88 594.05 567.57 21 256.92 227.72 256.49 227.65 22 868.86 854.74 868.96 854.88 23 376.79 354.91 376.57 354.48 24 231.54 215.12 231.45 214.74 total cost ($/24 hr) 13584.43 13252.97 13579.76 13248.43 fig. 6. generator sensitivity factor with wcaes fig. 7. mva flow in congested line with and without wcaes table vi. system parameters after rescheduling using mfo algorithm hour without wcaes with wcaes vmin(p.u) ploss(mw) vmin(p.u) ploss(mw) 1 0.945 58.672 0.967 58.254 2 0.946 58.025 0.946* 58.025* 3 0.947 58.342 0.947* 58.342* 4 0.947 58.439 0.947* 58.439* 5 0.949 58.023 0.949* 58.023* 6 0.954 58.025 0.954* 58.025* 7 0.951 58.351 0.951* 58.351* 8 0.945 58.672 0.964 57.746 9 0.936 59.045 0.941 58.862 10 0.935 59.086 0.940 58.889 11 0.935 59.087 0.941 58.874 12 0.934 59.088 0.940 58.872 13 0.934 59.166 0.935 59.132 14 0.934 59.212 0.936 59.120 15 0.935 59.091 0.938 59.001 16 0.935 59.042 0.937 58.988 17 0.946 58.762 0.948 58.523 18 0.948 58.688 0.952 58.547 19 0.945 58.672 0.967 58.455 20 0.946 58.674 0.952 58.465 21 0.948 58.579 0.974 58.023 22 0.952 58.564 0.976 58.012 23 0.958 58.485 0.978 58.016 24 0.945 58.672 0.966 58.255 fig. 8. caes operational vi. conclusion congestion in transmission systems is a real life problem and a burning issue in power sector reliability. misbalanced power generation and demand is the cause of congestion. to maintain the balanced system profile for a long run, alleviation of congestion is essential. the key element for the solution considered in this paper is the incorporation of wcaes. this helps to not only mitigate congestion but also to reduce congestion cost. the obtained results reflect the effective utilization of wcaes in the 39 bus new england test system. bsf is used for the optimal placement of wcaes in the most sensitive bus of the system. gsf with mfo algorithm in the presence of wcaes is implemented for generation rescheduling and to mitigate transmission congestion. results obtained by the mfo algorithm are compared with ones obtained from applying the pso algorithm and it is shown that the mfo algorithm gives slightly better results. the proposed engineering, technology & applied science research vol. 7, no. 4, 2017, 1746-1752 1752 www.etasr.com gope et al.: transmission congestion management using a wind integrated compressed air energy … method is used for a 24 hour scheduling period in order to explain the effectiveness of the technique more accurately. less congestion cost and reduced line mva flows are achieved. the proposed approach is economically feasible and easy to incorporate. nomenclature vti voltage magnitude at bus-i at tth time interval vtj voltage magnitude at bus-j at tth time interval t i angle at bus-i at t th time interval ptij change in active power flow at t th interval cgi congestion cost of individual generator pg max maximum active power generation limits mvak m ax maximum mva flow limit of kth transmission line pcgt power generation from caes in simple cycle mode at time interval t. pcdt power generation from caes in discharging mode at time interval t α electrical conversion factor of caes pccmax maximum compression capacity of compressor, emin minimum level of air storage eint initial level of air storage yij magnitude of ijth element of ybus matrix at tth time interval j angle at bus-j at t th time interval ij angle of ybus matrix at ij th element at tth time interval ∆ptgi active power adjustment of individual generator at time interval t, pg min minimum active power generation limits mvak 0 actual mva flow in the transmission line k pwindt wind power generation at time interval t pcct power consumption by caes in the time interval t t cc charging mode of caes at t th interval, [0 or 1] t cd discharging mode of caes at t th interval, [0 or 1] t cg simple cycle mode of caes at t th interval, [0 or 1] pmaxexp maximum generation capacity of expander ptdl dump load power consumption at time interval t emax maximum level of air storage t index of hour or interval m number of moths n number of variables  position vector matrix of moth fm fitness vector matrix of moth fl position vector matrix of flame flm fitness vector matrix of flame ,m n position of moth fm m fitness of moth , fl m n position of flame flm m fitness of flame ccf conversion factor of compressor cdf conversion factor of turbine references [1] s. dutta, s. p singh, “optimal rescheduling of generators for congestion management based on particle swarm optimization”, ieee transaction on power system, vol. 23, pp. 1560-1569, 2008 [2] a. kumar, c. sekhar, “congestion management with facts devices in deregulated electricity markets ensuring loadability limit”, electrical power and energy systems, vol. 46, pp. 258-273, 2013 [3] m. esmaili, h. a. shayanfar, r. moslemi, “locating series facts devices for multi-objective congestion management improving voltage and transient stability”, european journal of operational research, vol. 236, pp. 763-773, 2014 [4] a. kumar, r. k. mittapalli, “congestion management with generic load model in hybrid electricity markets with facts devices”, electrical power and energy systems, vol. 57, pp. 49-63, 2014 [5] g. yesuratnam, d. thukaram, “congestion management in open access based on relative electrical distances using voltage stability criteria,” electrical power systems research, vol. 77, pp. 1608-1618, 2007 [6] a. kumar, s. c. srivastava, s. n. singh, “a zonal congestion management approach using real and reactive power rescheduling”, ieee transaction on power systems, vol. 19, pp. 554-562, 2004 [7] a. kumar, s. c. srivastava, s. n. singh, “congestion management in competitive power market: a bibliographical survey”, electrical power systems research, vol. 76, pp. 153-164, 2005 [8] c. luo, y. hou, j. wen, s. cheng, “assessment of market flows for interregional congestion management in electricity markets”, ieee transactions on power systems, vol. 29, pp. 1673-1682, 2014 [9] a. k. singh, s. k. parida, “congestion management with distributed generation and its impact on electricity market”, electrical power and energy systems, vol. 48, pp 39-47, 2013 [10] s. deb, s. gope, a. k. goswami, “generator rescheduling for congestion management with incorporation of wind farm using artificial bee colony optimization technique”, ieee india conference, pp. 1-6, 2013 [11] s. deb, s. gope, a. k. goswami, “congestion management considering wind energy sources using evolutionary algorithm”, electric power components and systems, vol. 43, pp. 723-732, 2015 [12] m. ghofrani,, a. arabali, m. etezadi-amoli, m. s. fadali, “a framework for optimal placement of energy storage units within a power system with high wind penetration”, ieee transactions on sustainable energy, vol. 4, no. 2 , pp. 434-442, 2013 [13] h. lund, g. salgi, b. elmegaard, a. n. andersen, “optimal operation strategy of compressed air energy storage (caes) on electricity spot market with fluctuating price”, applied thermal engineering, vol. 29, pp. 799-806, 2009 [14] g. grazzini, a. milazzo, “thermodynamic analysis of caes/tes systems for renewable energy plants”, renewable energy, vol. 33, pp. 1998–2006, 2008 [15] h. ibrahim, r. younès, a. ilinca, m. dimitrova, j. perron, “study and design of a hybrid wind–diesel-compressed air energy storage system for remote areas”, applied energy, vol. 87, pp. 1749–1762, 2010 [16] s. mirjalili, “moth flame optimization algorithm-a novel nature inspired heuristic paradigm”, knowledge based system, vol. 89, pp. 228-249, 2015 [17] “database: world temperaturesweather around the world”, available at www.timeanddate.com/weather [18] s. dawn, p. k. tiwari, “improvement of economic profit by optimal allocation of tcsc & upfc with wind power generators in double auction competitive power market”, electric power and energy systems, vol. 80, pp. 190-201, 2016 microsoft word etasr_v12_n2_pp8382-8387 engineering, technology & applied science research vol. 12, no. 2, 2022, 8382-8387 8382 www.etasr.com bora et al.: the design of closed square rr loaded 2-port mimo for dual band applications the design of closed square rr loaded 2-port mimo for dual band applications pronami bora antennas and liquid crystals research centre department of ece koneru lakshmaiah education foundation andhra pradesh, india pronamiz@gmail.com p. pokkunuri antennas and liquid crystals research centre department of ece koneru lakshmaiah education foundation andhra pradesh, india pspokkunuri@kluniveristy.in b. t. p. madhav antennas and liquid crystals research centre department of ece koneru lakshmaiah education foundation andhra pradesh, india btpmadhav@kluniveristy.in received: 17 january 2022 | revised: 16 february 2022 | accepted: 16 february 2022 abstract-in this paper, a closed square ring resonator loaded 2port multi input multi output (mimo) is proposed for dualband applications in the s and c band. the presented antenna model is designed by loading it in fr-4 substrate with a feedline of 50ω and loaded with srr for the enhancement of isolation and radiation pattern. ansoft hfss is used to obtain the simulated parameters of the model for the frequency ranges of 2.2-2.5 and 6-6.3ghz. measurements confirm the characteristics of the fabricated antenna that were speculated with the simulation results with a little shift in frequencies. the diversity parameter performance analysis justifies the working performance of the 2port mimo for wifi, wlan, and ism band applications. keywords-dual band; microstrip; rr; mimo; ecc i. introduction wireless communications play a very important and significant part in our daily life [1-3]. in this time of global crisis due to the covid-19 pandemic, telecommunication infrastructure is connecting people and helping transfer necessary data from physical structures to digital platforms. antennas play a very important part in the telecommunication network by acting as a transducer in sending and receiving electromagnetic waves [4-5]. as the requirement of compact and portable devices for wireless communication is increasing, microstrip patch antennas prove to be a potential candidate and are preferred over the conventional antennas [6]. these antennas have the advantages of being light weight, smaller in size, they have a low profile, and the potential to be fabricated and incorporate easily on other external devices. however, mimo antennas have evolved as a potential aspirant in meeting the demands of high data rates and high speed with the significant advantages of decreased fading and link reliability in multipath environments. the use of mimo antennas results in better spatial and pattern diversity with increased channel capacity [7-10]. the main challenge for the researchers lies in increasing the isolation between the ports so that there is minimum interference between the transmitting and receiving signals. the increased correlation between the ports will affect the antenna efficiency, so mutual coupling needs to be reduced for the better performance of the antenna. moreover, even in the conventional microstrip patch antennas, the most common limitations are low impedance bandwidth, solo resonating frequency, and low gain. different techniques have been reported for enhancing the isolation and improving antenna parameters like dgs, resonators, amcs, meander line, metamaterials, etc. [11-12]. a mimo antenna with v shaped ground for application in the wlan band has been presented in [13], whereas in [14], an mimo antenna loaded with csrr is proposed. another mimo antenna with symmetrically placed patch elements is described in [15]. ring resonators proved to be a suitable candidate among all the techniques reported for enhancing the antenna parameters due to their simple structural design. in this paper, the use of triple closed square rr has been shown for the reference port antenna and also for the proposed 2-port design. return loss, reduced dimensions by maintaining its characteristics, and promoting the effect of the capacitive filter can be achieved by the application of ring resonators on the micro strip patch antenna [16]. the main aim of using closed square rr-inspired antennas is to minimize the antenna size, enhance the isolation, and increase the bandwidth making them more desirable for applications. when ring resonators are loaded in microstrip antennas, a capacitive filter effect is induced which works in increasing the antenna return loss, reducing the dimensions of antenna by retaining its main attributes, and other effects [17corresponding author: pronami bora engineering, technology & applied science research vol. 12, no. 2, 2022, 8382-8387 8383 www.etasr.com bora et al.: the design of closed square rr loaded 2-port mimo for dual band applications 18]. the use of various ring resonators implemented in microstrip antennas has been reported by many authors in the literature [19-20]. various non-homogenous elementary geometries have been used like split ring resonators and complimentary split ring resonators in various shapes [21-22]. the proposed antenna design loaded with square closed ring resonators exhibits advantages in terms of isolation, compact size, low-fabrication cost, low-cross polarization level, and dual-band operation. ii. antenna design a. model the present section illustrates the design of the single antenna element taken as a reference. figure 1 represents the configuration of the antenna embedded on a fr-4 substrate having relative permittivity of 4.4 and a loss tangent of 0.025 along with the fabricated prototype. the substrate height is taken as 1.6mm with a 25×25mm 2 patch. the antenna dimensions are mentioned in table i. testing of the fabricated prototype has been conducted with the vector network analyzer and it shows satisfactory correlation among the fabricated and the simulated results. the geometry of the closed square rr is given in figure 2(a) and the unit cell electrical equivalent is shown in figure 2(b). the resonating frequency fo of the square rr is given as: fo = �������� (1) (a) (b) fig. 1. geometry of the reference antenna. (a) simulated design, (b) fabricated antenna. (a) (b) fig. 2. (a) ring resonators, (b) equivalent circuit. table i. antenna dimensions antenna dimensions size in mm pw1 40 pl 50 sw 25 sl 25 a 6 b 5 fl 16 fw 3 b. design specifications the parameters of the antenna are obtained from the conventional formulas given below [15]. the width (w) is calculated as: w �� ���� � � � ��� �� � � � ��� (2) where c is the free space velocity of light and εr the dielectric constant of the substrate. the effective dielectric constant of the microstrip patch antenna is: ε� ���� � ���� � �������� � (3) the actual length of the patch (l) is: l l� � 2δl (4) where l� �� �� � (5) !�" 0.412 ' � �(.)*+ �� �(.�,-.' � �(.�/0*+�� �(.0. (6) the simulated and fabricated return loss for this antenna is shown in figure 3 which shows that this single element antenna is operating at 2.4ghz for ism band applications. fig. 3. measured and simulated reflection coefficient for the single element antenna. engineering, technology & applied science research vol. 12, no. 2, 2022, 8382-8387 8384 www.etasr.com bora et al.: the design of closed square rr loaded 2-port mimo for dual band applications figure 4 shows the proposed mimo antenna. testing of the fabricated prototype has been conducted with the vector network analyzer and it shows satisfactory correlation among the fabricated and the simulated results. the electrical equivalent circuit for one element is shown in figure 5. a tank circuit of inductor l and capacitor c is formed by each unit cell of the resonator. l is resulted due to the current flow through the main feedline. the shunt capacitances c2� and c2� are formed due to the gap in the ground plane and patch. (a) (b) fig. 4. geometry of the proposed antenna. (a) simulated design, (b) fabricated antenna. fig. 5. equivalent circuit of one patch element. iii. parametric analysis for the best probable performance of the proposed antenna, its dimensions have been optimized and this is evident from the following observations. the variations in the return loss have been observed by varying several parameters as discussed below. a. outcome of changing length of feed the proposed line fed antenna’s return loss is observed by changing the length to 15mm and 17mm. the feed length fl (16mm) of the proposed design is giving the optimum results as shown in figure 6. fig. 6. reflection coefficient by varying feed length. b. outcome of changing width of feed return loss variations have been observed by increasing and decreasing the feed width to 2.8mm and 3.2mm. optimum return loss is observed for the feed width of 3mm as designed in this paper. fig. 7. reflection coefficient by varying feed width. c. outcome of changing the width of the ring resonator slot width of the ring resonators was varied to 0.5mm and 1.5mm to obtain the variations in return loss characteristic as shown in figure 8. it is noticed that slot width of 1mm is providing the best results. iv. results and discussion for simulating the antenna parameters, finite element based ansoft hfss is used and for the fabricated results and the vector network analyzer manufactured by anritsu is utilized. the model number is ms2073c offering a frequency range from 5khz to 15ghz and 350µs/data point sweep speed. engineering, technology & applied science research vol. 12, no. 2, 2022, 8382-8387 8385 www.etasr.com bora et al.: the design of closed square rr loaded 2-port mimo for dual band applications fig. 8. reflection coefficient by varying resonator width. a. reflection coefficient and radiation patterns figure 9 shows the measured and simulated reflection coefficient for the proposed mimo antenna. the antenna provides return loss> –20db and isolation of more than 20db to tune over frequency bands between 2.3–2.4ghz and 5.9– 6.3ghz. fig. 9. measured and simulated reflection coefficient of the proposed antenna. the radiation patterns for the e plane and h plane of the proposed antenna for both operating frequencies are shown in figure 10. it is observed that the proposed design shows good radiation performance and cross polarization is less compared to the co-polarization in both planes. b. gain figure 11 shows the gain of the proposed antenna. it can be observed that the proposed design has a maximum gain of 7dbi at 2.4ghz resonating frequency and a gain of 4.5dbi at 6.1ghz frequency. (a) (b) (c) (d) fig. 10. radiation patterns of the proposed antenna: (a) 2.4ghz e plane, (b) 2.4ghz h plane, (c) 6.1ghz e plane, (d) 6.1 ghz h plane. (a) (b) fig. 11. gain of the proposed antenna. (a) 2.4ghz, (b) 6.2ghz. c. diversity parameters the various performance metrics for justifying the performance of the proposed mimo antenna, like envelope correlation coefficient (ecc), diversity gain (dg), and group delay (gd) were computed. it is observed from figure 12 that the proposed mimo antenna is having good performance metrics as ecc is below 0.05 with dg of more than 9.98, and gd less than 2ns. ecc defines the amount of correlation between an antenna and the others and can be expressed as: ρ� | ∑ 6∗8,: ∗ 6∗<,: =:>� |�∏ @�� ∑ 6∗8,:6:,ab=:>�:a>'8,<* (7) where n is the number of antenna elements, and a, b are the antenna elements. the measured ecc for the proposed antenna is below 0.05 which justifies its use for practical applications. the proposed design provides a maximum gd of 2ns which is well within limits. another important performance parameter in mimo antennas is dg which defines the amount of obtained improvement in mimo compared to siso and can be expressed as: engineering, technology & applied science research vol. 12, no. 2, 2022, 8382-8387 8386 www.etasr.com bora et al.: the design of closed square rr loaded 2-port mimo for dual band applications dg 10√1 � ecc� (8) dg should be more than 9.95 for any practical applications and the computed results shows that dg is more than 9.96 as can be seen in figure 12. a comparison of some of the existing works for isolation enhancement is presented in table ii for different applications. fig. 12. diversity gain and group delay of the proposed antenna. table ii. comparison with existing works ref no. size (mm) minimum isolation (db) resonant frequency (ghz) [19] 100×50 15 1.73, 2.8 [20] 100×50 10 2.4-2.5 [21] 80×40 15 2.9-3.3, 3.2-3.6 [22] 100×60 10 2.4-2.6, 3.4-3.6 this paper 80×50 20 2.2-2.5, 6-6.3 v. conclusion a triple closed rr of square shape, embedded on a microstrip patch antenna for s and c band applications is presented in this work. the resonating frequency band at return loss >20db is 2.3-2.4 ghz and 5.9-6.3 ghz with good impedance matching and gains of 7.5db and 5db respectively. the proposed antenna model is befitting for applications in s and x bands covering wifi, wlan, and ism band applications with isolation of more than 20db in the operating bands. the performance parameters of the proposed mimo antenna are satisfactory with ecc < 0.1, dg > 9.93db and a maximum gd of 2ns. references [1] j. liu, y. cheng, y. nie, and r. gong, "metamaterial extends microstrip antenna," microwaves & rf, vol. 54, no. 5, pp. 58–64, nov. 2013. [2] i. b. t. da silva, h. d. de andrade, j. l. da silva, h. c. c. fernandes, and j. p. p. pereira, "design of microstrip patch antenna with complementary split ring resonator device for wideband systems application," microwave and optical technology letters, vol. 57, no. 6, pp. 1326–1330, 2015, https://doi.org/10.1002/mop.29081. [3] h. t. zhang, g. q. luo, b. yuan, and x. h. zhang, "a novel ultrawideband metamaterial antenna using chessboard-shaped patch," microwave and optical technology letters, vol. 58, no. 12, pp. 3008– 3012, 2016, https://doi.org/10.1002/mop.30200. [4] x. cheng, j. j. whalen, and y.-k. yoon, "rectangular waveguide shape folded patch antenna," in 2010 ieee antennas and propagation society international symposium, toronto, on, canada, jul. 2010, pp. 1–4, https://doi.org/10.1109/aps.2010.5562063. [5] j. d. baena et al., "equivalent-circuit models for split-ring resonators and complementary split-ring resonators coupled to planar transmission lines," ieee transactions on microwave theory and techniques, vol. 53, no. 4, pp. 1451–1461, apr. 2005, https://doi.org/10.1109/ tmtt.2005.845211. [6] x. cheng, d. e. senior, c. kim, and y.-k. yoon, "a compact omnidirectional self-packaged patch antenna with complementary split-ring resonator loading for wireless endoscope applications," ieee antennas and wireless propagation letters, vol. 10, pp. 1532– 1535, 2011, https://doi.org/10.1109/lawp.2011.2181315. [7] z. ying, c.-y. chiu, k. zhao, s. zhang, and s. he, "antenna design for diversity and mimo application," in handbook of antenna technologies, z. n. chen, ed. singapore: springer, 2014, pp. 1–43, https://doi.org/10.1007/978-981-4560-75-7_53-1. [8] a. ramachandran, s. mathew, v. p. viswanathan, m. pezholil, and v. kesavath, "diversity-based four-port multiple input multiple output antenna loaded with interdigital structure for high isolation," iet microwaves, antennas &amp; propagation, vol. 10, no. 15, pp. 1633– 1642, dec. 2016, https://doi.org/10.1049/iet-map.2015.0828. [9] z. niu, h. zhang, q. chen, and t. zhong, "isolation enhancement in closely coupled dual-band mimo patch antennas," ieee antennas and wireless propagation letters, vol. 18, no. 8, pp. 1686–1690, dec. 2019, https://doi.org/10.1109/lawp.2019.2928230. [10] m. o. dwairi, "increasing gain evaluation of 2×1 and 2×2 mimo microstrip antennas," engineering, technology & applied science research, vol. 11, no. 5, pp. 7531–7535, oct. 2021, https://doi.org/ 10.48084/etasr.4305. [11] s. p. r. shastri, r. r. singh, and k. v. ajetrao, "coplanar stripline loaded reconfigurable loop antenna for wlan and wimax applications," engineering, technology & applied science research, vol. 8, no. 5, pp. 3479–3483, oct. 2018, https://doi.org/10.48084/ etasr.2314. [12] a. bousselmi, a. gharsallah, and t. p. vuong, "a novel high-gain quad-band antenna with amc metasurface for satellite positioning systems," engineering, technology & applied science research, vol. 9, no. 5, pp. 4581–4585, oct. 2019, https://doi.org/10.48084/etasr.2933. [13] s. r. thummaluru and r. k. chaudhary, "reducing the rcs of mimo antenna using angularly stable fss," in 2019 ursi asia-pacific radio science conference (ap-rasc), new delhi, india, mar. 2019, pp. 1–4, https://doi.org/10.23919/ursiap-rasc.2019.8738419. [14] a. ramachandran, s. valiyaveettil pushpakaran, m. pezholil, and v. kesavath, "a four-port mimo antenna using concentric square-ring patches loaded with csrr for high isolation," ieee antennas and wireless propagation letters, vol. 15, pp. 1196–1199, 2016, https://doi.org/10.1109/lawp.2015.2499322. [15] x. zhao and s. riaz, "a dual-band frequency reconfigurable mimo patch-slot antenna based on reconfigurable microstrip feedline," ieee access, vol. 6, pp. 41450–41457, 2018, https://doi.org/10.1109/ access.2018.2858442. [16] a. reddaf, f. djerfaf, k. ferroudji, m. boudjerda, k. hamdi-chérif, and i. bouchachi, "design of dual-band antenna using an optimized complementary split ring resonator," applied physics a, vol. 125, no. 3, p. 186, oct. 2019, https://doi.org/10.1007/s00339-019-2483-2. [17] d. samantaray, s. bhattacharyya, and k. v. srinivas, "a modified fractal-shaped slotted patch antenna with defected ground using metasurface for dual band applications," international journal of rf and microwave computer-aided engineering, vol. 29, no. 12, 2019, art. no. e21932, https://doi.org/10.1002/mmce.21932. [18] h. zhang, d. chen, y. yu, c. zhao, and g. tian, "a novel compact microstrip antenna with an embedded λ/4 resonator," international journal of antennas and propagation, vol. 2019, p. e2431760, dec. 2019, https://doi.org/10.1155/2019/2431760. engineering, technology & applied science research vol. 12, no. 2, 2022, 8382-8387 8387 www.etasr.com bora et al.: the design of closed square rr loaded 2-port mimo for dual band applications [19] r. anitha, v. p. sarin, p. mohanan, and k. vasudevan, "enhanced isolation with defected ground structure in mimo antenna," electronics letters, vol. 50, no. 24, pp. 1784–1786, 2014, https://doi.org/10.1049/ el.2014.2795. 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[23] c. a. balanis, antenna theory: analysis and design, 3rd ed. hoboken, nj, usa: wiley, 2005. microsoft word 03-pylarinos.doc etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 63-69 63 www.etasr.com pylarinos et al: investigation of lc waveforms recorded in a coastal hv substation investigation of leakage current waveforms recorded in a coastal high voltage substation d. pylarinos dept of ece university of patras greece dpylarinos@yahoo.com k. siderakis dept of ee tei of crete greece e. pyrgioti dept of ece university of patras greece e. thalassinakis assistant director p.p.c. greece i. vitellas director p.p.c. greece abstract— leakage current monitoring is a widely employed technique to monitor the performance of outdoor insulation. the investigation of leakage current waveforms offers significant information since the waveforms’ shape has been well correlated with different types of surface activity. field waveforms are not often considered and investigated due to technical difficulties and the long term monitoring required for recording activity portraying waveforms. therefore, the basic stages of activity have been defined mostly through accelerated lab tests. however, lab tests do not reproduce exact field conditions and therefore field activity may differ from the one recorded in the lab. in this paper, an investigation of lc waveforms recorded in a heavily polluted site, over more than 6 years of monitoring, is presented. a large variety of waveform shapes are portrayed and various correlations with world experience are made. in addition, recorded data is also investigated in order to identify field related noise. the need for added categorization criteria in the case of field measurements is discussed. keywordsfield; insulator; leakage current; noise; waveform; monitoring; pollution; i. introduction one of the main problems concerning outdoor insulation is the pollution phenomenon, which is rather intense in areas located near the sea. leakage current (lc) monitoring is a widely employed tool, used to monitor and investigate surface activity and insulation’s performance. contamination combined with wetting, in the case of ceramic insulators, results to the formation of a conductive film on the insulator’s surface, which permits the flow of leakage current which in turn can result to the formation of dry bands, arcing and eventually flashover [1]. polymer insulators and coatings are used as an improvement to ceramic insulators because of their hydrophobic surface which results to the formation of water droplets on the surface, instead of a film [2-5]. however, hydrophobicity is suppressed and recovered due to aging and the environmental and electrical stress applied [2, 3]. therefore, activity similar to the one recorded on ceramic insulators, is recorded on polymer insulators during hydrophobicity loss periods. leakage current waveforms portraying different stages of activity have been described by various researchers. a detailed review can be found in [6]. the basic discrete stages of activity consists of resistive sinusoid waveforms due to the presence of a conductive film on the insulator surface, distorted sinusoid waveforms as an intermediate stage and dry band arcing that causes a time lag of current onset. pulses have been reported to superimpose on lc and the appearance of such pulses has been correlated with corona discharges and short arcing [6]. recorded waveforms however do not always correspond clearly to a certain stage. this may not be reported in accelerated lab tests, but becomes evident in case of field lc waveform monitoring [7]. in the field, activity is not straight forward, surface conductivity may change rapidly or gradually, different parts of the insulator may be subjected to different conditions and surface condition may also vary from part to part. all these factors result to a variety of complex waveforms. in this paper, an investigation of lc waveforms recorded in a heavily polluted site over a significant time period, that exceeds 6 years, is presented. a large variety of waveform shapes are portrayed and various correlations with world experience are made. rcorded data is also investigated in order to identify field related noise. ii. experimental set up the lc measurements under investigation have been performed in the 150 kv linoperamata transmission substation which is located in heraklion, crete right next to the sea coast [8], and therefore suffers intense marine pollution. the waveforms investigated and presented in this paper are recorded on 150kv post insulators (porcelain, composite and porcelain coated with rtv sir) which are part of the grid. no distinction is made in this paper regarding the material of the insulator. the measurement of leakage current is acquired by inserting a collection ring and a hall sensor in the lc path. the acquired data are transmitted to a central data acquisition system (das). the waveform portraying the highest lc peak value in a user-defined time window is recorded [9]. each waveform has time duration of 480ms. custom-made software was developed to manage lc waveforms [10]. the measuring system is shown in figure 1. specifications of the monitoring system are shown in table 1. etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 63-69 64 www.etasr.com pylarinos et al: investigation of lc waveforms recorded in a coastal hv substation table i. specifications of the monitoring system leakage current inputs number of channels: 9 x current inputs input measuring range: 2 ranges ±500 ma and 3a peak sensor packaging: weatherproof metal enclosure safety features: galvanically isolated up to 6kv resolution: 350ua / 2ma signal acquisition resolution: 12 bit or 0.05% of full scale overall accuracy at 25°: 0.5% of full scale sampling rate: 2 khz continuously sampling methods: all channels sampled continuously & simultaneously other communication: rs232 communication speed: 56k baud packaging: metal enclosure time stamping: battery backed real time clock storage device: on-board flash memory base unit dimensions: 175 x 290 x 370 mm weight: 15 kg ac power supply: 110/230 vac, 50/60 hz (with dip/sag ride through capability) power usage: 30 va dc power input: 12 vdc (no dip ride through capability) operating system: microsoft windows 95/nt4+ data representation: graphical + ascii format fig. 1. the measuring system: 1. the collection ring 2. the hall sensor 3. the das iii. investigation of field lc waveforms leakage current waveform monitoring has been performed by various researchers both in lab and field and a detailed review of measuring and analyzing lc on insulators and specimens can be found in [6]. as a general rule, it is reported that as activity advances, the amplitude of the leakage current increases and that initial activity (resistive sinusoid current) is usually rather small. in the field, pollution, stress and surface condition vary with location (different parts of the insulator) and also with time. therefore, further investigation is performed in order to get an exact image of the activity experienced in the field and the resulting lc waveforms. a. sinusoid waveforms typical sinusoid waveforms recorded are shown in figure 2. the vast majority of the sinusoid waveforms recorded, portrayed small amplitude (under 2ma) similar to the one shown in figure 2a. however the amplitude range varies due to its dependence on the electric resistance of the conductive film on the insulator’s surface. because of this, sinusoid waveforms of amplitude much higher than usually reported [6] have been recorded in the considered site, due to heavy pollution and the high voltage stress applied. the amplitude of the largest recorded sinusoid (figure 2d) slightly exceeds 29ma. b. distorted sinusoid waveforms a large variety of distorted sinusoid waveforms have been recorded and some typical waveforms are illustrated in figure 3. no correlation could be established between waveform amplitude and type of distortion. distorted waveforms of large amplitude have also been recorded. the amplitude of the largest recorded distorted sinusoid (figure 3d) slightly exceeds 49ma. c. dry band arcing formation of a dry band results to a large part of the voltage applied on the band and arcing occurs when the surrounding air of the dry band cannot withstand that voltage. the resulting waveform illustrates a time lag of current onset and higher lc peaks as shown in figure 4. investigation of the waveforms showed that arcs can extinct gradually (figure 4a) or rapidly (figure 4d), and also ignite gradually (figure 4d) or rapidly (figure 4c). arcs can be distinct (figure 4c and figure 4d) or consequent (figure 4e). the amplitude of an arc can exhibit gradual increase and decrease before its extinction (figure 4a, figure 4b, figure 4e). finally arc duration can exceed the length of the time window (figure 4f). d. pulses pulses are recorded superimposed on various waveform types, as illustrated in figure 5. pulses have been recorded superimposed on waveforms portraying null activity (figure 5a), sinusoid and distorted sinusoid waveforms (figure 5b5k) and they can appear in the same waveform with a dry band arc-like discharge (figure 5i, figure 5k). the frequency of pulses’ appearance varies and pulses can appear on consequent half cycles (figure 5c, figure 5f, figure 5g), on consequent cycles in the negative of positive part (figure 5d, figure 5e, figure 5k) or on non-adjacent cycles (figure 5b). the amplitude of pulses also varies. the smallest pulse recorded portrays a peak value of about 5ma, while pulses in the area of 100ma have also been recorded (figure 5c, figure 5e). the size of pulses compared to the amplitude of the waveforms that are superimposed to, also varies. pulses can illustrate comparable (figure 5f, figure 5g, figure 5h, figure 5i, figure 5k), noticeably larger (figure 5b, figure 5d) or exceptionally larger amplitude than the rest of the waveform (figure 5a, figure 5c, figure 5e). the position of pulses is always at the peak of half-cycles, but sometimes exhibit a small shift to the right (figure 5f, figure 5h, figure 5i, figure5k), remaining however at the crest of the waveform. the duration of pulses also varies, and pulses may appear narrow (figure 5e, figure 5f, figure 5h) or broad (figure 5a, figure 5b). both narrow and broad pulses can appear in the same waveform in different cycles (figure 5c, figure 5i, figure 5k). the orientation of pulses also varies, and waveforms that portray mainly positive (figure 5b, figure 5c, figure 5g, figure 5i, figure 5k) or negative pulses (figure 5d, figure 5e) have been recorded. some or all of these behaviours can co-exist in etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 63-69 65 www.etasr.com pylarinos et al: investigation of lc waveforms recorded in a coastal hv substation the same waveform (figure 5c, figure 5g, figure 5h, figure 5i, figure 5k). even isolated pulses have been recorded (figure 5a). e. complexity of field lc waveforms’ shape the waveform shape does not always safely correlate to one of the basic stages. different types of activity can be present on the same waveform, exhibiting similar amplitude but different shape. in addition the transition sequence between different types of activity can vary. figures 6a-6f and figures 7a-7f are presented to better illustrate the complexity that can be recorded in field waveforms. fig. 2. sinusoid waveforms portraying a. low amplitude b. rapid conductivity increase c. gradual conductivity increase d. large amplitude fig. 3. a-b. distorted sinusoids, c. distorted sinusoid portraying conductivity increase d. the largest recorded distorted sinusoid fig. 4. waveforms portraying dry band arcing etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 63-69 66 www.etasr.com pylarinos et al: investigation of lc waveforms recorded in a coastal hv substation fig. 5. pulses superimposed on the waveforms’ crest fig. 6. various leakage current waveforms fig. 7. various leakage current waveforms etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 63-69 67 www.etasr.com pylarinos et al: investigation of lc waveforms recorded in a coastal hv substation iv. field noise limited access, long term monitoring and field conditions result to a variety of noise related waveforms. investigation of the recorded waveforms lead to the identification of three different types of noise: typical noise, dysfunction generated noise and single point noise [9]. typical noise (noise which is always present) consists of random minor peaks that exhibit amplitude in the range of 1ma, as illustrated in figure 8a and figure 8b. that means that measurements in the typical noise area are usually incoherent and that, since meagre or no activity is the usual case, a large number of typical noise waveforms are recorded [9]. single point noise results to a single point recorded far from the rest of the waveform. such single points are found superimposed on all types of waveforms (figures 8c-8f), even those portraying typical noise (figure 8c) and dry band arcing (figure 8f). such points do not always follow the current trend as shown in figure 8d and figure 8e. a large amount of dysfunction generated waveforms has been recorded and some typical waveforms are shown in figures 9a-9f. their origin cannot be strictly defined, since monitored insulators are part of the grid and any crucial event happening on the grid (e.g. switching, faults etc) could lead to a temporary chaotic lc measurement as the ones shown in figure 9. it should be noted that two sensor faults occurred during the monitoring time. the sensors were replaced shortly after their damage. however, dysfunction generated waveforms have been recorded on all channels, even those that didn’t suffer from a sensor fault, and during different time periods. it is not unusual for normal waveforms to be recorded shortly after the recording of a dysfunction generated waveform, frequently at the very next time window. fig. 8. a-b. typical noise c-f. single point noise fig. 9. dysfunction generated noise etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 63-69 68 www.etasr.com pylarinos et al: investigation of lc waveforms recorded in a coastal hv substation v. discussion & future work a large variety of lc waveform shapes and several parameters influencing the waveform shape have been recorded and investigated. several waveform shapes have been presented in order to highlight certain attributes such as: • the portrayed noise generated waveforms hints that a field reduction/removal stage should be designed to cope with the noise problem. a possible solution for this problem has been proposed by the authors in [9]. • sinusoid waveforms that portray gradual and rapid amplitude changes have been recorded (figure 2b-2c), reflecting the changes in surface film’s conductivity, which in turn can be gradual or rapid. this should be expected in field measurements where the insulator is subjected to field conditions and should be considered if differential current values are calculated in order to detect arcing as in [11]. • in the case of distorted waveforms, rapid transitions between different distortion types and amplitudes have been recorded, as shown in figure 3c. it should be mentioned that no distinct correlation could be established between waveform amplitude and type of distortion. such changes may be attributed to chemical changes in the pollutant layer as described in [12] or to hydrophobicity class changes as described in [13]. • the appearance of pulses has been correlated with the severity of the test conditions, the existence of high saltdensity fog, short strong discharges and corona discharges [6]. however, it should be noted that the waveforms shown in this papers hints that yet undefined conditions seem to favour either positive or negative pulses. • the existence of complex waveforms hints that further categorization of lc waveforms may be necessary in the case of field measurements. it has been proposed in [14] that the duration of the activity can be used to further categorize waveforms, and that seems to be the next logical step. such a criterion can be used to categorize waveforms as e.g. intense or short discharges based on whether the activity exceeds an arbitrary selected number of half-cycles. however, investigation of field waveforms in this paper shows that discrimination between e.g. a heavily distorted half-cycle and a discharge portraying half-cycle may be difficult and therefore an added criterion should be applied for that discrimination. vi. conclusion the measurement of leakage current is a well established technique, employed worldwide in order to monitor and investigate surface activity and field performance of high voltage insulators. in this paper, an investigation of lc waveforms recorded over a significant time period, in a coastal transmission substation is performed. the insulators monitored are part of the grid, installed in the 150 kv side of the substation, suffering from intense marine pollution. investigation of the recorded waveforms verified the basic waveform shapes described in the literature. however, several new attributes of such waveforms are reported and discussed in this paper. it is shown that further categorization could prove necessary in the case of long term field measurements. references [1] cigre sc 33 tf 33.04.01, “polluted insulators: a review of current knowledge”, technical brochure no158, 2000 [2] n. yoshimura, s. kumagai, s. nishimura, “electrical and environmental aging of silicone rubber used in outdoor insulation”, ieee trans. dielectr. electrical insulat., vol. 6, no. 5, pp. 632–650, 1999 [3] h. hillborg, u. w. gedde, “hydrophobicity changes in silicone rubbers”, ieee trans. dielectr. electrical insulat., vol. 6, no. 5, pp. 703–717, 1999 [4] k. siderakis, d. agoris, “performance of rtv silicone rubber coatings installed in coastal systems”, electr. power syst. res., vol. 78, no. 2, pp. 248-254, 2008 [5] k. siderakis, d. pylarinos, e. thalassinakis, i. vitellas, e. pyrgioti, “pollution maintenance techniques in coastal high voltage installations”, eng. technol. appl. sci. res., vol. 1, no. 1, pp. 1-7, 2011 [6] d. pylarinos, k. siderakis, e. pyrgiot, “measuring and analyzing leakage current for outdoor insulators and specimens”, rev. adv. mater. sci., vol. 29, no. 11, 2011 [7] d. pylarinos, k. siderakis, e. pyrgioti, e. thalassinakis, i. vitellas, “monitoring leakage current waveforms in the field”, demsee 5th international conference and technical exhibit on deregulated electricity market issues in south-eastern europe, sitia, greece, 2010 [8] d. pylarinos, k. siderakis, e. thalassinakis, i. vitellas, e. pyrgioti, “recording and managing field leakage waveforms in crete installation, measurement, software development and signal processing”, ieee 16th international conference on intelligent system application to power systems, hersonissos, greece, 2011 [9] d. pylarinos, k. siderakis, e. pyrgioti, e. thalassinakis, i. vitellas, “impact of noise related waveforms on long term field leakage current measurements”, ieee trans. dielectr. electr. insul., vol. 18, no. 1, pp. 122-129, 2011 [10] d. pylarinos, “a custom-made matlab based software to manage leakage current waveforms”, eng. technol. appl. sci. res., vol. 1, no. 2, pp. 36-42, 2011. [11] m. otsubo, t. hashiguchi, c. honda, o. takenouchi, t. sakoda, y. hashimoto, “evaluation of insulation performance of polymeric surface using a novel separation technique of leakage current”, ieee trans. dielectr. electrical insulat, vol. 10, no. 6, pp. 1053 – 1060, 2003 [12] waluyo, p. m. pakpahan, suwarno, m.a. djauhari, “study on leakage current waveforms of porcelain insulator due to various artificial pollutants”, world academy of science, engineering and technology, vol. 32, pp. 293 – 298, 2007 [13] m. a. r. m. fernando, s. m. gubanski, “leakage current patterns on contaminated polymeric surfaces”, ieee trans. dielectr. electrical insulat., vol. 69, no. 5, pp. 688–694, 1999 [14] m. sato, a. nakajima, t. komukai, t. oyamada, “spectral analysis of leakage current on contaminated insulators by auto regressive method”, conference on electrical insulation and dielectric phenomena, annual report, pp. 64 – 66, 1998 authors profile dionisios pylarinos was born in athens in 1981. he received a diploma degree in electrical and computer engineering from the university of patras in 2007. presently he is with the high voltage laboratory of the department of electrical and computer engineering at the university of patras. he has worked as a scientific consultant for ppc. his research interests include outdoor insulation, electrical discharges, signal processing and pattern recognition. kiriakos siderakis was born in heraklion in 1976. he received a diploma degree in electrical and computer engineering in 2000 and the ph.d. degree in 2006 from the university of patras. presently, he is an application etasr engineering, technology & applied science research vol. 1, �o. 3, 2011, 63-69 69 www.etasr.com pylarinos et al: investigation of lc waveforms recorded in a coastal hv substation professor at the department of electrical engineering, at the technological educational institute of crete. his research interests include outdoor insulation, electrical discharges, high voltage measurements and high voltage equipment diagnostics and reliability. eleftheria pyrgioti was born in 1958 in greece. she received her diploma degree in electrical engineering from patras university in 1981 and the ph.d. degree from the same university in 1991. she is an assistant professor at the department of electrical and computer engineering at the university of patras. her research activity is directed to high voltage, lightning protection, insulation coordination and distributed generation. emmanuel thalassinakis received the diploma in electrical and mechanical engineering and also the ph.d. degree from the national technical university of athens. after working for the ministry of the environment, in 1991 he joined the public power corporation (p.p.c.) where he is now assistant director of the islands network operations department. isidoros vitellas was born in 1954 in greece. he has a diploma in electrical engineering and the ph.d. degree in the same field. he is currently director of the islands network operations department in p.p.c. (public power corporation) athens, greece. microsoft word etasr_v12_n3_pp8791-8795 engineering, technology & applied science research vol. 12, no. 4, 2022, 8791-8795 8791 www.etasr.com usha & mahesh: monitoring and analysis of agricultural field parameters in order to increase crop … monitoring and analysis of agricultural field parameters in order to increase crop yield through a colored object tracking robot, image processing, and iot s. m. usha electronics and communication engineering jss academy of technical education bengaluru, india ushasm@jssateb.ac.in h. b. mahesh computer science engineering pes university bengaluru, india hbmahesh@pes.edu received: 29 april 2022 | revised: 9 may 2022 | accepted:15 may 2022 abstract-adequately watering plants is a challenging task. over and under-watering may harm plants and seeds, as excess or restraint watering reduces crop production and yield. this study presents a method to remotely monitor and efficiently water agricultural fields to increase crop production by utilizing advanced technologies such as internet things, robotics, image processing, and neural networks. accurate smoothing and image segmentation techniques were employed to study the plants' conditions. color median, gaussian, and hybrid median filters were employed to preprocess the data before segmentation and classification. the hybrid median filter and multilevel luminance grading system were employed to increase the quality of the image. the k-means clustering approach was used for image segmentation. the signal-to-noise ratios of the original and recreated images were compared and analyzed. keywords-image clustering; hybrid median image smoothing; iot; robotics; agricultural applications i. introduction throughout most of history, farmers used to water plants manually through canals. it is not easy to analyze the amount of manual required drenching, and water the plants to their exact need. βoth overand inadequate watering may lead to the degradation of crop production and reduce crop yield. the current work is a combination of robotics, internet of things (iot), and image processing to reduce the manual effort of the farmers and provide an optimal solution to agricultural field watering. this work was designed for an arduino board, fitted with different types of sensing and processing units. the motor driver l293d was interfaced with the arduino board to control a water pump. the robot's movements were controlled using the opencv software. the built-in camera captures images and processes them using gaussian, median, and hybrid median filters to improve their quality. k-means clustering segmentation was used for image segmentation. the objective was to give farmers the ability to analyze remotely the soil conditions and drench the appropriate amount of water depending on soil and plant conditions. this work is more accurate than similar studies. it utilizes three filter stages for image smoothing and k-clustering for image segmentation. ii. related work a prototype fuzzy rule-based irrigation controller that helps farmers save water by providing an ideal watering environment was demonstrated in [1, 2]. two control units were designed, a wireless sensor and a wireless information processing unit. the wireless sensor unit determined the climate and clay constraints. during summer the water evaporation in soil increases [3, 4]. based on weather and soil conditions, the sensor detects the water level and sends a signal to the controller. the wireless information processing unit analyzed the information received from the sensor regarding the water level conditions [5, 6]. based on the obtained parameters, it enables the actuator devices to supply the plants with the required amount of water. the results showed that it reduced the water loss by 27% and increased the yield by 40%. due to the scarcity of water, different kinds of diseases can be noticed in various plants. in [7, 8], the leaf disease of the guava plant was analyzed using the dcnn framework. in [9, 10] the soil and weather-related features were determined by analyzing various types of soil conditions. various sensors were used to examine the quality and conditions of various soil types. this study also defined soil suitability for various crops and analyzed the crop production, irrigation, and soil type and condition. accurate information for the farmers regarding the soil and water conditions was presented in [11, 12]. various water monitoring and conservation techniques were presented in [13-17]. iii. system design the system model consists of the functional blocks shown in figure 1. initially, real-time videos are acquired through the device's built-in camera. image smoothing is carried out using median, gaussian, and hybrid median filters. the region of corresponding author: s. m. usha engineering, technology & applied science research vol. 12, no. 4, 2022, 8791-8795 8792 www.etasr.com usha & mahesh: monitoring and analysis of agricultural field parameters in order to increase crop … interest is captured and image segmentation is performed. after the segmentation, the edges are detected and the contours are identified. soil moisture, temperature, and humidity are monitored, and finally, plants are appropriately watered by the robot vehicle control. fig. 1. block diagram of the proposed work. a. image smoothing image filtering and smoothing techniques improve an image's quality by removing noise. gaussian filter reduces the salt and pepper noise. noise can be appropriately minimized by keeping the image's edges through median filtering [18]. the brightness of the pixel can be enhanced through median filtering. figure 2 shows a leaf image before and after applying the median filter. in hybrid-filter, images can be extended symmetrically in horizontal and vertical directions. additional columns can be added to the left and the right and additional rows can be added at the bottom and the top. due to this adaptability in image size, this filter is more suitable for fastmoving image smoothing. the block diagram shown in figure 1 of [19] depicts the hybrid median filter used to recover the image. impulse noise is added to the input image. then, the hybrid median filter is applied to the noisy image and effectively eliminates the impulse noise. fig. 2. images before and after applying the median filter. in the hybrid median filter, the original pixel values are considered to frame + and x-shaped sub-neighborhoods. the first ranking stage is created by considering the + and x subneighborhoods. the second stage is created by taking the pixels from the first stage and the original pixel. the new pixel value is determined using the median values from the subneighborhoods and the original pixel. this filter removes the impulse noise effectively and preserves the edges. the hybridmedian filter performs three-stage operations on pixels to preserve the edges better than the median filter [19]. the calculated median values were: • median of horizontal and vertical pixels (mhvp) • median of diagonal pixels (mdp) • centre pixel (cp) for an n×n matrix, considering n=5, the output pixel is the median of {mhvp, mdp, cp}. noise is removed using a gaussian filter. gaussian smoothing has a similar effect to the median filter in smoothing a picture. the standard deviation determines the degree of smoothing as shown in (1) and (2). low-pass filtering suppresses high-frequency noise while maintaining the lowfrequency elements of an image. the gaussian filter output is shown in figure 3. ���� � � √� � � � ��� (1) ���, �� � � � � � ��� �����/�� � � (2) fig. 3. ιmage before and after applying the gaussian filter. b. creating binary mask image the pixels in the region of interest (roi) are set to logic 1 and the remaining pixels of the image are set to logic 0. c. image thresholding and k-means clustering segmentation segmentation of a captured image is the process of breaking it down into its constituent parts using edge detection, threshold processing, areas-based segmentation, and other techniques. a simple picture segmentation approach is image thresholding. this approach divides foreground from background pixels when converting a greyscale or color image to a binary. the threshold values are compared with the pixel values. logic 0 is set for the pixels which exceed the cut-off value. if the pixel value falls below the cut-off, then it is set as the logic high value. the k-means unsupervised clustering algorithm was used to classify the dataset. the following steps define the k-means set of rules. figure 4 shows the flowchart representation of the k-means clustering algorithm. engineering, technology & applied science research vol. 12, no. 4, 2022, 8791-8795 8793 www.etasr.com usha & mahesh: monitoring and analysis of agricultural field parameters in order to increase crop … fig. 4. flow chart showing the k-means algorithm d. color detection, extraction, and grid formation color is extremely important in image processing. each image made up of an m×n pixel array is split into m rows and n columns. the red, green, and blue values of each pixel are unique. the rgb colors are identified using thresholds. the intended color of the image is identified using the color recognition process. figure 5 shows grid formation and robot vehicle control. the user controls the motion of the robot by creating a 3×3 grid matrix. the robot's movement in different directions such as right, left, top, and bottom is controlled by sending commands. fig. 5. color detection, extraction, grid formation, and robot vehicle control. e. edge detection and contour finding edge detection and contour finding were conducted using opencv and python. as shown in figure 6, many dots with the same color are joined to form a curve. the different shapes formed are triangle, rectangle, and square by drawing curves, which joins the subsequent points. the following steps are used to identify the shape: • create a grayscale version of the image. • make a binary representation of the image. • determine the contour. fig. 6. edge detection and contour finding. f. monitoring parameters parameters such as soil, weather, temperature, humidity, and moisture level of the soil are sensed by different sensors. the sensors capture the data and send them to the data processing units. the image smoothing filter is applied to the captured images and then they are segmented and analyzed properly. iv. experiment and analysis the camera records a photograph which is a point of reference for the specified user interface. the robot moves forward, backward, left, and right according to the obtained instructions. the movements of the robot are recorded and stored in memory by connecting a wifi module to the arduino board. the required object is tracked from the captured image. if the object is red, the robot is moved accordingly in the grid. the block diagram shown in figure 7 explains the procedure to find the number of clusters. fig. 7. the process of finding the clusters. the procedure for the experimental analysis is shown in figure 9. figure 8 depicts the number of clusters versus the wcss list. as shown in the bar graph below, as the number of clusters increases, the sum of squares decreases. fig. 8. number of clusters vs wcss_list. engineering, technology & applied science research vol. 12, no. 4, 2022, 8791-8795 8794 www.etasr.com usha & mahesh: monitoring and analysis of agricultural field parameters in order to increase crop … the implementation of the prototype model is shown in figure 10. in this prototype model, the image is captured using the webcam of a laptop. the region of interest is selected and red color is identified. the grid is formed to control the movements of the robot. the chosen parameters are monitored and analyzed. fig. 9. flow chart of the experimental procedure. fig. 10. prototype implementation. v. result discussion and comparison the obtained results were analyzed. the captured image signal-to-noise ratio was 30.12db and the noisy image's snr was 12.3db. after passing the noisy image through the median filter, the obtained snr was 27.7db. the output of the median filter was applied to the hybrid median smoothing filter. the snr of the hybrid-median filter was 29.999db. the snr of the original and the final processed image were approximately the same. these results were compared with [18]. table i shows the comparison of snr of the original with the filtered images. the snr of the proposed method was 99.59%, whereas the snr of the previous work was 98.78%. this method improved the snr value compared to the previous work. the snr values are graphically represented in figure 11. table i. snr comparison of original with filtered image parameters snr in db [18] current paper captured /original image 20.1408 30.12 noisy image 13.4343 12.3 median smoothing filter 19.1523 27.7 hybrid median filter (hmf) smoothing 19.8964 29.999 percentage increase 98.78 % 99.59% fig. 11. signal to noise ratio of the proposed method. vi. conclusion an irrigation system using iot and robotics completes the prototype design. in this work, robotics, iot, and image processing are utilized. the designed robot is user-friendly and data from different units can be accessed with less delay in real-time. in the image smoothing process, the picture is passed through a median filter, a gaussian filter, and a hybrid-median filter to remove noise and improve its quality. the raw captured image was filtered by a median filter since it smoothens the image without blurring it. a hybrid-median filter removes effectively the impulse noise, keeps corner features, and does not delete outer boundary lines. the snr of the captured image was compared with the snr of the noisy image, median smoothing, and hybrid-median smoothing. the snr of the captured, noisy, median, and hybrid-median smoothing images was 30.12, 12.3, 27.7, and 29.999 respectively. the snr of the proposed method was 99.59%, while the snr of [18] was 98.78%. these results indicate that the proposed method is a feasible alternative for practical applications including picture restoration, medical image deengineering, technology & applied science research vol. 12, no. 4, 2022, 8791-8795 8795 www.etasr.com usha & mahesh: monitoring and analysis of agricultural field parameters in order to increase crop … speckling, and image enhancement. the k-means clustering algorithm was employed since it gives a better result in terms of accuracy as compared to traditional methods. the proposed method offers a viable solution to problems associated with agricultural applications. acknowledgments the authosr would like to acknowledge the jss academy of technical education for providing the lab support to carry out this research. references [1] s. murawwat, a. qureshi, s. ahmad, and y. shahid, "weed detection using svms," engineering, technology & applied science 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[19] m. r. rakesh, b. ajeya, and a. r. mohan, "hybrid median filter for impulse noise removal of an image in image restoration," international journal of advanced research in electrical, electronics and instrumentation engineering, vol. 2, no. 10, pp. 5117–5124, oct. 2013. microsoft word proposal_etasr_mlch-ed.doc etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 182-189 182 www.etasr.com chew et al: a decision-analytic feasibility study of upgrading machinery at a tools workshop a decision-analytic feasibility study of upgrading machinery at a tools workshop m. l. chew hernández dept. of grad. studies and research tech. of high studies of coacalco méxico city, méxico mchew@tesco.edu.mx e. k. velázquez hernández dept. of industrial engineering tech. of high studies of chalco chalco, méxico ing.evelazquez@yahoo.com.mx s. león dominguez dept. of industrial engineering tech. of high studies of chalco chalco, méxico chavalol@msn.com abstract— this paper presents the evaluation, from a decision analysis point of view, of the feasibility of upgrading machinery at an existing metal-forming workshop. the integral decision analysis (ida) methodology is applied to clarify the decision and develop a decision model. one of the key advantages of the ida is its careful selection of the problem frame, allowing a correct problem definition. while following most of the original ida methodology, an addition to this methodology is proposed in this work, that of using the strategic means-ends objective +etwork as a backbone for the development of the decision model. the constructed decision model uses influence diagrams to include factual operator and vendor expertise, simulation to evaluate the alternatives and a utility function to take into account the risk attitude of the decision maker. three alternatives are considered: base (no modification), c+c (installing an automatic lathe) and cf (installation of an automatic milling machine). the results are presented as a graph showing zones in which a particular alternative should be selected. the results show the potential of ida to tackle technical decisions that are otherwise approached without the due care. keywords-decision analysis; equipment replacement; integral decision analysis; maximum expected utility i. introduction this work presents a study of the feasibility of the inclusion of automated equipment into an existing metal manufacturing workshop located near méxico city. the feasibility analysis is approached from a decision analysis (da) perspective. da is a discipline which aims to bring clarity, insight and definition to messy decision situations [1-3], and has been viewed as a mixture of systems analysis and decision theory [1]. it´s usage for decision making guarantees the satisfaction of a set of desiderata (axioms) of rational choice [4]. in the context of da, several methodologies for problem analysis have been proposed, as is the case of the proact [5], the integral decision analysis (ida) [2] and value focused thinking (vft) [6]; similar methodologies are discussed in [7]. these methodologies aim to convert an initially blurry situation (in which the stakeholders don´t know exactly which consequences they care about or what can be done), into a structured decision model, in which alternatives and objectives have been clearly defined and measured [7]. the ida consists of the following steps: 1) problem framing; 2) analysis of objectives; 3) creation of alternatives; 4) identifying uncertainties; 5) decision modeling; 6) alternative evaluation; 7) alternative selection and 8) implementation. a distinct feature of the ida is its careful determination of the decision frame, involving the creation of several frames of different sizes and emphases, using a graphic tool called diagram of decision frames. there is a vast body of work related to the problem of finding an optimal replacement policy of industrial machinery [8-17]. a more complicated problem arises when incorporating the effects of technological change [18-20], inflation and taxes [21], a limited budget [22], imperfect repairs [23-24] or warranties from the equipment supplier [25-27]. other researchers have approached the problem through fuzzy models [28-29] or treated the replacement of several equipments [3132]. the consideration of several objectives can be found in [33-39] while the introduction of risk attitude is shown in [40]. the decision treated here is whether or not to include new equipment at a workshop, and it can be considered equivalent to the problem of determining a policy of equipment replacement. however, the above mentioned research starts with a problem that is already structured, that is, objectives and alternative courses of action are taken as a given. related to this, a four-step method for selecting a model for a replacement problem is shown by fraser and posey [41] while hart and cook [42] propose a systematic approach to the decision process with stages of objective identification, indicators of achievement, alternatives and problems of implementation. these methodologies, however, do not treat problem framing explicitly and don´t take advantage of any of the wellestablished tools of the da discipline. by contrast, in a real life situation, once the idea of replacing equipment comes to mind, the engineer should proceed to carefully define a decision frame for the situation, so relevant objectives and alternatives are uncovered. these steps are omitted in the previous works and are presented here, as they are part of the ida methodology. also, in this work, etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 182-189 183 www.etasr.com chew et al: a decision-analytic feasibility study of upgrading machinery at a tools workshop relevant uncertain knowledge from the plant engineers and vendors are expressed as subjective probabilities and incorporated to the model. in this respect, except for arueti and okrent [39], none of the previous authors explicitly use subjective probabilities in the decision. finally, while this work follows the original ida methodology for the most part, the ida methodology is here expanded by adding the usage of the strategic meansobjectives network as a map for decision-model building. to the best of our knowledge, there are no reports of the application of the ida, or other da methodology with a similarly careful procedure for problem framing, to an industrial equipment replacement problem. ii. problem statement the workshop under study is located near the town of chalco, méxico. it produces several types of iron and steel tools: manual and bench drills, vises, clamps, etc. its customers are mainly local carpenters and the nearby wood furniture industry. the main concern of the manager is a perceived low efficiency in the processing of bench vises, which happens to be the top seller product of the company. one proposal for improving this situation is to substitute old equipment with modern one, thus allowing operation with fewer workers and an increased productivity, as the modern machinery is more automated. several issues need to be settled so the problem can be modeled correctly 1. the metric over which the modifications should be evaluated: it can be productivity, production costs or profits. the adequate metric depends on the manager’s objectives. 2. the modifications that are to be considered when evaluating each proposal (i.e. are changes in inventory or layout to be considered in the decision?) 3. are there any uncertainties that should be considered in the model? if so, the stakeholder´s dislike of uncertainty should be introduced in the model. in the following we apply the ida steps to the problem, showing how it helps to clarify the decision. all shown tables and figures are the authors’ own production. iii. development and results a. problem framing in order to define a decision frame (what to decide and with which objectives), several frames should be explored. this can be conveniently done using a frames diagram. the construction of this diagram starts with the base frame, which represents the current understanding of the decision situation, and then several other frames are defined by changing the amplitude and emphasis of the base frame. figure 1 shows a decision frames diagram, whose parts are explained below. base frame: the trigger of the decision is the idea of automating the manufacture process, thus this frame is stated as: deciding the automation of the manufacture process. it comprises the decision of whether or not to automate, and the type and size of the new machines. its objective is to maximize the plant productivity. +arrow frames e1 and e2: the decision frame e1 is deciding the degree and extent of the automation and e2 is deciding the equipment provider. the objective of e1 is to maximize productivity and that of e2 is to minimize the time and costs involved in fixing possible equipment failures. wide frame a1: deciding about improving the manufacture process contains the base frame plus other alternatives, like modifications of inventory, staff, policies of inspection and outsourcing. the objective of this frame is to maximize product quality and to minimize costs. frames b1, b2, b3, b4 and b5: these frames are contained into a1, so their amplitude is similar to that of the base frame but their emphases are different: b1 emphasizes layout, b2 inspection, b3 staff, b4 inventory and b5 outsourcing. the objectives of b1-b5 are means of the objective of a1, related to the scope of each frame. fig. 1 diagram of decision frames wide frames a2 and a3: these frames shift the focus to different aspects of plant operation. a3 is decide about raw material procurement and a2 is decide marketing and a4. deciding about mid and long term company operation a) raw material providers b) improvements of manufactures process c) marketing and distribution d) new products and installations a3. deciding raw material provider a1. deciding about improving manufacture process a) automation decisions b) layout c) inspection d) staff decisions e) inventory f) outsourcing a2. decide about marketing and distribution a) distribution channels b) sales policies c) promotions, warranties b1. deciding workshop layout modify the machines layout and facility location. b2. deciding product inspection policies a) sampling policies b) type and frequency of inspections b3. staff decisions a) number of workers/ supervisors b) training of the workers/ supervisors base. deciding the automation of the manufacture process a) degree and extent of the automation b) provider of technology b4. inventory decisions modify the number and type of parts at the warehouses e2. deciding the provider of the automation technology national or foreign provider, distance to nearest offices etc. e1. decide the degree and extent of the automation a)degree: total or partial reduction of the number of workers b) extension: total or partial automation of the process b5. outsourcing decisions parts of the process to be outsourced etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 182-189 184 www.etasr.com chew et al: a decision-analytic feasibility study of upgrading machinery at a tools workshop distribution policies. the objectives of a3 are to minimize purchase costs, maximize availability and quality of raw material while those of a2 are to maximize sales and minimize marketing and distribution costs. wide frame a4: a4 is the widest frame to consider, including frames a1, a2 and a3 plus additional decisions, like the installation of more workshops and new product development. a4 objective is to maximize profits. once the decision frames diagram is complete, the generated frames are analyzed. a key element of our problem is that we haven´t decided whether or not to automate the process, and the automation will proceed only if it has a reasonable chance of generating economic benefits. thus we discard the narrow frames e1 and e2, as these assume that it has been decided to automate the process. the objective of the base frame is to increase productivity. while automating the process may increase productivity, the costs of the new equipment may outbalance the economic benefits of that increase. this would be an unacceptable scenario for the stakeholders, so the objective of the base frame is inadequate, as it doesn´t refer to costs. frame a1 objective (maximize quality and minimize costs) is more appropriate than the objective of the base frame. however, not all the decisions of a1 are to be considered in the present problem: we are not allowed to change inventory, inspection or outsourcing. by pruning the decisions of a1, we produce the frame a1* which has the same objective of a1 but only decisions in the context of our problem (figure 2). a1* is not yet adequate, as the decisions should be assessed by their economic implications and a1* has the objective of maximizing quality and minimizing costs. a4 has the adequate objective (maximize profits) but the decisions included in it are too wide. we thus define a4*, eliminating the decisions of a4, not included in a1*. the decision frame to be used a4*, shown in figure 3. fig. 2 reduced diagram of decision frames b3. staff decisions a) number of workers/ supervisors b) training of the workers/ supervisors b1. deciding workshop layout modify the machine, warehouse and general facility location. base. deciding the automation of the manufacture process a) degree and extent of the automation b) provider of automation technology a4* deciding about increasing plant profitability a) decision about automation b) decision about layout c) decisions about staff fig. 3 final decision frame b. objective analysis the first stage of the clarification of objectives is their identification [6]. to do so we begin with a “wish list” that provides the following 19 objectives 1. maximize profits 2. minimize total costs 3. maximize incomes 4. maximize sales 5. maximize product quality 6. minimize the number of jobs that need re-work 7. maximize productivity 8. minimize process times 9. minimize transport time 10. minimize delivery times 11. minimize raw material waste 12. optimize facility lay-out 13. minimize required man-hours 14. minimize inventory costs 15. minimize inspection cost 16. maximize market share 17. maximize competitiveness of company 18. maximize skill of work force 19. minimize delays in product delivery one of the most important steps in a da approach to problem solving, is to understand the relationships among the identified objectives. the objectives that are important by themselves are called fundamental objectives, and are organized into a hierarchy shown in figure 4. the objectives of the wish list that are not fundamental should either be a3. deciding raw material providers a4. deciding about mid and long term company operation a) raw material providers b) improvements of manufactures process c) marketing and distribution d) new products and installations a1* deciding about improvements of the manufacture process a) decision about automation b) decision about layout d) decisions about a2. decide about marketing and distribution a) distribution channels b) sales policies c) promotions, warranties b3. staff decisions a) number of workers/ supervisors b) training of the workers/ supervisors base. deciding the automation of the manufacture process a) degree and extent of the automation b) provider b1. deciding workshop layout modify the machine, warehouse and facility location. etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 182-189 185 www.etasr.com chew et al: a decision-analytic feasibility study of upgrading machinery at a tools workshop equivalent to a fundamental objective, or be a mean to accomplish one. in this latter is true they are called means objectives and are structured in the mean-end objectives network of figure 5. fig. 4 hierarchy of fundamental objectives min. number of reworks max profits raw material process distribution equipment min costs min. penalties max. sales max income inventory min. waste min. manhours min. inventory costs min. delays in deliveries max. quality min. process and transport times min. inspection costs max. productivity max. market share min. number of workers fig, 5 mean-ends objective network automate process min. number of reworks max profits raw material process distribution equipment min costs min. penalties max. sales max income inventory min. waste min. manhours min. inventory costs min. delays in deliveries max. quality min. process and transport times min. inspection costs max. productivity max. market share min. number of workers fig 6. alternatives and mean-ends objectives network c. alternatives the means-ends objective network is useful for generating alternatives; however, in this case the class of alternatives to be considered has already been identified by the framing process. the alternative “automating the process” implies either the introduction of automated machines that substitute the workers in a part of the process or changing the existing machines for new automated ones that require less supervision or fewer workers. this alternative implies purchase, installation, start up and maintenance costs, and, potentially, costs of worker training. to indentify all effects of this alternative on the objectives, we locate the alternative to the right of the mean-ends objective network and draw arrows to the objectives affected (figure 6) once the general class of alternatives has been set, the following three concrete alternatives are defined for further consideration 1. c+c: introduce an automatic lathe. 2. cf: introduce an automatic milling machine. 3. base: keep using the current machinery d. analysis of uncertain events the main uncertainties to be considered can be identified from the means-ends objective network of figure 6. the decision should be valued by its economic implications, so we´ll need to model the arrow paths that go from “automate process” to “max. profits”. the arrow between “max. productivity” and “max. sales” and that between “min. process and transport times” and “max. productivity” inventory raw material process distribution equipment min costs gas electricity staff min. penalties max. sales max income max profits etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 182-189 186 www.etasr.com chew et al: a decision-analytic feasibility study of upgrading machinery at a tools workshop represent uncertain relations. while the latter may be dealt with by a simulation model, for the former we will likely have to rely on subjective probabilities from the vendor staff. e. decision modeling as the decision should be justified economically, it should be evaluated by its effect on profits profits=income−cost (1) income equals the number of tools (vises) sold 'v (vises/day) times the selling price of each vise pv ($/vise). income='v×pv (2) if 'm is the size of the vise market (the maximum number that can be absorbed by the market on a daily basis) and 'prod the daily production then 'v=min('m , 'prod). the expertise of the company vendors can be used to construct the following contingency table of 'v. table i. example of contingency table for 'v �m probability of nm,k �v nm.1 p(nm,1) nm,1 nm.2 p(nm,2) nm,2 : : : nm.i p(nm,i) nm,i nm.i+1 p(nm,i+1) 'prod : : : nm.n p(nm,n) 'prod being nm,i such that nm,i < 'prod<nm,i+1. the daily costs for each automation option are ( ) ma'e'matprod eq eq ccc' v c cost ++×+ × =         360 (3) where ceq and veq are respectively the total cost and the life span (in years) of the new equipment, cmat and ce' are the raw material and energy costs of manufacturing one vise. cma' is the daily staff cost and depends on the number of workers nt and the daily wage swork ($/day-worker) cma' = nt× swork (4) if the process is automated, the required number of workers changes, whereas both the automation and number of workers affect the productivity. these relations are uncertain and are modeled as follows: for an automation option, let 'prod,max be the maximum achievable daily productivity. using the expertise of the plant engineers, a contingency table is elicited, in which different levels of 'prod are defined as fractions of 'prod,max. the table shows, for the relevant automation option, the probability of the 'prod levels conditional on the number of workers. the structure of such a table is shown in table 2, for a high (nt, high), medium (nt, med) or low (nt, low) number of workers. table ii. example of conditional probabilities of 'prod for a choice of machinery upgrade +umber of workers nt,low nt,med nt,high 0.8×'prod,max --- 0.9×'prod,max ---'prod 'prod,max --- the actual values of nt,low , nt,med and nt,high depend on which automation choice is being considered. as summary, an influence diagram of the model is shown in figure 7. in this diagram rectangles represent decisions; ovals mean uncertain variables and double-bordered ovals stand for deterministic calculations. the value of 'prod,max is obtained by simulating the system for the proposed automation choice. finally, the risk attitude of the company is introduced by translating the profits into a utility using an exponential risk averse function (5)         − −= r profitprofit u 0 exp1 (5) fig. 7. influence diagram for profits profit 0 is the minimum profit that can happen and r is the risk tolerance. the alternative to be selected is the one that has the maximum expected utility [43]. f. assessment of alternatives the manufacture of vises, as currently done, is shown in figure 8. the name of the operation, the tag of the equipment used, and the mean time (minutes) of the operation are also shown, while the name of each vise part is shown in the arrowlike shapes at the left. to calculate the maximum number of vises produced daily, arena [44] simulation models of the original and modified systems were set up. the model of the cnc option is produced by substituting the lathes (1-m, 2-m, 3-m, 5-m and 7-m) by a single one that processes each part in half the time [45]. the cf option is modeled by taking out the existing milling machines of the model (5-f, 4-f and 3-f) and introducing a single one that can process the parts twice as fast as the formers [46]. the simulated maximum number of vises per day is shown in table 3. it is interesting to note that the cnc option did not increase the productivity, as did the cf option. this is because the ¿automate? nprod,max nprod nt nm nv cost profits etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 182-189 187 www.etasr.com chew et al: a decision-analytic feasibility study of upgrading machinery at a tools workshop lathes are not an important bottleneck in the process. probabilities of 'prod and 'v, elicited from the plant engineers and vendors, respectively, are shown in tables 4-7. table iii. simulated 'prod,max for choice of automation base c+c cf 'prod,max 10 10 15 table iv. conditional probabilities of 'prod for base case +umber of workers 10 12 14 0.6×'prod,max 0.5 0.2 0.1 0.8×'prod,max 0.4 0.6 0.1 'prod 'prod,max 0.1 0.2 0.8 table v. conditional probabilities of 'prod for upgrade choice “cnc” +umber of workers 6 8 10 0.6×'prod,max 0.2 0.0 0.0 0.8×'prod,max 0.3 0.3 0.1 'prod 'prod,max 0.5 0.7 0.9 table vi. conditional probabilities of 'prod for upgrade choice “cf” +umber of workers 8 10 12 0.6×'prod,max 0.5 0.2 0.1 0.8×'prod,max 0.4 0.6 0.3 'prod 'prod,max 0.1 0.2 0.6 table vii. probability of vise market level �m probability 6 0.2 9 0.3 12 0.4 15 0.1 the values of pv, (cmat + ce'), swork and veq are respectively $1000, $300, $100 and 15 years. the risk tolerance (r) was evaluated as $3000, using the method in [3]. g. selection of alternatives the results are shown in figure 9, which is a graph over possible values of equipment cost per day (ceq/360×veq) for the cnc and cf alternatives. the graph shows zones in which the decision should be “cnc”, “cf” or leave the system as it is (“base”). for example, if the cost per day of the cnc is $700 or more and that of cf is more than $600, the best choice is to leave the system as it is, while if both the cnc and cf cost $400, then the best choice is cnc. fig. 8 vise processing clamp s lathe 1-m (4:21) bore (2:24) (2) (2) send to fusing clean (2:50) joint body rail (8:49) mill 3-f (3:55) broach 1-b (4:36) bore 1-3t; 1-5t (2:87) cut 1-s (2:55) bore 1-3t, 1-5t (2:59) notch 1-ph (1:09) bore 1-tr;2-tr (8:13) 3 step-drilling 1-tr; 2-tr (13:25) lathe and polish 3-m; 5-m;7-m (1:94) forge 2nd ball 1-ph (1:08) joint polish 3-m; 5-m; 7-m (1:39) joint cut 1-s (0:23) forge 1rst ball 1-ph (1:05) head thread 1rst side 1-m (3:18) thread 2nd side 2-m (2:26) joint cut 1-s (0:27) groove 4-f (1:99) bore 1-5t; 1-3t (2:82) rotation base bore 1-5t,1-3t (2:10) polish 2-e (1:54) rotating disc clean (2:1) subjection handle cut 1-ph (0:06) forge 1rst side 1-ph (0:45) lathe 1-m (2:39) bore 1-5t, 1-3t (1:54) joint forge 2nd side 1-ph (0:60) polish 2-e (7:36) bore 1-3t; 1-5t (8:08) joint paint joint screw handle screw body rail joint joint subjection nut rectifying mill 5-f (6:56) polish (1:05) polish (1:05) polish (1:05) etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 182-189 188 www.etasr.com chew et al: a decision-analytic feasibility study of upgrading machinery at a tools workshop fig 9. feasibility zones for choices “cnc”, “cf” and “base” iv. conclusions and further work from the application shown here, it can be concluded that the ida, proposed by ley-borrás [2], is a valuable tool in the clarification and structuring of real life engineering problems. by following its steps, it guarantees that the correct decision is tackled and that the adequate objectives, risk attitude and factual information are included and modeled. it was also shown how two of the steps of the ida methodology (“alternatives” and “analysis of uncertain events”) can be improved by using the means-ends objectives network to identify the relations and uncertainties that should be modeled. thus, the means-ends objectives network provides a blueprint for the construction of the decision model. currently, the simulation model is being extended with probabilistic vise process times. also, a decision model that considers decisions about the layout of the workshop simultaneously with decisions of equipment replacement is being developed. v. references [1] r. a. howard, “decision analysis: practice and promise”, management science, vol. 34, no. 6, pp. 679-695, 1988 [2] r. ley borrás, integral decision analysis, decision consulting, 2009 [3] r. t clemen, making hard decisions: an introduction to decision analysis, duxbury press, 1996 [4] m. d. resnik, choices: an 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operations management, vol. 3, no. 3, pp. 149-154, 1983 [12] j. m. a. tanchoco, l. c. leung, “an input-output model for equipment replacement decisions”, engineering costs and production economics, vol. 11, no. 2, pp. 69-78, 1987 [13] n. ebrahimi, “two new replacement policies”, ieee transactions on reliability, vol. 42 , no. 1, pp. 141-147, 1993 [14] v. legát, a. h. žaludová, v. červenka, v. jurča, “contribution to optimization of preventive replacement”, reliability engineering & system safety, vol. 51, no. 3, pp. 259-266, 1996 [15] w. g. sullivan, t. n. mcdonald, e. m. van aken, “equipment replacement decisions and lean manufacturing”, robotics and computer-integrated manufacturing, vol. 18, no. 3–4, pp. 255-265, 2002 [16] m. chen, c. -y. cheng, “sensitivity analysis for the optimal minimal repair/replacement policies under the framework of markov decision process”, ieee international conference on industrial engineering and engineering management, pp. 640 – 644, 2007 [17] x. cao, a. jouglet, d. nace, “a multi-period renewal equipment problem”, european journal of operational research, vol. 218, no. 3, pp. 838-846, 2012 [18] s. k. nair, w. j. hopp, “a model for equipment replacement due to technological obsolescence”, european journal of operational research, vol. 63, no. 2, pp. 207-221, 1992 [19] t. cheevaprawatdomrong, r. l. smith, “a paradox in equipment replacement under technological improvement”, operations research letters, vol. 31, no. 1, pp. 77-82, 2003 [20] i. e. schochetman, r. l. smith, “infinite horizon optimality criteria for equipment replacement under technological change”, operations research letters, vol. 35, no. 4, pp. 485-492, 2007 [21] e. e. karsak, e. tolga, “an overhaul-replacement model for equipment subject to technological change in an inflation-prone economy”, international journal of production economics, vol. 56–57, pp. 291301, 1998 [22] r. pascual, v. meruane, p. a. rey, “on the effect of downtime costs and budget constraint on preventive and replacement policies”, reliability engineering & system safety, vol. 93, no. 1, pp. 144-151, 2008 [23] f. i. d nodem, j. p. kenne, a. gharbi, “a replacement policy of deteriorating production systems subject to imperfect repairs”, 3rd ieee conference on industrial electronics and applications, iciea, pp. 611, 2008 [24] m. bartholomew-biggs, m. j. zuo, x. li, “modelling and optimizing sequential imperfect preventive maintenance”, reliability engineering & system safety, vol. 94, no. 1, pp. 53-62, 2009 [25] r. pascual, j. h. ortega, “optimal replacement and overhaul decisions with imperfect maintenance and warranty contracts”, reliability engineering & system safety, vol. 91, no. 2, pp. 241-248, 2006 [26] s. wu, p. longhurst, “optimising age-replacement and extended nonrenewing warranty policies in lifecycle costing”, international journal of production economics,vol. 130, no. 2, pp. 262-267, 2011 [27] y. pan, m. u. thomas, “repair and replacement decisions for warranted products under markov deterioration”, ieee transactions on reliability, vol. 59 , no. 2, pp. 368-373, 2010 [28] p. -t. chang, “fuzzy strategic replacement analysis”, european journal of operational research, vol. 160, no. 2, pp. 532-559, 2005 [29] p. v. suresh, d. chaudhuri, b. v. a. rao, “fuzzy-set approach to select maintenance strategies for multistate equipment”, ieee transactions on reliability, vol. 43 , no. 3, pp. 451-456, 1994 [30] j. c. hartman, “multiple asset replacement analysis under variable utilization and stochastic demand”, european journal of operational research, vol. 159, no. 1, pp. 145-165, 2004 [31] l. c. leung, j. m. a. tanchoco, “multiple machine replacement analysis”, engineering costs and production economics, vol. 20, no. 3, pp. 265-275, 1990 0 200 400 600 800 1000 0 200 400 600 800 1000 cnc cost ($/day) cf cost ($/day) cnc base cf etasr engineering, technology & applied science research vol. 2, �o. 2, 2012, 182-189 189 www.etasr.com chew et al: a decision-analytic feasibility study of upgrading machinery at a tools workshop [32] b. wang, d. liu, “rolling horizon procedure for large-scale equipment replacement problems with multiple alternatives”, control and decision conference (ccdc), pp. 2741-2746, 2011 [33] i. nosoohi, s. reza hejazi, “a multi-objective approach to simultaneous determination of spare part numbers and preventive replacement times” applied mathematical modelling,vol. 35, no. 3, pp. 1157-1166, 2011 [34] h. oeltjenbruns, w. j. kolarik, r. schnadt-kirschner, “strategic planning in manufacturing systems ahp application to an equipment replacement decision”, international journal of production economics, vol. 38, no. 2–3, pp. 189-197, 1995 [35] t. w. sloan, “green renewal: incorporating environmental factors in equipment replacement decisions under technological change”, journal of cleaner production, vol. 19, no. 2–3, pp. 173-186, 2011 [36] n. c. suresh, s. kaparthi, “flexible automation investments: a synthesis of two multi-objective modeling approaches”, computers & industrial engineering, vol. 22, no. 3, pp. 257-272, 1992 [37] w. a. sarache castro, o. d. castrillón, g. gonzales, a. viveros folleco, “a multi-criteria application for an equipment replacement decision”, ingeniería y desarrollo, vol. 25, pp. 80-98, 2009 [38] m. rausch, h. liao, “joint production and spare part inventory control strategy driven by condition based maintenance”, ieee transactions on reliability, vol. 59 , no. 3, pp. 507-516, 2010 [39] s. arueti, d. okrent, “a knowledge-based prototype for optimization of preventive maintenance scheduling”, reliability engineering & system safety, vol. 30, no. 1–3, pp. 93-114, 1990 [40] g. avila-godoy, a. brau, e. fernandez-gaucherand, “controlled markov chains with discounted risk-sensitive criteria: applications to machine replacement” proceedings of the 36th ieee conference on decision and control, vol. 2, pp. 1115-1120, 1997 [41] j. m. fraser, j. w. posey, “a framework for replacement analysis” european journal of operational research, vol. 40, no. 1, pp. 43-57, 1989 [42] d. t. hart, e. d. cook, “upgrade versus replacement: a practical guide to decision-making”, ieee transactions on industry applications, vol. 31 , no. 5, pp. 1136-1139, 1995 [43] r. l keeney, h. raiffa, decisions with multiple objectives: preference and value tradeoffs, john wiley and sons, 1998 [44] t. altiok, b. melamed, simulation modeling and analysis with arena, academic press, 2007 [45] v. martínez, modern industrial automation, alfaomega, 2001 [46] a. garcía, “automatic control in industry”, science and technology collection, vol. 48, universidad de castilla-la mancha. 2005 authors profile mario l. chew hernandez was born in méxico city, on july 27, 1975. he graduated as chemical engineer from the national university of méxico, and holds degrees of m. of sc. in process and project engineering and phd from the university of nottingham, united kingdom. he has worked at the mexican petroleum institute and is a full time researcher at the technological of high studies of coacalco. his main interests are applications of decision analysis to engineering problems. emma k. velázquez hernández was born in tlalmanalco, mexico, on june 4, 1977. she is an industrial engineer from the technological of high studies of chalco and a final year graduate student of industrial engineering. she has worked as a process engineer at a tool manufacturer for more that four years. her interests are application of simulation and decision analysis to improve productivity of the metal-machinery industries. salvador león domínguez was born in mexico city, on may 28, 1959. he is an industrial engineer from the national politechnic institute and a final year graduate student of industrial engineering. he has more than ten years of experience as process engineer at several manufacturing industries. he is currently a full time teacher at the technological of high studies of chalco. engineering, technology & applied science research vol. 7, no. 6, 2017, 2167-2170 2167 www.etasr.com khan et al.: development and experimental investigation on delay time consistency of modified … development and experimental investigation on delay time consistency of modified si/pbo/pb3o4/fg pyrotechnic delay composition azizullah khan school of chemical and material engineering national university of sciences and technology islamabad, pakistan aziz.phd@scme.nust.edu.pk zulfiqar h. lodhi school of chemical and material engineering national university of sciences and technology islamabad, pakistan abdul qadeer malik school of chemical and material engineering national university of sciences and technology islamabad, pakistan aqmalik@scme.nust.edu.pk abstract—in the present study, experimental investigation was carried out on the delay time consistency of modified si/pbo/pb3o4/fg pyrotechnic delay composition in a delay tube. where si is the fuel, pbo/pb3o4 are oxidizers and fish glue (fg) is the binder. ingredient mixing and loading pressure were studied. results revealed that homogenous mixing of the delay composition is a very critical parameter for controlling the time consistency of pyrotechnic delay composition. the delay time accuracy was improved from 25% to about 7.42% by ensuring homogenous mixing of the ingredients. results also show that loading pressure ranged from 30,000 to 65,000 psi did not affect much the delay time of this pyrotechnic composition and the burning rate. keywords-delay composition; loading pressure; time consistency; delay time; burning rate i. introduction pyrotechnic is a general term for a mixture that burns at a selected, reproducible rate, providing a predetermined time delay between ignition and delivery of main effects [1, 2]. the modern practice requires pyrotechnic delays to function very accurately. this has led to an intensive research into the mechanism and combustion control of both gas producing and gasless pyrotechnic mixtures. moreover, it has narrowed the field of investigation to the relatively few combustible materials that can be considered. pyrotechnic compositions are mixtures of ingredients, which usually are not themselves explosive, and are designed to burn but not to detonate. typical burning rate of pyrotechnics can vary from below 1 mm/sec to over 1,000 mm/sec. they are commonly used as delay devices in sophisticated missile systems to provide the required delay time before performing certain functions and to detonate the warhead after the predetermined delay time. the end result of any weapon or missile system is greatly dependent on accurate and consistent delay time. propagation or burning of a pyrotechnic delay device depends on a number of factors such as confinement, particle size, fuel percentage, diameter, thickness, conductivity and geometry of the delay body, nature and ratio of ingredients, initial temperature, ambient temperature, ambient pressure, consolidation pressure, moisture, terminal charge, ignition composition, delay body material, storage condition, charge increment, additives, intimate contacts of ingredients etc. [3-8]. repeatability and accuracy of any pyrotechnic delay device depends on design and development of the pyrotechnic delay composition which in turn depends on mixing, ingredient particle size, grain size and type, internal diameter and length of the delay tube. the main problem in pyrotechnic delay compositions is the accuracy ranging from ±10% to ±20% of the average value over the normally military operating temperature of -40oc to + 60oc [10]. in some pyrotechnics the time delay increased up to 25% from mean at -54°c [11-13]. the main objectives of this research were: (i) the development of a modified fast pyrotechnic delay composition comprising si as fuel, pbo/pb3o4 as oxidizers and fish glue as a binder. (ii) the experimental investigation of the effects of mixing and loading pressure on delay time consistency of this pyrotechnic delay composition in a pyrotechnic delay device. ii. experimental part a. materials analytical grade fuel silicon powder and oxidizers lead (ii) oxide (pbo) and lead oxide pb3o4 purchased from sigma aldrich company and commercial grade fish glue binder were used during this research work. the purity of these ingredients was greater than 99%. the particle size of si, pbo and pb3o4 were ≤44 µm, 1~2 µm and < 10 µm respectively. distillation was used for the preparation of binder solution. b. preparation of pyrotechnic delay composition two methods were used for the preparation of the pyrotechnic delay composition. engineering, technology & applied science research vol. 7, no. 6, 2017, 2167-2170 2168 www.etasr.com khan et al.: development and experimental investigation on delay time consistency of modified … 1) (3-d) automatic tumbler mixing machine the different chemicals (fuels and oxidizer) were individually dried out in a heating oven at 80°c for two hours to remove the moisture. the required quantities of the different ingredients were weighed according to the required percentages and blended thoroughly. the ingredients were mixed in the 3-d automatic tumbler mixing machine for 3 hours. a binder solution of 0.3% fish glue was prepared in distilled water. the binder solution was mixed in the already mixed composition to form a homogenous paste by using the spatula in agate container. then the composition was semi dried in the drying oven at 80 °c. semi dried composition was broken in to lumps by spatula in an agate container carefully. the composition was passed carefully through -212 mesh sieves to get grain size of ≤ 65 µm. then the grains dried out for four hours at 80 °c to remove the water/moisture. the finished composition was stored in container and placed it in desiccator. 2) manual mixing mortar and pestle: the individual chemicals (fuels and oxidizer) were dried in a heating oven at 80°c for two hours to remove the moisture. the chemicals were weighted according to the required percentages. small batches of 5 gram were prepared and the chemicals were mixed in mortar and pestle for 30 minute to get homogenous mixture. then a binder solution of 0.3% fish glue was prepared in distilled water. the binder solution was mixed in the already mixed composition to form the homogenous paste by using spatula in agate container. then the composition (paste) semi dried in the drying oven at 80 °c. the semi dried composition was broken into lumps by spatula in an agate container carefully. the composition passed carefully through -212 mesh sieves by using haver test shaker eml 200 to get grain size of ≤ 65 µm. [14, 15]. then the grains dried for eight hours at 80 °c to remove the water/moisture. the finished composition was stored in container and placed in desiccator for 24 hours to become stable. 3) safety during manual preparation of delay composition: this delay composition is very sensitive to friction, especially during manual mixing/grinding of the ingredients in the mortar and pestle and at the time of grain formation when the composition is passed through a particular sieve to get the desired grain size. the following safety precautions are very essential in order to avoid injuries:  ensure the exposure of minimum number of operators during processing steps  as this is a manual process, the quantity of pyrotechnic composition for each batch was kept to 5 grams in order to minimize the risks.  use specially designed mortar and pestle  use bullet proof screen while dry mixing the composition  use goggle and gloves while handling and preparing the composition 4) filling of delay body: stainless steel delay elements were made by drilling 0.157 inch diameter holes through stainless steel rods. the tube length was kept at 0.787 inches. the finished composition was then loaded into stainless steel delay tube in five equal increments. each increment was accurately weighted separately and pressed in a delay tube one by one. the surface of the delay column was kept flushed with the end of the delay tube. excess delay composition was removed by sliding the end of the delay tube. a hydraulic press machine installed with a calibrated gauge was used to consolidate the delay composition in the delay tube. at compaction loads from 10,000 to 65,000 psi, the pyrotechnic mixture ignited and burned in a satisfactory manner. consequently, for most of the tubes prepared in this way, the pressure was set at approximately 30,000 psi. a dwell time of about 2 s was used before relieving the stress. a mechanically initiate percussion assembled in the holder was then installed in the delay tube. a rubber o-ring was used to prevent the composition from environmental effect. the other end of the delay body was crimped. c. testing and measurement: the percussion cap was hit with a striking pin. the firing mechanism is an electromechanical switch. the delay time starts when the pin hits the percussion and stops when the light dependent resistor (sensor) detects the flame of the delay composition when it is completely burnt. in order to protect the senor from the slag a perspex disc was installed in front of it. the delay time was measured with a digital oscilloscope. channel 01 of the oscilloscope was connected with the firing switch and channel 02 was connected to the detector. a minimum of five measurements for each composition was kept. the mean delay time and mean burning rate were measured. maximum variation from mean and standard deviation were calculated. iii. results and discussion pbo/pb3o4/si/fg is a gasless delay mixture. the propagative burning of pressed column of this gasless delay composition is a combustion reaction in which pbo, pb3o4 and si react to give solid products. some of the heat produced during the chemical reactions is lost through the delay body to the surrounding and the remaining heat is transferred to the unreacted mixture through conduction that sustains propagation. the variation in the inner diameter and length of the delay tube was kept at minimum. the ingredients and the percentages used during preparation of this modified delay composition are shown in table i. table i. ingredients and their percentage s# ingredients percentage 1 silicon 18.0 2 pbo 21.0 3 pb3o4 60.7 4 fish glue 0.30 engineering, technology & applied science research vol. 7, no. 6, 2017, 2167-2170 2169 www.etasr.com khan et al.: development and experimental investigation on delay time consistency of modified … a. effect of ingredient mixing on delay time 1) test results of composition mixed in (3-d) automatic tumbler mixing machine the delay composition was prepared in a 3-d automatic tumbler mixing machine and then loaded in a delay tube of 0.157 in internal diameter. the length of the column was 0.787 in. the burning rate, delay time along with maximum variation in delay time and burning rate from mean are presented in table ii. all the tests were conducted at temperature range between 18~24 c°. results are summarized in table ii. as shown, the mean delay time and burning rate are 0.569 sec and 1.395 in/sec. the maximum variation in delay time and burning rate are 23% and 24.3% respectively. these variations in delay time and burning rate are very high. it means that the delay composition prepared in the 3-d automatic tumbler mixing machine did not produce consistent delay time. the reason could be the non-uniform mixing of the composition ingredients. table ii. test results of delay mixture mixed in (3-d) automatic tumbler mixing machine sample no delay time (sec) burning rate (inch/sec) 1 0.588 1.339 2 0.626 1.258 3 0.536 1.469 4 0.493 1.597 5 0.600 1.312 mean 0.569 1.395 max variation from mean 23% 24.3% the delay composition was then subjected to different loading pressures in the delay column in order to determine the effect of loading pressure on the delay composition in the delay tube. for this reason different loading pressures of 10,000, 12,000, 14,000, 20,000, 24,000 and 40,000 psi were applied to consolidate the composition in the delay column. pressing the delay composition in the column increases compaction and hence increases density. results in figure 1 show that the burning rate and hence the delay time was not much effected by changing the applied loading pressure. the maximum variation in delay time from mean at different loading pressures ranged from 15% to 25%. this variation in delay time though not very large is still very high considering our goal. the conclusion being that the time consistency of this delay mixture could not be achieved by varying the loading pressure. figure 2 also shows the mean delay time and mean burning rate at different loading pressures. the burning time and burning rate varied from 0.569 to 0.715 sec and 1.011 to 1.384 inch/sec respectively. the delay time and burning rate are inversely proportional to each other, when the delay time reduced the burning rate increased and vice versa. these results reveal that mixing through tumbler mixing machine is useful where large amounts are required to be prepared and where delay time consistency is not required. 2) test results of composition manually mixed in mortar and pestle. the ingredients of the pyrotechnic composition were mixed in mortar and pestle, the mixing procedure been discussed in section ii.b.2. the composition was then loaded in the delay body with internal diameter and length of 0.157 and 0.787 in respectively. the composition was then consolidated at 30,000 psi by using oil operated hydraulic press with calibrated pressure gauge. dwell time of two sec was applied for each increment. fig. 1. plot of maximum percent variation of delay time from mean against applied loading pressure fig. 2. plot of burning rate and delay time against applied loading pressure results in figures 3 and 4 show that, the variation in delay time of each sample range from 0.162% to 4.376%. results also show that burning rate of the delay mixture varies from 1.222 in/sec to 1.335 in/sec. the mean delay time and burning rate are 0.617 sec and 1.276 in/sec respectively. the standard deviation in delay time and burning rate are 1.316 and 0.0269 respectively. the maximum variation in delay time reduced from 25% to 8.75%. the intimate contact of the fuel and oxidizers resulted in the reduction in delay time variation. the intimate contact was ensured through manual dry mixing in mortar and pestle followed by wet mixing. additionally, the laboratory operating conditions i.e. controlling dry mixing time, wet mixing, drying time, stabilizing the composition for a specific time, controlling the weighing of the individual ingredients, controlling the weighing of delay composition, using calibrated measurement equipment were also ensured to be the same each time. homogeneity and intimate contacts of ingredients played a key role in time reproducibility of this pyrotechnic delay composition. intimate ingredient contact was ensured by dry mixing of fine and uniform particle sizes of the fuel and oxidizers followed by wet mixing with the binder solution. dry mixing of the ingredients is not a very safe engineering, technology & applied science research vol. 7, no. 6, 2017, 2167-2170 2170 www.etasr.com khan et al.: development and experimental investigation on delay time consistency of modified … method as compared to automatic mixing, therefore safety precautions were ensured during this critical operation. the composition was made slurry which was then stirred thoroughly to ensure even distribution of the fuel and oxidizers. the fuels and oxidizers have different densities and if binder is not used then the fuel and oxidizer separate due to their density difference. the main reason of adding fish glue as binder is to protect the fuel and oxidizer from environment effects such as humidity. binder also increases cohesion between particles of fuels and oxidizers to protect them from being segregated due to their density difference. the grains also provided ease of loading of the composition in the cartridge body. fig. 3. plot of percent variation of delay time from mean for each sample fig. 4. plot of burning rate and delay time for each sample 3) effect of loading pressure on delay composition (manually mixed in mortar and pestle) the data presented in table iii, show that the maximum variation in delay time is from 7.42% to 9.38% by varying the loading pressure from 20,000 to 65,000 psi. it means that if the composition is homogenously mixed, then this pyrotechnic delay composition is not much effected by the loading pressure and hence the burning rate is relatively insensitive to loading pressure. for varying loading pressure from 20,000 to 65,000 psi, only about 2% variation in mean delay time was recorded. results in table iii also show that even at 65,000 psi, the composition did not become insensitive, ignited by the standard percussion primer and functioned successfully. iv. conclusions the result analysis showed that ingredient mixing along with thorough controlling of the laboratory operating conditions are critical parameters for controlling the delay time variation and burning rate of pyrotechnic delay composition in a delay device provided that the variation in internal bore size and length of the delay tube is controlled. the manual mixing is much better than mixing in automatic tumbler mixer because the tumbler mixer did not produce intimate contact of the ingredients. the delay time and burning rate of this pyrotechnic delay composition was not much effected by the varying of the loading pressure. only about 2% variation in mean delay time was recorded when the loading pressure varied from 30,000 to 65,000 psi. these experimental results can be applied as design guidelines for the developing of any pyrotechnic delay composition. table iii. test results of delay time at different loading pressures s # mean delay time (sec) maximum % variation in delay time mean burring rate (inch/sec) loading pressure (psi) 1 0.635 8.66 1.240 20000 2 0.629 9.38 1.252 24000 3 0.617 8.75 1.276 30000 4 0.634 7.42 1.242 60000 5 0.618 7.93 1.274 65000 references [1] j. c. poret, a. p. shaw, c. m. csernica, k. d. oyler, j. a. vanatta, g. chen, “versatile boron carbide-based energetic time delay composition”, acs sustainable chemisrty and engineering, vol.1, no. 10, pp.1313-1338, 2013 [2] h. ren, q. jiao, s. c chen, “mixing si and carbon nanotubes by a method of ball-milling and its application to pyrotechnic delay composition”, journal of physics and chemistry of solids, vol. 71, no. 2, pp. 145–148, 2010 [3] a. bailey, s. g. murray, explosives, propellants and pyrotechnics, brassey's: putnam aeronautical, 1988 [4] c. g. morgan, c. rimmington, production of pyrotechnic delay composition, us patent 0314397 a1, 2009 [5] j a. conkling, chemistry of pyrotechnics basic principles and theory, marcel dekker inc, new york, 1985 [6] l. kalombo, “evaluation of bi2o3 and sb6o13 as oxidants for silicon fuel in the delay detonators”, msc thesis, university of pretoria, 2008 [7] r. aube, delay composition and detonation delay device utilization, patent-us 0223242 a1, 2008 [8] b. j. kosanke, k. l. kosanke, “control of pyrotechnic burn rate”, second international symposium on fireworks, 1994 [9] y. li, y. ceng, y. l. hui, s. yan “the effect of ambient temperature and boron content on the burning rate of the b/pb3o4 delay compositions”, journal of energetic materials, vol. 28, no. 2, pp.77-84, 2010 [10] s. m danali, r. s. palaiah, k. c. raha, “developments in pyrotechnics”, defense science journal, vol. 60, no. 2, pp.152-158, 2010 [11] military specification, manganese delay composition, mil-m-21383a, 1976 [12] military specification, delay composition t-10, mil-d-85306a (as), 1991 [13] military specification, delay composition, tungsten-fluorocarbon copolymer, mil-d-82710(os), 1984 [14] operating instructions, haver test shaker eml 200-89 digital, 1993 [15] s. s. al-kazraji, g. j. rees, “the fast pyrotechnic reaction of silicon and red lead”, fuel, vol. 58, no. 2, pp. 139-143, 1979 engineering, technology & applied science research vol. 8, no. 1, 2018, 2546-2554 2546 www.etasr.com behshad and shekari: seismic performance evaluation of concrete gravity dams with penetrated … seismic performance evaluation of concrete gravity dams with penetrated cracks considering fluid– structure interaction amir behshad faculty of industry and mining yasouj university choram, iran a.behshad@mail.yu.ac.ir mohammad reza shekari department of civil engineering estahban higher education center estahban, iran shekari.2291@gmail.com abstract—in this paper, a comprehensive study on the seismic behavior of fractured concrete gravity dams during ground shakings is carried out considering dam–reservoir interaction effects. to gain the seismic behavior of the whole system, finite and boundary elements are employed to model the liquid region and the cracked structure, respectively. formulation and different computational aspects of the suggested staggered hybrid approach are thoroughly argued. a computer code was developed in order to discuss the presented hybrid be–de technique and comparisons are made between the obtained results and those reported in the literature. to gain this goal, several problems of seismic excitations in frequencyand timedomains are presented employing the proposed approach, showing that the present results agree well with the results from other numerical procedures. the cracked koyna dam is scrutinized, considering the dynamic interaction between dam and reservoir with focus on the nonlinear behavior due to its top profile crack. the developed numerical model is rigorously validated by extensive comparisons with available results in the literature in which the dam–reservoir interaction were simplified by added masses. it can be concluded that there is significant disparity between the overturning and sliding response schemes of the nonlinear analysis and those of added mass technique. keywords-seismic behavior; concrete gravity dams; boundary elements; distinct elements; dam–reservoir interaction i. introduction concrete gravity dams behave differently from other structures because of their size and their interactions with the reservoir and foundation. in fact, concrete gravity dams might have well cracked at their foundation or at a specific height caused by seasonal temperature variations, concrete shrinkage or earlier earthquakes. apart from those cracks with confined depth that exist on both the upstream and downstream faces and which will possibly develop subjected to static or dynamic conditions, some cracks may have expanded so much that they almost penetrate the monoliths. consequently, these existing cracks weaken the stability of concrete gravity dams principally due to the nonlinear behavior of sliding and overturning, during strong earthquakes. therefore, nonlinear response of cracked concrete gravity dams has been investigated by different techniques to study the propagation of cracks in this type of dams. a number of researches focused on the propagation of cracks in the dam, something that includes opening and closing of the cracks [1-3]. several researches have been conducted based on experiments, focusing mainly on the process of crack initiation and propagation [4-6]. on the other hand, little attempts have been made for the case in which cracks are expected to penetrate from upstream to downstream in non-overflow monoliths of the dam. in comparison with various researches concerning crack event and propagation in concrete gravity dams, little efforts have been done to demonstrate the seismic behavior of cracked concrete gravity dams. the overturning analysis of the koyna dam was first investigated by authors in [8] assuming no sliding of the top block, which was regarded as a rigid body, ignoring the interaction between the top and bottom blocks and adopting a horizontally penetrated crack. their results indicated that under these assumptions the top block remained stable and overturning of the top profile would not happen under future earthquake of similar magnitude. however, the top block is comparatively large, and the interaction between the two blocks may considerably affect their behavior. authors in [9] employed contact elements located at the dam–foundation interface in order to ascertain the seismic sliding and uplifting response of concrete gravity dam monoliths. authors in [10] scrutinized the frictional base sliding of concrete gravity dams subjected to seismic ground motion, in which the whole dam was modeled as a singledegree-of-freedom system. presented results indicate that the dam flexibility affects significantly the sliding displacement in the downstream direction. based on the single-degree-offreedom system criterion, authors in [11] developed an empirical formula for estimating the seismic induced slip of concrete gravity dams at the rock interface with finite-element analysis. employing finite element method (fem), authors in [12] calculated the base sliding of the gravity dams during ground excitation. results of their parametric study of typical gravity dams revealed how the earthquake-induced sliding is engineering, technology & applied science research vol. 8, no. 1, 2018, 2546-2554 2547 www.etasr.com behshad and shekari: seismic performance evaluation of concrete gravity dams with penetrated … affected by the characteristics of the ground motion and dam system. by using fem, authors in [13] investigated experimentally the friction model of concrete lift joint interfaces and applied the model to assess the static and dynamic behavior of concrete gravity dams. they simulated the contact conditions with gapfriction elements that are appropriate for the case of small displacement and concluded that the sliding displacement is reduced in multi-crack cases. using the continuous mass of liquid as lumped masses in the horizontal direction for the reservoir effects, authors in [14] investigated some important phenomena such as the jounce of the upper block of the fractured koyna dam in detail, by using the distinct element method (dem). afterwards, authors in [15] developed a rigid model with three-degrees-of-freedom considering sliding, rocking, rock-sliding, and drifting modes. they concluded that a large coefficient of friction does not surely prevent sliding, and rocking and drifting modes should be mainly considered in estimating the stability of cracked concrete gravity dams. employing rigid block models, authors in [16] suggested a convenient and simple tool to supply a conservative estimate of upper cracked block residual sliding displacements. authors in [17] inspected the stability of a gravity dam on jointed rock foundation and also the seismic stability of the upper part of the fractured konya dam using discontinuous deformation analysis (dda). authors in [1] examined the seismic response of pine flat dam with penetrated cracks using the finite element modeling technique but limited in scope to small deformation of the continuum. hydrodynamic interaction in dam–reservoir system is a significant aspect in seismic response of concrete gravity dams that may be taken into account by various numerical methods [18, 19]. a number of previous researches on the dynamic behavior of concrete gravity dams with penetrated cracks were performed considering the simplified added mass technique for reservoir effects [14, 16, 20]. in fact this technique, applying the results of rigid dam–incompressible fluid interaction, leads to approximate results in the seismic response of fractured concrete gravity dams. more authentic results may be achieved through the use of numerical methods, among which fem and bem (boundary element modeling) are most popular. to particularly perform the nonlinear dam analysis, due to the needs for iterative solutions and very short consecutive time steps, minor degrees of freedom for reservoir domain is a more proper way. besides, in the fem modeling of reservoir, a radiating condition (for instance, sommerfeld condition) should be employed to the far-field truncated boundary of reservoir to consider radiation damping. thanks to substantial characteristic of bem that is more felicitous for boundless domains, the technique is able to consider the radiating damping with much less additional attempt compared with the fem analysis of reservoir. consequently, the dynamic analysis of dam–reservoir system is achieved by employing the be equations governing the reservoir region coupled with the dam fe equations of motion as a straightforward approach for observation of the whole system behavior [21, 22]. using a hybrid de–be method, authors in [23] modeled the seismic behavior of the cracked koyna dam focusing on the upper profile crack. with the significant improvements of discontinuous media methods like dem, it becomes not very difficult to investigate the stability of fractured dams in destructive earthquakes. in this paper, dem is employed to assess the seismic response of the koyna dam with penetrated cracks subjected to earthquakes. this analysis method allows relative motion between elements, and is specifically appropriate for problems in which the relative motion between blocks contributes considerably to the general structure deformation. as a result, reservoir effects are accurately modeled by the use of bem, and then a coupled bem–dem algorithm is developed to analyze the seismic behavior of cracked gravity dams examining dam–reservoir interaction effect. ii. hybrid formulation a coupled numerical method which combines the distinct elements for the fractured concrete gravity dam and the boundary elements for the reservoir domain is developed in the time domain. a sketch of dam-reservoir system is exposed in figure 1. fig. 1. cracked dam scheme on rigid foundation. the following assumptions are considered in the formulation of governing equations:  seismic response analyses are carried out using the horizontal acceleration component.  the dynamic dam-foundation interaction is ignored.  the dam–reservoir system is analyzed under twodimensional (2d) condition.  the liquid in the reservoir is inviscid and compressible resulting in an irrotational flow with negligible amplitudes.  the nonlinear analysis of the dam is employed for the existing cracked zone and the linear elastic analysis is adopted for the deformable blοcks.  uplift pressures are disregarded in the cracked zone. a. bem formulation for the reservoir domain a short explanation of the reservoir bem follows. emphasis is principally devoted to the important aspects of the method, subjected to some modifications compared to previous works [24, 25]. these modifications may be remarked as: engineering, technology & applied science research vol. 8, no. 1, 2018, 2546-2554 2548 www.etasr.com behshad and shekari: seismic performance evaluation of concrete gravity dams with penetrated …  at the far away from the upstream face of the dam, the domain is left opened because the radiation boundary condition is automatically satisfied by employing the hankel fundamental solution as the most exact green’s function of boundless domains.  dynamic boundary conditions of the free surface gravitational waves and the bottom partial absorption are considered. for a compressible, irrotational and inviscid fluid, the governing equation of liquid motion is expressed by the wellknown helmholtz differential equation (1): 0 1 2 2 2 2     tc (1) in which,  is the velocity potential, and c denotes the acoustic wave velocity in fluid. considering harmonic ground motion, the velocity potential in the reservoir can be described in the frequency domain as φ(t) = φ(ω)exp(iωt), where ω represents the exciting frequency and φ(ω) the complex-valued frequency response function for the velocity potential. the boundary element method is used to solve the helmholtz equation with the following boundary conditions (see figure1): a) dynamic and kinematic boundary condition of the reservoir free surface (s4):      gn 2 (2) b) the boundary condition at the fluid–solid interface (s1): nan    (3) where n is the unit normal vector, an is the normal acceleration on the interface and ρ is the mass density of the fluid. c) the boundary condition at the foundation–reservoir interface (s2) for the reservoir bottom partial absorption:       c i n (4) in which, β=(ρbcb/ρc) is the acoustic impedance ratio of the foundation to reservoir water, ρb and ρ represent the mass densities of foundation material and water respectively, and cb represents the compression wave velocity of the foundation. d) and eventually, for the reservoir up stream radiation condition (s3) of acoustic waves, no additional discretization is required as elucidated above. the linearized bernoulli equation for pressure represents the hydrodynamic pressure acting on the dam system. p t      (5) employing the constant boundary element formulation, the following equations may be derived to solve the motion of liquid in discretized form [25]. hφ gq (6) where h and g stand for boundary element coefficient matrices for the potential vector φ and the flux vector q, respectively. the components of h and g coefficient matrices can be obtained as followings: ( ) 1 2 i i i ij i i s ii i i s ij i i s h q ds i j h q ds g φ ds             (7) in which si is the boundary of the ith constant element, and φi* and qi*denote the values of the fundamental solution φ*and q*at the ith constant element respectively. the fundamental solution φ* and its normal derivative q* are: (1) 0 (1) 1 ( ) 4 ( ) 4 * * * i φ h kr φ ik r q h kr n n         (8) in which r is the distance between the points on the boundary, i.e. source and field, h0(1) (kr) and h1(1)(kr) show the hankel functions of the first kind of order zero and of order one respectively, and n represents the outward normal to the boundary. discretized form of boundary element equations of the reservoir domain may be written and separated into the following expressions, according to three types of assumed boundary conditions:    , , . , , . w w w i b i w i b i b b                  φ q h h h φ g g g q φ q (9) where the subscripts w, i and b indicate the boundary nodes on the reservoir free surface, dam–reservoir interface and reservoir bottom surfaces, respectively. substituting (2) – (4) into (9) the following expression is obtained: -1 s s 2 , w w i b g i c       φ d g q d h g h g (10) inspection of (10) reveals that φ could be determined, since all sub-matrix components of d are known. engineering, technology & applied science research vol. 8, no. 1, 2018, 2546-2554 2549 www.etasr.com behshad and shekari: seismic performance evaluation of concrete gravity dams with penetrated … b. distinct element method the distinct (or discrete) element method (dem) has been exhaustively illustrated in many papers. this method was primarily proposed in [20] for the investigation of jointed and cracked rock masses. in this section, a brief review of some substantial aspects, especially those that would be subject to modification for their usage to the coupled dam–reservoir system, are reviewed. the openings are considered as interface boundary conditions between distinct blocks, and put into the problem domain according to their locations and orientations. the domain in dem is divided into polygonal blocks by joints and the blocks are supposed to be quite deformable. deformable blocks are discretized into a mesh of finite difference triangular elements in the dem program [26] for stress-strain analysis, whose formulation is similar to the socalled constant strain triangle (cst) finite element. failed contacts will be effaced and new contacts will be recognized and established when the block contact relationship varies. normal and shear springs and dashpots are placed between contact elements for simulating the interaction behavior of contact points of block elements (see figure 2). fig. 2. spring-dashpot contact model. the normal spring is linear-elastic in compression. zero tension in the normal direction of contacts is presumed in the normal springs for modeling penetrated cracks. when normal compressive forces attain zero, joints open and blocks separate at that point. as a result, the analogous contact will be deleted. the shear spring is specified as linear elastic–perfectly plastic and assumed to follow coulomb’s friction law. the stiffness damping forces regarding the normal and shear dashpots are linearly related to the corresponding normal and shear velocities of the blocks at contact. the linear coefficients may be supposed to be identical for both normal and shear dashpots. the increments of normal and tangential spring forces in each time step (δt) at the interfaces of blocks are found for updating the normal and shear contact spring forces at time (t+δt). to investigate the motion of each point in all the blocks newton’s second law is used which is resulted from the known forces acting on them. explicit time marching scheme is applied to solve the dynamic equilibrium equations, which by employing the central difference method the movement of the ith grid point can be described individually as ( / 2) ( / 2) ( / )t t t ti i xiu u f g t      (11) and ( / 2) ( / 2) (( / ) )t t t ti i yi iv v f g m t       (12) where mi is the lumped mass of the ith grid point and g is the ground acceleration. ( / 2)t tiu  and ( / 2)t tiv  indicate the horizontal and vertical velocity which may be used to attain the displacement components at the next time step as ( / 2) ( ) ( / 2)t t t t t i i iu u u t     (13) and ( / 2) ( ) ( / 2)t t t t t i i iv v v t     (14) the resultant forces fxi and fyi in (11) and (12) represent the summation of forces applied at the ith grid point including the resultant contact force if the grid point is on the boundary of the block, and the elastic forces owing to elastic deformation of the block. dynamic response is achieved by using an explicit time marching scheme, which is equal to that used by the explicit finite difference method for continuum analysis. this usually requires a sufficiently small time step to overcome numerical instabilities principally caused by disturbances propagation between adjacent discrete elements during a single step [20, 27]. c. hybrid bem–dem algorithm in present section, the proposed hybrid bem–dem algorithm is described. in order to consider the dam–reservoir interaction, the influence of the reservoir when the dam is subjected to ground excitation should be taken into account. this may be achieved by the assessment of hydrodynamic pressure at any instant of time t, by solving the fluid domain applying (10). in this equation, qs depends on the horizontal (ui) and vertical (vi) displacement components of the dam upstream face under water which are calculated by (13) and (14). the foregoing equations are, in turn, updated employing (11) and (12) in which, the resultant forces fxi and fyi are functions of hydrodynamic pressures caused by ground excitation at the dem grid points of the dam upstream face. to vanquish this problem, a staggering solution technique is used, in which at each time step (δt), both the hydrodynamic pressure and the dam displacement components are iterated concurrently till a desired level of convergence is attained. for displacement iterations in the staggering scheme, in all nodes of the dam upstream face, the convergence criterion is prescribed by the following norm:       j tt i j tt ij tt i u uu )( )( 1 )( (15) in which j shows the iteration number and ε is a small convergence tolerance value. thanks to intrinsic non-linear behavior of the whole system (i.e., hydrodynamic interaction problem coupled with cracked concrete dam) dynamic response, the most straightforward procedure may be engineering, technology & applied science research vol. 8, no. 1, 2018, 2546-2554 2550 www.etasr.com behshad and shekari: seismic performance evaluation of concrete gravity dams with penetrated … considered as the time domain analysis of bem–dem formulation. since the time domain analysis of be formulation is more intricate in comparison with the frequency domain formulation, the latter has been selected to construct the coupled formulation in the present research [25]. this frequency domain analysis (i.e., forward and inverse fourier transformations) is carried out for very short consecutive time steps of δt (e.g. 0.1s) of ground motion time history to permit the algorithm to follow the correct path of a non-linear phenomenon. it is gainful remarking that, as the maximum sliding displacement occurring does not exceed a couple of centimeters, no considerable errors may be resulted in the boundary elements whose lengths are of the order of several meters. in fact, the present method is an euler–lagrangian one, in which an eulerian and lagrangian formulation are applied for the reservoir and the cracked concrete gravity dam respectively. in this method, the cracked dam is explained in a lagrangian frame of reference, which deforms under the reservoir forces, while the eulerian reservoir mesh does not need re-meshing since the sliding displacements are very small. iii. benchmark examples for accuracy verification a program has been developed to implement the proposed algorithm. several numerical examples are scrutinized to determine the validity and accuracy of the proposed modeling technique. a. rigid dam example in this section, a rigid dam example with infinite reservoir whose depth (h) has a constant value of 180m is excited by ramp acceleration, in which the reservoir foundation is assumed to be rigid. in the analysis, the effects of surface waves are neglected, as in the exact analytical solution [29], which is employed for comparison. the time variation of hydrodynamic pressure on the dam–reservoir interface is acquired by the present algorithm considering both constant and linear boundary elements, and is shown in figure 3. fig. 3. comparison of hydrodynamic pressure acting on the base of the dam. in the figure, the dimensionless hydrodynamic pressure is given by /pc p ah , where a indicates the maximum value of the ramp acceleration and h is the height of the reservoir. b. flexible dam example a time history analysis for a flexible dam with infinite horizontal reservoir of 180 m in height, 15 m in width and a constant depth extending to infinity is carried out as the second verification example, using the 1940 el centro earthquake as input ground motion. the reservoir and the dam bottoms are assumed to be rigid, the sound velocity of reservoir c is 1440 m/s and the water is assumed to be compressible and inviscid with a mass density of 1000 kg/m3. figure 4 shows the time variation of hydrodynamic pressure at the base of the dam for the present study and the same fe-fe model in which, the reservoir is modeled by finite elements in the same method as the dam. one can judge by considering the figure, that the present algorithm gives good results in comparison with benchmark solution results. fig. 4. variation of hydrodynamic pressure at the bottom of the dam under el centro earthquake’s ground acceleration. iv. seismic analysis of fractured koyna dam koyna dam experienced a strong earthquake of 6.5 r magnitude on december 11, 1967. during the earthquake, the dam suffered severe damage encompassing horizontal cracks on both the upstream and downstream faces on a number of non-overflow monoliths. in this section, seismic analyses are carried out to observe the dynamic behavior of non-overflow monoliths of cracked koyna dam (figure 5) with a penetrated horizontal crack subjected to various ground motions. for this purpose, two real earthquake ground motions are selected: the 1967 koyna earthquake in the stream direction with a pga of 0.49g and the1994 newhall earthquake with a pga of 0.678g (figure 6). the material properties of the koyna dam concrete are: mass density = 2640 kg/m3, elastic modulus = 31.0 gpa, poisson ratio=0.2, tensile strength at crack surface = 0, dynamic friction angle = 45o and viscous damping ration=0.05. sound velocity of reservoir = 1440m/s, and wave reflection coefficient = 1.0. engineering, technology & applied science research vol. 8, no. 1, 2018, 2546-2554 2551 www.etasr.com behshad and shekari: seismic performance evaluation of concrete gravity dams with penetrated … fig. 5. details of fractured koyna dam with a penetrated horizontal crack from upstream to downstream, at its top profile. (a) (b) fig. 6. ground acceleration time histories of the earthquakes considered in this study: (a) 1967 koyna earthquake, (b) 1994 newhall earthquake figure 7 reveals the plots of time histories of hydrodynamic pressure acting at the bottom of the dam expressed as a ratio of the maximum hydrostatic pressures under above ground motions considering the shell structure to be rigid and/or flexible. it can be observed that the effect of dam flexibility on the hydrodynamic pressure is considerable and should be taken into account. the time variation of horizontal acceleration histories of both bottom and top block at the crack level is illustrated in figure 8. the time variation of horizontal acceleration histories of bottom block, top block at crack level and the top levels of the dam under foregoing ground motions is illustrated in figure and 9. it is observed that the peak value of bottom block’s acceleration due to koyna earthquake at the crack level is approximately 2.89 g which is about 5.9 times the value of the earthquake input, while the analogous acceleration of the top at the same level is a little smaller at 2.41 g. furthermore, the shape of the acceleration at the top of the dam is mostly different from those at the crack level while the peak value is approximate. similarly, due to newhall earthquake, the corresponding accelerations of bottom and top blocks at the crack level are 4.35 g and 3.62 g respectively. according to above results, the ground motion has been amplified about 5.4 and 5.88 times under koyna and newhall earthquakes respectively. figures 10 and 11 plot the horizontal and vertical displacement histories of the crest of the cracked koyna dam obtained by the present hybrid be–de method compared to the results of fe-de technique, in which, the positive values of the horizontal and vertical displacement are in the downstream and upward directions respectively. it is observed that there is no damage during the moderately small amplitude shaking. the first large horizontal displacement of the dam in the downstream direction based on present algorithm is 2.65 cm at 4.02 s due to koyna earthquake, while the corresponding value due to the other earthquake is 5.56 cm at 4.72 s. figure 12 shows the results of horizontal sliding of the top block under foregoing ground motions obtained by the two numerical coupling models. the figure denotes that the residual displacements calculated by using the present hybrid be–de approach due to koyna earthquake is 13.1mm, which is comparable to the residual displacement of fe–de analysis (12 mm). (a) 1967 koyna earthquake (b) 1994 newhall earthquake fig. 7. hydrodynamic pressure time histories at the dam bottom for different conditions under various ground motions engineering, technology & applied science research vol. 8, no. 1, 2018, 2546-2554 2552 www.etasr.com behshad and shekari: seismic performance evaluation of concrete gravity dams with penetrated … (a) bottom block at crack level (b) top block at crack level (c) top of the dam fig. 8. acceleration time histories at different positions under the 1967 koyna earthquake. similarly the corresponding displacement due to newhall earthquake is 20.3 mm for the present study and 18.4 mm for the fe–de model. although the present study results are in reasonable agreement with the results of fe-de model, details of the two plots are somehow different mainly because dam– reservoir interaction has been evaluated using fe analysis. time variation of upper block rotations of the cracked koyna dam under both ground motions is illustrated in figure 13. we observe that the upper block is safe against overturning, as the peak rotations of the top block are 0.0018 and 0.0026 under koyna and newhall earthquake records, respectively. (a) bottom block at crack level (b) top block at crack level (c) top of the dam fig. 9. acceleration time histories at different positions under the1994 newhall earthquake. v. conclusion a numerical method has been developed to analyze the seismic response of cracked concrete gravity dams placed on rigid foundation subjected to the excitation of horizontal seismic waves including dam–reservoir interaction effects. this is achieved by coupling dem, employed to model the cracked dam, and bem, used to analyze the dynamic behavior of the reservoir. in the proposed method, the two different media of cracked dam and reservoir are solved independently and coupling effects are taken into account through the propounded iterative scheme where equilibrium condition at the dam– reservoir interface is satisfied. the proposed hybrid dem– bem approach elucidated in this paper presents the following chief advantages in comparison with other numerical techniques accessible for seismic analysis: engineering, technology & applied science research vol. 8, no. 1, 2018, 2546-2554 2553 www.etasr.com behshad and shekari: seismic performance evaluation of concrete gravity dams with penetrated … (a) horizontal displacement (b) vertical displacement fig. 10. horizontal and vertical displacement time histories at the dam crest subjected to the 1967 koyna earthquake. (a) horizontal displacement (b) vertical displacement fig. 11. horizontal and vertical displacement time histories at the dam crest subjected to the1994 newhall earthquake. (a) 1967 koyna earthquake (b) 1994 newhall earthquake fig. 12. horizontal sliding of top block of the cracked koyna dam subjected to various ground motions. (a) 1967 koyna earthquake (b) 1994 newhall earthquake fig. 13. rotation of top block of the cracked koyna dam under various ground motions. engineering, technology & applied science research vol. 8, no. 1, 2018, 2546-2554 2554 www.etasr.com behshad and shekari: seismic performance evaluation of concrete gravity dams with penetrated … 1. due to the reduction of problem dimensions in bem, this numerical method performs the dynamic analysis with very small size of matrices of reservoir domain and considerably less computational efforts. 2. reservoir domain dimensions may be remarkably reduced as the far end of the infinite fluid domain is directly considered with no boundary elements. 3. dem is applied to model the fractured concrete gravity dam, which is widely employed for the investigation of blocky media. 4. a satisfying level of convergence is simply attained through a few iterations. several harmonic and transient excitation problems are examined employing the proposed method, and are compared with the results from other analytical solutions and numerical methods existing in the literature to appraise the accuracy and validity of the present method. result comparison shows that the present method works well. furthermore, considering dam–reservoir interaction effects, seismic performance of the koyna dam with a horizontal crack at a height has been evaluated. it can be concluded that the appropriate modeling of the dam– reservoir interaction is necessary in the seismic behavior of fractured gravity dams. considering the above, this method seems to be well adapted to handle more complex discontinuous fluid–structure domains involving finite and semi–infinite subdomains. of course, more parametric studies are proposed in order to calculate optimized time steps that may significantly improve the present algorithm. references [1] b. el-aidi, j. hall, j, “non-linear earthquake response of concrete gravity dams part 2: behaviour”, earthquake engineering and structural dynamics, vol. 18, no. 6, pp. 853–865, 1989 [2] s. s. bhattacharjee, p. leger, “seismic cracking and energy dissipation in concrete gravity dams”, earthquake engineering and structural dynamics, vol. 22, no. 11, pp. 991–1007, 1993 [3] m. l. ayari, v. e. saouma, “a fracture mechanics based seismic analysis of concrete gravity dams using discrete cracks”, engineering fracture mechanics, vol. 35, no. 1-3, pp. 587–598, 1990 [4] s. s. bhattacharjee, p. leger, “application of nlfm models to predict cracking in concrete gravity dams”, journal of structural engineering (asce), vol. 120, no. 4, pp. 1255–1271, 1994 [5] j. f. hall, “the dynamic and earthquake behaviour of concrete dams: review of experimental behaviour and observational evidence”, soil dynamics and earthquake engineering, vol. 7, no. 2, pp. 58–121, 1988 [6] q. s. li, z. n. li, g. q. li, j. f. meng, j. tang, “experimental and numerical seismic investigation of the three george dam”, engineering structures, vol. 27, no. 4, pp. 501–513, 2005 [7] m. rochon-cyr, p. leger, “shake table sliding response of a gravity dam model including water uplift pressure”, engineering structures, vol. 31, no. 8 pp. 1625–1633, 2009 [8] s. s. saini, j.krishna, “overturning of top profile of the koyna dam during severe ground motion”, earthquake engineering and structural dynamics, vol. 2, no. 3, pp. 207–217, 1973 [9] p. leger, m. katsouli, “seismic stability of concrete gravity dams”, earthquake engineering and structural dynamics, vol. 18, no. 6, pp. 889–902, 1989 [10] chopra, a.k. and zhang, l. 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element modeling for rock engineering”, in: j. a. hudson, comprehensive rock engineering: principles, practice and projects, vol. 2, pergamon press, pp. 245–261, 1993 [28] p. a. cundall, “distinct element models of rock and soil structure”, in: e. t. brown et, analytical and computational methods in engineering rock mechanics, allen &unwin, 127–163, 1987 [29] c. s. tsai, g. c. lee, r. l. ketter, “a semi-analytical method for time domain analyses of dam–reservoir interactions”, numerical methods in engineering, vol. 29, pp. 913–933, 1990 engineering, technology & applied science research vol. 8, no. 1, 2018, 2508-2513 2508 www.etasr.com hafizi and nasr: the effect of zinc oxide nanoparticles on safflower plant growth and physiology the effect of zinc oxide nanoparticles on safflower plant growth and physiology zeinab hafizi department of biology paymenoor university tehran, iran nasrin nasr department of biology payamenoor university tehran, iran abstract—in this paper, a study of the effect of zno nanoparticles on safflower growth and physiology was performed. each of these elements plays a particular role in the plant life, the presence of these elements is necessary for plant’s life cycle and growth. zinc deficiency causes the biggest problems in safflower’s production. considering the importance of nanoparticles in today's world, this research investigated the effect of zinc oxide nanoparticles on the concentration of guaiacol peroxidase, polypeptide oxidase, dehydrogenase and malondialdehyde in four plant sample groups in greenhouse and laboratory conditions. results of showed that malondialdehyde enzyme increased with different treatments of various concentrations of zinc oxide. the enzyme guaiacol oxidase increased at concentrations of 100 mg/l and polyphenol oxide at concentrations of 10 and 500 mg/l and dehydrogenase in 1000 mg/l and decreased in other treatments. in addition to showing the effect of nanoparticles in plants, these findings determine the beneficial concentrations of nanoparticles that have a positive effect on the level of enzymes in plants. keywords-nanoparticles; malondialdehyde; guaiac peroxidase; polyphenol oxidase; dehydrogenase i. introduction nanotechnology is a science and technology that has the ability to produce new materials, tools, and systems with atomic and molecular levels and has the potential to revolutionize agriculture. nanotechnology properties, their use, and their probable harmful effects in the environment, have created concerns [1]. most studies have been conducted on the effects of nanoparticles on aquatic systems. nanoparticles enter the food chain through plants. although the level of these nanoparticles is not remarkable at present, one day it can reach a critical level. some of the aims of the use of nanoparticles are plant pathology, specific agricultural problems related to pathogens, and the creation of new ways of product’s protection [2]. nanoparticles are used in many agricultural and biomedical departments [3]. nanoparticles are also used in a variety of biological programs [4]. nanotechnology, as the science of working with the smallest particles, has increased hopes for overcoming the problems the agricultural sector is facing. nanotechnology has significant impact on important areas of the agricultural sector, such as the modernization of new cultivars, the development of intelligent chemical delivery systems and pesticides, the integration of intelligent systems for food processing and packaging, the removal of herbicide debris from plants and soil [5]. safflower (carthamus tinctorius l.) raceme is of dense clump type, covered by a number of involucres [6, 7]. the cultivation of safflower was initially done to extract the color of its petals in order to color the fabric and decorate the food, but today it is also cultivated for the production of oils, meal, pharmaceuticals, cosmetics and ornament [8]. safflower has 8 species and 50 different cultivars and high alkaloids content. in the past, its infused leaves have been used to treat bee stings and prevent uterine bleeding [9]. all plant parts have alkaloids. ajmalicine, placed at the root of this plant, is used to treat high blood pressure [10]. serpentine is also used to treat circulatory system abnormalities [11]. among the 300 types of terpenoid indole alkaloids identified in safflower, vinblastine and vincristine are of particular importance: these two alkaloids have antitumor activity by binding to the microtubules and stopping cell division during mitotic metaphase and they are used in chemotherapy of many cancers for over 40 years [1214]. a small amount of these two alkaloids in the safflower plant, complexity and multi-stage synthesis path of these two alkaloids, the lower effectiveness of semi-synthesis drugs and high demand for this two drugs are some of the most important reasons for attracting researchers to the use of biotechnology and tissue culture techniques to increase the production of these vital alkaloids in the plant. finding the factors affecting the increase in the biosynthesis of vinblastine and vincristine or their monomers, such as catharanthine and vindolin, are always important research objectives [15]. ii. theoretical foundation a. zinc in plants 1) physical and chemical zinc characteristics zinc is a transition metal with an atomic number of 30 and it is the 23rd element on the earth's crust in terms of frequency. the zinc element has five stable isotopes. heavy isotopes exist at the roots and light isotopes exist in the stems of the plant. 30 zinc radioisotopes have been identified. among these radioisotopes, zn65 radioisotope has the highest half-life and is used as a tracer in plants. zinc has the characteristic of lewis acid, that is, its radius relative to rainfall is smaller than that of other elements. the electron configuration of the zinc organic complexes is in the form of a hexagonal octahedral, although engineering, technology & applied science research vol. 8, no. 1, 2018, 2508-2513 2509 www.etasr.com hafizi and nasr: the effect of zinc oxide nanoparticles on safflower plant growth and physiology there are pentagonal and tetragonal shapes [16]. in solutions, zinc is in the form of zn2+, and unlike fe2+ and cu2+ in physiological conditions, it has a stable oxidation and resuscitation mode due to the fact that its organic electrons are complete [16, 17]. zinc creates salts with halides, sulfates, nitrates, ferrates, acetates, thiocyanates, perchlorates, flocyls, and cyanides [16, 18]. 2) zinc and soil zinc concentrations in soils typically range from 10 το 300 mg/g in organic and mineral soils respectively, and in most agricultural soils it varies from 50 to 66 mg/g [19, 20]. 3) the sources of zinc entry into soil zinc entry to soil is done by different sources: • zinc entry to soil can be the result of blasting of rocks like asphalite (zns), smithsonite (znco3), hemorhphyte (zn4 (oh) 2 si2 o7 h2o) [16]. • zinc in the soil can be the result of natural phenomena such as volcanoes, forest fires, surface dust, etc. [21]. • zinc enters soil through fossil fuels, mining waste, phosphate fertilizers, limestone, agricultural fertilizers and elastic coating [19, 22]. 4) zinc shapes in soil zinc can be seen in soil in the following forms: • as a building part of some clay minerals, it can be replaced with magnesium in a crystalline network. • a portion of zinc in the form of cation is exchangeable with surface absorption of clay minerals. • a part of zinc in the soil is seen as a mixture of organic material. • an amount of exists zinc in the soil solution in the form of zn2+ [23]. 5) factors of zinc accessibility to plants some of the factors that control the accessibility of zinc to plants are the total amount of zinc in the soil, soil ph, the amount of organic material, the amount and type of clay, the amount of calcium carbonate, oxidation and regeneration conditions, microbial activity in the rhizosphere, soil moisture, other element accumulation and weather [24]. soil ph: soil ph is one of the most important factors for zn access to plants. zinc activity in the soil is controlled by ph. increase of the soil ph causes a significant reduction in the zinc dissolution. when ph increases, zinc concentration decreases rapidly [18]. organic material: soil organic material plays an important role in the zinc accessibility to growing plants. soil organic material improves the physical properties of the soil, and also helps the maximum increase of the absorption of metal ions by plants with the formation of soluble complexes with metal ions. with the reduction of soil organic material, the dissolution of zinc also reduces. the usage of organic material to increase the access of elements in soil depends on the type of source and the formation of organic material [25]. calcareous soils: zinc deficiency in calcareous soils is due to the strong absorption of zinc on the surfaces of calcium carbonate (caco3) because the levels of calcium carbonate are sites for deposition and adsorption of metal ions. zinc emission factor in the calcareous soils is 5 times lower than that of acidic soils [26]. soil salinity: the problem of zinc deficiency in the dry and semi-arid lands is due to soil salinity. salinity increases the absorption of cadmium and reduces zinc absorption. because there is an antagonistic relationship between zn and cd, the increase of cd absorption under salinity stress (nacl) is due to the formation of the cdcl2-n solution complex and is easily absorbed by the root. application of zn2+ under salinity conditions improves plant growth. zinc controls the entry and exit of sodium [28] due to its role in protecting the membrane [27]. in addition to this, zinc takes part in the detoxification of reactive oxygen species (ros), which may be due to salinity stress [29]. clay soils: zinc accessibility to the soil is also associated with clay material, the presence of iron oxides and manganese in the soil. the researchers observed that zinc containment in the kaolinite clay soils is less than illite and montmorillonite, and this may be due to homogeneous material and permanent load of clay in the illite and montmorillonite compared to that of kaolinite. due to its similarity with elements of two-capacity cations such as mg, cu, fe, mn, zn accessibility can change physiological balance by local competition in different places [30]. b. the role of zinc in plants zinc is an essential micronutrient element for organisms [31] and plays an important role in plant processes [24, 32]. zinc is necessary for producing chlorophyll, pollen performance, fertility and germination [27, 33], as well as for lipid metabolites, nucleic acid, rna metabolism, stability and dna simulation and gene expression regulation. zinc plays an important role in cell proliferation [27] and plant roughness [34]. zinc tends to form tetragonal complexes with o, n, and especially s ligands, which affects the metabolic activity. zinc as a catalyzer, has an activating or building role in many enzymes in plants [31]. zinc is involved in the structure of more than 300 enzymes [35] and is the only metal that is present in all 6 enzyme grades [17]. iii. methodology fertile soil in the analogy of 50:50 soil and sand ratio was used in order to plant isfahan cultivar safflower seeds, obtained from isfahan's pakan co. four pots were taken for each treatment, and 15 seeds were planted at a depth of 2 cm in each pot. the steps were done in the greenhouse and the laboratory of the faculty of science of azad university of mashhad. the greenhouse temperature was 25°c and the samples were irrigated once a day with urban water. in the two leaf stage of the plant, the first spray of zinc oxide nanoparticles was given at concentrations 0, 10, 100, 500, and 100. the second and third sprays were performed at 14 day intervals. engineering, technology & applied science research vol. 8, no. 1, 2018, 2508-2513 2510 www.etasr.com hafizi and nasr: the effect of zinc oxide nanoparticles on safflower plant growth and physiology a. measurements 1) measuring the activity of the enzyme guaiacolat oxidase in order to measure the activity of the enzyme guaiacolat oxidase the method described in [36] was followed. in order to maintain the activity of the enzyme, all the steps were performed in temperature 1±1oc [36]. 2) measuring the activity of the enzyme guaiac peroxidase in order to measure the enzyme activity, phosphorus buffer solution of 0.1m and 50 μl of guaiacol followed by 50 μl of 3% hydrogen peroxide were added to 3mm enzyme extract. the change in optical absorption was recorded by a spectrophotometer (shimaduz model uv/110) [36]. 3) measuring the activity of polyphenol oxidase enzyme in order to maintain the activity of the enzyme, all enzyme extraction steps were carried out in 1±1oc. measuring the activity of polyphenol oxidase was done by the method described in [37]. 4) measuring malondialdehyde level 2.0 g of leaf tissue were eroded in 10 milliliters of 0.1% (w/v) trichloroacetic acid (tca) and centrifuged at 10,000 rpm for 5 minutes. for each 1 mm of the resulting solution, 4 mm 20% tca containing 0.1% thybutriracic acid were added. the product mixture was then placed at 90°c for up to 30 minutes. the samples were cooled for 5 minutes on ice and then centrifuged again for 10 minutes at 10000 rpm. the absorbance of the samples was measured at 532 nm and 600 nm by a spectrophotometer. the malondialdehyde value was obtained by differentiating the absorbance value of 600 from 532 and multiplying in 1.55x105 (unit: μmol/gfw). 5) measuring the dehydrogenase level the dehydrogenase’s activity was measured using triphenyltetrazolium chloride (ttc) reduction to trifluoromethane (tpf). the level of young roots was washed and dried, and then the weight was measured. roots were placed in tubes containing 2 mm 0.4% ttc and 1 ml phosphate buffer 0.6 m, with ph=7 and then were placed at 7°c for 3 hours. in the next step, 1 mm solution of sulfuric acid 1m was added to the tubes and tpf was formed. then, the absorbing was read at 485 nm [38]. iv. results a. statistical analysis data statistical analysis was done by using spss. for comparing averages, duncan minimum significance level test was used at the error probability level of 5% (p≤0.05). charts were drawn in microsoft excel. data statistical analysis on the effect of different zinc oxide nanoparticles levels on the level of malondialdehyde showed a significant increase compared to control. the highest rate in the treatment was at 100 mg/l treatment (figure 1). comparison on the amount of guaiac peroxidase in treatment of 100 mg/l zno and in treatments of 10, 500 and 1000 mg/l showed a decrease compared to control (figure 2). data analysis showed that the amount of polyphenol oxidase increased at concentrations of 10 and 500 mg/l and decreased at concentrations of 1000 and 100 mg/l, compared to control (figure 3). dehydrogenase increased in the treatment of 1000 mg/l and decreased in treatments of 10, 100 and 500 mg/l (figure 4). fig. 1. the enzyme levels of malondialdehyde in safflower under zinc oxide nano treatment, the columns with similar letters at the 5% probability level (p≤0/05) have no significant difference. fig. 2. the amount of enzyme of safflower guaiacol peroxidase under the treatment of zinc oxide, the columns with similar letters at the probability level of 5% error (p≤0/05) have no significant difference. v. discussion the production of malondialdehyde due to lipid peroxidation has been reported in many plants under stress of various types of nanoparticles [39]. reduced activity of antioxidant enzymes such as glutathione reductase and catalase and increased levels of malondialdehyide is believed to cause oxidative stress and, consequently, to reduce the plant growth under cadmium treatment [40]. investigation of nanoparticles of iron oxide on the lawn and pumpkin was done in [41]. according to authors, iron oxide nanoparticles cause a higher oxidative stress and high induction of antioxidant activity in comparison to the mass of iron oxide in lawn and pumpkin. one of the reasons for oxidative stress in these two plants is the absorption of iron oxide nanoparticles on the root surface, or on the account of absorption of this nanoparticle, the physiological root functions like respiration are impaired while it causes instability on the two-layer lipid membrane. due to increased engineering, technology & applied science research vol. 8, no. 1, 2018, 2508-2513 2511 www.etasr.com hafizi and nasr: the effect of zinc oxide nanoparticles on safflower plant growth and physiology activity of the catalase and superoxide dismutase enzymes, lipid peroxidation decreases followed by a reduction in the level of malondialdehyde (the index for determining the lipid peroxidation rate) [41]. fig. 3. the amount of safflower polyphenol oxidase under zinc nano oxide treatment, the columns with similar letters at the level of 5% error probability are not significantly different. fig. 4. the amount of safflower dehydrogenase enzyme under zinc nano oxide treatment, the columns with similar letters at the 5% probability level are not significantly different. a. guaiacol peroxidase peroxidases belong to a large family of enzymes found in plants and fungi. these proteins usually include a prostatic group of protopourfirin ix, which oxidizes several substrates in the presence of hydrogen peroxide (h2o2) [42]. many of the internal cellular and external cellular oxidases are easily identified [43]. peroxidase catalyzes the oxidation reactions of the resuscitation and restores h2o2. therefore, polyoxides are oxidoreducts that use h2o2 as an electron receptor to catalyze different oxidative reactions [44]. after applying a mixture of two nano particles of copper oxide less than 50 nm in size and zinc oxide with a size less than 100 nm with different degrees, the root growth was significantly decreased. oxidative stresses were observed in the plant under the treatment of nanoparticles. by increasing lipid peroxidation and glutathione oxidation in the roots, the chlorophyll level decreased and the activity of peroxidase and catalase increased. nano particles increased ros production [45]. authors in [46] showed that during the germination stage of bean, cadmium treatment caused the increase of the induction peroxidase guaiacol enzyme activity. generally, guaiacol peroxidase is known as a tensile enzyme and the increase of its activity has been reported under stress conditions such as cadmium treatment [47]. b. polyphenol oxidase authors in [48] also observed the increase of the antioxidant enzymes of guaiacol peroxidase and polyphenol oxidase in labrad purpurcus plant under cadmium treatment. polyphenol oxidase activity in arabidopsis thaliana plants also increased under cadmium stress. the enzyme uses polyoxyethylene peroxidation as a coagulant substrate [49]. polyphenol oxidase causes oxidation of phenolic compounds to quinones and thus reduces the amount of these compounds in the leaves and roots of plants under stress. this action, by changing the peroxidation, leads to a decrease in the fluidity of the membrane and prevents the diffusion of the released radicals and thereby increases the plant's stress [48]. c. dehydrogenase analysis of data variance showed that treatment with 1000 mg/l nanoparticles of zinc oxide showed a significant increase compared to control, but treatments of 10, 100 and 500 showed an insignificant decrease. dehydrogenases are a group of enzymes that play a role in biological cycles and synthesis pathways of various compounds in plants. pyruvate dehydrogenase, molathase dehydrogenase, isocyte dehydrogenase, suction dehydrogenase and alpha-keto glutarate dehydrogenase are dehydrogenase in the tca cycle. dehydrogenases are responsible for water absorption and biomass increase in plants, and thus contribute to plant growth. dehydrogenase regulates the absorption of the substances in the plants. the activity of dehydrogenase is an important indicator for root canal survival [50]. dehydrogenase activity in plants increased affected by titanium dioxide [51]. authors in [38] investigated the effects of multi-wall oxidized carbon nanotubes on wheat. increase of electron transport reactions by the enzyme dehydrogenase was caused by these nanoparticles on wheat. vi. conclusion in this study, the effect of different concentrations of zinc oxide on some biochemical properties of safflower was investigated. the purpose of this stress was to study plant response to these particles. according to the results, it was found that the presence of these particles increased the level of malondialdehyde in the safflower plant. the amount of guaiacol peroxidase increased at concentration of 100 mg/l and decreased at concentrations of 10 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[50] l. wei, m. thakkar, y. chen, s. a. ntim, s. mitra, x. zhang, “cytotoxicity effects of water dispersible oxidized multiwalled carbon nanotubes on marine alga, dunaliella tertiolecta”, aquatic toxicology, vol. 100, no. 2, pp. 194-201, 2010 [51] v. kumar, a. kumari, p. guleria, s. k. yadav, evaluating the toxicity of selected types of nanochemicals, in: reviews of environmental contamination and toxicology, pp. 39-121, springer, 2012 engineering, technology & applied science research vol. 7, no. 5, 2017, 1930-1933 1930 www.etasr.com adekunle et al.: utilization of construction waste tiles as a replacement for … utilization of construction waste tiles as a replacement for fine aggregates in concrete adebola a. adekunle department of civil engineering federal university of agriculture abeokuta, nigeria adebolamay@gmail.com kuye r. abimbola department of civil engineering federal university of agriculture abeokuta, nigeria kuyeabimbola06@gmail.com ayo o. familusi department of civil engineering federal university of agriculture abeokuta, nigeria ayomacfamilson@gmail.com abstract—ceramic wastes are found to be suitable for usage as substitution for fine and coarse aggregates in concrete production. this study is an investigation into the utilization of waste tiles as partial replacement for fine and coarse aggregates in concrete. the control mix and other mixes containing cement, water, granite and partial replacement for sand with crushed tiles (in 5%, 10%, 15% and 20% proportions) were cast, cubed, cured and crushed. also, another mix containing cement, water, sand and partial replacement of granite with crushed tiles (in 25%, 50% and 75% proportions) were cast, cubed, cured and crushed. the specimens were tested for their respective compressive strengths using the universal testing machine (utm) on the 7th, 14th, 21st and 28th days of curing. at 28 days, the compressive strength value of 5% of fine-waste tiles replacement was 20.12 n/mm2 while that of 10%, 15% and 20% were 14.24 n/mm2, 11.04 n/mm2 and 10.12 n/mm2 respectively. moreover, at 28 days, the compressive strength of 25% of coarsewaste tiles replacement shows an increase to 22.45 n/mm2 while that of 50% and 75% were 18.4 n/mm2 and 12.2 n/mm2 respectively. thus it can be concluded that fine aggregates can be substituted at 5% waste tiles while coarse aggregates can be substituted at 25% waste tiles. keywords-concrete; deviation; gradation; replacement; waste tiles i. introduction aggregate is one of the most important materials in use for concrete production as it profoundly influences concrete properties and performance. and not much research has been done on incorporating normal ceramic wall tiles waste as partial substitute of fine aggregates or cement, in the production of structural concrete. the current research is a bid towards exploring the possibility of incorporating wastes from ceramic wall tiles as partial substitute of fine aggregates or cement in the making of concrete. from economic point of view, cement and fine aggregates contribute a bigger portion of costs in the production of concrete, thus to have them replaced by waste material of similar characteristics is a major economic gain, while being more environment friendly. ceramic wastes are found to be suitable for usage as substitution for fine and coarse aggregates and partial substitution in cement production. researchers have indicated their potential for usage in both structural and non-structural concrete and even for mortars. they were found to be performing better than normal concrete, in properties such as density, durability, permeability and compressive strength [1]. the usage of waste tiles partially as a replacement for coarse aggregates will clear the wastes from construction and production site, also environmental pollution is reduced as impact of mining is reduced, natural resources are conserved and power consumption required for quarrying is minimized [2]. compressive strength of concrete gradually increased with the increase of quantity of coarse waste ceramic tile aggregate up to certain limits i.e. 20% for water-cement ratio of 0.4, 30% for water-cement ratio of 0.5 and 40% for water-cement ratio of 0.6. the greatest compressive strength was observed for c5-10 concrete. it was noticed that the flexural strength of optimal waste ceramic concrete was 32.2% higher than flexural strength of reference concrete. therefore, it can be concluded that the use of coarse waste ceramic tile content in the concrete enhanced the flexural strength considerably. also, it can be seen that using waste ceramic tiles in concrete production causes no remarkable negative effect in the properties of concrete. the optimal case of using waste ceramic tiles as coarse aggregates is found to vary from 10 to 30 percent. in these measures, not only an increase happens in compressive strength, but also a decrease in unit weight occurs. finally, using waste ceramic tiles in concrete is an effective measure regarding to reducing the costs of concrete and is environmentally cleaner clean along with wastage management and decreasing the use of natural raw materials [3]. in [4] it is affirmed that the increase in tiles powder leads to the increase in workability of concrete. tile powder behaves like admixtures, which can be used to produce ready mix concrete. when crushed tiles replace coarse aggregate, compressive strength increases up to 10%, but after that it decreases. the authors in [5] further confirm that ceramic waste can be used as coarse aggregate as the properties of ceramic waste coarse aggregate are within the range of the values of concrete making aggregate according to indian standards. the use of crushed tile aggregate (cta) caused a 40% loss in compressive and splitting tensile strengths. cta has negatively affected abrasion and freezethaw durability. according to these results, 100% replacement of cta as a coarse aggregate is not appropriate. the use of cta in concrete has positive effects on the environment and obtaining lower costs [6]. tile aggregate concrete is little bit more economical as compared to conventional concrete. as an estimate for making 1m3 of concrete by substituting 20% engineering, technology & applied science research vol. 7, no. 5, 2017, 1930-1933 1931 www.etasr.com adekunle et al.: utilization of construction waste tiles as a replacement for … normal 20 mm aggregates with tile aggregates about 16% money can be saved on total amount of 20 mm aggregates. by addition of ceramic tile waste into concrete, proper effective utilization of ceramic tile waste can be achieved [7]. ii. materials and methods a. materials used for the study these include ordinary portland cement, waste tiles (which were collected from building site in lagos, nigeria), coarse aggregates (granite) and fine aggregates (sand). b. experimental procedure the sieve analysis was carried out in accordance with the procedure given in bs 812 and the gradation test was performed on the samples of aggregates (sand, granite and waste tiles) in the laboratory. the batching of concrete test samples was by weight in order to eliminate errors due to variations the mix proportion adopted was 1:2:4 by weight of cement, fine and coarse aggregates and the water/cement ratio by weight of 0.6, crushed granite aggregate with maximum size of 12.7 mm was mixed with sand-cement mixture. the control mix containing cement, sand, granite and water was mixed and cast. cubes were then made from the mix and cured for 7, 14, 21 and 28 days respectively before they were crushed using the universal testing machine. table i. weight of crushed tile as replacement for fine aggregates tile replacement (%) cement (kg) sand (kg) granite (kg) tiles (kg) 0 13.89 27.77 55.54 5 13.89 26.38 55.54 1.39 10 13.89 24.99 55.54 2.78 15 13.89 23.6 55.54 4.77 20 13.89 22.22 55.54 5.55 table ii. weight of crushed tile as replacement for coarse aggregates tile replacement (%) cement (kg) sand (kg) granite (kg) tiles (kg) 0 13.89 27.77 55.54 25 13.89 27.77 41.68 13.86 50 13.89 27.77 27.77 27.77 75 13.89 27.77 13.89 41.66 other mixes as shown in table i containing cement, water, granite and partial replacement for sand with crushed tiles (in 5%, 10%, 15% and 20%) were also cast, cubed, cured and crushed following the same process for the control mix. also, another mix as shown in table ii containing cement, water, sand and partial replacement of granite with crushed tiles (in 25%, 50% and 75%) were also cast, cubed, cured and crushed using the same process above. the specimens were tested for their respective compressive strengths using the universal testing machine (utm) on the 7th, 14th, 21st and 28th days of curing and data for their respective compressive strengths were collated from the tests. iii. results and discussion the sieve analysis revealed that most of the coarse waste tile materials were within the range between 2.5 mm to 19 mm in particle size diameter with a fairly good gradation pattern, and the nominal maximum particle size diameter was 12.5 mm. while for fine materials, the analysis showed that most of the fine waste tiles material was within the range between 0.2 mm to 2.5 mm in particle size diameter with a very good gradation pattern, and the nominal maximum particle size diameter was 4.75 mm, as shown in figures 1 and 2. fig. 1. grain size distribution curve of waste tile coarse aggregates. fig. 2. grain size distribution curve of waste tile fine aggregates at 7 days, the compressive strength value of 5% of waste tiles replacement showed a considerable high compressive strength of 14.57 n/mm2 as compared to the other three batches which were 12.9 n/mm2, 12.6 n/mm2, 8.85 n/mm2 respectively while at 14 days, the compressive strength value of 5% of waste tiles replacement had increased to 14.89 n/mm2 while that of 10%, 15% and 20% were 14.69 n/mm2, 11.14 n/mm2 and 9.39 n/mm2 respectively. at 28 days, the compressive strength value of 5% of waste tiles replacement was 20.12 n/mm2 while that of 10%, 15% and 20% were 14.24 n/mm2, 11.04 n/mm2 and 10.12 n/mm2 respectively as these were evident from figure 3. these results when compared with a grade 20 concrete which was the target, showed that 5% waste tile replacement were adequate as fine aggregate replacement. engineering, technology & applied science research vol. 7, no. 5, 2017, 1930-1933 1932 www.etasr.com adekunle et al.: utilization of construction waste tiles as a replacement for … moreover, there were variations in the compressive strength of the concrete with partial replacement of waste tiles as coarse aggregates. at 7 days, the compressive strength of 25% of waste tiles replacement showed a considerable high compressive strength of 19.2 n/mm2 as compared to the other two replacement batches which were 9.51 n/mm2 and 6.52 n/mm2 respectively and while at 28 days, the compressive strength of 25% of waste tiles replacement shows an increase to 22.45 n/mm2 while that of 50% and 75% were 18.4 n/mm2 and 12.2 n/mm2 respectively. these results when compared with a grade 20 concrete which was the target, showed that 25% waste tile replacement were adequate as coarse aggregate replacement. fig. 3. compressive strength of concrete with waste tiles as fine aggregates it can be deduced that 5% fine-waste-tiles-concrete samples showed a small deviation in compressive strength of about 11.37% from the control sample compared with the other 10%, 15% and 20% which gave 37.27%, 51.37% and 55.42% reduction in the compressive strength at 28 days respectively. this deviation when compared with the control samples showed that 5% fine-waste-tiles-concrete samples were within the range of grade 20 concrete, while 20% replacement showed the largest deviation as shown in table iii. from table iv below, it can be deduced that 25% coarse-waste-tiles concrete showed a minimal deviation of about 18.66% from the control sample compared with the other 50% and 75% which showed a reduction in the compressive strength of the control sample with 33.3% and 55.8% respectively. this deviation when compared with the control samples shows that 25% coarsewaste-tiles concrete samples were within the range of grade 20 concrete, while 75% coarse-waste-tiles concrete samples showed the largest deviation . table iii. deviation of the fine-waste-tile-concrete from the control sample fine-waste-tilecontent (%) % reduction in compressive strength 5 11.37 10 37.27 15 51.37 20 55.42 table iv. deviation of the coarse-waste-tile-concrete from the control sample coarse-waste-tiles content (%) % reduction in compressive strength 25 18.66% 50 33.3% 75 55.8% iv. conclusions and recommendations the suitability of ceramic waste as substitution of concrete aggregate elements varies and depends on the material being substituted and the percentage composition of the new mixure. from the experimental results, the following conclusions can be drawn: • the compressive strength of 5% fine-waste-tiles concrete showed a minimal deviation of 11.37% from the strength of the control sample at 28 days, thus it can be concluded that fine aggregates can be substituted at 5% waste tiles. • the compressive strength of 25% coarse-waste-tiles concrete showed a minimal deviation of 18.66% from the strength of the control sample at 28 days, thus it can that concluded that coarse aggregates can be substituted at 25% waste tiles. • fine-waste-tile concrete 15% and 20% shows 51.37% and 55.42% reduction in the concrete strength to values of 11.04 n/mm2 and 10.12 n/mm2, values which were below the target grade 20 concrete. thus, it cannot be recommended to substitute fine aggregates in concrete with these percentage replacements. • coarse-waste-tile concrete of 50% and 75% showed 33.3% and 55.8% reduction in the concrete strength to values of 18.4 n/mm2 and 12.2 n/mm2, values which were below the target grade 20 concrete. thus, it cannot be recommended to substitute coarse aggregates in concrete with these percentage replacements. • adequate replacement of fine aggregate with waste tiles has been found to be 5%. beyond this limit, the concrete cube strengths did not meet code requirements for grade 20 concrete strength as per bs 1881 part 4 (1997). • adequate replacement of coarse aggregate with waste tiles has been found to be 25%. beyond this limit, the concrete cube strengths did not meet code requirements for grade 20 concrete strength as per bs 1881 part 4 (1997). • with 5% and 25% waste-tile substitution of fine and coarse aggregate respectively, a cost reduction of 2.3% was achieved for every cubic meter of concrete produced. further study is recommended to extend this research to a wider perspective in order to be able to consider more parameters governing the effect on the behavior and engineering properties of fresh and hardened concrete containing different types and sizes of waste tile materials. references [1] o. zimbili, w. salim, m. ndambuki, “a review on the usage of ceramic wastes in concrete production”, world academy of science, engineering and technology international journal of civil, engineering, technology & applied science research vol. 7, no. 5, 2017, 1930-1933 1933 www.etasr.com adekunle et al.: utilization of construction waste tiles as a replacement for … environmental, structural, construction and architectural engineering vol. 8, no. 1, pp. 91-95, 2014 [2] p. c. shetty, varun, v. kumar, n. shetty, s. b. poojary, “study of strength properties using tile waste in concrete”, international journal of combined research and development, vol. 5, no. 4, pp. 659-662, 2016 [3] m. daniyal, s. ahmad, “application of waste ceramic tile aggregates in concrete”, international journal of innovative research in science, engineering and technology. vol. 4, no. 12, pp. 12808-12815, 2015 [4] k. c. hemanth, r. k. ananda, b. k. sateesh, t. guravaiah, n. naveen, s. jani, “effect of waste ceramic tiles in partial replacement of coarse and fine aggregate of concrete”, international advanced research journal in science, engineering and technology vol. 2, no. 6, pp 13-16, 2015 [5] p. malik, j. malhotra, a. verma, p. bhardwaj, a. dhoundiyal, n. yadav, “mix design for concrete with crushed ceramic tiles as coarse aggregate”, international journal of civil engineering research, vol. 5, no. 2, pp 151-154, 2014 [6] i. b. topcu, m. canbaz, “utilization of crushed tile as aggregate in concrete”, iranian journal of science & technology, transaction b, engineering, vol. 31, no. b5, pp. 561-565, 2007 [7] p. singh, r. k. singla, “utilization of waste ceramic tiles as coarse aggregate in concrete”, journal of multidisciplinary engineering science and technology (jmest) vol. 2, no. 11, pp. 3294-3300, 2015 microsoft word 03-odhiambo-ed.doc etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 302-309 302 www.etasr.com odhiambo and umenne: net-computer: internet computer architecture and its application … net-computer: internet computer architecture and its application in e-commerce marcel o. odhiambo dpt of electrical and mining engineering university of south africa (unisa) pretoria, south africa ohangmo@unisa.ac.za patrice o. umenne dpt of electrical and mining engineering university of south africa (unisa) pretoria, south africa umennpo@unisa.ac.za abstract— research in intelligent agents has yielded interesting results, some of which have been translated into commercial ventures. intelligent agents are executable software components that represent the user, perform tasks on behalf of the user and when the task terminates, the agents send the result to the user. intelligent agents are best suited for the internet: a collection of computers connected together in a world-wide computer network. swarm and hydra computer architectures for agents’ execution were developed at the university of surrey, uk in the 90s. the objective of the research was to develop a software-based computer architecture on which agents execution could be explored. the combination of intelligent agents and hydra computer architecture gave rise to a new computer concept: the net-computer in which the computing resources reside on the internet. the internet computers form the hardware and software resources, and the user is provided with a simple interface to access the internet and run user tasks. the agents autonomously roam the internet (net-computer) executing the tasks. a growing segment of the internet is ecommerce for online shopping for products and services. the internet computing resources provide a marketplace for product suppliers and consumers alike. consumers are looking for suppliers selling products and services, while suppliers are looking for buyers. searching the vast amount of information available on the internet causes a great deal of problems for both consumers and suppliers. intelligent agents executing on the net-computer can surf through the internet and select specific information of interest to the user. the simulation results show that intelligent agents executing hydra computer architecture could be applied in e-commerce. keywordsintelligent agents; internet; hydra computer architecture; net-computer; cloud computing; e-commerce i. introduction agents’ technology was developed from related works on distributed artificial intelligence (ai), in which researchers aimed at spreading intelligence behavior through distributed computer systems to tackle inherently distributed problems. they developed intelligent software programs (or agents), the most advanced of which can communicate, collaborate and even learn from each other as they use their knowledge for problem solving. research on intelligent agents has been ongoing for sometime yielding interesting results. research at university of surrey, uk in late 90s resulted in hydra and swarm computer architectures for intelligent agents execution. the motivation was to develop a software-based computer architecture based on compiled code (program) as opposed to interpreted code for intelligent agents execution. in addition there was a need to extend the developed architecture for agents execution in parallel and distributed environments. the agents executing on swarm or hydra computer architecture traverse the network of hosts carrying the user rights or permissions and execute user tasks and, when the task terminates, the agents carry the results back to the user. the internet provides an inter-connected worldwide network enabling the user to log onto and browse documents on a remote machine several thousands of miles away. combining information processing with the internet opens the door for all sorts of communication and information processing possibilities. automatic banking or automatic teller machines (atm), imaging, remote teaching and telemarketing are among the many services that can be provided [1]. a growing segment of the internet is electronic commerce. consumers are looking for suppliers selling products and services on the internet. meanwhile, suppliers are looking for buyers to increase their market share. the vast amount of available information, however, causes a great deal of problems for both the consumer and the supplier. often, a task executed online is not only time consuming but boring as well. intelligent agents are best suited for this type of task, since they can surf through the internet selecting specific information of interest to the user [1]. the ultimate objective of intelligent agents is for the user to log on to the proposed net-computer (based on intelligent agents and the hyrda computer architecture), issue task(s) to be autonomously executed, log off and then, at a later time, log on to collect the results. the agents autonomously execute and locate items on the internet while the user is offline and free time to carry out tasks requiring user intervention. the simulation results show that the combination of intelligent agents and hydra computer architecture could be used to implement the net-computer in which the computing resources reside on the internet and that the proposed netcomputer architecture could be applied in e-commerce. this paper is structured as follows: section i introduces the topic etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 302-309 303 www.etasr.com odhiambo and umenne: net-computer: internet computer architecture and its application … covering the objectives and the relevance of intelligent agents, the hydra computer architecture, the net-computer and electronic commerce. section ii provides a definition of intelligent agents, their characteristics and motivation and concludes with a brief mention of architecture models. section iii provides a brief description of hydra computer architecture. section iv describes the concept of the netcomputer architecture based on a combination of intelligent agents and hydra computer architecture. section v describes how the net-computer could be applied in ecommerce. section vi provides a brief mention of cloud computing (not based on intelligent agents) as an indication of the trend towards internet computing. section vii describes the simulation of intelligent agents execution and section viii concludes the paper and provides suggestions for further work. ii. intelligent agents the definition of an agent falls everywhere along a continuum, from simple macros in which the user enters a few parameters to truly intelligent agents, which demonstrate learning abilities and artificial intelligence. an agent [2, 3] is a software entity with some degree of autonomy, which carries out operations on behalf of the user or another program, and thus, represents or has knowledge of the user's goals or wishes. agents are the user's personal representatives or assistants on the internet carrying the user identity, access rights (permissions) and responsibilities. agents act on behalf of the user at the user's request or using some agreed user protocol. agents communicate with their peers by exchanging messages on behalf of the user [4]. while agents can be as simple as subroutines, typically they are larger entities with some sort of persistent control (e.g. distinct control threads within a single address space, distinct processes on a single machine or separate processes on different machines). the characteristics of an agent can be broken down into three main dimensions: agency, intelligence and mobility [5]. • “agency” describes the agents’ degree of independence. agents must be able to operate on the internet while the user is disconnected or, in any case, not interacting with the web. the most basic agent represents the user in some way and proceeds to complete a task with that information in mind. more complex agents can interact with other programs and data. • “intelligence” is the amount of learned behavior or possible reasoning capacity that an agent may possess. at the basic level, the agent may follow a set of rules that are pre-defined by the user. • “mobility” is the dimension which makes agents useful for internet applications, yet poses many privacy and security issues. an agent can be static and reside on the client computer to manage and gather information on that machine. a more mobile agent may be composed on one computer (at the client or server end) and then sent to another to gather data and then return the data to the client. agents are divided into three main categories: advisory, assistant and internet [1]. • “advisory agents” don't actually carry out tasks but they offer instructions and advice to help users do their work. these agents are experts in a particular domain, but in the beginning, they have only rudimentary knowledge of the user, user’s work patterns, and user preferences. • “assistant agents” are more ambitious than advisory agents because they often act without direct feedback from the user. while this allows them to be much more powerful, it also raises a lot of technical and social issues that are yet to be resolved. • “internet agents” and their related issues are especially relevant on the internet. along with the explosive growth of the web, has come the demand for tools to help manage and to sift through the vast amounts of available information, and agents (variably known as web crawlers, spiders, and robots) often fit the bill. some internet agents attempt to present an integrated view of the internet as a whole, but the most common to date are information gatherers. some of the currently available agents can save the user time by performing repetitive tasks such as gathering and processing information. with the help of an intelligent agent, the user input could decrease to the time required to fire the agent on the internet. the agent can work on/offline thus freeing the user to work on other projects or more enjoyable endeavors. a. agents execution on the internet agents freely roam the internet searching for relevant information or services that are of interest to the user. agents provide the user with the information, and the user is free to act otherwise. however, a higher level of agent sophistication involves service performing agents which execute the specific tasks on behalf of the user e.g. “find me the nearest chinese restaurant and book me a dinner table for two this evening”. finally there are predictive agents that volunteer information or services to the user without explicitly being asked [3]. for example, the agent may monitor the stock exchange and return information pertaining to a particular item which might be of interest to the user. agents’ execution on the internet raises a lot of issues which needs to be addressed if agents processing is to be widely accepted. such issues include: authentication, or how much should the user trust the agent especially when the agents are delegated important decisions such as making financial commitments. security of such a transaction should be guaranteed. in traversing the network searching for information, the agents will need access permission at every site they visit in addition to the site authenticating the identity of the user that the agent purports to represent [6]. this is to prevent agents masquerading as some other user's representative. the need to guard against wayward programs that install viruses, compromise host, or pilfer the database. the resources used by the agent at each site needs to be charged to the user. these and many others are the issues which must be addressed. etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 302-309 304 www.etasr.com odhiambo and umenne: net-computer: internet computer architecture and its application … b. agents motivation four main motivations exist for the agent paradigm. the first important motivation is performance improvement [4]. in figure l(a), we have the common situation where the client and the server are located on two different nodes. to carry out computation, several messages will often be transferred back and forth between the two parties. there are performance advantages in moving the client to the server side of this connection. the amount of network interactions is reduced as a result of co-locating service requesters and service providers heavily engaged in communication. this scenario is illustrated in figure 1(b). fig. 1. clientserver agent model a second motivation for the agent model is that it is intuitive. agents acting more or less independently on behalf of somebody are a well-known concept. figure l(c), represents a similar situation as in figure l(b), but now the client itself does not move. it sends a representative to the server side to do the actual computation. the agent will typically reduce the amount of data to be transferred over the network. in this example, the result is finally sent back to the client. a third motivation for the agent paradigm is that communication is reduced to a local site issue. all that is needed is to move, or co-locate, agents that wish to communicate. locality of agents is not hidden, but communication channels are. finally, this model gives cleaner and simpler failure semantics. in a regular distributed system, the state between the client and the server is normally distributed. a failure half-way makes it tricky to ensure that both parties roll back their state to maintain consistency. alternative agent architecture, such as server-server models shown in figure 2, also exist. in the server model, the agent server co-ordinates the activities of local agents arriving from other hosts. nevertheless, it is not the intention of this paper to carry out a comparative analysis of the advantages/disadvantages of the two agent models. the inclusion of the agent-server only serves the purpose of informing the reader of the existence of alternative agent model. a number of agent-based systems have been implemented, tested and the simulation results obtained point to the feasibility of agents processing. agent systems are implemented either as interpreted program code, e.g. wave [7], tacoma [8], telescript [9-11], agent tcl [12], or compiled program code, e.g. swarm [13], hydra [14]. in the interpreted program code version, the execution engine runs on each host, receiving, interpreting user programs (strings) and executing user commands. in the compiled program code version, the compiled program and user commands (compiled code) are uploaded and executed by the execution engine fig. 2. server – server agent model iii. hydra computer architecture parallel and distributed swarm computer architecture for agent execution [14] is based on the swarm computer architecture [13]. the hydra computer shown in figure 3, consists of four modules: access point (ap) through which the user can access the hydra computer to issue tasks and collects the results after task termination, routing module (rm) responsible for routing agents to local destinations, processing module (pm) is the execution engine and also the destination of an executing agent, and network router (nr) that connects hosts on the network, routes agents between the hosts and ensures message delivery to correct destinations. the network router and routing module together form the communication router (cr). the cr uses an interconnection scheme to connect hosts in the network, assign host numbers to host names and creates communication channels among the hosts. the hosts in the network are grouped into domains, and the domains interconnected together form a distributed network. the nr then starts the rm running at each host, creates a connection point for access point (user interface) at each host and then, enters a continuous loop monitoring network hosts for user connection. during start up, the cr, starts the routing module at each host, establishes a listening end-point at each host and monitor message arrival at the end-points. the cr identifies both local and remote destinations to reliably deliver messages to these destinations. the communication router (cr) reliably delivers messages to the hosts. etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 302-309 305 www.etasr.com odhiambo and umenne: net-computer: internet computer architecture and its application … fig. 3. configuration of the net-computer agents navigate a network of hosts using hosts’ addresses (pm number or hostname), executing a task, and when the task terminates, the agents collects the result and sends them to the user. the hydra computer is a software implementation coded in c, running in the unix/linux environment using the tcp/ip transport protocol. the hydra computing environment consists of network hosts connected together by an interconnection scheme to provide a distributed computer system. the hydra computer prototype adopts a spmd (single program multiple data) approach. at the beginning of task execution, the program is broadcasted to all hosts in the network running the prototype. the agents then navigate the network carrying only the minimum status information comprising of task identification, destination address, status word, instruction pointer and/or data. the objective was to develop and implement a parallel and distributed computer architecture on which agents execution or characteristics can be simulated. hydra computer prototype was simulated on a network of hosts running other applications and being used by other users. hence, performance analysis/comparison was not an objective. the main objective of the simulation was to verify that agents executing on a hydra computer prototype could navigate the network to reach their destination using host address/name, execute the task and after task termination, collect the results and send them to the user. in essence, a computer prototype on which agenst characteristics: intelligence, mobolity and agency can be demonstarted iv. the net-computer system the motivation for developing the net-computer is to shift the computing resources to the internet and provide users a simple interface to access the internet computing resources. the concept of internet computing [15] is based on intelligent agents traversing the internet executing user tasks. current estimates indicate that: • nearly 90% of the users run document processing applications. • in an 8-hour office working day, effective computer usage is about 40% (when the computer is actively in use). in the home environment, this is less than 20%. • the ordinary user uses less than 10% of the computing resources e.g. processor speed etc (except for scientific or data processing applications). from the above statistics, it can rightly be argued that there is no point in providing the user with a powerful machine which spends most of its time idle. thus, it would be worthwhile to concentrate the computing resources on the internet and provide the user with a simple interface to access the computing resources. the user interface can be as simple as a pager, ipad, tablet, personal organizer, etc. the net-computer [16] is a collection of internet computers (servers) running user programs on demand. both the hardware and software resources reside on the internet. the user does not need to be aware of the exact location of the resources. the hydra computer architecture attached to the internet servers shown in figure 4(a) receives and executes the agents. the internet servers are connected together to form the internet computing resources as shown in figure 4(b). the user interface to the net-computer is a simple device with less complexity in hardware and software since the computing resources reside on the internet. fig. 4. configuration of the net-computer v. cloud computing cloud computing [17] is all the rage. "it's become the phrase du jour," says gartner senior analyst ben pring, echoing many of his peers. the problem is that (as with web 2.0) everyone seems to have a different definition. etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 302-309 306 www.etasr.com odhiambo and umenne: net-computer: internet computer architecture and its application … as a metaphor for the internet, "the cloud" is a familiar cliché, but when combined with "computing", the meaning gets bigger and fuzzier. some analysts and vendors define cloud computing narrowly as an updated version of utility computing: basically virtual servers [17] available over the internet. others go very broad, arguing anything outside the firewall is "in the cloud", including conventional outsourcing. cloud computing comes into focus only when one considers what it always needs: a way to increase capacity or add capabilities on the fly without investing in new infrastructure, training new personnel, or licensing new software. cloud computing encompasses any subscriptionbased or pay-per-use service that extends it's existing capabilities. cloud computing is at an early stage, with a motley crew of providers, large and small, delivering a slew of cloud-based services, from full-blown applications to storage services and spam filtering. yes, utility-style infrastructure providers are part of the mix, but so are saas (software as a service) providers. today, for the most part, it must plug into cloudbased services individually, but cloud computing aggregators and integrators are already emerging. today, with such cloud-based interconnection seldom in evidence, cloud computing might be more accurately described as "sky computing", with many isolated clouds of services which it customers must plug into individually. on the other hand, as virtualization permeate the enterprise, the idea of loosely coupled services running on an agile, scalable infrastructure should eventually make every enterprise a node in the cloud. it's a long-running trend with a far-out horizon. but among big metatrends, cloud computing is the hardest one to argue with. cloud computing is thus an example of internet computing though not based on intelligent agents. the inclusion of cloud computing is to provide an indication of the move towards internet computing. vi. application of the net-computer in e-commerce a growing segment of the internet is electronic commerce or e-commerce [18]. consumers are looking for suppliers selling products and services on the internet. meanwhile, suppliers are looking for buyers to increase their market share. the vast amount of available information causes a great deal of problems for both ends. searching, a task executed online, is not only time consuming but boring as well. intelligent agents are best suited for this type of task. a typical campus internet infrastructure shown in figure 5 is a collection of communication devices and networks of varying types and configurations connected together to form one network: the “internet”. the tower and the high speed disk are used as a data warehouse for suppliers’ products and consumers’ needs and services. the remaining devices on the network provide user interface to the network clients. intelligent agents executing on such network will surf through the information on the internet, resulting in the selection of specific information of interest to the user. intelligent agents provide a mechanism for conducting ecommerce. using intelligent agents, the user composes the task offline, logs to the internet to issue the task and logs off. at a later time the user can log to the internet to collect the results of the task execution. fig. 5. typical internet infrastructure vii. simulation test the net-computer was simulated in a network of three hosts: ainur, kira and yavanna connected as shown in figure 6. the hosts connected to networks a, b and c shown in figure 7 are located on different floors of the same building and run unix operating systems. fig. 6. simulation test network the objective of the simulation test is to test the following agents characteristics: • mobility: agents navigate the network and reach destination address (host). • agency or task execution: agents carry out useful work on behalf of the user. • intelligence: agents follow a set of rules predefined by user. in addition, the user is at liberty to configure and select the hosts making up the hydra computer system as explained in section iii. at the beginning of execution, a node file containing node distribution (pm number and links to other nodes in the network) is prepared for each pm. at each pm a unique number is stored which is accessed by agents visiting the node. the aim here is to demonstrate the ability of the etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 302-309 307 www.etasr.com odhiambo and umenne: net-computer: internet computer architecture and its application … agents to access a stored data item. the unique number is stored in the persistent workspace 3 (pw3) which is accessible and can be modified by agents belonging to the same task. the unique number is retrieved by the agents and used in a simple addition routine. in the test routine, the agents load a value of 0000001ahex to the agent’s workspace 2 (aw2), the agents then navigate the network to node 1 in all pms. on reaching its destination, the agents retrieve the number stored at pw3 and add it five times to the number carried by the agents in aw2 and store the result in pw3 as shown in table i. the agents then navigate through the network to node 1 in pm3 where each agent adds the contents of aw2 to the contents of pw3 in pm3 and stores the result in aw3. the final result is stored in pw4 in pm3 as shown in table ii. the test program is described as follows: aw2, aw3, aw4 agent variables in the agent workspace. pw3, pw4 persistent workspace (nodal variables) 01 assign a value to aw2 02 insert destinations pm (pm1-3) address in the destination list (dl). 03 insert destination node address (node 1) in the destination list (dl). 04 spawn to destination address in the destination list. 05 load a value from persistent workspace pw3 to aw3. 06 add contents of aw3 to contents aw2 and store the result in aw2. 07 add one (1) to contents of aw4. 08 test if contents of aw4 equal 5. 09 if contents of aw4 are less than 5, go back to 06. 10 store the contents of aw2 in persistent workspace pw3. 11 store the value 0 in persistent workspace pw4. 12 insert destination pm (pm3) address in the destination list. 13 insert destination node (node 1) address in the destination list. 14 spawn to the address in the destination list. 15 load a value from persistent workspace pw3 to aw3. 16 add contents of aw3 to contents aw2 and store the result in aw3. 17 load a value from persistent workspace pw4 to aw4. 18 add contents of aw3 to contents aw4 and store the result in aw3. 19 store the contents of aw3 to persistent workspace pw4 20 terminate. 21 conclusion during the simulation test, the agents carrying a data item traversed the network using destination addresses (pm number). at each visited pm, the agents retrieved the data item stored at the site and added the data to the data item carried by the agent, executing the addition loop five times and stored the final result at the visited site. at the end of the addition, the agent retrieved the final result. the agent then traversed the network to pm3. at the final destination in pm3, the agent retrieved the stored data, added it to the data carried in the agents workspace and stored the result at pm3. the results are presented below in tables i and ii. fig. 7. the net-computer execution network table i. agents add contents of aw2 to the contents of pw3 pm number pm1 pm2 pm3 value in pw3 90 120 150 value in aw2 0000001a 0000001a 0000001a loop count sub total in aw2 000000aa 0000013a 0000016a 1 sub total in aw2 0000014a 0000025a 000003ba 2 sub total in aw2 000001da 0000037a 0000051a 3 sub total in aw2 0000027a 0000049a 0000066a 4 sub total in aw2 0000031a 000005ba 000007ba 5 total in pw3 0000031a 000005ba 000007ba table ii. agents add contents of aw2 to the contents of pw3 and store the results in pw4 in pm3 pm1 pm2 pm3 sub total total in pm3 0000031a (aw2) 000007ba (pw3) 00000ade (aw3) 00000ade (pw4) 000005ba (aw2) 000007ba (pw3 00000d85 (aw3 00001974 (pw4) 000007ba (pw3) 000007ba (aw2) 00000f55 (pw3) 000029c9 (pw4) the simulation tests were carried out to test agents ability to traverse the network using destination (pm) addresses, access a data item stored at a site, manipulate the data item and store the final result at the site or communicate the data item (result) to a different location. in the proposed net-computer, the computing resources are distributed over a wide geographical area. thus, agents navigated the network to reach their execution environment and the user at the end of the task execution to deliver the results. the hosts used in the simulation test are connected to physically separated networks. we can therefore conclude that the agents traversed the network to reach their destinations. thus, confirming agents navigation ability in the hydra etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 302-309 308 www.etasr.com odhiambo and umenne: net-computer: internet computer architecture and its application … computer architecture. the simple addition exercise demonstrated that agents can be used to carry out some useful work such as manipulating the user program. the ability of the agents to access stored information (data), manipulate the data and carry the data to different locations within the network, demonstrates the agents’ ability to collect/access, modify data and communicate the same. the simulation test results have demonstrated the feasibility of the net-computer based on hydra computer architecture and intelligent agents. however, more research work is needed to adapt the hydra architecture for deployment on the internet. the simulation results confirmed agents characteristics of mobility (traversing the network to reach destination host and user), agency (carrying out addition loop on behalf of the user) and intelligence (accessing stored information/date). a. application of the research searching for a service on the internet is a difficult task given the vast amount of information available; this is further complicated by the duplication of sites offering the same service. the ability to execute parallel search on the internet and to receive the results that matches the user interest is a very welcome help. the characteristics of agents autonomously roaming the network with no central control best suits applications such as relational and network databases, processing in graph-like structures, intelligent and mobile communication amongst others. the simulation results show that the hydra computer prototype could be used to implement distributed and parallel computer based lans, wans and the internet, in which the computing resources residual on the net side. agent-based processing could be a major development on the internet supporting electronic commerce/shopping and information processing amongst others. b. implication of the research the internet consisting of a collection of computers interconnected together has made it possible for service providers to electronically avail services to the users. for example, a number of organizations have sprung up offering electronic mail and internet related services. users of these services log on to the mail servers to both send and receive mail and then log off. the user terminal serves as a simple input/output device through which the user can compose their mail offline, log on to the mail server to send/receive mail then log off. in the hydra computer prototype, the access point serves as the input/output device. the processing modules are akin to the internet computers. it is thus feasible to build a distributed computer system based on a hydra computer prototype and intelligent agents. the computing power of such a computer system resides with the internet computers and the user is provided with a simple input/output terminal with minimal computing power. c. future studies and recommendations security and fault tolerance are desirable and important characteristics in distributed systems however, these were not taken into account in the hydra prototype. the security of the site (host) and agents must be guaranteed before a guest agent is permitted to execute at a site. fault-tolerance would enable the system to operate (though down-graded) in the presence of a fault or to be brought down gracefully. routing tables as currently implemented are based on immediate neighborhood (network hosts directly connected to each other). it would be infeasible to implement such routing tables on the internet, considering the vast number of connected computers. the network could be partitioned into sections, each with a unique number or address. gateway hosts would then be assigned to handle a section of the network depending on the assigned address or number. the program executed in the hydra computer prototype is written in swarm instruction (assembler language) which is very tedious, time consuming and prone to errors. having a translator to translate programs from and to high-level language would make writing of the code user friendly and easier to spot and correct errors. moreover, the delays experienced when sending agents and during execution of user tasks and the fact that the participating hosts run other programs as well, have not been taken into account in the hydra computer architecture. these and other matters will be the subject of further investigation in the next phase of the research. further, the simulation was run with the user connected online. the next phase of the research will investigate the feasibility of the user to log to the netcomputer, issue a task and log off. at a later time, the user can log to the net-computer to collect the results of the task execution. through cloud or sky computing technologies, the internet computing concepts described in [16] are beginning to become a reality. the combination of intelligent agents and the netcomputer might just provide the mechanism for furthering electronic commerce on the internet. however, a lot of work still needs to be done to make agents processing on the internet feasible. issues such as security, accessibility, faulttolerance, authentication, charges for consumed resources etc still need to be adequately addressed. references [1] k. indermaur, “baby steps: they may not fulfill our dreams yet, but agents and smart software are beginning to help us find information and do our jobs more effectively”, byte, vol. 20, no. 3, pp. 97-104, 1995 [2] s. russell, p. norvig, artificial intelligence: a modern approach, upper saddle river, new jersey: prentice hall, 2003 [3] intelligent agents. mit encyclopedia [4] m. r. genesereth, s. p. ketchpel, “software agents”, comms. of the acm, vol. 37, no.7, pp. 48-54. 1994. [5] n. jennings, m. wooldridge, “software agents”, iee review, vol. 42, no. 1, pp. 17-20, 1996 [6] p. wayner, “free agents: a new generation of light-weight, multithreaded operating environments provide security and interoperability for agent developers”, byte, vol. 20, no. 3, pp. 105114, 1995 [7] p. s. sapaty, p. m. borst, an overview of wave language and systems for distributed processing in open networks, university of surrey, department of electronic and electrical engineering, technical report, 1994. etasr engineering, technology & applied science research vol. 2, no. 6, 2012, 302-309 309 www.etasr.com odhiambo and umenne: net-computer: internet computer architecture and its application … [8] r. renesse, d. johansen, f. scheneider, an introduction to the tacoma distributed system version 1.0, technical report: university of tromso (norway) and cornell university (usa), june, 1995. [9] j. e. white, “telescript technology: the foundation for the electronic marketplace”, general magic white paper. general magic inc., 1994 [10] j. e. white, “telescript technology: scene from the electronic marketplace”, general magic white paper. general magic inc, 1996 [11] j. e. white, “telescript technology: mobile agents”, general magic white paper. general magic inc., 1996 [12] r. s. gray, agent tel: a transportable agent systems, department of computer science, dartmouth college, 1995. [13] l. de errico, agent based distributed parallel processing, dissertation for the degree of doctorate of philosophy, department of electrical and electronic engineering, university of surrey, 1996. [14] m. o. odhiambo, “hydra: parallel and distributed swarm computer architecture”, rovpia ’99” international conference on robotics, vision and parallel processing for automation, ipoh, malaysia, 1999. [15] m. o. odhiambo, “intelligent agents: the advent of the netcomputer”, kenya engineer. a journal of the institution of engineers of kenya, 1999. [16] m. o. odhiambo, “net-computer: internet computer architecture based on intelligent agents”, worldcomp'11: the 2011 world congress in computer science, computer engineering, and applied computing (internet computing (icomp’11), las vegas, usa, 2011. [17] e. knorr, g. gruman, “what cloud computing really means”, inforworld, http://www.infoworld.com/d/cloud-computing/what-cloudcomputing-really-means-031 [18] m. o. odhiambo, p. umenne, p. a. rayolla. “application of intelligent agents in e-commerce”, the 7 th annual international conference, knowledge creation and dissemination for the realization of millennium development goals, moi university, eldoret, kenya, 2011. . engineering, technology & applied science research vol. 8, no. 3, 2018, 2954-2957 2954 www.etasr.com khan et al.: analysis of children’s prosodic features using emotion based utterances in urdu language analysis of children’s prosodic features using emotion based utterances in urdu language sallar khan department of computer science sir syed university of engineering and technology karachi, pakistan sallarkhan_92@yahoo.com syed abbas ali department of computer information system, ned university of engineering and technology karachi, pakistan saaj.research@yahoo.com jawaria sallar department of computer science sir syed university of engineering and technology karachi, pakistan h.jawaria@yahoo.com abstract—emotion plays a significant role in identifying the states of a speaker using spoken utterances. prosodic features add sense in spoken utterances providing speaker emotions. the objective of this research is to analyze the behavior of prosodic features (individual and in combination with others’ prosodic features) with different learning classifiers on emotion based utterances of children in the urdu language. in this paper, three different prosodic features (intensity, pitch, formant and their combinations) with five different learning classifiers(ann, j-48, k-star, naïve bayes, decision stump) and four basic emotions (happy, sad, angry, and neutral) were used to develop the experimental framework. demonstrative experiments expressed that, in terms of classification accuracy, artificial neural networks show significant results with both individual and combination of prosodic features in comparison with other learning classifiers. keywords-speech; emotion; recognition; learning; classifiers; prosodic; features; language; urdu; pakistan i. introduction and related work speech is commonly known as an effective way of communication between human beings [1]. emotion is an application which is very much concerned with the speech in which we can perceive the speaker’s mental state through his/her spoken utterances and this term is known as speech emotion recognition (ser). using machine learning systems with partial computational resources we can identify speech emotion by the usage of a few emotions (happy, sad, angry, and neutral) [2]. the efficiency of human machine interface in the field of human machine interaction can significantly be improved by the help of automatic ser with the assistance of learning machines [3]. speech signal and its acoustic features such as timing, intensity, voice quality, pitch and articulation are highly associated with fundamental emotion [5]. speech emotion recognition systems have numerous applications which include: 1) telephonic conversations and their emotion analysis 2) psychiatric patient’s medical diagnosis 3) student emotional condition e-learning system 4) analysis of mental stress level during an exchange of conversations. there are 3 core phases leading ser as a pattern recognition statistical problem: 1) feature extraction from speech, 2) feature selection, 3) pattern classification [5]. for the evaluation and impact of spectral and prosodic features of emotional speech on classification, gaussian mixture models (gmm) were used in [6]. three fundamental parts which could enhance the design of a speech emotion recognition system are discussed in [7]: 1) selection of suitable features for speech, 2) appropriate classification scheme’s design and 3) system performance has been evaluated through the presentation of a database designed for emotional speech. speech emotion recognition review and analysis are presented in [8] by the use of different learning classifiers. extraction of both local and global prosodic features from sentences are addressed in [9], furthermore, different words and syllables are suggested for analyzing the speech recognition or affect recognition. the technology of emotion as a crucial component of artificial intelligence is advised in [10]. furthermore, distinct context must be considered by artificial intelligence for emotion recognition. five different emotions have been investigated in [11] which are associated with acoustic properties of the prosody of speech. this investigation comes to a result that those speeches which are associated with emotion “love” and “sad” are identified by higher pitch and utterances with lengthier duration. similar to [11], prosody is recognized as the most fundamental feature of emotional expression in any specific speech in [12]. ii. research methodology a. corpus collection and specification of recording the structure for this research is to conduct interviews from primary level school going children, while the medium chosen will be the regional language of pakistan urdu. the same sentence will be asked from all of the participated children. itu recommendations which were chosen for the recording of the corpus with following specifications are a) 24120 bps and b) snr>=45 db [13]. for the experiment analysis, a noise free room will be utilized for taking recording samples by using a microphone, and the entire speech emotion utterances are recorded in the recording format of 2.4 ohms; sensitivity and 48 khhz; sampling rate. with four different emotions (happy, sad, angry, and neutral) the urdu language sentence which is used for experiment is: “i want to play” ("ميں کهيلنا چاہتا ہوں”) engineering, technology & applied science research vol. 8, no. 3, 2018, 2954-2957 2955 www.etasr.com khan et al.: analysis of children’s prosodic features using emotion based utterances in urdu language b. population children were chosen randomly from a primary level school with the age group of the population of this research being 5-10 years. c. sampling frame sufficient ratio of sampling frame is chosen which can produce the desired result. it is selected from past studies from the realm of ser. for analysis purpose in this research, the data will consist of approximately 10 participants with 40 speech samples (consisting all four emotions). d. procedure 1) feature extraction the extraction process of prosodic features (pitch, intensity and formant) is done through testing of these samples on praat, while only mean values of prosodic features were extracted in the experimental section. 2) learning classification we have used 5 different machine learning classifiers for classification purpose which are artificial neural network (ann), naïve bayes (nb), decision stump (ds), j-48, and kstar. 3) pilot study of the proposed research for getting familiarized with the software/tools which we have utilized for this study, we have collected the speech samples. the .wav file format was used for the recorded samples, while praat will generate the desired result accordingly. whereas, weka classifier will process these values to generate the classification result. iii. experimental results and discussion a. extracting prosodic features to analyze the overall impact of prosodic features (intensity, pitch, and formant) on learning classifiers the experimental phase of this research is divided into two portions. in the first portion, the four emotions (happy, sad, angry, and neutral) which are present in the utterances of the speaker have been observed by using the praat software [14]. speech emotion corpuses which are used in the experimental study consist of initially 40 samples appropriated from a children recording in the age group of 5-10 years in regional language urdu with four different emotions. to evaluate the dependency of emotions on each prosodic feature (pitch, intensity, and formant) is the primary motivation through these experiments. the extraction process of prosodic features from spoken speech emotion utterances in regional langue urdu are shown in figures 1 to 3. these observations are demonstrating the behavior of all three prosodic features which are extracted by using praat software [1]. not all the total 40 samples are being demonstrated in this section but just a portion to show an aroma that how these features were extracted with the use of praat. fig. 1. extracting prosodic feature (pitch) using praat. fig. 2. extracting prosodic feature (intensity) using praat. b. classification and precision accuracy the second portion is further divided into two parts, in first part we will discuss the overall calculation of classification accuracy of each learning classifier (ann, nb, ds, j-48, and k-star) against each prosodic feature individually as shown in table i and in combination as shown in table ii. in the second part, we will discuss the precision accuracy against each emotion (happy, sad, angry, and neutral) which are produced by different learning classifiers. 1) overall classification accuracy the overall result is satisfactory in terms of classification accuracy. it has been observed (figure 5) that learning classifiers performed well when we jointly analyzed prosodic features and can classify correctly up to the accuracy of 45% meanwhile separately they produce accuracy of 40% which is shown in figure 4. furthermore in terms of learning classifiers, j-48 gave best classification accuracy of 35% for the prosodic feature pitch, while on the other hand ann and nb both held their classification accuracy higher up to 40% for the prosodic feature intensity and for the third prosodic feature, formant, ann and ds both have produced classification accuracy around 33%. during the process of analyzing prosodic features jointly, it has been recognized that the combination of intensity engineering, technology & applied science research vol. 8, no. 3, 2018, 2954-2957 2956 www.etasr.com khan et al.: analysis of children’s prosodic features using emotion based utterances in urdu language and formant produced the finest classification accuracy of 45% with ανν, while combinations of pitch and formant against j48, as well as pitch, intensity, and formant with ann came second, both with accuracy around 43%. lastly the combination of pitch and intensity produced classification accuracy around 38% with ann classifier which comes third. fig. 3. extacting prosodic feature (formant) using praat. fig. 4. classification accuracy of emotions on pitch, intensity and formant. fig. 5. classification accuracy of emotions on combination of pitch, intensity and formant. table i. comparative analysis of individual prosodic features using machine learning classifiers classifier precision accuracy happy sad angry neutral pi tc h ann 0.333 0 0 0.316 20% nb 0.125 0 0.222 0.417 12.50% ds 0.217 0 0.25 0.273 22.50% j-48 0.231 0 0.455 0.429 35% k-star 0.2 0 0.222 0.417 22.50% in te ns ity ann 0.286 0 0.545 0.4 40% nb 0.25 0 0.5 0.375 40% ds 0.143 0 0.545 0.273 32.50% j-48 0.125 0 0.462 0.263 30% k-star 0.111 0.2 0.545 0.333 32.50% fo rm an t ann 0.4 0.75 0.182 0.2 32.50% nb 0.385 0.385 0.267 0 30% ds 0 1 0.27 0 32.50% j-48 0 0 0.242 0 20% k-star 0.231 0.5 0.308 0.125 27.50% table ii. comparative analysis of prosodic feature combinations using machine learning classifiers classifier precision accuracy happy sad angry neutral p+ i ann 0.385 0 0.455 0.333 37.50% nb 0.25 0 0.467 0.333 35% ds 0.143 0 0.545 0.273 32.50% j-48 0.133 0 0.556 0.188 25% k-star 0.083 0.2 0.5 0.2 22.50% p+ f ann 0.25 0.429 0 0.412 30% nb 0.182 0.429 0.154 0.222 22.50% ds 0.25 0 0.25 0.25 25% j-48 0.417 0.333 0.444 0.462 42.50% k-star 0.375 0.429 0.143 0.273 27.50% i+ f ann 0.375 0.667 0.545 0.417 45% nb 0.375 0.333 0.5 0.429 42.50% ds 0.143 0 0.545 0.273 32.50% j-48 0.083 0 0.462 0.2 25% k-star 0.154 0.2 0.5 0.167 25% p+ i+ f ann 0.385 0.5 0.444 0.429 42.50% nb 0.25 0.286 0.455 0.357 35% ds 0.143 0 0.545 0.273 32.50% j-48 0.182 0 0.5 0.125 22.50% k-star 0.222 0.222 0.5 0.333 32.50% p: pitch, i: intensity, f: formant 2) precision accuracy the plot of precision against each emotion (happy, sad, angry, and neutral) is shown in figures 6 to 9. analyzing process shows that j-48 kept the highest precision rate of around 0.45 regarding the happy emotion with the combination of pitch and formant features, while classifiers didn’t produce well enough results for the emotion sad except ann which produced precision rate of around 0.8. for the angry emotion, every classifier produced their best possible results against almost every feature (individually or jointly) but j-48 produced a slightly better precision rate of 0.6 for the combination of pitch and intensity. in the end, for neutral emotion, again j-48 achieved the highest precision rate of around 0.5 with the combination of pitch and formant. iv. conclusion speech emotion corpuses were recorded in the urdu language with separate regard of four basic emotions. the main motivation behind this research is to analyze the impact of prosodic features (pitch, intensity and formant) on five different learning classifiers. the praat software weka tool was used in the experimental framework for emotion engineering, technology & applied science research vol. 8, no. 3, 2018, 2954-2957 2957 www.etasr.com khan et al.: analysis of children’s prosodic features using emotion based utterances in urdu language observation in spoken utterances and as learning classifier for the classification purpose. experimental results made evident that by combining prosodic features (intensity and formant) we can achieve a classification rate up to 45% while 40% classification accuracy can be achieved from an individual prosodic feature (intensity). in terms of classification accuracy, the ann has been proved overall to perform better than others with a classification accuracy of 45%. fig. 6. precision of emotion ‘happy’ on all three prosodic features. fig. 7. precision of emotion ‘sad’ on all three prosodic features fig. 8. precision of emotion ‘angry’ on all three prosodic features. fig. 9. precision of emotion ‘neutral’ on all three prosodic features. references [1] s. a. ali, a. khan, n. bashir, “analyzing the impact of prosodic feature (pitch) on learning classifiers for speech emotion corpus”, international journal of information technology and computer science, vol. 2, pp. 54-59, 2015 [2] p. ekman, “an argument for basic emotions”, cognition & emotion, vol. 6, no. 3. pp. 169–200, 1992 [3] i. chiriacescu, automatic emotion analysis based on speech, msc thesis, delft university of technology, 2009 [4] m. b. mustafa, r. n. ainon, r. zainuddin, z. m. don, g. knowles, s. mokhtar, “prosodic analysis and modelling for malay”, malaysian journal of computer science, vol. 23, no. 2, pp. 102–110, 2010 [5] j. rong, g. li, y. p. p. chen, “acoustic feature selection for automatic emotion recognition from speech”, information processing & management, vol. 45, no. 3, pp. 315–328, 2009 [6] j. pribil, a. pribilova, “determination of formant features in czech and slovak for gmm emotional speech classifier”, radioengineering, vol. 22, no. 1, pp. 52–59, 2013 [7] m. el ayadi, m. s. kamel, f. karray, “survey on speech emotion recognition: features, classification schemes, and databases”, pattern recognition, vol. 44, no. 3, pp. 572–587, 2011 [8] a. utane, s. nalbalwar, “emotion recognition through speech”, 2nd national conference on innovative paradigms in engineering & technology, international journal of applied information systems, pp. 5-8, 2013 [9] k. s. rao, s. g. koolagudi, r. r. vempada, “emotion recognition from speech using global and local prosodic features”, international journal of speech technology, vol. 16, no. 2, pp. 143–160, 2013 [10] p. olivier, j. wallace, “digital technologies and the emotional family”, international journal of human-computer studies, vol. 67, no. 2, pp. 204–214, 2009 [11] p. pattnaik, “impact of emotion on prosody analysis”, iosr journal of computer engineering, vol. 5, no. 4, pp. 10–15, 2012 [12] w. l. jarrold, towards a theory of affective mind: computationally modeling the generativity of goal appraisal, phd thesis, university of texas at austin, 2004 [13] s. a. ali, m. andleeb, n. g. haider, d. r. khan, “evaluating the performance of learning classifiers and effect of emotions and spectral features on speech utterances”, international journal of computer science and information security, vol. 14, no. 10, pp. 406– 412, 2016 [14] p. boersma, d. weenink, praat: doing phonetics by computer, available at: http://www.fon.hum.uva.nl/praat/ microsoft word etasr_v12_n1_pp8017-8022 engineering, technology & applied science research vol. 12, no. 1, 2022, 8017-8022 8017 www.etasr.com rafi et al.: an evaluation of the extreme rainfall event of 2010 over the kabul river basin using the … an evaluation of the extreme rainfall event of 2010 over the kabul river basin using the wrf model fehmida rafi u.s.-pakistan center for advanced studies in water mehran university of engineering and technology jamshoro, sindh, pakistan fehmida.rafi850@gmail.com ghulam h. dars u.s.-pakistan center for advanced studies in water mehran university of engineering and technology jamshoro, sindh, pakistan ghdars.uspcasw@faculty.muet.edu.pk courtenay strong department of atmospheric sciences university of utah salt lake city, utah, usa court.strong@utah.edu kamran ansari u.s.-pakistan center for advanced studies in water mehran university of engineering and technology jamshoro, sindh, pakistan kansari.uspcasw@faculty.muet.edu.pk syed hammad ali glacier monitoring and research center (gmrc) water and power development authority (wapda) lahore, pakistan syedhammadali2001@yahoo.com abstract-extreme precipitation events are among the most severe weather hazards. knowledge about the spatial patterns underlying such events in the upper indus basin is limited because estimating precipitation is very challenging due to the data scarcity and the complex orography. numerical weather prediction models can be applied at a fine resolution to overcome this issue. the advanced research weather research and forecasting (wrf) model version 3.8.1 was applied over the kabul river basin to simulate the temperature and precipitation of monsoon season 2010, i.e., 1 st may to 16 th september 2010. we considered the may month as a spin-up period. the initial and boundary conditions were derived from the national oceanic and atmospheric administration, climate forecast system reanalysis data. the model was set up by using two-nested domains with increasing horizontal resolution moving inward from 15km on domain d01 to 5km on domain d02. the simulations were compared with trmm 3b42, and station data collected from the pakistan meteorological department and water and the power development authority using bias, percentage bias, root mean square error, and pearson correlation. the results revealed that the simulated precipitation was improved from d01 to d02. however, the model showed mixed results with overestimation of precipitation at some stations and underestimations at others. simulated precipitation generally agreed better with trmm than with station data. overall, the results indicate that the wrf model can be used to simulate heavy precipitation in complex terrain. keywords-wrf-arw model; upper indus basin; kabul river basin; pakistan; climate change i. introduction the indus basin is prone to floods and has been hit by massive and destructive flood events in the past. the main causes of floods in various regions of himalayan karakoram and hindukush (hkh) is the intense monsoon rainfall and the rapid snowmelt due to the rising temperatures [1-4]. pakistan faced an unprecedented and most devastating flood in 2010, which inundated 100,000km 2 , affecting more than 20 million people, with a death toll of 1,980 [5]. many factors are responsible for the 2010 flood occurrence, however the primary cause was extreme monsoon precipitation [7, 8]. in the early july of 2010, a strong ridge of high pressure was developed over russia, which moved southward and was combined with the monsoon track and the phet cyclone [9, 10]. the combination of these three factors caused unprecedented rainfall in pakistan. the northwestern parts of the country, especially kabul river basin (krb), were struck first by the flooding event of 2010, which then traveled to the south, causing severe damage to houses, crops, and livestock [8]. authors in [9] reported that on 29 july 2010, khyber pakhtunkhwa (kpk) province received more than 200mm of rainfall, which caused severe flash floods. many stations in kpk received more than 150% of their climatological monthly july rainfall on 29 july. the krb is a data-scare region, and the lack of sufficient meteorological stations makes performing climate and hydrological studies very challenging [10]. global climate models (gcms) are basic tools that assess climate change, but their coarse resolution limits their utility corresponding author: fehmida rafi engineering, technology & applied science research vol. 12, no. 1, 2022, 8017-8022 8018 www.etasr.com rafi et al.: an evaluation of the extreme rainfall event of 2010 over the kabul river basin using the … for studying hydrology processes that are sensitive to sub-grid scale variations in precipitation. the complex terrain in the mountainous areas exhibit variations at much finer scales than the grid spacing of gcms. therefore, regional climate models (rcms) are used to perform hydro-climate studies in complex terrain [11, 12]. numerical weather prediction (nwp) models can be applied at higher resolutions to overcome the data scarcity issue and enhance the knowledge of atmospheric variability. the wrf model has been used worldwide for different applications [13, 14], but its application to the indus river basin (irb) or even pakistan is minimal [9, 15]. pakistan is among the top 10 countries affected by climate change. extreme events due to climate change cannot be completely avoided [16, 17], but their impacts can be reduced by developing effective and efficient forecasting techniques through sophisticated tools. this study has been conducted to simulate the flood-producing rainfall event of 2010, which occurred in krb by using the wrf model with a two-nested domain with a horizontal resolution of 15km and 5km. the event of 2010 is used as a case study to examine the applicability of the wrf model to simulate extreme precipitation events. the study will help in overcoming the lack of gauge data for forecasting heavy precipitation in complex terrains, such as krb. we believe that this study will improve the understanding of the flood-producing rainfall event of 2010 and may serve as a baseline for the authorities to devise better strategies to reduce the adverse effects of heavy precipitation events. ii. materials and methods a. study area the kabul river is a 700-kilometer long river which is located between 33°36’ n 36°55’ n and 67°36’ e 73°54’ e. the river starts from the sanglakh range of hindukush mountains in afghanistan and enters pakistan through mohmand agency, where it is first gauged at warsak dam, then passes through nowshera and finally drains into the indus river near attock. it contributes about 10% to 20% of its annual flows to the indus river system [17]. the total catchment area of the kabul river basin (krb) is about 76,908km 2 , out of which 14,000km 2 are located in pakistan (figure 1). the basin has elevation of 305-7690m [18]. higher discharge in the river is observed in july and august due to the heavy rainfall and, due to the higher temperature of these months, glacier melting. the main cause of flooding in the region is the combination of rainfall and glacier melting [19]. the climate of the basin is semi-arid. the maximum temperature of 28°c is observed in june-august, whereas the mean minimum temperature is -6°c. due to the complex terrain and the variation in elevation, precipitation varies throughout the basin. the maximum precipitation occurs during winters in the form of snowfall, with an average of 110mm [20, 21]. chitral, swat, and lower parts of the kabul river experience the indian summer monsoon, on the contrary, the upper kabul is influenced by western disturbances [17]. fig. 1. map of the two nested domains of wrf simulations at the kabul river basin (d01 = 6km, d02 = 2km). b. wrf model and setup in this study, the advanced research weather research & forecasting (wrf) model [21] is used. the wrf model is a next-generation mesoscale numerical weather system, which is used for short-term weather forecasts and long-term climate simulations. the wrf has been developed by the national center for atmospheric research (ncar) in partnership with national oceanic and atmospheric administration (noaa) and the us department of defense. the wrf model was set up by using two nested domains, domain 1 (d01) and domain 2 (d02) with increasing resolution moving inward from 15km to 5km grid spacing (figure 1). the lambert map projection type is chosen for both domains. the inner domain (d02) is centered over northwest pakistan to represent krb with two-way nesting. the simulation started at may, 1 at 00:00 hours and ended at september, 16 at 20:00 hours. the hourly simulated data were converted into daily data for the validation process. initial and boundary conditions for the simulations were derived from the noaa climate forecast system reanalysis (cfsr) data [22], which has a 38km horizontal resolution. the research shows that the cfsr dataset performs well in simulating atmospheric changes over the hkh region [11, 22]. the wrf model is a non-hydrostatic model that has many options for physical parameterization schemes. the model is configured with the noah multi-parameterization (noah-mp) land surface model [23], yonsei university (ysu) planetary boundary layer scheme [24], thompson microphysics scheme [25], rapid radiative transfer model (rrtm) longwave radiation scheme [26], dudhia shortwave scheme [27], surface layer scheme [28], and betts-miller-janjic cumulus scheme [29]. all these schemes were applied for both domains, however the resolution of the inner domain (d02) is small enough to allow switching off the convective parameterization. c. model validation we evaluated the simulations with the station meteorological data obtained from the pakistan meteorological station (pmd) and water and power development authority engineering, technology & applied science research vol. 12, no. 1, 2022, 8017-8022 8019 www.etasr.com rafi et al.: an evaluation of the extreme rainfall event of 2010 over the kabul river basin using the … (wapda). the daily data come from 11 stations, namely balakot, chitral, drosh, dir, saidu-sharif, peshawar, ushkore, yasin, phulra, beshamqila, and daggar. the wrf precipitation output was also assessed with the tropical rainfall measuring mission (trmm) 3b42 version 7 gridded precipitation data at a monthly time scale. trmm is considered a reliable gridded precipitation dataset in the himalayan karakoram region. the trmm dataset has the best performance among the other remote sensing datasets in the indus basin [30]. similarly, authors in [31] revealed that trmm 3b42v7 is better than the other products when evaluated in the hunza river. the wrf simulations were assessed by the percentage bias (pbias), root mean squared error (rmse), and pearson correlation coefficient (r), and bias. ���� � �∑ �� �������� (1) � � ∑ � �ō����� ��͞ � �∑ ��ō����� � ∑ ��͞ ����� � (2) ���� � �� ∑ �� � ������� (3) pbias � 100 ∗ (∑ �� �� �∑ �� ) (4) where si denotes the simulated values, oi denotes the observed values and n is the number of days. iii. results in this section, the wrf-simulated precipitation is evaluated by using the pmd meteorological data and the trmm dataset. a. precipitation at specific location this section compares the wrf predicted precipitation to values observed by gauges and trmm. the main results for both domains are shown in figure 2. the wrf and trmm data were bilinearly interpolated to the 11 gauge stations. for the wrf data, interpolations were performed separately for the 15km data from d01 and the 5km data from d02. the wrf reproduced the precipitation from may, 1 to september, 16 at each station at 22 different resolutions. it was seen that more precipitation was simulated by the wrf model on 29 july in each station in both domains. fig. 2. time series comparison between the wrf simulated precipitation (blue), observed gauge precipitation (red), and trmm precipitation (green) for d01 (left column) and d02 (right column). before presenting the summarized statistics of the wrf performance, we begin with the specific results for july, 29, 2010, which feature exceptionally high precipitation totals as discussed in the introduction. when the simulations of each station were compared for d01, the simulated rainfall on july, 29 was 55mm (balakot), 65mm (besham qila), 27mm (chitral), 47mm (daggar), 58mm (dir), 38mm (drosh), 49mm (phulra), 63mm (saidu sharif), 16mm (ushkore), and 17mm (yasin), with the highest rainfall predicted in peshawar (120mm). similarly, in domain d02 the rainfall predicted at each station was 46mm, 55mm, 22mm, 40mm, 84mm, 30mm, 53mm, 67mm, 10mm, and 12mm respectively, with the highest rainfall again predicted in peshawar (153mm). on the other hand, the observed data show that the maximum precipitation recorded on july, 29 was 45mm, 128mm, 41mm, 99mm, 149mm, 61mm, 90mm, 187mm, 0mm, and 2mm for the same stations, with the highest rainfall predicted in peshawar (274mm). in addition, when simulated precipitation and gauge data were compared for d01, it was found that the wrf model under-predicted the precipitation at all the stations on july, 29, whereas there was over-prediction at balakot, ushkore, and yasin. engineering, technology & applied science research vol. 12, no. 1, 2022, 8017-8022 8020 www.etasr.com rafi et al.: an evaluation of the extreme rainfall event of 2010 over the kabul river basin using the … for the gauge data, the results showed that the pbias decreased in magnitude in domain d02 at balakot, chitral, daggar, drosh, peshawar, phulra, saidu sharif, and ushkore, whereas it increased at besham qila, dir, and yasin. this means that the resolution increase from d01 to d02 lessened the bias against the gauge data for 8 stations and worsened the bias for 3 stations. on the other hand, when the simulated precipitation was compared with the trmm dataset, it was found that there were 4 stations (balakot, peshawar, dir, and yasin) where the bias was decreased in magnitude on d02 and 7 stations (chitral, saidu sharif, ushkore, besham qila, phulra, drosh, and daggar) where the bias was larger in magnitude on d02. overall, the gauge data comparison provided a stronger indication of bias reduction on d02 than the trmm data comparison. similarly, when the wrf predicted precipitation was compared with the gauge data, the correlation between the simulated and the observed data varied for each station. the wrf showed a high correlation (r ≥ 0.5) to 5 stations (balakot, chitral, besham qila, dir, and drosh), whereas the rest of the wrf results had a lower correlation with the station data. the highest correlation was observed in besham qila (r = 0.8) and the lowest in phulra (r = 0.2). on the other hand, when the correlation was considered for the simulation precipitation and trmm dataset, 8 stations (balakot, chitral, yasin, besham qila, dir, drosh, saidu shaarif, and daggar) showed high correlation to the trmm dataset, whereas 3 (peshawar, ushkore, and phulra) did not. the highest correlation was observed in besham qila and peshawar with r = 0.8, whereas the lowest was observed in phulra with r = 0.3. overall, at each location, the correlations with station data were similar in domains d01 and d02. fig. 3. wrf precipitation percent bias against gauge data in domain d01 and domain d02. to illustrate how the performance statistics were organized on the topography in each domain, figure 3 shows the pbias of wrf simulated precipitation relative to gauge data as a function of elevation. the shape of the pbias graphs as a function of elevation was similar on both domains, and the largest magnitude biases were positive and occurred at higherelevation stations above approximately 1500m. at all but one station, as shown in figure 3, the pbias was smaller in d02, which shows that at all stations there was a smaller bias between modeled and observed precipitation in d02 as compared to d01. the pbias averaged -9% in d02 and 17% in d01. the t-test was used to identify cases where the mean precipitation simulated by wrf differed significantly from the observed precipitation at the 95% confidence level (p ≤ 0.05). for most gauge data, the null hypothesis of no difference in mean could not be rejected at the 95% confidence level. however, in domain d01, a significant difference in mean was found at 3 stations: chitral, drosh, and ushkore. when the wrf predicted precipitation was compared with station data in domain d02, significant differences were found at dir and ushkore. for trmm data, no significant differences were found in d01, and only 2 locations (drosh and besham qila) had significantly different results in d02. the patchy significance of these t-test results indicates the encouraging performance of wrf, especially given that we assumed one degree of freedom per day (i.e. use of effective degrees of freedom reduced to account for autocorrelation would be less likely to reject the null). table i lists the p values associated with the t-test comparing the mean wrf precipitation to gauge (trmm) precipitation in d01 and d02. table i. p values for d01 and d02 station p-value d01 (trmm) p-value d02 (trmm) balakot 0.12 (0.14) 0.3 (0.2) chitral 0.004 (0.7) 0.1 (0.3) dir 0.2 (0.2) 0.003 (0.2) drosh 0.002 (0.3) 0.9 (0.02) saidusharif 0.7 (0.07) 0.8 (0.3) peshawar 0.8 (00.5) 0.6 (0.3) ushkore 0.0005 (0.06) 0.03 (0.6) yasin 0.86 (0.4) 0.4 (0.8) phulra 0.4 (0.5) 0.6 (0.3) beshamqila 0.3 (0.1) 0.1 (0.02) daggar 0.5 (0.6) 0.7 (0.4) b. multilocation mean precipitation this section examines the precipitation averaged across the station locations for wrf, trmm, and gauge data. wrf, trmm, and gauge data were averaged at the 11 gauge location. wrf over-predicted the precipitation at some days and under-predicted at others (figure 4). similarly, it was observed that wrf under-predicted the average precipitation on july, 29 in both d01 and d02. the trmm value for this extreme event was intermediate between the wrf and the station values (the station average precipitation for both domains on july 29 was 98mm, and the trmm dataset indicate 76mm in both d01 and d02, whereas the wrf model simulated 50mm in d01 and 49 mm in d02). iv. discussion in this paper, the wrf model was used to simulate the precipitation of the flood-producing rainfall event of 2010. it was found that there were 3 heavy precipitation events observed during these 5 months, namely may 17, june 3, and july 29. the findings of the study revealed that the precipitation event of july, 29 was the main cause of the flood of 2010, which was consistent with [8, 9]. the results showed that the precipitation simulations were improved from d01 (15km) to d02 (5km), which is attributable to the increased resolution or the combination of the parameterization schemes, engineering, technology & applied science research vol. 12, no. 1, 2022, 8017-8022 8021 www.etasr.com rafi et al.: an evaluation of the extreme rainfall event of 2010 over the kabul river basin using the … which is consistent with [32], in which it was found that wrf simulates convective precipitation quite effectively using noah lsm, which predicts both soil temperature and moisture. the findings are also consistent with [33], the authors of which found that at higher resolution the wrf model shows better results. the results of the study are similar to that of [34], in which it was found that complex terrains need higher resolution to accurately forecast precipitation. the study showed that the wrf has a weak positive correlation (r = 0.3) with the observed data at high-elevation stations (ushkore and yasin). however, the wrf results tend to have a stronger positive correlation with the observed datasets at some of the low-elevation stations (e.g. besham qila and peshawar). this is consistent with [34-36]. in addition, the wrf showed a higher overall correlation with the trmm dataset than with the gauge data. the station-averaged precipitation indicated a mix between over-prediction and under-prediction. for the extreme event on july, 29, wrf's simulated precipitation (~50mm) was smaller than the trmm (76mm) and gauge results (98mm). discrepancies from observations may stem from not resolving subgrid-scale terrain effects or limitations of the chosen physical parameterization schemes [36]. the high-elevated stations showed more pbias except for yasin and dir station, where the wrf showed a low pbias of 3.8% in d01 and -18% in d02 in yasin and -21% in d01 and -51% in d02 in dir. in addition, the wrf showed less bias at the low-elevated stations except from saidusharif and beshamqila stations where the model showed underestimation of precipitation, as large as-34%. overall, it was concluded that the wrf model performed well with higher resolution with slightly overestimation at some locations and underestimation at others, which is consistent with [38]. hence, it can be said that wrf can be used to predict the extreme precipitation events over complex regions such as the upper indus basin. v. conclusion and recommendations kabul river basin is an integral part of the indus basin and has been frequently hit by massive floods in the past. the worst flood in krb was the flood of 2010. it is expected that due to the climate change, the frequency and intensity of floods will increase in the future. this study was conducted to simulate the flood of 2010 by using the wrf model over the krb. the findings of the study revealed that the wrf model was able to predict the extreme precipitation event of 2010. the overall favorable performance indicates that the one-month spin-up period was sufficient for short-term simulations. two domains were used to simulate the precipitation over the region, and the result showed that the wrf model performed better in the higher resolution domain. it was concluded that the model proved to be useful for precipitation simulations in the hkh region. although the wrf model performed well in the krb, substantial biases were found at some of the higher elevation 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[38] g. skok, j. tribbia, and j. rakovec, "object-based analysis and verification of wrf model precipitation in the lowand midlatitude pacific ocean," monthly weather review, vol. 138, no. 12, pp. 4561– 4575, dec. 2010, https://doi.org/10.1175/2010mwr3472.1. engineering, technology & applied science research vol. 8, no. 2, 2018, 2735-2740 2735 www.etasr.com soomro et al.: fading legacy of the architectural heritage of the historic core of karachi fading legacy of the architectural heritage of the historic core of karachi tania ali soomro department of architecture and planning dawood university of engineering & technology karachi, pakistan mohsin ali soomro department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan drmohsin@quest.edu.pk abdul nasir laghari department of chemical engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan daddan k. bangwar department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan mukhtiar ali soomro department of civil engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan abstract-in 1839 british east india company captured the town of karachi. after an effortless resistance from the locals the fort was conquered by the british commander sir charles napier. the village of kolachi then was annexed to british india and the city was labeled as karachi. with the british occupation a phase of new sophisticated architecture and development started. before that the city was based upon the vernacular mud architecture. these developments resulted in an influx of economic migrants who helped in making karachi as a multinational and a multicultural city. this paper investigates the architectural attributes that the historic core of the city offers. it also discusses the side by side development of the native and british towns. the paper also researches about the existing state of the architecture precedent of the british colonial past of the city and the urban blight occurred to them over time in various forms like vandalism, encroachments, illegal repairs, etc. keywords-architecture; karachi; legacy; urban; development i. introduction the city of karachi was established in 1729 as a fortified port settlement which used to be part of the greater british raj together with the present day countries of india and bangladesh. although the city is only 250 years old, there are places of pilgrimage within that go back to more than 2000 years. most of them are still active [1]. karachi used to be a small fishing village at the time when it was occupied by the british in 1839 and with this annexation a new era of development and construction started. karachi remained a british colony from 1839 to 1947 for 108 years. in 1843 the whole province of sindh was captured by british and karachi was made its capital. new business opened up with the development of its harbor for shipping. the foundations of a city municipal government were laid down and infrastructure development was undertaken. at that time, the british realized the significance of the city as a military cantonment and laid foundation of a new division. the cantonment was a mock-up of an english industrial parent-city, in other words, a basis of the 'white' town, where the local population had restricted rights of entry, where work and residential spaces were separated [2]. at present day the city is divided into 6 different zones and each of the zones is divided further into towns/municipalities. altogether there are 18 elected municipal administrations for infrastructure and spatial planning, development facilitation, and municipal services with some functions being retained by the kmc. the towns are further sub-divided into 178 localities (each town has its own number of localities). ii. introduction to the historic core of karachi historically, the city was divided into 18 different quarters as it grew after the british annexation (demarcated by alexander f. bailie, the municipal engineer then). these 18 parts are now referred to as the historic core or the center of the city. among 18 quarters, 13 are closely located and the rest are located at a distance. the boundaries of these quarters do not usually coincide with the town boundaries. therefore, the saddar town and the saddar bazaar quarter should not be confused to be the same. these quarters contain much of the oldest parts of the city which signifies the colonial history of karachi, in particular the saddar bazaar and the neighboring areas of kharadar and mithadar. the town is further subdivided in 11 municipal localities, including saddar bazaar as one of the locality. the present day historic center was developed by the british during the colonial era and housed magnificent stru dis wo or bec sta nei au we gri dem stru (de eas rup loc nam som sc vir an nor mi acc the she the all gov the nu sa of con inc off ho ob pa con tra wa tra mi mi evi zo her apa lib the his un pro sta sup qu sa engineerin www.etasr ructures of gre strict of the ci ord saddar is the supreme came a main alls under on ighborhood co uthor in [3] rem ell planned set id iron pattern marcations. h ructures within emolished late stern end of t pees and the cated along the med after the me of the very otch presbyte r baijee soo nother quarter rthwest (back) ilitary arsenal cess from pre e quarter was eds, some cell e quarter was ocated for vernment adm e sindh asse mber of emba cantonment addar bazaar w sindh. it wa ntaining all b cluding britis ficers, british/ spitals, churc servatory etc. atrick’s cathed nnected and a ansportation sy as discontinue ams were cons iddle of the ro ix of the peo ident from th oroastrian fire ritage consists artments, man braries etc. at e rest of the c storic properti derstand the operties a surv ate is develop pposed to be e arters but due addar bazaar q ng, technology r.com eat importance ity with sadda derived from and it develo bazaar of the ne roof, but ontaining a n members sadd ttlement havin ns with proper he mentions n that area spec er, location un the bazaar), b parsi infant e southeast (fr first ‘bazaar y important str erian church, k opariwalla pa r is artillery ) side of the s that was locat edy street. du s dedicated to ls for detention just a large gr government ministrative bu embly buildin assies [2]. from the sout was developed as essentially t building type sh army offi /native adminis ches, canteen one of the dral and the sc accessed well ystem. there ed during the sidered a traff ad [4]. moreo ople from var he presence of e temple with s of both priv nsions, instituti present, the q city but unlike ies have gon present con vey is conduct ped. the scop extended to the e to constrain quarter only. th y & applied sci e. it became a ar as the main arabic which oped as a baz e town, not o t it grew a number of sto dar as the mo ng wide stone r pedestrian a about few cifically the c nknown proba built in 1861, school. pree ront) side of th master’ of ka ructures includ known as st. arsi (bvs) b maidan whic saddar bazaar ted in the north uring the late o the horse k n and a small round. later t purposes, an uildings were b ng, high cou theast to the n d shortly after t the domain o es necessary cer’s resident stration, reside ns, stores, p magnificent s chool complex by other loc used to be a 1960s. as a fic hazard as t over these quar rious religiou f mosques, ch hin them. the vate and publi ions of dispen quarters are w e their original ne through dr servation stat ted and a map e of the exer e saddar baza nt of time, it he survey show ience research soomro et a a highly fashio n market place h means chief, zaar that ultim only as a mark as a sophist ores and shop st sophisticate paved streets and vehicular t of the land cunynghame m ably situated o at a cost of 1 edy quarter th he saddar baz arachi [2]. it h ding the magni andrew’s an boys high sc h is located t r. it used to ho h – east corne 1880s, one p keeper’s lines hospital and r that empty par nd a numbe built there incl urt building a northeast side the british con of the british for their com tial colony, j ential lines, sc parade ground structures is th x. these quarte calities via a p tram system w matter of fac they stopped rters are a harm us groups wh hurch, hindu e rich archite ic premises su sary, schools, well connected l state, even th rastic change te of the he pping of the c rcise was orig aar and its adjo was limited t ws that the ma h v al.: fading lega onable e. the , main mately ket of ticated ps [3]. ed and set of traffic dmark market on the 17,500 hat is zaar is houses ificent nd bai chool. to the ouse a er with part of s, gun rest of rt was er of luding and a of the nquest army, mfort, junior hools, d, an he st. ers are public which ct, the in the monic ich is and a ectural uch as office d with hough es. to eritage current ginally oining to the ajority of t sma mai con sho rath hist tim few seen suc dete high a. freq arch styl then with is c iden mor way the kar bui to app form the to phi alre edif colo ope to t ped gril wor are giz fini vol. 8, no. 2, 20 acy of the arch the buildings, all number of intained’. the ndition of the r ould not be con her a state tha toric building me. a few of t w are under co n as having ju ch type of eriorated’, the h threats of co fig. 1. kris iii. archit description o anglo vernac quent termin hitecture (prio les imitate a ce n contempora h the regional concerned, th ntified in kara re as a respon ys rather than city as a po rachi became lders, masons travel to kar proach is refle m of an innov built environm karachi play lanthropist eady well-kno fices inspired the most fre onial period enings, recesse the certain lev diments. regi ll iron works a rk in fine woo often seen w zri stone as a ish, is most c 018, 2735-2740 hitectural herita almost 60% o f buildings fa e degree of th rest of the buil nsidered as a p at is distinguis gs have been them have new onstruction. a ust standing fa buildings a ey are in a hig omplete demol shna mansion in s tectural ana of the colonial cular, colonial nologies by or to 1947) o ertain type of a ary europe, p context of the here is no co achi. this cou nse to the gro n a planned sc ort town in la a dynamic co s, craftsmen an rachi to avail ected in the h vative mix of ment of karac ed their part the qualities own in bomb by the europe equent recurrin are the arca ed windows, cr vel and the use onal features and the orname od strips and th with the semic main building ommonly see age of the histo of them, are pa all under the he maintenanc ldings in the q perfectly resto shing from oth demolished o wly constructe certain numb acades of the are identified ghly vandaliz lition (figure 1 saddar bazaar (hi alysis of the l architecture l or the dome which the of karachi is architectural a particularly in e area. as far a oncept of the uld be because owing needs in cheme. with th ate 19th and e ommercial cen nd others from l the work o hybrid archite imported and chi. parsi fam as the great for which th bay [2]. they ean forms. ng architectur aded colonna rowning corni e of pilasters include jodh entation in flor he intricate con circular gothic g component, n. moreover 2736 oric core of ka artly maintaine category of e is relative t quarter. howev ored condition her buildings. over the perio ed structures a ber of building original prope d as the ‘h ed state and u 1). ighly deteriorated e historic co of karachi estic gothic ar pre independ referred to. t approach popu england, ado as the city plan e parallel plan the city devel n many unpla he developme early 20th cen nter. this attr m different re opportunities. ectural approac d regional form milies who mig t builders and he community y built impre al attributes o aded porticos ices that projec and sometime hpuri style tu ral patterns. l ncrete mashra c arched open in dressed su most sources arachi ed. a ‘well to the ver, it n, but, few od of and a gs are erties. highly under d) re re the dence these ular in opted nning nning loped anned ent of ntury, racted gions such ch in ms to grated d the y was essive of the and ct out es the urrets, attice abiyas nings. urface have als ita col com the ka orn dem res inn app sou adm con adm als sup sys for lig lam tho len exc trib and on br tow ar for had da kn wa tow the dev adm bu wo str and the the wa nat clo its cov ma wa hin arc mo engineerin www.etasr so quoted the alian renaiss lonnaded por mmon in the b e buildings of atrakparsi ma namental as th monstrate a spect to the novation of propriately use und knowledg ministrators to nstruction o ministrators n so executed s pply system stems, road ne rm of tram. ghting. he has mps every nig ousand lamps ngth of over 6 changed for ke iv. today’s met bes from balo d was named e of the ruling ritish conques wnship and b rabian sea wi rtified by a fo d two entran arwaaza (brac own as meet ater of the rive wn area is still e conquest o velopment aro ministrators e ilt stone struc orks of sanitat reets, proper d d horse-drawn ese amenities w e elite. native the british alled city of k tive city and t ose to the port suburbs. it w vering every aneuvering. du as less space ndu and musl chitecture was ost often the ng, technology r.com late 19th earl sance architec rticos, vestib buildings cons f mitharam ho ansion. thou hey are in ita blend of the regional con f the italia ed here is the ge of using th o achieve extr of magnifice not only emph some of the p for the settle etworks and pu author in [4 s expressed tha ght. he has fu are installed in 60 miles, for w erosene oil in chronolo tropolitan city ochistan and m kolachi. it w g dynasties in st. the villag by late 1720 ith oman an ort built by the nces, one fac ckish gate) an tha darwaaza er). the fort do l referred to as of karachi ose and the vil established eu ctures. they tion and trans drains, street sw n trolleys, etc. were only acc people were d built separate kolachi and cl the british nei t and consisted was extremely y bit of sp ue to the dens for vegetation lim merchants a mix of low houses were y & applied sci ly 20th century ctural approa ules and co structed during ostel, sewajunj ugh the churc aly, but in cer e renaissance ntext of kara an romane ‘vault’. vaults hem together, raordinary acc ent structure hasized on the public works ements, sewe ublic transport 4] has elabora at the city is l further added n the roads and which, since 1 the lamps. ogical develo was founded makran as a sm was ruled by t the province ge developed s, it started nd persian gu e local sindhi cing the sea, nd other facin a (sweet gate oes not exist a s kharradar an a new phas llage upgraded uropean inhab also set up a sportation, suc weepers, and . one downsid cessible by the deprived of suc e settlements early created ighborhoods. t d of the old p y congested an pace with n se developmen n. as it was as well as the mud hovels a made of win ience research soomro et a y architecture ach. the us ourtyards are g this phase su j, mendoza an ches are not rtain ways, th e forms used achi. the for esque archit s and arches an helped the co complishment es. the co e built structur such as the erage and dra tation facility ated the syste lightened by t that approxim d streets, cove 1870, coconut opment by the local b mall fishing v the talpur dy of sindh befo into a small trading acros ulf. the town i populace. th known as k ng the lyari because of anymore but th nd meethadar. se of archite d to a city. co bited quarters a number of p ch as gravel a network of de was that m e british or so ch facilities. next to the n a bifurcation the native cit re-british tow nd highly den narrow streets nt in the town, dominated by e working clas and tall mud ho dowless mud h v al.: fading lega as the se of seen uch as nd the t that hey do d with remost ecture nd the olonial in the olonial re but water ainage in the em of the oil mate a ering a t oil is baloch village ynasty, ore the l port ss the n was he fort kharra river sweet he old . with ectural olonial s, and public paved trams most of ome of native as the ty was wn and nsified s for , there y both ss, the ouses. walls with surr bui sign who can mo gro city very com min pop spa of b the mar ann the civi eur the eur city all tod brit con fig. sern trou ind of sign nee acc esta baz area bab vol. 8, no. 2, 20 acy of the arch h flat roofs. rounded by a lt upon humb nificant archit olesale marke ntonment, civi st part was i oup of parsi an y. it contained y similar to mmunities w norities). this pulated low-ris aces and little british neighb occupation o rkets in the nexation of sin european pop il servants ropeanized ind time of part ropean city an y over flown th the directions day’s city is tish. at prese nsidered as the 2. top left: nagati building ( ugh. v. histor the city rec dian subcontine newly forme nificant physic ed of developin commodating ablished in th zaar. most cou a. also a uni ba-i-urdu road 018, 2735-2740 hitectural herita bad-girs or a tumble-down ble platform tectural featur ets of the city il lines and th inhabited by t nd goan elite c d posh retail m those in eu who still re s part of k se settlement, plantation. sa borhood was cr of karachi as native city ndh in 1843, pulation of ka and military dian communi tition karachi nd native city he boundaries having new c much bigger ent the british e historic nucle mendoza buildi (used to house b ric city cent eived a sudd ent partition, w ed pakistan i cal and cultur ng new institu the federal he artillery m untries establis iversity was e d in the aramb age of the histo the ventilator n curtain-cum of mud-cove re [5]. it cont y. british city he saddar ba the british po came to settle d markets, shops urope (the m main have karachi develo with wide th addar bazaar, reated in 1839 a competitor y. however, it evolved as arachi which c y personnel ities made sad i was clearly . with further s of british tow colonies and sa than the one h town along eus of the city ing in rambagh british council ter present den change o when karachi in 1947. thi ral changes to utions in the ci government maidan quarte shed their emb established on bagh quarter ( 2737 oric core of ka rs (wind catc m-bastions of ered rock wa tained most o y consisted o azaar quarters. opulation. a down in the b s and eating p members of become cu oped as a t horoughfares, g one of the qua 9 immediately r to the whol after the b a retail marke consisted main [5]. over ddar their hom divided into r developmen wn and extend atellite towns developed by with the nati of karachi. h quarter. bottom library), right: day situatio f census afte became the ca is change bro the city. wit ity, a secretari institutions er next to sa bassies in civil n what is now (formerly ram arachi chers) mud, s the of the of the . the large british places these ultural thinly green arters y after lesale british et for nly of time, me. at two: nt, the ded in built. y the ive is m left: water on er the apital ought th the at for was addar lines w the mbagh engineering, technology & applied science research vol. 8, no. 2, 2018, 2735-2740 2738 www.etasr.com soomro et al.: fading legacy of the architectural heritage of the historic core of karachi quarter). the refugee population occupied most of the buildings abandoned by hindus including public and religious in the native city and the open spaces in the cantonment and lines area near sadder in a multi-class settlement structure. they included government officers, poets, artists, journalists and intellectuals. people from all walks of life made karachi a multi-class high density metropolis with the saddar bazaar as a rising intellectual and entertainment center. a. current status of the colonial architecture in karachi the saddar bazaar, which developed as the cultural hub of the city along with the rest of the quarters is now a victim of environmental degradation. the change of land and building use by laws has transformed the majority of the low rise historic structures into high rise plazas. the process of dilapidation started when the wealthier people moved out of center to the newly developed cooperative societies during the 1960s, leaving the earlier inhabited area as a transit area of the movement between the newly developed satellite towns of korangi and landhi and the work areas of the city [6]. the colonial buildings after the indian subcontinent partition went through a lot of transformations, in the worst cases they were demolished. the demolition process stopped due to the enlistment system for the protected heritage in 1970s. perhaps this act helped structures to sustain but the vandalism kept on going in the form of inappropriate changes in historic significance properties. for instance, the empress market along with a few nearby structures has survived despite the additions and modifications having largely retained the function for which they were originally constructed. eduljee-dinshaw dispensary building a few blocks away from the empress market has undergone several changes from the adding up of minor alterations to the addition of masses to its fabric. the same happened to the khyber hotel building, which is a magnificent corner building with impressive arcaded openings on ground floor. it had gone through several alterations such as the closing of the arcade permanently, application of ceramic tiles over stone wall and so on. b. urban blight of the heritage properties in the historic center based upon the study of the present conservation status of the heritage buildings, an analysis of the urban decay in the historic core of the city is made which illustrates how this decay eventually threatens the city’s heritage properties. within a decade of the independence the city extended its limits as new cooperative housing societies and satellite towns for the working class refugee population were established on the fringes of the city. this deprived the historic center of its elite class population as more influential and wealthier families in the refugee colonies shifted to those colonies leaving behind the historic buildings occupied by them earlier. on the one hand, when city grew outward for residential purpose, at the same time it grew inward from the commercial point of view. the major whole sale markets located within the city center extended their limits over time. as there was no more space for their extension they eventually occupied the historic structures and converted them into godowns and storage spaces, etc. transportation crises emerged as to cater the distant located colonies and towns to the city center. since there was no proper transportation network, the whole movement was through saddar. this transformed saddar into a transit camp, congested with people, badly maintained busses and badly maintained traffic [5]. in the 1960 the university was moved from the rambagh quarter to its present location. this caused a rundown of student population and academic life in rambagh. moreover, amendments in the building by laws and land use regulations in 1972 caused a great deal of damage to the heritage buildings as well as open spaces. earlier the plots which were eligible for ground floor construction are now qualified to go till g+8 structures. this put a great threat to the historic structures. a large number of important heritage buildings are pulled down and replaced by new high and medium rise structures. the changing demographic patterns have a great impact on the city. it has always been a threatening factor to the wellbeing of historic structures. karachi being the metropolitan city and a commercial hub has to cater a large number of population. apart from the annual rural urban migrations, the city has received three phases of the influx of refugees:  phase 1. refugees from indian subcontinent partition in 1947  phase 2. refugees from pakistan bangladesh partition in 1971  phase 3. refugees from afghan russian war in 1980. apart from this the population tends to increase every year as the average household size increases. according to a recent research on the population division (2014), world urbanization prospects: the 2014 review by the united nations department of economics and social affairs, the city of karachi is considered among world’s top 10 populated cities. its population is estimated to be 24,837,881 in 2030 from 16,125,936 in 2014 [8]. constant population growth with increasing economic pressures and least economic incentives exerts pressure on the buildings in order to fulfill the requirements of the dwellers,and under the inadequate law enforcement, the situation results in the poor state of conservation of architectural heritage.in the historic center of karachi, exists an informal renting system called pugree or the good-will system. in this system the property is leased for over 99 years with a condition of bare minimum rental amount per month. most of the historic premises in the historic core are rented on pugree that means they are rented and owned by different persons. the owner receives almost nothing whereas on the other hand the situation is pretty fair for the tenant who has to pay very little amount. the arrangement wields a great threat to the wellbeing of the architectural heritage. as the owner gets the minimal amount, it makes him least bothered about the well-being of his property and the tenant considers it as a rented property and not his own. in the end the property suffers. c. repercussions of the urban blight in the historic center 1) urban densification the historic center of the city is densely populated with high rise structures giving a portrait of a thick concrete jungle wit dev stru of no 2) wit ter inh exp con inc inf the rea thi enc 3) all tra vie inc act spa the 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uarters have ionality and ap ential apartme ion have acq many religious nstruct new b ave survived a ep the buildin ace, these build alterations. th apid as these a quality mater to the existing ity of the stru es are therefo ead load applie severely [9]. f ddar was linke nnected one en able for those the major ch using schemes ot enough and services were ncreased vehi ces used to en a landmark th t was at walk n artillary ma new satellite t on the trans arge transit m pt on growing rivate) could ience research soomro et a oric premises at to those hi untouched, th w rise structure ncreasing hous ressure buildin quirements o priate conserv ults in poor st uarter. moreov on the p of roads, park n and several have failed to few example pansion with ti undergone s ppearance poi ent buildings d quired comm buildings and buildings. how and sustained ngs still going a dings have acq he decaying pr added structur rial. at some p g structures w cture to which re over loade ed to them and figure 4 show ed to the rest o nd of the city e who worked hange occurred s that were o d a proper veh added to me cular traffic i nd in the vicin hat had open s king distance aidan quarter. towns develop sportation net movement took g and the tran not cope wit h v al.: fading lega s. the istoric he rest es are sehold ngs in of the vation tate of ver the public ks and other o stop es of ime in everal ints of due to mercial d open wever, d their and to quired rocess res are places without h they ed and d may ws one of city to the in the d with outside hicular eet the in the nity of spaces to the with ped on twork. k place nsport th the hug intr wis no of p per incr mo till in t in term tran fig. histo fig. surfa 5) pro whi com and peo for fina bui of cha of t vol. 8, no. 2, 20 acy of the arch ge increase in roduced a fre shing to opera subsidies and proper large b mits for affo rease of popu st important t today. this m the absence of the emergen minals and bu nsport. 3. images sh oric buildings. 4. image sho face decoration ov commercializ during the pa operties has be ich puts the mmercializatio d their replacem ople prefer dem a systematic ancial capabili ldings is also a the demolish anging buildin the heritage p 018, 2735-2740 hitectural herita n commuters ee transport p ate a bus could bank loans or busses were of ordable mini-b ulation in year transport mod massive overcro f a rational tra nce of hawke us stops and a howing encroachm owing unwanted r ver stone facade zation pressur ast decades the en transforme whole area u on. the rate of ment by high r molition as an conservation ity being the m an approach to hed constructio ng regulations properties of k age of the histo . as a resul policy whereb d be given a r r even any aud ffered, individu buses and sm s ahead mini de in karachi owding of com ansport plan fo ers, encroach an aggressive ments and various repairs in form of re e function of m d from residen under a great f demolition of rise structures n easy way ou strategy due most importan o earn easy rev on materials are also threa karachi paving 2739 oric core of ka lt the govern by any indiv route permit. s dit for the purc uals acquired mall coaches. busses becam which is prev mmuters and b or the city, res hers, informal services sect s forms of vandali f application of pa most of the his ntial to comme t threat of fu f historic struc is alarmingly ut rather than g to several rea nt. demolishin venue as antiqu can be sold. atening the sur g the way for arachi nment vidual since chase route with me the valent buses, sulted l bus tor to ism on aints as storic ercial urther ctures high. going asons, ng old uities the rvival r new dev of hav un 6) att set com pre bei rec acc but new 7) to is cha bil ins sho def fig em and fun inh the con and com inc per pro his col [1] [2] engineerin www.etasr velopment pro technology, m ve played a g wanted for pre violence violence in acks, vandali tting fire to b mmon phenom ecious buildin ing restored, construct the b ceptable if th t reconstructin w objective ca political pre one of the ve historic build referred to a alking in for llboards defac serted in ever own in the fi facement. g. 5. image sh mpress market over time m d what remain nctioning. the habited. the m e state of the nsolidated wit d the user con mmercializatio creasing numb rplexing. the omote awaren storic premise lonial architec j. ruskin, the h. khuhro, a oxford univer ng, technology r.com ojects. the ec modernism an great part in esent day worl case of herita isms etc. the buildings, in menon. there h ngs were burnt the damage building. the e building ha ng the deliber an only be clas essure ery widesprea ings is politic a combination rm of graffiti cing the bui ry corner. the igure 5 is a p howing graffiti vi. c much of the arc ns is either in v e buildings wh main conclusio e urban bligh th the non-pre nflicts. the gr on forces, la mber of users e best solution ness on local le s because des cture still offer refe seven lamps of . mooraf, karach rsity press, 2010 y & applied sci conomic chan nd the changin making old ( ld. age properties e intentionall order to get have been cas t and then van ed edifices w process of rec ad been dama rately damage ssified as vand ad and powerfu al pressure. t n of damages of the polit ilding facades e image of th erfect descrip and flags of po conclusion chitectural heri very dilapidate hich are structu on drawn throu ht to the her evailing situat round realities ack of awaren make this s n to mitigate evel regarding spite enduring rs preservation erences architecture, cou hi; megacity of o ience research soomro et a nges, transform ng human beh (historic) stru manifests as ly and malic rid of them ses in the past w ndalized. inste were dismantl construction is aged unintentio ed buildings w dalism. ul causes of da this type of da s such as the tical slogans, s and party he empress m tion of this ty olitical parties h itage has gone ed state or no l urally sound ar ugh this study ritage propert tion of heritag s like overpow ness and the subject even this situation g the significan severe chang n potential. urier corporation our times, 2nd e h v al.: fading lega mation havior uctures arson iously m, is a where ead of led to s only onally with a amage amage e wall party flags market ype of hung in e away longer re still is that ties is ge law wering e ever more n is to nce of ges the n, 1989 edition, [3] [4] [5] [6] [7] [8] [9] vol. 8, no. 2, 20 acy of the arch a. w. hughes, sons, 1876 a. hasan, a. s publishing inter f. s. aijazuddi 1992 a. hasan, und city press publ h. haroon, m. empire, pakista united nations division, world k. v. balen, “f other way aro consolidation restoration, vo 018, 2735-2740 hitectural herita , gazetteer of th . polak, c. polak rnational, 2008 in, historical im derstanding karac ication, 1999 a. baig, karach an herald publica department of e d urbanization pr from conservatio ound: how is m of masonry: a ol. 1, pp. 135-144 age of the histo he province of s , the hawkers of mages of pakistan chi, planning & r hi under the raj ations (pvt) ltd, economic and so rospects: the 201 on principles to materialization gu advances in m , 2003 2740 oric core of ka sindh, george be f saddar bazaar, n, ferozsons (pvt reform for the f j 1843-1947 visi 2004 ocial affairs/popu 4 revision, 2014 materialization ( uided by princip materials science arachi ell and ushba t) ltd., future, ions of ulation 4 or the ples?)”, e and microsoft word etasr_v12_n6_pp9670-9675 engineering, technology & applied science research vol. 12, no. 6, 2022, 9670-9675 9670 www.etasr.com nagaraja et al.: pv and wind energy conversion exploration based on grid integrated hybrid … pv and wind energy conversion exploration based on grid integrated hybrid generation using the cuttlefish algorithm y. nagaraja department of eee annamacharya institute of technology and sciences kadapa, india nagarajaeps@gmail.com t. devaraju department of eee sree vidyanikethan engineering college (autonomous) tirupathi, india devaraj_t@yahoo.com a. muni sankar department of eee sree rama engineering college tirupathi, india naac.co-ordinator@sreerama.ac.in v. narasimhulu department of eee rajeev gandhi memorial college of engineering and technology (autonomous), nandyal, india narasimhapid@gmail.com received: 22 september 2022 | revised: 28 september 2022 | accepted: 1 october 2022 abstract-this paper focuses on the exploration of grid integrated hybrid generation comprising of photovoltaic (pv) and wind energy conversion systems (wecss) using the cuttlefish algorithm (cfa). pv and wind energies are opposite because sunny days are normally calm, and strong winds frequently occur on cloudy days or at night. hence, a hybrid pv and wind power system is more reliable than either individual source in terms of delivering uninterrupted power. the regulation of the dc voltage is the key issue in this configuration. the conventional pi controller is inaccurate in regulating the dc voltage. the pi controller gain tuning using optimization techniques provides good dc voltage regulation and less total harmonic distortion (thd). hence, cfa is proposed for the tuning of pi gains. the performance parameters such as dc voltage regulation and thd of cfa are analyzed. keywords-photovoltaic; wind energy conversion system; pwm; pi; awt; pr; pso; cfa i. introduction the quick advancement of power electronics has increased the amount of solar and wind energy applications. solar energy and wind energy are generally considered to be incompatible with one another due to the fact that calm winds are more typical on cloudy days or at night, whereas sunny days typically include calm conditions. as a result, a hybrid pv and wind power system is more reliable than any independent source in terms of delivering continuous electricity. conventionally, a large energy storing battery bank [1] is adopted to reliably supply power and maximize power from pv arrays or wind turbines [1, 18], both of which are intermittent. the battery is not an environmentally friendly product, it is expensive, has a limited life cycle, it is large and heavy [2], and, pollutes the environment with chemical waste. as a consequence, it is fairly usual practice to link renewable energy sources like solar or wind to the main power grid directly. the integration of wind and solar power hybrids into the grid system is an area that is explored in this study. ii. modeling of the hybrid generation system the structure of the projected pv and wind based hybrid renewable generation power system is depicted in figure 1 and its comprehensive stipulations are listed in table i [3]. fig. 1. schematic representation of a hybrid generation system connected to the grid. the block diagram of the hybrid renewable generation power system including wec, pv, inverter, and grid is depicted in figure 1. the wind energy based power is corresponding author: y. nagaraja engineering, technology & applied science research vol. 12, no. 6, 2022, 9670-9675 9671 www.etasr.com nagaraja et al.: pv and wind energy conversion exploration based on grid integrated hybrid … converted to the dc supply and then the pv supply is integrated [4]. the combined voltage at the dc link is converted to ac supply using a standard inverter for the integration of the ac power grid. the filter is used between the inverter and the grid for obtaining quality signal. two converters are brought together to form a back-to-back converter. the connection between a grid side converter (gsc) and a machine side converter is made via a dc-bus capacitor (msc) [3]. the vector control method is utilized so that the vsi can be controlled. the vector control is constructed using two different loops. the first loop is responsible for regulating the dc-link voltage and the second loop is in charge of controlling the amount of the current that is injected. when compared to the voltage loop, the current loop is intended to react more quickly to any disturbance that may occur [3]. wind turbines generate mechanical power by capturing wind [11], as shown in (1): �� � �� ���� ��, ���� (1) where r and ρ denote the radius of blades and air density, β is the pitch angle, and λ the tip-speed ratio. the wind speed is denoted by v. � represents the utilization coefficient of wind energy [11]. equation (2) expresses the wind turbine mechanical acting torque [11]: �� � ��� � �� ���� ��, �� �� �� (2) where �� � ��� denotes the mechanical angular velocity. the pmsg is a type of power conversion machinery that converts mechanical energy to electrical energy. the park transformation, also known as dq transformation, is used to transform the time varying quantities into dc quantities. equations (3) and (4) present the voltage expression of pmsg in a 2-phase rotating d-q axis system [3]: ��� �� !�" � #��$�� % �&��' $�' % (�� (3) ��' �� )�" � #��$�' # �&��� $�� # �& * % (�' (4) where (�� and (�' are the stator voltages in the d-q components and $�� and $�' are the d and q current components in the rotor flux. the stator resistance is denoted by rs. lsd and lsq are the equal inductances of stator d-q axis in the surface mounted pmsg. �& and * denote the electrical angular speed and permanent magnet chain respectively. equation (5) represents the electromagnetic torque of pmsg [11]: �& � 1.5.� /0��� # ��' 1$�� $�' % *$�' 2 (5) equation (6) expresses the mechanical properties of a system that employs a dynamic one-mass model: �� � 3 ����" % 4�� % �& (6) the transmission system's moment of inertia and the coefficient of self-damping are denoted by j and b respectively. the pv array is depicted in figure 1, where ns represents the number of cells connected in series and np the number of modules connected in parallel. in this particular instance, the array denoted by ipv can be written as: $�� � 5 $ # 5 $� 6789 6: ;<=>? % � �=>?= @a # 1a #?=� b ;<=>? % � �=>?= @ (7) considering zero sequence components in a 3-phase system is not necessary because there is no circulation path. equation (8) depicts the three-phase balanced voltage: c(de(df(dg h � (� i sin �msin��m % 120p�sin��m # 120p�q (8) control systems make it possible to improve the effectiveness as well as the quality of the electricity that is generated by a wind energy conversion system. they are closed-loop feedback systems that control switching elements in active power conversion stages. initially, the rotational speed of the generator can be sensed and controlled using an active rectifier and a proportional integral (pi) controller. also, the grid-side inverter pwm signal can be used to regulate the system. it can be adopted to keep the dc link at a constant voltage [13-17], which will decouple the grid from power fluctuations caused by wind variations. (a) (b) fig. 2. overall control block illustration for msc. (a) reference generation of $' , (b) control block illustration. the overall control method for the pmsg [1, 4, 9-12] based wind energy power system is depicted in figure 2. the reference torque is generated in a torque control scheme by measuring the generator speed. the park transformation is used to convert the measured 3-phase current in the stator into a d-q component. thus, the stator current is equal to the q-axis component. thus, torque is controlled by only changing the stator current in the q-axis direction. it is determined whether the measured d-q stator currents are greater than the reference engineering, technology & applied science research vol. 12, no. 6, 2022, 9670-9675 9672 www.etasr.com nagaraja et al.: pv and wind energy conversion exploration based on grid integrated hybrid … d-q currents in the stator, and the difference is connected to the pi controllers [8], which produce the stator reference voltages in the d-q components. the reference voltages in stator of d-q components are transformed to the reference 3-phase stator voltages va, vb, and vc and are sent to the pwm, which generates the converter switching pulses. fig. 3. control block diagram of the gsc. the gsc's role is to ensure that the dc-link voltage stays the same all the time [5]. figure 3 depicts the block diagram of the control of gsc. the current reference (idg_ref) is generated using the pi+awt method. the gsc output current is converted from abc signal to dq signal and the components of this current are compared with the reference currents $�d_s&t and $'d_s&t. this design is made up of one outer voltage loop and two inside current loops, which are connected. the dc-link voltage loop provides the reference d-axis component of grid current. it is necessary to match the reference and measured dclink voltages, and vector control is used to handle errors. the reference d-axis grid current is produced by the pi+awt controller. the inner proportional-resonant (pr) controller produces the d-q axis grid voltage from the d-axis reference grid current and the actual d-axis grid current. park transformation is adopted to convert the d-q voltage components into natural abc grid components. the actual 3phase abc grid voltage components are then sent to the pwm generator, which generates the firing pulses to the vsc. figure 4 depicts the pr controller's block diagram. the pr control method has a high gain at the resonant frequency, which ensures that a little steady-state inaccuracy is presented between the actual and the reference signal. the pr controller is composed of a proportional and a resonant term. fig. 4. block diagram of the pr current controller. iii. cuttlefish optimization scheme cuttlefish is a species of mollusk and it is well-known for its ability to change color in such a way that it either blends in with its surroundings or puts on a spectacular show. the program is designed to function in a manner analogous to the color-changing systems that are present in cuttlefish. the patterns and colors that can be observed on cuttlefish are the result of light being reflected off of the several layers of cells within the animal, including chromatophores, leucophores, and iridophores. reflection and visibility are both taken into consideration by the cfa as important activities. the visibility process replicates the visibility of matching patterns, whereas the reflection process models the mechanism that controls how the light is reflected. the patterns and colors that may be seen in cuttlefish are the results of light being reflected from multiple layers of cells. the complete steps of the cfo algorithm are depicted in the flowchart of figure 5. fig. 5. flowchart of the cfo algorithm. iv. simulation results and discussion the performance of proposed grid-connected hres is analyzed using the matlab simulation results. the proposed work was simulated in 4 cases: constant wind speed and engineering, technology & applied science research vol. 12, no. 6, 2022, 9670-9675 9673 www.etasr.com nagaraja et al.: pv and wind energy conversion exploration based on grid integrated hybrid … irradiation, variable wind speed and constant irradiation, constant wind speed and variable irradiation, and variable wind speed and variable irradiation. the pr controller was adopted as the current controller. the cfa was adopted for dc voltage regulation and its performance was compared with conventional controllers', such as the awt controller and the pso algorithm. the simulation parameters are listed in table i [7]. table i. simulation parameters description value pmsm parameters stator phase resistance rs 2.8750ω ld (h), lq(h) 8.5mh, 8.5mh inertia (kg.m 2 ) 0.0019 friction factor (n.m.s) 0.001 no. of poles 4 flux linkage 0.175 v.s dc link parameters dc link capacitor 4700 µ f reference dc voltage 800v gsc parameters switches igbt switching frequency 7000hz filter inductance 6 mh grid parameters voltage 400v (r.m.s) frequency 50 hz source resistance 0.01ω source inductance 2µh turbine parameters reference wind speed 12m/s reference voltage 1.2 p.u pv parameters open circuit voltage voc 43.5 v short circuit current isc 2.783 a a. case 1: constant wind speed and irradiation in this case, the wind speed value was set at 12m/s and the pv irradiation was maintained constant and equal to 1000w/m 2 throughout the simulation as shown in figures 6 and 7 respectively. fig. 6. constant wind speed. fig. 7. constant pv irradiation. the cfa response curves are presented in figure 8. the dc link voltage when using the cfa algorithm has a value of 800v and it is tracking the reference voltage after 0.06s. all the grid voltages are sinusoidal in nature and balanced. the response curves of the grid voltage and current are also presented in figure 8. (a) (b) (c) fig. 8. response curves of cfa (case 1): (a) dc link voltage, (b) grid voltage, (c) grid current. b. case 2: variable wind speed and constant irradiation in this case, the variable wind speed depicted in figure 9 was applied. the wind speed was 12m/s from 0 to 0.2s, it reduced to 8m/s at 0.2s, changed to 10m/s at 0.5sec, and changed back to the initial value at 0.8s. fig. 9. variable wind speed. (a) (b) (c) fig. 10. response curves of cfa (case 2): (a) dc link voltage, (b) grid voltage, (c) grid current. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 4 8 12 time (s) w in d s p e e d ( m /s ) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 500 1000 time (s) ir ra d ia ti o n ( w /m 2 ) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 200 400 600 800 time (s) v o lt a g e ( v ) vdcref vdc 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 -400 0 400 time (s) v o lt a g e ( v ) vga vgb vgc 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 -220 -100 0 100 220 time (s) c u rr e n t (a ) iga igb igc 0 0.2 0.4 0.5 0.6 0.8 1 1.2 1.4 0 4 8 12 14 time (s) w in d s p e e d ( m /s ) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 200 400 600 800 time (s) v o lt a g e ( v ) vdcref vdc 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 -400 0 400 time (s) v o lt a g e ( v ) vga vgb vgc 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 -220 100 0 -100 220 time (s) c u rr e n t (a ) iga igb igc engineering, technology & applied science research vol. 12, no. 6, 2022, 9670-9675 9674 www.etasr.com nagaraja et al.: pv and wind energy conversion exploration based on grid integrated hybrid … the response curves using cfo are presented in figure 10. the dc link voltage using the cfa algorithm has a value of 800v and it is tracking the reference voltage after 0.06s. all the grid voltages are in sinusoidal nature and balanced. the response curves of the grid voltage and current are also presented in figure 10. c. case 3: constant wind speed and variable irradiation in this case, the change of pv irradiation is applied as illustrated in figure 11. a constant irradiation of 1000w/m 2 is applied from 0 to 0.5s, it is then reduced to 700w/m 2 , and is again 1000w/m 2 at 0.8s. the response curves using cfo are presented in figure 12. the dc link voltage using cfa algorithm has a value of 800v and it is tracking the reference voltage after 0.06s as depicted in figure 12(a). all the grid voltages are sinusoidal in nature and balanced. the response curves of grid voltage and current are also presented in figure 12. fig. 11. variable pv irradiation. (a) (b) (c) fig. 12. response curves of cfa (case 3): (a) dc link voltage, (b) grid voltage, (c) grid current. d. case 4: variable wind speed and variable irradiation in this case, variable wind speed as depicted in figure 6 and variable pv irradiation as illustrated in figure 11 are applied. the response curves using cfo are presented in figure 13. the dc link voltage using cfo algorithm has a value of 800v and it is tracking the reference voltage after 0.06s as depicted in figure 13. all the grid voltages are sinusoidal in nature and balanced. the response curves of grid voltage and current are also presented in figure13. further, comparative performance analysis was conducted with thd. the fft spectrum using the pi+awt controller, the pso algorithm, and cfa are presented in figure 14. the thd when using the pi+awt controller, pso, and cfa is 1.97%, 1.62%, and 1.56% respectively. the proposed controller (cfa) performed better than the pi+awt controller and the pso algorithm. the comparative performance indices are listed in table ii. it is observed that the cfa has performed well in regulating the dc voltage. the dc voltage reached the reference voltage at 0.04s which is less compared than the time it took in both pi+awt and pso. (a) (b) (c) fig. 13. response curves of cfa (case 4): (a) dc link voltage, (b) grid voltage, (c) grid current. (a) (b) (c) fig. 14. thd comparison. fft spectrum of grid current using (a) awt controller, (b) pso algorithm, (c) cfa. table ii. performance comparison controller dc voltage settling time (s) %thd in current signal awt 0.15 1.97 pso 0.1 1.62 cfa 0.04 1.56 v. conclusion the concept of hybrid solar and wind power generation was described in detail in this paper, and the training procedure of a 0 0.2 0.4 0.5 0.6 0.8 1 1.2 1.4 0 700 1000 time (s) ir ra d ia ti o n ( w /m 2 ) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 200 400 600 800 time (s) v o lt a g e ( v ) vdcref vdc 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 -400 0 400 time (s) v o lt a g e ( v ) vga vgb vgc 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 -220 -100 0 100 220 time (s) c u rr e n t (a ) iga igb igc 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 200 400 600 800 time (s) v o lt a g e ( v ) vdcref vdc 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 -400 0 400 time (s) v o lt a g e ( v ) vga vgb vgc 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 -220 -100 0 100 220 time (s) c u rr e n t (a ) iga igb igc 0 10 20 30 40 50 60 70 80 90 100 0 0.5 1 1.5 harmonic order fundamental (50hz) = 217 , thd= 1.97% m a g ( % o f f u n d a m e n ta l) 0 10 20 30 40 50 60 70 80 90 100 0 0.5 1 1.5 harmonic order fundamental (50hz) = 215.1 , thd= 1.62% m a g (% o f f u n d a m e n ta l) 0 10 20 30 40 50 60 70 80 90 100 0 1 2 3 harmonic order fundamental (50hz) = 218.8 , thd= 1.56% m a g (% o f f u n d a m e n ta l) engineering, technology & applied science research vol. 12, no. 6, 2022, 9670-9675 9675 www.etasr.com nagaraja et al.: pv and wind energy conversion exploration based on grid integrated hybrid … cfa-based optimization algorithm is presented. from the results, it is realized that the cfa performed better than pi+awt and pso. optimum dc voltage regulation is achieved with the use of the cfa algorithm. in order to demonstrate the applicability of the suggested controller, simulations were carried out in matlab/simulink. references [1] y.-m. chen, y.-c. liu, s.-c. hung, and c.-s. cheng, "multi-input inverter for grid-connected hybrid pv/wind power system," ieee transactions on power electronics, vol. 22, no. 3, pp. 1070–1077, feb. 2007, https://doi.org/10.1109/tpel.2007.897117. 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[18] n. regis, c. m. muriithi, and l. ngoo, "optimal battery sizing of a grid-connected residential photovoltaic system for cost minimization using pso algorithm," engineering, technology & applied science research, vol. 9, no. 6, pp. 4905–4911, dec. 2019, https://doi.org/ 10.48084/etasr.3094. microsoft word etasr_v13_n4_pp11360-11365 engineering, technology & applied science research vol. 13, no. 4, 2023, 11360-11365 11360 www.etasr.com gopi & karthikeyan: effectiveness of crop recommendation and yield prediction using hybrid moth … effectiveness of crop recommendation and yield prediction using hybrid moth flame optimization with machine learning subbu raman gopi department of computer and information science, faculty of science, annamalai university, india gopipss@gmail.com (corresponding author) mani karthikeyan department of computer and information science, faculty of science, annamalai university, india karthiaucse@gmail.com received: 5 june 2023 | revised: 16 june 2023 | accepted: 21 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6092 abstract agriculture is the main source of income, food, employment, and livelihood for most rural people in india. several crops can be destroyed yearly due to a lack of technical skills and changing weather patterns such as rainfall, temperature, and other atmospheric parameters that play an enormous role in determining crop yield and profit. therefore, selecting a suitable crop to increase crop yield is an essential aspect of improving real-life farming scenarios. anticipating crop yield is one of the major concerns in agriculture and plays a critical role in global, regional, and field decision-making. crop yield forecasting is based on crop parameters and meteorological, atmospheric, and soil conditions. this paper introduces a crop recommendation and yield prediction system using a hybrid moth flame optimization with machine learning (hmfo-ml) model. the presented hmfo-ml method effectively recommends crops and forecasts crop yield accurately and promptly. the proposed model used a probabilistic neural network (pnn) for crop recommendation and the extreme learning machine (elm) method for the crop yield forecasting process. the hmfo algorithm was used to improve the forecasting rate of the elm approach. a wide-ranging simulation analysis was carried out to evaluate the hmfo-ml model, showing its advantages over other models, as it exhibited a maximum r 2 score of 98.82% and an accuracy of 99.67%. keywords-agriculture; crop yield prediction; crop recommendation; machine learning; moth flame optimizer i. introduction the estimation of crop production has attracted a lot of research interest recently. the most outstanding aspect of crop yield is climatic situations [1]. if the climate-established forecast is accurate, farmers can be notified and mitigate damage, which can help economic progress [2]. proper anticipation can serve as an aiding factor for farmers in substituting crop selection or abandoning a crop in its initial phase in severe circumstances [3]. in addition, crop yield forecasts could provide farmers with a good idea of harvesting seasonal crops and their preparation [4]. achieving an ultimate crop harvest rate by employing inadequate field capacity is a target of agronomic scheduling in an agro-based nation. crop pickers can reduce their financial damage during adverse situations or expand the degree of crop harvest when there is the possibility of encouraging conditions [5]. therefore, it is necessary to predict crop yields before harvest to achieve efficient crop administration and predicted results [6]. as there is a non-sequential link between crop yield and the factors persuading crops, ml might be efficient for yield prediction. ml is a subdivision of ai that focuses on education and is a real-world method that can offer good harvest forecasts [7]. ml can also regulate outlines and associations from data that represent results from previous practice. the analytical approach is constructed by adopting many procedures, and the parameters are decided using previous records during the training stage [8]. the testing stage uses a fragment of the record that was not used for training. ml can be definitive or predictive [9]. descriptive methods are used to describe what has happened, while predictive methods are used to forecast the future. ml incorporates various risks when trying to construct a high-performance predictive method [10]. it is significant to pick the appropriate process/algorithm to resolve the given issue, along with the algorithms and basic platforms required to manage data capacity. this paper introduces an intelligent crop recommendation and yield prediction system using the hybrid moth flame optimization with machine learning (hmfo-ml). the presented hmfo-ml model effectively recommends crops and forecasts crop yield promptly and accurately. the hmfoml model uses a probabilistic neural network (pnn) for crop engineering, technology & applied science research vol. 13, no. 4, 2023, 11360-11365 11361 www.etasr.com gopi & karthikeyan: effectiveness of crop recommendation and yield prediction using hybrid moth … recommendation and the extreme learning machine (elm) method for the crop yield forecasting process. the hmfo algorithm was used to improve the prediction rate of the elm approach. a wide-ranging simulation analysis was carried out to demonstrate and evaluate the results of the hmfo-ml method. ii. related works in [11], a crop recommendation method was presented that used cnn and rf techniques to predict better crop yield, exploring several parameters, such as harvest, area, selling price, soil variety, etc. in [12], a hybrid dl-based crop yield forecasting method was proposed using fnn and dbn techniques to overcome the problems of nonlinearity and gradient diffusion. dbn incorporates statistics and probability with nns. this method primarily executed an effectual pretrained system by dbn to improve model progress and feature vector generation. in [13], a system was proposed to predict crop yield in earlier data using ml approaches, such as random forest and svm in agriculture data, and to recommend appropriate fertilizers for specific crops. this study emphasized the design of a predictive method that could be used for future crop prediction. in [14], a dl algorithm was presented for crop production, using previous information on crops and climate. this method was a hybrid mechanism that used ant colony optimization (aco) to optimize deep convolution neural network (dcnn) and lstm network inputs for crop prediction. based on the number of layers used in processing, dcnn achieved a higher level of accuracy but had a higher computational complexity. in [15], a dl method based on gray wolf optimization (gwo) was proposed that could suggest the best crop depending on the chemical and climatic situations. this study considered many chemical features, namely nitrogen, ph, potassium, and phosphorus, and different climate factors, namely humidity, rainfall, and temperature, to recommend crops to farmers. the method was established in diverse folds: a cnn was initially used to extract and categorize the main characteristics, and then the gwo was used to optimize the features to recommend an improved crop based on various factors. in [16], a fusion intellectual model for soil was established and examined with different baseline methods on the south australian soil dataset to assess forecasting. semantic similarity can be evaluated using the semantosim measure, jaccard, and cosine similarity in the squirrel search process to ensure that the related results and set entity generated from a set of recommendations are improved. iii. the proposed model this study presents the hmfo-ml method for robust crop recommendation and yield forecasting. the proposed hmfoml method effectively recommends crops and forecasts crop yield accurately and promptly, encompassing pnn-based crop recommendation, elm-based yield forecasting, and an hmfobased tuning process. figure 1 shows the workflow of the hmfo-ml approach. fig. 1. workflow of hmfo-ml approach. a. crop recommendation using pnn the proposed hmfo-ml method uses a pnn model for crop recommendation. an ann can characterize any nonlinear relation between input and output via proper training and a flexible model [17]. ann is used for real-time prediction and classification problems. the pnn is a kind of ann that depends on bayesian classification and has similarities to the backpropagation method in the way they progress. however, the model has variations in the learning process. the structure of the model includes the summation, input, output, and pattern layers. the summation layer is similar to the competitive network and has similar neurons to the targeted class, but the pattern layer is similar to rbn and has several neurons identical to the input sample number. the input layer neuron takes input from an input vector: � = (���� , � , � ), ∈ �� , � = 9 where mi = (r, g, b) signifies a color map for i = 1, 2, 3. this input is sent to the patterning layer where the neuron is split into an amount of classes c. the resultant of the j-th pattern neurons c-th class evaluated by the gaussian kernel: ��� (�) = �(����)�� exp − ‖#$#%,&‖ � ��� ' (1) engineering, technology & applied science research vol. 13, no. 4, 2023, 11360-11365 11362 www.etasr.com gopi & karthikeyan: effectiveness of crop recommendation and yield prediction using hybrid moth … where �( ,) *�� denotes the center of the kernel, and σ indicates spread (smoothing) parameters, defining the magnitude of the corresponding kernel area. the summary layer calculates the conditional class probability estimation function with a fusion of the formerly calculated density: +� (�) = ∑ ��,)-%).� (�), / ∈ 01,2, … 45 (2) where wcj indicates positive coefficient satisfying, nc denotes the pattern neurons number of class c and ∑ 6�)-%).� = 1. the patterning vector x is categorized in class respectively to the unit of summary with the maximal result: 0(�) = arg max�<�<( (+( ) (3) this is the diagrammatic representation of the presented method. the images are chosen sequentially, and their features will be extracted. the feature was used for training the pnn network for classification. b. elm-based crop yield forecasting the elm model was applied to the crop yield forecasting process [18]. consider a learning issue of evaluating an arbitrary targeting function with an unknown relation amongst input � ⊂ �� and output > ⊂ �� . the objective of the learning is to find an appropriate non-linear mapping �?(@) ≈b(@ ∈ �, b ∈ >) with the presented dataset 0(@� , b� )5�.�⊂ �� ×�� with n identically distributed and independent samples. elm integrates a three-layer framework, was initially developed for slfn, and expanded to widespread slfn where the hidden layer (hl) should not be the same. unlike other traditional methods to train slfn, its hl variables (ai, bi) are produced randomly. therefore, the learning problem is reduced to evaluate the optimum output weight β. t and β are the elm output and target weight matrix, respectively. in general, elm is processed as a linear integration of the l activation function: �d (@) = ∑ e�d�.� ℎ� (@) = ℎ(@)e (4) where l indicates the hl number of elm, and hi(x) = g(x, ai, bi). the abovementioned formula is expressed as follows: ge = > (5) where h denotes the hl output matrix: g = hℎ(@�)⋮ℎ(@)j = h ℎ�(@�) … ℎd (@�)⋮ ⋱ ⋮ℎ�(@) … ℎd (@)j (6) > = hb�l⋮b-l j m�n e = h e�l⋮edl j (7) unlike other traditional ml methods, elm aims to obtain the smallest norm of the output weight and the most minor training error. the objective function can be formulated as: op� ∶ rsdt = �� |e‖� + �� 4 ∑ w��-�.� (8) x. b. ℎ(@� )e = b� − w� , p = 1, … , z where ξι= [ξ1,m, … ,ξi,m] represents the m output node’s training error vector regarding the training instance xi, and c shows the regularization factor to improve the overall performance. based on the karush‐kuhn‐tucker (kkt) formula: e = [gl(�( + ggl )$�>, z < r(�( + gl g)$�gl >, z > r’ (9) where i indicates the unity matrix. c. parameter tuning using the hmfo algorithm the hmfo method was used to improve the forecasting rate of the elm method. mfo uses the moth transverse orientation navigation algorithm [19]. a moth flies a long distance during night-time by keeping a stable angle toward the sky. in this problem, the solution candidate is a moth and the problem variable is its spatial placement. moths might fly in a hyper-dimensional space of 1d, 2d, or 3-d by adjusting their location vectors. the mfo algorithm is robust and computationally efficient and can be scientifically represented in the following: _ = ⎣⎢ ⎢⎢ ⎡4c�,� 4c�,� … … 4c�,d4c�,� 4c�,� … … 4c�,d⋮ ⋮ ⋮ ⋮ ⋮⋮ ⋮ ⋮ ⋮ ⋮4ce,� 4ce,� … … 4c�,d ⎦⎥ ⎥⎥ ⎤ (10) where h denotes the dimension numbers, and a denotes the moths’ numbers. i = ⎣⎢ ⎢⎢ ⎡i�,� i�,� … … i�,di�,� i�,� … … i�,d⋮ ⋮ ⋮ ⋮ ⋮⋮ ⋮ ⋮ ⋮ ⋮ie,� ie,� … … i�,d ⎦⎥ ⎥⎥ ⎤ (11) mfo is a three‐stage process for universal optimization: _�c = (j, �, >) (12) where i denotes the function, f represents the moth flight in the search space, and t represents the termination condition criteria. �� = bk4� , i) l (13) where ci specifies the count of the i-th moth, sj denotes the count of the j-th flames, and r represents the twisting function. ik4� , i) l = m� . n op . cos(2tb) + i) (14) where zi denotes the distance between the moth and flame, b indicates constant values, and t shows a random number within [−1, 1]. mp = ui) − �� u (15) particles in pso with a specific random solution follow the present optimal particles to search for global optimization. with n particles in a search space of d-dimension at the t-th iteration, v�p and @w�p denote the velocity and location, respectively. correspondingly, at the i-th iteration, xynxb�p engineering, technology & applied science research vol. 13, no. 4, 2023, 11360-11365 11363 www.etasr.com gopi & karthikeyan: effectiveness of crop recommendation and yield prediction using hybrid moth … indicates the personal solution attained for the i-th particle, and zynxb�p shows the optimum solution attained. the following equations were used to calculate the upgraded value for the i-th particle’s velocity and position: v�p{� = 6v�p + /�w� + (xynxb�p − @�p ) + /�w� +(zynxb�p − @�p ) (16) @�p{� = @�p + v�p{� (17) where r1 and r2 denote the random number [0, 1], c1 and c2 indicate constant terms, and w represents the inertia weight. the early convergence problem is addressed by integrating the idea of local attractors from pso, including the locationadjusting method of a moth around the flame from mfo. it is shown that the pso method was ensured to converge if every particle converged towards the local attractor |�p : |�p = ~xynxb�p + (1 − ~�zynxb�p (18) where ~ denotes a vector. i�4� , |� p � = m� . n op . cos�2tb� + |� p (19) mp = ||� p − 4� | (20) fitness selection is a crucial factor in the hmfo algorithm. the encoded solution was used to develop aptitude or candidate goodness outcomes. at present, the accuracy value is an essential situation exploited for scheming a fitness function. �pb�nxx = max ��� (21) � = l� l�{�� (22) where tp and fp signify the true positive and false positive values, respectively. iv. results analysis this study used the crop recommendation dataset [20] to evaluate the performance of the hmfo-ml method. this dataset was constructed by improving databases of weather, rain, and manure information for india [21]. the dataset was split into 70:30 subsets for training and testing. the modes presented were simulated using python 3.6.5 on an i5-8600k, geforce 1050ti 4gb, 16 gb ram, 250 gb ssd, and 1tb hdd pc. the parameter setups were: rate of learning: 0.01, epochs count: 50, size of the batch: 5, rate of dropout: 0.5, and activation: relu. figure 2 shows the classifier outputs of the hmfo-ml method under the test data. figure 2(a)-(b) show the confusion matrices presented by hmfo-ml. the hmfoml method recognized distinct instances under 21 class labels. figure 2(c) shows the pr investigation of the hmfo-ml method. the figures show that the hmfo-ml approach achieved maximal pr under total classes. figure 2(d) shows the roc investigation of the hmfo-ml model, showing its effectiveness with maximum roc values under discrete class labeling. figure 3 shows the comprehensive outputs of the hmfo-ml method on training. the results indicate that the hmfo-ml method recognized all 20 classes. it is also noticed that the hmfo-ml model accomplished an average accuy of 99.67%, precn of 96.43%, recall of 96.39%, fscore of 96.40%, and mcc of 96.23%. fig. 2. (a), (b) classifiers for 70:30 training/testing of the dataset, (c): pr curve, and (d): roc curve. fig. 3. average results of the hmfo-ml method in training. figure 4 shows the overall outputs of the hmfo-ml method on testing. the outputs indicate that the hmfo-ml method recognized all 20 classes and accomplished an average accuy of 99.66%, precn of 96.07%, recall of 96.23%, fscore of 96.08%, and mcc of 95.94%. fig. 4. average results of hmfo-ml approach under 30% of testing. engineering, technology & applied science research vol. 13, no. 4, 2023, 11360-11365 11364 www.etasr.com gopi & karthikeyan: effectiveness of crop recommendation and yield prediction using hybrid moth … table iii shows a brief comparative study of the hmfoml method with others [22-24]. based on accuy, the hmfoml method achieved a higher accuy of 99.67% while the svm, svm-kernel, ssae and pca cnn, nc-sae, and dt methods obtain lesser accuy of 94.64%, 91.73%, 90.85%, 89.49%, 88.62%, and 85.07%, respectively. table i. comparative result of hmfo-ml with other methods methods accuy precn recall fscore hmfo-ml 99.67 96.43 96.39 96.40 nc-sae 94.64 94.06 94.78 95.49 svm-kernel 91.73 91.13 92.42 93.80 svm 89.49 88.17 88.70 88.46 ssae-cnn 90.85 93.86 90.60 92.94 pca-cnn 88.62 89.27 87.75 89.08 dt 85.07 84.73 85.91 85.39 table iv shows the results of the hmfo-ml approach in terms of r 2 . the hmfo-ml method reached a higher r 2 of 98.82%, while the svm, knn, mlr, and ann methods obtained a lower than 91.99% r 2 , respectively, 87.05%, 89.10%, and 91.97%. these results demonstrate the improved efficiency of the hmfo-ml model. table ii. r2 of the hmfo-ml with other methods methods r 2 hmfo-ml 98.82 svr 91.99 knn 87.05 mlr 89.10 ann 91.97 v. conclusion this study proposes an hmfo-ml model for robust crop recommendation and yield forecasting. the introduced hmfoml method effectivelly recommended the crops and forecasted crop yield accurately and promptly. the hmfo-ml method exploited a pnn model for crop recommendation purposes and an elm model for the crop yield forecasting process. the hmfo algorithm was used to improve the forecasting rate of the elm method. the results of the proposed method were evaluated and compared with other methods, showing its superiority. in the future, the hmfo-ml method can also embed ensemble ml methods. references [1] r. jeevaganesh, d. harish, and b. priya, "a machine learning-based approach for crop yield prediction and fertilizer recommendation," in 2022 6th international conference on trends in electronics and informatics (icoei), tirunelveli, india, apr. 2022, pp. 1330–1334, https://doi.org/10.1109/icoei53556.2022.9777230. 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[24] p. s. maya gopal and r. bhargavi, "a novel approach for efficient crop yield prediction," computers and electronics in agriculture, vol. 165, oct. 2019, art. no. 104968, https://doi.org/10.1016/j.compag.2019. 104968. engineering, technology & applied science research vol. 8, no. 1, 2018, 2351-2355 2351 www.etasr.com maslougkas and danikas: study of water droplets behavior on electrical machine insulation under … study of water droplets behavior on electrical machine insulation under the influence of uniform electric fields: the influence of some parameters on mica sheets s. maslougkas democritus university of thrace, department of electrical and computer engineering, power systems laboratory, 67100 xanthi, greece sotimasl@ee.duth.gr m. g. danikas democritus university of thrace, department of electrical and computer engineering, power systems laboratory, 67100 xanthi, greece mdanikas@ee.duth.gr abstract—mica sheets are a vital component of electrical machine insulation. although great attention has been paid to partial discharges and their deteriorating effect on such insulation, relatively little attention has been given to surface discharges. this paper investigates the effect of water droplets, their volume, their conductivity, their positioning as well as their number on the flashover voltage of mica sheets. it is indicated that all the above mentioned parameters influence the flashover voltage. keywords-insulation; machine; field; electric; mica;discharge; water; droplet; flashover i. introduction electric machines are a crucial part of an electric power system and their reliability highly depends on the durability of the insulation. the maximum operating temperature of an electric machine is about 200oc . an electrical machine is subjected also to mechanical vibrations. the presence of humidity and chemicals can also corrode the insulation of an electrical machine. one can easily conclude that the role of the electric machine insulation is not only to keep the live parts separated from the grounded ones but also to endure the mechanical, thermal and chemical stresses. in other words, such insulation may suffer from multiple stresses, which far too often apply at the same time. the result of these stresses is the creation of voids that lead to the increase of partial discharges [1-4]. the combination of mica and epoxy resin constitutes the basic insulation component of an electric machine due to its ability to withstand the harsh conditions of the operating environment. in this study, a series of experiments was conducted with mica sheets, which are the hardest part of electrical machine insulation. the behavior of water droplets on mica sheets under the influence of uniform electric fields was studied. the experimental parameters studied were the water conductivity, the number, the position and the volume of the droplets and the surface roughness of the mica sheets [5]. ii. experimental setup a. high voltage supply the voltage source (power grid) is connected to the insulation transformer. next, the variable autotransformer decreases the voltage between 0-140 v and supplies the low voltage winding of the 100v/20 kv step up transformer. the step up transformer is a dry type transformer insulated by epoxy resin. the maximum voltage can be reached is 24kv (1.2 times the nominal output voltage). on the low voltage side of the step up transformer there’s a digital voltmeter. a circuit breaker interrupts the circuit before the insulation transformer (figure 1). b. electrodes the electrodes are made of brass and their shape is that of a half cylinder with rounded edges. during their construction, attention was given on the surface smoothness because a smooth surface creates a uniform electric field (figure 2). fig. 1. high voltage supply. fig. 2. the electrodes of the experimental setup. their distance is 2.5 cm. engineering, technology & applied science research vol. 8, no. 1, 2018, 2351-2355 2352 www.etasr.com maslougkas and danikas: study of water droplets behavior on electrical machine insulation under … c. water samples the values of electric conductivity of the water samples used were 1,4 μs/cm, 100 μs/cm, 200μs/cm, 500 μs/cm, 1000 μs/cm, 2000 μs/cm,5000 μs/cm and 10000 μs/cm. distilled water conductivity is approximately 1,4μs/cm at 25oc and it is increased when nacl is added. by adding nacl and counting the conductivity (using a digital conductivity meter) the above mentioned values were obtained. d. surface roughness the surface roughness is calculated by the vertical divergence of the real surface from the ideal one. if the vertical distances are high, the surface is rough. using pertometer m4p, the roughness of the mica paper samples was specified (figure 3). the needle of the device moves on a line segment on the sample surface while the surface abnormalities move the needle vertically. a sensor converts the needle movement to an electric signal which is processed by the microprocessor. after completing the calculations the device prints the results on a paper stripe. three samples were examined. the first one was unused and the other two were used samples. one of the two samples was used during the first half of the experimental procedure and the other one during the second half. on each mica sample the roughness sampling implemented across the length of five 4,8mm line segments. three of these line segments were parallel to the large side of the rectangle and two of them were perpendicular to it. the calculated roughness parameters were the average roughness, the mean roughness depth and the maximum roughness depth and the respective results are shown below (table i). table i. results of surface roughness measurements average roughness ra (μm) mean roughness depth rz (μm) maximum roughness depth rmax (μm) unused sample 5.46 20.89 24.48 3.31 14.91 28.48 3.1 12.64 18.16 2.82 14.04 21.28 4.69 21.37 31.68 used sample 1 3 12.92 16.96 3.68 14.33 17.28 4.86 19.71 30.40 4.86 20.89 28.16 3.98 17.37 21.92 used sample 2 3.18 15.07 16.32 4.47 19.42 24.8 3.49 16.68 22.56 3.45 18.9 19.2 3.86 14.68 19.36 average roughness: the arithmetic average of the absolute values of the roughness profile ordinates: 1 ( ) i a o r z x dx i   mean roughness depth: the arithmetic mean value of the single roughness depths rzi of consecutive sample length: 1 2 1 ( ... ) z z z zn r n r r r     maximum roughness depth: the largest single roughness depth within the evaluation length [6]. fig. 3. perthometer m4p. the measurements took place at the machine tools and quality control laboratory of the technological educational institute of eastern macedonia and thrace. e. experimental procedure the electrodes were positioned on the mica paper sample at a distance of 2.5 cm. the water droplets were positioned between the electrodes by a syringe. the purpose of the experimental procedure was to measure the flashover voltage. the arrangements of the water droplets were the following:  one 0.05 ml droplet with a distance of 1.25 cm from the electrodes  two 0.05 ml droplets with a distance of 0.8 cm from the nearest electrode and their centers  three 0.05 ml droplets forming a triangle.  four 0.05 ml droplets forming a square.  one droplet of 0.1 ml with a distance of 1.25 cm from the electrodes  two 0.1 ml droplets with a distance of 0.8 cm from the nearest electrode and their centers (figure 4) fig. 4. the water droplet arrangements engineering, technology & applied science research vol. 8, no. 1, 2018, 2351-2355 2353 www.etasr.com maslougkas and danikas: study of water droplets behavior on electrical machine insulation under … after putting the droplets on the mica paper the voltage was raised until flashover occurred. the value was recorded. after the flashover the surface and the electrodes were cleaned, new droplets were put and the voltage was raised at a value lower than the previous breakdown value by 1.2 kv. at this point the voltage stayed at this value for 5 min. if no flashover occurred, the voltage was raised by 0.4kv and the procedure was repeated until flashover occurred. after the flashover the value was recorded. during the 5 min interval there was a smooth progress of the droplet oscillation and deformation until the occurrence of partial discharges and the flashover. iii. experimental results from the flashover voltage-conductivity diagrams it is understood that the flashover voltage depends on the number of droplets, their distance from the electrodes and their conductivity. as the number of the 0.05 ml droplets is increased their distance from the electrodes is decreased leading to a flashover (figures 5 and 6). the mica surface is highly hydrophilic and as a result the water droplets stick on it with a contact angle lower than 90o. putting the droplets was quite difficult during the experiment due to the fact that they were spreading over the mica surface. hydrophilicity might be the reason of this stability problem. a possible explanation is that the residual humidity on the mica surface did not let the water droplet be in contact with the mica. thus, there were no adhesive forces to hold the droplets [7, 8]. fig. 5. comparative results of the various droplet arrangements fig. 6. comparative results of two different droplet arrangements another crucial factor was the surface roughness on the mica paper samples. there are plenty of abnormalities on the mica paper surface forming hills and valleys of μm order. the water fills the space between the abnormalities and as a result the droplet movement is affected in two ways: i) the droplet is elongated across the surface valleys and, ii) the droplet spreading is blocked by the surface hills. the applied electric field made the droplets oscillate and emit sound waves. by raising the applied voltage the droplet oscillation and elongation became more intense. some very common droplet types of behavior were the merging and the spreading of the adjacent droplets while some single droplets were moving close to the nearest electrode. the oscillation frequencies before the surface flashover were higher than 50 hz (power grid frequency) and they were changing while the applied voltage was rising. the spectrum of the oscillation and flashover emitted sound signal was analyzed on matlab. the spectrum analysis showed that the emitted frequencies were multiples of 100hz (twice the power frequency). in order to understand the evolution of the emitted sound frequencies during the experiment a spectrogram was extracted. on the spectrogram one may see that the high frequency amplitudes increase before flashover occurs. the droplet oscillations were more intense and the flashover voltage decreased while the water salinity increased. after the surface flashover the water was spread on the mica paper bridging the two electrodes (figures 7-9). fig. 7. the sound wave recorded during the experiment fig. 8. signals of the oscillations and the flashover and their fft. looking at the mica paper samples there are no signs of degradation after the implementation of the experiment. some surface changes shown after scanning the samples with the digital microscope dino lite pro hr am7000. the two used samples probably deteriorated by the electric arc by-products. engineering, technology & applied science research vol. 8, no. 1, 2018, 2351-2355 2354 www.etasr.com maslougkas and danikas: study of water droplets behavior on electrical machine insulation under … the main arc by-products are the nitrogen monoxide and nitrogen dioxide. when nitrogen dioxide is combined with water, nitric acid is formed. the presence of nitric acid corrodes the mica surface since a substitution reaction occurs (mica’s potassium is substituted by hydrogen and potassium nitrate is formed). surface corrosion can also occur when particles are accelerated due to the partial discharges and bombardment of the surface. thus, mica flakes get gradually delaminated. the differences between the images of the unused and used mica samples are shown below (figures 10-12). fig. 9. spectrogram of the emitted sound signal fig. 10. unused sample magnified by 50 times (photos a, b and f) and 200 times (photos c, d and e). the f photo was taken without the microscope’s light source. the relatively dark spots in the a and d photos are impurities of the mica structure fig. 11. the first used sample magnified by 50 times (photos a, b, f) and 220 times (photos c, d, e). in the d and e images there are some indications of flake delamination and chemical degradation. fig. 12. the second used magnified by 50 times (photos a, b, d) and 220 times (photos c, e, f). in the e and f photos the deterioration is obvious. a b c d e f a b c d e f a b c d e f engineering, technology & applied science research vol. 8, no. 1, 2018, 2351-2355 2355 www.etasr.com maslougkas and danikas: study of water droplets behavior on electrical machine insulation under … iv. discussion in the present paper, a series of experiments were conducted on the basic insulating material of the electric machines. the measurements showed that among the factors determining the surface flashover are the conductivity, the number and the arrangement of the water droplets with respect to the electrodes, and the surface roughness on the insulation material. more specifically, it was observed that the flashover voltage of a single droplet with a volume of 0.05 ml had the same value as the one of the single droplet with a volume of 0.1 ml. comparing the flashover voltages of the two droplets of 0.05 ml and 0.1 ml it was observed that the 0.1 ml droplets had a larger flashover voltage although their overall droplet volume was the largest one. additionally, the flashover voltages of the 0.5 ml droplet arrangements (except for the 100μs/cm droplets) were lower than the ones of the 0.01 ml. the increase of water conductivity tends to decrease the flashover voltage. on the other hand, the surface roughness contributes both to the decrease and the increase of the flashover voltage. the orientation of the surface abnormalities (hills and valleys) plays a crucial role regarding these procedures. there were some cases where the roughness was trapping the droplets and did not let them move towards the electrodes. in this case the flashover voltage tended to increase. in other cases, the roughness let the droplets elongate and move towards the electrodes. the result of this elongation was the creation of sharp edges where corona effect took place. in this case the flashover voltage decreased. the experimental results presented here indicate that there is a relationship between flashover voltage and the above mentioned parameters. the effect of water conductivity, surface roughness, droplet volume and number of droplets was studied elsewhere with both traditional polymers materials and with nanocomposite materials [7–12]. the results of the present study are qualitatively not that different from the experimental results of the references [7–12]. one may object to the fact that in this paper only mica sheets were investigated and not mica sheets impregnated with epoxy resin. to this the reply is that mica sheets consist the main strong insulation component in an electrical machine insulation system and thus investigating water droplets on mica sheets to a great extent gives enough information regarding the electrical behavior of the whole system. a second objection may be that surface discharges and flashovers constitute a smaller danger to machine insulation than partial discharges. to this, the reply is that there is a great amount of published research on the aforementioned subject (e.g. [1-4]) and, nevertheless surface discharges and flashovers are also a danger to electrical machine insulation admittedly smaller but with no great amount of published work about this subject. another parameter that affects the water droplet behavior was the frequency of the applied voltage. electric motors are usually supplied by power electronic devices such as converters and inverters. this means that the applied frequency is variable. in a future research the behavior of water droplets under different frequencies and waveforms (e.g. pwm or spwm) may be studied [13-15]. experiments like the ones conducted in this paper can also take place on real stator bars insulated by mica, epoxy resin and glass fibers. v. conclusions flashover voltages on mica sheets were investigated under the influence of uniform electric fields and taking into account parameters, such as water droplet conductivity, positioning of the droplets w.r.t. the electrodes, mica surface roughness and droplet volume. the above mentioned parameters affect the flashover voltage in an expected way, except perhaps from the surface roughness, which on other occasions may provoke an increase of the flashover voltage and in other cases a decrease of it. references [1] d. kind, h. kaerner, insulating materials in high voltage technology, eds. vieweg & sohn, braunschweig/wiesbaden, 1985 [2] c. l. wadhwa, high voltage engineering, eds. new age international (p) limited, publishers, new delhi, 1994 [3] m. s. naidu, v. kamaraju, high voltage engineering, eds. tata mcgraw-hill publishing company limited, new delhi, 2000 [4] d. koenig, y. narayana rao, teilentladungen in betriebsmitteln der energietechnik, eds. vde verlag, berlin und offenbach, 1993 [5] s. maslougkas, “study of droplet behavior in electrical machine insulation”, diploma thesis, democritus university of thrace, department of electrical & computer, engineering, power systems laboratory, xanthi, greece, 2017 (in greek) [6] mahr gmbh, perthometer. surface texture parameters. new standards din en iso/asme, germany 1999 [7] m. g. danikas, p. rakitzis, k. karakoulidis, “study of parameters related to deterioration phenomena due to water droplets on polymeric surfaces”, journal of electrical engineering, vol. 57, no. 3, pp. 130-137, 2006 [8] m. g. danikas, p. ramnalis, r. sarathi, “a study of the behavior of water droplets on polymeric surfaces under the influence of electric fields in an inclined test arrangement”, journal of electrical engineering, vol. 60, no. 2, pp. 94-99, 2009 [9] m. g. danikas, “surface phenomena on resin-type insulators under different electrical and non-electrical stresses in the early stage of ageing”, facta universitatis, vol. 13, no. 3, pp. 335-352, 2000 [10] y. cheng, x. zhao, m. g. danikas, d. christantoni, p. zairis, “a study of the behaviour of water droplets under the influence of uniform electric field in epoxy resin samples”, journal of electrical engineering, vol. 63, no. 3, pp. 196-200, 2012 [11] a. bairaktari, m. g. danikas, x. zhao, y. cheng, y. zhang, “behaviour of water droplets under the influence of a uniform electric field in nanocomposite samples of epoxy resin/tio2”,engineering, technology & applied science research, vol. 3, no. 5, pp. 511-515, 2013 [12] s. c. kechagia, m. g. danikas, r. sarathi, “water droplets and breakdown phenomena on polymer nanocomposite surfaces under the influence of uniform electric fields”, malaysian polymer journal, vol. 8, no. 2, pp. 41-47, 2013 [13] a. cavallini, d. fabiani, g. c. montanari, “power electronics and electrical insulation systems – part 1: phenomenology overview”, ieee electrical insulation magazine, vol. 26, no. 3, pp. 7-15, 2010 [14] a. cavallini, d. fabiani, g. c. montanari, “power electronics and electrical insulation systems – part 2: life modelling for insulation design”, ieee electrical insulation magazine, vol. 26, no. 4, pp. 33-39, 2010 [15] a. cavallini, d. fabiani, g. c. montanari, “power electronics and electrical insulation systems – part 3: diagnostic properties”, ieee electrical insulation magazine, vol. 26, no. 5, pp. 30-40, 2010 engineering, technology & applied science research vol. 8, no. 3, 2018, 2879-2881 2879 www.etasr.com memon et al.: a survey on the criteria for measuring the profitability of a construction organization a survey on the criteria for measuring the profitability of a construction organization aftab hameed memon department of civil engineering engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan aftabm78@hotmail.com mohsin ali soomro department of civil engineering engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan nawab ali lakho department of civil engineering engineering quaid-e-awam university of engineering, science & technology nawabshah, pakistan ammaar noor memon indus university karachi, pakistan muhammad aslam bhutto department of civil engineering ned university karachi, pakistan abstract—any organization’s performance depends on profitability which depends on several adopted criteria. the preference and level of adoption of these criteria varies, on different industries. this study focuses on investigating the criteria of profitability in the construction industry. this investigation involves a survey to seek the perception of the contractors involved in handling physical activities of construction works. the survey considered 63 questionnaire forms. statistical analysis was performed to compute the frequency and the relative importance index. the results indicated that structural capital, lifetime values, capital structure and competitor actions are the top 4 criteria implemented in construction organizations to measure profitability. keywords-profitability; criteria of profitability; construction organization i. introduction profitability is considered a fundamental aspect for any enterprise. the same apply for organizations in the construction industry, which is a very fast growing industry, especially in developing countries such as pakistan. several researchers have identified various metrics of profitability measurement such as intellectual capital, relational capital, human capital and structural capital [1]. another study showed that criteria for measuring profitability include unexpected product reliability failures, firm innovativeness, product reliability, warranty costs, unexpected product failure costs, moderating effect of industry innovativeness and firm return on assets (roa) as the major metrics of profitability measurement [2]. comprehensive review of literature resulted in finding 24 criteria for measuring organization profitability which are presented in table i. ii. methodology data was collected by conducting a survey amongst the representatives of contractor organizations handling construction projects in pakistan. the survey was done using a structured questionnaire form designed based on literature review as discussed in table i. for collected completed questionnaire forms, frequency was computed with spss. using this, frequency, average index (ai) for each criterion was calculated using the following equation: . . .= ∑ (1) where: a=constant expressing the weight assigned to each response, n=frequency of each response, n=total number of responses table i. criteria for measuring profitability criterion references intellectual capital [1, 3-8] relational capital [1, 9-13] human capital [1, 9-13] structural capital [2, 9-14] unexpected product reliability failures [2, 14-17] firm innovativeness [2, 14, 18-19] product reliability [2, 15-16, 18, 20] warranty costs [2, 17, 21-23] unexpected product failure costs [2, 21-22, 24] moderating effect of industry innovativeness [2, 14, 19, 20] firm return on assets (roa) [2, 17, 21-22, 25] capital structure [26-28] return on equity (roe) [26, 29-31] short term debt/total assets [26, 29-31] long term debt/total assets [26, 29-31] sales growth [26, 29-31] retention resources [32-34] customer actions [32-35] competitor actions [32-35] industry type [26, 29-30, 32] annual revenue [32-33, 35] firm size [26, 29-30, 32] cross-buying [32-35] lifetime values [32-34] engineering, technology & applied science research vol. 8, no. 3, 2018, 2879-2881 2880 www.etasr.com memon et al.: a survey on the criteria for measuring the profitability of a construction organization iii. results and discussion a. demographic information of the respondents. demographic information presents the characteristics of the participating respondents. during the survey, 100 questionnaire forms were distributing and 63 completed forms were received back and analyzed. the results of various characteristics of the respondents which include academic qualification and experience are presented in table ii. table ii. demography of the respondents metrics of profitability r.i.i. value % age cumulative %age academic qualification diploma 18 28.6 28.6 b. e 34 54.0 82.5 masters 8 12.7 95.2 b. tech 3 4.8 100 experience (years) 0–5 23 36.5 36.5 6–10 15 23.8 60.3 11–15 9 14.3 74.6 >15 16 25.4 100 table iii. level of implementation metrics of profitability level of implementation r.i.i. value rank 1 2 3 4 5 structural capital 2 8 16 21 16 0.73 1 lifetime values 6 7 14 17 19 0.71 2 capital structure 2 12 16 19 14 0.70 3 competitor actions 3 10 17 20 13 0.70 3 unexpected product failure costs 3 12 16 19 13 0.69 4 return on equity (roe) 1 14 18 17 13 0.69 4 industry type 5 8 17 21 12 0.69 4 firm return on assets (roa) 4 10 18 18 13 0.68 5 firm size 7 6 16 23 11 0.68 5 moderating effect of industry innovativeness 2 11 20 21 9 0.68 5 firm innovativeness 3 12 17 22 9 0.67 6 long term debt/total assets 2 13 19 19 10 0.67 6 sales growth 4 11 16 24 8 0.67 6 annual revenue 3 11 20 20 9 0.67 6 product reliability 6 10 12 28 7 0.66 7 human capital 3 12 22 15 11 0.66 7 warranty costs 4 8 22 23 6 0.66 7 retention resources 7 7 22 15 12 0.66 7 short term debt/total assets 6 8 21 19 9 0.65 8 customer actions 7 12 14 17 13 0.65 8 cross-buying 3 15 19 15 11 0.65 8 relational capital 10 8 19 14 12 0.63 9 intellectual capital 10 11 20 13 9 0.60 10 unexpected product reliability failures 8 14 21 12 8 0.59 11 b. level of implementation the respondents were asked to rank the level of implementation for each criterion of profitability adopted by their organization. the results obtained are presented in table iii. from table iii it can be perceived that ‘structural capital’ is the most commonly implementing metric in the construction projects of pakistan . table iv. level of influence criteria of profitability level of influence r.i.i. value rank 1 2 3 4 5 lifetime values 5 9 11 14 24 0.74 1 structural capital 2 10 11 27 13 0.72 2 human capital 4 9 16 14 20 0.72 2 firm size 4 11 15 14 19 0.70 3 industry type 1 9 24 15 14 0.70 3 retention resources 3 6 23 19 12 0.70 3 annual revenue 6 6 18 18 15 0.70 3 product reliability 4 7 20 20 12 0.69 4 cross-buying 5 8 17 22 11 0.68 5 long term debt/ total assets 4 12 17 15 15 0.68 5 sales growth 3 9 24 17 10 0.67 6 capital structure 4 14 16 15 14 0.67 6 relational capital 3 12 17 24 7 0.66 7 firm innovativeness 3 10 24 16 10 0.66 7 unexpected product reliability failures 3 13 22 13 12 0.66 7 customer actions 2 15 18 19 9 0.66 7 competitor actions 6 10 18 18 11 0.66 7 short term debt/ total assets 6 11 18 16 12 0.65 8 firm return on assets (roa) 1 16 21 16 9 0.65 8 intellectual capital 7 10 19 17 10 0.64 9 warranty costs 5 14 18 16 10 0.64 9 moderating effect of industry innovativeness 5 10 29 8 11 0.63 10 return on equity (roe) 4 15 21 13 10 0.63 10 unexpected product failure costs 8 6 26 19 4 0.62 11 c. level of influence of criteria on profitability influence level of each criterion on profitability was measured according to the 5 point likert scale and analysis results based on relative importance index values are shown in table iv. from table iv it is observed that the criterion ‘lifetime values’ cause extremely high influence on the company’s profitability. iv. conclusion this study investigated the level of implementation and influence of various criteria used to measure profitability. investigation involved a survey through structured questionnaires. against 100 distributed questionnaire forms 63 were finally received and then statistically analyzed to calculate frequency and relative importance index values. the results indicated that ‘structural capital’, ‘lifetime values’, ‘capital structure’ and ‘competitor actions’ are the top 4 criteria implemented in construction organization to measure profitability. engineering, technology & applied science research vol. 8, no. 3, 2018, 2879-2881 2881 www.etasr.com memon et al.: a survey on the criteria for measuring the profitability of a construction organization references [1] r. sydler, s. haefliger, r. pruska “measuring intellectual capital with financial figures: can we predict firm profitability?”, european management journal, vol. 32, pp. 244– 259, 2014 [2] a. w. mackelprang, m. habermann, m. swink, “how firm innovativeness and unexpected product reliability failures affect profitability”, journal of operations management vo. 38, pp. 71–86, 2015 [3] n. 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customer selection and resource allocation strategy”, journal of marketing, vol. 68, pp. 106–125, 2004 [35] r. t. rust, k. t. lemon, v. a. zeithaml, “return on marketing: using customer equity to focus marketing strategy”, journal of marketing, vol. 68, pp. 109–127, 2004 engineering, technology & applied science research vol. 8, no. 2, 2018, 2693-2698 2693 www.etasr.com hussain et al.: analysis of d2d communications over gamma/nakagami fading channels analysis of d2d communications over gamma/nakagami fading channels zakir hussain national university of computer and emerging sciences karachi, pakistan asim ur rehman khan national university of computer and emerging sciences karachi, pakistan haider mehdi national university of computer and emerging sciences karachi, pakistan syed muhammad atif saleem national university of computer and emerging sciences karachi, pakistan abstract—in this paper, we investigate the outage probability, channel capacity and symbol error rate (ser) performance of device-to-device (d2d) communication systems. the d2d communication system is affected by several co-channel interferers. gamma fading channel is considered for the d2d communication system. the channel for the co-channel interference is assumed to be nakagami faded. an expression for the probability density function (pdf) of the signal-tointerference ratio (sir) is presented. the pdf is a function of distances between various devices in the d2d system, path-loss, channel fading conditions and signal powers. based on the pdf expression, we present the expressions for the outage, channel capacity and ser. with the help of numerical results the performance of d2d communication system is discussed under various conditions of interference, path-loss and channel fading. keywords-channel capacity; co-channel interference; d2d communication; outage; gamma fading; nakagami fading i. introduction the rapid growth of interconnected wireless devices needs efficient wireless networks to fulfill demands of high data rates [1-5]. for this purpose device-to-device (d2d) communication system is one of the promising technologies introduced [6-10]. d2d communication is a 5g cellular communication standard that facilitates nearby active devices to communicate directly without going through a base-station (bs) [11-15]. services such as multimedia sharing, online gaming and cloud computing etc., have become vital part of daily communications. d2d communication is one of the communication systems which enable these services. d2d communication can also be used to encounter the excessive user density [16-20]. due to the large number of wireless devices always competing for the limited wireless resources, any lack of coordination or management between them, may result in a scenario of unintentionally jamming of wireless signals due to co-channel interference (cci). cci causes degradation in the performance of the system. therefore, effects of cci should be taken into consideration while analyzing the performance of wireless communication systems [21-23]. d2d communication system also suffers from cci [24]. communication system performance can be analyzed using well known metrics like outage performance, channel capacity and symbol error rate (ser) [25, 28]. outage performance of multi-antenna d2d system is studied in [25] over a rayleigh fading channel with cci. in [26], authors investigate outage probability of d2d multichannel systems over raleigh fading channels in the presence of interference. the outage analysis of d2d systems with suzuki fading channel and interference is presented in [27]. channel capacity of d2d communication system is studied in [28] over a rician fading channel and cci. in [29], channel capacity of d2d system is presented over a rician/rayleigh channel and cci. in [29], ser analysis of m-ary phase-shift keying (mpsk) for d2d systems over a rician/rayleigh channel is studied. in this paper, we study outage probability, channel capacity and ser performance of d2d communication systems with multiple co-channel interferers. based on the probability density function (pdf) expression of signal-to-interference (sir) of the d2d system, expressions for the outage, channel capacity and ser are presented. channel for d2d communication system is assumed to be gamma distributed. the generality of gamma distribution makes it feasible for the analysis of d2d communication system. it can be used to model severe channel fading conditions. in this work, we assume channel for the interferers to be nakagami faded. ii. system model we consider an interference limited system where an active pair of d2d communication devices is communicating [30]. system layout is shown in figure 1. we consider several cochannel interferers in the system. these interferers are assumed to be equidistant from the d2d receiver. the channel for cochannel interferers is considered to be nakagami faded. channel gains for the co-channel interferers are assumed to be independent and identically distributed (iid) [31]. the pdf of nakagami fading is given as [32] 2 1 22 1( ) exp , 0, 0 ( ) 2 m m x m m f x x x , m x m                  where m is the fading parameter which describes the severity of the channel fading conditions,  is the average power of fading and (.) is gamma function [32, 33]. the channel for engineering, technology & applied science research vol. 8, no. 2, 2018, 2693-2698 2694 www.etasr.com hussain et al.: analysis of d2d communications over gamma/nakagami fading channels the d2d pair is assumed to be gamma distributed. the pdf of gamma distribution is [34]: 1 ( ) , 0, > 0, > 0, ( ) x k k e x f x x k k         where k is the shape parameter, related to the intensity of the channel fading and  is the scale parameter of gamma distribution [35]. path-loss is another factor which affects the performance of communication systems. in this paper, we consider a simplified path-loss model. the received power of the d2d communication system is: 2 0 1 0 4 a d c s p c c               (1) where p1 is the d2d signal power, c is the distance between sender and receiver of d2d pair,  is the wavelength, a is the path-loss exponent (2 5)a  and c0 is the reference distance (1 to 100 meters) [36]. similarly, power of the i-th interferer at the d2d receiver is given as 2 0 .2 0 = 4 b d i p d d              (2) in (2), p2 is the interference signal power, d is the distance between the receiver of d2d pair and the i-th interferer, b is the path-loss exponent and d0 is the reference distance. using expressions (1) and (2) the sir of considered d2d communication system is given as     22 2 0 2 2 1 0 1 , , aa n b b i i ch p c g= p d dg             (3) where h is the independent gamma fading variable of the desired d2d signal, i is an independent nakagami fading variable of the i-th interferer and n is the number of co-channel interferers in the system. the pdf of the sir of our system, i.e.,  f r , is determined by using the formula       0 s irf x f rx f x dx     [37] as         1 12 0 exp( ) , 2 ( ) ( ) t t s i rx m m t f rx f x rx e x f x x dx m r                  ( 2 ) 2 1 2 2 2 ( 2 ) ( ) ( ) ( ) 2 1 , , 2 2 4 t m t t t m f r r m m r                          (4) in (4), and  are the shape and the scale parameters of the desired signal, respectively,  . is kummeru function [33] and tm nm , where m is the fading parameter for the interferer signals. also, ,g  where m   in which  is the average power of the interference fading channel. based on (4), the expression of cumulative distribution function (cdf) of our system, after some mathematical manipulation, is given as ( 2 ) 2 2 2,2 2,3 2 2 ( 2 ) ( ) 2 2 1 ( ) ( ) 2 2 2 ( 2 ) 1 ,1 2 2 14 0, , 2 2 t m t t t t t m r f r m m m m r g                                                (6) in (5), ,w xy,zg is the meijer-g function [33]. the probability of drop-down of the sir of a system below a predefined threshold r is termed as the outage probability. by using 0 ( ) r outp f r dr  [38] the expression for the outage probability of our d2d communication system is : ( 2 ) 2 2 2,2 2,3 2 2 ( 2 ) 2 2 1 ( ) ( ) 2 2 2 ( 2 ) 1 ,1 2 2 14 0, , 2 2 t m t out t t t t m r p m m m m r g                                                (6) by using the channel capacity expression 2 0 log (1 ) ( )c r f r dr    [41], the expression for the channel capacity of our d2d communication system is: ( 2 ) 2 4,2 3,4 2 2 ( 2 ) 2 2 1 ln(2) ( ) ( ) 2 2 2 ( 2 ) 1 , ,1 1 2 2 2 14 0, , , 2 2 2 t m t t t t t m c m m m m g                                                   (7) the ser performance expression for the d2d system incorporating m-ary phase-shift keying (m-psk) modulation, after some mathematical manipulations, is [33]: engineering, technology & applied science research vol. 8, no. 2, 2018, 2693-2698 2695 www.etasr.com hussain et al.: analysis of d2d communications over gamma/nakagami fading channels 2 1 ( 2 ) 2 2 ( 1) 2 0 1 2 ( 2 ) 2 2 1 ( ) ( ) sin 2 sin sin 2 1 (sin ) , ; ;1 2 2 2 4 t m t e t t m m t t m p m m m m m f m d                                                                                       (8) where m is the order of modulation and 2f1 is hypergeometric function [33]. fig. 1. d2d communication system layout where device-to-device pair n interferers (in) desired signal communication between d2d pair distance between d2d pair (c) interference signal distance between an interferer and d2d receiver (d) iii. numerical results in this section, numerical results are presented and discussed based on the expressions in section ii. our expressions are valid for arbitrary values of the channel and interference parameters. for the analysis the reference distances c0 and d0 are assumed to be 1m. for the outage probability analysis, the sir threshold is assumed to be 10dbm. the outage performance of our d2d communication system is shown in figure 2. the values of p1, δ and a, are assumed to be 20dbm, 3 and 3, respectively. the values of p2, b and m are considered to be 13dbm, 2.8 and 2, respectively. we consider 5 interferers in the system. from the figure, we observe that as the distance between d2d devices increases the outage performance degrades due to worsening of sir performance. we also observe that as interferers move away from the receiver the outage performance improves. fig. 2. outage probability comparison with varying distance between the receiver and the interferers figure 3 shows the outage performance with varying fading conditions for the interference. the values of p1, δ, p2, a, b and d are considered to be 20dbm, 3, 13dbm, 3.5, 2.7 and 50m, respectively. we consider 5 interferers in the system. from the figure, we observe negligible change in the outage performance of our system when the interference channel fading conditions are varied. hence, our system is mostly insensitive to the variations in the fading conditions of the interferers. figure 4 shows the outage performance with varying path-loss exponent values of the interfering signals, b. the values for p1, δ, p2, m, a and d are fixed at 20dbm, 3, 13dbm, 2, 3.5 and 50m, respectively. we consider 5 interferers in the system. from the figure, it can be observed that by increasing the path-loss exponent value of the interference signal, the outage performance improves. it is due to the weakening effect of the interference signal strength at the receiver when path-loss exponent value is increased. there is an inverse relation between the received signal strength and the path-loss exponent value. channel capacity performance of our system with varying numbers of co-channel interferers and d2d signal power is shown in figure 5. the values for δ, a, m, b, c, d and p2 are considered to be 3, 2.7, 2, 3, 60ms, 30m and 16dbm, respectively. from the figure, it can be seen that when the strength of the d2d signal is increased, capacity performance improves due to the improved sir conditions of the system. however, when the number of interferers in the system is increased, capacity performance deteriorates due to degraded sir conditions. channel capacity performance comparison with varying path-loss exponent values of co-channel interferers is shown in figure 6. we also vary the number of interferers in the system. the values for p1, δ, a, m, b, c, d and p2 are considered to be 20dbm, 3, 2.8, 2, 3.5, 60m, 30m and 16dbm, respectively. it can be observed that by increasing the path-loss exponent values of co-channel interferers the capacity performance improves. it is due to the weakening of the interference signals when path-loss exponent value increases. engineering, technology & applied science research vol. 8, no. 2, 2018, 2693-2698 2696 www.etasr.com hussain et al.: analysis of d2d communications over gamma/nakagami fading channels fig. 3. outage performance comparison with varying fading parameters of the interferers. fig. 4. outage probability comparison with varying path-loss exponent values of the interferers. performance analysis of 8-psk modulated d2d system with varying values of shape parameter and path-loss exponents of desired signal is shown in figure 7. the values of p1, p2, m, b, c and d are assumed to be 20dbm, 13dbm, 2, 4, 30 m and 70 m, respectively. we consider 5 interferers in the system. from the figure, we observe that the ser performance degrades as the path-loss exponent value is increased. |this is due to the weakening of the received d2d signal. we also observe that under better channel fading conditions ser performance of our system is improved. performance analysis of 8-psk system with varying d2d signal power and d2d signal path-loss exponent values is shown in figure. 8. the values for p2, m, b, c and d are assumed to be 13dbm, 2, 3.5, 30m and 70 m, respectively. we consider 5 interferers in the system. it can be seen from the figure that when the d2d signal strength is increased, improved ser performance is observed due to better sir conditions. fig. 5. capacity performance comparison with varying number of cochannel interferers fig. 6. capacity performance with varying number of path-loss exponent values of interferers fig. 7. ser performance of 8-psk system with varying shape parameters of d2d signal engineering, technology & applied science research vol. 8, no. 2, 2018, 2693-2698 2697 www.etasr.com hussain et al.: analysis of d2d communications over gamma/nakagami fading channels fig. 8. ser performance of 8-psk system with varying path-loss exponents of d2d signal iv. conclusion we studied and analyzed the outage probability, channel capacity and ser performances of d2d communication systems over gamma fading channels in the presence of multiple nakagami faded co-channel interferers. we also considered path-loss effects in our system. we presented a pdf of the sir of our system. based on this pdf, expressions for the outage probability, channel capacity and ser are presented. with the help of numerical results based on our expressions, we discussed the effects of various channel parameters, like fading and path-loss, on the outage, channel capacity and ser performances of our d2d communication system. we also observed that our d2d communication system performance is largely insensitive to the variations in the channel fading conditions of the interferers. however, variation in the pathloss exponent values of the interference signal show variation in the overall d2d system performance. references [1] c. gao, h. 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mh.mahshidnia@yahoo.com ahmad jafarian department of mathematics, urmia branch, islamic azad university, urmia, iran. jafarian5594@yahoo.com abstract—wastewaters caused by industrial and manufacturing production containing pollutants which beside degradation and depletion of natural resources, impose excessive pressure on the earth's ecosystems and exacerbate water shortages. one of the pollutants is a toxic substance named malachite green (mg). wastewater treatment means to obtain usable water by separating contaminants of contaminated water. one of its main purposes is the recovery and re-use of wastewater for a variety of uses including agriculture and aquaculture, especially in arid and semi-arid countries, as well as providing environmental protection. the main purpose of the present study was to investigate mg separation efficiency by nano composite materials. poly-aniline was covered on wheat husk ash in order to prepare this type of nano composite. the material was analyzed by x-ray radiation and scanned by an electron microscope. the level of separation depends on the initial value of wheat husk ash and poly-aniline and the initial concentration of mg and the intensity of ultraviolet radiation and radiation time. the effect of these parameters was investigated and optimum operating conditions were obtained. an adaptive neural fuzzy intelligent system was used to forecast the results of the mg separation process. the comparison between the results forecasted by the designed model and experimental data strengthens the validity of the process. keywords-malachite green (mg); industrial wastewater treatment; adaptive neural fuzzy intelligent system; anfis i. introduction wastewaters caused by industrial and manufacturing production contain various pollutants and have a huge environmental impact. therefore, treatment should be applied before discharging wastewaters into the environment. the issue of reducing the volume of pollution and removing pollutants and toxins and colored wastewaters has been one of the most important research topics in recent years and many works has been done in this field. [1-3, 5-21, 25-26]. polymer and nano materials are bound to play an important role in such treatments, therefore specific works in this field [4, 22-24, 2729] are of interest for researchers focusing on wastewater treatment. as a detail laboratory evaluation of different treatments is time and cost consuming, advanced forecasting techniques are often employed for assessment [1-3, 15, 17, 20, 21 in this study, a new method, using an anfis model is proposed to forecast treatment results. anfis is a fuzzy inference tool that has been implemented within the framework of adaptive networks. this method combines the ability to fuzzy learning with the versatility and the self-learning of neural networks. in this study, a subtractive clustering method was also employed to increase forecasting speed and efficiency. ii. methods and materials a. industrial wastewater the quality of industrial wastewater is very diverse because of a large variety of chemicals are used and it highly depends on the related industry. in the metal industry for example, production process or coating metal parts create a large amount of wastewater contaminated with heavy metals such as copper, cadmium, silver, mercury, chromium or nickel which are considered as most dangerous pollutants. in the dairy industry, a lot of fat-soluble wastes are generated different parts of the production unit which. in textile, leather, cosmetics and personal care and paper making industries, colors and organic materials are the most often found pollutants. industrial wastewater is usually divided into the following groups: • wastewater related to the industrial process for the production line • wastewater of utilities sector related to the process of water treatment, water boiler and cooling tower and public facilities • sewage of washing tanks, premises and sudden discharge which are similar to the wastewater of production line. the concentration of industrial wastewaters is usually measured by contaminants. since, the nature of the above pollutions are mostly different, there are different methods to treat the industrial wastewaters. 1) malachite green (mg) one of contaminants in industrial wastewaters is a toxic substance named malachite green (mg). malachite green is usually used for dyeing cotton, cream, silk and paper stuck. engineering, technology & applied science research vol. 6, no. 5, 2016, 1175-1181 1176 www.etasr.com mahshidnia and jafarian: forecasting wastewater treatment results with an anfis intelligent system malachite green filtration and separation process is done using poly-aniline nano-composites. composite is a compound material with a few structures. wheat husk ash in combination with poly-aniline forms a composite. poly-aniline polymerase is derived from aniline, which is a chemical substance and used to treat wastewater. wastewater treatment means to obtain usable water by separating and removing pollutants from contaminated water. 2) industrial wastewater treatment the first step of industrial wastewater treatment is to carry out qualitative analysis and identifying the type of contamination. in the next step, the wastewater treatment system is designed and implemented based on the type of contamination. at present, in gas (air), liquid (water) and solid (soil) phases there are three kinds of treatment method which can be used separately or in combination with each other: • chemical methods • physical methods • biological methods chemical methods can be expensive or produce dangerous excipients and in the case of facing a pollutant with excessive construction, the condition will be more critical, because of high costs, low rate of chemical reaction, the need of building reactors with certain characteristics and the possibility of chemical substance remaining on the process which itself can be dangerous. whatever the size of pollutant’s particles is smaller, its physical removal needs more costs. on the other hand most physical methods are not able to remove contaminants with very small sizes. biological methods have low costs and are commonly used, but they are sufficient for all pollutants and they also suffer in terms of speed, controllability and efficiency. 3) supplying and preparing the materials aniline, potassium iodates (kio3), ferric chloride (fecl3), sodium hydroxide (na-oh), sulfuric acid and malachite green were obtained from merck (germany) and used without any purification. wheat straw (wha) is a by-product obtained using a wheat mill. the sem image of wheat straw is shown in figure 1. distilled water was used to wash wheat crust, which was then dried in the oven at c ° 60 for 2 hours. at the next step, it was washed using acetone and sodium hydroxide (m0.3) to separate dust and other contaminants in it and was dried in the oven at c ° 60 for 24 hours [21]. fig. 1. sem image of a wheat straw 4) nano-composites / poly-aniline synthesis wha 1 g of kio3 was added to 100 ml of sulfuric acid to prepare the nano-composites of aniline/wheat straw and then a uniform solution was obtained using a magnetic stirrer. in continue, 1 g of wheat husk ash was added to the solution and then 1 ml of fresh distilled aniline monomer was added to the solution. the reaction lasted for 5 hours at room temperature. as a result, the product was filtered on filter paper and washed with distilled water for several times to isolate the oligomers and impurities. then, it was dried in the oven at c ° 60 for 24 hours. the sem and ir spectrum are shown in figures 2 and 3 respectively [2127]. fig. 2. sem image of wha nano-composite/polyaniline fig. 3. ir spectrum of wha nano-composite/poly-aniline 5) analytical method the nano-composite of mg was used as pollutants in the vicinity of pan/wha. all samples were gathered and analyzed at 690 nm using a uv-vis spectrophotometer (200, high settings of england biotech). the linear correlation between the concentration and absorption of mg in the range of 1-10 mg was obtained at correlation coefficient level of r2=0.9. the following equation was used to calculate the photo-catalytic removal efficiencies (r %) in the experiment [21]. 100   o to c cc r where co (mg/l) and ct (mg/l) are the initial concentration of mg and mg concentration at the time of t, respectively. 6) wastewater treatment using poly-aniline nano-composite cheap raw materials, cheap and environmentally friendly methods of preparation are among advantages of the nanocomposites. the synthesize of suitable nano-composites was engineering, technology & applied science research vol. 6, no. 5, 2016, 1175-1181 1177 www.etasr.com mahshidnia and jafarian: forecasting wastewater treatment results with an anfis intelligent system done using poly-pyrrole and aniline monomers and base materials. different nano-composites polymers were synthesized and different effects such as the type of oxidizing, synthesis environment, temperature conditions, etc. were investigated to obtain the most proper composite. among the most striking characteristic of this nano-composite, is removing color, odor, anionic and cationic only in one stage and in a very short time period. b. adaptive neural fuzzy intelligent system (anfis) the anfis system was firstly proposed in [30]. in such a system, fuzzy logic is combined with artificial neural networks to facilitate the learning and adaptation process. an adaptive network which generally is a leading multi-layer neural network is used in fuzzy-neural models to solve the problem of fuzzy inference system parameters' identifying. an adaptive network is a leading multi-layer structure which the overall output behavior of it is determined by a number of modifiable parameters. the main form of fuzzy systems' usage which is fuzzy " if and then" rules and optimizing model's parameters is gained by using adaptive neural network. the most common type of fuzzy inference systems which can exposure in an adaptive is the takagi-sugeno fuzzy system. to simplify, it is assumed that the under investigation fuzzy inference system includes inputs of x and y and an output of "f" with rule base of "if and then". the rules of this system are:  the first rule: if x is a1 and y is b1, then: f1 = p1x + q1 + r1  the second rule: if x is a2 and y is b2, then: f2 = p2x + q2y + r2 where, a1 and a2 are the membership functions of input x and b1 and b2 are the membership functions of input y and p1, q1 , r1 , p2 , q2 and r2 are the parameters of output function. the overall structure of a fuzzy inferenceneural system is shown in figure 4 where n is the input variable (here n is equal to 4). five layers have been used to make this model. each layer includes e few nodes which has been defined by the function of the node. the compatible nodes signed with squares show the parameters sets which are adaptable in the nodes. in contrast, the fixed nodes signed with circles indicate the fixed parameters of model. fig. 4. the fuzzy inferenceneural system layer1: the first layer is a fuzzy layer which turns inputs to a fuzzy set by membership functions. these layers are adaptive nodes which are as follow: i i-2 1,i a 1,i b o =μ (x), for i=1,2 (1) o =μ (y), for i=3,4 (2) where, x and y are the input nodes of "i". a and b are time tags corresponding to each node. μ(x) and μ(y) are membership functions. layer2: each node in this layer is a fixed node tagged by п. o2,i is the output of the second layer:   i i-22,i i a b o =w =μ (x).μ (y), for i=1,2 3 layer3: each node in this layer is a fixed node tagged by n. o3,i is the output of third layer: i 3 , i 1 2 w o = w = , f o r i = 1 , 2 ( 4 ) w + w layer4: each node in this layer is an adjustable node. o4,i is the output of third layer: 4,i i io =w .f , for i=1,2 (5) layer5: each node in this layer is a fixed node and the output is: i i 5,i i i i w .f io = w .f = =fout=overall output (6) i w   the simplest rule of fuzzy-neural inference system is "back-propagation" which calculates the error signals in a propagation manner from output layer (layer5) backward to input nodes (layer1). in training of these systems, with utilizing from training data the non-linear parameters of fuzzy membership functions in the first layer and the linear parameters of fourth layer are determined in a way that the desired output is reached for each arbitrary input. this hybrid training method is one of the most important training methods of adaptive neural network-based fuzzy inference systems. in this method, the error back propagation approach in the first layer and the least squares estimator approach in the fourth layer are used to training. the actual structure of the anfis model used is shown in figure 5. fig. 5. the structure of the anfis model engineering, technology & applied science research vol. 6, no. 5, 2016, 1175-1181 1178 www.etasr.com mahshidnia and jafarian: forecasting wastewater treatment results with an anfis intelligent system c. subtractive clustering the aim of clustering is to find similar clusters of objects among input samples [31-32]. although, there is no clear idea about the number of clusters, subtractive clustering is a quick method to solve this problem [33-34]. sometimes, the centers estimated by this method are considered as initial points of other clustering algorithms. the subtractive clustering is in fact a modified form of mountain method. in this algorithm, each point is considered as a potential to cluster's center. the measurement of potential is carried out and the the allocated potential to each cluster depends on its distance from other points and in the cases with integrated neighborhood leads to clusters with high potential. after calculating the potential of each point, point with the highest potential is selected as cluster centers. then potential reduction is performed and the process is repeated until a stop criterion is satisfied. iii. results a. data preparing & forecasting scheme the model includes four parameters of the initial concentration of mg, the initial amount of poly-aniline and wheat husk ash and time and intensity of uv radiation as input variables and removal percentage of mg as output variable as shown in table i. the forecasting scheme is shown in figure 6. as shown, inputs and outputs presented in table i were logged on a neuron-fuzzy inference system for training and diagnosis. the training errors have been comprised based on anfis structure in combination with the 3 ways of network partitioning, clustering and fuzzy clustering and the system was trained by two algorithms (postpropagation and hybrid). then the structure and algorithm of suitable training have been used to forecast the removal percentage of mg by comprising each of forecasted outputs with the real output. b. forecasting results since the training data error in the structure of neural adaptive fuzzy inference system have 0.008 error reduction in 100 iterations based on subtractive clustering structure, this structure was selected and re-trained considering training algorithms which its results have been represented in this section. the results from different structures for the back propagation case are shown in figures 7-12 whereas the results from different structures for the hybrid case are shown in figures 13-18. as shown, the difference between the obtained output and the real output is negligible in all cases. table i. variables variable range input layer x1=pani/wha-initial dosage (g/l) 0.1-1.5 x2=mg-initial concentration (mg/l) 1-12 x3=uv-light intensity (w/m2) 8.3-40.6 x4=irradiation time (min) 0-60 output layer range y=removal of mg (%) 0-100 fig. 6. the forcasting scheme fig. 7. difference between anfis output and detailed output during the training stage fig. 8. difference between anfis output and detailed output during the testing stage fig. 9. difference between anfis output and detailed output during the training stage of fis1 engineering, technology & applied science research vol. 6, no. 5, 2016, 1175-1181 1179 www.etasr.com mahshidnia and jafarian: forecasting wastewater treatment results with an anfis intelligent system fig. 10. difference between anfis output and detailed output during the testing stage of fis1 fig. 11. difference between anfis output and detailed output during the training stage of fis2 fig. 12. difference between anfis output and detailed output during the testing stage of fis2 fig. 13. difference between anfis output and detailed output during the training stage of fis fig. 14. difference between anfis output and detailed output during the testing stage of fis fig. 15. difference between anfis output and detailed output during the training stage of fis1 fig. 16. difference between anfis output and detailed output during the testing stage of fis1 fig. 17. difference between anfis output and detailed output during the training stage of fis2 engineering, technology & applied science research vol. 6, no. 5, 2016, 1175-1181 1180 www.etasr.com mahshidnia and jafarian: forecasting wastewater treatment results with an anfis intelligent system fig. 18. difference between anfis output and detailed output during the testing stage of fis2 iv. discussion the anfis intelligent model was utilizing in matlab. three different structures (anfis-gp, anfis-sub, anfisfcm) were compared and the anfis-sub structure was finally chosen and trained by two methods (bp, hybrid). the proposed model was trained by receiving actual data (70% of data) and then evaluated (30% of data). then the forecast was compared to actual values. according to the histogram diagrams of error values, the adaptive neuron-fuzzy inference system trained by hybrid method led to better results. according to the training performance and evaluation, the difference between output data of anfis and detailed (real) output data in training and testing stages of anfis is negligible. the diagrams have high overlap on each other in the hybrid method and it can be concluded that utilizing from the subtractive clustering-based structure of adaptive neuron-fuzzy inference system trained by hybrid method provides better results. as shown, it is possible to provide an accurate and detailed forecasting about the removal percentage of malachite green and also, it is possible to use this factor in other similar cases after training the system. v. conclusion forecasting the results of wastewater treatment using an anfis model was investigated in this paper. different schemes and training algorithms were evaluated. finally, it was derived that the anfis-sub structure trained under a hybrid algorithm provided the best results. the results showed a rather satisfying efficiency for the forecasting scheme. the pollutant tested was malachite green and actual data was used to train and evaluate the system. a similar approach however, could be used for other pollutants. references [1] j. wan, m. huang, y. ma, w. guo, y. wang, h. zang, w. li, x. sun, “prediction 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aerospace university «khai» kharkiv, ukraine k105@d1.khai.edu abstract—the effects of uncertainty on a project and the risk event as the consequence of uncertainty are analyzed. the uncertainty index is proposed as a quantitative measure for evaluating the uncertainty of a project. this is done by employing entropy as the indicator of system disorder and lack of information. by employing this index, the uncertainty of each activity and its increase due to risk effects as well as project uncertainty changes as a function of time can be assessed. the results are implemented and analyzed for a small turbojet engine development project as the case study. the results of this study can be useful for project managers and other stakeholders for selecting the most effective risk management and uncertainty controlling method. keywords-project uncertainty index; entropy; risk management; rework risk; research and development project i. introduction one of the most prominent aspects of each project and especially complex projects is the influence of uncertainty on achieving the project goals. in a project, the uncertainty is maximum at the beginning and as the information and knowledge about the project is attained and as activities terminate, uncertainty decreases and reaches its minimum value at the project’s end [1]. a well-known aspect of uncertainty is imprecision or variation of project parameters such as duration, cost, work amount (effort). another aspect is foreseen uncertainty, which causes risks [2]. risk is defined as an uncertain event or condition that, if occurs, has a positive or a negative effect on at least one project objective, such as time, cost, scope, or quality [1]. therefore, due to the significant impact of uncertainty on project goals, quantification and monitoring this concept can be very useful and informative for project manager and other stakeholders. however, in this area and its practical use in project management, little progress has been achieved so far [3]. considerable part of limited researches on this field employed the entropy concept [3-8]. however, these researches do not investigate the contribution of each activity on project uncertainty depending on its position in the project’s schedule. in addition, the effect of complex combination of risks, which affects the distributions of activity durations and costs have not been analyzed in detail. one of the first works on quantification of uncertainty in a project was performed in [4] where the authors proposed the entropy as a measure of project uncertainty and implemented entropy concept for a project with deterministic pert distribution and uncertain durations. they suggested decreasing project entropy level at project milestones and implemented the results in a petroleum plant project in russia. in [8], entropy was employed and a detailed description of uncertainty for organizational and economic systems was proposed. a method for estimating uncertainty was proposed that consisted of four parts: the uncertainty of the environment; uncertainty of managerial decision-making; uncertainty of consequences and future implementation of management decisions and vartational uncertainty. in [9, 10], authors proposed the use of entropy for evaluating the risks and uncertainties of a project. in [3], authors offered three entropy-based uncertainty measures for evaluating the project uncertainty: aggregate uncertainty, weighted aggregate uncertainty and deviation uncertainty. the proposed method is based on the number of unknown risk factors and their weight at each project stage, which is evaluated by experts. the employment of entropy as the third risk characteristic (besides probability and impact of risk) for assessing risks of software development projects is suggested in [5]. authors introduced entropy as a measure of uncertainty about the probability of risk occurrence. they assessed the entropy of risks by a questionnaire survey and implemented a risk fuzzy judgment method for a group of software projects. in [11], authors used fuzzy entropy and the vikor technique for evaluation and prioritizing risks of engineering, procurement and construction (epc) projects. in their work, fuzzy entropy is used for calculating the weights of criteria. in [6], authors employed a weighted linear average of expected utility and entropy (eu-e) decision model for measuring uncertainty of different possible variants for realization of resource constrained project with uncertain activity durations. in [12], authors proposed a markov chain model for assessing the risks of life safety projects, which allows moving from onedimensional to multi-dimensional assessments of the level of security in organizational and technical systems. finally, in [7], entropy was applied as a measure of uncertainty for two project parameters, i.e. project completion time and critical path probability. the required distributions are obtained by arena simulation software for a project network with pert distributions. engineering, technology & applied science research vol. 7, no. 5, 2017, 2083-2088 2084 www.etasr.com chenarani and druzhinin: a quantitative measure for evaluating project uncertainty under … a measure for project uncertainty that takes into account the mentioned factors is proposed in this work. the results are implemented in practice for a small turbojet engine development project. ii. proposed approach a. basics, entropy as a measure of uncertainty entropy concept is used widely as a measure of uncertainty in different fields. for the first time, boltzmann in 1872 in his work on theory of gases introduced entropy. his famous equation relates the entropy of an ideal gas to the number of real microstates consistent with its macrostate properties. this way, the entropy value represents the number of possible statuses of a system, and consequently the degree of disorder and disorganization of a system. in [13], the concept of entropy for measuring information uncertainty was developed. the information was defined as removed uncertainty and the use of entropy as a measure of information related to the message was suggested. in other words, the uncertainty of a system decreases by receiving information about the possible outcomes of the system. entropy formula has the following form: i n 1i i plnph    (1) where: h: entropy of system, n: the number of possible outcomes or states of a given system, pi: probabilities of those outcomes or states and we have   1pi . in [4], the entropy concept in project management field was developed and calculating entropy of each activity regarding to duration, cost and other project parameters and adding the entropy of activities for obtaining the total entropy of project was suggested. in other words:  id idhh (2) where: hid is the entropy of an individual activity and ...hhhh qualitytcosscheduleproject  (3) in next section, we will further develop this concept along with introducing other aspects, which contribute to the uncertainty of the project. hence, we suggest an uncertainty index for project by employing these factors. b. developing the project uncertainty index in this research, a project simulation program which is presented in [14] has been employed. this program uses a discrete event based monte carlo method and models the project with and without considering risk factors when activities have uncertain cost and duration values. durations and cost of activities can be determined by probability distributions such as triangular, normal or beta-distribution. as noted before, this aspect of uncertainty is called variation [2]. on the other hand, risks are consequences of uncertainty, which are specified by two parameters, probability of occurrence (p) and impact of risk (i). for simulating risks in project, depending on their effect on main project constraints we categorized them into four types (delay risks, cost risks, excess work risks and rework risks). as the result of simulation, the duration and cost of each activity as well as cumulative time and cost of project are obtained in form of histogram distributions or cdfs (cumulative distribution function). figure 1 shows a summary of simulation program inputs and outputs. fig. 1. summary of simulation program inputs and outputs in order to formulate the uncertainty index, for example we consider the uncertainty of activities with respect to their durations. we define itu as duration uncertainty index of activity i as: )i1(thu ititit i  (4) where it h =non-dimensional entropy of activity i with respect to its duration distribution, it = average (mean) value for duration of activity i, iti = uncertainty propagation factor of activity i with respect to duration each part of (4) is obtained as follows: it h for each activity is calculated by using the distribution of that activity’s duration, which is achieved by simulation results. figure 2 shows an example of obtained distribution for duration of an activity for two cases i.e. simulation with and engineering, technology & applied science research vol. 7, no. 5, 2017, 2083-2088 2085 www.etasr.com chenarani and druzhinin: a quantitative measure for evaluating project uncertainty under … without considering risk factors. in this case, the initial distribution for duration of activity was triangular distribution (white histograms), after simulating the effect of project risks, the yellow histogram is obtained for duration of activity. we calculate the non-dimensional entropy of this activity’s duration as:    t max i i n 1j jj tt t t plnp nln 1 h h h (5) where t )tt( t t n minmaxt       (6) and 0)pln(p jj  when 0p j  the coefficient tnln is maximum possible entropy value and happens for uniform distribution. equation (5) is used for calculating the entropy of both distributions, i.e. with and without considering risk effects. fig. 2. histograms for duration of an activity selecting the appropriate value of t is important for achieving the suitable results [4]. for determining this parameter, we must take into account two considerations. the first consideration is that the size of t compared with sampling interval )tt( minmax  must be small enough in order to properly reflect the form of distribution. another consideration is that t value cannot be so small as it causes the low density of samples in intervals. these considerations can be expressed by next inequality: tt n t   (7) where n is the total number of samples (in our simulation program it is equal to iteration number) and )tt(t minmax  . the suitable value of t can be obtained by a simple try and error process. in cases where the order of durations for different activities differ significantly, this process can be more complex. the value of t must be equal in both cases of figure 2 in order to compare their entropies. the next coefficient in (4) is it i or uncertainty propagation factor which shows the potential ability of an activity in propagating the uncertainty through the project. for first activities, this parameter is higher than last activities. for example for the network diagram of a project which is shown in figure 3, the uncertainty about the third activity affects 8 successor activities but for activity 12 only 2 activities are affected. for computing this coefficient, we use graph theory for searching and finding the affected activities for each activity. fig. 3. example of a project’s network diagram if the directional graph of project is represented by: )a,v(g  (8) we have:  n,...,2,1v  , set of vertices (project activities) (9) vn  is graph order (number of project activities) and   vu,nv1,nu1|v,ua  (10) set of edges (activity dependencies) for calculation of it i in (4) for each activity, we create a directional subgraph, which corresponds to vertex i. this is performed via a graph traversal algorithm. in present study, we used bfs (breadth first search) method and as the result, all vertices (project activities) and edges (activity dependencies) which start from i th vertex (activity) are found. therefore, the obtained subgraph )a,v(g iii  is directional subgraph that starts from i th vertex and we have:    n,...,ij,jv,vv ii  (11) iv is the set of activities affected by activity i and it’s order (number of project activities dependent on that activity) is represented by ii vn  . in addition, we have:      n,...,1iv,1n,...,iu,)v,u(a,aa iiiiii  (12) after obtaining ig , the iti value is calculated as follows:     i ii n 1j ii)j(ut ))j(v),j(u(iti (13) 1 i max i i t t t t t i i i i i  (14) (the maximum value of this coefficient belongs to first activity because all project activities are affected by it). engineering, technology & applied science research vol. 7, no. 5, 2017, 2083-2088 2086 www.etasr.com chenarani and druzhinin: a quantitative measure for evaluating project uncertainty under … )v,u(i ii in (13) is an estimate of predecessor activity ( iu ) impact on successor activity ( iv ) in form of the ratio of received and used data, documentation, raw material etc. and can be determined by different methods. in this work, we employed the expert method. finally, the last part of (4) is the mean value for duration of i th activity ( it ) which is obtained by the simulation program. this part is employed for the evaluation of each activity’s contribution in project uncertainty with respect to the assumed parameter (project duration is this case). after calculating uncertainty index for all activities with (4), the duration uncertainty index of project as a function of time, is obtained as:    i ti 0t t t i project project uk u 1 )t(u (15) where  0w|n,...,2,1i i  , n= the total activity number of project , 0t t project u  = maximum value of duration uncertainty index of project, which occurs at the beginning of project (t=0). coefficient ik is the remained work fraction of i th activity (wi) at time t. in other words, the summation is performed over unfinished parts of activities. the unfinished activity set and their ik coefficients are obtained by project simulation program at every time step. the calculated uncertainty index is maximum at the beginning of project and as an activity accomplishes, the corresponding uncertainty index value is subtracted. when project finishes, the uncertainty index equals zero. similarly, uncertainty index for cost of activities and project can be obtained as follows: )i1(chu iii cicc  (16) where ic u is the cost uncertainty index for activity i    c max i i n 1j jj cc c c plnp nln 1 h h h (17)    i ci 0t c c i project project uk u 1 )t(u (18) where: )t(u projectc is the cost uncertainty index of project. then, we represent the overall index of project uncertainty as follows:  )t(ku)t(u 1k 1 u projectproject ctproject         (19) 1u0 project  . coefficient k shows the importance of project cost uncertainty in relation with duration uncertainty. depending on project type, the manager can determine whether the cost uncertainty or duration uncertainty is more important and assign the degree of that importance relationship. in order to have a good representation of risk effects on a project, these calculations are performed for two cases: without considering risk effects and with risk effects (these two cases are illustrated in figure 2). if there is another important aspect or parameter of project uncertainty (for example quality, work volume, technical characteristics etc) the overall concept can be applied provided that the distribution of that parameter for each activity can be evaluated or measured. iii. case study results the results of this study were implemented for a small turbojet engine development project as the case study. this engine type can be installed on unmanned aerial vehicles or ultralight sport planes. the project consists of 5 phases and 63 activities. the overall project duration and cost without existing risk factors and with determined (certain) duration of activities are 4 years and 1 million dollars respectively. the gantt chart diagram for this project is shown in figure 4. for representing the uncertainty about activity durations and cost, triangular distribution is considered for each activity. each triangle distribution is characterized by three parameters: optimistic estimate, most likely estimate and pessimistic estimate. in addition, for this project, a total number of 41 possible risks are identified by experts and are listed in detail in table i. fig. 4. project gantt chart table i. number of indentified risks for case study project project phase number of risks delay risk cost risk excess work risk rework risk technical proposal 1 0 1 3 schematic design 2 1 1 7 technical project and detail design 1 0 1 1 preparing engine prototypes 4 3 2 0 ground and flight tests 2 1 2 9 total 10 5 7 19 the estimated probabilities and impacts of risks are entered in corresponding probability and impact matrices (simulation inputs, figure 1). we obtained distributions of duration and cost of each activity with and without risk effects by employing the simulation program. the entropy of each activity is calculated by averaging the values of it h in (5) and ic h in engineering, technology & applied science research vol. 7, no. 5, 2017, 2083-2088 2087 www.etasr.com chenarani and druzhinin: a quantitative measure for evaluating project uncertainty under … (17). the entropy increase for each activity due to risk effects is shown in figure 5. fig. 5. entropy increase of activities because of risk effects figure 5 shows the uncertainty increase for each activity when simulation program models all possible risks. in order to investigate the effects of each phase’s risks on overall project uncertainty index, figure 6 is represented. for this end, the simulation program was executed five more times. each time, risks of one phase were ignored and the project uncertainty index at the project start was calculated for duration and cost uncertainty (i.e. 0t t project u  in (15) and 0t t project u  in (18)). the ratios of uncertainty increase due to ignoring risks of each phase to its maximum value (which obtains after modeling all possible risks) are calculated and shown in figure 6. fig. 6. effect of each phase’s risks on project uncertainty by using (4) and (15), we obtain the curves of duration uncertainty index (figure 7). the value of t in (7) is set to 0.1 week. similarly, figure 8 represents cost uncertainty index that are obtained from (16) and (18). here, we used 50 dollars as the value of c for calculating cost entropy of activities. table ii represents the portion of each phase in uncertainty index of project for duration and cost uncertainties. fig. 7. duration uncertainty index curve with and without risk effects fig. 8. cost uncertainty index curve with and without risk effects table ii. portion of project phases in project uncertainty project phase duration uncertainty cost uncertainty technical proposal 4.3% 1.3% schematic design 14.9% 3.9% technical project and detail design 19.8% 6.2% preparing engine prototypes 36.7% 62.5% ground and flight tests 24.3% 26.1% the results are obtained with considering risk effects (black curves in figures 7,8) finally, by results of uncertainty index for duration and cost of project (figures 7 and 8) and using (19), overall project uncertainty index is obtained (figure 9). here, we assumed k=1 in (19) which means that on-time completion of project and within determined budget have the same importance. fig. 9. overall project uncertainty index curves (for k=1) iv. discussion as shown in figure 5 the relative uncertainty increase as the result of risk factors is higher for first phases (design activities) in comparison with last activities. this is mainly due to the nature of the design phase in these project types, which is associated with high uncertainty and the need for repeating or increasing the work amount. moreover, this figure shows us that activities 6, 18, 39, 48 and 57 are the most sensitive activities of each phase to risk factors. in performing each phase, special attention must be paid to risk management strategies for these activities. the influence of rework risk types on project uncertainty is higher than other risk types as they affect set of activities and not a single one. given that out engineering, technology & applied science research vol. 7, no. 5, 2017, 2083-2088 2088 www.etasr.com chenarani and druzhinin: a quantitative measure for evaluating project uncertainty under … of 19 rework risks 7 reworks start from schematic design (second phase) and 9 reworks from ground and flight tests (fifth phase) it does not seem surprising that in figure 6 these phases has higher effects on project uncertainty. for managing project risks, this risk type must be considered more seriously. analyzing figures 7 and 8 and the corresponding values on table ii show that at first 3 phases, the project uncertainty due to activity durations is 3%, 11%, 13.6% more than uncertainty due to activity costs for the first, second and third phases respectively. however, this is because of the fact that for design activities the activity cost aspect is not as significant and prominent as activity durations. figure 9 can be employed as an effective quantitative tool for investigating the impact of different risk management methods on project uncertainty level. the result of implementing risk management methods that attempt decreasing probability or impact of risks, can be represented by a curve between two curves of figure 9 (without risk effects and with all possible risks). the relative area between two curves that is decreased by implementing risk management method can be considered as a quantitative measure for evaluating the effectiveness of that risk management method. v. 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approach for risk identification and prioritization simultaneously in epc projects”, in: risk management in environment, production and economy, intech, 2011 [12] v. gogunsky, y. s. chernega, e. rudenko, “markov model of risk in the life safety projects”, odes’kyi politechnichnyi universytet. pratsi, vol. 41, no. 2, pp. 271-276, 2013 [13] c. e. shannon, “a mathematical theory of communication”, bell system technical journal, vol. 27, pp. 379-423, 1948 [14] a. chenarani, e. a. drughinin, d. n. kritskiy, “simulating the impact of activity uncertainties and risk combinations in r&d projects”, journal of engineering science and technology review, vol. 10, no. 4, pp. 1-9, 2017, engineering, technology & applied science research vol. 7, no. 2, 2017, 1486-1495 1486 www.etasr.com nejad and keshtkar: entropy generation analysis of natural convection in square enclosures with… entropy generation analysis of natural convection in square enclosures with two isoflux heat sources saeed zaidabadi nejad department of mechanical engineering, kerman branch, islamic azad university, kerman, iran mohammad mehdi keshtkar department of mechanical engineering, kerman branch, islamic azad university, kerman, iran abstract-this study investigates entropy generation resulting from natural convective heat transfer in square enclosures with local heating of the bottom and symmetrical cooling of the sidewalls. this analysis tends to optimize heat transfer of two pieces of semiconductor in a square electronic package. in this simulation, heaters are modeled as isoflux heat sources and sidewalls of the enclosure are isothermal heat sinks. the top wall and the non-heated portions of the bottom wall are adiabatic. flow and temperature fields are obtained by numerical simulation of conservation equations of mass, momentum and energy in laminar, steady and two dimensional flows. with constant heat energy into the cavity, effect of rayleigh number, heater length, heater strength ratios and heater position is evaluated on flow and temperature fields and local entropy generation. the results show that a minimum entropy generation rate is obtained under the same condition in which a minimum peak heater temperature is obtained. keywordsnatural convection;enclosure; finite volume method; rayleigh number; entropy nomenclature pr prandtl number (=ν/α) (dimensionless) ec eckert number (=α 2 k/h3 cp q1) ra rayleigh number (=gβq1 h 4/kαν) g acceleration due to gravity (m/s2) h height of cavity (m) k thermal conductivity (w/mk) lh,1 width of left heater (m) lh,2 width of right heater (m) lh,1 dimensionless width of left heater (lh,1 /h) ns dimensionless rate of entropy generation (=sgen h2/k) p* effective pressure (= ( )ap gy p p dimensionless effective pressure (=p* h2/α2) q1 flux over left heater (w/m2) q2 flux over right heater (w/m2) qr heat flux ratio (=q2/q1) tc cold wall temperature (k) t ambient temperature (k) *t dimensionless ambient temperature (=tc k/q1 h) u dimensionless horizontal velocity (=uh/α) v dimensionless vertical velocity (=vh/α) x dimensionless horizontal coordinate (=x/h) y dimensionless vertical coordinate (=y/h) α thermal diffusivity (m2/s) β volumetric expansion coefficient (k-1) εr heater length ratio (lh,2/lh,1) μ dynamic viscosity (pa.s) ν kinematic viscosity (m2/s) θ dimensionless temperature (=(t-tc)k/q1 h)  ambient density (kg/m 3) i. introduction entropy generation minimization (egm) in a closed enclosure filled with fluid is the interaction of heat transfer, fluid mechanics, and engineering thermodynamics. this approach is considered as a part of exergy analysis, since exergy destruction is proportional to entropy generation. various precise works on natural convection in enclosures have been published. in [1-2] authors numerically solved free convection problem in a square enclosure with insulated horizontal walls and vertical walls under two different temperatures. in [3] authors studied laminar free convection in a rectangular enclosure with discrete heat sources. they showed that constant temperature heat sources are generally more significant than constant flux. passive systems such as fin or baffle are simple methods used to control fluid flow and heat transfer due to natural convection in enclosures. in [4], authors studied two-dimensional laminar natural convection heat transfer in an inclined fin located cavity. they observed that the inclination angle of the fin is an important parameter for controlling heat and fluid flow. in natural convection process, entropy generation should be minimized in thermal processing to achieve an optimal processing with minimum irreversibility. optimal conditions can be evaluated by egm. in [5–6], authors comprehensively discussed the analysis of entropy generation for various problems. in [7], authors studied entropy generation due to heat transfer and fluid low irreversibility in natural convection into diverse cavities. in [8] natural convection in closed enclosures with heating in corners was evaluated. it was documented that heat transfer depends on the length of the heating body and that the effect of prandtl number on average nusselt number is more significant in prandtl numbers lower than 1. in [9], authors studied entropy generation due to natural convection in a square enclosure heated by a protruding heat source and filled with nanofluid. it was shown that heat transfer performance could be maximized and entropy generation could be minimized by positioning the heat source on the lower wall of the enclosure. in [10], authors investigated free convection in a rectangular system with hot sidewall in nine different positions of heat source. in [11], authors numerically analyzed engineering, technology & applied science research vol. 7, no. 2, 2017, 1486-1495 1487 www.etasr.com nejad and keshtkar: entropy generation analysis of natural convection in square enclosures with… free convection in a 3d square enclosure with a cubic body producing heat at the center of the enclosure. they found out that fluid flow inside the enclosure results from two temperature differences; one, temperature difference between hot and cold wall of the enclosure and the other temperature difference caused by heat generating body. in [12], entropy generation due to natural convection in square enclosures with two discrete heat sources was generated. recently, different studies have been conducted on mixed convection in nanofluid-containing enclosures with moving wall and different geometry and boundary conditions [13-15]. in [16], authors addressed heat transfer in the space between cold outdoor square cylinder and hot indoor elliptical cylinder in the presence of a uniform magnetic field and reported the results relative to particle volume fraction, rayleigh number and hartman. in [17], authors simulated natural magne-tohydrodynamic convection in a square enclosure full of alumina water nanofluid using the lattice-boltzmann method. this simulation is different from similar cases in a place-dependent sine temperature distribution in vertical walls of the enclosure. their results showed that heat transfer is directly proportional to rayleigh number and inversely proportional to hartmann. in [18], authors studied free convection in a steep chamber with two adjacent walls at two different temperatures. they found that the effect of the enclosure angle is negligible on lines of current and temperature in small rayleigh numbers, while free convection considerably increases in large rayleigh numbers. in [19], authors numerically investigated a mixed convection fluid flow, heat transfer and entropy generation inside a triangular enclosure filled with cuo-water nanofluid with variable properties. this study tends to minimize operating heater temperatures and rate of entropy generation in the system. this study optimizes the relationship between locations of heaters, heater length ratios as a function of heater strength ratios. ii. methodology in this simulation, the electronic components and side walls were modeled as constant flux heat sources and isothermal thermal heat sinks, respectively. the flow and temperature fields were obtained by numerical simulation of mass conservation, momentum, and energy equations. simplifying assumptions are: • incompressible and newtonian fluid. • 2d, steady state and laminar flow field. • constant thermo physical properties. • neglect the radiation effects. • for elimination of density as a variable, the correlation between variation in density and temperature is given by boussinesq approximation. the numerical simulation was performed in matlab. the governing equations were discretized by finite volume method, and were solved using the simpler algorithm. in finite volume method (fvm) integral forms of governing equations derived directly from conservation laws are used for discretization in the considered space. fvm contains simple discretization and applicability to complex networks. the most fundamental problem of fvm is the definition of variables in sides of control volume, particularly second order derivatives. in this method, interpolation methods are often used to obtain flux. it is proved that if domain mesh resolution is less than 100×100, inverse matrix method performs better than other methods in obtaining linear algebraic equations. the current study uses this method. a uniform 50×50 staggered grid was used to store velocities and scalar variables. the power law scheme was also used to define the relationships between convection-diffusion terms. at the beginning, the required parameters and matrices such as physical parameters, velocity and pseudo-velocity matrix are defined. this section defines convergence conditions for conservation equations of mass, momentum and energy. then, pseudo-velocity field is obtained by simpler algorithm. step 1: calculate pseudo velocities: however, calculations are different for internal nodes and boundary conditions. calculations are done separately. the next step of the simpler algorithm is to calculate pressure field. step 2: solve pressure equation: since navier-stokes equation and consequently discretized equation only contains pressure gradient, unknown pressure values may be considered as difference of two very large numbers (for example, 100100-1000000), which may cause problems in numerical solution. to avoid this problem, pressure value of a certain node is considered zero in the solution. in the third step of simpler algorithm, the obtained pressure field is considered as speculative pressure field; then, infrarelease factor is applied on pressure field. step 3: p = p* in the fourth step, velocity field is calculated by solving discretized momentum equation: step 4: solve discretized momentum equations: next, pressure correction field is calculated to correct velocity field. then, temperature field is obtained by corrected velocity values. finally, convergence conditions are checked. entropy field is obtained by calculating velocity and temperature fields. fdm and second-order cds are used for discretization. to discretize term of entropy generation due to heat convection, temperature derivatives of cds are substituted. to discretize term of entropy generation due to fluid friction, velocity derivatives of fds are substituted. finally, the resulted the linear algebraic set of equations was solved using inversion matrix method. process simulation and problem solving is shown in figure 1. engineering, technology & applied science research vol. 7, no. 2, 2017, 1486-1495 1488 www.etasr.com nejad and keshtkar: entropy generation analysis of natural convection in square enclosures with… in this optimization, the parameters prevailing in the flow field, temperature, and entropy were examined as the following: • the effect of changing dimensionless parameter of rayleigh number (ra) on flow field, temperature, and entropy was investigated in constant length and strength ratios of the heaters (εr=qr=1). • the effect of changing strength ratio of the heaters (qr) on flow field, temperature, and entropy was investigated in constant length ratio of the heaters (εr=1). • the effect of changing length ratio of the heaters (εr) on flow field, temperature, and entropy was investigated in constant strength ration of the heaters (qr=1). • the effect of changing the dimensionless parameter of distance between centers of the heaters (xc) on flow field, temperature, and entropy was investigated in constant length and strength ratios of the heaters (εr=qr=1). fig. 1. the flow chart of the method steps in this study iii. geometry and boundary conditions the geometry of the problem and details of boundary conditions, illustrated in figure 2, involves a square chamber with 15 cm side length having two heat sources on the bottom wall. the length of left-hand and right-hand heaters are lh,1 and lh,2 , respectively. the distance between centers of the heaters is indicated by xc. the fluid inside the chamber is air with pr=0.7. all chamber walls are fixed, having no movement. the temperature of leftand right-hand walls is equal to the constant cold wall temperature (tc). the environment temperature is assumed to be 300 k (t∞=300k). the upper wall and not-heating part of the lower wall are insulated. the following boundary conditions were used to solve the governing equations: • the boundary condition of no slippage and impermeability for all walls (u=v=0). • the thermal boundary condition of θ=0 for cold side walls. • the thermal boundary condition of 0 y    for the upper wall and non-heating part of the lower wall. • the thermal boundary condition of 1 y     for the position of mounting the left-hand heater. • the thermal boundary condition of rq y     for the position of mounting the right-hand heater. fig. 2. problem geometry and boundary conditions iv. dimensionless governing equations characteristic quantities which are constant in the field of flow and temperature are used to make dimensionless constant and independent variables; these quantities include , ,, , , ,sg l t t p v    . dimensionless independent and constant variable are defined as follows:       * * * 2 s p p t tv v p t v t tv            * * * vg x g t t x g l l      the subscript ∞ refers to the characteristic distance of the object. the dimensionless form of operators is defined as follows: * * * * 1 1 1 1 l l l lx y z             molding: modeling of cooling process of two semiconductors in the form of natural convection in enclosure. modeling of electronic components in the form of isoflux heat sources. modeling sidewalls in the form of isothermal heat sinks derivation of governing equations: derived differential form of conservation equations of mass, momentum and energy in state of steady, two-dimensional and laminar flow discretization of governing equations: using finite volume method, approximation of power law, simpler algorithm and staggered grid solving set of algebraic equations obtained: using matrix inversion methods control convergence and grid independence analysis the results engineering, technology & applied science research vol. 7, no. 2, 2017, 1486-1495 1489 www.etasr.com nejad and keshtkar: entropy generation analysis of natural convection in square enclosures with… 22 * 2 * * 1 ( ) vd d d d t ll l t d t d v        dimensionless form of continuity equation: * * . 0 d v d t     dimensionless form of momentum equation: 2 * * * * * * * 2 1dv gr t g p v redt re      dimensionless form of energy equation: 2 * * * *1 d t e c t d t r ep r r e     dimensionless reynolds number: v l v l re       dimensionless grashof number:   3 2 sg t t l g r      3 . sg t t l ra gr pr     rayleigh number is defined as the ratio of buoyancy force to heat spreader in the fluid. rayleigh number determines laminar or turbulent flow in the free convection. v. governing equations the governing equations of this this problem include mass conservation, momentum, energy conservation, and the rate of generated entropy. the stable and dimensionless form of the governing equation is: 0 u v x y       (1) 2 2 2 2 [ ] 0 u u p u u u v u v x y x x yx y                     (2) 2 2 2 2 p r[ ] p r v v p v v u v r a x y y x y                  (3) 2 2 2 2 u v x y x y               (4) 2 2 2 2 2 2 pr1 [( ) ( ) ] [2{( ) ( ) } ( ) ( ) c s e u v u v n x y x y x yt t                         (5) where, x=x/h and y=y/h are dimensionless horizontal and vertical coordinate components respectively. u=uh/α and v=vh/α are the dimensionless velocity components in the x and y directions. p is the dimensionless effective pressure, θ is the dimensionless temperature, θ=(t−tc)k/q1h , where tc is the cold wall temperature. in (5), the first phrase demonstrates entropy generation due to conduction heat transfer (ns,conduction) and the second phrase demonstrates the entropy generation due to viscous dissipation (ns,viscous). vi. results in order to validate the computational code, the results were compared with the results of reference [12] and it was observed that, in the same conditions, there is good agreement between the results. minimal difference between the results is due to differences in applied methods and approximations solution. the result of this comparison is shown in figure 3. the summary of the states investigated in this study is shown in table i. convergence velocity and temperature fields controlled with relationship root square. the remaining amount is defined as follow: max max 2 8 2 , 1 1 ( ) 10 i i j j i j i j l b = = = = = £å å fig. 3. comparing the results of preseny study with reference [12] in numerical simulations, one of the important points the independence of the results is the number of grid points. to evaluate the grid independence, the nondimensional maximum temperatures in a particular case and for two different grids obtained, and compared with results of the 100×100 grid. result of this investigation are shown in table ii. once the results were obtained and compared for several grids, it was concluded that the 50×50 grid occupied minimal memory or lower runtime provided reasonable results compared to other grids. a. the effect of rayleigh number on flow field, temperature distributuon and entropy generation figure 4 shows the streamlines and isotherms contours for different rayleigh number. in this case, heaters have equal length and strength ratios (εr=qr=1). also the distances between heaters and sidewalls are equal. the trend of streamlines reveals that in low rayleigh numbers (ra=103 and ra=104), the viscous force is partly dominant over buoyancy force, and buoyant flow is weak. as well as, and the upper half of enclosure hasn't been practically affected by the heat sources. the cores of created vortices move upward by increasing rayleigh number due to forming a stronger rotating flow and increasing buoyancy force. when ra=106, the isothermal curves are thinner that other states, which is due to increased energy transmission. in all states engineering, technology & applied science research vol. 7, no. 2, 2017, 1486-1495 1490 www.etasr.com nejad and keshtkar: entropy generation analysis of natural convection in square enclosures with… related to figure 3, heaters have equal length and strength ratios and the boundary condition of side walls is also symmetrical, therefore, there is similar heat loss from cold side walls and expected that heater temperatures are equal. dominant over buoyancy force, and buoyant flow is weak. in this case, the isothermal curves are rather flat, and the upper half hasn't been practically affected by the heat sources. the cores of created vortices move upward by increasing rayleigh number due to forming a stronger rotating flow and increasing buoyancy force. furthermore, by increasing rayleigh number, the isothermal curves divert from those of pure conductance, and fluid flow results in transmission of hot air to near the upper wall. when ra=106, the isothermal curves are thinner that other states, which is due to increased energy transmission. in all states related to figure 4, heaters have equal length and power ratios and the boundary condition of side walls is also symmetrical, therefore, there is similar heat loss from cold side walls and the temperature of heaters are expected to be equal. table i. the summary of the states investigated εr qr lh xc xl ra stat e figure no. 1 1 1 1 0.3 0.6 1.5 2 1 1 1 1 0.3≤ εr≤ 1.7 0.3≤ εr≤ 1.7 0.3≤ εr≤ 1.7 1 1 1 1 1 1 1 1 1 1 1 1 1 0.5 1 2 1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.1 0.3 0.6 0.9 0.5 0.5 0.5 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.45 0.35 0.2 0.025 0.25 0.25 0.25 0.5-( xc/2) 103 104 105 106 1.5×106 1.25×106 8×105 6.66×105 106 106 106 106 2×106/(1+ εr× qr) 2×106/(1+ εr× qr) 2×106/(1+ εr× qr) 106 a b c d a b c d a b c d a b b a 2 and 3 2 and 3 2 and 3 2 and 3 5 and 7 5 and 7 5 and 7 5 and 7 8 and 10 8 and 10 8 and 10 8 and 10 6 6 6 9 and 11 table ii. the results of grid independence %change (absolute) in max .ra q max.ra q grid size 7.73×104 50×50 3 0 0.2 7.5×104 7.4×104 100×100 150×150 figure 5 shows the trend of changing entropy generation contours resulted from fluid friction irreversibility (ffi) and conductive heat transfer irreversibility (hti) by rayleigh number. the contours are plotted using normalized values. these values are obtained by dividing the entropy resulted from conductive heat transfer (ns,conduction) or fluid friction (ns,viscous) to the maximum generated entropy (ns,max). these contours show that the maximum entropy is generated near heaters and is due to hti. the conductive heat transfer process was resulted by two temperature differences. these two temperature differences, caused by creation of the internal and external irreversibility due to heat transfer in the system, involve the temperature difference (conduction heat transfer) created between heaters and the fluid inside the enclosure, as well as the temperature difference created between the hot fluid and cold enclosure walls. the plot of entropy generated by heat transfer shows that the value of hti is negligible near the upper wall, which is due to the little temperature gradient in these areas. the rate of entropy generation due to heat transfer increases by rayleigh number. the plots of entropy generated by ffi show that the friction irreversibility is higher near the walls because of forming a boundary layer and velocity gradient. the fluid flow and thickness of the hydrodynamic boundary layer formed on the walls increases by rayleigh number, and the ffi value increases as a result. in all states investigated in figure 5, the magnitude of entropy generated by heat transfer is higher than the entropy generated by fluid friction. therefore, the bejan number, which represents the relative importance of heat transfer irreversibility over total irreversibility, can be considered equal to 1 for all states investigated in this study. this issue is consistent with the results of [12], whose authors found out that the magnitude of entropy generated by fluid friction is several orders of magnitude less than the entropy generated by heat transfer. figure 6 shows the contours of changing total entropy generation by rayleigh number. as it can be seen, the total entropy generation in the enclosure increases with rayleigh number, which is the result of simultaneous rise in the value of entropy generated by fluid friction and conduction heat transfer with increasing rayleigh number. engineering, technology & applied science research vol. 7, no. 2, 2017, 1486-1495 1491 www.etasr.com nejad and keshtkar: entropy generation analysis of natural convection in square enclosures with… state (b): ra=104 state (a): ra=103 state (d): ra=106 state (c): ra=105 fig. 4. plots of changing flow curved (left column) and isothermal curves (right column) versus rayleigh number state (b): ra=104 state (a): ra=103 state (d): ra=106 state (c): ra=105 fig. 5. the trend of changing entropy resulted from fluid friction (left column) and conductive heat transfer (right column) versus rayleigh number state (d): ra=106 state (c): ra=105 state (b): ra=104 state (a): ra=103 fig .6. the trend of changing total entropy versus rayleigh number engineering, technology & applied science research vol. 7, no. 2, 2017, 1486-1495 1492 www.etasr.com nejad and keshtkar: entropy generation analysis of natural convection in square enclosures with… b. the effect of length ratio on flow field, temperature distributuon and entropy generation figure 7 shows the effect of inequality of heaters' length a flow field and entropy. the power ratio of the heaters are equal in all states related to this figure (qr=1), and only their length ratio changes. the current study differs from [12] in: • evaluating effect of heater length ratio on flow, temperature and entropy fields • evaluating entropy generation due to fluid friction (ffi) in all scenarios • solving linear algebraic equations obtained in practice, the studied problem is similar to [12]; thus, structure of this study is also similar to [12]. as a result, the length of vortices formed on heaters changes an asymmetric heat loss occurs from the sold side walls. when εr=0.3, the length of right-hand heater is 0.3 of that in the left-hand heater, so the rate of input thermal energy to the right-hand heater is 0.3 of that to the left-hand heater. on the other hand, the convective flow creates stronger vortices on the shorter heater, therefore, more heat would be lost from the surface and walls of the right-hand heater. so, for any power ratio of the heaters, the temperature of the left-hand heater decreases with εr , while the temperature of the right-hand heater increases. figure 8 confirms the above statements. comparing different states of figure 8 shows that the temperature of the heaters will be equal and at minimum if their length and power ratios are equal. in other words, the optimum length and power ratios, which prevents creation of hot spot and early failure in the system, is equal to 1 (εr= qr=1). figure 9 shows the trend of changing the total entropy generation and the entropy generated by fluid friction versus length ratio of the heaters. as it was mentioned earlier, changing heaters' length results in changed length of the vortices formed on them and an asymmetrical heat loss from the cold side walls. so, the area of the surface in which the temperature gradient and irreversibility is important increases with heaters' length ratio. the contours shown in figure 9, besides confirming the statements above, reveal that for the states related to εr<1, increasing the heaters' length ratio results in approaching to the optimum state of εr=1 and decreasing entropy generation in the chamber. furthermore, for the states related to εr>1, increasing the heaters' length ratio results in diverting from the optimal state and increasing entropy generation. c. the effect of distance between heaters on flow field, temperature distributuon and entropy generation figure 10 shows the effect of positioning of the heaters on the flow and temperature fields. in all states related to this figure, the length and strength ratios of the heaters are equal (εr=qr=1), and their positioning related to the sidewalls are equal. the rayleigh number is also constant and equal to ra=106. so, for a given value of xc, the temperature differences between each heater and the fluid inside the enclosure are equal, and the vortices formed on the heaters will be the same. this can be inferred from the patterns of flow curves. the isotherms show that by decreasing xc, the resulted interaction between the heaters reduces the rate of heat transfer from them, therefore, the surface temperature of the heaters increases and the hot fluid can move upward near to the upper wall. as xc increases, the greater distance between the heaters results in increasing the rate of heat transfer from them, and the surface temperature of the heaters decreases as a results. on the other hand, if the distance between the heaters exceeds a certain value, the buoyancy force and fluid flow created in the enclosure weak, the heat transfer from surface of the heaters decreases and their heat loss increases, and heaters temperature decreases again. the contrast of these two effects is shown in figure 11. state (b): εr=0.6 state (a): εr=0.3 state (d): εr=2 state (c): εr=1.5 fig .7. plots of changing flow curves (left column) and isothermal curves (right column) versus heaters' length ratio engineering, technology & applied science research vol. 7, no. 2, 2017, 1486-1495 1493 www.etasr.com nejad and keshtkar: entropy generation analysis of natural convection in square enclosures with… state (c): qr=2 state (b): qr=1 state (a): qr=0.5 fig .8. plots of heaters' temperature change versus their length ratio state (b): εr=0.6 state (a): εr=0.3 state (d): εr=2 state (c): εr=1.5 fig .9. the trend of changing the total entropy (right column) and the entropy generated by fluid friction (left column) versus the heaters' length ratio state (b): xc=0.3 state (a): xc=0.1 state (d): xc=0.9 state (c): xc=0.6 fig .10. plots of flow curves (left column) and isothermal curves (right column) versus distance between the heaters figure 12 shows the contours of the total entropy generation versus distance between the heaters. the contours in this figure show that by increasing distance between the heaters, first, the entropy generation decreases, but then increases with approaching the to the side walls. so, the changes in the total entropy generation with the distance engineering, technology & applied science research vol. 7, no. 2, 2017, 1486-1495 1494 www.etasr.com nejad and keshtkar: entropy generation analysis of natural convection in square enclosures with… between the heaters is mainly a function of the entropy generated by heat transfer. this can also be inferred from figure 13. figure 11 shows the trend of changing the heater temperature and the rate of entropy generation versus distance between the heaters. the rate of total entropy generation is derived by integrating the rate of local entropy generation rate. this figure shows that changing the rate of entropy generation versus distance between the heaters is almost similar to the change in the peak temperature of the heaters versus their distance. this figure also indicates that the spacing between the heaters is the most important parameter in terms of optimal thermal management. the most important factor in controlling the irreversibility is the positioning of the heaters. therefore, in the perspective of thermal management of the electronic components, mounting heaters near the chamber's central line is unfavorable since the peak temperature and generated entropy are high in this area. on the other hand, on order to minimize the peak temperature and entropy generation, heaters have to be mounted near cold side walls, or the distance between the heaters has to be half of the chamber width. in terms of efficiency, when the length and power ratios of the heaters are equal, presence of a number of heat sources results in equal power loss compared to presence of one heat source in the center. the studies carried out in this context confirm this issue. fig. 11. plot of changing surface temperature of the heaters versus their distance state (d): xc=0.9 state (c): xc=0.6 state (b): xc=0.3 state (a): xc=0.1 fig .12. the trend of changing the total entropy generation versus distance between the heaters fig .13. plot of changing heater temperature and the total entropy generation versus distance between the heaters vii. conclusions this study investigates numerically the entropy generated by natural convection in a square electronic package with two pieces of semiconductor. the flow field, temperature, and entropy maps were obtained by numerical simulation of the governing equation using finite volume method and simpler algorithm in matlab. results show that dominant heat transfer mechanism is conduction in low rayleigh numbers, while heat transfer mechanism changes to convection by increasing rayleigh number and effect of conduction disappears. conduction heat transfer and fluid movement increased with rayleigh number; as a result, fluid friction irreversibility and heat transfer irreversibility increased. in this study, entropy generation mainly resulted from heat transfer irreversibility, which was partially associated with fluid friction. for all scenarios investigated, the arrangement producing minimum peak temperature also produced minimum irreversibility. among the examined scenarios, minimum rate of entropy generation was seen in a scenario in which heaters had equal length and strength ratios, and the heaters were mounted close to cold sidewalls. future works can: 1. study this subject in three dimensions and compare the results with current results 2. add a fan to the system and re-optimize the problem in order to achieve optimal location of the fan and minimize power consumption 3. apply a gradient to the enclosure and re-optimize the problem in order to achieve optimal gradient (the gradient for which entropy generation is minimized in the enclosure) 4. create an obstacle (baffles) in the enclosure and evaluate the role of sizes and location of obstacles in flow, temperature and entropy fields 5. evaluate different thermal boundary conditions for walls in order to achieve uniform temperature distribution and to minimize entropy generation in the enclosure 6. evaluate the role of round corners in the enclosure and compare the results with current results engineering, technology & applied science research vol. 7, no. 2, 2017, 1486-1495 1495 www.etasr.com nejad and keshtkar: entropy generation analysis of natural convection in square enclosures with… references [1] t. saitoh, k. hirose, “high-accuracy benchmark solutions to natural convection in a square cavit”, comput. mech, vol. 4, pp. 417-427, 1989 [2] g. de vahl davis, “natural convection of air in a square cavity: a bench mark numerical solution”, int journal for numerical methods in fluids, vol. 3, no. 3, pp. 249-264, 1983 [3] q. h. deng, g. f. tang, y. li, “a combinedtemperature scale for analyzing natural convection in rectangular enclosures with discrete wall heatsources”, international journal of heat and mass transfer, vol. 45, no. 16, pp. 3437-3446, 2002 [4] y. varol, h. f. oztop, f. ozgen, a. koca, “experimental and numerical study on laminar natural convection in a cavity heated from bottom due to an inclined fin”, heat mass transfer, vol. 48, pp. 61–70, 2012 [5] a. bejan, “entropy generation minimization: the new thermodynamics of finitesize devices and finite-time processes”, j. appl. phys., vol. 79, pp. 1191–1218, 1996 [6] a. bejan, shape and structure from engineering to nature, cambridge university press, new york, 2000 [7] m. alipanah, p. hasannasab, s. f. hosseinizadeh, m. darbandi, “entropy generation for compressible natural convection with high gradient temperature in a square cavity, international communications in heat and mass transfer, vol. 37, no. 9, pp. 1388–1395, 2010 [8] o. aydin , a. unal, t. ayhan, “natural convection in rectangular enclosures heated from one side and cooled from the ceiling”, international journal of heat and mass transfer, vol. 42, no. 13, pp. 2345-55,1999 [9] m. shahi, a. h. mahmoudi, a.h. "raouf, “entropy generation due to natural convection cooling of a nanofluid”, international communications in heat and mass transfer, vol. 38, pp. 972–983, 2011 [10] n. nithyadevi, p. kandaswamy, j. lee, “naturalconvection in a rectangular cavity with partially active side walls”, international journal of heat and mass transfer, vol. 50, pp. 4688-4697, 2007 [11] h. yeong, m. jung, “a numerical study on three-dimensional conjugate heat transfer of natural convection and conduction in a differentially heated cubic enclosure with a heat-generating cubic conducting body”, international journal of heat and mass transfer, vol. 1, pp. 4229-4248, 2000 [12] a. mukhopadhyay , “analysis of entropy generation due to natural convection in square enclosures with multiple discrete heat sources”, international communications in heat and mass transfer, vol. 37, pp. 867-872, 2010 [13] f. talebi, a. h. mahmoudi, m. shahi “numerical study of mixed convection flows in a square lid-driven cavity utilizing nanofluid”, international communications in heat and mass transfer, vol. 37, pp. 79-90, 2010 [14] e. abu–nada, a. j. chamkha, “mixed convection flow in a liddriven square enclosure filled with a nanofluid”, eur. j. mech. bfluid, vol. 29, pp. 472-482, 2010 [15] m. mahmoodi, “mixed convection inside nanofluid filled rectangular enclosures with moving bottom wall”, therm. sci., vol. 15, pp. 889-903, 2011 [16] m. sheikholeslami, m. gorji-bandpy, g. domairry, “free convection of nanofluid filled enclosure using lattice boltzmann method (lbm)”, applied mathematics and mechanics, vol. 34, no. 7, pp. 833-846, 2013 [17] a. mahmoudi, i. mejri, m. a. abbassi, a. omri, “lattice boltzmann simulation of mhd natural convection in a nanofluidfilled cavity with linear temperature distribution”, powder technology, vol. 256, no. 10, pp. 257-271, 2014 [18] s. m. aminossadati, b. ghasemi, “the effects of orientation of an inclined enclosure on laminar natural convection”, heat and technology, vol. 23, no. 2, pp. 43-49, 2005 [19] a. aghaei, s. h. ghanbarali, e. hamidreza, m. hajiahmadi, “numerical investigation of mixed convection fluid flow heat transfer and entropy generation in triangular enclosure filled with nanofluid”, journal of applied fluid mechanics, vol. 9, no. 1, pp. 147-156, 2016 microsoft word etasr_v11_n6_pp7881-7886 engineering, technology & applied science research vol. 11, no. 6, 2021, 7881-7886 7881 www.etasr.com basheleishvili & bardavelidze: design and development of a group decision support system for the … design and development of a group decision support system for the evaluation and selection of research projects irakli basheleishvili department of computer technology akaki tsereteli state university kutaisi, georgia irakli.basheleishvili@atsu.edu.ge avtandil bardavelidze department of computer technology akaki tsereteli state university kutaisi, georgia avtandil.bardavelidze@atsu.edu.ge abstract-the current paper deals with the design and development of a web-based group decision support system for the evaluation and selection of research projects. the paper involves the analysis of the system’s requirements, the definition of its functional structure, the development of an algorithm for the evaluation and ranking of research projects, the development of a related database and of a user interface along with the writing of the business logic of the system. keywords-research projects; group decision; evaluation; selection; multi-criteria analysis i. introduction decision-making is one of the most difficult problems of human activity, whose solution depends on the effective implementation of relevant activities. decision-making problems are analytical problems that allow, relying on the primary information base, gaining new knowledge concerning the new situation, deeply understanding the current processes and, consequently, making the right decision [1]. in order to solve such problems, it is important to use the information systems called decision support systems [1-4] which are the model-based or knowledge-based systems designed to assist in decision-making [2]. the current paper deals with the design and development of a group decision support system for the evaluation and ranking of research projects. in decision-making theory and practice, great importance is attached to the so-called group decisions made by several individuals. there is particular interest in group decisions due to the fact that there is a high level of professionalism in society, and at the same time, the physical and informational capacities of an individual are quite limited. the use of this type of system is mainly needed by organizations that announce research grant competitions. the grant competition process can generally be described as follows: the granting organizations announce a scientific grant competition in various fields of science and define the requirements for the research projects. after the announcement of the grant competition, the applicants submit their project proposals according to the area of research, after which the granting organization appoints a group of experts for the relevant projects, and the experts review and evaluate the submitted project proposals. the granting organization makes the decision to select the best research projects based on the experts’ evaluation. today there are numerous management information systems used by the organizations providing research grants [8]. the functionality of these systems is largely limited to allowing the grant applicants meet the requirements of a grant project in accordance with the requirements of the organization providing these grants, that is, they are mostly engaged in data collection and submission. these systems do not support decision-making on grant selection. the proposed system, in addition to all these, has the novelty of decision-making support which increases its practical value, making the activities of the grant-proving organizations more effective. the aim of the current paper is the design and development of a web-based group decision support system that provides support for the research grant competition processes with a view to conduct the research grant competition in an efficient and fair manner. a web-based group decision support system will allow the involvement in this competition of applicants from various and distant geographical locations. ii. identifying the system’s requirements a use case diagram (figure 1) was developed to specify and analyze the requirements of the group decision support system for the evaluation and selection of research projects. the diagram illustrates the requirements and the functionality that will be imposed on the design system. as shown in this use case diagram, there are four types of roles in the system: • administrator: manages the users of the other levels of the system and ensures the efficient operation of the system. • manager: represents the organization that announces the research grant competition. the user having this this role: o defines the areas of the research grant competition. corresponding author: irakli basheleishvili engineering, technology & applied science research vol. 11, no. 6, 2021, 7881-7886 7882 www.etasr.com basheleishvili & bardavelidze: design and development of a group decision support system for the … fig. 1. use case diagram. o identifies the requirements and necessary documents for the submission of the research project. o defines the evaluation criteria and their weights in accordance with the areas of the research grant competition. o nominates the experts in accordance with the scientific areas of the submitted research projects. o ranks the research projects based on the experts’ evaluation. o makes the decision of selecting the research projects. • submitter of the research project: this user is registered in the system and submits the information and documentation required for the submission of the grant research project. the submitter of the research project in the system can get information about the evaluation of his research project and the decision on selecting the project, after the evaluation of the project by experts. • experts: are registered users in the system and their main function is to evaluate research projects in accordance with the previously defined evaluation criteria, for the projects of the scientific fields that they were nominated for by the manager. the users of the system can use the above mentioned functions if they are authorized by the system. to do this, it is necessary for them to register and get a confirmation from the administrator. iii. development of the required algorithm for the operation of the system the main issue when designing decision support systems is the development of the mathematical models and the algorithms necessary for its operation. the decision-making problems, in which the possible alternatives are evaluated according to several criteria, are of particular interest. in this case we are dealing with multi-criteria decision-making problems [10]. the problem of evaluating and ranking research projects is a multi-criteria problem, in which the research projects are considered to be the alternatives, while the research project evaluation criteria are considered to be the alternative evaluation criteria. therefore, multi-criteria decision analysis methods are used to develop an algorithm for evaluating and ranking research projects [3]. many theoretical studies have been dedicated to this problem, but the analysis reveals that their application in practice is not always possible and is time consuming. therefore, it is relevant to develop user-friendly, multi-criteria decision-making algorithms and the appropriate software system for practical use, which will allow the decision-makers to promptly evaluate the multi-criteria alternatives and make optimal decisions. a. the ranking algorithm the ranking of the research projects is carried out once the group of experts evaluates the research projects according to the relevant criteria, based on which it will be possible to form a decision matrix: engineering, technology & applied science research vol. 11, no. 6, 2021, 7881-7886 7883 www.etasr.com basheleishvili & bardavelidze: design and development of a group decision support system for the … �� �� �� ⋯ �� �� �� �� �� ⋯ �� �� �� �� �� ⋯ �� �� �� �� �� ⋯ �� ⋮ ⋮ ⋮ ⋮ ⋱ ⋮ �� �� �� �� ⋯ �� � � � ⋯ � (1) where ��, i=1,….,n, j=1,…., m represent the assessment of the i alternative in accordance with the j criterion, defined by the experts. the value of �� is calculated as: where , k=1, t is the kth – expert's assessment of the j criterion of the i alternative. the multi-criteria decision analysis method ahp is used to calculate the weights of the alternative evaluation criteria [2, 58]. the vikor method [9] was used to identify the research projects. it includes the following steps: step 1: determine the best + j x and the worst − j x values of all criteria: 1 j ij x max( x ), j ,...,m + = = (2) 1 j ij x min( x ), j ,...,m − = = (3) step 2: calculate i s and i r using (4) and (5): 1 m j ij i j j j j x x s ( w * ) x x + + − = − = ∑ − (4) j ij i j j j j x x r w *max x x + + −  − =    −  (5) step 3: compute the values iq using (6): 1i i i s s r r q v* ( v )* s s r r + + − + − + − − = + − − − (6) where i i s smin + = , i i s smax − = , i i r rmin + = , i i r rmax − = , and v=0.5 step 4: ranking of the alternatives for the i q values: the rank of alternatives is determined by sorting the obtained values from small to large. b. numerical experiment to demonstrate the work of the presented algorithm, lets consider a practical case , let’s assume we want to evaluate five projects (��,.., ��) that are evaluated according to four criteria (��,.., ��). let's assume that the decision matrix based on the experts' evaluations has the form exhibited in table i. table i. decision matrix �� �� �� �� �� 90 70 85 79 �� 87 75 96 89 �� 80 79 74 75 �� 75 80 92 78 �� 82 75 69 96 the pairwise comparison matrix of the criteria of assessment is shown in table ii and the normalized pair-wise comparison matrix in table iii. the vector of the weights is determined as: �� = 0.48 �� = 0.29 �� = 0.13 �� = 0.09 the calculated weighted normalized decision matrix is shown in table iv. the calculated sum of the weighted values is: c� = 1.97 c� = 1.21 c� = 0.54 c� = 0.38 the calculated &�'( is 4.077618. the calculated consistency index (ci) is 0.025873 and the consistency ratio (cr) is 0.028748. because the cr value is less than 0.1 it is acceptable. the determined best � ) and the worst � * values of all criteria are shown in table v. then, +� , ,�, and .� are calculated. the final result is shown in table vi. table ii. pairwise comparison matrix �� �� �� �� �� 1.00 2.00 4.00 4.00 �� 0.50 1.00 3.00 3.00 �� 0.25 0.33 1.00 2.00 �� 0.25 0.33 0.50 1.00 table iii. normalized pairwise comparison matrix �� �� �� �� �� 0.50 0.55 0.47 0.40 �� 0.25 0.27 0.35 0.30 �� 0.13 0.09 0.12 0.20 �� 0.13 0.09 0.06 0.10 table iv. weighted normalized matrix �� �� �� �� �� 0.48 0.59 0.53 0.37 �� 0.24 0.29 0.40 0.28 �� 0.12 0.10 0.13 0.19 �� 0.12 0.10 0.07 0.09 table v. best and worst values of all criteria �� �� �� �� /0 ) 90 80 96 96 /0 * 75 70 69 75 table vi. result 12 32 42 rank �� 0.423997 0.294041 0.467016 2 �� 0.274038 0.147021 0 1 �� 0.550943 0.319506 0.713381 4 �� 0.579133 0.479259 1 5 �� 0.535828 0.255605 0.592444 3 1 2 31( )t ij ij ij ij ij x x x x x t = + + + +l k ij x engineering, technology & applied science research vol. 11, no. 6, 2021, 7881-7886 7884 www.etasr.com basheleishvili & bardavelidze: design and development of a group decision support system for the … iv. system software the system’s software package presented in this paper was developed using the asp.net core technology. one of the most important components of a decision-making system is the database, which contains the data on the basis of which the entire system works. the entity relationship (eer) model of the database is presented in figure 2, and is designed with the visual studio 2017 ado.net entity data model. the database was implemented on an sql server. the system’s database and business logic have been designed in such a way that it is easy to add new modules to it and improve the system. the system’s software, according to the system roles, consists of 4 modules: administrator module, expert module, manager module, and research project submission module. some fragments of the system software are given in figures 3-8. figure 3 presents the form of the determination of the evaluation criteria according to the scientific directions. figure 4 presents the form of the determination of the weights of the evaluation criteria. figure 5 presents the form of the assignment of experts according to the scientific directions. figure 6 shows the upload page of a scientific project. figure 7 presents the evaluation form of the scientific projects by the experts, and figure 8 presents the ranking form of the scientific projects. fig. 2. the eer model of the database. fig. 3. the evalution criteria. fig. 4. the weights of the evaluation criteria. engineering, technology & applied science research vol. 11, no. 6, 2021, 7881-7886 7885 www.etasr.com basheleishvili & bardavelidze: design and development of a group decision support system for the … fig. 5. the assignment of experts. fig. 6. project submission. fig. 7. evaluation of the scientific projects by the experts. fig. 8. ranking of the scientific projects. v. conclusion the current paper presents a group decision support system for the selection of research projects, which can be effectively used by organizations to conduct research grant competitions fairly and effectively. the resulting system is designed in such a way that it is easy to add new functionalities in order to make it more convenient for a particular organization. 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[16] s. alshehri, "multicriteria decision making (mcdm) methods for ranking estimation techniques in extreme programming," engineering, technology & applied science research, vol. 8, no. 3, pp. 3073–3078, jun. 2018, https://doi.org/10.48084/etasr.2104. microsoft word 4-442.doc engineering, technology & applied science research vol. 4, no. 3, 2014, 644-648 644 www.etasr.com khelil et al.: a numerical approach for the determination of mode i stress intensity factors … a numerical approach for the determination of mode i stress intensity factors in pmma materials f. khelil laboratory lml of lille, university of lille1, france foudil.khelil@univ-lille1.fr m. belhouari laboratory lmpm, university of sidi bel abbes, algeria belhouari@yahoo.com n. benseddiq university of lille1, france noureddine.benseddiq@ univ-lille1.fr a.talha hei university lille, france abderrahim.talha@hei.fr abstract—an evaluation technique of the ki stress intensity factors (sif) by a numerical investigation using line strain method is presented in this paper. the main purpose of this research is to re-analyze experimental results of fracture loads from polymethyl-metacrylate (pmma) specimens (fully finite plates). stress intensity factor equation calculation is derived from the williams stress asymptotic expansion. possible error caused by strain gradients across the gage length is minimized by integrating the equation in the ki calculation. theoretical and computed values using finite element analysis of stress intensity factors are compared with experimental results. a good agreement is observed between the present approach and experimental values. it is shown that, in the case of a throughplate crack, the stress intensity factor can be calculated with adequate accuracy using the proposed method. keywords-finite element; strain gage method; ki; pmma edge crack i. introduction all standard paper components have been specified for three reasons: the measurement of the stress intensity factor with strain gages was first suggested by irwin in 1957 [1]. due to the local yielding effect in the crack vicinity, little progress has been made in implementing irwin's suggestion. a valid strain gage technique for calculating the stress intensity factor ki was first presented in [2-4]. in this method, a valid region was specified for locating the gages to get rid of the elasticplastic crack-tip state caused by local yielding in the innermost region close to the crack tip. the error caused by strain gradient was minimized by placing the virtual strain gages sufficiently far from the crack tip. an extended over-deterministic approach was later proposed to significantly improve the accuracy [5]. a specified strain gage pattern has been proposed to measure the stress intensity factors of mixed mode problems [6]. moreover, different strain gage approaches have been introduced to measure the variation of stress intensity factor of a propagating crack [7-12]. it has long been acknowledged that in plates of finite thickness the stress field near the crack tip is three-dimensional in nature. from the finite element results of [13, 14, 26-30] and the experimental results of [15] it has been shown that the local yielding effect is only significant within a radial distance about one-half thickness from the crack tip. for the rest of the area, the plane stress condition is expected to dominate. the choice of the position and orientation of the point p for the calculation of ki are studied by using virtual gages with two orientation angles (ѳ, α), as shown in figure 1, when considering a line segment in a strain field near the crack tip. a different load and geometry of specimen are also employed to visualize the geometry effect on the evaluated stress intensity factors. fig. 1. deferent area delimiting the vicinity of a crack tip. in this work, we investigate the feasibility of the numerical determination of accurate opening mode of stress intensity factors using the dally–sanford method [2] for the cracked polymethyl-methacrylate (pmma) specimens. in this procedure, gages can be placed at low strain gradient zones. in contrast with past research described in [2, 16-19] this work attempts to accurately calculate the sif using a relative large strain points method (virtual strain gage) under monotonic increasing loads in fully finite edge-cracked plates subject. to validate the proposed method for the determination of sifs, we compare experimental results [10] with our computercalculated values obtained using abqus finite-element software. ii. basic theory and mathematical formulation of the model the area adjacent to the crack tip was divided into three regions as shown in figure 2. region i very near the crack tip is invalid because of three-dimensional effects. region iii far from the crack tip is invalid because the truncated series engineering, technology & applied science research vol. 4, no. 3, 2014, 644-648 645 www.etasr.com khelil et al.: a numerical approach for the determination of mode i stress intensity factors … solution does not adequately describe the strain field. region ii located between regions i and iii is a valid area where the truncated-series solution represents the strain field to a specified accuracy. the size and shape of region ii is presented for the compact-tension geometry. to identify a valid location for the virtual strain gages, region ii was subdivided into regions iia and iib. region lib was discarded because the strains in this area are too low for accurate measurement [2, 20]. fig. 2. deferent area delimiting the vicinity of a crack tip. dally and sanford [7] adopted an approach to three parameters and assumed that the deformation field in region ii can be represented with sufficient accuracy by the three terms of the william's series [20]. the deformation field in this region for a state of plane stress is then written in the following form [9]:   1/ 2 xx 0 1/ 2 2 0 1 e =a r cos( / 2 ) [(1) (1 ) sin( / 2 ) sin( 3 / 2 )] 2b a r cos( / 2 )[( 1 ) ( 1 ) sin ( / 2 )] 1                     1/ 2 yy 0 1/ 2 2 0 1 e =a r cos( / 2 )[(1) (1 ) sin( / 2 ) sin( 3 / 2 )] 2 b a r cos( / 2 )[( 1 ) ( 1 ) sin ( / 2 )] 2                      1/ 2 1/ 2 2 xy 0 1=a r sin cos( 3 / 2 ) a r s in( / 2 )cos( / 2 ) 3       where a0, a1 and b0 are unknown coefficients which can be determined by using the specimen geometry and boundary conditions. using the definition of ki one can easily show that it is related to a0 by: i 0k 2 a [2-11].  a single strain gage is sufficient to evaluate the constant a0 (hence ki ) by placing and orienting the strain gage as given below. using transformation equations of the deformation component xx at the point p located at r and θ (figure 1) [2, 4, 10] is given by:   1 / 2 1 / 2 xx 0 1 1 / 2 0 1 / 2 2 1 0 e (1)[a r [cos( / 2 )] a r [cos( / 2 )] -(1 ) [a r sin( 3 / 2 ) sin( / 2 ) cos( / 2 ) a r sin ( / 2 ) cos( / 2 ) ] 2 b 4                    1 k 1       (5) the b0 coefficient of (3) can be removed by selecting the angle α, so that 1 cos 2 k 1           (6) the coefficient a1, can also be made zero by replacing α using: tan( / 2 ) cot 2   (7) deformation εx'x' is given by: i x' x' k 2g (k cos sin / 2 sin 3 cos 2 2 22 r 1 sin cos 3 sin 2 ) 2 2             (8) the angles α and θ depend only on the poisson's ratio of the material. the location of the radius rp strain gauge is chosen taking into account the effects of strain gradient [2-10]. iii. numerical procedures a. material constitutive model specimens are made of polymer pmma (plexiglas sheet) [10]. material properties are e=2300 mpa, υ=0.37, kic = 1.9 mpam0.5 and gic= 0.4 kjm -2. b. finite element model natural elements iso-parametric quadratic triangular (t6) and the singular point due to symmetry is used and only half of the plate was taken into account in the analysis. figure 4 shows a typical mesh used for determining the standard sif. these meshes were used for all values of a/w and h/w. when the mesh was refined significant improvements were noted in the values of sif [25]. the sif of a plate of finite width cracked edge is given by:  i 1 a h k 2 f , w w         (9) where 1 a h f , w w       is the normalized function which shows the effect of the geometry of the specimen [10, 32]. c. loading and boundary conditions fully finite edge-cracked plates specimen with key dimensions are shown in figure 3b. the thickness was 6 mm in a plane strain state. the width of all samples was maintained at w = 150 mm, while the length of the crack and the height h of the sample were changed. for the simulation, engineering, technology & applied science research vol. 4, no. 3, 2014, 644-648 646 www.etasr.com khelil et al.: a numerical approach for the determination of mode i stress intensity factors … the values of a/w were 0.3 and 0.5, and the value of h/w was equal to 0.2 to 1.1 in step of 0.1. the load is pointed and semi distributed uniformly as shown in figure 3c. a) specimen studie b) geometry of the specimen. c) load and boundary conditions of half specimen. figure.3 centrally notched rectangular specimen under uniaxial tension. d. computational code a finite element analysis using abaqus 6.11.1 [25] was conducted. the extrapolation method of integral j was used to calculate standardized sif mode i opening [31]. we know that this method is consistent and profitable for a very specific sif. corresponding to the element the value of 0.25 was used [24]. fig. 4. a typical finite element mesh used for modeling the specimen, the integration contours for evaluation of the m-integral and the line strain. θ and α in (4) and (5) are equal to 58.69° and 54.76° respectively. the radial position of the strain gage r=10 mm was chosen in all tests based on the stress gradient analysis presented in [12]. some results of sif calculated in digital studied samples are shown in figures 5 and 6. figure .5: a comparison between the variations values of normalized and experimental sif [10] and with different values of h/w; parameters adopted: a / w = 0, 3 (a) h/w =0,3 et (b) h/w =0,5 (c) h/w = 0,7 et (d) h/w =1,0 a) b) c) d) engineering, technology & applied science research vol. 4, no. 3, 2014, 644-648 647 www.etasr.com khelil et al.: a numerical approach for the determination of mode i stress intensity factors … figure.6: a comparison between the variations values of normalized and experimental sif [10] and with different values of h/w; parameters adopted: a / w = 0, 5 (a) h/w =0,3 et (b) h/w =0,5 (c) h/w = 0,7 et (d) h/w =1,0 iv. results and discussion figures 5 and 6 show the deformation data measured experimentally [10] and the results obtained by the proposed model for a/w = 0.3 and 0, 5 with h/w = 0.3, 0.5, 0.7, 1.0. a very good linear relationship can be noted between the load and the deformation in all figures for the eight samples. from the linear equation presented in the literature, the deformations (measured) were calculated using the proposed model for different loads. thereafter, sif values were determined by finite elements analysis (abaqus). figures 5 and 6 shows the dependence between sif (ki) and the different loads. the figures show that the measured strains are linearly proportional with the applied load. v. conclusions the results of this work allow us to draw the following conclusions:  the digital program that was used for the study of a pmma's sample applying a process of the single virtual strain gage, had showed that this latter is the most powerful tool for the measurement of the sif (ki ) in the pmma's specimen as was demonstrated in the present study.  the latter conclusion is confirmed by the relative consistency between the fic values calculated based on this approach, and those obtained experimentally.  that said, the proposed approach represents an alternative tool in the sense of quantitative and qualitative effectiveness for the accurate measurement of fic in a polymer plate with finite dimensions.  the results obtained in this study show that the use of a single strain gage is very effective in the case of pmma. the major interest of this technique is its ability to approach the problem in more complex configurations. a continuation of this work suggests a coupling between the t-stress and ki, with more complicated loading. an extension will be proposed for different geometries, and of course, a validation on polymeric materials other than pmma will be considered in order to make a conclusion on the generalization of the proposed approach. references [1] g. r. irwin, “analysis of stresses and strains near the end of a crack traversing a plate”, journal of applied mechanics, vol. 24, pp. 361-364, 1957 [2] j. w. dally, r. j. sanford, “strain gage methods for measuring the opening mode stress intensity factor ki”, experimental mechanics, vol. 27, pp. 381-388, 1987 [3] j. w. dally, r. j. sanford, “measuring the stress intensity factor for propagating cracks with strain gages”, journal of testing and evaluation, vol. 18 no. 4, pp. 240–249, 1990 [4] j. w. dally, w. f. riley, experimental stress analysis, mcgraw-hill, new york, 1965 [5] j. r. berger, j. w. dally, “an overdeterministic approach for measuring ki using strain gages”, experimental mechanics, vol. 28, no. 2, pp.142145, 1988 a) b) c) d) engineering, technology & applied science research vol. 4, no. 3, 2014, 644-648 648 www.etasr.com khelil et al.: a numerical approach for the determination of mode i stress intensity factors … [6] y. z. itoh, t. murakami, h. kashiwaya, “experimental determination technique of stress intensity factor and its application”, journal of engineering materials and technology, vol. 111, no. 1, pp. 81-86, 1988 [7] r. j. sanford, principles of fracture mechanics, prentice-hall, englewood cliffs, nj, 2002 [8] r. j. sanford, principles of fracture mechanics, prentice hall, upper saddle river, nj, 2003 [9] r. j. sanford, “a critical re-examination of the westergaard method for solving opening-mode crack problems”, mechanics research communications, vol. 6, no. 5, pp. 289–294, 1979 [10] s. swamy, m. v. srikanth, k. s. r. k. murthy, p. s. robi, “determination of mode i stress intensity factors of complex configurations using strain gages”, journal of mechanics of materials and structures., vol. 3, no. 7, pp. 1239-1255, 2008 [11] m. j. maleski, m. s. kirugulige, h. v. tippur “a method for measuring mode i crack tip constraint under static and dynamic loading conditions”, experimental mechanics, vol. 44, no. 5, pp. 522–532, 2004 [12] a. shukla, r. chona, r. k. agarwal, “investigation of dynamic fracture using strain gage”. proc. sem spring conf. houston, tx, usa 1987 [13] n. levy, p. v. marcal, j. r. rice, “progress in three-dimensional elastic-plastic stress analysis for fracture mechanics”, nuclear engineering and design, vol. 17, no. 1, pp. 64-75, 1971 [14] t. nakamura, d. m. parks, “three dimensional stress field near the crack front of a thin elastic plate”, journal of applied mechanics, vol. 55, no. 4, pp. 805-813, 1988 [15] a. j. rosakis, k. ravi-chandar, “on crack-tip stress state: an experimental evaluation of three-dimensional effects”, international journal of solids and structures, vol. 22, no. 2, pp.121-134, 1986 [16] j. wei, j. h. zhao, “a two-strain-gage technique for determining mode i stress-intensity factor”, theoretical and applied fracture mechanics, vol. 28, no. 2, pp. 135–140, 1997 [17] j. h. kuang, l. s. chen, “a single strain gage method for ki measurement”, engineering fracture mechanics, vol. 51, no. 5, pp. 871–878, 1995 [18] c. h. chen, c. l. wang, “stress intensity factors and t-stresses for offset double edge-cracked plates under mixed-mode loadings”, international journal of fracture,vol. 152, no. 2, pp. 149–162, 2008 [19] p. v. jogdand, k. s. r. k. murthy, “a finite element based interior collocation method for the computation of stress intensity factors and tstresses” , engineering fracture mechanics vol. 77, no. 7, pp. 1116– 1127, 2010 [20] m. l. williams, “on the stress distribution at the base of a stationary crack”, journal of applied mechanics, vol. 24, pp. 109-114, 1957 [21] r. chona, g. r.irwin, r. j. sanford, “influence of specimen size and shape on the singularity-dominated zone,” fracture mechanics 14th symposium, vol. 1: theory and analysis, astm-stp, vol. 791, american society for testing and materials, philadelphia, pa, 492–502, 1983 [22] p. v. jogdand, “\an investigation on overdeterministic approaches for determination of the mixed mode stress intensity factors and t-stresses, masters thesis, indian institute of technology guwahati, india, 2009 [23] h. v. tippur, s. krishnaswamy, a. j. rosakis, “optical mapping of crack tip deformations using the methods of transmission and reflection coherent gradient sensing: a study of crack tip k-dominance”, international journal of fracture, vol. 52, no. 2, pp. 91–117, 1991 [24] l. parnas, o. g. bilir, “strain gage methods for measurement of opening mode stress intensity factor”, engineering fracture mechanics, vol. 55, no. 3, pp. 485–492, 1996 [25] abaqus, theory reference manual, release 11. swanson analysis systems, inc, 2009 [26] t. fett, g. rizzi, “weight functions for stress intensity factors and tstress for oblique cracks in a half-space”, international journal of fracture, vol.132, no. 1, pp. l9–l16, 2005 [27] t. fett, “stress intensity factors and t-stress for internally cracked circular disks under various boundary conditions”, engineering fracture mechanics , vol. 68, no. 9, pp. 1119–1136, 2001 [28] t. fett, “t-stresses in rectangular plates and circular disks”, engineering fracture mechanics, vol. 60, no. 5-6, pp. 631–652, 1998 [29] k. s. r. k. murthy, m. mukhopadhyay, “unification of stress intensity factor (sif) extraction methods with an h-adaptive finite element scheme”, communications in numerical methods in engineering, vol. 17, no. 7, pp. 509–520, 2001 [30] l. banks-sills, d. sherman, “comparison of methods for calculating stress intensity factors with quarter-point elements”, international journal of fracture, vol. 32, no. 2, pp. 127–140, 1986 [31] h. tada, p. c. paris, g. r. irwin, the stress analysis of cracks handbook, new york, asme, 2000 [32] m. isida “effect of width and length on stress intensity factors of internally cracked plates under various boundary conditions”. engineering fracture mechanics, vol . 7, no. 3, pp. 301–16, 1971 engineering, technology & applied science research vol. 7, no. 4, 2017, 1863-1869 1863 www.etasr.com kimiagari and saleh: ranking tehran’s stock exchange top fifty stocks using fundamental indexes and … ranking tehran’s stock exchange top fifty stocks using fundamental indexes and fuzzy topsis ali mohammad kimiagari dpt of industrial engineering & management systems amir kabir university of technology (tehran polytechnic) tehran, iran elham sabeti saleh dpt of industrial engineering & management systems amir kabir university of technology (tehran polytechnic) tehran, iran abstract—investment through the purchase of securities, constitute an important part of countries economic exchange. therefore, making decisions about investing in a particular stock has become one of the most controversial areas of economic and financial research and various institutions have began to rank companies stock and determine priorities of stock purchase to investment. the current research, with the determination of important required indexes for companies ranking based on their shares value on the tehran stock exchange, can greatly help to the accurate ranking of fifty premier listed companies. initial ranking indicators are extracted and then a decision-making group (exchange experts) with the use of the delphi method and also non-parametric statistic methods, determines the final indexes. then, by using fuzzy anp, weight criteria are obtained with taking into account their interaction with each other. finally, using fuzzy topsis and information extraction about the premier fifty listed companies of tehran stock exchange in 2014 are ranked with the software "rahavard novin”. sensitivity analysis to criteria weight and relevant analysis presentation was conducted at the end of the study procedures. keywords-performance evaluation; stock efficiency; companies ranking; anp fuzzy; topsis. i. introduction much research in ranking and evaluating companies has been conducted, especially on stock exchange companies. in [1], authors applied time series analysis and multi-criteria decision to anticipate the financial performance of companies. the aim of this study was to estimate the financial performance of companies in turkey between 2012 and 2015. for this purpose, two time series analysis and multi-criteria decision approach analysis were used. in [2], authors checked to evaluate the efficacy data on the value of stock options in the taiwan market. in [3], authors began to combine soft computing and fundamental analysis to select stocks. the results show that the proposed method could pay to stock selection, well. in [4], using cbr select stocks was investigated. the study results show that the proposed model could select the stock's choice based on the determined indexes very well. in [5], the performance of banks was evaluated with fuzzy hierarchical analysis and fuzzy topsis. in [6], authors surveyed the topsis approach as a ranking approach. in this paper, the 2014 tehran stock exchange market is considered and its statistical population is the heads of 87 tehran stock exchange agencies. also for the financial information extraction of the companies, the "rahavard novin" software is used. two fuzzy network analysis and fuzzy topsis technique are used to analyze the results and rank companies. two matrix (middle number and near fuzzy number) of each matrix are derived and then an adaption of each matrix based on the computing hours is computed. ii. basics of used analysis methods the steps of computing fuzzy matrix pairwise comparison compatibility rate are: a. step 1 in the first phase divide triangular matrix to two matrixes. first matrix is formed of middle numbers of triangular inferences ][ ijm m aa  and the second matrix contains geometric mean of the upper and lower triangular numbers, ijliju g aaa . . b. step 2 each vector weight vector with using saati method is computed as below:     n j n i ijm ijmm i a a n w 1 1 1 which in it ][ m i m ww      n j n i ijliju ijlijug i aa aa n w 1 1 . .1 which in it ][ g i g ww  c. step 3 the biggest eigen vector for each matrix is calculated with below relations: engineering, technology & applied science research vol. 7, no. 4, 2017, 1863-1869 1864 www.etasr.com kimiagari and saleh: ranking tehran’s stock exchange top fifty stocks using fundamental indexes and … )( 1 1 1 max m i m j n i n j ijm m w w a n λ      )(. 1 1 1 max g i g j n i n j ijliju g w w aa n λ      d. step 4 consistency index is calculated with using below relations. )1( )( max    n nλ ci m m )1( )( max    n nλ ci g g e. step5 to calculate the consistency rate (cr), the ci index is divided to random index (ri). if the result value is less than 0.1, matrix diagnosed consistent and usable. to produce random matrixes, first the middle value of triangular fuzzy number produced randomly in [1/9, 9] interval mutually. then, low bound of each triangular number in [produced middle value, 1/9] interval and upper bound value in [1/9, produced middle value] interval is produced randomly and at last, their random index value was obtained by dividing resultant random matrix to two middle bound matrix and geometric mean of up and low bounds matrix. we compare computed consistency rate for two matrix based on below relations with threshold 0.1: g g g ri ci cr  m m m ri ci cr  if both indexes were lower than 0.1, fuzzy matrix is consistence. while both were more than 0.1, decision-making will be asked to reconsider the priorities presented and while only crm(crg) was more than 0.1, decision-making of reconsidering in middle values (bounds) make fuzzy inference. iii. steps of obtaining component weights with fuzzy network analysis based on super-matrix, steps of component weights computing include: the first step is to bring together experts comments, the paired comparisons of geometric mean respondents is taken. second: the eigen vector comparison: to calculate eigen vector comparison each pairwise comparisons tables aggregated, according to equation logarithmic least squares method is used.  umls a a w n i nn j m ij nn j s kj s k ,,, 1 1 1 1 1                         as: nkwwww uk m k l kk ,...,3,2,1),,( ~  third: forming eigen vector matrixes (wij): these matrixes include eigen vectors which obtained from second step of pairwis comparisons. fourth step: computing final levels weights: for computing final weight of each level component ( *iw ) the multiplication of eigen matrix-vector of inner relation in same level of eigen vector must be multiplied by the higher level of upper level. * 1)1( *   iiiiii wwww while, there was not one level iiw matrix , it is necessary to substitute identity matrix with the same degree of that matrix. in the other word, below formula is used. * )( * 11   iiii wwiw topsis method is a common approach in decision making multi-criteria (madm) to the development phase space. this method requires a decision-making matrix which rows of this matrix is options and columns of the matrix are the criteria [7, 8, 9]. with a systematic approach, we can develop a topsis decision making method to fuzzy space. to increase the accuracy of calculations, we can assume that the degree of importance of decision criteria and qualitative variables rates as linguistic variables were collected. in fuzzy space, linguistic variables can be defined in the form of fuzzy numbers. many decision-making techniques in fuzzy space rather profit paired comparisons to reach a decision matrix. always a multi-criteria decision-making problem in fuzzy space can be shown in matrix form as below.                      mnmm n n xxx xxx xxx d ~~~ ~~~ ~~~ ~ ... . . . ... . . . . . . ... ... 21 22221 11211 ],...,,[ ~ 2 ~ 1 ~~ nwwww  note that each of the linguistic variables xij and wj can be in the form of triangular fuzzy numbers is defined as follows: ),,( ~ ijijijij cbax  ),,( 321 ~ jjjj wwww  for the topsis technique, it is necessary to normalize obtained data in decision-making matrix using euclidean norms. this normalization method has high complexity. but if we want to use this technique in a fuzzy space, we can use simpler norms such as linear to data homogenization. thus, normalized fuzzy decision matrix is obtained as follows engineering, technology & applied science research vol. 7, no. 4, 2017, 1863-1869 1865 www.etasr.com kimiagari and saleh: ranking tehran’s stock exchange top fifty stocks using fundamental indexes and … nm ijrr      ~~ if we define b and c respectively as set of same direction criteria with cost and profit, we have: bj c c c b c a j ij j ij j ij ijr  ),,( *** ~ cj c ca b a c a ij j ij j ij j ijr   ),,( ~ bjifcc ijj   max cjifaa ijj   min by using this normalizing method, we can now homogenize all fuzzy data based on obtained triangular numbers in a range between zero and one. now, based on row vector of criteria weights (w) and normalized decision matrix r can be obtained the decision weighted matrix. nm ijvv      ~~ so that each of the elements of this matrix are equal: n,,1,2,j m,,1,2,i. ~~~  jijij wrv each of the weighted normalized decision matrix elements are fuzzy triangular numbers which their numbers are homogenized between zero and one. based on this matrix, positive and negative ideal options can be defined: ),...,,( ),...,,( ~ 2 ~ 1 ~ ~ 2 ~ 1 ~       n n vvva vvva where: )0,0,0( )1,1,1( ~ ~     j j v v after calculating positive and negative ideal options, the distance of each options of these two ideal choices will be achieved mivvdd j n j iji ,...,2,1)( ~ 1 ~      mivvdd j n j iji ,...,2,1)( ~ 1 ~      at last, the closeness coefficient is calculated to determine the priorities of options. this coefficient can be obtained based on the values * ,i id d  of each alternative as follows: mi dd d cc ii i i ,...,2,1    now, we can sort all options based on higher value of cci. iv. data analysis results in this step, the most important financial ratios were identified as primary indexes. these indexes are mentioned in 12 criteria-groups in below and were offered to experts by questionnaire to each experts mention their opinions about importance of this criterion in the ranking process of tehran stock exchange company’s shares (table i). answers of 51 completed questionnaires regarding the importance of criteria of ranking tehran stock exchange company shares is shown as table and graph with delphi method by descriptive approach. in this questionnaire, the importance of intended indexes in the direction of the research purposes has been questioned. in this part, with considering figure 1, we calculate each fifty premier company ranking indexes weight and active company of tehran stock exchange with anp fuzzy approach for group decision making. table i. the identified primary criteria for ranking company stocks table ii. common paired comparisons average fuzzy in ranking indicators of active companies and top stocks (matrix) prioritizing indicators beta coefficient earnings per share (eps) sales growth price to earnings ratio p/e dividend per share (dps) growth in profit margins beta coefficient )1 ,1 ,1( )6.22 ,5.13 ,4( )2.89 ,2.47 ,2( )8 ,7 ,6( )5.77 ,4.72 ,3.64( )6.61 ,5.6 ,4.58( earnings per share (eps) )0.25 ,0.2 ,0.17( )1 ,1 ,1( )0.5 ,0.41 ,0.33( )1.36 ,1 ,0.8( )2.63 ,2.03 ,1.59( )2.72 ,2.09 ,1.59( sales growth )0.5 ,0.41 ,0.35( )3.11 ,2.47 ,2( )1 ,1 ,1( )6.22 ,5.13 ,4( )3.42 ,2.76 ,2.29( )8.44 ,7.4 ,6.35( price to earnings ratio p/e )0.17 ,0.15 ,0.13( )1.26 ,1 ,0.74( )0.25 ,0.2 ,0.17( )1 ,1 ,1( )1 ,0.85 ,0.7( )0.8 ,0.7 ,0.63( dividend per share (dps) )0.28 ,0.22 ,0.18( )0.63 ,0.5 ,0.39( )0.44 ,0.37 ,0.3( )1.45 ,1.19 ,1( )1 ,1 ,1( )1.26 ,1.12 ,1( growth in profit margins )0.22 ,0.18 ,0.16( )0.63 ,0.49 ,0.37( )0.16 ,0.14 ,0.12( )1.59 ,1.45 ,1.26( )1 ,0.9 ,0.8( )1 ,1 ,1( indexrow indexrow returns7 beta coefficient (systematic risk) 1 risk and return 8 financial ratios (liquidity, efficiency, etc.) 2 earnings per share (eps) 9 dividend per share (dps) 3 sales growth 10 capital increase 4 growth in profit margins 11 balance sheet 5 price to earnings ratio (p/e) 12 profit and loss 6 engineering, technology & applied science research vol. 7, no. 4, 2017, 1863-1869 1866 www.etasr.com kimiagari and saleh: ranking tehran’s stock exchange top fifty stocks using fundamental indexes and … fig. 1. company ranking indexes weight and active company of tehran stock exchange with anp fuzzy then, pairwise comparison of 6 final criteria is defined, rather than goal and other criteria (control criteria) including 7 tables in second questionnaire were offered to persons who complete the first questionnaire and decisionmaking group members compared criteria pairwise comparison in verbal terms forms "same preferences, small preferred, the strong preference, preferred very strong "which respectively represent fuzzy numbers are 1,3,5,7,9. it should be noted that the decision group members were asked to fill out entries above the main diagonal of pair-wise comparison tables, because in considered fuzzy anp approach, pairwise comparison matrices elements are reversed in comparison to the main diameter. summarizing shows the pairwise comparison of indexes for 22w matrix (table ii-viii). table iii. common paired comparisons average fuzzy in ranking indicators in relation to beta coefficient index beta coefficient earnings per share (eps) sales growth price to earnings ratio p/e dividend per share (dps) growth in profit margins earnings per share (eps) )1 ,1 ,1( )0.5 ,0.41 ,0.33( )0.75 ,0.64 ,0.56( )1.45 ,1.19 ,1( )1.96 ,1.71 ,1.48( sales growth )3.11 ,2.47 ,2( )1 ,1 ,1( )7.27 ,6.26 ,5.25( )2.89 ,2.27 ,1.82( )0.86 ,0.72 ,0.61( price to earnings ratio p/e )1.82 ,1.58 ,1.34( )0.2 ,0.16 ,0.14( )1 ,1 ,1( )1.82 ,1.58 ,1.34( )0.28 ,0.22 ,0.18( dividend per share (dps) )1 ,0.85 ,0.7( )0.56 ,0.45 ,0.35( )0.75 ,0.64 ,0.56( )1 ,1 ,1( )0.75 ,0.64 ,0.56( growth in profit margins )0.68 ,0.59 ,0.52( )1.66 ,1.41 ,1.17( )5.77 ,4.72 ,3.64( )1.82 ,1.58 ,1.34( )1 ,1 ,1( table iv. common paired comparisons average fuzzy in ranking indicators in relation to earnings per share (eps) earnings per share (eps) beta coefficient sales growth price to earnings ratio p/e dividend per share (dps) growth in profit margins beta coefficient )1 ,1 ,1( )1 ,0.85 ,0.71( )2.24 ,1.74 ,1.42( )6 ,5 ,4( )1.59 ,1.35 ,1.16( sales growth )1.42 ,1.19 ,1( )1 ,1 ,1( )4 ,3 ,2( )1 ,0.85 ,0.71( )1.16 ,1 ,0.87( price to earnings ratio p/e )0.71 ,0.58 ,0.45( )0.5 ,0.34 ,0.25( )1 ,1 ,1( )1.23 ,1 ,0.82( )1.23 ,1 ,0.82( dividend per share (dps) )0.25 ,0.2 ,0.17( )1.42 ,1.19 ,1( )1.23 ,1 ,0.82( )1 ,1 ,1( )1.16 ,1 ,0.87( growth in profit margins )0.87 ,0.75 ,0.64( )1.16 ,1 ,0.87( )1.23 ,1 ,0.82( )1.16 ,1 ,0.87( )1 ,1 ,1( table v. common paired comparisons average fuzzy in ranking indicators in relation to sales growth sales growth beta coefficient earnings per share (eps) price to earnings ratio p/e dividend per share (dps) growth in profit margins beta coefficient )1 ,1 ,1( )0.71 ,0.58 ,0.45( )8.95 ,7.94 ,6.93( )6.93 ,5.92 ,4.9( )1.42 ,1.19 ,1( earnings per share (eps) )2.24 ,1.74 ,1.42( )1 ,1 ,1( )10 ,9 ,8( )6.33 ,5.2 ,4( )6 ,5 ,4( price to earnings ratio p/e )0.15 ,0.13 ,0.12( )0.13 ,0.12 ,0.1( )1 ,1 ,1( )0.41 ,0.38 ,0.36( )0.15 ,0.13 ,0.12( dividend per share (dps) )0.21 ,0.17 ,0.15( )0.25 ,0.2 ,0.16( )2.83 ,2.65 ,2.45( )1 ,1 ,1( )0.18 ,0.15 ,0.13( growth in profit margins )1 ,0.85 ,0.71( )0.25 ,0.2 ,0.17( )8.95 ,7.94 ,6.93( )7.75 ,6.71 ,5.66( )1 ,1 ,1( engineering, technology & applied science research vol. 7, no. 4, 2017, 1863-1869 1867 www.etasr.com kimiagari and saleh: ranking tehran’s stock exchange top fifty stocks using fundamental indexes and … table vi. common paired comparisons average fuzzy in ranking indicators in relation to price to earnings ratio p/e price to earnings ratio p/e beta coefficient earnings per share (eps) sales growth dividend per share (dps) growth in profit margins beta coefficient )1 ,1 ,1( )2.83 ,2.65 ,2.45( )2.83 ,2.65 ,2.45( )2 ,1.53 ,1.23( )4.9 ,3.88 ,2.83( earnings per share (eps) )0.41 ,0.38 ,0.36( )1 ,1 ,1( )2 ,1.74 ,1.42( )2 ,1.74 ,1.42( )0.82 ,0.66 ,0.5( sales growth )0.41 ,0.38 ,0.36( )0.71 ,0.58 ,0.5( )1 ,1 ,1( )0.5 ,0.45 ,0.41( )0.82 ,0.66 ,0.5( dividend per share (dps) )0.82 ,0.66 ,0.5( )0.71 ,0.58 ,0.5( )2.45 ,2.24 ,2( )1 ,1 ,1( )1 ,0.78 ,0.58( growth in profit margins (0.36 ,0.26 ,0.21) )2 ,1.53 ,1.23( )2 ,1.53 ,1.23( )1.74 ,1.3 ,1( )1 ,1 ,1( table vii. common paired comparisons average fuzzy in ranking indicators in relation to dividend per share (dps) dividend per share (dps) beta coefficient earnings per share (eps) sales growth price to earnings ratio p/e growth in profit margins beta coefficient )1 ,1 ,1( )2.45 ,2.24 ,2( )6 ,5 ,4( )1.74 ,1.3 ,1( )1.23 ,1 ,0.82( earnings per share (eps) )0.5 ,0.45 ,0.41( )1 ,1 ,1( )2 ,1.74 ,1.42( )0.36 ,0.26 ,0.21( )0.82 ,0.66 ,0.5( sales growth )0.25 ,0.2 ,0.17( )0.71 ,0.58 ,0.5( )1 ,1 ,1( )0.21 ,0.17 ,0.15( )0.82 ,0.66 ,0.5( price to earnings ratio p/e )1 ,0.78 ,0.58( )4.9 ,3.88 ,2.83( )6.93 ,5.92 ,4.9( )1 ,1 ,1( )1.59 ,1.35 ,1.16( growth in profit margins )1.23 ,1 ,0.82( )2 ,1.53 ,1.23( )2 ,1.53 ,1.23( )0.87 ,0.75 ,0.64( )1 ,1 ,1( table viii. common paired comparisons average fuzzy in ranking indicators in relation to growth in profit margins growth in profit margins beta coefficient earnings per share (eps) sales growth price to earnings ratio p/e dividend per share (dps) beta coefficient )1 ,1 ,1( )2.45 ,2.24 ,2( )1.42 ,1 ,0.71( )2.83 ,2.65 ,2.45( )2 ,1.53 ,1.23( earnings per share (eps) )0.5 ,0.45 ,0.41( )1 ,1 ,1( )0.36 ,0.26 ,0.21( )0.5 ,0.45 ,0.41( )0.5 ,0.34 ,0.25( sales growth )1.42 ,1 ,0.71( )4.9 ,3.88 ,2.83( )1 ,1 ,1( )0.71 ,0.58 ,0.5( )2.45 ,2.24 ,2( price to earnings ratio p/e )0.41 ,0.38 ,0.36( )2.45 ,2.24 ,2( )2 ,1.74 ,1.42( )1 ,1 ,1( )2.45 ,2.24 ,2( dividend per share (dps) )0.82 ,0.66 ,0.5( )4 ,3 ,2( )0.5 ,0.45 ,0.41( )0.5 ,0.45 ,0.41( )1 ,1 ,1( fuzzy weight for each factor of prioritizing top and active companies in stock exchange is as shown in table ix. the fuzzy weight of each prioritizing indicator of active and top companies in stock exchange is shown in table x. in the next phase, ranking of companies using topsis fuzzy approach is determined with respect to the decision criteria specified above and the above weights (tables xii-xii). table ix. fuzzy weight for each factor of prioritizing top and active companies in stock exchange weight of each indicator                        6 1 6 1 6 1 6 1 6 1 i j m kj j s kj s k a a w umlsa j s kj ,,         6 1 6 1 prioritizing indicators u m l u m l )0.21 ,0.15 ,0.11( 0.218 0.158 0.114 1.849 1.338 0.967 beta coefficient )0.29 ,0.22 ,0.16( 0.299 0.221 0.160 2.533 1.870 1.355 earnings per share (eps) )0.26 ,0.19 ,0.13( 0.263 0.191 0.136 2.227 1.621 1.154 sales growth )0.15 ,0.10 ,0.78( 0.148 0.107 0.078 1.251 0.909 0.659 price to earnings ratio p/e )0.15 ,0.11 ,0.08( 0.151 0.111 0.080 1.281 0.940 0.677 dividend per share (dps) )0.28 ,0.21 ,0.15( 0.287 0.211 0.152 2.429 1.789 1.288 growth in profit margins 8.467            6 1 6 1 6 1i j m kja engineering, technology & applied science research vol. 7, no. 4, 2017, 1863-1869 1868 www.etasr.com kimiagari and saleh: ranking tehran’s stock exchange top fifty stocks using fundamental indexes and … table x. fuzzy weight of each prioritizing indicators priority absolute weight of indicators prioritizing indicators 4 0.161 beta coefficient 1 0.224 earnings per share (eps) 3 0.194 sales growth 6 0.109 price to earnings ratio p/e 5 0.113 dividend per share (dps) 2 0.214 growth in profit margins table xi. fifty premier company data ranking indexes beta coefficient eps sales growth p/e dps growth in profit margins beta coefficient eps sales growth p/e dps growth in profit margins 0.033 28.145 27.430 2.583 520.000 8.333 1.510 39.735 52.975 6.143 128.750 11.998 0.320 20.655 21.105 2.483 668.750 -0.515 0.670 29.613 13.735 3.363 127.000 -3.888 0.953 63.478 412.638 7.040 307.500 -55.113 0.513 18.243 43.523 9.035 117.500 13.523 0.528 5.928 21.048 5.390 1680.000 5.040 0.580 21.830 22.023 6.888 605.750 1.213 0.798 13.655 14.310 7.630 781.250 3.583 0.438 73.353 67.127 6.077 205.000 1.240 1.295 16.963 12.698 4.615 2375.000 1.713 -0.002 -9.910 -6.750 18.680 132.500 3.517 0.195 22.595 16.793 7.105 722.500 9.358 0.000 71.138 49.868 4.780 500.000 -34.055 0.280 281.380 57.210 6.763 196.333 178.428 1.325 37.140 23.775 5.815 520.000 30.235 0.435 18.253 44.020 3.938 775.000 -22.458 0.168 57.987 60.427 2.733 342.500 -18.305 1.305 49.795 49.735 9.513 642.500 0.220 0.130 62.240 10.725 5.028 215.000 -3.257 0.240 27.445 30.088 6.115 750.000 6.305 0.460 13.005 17.143 51.660 3500.000 44.873 1.058 15.055 42.238 2.658 1369.000 -16.990 0.060 -8.118 30.675 15.263 332.500 -18.065 0.485 1.723 14.315 2.855 739.250 -4.443 -0.073 51.248 23.855 5.103 197.500 -48.018 -0.770 -4.450 33.123 4.770 840.000 -29.158 0.273 -6.185 30.215 3.180 1300.000 25.350 1.163 12.208 9.443 5.250 275.000 1.243 1.180 2.095 40.620 2.948 362.500 2.608 0.873 48.287 3.505 3.470 116.667 -84.318 0.083 6.553 -5.480 6.298 104.000 -26.118 0.255 9.225 10.935 2.755 295.500 -0.783 0.550 39.855 25.160 6.903 432.500 45.248 0.745 10.088 14.435 5.695 170.500 -3.268 -0.163 1.323 -6.813 3.995 242.500 29.088 1.293 40.838 73.783 3.805 76.500 -8.405 0.343 6.175 433.520 3.590 420.000 15.455 0.243 1.023 3.773 3.388 431.250 43.045 2.133 28.333 31.773 8.153 562.500 596.525 0.295 102.623 24.575 6.063 71.250 71.525 1.243 33.588 20.638 5.473 587.750 -0.508 0.983 486.618 5.295 3.783 135.000 434.108 0.338 0.443 4.443 2.858 440.000 15.725 0.723 38.383 32.937 5.190 105.000 3.497 0.313 16.175 18.400 3.410 328.250 -5.027 0.238 25.765 33.693 4.713 247.500 9.613 1.043 1.100 27.255 5.000 2800.000 -1.638 0.765 9.003 1.503 9.205 215.000 8.333 0.985 39.735 52.975 6.350 1650.000 -21.625 table xii. the results of prioritizing top and active companies in stock exchange  id  idicc rank  id  idiccrank  id  id icc rank 3.350 2.204 0.397 45 3.266 2.321 0.415 23 2.805 2.545 0.476 1 3.191 2.099 0.397 46 3.225 2.287 0.415 24 2.797 2.492 0.471 2 3.272 2.117 0.393 47 3.194 2.265 0.415 25 2.803 2.405 0.462 3 3.281 2.098 0.390 48 3.237 2.294 0.415 26 2.897 2.337 0.447 4 3.375 2.049 0.378 49 3.217 2.277 0.414 27 2.952 2.285 0.436 5 3.157 1.853 0.370 50 3.232 2.284 0.414 28 3.155 2.389 0.431 6 3.160 2.232 0.414 29 3.093 2.310 0.428 7 3.162 2.194 0.410 30 2.999 2.232 0.427 8 3.241 2.237 0.408 31 3.119 2.318 0.426 9 3.174 2.188 0.408 32 3.103 2.303 0.426 10 3.210 2.201 0.407 33 3.059 2.258 0.425 11 3.170 2.171 0.406 34 3.160 2.330 0.424 12 3.207 2.190 0.406 35 2.997 2.195 0.423 13 3.297 2.247 0.405 36 3.067 2.237 0.422 14 3.174 2.151 0.404 37 3.162 2.299 0.421 15 3.044 2.061 0.404 38 3.128 2.263 0.420 16 3.175 2.140 0.403 39 3.141 2.253 0.418 17 3.170 2.126 0.401 40 3.133 2.247 0.418 18 3.257 2.183 0.401 41 3.202 2.294 0.417 19 3.215 2.155 0.401 42 3.114 2.231 0.417 20 3.120 2.066 0.398 43 3.185 2.272 0.416 21 3.252 2.145 0.397 44 3.196 2.275 0.416 22 engineering, technology & applied science research vol. 7, no. 4, 2017, 1863-1869 1869 www.etasr.com kimiagari and saleh: ranking tehran’s stock exchange top fifty stocks using fundamental indexes and … v. discussion & conclusion company stock ranking is a method to convert raw data into relevant information for decision-making. ranking can be performed based on different parameters such as the criteria and fundamental analysis elements. the aim of this study is to provide a fuzzy multi-criteria decision making model to rank the stocks of companies of tehran stock exchange. at first by using stock exchange experts as a decision-making group and then by using non-parametric statistical analysis to establish ranking criteria. then, the anp multi-fuzzy technique is used to determine their weight. then, the fuzzy topsis technique is used and the fifty top stocks in the stock exchange were ranked. after performing the ranking for sensitivity analysis of criteria weight, their weights are shifted mutually with each; hence, the rank of companies will be compared in fifty-one situations, by selecting two criteria of six criteria. a consistency is shown. the company that was placed in the second rank in main ranking occupied the first rank in all 51 situations and the company occupied the second rank in all 51 situations was placed in the first rank in main ranking. it is noteworthy that the decision maker can present a ranking by giving the desired amount of six indicators of the company. one can even begin to analyze the sensitivity of rate changes by criteria weight shift. the first ranking company has a higher special value per share and d/e allocation ratio in comparison to other companies.. in the same manner, comparing financial ratios with other companies will uncover confirm acceptability and accuracy of ratings. moreover, the results of interviews with the authorities on the final indicators of the research represent that the criteria are the most basic possible indicators for ranking stocks so that some experts believe that 80 percent of ranking result depends on three first factors that have more weights. in addition, the results of surveying experts about shares’ obtained ranks in the ranking express that the results are very much close to reality; especially, companies with higher ranks can meet the demands of shareholders largely. vi. suggestions for future studies further studies can define subscales for each scale through more investigations; they can also solve the model according to mutual impacts of subscales of each group on each other as well as on other scales and subscales. as there are many problems in estimating the beta value in tehran stock exchange, one can extract beta coefficient from other models like dimson instead of using rahavard novin software in order to obtain better results. references [1] e. onder, a. hepsen, “combining time series analysis and multi criteria decision making techniques for forecasting financial performance of banks in turkey”, international conference on applied business and economics (icabe-13), pp. 530-555, october, 2013 [2] c. kao, r. e. steuer, “value of information in portfolio selection, with a taiwan stock market application illustration”, european journal of operational research, vol. 253, no. 2, pp. 418-427, 2016 [3] k. y. shen, g. h. tzeng, “combined soft computing model for value stock selection based on fundamental analysis”, applied soft computing, vol. 37, no. 1, pp. 142-155, 2015 [4] h. ince, “short term stock selection with case-based reasoning technique”, applied soft computing, vol. 22, no. 2, pp. 205-212, 2014 [5] m. amile, m. sedaghat, m. poorhossein, “performance evaluation of banks using fuzzy ahp and topsis, case study: state-owned banks, partially private and private banks in iran”, caspian journal of applied sciences research, vol. 2, no. 3, pp. 10-15, 2013 [6] s. ansari, m. kazemi, a. eshlaghy, “an application of fuzzy topsis for ranking strategies”, management science letters, vol. 4, no. 4, pp. 663-668, 2014 [7] k. y. shen, m. r. yan, g. h. tzeng, “combining vikor-danp model for glamor stock selection and stock performance improvement”, knowledge-based systems, vol. 58, no. 4, pp. 86-97, 2014 [8] x. bi, r. a. isaili, q. zheng, “evaluation of wastewater treatment quality in the west bank-palestine based on fuzzy comprehensive evaluation method”, 21st international conference on industrial engineering and engineering management, pp. 219-221, 2015 [9] a. e. la plante, j. c. paradi, “evaluation of bank branch growth potential using data envelopment analysis”, omega, vol. 52, no. 2, pp. 33-41, 2015 microsoft word etasr_v12_n1_pp8033-8038 engineering, technology & applied science research vol. 12, no. 1, 2022, 8033-8038 8033 www.etasr.com salamh & akyuz: a novel feature extraction descriptor for face recognition a novel feature extraction descriptor for face recognition ahmed b. salem salamh material science and engineering department kastamonu university kastamonu, turkey nuclear_2010@hotmail.com halil ibrahim akyüz computer and teaching technologies education dpt. kastamonu university kastamonu, turkey hakyuz@kastamonu.edu.tr abstract-this paper presents a new feature extraction technique for face recognition. the new model, called multi-descriptor, is based on the well-known method of local binary patterns. it involves many different neighborhoods of the central pixel. its unique advantage is that this descriptor allows the use of different neighborhood sizes instead of only one point. this structure ensures reasonable effectiveness and also provides the possibility to obtain a different distribution of features. based on the new descriptor, a face recognition model using the pairwise feature descriptor based on the proposed descriptor was developed in this work, and local binary patterns were created to investigate the similarity and dissimilarity between the two models. for both models, the training was done using the support vector machine method on different face databases to overcome face recognition problems such as camera distance, expression, large head size, and illumination variations. the proposed technique achieved perfect accuracy on almost all tested databases including the extended yale b and grimace database. keywords-multi descriptor model; local binary pattern; face recognition; feature extraction i. introduction face recognition has been intensively researched and developed to introduce models that lead to more accurate results [1]. the great importance of face recognition lies in the identification and authentication, especially in security and registration systems. the main idea in any recognition technique is to interpret the physical characteristics of the object to be recognized [2]. biometric recognition is widely used. face recognition outperforms fingerprint and iris recognition [3]. most problems in face recognition usually involve pose, scale, orientation, illumination, and facial expression. over time, numerous methods have been proposed to solve these problems [4]. moreover, constrained and unconstrained environments have become complicated due to different lighting conditions, pose, occlusion, and distance from the camera [5]. different angles and illuminations affect facial features as the physical characteristics of the human face change [6]. there are many methods that have been used for face recognition under different illumination conditions during the last decades [7]. the performance of the recognition techniques has achieved significant results under controlled and uncontrolled environments such as under illumination and pose variations, which are challenging situations. variations in the illumination of the face images occur when the light source is at different angles to the direction of the face [8]. moreover, face recognition accuracy and recognition time are two major factors that affect the quality of face recognition algorithms [9]. deep learning has been developed with higher accuracy and complex structure, but common deep learning techniques require large databases, much computation time for training, and high power consumption. deep learning, local features, and geometric techniques are used in facial feature extraction. the function of facial feature extraction is to identify facial features such as structure, size, and shape of the facial image after face recognition. features such as nose, mouth and eyes or geometry calculations, represent the face. feature based descriptor techniques have been successfully used for face recognition due to their robustness, efficiency and simplicity. scale invariant feature transform (sift) [10], local binary patterns (lbp), and histogram of oriented gradients (hog) [11] in combination with nearest neighbors, support vector machine (svm) technique are used for person recognition [12]. the lbp technique, was proposed in [13] for texture description and has the advantage of being robust and simple. lbp continues to be used for face recognition as it gives very good results compared to other techniques, while it has improved its performance many times over [14]. moreover, with the increasing use of machine learning techniques, researchers have integrated algorithms such as lbp and ensemble ad boosted strategy to achieve accurate results in face recognition. moreover, the use of more than one strategy, for example lbp and gabor wavelet filter, for feature extraction has led to better results, and the integration of different techniques is said to give much better performance. lbp describes smaller details of appearance, while gabor processes the structure of faces over a wider range of scales [15]. lbp is recognized as a powerful feature extraction method for face recognition and texture classification [16]. lbph uses a histogram by dividing the cropped face image blocks and counting the histogram for each block by integrating the histogram blocks to introduce the final feature vector. the lbph process is applied to each face image to represent vectors for each image and finally compare the tested face vector with the total trained vectors to compare two face images [17]. in the field of face recognition, there are corresponding author: ahmed b. salem salamh engineering, technology & applied science research vol. 12, no. 1, 2022, 8033-8038 8034 www.etasr.com salamh & akyuz: a novel feature extraction descriptor for face recognition many face databases with different features, and selecting the databases that are suitable for evaluating the new technique is challenging. in this work, most face recognition problems were considered. to ensure the diversity, 6 databases were selected for the evaluation of the algorithms. the derivation is based on the mathematical theory derived from the equation for local binary patterns to achieve perfect accuracy in face recognition. for this purpose, different descriptors were used to extract features, to calculate the histogram for each descriptor, and to generate a pair of feature vectors considering the proposed face recognition model. ii. methodology in this part, the combination of multi-descriptor and svm is presented in detail. in this work, known databases have been used to evaluate the performance of descriptors while ensuring the diversity of data. each database contains a different number of subjects. each subject is called a class and is denoted by c. the number of subjects in each database is different. for each class, there is a different number of samples, denoted by s. the face databases contain a variety of features. the databases used in the study were cropped and reformatted into images of 128×128 pixels. iii. the proposed method appearance based feature extraction works on representing facial details. it stands out for its efficiency, accuracy, and robustness. the initial lbp method simply works by threading central pixels of 3×3 neighborhoods to binary encode the value of the central pixel. the value of the central pixel is denoted by gp and its 8 neighbors by gc [18]. subtracting (gp-gc) gives a negative or a positive value. the resulting value is encoded to 0 if it is negative and to 1 otherwise. finally, the binary code is converted to decimal value to represent the feature. the main functionality of the proposed feature extraction based on appearance considers the mean value as a threshold value and compares it with the 8 neighboring values to generate a new value, which represents the new value as a feature. the advantage of multi-descriptor models md1 and md2 is that they generate distinguishing features by determining the value that describes the facial image. the proposed technique starts by introducing a new mathematical equation to describe the facial structure in different distributions as shown in figure 1, by comparing 8 neighbors with the mean value in a gray scale image representing the value from 0 to 255 pixel intensity. the variety of x values is to ensure the distribution of the data, that is, the values of x8 and x0 are variable depending on the application. the application of the multi-descriptor equations (1)-(3) to the original images of the extended yale b database is shown in figure 2. the results are shown in figures 3-4. mdn � �x�f g� � g � � �∑ ������� f g� � g ��� ∗ 2.55 ��� �� (1) f(x) = !new value if x * 0, 0 otherwise. (2) f(x) = !new value if x 2 0, 0 otherwise. (3) fig. 1. multi structures of descriptor. fig. 2. some samples per person with illumination variation from the extended yale b database. fig. 3. samples from the extended yale b produced by the md1 model. fig. 4. samples from the extended yale b produced by the md2 model. iv. support vector machine machine learning has become a desirable technique in most areas of recognition. one of these techniques is svm. svm is a supervised learning algorithm for handling regression and classification problems, which performs classification by finding a hyperplane that can separate two classes. in this paper, svm [19] is used to databases which are divided into two categories, training and testing, to perform classification. svm uses error-correcting output codes (ecoc), binary classification, and an ensemble method for multi-class classification problems. two methods used in ecoc are one against one and one against all, which was used in this work. v. face recognition with multi-descriptor figure 5 shows the overall architecture using a multidescriptor model for classification consisting of two main parts, namely a training set and a test set. the same model was used engineering, technology & applied science research vol. 12, no. 1, 2022, 8033-8038 8035 www.etasr.com salamh & akyuz: a novel feature extraction descriptor for face recognition for face feature extraction to represent the face structure. multidescriptor one (md1) has different parameters than multidescriptor two (md2). based on the flexibility of the derived equation, it was explained how to generate facial features. the md1 uses a value of x8 equal to 50 and x0 equal to 0 and the md2 uses a value of x8 equal to 60 and x0 equal to 0. together, they brought different representations of facial images. the evidence of the differences between mdn and the pair-lbp model is doubted. for this reason, a new lbp architecture for face recognition was introduced, as shown in figure 6. the classification of both models was conducted with the use of svm. vi. performance evaluation to compute and evaluate the performance of face recognition models using machine learning techniques, the most commonly used metrics [20] are defined in this work as follows: for all matrices, consider p as the number of positive samples, n as the number of negative samples, t as true, and f as false. accuracy (acc) is an indicator used frequently to measure classification performance. acc � 5675856758796798 (4) sensitivity or true positive rate (tpr) reflects the samples positively classified in the total number of positive samples, also known as actual positive samples. tpr � 5656798 (5) positive predictive value (ppv) or precision indicates the proportion of positive samples classified correctly in the total number of positive predicted samples. ppv � 56 96756 (6) f-measure or f1 score reflects the harmonic mean of precision and recall. the value of f1 is ranged from 0 to 1. high values of the f-measure indicate high classification performance. f1 � @56 @56796798 (7) fig. 5. face recognition architecture using the multi descriptor model. engineering, technology & applied science research vol. 12, no. 1, 2022, 8033-8038 8036 www.etasr.com salamh & akyuz: a novel feature extraction descriptor for face recognition fig. 6. face recognition architecture using the local binary pattern model. vii. facial recognition data the yale face database consists of 15 subjects with 11 images taken under different conditions for each class, giving a total of 165 grayscale images [21]. extended yale b has 28 classes, with each class containing 9 poses and 64 illumination conditions for a total of 16128 face images [22]. the university of essex has introduced 4 folders of data (faces94, faces95, faces96, and grimace) [23]. the total face database contains 395 faces of people of both sexes with 20 images for each subject. it contains photos of people from different ethnic backgrounds, mainly first-year university students. most of the subjects are between 18 and 20 years old, while there are also some older subjects. some persons wear glasses or have beards. table i. summary of facial recognition datasets dataset number of subjects number of images yale 15 165 extended yale b 28 16128 faces94 152 3060 faces95 72 1440 faces96 72 3013 grimace 18 360 viii. results and discussion figure 7 presents the performance of the two models. both show good performance in terms of sensitivity, precision, and f1 score and excellent results on the challenges encountered in each database, especially when the subject moves during the acquisition of the image. fig. 7. multi-descriptor and lbp performance comparsion using sensitivity, precision, and f1 score. figure 8 shows the accuracy of the md and the lbp models. both models showed excellent performance, with the proposed md either coming close or outperforming the lbp. engineering, technology & applied science research vol. 12, no. 1, 2022, 8033-8038 8037 www.etasr.com salamh & akyuz: a novel feature extraction descriptor for face recognition fig. 8. performance comparison of the md and the lbp models for face recognition. the results show that the new descriptor, which uses a new feature extraction equation, is more efficient on different poses, illuminations, facial expressions, and glasses, than the lbp model. this means that the new model is suitable to face the challenges of face recognition and other tasks when feature extraction is required for description, verification, and identification. the descriptor was tested and verified on several face images in the first part, which clearly shows how well it can describe face details. this is very important and shows the ability to represent all the features of a face. the new descriptor may contribute to the recognition of other tasks, such as covid19, retinal vessels, and texture classification, which we plan to study in the future. ix. conclusion this paper presented a new feature extraction model called multi-descriptor (md) model. a key finding was the use of the derived equations to describe facial features with pair technique and different distribution. the technique was developed for face feature extraction, but is certainly suitable for most other types of texture description with more descriptors. the classification for face recognition was performed using svm. the proposed descriptor outperformed the lbp model in extended yale b, face94 and grimace databases, having accuracy of 99.437%, 98.814%, and 100% respectively. this shows that the proposed descriptor is completely different from the conventional lbp and improves the recognition accuracy of faces and handles perfectly the challenge of poses, illuminations, expressions, face position, and camera distance. combinations of mdn and lbp models with different structures and distributions of data could be used in future work. authors’note the authors announce that they have complete access to all the 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[23] "libor spacek’s facial images databases." https://cmp.felk.cvut.cz/ ~spacelib/faces/ (accessed dec. 11, 2021). engineering, technology & applied science research vol. 7, no. 3, 2017, 1670-1675 1670 www.etasr.com naderpour et al.: application of fuzzy expert systems to manage the projects time in iranian gas refineries application of fuzzy expert systems to manage the projects time in iranian gas refineries abbas naderpour department of civil engineering islamic azad university central tehran branch, iran aba.naderpour.eng@iauctb.ac.ir javad majrouhi sardroud department of civil engineering islamic azad university central tehran branch, iran j.majrouhi.eng@iauctb.ac.ir masood mofid department of civil engineering sharif university of technology tehran, iran mofid@sharif.edu abstract-the national iranian gas company (nigc) is one of the top ten gas companies in the gas industry in the middle east and is comprised of 7 gas refineries. so this company needs to apply the most optimum time management methods to achieve its goals. custom scheduling calculation of project planning uses the critical path method (cpm) as a tool for planning projects activities. cpm is now widely used in planning and managing projects but in spite of its wide application, this method has a critical weak point of not taking into account the uncertainties in scheduling calculation. this article aims to present a precise method based on the application of fuzzy expert systems in order to improve the time estimation method in construction projects and in this regard, reviews the results of the implementation of this method in construction projects of iranian gas refineries. the results show that the proposed method increases the accuracy of time estimation about 7 to 22 percent. keywords-critical path method; fuzzy expert systems; uncertainty; time estimation method i. introduction time management can be effective in a project when the project schedule is based on reasonable and comprehensive time estimation. in industries with complex processes such as gas refineries, considering limitations and risks involved in the project implementation and also many uncertainties that affect the project activities, the importance of the time management is great. as the ongoing projects are directly or indirectly linked with continuous production in gas refineries, operational condition and site classification based on the hse risks, increases more uncertainties to the project schedule. considering the very low reliability of planning with certainty and project control by this approach, using more secure methods for control and interaction with uncertainty is to be placed on the agenda. this article presents a method for implementing an extended method of cpm based on the application of fuzzy expert systems (fcpm) to manage schedule uncertainties in iranian gas refinery projects. the concept of fcpm is explained by a real and applicable example and then, the proposed model and the method of its implementation in projects will be described. ii. fuzzy critical path method (fcpm) fcpm is an extension of critical path method in terms of fuzzy approach. in this method, fuzzy function defines the time of project activities to manage their uncertainties. for understanding the main concepts of fcpm, consider the project network indicated in figure 1. this project network is a part of a small one-story building construction planning that contained excavation, concreting and installing the building structures. the resistance system against the earthquake is a.d.a.s bracing. the description of all activities regarding the mentioned project is presented in table ι. fig. 1. cpm of small one-story building construction as it could be seen from table ι, 10 out of whole 11 activity times have triangular fuzzy type format and only the remaining one (related to a.d.a.s braces) is in trapezoidal form. equations (1) to (8) represent the stages of fcpm calculations of the project network. the calculations indicate that the project total time is the maximum of three fuzzy numbers (eq.8). consequently, in order to determine the project time, it is necessary to rank the fuzzy numbers and select the maximum. fes1 = (0, 0, 0) + (1, 2, 4) = (1, 2, 4) (1) engineering, technology & applied science research vol. 7, no. 3, 2017, 1670-1675 1671 www.etasr.com naderpour et al.: application of fuzzy expert systems to manage the projects time in iranian gas refineries fes2 = (0, 0, 0) + (1, 5,10) = (1, 5,10) (2) fes3 = (0, 0, 0) + (1, 2, 3) = (1, 2, 3) (3) fes5 = (0, 0, 0) + (2,14,18) = (2,14,18) (4) fes4 = max ((1, 2, 4) + (2 , 3 ,4) , (1, 4,10) + (1, 2, 3) , (1, 2, 3) + (1, 2, 3)) = (2, 6,13) (5) fes6 = (2, 6,13) + (3, 4, 5) = (5 ,10,18) (6) fes7 = max ((5,10,18) + (4, 5, 9), (2,14,18) +(1, 4, 6), (0, 12, 21, 24)) (7) fes7 = max ( a , b, c) st: a= (9, 15, 27) ; b= (3, 18, 24) & c =(0, 12, 21, 24) (8) the calculations indicate that the project total time is the maximum of three fuzzy numbers (8). consequently, in order to determine the project time, it is necessary to rank the fuzzy numbers and select the maximum. since fuzzy numbers do not form a natural linear order (similar to real numbers) a key issue in applications of fuzzy set theory is how to compare fuzzy numbers. various approaches have been developed for ranking fuzzy numbers up to now. initially a method using the concept of maximizing set to order the fuzzy numbers was proposed in [1]. in [2] four indices which may be employed for the purpose of fuzzy ranking were introduced. in [3], an index for ordering (ranking) fuzzy numbers was proposed. in [4] a new method of fuzzy numbers ranking with integral value was described. in [5], fuzzy sets were ranked based on the concept of existence of vibration frequencies. in [6] a new approach for ranking fuzzy numbers by distance method was proposed. in [7], ranking alternatives with fuzzy weights by maximizing and minimizing set was introduced. a new methods for ranked fuzzy sets was described in [8]. in [9], authors ranked fuzzy numbers with an area between centroid point and original point while in [10] authors used fuzzy distance measure for fuzzy numbers comparison in the same year. in [11], authors proposed another fuzzy ranking method based on distance method. in [12], authors ranked fuzzy numbers by sign distance. in [13], authors ranked fuzzy numbers by distance minimization. in [14], authors ranked trapezoidal fuzzy numbers with integral value. in [15], authors published the result of their research about fuzzy ranking. in [16], authors ranked fuzzy numbers with an area method using a radius of gyration in torsion stiffness. in [17], authors ranked trapezoidal fuzzy numbers based on mode, spread, and weight. in [18], authors improved the ranking method for fuzzy numbers based on centroid-index. in [19], authors proposed a new method based on angle measure and finally in [20] a new lexicographical approach for ranking fuzzy numbers was proposed. for ranking the three fuzzy numbers of (8), five methods were considered. table ii shows the results of this ranking and figure 2 compares the results in bar charts. also, the project total time and critical path for each method are indicated in table iii. table i. the project information of activities activity activity description time (days) 0 1 steel bars cutting (1, 2, 4) 0 2 excavation (1, 5, 10) 0 3 base plate making (1, 2, 3) 0 5 making the beams (2, 14, 18) 0 7 making & installation of a.d.a.s braces (0, 12, 21, 24) 5 7 installing the beams (1, 4, 6) 1 4 making reinforce cage (1, 2, 3) 2 4 foundation forming (1, 2, 3) 3 4 base plate installation (1, 2, 3) 4 6 concreting (3, 4, 5) 6 7 columns making and installation (4, 5, 9) table ii. results of fuzzy ranking by 5 methods fuzzy ranking method result of ranking method calculation a b c result choobineh & li 17.5 18.33 15 18.33 c < a < b yager 15.75 16.5 13.5 16.5 c < a < b cheng 21.77 21.72 21.32 21.77 c < b < a chen & sanguansat 17.1 18.75 15.6 18.75 c < a < b abbasbandy & hajjari 15.75 15.73 14.25 15.75 c < b < a table iii. results of project critical path fuzzy ranking method project critical path project time (days) choobineh & li 0 – 5 – 7 18.33 yager 0 – 5 – 7 16.5 cheng 0 – 2 – 4 – 6 7 21.77 chen & sanguansat 0 – 5 – 7 18.75 abbasbandy & hajjari 0 – 2 – 4 – 6 7 15.75 fig. 2. project time calculation by various fuzzy ranking methods according to the results of fcpm calculations, selecting the fuzzy ranking method for project scheduling has a great influence on the determination of project total time and critical path. as a result, a suitable fuzzy ranking method, compatible engineering, technology & applied science research vol. 7, no. 3, 2017, 1670-1675 1672 www.etasr.com naderpour et al.: application of fuzzy expert systems to manage the projects time in iranian gas refineries to project nature should be considered by project management team. iii. fuzzy time estimation several methods have been proposed for finding the fuzzy time management. the main common topic in all of these methods is converting the classic time of project activities to fuzzy numbers for schedule calculation. for the reason that cpm calculation needs to compare the time of activities to determining critical path, ranking of fuzzy numbers is necessary. consequently, fuzzy numbers ranking is the most important factor in these methods. in [21], authors introduced the preliminary concept of fuzzy cpm. they presented the time of project activities by fuzzy set in the time space. their method provides more direct processing verbally expressed opinions of experts. the significant problem not quite solved in their method was the question of deriving membership functions for activity duration times. in [22] algebraic operators were used to estimate the time of project activities and project critical path. in [23] a way to to compute total floats and find critical paths in a project network by the fuzzy approach was described. in [24], a methodology to calculate the fuzzy completion project time was presented and in [25] an extension of fuzzy schedule networks was proposed. new methods were recently introduced in [26]. they proposed a method for ranking fuzzy numbers without the need for any assumptions and used both positive and negative values to define ordering which is applied to cpm. in [27], authors presented an approach to the critical concept in a network with fuzzy activity times. in [28], a taxonomy of fuzzy graphs that treated fuzziness in vertex existence, edge connectivity and edge weight was presented. in [29], a new approach to implementing a fuzzy cpm for activity networks based on statistical confidence interval estimates and a ranking method for level fuzzy numbers was introduced. in [30], authors presented an algorithm to perform fuzzy critical path analysis for project network problem. in [31], authors presented another method to calculate fuzzy critical paths and critical activities and activity delays and in [32] authors extended some results for interval numbers to the fuzzy case for determining the possibility distributions to describe latest starting time of activities. in [33], authors proposed an approach based on the extension principle and linear programming (lp) formulation to critical path analysis in networks with fuzzy activity durations. in [34], authors introduced the problems of determining possible values of earliest and latest starting times of an activity in networks with minimal time lags and imprecise durations that are represented by means of the interval of fuzzy numbers. in [35], authors proposed a new approach based on fuzzy critical path calculation. they used fuzzy arithmetic and the fuzzy ranking method to determine the fuzzy critical path of the project network without converting the fuzzy activity times to classical numbers and compared their method with other methods. in [36], authors proposed a new method of fuzzy critical path analysis based on the centroid of centroids of fuzzy numbers and in [37] authors proposed new algorithms identify the critical path in a fuzzy environment of project network.. iv. proposed fuzzy base method the uncertainties that must be managed in each project are categorized into two main groups; the first group includes probable uncertainties which are managed by risk management and the second group covers non-probable uncertainties that are related to project nature and its complexity. many industries, such as gas refineries manage probable uncertainties in their projects by risk management but in the field of non-probable uncertainties, actions are very scarce. this article considers the managing of non-probable uncertainties in gas refineries projects. the diagram of proposed model is shown in figure 3. fig. 3. diagram of the proposed model for implementing the models, at first, two professional questionnaires were distributed between a professional team which was selected by the staff of 70 contractors, consultant and employer companies. the first questionnaire was designed to identify effective factors such as site organization, weather, labor skills and quality of equipment on doing project activities. then obtained linguistic variables were translated into mathematical measures. for instance, the questionnaire was designed for excavation activity is presented in table iv. table iv. questionnaire of excavation activity please determine the effect of each factor in the time of excavation activity. 1excavation equipment (hand tools, loader, backhoe, excavator, dozer) very poor poor medium high very high 2climatic condition (very warm, warm, moderate, cold, very cold) very poor poor medium high very high 3hse criteria (classification of site in operational zones) very poor poor medium high very high 4classification of rock (earthy, soft, moderate, hard, very hard) very poor poor medium high very high 5the level of underground water in meter (>15, 10-15, 5-10, 1-5, <1) very poor poor medium high very high 6depot distance in meter (>10000,1000-10000, 500-1000, 100-500,<100) very poor poor medium high very high 7depth of excavation in meter (>15, 10-15, 5-10, 1-5, <1) very poor poor medium high very high 8years of driver experience of (>20, 15-20, 10-15, 5-10, <5) very poor poor medium high very high engineering, technology & applied science research vol. 7, no. 3, 2017, 1670-1675 1673 www.etasr.com naderpour et al.: application of fuzzy expert systems to manage the projects time in iranian gas refineries as it can be seen in table iv, the value of the linguistic variables is classified into 5 types (figure 4). as it could be seen in table iv, a large number of factors are considered to estimate the time of excavation activity. to examine the reliability of the questionnaire, data analysis was done by spss. the results of this analysis are shown in table v. according to spps analysis, the cronbach's alpha (reliability index) was 0.387, while it should be greater than 0.7. the results show that factors 2, 3, 5, 6 and 8 do not have an effective influence on the timing of excavation activity. so these factors were eliminated and the calculations were repeated. in the new analysis, the index rose up to 0.888 which is desirable. so the main factors of excavation activity are excavation equipment, classification of rock and depth of excavation. in the next step, the second questionnaire which relates to estimating activity durations was distributed among team members. after summing up the results of the first and second questionnaires, obtained results were examined by a team of experts (composed of 8 expert project managers) to determine its content validity. then, according to satisfactory results, the structural validity of survey questionnaires was evaluated by factor analysis method. according to the kmo index, the acceptable construct validity of research was approved. the analysis results are summarized in table vi. also, the results of the total variance of analysis explained that these three factors are not reducible to the number of agent-less (table vii). fig. 4. the value of the linguistic variables classification table v. results of reliability index calculated by spss scale mean if item deleted scale variance if item deleted total correlation cronbach's alpha if item deleted s01 12.11 5.951 0.443 0.290 s02 13.75 8.639 0.136 0.449 s03 13.75 9.231 0.110 0.505 s04 11.86 5.460 0.621 0.190 s05 13.25 8.120 0.000 0.526 s06 13.68 8.300 0.109 0.457 s07 12.75 6.861 0.368 0.153 s08 13.61 7.803 0.276 0.404 table vi. the results of kmo test kaiser-meyer-olkin measure of sampling adequacy 0.692 bartlett's test of sphericity approx. chi-square 13.522 df 3 sig. 0.003 table vii. the results of total variance component total variance explained total % of variance cumulative % 1 1.823 46 46 2 1.076 28 74 3 1.041 26 100 according to the results obtained from computing of the pearson correlation coefficient, the correlation between these factors is also desirable. table viii indicates related results. table viii. the results of correlation index correlation results s01 s04 s07 s01 pearson correlation 1 0.910 0.576 sig. (2-tailed) 0.000 0.001 n 28 28 28 s04 pearson correlation 0.910 1 0.511 sig. (2-tailed) 0.000 0.005 n 28 28 28 s05 pearson correlation 0.576 0.511 1 sig. (2-tailed) 0.001 0.005 n 28 28 28 in later stages of the proposed model, membership functions of these factors were drawn according to the second questionnaire. the second questionnaire is about estimating the time of each activity based on the experience of the professional team. in this research, fuzzy diagrams were of triangular and trapezoidal types. in the present example, figures 5 to 7 indicate the fuzzy membership functions of excavation activity factors. these diagrams are considered as the input of analysis. fig. 5. fuzzy membership of excavation equipment factor fig. 6. fuzzy membership of classification of rock factor fig. 7. fuzzy membership of excavation depth factor then the results of the previous step as input were analyzed in fuzzy toolbox of matlab. this toolbox follows a rule base system. analysis of model is presented in figure 8. as it engineering, technology & applied science research vol. 7, no. 3, 2017, 1670-1675 1674 www.etasr.com naderpour et al.: application of fuzzy expert systems to manage the projects time in iranian gas refineries can be seen in figure 8, inputs are processed by a smart and rule base system. fig. 8. a pictorial view of analysis model in matlab “if …then …” rules were set by the expert team in rule base system. for example, for these three factors, about 125 operating modes may occur. three states of these rules are observed in table ix and software environment can be seen in figure 9. table ix. an example of analysis rules rule no the rule rule 1 if excavation equipment is a dozer and classification of rock is very hard and depth of excavation is more than 15 meter thenthe time of excavation is very long. rule 2 if excavation equipment is a backhoe and classification of rock is soft and depth of excavation is less than 1 meter thenthe time of excavation is very short. rule 3 if excavation equipment is a dozer and classification of rock is hard or depth of excavation is between1 to 5 meter thenthe time of excavation is moderate. fig. 9. a pictorial view of setting the rules in the software after analysis, the duration of activities under uncertainty and fuzzy approach can be achieved. for example, this time for an above-mentioned activity (excavation) will be 4.5 days for each 200 cubic meters of concrete. (figures 10-11). finally, after calculating the time of all activities by this method, project schedule was run and the total time of project was calculated. fig. 10. a pictorial view of analysis output fig. 11. a pictorial view of matlab output diagram v. results the proposed model of the research has been implemented in one gas refinery in the north east of iran. the study period was between 2014 and 2016 and the population of this study was composed of 30 projects by cochran formula. the result of the research shows the estimated project duration is about 7 to 22percent closer to actual time. figure 12 indicates the percent of improvement in project time estimation. fig. 12. diagram of improvement in project time estimation new method vi. conclusion this study investigated a new method for precise time estimation in construction projects of the iranian gas refineries. a gas refinery has a complicated process and engineering, technology & applied science research vol. 7, no. 3, 2017, 1670-1675 1675 www.etasr.com naderpour et al.: application of fuzzy expert systems to manage the projects time in iranian gas refineries ongoing projects are directly or indirectly linked with continuous production in this industry. consequently managing the project time is a critical issue and considering the very low reliability of the project planning with certainty, using more secure models for control and interact with uncertainty is a necessity. it is obvious that successful project time management should be based on comprehensive time estimation. therefore, considering the uncertainty in the estimation of project time is the main object. from the above discussion, the following conclusions were derived: 1. many industries, such as gas refineries manage probable uncertainties in their projects by risk management but in the field of non-probable uncertainties, actions are very scarce. 2. this research considered the managing of non-probable uncertainties in gas refineries projects by a proposed method based on fuzzy critical path method. 3. the result of the implementation of proposed method shows that the accuracy of project time estimation increases about 7 to 22 percent. finally, due to successful results of this research, it has been suggested that the proposed method could be generalized to other industries projects. references [1] r. jain, “decision-making in the presence of fuzzy variables”, ieee transactions on systems man and cybernetics, vol. 6, pp. 698-703, 1976 [2] r. yager, “a procedure for ordering fuzzy subsets of the unit interval”, information science, vol. 24, pp. 143-161, 1981 [3] f. choobineh, h. li, “an index for ordering fuzzy numbers”, fuzzy sets and systems, vol. 5, pp.1-19, 1985 [4] s. l. liou, m. j. wang, “ranking fuzzy numbers with integral value”, fuzzy sets, and systems, vol. 50, pp 247-255, 1992 [5] p. t. chang, e. s. lee, “ranking of fuzzy sets based on the concept of existence”, computers and mathematics with applications, vol. 27, no 9, pp.1-21, 1994 [6] c. h. cheng, “a new approach for ranking fuzzy numbers by distance method”, fuzzy sets and systems, vol. 95, pp. 307-317, 1998 [7] p. a. raj, a. kumar, “ranking alternatives with fuzzy weights using maximizing set and minimizing set”, fuzzy sets and systems, vol. 105, pp. 365-375, 1999 [8] j. s. yao, f. t. lin, “fuzzy critical path method based on signed distance ranking of fuzzy numbers”, ieee transactions on systems, man, and cybernetics-part a: systems and humans, vol. 30, no 1, pp.76-82, 2000 [9] t. c. chu, c. t. tsao, “ranking fuzzy numbers with an area between the centroid point and the original point”, computers and mathematics with applications, vol. 43, pp.111-117, 2002. 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between generalized fuzzy numbers”, expert systems with applications, vol. 38, pp. 2163-2171, 2011 [17] p. rao, n. ravi shankar, “fuzzy critical path analysis based on centroid of centroids of fuzzy numbers and new subtraction method”, international journal of mathematics in operational research, vol. 5, no. 2, pp. 205-224, 2013 [18] l. q. dat, s. y chou, “an improved ranking method for fuzzy numbers based on the centroid-index”, international journal of fuzzy systems, vol. 14, pp. 413-419, 2012 [19] m. barkhordary ahmadi, “ranking of fuzzy numbers based on angle measure”, international journal of information, security and system management, vol. 3, no 1, pp. 259-265, 2014 [20] u. a. sharma, “new lexicographical approach for ranking fuzzy numbers”, mathematical theory and modeling, vol. 5, no 2, pp. 143-153, 2015 [21] s. chanas, j. kamburowski, “the use of fuzzy variables in pert”, fuzzy sets and systems, vol. 5, no 1, pp. 11-19, 1981 [22] i, gazdik, “fuzzy network planning-fnet”, ieee 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355-368, 2002 [29] j. s. yao, f. t. lin, “fuzzy critical path method based on signed distance ranking of fuzzy numbers”, the journal of supercomputing, vol. 24, pp. 305-325, 2003 [30] g. s. liang, t. c. han, “fuzzy critical path for project network”, information and management sciences, vol. 15, no 4, pp. 29-41, 2004 [31] a. oliveros, a. robinson, “fuzzy logic approach for activity delay analysis and schedule updating”, journal of construction and management, vol. 131, no. 1, pp. 42-51, 2005 [32] s. chanas, p. zielinski, “critical path analysis in the network with fuzzy activity times”, fuzzy sets and systems, vol. 122, pp. 195204, 2006 [33] s. p. chen, y. j. hsueh, “a simple approach to fuzzy critical path analysis in project networks, applied mathematical modelling”, vol. 32, no. 7, pp. 1289-1297, 2008 [34] s. h. yakhchali, s. h. ghodsy pour, “on latest starting times of activities in networks with imprecise durations and generalized precedence relations”, applied mathematical modelling, vol. 34, no. 8, pp. 2044-2058, 2010 [35] s. sathish, k.ganessan, “a simple approach to fuzzy critical path analysis in project networks”, journal of scientific & engineering research, vol. 2, no. 12, pp. 1-6, 2011 [36] p. rao, n. ravi shankar, “fuzzy critical path analysis based on centroid of centroids of fuzzy numbers and new subtraction method”, international journal of mathematics in operational research, vol. 5, no. 2, pp. 205-244, 2013 [37] s. elizabet, l. sujatha, “project scheduling method using triangular fuzzy numbers and triangular fuzzy numbers”, applied mathematical science, vol. 9, no. 4, pp. 185-198, 2015 microsoft word etasr_v12_n4_pp8817-8824_1 engineering, technology & applied science research vol. 12, no. 4, 2022, 8817-8824 8817 www.etasr.com rahmani & mostefai: multi-objective mpso/ga optimization of an autonomous pv-wind hybrid … multi-objective mpso/ga optimization of an autonomous pv-wind hybrid energy system nassima rahmani department of electrical engineering automatic laboratory of setif (las) ferhat abbas university setif 1 setif, algeria rahmani_nassima@yahoo.com mohammed mostefai department of electrical engineering automatic laboratory of setif (las) ferhat abbas university setif 1 setif, algeria mostefai@univ-setif.dz received: 2 march 2022 | revised: 21 april 2022 | accepted: 26 april 2022 abstract-this article presents a study of the optimal sizing of an autonomous hybrid energy system (pv-wind-battery) as a power source for a typical household in an isolated village in adrar, algeria using the multi-objective particle swarm optimization (mpso) algorithm and genetic algorithm (ga). this study presents a new approach to obtain an optimal configuration and sizing of the main components integrated into the autonomous hybrid system (pv/wind) which meets the requirements of the desired system. in the first phase, the reliability criterion (lpsp) is met with the lowest energy cost (ec) value (min total net present cost (tnpc)). the required storage bank must have a low rate of aging in order to extend the battery life, which contributes to the reduction of the overall cost of the system. keywords-autonomous hybrid system; optimization and sizing (pv/wind); minimum energy cost; trnsys i. introduction many isolated sites are powered by autonomous electricity generation systems, using local renewable sources, such as photovoltaic (pv) panels, wind turbines, and micro turbines. electricity from renewable sources is intermittent, dependent on weather conditions. these renewable generators are coupled to a storage system ensuring the continuous availability of energy. the renewable generators selected for our study is a hybrid system (pv/wind) with storage. generally, the storage is ensured by batteries which currently consist one of the most used solutions. the batteries have very good yields, around 8085%, and have a very competitive price, if we consider lead technology. the optimization of these systems is based on sizing criteria, maximizing the power generated to have a good yield and cost minimization. knowing that the main research goal is the overall improvement of the performance of pv and wind conversion systems, the equivalence between the admissible efficiency and the average operating cost determines the degree of efficiency of use of these systems. several criteria for optimizing the efficiency of hybrid systems (pv/wind) as well as techniques have been applied in order to have a good adaptation and a high efficiency. authors in [1] recommended an optimal design model for the design of hybrid solar-wind-battery systems for powering a telecommunication relay station. to assess the optimal system configuration and ensure that the annualized cost of the system is minimized while satisfying the probability of loss of required power. the five decision variables for loss of power supply probability (lpsp) included in the optimization process are the pv module number, pv module slope angle, wind turbine number, installation height of the wind turbine, and battery capacity. an iterative method to determine the optimal dimensioning of autonomous photovoltaic (pv-battery) is proposed in [2, 4], linear programming is used in [3] to design and optimize the components of a hybrid system (pv/wind/micro-hydro) which minimize the size and initial cost. a new approach to designing an autonomous hybrid wind pv/battery system is proposed in [5] taking into account both economic and ecological aspects. a technical-economic analysis of the complete study of the hybrid system (pv/diesel generator/battery) was done by the authors in [6] to minimize the cost and meet charging requirements and the optimal tilt angle of the pv panel in order to increase the energy generated by the use of a genetic algorithm. in [7], feasibility study and techno-economic evaluation of an autonomous hybrid system (pv/wind) with battery energy storage for a remote island were conducted using the homer software to obtain an optimal configuration of the autonomous system in terms of energy cost (coe) and system net present cost (npc). an iterative approach following the total energy deficit (ted), the total npc (tnpc), and ec was developed in [8] to size the components of an autonomous hybrid system (pv/wind/diesel/battery) to satisfy the charge demand in a more cost-effective manner. an iterative optimization technique was used in [9] to determine the optimal configuration of an autonomous system (pv/wind/hydrogen) supplying a desalination unit which would guarantee a reliable energy supply with the lowest initial investment cost for any site. optimal sizing and techno-economic evaluation of the pumped storage-based pv power generation system was presented in [10] to maximize power supply reliability and minimize lifecycle cost. the pigeon inspired optimization (pio) algorithm was used for optimization sizing of a pv-wind hybrid power system in [11]. several thermal insulation solutions have been proposed [12-14] in order to ensure excellent thermal comfort of a home and to minimize energy needs while improving energy efficiency. corresponding author: nassima rahmani engineering, technology & applied science research vol. 12, no. 4, 2022, 8817-8824 8818 www.etasr.com rahmani & mostefai: multi-objective mpso/ga optimization of an autonomous pv-wind hybrid … this paper presents a comprehensive and integrated study divided into two phases. at first, a study of the optimal sizing of an autonomous hybrid energy system (pv/wind/battery) as a power source for a typical algerian village household is conducted using mpso and ga. this work relates to the development of a technical and economic analysis and evaluation methodology carried out for a hybrid system (pv/wind). the results are compared and discussed. our study is based on two models: the reliability model developed according to the concept of lpsp and the economic model based on tnpc and the battery aging model. in order to achieve our objective, we proposed two essential contributions which are mpso algorithm and ga. a case study is being investigated for the analysis of an autonomous hybrid system (pv/wind) intended to supply a village of habitats in adrar algeria. the simulation results relating to the different system configurations and their corresponding costs are presented. the type of storage used in our system is the lead acid battery. in the next phase, in order to guarantee the state of health of the storage batteries, we have chosen a configuration which ensures longer battery lifetime and minimum aging rate from a study of its state of charge (soc). the application of the rainflow algorithm allows extracting the number of cycles of the signal with its corresponding depth of discharge. the operating cycles used to study the aging of the battery were based on the battery life given by the manufacturer. ii. model of the hybrid system components the solar/ wind hybrid energy production system consists of a pv generator, a wind turbine, a storage battery bank, ac/dc converters, dc/dc converters, a controller, and cables. in order to predict the performance of the hybrid system, the individual components must first be modeled. fig. 1. block diagram of the hybrid system. the power delivered by the different energy sources depends on several parameters. for the solar generator, the parameters influencing the power supplied by the generator are: the metrological data of the site: ambient temperature ta and irradiation ir and the apv surface of the solar panel field. for the wind generator, the supplied power is influenced by the metrological data of the site: ambient temperature ta and wind speed ws and the surface swept by the rotor of the wind turbine awt. a. modeling of the pv system the model of the solar generator is given by [5, 15, 17, 18]: ��� �� ��⁄ � ��� �� (1) where � is the overall efficiency of the generator given by: � �� ��� �1 � �� ��� � ����� � (2) where �� is the reference efficiency of the solar generator, ��� is the degradation factor of the solar generator according to its lifetime, �� is the coefficient of the influence of the temperature of the pv cells on the efficiency of the generator. the temperature of the junction or the cell of the pv panel is given by: �� 30 � 0.075�300 � �� � � 1.14��$ � 25� (3) where ����� is the nominal operating cell temperature and �� the irradiation or solar sunshine. b. modeling of the wind generator the power model of the wind generator is given by the following expressions [5, 15]: �&' ()*��'+ �' , �&� �. (4) �&' ()� , �&� �. (5) where c0 is the turbine efficiency, η23 is the efficiency of the speed variator (drive controller), �' the generator efficiency, �&� �m� , is the surface swept by the rotor of the turbine, ��m/s the wind speed, 7�m is the altitude , �$ is the ambient temperature, and , �kg/m. the air density: , �353.049 �$⁄ �. exp ��0.034�7 �$⁄ � (6) c. modeling of the storage system the charge-discharge expression of the lead-acid battery is given by the following expression: >?@+$� >?@+$� �a � 1� � bc�� �a� ∗ �e�e� � c&� �a� ∗ �$�e� � fgh ijkl m ∗ ��n$ (7) where epv(t)=ppv(t)*∆t, ewt(t)=pwt(t)*∆t, eld(t)=pld(t)*∆t, and ppv(t), pwt(t), pld(t) are respectively the pv generator power, the wind generator power, and the load demand in an instant t. ∆t is the step time of the simulation, ηinv is the inverter efficiency, ηcha is the battery charging efficiency, which generally depends on the charging current and is between [0.65 and 0.8]. when the load demand is greater than the available generated energy, the battery bank is in discharging state. thus, the >?@+$� at instant t can be expressed as: engineering, technology & applied science research vol. 12, no. 4, 2022, 8817-8824 8819 www.etasr.com rahmani & mostefai: multi-objective mpso/ga optimization of an autonomous pv-wind hybrid … >?@+$� >?@+$� �a � 1� + bc�� �a� ∗ �e�e� + c&� �a� ∗ �$�e� − foh ijkl m ∗ pihjqrs (8) where ηdisch is the battery discharging efficiency, it is supposed to be equal to 1. in all cases the state of batteries charging must satisfy the following condition: >?@+$�_uvw < >?@+$� �a� < >?@+$�_u$y where >?@+$�_uvw and >?@+$�_u$y are the limit states of battery charging. >?@+$�_u$y is considered as the nominal capacity of the storage system: >?@+$�_u$y = cbat_n. the inferior limit is given by: >z*+$�_uvw = [z[ ∗ *+$�_w where dod(%) is the battery depth of discharge [17]. iii. sizing and optimization procedure the developed process was used to calculate the optimum value of the pv module area, the wind turbine, and the optimal battery capacity for a standalone pv/wind hybrid system. a. enunciation of the optimal sizing problem the estimate of the hybrid pv/wind energy/battery size is formulated as an optimization problem where the express of the objective function is according to the constraints and the performances of the system. the objective function and the constraints are detailed in the following subsections. b. objective function the objective functions of the optimization problem must minimize the total economic cost of the tnpc and ec of the system and to satisfy the energy needs. we are focused on finding the best combination of multiple sources for a hybrid system, i.e. the pv panel surface (apv), the area swept by wind turbines (awt) and the nominal storage capacity of the battery bank (cn). 1) economic evaluation this assessment is based on the concept of the current global net cost: the cumulative cost of a product throughout its life cycle, from the start of its conception until its dismantling. it includes the initial cost (acquisition + installation) of all system components, the cost of all component replacements required during the lifetime of the system, and the cost of maintenance. the lifetime of the system is usually considered to be the lifetime of the element with the longest lifetime. in this article, the economic approach used based on the tnpc and the ec taking into account the lifetime and replacement costs of each element of the system. 2) total net present cost the current tnpc in $, can be expressed as follows according to [8]: �\�* �$� = �* + � �̂�_� + � �̂w`w�_� (9) where ic is the initial cost of the system components. �* = *v�� ∗ ��� + *v& ∗ �& + *v+$� + *vvw� (10) where cipv is the initial cost of the photovoltaic system, ciw the initial cost of the wind system, cibat the initial cost of the storage system, ciinv the initial cost of the inverter. pwcrec and pwcnonrec are factors for the conversion of the recurring and non-recurring costs to their present value, defined by [8]. the component cost assumptions on which we based our calculations are given in table i [6, 8]. table i. cost of the system components component unit price (us$/w) maintenance cost during the first year (%) life time (years) interest rate d (%) pv array a 2.29 1% of price 25 8 wind turbine b 3.00 3% of price 20 battery a 0.213 1%of price 4 inverter a 0.711 0%of price 10 a http://www.solarbuzz.com. b mean value of the literature data. 3) energy cost ($/kwh) the cost per kwh of the ec produced in $/kwh can be determined by the ratio of the annualized total cost (tac) to the annual energy produced by the system [7-9, 15,16]. ec can be calculated according to (11), (12). c* b$ a�ℎc m = �d� ∑ ffg ���hijklm( = �\�*∗*no ∑ cpq�a�8760a=1 (11) crf is the recovery factor, expressed as: *no�t, v� = v�pwv� k �pwv�kxp (12) where i is the interest rate and n the lifetime of the system in years. for this study, we have assumed an interest rate of 8% and n = 20 years. c. the constraints to find solutions for the optimization problem, a set of constraints must be satisfied with any feasible solution throughout the system operations as follows: the soc of the battery bank must satisfy the following constraints at any times: >?@uvw < >?@ < >?@u$y the system's lpsp must be less than the allowed lpsp reliability index: lpsp < lpspindex 1) reliability estimation according to lpsp lpsp is defined as the fraction of all energy losses and energy demand in a defined period of operation (in our study we used t = 1year) [16]: y�>� = �� zc+$� ≤ c+$�|jk } = ∑ ~������lm( ∑ �g�lm( ���∗∆� (13) lps (loss of power supply) can be calculated with the following relation: engineering, technology & applied science research vol. 12, no. 4, 2022, 8817-8824 8820 www.etasr.com rahmani & mostefai: multi-objective mpso/ga optimization of an autonomous pv-wind hybrid … y�>�a� = ��� �a� − �& �a�� ∗ ∆a −���� �a� ∗ ∆a + *+$� �a − 1� − >z*+$�_uvw � ∗ �vw� (14) iv. implementation of the pso algorithm pso is a new evolutionary algorithm, which was originally inspired by the regularity of the cluster activities of birds. thus, a simplified model using group intelligence was established. pso is initialized as a set of random particles, each particle having its own position and velocity vectors. the optimal solution is searched for iteratively. in each iteration, the particles update themselves by tracking two "extremes". the first extreme, called pbest, is the best solution found by the particle itself. the other extreme, called gbest, is the best solution currently found by the entire swarm [21-25]. the position and velocity vectors of each particle can be calculated as: �v �a + 1� = ��v �a� + �*pqp�p���av �a� − �v �a�� + *�q������av �a� − �v �a�� (15) �v �a + 1� = �v �a� + �v �a + 1� (16) � = � �x�x��)x�� (17) � = *p − *� (18) � � 4 (19) c1 and c2 are the cognitive and social parameters respectively in this study c1=c2=1. r1 and r2 are random numbers between 0 and 1. in this article, the objective functions are defined as minimum {ec, tnpc}, under the constraint of inequality, the main program is developed in matlab. v. site description the meteorological data used in this study have been recorded at the new energy algeria (neal) station installed at the roof top of the research unit in renewable energies in the saharan medium (urerms) located in adrar (figure 2). fig. 2. neal station. fig. 3. algeria wind map. adrar is the administrative capital of adrar province, the second largest province in algeria. the commune is sited around an oasis in the tuat region of sahara desert. according to the 2008 census, it has a population of 64,781, with an annual growth rate of 4.0%. adrar lies at an elevation of 258m above sea level. its geographical coordinates are 27°52′n, 0°17′w. adrar has a hot desert climate, with long, hot summers and short, warm winters, and averages just 15mm of rainfall per year. summer temperatures are consistently high as they commonly approach 40°c. the temperatures at night are still hot at around 27°c. even in early may or in late september, daytime temperatures can rise up to 45°c. figure 3 shows the annual wind map. a. wind potential to evaluate the wind potential of the site, measurements of wind speeds were taken on site during the year 2015, with half hour intervals. figure 4 shows the wind profile during january. fig. 4. wind profile during january, 2015. b. solar potential measurements of the solar irradiation were also taken on site, by using the orientation and inclination of the pv modules, the latitude of the place, and the values of the global radiation engineering, technology & applied science research vol. 12, no. 4, 2022, 8817-8824 8821 www.etasr.com rahmani & mostefai: multi-objective mpso/ga optimization of an autonomous pv-wind hybrid … were calculated. the quantity of the global irradiation received per day for 1m of horizontal surface is indicated, the mean value of the radiation measured every hour of january and july is given in figure 5. (a) (b ) fig. 5. global irradiation in (a) january and (b) july. c. potential analysis the annual solar irradiation profile for the proposed site shows that there is a marked seasonal variation in solar irradiation (greater in summer). the adrar region has an acceptable wind potential. this feature has led the region to favor initiatives in wind energy generation. d. load profile the exact identification of the consumer's charge profile will facilitate the determination of the size of our generators. the system under study is supposed to supply a load for domestic use. the power demanded by a particular kind of household is not fixed throughout the year. the time of maximum loading of the energy system by the load varies according to the season as a consequence of the variation of the duration of the day. for our part, we consider that the total load demand for usable electrical energy for lighting, refrigeration, air conditioner, tv, radio, hair dryer, and iron is 6.126kwh/d. the load profile taken into account in our study is for a typical adrar village household. figure 6 illustrates the monthly electrical energy demand. fig. 6. monthly load profile. vi. results and discussion in order to find the optimum design of the hybrid system (pv/wind/battery), the proposed algorithm is implemented using matlab/simulink. the optimal sizing results for the desired loss of lpsp of 5% in both cases of optimization are presented in the following paragraphs. the fitness function is defined as the minimum cost of electricity produced by the hybrid system. in the case of a single-objective optimization using the pso and ga optimization algorithms, we have considered the following parameters: • lower and upper limits of decision variables: spvmin < spv < spvmax (20) swmin < sw < swmax (21) cbmin < cb < cbmax (22) where spvmin=1m 2 , spvmax=12m 2 , swmin=1m 2 , swmax=12m 2 , cbmin=150ah, cbmax=200ah • maximum probability of dissatisfaction of the tolerated demand lpsp <5. the sizing results using pso algorithm for different value of tolerated lpsp are given on table ii. table ii. pso results lpsp spv swt cb lpsp cost $/kwh*10 -1 <2 7.45 8.91 155.2 1.99 2.70 <3 6.50 8.47 154 2.99 2.47 <4 6.04 7.76 150 3.97 2.44 <5 6.03 6.63 150 4.95 2.74 to validate the optimization method and ensure the good convergence of the algorithm, we applied another optimization algorithm, the ga. the results are shown in figure 6. they show that the obtained solution is indeed in the optimal zone. the solution was obtained at the 40th iteration starting from the initial conditions after 80 evaluations of the objective function. the simulation results given by the ga algorithm are summarized in the table iii for lpsp <5. engineering, technology & applied science research vol. 12, no. 4, 2022, 8817-8824 8822 www.etasr.com rahmani & mostefai: multi-objective mpso/ga optimization of an autonomous pv-wind hybrid … fig. 7. ga convergence. table iii. ga results lpsp spv swt cb lpsp cost $/kwh *10 -1 <2 8.88 6.11 166 1.96 2.62 <3 8.68 5.59 156.74 2.63 2.42 <4 6.9 6.4 154 3.86 2.66 <5 6.7 5.57 153.15 4.98 2.34 the simulation results show that the cost, the size of the generators (pv, wind), and the battery capacity depend on the desired lpsp. they are important for low lpsp values. in view of establishing optimal system dimensioning, another parameter was proposed, which allows the estimation of the rate of aging of the battery for each configuration. vii. calculation of the number of cycles according to the depth of discharge the study is based on the mathematical model of a gel vrla solar type plate battery given by [26, 27]: \������ = 12850� x��.�.�∗���� + 3210� x�p.���∗���� (23) to extract the number of cycles (nc) and the corresponding dod, the rain flow algorithm has been applied to the soc of our system . a. calculation of aging the aging rate per cycle (ar/c(dod)) is calculated based on the life cycle of the battery and the dod. the expression is written in the following form [26, 27]: ��/������ = p �r����� (24) b. simulation results table iv. pso/ga results lpsp pso ga ar % ar (year) ar % ar (year) <2 6.11 16.36 8.07 12.39 <3 7.47 13.38 8.80 11.36 <4 7.39 13.53 7.73 12.92 <5 8.08 12.38 9.12 10.96 in our case and for a lpsp ≅5 we choose the results given by the pso algorithm which gives a lifetime of 12.38 years and an aging rate of 8.08%. the surface of pv panels installed was apv=6.03m 2 , the surface swept by the rotor of the wind turbine was awt=6.63 m 2 , and the storage capacity was cb=150ah. to see the effectiveness of the optimal result found, we present the soc of the batteries during the year in figure 8. fig. 8. soc vs time. this curve shows the complete exploitation of the batteries in the unfavorable period. the wind energy produced is equal to 2471.9kw per year, i.e. 8.58w per hour on average, which represents 56% of the energy demanded by the consumer. the pv energy produced by the panels is equal to 1760.4kw. comparing to the energy demanded (4386.6kw per year), we find that there is an excess energy at an annual level. the latter is explained by the random nature of the renewable energy sources. fig. 9. the new soc. engineering, technology & applied science research vol. 12, no. 4, 2022, 8817-8824 8823 www.etasr.com rahmani & mostefai: multi-objective mpso/ga optimization of an autonomous pv-wind hybrid … viii. conclusion given the geographical location, the nature of the terrain and the duration of the sunshine, algeria is a most suitable country for the production of renewable energy. the work presented in this article concerns the production of electricity from a hybrid system (pv/wind) with a completely autonomous storage system to supply the households of an isolated village in the adrar region of southern algeria. the objective was to maintain a high level of reliability with a minimum cost thanks to the optimal dimensioning of the hybrid system for a load and a given probability of energy loss under the 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[27] r. dufo-lopez, j. m. lujano-rojas, and j. l. bernal-agustin, "comparison of different lead–acid battery lifetime prediction models for use in simulation of stand-alone photovoltaic systems," applied energy, vol. 115, pp. 242–253, feb. 2014, https://doi.org/10.1016/ j.apenergy.2013.11.021. microsoft word 5-447.doc engineering, technology & applied science research vol. 4, no. 3, 2014, 649-655 649 www.etasr.com nehari et al.: numerical study of the effect of the penetration of a crack in the matrix of a composite numerical study of the effect of the penetration of a crack in the matrix of a composite taieb nehari dept. of mech. eng. djillali liabes university of sidi bel abbes, algeria nehari1976@gmail.com abdelkader ziadi lab. of smart. st. cent. univ. ain temouchent, algeria aekziadi@yahoo.com djamel ouinas dept. of mech. eng. university of mostaganem, algeria douinas@netcourrier.com benali boutabout dept. of mech. eng. djillali liabes university of sidi bel abbes, algeria bboutabout@yahoo.fr abstract—in this numerical investigation, the effect of the penetration of a crack in a matrix reinforced by aluminum silicon carbide particles in a composite is studied in order to determine the thermo-mechanical behavior under the effect of different temperature gradients during cooling. to realize this, the thermal residual stresses are calculated by considering a wide range of cracks of different penetrations. the results of this investigation compared to a case without geometric discontinuity, have revealed no meaningful effect of the distribution of the stresses along a main direction perpendicular to the direction of the crack. on the other hand, regarding the distribution of the stresses along the plane of the crack and in vicinity of the particle, results show that the penetration of the crack in the matrix causes an asymmetry. keywordsmetal matrix composites; al/sic; thermal residual stress; penetration; crack i. introduction since the last decade, metal matrix composite (mmc) materials have become increasingly important in enormous applications in the aerospace, automotive and military industries, due to their high strength-to-density ratio and excellent wear resistances [1, 2]. the main concern about mmcs is related to relatively high states of residual stresses. during cooling down from the manufacturing temperature to room temperature, due to the fact that the constituent materials have different coefficients of thermal expansion, thermal residual stresses are produced, and this affects the mechanical behavior of mmcs [3]. several analyses of residual stresses have been carried out, both experimentally using neutron diffraction and x-ray diffraction and theoretically, by computer simulation [4]. nowadays, there is a wide variety of modeling approaches to the behavior of mmc. most of them are based on the distinct properties of the constituent materials – the matrix and the reinforcement materials. these models are micromechanical models and are based on the topology and geometrical distribution of the reinforcement components. moreover, the micromechanical analysis provides better understanding of formation and distribution of thermal residual stress within the mmcs. the distribution of these stresses in the mmcs depends on several parameters such as inclusion shape, particles volume fraction, cooling rate during manufacturing process, and fabrication temperature. a spherical symmetric model has been employed to calculate thermal residual stresses in al/sic particle metal matrix composites [4]. the numerical analysis revealed that residual stresses within the matrix increases when the particulate volume fraction is enhanced. meijer et al. [5] have studied the effects of inclusion shape on residual stresses of mmcs by finite element analysis. results showed that the use of a cube shaped particle, with sharp corners and edges in the unit cell model, lead to much greater initial hardening behavior than the spherical inclusions and therefore to a greater 0.2% offset yield stress due to stress/strain localization at the particle corners and edges. the elastic behavior of materials is significantly affected by the presence of defects which can entail the weakening of the structure and cause its destruction. strong stress concentrations arising from geometrical or metallurgical failings, may result in the appearance of microcracks. indeed, fracture is the consequence of the various mechanisms related to the development of the damaged zones [6]. the presence of inclusions is also investigated, as they are responsible for stress concentration, crack initiation and propagation, and therefore for the fracture of the material [7]. experimental observations on metal-matrix composites reinforced with particles have demonstrated that damage is always generated at the reinforcement space [8, 9]. according to [10], further improvements in the modeling of particle-reinforced composites should aim at including the damage effect, which is known to control many critical mechanical properties such as ductility and fracture toughness. from the above literature review and to the best of our knowledge the effect of the penetration of a crack on the thermo-mechanical behavior of a metal matrix composite is not clear. the present paper deals with the investigation and the analysis of the effect of the penetration of a micro-crack on the thermo-mechanical behavior of a microstructure of a composite of aluminum matrix reinforced with silicon carbide particles subjected to different temperature gradients (cooling process). this was done using the finite element method to numerically engineering, technology & applied science research vol. 4, no. 3, 2014, 649-655 650 www.etasr.com nehari et al.: numerical study of the effect of the penetration of a crack in the matrix of a composite predict the residual thermal stresses acting on the microstructure. only the damage in the aluminum matrix was considered in the present investigation. the simulations were done with abaqus [11]. ii. modelling procedure until now, it is still not practical to model a three dimensional random distribution of reinforcement particles, of various geometries in a matrix. therefore, to overcome this difficulty, the unit cell analysis method is used. in this study we use a special design of matrix (al) and reinforced particles (sic) [12] as it is shown in figure 1a. the length, width and thickness of our micro-structure are respectively c=160 μm; c=160 μm and c/2=80 μm. the diameter of the reinforced particle (sic) is equal to d=2r0=20 μm. the bonding between the inclusions and the matrix is assumed to be perfect; the debonding on the inclusion-matrix interface is not studied. the matrix (al) was defined as an elastic–plastic material with a modulus of elasticity of 70 gpa, poisson ratio of 0.3, yield strength of 275 mpa and a coefficient of thermal expansion of 23.410-6 °c-1. the particle (sic) was considered as an isotropic elastic material. the particle was assumed to have a modulus of elasticity of 408 gpa and a poisson ratio of 0.2, corresponding to silicon carbide (sic) properties. the coefficient of thermal expansion (hereafter cet) of sic was considered as 5.1210-6 °c-1. therefore, the cet of aluminum is about four times higher than sic. this composite has been subjected to a thermal cycle of preheating to t0 followed by cooling to the ambient temperature. it is assumed that the absolute temperature field is homogeneous and that its evolution is given by: 0 ( ) .t t t t t   (1) where t0 is the initial temperature, t is time and t ~ is the temperature rate, which is considered constant during cooling. here, the initial temperature is considered for several cases t0 = 120°c, 220°c, 320°c, 420°c, 520°c and 620°c, whereas the final temperature is maintained equal to the ambient temperature (tend = 20°c), and the constant cooling rate was considered t ~ =-100°k.s-1. (a) (b) (c) fig. 1. modeling a particle-reinforced composite: (a) the assumed mmc model, (b) the boundary condistions used (c) the finite element mesh on the other hand, the boundary conditions applied to the microstructure are as follows: a fixed boundary condition of the plane surface of the bottom, a tensile pressure force of 10mpa is applied on the upper surface plane, and a symmetric condition has been used for the vertical plane which passes through the inclusion. however, free conditions are applied to the other boundaries planes (see figure 1b) the calculations were performed using abaqus version 6.11 [11]. due to stress concentration, the precision of numerical method is strongly related to the quality of the designed mesh surrounding the particles and also to the zone containing the crack. therefore, a 4 node linear tetrahedron (c3d4) finite element was used for modeling. the accuracy of the model was verified by comparing stress results with two other mesh densities, one with twice the number of elements and one with a coarse mesh having half the number of elements. the satisfactory model containing a spherical inclusion, shown in figure 1c, consists of 52750 elements. all simulations with the meshes described above were performed with al/sic composites with 20 percent volume fraction of reinforcement material. iii. results and discussion a. distribution of residual stress for the sic/al composite under investigation, the coefficient of thermal expansion of aluminum is about four times greater than that of sic. therefore, according to [12], the generations of thermal residual stresses are inevitable during cooling from the high operating temperature, resulting in engineering, technology & applied science research vol. 4, no. 3, 2014, 649-655 651 www.etasr.com nehari et al.: numerical study of the effect of the penetration of a crack in the matrix of a composite tensile stress in the matrix and compressive ones in the reinforcement particles. the micro-structure of the composite is subject to complex residual stresses. there are three "principal stresses" that can be calculated at any point, acting in the x, y, and z directions which are respectively xx, yy and zz. the von mises stress, vm, which is the combination of these three stresses into an equivalent stress, is used in this investigation. figure 2 shows the three-dimensional distribution of the thermal residual stresses vm, xx, yy and zz on the micro-structure of the composite for the case a=5 μm, d=2μm, t=300°c . it should be noted that the distribution of the von mises stress is symmetrically spherical to the three planes from the center of the inclusion. it takes high values in the inclusion and at the vicinity of the matrix–particle interface. in addition, the considered stress decreases radically away from the center of the inclusion and tends to a negligible value to the extremity of the elementary volume. on the one hand, the distribution of the xx stress, is symmetric in the matrix relative to the x-axis and highly important on either side of the inclusion. this stress is negative due to the compression created on inclusion by the presence of the geometric discontinuity. on the other hand, the compressive stresses in the inclusion are twice higher than those obtained in the matrix. for this purpose, the plastic zone in the matrix surrounding the inclusion systematically generates the debonding of the interface matrix-inclusion along the x-axis. it should be noted that the yy residual stresses distribution is significantly asymmetric with respect to the vertical axis in the presence of the effect of the crack appeared with the creation of the tension zone in the vicinity of the inclusion in the opposite side of crack. the compressive stresses are twice higher on both sides of the inclusion on the ordinate axis. the compressive stresses located in the particle are comparable to those shown in figure 2b (xx). the difference in tensilecompressive stresses on the opposite side of the crack can produce the generation of cracks by debonding in the inclusionmatrix. figure 2d shows the evolution of the normal stresses along the z axis (zz). it is clear that the tensile stresses distribution in the matrix is homogeneous and spherical with respect to center of the inclusion whose values are comparable to the xx stresses. the compressive stresses are in the interior of the inclusion and are of the order of five times greater than those of the tensile. far from the particle, this stress takes low values in the matrix. (a) (b) (c) (d) fig. 2. von-mises and normal residual stress distribution for d=2μm, a=5 μm,t=300°c:(a)vm; (b) xx;(c)yy and (d)zz. engineering, technology & applied science research vol. 4, no. 3, 2014, 649-655 652 www.etasr.com nehari et al.: numerical study of the effect of the penetration of a crack in the matrix of a composite b. effect of the temperature gradient for the microstructure without crack case the composite at high temperature can plasticize, and consequently, it is necessary to model and to analyze the effect of different reheating temperatures on the generated thermal residuals stresses. first, we analyze the case without geometric discontinuity, which is displayed in figure 3, that describes the stresses distribution along the vertical path (mentioned in figure 2a) that act on the microstructure namely vm, xx, yy and zz for different temperature gradients ranging from 100 °c to 600 °c. it should be noted that the shape of all these stresses is almost symmetrical about the center of the inclusion. the maximum stresses are proportional to the temperature gradient that replicates the difference in thermal expansion and mechanical properties of radically different materials. thus, regardless of the different temperature gradients, the magnitudes of the stresses are insignificant away from the inclusion. it should be noted that these stresses are maximum at the interface between the inclusion and the matrix, and that they are very small or reaching zero when the distance is greater than 0.3 μm. it is clear that the temperature gradient has a direct and significant effect on the stresses in the vicinity close to the inclusion. the von mises stresses decrease significantly within the particle to a value close to zero at the center of the particle which shows that the effect of the temperature gradient is negligible within the inclusion. an inverse behavior occurs for the xx, yy and zz, stresses as they are practically constant within the particle and comparable to the maximum value obtained in the vicinity of the interface. it should be noted that the temperature gradient affects considerably on the stresses within the inclusion. the same behavior is found for the vm , xx , yy and zz stresses distribution along the horizontal path (as mentioned in figure 2a) that act on the microstructure, for the same different temperature gradients as it is found for the case of vertical path (not shown here). c. interaction fissure-inclusion the effect of crack-inclusion interaction is highlighted in the present study. it should be noted that in the case of a vertical patch, the profiles of the stresses are identical with and without the presence of geometrical discontinuity (crack). a slight difference of the stresses should be reported near the vicinity of the matrix-inclusion interface. concerning the stresses evolution along the horizontal direction, iare found to be significantly affected by the presence of crack. the stress values are higher compared to those obtained in the no-cracks case. this means that a crack generates aditional residual stresses caused by the stresses at the crack tip and the plastic strain in the matrix in the vicinity very close to the inclusion. an increase in stresses at the surroundings of the matrix0 0.2 0.4 0.6 0.8 1 normalized distance 0 100 200 300 v o n m is es r es id u a l s tr es s  v ,m (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c (a) 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n o rm a l r es id u a l s tr es s  x, x (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c (b) 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 n o rm a l r es id u a l s tr es s  y, y (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c (c) 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n o rm a l r es id u a l s tr es s  z, z (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c (d) fig. 3. von-mises and normal residual stress distribution along the vertical path (case without crack) engineering, technology & applied science research vol. 4, no. 3, 2014, 649-655 653 www.etasr.com nehari et al.: numerical study of the effect of the penetration of a crack in the matrix of a composite inclusion interface is noticed with the presence of the crack (as shown in figure 4). this increase is inversely proportional to the crack-inclusion gap. the simultaneous effect of the plasticity zone at the tip of the crack near the interaface and the strong stresses on the inclusion provoke an increase of the residual stresses under the effect of the temperature gradient. figure 5 displays the distribution of residual stresses in the vertical direction through the centre of the inclusion, in the presence of a longitudinal plane crack of width 'a = 5 m’. the gap between the tip of the crack and the particle (in the horizontal plane passing through the centre of the particle, see figure 1a) is noted as "d",. three gap values are considered namely d= 0.2, 0.5 and 2m. it should be noted that whatever the gap "d", the paces of the stresses vm, xx, yy and zz are almost similar under the effect of the temperature gradient with those without the presence of crack. the effect of the presence of the crack is negligible on the magnitude of stresses. gap d=0,2 d=0,5 d=2 v on m is es 0 0.2 0.4 0.6 0.8 1 normalized distance 0 100 200 300 v on m is es r es id u a l s tr es s  v ,m (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance 0 100 200 300 v o n m is es r es id u al s tr es s  v ,m (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance 0 100 200 300 v o n m is es r es id u al s tr es s  v ,m (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c  xx 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n or m a l r es id ua l s tr es s  x, x (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n o rm a l r es id u a l s tr es s  x, x (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n o rm a l r es id u a l s tr es s  x, x (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c  y y 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 n or m a l r es id ua l s tr es s  y, y (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 n or m a l r es id ua l s tr es s  y, y (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 n or m a l r es id ua l s tr es s  y, y (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c  zz 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n o rm al r es id u a l s tr es s  z, z (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n o rm al r es id u a l s tr es s  z, z (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n o rm al r es id u a l s tr es s  z, z (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c fig. 4. normal residual stress distribution along the vertical path in the case a=5 μm and for d=0.2, 0.5 ,2μm engineering, technology & applied science research vol. 4, no. 3, 2014, 649-655 654 www.etasr.com nehari et al.: numerical study of the effect of the penetration of a crack in the matrix of a composite fig. 5. interaction crack-particle(crack tip region) in the case (a=5µm, d=0.2 µm, t=300°c) concerning the effect the crack in the longitudinal direction, figure 6 shows the distribution of residual stresses along such direction (path) passing through the centre of the particle, in the presence of a longitudinal plane crack of width "a = 5μm" and for different temperature gradients (from 100°c to 600°c). as previously noted, "d" is the gap of crackinclusion (see figure 1a). we have considered three values of the gap (d=0.2, 0.5 and 2 μm). for the three cases of figure 6, we see that the four stresses vm, xx, yy , zz have the same shape, and variation under the effect of temperature gradient, but are invariable in gap d=0,2 d=0,5 d=2 v on m is es 0 0.2 0.4 0.6 0.8 1 normalized distance 0 100 200 300 v on m is es r es id u a l s tr es s  v ,m (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance 0 100 200 300 v on m is es r es id u a l s tr es s  v ,m (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance 0 100 200 300 v on m is es r es id u a l s tr es s  v ,m (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c  xx 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 n o rm a l r es id u a l s tr es s  x, x (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 n o rm a l r es id u a l s tr es s  x, x (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 n o rm a l r es id u a l s tr es s  x, x (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c  yy 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n o rm a l r es id ua l st re ss  y, y (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n or m a l r es id ua l s tr es s  y, y (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n or m a l r es id ua l s tr es s  y, y (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c  zz 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n o rm al r es id u a l s tr es s  y, y (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n o rm al r es id u a l s tr es s  z, z (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c 0 0.2 0.4 0.6 0.8 1 normalized distance -500 -400 -300 -200 -100 0 100 n o rm al r es id u a l s tr es s  z, z (m p a ) t=100 0c t=200 0c t=300 0c t=400 0c t=500 0c t=600 0c fig. 6. normal residual stress distribution along the longitudinal path in the case a=5 μm and for d=0.2, 0.5 ,2μm engineering, technology & applied science research vol. 4, no. 3, 2014, 649-655 655 www.etasr.com nehari et al.: numerical study of the effect of the penetration of a crack in the matrix of a composite comparison with the no-cracks case. in contrast, in the vicinity close to the particle, we notice that the penetration of the crack in the matrix causes an asymmetry of the stresses distribution due to the presence of the geometric discontinuity (crack). it is noted that the effect of the gap is more dominant for small and medium values and thus, a more significant asymmetry in the distribution of stresses vm and xx. concerning the extreme values of stresses, it is noted that the reduction of the gap affects only the stress zz which it falls slightly with the reduction of the "d" gap (or the increase penetration crack) iv. conclusion the objective of this investigation is to determine the influence of crack penetration and gradient temperature on the generation of residual thermal stresses and the subsequent mechanical behaviour for the al–sic composite. the present stuy is purely numeric and uses a three dimensional finite element method. the following conclusions are drawn from the results presented above:  the thermal residual stresses have high values in the inclusion and in close vicinity to the particle-matrix interface and decrease gradually as we move away from the centre of the inclusion until they vanish to the limit of the microstructure.  for the distribution of the stresses vm, xx, yy, zz along the vertical path, it is noted that whatever the gap "d", the profiles of the stresses are almost identical under the effect of temperature gradient with those found in a no-cracks case, and also the temperature gradient increases significantly the intensity of stresses specially for xx, yy, zz.  for the distribution of the four stresses (vm, xx, yy, zz) along the longitudinal direction belonging to the plane of the crack, we notice that they have the same shape and variation under the effect of the temperature gradient and similar to those found for the no-cracks case. on the other hand, in the vicinity of the particle we notice that the penetration of the crack in the matrix causes an asymmetry. furthermore, the values of these stresses are significantly higher compared with those obtainedfor the no-cracks case. this means that the crack generates an additional residual stress caused by stresses at the crack tip and the plastic strain in the matrix at close vicinity of the inclusion. references [1] d. j. chellman, s. l. langenbeck, “aerospace applications of advanced aluminum alloys”, key engineering materials, vol. 77–78, pp. 49–60, 1993 [2] m. shanthi, c. y. h. lim, l. lu, “effects of grain size on the wear of recycled az91 mg”, tribology international, vol. 40, no. 2, pp. 335338, 2007 [3] p. kenesei, a. borbély, h. biermann, “microstructure based threedimensional finite element modeling of particulate reinforced metal– matrix composites”, materials science and engineering a, vol. 387– 389, pp. 852–856, 2004 [4] m. surry, c. teodosiu, l. f. menezes, “thermal residual stresses in particle-reinforced /viscoplastic metal matrix composites”, materials science and engineering a, vol. 167, no. 1-2, pp. 97-105, 1993 [5] g. meijer , f. ellyin, z. xia, “aspects of residual thermal stress/strain in particle reinforced metal matrix composites”, composites part b: engineering, vol. 31, no. 1, pp. 29–37, 2000 [6] d. ouinas, b. bachir bouiadjra, n. benderdouche, “interaction effect of a main crack emanating from a semicircular notch and a microcrack”, computational materials science, vol. 43, no. 4, pp. 1155–1159, 2008 [7] d. ouinas, b. bachir bouiadjra, n. benderdouche, b. ait saadi, j. vina, “numerical modelling of the interaction macro–multimicrocracks in a plate under tensile stress”, journal of computational science, vol. 2, no. 2, pp. 153-164, 2011 [8] j. llorca, c. gonzalez, “microstructural factors controlling the strength and ductility of particle reinforced metal-matrix composites”, journal of the mechanics and physics of solids, vol. 46, no. 1, pp. 1–28, 1998 [9] j. llorca, j. segurado, “three-dimensional multiparticle cell simulations of deformation and damage in sphere-reinforced composites”, materials science and engineering a, vol. 365, no. 1-2, pp. 267–274, 2004 [10] j. segurado, j. llorca, “a new three-dimensional interface finite element to simulate fracture in composites”, international journal of solids and structures, vol. 41, pp. 2977–2993, 2004 [11] abaqus, user’s manual, 6.11, dassault systèmes simulia corp, 2011 [12] f. bouafia, b. serier, b. bachir bouiadjra, “finite element analysis of the thermal residual stresses of sic particle reinforced aluminum composite”, computational materials science, vol. 54, pp. 195-203, 2012 engineering, technology & applied science research vol. 7, no. 5, 2017, 2089-2093 2089 www.etasr.com vosoughi et al.: investigating appropriate financing methods in collaborative projects of water … investigating appropriate financing methods in collaborative projects of water and wastewater with ahp approach vandad vosoughi department of civil engineering nour branch, islamic azad university, nour, iran. vandadvosoughi@gmail.com heydar dashti nasserabadi department of civil engineering chalus branch, islamic azad university, chalus, iran dashti@iauc.ac.ir abbas babaei department of civil engineering nour branch, islamic azad university, nour, iran ababaei@iaunour.ac.ir abstract—a mix of public and private funding is employed worldwide to enable the construction of large public projects and even, in some cases, the work of public services. in this study, the selected methods of financing of participatory projects of water and water wastes were studied and prioritized. questionnaires and comments of experts were used along with ahp decisionmaking and expert choice software. different financing methods include: bot and boo and its types, the publication of bonds, foreign direct investment, the method of buyback, internal financing, current financing, development banks, barter transactions, new tax resources and foreign financing. results are shown and discussed and a final ranking is provided. keywords-financing; public-private partnership contracts; water and sanitation projects; ahp methods i. introduction with rapid population growth and the increasing need for drinking water and wastewater disposal, in most countries, the governments are obliged to carry out infrastructure projects. historically, public funds were used for such projects. however, the past years a mixed (public and private) funding is followed in most such cases [1]. the justification for private participation in the funding is the state’s financial situation, the ability to move forward multiple projects and the high expertise that private sector is supposed to offer [2]. the original contract is between the public and private parties. the participation contract is the risk divider between associated risks with the projects of the parties and is determined by the general conditions of the assignment, tariffs, and payments, regulations and performance standards for the design, construction, operation and maintenance of constructions. public private partnership (ppp) is a model in which, the government-sector in partnership with the private sector, attempt to design, implement, manage and support large projects [3]. public-private partnership includes a contract that takes place between a governmental agency and a private party in which the parties are involving in using their abilities and assets, to provide services and facilities and public use. in addition to the sources, the participation takes place in the risk sharing and harvesting interests [4]. ii. method layout scheme a research method includes the set of rules, the tools, the reliable and systematic ways for achieving solutions [5]. in this research, suitable financing methods for participatory projects of water and water waste projects are investigated, considering the special characteristics of such projects. for this purpose, some criteria for evaluating the types of financing methods is introduced and explained. ten such methods are chosen and indicators are introduced through a questionnaire handed to experts in this area. results are analyzed using expert choice software. a. effective indicators the effective indicators were identified using a set of literature review and case studies. 1) efectiveness area the effect's value of water and water waste projects on its climate conditions has a direct relationship with the desired objectives from the implementation of the plan. plans for water are designed for a specific region (directly) but the impact weighs in the whole country (indirectly), thus the effectiveness area is both the region and the country [6]. 2) fairness the fair term reflects the fact that the preparation of required funds to build infrastructure facilities should be divided fairly between the consumers. this means that everyone to the extent that benefited from this structure (direct and indirect users), must pay its fee [6]. from this perspective, the method of selling products is considered as the fairest method. as the payment groups to move away from the circle of direct consumers, the fairness value is reduced [6]. 3) effectiveness during the process of choosing a financing method, the impact on the project’s success and the development of the near engineering, technology & applied science research vol. 7, no. 5, 2017, 2089-2093 2090 www.etasr.com vosoughi et al.: investigating appropriate financing methods in collaborative projects of water … area is to be considered. however, additional care should be provided so that the extra costs are not imposed on the consumers [6]. correlating the level of satisfaction to the price is a well established method [7]. whatever the difference between the cost that satisfies the consumers and the actual cost, the consumers will most likely try to modify the conditions to their advantage [8]. in the ideal case that no difference is documented, the value of this index is set to 1. 4) financial sustainability the values of stability and sustainability of used resources are also to be considered (8). the main focus of the project executive is on the determining the fluctuations in the resources of the selected method. several factors are involved in causing these fluctuations and the result of activating these factors is imposing additional costs to the project. the most prominent risks during the financing of a project, can be divided into 5 main groups: political, financial, construction, risks, operational and market [8]. b. financing methods in this study, to evaluate the most appropriate method of financing, ten methods are considered. these are the following: (1) new tax resources, (2) current finance payback method, (3) barter transactions, (4) foreign investors, (5) bonds, (6) internal financing, (7) buyback methods, (8) bot, boo etc, (9) development banks, (10) foreign direct investment. c. familiarity with ahp analytical method analytical hierarchy process (ahp) method is a multicriteria decision-making technique. this method can be rather useful when faced with few options and decision criteria. indicators can be quantitative or qualitative. the basis of this method is pair comparisons [9]. the process of ranking and prioritization of options in ahp methods includes the following steps: 1) setting the hierarchy at this stage, the problem is defined and the purpose of decision-making is drawn with a hierarchy of factors and elements of the decision. for this purpose, a decision tree is used [9] (figure 1). fig. 1. making hierarchy determine the most appropriate method of financing 2) paired comparisons at this stage, the experts make comparisons between scales and sub-scales of decision making and determine its scores to each other. 3) calculation of relative weight the next step in the analytic hierarchy process (ahp) is the required calculations to determine the priority of any decision elements by using the information of the matrixes of paired-calculations. 4) the final weigh of options the final weight of options is obtained from the sum of criteria importance in the weight of options (9). 5) calculation of data validation (incompatible rates) inconsistency rate (i.r.), is a mechanism by which the validity of the answers of respondents to the pair wise comparisons is measured. almost all the ahp calculations based on a preliminary judging decision that appears in the form of pairwise comparison matrix and any error and incompatibility between options and indicators would skew the final obtained results of calculations [9]. d. questionnaires 1) structure the questionnaire includes a set of frequently asked questions that by utilizing various scales, comment, perspective, and insight of individuals assesses the respondent. the measurement scale is a set of principles for assigning the subjects to the category or assigning the figures to the subjects. the relative scale has been chosen as the used scale in the questionnaire. relative scale is the most precise scale for measurement. this scale has a value of true zero that is a point on the scale that shows a complete shortage of the features on measurement. by this scale either the difference between the figures and their relative importance could be compared [10]. engineering, technology & applied science research vol. 7, no. 5, 2017, 2089-2093 2091 www.etasr.com vosoughi et al.: investigating appropriate financing methods in collaborative projects of water … 2) validity standard questionnaires were used in this study and after receiving the comments of the experts in the stage of validation, the accuracy, clarity, and transparency of made questions, were revised and the questionnaires were prepared for distribution. 3) the sample size in order to obtain the opinions of the experts, 20 questionnaires were distributed between them. among the distributed questionnaires, 14 of them were returned. 5 numbers of questionnaires due to defects in completion and improper method of inserting information were excluded from the analysis process. therefore, the analysis was conducted on the remaining 9 questionnaires. 4) limitations in information gathering data collection from different experts involved in different projects is bound to face constraints due to confidentiality. personal involvement is also an issue. 5) reliability one of the most well known methods for calculating reliability is using cronbach's alpha. the method is used for calculating the internal consistency of measurement tools, including questionnaires. cronbach's alpha has been used to determine the reliability of the questionnaire with emphasis on internal consistency. provided that the alpha coefficient is more than 0.7 the test has acceptable reliability. 6) analysis of questionnaire data the ahp method is used for converting the qualitative comments of experts to quantitative values that can be calculated and compared. for ranking, all questions were summarized in the form of four separate matrices, then the different ahp methods were implemented on the data. the raw data was analyzed using expert choice software. iii. results the expert choice software results for each of the comparison criteria and for the questionnaire of ahp coefficient is shown in figures 2 to 6 and tables i to v. as it can be seen the participatory methods such as bot, boo have the highest value. the mean, variance and standard deviation (std) of the available data for each indicator are also calculated. an overall comparison is given in figure 7. iv. conclusion in this study, ten methods of financing for water and water wastes projects were studied and prioritized. questionnaires were used along with ahp decision-making and expert choice software. the final ranking is as follows: (1) bot, boo etc, (2) bonds, (3) foreign direct investment, (3) buyback, (4) internal financing, (5) current financing, (6) developmental banks, (7) barter transactions, (8) new tax resources, (10) financing from foreign finance. fig. 2. ranking based on effectiveness fig. 3. comparison fig. 4. ranking on fairness fig. 5. ranking on financial sustainability fig. 6. percentage of ahp coefficients for each of the financing methods engineering, technology & applied science research vol. 7, no. 5, 2017, 2089-2093 2092 www.etasr.com vosoughi et al.: investigating appropriate financing methods in collaborative projects of water … table i. ahp coefficients derived from the analysis criteria 9 8 7 6 5 4 3 2 1 number of questionnaire 0.379 0.187 0.08 0.99 0.056 0.17 0.078 0.073 0.064 effectiveness 0.508 0.07 0.609 0.537 0.62 0.123 0.205 0.205 0.237 fairness 0.113 0.743 0.311 0.364 0.324 0.707 0.722 0.722 0.699 sustainability table ii. total obtained ahp coefficient for each financing method f o re ig n f in an ce n ew t ax r es o u rc ed c u rr en t fi n an ce b o n d s f o re ig n d ir ec t in v es tm en t b u y b ac k b ar te r tr an sa ct io n s in te rn al f in an ce f in an ci n g b y d ev el o p m en ta l b an k s b o t ، b o o e tc financing method number of questionnaires 0.049 0.068 0.083 0.137 0.03 0.169 0.012 0.102 0.108 0.239 1 0.045 0.068 0.088 0.147 0.033 0.167 0.014 0.103 0.104 0.239 2 0.036 0.06 0.11 0.149 0.046 0.156 0.017 0.112 0.083 0.208 3 0.025 0.068 0.145 0.173 0.094 0.118 0.03 0.125 0.031 0.193 4 0.025 0.071 0.145 0.166 0.094 0.121 0.034 0.122 0.034 0.194 5 0.027 0.066 0.141 0.182 0.09 0.115 0.04 0.109 0.038 0.198 6 0.023 0.062 0.128 0.183 0.115 0.09 0.048 0.138 0.06 0.153 7 0.026 0.072 0.14 0.2 0.124 0.107 0.056 0.144 0.064 0.16 8 0.023 0.077 0.122 0.168 0.12 0.108 0.052 0.139 0.062 0.138 9 fig. 7. overall comparison table iii. the scores of comparing indexes sustainability fairness effects average score for each indicator 0.467 0.346 0.132 percentage of each indicator 49.4 36.60 14 table iv. comparing indices sustainability fairness effects variance 0.052 0.043 0.0096 standard deviation 23.47 % 20.67 % 9.78 % engineering, technology & applied science research vol. 7, no. 5, 2017, 2089-2093 2093 www.etasr.com vosoughi et al.: investigating appropriate financing methods in collaborative projects of water … table v. the values of mean, variance and standard deviation for financing methods financing method mean var std (%) financing method mean var std (%) bot, boo etc 0.17 0.0011 3.38 internal finance 0.10 0.0012 3.4 bonds 0.13 0.001 3.16 buyback 0.08 0.0006 2.5 current finance 0.12 0.001 3.16 foreign direct investment 0.07 0.0014 3.7 development banks 0.11 0.0009 3.02 using foreign finance 0.07 0.0003 1.7 new tax resources 0.11 0.00055 2.54 barter transactions 0.04 0.003 1.7 references [1] m. g. r. h. falamaryzi, “the treaty on public-private partnership (public-private partnership) in infrastructure projects”, sixth international conference on project management, tehran, iran, 2010. [2] management and planning organization, public-private partnership framework agreement, 201. [3] h. ashkuh, m. h. sobhieh, h. s. zargarpur, p. zarabad, “the challenges of financing power projects in public-private partnership”, sixth conference of financial system development in iran, tehran, iran, 2013 [4] s. m. mousavi, m. ahmedi, r. farhadi, “pathology providing publicprivate partnership approach”, municipal finance conference, tehran, iran, 2010 [5] e. seyed hoseini, review of contracts in the free zones development projects (case study: kish free zone), msc thesis, university of isfahan (khorasgan), iran, 2015 [6] m. a. saglio, financing public infrastructure in the united states and france; a comparative analysis and policy recommendations, msc. thesis, massachusetts institute of technology, usa, 1995 [7] j. krajne, “cost recovery vs. marginal social cost toll calculation motorway operator's perspective", secap pula, 2006, slovenia. [8] m. s. miri,. new methods of financing highway projects and provide appropriate manner, msc thesis, civil engineering and construction management engineering, university of technology (tehran polytechnic), 2008. [9] s. h. qodsipour, discussions on multi-criteria decision-making, amir kabir university press, 2002 [10] m. r. ebrahiami,”financial and economic evaluation”, committee report no. 9 pyark, publications center of higher education and research institute for management and planning, 2004. microsoft word etasr_v12_n2_pp8421-8425 engineering, technology & applied science research vol. 12, no. 2, 2022, 8421-8425 8421 www.etasr.com saxena & roy: suitability analysis of stone column materials with plaxis suitability analysis of stone column materials with plaxis shivangi saxena department of civil engineering national institute of technology patna, india shivangisaxenacivil0049@gmail.com lal bahadur roy department of civil engineering national institute of technology patna, india lbroy@nitp.ac.in received: 17 january 2022 | revised: 21 february 2022 | accepted: 27 february 2022 abstract-stone columns are usually provided in groups to support various geotechnical structures, such as embankments, storage tanks, etc. several experimental and numerical studies have been performed to study the response of stone columns as soil reinforcement. for relatively moderate loading of a structure, application of stone columns either singly or in groups is widely used. the enhancement of strength of the soil is governed by the type of original subsoil and the properties of the coarse aggregate materials used for the stone columns. several researchers have analyzed different coarse-grained materials using various plane strain approaches to model the stone columns. this article deals with the non-linear analysis of an isolated stone column embedded in a semi-infinite medium of sandy soil. the parameters which crucially affect the settlement characteristics and the bulging failure of stone columns have been determined. the suitabilities of two different natural aggregates, pebble gravels, and crushed pebble gravels as materials for the stone column have been compared on the basis of their settlement behavior using 2d numerical modeling with the plaxis software. keywords-soil improvement; stone columns; numerical modeling; natural aggregates i. introduction engineers face challenges due to the presence of low bearing soils. these marginal soils have low bearing capacity and high compressibility characteristics. in order to make these marginal soils suitable for construction, ground improvement techniques need to be applied [1-3]. stone column is such a technique to treat the weak soil. stone columns are constructed by compacting coarse aggregates in bore holes. granular stone columns have been used as a soil reinforcement technique for soft clay improvement to improve the bearing capacity of the native soil [4, 5]. an analytical method to assess the stone column load bearing mechanism for calculating the immediate settlement and rate of consolidation for stone columns embedded in soft soil was developed in [6, 7]. the ultimate bearing capacity of columns depends on the geometry of the column, its material properties, and the properties of the soft soil. the effect of the length of the stone column is almost negligible on bearing capacity because most of the load is transferred from the column to the surrounding soil through sides and very little load is transferred to the bottom which is similar to the effects of piles in granular soil [8-12]. the general range for the diameter of the stone column ranges from 0.9 to 1.2m and the length of stone column from 4 to 10m [13, 14]. bulging failure is most common in long columns where, length to diameter (l/d) ratio is more than 4 to 6 [15]. various researchers have analyzed the failure of reinforced ground. the numerical modeling of a single and a group of stone columns has been analyzed using finite element software in [16-20]. three different coarse grained materials were analyzed in [21] to assess their suitability for stone column materials by performing large scale site tests and laboratory tests. important results from these works have been considered as input properties in the model presented in this study to analyze the behavior of pebble gravels and crushed pebble gravels as stone column material. ii. experimental setup and material properties several in-situ and laboratory tests were performed by the authors in [21] to determine the properties of soft soil and coarse-grained aggregates used in the analysis of stone columns. they determined the bulk density of natural aggregates using pit tests on already existing columns. the density index of the stone columns was determined in the laboratory. the obtained results from the tests are presented in table i. to find the shear strength properties of column material, direct shear test was performed. the dimensions of the apparatus were 300×300mm with a height of 200mm. shear stresses have been calculated by applying normal stresses with 50kn/m 2 increments. the angle of internal friction for pebble gravel was calculated to be 50° and it came out as 52° for the crushed pebble gravel. the influence of angle of shear (φ), l/d ratio, and undrained cohesion (cu) have been considered in parametric study section. the analysis is followed by different materials study and the load – settlement curve. iii. problem statement two dimensional linear finite element models were used to analyze the behavior of stone column in clay soil. stone columns with two different granular materials were used in two separate cases. the analysis was carried out with pebble corresponding author: shivangi saxena engineering, technology & applied science research vol. 12, no. 2, 2022, 8421-8425 8422 www.etasr.com saxena & roy: suitability analysis of stone column materials with plaxis gravels and crushed pebble gravels. the elementary boundary condition has been used for the analysis where radial deformation (ux = 0) is restricted but settlement is allowed. fixity condition was applied at the bottom of the model i.e. ux = 0, uy = 0. the stone column is modeled as axisymmetric and mohr-coulomb’s criteria considering elasto-perfectly plastic behavior for soft clay were considered. drained condition is assumed for both aggregates. table i. material properties [21] parameter unit materials clay pebble gravel crushed pebble gravel γ kn/m 3 19 18 17.36 γsat kn/m 3 20.45 19.9 19.55 eoed kn/m 2 5170 45300 65800 φ o 26.6 49.9 51.8 ψ o 0 19.9 21.8 c kn/m 2 10.8 1 1 kx = ky m/day 0.01037×10 -3 864 864 µ 0.355 0.23 0.23 properties of loading plate normal stiffness (ei) 5×10 6 kn/m flexural rigidity (ea) 8500knm 2 /m it was considered that sufficient time has passed since the load has been applied, hence stress concentration and settlement have become steady. at the junction of stone column and soft clay there is no interface element due to deformation. this is found to occur mainly due to the radial bulging of the stone column. finite element analysis for the stone column without considering any interface material has been performed in [22, 23]. figure 1 shows the geometrical dimensions of the model problem. the model geometry is 325mm×350mm. length and diameter of the stone columns were taken as 225mm and 25mm respectively. stone columns are provided at the center of the clay bed and loading has been done through a flat plate double the size of the stone column. displacement of 75mm is applied at the top of the stone column. fig. 1. problem dimensions. iv. numerical model finite element linear elastic-perfectly plastic analysis is carried out in the clay medium soil. mohr-coulomb’s material model is used to observe the response of clay and stone column. according to the mohr-coulomb failure criteria, when the shear stress on the soil element becomes equal to the critical value of stress, then the soil will fail. in mohrcoulomb, effective cohesion (c) and effective internal friction angle (φ) are modeled for both types of behavior, drained or un-drained. to do an effective stress analysis of the soil, friction angle and effective cohesion are taken in terms of effective stress. the total stress analysis value of cohesion parameter has been taken equal to the un-drained shear strength of the soil, in combination with φ equal to 0 o . the finite element program plaxis v8 was used for the analysis. the stone column and clay soil were modeled as axisymmetric 2d structures. the finite element mesh is generated with 15-node triangular elements having fine mesh size. there are 3 types of loading that can be applied in plaxis: (i) distributed load, (ii) point load, (iii) prescribed displacement, which provides more information to draw the load-settlement response, so it is considered as the loading type in this study. since we are using axisymmetric model, 2π is multiplied with the load recorded by the plaxis to get the actual load in the field. plaxis has the fixities option to apply the boundary condition. v. results a. analysis for stress concentration gravel pebbles and crushed gravel pebbles were used as materials for the stone columns and their effectiveness was analyzed on the basis of their stress concentration and settlement occurring in the stone column-soil system up on the application of load. 1) using pebble gravel as stone column material effective stress analysis was carried out and the deformation behavior of the finite elements was observed. figure 2 shows the deformed mesh at the failure when pebble gravel is used as stone column material. the extreme total displacement in the deformed shape is 50.68mm. the value is observed on scale factor of 0.5. the length of each line represents the magnitude of principal stress and the direction indicates the principal direction. the observed effective principal stress is 3.42×10 3 kn/m 2 as shown in figure 2(b). 2) using crushed pebble gravel as stone column material figure 3 shows the deformed mesh at failure. extreme total displacement in the deformed mesh is 38.71mm. here, total displacement means absolute accumulated displacement combined from the horizontal and vertical displacement components at all nodes at the end of the calculations. the relative deformation decreases by almost 31% in case of crushed pebble gravels. the stress concentration is less localized in the case of crushed pebble gravels. hence, crushed pebbles gravel is more suitable material for stone column than pebbles gravel. the observed effective stress is 2.5×10 3 kn/m 2 as shown in figure 3(b). b. analysis for load-settlement curve load settlement behavior was monitored in order to find out the most suitable material for stone columns. based on the axial stress developed in the stone column and the settlement behavior, it can be concluded that stone column reaches the engineering, technology & applied science research vol. 12, no. 2, 2022, 8421-8425 8423 www.etasr.com saxena & roy: suitability analysis of stone column materials with plaxis failure stage at the top. settlement behavior of stone column with respect to load on the top of stone column is shown in figure 4. it can be observed from the load-settlement curve that the stone column with pebble gravels settled more than the stone column with crushed pebbles gravel for the same value of stress. crushed pebble gravel can be treated as a more suitable material for stone column than pebble gravels. (a) (b) fig. 2. pebble gravel deformation and principal effective stress: (a) deformed mesh, (b) effective stress contour. c. parametric study the physical parameters of the stone columns, φ, l/d ratio, and cu of soft clay are varied to study their influence on the load settlement behavior of stone columns. 1) angle of internal friction of granular material figure 5 shows the influence of the angle of internal friction (φ) of natural aggregates on the load-settlement behavior. this effect has been shown by varying φ from 47.9° to 51.9°. (a) (b) fig. 3. crushed pebble gravel deformation and principal effective stress: (a) deformed mesh, (b) effective stress contour. fig. 4. stress vs settlement curve for different materials. engineering, technology & applied science research vol. 12, no. 2, 2022, 8421-8425 8424 www.etasr.com saxena & roy: suitability analysis of stone column materials with plaxis fig. 5. stress-settlement curve for different values of φ. with increase in the shearing angle of the granular material, the settlement value of the stone column material is reduced for a particular value of load. this is mainly due to the increase in shearing resistance offered by the granular material with increase in φ. at the same time, for lower values of stress, the angle of internal friction does not influence the settlement of stone column significantly. 2) undrained cohesion of clay bed the behavior of load settlement curve is analyzed in figure 6 with increments of 2kn/m 2 in the value of undrained cohesion of the soil. cu ranges from 8.8kn/m 2 to 12.8kn/m 2 . fig. 6. stress-settlement curve for different values of cu. 3) l/d ratio to study the effect of l/d ratio on the load settlement behavior, the l/d ratio varied from 2 to 9 (figure 7). it is observed that when the l/d ratio is increased, the settlement of stone column is decreased for the same applied load up to l/d = 4. after l/d = 4, there is no significant decrease in the settlement. vi. discussion the comparison of different types of coarse-grained materials explains the utility of pebble gravels and crushed pebble gravels for stone columns. no such previous work has been carried out on the above specified aggregates, hence the study is unique within the area of stone columns. the results obtained from the current study state that the effect of the angle of internal friction, the undrained cohesion of surrounding clay, and the l/d ratio on the load settlement response are approximately the same with the findings in [3, 21]. fig. 7. stress-settlement curve for different values of l/d ratio. vii. conclusions the increased requirement for ground improvement by stone columns led to the incorporation of various types of natural aggregates as material for stone columns. the comparative analysis of the load-settlement response for gravel pebbles and crushed pebble gravels shows that: • relative deformation and settlement in the case of crushed pebble gravels are less than those imposed by pebble gravels. hence, crushed pebble gravels are more efficient as a material for stone columns in soft soils. • the settlement tendency of stone columns on the application of load was found to decrease with the increase of the angle of internal friction. • when the value of undrained cohesion of the surrounding clay increases, the settlement of the stone column for the same value of load decreases. • with the increase in the value of the l/d ratio, the settlement of the stone column for the same value of load decreases and there is no significant response on the load settlement curve of the stone column when the l/d ratio is increased beyond 4. references [1] n. p. balaam and j. r. booker, "analysis of rigid rafts supported by granular piles," international journal for numerical and analytical methods in geomechanics, vol. 5, no. 4, pp. 379–403, 1981, https://doi.org/10.1002/nag.1610050405. 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[23] j. t. shahu and y. r. reddy, "clayey soil reinforced with stone column group: model tests and analyses," journal of geotechnical and geoenvironmental engineering, vol. 137, no. 12, pp. 1265–1274, dec. 2011, https://doi.org/10.1061/(asce)gt.1943-5606.0000552. engineering, technology & applied science research vol. 7, no. 5, 2017, 1980-1986 1980 www.etasr.com jakhrani et al.: analysis and fabrication of an active cooling system for reducing photovoltaic … analysis and fabrication of an active cooling system for reducing photovoltaic module temperature abdul qayoom jakhrani department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan aqunimas@hotmail.com abdul rehman jatoi department of energy and environment engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan arjatoi@quest.edu.pk sadam hussain jakhrani department of civil engineering comsats institute of information technology, sahiwal, punjab, pakistan sadamhussain@ciitsahiwal.edu.pk abstract—the purpose of this study is to fabricate and analyze an active cooling system for reducing photovoltaic (pv) module temperature and increasing its efficiency. an active cooling system was devised to cool the pv module. two modules of same specifications were used for this study. one module was cooled, and other was left un-cooled for performance comparison. solar radiations, wind speed, ambient temperature and temperatures at different points of the fabricated system were measured. the modules were mounted on a frame facing true south at the inclination of the latitude of the location. the measurements were taken during daytime with one hour intervals for two weeks. the temperatures at various points on cooled and un-cooled photovoltaic modules were noted using two different flow rates with 1 lit/min and 2 lit/min. it was discovered that the efficiency of pv module was enhanced from 6% to 7% during study period. the flow rate of 1lit/min was found more feasible for heat extraction as compared to the flow rate of 2lit/min. the wind speed was found to be more helpful for heat extraction from the modules as compared to other climatic parameters. keywords-active cooling system; photovoltaic module; module temperature i. introduction solar energy is an environmental friendly source of electric power generation and at the same time cannot be affected by escalation of fuel price. a solar photovoltaic (pv) system converts sunlight directly into electricity. it comprises of cells, modules, panels, arrays and other auxiliary components, such as storage batteries, inverter/convertor and charge controller. solar cells are fundamental component of pv systems. a solar cell is a tiny semi-conductor device which has a light sensitive p-n junction. when solar radiation hit the p-n junction, dc electric motive force is generated with p-terminal as positive and n-terminal as negative. a single solar cell has a rated voltage of about 0.45 volts dc, current of about 0.75 amperes dc, and a rated power of 0.33 watts [1]. when the cells are arranged in series or parallel or combination of both constitute a solar photovoltaic module or panel. photovoltaic modules usually have a glass pane on the sun-facing side, permitting light to pass through its cover and shielding the semiconductor wafers from deterioration. solar cells for remote applications are normally made from silicon as single-crystalline, polycrystalline or amorphous solids, however, thermophotovoltaics are also in research and development stage and may be commercialized soon. the monocrystalline cells are made up of single-crystalline silicon that has a distinct continuous crystal lattice structure with almost no defect of impurities. although, it is more expensive to manufacture, it has higher efficiency of around 15% compared to its counterparts. polycrystalline cells are produced using several particles of single-crystalline silicon, and they have more disarranged atomic structure, leading to lower efficiency of about 12%. these are less expensive and more resistant to degradation due to irradiation. in amorphous or thin film silicon cells, the silicon particles are spread over the transparent surface. an amorphous silicon cell is composed of silicon atoms in a thin identical layer and absorbs light more effectively than crystalline silicon. these cells have lower efficiency of around 6%. for thin film cells, a very thin layer of silicon is required with a mixture of another material like glass for holding the silicon. at present, the efficiency of commercial thin film modules is around 5-7% [1-5]. moreover thermophotovoltaics are photovoltaic devices that use infrared radiations. besides the above type of cells, numerous other favorable materials, such as cadmium telluride and copper indium diselenide are used currently for photovoltaic applications [3]. a. working principle of photovoltaic cell photovoltaic cell is a light sensitive, two terminal semi conducting n-p junctions, made up of semi-conducting material such as silicon. a solar cell has two layers, one is n-type and other is p-type and two subsequent electrodes, negative and positive. n-type material is achieved by the doping silicon crystal with n-type impurity, whereas, p-type material by doping silicon crystal with p-type impurity. p-type layer is engineering, technology & applied science research vol. 7, no. 5, 2017, 1980-1986 1981 www.etasr.com jakhrani et al.: analysis and fabrication of an active cooling system for reducing photovoltaic … thick and the n-type layer is thin and ostensible. when the sun light hit the n-type thin layer, some of the waves of light energy enter up to p-type layers. the electrons are freed from n-type material and holes are created in p-type material. the electrons are negatively charged and holes are positively charged. when external electric circuit is finalized by joining electrodes to the load, the electrons flow in the closed external circuit from ntype terminal (-ve) to p-type terminal (+ve). the direction of current, by conversion, is from (+ve) terminal p-type to (-ve) terminal n-type in the external circuit, thus, electron hole pairs are generated within n-p junction regularly during the incidence of the sun-light [2-4]. hence, energy from solar rays is captured by photovoltaic cells and is converted directly to electrical energy [4]. b. power output of photovoltaic modules power output is an important factor to be considered for selection of photovoltaic (pv) modules. the performance of pv modules is a function of the amount of available and received solar radiation, ambient temperature and air mass. the power output of pv modules is almost proportional to the sun’s intensity. at a given solar intensity, the output current and operating voltage of pv module can be determined with the help of load characteristics. if that load is a battery, then its internal resistance will govern the module’s operating voltage. the photovoltaic energy generation and the corresponding efficiency of pv modules can be defined as the ratio of the output energy produced by the pv modules to the incident solar radiation. the principal advantages of pv systems includes low maintenance cost, zero operation cost, conservation of energy, protection of environment, no noise production and more reliable as compared to other power generating sources. it is reported that a photovoltaic system installed with a maximum power output of 1 kw for an entire year period, can save around 1300 kwh of electrical energy and 800 kg of co2 emissions [4-5]. c. factors affecting performance of photovoltaic modules the performance of pv modules can be evaluated from the performance of its components which can be affected by climatic factors and associated losses. the rated power of pv modules are homogenized under standard test conditions, stc, with the solar irradiance of 1000 w/m2, air mass of 1.5 and temperature of 25°c. nevertheless, the outdoor environment is varied due to random nature of climatic conditions [4]. the solar energy reaching earth’s surface is equivalent to 1367 w/m2, which is almost constant. however, many factors contribute the efficiency loss of pv modules except the reflection of clouds and earth’s own surface as given in table i [5-6]. d. influence of temperature on photovoltaic modules the operating temperature is one of the most important parameters in the conversion process of photovoltaic cells. as the cell temperature increases there is reduction of its voltage output. since the output current is quite stable, the drop of voltage leads to a decrease of electrical conversion efficiency. photovoltaic cells perform better in cold rather than in hot climate. for each degree rise in temperature above 25ºc, the pv module output decays nearly 0.25% for amorphous and around 0.4-0.5% for crystalline (mono or poly) cells. it shows that the pv modules will produce 25% less power as compared to the rated power of 25ºc. thus, a 100 w module will produce only 75 w in hottest months when temperatures reach up to 45ºc or more. photovoltaic modules are made by the assemblage of solar cells, which operate as a quantum device exchanging photons for electrons. the output of solar cells is affected by various external (climatic) and internal (material properties) factors. the open circuit voltage, voc, and short circuit current, isc, depends upon the solar irradiance and the temperature as shown in 1 and 2. o sc oc i i q kt v ln (1) bhi sc  (2) where, io is the saturation current, q is the electronic charge k is the boltzmann constant, t is the absolute temperature, h is the incident solar radiation and b is a constant depends on the properties of the semiconductor material [7]. ominously, a pv module converts only 6-20% of the incident solar radiation into electricity, the rest is converted into heat, which significantly increases the temperature of the module and reduces its efficiency. several researches have been carried out in order to discover the effect of temperature on the efficiency of pv modules and to reduce its consequences. table i. factors affecting performance of pv module effect range temperature 1-10 % incidence angle 1-5 % solar spectrum 1-3 % mismatch 2% soiling 0-15 % snow and shading location dependent ageing 5% over lifetime power rating 0-5 % or more diodes & wiring 3% e. methods for reducing temperature of pv module a decrease in the pv module temperature will lead to an increase in electrical efficiency. the efficiency which drops with the rise of temperature is approximately 0.5%/°c. increase in electrical efficiency is mainly dependent on different cooling techniques, types and size of the module, geographical location/position and season of the year. the construction and maintenance of cooling systems are main issues. these expenses may outweigh the benefits of the improved electrical yield. therefore, care must be taken at the time of selection and implementation of any cooling method. the two most famous engineering, technology & applied science research vol. 7, no. 5, 2017, 1980-1986 1982 www.etasr.com jakhrani et al.: analysis and fabrication of an active cooling system for reducing photovoltaic … pv cooling methods comprise of either passive or active techniques. passive cooling uses natural convection/conduction to enable heat extraction, whereas, the active cooling consumes energy (pump, fan, etc). 1) passive cooling techniques passive cooling is a natural technique for heat dissipation and modulation without utilization of energy source or power. the procedure involves transporting heat from where it is generated and dissipating it to the environment. the simple passive cooling techniques include the use of high thermal conductivity metals (aluminum and copper), or fins or other extruded surfaces to enhance heat transfer to the ambient atmosphere. the complex systems comprised of the phase change materials (pcms) and use of heat pipes to transfer heat efficiently through a boiling-condensing process. passive cooling techniques can be further divided into three categories: air passive cooling, water passive cooling and conductive passive cooling. authors in [8] studied the behavior of polycrystalline pv cells in controlled conditions. for that, two pv cells were used, one with aluminum fins as a heat sink with thermal grease and other without a heat sink. illumination was varied from 200 to 800 w/m2. a relative increase in electric efficiency of 9 % has been gained via usage of passive cooling with a heat sink. authors of [9] reported that the depth of flow channel beneath pv cells has significant influence on passive cooling, for larger pv surface (1.95 m2). it has been shown that, for a length-to-depth ratio of 0.085, the pv module heats up by 5-6°c when compared with a pv module on a regular mount. it has been noted that the temperature difference rises with the increase of insulation. in other words, passive flow channels can have the reverse effect on pv module cooling. a special type of passive conductive cooling is phase change material cooling, pcm, which is considered as a complex type of cooling. although this can’t be viewed as cooling in the strict sense, it keeps maintaining the same temperature. it can still be counted as a passive technique mainly because of the fact that no additional work or energy is needed to take away the heat-it is dissipated mostly conductively. author in [10] reported that the use of proper pcm material could decrease 15°c temperature of pv cell as compared to reference conditions and with the insolation of 1000 w/m2. pv modules with nominal power of 65w were used, with 50 mm of pcm material from the back, with vertical aluminum fins to enhance conduction. the power gained was more than 9.7 % from a reference pv module. authors in [11] investigated the performance and costs for a passively cooled, single cell high concentrated pv receiver, whose concentration range is between 100 and 1000. it has been found that aluminum performs better than copper as a heat sink material. the optimized finned heat sinks made of aluminum have shown the ability to keep a 3mm x 3mm cell temperature below 60°c and 80°c degrees under standard conditions of 1000 w/m2 with material costs of 0.57$/wp and 0.18$/wp, respectively. in [12] the operating temperature of pv modules were reduced by means of ribs at different angles. moreover, the temperature of the pv module was also decreased using heat sinks, which accounted the reduction of 10°c from the base case. thus, the maximum power produced was more than 90% of the nominal one. authors in [13] investigated thermal and electrical performance of flat pv module with cotton wick cooling system in combination with water, al2o3/water nanofluid and cuo/water nanofluid. they have got module temperature reduction in between 11% and 17% as compared to the module temperature obtained without cooling. 2) active cooling techniques active cooling systems involve the use of energy and consume power in order to cool the photovoltaic module. in this system, a coolant is used to circulate and transfer heat from one place to another. the coolant is either a gas (air) or a liquid (water or other chemical). in the case of liquid, this in turn is cooled by passing air over it. most of the methods are based on the air or water cooling. hence, the main consumption system is pump or fan needed for maintaining fluid circulation. in general, active cooling systems give more production of power and thermal energy, however, power is also consumed in the system itself, which must be taken into account. authors in [14] worked on the cooling of four polycrystalline modules with the rated power of 55 w from back side. the surface of pv module was 0.78 m2. special flow channel was made and cfd analysis was used to optimize its shape. total efficiency gain was around 1%, depending of the solar irradiation. optimal air flow beneath the panel was 0.055 kg/s, although no ambient temperature was given. this information is therefore reliable only for this specific case. nevertheless, it can be valuable when trying to evaluate the amount of air needed to cool down the standard pv module. as for water cooling, two distinct techniques can be applied, for example, front side and back side cooling. authors in [15] created a thin water film at front side of a monocrystalline pv module and gained total efficiency increase of about 1%. the total area of module was 0.44 m2 and maximum water flow was kept around 1 lit/min. the pump used for circulating water was 0.25 hp. a decrease in temperature of 20°c was achieved. they did not mention the amount of heat taken off by evaporation, which should be taken into account when cooling is done from the front side. authors in [16] worked on the active cooling technique for concentrated monocrystalline pv cell of 0.152 m2. the concentration was at the intensity of 8.5 suns. the cooling technique used was back side cooling via two aluminum pipes on aluminum mounting. peak efficiency gain was 0.8 % for mass flow of 0.035 kg/s of water. peak pv temperature was around 60°c. authors in [17] performed an experimental work on the cooling of a monocrystalline pv module with an area of 1.24 m2 from back side, via closed casing through which a flow of water was established. in experiment, a jet entrainment of water was considered. water pump demanded 0.5 hp at the maximum mass flow of 0.06 kg/s. the maximum efficiency obtained was 2.8 % as compared with non-cooled module with a decrease of 10°c in pv module temperature. considering the size of the module, the rise in efficiency was significant and a substantial change in temperature was achieved. authors in [18] worked on active cooling of pv module by passing the water on the surface of the module. they used monocrystalline pv panel of 1.25 m2 surfaces, and cooled it with a water flow on the front side of the panel. the pump demand was around 1 hp. flow of the water was fixed at 0.48 kg/s. the cooling was made in intervals of 5 minutes, with 15 minute pauses. the engineering, technology & applied science research vol. 7, no. 5, 2017, 1980-1986 1983 www.etasr.com jakhrani et al.: analysis and fabrication of an active cooling system for reducing photovoltaic … cooling rate was found 2°c/min. the total increase in efficiency, as a result of cooling was about 1.5%. it was proposed that an optimal temperature for cooling initiation should be 45°c. the front of the panels should be cleaned, especially for dusty regions such as sahara or middle east. solar energy is one of the cheap, ever-present and environmental friendly sources of energy. it can be utilized for generation of heat, and electricity either by means of thermal technologies or pv modules. however, the power out of photovoltaic modules is being affected externally by climatic factors or internally by module materials. moreover, the performance can also be decreased by the heat buildup beneath the pv modules, which may lead to decrease electrical power output and life span of module. therefore, cooling of pv modules not only increases the power output of pv module but also life of these generating units. ii. materials and methods a. materials and instruments the materials used for fabrication and installation pv module cooling system were monocrystalline module, air duct, heat exchanger, thermoset, silicone gel, water tank, water pump, metal stand and structure. two monocrystalline pv modules, each with a rated power of 10 w were used for this study, and their electrical characteristics are given in table ii. the materials for metal stand include metal rods, pulley, screws, bearings, frame etc. duct fitted with silicon jell on the stand. an electrical switch button was made up of plastic used to turn on and off the data logger and motor when they were not in use. the instruments used for the analysis were data logger, anemometer and lux meter. an arduino uno r3 data logger was used for data logging purpose and its specifications are shown in table iii. table ii. specifications of monocrystalline pv module type solar module model jh10-18m rated maximum power 10 watt rated voltage 9 volt rated current 1.11 ampere opened-circuit voltage 10.8 volt short-circuit current 1.19 ampere table iii. specifications of arduino uno r3 datalogger parameters description microcontroller atmega328 effective voltage 5 v suggested input voltage 7-12 v voltage limit 6-20 v digital input/output pins 14 (of which 6 provide pwm output) analog input pins 6 dc current per input/output 40ma dc current for 3.3 v pin 50ma flash memory 32kb (atmega328) of which 0.5 kb used by boot loader sram, eeprom 2kb (atmega328), 1kb (atmega328) clock speed 16mhz the sensors were pasted at different points on the fabricated system to examine pv modules temperature, water inlet and outlet temperature from radiator, heat exchanger temperature and air temperature when existing from pv module. the unit was interfaced with computer to store data. the data from the digital logger was stored in a memory card. the data of memory card was extracted through a computer and were further analyzed. a digital anemometer, model prova avm05 was used, its specifications are given in table iv. solar radiations were measured with the help of a lux meter on horizontal as well as on tilted surface. the fabricated system was installed over the roof of energy and environment engineering department, nawabshah. the system was placed at latitude angle facing true south with the help of compass as shown in figure 1. fig. 1. fabricated active cooling system. b. procedure adopted for data recording the installed unit was oriented at an inclination of 26.24° to the horizontal facing true south. two main parameters of system, namely pv module temperatures at different points and weather conditions were considered for this study. the temperatures at different points of systems, such as, cooled pv module temperature (tcc), without cooled pv module temperature (tcw), air temperature inlet pv module after radiator (tci), air temperature outlet pv module (tco), water temperature inlet of radiator (tri), and water temperature outlet of radiator (tro) were observed at two different flow rates of 1lit/min and 2lit/min. weather conditions, such as solar radiations on horizontal surface and on tilted surface, wind speed and ambient temperature were recorded from 08:00 to 17:00 hours with one hour interval, thus allowing the knowing of the effect of atmospheric air cooling on the cooling of pv module and ultimately the performance improvements of pv modules. the experimental work was conducted for two weeks from octomber 21st until the november 4th, 2016. the weather conditions and temperatures at various points of installed pv system at the flow rate of 1lit/min were observed for five days, and at the flow rate of 2lit/min were also measured for another five days. the temperatures at different points of installed unit were recorded by the data logger and was extracted at the end of each day for analysis. the weather conditions were observed using lux meter and anemometer from 8:00 to 17:00 hours regularly. engineering, technology & applied science research vol. 7, no. 5, 2017, 1980-1986 1984 www.etasr.com jakhrani et al.: analysis and fabrication of an active cooling system for reducing photovoltaic … table iv. specifications of digital anemometer parameters description type of battery 9v demonstration 2 x 4 digits dual display lcd bearing sapphire jewel bearing temperature sensor k-type thermocouple temperature range meter: 0 ~ 50 ( 32 ~122 ) vane: 0 ~ 60 ( 32 ~140 ) humidity range less than 80% rh storage temperature range 40 ~ 60 (40 ~140) power consumption approx. 3ma size 88x168x26.2mm vane: 66x132x29.2mm weight 141g iii. results and discussions the results obtained from the installed pv modules are illustrated with respect to two main parameters of system configurations, namely pv module temperatures at different points and weather conditions. the temperature of cooled and un-cooled pv module, air temperature at inlet and outlet of pv module, water temperature at inlet and outlet of radiator were observed at two different flow rates with 1 lit/min and 2 lit/min. a. weather conditions and results with flow rate of 1 lit/min the results of average weather conditions and temperature of pv module at the flow rate of 1 lit/min are illustrated in figures 2 and 3. the maximum average temperature of cooled (tcc) and un-cooled (tcw) pv module at flow rate of 1lit/min was recorded as 50.6°c and 54.5°c respectively. the average ambient temperature (ta) was found 33°c with the average wind speed (ws) of 0.9 m/sec. the average solar radiations on horizontal surface (gh) were found 604.4 w/m2, and on the tilted surface (gt) 754.8 w/m2. likewise, the minimum average tcc and tcw pv module recorded was 48.34°c and 51.9°c respectively. the average ambient temperature (ta) was 33.5 °c, average ws 1.32 m/sec, and the average solar radiations on gh 588.2 w/m2, and on gt was 731.8w/m2. similarly, the overall average of mean temperature of cooled tcc and tcw pv module throughout these days was found as 49.2°c and 52.7°c respectively. the average ta recorded was 32°c, average ws 1.1m/sec, and the average gh was 572.7w/m2, and gt was 705w/m2. b. weather conditions and results with flow rate of 2 lit/min the results of average weather conditions and temperature of pv module at the flow rate of 2lit/min are illustrated in figures 4 and 5. the mean maximum average tcc and tcw pv module during data recording period with the flow rate of 2lit/min was recorded as 48.86°c and 52.3°c respectively. the average ta was found 31.2°c with the average wind speed of 0.5m/sec. the average solar radiation on horizontal surface was found 598.3w/m2, and on the tilted surface 754.3w/m2. likewise, the mean minimum average temperature of tcc and tcw pv module recorded was 46.8°c and 50°c respectively. the average ta was 31.4°c, average ws 0.4m/sec and the average solar radiations on gh was 514.3 w/m2, and on gt was 645 w/m2. similarly, the overall average of mean tcc and tcw pv module throughout these data recording period with the flow rate of 2lit/min was found as 48°c and 51.3°c respectively. the average ta recorded was 32°c, average ws 0.5m/sec, and the average solar radiations on gh was 548w/m2, and on gt was 688.2w/m2. fig. 2. temperature at different points on pv system using flow rate of 1lit/min. fig. 3. weather conditions of the site with the flow rate of 1lit/min c. comparision of results with different flow rate conditions the average maximum, minimum and mean values of weather conditions and temperature of pv modules at the flow rate of 1lit/min and 2lit/min are presented in figures 6 and 7. both flow rates were maintained for five days period individually and then average results were framed for comparison purpose. the mean maximum average temperature of cooled (tcc) and un-cooled (tcw) pv module was recorded as 49.1°c and 52.7°c respectively at flow rate of 1 lit/min. the average ambient temperature (ta) was found 32°c with the average wind speed (ws) of 1.1m/sec. the average solar radiations on horizontal surface (gh) was found 572.7 w/m2, and on the tilted surface (gt) 705w/m2. likewise, the minimum average temperature of cooled (tcc) and un-cooled (tcw) pv module recorded was 48°c and 51.3°c respectively at flow rate of 2lit/min. the average ambient temperature (ta) was 32°c, average wind speed (ws) 0.5 m/sec, and the average solar radiations on horizontal surface (gh) 547.7w/m2, and on the tilted surface (gt) was 688.2w/m2. similarly, the overall engineering, technology & applied science research vol. 7, no. 5, 2017, 1980-1986 1985 www.etasr.com jakhrani et al.: analysis and fabrication of an active cooling system for reducing photovoltaic … average of average temperature of cooled (tcc) and un-cooled (tcw) pv module throughout the data recording days at both flow rates of was found as 48.6°c and 52.01°c respectively. the average ambient temperature (ta) recorded was 32°c, average wind speed (ws) 0.8m/sec, and the average solar radiations on the horizontal surface (gh) was 560.2w/m2, and on the tilted surface (gt) was 696.6 w/m2. fig. 4. temperature at different points on pv system using flow rate of 2lit/min. fig. 5. weather conditions of the site during flow rate of 2lit/min. fig. 6. temperature at different points on pv system using variable flow rates fig. 7. weather conditions during study period with variable flow rates. iv. conclusions based on daily analysis, the maximum average temperature of cooled (tcc) pv module recorded was 50.6°c and un-cooled (tcw) was 54.5°c, at the flow rate of 1lit/min. the heat extracted from the module was 7.2%. similarly, the minimum average temperature of cooled (tcc) pv module recorded was 46.8°c and un-cooled (tcw) 49.9°c at the flow rate of 2lit/min. it indicated the efficiency of 6.2% of heat extraction from the pv module. based on overall average of all data collection days, the maximum average temperature of cooled module was 49.16°c and un-cooled module was 52.73°c at a flow rate of 1 lit/min, with indicates the heat extraction of 6.8%. since, the minimum average temperature of cooled pv module recorded was 47.9°c and un-cooled was 51.3°c, which shows the heat extraction of 6.6%. it was discovered from the analysis that the flow rate of 1lit/min is more feasible for heat extraction as compared to the flow rate of 2lit/min. as far as weather conditions are concerned, the wind speed was found to be more helpful for heat extraction from the modules compared to other climatic parameters. in general, it is revealed that cooled monocrystalline pv module perform better with 6.7% more efficiency than un-cooled pv module. the present study was conducted by setting the pv module structure at the slope of 26º with respect to horizontal surface, and the heat exchanger at 90º. further study can be undertaken by changing the slope of the pv module structure and heat exchanger. the measurements were taken persistently for two weeks from 8:00 am to 5:00 pm with an interval of 1 hour during the months october and november. it is recommended that the measurements may be taken during summer months, so as to know the effect of atmospheric air cooling on the cooling of pv module during the hottest season of the year. the aluminum air cooled (radiator) heat exchanger is used in order to dissipate the heat of the air in to the water present in the tubes of heat exchanger. it is suggested that different types of heat exchangers may be tested for cooling of pv modules. acknowledgment the authors acknowledge the financial support provided by the authorities of quaid-e awam university of engineering, science and technology nawabshah for the fabrication and analysis of the pv module cooling system. engineering, technology & applied science research vol. 7, no. 5, 2017, 1980-1986 1986 www.etasr.com jakhrani et al.: analysis and fabrication of an active cooling system for reducing photovoltaic … references [1] s. rao, b. b. parulekar, energy technology non conventional, renewable and conventional, third revised and updated edition, khanna publishers, 2007 [2] a. q. jakhrani, a. k. othman, a. r. h. rigit, s. r. samo, s. a. kamboh, “a novel analytical model for optimal sizing of standalone photovoltaic systems”, energy, vol. 46, no. 1, pp. 675-682, 2012 [3] s. a. kalogirou, solar energy engineering, processes and systems academic press, 2013 [4] b. mondoc, f. pop, “factors influencing the performance of a photovoltaic power plant”, 3rd international conference on modern power system, romania, may 18-21, 2010 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bahram heydari department of computer engineering zanjan branch, islamic azad university zanjan, iran bh.heydari2016@gmail.com mojtaba aajami department of computer engineering zanjan branch, islamic azad university zanjan, iran m.aajami@gmail.com abstract—due to its efficient, flexible, and dynamic substructure in information technology and service quality parameters estimation, cloud computing has become one of the most important issues in computer world. discovering cloud services has been posed as a fundamental issue in reaching out high efficiency. in order to do one’s own operations in cloud space, any user needs to request several various services either simultaneously or according to a working routine. these services can be presented by different cloud producers or different decision-making policies. therefore, service management is one of the important and challenging issues in cloud computing. with the advent of semantic web and practical services accordingly in cloud computing space, access to different kinds of applications has become possible. ontology is the core of semantic web and can be used to ease the process of discovering services. a new model based on ontology has been proposed in this paper. the results indicate that the proposed model has explored cloud services based on user search results in lesser time compared to other models. keywords-cloud; computing; service; semantic; web; ontology i. introduction cloud computing includes a lot of remote servers which make a network and cause focused data storage and online access to services and computer sources [1]. to put it in another way, cloud computing is access to calculation sources through the internet and in effect instead of saving your data on the hard disc or updating your practical applications constantly, you can use an internet service to meet such needs [2]. cloud computing is a calculating pattern in which numerous systems are linked in the form of private or public networks to make a dynamic and comparable substructure for practical applications for the purpose of saving data and files [3]. with the emergence of this technology, hosting practical applications, saving content and delivering services has reduced remarkably. the idea of cloud computing in fact is on the basis of “reusing technology capabilities”. ontology is a kind of structured knowledge about a specific area which is made by presenting concepts and relations among them [4]. nowadays, because of designing ontology in different fields, offering criteria for the selection of the most appropriate ontology is essential. ontology is a branch of philosophy which studies essence of existence and structure of reality, but, in semantic web space, ontology investigates the classification of topics or the elements in a specific field and offers a list of them. few studies have been conducted on cloud service discovery [5, 6] all of which have aimed to upgrade the quality of exploration process and combine cloud services from various perspectives. with the improvement of communicational substructures and educational practices, the use of cloud computing has increased. given the widening use of the internet, cloud services have become a major data tool on the internet. the first major problem in exploring cloud services is the necessity of identification, exploration, and optimal selection from among a wide range of services. hence, the more accurate the process of cloud service discovery, the more efficient the system functioning. the second problem is the lack of access to the exploration of the users’ favorite services. in the majority of cases, cloud service is not able to explore the best service. as a result, ontology is a new method for exploring co-related services based on semantic relations. a lot of companies offer cloud computing services. cloud space is a service for offering storage space to the users so that they can save their information on the internet in order to have access to them from anywhere or by different devices [7]. cloud computing makes it possible for users and developers to use them without getting involved with technical information or control of the needed technological substructures. one of the major issues in cloud computing is service exploration. sharing, source allocation, purification and service exploration are of great prominence while data and software are offered in the form of service in cloud computing. under-exploration of appropriate services for the various user needs is the main problem in using cloud computing services. with the emergence of semantic web and semantic web services after that, exploring cloud web service has gained crucial importance. ontology is the core of semantic web and can be used to ease the process of exploring web services [8]. the aim of exploring web services is to search and find the appropriate web services which meet the users’ needs. ii. related works the aim of developing semantic web services is to use the technological capabilities of semantic web to auto-explore, engineering, technology & applied science research vol. 7, no. 6, 2017, 2268-2272 2269 www.etasr.com heydari and aajami: providing a new model for discovering cloud services based on ontology combine, monitor, and run them. few studies have been done in this regard, and different solutions have been proposed to explore cloud service. authors in [9] proposed a multi-factor ontology-based system to explore cloud service. a multi-factor system is composed of several interactional intelligent factors. multi-factor systems can be used to solve problems, the solution of which is difficult or impossible for a pure system. multi-factor systems have better efficiency in searching, parallel, or algorithmic processing. in the hybrid model, the semantic relations between services are based on ontology being explored based on a multi-factor system. a model has been proposed on the basis of ontological clustering to explore cloud substructure services [10]. substructure-based clusters have been created as a service and the ontology of the semantic relations among them has been established. calculation sources have been considered as the provider of the service and storage space in ontological clustering. the results indicate that the clustering model has explored cloud substructure services in less time than the normal method. authors in [11] proposed a hybrid model based on ant colony optimization and learning automaton to explore the cloud semantic relations. ant colony optimization has been used to find the shortest paths and reach the intended service in the hybrid model. learning automaton has been used to improve ant colony optimization algorithm and to make it intelligent. the results indicate that the hybrid model obtains better outcomes in less time. a model has been proposed based on xml substructure for cloud service discovery [12]. it aims to provide cloud services based on xml files. in this model, xml file consists of 3 parts including memory, processor, and cloud space services. each part in xml files is labeled and the users can select their favorite service. authors in [13] proposed a model based on semantic web for educational spaces in cloud computing. since search engines are used to internet search and they show information unrelated to the search, the data searched are only recognized by the motor engine and they cannot be interpreted by the motor engines. consequently, semantic web model which is used as the new technology has a major impact on cloud education services and ontology investigation in the retrieval and extraction of data. ontology describes different aspects of the learning process in cloud space. specifically, the manager of a database considers the cloud knowledge as the core of learning which instructs the learner to find the educational services in cloud with the help of ontology. data production and maintenance in cloud knowledge dataset is managed by ontological techniques. authors in [14] proposed a new model based on argumentation factors for cloud service discovery based on ontology. word frequency has been used to relate the data in this model. the data whith higher frequency and closer semantic relation for service exploration is retrieved. saas, paas, and iaas interact based on ontology and the best service is retrieved. iii. the proposed model ontology is the structured study of a specific field which is formed by proposing the concepts and the relations among them. in the proposed model, the relations among the cloud services are explored based on ontology, and the best services are selected for a specific function. cloud-based services are done at saas, paas, and iaas levels. in the first level, the user inserts his/her request. according to the user’s request, the process is done in a xml file. in the proposed architecture, the task of xml dataset is to store a mass of services, return the results intended by the users as soon as possible and in some cases process some of the saved services. as the data are heterogeneous and complex in xml, inquiries are made to enhance the quality of retrieval. rdf can be used to develop inquiries. in the proposed model, the services requested by the user are sent to the cloud provider based on ontology, and the cloud provider must provide the sources needed based on the wanted services. the flowchart of the proposed model is shown in figure 1. the most important services for the users lie in iaas level. this level includes such services as storage space, memory, and central processing module. based on user operation, he/she needs memory and a processing system. therefore, service selection must be done in a way that the most optimal and the most appropriate services get selected. by selecting the services on behalf of the users, cloud providers can offer the certificate needed so that users can have access to cloud space. fig. 1. the proposed model for service exploration based on ontology iv. evaluation and results using sparql, modelling the proposed architecture was carried out on protégé 5.0.0 software. protégé is a software used in semantic web. the major task of this software is to produce content which suits the semantic web and ontology. furthermore, there is the likelihood of retrieving ontology, developing it, making inquiries, graphical presentation of the classes, their identities, and the relations among them. 15 cloud providers and 150 different services have been used in the proposed architecture. the simulation scenario is shown in figure 2. ontology of the proposed architecture for cloud service discovery is shown in figure 3 based on ontograf chart. ontology of the cloud services is shown in figure 4 based on ontograf chart. each cloud service has practical subclasses which are used to explore services and build engineering, technology & applied science research vol. 7, no. 6, 2017, 2268-2272 2270 www.etasr.com heydari and aajami: providing a new model for discovering cloud services based on ontology ontology relations. ontology model of the cloud services is shown in figure 5 based on owlviz chart. ontology model of cloud services is shown in figure 6 based on owlviz chart. fig. 2. simulation scenario fig. 3. ontology of the proposed architecture for cloud service discovery on the basis of ontograf chart inquiries (1), (2), (3), (4), (5), and (6) are examples of spralql instructions which are written in protégé space to explore cloud services based on the proposed model (table i). in instruction (1), cloud service discovery is done based on saas. in (2), cloud service discovery is done based on paas. in (3), cloud service discovery is done based on iaas. in (4), service exploration is done based on saas, paas, and iaas. in (5), explored services are classifies based on iaas. services are shown based on numbers in classification. in instruction (6), filtering operation is done on the explored services. in instruction (6), services are saved in the memory for the purpose of retrieval. a comparison of the search time is made for the exploration of services in table ii based on the number of providers and services. the search time period is different based on the number of providers and services. if the number of providers is high, the time period for searching will be more. this is because the search for exploring services is made among greater number of providers. fig. 4. ontology model of the cloud services based on ontograf chart fig. 5. ontology model of the cloud services based on owlviz chart engineering, technology & applied science research vol. 7, no. 6, 2017, 2268-2272 2271 www.etasr.com heydari and aajami: providing a new model for discovering cloud services based on ontology a. comparison and evaluation the main advantage of the proposed model is the reducing of the search time for service discovery. in the proposed model, based on ontology, services are discovered at a faster time. the search time for service discovery is very important for users, so service discovery should be done in the shortest possible time and with the best response time. figure 7 shows the comparison of service discovery time of proposed model with others. the comparison is shown on the basis of 20 suppliers and 194 services. the search time for the discovery of the service in the cluster-free clustering model is 10152 and 5021 milliseconds, respectively. in the clustering model, services are clustered based on similarity, and each cluster includes a set of services. the clustering model is 50% faster than the model without clustering. the search time for service discovery in the proposed model is based on 20 suppliers and 194 services equals to 3800 milliseconds. the proposed model is operating 75% faster than the uncluttered model for discovering services. compared to the clustering model, it can search for query services for service discovery by 35% faster. in figure 8, the comparison of the proposed model with other models is shown on the basis of 15 suppliers and 150 services. the search time for the discovery of services in the proposed model is equal to 1,000 milliseconds. the proposed model with 15 suppliers and 150 services compared to no clustering model operates 90% faster. if the number of suppliers and services is lower, the search time for services to be discovered will be less because the number of comparisons will be less. on the other hand, if the number of suppliers and services is higher, users are more likely to discover their service. fig. 6. ontology model of cloud service discovery on the basis of owlviz chart table i. examples of spralql instructions based on the proposed model select ?saas where {?cloud_service ?saas. ?cloud_service rdfs:ontlogy ?xml. ?cloud_service rdfs:xml?saas.} (1) select ?paas where {?cloud_service ?paas. ?cloud_service rdfs:ontlogy ?rdf. ?cloud_service rdfs:xml ?paas.} (2) select ?iaas where {?cloud_service ?iaas. ?cloud_service rdfs:ontlogy ?rdf. ?cloud_service rdfs:xml ?iaas.} (3) select ?saas ?paas ?iaas where {?cloud_service ?saas. ?cloud_service rdfs:ontlogy ?xml. ?cloud_service rdfs:xml ?iaas.} (4) select ?iaas (count(?cloud_service) as ?count) where {?cloud_service ?iaas.} group by ?iaas (5) select ?iaas where { ?cloud_service ?saas. filter( contains(?iaas, "ram")) } (6) fig. 7. comparison of proposed model with other models based on 20 suppliers and 194 services fig. 8. comparison of the proposed model with other models based on 15 suppliers and 150 services. v. conclusion and future works cloud computing is a model developed for easy, distributed, and comprehensive access to aggregate computing resources. in cloud computing, it-based capabilities are engineering, technology & applied science research vol. 7, no. 6, 2017, 2268-2272 2272 www.etasr.com heydari and aajami: providing a new model for discovering cloud services based on ontology presented as services that are accessible without the need for accurate knowledge of infrastructure technologies and the least managerial effort available. in cloud computing, cloud service discovery can satisfy user needs. considering the relationships between cloud services based on ontology leads to the discovery of optimal cloud services. in addition to semantic relationships, standards such as xml, in the discovery of cloud services, also lead to enhanced service discovery. in this paper, we proposed a model for the discovery of cloud services based on ontology. we hope that in the future we will provide a system for discovering cloud services based on the ontology evolution and with applying techniques for the service interpretation, extraction and classification. table ii. a comparison of search time for discovering services based on the number of services and providers search time (ms) number of service number of suppliers no 1000 150 15 1 1500 100 15 2 1600 120 15 3 1800 100 20 4 2500 150 20 5 3800 194 20 6 2700 100 25 7 3000 120 25 8 3500 150 30 9 4500 150 40 10 6500 100 45 11 7500 100 50 12 8500 150 50 13 references [1] p. samimi, y. teimouri, m. mukhtar, “a combinatorial double auction resource allocation model in cloud computing”, information sciences, vol. 357, pp. 201-216, 2016 [2] x. ji, f. zeng, m. lin, “data transmission strategies for resource monitoring in cloud computing platforms”, optik international journal for light and electron optics, vol. 127, no. 16, pp. 6726-6734, 2016 [3] w. kong, y. lei, j. ma, “virtual machine resource scheduling algorithm for cloud computing based on auction mechanism”, optik international journal for light and electron optics, vol. 127, no. 12, pp. 5099-5104, 2016 [4] m. rani, r. nayak, o. p. vyas, “an ontology-based adaptive personalized e-learning system, assisted by software agents on cloud storage”, knowledge-based systems, vol. 90, pp. 33-48, 2015 [5] r. guerfel, z. sbai, r. b. ayed, “towards a system for cloud service discovery and composition based on ontology”, in: lecture notes in computer science, vol. 9330, pp. 34-43, springer, 2015 [6] a. alfazi, t. h. noor, q. z. sheng, y. xu, “towards ontologyenhanced cloud services discovery”, in: lecture notes in computer science, vol. 8933, pp. 616-629, springer, 2014 [7] y. m. afify , i. f. moawad, n. l. badr, m. f. tolba, “cloud services discovery and selection: survey and new semantic-based system”, in: bio-inspiring cyber security and cloud services: trends and innovations, vol. 70, pp. 449-477, springer, 2014 [8] t. labidi, a. mtibaa, f. gargouri, “ontology-based context-aware sla management for cloud computing, model and data engineering”, lecture notes in computer science, vol. 8748, pp. 193-208, springer, 2014 [9] m. parhi, b. k. pattanayak, m.r. patra, “a multi-agent-based framework for cloud service description and discovery using ontology”, in: intelligent computing, communication and devices, vol. 308, pp. 337-348, springer, 2015 [10] t. uchibayashi, b. apduhan, n. shiratori, “towards a cloud ontology clustering mechanism to enhance iaas service discovery and selection”, international conference on computational science and its applications, part i, pp. 545-556, springer, 2015 [11] m. olaifa , s. ojo, t. zuva, “an adaptive multi agent service discovery for peer to peer cloud services”, in: emerging trends and advanced technologies for computational intelligence, studies in computational intelligence, vol. 647, pp. 147-163, springer, 2016 [12] j. shetty, d. a. d’mello, “an xml based data representation model to discover infrastructure services”, international conference on smart technologies and management for computing, communication, controls, energy and materials, pp.119-125, 2015 [13] m. rani, r. nayak, o. p. vyas, “an ontology-based adaptive personalized e-learning system, assisted by software agents on cloud storage”, knowledge-based systems, vol. 90, pp. 33-48, 2015 [14] t. han, k. m. sim, “an ontology-enhanced cloud service discovery system”, international multiconference of engineers and computer scientists, vol. 1, pp. 1-6, 2010 microsoft word etasr_v12_n1_pp8090-8095 engineering, technology & applied science research vol. 12, no. 1, 2022, 8090-8095 8090 www.etasr.com nhung et al.: load shedding in microgrids with dual neural networks and ahp algorithm load shedding in microgrids with dual neural network and ahp algorithm le thi hong nhung electrical and electronics department hcmc university of technology and education ho chi minh city, vietnam nhunglth@hcmute.edu.vn hoang minh vu nguyen urban engineering department hcmc university of architecture ho chi minh city, vietnam vu.nguyenhoangminh@uah.edu.vn thai an nguyen electrical and electronics department cao thang technical college ho chi minh city, vietnam nguyenthaian@caothang.edu.vn trieu tan phung electrical and electronics department cao thang technical college ho chi minh city, vietnam phungtrieutan@caothang.edu.vn trong nghia le electrical and electronics department hcmc university of technology and education ho chi minh city, vietnam trongnghia@hcmute.edu.vn vo tan danh electrical and electronics department hcmc university of technology and education ho chi minh city, vietnam 2080602@student.hcmute.edu.vn abstract-this paper proposes a new load shedding method based on the application of a dual neural network (nn). the combination of a back-propagation neural network (bpnn) and of particle swarm optimization (pso) aims to quickly predict and propose a load shedding strategy when a fault occurs in the microgrid (mg) system. the pso algorithm has the ability to search and compare multiple points, so the proposed nn training method helps determine the link weights faster and stronger. as a result, the proposed method saves training time and achieves higher accuracy. the analytic hierarchy process (ahp) algorithm is applied to rank the loads based on their importance factor. the results of the ratings of the loads serve as a basis for constructing the load shedding strategies of a nn combined with the pso algorithm (ann-pso). the proposed load shedding method is tested on an ieee 25-bus 8-generator mg power system. the simulation results show that the frequency recovery of the power system is positive. the proposed neural network adapts well to the simulated data of the system and achieves high performance in fault prediction. keywords-load shedding; ann-pso; bpnn; dual neural network; ahp i. introduction the increase in load consumption over time poses problems of power system stability. to ensure balance in terms of power, the power system must constantly change in size and structure [1]. however, in some unexpected cases such as serious problems in the power system leading to an imbalance of active power, it is necessary to have temporary solutions to restore the equilibrium of the system. there are many solutions to this problem, as shown in [2], the self-healing ability of the power system depends on the load adjustment based on the voltage, frequency and governor characteristics of the generating sets. in [3-4], traditional load shedding methods are presented using under frequency load shedding relay to set the threshold of the shedding frequency. currently, many new load shedding methods apply intelligent algorithms. in [5], the decisionmaking technique in load shedding is presented using the ahp algorithm. in [6], the application of the ant colony optimization (aco) algorithm is presented in optimizing the amount of load shedding power. in [7-8], the pso algorithm is applied to optimize the inertia weights and train coefficients to get the optimal settings for the system and improve the voltage quality. in [9], a new adaptive load shedding method based on anns and proposed shedding power detection is presented. the ann is used to estimate the total amount of active power that causes unbalance over the attenuation frequency period, equivalent from the rated value to the threshold value. in [10], the genetic algorithm (ga) is also applied to optimal shedding against voltage collapse. however, the ga algorithm has the disadvantage of a very long training time compared to pso algorithm. the above studies often use intelligent methods and algorithms individually. therefore, the results obtained are usually satisfactory but not the best because of the limitations of each method and algorithm. the proposed idea is to combine methods together, thereby using the advantages of one method corresponding author: trong nghia le engineering, technology & applied science research vol. 12, no. 1, 2022, 8090-8095 8091 www.etasr.com nhung et al.: load shedding in microgrids with dual neural networks and ahp algorithm to overcome the disadvantages of the other method. in this paper, a new load shedding method is proposed based on the application of a dual nn system structured from a bayesian nn (bnn) and a nn combined with pso (ann-pso), thereby quickly predicting incidents and recommending load shedding strategies. in the structure of the proposed neural network, the bnn is responsible for classifying the fault types in the system to make a decision whether or not to shed the load. the nn combines the pso with the task of determining the load shedding strategies based on the fault type and fault location in the system, so the proposed nn training method can determine the link weights faster and stronger. tthe training time is saved and the accuracy is high. the ahp algorithm is applied in this paper to rank the loads based on a hierarchical model of comparing their importance to each other. the ranking results of the loads are the basis for constructing the load shedding strategies of the ann-pso. the proposed method in the article helps solve the integration problem in the load shedding issue, quickly determining whether or not to shed the load and propose a strategy for shedding the load quickly. the effectiveness of the proposed method is simulated and tested on the ieee 25-bus 8-generator mg system. the simulation results show the efficiency of the power system in frequency recovery. the frequency value quickly returns to the allowable range when a fault occurs after the intervention of load shedding according to the proposed method. the proposed nn adapts well to the simulation data of the ieee 25-bus 8generator mg system and achieves high performance in fault prediction. ii. the load shedding control strategy construction based on the ahp algorithm ahp algorithm is a method of weight calculating applied to multi-criteria decision problems with the idea of using knowledge and importance priority to rank objects in a system [11-13]. here, the ahp algorithm is applied to determine the importance factor and rank load unit in the ieee 25 bus power system. a hierarchical model of the importance comparison of load centers and loads to each other proposed by a system expert or operator is shown in figure 1. the steps to implement the ahp algorithm are detailed in [5]. fig. 1. the ahp hierarchical model includes load centers and load units. the construction of a judgment matrix of the importance factor of the load centers and of the loads in each load center is presented in tables i and ii. the ahp algorithm is applied to calculate the importance factor of the load centers and the load nodes in each load center. the result and load’s rank are presented in table iii. table i. judgment matrix of load centers load center 1 load center 2 load center 3 load center 4 load center 1 1 1 1/3 1/5 load center 2 1 1 1/2 1/3 load center 3 3 2 1 1/3 load center 4 5 3 3 1 table ii. judgment matrix of load units in the load centers lc1 load 1 load 2 load 4 load 5 load 1 1 1 1/3 1/2 load 2 1 1 1/3 1/2 load 4 3 3 1 2 load 5 2 2 1/2 1 lc2 load 6 load 7 load 8 load 6 1 1/3 1/3 load 7 3 1 1/2 load 8 3 2 1 lc3 load 9 load 10 load 11 load 12 load 9 1 2 2 1/2 load 10 1/2 1 2 1/3 load 11 1/2 1/2 1 1/2 load 12 2 3 2 1 lc4 load 14 load 15 load 16 load 17 load 14 1 2 2 3 load 15 1/2 1 2 3 load 16 1/2 1/2 1 2 load 17 1/3 1/3 1/2 1 table iii. ranking of load shedding according to the ahp rank load load center wlj wlci weights of the importance factor wij 1 load 1 lc1 0.14114490 0.10314687 0.014558655 2 load 2 lc1 0.14114490 0.10314687 0.014558655 3 load 6 lc2 0.13964794 0.12970033 0.018112384 4 load 5 lc1 0.26270020 0.10314687 0.027096703 5 load 11 lc3 0.13498819 0.24139951 0.032586083 6 load 10 lc3 0.17249955 0.24139951 0.041641307 7 load 7 lc2 0.33251593 0.12970033 0.043127426 8 load 4 lc1 0.45501010 0.10314687 0.046932868 9 load 17 lc4 0.10779910 0.52575330 0.056675733 10 load 9 lc3 0.26997638 0.24139951 0.065172166 11 load 8 lc2 0.52783613 0.12970033 0.068460520 12 load 16 lc4 0.18671352 0.52575330 0.098165249 13 load 12 lc3 0.42253588 0.24139951 0.101999954 14 load 15 lc4 0.29222244 0.52575330 0.153636912 15 load 14 lc4 0.41326494 0.52575330 0.217275406 based on the results of loads' rank, the load that has a lower importance factor will be prioritized for shedding and vice versa. in detail, based on the results in table i, the load 1 will be prioritized for shedding first and load 14 which has the highest importance factor will be shedding last. the implementation of load shedding is performed when the grid frequency attenuation is less than the allowable value and corresponds to the cases in which the mg operates in the island engineering, technology & applied science research vol. 12, no. 1, 2022, 8090-8095 8092 www.etasr.com nhung et al.: load shedding in microgrids with dual neural networks and ahp algorithm grid separation mode or a generator failure requires implement load shedding. the process of implementing this load shedding strategy is carried out until the frequency recovers to the allowable range from 49.8hz to 50.2hz. iii. backpropagation neural network the structure of the ann network consists of 3 main parts, the input layer, the hidden layer, and the output layer. the signal will be the input of the network and will be processed to give the answer. the number of nodes of the layers and the network structure is chosen to suit each problem and training data. bpnn is a feedforward multilayer network using the back propagation error training algorithm proposed in 1986. it is used in many fields. thanks to its ability to self-learn from errors, the network structure is very suitable for nonlinear problems. the flowchart of the training process of a bpnn can be seen in [14]. however, it also has some disadvantages such as low convergence speed and instability [15]. in order to solve the limitation bpnn the author in [16] proposed to combine it with the genetic algorithm (ga) to improve its structure. however, in ga, chromosomes exchange information with each other through crossover, which is a two-way information sharing mechanism with long loop times. pso algorithm uses multi-point comparison search, so the proposed training method can determine the link weights faster, saving training time and achieving high accuracy [17]. iv. particle swarm optimization algorithm the pso algorithm was proposed in [18]. in the field of power systems, algorithms are often applied in optimization problems [17]. with pso, each element in the swarm is represented as a vector. in the nn structure optimization problem, each weight vector represents the ann structure consisting of the weight values of all the nodes in the neural network. each particle (element) remembers its individual best historical location, called pbest. for each iteration, the best global position gbest is found. once the best global position is found, each element will move closer to its individual best position and best global position. after many iterations, this process finds a good network structure for the objective function, since the elements converge to a quasi-optimal solution. the speed and position of each individual are calculated as: vi k+1 = w.vi k + c1.rand1().(pbesti – xi k ) + c2.rand2().(gbest – xi k ) (10) after each cycle, the position of each individual will be updated as follows: xi k+1 = xi t + vi k+1 (11) where w is the inertial weight, c1, c2 are the acceleration coefficients, and rand1, rand2 are random number between 0 and 1. v. constructing dual nn combined with pso although nns have strong non-linear learning and representation capabilities, a traditional nn does not take into account the uncertainties of the weights in the network and only obtain point estimates of the weights [19]. there are many methods to reduce network complexity and increase efficiency in classification and forecasting. from [19], this paper utilizes a new cyclic nn called dual nn, in order to classify system failure and release shedding strategy. in detail, the ann network uses the back propagation (bp) algorithm to forecast power system whether load shedding or not. another ann uses the pso algorithm to determine the load quantity needed to load shedding. we combine these 2 nns to establish forecast value and load shedding in the power system. vi. simulation and results the proposed method is tested on the microgrid ieee-25 bus diagram. this test system consists of 8 synchronous machines with excitation types ac5a and ac8b [20], 25 buses, 25 transmission lines, 9 transformers, and 11 constant impedance loads. the total load demand is 393kw [21]. the diagram of the mg system is shown in figure 2. fig. 2. microgrid diagram of the ieee 25 bus system. the construction of the dataset to train the dual ann is done with loads ranging between 50% and 100% of the load. for each load level, the power grid provides sample data with island operation cases and generator failure cases. the process of training the dual ann is shown in figure 3. about load shedding cases, each different load level has a load combination and the sequence of shedding these loads which is ranked follows the priority based on the ahp algorithm. the load shedding process is conducted based on the results of load rank and is implemented until the frequency is restored to the allowable range. the summary results of load shedding strategies for different load levels are presented in table iv. consider a case study at 95% load, assuming that when there is a dg5 generator problem, the load shedding combination is ls1: load1, load2, load6, load5, load11, load10. for a dg8 generator problem, the load shedding combination is ls3: load1, load2, load6, load5, load11, load10, load7, load4. load shedding is conducted similarly for different generator problem cases. recovery frequency value and frequency recovery time are within the allowable range. engineering, technology & applied science research vol. 12, no. 1, 2022, 8090-8095 8093 www.etasr.com nhung et al.: load shedding in microgrids with dual neural networks and ahp algorithm fig. 3. supplemental flowchart for sampling and clustering load shedding using dnn. the results of the implementation of load shedding strategies are presented in table v. the comparison of recover frequency for the case with and without load shedding is shown in figure 4. as the comparison result, when load shedding is not conducted, frequency will decrease deeply and out of the allowable range. meanwhile, if the load shedding is performed according to the proposed method, the frequency is recovered to the allowable value ranges within 21s to 30s. table iv. strategies for load shedding according to the ahp load shedding control strategy load ls1 load1, load2, load6, load5, load11, load10 ls2 load1, load2, load6, load5, load11, load10, load7 ls3 load1, load2, load6, load5, load11, load10, load7, load4 ls4 load1, load2, load6, load5, load11, load10, load7, load4, load17 table v. fault statisticcs and load shedding implementation case study ls recovery frequency (hz) amount of load shedding power (kw) frequency recovery time (s) island operation ls2 50.004 141.25 23.97 island operation and loss dg1 ls3 50.034 197.84 22.08 island operation and loss dg2 ls4 50.020 215.83 20.09 island operation and loss dg3 ls3 50.026 197.84 28.08 island operation and loss dg4 ls3 50.007 197.84 25.08 island operation and loss dg5 ls3 50.066 197.84 30.08 island operation and loss dg6 ls3 50.064 197.84 25.08 island operation and loss dg7 ls3 50.065 197.84 23.08 island operation and loss dg8 ls3 50.090 197.84 21.08 all the data collected through the simulation process were used for the training of the nn. the data consist of 459 training engineering, technology & applied science research vol. 12, no. 1, 2022, 8090-8095 8094 www.etasr.com nhung et al.: load shedding in microgrids with dual neural networks and ahp algorithm samples and 123 input variables including 5 system parameters, i.e. line capacity, generator, load, frequency, and each bus voltage. the output of each training sample has 15 variables consisting of: yes/no recognition status (value 1 or 0), load shedding, and 4 load shedding strategies. all the data are processed and 2 separated datasets are established. the first dataset includes 459 samples, with 123 input variables and 1 output variable. the first dataset used bpnn with many different improved algorithms to forecast whether load shedding should be performed or not. the second dataset includes the cases of load shedding. this dataset consists of 167 samples, with 123 input variables and 14 output variables corresponding to the state of load shedding or not. the psoann is utilized to predict load shedding strategies. the result of the 2 networks will be combined to show the forecast of whether load shedding or not and the suitable strategy. (a) (b) fig. 4. frequency characteristics at bus 3 (a) without load shedding and (b) with load shedding based on the proposed method. the training results in figure 5. we can see that the result of the nn-pso algorithm in figure 5(a) has many advantages and is more suitable than the ga-nn with 95.59% testing and 99.74% training accuracy considering 40 input variables. the result (b) network of the improved algorithm gives good results. the bayesian algorithm performs better with accuracy 100% in training and 96% in testing with 20 input variables. so, the bpnn will use the bayesian algorithm to improve the network structure. vii. disccussion the application of dnn combining pso and ahp algorithms has supported the decision to load shedding quickly. that makes the power system able to keep the frequency in a steady state. the frequency of the system recovers to the allowable value. the ahp algorithm is applied to build load shedding strategies by ranking loads based on their relative importance. (a) (b) fig. 5. comparison chart of the training results of the proposed method with (a) comparison of ann-pso and ann-ga, (b) comparison of the improved algorithms in bpnn network. the proposed load shedding method used two nns. the first (ann1), is responsible for determining whether or not to shed the load. the second (ann2) is responsible for determining the load shedding strategies. the training results show that using a dnn to separate the information to process, achieves training results which exhibit good performance and increase the processing speed. meanwhile, other methods [21] perform only one task, the one of shedding the load. this shows that the proposed method is more general. however, the problem is that when the load changes continuously over time, the construction of an adaptive nn, or a nn that learns and self-adjusts the network structure, will be the solutions to the above problem. viii. conclusion a new load shedding method based on the use of dual neural networks is proposed in this paper. a bpnn network is used to determine the severity of the failure. the result makes a yes/no decision to shed the load. the ann-pso network supports the proposal load shedding strategy. pso algorithm is applied to optimize the link weights of the network, which makes accelerates the training and the accuracy of the network. the effectiveness of proposed load shedding was tested on the ieee 25-bus 8-generator. it was shown that the proposed load shedding maintained the frequency stability in the power system. in the future, the proposed load shedding method will be improved and along with solving the optimizing load shedding power problem, it will also reduce economic losses. engineering, technology & applied science research vol. 12, no. 1, 2022, 8090-8095 8095 www.etasr.com nhung et al.: load shedding in microgrids with dual neural networks and ahp algorithm acknowledgment this work was funded by the project grant no: t202145tđ by ho chi minh city university of technology and education, vietnam. references [1] n. voropai, "electric power system transformations: a review of main prospects and challenges," energies, vol. 13, no. 21, jan. 2020, art. no. 5639, https://doi.org/10.3390/en13215639. 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[21] c. wang, h. yu, l. chai, h. liu, and b. zhu, "emergency load shedding strategy for microgrids based on dueling deep q-learning," ieee access, vol. 9, pp. 19707–19715, 2021, https://doi.org/10.1109/ access.2021.3055401. engineering, technology & applied science research vol. 7, no. 3, 2017, 1623-1628 1623 www.etasr.com egba et al.: temperature response in hardened concrete subjected to tropical rainforest… temperature response in hardened concrete subjected to tropical rainforest environment ernest ituma egba faculty of civil engineering universiti teknologi malaysia 81310 skudai johor, malaysia and ebonyi state university, abakaliki, pmb 53, ebonyi state nigeria letschartup@gmail.com mohammad ismail faculty of civil engineering universiti teknologi malaysia 81310 skudai johor, malaysia mohammad@utm.my norhisham bakhary faculty of civil engineering universiti teknologi malaysia 81310 skudai johor, malaysia and institute of noise and vibration universiti teknologi malaysia norhisham@utm.my abstract—the objective of this paper is to characterize the microenvironment temperature response to the natural climate of the tropical rainforest. the peculiar warmth, high humidity, and low pressure nature of the tropical rainforest necessitated the present study. temperature probes were inserted into concrete specimens subjected to the sheltered and unsheltered environment to measure the micro-environment temperature of the concrete, and study the hysteresis characteristics in relation to the climate temperature. some mathematical relationships for forecasting the internal temperature of concrete in the tropical rainforest environment were proposed and tested. the proposed relationships were found reliable. it was observed that the microenvironment temperature was lower at the crest, and higher at the trough than the climate environment temperature with a temperature difference of 1-3 oc. also, temperature response in concrete for the unsheltered micro-environment was 1.85 times faster than the response in the sheltered micro-environment. the findings of the study may be uses to assist the durability assessment of concrete. keywords-natural climate temperature; concrete microenvironment temperature; concrete deterioration; rainforest tropical climate i. introduction temperature has been identified as a major factor that influences the performance of concrete as a result of the constant periodic, daily, and seasonal temperature variation. previous studies have shown various ways that temperature influenced concrete deterioration and service life reduction of concrete structures [1-7]. it has been revealed that the temperature effect on concrete durability was stirred by the concrete micro-environment temperature [3, 8-15]. the submission of previous researchers in [3] showed the relevance of describing the environment parameters in the natural climate and concrete micro-environment based on climate zones. this paper describes the analysis of temperature response in hardened concrete subjected to the natural environment of the tropical rainforest of johor, malaysia. the paper also explains the likelihood of concrete deterioration in the tropical rainforest as a result of the influence of the natural climate temperature. authors in [9] studied the hysteresis characteristics of temperature response of concrete. but the study was pertinent to the subtropical climate that is branded by warm and dry air whereas the tropical rainforest environment is characterized by unusual warmth, high humidity and low pressure. the study aims to assist the description of temperature effect on concrete and efficient concrete durability design. ii. methodology a. concrete specimen preparation a grade 20 concrete was prepared with ordinary portland cement, 20 mm maximum size crushed granite, natural river sand of 5 mm maximum size, and clean water. table i shows the composition of the concrete. 100 mm x 150 mm x 150 mm concrete size specimens with water to cement ratio of 0.6 were prepared, demoulded after 24 hours, and cured in water for 28 days. a temperature probe was inserted into 10 mm diameter hole, 25 mm from the surface of the concrete specimen. the 25 mm was assumed as the approximate reinforcement bar location in reinforced concrete. the specimens were oven dried at the temperature of 105 oc after the 28-days water curing, to achieve moisture content free concrete. table i. concrete composition material quantity (kgm-3) cement 350 river sand 717.6 crushed granite 1122.4 water 210 b. exposure condition the specimens that were placed 1500 mm above the ground level to avoid sorption of ground water were subjected to two exposure conditions, the sheltered, and the unsheltered natural climate exposure conditions. the two exposure conditions were selected to characterize the effect of sunshine and daylight hour on temperature response in concrete. c. data acquisition and analysis the concrete micro-environment temperature was measured with the xr5-se data logger at time intervals with engineering, technology & applied science research vol. 7, no. 3, 2017, 1623-1628 1624 www.etasr.com egba et al.: temperature response in hardened concrete subjected to tropical rainforest… the use of temperature probe. xr5-se data logger with a dimension of 124 mm x 56.2 mm x 32.5 mm has 20 positions screw input terminals and an operating limit of -40 oc to 78 oc and above 5 % relative humidity. the test setup is shown in figure 1. the natural climate temperature data were collected from the johor meteorological service. statistical data analysis was conducted to describe the extent of likelihood of concrete deterioration in the tropical rainforest environment, as well as the hysteresis characteristics of temperature in concrete. fig. 1. test set-up iii. results and discussion a. natural climate temperature the natural climate temperature t values for the month of june, and july are presented in figures 2a and 2b respectively. the temperature envelope for june 2016 as presented in figure 2a has the highest and lowest boundaries of 38 oc and 23 oc respectively. the june 2016 temperature data was used as the training data set to perform a waveform nonlinear curve fitting analysis to explain the temperature t and time t relationship. the function in (1) was deduced. t=30.253+5.385sin[π(t+6.981)/12.003] (1) the function explained 80.61% of the envelope. the function was used to predict the july natural climate temperature data to ascertain its validity. the result as shown in figure 2b indicated that it explained 84.46% of the july 2016 measured temperature with a mean square error of 2.81. figures 2a and 2b revealed that the average temperature within the period of test is 30.48 oc while the difference of the amplitude crest and trough is 15 oc with the daily temperaturerise period of about 8.33 hours. the result showed that value of the difference of the amplitude crest and trough differ by 85.2% compared to the case at changsha described in [8]. this suggests varying impact of temperature on concrete performance as a result of different degrees of daily temperature fluctuation in the environment. it supports the proposition of researchers that characterization of environmental parameters in the natural climate, and concrete micro-environment should be based on climate zones for adequate design of durable concrete structures [3, 9]. fig. 2. natural climate temperature values: (a) month of june 2016, (b) measured and predicted values for the month of july 2016 also, the cluster analysis chart of the natural climate temperature for the month of june, and july 2016 are presented in figures 3a, and 3b respectively. the chart showed that the natural climate temperature was above 30 oc for 53.70% of the studied period. the results indicated that the environment favours significant carbonation, and corrosion of concrete. the deduction was made based on arrhenius theory and the submission of researchers that concrete deterioration, carbonation and corrosion increase as temperature increases [10-12]. also, it was opined in [12] that the corrosion of reinforced concrete aggravates from temperature of 20 oc; intensifies as the temperature approaches 40 oc; and decreases above 40 oc. the implication is that the tropical rainforest environment of johor in malaysia is absolutely conducive for concrete deterioration and corrosion, since the natural climate temperature envelop falls within 20 to 40 oc. in addition, the environment permits intensified rate of corrosion, since the temperature is above 30 oc, 53.70% of the time. b. concrete micro-environemnt temperature the daily temperature variations in the climate environment, and the micro-environment for the sheltered and unsheltered concrete specimens are presented in figure 4. it shows the hysteresis characteristics of temperature response in (a) (b) engineering, technology & applied science research vol. 7, no. 3, 2017, 1623-1628 1625 www.etasr.com egba et al.: temperature response in hardened concrete subjected to tropical rainforest… concrete micro-environment. figures 4a and 4b reveal that the climate environment temperature rises at a faster rate than the micro-environment temperature from the sunrise time to the maximum temperature some hours after the noon time; and falls faster than the micro-environment temperature through the sunset time to the night period. this behaviour could be attributed to the change of transmission medium of temperature, and the coupled effect of heat convection, and conduction. it was observed that the micro-environment temperature was lower at the crest, and higher at the trough than the climate environment temperature with a temperature difference of 1-3 oc. it was deduced from figure 4c that temperature response in concrete for the unsheltered microenvironment was faster 1.85 times more than the response in the sheltered micro-environment. also, figure 4a shows that it took the micro-environment temperature a minimum of 9 hours to attain the climate environment temperature. the findings agreed with the observation of previous studies that the peak and valley points of micro-environment temperature lag behind the corresponding climate environment temperature with varying values of the range of 1-7 oc [8-9, 13]. fig. 3. cluster analysis of natural climate temperature values: (a) month of june 2016, (b) month of july 2016 the micro-environment temperature data of 1st – 3rd june 2016 was used as the training data to perform a waveform function nonlinear curve fitting analysis to explain the temperature and time relationship. the mathematical expressions for the unsheltered and sheltered microenvironment are presented in (2) and (3) respectively. tu=31.481+4.531sin[π(t+9.208)/12.035] (2) ts=30.943+4.046sin[π(t+9.129)/12.040] (3) where tu and ts denote unsheltered micro-environment temperature, and sheltered micro-environment temperature respectively. equations (2) and (3) were used to predict the unsheltered and sheltered micro-environment temperatures respectively, for july 4 – july 6. the result shown in figure 5 indicated that (2) explained 83.72% of the july 2016 measured unsheltered micro-environment temperature with a mean square error of 2.79; while (3) described 85.82% of the july 2016 measured sheltered micro-environment temperature with a mean square error of 2.00. the result indicated that the expressions were valid for predicting concrete micro-environment temperature. the daily temperature range for the climate environment is presented in figure 6. it is indicated that the daily temperature varied most and least at the range of 14 oc and 6 oc respectively, with the average range at 10.84 oc. figure 7 shows the temperature difference for the unsheltered and sheltered micro-environment. temperature difference described the extent the micro-environment temperature varied from the average daily natural climate temperature. the diagram revealed lesser temperature difference for the unsheltered environment than the sheltered environment. the finding affirmed the claim that temperature response in unsheltered concrete micro-environment is higher than the sheltered micro-environment as a result of sunshine and daylight effects [8-9]. nevertheless, relationships amongst temperature difference and temperature range are presented in figures 8(a) and 8(b). the following mathematical expressions were deduced from the relationship by linear regression; δtu=-0.024r-0.009 (4) δts=0.041r-0.190 (5) the relationship amongst temperature difference and temperature range for the unsheltered concrete and sheltered concrete are explained in (4) and (5) respectively. the mathematical expressions are useful for predicting concrete micro-environment temperature, providing the daily natural climate temperature range r is known. be that as it may, the statistics above revealed that the concrete micro-environment temperature was higher than 30 oc for 80.33% exposure duration. this value is far from 53.70% recorded for the natural climate temperature. this suggests that concrete microenvironment temperature is much more responsible for temperature effect on concrete durability. the result is in agreement with earlier studies [8-9, 13-15]. (b) (a) engineering, technology & applied science research vol. 7, no. 3, 2017, 1623-1628 1626 www.etasr.com egba et al.: temperature response in hardened concrete subjected to tropical rainforest… fig. 4. hysteresis behaviour of temperature: ture values: (a) 31st may – 3rd june 2016, (b) 4th june – 6th june 2016, (c) daily mean temperature values for june and july 2016 fig. 5. prediction of temperature response in concrete micro-environment fig. 6. temperature range in the natural climate environment (1st june – 31st july 2016) fig. 7. temperature difference (1st june – 31st july 2016) (b) (c) (a) engineering, technology & applied science research vol. 7, no. 3, 2017, 1623-1628 1627 www.etasr.com egba et al.: temperature response in hardened concrete subjected to tropical rainforest… fig. 8. relationship between daily temperature range and temperature difference: (a) unsheltered natural environment, (b) sheltered natural environemnt iv. conclusion the present study focused on the analysis of temperature response in concrete. it scrutinised the favourable chances of tropical rainforest environment for concrete deterioration. it also examined the hysteresis behaviour of temperature in concrete. the following deductions were made:  the natural climate temperature envelop in the tropical rainforest environment of johor in malaysia falls within 20 oc to 40 oc, which is absolutely conducive for concrete deterioration,  the tropical rainforest environment permits intensified rate of corrosion, since the temperature is often above 30 oc, 53.70% of time.  the climate environment temperature rises at a faster rate than the micro-environment temperature from the sunrise time to the maximum temperature some hours after the noon time; and falls faster than the micro-environment temperature through the sunset time to the night period; as a result of change of transmission medium of temperature, and the coupled effect of heat convection, and conduction.  the micro-environment temperature was lower at the crest, and higher at the trough than the climate environment temperature with a temperature difference of 1 to 3 .  temperature response in concrete for the unsheltered micro-environment was 1.85 times faster than the response in the sheltered micro-environment.  the daily temperature varies most and least at the range of 14 oc and 6 oc respectively, with the average range of about 10.84 oc at the tropical rainforest environment.  the temperature response in unsheltered concrete microenvironment is higher than the sheltered micro-environment as a result of sunshine and daylight effects. acknowledgment the authors gratefully acknowledge the support of ministry of higher education malaysia for the financial assistance, grant no: 4f528 for this research; and the financial support received from the research management centre (rmc) universiti teknologi malaysia (utm), grant no: 10h06, faculty of civil engineering utm. also, appreciated are the support of the management of ebonyi state university, abakaliki, nigeria; the management of tertiary education trust fund (tetfund), nigeria; as well as the technicians, faculty of civil engineering utm. references [1] j. ortiz, a. aguado, l. agullo, t. garcia, “influence of environmental temperatures on the concrete compressive strength: simulation of hot and cold weather conditions”, cement and concrete research, vol. 35, pp. 1970-1979, 2005 [2] a. alhozaimy, r. r. hussain, r. al-zaid, a. al-negheimish, “coupled effect of ambient high relative humidity and varying temperature marine environment on corrosion of reinforced concrete”, construction and building materials, vol. 28, pp. 670-679, 2012 [3] m. n. haque, h. al-khaiat, b. john, “climate zone – a prelude to designing durable concrete structures in the arabian gulf”, building and environment, vol. 42, pp. 297-321, 2007 [4] o. b. hwan, j. s. yup, “effect of material and environmental parameters on chloride penetration profile 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temperature response in concrete in a natural climate environment”, construction and building materials, vol. 25, pp. 3159-3167, 2011 [14] c. y. chang, s. s. hung, “implementing rfic and sensor technology to measure temperature and humidity inside concrete structures”, construction and building materials, vol. 26, pp. 628-637, 2012 [15] j. jiang, y. yuan, “prediction model for the time-varying corrosion rate of rebar based on micro-environment in concrete”, construction and building materials, vol. 35, pp. 625-632, 2012 microsoft word etasr_v12_n2_pp8354-8358 engineering, technology & applied science research vol. 12, no. 2, 2022, 8354-8358 8354 www.etasr.com mouafki et al.: porous silicon antireflective coatings for silicon solar cells porous silicon antireflective coatings for silicon solar cells achoura-mouna mouafki department of matter sciences faculty of exact sciences and sciences of nature and life university larbi ben m’hidi oum el bouaghi, algeria mouafki.mouna17@gmail.com faiza bouaïcha laboratory of the active components and materials institute of science and applied techniques university larbi ben m’hidi oum el bouaghi, algeria f_bouaicha@yahoo.com abouelfath hedibi materials science and informatics laboratory faculty of science university of djelfa djelfa, algeria abouelfath.hedibi@gmail.com ahmed gueddim materials science and informatics laboratory faculty of science university of djelfa djelfa, algeria ahmed_gueddim@yahoo.fr received: 3 february 2022 | revised: 11 february 2022 | accepted: 13 february 2022 abstract-this study presents a numerical investigation of the reflectivity of a single anti-reflective layer (sarl) and a stack of antireflective layers made of porous silicon. the stack consists of a certain number of periods, and each period contains two layers with different porosity. the simulations were conducted using the well-known stratified medium theory (smt) framework and the effect of porosity was studied. the optimal value was determined at 60% for the sarl and 65/55% for the stack of 12 periods and 6 layers. the angle of incidence was found to have more influence on the stack reflection than on the sarl reflection. the results of this investigation show that porous silicon can be used as an effective anti-reflective coating for silicon solar cells. keywords-porous silicon; silicon; solar cell;reflectivity i. introduction the photovoltaic effect is defined as the direct transformation of electromagnetic energy (solar radiation) into directly usable continuous electrical energy, and it was discovered in 1839 [1]. the photovoltaic effect has been exploited for the design of photovoltaic solar cells. since the 1990s, photovoltaic energy has attracted growing interest and many technological advances have been made through several technological sectors. photovoltaic electricity production has increased exponentially since 2001, and projections are quite optimistic for the coming years [2]. cell efficiency will certainly increase and, according to the community research and development information service (cordis), the lifespan of cells in 2030 will be 40 years with an energy payback time of only one year and very satisfactory efficiency [3]. the efficiency of a solar cell is mainly limited by the various losses that occur in the cell. among these losses, the reflection of incident photons at the surface of the cell (emitter, or window layer) contributes to the degradation of the collection efficiency of the cell. to remedy this problem, antireflection layers are often used on the front face of the cell to reduce the reflected fraction of incident radiation and improve the transport of carriers via the passivation of defects inside the cell [4-6]. the simplest way to create an anti-reflective coating is to deposit a quarter-wave layer of a dielectric with an intermediate refractive index between that of the emitter (or the window) and the air (tio2, si3n4, ta2o5, etc). for silicon, for example, a layer of si3n4 quarter wavelength centered on the maximum of the solar spectrum am1.5 reduces the reflection by 12% on average in the wavelength range 400-1100nm, increasing the photocurrent by 45% [7]. it should be noted that the reflection of silicon is between 35-40%, depending on the synthesis process [7-10]. in addition, porous silicon can be used as an alternative antireflective coating for silicon solar cells since the basis material is the same. porous silicon was accidentally discovered in the 1950s in an attempt to develop an electrochemical method to fabricate silicon substrates for microelectronic devices. under the appropriate electrochemical conditions, the silicon substrate did not dissolve uniformly as expected. however, fine holes appeared, propagating primarily within the material in the [100] direction. since this did not provide the desired smooth polish, the material was somewhat abandoned. during the 1970s and 1980s, significant interest arose because the high surface area of porous silicon was found to be useful as a model of the crystalline silicon surface in spectroscopic studies [11-14], as a precursor to generate thick oxide layers on silicon, and as a dielectric layer in capacitance-based chemical sensors [15]. interest in porous silicon, and in particular its corresponding author: achoura-mouna mouafki engineering, technology & applied science research vol. 12, no. 2, 2022, 8354-8358 8355 www.etasr.com mouafki et al.: porous silicon antireflective coatings for silicon solar cells nanostructure, exploded in the early 1990s when ulrich goesele at duke university identified quantum confinement effects in the absorption spectrum of porous silicon, and almost simultaneously leigh canham in england reported efficient bright red-orange photoluminescence from the material [16, 17]. the quantum confinement effects arise when the pores become extensive enough to overlap with each other, generating nanometer-scale silicon filaments. as expected from the quantum confinement relationship [18], the red to green color of photoluminescence occurs at energies significantly higher than the bandgap energy of bulk silicon (1.1ev, in the near-infrared). a little after, enormous work focused on creating silicon-based optoelectronic switches, displays, and lasers. at the same time, the unique properties of the material, such as large surface area, controllable pore sizes, convenient surface chemistry, and compatibility with conventional silicon microfabrication technologies, prompted research into novel applications: various biomedical sensors, optics, and electronics applications emerged [19]. this study examines the use of porous silicon with different porosity values as an antireflection coating to reduce light reflection and improve the conversion efficiency of silicon solar cells. two different cases were considered: single antireflection layer and multilayered stack antireflection coating. the effect of the incidence angle was examined along with the determination of the reflectivity in each case. ii. computational methodology the stratified medium theory (smt) was used for the calculation of the reflectivity of the studied arcs. this approach is known to combine a simple formalism and great flexibility of use. more insights and details about smt are given in [20-22]. within smt, the inhomogeneous medium is subdivided into n inhomogeneous strata with refractive index ��� . each stratum is represented by a complex characteristic matrix �� . matrices �� and �� correspond to ambient and substrate semi-infinite media, respectively, as detailed in [21,22]. the simplified relation: �ab � m� ∏ m����� �m� (1) can be written more explicitly: �ab � � p��� p���� ∏ � cosδ� p���sinδ� ip�sinδ� cosδ� " ���� � 1p�� (2) where $� is the phase shift due to the jth stratum: δ� � %&' n��d�cosθ� (3) and +� is determined from the incidence angle +� according to the snell-descartes law: n��sinθ� � n��sinθ� (4) for transverse electric (te) polarization, ,� � ���-./+�, and for transverse magnetic (tm) polarization, ,� � ���/-./+�. fresnel coefficients are calculated for both polarizations and each wavelength using: r23 � 4ab523 and r26 � 478526 (5) reflectivity can then be expressed as [21,22]: r � �% 9r23 r23∗ ; r26r26∗ < (6) iii. results and discussion a. single antireflection layer figure 1 represents the reflectivity as a function of the incident wavelength for a single antireflection layer made of porous silicon with different values of porosity ranging between 55 and 80%. as can be noted, the reflectivity at first increases, reaching a maximum value for wavelengths below 400nm and then decreases until the wavelengths approach 630nm. beyond 630nm, the reflectivity increases again. furthermore, the lowest reflectivity is obtained in the vicinity of 630nm and corresponds to porosity values of 55, 60, and 65%. the best-retained result corresponds to a porosity of 60% and therefore to a refractive index of 1.96. this is in agreement with the findings reported in [23]. however, the reflectivity in the vicinity of 630nm in this study is better than the one obtained in [23]. in general, good agreement is recorded for other wavelengths. fig. 1. reflectivity vs wavelength for a single porous silicon antireflection layer for different porosity values. b. effect of the number of layers in the stack the anti-reflective coating is obtained by stacking a certain number of periods, each of them consisting of two layers of porous silicon with different porosity values. the effect of the number of layers of the stack on the reflectivity is illustrated in figure 2. as can be noted, the stack of layers with minimum reflectivity consists of alternating layers of respective porosities 65/60% with nl=6 periods. however, the corresponding wavelength range is relatively narrow. the stack with 6 layers engineering, technology & applied science research vol. 12, no. 2, 2022, 8354-8358 8356 www.etasr.com mouafki et al.: porous silicon antireflective coatings for silicon solar cells of respective porosity values of 65/55% is preferable as it is characterized by a wider range of wavelengths extending from 580 to 690nm. the corresponding minimum reflectivity is as low as 1.46%. this can be traced back to the effect of the quantum confinement phenomenon. more details about this phenomenon can be found in [24-28]. these results are qualitatively similar in trend to the requirements reported in [29-35]. fig. 2. reflectivity vs wavelength for a stack of porous silicon antireflection coatings for different porosity values. c. effect of the angle of incidence for a single arl the influence of the angle of incidence on the reflectivity of a simple porous silicon antireflection layer of 60% porosity with refractive index 1.96 is shown in figure 3. fig. 3. reflectivity as a function of the angle of incidence for a single porous silicon anti-reflection coating with a porosity of 60%. as it can be observed, the reflectivity is almost zero for angles of incidence less than 30°. this reflectivity increases up to 0.05 for angles between 30° and 53°, then it increases more for higher values of the angle of incidence. therefore, it can be concluded that the angle of incidence affects the reflectivity only slightly until the angle of incidence exceeds 55°. qualitatively similar behavior was reported in [22]. this result is confirmed in figure 4 which represents the dependence on the wavelength of the reflectivity of a single layer of porous silicon used as an antireflection coating on a silicon-based photovoltaic cell, for different angles of incidence ranging from 0 to 80°. it is noted that the lowest reflectivity is recorded for normal incidence, and increasing the angles to more than 30° deteriorates the reflectivity. fig. 4. reflectivity vs. wavelength for a single porous silicon antireflection layer with 60% porosity for different incidence angles. d. effect of the angle of incidence for a stack of antireflection layers the chosen stack of layers was the optimal one consisting of stacking of porosity 65/55% with 1.78/2.14 refractive indices and nl=6 (nl being the number of layers in the stack). the corresponding reflectivity is plotted as a function of the angle of incidence in figure 5. fig. 5. reflectivity as a function of the angle of incidence for a stack of porous silicon antireflection layers with a porosity of 65%/55%. engineering, technology & applied science research vol. 12, no. 2, 2022, 8354-8358 8357 www.etasr.com mouafki et al.: porous silicon antireflective coatings for silicon solar cells fig. 6. reflectivity vs. wavelength for a stack of porous silicon antireflection layers with a porosity of 65%/55% for different incidence angles. as can be observed, the reflectivity is between 1.66% and 18% for angles of incidence less than 20°, and between 18 and 22.7% for angles between 20°-30°, and increases rapidly for angles above 30°. this confirms that the lowest reflectivity corresponds to the normal incidence, while the reflectivity of the stack increases when moving away from normal incidence. figure 6 shows the reflectivity as a function of wavelength for angles of incidence ranging from 0 to 80°, for a stack of porous silicon anti-reflection layers with a porosity of 65/55%. it can be noted that the lowest reflectivity is recorded for the case of normal incidence. furthermore, as the angle of incidence exceeds 20°, the reflectivity increases and shifts towards the lowest wavelengths. the conversion efficiency of a solar cell can be improved by making a judicious choice of the number of junctions in the cell and the materials whose energy gap can be controlled. this control can be easily obtained by alloying binary compounds to obtain ternary semiconductor alloys such as gaas1-xnx, gasb1xnx, or inas1-xnx [36-39]. other alloys that contain low concentration magnetic elements, called dilute magnetic semiconductors, can also be 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[43] s. zerroug, a. gueddim, and n. bouarissa, "composition dependence of fundamental properties of cd1-xcoxte magnetic semiconductor alloys," journal of computational electronics, vol. 15, no. 2, pp. 473–478, mar. 2016, https://doi.org/10.1007/s10825-016-0802-9. engineering, technology & applied science research vol. 8, no. 4, 2018, 3098-3102 3098 www.etasr.com yazdanifar: effect of social capital on innovation: a mediating role of employee motivation effect of social capital on innovation: a mediating role of employee motivation mohsen yazdanifar faculty of management department of mba university of tehran tehran, iran abstract—enterprises’ survival depends on their ability to selfreconstruct. this reconstruction regards coordinated goals with the current situation and improved methods used to achieve these goals. companies have to improve processes of innovation and creativity in order to adapt to changes. this study tends to examine the effect of social capital on innovation with emphasis on the mediating role of employee motivation. through a descriptive-correlational study, 196 sso employees in tehran were randomly recruited and were asked to fill out relative questionnaires. the validity and reliability of the questionnaires were determined by using cfa and calculating cronbach’s alpha. data were tested by using descriptive tests (mean and standard deviation) and analytic tests (path analysis). the effect of social capital and employee motivation was positive and significant on organizational innovation (p<0.01). employee motivation had the highest direct effect on organizational innovation (0.59). findings imply the effect of variables on organizational innovation. using these results, sso planners and managers can improve organizational innovation. keywords-social capital; employee motivation; organizational innovation i. introduction innovation is an important issue for people, institutions and societies, because of its association with flexibility and production. innovation and creativity are two of the most important factors of growth and progress in competitive environment. organizational innovation refers to creation or selection of an idea or behavior and its successful implementation [1]. creativity and innovation are necessary for the survival of any enterprise. it is essential to examine effective variables on organizational innovation and recommendations in this area [2]. one of the effective variables on organizational innovation is employee motivation. motivation is an important, yet vague concept in work and organizational science. employee motivation is considered a main factor of organizational innovation [3]. motivation is an internal factor which drives employees. its definitions vary. motivation is a psychological process which leads to arousal, direction, intensity and persistence of behavior. given the importance of tacit knowledge and its utilization to establish effective communications in order to perform activities better, a main factor for using tacit and explicit knowledge of employees for innovation is motivation and enthusiasm for participation in the company’s development [4]. another influential variable on innovation is social capital. social capital is useful for people, groups and organizations which have it in abundance. in fact, high quality of social capital helps businesses improve their performance and stable behavior [5]. proper social capital enables management to resist more successfully against competition. high quality of social capital helps organizations improve their performance and stable behavior [6]. the current study tends to examine the effect of social capital on organizational innovation focusing on the mediating role of employee motivation. ii. theoretical framework a. social capital if physical capital exists in the building and generating equipment, financial capital is what a person has in the bank (money), human capital exists in the mind (education and skills), social capital exists in relations or networks. social capital exists neither in people nor in physical tools of production. bourdieu introduced one of the most powerful social analyses in contemporary sociology. he had an instrumental view of social capital and focused on two aspects: 1) individual benefits from participating in the group and 2) intentional social communications to provide greater access to these resources and individual benefit. social capital results from: mutual trust, mutual social interaction, social groups with a sense of collective identity, a sense of shared picture of the future, and teamwork. through an organizational approach, two forms of social capital were identified: intra-organizational social capital and extra-organizational social capital. network structure and relational aspects of social capital tended to be incorporated to this approach. using these two types of social capital, an enterprise can collect and transform its intellectual capital into a competitive advantage. through an organizational approach, authors in [7] defined three dimensions of intraorganizational social capital including cognitive, relational and structural dimensions: structural dimension: structural dimension refers to properties of social systems and networks of relationships as a engineering, technology & applied science research vol. 8, no. 4, 2018, 3098-3102 3099 www.etasr.com yazdanifar: effect of social capital on innovation: a mediating role of employee motivation whole. this term describes the configuration or non-personal condition of connections between people or units. in other words, this dimension refers to the general pattern of communications between the members of the organization i.e. who is available and how he is available, or whether people in the organization know each other [7]. this dimension indicates the extent to which people communicate in the enterprise [8]. the most important aspects of this dimension are the presence or absence of network links between members. this dimension describes the pattern of communications in terms such as intensity, connection and hierarchy and organization [7]. overall, it focuses on whether people communicate with each other [8]. relational dimension: relational dimension describes the type of personal relationships with others expanded through a history of interactions. this concept focuses on certain relationships, such as respect and friendship, which influence behavior. through these personal relationships, people meet social incentives such as socialization, ratification and prestige. trust and trustworthiness, norms and guarantees, requirements and expectations, identity and identification are the most important aspects of this dimension [7]. unlike structural dimension which emphasizes on quantity of relationships, this dimension focuses on nature and quality of relationships [8]. cognitive dimension: cognitive dimension refers to resources which provide representations, interpretations and shared meaning systems among members, such as common codes, language, and jokes [7]. in other words, cognitive dimension deals with the extent to which employees share a vision and common understanding within a social network. therefore, as relational dimension, cognitive dimension of social capital deals with the nature of relationships between people. unlike relational dimension, however, this dimension focuses on whether quantity and quality of relationships have a cognitive component for members [8]. two components of this dimension include common goals and a common culture among members of the organization (a set of institutionalized behavioral norms) [9]. b. organizational innovation in general, the term organizational innovation refers to the emergence or acceptance of a behavior or new idea. innovation involves creation, adoption and implementation of new ideas in processes, new products and services or marketing. in fact, organizational innovation is defined as implementation of new ideas, whether it comprises products, services, processes, management or marketing systems. enterprises follow different innovations to achieve competitive advantage, for example, innovation in goods and services, innovation in strategy and structure, innovation in culture and technology. these innovations are manifested in various forms and are followed by certain advantages. the strategic advantage of types of innovation is presented in table i. author in [10] distinguishes two types of innovation: technical innovation and administrative innovation. technical innovation includes new processes, new products and services. administrative innovation refers to new policies, procedures and forms [10]. since this model is used in the current study, these dimensions are described here (figure 1). product innovation: product innovation provides a means of production [11]. product innovation refers to development of new and improved products and services. in fact, product innovation shows the extent to which an enterprise is providing new services, allocating financial resources to research and development and so on. process innovation: process innovation provides a tool in order to maintain and improve quality and cost saving [11]. it involves adoption of new or improved methods of production, distribution or service delivery. in fact, process innovation is the extent to which an enterprise uses new technologies and experiments new ways of doing things. administrative innovation: administrative innovation refers to new procedures, policies and organizational forms [11] and involves changes which influence policies, resource allocation and other factors related to the social structure of the organization. in fact, administrative innovation is the extent to which managers use modern management systems. table i. strategic advantage of innovation types type of innovation strategic advantage novelty offering a new product or service promotion of competence rewriting the rules of the competitive game complexity keeping entry barriers high robustness improving the basic model by extending its life and reducing overall cost continuous incremental innovation continuous improvement in performance c. job motivation job motivation is defined as a desire to achieve goals related to difficult and socially approved jobs. author in [12] considers job motivation as a series of energizing forces which originate from within and beyond a person and begin workrelated behavior and determine its shape, intensity, direction and persistence. author in [13] defined job motivation as one’s willingness to exercise and keep trying to achieve organizational goals. he believes that job motivation is a set of psychological processes which influence allocation of personal resources to achieve those goals. this influences effectiveness and productivity. job motivation exists when personal goals align with organizational goals. motivation and cognition are internal regulators of human actions. four points are noted in relation to motivation of certain behaviors: 1) motivation has a strong and difficult aspect of guiding. 2) people work harder when they are motivated. motivation leads to endeavor. 3) motivation leads to persistence. 4) motivation leads to task strategies, namely behavioral patterns produced in order to achieve a particular goal [12]. d. conceptual model considering the theoretical framework, the conceptual model is depicted in figure 2. this model considers social capital as an independent variable, employee motivation as mediating variable and organizational innovation as dependent variable. therefore, the hypotheses can be written as: h1: social capital has a positive effect on employee motivation, h2: employee motivation has a positive effect on organizational innovation, h3: social capital has a positive effect on organizational innovation. engineering, technology & applied science research vol. 8, no. 4, 2018, 3098-3102 3100 www.etasr.com yazdanifar: effect of social capital on innovation: a mediating role of employee motivation fig. 1. components of organizational innovation fig. 2. conceptual model iii. materials and methods the studied population included all the employees of the social security organization (sso) in tehran (n=400). simple random sampling was used in this study (n=196). questionnaires were used to collect the data required for analysis. the questions were measured on a 5-point likert scale from strongly disagree to strongly agree. the questionnaire was distributed among sso employees. out of 196 questionnaires, 190 were completely responded and further analyzed and 6 questionnaires were excluded from analysis because many questions were not answered. confirmatory factor analysis (cfa) was used to ensure the validity of the instruments. table ii lists the cfa findings. these findings show factor loadings of cognitive dimension (0.71), structural dimension (0.66) and relational dimension (0.57) on social capital (p<0.01) as significant. moreover, findings show factor loadings of administrative dimension (0.74), product dimension (0.69) and process dimension (0.54) on organizational innovation. in addition, factor loadings of the questions 1 to 15 related to employee motivation are significant (p<0.01). furthermore, cronbach’s alpha suggests good reliability of the questionnaire. table iii lists fit indexes related to constructs. this table shows the acceptable and estimated values for each construct. the results suggest that fit indexes of social capital, employee motivation and organizational innovation are acceptable. iv. methodology social capital: a 24-item questionnaire was developed to measure social capital based on questionnaires developed in [7]. in this questionnaire, 7 items measure structural dimension, 11 items measure relational dimension and 6 items measure cognitive dimension. organizational innovation: a 17-item questionnaire was developed to measure organizational innovation based on questionnaires developed in [10]. in this questionnaire, 7 items measure product innovation, 6 items measure process innovation and 4 items measure administrative innovation. job motivation: this study used mps index to measure employee motivation. based on this index, attitude of employees to their current job in the organization is formed of various aspects (diversity of skills, job identity, significance, autonomy, feedback). all questions are measured on a 5-point likert scale from strongly disagree to strongly agree. table ii. cfa results factors loadings on constructs α variable employee motivation organizational innovation social capital 0.87 social capital 0.66 structural dimension 0.57 relational dimension 0.71 cognitive dimension 0.91 organizational innovation 0.69 product 0.54 process 0.74 administrative 0.80 employee motivation 0.69 m 1 0.75 m 2 0.65 m 3 0.58 m 4 0.62 m 5 0.60 m 6 0.72 m 7 0.66 m 8 0.63 m 9 0.59 m 10 0.78 m 11 0.58 m 12 0.64 m 13 0.71 m 14 0.60 m 15 all factor loadings are significant at p<0.01. table iii. fit indexes calculated for cfa index social capital innovation motivation 2/df 3.22 2.85 1.57 (nfi) 0.95 0.92 0.94 (nnfi) 0.94 0.95 0.98 (cfi) 0.94 0.96 0.96 (gfi) 0.92 0.93 0.96 (agfi) 0.95 0.94 0.98 (rmsea) 0.047 0.051 0.068 v. results table iv lists the results related to demographic variables. once descriptive indexes were calculated, path analysis was engineering, technology & applied science research vol. 8, no. 4, 2018, 3098-3102 3101 www.etasr.com yazdanifar: effect of social capital on innovation: a mediating role of employee motivation used to examine causal relationships between variables. moreover, spss23 and lisrel8 were used to analyze data. analysis of causal models is based on the correlation matrix. table v shows the correlation matrix, the mean and standard deviation of the variables. as shown in table v, social capital (r=0.47) and employee motivation (r=0.51) have the highest positive and significant correlation with organizational innovation (p<0.01). figure 3 shows the fitted model; the numbers on paths are standardized parameters. according to figure 3, all paths are significant (p<0.01). since this study tended to examine the effect of social capital on organizational innovation by focusing on the mediating role of employee motivation using path analysis, table vi lists coefficients of direct effect, indirect effect and total effect and significance level of variables. as shown in table vi, direct effect of social capital (β=0.51) is positive and significant on employee motivation (p<0.01). direct effect of social capital (β=0.42) is positive and significant on organizational innovation (p<0.01). direct effect of employee motivation (β=0.59) is positive and significant on organizational innovation (p<0.01). indirect effect of social capital (β=0.11) is positive and significant on organizational innovation (p<0.01). table vii lists fit indexes of path analysis model. according to table vii, 2/df=1.53, gfi=0.96, agfi=0.98 and rmsea=0.021 are good. thus, the model is well fitted to data. table iv. demographic findings variable n % gender male 137 72.2 female 53 27.8 age 25-31 80 42.1 31-35 65 34.2 36-40 35 18.4 >41 10 5.2 table v. correlation matrix variable social capital motivation innovation social capital 1 motivation 0.51** 1 innovation 0.47** 0.39** 1 mean 3.24 3.42 3.60 sd 0.91 1.17 1.11 ** p<0.01; * p<0.05 table vi. estimate of the standardized coefficients of direct, indirect and total effects path direct effect indirect effect total effect on employee motivation vie social capital 0.51** 0.51** on organizational innovation vie social capital employee motivation 0.42** 0.59** 0.30** 0.72** 0.34** ** p<0.01; * p<0.05 table vii. fit indexes of path analysis model 2/df rmsea gfi agfi cfi nnfi 1.53 0.021 0.96 0.98 1 0.99 fig. 3. the fitted model vi. discussion and conclusions this study examined the effect of social capital on innovation with an emphasis on mediating role of employee motivation using path analysis. path analysis results showed that the suggested model is well fitted to data. the results showed that social capital has a positive and significant effect on organizational innovation. this finding is consistent with the findings in [14-18]. the main proposition of social capital is that social networks (personal communications) are developed over time, underlie trust and cooperation and include actual and potential valuable resources which contribute to social relations. in fact, social capital leads people to unite, makes them work together successfully and establishes cooperation-based working relations and facilitating working practices. therefore, increase in social capital increases organizational innovation and empowers employees, because it leads to cohesion of employees and managers and creates value-added by facilitating successful collective activities. the results showed that employee motivation has also a significant and positive effect on organizational innovation. this finding is consistent with [19]. enterprises with motivated employees will be better able to adapt to change. increased employee motivation is the healthiest way to share power. this leads to self-esteem, additional energy, commitment and selfreliance in people, increased sense of participation and finally increased innovation and improved performance. high motivation of employees provides potential capacities and suggests a balanced way between applying full control of the management and staff complete freedom of action in a healthy environment. in conclusion, employee motivation has a positive effect on organizational innovation. based on findings, the following strategies can be suggested: this study supports the direct and indirect role of social capital in organizational innovation. thus, sso managers are recommended to evaluate their social capital and improve its components in the organization and increase organizational innovation. the results also showed that social capital plays an important role in increasing employee motivation. therefore, sso senior executives are recommended to increase employee motivation by providing training for managers and increasing their awareness of social capital. it is also recommended to establish a culture in which employees can record their work experiences. it is difficult to generalize findings. this study considered only the social security organization in tehran. therefore, the findings cannot be generalized to other populations. moreover, findings are based on self-reported data. it is recommended to use qualitative and mix engineering, technology & applied science research vol. 8, no. 4, 2018, 3098-3102 3102 www.etasr.com yazdanifar: effect of social capital on innovation: a mediating role of employee motivation methodologies in future studies to understand effective factors on organizational innovation. references [1] s. laforet, “effects of organisational culture on organisational innovation performance in family firms”, journal of small business and enterprise development, vol. 23, no. 2, pp. 379-407, 2016 [2] a. monavarian, n. asgari, organization in the era of industry, information and knowledge, tehran tehran university publications, 2009 [3] m. a. mawoli, a. y. babandako, “an evaluation of staff motivation, dissatisfaction and job performance in an academic setting”, australian journal of business and management research, vol. 1, no. 9, pp. 1-13, 2011 [4] a. hecker, a. ganter, “organisational and technological innovation and the moderating effect of open innovation strategies”, international journal of innovation management, vol. 20, no. 2, pp. 165-169, 2016 [5] t. blokland, networked urbanism: social capital in the city, routledge, 2016 [6] a. danchev, “social capital and sustainable behavior of the firm”, industrial management & data system, vol. 106, no. 7, pp. 953-965, 2006 [7] j. nahapiet, s. ghoshal, “social capital, intellectual capital, and organizational advantage”, the academy of management review, vol. 23, no. 2, pp. 242-266, 1998 [8] c. bolino, m. turnley, h. william, m. bloodgood, m. james, “citizenship behavior and the creation of social capital in organizations”, academy of management review, vol. 27, no. 4, pp. 505-522, 2002 [9] m. lazarova, s. taylor, “boundary less careers, social capital and knowledge management: implications for organizational performance”, journal of organizational behavior, vol. 30, no. 1, pp. 119-139, 2008 [10] d. jimenez-jimenez, r. sanz valle, m. hernandez-espallardo, “fostering innovation: the role of market orientation and organizational learning”, european journal of innovation management, vol. 11, no. 3, pp. 389-412, 2008 [11] j. ojasalo, “management of innovation networks: a case study of different approaches”, european journal of innovation management, vol. 11, no. 1, pp. 51-86, 2008 [12] c. c. pinder, work motivation in organizational behavior, psychology press 2014 [13] r. dwivedula, c. n. bredillet, r. müller, “work motivation in temporary organizations: a review of literature grounded in job design perspective”, in: leadership, innovation and entrepreneurship as driving forces of the global economy, pp. 609-618, springer international publishing, 2017 [14] k. abili, h. faraji-dehsorkhi, k. shateri, a. youzbashi, “the relationship between social capital and organizational innovation in tehran university employees”, journal of shahed university, 2010 [15] m. rezvani, m. t. toghrai, “the role of social capital on organizational innovation in knowledge-based companies”, transformation management, vol. 3, no. 6, pp. 28-33, 2011 [16] g. schiuma, a. lerro, “knowledge-based capital in building regional innovation capacity”, journal of knowledge management, vol. 12, no. 5, pp. 121-136, 2008 [17] m. zerenler, s. burak hasiloglu, m. sezgin, “intellectual capital and innovation performance: empirical evidence in the turkish automotive supplier”, journal of technology management & innovation, vol. 3, no. 4, pp. 31-40, 2008 [18] r. ngah, a. r. ibrahim, “the relationship of intellectual capital, innovation and organizational performance: a preliminary study in malaysian smes”, international journal of management innovation systems, vol. 1, no. 1. 2009 [19] c. r. leana, f. k. pil, “social capital and organizational performance: evidence from urban public school”, organizational science, vol. 17, no. 3, pp. 353-366, 2006 engineering, technology & applied science research vol. 7, no. 6, 2017, 2231-2235 2231 www.etasr.com boubaker et al.: assessment of electrical safety beliefs and practices: a case study assessment of electrical safety beliefs and practices: a case study sahbi boubaker souad mekni houssem jerbi research unit on study of systems and renewable energy, national college of engineering of monastir, tunisia and hail university, hail city, saudi arabia s.boubaker@uoh.edu.sa laboratory of automation and control of systems national college of engineering of tunis tunisia msouadpop@gmail.com hail university hail city, saudi arabia h.jerbi@uoh.edu.sa abstract—in this paper, the electrical safety beliefs and practices in hail region, saudi arabia, have been assessed. based on legislative recommendations and rules applied in saudi arabia, on official statistics regarding the electricity-caused accidents and on the analysis of more than 200 photos captured in hail (related to electrical safety), a questionnaire composed of 36 questions (10 for the respondents information, 16 for the home safety culture and 10 for the electrical devices purchasing culture) has been devised and distributed to residents. 228 responses have been collected and analyzed. using a scale similar to the one adopted for a university student gpa calculation, the electrical safety level (esl) in hail region has been found to be 0.76 (in a scale of 4 points) which is a very low score and indicates a poor electrical safety culture. several recommendations involving different competent authorities have been proposed. future work will concern the assessment of safety in industrial companies in hail region. keywords-electrical safety; assessment; statistics; survey; hail region; beliefs; practices i. introduction electricity has become essential in modern living, so much attention should be allocated to its potential hazards [1]. assessing electrical safety practices has to be based first on strong regulations and safety requirements. as example, the study conducted in [2] aimed to implement a practical and adaptive electrical security risk assessment system based on electricity regulation in guangdong (china) power system. the results show that the studied electrical power system faces a moderate risk. although the study in [3] is relatively old, it has been reported that, as per the general civil defense administration (gcda) reports, electrical shock is the major cause of fire accidents. both the occupational safety and health administration (osha) and the national fire protection association (nfha) are the two organisms responsible of safety in usa. they establish, publish and revise periodically the safety related regulations [4]. many countries around the world (among them saudi arabia) adopt these regulations. in canada, the nfpa and the canadian standards association (csa) have recently (in 2016) integrated occupational health, safety management system and risk management principles in a unified framework to enable sustainable prevention of electrical incidents and injuries [5]. the severity of electrical occupational accidents in the primary, secondary and tertiary sectors has been assessed based on 14022 electrical accidents which occurred in spain between 2003 and 2012 [6]. the obtained results show that the competent authorities must promote actions to ensure agreement between the real workplace equipment and installations safety practices and those indicated by legislation. moreover, workers have to be educated and trained to their work circumstances. similarly to the study in [6], the severity of electricity accidents in the construction industry in spain has been evaluated based on statistics [7]. the findings of the study showed how several variables including age, occupation, company size, etc, are the most related to the electrical accidents severity. training is proposed as the most practical measure in order to limit the severity of electrical accidents in the construction industry in spain. fire safety risk assessment in hotels has been investigated based on qualitative approaches [8]. the paper provides a fire safety code in hotels consisting of 76 items. the electrical part is composed of 14 items (18.42%). this safety code represents a methodical approach that can be followed by safety fire inspectors. some aspects of safety culture held by subcontractors in the domestic building industry in australia have been assessed in [9]. the resistance of the subcontractors to safety practices has been found to be caused by seven causes including methods, personal, culture and materials. the recommendations proposed are particularly built around the integration of ohs in the design stage as well as on providing free training of the subcontractors‘workers. based on a survey, authors in [10] studied the relationship between the manager’s opinion and the existing safety cultures in n. cyprus manufacturing companies. it has been concluded that although the safety situation is in a relatively good level, there is room for improvement. assessing safety beliefs of australian electrical workers has been investigated using a qualitative methodology. interviews and focus groups with 46 licensed electrical workers have conducted to classify their beliefs into advantages, disadvantages, referents, barriers and facilitators. this theory is known as planned behavior [11]. the obtained engineering, technology & applied science research vol. 7, no. 6, 2017, 2231-2235 2232 www.etasr.com boubaker et al.: assessment of electrical safety beliefs and practices: a case study results show that the identified beliefs can inform about the principal factors influencing safe work decisions. safety on the job site has been assessed in a sample of sites in saudi arabia [12]. it has been through filling a safety checklist that large projects have much better safety awareness level. however, both small and large projects generally agree on the safety ranking. safety practices have been also evaluated in residential buildings in saudi arabia. for this aim, a questionnaire has been devised [13]. unfortunately, the obtained results have shown the design offices to be unaware about the requirements when designing buildings. number of recommendations is thus reported mainly for involving the necessity of respecting such rules. ii. research methodology the main objective of this study is to assess the level of electrical safety in hail region and to present adequate recommendations to improve it. five principal activities have been performed: 1. collecting the main legislative texts, requirements, rules and recommendations related to electrical safety applied in saudi arabia. 2. analyzing official safety reports issued by the local safety authorities. 3. meeting with officials from the general civil defense administration of hail region as well as with officials from the saso. several interviews and discussion groups have been organized. 4. analyzing more than 200 photos related to ‘bad’ electrical safety practices/situations collected from hail region. 5. conducting a survey among persons living in hail region in order to evaluate their electrical safety beliefs and practices. a. electrical safety legislative aspects the civil defense department in saudi arabia is the main authority responsible of safety (including electrical safety). the civil defense council has issued in 1990 g/1410 h a code of safety requirements and protections that must be available in residential administrative buildings [14]. in chapter (subsection 2), entitled “wiring and equipment”, it has been reported that “the design and installation of electrical and mechanical devices must follow the saudi standards and must be done by specialists”. six general requirements have been defined including wires, equipment, grounding, breaks and lights. during this research, it has been found that all the checklists used for assessing safety used this code. b. meetings several meetings have been organized with officials from the gcda. many aspects including the safety auditing activities have been discussed. their experiences in the domain of safety was interesting for this study. moreover, some meetings with safety field inspectors have revealed several key points that helped us in designing the questionnaire. c. statistical analysis the statistical analysis performed in this section is based on the report collected from the gdcd of hail region on august 21, 2016. this report is summarized in table i. for brevity, only the total number of electricity-caused accidents, the estimated costs and the secondary causes are cited. the electrical accidents are classified according to the requirements mentioned in section ii.a. note that this report includes only the accidents handled by the gdcd. twelve causes are mentioned in this report. the three important secondary causes are respectively “bad electrical wiring”, “high electrical load” and “high wire temperature”. according to the estimated costs, the “bad electricity wiring” is the most costly (5401140 sar) and the “faulty electrical devices” is the second one (3079750 sar). it could be also noted that the causes are respectively related to “safety practices” (1, 2, 4, 5, 6, 9, 10) and “faulty devices” (3, 7, 8, 11). “bad electrical wiring” is classified first in both number of accidents and cost. an obvious limitation is observed in the gdcd report. in fact, 628 accidents are classified as “other”. the estimated cost of this sub-class is relatively high (2746300 sar). table i. statistics of the electrical accidents recorded by the gdcd in hail region # cause of electrical accidents number of accidents estimated cost (sar) 1 bad electrical wiring 919 5401140 2 high wire temperature 270 797522 3 bad quality of devices and wires 127 1345500 4 high electrical load 465 2010100 5 liquid leakage on cables 22 700 6 static electricity 3 1000 7 no existence of automatic breaker 18 215700 8 faulty electrical devices 126 3079750 9 bad maintenance 61 313015 10 high voltage wires touching 40 51500 11 fault in rings 2 0 12 other 628 2746300 total 2681 15962227 engineering, technology & applied science research vol. 7, no. 6, 2017, 2231-2235 2233 www.etasr.com boubaker et al.: assessment of electrical safety beliefs and practices: a case study d. electrical safety survey the objective of the present study is to evaluate the electrical safety level in hail region. based on previous subsections a questionnaire has been devised. the survey conducted during this study has concentrated on both “beliefs” and “practices” of electrical safety. a total of 36 questions have been included in a checklist where the responses are “yes” or “no” except of the questions related to some information about the participants (questions 1-10). the questionnaire was distributed via social-media. 228 responses have been received and statistically analyzed. the first 10 questions are related to the responder information (age, sex, nationality, house category, education level, number of rooms, number of persons living in the house and the number of children living in the house). questions 11-26 are concerned with the electrical safety (at home) beliefs and practices. questions 27-36 are related to the degree of awareness about electrical safety when buying and using electric and electronic devices. the results of the survey are presented and analyzed below. 1) survey participants the general information of the survey’s participants is summarized in table ii. by analyzing the survey’s participants’ general information, the following conclusions should be drawn:  male participants are about 86.4% which is beneficial for the study because in arabic societies, male are in general responsible of all facts concerning the family including the house and its safety. the obtained percentage is highly correlated with the “yes” response of question 7 (“are you responsible in the house (father for example)”).  saudi participants were of 82.9%. this constitutes a positive point of the study. the surveyed sample covered high number of saudi population. the obtained results will be more significative.  house owners are of about 64.9% (against house tenants 35.1%). in general, a house owner would be more aware regarding safety questions.  the majority of surveyed persons live in relatively huge houses (with more than 4 rooms) and a relatively high number of persons living in it (more than 4 persons/house). table ii. general information of the survey's participants 1 age (years) less than 25: 18.4% between 26 and 50: 64% more than 50:17.5% 2 gender male: 86.4% female: 13.6% 3 nationality saudi: 82.9% non-saudi: 17.1% 4 educational level secondary and less: 12.7% university: 87.3% 5 house owner: 64.9% tenant: 35.1% 6 house category independent villa: 65.4% apartment: 34.6% 7 are you responsible (father) yes: 76.3% no: 23.7% 8 number of rooms 3 or less: 13.6% more than 4: 86.4% 9 number of persons living in the house 3 or less: 17.5% more than 4: 82.5% 10 number of children in the house 3 or less: 73.7% more than 4: 26.3% 2) survey results in this paper, the assessment of electrical safety attitudes (practice and beliefs) is based on the positive behaviors. each question is posed so that it allows to measure one aspect of the considered attitudes. for all questions, the “yes” response represents the “good” attitude except of questions 20, 21, 22, 24, 29, 31 and 36 (see table iii) where the positive attitude corresponds to the “no” response. in what follows, the electrical safety level (esl) in hail region is calculated using the following procedure:  each question is assigned a grade and a weight as a 4-point average scale used to assess the results of a university student (see table iii).  the esl is calculated using the same formula of a student grade point average (gpa). based on the assessment scale of table iii, the questions 11-36 are assigned a level, a grade and a weight. the details are reported in table iv. table iii. electrical safety level assessment scale grade meaning range weight a+ exceptional 95-100 4 a excellent 90-94 3.75 b+ superior 85-89 6.50 c very good 80-84 3.00 c+ above average 75-79 2.50 c good 70-74 2.00 d+ high pass 65-69 1.500 d pass 60-64 1.00 f fail less than 60 0.00 3) results analysis the questions related to the electrical safety attitudes (practices and beliefs) are divided in such a way that they cover the safety home culture (questions 11-26) and the engineering, technology & applied science research vol. 7, no. 6, 2017, 2231-2235 2234 www.etasr.com boubaker et al.: assessment of electrical safety beliefs and practices: a case study electric devices purchasing culture (questions 26-36). the overall electrical safety score is found to be 0.76 (using a scale of 4 points). according to table iii classification, this score is poor which incites suitable recommendations to improve it. the sale culture is relatively better (1.45 out of 4) than the home safety culture (0.45 out of 4). however, the two aspects of electrical safety culture are obviously poor. although 87.3% of respondents have at least one university degree, their electrical safety culture is very poor. despite that 66.7% of respondents know that the current used at home must be under an allowed value, 57.6% of them did not check the correspondence between the receptacles and sockets and the current to be fed. the “grounding” culture is also poor since almost 50% of the respondents said that some of their domestic appliance is not grounded which can be a source of dangers for them and for their families. a positive aspect has been noticed according to the children electrical safety consideration. in fact, 67.5% of respondents take into consideration their children electrical safety (they cover the switches and sockets and mount them far away from their children). table iv. calculation of the electrical safety level (esl) of hail region based on the designed questionnaire # question yes (%) no (%) grade weight 11 did you know that the current allowed at home must be under a value predefined by the electricity feeder? 51.9 48.1 f 0 12 did you know that if you exceed the allowed current, harmful danger on human and equipment can occur? 66.70 33.3 d+ 1.5 13 did you have examined the electrical wiring in your home by a specialist? 35.1 64.9 f 0 14 did you check the correspondence between the socket and the current to be provided from it? 57.6 42.4 f 0 15 have you ever heard the term “earthing”? 49.8 50.2 f 0 16 are all your domestic appliances connected to the earth? 43.3 56.7 f 0 17 are all the switches and sockets covered by plastic covers? 51.9 48.1 f 0 18 are all switches and sockets far away from children? 67.5 32.5 d 1 19 are all light lamps well fixed? 91.8 8.2 a 3.75 20 were you subject to an electrical shock? 61.5 38.5 f 0 21 did a short circuit occur before in your house? 47.6 52.4 f 0 22 did you switch on the electricity source after a short circuit without checking for the cause? 43.3 56.7 f 0 23 did you know that if you don’t check for the cause, a high danger will occur? 64.1 35.9 d 1 24 did an electricity-caused fire occur before in your house or in neighbor or parent house? 47.2 52.8 f 0 25 are the breaker and the electrical cabinet in your house of high quality? 59.3 40.7 f 0 26 did you have an extinguisher for electricity-caused fires? 18.2 81.8 f 0 27 did you check the technical features of an electrical device (provider, country, and model) before buying it? 80.9 19.1 b+ 3.5 28 did you check the maximum current supported by the sockets and switches before buying them? 58.7 41.3 f 0 29 did you bought before an electrical device from an unknown source? 57.7 42.3 f 0 30 did you know that the bad quality of electrical devices can cause fires? 93.2 6.8 a 3.75 31 were you subject of an accident caused by a bad electrical device? 44.7 55.3 f 0 32 did you know that the overall load of devices connected to the same electrical socket is not allowed to go over the maximum load of this socket? 79.9 20.1 c+ 2.5 33 did you read the technical datasheet (book) of any device you buy? 52.6 47.4 f 0 34 did you obey to the safety rules included in an electrical device book? 53.2 46.8 f 0 35 did you consider that the electrical devices you use are of good quality? 91.8 8.2 a 3.75 36 did you let the mobile phone charging for a long time? 79.5 20.5 f 0 electrical safety level (esl) 0.76 out of 4 although 64.1% of the survey participants responded knowing “they have to check for the cause of current interruption” (culture aspect), 56.7% practice this safety aspect. 80.9% of respondents have declared that they check the technical features of an electrical device before purchasing it. this practice is clearly good. however, 58.7% have recognized that they did not check the maximum current required by this device (or supported by it). despite that 93.2% have the culture of purchasing devices with good quality, 42.3% of respondents have recognized buying electrical devices from an unknown source. finally, the culture of letting the cell phone charging during a long period is spread since 79.5% responded “yes” to this question. iii. conclusions and recommendations the results of the present study have demonstrated that the electrical safety culture (practices and beliefs) in hail region, saudi arabia, is very poor. this fact has been confirmed by the official general directorate of civil defense (gdcd) records of electricity-caused accidents in hail region, and by the questionnaire we have devised and distributed to persons living in hail. therefore, based on the results of this study, plans aiming to improve the electrical safety score are necessary. the competent authorities should promote specific actions following the below recommendations: engineering, technology & applied science research vol. 7, no. 6, 2017, 2231-2235 2235 www.etasr.com boubaker et al.: assessment of electrical safety beliefs and practices: a case study  from a legislative point of view, new rules and sanctions have to be included and applied to organisms that do not obey rigorously to the electrical safety requirements.  the gdcd, as the authority responsible of safety matters, has to intensify the inspections. this requires highly qualified inspectors.  the safety culture (including the electrical safety) has to be developed during the primary and secondary schools by specialized courses or trainings. this task can be adopted by the ministry of education.  brochures explaining the dangers of electricity and the rules to be applied in order to avoid accidents should be prepared and distributed.  campaigns aiming to improve the awareness level should be organized by the civil community associations and the scientific chairs of the university of hail.  more research studies on the field of safety should be conducted by hail university faculty members.  the culture of occupational safety and health (osh) should be improved, particularly in the family level.  since fire is the most dangerous consequence of an electrical accident, homes, schools, administrative buildings, hospitals, hotels etc. should be equipped with specific extinguishers (for electricity-caused fires).  the residents should be provided with free training on safety awareness by the deanship of community service of hail university in collaboration with the concerned faculties. acknowledgement this research project has benefited from a research grant awarded by the deanship of scientific research of hail university, saudi arabia under the number 150462. the authors would like also to thank mr. abdullah aly al-amer from the general directorate of civil defense of hail region, saudi arabia for the data and photos he has provided. references [1] d. k. neitzel, “electrical safety basics for non-electrical personnel”, 61th ieee pulp and paper industry conference, milwaukee, pp. 1-4 2015 [2] a. dahai you, b. qingqian chen, c. xianggen yin, d. bo wang, “a study of electrical security risk assessment based on electricity regulation”, energy policy, vol. 39, no. 4, pp. 2062-2074, 2011 [3] m. s. al-homoud, m. m. khan, “assessing safety measures in residential buildings in saudi arabia”, building research & information, vol. 32, no. 4, pp. 300-305, 2004 [4] d. k. neitzel, “electrical safetyupdate-osha 29 cfr 1910.269 and nfpa 70e-2015 revisions”, ieee transactions on industry applications, vol. 52, no. 4, pp. 2753-2758, 2016 [5] d. t. roberts, “risk assessment and your electrical safety program: performance at the organizational and worker levels”, ieee ias electrical safety workshop, louisville, pp. 1-6, 2015 [6] j. castillo-rosa, m. suraz-cebador, j. rubio-romero, j. a. aguado, “personal factors and consequences of electrical occupational accidents in the primary, secondary and tertiary sectors”, safety science, vol. 91, pp. 286-297, 2017 [7] m. suarez-cebador, j. c. rubio-romero, a. lopez-arquillos, “severity of electrical accidents in the construction industry in spain”, journal of safety research, vol. 48, pp. 63-70, 2014 [8] m. a. hassanain, “approaches to qualitative fire safety risk assessment in hotel facilities”, structural survey, vol. 27, no. 4, pp. 287-300, 2009 [9] p. wadick, “safety culture among subcontractors in the domestic housing construction industry”, structural survey, vol. 28, no. 2, pp. 108-120, 2010 [10] i. n. isik, e. atasoylu “occupational safety and health in north cyprus: evaluation of risk assessment”, safety science vol. 94, pp. 17-25, 2017 [11] k. m. white, n. l. jimmieson, p. l. obst, p. gee, l. haneman, b. o’brien-mcinally, w. cockshaw, “identifying safety beliefs among australian electrical workers”, safety sience, vol. 82, pp. 164-173, 2016 [12] m. o. jannadi, s. assaf, “safety assesment in the built environment of saudi arabia”, safety sience, vol. 29, pp. 15-24, 1998 [13] m. s. al-homoud, a. a. abdou, m. m. khan, “safety design practices in residential buildings in saudi arabia”, building research & information, vol. 32, no. 6, pp. 538-543, 2004 [14] safety requirement code & the safety rules required in residential and administrative buildings in saudi arabia, ministry of interior, civil defense council, 1410 h [15] statistics of electricity-caused accidents from 1/1/1431 h to 1/12/1437 h, internal report of general directorate of civil defense in hail region, 2016 [16] m. h. noweir, m. m. alidrisi, i. a. al-darrab, m. a .zytoon, “occupational safety and health performance of the manufacturing sector in jeddah industrial estate, saudi arabia: a 20-years follow-up study”, safety sciuence, vol. 53, pp. 11-24, 2013 engineering, technology & applied science research vol. 7, no. 5, 2017, 1934-1939 1934 www.etasr.com αhmadi et al.: optimal resources planning of residential complex energy … optimal resources planning of residential complex energy system in a day-ahead market based on invasive weed optimization algorithm pouria αhmadi electrical engineering dpt amirkabir university of technology tehran, iran pouria7091@aut.ac.ir mohammad ηassan νazari electrical engineering dpt amirkabir university of technology tehran, iran nazary@aut.ac.ir seyed ηossein ηosseinian electrical engineering dpt amirkabir university of technology tehran, iran hosseinian@aut.ac.ir abstract—this paper deals with optimal resources planning in a residential complex energy system, including fc (fuel cell), pv (photovoltaic) panels and the battery. a day-ahead energy management system (ems) based on invasive weed optimization (iwo) algorithm is defined for managing different resources to determine an optimal operation schedule for the energy resources at each time interval to minimize the operation cost of a smart residential complex energy system. moreover, in this paper the impacts of the sell to grid and purchase from grid are also considered. all practical constraints of the each energy resources and utility policies are taken into account. moreover, sensitivity analysis are conducted on electricity prices and sell to grid factor (sgf), in order to improve understanding the impact of key parameters on residential chp systems economy. it is shown that proposed system can meet all electrical and thermal demands with economic point of view. also enhancement of electricity price leads to substantial growth in utilization of proposed chp system. keywords-combined heat and power system (chp); electricity tariff; energy management system; smart home i. nomenclature i time interval ,battery ic total cost of battery in the i th interval ,gas ic total cost of purchasing gas in the ith interval ,fc ic total cost of fuel cell in the i th interval ,i pur gridc total cost of utility in the ith interval ,i sell gridc total revenue of utility in the ith interval u length of time interval gasb cost of purchasing natural gas per kw ,gas ip heat power produced directly from gas mu normalized price of electricity tariff gridb maximum value of utility purchasing electricity cost per kw ,grid ip purchased power from utility by home batteryb operation and maintenance cost of battery (kw) ,battery ip output power of battery plr part load ratio ,efc ip electrical power produced by fuel cell ,fc iή efficiency of fuel cell. ,el ip electrical load demand loadq thermal load power ,fc iq heat power produced by fuel cell minw minimum energy limit of battery maxw maximum energy limit of battery soc available energy in battery , ,battery dch maxp maximum limit of battery discharging rate , ,battery ch maxp maximum limit of battery charging rate dchή efficiency of battery discharging. chή efficiency of battery charging  hourly self-discharge rate ,fc up upper limit of ramp rate of fuel cell ,fc dp lower limit of ramp rate of fuel cell ,fc minp minimum limit of fuel cell generated power ,fc maxp maximum limit of fuel cell generated power chή efficiency of battery charging ,fc ir electrical to thermal power ratio of fuel cell dchή efficiency of battery discharging ,t ig reference irradiation ,c it environment temperature sgf sell to grid factor engineering, technology & applied science research vol. 7, no. 5, 2017, 1934-1939 1935 www.etasr.com αhmadi et al.: optimal resources planning of residential complex energy … ii. introduction chp (combined heat and power) system is a lucrative alternative which offers lower energy costs, higher efficiency, higher reliability, stability in the face of uncertain electricity costs and lower greenhouse gas (ghg) production. the application of chp systems for residential loads will be promoted if optimal operation of the integrated energy system is completely investigated. authors of [1] have proposed a mixed integer nonlinear programming approach to minimize annual cost of the system for a given residential customer equipped with the chp plant, combining with a back-up boiler. authors in [2] have presented optimal sizing of rers (renewable energy resources) including pv/wt beside chp units in a grid connected to residential complex using simulated annealing optimization (sa). it has been shown in [2] that rers and chp unit can properly complement each other. authors of [3] have proposed operational strategy for a chpbased grid-tied mg (microgrid) including pv/fc/wt and mt (micro-turbine). it has been presented in [3] that an increase in the price of electricity encourages the utilization of mgs based on rers. also in order to have a higher level of reliability, a higher number of dgs must be employed in mgs. in [4], a hybrid electrical/ thermal home energy system including fc, chp and battery is studied using hyper-spherical search algorithm. it has been shown that the battery and variable electricity tariffs have substantial effect on system operating costs. in [5] optimal scheduling of home energy system has been shown that the efficiency of battery has a major effect on the system operating cost; however, the impact of selling electrical energy to grid is not considered. in this paper, an optimal resources planning in the hybrid thermal/electrical grid-connected residential complex including a fc, pv and battery is studied. a day-ahead power scheduling based on invasive weed optimization (iwo) algorithm for managing different resources is developed to generate an efficient look-up table that determines an optimal operation schedule for the distributed energy resources at each time interval, in order to minimize the operation cost of the system. the impacts of bilateral trading to grid during different tariffs are taken into account and all practical constraints of the energy resources and utility are considered. also accurate models of each energy resources including upper and lower limits of ramp rates of fc and charge and discharge ramp rates of battery are also applied. moreover, in order to examine different energy price policies, sensitivity analysis have been conducted on electricity prices and sell to grid factor (sgf). it should be noted that the model of this study is formulated in general terms, so it can be easily adapted to various residential building systems by applying hourly load data, meteorological data, energy price policies etc. this paper is structured as follows. firstly the system architecture and operation is given in section iii. energy management system (ems) is explained in section iv. problem formulation is outlined in section v. results and discussion are investigated in section vi and section vii draws the concluding remarks. iii. system configuration and operation figure 1 shows the configuration of the proposed hybrid residential energy system. the system includes of pv panels as a renewable energy source, a fc as a chp system and battery to store surplus energy and improve the system reliability. the thermal load can be supplied by either natural gas or recovered heat from the fc. the electrical load can be supplied by the pv, fc, battery or main grid. sell to grid is also taken into account. fig. 1. residential building multi-carrier energy system a. modeling the system components 1) pv system the output power of pv (ppv) at each time (t) can be calculated [6, 7]: , ,i pvpv ip a g   (1) where g is solar radiation, a is pv area and pv is overall efficiency of solar panel without considering efficiency of dc/ac converter. the pv in each time can be determined using following equation:  , 10 ,[1 ]pv ref ref c i ref t iή ή t t ylog g    (2) 2) fc the maximum electrical power of the fc is restricted by maximum capacity of fc given in table ii. if output power of fc becomes less than a lower threshold, the fc cannot work and it should be switched off. the efficiency of the fc is a function of part load ratio (plr). plr is ratio of electrical generation to maximum fc power rating. the efficiency and ratio of the electrical to thermal energy of fc are also function of plr [8] and can be obtained by following equations: 0.05iif plr  ,i ,0.2716 0.681fc fc iή r  (3) 0.05iif plr  5 4 , 3 2 0.9033plr 2.9996plr 3.6503plr 2.0704plr 0.4623plr 0.3747 fc i i i i i i ή       (4) engineering, technology & applied science research vol. 7, no. 5, 2017, 1934-1939 1936 www.etasr.com αhmadi et al.: optimal resources planning of residential complex energy … 4 3 , 2 1.0785plr 1.9739plr 1 .5005plr 0.28 ( 17plr 0. ) 6838 fc i i i i i tr      (5) therefore, thermal energy provided by fc in each time interval is: , ,,fc ifc i fc iprq   (6) in this paper, as an accurate model of the energy resources is considered, upper and lower limits of ramp rates of fc are taken into account. therefore following equations are considered through simulation procedures. , , 1 , efc t efc t fc u p p u p    (7) , 1 , , efc t efc t fc d u p p p    (8) 3) battery the battery bank capacity is presented in table ii. in this study an accurate model for battery is considered in which battery and converter efficiencies, self-discharge rate and charge and discharge ramp rates of battery are taken into account. the charge and discharge quantity of the battery bank at time t can be determined by following equations, respectively. 1 ,i(1 )i battery hi csocsoc p ή     (9) ,i 1 (1 ) batter i y i dch p so ή so cc    (10) the following inequalities represent limitations of discharging and charging ramp rates for the battery, respectively: ,1 ,1 ch maxi battery dch maxi batter i y i soc u soc soc p soc p u       (11) iv. energy management system (ems) the main role of the ems is to minimize the operating cost while satisfying all thermal and electrical demands of residential complex. in order to use available energy resources effectively, operation scheduling should be determined one day or longer in advance. it is assumed that the predicted values of heat and electricity demands are available one day ahead in the optimization model studied in this paper. it should be noted that as the objective of this study is to minimize the operating cost of residential complex energy system, the components of system are previously installed and there is no need to consider installation costs. in this study, the model is formulated in general terms, so it can be easily adapted to various systems by applying hourly load data, meteorological data tariffs, natural gas price etc. a. cost function the objective of ems is to minimize following cost function.   ,i ,i ,i ,i ,i )( pur sellfc battery grid grid gasimin f x c c c c c     (12) where ,fc tc , ,battery tc , , pur grid tc , , sell grid tc and ,gas tc can be calculated using following relations: ,i , ,i efc fc t f ga c s p c u c ή          (13) also, in this study startup cost and shutdown costs of fc are taken into account. ,i ,i battery battery batteryc u b p  (14) ,i ,i pur grid grid gridc u m pbu    (15) ,i ,i sell grid grid gridc u m s fpb gu     (16) ,i ,igas gas gasc u b p  (17) b. constraints following constraint should be satisfied. , ,i ,fc min fc fc maxp p p  (18) min xi masoco socs c   (19) c. power balance in this study, the load shedding is not considered, so all the electrical and thermal demands must be supplied. , ,, , , 0fc i battery ip grid i l iv ai o dp p p pp     (20) , , , 0gas i fc i load iqq q   (21) it is assumed that sell to and purchase from grid must not be occurred simultaneously. namely, at each t , the residential complex energy system should only sell energy to grid or purchase electricity from grid. d. electricity tariff in this paper, three different tariffs are considered for electricity price: peak, intermediate, and off-peak tariffs. all of the tariffs are normalized regarding the maximum electricity tariff defined in the “peak” period. normalized values of these tariffs and their pertaining time intervals are listed in table i [9]. in this study, electricity price during on-peak hours is 0.13($/kwh) [5]. in base scenario, sell to grid (sgf) factor is assumed to be 0.9 [10]. v. invasive weed optimization algorithm a. terms used • seeds – all units in the optimization problem that are assigned a value pertaining to the limiting conditions. • plants – seeds that grow into plants before being evaluated. engineering, technology & applied science research vol. 7, no. 5, 2017, 1934-1939 1937 www.etasr.com αhmadi et al.: optimal resources planning of residential complex energy … • fitness value – a value that determines how good the plant is, i.e. how much optimized the solution is. table i. electricity tariff [8] period time range normalized electricity purchase price peak (9:00-12:00), (17:00-22:00) 1pu intermediate (13:00-16:00) 0.9pu off-peak (23:00-08:00) 0.78pu the iwo algorithm is inspired from the biological growth of weed plants. this technique is based on the colonizing behavior of invasive weed plants [13]. weed plants are called invasive because the growth of weed plants is extensively invading in the growth area. iwo is known to be highly converging in nature since it a derivative free algorithm. it also converges to the optimal solution thereby eliminating any possibilities of sub optimal solutions with easy coding implementation. iwo has been so far implemented for applications like dna computing and antenna system design [14]. in this algorithm, the number of decision variables are taken in the form of seeds and then randomly distributed in the feasible space [15]. these seeds are then permitted to grow into plants and the fitness of each individual plant is determined. depending upon these fitness values, new seeds are generated by each plant in accordance with a normalized standard deviation σ. in the next step the combined fitness values of seeds and plants is calculated until the fitness value converges to an optimal solution. the objective function is utilized as the fitness function to achieve the optimized results using convergence technique. simulation procedure of iwo algorithm has been explained below. step 1: the seeds are initialized based on the number of selected variables involved in the process over the probable search boundary. the seeds are randomly initialized based on feasible space. step 2: the fitness of the seeds initialized is evaluated depending upon the fitness function. these seeds then evolve into weed plants capable of producing new units. step 3: the evolved plants are arranged in a definite order (increasing or decreasing) and new seeds are produced by these plants depending upon its position in the sorted list of plants, starting with the maximum number of seeds produced by the best fit plant. step 4: the number of seeds to be produced by the plants varies linearly from nmax to nmin which is obtained by given formulation: max min min( ) i worst best worst number of se f f n n n f f eds      (22) step 5: the generated seeds are distributed normally over the feasible space with zero mean and a standard deviation that is updated during each iteration using: max 0 max ( ) n iter f f iter iter iter             (23) where n is used to help algorithm to traverse around the feasible space more efficiently and is generally assumed to be between 2 and 3. step 6: the fitness of each seed generated in the above steps is calculated along with the parent weeds and by means of competitive exclusion, the seed-parent combinations that are least in fitness are eliminated and the number of weed plants is limited to the maximum of number of weeds allowed. step 7: the above steps are repeated until convergence criteria is reached, so that the plant with the best fitness value is the optimized solution. the simulation procedure of iwo algorithm is given in figure 2. vi. results and discussion a. operation behavior the simulation has been conducted for 24 hours in matlab software environment. the profile of thermal and electrical load demands of the residential complex in a typical day in spring has been presented in [2]. for this system, the peak of thermal and electricity demands are 34 kw and 78 kw, respectively. the parameters of the system are presented in table ii. figure 3 shows the optimal operation of each energy resources in a typical day. according to this figure, in early hours of the day, as the price of electricity is low, the residential complex energy system purchases electrical energy to supply the load and store in battery. then, during the highcost hours, the ems orders the sell of electrical energy in order to make the operation of the system more economic. in addition, this sold energy contributes to power system for supplying electrical demand of the system during peak hours. namely, in the first eight intervals, as the utility electrical cost is at its lowest level, the battery is charged and the major part of electrical demand is supplied by the utility. fc does not generate at its maximum capacity and generates the limited power such that its cost becomes less than the utility. in other words, if fc generates more power, its efficiency is reduced and it causes higher cost compared to the utility cost. also as ramp rate of fc is taken into account, fc needs to increase its power generation at interval 6th and 7th, so that there will be no limit on high-cost hours to generate at its maximum capacity. during the 13th to 16th intervals that the electricity tariff is in the intermediate period, only fc and pv supply the electrical load. also natural gas contributes to recovered thermal energy from fc to meet thermal demand. in the 9th to 12th and 17th to 22th intervals, the electricity tariff is in the peak period. therefore, the battery delivers all of its stored energy, fc generates at its maximum power limit and pv panel contributes to other energy resources to supply the load and sell electrical energy to grid. so it can be concluded proposed residential energy system sells energy to grid only in high-cost periods and purchase energy from grid in low-cost intervals. as a result, proposed residential system can help to have smoother engineering, technology & applied science research vol. 7, no. 5, 2017, 1934-1939 1938 www.etasr.com αhmadi et al.: optimal resources planning of residential complex energy … load profile in power system. the power generations of each energy resource are listed in table iii. no yes fig. 2. the simulation procedure of iwo algorithm b. sensitivity analysis sensitivity analysis improves the understanding of impact of key parameters on the behavior of proposed residential chp systems. in this study, sensitivity analyses have been performed on electricity prices and sell to grid factor parameters. an imperative parameter of the operation cost for residential energy system is electricity price, which also has an important effect on the adoption of residential chp systems. figure 4 shows the result of sensitivity analysis. it is clear that electricity price and sell to grid factor strongly affect the economy of residential chp system operation. according to figure 4, while the electricity price is low, sell to grid factor has a negligible effect on operation cost of residential chp system, because of low electricity price, the ems provides the majority of required electrical energy of system from utility. in fact, purchasing electricity from utility is more economic than operation of fc close to its maximum capacity and system. therefore after this point, by increasing the electricity price, the operation of residential chp system becomes more economic and operation of fc near its maximum power gradually becomes more economic. also figure 4 demonstrates that by increasing the electricity price, the impact of sell to grid factor on operation cost of residential chp system will be increased. therefore, enhancement of electricity price encourages other residential buildings to install proposed chp system. fig. 3. optimized resources power generations table ii. system parameters [5, 11,12 ] ,fc up , upper limit of ramp rate of fuel cell 0.15 ,fc dp , lower limit of ramp rate of fuel cell 18 ,fc maxp , maximum limit of fuel cell generated power 25 ,fc minp , minimum limit of fuel cell generated power 0.05 maxw , maximum energy limit of battery 40 gasb , cost of purchasing natural gas per kw 0.04 gridb , maximum value of utility purchasing electricity cost per kw 0.13 dchή , efficiency of battery discharging 0.971 chή , efficiency of battery charging 0.921 , ,battery dch maxp , maximum limit of battery discharging rate 15 , ,battery ch maxp , maximum limit of battery charging rate -15 reft , reference temperature (°c) 25 ref 0.0044 refή , reference efficiency of pv 0.125 fig. 4. operation cost sensitivity related to different electricity prices and sgfs initialize input data the distributed seeds grow into weed plants calculated fitness of each individual plant sort the fitness in descending order and rank the plants generate new seeds using spatial distribution based on the rank of the plant determine the new fitness of the seed plant combination competitive exclusion convergence criteria is satisfied stop start engineering, technology & applied science research vol. 7, no. 5, 2017, 1934-1939 1939 www.etasr.com αhmadi et al.: optimal resources planning of residential complex energy … table iii. simulation results interval pbat pefc phfc pgas ppv pu 1 -0.342 5.864 3.985 0 0 7.645 2 -16.174 5.8641 3.985 0 0 23.477 3 -16.181 5.8637 3.985 0 0 23.484 4 -10.451 5.8644 3.985 0 0 17.753 5 0 5.8641 3.985 0 0 7.469 6 0 5.8643 3.985 0 0.802 14.999 7 0 5.8642 3.985 0 2.407 18.228 8 0 9.3859 6.666 0 5.778 15.169 9 9.105 23.0037 22.185 47.8147 9.1485 -8.757 10 12.3867 23.0037 22.185 56.148 11.395 -13.45 11 8.4253 23.0039 22.185 52.8143 13.0005 -10.59 12 3.5214 23.0033 22.184 49.4822 13.482 -6.59 13 -1.0473 21.0413 18.877 51.1221 12.84 -0.0006 14 0 21.265 19.220 50.7793 11.23 0 15 0 22.3577 21.016 38.9837 9.309 0 16 0.0002 22.0736 20.528 29.4712 6.259 0 17 0.4367 23.0035 22.185 16.1484 3.21 -0.483 18 0.1085 23.0036 22.185 14.4816 0.8025 -0.581 19 2.5615 19.4696 16.666 0 0 -0.364 20 1.7907 12.7233 9.5076 0 0 -0.014 21 1.4468 12.724 9.5082 0 0 -0.004 22 0 13.6667 10.371 0 0 0 23 0 5.8642 3.9853 0 0 7.635 24 0 5.8641 3.9853 0 0 7.469 vii. conclusion in this paper, a new configuration for a residential building energy system has been proposed, including a fc, pv and a battery connected to the utility. an optimization model has been established based on deterministic prediction of electrical and thermal power demands and utility prices. a day-ahead ems based on iwo algorithm has been defined for managing different resources to determine an optimal operation schedule for the energy resources at each interval to minimize the operation cost of the system. the impacts of the sell to grid and purchase from grid have been considered and all practical constraints of the each energy resources and utility policies have been taken into account. sensitivity analyses have been conducted on electricity prices and sgf. it has been shown that proposed system can meet all electrical and thermal demands with economic point of view. also it has been proved that with the increase in electricity price, the operation cost of proposed system has been increased. but from one particular point on, by increasing the electricity price, the operation of residential chp system has been more economic and operation of fc near its maximum power gradually has become more economic. also it has been offered that by increasing the electricity price, the impact of sell to grid to factor on operation cost of residential chp system will be increased. therefore, enhancement of electricity price encourages other residential building to install proposed chp system. references [1] h. ren , w. gao, y. ruan, “optimal sizing for residential chp system”, applied thermal engineering, vol. 28, no. 5-6, pp. 514–523, 2008 [2] y. yang, w. pei, z. qi, “optimal sizing of renewable energy and chp hybrid energy microgrid system”, ieee innovative smart grid tech. asia conf., pp. 1-5, china, may 21-24, 2012 [3] m. h. moradi, m. eskandari, m. hossenian, “operation strategy optimization in an optimal sized microgrid”, ieee transactions on smart 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mojallali, r. izadi-zamanabadi, “state estimation of nonlinear stochastic systems using a novel meta-heuristic particle filter”, swarm & evolutionary computation, vol. 4, pp. 44–53, 2012 [14] s. karimkashi, a. a. kishk, “invasive weed optimization and its features in electromagnetics”, ieee transactions on antennas and propagation, vol. 58, no. 4, pp. 1269–78, 2010 [15] s.g. tichi, m. m.ardehali, m.e.nazari, “examination of energy price policies in iran for optimal configuration of chp and cchp systems based on particle swarm optimization algorithm”, energy policy, vol. 38, no. 10, pp. 6240–6250, 2010 microsoft word etasr_v12_n4_pp9038-9041 engineering, technology & applied science research vol. 12, no. 4, 2022, 9038-9041 9038 www.etasr.com chami et al.: a new miniature micro-strip two-layer band-pass filter using aperture-coupled … a new miniature micro-strip two-layer band-pass filter using aperture-coupled hairpin resonators n. chami electrical engineering department university of m’sila algeria nourchami@gmail.com d. saigaa electrical engineering department university of m’sila algeria djamel.saigaa@univ-msila.dz a. djaiz electronics and instrumentation engineering technology department yanbu industrial college saudi arabia djaiza@rcyci.edu.sa received: 3 may 2022 | revised: 25 june 2022 | accepted: 29 june 2022 abstract-the goal of this project was to provide novel band-pass filter design techniques for mobile communications, which allow a significant reduction in the size of the filters produced. the novelty comes from the transformation of the single layer technique into a double layer technique by inserting coupling slots in a common mass plane. because of their tiny size, these filters are suitable candidates for integration into mobile communication systems. indeed, when compared to the dimensions of a single-layer planar filter, the multilayer construction allowed us to reduce the size of the filter by more than 40%. five u-shaped hairpin resonators were placed on two micro-strip layers in the planned filter. two apertures etched on a common ground plane positioned between the two layers allow varied couplings between the upper and bottom layer resonators. a five-pole hairpin band-pass filter was created as a result. keywords-micro-strip filters; miniature circuits; hairpin resonator; multilayer structure; apertures; resonator filters i. introduction the field of wireless communications is continuously expanding and improving. indeed, since the introduction of cellular systems, particularly 4g systems [1, 2], downsizing of rf components in general, and filters in particular, has piqued interest and has become a critical requirement. filtering at 4g operating frequencies is considered a challenge itself: waveguides and, more broadly, three-dimensional (3d) approaches, which are widely used in mobile communications, are not available in 4g cellular networks, whereas planar filters, which are generally not used in 4g systems due to their relatively high losses, tuning difficulties, and low operating powers, become more appealing. several strategies have been presented to address this demand. micro-strip line filters are particularly appealing for mobile radio applications due to their efficiency and repeatability [3]. the latest generation of cellular systems is characterized by a constant reduction in cell size. this tendency, on the one hand, increases the market volume of base stations, while, on the other hand, reduces the power supply demand for wireless communication networks [4, 5]. special attention must be paid in this context to the types and qualities of employed equipment, such as weight and size, which are becoming an increasingly strong limitation for the realization of current cellular telephone circuits [3, 4, 6, 7]. planar technology has sparked interest in the design of microwave circuits in this context, due to the multiple benefits of these structures, which include low cost, small size, light weight, ease of design, and reproducibility. filters are also the first, out of all the components, of the microwave block circuit to be explored in planar technology [3]. the current work proposes and investigates a unique fivepole micro-strip band-pass filter with a two-layer structure and aperture-coupled hairpin resonators operating at 2.45ghz [9]. the suggested filter architecture consists of five hairpin resonators etched on two stacked layer substrates, with two slots in the common ground plane providing coupling between the upper and bottom layer resonators [8-10]. ii. design approach to demonstrate our approach, a five-pole u-shaped band pass filter with hairpin resonators was designed with the specifications listed in table i. the proposed filter is designed to have a 5% fractional bandwidth (fbw) and a median frequency f0 of 2.45ghz [12-14]. a five-pole chebyshev lowpass filter prototype with a bandwidth ripple of 0.1db was chosen. a five-pin resonator on two stacked micro-strip layers was used to meet these requirements. the coupling between the resonators on the upper and lower layers is accomplished by etching two coupling apertures on a common ground plane between the two layers. the proposed stacked five-pole bandpass filter of aperture-coupled hairpin resonators on the outer corresponding author: n. chami engineering, technology & applied science research vol. 12, no. 4, 2022, 9038-9041 9039 www.etasr.com chami et al.: a new miniature micro-strip two-layer band-pass filter using aperture-coupled … surfaces of the two dielectrics is shown in exploded view in figure 1. the substrate thickness is h, and the aperture dimensions on the common ground plane are dx and dy. table i. the proposed bandpass filter specifications center frequency (f0) 2.45ghz fbw 5% insertion loss 3db maximum bandwidth (at -3db) 120mhz stopband rejection (db) < -30db to design this filter, numerical simulations were performed using the full-wave simulator advanced design system (ads) for hp-agilent [9, 15] to simulate the frequency responses of these fundamental couplings, and thus to acquire the varied spacing between resonators and coupling aperture dimensions. the typical resonant responses between the second and third or third and fourth coupled resonators are shown in figure 2(a). the typical resonant responses between the first and second resonators, or between the fourth and fifth resonators, are shown in figure 3(b). the coupling coefficient can be then extracted by using the following relation [8]: ��� � ∓ �� � � � �� ��� � (1) where fe and fm are the two split resonant frequencies. (a) (b) (c) fig. 1. structure of the proposed filter. the proposed band-pass filter uses u-shape hairpin resonators [15]. to produce necessary coupling between adjacent resonators, these resonators were placed near each other in a specified space s [16]. (a) (b) fig. 2. typical resonant responses: (a) horizontal coupling, (b) aperture coupling. iii. results and discussion to demonstrate the proposed approach, the proposed five pole βand-pass filter [17] using identical miniaturized hairpin resonators is designed in the ism band with center frequency fo at 2.45ghz, band-pass bandwidth of 150mhz (fbw= 5%), and stop-band rejection of 20db at +70mhz from the center frequency. this rejection is achieved in the design by replacing the transmission zero at 75mhz from the center frequency [18]. the circuit was designed and optimized using a substrate with relative dielectric of εr = 6.15, loss tangent of 0.0027, and thickness 50mil (1.27mm). the filter can be synthesized using the method reported in [10, 19] from which the lumpedelement values of low pass prototype filter were determined as: g0 = g6 = 1, g1 = g5 = 1.1468, g2 = g4 = 1.3712 g3 = 1.975 the coupling coefficients and qext can be calculated as follows: � �� � ���� ��� (2) ��,� � ��,� � ��� √���� (3) ��,� � ��,� � ��� ���� (4) 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 -50 -40 -30 -20 -10 0 in s e rt io n l o s s ( d b ) frequency (ghz) s= 2.0 mm s= 1.5 mm s= 1.0 mm 1.8 2.0 2.2 2.4 2.6 2.8 3.0 -75 -70 -65 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 in s e rt io n l o s s ( d b ) frequency (ghz) dy=7.0 mm dy=5.0 mm dy=9.0 mm engineering, technology & applied science research vol. 12, no. 4, 2022, 9038-9041 9040 www.etasr.com chami et al.: a new miniature micro-strip two-layer band-pass filter using aperture-coupled … the coupling coefficient m1,2 and m4,5 values are used to determine the dimensions of the apertures (dx, dy), between the resonators 1 and 2 and 4 and 5 respectively. the coupling coefficient m2,3 = m3,4 is used to find the spacing between the resonators 2 and 3. the input/output loads are achieved via tapped feed lines. figure 3 shows the coupling coefficients of different spacings. 0.1 0.2 0.3 0.4 0.5 0.6 0.050 0.075 0.100 0.125 0.150 0.175 0.200 0.225 spacing s (mm) fig. 3. coupling coefficients of different couplings. fig. 4. bandwidth versus resonator spacing s. as depicted in figure 5, it should be noted that the suggested filter's bandwidth varies inversely with the separation between resonators. a five-pole u-shape hairpin resonator band-pass filter prototype with two layers was manufactured utilizing the design technique. experiments were carried out utilizing an hp8722 network analyzer to evaluate the suggested filter's performance. filter responses that have been measured are provided and compared to simulation results. figures 5 and 6 show the simulated and measured s parameters of the proposed filter. from these curves, it can be observed that good agreement is achieved between simulation and experimental results. the band-pass insertion loss fluctuates around 1.65db, the return loss is less than -11db, which are higher than the simulated results (0.8db, 15db). fig. 5. simulated s parameters s11 and s21 of the filter. fig. 6. measured s parameters s11 and s21 of the filter. these small differences are mainly due to the effect of input/output sma connectors, the dielectric conductance, and the resistance of the conductor which were neglected in the simulations [14]. also, a fractional bandwidth of 4.75% at 2.5ghz is achieved. with such features, the proposed miniaturized filter is suitable for wireless communication systems. it can be seen that the bandwidth of the proposed band-pass filter is slightly wider than that of the conventional filter. moreover, a slight frequency shift between the two responses can be observed, which should be attributed to the accuracy of the dimensions of the opening, and leads to a stronger coupling. from these responses, two desirable transmission zeros can be observed, and a symmetrical characteristic of the frequency responses is obtained [19]. the proposed filter has a size of 21.8mm×21.6mm. this structure provides 40% reduction in size compared to the single layer filter structure. iv. conclusion the goal of this project was to provide a novel band-pass filter design technique for mobile communications. the design procedure allows a significant reduction in the size of the produced filters. the approach's novelty comes from the 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 -50 -40 -30 -20 -10 0 r e tu rn & i n s e rt io n l o s s e s ( d b ) frequency (ghz) simulated s 21 simulated s 11 engineering, technology & applied science research vol. 12, no. 4, 2022, 9038-9041 9041 www.etasr.com chami et al.: a new miniature micro-strip two-layer band-pass filter using aperture-coupled … transformation of a single layer technique into a double layer technique by inserting coupling slots in a common mass plane. because of their tiny size, these filters are suitable candidates for integration in mobile communications systems. indeed, when compared to the dimensions of a single layer planar filter, the multilayer construction allowed us to reduce the size of the filter by more than 40%. references [1] y. clavet, "définition de solutions de filtrage planaires et multicouches pour les nouvelles générations de satellites de télécommunications," ph.d. dissertation, université de bretagne occidentale, 2006. [2] r. levy and s. b. cohn, "a history of microwave filter research, design, and development," ieee transactions on microwave theory and techniques, vol. 32, no. 9, pp. 1055–1067, sep. 1984, https://doi.org/10.1109/tmtt.1984.1132817. [3] i. c. hunter, l. billonet, b. jarry, and p. guillon, "microwave filtersapplications and technology," ieee transactions on microwave theory and techniques, vol. 50, no. 3, pp. 794–805, mar. 2002, https://doi.org/ 10.1109/22.989963. [4] m. nahas, "a super high gain l-slotted microstrip patch antenna for 5g mobile systems operating at 26 and 28 ghz," engineering, technology & applied science research, vol. 12, no. 1, pp. 8053–8057, feb. 2022, https://doi.org/10.48084/etasr.4657. [5] j. d. rhodes, theory of electrical filters. london, uk ; new york, ny, usa: john wiley & sons, 1976. [6] g. matthaei, e. m. t. jones, and l. young, microwave filters, impedance-matching networks, and coupling structures. norwood, ma, usa: artech house, 1980. 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[11] s. mallavarapu and a. lokam, "circuit modeling and analysis of wearable antennas on the effect of bending for various feeds," engineering, technology & applied science research, vol. 12, no. 1, pp. 8180–8187, feb. 2022, https://doi.org/10.48084/etasr.4699. [12] a. basti, "développement de méthodes de synthèse pour la conception de filtres hyperfréquences compacts et optimisés en pertes," ph.d. dissertation, université de limoges, limoges, france, 2014. [13] t. l. duong and t. t. nguyen, "network reconfiguration for an electric distribution system with distributed generators based on symbiotic organisms search," engineering, technology & applied science research, vol. 9, no. 6, pp. 4925–4932, dec. 2019, https://doi.org/10.48084/etasr.3166. [14] p. f. combes and r. crampagne, "circuits passifs hyperfréquences filtres et cavités," techniques de l’ingénieur. https://doi.org/10.51257/av1-e1402. [15] s. bahrami, "design of a mobile agents based solution to distributional management of computer networks, taking into account the security mechanisms," engineering, technology & applied science research, vol. 7, no. 5, pp. 2026–2029, oct. 2017, https://doi.org/ 10.48084/etasr.829. [16] m. k. mohd salleh, "contribution à la synthèse de résonateurs pseudoelliptiques en anneau : application au filtrage planaire millimétrique," ph.d. dissertation, university of toulouse, toulouse, france, 2008. [17] r. saal and e. ulbrich, "on the design of filters by synthesis," ire transactions on circuit theory, vol. 5, no. 4, pp. 284–327, dec. 1958, https://doi.org/10.1109/tct.1958.1086481. [18] j.-s. hong, microstrip filters for rf / microwave applications, 2nd ed. hoboken, n.j, usa: wiley, 2011. [19] α. bairaktari, m. danikas, x. zhao, y. cheng, and y. zhang, "behaviour of water droplets under the influence of a uniform electric field in nanocomposite samples of epoxy resin/tio2," engineering, technology & applied science research, vol. 3, no. 5, pp. 511–515, oct. 2013, https://doi.org/10.48084/etasr.373. engineering, technology & applied science research vol. 8, no. 2, 2018, 2818-2820 2818 www.etasr.com shah et al.: ann and anfis for short term load forecasting ann and anfis for short term load forecasting s. shah electrical engineering department iite, indus university ahmedabad, india shah.sweta21@gmail.com h. n. nagraja electrical engineering department graphic era university uttarakhand, india nagraj_hp@yahoo.com jaydeep chakravorty electrical engineering department indus university ahmedabad, india jaydeepchak@yahoo.co.in abstract—load forecasting has become one of the major areas of research in electrical engineering. short term load forecasting (stlf) is essential for power system planning and economic load dispatch. a variety of mathematical methods has been developed for load forecasting. this paper discusses the influencing factors of stlf and an artificial intelligence (ai) based stlf model for mgvcl load. it also includes comparison of various ai models. our main objective is to develop the best suited model for mgvcl, by critically evaluating the ways in which the ai techniques proposed are designed and tested. keywords-load forecasting; neural network; adaptive neuro fuzzy interface system i. introduction electric load forecasting is the process used to forecast future electric load from the given historical load and weather information. in the last few decades, several models have been developed to forecast electric load more accurately than analytical methods. load forecasting can be divided into three major categories [1]: 1. long-term electric load forecasting, used to supply electric utility company management with prediction of future needs for future expansion, equipment purchases, or hiring of new staff. 2. medium-term forecasting, used for the purpose of scheduling fuel supplies and maintenance. 3. short-term forecasting used to supply necessary information for the system management of day-to-day operations and unit commitment for economic load dispatch. short term load forecasting mainly aims at one hour to one week forecast. as daily load pattern is highly non linear and random, it is very difficult to obtain higher accuracy using analytical methods. application of artificial intelligence (ai) techniques like neural networks and adaptive neuro fuzzy interface systems is an advanced approach for accurate short term load forecasting. ii. artificial neural networks a. introduction artificial neural networks (anns) have been used for many years in sectors like medical science, defense industry, robotics, electronics, economy, forecasts etc. the learning property of anns in solving nonlinear and complex problems is the cause of their application to forecasting problems. b. learning algorithm anns work through optimized weight values [2]. the method by which the optimized weight values are attained is called learning. in the process of learning we present to the neural network pairs of input and output data and try to teach the network how to produce the output when the corresponding input is presented. when learning is complete, the trained neural network, with the updated optimal weights, should be able to produce the output within desired accuracy. there are several learning algorithms. they can be broadly categorized into two classes: supervised and unsupervised. supervised learning means guided learning, i.e. when the network is trained by showing the input and the desired result side by-side. this is similar to the learning experience in our childhood. as children we learn about things (input) when we see them and simultaneously are told (supervised) their names and the respective functionalities (desired result). this is unlike the unsupervised case where learning takes place from the input pattern itself. in unsupervised learning the system learns about the pattern from the data itself without a priori knowledge. this is similar to our learning experience in adulthood. for example, often in our working environment we are thrown into a project or situation which we know very little about. however, we try to familiarize with the situation as quickly as possible using our previous experiences, education, willingness and similar other factors. this adaptive mechanism is referred to as unsupervised learning. c. ann model traning process multilayer feed forward neural network (having input layer, hidden layer and output layer) is used for stlf. the training goal was set at 0 in order to ensure zero tolerance to network computational errors [3]. the transfer function used was the tan-sigmoid in the hidden layer while a linear function was used in the output layer neurons so as not to constrain the output's values. the learning function used is the steepest gradient descent method. the levenberg-marquardt learning function was used as it has better learning rate compared to the other available functions in forecasting problems. the training function used was the steepest gradient descent function and in some tests the steepest gradient descent method with momentum. net art inf fuz of to app to a. lay inp ass be par fun op giv rul sum cal nor the pre an inc engineerin www.etasr iii. ada an adaptive twork-based f tificial neural n ference system zzy logic princ both in a sing a set of fuzzy proximate non be a universal anfis archi in anfis ar yer has the ana put in terms sociated. this defined by su rameters. th nctions are cal layer 2 show erator on the ven as oi wi the output o le of firing po mmation of t lculated in la rmalization. toi wi the output ooi w1d1 in this, result e anfis. the emise and resu nfis which coming signalsoi ∑ w1 ng, technology r.com aptive neuro e neuro-fuzzy fuzzy inferenc network that i m. since it inte ciples, it has th gle framework. y if–then rules nlinear functio l estimator. itecture chitecture [4] alogous functi of its associ is also called uitable membe he foundation lled nonlinear fig. 1. an ws fuzzy and input signals μpi x μqi x of this level is n ower. the ratio the firing str ayer 3. this i the throughput ; i of layer 4 is giv1 w1 aix ting parameter amount of pa ultant paramet can be give s. 1di ∑∑ y & applied sci o fuzzy inter y inference s ce system (an is based on ta egrates both n he potential ca . its inference s that have lea ons. hence, a (figure 1), ea ion. level 1 sh iation grade membership g ership functio n parameters parameters. nfis architecture d operations u s to generate ; i 1,2 normally know o of a rule’s f rengths of all is known as t of layer 3 cani 1,2 ven by: biy ci ; rs are ai, bi an arameters of a ters. in layer n below is ience research rface system system or ad nfis) is a ki akagi–sugeno neural network apturing the be system corres arning capabil anfis is consi ach joint in the hows that with a linguistic t grade [5] and ns with appro s associated e using an appro the output c (1) wn as the anal firing strength l the rules a firing strengt n be given by: (2) i 1,2 (3) nd ci where i=1 anfis is the s 5, overall outp the summatio (4) h v m aptive ind of fuzzy ks and enefits sponds lity to idered e same h each tag is it can opriate with opriate can be logous is the and is ths of 1, 2 of um of put of on of fun pos netw b. con util mat spa init ada fuz com squ mea betw whe obt for algo con esti bac gra are com whi con esti der outp laye upd a. fore and an sho nov sma com 0.3% imp feb for betw vol. 8, no. 2, 20 shah et al.: a the anfis s nctions and b ssible. anfis work holding learning pro as mentione nsequent (linea lizing the learn thematical rela ace. normally, tiated by the s aptive learning zy model and mbining gradie uares optimiza asure, usually ween actual a en either the tained. there a anfis. in orithm, functi nsequent para imate. in the ckward and t adient descent. learned, the o mbination of th 1 1 2 1 1 1 2 2 2 ( ) ( ) w f w w w x m w x n       ich is linear. i nsequent para imate. in the b rivatives of th tput, propagate er. in this b dated by the gr ann model r table i show ecasted error. d forecasted er nn error is 0.1 ows the compa vember and d all compared mparison of er % to 0.5%. it proves the ac bruary and ma the entire yea ween errors is 018, 2818-2820 nn and anfis structure is a because of t is an amalgam the benefits of ocess d above, both ar) parameters ning process, t ationships bet , as a first step system and the g process. ba d tunes it by ent descent ba ation algorith y defined as th and desired ou predefined e are two passes the forward ional signals ameters are i e backward p the premise p . when the va overall output he consequent 2 1 1 2 1 1 1 2 2 ( ) w f w w w x n w w q      in the forward ameters are i backward pass he squared er e backward fr backward pas radient descen iv. results ws the compar average ann rror is -1.346% 34% and forec arison of ann december. it to forecasted rrors for the en t indicates tha curacy of for arch (figure 2 ar could be sim also shown in 0 is for short ter meaningful a this several c mation of fuzz f both. h the premise s of the anfi to optimally re tween the inpu p, an approxim en improved th asically, anfi y means of a ack propagatio hms. at each he sum of the utput, is reduc epoch numbe in the hybrid d pass of the go forward ti dentified by pass, the erro parameters ar alues of the p t (f) can be ex parameters as 2 1 1 1 1 2 2( ) f w f w w q w x m      d pass of the l dentified by s, the error sig rror with resp rom the output s, the premis nt algorithm. results rison of ann n error for 6th % while for 7 casted error is n error and f shows that a error. figure ntire year whic at application recasting. the 2) varies up to milarly develop n figure 2. 2819 rm load foreca assignment of configurations zy logic and n e (non-linear) is should be tu epresent the fa ut space and o mate fuzzy mo hrough an iter is takes the i a hybrid techn on and mean h epoch, an squared differ ced. training er or error ra learning proce e hybrid lea ill layer 4 and the least sq or rates prop re updated by premise param xpressed as a l s: 2 2 2 w f m  (5) learning algor the least sq gnals, which ar pect to each t layer to the se parameters n model error h january is 0 7th january av s -1.566%. fig forecasted erro ann error is e 2 also show ch varies betw of ann for s e anfis erro o 0.07%. a m ped. a compa asting node s are neural ) and uned, actual output del is rative initial nique leasterror rence stops ate is edure arning d the quares pagate y the meters linear rithm, quares re the node input s are r and 0.05% erage gure 2 or for very ws the ween stlf or for model arison engineerin www.etasr t hour 6th er (an 1 0.3 2 -0. 3 0.0 4 0.0 5 0.0 6 0.3 7 0.9 8 0.8 9 0.4 10 0.2 11 -0. 12 0.7 13 -0. 14 -1. 15 1.3 16 -0. 17 1.4 18 -0. 19 -0. 20 -2. 21 1.0 22 0.2 23 0.3 24 0.2 ng, technology r.com fig. 2. table i. a jan rror nn) 6th j err (forec 390 -2.1 .986 -0.6 050 -0.6 056 -0.8 089 -0.0 324 0.17 904 -2.9 872 -3.2 422 -6.4 285 -6.1 .413 -4.7 779 -2.5 .577 -3.6 .671 -2.9 366 -2.6 .407 -0.4 429 0.83 .394 2.27 .809 -2.7 .410 -1.6 091 4.1 275 2.74 383 0.19 240 1.94 y & applied sci error graphs ann results for jan ror cast) 7th ja erro (ann 81 -0.04 658 0.047 695 -0.02 823 0.048 060 2.178 78 -1.51 935 0.000 281 0.019 404 0.000 42 0.000 782 1.948 515 0.036 640 0.019 938 0.018 647 -1.87 455 -3.28 39 -5.02 70 -0.03 777 0.018 692 0.036 14 -1.01 45 -0.04 92 11.67 43 0.02 ience research r january. an or n) 7th jan error (forecas 46 -1.899 7 -1.129 24 -1.335 8 -1.278 8 -2.683 2 -1.351 0 -2.145 9 -1.780 0 -3.800 0 1.042 8 -0.842 6 -2.504 9 -3.656 8 1.575 77 2.217 87 0.263 21 0.436 7 -0.405 8 -0.339 6 -2.123 8 -3.306 40 -6.583 77 -3.935 1 -2.019 h v n st) 9 9 8 0 0 2 4 6 9 6 9 [1] [2] [3] [4] [5] vol. 8, no. 2, 20 shah et al.: a k. kalaitzakis, forecasting base electric power m. markou, e. load forecasti deregulated ele 2008 e. banda, k. a neural network pp. 108-112, ju z. souzanchi-k multi adaptive forecasting by on electronics 54-57, august 1 h. p. oak, s. j international jo no.3, pp. 1878018, 2818-2820 nn and anfis refer g. s. stavrakaki ed on artificial ne systems research kyriakides, m. p ing using multip ectricity market i a. folly, “short-t k”, ieee lausan uly 1-5, 2007 k, h. fanaee-t, m e neuro fuzzy i using previous d and information 1-3, 2010 . honade, ‘anfi ournal of current -1880, 2015 0 is for short ter rences s, e. m. anagnos eural networks pa h, vol. 63, no. 3, polycarpou “24-h ple mlp’, intern issues in south-e term load forec nne power tech, m. yaghoubi, m inference system day features”, in engineering, ky is based short t t engineering an 2820 rm load foreca stakis, “short-term arallel implementa , pp. 185-196, 200 hour ahead short rnational worksh eastern europe, p casting using ar lausanne, switze . r. akbarzadehm for short term nternational conf yoto, japan, vol. erm load foreca nd technology, v asting m load ation”, 02 t term hop on p. 1-6, rtificial erland, -t, “a m load ference 2, pp. asting’, vol. 5, microsoft word etasr_v12_n1_pp7988-7992 engineering, technology & applied science research vol. 12, no. 1, 2022, 7988-7992 7988 www.etasr.com jadhav & deshpande: a tri-band planar inverted-f antenna with complementary split ring … a tri-band planar inverted-f antenna with complementary split ring resonator and reactive impedance surface for wireless application tejaswi jadhav electronics engineering department walchand college of engineering sangli, maharashtra, india tejaswi.jadhav@walchandsangli.ac.in shraddha deshpande electronics engineering department walchand college of engineering sangli, maharashtra, india. shraddha.deshpande@walchandsangli.ac.in abstract-in this paper, a compact, tri-band planar inverted-f antenna (pifa) using complementary split ring resonator (csrr) and reactive impedance surface (ris) is presented for multiband application. the structure of the pifa consists of a metallic csrr and 5×6 periodic unit ris cells, which accomplishes miniaturization and improves bandwidth and multiband. the ris metamaterial plane lies between two substrates and acts as a loading function, reducing the volume of the antenna. the measured and simulated results are consistent for a manufactured prototype. the overall size of the antenna is 22.71×3.451×2.59mm. the pifa shows a tri-band with an s11 < −10db bandwidth of approximately 17.08% (2.26-2.67ghz), 5.14% (6.85-7.21ghz) and 19.44% (7.44-9.19ghz) under measurement. the antenna radiates a wave in a preset direction with realized gains ranging from 3.21 to 8.1dbi. the csrr and ris improve the performance of the antenna for wlan, c-band, and x-band applications. keywords-complementary split ring resonator; gain; multiband; planar inverted-f antenna; reactive impedance surface; wideband i. introduction with the rapid advancement of wireless applications, lightweight, low-cost, and often omnidirectional radiation pattern antennas are becoming increasingly popular. with its low profile and ease of implementation, the planar inverted-f antenna (pifa) is a good radiator for applications such as handheld communication, global positioning system (gps), microwave sensors, wireless local area networks (wlans), synthetic aperture radar (sar), etc.. the pifa has been used in wireless networking applications, such as wlan, radiofrequency recognition (rfid), and satellite navigation systems because of its low profile and light weight. broadside coupled split-ring resonator (srr) inclusions in the magnetic superstrate were studied in [1] and a lower resonance frequency was utilized using a metamaterial-based dual-band in [2], an asymmetrical meander lines srr [3], and a cross-coupled interlinked srr based metamaterial [4]. the combination of the thickness and feed position substantially increases the bandwidth of the desired frequencies discussed in [5] and a cross-shaped slot with a t-shaped patch is used for wideband in [6]. a dual-band operation is addressed by additionally loading an electrically small csrr structure in [7]. a metamaterialbased ris has been used in the slot-loaded patch for antenna optimization in [8]. a tri-band antenna was presented in [9] and a csrr loaded multiple-input–multiple-output antenna with electrically small elements and reduced mutual coupling in [10]. a fractal pifa and srr printed on a conductor-backed dielectric substrate were used to create an artificial magnetic conductor in [11, 12]. a four-port diversity-based multiband antenna with high element isolation was presented in [13]. a csrr has been used for miniaturization including the ground plane in [14]. a rectangular csrr for the pifa using a branch line and quad-band elements was arranged properly to implement a four-element mimo configuration in [15, 16]. improved narrow bandwidth and size reduction of an antenna were discussed in [17, 18]. three resonant modes using an f-tshaped radiating structure by a trapezoidal feeding plate were presented in [19, 20]. the portable wireless device system referred to in [21] is small in size and multi-band. the antenna structure is built around capacitive slots, which allow the multiband behavior described in [22]. a loop antenna loaded with a coplanar strip (cps) line was added along with two switches that allow the antenna perimeter to be varied to cover 7 different bands [23]. the cps line is combined with two switches to vary the antenna perimeter to cover 7 different bands, and an artificial magnetic conductor (amc) was used as the reflector plane in [24]. the pifa is a built-in mobile antenna that compensates for polarization issues, narrow bandwidth, lower gain, and operates multiple frequency bands. in this paper, the csrr and the ris metamaterial are used to reduce the antenna size while improving the impedance bandwidth and multiband application. the drawbacks of the pifa are reduced with an optimization technique, and a new, advanced, low-profile, and effective design of a pifa with csrr and ris for multiband operations is implemented. ii. the pifa a. conventional antenna the proposed tri-band pifa using csrr and ris is shown in figure 1. the overall dimensions of the antenna are 22.71 × 3.456 × 2.59mm, which allows its use in portable corresponding author: tejaswi jadhav engineering, technology & applied science research vol. 12, no. 1, 2022, 7988-7992 7989 www.etasr.com jadhav & deshpande: a tri-band planar inverted-f antenna with complementary split ring … systems. the standard pifa consists of only a metallic patch element positioned above a ground surface, a dielectric constant, a microstrip line feeding mechanism on the ground surface, and a short-circuiting pin. the basic characteristic of the antenna, is the form of the letter f in english, thus it is called the inverted-f antenna. the pifa is attached to the antenna ground plane. the pifa ground plane scale on the pcb board has average dimensions of 56.4mm×33.5mm with a 1.59mm antenna height of fr4 dielectric substrate (�r = 4.4, tan δ = 0.02). the overall dimensions of the antenna substrate are 70×50 mm. (a) (b) (c) (d) (e) fig. 1. the proposed pifa with csrr and ris. the pifa is made up of a metallic module that is mounted on the bottom side of the substrate. ris is a periodic structure designed, which can significantly improve the bandwidth and radiation characteristics. as shown in figure 1(b), the ris substrate is made up of two-dimensional periodic metallic patches printed on a metal-backed high dielectric substance. the csrr is etched on the metal-plane resonator. figure 1(c) shows a schematic view of the rectangular csrr. b. pifa with csrr and ris the metallic square unit structure is mounted on the top side of the dielectric material in the pifa configuration (fr4). table i. geometric dimensions of the proposed pifawith csrr and ris parameters value (mm) parameter value (mm) lp 22.71 wp 3.45 lg 56.4 wg 41.68 ls 4.6 ws 2.1 lf 4.6 wf 2.1 b1 5.5 w1 1 b2 9 w2 1 g1 1.5 g2 1.5 a1 0.8 g1 0.34 a2 0.9 g2 0.28 h1 1.59 h2 1 the design of the ris contains 5×6 periodic unit cells. the ris uses episodic metallic square unit cells that are joined and organized one after another on a dielectric substrate. the surface of ris is perpendicular to the plane. the lateral dimensions of the pifa are almost the same size as the ground element for the pifa configuration. using the exact picture formulation will reduce the interaction between its image and the elemental source in the ris. the ris can enhance impedance bandwidth and reduce the size of the pifa antenna. it is between perfectly electric and magnetic conductor (pec and pmc) surfaces. for better impedance matching, the pifa has a single side-feed spot. the csrr is a mirror image of an srr in a metasurface resonator. it consists of two concentric metallic rectangles, each with a slit in the middle. a rectangular csrr structure is engraved on the dielectric substrate of the proposed antenna, as shown in figure 1(d). the widths of the rectangular inner and outer csrr are w1 and w2 and the distances between the rectangular gap are g1 and g2. therefore the gap between the rectangular csrr is 1–1.5mm. the width of the metallic slot is between 0.9 and 1mm. the proposed pifa with csrr and ris design parameter dimensions is described in table i. a fixed metallic inverted-f patch on the top is adjacent to the substrate (h2) and a ground plane of the antenna is on the bottom side of the antenna substrate (h1). the rectangular patch is fed by an electromagnetically coupled microstrip feed line that is sandwiched between two fr4 dielectric substrates, each with a thickness h1 of 1.59mm and an h2 of 1mm. figure 1(e) shows the front view (cross-section) of the modified pifa with csrr and ris. the metamaterial unit cell has extracted relative negative permittivity at its resonance frequency. iii. design of the proposed pifa a. proposed antenna equation the design of the pifa is using the transmission line model, which has 3 essential parameters, resonance frequency (f0), selection of a dielectric substrate (εr), and substrate height (h). the geometric radiating patch length (lp), patch width (wp), ground length (lg), and ground width (wg) have been calculated by using the mathematical model in [21]. the patch width (wp) of the pifa is: �� � � �� √ �� �� � (1) the patch length (lp) of the pifa is calculated by: � � �� � (2) engineering, technology & applied science research vol. 12, no. 1, 2022, 7988-7992 7990 www.etasr.com jadhav & deshpande: a tri-band planar inverted-f antenna with complementary split ring … frequency (a) frequency (b) fig. 2. (a) simulated return loss of pifa with and without crss and ris. (b) simulated vswr of pifa with and without crss and ris. frequency (ghz) (a) frequency (ghz) (b) fig. 3. (a) measured and simulated return loss of pifa with csrr and ris. (b) measured and simulated vswr of pifa with csrr and ris. (a) (b) (c) fig. 4. surface current distribution of the proposed pifa at (a) 2.4ghz, (b) 7ghz, (c) 9ghz. b. parametric study the pifa with and without csrr and ris has undergone parametric analysis and the results of the simulation are presented in figure 2. the study was carried out by placing metamaterial surfaces on an antenna dielectric substrate while keeping all other measurements stable. figures 3(a) and 3(b) display the simulation return loss and vswr of the pifa, which is tuned to resonate at 2.45ghz, 7ghz, and 9ghz with the csrr’s dimensions modified. all geometric dimensions of the inside and the outside rectangle of the csrr are listed in table i. as a result, the slit width was held at 1.5mm. the resonant frequency of the antenna decreased as the length of the rectangular csrr increased. the antenna resonant frequency increased, multiband was generated by increasing the width of the csrr and the distance between the two squares. the antenna was tuned for multiband by adjusting these parameters. the patch’s presence on the top of the csrr produced a lower than the actual patch’s resonant frequency. this behavior is observed for different csrr parameters in the proposed study and is consistent with previous findings. iv. experimental results and disscussion a. return loss the pifa shows a tri-band with an s11 <-10db bandwidth of approximately 27.25% (2.1467-2.80ghz), 5.71% (6.707.10ghz), and 22.46% (7.309.3214ghz) under simulated and 17.08% (2.26-2.67ghz), 5.14% (6.85-7.21ghz) and 19.44% (7.44-9.19ghz) under measurement respectively. bandwidth, polarization, gain, vswr, and return loss of the pifa antenna were measured in a vector network analyzer (vna). the simulated and fabricated results obtained from the output parameters are presented in figure 3(a)-(b). the developed antenna is demonstrating high impedance matching in mobile application. table ii represented the comparison of the pifa with previous works in terms of geometric measurements, miniaturization, frequency spectrum, gain, and bandwidth. b. voltage standing wave ratio the voltage standing wave ratio (vswr) of the pifa is shown in figure 3(b). the vswr values at 2.4ghz, 7ghz, and 9ghz are almost 1.32, 1.92, and 2.07 respectively, which is very effective in the fabrication process. vswr should lie in the range of 1 to 2, indicating best antenna performance. it has used the input power of an antenna transmitted to the patch, as well as better impedance matching. c. current distribution the current distribution of pifa with csrr and ris is determined through hfss simulations. figure 4 indicates the surface current distribution of the pifa to determine the current with the ris and the ground surface. the ground surface disrupts the current distribution of pifa, causing csrr. as a result, the propagation of electromagnetic waves was controlled by the substrate layer, port excitation, and changes in resonant response. the current distribution of 2.4ghz, 7ghz, and 9ghz is shown in figure 4. d. gain for a handheld unit, the gain of the pifa, as shown in figure 5 is acceptable for a good multiband antenna. for operating bands 2.4, 7, and 9ghz, the pifa gain is 8.1, 3.13, and 7.26dbi, respectively. the average gain of an antenna across its operating bandwidth for a quad-band is 6.16dbi. frequency [ghz] fig. 5. measured gain of the pifa with csrr and ris. v s w r engineering, technology & applied science research vol. 12, no. 1, 2022, 7988-7992 7991 www.etasr.com jadhav & deshpande: a tri-band planar inverted-f antenna with complementary split ring … table ii. comparison with previous works ref. size no of bands operating frequency (ghz) gain (dbi)) [5] 25.6×26×3.57 3 2.09/3.74/5 2.05/2.32/3.47 [8] 34×17×8 3 0.94/1.79/2.46 0.4/1.7/1.1 [11] 16.5×11.5×5 3 2.4/5.2/5.8 4.44/4.91/4.94 [15] 90×42×7.5 4 1.15/2.42/3.6/5.3 1.45/1.6/3.56/4 [16] 18.35×16.4×4.0 3 2.1/2.6/3.5 2.73/3.84/4.8 [20] 25×11×8 3 2.4/5.2/5.75 1.6/2.3/4.4 [21] 26×20×1.6 3 2.4/3.5/5.8 2.24/2.8/2.6 proposed 22.7×3.45×2.59 3 2.4/7/9 8.1/3.213/7.26 d. radiation pattern figure 6 indicates the e-plane and h-plane antenna radiation patterns (phi=0°and phi=90°) simulated in hfss. the electric or magnetic field of the pifa affects the radiation pattern with csrr and ris. fig. 6. radiation pattern of the x-z and y-z planes of the proposed pifa at 2.4, 7, and 9ghz. the verified pifa radiation patterns with metasurface for wireless applications are 2.4, 7, and 9 ghz. the wave path of the maximum antenna radiates along the z-axis, and the wave port 1 exits the simulation. the radiation pattern of the antenna (co-plane and cross-plane) is illustrated in figure 6 for φ = 0 0 and φ = 90 0 at 2.4, 7 and 9ghz. the radiation pattern of the pifa (co-plane and cross-plane) in the φ = 0 0 and φ = 90 0 of the xy plane. figures 7(a)-(b) show a photograph of the manufactured cp-pifa with csrr and ris. (a) (b) fig. 7. photograph of the fabricated pifa with csrr and ris. v. conclusion a compact, tri-band, pifa with csrr and ris, suitable for wlan, c-band, and x-band applications pifa was presented in this paper. the pifa has multiple bands with s11 < -10 and bandwidth of approximately 17.08%, 5.14%, and 19.44% measured at 2.4, 7, and 9ghz respectively. the antenna radiates a wave in a preset direction with realized gains ranging from 3.21 to 8.1dbi. the parametric analysis indicates that a small change in the rectangular csrr has a significant impact on the antenna impedance mapping. it also increases the bandwidth and provides better gain with the same dielectric substrate and radiating patch. the benefit of the multiple bands on the pifa is shown on the radiation pattern, broadband, impedance adequacy, and gain of their operating bandwidth. references [1] h. attia, m. bait-suwailam, and o. ramahi, "enhanced gain planar inverted-f antenna with metamaterial superstrate for umts applications," piers online, vol. 6, no. 6, pp. 585–588, jan. 2010, https://doi.org/10.2529/piers100422003051. 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[24] a. bousselmi, a. gharsallah, and t. p. vuong, "a novel high-gain quad-band antenna with amc metasurface for satellite positioning systems," engineering, technology & applied science research, vol. 9, no. 5, pp. 4581–4585, oct. 2019, https://doi.org/10.48084/etasr.2933. microsoft word etasr_v12_n1_pp8180-8187 engineering, technology & applied science research vol. 12, no. 1, 2022, 8180-8187 8180 www.etasr.com mallavarapu & lokam: circuit modeling and analysis of wearable antennas on the effect of bending … circuit modeling and analysis of wearable antennas on the effect of bending for various feeds sandhya mallavarapu department of electronics & communication engineering national institute of technology warangal warangal, telangana, india sandhyamallavarapu@student.nitw.ac.in anjaneyulu lokam department of electronics & communication engineering national institute of technology warangal warangal, telangana, india anjan@nitw.ac.in abstract-the promising utilization of wearable antennas has experienced gigantic growth during the last decade. an antenna is one of the most significant and crucial components of wireless wearable devices. they need to be particularly designed to work while worn on and off the body. the wearable antenna embedded into clothing finds its use in wireless communications including tracking and navigation, mobile and wearable computing, and public safety and security. for user accessibility, there is a growing requirement for incorporating antennas on or in clothing. determining the dielectric characteristics of the flexible substrates utilized in the design of the wearable antenna is also essential. in this paper, a microstrip ring resonator (mrr) is employed to determine the dielectric properties of fabric substrates followed by state-of-the-art designs of wearable antennas and their bending effects at ism band frequencies. an electrical equivalent model is designed to realize the potentials inside the geometry of an antenna under bending environment. this is followed by observing the effect of bending for different feeding methods on the wearable antenna's parameters when bending on a certain radius. the robustness of the proposed wearable antenna is examined by measuring the antenna under various bending curvatures for return loss, gain, and efficiencies. this will disclose the various contemplations for designing a wearable antenna from different feeding mechanisms with different materials and exemplifying the antenna's outcomes to dynamic moments of the human body. the performance of the proposed wearable antenna is acceptable even in a deformation environment, and there is a good agreement between the measured and the simulation results. keywords-wearable antenna; wireless body area networks (wban); microstrip ring resonator (mrr); industrial; scientific and medical (ism) band; aperture coupled wearable antenna (acwa) i. introduction the evolution of wearable antennas originates from the concept of wearable computing systems as a part of clothing that enables the wearer continuous hassle-free data transfer. in recent times, a wearable antenna receives a noteworthy development in technologies such as wi-fi, bluetooth, wireless local area networks (wlans), and wireless body area networks (wbans). in general, a wearable antenna is stated to have high flexibility and competence in a system connected with the human body. well-being, health, and lifestyle are the primary interests while implementing these systems [1-5]. usually, wearable antenna desires for all modern applications must be lightweight, economical, almost maintenance-free, and do not require installation. several specialized activity segments apply body area communication network systems, for instance, paramedics [6], firefighters [7], astronautics [8], military [9], and public safety. in addition, wearable antennas can also be applicable for teenagers, the elderly, and sportspersons to monitor vital signs such as temperature, heart rate, etc. when worn on the body, wearable antennas can establish a wireless link between the body and the external world. the most appropriate topology for wearable antennas, ensuring the most favorable integration into clothing and wearer's ease, is the planar patch antenna [8, 9]. on-body antennas are preferably made of flexible textiles and wearable materials [12], which can naturally conform to the surface of the body. this involves information related to the dielectric characteristics, namely permittivity and loss tangent of the fabric. the measurement of the dielectric properties of flexible materials characterized by their complex values is a challenging task and special measuring instruments are required [13]. a simple but effective technique is considered to characterize the flexible substrates and electromagnetic properties of some fabrics [14, 15]. wearable antennas are usually designed in the ideal flat state. still, when integrated into clothing and worn they are likely to be subjected to deformations such as bending and stretching, which cause variations in the performance of the antenna, leading to potential performance degradation related to the resonant frequency, impedance bandwidth, and efficiency [16, 17]. though the antenna is designed for a certain curvature, the variation of the radius of the curvature can influence the antenna's performance. therefore there is a need to explore the influence of bending on various factors starting from scratch. the effect of bending on the antenna performance is sensitive to the different dielectric value of substrates [18], in which the dielectric constant near the air shows stable performance under bending. the impact of different thicknesses is explored in [19], and the influence of different radiator shapes is explored in [20]. further, the wearable antenna undergoes the effect of being near to the body as the relative permittivity of the body changes [21]. to mitigate the human body coupling, corresponding author: n sandhya mallavarapu engineering, technology & applied science research vol. 12, no. 1, 2022, 8180-8187 8181 www.etasr.com mallavarapu & lokam: circuit modeling and analysis of wearable antennas on the effect of bending … electromagnetic bandgap (ebg) structures / amc structures are placed on the backside of the wearable antenna, which can improve its fbr [22]. therefore, the fundamental step in ensuring that the antenna can perform well is to ascertain the most suitable feeding method [23]. mostly, any efficient antenna design involves a maximum power transfer between the end terminals, i.e. from the source to the antenna, where the antenna is fed at a point where the antenna impedance is 50ω. by considering these conditions, the wearable antenna should be designed carefully in every aspect, including the feeding mechanism. however, the approach of estimating the antenna behavior using electromagnetic simulators has relatively high computational costs depending on the complexity of the radiating structure. thus, an electrical equivalent circuit model is useful while characterizing such complex structures. in addition, the matching potentials of the antenna are estimated with the knowledge of equivalent circuit models. in this paper, the advanced design system (ads) software is utilized to develop the equivalent circuit and predict the return loss, while the antenna is simulated in cst mw software before fabrication. ii. dielectric properties of fabrics several techniques are available in the literature to identify the dielectric properties of fabrics. one simple technique adopted here is the microstrip ring resonator (mrr), which is useful for analyzing the electromagnetic properties of the materials due to its feasible geometry, ease in prototyping, low price, small volume, and adaptability [24, 25]. the proper usage of the fabric material as substrate while designing wearable low-profile antennas makes them efficient. the mrr method uses the resonant frequency and the quality factor to calculate the permittivity and loss tangent of the substrate, which gives accurate results due to the absence of end effects and the high q factor. this makes the proposed method advantageous compared to previously published [26, 27] methods. a straightforward resonant technique to characterize sample fabric’s electromagnetic properties is based on the mrr and another method is based on the patch radiator, which is used to validate the results of the first. the geometry of the mrr involves the ring and two feed lines separated by a gap (∆), which are placed on top of the substrate of size 50×50mm 2 . on the back of the substrate, ground plane is placed. adhesive copper foil is utilized for the metal parts such as the ring and the two feed lines, whereas flexible jeans is the substrate as shown in figure 1. the optimized dimensions are obtained with the help of traditional equations (table i). r1 r2 ∆ (a) (b) fig. 1. (a) schematic of the mrr, (b) prototype. table i. optimized dimensions of the mrr model theoretically, the n th resonance peak takes place at [28]: 2 n r nc f rπ ε = (1) where r is the average radius, c is the speed of light in the vacuum, and εr is the required dielectric constant. also, the insertion loss (il) s21 (db) is given by: il 20log 1 l u q q   = −    (2) where ql, qu represent the loaded and unloaded quality factors respectively. from the s21 curve, the loaded quality factor given by: 0 l f q f = ∆ (3) where f0 is the resonance frequency, ∆f is the difference between the upper and lower of the s21 (db) curve. the loss tangent can be calculated by determining the unloaded quality factor qu from (2) and substitute in (4): 1 1 1 u c d q q q = + (4) 0 0c c q h f µ πσ= (5) where qd and qc are the quality factors of the dielectric and the conductor respectively. then, the loss tangent is calculated from: 1 tan d q δ = (6) figure 2 shows the measurement setup on the network analyzer and the transmission coefficient of the proposed method. it is observed that there are two resonance peaks obtained at 4.27ghz and 8.9ghz, with a corresponding return loss of -35.94 and -22.48db for the jeans textile. based on the resonant peaks that appeared in s21, the dielectric properties are calculated by substituting in (1)-(6) (table ii). the simulated and measured values are in good agreement. this result is also verified by the second method, which is focused on designing the patch antenna on the desired substrate [14]. in general, the fabric material is said to be lossless when the loss tangent is significantly small. according to the obtained results, the dielectric constant and loss tangent are 1.729 and 0.025 respectively [29-30]. usually, the substrate's relative permittivity plays a substantial part in the design of the antenna, and variations in its value tend to change the operating ring dimensions mean radius (r) feed line width (wf) feed line length (lf) gap (∆) value (mm) 8.5 3 14 1 engineering, technology & applied science research vol. 12, no. 1, 2022, 8180-8187 8182 www.etasr.com mallavarapu & lokam: circuit modeling and analysis of wearable antennas on the effect of bending … frequency of the antenna to more or less of the desired center frequency. however, the variation in loss tangent has a negligible effect on the antenna resonant frequency, affecting mostly the magnitude of return loss. fig. 2. s21 (db) vs. frequency of the mrr mode. table ii. resultant dielectric properties of jeans substrate using the mrr method mode resonant frequency (ghz) il s21 (db) dielectric constant (εr) tanδ n=1 4.2716 -35.94322 1.729 0.078 n=2 8.916 -24.9838 1.687 0.025 iii. design and electrical equivalents of the wearable antenna ideally, a wearable antenna should be highly flexible, lightweight, and small in volume. it should have no installation requirements, high durability, and support bending and stretching at certain strain levels, but simultaneously it must be able to still function efficiently without compromising its rf characteristics. two wearable antennas were designed with different feeding mechanisms and their equivalent circuits were obtained. a. inset fed wearable antenna for the implementation of a textile antenna, a planar patch antenna of a rectangular shape is chosen because of its planar structure and compactness [31]. substrate selection is the key parameter while designing a microstrip antenna. by proper selection of the substrate dielectric properties and dimensions, a good antenna design is possible. the elementary form of the microstrip patch antenna consists of two metallic layers and a dielectric layer sandwiched between them as shown in figure 3. the full ground plane attached to the back of the substrate shields the user from unwanted radiation. the radiating patch and the feed line are attached to the top of the substrate. the patch antenna with the inset feed is designed with flexible jeans as substrate and adhesive copper foil as the radiating patch. the proposed wearable patch antenna is designed to resonate at 2.5ghz, which is suitable for wi-max applications. the transmission line model is used to find the input impedance of the inset-fed microstrip patch antenna. the microstrip patch antenna operates on the same principle, where the length of the patch has a greater influence in deciding the resonant frequency. the fringing fields’ forms at both the ends along the length of the patch tend to increase the effective length of the patch. therefore, the impedance at the edges is very high and decreases as the inset distance moves towards the center of the patch. by adjusting the inset distance, proper impedance matching is achieved. the optimized dimensions are obtained from the standard equations [32] as shown in table iii. to get more insight, the textile antenna can be described in its electrical equivalent. using the transmission line model in [32], the equivalent circuit of the inset-fed patch element is modeled as a parallel rlc resonant network with a series inductance representing the near field effect of the microstrip feed line. the electromagnetic fields' parameters l and c can be determined in the antenna's near field, where they can represent the ability to deposit magnetic and electric energy in the circuit throughout resonance. the circuit simulations were carried out in ads software. the optimized parameter values are directly shown with the elements in the circuit in figure 4. table iii. dimensions of the inset fed wearable patch antenna parameter lp wp w l feed width thickness dimensions (mm) 46.6 53.6 100 100 13 3.5 (a) (b) fig. 3. (a) schematic view, (b) fabricated prototype of the inset fed wearable patch antenna. (a) (b) fig. 4. (a) simulated equivalent circuit in ads, (b) s11 plot of the inset fed microstrip patch antenna. engineering, technology & applied science research vol. 12, no. 1, 2022, 8180-8187 8183 www.etasr.com mallavarapu & lokam: circuit modeling and analysis of wearable antennas on the effect of bending … from the circuit, the feed point impedance at the specific frequency band can be modeled as an inductance (l) at highfrequency and a capacitor at low-frequency (which is neglected and not shown in the circuit) in series. the circuit parameters ra, la, and ca are the equivalent resistance, inductance, and capacitance and are given by the standard relations given below [33]: 0 2 1 . 2 cos ( ) e p p a l w c h ε ε β = , p zo l π β = (7) 1 2 r a la f cπ = (8) 2 r a q ra f cπ = (9) the input impedance at the feed location from the circuit is noted as: 1 ( ) 1 1 in f a a a z f x jwc r jwl = + + + (10) where lp is the length of the patch, wp the width of the patch, h the substrate thickness and z0 the feed location impedance. from figure 4(b), it is observed that there is a good agreement between the simulated and the measured values. however, a small discrepancy is accountable for fabrication errors. with a flexible substrate, it is always a challenging task to shape the material in the required dimensions with the help of scalpel/cutting tools. while cutting the edges of the substrate, due to parallax error, the slides and edges may not be straightly cut or some threads may come out. all these complications may affect the antenna matching and performance. therefore the wearable antenna is fabricated with the right tools and with utmost care. b. aperture coupled wearable patch antenna the present generation clothing can monitor the bio signals of the wearer and enables continuous communication between the attached antenna and the outer world regarding the person’s state of health. many of the existing models involve a singlelayer design and regularly a coaxial feed [34, 35] is utilized to attach the antenna to the transceiver. this type of feed structure is firm and is often annoying to the wearer. similarly, using microstrip feed to the antenna is not the greatest solution because of the unnecessary parasitic radiations from the feed line and the radiating element. however, these problems can be mitigated by situating the feed line beneath the antenna ground plane, which can protect the feed line and the transceiver from the radiating antenna. the power is transferred from the feed line to the radiating element through an aperture in the ground plane that leads to an aperture-coupled patch antenna. the aperture coupled wearable patch antenna (ac-wpa) serves the purpose. its structure involves a ground plane sandwiched between two different substrates. the radiating patch is placed on the antenna substrate and a feed line is seated on the base of the feed substrate as shown in figure 5. fig. 5. ac-wpa: (a) scheme, (b) front view and (c) back view of the fabricated prototype, (d) experimental setup. all the rigid cables are replaced with a simple transmission line, and the power is coupled through a small aperture of arbitrary shape in the ground plane, which justifies the name of the antenna. flexible jeans and wash cotton were chosen as the feed and antenna substrates since they are typical, durable, inelastic, and of low cost. design studies were carried out using the electromagnetic simulator cst mw studio and the acquired optimized dimensions are tabulated in table iv. table iv. optimized dimensions of the ac-wpa patch adhesive copper wp (mm) lp (mm) 43 40 antenna substrate wash cotton h (mm) ɛr tanδ 2.56 1.5 0.025 ground plane adhesive copper wg (mm) lg (mm) 65 65 aperture wap (mm) lap (mm) 3.5 20 feed substrate jeans h (mm) ɛr tanδ 1.15 1.7 0.02 feed line adhesive copper wf (mm) lf (mm) 1.5 22.5 the adopted feeding method produces a higher bandwidth than the other feeding methods because of its impedance transformation behavior. in practical applications, the transceiver is directly connected to the feed line which couples the power to the patch through an aperture placed exactly in the middle under it. the prototype is built according to the specifications and is shown in figure 5. the ac-wpa is represented in its electrical equivalent circuit model to gain insight into the underlying electromagnetic behavior. the equivalent circuit of ac-wpa practically is complex and consists of lumped rlc elements, ideal transformer, and transmission line segment to represent the radiating patch and coupling slot. a simple equivalent model is adopted here, in which the optimized parameter values are shown directly in the circuit. the circuit simulations were carried out in ads, whereas the electromagnetic simulator cst mws was applied to achieve the ac-wpa design and optimization, which are shown in figure 6(a). engineering, technology & applied science research vol. 12, no. 1, 2022, 8180-8187 8184 www.etasr.com mallavarapu & lokam: circuit modeling and analysis of wearable antennas on the effect of bending … (a) (b) fig. 6. (a) circuit model, (b) reflection coefficient curve of ac-wpa. it can be observed that there is a close relationship between the simulated and the measured values. however, proper care and attention must be given while assembling the multilayer structure manually, because even for small misalignment between the feed line, the slot, and the patch there is variation in the performance result. moreover, high fabrication tolerances exist while working on textiles compared to the traditional substrates. all these circumstances lead to some measurement deviation in the resonance frequency as can be seen in figure 6(b). iv. bending characterization and electrical modeling the bent wearable patch antenna's geometry is modeled as a cylindrical cavity [36]. the geometry of the foam cylinders upon which the textile antennas are wrapped around is shown in figure 7(a). for both inset fed and aperture coupled antennas, patch and ground planes were modeled as perfect electric conductors and the remaining four sides as perfect magnetic conductors. hence this arrangement forms a cavity bounded by electric and magnetic walls at: ρ = r, ρ = r +h, � � � � � , and �.� � /2 (11) the maxwell's field equations are: ( ) 1 .e xf jw a a jw µ ε = −∇ − + ∇ ∇ (12) ( ) 1 .h xa jw f f jw µ ε = −∇ − + ∇ ∇ (13) the fields inside the cylindrical cavity are obtained by imposing the boundary conditions on maxwell's equations. by solving these equations, one can get the relations for t.e. and t.m. modes, from which a relation between resonant frequency and bending radius was found analytically. to give an outlook to wban applications, it is essential to explore certain bending radius/angles per antenna width/length. from the circuit analysis point of view, the bending of the patch antenna changes length, thereby altering the antenna's e-field, which can be validated by changing the capacitance between the antenna element and the ground plane. in general, bending of the antenna brings discontinuity, i.e. the electric field becomes strongest in that particular part while the magnetic field shows a minimal effect. this indicates that the inductive loading doesn't get affected. the capacitive loading, also known as tuning capacitor, is denoted by ct. as the bending radius increases, the capacitive loading becomes small [37]. the simulated circuit parameters for the patch antenna bent in the e-plane are shown in figure 7(b). comparing the flat case with the bent cases, it is observed that the capacitance c2 decreases and l2 increases. the product l.c increases when bending becomes critical, which means that the resonance frequency shifts to a lower frequency band. (a) (b) fig. 7. (a) antennas wrapped around foam cylinders in e, h-plane directions, (b) equivalent circuit of a bent patch antenna. v. results and discussion although the performance of the flexible antennas can be upgraded with united solutions for wearable applications, the development and optimization of such materials still require further characterization and improvement. here a comparison is made for bending variations for different feeds of patch antennas where four different scenarios are considered. these radii are sensibly considered to mimic the chest and arm sizes of the human body [38]. these deformations were conducted to test their capability to resist a certain amount of structural bending. a. effect on resonant frequency and impedance match simulations were carried out over the frequency range of 1.0–3.0ghz. the proposed textile antennas have been fabricated, and the resultant reflection coefficient is measured using the vector network analyzer (vna) hewlett packard 8719a. when these antennas are wrapped around the cylindrical foam surfaces, the simulated resonant frequency appears to be dependent on the antenna curvature, more particularly for the antenna bending in the direction of length as for a microstrip radiator the electric field lines are oriented s-parameters ct l1 l2c2 r1 term1 sp1 c=1 pf {t} l=1 nh {t} r= l=1.5 nh {t} r= c=3.14 pf {t} r=50 ohm {t} num=1 z=50 ohm start=1.0 ghz stop=3 ghz step=100 mhz c l lc r term s_param engineering, technology & applied science research vol. 12, no. 1, 2022, 8180-8187 8185 www.etasr.com mallavarapu & lokam: circuit modeling and analysis of wearable antennas on the effect of bending … along the length and magnetic field lines along the width. therefore a shift in resonant frequency appeared as the effective length of the patch is decreased when it is bent lengthwise. (a) (b) (c) (d) fig. 8. return loss variations for different bending cases for (a) ac-wpa, on the e-plane, (b) inset fed patch antenna on the e-plane, (c) ac-wpa on the h-plane, and (d) inset fed patch antenna on the h-plane. if the tendency of detuning of the simulated resonant frequency is considered and graphed for different bending cases, it is worth noting that the more the antenna is bent in the e-plane, in general, the more the effective length gets reduced, and so the resonant frequency gets shifted to the higher band as shown in figure 8(a) and 8(b) for the ac-wpa and the inset fed patch antenna respectively [39]. on the other hand, the hplane bending shows minute, almost negligible, variations in resonant frequency (figure 8(c), 8(d)). it can be seen that the reflection coefficient increases as the bending becomes critical, i.e. the antenna operates ordinarily. for the ac-wpa, the frequency detuning is approximately 16% for severe bending in the e-plane, and the deviation in the resonant frequency is small in the h-plane. the return loss of the bent ac antenna is large, so a large amount of energy enters the antenna and hence efficient antenna performance is obtained. the same is applicable for any candidate antenna. b. effect on electric field intensity the electric field intensity can be better understood when the antenna bending occurs on a foam cylinder. the distribution of the e-field for both the proposed antennas under different bending radii is shown in figure 9. it can be observed that the e-field is small at the center, and maximum at the sides of the patch for the flat antenna candidates. instead, for both the antennas, there is an insignificant effect on their e-field behavior under bending situations, in which maximum occurs at the sides of the patch. generally, for the inset fed patch antenna, the electric field, and thus the current flow, is associated with the length, whereas the magnetic field with the width. exposing antennas to lengthwise bending, influences on the current flow and the electric field are expected, while there is marginal impact when the bending occurs in the width direction. the change in the distance traveled by the current between the opposing ends of the patch antenna due to the bending of the materials leads to a reduction in the length of the patch. (a) (b) fig. 9. electric filed variations of (a) inset fed antenna, (b) ac-wpa on different bending fixtures. c. effects on the radiation pattern figure 10 shows the e-plane 2d radiation patterns for the planar and bent antennas. meanwhile, for all the bending cases, the forward gain shows slight variations due to the high bending radius, which gives some difficulties to the antenna to radiate appropriately. it is instinctively clear that antenna 1.0 1.5 2.0 2.5 3.0 -20 -10 0 s 1 1 ( d b ) f (ghz) sim.r 70mm sim.r 50mm sim.r 40mm sim.r 35mm meas.r 70mm meas.r 50mm meas.r 40mm meas.r 35mm 1.0 1.5 2.0 2.5 3.0 -15 -10 -5 0 s 1 1 ( d b ) f (ghz) sim.r 70mm sim.r 50mm sim.r 40mm sim.r 35mm meas.r 70mm meas.r 50mm meas.r 40mm meas.r 35mm 1.0 1.5 2.0 2.5 3.0 -40 -30 -20 -10 0 s 1 1 ( d b ) f (ghz) sim.r 70mm sim.r 50mm sim.r 40mm sim.r 35mm meas.r 70mm meas.r 50mm meas.r 40mm meas.r 35mm 1.0 1.5 2.0 2.5 3.0 -30 -20 -10 0 s 1 1 ( d b ) f (ghz) sim.r 70mm sim.r 50mm sim.r 40mm sim.r 35mm meas.r 70mm meas.r 50mm meas.r 40mm meas.r 35mm engineering, technology & applied science research vol. 12, no. 1, 2022, 8180-8187 8186 www.etasr.com mallavarapu & lokam: circuit modeling and analysis of wearable antennas on the effect of bending … bending widens the radiation pattern in the bending plane, which leads to gain reduction. different bending radii do not have a significant effect on the antenna radiation pattern. however, the efficiency of the proposed antenna is marginally reduced as the antenna bending is increased, but the antenna still operates efficiently at an acceptable level as shown in table v. another main consequence was obtained in terms of 3db angular beam width, which is experienced as an increment when bending becomes critical. (a) (b) fig. 10. 2d radiation pattern variations of (a) aperture coupled, (b) inset fed wearable patch antenna in different bending situations. table v. gain and efficiency variations of the proposed antennas for different bending radii cylinder radius(mm) gain (dbi) efficiency (%) inset fed aperture coupled inset fed aperture coupled flat 6.12 4.84 58.61 53.95 70mm 6.01 4.50 58.34 46.02 50mm 5.74 4.46 58.47 55.08 40mm 5.41 4.41 59.56 55.08 35mm 5.03 4.13 60.06 52.72 vi. conclusions this paper focused on developing electrical equivalents of bending and its feeding effects on wearable textile antennas when bending occurs on a certain radius. two exciting feed types were selected on the textile patch antenna and input impedance, resonance frequency, electric field intensity, and radiation pattern were investigated. these are the most significant parameters to be observed before focusing on the bending effects. it was found that the e-plane bending has a dominant impact on the impedance matching for both textile antennas. this result holds for all antenna candidates because the resonant length changes when the antenna is bent. the results showed that the aperture coupled antenna has a minimal bending influence on the impedance matching and resonant frequency, proving the robustness of the antenna under these effects at the cost of complexity. moreover, the feed type removes the usage of rigid cables and unnecessary radiation from the feeds. the less cross-polar level makes it a better candidate for wearable applications. also, the electric field intensity and gain have minimal effect on bending for both the antenna candidates. therefore, aperture coupled wearable antennas are far better regarding the bending performance despite their structural complexity. references [1] a. sabban, "small wearable antennas for wireless communication and medical systems," in ieee radio and wireless symposium, anaheim, ca, usa, jan. 2018, pp. 161–164, https://doi.org/10.1109/rws. 2018.8304974. 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[39] l. z. tung, g. a. mahdiraji, and l. c. ping, "comparative study between planar and bent antenna characterization," matec web of conferences, vol. 152, 2018, art. no. 03002, https://doi.org/10.1051/ matecconf/201815203002. microsoft word 12-746.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1099-1102 1099 www.etasr.com vukotic and babic: estimation of length and order of polynomial-based filter implemented in the form … estimation of length and order of polynomial-based filter implemented in the form of farrow structure selena vukotic school of computing university union belgrade 11000, serbia svukotic@raf.edu.rs dorde babic school of computing university union belgrade 11000, serbia djbabic@raf.edu.rs abstract—digital polynomial-based interpolation filters implemented using the farrow structure are used in digital signal processing (dsp) to calculate the signal between its discrete samples. the two basic design parameters for these filters are number of polynomial-segments defining the finite length of impulse response, and order of polynomials in each polynomial segment. the complexity of the implementation structure and the frequency domain performance depend on these two parameters. this contribution presents estimation formulae for length and polynomial order of polynomial-based filters for various types of requirements including attenuation in stopband, width of transitions band, deviation in passband, weighting in passband/stopband. keywords-digital filters; filter design; polynomial-based filters; farrow structure i. introduction the digital polynomial-based interpolation filters are used in signal processing applications whenever it is required to calculate signal samples at arbitrary positions between existing samples. the impulse response of digital polynomial-based interpolation filters is derived by using piecewise polynomial analogue model [1]. an underlying continuous-time impulse response ha(t) has the following properties [1]: first, ha(t) is nonzero only in a finite interval 0≤t≤nt with n being an integer which determines the length of the filter. second, in each subinterval nt ≤t<(n+1)t, for n= 0,1…, n-1, ha(t) is expressible as a polynomial of t of a given order m. third, ha(t) is symmetric with respect to its middle point t = nt/2, to guarantee phase linearity of the resulting overall system. the advantage of the above impulse response is in the fact that the actual implementation can be efficiently performed by using the farrow structure [2] or its modifications such as transposed farrow structure, prolonged farrow structure etc [1, 3]. the number of multipliers in any modification of farrow structure is directly proportional to polynomial order m and number of polynomial segments n. the polynomial-based interpolation filters can be designed using time domain or frequency domain design methods [1]. the time-domain design methods are based on lagrange and b-spline interpolations, where the approximating polynomial is fitted to the discrete-time samples. in the frequency domain design methods, the coefficients of the polynomials, i.e. coefficient of the farrow structure, are optimized directly in the frequency domain [1, 3]. in all these design methods, there are two basic parameters that control performance of the filter and its complexity. these two basic parameters are the number of polynomial segments n and polynomial order m. as stated above, polynomial order m and filter length n are directly proportional to the number of multipliers in farrow based structure. thus, the system complexity measured in number of operations is directly related to these two parameters. furthermore, the system performance in the frequency domain measured by stopband attenuation and passband ripple is also related to n and m. therefore, it is very important to estimate polynomial order m and filter length n according to given system parameters. this paper presents the estimation formulae for the length n and polynomial order m for various types of requirements. the formulae presented below can save time for the filter designers, because they get suitable starting values for n and m for the given set of requirements. they can serve to estimate the filter complexity for given set of system requirements. similar order estimation formulae exist for fir filters, for example kaiser order estimation [4]. in the actual digital implementation, polynomial-based filters can be modeled as fir filters [1], thus we can use similar methodology for analysis. the estimation formula for n, which can be found in [5] is good starting point for filter length n. in [6], the estimation formulae for both n and m have been proposed. the work presented in [6], has been the main motivation for the research presented here. however, the formulae presented in [6] are obtained using trial and error method, and they have some conditional restrictions. namely, the estimation formulae this work is supported by the ministry of education, science and technological development of republic of serbia under technology development project: tr32028 – “advanced techniques for efficient use of spectrum in wireless systems”. engineering, technology & applied science research vol. 6, no. 4, 2016, 1099-1102 1100 www.etasr.com vukotic and babic: estimation of length and order of polynomial-based filter implemented in the form … of [6] cannot be used in the case when filter with narrow transition band is designed. in [7], the estimation formulae for the prolonged farrow structure has been proposed. hence, in this paper we propose the more general and accurate formulae for estimation of polynomial order m and filter length n based on the system requirements including attenuation in stopband, width of transitions band, deviation in passband, weighting in passband/stopband. ii. estimation of polynomial order m and filter length n in the previous section, we have seen that the number of polynomial segments n and the order m of the polynomial are the design parameters that highly influence the performance of the filter in the frequency domain. furthermore, the cost of realization, i.e. the number of multipliers, of a filter can be estimated by determining required values for n and m. in this section, we present the estimation formulae and explain in detail an experimental method used to derive the formulae. the estimation formula from [6] for the number of polynomial segments n is rather similar to the kaiser formula for order estimation of fir filters [4], thus we can use it as good starting point. in this way, we can start from the kaiser formula and adapt it to polynomial-based filters. similarly to other approaches [6, 8], we use experimentally obtained results in order to determine the estimation formulae. to this end, a lot of filters were designed, by using different system specifications, in order to adapt the kaiser formula to the polynomial-based case. the polynomial based filters are designed using the minimax optimization routine explained in [1] for the following design parameters. the passband edge is varied from fp to f/2-fp with step equal to fp =0.05 normalized to f, where f is output/input sampling rate in decimation/interpolation case. the stopband edge fs is determined according to case a specification defined in [1], thus fs=0.5 normalized to f. the weighting function w(f), which is used to differentiate precision of design in passband and stopband, is also varied from w(f)=[wp ws]=[1 0.1] to w(f)=[1 1000], where wp and ws are weights in passband and stopband region respectively. finally, we used different values for the number of polynomial segments n ranging from n=2 to n=24 with step two, taking only even values of n. the polynomial order m takes values from m=0 to m=7 with unity step. in this way, in our experiment we use 9 different values of fp, five values of w(f), 12 values of n, and 8 values of m. all together, we have designed 9∙5∙12∙8=4320 filters. for each set of requirements, we have determined obtained performance in terms of passband ripple p, and stopband ripple s. figures 1 and 2 illustrate the stopband attenuation as a function of used system parameters for case a specifications from [8]. from figure 1, one can see that for a given m, fp, and w(f) there is a certain value of n after which the stopband attenuation s saturates in value. therefore, there is no point to design filters with higher n for given set of m, fp, and w(f). from figure 2, it is also possible to see that for given n, fp, and w(f) there is a certain value of m after which the stopband attenuation s saturates in value. therefore, there is no point to design filters with higher m for given set of n, fp, and w(f), as well. these border values of n and m are actually the optimal values to be used in design for given s, fp, and w(f). therefore, we take these border values for n with appropriate system parameters to curve fitting toolbox assuming the same type of function as in the case of kaiser estimation formula. the starting formula can be represented as: bnas  )(log20 10    with coefficients a and b, which should be determined. fig. 1. case a specifications: the curves are shown for m equals 0 to 7. dashed line is obtained from the estimation formula for n shown in (2). the stopband edge is at fs=0.5 normalized to f, passband edge and stopband weighting are at: (a) fp=0.15f and w=0.1; (b) fp=0.3f and w=10. the curve fitting toolbox is applied with experimental data, and the following estimation formula is obtained:                                        w ff w ff n psps s 5.0 )( 45.0 )(28 )(log20 5.02 10    where p and s are the maximum deviations of the amplitude response from unity for f[0, fp] and the maximum deviation from zero in stopbands, respectively, and w=1-log10(w). here, engineering, technology & applied science research vol. 6, no. 4, 2016, 1099-1102 1101 www.etasr.com vukotic and babic: estimation of length and order of polynomial-based filter implemented in the form … x stands for the smallest integer which is larger or equal to x. it has been observed that in the most cases the above estimation formula is rather accurate. however, if the transition band is narrow, i.e., in the case when (fs-fp)/f≤0.1, the required value of n should be increased by 2. a dashed line in figure 1 is a plot obtained from the estimation formula for n shown in (2). one can see that the dashed line represents the border values of n when performance saturates as explained above. fig. 2. case a specifications: the curves are shown for n equals 2 to 24. dashed line is obtained from the estimation formula for m shown in (4). the stopband edge is at fs=0.5, passband edge and stopband weighting are at (a) fp=0.15f and w=0.1; (b) fp=0.3fand w=10. the next problem is to find the minimum value of the polynomial order m to meet the specifications, which is actually border value of m in figure 2 when performance saturates. it has been observed that the required value of m depends on the type of requirements. never the less, it is possible to consider the following estimate as a good starting point for all three types of requirements: emdmcs  2 10 )(log20   the coefficients c, d and e are adjusted using experimentally obtained data within curve fitting toolbox. the case a estimation formula can be expressed as: 3 13.0 5.1 10)40)(log10( 10              f fwa m s  where f=(fs-fp). it has been observed that if transition band is relatively large to the sampling frequency, that is when (fs-fp)/f ≥0.5, the required value of polynomial order m can be lowered by one. the estimation formula cannot be used when the transition band is very small, i.e., in the case when (fs-fp)/f <0.1. (lower bound for the transition bandwidth in the experiment is (fs-fp)/f =0.1, thus we do not have data for the case when (fs-fp)/f <0.1). a dashed line in figure 2 is a plot obtained from the estimation formula for m shown in (4). one can see that the dashed line represents the border values of n when performance saturates as explained above. iii. design examples this section gives an example in order to illustrate how to use the presented formulae. at the same time we can estimate the performance of the proposed estimation formulae. the following system requirements are considered: passband and stopband edges are at fp=0.4f and at fs=0.5f, the filter is to be designed in minimax sense with stopband attenuation as=60db, passband weighting equal to unity and stopband weightings of w=100. in order to design the filter according to the specifications given above, first, we use (2) to estimate the number of intervals for the case a specifications, and we obtain n=18. the degree of the polynomial in each subinterval m=4 is estimated using (4). we design filter using obtained n and m with earlier defined system requirements. figure 3 gives the frequency response for case a filter with achieved stopband attenuation as=59.5db and passband ripple p=0.1065 in linear scale. it can be observed that the estimation formulae are relatively good, as they estimate the border performance for the given set of requirements. fig. 3. design example: the frequency domain performance of filter whose parameters are estimated using the presented formulae. the filter specifications are: stopband attenuation as=60db, passband weighting equal to unity and stopband weighting is w=100, passband edge fp=0.4f. case a filter of length n=18, and m=4 with achieved as=59.5db and p=0.1065. engineering, technology & applied science research vol. 6, no. 4, 2016, 1099-1102 1102 www.etasr.com vukotic and babic: estimation of length and order of polynomial-based filter implemented in the form … iv. conclusion in this paper, the estimation formulae for the number of polynomial segments n and the polynomial order m of polynomial-based filter are presented. it has been shown that these estimates give the border performance of the filter for the given set of specifications. formulae for n and m can be used to estimate the starting value of these two parameters in minimax optimization used to design the farrow structure. this is significant information which can save time for filter designers. furthermore, the formulae for n and m can be used to estimate implementation costs of the farrow based filters for the given set of requirements. the formulae can also be used to estimate implementation costs of multistage sampling rate converters containing farrow filter. estimation formulae for case b and case c requirements with minimax optimization, as well as, least-mean-square optimization are part of future work. references [1] j. vesma, t. saramaki, “polynomial-based interpolation filters-part i: filter synthesis”, circuits, systems, and signal processing, vol. 26, no 2, pp. 115-146, 2007 [2] c. w. farrow, “a continuously variable digital delay element”, ieee international symposium on circuits and systems, pp. 2641-2645, espoo, finland, june 7-9, 1988 [3] d. babic, t. saramaki, m. renfors, “conversion between arbitrary sampling rates using polynomial-based interpolation filters”, 2nd international ticsp workshop on spectral methods and multirate signal processing, pp. 57-64, toulouse, france, 2002 [4] j. f. kaiser, “nonrecursive digital filter design using the i0-sinh window function”, ieee international symposium on circuits and systems, pp. 20-23, 1974 [5] t. saramaki, multirate signal processing, lecture notes, tampere university of technology, finalnd, 2012 available at: http://www.cs.tut.fi/~ts/ [6] d. babic, h. g. gockler, “estimation of the length and the polynomial order of polynomial-based filters”, 8th international conference on sampling theory and applications, marseille, france, may 18-22, 2009 [7] d. babic, “estimation of the number of polynomial segments and the polynomial order of prolonged farrow structure”, 22nd telecommunications forum telfor (telfor), belgrade, serbia, pp. 461 464, november 25-27, 2014 [8] t. saramaki, “finite impulse response filter design”, in handbook for digital signal processing, john wiley & sons, new york, usa, 1993 microsoft word 08-812-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1249-1252 1249 www.etasr.com broujeni et al.: construction and demolition waste management (tehran case study) construction and demolition waste management (tehran case study) babak rouhi broujeni ghassem ali omrani reza naghavi salar s. afraseyabi environmental engineering science and research branch, islamic azad university, tehran, iran tehran university of medical science science and research branch, islamic azad university, tehran, iran islamic azad university, tehran, iran. civil and environmental engineering islamic azad university, estahbān, fars, iran abstract—increasing building construction raises concerns about construction and demolition (c&d) waste management. to assess this issue the building components, the collection schemes, their recycling and disposal should be investigated. in order to manage c&d wastes, paying attention to how this kind of wastes is disposed is imperative for their correct identification. inattention, lack of organization and proper transport and sanitary disposal of construction and demolition waste lead to problems such as accumulation of construction waste in the streets. however, more than 90 percent of the potential for recycling and re-using as raw materials is provided. environmental protection agency (epa) has classified c&d wastes into three categories: non-dangerous waste, hazardous wastes and semi-hazardous wastes. currently in tehran, an average of about 50,000 tons per day of construction and demolition wastes are produced from which over 30,000 tons per day are dumped in landfills. according to this research more than 57% of these wastes are placed in the first category (non-dangerous waste) and have the potential for being recycled and reused. on the other hand, items that are placed in the second category shall be managed based on the existing laws. this article provides some management solutions including proposing methods for collecting and reusing construction waste in accordance with current market needs in iran. keywords-construction; demolition; waste; recycling; re-use i. introduction solid wastes produced by construction and demolition (c&d) activities, are a significant portion of total municipal solid wastes [1]. in developing countries, population growth, urbanization and rising construction process on one hand, and lack of appropriate space for landfill sites on the other hand, intensify the need of recycling and reusing c&d wastes management, while, much of the urban fabric of these countries, such as iran, are old and in need of demolition or renovation. in addition, natural disasters such as floods, earthquakes and hurricanes increase c&d wastes [2, 3]. due to the characteristics of c&d wastes, separating them from other wastes product (waste products) in a city is a very critical step in waste management [4-6]. from 2000 extensive studies have been done to assess solid waste management technology in order to reduce c&d wastes from civil projects or reuse them in to reduce the consumption of raw materials. in 2002, about 11 million tons of c&d wastes were produced in the united states [4]. based on figures, in tehran about 18,250,000 tons of c&d wastes are produced annually, which in the absence of this type of waste management, average space for burial is 20768055 cubic meters annually. this study attempts to examine an appropriate situation for managing c&ds wastes. according to the u.s. environmental protection agency c&d wastes consist of three types of waste: (1) nonhazardous waste; (2) hazardous waste as regulated by the resource conservation and recovery act (rcra); and (3) items that contain hazardous components that might be regulated by some states [7]. most c&d debris is nonhazardous and is not regulated by epa. in u.s under rcra, however, many states have specific definitions of c&d debris that effectively determine what materials are allowed to be disposed in nonhazardous waste landfills, c&d landfills, or incinerators. table i show some examples of c&d wastes that may not be considered as hazardous wastes according to epa’s definition [6]. in some countries (such as iran), hazardous c&d wastes management task is the responsibility of municipalities [8]. ii. management strategies a. the proposed method for reusing c&ds reusing is the use of an item again after it has been used [9, 10]. this includes conventional reuse where the item is used again for the same function, and creative reuse where it is used for a different function [11]. it prevents the consumption of resources, raw materials, energy and reduce waste production. table ii shows c&d wastes that are reusable. bet reuse of these materials is being intact and having an acceptable quality [12-14]. some c&d wastes can be used in new construction projects only by imposing certain limitations. these types of c&d wastes are shown in table iii [12-14]. engineering, technology & applied science research vol. 6, no. 6, 2016, 1249-1252 1250 www.etasr.com broujeni et al.: construction and demolition waste management (tehran case study) table i. some examples of hazardous c&ds wastes activity wastes generated possible rcra waste codes land-clearing, wrecking and demolition ignitable or toxic wreckage and debris, and lead pipe d001 (ignitable wreckage and debris), d008 (lead pipe, toxic wreckage and leadbased paint debris), d009 (mercury-containing fluorescent lamps), d023-d026 (toxic wreckage and debris containing cresols). heavy construction asphalt wastes, petroleum distillates, and used oil. (asphalt is widely recycled.) d001 (asphalt wastes, petroleum distillates, used oil sent for disposal), d004 (arsenic), d006-d008 (used oil sent for disposal containing cadmium, chromium, or lead), d018 (asphalt wastes containing benzene). carpentry and floor work acetone, adhesives, coatings, methylene chloride, methyl ethyl ketone (mek), methyl treatisobutyl ketone (mik), mineral spirits, sol vents, toluene, treated wood. d001 (acetone, adhesives, coatings, methylene chloride, mek, mik, mineral spirits, solvents, trichloroethylene, toluene, xylene), d004 (treated wood), d023d026, d037 (treated wood), d035 (mek), d040 (trichloroethylene), f001 or f002 (trichloroethylene, methylene chloride), f003 (acetone, xylene, mik), f005 (toluene, mek), u002 (unused acetone), u159 (unused mek), u161 (unused mik), u239 (unused xylene), u220 (unused toluene), u080 (unused methylene chloride). paint preparation and painting acetone, chlorobenzene, glazes, methanol, mek, methylene chloride, paint, petroleum distillates, pigments, solvents, strippingcompounds, toluene, and wastewater. d001 (acetone, chlorobenzene, glazes, methanol, mek, methylene chloride, paint, petroleum distillates, solvents, stripping compounds, toluene, wastewater), d007 (chromium pigments), d008 (lead pigments), d021 (chlorobenzene), d035 (mek), f001 and f002 (chlorobenzene), f003 (acetone, methanol), f005 (mek, toluene), u002 (unused acetone), u037 (unused chlorobenzene), u159 (unused mek), u220 (unused toluene). specialty contracting activities acetone, adhesives, coatings, hexachloroethane, kerosene, mek, mik, pigments, solvents, toluene, wastewater, and xylene. d001 (acetone, adhesives, coatings, mek, mik, kerosene, solvents, toluene, wastewater, xylene), d007 (chromium pigments), d008 (lead pigments), d034 (hexachloroethane), d035 (mek), f003 (acetone, mik, xylene), f005 (toluene, mek), u002 (unused acetone), u131 (unused hexachloroethane), u159 (unused mek), u161 (unused mik), u220 (unused toluene), u239 (unused xylene). table ii. c&d wastes which can be reused c&ds bricks, clay pipes, clay blocks alone or attached to the cement concrete, cement blocks, tiles, stepping stones, concrete pipes, cement sand mortar metal components and facility parts aggregates and building stone parquet and other wood materials b. the proposed method for recycling c&d wastes currently in tehran, about 30,000 tons of c&d wastes are daily produced by the civil project and table iv shows the components of these c&d wastes. more than 57% of these c&d wastes are recycled. about 16.7% of these c&d wastes are soil and rubble which are recycled and converted in situ into sand and gravel. figure 1 shows the percentage curve of materials which are recycled separately. the main purposes of recycling c&d wastes are making good materials with cheap price (subject to compliance with the standard), to avoid filling landfills, and reducing environmental impact and job creation. the most useful c&d waste that is recycling is mixed soil and rubble which can be considered as the main material in many civil projects after recycling. mixed soil and rubble recycling process is shown in figure 2. it should be noted that during the recycling process, environmental tips such as not engaging contaminated materials should be considered (table v). fig. 1. percentage of recycled materials (numbers refer to table iv) table iii. c&d wastes which can be reused c&ds kind of limitation doors, windows and frames compliance dimensions steel profile just can be used in minor non-structural parts of buildings. if any features such as corrosion, deformation and twist not be visible. gravel and sand just for floors leveling table iv. recycled products and rates recycling products the weight of recycled products (ton) percent of recycling from total c&ds 1 gravel and sand 5000 16.7 2 brick 50 0.2 3 ironware 3500 11.7 4 plastics 2000 6.7 5 cardboard 2000 6.7 6 plaster 1000 3.3 7 sack 2000 6.7 8 wood 1600 5.3 engineering, technology & applied science research vol. 6, no. 6, 2016, 1249-1252 1251 www.etasr.com broujeni et al.: construction and demolition waste management (tehran case study) fig.2. flowchart of mixed soil and rubble recycling process fig.3. comparing the amount of left in landfill and c&d wastes which has been recycled and reused in tehran. table v. how to recycle solid and rubble recycled materials how to use washed sand with grain size less than 5 mm concrete, foundation insoles sand use as drainage, reinforced concrete columns with low load on oval gravel from 13 to 25 mm concrete, block and brick construction, foundation normal gravel 7 to 30 mm concrete, foundation rubble parking floor iii. suggestions to protect the environment against pollution and create safety in construction projects in which the recycled materials are used the following strategies are recommended:  selecting and applying appropriate management plans through appropriate tools.  making a good market for recycled products.  guaranteeing the quality of recycled materials by valid organizations. in order to reduce the amount of c&d wastes creation, the following suggestions are intended:  correcting storage and use of construction materials.  using packaged materials instead of bulk materials.  keeping material packages safe till to use.  using appropriate materials with long service life. iv. conclusion the aim of this paper was to show that the existing c&ds have good potential for being reused and recycled. additionally, this research proposes reuse and recycling of c&d wastes in order to increase the amount of landfill capacities and reduce the use of raw materials. the way which c&d wastes can recycle and the way of reuse are proposed also. statistics show the capability of methods which are used for recycling and reuse of c&d wastes in this study. coincided with the rise of recycled and reused c&d wastes, accumulation of the amounts of c&d wastes in existing landfill has declined. references [1] a. abbas, g. fathifazl, o. isgor, a. razaqpur, b. fournier, s. foo “environmental benefits of green concrete”, ieee climate change technology conference, pp. 1–8, 2006 [2] m. osmani, “construction waste minimization in the uk: curent pressure for change and approaches”, procedia social and behavioral sciences,vol. 40, pp. 37-40, 2012 engineering, technology & applied science research vol. 6, no. 6, 2016, 1249-1252 1252 www.etasr.com broujeni et al.: construction and demolition waste management (tehran case study) [3] j. d. goedert, p. meadati, “integrating construction process documentation into building information modeling”, journal of construction engineering and management, vol. 134, no. 7, pp. 509– 516, 2008 [4] m. osmani, g. glass, a. proce, “architect and contractor attitudes towards waste minimisation, waste and resource management”, proceedings of the institution of civil engineers waste and resource management, vol. 59, no. 2, pp. 65-72, 2006 [5] p. o. quantity of construction and demolition waste collected, https://www.wasterecycling.org [6] resource conservation and recovery act of 1976 (rcra), rcra hazardous waste resources, construction, demolition, and renovation, www.epa.gov/osw/topics.htm [7] u. bogenstatter, “prediction and optimisation of life-cycle costs in early design”, building research and information, vol. 28, pp. 376-386, 2000 [8] o. faniran, g. caban, “minimising waste on construction project sites”, engineering, construction and architectural management, vol. 5, no. 2, pp. 182-188,1998 [9] hm government, strategy for sustainable construction, uk, 2008, http://webarchive.nationalarchives.gov.uk/+/http:/www.bis.gov.uk/files/f ile46535.pdf [10] wrap, 2007a, “waste recovery quick win case studies” http://www.wrap.org.uk/construction/construction_waste_minimisation_ and_management/wrqw_case_studies.html [11] wrap, designing out waste: a design team guide for buildings, 2009 [12] m. l. tseng, “an assessment of cause and effect decision making model for firm environmental knowledge management capacities in uncertainty”, environmental monitoring and assessment, vol. 161, pp.549-564, 2010 [13] m. l. tseng, “importance-performance analysis on municipal solid waste management in uncertainty”, environmental monitoring and assessment, vol. 172, no. 1-4, pp.171-187, 2011 [14] j. holmes, g. capper, g. hudson, “21st century health care centres in the united kingdom”, journal of facilities management, vol. 4, pp. 99109, 2006 [15] c. s. poon, “reducing construction waste”, waste management, vol. 27, pp. 1715-1716, 2007 . microsoft word etasr_v12_n6_pp9760-9765 engineering, technology & applied science research vol. 12, no. 6, 2022, 9760-9765 9760 www.etasr.com ky: a study on the influence of plasma nitriding technology parameters on the working surface … a study on the influence of plasma nitriding technology parameters on the working surface deformation of hypoid gears le hong ky vinh long university of technology education vinh long, vietnam kylh@vlute.edu.vn received: 23 september 2022 | revised: 15 october 2022 | accepted: 17 october 2022 abstract-this paper presents the results of the research on the influence of plasma nitriding technology parameters on the working surface deformation of hypoid gears. blue light technology with non-contact measuring devices is used to determine the working surface deformation of hypoid gears after plasma nitriding. the study has determined a regression equation showing the influence of plasma nitriding technology parameters on the deformation of the working surface of the hypoid gear. the minimum deformation optimization value at the planning area is 0.0071746 at permeation temperature tl=4.89 o c, permeation time h=510h, and gas flow 1 g1=6.02l/h. keywords-hypoid gear; surface deformation; computer aided verification; plasma nitriding i. introduction the hypoid gear pair has some special features: the axes of the gears are diagonal, the average helix angle of the active gear and the passive gear are not equal, and the tangential module of the active gear is larger than those of the passive gear. the constraining forces at the contact trace acting on the active and passive gears are equal, but the tangential forces are not equal [1]. hypoid gears are shaped by milling [2] (figure 1(a)). this study uses plasma nitriding to improve the working surface quality of hypoid gears. plasma nitriding is an advanced and environmentally friendly technology that is very effective for products with simple structures. the advantage of this technology is that it can control the white layer, so it is very suitable for impregnating products that require high quality. the disadvantage of the plasma nitriding method is the occurrence of plasma amplification during the penetration of the surface. this disadvantage can be completely eliminated by controlling the plasma thickness [3, 4]. plasma nitriding is the process of alloying the surface with nitrogen. the permeation process is carried out in a vacuum furnace at low pressure with a mixture of h2, n2, ch4, and ar gases [3, 4]. under high voltage, the gases are ionized, creating a plasma flow. nitrogen ions are accelerated during plasma collision with the sample. this ion bombardment process heats, cleans and forms a hard layer with good wear resistance, increasing fatigue strength [5]. the eltropul permeation furnace [6] uses a pregenerated plasma pulse source. it creates stable plasma under all circumstances, permeates parts with complex geometries, lowers temperatures providing for the lowest permeation and the most treated surfaces. the surface layer that is nitrified after ion nitriding is a thin, solid white layer outside and a diffuse domain inside. the properties of the surface layer (deformation, hardness, roughness, cleanliness), permeation layer depth, permeation layer properties, microscopic hardness of the material, etc. are influenced by input parameters such as voltage, current density, permeation time, permeation temperature, compositions of gas mixture, gas pressure, etc. authors in [7] used plasma nitriding treatment to reduce wear occurring in hot forging applications, but there is a need for further optimization of the processes to achieve suitable properties for different loaded forging tools. this work presents the influence of the main process parameters on the wear properties of the mold. the effects of nitriding parameters such as temperature, nitrogen flow, and time on nitriding depth, hardness, and crack sensitivity were investigated. authors in [8] studied the surface properties of the fe4n layer on steel modified by pulsed plasma nitriding [8]. authors in [9] studied the phase structure and surface hardness value of aisi h13 ion nitrided steel under different temperatures. authors in [10] worked on nitriding of tertiary alloys based on iron (fe-cr-ti and fe-cr-al) and other alloy steels [10]. there have been many studies on the mechanical properties of steel after plasma nitriding [9-11]. to the best of our knowledge, there are no studies that consider plasma nitriding of hypoid gears made of 18xгt alloy steel. precision inspection has been widely used in manufacturing to measure the dimensional accuracy of parts and products to meet the quality requirements. for regular geometric features, coordinate-measuring machines can be used effectively to assess the accuracy and tolerances. for parts with free-form surfaces, the inspection becomes complex. therefore, numerous researches have been carried out to tackle both fundamental and application issues concerning free-form surface inspection. in addition to academic research, some commercial packages have also been developed [12]. this corresponding author: le hong ky engineering, technology & applied science research vol. 12, no. 6, 2022, 9760-9765 9761 www.etasr.com ky: a study on the influence of plasma nitriding technology parameters on the working surface … study used atos's non-contact measuring instrument to collect point cloud data of samples before and after plasma nitriding. the evaluation of surface deviations is handled by gom software, also of atos. this application has never been used before with hypoid gear working surfaces. ii. plasma nitriding for hypoid gear samples a. experimental samples the plasma nitriding sample consists of passive gear teeth, which have been machined from 18xгt and improved to a uniform hardness of 34 – 36 hrc (figure 1). each tooth is cut separately by wire cutting. the teeth are marked in order from 1 to 41 corresponding to the total number of teeth of the gear, as shown in figure 1(b). (a) (b) fig. 1. sample preparation for the experiment: (a) passive hypoid gear, (b) teeth that are cut apart. b. experiment planning 1) selection of input parameters h4580 eltrolab is used to perform plasma nitriding. many parameters affect the surface quality [13]: h is the number of hours executed in each step of the program (h), m is the number of minutes executed in each step of the program (min), p is the pressure (pa), tl the permeation temperature ( o c), tg the detailed temperature rising rate over time ( o c/min), tw the furnace wall temperature ( o c), wg the furnace wall temperature rising rate over time ( o c/min), v is the voltage (v), pd the pulse duration (s), pr the number of repetitions of the pulse, and g1-g4 are gas flows 1-4 respectively (l/h). in reality, in permeation with samples of the same material and size with little change, the voltage v and pressure p are fixed. detailed temperature rising rate over time tg, furnace wall temperature tw, and furnace wall temperature rising rate over time wg depend on tl and h. g1-g4 are proportional to each other [14]. according to the requirements for selecting input factors, the experimental variables were selected including tl, h, and g1. the remaining factors remain unchanged. the influence relationship of plasma nitriding technology parameters on the deformation of the working surface of hypoid gears is: �  =  �(ℎ, � , 1) (1) where ɛ is the absolute deviation due to thermal deformation of tooth working surface (mm). 2) the permeation process when the power supply is closed under high voltage and low pressure, the first heating process, until reaching a temperature of 250-300 o c, passes through the surface activation stage, followed by the second heating stage until reaching the permeation temperature (510-550 o c). the end of the permeation period, lasting from 4 to 8h (depending on the installation program), is the automatic cooling phase. (a) (b) fig. 2. plasma nitriding of hypoid gear tooth samples annd scanning of samples after permeation. (a) samples in the permeation furnace, (b) measuring and scanning of samples after permeation. 3) the conduct of permeation of the test samples level 2 planning with 27 experiments and programming to control the permeation process on h4580 eltrolab are shown in table i. plasma nitriding of hypoid gear tooth samples was carried out as shown in figure 2(a). 4) test samples measuring and scanning one of the development applications of the technique is non-contact measurement using computer aided verification (cav) to determine the deformation of the surface. here, deformation is understood as the differences from the origin (standard). the basic cav steps include data collection (point cloud) from the original object, data after machining (here, after permeation), superposition of 2 cloud data according to predetermined standards, and deviation evaluation. in this study, capture 3d–atos blue light iii triple non-contact measuring device with blue light technology were used to collect point cloud data of samples before and after plasma nitriding, as shown in figure 2(b). iii. results and discussion after loading the sample point cloud data before and after permeating into the software and superimposing these two data sets, automatic comparison was made with the two tooth surface point cloud data, displaying the measurement results of deviation due to deformation on the tooth surfaces of each test sample as shown in figure 3. the software produces a statistical report on the measurement results of deviation due to deformation at specified points on the gear tooth surface of each measured sample. the deviation due to surface deformation of each measured sample is the average value of the specified points on the gear tooth surface. measurement results with 27 samples are summarized in table ii. engineering, technology & applied science research vol. 12, no. 6, 2022, 9760-9765 9762 www.etasr.com ky: a study on the influence of plasma nitriding technology parameters on the working surface … table i. control program of the permeation process ps h m opt p tl tg tw wg v pd pr g1 g2 g3 g4 1 4 2 144 250 510 10 530 10 470 50 100 4 12 0 0 2 4 2 144 250 510 10 530 10 470 50 100 6 18 0 0 3 4 2 144 250 510 10 530 10 470 50 100 8 24 0 0 4 4 2 144 250 530 10 530 10 470 50 100 4 12 0 0 5 4 2 144 250 530 10 530 10 470 50 100 6 18 0 0 6 4 2 144 250 530 10 530 10 470 50 100 8 24 0 0 7 4 2 144 250 550 10 530 10 470 50 100 4 12 0 0 8 4 2 144 250 550 10 530 10 470 50 100 6 18 0 0 9 4 2 144 250 550 10 530 10 470 50 100 8 24 0 0 10 6 2 144 250 510 10 530 10 470 50 100 4 12 0 0 11 6 2 144 250 510 10 530 10 470 50 100 6 18 0 0 12 6 2 144 250 510 10 530 10 470 50 100 8 24 0 0 13 6 2 144 250 530 10 530 10 470 50 100 4 12 0 0 14 6 2 144 250 530 10 530 10 470 50 100 6 18 0 0 15 6 2 144 250 530 10 530 10 470 50 100 8 24 0 0 16 6 2 144 250 550 10 530 10 470 50 100 4 12 0 0 17 6 2 144 250 550 10 530 10 470 50 100 6 18 0 0 18 6 2 144 250 550 10 530 10 470 50 100 8 24 0 0 19 8 2 144 250 510 10 530 10 470 50 100 4 12 0 0 20 8 2 144 250 510 10 530 10 470 50 100 6 18 0 0 21 8 2 144 250 510 10 530 10 470 50 100 8 24 0 0 22 8 2 144 250 530 10 530 10 470 50 100 4 12 0 0 23 8 2 144 250 530 10 530 10 470 50 100 6 18 0 0 24 8 2 144 250 530 10 530 10 470 50 100 8 24 0 0 25 8 2 144 250 550 10 530 10 470 50 100 4 12 0 0 26 8 2 144 250 550 10 530 10 470 50 100 6 18 0 0 27 8 2 144 250 550 10 530 10 470 50 100 8 24 0 0 table ii. synthesis of the deviation measurement results due to thermal deformation of work surface trial tl ( o c) h (h) g1 (l/h) ɛ (mm) 1 4 510 4 0.0080 2 4 510 6 0.0071 3 4 510 8 0.0082 4 4 530 4 0.0086 5 4 530 6 0.0085 6 4 530 8 0.0093 7 4 550 4 0.0103 8 4 550 6 0.0099 9 4 550 8 0.0114 10 6 510 4 0.0082 11 6 510 6 0.0078 12 6 510 8 0.0080 13 6 530 4 0.0090 14 6 530 6 0.0083 15 6 530 8 0.0092 16 6 550 4 0.0105 17 6 550 6 0.0099 18 6 550 8 0.0111 19 8 510 4 0.0096 20 8 510 6 0.0087 21 8 510 8 0.0098 22 8 530 4 0.0099 23 8 530 6 0.0099 24 8 530 8 0.0101 25 8 550 4 0.0119 26 8 550 6 0.0111 27 8 550 8 0.0139 1) influence of input parameters on surface deformation the experimental results (table iii) were processed using minitab software and were preliminarily analyzed [15, 16]. fig. 3. measurement result display on two gear tooth surfaces. table iii. experimental results analysis term coef se coef t-value p-value vif constant 0.008207 0.000194 42.36 0.000 tl 0.000756 0.000090 8.42 0.000 1.00 h 0.001367 0.000090 15.24 0.000 1.00 g1 0.000278 0.000090 3.10 0.007 1.00 tl×tl 0.000678 0.000155 4.36 0.000 1.00 h×h 0.000544 0.000155 3.50 0.003 1.00 g1×g1 0.000811 0.000155 5.22 0.000 1.00 tl×h 0.000042 0.000110 0.38 0.709 1.00 tl×g1 0.000033 0.000110 0.30 0.765 1.00 h×g1 0.000292 0.000110 2.66 0.017 1.00 it was found that there were some coefficients with p-value greater than the precision a=0.05, so these coefficients were discarded, and the experimental results were reanalyzed (table iv). engineering, technology & applied science research vol. 12, no. 6, 2022, 9760-9765 9763 www.etasr.com ky: a study on the influence of plasma nitriding technology parameters on the working surface … table iv. experimental results second analysis term coef se coef t-value p-value vif constant 0.008207 0.000185 44.48 0.000 tl 0.000756 0.000085 8.85 0.000 1.00 h 0.001367 0.000085 16.00 0.000 1.00 g1 0.000278 0.000085 3.25 0.004 1.00 tl×tl 0.000678 0.000148 4.58 0.000 1.00 h×h 0.000544 0.000148 3.68 0.002 1.00 g1×g1 0.000811 0.000148 5.48 0.000 1.00 h×g1 0.000292 0.000105 2.79 0.012 1.00 fig. 4. the influence of input parameters (tl, h, g1) on surface deformation (ɛ). the influence of the input parameters on the surface deformation is presented in figure 4. corresponding to the three levels (-1), (0), and (+1) of each factor, the software calculates the average value of the output response and displays it as a point (figure 4). from there, to find out the parameter that has the most influence on the output value, it is possible to make a brief comment on the influence of the input parameters on the surface deformation. with the permeation temperature tl, the influence on the output is parabolic, with the minimum near the value 0, and the influence chart goes from a minimum of about 0.0080 to the maximum value of 0.0095 at the value area +1 of the planning. for permeation time h, the influence on the output is parabolic, with the minimum near the value 0 and the influence chart goes from the minimum value around 0.0075 towards the maximum value of 0.0100 at the value area +1 of the planning. with a gas permeation concentration of 1 g1, the influence on the output is parabolic, with the minimum near the value 0 and the influence chart goes from about 0.0085 to a minimum and to the maximum value of 0.0095 at the value area +1 of the planning. with the pareto chart in figure 5, it is found that the parameters that greatly affect the surface deformation are h and tl. these parameters interact at level 2 of g1. in the standard distribution chart in figure 6, the effect parameters are standardized. these are the parameters that affect the regression equation. 2) regression equation of experimental data the variance (anova) of the regression equation for the output object is analyzed, with the selection of removing the parameters that do not affect the determined regression equation (table v) [17]. the variance analysis table has all pvalues less than 0.05. this shows that these parameters all have an influence on the regression equation. fig. 5. pareto chart of input parameters. fig. 6. standard distribution chart of the standardized effect parameters. table v. analysis of variance source df adj ss adj ms f-value p-value model 7 0.000055 0.000008 59.59 0.000 linear 3 0.000045 0.000015 114.93 0.000 tl 1 0.000010 0.000010 78.24 0.000 h 1 0.000034 0.000034 255.98 0.000 g1 1 0.000001 0.000001 10.57 0.004 square 3 0.000008 0.000003 21.53 0.000 tl×tl 1 0.000003 0.000003 20.99 0.000 h×h 1 0.000002 0.000002 13.54 0.002 g1×g1 1 0.000004 0.000004 30.05 0.000 2-way interaction 1 0.000001 0.000001 7.77 0.012 h×g1 1 0.000001 0.000001 7.77 0.012 error 19 0.000002 0.000000 total 26 0.000057 the suitability of the data was evaluated using a set of r 2 , adjusted r 2 , and predicted r 2 parameters. these parameters all have a value bigger than 90%, which means that the regression equation is completely consistent with the experimental data. engineering, technology & applied science research vol. 12, no. 6, 2022, 9760-9765 9764 www.etasr.com ky: a study on the influence of plasma nitriding technology parameters on the working surface … table vi. suitability s r 2 r 2 (adj) r 2 (pred) 0.0003624 95.64% 94.04% 91.01% then the general equation (1) is rewritten as a regression equation in natural form: ɛ = 0.388 � 0.001656 � � 0.001418 ℎ � 0.00616 1 � 0.000169 � � � 0.000001 ℎ� � 0.000203 1� � 0.000007 ℎ � 1 (2) the chart in figure 7 shows the domain of double interactions between the parameters. based on these charts, the changing trend of surface deformation can be seen when changing separately the two parameters shown in each chart. fig. 7. interaction charts between parameters. 3) optimization of permeation technology parameters with the regression equation found, minimum deformation optimization is carried out with the following contour conditions: min �: 4 ! � ! 8510 ! ℎ ! 5504 ! 1 ! 8 minitab software gives the optimization results shown in table vii: table vii. minitabl results tl h g1 ɛ fit 4.89 510 6.02 0.0071746 fig. 8. software result of minimizing deformation in the planning area. iv. conclusion blue light technology with a non-contact measuring device is used to determine the working surface deformation of hypoid gears after plasma nitriding. the current study has determined the regression equation showing the influence of plasma nitriding technology parameters on surface deformation. research results show that the parameters of plasma nitriding technology that have a great influence on surface deformation are permeation time h and permeation temperature tl. the gas permeation concentration 1 g1 has little effect on the surface deformation and the level 2 interaction with h and tl. the minimum deformation optimization value in the planning area is 0.0071746 for tl=4.89 o c, h=510h, and g1= 6.02l/h. thus, the working surface deformation of hypoid gears after permeation is very little influenced by plasma nitriding technology parameters. to the best of our knowledge, plasma nitriding of hypoid gears along with the use of blue light technology with noncontact gauges to determine the gear working surface deformation have not been studied before. with the technological parameters determined as above, it is possible to proceed to set up the hypoid gear plasma nitriding technology process in industrial production. references [1] m. kolivand, development of tooth contact and mechanical efficiency models for face-milled and face-hobbed hypoid and spiral 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[17] v. c. nguyen, t. d. nguyen, and d. h. tien, "cutting parameter optimization in finishing milling of ti-6al-4v titanium alloy under mql condition using topsis and anova analysis," engineering, technology & applied science research, vol. 11, no. 1, pp. 6775–6780, feb. 2021, https://doi.org/10.48084/etasr.4015. engineering, technology & applied science research vol. 7, no. 4, 2017, 1775-1780 1775 www.etasr.com singh and sharma: a novel energy efficient clustering algorithm for wireless sensor networks a novel energy efficient clustering algorithm for wireless sensor networks santar pal singh electronics and computer discipline, dpt indian institute of technology roorkee roorkee, india spsingh78@gmail.com subhash chander sharma electronics and computer discipline, dpt indian institute of technology roorkee roorkee, india scs60fpt@iitr.ac.in abstract—wireless sensor networks (wsns) are composed of huge amount of tiny resource constrained devices known as sensors. the demand for an energy efficient structure is becoming gradually more essential in wsns. energy efficient clustering is a distinguished optimization problem which has been studied extensively to expand the life span of wsns. in this manuscript, a new energy efficient clustering scheme for wsns with the use of particle swarm optimization (pso) is proposed. the clustering algorithm is implemented with the goal of concurrently minimizing the intra-cluster distance along with optimizing the usage of network energy. the presented algorithm is tested widely and results are analyzed and compared with previous ones to show the supremacy in term of alive nodes, energy consumption, packet delivery ratio, and system throughput. simulation results show that the proposed algorithm outperforms other existing algorithms. keywords-wireless sensor networks; clustering algorithms; energy efficiency;particle swarm optimization i. introduction latest advancements in wireless and embedded technologies allow the use of micro autonomous system comprised of small tiny devices known as sensors. these sensors can detect, compute and communicate via suitable sensor technology which results to a wireless sensor network. deployment ease and low cost sensors make wireless sensor network suitable for many applications like health care, transportation, smart building, and environmental monitoring etc. regarding the wsn design, there are lots of significant aspects that ought to be considered such as the size of nodes, hardware complexity and low energy utilization [1, 2]. energy efficiency is considered to be the main design objective, in view of the fact that a wireless node can only be outfitted with a restricted power supply. in several applications, replacement of energy sources is not possible, and thus the node’s life span demonstrates a strong reliance on battery life [2, 3]. clustering is among the design schemes utilized to handle the energy utilization proficiently, via minimizing the amount of nodes to be included in long-haul transmission with sink and allocating the energy expenditure uniformly amid the nodes. in this scheme, every set of nodes has a head node recognized as cluster head (ch) that performs data aggregation on data as of its relevant group and forwards it to sink or base station (bs). thus, the clustered schemes have the advantages of decreasing the total information that requires to be disseminated, besides improving resource allocation as well as bandwidth reusability [4-7]. lots of algorithms have been reported with the goal of exploiting the network life span by implementing clustering designs [6-10]. probably the most renowned hierarchical protocol is low energy adaptive hierarchy (leach). leach is a hierarchical scheme that introduces disseminated cluster establishment; at some stage in it, nodes choose themselves as head node with some possibility [11]. this algorithm is executed sporadically and the possibility of becoming ch for every epoch is elected to insure that each node turn out to be a ch at least on one occasion in 1/p rounds, wherever p is preset proportion of chs. it gives considerable energy saving and lengthened network life span over traditional routing methods for example minimum transmission energy (mte) scheme. however, leach does not ensure that preferred amount of chs is elected and chs are not uniformly placed in the network. the most important drawback of leach is that a sensor node with incredibly low energy might be designated as ch and the chs send the data to base station in one-hop manner [11]. thus, this scheme increases the energy utilization of the chs. various methods have been designed to improve leach i.e. leach-c, pegasis, heed etc. [1214]. leach-c behaves superiorly compared to leach because of the appropriate election of ch by bs. in the selection of ch, it considers the energy as well as distance into account [12]. hence, leach-c can efficiently choose the ch by taking into consideration of energy competence and be capable of extending the network life span. pegasis arranges the nodes into chain with the intention that every node sends and/or receives the data merely as of its nearby nodes. in every round an arbitrarily chosen node from chain is elected as cluster head. pegasis improves the network lifetime engineering, technology & applied science research vol. 7, no. 4, 2017, 1775-1780 1776 www.etasr.com singh and sharma: a novel energy efficient clustering algorithm for wireless sensor networks compared to leach but data delay is considerably high [13]. so, it is not suitable for large area networks. the heed periodically chooses the chs on the basis of node’s remaining energy along with connectivity measure of nearest node or node degree [14]. other leach based clustering algorithms have been presented [15-18]. in the present paper, a novel energy efficient clustering algorithm for wsns with help of the pso algorithm is investigated aiming to maximize the life span of network. the key idea of the proposed algorithm is the election of a ch that focuses on minimization of intra-cluster distance and optimization of network energy. the proposed method uses a high energy node as ch and makes clusters which can be uniformly placed in the sensor region. the use of pso has been suggested earlier in [19, 20]. in the current approach, we attempted to optimize the energy usage of nodes whereas maximizing the data communication. the main difference among this work and earlier works is the use of pso to decide the optimum nodes as chs to expand the life span of the system ii. system model here, we illustrate the network model and energy model used in the proposed algorithm. a. network model let us consider a net model alike to that utilized in leach with the following characteristics:  every node carry out sensing tasks sporadically and all the time send data to bs.  a fixed bs can be placed inside or outside the wsn area.  each and every node is fixed and energy restrained.  each and every node is capable of working in ch mode as well as in sensing manner.  fusion of data is utilized to lessen the overall data. b. radio energy model in this work, we employ energy model of radio (rem) as given in figure 1. fig. 1. radio energy model in rem, transmitter depletes energy to operate radio as well as power amplifier, moreover the receiver uses up the energy to operate radio [21, 22, 25]. the radios can carry out the power control and thus utilize minimum energy needed to get to the destined recipients. because of attenuation, energy loss model is applied for small and long distances. hence, to realize signal-to-noise (snr) ration during broadcasting l-bit packet over distance d, then energy dissipated in radio is specified as:   2 0 4 0 , , , elec fs tx elec mp le l d if d d e l d le l d if d d          (1) where eelec represents energy depleted per bit to operate the electronic circuitry, εfs and εmp depends on amp model, d denotes the distance among sender and receiver, and d0 denotes threshold transmission distance. the threshold distance d0 is given by: equating the equation (1) for d=d0 2 4 0 0elec fs elec mple l d le l d    0 fs mp d    to obtain l-bit packet, radio uses   .rx elece l l e (2) iii. particle swarm optimization pso is a swarm intelligence and collective intelligence based scheme, modeled behind the social foraging behavior of some animals like flock of birds or schools of fishes [23, 24]. in pso, a swarm specifies the number of probable solutions to a complex problem, where each probable solution is known as a particle. the key objective of this method to discover the particle location that outcomes the finest assessment of a specified fitness function. during the initialization phase of swarm optimization, every particle set opening parameters in random fashion and is flown throughout the multidimensional search space. in every generation, every particle make use of the info about its earlier personal best position as well as global best position to maximize the possibility of moving in the direction of a better answer space that will results in improved fitness and update its candidate solutions in accordance with the subsequent equations:   1 1 1 ..) 1 .( ( )id i d id i dc r xpbestv x tt v t          2 2 .... 1idc r xgbest x t     (3)      1id id idx t x t v t   (4) where v and x represents particle’s velocity and place, t is time, c1, c2 are learning coefficients, ω is the inertia parameter. r1, r2 denotes the numbers generated randomly among 0 and 1. the idxpbest be the particle’s best position individually and xpbest be the particle’s best position globally. engineering, technology & applied science research vol. 7, no. 4, 2017, 1775-1780 1777 www.etasr.com singh and sharma: a novel energy efficient clustering algorithm for wireless sensor networks iv. proposed algorithm the flow sheet of proposed algorithm is revealed in figure 2. the proposed algorithm is comprised of three core phases given as: phase 1: cluster formation the cluster is formed by the bs or sink node on the basis of centralized clustering. for clustering bs transmit a message to every node. the nodes after receiving this message starts to send its information like node id, location, energy loss ratio, and current energy to sink. based on such info, the bs estimates moderate energy level of every node. to assure that nodes that have acceptable energy level are likely to be a ch aspirant for present round. later the sink uses the pso scheme to identify the best k chs which can minimize the cost function defined as:  1 21cost func func      (5) where func1 denotes the maximum average distance of nodes to their corresponding chs and can be expressed as:   , 1 1 , ,max , / i p k k k i p k p k n c func dist n ch ch              (6) where |chp,k| denotes the amount of nodes be owned by cluster ck for particle p. the func2 represents the proportion of entire initial energy of the network with whole energy of ch candidates in present round. α is an user described constant utilized to weigh the effort of every sub-objective. the func2 can be expressed as:     1 2 ,1 n ii k p kk e n func e ch      (7) the fitness function has an aim of concurrently minimizing the intra-cluster distance among sensor nodes and relevant chs and as well optimizing the network energy competence. in accordance with cost function, small rate of func1 and func2 recommend compact clusters through optimal set of nodes which have enough energy to execute the ch jobs. for the wsn with n number of nodes along with k no. of clusters, the clustering schemes can be shown as: step1: initializing particles to have k arbitrarily chosen chs amid the entitled ch aspirants. step2: estimate the function of cost of every particle: (i) for every node ni ,i=1,2,…,n  compute distance dist(ni , chp,k ) among node ni and every heads chp,k  allocate node ni to leader chp,k ,wherever     , 1 ,, min ,i p k k k i p kdist n ch dist n ch   (8) (ii) evaluate the cost function through equation (5) to (7) step3: discover the individual and overall best for every particle. step4: updations of the velocity and position of particle with equation (3) and (4). step5: updating the change in the particle’s position assessment. step6: depict the new updated location with nearby coordinates step7: repeats steps 2 to 6 until the highest amount of iterations is achieved. phase 2: intra-cluster communication after clustering, routing procedure is invoked during data transmission stage. routing consists of two steps: first one is route establishment and other one is forwarding sensed data. in route establishment phase route request message is broadcasted to all nodes with single hop transmission and unicast route reply message is sent in reverse path to source node. once the route is established data transmission with multi-hop routing is commenced. in this work, the multi-hop communication protocol is utilized for data communication between nodes and chs (intra-cluster communication) and chs to bs. data aggregation is accomplished by the head node in each cluster for the intention of saving the remaining energy of nodes. fig. 2. flow sheet of the proposed algorithm phase 3: data transmission to sink when the cluster heads have been chosen, the networks go into data communication phase. in this work, multi-hop communication protocol is utilized for communication among chs and bs. the cluster head set up a threshold value i.e. d. in case of the transmission distance among ch and bs is lesser than the threshold value then the ch is committed to forward the calculated aggregated data to the head. otherwise, ch will find next with minimum cost neighbor as a relay node. the minimum cost path and highest residual energy is calculated by using the formula given as:                      , , , maxmax 1 maxmaxmaxmax , i j j i j j d s h d h bs e j e j cost j e jd s h d h bs           (9) engineering, technology & applied science research vol. 7, no. 4, 2017, 1775-1780 1778 www.etasr.com singh and sharma: a novel energy efficient clustering algorithm for wireless sensor networks where γ is a randomized tuning parameter in the range [0,1], si, hj are the sensor node and current head node respectively. relay ch node is selected with minimum cost to send data to destination and inter-cluster routing is established when relay node is selected. v. results and analysis the performance analysis of the proposed method is done with the help of ns-2.35. in the network, 100 nodes are organized in random fashion in 100m×100m area where bs is situated in network region. the performance assessment of proposed work is done as per the certain parameters given as:  energy consumption: total energy used by the entire nodes in their intra-cluster and intercluster activities.  no. of alive nodes: quantity of nodes that have not so far exhausted their power.  packet delivery ratio: ratio of actual packet delivered to total packet sent.  end to end delay: time utilized for message to be communicated transversely in network from source to destination.  throughput: quantity of packets per bytes received by source per unit time. the proposed algorithm is evaluated with leach, leach-c, in term of alive nodes over rounds, packet delivery ratio, energy expenditure, end-to-end delay, throughput. the total rounds used in experiment are 500. the simulation parameters are summarized in table i. in pso scheme, we use 30 particles, c1=c2=2.05, ω=0.9, and use this for 100 iterations and set α= 0.5 to provide equal involvement of every subobjective. table i. network parameters parameter value nodes 100 network size 100m×100m bs position (50,100) initial node energy 2 j eelec 5 nj/bit etx=erx 50 nj/bit εfs 10 pj/bits/m2 εmp 0.0013 pj/bits/m4 eda 5 nj/bit packet size 500 bytes no. of chs 5 no. of rounds 500 figure 3 shows the comparative analysis of energy consumption of the proposed algorithm with leach along with leach-c and it is clear that our algorithm have better energy usage in comparison to leach and leach-c. figure 4 demonstrates the amount of nodes alive per round demonstrating stability of the system. figures 5 and 6 illustrate the pdr and end-to-end delay over rounds in the network respectively. figure 7 illustrates the throughput demonstrating the efficiency of the network. fig. 3. energy consumption over rounds fig. 4. number of nodes alive over rounds fig. 5. packet delivery ratio over rounds engineering, technology & applied science research vol. 7, no. 4, 2017, 1775-1780 1779 www.etasr.com singh and sharma: a novel energy efficient clustering algorithm for wireless sensor networks fig. 6. end fig. 7. end-to-end delay over rounds fig. 8. throughput over rounds vi. conclusion in this work, a novel clustering algorithm for wsns with pso method is presented. a new function of cost with the consideration of the maximum distance among a member node and their ch and the left over energy of ch aspirants in the ch election method is delineated. the results show that the proposed method offers better network stability in comparison to leach and leach-c. moreover, the proposed algorithm induces better clustering via the uniform allocation of ch throughout the network. so, the proposed algorithm has improved energy efficiency and is useful in extending the network life span. acknowledgment the authors like to thank mhrd (govt. of india). this work is supported in part through a doctoral studies funding from ministry of human resource development. references [1] i. f. akyildiz, w. su, y. sankarasubramaniam, e. cyirci, “wireless sensor networks: a survey”, computer networks, vol. 38, no. 4, pp. 393-422, 2002 [2] j. yick, m. biswanath, d. ghosal, “wireless sensor network survey”, computer networks, vol. 52, no. 12, pp. 2292-2330, 2008 [3] d. gosain, i. snigdh, “performance comparison of protocols in bipartite wireless sensor networks”, international journal of electrical and computer engineering, vol. 5, no. 6, pp. 1417-1423, 2015 [4] a. a. abbasi, m. younis, “a survey on clustering algorithms for wireless sensor networks”, computer communication, vol. 30, no. 14, pp. 2826-2841, 2007 [5] x. liu, “a survey on clustering routing protocols in wireless sensor networks”, sensors, vol. 12, no. 8, pp. 11113–11153, 2012 [6] s. p. singh, s. c. sharma, “cluster based routing algorithms for wireless sensor networks”, international journal of engineering & technology innovations, vol. 1, no. 4, pp. 1-8, 2014 [7] s. p. singh, k. bhanot, s. sharma, “critical analysis of clustering algorithms for wireless sensor networks”, advances in intelligent systems and computing, vol. 436, pp. 783-793, 2015 [8] x. liu, j. shi, “clustering routing algorithms in wireless sensor networks: an overview”, ksii transactions on internet and information systems, vol. 6, no. 7, pp. 1735-1755, 2012 [9] s. p. singh, s. c. sharma, “a survey on cluster based routing protocols for wireless sensor networks”, procedia computer science, vol. 45, pp. 687-695, 2015 [10] w. k. lai, c. s. fan, l. y. lin, “arranging cluster sizes and transmission ranges for wireless sensor networks”, information sciences, vol. 183, no.1, pp. 117–131, 2012 [11] w. r. heinzelman, a. chandrakasan, h. balakrishnan, “energyefficient communication protocol for wireless microsensor networks”, ieee 33rd hawaii international conference on system sciences, hawaii, usa, pp. 1–10, 2000 [12] w. b. heinzelman, a. p. chandrakasan, h. balakrishnan, “application specific protocol architecture for wireless microsensor networks”, ieee transactions on wireless networking, vol. 1, no. 4, pp. 660-670, 2002 [13] s. lindsey, c. raghavendra, k. m. sivalingam, “data gathering algorithms in sensor networks using energy metrics”, ieee transactions on parallel and distributed system, vol. 13, no. 9, pp. 924-935, 2002 [14] o. younis, s. fahmy, “heed: a hybrid, energy-efficient, distributed clustering approach for ad hoc sensor networks”, ieee transactions on mobile computing, vol. 3, no. 4, pp. 366-378, 2004 [15] m. xiaoyan, study and design on clustering routing protocols for wireless sensor network, ph.d dissertation, zhejiang university, hangzhou, china, 2006 [16] x. fang, y. song, “improvement on leach protocol of wireless sensor network (e-leach)”, international conference on sensor technologies and applications, valencia, spain, 2007 [17] m. b. yassein, a. alzou, y. khamayseh, w. mardini, “improvement on leach protocol of wireless sensor network (vleach)”, international journal of digital content: technology and its applications, vol. 3, no. 2, pp. 132–136, 2009 [18] g. ran, h. zhang, s. gong, “improving on leach protocol of wireless sensor network using fuzzy logic”, journal of information science, vol. 7, no. 3, pp. 767-775, 2010 [19] n. m. a. latiff, c. c. tsimenidis, b. s. sharif, “energy aware clustering for wireless sensor networks using particle swarm optimization”, 18th annual ieee international symposium on personal, indoor, and mobile radio communications, athence, greece, 2007 [20] j. tillet, r. rao, f. sahin, “cluster head identification in ad-hoc sensor networks using particle swarm optimization”, ieee international conference on personal wireless communications, new delhi, india, pp. 201-205, 2002 [21] m. azharuddin, p. k. jana, “particle swarm optimization for maximizing lifetime of wireless sensor network”, computers and electrical engineering, vol. 51, pp. 26-42, 2016 [22] s. chelbi, m. abdouli, m. kaddes, c. duvallet, r., bouaziz, “an unequal cluster based routing protocol based on data controlling for engineering, technology & applied science research vol. 7, no. 4, 2017, 1775-1780 1780 www.etasr.com singh and sharma: a novel energy efficient clustering algorithm for wireless sensor networks wireless sensor network”, international journal of electrical and computer engineering, vol. 6, no. 5, pp. 2403-2414, 2016 [23] j. kennedy, r. c. eberhart, “particle swarm optimization”, ieee international conference on neural networks, piscataway, nj, usa, pp. 1942-1948, 1995 [24] r. v. kulkarni, g. k. venayagamoorthy, “particle swarm optimization in wireless sensor network: a brief survey”, ieee transactions on system, man, and cybernetics-part c: applications and reviews, vol. 41, no. 2, pp. 262-267, 2011 [25] k. khan, w. goodridge, “energy aware ad-hoc on demand multipath distance vector routing”, international journal of intelligent systems and applications, vol. 7, no. 7, pp. 50-56, 2015 [26] http://file.scirp.org/html/41-7601045_70085.htm authors profile santar pal singh is a ph.d. student in computer engineering discipline, dpt, indian institute of technology roorkee (india) since july 2013. he received the b.tech in computer sc. & engineering from kamla nehru institute of technology, sultanpur (u.p.) in 2001 and the m.tech in computer sc. & engineering from samrat ashok technological institute, vidisha (m.p.) in 2006. he has more than 10 years of teaching and research in area of computer science and engineering his present research interest includes ad-hoc and wireless sensor networks, network security. professor subhash c. sharma received the m.sc. (electronics), m.tech. (electronics & communication engg.) and ph.d. (electronics & computer engg.) from iit roorkee (erstwhile university of roorkee). he has published over two hundred research papers in national and international journals/conferences and supervised more than 30 projects/dissertation of pg students. he has supervised 14 phds in the area of computer networking, wireless network, computer communication and continuing supervising ph.d. students in the same area. he has successfully completed several major research projects independently funded by various govt. agencies like aicte, csir, mhrd, dst, and drdo. engineering, technology & applied science research vol. 8, no. 1, 2018, 2459-2463 2459 www.etasr.com hassan et al.: sla management for virtual machine live migration using machine learning with … sla management for virtual machine live migration using machine learning with modified kernel and statistical approach m. k. hassan a. babiker m. b. m. amien m. hamad future university khartoum, sudan memo1023@gmail.com neelain university khartoum, sudan amin.31766@hotmail.com university of gezira wad madani, sudan magdy_baker@yahoo.co.uk universiti teknologi malaysia johor bahru, malaysia taza1040@gmail.com abstract—application of cloud computing is rising substantially due to its capability to deliver scalable computational power. system attempts to allocate a maximum number of resources in a manner that ensures that all the service level agreements (slas) are maintained. virtualization is considered as a core technology of cloud computing. virtual machine (vm) instances allow cloud providers to utilize datacenter resources more efficiently. moreover, by using dynamic vm consolidation using live migration, vms can be placed according to their current resource requirements on the minimal number of physical nodes and consequently maintaining slas. accordingly, non optimized and inefficient vms consolidation may lead to performance degradation. therefore, to ensure acceptable quality of service (qos) and sla, a machine learning technique with modified kernel for vms live migrations based on adaptive prediction of utilization thresholds is presented. the efficiency of the proposed technique is validated with different workload patterns from planet lab servers. keywords-virtual machine; migration; machine learning; sla i. introduction resource optimization has been improved significantly by virtualization. it introduced isolation between application and the physical resource [1], it allows live virtual machines (vms) to seamlessly move between physical hosts. this allows service providers to host high availability applications and to better commit to their level of service governed by a service level agreement (sla). most applications in telecommunication industry permit small fraction of downtime or no downtime at all [2]. sla violation may occur due to server’s resources being over utilized. therefore, high availability and faulttolerant systems are crucial in order to maintain such a demanding policy which is costly in terms of capital and operational expenses. tightly controlled live migration can provide solution to this problem by moving vms with little or no interruption but that is often against the agreed sla. however, these interruptions can cause performance degradation which varies between applications [3-4]. thus, predicting live migration at the earliest time possible will significantly contribute to reducing any performance degradation due to sla violation or from the duration of any interruption. our objective is to provide a machine learning and statistical based predictive model to predict vm migration and consequently maintaining the sla. it is a heuristic based predictive model where future sla violation is to be predicted, then migration decision will be made by a machine learning algorithm classifier. cpu utilization, inter vm bandwidth utilization and memory utilization will be used as potential classifiers. ii. related work resource optimization in cloud based data center has been extensively investigated in recent years. authors in [5] suggested that live migration is to be handled by global policies applied to redistribute the vms, suggestion based on resources classification into local and global policies. authors in [6] have adopted priority based approach to allocate the resources in the virtualized clusters. in [9] dynamic consolidation problem was addressed by using a heuristic based approach for the bin packing problem. in [8] a threshold-based reactive approach to dynamic workload consolidation has been proposed. however it was applicable for certain types of applications. popular approaches such as vmware distributed power management [7] have the drawback that they operate on fixed threshold values which is not suitable for dynamic and unpredictable workloads [9]. in our proposed model, we introduce an approach to set the threshold values dynamically, depending on vms historical predicted data of the resource usage by each vm and machine learning as a decision making approach. static and dynamic resource assignment policies in virtualized data centers is discussed in [10, 11]. authors in [12-15] classified vm consolidation as centralized and decentralized. it was suggested vm migration trigger point to be based on predefined threshold, where on other hand other approaches [13, 15] trigger migration after workload analyzed based on learnedintelligent qos-based threshold and predictive heuristic methods [16]. nevertheless, a few set of approaches [14, 15] studied workload-independent qos-based threshold approaches for the purpose of sla violation avoidance and efficient migration management. in [16] vm placement problem with traffic-aware balancing (vmpptb) has been discussed and a longest processing time based placement algorithm (lptbp algorithm) is designed to solve it. in addition to that, localityaware vm placement problem with traffic-aware balancing engineering, technology & applied science research vol. 8, no. 1, 2018, 2459-2463 2460 www.etasr.com hassan et al.: sla management for virtual machine live migration using machine learning with… (lvmpptb) is proposed. authors in [17] proposed a vm placement algorithm named atea (adaptive three-threshold energy-aware algorithm) to reduce the energy consumption and sla violation. it is based on historical data collected from resource usage by vms to migrate vms on heavily loaded to lightly loaded hosts. all previous works did not consider inter vm bandwidth and memory utilization effects on vm consolidation problem and on sla definition especially in applications that do not tolerate any downtime or performance degradation like the telecommunication applications [18]. iii. sla violations detection the vms experience dynamic variable workloads, in a way that hardware resources consumed by a vm arbitrarily change over time. during this variation sla can be breached or the host can be over utilized, i.e. if all the vms request their maximum allowed physical resources. in such case, the algorithm must have perfect knowledge of the time when the sla violation will occur before it actually occurs. live migrations can have negative impact on the performance of applications in a vm during a migration. the length of a live migration depends on the total amount of memory used by the vm and the available network bandwidth. the migration time and performance degradation experienced by a vmj is expressed in (1) [15]. /j j jtm m b (1) 0 0.1 ( ) ( ) m o t t dj j t u u t d t    (2) where udj is the performance degradation by vmj during migration, t0is the time when the migration starts, tmj is the time taken to complete the migration,uj is the cpu utilization by vmj , mj is the amount of memory used by vmj and bj is the available network bandwidth.[15] j dj djs x u  (3) in (3) xdj is the performance degradation when the allocated resource utilization for vmj is not aligned with the agreed sla and sj is the total performance degradation by vmj. thus, from (3) in order to minimize the total performance degradation, either udj or xdj should be minimized. in this work we concentrate on minimizing xdj as udjis not only influenced by the cpu utilization uj, but is also depended on the amount of memory used and the available network bandwidth as well. moreover, it is more likely that vmj will experience performance degradation while the host resources utilization is above the agreed sla more than during the actual live migration. in order to avoid sla violation and performance degradation, host should perform regular check on the system utilization where an sla violation detection algorithm should be executed. one of the earliest methods relied on setting static cpu utilization threshold to differentiate between overload and non-overload states of the host. it is simple but inefficient for dynamic workloads, particularly when different types of applications share a physical node. in such case the system should be able to automatically adjust its behavior based on the workload patterns adopted by the applications [15]. a. local regression our approach, as depicted in figure 1, relies firstly on work load prediction based on statistical analysis of historical data collected during the vms’ lifetime. local regression (lr) has proved its efficiency as predictor method [17]. it is a model used to build up a curve from localized subsets of data that approximate the original input with the original data. lr algorithm, derived from local regression algorithm. for each new observation a new trend line is found [15] ( ) = + (4) this trend line is used to predict the next observation ( ) . the new observation can be a host resource utilization such as cpu and memory ( ) ≥ 1, − ≤ (5) where tm is the maximum time required for a vm migration fig. 1. proposed method b. classification trees when a class is already known on prior in the training samples, classification trees are effective. let tp be a parent node and tl, tr left and right child nodes of the parent node respectively. assume the learning sample with variable matrix x with m number of variables xj and n observations. let class vector y consist of n observations with total amount of k classes. classification tree is based on splitting rule that performs the splitting of learning sample into smaller parts. we already know that each time data have to be divided into two parts with maximum homogeneity of left and right child nodes will be equivalent to the maximization of change of impurity function δi(t): [19]   ( ) [ ( )]p cit t e ii t  (6) where tc represents the left and right child nodes of the parent node. assuming that the pl, pr probabilities of right and left nodes, we get:[19]   ( ) ( ) ( )p l l r ri t pi t p i ti t    (7) therefore, at each node classification trees solves the following maximization problem:[20] arg max , j=1,..., m [i(t ( ) ( )] r j j p l l r r x x pi t p i t    (8) engineering, technology & applied science research vol. 8, no. 1, 2018, 2459-2463 2461 www.etasr.com hassan et al.: sla management for virtual machine live migration using machine learning with… from (8) all possible values of all variables in matrix x for the best split question will be searched through xj<xk k which will maximize the change of impurity measure δi(t) [19]. c. support vector machine support vector machines (svms) support nonlinear classification and can find the hyper plane of maximal margin. given a training set of n data points 1{ } n k k ky x  where xk є n is the kth output pattern, the support vector method approach aims at constructing a classifier of the form: 1 ( ) [ ( , ) ] n k k kk y x sign a y x x b     (9) input (10) shows an example of hard-margin svm with noise free training data to be correctly classified by a linear function. data points d (or training set) are represented mathematically [20, 21] 1 1 2 2{( , ), ( , ),.........., ( , )}m md x y x y x y (10) where xi is a n-dimensional real vector, yi is either 1 or -1 indicating the class to which the point xi belongs to. the svm classification function f(x) takes the form [20] f(x) = w·x−b (11) where b is the bias and is the weight vector , which will be calculated during the training process. first, to correctly classify the training set f(x) (or w and b) we must return negative numbers for negative data points and positive numbers otherwise, for every point xi in d in (12) [20] wx-b>0 if yi = 1 , wx-b<0 if yi = -1 (12) d. k-nearest neighbors the k-nearest neighbors (knn) is one of the simplest methods for pattern classification. when combined with prior knowledge it can be used to produce significant results [22]. in the knn each unlabeled example is classified by the majority label among its k nearest neighbors in the training set. therefore its classification performance depends on the distance metric used to identify nearest neighbors. in the case of missing prior knowledge, euclidean distances between examples represented as vector inputs are used to measure the similarities in most knn classifiers. let 1{ , } n i i ix y   denote a training set of n labeled examples with inputs ix  є and discrete (in our case binary) class labels yi. we use the binary matrix yij є {0,1} to indicate whether or not the labels match. our goal is to learn a linear transformation which we will use to compute squared distances as [21]: 2( , ) || ( ) ||i j i jd x x l x x     (13) iv. results and analysis in this work, workload was collected from comon project [16]. extracted data was part of more than a thousand vms's resource uilization distributed across the world. samples were selected from 6 servers for a period of one week with 5 minutes measurement interval. cpus and other resources were adjusted manually with different resource utilizations for the purpose of this experiment. the collected data did not contain memory and inter vm bandwidth utilization. in this work average tpr, friedman rank summations and average ranking were used as performance metrics. tpr is defined as vm migration being correctly classified due to high utilizations. since the provided training set is not very large, cross validation has been used to train, test and validate the classification techniques, the provided data is divided into 5 folds and each fold is held out in turn for training and testing. at the initial stage, data is predicted using local regression provided that prediction window is less than or equal to the migration time as in the bond xk+1 xk≤ tm and this is crucial to maintain the sla then different classification techniques are investigated. sample data were collected for the six servers named 146cs4, cs-planetlab3, cs-planetlab4, fobos, jupiter_cs and node1. figure 2 shows sample resource utilization for 146cs4 for one week. for the purpose of the experiment, sla has been identified as 90%, 80% and 70% for the 146cs4, csplanetlab3 and cs-planetlab4 servers and 80%,70% and 60% for fobos, jupiter_cs and node1 severs for the cpu, memory and inter vm bandwidth utilization respectively. using the workload data described above, all algorithms mentioned in table i have been applied and analyzed. tpr results are shown in tables ii and iii respectively and final ranking is shown in table iv. friedman test was conducted to assess the statistical significance for the obtained results. friedman test was chosen for multi classifier performance assessment due to it is non parametric nature and wide use in multi domain analysis [22]. the null-hypothesis tested is defined as that all classifiers perform the same and the obtained differences are not significantly random. algorithms will be ranked for each data set separately. under the null-hypothesis, all the algorithms are equivalent and so their ranks rj should be calculated as [22]: 2 2 1 12 [ ] ( ) 3 ( 1) ( 1) k f j j x r k k nk k       (14) table i. classification algorithms algorithm table column head complex tree fine distinction with maximum number of leave splits 100 medium tree maximum number of leave splits 20 simple tree coars distinction with maximum number of leave splits 4 knn coars coars distinction between classes wih neightbours set to 100 knn cosine uses cosine distance metrics knn cubic uses cubic distance metrics knn fine uses fine detailed distance metrics with neighbour set to 1 knn medium neighbour set to 10 svm coars gausian coars distinction with gausian kernel svm cubic uses cubic kernel svm fine gausian fine detailed distinction gausian kernel svm liner uses linear kernel svm medium fewer distinctions are used svm quad uses quadretic kernel engineering, technology & applied science research vol. 8, no. 1, 2018, 2459-2463 2462 www.etasr.com hassan et al.: sla management for virtual machine live migration using machine learning with… (a) (b) (c) fig. 2. 146cs4 server resource utilization: (a) cpu (b) memory (c) intervm table ii. tpr results algorithm tpr 146cs4 (90-8070)_105 cs-planetlab3 (90-8070)_54 cs-planetlab4 (90-80-70)_117 complex tree 89.7 96.4 95.9 medium tree 89.7 96.4 97.5 simple tree 89.7 96.4 96.7 knn coars 88.9 0 57.4 knn cosine 89.7 0 96 knn cubic 89.7 94.6 95.1 knn fine 82.9 96.4 98.4 knn medium 89.7 94.6 95.1 svm coars gausian 97.5 100 98.4 svm cubic 98.4 98.2 95.1 svm fine gausian 97.5 94.6 98.4 svm liner 89.7 98.2 96.7 svm medium 98.4 98.4 98.4 svm quad 89.7 96.4 98.4 the friedman statistic is distributed according to xf 2 with k−1 degrees of freedom. level of significance at p < 0.05 is chosen. if the null-hypothesis is rejected, then we can proceed with a post-hoc test. the nemenyi test is used to compare classifiers to each other. if the corresponding average ranks differ by at least the critical difference, the performance of two classifiers will be considered significantly different. in this work average tpr, friedman rank summations and average ranking are used as performance metrics. table iii. tpr results algorithm tpr fobos(8070-60)_25 jupiter_cs (80-7060)_17 node1 (80-7060)_57 complex tree 96 88.2 100 medium tree 96 88.2 100 simple tree 96 88.2 100 knn coars 0 0 0 knn cosine 52 10 59 knn cubic 92 20 86 knn fine 92 47.1 93 knn medium 92 10 86 svm coars gausian 100 10 80.7 svm cubic 96.5 64 93 svm fine gausian 44 5 75.4 svm liner 96 11.8 68.4 svm medium 88 41.2 41.2 svm quad 88 52.9 96.5 table iv. final ranking algorithm final ranking average tpr friedman rank summations average ranking medium tree 94.63333 13 2.166667 simple tree 94 14 2. 333333 complex tree 94.3 16 2.666667 svm cubic 90 16 2.666667 svm coars 79.4 17 2.833333 svm quad 86.89 17 2.833333 knn fine 84.96 20 3.333333 svm medium 77.26 23 3.833333 svm liner 76.8 24 4 svm fine 68.3 27 4.5 knn cubic 76.2 28 4.666667 knn medium 76.2 28 4.666667 knn cosine 49.6 33 5.5 knn coars 24.2 41 6.833333 from table iv we see that the tree based algorithms show better performance compared to other algorithms, whereas knn shows the worst performance. medium tree has average tpr of 94.63% with friedman rank summations of 13 and overall friedman ranking of 2.166667. now to measure statistical significance using friedman test xf 2 was calculated as 154.66 and found to be larger than the critical value of p=23.68 which indicates the statistical significance of the obtained tpr values. accordingly null hypothesis that tested classifiers have the same performance is rejected. thus, nemenyi test is used to pinpoint where the significance lies. qa is found to be 3.353 and based on two pair testing ,we failed to reject the null hypothesis between medium, simple and complex tree in addition to svm cubic, svm coars, svm quad and knn fine. however, medium tree shows better performance in terms of average tpr, friedman rank engineering, technology & applied science research vol. 8, no. 1, 2018, 2459-2463 2463 www.etasr.com hassan et al.: sla management for virtual machine live migration using machine learning with… summations and average friedman ranking. in addition to that, medium tree algorithm results were consistent among all tested data. v. conclusion in this work, machine learning based approach with modified kernel along with friedman rank summation and average ranking have been used for dynamic live migration based on adaptive prediction of utilization thresholds. from the analysis of the proposed approach different classification techniques have been used to predict vm migration. it is shown that the regression trees have more accuracy compared to svm and knn. this approach can be used to manage sla in virtualized cloud based data centers for critical applications like telecommunication ones, especially applications with strict sla. further analysis can be made on other dynamic consolidation problems such as vm placement following the approach presented in this paper. references [1] p. barham, b. dragovic, k. fraser, s. hand, t. harris, a. ho, r. neugebauer, i. pratt, a. warfield, “xen and the art of virtualization”, 19th acm symposium on operating systems principles, pp 164-177, 2003 [2] s. akoush, r. sohan, a. rice, a. w. moore, a. hopper, “predicting the performance of virtual machine migration”, ieee international symposium on modeling, analysis & simulation of computer and telecommunication systems, 2010 [3] c. clark, k. fraser, s. hand, j. g. hansen, e. jul, c. limpach, i. pratt, a. warfield, “live migration of virtual machines”, 2nd symposium on networked systems design and implementation, pp 273-286, 2005 [4] a. b. nagarajan , f. mueller, c. engelmann, l. scott, “proactive fault tolerance for hpc with xen virtualization”, 21st annual international conference on supercomputing, pp 23–32, 2007 [5] r. nathuji, k. schwan, “virtual power: coordinated power management in virtualized enterprise systems”, acm sigops operating systems review, vol. 41, no. 6, pp. 265-278, 2007 [6] y. song, h. wang, y. li, b. feng, y. sun, “multi-tiered on-demand resource scheduling for vm-based data center”, 9th ieee/acm international symposium on cluster computing and the grid, pp. 148155, 2009 [7] vmware inc, vmware distributed power management concepts and use, 2010 [8] a. beloglazov, r. buyya.,adaptive threshold-based approach for energy-efficient consolidation of virtual machines in cloud data centers, dept. of computer science and software engineering, university of melbourne, 2010 [9] t. c. ferreto, m. a. s. netto, r. n. calheiros, c. a. f. de rose, “server consolidation with migration control for virtualized data centers”, future generation compute systems, vol. 27, no. 8, pp 1027–1034, 2011 [10] t. wood, g.tarasuk-levin, p. shenoy, p. desnoyers, e. cecchet, m. d. corner, “memory buddies: exploiting page sharing for smart co-location in virtualized data centers”, acm sigplan/sigops international conference on virtual execution environments, pp. 31-40,2009 [11] t. hirofuchi, h. nakada, s. itoh, s. sekiguchi, “reactive consolidation of virtual machines enabled by post copy live migration”, 5th international workshop on virtualization technologies in distributed computing, pp 11-18, 2011 [12] d. kakadia, n. kopri, v. varma, “network-aware virtual machine consolidation for large data centers”, 3rd international workshop on network-aware data management, 2013 [13] h. mi, h. wang, g. yin, y. zhou, d. shi, l. yuan, “online selfreconfiguration with performance guarantee for energy-efficient largescale cloud computing data centers”, ieee international conference on service computing, pp. 514-521, 2010 [14] m. sindelar, r. k. sitaraman, p. shenoy, “sharing-aware algorithms for virtual machine co location”, amc 23rd symposium on parallelism in algorithms architectures, pp. 367-378, 2011 [15] a. beloglazov, “energy-efficient management of virtual machines in data centers for cloud computing”, phd thesis, department of computer science, melbourne university, 2013 [16] t. chen, x. gao, g. chen, “optimized virtual machine placement with traffic-aware balancing in data center networks”, scientific programming, vol. 2016, article id 3101658, 2016 [17] z. zhou, z. hu, k. li, “virtual machine placement algorithm for both energy-awareness and sla violation reduction in cloud data centers”, scientific programming, vol. 2016, article id 5612039, 2016 [18] m. khalaf alla h. m., a. babiker, m. b. m. amien, m. hamad, “review in cloud based next generation telecommunication network”, jurnal teknology, vol. 78, no. 6, pp. 51–57, 2016 [19] r. timofeev, classification and regression trees (cart). theory and applications, msc thesis, humboldt university, berlin, 2004 [20] h. yu, s. kim, “svm tutorial: classification, regression, and ranking”, in: handbook of natural computing, pp. 479-506, springer, 2012 [21] k. q. weinberger, l. k. saul, “distance metric learning for large margin nearest neighbor classification”, journal of machine learning research, vol. 10, pp. 207-244, 2009 [22] n. japkowicz, m. shah, evaluating learning algorithms: a classification perspective, cambridge press, 2011 microsoft word etasr_v12_n3_pp8574-8577 engineering, technology & applied science research vol. 12, no. 3, 2022, 8574-8577 8574 www.etasr.com da silva júnior et al.: numerical simulation of a one-dimentional non-linear wave equation numerical simulation of a one-dimentional nonlinear wave equation adalberto gomes da silva júnior department of basic science and environmental engineering school at lorena, university of são paulo são paulo, brasil adalbertogomes.eq@usp.br jairo aparecido martins research & development desch north america cambridge, ontario, canada jairo.martins@desch.com estaner claro romão department of basic science and environmental engineering school at lorena, university of são paulo são paulo, brasil estaner23@usp.br received: 15 march 2022 | revised: 24 march 2022 | accepted: 27 march 2022 abstract-in this paper, numerical simulations via regressive and central finite differences of different orders were produced using fortran code and a one-dimensional non-linear wave equation was solved. the errors obtained during simulations, when using different refinements, were listed and compared in order to determine the validity of the simulation, which demonstrates that the proposed formulation presents satisfactory results. keywords-finite difference method; wave equation; numerical simulation i. introduction in order to better understand phenomena in physics, engineering, and even mathematics, it is often necessary to apply mathematical modeling, which most of the times requires solving partial differential equations (pdes). due to the high complexity of these models, an analytical solution is infeasible, requiring the use of numerical methods. among many methods available, the most friendly, accessible, and accurate, and therefore used for multiple purposes in engineering, is the method of finite differences [1-7]. it relies in a substitution of partial derivatives at a point by its incremental reasons. moreover, it is important to highlight that numerical simulations involving equations which guide transference of energy usually have their values matching with the analytical solution. authors in [8] for instance, analyzed the temperatures inside a concrete dam by using an explicit method, where a transition between stationary to transient regime could be detected. another example is described in [9], when using finite differences at sixth order, applied in an equation of convection-diffusion-reaction an implicit method, obtained low absolute errors, most of them diffusive when using more refined meshes. by using the same approximation order, authors in [10] obtained deviations of 10 -14 in problems which considered reaction-diffusion equations in singly disturbed systems. many other papers have demonstrated success when using the difference finite method for the solution of problems of transport phenomena such as [11-14], however, we did not find in the open access bibliography other works that compare explicit methods in the solution of the equation proposed in this work. since many papers have described high precision on outputs when covering transport phenomena via finite difference methods, this paper applied this method to simulate a one-dimensional non-linear wave equation, while also checking whether this method is valid for this application. in addition, the maximum error obtained with a discrete mesh was evaluated and demonstrated the accuracy of the proposed method. ii. method of finite differences one of the most common methods to solve pdes is the finite difference method, which consists of an approximation of differences by incremental reasons that utilizes expansions from taylor’s series. furthermore, a finite differences method can be classified as regressive, progressive, or central. assume that y is a function, i a point which belongs to a mesh and �� an incremenal reason between two points: ���� and ��, both included in the mesh. a regressive finite difference makes use of values of a function in i and of i-1 to calculate a variation rate at the point. a progressive finite difference uses i and i+1 and finally it is also possible to know an approximate value of a differential by applying central differences, which applies values such as: i+1 and i-1 [15]. the three described equations are: • regressive finite differences: ���� � = ����� � ∆ + ����� (1) corresponding author: estaner claro romão engineering, technology & applied science research vol. 12, no. 3, 2022, 8574-8577 8575 www.etasr.com da silva júnior et al.: numerical simulation of a one-dimentional non-linear wave equation • progressive finite differences: ���� � = ������� ∆ + ����� (2) • central finite differences: ���� � = ������� � �∆ + ������ (3) iii. model equation and formulations an equation of one-dimensional non-linear wave, obeying the continuity and euler’s principles, was used in the simulations. it is important to highlight that functions such as ���,�� and ���,�� were applied in order to allow an easier way to build a precise solution when processing computational tests. the equations of the one-dimensional non-linear wave are: �� �� + � �� � + � �� � = ���,�� (4) �� �� + � �� � + ! � �� � = ���,�� (5) note that (4) and (5) are only a reduction of the motion and continuity equation (navier stokes equations). for the formulations below, the explicit method is employed, which allows calculating variables � and � at point xi in a mesh, by using data from previous steps. this procedure allowed considering independent equations and guaranteed a quicker computerized solution when comparing with the implicit method, which implies a linear system of algebraic equations [16]. a. formulation i : regressive finite difference in (4): ��"���" � ∆� + ��#�� � ��" ���� �" � ∆ + ��#�� � ��" ���� �" � ∆ = ����,�� (6) ��# = $����,�� − ��#�� ��� " ���� �" � ∆ − �� #�� ���" ���� �" �∆ + ��" � ∆� &∆� (7) and in (5) : ��"���" � ∆� + �� #�� ���" ���� �" �∆ + ! ��" � ���" ���� �" �∆ = ����,�� (8) ��# = '����,�� + �� " � ∆� − ��#�� � ��" ���� �" � ∆ + ! ∆ ( �� �" � ��" � − 1*+∆� (9) b. formulation ii: central finite difference in equation (4): ��"���" � ∆� + ��#�� � ����" ���� �" � �∆ + ��#�� � ����" ���� �" � �∆ = ����,�� (10) ��# = $����,�� − ��#�� ����� " ���� �" � �∆ − �� #�� �����" ���� �" ��∆ + ��" � ∆� & ∆� (11) and in (5): ��"���" � ∆� + ��#�� � ����" ���� �" � �∆ + ! ��" � �����" ���� �" ��∆ = ����,�� (12) ��# = '����,�� + �� " � ∆� − �� #�� �����" ���� �" ��∆ − ! ��" � �����" ���� �" ��∆ +∆� (13) iv. results and discussion the formulations presented above were processed with fortran programming language. by computational code was possible to obtain results for values of u (speed) and � (specific mass) for both the conducted tests, i.e. with regressive finite differences and central finite differences. furthermore, in order to make the test simpler, sound speed was assumed as , = 1 and the size of spatial and time domains as 0.2. meanwhile, for the numerical tests the following equations were adopted for u and ρ: ���,�� = -./�� + �� (14) ���,�� = 01-�� + �� (15) as a result, (4) and (5) were written as: ���,�� = 01-�2� + 2�� − -./�� + �� (16) ���,�� = 01-�� + �� + -./�� + ��01-�� + �� + ! 345� 6�� 7−-./�� + ��8 (17) notice that, the previous equation is valid if: � + � ≠ :�. for both numerical simulations, the values of maxu and max � were calculated, which represent the highest error incurred when comparing the calculated value, by finite differences, and the real value (the exact solution) from equations which contain all the points in the discrete mesh. some of data for maximum errors were very high and they were considered as divergent. further, for finite differences there were only a few values of maxu and max� that were not divergent (see tables i and ii). in addition, there was an homogeneous trend of divergences among the meshes worked along the tests. a notable feature verified for central finite differences was the lower values for maxu and max� for smaller increments of time, while for higher spatial increments values of maxu and max� showed divergent values, see tables iii and iv. table i. maximum error for function ���, �� using regressive finite differences ;< ;= 0.01 0.02 0.01 0.001 0.0001 0.00001 0.000001 0.2 1.56e+00 5.76e-01 div 4.99e+00 1.03e+01 6.68e+00 div 0.1 div 9.51e-01 div div 9.88e+00 1.07e+01 div 0.05 div div div div div div div 0.02 div div div div div div div 0.01 div div div div div div div 0.005 div div div div div div div engineering, technology & applied science research vol. 12, no. 3, 2022, 8574-8577 8576 www.etasr.com da silva júnior et al.: numerical simulation of a one-dimentional non-linear wave equation table ii. maximum error for function ρ�x,t� using regressive finite differences ;< ;= 0.01 0.02 0.01 0.001 0.0001 0.00001 0.000001 0.2 9.85e-02 5.94e-02 div 2.01e-01 2.50e-01 2.23e-01 div 0.1 div 1.17e-01 div div 3.88e-01 3.92e-01 div 0.05 div div div div div div div 0.02 div div div div div div div 0.01 div div div div div div div 0.005 div div div div div div div table iii. maximum error for function ���,�� using central finite differences ;< ;= 0.01 0.02 0.01 0.001 0.0001 0,00001 0,000001 0.2 2.24e-01 2.02e-02 9.25e-03 8.74e-04 1.06e-04 3.82e-05 4.24e-05 0.1 4.22e+01 1.31e-01 5.99e-02 5.63e-03 5.62e-04 5.86e-05 8.74e-06 0.05 div 7.02e-01 1.63e-01 1.46e-02 1.43e-03 1.41e-04 1.20e-05 0.02 div div div 4.77e-02 4.50e-03 4.48e-04 4.44e-05 0.01 div div div 1.55e-01 8.88e-03 8.72e-04 8.70e-05 0.005 div div div div 1.86e-02 1.77e-03 1.77e-04 table iv. maximum error for function ���,�� using central finite differences ;< ;= 0.01 0.02 0.01 0.001 0.0001 0,00001 0,000001 0.2 2.68e-01 5.02e-02 2.44e-02 2.40e-03 2.63e-04 5.00e-05 3.87e-05 0.1 9.60e+01 4.58e-02 1.68e-02 1.34e-03 1.36e-04 2.50e-05 1.39e-05 0.05 div 4.36e-01 8.20e-02 3.48e-03 3.19e-04 3.16e-05 5.79e-06 0.02 div div div 1.01e-02 7.30e-04 7.07e-05 7.04e-06 0,01 div div div 1.31e-01 1.62e-03 1.49e-04 1.48e-05 0.005 div div div div 4.18e-03 3.18e-04 3.10e-05 v. conclusions the results obtained with both numerical simulations allow inferring about the validity of finite different methods to analyze one-dimensional non-linear wave equations. for regressive differences, the values of maxu and max� for many simulations showed divergence, most likely due to the truncation error, very common for cases where taylor series are utilized. for central finite differences, very small values of maxu and max � , close to 10-3, appeared during the simulations with spatial meshes as well as during the time dependent simulations with refined meshes. these values could be driven by choosing ∆� within the range of stability requirements. in conclusion, the finite differences methods are valid to solve the one-dimensional non-linear wave equation but they are spatial restricted and time dependent, with few increments and finite differences 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[16] a. d. o. fortuna, técnicas computacionais para dinâmica dos fluidos. conceitos básicos e aplicações, 2nd ed. sao paolo, brazil: edusp, 2020. engineering, technology & applied science research vol. 8, no. 2, 2018, 2755-2757 2755 www.etasr.com tsolov and marinova: optimal power factor for the reactive load of small hydro power plants optimal power factor for the reactive load of small hydro power plants angel tsolov faculty of electrical engineering technical university of sofia sofia, bulgaria abc@tu-sofia.bg boryana marinova department of electrical power engineering technical university of sofia sofia, bulgaria b_marinova@tu-sofia.bg abstract—this article explores the operation algorithm of an excitation regulator of synchronous generators of small hydro power plants (hpps). the aim is to provide optimum economic parameters, consistent with the dynamically changing requirements of electric supply companies. an integral method for maintaining the power factor has been introduced. the proposed method ensures stable operation of generators in different working modes. it is implemented and the economic effect proved significant. keywords-small hpp; power factor; reactive load; excitations; avr i. introduction the difference between small and large hydro power plants (hpps) is the electrical network length. small hpps are connected to open radial peripheral junctions in the distribution network, where the impedance can be high with a large resistor and little / ratio. the production of small hpps is fragmented, seldom centralized and power generation is dependent on water flow. the hourly, daily and monthly power changes will lead to unobstructed reactive power in both network directions. therefore, fluctuations in the voltage of the busbars are likely to arise in this network part [1-3]. if these voltage fluctuations are not limited, the power quality requirements delivered to the consumer might be violated. with regard to the work of small-scale generators, connected to a medium voltage grid, a requirement is set. the mode of operation has to restrict the generator’s voltage increase above a certain point while generating maximum possible real power [7]. then the excitation system should ensure a mode of operation maintaining the maximum allowed bus voltage of 20kv with restriction of maximum generator voltage, maximum and minimum field current [4]. in practice, the structure of excitation regulators (avr controller) is used (figure 1). regulation of excitation is made either by voltage or by power factor (lagging or leading). 1) by voltage in this mode, the stator voltage of the generator is regulated with a static characteristic. the stable operation depends on the coefficient of the stasis and its sign. 2) by reactive power when this mode is in use, the generator works parallel with the network at constant reactive power. this is recommended when the generator works for a long time with load close to the nominal one. 3) by power factor () there is a restriction regarding the mode of operation for small generators connected to a medium voltage grid. it should not allow a power factor under certain value – e.g. 0.9. in this case, an excitation system with constant cos () mode of operation is advisable. the set value should be compliant with the given minimal value. 4) by field current this mode could be performed if the regulation is on the field current. the assigned current value changes according to the power line voltage connecting the plant to the power substation. the set value should consequently be adjusted to the maximum voltage value of the 20kv busbar. fig. 1. excitation regulator (avr controller) scheme assuming that this structure provides reliable operation with a properly-tuned regulative parameter, the question of optimal management, consistent with the economic requirements, remains. the importance of power factor [5] is taken into account. depending on the registered deviation between the prescribed power factor and the power factor achieved, utility companies apply different criteria and requirements for the mode of operation. in case of deviations of pid1 mode ifsens cos(φ) estimation iflimits cos(φref) ifref qref uref cos(φ) q protections control pid2 pid3 pid4 u if f t cos(φ) criteria co tim ma the wit ma exc exc ma ma is vo vo is an ana pre exc exa ma the mo syn of the re con dis im ho rem fac rec engineerin www.etasr s () from the me, the static aintained, keep e manufacture th the regimes restrictions aximal and m citation), maxi citation syste aximum real p aintenance of parallel, the ltage on the 2 ltage is within in the range i operation mo alogous to the eset paramete citation curren the study of amined w atlab/simu e model is give odes research nchronous gen operation are e research are esults analysis nstant level o stribution of mplementation owever, long-t mains a proble iii. integr in a 24-hour ctor (cos()) cord of voltage ng, technology r.com e concurred, f c 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distribution, fr i. tamrakar, l. frequency cont induction gene generation, tra 2007 d. dobrilov, co international e electrical mach synchronous m mathworks, he ] p. kundur, pow ] r. grondin, i “modeling and band pss”, iee pp. 1809, 2003 ] h. wu, g. t. system stabiliz engineering so 1709, july 13-1 018, 2755-2757 or the reactive iv. co tor correction m moment rea operation of re steadily as t ter field curre occur. the po ic characteris ll fluctuations implementatio the power fact ble operation w ic parameters. possibility o anging requi method is a all hpp “vlah ffect is highly e introduction refer tsolov, a. krum enerators an electr – mathematical fia, vol. 59, no. nakabayashi, y. aya, m. yamane, smes for lo n applied superco a. tsolov, means of the technical u means of reactive p al university of so o. samuelsson, “v uction generators rankfurt, germany . b. shilpakar, b. trol of parallel erator with stat ansmission & d ontrol for small h electrotechnical hines part 3: sp machines, 1996 elp for matlab sim wer systems stabi i. kamwa, g. closed-loop valid ee power engine heydt, “design zer using the g ociety general m 7, 2003 7 load of small onclusions field current m active power a parallel bus the regulation ent . restrict ower distribut tics are eithe with a decrem on of an int tor gives very within a certai an additiona of regulation irements of applied in the i” and small positive (no s of this princip rences mov, “distribution ric power plant un model”, proceed 1, pp. 151, 2009 nijo, t. tamada, , y. ishii, t. nitta oad fluctuation onductivity,vol. 1 s for reactive pow university of sof power compensat ofia, vol. 64, no. voltage and frequ s”, cired sem y, june 23-24, 200 . g. fernandes, r operated synch tcom in micro istribution,vol. 1 hpp in limited mo commission, i pecific requirem mpower system, 2 ility and control, trudel, l. geri dation of a new p eering society g n of delayed-inp gain scheduling m meeting, toronto 2757 hydro power p mode, it is en is 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power power 3, pp. microsoft word etasr_v11_n6_pp7841-7845 engineering, technology & applied science research vol. 11, no. 6, 2021, 7841-7845 7841 www.etasr.com tomescu & bucur: numerical investigation of oil gas separation with the use of vof cfd numerical investigation of oil gas separation with the use of vof cfd sorin tomescu screw compressors department nrdi for gas turbines comoti bucharest, romania sorin.tomescu@comoti.ro ioana octavia bucur computational fluid dynamics department nrdi for gas turbines comoti bucharest, romania ioana.bucur@comoti.ro abstract-in this research paper, a numerical study regarding gas-oil separation is presented. employing the geometry of a classic separator used by the nrdi for gas turbines comoti and a computer-aided design (cad) software, the computational domain was defined. to perform the computational fluid dynamics (cfd) investigation, the mesh was created with the ansys meshing tool, and the ansys cfx was employed as a solver. the computational domain was split into 5 subdomains, 3 were fluid and 2 were defined as porous media. the volume porosity, loss model, and permeability were set up. in terms of turbulence flow, the standard k–ε model was adopted. the results of the numerical calculations in terms of oil volume fraction and streamline profiles were used to analyze the separator configuration. the results show that the numerical investigation with the vof (volume of fluid method) cfd model is capable of analyzing the performance of a two-phase separator equipped with two demisters-porous media. keywords-two-phase separator; computational fluid dynamics; volume of fluid; porous media; demister i. introduction technological evolution is currently mainly based on fossil fuels and their impact will continue to persist, although the trend is to redirect to the use of renewable energy with low environment impact and reduced pollution emissions [1]. in the petroleum extraction industry, air at high pressure is often employed in the oil extraction and recovery processes, which are complex procedures that require advanced installations [2]. systems that can provide the needed amount of pressurized air for the extraction process, can be screw compressors with oil injection, which can raise the air pressure up to 40 bars [3]. in general, an oil-injected screw compressor developed for the petroleum and petrochemical industries is provided with a complex lubrication oil system that incorporates separator vessels. the separator vessels mainly consist of an inlet, a demister pad, and an outlet and they should ensure an efficient oil-gas separation. the process along with various configurations for the separator, are discussed broadly in [4]. figure 1 illustrates a complex screw compressor with oil injection equipment, developed by the nrdi for gas turbines comoti. the use of such a system implies oil-air separation, which can be done using a separator vessel [5] that is provided with filters capable to retain the oil particle and separate them from the pressurized air [6]. a schematic presentation of a classic two-phase separator can be observed in figure 2. fig. 1. screw compressor installation. fig. 2. two-phase separator principle. the efficiency evaluation of a two-phase separator can be done by employing the volume of fluid (vof) method. this method is broadly applied in computational fluid dynamics (cfd) for various flow applications such as the dam-break problem or the surge propagation in a dry channel, as well as the one identified above, i.e. the efficiency evaluation of a twophase separator. the method is best suited for the mentioned applications as it manages to track vapor-liquid interference while giving various alternatives for the reconstruction of the interface with precision whilst preserving the fractional volume corresponding author: ioana octavia bucur only vapor gets through the demister engineering, technology & applied science research vol. 11, no. 6, 2021, 7841-7845 7842 www.etasr.com tomescu & bucur: numerical investigation of oil gas separation with the use of vof cfd of the fluid [7]. cfd tools have been proven to be reliable flow investigation instruments and have an important role in the design and optimization processes of complex systems, having large applications in the turbomachinery industry [8]. the use of cfd methods for the investigation of oil particles behavior in a separator vessel is studied in [9, 10]. in [9], the conducted research confirms that cfd tools and methods are accurate by comparing the numerical results with the experimental data. on the other hand, the authors in [10] largely present various cfd studies of separators using the vof method, concluding that the numerical approach has numerous benefits, being cost effective and flexible with regard to design alterations. furthermore, using the numerical results, the optimization of oil-air separation process leads to enhanced separator vessel designs capable to capture up to 10 micrometer oil particles [11]. in [12], the authors use the rosin rammler distribution [13] to conduct a numerical investigation employing the ansys fluent, for the oil droplet distribution at the inlet of a separator vessel using a multiphase model. in [14], the authors apply cfd tools for the investigation of the flow through a separator vessel with different inlet designs, concluding that cfd methods represent a valuable tool for the performance evaluation and optimization processes of separator vessels. besides numerical alternatives, the flow in such systems can also be investigated using advanced measurement techniques as the capacitance wire mesh sensor (wms) and the electrical capacitance tomography (ect) [15]. this paper aims to numerically investigate the oil/air separation process in a separator vessel by using ansys cfx, employing the vof method. ii. methodology this section addresses the computational domain creation, mesh generation, and case set up for the numerical investigation of the oil/air separation process. a. computational domain creation the computational domain was generated using the 3d cad model of the separator vessel by utilizing the boolean function. figure 3 depicts the computational domain that is divided into 5 subdomains: 3 defined as fluid and 2 with porous media proprieties. b. mesh generation and boundary conditions the grid was generated based on a hybrid scheme by combining tetrahedral and hexahedral elements. due to the complex geometry of the inlet and outlet domains, the mesh for these zones was automatically generated with ansys meshing. the maximum element size was set at 50mm. for the demister domains, with porous media characteristics, the blocking method was employed in icem in order to generate the grid. mesh statistics are detailed in the figure 4 and the resulting mesh is illustrated in figure 5. the quality of the grid is visualized in figure 6, for both types of elements tetrahedral and hexahedral. it can be observed that only a negligible fraction of cells had poor quality. (a) (b) (c) fig. 3. computational domain. (a) 3d cad model for the separator vessel, (b) computational domain prepped for cfd, (c) computational domain cross plane: 1, 3, 5 fluid subdomains; 2, 4 porous media properties subdomains. fig. 4. mesh statistics. (a) (b) (c) fig. 5. mesh for the numerical investigation. (a) separator mesh, (b) cross plane view, (c) close-up on demister mesh. the boundary conditions for the case set-up are described in table i. a static pressure inlet boundary type and the volume fraction for each phase were defined for the fluid inlet. regarding the porous media zones, the volume porosity was set at 0.7 with isotropic loss model and 3.8e-05m 2 . figure 7 illustrates the boundary conditions that were previously described. engineering, technology & applied science research vol. 11, no. 6, 2021, 7841-7845 7843 www.etasr.com tomescu & bucur: numerical investigation of oil gas separation with the use of vof cfd fig. 6. element quality. table i. boundary conditions location bc description inlet boundary type: static pressure relative pressure [bar]: 22.5 static temperature [ºc]: 80 outlet boundary type: bulk mass flow rate mass flow rate [kg/s]: 0.2 oil outlet boundary type: bulk mass flow rate mass flow rate [kg/s]: 2.25 walls boundary type: wall no-slip condition (a) (b) fig. 7. (a) computational domain, (b) boundary conditions. the flow through the gas-oil separator equipped with two demisters was numerically modeled by solving the unsteady reynolds-averaged navier stokes (urans) equations with the standard k-ɛ turbulence model. the transport equations for this turbulence model are presented below. the transport equation for the turbulent kinetic energy (k) is: 1 1 k k k k u v w t x y z k k kt t t x x y y z z k k k __ u i tij xi, j j ∂ ∂ ∂ ∂ + + + = ∂ ∂ ∂ ∂            µ µ µ∂ ∂ ∂ ∂ ∂ ∂           = µ + + µ + + µ + +            ρ ∂ σ ∂ ∂ σ ∂ ∂ σ ∂             ∂ + τ − ε∑ ρ ∂ (1) where ρ represents the density, µ the dynamic viscosity, tµ the turbulent viscosity, and kσ the turbulent prandtl number for kinetic energy. the transport equation for the turbulent kinetic energy dissipation (ɛ) is: 2 1 2 1 t t t __ i tij i , j j u v w t x y z x x y y z z u c c k x k ε ε ε ε ε ∂ε ∂ε ∂ε ∂ε + + + = ∂ ∂ ∂ ∂            µ µ µ∂ ∂ε ∂ ∂ε ∂ ∂ε = µ+ + µ + + µ + +                ρ ∂ σ ∂ ∂ σ ∂ ∂ σ ∂             ∂ε ε + τ − ρ ∂ ∑ (2) where εσ is the turbulent prandtl number for dissipation and 1εc and 2εc are constants. c. results the 3d cfd investigation was a transient one with a total flow time duration of 50s and a time step size that was set at 0.01s. for this study, a multiphase homogeneous model with no heat transfer from the working fluid to the vessel walls was adopted. the evolution of the volumetric mass fraction of oil was investigated, as well as the development of the streamlines. figure 8 describes the oil volume fraction for different moments of time in the simulation. the regions where only oil is present are depicted with red, whereas the dark blue zones represent the areas without oil. it can be observed that the separation process is efficient. after the initialization stage (figure 8(a), time = 0s), where the oil level is defined according to the real operational conditions, the mixture of oil and gas is noticeable in the feeding pipe, but oil particles detectable above the region 2 (demister) are within reasonable boundaries at any moment of time. after region 4 (second demister), only a ratio of 0.1% of the inlet oil eludes the separation process and slips through the gas outlet. in [16], the authors investigated numerically the performances of a two-phase separator and improved its internal configuration, reaching an efficiency of 99.49%. the high efficiency of 99.9% of the system evaluated in this paper can save up to 33.2kg/h of oil in comparison with the enhanced geometry from the mentioned paper. thus, the oil gas separation procedure is fulfilled properly and the methodology adopted for numerical evaluation is accurate. engineering, technology & applied science research vol. 11, no. 6, 2021, 7841-7845 7844 www.etasr.com tomescu & bucur: numerical investigation of oil gas separation with the use of vof cfd (a) (b) (c) (d) fig. 8. oil volume fraction for different moments in the simulation: (a) 0s, (b) 10s, (c) 20s, and (d) 30s. the 2d streamlines are illustrated in figure 9. cross planes multiple recirculation zones can be identified, but this phenomenon does not have a negative influence on the overall performance of the separator as the vortexes are developed for low values of velocity. according to the presented streamlines, the velocity of the mixture slightly accelerates as it exits the feeding pipe and enters the separator. an increase in velocity is also noticeable at the liquid outlet, which is explained by the abrupt area reduction. regarding the velocity of the gas, it is conspicuous from figure 9 that its velocity increases slightly in time after the first demister (figure 8(a), region 2) and more obvious after the second one (figure 8(a), region 4) at the gas outlet duct (figure 8(a), region 5). (a) (b) (c) (d) fig. 9. streamlines for different moments in the simulation. (a) 0s, (b) 10s, (c) 20s, and (d) 30s. the flow behavior of the investigated phenomenon and the obtained results are in agreement with the results from similar works in the field [17]. in [18], a similar cfd investigation is conducted but in terms of particle size it can only capture oil particles that are bigger than 100µm, whereas the method adopted for the current cfd analysis is more precise, as it allows the visualization of oil particles bigger than 10µm. iii. conclusions in this paper, the efficiency of a gas-oil separator was numerically investigated with the use of the ansys cfx software. a two-phase homogeneous model was defined for a computational domain with 5 subdomains, 3 defined as fluid and 2 as porous media, capable to capture the oil particles that are bigger than 10µm. for the study of the oil flow in the separator vessel, a volume fraction evolution is presented engineering, technology & applied science research vol. 11, no. 6, 2021, 7841-7845 7845 www.etasr.com tomescu & bucur: numerical investigation of oil gas separation with the use of vof cfd throughout the simulation. after a flow time of 50s only 0.1% of the inlet oil is escaping through the gas outlet. the present research contribution for the addressed field consists in a welldefined methodology for the numerical investigation of oil gas separation, with the addition of successfully employing the vof method for this application. the paper’s contents broadly describe the stages leading to the numerical evaluation, concentrating on mesh generation and characteristics, as well as on case set-up and turbulence model selection. future work will consist of a grid influence study and the results will be compared with the experimental data from testing campaigns. the testing facility is depicted in figure 10. fig. 10. testing facility. acknowledgment this research was supported by the "nucleu" program turbo 2020+, grant number 2n/2019, supported by the romanian ministry of research, innovation and digitalization. references [1] c. zou, q. zhao, g. zhang, and b. xiong, "energy revolution: from a fossil energy era to a new energy era," natural gas industry b, vol. 3, no. 1, pp. 1–11, jan. 2016, https://doi.org/10.1016/j.ngib.2016.02.001. 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[18] v. vijayan, m. vivekanandan, r. venkatesh, k. rajaguru, and a. godwin antony, "cfd modeling and analysis of a two-phase vapor separator," journal of thermal analysis and calorimetry, vol. 145, no. 5, pp. 2719–2726, sep. 2021, https://doi.org/10.1007/s10973-02009825-2. microsoft word 03-lajimi-ed .doc etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 121-125 121 www.etasr.com lajimi et al: modeling and control of a dfig-based wind turbine during… modeling and control of a dfig-based wind turbine during a grid voltage drop a. babaie lajimi department of electrical and computer engineering babol university of technology babol, iran reza.lajimi@gmail.com s. asghar gholamian department of electrical and computer engineering babol university of technology babol, iran gholamian@nit.ac.ir m. shahabi department of electrical and computer engineering babol university of technology babol, iran shahabi.m@nit.ac.ir abstract— doubly-fed induction generators (dfig) are widely used in wind energy generation systems. during a grid voltage drop, performance is degraded with rotor over current deteriorating the fault-ride through (frt) capability of the dfig wind-energy generation system. in this paper, a complete mathematical dfig model is proposed. the rotor is considered fed by a voltage source converter whereas the stator is connected to the grid directly. output power and electromagnetic torque are controlled using field-oriented control (foc). simulation results show the efficiency of the controller in exploiting the maximum power of wind. keywordsdoubly-fed induction generator (dfig); fieldoriented control (foc); dfig protection; i. introduction wind energy systems employ various installations to exploit wind energy such as synchronous or squirrel-cage and doubly fed asynchronous machines. the changing of wind speed has an effect on the considered power transfer [1]. in general, the efficiency of variable-speed systems is higher compared to the one of fix-speed systems. in this paper, a doubly-fed induction generator (dfig) is used to regulate the turbine speed. when using conventional squirrel cage asynchronous machines, very high magnetizing currents are drawn from the power grid when recovering from a nearby fault in the power system. if the power system cannot provide a sufficient magnetizing current in the post-fault transient state, the squirrel cage asynchronous machine keeps on accelerating. the asynchronous machine draws as much magnetizing current as possible from the grid, and a severe voltage drop takes place. the voltage drop will stop only when the protection system disconnects the wind turbine from the grid [12]. an alternative is to use an asynchronous generator with its rotor connected to a vsc via slip rings, a so-called doubly fed induction generator. in this concept, the vsc is connected to a control system that determines the voltage that the vsc impresses onto the rotor of the induction generator. this concept also provides variable-speed capability, which makes it possible to optimize power production and electromagnetic torque [2]. according to recent grid codes, wind turbines are required to be provided with low voltage ride through (lvrt) capability, which means that wind power generators have to keep being connected with the grid and provide the required power into electric power systems during external grid faults. direct prediction of the transient performance of dfig under grid fault conditions is extremely important for design and coordination of control strategies and protection devices. therefore, an integrated dfig model is required during the process of the fault analysis and lvrt operation [3]. the main goal of this paper is to propose an integrated and particular dfig model. simulation was carried out on a 2 mw wind-turbine driven dfig system. results show that the proposed dfig model fairly approaches the actual dfig. ii. general form of generation system the general scheme of electrical energy’s generation from the wind power on the basis of using doubly-fed induction generator is shown in figure 1. the stator is considered to be connected to the grid directly whereas the rotor is connected to it via back-to-back converter [4]. rotor side converter is a current regulate-voltage source inverter [5] and grid side converter is a pwm inverter. fig. 1. general form of electrical energy’s generation from the wind power on the induction generator etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 121-125 122 www.etasr.com lajimi et al: modeling and control of a dfig-based wind turbine during… iii. model and equations of wind turbine amount of power that wind turbines can extract from wind can be expressed as: m p w p c p= 2 31 2 w w p r vπρ= (1) where m p is the mechanical power that is extracted from the wind by the wind turbine, w p is the actual wind power, ρ is the air density, r is the blades radius of the wind turbine, w v is the wind speed and p c is the efficiency index [6]. the efficiency index ( p c ) represents the part of the actual wind energy that is extractable by wind turbine and is depended to the blade’s aerodynamic form, as described by: ( ), p c f λ β= t w r v ω λ = (2) where λ is the ratio of turbine blades tip speed to wind speed, β is the blade angle and t ω is the turbine blades rotational speed. in a wind turbine, p c can be represented by a nonlinear curve in terms of λ in place of different β or the following relationship [7]: ( ) ( )2 0.44 0.0167 sin 13 0.3 p c π λ β β − = − −       ( )0.00184 2λ β− − (3) fig. 2. nonlinear curve in terms of λ in place of different β in wind turbine simulation, generation torque is modeled in variable-speed of turbine as is represented below: 2 3 1 2 p wm a t t r c vp t ρπ ω ω = = (4) where a t is the torque in turbine shaft. iv. machine equations the equations of induction machines in the dq reference frame, with the speed of and neglecting zero parameter is given by [8]: ds ds s ds qs dψ r i ωψ dt v = − + qs qs s qs ds dψ r i ωψ dt v = + + ( ) dr dr r dr r qr d v r i dt ψ ω ω ψ= − − + ( ) qr qr r qr r dr d v r i dt ψ ω ω ψ= − − + (5) where ds v and qs v are the dand q-axis stator voltages, dr v and qr v are the dand q-axis rotor voltages, ds i and qs i are the d-and q-axis stator currents, and dr i and qr i are the d– and q-axis rotor currents. s r and r r are the per-phase stator and rotor resistances referred to the stator, ds ψ and qs ψ are the dand q-axis stator flux linkages ,and ψ dr and qr ψ are the d– and q-axis rotor flux linkages. ω is the speed of rotation of the dq frame, and r ω is the rotor electrical angular velocity. the rotor electrical angular velocity is related to the rotational speed of the machine through the relationship 2 ( ) m r p ω ω= , where p is the number of machine poles. the developed electromagnetic torque em t is given by: ( )3 4 em qs ds ds qs p t i iψ ψ= − (6) the equation relating the speed of rotation of the machine to the electromagnetic and applied mechanical torque is given by: m mech em d j t t dt ω = + (7) where in this relationship j is the polar moment of inertia of the machine and prime mover referred to the inductionmachine shaft. etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 121-125 123 www.etasr.com lajimi et al: modeling and control of a dfig-based wind turbine during… v. field-oriented control (foc) the induction-machine model presented in this section may also be used to simulate the operation of a doubly fed induction machine. in addition to the machine model, a model of the power converter and its associated controls must also be included. the controller of a dfig is typically configured to allow the adjustment of the rotation speed of the wtg. however, employing an appropriate choice of reference frame, the task can be simplified, upon which control of the field-oriented quantities allows for independent control of the electromagnetic torque. this technique is known as foc. the controlled back-to-back converter of a dfig is typically connected through slip rings to the rotor windings, and independent torque control is usually achieved through control of the rotor current [9]. the model of the foc can be developed for the dfig by rewriting equation (1) as: s m ds ds qs dr s r l ψ ωψ i l s s r v p l = + − −       (8) s m qs ds qs qr s r l ωψ ψ i l s s r v p l = + + −       (9) ( ) dr m m ds r qs s s v l l p p l l ψ ω ω ψ= − − ( ) r dr r qr s s l l r p i i l l α αω ω+ − + −       (10) ( ) qr m m r ds qs s s v l l p p l l ω ω ψ ψ= − + ( )r dr r qr s s l l i r p i l l α αω ω   − − + −    (11) where s l is the per-phase stator inductance, r l is the rotor inductance per-phase referred to the stator, and m l is the mutual inductance per-phase and 2 m r s l l l l α = − . the expression for electromagnetic torque (6) can also be rewritten in terms of rotor current as: ( )mem qr ds dr qs s 3p i ψ i ψ 4 l l t = − + (12) examining (12), it can be seen that in order to have control over the electromagnetic torque, it is desirable to have ds ψ 0= . the torque equation reduces to: 3 4 m em dr qs s lp t i l ψ= (13) allowing the electromagnetic torque to be controlled by adjusting dr i . the speed of the rotation of the reference frame can be calculated as: s m ds dr qs s qs l v ω i ψ l ψ r = − − (14) a mean of controlling can be established by examining (10) and (11) with the condition that ds ψ 0= . ( ) dr v m r qs r dr s s l l p r p i l l αω ω ψ= − − + −       ( )r qr s l i l αω ω+ − (15) qr v ( )m qs s r dr s l p l l i l αψ ω ω= − − r qr s l r p i l α+ −       (16) many foc dfig models, use an induction-machine model as described in this section coupled with a model of the foc, and ultimately, yielding the final dynamic equation in the equivalent foc dfig model [9]: s m qs qs qr s r l ψ i l s s r v p l = + −       (17) if the closed-loop response of the current control loops are represented by the transfer functions: ( ) * dr d dr i g s i = (18) ( ) * qr q qr i g s i = (19) where * dr i and * qr i are the reference dand q-axis rotor currents and the reference signal * dr i is derived from a required electromagnetic torque set point * em t according to (13), with * qr i derived from a stator reactive power set point. first-order current-controller response was assumed for the foc dfig model as below [10, 11]: ( ) ( ) 1 1d d g s sτ = + (20) ( ) ( ) 1 1 q q g s sτ = + (21) where d τ and q τ are the dand q-axis times constant of current-controller. etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 121-125 124 www.etasr.com lajimi et al: modeling and control of a dfig-based wind turbine during… vi. simulations results in this part, the effect of voltage drop has been evaluated using the presented model. the applied voltage drop is about 20 percent and its effect on the rotor rotational speed m ω , the electromagnetic torque em t , and electrical power is examined. it was assumed that the wtg was connected to an infinite bus bar, and thus, the system frequency at the point of connection of the wind turbine remains constant during the event. the foc and dfig models were simulated in matlab/simulink using the parameters from a 2-mw wtgbased induction machine, listed in table i. it was also assumed that the wtg is largely insensitive to small variations in rotational speed, and thus, mech t was held constant during the voltage drop. during normal operation of a wtg, the signal * em t is supplied from an external control loop, which adjusts the speed of the wtg. this way maximum energy is extracted at below rated wind speeds, and power smoothing is achieved at and above rated wind speed. as the wind speed was assumed constant during the voltage drop, the reference torque * em t remained constant during the event. the resulting closed-loop current-controller response for the voltage drop, is shown in figure 3. figure 4 shows the effect of the measured system’s voltage drop on the rotational speed of foc dfig-based wtg model. table i. 2-mw wtg induction machine parameters parameter value rs 2 1 . 7 4 8 1 0 −× ω rr 2 3 . 2 5 3 1 0 −× ω ls 22 . 5 8 9 1 0 −× h lr 22 . 6 0 4 1 0 −× h lm 22 . 4 9 2 1 0 −× h p 6 j 21 . 3 9 1 0× 2.k g m ρ 1.25 2k g m r 33 m vw 8 m s vs 690 v rated power 2mw the effect of the reduction in system voltage on the electromagnetic torque can be seen in figure 5. the inertial response that results from the decrease in rotational speed and release of kinetic energy can be seen by observing the generated electrical power, as shown in figure 6, where an increase in generated electrical power can be observed immediately following the voltage drop. fig. 3. current-controller response fig. 4. foc dfig rotational speed in response to grid voltage drop fig. 5. foc dfig electromagnetic torque in response to grid voltage drop fig. 6. foc dfig-generated electrical power in response to grid voltage drop etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 121-125 125 www.etasr.com lajimi et al: modeling and control of a dfig-based wind turbine during… vii. conclusion this paper investigated the transient performances of dfig during grid voltage dips. on the basis of an ideal model, an integrated dfig model is proposed. from the simulation results, it is shown that the dfig model approaches the behavior of the actual dfig. the presented results can be used in order to fully evaluate the fault degrees when designing protection schemes and also for future research on improved control strategies and the fault ride through capability for dfig-based wind power generation systems. references [1] a. mullane, g. lightbody, r. yacamini, “adaptive control of variable speed wind turbines”, n proceedings of 36th universities power engineering conference, swansea, 2001 [2] t. ackermann, wind power in power systems, john wiley & sons, 2005 [3] j. zhao, w. zhang, yikang he, j.hui, “modeling and control of a windturbine-driven dfig incorporating core saturation during grid voltage dips” international conference on electrical machines and systems (icems 2008), pp. 2438 – 2442, 2008 [4] w. hofmann, "optimal reactive power splitting in wind power plants controlled by double-fed induction generator" ieee africon, pp 943948, south africa, 1999 [5] a. petersson, "analysis, modeling and control of doubly-fed induction generators for wind turbines", technical report no. 464l, school of electrical engineering, chalmers university of technology, goteborg, sweden, 2003 [6] chee-mun ong, dynamic simulation of electric machinary using matlab/simulink, prentice hall, 1998 [7] p. kundur, n. j. balu, m. g. lauby, power system stability and control, mcgraw-hill, 1994 [8] p. kundur, power system stability and control, mcgraw-hill, 1994 [9] n. hur, j. jung, k. nam, “a fast dynamic dc-link power-balancing , scheme for a pwm converter-inverter system”, ieee transactions on industrial electronics., vol. 48, no. 4, pp. 794–803, 2001 [10] a. mullane, m. o’malley, “the inertial response of inductionmachine-based wind turbines,” ieee transactions on power systems, vol. 20, no.3, pp. 1496 15033, 2005 [11] m. cichowlas, m. kamierkowski, “comparison of current control techniques for pwm rectifiers”, ieee international symposium on industrial electronics, vol. 4, pp. 1259–1263, 2002 [12] v. akhmatov, “variable-speed wind turbines with doubly-fed induction generators, part i: modelling in dynamic simulation tools”, wind engineering, vol. 26, no. 2, pp. 85–108, 2002 engineering, technology & applied science research vol. 7, no. 3, 2017, 1615-1618 1615 www.etasr.com farhat et al.: a low cost automated weather station for real time local measurements a low cost automated weather station for real time local measurements mohamad farhat school of engineering the australian college of kuwait, kuwait m.farhat@ack.edu.kw mohammed abdul-niby school of engineering the australian college of kuwait, kuwait m.nibi@ack.edu.kw mohammed abdullah school of engineering the australian college of kuwait, kuwait 1210813@go.ack.edu.kw abdelbaset nazzal school of engineering the australian college of kuwait, kuwait 1108945@go.ack.edu.kw abstract—in this paper, we present an automated weather station for real time and local measurements, based on an embedded system that continuously measures several weather factors such as temperature, humidity, barometric pressure, wind speed, wind direction, and rainfall. this weather station consists of two parts which are located indoor and outdoor and connected together wirelessly. the outdoor weather station measures the current temperature, humidity, barometric pressure, wind speed, wind direction and recent rain amount. the indoor station displays the outdoor reading as well as the temperature and humidity for the room it is located in, on a graphic liquid crystal display. in addition, this weather information can be accessed from any place through an ios and android application called blynk. keywords-automated weather station;embedded system i. introduction horticulture, agriculture, and ranching are all rely on weather conditions to determine when to carry a specific kind of work in a related field, such as crop irrigation, planting, harvest and spray to prevent diseases [1]. in addition, renewable energy sources such as wind, hydro and solar energy are on high demand globally. to choose the prospective location of such projects, it is crucial to gather and analyze all associated weather information to ensure the sustainability and viability of the project. for these purposes and many more, it is important to continuously collect the weather data, study and analyze them to obtain the necessary predictions. therefore, the challenge is to find suitable weather measurement devices with the least of hassles in obtaining weather data, considering most applications are remotely located and measurements are to be carried out for long periods. most low-cost weather stations are hand-held while the sophisticated once are quite expensive [2]. also, weather information provided by local authorities [3] are general and inaccurate for such applications, as they are based on automated weather stations (aws) located on specific locations. in this paper, an accurate, reliable, user friendly low cost automated weather system was developed to overcome such issues. ii. system description and operation the system described in this paper aims to provide full weather information for certain areas through a convenient user friendly mobile device or a graphic liquid crystal display. it consists of two weather stations, indoor and outdoor connected together wirelessly. they provide the outdoor information of the current state of the weather such as temperature, relative humidity, barometric pressure, wind speed, wind direction, and rain fall. the indoor station measures the indoor temperature and relative humidity. the system is an internet of things system as all the weather measurements are uploaded to the internet for display and analysis using smartphones, tablets, pc, and even for sharing through social media. also, the system sends notification to the user through an application if a certain weather parameter exceeds certain limits. the system basic operation can be summurized as shown in figure 1. the outdoor weather station measures the current weather factors and send them wirelessly to the indoor station. the indoor station displays the outdoor reading as well as the temperature and humidity for the room it is located in, on a graphic liquid crystal display. in addition, the indoor station uploads the indoor and the outdoor weather information to the internet in order to access them anywhere through an ios and android application called blynk. fig. 1. block diagram for the general system functions. iii. system implementation the system consists of two developments boards as shown in figure 2, in additional to several peripherals. arduino uno board [4] was used for the indoor weather station, where a red board from sparkfun [5] was used for the outdoor station. both boards are programmed using the arduino ide. these two boards consist of 14 digital input/output pins with 6 pwm pins, and 6 analog inputs. they can be powered either by usb or the barrel jack; also, they have an on-board power regulator which can handle anything from 7 to 12 vdc for the arduino and 7 to engineering, technology & applied science research vol. 7, no. 3, 2017, 1615-1618 1616 www.etasr.com farhat et al.: a low cost automated weather station for real time local measurements 15 vdc for the red board. these development boards are used to control the sensors, wireless modules, and the graphic screen to perform their function in this system. fig. 2. main boards used for system development. a. particle photon kit to link the system to the internet, the particle photon kit figure 3 was used. it has a 120 mhz arm cortex m3 microcontroller with a broadcom wi-fi chip in a tiny thumbnail sized module called the p-zero. each photon comes with headers to be easily installed on breadboard and access to the particle cloud which have great features for building a connected system like over the air updates and data storage. there are two ways to program the photon using either an online or local ide. the photon is ideal to build an internet of things system. fig. 3. particle photon kit b. weather shield and sensors the weather shield (figure 4b) is an arduino shield with sensors to measure the temperature, relative humidity, and barometric pressure. it has htu21d humidity and mpl3115a2 barometric pressure sensors. also, it has optional rj11 connections to other sensors like a wind speed, wind direction, rain gauge and gps. this connector used to connect the wind direction, speed and rain fall sensors to the board (figure 4c). each shield can operate from 3.3v up to 16v and has built in voltage regulators. the shield is designed to work with the sparkfun and arduino uno. the indoor station use dht11 (figure 4b) which is a low-cost temperature and relative humidity sensor. it has a digital output on the data bin based on the readings of a capacitive humidity sensor and a thermistor to measure the surrounding air. c. 434mhz wireless module these 434mhz wireless modules (figure 5) fit into breadboards and configures with microcontrollers to create a simple wireless data link. the theoretical communication range of these two modules is 152.4 meters given perfect conditions. they also have 4800 bps data rate and operate with 5v supply voltage, thus this module is ideal for this system. d. power source the system uses multi-voltage power sources that provide each component with its corresponding power. the outdoor station uses solar power, while the indoor uses 9 volt battery or power adapter. fig. 4. weather shield, dht11, and wind-rain sensor. fig. 5. wireless module iv. system operation in detail a. outdoor station the outdoor station is connected according to figure 6. the data pin is connected to pin 12 on the red board, while the rain gauge, wind direction and wind speed sensors are connected through rj 11 cables. gnd and vcc are connected to power source. b. indoor station the indoor weather station is connected as shown in figure 7. the receiver, photon and dht11 are connected to arduino board through their desired pins. a nine-volt adaptor or battery is used to power up the circuit. c. system operation to reduce power consumption, both stations takes reading every 10 minutes as explained in figure 8. first, the outdoor station takes all outdoor weather information and sends them wirelessly to the indoor station. the indoor station receives the outdoor measurements and measure the indoor temperature and relative humidity. then it displays all information using the graphic lcd. information then moved to the particle photon (a) (b) (c) engineering, technology & applied science research vol. 7, no. 3, 2017, 1615-1618 1617 www.etasr.com farhat et al.: a low cost automated weather station for real time local measurements through serial connection to upload them to the internet. therefore, an application called blynk [6] which is a platform with ios and android to control arduino, particle photon and the likes over the internet. it's a digital dashboard where a graphic interface simply can be built by dragging and dropping widgets. thus, benefitting from these features of blynk, a userfriendly interface was built (figure 9), where all information can be accessed from anywhere using smart devices. in addition, the weather information data can be saved using blynk app servers or any computer server for study and analysis. furthermore, having data on the internet, opens many possibilities for system enhancements, such as sharing weather information publicly over social media. therefore a twitter account that tweets all these information automatically once per hour was developed for this purpose (figure 10). also, the system has the ability to send a warning message through blynk app if a certain weather parameters exceed any preset limits (figure 11). actual pictures from the stations are shown in figures 12 and 13. v. conclusion the weather station described in this paper provides a low cost, flexible and user friendly system for different applications. the weather information provided by this system can be accessed through different ways, such as lcd, smart devices, pc, social media and alert messages. the outdoor station was power using solar power while the indoor station can be powered using main power. fig. 6. outdoor practical connection between the different circuitry fig. 7. indoor practical connection between the different circuitry fig. 8. system operational flow chart fig. 9. blynk interface for indoor and outdoor information fig. 10. sharing weather measurements through automatic tweets fig. 11. sending mobile notification inside and outside the application engineering, technology & applied science research vol. 7, no. 3, 2017, 1615-1618 1618 www.etasr.com farhat et al.: a low cost automated weather station for real time local measurements fig. 12. the outdoor station fig. 13. the indoor station references [1] australian government–bureau of meteorology, “automatic weather station for agricultural and other applications”, 1995 http://www.bom.gov.au/inside/services_policy/pub_ag/aws.shtml. [2] c. liu, h. lee, j. yang, j. huang, y. fang, b. lee, c. king, “development of a long-lived, real-time automatic weather station based on wsn”, in proceeding of sensys, pp. 401-402, 2008 [3] kuwait meteorological department:, http://www.met.gov.kw/ [4] http://arduino.cc/en/main/arduinoboarduno [5] sparkfun electronics online store, https://www.sparkfun.com/ [6] blynk application for ios and android, http://www.blynk.cc/ engineering, technology & applied science research vol. 7, no. 6, 2017, 2345-2350 2345 www.etasr.com shabbir et al.: design and performance analysis of multi-tier heterogeneous network through … design and performance analysis of multi-tier heterogeneous network through coverage, throughput and energy efficiency amna shabbir department of electronic engineering, n.e.d. uet, pakistan aamna@neduet.edu.pk h. r. khan department of electronic engineering, n.e.d. uet, pakistan hashim@neduet.edu.pk syed abbas ali department of computer & information systems engineering, n.e.d uet, pakistan safdar rizvi department of computer science, bahria university, pakistan safdar.bukc@bahria.edu.pk abstract—the unprecedented acceleration in wireless industry strongly compels wireless operators to increase their data network throughput, capacity and coverage on emergent basis. in upcoming 5g heterogeneous networks inclusion of low power nodes (lpns) like pico cells and femto cells for increasing network’s throughput, capacity and coverage are getting momentum. addition of lpns in such a massive level will eventually make a network populated in terms of base stations (bss).the dense deployments of bss will leads towards high operating expenditures (op-ex), capital expenditure (cap-ex) and most importantly high energy consumption in future generation networks. recognizing theses networks issues this research work investigates data throughput and energy efficiency of 5g multi-tier heterogeneous network. the network is modeled using tools from stochastic geometry. monte carlo results confirmed that rational deployment of lpns can contribute towards increased throughput along with better energy efficiency of overall network. keywords-energy efficiency; 5g networks; heterogeneous networks; stochastic geometry i. introduction the accelerating demands of faster data connectivity and explosive growth in high speed applications results in staggering contribution towards energy consumption in today’s information and communication technology (ict) sector [1]. currently, ict alone generates 10% of global co2 foot print and within ict sector, 0.5% is consumed by mobile networks alone. according to the survey done in [2, 3] wireless sector is expected to increase by 75% latest by 2020. many documented studies show that in near future there will be a situation where number of bs will exceed the number of mobile users [2-5]. in the coming five year mobile data traffic expects a 20 to 30-fold increase which is expected to exceed 250-1.000 fold by 2020 [2]. to facilitate such a massive number of mobile users, 5g hetnets capacity have to increase dramatically in a significant manner. data traffic volume in 5g networks is expected to increase exabyte monthly [5]. this increase in data rate requirement puts urgency on network operator side to increase data rate without compromising the cost and quality of service. while focusing on high data rate services, the energy consumption by network is increasing naturally which pose not only serious environmental concerns but also major economical burden on networks side as well. for more than a decade the primary focus in designing of wireless networks was high capacity, coverage, data rate, throughput maximization and low latency, whereas in recent years energy efficiency (ee) of wireless network has become the foremost figure of merit due to environmental, economical and operational [4, 10-12]. hence in design of future generation 5g heterogeneous networks (hetnets), ee is one of the major performance markers. as illustrated in figure 1, energy consumption reduction is important from three different perspective which consumer’s side, operator’s side and ecological side. fig. 1. energy efficient network’s concerns a. consumer’s side perspective from the perspective of mobile consumers the ee of cellular network is one of the major concern when it comes to 3g data services. the mobility of users becomes questionable when it comes to battery life. a recent survey done in 2016 about satisfaction of smart-phone’s customers shows that iphone received lowest marks in battery drainage [6]. the engineering, technology & applied science research vol. 7, no. 6, 2017, 2345-2350 2346 www.etasr.com shabbir et al.: design and performance analysis of multi-tier heterogeneous network through … article [7] also emphasis on the same issue and discusses some of the potential solutions regarding wireless power transmission form energy efficient network. in a nut shell, battery life of users will be the biggest limitation for high speed or high or energy hungry devices (like 3d services, video streaming, mobile tv and multimedia), if it is not addressed quickly. b. operators side perspective in a wireless network, the biggest contributor towards energy consumption is macro bs, which is generally placed at the center of cell for providing basic network coverage. usually network capacity is scaled up by increasing number of macro bs which eventually leads to higher electricity bills due to high energy consumption. around 18% to 20% operating expenditures (opex) come from bss only. [8-11, 15]. therefore addressing the energy crisis quickly will have significant economic benefits from operator side as well. c. ecological side perspective currently ict is solely responsible for one tenth percent of worlds total energy consumption. this percentage is continued to increase with the increasing number of cellular subscribers. latest by 2020, three fourth sector of ict will be wireless [12] which puts an urgency to reduce ict related co2 emissions as soon as possible. figure 2 represents the detailed insight into the portion of energy consumed by ict, telecom network, cellular networks and base stations [16]. recognizing the importance of ee in current cellular network, this research work aims to analyze an energy aware heterogeneous network along with its data throughput. fig. 2. the proportions of energy consumption by different subsectors ii. mathematical preliminaries a typical 5g hetnet consists of multiple tiers, each tier differ on the basis of its coverage , transmit power and density. heterogeneous networks are designed and analyzed from an advance mathematical tool known as stochastic geometry [17, 18]. some of the mathematical preliminaries of stochastic geometry are briefly discuss before moving into detail analysis. a. point process (pp) random collection of points in n-dimensional isolated points either in time or in geographical space is known as point process (pp). mathematically, in a space of real isolated points (only integer values) point measures it is a measurable mapping φ from one probability space to another point measure’s space. the space is usually taken as rd where d>1. discrete sum of dirac measure is used expressed each measure on euclidean space e. ii x    where xi are the collection of random variable in euclidian space of φ . b. poisson point process (ppp) poisson point process is a random point having as a parameter. if is constant than the ppp is called stationary ppp. is the average no. of pp inside a boundry region. it is not nesessary for every ppp to follow poison distribution. for real, finit a pp can be a ppp iff  all points of disjoint subsets s1,…,sn,are independent;  all random variables φ(s) all sets s e , follows poisson distribution. in this paper homogeneous ppp is considered. where homogeneous forms stationary motion invariant and density points. λ is held to be constant throughout the space. c. voronoi tessellation voronoi diagrams, voronoi tessellations are used to analyze the cellular network performance when nodes are distributed thru stochastic geometry techniques [20]. a voronoi tessellation is the distribution of a plane is such a way that each polygon contains at least one generating point. in a polygon under consideration points should be placed close to the generating point. dirichlet tessellation is another name of voronoi diagram. dirichlet tessellation consists of multiple points in space r2. in this paper voronoi tessellation on rd space and random variables are modelled through matlab tools. d. throughput successful transmission of data from base station to mobile user in specific time is termed as throughput. unit of throughput is bits per second (bps), where as in cellular network data throughput is measured typically measured in kilobits per seconds (kbps), megabits per second (mbps) or gigabits per second (gbps). sometime throughput is considered as a benchmark for measuring network performance. iii. system model a. network model network considered in this paper is the multi-tier network which consist of three tiers namely macro, pico and femto tiers, as shown in figure 3. all three tiers differ in term of their densities, coverage and size. all bs are located according to ppp reflecting a heterogeneous network. b. equations power consumption model 1) single tier network model single tier network mainly consist of macro bs and ms. macro bs consume most of the energy [15]. around 70% 80% of macro bs energy is consumed by power amplifiers. the power consumption at each macro bs is given as: engineering, technology & applied science research vol. 7, no. 6, 2017, 2345-2350 2347 www.etasr.com shabbir et al.: design and performance analysis of multi-tier heterogeneous network through … t static txp =p +γ p (2) pt and ptx represents the total average power consumed and transmitted power by macro bs respectively. pstatic is the fixed power includes miscellaneous power consumptions due to signal processing, cooling of site etc. γ is the scaling factor of different radiated power losses likes feeder losses. for the sake of simplicity is assumed to be same throughout the network. fig. 3. a multi-tier heterogeneous wireless network 2) multi-tier network model a multi-tier network is further divided in to two parts:  2-tier network: which consists of macro bs under laid by pico bs  3-tier network: which consists of macro bs under laid by pico bs and femto bs the bs in each tier of hetnet are distributed according to homogeneous and independent ppp φi with density λi and pi is the transmitting power transmitted of ith tier. bss of every tier share same bandwidth. in ith any ms can connect to bs x if its sinr is greater with respect to intended bs.. the threshold in ith tier is represented by βi. each tier can be characterized by its transmitting power, density and sinr threshold {pi, λi, βi}. mobile stations are randomly placed according ppp distribution φm with λm being its density. the channel between ms and bs is rayleigh. bs are placed at the center with i.i.d exponential distribution. complex channel will be considered in future work. the average received power pi of ms located at some point th ip i is: ii i i p h xy x   (3) where α represents standard path loss exponent and ranges from 2 to 4. in free space α=2. the average power consumption of the ith tier is given by ihetnet,i i static,λ i t p =λ (p +γ p )x  (4) where λi, pstatic, i and it p x are is the bs density, fixed power consumption, scaling factor of different losses and output rf transmitted power in ith tier respectively. c. signal-to-interference and noise ratio (sinr) assuming that ms is connected in bs, the expression for sinr will be given in equation 4 ii i 2 p h sinr i+σi x x x   (5) where ι is the interference received by xi and σ 2 is awgn power in the ith tier. the resulting interference is given in ii i 1 \ p h i i m x j x x i x       (6) therefore, resulting sinr is given by i i i i 2 i i 1 \ p h sinr (7) p h σ i i i x x m x j x x x x          assuming i h ~ exp(1)x for simplicity in τηε rest of the paper. ms can connect to any bs which provides strongest signal. a typical ms is said to be in coverage region if: imax ( )>β (8)isinr x x  where βi is the threshold, for simplicity it is also assume that βi >1, which means that in entire network at most one bs can provide sinr larger than threshold allowing any ms to connect with at most one bs at one time. for the sake of simplicity interference effect is ignored in simulated results. d. energy efficiency (ee) and throughput the ee of any network is defined as the ratio of maximum achievable data rate per unit of transmitted power. mathematically, r ee:= p (9) where r and p average data rate and consumed power by network respectively. ee is measured in bits/sec/watt or commonly known as bits/joule. the maximum achievable data rate commonly known as maximum throughput achievable in the network. the maximum throughput of mth user in a single tier can be defined in terms of shannon capacity cm m m 2 mc =b log (1+sinr )  where bm is the assigned bandwidth of the m th user. in case of multi-tier hetnet, this capacity will be scaled by factor ni, where n is the no of pico or femto bs in a i th tier im m 2 m c =n b log (1+sinr )i (11) engineering, technology & applied science research vol. 7, no. 6, 2017, 2345-2350 2348 www.etasr.com shabbir et al.: design and performance analysis of multi-tier heterogeneous network through … the average ee of two tier i-e macro under laid by pico cells is given as i,k i,k k macro p k=1 two-tier k macro p k=1 r + r ee = (12) p + p    where rmacro is the average throughput and pmacro is the average consumed power by macro bs respectively. i,kp r and i,kp p represents the average throughput and average consumed power by kth pico station respectively. likewise, the ee of three tier network can be calculate as i,m i,m m macro pico p m=1 three-tier m macro p m=1 r +r + r ee = (13) p + p   i,mp r and i,mp p present the average throughput and average consumed power by mth femto station respectively. iv. results and analysis in this section coverage tessellation, throughput and ee of single, two tier and three tier network is analyzed. data throughput and ee are explored in detail for two tier and three tier network, with special focus on how number of base station and number of tiers effect on ee and data throughput of multitier hetnet. table i. simulation parameters for macro cells cellular layout hexagonal grid, 3 sectors per site inter-site distance 500 m ue power class 23 dbm (200 mw) ue distribution 80% inside the building table ii. simulation parameters for pico cells carrier frequency 2000 mhz bandwidth 10 mhz path loss model l = 38 + 30 log10(r); r in m max pico tx power 24dbm 24dbm antenna gain 0 dbi or 2 dbi outdoor wall penetration loss 10 db pico bs noise figure 6 db min separation ue to pico bs 2 m table iii. simulation parameters for femto cells max output power 20dbm propagation model pl(db) = 127+30log10(r/1000), r in m log-normal shadowing standard deviation 10 db fig. 4. single tier network with bs distribution as ppp the simulations parameters for network under consideration follow that in 3gpp tr 36.931 version 9 and 3gpp tr 36.922 version 10 [14-15] which are given in table [i-iii]. for single tier network, i-e macro bss only. coverage tessellation plot is shown in figure 4. macro bss are distributed according to ppp throughout the network. similarly, coverage tessellation for two tier network is shown in figure 5. figure 5 consist of two tier network macro and pico only. it comprises of macro (blue dots) underlaid by pico cell (red dots) only. the bs density of pico cells are twice than macro bs. through monte carlo simulation, throughput of two tier network is investigated. macro bss are placed homogeneous whereas pico cells are distributed according to ppp with twice bs density of macro cells. the total bw is divided uniformly across all ms. the data throughput is calculated with known snir at the receiver. figure 6 shows data throughput in mbps, which shows that while increasing number of pico bs gradually the throughput of two tier network is increased. fig. 5. two tier network pico (red) and macro (blue) with (λpico=2λmacro) figure 7 shows the ee of two tier network using equation 11. comparison of ee in bits/joule is plotted for different number of pico bs. two tiers network’s ee can be increased if number of pico bs are increase reasonably e.g. 6 to 10. however, increasing pico base station will results in increased co-channel interference in some over lapping areas due to its smaller size and placement inside a macro cell. nevertheless engineering, technology & applied science research vol. 7, no. 6, 2017, 2345-2350 2349 www.etasr.com shabbir et al.: design and performance analysis of multi-tier heterogeneous network through … capacity of hetnet will improves significantly if rational numbers of pico station are placed. three tier network is designed by placing femto cells inside two tier network forming a three tier network which consist of macro, pico and femto bs. average data throughput and ee of three tier network is analyzed below. figure 8 represents coverage tessellation plot for three tier network. macro and pico bss underlaid by femto bss (green). the density of femto bss is ten times higher than macro bss. all tiers are modelled by ppp distribution. figure 9 show the average throughput generated by femto cells as a function of transmitting power. it is observed that in a three tier network when transmitting power rises from 10dbm to 20dbm, there is linear increase in data throughput whereas increasing its transmitting power from 20dbm to 28dbm will result in exponential growth in data rate. for assessing ee attained by femto cells only, keeping transmitting power constant, statistical comparison of data rate and energy in bits/joule has been done for multiple femto bs as depicted in figure 10. from the statistical plot it is evident that increasing the number of small cell i-e femto cells will results in increase energy efficiency due to the reduce distance between bs and mobile user. table iv shows the data rate and energy when femto bs increases from one to six in three tier hetnet. fig. 6. average throughput of two-tier network fig. 7. energy efficiency of two tier network. fig. 8. three tier network with (λpico=2λmacro). pico (red) and macro (blue) ppp with (λpico=2λmacro) and (λfemto=10λmacro). femto (green), pico (red) and macro (blue) fig. 9. femto cells data throughput fig. 10. statistical comparison of data rate and energy for three tier network table iv. data rate and energy comparision for multiple femto cells parameter femto= 1 femto=2 femto=4 femto=6 data rate in mpbs 0.2031 0.7187 1.133 1.769 energy in bits/joule 1.016 3.594 5.665 8.843 engineering, technology & applied science research vol. 7, no. 6, 2017, 2345-2350 2350 www.etasr.com shabbir et al.: design and performance analysis of multi-tier heterogeneous network through … v. conclusion in this research paper coverage tessellations, data throughput and energy efficiency is being investigated through deployment of multi-tier heterogeneous network. a multitier network is form by two different topologies namely two-tier (macro-pico) and three-tier (macro, pico and femto). all networks are modeled using stochastic geometry. coverage tessellations, data throughput and energy efficiency analyses of both networks. in particularly effect of number of pico and femto base stations on data throughput and on energy efficiency is explored in detail. statistical and numerical analysis confirmed that 5g heterogeneous network throughput can be enhanced to greater extent if small base stations i-e pico and femto cell are increased in rational manner. in addition, wise deployment of optimal number of bss can lead to higher energy efficiency. moreover, in this research work energy efficiency investigation is only dependent on power transmitted by base stations within the tier under consideration. it is expected that energy efficiency and data throughput can further be improved if optimal power transmission and adaptive power control strategies are use. references [1] d. muirhead, m. ali imran, k. arshad, “a survey of the challenges, opportunities and use of multiple antennas in current and future 5g small cell base stations”, ieee access, vol. 4, pp. 2952-2964, 2016 [2] s. provider, w. papers, “cisco visual networking index: global mobile data traffic forecast update, 2015–2020 white paper”, cisco, 2016 [3] j. zhu, “energy efficiency analysis of cellular downlink transmission with network coding over rayleigh fading channels", ksii transactions on internet and information systems, vol. 7, no. 3, pp. 446-458, 2013 [4] k. davaslioglu, r. d. gitlin, “5g green networking: enabling technologies, potentials, and challenges”, 2016 ieee 17th annual wireless and microwave technology conference (wamicon), pp. 16, usa, 2016 [5] s. buzzi, c. i. t. klein, h. poor, c. yang, a. zappone, “a survey of energy-efficient techniques for 5g networks and challenges ahead”, ieee journal on selected areas in communications, vol. 34, no. 4, pp. 697-709, 2016 [6] j. d. power, 2016 u.s. wireless smartphone satisfaction study volume 1, 2016 [7] k. huang, x. zhou, “cutting the last wires for mobile communications by microwave power transfer”, ieee communications magazine, vol. 53, no. 6, pp. 86-93, 2015 [8] a. fehske, g. fettweis, j. malmodin, g. biczok, "the global footprint of mobile communications: the ecological and economic perspective", ieee communications magazine, vol. 49, no. 8, pp. 5562, 2011 [9] a. shabbir, h. r. khan, s. a. ali, s. rizvi, “a stochastic geometrical approach for performance analysis of heterogeneous cellular network”, international journal of computer science and information security, vol. 14, no. 8, pp. 467-475, 2016 [10] research focus magazine, why the eu is betting big on 5g, digital single market, 2016. [11] g. auer, v. giannini, c. desset, i. godor, p. skillermark, m. olsson, m. imran, d. sabella, m. gonzalez, o. blume, a. fehske, "how much energy is needed to run a wireless network?", ieee wireless communications, vol. 18, no. 5, pp. 40-49, 2011 [12] d. feng, c. jiang, g. lim, l. cimini, g. feng , g. li, “a survey of energy-efficient wireless communications”, ieee communications surveys & tutorials, vol. 15, no. 1, pp. 167-178, 2013 [13] s. verdu, “on channel capacity per unit cost”, ieee transactions on information theory, vol. 36, no. 5, pp. 1019-1030, 1990 [14] d. lister, “an operator’s view on green radio”, the proc. ieee int. workshop on green communications, 2009 [15] g. rittenhouse, “green wireless networks”, ieee wcnc, paris, france, 2012 [16] m. haenggi, stochastic geometry for wireless networks. cambridge university publishers, 2012 [17] m. haenggi, j. g. andrews, f. baccelli, o. dousse, m. franceschetti. “stochastic geometry and random graphs for the analysis and design of wireless networks”, ieee journal on selected areas in communications, vol. 27, no. 7, 2009 [18] k. huang, j. g. andrews, “a stochastic-geometry approach to coverage in cellular networks with multi-cell cooperation”, ieee global telecommunications conference, globecom 2011, nepal, 5-9 dec. 2011 engineering, technology & applied science research vol. 7, no. 5, 2017, 1900-1903 1900 www.etasr.com ilerisoy and takva: nanotechnological developments in structural design: load-bearing materials nanotechnological developments in structural design: load-bearing materials zeynep yesim ilerisoy architecture department faculty of architecture, gazi university ankara, turkey zyharmankaya@gazi.edu.tr yenal takva architecture department faculty of architecture, gazi university ankara, turkey yenal.takva@gazi.edu.tr abstract—nanotechnology has a wide field of possible applications that includes the design, manufacture and application of nanomaterials and nanostructures. the selection of materials is an issue of significant importance to the construction industry. concrete, steel and wood materials are considered as the main load-bearing materials in building construction and due to nanotechnological developments advanced application possibilities have been provided. the aim of this study is to systematically examine the nanotechnological developments on concrete, steel and wood which are used as load-bearing materials. the materials’ properties and the steps that enable these properties are considered and the advantages brought by the use of nanotechnology are tabulated. the differences in the molecular level of materials exhibiting behaviors different from those of conventional scale equivalents are shown. keywords-architecture; load-bearing system; concrete; steel; wood i. introduction considered as the industrial revolution of the 21st century, nanotechnology is related to controlling the materials in very small dimensions [1] and has become one of the fastest growing industrial sectors in the world with an impact to a vast variety of science and technology fields such as materials, medical sciences, computers, textiles, economics, environment, sustainable energy, etc. the incorporation of nanotechnology into future plans of major industrial countries emphasizes the importance that nanotechnology represents in terms of power and wealth of those countries in the near future [2]. multifunctional and smart materials that are rapidly developed can be employed to add extraordinary features to building materials. nanotechnology contributes to many features such as maximizing the quality and performance of existing products, extending physical life by preventing material damage, reducing material weight or volume, reducing the number of manufacturing steps by improving production methods, ensuring production with more efficiently usable materials, minimizing the operating costs of maintenance and repair [3]. nanotechnology is the creation of materials and devices by providing control of the material at atomic, molecular and nano level (one billionth of a meter) [4]. in other words, it is using very small particles of material to obtain new, large materials [5]. the term “nanomaterials” is emerging as a general name given for such materials. some examples of improved nanomaterials include copper which is normally opaque but it becomes translucent at nano-level, silicon that is an insulator at the macro level but conductive at nano-level and gold which normally doesn't react with anything at macro level but it transforms into a very active element in nano-level [6]. there are two main objectives in developing new nanomaterials. the first is to make use of the different properties of nano materials developed using special production techniques; and the second is to manipulate the inner structures of largescale materials at the atomic level and to control them, therefore giving them extraordinary properties [6]. in this direction, there are two main approaches in the production of nanomaterials aiming to form functional structures with individual atoms and molecules. the first approach, which is used to produce nano-scale structures from top to bottom, involves the process of separating the material in its entirety into small pieces. the entire material is reduced to a nanometer scale and miniaturized by chemical abrasion methods. the second approach, which is characterized as from bottom to top, is the process of dimensionally growing material atoms and molecules by chemical synthesis methods [7]. the architecture, engineering and construction sectors collectively represent a broad application area of nanotechnology and nanomaterials. such materials when used as load-bearing system materials exhibit different behaviors from those of conventional scale equivalents, thus creating new possibilities in the construction industry, which are further discussed in this paper. ii. nanomaterials in the construction industry the choice of materials in the construction sector is of great importance. advances in nanomaterials have brought forward innovations that improved the performance of buildings and infrastructure facilities. through nanotechnology, building materials have gained features such as higher strength, durability, permanent and quick constructability and environmental impact reduction. engineering, technology & applied science research vol. 7, no. 5, 2017, 1900-1903 1901 www.etasr.com ilerisoy and takva: nanotechnological developments in structural design: load-bearing materials a. concrete concrete, which is a cement based and multi-phase composite material and have been widely used for many years, are gaining important new features with the use of carbon nanotubes and nanoparticles. carbon nanotubes are graphite planes wrapped around pipes and have a cylindrical surface containing regular hexagons with carbon atoms at their corners [8]. carbon nanotubes have superior properties such as surface chemistry and high stability due to its higher conductivity than copper, elastic deformation and durability stronger than steel [9]. carbon nanotubes, ranging in length from about a few micrometers to 550 micrometers and ranging in diameter from about 1 to 50 nm, are in the form of cylinders and are classified as single (swcnt) or multilayer (mwcnt). adding carbon nanotubes to the cement in a small amount significantly improved the mechanical properties of the concrete [8]. multilayered nanotubes provide the highest increase in compressive strength and bending strength of concrete. they have yielded an advantage of +25 n/mm2 in compressive strength and +8 n/mm2 in bending strength compared with conventional samples [10]. nanoparticles can be defined as particles whose size ranges from 1 to 100 nm [6]. the first of these particles used to improve concrete material properties is titanium dioxide (ti̇o2). in most applications, the concrete surface is exposed to liquids such as water, mineral solutions, oil, solvents, etc., which results in wear, exposure to environmental influences, and erosion. when dry concrete is exposed to liquid, most of the fluids are absorbed by the pores due to capillary forces. for this reason, it is important to synthesize concrete with water repellent property in order to increase the durability [11]. tio2 is a white pigment that can be used as a reflective coating material that can decompose organic pollutants and volatile organic compounds by strong photocatalytic reactions. it reduces airborne contaminant concentration when used outside the building. tio2 is a hydrophilic material that allows the surface to be cleaned and used to keep the whiteness and gloss of the material for a long time [12]. another nanoparticle used in concrete is silica. this compound, with the chemical formula sio2, is crystal-like, just like diamond. this material, which is found abundantly in the earth's crust, has a relatively high melting and boiling point and exists in two forms in nature, as crystalline and amorphous. the production of high quality concrete depends on the type and size of the silicon particles. adding this nanoparticle into the cement mortar makes the compressive and bending strength of the cement mortar better than conventional mortar. in the concrete material, it ensures the control of the csh (calciumsilicate-hydrate) dissociation reaction and increases the strength of the concrete by preventing the water from penetrating into the concrete [13]. another nanoparticle used in the concrete industry is nano amorphous silica. amorphous silica is one of the allotropes of silicon. it is an important material used primarily for increasing adherence and obtaining high performance concrete. the other advantages that it provides to concrete can be listed as resistance against abrasion, non-slip surface acquisition, resistance to fire and anti-reflective properties. concrete is a brittle material and its repair in case of cracking can be very difficult. however, latest studies used bacteria to repair cracks in the material so that concrete was able to renew itself. in this method, the concrete is renewed with the help of a special bacteria that can live in the alkaline (basic) concrete environment within nature. an example of these bacteria is known as bacillus, which lives in alkaline lakes in russia and egypt. these bacteria are embedded in small ceramic trenches and are incorporated into the wet concrete mix. staying dormant in concrete, these bacteria become active with the increase of cracks and water leaks. the resulting calcium carbonate from their reactions penetrates into the cracks and closes the pores. by adding the anaerobic microorganisms used in this application to the mixture of water and concrete, the resistance of 28 days cured concrete increases by 25% [12]. b. steel steel is one of the most important materials widely used in the building industry. its properties such as strength, corrosion resistance and weldability are very important in design and construction [14]. fatigue under constant load creates deformations in the material. increased tension causes cracking. in this case, the physical life of materials used in the construction is reduced. research has shown that the use of copper nanoparticles reduces cracking caused by fatigue. it is also revealed that the addition of copper nanoparticles to the steel prevented the stresses and corrosion effects from the pressure-induced stress [15]. the steel produced with these nanoparticles has been used primarily in the building industry and bridges. in addition to the increase in durability, surface roughness is reduced and features of fingerprint remnant prevention and anti-corrosion properties are also obtained. it is important to ensure sufficient strength at the connection points used to connect the different load-bearing system components to each other in steel structures. concerning this issue, nanoparticles of vanadium and molybdenum reduce fracture problems and hydrogen brittleness at the connection points with the use of high strength bolts, and allow cracking problems to be postponed [16]. when it is considered that the welded parts are fragile, the strength of these parts under dynamic loads is increased by using magnesium and calcium nanoparticles [17]. in particular, carbon nanotubes can be used to strengthen high strength steel cables used in suspension bridge constructions. the use of strong cables in the buildings reduces construction costs and saves time. nano scale strong cables were produced in conducted studies by using phase correction cementite (fe3c). the use of tio2 has also led to a major transformation in the manufacture of nano-wires, nano-coatings and bolts used in construction [12]. the increase in yield strength increases the physical life of steel material. oxides which are commonly used in spray coating techniques are used to increase yield strength. the alloys used increase the yield strength of the steel 100 times. the alloy uses carbon-nitrite alloy containing yttrium oxide nanoparticles [14, 15]. in addition, stainless steel castings have been produced in nanotechnology using different compounds such as manganese, nitrogen and niobium carbide. the steel produced with this method has high heat tolerance. engineering, technology & applied science research vol. 7, no. 5, 2017, 1900-1903 1902 www.etasr.com ilerisoy and takva: nanotechnological developments in structural design: load-bearing materials finally, the mmfx2 steel, obtained by modifying the conventional steel microstructure, is three times stronger than conventional steel, more flexible, has higher strength and higher resistance to corrosion [12]. in this product, the formation of microgalvanic cells, which have a significant contribution to accelerating the corrosion activity in material composition and production processes, is minimized [15]. increasing the resistance to corrosion has made the use of this material economically more advantageous. the properties of this modified steel can be summarized as being cheaper than ordinary steel, more malleable, having better energy absorptive properties and higher durability . c. wood wood is a living material used as a daily building material from the past ages to present day and consists of nanotube or nano fibrillation. the lignocellulosic structure (woody texture) formed by the combination of lignin and cellulose, which strengthen plant cells, is extremely strong. nanoscale lignocellulosic surfaces create new opportunities for appropriate for self-cleaning surfaces, self-repairing features, high-level water repellent coatings containing silica and alumina nanoparticles, and wood materials with hydrophobic polymers [1, 18]. with nanotechnology, scientists aim to control fiber bonding at the microscopic level and improve the structural performance and usability of the wood by providing nanofiber bonding. nanotechnology can reduce or eliminate the occurrence of random defects that limit the performance of wood. nanocatalysts that trigger chemical reactions and make the wood more functional than its current properties make these reactions faster, easier and more effective. in addition, natural nanoparticle insecticides and repellents, self-cleaning wood surfaces, and nanosensors that define photocatalytic degradation of contaminants are at the forefront of nanotechnological uses in wood materials [19]. iii. application and evaluation the construction sector is one of the most prominent application area of nanotechnology. according to [20], the construction sector is the primary potential consumer of nanostructured materials, although many materials have not yet cleared the laboratory phase. table i compares the advantages of the nanoparticles used in the nanotechnological production process on the load-bearing materials. nanomaterials’ advantages can be summarized as follows: • in case of concrete: self-repair, faster stiffening and hydration, high strength, reduction of air pollutant concentration, easy cleaning and self-cleaning, water repellent property, resistance against fire and abrasion. • in case of steel: cracking and corrosion control, fingerprinting, high ductility and yield strength, high heat tolerance, better weldability and high strength steel cable production, as well as high resistance to fire, delayed cracking problems in high strength screws, high flexibility and scratch resistance. • in case of wood: rot retardancy, water repellency, preservation of color, fire protection, easy cleaning and selfcleaning. table i. properties of different nanomaterials n a n o p a rt ic le s property n a n o -c o n cr et e n a n o -s te el n a n o -w o o d self-repair faster stiffening faster hydration high strength √ rot retardancy water repellency √ si̇o2 resistance against fire √ √ cnt high strength √ reduction of air pollutant concentration √ easy cleaning, selfcleaning water repellent property √ √ ti̇o2 preservation of color fire protection √ nano amorphous silica resistance against fire resistance against abrasion √ vanadium molybdenum delayed cracking problems in high strength screws √ copper high flexibility scratch resistance cracking and corrosion control fingerprinting √ carbon-nitrite alloy high ductility and yield strength √ manganese, nitrogen niobium carbide high heat tolerance √ mg ca better weldability √ phase correction cementite (fe3c) high strength steel cable √ alumina rot retardancy √ iv. conclusion nanotechnology can be used to provide significant improvements to the properties of materials widely used in the construction industry, such as concrete, steel and wood. along with maximizing the quality and performance of existing products, they contribute to many criteria such as extending the physical life by preventing damage to materials, providing production with more efficient use of materials, minimizing operating or maintenance-repair needs. along with the fact that nanotechnology produced products have unique characteristics; significant reduction of existing construction problems, the shortening of construction time and effecting the long-term costs are also possible. in professional terms, these progresses should be followed carefully. engineering, technology & applied science research vol. 7, no. 5, 2017, 1900-1903 1903 www.etasr.com ilerisoy and takva: nanotechnological developments in structural design: load-bearing materials references [1] a. s. y. mohamed, “nano-innovation in construction, a new era of sustainability, international conferance on environment and civil engineering ( iceace’2015) pattaya, thailand, april 24-25, 2015 [2] a. mnyusiwalla, a. s. daar, p. a. singer, “‘mind the gap’: science and ethics in nanotechnology”, nanotechnology, vol. 14, no. 3, 2003 [3] s. leydecker, nano materials in architecture, interior architecture and design, birkhauser, boston, 43, 2008 [4] iwgn workshop report, nanotechnology research directions: vision for nanotechnology r&d in the next decade, iwgn research report, committee on technology, interagency working group on nanoscience, engineering and technology (iwgn), national science and technology council, usa, 1999 [5] iso/ts 800004-1 nanotechnologies—vocabulary—part 1: core terms. geneva, 2011 [6] s. gullapalli, m. s. wong, “nanotechnology: a guide to nano-objects”, chemical engineering progress, vol. 107, no. 5, pp. 28–32, 2011 [7] b. gordijn, “nanoethics: from utopian dreams and apocalyptic nightmares towards a more balanced view”, science and engineering ethics, vol. 11, no. 4, 521-533, 2005 [8] x. wang, q. li, j. xie, z. jin, j. wang, y. li, k. jiang, s. fan, “fabrication of ultralong and electrically uniform single-walled carbon nanotubes on clean substrates”, nano letters, vol. 9, no. 9, pp. 3137– 3141, 2009 [9] j. lee, s. mahendra, p. j. j. alvarez, “nanomaterials in the construction industry: a review of their applications and environmental health and safety considerations”, acs nano, vol. 4, no. 7, pp. 3580–3590, 2010 [10] k. a. alsafar, “review of the use of nanotechnology in construction industry”, international journal of engineering research and development, vol. 10, no. 8, pp. 67-70, 2014 [11] y. kothari, s. dewalkar, “application of nanotechnology in smart civil structures”, international journal of technical research and applicatons vol. 4, no. 3, pp. 13-17, 2016 [12] a. kazempour, “the impact of nanotechnology in reinforced structures: the structure of concrete and steel”, journal of current research in science, vol. s(1), pp. 421-430, 2016 [13] t. ji, “preliminary study on the water permeability and microstructure of concrete incorporating nano-sio2”, cement and concrete research, vol. 35, no. 10, pp. 1943-1947, 2005 [14] a. khitab, m. t. arshad, “nano construction materials: review”, reviews on advanced materials science, vol. 38, pp. 181-189, 2014 [15] saurav, “application of nanotechnology in building materials”, international journal of engineering research and applications, vol. 2, no. 5, pp.1077-1082, 2012 [16] r. olar, “nanomaterials and nanotechnologies for civil engineering, buletinul institutului politehnic din iasi, vol. liv (lviii), no. 4, pp. 109-117, 2011 [17] a. shakibabarough, m. valinejadshoubi, m. valinejadshoubi, “useable and precautionary aspect of using nanotechnology and nano-materials in the construction industry”, international journal of science, engineering and technology research, vol. 3, no. 4, pp. 841-848, 2014 [18] p. khandve, “nanotechnology for building material”, international journal of basic and applied research, special vol. 04, pp. 146-151, 2014 [19] v. pents, “application of nanotechnology in building materials”, available at: http://civilpents.blogspot.gr/2012/10/application-ofnanotechnology-in.html [20] p. j. m. bartos, “nanotechnology in construction: a roadmap for development”, proceedings of the 2nd international symposium on nanotechnology in construction, bilbao, spain, 27–36, 2005 engineering, technology & applied science research vol. 7, no. 4, 2017, 1879-1882 1879 www.etasr.com li et al.: an appraisal of asia-pacific cities as control and command centres embedded in world … an appraisal of asia-pacific cities as control and command centres embedded in world city network zeyun li geography section, school of humanities, universiti sains malaysia penang, malaysia lizeyun@yahoo.com sharifah rohayah sheikh dawood geography section, school of humanities, universiti sains malaysia penang, malaysia sdawood@usm.my xiaoxiao zhang tesol, school of educational studies universiti sains malaysia penang, malaysia 2390965168zxx@gmail.com abstract—since the globalization trend is proliferating at a staggering rate, world cities have emerged as the most dominant vanguard incorporated into global economy. control and command function is one of the robust integral parts of world city formation, which is closely associated with the corporate headquarter status of some dominant multinational companies. previous research works on this topic tend to concentrate on the western europe and north american arenas neglecting the asiapacific region. hence, the objective of this paper is to explore control and command functions of asia-pacific cities with reference to headquarters’ locations of multinational companies. the methodology will utilize the forbes global 2000 dataset from the seminal study of gawc research group, and apply the control and command center model and the interlocking city network model to discover the control and command index, as well as network connectivity of asia-pacific cities. based upon the empirical study of this research, we could identify the hierarchical structure and spatial structure of asia-pacific world cities to emerge as some control and command centers embedded in world city network. keywords-control and command center; world city network; globalization; multinational companies headquarters; forbes global 2000 i. introduction in the dynamic context of globalization, headquarter function of the predominant multinational companies（mnc) is an integral part of world city studies. in line with contemporary transformation of urbanization and industrialization, it is conspicuous that the majority of mnc tend to concentrate on some world cities, particularly pertinent to the economic base and the vibrant market environment of these cities. hence, the study of some control and command centers’ formation with reference to their headquarter function is perceived to be increasingly significant, especially related to their network connections on the basis of the world city network. based on pioneering studies of global urban hierarchy [6] , global city and advanced producer services formation [10] command and control function of world city is elucidated in many articles, notably for the presences of the mnc headquarters in these cities [1,7,17]. due to the spatial organization of mnc headquarters, [15] it is proposed that control and command center formation is closely associated with the headquarter status of the city. in spite of the 2008 financial crisis, geo-economic restructuring is transited at a staggering rate, and the financial sector still maintains its preeminent position [16, 18]. previous studies on control and command centers tend to restrict to europe [14] and north america [13]. in this article, we will explore the control and command function of asiapacific cities with regard to their multinational company’s headquarters agglomeration. in addition to finding the control and command functions of asian-pacific world city based upon the hierarchical method, we also seek to explore control and command function embedded in world city network with regard to its relevant connectivity in asia-pacific region. following [2], since the majority of world city study tends to focus on the hierarchical structure of urban relationship based upon the attributed data, this form of study is usually ascribed to the dearth of relational data [8,12]. in this sense, some scholars are intended to explore the increasingly inter-city connections in the age of globalization. this pattern of network structure is presented in the pattern of seamless office network of global business firms, and the details are explored in [5, 13]. most importantly, this ramification of business network conceptualizes the inter-city connections in the form of world city network. in this research, we would examine the network connectivity of asia pacific city embodied in the world city network. ii. methodology a. control and command center model this article applies the control and command center model from the globalization and world city research network (gawc) by utilizing the dataset 26 from gawc’s website based upon “forbes global 2000” information of year 2011 [3, 4]. according to this model, we can straightforwardly examine the general ranking of the leading 2000 firms in the world and the spatial distribution of their headquarters in the global engineering, technology & applied science research vol. 7, no. 4, 2017, 1879-1882 1880 www.etasr.com li et al.: an appraisal of asia-pacific cities as control and command centres embedded in world … territory. specifically, the general ranking is attributed to the comprehensive information of sales, profits and market values of forbes database and headquarters’ distribution is derived from company websites, and some business websites, as well as google map. in practice, in order to avoid some hidden and ambiguous results in this research, we will draw on the previous gawc experience in the control and command center research. generally, since bunds of companies’ headquarters are not concentrated in the core city area, they are decentralized in the suburban locations or satellite city of core city. in this multi-layered analysis, we will initiate the metropolitan area to replace the concept of city in our research. for instance, as some headquarters in kuala lumpur of malaysia are located in its satellite city petaling jaya or its neighboring state selangor, hence, we will qualify a notable metropolitan area kuala lumpur-petaling jaya-selangor to represent our sourced headquarters in the kuala lumpur area. in other words, in this research, city is replaced by its corresponding metropolitan area for deep analysis. according to these two streams of information, we can clearly calculate the quantity of forbes global 2000 companies in each asia-pacific metropolitan area. in line with the quantitative calculation, we will incorporate firm size and other essential information in our analysis. eventually, a control and command index （ cci ） is proposed in our article which derived from gawc research network. along with general hierarchical ranking, cci is able to simplify the ranking of the control and command centre in asia-pacific area with reference to a more rigorous evaluation method. specifically, a measurement of linear combination about control and command index is not restricted to simple count of headquarters and one variable in a city. in such an index, we invariably approach some other dominant variables in the forbes global 2000 database. hence, this index is equal to the sum of percentage of four critical variables along with quantity of headquarters, which are revenues, assets, profit, as well as market value. the major formula is summarized as followings: , , , , , , , , , 1 (1) 4 n i x y i x y i x y i x y x y i r a p mw cci       where ri,x,y refers to the percentage of revenues derived from total database; ai,x,y is the percentage of assets in the total database, pi,x,y and mwi,x,y are the percentage of profit and market value from the total database respectively. apart from four variables, i denotes the quantity of global 2000 company headquarters in a city and n represents the total number of headquarters in city x in given year y. in addition to formal specification of control and command centre model, gawc research network also simplify the 80 industries in forbes global 2000 database into 10 ordinary sectors using the global industrial classification standard (gics). in our research, we homogenise the asia-pacific cities with reference to 10 ordinary sectors in order to find the sectoral structure of control and command centres in the asia-pacific region b. interlocking city network model generally, world city tends to deemed as a global service center integrated in the global economy, interlocking city network model is initiated in this research so that we could measure the global network connectivity of asia-pacific cities embedded in world city network. building upon the model specification of gawc research network [13, 14] and theory of world city network, we specify the model in the matrix of vij. clearly, this matrix demonstrates the presence of j firms in i cities, and vij is considered as the service value of firm j with reference to city i; practically, the network connectivity of each paired cities are indicated as followings: rab,j=vaj×vbj (2) where vaj and vbj refer to service value of firm j with regard to city a and city b in the city dyad network. apart from the paired city connectivity derived from one firm, we also need to gauge the aggregate city connectivity of all advanced producer services firms between city a and b in the interlocking city network model. the formula is developed in details as followings: ,ab ab jr r  (3) finally, in order to identify the global network connectivity of single city drawn from the interlocking city network model. the formula is elucidated below: ( )a aignc r a i  (4) where gnca is network connectivity of city a with regards to all cities and all advance producer services firms. therefore, the result is indicated in the relative value in this table i in terms of the connectivity of top 10 cities in the asia-pacific region. based upon model specification of interlocking city network, gawc research network collect the relational data for the subsequent calculation and analysis. in order to produce the interlocking network about location strategy of multinational companies in the global scale, the notable of data collection procedure is constituted of three parts, which are detailed as followings: at the beginning, gawc research network select the 526 cities covering all of global arenas. these cities tend to be some capital cities, metropolises and some other dominant cities of each country. in addition to city selection, gawc implemented the procedure to select the firms for constructing a matrix. the criterion is determined by the ranking of firm size. consequently, a dataset of global producer service firms are qualified with the branches above 15 different cities and at least one branch in each of the three global arenas, which are east europe, north america and asia pacific. based upon the rigorous detection process, a number of 175 leading advanced producer service firms are identified in this database. in line with the cities and firms selection, meanwhile, we also assign the service value in terms of an advanced producer services firm in a city. two kind of secondary information are collected by gawc research network. the first information refers to the size of firm office or branch in a city, notably for the number of practitioners and quantity of offices in a city. besides, the second spectrum of information is collected based on extraengineering, technology & applied science research vol. 7, no. 4, 2017, 1879-1882 1881 www.etasr.com li et al.: an appraisal of asia-pacific cities as control and command centres embedded in world … locational functions of branches or offices in a city, for instance, national headquarter, regional headquarter and local branches. according to the above two types of information, we assign the service value of a firm’s presence in a city covering a range between 0 and 5. specifically, a city with a firm’s headquarter is assigned with 5 whereas a normal office or branch is deems as 2 in the scoring system. besides, if an office with no partner, the mark will reduce to 1. in contrast, if an office possesses large pattern of size, the score is increased to 3. finally, an office is considered as regional headquarters, the mark will be 4. iii. results and discussion table i summarizes the major indicators of top 10 asiapacific control and command centers based upon the forbes 2000 corporations’ headquarters’ ranking. this table encompasses the information of pilot study about number of sectors from gics, number of firms’ headquarters, control and command index, as well as the network connectivity of each city. accordingly, we can demonstrate that the tokyo is the leading control and command center in the asia-pacific region. based on this table, it is conspicuous that this world city possesses the highest quantity of the global 2000 companies’ headquarters and number of gics sectors. clearly, the quantity of headquarters is twice over the second position cityseoul. this trend of hierarchy is attributed to the robust economic base and multifarious industry structure of japan in the world economy. not surprisingly, this diversity of industry and economy development of japan enables its strategic center (tokyo) to attract huge amount of multinational companies pertaining to japan’s economy development. apart from tokyo’ irreplaceable position in the asia-pacific world city network, some other capital cities of emerging counties are also embodied in an incipient power integrated in the asia-pacific economy. in this situation, we could find that korea, hong kong and china aggressively strive to attract the mnc headquarters in their capital cities in the era of globalization. this unprecedented framework of the mnc agglomeration in some capital cities tend to be associated with a structural amalgam of spatial dispersal and global integration in these countries [9, 11]. since these capital cities entail a network power in the world city network, this network power significantly contributes to its control and command center formation. in other words, network power is correlated with the control and command center development. in general, the ranking of connectivity has implications on the power of a city; meanwhile, instructional power is the major determinants for the control and command center development [14]. in this article, we will examine the interrelationship between the control and command index and network connectivity. according to table i, we could find that the ranking of control and command index tends to epitomize an inconsistent correlation with the network connectivity. clearly, some cities maintain a conspicuous higher ranking in the control and command index whereas they are only featured a lower ranking in the batch of network connectivity. for instance, osaka is classified in this group with a lower network connectivity of only 18.79 as compared to other competitors in the world city network. with the exception of some slight distinctions between cci and network connectivity in most cities, hong kong performs a notable position in the status of highest connectivity of world city network in spite of relative average ranking in the cci. hence, the preliminary glimpse of general ranking of control and command is not enough to discover the intrinsic hierarchical structure of control and command center embedded in world city network, the next section attempts to elucidate the sectoral structure of control and command center embedded in the world city network based upon gics sectors. according to table ii., we can find tokyo is by far the most dominant control and command center in the majority sectors in the face of the competition with other asia-pacific cities. the successful of tokyo in the majority rankings tends to attributed to its unprecedented economic power, industrialization and urbanization in the context of globalization. apart from tokyo, beijing is another critical city in several spectrums of sectoral ranking, notably for the financial and utilities sectors. beijing has powerful financial and utilities market in the asian arena as so far, possibly reflecting the trend of rapid economic transformation, industrial consolidation, as well as urban restructuring of china. on the other hand, this sectoral ranking also implies that beijing is the preeminent world city in the global scale. apart from tokyo and beijing, some other cities are embodied by a complementary ranking in the different sectors, which means some cites are ranking higher in one sector whilst they are possible ranking lower in other sectors, the other competitors will replace or complement its position in the respective sectoral ranking. table i. top 10 headquarter cities in asia-pacific region ranking city no of gics sectors no of hqs cci network connectivity london=100 1 tokyo 10 154 23.15 65.22 2 seoul 9 60 7.16 53.42 3 hong kong 8 48 8.11 77.91 4 beijing 7 45 18.68 62.19 5 taipei 6 27 2.55 43.88 6 mumbai 9 26 3.28 59.42 7 osaka 7 23 2.70 18.79 8 sydney 5 21 3.57 62.91 9 shanghai 6 19 2.49 64.52 10 singapore 5 18 2.36 67.63 source: compiled and analysed by authors from dataset 26 of the gawc research network engineering, technology & applied science research vol. 7, no. 4, 2017, 1879-1882 1882 www.etasr.com li et al.: an appraisal of asia-pacific cities as control and command centres embedded in world … table ii. top 5 headquarter cities in asia-pacific region by gics sectors r an ki ng c on su m er d is cr et io na r y h q s c on su m er st ap le s h q s e ne rg y h q s fi na nc ia ls h q s h ea lth c ar e h q s in du st ri al s h q s 1 tokyo 23 tokyo 11 beijing 6 tokyo 30 tokyo 9 tokyo 43 2 seoul 8 sydney 3 tokyo 6 hong kong 21 mumbai 2 seoul 18 3 hong kong 6 singapore 3 mumbai 5 beijing 15 nagoya 1 beijing 11 4 osaka 6 bangkok 3 seoul 4 sydney 13 osaka 1 hong kong 8 5 kariya 4 hong kong 2 bangkok 3 seoul 13 shanghai 1 osaka 8 in fo rm at io n t ec hn ol og y h q s m at er ia ls h q s t el ec om m un ic at io n se rv ic es h q s u til iti es h q s o ve ra ll ra nk in g in du st ry h q s 1 taipei 5 tokyo 23 tokyo 3 beijing 6 tokyo industrials 43 2 seoul 3 seoul 8 seoul 3 hong kong 6 tokyo financials 30 3 tokyo 3 melbourne 6 hong kong 2 delhi 4 tokyo consumer discretionary 23 4 beijing 3 osaka 4 riyadh 2 kuala lumpur 3 tokyo materials 23 5 taoyuan 2 mumbai 3 taipei 2 osaka 2 hong kong hong kong 21 source: compiled and analysed by authors from dataset 26 of the gawc research network iv. conclusion based upon progressive hierarchical analysis of control and command centers in asia-pacific arena, the fascinating hierarchical structure of control and command centers were clearly corroborated. control and command centers are the major cities that facilitate the development of multinational companies in different countries with access to global market, espousing to the international network. accordingly, the hierarchical structure of control and command center in asiapacific area can be classified into 3 tiers. tokyo is the irreplaceable apex location in this urban hierarchy inferred by considering general ranking and sectoral ranking. the enormous quantity of multinational companies is attributed to a vast number of foreign direct investments. on the other hand, since the majority of multinational companies’ headquarters tend to agglomerate in some financial centers or industrial centers, the spectacular updating of japanese economy have moulded its capital city (tokyo) to sustain the financial center and industrial center in the asia-pacific region. thus, all of above centripetal forces contribute to higher control and command index and network connectivity of tokyo. apart from the tokyo’s position in the urban hierarchy of control and command centers, meanwhile, seoul, hong kong and beijing maintain their second tier’s position in the hierarchy. seoul and hong kong are two cities with the consolidated economic base in the asia region so that they can facilitate the high amount of multinational company regional headquarters. the only exception is beijing, due to the fact of the rising of industrial transformation of chinese industries, and west to east shift of world economy. chinese economy is overwhelmingly acquiring benefits from these opportunities. consequently, the apex city of china (beijing) will attain more chances to linkage with other world cities and attracting of mnc. these all are indispensable benefits affecting the control and command center formation in beijing. in addition to first and second tiers of leading control and command centers embedded in world city network, the third tier is characterized by some other capital cities and metropolises in some asia emerging economy, as well as some developed counties, such as australia and singapore. furthermore, with the exception of hierarchical structure of control and command centers in asia-pacific region, spatial structure is also essential to be explored. the spatial structure of control and command centers could reflect a west-east disparities of spatial pattern, which means all of leading control and command are concentrated in the east asia and pacific regions, there are no candidates are reflected in the west and middle asia regions. in spite of fuzzier borders for the space of flow and transnational economy, asiapacific region still indicates a tendency of uneven regional development. therefore, the majority of multinational companies’ headquarters are concentrated in east asia district albeit some prosperous counties in middle-east area. this uneven spatial disparity corroborates the importance in terms of location and information of the control and command center formation. since east asia and pacific areas have the convenient location for the transportation and infrastructure development, as well as proximity to global and regional information, they attract the higher quantity of mnc headquarters thereby enhancing their control and command development. although this empirical study identifies the hierarchical structure and spatial structure of control and command in the asia-pacific region, there still exits some deficiency. in the future research, we will conduct some other spatial analysis and quantitative analysis methods to discover the spatial-temporal structure of control and command centers embedded in world city network. acknowledgment the authors would like to thank universiti sains malaysia for providing financial assistance through the usm fellowship to engineering, technology & applied science research vol. 7, no. 4, 2017, 1879-1882 1883 www.etasr.com li et al.: an appraisal of asia-pacific cities as control and command centres embedded in world … conduct this research smoothly. the data were produced by g. csomós and constitute data set 26 of the globalization and world cities (gawc) research network (http://www.lboro.ac.uk/gawc/) publication of inter-city data. references [1] a. alderson, j. beckfield, “power and position in the world city system”, american journal of sociology, vol. 109, no. 4, pp. 811-851, 2004 [2] j. v. beaverstock, r. g. smith, p. j. taylor, “world-city network: a new metageography?”, annals of the association of american geographers, vol. 90, no. 1, pp. 123-134, 2000 [3] g. csomós, “the command and control centers of the united states (2006/2012): an analysis of industry sectors influencing the position of cities”, geoforum, vol. 50, pp. 241-251, 2013 [4] g. csomós, b. derudder, “european cities as command and control centres, 2006–11”, european urban and regional studies, vol. 21, no. 3, pp. 345-352, 2014 [5] b. derudder, p. j. taylor, f. witlox, g. catalano, “hierarchical tendencies and regional patterns in the world city network: a global urban analysis of 234 cities”, regional 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“development of the regional financial centers in china: a quantitative study based on the province-level data”, mediterranean journal of social sciences, vol. 7, no. 3 s1, pp. 374-382, 2016 engineering, technology & applied science research vol. 7, no. 5, 2017, 2010-2013 2010 www.etasr.com panchal and debbarma: rail-route planning using a geographical information system (gis) rail-route planning using a geographical information system (gis) sandeep panchal department of civil engineering nit hamirpur, hamirpur, himachal pradesh 2290sandy@gmail.com asim debbarma department of civil engineering, nit hamirpur, hamirpur, himachal pradesh 2290sandy@gmail.com abstract—the aim of this study is to analyse the potential of geographical information system (gis) in decision making in rail route planning process. the various parameters affecting the alignment of rail route are considered in this study and a feasibility map is prepared considering the cumulative effect of these factors. the factors considered in this study are road network, slope, topographical characteristics and drainage characteristics of study area. each parameter is given weights according to analytic hierarchy process (ahp) in gis environment. the layers of parameters affecting the feasibility of route are overlaid in gis environment to find a feasibility map. feasibility map is divided into five categories i.e. very low, low, moderate, high and extremely feasible on the basis of feasibility index. keywords-route; planning; ahp; gis; high speed rail; transport i. introduction route planning is a very difficult task in hilly regions. the uncertainty of various factors which affect the route alignment makes this process more complicated. alignment of a route is to be decided by balancing the economical and engineering considerations. conventional processes of route planning are very difficult and the results are not much accurate. it is difficult to find the cumulative effect of the factors like slope, drainage pattern of area and topographical characteristics of study area. transportation and highway engineering is one field which has been affected by developments in gis aspects, as spatial variables including environment, topography, built-up areas, land use/land cover, can be easily modeled. the first concept of gis application in rail track planning developed from location map through digitizing, geo-referencing and entering considered data. the factors considered are weighted according to giss’ criteria and importance with the help of different methods. the weighted factors are now standardized and overlaid in the proposed map by the help of arc gis tools. so the use of gis application has very much important role to take place in the development and making of a new rail track or road at any type of topological conditions on earth. geographical information system (gis) is a very efficient tool in route planning. it is easy to model the various factors affecting the route alignment in gis environment [1]. the inputs in gis environment can be varied to change the output until the planner is satisfied with the results. effect of engineering, social, economic and environmental factors can be considered in route planning of highways [2]. route selection is a critical first step in the process of design and construction and has a potentially significant impact to the construction and environment of the area. the various methods of route alignment in gis can be considered and a best method can be found out by comparing them [3]. multi-criteria decision analysis is a good way to consider the effect of economic and engineering factors. cosima is a model that considered the cost benefit analysis as a factor and then modeled the route alignment in gis environment [4]. the methods suggested by various researchers are applied in plain terrains but the study area considered in this study is hilly. the study area lies in lower shiwaliks in india. during the past decade the study area has become a development hub. the main assumption in this study is that the rail route should align as near as possible to the state highway 32 (sh-32). so, the study is restricted up to 1 km2 area along sh-32. the reason behind this assumption is that the important places and cities are along sh-32 and also that the construction site will thus be easily accessible for the transporting of raw materials. in nutshell, the various factors affecting the alignment of rail route are considered in this study. these factors are digitized and each factor is represented by a layer in gis environment. these factors and their subfactors are given weightage according to analytic hierarchy process. the reclassed layers are overlaid to get the final feasibility map. the feasibility map is divided into five parts according to the feasibility index. the feasibility map is an output of cumulative effect of factors affecting route feasibility. ii. material and methods the various parameters considered in this study are slope, nearness to important places, nearness to stream, nearness to routes, lithology and properties of soil in study area. analytic hierarchy process is used to know the relative importance of each criterion. engineering, technology & applied science research vol. 7, no. 5, 2017, 2010-2013 2011 www.etasr.com panchal and debbarma: rail-route planning using a geographical information system (gis) a. parameters of route feasibility the various factors affect route planning in different ways. each factor and its effect on route alignment are explained below. 1) slope the proposed railway line should not go from the areas which have high slope. if the slope in the study area is more than 25o, then it affects the economy of the project as the chances of landslides near railway track increases. slope layer of the study area is shown in figure 1. 2) nearness to important places: the proposed railway line should be near to the important cities or villages because of accessibility concerns. if the railway facility is much away from the important places, it will be difficult to use. figure 2 shows the nearness to important places. fig. 1. slope layer fig. 2. nearness to places 3) nearness to streams the proposed railway section should not be near to streams or high water level. high water level near the construction site is not preferred because it causes problem during construction. figure 3 shows the nearness to streams. fig. 3. nearness to streams 4) gradient gradient of the area should be gentle if possible. the lower gradient values are preferred from the economic point of view. 5) lithology the rocks encountered in the hilly region are a big challenge to deal with. alluvium can be cut easily but boulder and shales are hard to cut. so, it is preferred that the route should go through soft rocks. figure 4 shows lithology of the study area. fig. 4. lithology of area 6) type of soil the top soil should be soft but there should be firm strata beneath the soil so that the foundation can rest on it. so, soil is also taken as a factor which affects the feasibility of rail route. 7) nearness to route the proposed railway track should be well connected. so, nearness to routes is also an important factor considered in this study. figure 5 shows the nearness to route. engineering, technology & applied science research vol. 7, no. 5, 2017, 2010-2013 2012 www.etasr.com panchal and debbarma: rail-route planning using a geographical information system (gis) 8) landuse/landcover the landuse and landscover of the study area is another important factor that affects the route planning process. the route should go through barren land instead of agricultural and forest area. fig. 5. nearness to routes b. analytic hierarchy process(ahp) analytic hierarchy process is a multi-criteria decision making technique which is used to find the relative importance of criteria [5]. a 1-9 scale is used for calculating relative importance of the criteria like slope, lithology etc. table i shows the scale of reference proposed [5]. the preference criteria given in table i are used to compare the various parameters. table i. scale of reference scale degree of preference explanation 1 equal two activities contribute equally to an objective 3 moderate experience and judgment slightly to moderately favour one activity over the other 5 strong experience and judgment strongly favour one activity over other. 7 very strong experience and judgment very strongly favour one activity over other 9 extreme the one activity affect the objective with the highest degree that is possible 2,4,6,8 intermediate value used to present the compromise between values 1,3,5,7,9 reciprocal opposites used for inverse comparison consistency ratio (cr) is calculated to measure the consistency of the solution. if the value of cr<10%, then the ratio is defined as reasonable level of consistency. it means that the values assigned to the parameters are considered correct. if the value of cr is more than 10% then the preferences are to be revised to get the consistence result. when cr value is less than 10% then the results are considered as consistent and can be used for the analysis. the final weightage to be assigned to the criteria like slope, nearness to streams etc. are found by their relative comparison. the solution is checked for consistency. if it is found consistent, then the calculated weights can be assigned to each criteria and sub-criteria. c. role of gis the various parameters affecting the feasibility of rail route are converted in layers using gis. slope layer can be driven from the digital elevation model (dem) of the study area. the maps of the study area are collected from survey of india (soi). the maps are scanned and imported in arcgis 10. the maps are georeferenced and the factors like streams; places etc. are digitized using linear and polygon tools. the digitized data is converted into raster format. all the layers prepared in gis environment are given weightage calculated using ahp. the layers prepared in gis are overlaid using the weighted overlay. as the layers are overlaid, a final map is formed by the combination of various layers. the combination of weightage of layers is called feasibility index. the output map which is the output of the combination of layers is based on the feasibility index and shows the cumulative effect of the factors which are considere. the final map can be reclassed into five parts i.e. lest feasible, low feasible, moderately feasible, highly feasible and extremely feasible. iii. results and discussion the final result of the study is a feasibility map which shows the feasibility of rail route with different colours. it is found that the study area in the beginning of sh-32 is extremely feasible for the construction of railway line. it is because this area is almost flat and there are not much hills. the gradient is small and also the slopes in the area are gentle. about 35-40% of the area is found to be suitable for the alignment of the rail route. the terrain and land-use characteristics of the area are supporting the construction of railway line. there is almost 20% area which is least and low feasible for rail route construction. the terrain and lithology of the area proved challenging. it is difficult to construct the rail route in the least feasibility region due to its challenging terrain conditions. figure 6 shows the feasibility map. the most feasible route in the study area should be through the best options according to the feasibility map. a final route is also proposed according to the feasibility map. figure 7 shows a proposed feasible route. the most feasible route passes through the best alternative which is available at any point. iv. conclusions it can be concluded from this study that geographical information system (gis) can be used for route feasibility studies. it is easy to model the various factors affecting route feasibility in gis environment. the advantage of using the gis for route feasibility studies is that the planner can vary the input to change the output. the inputs can be varied until the planner gets satisfied by the results. the main limitation of this study is that the output of the study depends upon the accuracy engineering, technology & applied science research vol. 7, no. 5, 2017, 2010-2013 2013 www.etasr.com panchal and debbarma: rail-route planning using a geographical information system (gis) of the parameters. if the input is erroneous the output will also be erroneous. the output of the study can be modified by considering the other factors which affect the route feasibility. fig. 6. feasibility map fig. 7. most feasible route acknowledgment authors are thankful to dr. vijay shankar dogra, head of department, civil engineering, nit hamirpur for providing research friendly environment in the institute. authors are also thankful to the department of civil engineering, nit hamirpur for providing the resources for the research. references [1] g. della acqua, “using fuzzy inference systems to optimize highway alignments”, international journal for traffic and transport engineering, vol. 2, no. 1, pp. 44-59, 2008 [2] r. mateus, j. a. ferreira, j. carreira, “multi criteria decision analysis (mcda): central porto high-speed railway station”, european journal of operational research, vol. 187, pp. 1-18, 2008 [3] j. barzilai, “deriving weights from pair wise comparison matrices”, journal of the operational research society, vol. 48, no. 12, pp. 12261232, 1997 [4] i. ambrasaite, m. b. barfod, k. b. sallin, “mcda and risk analysis in transport infrastructure appraisals: the rail baltica case”, proscenia social and behavioral sciences, vol. 20, pp. 944–953, 2011 [5] t. l. saaty, “how to make a decision: the analytic hierarchy process”, european journal of operation research,vol. 48, no.1, pp. 926, 1990 [6] t. kara, m.cengiz savas, “design and simulation of decentralized railway traffic control system”, engineering, technology and applied science research, vol. 6, no. 2, pp. 945-951, 2016 [7] a. predo, m. ronkko, s. pickl, m. kolehmainen, “gis-based route planning for hazmat transportation”, ifip advances in information and communication technology, vol. 413. springer, berlin, heidelberg, 2013 [8] y. h. wu, h. miller, m. c. hung, “a gis-based decision support system for analysis of route choice in congested urban road networks”, journal of geographical systems, vol. 3, no. 3, pp. 3-24, 2001 [9] r. huang, “a schedule-based pathfinding algorithm for transit networks using pattern first search”, geoinformatica, vol. 11, no. 2, pp. 269-285, 2007 [10] c. macharis, a. de witte, l. turcksin, “the multi-actor multi-criteria analysis (mamca) application in the flemish long-term decision making process on mobility and logistics”, transport policy, vol. 17, no. 5, pp. 303-311, 2007 [11] i. ambrasaite, m. b. barfod, k. b. sallin, “mcda and risk analysis in transport infrastructure appraisals: the rail baltica case”, procedia social and behavioral sciences, vol. 20, pp. 944–953, 2011 [12] x. chen, m. zhang, “high-speed rail project development processes in the united states and china”, 2010,transportation research record, no. 2159, pp. 9-17, 2010 microsoft word 2-483-ed.doc engineering, technology & applied science research vol. 4, no. 5, 2014, 696-701 696 www.etasr.com mahmoud and el-labban: microstructure and wear behavior of tic coating deposited on … microstructure and wear behavior of tic coating deposited on spheroidized graphite cast iron using laser surfacing essam r. i. mahmoud welding and ndt lab., department of manufacturing technology, central metallurgical research & development institute (cmrdi), cairo, egypt essamibrahim2@yahoo.com hashem f. el-labban department of production engineering, alexandria university, alexandria, egypt dr_labbanh@yahoo.com abstract—spheroidal graphite cast iron was laser cladded with tic powder using a yag fiber laser at powers of 700, 1000, 1500 and 2000 w. the powder was preplaced on the surface of the specimens with 0.5 mm thickness. sound cladding and fusion zones were observed at 700, 1000 and 1500 w powers. however, at 2000 w, cracking was observed in the fusion zone. at 700 w, a build-up zone consisted of fine tic dendrites inside a matrix composed of martensite, cementite (fe3c), and some blocks of retained austenite was observed. in this zone, all graphite nodules were totally melted. in the fusion zone, some undissolved and partially dissolved graphite nodules appeared in a matrix containing bainite, ferrite, martensite and retained austenite. at 1500 w, the fusion zone had more iron carbides and ferrite, and the haz consisted of martensitic structure. at 2000 w, the buildup zone was consisted of tic particles precipitated in a matrix of eutectic carbides, martensite plus an inter-lamellar retained austenite. the hardness of the cladded area was remarkably improved (1330 hv in case of 700 w: 5.5 times of the hardness of substrate). keywordsspheroidal graphite cast iron; laser cladding; tic particles; yag fiber laser; wear resistance i. introduction spheroidal graphite cast iron has an excellent castability, good machinability, adequate wear resistance, high strength-toweight ratio, good combination of strength and toughness and high fatigue endurance [1-3]. such desirable properties widen its applications in machine, automobile, and mining industries. some applications include machine tool beds, rolling mill rolls, pistons, cylinders, sea water pump housings, and parts of earth moving equipment [4-5]. however, under severe service conditions, its performance and reliability can be limited by various forms of wear, which affect the life of a component and reduce its performance. improving the surface properties of ductile irons can help coping with these problems [4, 6]. many different traditional surface modifications such as surface hardening [7] and surface cladding [8, 9] are applied to improve the wear and erosion characteristics of ductile irons’ surfaces. various techniques such as thermal spraying [10], plasma spraying [11], traditional arc welding [8, 9] and focused energy technologies like electron beam [12] and laser [2, 4-5], have also been employed. the metallurgical bonding between the thermal spraying layers and the substrate is relatively weak, which causes the sprayed material to peel off under high bending stress or heavy loads [13]. the excessive energy input from the traditional welding processes such as shielded metal arc welding or even gas tungsten arc welding may cause some undesirable distortion and residual thermal stresses which may cause cracks in the hardened layer [8-9]. laser surfacing has been suggested as a potential technique to produce a hard surface layer of ductile irons for a number of reasons. the most important one arises from the fact that this technique provides rapid heating and cooling, which can easily produce special types of microstructures with novel properties that cannot be produced by other conventional processing techniques [14, 15]. generally, the obtained microstructure in the laser treated area depends on the heating and cooling cycles that take place during the process, which in turn depends on the laser parameters [16]. other merits of the laser surfacing are to produce a hard layer with low dilution and deformation, relative cleanliness, lack of quenching medium and limited grain growth during heating [2]. laser cladding is considered one of the laser surfacing techniques that can produce ductile iron-based-composites clad layers, where hard particles such as carbides, borides, and nitrides are used to reinforce the ductile iron [17]. in this case, the wear properties can be improved by the combination of embedded hard carbide particles and the rapid heating and cooling which forms hard structure matrix. the widely used carbide particles reinforcement is tic. it has low density, excellent mechanical properties, especially at high temperatures, good thermal stability and high wear resistance [18]. tic powder has been used previously on a variety of substrates. liu et al. [19] clad tic powder on the normal carbon steel substrate; jiang and kovacevic [20] clad tic powder on the tool steel alloy substrate; gu et al. [21] clad tic powder on the al alloy substrate; and ravnikar et al. [22] clad tic powder on the ti alloy substrate. this indicates that the engineering, technology & applied science research vol. 4, no. 5, 2014, 696-701 697 www.etasr.com mahmoud and el-labban: microstructure and wear behavior of tic coating deposited on … wear resistance of the substrate can be improved significantly by cladding tic powder. thus, in the present study, we aim to investigate the effects of main laser parameters and rapid solidification on the microstructure, hardness and wear behavior of spheroidal graphite cast iron surface cladded by tic powder. microstructural changes in the build-up melted and heat affected zones are examined in details. ii. exprimental work spheroidal graphite cast iron samples, with dimensions of 100 mm×50 mm×6 mm were used as substrate, with chemical compositions listed in table i. tic powder with purity of 99% and particle size of 3-10 μm, as shown in figure 1, was used as reinforcement. laser surface cladding using a 3 kw yag fiber (nd:yag) laser with a defocusing distance of 24 mm was employed for processing the samples. before laser treatment, the sample surfaces were mechanically ground and cleaned to remove any contaminates. the tic powder was preplaced on the surface to form a 0.5 mm thick film. the experiments were carried out at a fixed traveling speed of 4 mm/s and different laser processing powers of 700, 1000, 1500 and 2000 w. to produce oxide-free coatings in all experiments, argon shielding gas was used during and after laser cladding at a gas flow rate of 15 l/min. the transverse cross sections of the deposited beads were cut for microstructural examination. the depths and width of laser treated beads were measured on the cross-sections of treated samples under the given range of processing conditions. fig. 1. sem micrograph of the tic powder. the microstructures of the coated layer and substrates were investigated using an optical microscope, a scanning electron microscope equipped with an edx analyzer and standard methods of metallography. the substrate and the laser treated area were analyzed by x-ray diffractometer (xrd) to identify experimentally the existent phases that were originally found or in situ formed during laser processing. the micro-vickers hardness in the coated layer cross-section and the substrate were measured with an indentation load of 9.8 n and loading time of 15s at room temperature. the wear behavior of the laser cladded zone was evaluated using a pin-on-disk dry sliding wear tester in air at room temperatures. a stationary sample with a diameter of 2.5 mm was slid against a rotating disk with a rotational speed of 265 rpm for 15 minutes. the tests were carried out at a fixed load of 1 bar applied to the pin. before the test, all the specimens were ground using emery paper up to #600 to get smooth and flattened surface. the specimens were weighted before and after the test with a sensitive electronic balance with an accuracy of 0.001 g. the differences in average mass loss before and after the wear test were measured and accounted. three specimens of each laser power were chosen for wear tests. the untreated cast iron base metal was selected as the reference material for the wear test. table i. chemical composition of the spheroidal graphite cast iron substrate, wt.%. c si mn p s cr 3.82 2.7 0.237 0.02 0.014 0.03 ni mg al v cu fe 0.03 0.05 0.02 0.007 0.02 bal. iii. results and discussion a. macro/microstructure analysis the basic microstructure of the substrate, as shown in figure 2, consists of typical spheroidized graphite, surrounded by a narrow crescent of ferrite phase, embedded in a pearlite matrix. this microstructure was confirmed by the xrd analysis shown in figure 3. in this xrd peaks, alpha phase was the dominant phase together with cementite, which represents the constituents of pearlite, and graphite. fig. 2. optical micrographs (a) and (b), and sem images (c) and (d) for microstructure of the base metal. macro-views of the cross-sections of the surface laser treated layer at different laser powers of 700, 1000, 1500, and 2000 w are illustrated in the macrographs shown in figure 4. from these figures, four distinctive zones were observed. these regions are: (i) the build-up zone which refers to the areas enriched in tic particles and completely melted by laser heating and then solidified, (ii) the fusion zone which appeared engineering, technology & applied science research vol. 4, no. 5, 2014, 696-701 698 www.etasr.com mahmoud and el-labban: microstructure and wear behavior of tic coating deposited on … as a narrow band around the tic rich zone in which the substrate material is melted and then solidified, (iii) the heataffected zone (haz) which is just beyond the fused zone, which experiences an elevated temperature, but does not melt, and (iv) the substrate, whose microstructure remains unaffected during the laser treatment. the depth and width of the treated layers at different laser powers are shown in table ii. the depth of the treated layer is in direct proportion to the laser power. on the other hand, the laser power has no great effect on the treated zone width. fig. 3. xrd of the base metal. fig. 4. optical macrographs of the laser-treated zone cross-sections at different laser processing powers of: (a) 700 w, (b) 1000 w, (c) 1500 w, and (d) 2000 w. the microstructures of the build-up zone of the sample treated by a laser power of 700 w are shown in figure 5. in contrast to the microstructure of the substrate, the laser treated build-up zone was consisted of precipitated particles appeared as a dendritic morphology inside a fine matrix composed of martensite, cementite (fe3c) and some blocks of retained austenite. generally, all the constituents have fine microstructure due to the extremely high cooling rate after laser treatment. the edx analysis of the precipitated dendrites shows that they are tic, as shown in figure 6. this means that the tic particles are melted and then re-solidified during the laser processing. table ii. dimensions of the laser build-up zone at different laser powers. laser power, w width, mm depth, mm 700 0.51 1.21 1000 0.52 1.29 1500 0.54 1.45 2000 0.55 1.52 fig. 5. sem micrographs of the laser treated areas by processing power of 700 w where: (a) & (b) build-up zone, (c) the interface between the fusion zone and heat affected zone (haz), and (d) enlarged zone in (c). (m: martensite; d: carbides; ld: ledeburite). as it is well known, laser technology is characterized by a high energy density and ceramics have a much higher capability to absorb laser energy than metals. [23]. therefore, tic particles were melted (or partially melted) in spite of their extremely high melting point. tic solidified in a dendritic morphology due to high solidification rates after laser processing, and these results agree well with previously published results [24-26]. it is obviously to note here that all the graphite nodules are totally melted and are no longer formed again during re-solidification. by going down to the fusion zone, as shown in figures 5(c) and 5(d), the tic particles/dendrites have disappeared. its microstructure reveals a martensitic microstructure plus an interlamellar austenite between lathes of cementite, which is called ledeburite. at the bottom of the fusion zone, as shown in figure 7, some undissolved and partially dissolved graphite nodules appeared in a matrix containing bainite, ferrite, martensite and retained austenite. in this region, complete melting was not achieved but solid-state transformations are occurred. on the other hand, the heat affected zone shows a martensitic structure as shown in the lower part of figures 5(c), 5(d) and 7. moreover, the results show that there was no noticeable cracks in the interface of the laser treated zone which appeared to have good engineering, technology & applied science research vol. 4, no. 5, 2014, 696-701 699 www.etasr.com mahmoud and el-labban: microstructure and wear behavior of tic coating deposited on … adherence to the substrate. this interface appeared to have irregular shape, as shown in figures 4 and 7. this may be due to the extra carbon that came from the dissolution of graphite nodules into their adjacent areas, which lower the local melting point of these areas. melting occurs first in those carbon enriched areas, and then in the other areas [27]. fig. 6. eds spectra (b) of the area x in the enlarged sem micrograph (a) of the build-up zone in the laser treated zone by processing power of 700 w. (m: martensite) figure 8 shows the xrd patterns of the laser treated area at a processing power of 700 w. the laser treated zone showed peaks of titanium carbide, martensite, cementite and retained austenite in different ratios in addition to some traces of ferrite. the rapid cooling after laser treatment forces the nucleation during solidification to occur to temperatures below the liquidus temperature (undercooling) [3]. for this reason, grain refinement and more meta-stable phases can be achieved. on the other hand, carbon diffuses from higher concentration areas to lower concentration areas, where it forms in one hand large amounts of iron carbide (cementite) and in the other hand, leaving behind a low carbon area of ferrite. fig. 7. optical micrographs of the interface between fusion zone and heat affected zone at laser power of 700 w. fig. 8. xrd of the laser treated zone at processing power of 700 w. by increasing the laser power to 1500 w, the fusion zone resulted in iron carbides (fe3c) and ferrite, in addition to martensite (figure 9). this result can be attributed to the decrease of the cooling rate with increasing laser power. this relatively slow cooling rate gave the chance to the carbon of the dissolved graphite to diffuse into a higher concentration area, forming local batches of iron carbides. ferrite grains were more pronounced around these batches. martensite plates were also observed in these areas. moreover, some pores were found at the interface between the melted zone and the heat affected zone (figure 9(a)). during the laser treatment, combustion of graphite nodules can occur and consequently the graphite can be removed by the shielding gas [5]. the heat affected zone of the sample treated under this condition (1500 w) is composed of martensite structure (figure 9(b)). at a laser power of 2000 w, the build-up zone consisted of tic particles precipitated in a matrix of eutectic carbides, martensite plus an inter-lamellar retained austenite (figures 10(a) and 10(b)). the fusion zone appeared as a wide area and its structure, (figures 10(c) and 10(d)), was consisted of martensite-transformed primary dendrites, plate-like eutectic carbides, and some ledeburite between the interdendritic structures. this fusion zone structure is very similar to that of white cast iron. some transverse cracks were detected in the fusion zone (figure 10(c)). this may be attributed to the coarse carbides which solidified directly from the liquid and formed a continuous brittle network inside the fused area. moreover, the thermal stresses generated from this higher laser power (2000 w) can contribute to the formation of cracks in this condition. fig. 9. sem micrographs of the laser treated zone by processing power of 1500 w fig. 10. sem micrographs of the laser treated zone produced by 2000 w where: (a) and (b) build-up zone, and (c) and (d) fusion zone. engineering, technology & applied science research vol. 4, no. 5, 2014, 696-701 700 www.etasr.com mahmoud and el-labban: microstructure and wear behavior of tic coating deposited on … b. hardness measurements the microhardness of the base metal was about 240 hv. figure 11 shows the microhardness profiles through the depth of the laser treated zone obtained at different laser powers. the hardness along the depth of the treated zone is found to vary with the distance from the free surface. as the distance from the free surface increases, the hardness decreases. this decreasing of the hardness along the distance may be attributed to the microstructural changes along the depth of the treated layer. it can be seen that the free surface have much higher hardness than that of the substrate, which is related to the combined effect of the added tic particles and the formation of hard phases during the re-solidification after the laser surface treatment. the average hardness value at the surface treated with 700 w and 2000 w was about 1330 hv and 1100 hv, respectively. decreasing laser power was found to increase the hardness of the treated-zone, which may be attributed to an increased cooling rate. fig. 11. microhardness profiles through the depth of the laser treated zone obtained at different laser powers. c. wear resistance figure 12 shows the variation of wear weight loss of the laser cladded cast iron using different powers together with the base metal, after subjected to pin-on-disk dry sliding wear test at a fixed load of 1 bar in air at room temperature. compared with the cast iron base metal, all the investigated laser cladded samples have far better wear properties under the dry-sliding wear test condition. the weight loss of the sample treated by a laser power of 700 w was almost 1:40 compared to the untreated sample. this exceptional wear resistance improvement came from the hard, stable, wear resistant tic dendritic particles which were formed in-situ and were homogenously distributed inside the hard martensite matrix. the experimental results show that the weight losses are increased when increasing the laser power. the relatively faster cooling rate under the lower laser power resulted in refinement of both the reinforcement (tic particles) and the matrix (full martensite microstructure), which helped to improve the wear characteristics. on the other hand, the relatively slower cooling rate under the higher laser power resulted in relatively course tic particles inside a matrix of large martensite lathes and retained austenite. fig. 12. wear weight loss of untreated and laser cladded specimens with different laser powers. iv. conclusion spheroidal graphite cast iron was laser cladded with tic powder of 99% purity and particle size of 3-10 μm. the powder was preplaced on the surface of the specimens with 0.5 mm thickness. laser surface cladding was carried out using a 3 kw yag fiber laser at 700, 1000, 1500 and 2000 w processing powers and fixed traveling speed of 4 mm/s. to prevent the oxidation, argon gas was used as a shielding gas. the results lead to the following conclusions: 1. the treatment resulted in three zones: build-up (cladding), fusion, and the heat affected zone (haz). the depth of the treated layer is in direct proportion to the laser power. sound cladded layers were formed when applying 700, 1000 and 1500 w processing powers. the treatment under 2000 w caused cracking in the fusion zone. 2. at 700 w, the laser treated build-up zone microstructure was consisted of fine precipitated tic particles appeared with a dendritic morphology inside a fine matrix composed of martensite, cementite (fe3c), and some blocks of retained austenite. in the cladded zone, all graphite nodules were totally melted and were no longer formed again during the re-solidification. the fusion zone microstructure reveals a martensitic microstructure plus an interlamellar austenite between lathes of cementite. 3. by increasing the laser power to 1500 w, coarse grains and more iron carbides (fe3c) and ferrite appeared in the fusion zone. the heat affected zone showed a martensite structure. 4. at 2000 w, the build-up zone was consisted of tic particles precipitated in a matrix of eutectic carbides, martensite plus an inter-lamellar retained austenite. the fusion zone appeared as a wide area and its structure was consisted of martensite-transformed primary dendrites, plate-like eutectic carbides, and some ledeburite between the interdendritic structures. engineering, technology & applied science research vol. 4, no. 5, 2014, 696-701 701 www.etasr.com mahmoud and el-labban: microstructure and wear behavior of tic coating deposited on … 5. the hardness and thus the wear resistance of the cladded layer was remarkably improved due to the combined effect of the added tic particles and the formation of hard phases during the re-solidification after the laser surface treatment. the average hardness value at the surface treated by 700 w was about 1330 hv (5.5 times of the hardness of the substrate). the wear resistance of the sample treated by a laser power of 700 w was improved almost forty times compared to the untreated sample. references [1] m. shamanian, s. m. r. mousavi abarghouie, s. r. mousavi pour, “effects of surface alloying on microstructure and wear behavior of ductile iron”, materials & design, vol. 31, no. 6, pp. 2760–2766, 2011 [2] g. sun, r. zhou, p. li, a. feng, y. zhang, “laser surface alloying of cb-w-cr powders on nodular cast iron rolls”, surface and coatings technology, vol. 205, no. 8-9, pp. 2747–2754, 2011 [3] j. h. abboud, “microstructure and erosion characteristic of nodular cast iron surface modified by tungsten inert gas”, materials & design, vol. 35, pp. 677–684, 2012 [4] b. podgornik, j. vizintin, i. thorbjornsson, b. johannesson, j. t. thorgrimsson, m. martinez celis, n. valle, “improvement of ductile iron wear resistance through local surface reinforcement”, wear, vol. 274– 275, pp. 267–273, 2012 [5] a. fernandez-vicente, m. pellizzari, j. l. arias, “feasibility of laser surface treatment of pearlitic and bainitic ductile irons for hot rolls”, journal of materials processing technology, vol. 212, no. 5, pp. 989– 1002, 2012 [6] x. qi, s. zhu, h. ding, z. zhu, z. han, “microstructure and wear behaviors of wc–12%co coating deposited on ductile iron by electric contact surface strengthening”, applied surface science, vol. 282, pp. 672–679, 2013 [7] k. f. alabeedi, j.h. abboud, k. y. benyounis, “microstructure and erosion resistance enhancement of nodular cast iron by laser melting”, wear, vol. 266, no. 9-10, pp. 925–933, 2009 [8] m. heydarzadeh sohi, m. ebrahimi, h. m. ghasemi, a. shahripour, “microstructural study of surface melted and chromium surface alloyed ductile iron”, applied surface science, vol. 258, no. 19, pp. 7348– 7353, 2012 [9] k. y. benyounis, o. m. a. fakron, j. h. abboud, a. g. olabi, m. j. s. hashmi, “surface melting of nodular cast iron by nd-yag laser and tig”, journal of materials processing technology, vol. 170, no. 1-2, pp. 127–132, 2005 [10] d. womersley, “thermal spraying and powder spray welding processes for the hardfacing of grey cast iron”, materials & design, vol. 11, no. 3, pp. 153-155, 1990 [11] y. hoshiyama, t. miyazaki, h. miyake, “zirconium carbide dispersed high cr–ni cast iron produced by plasma spraying”, surface and coatings technology, vol. 228, no. s-1, pp. s7-s10, 2013 [12] r. zenker, a. buchwalder, k. rüthrich, w. griesbach, k. nagel, “first results of a new duplex surface treatment for cast iron: electron beam remelting and plasma nitriding”, surface and coatings technology, vol. 236, pp. 58-62, 2013 [13] p. fauchais, g. montavon, “plasma spraying: from plasma generation to coating structure-review article”, in: advances in heat transfer, vol. 40, pp. 205-344, 2007 [14] n. yasavol, a. abdollah-zadeh, m. ganjali, s. a. alidokht, ”microstructure and mechanical behavior of pulsed laser surface melted aisi d2 cold work tool steel”, applied surface science, vol. 265, 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tool steel composite coatings and their erosion resistance”, journal of materials processing technology, vol. 186, no. 1-3, pp. 331–338, 2007 [21] s. t. gu, g. z. chai, h. p. wu, y. m. bao, “characterization of local mechanical properties of laser-cladding h13–tic composite coatings using nanoindentation and finite element analysis”, materials & design, vol. 39, pp. 72-80, 2012 [22] d. ravnikar, n. b. dahotre, j. grum, “laser coating of aluminum alloy en aw 6082-t651 with tib2 and tic: microstructure and mechanical properties”, applied surface science, vol. 282, pp. 914-922, 2013 [23] j. sampedro, i. pérez, b. carcel, j. a. ramos, v. amigó, “laser cladding of tic for better titanium components”, physics procedia, vol. 12-a, pp. 313–322, 2011 [24] a. chehrghani, m. j. torkamany, m. j. hamedi, j. sabbaghzadeh, “numerical modeling and experimental investigation of tic formation on titanium surface pre-coated by graphite under pulsed laser irradiation”, applied surface science, vol. 258, 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[26] r. m. mahamood, e. t. akinlabi, m. shukla, s. pityana, “scanning velocity influence on microstructure, microhardness and wear resistance performance of laser deposited ti6al4v/tic composite” materials and design, vol. 50, pp. 656–666, 2013. [27] h. yan, a. wang, z. xiong, k. xu, z. huang, “microstructure and wear resistance of composite layers on a ductile iron with multicarbide by laser surface alloying”, applied surface science, vol. 256, no. 3, pp. 7001–7009, 2010 microsoft word etasr_v11_n5_pp7709-7713 engineering, technology & applied science research vol. 11, no. 5, 2021, 7709-7713 7709 www.etasr.com abd al kareem & ahmed: impact resistance of bendable concrete reinforced with grids and … impact resistance of bendable concrete reinforced with grids and containing pva solution shrooq abd al kareem department of civil engineering college of engineering university of baghdad baghdad, iraq s.shetan1901m@coeng.uobaghdad.edu.iq ikram faraoun ahmed department of civil engineering college of engineering university of baghdad baghdad, iraq ikram.faroun@coeng.uobaghdad.edu.iq abstract-the development of new building materials, able of absorbing more energy is an active research area. engineering cementitious composite (ecc) is a class of super-elastic fiberreinforced cement composites characterized by high ductility and tight crack width control. the use of bendable concrete produced from portland limestone cement (plc) may lead to an interest in new concrete mixes. impact results of bendable concrete reinforced with steel mesh and polymer fibers will provide data for the use of this concrete in areas subject to impact loading. the experimental part consisted of compressive strength and impact resistance tests along with a result comparison with unreinforced concrete. concrete samples, with dimensions of 100×100×100mm (cubes), and 500×500×50mm (slabs), were poured and were treated at ages of 28, 56, and 90 days. the compressive strength increased by 36.11%, 45.5%, and 52.4% respectively, whereas the impact resistance for samples reinforced with steel mesh and polypropylene fibers gave superior results to the conventional mixes. keywords-ecc concrete; impact resistance; polypropelene fiber i. introduction in comparison with other building materials, concrete is more practical, durable, and economical [1]. concrete is widely used as a building material due to its high durability, easy accessibility, and low cost [2] and is commonly used in almost every kind of construction [3]. cracks are inevitable during the life of a concrete structure. structures exposed to the external environment are more susceptible to cracking because they are affected by shrinkage or expansion in weight and drying in addition to other environmental conditions along with the overloading factor. these cracks affect the strength of the structures by weakening them and the mechanical properties and its durability are reduced as these cracks create a path for the penetration of harmful factors into the core of the structures [4]. attempts have been made to reduce cracks and improve the tensile properties of concrete members by using traditionally reinforced steel bars and also through the application of restraining techniques. although both methods provide more tensile strength to the concrete members, they do not increase the tensile strength of the concrete itself. in normal concrete and similar brittle materials, fine structural cracks develop even before loading due to drying shrinkage or other causes of volume changes. upon loading, these micro cracks spread and open due to the stress concentration effect [5]. to give the concrete flexibility we have to modify the traditional material. this type of concrete is softer than conventional concrete and is known as the engineered cementitious composite (ecc). developed at the end of the twentieth century, the ecc demonstrates the unique properties of high strength concrete, including excellent stress-hardening properties, multiple cracking properties, and fiber bridging properties which in turn increase the ductility of a structure. ecc, also called ultra-hard cementious composite, flexible concrete, or conflexpave, is a matrix-based composite material reinforced with short fibers with a maximum volume fraction of 2.0%. ecc blends are generally developed by adding polyvinyl alcohol (pva) solutions, polypropylene (pp), and polyethylene (pe) fibers. the introduction of fibers aims to reduce the damage in the concrete structure that is exposed to seismic and impact loads [6]. ecc concrete, is an easy-to-form mortar-based composite reinforced with specially selected short polymer fibers. ecc acts more like ductile metal than brittle glass which leads to a wide variety of applications. the tensile stress capacity of ecc can reach 3-5%, which is much higher than the 0.01% of ordinary concrete. the compressive strength of ecc is similar to that of normal to high strength concrete. ordinary concrete is brittle by nature while ecc is ductile. due to this property, it has wide applications and future scopes in various fields [7]. the associated high fracture toughness and controlled slit width (typically less than 100µm) make ecc an ideal material for improving the serviceability and durability of infrastructures [8]. ii. material characterization a. cement the cement employed in the current research was ordinary portland cement (opc) and portland limestone cement (il). the il was produced by lafarge and conforms to european standard en-197-1 & european standard no 196-2-type il [9]. tables i-iv show the properties and specifications of the two types of cement. corresponding author: shrooq abd al kareem engineering, technology & applied science research vol. 11, no. 5, 2021, 7709-7713 7710 www.etasr.com abd al kareem & ahmed: impact resistance of bendable concrete reinforced with grids and … table i. physical tests of il according to european standard en-197-1 for grade (42.5) test test result specification limits compliance finance (blain) cm 2 /gm 5105 at least matching initial setting time (min) 90 min at least 45min matching compressive strength (mpa) 2days curing 8 at least (10-20) not matching 28 days curing 34 at least 42.5 not matching table ii. chemical analysis of il according to european standard no 196-2 oxides and phases karasta test results (%) specification limits compliance cao 62.22 sio2 17.18 al2o3 4.19 fe2o3 2.91 mgo 1.95 not more than 5% not matching so3 2.44 not more than 2.5% not matching loi 6.21 not more than 4% not matching total 98.43 ci0.011 c3a 6.18 less than 0.1% i.r 0.47 not more than 1.5% table iii. chemical analysis of opc oxide composition test results limits of iqs no.5 /2019 for opc cao 62.32 sio2 21. 34 al2o3 4.93 fe2o3 5.43 mgo 2.12 < 5% so3 2.35 < 2.8% loi 1.72 < 4% lsf 0.86 0.66 – 1.02% ir 0.83 < 1.5% main compounds (bogue's equation) c3s 76.28 c2s 3.73 c3a 6.72 c4af 16.5 table iv. physical tests of opc physical properties test results requirements of iqs no.5/2019 for opc specific surface area (blaine method) m 2 /kg 376 > 250 initial setting (h) 2:45 > 45min final setting (h) 4:20 ≤ 10h soundness (autoclave method) % 0.12 < 0.8 compressional strength (mpa) at 2 days 20 ≥ 10 compressional strength (mpa) at 28 days 37 ≥ 42.5 b. sand ekhaider natural sand was employed as fine aggregates in this study. its physical and chemical properties are shown in table v. sieve analysis shows that the sand lies in zone 2 from the tests that were carried according to the requirements of [10] as shown in table vi. table v. physical and chemical tests of fine aggregates property test result i.q.s.45: 1984 limits specific gravity 2.6 absorption % 0.72 density (kg/m 3 ) 1580 so3 0.2% 0.50% (max) table vi. grading tests of fine aggregates sieve no. passing % limits of iraqi specification no.45/1984 zone 2 10mm 100 100 4.75mm 93.3 100-90 2.36 mm 77.7 100-75 1.18 mm 66.6 90-55 600 µm 54.4 59-35 300 µm 26.3 30-8 150 µm 3.1 10-0 c. silica fume silica fume (sf) (condensed micro-silica) with an activity index of 121% conforming to astm c1240-15 [11] was used. the technical data for the sf are shown in tables vii and viii. table vii. physical tests of silica fume physical properties silica fume limit of specification requirements astm c-1240 percent retained on 45µm (no. 325) sieve, max.% 7 ˂ 10 accelerated pozzolanic strength activity index with portland cement at 7 days, min. percent of control 121 ˃ 105 specific surface, min (m 2 /g) 15 ˃ 15 table viii. chemical analysis of silica fume sio2 % loss on ignition % moisture content % sample 92.84 1.59 0.33 chemical requirement according to astm c1240-2012 85% min 6% max 3%,max d. superplasticizer a third-generation superplasticizer (sika viscocrete -5930) was employed, which conforms to the specifications of astmc494 types g and f [12]. superplasticizers are employed to attain sever decrease of water, enhanced flowability, and optimal cohesion. the decrease in water-cement (w/c) ratio means that the cement paste permeability reduces noticeably, hence superplasticizers can be effectively employed to enhance the properties of concrete and prevent specific defects such as honeycombing. e. water tap water was used conforming [13] f. polypropylene fibers pp fibers absorb water and resist alkalis, chemicals, and chloride. table ix shows the properties of pp fibers. engineering, technology & applied science research vol. 11, no. 5, 2021, 7709-7713 7711 www.etasr.com abd al kareem & ahmed: impact resistance of bendable concrete reinforced with grids and … table ix. properties of pp fibers length 12mm diameter 0.032 density kg/m 3 910 tensile properties 600 700 g. polyvinyl alcohol (pva) solution pva is a water-soluble and biodegradable artificial polymer. pva is an excellent adhesive with superior bonding strength and film forming and emulsifying properties. it has excellent adhesion to both hydrophilic and hydrophobic materials. the solution was prepared to employ closely 80g of pvc in 2lt of boiled water until it disappeared completely. h. reinforcement grids two kinds of grid reinforcement were employed, steel and polymer with 12.7mm square opening size and 0.2mm diameter. iii. experimental work a. mixures two major categories of ecc mixtures have been designed and chosen. the first mixture was composed of opc, sand, sf, pva solution, and the optimum dosage of superplasticizer of about 1.3% which is within the acceptable range which is between 0.2 and 1.5% by weight of cement. the mix was reinforced with pp fibers. the second mixture was composed of the same components except that it was produced from il cement. the mix designs are described in detail in table x. table x. mix proportions type ref. ecc cement (kg/m 3 ) opc 356 356 il sand (kg/m 3 ) zone 2 320 320 sf (kg/m 3 ) 285 285 vf (kg/m 3 ) ppm 18 water (kg/m 3 ) 288 288 s.p (kg/m 3 ) 5930 4.6 4.6 acetate (kg/m 3 ) pva 3.56 b. molds preparation for compressive strength tests, 100×100×100mm cubes were used, and for the impact resistance test, 500×500×50mm molds were used. iv. results and discussion a. compressive strength the compressive strength test was conducted according to the british standard b.s.1881: part116 [14] by using 3 cubes specimens with dimensions of 100×100×100mm and with a testing machine of 2000kn capacity with loading rate of 2.5mpa/s, at a position perpendicular to the direction of casting (figure 1-2). the compressive strength test was conducted at the ages of 28, 56, and 90 days. it can be noted that the samples reinforced with pp fibers have better results than the reference mixtures. the increase in compressive strength was 36.11%, 45.5%, and 52.4% at 28, 56, and 90 days of water curing respectively. the difference between the two types of cement is the change in the chemical compounds of the cement the interpretation of the compressive strength test results is divided into three stages: fig. 1. the typical failure behavior of reference concrete specimens. fig. 2. the typical failure behavior of concrete specimens with 2% pp fibers under compression. fig. 3. compressive strength vs curing age of mixes containing opc. fig. 4. compressive strength vs curing age of mixes containing il. at first, there is the addition of pp fibers. these fibers were combined with the cement paste and enhanced the ability of micro cracks to spread without breaking or pulling the fibers and therefore reduced the cracks in the concrete. engineering, technology & applied science research vol. 11, no. 5, 2021, 7709-7713 7712 www.etasr.com abd al kareem & ahmed: impact resistance of bendable concrete reinforced with grids and … the second stage is the addition of small amounts of watersoluble polymers (pva solution) that enhance the bonding strength and durability of cementing materials. in the third stage, and keeping in mind the recent focus on the sustainable influence on unstable constructions, the environmentally friendly sf decreases carbon dioxide emissions by decreasing the amount of cement used. sf is a material with a volume twice smaller than cement, which can easily fill the voids between cement particles, and is also a highly active pozzolanic material that reacts easily with ca(oh)2 and water to form secondary csh through a pozzolanic reaction whereby the generated csh fills the capillary voids and a denser microstructure and high compressive strength can be achieved (figure 2). timedependent deformation behavior of bendable concrete produced by il cement was studied in [15]. two types of il cement were used and pp fibers and pva solution were utilized. the best results obtained were for mixes containing pp fibers and pva solution [15]. b. impact resistance the device used to measure impact resistance contains three parts that can be described as follows: • the main support part: it consists of an iron bracket that is strong enough to support the examination device during the examination and withstand the impact. it also contains another support on which the examination form is placed, which is of angle iron and is well fixed to prevent the movement of the form during the examination. • the iron structure for dropping the block: it is a cylindrical tube with an inner diameter of 10.5cm. it is fixed with supports that prevent it from moving during the examination. this tube contains an opening of 1.5m height. • the falling block: it is an iron ball, weighing 3.4kg with a diameter of 9.5cm. this mass is thrown from the height of 1.5m on the model several times. the model is placed on the supporting iron structure, and then the iron block is dropped from the specified height of 1.5m on the model. the number of blows at which the first crack appears and the number of blows to cause failure were recoded. the average of three 50×50×5cm specimens was considered. the test was carried out at the ages of 28, 56, and 90 days according to aci c-544 [16]. the results are shown in table xi. table xi. impact resistance test results mix reinforcement impact resistance no. of blows to cause: 1 st crack at day failure at day 28 56 90 28 56 90 reference (opc) plain 2 4 6 3 5 6 ecc opc steel 6 8 9 67 93 118 polymer 5 7 9 32 50 67 reference (il) plain 2 4 5 3 5 6 ecc il steel 5 7 8 50 53 55 polymer 5 7 8 23 31 38 dimensions: 50×50×5cm fig. 5. impact resistance with curing age of reference and ecc concrete mixes containing opc. fig. 6. impact resistance with curing age of reference and ecc concrete mixes containing il. according to the test results shown in table xi and figures 5 and 6, the samples reinforced with steel mesh and pp fibers have the greatest results with 67, 93, and 118 blows at 28, 56, and 90 days of water curing respectively, unlike the conventional mix which showed the lowest results. the mix reinforced with a plastic mesh had mid-values of 32, 50, and 67 blows respectively. the impact resistance test results interpretation is again divided into three stages: at first, the addition of pp fibers: these fibers incorporated with the cement paste, enhanced the ability of micro cracks to spread without breaking or pulling the fibers and therefore the cracks in concrete were reduced. the addition of small amounts of water-soluble polymers (pva solution): enhances the bonding strength and durability of cementing materials. the presence of steel mesh that has higher tensile strength: the bonding between concrete and reinforcing mesh plays a major role in impact resistance, as the number of blows required to cause first crack and failure increases. this can be attributed to the effect of the reinforcement mesh which helped absorb more impact energy efficiently (figures 7-9). the behavior of superplasticized concrete slabs reinforced with different types of polymer grids and subjected to low velocity impact loading was studied extensively in [17]. the tested 500×500×50mm and 500×500×25mm slabs had either imported or local polymer grids. the adopted falling steel mass was 3.36kg in weight and 9.5cm in diameter and the falling height was 1.2m. three mixes were used. many properties were tested during this research, including compressive strength and impact resistance. the test results indicated that the presence of polymer grids as concrete reinforcement enhances significantly the mechanical properties of concrete. it increases the number of blows required to cause impact failure and delays first crack and final scabbing and spalling to take place [17]. engineering, technology & applied science research vol. 11, no. 5, 2021, 7709-7713 7713 www.etasr.com abd al kareem & ahmed: impact resistance of bendable concrete reinforced with grids and … fig. 7. typical failure behavior of reference concrete specimens under impact. fig. 8. typical failure behavior of concrete specimens including 2% pp fibers and polymer grids under impact. fig. 9. typical failure behavior of concrete specimens including 2% pp fibers and steel grids under impact. v. conclusions according to the obtained experimental results, the following are the most notable outcomes of the current study: • compressive strength increased by 36.11%, 45.5%, and 52.4% over the traditional mixture at the age of 28, 56, and 90 days of water curing respectively. • the fiber-reinforced slab and steel mesh showed superior performance in impact resistance compared to the traditional mixture and required 67, 93, and 118 blows at 28, 56, and 90 days respectively, while the slab reinforced with fiber and polymer mesh showed satisfactory results compared to the traditional mixture with 32, 50, and 67 respectively. • the cost of bendable concrete was reduced by using il cement. • bendable concrete made with locally available materials and reinforcements can be widely used instead of conventional concrete at complex construction sites. • it is possible to use locally manufactured il cement in producing bendable concrete with acceptable mechanical properties reinforced with locally available grids. references [1] m. t. lakhiar, s. sohu, i. a. bhatti, n. bhatti, s. a. abbasi, and m. tarique, "flexural performance of concrete reinforced by plastic fibers," engineering, technology & applied science research, vol. 8, no. 3, pp. 3041–3043, jun. 2018, https://doi.org/10.48084/etasr.2084. [2] m. t. lakhiar, n. mohamad, m. a. b. shaikh, a. a. vighio, a. a. jhatial, and a. a. a. samad, "effect of river indus sand on concrete tensile strength," engineering, technology & applied science research, vol. 8, no. 2, pp. 2796–2798, apr. 2018, https://doi.org/ 10.48084/etasr.1869. [3] a. s. buller, a. m. buller, t. ali, z. a. tunio, s. shabbir, and m. a. malik, "experimental characterization of bacterial concrete against mechanical and durability performance," engineering, technology & applied science research, vol. 11, no. 1, pp. 6703–6707, feb. 2021, https://doi.org/10.48084/etasr.3983. [4] v. c. li, "on engineered cementitious composites (ecc) a review of the material and its applications," journal of advanced concrete technology, vol. 1, no. 3, pp. 215–230, jun. 2011. [5] p. archana, a. n. nayak, s. r. nayak, h. vaddar, and d. s. magnur, "study of strength of polypropylene fiber reinforced concrete," international journal of engineering research & technology, vol. 6, no. 6, may 2017. [6] k. ramasamy, s. kandasamy, and k. mani, "influence of polymeric and non-polymeric fibers in hybrid engineered cementitious composites," romanian journal of materials, vol. 48, no. 4, pp. 507–513, jan. 2018. [7] a. chaudhary and a. k. sharma, "experimental study on flexural behaviour of engineering cementitious composite as bendable concrete," international journal for research in applied science and engineering technology, vol. 7, no. 6, pp. 1274–1278, jun. 2019, https://doi.org/10.22214/ijraset.2019.6219. [8] v. c. li, "strategies for high performance fiber reinforced cementitious composites development," in proceedings of international workshop on advances in fiber reinforced concrete, bergamo, italy, sep. 2004. [9] cement -part 1: composition, specifications and conformity criteria fo rcommon cements. cen, 2011. [10] iraqi specification, no. 45 aggregate from natural sources for concrete and construction. baghdad, iraq, 1984. [11] c09 committee, "astm c1240 03a: specification for silica fume used in cementitious mixtures," west conshohocken, pa: astm international. https://doi.org/10.1520/c1240-03a. [12] astm c494 / c494m-15, standard specification for chemical admixtures for concrete. west conshohocken, pa: astm international, 2015. [13] iraqi specification, no .1703: water used in concrete. baghdad, iraq: central organization for standardization and quality control, 1992. [14] "testing concrete — part 116: method for determination of compressive strength of concrete cubes," in british standard, bsi, 1983. [15] s. s. saeed, "time-dependent deformation behavior of bendable concrete produced by portland limestone cement," m.s. thesis, university of baghdad, baghdad, iraq, 2016. [16] aci committee 544, "design considerations for steel fiber reinforced concrete," aci, west conshohocken, pa, usa, aci 544.4r-88, 1988. [17] i. f. a. almulla, "behaviour of concrete units containing polymer grids’," m.s. thesis, university of baghdad, baghdad, iraq, 2002. microsoft word etasr_v13_n4_pp11375-11386 engineering, technology & applied science research vol. 13, no. 4, 2023, 11375-11386 11375 www.etasr.com aljaloud & razzaq: an innovative metric-based clustering approach for increased scalability … an innovative metric-based clustering approach for increased scalability and dependency elimination in monolithic legacy systems abdulaziz aljaloud college of computer science & engineering, university of ha’il, saudi arabia a.aljaloud@uoh.edu.sa abdul razzaq ocean technology and engineering, ocean college, zhejiang university, pr of china 11934071@zju.edu.cn received: 16 may 2023 | revised: 30 may 2023 | accepted: 8 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6048 abstract scalability is one of the system’s characteristics highlighted in the recent literature, and it is directly related to issues that are encountered in state-of-the-practice technology. the scalability of a system is challenging because monolithic legacy systems are hard to scale due to the high level of component dependencies. to the best of our knowledge, there is no published work available that can identify the components from a monolithic legacy system in the context of dependent and independent components and scale them accordingly. the main contribution of this paper is the proposal of a novel approach for the exclusive identification of dependent and independent monolithic legacy system components. the proposed approach also helps to remove the dependency among components of monolithic legacy systems. as a result, it establishes a precise method that identifies all the components of an application and removes the dependency among components, helping to increase the scalability of the resulting application. this approach was validated by several experiments, and the key findings were the identification of dependent and independent components, the identification of relationships among components, and the identification of the abstract level architecture of the monolithic legacy system. in future work, the proposed method will be enhanced toward the recovery of the whole system’s architecture. keywords-monolithic application upgradation; system components; architecture recovery; dependency; scalability of monolithic systems; reverse engineering i. introduction scalability is a needed quality attribute of a process or system of non-functional requirements that describes the ability of the software to scale analogous to the demands (load scalability, structural scalability) [1-5]. scalability saves resources in terms of the time required to scale the software [6]. if scalability issues are not fixed rapidly and timely, the system can become unmaintainable [5]. at the point when scalability isn't altogether disregarded, requirements regularly are described distinctly regarding application boundaries.  load scalability: a component of a monolithic legacy system can be added, removed, or modified to accommodate changing loads. the system has the ability to adapt graciously as the presented circulation increases [4].  structural scalability is the capacity of a system to extend in a picked measurement without significant modifications to its architecture, and its usage or models don't impede the development of the number of objects it encompasses [4]. a monolithic legacy system architecture is the traditional unified model for software development and design. traditional software is intended to be self-contained. software components are interconnected and related as opposed to loosely coupled just like the case with a software modular [7]. this can create many challenges for groups working in a similar environment [8]. a monolithic legacy system is simple to develop and to test and has numerous obligations, e.g. it is independent from other applications and self-contained. these traditional architectures are commonly hard to upgrade, deploy, and maintain, and difficult to understand [9]. after the evaluation of the relevant research, it has been established that dependency removal of a component to increase the scalability of a system is an area where a serious effort is required to bridge the identified knowledge gaps. engineering, technology & applied science research vol. 13, no. 4, 2023, 11375-11386 11376 www.etasr.com aljaloud & razzaq: an innovative metric-based clustering approach for increased scalability … a. components components play a significant role in reducing the scalability issues of monolithic legacy systems [10]. components are defined as the smallest self-managing, autonomous, and helpful sets of a system that works in various environments. components are regularly circulated objects consolidating propelled self-administration features [11]. the components utilized in these essential programming applications are comprised of central blocks that can be joined together, relying on the prerequisite [12]. components increase the productivity of application developers and improve the programming quality due to the high level of reusability [13]. it is vital for an application developer to alter parts since it is uncommon to discover the components coordinating their nonfunctional and functional requirements in new system applications [13]. software engineering is favored due to these reasons. it can address these worries beginning from the prerequisite of the undertaking. the activities are to be executed by the product of a specific business for which it is planned [14]. additionally, it can likewise guarantee the duty regarding individual groups. software development based on components has emerged as a successful way to deal with building an adaptable system. component-based work has risen as a compelling way to deal with complex programming systems [15]. its advantages incorporate decreased improvement costs through reusing off-the-shelf components and expanded flexibility through including, evacuating, or replacing components [16, 17]. the system applications are to be kept running in the cloud with effectiveness. this requires substantially more expertise than what is essential to convey any programming in virtual machines. it is continuously prescribed to oversee cloud applications consistently to use their assets as per the approaching burden and to confront the disappointments, to duplicate and rehash every one of the segments to give flexibility if there should arise an occurrence of inconsistent framework [18]. when a program is planned to keep in view every one of the prerequisites, it turns out to be very extreme for the software architect to present radical changes which are later on requested by plans of action or clients as often as possible since it turns out to be progressively entangling for the designer to make changes when the code begins extending as a result of the inclusion of various individuals who make changes in the product [19]. as increasingly more exertion is required to facilitate updating in the highly coupled architecture of a monolithic design. this entire procedure, makes the discharge cycle of the application moderate [20] and the model delicate and untrustworthy. versatility is an essential element that requires the task and advancement of large enterprise applications [21]. the major downside of the monolithic application is its deficiency of scalability when a specific errand is to be performed inside the components [22]. the lengthy software cycle in light of the multifaceted nature of the framework is an obstacle in current, dependable administrations. in this strategy, the figuring method delivers the wanted outcomes. the method utilized is bunching, which is considered the least essential and challenging procedure utilized in building and science [12]. the primary and most essential target of executing this system is to mention the objective facts clearer to build up a superior comprehension. this robust understanding makes it simple to create complex information structures from given directives. a grouping strategy or technique is commonly used to distinguish all the related segments of monolithic legacy systems alongside their duties. as the info utilized in this procedure features the interconnectivity of every one of these parts, this grouping strategy is beneficial to limit the interconnection among various components to create ideal outcomes. b. clustering in the proposed method, reverse engineering is used to produce the wanted outcome. this method utilized with the end goal of reverse engineering is considered the least complicated and the primary method utilized in engineering and science [12, 23]. the primary and most imperative target of implementing this method is to mention the objective facts clearer in order to build up a superior understanding. this awareness makes it simple to create a sophisticated learning structure from given highlights. bunching strategy or technique is commonly liked to recognize all the related parts of monolithic legacy systems alongside their obligations [24]. as the information utilized in this strategy features the interconnectivity of every one of these components, this metric-based clustering method is very valuable to limit the interconnection among various parts in order to create the ideal outcome [25, 26]. clustering is a procedure in which huge frameworks are divided into pieces. this sensible framework exhibits that the substances which bear closeness with each other have a place in a similar subsystem, while the elements with a contrast among each other are ordered into various subsystems [12]. the clustering procedure is commonly utilized in distinguishing the product parts [18, 27]. a software developer with vast experience may highlight two kinds of issues in practice. the first issue is that it is challenging to decide on an explicit cluster, which is utilized for profoundly coupled parts [26, 28]. the second issue is to decide on the bunch mapping, which connects the software components [29]. c. metrics metrics are tools for gathering and organizing data into coherent groups. in the context of this particular research, metrics assume a crucial role in assessing the various components of a monolithic legacy system [32, 33]. by employing metrics, we are able to effectively categorize and cluster all relevant system components. through this process, we discover the intricate relationships between these components, identifying dependencies and independencies among them. these metrics provide us with a comprehensive understanding of the system's inner working and enable us to gain insight into its overall structure and functionality. by mapping out the interdependencies, we are able to discern the impact that changes or modifications in one component could have on others, aiding us in making informed decisions regarding system maintenance, optimization, or potential refactoring efforts. furthermore, the metrics serve as a means to quantify the system's performance, highlighting areas of strength and potential weaknesses or bottlenecks. this information is proved to be invaluable in the pursuit of improving a system's overall efficiency and reliability. through engineering, technology & applied science research vol. 13, no. 4, 2023, 11375-11386 11377 www.etasr.com aljaloud & razzaq: an innovative metric-based clustering approach for increased scalability … the diligent utilization of metrics, we are able to extract meaningful insight and enhance our comprehension of a monolithic legacy system, ultimately contributing to its enhancement and evolution. d. related work there are many approaches in identifying the software components of monolithic legacy systems. authors in [34] find the components based on classes and use a clustering algorithm. the approach presented in [35] makes use of only variables related directly to components. however, this can lead to low component quality. the identified components do not fulfill the requirements of scalability. authors in [34] relied extensively on uml diagrams only, which may not mirror the original structure of a system [36, 37]. however, our method is general and based on the investigation of the source code [38], which leaves the leading software design curio that mirrors the truth of a system. to the best of our knowledge, there is not a method/technique in the literature for identifying the components of a monolithic legacy system in the context of dependent and independent components and relationships among them. it is necessary to scale the developed monolithic legacy system. by using the proposed method, we identified the components and also found the relations among them and made an abstract-level architecture of the monolithic legacy system. in this way, software architecture, open-source advancement, authoritative structure, and obligation are vertically disintegrated [27]. during the time spent on software development, a complex system is challenging to be architected expertly. so, architecture refinement plays a critical job in the description of software architecture [12]. in a stepwise refinement, a succession of steps beginning from a unique detail of the design prompts a reliable, execution-focused, and building model [39]. to the point of a component, the conceptual architecture could be refined to a progressively robust design by sets. the architecture comprises two parts and a connector. the reality of software architecture representation gives numerous points of interest amid all the periods of the programming life cycle [20, 40]. for some systems, like the inheritance ones, there is no available representation of their architecture [41, 42]. the interface of a component should be the essential concern of its designer or developer. since the components are intended for use in an assortment of systems and need to give the administrations the ability to pay a little heed to the setting, designers endeavoring to utilize a segment must almost certainly distinguish the capacity of a component and the methods for invoking its behavior [43]. monolithic applications come up with failures when the number of clients getting to a system becomes excessively high or when too many features are integrated into a single system [20]. component architecture gives software engineers a way to deal with the multifaceted nature of vast-scale logical recreations and to push toward a fitting and-play condition for elite figuring [44]. some vast and expensive software systems work in a constant domain under requesting execution prerequisites. often a large portion of the expense for an item is spent on support [45]. numerous advantages can be picked up by partitioning a system into components. additionally, maintainability and scalability are accomplished [46, 47]. a comparison of some appropriate methods is shown in table i. table i. comparison of previous and present work previous works present work -identification of only components -no identification of dependent components & relationships among components -no identification of the architecture of the system -identification of independent components -identification of dependent components -identification of relationships among the components -identification of abstract level architecture of the monolithic legacy system e. contribution of this study  method creation: a method was developed to identify dependent and independent components in a monolithic legacy system using metrics and clustering techniques.  scalability enhancement: the method was successfully applied in a multinational industrial project, resulting in increased scalability.  dependency removal: the dependent and independent components were identified and dependencies among the dependent components were eliminated by adding a few lines of code.  abstract-level architecture: an abstract-level architecture derived from the monolithic legacy system was achieved, providing higher-level insight into the system's design.  solution applicability: considering the applicability of the solution in terms of methods, dependencies, and architecture level refactoring, the solution needs to be further evaluated in terms of legacy migration for emerging software. specifically, we focused on evaluating refactoring or modernization of the existing software to modern computing platforms such as mobile computing [43] and architecture-level refactoring of quantum software [44].  featured method: this research is an effort to fill the identified gap in the literature. scaling a monolithic legacy system can be useful for academic and industrial works. the monolithic legacy system can be scaled after its components are identified. it is useful for monolithic legacy systems that have no documentation and their components are unknown, to know how can the system be scaled further. this method helps achieve high cohesion and low coupling of the monolithic legacy system’s components. ii. research method and component mapping a. research method 1) research questions (rqs)  rq1. what techniques/methods are reported in the literature regarding the identification of the components of the developed monolithic legacy system and the removal of the dependencies of applications’ components?  rq2. why is it necessary to find and remove the dependency on the monolithic legacy systems application’s components? engineering, technology & applied science research vol. 13, no. 4, 2023, 11375-11386 11378 www.etasr.com aljaloud & razzaq: an innovative metric-based clustering approach for increased scalability …  rq3. how to resolve the dependency issue of the application’s components in order to increase the scalability of the monolithic legacy system?  rq4. what is the impact of the novel proposal when compared with the state of the art? table ii. rqs discussion rqs discussion rq1 we did not find any method or technique for finding the components of developed systems and for removing component dependencies. rq2 scalability is the primary quality attribute to achieve by removing the dependencies of the application’s components. rq3 we developed the metrics-based clustering method to identify the dependent and independent components of the applications and added a few new lines of code to remove dependencies. rq4 we identified the conceptual architecture of the monolithic legacy system and identified the relations among all components of the application. it’s abstract level architecture. the research method comprises the following components:  critical literature evaluation and analysis.  a method for proof of concept is built in order to validate results.  case study results and analysis of data for answering the raised research questions.  concluding the research based on analyzed data and own interpretive deductions. 2) rationale table ii discusses the research questions. we undertook the study in order to find the dependent and independent components of a monolithic legacy system. after finding all the components of the system, we removed the dependencies of components and classes by using the proposed model with metrics-based clustering. the monolithic legacy system can scale by using the proposed method. 3) type of study the contextual investigation is similar in nature to what will be utilized in the current study. comparative study is conducted to find out the impact of large and small projects in order to remove the component dependencies. 4) study analysis we measured and compared the results of the project keeping in mind the reusability of components and the achievement parts (e.g. dependent and independent components, relationships among components, and abstract level system’s architecture) of the proposed model. 5) case study context proposing a new technique is the primary context of the case study. 6) expected result by using the proposed method for increasing the scalability of a monolithic legacy system, the expected result was completed successfully. 7) component mapping to identify the software components of monolithic legacy systems, we made the component model of figure 2 and showed the relationships among all methods (figure 1). b. attribute relations attributes are variables where data are stored temporarily. the first step of the proposed method is to start from the variables in order to find the dependent and independent components of the monolithic legacy system. we provide a list of attributes in figure 1 (v1-13, v1-v59, v60-v67). a = attribute, v= variable c. methods in the second step, we list down all the methods (table iii). we identified the relationships between methods and attributes (figure 1). d. attributes to methods we listed down all the attributes and created relevant groups. we define the groups of methods with relevant attributes (figure 1). e. mapping methods to component the different method collections are defined (figure 1). each silhouette is composed of different sets of methods. the silhouette interface is the boundary of methods and sets of attributes inside the silhouette center. these interfaces have a link with other methods from the outside of the silhouette. figure 2 describes the attribute mapping component model. this model shows the mapping structure of the components. f. lack of cohesion of methods (lcom) the single obligation rule expresses that a class should not have more than one motivation to change. such a class is said to be durable. a high lcom esteem, by and large, pinpoints an inadequately cohesive class. lcom: max ((1-2), 0) (1) maximal cohesion: attributes are accessed by all methods lcom = 0 (2) no cohesion: a unique attribute is accessed by each method lcom = 1 (3) ������� = � − � if > �0 otherwise (4) where j is the number of pairs of discrete strategies in c which don't share instance attributes, q is the number of pairs of discrete strategies in c which share the instance attributes, m is the number of methods, a the number of attributes, m(ai) the number of methods that access ai m(ai) = ��� ∑ ����� � ��� !� "!� (5) maximal cohesion: all methods access all attributes m(ai) = m and lcom = 0 (6) no cohesion: each method accesses a unique attribute m(ai) = 1 and lcom = 1 (7) engineering, technology & applied science research vol. 13, no. 4, 2023, 11375-11386 11379 www.etasr.com aljaloud & razzaq: an innovative metric-based clustering approach for increased scalability … if some attributes are not accessed at all, then: m(ai) = 0 (8) and if no attributes are accessed: ��� ∑ ����� � ��� !� "!� = !� "!� = 1 $ " �!" (9) fig. 1. method relationships and structure. iii. proposed solution model a. solution brief in this proposed method, we used different techniques (clustering, matrices, and lcom matrix formula). this approach is divided into different categories. first, we extract the abstract-level solution model for understanding the method flow and its different sections (figure 1) in an abstract-level model design. after this, we made a detailed solution design model with different sub-phases, which shows the holistic flow of the solution design. fig. 2. attribute and object mapping component model. b. project brief the monolithic legacy system is a .net project. there were two projects, the first one a small pilot study, and the second is one of medium level. the proposed technique was applied to both projects. we measured the results and the type of impact on through this proposed method. we used the proposed method on classes and methods/functions to find the similarities and dependencies of every class and method/function. this helped us to recognize the components of the monolithic legacy system. to identify the monolithic legacy system components, two sets of categories of components were made, independent components and dependent components. the way to verify dependent components is mentioned below. finally, we removed the component dependencies (figure 1) and scaled the monolithic legacy system by adding a new component. the medium level project development was made in the mvc .net framework. the duration of this project was four months and two developers were employed. the number of code lines was 7,944 and a total of 330 classes formed the depth of inheritance. further details and significant parts of the project are mentioned in table iii. fig. 3. abstract model of the proposed solution. table iii. project code details parts (operations) class coupling loc areas admin section 7 29 admin controller 82 1117 admin models 95 1906 approval 4 4 approval controllers 57 912 budget 4 4 budget controllers 2 7 budget models 17 71 request 4 4 request controllers 29 109 request models 24 217 user management 4 4 user management controllers 117 1638 user management models 70 807 vendor 4 4 vendor controllers 35 170 vendor models 31 213 figure 3 shows the procedure at the abstract level of our proposed method and its flow. the proposed method has five processes. the first process is the project. projects must have classes or methods/functions. the second process is the clustering technique, which we used with metrics in our method. the third process is identifying components by applying the proposed method. the fourth process gives us an engineering, technology & applied science research vol. 13, no. 4, 2023, 11375-11386 11380 www.etasr.com aljaloud & razzaq: an innovative metric-based clustering approach for increased scalability … abstract-level architecture model of component relations. in the last process, we identify dependent and independent components. we add a few lines of code to remove the dependencies where it is necessary. fig. 4. holistic proposed solution model. the project in the first process is a monolithic legacy system that can be a web application or desktop software and can be written in any programing language. the second process is the basis of the proposed method, which we designed using the clustering technique. the proposed method is based on metrics. we used clustering techniques in our method for making groups or related methods that are being used in a monolithic legacy system. we find the code methods/functions and insert each method/function in the metric. we also write the value of each method, i.e. how many times this method/function is used in other methods. also, we checked and wrote the accessibility of each method for another method. we counted the number of usage values by applying intersection and writing down the exact values in the metric and how many times it is being used in other methods. the third process is defining a monolithic legacy system’s components. in this process, we find components based on our metrics, check the relations, and make groups by using the clustering technique and further separate them into groups. each group expresses its related component. we measured the relationships among methods/functions and found the relations among components that show the dependency among them. the independent components were also found. the fourth process is a component architecture model of the monolithic legacy system. to reach this process, we have identified the dependent and independent components of the monolithic legacy system and the relationships among all components. we see the complexity of the methods and the complexity of the components’ relationships to make them independent. we make new classes or write code for methods to make them independent. we make the abstract-level architecture model of components by using their relationships. it is a high-level architecture model. iv. results and discussion we performed experiments on an industry-based monolithic legacy system and a pilot study. we found that the impact was the same in both studies. our approach helps the developer identify components and the system’s structure. it also allows the architect to create abstract-level architecture. we performed the clustering technique with metrics on components to find the similarity and dependency of each method used in the monolithic legacy system. based on the proposed method, we identified the monolithic legacy system’s components in two different categories of components, independent, and dependent. independent components are easily scaled and reused without any risk, but dependent components cannot be easily scaled or upgraded in the monolithic legacy system, so it was needed to make the dependent components independent. we also identified the abstract level architecture of the monolithic legacy system. once we identified all the system’s components, we created the architecture of the monolithic legacy system based on the components’ relations and the method’s logic (figure 7). fig. 5. ttms component abstract architecture model. figure 5 shows all the components used in this project. these components are fully functional in the system. we designed all component models with the enterprise architect tool. we used the standard rules, the "provider," and the "required" interfaces. details about figure 5 are described below:  request: it has the functionality to execute a request by employee, admin poc, or approver. requests can be generated under different conditions like priority, category, and location wise.  employee: it creates the request and checks its progress. emails are generated on the biases of each request’s action. an employee can communicate directly to its related poc based on the request. an employee can only create a request based on an auto-detected location, authenticated by an active directory (ad).  admin poc: it can create a request for itself and also on behalf of an employee. it has the capability to make the request on behalf of employees who are under the poc. once a request is created on behalf of an employee, an email is sent to the employee about its update. the poc also has limited rights based on locations and category. the poc can only create or proceed with a request which is under the categories and locations' rights. the poc proceeds with the request that is created by the employee or itself. the poc can entertain any request which comes under its roles. it can reject the request made by the and system application metrics clustering • clustering • components system application’s components • independent components • dependent components system application component model • identify relationships among components • add new loc • remove dependency engineering, technology & applied science research vol. 13, no. 4, 2023, 11375-11386 11381 www.etasr.com aljaloud & razzaq: an innovative metric-based clustering approach for increased scalability … send a comment about the rejection whereas it can also communicate for further information about the request. after completion, of all proceedings of request and return from the vendor, the poc verifies the request and generates the invoice according to verification. all details of the invoice were automatically fetched from the database, which has been updated by the vendor. the poc can adjust the amount if something is missed by the vendor and let them know. this adjustment history is maintained with previous and new records. a poc can generate reports in detail or summary and with different filters to see things like categories, locations, and dates.  approver: it can proceed with the new request by itself. the approver can proceed with the request, which is forwarded by the poc for approval. the approver can entertain any request amd submit it to the vendor, which comes under its roles and amount limit. the approver can communicate with poc regarding requests or can reject the request back to poc with reasons. an approver can check the request’s details. the approver also has the role of seeing the reports.  vendor: the vendor must deliver the required items in requests. if a vendor does not have a task, it can update the missing items in a request. the vendor can communicate with the poc if it needs more details about the request’s items. the vendor can respond to the request and can check its progress. once the job is done and all the items of the request are delivered, the vendor closes the request as completed. if some items are delivered, the vendor can update the request’s status as a partial and can close it. figure 6 displays the intersection point between the admin poc and the approver components with the employee component. this diagram visually represents the interdependencies that exist among these components, particularly their reliance on the employee (request) component. the admin poc and approver components are intricately connected to the employee component, as they rely on its functionalities to perform their respective tasks. fig. 6. intersection among components. figure 7 provides a visual representation of the interfaces, requirements, and providers associated with each component within the system. it is important to note that figure 7 represents the dependent component model prior to implementing the proposed method. within this model, a clear observation is made: all components, namely employee, admin poc, and approver do not depend on the request component. this dependency indicates that the functionality and proper operation of these components rely on the availability and proper functioning of the request component. fig. 7. ttms component relation architecture design with required and provider interface. fig. 8. independent component model. fig. 9. employee request component. figure 8 shows the independence of the requester component among all components. this component model is created after applying our proposed model, which clearly shows the elimination of component dependencies. employee, admin poc, and approver components were dependent on the request component before. now, after removing the dependency, the employee component is separated from the request component. figure 9 presents a comprehensive overview of the dependencies within the system, showcasing the intricate interconnections among various methods and components. this diagram elucidates the profound bond engineering, technology & applied science research vol. 13, no. 4, 2023, 11375-11386 11382 www.etasr.com aljaloud & razzaq: an innovative metric-based clustering approach for increased scalability … established with a specific method and how it affects the functioning of other components. interdependencies with other components create a web of relationships that significantly impact the overall system's functionality and performance. this depiction of dependencies in figure 9 reinforces the need for a comprehensive approach to system design and maintenance, where careful consideration is given to understanding and managing these intricate bonds. by recognizing the significance of these dependencies, system architects can make informed decisions to optimize system performance, enhance modularity, and enable seamless integration of future enhancements or modifications. fig. 10. admin poc dependent component. fig. 11. approver dependent component. figure 10 provides a clear visualization of the dependencies between all methods within the system and the request component. this diagram highlights the crucial role of the request component as a central entity, upon which various methods rely for their operations. it demonstrates the intricate network of dependencies, emphasizing that each method requires the functionality and data provided by the request component to fulfill its purpose effectively. moreover, it is worth noting that a significant change has been implemented concerning the dependency of the admin poc component, as indicated in figure 15. this change removes the dependency of the admin poc component on the request component, which was previously present. this alteration reflects a modification in the system's architecture, enabling the admin poc component to operate independently, without relying on the request component for its functionalities. by visualizing the dependencies in figure 10, system designers and developers can gain valuable insight into the relationships among methods and components. it provides a basis for identifying potential areas of optimization, enhancing modularity, and improving the overall efficiency of the system. the removal of the dependency of the admin poc component, as depicted in figure 15, demonstrates a proactive approach to decoupling dependencies and refining the system's architecture for enhanced flexibility and adaptability. figure 11 visually illustrates the dependencies between all methods and the approver component within the system. this diagram showcases the vital role of the approver component as a central entity that various methods rely on for their functionality. it effectively portrays the intricate network of dependencies, emphasizing that each method requires the request component to fulfill its specific tasks effectively. engineering, technology & applied science research vol. 13, no. 4, 2023, 11375-11386 11383 www.etasr.com aljaloud & razzaq: an innovative metric-based clustering approach for increased scalability … fig. 12. admin poc component dependent on request creating method. figure 16 illustrates a significant modification made to the system's architecture, specifically the removal of the dependency on the approver's component. this change, as depicted, enables the approver's component to function independently, freeing it from relying on the request component for its operations. the visual representation in figure 11, combined with the adjustment showcased in figure 16, emphasizes the system's adaptability and flexibility. it reflects the effort to reduce dependencies and enhance the modularity within the system's design. by removing the dependency on the approver's component and accommodating different request models, the system becomes more versatile and capable of handling diverse scenarios effectively. these modifications not only improve the overall efficiency and maintainability of the system but also pave the way for future scalability and extensibility. system designers and developers can utilize the insights provided by figures 11 and 16 to optimize the system's architecture, ensuring smooth operation and facilitating seamless integration of additional features or enhancements. table iv serves as a valuable qualitative representation of the dependency relationships among all components within the system. it provides insightful information about the ways different components rely on each other to fulfill their functionalities. by examining table iv, we can observe that the employee (request) and admin components depend on each other, implying that their operations are closely intertwined. additionally, the approver's method is primarily reliant on the create() method, indicating a more specific dependency within the system. table v showcases the transformative outcome after applying the proposed method and removing the dependencies among components. the table clearly demonstrates that the monolithic legacy system's components have become independent, marking a significant shift in the system's architecture. table v represents the main result of the decoupling process, highlighting the successful attainment of independent components that were previously dependent. the removal of dependencies has freed the components from relying on each other, enabling them to operate autonomously. this newfound independence among the components has substantial implications to the system. it enhances modularity, flexibility, and scalability, allowing for easier maintenance and future modifications. each component can now be modified, updated, or replaced without causing disruptions to other components, fostering a more efficient and adaptable system. the results as presented in table v, reinforces the success of the proposed method in decoupling the components and transforming the monolithic legacy system into a more independent and robust architecture. system designers can refer to this table in order to understand the impact of the applied changes and assess the overall effectiveness of the method in achieving the desired outcome. table iv. dependent components of the monolithic legacy system components methods employee admin poc approver employee admin poc approver create() //new request yes yes yes inprocessrequests() yes yes no returnedrequests() yes yes no editreturnedrequests yes yes no rejectecdrequests() yes yes no completedrequests() yes yes no table v. independent components of the monolithic legacy system components methods employee admin poc approver employee admin poc approver create() //new request yes no no inprocessrequests() yes no no returnedrequests() yes no no editreturnedrequests yes no no rejectecdrequests() yes no no completedrequests() yes no no engineering, technology & applied science research vol. 13, no. 4, 2023, 11375-11386 11384 www.etasr.com aljaloud & razzaq: an innovative metric-based clustering approach for increased scalability … figure 12 depicts the dependency relationship with a requester component within the system. this diagram visualizes how other components rely on the requester component for certain functionalities. it highlights the integral role played by the requester component in facilitating communication and data exchange within the system. the basis for this transformation is reflected in table v, which likely served as a reference for identifying and resolving dependencies. by eliminating the dependency on the requester component, the system achieves greater independence and modularity. this architectural change enables the requester component to function autonomously, without relying on external dependencies. figure 15 represents the culmination of these efforts, illustrating the requester component as dependency-free. this revised graph demonstrates the success of the proposed method in removing dependencies and streamlining the system's architecture. the removal of dependencies offers several advantages, including enhanced flexibility, improved maintainability, and the ability to modify or update individual components without affecting the entire system's functionality. by referring to figures 12 and 15, system designers and developers can gain valuable insight into the evolution of the system's dependency structure and the resulting benefits of removing dependencies. these visual representations provide a clear understanding of the architectural improvements achieved through the proposed method, facilitating a more efficient and adaptable system design. figure 12 presents the dependency relationship between the create() method and the request component within the system. this diagram visually depicts how the create() method relies on the functionality provided by the request component. it highlights the integral role played by the request component in facilitating the execution of the create() method. the removal of dependencies between the create() method and the request component offers several benefits. it enhances the modularity and flexibility of the system, allowing for independent modifications and updates to each component without affecting the others. it also simplifies maintenance and reduces the risk of cascading failures that could arise from interdependencies. by referring to figure 13 and figure 16, system designers and developers can gain valuable insight into the evolution of the system's dependency structure. these visual representations effectively showcase the successful implementation of the proposed method in removing dependencies and optimizing the system's architecture. fig. 13. approver component dependent on the request creating method. fig. 14. employee request independent component. fig. 15. admin poc component independent from the employee request component. engineering, technology & applied science research vol. 13, no. 4, 2023, 11375-11386 11385 www.etasr.com aljaloud & razzaq: an innovative metric-based clustering approach for increased scalability … fig. 16. approver component independent from the employee request component. figure 14 provides a clear representation of the independent components within the system. it illustrates the components that are completely detached from the admin poc and approver components. this diagram effectively conveys the autonomy and independence of these components, demonstrating their ability to operate independently without relying on the admin poc and approver components. the visual depiction in figure 14 emphasizes the distinct separation of these components from the rest of the legacy system, underscoring their self-sufficiency and freedom from external dependencies. figure 15, on the other hand, showcases an independent component that is entirely detached from the employee requester component. this diagram illustrates the clear separation of this component from the employee requester component, highlighting its autonomy and self-reliance. from figure 15, it becomes evident that this independent component's methods are distinct and separate from those of the employee requester component. this delineation emphasizes the component's ability to function independently, without any reliance on the employee requester component. in contrast, figure 16 presents a component that is entirely independent of the employee requester component, but it remains dependent on the admin poc. this diagram depicts the component's autonomy and independence from the employee requester component, while also highlighting its reliance on the admin poc component. by examining figures 14-16, system designers and developers can gain a comprehensive understanding of the independence and interdependencies among components within the system. these visual representations offer valuable insight into the architecture and relationships between components, enabling informed decision-making for system optimization, modularity, and scalability. v. conclusion the current work presents a novel approach in identifying the dependent and independent components of a monolithic legacy system. this research gives awareness to understand and increase the scalability of an already developed monolithic legacy system. the favorable primary position of the proposed method is the accomplished high cohesion and low coupling of components. these useful points assume the job of tackling the issues which require software evolution. to the best of our 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[42] d. p. lupp, m. hodkiewicz, and m. g. skjaeveland, "template libraries for industrial asset maintenance: a methodology for scalable and maintainable ontologies," ceur workshop proceedings, vol. 2757, pp. 49–64, 2020. microsoft word etasr_v11_n5_pp7658-7664 engineering, technology & applied science research vol. 11, no. 5, 2021, 7658-7664 7658 www.etasr.com nagao: variation evaluation of path characteristic and site amplification factor at four sites in … variation evaluation of path characteristic and site amplification factor of earthquake ground motion at four sites in central japan takashi nagao research center for urban safety and security kobe university kobe city, japan nagao@people.kobe-u.ac.jp abstract-the considered parameters in seismic design vary, with the earthquake ground motion (egm) having the largest variation. since source characteristic, path characteristic, and site amplification factor (saf) influence the egm, it is crucial to appropriately consider their variations. source characteristic variations are mainly considered in a seismic hazard analysis, which is commonly used to evaluate variations in egm. however, it is also important to evaluate variations in path characteristic and saf with only a few studies having individually and quantitatively examined the variations of these two characteristics. in this study, based on strong-motion observation records obtained from four sites in central japan, the three characteristics were extracted from seismograms using the concept of spectral inversion. after removing the source characteristic, the path characteristic and saf were separated, and the variations in these two characteristics were quantified. to separate and obtain each characteristic from the observed record, one constraint condition must be imposed, whereas the variations in the constraint condition must be ignored. in that case, the variations in the constraint condition are included in the variations of the separated characteristics. in this study, this problem was solved by evaluating the variation in the constraint condition, which is the saf at a hard rock site, by the use of the vertical array observation record at the site. keywords-earthquake ground motion; path characteristic; site amplification factor; variation i. introduction in seismic design, the cross-section of a structure is determined in such a way that the cross-sectional resistance exceeds the section force caused by an earthquake. since the parameters to be considered in seismic design vary, the crosssection of a structure should be set considering the possibility that the seismic load acting on the structure exceeds the design value. the earthquake ground motion (egm) has the largest variation among the considered parameters in seismic design. therefore, it is critical to accurately evaluate the variation in egm. seismic hazard analysis [1] is a method for considering variations in egm. in seismic hazard analysis, probabilistic egm is evaluated by considering variations in parameters such as seismic magnitude and hypocenter location. egm is determined by three characteristics: source characteristic, path characteristic, and site amplification factor (saf). these three characteristics must be considered carefully because the egm varies significantly depending on the evaluation method of these characteristics [2]. in seismic hazard analysis, source characteristic is the major variation evaluation object, and path characteristic and saf are treated deterministically. however, since these two characteristics vary in reality, it is necessary to evaluate the variations in path characteristic and saf separately in order to conduct rational seismic design. although there are many research cases on the variation in amplification characteristics, the definitions of amplification characteristics vary, such as the ratio of spectral acceleration to the predicted value by ground motion prediction equations [3], the amplification at the object location with respect to the reference location [4], the ratio of the vertical array strong-motion observation record on the ground surface to the borehole [5, 6], and the residual of the observed egm to the probabilistically evaluated egm [7]. the saf to be considered when the egm is separated into the three characteristics must include not only the amplification by the shallow subsurface but also that by the deep subsurface, because the amplification factor by a shallow subsurface is significantly smaller than the actual saf [8, 9]. therefore, the variation in saf for each frequency, including the effect of deep subsurface must be evaluated. there are cases in which the variations of saf, including the effect of deep subsurface, were studied using the spectral ratio of seismograms observed at two sites [10, 11]. however, these studies did not separate path characteristic and saf, and because path characteristic was treated deterministically, their results included variations of path characteristic and saf. there are no case studies in which the variations in path characteristics and saf were quantified after separation. spectral inversion [12, 13] is a technique for separating each characteristic from the observed records. the current study separates path characteristic and saf based on the concept of spectral inversion and conducts quantitative evaluation of each variation. corresponding author: takashi nagao engineering, technology & applied science research vol. 11, no. 5, 2021, 7658-7664 7659 www.etasr.com nagao: variation evaluation of path characteristic and site amplification factor at four sites in … ii. method a. target sites and target earthquakes this study focuses on four sites (gifh20, gifh24, gifh28, and ngnh20) in central japan that are part of the kik-net [14] strong-motion seismograph network as shown in figure 1. kik-net provides egms recorded at the ground surface and in the borehole simultaneously, and p-s logging reveals the s-wave velocity profile leading to the seismograph installation position in the borehole. strong-motion records and ground data were made available to the public by [15]. however, seismographs in boreholes are rarely installed at seismic bedrock in which s-wave velocity exceeds 3km/s. therefore, the s-wave velocity profile from the ground surface to the seismic bedrock was obtained by combining the information from kik-net and j-shis [16] as described in [8]. the obtained s-wave velocity profiles are shown in figure 2. among the sites, gifh28 has the thickest and ngnh20 the thinnest sediment site. in gifh24, the depth at which the swave velocity exceeds 1500m/s is shallower than that in ngnh20. the multiple reflection theory calculates transfer functions assuming horizontally stratified ground conditions (figure 3). in the frequency range of 0.1–10hz, which is important in seismic engineering, the amplification factor of gifh24 is the smallest with values less than 2 in the frequency range lower than 7hz. because the soil layer thickness with an s-wave velocity of 720m/s is relatively thick (= 25m), the amplification factor is as high as 5 at 6hz in ngnh20. firstorder peaks occur at 2hz in gifh20 and 0.6hz in gifh28, in which the sedimentary layer is the thickest. fig. 1. target sites. fig. 2. s-wave velocity profiles. table i shows the list of the considered events. the epicenters of the target events, as well as the locations of the observation sites, are shown in figure 4. the red circles indicate seismograph installation sites, and the blue cross marks indicate the epicenters. the epicenters do not exist on the west side of the observation sites, but they are distributed evenly in the other directions. fig. 3. transfer functions. table i. target earthquakes no date time lon (deg) lat (deg) depth (km) m site* 1 sep/27/2020 13:13 137.80 35.10 45 5.3 b, c, d 2 apr/23/2020 13:44 137.32 35.64 3 5.5 b, d 3 feb/13/2018 14:39 137.59 35.87 3 4.1 b, c, d 4 dec/6/2017 00:13 137.97 36.38 10 5.3 b, d 5 jun/25/2017 07:02 137.59 35.87 7 5.6 b, c, d 6 dec/6/2016 09:05 137.34 36.01 5 4.5 b, c, d 7 may/25/2015 14:28 139.64 36.05 56 5.5 a, b, d 8 mar/4/2015 00:04 136.80 35.34 40 4.6 a, b, c 9 dec/3/2014 23:19 137.12 35.29 45 4.2 a, b, c, d 10 sep/16/2014 12:28 139.86 36.09 47 5.6 a, b, d 11 jun/1/2012 17:48 139.88 36.03 44 5.1 a, b, c, d 12 apr/25/2012 05:22 140.68 35.72 43 5.5 a, b, d 13 jan/28/2012 07:43 138.98 35.49 18 5.4 a, b, c, d 14 jun/30/2011 08:21 137.95 36.19 4 5.1 a, b, d 15 apr/16/2011 11:19 139.94 36.34 79 5.9 a, b, c, d 16 mar/16/2011 03:33 137.30 36.00 0 4.0 a, b, c, d * a: gifh20, b: gifh24, c: gifh28, d: ngnh20 fig. 4. target sites and epicenters. because egm records of small seismic magnitude (m) have a low signal-to-noise (s/n) ratio, events of seismic magnitude m = 4.0 or larger are considered. additionally, egm records of m = 6.0 or larger are excluded to avoid the effect of the rapture process at the fault plane. with the ω −2 model [17], only egm records with good s/n ratios in the range of 0.3hz or higher were used. to discuss the amplification characteristics of s-waves, 10.24s records were extracted for the s-wave arrival. before calculating the fourier spectra, baseline correction was conducted, and the extracted 136 137 138 139 140 141 34 35 36 37 longitude (deg) l a ti tu d e ( d e g ) engineering, technology & applied science research vol. 11, no. 5, 2021, 7658-7664 7660 www.etasr.com nagao: variation evaluation of path characteristic and site amplification factor at four sites in … records were tapered. based on the root mean square of the fourier spectra of seismograms recorded horizontally in two directions, a parzen window with a bandwidth of 0.3hz was used to smooth the spectra. b. separation method of the three characteristics the three characteristics are separated from the observed records according to the concept of spectral inversion. this study focuses on seismograms of the same event recorded at multiple stations. the fourier spectra of the observed records can be expressed as the product of the source characteristic, path characteristic, and saf as shown in (1): ij i ij j o ( f ) s ( f )p ( f )g ( f )= (1) where o is the observed egm, s is the source characteristic, p is the path characteristic, g is the saf, i is the event number, j is the station number, and f is the frequency. the values of each characteristic for each frequency can be obtained by solving the equations simultaneously using (2) in which the equation is expressed as a common logarithm. ij i ij j logo logs logp logg= + + (2) the path characteristic can be expressed by (3): ( ) 1 ij ijn ij p ( f ) exp f r / qvs r = −π (3) where r is the hypocentral distance and n is a value representing the geometric attenuation of the body wave, with its typical value being 1.0, but it is pointed out that n = 2 when the hypocentral distance is significantly long [18]. in this study, n = 2 was assumed for a dataset with hypocentral distances of 120km or more. vs is the average s-wave velocity along the propagation path, and vs = 3.8km/s in the target area. q is the q-value, which represents the inelastic attenuation of egm. there is a trade-off relationship among the characteristics: for example, a product of large path characteristics and small saf can result in the same value as a product of small path characteristics and large saf. therefore, one constraint condition must be imposed to solve the equations simultaneously. the constraint condition is set as the saf at one station and calculated as a theoretical saf assuming onedimensional (1d) ground structure [19]. the saf of a significantly small rock site is chosen for the constraint condition. however, even at rock sites, egm is amplified in many cases because of weathering [20]. furthermore, because of the heterogeneity of a three-dimensional (3d) ground structure, the saf assuming 1d ground structures often underestimates the actual saf [2, 21]. therefore, it is desirable that the saf used as a constraint condition to be as small as possible and the s-wave velocity profile down to seismic bedrock is disclosed. as shown in figure 3, the amplification factor at gifh24 is significantly small in the frequency band below 10hz, and we can assume that the difference in saf between the actual and the one calculated by assuming a 1d structure is negligible. as a constraint condition, this study uses the 1d amplification factor (1da) at gifh24. iii. results and discussion a. saf variation in low-frequency bands at hard rock sites path characteristic and saf can be separated in the spectral inversion and variations of the two characteristics can be discussed. however, the variation cannot be evaluated for the constraint condition. the constraint condition, which is the saf at the reference hard rock site, also varies. therefore, variations in the obtained characteristics include variations in the constraint conditions. because seismographs are installed at the ground surface (s) and in boreholes (b) at kik-net sites, the variation can be evaluated using the spectral ratio (s/b). however, even if the seismograph in the borehole is installed on the seismic bedrock, s/b cannot be considered as the saf because borehole records include the upward egm (e) and downward egm (f), which are reflected at the layer boundary (e + f). because e and f are identical on the ground surface, egm is 2e, and the s/b becomes 2e/(e + f). however, the saf is defined as the spectral ratio of the egm at the ground surface to that obtained by doubling the incident egm (e) at the bedrock (2e/2e). figure 5 compares the s/b (= 2e/(e + f)) with the saf (= 2e/2e) under horizontally stratified ground conditions, using gifh24 and ngnh20 as examples. the red line represents the saf, and the blue line represents the s/b. although the difference between the two is large in the frequency band higher than 1hz, it is tiny in the frequency band lower than 1hz. therefore, the variation in s/b in the frequency band lower than 1hz of these two sites is the variation in the saf. figure 6 shows the variation in s/b calculated with the observation record. the gray line represents the individual s/b and the red line represents the average value. each characteristic is separated on a logarithmic scale in the spectral inversion, as shown in (2). therefore, unless otherwise specified, these results are on a logarithmic scale hereafter. the value of s/b agrees with the theoretical value on average in the frequency band of 1hz or lower, although there is some dispersion. fig. 5. comparison of 2e/(e + f) and (2e/2e). fig. 6. variation in s/b. engineering, technology & applied science research vol. 11, no. 5, 2021, 7658-7664 7661 www.etasr.com nagao: variation evaluation of path characteristic and site amplification factor at four sites in … fig. 7. sd of s/b. figure 7 shows the standard deviation (sd) of s/b in the frequency band lower than 1hz. the sd is large in frequencies lower than 0.4hz because of the poor s/n ratio in the seismograms of small amplitude. the sd of the saf of hard rock sites in the frequency band lower than 1hz was determined to be 0.048 using the average sd in the range of 0.488 to 1.074hz. figure 8 shows the histogram of the s/b, referring to the results at frequencies 0.586 and 0.781hz. the probability distribution can be considered normal. fig. 8. histogram of s/b. b. evaluation of q-value and path characteristic variation because the variation in the saf at hard rock sites was obtained when considering the frequency band of 1hz or lower, the variation in the path characteristics can be evaluated based on the results. the q-value used to evaluate path characteristics varies by region, and its frequency dependence has been mentioned. there have been no previous studies on the q-value for the regions covered in this study, but the qvalues for other japanese regions are q = 83 f 0.73 [22] and q = 33 f 1.0 [23]. in this study, we first evaluate the q-value for the target area. based on the simultaneous records from two locations (i.e. gifh24 and ngnh20), we can evaluate the qvalue using (4) and combining (2) and (3). ( ) 10j k k j k j j k f r r log e vsq logo logo logg logg nlogr nlogr π − = − − + − + (4) where j and k are the observation stations. saf in the frequency band higher than 1hz cannot be determined at this point, but for frequencies lower than 1hz the saf of the two stations can be considered as 1.0. therefore, the q-value can be determined by (4). the q-value was obtained as in (5) regarding the average q-value for each frequency, and the minimum spectral residual, which is to be described later. q = 70 f 0.90 (5) figure 9 compares the average q-value with the value obtained by (5). the blue line represents the average q-value, and the red line represents the value according to (5). the variation in path characteristic is evaluated based on the obtained q-value. by applying (2) to the records of two sites j and k (i.e. gifh24 and ngnh20), the spectral residual (sr) is obtained as follows: j k j k j k sr logo logo log p log p logg logg= − − + − + (6) fig. 9. q-value. the sr distribution is displayed in the left panel of figure 10. the gray lines represent individual results, and the red line represents the average value. if path characteristic and saf do not vary, sr becomes zero. although the average sr is generally zero for frequencies lower than 1hz, the variation in sr is large. the sd of sr is shown in the right panel of figure 10. the average value of sd in the frequency band 0.2931.074hz was determined to be 0.184. the histograms of sr at frequencies 0.586 and 0.781hz are shown in figure 11. although the result at 0.586hz deviates from the normal distribution, the frequency distribution at 0.781hz can be considered normal. fig. 10. distribution and sd of sr. fig. 11. histogram of sr. 0.2 0.4 0.6 0.8 1 1.2 0 0.02 0.04 0.06 0.08 0.1 frequency(hz) st a n d a rd d e v ia ti o n 0.1 1 10 0 100 200 300 frequency (hz) q v a lu e engineering, technology & applied science research vol. 11, no. 5, 2021, 7658-7664 7662 www.etasr.com nagao: variation evaluation of path characteristic and site amplification factor at four sites in … this sr variation includes the variations in path characteristics and safs of the two sites. assuming that the path characteristic and saf at each site follow independent normal distributions, the following equation holds: ( )2 2 22sr p gσ = σ + σ (7) where σ is the sd. by using the sd of saf obtained in the previous section, the sd of the path characteristic was determined to be 0.121. c. saf and its variation based on the above results, the variation in saf at the site where the effect of the sedimentary layer cannot be ignored is evaluated. because the path characteristics vary slightly with frequency, the sd obtained in the previous section is assumed to be applicable at all frequencies. furthermore, because gifh24 is a site with a significantly small amplification factor in the frequency band lower than 10hz, it is assumed that the average value of saf at gifh24 agrees with the amplification factor assuming 1d ground structure (1da) considering ground structure leading to the seismic bedrock. regarding the variation in saf at gifh24, it is assumed that the sd value obtained in the previous section for the low-frequency band can be applied to all frequencies. based on the simultaneous records at gifh24 and ngnh20, saf and its variations of ngnh20 are evaluated by solving (6) for saf at ngnh20 as shown in the left panel of figure 12. the gray lines represent the individual results, and the red line represents the average value. the right panel of figure 12 shows the average value and the sd of saf. the red line represents the average value and the blue line represents the sd. the sd is less dependent on the frequency. the sd has an average value of 0.323 in the 0.195–10hz frequency band. because the sd here includes variation in path characteristics at two sites and variation in saf at gifh24, these variations are removed using the same approach as in (7). the average values of the sd of saf at ngnh20 in the frequency bands of 1–10hz and 0.195–10hz were determined to be 0.282 and 0.270 respectively. furthermore, the saf at gifh28 is discussed. the procedures are the same as in ngnh20. the left panel of figure 13 shows the saf, with the gray lines representing the individual results and the red line representing the average value. fig. 12. average and sd of saf (ngnh20). the right panel of figure 13 shows the average saf (red) and the sd (blue) lines. the sd in the frequency band higher than 2hz is slightly larger than that in the lower-frequency band. the average value of sd in the frequency band of 0.195– 10hz is 0.316. when the variation in the saf of gifh24 and path characteristics of the two sites were removed from the sd, the average value of sd of saf at gifh28 was 0.061 in the 0.195–1.1hz frequency band, 0.277 in the 1–10hz frequency band, and 0.262 in the 0.195–10hz frequency band. fig. 13. average and sd of saf (gifh28). fig. 14. average and sd of saf (gifh20). fig. 15. average sd of saf. the left panel of figure 14 shows the saf for gifh20, with gray lines representing the individual results and the red line representing the average value. the right panel of figure 14 shows the average value and sd of saf, with the red line representing the average value and the blue line the sd. the average sd in the frequency band from 0.195 to 10hz is 0.217. when the variation of the saf of gifh24 and the path characteristics of the two sites were removed from this sd, the average value of the sd of saf at gifh20 was 0.080 in the 0.195–1.1hz frequency band, 0.130 in 1–10hz, and 0.125 in 0.195–10hz. because the sd at each site varies with frequency, figure 15 shows the average sd in case of saf with frequency. the sd is small for frequencies lower than 2hz, in the range of 0.10–0.15, but a large value of approximately 0.30 can be obtained in the case of gifh28 and ngnh20 when considering frequencies higher than 3hz. however, at gifh20, the sd is almost constant in all frequency bands and is smaller than those at the other two sites. the average value of saf varies significantly with frequency at the three sites, but the sd 0 2 4 6 8 10 0 0.1 0.2 0.3 0.4 frequency (hz) s d engineering, technology & applied science research vol. 11, no. 5, 2021, 7658-7664 7663 www.etasr.com nagao: variation evaluation of path characteristic and site amplification factor at four sites in … does not vary significantly with frequency and is not dependent on the average value of saf. because the saf in the lowfrequency band is mainly determined by the deep subsurface structure, a low sd of the saf in the low-frequency band indicates a minor local change in the deep subsurface structure near the observation sites. however, the saf in the highfrequency band mainly depends on the shallow subsurface structure, implying that the shallow subsurface structure is changing in a complex manner around the site where the sd of the saf is large in the high-frequency band. however, the sites where the sds of safs do not increase even in the case of high-frequency bands, such as in gifh20, are considered to be sites at which the surrounding shallow subsurface structure does not change significantly. d. comparison of 1da and saf figure 16 compares the saf in this study to 1da used in design practice. the red line represents the average saf, the blue line represents the 1da considering shallow and deep subsurface, and the black line represents the 1da considering shallow subsurface only. note that those values are expressed on an arithmetic scale. compared to the 1da considering deep subsurface, the shallow subsurface 1da significantly underestimates the amplification factors. this result is in accordance with the findings in [8]. except for the secondorder peak at 1.5hz of gifh28, the 1da considering deep subsurface underestimates the amplification factor compared to the safs in this study. previous studies [2, 20] have also highlighted this trend. except for the very thin sediment site, ngnh20, the safs at the other two thick sediment sites have high amplification factors over a wide-frequency band, whereas 1da has large amplifications only at certain frequencies. therefore, when considering the egm amplification in seismic design, it is necessary to use a method capable of evaluating the actual amplification factors, such as spectral inversion, rather than 1da. fig. 16. saf and 1da. iv. conclusion in this study, the source characteristic, path characteristic, and saf were separated from observation records using the spectral inversion approach by utilizing the seismic records of four strong-motion observation sites in central japan. the variation in path characteristics and saf were quantified. the conclusions of this study are: • saf and path characteristic can be separated by spectral inversion by imposing a single constraint condition, namely, saf at a hard rock site. however, the variation cannot be evaluated for the constraint condition. therefore, the variations obtained for each characteristic contain the variation in the constraint conditions. in this study, the sd of the constraint condition was evaluated using the variation in the spectral ratio of seismograms at the ground surface to those in the borehole. the obtained sd of the constraint condition was 0.048. • the sds of the sr of two hard rock sites’ records were evaluated. the variation in path characteristic was evaluated by assuming that path characteristic and saf follow independent normal distributions. the sd of the path characteristic was estimated to be 0.121. finally, the variation in the saf was evaluated. the sd of the saf was independent of the average saf and ranged from 0.10 to 0.15 in the frequency band of 2hz or lower. in the highfrequency band, the sd of saf was approximately 0.30 at gifh28 and ngnh20 and approximately 0.10 at gifh20. the sd in the high-frequency region varies significantly from point to point. this difference in sd is due to the difference in the uniformity of the shallow subsurface around the site. • the 1da underestimates the saf even when the ground structure down to the seismic bedrock is considered. at thick sediment sites, large saf is observed in a widefrequency band, and the envelope of the saf is completely different from that of the 1da. therefore, precise evaluation of the saf is critical for rational seismic design. acknowledgment strong-motion records and ground data were provided by the national research institute for earth science and disaster resilience. data-sorting was aided by yusuke yamane. yasuhiro fukushima helped us evaluate the hypocentral distances. references [1] n. a. abrahamson, "state of the practice of seismic hazard evaluation," presented at the isrm international symposium, nov. 2000, art. no. isrm-is-2000-014. [2] t. nagao and y. fukushima, "sourceand site-specific earthquake ground motions: application of a state-of-the-art evaluation method," engineering, technology & applied science research, vol. 10, no. 4, pp. 5882–5888, aug. 2020, https://doi.org/10.48084/etasr.3612. [3] n. morikawa et al., "strong motion uncertainty determined from observed records by dense network in japan," journal of seismology, vol. 12, no. 4, pp. 529–546, oct. 2008, https://doi.org/10.1007/s10950008-9106-2. [4] k. kato, k. aki, and m. takemura, "site amplification from coda waves: validation and application to s-wave site response," bulletin of the seismological society of america, vol. 85, no. 2, pp. 467–477, apr. 1995. [5] t. satoh, h. kawase, and t. sato, "evaluation of local site effects and their removal from borehole records observed in the sendai region, japan," bulletin of the seismological society of america, vol. 85, no. 6, pp. 1770–1789, dec. 1995. 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[8] t. nagao, "seismic amplification by deep subsurface and proposal of a new proxy," engineering, technology & applied science research, vol. 10, no. 1, pp. 5157–5163, feb. 2020, https://doi.org/10.48084/etasr. 3276. [9] t. nagao, "maximum credible earthquake ground motions with focus on site amplification due to deep subsurface," engineering, technology & applied science research, vol. 11, no. 2, pp. 6873–6881, apr. 2021, https://doi.org/10.48084/etasr.3991. [10] y. fukushima and t. nagao, "variation of earthquake ground motions with focus on site amplification factors: a case study," engineering, technology & applied science research, vol. 9, no. 4, pp. 4355–4360, aug. 2019, https://doi.org/10.48084/etasr.2856. [11] t. nagao and p. lu, "a simplified reliability estimation method for pilesupported wharf on the residual displacement by earthquake," soil dynamics and earthquake engineering, vol. 129, feb. 2020, art. no. 105904, https://doi.org/10.1016/j.soildyn.2019.105904. [12] d. j. andrews, "objective determination of source parameters and similarity of earthquakes of different size," in earthquake source mechanics, washington dc, usa: american geophysical union (agu), 1986, pp. 259–267, https://doi.org/ 10.1029/gm037p0259. [13] t. iwata and k. irikura, "source parameters of the 1983 japan sea earthquake sequence," journal of physics of the earth, vol. 36, no. 4, pp. 155–184, 1988, https://doi.org/10.4294/jpe1952.36.155. [14] s. aoi, k. obara, s. hori, k. kasahara, and y. okada, "new strongmotion observation network : kik-net," eos, transactions, american geophysical union, vol. 81, 2000. [15] strong-motion seismograph networks (k-net, kik-net). https://www.kyoshin.bosai.go.jp/ (accessed sep. 10, 2021). [16] h. fujiwara, s. kawai, k. x. hao, n. morikawa, and h. azuma, "jshis an integrated system for sharing information on national seismic hazard maps for japan," in 16th world conference on earthquake, santiago chile, jan. 2017, art. no. 0372. [17] k. aki, "scaling law of seismic spectrum," journal of geophysical research (1896-1977), vol. 72, no. 4, pp. 1217–1231, 1967, https://doi.org/10.1029/jz072i004p01217. [18] k. aki and p. g. richards, quantitative seismology, 2nd ed. mill valley, ca, usa: university science books, 2009. [19] s. drouet, p. triantafyllidis, a. savvaidis, and n. theodulidis, "comparison of site-effects estimation methods using the lefkas, greece, 2003 earthquake aftershocks," bulletin of the seismological society of america, vol. 98, no. 5, pp. 2349–2363, oct. 2008, https://doi.org/10.1785/0120080004. [20] j. h. steidl, a. g. tumarkin, and r. j. archuleta, "what is a reference site?," bulletin of the seismological society of america, vol. 86, no. 6, pp. 1733–1748, dec. 1996. [21] y. fukushima, t. nagao, j. oshige, and i. suetomi, "ground motion evaluation for intra-plate earthquake by different site amplification factors and source models," in 7th international conference on earthquake geotechnical engineering, roma, italy, jun. 2019, pp. 2484–2492. [22] k. yoshimoto, h. sato, and m. ohtake, "frequency-dependent attenuation of p and s waves in the kanto area, japan, based on the coda-normalization method," geophysical journal international, vol. 114, no. 1, pp. 165–174, jul. 1993, https://doi.org/10.1111/j.1365246x.1993.tb01476.x. [23] a. moya, j. aguirre, and k. irikura, "inversion of source parameters and site effects from strong ground motion records using genetic algorithms," bulletin of the seismological society of america, vol. 90, no. 4, pp. 977–992, aug. 2000, https://doi.org/10.1785/0119990007. microsoft word etasr_v12_n2_pp8416-8420 engineering, technology & applied science research vol. 12, no. 2, 2022, 8416-8420 8416 www.etasr.com fathy: interfacial microstructure and bonding area of sn-based alloy-gg25 gray iron bimetallic … interfacial microstructure and bonding area of snbased alloy-gg25 gray iron bimetallic material using flux, sn, and sn-zn interlayer compound casting naglaa fathy department of physics college of science university of hail hail, saudi arabia naglaaf2002@yahoo.com received: 4 february 2022 | revised: 23 february 2022 | accepted: 2 march 2022 abstract-a bimetallic casting consisting of gg25 gray iron substrate and sn-based alloy using the liquid-solid technique has been studied in this paper. three different pretreatment processes of gray iron surface substrates including flux only, flux and sn powder, and flux and sn-8.8% zn powder eutectic alloy surface treatment were adopted for the aim of improving the quality of tinning, the interfacial structure, and the bonding area of the sn-based alloy/gray iron bimetallic composite in order to promote the bonding quality of bimetallic castings. microstructure characterization on the bonding interface was conducted. the novel tinning material for gray cast iron substrate comprising of sn-8.8% zn eutectic alloy powder in combination with flux interlayer improved the bonding area, the interfacial bimetal structure, and the shear stress. this improvement is due to the higher interface reaction of zn with fe that leads to the formation of a very thin layer of fe-zn and fesn intermetallic phases. keywords-sn-based alloy; gg25 gray iron; flux; sn-zn; bimetal; interface i. introduction nowadays, manufacturing techniques are more focused on fabricating materials of superior properties and the facilitation of their fabrication techniques. despite the intensive development of cast metal’s structure and properties, the possibilities of the existing monometallic alloys are practically exhausted for fabricating new materials of superior properties [1-3]. liquid-solid compound casting has been used to fabricate different ferrous and nonferrous functionally graded materials, and is considered the most economical fabrication process, which allows the fabrication of bimetal materials directly [4-8]. for bimetallic bearing materials, higher bonding strength is still required to meet the industrial application demands. more effort on the enhancements of the bimetallic composites interfacial structures and bonding area should be considered. the tin-based snsb8cu3 alloy is one of the most common bimetallic bearing materials used in thrust bearings with substrate shells. carbon steel alloys are commonly used as shell substrates in liquid-solid compound casting techniques [812]. although the gray cast iron has unique mechanical properties, it has limited applications in the liquid-solid compound casting as solid shells due to its free graphite flacks. gray iron is well known as flack graphite iron in which the graphite is present in a matrix of ferrite, pearlite, or ferritepearlite. compared with carbon steel substrates, the relatively higher silicon and carbon content, as well as the production processing parameters of gray iron, make eutectic graphite separate from the molten iron. as solid bimetal shells, grey irons have been used in liquid-solid configuration casting [13, 14]. the interfacial bonding strength of sn-based alloy/grey iron was investigated for bimetal composites fabricated by centrifugal casting process in [13]. in addition, al-si alloy/grey iron bimetallic composite has been fabricated. the optimum shear strength was achieved with the assist of hot dipping of the solid iron in a zn–0.2 wt. % bi melt [14]. in the current study, the sn-zn eutectic alloy was used due to its physical and mechanical properties. the sn-zn eutectic system is a promising candidate for the replacement of sn-pb solders due to its melting temperature (198°c), which is very close to the sn-pb eutectic alloy melting temperature (183°c), so it is suitable for electronic components without major modifications [15]. in addition, the sn-8.8% zn eutectic lower melting temperature is favorable and the cost of production is relatively low compared with other sn-ag and sn-in soldering materials [16]. for the aim of improving the interfacial structure and bonding area of sn-based alloy/gray iron bimetallic composite, the gray iron surface substrate is prepared using three pretreatment processes. gray iron surface substrates are treated with flux only, flux + sn powder, and flux + powder sn-8.8% zn eutectic alloy. the proposed sn-zn corresponding author: naglaa fathy engineering, technology & applied science research vol. 12, no. 2, 2022, 8416-8420 8417 www.etasr.com fathy: interfacial microstructure and bonding area of sn-based alloy-gg25 gray iron bimetallic … interlayer of sn-based alloy/gg25 gray iron bimetallic material using the tinning process is considered as an alternative new interlayer material designed for fast, easy, high bonding interface and low-cost surface improvement of the gray iron solid substrate. this newly designed sn-based alloy/gg25 gray iron with sn-zn interlayer is more suitable for bimetallic materials of flat and horizontal solid substrates. ii. experimental work the sn-based alloy/gg25 gray iron bimetallic composite specimens were prepared using the liquid-solid compound casting technique. sn-8.8% zn interlayer alloy samples were prepared by melting pure sn (99.97%), and pure zn (99.95%) in graphite crucibles using an electrical muffle furnace. the alloys were melted 2 times to ensure uniform mixing of the elements. table i shows the chemical compositions of the snbased alloy and the gg25 gray iron substrate used for the snbased alloy/gg25 gray iron bimetallic composite fabrication. table i. chemical compositions chemical composition c si mn cu pb sb sn fe sn-based alloyastm b-23grade2 3.04.0 0.00.35 7.08.0 bal g.g 25 gray iron substrate 3.03.25 1.852.10 0.40.7 bal. gray iron substrate specimens of solid cylindrical shape of 25.4mm diameter and 5.5mm thickness were cut and ground with up to 800 grades emery papers. the specimens were tinned with pure sn and with sn-8.8% zn alloy. the direct pretinning process of the gray iron substrate that involves sn powder or sn-zn alloy and flux mixture has been explained in detail in [17–18]. the current flux is fabricated with a mixture of chemicals listed in table ii mixed with the pure tin or sn-zn powders. the sn to flux ratio is 1:10 (1g of sn and 10g of flux). the necessity of using flux in the tinning process during bimetal fabrication is to remove the oxides for the sake of allowing the sn or sn-zn to stick directly to the gray iron surface. table ii. flux chemical composition wt.% ml zncl2 nacl2 nh4cl hcl h2o 24 gm 6 gm 3gm 1ml 1ml in order to study the effect of different pretreatments of gray iron surface on the quality of tinning, the interfacial structure and the bonding area of the sn-based alloy/gray iron bimetal, three groups of specimens were fabricated. • the first group of sn-based alloy/gray iron bimetal was produced by pretreated gray iron substrate with flux only. • the second group was produced by pretreated gray iron substrate with flux + sn (1g of sn powder and 8g of flux). • the third group was produced by pretreated gray iron substrate with flux + sn -8.8% zn (1g of sn-8.8% zn powder,8g of flux). during the tinning process, 0.2gm/cm 2 of flux and sn or sn-zn mixture was distributed on the gray iron shell substrate. then the substrate was placed on a preheated hot plate of 360 o c for 3min. after heating, the gray iron was removed from the hot plate and the tinned surface as cleaned using a towel and tap water and left to cool to room temperature. sn-based alloy with the chemical composition shown in table i was melted on a hotplate at 370 o c and after 30min the crucible of molten metal was removed from the hotplate and was poured onto a ceramic mold that contained a preheated (370 o c for 3min) tinned gray iron substrate. the volume of liquid snbased alloy to gray iron substrate ratio was kept to 3:1 for all casting groups. fig. 1. sn-based alloy/gg25 gray iron bimetallic casting: (a) gray iron substrate after cutting and grinding, (b)-(c) gray iron substrate during tinning with a hot plate, (d) gray iron substrates after tinning, (e) inserting the tinned gray iron substrate into the ceramic mold, (f) pouring the molten sn-based alloy onto the ceramic mold. the microstructure of the sn-based alloy/gray iron bimetal, especially the interfaces region between the alloy and the gray iron substrate was examined with an olympus optical microscope with a maximum magnification of 1000x. the optical examination was conducted after grinding, polishing, and etching with 4% nital to define interlayers, lack of bonding, and voids. measurements of the as-cast specimens of the three groups of the sn-based alloy/gray iron bimetal composites were taken. iii. results and discussion a. macro-and micro-structures of base bimetallic materials figure 2 shows photographs of the sn-based alloy/gg25 gray iron bimetal composite specimens and the cross section of the three fabricated specimens. clear and regular bimetal interface for gray iron substrate treated with pure sn and sn8.8% zn alloy and an irregular bimetal interface for the gray iron substrate treated with flux only were monitored. microstructures of the materials used in the fabrication of tin-based alloy/gray cast iron bimetallic composite are shown in figure 3. figure 3(a) shows the optical microstructure of snengineering, technology & applied science research vol. 12, no. 2, 2022, 8416-8420 8418 www.etasr.com fathy: interfacial microstructure and bonding area of sn-based alloy-gg25 gray iron bimetallic … based alloy revealing cu6sn5 and snsb phases reinforced in the solid solution of the sn matrix. the cu6sn5 phase has the shape of asterisks. the microstructure of a matrix of solid solution with hard-embedded phases of cu6sn5 and snsb make a metal matrix composite possessing fatigue-resistant properties [19– 21]. fig. 2. (a) sn-based alloy/gg25 gray iron bimetal composite specimens, (b) cross sections of three specimens. fig. 3. microstructures of (a) tin-based babbitt alloy and (b) gray cast iron substrate, used for preparing the bimetallic casting. previous studies [22–24] reported that the variation in the chemical composition of tin-based alloy modifies the microstructure. tin-based alloys containing less than 8% sb are characterized by a solid solution with distributed asterisks and needles of cu6sn5, copper-rich constituents, and fine precipitates of sbsn. on the contrary, the tin-based alloys containing greater than 8% sb exhibit a primary cuboid phase of sbsn. the microstructure of sn-based babbitt alloy acquired in the present study is in good agreement with those available in the literature [22–24]. the microstructure of gray cast iron substrate (figure 3(b)) shows the three common phases of ferrite, pearlite, and free graphite. the higher percentage of the pearlite verifies the mn and cu content in the gray cast iron chemical composition. b. microstructures of interfacial sn-based alloy/gray cast iron bimetallic composites the microstructures of the interfaces of bimetallic composites containing tin-based alloy/gray cast iron substrate with different surface pre-treatments of gray cast iron solid substrates are shown in figure 4. visual observation of the interfacial microstructures of the bimetallic interface fabricated using flux only shows poor bonding between the two metallic parts (figure 4(a)). some small voids were observed in the interface area of bimetal composites fabricated using flux + sn interlayer (figure 4(b)). a uniform interfacial bonding free of defects is observed in bimetallic composites fabricated using flux + sn8.8% zn alloy (figure 4(c)). tin-based alloy/gray cast iron composites fabricated with flux + sn-8.8% zn alloy revealed a good quality of interfacial bonding compared with other previous gray cast iron pre-treatment conditions. figure 5 shows the interfacial bonded areas of the three fabricated snbased alloy/ gray cast iron bimetallic composites with three different surface pre-treatments of gray cast iron solid substrate. it can be seen that substrate treated with flux only has the lowest value, while the substrate treated with flux + sn shows comparable results. gray cast iron substrate treated with flux + sn-8.8% zn exhibited a comparatively higher value. both fesn2 and fesn intermetallic compounds (imcs) could be formed in temperatures ranging from 300 to 500°c. fe-zn coating grows because of a rather complicated process of atomic diffusion of both metals with the formation of elementary intermetallic bonds and subsequent phase transformations. layers consisting of these compounds have different compositions and thicknesses. they are usually marked with greek alphabet letters, i.e. gamma (γ), gamma1 (γ1), delta (δ), zeta (ζ), and sometimes eta (η). individual phases differ significantly not only by composition and morphology of the grain but also by mechanical characteristics. the formation of individual phases in the coating is ruled by the binary phase diagram fe – zn shown in [25-27]. fig. 4. optical microstructure interfaces of tin-based alloy/gray cast iron specimens with different interlayer compositions: (a) flux only, (b) flux with sn, (c) flux with sn-8.8% zn alloy. engineering, technology & applied science research vol. 12, no. 2, 2022, 8416-8420 8419 www.etasr.com fathy: interfacial microstructure and bonding area of sn-based alloy-gg25 gray iron bimetallic … 1 2 3 0 20 40 60 80 100 substrate treated with fulx + sn-8.8% zn alloy substrate treated with fulx + sn substrate treated with fulx only bonding area % fig. 5. sn-based alloy/ gray cast iron bimetallic interfacial bonded areas as a function of interlayer pre-treatment compositions for the 3 sample groups. c. mechanical properties of sn-based alloy/gray cast iron bimetallic composites the shear strengths of the sn-based alloy/gg25 gray iron bimetallic composites with sn and sn-8.8% zn interlayer compositions are shown in figure 6. the shear strength of the bimetal fabricated with sn-8.8 % zn interlayers is significantly more by 20% than the one fabricated with sn interlayer, which is mainly due to the improvements of the interface bond area of sn-8.8% zn interlayers. fig. 6. shear stress-strain curves of the tin-based alloy/gray cast iron specimens with sn and sn-8.8% zn interlayer compositions. iv. conclusion in this paper, bimetallic specimens of sn-based alloy/gray cast iron were successfully prepared by liquid-solid compound casting after depositing the molten sn-based alloy on the solid gray cast iron substrate. a novel tinning material for gray cast iron substrate comprising of the sn-8.8% zn eutectic alloy powder in combination with flux was performed. sn-8.8% zn eutectic alloy interlayer improved the bonded area and interfacial bimetal structure, due to the higher interface reaction of zn with fe that led to the formation of very thin fe-zn and fe-sn intermetallic phases. higher shear stress was achieved using sn-8.8% zn interlayer as tinning material. the optimum zn content in snzn alloy interlayer should be considered for future work in order to optimize the fabrication of sn-based alloy/gray cast iron bimetallic composite with high quality and long life bimetal bonding. acknowledgement the author would like to thank dr. mohamed ramadan of mechanical engineering department, university of hail for the useful discussions and the technical support. references [1] m. ramadan and n. fathy, "solidification microstructure of rheocast hyper‐eutectic al–18si alloy," journal of metallurgical engineering, vol. 2, no. 4, pp. 149–154, 2013. 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[20] n. p. barykin, f. a. sadykov, and i. r. aslanian, "wear and failure of babbit bushes in steam turbine sliding bearings," journal of materials engineering and performance, vol. 9, no. 1, pp. 110–115, oct. 2000, https://doi.org/10.1361/105994900770346367. [21] f. a. sadykov, n. p. barykin, i. sh. valeev, and v. n. danilenko, "influence of the structural state on mechanical behavior of tin babbit," journal of materials engineering and performance, vol. 12, no. 1, pp. 29–36, oct. 2003, https://doi.org/10.1361/105994903770343448. [22] r. r. dean and c. j. evans, "plain bearing materials: the role of tin," tribology international, vol. 9, no. 3, pp. 101–108, mar. 1976, https://doi.org/10.1016/0301-679x(76)90032-3. [23] g. c. pratt, "materials for plain bearings," international metallurgical reviews, vol. 18, no. 2, pp. 62–88, mar. 1973, https://doi.org/ 10.1179/imtlr.1973.18.2.62. 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[27] l. zhu, s. honrao, b. rijal, r. g. hennig, and m. v. manuel, "phase equilibria and diffusion coefficients in the fe-zn binary system," materials & design, vol. 188, nov. 2020, art. no. 108437, https://doi.org/10.1016/j.matdes.2019.108437. microsoft word etasr_v12_n1_pp8086-8089 engineering, technology & applied science research vol. 12, no. 1, 2022, 8085-8089 8085 www.etasr.com bashir et al.: understanding the seepage behavior of nai gaj dam through numerical analysis understanding the seepage behavior of nai gaj dam through numerical analysis afsheen bashir us-pakistan center for advanced studies in water mehran university of engineering and technology jamshoro, sindh, pakistan afsheenbasheer@yahoo.com rabia chaudhry phd researcher/expert in geotechnical engineering water & power development authority punjab, pakistan rabiach100@gmail.com abdul latif qureshi us-pakistan center for advanced studies in water mehran university of engineering and technology jamshoro, sindh, pakistan alqureshi.uspcasw@faculty.muet.edu.pk uroosa memon us-pakistan center for advanced studies in water mehran university of engineering and technology jamshoro, sindh, pakistan uroosamemon11@gmail.com naraindas bheel department of civil and environmental engineering universiti teknologi petronas perak, malaysia naraindas04@gmail.com abstract—this study presents the seepage patterns of earth-fill dams, using critical situations by employing the finite element approach. the nai gaj dam is 65km northwest of dadu city in sindh province, pakistan. in this study, the seepage through the main dam body and foundation is computed and simulated for different scenarios, i.e. maximum, normal, and minimum reservoir level. seepage analysis was conducted by using the seep/w sub-program of geo-slope software. dam design parameters and dam geometry data were used as input data to compute the unknown seepage. the seepage behavior of the nai gaj dam is shown in terms of net flow which consists of equipotential lines, streamlines, velocity vectors, and phreatic lines. the results show the seepage flux, maximum seepage, and exit gradient at different reservoir levels. the results show that the average flow rate at normal, maximum, and minimum reservoir levels are 1.49×10 -7 cumec/m, 3.38×10 -7 cumec/m, and 2.108×10 -8 cumec/m respectively. in addition, the overall stability of the side slope of the dam is discussed. keywords-seepage; earth fill dam; phreatic line; seep/w; finite element modelling i. introduction pakistan is basically an agricultural country. the agriculture in pakistan depends mainly on water irrigation. in this regard, many dams have been constructed in the past and some others are planned to be constructed in the future. embankment dams are important and costly civil engineering structures that provide an essential infrastructure for the management of water [1, 2]. one of the critical aspects of dam design is the analysis of stability and safety of the earth structure under various operating conditions. dams are built for specific functions, i.e. storage of water for domestic use and irrigation, flood control, entertainment, fishing, and hydroelectric power generation. design and construction of dams have to meet safety criteria and satisfy specific requirements. stability of the dam against slope failure is an essential component for the design, operation level under all flood and drought circumstances [3, 4]. the estimated number of the earth fill dams around the world is 11192 [5, 6]. a review of historical dam failures indicates that nearly half of all failures of embankment dams have occurred due to seepage induced internal erosion. detailed studies of seepage analysis through and beneath the dam body need to be parts of design, construction, and maintenance of any dam component. most geotechnical studies related to dams involved seepage and stability analysis considering the pore pressure variations in unsaturated soil conditions. seepage failures occur by rainfall or water infiltration that changes the distribution of pore water pressure. this effect leads to changes in the stress and affects the seepage process of the soil. an analyst must have a good understanding of seepage, its solutions, and the preventive measures for its monitoring. finite element analysis is extensively used in the geotechnical studies for seepage and stability analysis considering the pore pressure variations. in case of dam seepage, failures occur by rainfall or water infiltration that changes the distribution of pore water pressure. this effect leads to changes in the stress and affects the seepage process of the existing soil. to make the dam safe, it is important to take great care on stability and seepage control corresponding author: naraindas bheel engineering, technology & applied science research vol. 12, no. 1, 2022, 8085-8089 8086 www.etasr.com bashir et al.: understanding the seepage behavior of nai gaj dam through numerical analysis while designing embankment dams. embankment dams are generally constructed with various zones of materials such as two permeable shells and impermeable core in the middle [7]. the main reasons behind embankment dams’ failures are seepage, hydraulic failures, piping through the dam body, and structural damage due to earthquakes [8]. permeable materials such as gravel or coarse sand when used in dam foundation lead to heavy seepage [5, 9-11]. in the past, embankment dams mostly faced seepage problems. as water in the reservoir seeks the paths of least resistance through the dam body and its foundation, it may pose some hazards on the dam safety. excessive seepage may lead to dam failure if it is not treated and controlled properly. if seepage flow can continue unhindered in appreciable quantities, then the seepage force may erode fine soil particles and wash them out causing piping failure of the dam or create uplift problems. seepage, therefore, may be considered as one of the most common safety hazards for embankment dams. the basic problem the designers and operators face are to discern how seepage is affecting a particular dam and what measures, if any, must be taken to ensure that the seepage does not unfavourably affect the safety of the dam. this paper presents a case study of the nai gaj dam and highlights the probability of pre and post seepage issues. the seep/w geo-slope software was utilized. it can work quite well on seepage analysis in homogenous and nonhomogenous embankment dams [12]. slope stability analysis confirms the safety of the embankment dam. different loading conditions can be studied, for example end of construction, steady state, rapid draw down, and the earthquake loading scenario. the aim of this study is to analyze the steady state seepage behavior of the dam foundation of the nai gaj dam for various scenarios, namely normal, maximum, and minimum reservoir level conditions. in addition, the stability of the dam was analyzed. ii. description of the study area nia gaj dam is located on the gaj river in the kirther mountain range. it is located 65km north-west of the dadu city, sindh province. the purpose of the dam project is to provide irrigation to agriculture lands downstream of the dam. the foundation rocks of this dam project are generally weak and fragile. sandstone and silty sandstone beds encountered at the core trench are weak and friable with jointings and open bedding planes [13, 14]. these rock characteristics may indicate poor rock conditions, low shear strength, and probability of increased seepage through the foundation [15]. iii. materials and methods initially, the cross section of the dam was drawn in cad format and imported in seep/w as shown in figure 1. the material zones in the dam are sandy gravel, random fill, central impervious clay core, sand filter, coarse filter, and drainage blanket. the foundation of the dam mainly consists of sandy siltstone. the dam is 59m high, 1137m long, having a maximum design water level of 56.6m with 10m crest width. the core has an upstream side slope of 1h:3v, and a downstream slope of 1h:4v. the upstream and downstream shoulders have slopes 1v:2.5h. drainage features, including a chimney drain and horizontal drainage blanket below the downstream shell, have been incorporated in the design to relieve the pore water pressure within the dam body and to dispose the seepage water in a safe manner to prevent erosion and boiling. numerical analysis was carried out on a typical section of the dam. a nonhomogenous section is selected for the analysis of the response of complex materials by varying the water levels in order to understand and analyze the seepage phenomenon. the physical, mechanical and index characteristics of the materials were taken from the references mentioned in table i. these material properties were assigned to the finite element model of the dam. the generated fem mesh is shown in figure 2. dirichlet and neumann boundary nodes were assigned at the inlet and outlet boundary conditions [16, 17]. it was accepted that the discharge is gravity driven flow while the capacity changes due to water compressibility, soil structure compressibility, and changes in matric suction (i.e. drainage), in spite of the fact that soil structure compressibility is related to pore water pressure changes. subsequently, all the stresses inside the domain are accepted as constant. no loading and unloading of soil mass is included. once the required data were imported to the seep/w, it verified the mesh development (7047 nodes and 6913 elements). therefore, now the model can be used for simulations and analysis of the results. fig. 1. x-section of th enai gaj dam. cl crest el=184.00 1 2.50 2.50 1 d / s u / s 1 4 1 3 h.f.l el=181.700 mcl=177.50 1 2 4a 5r2 5r1 3 4b 2 6 7 consolidation grouting curtain grouting engineering, technology & applied science research vol. 12, no. 1, 2022, 8085-8089 8087 www.etasr.com bashir et al.: understanding the seepage behavior of nai gaj dam through numerical analysis fig. 2. mesh formation for the selected non-homogeneous section. results are generated for the following scenarios: (i) normal reservoir level (150m), (ii) maximum reservoir level (177.5m), and (iii) minimum reservoir level (130m). the boundary conditions which are used in the analysis are: • dirichlet and neumann boundary nodes are assigned at the inlet and outlet boundary conditions [17]. • zero flux (neuman) condition is considered as the boundary node at the bottom of foundation for the all the given conditions. the results are analyzed in terms of development of net flows for different scenarios, along with velocity vectors, quantity of seepage value through the core and foundation of the dam for different scenarios, and exit gradient. in addition, the stability of the dam was determined based on slope stability analysis. a. fundamental equations in this study, finite element method is used for the modelling of the groundwater flow in porous media by utilizing the following differential equations to analyze the seepage through the body of the dam at its foundation. equations are derived on the principle of mass conservation law [17, 18]. the partial differential equation (1) is used in seep/w: � �� (kx �� �� � + � �� � �� �� � � � �� �� (1) where h is the hydraulic head, kx and ky are the horizontal and vertical hydraulic conductivity respectively, q is the discharge, t is the time θ-domain and volumetric water content. the above equation is a two-dimensional and nonlinear 2 nd order pde and is used for transient flow. it is derived from darcy’s law: v = − k ∇h (2) where: ∇h � � �� ���� �� � (3) where v is the darcian velocity, k is the hydraulic conductivity of the soil material, and ∇h is the hydraulic gradient. equation (1) is dependent on time, and tells that the flow that enters an elemental volume minus the flow leaving the elemental volume at a point is equal to the volumetric water content at that point. if the volume of water that enters is equal to the volume of water that leaves at steady state situations, then the right side of (1) becomes equal to zero. � �� ( kx �� �� � + � �� � k� �� �� � � q � 0 (4) iv. results and discussion the material properties which are used in the selected dam sections were taken from past studies and from a feasibility report on the nai gaj dam [19]. the inherent material parameters used in the dam are presented in table i. the mesh was generated by seep/w and got a no error report for further computations. also, the given upand down-stream boundary conditions were assigned. the physical and mechanical parameters of the materials during the time of construction were adopted. slope/w then verified the development model and found no error in the generation of the numerical model. table i. inherent material parameters of the nai gaj dam [1, 19-23] dam component material unit weight (kn/m 3 ) cohesion (kpa) friction angle (deg) hydraulic conductivity (m/day) c ᴓ foundation sandy siltstone 20.4* 12 29* 0.00063* upstream sandy gravel 21.5** 0 37* 86.4*** downstream random fill 18.85* 0 34* 0.0263* downstream shell riprap 19.5* 0 34* 8640*** core clay 18.85* 9.57 30* 0.000263* filter blanket sand filter 18.85* 0 36* 26.33* the seepage analysis of the nai gaj dam and its foundation at different reservoir levels was conducted with the use of the seep/w. it is assumed that the downstream drain will drain out the seepage and no seepage will develop downstream. for this purpose, flow net has been drawn as shown in figures 3-5 for the selected dam sections. it was found that if the reservoir is kept at 150m and 130m there is no pronounced seepage observed. engineering, technology & applied science research vol. 12, no. 1, 2022, 8085-8089 8088 www.etasr.com bashir et al.: understanding the seepage behavior of nai gaj dam through numerical analysis fig. 3. flow net of the selected section at maximum reservoir level (177.5m). fig. 4. flow net of the selected section at normal reservoir level (150m). fig. 5. flow net of the selected section at minimum reservoir level (130m). table ii. calculated seepage flux and exit gradient upstream reservoir level (m) water head (m) seepage flux (cumec/m) f o u n d a ti o n 177.5 (max) 177.5 1.29 x 10 -7 150 (normal) 150 4.53 x 10 -8 130 (min) 130 6.92 x 10 -9 c o r e 177.5 (max) 177.5 3.38 x 10 -7 150 (normal) 150 1.49 x 10 -7 130 (min) 130 2.106 x 10 -8 the exit gradient was calculated at the downstream toe of the dam for 3 reservoir levels, i.e. 177.5, 150, and 130 m (table iii). the factor of safety against piping is described as follows: fs = critical hydraulic gradient/exit gradient (5) the value of the critical hydraulic gradient is taken as 1. a dam is considered as safe against piping, if the value of the factor of safety is between 4 and 5. the results indicate that the values of factor of safety for normal, average, and maximum water level are 7, 6, and 5 respectively. this shows that the dam is safe against piping failure even at the maximum reservoir level of 177.5m. table iii shows that the exit gradient of the selected section was mostly found less than 1 for all the water levels which conforms the safety criteria of the dam. it further support the current design of the dam. from tables ii and iii, it can be observed that both the exit gradient and seepage flux are functions of water level. generally, the stability of a slope at the downstream embankment is critical at steady state seepage condition. it is assumed that the steady seepage condition may develop when the reservoir is full at maximum retention level, i.e. at el 177.5m. the phreatic surface is estimated using the flow net development by the seep/w program. furthermore, to support the outcomes, deterministic slope stability analysis was engineering, technology & applied science research vol. 12, no. 1, 2022, 8085-8089 8089 www.etasr.com bashir et al.: understanding the seepage behavior of nai gaj dam through numerical analysis performed for different loading conditions, such as the end of construction and steady state seepage. the material properties used are mentioned in table i and the results were discussed in terms of their factor of safety as shown in table iii. the computed foss at different loading conditions were further compared with the usace standards [24]. it was noted that in slope stability analysis, the computed foss for different loading conditions are greater than the standard values which indicates safety of the side slopes of the dam as given in table iii. table iii. exit gradient and factor of safety against piping upstream pond level (m) exit gradient (m) factor of safety against piping 177.5 (max) 0.19 5 150 (average) 0.16 6 130 (normal) 0.14 7 table iv. factor of safety load slope static equilibrium condition required* computed end of construction downstream 1.30 1.7 steady state condition downstream 1.50 1.8 v. conclusion in this paper, seepage analysis of nai gaj dam was carried out with the sub program seep/w of the geo-slope software. the flow rates of the seepage computed at the core of the dam at maximum (177.5m), normal (150m), and minimum (130m) reservoir level were found to be 1.49×10 -7 cumec/m, 3.38×10 -7 cumec/m, and 2.108× 10 -8 cumec/m respectively. it was observed that as the reservoir level increased, the seepage quantity also increased. for the three tested scenarios of the reservoir level, the value of the exit gradient was found to be less than 1 which confirms that the dam is safe against piping due to seepage. in addition, slope stability analysis shows that the dam is stable at the end of construction and at steady state seepage condition. acknowledgement the authors are thankful to the us-pakistan center for advanced studies in water, mehran university of engineering and technology, jamshoro, sindh, pakistan for providing the facilities to carry out this research 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[24] slope stability. washington, dc, usa: usace, 2003. engineering, technology & applied science research vol. 8, no. 1, 2018, 2399-2404 2399 www.etasr.com tiecher et al.: alkali-aggregate reaction: a study of the influence of the petrographic characteristics … alkali-aggregate reaction: a study of the influence of the petrographic characteristics of volcanic rocks francieli tiecher polytechnic school of civil engineering imed passo fundo brazil francieli.bonsembiante@imed.edu.br marcia e. b. gomes department of geology universidade federal do rio grande do sul porto alegre, brazil marcia.boscato@ufrgs.br denise c. c. dal molin department of civil engineering universidade federal do rio grande do sul porto alegre, brazil dmolin@ufrgs.br abstract—when the rock involved in the alkali-aggregate reaction (aar) is volcanic, the matter present in the interstices of the grains, called mesostasis is considered responsible for the expansions. mesostasis is a residue which consists of mineral phases rich in silica and alkalis (k and na) and in optical microscopy looks like amorphous matter. by means of scanning electron microscopy (sem) and with the aid of energy dispersive spectroscopy (eds), the presence of well-crystallized mineral phases in mesostasis can be observed. the objective of this study was to evaluate the amount, the chemical composition and the degree of crystallinity of mesostasis on the reactive potentiality of volcanic rocks. keywords: alkali-aggregate reaction; volcanic rocks; basalt; rhyolite i. introduction mesostasis originates from the abrupt cooling of magma when volcanic rocks form. it consists of micro-tocryptocrystalline phases, which in optical microscopy look like amorphous matter and is often confused with volcanic glass. in an alkali-aggragate reaction with basic rocks being used, alkalireactive phases appear to be in mesostasis state. if acid rocks are used quartz is mainly responsible for the reaction. alkaliaggregate reaction develops when the silica present in aggregates reacts with the alkali hydroxides coming from cement. using scanning electron microscopy, with the aid of eds, the presence of small crystals of k-feldspar and quartz can be identified in this interstitial material [1]. there seems to be no direct relationship between the amount of microcrystalline, or amorphous matter present in the rocks and the expansions resulting from the alkali-aggregate reaction (aar) [2]. a rock with hardly any mesostasis can represent expansions similar to other rock with a lot of mesotasis [3-5]. quantifying the silica present in the mesostasis can explain this behavior. the objective of this work was to analyze the characteristics of the interstitial matter present in the mesostasis and to correlate with the expansions triggered by the aar. ii. experimental program a. methods characterizing and quantifying the mineral phases in the rocks studied, as well as characterizing the mesostasis, were conducted by petrographic analysis, along with modal analysis (point counting by area). x-ray diffraction (xrd) assisted in the mineralogical characterization of the samples, but mainly in identifying clay minerals by the non-oriented powder method [6]. for the chemical analysis of the samples, x-ray fluorescence (xrf) was employed. scanning electron microscopy (sem), along with energy dispersion spectroscopy (eds), was used to analyze in greater depth the different features of mesostasis previously identified in petrographic analysis. for this analysis, the same 30μm-thick slides as in the petrographic analysis were used, and metalized with carbon. in order to quantify the alkali-reactive potential of each sample, the accelerated mortar bar test [7, 8] was used. b. materials two types of volcanic rocks were used in this study: a basalt (basic rock) and a rhyolite (acid rock). by using petrographic analysis, it was verified that the basalt has a fine granulation, consisting of plagioclase (44.1%), pyroxene (28.5%), opaque minerals (fe and ti oxides, 7.7%), clay minerals (5.8%) and mesostasis (13.8%). it was also possible to observe phenocrystals of plagioclase, pyroxene, fe and ti oxides and some traces of apatite and hematite. the xrd of this rock ratifies the mineralogy observed in the petrographic analysis and reveals the presence of quartz, indicating that there are grains that could not be identified with optical microscopy. in basalt, quartz is found in the interstitial mesostasis [9]. figure 1 shows the diffractogram of a fraction smaller than 2 μm in the oriented sample, thereby giving evidence of the clay minerals. the xrd of the sample in the natural form shows the presence of a peak around 15 å, which moves to the left (position 16.5 å) in the glycolated condition and disappears after calcination, a characteristic behavior of expansive, smectite clay minerals [10, 11]. these clay minerals can contribute to aar occurring in concrete, both because of the expansibility and the possibility of reaction with the alkali hydroxides. the xrf analysis (table i) shows that the basalt has a high amount of silica: 54.04%, which is common to tholeitic basalts [12]. this percentage corresponds mainly to the silica needed to form the main minerals of the rock, which are the plagioclases and pyroxenes. the 'free silica' (quartz), which is more prone to react, corresponds to a smaller percentage present in the mesostasis [13]. by using the petrographic analysis, with the help of the xrd, it was verified that the rhyolite consists of k-feldspar (1.2%), quartz (5.8%), engineering, technology & applied science research vol. 8, no. 1, 2018, 2399-2404 2400 www.etasr.com tiecher et al.: alkali-aggregate reaction: a study of the influence of the petrographic characteristics … plagioclase (8.9%), pyroxene (7.8%), ti-magnetite (9.4%), and mesostasis (15.2%), and contains traces of apatite, hematite and clay minerals (smectite figure 2). its granulation is fine and the intergranular mesostasis can be microcrystalline or filled with automorphic crystals of quartz and k-feldspars, this being more abundant in the vesicular levels. the xrf showed that rhyolite consists of 67.98% of silica. this silica represents the quartz of the matrix of the rock and also the grains in the microcrystalline form in the mesostasis. the percentage of k2o and na2o in the rhyolite sample is higher than in basalt, emphasis being given to k2o, due to the more expressive presence of k-feldspar in this rock. the presence of these constituents may increase the alkali hydroxides in the pores of the concrete if there is dissolution. thus, the rhyolitic sample could contribute both to the dissolution of silica and to the dissolution of alkalis. fig. 1. diffractogram of the clay minerals present in basalt fig. 2. diffractogram of clay minerals present in rhyolite table i. chemical composition of the rocks compound results basalt rhyolite sio2 54.04 67.98 al2o3 16.71 11.75 tio2 0.94 1.15 fe2o3 (total) 10.33 7.32 mno 0.18 0.12 mgo 4.81 0.74 cao 9.22 2.38 na2o 1.73 1.89 k2o 1.39 4.15 p2o5 0.14 0.18 loss to fire 0.70 1.01 total 100.21 98.68 iii. results and discussion a. interstitial matter analysis the reactivity of the volcanic rocks comes from the interstitial material of low crystallinity: volcanic glass and/or mesostasis [14-16]. after characterizing the rocks selected for the study (item ii), the mesostasis analysis was conducted. the first finding, obtained by the petrographic analysis, was the presence of different types of mesostasis in the same rock: microcrystalline mesostasis; mesostasis with better crystalized grains; mesostasis with predominance of clay minerals. the name microcrystalline mesostasis was given to the matter of low crystallinity, rich in silica and alkalis, and accompanied by small grains of hematite and needles of apatite, since optical microscopy cannot individualize grains of quartz or feldspar. the mesostasis with better crystalized grains is the one where there is dissemination of quartz grains that can be visualized in optical microscopy, associated to the matter that consists of feldspar, clay minerals and apatites. the mesostasis with predominance of clay minerals is the one formed by cryptocrystalline quartz-feldspar matter accompanied by an abundant amount of clay minerals, which form well-developed aggregates, with fibro-radiated forms, of greenish color, the smectites (xrd confirming this). table ii presents the percentages of each type of mesostasis in both rocks. the features observed, under petrographic analysis are shown in figure 3. table ii. rock mesostasis percentage mesostasis type sample basalt rhyolite mesostasis with predominance of clay minerals 3.00 0.20 microcrystalline mesostasis 7.00 10.00 mesostasis with better crystallized grains 0.25 5.00 total 10.25 15.20 on comparing the texture of the samples (figure 4), it can be seen that regions of the rhyolite have higher mesostasis concentrations, very often distributed radially. in the basalt, the mesostasis are completely disseminated among the grains. the chemical and mineralogical composition of the different mesostasis identified is also distinct, and may directly influence the potential of the expansion due to the aar. then, using optical microscopy, regions were selected for analysis by using sem and eds. figure 5 shows a basalt region containing mesostasis with clay minerals. this image, obtained by sem, of the relief of the region containing clay materials shows that they are different from the other minerals present (figure 5(c)). while the plagioclases and pyroxenes present a flat aspect, the clay minerals show scaling. this aspect is due to their lamellar shape and their very small size, which makes it difficult to polish the lamina used for the analysis. the clay minerals contribute to the aar due to silica and alkalis easily dissolving [17, 18]. the eds analysis presented in figure 5(d) confirms the presence of these clay minerals in the mesostasis, since the main constituents of the clays are na, k, ca, al, mg, si [19]. in order to explore the specific region of the mesostais in greater detail and to verify the possible presence of quartz micrograins in this region, a chemical elements mapping which could characterize clay minerals and quartz was carried out. in engineering, technology & applied science research vol. 8, no. 1, 2018, 2399-2404 2401 www.etasr.com tiecher et al.: alkali-aggregate reaction: a study of the influence of the petrographic characteristics … this case, the mapped elements were si, ca, k, fe (figure 6, which is an enlarged mesostasis region shown in figure 5). the analysis showed that there are regions in the mesostasis with clay minerals that are rich in si (figure 6(b)). in these regions, the amount of k, ca and fe is lower (figure 6(c), 6(d) and 6(e)). on comparing the si and k maps, it is observed that when there is a higher concentration of si, the concentration of k decreases, that is, even when it contains predominantly clay minerals, microcrystalline quartz occurs. (a) (b) (c) fig. 3. micrographs of the mesostasis of the basalt and rhyolite samples, where mm=microcrystalline mesostasis, mq=best crystallized mesostasis, q=matrix quartz, qmq=quartz of the mesostasis, ma=mesostasis with clay minerals. (a) mm, natural light, (b) mq, cross polarized, (c) ma, natural light. magnification 20x. (a) (b) fig. 4. texture of the samples, where m=mesastasis. (a) basalt, (b) rhyolite. 2.5x magnification, natural light. fig. 5. mesostasis with clay minerals of the basalt, where pl=plagioclase, px=pyroxene, ma=mesostasis with clay minerals. (a) and (b) micrographs obtained by light microscopy under natural light and crossed polarizer, magnification 20x, (c) micrograph obtained by sem, 250x, (d) analysis by using eds. (a) (b) (c) (d) (e) fig. 6. mapping of the chemical elements in a region containing mesostasis with clay minerals of basalt. (a) micrograph of the region of analysis, 2000x magnification, (b) concentration of si, (c) concentration of k, (d) concentration of ca, (e) concentration of fe. figure 7 shows, in the images obtained from sem, that the texture of the microcrystalline mesostasis is very homogeneous, unlike what was observed in the mesostasis with clay minerals. the differentiation between the mesostasis and the other minerals was made because of the difference of tonality, since the microcrystalline mesostasis forms a darker region (figure 7(c)). on using eds analysis (figure 7(d)), only si was identified in the region where the microcrystalline mesostasis is located. this findings show that the mesostasis characterized as microcrystalline basically consists of microcrystalline quartz, unlike what was identified in the mesostasis with clay minerals. the analysis conducted by mapping the chemical elements corroborates this statement, since there is a great concentration of si (figure 9(b)). another observation is the absence of clay minerals, evidenced by the low concentration of ca (figure 9(d)) [17]. the elements k, ca, and fe are found only in well crystallized minerals, in the plagioclase (k, ca) and in pyroxene (ca, fe) [20, 21]. the quartz present in the microcrystalline mesostasis is smaller than 1 μm, as shown in the analysis presented in figure 8. (a) (b) (c) (d) engineering, technology & applied science research vol. 8, no. 1, 2018, 2399-2404 2402 www.etasr.com tiecher et al.: alkali-aggregate reaction: a study of the influence of the petrographic characteristics … (a) (b) (c) (d) fig. 7. microcrystalline mesostasis of the basalt, where pl=plagioclase, px=pyroxene, mm= microcrystalline mesostasis. (a) and (b) micrographs obtained by light microscopy under natural light and crossed polarizer, magnification 20x, (c) micrograph obtained by sem, 250x, (d) analysis by using eds. (a) (b) (c) fig. 8. analysis by sem and eds in the region containing the microcrystalline mesostasis in basalt, where q=quartz, pl=plagioclase. (a) micrograph of the region of analysis, magnification 5000x, (b) quartz, (c) plagioclase. (a) (b) (c) (d) (e) fig. 9. mapping of the chemical elements in the region containing microcrystalline mesostasis of basalt. (a) micrograph of the region of analysis, magnification 500x, (b) concentration of si, (c) concentration of k, (d) concentration of ca, (e) concentration of fe. (a) (b) (c) (d) fig. 10. region containing mesostasis of greatest crystallinity, where q=quartz, mc=best crystallized mesostasis, pl=plagioclase, px=pyroxene. (a) micrograph obtained by optical microscopy under cross polarizer, 10x magnification, (b) micrograph obtained using sem, 150x, (c) quartz of the mesastasis, (d) plagioclase. (a) (b) (c) (d) (e) fig. 11. mapping of the chemical elements in a region with mesostasis containing quartz grains in the rhyolite. (a) micrograph of the region of analysis, magnification 500x, (b) concentration of si, (c) concentration of k, (d) concentration of ca, (e) concentration of fe. figure 10 shows that the texture of mesostasis of greatest crystallinity, in sem is homogeneous, similar to that observed in the microcrystalline mesostasis (figure 10(b)). however, small grains of quartz were observed in the mesostasis (figure 10(a)), which was confirmed by eds (figure 10(c)). the mapping of the chemical elements was carried out in a region of the best crystallized mesostasis. as in the other mappings presented, the identification of the presence of si coincided with the absence of other elements (k, ca and fe), indicating that this region consists of micrograins of quartz. engineering, technology & applied science research vol. 8, no. 1, 2018, 2399-2404 2403 www.etasr.com tiecher et al.: alkali-aggregate reaction: a study of the influence of the petrographic characteristics … b. analysis of the potential of development of aar figure 12 shows the expansions over time in the accelerated mortar bar test [6, 7]. it is observed that both are potentially reactive, in accordance with the classification of astm c 1260, which establishes that an aggregate is potentially reactive when the expansions are superior to 0.10% at 30 days. the basalt resulted in 26% higher expansions at the end of the test, even though it had a smaller amount of mesostasis than rhyolite. an important distinction between the mesostasis is their distribution on the rocks. while in basalt, they are disseminated among the grains, in rhyolite it is common to find regions with larger concentrations, where it is distributed radially. this may be an indication that the dissemination of the mesostasis among the minerals (as for basalt) increases its reaction potential with alkaline hydroxides due to the more uniform availability of material and ease of dissolution. there is also a great difference between the quantities of mesostasis with clay minerals of the rocks, where rhyolite has a very small amount. when there is a predominance of clay minerals, the amount of free silica (quartz) available to react is lower. however, the ease of making both silica and alkalis (constituents of clay minerals) soluble makes them important for enhancing aar. apparently the best crystallized mesostasis does not interfere with the intensity of the reaction. the fact of the grains being better crystallized hinders the attack of alkaline hydroxides. 0.62 0.46 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0 2 3 4 7 8 9 10 11 14 15 16 17 18 21 22 23 28 29 30 ex p an s io n ( % ) age (days) basal t rhyolite fig. 12. accelerated mortar bar test iv. conclusions at the end of the research it was verified that the interstitial matter present in the volcanic rocks can be very heterogeneous. in the rocks selected, three types of mesostasis were differentiated, namely: microcrystalline mesostasis which is rich in microcrystalline quartz grains, identifiable only by using sem and eds, mesostasis with predominance of clay minerals, and the best crystallized mesostasis, where the quartz present in the interstitial material can be identified by optical microscopy. according to the results of the expansion assay, the presence of microcrystalline mesostasis between the grains of the rock, as well as mesostasis with clay minerals increases its potential for expansion due to the aar. it was also verified that the amount of mesostasis is not a preponderant factor for the intensity of expansion resulting from the reaction. according to the obtained results, the constitution of the mesostasis and its distribution in the rock are the main characteristics that potentiate the reactivity of a volcanic rock. however, a larger number of samples needs to be analyzed in order to confirm these conclusions. acknowledgments the authors would like to thank imed for supporting the research, ufrgs for making materials, equipment and laboratories available and the national council for research (cnpq) for the financial support. references [1] m. e. b. gomes, mecanismes de refroidissement, structurat et processus post-magmatiques des basaltes du bassin du parana – region de frederico westphalen (rs) – bresil, phd thesis, universidade federal do rio grande do sul, 1996 [2] f. tiecher, reacao alcali-agregado: avaliacao do comportamento de agregados do sul do brasil quando se altera o cimento utilizado, msc. report, universidade federal do rio grande do sul, 2006 [3] l. valduga, influence of astm c 1260 test conditions to verify alkaliaggregate reaction, phd thesis, universidade federal do rio grande do sul, 2007 [4] l. valduga, d. c. c. dal molin, v. a. paulon, “basalts potential reactivity survey in brazil”, 2th simposio sobre reacao alcaliagregado em estruturas de concreto, 2006 [5] a. a. silveira, contribution to the study of rice husk ash admixtures on concretes submitted to alkali-agreggate reactions, phd thesis, ufrgs, 2007 [6] d. b. alves, “desenvolvimento da metodologia de preparacao de amostras para analise difratometrica de argilominerais no centro de pesquisas da petrobras”, boletim de geociencias da petrobras, rio de janeiro: petrobras, vol. 1, no. 2, pp. 157-175, 1987 [7] associacao brasileira de normas tecnicas, nbr 15577-4: agregados reatividade alcali-agregado parte 4: determinacao da expansao em barras de argamassa pelo metodo acelerado, 2008 [8] annual booking of american society for testing and materials, astm c 1260-01: standard test method for potential alkali reactivity of aggregates (mortar-bar method), annual book of astm standards, 2001 [9] y. wakizaka, “alkali-silica reactivity of japanese rocks”, developments in geotechnical engineering, vol. 84, pp. 293-303, 2000 [10] j. t. kloprogge, s. komarneni, j. e. amonette, “synthesis of smectite clay minerals: a critical review”, clays and clay minerals, vol. 47, no. 5, pp. 529-554, 1999 [11] a. r. v. silva, h. c. ferreira, “esmectitas organofilicas: conceitos, estruturas, propriedades, sintese, usos industriais e produtores/fornecedores nacionais e internacionais”, revista eletronica de materiais e processos, vol. 3, no. 3, pp. 1-11, 2008 [12] l. s. marques, m. ernesto, “magmatismo toleitico da bacia do parana”, geologia do continente sul-americano: evolucao da obra de fernanado flavio marques de almeida, pp. 245-263, 2004 [13] a. j. r. nardy, f. b. machado, m. a. f. de oliveira, “as rochas vulcanicas mesozoicas acidas da bacia do parana: litoestratigrafia e consideracoes geoquimico-estatigraficas”, revista brasileira de geociencias, vol. 38, no. 1, pp. 178-195, 2008 [14] m. korkanc, a. trugrul, “evaluation of selected basalts form the point of alkali-silica reactivity”, cement and concrete research, vol. 35, no. 3, pp. 505-512, 2005 [15] p. krivenko, r. drochytka, a. gelevera, e. kavalerova, “mechanism of preventing the alkali-aggregate reaction in alkali-activated cement concretes”, cement and concrete composites, vol. 45, pp. 157–165, 2014 [16] m. s. islam, m. s. alam, n. ghafoori, r. sadiq, “role solution concentration, cement alkali and test duration on expansion of accelerated mortar bar test (ambt)”, materials and structures, vol. 49, no. 5, pp. 1955-1965, 2015 engineering, technology & applied science research vol. 8, no. 1, 2018, 2399-2404 2404 www.etasr.com tiecher et al.: alkali-aggregate reaction: a study of the influence of the petrographic characteristics … [17] s. sujjavanich, t. meesak, d. chayasuwan, “effect of clay brick powder on asr expansion control of rhyolite mortar bar”, advanced materials research, vol. 931-932, pp. 441-445, 2014 [18] a. leemann, t. katayama, i. fernandes, m. a. r. broekmans, “types of alkali-aggregate reactions and products formed”, construction materials, vol. 169, no. 3, pp. 128-135, 2016 [19] c. igarashi, i. maruyama, y. nishioka, h. yoshida, “influence of mineral composition of siliceous rock on its volume change”, construction and building materials, vol. 94, pp. 701-709, 2015 [20] h. chamley, clay sedimentology, springer-verlang, 1989 [21] j. m. ponce, o. r. batic, “different manifestation of the alkali-silica reaction in concrete according to the reaction kinetics of the reactive aggregate”, cement and concrete research, vol. 36, no. 6, pp. 11481156, 2006 engineering, technology & applied science research vol. 7, no. 5, 2017, 2056-2061 2056 www.etasr.com riahi et al.: buckling stability assessment of plates with various boundary conditions under … buckling stability assessment of plates with various boundary conditions under normal and shear stresses farhad riahi department of civil engineering islamic azad university mahabad, iran riahi.farhad@gmail.com alaeddin behravesh department of civil engineering islamic azad university mahabad, iran behravesh@tabrizu.ac.ir mikaeil yousefzadeh fard department of civil engineering islamic azad university mahabad, iran mikaiel@ymail.com arasto armaghani department of civil engineering islamic azad university mahabad, iran aarmaghani@yahoo.com abstract—in the present paper, the buckling behavior of plates subjected to shear and edge compression is investigated. the effects of the thickness, slenderness ratio and plate aspect ratio are investigated numerically. effects of boundary conditions and loadings are also studied by considering different types of supports and loading. finally, the results of numerical methods are compared with the theoretical results. this work mainly investigates the buckling behavior of plates but also the capabilities of program of plate-buckling (ppb) and abaqus for performing linear and nonlinear buckling analyses. the results will be useful for engineers designing walls or plates that have to support intermediate floors/loads. keywords-steel plate; thin plates; buckling; finite element method; boundary condition i. introduction the problem of buckling of a plate subjected to in-plane compressive and shear loading is important in the shipbuilding, thin-walled structures and building industries. the term buckling refers to when a plate loses its stability, which may lead to a sudden and catastrophic failure, such as the complete collapse or breakage of the structure. when compressive loading is present, buckling may become a concern. buckling is a big problem, particularly in thin-walled structures where the membrane stiffness is much greater than the bending stiffness. an energy method to study the buckling behavior of rectangular plates subjected to in-plane shear load was utilized [1, 2]. later, author in [3], considered a uniaxial compressive loading with a parabolic distribution and obtained an energy solution [3, 4]. authors in [5] have performed elasto-plastic buckling analysis of simply supported plates subjected to uniaxial compression load [5]. authors in [6, 7], showed that the differential quadrature method can yield accurate buckling loads for rectangular plates under uniformly or non-uniformly distributed edge compressions [6, 7]. the present paper evaluates the buckling load of the plate, which is subjected to uniaxial compression and shear load using finite element method software abaqus and (ppb). the analysis is done using eurocode 3. the buckling load is evaluated by changing parameters such as aspect ratio a/b, thickness plate t, slenderness ratio β, slenderness parameter λ, mesh sizes and boundary conditions. the effects of these parameters are studied on buckling load. the accuracy of the current analysis is validated through comparison studies. several case studies are then performed in order to gain a better understanding of some uncovered aspects of buckling stability of such thinwalled structures. ii. plate geometry and mechanical properties all the fe models used in this part and their geometrical parameters are declared in table i. dimension of the length of the plate (a) are 750, 1500, 2250 and 3000 mm, the width of the plate (b) is 750 mm, therefore the ratio a/b for the plate is taken as 1, 2, 3 and 4 respectively thickness of the plate (t) is taken as 3, 5, 7.5 and 10 mm. naming specimens are presented as follows: p-i, plate specimens, as shown in table i, where (i) number of plate by different aspect ratios. for each boundary condition, four aspect ratios and four thicknesses of the plate and three mesh size are considered and total specimens are 96. table i. geometrical properties of plate models α =a/b plate model a (mm) b (mm) 1 p-1 750 750 2 p-2 1500 750 3 p-3 2250 750 4 p-4 3000 750 a. boundary conditions and load types the type of boundary condition used for the models is simple and clamped. three different types of load are considered in the fe models, in-plane shear load and uniaxial compression load and combined compression and shear, see figure 1. as magnitude, in all of the linear buckling analyses, a unit load is applied to the involved edges. in the nonlinear buckling analyses, the load is applied incrementally. engineering, technology & applied science research vol. 7, no. 5, 2017, 2056-2061 2057 www.etasr.com riahi et al.: buckling stability assessment of plates with various boundary conditions under … iii. modelling details and validation the modulus of elasticity analyses, is set to 210 gpa, the poisson’s ratio ν, is 0.3 and the yield stress of the metal is selected as 355 mpa. the introduced dimensionless variables, and parameters: plate in-plane (xy), of length (a) along x-axis, width (b) along y-axis and uniform thickness (t) along z-axis as shown in figure1 are considered. (a) in-plane shear load (b) uniaxial compression load (c) combined compression and shear loads fig. 1. three types of load are used in the parametric studies (a) abaqus (b) program of plate-buckling (ppb) fig. 2. typical of combined compression and shear loads the buckling of thin plate theory is used for calculating the critical buckling load of plates with various geometries, boundary conditions and exposed to loading types such as inplane shear and/or uniaxial compression [9, 10]. the program of plate-buckling (ppb) is used for every plate buckling analysis according to en 1993-1-5, the reduced stresses are implemented in plate buckling [11]. in nonlinear buckling analysis, the method for evaluating if a structure buckles or not is always done by using a force versus the out-of-plane displacement. program of plate-buckling and abaqus have both their own eight-node shell element formulation implemented [10, 12]. a. details mesh size the software abaqus cae 2016 [1] was used, with each model finite element defined by eight-node shell element (s8r5) with quadratic base function and reduced integration being selected for modeling the plates. in this study dimensions for the width of the plate for all models are taken 750 mm. three types of mesh are selected based on the width of the plate. small mesh with 16 elements in the width of the plate, medium mesh with 8 elements in the width of the plate, large mesh with 6 elements in the width of the plate. in this paper the effect of the type of mesh on buckling analysis plates is investigated. b. plates with simple and clamped edges it is necessary to perform verification and validation for the fem analysis results to ensure that the loading, buckling strength and acceptance criteria are suitably considered. for numerical comparison of the result of the program of platebuckling and abaqus, it is necessary to define of discrepancy parameter (d). 100fem ppb ppb esult esult d esult r r r        (1) the results of examination of the effect of length/ width of the plate ratio (a/b) on buckling loads of the plates subjected to external pressure and modeled with clamped boundary conditions for support are presented in table iii. the results of examination of the effect of length/width of the plate ratio (a/b) on buckling loads of the plates subjected to external pressure and modelled with simple boundary conditions for supports are presented in table iii and table iv. according to tables iii and iv it can be seen that the convergence between the results of ppb and fem models is explicit, but in the p1 model is a square plate and with the lowest number of mesh, the results were different. by increasing the aspect ratio and in the rectangular plates, differences between the results lessen. engineering, technology & applied science research vol. 7, no. 5, 2017, 2056-2061 2058 www.etasr.com riahi et al.: buckling stability assessment of plates with various boundary conditions under … iv. results and discussion a. general the buckling behavior of plates is investigated in this paper for different types of boundary condition, aspect ratios, slenderness parameters, mesh size and plate thickness. b. effect of slenderness parameter authors in [8] investigated the effect of slenderness parameter on metal plates subjected to in-plane shear load. slenderness ratio is used to describe the ratio between the width and thickness of the plate while the slenderness parameters also involve the yield stress and young’s modulus of the material; b t   (2) /y e   (3) where β is the slenderness ratio, b is the shortest side of the plate, t is the thickness, λ is the slenderness parameter, e is the elastic young’s modulus and σy is the yield stress. table ii. slenderness ratio ( ) and slenderness ( ) b (mm) t (mm) β λ 750 3 250 10.27 750 5 150 6.16 750 7.5 100 4.11 750 10 75 3.08 plates can be divided into three groups depending on geometrical dimensions: slender, moderate and stocky. the authors concluded that for slender plates with λ ≥ 6, elastic buckling loads predicted numerically using the finite element method are in total agreement with those obtained from theory. slender plates buckle at lower loads and bifurcate mainly due to geometrical instability within the elastic limits of the material. stocky plates, where λ ≤ 3, show a material bifurcation i.e., they buckle in an inelastic way closer to the yield limit implying that a linear buckling analysis approach is not sufficient to catch the buckling behavior. the slender plates show a load carrying capacity up to the ultimate load after the buckling load is reached [8]. c. buckling coefficients buckling coefficients of simply and clamped supported plates are calculated by the rayleigh–ritz method. table v summarizes the buckling coefficients kσ obtained by the ppb and by using abaqus. one can clearly see the effect of boundary conditions as well as aspect ratios on buckling loads. maximum of buckling coefficient kσ for plates with all edges simply and clamped supported subjected to normal stress respectively: kσ = 5.23 and kσ =12.41. this research showed that the actual ultimate carrying capacity was much larger than the critical load. this was most obvious with the slenderer plates. turning our attention to support conditions and geometric situation of several plates, it could be claimed that by the increase in length to width ratio of the plates, critical stress and buckling coefficient decline. table iii. discrepancy (%) between ppb and fem predictions of critical buckling stress with simply supported conditions (ssss). plate model thickness (mm) mesh size small medium large normal stress shear stress *combined normal stress shear stress *combined normal stress shear stress *combined p-1 3 0.37 4.68 0.25 0.57 13.37 1.42 0.82 26.77 3.11 p-2 0.28 -3.12 -0.57 0.42 -3.51 -0.71 0.12 -6.73 -1.42 p-3 0.24 -0.84 0.79 0.42 -1.05 -0.75 0.14 -2.97 -1.37 p-4 0.23 -0.49 -0.77 0.40 -0.66 -0.78 0.08 -2.19 -1.56 p-1 5 0.61 4.92 0.91 0.70 14.27 1.15 1.03 29.69 3.08 p-2 0.46 -3.01 -0.72 0.57 -3.22 -0.67 0.56 -4.74 -1.6 p-3 0.41 -0.73 -0.67 0.54 -0.86 -0.64 0.59 -1.73 -1.62 p-4 0.39 -0.39 -0.69 0.51 -0.50 -0.61 0.53 -1.18 -1.68 p-1 7.5 0.93 5.24 1.12 0.91 14.82 0.91 1.22 31.15 2.72 p-2 0.71 -2.85 -1.4 0.78 -2.99 -0.88 0.84 -3.85 -1.91 p-3 0.64 -0.58 -1.17 0.71 -0.68 -0.81 0.83 -1.18 -1.89 p-4 0.61 -0.24 -1.3 0.68 -0.33 -0.9 0.78 -0.73 -1.86 p-1 10 1.26 5.60 1.23 1.17 15.25 1.53 0.54 31.94 2.96 p-2 0.97 -2.66 -1.4 1.01 -2.78 -1.7 1.08 -3.38 -1.24 p-3 0.88 -0.40 -1.29 0.92 -0.49 -1.16 1.03 -0.86 -1.31 p-4 0.83 -0.06 -1.22 0.87 -0.15 -1.29 0.98 -0.45 -1.28 engineering, technology & applied science research vol. 7, no. 5, 2017, 2056-2061 2059 www.etasr.com riahi et al.: buckling stability assessment of plates with various boundary conditions under … table iv. discrepancy (%) between ppb and fem predictions of critical buckling stress with clamped supported conditions(cccc). plate model thickness (mm) mesh size small medium large normal stress shear stress *combined normal stress shear stress *combined normal stress shear stress *combined p-1 3 0.008 0.17 0.185 -0.033 -2.29 -1.26 -0.329 -15.05 -6.31 p-2 0.008 -3.24 -1.54 -0.041 -3.73 -2.43 -0.708 -8.05 -2.8 p-3 0.008 -0.95 0.9 -0.041 -1.25 -0.95 -0.757 -3.91 -1.64 p-4 0.008 -0.60 -0.087 -0.041 -0.83 -1.3 -0.708 -2.96 -0.92 p-1 5 0.024 0.23 0.42 0.006 -0.88 0.95 -0.110 -7.01 -1.30 p-2 0.024 -3.20 -2.72 0.003 -3.44 -2.4 -0.249 -5.47 -2.45 p-3 0.024 -0.91 -1.67 0.003 -1.07 -0.97 -0.270 -2.26 -0.96 p-4 0.024 -0.57 -1.09 0.003 -0.70 -1.05 -0.249 -1.64 -0.94 p-1 7.5 0.055 0.34 1.32 0.045 -0.26 -0.73 -0.014 -3.74 -1.87 p-2 0.055 -3.13 -2.54 0.043 -3.28 -1.47 -0.076 -4.39 -2.34 p-3 0.055 -0.85 -1.5 0.042 -0.96 -1.11 -0.087 -1.62 -0.82 p-4 0.055 -0.52 -1.2 0.043 -0.61 -1.32 -0.076 -1.13 -0.76 p-1 10 0.103 0.49 0.89 0.088 0.08 0.78 0.051 -2.24 -1.12 p-2 0.103 -3.03 -1.6 0.088 -3.15 -1.07 0.014 -3.89 -0.81 p-3 0.103 -0.77 -1.44 0.088 -0.86 -1.03 0.014 -1.32 -0.87 p-4 0.103 -0.43 -1.28 0.088 -0.52 -0.92 0.014 -0.88 -0.95 * combined normal and shear stress buckling coefficients kτ for plates with all edges simply supported subjected to in-plane shear load, are shown in (4).  2 4 5.34 / k a b    (4) as the plate is shortened, the number of local buckles is reduced and the value of buckling coefficients kτ for a plate simply supported on all four edges is increased from 5.36 for a very long plate to 9.94 for a square plate and for a plate clamped supported on all four edges is increased from 6.23 for a very long plate to 10.75 for a square plate. table v. buckling coefficient k  for plates under uniaxialdistributed edge compressions a/b 1 2 3 4 ppb fem ppb fem ppb fem ppb fem ssss 5.22 5.23 5.35 5.30 5.92 5.87 6.34 6.27 cccc 12.41 12.20 10.7 10.6 10.3 10.3 9.98 9.98 table vi. buckling coefficient k  for plates under in-plane shear load edge a/b 1 2 3 4 ppb fem ppb fem ppb fem ppb fem ssss 9.94 9.03 6.34 6.21 5.78 5.57 5.59 5.36 cccc 10.75 10.44 8.57 8.48 7.81 6.92 6.84 6.23 the aspect ratio of the plate determines the number of folds or lobes formed at buckling. considering that m and n are the number of half waves in x and y directions respectively, for the m-n buckling mode. for the lowest value of critical load, number of half waves along the width of the plate n is one, while the number of half waves formed along the length of the plate is governed by the aspect ratio of the plate. the value of k depends on the number of half waves m and the aspect ratio, as graphed in figure 3, shows the plots of the buckling coefficient (k) versus a/b for plates. (a) buckling factor (b) buckling modes fig. 3. variation of buckling factor with the plate aspect ratio the value of k is minimal at the integer values of aspect ratio for which the number of half waves is equal to the aspect ratio. at the aspect ratio of the plate more than the transitional value of α=a/b for m=1 to m=2, the number of half waves engineering, technology & applied science research vol. 7, no. 5, 2017, 2056-2061 2060 www.etasr.com riahi et al.: buckling stability assessment of plates with various boundary conditions under … which have been formed will change to 2 to maintain the lowest value of (k). d. local buckling load the local buckling stresses (σcr) are obtained from fem. the axial compression load versus out-of-plane displacement curves were used to obtain the local buckling load with different support condition as shown in figures 4 5. bifurcation curve was seen in the local buckling of plates. this lead to gradual out-of-plane displacement even at lower axial compression loads. in figure 4 and clamped support condition, the maximum and minimum out-of-plane displacement respectively was for plate with thickness of 3 and 10 mm. the highest and lowest values of out-of-displacement were 2 and 1.2 mm. in figure 5 and simply support condition the maximum and minimum out-of-plane displacement respectively was for plate with a thickness of 3 and 10 mm. the highest and lowest values of out-of-displacement were 2.2 and 1.6 mm. the axial compression load often dropped rapidly after reaching the ultimate strength. this might be due to the assumption of ideal perfect-plastic material behavior in abaqus. the first buckling modes and out-of-plane displacement plates with various aspect ratios are shown in figure 6. (a) plate with a thickness of 3 mm (b) plate with a thickness of 5 mm (c) plate with a thickness of 7.5 mm (d) plate with a thickness of 10 mm fig. 4. plot of normal stress load versus out-of-plane displacement with support condition: cccc e. interaction relation between / cr  and / cr  for combined loadings the general conditions for failure are expressed by (5): 1 2 1r r  (5) in this equation, 1 / crr   and 2 / crr   could refer to normal and shear stresses are applied to the edges of the plate. figure 7 shows the interaction relation curves for different aspect ratio between / cr  and / cr  for simply and clamped supported. (a) plate with a thickness of 3 mm (b) plate with a thickness of 5 mm (c) plate with a thickness of 7.5 mm (d) plate with a thickness of 10 mm fig. 5. plot of normal stress load versus out-of-plane displacement with support condition: ssss fig. 6. buckling modes of plates with out-of-plane displacement and different aspect ratios (a) support condition: ssss (b) support condition: cccc fig. 7. interaction relation between / cr  and / cr  when the aspect ratio a/b =1, the interaction relation curves lie slightly below the circular curve. the interaction between compression and shear is therefore significant due to the fact that the aspect ratio a/b =1 causes twisting buckling mode. as the aspect ratio increases, the interaction relation curves lie further above the circular curve. the interaction relation is therefore less significant. f. first eigen mode for various cases of plates this part of paper contains the results that are obtained by the fe models that were presented in the previous part. in the engineering, technology & applied science research vol. 7, no. 5, 2017, 2056-2061 2061 www.etasr.com riahi et al.: buckling stability assessment of plates with various boundary conditions under … paper, some selected contour plots are presented in order to illustrate the buckling modes for various cases of plates. the results for the first eigen mode (z-displacement magnitude) obtained in the paper where the aim was to perform a mesh convergence study. figure 8 shows square plates with two types of loads and mesh size and figure 9, shows rectangular plates for two types of loads and mesh size. fig. 8. the first eigen mode of square plate in abaqus fig. 9. the first eigen mode of rectangular plate in abaqus v. conclusion buckling analysis of plates with uniform distributed inplane shear and compressive loadings along edges is investigated. the plate aspect ratio was supposed that varies from 1 to 4 and with several loading states, 96 models were considered. abaqus and plate-buckling programs were used for modeling and analysis of the considered plate models. the numerical predictions of the two aforementioned programs were compared for verification purposes. the major findings of this research are summarized in the following:  fixity of the loading edges can be effective in improving the buckling strength of plates as the aspect ratio gets smaller than unity, while loading edges fixity does not seem to have a considerable effect on the buckling capacity in plates with aspect ratios larger than unity.  the buckling coefficients decrease when the aspect ratio increases. the decreasing in the buckling coefficients when the aspect ratio a/b =1 less than the decreasing in the buckling coefficients when the aspect ratio a/b >1. the decrease in the buckling coefficients in plate with boundary condition (ssss) is more than the decreasing in the buckling coefficient in plate with boundary condition (cccc).  the buckling loads and modes were evaluated numerically as stated above. eigenvalues were calculated for unit lineload (1 n/mm) and then the buckling load in each mode was calculated by multiplying the eigenvalue with the width of the plate.  buckling load decreases with the increasing aspect ratio.  buckling load increases with the increase in the thickness of the plates. the main objective of this research is to explore some uncovered aspects of buckling stability of plates by considering the effects of support conditions, aspect ratio, and slenderness ratio, which will consequently result in efficient design of such thin-walled structures. references [1] s. p. timoshenko, theory of elastic stability, mcgraw-hill book company, inc. new york, 1936 [2] m. stein, j. neff, buckling stresses of simply supported rectangular flat plates in shear, naca technical note, no.1559, 1947 [3] m. b. benoy, “an energy solution to the buckling of rectangular plates under non-uniform in-plane loading”, aeronautical journal, vol. 73, pp. 974–7, 1969 [4] t. m. shakerley, c. j. brown, “elastic buckling of plates with eccentrically positioned rectangular perforations”, international journal of mechanical sciences, vol. 38, no. 8-9, pp.825-38, 1996 [5] a. k. soh, , l. c. bian, j. chakrabarty, “elastic/plastic buckling of a composite flat plate subjected to uniform edge compression”, thinwalled structures, vol. 38, no. 3, pp. 247-265, 2000 [6] x. wang, x. wang, x. shi, “accurate buckling loads of thin rectangular plates under parabolic edge compressions by the differential quadrature method”, international journal of mechanical sciences, vol. 49, no. 4, pp. 447–453, 2007 [7] x. wang, differential quadrature and differential quadrature based element methods theory and applications, elsevier inc., united states, 2015 [8] a. gheitasi, m. m. alinia, “slenderness classification of unstiffened metal plates under shear loading”, thin-walled structures. vol. 48, no. 7, pp. 508-518, 2010 [9] b. torstenfelt, finite elements – from the early beginning to the very end, liu-tryck, linkoping, 2007 [10] k. hibbitt, abaqus/standard theory manual, sorenson inc, 2016 [11] euro code 3 en 1993-1-5, “design of steel structures. part 1.5 plated structural elements”, 2006 [12] d. beg, u. kuhlmann, l. davaine, b. braun,“design of plated structures, eccs euro code design manuals, ernst & sohn, berlin, 2010 microsoft word etasr_v12_n3_pp8803-8808 engineering, technology & applied science research vol. 12, no. 4, 2022, 8803-8808 8803 www.etasr.com bhalekar & bedekar: the new dataset mitwpu-1k for object recognition and image captioning tasks the new dataset mitwpu-1k for object recognition and image captioning tasks madhuri bhalekar school of computer engineering and technology dr. vishwanath karad mit world peace university pune, india madhuri.bhalekar@mitwpu.edu.in mangesh bedekar school of computer engineering and technology dr. vishwanath karad mit world peace university pune, india mangesh.bedekar@mitwpu.edu.in received: 5 may 2022 | revised: 19 may 2022 | accepted: 20 may 2022 abstract-in the domain of image captioning, many pre-trained datasets are available. using these datasets, models can be trained to automatically generate image descriptions regarding the contents of an image. researchers usually do not spend much time in creating and training the new dataset before using it for a specific application, instead, they simply use existing pre-trained datasets. ms coco, flicker, and pascal voc, are well-known datasets that are widely used in the task of generating image captions. in most available image captioning datasets, image textual information, which can play a vital role in generating more precise image descriptions, is missing. this paper presents the process of creating a new dataset that consists of images along with text and captions. images of the nearby vicinity of the campus of mit world peace university-mitwpu, india, were taken for the new dataset named mitwpu-1k. this dataset can be used in object detection and caption generation of images. the objective of this paper is to highlight the steps required for creating a new dataset. this necessitated a review of the existing dataset models prior to creating the new dataset. a sequential convolutional model for detecting objects on a new dataset is also presented. the process of creating a new image captioning dataset and the gained insights are described. keywords-convolutional model; dataset; image captioning; image labelling; object detection i. introduction many image datasets (e.g. ms coco, flicker, pascal) are available and can be used in image captioning systems. we wanted to explore the background and preprocessing required while creating such a dataset. for this purpose, we started to create a new dataset, called mitwpu-1k, of our university, mit world peace university, campus. currently, the dataset consists of around 1500 images which are object labeled and captioned manually. these labels are classes of objects present in the image. our dataset model is trained using the cnn (convolutional neural network) architecture to detect objects present in an image. the validation while consideration of image selection is also presented. currently, the mitwpu-1k dataset is having 4500 image descriptions, i.e. for each image, an average of three image annotations is provided. this dataset has a total of 68 objects and we are still working on its expansion. before creating a new dataset, we studied some of the prominent existing datasets used in image captioning. ii. related works many architectures have been proposed for generating captions for a given image. the reviewed research papers belong to the domains of machine learning and neural networks. most of the datasets which are used in object recognition tasks are developed by considering the task of object classification, detection, and labeling. in the image caption domain, the ms-coco [1] dataset is considered a benchmark, in which object recognition is enhanced by advancing scene understanding and by piping the annotation via picture labeling, instance spotting, and instance segmentation pipelines. in the ms-coco dataset, there are 91 frequent object types with 25,00,000 labeled instances in 3,28,000 images. the training set consists of 82,783 photos, whereas the validation set contains 40,504 images, and the testing set 81,434 images. the pascal voc [2] dataset consists of 11,000 pictures divided into 20 object groups, having 2,501 images in the training set, 2,510 images in the validation set, and 4,952 images in the testing set. imagenet [3] contains 14,197,122 images and almost 21,000 object classes. imagenet is built upon the hierarchical structure provided by wordnet. cifar-10 [4] dataset and contains 100 categories with almost 60,000 images. they have performed object classification on tiny images of size 32×32. the authors explain how they have trained a two-layer convolutional deep belief network (dbn) on a 1.6 million tiny images dataset. while analyzing these different dataset models, we come across the yolo architecture [5] and caffe framework [6]. yolo architecture is used for object detection. classification is done using cnns along with localization using regression. caffe convolutional architecture is used in region-based cnns (rcnns) for quick feature embedding framework. caffe has already been employed in several academic research projects. along with these papers, we also find some latest review papers on object detection methods used in deep learning [7, 8] which provide the metrics used for object detection along with the datasets used. the detailed review of many object detection survey papers is summarized in [7]. the authors observed that corresponding author: madhuri bhalekar engineering, technology & applied science research vol. 12, no. 4, 2022, 8803-8808 8804 www.etasr.com bhalekar & bedekar: the new dataset mitwpu-1k for object recognition and image captioning tasks for object detection, deep learning methods provide a prominent approach. the authors also highlight the future work that can be done in visual object detection like multi-domain object detection, silent object detection, and unsupervised object detection using a deep learning approach. in [8], authors provide the categorization of existing image captioning systems and commonly used datasets for image captioning. they provided the detailed statistics of the following datasets: ms coco, flickr30k, flickr8k, visual genome, iapr tc-12, stock3m, and mit-adobe fivek dataset. table i presents the details of some of the existing datasets mostly used in image captioning. table i. summary of prominent existing datasets used in image captioning dataset images objects / classes training set validation set testing set ms-coco [1] 3,28,000 80 categories 82,783 40,504 81,434 pascal voc [2] 11,000 20 2,501 2,510 4,952 imagenet [3] 14,197,122 21,000 classes 1.2 million 150,000 cifar-10 [4] 60,000 100 iii. methodology used in dataset creation after analyzing the existing dataset models, we have started creating our new dataset which consists of images of the nearby vicinity of the mit world peace university campus. we are creating a new dataset which can be further used in object recognition with labeled data and captions for the image. the flow of the creation of the dataset is shown in figure 1 and can be summarized as: • image collection and validation • interface to provide image description/annotations • labeling objects these steps are explained in the following sections. a. image collection for creating the new dataset, we collected images having diversity. the main objective of collecting diverse images was to proper train the dataset to avoid the problem of over fitting or under fitting during training. so, we tried to collect diverse images, like images with different brightness levels, having different foreground and background, containing multiple objects, etc. we took images that include different activities and events carried out on the mitwpu campus. while building this dataset we considered the images of posters and banners of various events on campus which contain some text information. the main goal was to use these textual data from the image to provide more detailed image descriptions during the caption generation task. initially, we collected the images with the use of a smartphone and a professional camera, due to which the gathered images have different resolution, size, and orientation. after collecting several images, we found that all images could not be considered for the new dataset, so the rectification of these collected images are carried out as mentioned below. fig. 1. system flow of dataset creation. b. validation images from different sources were collected (via a professional camera, smart phones, etc.) from which many had low resolution, poor brightness, whereas some images were redundant, i.e. captured with multiple clicks on the same view. while preparing the dataset we observed that images should provide a good representation of the classes which can further help in the classification process. to achieve this, these images were removed using manual filtration. after validating the selected images at present, we had 1500 images in the dataset. further, to speed up the process, the images were resized. some sample images are shown in figure 2. we also considered images containing text, like banners and posters, so that in the future we can develop an image captioning system for generating the description of an image along with text extraction as shown in figure 12. c. interface to provide image description as the dataset that can be utilized in an image captioning system was developed, we added descriptions for each image. to accomplish this task, a user interface was created in python as shown in figure 3. using this interface manually we provided captions for every image, which were stored in the form of csv and json files, and can be further used to train our dataset for image captioning (figure 4). while providing the engineering, technology & applied science research vol. 12, no. 4, 2022, 8803-8808 8805 www.etasr.com bhalekar & bedekar: the new dataset mitwpu-1k for object recognition and image captioning tasks manual captions we took care to provide different captions for the same image considering all visual elements of the image. for this, we provided a minimum of three captions for each images. finally, along with each new image, an image description file containing the image annotations was provided. fig. 2. sample mages from the dataset. fig. 3. dataset creation module. fig. 4. interface providing image description. d. image description format with the image identification number we keep track of its associated descriptions or annotations. we maintained track of image file as {"file_name": "img_100.jpg","id": 100}, and the included annotations for each image were in the format mentioned below in either csv or json file format: • {"image_id": 100, "id": 1,"caption": "description 1"}, • {"image_id": 100,"id": 2,"caption": " description 2"}, • {"image_id": 100,"id": 3,"caption": " description 3"}, this way, in the new dataset two folders were maintained, one which contains all the images and another that includes the manually assigned annotations for each image. for creating the ms coco dataset [1], huge crowdsourcing was involved in the annotation task and by using the precision-recall metric the quality of the annotation task was measured. we measured the quality of annotations of our dataset by applying the same concept. the quality of annotations was analyzed by a group of people including the authors of the paper. in some cases, we observed low precision and recall value, so we tried to search the false positive and false negative patterns and again perform the annotation correction task. for validation purposes, after assigning descriptions to all the images, we manually checked for redundancy the descriptions and verified them. presently, the new dataset contains 1500 images with 4500 descriptions/annotations. some image samples with the assigned captions are shown in figure 5. fig. 5. sample images with assigned captions from the created dataset. e. object labelling after acquiring images and their associated descriptions, the next task was to perform object detection, but before that, engineering, technology & applied science research vol. 12, no. 4, 2022, 8803-8808 8806 www.etasr.com bhalekar & bedekar: the new dataset mitwpu-1k for object recognition and image captioning tasks we performed labelling on the images as shown in figure 6. when multiple appearances of the same object occur in one image, only one label will be considered. before using the new dataset, we performed object detection. identifying objects from an image becomes complex when the image contains multiple objects. for this, we used the tensorflow object detector [9] and done the review process used during the imagenet dataset creation for detecting objects present in the image (figure 7) [3]. the process involves visually checking the objects assigned with the images in order to check the classification accuracy of the new dataset. fig. 6. labelling the objects of an image. fig. 7. review method of identifying objects present in the image. after performing the review method thoroughly, a complete list of classes in the new dataset was acquired. at present, our dataset contains 68 different object classes, such as person, chair, room, garden, plant, car, road, door, window, building, globe, printer, pen, notebook, bag, cupboard, book, bench, table, staircase, etc. iv. building and training the classification model to perform image classification, there are many existing pre-trained architectures available which are trained on huge size image datasets like ms coco [1] and imagenet [3]. instead of using these available pre-trained architectures, we have come up with a simple convolutional classifier model which was trained on the new dataset. the main reason to come up with a different convolutional classifier was to avoid the over fitting problem because currently our dataset size is limited. we have created a sequential convolutional model, which gives the flexibility to keep adding different layers to the model as per requirements. the basic steps we followed while creating our classifier model which was trained on the new dataset are: • build the model • compile the model • train the model with the new dataset • validate the model • measure the model's performance in terms of accuracy the classifier model summary is shown in figure 8. as already mentioned, in order to detect the 68 different object types present in our dataset, we have used a dense layer size (68). the model is trained to identify more than one object in an image. some samples of object detection are shown in figure 9. we initially started with bigger size objects, then proceeded towards smaller size objects. our trained classification model detected objects like monitor, mouse, and keyboard in the given image shown in figure 9. fig. 8. model summary of the sequential classifier. fig. 9. results of multiple detected objects. a. results the new dataset was created for image captioning tasks, but it can also be used in object detection. to perform object detection, we performed labelling on the images which are further used during the training phase. instead of using any pretrained classifier model, we presented the sequential classifier model. to check and compare the accuracy of the engineering, technology & applied science research vol. 12, no. 4, 2022, 8803-8808 8807 www.etasr.com bhalekar & bedekar: the new dataset mitwpu-1k for object recognition and image captioning tasks presented sequential model, we performed the review method of [3]. object detection with the sequential classifier model provided 84% accuracy. the comparative analysis graph plot of the review method and the sequential classifier model is shown in figure 10. fig. 10. object detection accuracy comparison. table ii. mitwpu-1k dataset summary dataset images objects image descriptions/annotations mitwpu-1k 1500 68 4500 fig. 11. sample images of identified objects in the mitwpu-1k dataset. fig. 12. sample images containing poster/banner. οur dataset contains 1500 images with 68 different objects and 4500 image descriptions (table ii). these objects are mostly present in any college or university campus. some of the samples of the identified objects in the created dataset are shown in figure 11. the dataset contains some images which contain text in the form of a banner or poster as shown in figure 12. using this dataset, we proposed a new deep learning model [10] for performing image captioning and text extraction. the obtained results of image captioning, including textual information present in the image, were satisfactory, giving accuracy up to 83% and performed as well as the state of the art methods. the new dataset mitwpu-1k can be used in a wide range of applications such as object detection, caption generation, text detection, etc. regarding future work, the size of the dataset will be increased by adding some domain-specific images along with captions. v. conclusions this paper presented the followed process while creating a new image dataset for image captioning generation. the main purpose was to explore the processing behind creating a dataset that can be used in generating image captions. before and during the creation of this new dataset, existing dataset models were studied in detail. at present, the new dataset consists of 1500 images and its name is mitwpu-1k in line with the current trend to name the dataset in a particular manner. the dataset includes 4500 annotations as we have assigned the minimum of three annotations for each image. the dataset has a subset of images that include text, so along with image description, text extraction can be done to further extend its application in domains like image captioning or other similar tasks. using a sequential convolutional model, we performed object detection tasks on the mitwp-1k dataset. the dataset creation model can be extended to include all images of a particular domain such as sports, night vision images, animals, automobiles, computers, etc. in the application of image captioning, all available datasets are mostly generic. the accuracy of such systems can be improved by creating or using domain-specific image datasets. acknowledgment the authors would like to thank the authorities of dr. vishwanath karad mit world peace university for their support. references [1] t.-y. lin et al., "microsoft coco: common objects in context," in computer vision – eccv 2014, 2014, pp. 740–755, https://doi.org/ 10.1007/978-3-319-10602-1_48. [2] m. everingham, s. m. a. eslami, l. van gool, c. k. i. williams, j. winn, and a. zisserman, "the pascal visual object classes challenge: a retrospective," international journal of computer vision, vol. 111, no. 1, pp. 98–136, jan. 2015, https://doi.org/10.1007/s11263-014-07335. [3] j. deng, w. dong, r. socher, l.-j. li, k. li, and l. fei-fei, "imagenet: a large-scale hierarchical image database," in 2009 ieee conference on computer vision and pattern recognition, miami, fl, usa, jun. 2009, pp. 248–255, https://doi.org/10.1109/cvpr.2009.5206848. [4] r. doon, t. kumar rawat, and s. gautam, "cifar-10 classification using deep convolutional neural network," in 2018 ieee punecon, pune, india, aug. 2018, https://doi.org/10.1109/punecon.2018. 8745428. engineering, technology & applied science research vol. 12, no. 4, 2022, 8803-8808 8808 www.etasr.com bhalekar & bedekar: the new dataset mitwpu-1k for object recognition and image captioning tasks [5] j. redmon and a. farhadi, "yolo9000: better, faster, stronger," in 2017 ieee conference on computer vision and pattern recognition (cvpr), honolulu, hi, usa, jul. 2017, pp. 6517–6525, https://doi.org/ 10.1109/cvpr.2017.690. [6] y. jia et al., "caffe: convolutional architecture for fast feature embedding," in mm ’14: proceedings of the 22nd acm international conference on multimedia, new york, ny, usa, aug. 2014, pp. 675– 678, https://doi.org/10.1145/2647868.2654889. [7] v. sharma and r. n. mir, "a comprehensive and systematic look up into deep learning based object detection techniques: a review," computer science review, vol. 38, nov. 2020, art. no. 100301, https://doi.org/ 10.1016/j.cosrev.2020.100301. [8] m. d. z. hossain, f. sohel, m. f. shiratuddin, and h. laga, "a comprehensive survey of deep learning for image captioning," acm computing surveys, vol. 51, no. 6, pp. 118:1-118:36, oct. 2019, https://doi.org/10.1145/3295748. [9] g. tanner, "creating your own object detector," towards data science, feb. 06, 2019. https://towardsdatascience.com/creating-your-ownobject-detector-ad69dda69c85. [10] m. bhalekar and m. bedekar, "d-cnn: a new model for generating image captions with text extraction using deep learning for visually challenged individuals," engineering, technology & applied science research, vol. 12, no. 2, pp. 8366–8373, apr. 2022, https://doi.org/ 10.48084/etasr.4772. [11] b. ahmed, g. ali, a. hussain, a. baseer, and j. ahmed, "analysis of text feature extractors using deep learning on fake news," engineering, technology & applied science research, vol. 11, no. 2, pp. 7001–7005, apr. 2021, https://doi.org/10.48084/etasr.4069. [12] s. nuanmeesri, "a hybrid deep learning and optimized machine learning approach for rose leaf disease classification," engineering, technology & applied science research, vol. 11, no. 5, pp. 7678–7683, oct. 2021, https://doi.org/10.48084/etasr.4455. microsoft word etasr_v12_n2_pp8316-8320 engineering, technology & applied science research vol. 12, no. 2, 2022, 8316-8320 8316 www.etasr.com khlifi et al.: investigation of a leakage reactance brushless dc motor for dc air conditioning … investigation of a leakage reactance brushless dc motor for dc air conditioning compressor mohamed arbi khlifi department of electrical engineering, faculty of engineering, islamic university of madinah, saudi arabia sime laboratory, ensit, university of tunis, tunisia mohamedarbi.khlifi@issatm.rnu.tn marwa ben slimene college of computer science and engineering, haï’l university, saudi arabia sime laboratory, ensit, university of tunis, tunisia benslimenemarwa@gmail.com ahmad alradedi department of electrical engineering faculty of engineering islamic university of madinah, madinah, saudi arabia a-raddadi@hotmail.com salah al ahmadi department of electrical engineering faculty of engineering islamic university of madinah, madinah, saudi arabia sa-alhmadi@hotmail.com received: 17 january 2022 | revised: 8 february 2022 | accepted: 11 february 2022 abstract-home appliances using brushless dc (bldc) motors, such as air conditioners (acs) and ceiling and pedestal fans, are gaining attention these days due to their low power consumption and low maintenance cost. this paper estimates and analyzes the leakage reactance of conventional and flux-switching permanent magnet bldc motors. the leakage magnetic field of a highpower bldc motor will be one of the main sources of interference. the magnetic field characteristics of the leakage field of a bldc motor must be analyzed in order to acquire correct geomagnetic data. we also show the rotor's leakage magnetic field while the bldc motor is static, the stator and rotor's leakage magnetic fields when the bldc motor is functioning, and the near-field characteristic of the bldc motor's leakage magnetic field. keywords-brushless dc (bldc); leakage reactance; parameter estimation; potier and sub-transient reactances i. introduction global urbanization, electrification, rising standards of living, and dropping air conditioner (ac) prices are all predicted to significantly increase direct and indirect emissions from ac refrigerants and ac energy use [1-3]. the increasing amount of energy consumption by buildings has caused widespread global attention to the social, environmental, and economic implications associated with it. from the scope of reducing global warming and other environmental concerns, there has been an increased demand for making energyconsuming equipment more energy-efficient. various manufacturers have been actively engaged in energy-saving advancements, particularly with regard to room acs, which are estimated to consume the most electrical energy in households. electric power rationalization entails reducing electrical loads in power plants and electric networks, resulting in an uninterrupted supply of electricity, significant cost savings, and environmental preservation. air conditioning consumes 75% of monthly energy consumption during the summer months, which is an excessively high amount [2, 4-6]. brush machines are generally inexpensive due to their established design and manufacturing technologies, as well as their simple control [7-10]. the brushes in a brush machine make mechanical contact with a set of mechanical commutators or slip rings that are attached to the rotor and give connections to various armature coils at various rotor positions. brushless machines, as the name implies, lack brushes, mechanical commutators, or slip rings, and instead rely on an electronic controller. brushless machines, in comparison to brush machines, have superior efficiency and dependability, lower noise, longer lifetime (no brush degradation), less ionizing sparks from the commutators, and less electromagnetic interference overall. they can run at a higher speed range because the mechanical limits have been removed [11-14]. because of their great efficiency, high power density, small size, and reliability, pm brushless motors have been widely employed for high-speed applications. three-phase brushless motors are the most often used pm brushless motors, as they offer the optimum balance of motor iron and copper use and inverter cost. pm brushless motors, on the other hand, can be relatively inexpensive, which is always desirable in costconscious home appliance applications [15-17]. the reactance due to the difference between the total flux produced by an armature current and the flux in the air gap produced by the same armature current is known as armature leakage. there are several factors that contribute to stator leakage. each component represents flux pathways into the rotor that do not cross the airgap [18-21]. the present contribution exposes a direct approach for parameter evaluation of salient or nonsalient pole synchronous machines. the information received from the constant excitation test is used in this paper to propose a straightforward approach for estimating the leakage corresponding author: mohamed arbi khlifi engineering, technology & applied science research vol. 12, no. 2, 2022, 8316-8320 8317 www.etasr.com khlifi et al.: investigation of a leakage reactance brushless dc motor for dc air conditioning … reactance. the technique theory is explained and applied to a variety of systems ranging from laboratories to hydroelectric power plants. the estimates are compared to the potier and sub-transient reactances in the absence of absolute values of the leakage reactance. ii. the proposed method bldc motors rotor is composed of magnetic steel and iron core. in order to study the magnetic field characteristics of the rotor and to obtain accurate values of the leakage reactance sx , an alternative testing method is adopted which was proposed in [1, 2]. in this method, the terminal voltage/armature current characteristic ( a av /i ) curve with the machine unloaded and unexcited is needed along with the d-axis open circuit characteristic curve (occc) of the machine (figure 1). 1 2 3 0 100 200 300 0.2 0.4 0.6 0.8 1 0 100 200 300 (a) (b) fig. 1. determination of the armature leakage reactance of the bldc motor. (a) characteristic with the machine unloaded and unexcited, (b) the occc. when the machine is unloaded and unexcited, the armature current equals to approximately its d-axis component since its q-axis component is approximately equal to zero. the nonlinear magnetic curve can be obtained at the rated speed by energizing the field circuit and closing the stator terminals, or vice versa. by neglecting copper and core losses, it is supposed that in ( ) a a v i , the armature current is a pure magnetizing component. consequently, for a given stator voltage, the corresponding if and ia are known, defining together the ratio alpha if /ia. neglecting the effect of the armature resistance of the machine, which is usually very small, the machine terminal voltage vt, in this case, is equal to the d-axis synchronous reactance voltage drop iaxd. the difference between the terminal voltage vt and the internal e.m.f. ei is the armature leakage reactance voltage drop, namely iaxl. thus: t i a lv e i x= + (1) the internal e.m.f. ei could be obtained from the d-axis occc of this machine. in the "xmd-base" per unit system [7, 12], the induced e.m.f. due to a certain armature current in per unit is by definition equal to the generated e.m.f. due to the field current ef which has the same per unit value as this armature current ia. thus, (1) could be rewritten as follows: t f a lv e i x= + (2) (a) (b) (c) (d) fig. 2. field/armature turns ratio versus armature current: (a) unload test, (b) short circuit test, (c) potier, (d) potier, c-c and o-c comparison. the field current if which has the same per unit value of the armature current ia (figure 2) can be expressed as follows: ( ) fu tu a l f a du a l a du l -i i = k k i -i k i e v x x x x x k = = = − (3) where fu f e k i = . in order to obtain a simpler expression for the armature leakage reactance, the following saturation factors can be used: t t tu v s v = (4) f fu e s e = (5) engineering, technology & applied science research vol. 12, no. 2, 2022, 8316-8320 8318 www.etasr.com khlifi et al.: investigation of a leakage reactance brushless dc motor for dc air conditioning … where st and s are the saturation factors found from the terminal voltage/armature current and open-circuit characteristics respectively. since tuv can be substituted by a dui x and fue can be substituted by fi k , (4) can be rewritten as (6) and (5) can be rewritten as (7): t t tu t a duv s v s i x= = (6) f fu fe se si k= = (7) start for armature current calculate choose an initial value of the leakage reactance , calculate by equation (3) find from the o .c.c.c calculate the saturation factor , s stop ts 0lx 1 t l du s s x x s − = − 4 0 10l lx x − − >0 0l l lx x x= +∆ no yes j fe si fig. 3. flowchart of the bldc motor leakage reactance estimation. fig. 4. armature leakage reactance. substituting (3) in (7), gives us: ( )f a du le si x x= − (8) substituting (6) and (8) in (2), results to: ( )t a du a du l a ls i x si x x i x= − + (9) equation (9) gives the following expression for lx : 1 t l du s s x x s − = − (10) iii. identification of the leakage reactance the proposed technology was tested on many synchronous machines of various rated sizes in laboratory and at several hydro power facilities. measurements were taken as soon as the machines were synchronized to the power system. the units were loaded while the excitation current was kept constant. voltage and active and reactive powers were recorded. the potier reactance has largely replaced the armature leakage reactance in many applications. it is calculated using the potier triangle, which is built using data from open circuit, short circuit, and zero power factor characteristics. fig. 5. armature leakage reactance with open inductor test. fig. 6. armature leakage reactance with the potier method. 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 30 35 40 45 is(a) p o ti e r r e a c ta n c e ( o h m s) potier reactance engineering, technology & applied science research vol. 12, no. 2, 2022, 8316-8320 8319 www.etasr.com khlifi et al.: investigation of a leakage reactance brushless dc motor for dc air conditioning … fig. 7. armature leakage reactance with open circuit test. fig. 8. comparison of the leakage reactance and potier reactance. the resulting leakage reactances were compared to the available potier reactance values or the direct axis subtransient reactance with the aim of evaluating the results. for steadystate conditions, computing the synchronous reactance first, then the mutual reactance, and finally the slot and differential leakage reactance as a difference between potier and mutual reactances yields similar accuracy. a standard approach for determining armature inductance is to remove the rotor. however, it would be tough to implement in those bldc computers. as a result, we offer an approach that includes a zero sequence reactance approximation. the potier reactance has a greater value than the leakage reactance, especially when the zero power factor test is performed at the rated voltage. furthermore, because it is an intrinsic element of the formers, the leakage reactance may have a lower value than the dand qaxis sub-transient reactances. as a result, when making comparisons, one has to keep in mind that the genuine leakage reactance value is lower than the potier and subtransient reactances. iv. conclusion using the constant excitation test and simple computations over the collected data, this research proposed a novel way to estimate the armature leakage reactance of a bldc motor. the procedure was applied to a variety of tests with excellent results. rather than providing any error measure, the resultant leakage reactances were simply compared to the values declared by the manufacturers, derived through normal procedures, or to the d-axis sub-transient reactance. this was done since the percentage errors appear to be bigger even for slight variations due to the modest values of the leakage reactance. it should be emphasized that the test is straightforward to perform and that it can be performed on a bldc machine in operation at virtually no cost or danger of damage. rather than prototypes or laboratory machines, the technology is ideal for medium to large scale power units that are currently installed or being built in the field. acknowledgment the authors extend their appreciation to the deputyship for research & innovation, ministry of education, saudi arabia for funding this research work through the project number (20/11). references [1] y. park, h. kim, h. jang, s.-h. ham, j. lee, and d.-h. jung, "efficiency improvement of permanent magnet bldc with halbach magnet array for drone," ieee transactions on applied superconductivity, vol. 30, no. 4, pp. 1–5, jun. 2020, https://doi.org/ 10.1109/tasc.2020.2971672. [2] g. boztas, m. yildirim, and o. aydogmus, "design and analysis of multi-phase bldc motors for electric vehicles," engineering, technology & applied science research, vol. 8, no. 2, pp. 2646–2650, apr. 2018, https://doi.org/10.48084/etasr.1781. [3] m. yildirim, h. kurum, d. miljavec, and s. corovic, "influence of material and geometrical properties of permanent magnets on cogging torque of bldc," engineering, technology & applied science research, vol. 8, no. 2, pp. 2656–2662, apr. 2018, https://doi.org/ 10.48084/etasr.1725. [4] s. mahdiuon-rad, s. r. mousavi-aghdam, m. r. feyzi, and m. b. b. sharifian, "analysis of pm magnetization field effects on the unbalanced magnetic forces due to rotor eccentricity in bldc motors," engineering, technology & applied science research, vol. 3, no. 4, pp. 461–466, aug. 2013, https://doi.org/10.48084/etasr.296. 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[21] d. b. minh, v. d. quoc, and p. n. huy, "efficiency improvement of permanent magnet bldc motors for electric vehicles," engineering, technology & applied science research, vol. 11, no. 5, pp. 7615–7618, oct. 2021, https://doi.org/10.48084/etasr.4367. microsoft word 10-751-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1162-1166 1162 www.etasr.com ebrahimi et al.: effect of pre-gelatinized wheat starch on physical and rheological properties of... effect of pre-gelatinized wheat starch on physical and rheological properties of shortened cake batter and cake texture fatemeh ebrahimi department of food science and technology, ayatollah amoli branch islamic azad university amol, iran. babak ghiassi tarzi department of food science and technology science and research branch islamic azad university tehran, iran maryam asghari department of food science and technology science and research branch islamic azad university tehran, iran abstract—the focus of this study was the effect of 1.5%, 3% and 4.5% pre-gelatinized wheat starch (based on the total weight of cake batter) on improving the qualitative properties of shortened cake batter. specific volume and viscosity of the shortened cake batter were measured for controls, 1.5%, 3% and 4.5% gelatinized starch; some important properties such as texture and sensory evaluation were examined. by increasing pre-gelatinized wheat starch used in the batter, a significant difference was observed in the rheological properties of the batter. cake batter properties were found improved compared to the control samples. the sample with 3% pre-gelatinized starch had a lower viscosity than other treatments. the treatment with 4.5% pregelatinized starch had the lowest specific volume compared to other treatments. the overall results showed that the shortened cake with 3% pre-gelatinized starch was the best treatment in terms of texture and sensory evaluation factors. keywords-pre-gelatinized wheat starch; rheological properties; shortened cake batter; viscosity i. introduction currently, there are many producers of baking products such as breads, cakes, muffins and biscuits in iran. according to the association of iranian confectionery manufacturing companies, over 240,000 tons of cake is produced annually for use in domestic and foreign markets [1]. one of the important problems with cakes is that they stale fast. they quickly lose their freshness within a few days and become leathery and hardly chewable. economically, it is important to keep cakes fresh. flat cakes have generally very short shelf life; thus, additives such as modified starch can improve their quality [2, 3]. the main ingredients of cake are flour, sugar, eggs and fat, each of which has an important role in the structure and quality of the product [4]. extensive research has been conducted on the material and process conditions of cake products. variety, quality and shelf life of cakes are always a concern of researchers. the improved cooking methods, storage at certain temperature and additives improve texture, strengthen the gluten network, provide softness and smoothness and postpone staling. instant starches or hydro-colloids added to baked goods can increase moisture survival [5, 6]. moisture content is an important parameter for staling, because retro gradation of the starch is reduced with increasing moisture content [5, 6]. in [7], wheat starch was replaced by 3, 5 and 7% retrograded waxy corn starch to produce bread and evaluated rheological properties of the batter and sensory properties of the breads by farinograph and extensographic after 24, 48 and 72 hrs. results of the rheological tests showed that this starch increase water absorption. in general, the replaced starch quickly increased viscosity; however, it was not able to keep its stability. the batter made by the replaced starch was weaker and less stable than the batter made by wheat starch. results of sensory evaluation showed higher acceptability for these breads; addition of 5-7% starch considerably improved shelf life of the bread. the breads remained softer and more humid during 6 days of storage time [7]. in [8], it was shown that that moisture content increase shelf life of the product by 2%. therefore, high moisture lost in bakery products is one of the reasons for accelerated staling of these types of products [8]. in [9], authors evaluated the effect of different types of starch (corn, potato, waxy maize and pre-gelatinized) added to cake formulation in order to delay staling of the cake and found that pre-gelatinized starch contributes to reduced moisture loss during cooking and storage and cakes containing pre-gelatinized starch are softer than the control cake. in [10], it was reported that the overall stiffness of cakes consists of two separate factors: 1) stiffness effects caused by moisture transfer to the crust and 2) internal stiffness of the cell wall matter associated with starch retro gradation during storage. in [11], authors studied the effect of rice starch on rheological properties of the batter at different temperatures. rice starch was gelatinized at 20, 40, 60 and 90 minutes. the results showed that gelatinization temperature increased by increasing the time to 60 minutes. the rice starch batter had higher viscosity and lower moisture content for a longer period of time. this is probably due to lower amylose and protein content of the modified starch batter. engineering, technology & applied science research vol. 6, no. 5, 2016, 1162-1166 1163 www.etasr.com ebrahimi et al.: effect of pre-gelatinized wheat starch on physical and rheological properties of... ii. materials and methods materials used to produce shortened cake batter included wheat starch, sugar, water, eggs, inverted sugar, oil, emulsifier, vanilla and baking powder as well as pre-gelatinized starch. materials and equipment used for production of pre-gelatinized wheat starch included wheat starch, water and extruder. materials used for physicochemical tests included buffer, petroleum ether, 2% boric acid, 0.1 n hydrochloric acid, 50%naoh, concentrated sulfuric acid, catalyst, reagent solution (methyl red + ethanol + methylene blue). a. production of pre-gelatinized wheat starch to produce the pre-gelatinized wheat starch, wheat starch and water were mixed and pre-gelatinized in an extruder at 70100 °c and 30-80 rpm. then, the water was evaporated in a dryer. the mixture was crushed to smaller pieces by a mill [12]. b. production of shortened cake batter to produce shortened cake batter, eggs, sugar and emulsifier were mixed by a mixer at high speed for 3 minutes (table i). then, oil and water were added to the mixture and stirredbya stirrerat high speed. next, starch, vanilla, baking powder, inverted syrup, pre-gelatinized starch and salt were added and the mixture was stirred at medium speed for 3 minutes [13]. to produce batter with the pre-gelatinized starch, three units of water per unit of pre-gelatinized starch minus the same amount of null flour were added to the mixture. table i. formulation of the control and sample cakes r aw m at er ia l c o n tr o l 1 .5 % p re g el at in iz ed st ar ch 3 % p re g el at in iz ed st ar ch 4 .5 % p re g el at in iz ed st ar ch starch 36 34.5 33 31.5 oil 10 10 10 10 sugar 20 20 20 20 baking powder 1 1 1 1 emulsifier 1.5 1.5 1.5 1.5 egg 11 11 11 11 water 19.5 24 28.5 23 invert syrup 3 3 3 3 vanilla 0.1 0.1 0.1 0.1 pre-gelatinized flour 0 1.5 3 4.5 c. tests for pre-gelatinized starch and starch used in the formulation moisture, ash and protein content of the starch were calculated by aacc 08-01, aacc 44-15 and aacc 46-13, respectively. starch fat was evaluated according to the national standard of iran. d. tests for batter determination of specific volume specific weight of the batter was calculated by measuring the weight ratio of 240 ml batter to 240 ml water [14]. specific volume was calculated by the following formula: waterdistilled 240ml ofweight batter 240ml ofweight = volumespecificbatter determination of batter viscosity viscosity of cake batter was measured by the brookfield model, dv-ii + programmable. since brookfield viscometer cannot easily measure viscosity of the cake batter, viscosity of batters was measured under certain conditions using a particular spindle. viscosity of the samples was measured using spindle 64, 1 rpm and 73 torque at 30 s [15]. e. tests for cake cake texture assessment texture analysis test was performed by texture profile analyzer with aacc 74-04 in days 15 and 30 of storage on controls and the samples treated with 1.5%, 3% and 4.5% pregelatinized starch. for the compression test, the samples were first cut into 2.5 cm cubes; then, the cubes were compressed by a plate probe by 50% at 1 mm/s. the compressive force applied to the samples was reported in newton. maximum force applied to the samples indicated higher stiffness of the samples. moreover, sensory properties of the cakes such as color, flavor and texture was tested by 8 trained evaluators using a 9-point hedonic method. in this test, number 1 represented the lowest score given by the evaluators and number 9 the highest [16]. all physical and chemical tests were performed 3 times on 3 different days. data obtained was analyzed using a completely randomized design (crd) by the spss software, version 19. the mean of treatments was compared by duncan's multiple range test to the average level of error 5%. moreover, the data obtained from sensory evaluation was analyzed by the friedman test. iii. results a. starch the results related to flour and pre-gelatinized starch are shown in table ii. the results are significantly different (p<0.05). table ii. results of the tests on null flour and the pregelatinized starch (each number indicates 3 iterations) test null flour pre-gelatinized starch protein (%) 11.89 13.91 ash (%) 0.5 0.5 moisture (%) 14.71 3.34 fat (%) 0.86 0.18 wet gluten 28.35 not measurable gluten index (%) 87.3 not measurable falling number 614.5 115 sedimentation number 25 32 pan 77.43 17.13 sieve 125 20.80 13.69 sieve 180 1.05 45.34 particle size sieve 475 1.08 24.28 ph 5.75 5.81 engineering, technology & applied science research vol. 6, no. 5, 2016, 1162-1166 1164 www.etasr.com ebrahimi et al.: effect of pre-gelatinized wheat starch on physical and rheological properties of... b. specific volume of batter the results related to the effect of pre-gelatinized starch on specific volume of batter are shown in figure 1 and table iii. statistically, there was no significant difference in specific volume of 1.5% and 3% treatments, while controls and 4.5% treatments were significantly different from each other and other treatments. specific volume of cake batter as a factor for assessing overall ability of the batter to maintain air provides limited information regarding the size and extent of the gas cells [16]. according to [17], higher specific volume of cake batter reflects lower volume of the cake. this report is consistent with the current study, where the increased amount of pregelatinized starch used reduced the specific volume of cake batter. eventually, an increase was observed in volume of the cakes containing more pre-gelatinized starch. according to observations, the increase in pre-gelatinized starch softened the batter texture which made the mixing easier. since mechanical factors (mixing) are one of the factors effective in increasing cake volume, the increase in pre-gelatinized starch and water content and a reduction in the amount of null flour used in the cake batter influenced aeration and thus the amount of air in the batter and reduced the specific volume. c. viscosity of batter as shown in figure 2, there is a significant difference in viscosity of all treatments. the 3% treatment had the lowest viscosity while the 1.5% treatment was the most viscose sample. according to the results, the pre-gelatinized starch added to the batter formulation reduced viscosity by 3%, while 4.5% pre-gelatinized starch added to the cake batter increased viscosity by3% compared to the sample. the results showed that the 3% treatment had the highest reduced viscosity compared to the control treatment. pre-gelatinized starch changes the elasticity of the batter and increases gas storage capacity, reducing the consistency of the batter. this means that the batter is softer, that is, its viscosity is reduced compared to the control sample. thus, the increased softness is followed by reduced viscosity of the batter. pre-gelatinized starch has a very high water holding capacity. therefore, addition of certain amounts of pregelatinized starch will result in increased residual moisture and reduced viscosity of the batter. the results indicate that the 3% treatment had the lowest viscosity compared to controls and other treatments. in [18] it was stated that the flour boiling happens simultaneously with partial drying of the starch molecular structure under heat, which is also true for the pregelatinized starch. the increased solubility of the pregelatinized starch can be due to partial breaking and increased mobility of the molecules by absorbing water as well as physical porous structure of this type of starch [19]. d. cake texture the cake samples produced were tested for f(max) which is a measure of the force on the cake samples. the changes related to maximum force were tested for all samples in three different days of storage (1, 15 and 30). it was observed that a larger increase in the pre-gelatinized starch used in the product structure and reduced amount of flour was followed by reduced stiffness of texture. therefore, 4.5% treatment had the softest tissues compared to other treatments. this can be attributed to water absorption of the pre-gelatinized starch. in addition, there is a direct relationship between moisture and stiffness. water absorption and thus moisture content will have a direct effect on textural properties of bakery products. pre-gelatinized starch changes elasticity of the batter and increases gas storage capacity. the increased gas storage capacity and consequently reduced consistency of the batter will soften the cake texture. thus, the pre-gelatinized starch plays an important role in reducing stiffness of the cake texture by reducing elasticity. moreover, texture analysis showed that the cake had higher stiffness in day 30 compared to day 1 and 15. e. sensory evaluation according to the results of the sensory evaluation test, 3% treatment obtained higher score for flavor, color and general acceptance compared to other treatments. in contrast, acceptance of texture was higher for 4.5% treatment compared to other treatments. the pre-gelatinized starch will improve taste, color and texture of the final product. fig. 1. effect of pre-gelatinized starch on specific volume of cake batters. letters indicate significant mean of treatments at 0.05 table iii. results related to batter specific volume treatment specific volume control sample 0.93c 1.5% treatment 0.83b 3% treatment 0.85b 4.5% treatment 0.70a fig. 2. effect of pre-gelatinized starch on viscosity of cake batters. letters indicate significant mean of treatments at 0.05 table iv. results related to specific viscosity of batter treatment viscosity control sample 14.42c 1.5% treatment 15.97d 3% treatment 12.15a 4.5% treatment 13.58b engineering, technology & applied science research vol. 6, no. 5, 2016, 1162-1166 1165 www.etasr.com ebrahimi et al.: effect of pre-gelatinized wheat starch on physical and rheological properties of... fig. 3. comparison of means of three days f-max (n) fig. 4. comparison of the effect of day on of-max (n) * letters indicate significant mean of treatments in 0.05. fig. 5. comparison of mean of sensory evaluation iv. discussion a significant difference was observed in specific volume of the 4.5% treatment and the control. due to its higher water absorption capacity, the 3% treatment had the lowest viscosity than other treatments. physicochemical tests on the cake samples indicated no significant difference in moisture, aw, volume, color and stiffness of the 1.5% treatment and the control (p>0.05), while a significant difference was observed in the results of physicochemical tests as the amount of pregelatinized starch was increased in the formulation (p<0.05); the increase in the amount of 3% pre-gelatinized starch was associated with an increase in moisture, aw and volume of the treatment. this led to an increase in quality of the 3% sample. results of cake texture assessment which were evaluated for the effect of various amounts of the pre-gelatinized starch on the cake texture showed that the increase in the pre-gelatinized starch used in the structure as well as the reduction in the amount of the used null flour was associated with a decrease in stiffness of the cake samples; the 4.5% treatment had the softest texture compared to other treatments. moreover, cake texture assessment for various amounts of the pre-gelatinized starch in days 1, 15 and 30 indicated no significant difference in stiffness (p>0.05). cake texture assessment showed that the control and treatments were more stiff in day 30 compared to day 1 (p<0.05). moisture of the null flour is higher than that of pre-gelatinized starch, because the pre-gelatinized starch is exposed to a combination of moisture, pressure, temperature and mechanical cuts during its production using extrusion process which is a special process in short time and high temperature and the pre-gelatinized starch loses its moisture [20]. v. conclusion the pre-gelatinized starch, as an improver, has a positive effect on nutritional value and leads to changes in physicochemical properties of the finished product. battersmixes with different percentages of pre-gelatinized wheat starch were investigated in this paper. the results presented in this paper showed that the increased amount of pre-gelatinized starch reduced the specific volume of cakes. the best results derived from a 3% pre-gelatinized starch. sensory evaluation of the cake samples, performed by trained sensory evaluators, showed that the cake produced by 3% pregelatinized starch had the highest score on flavor, color and general acceptance compared to other treatments. a better texture however was achieved with a 4.5% mix. as higher amount of pre-gelatinized starch replaced the null flour, some properties of the cake such as texture and general acceptance also improved. references [1] e. b. bennion, g. bamford, the technology of cake making, publication of agricultural sciences, 2008 [2] m. hogati, m. h. azizi, flat bread technology, tehran andishmand publiction, 2004 [3] n. ragab zadeh, bread technology, tehran university, 1996 [4] a. mastakidou, g. bekas, a. paraskevopoulou, “aroma and physical characteristics of cakes prepared by replacying margarine with extra virgin olive oil”, lwt-food science and technology, vol. 43, pp. 949957, 2010 [5] d. a. bell, l. w. steinke, “evaluating structure and texture effects of methylcellulose gums in microwave baked cake”, cereal food world, vol. 36, no. 11, pp. 941-944, 1991 [6] j. p. zallie, the role and function of starches in microwaveable food formulation microwave foods, chicago, 1988 [7] f. ahmadian, effect of retrograded waxy corn starch on dough rheological properties and quality of baguette bread, m.sc. thesis, national nutrition and food technology research institute, 2006 [8] c. e. stauffer, “emulsifiers as anti-staling agents”, cereal food world, vol. 45, no. 3, pp. 106-110, 1997 [9] n. seyhun, g. sumnu, s. sahin, “effects of different starch on retargation of staling of microwave–baked cakes”, food and bioproducts processing , vol. 83, no. c1, pp. 1-5, 2005 [10] r. c. e. guy, “factors affecting the staling of madeira slab cake”, journal of the science of food and agriculture, vol. 34, pp. 477-491, 1983 [11] m. s. rohaya, m. y. maskat, a. g. ma’aruf, “reologicalproperties of different degree of pregelitinized rice flour batter”, sains malaysiana. vol. 42, no. 12, pp. 1707-1714, 2013 [12] t. jaya shankar, s. bandyopadhyay, “process variables during singlescrew extrusion of fish and rice-flour blends”, journal of food processing and preservation, vol. 29, no. 2, pp. 151-164, 2005 [13] m. r. baeva, i. n. panchev, v. v. terzieva, “comparative study of texture of normal and energy reduced sponge cakes”, die nahrung, vol. 44, no. 4, pp. 242-246, 2000 [14] c. c. lee, h. f. wang, s. d. lin, “effect of isomaltooligosaccharide syrup on quality characteristics of sponge cake”, cereal chemistry, vol. 85, no. 4, pp. 515-521, 2008 engineering, technology & applied science research vol. 6, no. 5, 2016, 1162-1166 1166 www.etasr.com ebrahimi et al.: effect of pre-gelatinized wheat starch on physical and rheological properties of... [15] s. m. lakshminarayan, v. rathinam, l. krishna rau, “effect of maltodexterin and emulsifiers on the viscosity of cake batter and the quality of cakes”, j. sci. food agric., vol. 86, pp. 706-712, 2006 [16] c. c. lee, h. f. wang, s. d. lin, “effect of isomaltooligosaccharide syrup on quality characteristics of sponge cake”, cereal chemistry, vol. 85, no. 4, pp. 515-521, 2008 [17] i. l. des rochers, k. d. seitz, c. e. walker, c. wrigley, w. colin, “cakes, chemistry of manufacture”, encyclopedia of grain science, pp. 129-133, 2004 [18] s. e. harding, “the intrinsic viscosity of biological macromolecules; progress in measurement interpretation and application to structure in dilute solution”, progress in biophysics and molecular biology, vol. 68, pp. 207-262, 1997 [19] m. majzoobi, m. radi, a. farahnaky, j. jamalian, t. tongdang, g. h. mesbahi, “physicochemical properties of pre–gelatinized wheat starch produced by a twin drum drier”, journal of agriculture science technology, vol. 13, pp. 193-202, 2010 [20] a. anastasiades, s. thanou, d. loulis, a. stapatoris, t. d. karapantsios, “rheological and physical characterization of pregelatinized maize starches”, journal of food engineering, vol. 52, pp. 57-66, 2002 microsoft word etasr_v12_n3_pp8765-8771 engineering, technology & applied science research vol. 12, no. 3, 2022, 8765-8771 8765 www.etasr.com doufene et al.: hybrid grey wolf and finite element method (gwo-fem) algorithm for enhancing … hybrid grey wolf and finite element method (gwo-fem) algorithm for enhancing high voltage insulator string performance in wet pollution conditions dyhia doufene department of electrical engineering electrical and industrial system laboratory (lsei) university of science and technology houari boumediene bab ezzouar, algeria doufenedyhia@yahoo.fr samira benharat department of electrical engineering electrical and industrial system laboratory (lsei) university of science and technology houari boumediene bab ezzouar, algeria sbenharat@hotmail.fr slimane bouazabia department of electrical engineering electrical and industrial system laboratory (lsei) university of science and technology houari boumediene bab ezzouar, algeria sbouazabia@yahoo.fr sid ahmed bessedik department of electrical engineering université amar telidji de laghouat laghouat, algeria s.bessedik@lagh-univ.dz received: 12 april 2022 | revised: 29 april 2022, 3 may 2022, and 7 may 2022 | accepted: 12 may 2022 abstractthe presence of wet pollution on the upper surface of a string insulator increases the electric field on the insulator surface, especially at the triple junction (pin-cement, cementporcelain) as well as at the surrounding air of the insulator. the rise of the electric field leads to the ionization of the air surrounding the insulator. this phenomenon, called corona discharge, is accompanied by several consequences that are harmful to the electricity transmission network, such as electromagnetic interferences, energy losses, visible light, audible noise, and the destruction of materials by erosion. if favorable conditions are gathered, it may even cause the flashover of the insulator. designing an optimal insulator shape that reduces this electric field value at the triple junction will be an important achievement in enhancing the performance of electrical grids. the objective of this paper is to evolve a hybrid algorithm based on the gwo-fem for optimizing the shape and the electrical performance of a string insulator. to achieve this purpose, this work is structured in four parts. first, modeling of the insulator string geometry is conducted in comsol-multiphysics, then fem computation of the electric field on the polluted surface of the string insulator is completed, and the maximum electric field value at the triple junction is saved as the fitness function that will be sent to the gwo algorithm to be optimized (minimized). the third part of the work is devoted to the coding of the constrained (electrical and geometrical constraints) gwo algorithm in a matlab interface, and finally, coupling the gwo code with the fem code. this study is achieved in wet polluted conditions. the results are given in both 2d and 3d representations. from the obtained results we can confirm that the developed gwo-fem hybrid algorithm for optimizing insulator strings is a very promising tool for designing and enhancing the shape and the electrical performance of insulators. keywords-insulator design; grey wolf optimisation; finite element method; 3d electric field i. introduction transmission and distribution lines constitute the link between production and consumers. these lines are held by insulating strings [1]. their performance is crucial for the good functioning of the electrical network. it is well established by experimental studies and confirmed by simulations [2-8], that the highest electric field value around an insulating string is found on the last pin in contact with the high voltage conductor, more exactly at the triple junction (pin-cement, cement-porcelain), which also corresponds to the highest thermal point [9], therefore, these areas are very critical in high voltage lines. the presence of high electric field leads to corona discharges by ionizing the surrounding air of the insulator, resulting in energy losses, electromagnetic interferences, visible light, audible noise, and the destruction of materials by erosion [10-12]. when the electric field stress exceeds a threshold value, especially in the presence of pollution conditions [13], flashover of the insulator string may occur. thus, finding the insulating string design that can reduce the critical value of the electric field at the triple junction region, and at the same time reduce the weight of the insulator corresponding author: dyhia doufene engineering, technology & applied science research vol. 12, no. 3, 2022, 8765-8771 8766 www.etasr.com doufene et al.: hybrid grey wolf and finite element method (gwo-fem) algorithm for enhancing … constitutes, a considerable advantage for improving the performance of electrical networks. it is here where the contribution of the present paper is registered. designing an improved shape of the insulator string involves taking into account many constraints, such as electrical, mechanical, environmental and economic, so using simulations prior to real testing and manufacturing is money and time saving. recent works carried out concerning the improvement of the high voltage insulators performance based on optimization methods, are divided into two main categories: (i) optimizing the shape of the chain elements [14-23] and (ii) grading ring optimization [24-25]. this research aims to study a hybrid algorithm based on the grey wolf optimization and the finite element method (gwo-fem) for designing an insulator sting and enhancing its electrical and geometrical performance. the current paper brings a complementarity to fill some existing gaps in the field of designing high voltage insulators. its main contributions are: • the proposal of the new hybrid gwo-fem algorithm for insulator optimization. • corona ring optimization and one-element insulator optimization have been already done in previous studies, but, to the best of our knowledge, total string optimization is achieved for the first time in this paper. • by using optimization constraints, two goals are achieved, namely reduction of the electric field value at the triple junction and of the weight of the insulator string. • 3d geometry representation and electric field distribution were conducted. • the most significant contribution of this work is the pollution case study which is conducted for the first time in this paper. to accomplish the above contributions, this work is divided into four main parts: • modeling of the insulator string geometry in comsolmultiphysics. • fem computation of the electric field on the insulation surface of the insulator and saving the maximum electric field value at the triple junction as the fitness function that will be sent to the gwo algorithm to be optimized. • coding of the constrained gwo algorithm in matlab [2627]. • coupling of the gwo code with the fem code. ii. insulator geometry modeling figure 1 shows one element of the studied 6-element string insulator. the parameters of the insulators are given in table i. the model is a string insulator of 6 elements of an u400b glass insulator commonly used in the algerian power grid. the modeling of the insulator geometry in comsol-multiphysics is represented in 2d and 3d in figure 2. fig. 1. u400b model. table i. parameters of the insulator string dimensions [cm] applied voltage [kv] shed diameter (d) unit spacing (h) creepage distance (l) pin cap 32.0 20.5 435 100 0 (a) (b) fig. 2. the reference 6-element string insulator. (a) 2d, (b) 3d. a wet pollution layer (figure 3) is put on the upper surface of each element of the string. the thickness of the pollution layer is 0.5mm. the pollution layer is in contact with the earthed cap. the material parameters used for the simulation are given in table ii. engineering, technology & applied science research vol. 12, no. 3, 2022, 8765-8771 8767 www.etasr.com doufene et al.: hybrid grey wolf and finite element method (gwo-fem) algorithm for enhancing … fig. 3. zoom in the pollution layer. table ii. material parameters of the simulation model material permittivity conductivity [s/m] air 1 0 glass 5.59 10-14 iron 106 5,998.107 cement 5.9 10-12 pollution 80 10-4 iii. fem computation of potential and electric field after the meshing process, potential and electric field distributions are computed by solving (1) and (2) by using fem. ∆v=0 (1) e��� � ����� v (2) where e represents the electric field and v is the electric potential. the electric potential varies from 100kv from the pin to 0v on the cap as shown in figure 4 giving the potential repartition along the creepage distance of the insulator string. fig. 4. electric potential repartition on the creepage path of the insulator string. from the electric field repartition (figure 5), starting from the pin towards the cap, we record a maximum value of 190kv/cm at the last pin. this obtained result is in adequacy with the results from the literature review [2-9], which attest that the highest electric field value is located at the last pin of the string connected to the high voltage and exactly at the triple junction. so, for the optimization purpose, the maximum electric field emax recorded at this triple junction is saved as the fitness function and is sent to the gwo cod to be optimized (minimized). the potential and electric field distribution in 2d and 3d are given in figures 6 and 7 respectively. a zoom in the last pin shows clearly the triple junction with the highest electric field value. fig. 5. electric field repartition on the creepage path of the insulator string. (a) (b) fig. 6. electric potential distribution for the insulator sting. a) 2d, (b) 3d. engineering, technology & applied science research vol. 12, no. 3, 2022, 8765-8771 8768 www.etasr.com doufene et al.: hybrid grey wolf and finite element method (gwo-fem) algorithm for enhancing … (a) (b) fig. 7. electric field distribution for the insulator sting. a) 2d, (b) 3d. iv. optimization process using gwo the principle of the gwo algorithm [28] is based on reproducing the hunting technique of grey wolves and modeling mathematically their social hierarchy. four categories can be noticed in wolf population. the α (alpha), β (beta), and δ (delta) wolfs represent the optimal solutions for the optimization problem. the last category is the ω (omega) wolves, which are the followers [28, 30]. the mathematical modeling of the steps of the hunting process is given below. • encircling: (surrounding the prey while hunting), is modeled by (3) and (4): d��� � c ����.x���� �t� � x �����t�| (3) x �����t � 1� � x���� �t� � a ����.d��� (4) where t is the current iteration, xp and x are the positions of the prey and the grey wolf respectively, c and a are the coefficient vectors calculated by (5) and (6): a ���� � 2.a���t�.r�� � a���t� (5) c�� � 2.r�� (6) the elements of the vector a linearly decrease from 2 to 0, and r1, r2 are random vectors in [0,1]. • hunting: equations (7)-(9) reproduce the hunting model: �d���� � c��� .x���� -x �����t� d���� � c��� .x���� -x �����t� d���� � c�� .x���� -x �����t� (7) where c1, c2, and c3 are obtained by (6). !"# "$ x�����t�� x���� –a����.�d�����t�� x�����t�� x����-a����.&d�����t�' x��� �t�� x����-a��� .&d�����t�' (8) where xα, x(, and xδ are the first three best solutions at iteration t, a1, a2, and a3 are obtained from (5), and dα, d(, and dδ are obtained from (7). x �����t � 1� � )���*�+�,)���-�+�,)���.�/� (9) • attacking: when the prey representing the optimal solution, can no longer move, the wolves launch the attack, which marks the end of the hunt. this process is mathematically reproduced by decreasing the value of a linearly from 2 to 0. v. gwo and fem coupling the hybrid gwo-fem algorithm is obtained by following the different steps given in the flowchart of figure 8. fig. 8. flowchart of the gwo-fem algorithm process. vi. optimization results the different lengths (l1 to l4), shown in figure 9 are taken as the optimization variables. a constraint is imposed to the total creepage length to not exceed the reference length of the engineering, technology & applied science research vol. 12, no. 3, 2022, 8765-8771 8769 www.etasr.com doufene et al.: hybrid grey wolf and finite element method (gwo-fem) algorithm for enhancing … industrial model in order to obtain a shape with a reduced creeapage distance and as a consequence reduced weight of the insulator. the stopping criterion of the hybrid algorithm is 150 iterations [15]. the obtained shape of the optimized insulator string is given in figure 10. a comparative analysis of the results before and after optimization is established in table iii. fig. 9. the optimization variables. fig. 10. optimized shape of the string insulator. table iii. optimization results reference string optimized string l�1cm4 3.30 0.50 l��1cm4 3.40 0.60 l�1cm4 3.85 0.14 l��1cm4 4.03 0.32 l 1cm4 3.50 0.130 l51cm4 1.16 5 creepage distance 1cm4 435 324 creepage length reduction (%) 25 electric field at the triple junction [kv/cm] 190 177 electric field reduction at the triple junction region (%) 8 the diametrical surface of the insulating glass surface [cm 2 ] 435.7 369.7 reduction of the surface value of the insulating glass surface [%] 15.14 the potential and the electric field distributions after optimization are given in figures 11 and 12 respectively. the potential and electric field repartition along the creepage distance (from the pin to the cap) on the optimized insulator string are registered in figures 13 and 14 respectively. (a) (b) fig. 11. electric potential distribution for the optimized insulator sting. (a) 2d, (b) 3d. (a) (b) fig. 12. electric field distribution for the optimized insulator sting. (a) 2d, (b) 3d. engineering, technology & applied science research vol. 12, no. 3, 2022, 8765-8771 8770 www.etasr.com doufene et al.: hybrid grey wolf and finite element method (gwo-fem) algorithm for enhancing … fig. 13. electric potential repartition on the creepage path of the optimized string insulator. (a) (b) fig. 14. electric field repartition on the creepage path of the optimized string insulator. (a) on the creeapage path (from the pin to the cap), (b) zoom at the triple junction point (the last pin connected to the high voltage). vii. discussion from the comparative analysis between the cases before and after optimization (table iii), we can clearly notice the efficiency of the proposed optimization method since the two objectives set in this work, namely the reduction of the electric field and the creepage distance, have been correctly achieved. the developed gwo-fem hybrid algorithm for optimizing insulator strings is a promissing technique for designing and enhancing the shape and the electrical performance of insulators. the comparative analysis carried out between the reference string and the optimized one in the prensence of a wet pollution shows the following findings : • a decrease of 8% in the electric field at the triple junction of the last insulator connected to the high voltage was recorded. this reduction constitutes a major advantage with regard to the reduction of corona discharges at the surface of the insulator, and consequently a decline of the noise, the light, and the electromagnetic interferences issued from the ionization phenomenon of the air particles surounding the insulator sting. other positive consequences are the elongation of the insulator lifetime following the reduction of the corrosive effect of the crona discharges and the reduced risk of insulator flashover. • creepage length decreased by 25% and the diametral surface of the string insulator by 15.14%, which represent a huge advantage resulting in an important weight decrease and thus improving the economic aspect of the manufacturing of the insulators. • the 3d study gives a more realistic aspect to the achieved results. comparing the obtained results with [23, 24], where the objective function (the electric field at the pin region) is predicted using artificial neural networks, big similarity in the obtained shape after optimization is noticed. viii. conclusion the developed gwo-fem hybrid algorithm provides very satisfactory results, therefore it can be used as a powerful tool for desinging high voltage insulators in general. with this hybrid algorithm, optimal design of the insolator string is reached, satisfying two constraints: an electrical constraint (minimizing the maxium electric field value) and a geometrial constraint (minimizing the weight of the insulator string). the main advantage of the proposed hybrid algorithm is the possibility of combining other constaints that are involved in the flashover of high voltage insulators, such as the dry band formation, nsdd encapsulation, water draining, and also mechanical and thermal stresses can be taken into account, which is possible with the use of the computation interface of comsol-muliphysics that allows multiphysic studies at the same time and thus permitting the obtainment of an optimal design encompassing all the stresses undergone by the insulator string. acknowledgment the authors would like to thank the algerian ministry of higher education and scientific research and the directorate general for scientific research and technological development who provided the scholarship for visiting the high voltage laboratory at the school of engineering at cardiff university. references [1] d. pylarinos and i. pellas, "investigation of an insulator flashunder in an 150 kv otl of the power system of crete," engineering, technology & e le c tr ic f ie ld [ v /m ] e le c tr ic f ie ld [ v /m ] engineering, technology & applied science research vol. 12, no. 3, 2022, 8765-8771 8771 www.etasr.com doufene et al.: hybrid grey wolf and finite element method (gwo-fem) algorithm for enhancing … applied science research, vol. 9, no. 5, pp. 4851–4858, oct. 2019, https://doi.org/10.48084/etasr.3198. 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[30] s. arora, h. singh, m. sharma, s. sharma, and p. anand, "a new hybrid algorithm based on grey wolf optimization and crow search algorithm for unconstrained function optimization and feature selection," ieee access, vol. 7, pp. 26343–26361, 2019, https://doi.org/ 10.1109/access.2019.2897325. microsoft word etasr_7-1_1323-1328.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1323-1328 1323 www.etasr.com charalambous et al.: study of the behavior of water droplets under the influence of a uniform electric… study of the behavior of water droplets under the influence of a uniform electric field on conventional polyethylene and on crosslinked polyethylene (xlpe) with mgo nanoparticles samples c. charalambous m. g. danikas y. yin democritus university of thrace, department of electrical & computer engineering, power systems laboratory, greece crcharal@ee.duth.gr democritus university of thrace, department of electrical & computer engineering, power systems laboratory, greece mdanikas@ee.duth.gr shanghai jiao tong university, state energy smart grid r&d research center, shanghai, people’s republic of china yiny@sjtu.edu.cn n. vordos j. w. nolan a. mitropoulos hephaestus advanced laboratory, eastern macedonia and thrace institute of technology, greece vordosn@yahoo.com hephaestus advanced laboratory, eastern macedonia and thrace institute of technology, greece jnolan@teikav.edu.gr hephaestus advanced laboratory, eastern macedonia and thrace institute of technology, greece amitropoulos@teikav.edu.gr abstract—it is well known that polyethylene (pe) and crosslinked polyethylene (xlpe) are suitable insulating materials for underground cables. samples of pe and of xlpe with mgo nanoparticles were investigated regarding their flashover behaviour with a uniform electric field and water droplets of various conductivities. in the present paper, the effect of the mounting arrangement of the water drops on the value of the flashover voltage and the effect of the volume of dripping water on the flashover voltage were also studied. surface damages were analyzed using scanning electron microscopy (sem) studies and the study of the nano-structure of the samples was studied using the saxs system. keywords-polyethylene; cross-linked polyethylene; flashover; surface discharges; polymer nanocomposites i. introduction the insulating materials used for equipment of high voltages during operation for many years, are stressed by various factors. an important factor that contributes to the aging of the insulation is moisture, which in combination with the electrical stress causes changes in the condition of the insulating surface. these changes on the surface can cause the onset of partial discharges and eventually the gradual disintegration of the insulating material. in this paper, a comparison is made of the two types of insulation materials, i.e. between a conventional polymer material (pe) and a polymer nanocomposite material (xlpe with mgo nanoparticles. it is an experimental study using samples of pe and samples of xlpe with nanoparticles of magnesium oxide (mgo) [1, 2]. the purpose of the present work was to answer the question whether the addition of nanoparticles to a polymer insulator improves or not the flashover voltage. in the present study, the behavior of the said samples of insulating material with drops of water placed on the surface of samples of different conductivity from 0.8 μs/cm to 10000 μs/cm, under the effect of a uniform electric field. apart from the experimental measurements of water drops of different conductivities, some diagnostics are also reported regarding the results of surface erosion with the small angle x-ray scattering (saxs) technique and with a scanning electron microscope (sem). ii. experimental studies for the production of high voltage for carrying out the experiments, a high voltage power supply comprising a voltage transformer with dry insulation (epoxy resin) with a rated voltage of 20 kv. thus by controlling the voltage of the secondary winding through the autotransformer have the other side of the transformer voltages from 0 v to 28 kv. for the engineering, technology & applied science research vol. 7, no. 1, 2017, 1323-1328 1324 www.etasr.com charalambous et al.: study of the behavior of water droplets under the influence of a uniform electric… experiments two hollow electrodes were made of copper. the electrodes were bonded to the high voltage terminals of the feeder, and the distance between the two electrodes during the experimental measurements were constant at 2.5 cm. the dimensions of the electrodes are shown in figure 1. fig. 1. top view and transverse electrode section. the water droplets were positioned on the polymeric material surface with the aid of a special arrangement consisting of a metallic frame and three rules, one of which had two laser indicators. the water droplets were put on the surface with a 10 ml syringe. detailed information on the way the droplets were positioned on the polymeric surface is given in figure 2. the insulation materials investigated during the experiments were both conventional pe and xlpe with mgo nanoparticles (having 0.5 wt% nanoparticles). the water samples that were used for the experiments were eight, namely with conductivities of 0.8 μs/cm, 100 μs/cm, 200 μs/cm, 500 μs/cm, 1000 μs/cm, 2000 μs/cm, 5000 μs/cm and 10000 μs/cm. the apparatus used for measuring the conductivity was an electronic conductivity meter brand wtw inolab cond level 1 electrode (probe) wtw tetracon 325. fig. 2. water droplet arrangements between the electrodes. the arrangements shown in figure 2 implemented with both water drops of 0.05 ml and water drops of 0.1 ml. also measurements were made on arrangement of a droplet volume of 0.2 ml and 0.3 ml. after completion of the measurements with the water drops on the surface of the samples, the surface erosion was investigated by means of a saxs system (small angle x-ray scattering) and an scanning electron microscope (sem). iii. experimental methodology to perform the experiments followed the following procedure: once placed, the specified volume of water drops and conductivity on the insulating material in one of the aforementioned arrangements, the output voltage of the power supply was gradually increased until the flashover of the gap and recording of the breakdown voltage. after cleaning the insulating surface with alcohol, we repeated the same procedure by increasing the voltage of the power supply until the last recorded value reduced by 1.2 kv in order not to bring about the flashover of the gap. at this point we leave the output voltage of the power supply steady for five minutes to provide the necessary time for the process of deformation of the drop to be developed, the occurrence of partial discharges and ultimately overcome or not the gap. if there was not arcing and/or flashover, the voltage was increased at 0.4 kv steps until the occurrence of a flashover. this was the value of breakdown voltage that was finally recorded. variable parameters during the experiments were as follows: • the arrangement of water drops • the conductivity of the dripping water • the volume of water drops • the kind of the insulating material • the distance of the drops from the electrodes a. effect of water drops to the breakdown of insulating materials during operation the insulating materials are stressed by various environmental factors. one of the major factors of aging is moisture, which in combination with the electrical stress may cause changes on the surface of insulation. polymer insulation materials are widely used in high voltage applications. they are, however, sensitive to, among other factors, partial discharges. upon exposure of the polymer to rain or moisture, water droplets are formed on the surface of the insulation and hence the conductive contamination on the surface of insulation may follow. water droplets on the surface of a polymer material can cause –with an electric field present degradation of insulation even in low pollution conditions. this is due to the fact that water droplets on a polymer surface locally increase the applied electric field. an excessive increase in the localized electric field may result in certain local discharges and/ or arcs, which in turn make it possible to create the dry strips on the polymer surface. bridging of individual dry bands through the local electric arcs will eventually lead to a complete flashover [3]. this discharge mechanism can occur in both indoor insulations and outdoor insulations although engineering, technology & applied science research vol. 7, no. 1, 2017, 1323-1328 1325 www.etasr.com charalambous et al.: study of the behavior of water droplets under the influence of a uniform electric… each of these categories has its own peculiarities. generally, a combination of water droplets and dust as impurities on the surface of an insulating surface can lead to contamination, which may in turn result in significant reduction in flashover voltage. as shown in previous studies [4-7], the conductivity of the droplets, the roughness of the polymer surface, the volume of the droplets and the arrangement of the droplets in relation to the electrodes affect their behavior. b. forces applied on a drop of water on the polymer surface figure 3 shows the forces exerted on the droplet in case there is no applied electric field [4]. such forces are the surface tension of the liquid (τl), the surface tension of the solid (τs) and the interfacial tension between the liquid and solid (δsl). when an electric field is applied, the droplet is deformed due to an additional force applied to it. the tangential electric field on the insulation surface creates a force on the surface of the droplet causing deformation. the deformation of droplets adversely affects the uniform distribution of the electric field. droplet deformation could cause local increases in the electric field which in turn will cause local micro-discharges between the droplets. this is the beginning of the electrochemical deterioration of the insulation surface. hydrophobicity can be locally lost [8-10]. reduced hydrophobicity implies a higher risk of discharge [10]. solvable nitrates – the result of electrochemical deterioration – will cause a higher conductivity of the water droplets. dry zones may ensue. around the water droplets the electric field will be modified. the point where the electric field gets the highest value is the triple point. as was pointed out elsewhere [11], it is important to bear in mind that not only the influence of the applied electric field on the shape of the droplet is of great significance, but also the influence of the disintegrated droplet on the electric field distribution. micro-discharges, which eventually will develop into full partial discharges are among the major causes of insulation aging [12]. fig. 3. forces applied to a water drop on insulating surface. iv. sem and saxs analysis the pe and xlpe were studied with a jeol jsm 6390lv scanning electron microscopy (sem), in high vacuum mode at 20kv. before introduction to the sem for imaging, samples were coated with a thin layer of gold to reduce sample charging. ten images were selected from different areas on each surface. small angle x – ray scattering was performed in a saxs rig system provided by jj x – ray systems, with a cuka x ray source (λ=0.15056nm). the apparatus consists of the 2d rigaku smax -300 detector, vacuum chamber, pinholes to collimate the beam, and an x-ray source. each sample was measured at 2.5 m (detector-to-sample distance for 3600 sec exposure time). the background radiation and the matrix spectra were recorded for the same time period. silver behanate was used to calibrate the center and the q range of the detector. all measurements were corrected for background radiation, and transmission. v. results and discussion from figures 4 and 5, it is evident that the droplet volume plays a significant role in determining the flashover voltage in pe.. moreover, from figure 4 is indicated that the positioning of droplets influences the flashover voltage (if we compare the data of the 2 droplets put horizontally and of the 2 droplets put vertically on the sample). the droplet volume effect is even more dramatic in figure 5. needless to remark that it is obvious that the water conductivity affects greatly the droplet behavior and the flashover voltage. it is observed that the conductivity of the drops solution plays an important role in flashover voltage. the greater the conductivity of the water drops the smaller the value of the flashover voltage. fig. 4. flashover voltage for pure polyethylene sample with 0.05 ml volume droplets. fig. 5. comparison of results for two drops assembly horizontally volume 0.05 ml and 0.1 ml in pure polyethylene sample. figures 6 and 7 show the results for xlpe with 0.5 wt% nanoparticles of mgo. here again one may see the effect of water droplet conductivity on the flashover voltage as well the effect of droplet volume. for both materials (pe and the nanocomposite), it is evident that the distance of the droplets engineering, technology & applied science research vol. 7, no. 1, 2017, 1323-1328 1326 www.etasr.com charalambous et al.: study of the behavior of water droplets under the influence of a uniform electric… from the electrodes plays a role and it was noted that the nearer the droplets to the electrodes, the lower the flashover voltage. this phenomenon was noticed before with other insulating materials [5-7, 11]. in figures 8 and 9, a direct comparison between the two materials is made. it is clear that the nanocomposite xlpe (with 0.5 wt% mgo nanoparticles) tends to give higher flashover results than the conventional pe. this is a strong indication that nanoparticle addition improves the flashover voltage. this may be due to the gradual erosion of the surface and the emerging onto the surface of the nanoparticles, which in turn hinder the propagation of surface discharges. this explanation seems plausible and was given in [13, 14]. fig. 6. flashover voltages for xlpemgo sample with 0.05 ml volume droplets. fig. 7. comparison of results for three drops on triangle arrangement with volume 0.05 ml and 0.1 ml on xlpemgo sample. it seems that the addition of nanoparticles is beneficial for the flashover voltage. the addition of nanoparticle percentage depends on the polymer matrix as well on the type of the added nanoparticles. nevertheless, according to the literature, there is an optimum nanoparticle addition rate above which the properties of the insulating material deteriorate. this phenomenon is attributed to the formed nanoparticle aggregates within the polymer matrix which act negatively on the performance of the insulating material [15, 16]. in addition to experimental measurements made in the high-voltage laboratory for the study of the flashover voltage, the surface of the insulating materials tested was studied by using some well known diagnostic methods. these experiments relating to small angle x-ray scattering (saxs), and the study of samples of insulating material with a scanning electron microscope (sem). small angle x – ray scattering (saxs) is an analytical method for the determination of particle size and shapes in the nanoscale. typically, the saxs curves are divided in five regions (guinier, fractal, porod, micropore shoulder and near beam region). due to the nature of the sample, the saxs curves may have less than the 5 regions. according to guinier, the radius of gyration rg, can be calculated from the guinier plot (i(q) vs q2). rg is an indicator of how the mass of a particle is distributed around its center of mass [17]. fig. 8. comparison of the two insulating materials for three drops on triangle arrangement with volume 0.1 ml. fig. 9. comparison of the insulating materials for arrangement of a drop with volume 0.2 ml. figures 10 and 11 illustrate a graphical comparison of curves derived from the study of the polyethylene before and engineering, technology & applied science research vol. 7, no. 1, 2017, 1323-1328 1327 www.etasr.com charalambous et al.: study of the behavior of water droplets under the influence of a uniform electric… after the discharge (figure 10) and the xlpe with mgo nanoparticles (figure 11). in figure 10, the blue line shows the curve corresponding to the case of the material after the discharge, while curve in red corresponds to the case of the material that has not suffered a flashover, whereas in figure 11 the red line indicates the material that suffered flashover. in figures 10 and 11, we observe that more distortion occurs in the structure of the crosslinked polyethylene (xlpe) with mgo nanoparticles, but as shown in figure 11, the structure is somewhat more compact after discharge. as indicated in the studies [13, 14], this can be attributed to the fact that during the discharge the polymer matrix material decomposes and nanoparticles creating agglomerates gather near the surface. this makes the material more compact. fig. 10. comparison of two samples pe. fig. 11. comparison of two samples xlpe. from the electron density differences of the xlpe and pe samples the periodicity of the samples can be measured. the periodicity interprets the characteristic spacing of crystalline and non – crystalline domains for a two – phase system and represented as lp and called long period. the long period determined and lp=2π/qmax is the peak position of i(q) versus q plot [18]. the long period for the pe sample before and after discharge is 14.8nm. the xlpe long periods before and after discharge are 13nm and 48nm respectively. the increasing of crystallinity can be explained as an increasing of nanoparticles agglomerates due to destroying of the xlpe nanostructure. another diagnostic method used is the scanning electron microscopy (sem). electronic scanning microscopy is one of the modern and flexible methods of analysis of the microstructure of a large number of materials. fig. 12. sem micrographs of the polyethylene insulation surface: (a) virgin (b) damaged by arc (c) magnification of damaged area. fig. 13. sem micrographs of the xlpe mgo insulation surface: (a) virgin (b) damaged by arc (c) magnification of damaged area. figure 12 shows sem micrographs of the polyethylene insulation surface. figure 12(a) shows the surface before the discharge, figure 12(b) shows the damage of the surface caused by arc after the discharge and figure 12(c) shows a magnification of the damaged area. figure 13 shows sem micrographs of the xlpe–mgo insulation surface. figure 13(a) shows the surface before the discharge, figure 13(b) shows the damage of the surface caused by arc after the engineering, technology & applied science research vol. 7, no. 1, 2017, 1323-1328 1328 www.etasr.com charalambous et al.: study of the behavior of water droplets under the influence of a uniform electric… discharge and finally figure 13(c) shows a magnification of the damaged area. from the images obtained with the scanning electron microscope can be seen that in the case of the polyethylene sample, in contrast to the case of xlpe, in regions where they had undergone damage, the formation of pinholes in the surface of the insulating material was observed (figure 12 (c)). it is evident that xlpe with mgo nanoparticles behaves better that conventional pe. this generally agrees with previously published work, namely that small percentage additions of nanoparticles improve the electrical properties of conventional polymers [19-21]. vi. conclusions according to the results of the experiments, it is clear that by increasing the water conductivity, the value of the flashover voltage decreases. also an important role in the flashover voltage play the water droplets arrangement. the more droplets were, the smaller was the value of the flashover voltage. finally, from the results of the experimental measurements it is observed that by increasing the volume of water droplets, the flashover voltage decreases. as shown by the experiments made by saxs system, the largest alteration occurs in the structure of the crosslinked polyethylene (xlpe) with mgo nanoparticles, but it is observed that the structure becomes somewhat more compact after discharge. the scanning electron microscope indicated that in the case of the conventional polyethylene in contradistinction to the case of xlpe with mgo nanoparticles small holes have been observed, which may be the cause of further surface discharges. as a final conclusion, it can be suggested that the crosslinked polyethylene (xlpe) with addition of 0.5 wt% nanoparticles of magnesium oxide (mgo) has a higher flashover voltage than the conventional polyethylene (pe). acknowledgments the samples mentioned in the present paper were built by prof. yi yin’s research group at the state energy smart grid r&d research center, shanghai, people’s republic of china. references [1] g. chen, m. hao, z. xu, a. vaughan, j. cao, h. wang, ‘’review of high voltage direct current cables’’, csee journal of power and energy systems, vol. 1, no. 2, pp. 9-21, 2015 [2] m. g. danikas, r. sarathi, p. ramnalis, s. l. nalmpantis, “analysis of polymer surface modifications due to discharges initiated by water droplets under high electric fields”, world academy of science, engineering and technology, vol. 38, pp. 905-910, 2009 [3] m. s. naidu, v. kamaraju, high voltage engineering, eds. tata mcgraw-hill publishing co. ltd., new delhi, 2000 [4] h. -j. kloes, d. koenig, m. g. danikas, “electrical surface discharges on wet polymer surfaces”, proceedings of the 8th international symposium of gaseous dielectrics, virginia beach, virginia, usa, pp. 489-495, june 1998 [5] k. karakoulidis, m. g. danikas, p. rakitzis, “deterioration phenomena on insulating surfaces due to water droplets”, journal of electrical engineering, vol. 56, pp. 169-175, 2005 [6] m. g. danikas, p. rakitzis, k. karakoulidis, “study of parameters related to deterioration phenomena due to water droplets on polymeric surfaces”, journal of electrical engineering, vol. 57, no. 3, pp. 130– 137, 2006 [7] m. g. danikas, r. sarathi, p. ramnalis, s. l. nalmpantis, “analysis of polymer surface modifications due to discharges initiated by water droplets under high electric fields”, int. j. electr. power and energy syst. eng., vol. 3, no. 1, pp. 19-24, 2010 [8] w. t. starr, “polymeric outdoor insulation”, ieee transactions on electrical insulation, vol. 25, no. 1, pp. 125-136, 1990 [9] a. e. vlastos, s. m. gubanski, “surface structural changes of naturally aged silicone and epdm composite insulators”, ieee transactions on power delivery, vol. 6, no. 2, pp. 888-900, 1991 [10] m. g. danikas, “polymer outdoor insulators”, acta electrotehnica napocensis, vol. 40, no. 1, pp. 3-10, 1999 [11] m. g. danikas, p. ramnalis, r. sarathi, “a study of the behaviour of water droplets on polymeric surfaces under the influence of electric fields in an inclined test arrangement”, journal of electrical engineering, vol. 60, no. 2, pp. 94-99, 2009 [12] s. feier-iova, v. hinrichsen, “partial discharge inception voltage of water drops on insulating surfaces stressed by electrical field”, international symposium on high voltage engineering, pp. 21-25, 2009 [13] m. kozako, r. kido, n. fuse, y. ohki, t. okamoto, “difference in surface degradation due to partial discharges between polyamide nanocomposite and microcomposite”, ieee annual report of conference on electrical insulation and dielectric phenomena, pp. 398401, 2004 [14] m. kozako, r. kido, t. imai, t. ozaki, t. shimizu, t. tanaka, “surface roughness change of epoxy/tio2 nanocomposites due to partial discharges”, proceedings of 2005 international symposium on electrical insulating materials, pp. 661–664, japan, 2005 [15] j. k. nelson, dielectric polymer nanocomposites, eds. springer, heidelberg, germany, 2010 [16] i. plesa, p. v. notingher, s. schloegl, c. sumereder, m. muhr, “properties of polymer composites used in high-voltage applications”, polymers, vol. 8, 2016 [17] h. schnablegger, y. singh, the saxs guide. getting acquainted with the principles, anton paar gmbh, 2011 [18] m. jarvid, a. johansson, r. kroon, j. m. bjuggren, h. wutzel, v. englund, s. gubanski, m. r. andersson, c. müller, “a new application area for fullerenes: voltage stabilizers for power cable insulation,” advanced materials, vol. 27, no. 5, pp. 897–902, 2015 [19] l. a. utracki, “clay-containing polymeric nanocomposites and their properties”, ieee electrical insulation magazine, vol. 26, no. 4, pp. 615, 2010 [20] e. david, m. frechette, “polymer nanocomposites – major conclusions and achievements reached so far”, ieee electrical insulation magazine, vol. 29, no. 6, pp. 29-36, 2013 [21] e. a. cherney, “nanodielectrics applications–today and tomorrow”, ieee electrical insulation magazine, vol. 29, no. 6, pp. 59-65, 2013 microsoft word etasr_v12_n1_pp8136-8142 engineering, technology & applied science research vol. 12, no. 1, 2022, 8136-8142 8136 www.etasr.com ali et al.: an intelligent detoxification function of liver algorithm-partial transmit sequence … an intelligent detoxification function of liver algorithm-partial transmit sequence (idfla-pts) for the reduction of peak to average power ratio in underwater acoustic ofdm communication amir ali college of underwater acoustic engineering and key laboratory of marine information acquisition and security, ministry of industry and information technology, and acoustic science and technology laboratory, harbin engineering university, harbin, china amir@hrbeu.edu.cn baowei chen college of underwater acoustic engineering and key laboratory of marine information acquisition and security, ministry of industry and information technology, and acoustic science and technology laboratory, harbin engineering university, harbin, china cbwwin@163.com waleed raza college of underwater acoustic engineering and key laboratory of marine information acquisition and security, ministry of industry and information technology, and acoustic science and technology laboratory, harbin engineering university, harbin, china waleed@hrbeu.edu.cn asif ali college of nuclear science and technology harbin engineering university harbin, china aliasif@hrbeu.edu.cn haisen li college of underwater acoustic engineering and key laboratory of marine information acquisition and security, ministry of industry and information technology, and acoustic science and technology laboratory, harbin engineering university, harbin, china hsenli@126.com abstract-intelligent algorithms in artificial intelligence have brought several benefits to digital signal processing. the boom in machine learning and intelligent systems provides new perspectives and methods to solve many research problems in underwater acoustic (uwa) orthogonal frequency divisional multiplexing (ofdm) communication. partial transmit sequence is a tremendous technique for the mitigation of high peak-toaverage power ratio (papr) in ofdm communication systems, but finding the optimum phase factors has still a few problems. in this paper, a partial transmit sequence (pts) based on an intelligent detoxification function of liver algorithm-partial transmit sequence (idfla-pts) is proposed for the mitigation of papr in the uwa ofdm communication systems. this algorithm reduces the papr and the complexity of the proposed uwa ofdm model. the idfla-pts is also compared with the genetic algorithm-partial transmit sequence (ga-pts). besides this, the bit error rate (ber) performance of the idfla-pts is shown when a high power amplifier (hpa) is used for the bellhop channel model. the experimental results of the proposed idfla-pts method achieved nearly optimum results with fair complexity as compared to ga-pts and boosted the ber performance. keywords-underwater acoustic communication; ofdm; papr; intelligent detoxification function of liver algorithmpartial transmit sequence (idfla-pts) i. introduction the research on ofdm has been explored due to its distinct advantages over other techniques for wireless communication systems [1, 2]. due to its optimum results, now many kinds of research have taken steps in underwater communication and exploration [3]. for any communication network, a system should be noiseless, with less multipath delay, and with less doppler shift [4]. underwater acoustic sensing networks (uwasns) are formed by deploying different underwater acoustic transmitters and receivers which monitor the ocean. the battery deployed modems are installed, which consumes more power depending on its applications. for short-range communications this is not an issue, but for longcorresponding author: baowei chen engineering, technology & applied science research vol. 12, no. 1, 2022, 8136-8142 8137 www.etasr.com ali et al.: an intelligent detoxification function of liver algorithm-partial transmit sequence … range uwa applications, it is necessary to save battery power. the ofdm system is utilized for high-speed communication, but due to its major drawback of papr, researchers have contributed a lot to mitigate it up to the maximum level. papr has bit error degradation and leads to nonlinear distortion and affects the power efficiency of power amplifiers in the underwater communication systems [5]. therefore, the mitigation of papr has become a competitive and worth thinking research to have soft, reliable, and long-range communication in uwa communication. linearly operating powerful amplifiers are needed for high peaks, but designing and manufacturing those powerful amplifiers is comparatively costly [6, 7]. a power amplifier is in the saturation region during high papr creating inter-symbol interference among subcarriers, manipulates thus the original signal resulting in lower ber performance. to avoid this scenario, the average power of the transmitting signal is reduced. but reducing the average power will lead to a reduction of ber performance as well as the signal to noise ratio (snr). however, to reduce the peak power of the signal, much research has been done previously [8-11]. therefore, many researchers prefer to solve the problem of high papr by reducing the peak power of the transmitting signal. after experiments and simulations, many researchers have developed papr reduction methods like clipping, selective mapping, tone injection and reserved carriers, active constellation, coding, and partial transmit sequence [12-14]. although clipping is the simplest technique, it clips the signals with unwanted peaks and distorts the communicating signal and increases ber. on the other hand, few techniques cause inefficient energy increment of the signal, such as tone injection, tone reservation, and active constellation. selective mapping (slm) is also an efficient technique having better performance than others, as it has no energy increment and it does not distort the communication signal, but it still is rather complex [15-17]. the pts is the only efficient technique due to its distortionless feature with the least complexity. in this paper, we propose a pts technique based on the intelligent detoxification function of liver algorithm (idfla) to minimize papr and acquire better performance than the gapts system. the idfla is a self-efficacy algorithm that is extracted from medical science. it removes the toxic substances from the bloodstream and balances the hormonal level. besides this, it breaks down fats and makes them more easily digestible. ii. related work a lot of work has been proposed to mitigate papr, but few researches have been found to use intelligent computing techniques. therefore, the research on using various machine learning and deep learning algorithms still seeks attention for future generation networks. a few major articles are discussed below for both uwa ofdm communication networks and terrestrial networks. authors in [18] proposed a novel method to reduce papr and nonlinear distortion at the receiver side using a machine learning algorithm. this method is named frequentative decision feedback (ffb). this work was proposed for underwater acoustic ofdm communication. an energy-efficient underwater acoustic ofdm communication system was introduced in [19] without using any intelligent algorithm for the reduction of papr. the authors used pts as a papr mitigation tool. an artificial bee colony-based slm technique was proposed in [16]. the authors used selective mapping as a papr reduction technique. however, the computational complexity was too high. the particle swarm optimization (pso) method was used to mitigate the papr of the ofdm signal in [20]. this technique was based on adaptive pso. this method also lacked in reducing the complexity of the overall system while searching the optimal combination of phase factors. genetic algorithm (ga) was proposed in [21-24] for papr mitigation. an efficient method using slm wavelet-ofdm (wofdm) was used, which is based on a genetic machine learning algorithm. the optimum phase factors were searched using ga. in [25] the authors introduced a novel research, also based on ga. this technique performs well in reducing the peak signals in an ofdm system. the tone reservation (tr) method was used, which is based on the selection of the peak reduction tone (prt). however, finding an optimal prt set of data is problematic, because the complexity of the system is increased exponentially while searching the prt data set. this method also uses tr-based clipping which creates distortion and degrades the ber performance. the current paper proposes a novel idlfa approach with a lesser computational complexity. the proposed idlfa-pts based algorithm easily searches the optimum phase factors in pts method and gives improved performance. iii. system model the transmitted ofdm signal with n subcarriers in terms of the continuous-time domain can be expressed as: x(t) = � √� ∑ x� ��� �� e ������, 0 ≤ t < nt (1) where x(t) denotes the ofdm signal, f is the spacing of subcarriers, and nt indicates the data block interval, which carries useful information. the above equation can be written in terms of the discrete-time domain as: x(n) = � √� ∑ x� ��� ��� e ����� , n = 0,1,. . . ,n − 1 (2) here, the pts technique is utilized, which focuses on the discrete-time domain hence taking into consideration (2). the main drawback of the ofdm communication system is the varying high peaks. the varying power of such high peaks is much greater than the average power when the subcarriers are added after the modulation block. the papr is the resultant of the ratio of maximum transferred signal power (power of varying high peaks) to the average transferred power. papr = &'(|(*| + ,-|(*|+. (3) the mathematically expected value of the ofdm signal can be defined by the e[.] operator. a function used to observe the overall performance of papr reduction is known as a complementary cumulative distribution function (ccdf), which is the most prominent way in the reduction of papr. specifying papr(1) is higher than papr(0) (threshold level) and can be given as: ccdf = p(papr(1) > papr(0)) (4) engineering, technology & applied science research vol. 12, no. 1, 2022, 8136-8142 8138 www.etasr.com ali et al.: an intelligent detoxification function of liver algorithm-partial transmit sequence … ccdf � 1 " �1 " e�3435����� (5) in figure 1, the bit-stream of digitally inserted inputs is mapped with the constellation. after qpsk modulation symbols are further divided into subcarriers of length n. these subcarriers are added in a serial to parallel converter block to convert them into parallel for fast computation. the inverse fast fourier transform (ifft) is applied to reduce the computational complexity instead of the more complex inverse discrete fourier transform (idft). the signal is then passed through a parallel to serial conversion to transmit the generated signal serially. after adding a cyclic prefix (cp), the signal is transmitted through an underwater acoustic channel. the process at the receiver end is the reverse. after removing the cyclic prefix, the serial bit stream is modified into parallel form. the parallel moving data are then demodulated by fast fourier transform (fft). hence, the resulted data are converted from the frequency domain to the time domain. thus, the serial signal at the receiving end has been improved, which is then compared with the transmitted source generated signal. fig. 1. block diagram of the system model. iv. pts technique for papr reduction a block of input stream data n (symbols) is sub-divided into m disjoint sub-blocks using the partitioning method denoted as: x � ∑ x&6��&�� (6) generally, pts has adopted 3 primary partitioning methods for the better reduction performance of papr, which are the interleaving scheme, the adjacent scheme, and the pseudorandom scheme. to choose less complex and best papr reduction performance, a pseudo-random scheme has been implemented in our proposed model. sub-blocks are further oversampled by a factor of �l " 1�n zero paddings to estimate the value of papr in the continuous-time domain. ifft is applied on the oversampled sub-blocks of size ln and transferred sub-blocks as: x& � -x� &,x� &, . . . .x&8���. where 0 � m � "1 (7) the n-th symbols of x�n� signal can be generated by the product of the m-th sub-blocks (x&) with phase factors ( bm) and summed up after applying ifft. the ofdm signal after the pts technique of phase rotated sub-blocks with the lowest papr is: x�n� � ∑ bm6��&�� x & (8) where bm is the phase factor that can be defined as: bm � -b�,b�,b>, . . . . . ,b&��. � arg minbmaxc∑ bm6&�� x &cd (9) the partial transmit sequence is the ifft of sub-blocks (x&). the selection of phase factors is the real aim of the pts scheme. but comprehensively finding the optimal phase factors suffer from exponential complexity, so the choice is very much limited to specific elements to reduce the phase factor (bm) complexity. v. idfla for pts the idfla simulates the refining of blood and the maintenance of hormonal levels. the hepatic vein (a particular vein of the liver) carries alcohol and drugs to the liver for detoxification. here nutrients are equivalent to phase factors. be = -be�,be�, . . . . . . .b&��. , where i is taken up to the maximum number of substances denoted by max am, which represents the maximum substances carried out by the vein towards the liver. to obtain optimal nutrients (vitamins, i.e. b12), the hepatic vein carries out alcohol and drug substances, from which the liver utilizes vitamins and eliminates the toxic (waste) materials from the body. in idfla-pts, the source of the nutrients in terms of phase factor can be expressed as: x fg � θ�xijk " x�lmfnlijk� (10) where x�lmfnlijk is the threshold value up to which the liver controls the nutrients, xijk is the old value of substances for detoxification, and θ is the user-generated random variable within the specified limit of range taken as θ � -o1, . . . . "1.. the proposed idlfa-pts model is depicted in figure 2. fig. 2. block diagram of the proposed idfla-pts. the optimal value defines the beneficial nutrients (bn) required for a healthy body and will be considered as the best solution. the bn in terms of mathematical form can be given as: bn � � �q� , . . . . . ,x fg r 0 (11) and it does not operate if {halt, . . . ,x fg � 0} where x fg is the representation of the minimal expected value of papr in underwater acoustic communication. the liver collects all the substances to differentiate them with intelligent principles into beneficial nutrients and toxic substances, and then accepting the suitable nutrients according to their required level. the probability (pr) of accepting nutrients is: engineering, technology & applied science research vol. 12, no. 1, 2022, 8136-8142 8139 www.etasr.com ali et al.: an intelligent detoxification function of liver algorithm-partial transmit sequence … pr � 'uufv�'wjf x�mef �n nx&&'�ei i� 'jj 'uufv�'wjf x�mef �n (12) after accepting the nutrients, the liver looks for new alcoholic contaminated food and allows the food with nutrients. the liver repeats the whole detoxification process after some time in order to accept the remaining nutrients. an intelligent liver considers other substances as toxic and sends them to the waste part, and continues its function in order to maintain the health of the body. possible bn � �pr [ xijk� " tje&e��\ (13) if value is r threshold, then limit � "5 if value is � threshold, then put limit � 0 the steps defined are repeated in a continuous-time cycle to generate the possible beneficial nutrients. in the idfla-pts algorithm, continuous-time cycle and possible beneficial nutrients are made to find the desired phase factors. the steps of the proposed idfla-pts algorithm are: 1. set up the threshold value. 2. take a random number θ within the specified range to generate a new phase factor. 3. determine the best-fit phase factor by solving (11). 4. this value continues up to the given limit. 5. go back to step 2 until the halt condition is not achieved. this process continues to generate the possible solutions. 6. new generated phase factor is calculated by (10) and the best fit is solved using (11). 7. then the probability of beneficial nutrients can be achieved by (12). 8. considering the remaining substance as toxic after multiple iterations, it starts the detoxification of new random contaminated food using (13). 9. the whole process is repeated until the beneficial nutrients for maintaining the health of the body are acquired. 10. set and memorize the best fit values. vi. simulation and experimental results in order to achieve optimum results of our proposed model, experiments were carried out in an underwater tank, while simulations were performed in matlab 2017b using the bellhop channel. the experiments in the water tank proved to have better results. a. simulations in this section, simulation results and numerical analysis of the proposed idfla-pts are given. the matlab version 2017b was used, the number of subcarriers during simulations in an underwater ofdm system is n=512, and qpsk modulation was employed. the bellhop ray tracing communication channel was utilized. in the pts technique, the partitioning is random. the number of sub-blocks was m = 128, 256, 512, along with w=4 selected phase factors. the phase factors became bm ∈ ±1. the papr in idfla-pts and gapts were compared and their comparison with different numbers of sub-blocks was conducted in terms of complexity. the best fit phase factor was chosen and then the sequence was generated as bm = [ b1, b2, bm−1]. in ga-pts, the selection of b is random. the parameters that are implemented in the simulation are given in table i. figure 3 illustrates the performance of papr in the original ofdm signal and idfla-pts. in idfla-pts, by considering the sub-block number m = [128, 256, 512]. the papr of the conventional ofdm signal can be observed in the figure, which is 11.22db when the ccdf of papr is 10 -3 . the ideal exact idfla measurement is 7.4db, while the observed papr of the proposed idfla-pts with different sub-blocks, i.e. 128, 256, and 512 is 8.2db, 7.7db, and 7.59db respectively. it is observed that taking a greater number of m (sub-blocks) decreases papr. the improved performance and papr comparison of idfla-pts and ga-pts with m = [128, 256, 512] sub-blocks are shown in figure 4. table i. simulation system parameters serial number parameters data 1 length of fft points 8192 2 number of subcarriers 512 3 cyclic prefix time 21.56ms 4 sound speed 1500m/s 5 sampling frequency 96khz 6 signal modulation type qpsk 7 ofdm symbol number 24 8 modulation order 4 9 up sampling rate 2 10 maximum multipath delay 12ms 11 bandwidth 6khz fig. 3. papr comparison of idfla-pts, exact idfla-pts, and original ofdm signal. the simulation of ga-pts at m=2048 was an additional task in order to check the improved performance. after taking the mentioned sub-blocks, the papr values of ga-pts were 8.62db, 8.02db, 7.65db, and 7.5db respectively. so, the difference in the papr of both methods for the same number of sub-blocks was 0.42db, 0.32db, and 0.06db respectively. concluding after the comparison, one can see that the performance of the proposed idfla-pts method is better, faster, and more cost-effective, as it converges to 7.65db at m=512, which has similar papr at m=2048 in the ga-pts, i.e. 7.5db, so the cost is decreased 4 times in the idfla-pts method. in table ii, the papr of idfla-pts and ga-pts is illustrated with a different number of sub-blocks. the original engineering, technology & applied science research vol. 12, no. 1, 2022, 8136-8142 8140 www.etasr.com ali et al.: an intelligent detoxification function of liver algorithm-partial transmit sequence … signal has a papr of 11.2db, while the optimum exact papr is 7.4db. fig. 4. papr comparison of idfla-pts, ga-pts, and exact idflapts. table ii. reduction of papr with idfla-pts and ga-pts papr reduction method number of sub-blocks papr (db) idfla-pts 128 8.2 idfla-pts 256 7.7 idfla-pts 512 7.55 ga-pts 128 8.6 ga-pts 256 8.02 ga-pts 512 7.65 ga-pts 2048 7.5 table iii. uwa bellhop channel simulation parameters parameters processing data surface height 100 m transmitter side depth, transducer (tx) 25 m receiver side depth hydrophone (rx ) 40 m distance between tx and rx 3 km frequency range 8-12khz fig. 5. comparison of proposed idfla-pts, ga-pts, and conventionalpts in terms of ber. the parameters used in the bellhop channel configuration are mentioned in table iii. in the simulation, the bellhop channel is executed in matlab window containing all the features of shallow water. we supposed surface height (depth) of 100m, the transducer is dipped in water up to the depth of 25m, and the depth of hydrophone was kept at 40m while the distance of the hydrophone (rx) and transducer (tx) was 3km. for a better understanding of the proposed method, the ber vs. snr of idfla-pts with ga-pts and conventional pts are compared. the best-fit algorithm in uwa communication must produce less ber and higher snr thus creating a better environment for communication. figure 5 shows the ber performance over the range of snr. it is observed that idlfapts has better performance than the traditional methods. the parameters mentioned in table i are taken into consideration. the yellow line determines the ber curved line of the idflapts method that has better performance than ga-pts. the red curved line determines the ber of the ga-pts. it is noticed that using the ga gave a slightly more ber. the blue curve shows the ber of the conventional-pts. from figure 5, it is clear that the proposed method idfla-pts performs better with lower ber and higher snr, which determines the best performance for an underwater and acoustic system.. b. experiment to observe the simulated idea of the proposed idfla model, we did experiments at harbin engineering university on the june, 1, 2020. the transducer (transmitter) and receiver (hydrophone) were placed at different depths (25m and 40m respectively) in a water tank. the distance between the hydrophone and transducer was 3km, which is similar to the simulation parameters. the experimental layout is shown in figure 6, which portraits the experimental setup and the underwater acoustic tank channel. fig. 6. experimental setup in underwater acoustic tank channel. the transmitter was connected with the computer via a power amplifier. the parameters given in table i were employed in the experiments. the signal was generated from the signal generator and was transmitted through an underwater acoustic channel. after hitting the surrounding boundaries of the water tank, the acoustic signal creates various paths at the engineering, technology & applied science research vol. 12, no. 1, 2022, 8136-8142 8141 www.etasr.com ali et al.: an intelligent detoxification function of liver algorithm-partial transmit sequence … receiver side (multipath). when acoustic signals with different frequencies are transmitted, then peaks are overlapped, and high peaks are also observed which affects the performance of the signal’s ber. for papr reduction, we introduced the idfla-pts algorithm, which selects the optimum phase factors, and provides better ber performance. the transmission of the signal is efficient in the proposed method. during the signal transmission, multiple high peaks occurred in the underwater acoustic channel. the high peaks passed through the proposed algorithm block, where they were further calculated and informative peaks were reduced by the iterative process. in figure 7, the impulse response of the underwater tank channel is illustrated. it is mainly relying on the sound speed, ranging from 1490m/s to 1500m/s. hence, one can observe several time delays with normalized amplitude due to the nature of the uwa channel. the signal suffers from multipath when reaching the receiver side. figure 8 shows the simulated and experimental ber curves of the proposed idfla-pts algorithm. it is noted that the curves are close to each other with only a slight difference between them. this proves our method to be very feasible for practical applications. fig. 7. channel impulse response of the underwater tank with the idflapts algorithm. fig. 8. ber comparison of the proposed idfla-pts, simulation and experiment. vii. conclusion and future work in this paper, the idfla-pts is proposed for the uwa ofdm communication system. it is verified that the proposed method has better performance than other intelligent papr reduction techniques. the idfla algorithm is independent of other complex parameters that can affect in-band and out-band distortion. the proposed idfla-pts method was compared with ga-pts with varying number of sub-blocks and achieved optimum papr. it is concluded that the idfla-pts method proved to be efficient, less complex, while it reduces 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[28] j. jake, e. mwangi, and k. langat, "spectral re-growth suppression in the fbmc-oqam signal under the non-linear behavior of a power amplifier," engineering, technology & applied science research, vol. 9, no. 5, pp. 4801–4807, oct. 2019, https://doi.org/10.48084/etasr.3097. [29] a. elsanousi and s. ozturk, "performance analysis of ofdm and ofdm-mimo systems under fading channels," engineering, technology & applied science research, vol. 8, no. 4, pp. 3249–3254, aug. 2018, https://doi.org/10.48084/etasr.2209. authors profile amir ali received the be in electronic engineering from mehran university of engineering and technology, jamshoro, pakistan in 2016. he was a junior expert engineer in national engineering services pakistan from 2016 to 2018. currently he is pursuing his ms. in the college of underwater acoustic engineering, harbin engineering university, china. his research interests are wireless communications, machine learning, underwater image processing, 5g, iot, and blockchain technology. baowei chen received his phd from the harbin engineering university in 2012. currently, he is an associate professor of the college of underwater acoustic engineering, harbin engineering university. he has worked as a visiting scholar at the university of guelph, canada.his research interests include the design of underwater acoustic electronic systems and the research and implementation of underwater acoustic signal processing algorithms, the design of sonar electronic systems, and the acquisition technology of ocean environment information. waleed raza received his be in electronic engineering from the department of electronic engineering, dawood university of engineering and technology, karachi, pakistan in 2017. he is currently pursuing an ms in hydroacoustic engineering in the college of underwater acoustic engineering, harbin engineering university, china. his research areas of interests include underwater acoustic ofdm communication, machine learning, and digital signal processing. asif ali received his bs degree in physics from shah abdul latif university, khairpur, pakistan in 2017. currently, he is pursuing an ms degree in nuclear engineering at the harbin engineering university, china. his current research interests include system engineering, nuclear physics, and nuclear power plant safety. haisen li received his phd degree from harbin engineering university in 1999. from 2002 to 2003, he was a senior visiting scholar at the woods hole oceanographic institution (whoi), usa. he is currently a professor at the college of underwater acoustic engineering, harbin engineering university and the chief of the ti-heu dsp joint laboratory. his research interests include multi-beam echo sounder technology and underwater acoustic target detection and location. he is a fellow of the acoustical society of china, the standing director of the heilongjiang acoustics society, and the visiting research fellow of whoi. he is also a reviewer or a member of the editorial board for many prestigious international journals, such as technical acoustic, hydrographic surveying and charting, and the journal of harbin engineering university. he is currently a reviewer of the national natural science foundation of china. microsoft word etasr_v11_n6_pp7932-7937 engineering, technology & applied science research vol. 11, no. 6, 2021, 7932-7937 7932 www.etasr.com qasim et al.: producing green concrete with plastic waste and nano silica sand producing green concrete with plastic waste and nano silica sand mohammed fadhil qasim department of civil engineering college of engineering university of baghdad baghdad, iraq m.qasim1901m@coeng.uobaghdad.edu.iq zena k. abbas department of civil engineering college of engineering university of baghdad baghdad, iraq dr.zena.k.abbas@coeng.uobaghdad.edu.iq suhair kadhem abed building research directorate baghdad, iraq suhairkah@yahoo.com abstract-industrial and urban development has resulted in the spread of plastic waste and the increase in the emissions of carbon dioxide resulting from the cement manufacturing process. the current research aims to produce green (environmentally friendly) concrete by using plastic waste as coarse aggregates in different proportions (10% and 20%) and nano silica sand powder as an alternative to cement in different proportions (5% and 10% by weight). the results showed that compressive strength decreased by 12.10% and 19.23% for 10% and 20% plastic waste replacement and increased by 12.89% and 20.39% for 5% and 10% silica sand replacement respectively at 28 days. flexural strength decreased by 12.95% and 19.64% for 10% and 20% plastic waste replacement and increased by 11.16% and 19.86% for 5% and 10% silica sand replacement. splitting tensile strength decreased by 12.74% and 20.22% for 10% and 20% plastic waste replacement and increased by 10.86% and 19.66% for 5% and 10% silica sand replacement. dry density decreased by 4.51% and 7.83% for 10% and 20% plastic waste replacement and increased by 2.78% and 4.10% for 5% and 10% silica sand replacement respectively at 28 days. keywords-green concrete ; plastic waste; silica sand i. introduction green concrete was first produced in denmark in 1998. the term green concrete refers to the environmental concept in which waste is utilized and thus recycled in its production. the production of green concrete is usually cheap because of the use of waste as a partial substitute for cement and aggregates, reducing energy consumption and causing less harm to the environment [1, 12, 13]. the emission of carbon dioxide (co2) is an environmental problem. the cement manufacturing process produces about 8 to 10% of the total co2 emissions globally, so researchers resorted to the production of green concrete, which utilized recycled materials, e.g. pozzolanic materials, which are used to reduce the amount of cement in the mixture, thus reducing cement production and co2 emissions from cement factories. waste plastic, glass, ceramics, rubber, etc. have also been used as aggregates in the production of green concrete [2, 17]. the process of disposing of plastic waste causes major environmental problems due to the large disposed quantities and their low biodegradability, so research has focused on the disposal of plastic waste through its use in concrete [3, 14, 16]. plastic waste consisting of low-density polyethylene (ldpe), such as plastic bags, has become a major environmental problem due to the difficulty of its eco-friendly disposal. often plastic bags are burned, contributing to air pollution [4, 15]. green concrete developed with waste materials is an active area of research. fly ash has been used as cement replacement in green concrete made with partial replacement of conventional coarse aggregates with coarse aggregates from demolishing waste [5]. portland cement is considered a product most involved in environmental pollution. it is responsible for about 10% of global co2 emissions. limestone dust is a by-product of limestone plants and it is produced in thousands of tons annually as waste [6]. for sustainable development construction, recycle or reuse of waste materials is utilized. many researches tried to create an innovative green concrete, utilizing waste materials [7]. ii. material characterization a. cement ordinary portland cement (opc) 42.5 r from the al-mass company was used in all concrete mixes. the physical and chemical properties in accordance with the iraqi specification no. 5/2019 as shown in tables i and ii. b. fine aggregates using natural sand in saturated surface dry (ssd) condition was used as fine aggregates. it is conformable with the iraqi specification no.45/1984 zone three (tables iii and iv). corresponding author: mohammed fadhil qasim engineering, technology & applied science research vol. 11, no. 6, 2021, 7932-7937 7933 www.etasr.com qasim et al.: producing green concrete with plastic waste and nano silica sand table i. physical properties of opc physical properties test result iqs no.5/2019 requirements for opc fineness (blaine method) m 2 /kg 386 ≥ 280 initial setting (min) 165 ≥ 45 min final setting (min) 260 ≤ 600 min soundness (autoclave method), % 0.12 ≤ 0.8 compressive strength (mpa) at 2 days 28 ≥ 20 compressive strength (mpa) at 28 days 46 ≥ 42.5 table ii. chemical composition and main compounds of the cement used oxide composition and chemical properties test results iqs no.5 /2019 limits for opc lime (cao) 62.77 silica (sio2) 20. 65 alumina (al2o3) 4.87 iron oxide (fe2o3) 3.43 magnesia (mgo) 4.35 ≤ 5% sulfate (so3) 2.50 ≤ 2.8% for c3a > 3.5% loss on ignition (l.o.i.) 1.36 ≤ 4% insoluble residue (i.r.) 0.91 ≤ 1.5% main compounds (bogue's equation) tri calcium silicate (c3s) 53.77 di calcium silicate (c2s) 18.72 tri calcium aluminate (c3a) 7.10 tetra calcium aluminate ferrite (c4af) 10.43 table iii. fine aggregate grading test sieve size (mm) passing% iqs no.45/1984 zone 3 requirements 10 100 100 4.75 100 90– 100 2.36 93.8 85 – 100 1.18 80.8 75 – 100 0.6 61 60 – 79 0.3 21.8 12 – 40 0.15 1.8 0 – 10 table iv. chemical and physical properties of fine aggregates property test result iqs no.45/1984 requirements sulfate content, % 0.101 ≤ 0.5 fine materials passing from 75µm sieve, % 3.9 ≤ 5 specific gravity 2.58 fineness modulus, % 2.4 dry rodded density, kg/m 3 1694 absorption, % 0.8 c. coarse aggregates crushed gravel in ssd, of nominal maximum size of 14mm and conformable with the iraqi specification no.45/1984 was used as coarse aggregates. sieve analysis, and chemical and physical properties are shown in tables v-vi respectively. table v. coarse aggregate grading test sieve size (mm) passing % iqs no. 45/1984 5-14mm requirements 20 100 100 14 94 90 100 10 52.66 50 – 85 4.75 1.0 0-10 table vi. chemical and physical properties of coarse aggregates property test result iqs no .45/1984 requirements sulfate content as a so3, % 0.08 ≤ 0.1 specific gravity 2.62 impact value, % 2.405 ≤ 45 abrasion test (los angeles), % 17.4 ≤ 35 crushing value, % 17.77 dry rodded density, kg/m 3 1688 absorption, % 0.7 d. waste plastic aggregates the plastic waste used as coarse aggregates had nominal maximum size of 14mm obtained from cutting vegetable boxes, garbage containers, shampoo, and detergent bottles. sieve analysis, and the results of chemical and physical tests of the waste plastic aggregates are presented in tables vii and viii respectively. table vii. plastic waste aggregates grading test sieve size (mm) passing % iqs no. 45/1984 5-14mm requirements 20 100 100 14 96 90-100 10 63 50-85 4.75 4.5 0-10 table viii. chemical and physical properties of plastic waste aggregates property test result iqs no .45/1984 requirements sulfate content as a so3, % nile ≤ 0.1 specific gravity 0.95 impact value, % 0.00 ≤ 45 abrasion test (los angeles), % 0.00 ≤ 35 crushing value, % 0.00 dry rodded density, kg/m 3 455 absorption, % 0.00 thickness, mm max3 e. mixing and curing the water used for mixing and curing conforms to the iraqi specification no. 1703/1992. the chemical properties of the water used are shown in table ix. table ix. properties of the water used iraqi specification no.1703/1992 test result required tests ≤ 1000 316 sulfur salts so3 -2 , ppm ≤ 3000 978 total dissolved salts (tds), ppm ≤ 500 118 chlorides, ppm ≤ 1000 307 carbonate and bicarbonate, ppm f. high range water reducing admixture (superplasticizer) hyperplastic pc200 complying with astm c494-04 type a and g was used in this research. the dosage recommended by the manufacturer is 0.5 2.5lt/100kg of cement weight in the mix. engineering, technology & applied science research vol. 11, no. 6, 2021, 7932-7937 7934 www.etasr.com qasim et al.: producing green concrete with plastic waste and nano silica sand g. silica sand powder local silica sand was used in the form of powder. the particle size analysis test is presented in figure 1. chemical and physical tests for nano silica sand were carried out and were compared with astm c 618 as shown in tables x and xi respectively. fig. 1. practical size analysis for silica sand powder. table x. chemical composition of nano silica sand powder property test result chemical requirements for class n natural pozzolan, astm c618-19 sio2 plus al2o3 plus fe2o3, % 90.04 70.0 min. so3, % 2.10 4.0 max. loss on ignition, % 7.41 10.0 max. moisture content, % 1.8 3.0 max calcium oxide (cao), % 4.66 magnesium oxide (mgo), % 1.23 table xi. physical properties of nano silica sand powder physical requirements for class n natural pozzolan, astm c618-19 test result property 34 max. 0 amount retained when wet sieved on 45 µm, % 75 min. 87.46 strength activity index with portland cement at 7 days, percentage of control 75 min. 92.54 strength activity index with portland cement at 28 days, percentage of control iii. experimental part a. mixtures aci 211.1 code design was used to achieve compressive strength of 30mpa at 28 days for cylinder and 37.5mpa for cube specimens as the reference mix. the plastic waste was replaced in different proportions of the volume of the coarse aggregates (natural gravel), and the silica sand replaced cement in different proportions as shown in table xii. b. molds preparation cube steel molds having dimensions of 100×100×100mm were utilized for compressive strength tests, cylinder steel molds of 100×200mm for splitting tensile strength tests, and 100×100×400mm prisms for flexural strength tests. table xii. material content for the designed concrete materials kg/m 3 ref. 10% pl * 20% pl 5% ss ** 10% ss cement 400 400 400 380 360 fine aggregates 727 727 727 727 727 coarse aggregates 1020 918 815 1020 1020 plastic waste 0 27.5 55 0 0 silica sand 0 0 0 20 40 water 171 171 171 171 171 s.p. l/100kg cement 0.75 0.75 0.75 0.80 0.85 *pl: plastic coarse aggregates, **ss: silica sand iv. results and discussion a. compressive strength measurements compressive strength test was conducted according to bs en 12390-3:2019 (e) as shown in figure 2. the compressive strength was tested for three cubes at the age of 7, 28, and 90 days. fig. 2. compressive strength test machine. the results for the reference mix and the concrete containing plastic aggregates are plotted in figure 3. it was found that the compressive strength decreased by 10.84, 12.10, and 13.62% and by 18.18, 19.23, and 20.15% for 10% and 20% plastic waste replacement, respectively, at 7, 28, and 90 days. a possible reason for the decrease in the compressive strength is the weakness of the bonding strength between the smooth surface of the plastic aggregates and the cement paste, which leads to a weakening of the transition zone [21-23]. plastic waste (high density polyethylene) in concrete mixtures as aggregate replacement was studied in [8]. the authors used plastic waste in the concrete mixture with proportions of 10, 20, and 30% of the volume of coarse aggregates. the compressive strength decreased with increasing plastic waste proportion [8]. fig. 3. relationship between compressive strength and age for deferent percentages of plastic waste as coarse aggregates. 2000 kn capacity, 2.5 mpa/s loading rate engineering, technology & applied science research vol. 11, no. 6, 2021, 7932-7937 7935 www.etasr.com qasim et al.: producing green concrete with plastic waste and nano silica sand the compressive strength test results for the reference mix and the concrete containing the silica sand powder are plotted in figure 4. the compressive strength increased by 10.20, 12.89, and 12.64% and by 19.46, 20.39, and 19.11% for 5% and 10% silica sand replacement, respectively, at 7, 28, and 90 days. the reason for the increase in compressive strength is the reaction of calcium hydroxide (ca(oh)2), which is a product of the reaction of cement and water with silica sand, which leads to the formation of a secondary gel (c-s-h) [20]. the mechanical properties of concrete using silica sand as partial (5, 10, 15, 20 and 25% by weight) replacement of cement were studied in [9]. it was found that the best replacement ratio was 15% [9]. fig. 4. relationship between compressive strength and age for deferent percentages of silica sand powder. b. flexural strength flexural strength was determined according to astm c293-16 as shown in figure 5. the flexural strength average of three models per mixture was examined at the age of 7, 28, and 90 days. fig. 5. flexural strength test machine. the results of the flexural strength measurements for the reference mix and the concrete containing plastic aggregates are plotted in figure 6. flexural strength decreased by 12.26, 12.95, and 10.81% and by 21.63, 19.64 and 19.10% for 10% and 20% plastic waste replacement, respectively, at 7, 28, and 90 days. the reason is the same with the one mentioned in compressive strength analysis [24]. some properties of sustainable concrete with mixed plastic waste aggregates can be seen in [10]. when replacing aggregates with plastic waste at proportions of 5, 25, and 45% of volume, a decrease in flexural strength was observed with an increase in the replacement ratio. the flexural strength test results for the reference mix and the concrete containing the silica sand powder are plotted in figure 7. flexural strength increased by 11.1, 11.16, and 11.6% and by 17.78, 19.86, and 18.64% for 5% and 10% of silica sand replacement, respectively, at 7, 28, and 90 days. the reason is the one mentioned in compressive strength analysis [9, 19]. the use of silica sand in partial replacement of the fine material (sand) in concrete was studied in [20]. the best replacement ratio was found to be 15% [20]. fig. 6. relationship between flexural strength and age for deferent percentages of plastic waste as coarse aggregates. fig. 7. relationship between flexural strength and age for deferent percentages of silica sand powder. c. splitting tensile strength splitting tensile strength test was determined according to astm c496/c496m-17 at the age of 7, 28, and 90 days (figure 8). the average of three measurements was considered the final value of each mixture. fig. 8. splitting tensile strength test. the results of the splitting tensile strength tests for the reference mix and the mixtures containing plastic aggregates are plotted in figure 9. splitting tensile strength decreased by 11.77, 12.74, and 13.76% and 19.34, 20.22, and 20.63% for 10% and 20% of plastic waste replacement, respectively, at 7, 28, and 90 days. the reason is the same mentioned in compressive strength analysis [10, 25]. the use of plastic waste (high density polyethylene) in concrete mixture as aggregate 200 kn capacity, 1 mpa/min loading rate 2000 kn capacity, 1 mpa/min loading rate engineering, technology & applied science research vol. 11, no. 6, 2021, 7932-7937 7936 www.etasr.com qasim et al.: producing green concrete with plastic waste and nano silica sand replacement was studied in [8]. plastic waste was utilized in concrete mixtures with proportions of 10, 20, and 30% of the volume of coarse aggregates. it was found that splitting tensile strength decreased by increasing percentage of plastic waste [8]. splitting tensile strength for the reference mix and the concrete containing silica sand powder is plotted in figure 10. splitting tensile strength increased by 10.71, 10.86, and 11.37% and by 17.60, 19.66, and 18.50% for 5% and 10% of silica sand replacement, respectively, at 7, 28, and 90 days. the reason mentioned in compressive strength analysis [9, 18] also applies here. the use of silica sand as partial replacement of fine materials in concrete was studied in [20]. the best replacement ratio was proved to be 15% of cement weight [20]. fig. 9. relationship between splitting tensile strength and age for deferent percentages of plastic waste as coarse aggregates. fig. 10. relationship between splitting tensile strength and age for deferent percentages of silica sand powder. d. dry density dry density test was found by taking the average density of three cubs of 100×100×*100 dimensions at the age of 28 days according to bs 1881-114: 1983. the cubes were drying in the oven at 105 ± 5 ºc until constant mass. dry density decreased by 4.51% and 7.83% for 10% and 20% plastic waste replacement, respectively, at 28 days. this decrease in the dry density of concrete is caused by the decrease in the plastic density compared to the density of the natural coarse aggregate [26-28]. experimental investigation on recycled plastics as aggregates in concrete was conducted in [11]. it was found that dry density decreased with increasing plastic waste percentage [11]. silica sand powder was utilized at proportions of 5% and 10%. it was found that the density of dry concrete increases by 2.78% and 4.10% respectively at 28 days. the reaction of calcium hydroxide ca(oh)2 with silica sand powder leads to the formation of a secondary gel (c-s-h) that fills the voids in concrete, making the mixture more denser [9]. the effect of nanomaterials on the properties of limestone dust green concrete was studied in [6]. it was found that dry density increased with the increase in nano al2o3 percentage [6]. the dry density for the reference mix and the concrete containing plastic and silica sand powder are plotted in figure 11 fig. 11. relationship between dry density and deferent percentages of plastic waste and silica sand powder . v. conclusions based on the obtained experimental results, the most notable outcomes of the current study are: • compressive strength decreased by 10.84, 12.10, and 13.62% and by 18.18, 19.23, and 20.15% for 10% and 20% plastic waste replacement, and increased by 10.20, 12.89, and 12.64% and 19.46, 20.39, and 19.11% for 5% and 10% silica sand replacement, respectively, at 7, 28, and 90 days. • flexural strength decreased by 12.26, 12.95, and 10.81% and 21.63, 19.64, and 19.10% for 10% and 20% plastic waste replacement, and increased by 11.1, 11.16, and 11.6% and 17.78, 19.86, and 18.64% for 5% and 10% silica sand replacement, respectively, at 7, 28, and 90 days. • splitting tensile strength decreased by 11.77, 12.74, and 13.76% and 19.34, 20.22, and 20.63% for 10% and 20% plastic waste replacement and increased by 10.71, 10.86, and 11.37% and 17.60, 19.66 and 18.50% for 5% and 10% silica sand replacement, at 7, 28, and 90 days respectively. • dry density decreased by 4.51% and 7.83% for 10% and 20% plastic waste replacement, respectively, at 28 days. it increased by 2.78% and 4.10% for 5% and 10% silica sand replacement, respectively, at 28 days. • the cost of concrete was reduced by using local and recycled materials. • the concrete production had reduced pollution by using plastic waste as coarse aggregates. references [1] n. agarwal and n. garg, "a research on green concrete," ijirmps international journal of innovative research in engineering & multidisciplinary physical sciences, vol. 4, no. 4, jul. 2016, https://doi.org/10.17605/osf.io/9mbzn. engineering, technology & applied science research vol. 11, no. 6, 2021, 7932-7937 7937 www.etasr.com qasim et al.: producing green concrete with plastic waste and nano silica sand [2] b. suhendro, "toward green concrete for better sustainable environment," procedia 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[28] a. s. m. sayem, a. hasnat, m. j. islam, and t. tafsirojjaman, "a study of green concrete using waste plastic and stone dust," in international conference on recent innovation in civil engineering for sustainable development, gazipur, bangladesh: dhaka university of engineering and technology, 2015, pp. 110–115. microsoft word etasr_v12_n1_pp8045-8052 engineering, technology & applied science research vol. 12, no. 1, 2022, 8045-8052 8045 www.etasr.com muchande & thale: hierarchical control of a low voltage dc microgrid with coordinated power … hierarchical control of a low voltage dc microgrid with coordinated power management strategies shrishell muchande department of electrical engineering fr. conceicao rodrigues institute of technology navi mumbai, india skmuchande@git-india.edu.in sushil thale department of electrical engineering fr. conceicao rodrigues institute of technology navi mumbai, india sushil.thale@fcrit.ac.in abstract-a microgrid consists of a cluster of renewable energy sources, energy storage elements, and loads. one of the main objectives of a microgrid is to provide reliable and high-quality power to the loads. under normal operating conditions, this is achieved through suitable power management strategy (pms). however, under emergency conditions, such as the failure of any source, overloads, or faults, the pms may not be able to retain the microgrid in operating conditions. any emergency condition may demand a significant change in control and coordination between various subsystems of the microgrid to survive and continue the operation. this feature makes a microgrid "a fault resilient" system as visualized in its objectives. this paper proposes a novel coordinated power management (cpm) strategy based on three-layer hierarchical control for an autonomous low voltage dc (lvdc) microgrid. the proposed cpm strategy ensures the continuation of the microgrid operation under normal and emergency conditions. an emergency control layer is established to extend the microgrid operation during an emergency condition. the performance of the proposed control scheme is validated through simulation and experimental results. keywords-coordinated power management; dc microgrid; hierarchical control; fault resilient system i. introduction some of the challenges the conventional power generation faces are the environmental pollution, the reduction in the fossil fuels reservoirs, and the continuous increase in the power demand, which lead to increased penetration of the res based distributed generation (dg). the resultant large penetration of ress like solar photovoltaic (spv) panels and wind turbines in existing grid is subsequently challenging its stability due to their intermittent nature. small capacity sources with diverse nature integrated with energy storage systems (esss) feeding aggregated loads are controlled and coordinated as a single entity, referred to as a microgrid (mg). it facilitates the integration of free and locally available micro energy sources with suitable energy storage elements to meet the local load demand. in mgs, micro-sources are controlled through suitable power electronic converters. based on voltage type, an mg can be classified as an ac mg, a dc mg or dcmg, and a hybrid mg [1]. a dcmg possesses more advantages such as higher efficiency and natural interface with res, ess, and the loads. figure 1 shows a typical schematic of an lvdc mg configuration. boost converter spv boost converter bi-directional converter battery dc load m ic r o g r id d c b u s +48vfuel cell fig. 1. a typical lvdc mg configuration. the intermittent behavior of res along with the unpredictable load fluctuations generally results in imbalance between the power generation and the load demand which significantly affects the overall operation of the system. various power sharing control strategies have been presented in the past and are classified as decentralized, centralized and multilevel (hierarchical) control. in decentralized control, generally power management with droop control is adopted based on the capacity of individual sources. this method is simple and easy to implement with locally measured variables, but possesses some operational challenges like optimal load sharing (ls), voltage regulation, power regulation, real time source optimization etc. these challenges mainly persist due to the lack of information about source parameters. to address these issues, some improved droop control strategies have been proposed to enhance the load sharing accuracy, source optimization and voltage regulation achieved with low bandwidth communication [2, 3]. in centralized control, the sources are controlled by a remotely located centralized controller with high-speed communication links. the communication network with sufficiently large bandwidth plays an important role to exchange the information among the micro sources. however, the reliability of this centralized scheme suffers by the high probability of single point failures like the failures of the corresponding author: shrishell muchande engineering, technology & applied science research vol. 12, no. 1, 2022, 8045-8052 8046 www.etasr.com muchande & thale: hierarchical control of a low voltage dc microgrid with coordinated power … central controller or of the communication networks. the hierarchical control is a better approach which neither suffers a single point failure nor demands the use of a high-speed communication network. however, a low to medium bandwidth communication link is needed, which plays an important role in the overall optimization of the system operation. most of the difficulties associated with decentralized and centralized control are overcome in this approach. the hierarchical control provides continuous operation at suboptimal level during a failure of the controller or communication network. in the existing literature, various control schemes for dc mgs have been reported. authors in [2] presented the drawbacks of conventional droop control and showed the effect of different droop gains on the current sharing accuracy and voltage regulation. the current sharing accuracy changes with the higher value of line impedance while reduction in voltage. authors in [3] proposed and analyzed 3 nonlinear droop control techniques to obtain the optimal operation for load sharing accuracy and bus voltage restoration. a power distributed control method for proportional load power sharing and bus voltage restoration is reported in [4]. the proportional output power sharing with load voltage restoration is achieved by adjusting only the output source voltage instead of introducing the virtual impedance. however, poor load sharing at light load and voltage deviation in heavy load conditions persist in the system. frequency droop control method is proposed in [5]. fuzzy logic is used to define the frequency droop coefficient. authors in [6] proposed and evaluated a fault detection method which is independent of the mg topology. authors in [7] proposed a decentralized controller with low bandwidth communication to enhance high reliability, low voltage regulation, and equal load sharing. eigenvalue analysis and mathematical modal were derived. the conventional droop curve equation is shifted along with x-axis by adding additional voltage. a similar approach has been presented in [8], but the compensating average voltage of the identified critical busses is determined by the proposed modal analysis. the hierarchical architecture was proposed for dc microgrid with reliable and optimum utilization of resources in [9, 10]. primary level control is embedded in local controllers (lcs) directly acting on power converters according to the references generated by the secondary level controller with faster dynamics. the secondary level control facilitates functions like bus voltage regulation, power management, and overall system optimization. authors in [11] proposed a power management control strategy to dc mgs under different operating conditions. the developed control algorithm ensures optimal utilization of the available resources and maintains a healthy state of charge (soc) of the ess. a two-level hierarchical control algorithm is proposed in [12] that can operate the main source at constant power and reduce the fluctuations on the voltage-controlled source in system while maintaining the soc of the storage unit. authors in [13] addressed the adaptive dynamic power management strategy (adpms) for a self-reliant dc mg. authors in [14] presented the design and implementation of a low voltage autonomous mg integrating different res combination with suitable energy storage units to meet the electrical energy needs in remote locations. it consists of a single voltage source converter and a bidirectional dc converter (bddc) to manage the power flow in self-sustain low voltage mgs. emergency power and energy management system are essential in ensuring the optimal restoration process and continue the healthy operational amongst available ress, energy storage system. authors in [15] proposed a multi-level novel reconfigurable hierarchical architecture for an ac mg to transfer its functionalities from a source-level control to system level control to supports long-term optimization of mg operation under normal conditions and front-line switching roles in emergency conditions. authors in [16] proposed the design and control of integrated ress for energy management. the peak load demand problem was resolved with a combination of demand side energy management and esss. authors in [17] proposed a methodology of making a schedule of list of actions such that the distribution system operator is able to provide continuous electricity supply for classified customers. this is achieved by considering some power management options such as intentional load shedding, dispatch of expensive fossil fuel sources, system reconfiguration, and so on. authors in [18] presented a mathematical formulation based on mixed integer linear programming under normal and emergency operating conditions for an ac mg to improve the system resilience. as discussed above, the focus of the research in dc mgs is more on power management under steady-state operation. not much research is reported in operational management under emergency operating conditions. therefore, it is essential to make more investigations in emergency cases to extend the mg operation in such emergency. this paper describes the novel coordinated power management strategy (cpms) implemented on a typical lvdc mg architecture shown in figure 2. the proposed cpms facilitates lvdc mg operation under both steady-state and emergency conditions. the proposed strategy incorporates 3 levels of hierarchical control. the details of the proposed strategy are provided along with the simulation and the experimental results. the proposed strategy makes a lvdc mg a fault-resilient system able survive and perform under all operating conditions. ii. the coordinated power management strategy for the lvdc microgrid an mg's main objective is to provide reliable power under all operating scenarios and this demands the use of a failsafe power management strategy. it is also essential to use the locally available resources optimally. the main focus is to maximize the power extraction from res and to relieve the ess from its major share in supplying power to the loads. with the abovementioned objectives, a 3 layered hierarchical control strategy is proposed for an autonomous lvdc mg. the power topology of the proposed lvdc mg considered for this study integrates 2 solar pv power plants and a fuel cell-based source as res components while the ess consists of battery-based and ultra-capacitor based sources. engineering, technology & applied science research vol. 12, no. 1, 2022, 8045-8052 8047 www.etasr.com muchande & thale: hierarchical control of a low voltage dc microgrid with coordinated power … converter-1 (boost) local load-1 local controller-1 tms320f8069 vpv1 ipv1(in) vo(s1) converter-2 (bidirectional) local load-2 local controller-2 tms320f8069 vbat ibat-in vo(s2) converter-3 (boost) local controller-3 tms320f8069 vpv2 ipv 2 vo(s3) microgrid supervisory controller tms320f28379d communication link vload iload 48 v dc microgrid (mg) bus solar pv source (s1) battery source (s2) solar pv source (s3) network impedancenetwork impedance s1 s2 s3 ring switch mg bus load spv1 s2 spv2 local load-3 converter-4 (bidirectional) local controller-4 tms320f8069 vuc iuc-in vo(s4) ultracap source (s4) s4 uc converter-5 (boost) local controller-5 tms320f8069 vfc ifc-in vo(s5) fuel cell source (s5) s5 fc local load-4 ibat i(s1-s5) v(s1-s5) ipv1 ipv1 ibat ipv2(in) ipv2 iuc iuc ifc ifc fig. 2. mg power architecture of the proposed control strategy. the battery-based source is meant for long term power backup and the ultracapacitor-based source is designed to meet the transient load requirements. figure 2 shows the schematic of the complete lvdc mg. the boost converters with spv are designed to operate in two modes: maximum power point tracking (mppt) mode and constant current mode (ccm). similarly, a bidirectional converter (bdc) with battery and ultracapacitor is configured to operate in voltage control mode (vcm) as well as in ccm when absorbing the excess power. the fc-based source with the boost converter is configured to work in both vcm and ccm. a. the proposed three layer hierarchical control the hierarchical control is divided into 3 levels: local control, emergency control, and supervisory control as shown in figure 3. the local control acts as the primary control directly on the dc-dc converters interfaced with each source. this includes source optimization and local power/energy management of each source. the top layer consists of supervisor control which optimizes the overall system performance while ensuring system stability. the emergency layer monitors the source and system parameters to ensure that their values are within the limits. in case of any parameter crossing the set limits, the emergency control layer intervenes with the local or supervisory control to initiate the necessary actions. in case of emergencies like a severe mg bus fault, the emergency control initiates the actions directly to ensure no damage occurs to the system components. local control source optimization, local power/energy management emergency, transient condition monitoring and protection voltage, optimal power energy management, stability control emergency control supervisory control fig. 3. the proposed three layer hierarchical control structure. the converter of each source is designed with selfsustainable local control to work independently and feed the power to its own local loads. the supervisory control is responsible to control various primary controller parameters as and when required. the low band-width communication link between the supervisory and the local controller ensures the information exchange needed for the control and the coordination of power generation balancing and load demand. it also ensures the source and system level data for identifying the transient/emergency conditions for changing the mode of operations, as well as the calculation of the reference signals to source level primary controller parameters. the overall mg is designed to provide 3kw of dc load at 48v bus voltage. the specifications of the various power converter components and their ratings used in the hardware implementation are given in table i. table i. power converter details of the studied dc m g converter vs pout (kw) l (mh) esrl (mω) c (µf)/v esrc (ω) conv. switch battery bdc 24v 1 0.56 50a 10 470 / 200v 0.05 skm100 gb063d spv-boost conv.1&2 31v 1 0.26 50a 6 1000 / 200v 0.1 skm 100 gb 063d fuel cell 24v 1.2 0.56 50a 10 1000/ 200v 0.1 skm 100 gb 063d ultracapacitor 165f/48v 24v - 0.26 50a 6 470 / 200v 0.05 skm 100 gb 063d the switching frequency for all the converters is selected to be 20khz. the supervisory control is realized on a texas instrument’s tms320f28379d dual core controller board whereas the local control for each source is realized on tms320f28069 controller boards. based on hierarchical control strategy, the supervisory controller selects the mode of operation for each local converter through serial communication executed on the dsp. figure 4 shows the power and control scheme implemented for various converters. the details of design of both vcm and ccm are given in [10]. the emulated fuel cell source is designed to be similar to a battery based source except the unidirectional boost converter instead of the bdc. figure 5 shows a photograph of the engineering, technology & applied science research vol. 12, no. 1, 2022, 8045-8052 8048 www.etasr.com muchande & thale: hierarchical control of a low voltage dc microgrid with coordinated power … developed lvdc mg in hardware with the specifications listed in table i. the functionalities of the proposed control strategy were verified with simulations carried out in the psim platform. the simulations were carried out to investigate some technical operational challenges and the way they were addressed suitably. various operating scenarios under normal and emergency conditions were created as cases listed below. also, hardware implementation of power topology along with the proposed control scheme was carried out to validate the results. (a) vpv ipv spv c dc mg bus solar p v emulator + + supervi sory cont rol command l esr-l c esr-c kp+ki/s mode select mppt il* il ipv il vmgvpv rlocal + (b) l esr-l c esr-c kp+ki/s mode select type iii kp+ki/s il* il vo* vo ichrg* ichrg ichrg il vbusvs rlocal + + + ++ + dc mg bu s 24v/ 35ahr battery bank supervi sory control comma nd ultra-cap 165f/48v (c) fig. 4. (a) solar pv 1 and 2 boost converter with ccm and mppt control mode. (b) battery and ultra-capacitor boost converters with vcm and ccm control mode. (c) mode select control logic with communication received from the supervisory controller. b. cpms simulation results in normal operating conditions the hierarchical control based algorithm ensures the continuity of supply and efficient source utilization under all operating conditions. the supervisory control mentors the local variable parameters from the local controllers to perform the system level operating modes and passes the charging/discharging information. considering the different power generation and loading scenarios for the proposed dc microgrid for urban applications, a few normal operational scenarios (nos) are describing as below. sola r pv source emulator fc source emulator mg bus electronic load ccs platform for real-time debugging fc boost converter battery source bdc converter battery 2 x 12v/35ah pv source boost converter uc boost converter ultracapacitor microgrid supervisory controller mg dc bus fig. 5. photograph of the developed lvdc mg setup. nos-1: during the light load conditions, the mg bus load is fed from the spv and battery sources. as seen in figure 6, the spv source 1 is operating in mppt mode to supply the primarily load current. the battery source maintains the mg bus voltage by absorbing the excess power or delivering the deficit power. the load is reduced at t= 2s, the excess power from the spv 1 is absorbed by the battery. before t=2s, the load demand is met by spv 1 and the battery. fig. 6. nos 1: light load condition supported with spv and battery. nos-2: under light load conditions, load is fed by the spv and battery sources, but if the spv power is more than the connected mg bus load, then battery charging is carried out. figure 7 shows, the solar pv power generation changes as per solar insolation level. the spv source supplies the available power to the load in the mppt mode. fig. 7. nos 2: light load condition supported with spv and battery with opportunity charging scenario. dc/dc convpwm cc vc iact iref vact vref dc/dc convpwmvc vact vref signal from source failure d c b u s c o m m u n ic at io n c h an n el state-1 state-2 1 2 3 4 time (s) -20 0 20 40 60 ibat il ipv1 vmg spv-source1 current1000w/sqmt spv-source-1 current850w/sqmt battery charging with excess spv source 1 power load current @525 w load mg bus voltage48 v load current @1000 w load battery discharging to supply the load power 1 2 3 4 time (s) -60 -40 -20 0 20 40 60 80 ibat il ipv1 vmg ipv2 spv-source1(mppt mode) curren@800w/sqmt spv-source1(mppt mode) current@500w/sqmtbattery discharging to supply the load power load current @525 w mg bus voltage48 v load current @1000 w battery discharging to supply the load power load current @1500 wspv-source2(mppt mode) current@1000w/sqmt spv-source2(mppt mode) current@900w/sqmt engineering, technology & applied science research vol. 12, no. 1, 2022, 8045-8052 8049 www.etasr.com muchande & thale: hierarchical control of a low voltage dc microgrid with coordinated power … the battery source maintains the mg bus voltage by absorbing the excess power or delivering the deficit power. the battery can be availed with opportunity charging in case the pv power is more than the instantaneous load demand. at t= 2.5s the solar insulation level is changed and excess power from solar pv 1 and 2 is utilized to battery charging. nos-3: the mg bus load increased from 0.5kw to 2.8kw. the spv sources 1 and 2 are both operating in mppt mode primarily delivering the available power to the load. fuel cellbased source working in current controlled mode supplements the spv sources feeding the load. the battery source maintains the mg bus voltage by absorbing the excess power or delivering the deficit power. the simulation results for full load condition with the fuel cell operating in cc mode supplemented by both spv sources is shown in figure 8. under full load conditions, all the sources participate to feed the mfg bus load while both the spv sources deliver the available maximum power. fig. 8. nos 3:-full load condition supported with spv (mppt mode), fuel cell (cc mode), and battery sources (cv mode). nos-4: the mg bus load increased from 0.5kw to 2.8kw. spv sources 1 and 2 are both operating in cc mode. the fuel cell source is configured to deliver the available power to the load while maintaining the mg bus voltage. the battery source delivers no load power but is engaged in charging through the fc as can be seen in figure 9. fig. 9. nos 4: full load condition supported with spv (cc mode), fuel cell (cv mode), and battery sources (charging mode). nos-5: the spv sources 1 and 2 are both operating in cc mode. the battery source is configured to primary deliver the available power to the load while maintaining the mg bus voltage. at 1.5s, the capacitive load imposed on the mg bus results in large transient current requirement. the ultracapacitor source pumps the demanded transient current, thus relives the battery from supplying the transient load. the transient phase mitigation by the ultracapacitor source is shown in figure 10. fig. 10. nos 5: transient loading condition. c. cpms simulation results in emergency operating conditions emergency conditions such as mg short bus faults, failure of controllers/sources, loss of generation, and heavy overloads can occur in a dc mg. however, in the extreme case of a fault, the pms may not be capable of retaining the mg in normal operating condition. when it comes to improving the resiliency and the reliability of the dc mg, power management and coordination strategy play a vital role. it is assumed that the fault was occurred, detected, and isolated by the emergency control layer and then control and coordination actions have to react quickly ensuring stability. considering the different power generation and loading scenarios for the proposed dc mg, a few emergency operating scenarios (eoss) are described below. eos-1: the spv sources 1 and 2 are both operating in mppt mode. the battery source is configured to primarily deliver the available power to the load while maintaining the mg bus voltage. at 2.5s, due to passing clouds, the power available from the spv sources to zero. the battery source pumps additional load current to maintain the mg bus voltage. figure 11 shows the simulation results of a sudden loss of the non-dispatchable spv source. fig. 11. eos 1: sudden loss of the non-dispatchable spv source. 0 1 2 3 4 5 time (s) -60 -40 -20 0 20 40 60 80 ibat il ipv1 vmg ipv2 ifc spv-source1(mppt) current@1000w/sqmt spv-source1(mppt) current@500w/sqmt battery supplying the load power load current @2400 wmg bus voltage-48v load current @500 w battery absorbing the excess spv power load current @2800 w spv-source2(mppt) current800w/sqmt fc source current-17a battery source maintains mg bus voltage but supply zero load current 0 1 2 3 4 5 time (s) -40 -20 0 20 40 60 80 ibat il ipv1 vmg ipv2 ifc spv-source1 (cc mode) current battery supply the load power load current @2400wmg bus voltage-48v load current @500w battery source maintains mg bus voltage load current @2800w spv-source2 (cc mode) current fc source takes over as master source battery charging with fc/ spv1 & 2 sources power fc supply current limited by its capcity voltage scale-(volts) current scale-(amps) 1.46875 1.48438 1.5 1.51563 1.53125 1.54688 time (s) -50 0 50 100 150 200 ibat il iuc vmg mg bus voltage-48v uc source current during transient load condition uc source current before transient load condition transient mg bus load current (switching of capcitive load) mg bus voltage variation due to transient load battery source supply the mg bus load voltage scale (volts) current scale (amps) nominal load current 0 1 2 3 4 5 time (s) -80 -60 -40 -20 0 20 40 60 80 100 ibat il ipv1 ipv2 vmg mg bus voltage48 volts spv source 1&2 (mppt) supplying load current and charging the battery battery charging with excess power from spv source 1 and 2 spv source 1 & 2 both dropped due to passing clouds battery source takes over the entire mg bus load power requirement voltage scale (volts) current scale (amps) engineering, technology & applied science research vol. 12, no. 1, 2022, 8045-8052 8050 www.etasr.com muchande & thale: hierarchical control of a low voltage dc microgrid with coordinated power … eos-2: the spv sources 1 and 2 are both operating in mppt mode. the battery is assumed to be charging with the excess power from the spv sources. at 1.5s, the spv source 2 suffers from loss of generation. at 2s, due to the increase in load demands, the fuel cell source kicks in to supply the additional load current to maintain the mg bus voltage. the simulation results are shown in figure 12. fig. 12. eos 2: sudden loss of the dispatchable battery source. iii. hardware results a laboratory scaled prototype (figure 5) was designed and implemented for validation of the proposed mg with hierarchical control to supply 3kw dc load at 48v. some selected hardware results are presented in figures 13-16 indicating the various parametric measurements and their dynamic responses under different operating conditions (only few illustrative results are shown in this paper). figure 13 shows the spv source and battery source managing the overall load requirement of the mg under light load conditions. figure 13(a) shows the available spv power changes as per the variation in the solar insolation and the deficit power that is then delivered by the battery source ensuring the mg bus voltage is maintained within the specified allowable limit. figure 13(b) shows the spv source emulation with the mppt mode primarily delivering the available power to the load while maintaining mg bus at 48v throughout the operation. figure 14 shows the emulated fuel cell and battery sources managing the overall load requirements of the mg. the spv source is operating in mppt mode primarily delivering the available power to the load. this situation may arise when the spv source is not available, e.g. under rainy conditions or during the night. the fuel cell-based source working in current controlled mode supplements the battery source feeding the load. the battery source maintains the mg bus voltage by delivering the deficit power. in normal operating conditions, it is ensured that the spv and the battery handle the load requirement. under heavy load conditions, the fuel cell source along with the spv and battery sources are utilized to supply the net mg bus load, whereas in light load conditions, the spv source operating in mppt mode delivers the excess power to the battery. figure 15 shows the opportunity charging of the battery source when the spv source power at the mppt is more than the one demanded by the mg bus load. the battery source gets charged through the excess spv source power while maintaining the mg bus voltage. (a) (b) fig. 13. (a) the spv source is in the mppt mode primarily to supply the load current and the battery source maintains the mg bus voltage by absorbing the excess power or delivering the deficit powerage due to solar insolation changes. (b) spv emulation with mppt tracking. under transient loads, like switching of capacitive loads, or short term fault conditions, the current drained from the battery source can be very high which may lead to the faster deterioration of the battery cells thus reducing the life of the battery. as shown in figure 16, under such conditions the uc source gets engaged due to the faster current loop design and hence the faster dynamic response. under any transient current demand conditions, the uc source supplies the current, thus reducing the current requirement demanded from the battery source. the hardware setup of the lvdc mg with the proposed coordinated power management strategy implemented was tested under various other conditions as explained in the simulation results. 0 1 2 3 4 5 time (s) -20 0 20 40 60 ibat il ipv1 ipv2 vmg ifc mg bus voltage-48v load current spv source 1 current spv-source2 current loss of spv source 2 due to passing clouds battery charging (< 30% soc) with excess solar pv power battery charging stopped due to loss of spv power fc source kicks-in to supply the deficit power voltage scale (volts) current scale (amps) engineering, technology & applied science research vol. 12, no. 1, 2022, 8045-8052 8051 www.etasr.com muchande & thale: hierarchical control of a low voltage dc microgrid with coordinated power … (a) (b) fig. 14. (a) fc (cc mode) and battery (cv mode) under a particular loading condition. (b) the fc source feeds designated power to the load based on the command received from the cpm, and the battery source supply the deficit power. fig. 15. spv source with mppt mode delivering available power to load and excess power under light load condition is supplied to the battery source with opportunity charging. (a) (b) fig. 16. (a) capacitive load switching: the uc source contributes the transient current relieving the battery source. (b) expanded view of (a). the performance of the mg proved to satisfy the requirement of reliable mg bus supply under all the operating conditions. because a dc mg involves the integration of different types of renewable energy sources with dynamical changing characteristics and continuous changing in loads, mg control needs to be designed to ensure that the bus voltage stability is maintained all the time. the power sharing between the mg sources which ensures flat mg bus voltage profile under any operational conditions while reliably fulfilling the load requirements is a challenging task. most of the researchers focused on power sharing under normal operating conditions while at emergency conditions the focus was on the protection of the system. while some researchers have already addressed the suitable power management strategies like adaptive dynamic power management strategy, different combinations of ress with suitable energy storage units, demand side energy management and esss, intentional load shedding, dispatch of expensive fossil fuel sources, system reconfiguration by considering one by one the issues to be taken into the account under normal operating conditions. very few papers have reported a power sharing strategy under emergency operating conditions in dc mgs. under emergency conditions the demand in control and coordination between various subsystems of the mg to survive and extend the mg operation may significant change. this paper presented a highly effective hierarchical control with coordinated power management strategy for mg sources and esss to handle both normal and abnormal situations. the proposed control strategy was validated with simulation and experimental results in an implemented lvdc mg to showcase its reliable behavior under normal and emergency conditions. iv. conclusion this paper presented the implementation of a hierarchically controlled lvdc mg with spv, fuel cell source as res components, and ess comprised of battery based and ultracapacitor based sources. the proposed lvdc mg system can facilitate the integration of such ress to supply continuous power to the load. the proposed coordinated power management strategy based on hierarchical control for an autonomous lvdc mg ensures the reliable operation of the system with renewable energy sources, storage, and loads. the proposed strategy ensures the proper power sharing and the continuation of the mg operation under normal and emergency conditions. the hierarchically controlled dc mg operating in autonomous mode under normal and emergency conditions has been tested and some of the hardware results were reported. references [1] x. lu, k. sun, j. m. guerrero, j. c. vasquez, and l. huang, "state-ofcharge balance using adaptive droop control for distributed energy storage systems in dc microgrid applications," ieee transactions on industrial electronics, vol. 61, no. 6, pp. 2804–2815, jun. 2014, https://doi.org/10.1109/tie.2013.2279374. 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[17] d. q. oliveira, a. c. zambroni de souza, a. b. almeida, m. v. santos, b. i. l. lopes, and d. marujo, "microgrid management in emergency scenarios for smart electrical energy usage," in 2015 ieee eindhoven powertech, eindhoven, netherlands, jun. 2015, https://doi.org/10. 1109/ptc.2015.7232309. [18] m. alowaifeer, a. alamri, and a. p. s. meliopoulos, "microgrid energy management system for normal and emergency operating conditions," in 2019 north american power symposium (naps), oct. 2019, https://doi.org/10.1109/naps46351.2019.9000218. authors profile shrishell muchande completed his b.e. and m.e degrees in electrical engineering at the university of mumbai, mumbai, india, in 2008 and 2013, respectively. since 2016, he is a research scholar in the department of electrical engineering, fr. conceicao rodrigues institute of technology, navi mumbai, mumbai, india. he has over 4 years of experience in industry. his interest areas include power electronics, renewable energy systems, microgrids, and control in microgrids. from 1996 to 2012, he was worked at the lokmanya tilak collage of engineering, koparkhairane, navi mumbai. since 2013, he has been a member of the faculty of the department of electronics and telecommunication engineering, gharda institute of technology, lavel, ratnagiri, maharastra, india. sushil thale obtained his b.e. degree in electrical engineering in 1992 and m.e. in electrical engineering in 1996 from the university of mumbai, india. he completed his ph.d. at the indian institute of technology-bombay with specialization in power electronics and power systems in 2015. he is currently working as a professor (electrical) and dean (r&d) at fr. conceicao rodrigues institute of technology, navi mumbai, india. his areas of research include renewable energy systems, electric vehicle control, and microgrids. microsoft word etasr_v12_n5_pp9186-9191 engineering, technology & applied science research vol. 12, no. 5, 2022, 9186-9191 9186 www.etasr.com rohilla et al.: an empirical framework for recommendation-based location services using … an empirical framework for recommendation-based location services using deep learning vinita rohilla department of computer science and engineering, school of engineering and technology, sharda university, greater noida, india and department of cse, maharaja surajmal institute of technology, new delhi, india vinita_rohilla@msit.in mandeep kaur department of computer science and engineering school of engineering and technology sharda university greater noida, india mandeep.kaur@sharda.ac.in sudeshna chakraborty department of computer science and technology lloyd institute of engineering and technology greater noida, india sudeshna2529@gmail.com received: 8 june 2022 | revised: 8 july 2022 | accepted: 10 july 2022 abstract-the large amount of possible online services throws a significant load on the users' service selection decision-making procedure. α number of intelligent suggestion systems have been created in order to lower the excessive decision-making expense. taking this into consideration, aν rlsd (recommendation-based location services using deep learning) model is proposed in this paper. alongside robustness, this research considers the geographic interface between the client and the service. the suggested model blends a multi-layer-perceptron (mlp) with a similarity adaptive corrector (ac), which is meant to detect high-dimensional and non-linear connections, as well as the location correlations amongst client and services. this not only improves recommendation results but also considerably reduces difficulties due to data sparseness. as a result, the proposed rlsd has strong flexibility and is extensible when it comes to leveraging context data like location. keywords-location services; recommendation system; deep learning; similarity corrector i. introduction numerous corporations and organizations have started to wrap their created business apps into more and more widespread multiple online services [1-4]. many lightweight recommendation methods have also been created to reduce the expenses of consumer decision-making. generally, by evaluating available client data, a recommender system can deduce a person's approximated tastes and preferences and then offer reliable suggestions [5-9]. it efficiently captures the relevant information and preferences of service clients. location is an important component in decision recommendations since the quality of service (qos) is sometimes significantly dependent on client or service location. moreover, location-aware qos data frequently contain sensitive user information, such as a user's most recently requested service set, the amount of time it takes a user to summon a services located in a nation, etc. service-oriented architecture (soa) is commonly employed in decentralized computing environments [10], including cloud computing and mobile computing. location-based services are more successful to provide recommendations based on user's interests [12, 13]. collaborative filtering (cf) is a popular way for creating a recommendation system. in recommendation systems, the current user-based cf mechanism seeks for a comparable user based on their prior behavior. the ideas must be according to the user's interest. for example, a user's visited locations are denoted by pins of various forms. the 4 customers check in at 9 distinct locations: 'exhibition,' 'hotel,' 'campground,' 'shopping centre,' 'cineplex,' 'opera cinema,' 'cafe,' 'library,' and 'college.' the cf approach often creates a similarity measure between various users and offers suggestions based on the maximum value. let's create a suggestion for customer a1. we could observe that user a1s activities are more comparable to users a2s activities because both went into 'cineplex,' 'opera cinema,' and 'cafe.' based on the activities of user a2, the cf technique now recommends 'library' to user a1. unfortunately, this is not the greatest fit for user a1 when user a1's visiting information indicates a preference in 'entertainment' venues, like 'gallery.' to address this constraint, we will construct an interested profile for every customer so that suggestions may be made as needed. the following are the major contributions to this study: • an rlsd framework is developed, which blends an mlp with a similarity adaptive corrector in a new way. corresponding author: vinita rohilla engineering, technology & applied science research vol. 12, no. 5, 2022, 9186-9191 9187 www.etasr.com rohilla et al.: an empirical framework for recommendation-based location services using … • the performance of the suggested strategy was assessed and compared with 9 advanced options. • the proposed technique not only improves recommendation performance, but it also significantly reduces difficulties due to data sparseness. ii. literature survey authors in [14] focused mostly on the cold-start dilemma for service advice depending on user and service locations. to resolve this concern, they offered a service recommendation approach based on cf and geo location, which takes into account the characteristics of services at the edges, movement, and customer requests over time. to begin, they used a multidimensional weighted approach to synthesize the service quality for every dimension in different temporal chunks. in respect of recommendations accuracy, the empirical findings suggest that their multidimensional inverse similarity recommendation method (mditcf) built on time-aware cf surpasses the inverted cf recommendation method. authors in [15] suggested a novel deep cf approach to service recommendations, dubbed location-aware deep cf (ldcf). these main advancements included in this approach are: 1) the location attributes are located into high-dimensional dense imbed matrices. mlp encapsulates the hd and non linear features. similarity acs are integrated in the output nodes to first rectify the forecasting qos. with this, ldcf not only understands the high-dimension and non-linear correlation among the user and services, but it can also dramatically reduce data sparseness. extensive studies on a real-world web service [15] database show that ldcf's recommendations efficiency clearly exceeds 9 state-of-the-art services recommendations approaches. authors in [16] used location information in the factorization machine for qos predictions, while contextualized information helps the cf similarity calculation. these computations understand the lower dimension and linear characteristics of customers and service providers. authors in [17] suggested a tailored location-aware cf approach for web service recommendations. picking comparable neighbors for the user based service the suggested technique takes advantage of both customer location and online services. the technique also incorporated an improved similarity metric for user and web services through accounting for their customized contribution. the test findings demonstrate that this methodology greatly increases qos predictive performance and computing efficiency when compared to earlier cf-based systems. iii. proposed methodology the major problem in recommending services is estimating qos. cf is the most extensively utilized qos predicting technology currently available. conventional cf techniques, on the other hand, suffer from two flaws: 1) the similarity modeling approach used by conventional cf-based techniques can only gain knowledge of low-dimension and linear characteristics or features from previous networks of user and service and 2) the commonly used data sparseness dilemma in reality has a massive effect on recommendation systems' efficiency. this section provides a detailed description of the proposed model and methodology. the section briefly describes the loss function, the optimizer, and the algorithm used in this work. a. deep neural networks a deep neural network (dnn) is one type of neural network with more than 2 layers: an input layer, at least one hidden layer, and an output layer. in a process known as "feature hierarchy," every layer conducts certain kinds of sorting and ordering. handling with unorganized or unstructured input is among the most important applications of highly powerful neural network models [18]. fig. 1. recommendation based location services based on deep learning architecture. the rlsd model is a multiple-layered feed forward neural network with 3 main layers. an input layer is used to create the input variables needed from the intermediate layer and the similarities needed for the output nodes. the intermediate layer is employed for centralized training to ensure getting high-dimension and non-linear characteristics. 1) input layer the input layer's primary function is to regulate the initial input. the input contains user identification, location-based info, service identifiers, and service geo locations in keras1's embedding layer, that may be thought as a special fullyconnected layer lacking bias terms. essentially, the embedded layer uses one-hot encoding on the inputs to build a '0' vector with a given dimension, while the vector's i-th point is set to 1 [19]. the category characteristics are translated to highdimension fully connected embedding vectors using this procedure. the mapping procedure is depicted in (1) (4): ��� = ��(��� � + ��) (1) ��� = ��(��� �� + ��) (2) ��� = ��(��� � + ��) (3) ��� = ��(��� �� + ��) (4) where � and � are the user's identifier and the service’s identifier, correspondingly, �� and �� are the initial inputs for the user’s and service’s location, �� and �� are user's and service's embedding weighted matrices, �� is a bias term engineering, technology & applied science research vol. 12, no. 5, 2022, 9186-9191 9188 www.etasr.com rohilla et al.: an empirical framework for recommendation-based location services using … initialized to 0, �� is the embedding layer's activation function, which is considered as the identity function for this work, ��� and ��� are the k-dimensional user_id and location embedding vector correspondingly, and u and s are the k-dimensional service_id and location embedding vector correspondingly. these identifying feature vectors representations are integrated with the appropriate location features set to generate the user feature map and service feature map. next, we append both feature maps to generate the intermediate layers input vector sequence. the equation is written in the following form: � = ɸ(��� , ��� ) = � ��� ��� � (5) s = ɸ(��� , ��� ) = � ��� ��� � (6) x = ɸ(u, v) = ���� (7) where φ is the mergence operation, u and s are user and service embedding vectors, and x is the input vector. an adaptive corrector (ac) that computes similarities among user-location embedding and service-location embedding is present. the ac employs a similarity approach, including location similarities among consumers and services into the neural network's forward propagation phase. as a result, the ac bridges gaps across deep learning with cf. the ac's operation outcome is immediately transferred to the output nodes, bypassing the intermediate layer. the ac is adaptable and may be used for all other similarity computations like cosine and euclidean similarity. equations (8) and (9) describe the procedure: !" = cosider(�� , ��) = �� . �� $|��|$ ||��|| (8) !" = cosider(�� , ��) = &�� . �� (9) where !" is the ac similarity output. cosine and euclidean similarities are both present in this. when no specific comment is made, (8) is applied to determine the cosine similarity outcome of the ac. 2) intermediate layer the intermediate layer is responsible for processing the input vectors from the input nodes in order to capture nonlinear information. the high-dimensional non-linear correlation among consumers and services is learned using a densely integrated mlp architecture in this work. first but foremost, we must select the non-linear activation. the activation function selu (scaled exponential linear unit) presents numerous benefits. it allows building a map featuring qualities that led to snns (self-normalized neural networks). secondly, in order for the dnn to train and learn many attributes, the network structure must adhere to the standard tower architecture [20]. lastly, to avoid over fitting, we employ l2 regularization on weights. in the intermediate layer, the forward propagating of the input vector sequence is described by: '( )*+ = �((,(� + �() (10) '( )*+ = ��(,�� �('./� )*+ + ��), i = 3, 4,…,n -1 (11) '012 = '3−1 012 (12) where '6/� )*+ is the ith layer of the intermediate layer’s output, �� the intermediate layer bias term, and ')*+ the intermediate layer's output. 3) output layer the output layer is largely responsible for producing the overall forecast results. the frls paradigm divides users and services into two paths. we immediately combine the outcomes of these two paths, as in [20, 21]. we mix the similarity outcome ' !" with the output vector ')*+ to create a new output vector sequence o. finally, frls makes the final projections using a single-layered neural network. gaussian distribution is used to initialize the parameters of this layer, as illustrated in (13)-(14): o = ɸ(' !" , ')*+ ) = � 7897:;<� (13) �= �,� = �6(,6� ' + �6 ) (14) where �>�,� is the predicted qos values of user u raising the s service, and �6 is the ordinary identity function that signifies the activation function of the last layer. we get a typical matrix factorization network base gaussian matrix factorization (gmf) distribution on one side and an mlp network on the other. b. multi-layer perceptron networks an mlp network is simply a formal moniker for the most fundamental type of dnn. an mlp network is made up of 5 dense hidden layers and the selu activation function. we began by embedding the user and items, then flattened and appended them. afterwards, we added the first dropout layer, followed by 4 hidden layers with 64 neurons, 32 neurons, 16 neurons, 8 neurons, and finally one densely integrated neuron. then a dropout and batch normalization layer was added between hidden layers 1 and 2 and 2 and 3. lastly, we got our final output layer, which is nothing more than a one fullyconnected neuron. we utilized log cosh as the error function and nadam as optimizer. c. matrix factorization networks a gaussian mf networks is essentially a conventional point-wise mf that uses stochastic gradient decent (adam with this context) to approximate the factoring of a matrix (user×item) into two matrices, i.e. user×latent feature and latent feature×item. d. combining the two networks: neumf finally, the matrix factorization and mlp network are merged into the neumf network. essentially, this merely appends the results of two networks. the two networks are then fused, and a single output node is added to the newly integrated model. from this, the configuration is like above, with a binary log cosh loss and the nadam optimizer. engineering, technology & applied science research vol. 12, no. 5, 2022, 9186-9191 9189 www.etasr.com rohilla et al.: an empirical framework for recommendation-based location services using … to improve the accuracy of representing probability distributions, many variants have been proposed. an alternative approach for improvement is through the reconstruction loss: f(t: a) = � ?log(cosh(at)) = � ?log @ abc @ dab ( (15) nadam optimizer can be written as: (16) nesterov is used by nadam optimizer to modify the gradients 1 step forward by substituting the prior m_vec (mt-1) in (16) with the current m_vec (mt): (17) algorithm 1: rlsd (recommendation based location services using the deep learning algorithm. required: user_service request matrix (rm), density of matrix (dm), dnn topology design (t), learning rates (lr), decayed ratios (dr), no. of iterations (ni). output: weighted matrix and the bias ��, ��, ,�, …, ,6 , ��, �(, …, �6 . strategy: step 1. scarce rm based on dm step 2. make training inputs entries for efg?.6 and test input entries ef@�f step 3. create input attributes/features � , ��, �, ��; step 4. construct the dnn using t and (10)-(12) step 5. set �� , �� , ,� , …, ,6 according to the gaussian distribution; step 6. set ��, �(, …, �6 to 0; step 7. for each epoch = 1 to ni do step 8. for each user and service in rtrain do step 9. create embedding vectors sequence using (1)-(4); step 10. create input vector sequence using (5)-(7) step 11. create the ac output from either (8) or (9) step 12. make prediction, �>�,� using (13)-(14) step 13. end for step 14. give lr and dr to nadam optimizer step 15. modify parameters of the model using the nadam minimization (15) step 16. for each user and service in rtest do step 17. use (20)-(21) to measure the performance of the model step 18. end for step 19. end for iv. results and discussion this section discusses the experimentation results for location-based services on the ws-dream dataset using python programming. to assess the effectiveness of the proposed method, two evaluation measures are used. a. dataset we ran tests upon the ws-dream dataset which is a substantial web services dataset gathered and managed in [22], which consists of 19,74,675 qos values from 339 users on 5,825 services. this dataset includes information on users' and services' locations. qos data are presented in this work as a user-service matrix, with the row indicator representing the user identifier and the column indicator representing the services identifier. this work utilized response time and throughput as inputs to the rlsd. b. pre-processing this research makes use of two spatially relevant dataset features/attributes: country name (cn) and autonomous system number (asn). users were spread throughout 30 nations and 136 asns, whereas services were spread across 990 asns across 73 countries, according to database figures. for cn, we utilized sklearn3's category encoding to convert the classed characteristics into numerical embeddings, such that each classified attribute is expressed by a nation code. the data can be viewed like after pre-processing: � = (�_�i, �jkl, �ml) (18) k = (k_�i, kjkl, kml) (19) where u and s are the user input embedding vector and service input embedding vector correspondingly, u_id is the user identifier, uasn is an autonomous system numeric user code, ucn is the nationwide user code, and s_id, sasn, and scn are the same as above. c. parameter setting for cf methods (upcc, lacf, ipcc, regionknn, etc.),the best-k value is set to 10, the learning rate is fixed at 1e -3 , the total of implicit feature factors (size) is fixed to 10, the number of total iterations is fixed to 300, the regularization variables are fixed to 0.1, and the randomized factor for the rarefy matrix is fixed to 7. deep learning techniques (ncf, rlsd), can be developed using the keras api, wherein the gaussian distribution function is utilized (average is 0, stdev is 0.01) to set the model hyper parameters and (15) to modify the hyper parameters. then we configured the batch size to 256, learning rate to 1e -4 , 4 mlps, and nadam optimizer. d. evaluation metrics the recommendation success of the specified approach is measured using two fundamental statistical evaluation metrics: mean absolute error (mae) and root mean squared error (rmse): mae = ∑ |o�,��,� / o⏞�,�| q (20) rmse = � q ∑ (��,� − �⏞�,� )(�,� (21) where ��,� is the qos initial value for the user u raising the service s, �⏞�,� is the qos prediction value u raising the service s, and n is the overall qos value. tables i and ii show the obtained results by the algorithms performed in [21], with which the proposed model of this paper is compared to. the values in the tables show that the proposed model is better in mae and rmse for response time (rt) and tp (throughput). engineering, technology & applied science research vol. 12, no. 5, 2022, 9186-9191 9190 www.etasr.com rohilla et al.: an empirical framework for recommendation-based location services using … table i. response time experimental results approach density 0.5 0.10 0.15 0.20 0.25 mae rmse mae rmse mae rmse mae rmse mae rmse umean 0.876 0.853 0.873 1.857 0.874 1.857 0.873 1.858 0.874 1.858 imean 0.703 0.567 0.686 1.542 0.684 1.533 0.681 1.529 0.680 1.525 upcc 0.634 0.377 0.553 1.311 0.511 1.258 0.483 1.220 0.467 1.189 ipcc 0.633 1.397 0.591 1.341 0.507 1.258 0.454 1.208 0.431 1.175 uipcc 0.624 1.386 0.579 1.328 0.498 1.247 0.448 1.197 0.425 1.165 regionknn 0.594 1.641 0.577 1.637 0.569 1.627 0.569 1.617 0.562 1.619 lacf 0.682 1.500 0.650 1.468 0.610 1.416 0.582 1.381 0.562 1.357 pmf 0.568 1.537 0.487 1.321 0.451 1.221 0.430 1.171 0.416 1.139 ncf 0.440 1.325 0.385 1.283 0.372 1.253 0.362 1.205 0.349 1.138 ldcf 0.246 0.7398 0.2787 0.895 0.2291 0.7573 0.2370 0.8004 0.2585 0.8819 rlsd (proposed) 0.1765 0.4977 0.1699 0.530 0.1892 0.6155 0.1831 0.5977 0.1710 0.5643 table ii. throughput experimental results approach density 0.5 0.10 0.15 0.20 0.25 mae rmse mae rmse mae rmse mae rmse mae rmse umean 54.333 110.296 53.947 110.345 53.971 110.201 53.906 110.190 53.862 110.194 imean 27.342 65.844 26.962 64.843 26.757 64.266 26.669 64.069 26.595 63.873 upcc 27.559 60.757 22.687 54.598 20.525 50.906 19.243 48.834 18.253 47.135 ipcc 27.102 62.665 26.270 60.479 25.487 57.561 23.726 54.564 22.286 52.293 uipcc 27.070 60.510 22.440 54.506 20.256 50.585 18.888 48.238 17.863 46.392 regionknn 26.857 69.614 25.352 68.015 24.947 67.365 24.687 66.923 24.746 66.831 lacf 27.419 65.770 24.847 62.057 22.943 58.816 21.562 56.507 20.587 54.785 pmf 18.943 57.020 16.004 47.933 14.668 43.642 13.988 41.652 13.398 40.025 ncf 15.468 49.703 13.616 46.034 12.284 42.317 11.833 41.263 11.312 39.534 ldcf 17.629 57.746 14.711 50.730 13.952 48.871 13.199 47.323 12.332 45.142 rlsd (proposed) 19.517 61.822 16.154 53.344 14.958 50.681 14.388 49.393 14.332 49.195 figures 2 and 3 show the loss values obtained by both models in response time and throughput respectively. the lesser the loss value, the more accurate the simulation (unless the model was over fitted to the training set). the loss value can be computed during training and testing and is used to determine how good the model performs for the two different sets. loss, like accuracy, is also not a proportion. it is the summarization of the errors incurred in training and test sets with each sample. it is clearly visible that the proposed rlsd model performed better than the existing methods by reducing the loss values in both response time and throughput. fig. 2. loss values of response time. fig. 3. loss values of throughput. v. conclusion a recommendation system is the backbone for retrieving and processing information that aims to forecast user interests. this study offers a novel deep learning-based approach called rlsd to provide recommendation services to predict qos which incorporates a similarity ac to improve the prediction values. in the future, we plan to analyze and solve additional privacy concerns in location service recommendations, as well as improve the performance, using a parallel and distributed recommendations system to manage the required massive data. this model may also improve the results of [15, 23-29]. references [1] y. 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[29] n. kumar, "document clustering approach for meta search engine," iop conference series: materials science and engineering, vol. 225, dec. 2017, art. no. 012291, https://doi.org/10.1088/1757-899x/225/ 1/012291. microsoft word siderakis2.doc etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 1-7 1 www.etasr.com siderakis et al : pollution maintenance techniques in coastal hv installations pollution maintenance techniques in coastal high voltage installations k. siderakis dept of ee tei of crete heraklio, greece ksiderakis@stef.teicrete.gr d. pylarinos dept of ece university of patras patras, greece e. thalassinakis assistant director p.p.c. heraklion, greece i. vitellas director p.p.c. athens, greece e. pyrgioti dept of ece university of patras patras, greece abstract— pollution of outdoor high voltage insulators is a common problem for utilities, with a considerable impact to power system reliability. in an effort to prevent possible flashovers due to pollution, many methods have been applied, aiming to improve the insulation performance, either by suppressing the formation of surface conductivity or by increasing the possible insulation level. in the case of substations, the selection of the appropriate technique is complex due to certain issues correlated to the nature of the installation. in this paper, several techniques usually implemented by utilities, are investigated based on the experienced gained in the case of crete, a greek island in southern europe, where due to the coastal development of the power system, the majority of high voltage installations are exposed to intense marine pollution. the technique of coating insulators with room temperature vulcanized silicone rubber (rtv sir) has proved rather efficient and therefore is presented extendedly. correlation of the material behaviour with environmental conditions is discussed and results from long term monitoring, including environmental parameters and leakage current measurements, in a 150 kv substation are presented. it is shown that rtv sir coatings have remarkably suppressed surface activity and that porcelain insulators exhibit different activity period when coated. keywords: pollution; rtv sir; gis; substation; insulators; leakage current; i. introduction a possible outage in a high voltage substation usually corresponds to a severe impact to the power system [1]. therefore, from the reliability point of view, substation maintenance has a considerable importance, which increases with the corresponding increase of the correlated transmission circuits’ number. pollution of high voltage insulators is a problem experienced by many utilities worldwide. it originates from the environment and is capable of deteriorating the performance of outdoor insulation, under the nominal voltage stress. the first step of the pollution phenomenon is the accumulation of contaminants on the insulation surface [2]. in the case of hydrophilic insulation (e.g. porcelain), the presence of a wetting mechanism (e.g. rain, fog, humidity) transforms the contaminants layer into a conductive film which permits the flow of leakage current through it. the flow of current heats up the surface and localized changes in the surface conductivity occur. areas of higher resistance are formed, called dry bands, and discharges may appear (dry band arcs) which can ultimately lead to a complete flashover of the insulator [2]. several methods have been applied to cope with the pollution problem [2-4]. the most usual suppressing method is the cleaning of insulators. other methods employ different insulator and substationsdesign. polymer insulators and coatings can also be employed in order to prevent film formation, by retaining moisture in the form of droplets. however, periods of hydrophobicity loss and recovery are observed [5-8]. in addition, discharges may appear from and between scattered water droplets. one of the polymer materials frequently used as coating is the room temperature vulcanized silicone rubber (rtv sir). the power system in the greek island of crete suffers from intense pollution problems due to sea influence [9]. several techniques have been employed from the greek public power corporation (ppc) to cope with the problem [10]. in this paper a brief description of substation pollution maintenance techniques that have been employed in the power system of crete is presented. further, the use of rtv sir coatings is thoroughly investigated since a large scale application of such coatings has been issued by ppc in the cretan power systems. in addition, data from a field leakage current monitoring system that has been installed in a 150 kv substation are presented and the performance of coated insulators is further investigated. ii. the pollution problem within the design several methods can be applied to suppress the influence of the pollution phenomenon. the aspects usually considered within the design process are presented in table 1. the first step is the selection of the insulation’s parameters. usually, the leakage distance is the first parameter evaluated. the required value can be determined according to iec60815, depending on etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 1-7 2 www.etasr.com siderakis et al : pollution maintenance techniques in coastal hv installations the experienced problem intensity. however, the insulator geometry is also considerably important. an appropriate profile selection must take advantage of the self cleaning mechanisms present. otherwise, problems may be experienced, although the leakage distance criterion is satisfied. such a case has been experienced in crete and is presented in [11]. the use of composite insulators that provide a hydrophobic surface is also a considered improvement. however the material lifetime is an issue, considering the replacement cost and availability. further, the insulator geometry of the new insulators has to be evaluated. maintenance ability is an added issue. especially if live water washing is not possible, e.g. prohibited by law as in the case of greece, different substation schemes must be employed, in order to avoid power interrupts and thus maintain high levels of quality. the scheme usually implemented contains multiple bus systems and sectionalizing circuit breakers. table i. design remedies in the case of new substations design guideline problem intensity comments leakage distance low iec60815 geometry low physical cleaning mechanisms insulator selection material medium hydrophobicity resistive glazed substation scheme multiple bus systems sectionalizing cbs or isolators automatic washing systems medium capability of live washing partially enclosed in air increased medium voltage side fully rnclosed in air increased both mv and hv side enclosed substations fully enclosed in sf6 (gas insulated systems) extreme sophisticated systems, maintenance, cost if severe pollution problems are due to appear, then the construction of enclosed substations can also be considered. in the case of crete, the majority of the 150kv/20kv substations are partially enclosed, with only the 150kv side exposed to the environment. in addition there is one 66kv air insulated substation that is fully enclosed, a view of which is illustrated in figure 1. in both cases, the environment oriented problems are suppressed, however a control of the inner atmosphere is necessary considering that phenomena such as condensation may appear. the substation scheme that totally encounters pollution problems is a gis installation, a substation enclosed in sf6. in this case the possibility of a pollution related problem is totally eliminated and the save of space achieved is an added considerable advantage. however there are issues to consider, concerning the maintenance means and procedures and the installation cost. in crete at the moment there are two gis 150kv substations. a picture of the 150kv gis substation located in heraklion is shown in figure 2. figure 1. view of the 66kv enclosed air substation at linoperamata figure 2. view of the 150kv gis at heraklion crete iii. pollution maintenance methods in substations in the case of the already installed equipment, the financial investment required in order to apply any of the remedies reported in table 1 is considerable. therefore, to improve the performance of existing insulators, cleaning and coating application are usually employed. a sum of the pollution maintenance methods usually employed in the case of substations is presented in table 2. etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 1-7 3 www.etasr.com siderakis et al : pollution maintenance techniques in coastal hv installations table ii. maintenance methods in the case of substations a. cleaning and washing of insulators there are many different cleaning methods, and one has to consider parameters such as the number of insulators to be cleaned, the pollutant type, the possible by-products and the corresponding application cost in order to select the most appropriate in each case. the most common methods are summarized in table 3. the main problem concerning all methods included in table 3 is the selection of the optimum cleaning time. this is an exclusively experience oriented parameter, which depends on various factors regarding the local service conditions. if cleaning is performed earlier than required then a critical build up of contaminants is possible to develop in short time which means that the problem reappears quickly. on the other hand the more the cleaning is delayed, the higher the possibility of an outage due to pollution. further, there is a considerable financial cost related to the cleaning procedures, especially if they cannot be applied on live equipment. in the latter case a supply interruption is required, which corresponds to a deterioration of system reliability, since a part of a substation is set out of service and to an additional financial loss since it may be required to interrupt the power supply to a number of consumers. it is worth mentioning that this financial loss can be increased in the case of step up substations, if one or more power units are put out of operation for some hours, due to the supply interruption. the probable problems related to the power units operation can result to a significant additional cost [12]. table iii. insulator cleaning methods cleaning method deposit comments insulator washing high pressure washing deposits with poor adhesion time of washing live washing? work hours cost if power interruptions are required insulator cleaning dry cleaning cement fertilizers time of cleaning dry material deposits cost glaze damage and insulator shattering consequently, insulator cleaning is a method that can be applied in order to ensure the insulation performance under pollution conditions, but there are two significant parameters that must be considered. the first is the selection of the optimum cleaning time, since it is a suppressive method (not preventive) and the second is the correlated financial cost, especially if live washing cannot be applied. b. coating application different types of coatings are provided by various manufacturers, however the two types mainly used in the industry, are silicone grease and rtv silicone rubber coatings [13]. the improvement achieved is the application of a preventive method (instead of a suppressing one), since the coating can be installed at a time convenient for the utility and within its operational lifetime is capable of suppressing the pollution influence at any time. in both cases, the phenomenon suppression is possible by providing a water repellant surface, which as a result does not permit the formation of a conductive film on the insulator’s surface. the difference between the two types is the method employed in order to maintain the water repellency feature. in the case of silicone grease, the deposited contamination is encapsulated within the material volume and as a result the surface is kept hydrophobic. this means that there is a saturation point, when the maximum contaminants amount that can be encapsulated is achieved. at this point the end of the coating service lifetime is achieved and the material must be removed. otherwise, a performance even worse than an insulator without silicone grease, is probable to be experienced [13]. in the case of crete, the average lifetime of silicone grease coatings is six months. therefore, such a coating must be applied and further removed twice each year, something that limits a possible large scale application and it may only be applied on critical equipment. this limited coating service lifetime and the required man-hours for replacing the coating are the two primary drawbacks that limit the possible use of silicone grease. in the case of rtv sir coatings, a hydrophobicity transfer capability is present, sufficient to change the initial hydrophilic behavior of the deposited contamination to hydrophobic [1418]. as a result, although the deposited contaminants remain on maintenance method problem intensity comments insulator washing automatic or manual systems any live washing? time of washing work hours cost if power interruptions are required silicone grease medium method of preventive maintenance limited lifetime (encapsulation) necessary coating replacement power interruptions required work hours insulator coatings rtv sir medium method of preventive maintenance extended lifetime (hydrophobicity) aging and replacement are issues creepage extenders elastomeric high method of preventive maintenance specific design for each insulator geometry application cost etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 1-7 4 www.etasr.com siderakis et al : pollution maintenance techniques in coastal hv installations the surface (no encapsulation), the surface behavior is hydrophobic, suppressing the phenomenon development. this is a considerable improvement in comparison to silicone grease, since the accumulated contamination is still exposed to various cleaning mechanisms such as rain and therefore there is no saturation behavior. further the application lifetime is elongated and can exceed a period of 5 years, achieving in some cases a lifetime of more than 10 years. therefore, rtv sir coatings can be considered as a preventive measure that can provide an efficient solution in the case of substations. they can be applied on any insulator type, regardless of material, use and geometry. the application can take place at a time convenient for the utility and remain active for a period that most of the times exceed 5 years. certain concerns have to be answered in the case of application of rtv sir coatings, like material aging, maintenance, optimum time of replacement and the corresponding cost (labour and financial). however, the preventive feature and the large scale application capability are considerable advantages that distinguish this method from the rest. c. creepage extenders it is worth mentioning that coatings cannot fully counterbalance the lack of the required creepage distance. if the later is not sufficient then the use of elastomeric creepage extenders is obligatory. these extenders can be applied in any insulator type. but they must be specifically designed for the considered insulator geometry, something that limits the possibility of a large scale application and further corresponds to an increased application cost. therefore it is a method usually adopted in special conditions, when the methods already mentioned are not sufficient. iv. application of rtv sir coatings – the case of linoperama substation the first application of rtv sir coatings in crete started in 1998 at linoperamata 150kv step up substation, which was fully coated a few years later. the 150 kv transmission substation of linoperamata is located in the west side of the city of herakleion, right next to the sea coast. the substation suffers from intense marine pollution and the substation’s insulators had to be washed at least twice in each summer in order to avoid flashovers. live washing is prohibited by law in greece, and therefore the substation had to be washed in two parts. the economical profit of rtv sir coating application instead of washing, has proved rather significant [12]. in addition, more substations were coated and today, twelve years later, more than 6000kg have been installed in 66kv and 150kv substations, in crete and rhodes, as illustrated in figure 3. since application, surface activity has been remarkably suppressed and no flashovers have been experienced, although washing procedures have been suspended. hence, rtv sir coating application is considered rather successful. however, as the material age, concerns regarding the material reliability, evaluation and the necessary maintenance actions arise. therefore, a leakage current monitoring system was installed in the linoperamata substation to monitor and investigate field performance of insulators. figure 3. amount of installed rtv sir coatings per year in crete, greece etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 1-7 5 www.etasr.com siderakis et al : pollution maintenance techniques in coastal hv installations v. leakage current measurements and insulators performance in service conditions, the coatings evaluation was based mainly on empirical observations, such as surface discharges noise and visual observation. in order to monitor field performance, a leakage current monitoring system has been installed in linoperamata substation. a collection ring is placed at the bottom of each monitored insulator and the collected leakage current is driven through a hall sensor. a commercially available data acquisition system calculates and stores several leakage current related values. more details about leakage current monitoring in linoperamata substation can be found in [17, 19]. a representation of the measuring system is shown in figure 4a an actual photo of an installed collection ring is shown in figure 4b. figure 4. (a) leakage current measurement system setup, (b) installation of the current collection ring on a 150kv rtv sir coated voltage transformer. leakage current measurements verified the improvement achieved by the application of rtv sir coatings. the monthly distribution of the accumulated charge recorded over a 5-year period on the surface of the monitored insulators is shown in figure 5. all monitored insulators were 150kv post insulators of the same geometry, installed at the same location. the measurements concerning uncoated porcelain insulators are portrayed in figure 5a and the measurements concerning porcelain rtv sir coated insulators are portrayed in figure 5b. the improvement achieved in the latter case is evident. in addition, it is worth noticing that the period of activity is different in each case. in the case of uncoated porcelain insulators, surface activity is observed during the summer period and especially from august to october, as expected. in the case of rtv sir coatings the surface activity is increased during the winter and especially from november to march, although the main pollution problem is experienced during the summer. this behaviour has been correlated to the influence of different wetting mechanisms. during the summer, the main wetting mechanism present is condensation whereas during the winter is precipitation. figure 5. accumulated charge for the same time period in the case of 150kv post insulators of identical geometry, installed at the same location (a) in the case of porcelain and (b) in the case of rtv sir coated porcelain a typical example of the influence of the two mechanisms on the two different insulation surfaces is shown in figure 6 and figure 7, illustrating an incident where both wetting mechanisms are present. both insulators can be considered, originally, having the same contamination on their surface, since they are installed in the same place. as it can be seen in figure 6, in the case of condensation (high relative humidity), activity is observed only on the porcelain insulator, a fact that is attributed to the hydrophobic surface of the rtv sir coated insulators that prohibits the formation of conductive films. on the other hand, surface activity is initially present on both insulators during rain (high precipitation). the effect of rain can be seen more clearly after a zoom-in, as portrayed in figure 7. at the first incident of rain the activity on the coated insulator is considerably less than that on the porcelain. at the second incident of rain, however, the activity on the porcelain insulator has decreased whereas the activity on the coated insulator has slightly increased. however, the activity recorded (a) (b) (a) (b) etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 1-7 6 www.etasr.com siderakis et al : pollution maintenance techniques in coastal hv installations on rtv sir coated insulator was significantly lower in any case compared to the activity on the porcelain insulator. finally, at the third incident, activity is not present on either insulator. it is evident that the cleaning effect of rain is different in each case. the first incident of rain was able to remove an amount of contamination from the porcelain insulator and the levels of activity decreased. on the other hand, the levels of activity on the rtv sir coated slightly increased, which indicates that the same amount of rain could not clean the rtv sir surface effectively. on the contrary, it seemed to favor the development of surface activity, which means that temporary hydrophobicity loss probably occurred. as the rain activity increased, both insulators were finally cleaned and therefore no surface activity was observed at the third incident. in conclusion, it is shown that wetting mechanisms have different effects on each insulator. considerable activity can be observed on porcelain insulators in the presence of condensation, but not on rtv sir coated insulators. on the other hand, rtv sir coated insulators acquire higher precipitation to be cleaned, in comparison with porcelain insulators, and favor the development of surface activity during light rain. in any case, however, the experienced activity is significantly smaller in the case of rtv sir coated insulators. the effect of light rain explains the increased activity recorded on rtv sir coated insulators from november to march since light rain is rather usual in crete during the winter. figure 6. the impact of condensation and light rain on the surface behavior of both surface types (coated and not) in the case of two identical insulators, at the same place and time:(a) simultaneous measurements of the maximum and minimum surface leakage current observed on both insulators, (b) precipitation and relative humidity at the same place and time figure 7. an enhanced (zoomed-in) version of figure 6. (a) simultaneous measurements of the maximum and minimum surface leakage current observed on both insulators, (b) precipitation and relative humidity etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 1-7 7 www.etasr.com siderakis et al : pollution maintenance techniques in coastal hv installations vi. conclusions pollution maintenance of high voltage substations is an issue for every utility worldwide. the case of substations is rather complex due to the service features and the corresponding financial cost of the equipment included in such installations. several methods can be applied to cope with the problem in the design stage of new installations. the development of enclosed installations and especially gis can be considered as the optimum solution as far as pollution is concerned. in the case of already installed equipment, the employed remedies have to improve the performance of the existing insulation, since the cost of replacement is considerable. many methods can be employed in this direction. insulator cleaning and especially high pressure water washing are the first to consider. however, they both are time and money consuming and the selection of the appropriate cleaning time is still an issue. on the other hand, rtv sir coatings provide a cost effective predictive remedy combined with long lifetime. in crete, a large scale application has taken place and coatings that exceed a service period of 10 years are still in operation. the results from leakage current monitoring implemented on post insulators installed in a 150 kv substation indicate that coated insulators exhibit a much improved performance compared to non coated ones. further, the period of activity in the case of coated insulators was found different, due to the interaction of the hydrophobic coating surface to the present wetting mechanisms and especially light rain. references [1] r.e. brown, t.m. taylor, “modeling the impact of substations on distribution reliability”, ieee transactions on power systems, vol 14, no 1, february 1999 [2] cigre wg 33-04, tf 01, “a review of current knowledge: polluted insulators”, cigre publications, 1998 [3] ieee std 957-1987, ieee guide for cleaning insulators [4] j.s.t. looms, “insulators for high voltage”, iee power engineering series 7. [5] wankowicz j.g., gubanski s.m., lampe, w.d., “loss and recovery of hydrophobicity on rtv coating surfaces”, ieee transactions on dielectrics and electrical insulation, vol 1, no 4, august 1994 [6] h. hillborg, u.w. gedde, “hydrophobicity recovery of polydimethylsiloxane after exposure to corona discharges”, polymer, volume 39, issue 10, may 1998, [7] kim j., chaudhury m.k., owen m.j., “hydrophobicity loss and recovery of silicone hv insulation”, ieee transactions on dielectrics and electrical insulation, vol 6, no 5, october 1999 [8] kim s.h., cherney e.a., hackam r., “the loss and recovery of hydrophobicity of rtv silicone rubber insulator coatings”, ieee transactions on power delivery, vol 5, no 3, july 1990 [9] d.p. agoris, k.g. siderakis, e.j. thalassinakis, “influence of the environment to the pollution performance of rtv silicone rubber coatings in crete”, 13th ish, netherlands 2003 [10] e. thalassinakis, j. stefanakis, k. siderakis, d. agoris, “measures and techniques against pollution in the cretan transmission system”, european power and energy systems, iasted, crete, greece, 2002 [11] k. siderakis, d. agoris, j. stefanakis, e. thalassinakis, “influence of the profile on the performance of porcelain insulators installed in coastal high voltage networks in the case of condensation wetting”, iee proceedings on science, measurements and technology, vol 153, issue 4, july 2006 [12] e. thalassinakis, k. siderakis, d. agoris, “experience with new solutions to combat marine pollution in the power system of the greek islands”, world conf. on insulators, arresters and bushings, malaga, spain, 2003 [13] r.s. gorur, e.a. cherney, j.t.burnham, outdoor insulators, r.s.gorur inc, phoenix, arizona, usa [14] ieee std 1523 – 2002, ieee guide for the application, maintenance and evaluation of rtv sir coatings for outdoor ceramic insulators, ieee outdoor service environment committee, 2002 [15] e.a. cherney, r.s. gorur, “rtv sir coatings for outdoor insulators”, ieee transactions on dielectrics and electrical insulation, vol 6, no 5, october 1999 [16] e.a. cherney, “rtv silicone – a high tech solution for a dirty insulator problem”, ieee electrical insulation magazine, vol. 11, no. 6, november/december 1995 [17] k. siderakis, d. agoris, “performance of rtv silicone rubber coatings installed in coastal systems”, electric power systems research, vol. 78, issue 2, february 2008 [18] f. pratomosiwi, suwarno, “performance improvement of the ceramic outdoor insulators located at highly polluted environment using room temperature vulcanized silicone rubber”, international journal of electrical engineering and informatics, vol. 2, no. 1, 2010 [19] d. pylarinos, k. siderakis, e. pyrgioti, e. thalassinakis, i. vitellas, “impact of noise related waveforms on long term field leakage current measurements”, ieee transactions on dielectrics and electrical insulation, vol. 18, no. 1, 2011 authors profile kiriakos siderakis received a diploma degree in electrical and computer engineering in 2000 and a phd degree in 2006 from the university of patras. presently, he is working as a consultant with public power corporation in crete and also teaches high voltage engineering at the technical institute of crete. his research activities include high voltage insulation, composite materials and performance of insulators in polluted areas. dr siderakis is a member of cigre and the technical chamber of greece. dionisios pylarinos received a diploma in electrical and computer engineering from the university of patras in 2007. presently he is with the high voltage laboratory of the school of electrical and computer engineering at the university of patras. he has worked as a scientific consultant for ppc. his research interests include outdoor insulation, electrical discharges, high voltage measurements and high voltage equipment diagnostics and reliability. emmanuel thalassinakis received his diploma in electrical and mechanical engineering and also a ph.d degree from national technical university of athens. after working for the ministry of the environment, in 1991 he joined the public power corporation where he is now head of the crete and rhodes sector of the islands network operations department. his professional and research interests are reliability, high voltage transmission technology, power system operation and contamination of insulators. dr. thalassinakis is a member of the technical chamber of greece, ieee and cigre. isidoros vitellas is director of the islands network operations department in ppc (public power corporation) athens, greece. he was born in 1954 in greece and has obtained an diploma in electrical engineering and a phd in the same field. his research interests include electrical power generation and transfer, degradation and breakdown of insulating materials, electromagnetics. eleftheria pyrgioti was born in 1958 in greece. she received her diploma degree in electrical engineering from patras university in 1981 and the ph.d. degree from the same university in 1991. she is an assistant professor at the department of electrical and computer engineering at the university of patras. her research activity is directed to high voltage, lightning protection, insulation coordination and distributed generation. microsoft word yu_ed.doc etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 352-358 352 www.etasr.com yu and wang: generation of a �ew three dimension autonomous chaotic attractor and its four… generation of a new three dimension autonomous chaotic attractor and its four wing type fei yu college of information science and engineering hunan university changsha, china yufeiyfyf@yahoo.com.cn chunhua wang college of information science and engineering hunan university changsha, china wch1227164@sina.com abstract— in this paper, a new three-dimension (3d) autonomous chaotic system with a nonlinear term in the form of a hyperbolic sine (or cosine) function is reported. some interesting and complex attractors are obtained. basic dynamical properties of the new chaotic system are demonstrated in terms of lyapunov exponents, poincare mapping, fractal dimension and continuous spectrum. meanwhile, for further enhancing the complexity of the topological structure of the new chaotic attractors, the attractors are changed from two-wing to four-wing through making axis doubly polarized, theoretically analyzed and numerically simulated. the obtained results clearly show that the chaotic system deserves further detailed investigation. keywords3d chaotic attractor; chaotic system; hyperbolic sine; four-wing; axis doubly polarized i. introduction nonlinear analysis especially chaos analysis and applications in dynamical systems has been studied extensively within many fields, such as secure communication, synchronization and control [1-3]. since lorenz found the first chaotic attractor in a simple mathematical model of a weather system which was constituted of three-order ordinary differential equations in 1963 [4], in-depth researches to propose new chaotic attractors have been undergone in the last four decades. in 1976, rossler conducted important work that rekindled the interest in three-dimensional (3d) dissipative dynamical systems [5]. then, many lorenz-like or lorenzbased chaotic systems were proposed and investigated [6-17]. creating a chaotic system with a more complicated topological structure such as a multi-wing attractor becomes a desirable task and sometimes a key issue for many engineering applications. recently, some new four-wing chaotic systems were proposed. wang et al. discussed the methods to generate a four wing chaotic attractor in detail and gave some sufficient conditions, such as: (1) there is at least one quadratic term in every equation; (2) there are at least three independent variables, and there is at least one linear term in every equation of the system; (3) there are five equilibria [10]. the authors pointed out the quadratic terms are very important in creating a four-wing chaotic attractor [10]. in 2010, jia et al. reported a four-wing chaotic attractor and the chaotic characteristic of the system was proved by investigating the existence of a topological horseshoe in it, based on the topological horseshoe theory [11]. in 2011, wang et al. investigated a four-wing chaotic attractor and demonstrated that there existed heteroclinic orbits [12]. the four-wing chaotic attractors in [11, 12] all meet the four-wing standards proposed in [10]. in this paper, a novel approach to construct a four-wing chaotic attractor is proposed. firstly a new chaotic attractor is established. it is a 3d autonomous system which mainly relies on a quadratic hyperbolic sine (or cosine) nonlinear term and a quadratic cross-product term to introduce the nonlinearity necessary for folding trajectories, which can generate an attractor through theoretical analysis and detailed numerical simulation. nonlinear dynamic properties of this system are studied by means of nonlinear dynamics theory, numerical simulation, lyapunov exponents, poincare mapping, fractal dimension and continuous spectrum. the compound structure of the two-wing attractor obtained by merging together two simple attractors after performing one mirror operation is explored. finally, a four-wing type of the new chaotic attractor is realized by using z -axis doubly polarized. ii. new 3d autonomous chaotic system a new 3d autonomous chaotic system with a non-linear term in the form of a hyperbolic sine (or cosine) function is expressed as follows respectively: ( ) ( ) , , sinh , x a y x y bx cxz z xy dz = −  = −  = − ɺ ɺ ɺ (1) and ( ) ( ) , , cosh , x a y x y bx cxz z xy dz = −  = −  = − ɺ ɺ ɺ (2) etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 352-358 353 www.etasr.com yu and wang: generation of a �ew three dimension autonomous chaotic attractor and its four… fig. 1. phase portraits of system (1) at the initial conditions [ ]3,2,2 t . (a) x y z− − view, (b) x y− plane, (c) x z− plane, (d) y z− plane. fig. 2. phase portraits of system (2) at the initial conditions [ ]3,2,2 t . (a) x y z− − view, (b) x y− plane, (c) x z− plane, (d) y z− plane. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 352-358 354 www.etasr.com yu and wang: generation of a �ew three dimension autonomous chaotic attractor and its four… where , , ,a b c d are real parameters assuming that , , , 0a b c d > and , ,x y z are the state variables. systems (1) and (2) can generate a new two-wing chaotic attractor for the parameters 10, 30, 2a b c= = = and 2.5d = . the chaotic attractors are displayed in figures 1 and 2. it appears that the new attractor exhibits an interesting complex chaotic dynamics behavior. from figures 1 and 2, it can be seen that the nonlinear dynamic behaviors for systems (1) and (2) are very similar. so, below we mainly investigate the properties of system (1) since similar methods can be used for research on system (2). iii. basic properties of system (1) a. equilibria let: ( ) ( ) 0, 0, sinh 0, a y x bx cxz xy dz − =  − =  − = (3) if 0db c> > , the system has two equilibria points, which are respectively described as follows: ( )ln , ln ,e m m b c+ , ( )ln , ln , .e m m b c− − − where 2 4 2, 2m p p p db c= + + = . when 10, 30,a b= = 2, 2.5c d= = , we operate above those nonlinear algebraic equations and obtain that: ( )2.0779,2.0799,15e+ , ( )2.0779, 2.0799,15e− − − . for equilibrium point e + , system (1) are linearized, the jacobian matrix is defined as: ( ) ( ) 0 10 10 0 0 0 0 4.16 . cosh cosh 77.95 77.95 2.5 a a j b cz cx y xy x xy d + − −        = − − = −      − −   to gain its eigenvalues, we let 0i jλ +− = . these eigenvalues corresponding to the equilibrium point e + are 1 15.9997,λ = − 2 1.7498 +20.0468iλ = and 3 1.7498 -20.0468 .iλ = here 1 λ is a negative real number and 2 λ and 3 λ become a pair of complex conjugate eigenvalues with positive real parts. the equilibrium point e + is a saddle-focus point, and system (1) is unstable at this equilibrium point. for the equilibrium point e − , its jacobian matrix equals to: ( ) ( ) 0 10 10 0 0 0 0 4.16 . cosh cosh 77.95 77.95 2.5 a a j b cz cx y xy x xy d + − −        = − − = −      − −   the same we let 0.i jλ −− = these eigenvalues corresponding to the equilibrium point e − are 1 15.9997,λ = − 2 1.7498 +20.0468iλ = and 3 1.7498 -20.0468iλ = . apparently 1 λ is a negative real number and 2 λ and 3 λ form a complex conjugate pair and their real parts are positive. the equilibrium point e − is also a saddle-focus point, and system (1) is unstable at this equilibrium point. by the above brief analysis, the two equilibrium points of the non-linear system are all saddle focus-nodes. b. symmetry and invariance it is easy to see the invariance of system under the coordinate transformation ( ) ( ), , , , ,x y z x y z→ − − i.e., the system has rotation symmetry around the z-axis [16]. the orbit on the z-axis tends to the origin as t → ∞ . c. dissipativity and the existence of attractor the three lyapunov exponents and the divergence of the vector field is: ( ) 3 1 , i i x y z le v a d f x y z= ∂ ∂ ∂ = ∆ = + + = − + = ∂ ∂ ∂ ∑ ɺ ɺ ɺ (4) where ( )1,2,3ile i = denote the three lyapunov exponents of the system. note that ( ) 12.5f a d= − + = − is a negative value, so the system is a dissipative system and an exponential rate is: 12.5 . fdv e e dt −= = (5) from (5), it can be seen that a volume element 0 v is contracted by the flow into a volume element 12.5 0 t v e − in time .t this means that each volume containing the system trajectory shrinks to zero as t → ∞ at an exponential rate of 12.5− . therefore, all system orbits are ultimately confined to a specific subset having zero volume and the asymptotic motion settles onto an attractor [14, 15, 17]. etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 352-358 355 www.etasr.com yu and wang: generation of a �ew three dimension autonomous chaotic attractor and its four… d. lyapunov exponent and fractional dimension the lyapunov exponents refer to the average exponential rates of divergence or convergence of nearby trajectories in the phase space [13, 17]. if there is at least one positive lyapunov exponent, the system can be defined to be chaotic. the lyapunov exponents are calculated to be 1 0.6649,l = 1 0l = and 3 13.1763l = − . therefore, the lyapunov dimension of this system is: 1 1 2 31 0.6776 2 2 2.0514 13.1763 j i i l j l l l d j ll = + + = + = + = + = − ∑ (6) equation (6) means system (1) is really a dissipative system, and the lyapunov dimensions of the system are fractional. having a strange attractor and positive lyapunov exponent, it is obvious that the system is really a 3d chaotic system. e. time domain, spectrum map and poincare maps in the time domain, figure 3 shows an apparently chaotic waveform ( )x t of system (1) whilst, in the frequency domain, an apparently continuous broadband spectrum log x of system (1) is shown in figure 4. it can be seen from figures 3 and 4 that the new system exhibits chaotic behaviors. the poincare maps are shown in figure 5. from figures 5(a) and 5(b), it can be seen that the poincare maps consist of virtually symmetrical branches. we can further find that the section of the attractor looks like the tangled points from the poincare map of system (1) as shown in figures 5(c) and 5(d). f. lyapunov exponent spectrum figure 6 shows the lyapunov exponent spectrum versus increasing c . it can be observed that the system is undergoing some representative dynamical routes, such as stable fixed points, chaos and period-doubling bifurcation. for example, when the parameters 10, 30, 2.5a b d= = = , while c is varied on the closed interval ( ]0,20 , we can summarize as follows: • 1 2 1 0 1.04, 0, 0, 0,c l l l< ≤ = ≤ < there is a reverse period-doubling bifurcation route with a flip bifurcation, the system are some period-doubling bifurcation windows, one is shown in figure 7(a) • 1 2 1 1.04 6.66, 0, 0, 0,c l l l< ≤ > = < the system is chaotic as shown in figure 7(b), and there are several periodic windows in the chaotic band. • 1 2 1 6.66 9.11, 0, 0, 0,c l l l< ≤ = ≤ < the system are some period-doubling bifurcation windows, one is shown in figure 7(c). • 1 2 1 9.11 20, 0, 0, 0,c l l l< ≤ > = < the system is chaotic as shown in figure 7(d), and there are several periodic windows in the chaotic band. fig. 3. chaotic waveform of ( )x t . fig. 4. continuous broadband frequency spectrum of log x . g. forming mechanism of this new chaotic attractor structure compound structures of system (1) may be obtained by merging together two simple attractor after performing one mirror operation [8, 17]. such an operation can be revealed through the use of a controlled system of the form: ( ) ( )sinh x a y x y bx cxz u z xy dz = −  = − +  = − ɺ ɺ ɺ (7) where u is a parameter of control and the value of u can be changed within a certain range. here, we still select the initial values of the system as [ ]3,2,2 t . when 0.1u = , the attractor evolves into partial but is still bounded in this time, the corresponding strange attractors are shown in figure 8(a). when 4.2u = , the attractors are evolved into the single right etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 352-358 356 www.etasr.com yu and wang: generation of a �ew three dimension autonomous chaotic attractor and its four… scroll attractor, it is only one half the original chaotic attractors in this time, the corresponding strange attractors are shown in figure 8(b). then we set u to be a negative value. when 0.1u = − , the corresponding strange attractors are shown in figure 8(c), the attractor evolves into partial but is still bounded in this time. when 4.2u = − , the corresponding strange attractors are shown in figure 8(d), the attractors are evolved into the single left scroll attractor; it is only one half the original chaotic attractors in this time. fig. 5. poincaré maps in planes where (a) 0.5x = , (b) 0.5y = , (c) 18z = , (d) 22z = . fig. 6. lyapunov exponents spectrum of system (1) with ( ]0,20c ∈ fig. 7. phase portraits of system (1) with ( ) ( ), , 10,30,2.5a b d = at initial values [ ]3,2,2 t , (a) 0.5c = , (b) 4.7c = , (c) 8c = , (d) 16c = . etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 352-358 357 www.etasr.com yu and wang: generation of a �ew three dimension autonomous chaotic attractor and its four… fig. 8. phase portraits of system (6) in y z− plane at (a) 0.1u = , (b) 4.2u = , (c) 0.1u = − , (d) 4.2u = − . iv. a four-wing type of system (1) a four-wing type of system (1) is studied in this section. first, we simply introduce the anti-structure of system (1). then, two architectures are unified by one system. in order to connect with the up-attractor and down-attractor, we use z-axis doubly polarized, and the attractors of system (1) will be changed from two-wing to four-wing. the principle will be discussed in detail below. a. anti-structure of system (1) the anti-structure of system (1) can be expressed as: ( ) ( )sinh x a y x y bx cxz z xy dz = −  = +  = − − ɺ ɺ ɺ (8) under the same parameters conditions, system (8) is also chaotic. the chaotic attractor is displayed in figure 9(b). it appears that the new attractor locates in the quadrant of 0,z < while the attractor of system (1) is in the quadrant of 0z > (figure 9(a)). b. uniform structure of system (1) and system (8) by using sign function, the uniform structure of system (1) and system (8) can be expressed as: ( ) ( ) ( ) ( ) ( )( )sinh x a y x y bx cxz sign z z sign z xy dz sign z  = −  = −  = − ɺ ɺ i ɺ i i (9) under the same parameters conditions, system (9) is also chaotic. the chaotic attractor is displayed in figure 9(c). the full line is the trajectory of system (1) and the dotted line is the trajectory of system (8). it can be seen that the chaotic attractors can not evolve from negative half shaft to positive half shaft, and vice versa. so there are unable to produce a four-wing chaotic attractor. fig. 9. phase portraits of (a) system (1), (b) system (8), (c) system (9), (d) system (10) in y z− plane. c. a new four-wing chaotic attractor in order to connect with up-attractor and down-attractor, we do coordinate translation along the z-axis to zero point of system (9). then, we get a four-wing system which can be expressed as: ( ) ( )( ) ( ) ( ) ( )( )( ) 10 sinh 10 x a y x y bx cxz z sign z z h z xy d z sign z  = −  = − +  = − + ɺ ɺ i i ɺ i i i (10) where ( )h z is the hysteretic function, and the expression can be expressed as ( ) 1, 1 1, 1 z h z z → =  − → − (11) the four-wing chaotic attractor is displayed in figure 9(d). from figure 9(d), it can be seen that the four-wing chaotic attractor is symmetrical around the x y− plane. with further research, when the parameters 4.4, 46, 2.6a b d= = = , while c is varied, the four-wing chaotic attractor of system (10) can exhibit very interesting dynamics behavior. the system is undergoing some novel dynamical routes, such as downperiod-down-chaos (figure 10(c)), up-period-doubling-down etasr engineering, technology & applied science research vol. 3, �o. 1, 2013, 352-358 358 www.etasr.com yu and wang: generation of a �ew three dimension autonomous chaotic attractor and its four… chaos (figure 10(d)), up-period-doubling-down-perioddoubling (figure 10(e)) and down-sink (figure 10(f)), it notes that here up means the area of 0,z > down means the area of 0z < . using the same mathematical methods as presented in section 3 for analyzing system (10), system (10) also has some basic dynamical properties, such as equilibria, symmetry, invariance, dissipativity, fractional dimension and so on. fig. 10. phase portraits of system (10) in y z− plane at (a) 1.2c = , (b) 1.58c = , (c) 1.9c = , (d) 2.7c = , (e) 3.8c = , (f) 10c = . v. conclusion a new 3d autonomous chaotic system with a nonlinear term in the form of a hyperbolic sine (or cosine) function is presented. the dynamical behaviors of the new system are analyzed, both theoretically and numerically, including some basic dynamical properties, lyapunov exponents, poincare mapping, routes to chaos and so on. in addition, forming mechanisms of compound structures of the new chaotic attractor have been studied and explored. further, a new fourwing chaotic attractor is realized by using doubly polarized zaxis, more suitable for secure communication applications due too the complexity of its topological structure. references [1] a. a. zaher, a. abu-rezq, “on the design of chaos-based secure communication systems”, commun. nonlinear sci. numer. simulat., vol. 16, no. 9, pp. 3721-3737, 2011 [2] x. wang, j. song, “synchronization of the unified chaotic system”, nonlinear analysis: theory, methods & applications, vol. 69, no. 10, pp. 3409-3416, 2008 [3] c. zhu, “feedback control methods for stabilizing unstable equilibrium points in a new chaotic system”, nonlinear analysis: theory, methods & applications, vol. 71, no. 7-8, pp. 2441-2446, 2009 [4] e. n. lorenz, “deterministic non-periodic flow”, j. atmos. sci., vol. 20, no. 1, pp. 130-141, 1963 [5] o. e. rossler, “an equation for continuous chaos”, phys. lett. a, vol. 57, no. 5, pp. 397-398, 1976 [6] g. chen, t. ueta, “yet another chaotic attractor”, internat. j. bifur. chaos, vol. 9, no. 7, pp. 1465-1457, 1999 [7] j. lü, g. chen, “a new chaotic attractor coined”, internat. j. bifur. chaos, vol. 12, no. 3, pp. 659-661, 2002 [8] c. liu, t. liu, l. liu, k. liu, “a new chaotic attractor”, chaos, solitons fractals, vol. 22, no. 5, pp. 1031-1038, 2004 [9] s. celikovsky, g. chen, “on the generalized lorenz canonical form”, chaos, solitons fractals, vol. 26, no. 5, pp. 1271-1276, 2005 [10] z. wang, g. qi, y. sun, b. j. van wyk, m. a. van wyk, “a new type of four-wing chaotic attractors in 3-d quadratic autonomous systems”, nonlinear dyn., vol. 60, no. 3, pp. 443-457, 2010 [11] h. jia, z. chen, g. qi, “topological horseshoe analysis and the circuit implementation for a four-wing chaotic attractor”, nonlinear dyn., vol. 65, no. 1-2, pp. 131-140, 2011 [12] x. wang, j. li, j. fang, “the stability and chaotic motions of a fourwing chaotic attractor”, appl. mech. mater., vol. 48-49, no. 2, pp. 1315-1318, 2011 [13] z. wei, q. yang, “dynamical analysis of a new autonomous 3-d chaotic system only with stable equilibria”, nonlinear analysis: real world applications, vol. 12, no. 1, pp. 106-118, 2011 [14] x. f. li, k. e. chlouverakis, d. l. xu, “nonlinear dynamics and circuit realization of a new chaotic flow: a variant of lorenz, chen and lü”, nonlinear analysis: real world applications, vol. 10, no. 4, pp. 23572368, 2009 [15] w. zhou, y. xu, h. lu, l. pan, “on dynamics analysis of a new chaotic attractor”, phys. lett. a, vol. 372, no. 36, pp. 5773-5778, 2008 [16] s. dadras, h. r. momeni, “a novel three-dimensional autonomous chaotic system generating two, three and four-scroll attractors”, phys. lett. a, vol. 373, no. 40, pp. 3637-3642, 2009 [17] f. yu, c. wang, “a novel three dimension autonomous chaotic system with a quadratic exponential nonlinear term”, eng. technol. appl. sci. res., vol. 2, no. 2, pp. 209-215, 2012 engineering, technology & applied science research vol. 7, no. 3, 2017, 1605-1610 1605 www.etasr.com anagha and sunitha: influence of field spacer geometry on the performance of a high voltage coaxial… influence of field spacer geometry on the performance of a high voltage coaxial type transmission line with solid dielectric spacer in vacuum a. p. anagha electrical engineering department national institute of technology, calicut, india k. sunitha electrical engineering department national institute of technology, calicut, india karakkadsunitha@gmail.com abstract-with the development of more powerful high power electromagnetic sources, the transmission of high voltage power particularly between pulsed power systems to huge power rated microwave sources in absence of electrical breakdown and pulse distortion has begun to become a vital issue. a high voltage coaxial type transmission line with 500 kv peak voltage in vacuum is proposed. a novel proposal of configuration bearing a positive angle of 45o with socket-type filed shaper is being discussed in this paper in a manner to improve surface flashover properties and also to decrease the distortion seen in the pulse shape. this type of transmission line provides high capability of hold off voltage. the electric field distribution of the coaxial geometry with different field shaper configurations and different spacer parameters are also investigated using comsol software. keywords-field shaper; electromagnetics; surface flashover; triple junction; spacer; dielectrics. i. introduction the development stages of electromagnetic radiation in the wave band regions of microwave and millimeter of electromagnetic spectrum began with the inception of pulsed power technology during the 1960s. the applications of such sources range from plasma physics to communication, some of which being particle acceleration techniques, fusion energy research, high-power radars, etc. [1-5]. the recent trends in the research area of high power electromagnetic sources (hpem) are basically due to the unmatchable advantages of being capable to deliver high average and peak power [6-8]. recent trends showcased the development of still more powerful hpem sources which geared the possibility of transmitting high voltage quasi-square pulses without causing any electrical breakdown. the stress upon electrical breakdown is a quite significant factor in coaxial transmission lines where surface flashover along the dielectric spacer surfaces occurs galore. therefore, a more detailed study has to be done upon methods to deal with electrical breakdown and pulse distortion phenomenon, for delivering power efficiently along the high power transmission lines using pulsed power devices,. with proper alteration of the shapes of insulator and with the use of field shapers at triple junctions, significant reduction in surface flashover and dielectric breakdown has been observed. the conventional filed shaper designs are bump type, insertion type and the tangential type [9-13]. the main motive behind the installation of field spacers is to reduce the electric field strength seen at the triple junction where the electrode, dielectric and vacuum all come together. even though they may seem successful in reducing the huge electric field strength seen at the triple junction, the field strength is not brought down to near zero due to imperfections in the field spacer design. modification of insulator shape is done by proposing a new design of conical shaped insulator bearing an angle close to 45o and by increasing the length of surface of the insulator. electromagnetic pulse is a short burst of electromagnetic energy that may be originated as a natural or a man-made radiated electric, conducted electric or magnetic field based on the source. the interference of emp sources is very dangerous to electronic equipment, and high energy emp sources such as lightning strikes can damage structures like buildings and aircrafts. the medium used to transfer these pulses are mainly grouped as guided and unguided media [4]. guided media will provide a physical path to propagate the information, which includes twisted pair, coaxial cable and optical fiber. unguided media uses an antenna to transmit the information through air, vacuum or water. for applications such as high speed local area network and high capacity long distance trunk etc., coaxial cables are used mostly because of their capability of higher data rates over long distances. hence, the most common type of antenna feeder used today is definitely coaxial cable. the common applications of coaxial cables include: transfer of radio frequency energy, domestic connections between receivers and aerials, carry any level of high frequency signals to any distance etc. coaxial cable carries current through both inner and outer conductors, which are equal and opposite and as a result all the fields are confined within the cable. this is the basic principle of cable operation i.e. by propagating an electromagnetic wave engineering, technology & applied science research vol. 7, no. 3, 2017, 1605-1610 1606 www.etasr.com anagha and sunitha: influence of field spacer geometry on the performance of a high voltage coaxial… through it. the nearby objects are not affected by the interferences due to the absence of fields outside the coaxial cable. this is the main advantage of a coaxial cable compared to other forms. in this paper a new design of coaxial-type transmission line with socket type field shaper and a slight modification of the shape of the dielectric spacer is proposed to minimize the electric field strength and distortion of pulse. ii. coaxial type transmission line the high power coaxial transmission line is composed of both inner and outer conductors, a solid dielectric spacer for supporting the inner structure, and also a field shaper. the conventional and proposed coaxial transmission lines are shown in figure 1. a. basic design generally, parameters for the coaxial transmission line are based on other factors such as the strength of breakdown field and impedance. ideally, when losses are neglected, the field distribution pattern inside the coaxial line and also the characteristic impedance are expressed as [3]: ( ) ln( ) r v t e d r d = (1) ln( ) 2 coax r d z d h p e = (2) where r is the radius (d/2≤r≤d/2 ), v(t) is the applied voltage, d and d are the inner and outer diameters of the coaxial line, η is the intrinsic impedance, and εr is the relative permittivity of the material filling the space between the conductors. as keeping the objective to reduce the electric field strength, it is required to increase the outermost diameter of the coaxial line since the electric field is inversely proportional to the radius r. also, coaxial impedance is proportional to the ratio of the diameter of the inner and outer conductors but inversely proportional to the dielectric permittivity. this makes it necessary to decrease the inner diameter of the coaxial line in order to get an impedance match between the spaces filled with air and dielectric. b. surface flashover phenomenon insulators ranges in various dimensions are used to supplement the system with potential variations under certain circumstances. this makes the role of high-voltage hold off capability in insulators to be a vital one vastly in case of practical applications. vacuum gap will have, mostly, an edge over the solid insulators (of comparable dimension) while considering their high voltage hold off capacity. the phenomenon of surface discharge can be explained using three different phases: (a) initiation phase, (b) growth phase, and finally, (c) final phase. the instigation of the flashover occurs greatly by the discharge of electrons from the surface of a conductor under the influence of a strong electrostatic field, as a result of tunnel effect, which we call the whole process as initiation phase. a very few times, the cause for emission of electrons maybe due to a bunch of electrons or ions hitting the surface of the insulator. there still lies an ambiguity regarding the clarity of explanation for the next phase of event resulting in the growth of discharge, other than a few widely acclaimed interpretations. most researchers prefer the process of secondary electron emission avalanche mechanism to explain the development phase, where a few of the already presen t(emitted) electrons may hit the surfaces and walls of the insulator thereby adding much more electrons into play by secondary emission. this process will continue thus agglomerating the continuously producing electrons to form a series connection of string of electrons called as secondary electron emission avalanche (seea) which is a possible reason for a complete flashover [5]. fig. 1. coaxial type transmission lines: (a) coaxial geometry with bumptype field shaper, (b) coaxial geometry with socket-type field shaper the use of high voltage vacuum insulators is mainly in pulsed power generators for the separation of dielectric and vacuum. the vacuum dielectric can be broadly classified as: insulator stack and coaxial insulator; while the commonly used one is the second type mostly in tesla-type pulse power generator. our concern in this type of generator is the insulation difficulties which may even lead to the final rupture of vacuum dielectric. the breakdown mechanism can be well reasoned by the aforesaid theory of secondary electron emission avalanche. the breakdown point in the triple junction is shown in figure 2. the flashover may also be initiated due to anode side electrons at anode triple junction due to which flashover may occur at the surfaces in a predominantly high electric field. this may further increase the electric field intensity on the dielectric surface thus resulting in a huge rupture. this breakdown will build up across the surface on the way towards cathode until the flashover becomes complete [6]. rather than the dependence alone on the magnitude of the applied voltage, the flashover voltage will greatly depend upon the size and waveform of the voltage. likely, predominantly short pulses of nanosecond duration will have the highest flashover voltage while the comparatively longer pulses of microsecond duration and also dc pulses will have a medium (a) (b) engineering, technology & applied science research vol. 7, no. 3, 2017, 1605-1610 1607 www.etasr.com anagha and sunitha: influence of field spacer geometry on the performance of a high voltage coaxial… level of magnitude and ac voltages will be showing the lowest level of magnitude for flashover voltages. the complete time duration of flashover phenomenon depends on the time to initiate while the growth duration will be contributing very less to the total time duration. in addition to the waveform dependence of the flashover voltage, the shape and size of insulator will also exhibit a significant effect on the surface breakdown. lastly, the type of material also greatly affects the surface flashover phenomenon. generally, homogenous materials on top of non-homogeneous materials are preferred. fig. 2. the breakdown point at the ctj (cathode triple junction) iii. design of high power coaxial geometry different configurations of the coaxial type transmission line are discussed mainly the bump-type and socket type filed shaper design. the materials used for conductor, dielectric spacer and their relative permittivity are shown in table i. vacuum is used as the dielectric between the inner and outer conductor. the inner and outer conductor diameters are taken as 102 mm and 310 mm respectively [2]. table i. material specifications part material used relative permittivity conductor stainless steel 1 dielectric spacer nylon 66 3.2 a. design of the bumptype field shaper the configuration of the bump-type field shaper is shown in fig. 3. here, the place for field shaper is around the area of the ctj where the electrode and dielectric join in the vacuum [7]. this minimizes huge electric field strength experienced around the space. the dielectric spacer is realized using a coaxial type geometry bearing an angle of 45o to reduce the electric field seen on the dielectric spacer surface. fig. 3. configuration of the bump type field shaper design mt /mx=0.096, b/a=0.843 b. design of socket type field shaper figure 4 shows the improved high power geometry with socket-type field shaper. this is used to make the electric field strength value to almost zero at the ctj. the main advantage of this field shaper in comparison with the conventional one is that this can conceal the ctj effectively and also thus it can eliminate the emission seed electron starting at the ctj. a slight modification of the coaxial type dielectric spacer bearing a positive angle of 45o is done at both ends to enhance the support provided to both inner and outer conductors. this modification also makes it advantageous by effectively shielding the cathode structure and therefore keeps away the dielectric surface from the huge electric field around the region of the cathode field shaper. fig. 4. coaxial solid dielectric spacer mt/mx=0.079, hy/hx=1.9 and (b)socket type field shaper with fx/fy=0.375, fg/fy=0.25 c. modified design of socket type field shaper a modified design of the socket type field shaper is proposed in this paper to reduce the electric field mainly at the portion where the dielectric spacer and outer conductor meet. a socket type field shaper is used at ctj. instead of conical shaped dielectric with a positive angle of 45o a curved shape spacer is used. the proposed design is shown in the figure 5. fig. 5. modified design of socket type field shaper: fx/fy = 0.375, fg/fy=0.25, mt /mx = 0.179 and curved shape spacer iv. analysis of high power coaxial geometry to compare and verify the conventional and proposed high power coaxial geometry, simulation of different designs are carried out using the comsol multiphysics software. (a) (b) engineering, technology & applied science research vol. 7, no. 3, 2017, 1605-1610 1608 www.etasr.com anagha and sunitha: influence of field spacer geometry on the performance of a high voltage coaxial… electrostatic analysis of the different configuration is performed. an excitation of 500 kv is applied to the inner conductor and the outer conductor is grounded. fig. 6. electric field distribution of bump type field shaper the electric field distribution of the bump type and of the socket type design is shown in figures 6 and 7 respectively. the electric field distribution of socket type field shaper is more uniform compared to bump type field shaper along the coaxial solid dielectric. the bulged shape of the bump type field shaper makes the distribution more non-uniform and larger electrical stress is experienced in these regions. fig. 7. electric field distribution of socket type field shaper a. analysis of bump type design the dimensions of the bump shape are varied and the electric field distribution is observed. it is analyzed that as the bulged shape of the bump decreases, the electric field strength on its surface decreases and it becomes more uniform also. the simulation results are given in figure 8. we can clearly observe from the results that, the intensity of the shape of bumpiness and the electric field strength are inversely proportional. b. analysis of socket type design the bulged shape is completely removed and a new type of design called socket type design is proposed. 1) effect of spacing width of socket the spacing width of the socket is varied and the electric field distribution is simulated which is shown in figure 9. it is observed that a large variation in field distribution is not observed while varying the spacing, but a slight increase in the field strength as spacing decreases is analyzed. spacing dimensions affect least importantly in the case of analysis of the electric field strength and they pose minimum threat to the design scenario with regard to electric field strength. but always a minimum spacing has always to be maintained for safer field strength levels. fig. 8. analysis of bump type design 2) effect of radius of the socket the radius of the socket is also varied and observations are shown in figure 10.as the radius of the socket decreases a large increase in the electric field strength is observed. electric field strength and the socket radius length are again inversely proportional and therefore the radius has to be maintained at a safe level so as to reduce the effect of high electric field strength at that region. c. analysis of proposed modified design from comparison, it is observed that electric field distribution on the surface of the cathode filed shaper is reduced to a large extend in case of socket type field shaper design. but both geometries have high electric field strength at the portion of dielectric spacer which meets the outer conductor. in order to overcome this drawback a modified spacer design of socket type field shaper coaxial geometry is proposed. the electric field distribution of the proposed design is given in figure 11. a moreover uniform electric field engineering, technology & applied science research vol. 7, no. 3, 2017, 1605-1610 1609 www.etasr.com anagha and sunitha: influence of field spacer geometry on the performance of a high voltage coaxial… distribution is achieved by using the modified design of coaxial geometry. the simulation results for various dimensions of the new design are given in figure 12. from the results it is clear that spacer with wider gap has uniform field distribution. the other one has large field concentration at the portion where spacer and outer conductor meet. fig. 9. variation of electric field with spacing of the socket fig. 10. variation of electric field with radius of the socket fig. 11. electric field distribution of the modified design fig. 12. electric field for the modified design of spacer d. comparison of all designs comparing the electric field distribution of bump, socket and modified designs, it is observed that field distribution is more uniform with socket type field shaper and circular shape dielectric spacer. the range of maximum electric field as well as the minimum electric field is least for proposed modified design. the electric field is highest for bump type geometry and least for the modified geometry. this fact is better illustrated in table ii. table ii. results comparison field shaper geometry dielectric spacer difference between maximum and minimum field (mv/m) bump type rhombus type 91.7 socket type rhombus type 74 proposed modified design circular curved 6 v. conclusion a coaxial–type matched transmission line to transmit high power with reduced electrical breakdown and pulse distortion is proposed and analyzed. a comparison of different field engineering, technology & applied science research vol. 7, no. 3, 2017, 1605-1610 1610 www.etasr.com anagha and sunitha: influence of field spacer geometry on the performance of a high voltage coaxial… shaper designs is carried out and concluds that the socket type field shaper is more favorable. finally a modification is done for the spacer shape in the socket type filed shaper design. this has the basic advantage of reducing the electric field at the position where both spacer and outer conductor meet. this type of transmission line that can provide a significant reduction of electric field strength to near zero at the ctj and also good pulse shape may be very useful for high voltage pulse power applications. references [1] s. d. korovin, v. v. rostov, s. d. polevin, i. v. pegel, e. schamiloglu, m. i. fuks, r. j. barker, “pulsed power-driven high-power microwave sources”, proceedings of the ieee, vol. 92, no. 7, pp. 1082-1095, 2004 [2] r. kichouliya, m. joy thomas, “interaction of high power electromagnetic pulses with power cables and electronic systems”, ieee international symposium on electromagnetic compatibility, canada, july 25-29, 2016 [3] j. choi, y. kim, j. so, “design of low distortion high voltage coaxialtype transmission line for quasi-square wave nano-pulse with several hundred kilovolts in vacuum”, ieee transactions on dielectrics and electrical insulation, vol. 22, no.4, pp. 1809 – 1814, 2015 [4] s. f. mahmoud, electromagnetic waveguides: theory and applications, iet, 1991 [5] h. c. miller, “surface flashover of insulators”, ieee trans. electr. insul., vol. 24, no. 5, pp. 765–786, 1989 [6] l. zhao, j.-c. peng, y.-f. pan, x.-b. zhang, j.-c. su, “insulation analysis of a coaxial high-voltage vacuum insulator,” ieee trans. plasma sci., vol. 38, no. 6, pp. 1369–1374, 2010 [7] j. choi, y. kim, j. so, “design and experiments of the 600 kv coaxialtype matched divider for high-power microwave source array”, ieee trans. electron devices, vol. 61, no. 12, pp. 4240–4246, 2014 [8] l. g. christophorou, r. v. van brunt, j. k. olthoff, “sulfur hexafluoride and the electric power industry”, ieee electrical insulation magazine, vol. 13, no. 5, pp. 20-24, 1997 [9] l. niemeyer, f. y.chu, “sf6 and the atmosphere”, ieee transactions on electrical insulation, vol. 27, no. 1, pp. 184-187, 1992 [10] l. g. christophorou, r. v. van brunt, “sf6 /n2 mixture basic and hv insulation properties”, ieee transactions on dielectrics and electrical insulation, vol. 2, no. 5, pp. 952-1003, 1995 [11] t. nitta, y. shibuya, y. fujiwara, y. arahant, h. takahashi, h. kuwahara, “factors controlling the surface flashover in sf6 gas insulated systems”, ieee transactions on power apparatus and systems, vol. pas-97, no. 3, pp. 959-965, 1978 [12] t. s. sudershan, r. a. dougal, “a review of mechanism of surface flashover along solid dielectrics in compressed gases”, ieee transactions on electrical insulation, vol. ei-21, no. 5, pp. 727-746, 1986 [13] j. a. bakken, “determination of characteristics of voltage in impulse and switching surge testing”, ieee transactions on power apparatus and systems, vol. pas-86, no. 8, pp. 962-968, 1967 microsoft word etasr_v12_n3_pp8584-8591 engineering, technology & applied science research vol. 12, no. 3, 2022, 8584-8591 8584 www.etasr.com alhamdany et al.: statistical modeling of time headway on urban roads: a case study in baghdad statistical modeling of time headway on urban roads: a case study in baghdad mohammed alhamdany department of civil engineering college of engineering university of baghdad baghdad, iraq m.abdulrazzaq1901m@coeng.uobaghdad.edu.iq amjad hamad khalil albayati department of civil engineering college of engineering university of baghdad baghdad, iraq a.khalil@uobaghdad.edu.iq received: 2 march 2022 | revised: 22 march 2022 | accepted: 1 april 2022 abstract-time headway is an important feature of traffic engineering, determined by measuring the time elapsed between successive vehicles crossing a point on the road. this paper proposes a time headway modeling of urban roads for each lane of selected sites based on headway distribution. the study was carried out in the capital of baghdad, iraq, choosing the mohamed al-qassim and qanat al-jaish highways to collect field headway data. data were obtained using image processing and python for video analysis. each road consisted of six lanes divided into three lanes in each direction. the three lanes were studied in the forward movement of both highways. seven flow rates were considered for the headway data to evaluate the flow state of each lane. the easyfit 5.5 software was used to select an appropriate headway distribution for each flow rate, using a method depending on the kolmogorov-smirnov test for each lane. the results demonstrated that the proper model per lane was different. the selected distributions were used to develop a model through nonparametric regression using theil's slope estimator method. keywords-time headway; headway distribution; urban road; headway model; flow rate; traffic volume i. introduction traffic modeling is a fundamental tool in solving traffic engineering problems. traffic simulation depends on modeling of time headway because it represents important characteristics in microscopic flow theory. the temporal distance between two successive vehicles is known as time headway [1]. it is the time difference between the arrival of a leading vehicle and the following vehicle to a reference point. time headway depends on the flow rate of vehicles. a short time headway represents a high flow rate. this property are critical for roadway system planning, analysis, design, and operation [2]. time headways can be used in various traffic evaluations such as safety, capacity, and service level [3]. the minimum of time headway is obtained when traffic flow reaches its maximum. to increase route capacity and reduce vehicle delays, traffic engineers can employ detailed modeling and assessment of vehicle headway distribution. a statistical model of time headway is essential for theoretical and simulation-based traffic modeling. in addition, headway distributions are used in digital simulations that mimic multi-lane and highway traffic [4]. traffic volume, the proportion of big or heavy vehicles in the traffic, lane position, road layout, time, and weather affect the time headway distribution of vehicles and their appropriate models [5]. lane distribution and speed are affected by lateral clearance on the roadsides [6]. data are collected and analyzed using advanced technologies, such as image processing techniques, due to their effectiveness compared to sensor and loop detector methods [7]. several studies examined the modeling of time headway distribution. a study on the effect of lane position on time lane distributions at high levels of traffic flow was presented in [8]. based on headway distribution analysis, this study assessed driving behavior in several highway lanes in isfahan, iran. the results demonstrated that the fit model for the passing lane was distinct from the middle lane, due to drivers' behavior. numerous drivers adopted unsafe headways through carfollowing conditions in the passing lane, demonstrating the high risk ability of the driver population, which led to considerable distances in capacities and statistical distribution models of two lanes. the proper model for the passing lane was the shifted lognormal while for the middle was the shifted gamma.a traffic detector based on a laser beam sensor was used to model a suburban artery in south korea [9]. the observed data were divided into five flow states. the test rejected the randomness for a flow rate of 5-9veh/m. hence, theoretical modeling was performed for the remaining flow rates 10-14, 15-19, 20-24, and 25-29veh/m. the goodness of fit tests, examined using the kolmogorov-smirnov (k-s) method, revealed that the best fits were the johnson sb model for a flow rate of 10-14veh/m and the johnson su for the remaining three flows. the log-logistic model was the second-best fit for flow rates of 20-24 and 25-29veh/m. the progression of time under high flow conditions was studied on the palestinian arterial street in baghdad using two different periods for data collection [10]. the quality of fit was evaluated using the nonparametric chi-square test to determine the suitability of the logistic distribution of empirical data for the time headway distribution. the logistic probability distribution function described the time headway at the congested palestine street for corresponding author: mohammed alhamdany engineering, technology & applied science research vol. 12, no. 3, 2022, 8584-8591 8585 www.etasr.com alhamdany et al.: statistical modeling of time headway on urban roads: a case study in baghdad scale parameters ranging from 1.5 to 0.85. the differences in time headway distributions were studied in [11] for four flow levels, 0-600, 600-1200, 1200-1800, and 1800-2400pcu/h, for different two-lane and four-lane roads in assam using the traffic volume data collected by cameras on four-lane roads. the burr and log-pearson distributions were found to be suitable for 600-1200pcu/h, while the lognormal and loglogistic distributions fit the headway for traffic flows above 1200pcu/h. in [12], the mathematical distribution of vehicle headway was analyzed for freeway and arterial roads in riyadh city, saudi arabia, evaluating low-volume traffic conditions. the findings demonstrated that the shifted exponential and the gamma distributions appeared to fit data on freeways and arterials, respectively. the time headway distributions of vehicles traveling on the urban expressway in bangkok, thailand, were examined in [1], using exponential, lognormal, and generalized extreme value gev distributions. this study showed that the gev distribution could describe more than 90% of the empirical distributions on most lanes and sections of an expressway. on the other hand, the exponential was the less practical distribution, as it only described the experimental distributions during ultra-low traffic conditions. ii. data collection field data were collected at two sites, as shown in figures 1 and 2. the first site was the mohamed al-qassim highway, a 20km-long major arterial expressway, while the second was the qanat al-jaish highway, a 22km-long major arterial expressway in baghdad. the camera was mounted on the footbridges at approximately 10m height from the road surface to monitor traffic flow. fig. 1. site no.1 mohamed al-qassim highway. fig. 2. site no.2 qanat al-jaish highway. table i shows the camera coordinates. the selected sections consisted of six main lanes, three lanes in each direction, termed left or lane one, middle or lane two, and right or lane three. the study section was distant from ramps, loops, and horizontal or vertical curves. data were collected during daytime, under ideal weather and good visual conditions. data were selected to include different levels of traffic flow and the stop-and-go situation was neglected. traffic data for site one were collected for 21 hours over three days: 3, 4, and 5/5/2021. two hours of the second day, 1:00 pm and 2:00 pm, were excluded due to the stop-and-go condition of the vehicles. data for site two were collected for 18 hours over three days: 22, 23, and 24/2/2021. table i. camera coordinates camera location coordinates n e site one 33° 18' 44.87'' 44° 27' 03.30'' site two 33° 19' 58.94'' 44° 27' 52.95'' the spot speed of vehicles passing each site was measured using a bushnell 101911 speed gun. the speed gun was set to measure the speed in km/h and pointed in the direction of the moving vehicle. this speed gun transmits signals to moving objects and can capture a vehicle moving faster than 16km/h [13]. the average speed was determined for an interval of 15min. therefore, the sample size of speed data of 100veh/h/ln was randomly selected from each lane. figure 3 shows the direction and equipment used to record the data. the video clips were analyzed using python to extract the real data, as shown in figure 4. fig. 3. the layout of the video cameras and speed gun on the site. fig. 4. data extraction from video recording using python. engineering, technology & applied science research vol. 12, no. 3, 2022, 8584-8591 8586 www.etasr.com alhamdany et al.: statistical modeling of time headway on urban roads: a case study in baghdad the data were compared for their accuracy. the extracted data included the number of vehicles, vehicle classification, and time headway for each lane. figures 5 and 6 depict the traffic volume observed during the study. fig. 5. traffic volume of site 1 (mohammed al-qassim highway). fig. 6. traffic volume of site 2 (qanat al-jaish highway). seven flow rates were used to represent each lane's different flow state conditions and provide accurate headway data. tables ii and iii illustrate a few characteristics of the time headways average speed, defined by the spot speed for each flow rate. table ii. collected data for site 1 position rate of flow v/h/ln average speed (km/h) sample size av. headway (s) max headway (s) min headway (s) heavy vehicles (%) left lane: lane 1 937 91 937 3.84 44.74 0.37 15 1291 91.03 1291 2.788 19.65 0.33 10 1366 91.01 1358 2.636 21.63 0.27 10 1493 90.62 1485 2.411 17.38 0.23 16 1679 90.23 1675 2.143 17.4 0.2 9 1812 89.282 1808 1.986 20.353 0.166 24 2015 87.609 1997 1.786 14.65 0.23 13 middle lane: lane 2 903 83.53 902 3.988 26.33 0.3 37 1029 82.566 1024 3.497 21.57 0.2 29 1142 81.658 1137 3.152 20.17 0.2 19 1278 80.987 1278 2.816 13.31 0.23 20 1384 79.918 1359 2.6 16.28 0.17 31 1445 78.212 1433 2.491 15.58 0.2 29 1575 72.762 1574 2.286 13.01 0.27 31 right lane: lane 3 311 76.26 311 11.566 59.85 1.07 30 418 74.1 415 8.61 42.67 0.7 12 423 72.21 421 8.515 37.84 0.73 21 475 70 475 7.574 41.7 1 35 500 68.525 498 7.201 62.1 0.4 27 581 66.21 580 6.192 35.56 0.3 20 684 64.041 675 5.262 46.01 0.3 19 table iii. collected data for site 2 position rate of flow v/h/ln average speed (km/h) sample size av. headway (s) max headway (s) min headway (s) heavy vehicles (%) lane 1 985 91.158 983 3.655 22.12 0.2333 35 1286 89.285 1280 2.799 28.43 0.2 18 1568 87.677 1562 2.295 15.55 0.3 29 1757 86.773 1745 2.049 17.38 0.27 21 1935 85.732 1926 1.86 14.18 0.3 25 2106 83.846 2103 1.709 12.71 0.2 30 2345 82.333 2345 1.535 10.61 0.2 28 lane 2 841 83.325 840 4.278 29.23 0.33 31 932 82.187 926 3.862 25.92 0.4 37 1090 80.562 1081 3.303 16.82 0.4 26 1131 80.1 1128 3.182 21.65 0.23 18 1271 78.762 1270 2.831 19.92 0.33 38 1393 77.337 1392 2.583 14.48 0.27 19 1490 74.975 1484 2.415 19.48 0.23 31 lane 3 461 66.287 454 7.804 41.84 0.67 34 515 65.45 514 6.991 31.73 0.5 18 593 64.512 588 6.072 38.2 0.2 11 612 63.61 610 5.883 32.93 0.64 21 735 61.337 735 4.895 38.5 0.37 32 843 60.187 842 4.272 33.06 0.4 20 950 58.95 949 3.787 28.13 0.5 14 fig. 7. measurement of time headway. the flow rate was calculated using: ���� ��� �� ���� (1) where havg is the average headway in a lane. time headway was defined as the time between bumper to bumper of successive vehicle arrivals at a reference point or line on the lane playback screen. this time was simultaneously calculated for multiple lanes, as shown in figure 7. iii. automatic vehicle and classification method data were extracted from videos using python and imageprocessing technologies to analyze vehicle counting, vehicle classifications, and time headway for each lane. python and the opencv library were used to count the vehicles. the pycharm ide was used to develop the code, and prettify was used to display it. additionally, the numpy, cv2, and csv libraries were also used. the developed method combined grayscale and threshold algorithms to improve the quality and accuracy of vehicle detection. a dilate filter was used to track the position of each vehicle and categorize the detected vehicles into distinct classes, which were then tallied individually for each lane to offer helpful information for traffic flow analysis. the method's flowchart is depicted in figure 8. engineering, technology & applied science research vol. 12, no. 3, 2022, 8584-8591 8587 www.etasr.com alhamdany et al.: statistical modeling of time headway on urban roads: a case study in baghdad fig. 8. flowchart of the processing algorithm. the count of vehicles was executed when the contour areas touched the region of interest (roi). the roi was formed by drawing three imaginary lines diagonally across the road, connecting the two ends representing the three lanes [14]. when the front bumper of the vehicle touched this imaginary line, the value of the counter increased, indicating that the object's movement was observed. an imaginary was drawn diagonally by connecting two roi points. the virtual detector was used for the classification. this method consisted of a rectangle box, considering the roi, and the vehicles within that box were identified based on their dimensions, i.e., width and height [15]. table iv. results of automatic and manual counting site no. time date automated method (using python) manual method lane 1 lane 2 lane 3 total lane 1 lane 2 lane 3 total two 8:00 a.m. 24/02/2021 1579 1123 575 3277 1518 1269 619 3406 two 2:00 p.m. 24/02/2021 2345 1392 865 4602 2351 1437 865 4653 two 7:00 a.m. 23/02/2021 983 840 514 2337 976 874 534 2368 two 11:00 a.m. 23/02/2021 1991 1277 748 4016 1879 1348 801 4028 two 3:00 p.m. 22/02/2021 1729 1155 566 3450 1694 1224 600 3518 one 7:00 a.m. 03/05/2021 937 902 550 2389 931 918 552 2401 one 8:00 a.m. 03/05/2021 1358 1024 362 2744 1358 1077 358 2793 one 4:00 p.m. 04/05/2021 1797 1104 415 3316 1778 1127 419 3324 one 10:00 a.m. 05/05/2021 1808 1278 421 3507 1845 1302 447 3594 one 2.00 p.m. 05/05/2021 1752 1387 475 3614 1832 1443 463 3738 fig. 9. the fit distribution obtained using the easyfit v5.5 software. the colors were specified to track the object using a histogram-oriented technique. in this method, the contour properties, such as solidity and contour area, were extracted and compared with the assumed values to determine whether the vehicle is a passenger or a heavy vehicle. the contours represent the connected pixels in an image. the contours of the foreground objects were detected after performing background subtraction. the video was binarized into frames to obtain the foreground. the open cv method was used for the process of thresholding black and white images. the open cv algorithm operates in the form of thresholding, as it considers the frame into two levels, i.e. background and foreground. additionally, a binary threshold was used for the segmentation of a vehicle. the vehicle counting results were obtained and compared using manual and automated methods, and it was observed that the latter method provided accurate results quickly, as shown in table iv. engineering, technology & applied science research vol. 12, no. 3, 2022, 8584-8591 8588 www.etasr.com alhamdany et al.: statistical modeling of time headway on urban roads: a case study in baghdad iv. method the easyfit v5.5 software examined the collected data to select an appropriate distribution model, as shown in figure 9. the distributions for each flow are shown in table v. the analysis was carried out by evaluating the goodness of fit in the k-s test. it used the maximum likelihood method for the estimation parameters of fit distributions [16]. the k-s test is commonly used to detect whether two datasets are significantly different or not by calculating the probability of similarity between the two distributions [17]. since the k-s tests are nonparametric and do not require prior assumptions based on distribution, they were applied to the observed data for distribution fitting. in this study, five distributions were used, where most of them were previously used for time headway modeling of highways and freeways: pearson 6 [18], inverse gaussian [19], generalized pareto [20], dagum [21], and generalized gamma. table v. equations and parameters for distributions distribution equation parameters pearson 6 ���� �������������,����� �����!�� α1, shape parameter >0 α2, shape parameter >0 β, scale parameter >0 inverse gaussian ���� " #$%�&'(�) exp-− #�&'/'0��$0��&'(� 1 λ, continuous parameter >0 µ, continuous parameter >0 γ, continuous location parameter >0 generalized pareto ���� 23 4 35�6�1 + 9�� − :� '�'�; < ,9 ≠ 01 <exp?− �� − :� < @ ,9 0 k, shape parameter >0 σ, scale parameter >0 µ, location parameter dagum ���� �a�����;����� ������;!� k, shape parameter >0 a, shape parameter>0 β, scale parameter >0 generalized gamma ���� a�&'/�;����;�b��� ×exp �−��� −d�/f�a� k, shape parameter >0 α, shape parameter >0 γ, location parameter the following process was used to determine the appropriate time headway distribution model per lane: • the goodness of fit of the distribution of total headways collected from the lane was examined per lane. • the goodness of fit of the distribution of the headways occurring for every flow scope (veh/h/ln) was evaluated for each lane. the flow scopes are presented in tables ιι and ιιι. • the acceptable models were identified for each lane using the above two steps. • a standardized model was selected using the theil's slope estimator method for the flow ranges for each lane. the parameters of time headway distribution models were estimated based on the previous steps. v. results the appropriate distribution for the time headway modeling was determined by the k-s test for each flow scope, and the results are shown in tables vi and vii. the goodness of fit of the models was tested with a 5% level of significance. the hypotheses for each test were: the compatibility of the headway distribution with the fitted model is rejected (h=1) or not (h=0). the model parameters were estimated through the headway data for each test, as shown in tables viii and ix. each flow rate's parameter estimation was performed using the conventional maximum likelihood estimate (mle). the mle method was used because it is an unbiased estimator [22]. the results showed that the flow scope in the left lane of site 1 followed pearson type 6 distribution, where the p-value of flow rates 937, 1291, 1366, 1493, and 2015v/h/ln was greater than 0.05. however, the flow rates of 1679 and 1812veh/h/ln were less than 0.05, but greater than 0.02. the middle lane results demonstrated that the flow scope followed the inverse gaussian distribution. the results of the right lane showed that the flow scope followed the generalized pareto distribution. the left lane in site two followed the dagum distribution with a p-value greater than 0.05, except for the flow rate of 985veh/h/ln with a p-value less than 0.05 but greater than 0.02. the middle and right lanes showed that the flow scope followed the generalized gamma distribution. the p-value, rank, decision to reject or accept the distribution for each flow, and rank value to determine if the distribution is most compatible with the data were calculated. these results were used to determine the appropriate distribution for each flow rate. the estimation of parameters for each lane was performed using the theil slope estimator method in matlab. the parameters of the simple linear regression model were determined using the estimated parameters for each flow rate. a t-test was performed to compare the regression coefficients with the null hypothesis, as shown in tables x and xi. theil's slope estimator method was used for the parameters of the linear regression model because it is simple to perform in the case of small sample sizes [23]. subsequently, the mean flow rate (f) function, the f0g denoting the constant and f1g denoting the slope in the model were calculated. table vi. k-s test distribution of headway for site 1 lane 1 lane 2 lane 3 pearson 6 distribution inverse gaussian distribution generalized pareto distribution flow rate p-value rank reject flow rate p-value rank reject flow rate p-value rank reject 937 0.32 11 no 903 0.67 4 no 311 0.86 2 no 1291 0.104 3 no 1029 0.86 3 no 418 0.93 3 no 1366 0.23 2 no 1142 0.303 4 no 423 0.99 1 no 1493 0.14 1 no 1278 0.52 3 no 475 0.91 2 no 1679 0.041 2 yes 1384 0.17 4 no 500 0.64 9 no 1812 0.048 7 yes 1445 0.2 2 no 581 0.83 2 no 2015 0.102 6 no 1575 0.5 6 no 684 0.8 7 no engineering, technology & applied science research vol. 12, no. 3, 2022, 8584-8591 8589 www.etasr.com alhamdany et al.: statistical modeling of time headway on urban roads: a case study in baghdad table vii. k-s test distribution of headway for site 2 lane 1 lane 2 lane 3 dagum distribution generalized gamma fistribution generalized gamma distribution flow rate p-value rank reject flow rate p-value rank reject flow rate p-value rank reject 985 0.042 13 yes 841 0.99 1 no 461 0.91 4 no 1286 0.086 6 no 932 0.58 4 no 515 0.51 2 no 1568 0.13 9 no 1090 0.93 2 no 593 0.97 5 no 1757 0.34 1 no 1131 0.67 2 no 612 0.77 7 no 1935 0.37 1 no 1271 0.74 4 no 735 0.87 1 no 2106 0.13 1 no 1393 0.37 6 no 843 0.96 3 no 2345 0.13 3 no 1490 0.28 10 no 950 0.25 5 no (note: no=not rejected , yes=rejected) table viii. estimated parameters for fitted distrubution models – site 1 no. lane 1 lane 2 lane 3 pearson 6 distribution inverse gaussian distribution generalized pareto distribution 1 α1=10.102, α2=2.0324, b=0.4249 λ=7.125, µ=4.251, γ= -0.262 k=0.041, σ=10.187, µ=0.936 2 α1=19.641, α2=2.0443, b=0.1622 λ=6.218, µ=3.793, γ= -0.296 k=-0.0187, σ=7.945, µ=0.8104 3 α1=12.681, α2=2.3164, b=0.2888 λ=6.256, µ=3.405, γ= -0.253 k=0.0311, σ=7.3578, µ=0.9213 4 α1=19.9, α2=2.4289, b=0.18102 λ=5.971, µ=3.053, γ= -0.236 k=0.0116, σ=6.655, µ=0.84031 5 α1=8.3206, α2=2.8309, b=0.4846 λ=5.885, µ=2.815, γ= -0.214 k=0.1318, σ=5.412, µ=0.9672 6 α1=10.021, α2=2.8365, b=0.3710 λ=4.079, µ=2.517, γ= -0.043 k=0.02808, σ=5.409, µ=0.6263 7 α1=17.498, α2=3.2427, b=0.2309 λ=4.682, µ=2.369, γ= -0.082 k=0.0722, σ=4.3503, µ=0.5739 table ix. estimated parameters for fitted distribution models – site 2 no. lane 1 lane 2 lane 3 dagum distribution generalized gamma distribution generalized gamma distribution 1 κ=4.3043, α=1.468, β=0.688 k=0.5002, α=5.256, β=0.1224, γ=0.2544 k=0.743, α=1.651, β=1.659, γ=0.212 2 κ=2.0897, α=1.731, β=1.062 k=0.662, α=2.951, β=0.607, γ=0.368 k=0.881, α=1.335, β=1.715, γ=0.285 3 κ=2.536, α=1.810, β=0.831 k=0.784, α=2.007, β=1.115, γ=0.3748 k=0.899, α=1.429, β=1.804, γ=0.293 4 κ=2.045, α=2.161, β=0.994 k=0.681, α=2.922, β=0.560, γ=0.179 k=0.601, α=0.934, β=1.393, γ=0.135 5 κ=1.4229, α=2.5797, β=1.2363 k=0.441, α=6.710, β=0.0278, γ=0.2823 k=0.98068, α=1.27683, β=1.7327, γ=0.36667 6 κ=1.660, α=2.685, β=1.08 k=0.48265, α=5.679, β=0.05310, γ=0.216 k=0.956, α=1.709, β=1.713, γ=0.3323 7 κ=1.036, α=2.403, β=1.158 k=0.425, α=9.150, β=0.0103, γ=0.173 k=1.029, α=1.7431, β=1.824, γ=0.464 each estimated parameter corresponded to a mean flow rate (f). then, the parameters could be calculated as functions of the mean flow rate in each lane. for the first site (mohammed al-qassim highway): • the parameters of the pearson type 6 distribution model for the left lane (lane 1) were: �� −3.461+ 0.012×m (2) �$ 1.283+ 0.001 ×m (3) f 0.805−0.0004∗ m (4) • the parameters of the inverse gaussian distribution model for the middle lane (lane 2) were: q 9.212 −0.003∗m (5) : 7.289− 0.003 ∗m (6) t −0.347 +0.0001∗m (7) • the parameters of the generalized pareto distribution model for the right lane (lane 3) were: 9 0.085−0.00013∗ m (8) < 17.146−0.022085∗ m (9) : 1.0483− 0.00036∗m (10) for the second site (qanat al-jaish highway): • the parameters of the dagum distribution model for the left lane (lane 1) were: 9 6.8958−0.00276∗ m (11) u 0.594+0.00088∗ m (12) f 0.406−0.0003∗ m (13) • the parameters of the generalized gamma distribution model for the middle lane (lane 2) were: 9 −0.106+0.0007∗ m (13) u 11.155 −0.007∗ m (14) f −2.109+0.0023∗m (15) t = 0.37 − 0.0001 ∗ m (16) • the parameters of the generalized gamma distribution model for the right lane (lane 3) were: 9 0.5924+0.0005∗ m (17) u 0.9451+0.0008∗ m (18) f 1.2574+0.0009∗ m (19) t 0.1333+ 0.00028∗m (20) given the parameters of each model, the headway distributions can be obtained for different flow rates in each lane. at peak traffic flow hours, the maximum observed flow rate at which vehicles can reasonably pass site one was 2015veh/h/ln in the left lane. this demonstrates that the lane's engineering, technology & applied science research vol. 12, no. 3, 2022, 8584-8591 8590 www.etasr.com alhamdany et al.: statistical modeling of time headway on urban roads: a case study in baghdad true capacity is approximately this amount. in the middle and right lanes, the corresponding values were about 1575 and 684veh/h/ln, respectively. for site two, the maximum observed flow rates were 2345, 1490, and 950veh/h/ln in the left, middle, and right lanes respectively. the distinct behavioral pattern of drivers in the left lane, as well as their tendency to tailgate at high speeds, resulted in a disparity in lane capacity and safety. the flow rates and statistical criteria such as mean, median, and standard deviation values were calculated based on the selected models to better evaluate the reasons for the different models chosen per lane, and they were compared with the observed data, as shown in table xii. table x. estimation of parameters using nonparametric regression for each lane site 1 position parameters vwg vxg t-test p-value r2 parameter estimation lane 1 α1 -3.461 0.012 4.455 0.01 0.972 14.4215 α2 1.283 0.001 9.2 0.001 0.953 2.4931 β 0.805 -0.0004 4.619 0.0095 0.655 0.2331 lane 2 λ 9.212 -0.00258 7.9616 0.002 0.941 5.9747 µ 7.2894 -0.003314 45.091 1.20e-05 0.978 3.1436 γ -0.347 0.0001 2.119 0.009 0.687 0.3471 lane 3 k 0.085 -0.00013 2.654 0.038 0.412 0.0176 σ 17.146 -0.022085 15.29 0.0003 0.971 6.4441 µ 1.0483 -0.000359 2.5336 0.0125 0.59 0.8739 as seen in table xii, the convergence of the results for the flow values for each lane amongst the model and the real indicates the model's strength. at the same flows, the mean value of headways in the left lane is less than the middle, which is less than the right. the median value of headways in the left lane is lower than the median value in the middle, which is less than the right. this indicates that the mean and median relationship is directly proportional to each lane. this also shows that the driver's behavior is different in each lane, even when the flows are the same in different lanes. table xi. εstimation of parameters using nonparametric regression for each lane site 2 position parameters vwg vxg t-test p-value r2 parameter estimation lane 1 k 6.8958 -0.00276 11.97 0.0006 0.911 2.1705 α 0.594 0.00088 12.342 0.0005 0.986 2.1129 β 0.406 0.0003 6.372 0.003 0.891 2.1129 lane 2 k -0.106 0.0007 4.169 0.012 0.59 0.709 α 11.155 -0.007 2.9 3.10e-02 0.377 2.991 β -2.109 0.0023 4.818 9.00e-03 0.412 0.6378 γ 0.37 -0.0001 2.637 0.038 0.776 0.241 lane 3 k 0.5924 0.0005 8.3357 0.0018 0.963 0.8859 α 0.9451 0.0008 5.1 0.0073 0.95 1.4091 β 1.2574 0.0009 5.0689 0.0074 0.919 1.7522 γ 0.1333 0.00028 6.1401 0.0043 0.937 0.2934 table xii. comparison of characteristics of headways for the same lane site no. lane no. flow rate (v/h/ln) mean (sec) median (sec) std. deviation (sec) real model real model real model real model 1 1 1432 1591 2.514 2.363 1.714 1.504 2.5 3.11 2 1210 1261 2.974 2.855 2.29 2.17 2.328 2.284 3 459 484 7.846 7.438 5.504 5.423 2.414 2.6 2 1 1587 1608 2.268 2.239 1.62 1.518 2.01 2.83 2 1122 1125 3.207 3.199 2.428 2.403 2.641 2.691 3 635 641 5.671 5.62 4.085 3.907 2.3786 2.593 vi. conclusion this study investigated the characteristics of the time headway modeling for each lane on two urban highways in baghdad. the field observations used video recordings and simulations of the two sites exhibited different statistical distributions of time headways for varying flow level ranges under mixed traffic conditions. five probability distributions were considered for investigating the time headways. furthermore, the fitted models were different for different lanes depending on the driver's behavior while selecting the lane and their movement within it. the results are summarized as follows: • 39 hours of traffic data were collected and the ratio of heavy vehicles ranged from 9% to 38% of total flow. • according to the field observations, the results indicate that mohamed al-qassim highway's minimum and maximum time headways were 0.166 and 59.85sec, respectively. the qanat al-jaish highway had a minimum time headway of 0.2sec and a maximum of 41.84sec. compared to other countries, such as the usa, it is very difficult to follow a vehicle safely with a time headway of fewer than 2sec [24]. in germany, the recommended minimum distance headway is half the speedometer, which means that a car traveling at 80km/h should maintain a distance of at least 40m. in sweden, the national road administration recommends time headway of 3sec in rural areas. police uses a critical time headway of 1sec as an orientation to impose fines [25]. this reflects the behavior of drivers on iraqi roads. this is a traffic violation that may lead to traffic accidents while these violations increase with traffic volume. • the comparison between automated vehicle counting and the manual method showed accuracy results of 96% for total flow and 88-97% for each lane. these results, along with the less time to extract the data, show the effectiveness of the automated method. • several statistical models were selected using easyfit, and the parameters for each flow rate were estimated using mle. the k-s test was used to examine the goodness of fit tests. the parameters for each model in a lane were estimated using theil's slope estimator method. by getting engineering, technology & applied science research vol. 12, no. 3, 2022, 8584-8591 8591 www.etasr.com alhamdany et al.: statistical modeling of time headway on urban roads: a case study in baghdad the parameters of each model, headway distributions for different flow rates per lane can be obtained. • in the case of the mohammed al-qassim highway, the left lane had a mean flow rate of 1432veh/h/ln for the observed data and 1591v/h/ln for the modeled data using pearson's type 6 distribution, showing a 6% error. the middle lane had a mean flow rate of 1210veh/h/ln for the observed data and 1261veh/h/ln for the modeled data using an inverse gaussian distribution, having a 4% error. the right lane had a mean flow rate of 459veh/h/ln for the observed data and 484veh/h/ln for the modeled data using a generalized pareto distribution with a 5% error. • in the case of the qanat al-jaish highway, the left lane had a mean flow rate of 1587veh/h/ln for the observed data and 1608vrh/h/ln for the modeled data using the dagum distribution, giving an error of 1.3 %. the middle lane had a mean flow rate of 1122veh/h/ln for the observed data and 1125veh/h/ln for the modeled data using a generalized gamma distribution, with an error of 0.3 %. the right 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[25] r. s. shirazinejad and s. dissanayake, "speed characteristics in relation to speed limit increase and its influence on driver’s speed selection behavior," sustainability, vol. 12, no. 4, jan. 2020, art. no. 1369, https://doi.org/10.3390/su12041369. microsoft word etasr_v11_n5_pp7695-7701 engineering, technology & applied science research vol. 11, no. 5, 2021, 7695-7701 7695 www.etasr.com zdiri et al.: optimal shedding against voltage collapse based on genetic algorithm optimal shedding against voltage collapse based on genetic algorithm mohamed ali zdiri cem laboratory engineering school of sfax sfax, tunisia mohamed-ali.zdiri@enis.tn ahmed s. alshammari department of electrical engineering university of hail hail, saudi arabia ahm.alshammari@uoh.edu.sa ahmed a. alzamil department of electrical engineering university of hail hail, saudi arabia aa.alzamil@uoh.edu.sa mohsen ben ammar cem laboratory engineering school of sfax sfax, tunisia mohsen.benammar@enis.tn hsan hadj abdallah cem laboratory engineering school of sfax sfax, tunisia hsan.hajabdallah@enis.tn abstract-the prevalent tendency in power transmission systems is to operate closer and closer to the energy limit, rendering system voltage instability a commonly widespread phenomenon. it is, therefore, necessary that certain remedial corrective controls need be undertaken whenever these systems tend towards failure. in this respect, load shedding stands as a major correction mechanism and such a failure can be prevented and nominal system voltage can be resumed. it is worth noting however that load shedding must be implemented very carefully to ensure the satisfaction of both the customer and the electricityproduction company. in this context, our focus of interest is laid on load and machine shedding against voltage collapse as an effective corrective method. it is important to note that such a problem turns out to be commonly defined as an optimization problem under constraints. using genetic algorithms as resolution methods, the application of the proposed methods was implemented on the 14-node ieee test network, while considering a number of different case studies. keywords-power transmission; load and machine shedding; voltage collapse; genetic algorithm; 14-node ieee test network i. introduction electric power plays a crucial role in almost every domain, particularly lighting, communication, and transportation. however, electricity production and transmission are not without serious hazards, likely to disrupt their normal operation and continuity. actually, numerous disturbances are known to take place worldwide every year, often resulting in noticeable blackouts. large-scale blackouts, though very rare to occur, could cause huge losses and severe damages to the society and the economy. in this respect, the electrical grid might well undergo or experience a severe voltage collapse phenomenon, bringing about serious consequences [1]. such a phenomenon often finds its origin in unexpected cascades of events, causing sudden voltage drops, usually leaving little time, often just a few minutes, for the necessary protective measures to be implemented. hence, the voltage stability margins are assigned even a greater effective role to meet market needs [2-5]. the inherent difficulties in analyzing the various voltage collapse associated problems result primarily from the more or less non-linear behavior of the electrical grid various components. in this regard, the incident cases reported to take place over the past few decades prove that most of the voltage collapse problems have been recorded to occur after a significant disturbance or sudden increase in the electrical grid load, wherein the latter turns out to be weakened and its reactive consumption increased. accordingly, the phenomenon is characterized with a gradual voltage decrease in one or more consuming regions, immediately accelerating within a few minutes. hence, the voltage degradation, at the load level, turns out to be so significant that it leads to service interruptions, culminating directly in increased reactive grid losses and voltage drops as major outcomes. failure in voltage regulation, at the group terminal level, engenders an acceleration of the voltage plane degradation, likely to culminate in cascade tripping, of groups and lines, as well as voltage collapse of the general electricity network. such faults could well affect the corresponding author: mohamed ali zdiri engineering, technology & applied science research vol. 11, no. 5, 2021, 7695-7701 7696 www.etasr.com zdiri et al.: optimal shedding against voltage collapse based on genetic algorithm power converters’ operation, bringing about a total shutdown of the entire electrical production chain [6-9]. the electricity companies usually charge the transmitted energy to the consumer per mwh, while aspiring for an optimization of the production cost. accordingly, each of the generators’ and plants’ performance and contribution must be determined in such a way as to ensure the effective minimization of power producing cost throughout the power system operation process. in effect, the evolution in electrical energy consumption has resulted in significant increases in power transportation and generating costs, hence the importance of an efficient strategy aiming at minimizing the electrical energy exploitation and generation costs. the environmental impact of such processes turns out to be increasingly important and seriously considered when developing the electricity power production and transmission procedures. to achieve these goals, several optimization methods and strategies have been applied [10-11]. the classic methods would serve to solve the single-objective optimization problem (production cost optimization) whereas the most efficient generator supplied grid would not be useful. these methods were designed to obtain voltages in the necessary boundary zones reliable enough to ensure that the grid would remain in an operating point, far from a voltage collapse level, with maintained stability. in [12], for instance, the authors proposed a method in which the determination of the load shedding localization relies heavily on the two buses’ phase angle sensitivity. more recently, however, several researchers have developed distinct load shedding methods, enabling to adjust the frequency and voltage within the required or demanded limits while reducing the amount of load shedding [13-18]. in the present paper, we opted for the genetic-algorithm methods which are suitable for treating a single-objective optimization problem. noteworthy, this field of interest is very dynamic and is still exhibiting continuous development. accordingly, the study’s major objective is focused on applying these optimization methods through implementing genetic algorithms for optimal load and machine shedding against voltage collapses. hence, to ensure the system’s continuity within the available permitted limits while maintaining minimum production cost, two distinct shedding modes are envisaged, namely load shedding and machine shedding. in this context, the choice of the appropriate shedding scheme rests exclusively on the computation of the limit’s required power. to this end, a test is administered on the load distribution program to set the limit’s value. the process implementation procedure was conducted via the ieee 14-node standard test network. ii. shedding against voltage collapse with regard to the permanent mode, the study of voltage collapse provides a solution to the magnitudes of an electrical grid in normal balanced operation. in this respect, the relevant quantities involve the voltages, the node injected powers as well as the line flowing power, and the relevant currents and losses are deduced therefrom. voltage drops accompany the power transfer between the consumption and the production points, under normal operating conditions. these drops are usually of a small percentage of the normal voltage. actually, voltage collapse is most often due to increased load, lack of reactive power and/or short circuit. in effect, the process of shedding against voltage collapse depends on the knowledge of the required power limit value. at this level, an electrical grid is considered to be stable, from a voltage point of view, once each node’s respective voltages are set within the allowable limit. in the load-distribution scheme, the power required is gradually increased until exceeding the admissible voltage limits. in this case, the associated power value is dubbed as the demanded limit power. it is in terms of the pd value (the demanded power) that the fit shedding type can be actually defined. accordingly, for a pd greater than the demanded limit power (pdlim), the load shedding process is carried out, and, inversely, however, machine shedding is affected. figure 1 illustrates the way the appropriate shedding type can be selected against voltage collapse. fig. 1. shedding type. iii. formulation of the genetic algorithm based optimal shedding problem the loads' and generators’ optimal shedding with static constraints takes into account the nodes’ voltage limits, the lines’ powers transmitted, and the generators’ outputs. in our problem formulation, two objective functions persist, one related to the loads, while the other deals with machines. a. loads and machines’ shedding objective functions the objective function, relevant to the load nodes to be minimized is: ���� � ∑ ��� � � � � (1) where �� denotes the load shedding cost at node i, �� stands for the load-shedding factor at node i, and nl designates the number of consuming nodes. the loads' associated cost is fixed ahead in accordance with the nodes’ importance. engineering, technology & applied science research vol. 11, no. 5, 2021, 7695-7701 7697 www.etasr.com zdiri et al.: optimal shedding against voltage collapse based on genetic algorithm as for the generator node related objective cost function, it is formulated in the form of a generated power function, as illustrated through the following equation: ���� � ∑ �� �� �� � � �� � � �� �� (2) where �� designates the number of generators, �� stands for the generated power, and � , � and � are the generated powers' relevant coefficients. this problem type involves special control variables to be defined subsequently. control variables designate the problemassociated input variables, likely to be adjusted to optimize the loads' and machines’ objective functions as well as the constraints’ adjustment. these variables are of the form: � � �� , � � ! � ", where � represents the voltage at node i, � denotes the active power at node i, and � designates the shedding factor at node i. b. constraints 1) equality constraints for loads: �# $ �1 $ � � �& $ ∑ |( |)(*)�+ * *� cos/0 $ 0*1 � 2 * sin/0 $ 0*1� � 0 (3) with i = 1, ..., n is the number of loaded nodes, n denotes the set of nodes connected to i, �6 designates the load active power at node's i level, + * represents the real part of the element in the nodal admittance matrix (ybus) by corresponding row i and column j, 2 * is the imaginary part of the element in the nodal admittance matrix by corresponding row i and column j, and 0 stands for the ( voltage. for generators: �# �1 $ � � $ �& $ ∑ |( |)(*)�+ * *� cos/0 $ 0*1 � 2 * sin/0 $ 0*1� � 0 (4) where i = 1, ..., n designates the number of machine nodes, and n denotes the i connected nodes set. 2) inequalities constraints these constraints reflect the limits set on the power system physical devices, along with the limits created to ensure the system’s security. indeed, for the sake of maintaining the electrical system’s safety, transmission lines bear certain limits regarding the generated power, owing to thermal losses occurring at the conductor level, such as: �� 7 8 �� 8 �� 79: (5) where �� 7 and �� 79: designate the minimum and maximum generated power and �� denotes the power generated at the node i. additionally, the voltage level must be maintained within the allowable range to ensure the grid’s smooth running smoothly, while preserving customer satisfaction. any voltage drops would engender severe disturbances with respect to any load type, specifically: � 7 8 � 8 � 79: (6) where � 7 designates a minimum voltage equal to 0.9pu, � 79: denotes a maximum voltage of the range of 1.1pu, and � represents the node i corresponding voltage. as the load and generator shedding factors are limited to specific minimum and maximum values, the entirety of the � relevant values must be set between � 7 and � 79: ([0, 1]), such as: � 7 8 � 8 � 79: (7) where � stands for the shedding factor at the level of node i. c. the genetic algorithm genetic algorithms are optimization algorithms with natural evolution drawn techniques: crossing, mutation, selection etc.. they help provide solutions to unresolved problems likely to be computed in an algorithmic finite-time manner [19]. figure 2 depicts the genetic algorithm's structure, while the flowchart in figure 3 highlights our suggested problem-solving algorithm sample. �� and �� stand for the machine and load associated shedding factors respectively. fig. 2. genetic algorithm structure. the algorithmic steps shown in figure 3 are: population initialization if pd > pdlim calculation of the pc and qc load active and reactive power, respectively. solving these load values distribution problem: if the voltage is within its limit, we return to step 1, otherwise: formulate the optimization problem and determine the control parameters’ limits solve the optimization problem using the genetic algorithm. engineering, technology & applied science research vol. 11, no. 5, 2021, 7695-7701 7698 www.etasr.com zdiri et al.: optimal shedding against voltage collapse based on genetic algorithm the best ultimately withdrawn individual represents the load’s optimal shedding factor result. carry out the load shedding process. display the results. if pd < pdlim same work with the generators’ constraints and objective function. end. fig. 3. optimal load and machine shedding algorithm flowchart. iv. application and simulation results a. application on the 14-node ieee test network for the implementation purposes of our scheme, we considered the 14-node ieee test network, involving 5 generators, 9 loads and 20 lines, shown in figure 4. fig. 4. structure of the 14-node ieee test network. line data, production limits, specific coefficient of each generator, voltage limits relevant data, load shedding cost functions associated coefficients, and the node data are illustrated in tables i-iv. it is important to note that all the nodes limits’ shedding factors are set between 0 and 1. b. simulation results matlab was utilized to solve the voltage collapse problem. the pd used is equal to 8pu, which exceeded the limit demanded power pdlim=5.4pu. accordingly, the shedding type is loads shedding. table v highlights the applied genetic algorithm associated parameters. the relevant convergence profile is illustrated in figure 5. accordingly, one could well note that the genetic algorithm appears to converge starting from generation number 55, which corresponds to the most optimal solution. table i. node relev ant data line number liaison impedance (pu) line number liaison impedance (pu) 1 1-2 0.01335+j0.04211 11 10-2 0.05695+j0.17388 2 1-3 j0.20912 12 10-11 0.04699+j 0.19797 3 1-4 j0.55618 13 11-1 0.06701+j0.17103 4 3-4 j0.11001 14 12-6 0.09498+j0.1989 5 10-1 0.05811+j0.17632 15 12-7 0.12291+j0.25581 6 4-5 0.03181+j0.0845 16 12-8 0.06615+j0.13027 7 4-9 0.12711+j0.27038 17 12-2 j0.25202 8 5-6 0.08205+j0.19207 18 13-3 j0.17615 9 7-8 0.22092+j0.19988 19 14-10 0.01938+j 0.05917 10 8-9 0.17093+j0.34802 20 14-2 0.05403 +j0.22304 table ii. production limits and proper cost coefficient relevant to each generator node n° pgmin pgmax a($/h) b($/m.w.h) c($/m.(w 2 ).h) 10 0.1 0.7 1469 40 0.13 11 0.1 1.2 450 46 0.11 12 0.15 1 1050 40 0.028 13 0.2 1.4 1245 40 0.0354 14 0.1 2.5 1660 36 0.0211 engineering, technology & applied science research vol. 11, no. 5, 2021, 7695-7701 7699 www.etasr.com zdiri et al.: optimal shedding against voltage collapse based on genetic algorithm table iii. data relating to voltage limits and coefficients o f load shedd ing cost fun ctions node n° 1 2 3 4 5 6 7 8 9 10 11 12 13 14 vmin (pu) 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 vmax (pu) 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 cost (ct) ($) 100 400 200 550 900 250 450 500 50 * * * * * * see table ii. table iv. lin e relev ant d ata node n° type active power generated (pu) active power consumed (pu) reactive power consumed (pu) voltage (pu) 1 p-q 0 1.2 55 0 0.1 02 4 2 p-q 0 0.1 99 5 0.0 42 0 3 p-q 0 0 0 4 p-q 0 0.7 74 5 0.4 35 8 5 p-q 0 0.3 91 2 0.1 31 3 6 p-q 0 0.3 54 4 0.1 52 3 7 p-q 0 0.0 91 9 0.0 47 3 8 p-q 0 0.2 36 3 0.1 52 3 9 p-q 0 0.1 60 2 0.0 42 0 10 p-v 1.050 2 0 0 1.0 45 0 11 p-v 1.050 2 0.2 94 1 0.1 96 9 1.0 10 0 12 p-v 1.575 3 2.4 73 2 0.4 98 8 1.0 70 0 13 p-v 1.050 2 0 .569 7 0.3 34 0 1.0 90 0 14 balance 2.291 0 0 0 1.0 60 0 table v. genetic algorithm parameters population size 800 generation number 100 probability of mutation 0.05 crossover probability 0.9 fig. 5. the convergence curve of the genetic algorithm. the cost and load-shedding factor profile, relevant to each load node, is depicted in figure 6. we can see that the load shedding process proves to persist at the level of buses number 1, 3, 4, 6, and 9, displaying different importance degrees, specifically: • "low" with regard to nodes number 3 and 4, • "medium" with regard to node number 6, and, • "totally unloaded" regarding the nodes 1 and 9. it should be noted that any increase in the load-shedding factor turns out to be closely associated with a load-cost reduction. fig. 6. the cost and load-shedding factor profiles of consumer nodes. the pre and post load shedding power profiles of the aggregate node loads are highlighted in figure 7. it can be seen that each load respective power turns out to decrease: • slightly at the level of nodes 2, 5, 7 and 8 due to the very high cost, • totally at the level of nodes 1 and 9 due to the very low cost, and • around 40% and 60% at the nodes 4 and 6, as cost at the level of node 4 appears to be rather high as compared to the other nodes (1, 3, 6 and 9). the loaded nodes’ pre and post load shedding voltage profiles are illustrated in figure 8. it can be seen that there is an increase in the voltages of nodes 4, 5, 6, and 9, which is not within the allowable limit of stability before the load shedding. after load shedding, the voltages of the various engineering, technology & applied science research vol. 11, no. 5, 2021, 7695-7701 7700 www.etasr.com zdiri et al.: optimal shedding against voltage collapse based on genetic algorithm load nodes are within their allowable limits, something that maintains the stability and continuity of the electrical network. fig. 7. the consumer nodes’ pre and post load shedding power. fig. 8. the consumer nodes’ pre and post load shedding voltage. v. conclusion several known registered voltage collapse events indicate that most of the observed power grids operate closely to their stability limits. this issue turns out to be further compounded coupled with the electricity market liberalization. hence, for the sake of avoiding the electrical grid associated blackouts and for saving more energy, the implementation of an optimal shedding process on a 14-node ieee test network was undertaken in this paper. in this context, two shedding types have been considered, namely, load and machine shedding. for the shedding type determination, a test has been administered on the load distribution program to set the exact shedding types. in order to avoid the voltage collapse problem, an implementation of the genetic algorithm for the shedding of a 14-node ieee test network was realized. based on the obtained simulation results, we were able to highlight the advanced optimization approach's remarkable performance and achieved effectiveness in terms of avoiding the blackouts while minimizing the production cost. the valuable contribution of the present research lies not only in minimizing the production cost, but also in combatting overloading lines, for an effective balance between energy generation and consumption. in view of future development, the proposed work can be expanded to other electrical grids containing renewable energy sources. references [1] w. lu, "le délestage optimal pour la prévention des grandes pannes d’électricité," ph.d. dissertation, institut national polytechnique de grenoble, grenoble, france, 2009. 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[12] t. n. le, h. a. quyen, t. t. b. phan, n. a. nguyen, and t. p. trieu, "select location for load shedding in power system*," in 2018 4th international conference on green technology and sustainable development (gtsd), ho chi minh city, vietnam, nov. 2018, pp. 13–17, https://doi.org/10.1109/gtsd.2018.8595559. [13] y. tofis, s. timotheou, and e. kyriakides, "minimal load shedding using the swing equation," ieee transactions on power systems, vol. 32, no. 3, pp. 2466–2467, may 2017, https://doi.org/ 10.1109/tpwrs.2016.2614886. [14] j. wang et al., "strategy on interruptible load selection for precise load shedding system of source-grid-load friendly interaction system," in 2019 ieee 3rd conference on energy internet and energy system integration (ei2), changsha, china, nov. 2019, pp. 1765–1769, https://doi.org/10.1109/ei247390.2019.9062030. 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[19] f. a. alshammari, g. a. alshammari, t. guesmi, a. a. alzamil, b. m. alshammari, and a. s. alshammari, "local search-based nondominated sorting genetic algorithm for optimal design of multimachine power system stabilizers," engineering, technology & applied science research, vol. 11, no. 3, pp. 7283–7289, jun. 2021, https://doi.org/10.48084/etasr.4185. engineering, technology & applied science research vol. 7, no. 5, 2017, 1904-1908 1904 www.etasr.com alvarenga et al.: bim and lean construction: the evolution obstacle in the brazilian civil … bim and lean construction: the evolution obstacle in the brazilian civil construction industry thomas wünsch alvarenga civil engineering department fluminense federal university niterói, brazil twalvarenga@gmail.com edson neves da silva civil engineering department fluminense federal university niterói, brazil engproducao.edson@gmail.com luiz carlos brasil de brito mello civil engineering department fluminense federal university niterói, brazil luiz.brasil@gmail.com abstract—this article presents the teaching approach of different universities in the state of rio de janeiro regarding the dissemination of two civil construction learning paradigms: bim and lean construction. the article’s main purpose is to investigate the learning systems of the two techniques for the benefit of the construction industry, as well as to evaluate their level of recognition. the principal results show that civil engineers graduates acquire little or no knowledge of both techniques, which may become a barrier to their professional evolution and especially to their involvement with public works projects. keywords-bim; lean construction; universities i. introduction the brazilian construction industry is known as the least technological, compared to industries in other segments, and deficient in the management of its ventures. the perception of a high level of production within the sector in recent years is not characterized by a high level of productivity. although production and productivity are closely linked, a company, an economic sector, or a country, are said to be competitive if they produce efficiently, that is, they make the best use of available resources [1]. increased production cost can be the result of increased costs of hiring of employees, materials, and equipment. in order to organize this discussion about productivity, authors in [2] reported seven points of leverage relevant to such objectives: planning project execution, management methods adoption, equipment, materials, constructive methods, project improvements and workforce qualification. the study revealed the urgent need for increased productivity in construction in brazil. thus, companies need to adopt a comprehensive productivity-enhancing program with multiple coordinated initiatives. all relations addressed toward improving productivity point to the improvement of efficiency in the construction sector by means of using new technologies, new construction processes, specialized labor, materials, manpower and equipment coordination. in order to bring construction to a satisfactory level of efficiency and productivity, new paradigms in civil construction are presented, such as building information modeling (bim) and lean construction philosophy. these two approaches are shown as the grand proposal to improve efficiency in the construction industry. however, for this to happen, it is necessary to evaluate how much is known about these techniques, the recognition of their benefits, and what type of dissemination strategy is being used within a context such as universities, whose main objective is to train professionals working in the construction sector, such as civil engineers. the objective of this research is to investigate the extent to which universities in the state of rio de janeiro support the dissemination of bim and lean construction. ii. theoretical background a. bim (building information modeling) bim technology presents itself as a solution with great potential for the construction industry, since it enables the sharing of a digital model that is common to all those involved in its process, in a consistent way, and that can handle the whole life cycle of the construction project [3]. most recent works present many definitions to describe bim. the most recognized one, is bim as a product or intelligent digital representation of a set of structured data that define a building [4]. another one is bim as a collaborative process that represents a business structure for work and communication based on the use of open standards of information sharing, which improves quality and efficiency in projects [3]. one more definition presents bim as a facility management tool throughout the enterprise lifecycle, providing a reliable, verifiable, transparent and sustainable information base which teams use in the operation of the facility throughout its entire life cycle [5]. bim brings numerous benefits to the construction industry, such as significant productivity improvements, projects that are more efficient, faster production and details, improved support for automating and reducing errors due to internal coordination [6]. when adopted with full awareness of its potentialities, bim enables the integration of the design and construction process, resulting in better quality works, lower costs and shorter project execution time [7]. b. lean construction with the publication of [8] began the transfer and adaptations of concepts and principles from the toyota engineering, technology & applied science research vol. 7, no. 5, 2017, 1904-1908 1905 www.etasr.com alvarenga et al.: bim and lean construction: the evolution obstacle in the brazilian civil … production system into the construction industry [9-11]. the study challenges construction professionals to break their management paradigms and adapt techniques and tools successfully developed in the tps [12]. production is defined as a flow of materials and/or information from raw material to finished product [8]. lean construction emphasizes the importance of production process flow, based on three concepts.  the transformation of input into output, in which production management equalizes the total decomposition of transformation into elementary transformations by task, seeking minimum cost and maximum efficiency [14].  the activities of waiting, inspection and movement to the next stage, in which production management seeks to reduce this variability in the production flow [14].  the fulfillment of customer needs, in which production management seeks to translate customer needs into product or service [14]. lean construction is defined by a set of interconnected principles that should be applied in an integrated way in the management of processes to obtain the expected results [8]. these principles are basically: reduce the share of activities that do not add value, increase product value by considering costumer needs, reduce process variability, reduce cycle time, simplify by reducing the number of steps or parts, increase output flexibility, increase process transparency, focus control on overall process, introduce continuous process improvement, maintain balance between improvements in flows and conversions, and finally benchmarking [8]. the lean concept is one of the most successful philosophies for production systems such as construction, as it depicts, through its tools, ways of controlling waste and anticipating uncertainties [15]. c. universities and engineering education. universities' main function is to train professionals. national curricular guidelines for engineering programs include a generalist, humanistic, critical and reflexive education, capable of absorbing and developing new technologies, stimulating their critical and creative role in identifying and solving problems [16, 17]. with a complete higher education, the engineer is a professional who develops his/her activity in a technology area, whose responsibility is to produce technology and to operate the industrial processes generating goods for society, from the available scientific production systems [18]. however, constant updates and radical changes may be required in order for courses to follow the vast changes in the industry and economy [19]. four major challenges to engineering programs are presented by several authors:  the challenge to change teachers' and students' perception that the degree program is merely business training, denying the validity of basic subjects and humanistic conception for the academic training of the engineer [18, 19]  the challenge of adding flexibility to engineering programs, since their technological aspect has been advancing with increasing rate [19]  the challenge of the acquisition of an interdisciplinary technological curriculum, aimed at the integration of theoretical and empirical knowledge such as project courses that make use of established methods and technology whilst introducing groundbreaking tools (bim software, for instance) that will improve production, quality and cost. that is necessary in order to avoid performing activities without a systemic direction and teaching subjects without connection, with repeated and autonomous content.  the challenge of the determination of a pedagogical line for this curriculum, defined and assimilated by the entire community involved in a participatory, democratic and conscious process, with autonomy to define and approve parameters and regulations inherent to the curricular process. iii. research metodology this research is presented as exploratory, where the objective is to carry out a survey of relevant information on the topics addressed. the case study focused on assessing, through a questionnaire sent to public universities (state and federal), questions regarding the degree of knowledge, recognition and actions for the dissemination of concepts, techniques and tools of bim and lean construction. questionnaires were prepared, tested and sent individually to 6 universities in the state of rio de janeiro that offer bachelor degrees in civil engineering. the sampling plan was classified as non-probabilistic and the questionnaire was sent to the entire sample. the sample size was stablished by considering the universe (metropolitan area of rio de janeiro and adjacencies) thereby granting a population of approximately 560 professors of civil engineering and architecture. the obtained sample size was a total of 89 respondents. in the exploratory analysis of qualitative data, the usual measure is mode, and thus the results are represented by bar graphs or circular diagrams [11]. iv. case study a. general aspects the research focuses on public universities (state and federal) located in the metropolitan area of rio de janeiro and adjacencies that had civil engineer and architecture courses. there are 6 institutions inside the considered area and they were all included in the research. the capital of the state of rio de janeiro has significant importance within the national and international level. it is the second largest metropolis in brazil, and one of the main economic, cultural and financial centers, and representing the country's second largest gross domestic product contributor (gdp). the study was conducted between april and november 2016, and return rates were 83.3% for the bim survey and 66.0% for the lean construction survey in a sample field of 6 educational institutions. for reasons of confidentiality, interviewees and institution names will not be disclosed. items addressed in the first stage of surveying interviewee and institutional profiles are summarized below: engineering, technology & applied science research vol. 7, no. 5, 2017, 1904-1908 1906 www.etasr.com alvarenga et al.: bim and lean construction: the evolution obstacle in the brazilian civil …  respondent posts: 100% undergraduate course professors in civil engineering.  time in position: 100% above 5 years.  educational degree: 100% phds. b. results obtained through the lean construction research. results are shown in figures 1-5 and further discussion follows. figure 1 shows how the statement by the universities was divided on the issue of whether content about the lean construction philosophy is actually taught. the chart shows unanimity in the outcome of the issue, as all 4 universities agree that lean construction is taught at the universities of rio de janeiro state. this question did not seek however to measure how much of this content is taught, which is seen in figure 2. the result demonstrates that such content involving concepts, techniques and tools is taught at low to very low, within the civil engineering program. figure 3 demonstrates the assessment as to the proof of the effectiveness level of lean techniques and tools for the benefit of civil construction. respondent insights indicate them to range from mid to high. the result shows an understanding by portions of the respondents, ranging from high to very high, of the philosophy's relevance to current and future civil engineers in the construction industry context. fig. 1. result obtained on declaration of teaching lean construction at the universities fig. 2. result obtained on the level of teaching of lean construction at the universities figure 5 demonstrates the results about what types of disciplines the lean construction philosophy content would fit better, in the opinion of academics. the result shows that there is a division among respondents about the kind of program where lean content could be presented. among their responses, 50% indicated it as an optional course subject in the civil engineering program, and the other 50% as an optional course subject in all engineering programs. there was no indication for lean construction concepts in compulsory courses. this question was aimed at analyzing, in another way, the level of importance of the lean construction philosophy for the academics. figure 4 demonstrates the importance of lean construction for the current and future civil engineer as perceived by the university. an evaluation of the importance of disseminating the concepts of the philosophy to professionals was sought. fig. 3. result obtained on the proof of efficacy level of lean construction philosophy at the universities fig. 4. result obtained on the importance of lean construction for the engineering profession fig. 5. result obtained on identifying the type of material for lean construction at the universities c. results obtained through the bim (building information modeling)rresearch. figure 6 shows how the statement of the universities was divided on the issue of whether content about the bim philosophy is taught at the universities. the graph shows unanimity in the question's result. all 5 respondent universities stated that bim is taught at the universities in rio de janeiro. this question did not seek to measure how much of this content is taught, which can be seen in figure 7 which shows that bimrelated content involving concepts, principles, techniques and engineering, technology & applied science research vol. 7, no. 5, 2017, 1904-1908 1907 www.etasr.com alvarenga et al.: bim and lean construction: the evolution obstacle in the brazilian civil … tools are taught at very low levels. figure 8 demonstrates the perception by the university of the importance of bim. the aim was to evaluate the perceived importance of disseminating concepts of the philosophy among professionals. the graph shows that most participants declare that it is very important to disseminate bim concepts, techniques and tools to civil engineering professionals. figure 9 illustrates the percentage distribution of benefits associated with the implementation of bim from the respondent’s perspective. integrated collaboration of all involved parties in the project is perceived as the main benefit that bim can promote for civil construction projects, with a 69% indication, followed by the possibility of use throughout the life cycle of a project, with a 14% indication. in a manner similar to that for the benefits of bim, respondents were asked to point out the following barriers to the dissemination of bim. figure 10 illustrates the percentage distribution associated with the main constraints associated with bim implementation from the respondent’s perspective. according to the respondents, the lack of technical knowledge on the part of the teachers represents the greatest obstacle in the implementation of bim at the universities, followed by the impossibility of teaching bim content in the current curriculum. fig. 6. result obtained from the declaration on teaching bim at the universities fig. 7. results obtained on bim teaching level at the universities fig. 8. result obtained on the importance of bim for the civil engineering professional. fig. 9. percentage representation associated with the main benefits coming from bim implementation as perceived by respondents. fig. 10. percentage representation associated with the main obstacles for bim implementation, as perceived by respondents. v. conclusions building information modeling and lean construction are two rather promising approaches aiming to improve efficiency in the construction industry. thus, incorporating their teaching in civil engineering courses is rather important for both industry and academia. the present paper focuses at universities located rio de janeiro and their aspects on these two techniques. results show that although both aspects are known and their value is recognized, the level of the content taught is evaluated as low to very low. this is attributed to the relatively low technical knowledge of the teaching staff and to the high investment costs required. references [1] camara brasileira da industria da construcao, produtividade da construcao civil, brasília, fgv projetos, 2012 [2] ernst & young, estudo sobre a produtividade na construcao civil – objetivos e tendencias no brasil, sao paulo, 2014 [3] c. eastman, p. teicholz, r. sacks, k. liston, bim handbook – a guide to building information modeling for owners, managers, designers, engineers and contractors, 2nd edition, bookman, 2014 [4] general services administration (gsa) gsa bim guide series 01 – bim guide overview, 2007. engineering, technology & applied science research vol. 7, no. 5, 2017, 1904-1908 1908 www.etasr.com alvarenga et al.: bim and lean construction: the evolution obstacle in the brazilian civil … [5] national institute of building sciences, united states national building information modeling standard, version 1 part 1: overview, principles, and methodologies, 2007. [6] c. eastman, g. lee, r. sacks, “development of a knowledge-rich cad system for the north american precast concrete industry”, proceedings of the 2003 annual conference of the association for computer aided design in architecture, indianapolis, 2003 [7] r. sacks, b. dave, l. koskela, r. owen, “analysis framework for the interaction between lean construction and building information modeling”, 17th international group for lean construction conference, 2009 [8] l. koskela, application of the new production philosophy to construction. center for intergrated facility engineering technical report #72, stanford university, palo alto, california, 1992 [9] v. d. s. d. azevedo, planejamento de atividades da construcao predial visando a reducao de perdas de processo na otica da construcao enxuta, programa de pos-graduacao em engenharia civil area de concentracao, estruturas, dissertation, universidade do estado do rio de janeiro, 2010 [10] i. r. bulhoes, diretrizes para implementacao de fluxo continuo na construcao civil: uma abordagem baseada na mentalidade enxuta, phd thesis, universidade estadual de campinas, campinas, 2009 [11] p. a. c. miguel, l. l. ho, metodologia de pesquisa em engenharia de producao e gestao de operacoes, 2nd edition, rio de janeiro, 2012 [12] c. t. formoso, “lean construction: principios basicos e exemplos, in: construcao mercado: custos, suprimentos, planejamento e controle de obras”, porto alegre, vol. 15, p. 5058, 2002 [13] l. s. carvalho, adocao dos princípios lean pelo setor da construcao civil, msc thesis, federal university of rio de janeiro, 2013 [14] l. koskela, an exploration towards a production theory and its application to construction, phd thesis, helsinki university of technology, finland, 2000 [15] j. m. f. pinto, “lean construnction proposta de metodologia de avaliacao de projetos de construcao”, msc thesis, university of porto, 2012 [16] e. padilha, “o papel das entidades de classe na nova visao do sistema confea/crea”, 8th national congress of professionals, brasilia, 2013 [17] brasilian ministry of the environment, sustainable construction, 2012, available at: http://www.ambiente.gov.br/cidades-sustentaveis/urbani smo-sustentavel/itemlist/category/66-urbanismo-sustentavel [18] j. b. laudares, a formacao do engenheiro em duas instituicoes mineiras: o centro de educacao tecnologica de minas gerais e o instituto politecnico da pontifícia universidade catolica de minas gerais, centro federal de educao tecnologica de minas gerais, 1992 [19] j. p. batista, um estudo comparativo dos cursos de engenharia civil e engenharia de producao civil em oferta em belo, msc thesis, 2003 engineering, technology & applied science research vol. 7, no. 6, 2017, 2296-2302 2296 www.etasr.com mir et al.: aspect βased classification model for social reviews aspect βased classification model for social reviews jibran mir computer science dept shaheed zulfikar ali bhutto institute of science and technology islamabad, pakistan jibmir@gmail.com azhar mahmood computer science dept shaheed zulfikar ali bhutto institute of science and technology islamabad, pakistan azharmahmood8@hotmail.com shaheen khatoon college of computer science and information technology king faisal university al ahsa, saudi arabia sha.xin@live.com abstract—aspect based opinion mining investigates deeply, the emotions related to one’s aspects. aspects and opinion word identification is the core task of aspect based opinion mining. in previous studies aspect based opinion mining have been applied on service or product domain. moreover, product reviews are short and simple whereas, social reviews are long and complex. however, this study introduces an efficient model for social reviews which classifies aspects and opinion words related to social domain. the main contributions of this paper are auto tagging and data training phase, feature set definition and dictionary usage. proposed model results are compared with cr model and naïve bayes classifier on same dataset having accuracy 98.17% and precision 96.01%, while recall and f1 are 96.00% and 96.01% respectively. the experimental results show that the proposed model performs better than the cr model and naïve bayes classifier. keywords-pos; chunking; word case; feature set; dictionary; ner; iob tagging i. introduction opinions are the key elements that influence a person’s decision making capability. it is natural for people to consult with friends or family whenever they make a decision, and so, to have access to diverse opinions. similarly, to gain better business insight, organizations conduct surveys, opinion polls and focus groups discussions to better understand their customer opinions about a product or service. in the same way, an individual customer, before buying a product tries to find his family’s or friend’s opinion about it [1]. hence, for marketing, public relations, and political campaign, gathering public and customer opinions has become a profitable business. recently it has been made possible for everyone to have internet access and therefore express his/her opinion about something in a matter of one click on social networks or other sites [2]. as a result, one can find huge amounts of user experience about usage of a product and/or service online. now, instead of consulting friends or family, people prefer to read reviews online in order to make a purchase decision about a product or service. consequently, companies can utilize these reviews to understand their customer response about the product usage instead of conducting traditional surveys to collect customer feedback. however, due to the huge amount of user generated contents it is almost impossible for companies to go through each review and respond accordingly. therefore, there is a need to extract useful information from this huge amount of data. given the size and growth rate of this kind of data, this could only be possible by using an automated system. the opinions expressed in social networking sites or product review sites have already assisted in reshaping the political and businesses structure. it was social networking sites like facebook that had changed the political thinking of arab people in 2011 [1]. consequently, sentiment analysis is a new trend in information science. the sentiment analysis is a process of classifying and identifying the opinions related to a topic. in addition to this, sentiment analysis is conducted at three main levels such as: document level, sentence level and aspect based level [3].the document level determines the overall sentiment of product as a whole, whereas, sentence level sentiment analysis evaluates whether each sentence expressed positive, negative or neutral opinion. in contrast to this, aspect level sentiment analysis investigates opinions on bases of some specific aspect. for instance: “the price of the canon is very reasonable.” here “canon” is a product, “price” is an aspect and “very reasonable” is a sentiment word. therefore, aspect based opinion mining investigates opinions about specific features of a product or service. however, identifying features from a sentence is another challenge. therefore, this research work will focus on aspect based opinion mining. there are different types of aspect based opinion mining such as regular and comparative, explicit and implicit, and multi-aspect sentiment analysis. each type comes with huge challenges due to natural language processing issues. analysis of human text is so complex, that none of the aspect based opinion mining techniques can accommodate all the types mentioned above. that is the reason why aspect based opinion mining researchers worked in different directions. some work on domain adaptability and some work only on sentiment analysis, however, most of them work on aspect identifications. there are some challenges in aspect based opinion mining: the first challenge is the identification of implicit feature. implicit features are those that are not used in a sentence engineering, technology & applied science research vol. 7, no. 6, 2017, 2296-2302 2297 www.etasr.com mir et al.: aspect βased classification model for social reviews directly instead they are implied in a sentence. for instance: “this mobile is too expensive” so here author refers expensive to the aspect “price”. the second challenge is multi-aspect sentence detection, where a sentence holds one explicit and one implicit aspects or both explicit or both implicit. for instance: “this phone’s battery life is great but it is too expensive”, this sentence is a multi-aspect sentence which contains one explicit and one implicit aspect. the third challenge is the detection of a comparative sentence, the example of this sentence is, “the canon camera is better than the nikon camera”. another challenge is domain and language adaptability. if an aspect based opinion mining is designed for chinese language it should be equally applicable to other languages. similarly, if an aspect based opinion mining algorithm is designed for product domain it should be easily applicable to other domains such as hotel accommodation. since, aspect based opinion mining has been applied in business domain, therefore, this study initiated an aspect based opinion mining model that will classify aspects and features of social reviews. in addition to this, the proposed model is able to classify explicit aspects efficiently and can identify and classify aspects from complex social reviews. the rest of the paper is organized as follows: section ii presents the literature review of different aspect based opinion mining algorithms. section iii presents the proposed model design. section iv shows the experimental results and section v offers the conclusion. ii. literature review authors in [4] proposed a feature based opinion mining using ontologies. moreover, this research, introduced a vector based sentiment analysis method. domain of the dataset is very important, if we know the domain of dataset in advance that will be helpful to find the domain aspects and sentiment words. however, there is no vibrant way to find dataset domain before sentiment analysis. the main contributions of this research are divided in to four parts: nlp, ontology based aspect detection, polarity assignment and opinion mining. this research successfully addresses the semantic relation in aspect identification process. furthermore, they developed a mathematical solution for sentiment analysis. there is no discussion of implicit aspect identification method neither there is any method for multi-aspect sentence and comparative sentence detection. domain independent method has been developed for electronic products in [5]. the crucial focus of this study is to develop a system of electronic product domain independent and explicit/implicit aspect identification from online customer’s reviews. there are a few limitations to this research, there is no method defined that can handle multiaspect sentences. it is domain independent only for camera, mobile phone and dvd player. it is not language adaptable. it does not group to gather semantically related aspect terms [6] and utilizes supervised approach with a balanced dataset[7]. aspect identification and classification is a basic step in sentiment analysis, moreover, to make a domain adaptable, aspect method classification is important. therefore, authors in [8] introduced an approach which will classify aspects with respect to domain. the main purpose of this research is to develop a model that will establish an association between product feature and domains. this will assist to build a domain independent solution. there is no discussion of implicit feature identification. in addition to this, there is no mechanism defined to handle multi-aspect and comparative sentences nor it is language adaptable. the strengths of this model are: aspect identification and sentiment analysis. one weakness of this approach is that the polarity assignment is done by global lexicon, however the global lexicon is unable to define polarity of polysemous words [9]. today, in aspect based opinion mining, most of the researchers carried out their work in explicit and implicit aspect detection. authors in [10] introduced a semi supervised model for aspect identification. they have introduced two statistical methods such as “seeded aspect and sentiment model” and “maximum entropy sas model” in order to discover explicit/ implicit features. this model is not automatic as it requires users to provide some prior knowledge and user may be not aware of that domain knowledge [11]. general aspects can be found by this method, however, it is unable to find domain specific aspects [12]. according to authors in [13] in information retrieval, although facts such as finding the relevant information are based upon precision and recall play an important role, opinions also play a crucial role to know the sentiments about the searched item. therefore, they established a search engine that not only brings out facts about the searched items but also mines opinions about them. the limitations of this study are that there is no discussion about implicit feature identification, no discussion about multi-aspect sentence detection and that it is neither domain nor language adaptable. the weakness of this study is that by using the tftfid algorithm sentiment analysis cannot be evaluated properly [14]. as mentioned above there are many challenges in aspect based opinion mining, however, authors in [15] initiated a method for implicit aspect identification for reviews in chinese only. there is no discussion of multi-aspect sentence detection. it is not domain or language adaptable. this method is not tested on bigger corpora. it should be adaptable for different domains and languages [16]. aspect based opinion mining is widely used in business intelligence, where the interest is to discover the customer’s opinion about the product. authors in [17] described a model that finds the product’s weaknesses and its competitive features found online in chinese reviews. it is domain specific and single lingo supportive. authors manually discriminated positive and negative opinion words. the method proposed in this paper is not able to properly discover customer satisfaction [18]. so far, aspect based opinion mining has been used in product domain, however, authors in [19] transformed the aspect-based opinion mining technique presented in [20] to be applicable on tourism domain. most of the work has been conducted on physical items, however, for intangible services there is no opinion mining system. there is a difference in the reviews of physical items and service products, for instance hotels. the reviews of physical products are usually short and easy to handle whereas, service domain reviews are verbose and difficult to handle. this technique is domain specific and single lingo supportive. neither there is a discussion of implicit nor multi-aspect identification. there is no mechanism defined to handle comparative sentences. the model described in [19] is unable to identify confusing and ambiguous terms in tourism engineering, technology & applied science research vol. 7, no. 6, 2017, 2296-2302 2298 www.etasr.com mir et al.: aspect βased classification model for social reviews reviews [21]. moreover, hardly 35% of the explicit aspects are detected by this model [22]. aspect identification is an important step in aspect based opinion mining because it is a fundamental step in fine grain sentiment analysis. most of the researches have been conducted in explicit aspect identification. however, they ignored the detection of implicit aspect. therefore, authors in [23] focused on the identification of implicit aspect in chinese reviews by using hybrid association rule mining. there is no discussion of comparative sentences, the model is not language adaptable while some of the features are extracted manually. this model used the most occurring explicit features as implicit feature indicators, however, it ignored the features that occur less often, even if they are most important [24]. aspect based sentiment analysis is an emerging science and different scientists have adopted different ways to identify implicit and explicit aspects. this requires extensive prior knowledge of the dataset domain, however, some studies like [24] stated that this issue can be solved without prior knowledge, whereas previous studies require extensive prior knowledge. the main contribution is that they introduced an algorithm that discriminates the sentences that have implicit feature and the ones that don’t have. they defined a threshold for the value of an aspect. there is no discussion of multi-aspect sentence detection or of comparative sentences. it is neither language nor domain adaptable. the removal of miss-spelling and the reduction of similar implicit features have been done by manual clustering. a detailed comparison of model based methods and statistical based methods have been given in [25]. it must be noted that the research is biased towards model based methods. hence, they have implemented and tested crf model based technique. the research results are quite satisfying compared with other model based and statistical based methods. their main contribution was the classification of feature words, opinion words and intensifiers and the feature set definition. disadvantages of this research are that this model will not give fine results when applied to other domains, there is no detail discussion about implicit aspect identification and comparative sentences. the biggest disadvantage of this method is that the dataset training is very complicated and required a great need of care. iii. proposed model most of the previous studies developed different aspect based opinion mining models for product and service domain [1-8]. in this study, aspect based opinion mining model for social reviews is proposed. it consists of five main phases where information flow is top down similar to water fall approach as shown in figure 1. social reviews are more complex and it is difficult to extract aspects from them. that is the reason model structure is more complex and divided into five phases namely pre-processing, auto tagging, training and classifier, testing and dictionary phase. the selection of classifier is very important in any machine learning problem. this research used conditional random fields (crf) [26] which requires well-trained dataset and features set as input. the model’s performance is highly depended on these two inputs. the core reason for using this classifier is to solve the ner (name entity recognition) problem. crf is proven good in detecting ner in plain text [26]. since, the dataset is consisted of social movie reviews which contain names of movies, actors, directors and writers, therefore, crf is the right choice for this ner problem. a. pre-processing the dataset for movie social reviews have been crawled from social websites and each review has been saved in a separate text file. approximately, 2000 reviews have been crawled for 2000 different movies. these movie reviews are recent and written by different writers. the movie reviews are complex and detailed in contrast with the product reviews that are usually short and simple. for instance “this phone is light weight and cheaper in price”. it can be observed from this example that this is a simple and short sentence. the review is talking about aspects, such as “weight and price”, of a particular phone. in addition to this, “light” and “cheaper” are opinion words. however, the social review example is: “the mayan empire grew from about the year 400 to 900. at their height they became a people very advanced in science. mayan notation for numbers made arithmetic easier for mayan children than our numbers make it for our children. the dresden codex shows that they may not have understood exactly what eclipses were, but they knew when they were coming”. it can be observed that this is complex and detailed comparing to common product review. therefore, this requires a great deal of effort to find feature words and opinion words from social reviews. b. auto tagging and dataset training supervised machine learning methods are effective but they require a well-defined example dataset for training, moreover, preparing dataset for training is usually a manual and tedious task [26]. therefore, an automated process has been developed to prepare the dataset. it involves five subtasks such as tokenizing, pos tagging, chunking, word case and iob tagging (inside outside beginning). the nlp [27] tasks such as tokenizing, pos tagging and chunking are all performed by using opennlp software. in first step each review is tokenized into a list of tokens and saved into a text file for further processing. next each token part of speech (pos) tag is assigned something which is required for the next step to identify named entity. in next step pos tagged tokens are used to detect entity using chunking. in next step word case is assigned to each chunk. for instance: if the token starts with a capital letter then the word will be tagged as tc (title case), and if all the letters of the token word are capitals, then the word will be tagged with uc (upper case). the other will be tagged as lc (lower case). the reason for using the ‘word case tag’ is to identify the movies and person names, since it is observed that people used title case for person name and upper case for movie name. the last column of figure 2 presents the iob tagging. iob label is given based upon pos and word case information for given token. for instance, for the token “cornell” its corresponding pos is “nnp” and if its word case is “tc” therefore, iob tag shouldbe “b-pers”. twenty one (21) such patterns are derived as shown in table i. as a result of tagging each token is annotated with token name, pos tagger, chunk, word case and iob tagging. moreover, engineering, technology & applied science research vol. 7, no. 6, 2017, 2296-2302 2299 www.etasr.com mir et al.: aspect βased classification model for social reviews figure 2 is an excerpt of the trained file. the annotation of dataset with these five columns is the major contribution of this work. the same process will be repeated for test file. fig. 1. the proposed model of aspect identification and classification for social reviews fig. 2. example of iob tagging fig. 3. example of output file c. training classifier crf++ cli software [28] has been used to train and test the proposed model. this classifier takes two inputs, the template file and the trained file and outputs the model file for training purposes as shown in figure 1.trained file will be the output of previous phase, however, template file will be developed according to the trained file. template file contains a set of rules regarding the training of the classifier. in this way, classifier looks at trained file by following the feature set or set of rules defined in template file. table ii shows an excerpt of the template file. forty feature sets have been written in template file. the model file is a binary file and will be used for testing purposes. in order to perform testing crf++ software takes two inputs, the model file and the test file. after performing the testing, crf++ output would be a six column text file as shown in figure 3.therefore, the last column in figure 3 is labeled by crf classifier and the previous column is label by iob tagging subtask in phase ii. in this way these two columns can be compared in order to calculate accuracy. d. testing the output text file produced by training classifier phase, will be used for evaluation purposes. the output text file will be given to perl script and it will calculate precision, recall and f1 measures for movie name, person name, opinion words and engineering, technology & applied science research vol. 7, no. 6, 2017, 2296-2302 2300 www.etasr.com mir et al.: aspect βased classification model for social reviews feature words. to know the proposed model accuracy, performance evaluation is crucial. table i. a list of patterns discovered from dataset sr.no pattern entity name 1 if wc[0] = uc movie 2 if pos[0] = jj or pos[0] =nnp or pos[0] = nn and wc[0] = tc person 3 if pos[0] = pos and pos[-1] = nnp or pos [-2] = nnp and wc[0] = tc person 4 if pos[0] = jj or pos[0] = nnp or pos[0] = nn and wc[0]=tc and wd[-1] = by and ck[-2] = i-vb or ck[-1] = b-vb person 5 if pos[0] = jj or pos[0] = nnp or pos[0] = nn and wc[0]=tc and wd[-1] = by and pos[-2] = rb and ck[-3] = b-vp and ck[-3] = i-vp person 6 if pos[0] = jj or pos[0] = nnp or pos[0] = nn and wc[0]=tc and wd[-1] = by and pos[-2] = nn person 7 if pos[0] = jj or pos[0] = nnp or pos[0] = nn and wc[0]=tc and pos[-1] = jj or pos[-1] = nn and pos[-2] = dt person 8 if ck[0] = b-vp and not ch[3] = b-np and wc[0] = tc person 9 if pos[0] = nn and pos[-1] = nnp and wc[0] = tc person 10 if pos[0] = cc and pos[-1] = nnp and pos[-2] = nnp and wc[-1] = tc and wc[-2] = tc person 11 if pos[0] = cc and pos[+1] = nnp and pos[+2] = nnp and wc[+1] = tc and wc[+2] = tc person 12 if wd[0]= , and pos[+1] = nnp and pos[+2] = nnp and wc[+1] = tc and wc[+2] = tc person 13 if wd[0]= , and pos[-1] = nnp and pos[-2] = nnp and wc[1] = tc and wc[-2] = tc person 14 if wd[0] = , and pos[+1] = nnp and wc[+1] = tc person 15 if wd[0] = , and pos[-1] = nnp and wc[-1] = tc person 16 if ck[0] = b-np and wc[0] = lc or wd[-1] = . and pos[0] = dt and pos[+1] = nn and wc[+1] = lc feature word 17 if pos[+1] = jj and wc[+1] = lc feature word 18 if pos[0] = nn feature word 19 if pos[0] = dt and ck[0] = bnp and wc[0] = lc and pos[+1] = rbs and wc[+1] = lc opinion word 20 if ck[0] = b-ad and wc[0] = lc opinion word 21 if ck[0] = b-vp and wc[0] = lc opinion word table ii. a list of feature set definition sr.no feature set word token 1 u00:%x[-2,0] the 2 u01:%x[-1,0] movie 3 u02:%x[0,0] seems 4 u03:%x[1,0] amazing e. dictionary phase at this level, model will classify all the explicit aspects but it will not be able to discriminate a person as actor, actress, director or writer. the reason for this is the availability of the less information about a person’s gender and job title in the review text. for that reason a dictionary has been used to identify gender and job title. iv. experimental results the dataset consists of 2000 movie reviews crawled from internet movie database (imdb) official website imdb.com/reviews/index. moreover, the proposed model, cr model and naïve bayes have been implemented on the movie reviews dataset. this dataset has been annotated with iob tagging scheme. there are basically 9 different tags been used. b-movie i-movie, b-pers i-pers, b-opinion iopinion, b-feature i-feature and o. they stand for movie name, person name, opinion word and feature word. here “b-” stands for beginning of entity name, “i-” stands for continuity of the entity name and “o” shows it doesn’t belong to any entity name. an example of tagging scheme is the movie name “v for vendatta” which will be annotated like “v b-movie for i-movie vendatta i-movie”. for experimental purposes 119 movie reviews have been taken for training and 51 movie reviews have been taken for testing. therefore, the ratio is 70% and 30% for training and testing. at this stage, 170 review comments have been used for training and the overall accuracy is 97.48% of the proposed model. now, there is no need to train the classifier by using iob tagging subtask from phase ii, moreover, there is no need to further define any new feature set. the crf classifier accomplished this job on its own. in other words, the last column in figure 2 will be labeled by crf classifier and not by phase ii, this whole process is called self-tagging. manually, quality check has been done at every 100 self-tagging reviews. if the crf classifier self-tagged 100 reviews correctly and there is no error then these 100 reviews are added to the already trained dataset. in this way, 700 reviews have been trained and the rest of the 1300 reviews was kept for testing. the overall accuracy of 2000 reviews of the proposed model was 98.17%. tables iii v show the classified aspects for the proposed model, cr model and naive bayes. the proposed and cr model use the crf classifier for aspect classification. the results show that the proposed model outperforms the cr model and naive bayes classifier. the reason why cr model is not performing well on this social review dataset is because it was not designed for the social domain. it doesn’t provide a well-defined method for dataset training, no method is defined for the name entity recognition problem and finally there is no feature set definition in it. that is why, the feature word and engineering, technology & applied science research vol. 7, no. 6, 2017, 2296-2302 2301 www.etasr.com mir et al.: aspect βased classification model for social reviews opinion word precision, recall and f1 is pretty good, while movie name and person name precision and recall is not quite satisfactory. similarly, the results show that the naive bayes classifier is not efficient regarding ner problem. the incorrectly identified aspects are 6,491 only by the proposed model, whereas, the cr model incorrectly identified aspects are 37,388. finally, the naive bayes incorrectly classified aspects are 71,121 as shown figure 4. table vi depicts the overall precision, recall, f1 and accuracy for the proposed model, cr model and naive bayes classifier. the proposed model’s overall accuracy is 98.17% which is way better than the cr model and naïve bayes classifier. figure 5 shows the graphical representation of the overall accuracy. table iii. 2000 reviews results for proposed model aspects precision recall f1 feature word 96.12% 95.74% 95.93% movie name 96.15% 96.19% 96.17% opinion word 97.34% 97.53% 97.43% person name 91.08% 91.36% 91.22% table iv. 2000 reviews results for cr model aspects precision recall f1 feature word 82.72% 89.20% 85.84% movie name 54.11% 19.42% 28.58% opinion word 76.46% 81.93% 79.10% person name 73.83% 81.94% 77.67% table v. 2000 reviews for naive bayes classifier aspects precision recall f1 feature word 43.5% 79% 55.6% movie name 74.5% 45.8% 56.6% opinion word 56.5% 65.2% 59.8% person name 57.37% 65.47% 57.8% table vi. comparison of results for the proposed model, cr model and naive bayes classifier precision recall f1 accuracy pm 96.01% 96.00% 96.01% 98.17% cr 77.95% 81.35% 79.62% 91.25% nb 57.37% 65.47% 57.8% 68.9% fig. 4. number of incorrectly identified aspects for proposed model, cr model and naive bayes fig. 5. a comparison of the proposed model, crf model and naive bayes classifier v. conclusion nowadays more people are engaged in generating online data. with the availability of plenty of data, the need of a mechanism that will extract useful information automatically emerged. this has opened the doors for aspect based opinion mining. this research has implemented an aspect based opinion mining method for identifying aspects from a social movie reviews dataset. the main contributions of this research were data training (phase ii), feature set definition (phase iii) and dictionary (phase v). the overall accuracy of our proposed method is 98.17% and precision, recall and f1 respectively are: 96.01%, 96.00% and 96.01%. the experimental results show that the proposed model performs much better than the cr model and the naive bayes classifier. future work involves implementation of a model that will identify implicit aspects and calculate aspect wise sentiment analysis. moreover, we will avoid the dictionary usage and find out the patterns for deep aspect classification. there are some other issues which are more challenging and tedious, for instance, comparative sentences, 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[25] l. chen, l. qi, f. wang, “comparison of feature-level learning methods for mining online consumer reviews”, expert systems with applications, vol. 39, no. 10, pp. 9588-9601, 2012 [26] c. sutton a. mccallum, an introduction to conditional random fields, now publishers, 2012 [27] j. baldridge, “the opennlp project”, url: https://opennlp.apache.org, (accessed 2 february 2012), 2005 [28] t. kudo, “crf++: yet another crf toolkit”, software available at http://crfpp. sourceforge. net, 2005 microsoft word etasr_v12_n6_pp9491-9495 engineering, technology & applied science research vol. 12, no. 6, 2022, 9491-9495 9491 www.etasr.com khan et al.: classification of macromolecules based on amino acid sequences using deep learning classification of macromolecules based on amino acid sequences using deep learning sarwar khan department of computer science national chengchi university taipei, taiwan sarwar@iis.sinica.edu.tw imad ali department of computer science university of swat khyber pakhtunkhwa, pakistan imadali@uswat.edu.pk faisal ghaffar system design engineering department university of waterloo waterloo, canada faisal.ghaffar@uwaterloo.ca qazi mazhar-ul-haq national taipei university of technology taipei, taiwan qazi@ntut.edu.tw received: 31 july 2022 | revised: 26 august 2022 | accepted: 28 august 2022 abstract-the classification of amino acids and their sequence analysis plays a vital role in life sciences and is a challenging task. deep learning models have well-established frameworks for solving a broad spectrum of complex learning problems compared to traditional machine learning techniques. this article uses and compares state-of-the-art deep learning models like convolution neural networks (cnns), long short-term memory (lstm), and gated recurrent units (gru) to solve macromolecule classification problems using amino acid sequences. the cnn extracts features from amino acid sequences, which are treated as vectors with the use of word embedding. these vectors are fed to the above-mentioned models to train robust classifiers. the results show that word2vec as embedding combined with vgg-16 performs better than lstm and gru. the proposed approach gets an error rate of 1.5%. keywordscnn; lstm; amino acid; macromolecules i. introduction the last decade has witnessed the great success of deep learning as it has brought revolutionary advances in many application domains including computer vision, natural language processing, and signal processing. the key idea behind deep learning is the consideration of feature learning and classification in the same network architecture, using backpropagation to update model parameters and learn discriminative feature representations. notably, many novel deep learning methods have been proposed, which improve classification performance significantly [1-3]. studying deoxyribonucleic acid (dna) in life sciences is essential for understanding organisms. current sequencing technologies make it possible to read dna sequences at a lower cost. dna databases are increasing daily, and the power of modern computing is required. classifying dna sequences is a critical and essential task. four major classes of organic macromolecules are always found in all life forms on earth: carbohydrates, lipids (or fats), proteins, and nucleic acids. the significant macromolecule classes are similar in that they are large polymers assembled from small repeating monomer subunits. proteins are large, complex molecules that play many critical roles in the body. they are made up of hundreds or thousands of smaller units called amino acids, which are attached in long chains. twenty different types of amino acids can be combined to make a protein. the sequence of amino acids determines each protein's unique 3-dimensional structure and specific function. the interaction of protein with protein and protein with dna/rna (ribonucleic acid) plays a pivotal role in protein function. experimental detection of residues in protein-protein interaction surfaces must come from determining the structure of protein-protein, protein-dna, and protein-rna complexes. however, experimental determination of such complexes lags far behind the number of known protein sequences. hence, there is a need to develop reliable computational methods for identifying protein-protein, proteinrna, and protein-dna interface residues. identifying macromolecules and detecting specific amino acid residues that contribute to the strength of interactions is a fundamental problem with broad applications ranging from rational drug design to the analysis of metabolic and signal transduction networks. this article aims to utilize deep learning models to classify the macro molecule types based on the amino acid sequence and residue count. we used state-of-the-art deep learning models like cnn [4], lstm [5], gru) [6]. we used word embedding to represent the amino acid sequences as vectors. the cnn extracts features from amino acid sequences, which are treated as vectors. these vectors are then fed to the models mentioned above to train robust classifiers. our results show that word2vec embedding combined with vgg-16 performs better than lstm and gru. corresponding authors: sarwar khan engineering, technology & applied science research vol. 12, no. 6, 2022, 9491-9495 9492 www.etasr.com khan et al.: classification of macromolecules based on amino acid sequences using deep learning ii. literature review the revolution in machine learning, mainly deep learning [7-10], allowed the study and extraction of complex patterns from data and made the machine models more robust. for instance, authors in [7] proposed deep learning techniques to perform brand and logo recognition tasks using multiple modern cnn models. in [8], a cnn model was applied to handwritten character recognition and was compared to a standard handwritten digit recognition task. it was found that cnns efficiently deal with the variability of 2d shapes and outperform the other techniques. a variable size replicated cnn in [9] gathers relevant input information and eliminates irrelevant variabilities. a cnn model was proposed in [10] for the study and investigation of the accuracy and efficiency of new image datasets via transfer learning. authors in [11] targeted learning as an informative feature representation of protein sequence as the input of neural network models to obtain the final predicting output of the belonging protein family. authors in [12] proposed a framework with a deep 1d cnn, which is robust in both fold recognition and the study of sequence-structure relationships to classify protein sequences. authors in [13] developed a framework with a cnn that used the idea of translation to convert dna sequences to word sequences for final classification. likewise, recurrent neural networks have shown promising results in many machine learning tasks. for example, an lstm-based end-to-end approach was proposed in [14] for sequence learning, where the model makes nominal assumptions on the sequence structure. similarly, authors in [15] described that recurrent neural networks could perform better on a challenging machine translation task. in the current article, we aim to evaluate the deep leaning techniques cnn, lstm, and gru for macromolecule classification. it is well established that these techniques work well on sequence-based tasks, even with longterm dependencies. iii. materials and methods a. dataset we used the protein data bank dataset [21]. a dna molecule consists of two long polynucleotide chains composed of 4 types of nucleotide subunits, called a dna chain. these may be adenine (a), cytosine (c), guanine (g), or thymine (t). the dataset contains two files with a different number of entries. one file has 467304 entries with 5 columns (table i). the other file contains protein meta-data, i.e. resolution, extraction method, experimental technique, etc. with 141401 entries and 14 columns. we merged the two files based on structure ids. the pre-processing step is to drop all the entries with nan value or if a label or sequence is missing. after removing the missing values, the sequence is checked for the removal of tags and numbers. once the dataset is cleaned, the sequence is divided into tri-gram, each sequence now combining three character strings. for example, cgc gaa ttc gcg. the final block may not have all three, and we added 0 to make it an equal slice (padding). the final output contains two columns, one for sequence and one for the label. as discussed above, there are 432474 rows in the processed data with 4 labels. these are all unbalanced data, and this issue will be discussed below. table i. types of macromolecule proteins type label data structure entries structure id structureid object 140250 chain id chainid object 2837 sequence protein sequence object 104813 residue count no. of residues atcg's integer 4737 macromolecule type macromolecule type object 14 b. biological structures in the dataset the central dogma of life if that dna makes rna, rna makes amino acids, and amino acids make proteins. dna and rna are made of four types of nucleotides (a, t, c, g). the nucleotide sequence is the combination of these nucleotides in a row. three nucleotides combine to form a codon, building a block of amino acids. the amino acids then are combined to form proteins. to make a protein, at least 20 amino acids are necessary. consider the following real example. att is a codon, which consists of three nucleotides. this codon represents amino acid (isoleucine) represented by the letter "i." ttt is another codon, i.e. another amino acid (phenylalanine) and is characterized by the letter "f." these "if"s are combined with others to make proteins. the letters in the codon represent nucleotides, while the letters in the protein sequence represent amino acids. at least 20 amino-acids must be combined to make a functional protein. the maximum number depends on when a stop codon is met. such a codon can be met after 20 or after 500 amino acids. the amino acid sequence determines the type of proteins. iv. the proposed method figure 1 shows the block diagram of the proposed system. this system can be broadly divided into 3 tasks. the first 2 are dataset processing and embedding. we have different choices in embedding, but word2vec [16], fast-text [17], and glove [18] are well-known embedding techniques in natural language processing (nlp). these embedding techniques have been tested in different bioinformatics tasks with promising results. another famous embedding method is onehot vector. we used word2vec in this study. the final task is the cnn, in which the number of network layers must be determined. we also need to find hyper-parameters along with the model's size, height, and width. the output layer is a softmax layer used to classify the sequence. classifying macromolecule types using sequences can be seen as a sequence classification problem. this is analogous to the sentence classification task in nlp. thus, we apply a skipgram analysis from nlp research to model our problem. there are various sequence models in the deep learning domain. we used lstm, gru, and 1d convolution for our problem. recurrent neural networks, such as lstm, are specifically designed to support input data sequences. figure 2 shows the layout of the model. cnns can learn the complex dynamics within the temporal ordering of input sequences and use internal memory to remember or use information across long input sequences. as it is crucial to any deep learning task, we applied data prepossessing before feeding them to our model. prepossessing includes handling missing values and downsampling the dominant class to balance data distribution. engineering, technology & applied science research vol. 12, no. 6, 2022, 9491-9495 9493 www.etasr.com khan et al.: classification of macromolecules based on amino acid sequences using deep learning fig. 1. the blog diagram of the proposed method. fig. 2. lstm model using embedding at the input. fig. 3. word2vec model relation between sequences. a. word embedding we used word2vec as the embedding technique in this work [17]. we need embedding techniques because deep learning or machine learning models only deal with real numbers. embedding not only converts these texts or sequences into numbers but also produces relationships between them. we have two algorithms for word2vec, skip-gram and common bag of words (cbow). after using both these algorithms in the 3 models, we find that skip-gram suits better in our case. we used the tri-gram data to generate our word2vec model. figure 3 shows the relationship between the sequences. we used different output dimensions, i.e. 100, 150, and 300. we find that the 300-dimension output has better performance. b. convolution neural network the cnn is the most famous deep learning method. we used the network architecture of vgg [19, 20]. fig. 4. cnn model parameters with dimensions. we are using convolution1d as the data dimension is 1d. this network has 4 convolution layers, each layer followed by a max-pooling layer. the network also includes batch normalization and dropout to prevent the model from overfitting. two dense layers follow the final max-pooling layer. the hyper-parameters which give the best results were set as: learning rate: 0.001, batch size: 512, loss function: crossentropy, optimizer: adam, number of epochs: 20, dropout rate: 0.5, activation: relu. the final layer is softmax. figure 4 shows the model architecture along with the model parameters. v. experiments and results we evaluated our models on a protein data bank [21], a database for the three-dimensional structural data of large biological molecules, such as proteins and nucleic acids. performance comparison between different models will only make sense if we keep the same pre-processing and embedding. our experiments show that word2vec with output dimension of engineering, technology & applied science research vol. 12, no. 6, 2022, 9491-9495 9494 www.etasr.com khan et al.: classification of macromolecules based on amino acid sequences using deep learning 300 performs better, and we will keep this setting unless mentioned otherwise. a. cnn model results figure 5 shows the validation and training loss over the 50 epochs with an embedding dimension of 50. we used an early stopping algorithm to save and use our best model. training loss is 0.028, while validation loss is 0.034. fig. 5. training and validation loss. fig. 6. model training and validation accuracy. fig. 7. confusion matrix for all classes. figure 6 shows the accuracy curve for the same setting, where the final training accuracy is 99.2% and the test accuracy is 98.8%. the micro-average and macro-average are almost the same. to further dig out the details, we drew the confusion matrix of all four classes, as shown in figure 7, where the accuracy of each class is nearly the same, as we can see from the diagonal color. figure 8 shows the cnn model's precision, recall, and f1-score. the model has precision of 0.98, 0.97, 0.98, and 1.00 for classes of dna, hybrid, rna, and protein respectively. recall and f1-score can also be easily observed in figure 8. fig. 8. precision, recall, and f1-score. b. additional simulations one hundred estimators initialized random forest (rf) [22], showing 96.83% test accuracy for more than 90,000 test sequences. we tested the rf for balanced and unbalanced data, and the results were almost identical. table ii shows each class's precision, recall, and f1-score. the results are not good enough compared to cnn, but rf is much faster and less expensive than cnns. we are reporting these results to show that traditional machine learning algorithms also work better for some visual question answering times. table ii. random forest results label precision recall f1-score protein 0.96 0.99 0.97 dna 0.90 0.80 0.85 rna 0.93 0.69 0.79 hybrid 0.94 0.88 0.91 macro-avg. 0.93 .84 0.88 weighted-avg 0.96 0.96 0.96 table iii. performance of different networks model t. acc. t. loss val-acc. val-loss cnn 98.19% 0.0486 97.74% 0.0819 gru 90.79% 0.2691 89.70% 0.2715 lstm 95.12% 0.3982 95.14% 0.1962 cnn-gru 94.85% 0.1509 92.74% 0.1962 rf 95.17% 0.4019 94.87% 0.4906 vgg16 99.11% 0.0288 98.10% 0.0297 the next step is to compare different state-of-the-art algorithms like lstm, rf, and gru with the proposed cnn. we used tensorflow embedding in this case with 50dimension vectors. in this case, the lstm and gru have the same network structure and use the same number of cells, i.e. 512. table iii shows the comparison of accuracy and loss across the different networks. the table shows that vgg-16 [19] performs better with word2vec as embedding. for example, the training accuracy (t. acc.) and the validation accuracy (val. acc.) for the vgg-16 are 99.11 and 98.10 engineering, technology & applied science research vol. 12, no. 6, 2022, 9491-9495 9495 www.etasr.com khan et al.: classification of macromolecules based on amino acid sequences using deep learning respectively. moreover, the training loss (t. loss) and the validation loss (val. loss) for the vgg-16 are 0.0288 and 0.0297 respectively. the 7-layer cnn also performs better compared to lstm and gru. all cnns are of one dimension. the other models' results can be easily read in table iii. vi. conclusion in this article, we used nlp techniques to classify the protein sequences and very good results based on accuracy and precision were achieved. the cnn and cnn-fru models have better performance than the other models. although we didn't train the models for long epochs, we still obtained high accuracy with cnn. moreover, the data are highly nonnormalized. these models perform much better when the data are normalized. future work includes classifying the data with more models. references [1] k. he, x. zhang, s. ren, and j. sun, "deep residual learning for image 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[22] l. breiman, "random forests," machine learning, vol. 45, no. 1, pp. 5– 32, oct. 2001, https://doi.org/10.1023/a:1010933404324. microsoft word etasr_v13_n4_pp11419-11425 engineering, technology & applied science research vol. 13, no. 4, 2023, 11419-11425 11419 www.etasr.com karasu et al.: an investigation of the effect of embedded gold nanoparticles in different geometric … an investigation of the effect of embedded gold nanoparticles in different geometric shapes on the directivity of thz photoconductive antennas yunus emre karasu faculty of engineering, karabuk university, turkiye yekarasu@karabuk.edu.tr (corresponding author) ihsan uluer faculty of engineering, ostim technical university, turkiye ihsanuluer@gmail.com turgut ozturk faculty of engineering, karabuk university, turkiye t.ozturk@karabuk.edu.tr received: 11 june 2023 | revised: 21 june 2023 | accepted: 2 july 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6116 abstract this study aims to show how terahertz (thz) photoconductive antennas (pcas) affect the radiation directivity when gold nanoparticles of various geometric shapes are embedded in the gap region between the electrodes of thz pcas. three different pcas, in the frequency range of 0.1 to 2 thz, conventional and after the addition of cylindrical, triangular, square, and hexagonal geometric gold nanoparticles to the antenna gap region between the electrodes, were built and simulated. the antenna directivity increased from 4.71 dbi to 4.92 dbi when square nanoparticles were added to the bowtie pca, from 4.33 dbi to 4.45 dbi when triangular nanoparticles were added to the dipole pca, and from 7.18 dbi to 7.52 dbi when square nanoparticles were added to the vivaldi pca. keywords-photoconductive antenna; terahertz waves; nanoparticles i. introduction the thz gap is the area between far infrared (10 thz) and microwave rays (100 ghz) in the electromagnetic spectrum. thz rays have been used in a very important and wide range, from imaging for security purposes to food spectroscopy and from space communication to drug and explosive material detection [1]. many devices can radiate at thz frequency. however, most are complex, expensive, inefficient, and cannot function at room temperature [2]. until recently, there has been no progress in thz applications for these reasons. with the production of ultra-fast lasers, pcas have become ideal devices that can be used as a source and detector for thz radiation and operate at room temperature [3, 4]. the pca is obtained as follows: electrodes are added on top of the semiconductor substrate. a dc bias is applied to the electrodes. an optical pulse of a certain frequency is applied to the semiconductor material at a certain time interval. the energy of the applied optical radiation should be sufficient to transfer the electrons from the valence band of the semiconductor material to the conduction band. electrons and holes emerge in the material when the semiconductor surface is illuminated with an optical laser. with dc bias, electrons and holes are aligned and accelerated. when the radiation ends, electrons and holes recombine and slow down. with the acceleration of electrons and holes, photocurrent occurs in the antenna gap. due to the photocurrent's emergence and change, radiation occurs from the side of the substrate to space [5, 6]. with the enhancement of ultrafast pulsed lasers [4] and the development of low-temperature grown gaas (lt-gaas) [7] the use of pcas as a room-temperature source and detector for thz radiation has become very common. according to the geometric shape of the thz pca electrode, it can be divided into bowtie, vivaldi, log spiral, and dipole. semi-insulating gaas (si-gaas), gaas, lt-gaas, graphene, and quartz were used as photoconductive materials [3, 8]. enhancement of high power of thz radiation produced from pcas or increasing optical-thz conversion efficiency is based on two principles: engineering, technology & applied science research vol. 13, no. 4, 2023, 11419-11425 11420 www.etasr.com karasu et al.: an investigation of the effect of embedded gold nanoparticles in different geometric … the first is the change in the density of the photocarrier, and the second is the change in its velocity [9, 10]. something that limits the increase in the photocarrier density in the pca and thus reduces the power and directivity of the radiation is the phenomenon known as delay saturation or screening effect. to reduce the screening effect, conductive nanoparticles have been added to the gap between electrodes where the optical pulse is applied. adding conductive nanoparticles increases the absorption of the ultrafast optical pulse, and a shorter lifetime photocarrier is obtained. to reduce the screening effect, the nanoparticles should not be placed on the gap in a threedimensional manner but should be embedded in the gap [11]. the added nanoparticles should have high conductivity [12]. a part of the power used for radiation in the pca is consumed in the substrate material. to overcome this problem, slots are opened on the antenna surface in order to reduce the surface wave loss and increase the optical-thz conversion ratio and directivity. when opening a slot, it is more efficient to open it in certain geometric shapes instead of a random shape [13, 14]. in this study, gold nanoparticles in certain geometric shapes were added to the antenna's gap to increase the pca's directivity. the chosen geometric shapes of the added gold nanoparticles were as cylinder, triangle, square, and hexagon. as antenna type, studies were carried out on bowtie, dipole, and vivaldi antennas. first, conventional antennas were analyzed in the cst mw studio simulation program. then, the geometric shapes were added, and the new pcas were analyzed. with the addition of nanoparticles to the antennas, its directivity increased. the highest directivity was achieved in the bowtie and vivaldi antennas when square-shaped particles were added. the highest directivity in the dipole antenna was achieved when triangular gold nanoparticles were added. ii. mathematical model of thz pca the current density ���� in the pca gap is given as [13]: ���� = ����. ��� ⋅ � (1) where ��� = � ���. �� is the average velocity of the carrier, � is the electron charge, � ��� is the electric field in the conductive antenna gap, �� is the electron mobility, and n(t) is the time-dependent carrier density. the time-dependent carrier density is expressed using the drude model [15]: ����� �� = − ���� �� + ���⋅� ����� (2) where � is represented by laser frequency, optical absorption coefficient �� , carrier lifetime � , and peak laser intensity �����. the electric field in the antenna gap is screened by the increase in the separation of charge carriers. the photoconductive substrate can be considered as a current source, dependent on the source resistance and time. the resistance depends on the optical source and substrate material and is also a time dependent variable, denoted as r(t): !��� = "#��� (3) where g(t) is the time-varying source conductivity, given by: $ = %&,(,�)& �1 − � +�,��� exp�−2� �1 − !� × √45 6�7 r� exp 9− :�; �� < =erf =√4�?� − √4?� 6�� @@ + 1 (4) where ab and cb are the width and length of the antenna gap, respectively, � is the optical absorption coefficient, � is the electron mobility, � is the electron charge, is the frequency, ℎ is the planck constant, �� is the peak laser intensity, ef is the skin depth of the excitation region, r� is the laser pulse duration, and ! is the reflection coefficient of the substrate [16]. the voltage across the time-varying pca range is given as follows: �gh��� �� = " ih j��� k − "ih j��� kl ��� − m��� ih j��� kl ��� − #��� j��� kl ��� − " j��� �j ��� �� (5) where k is the bias voltage and n��� is the time-dependent capacitance [17]: n��� = �oih p1 + (⋅�⋅ih⋅q⋅���� )r s (6) where �� is the recombination time, t is the active area, and c� is the dipole length of the antenna. the voltage-controlled time-dependent resource coefficient u��� depends on the recombination time and carrier density: u��� = �o(vw���xy (7) the produced photocurrent is given by: z���� = � ⋅ � ⋅ ���� ⋅ kl ��� ⋅ q)r (8) where ���� is the photocarrier density and kl ��� is the timedependent voltage at the antenna gap [15]. iii. thz pca design a. design of the bowtie pca the parameters of the conventional bowtie pca in figure 1 without nanoparticles are shown in table i. gold was used as the electrode material. while designing the bowtie antenna, simulations were made in the cst mw studio program using quartz, gaas, graphene, and lt-gaas as substrates. the best s11 and directivity values were obtained when lt-gaas was used as substrate. for this reason, lt-gaas was used as the substrate material in this antenna. to increase the directivity of the conventional bowtie pca, cylindrical, triangular, square, and hexagonal gold nanoparticles were added to the gap between the electrodes and simulated in the cst mw studio. the highest directivity value was obtained in the bowtie pca with square gold nanoparticles added. the bowtie antenna with square gold nanoparticles inserted between the electrodes can be seen in figure 2. the side length of the gold square added in figure 2(b) is 500 nm. the distances between the frames are equal and 500 nm. the nanoparticles of interest have been embedded in the substrate and have a depth of 10 nm. the return loss value (s11) of the pca with bowtie antenna and square gold added nanoparticles is shown in figure 3. engineering, technology & applied science research vol. 13, no. 4, 2023, 11419-11425 11421 www.etasr.com karasu et al.: an investigation of the effect of embedded gold nanoparticles in different geometric … fig. 1. shape and parameters of conventional bowtie pca. table i. parameter values of conventional bowtie pca parameter parameter explanation value (µm) ws substrate width 280 hs substrate height 240 ds substrate depth 1.5 hel height of the long side of the electrode 200 hes height of the short edge of the electrode 10 we width between the long edge and the short edge of the electrode 100 de depth of the electrode 0.01 g gap between electrodes 10 hes height of the short edge of the electrode 10 fig. 2. (a) zoomed-out view of bowtie pca with added square nanoparticles. (b) zoomed in view of the attached region of square-shaped gold nanoparticles between the electrodes. fig. 3. return loss information of conventional bowtie pca and square attached bowtie pca (s11). as seen in figure 3, when square nanoparticles are added to the conventional bowtie pca, the s11 value increased from -64.5 db to -42.27 db, the bandwidth increased from 1.65 thz to 1.66 thz, and the resonant frequency increased from 1.36 thz to 1.41 thz. the directivity of the conventional bowtie pca increased from 4.71 dbi to 4.92 dbi, as seen in figure 4, whereas the directivity of the bowtie pca with the addition of square gold nanoparticles can be seen in figure 5. fig. 4. 3d radiation patterns of conventional bowtie pca. fig. 5. 3d radiation patterns of square attached bowtie pca. b. design of the dipole pca the parameters of the conventional dipole pca (figure 1) without nanoparticles are shown in table ii. gold was used as the electrode material. while designing the bowtie antenna, simulations were made in the cst mw studio using quartz, gaas, graphene, and lt-gaas substrates. the best s11 and directivity value were obtained when gaas was used, so gaas was used as the substrate material in this antenna. to increase the directivity of the conventional dipole pca, cylindrical, triangular, square, and hexagonal gold nanoparticles were added to the gap between the electrodes and were simulated in cst mw studio. the highest directivity value was obtained in the dipole pca with triangular gold nanoparticles added. the bowtie antenna with triangular gold nanoparticles inserted between the electrodes is shown in figure 7. the side length of the gold triangular added in figure 7 is 1 µm. the distances between the frames are equal and 500 nm. the nanoparticles of interest were embedded in the substrate and have a depth of 10 nm. the s11 of the conventional dipole pca with triangular gold nanoparticles added is shown in figure 8. engineering, technology & applied science research vol. 13, no. 4, 2023, 11419-11425 11422 www.etasr.com karasu et al.: an investigation of the effect of embedded gold nanoparticles in different geometric … fig. 6. shape and parameters of conventional dipole pca. table ii. parameter values of conventional dipole pca parameter parameter explanation value (µm) ws substrate width 350 hs substrate height 340 ds substrate depth 1.5 hel height of the long side of the electrode 220 hes height of the short edge of the electrode 10 wel width between the long edge and the short edge of the electrode 80 wes width of the long electrode 30 de depth of the electrode 0.02 g gap between electrodes 10 fig. 7. a. zoomed-out view of bowtie pca with added triangular nanoparticles b. zoomed in view of the attached gap of triangular -shaped gold nanoparticles between the electrodes fig. 8. s11 of conventional dipole pca and triangular attached dipole pca. as can be seen in figure 8, when triangular nanoparticles were added to the conventional dipole pca, the s11 value increased from -33.27 db to -31.2 db, the bandwidth decreased from 0.28 thz to 0.27 thz, and the resonant frequency remained constant at 1.63 thz. the directivity of the conventional dipole pca (figure 9) increased from 4.33 dbi to 4.45 dbi. the directivity of the dipole pca with the addition of triangular gold nanoparticles is shown in figure 10. fig. 9. 3d radiation patterns of conventional dipole pca. fig. 10. 3d radiation patterns of triangular attached dipole pca. c. design of the vivaldi pca the parameters of the conventional vivaldi pca without nanoparticles in figure 11 are shown in table iii. gold was used as the electrode material. while designing the vivaldi antenna, simulations were made in the cst mw studio using quartz, gaas, graphene, and lt-gaas as substrates. the best s11 and directivity values were obtained when gaas was used as substrate, so gaas was used as the substrate material in this antenna. to increase the directivity of the conventional vivaldi pca, cylindrical, triangular, square, and hexagonal gold nanoparticles were added to the gap between the electrodes and the structure was simulated in the cst mw studio. the highest directivity value in the vivaldi pca was obtained with square gold nanoparticles added. the vivaldi antenna with square gold nanoparticles inserted between the electrodes is shown in figure 12. the side length of the gold square added in figure 7 is 500 nm. the distances between the frames are equal and 500 nm. the nanoparticles used had a depth of 50 nm. the s11 of the conventional vivaldi pca and of the square gold added nanoparticles is shown in figure 13. engineering, technology & applied science research vol. 13, no. 4, 2023, 11419-11425 11423 www.etasr.com karasu et al.: an investigation of the effect of embedded gold nanoparticles in different geometric … fig. 11. shape and parameters of conventional vivaldi pca. table iii. parameter values of the conventional vivaldi pca parameter parameter explanation value (µm) ws substrate width 150 hs substrate height 180 ds substrate depth 1.5 he electrode height 69,4 wel width of the long side of the electrode 77.5 wes width of the short edge of the electrode 10 de depth of the electrode 0.05 g gap between electrodes 10 c length of antenna curve 96.81 as seen in figure 13, when square nanoparticles were added to the conventional vivaldi pca, the s11 value decreased from 32.08 db to -31.2 db, the bandwidth decreased from 0.28 thz to 0.27 thz, and the resonant frequency increased from 1.57 thz to 1.58 thz. the directivity of the conventional vivaldi pca (figure 14) increased from 7.18 dbi to 7.52 dbi (figure 15). fig. 12. (a) zoomed-out view of the vivaldi pca with added triangular nanoparticles. (b) zoomed in view of the attached gap of square -shaped gold nanoparticles between the electrodes. the analysis results of all the studied pcas, such as the substrate material used, the electrode material, the type of nanoparticle material added, the nanoparticle shape, s11, resonance frequency, bandwidth, and directivity are shown in table iv. the electroded and the added nanoparticles are gold in all designs. fig. 13. s11 of conventional square attached vivaldi pcas. fig. 14. 3d radiation patterns of conventional vivaldi pca. fig. 15. 3d radiation patterns of square attached vivaldi pca. iv. discussion various efforts have been made to increase the output power, optical to thz conversion ratio, and antenna directivity of the thz pcas [13, 18]. the addition of metal nanoparticles to the photoconductive gap between the electrodes is one of these efforts [19, 21]. in this article, it has been shown that there is a relationship between the shape of the nanoparticle added to the photoconductive gap and the electrode shape of the antenna. in the bowtie and vivaldi pca, the highest directivity was reached when square-shaped nanoparticles were added, while in the dipole pca, the highest directivity was reached when triangular-shaped nanoparticles were added. engineering, technology & applied science research vol. 13, no. 4, 2023, 11419-11425 11424 www.etasr.com karasu et al.: an investigation of the effect of embedded gold nanoparticles in different geometric … table iv. result summary pca type substrate used shape of the added nanoparticles s11 (db) bandwidth (thz) resonance frequency (thz) directivity (dbi) bowtie lt-gaas no add -64,5 1.65 1.36 4.71 bowtie lt-gaas cylinder -38,51 1.67 1.41 4.91 bowtie lt-gaas triangle -36,85 1.65 1.4 4.88 bowtie lt-gaas square -42,27 1.66 1.411 4.92 bowtie lt-gaas hexagon -45,9 1.66 1.40 4.88 dipole gaas no add -33,27 0.28 1.631 4.33 dipole gaas cylinder -31,62 0.28 1.629 4.26 dipole gaas triangle -31,2 0.27 1.631 4.45 dipole gaas square -31,37 0.27 1.629 4.39 dipole gaas hexagon -33,55 0.27 1.625 4.37 vivaldi gaas no add -32,08 0.58 1.572 7.18 vivaldi gaas cylinder -33,39 0.59 1.568 7.5 vivaldi gaas triangle -34,2 0.58 1.570 7.46 vivaldi gaas square -48,75 0.55 1.582 7.52 vivaldi gaas hexagon -38,02 0.55 1.576 7.41 authors in [18] showed that plasmonic contact electrodes could significantly reduce photoconductive thz optoelectronics' low quantum efficiency performance. authors in [12] further increased optical to thz conversion efficiency by adding silver nanoparticles to the gap between antenna electrodes. authors in [19] proposed a photoconductive logarithmic spiral antenna with saw-toothed plasmonic contact electrodes to provide higher thz radiation than a conventional pca. authors in [20] showed that by integrating split-ring resonators like metallic structures into the coplanar lines of the pca transmitter, the spectral characteristic of the generated thz radiation could be significantly manipulated. author in [21] developed thz pca arrays to increase their output power. improved arrays were designed according to the crossfingers structure as a high-power thz generator. in these studies, nanoscale metal particles were added to the surface of the gap region of the pca. however, they were not embedded in the substrate. in our study, gold nanoparticles were embedded in the substrate, reducing the screen effect formed in the substrate, resulting in more antenna directivity. authors in [22] increased the radiation intensity by adding he+ ions to the semiconductor substrate in the pca, increasing thus the radiation intensity up to a certain dose and decreasing it after a certain point. in this study, the he+ element was embedded in the substrate at the gap. however, embedding an element is quite difficult in the manufacturing process. in our study, embedding of metal nanoparticles into the substrate is easier thanks to the e-beam lithography [23]. authors in [24] examined a photoconductive bowtie antenna with graphene electrodes on a photonic crystal substrate for thz radiation. the photonic crystal structure was formed by the periodic arrangement of cylindrical air holes in the gallium arsenide substrate to improve the performance of the basic antenna design. authors in [13] studied photonic crystal substrates with cylindrical, square, triangular, and hexagonal shapes. it was shown that hexagonal-shaped photonic crystals provide the highest directivity and bandwidth, confirming their suitability for thz pca. in the above mentioned studies, photocrystals in the form of an air gap were added to the antenna. photocrystals in the antenna can cause the s11 value to increase. in our study, the addition of conductive nanoparticles instead of the air gap caused the pca to work more effectively. v. conclusion in this article, embedding different shaped nanoparticles to the substrate was proposed for increasing the directivity of thz pcas. the proposed pcas have been designed and their performance was analyzed and compared with the conventional pcas. it was shown that the geometric shape of the embedded nanoparticles in the gap between the antenna electrodes caused different effects depending on the antenna type. embedding nanoparticles in the antenna gap increased antenna directivity from 4.71 dbi to 4.92 dbi in bowtie pca, from 4.33 dbi to 4.45 dbi in dipole pca, and from 7.18 dbi to 7.52 dbi in vivaldi pca. the highest directivity was obtained when triangular gold nanoparticles were added to the dipole antenna and square gold nanoparticles were added to the bowtie and vivaldi pcas. in previous studies, nanoparticles were either added to the surface or inserted into the antenna gap with random shape. however, in this study, the nanoparticles were embedded in the gap and placed in the antenna gap with certain geometric shapes. for this reason, a more significant increment was established in antenna directivity. our future work will aim to 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[24] m. shalini and m. g. madhan, "photoconductive bowtie dipole antenna incorporating photonic crystal substrate for terahertz radiation," optics communications, vol. 517, aug. 2022, art. no. 128327, https://doi.org/ 10.1016/j.optcom.2022.128327. microsoft word etasr_v12_n3_pp8688-8693 engineering, technology & applied science research vol. 12, no. 3, 2022, 8688-8693 8688 www.etasr.com mellah et al.: the effect of stator inter-turn short-circuit fault on dfig performance using fem the effect of stator inter-turn short-circuit fault on dfig performance using fem hacene mellah department of electrical engineering akli mohand oulhadj university of bouira bouira, algeria has.mel@gmail.com serdal arslan organized industrial zone vocational higher school harran university sanliurfa, turkey elkserdal@gmail.com sahraoui hamza department of electrical engineering benbouali hassiba university of chlef chlef, algeria hamzasahraoui@gmail.com kamel eddine hemsas department of electrical engineering ferhat abbas sétif 1 university sétif, algeria hemsas.kamel@gmail.com saoudi kamel department of electrical engineering akli mohand oulhadj university of bouira, bouira, algeria k.saoudi@univ-bouira.dz received: 24 march 2022 | revised: 15 april 2022 | accepted: 18 april 2022 abstract-doubly-fed induction generators (dfig) are operated for wind energy production, and as their capacity is increasing, their safety and reliability become more important. several faults affect the performance of dfig. the stator winding inter-turn short-circuit fault (itscf) is one of the most prevalent electric machine failures. this study examined the stator itscf effects on dfig performance for different cases. the dfig was designed and engineered using the finite element method (fem) and the maxwell software, and was examined in healthy operation and four defective cases with various numbers of inter-turn short circuit faults (nitscf): 4, 9, 19, and 29. these models allowed the examination of the effects and the comparison of each case separately from the healthy state. the comparison was plotted in matlab to show the effects of the faults. the novelty of this study was that it investigated the effects of different nitscf on the performance of dfig and not only on their effect on the stator current and distribution of magnetic flux density. a better understanding of the short circuit effects on the performance of the dfig can be exploited for subsequent implementations of early fault detection systems. keywords-doubly-fed induction generators (dfig); stator winding; inter-turn short circuit fault (itscf); number of itscf; finite element method (fem); finite element analysis i. introduction since the 1970s, modern wind power conversion technology has been developed, especially at the end of the last century. several wind turbine system (wts) concepts were explored and different wind turbines were built [1]. since the '90s, when the renewable energy is classified based on increasing installed capacity, wind energy occupies the first place among all types of renewable energy [2]. the ten leading countries in wind power at the end of 2017 had installed more than the three-quarters of all new wind turbines in the world [2]. dfigs, with external [3] or inner rotors [1], are used in wind power production. as their capacity increases, their safety and reliability become more important. the variation in speed is possible due to power electronics, which are required to provide a connection to the grid. many studies dealt with dfig grid connection issues for different purposes [4-7]. the itscf of the stator or rotor windings is among the most common faults of dfigs. the effect of itscf on the properties of dfig has attracted much attention during the past decade. on the other hand, many researchers investigated how to detect and localize such faults [8-12]. however, the difference in the behavior of electrical machines between normal and fault conditions must first be understood before detection and localization can be accomplished. according to [8-17], two methods exist for analyzing the itscf by simulation in dfig: the analytical and the numerical. the analytical approach is based on the multi-circuit theory [18-20], and the numerical approach is usually based on fem [21, 22]. it's critical to understand the dfig fault simulation models and features to investigate failure mechanisms. several studies examined a fem simulation model of an itscf stator or rotor winding in dfig [11, 23-24]. in [12], the itscf in the stator winding with different nitscf was examined, but this study was limited to the stator current behavior and only took into account two stator slots: 4 and 19. in [10], the stator itscf was validated both by fem simulation and experiment, however, this study was limited to the itscf effect on the current and only for some turns. other studies focused only on the effect of turn-to-turn short-circuit defects on the magnetic field [25]. authors in [23] only focused on the rotor itscf effect on the magnetic flux density distribution and the rotor current. in [26], two closely related phenomena of the current spectrum of the stator and rotor were studied: itscf and high corresponding author: hacene mellah engineering, technology & applied science research vol. 12, no. 3, 2022, 8688-8693 8689 www.etasr.com mellah et al.: the effect of stator inter-turn short-circuit fault on dfig performance using fem resistance connections, as well as their effect on the energy injected into the network in sub and super synchronous operation, and a discussion on how to tell them apart. in [24], a quantitative study was conducted on mechanical vibration, stator currents, and stator copper loss in healthy and itscf cases of one-third of a stator turn of dfig using fem. the effect of itscf on stator branch currents and its expression by the total harmonic distortion (thd) and the vector trajectory of park under various itscf cases of stator winding was studied in [27]. the current study used fem to model and simulate the healthy and faulty state in several cases, simulating the same dfig but with several nitscf of one stator phase a. a comparison between healthy and faulty stator flux linkages and current of phase a and torque were examined for constant speed. ii. dfig geometry and the fem model dfig is widely used as a principal component in a wind turbine, as shown in figure 1, where both the stator and the rotor are connected to the power grid. wind power (pw) is transformed into mechanical energy by the wind turbine, and dfig converts this mechanical energy into electric energy [1]. fig. 1. typical configuration of a dfig wts. the first step in fem is to create and draw the geometric outlines of the dfig model based on the parameters of a selected device. some of these parameters are listed in table i. table i. dfig rated values and design parameters electrical and dimensional parameters value nominal output power 550 w nominal voltage 220 v given rated speed 1500 rpm number of pole pair 2 number of stator slots 30 number of rotor slots 24 the next step was to assign specific materials and their properties to each region, including copper to conductors and air to air gaps. the next step incorporated phenomena and parameters including current sources, rotor speed, boundary conditions, eddy currents, and magnetic circuit saturation. a finite element mesh was created for each dfig part with a very fine mesh for the air gap to obtain the best results. finally, the simulation parameters such as relative and absolute error, simulation step, and stop time were set. a 3d view of the designed dfig is presented in figure 2. fig. 2. 3d view of the designed dfig. iii. simulation results this section introduces the results from the simulation of normal and faulty cases in phase a of the stator winding. various degrees of itscf in the dfig were simulated to show the effect of the nitscf on the dfig performance. the 2d finite element mesh of the dfig is shown in figure 3. afterward, these results were used to solve the electromagnetic field equation of the dfig. figure 4 compares the flux linkage in the stator phase a for the normal and different numbers of itscf. it was observed that a greater number of short-circuit inter-turn faults increased the error between the normal and fault value, with the flux magnitude for 29 short-circuit faults being the smallest of all cases. figures 5 and 6 demonstrate the effect of the faults in phases a, b, and c in terms of the flux. as can be observed, this effect is small but not negligible. fig. 3. 2d finite element mesh of the dfig fig. 4. flux linkage of the stator phase a in normal and under different nitscf conditions. figure 7 shows the comparison of a faulty-healthy root mean square (rms) ratio of the flux linkage of stator phases for different nitscf. in phase a, where the different defaults are created, the flux linkage rms value decreased for each 0 50 100 150 200 250 300 350 400 450 500 -1 -0.5 0 0.5 1 flux linkages a (wb) t(ms) fl u x (w e b ) healthy 4 titf 9 titf 19 titf 29 titf 102 104 106 108 110 112 114 -0.5 0 0.5 1 flux linkages a -zoom-(wb) t(ms) fl u x (w e b ) healthy 4 titf 9 titf 19 titf 29 titf engineering, technology & applied science research vol. 12, no. 3, 2022, 8688-8693 8690 www.etasr.com mellah et al.: the effect of stator inter-turn short-circuit fault on dfig performance using fem nitscf increase. this decrease in flux can be explained by the decrease in the number of turns of phase a. fig. 5. flux linkage in stator phase b for normal and various nitscf conditions in phase a. fig. 6. flux linkage in a stator phase c for normal and various nitscf conditions in phase a. fig. 7. comparison of the faulty-healthy rms ratio of stator phases for different nitscf. however, the opposite is noticeable for both healthy phases b and c, where the effective flux binding values increase with each nitscf increase, especially for phase b starting from the case of 9 nitscf. figure 8 shows the stator current in phase a for normal and various nitscf in the stator winding. a shortcircuit would increase the stator current and result in overheating of the winding. this can be detrimental to the machine and decrease its lifetime, and if the current exceeds the maximum short-circuit can result in its destruction. figures 9 and 10 show the effect of nitscf in phase a on current in phases b and c respectively. it can be observed that the effects in phases b and c are important, as the current amplitude in the condition of short-circuit results in system unbalance. figure 11 shows a comparison of the faulty-healthy rms ratio of the stator phases current for different nitscf. the partial shortcircuit of turns in phase a increases rapidly the current rms value for each nitscf rise. moreover, at the same time, the current rms value of the two healthy phases continues to increase with each increase in nitscf, but in a lower order compared to the rms value of the defective phase. figure 12 shows the induced voltage of phase a in healthy and faulty operation. the induced voltage in phase a decreases with each nitscf increment because the total induced voltage is a sum of the induced voltage for each turn. figure 13 shows the induced voltage of phase b in healthy and faulty operation. fig. 8. stator currents of phase a for healthy and various nitscf conditions. fig. 9. stator currents of phase b in healthy and under various nitscf in phase a of the stator. 0 50 100 150 200 250 300 350 400 450 500 -1 -0.5 0 0.5 1 flux linkages b (wb) t(ms) fl u x ( w e b ) 100 102 104 106 108 110 112 114 116 118 120 -1 -0.5 0 0.5 1 flux linkages b-zoom(wb) t(ms) fl u x ( w e b ) healthy 4 titf 9 titf 19 titf 29 titf healthy 4 titf 9 titf 19 titf 29 titf 0 50 100 150 200 250 300 350 400 450 500 -1 -0.5 0 0.5 1 flux linkages c (wb) t(ms) fl u x ( w e b ) healthy 4 titf 9 titf 19 titf 29 titf 100 102 104 106 108 110 112 114 116 118 120 -1 -0.5 0 0.5 1 flux linkages c-zoom(wb) t(ms) fl u x ( w e b ) healthy 4 titf 9 titf 19 titf 29 titf 0 5 10 15 20 25 30 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 nitscf ra ti o o f fa u lt y r m s t o h e a lt h y r m s fa fb fc 0 50 100 150 200 250 300 350 400 450 500 -20 -10 0 10 20 30 stator current (ia) t(ms) ia ( a ) healthy 4 titf 9 titf 19 titf 29 titf 100 105 110 115 120 125 130 -4 -2 0 2 4 stator current (ia)-zoomt(ms) ia ( a ) healthy 4 titf 9 titf 19 titf 29 titf 0 50 100 150 200 250 300 350 400 450 500 -20 -10 0 10 20 stator current (ib) t(ms) ib ( a ) healthy 4 titf 9 titf 19 titf 29 titf 100 105 110 115 120 125 130 -4 -2 0 2 4 stator current (ib)-zoomt(ms) ib ( a ) healthy 4 titf 9 titf 19 titf 29 titf engineering, technology & applied science research vol. 12, no. 3, 2022, 8688-8693 8691 www.etasr.com mellah et al.: the effect of stator inter-turn short-circuit fault on dfig performance using fem fig. 10. stator currents of phase c in healthy and various stator winding fault conditions of phase a. fig. 11. comparison of the faulty-healthy rms ratio of the stator phase currents for various nitscf. fig. 12. stator induced voltage of phase a in healthy and under various stator winding fault conditions. figure 14 displays the induced voltage of phase c in healthy and faulty operation, while figure 15 shows the rotor currents. as can be noted, the rotor currents are not affected by the stator itscf. figure 16 displays the torque curves of the dfig at nominal load in healthy and under various nitscf cases. this figure summarizes the effect of inter-turn faults on dfig torque. as can be observed, the inter-turn faults create an oscillation that increases with increasing nitscf. fig. 13. stator induced voltage of phase b in healthy and various nitscf conditions in phase a of the stator. fig. 14. stator currents of phase c in healthy and various nitscf in phase a of the stator. fig. 15. rotor currents. figure 17 shows the distribution of the magnetic flux density for normal and different stator winding fault conditions in phase a. as can be noted, the magnetic field is concentrated in both the stator and rotor regions and will increase both rotor and stator leakage reactance. the magnetic saturation will also increase in these regions. in the faulty state, asymmetric behavior will occur in the torque induced by the generator due to the change in currents passing through the stator winding. in this case, nitscf increase causes an increase in torque ripple, as can be observed in figure 17. 0 50 100 150 200 250 300 350 400 450 500 -10 -5 0 5 10 stator current (ic) t(ms) ic ( a ) healthy 4 titf 9 titf 19 titf 29 titf 100 105 110 115 120 125 130 -4 -2 0 2 4 stator current (ic)-zoomt(ms) ic ( a ) healthy 4 titf 9 titf 19 titf 29 titf 0 5 10 15 20 25 30 0 1 2 3 4 5 6 nitscf ra ti o o f fa u lt y r m s t o h e a lt h y r m s ia ib ic 0 100 200 300 400 500 -200 -150 -100 -50 0 50 100 150 200 induced voltage a time [ms] in d u c e d v o lt a g e a [ v ] healthy nitscf4 nitscf9 nitscf19 nitscf29 0 100 200 300 400 500 -300 -200 -100 0 100 200 300 induced voltage b time [ms] in d u c e d v o lt g e [ v ] healthy nitscf4 nitscf9 nitscf19 nitscf29 0 100 200 300 400 500 -300 -200 -100 0 100 200 300 induced voltage c time [ms] in d v o lt [ v ] healthy nitscf4 nitscf9 nitscf19 nitscf29 0 100 200 300 400 500 -10 -5 0 5 10 rotor currents time [ms] c u rr e n t a cur u cur v cur w engineering, technology & applied science research vol. 12, no. 3, 2022, 8688-8693 8692 www.etasr.com mellah et al.: the effect of stator inter-turn short-circuit fault on dfig performance using fem fig. 16. torque in healthy and various stator winding fault conditions. (a) (b) (c) (d) (e) fig. 17. the magnetic field for healthy and faulty dfig on different cases of inter-turn short-circuited numbers: (a) 29 inter-turn faults, (b) 19 inter-turn faults, (c) 9 inter-turn faults, (d) 4 inter-turn faults, (e) healthy. iv. conclusion fem is a numerical method that allows the analysis of complex and non-linear systems and is frequently used for modeling and simulating electrical machines. this study used a fem model to simulate and obtain a comparative analysis between the normal and several cases of itscf for one stator phase of dfig. a comparison of stator flux, currents, induced voltage, and torque between normal and fault conditions was presented at a constant speed. itscf in the stator winding causes a substantial increase in branch current and a small increase in currents of b and c stator phases. itscf in phase a of the stator winding causes a decrease in flux in this phase and a smaller decrease in the other two phases. moreover, itscf creates oscillations in the torque that increase with increasing nitscf. an increasing number of inter-turn short-circuits causes dfig characteristics to deviate further from normal. this study provides insight into the effects of itscf and can be exploited to allow the development of reliable fault detection systems and improve the quality of the electrical power injected into the power grid by wts. acknowledgment the authors express their gratitude and acknowledge the financial support received from the university of setif-1 in algeria for the prfu research project under grant a01 l07 un1901 2019 0002. references [1] h. mellah and k. e. hemsas, "design and simulation analysis of outer stator inner rotor dfig by 2d and 3d finite element analysis," international journal of electrical engineering and technology, vol. 3, no. 2, pp. 457–470, sep. 2012. 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[27] y. chen et al., "fem simulation and analysis on stator winding interturn fault in dfig," in 2015 ieee 11th international conference on the properties and applications of dielectric materials (icpadm), sydney, nsw, australia, jul. 2015, pp. 244–247, https://doi.org/10.1109/ icpadm.2015.7295254. engineering, technology & applied science research vol. 8, no. 2, 2018, 2680-2684 2680 www.etasr.com abdullah: formulation of low peclet number based grid expansion factor for the solution … formulation of low peclet number based grid expansion factor for the solution of the convection-diffusion equation aslam abdullah department of aeronautical engineering universiti tun hussein onn malaysia batu pahat, malaysia aslam@uthm.edu.my abstract—convection-diffusion problems, due to its fundamental nature, are found in various science and engineering applications. in this research, the importance of the relationship between grid structure and flow parameters in such problems is emphasized. in particular, we propose a systematic technique in the selection of the grid expansion factor based on its logarithmic relationship with low peclet number. such linear mathematical connection between the two non-dimensional parameters serves as a guideline for more structured decision-making and improves the heuristic process in the determination of the computational domain grid for the numerical solution of convection-diffusion equations especially in the prediction of the concentration of the scalar. results confirm the effectiveness of the new approach. keywords-convection-diffusion equations; finite difference method; non-uniform grid; grid-expansion factor; thomas algorithm i. introduction in cartesian coordinates and tensor notation following the einstein convention, the generic conservation equation in the partial differential form is ( ) + − − = 0  where is the density, is the conserved property, are velocity components of the fluid in the axes directions at the point ( , , ) at time , is the diffusivity of , and is the source or sink of . navier-stokes equations, which have special features of mass and momentum conservations, are extensions of this equation. the convection-diffusion equation (cde) takes the simplified form of (1)  ( ) − = 0  where zero source/sink is assumed. the first term in (2) is called the substantial derivative  ( ) = ( ) +   the substantial derivative ( ) is physically interpreted as the time rate of change in ( ) following a moving fluid element. the first and second terms on the rhs of (3) are called the local derivative ( ) (i.e. the physical change in ( ) with time at a fixed position), and the convective derivative (i.e. the physical change in ( ) with time due to the mass transfer and change in its properties from one spatial position to another), respectively. substituting (3) into (2) we have  ( ) + − = 0  in case of fluids at rest, or of small velocity ( ≈ 0), or large diffusivity , as well as solids, (4) is further simplified into  ( ) − = 0, representing the pure diffusion process where the local derivative ( ) is balanced by the diffusive derivative . in this paper, we consider the steady one-dimensional convection-diffusion problem where (4) reduces to  ( ) − ( ) = 0,  involving the scalar whose concentration is denoted by . such scalar is carried along with the moving fluid element (convection) and spreads due to diffusion. given appropriate boundary conditions, it can be shown that at relatively high velocity , or low diffusivity , the scalar concentration initially grows slowly in space and then suddenly rises over a defined distance. the sudden growth of not only provides a severe test of the discretization method, but also in the selection of compatible grid structure over the computation domain. note that the solution of (5) is linear in space when is negligible. we investigate the relationship between the flow parameter of interest (i.e. the peclet number ) in cde and the expansion factor based grid structure in finite difference engineering, technology & applied science research vol. 8, no. 2, 2018, 2680-2684 2681 www.etasr.com abdullah: formulation of low peclet number based grid expansion factor for the solution … numerical scheme, and formulate the mathematical relationship between and which is necessary in achieving numerical accuracy in the solution of the equation, thus unify the deduction of heuristic selections of grid expansion factor for solving the contaminated fluids problem that leads to less precomputation time. note that the relatively smaller grid expansion factor does not unconditionally lead to higher numerical accuracy. ii. convection diffusion problems various numerical methods for solving cde are by now well formulated and many useful schemes can be found such as finite differences, finite elements, spectral procedures, and the method of lines [1-12]. for instance, [1] presented a comparative study between the two most popular lattice boltzmann (lb) models for cde (i.e. those in two dimensions with five and nine discrete lattice velocities, respectively). other variants include multiple-relaxation-time lb model for the axisymmetric, as well as isotropic and anisotropic diffusion processes whose both applicability and accuracies have been investigated by [2] and [3] respectively. for the latter case, [4] proposed a finite-difference lb model for nonlinear equations. in the problem where no scalar or flux jump exists, [5] introduced a numerical scheme for dealing with curved interfaces with second-order spatial accuracy in conjunction with the lb method. authors in [6] summarized well-known a priori error estimates for the discontinuous galerkin approximation which carry over to the subspace of the discontinuous piecewise-quadratic space, while authors in [7] proposed the approximation of high order alternating evolution. both [8] and [9] considered compact difference scheme for solving cde. authors in [8] claimed that the fourth-order scheme requires only 15 grid points, while authors in [9] successfully proved that it is computationally more efficient than the standard second-order central difference scheme. recent methods include those that solve nonlinear fractional cde, as homotopy analysis transform and homotopy perturbation sumudu transform methods whose reliability and efficiency were clearly demonstrated in [10], and that based on the operational matrices of shifted jacobi polynomials of high accuracy [11]. author in [12] introduced a schwarz waveform relaxation algorithm for the cde that converges without overlap of the subdomains. the choice of suitable computational grid to discretize the governing partial differential equations (e.g. by means of polynomial fitting, taylor series expansion and compact scheme to obtain approximations to the derivatives of the variables with respect to the coordinates) is necessary at the onset of numerical modeling of the convection-diffusion problems as in [1-17]. it is worth noting that the variable values at locations other than the defined grid nodes can also be determined by interpolation. another important aspect is the method to solve the discretized algebraic equations. the solution is obtained via either direct [18-20] or iterative [21-24] methods. in this paper, the steady one-dimensional cde is discretized by finite difference techniques on non-uniform grids with a defined number of nodes, and the solutions are obtained by using thomas’ algorithm (i.e. direct method). iii. discretization and solution the starting point is the cde in differential form as given by (5). defining the boundary conditions as  (0) = 0,(1) = 1  here we define the peclet number as  =  the influence of the peclet number on the diffusivity coefficient can be found in [25]. the profiles for different ranges of are illustrated in figure 1. fig. 1. boundary conditions and solution profiles as a function of the peclet number. the corresponding solution domain is covered by a grid. we define the independent variables whose domain is discretized. the interval = 0, ( − 1) is subdivided into ( − 1)/ℎ subintervals where and ℎ are odd and even integers, respectively. the nodes are defined by  = + ∆  where 1 ≤ ≤ ( − 1) , ∈ ℤ , and is the grid expansion factor. clearly ∑ ∆ = ( − 1) . the grid is shown in figure 2. fig. 2. computational molecules. at each node, the governing equation is approximated by replacing the partial derivatives with nodal values. the result is an algebraic cde per node, in which the variables at that and immediate nodes appear as unknown. the equation system of is expressed by  + ∑ =   where p signifies the nodes at which the equations are assigned and index runs over the immediate nodes. the corresponding matrix in (7) has non-zero terms only on its main diagonal (represented by ) and the diagonals immediately above and below it (represented by and , engineering, technology & applied science research vol. 8, no. 2, 2018, 2680-2684 2682 www.etasr.com abdullah: formulation of low peclet number based grid expansion factor for the solution … respectively). the matrix elements are stored as three × array. using the three-point computational molecules, (7) becomes  + + =   since the convection-diffusion differential equation is linear, then the approximation contains only linear terms, and the numerical solution will not require linearization. the central difference scheme (cds) is used to discretize the diffusion term, both for the outer derivative  − ( ) ≈ ( ) ( )( )   and the inner derivative  ( ) ≈−( ) ≈   as well as the convection term  − ( ) ≈   the contributions of the diffusion and convection terms to the coefficients of the algebraic equation (8) are therefore; = + = − − 2( − )( − ) = + = − − − 2( − )( − ) = + = − +  tridiagonal matrix algorithm is applied for solving linear system of the algebraic equation (8). we set  = 1.0, = 1.0, = 11.  iv. sequences of the peclet numbers and the grid expansion factors the range of low peclet numbers is 0,100 . the mathematical relationship between and grid expansion factors is represented by a set of ordered pairs , , =1,2, … , n. we define a sequence of by  , = ⁄ ,= ⁄ ,= ⁄ ,   . . . = ⁄ , where the constants , ∈ ℤ . next, defining a sequence of by  , = + , = + , = + ,   .  .  . = + , where the constants , ∈ ℤ . let w and x be the domain and the target of , respectively, where the function from w to x is a collection of ordered pairs of the form ( , ). note that and are in w and x, respectively. the following conditions need to be satisfied by the collection: condition a for each in w, there is an element in x such that ( , ) is one of the ordered pairs. in other words, each element in the domain of has a value ( ) under . condition b if ( , ) and ( , ) are both among the ordered pairs that make up the function, then = . this means that every element of the domain has at most one value under . the function is therefore a mechanism that assigns to each element of the domain a unique element ( ) of the target. we write = ( ), indicating that the ordered pair ( , ) is in the collection of ordered pairs which define the function . thus the set { ( ): is a real number in w} of values of is the image of . let = 1, = 6, = 100, = 0.5, = 2 and = 0.1  such that the sequence in (13) and (14) become 100, 50, 25, 12.5, 6.25, 3.125; and 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 respectively. proposition a the sequences’ elements in (13) and (14), whose boundary values and independent variables are given in (15), form the ordered pairs (pe, r ) which satisfy condition a and b such that; ( , ), ( , ), … . . , ( , )= (100, 0.5), (50, 0.6), (25, 0.7),(12.5,0.8),(6.25, 0.9), (3.125, 1.0)  proposition b if 0 ≤ ≤ 3.125, then the ordered pair ( , ) = ( , 1). engineering, technology & applied science research vol. 8, no. 2, 2018, 2680-2684 2683 www.etasr.com abdullah: formulation of low peclet number based grid expansion factor for the solution … v. results of calculations the boundary conditions and other parameter settings for cde (i.e. equation in (5)) are given in (6), (12), (13), and (15). the concentration profiles which are numerically calculated for of interest are plotted in figure 3, and show good agreement with the exact solutions. this proves proposition a. the results vary exponentially in x-direction, and the area under the curve represented by the integral (x) x is inversely proportional to . note that since r = 1.0 matches pe = 3.125, then r = 1.0 is appropriate for 0≤ pe ≤ 3.125 where φ profile is close to linearity with respect to x . the uniform grid is therefore sufficient for the correct prediction of pe within the range. proposition b is thus proven. fig. 3. concentration profiles in this numerical calculation of a low peclet number convection-diffusion flow, it is found that the expansion factor is inversely proportional to the logarithm of as shown in figure 4. fig. 4. grid expansion factor as a function of logarithm of the peclet number theorem let 0 ≤ pe ≤ 100, the grid expansion factor r for solving the convection-diffusion equation in (5), with the flow conditions in (6) and (12), is expressed as a linear function of lg pe; r = m lg pe + b, for 3.125 ≤ pe ≤ 100, and as a constant; r = 1 for 0 ≤ pe ≤ 3.125 , where m and b are curve slope and a constant, respectively. vi. final remarks a new technique in the determination of grid expansion factor which represents a quantitative guideline for the numerical solution of the convection-diffusion equations is proposed. the understanding on the influence of the peclet number on the grid expansion factor formes a basis for a more effective approach in the selection of grid type for the computational procedure. the key aspect in this research is the formulation of the special function as a collection of ordered pairs of the 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state parameters for road construction of mswi bottom ash a study of state parameters for road construction of mswi bottom ash thi kieu vinh nguyen faculty of construction vinh university vinh city, vietnam kieuvinhkxd@vinhuni.edu.vn thi thuy huong doan faculty of construction vinh university vinh city, vietnam doanhuongkxd@vinhuni.edu.vn thi hao cao faculty of construction vinh university vinh city, vietnam caohaokxd@gmail.com hong son pham faculty of construction vinh university vinh city, vietnam hongsonkxd@vinhuni.edu.vn abstract-the current work tries to valorize the bottom ash from municipal solid waste incineration (mswi). the bottom ash from waste incineration consists of atypical granular materials. they are industrial by-products resulting from the incineration of domestic waste and the way of the considered valorization is road gravel. in this paper, we present the state parameters of bottom ash taken from a recycling company in the north of france. these features can help us evaluate our bottom ash according to the technical guide of realization of embankments and subgrades. keywords-bottom ash; compaction characteristics; valorization; incineration; road gravel i. introduction municipal solid waste management technologies include landfilling, recycling/recovery, and incineration. in many countries such as france, sweden, denmark, and taiwan, municipal solid waste incineration (mswi) for energy recovery represents the most common waste management technology [1]. the incineration reduces the mass and volume of the solid waste dramatically, thus the requirement for landfilling is decreased [2-7]. however, there is still a considerable amount of solid incineration residue, generated after the combustion, typically bottom ash, fly ash, boiler ash, etc. of which bottom ash accounts for about 80% [8]. in the past, mswi bottom ash was mostly treated by sanitary landfilling. possibilities other than landfilling have been sought since mswi started, and reutilization of incinerator bottom ash has already been considered many years ago. in civil engineering, the road field consumes a significant quantity of aggregates [9]. however, the aggregate reserves are not always exploitable for various reasons: they are often inaccessible, they must be integrated into an urban area, in classified or protected sites, and they have too expensive exploitation and risks of environmental impact. in this context, the valorization of the bottom ash in road field is an interesting alternative. bottom ash is mainly used in civil engineering for constructing embankments, road layers, and parking areas [9, 10]. in france, about 3 million tons of bottom ash are produced annually [11]. the use of bottom ash began during the late '50s. the expansion of its use throughout the country occurred in the late '80s-'90s [12]. this article presents the state parameters by particle size distribution, moisture content, absolute density, proctor compaction and bearing capacity index tests. these tests results are evaluated according to the technical guide of realization of embankments and subgrades. ii. the material the mswi bottom ash used in this study originated from the platform of recycling of the préfernord company located in fretin, france. préfernord recovers "slag" resulting from the combustion of 5 incineration plants. to calibrate the materials, pre-treatment of this bottom ash like sifting, removal of ferrous, and non-ferrous elements, was carried out on site. after, the bottom ash was left to mature for 3 months (figure 1). the particle sizes range from 0 to 20mm and approache the size range of natural aggregates which are usually used in the road field. fig. 1. bottom ash. corresponding author: n thi hao cao engineering, technology & applied science research vol. 11, no. 5, 2021, 7624-7627 7625 www.etasr.com nguyen et al.: a study of state parameters for road construction of mswi bottom ash iii. the experimental method the particle size distribution was obtained by sieving at 80µm of diameter three samples that were taken after quartering and washing. moisture content, absolute density and compaction characteristics are the state parameters of bottom ash. the moisture content is equal to the ratio of the mass of water contained in the sample and the dry mass of the sample and is expressed in %. the samples were dried in an oven for 3 days at a temperature of 105oc. the moisture content corresponds to the natural moisture content of the collected bottom ash. the absolute density of bottom ash was determined by using a helium pycnometer of accupyc 1330 type. this test is to measure the volume of solid grains from the change of helium pressure by applying the perfect gas law: pv = nrt. by knowing the mass of the sample, the absolute density is determined by the ratio between the mass of the solid grain and volume. the measurement was carried out on ground and dried bottom ash. the compaction is the densification of the soil by applying pressure to it. it contributes in particular to translate or eliminate compaction risk, increase the resistance of soil and slope stability, improve the bearing capacity of road, limit unwanted volume changes, for example, by the action of frost, swelling, or shrinkage [13]. the compaction capacity of the material is assessed through the normal proctor and the modified proctor tests. both trials are identical in principle, apart from the difference of the parameters defining the applied compaction energy. the principle of the test is to compact the material at varying moisture content and process energy. for every moisture content, wet and dry masses were determined and compaction characteristics (dry density and optimum moisture content) were determined. the bearing capacity index is the quantity used to assess the capacity of a material to bear directly on its surface the movement of construction equipment. in conjunction with modified proctor testing, punching action on compacted specimens was performed to estimate the bearing capacity index. iv. results a. particle size distribution the results of the particle size distribution presented in figure 2 show that the bottom ash is characterized by a spread out size distribution (coefficient of uniformity cu = 35.5) along with the too many coarse elements which generate much vacuum (coefficient of curvature cc = 2,3). the cu and cc are defined by: 2 30 10 60 u d c d * d = (1) 60 10 c d c d = (2) where dx is the diameter of particles for x% of cumulative passing. table i represents the useful parameters for the classification of the acquired bottom ash. the tested bottom ash is a granular material with continued grain size distribution and low proportions of non-plastic fine (< 63µm,) and coarse (> 20mm) fractions. therefore, this may be easily compacted to obtain a higher resistance. bottom ash could be considered a well-graded material. the obtained remarks are similar to those obtained by [14, 15]. fig. 2. particle size distribution by sieving. table i. particle size necessary for classification dmax 20mm passing to 80µm 6.3% passing to 2mm 33.2% b. moisture content table ii represents the moisture content of the studied bottom ash. the main cause of this high moisture content is the influence of rain before samples were taken from storage. table ii. moisture content values wet mass (g) dry mass (g) moisture content (%) sample 1 643 542 18.6 sample 2 697 602 15.8 sample 3 810 675 20 average 18.1 c. absolute density the obtained value of the absolute density of the studied bottom ash is about 2.70t/m3 (table iii). this value is similar to that of quartz-based sand. the obtained density lies in the range of values measured by [16, 17]. this value classifies bottom ash as an aggregate that is lighter than natural ones like sand and gravel. the density is an added benefit that may reduce settlement in use, due to the lower normal stresses caused by the self-weight [18]. table iii. absolute density sample 1 sample 2 sample 3 average absolute density (g/cm3) 2.70 2.70 2.69 2.70 d. proctor compaction figures 3 and 4 show the normal and modified proctor compaction curves. table iv shows the obtained characteristics with optimal normal proctor (opn) and optimal modified 0 10 20 30 40 50 60 70 80 90 100 0,01 0,1 1 10 100 particle size (mm) p e rc e n ta g e p a s s in g ( % ) engineering, technology & applied science research vol. 11, no. 5, 2021, 7624-7627 7626 www.etasr.com nguyen et al.: a study of state parameters for road construction of mswi bottom ash proctor (opm). the obtained values of compaction characteristics of bottom ash fall within the variability of the field defined by information note of setra on the use of bottom ash in road construction. based on proctor test results, bottom ash may be considered as a highly compactable material, which is desirable for preventing future settlements and for increased strength and stability of the layer. fig. 3. normal proctor compaction curve. fig. 4. modified proctor compaction curve. table iv. compaction characteristics opn opm optimal moisture content (%) 15.0 12.5 optimal dry density (g/cm3) 1.78 1.87 e. bearing capacity index fig. 5. bearing capacity index curve. figure 5 shows the variation of the bearing capacity index with moisture content. according to the recommendations of the french standard (nf p 98 115) [19], to ensure the normal circulation of the machines on a construction site, the desirable values of the bearing capacity index are at least 45 for the base layers and 35 for the foundation layers. this standard also defines the minimum values that must not be less than 35 for the base layers and 25 for the foundation layers. with bearing capacity index of 102 (figure 5), bottom ash can be considered stable. v. conclusions the state parameters of the studied bottom ash were analyzed and presented in this paper. from the analysis, the following conclusions can be drawn: • the bottom ash is characterized by spread out size distribution. bottom ash can be considered a well-graded material. • the main cause of its high moisture content is the influence of rain. • bottom ash is lighter than natural ashes like sand and gravel. the density is an added benefit that may reduce settlement in use, due to the lower normal stresses caused by the self-weight. • the obtained values of compaction characteristics of bottom ash fall within the variability of the field defined by information note of setra on the use of bottom ash in road construction. based on proctor test results, bottom ash may be considered as a highly compactable material, which is desirable in order to prevent future settlements and to increase the strength and the stability of the layer. • with bearing capacity index of 102, bottom ash can be considered stable. references [1] c.-l. lin, m.-c. weng, and c.-h. chang, "effect of incinerator bottomash composition on the mechanical behavior of backfill 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[12] r. badreddine and d. françois, "assessment of the pcdd/f fate from mswi residue used in road construction in france," chemosphere, vol. 74, no. 3, pp. 363–369, jan. 2009, https://doi.org/10.1016/j. chemosphere.2008.09.028. [13] f. bernard and n.-e. abriak, "etude physique, géotechnique et mécanique d’un mâchefer d’incinération d’ordures ménagères," journal of catalytic materials and environment, vol. 1, pp. 9–18, jan. 2003. [14] m. izquierdo, á. lópez-soler, e. v. ramonich, m. barra, and x. querol, "characterisation of bottom ash from municipal solid waste incineration in catalonia," journal of chemical technology & biotechnology, vol. 77, no. 5, pp. 576–583, 2002, https://doi.org/ 10.1002/jctb.605. [15] i. maria, e. vázquez, x. querol, m. barra bizinotto, l. ángel, and p. felicià, "use of bottom ash from municipal solid waste incineration as road material," in international ash utilization symposium, 2001. [16] c. j. lynn, g. s. ghataora, and r. k. dhir obe, "municipal incinerated bottom ash (miba) characteristics and potential for use in road pavements," international journal of pavement research and technology, vol. 10, no. 2, pp. 185–201, mar. 2017, https://doi.org/ 10.1016/j.ijprt.2016.12.003. [17] b. muhunthan, r. taha, and j. said, "geotechnical engineering properties of incinerator ash mixes," journal of the air & waste management association (1995), vol. 54, no. 8, pp. 985–991, aug. 2004, https://doi.org/10.1080/10473289.2004.10470959. [18] m. arm, "variation in deformation properties of processed mswi bottom ash: results from triaxial tests," waste management, vol. 24, no. 10, pp. 1035–1042, jan. 2004, https://doi.org/10.1016/j.wasman. 2004.07.013. [19] m. izquierdo, x. querol, and e. vazquez, "procedural uncertainties of proctor compaction tests applied on mswi bottom ash," journal of hazardous materials, vol. 186, no. 2, pp. 1639–1644, feb. 2011, https://doi.org/10.1016/j.jhazmat.2010.12.045. engineering, technology & applied science research vol. 7, no. 5, 2017, 1940-1945 1940 www.etasr.com oudrane et al.: study and simulation of the density of the incident solar flux on … study and simulation of the density of the incident solar flux on the walls of a building in adrar, algeria a. abdellatif oudrane center university of tissemsilt, tissemsilt, algeria abdellatif.habadat@gmail.com b. aour laboratory of applied biomechanics and biomaterials, department of mechanical engineering, enp oran, algeria ben_aour@yahoo.fr b. zeghmati laboratory of mathematics and physics, university of perpignan via domitia, france zeghmatib@univ-perp.fr x. chesneau laboratory of mathematics and physics, university of perpignan via domitia, france chesneaux@univ-perp.fr h. messaoud research unit in renewable energy in saharan medium adrar, algeria jhamouda@yahoo.fr abstract-in this work, we studied the effect of external climatic conditions on the evolution of the daily solar flux incident on the walls of a building located at adrar region in the south of algeria. this building is designed for heating or air conditioning applications. numerical simulations allowed to compare the variation of the incident solar flux over a full day on the south, east, north and west walls of the building to the values of the solar flux on a horizontal wall (the outer ceiling). the horizontal global solar flux is calculated using a gaussian sinusoidal function. the simulations were carried out in the case of a building located in a desert zone. the results of the numerical simulation showed the effect of the orientation of the building on the evolution of the incident daily solar flux. keywords-solar flux; adrar; heating; simulation; desert zone i. introduction the use of solar energy in sunny countries is an effective tool to compensate the energy lack and has also environmental interest because pollution has become a major problem [1]. knowledge of the solar energy potential at a given site is an important parameter for designers of solar energy systems. the long-term evaluation of the performance of solar energy conversion systems is established using numerical simulation programs. in algeria, the software for dimensioning photovoltaic and thermal installations claim, in most cases, integrated databases to calculate solar flux, based essentially on capderou’s model of the solar atlas of algeria [2]. the optimal dimensioning and the best management of energy systems requires knowledge of meteorological conditions for which extensive studies are carried out in several regions of the world to assess and model the solar potential. the first step is to determine the different astronomical parameters, and more precisely the exact position of the sun during the year. first of all, it is necessary to define the two indispensable concepts in order to locate a place in the world: latitude and longitude [3]. then, it seemed useful to us to study the theoretical modeling of the solar flux which allowed to carry out a comparative study between the different days in the season. the determination of the incident solar flux on the walls for different orientations of a building intended for heating in this desert region was studied by analyzing the effect of the climatic conditions of the region on the evolution of the solar flux. results will be presented with a view to good dimensioning and optimum orientation of a building with a solar heating system. in this work, some fundamental notions of astronomy are presented which give information on the radiation received by the ground (diffuse, direct and global). the data required for the establishment of the solar energy balance (direct and diffuse flux calculations) are obtained by considering a sinusoidal variation of the ambient temperature and of the overall flux received on a horizontal wall and by considering the actual data of the maximum solar flux and the minimum and maximum temperatures recorded for the considered months on the adrar site. ii. experimental data currently, in algeria, the measurement of solar radiation data is carried out in an instantaneous way on certain sites in algeria. we chose the site of adrar φ = 27088' n and λ = 0027' w for this study. the choice of this site is based on the fact that adrar is a city very rich in solar energy, given its average sunshine rate which reaches about 9963wh / m2·j [4]. for this reason, we have chosen this region in order to develop a building with a solar installation with maximum efficiency by playing on the climatic conditions. the data of the solar radiation (the mean ambient solar flux, the average ambient temperature) used were provided by the adrar renewable energy research unit in the saharian medium (rerusm). engineering, technology & applied science research vol. 7, no. 5, 2017, 1940-1945 1941 www.etasr.com oudrane et al.: study and simulation of the density of the incident solar flux on … iii. mathematical modeling a. modeling of geometric and atmospheric parameters 1) hour angle the hour angle ω (also denoted ha) of the sun is determined by the diurnal rotation of the earth around its axis. it is the measure of the arc of the solar trajectory between the sun and the meridian plane of the spot. expressed in (°) angle, by the following expression [5, 6]:  1215  tsv (1) where tsv: represents the true solar time expressed in hours. 2) solar declination the declination of the sun δ is the angle that the direction of the sun makes with the equatorial plane of the earth [5, 6]. the declination varies from -23°27' at the winter solstice to +23°27' at the summer solstice and is zero at the equinoxes. its value can be calculated by the formula of cooper (1969) [5, 6]:  36023 , 45 sin 284 365 j            (2) where j is the number of days elapsed since january 1st. 3) height of the sun it is the angle (h) formed by the horizontal plane at the place of observation and the direction of the sun. it is given by the relation [5, 7]: )cos()cos()cos()sin()sin()sin(  h (3) where φ is the latitude of the place in decimal degrees, δ the sun declination in degrees and ω the hour angle of the sun in degrees. from the height (h), we can deduce the hours of sunrise and sunset. we find, by making h = 0 [8]: )()()0cos(  tgtg  (4) the astronomical duration of the day is obtained just as easily by making [8]:  )()(cos 15 2 0  tgtgarcd  (5) 4) azimuth of the sun it is the angle a between the meridian of the place and the vertical plane passing through the sun. knowledge of the azimuth is essential for the calculation of the incidence angle of the rays on a non-horizontal surface. the origin of the azimuths corresponds to the direction of the south in the northern hemisphere. the azimuth angle is positively counted towards the west. the azimuth is related to the hour angle, height and declination by the relationship [9]: )cos( )sin()cos( )sin( h a    (6) 5) time equation to calculate the height of the sun and its azimuth, the time equation is necessary. the solar noon is the moment when the sun is at its maximum height. at this moment, it is positioned in the south or north direction, depending on whether it is in the northern or southern hemisphere. the solar noon differs from the local noon. this difference is called the time equation, it varies as a function of day and longitude and is given by the following expression [10]:                                            365 81 360sin5,1 365 81 360cos 53,7 365 81 720sin87,9 jj j et (7) 6) real solar time it is the solar time local corrected of the time equation. universal astronomical data related to the eccentricity of the orbit of the earth around the sun [10]:              1560 et dehtlgtsv (8) where deh is the time difference, equal to 1h for algeria and tlg: the local time in hours. b. modeling incident solar radiation on any plane for a clear sky 1) angle of incidence in solar applications the question is therefore to calculate the angle between a ray arriving directly from the sun and the normal at any plane. the orientation of the plane is defined by [11] its inclination (β) which is angle that the plane makes with the horizontal and its azimuth (γ). the angle of incidence (θ) is the angle between the direction of the sun and the normal of the plane and is determined by the knowledge of the direction cosines of the incident ray and the normal. in hourly coordinates [11]: )sin()sin()sin()cos()cos( )cos()sin()sin()cos()cos( )cos()cos()cos()cos()sin( )cos()sin()cos()sin()sin()cos(         (9) 2) calculation of radiation for any plane of inclination a) calculation for a clear sky on a horizontal plane the global radiation (rgh) received by a horizontal plane is divided into two terms:  direct radiation (i) where (hirb) (luminance corrected for atmospheric phenomena);  the diffuse radiation (d) where (rdifh) comes from the whole celestial vault. we will therefore have on a horizontal plane [8, 12]: hdhihdhihg  )sin( (10) engineering, technology & applied science research vol. 7, no. 5, 2017, 1940-1945 1942 www.etasr.com oudrane et al.: study and simulation of the density of the incident solar flux on … b) diffuse radiation for a horizontal plane the diffuse radiation for a horizontal surface is given by the expression [7]:           )sin(4511.0 1 120 h exprdifhdh (11)         284 365 360 sin01.0796.0 j (12) where γ is the nebulosity. c) radiation calculation for an inclined plane in practice, the global solar radiation on an inclined plane is expressed by the following form [13, 14]:                 2 )cos(1 .. 2 )cos(1 ..    hghdbrhiig (13) where ρ is the coefficient of reflection of the soil or albedo which varies according to the nature of the soil, and whose mean value is estimated to ρ = 0.25, br is the geometric factor. the ratio between the incidence angle of solar radiation on the inclined wall and the cosine of the zenith angle cos(θ) is: )cos( )cos( z br    (14) and: )cos()cos()cos()sin()sin()cos(  z (15) the algebraic relative error can be defined as the quotient of the absolute error at the real value [14]: measuredg measuredgvaluedg err   (16) where: valuedg is the total solar flux density calculated in (w/m 2) measuredg the total solar flux density measured by the radiometric station in (w/m2) and err the relative error. iv. results and discussion a. validation to test the validity of the models used to estimate the density of the solar flux, investigations were carried out on the global and direct solar flux density for a horizontal plane. the caliber models are used in the typical day of july 17, 2014 in order to validate these estimating models by making a comparison with the measured data. figure 1 shows the calculated densities of the global (a) and direct (b) solar fluxes incident on a horizontal plane compared to those measured by the adrar rerusm radiometric station. (a) density of the total solar flux incident on a horizontal plane 0 2 4 6 8 10 12 14 16 18 20 22 24 0 200 400 600 800 1000 0 200 400 600 800 1000 d en si ty o f so la r fl u x in ( w / m 2 ) duration of day in local time (h) density of calculated direct flux (hor.) density of the measured direct flux (hor.) (b) density of direct incident solar flux on a horizontal plane (c) density of the total flux and direct flux on a horizontal plane fig. 1. calculated and measured solar flux densities for a horizontal surface during the 17th of july 2014 in the region of adrar. engineering, technology & applied science research vol. 7, no. 5, 2017, 1940-1945 1943 www.etasr.com oudrane et al.: study and simulation of the density of the incident solar flux on … it can be observed that there is an acceptable agreement between the theoretical results and the experimental data, particularly in the middle of the day where the maximum relative difference does not exceed 1.8% for the case of the global solar flux and 1.5% for the case of the direct solar flux. moreover, it can be also noted that the two types of flux have the same variation trend. b. meteorological conditions figure 2 shows the evolution of the outside ambient temperature of the city of adrar. the peak of the ambient temperature in june and july is recorded exactly at solar noon, whereas in august is recorded at 11 solar time. this difference between the two peaks is due to the fact that the duration of the day of august is smaller than that of june and july. figures 3 and 4 represent the evolution of the density of the incident solar flux on the sunniest walls (east, west, south and ceiling). during the diurnal period, it initially increases, passes through a maximum towards solar noon (figure 3(a, b)), decreases and finally drops to zero at night. but what differs from one wall to another is the maximum value and the corresponding instant, which vary according to the wall orientation. the flux is maximum in the morning on the east wall (figure 3(a)), at noon on the south wall (figure 4(a)) and in the afternoon on the west wall (figure 3(b)). at midday, the incident solar flux is identical on both walls, but the maximum values differ from one month to another. for the south wall and the ceiling (figure 4(a, b)), the incident solar flux density has a symmetry with respect to noon tsv. fig. 2. evolution of the outside ambient temperature for the typical day of the month (city of adrar). c. evolution of solar flux in july a) evolution of the outside ambient temperature figure 5 shows the evolution of the mean outside air temperature as a function of the hour for the month of july. the outside temperature of the building at solar noon is visibly greater than that of the periods before noon and afternoon and especially greater compared to the night period. this difference is due to the effect of the sun during a day in the summer season which allows the temperature increase to 47° c around noun. figure 6 shows the instantaneous variations of the solar fluxes incident on the walls of the building for different orientations. this temporal evolution of the solar fluxes is calculated during the day of july 17, 2014. it is observed that the evolution of the incident solar flux on the walls is totally linked with the orientation of each wall of the habitable enclosure as well as with the position of the sun during the day. (a) east wall (b) west wall fig. 3. evolution of the incident solar flux density on the east and west walls. b) evolution of the incident solar flux on the walls of the building the solar flux in the walls of the building, during a 24-hour period is shown in figure 6. v. conclusion this work allows the study of evolution of the daily solar fluxes incident on the walls of a habitable enclosure located in adrar according to the variation of the actual climatic conditions of this desert zone and also to the different possible wall orientations. the influence of meteorological conditions engineering, technology & applied science research vol. 7, no. 5, 2017, 1940-1945 1944 www.etasr.com oudrane et al.: study and simulation of the density of the incident solar flux on … such as the external ambient temperature, the solar flux and the wall orientation on the evolution of the total horizontal and incident solar flux were studied and analyzed. the results have mainly shown that the outside temperature has a large variation according to the selected months. moreover, it has been found that the orientation of the structure of the habitable enclosure must also be taken into account in order to optimize the capture of solar radiation. thus, this orientation must be south-facing in an ideal way to have a maximum of 400 w/m2 towards solar noon and a maximum of 650w/m2 before noon for an orientation towards the east and the same value in the afternoon for an orientation towards the west. however, the surrounding obstacles must be taken into account. αcknowledgment we would like to thank the director of the urems of adrar for the supply of climate data and the ministry of higher education and scientific research of algeria for the financing of the finalization project of the thesis of mr. a. oudrane. 0 2 4 6 8 10 12 14 16 18 20 22 24 0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 o ve ra ll s ol ar f lo w i n ( w /m 2 ) duration of the day intsv (h) flow-wall_ south ( june) flow-wall_ south ( july) flow-wall_ south ( august) (a) south wall 0 2 4 6 8 10 12 14 16 18 20 22 24 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 h o ri zo nt al o ve ra ll s o la r fl ow i n (w /m 2 ) duration of the day in tsv (h) flow(gh)-ext._ wall roof ( june) flow(gh)-ext._ wall roof ( july) flow(gh)-ext._ wall roof ( august) (b) external wall roof fig. 4. evolution of the incident solar flux density on the south wall and the ceiling. 0 2 4 6 8 10 12 14 16 18 20 22 24 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 t em p er at u re i n (° c ) duration of day in solar time (h) tamb(july) fig. 5. evolution of the mean outside air temperature as a function of time. 0 2 4 6 8 10 12 14 16 18 20 22 24 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 o ve ra ll s ol ar f lo w i n (w /m 2 ) duration of the day in tsv (h) flow-gh_( july) flow(gi)east( july) flow(gi)north ( july) flow(gi)west ( july) flow(gi)south ( july) fig. 6. incident solar fluxes for different orientations during the 17th of july 2014 in the region of adrar. references [1] m. ghodbane, n. moummi, b. boumeddane, s. largot, h. berkane, “study and numerical simulation of solar system for air heating’’, journal of fundamental and applied sciences, vol. 08, no. 01, pp. 4160, 2016 [2] f. yettou, a. malek, m. haddadi, a. gama “etude comparative de deux modeles de calcul du rayonnement solaire par ciel clair en algerie”, revue des energies renouvelables vol. 12, no. 2, pp. 331–346, 2009 [3] m. hamdani, s. m. a. bekkouce, t. benouaz, m. k. cherier, “etude et modelisation du potentiel solaire adequat pour l’estimation deseclairements incidents a ghardaia”, revue internationale d'heliotechnique, no. 43, pp. 8-13, 2011 [4] m. capderou, atlas solaire de l'algerie, tome 2, 1985 [5] r. j. alain, gisement solaire et transferts energetiques, universite de cergy-pontoise, 2011 [6] aghilas brahimi, etude de performances d’un capteur solaire plan a eau, msc thesis, university of lorraine, 2016 engineering, technology & applied science research vol. 7, no. 5, 2017, 1940-1945 1945 www.etasr.com oudrane et al.: study and simulation of the density of the incident solar flux on … [7] y. el mghouchi, a. el bouardi, z. choulli, t.ajzoul “new model to estimate and evaluate the solar radiation”, international journal of sustainable built environment, vol. 3, no. 2, pp. 225–234, 2014 [8] l. yuehua, j. yingni, c. xinxiao, “evaluation of three models for calculating daily global solar radiation at yushu, tibet”, ieee international conference on consumer electronics, communications and networks (cecnet), pp. 1252-1255, 2011 [9] k. kabidi, experimentation et modelisation du comportement energetique et thermique d’un sechoir solaire sous le climat de la region de rabat, phd thesis, universite mohammed v – agdal, 2014 [10] k. kerkouche, f. cherfa, a. hadj arab s. bouchakour, k. abdeladim, k. bergheul “evaluation de l’irradiation solaire globale sur une surface inclinee selon differents modeles pour le site de bouzareah”, revue des energies renouvelables vol. 16 no. 2, pp. 269-284, 2013 [11] f. chabane, modelisation des paramètres de conversion thermique de l’energie solaire, phd thesis, university of biskra, 2015 [12] a. kaddour, modelisation et simulation d’un concentrateur parabolique solaire a moteur stirling en vue d’un rendement optimal, phd thesis, university of abou bekr belkaid, 2013 [13] a. moummi, n. hamani, n. moummi, z. mokhttari, “estimation du rayonnement solaire par deux approches semi empiriques dans le site de biskra”, 8th international meeting on energetical physics, algeria, 2006 [14] m.r yaiche, s. m. a bekkouche, “estimation du rayonnement solaire global en algerie pour differents types de ciel”, revue des energies renouvelables, vol. 13, no. 4, pp. 683–695, 2010 microsoft word etasr_v12_n4_pp8949-8953 engineering, technology & applied science research vol. 12, no. 4, 2022, 8949-8953 8949 www.etasr.com hamdani et al.: design and implementation of a medical telemonitoring system based on iot design and implementation of a medical telemonitoring system based on iot mostefa hamdani university of tissemsilt tissemsilt, algeria mustapha.hamdani@gmail.com mohammed youcefi saad dahlab bilba 1 university tiaret, algeria profmohamed.univ@gmail.com abdelaziz rabehi university of tissemsilt tissemsilt, algeria rab_ehi@hotmail.fr bachir nail university of tissemsilt tissemsilt, algeria nail_bachir@yahoo.fr abdelmalek douara university of tissemsilt tissemsilt, algeria abdelmalekreal@gmail.com received: 5 may 2022 | revised: 22 may 2022 | accepted: 11 june 2022 abstract-with the advancement of technology, healthcare and monitoring systems face significant issues. internet of things (iot) in healthcare enables real-time health monitoring at a low cost. this paper aims to provide a medical telemonitoring system based on iot for healthcare applications for doctors and paramedical staff. the system is made up of many sensors that can capture electrocardiograms (ecgs) in real-time and measure the temperature of the human body. the designed circuit is implemented and the obtained results are analyzed and discussed. keywords-e-health; internet of things; ecg i. introduction with the rapid development of data and it technology, healthcare monitoring systems are becoming of great concern [1, 2]. the modern human lifestyle among others, leads to many heart disorders such as arrhythmia, coronary occlusion, cardiac arrest, and heart inflammation. the early diagnosis of a heart disease may lead to minimization of deaths [3, 4]. modern technologies such as the iot, artificial intelligence (ai), and robotics systems play a vital role in revolutionizing the health care system [5]. smart health monitoring can be an effective solution to the above challenges as it may takes less time and is more accurate [6, 7]. several solutions based on ecg measurement systems allow to record and process the cardiac signal by placing skin electrodes on chest and limbs [8]. many researchers worked on developing and designing a hardware-based ecg acquisition system [3]. authors in [9] provide a fascinating review of the existing technologies that characterize commercial wireless ecg systems. the purpose of this study is to review the solutions described in the literature, besides commercially available devices and electronic components useful to setup laboratory prototypes. authors in [10] proposed an iot-based patient health monitoring system linked to the cloud talk platform. the proposed system streamlines the traditional workflow by providing all medical checkups, facilities, and tests in one location. authors in [11] present an approach based on the intel galileo development board to gather and upload various data into a database for use by patients and doctors, making the traditional checkup process more convenient. authors in [12] propose an automatic contactless thermometer to replace the traditional temperature measuring techniques and safeguard from human-to-human transmission diseases. the advantage of the proposed model is that it uses gps coordinates and population density values towards identifying the most crowded areas. authors in [13] proposed a system prototype for monitoring the heartbeat rate and body temperature of chronic patients using sensors. the monitored data are sent to a cloud database in real-time. in this paper, we present an interactive virtual interfacebased medical tele-monitoring system for doctors and paramedical staff, which is implemented using virtual interface-based software, labview, and iot. the system aims to contact a hospital emergency room for asking for first aids in case of positive diagnosis. patient path estimation, ecg signal capture, human-body temperature, and hospital alarm management are the four main components of the system. corresponding author: mostefa hamdani engineering, technology & applied science research vol. 12, no. 4, 2022, 8949-8953 8950 www.etasr.com hamdani et al.: design and implementation of a medical telemonitoring system based on iot ii. the ecg acquisition system in this section, we explain the methodology followed to design and simulate the ecg acquisition system. the ecg is the most used non-invasive method for making a preliminary clinical diagnosis of cardiac diseases. it is a method of recording the electrical activity of the heart, which is generated by the heart's cells, during the cardiac cycle (both normal and abnormal) [14, 15]. the electrical activity of the heart is measured because every time the heart beats, an electrical signal flows through it. electrodes are placed on the chest to record the signal. the architecture of the proposed system is shown in figure 1. this system consists of sensors, which interface with an arduino uno r3 module. the module transmits the sensor data to labview. the proposed approach is structured in two main phases: • labview software was used to write the code of the application. the aim of the simulation is to evaluate the operation of the card, and know, beforehand, the quality of the results and develop design guidelines. simulations were conducted on win 10, ni multisim release 12.0.1, arduino ide compiler 1.8.19 and ni labview14. • realization of the prototype and the physical implementation of the proposed system. in this step, we used the following tools to evaluate our algorithm: electrodes to capture the signal from the human heart, passive components (resistor and capacitor), an arduino board, a low frequency generator, an oscilloscope and a computer with i5 processor and 8gb ram. fig. 1. ecg data acquisition system. fig. 2. ecg amplifier, high-and low-pass filters. there are three stages in the process of simulation, i.e. preamplification, filtering, and amplification. the analog to digital converter (adc) is a significant data converter system. it is one of the main building blocks of the ecg detection system and health care integrated circuits [16]. figure 2 depicts the ecg amplifier, consisting of high-and low-pass filters. we used the multisim software to generate the circuit simulation results. multisim is an industry standard spice simulation and circuit design software for analog, digital, and power electronics in education and research [17]. figure 3 describes the framework used to develop and implement the proposed approach. figure 4 represents the simulation model of the proposed system circuit in ni multisim before assembling on a printed circuit board (pcb). fig. 3. stages of the acquisition card. fig. 4. circuit diagram of the system. a. pre–amplification the pre-amplification stage raises the amplitude of the sensed ecg signal from about 0.02mv to about 5mv. the first stage consists of pre-processing the signal using a low pass filter to reduce noise. the pre-amplifier plays an important role in the circuit design. it not only extracts the useful eeg signal, but also reduces the interference signals to the lowest level. pre-amplification is done using the well-known ad620 amplifier. the ad620 is highly suited for medical applications, such as ecg and non-invasive blood pressure monitors, due to its low noise, low cost, low input bias current, and low power [18]. three different sinusoidal signals are generated: • a signal with 50mvpp amplitude and a frequency of 20hz (main signal). • a signal with variable amplitude and a frequency of 100hz which is supposed as noise and reacts on the main signal. • a signal with variable amplitude and a frequency of 150mhz, considered as noise. engineering, technology & applied science research vol. 12, no. 4, 2022, 8949-8953 8951 www.etasr.com hamdani et al.: design and implementation of a medical telemonitoring system based on iot the three signals were introduced to the ad620 through pin 3. then, a balanced 9v supply was applied to the ad620. a resistance r1 of 470ω was added to have a gain equal to 106 according to: g��� = ��.� ω �� + 1 (1) figure 5 shows the circuit design. figure 6 illustrates the pre-amplification block results, the results show an informative signal with a main frequency of 20hz, to which noise signals of 100hz and 150mhz is superimposed. fig. 5. pre-amplification circuit. fig. 6. pre-amplification block results. ecg signals are frequently affected by various sources of noise, and baseline drifting is typical. signal conditioning is unquestionably required to permit automated ecg analysis. a filtering approach is employed to provide baseline correction and noise suppression with minimal signal distortion. b. filtering generally, the ecg signal can be corrupted by different types of noise and artifacts that can occur within the frequency band of interest and have comparable properties to the ecg signal itself. we must process the raw ecg data in order to obtain valuable information from the noisy ecg signals. filters are used to remove many forms of noise, including baseline wander, 60hz power line interference, muscle noise, and motion artifacts. in this section, we use two filters to eliminate the frequencies considered as noise. two passive filters are placed in series, as shown in figure 7. the cutoff frequency fc of the filter is calculated according to: fc = � ���� (2) the two filters used for this block are: • first, a low-pass filter around the cutoff frequency of fc=36hz to eliminate the 50hz noise. • second, a high-pass filter around the cutoff frequency fc=0.15hz. we cannot eliminate frequencies higher than 1hz since sometimes we find cases where the ecg frequency takes a value of 2 or 3hz. so, it is not recommended to eliminate these frequencies since we risk losing information. figure 8 describes the result obtained at the output of the filter. it can be seen that the noise has been largely attenuated by this filter, especially the ripples, which have frequencies of 100hz and 150mhz. fig. 7. pre-amplification and filters. fig. 8. filtering result. c. amplification this section is devoted to the design of an instrumentation amplifier of low frequency biomedical signals. an ecg signal is weak, with a magnitude of about 1mv, so a high gain amplifier is required to acquire this small signal. the amplification gain remains adjustable and also the reference value. practically, to vary the gain and the reference voltage we use two 10kω potentiometers, one placed in pins 1 and 8 to adjust the gain and the other placed on reference pin 5. the block diagram and related voltage gains of the circuit for engineering, technology & applied science research vol. 12, no. 4, 2022, 8949-8953 8952 www.etasr.com hamdani et al.: design and implementation of a medical telemonitoring system based on iot different values of resistances are depicted in figure 9. we obtain an amplified signal at 6.13vpp and totally detached from the noise as shown in figure 10. fig. 9. diagram of ecg signal detecting, amplification, and filtering. fig. 10. amplified and filtered output signal. fig. 11. arduino hardware board. d. analog to digital conversion an adc is interfaced to an arduino uno via serial peripheral interface. figure 11 shows the breadboard allowing to convert signals sent from the ecg sensor to the arduino through the adc. iii. temperature detection system lm35 is a temperature measuring device having an analog output voltage proportional to the temperature. in general, normal body temperature is 36.1°c or above. pin 1 of the lm35 is linked to the voltage pin (vcc) of the arduino uno board in the circuit diagram to receive a 5v supply voltage. both the pulse sensor and the arduino board's ground pin (gnd) are interconnected. the arduino's output pin (vout) is linked to the analog pin (a0) and gives a voltage output, which is then converted to temperature. iv. labview interface the adc converts the analog output of the instrumentation amplifier to a digital signal. we propose a graphical user interface (gui) in labview to display the ecg wave forms and to record the ecg data over a period of time. the ecg output from the circuit will be the input data in the labview interface where the data can be processed, stored, and displayed. figure 12 shows the block diagram of the ecg system using system on chip. fig. 12. block diagram made with the labview. figure 13 shows the result obtained by our card from a test on a teenager. it clearly shows that the ecg signal obtained is correct and totally detached from the noise source. it is noted that the treatment and diagnosis of this signal remains the work of specialist cardiologists. fig. 13. ecg signal after filtering. in the patient table system, the collected data are saved and updated in real time. ecg signals are sent from the patient's mobile device to the hospital's remote database server. the following information appears on each patient's table: • patient id • temperature engineering, technology & applied science research vol. 12, no. 4, 2022, 8949-8953 8953 www.etasr.com hamdani et al.: design and implementation of a medical telemonitoring system based on iot • ecg data acquisition • patient location • predicted states v. conclusion the current paper presents the design and implementation of a medical telemonitoring system based on iot and its integration with labview for recording the ecg data and measuring body temperature. labview was used to acquire the ecg signal samples from the data acquisition card, to save the data, and to display information about the patient health. references [1] m. hamdani and y. aklouf, "enhanced active vm load balancing algorithm using fuzzy logic and k-means clustering," multiagent and grid systems, vol. 17, no. 1, pp. 59–82, jan. 2021, https://doi.org/ 10.3233/mgs-210343. [2] m. hamdani, y. aklouf, and h. a. bouarara, "improved fuzzy loadbalancing algorithm for cloud computing system," in proceedings of the 9th international conference on information systems and technologies, new york, ny, usa, nov. 2019, https://doi.org/10.1145/ 3361570.3361589. [3] j. datta, s. saha, s. chowdhury, and a. acharya, "development of an ecg signal acquisition module," in 2017 devices for integrated circuit (devic), kalyani, india, mar. 2017, pp. 419–421, https://doi.org/ 10.1109/devic.2017.8073983. [4] a. s. almejrad, "the development of an ethernet-based portable embedded isolated ecg system," engineering, technology & applied science research, vol. 11, no. 3, pp. 7125–7129, jun. 2021, https://doi.org/10.48084/etasr.4128. [5] r. panwar and b. mallick, "a comparative study of load balancing algorithms in cloud computing," international journal of computer applications, vol. 117, no. 24, pp. 33–37, may 2015, https://doi.org/ 10.5120/20890-3669. 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[9] g. cosoli, s. spinsante, f. scardulla, l. d’acquisto, and l. scalise, "wireless ecg and cardiac monitoring systems: state of the art, available commercial devices and useful electronic components," measurement, vol. 177, jun. 2021, art. no. 109243, https://doi.org/10.1016/j.measurement.2021.109243. [10] s. gera, m. mridul, and s. sharma, "iot based automated health care monitoring system for smart city," in 5th international conference on computing methodologies and communication (iccmc), erode, india, apr. 2021, pp. 364–368, https://doi.org/10.1109/iccmc51019.2021. 9418487. [11] p. gupta, d. agrawal, j. chhabra, and p. k. dhir, "iot based smart healthcare kit," in 2016 international conference on computational techniques in information and communication technologies (icctict), new delhi, india, mar. 2016, pp. 237–242, https://doi.org/ 10.1109/icctict.2016.7514585. [12] n. k. al-shammari, h. b. almansour, and m. b. syed, "development of an automatic contactless thermometer alert system based on gps and population density," engineering, technology & applied science research, vol. 11, no. 2, pp. 7006–7010, apr. 2021, https://doi.org/ 10.48084/etasr.4103. [13] j. o. obira and r. sinde, "development of a sensor-based heartbeat and body temperature monitoring system for remote chronic patients," engineering, technology & applied science research, vol. 11, no. 4, pp. 7375–7380, aug. 2021, https://doi.org/10.48084/ etasr.4216. [14] n. tasneem and i. mahbub, "dry electrode based low-power ecg acquisition system with adaptive motion artifacts cancellation," in 2020 ieee 63rd international midwest symposium on circuits and systems (mwscas), springfield, ma, usa, dec. 2020, pp. 913–916, https://doi.org/10.1109/mwscas48704.2020.9184681. [15] k. h. hii, v. narayanamurthy, and f. samsuri, "ecg noise reduction with the use of the ant lion optimizer algorithm," engineering, technology & applied science research, vol. 9, no. 4, pp. 4525–4529, aug. 2019, https://doi.org/10.48084/etasr.2766. [16] t. b. nazzal, s. a. mahmoud, and m. o. shaker, "a 200-nw 7.6-enob 10-ks/s sar adc in 90-nm cmos for portable biomedical applications," microelectronics journal, vol. 56, pp. 81–96, oct. 2016, https://doi.org/10.1016/j.mejo.2016.08.004. [17] f. asadi, "simulation of electric circuits with multisimtm," in essential circuit analysis using ni multisim tm and matlab®, f. asadi, ed. cham: springer international publishing, 2022, pp. 91–428, https://doi.org/10.1007/978-3-030-89850-2_2. [18] "ad620 low-power instrumentation amplifier," components101. https://components101.com/ics/ad620-instrumentation-amplifier. microsoft word etasr_v12_n3_pp8559-8566 engineering, technology & applied science research vol. 12, no. 3, 2022, 8559-8566 8559 www.etasr.com said et al.: modeling and simulation of a uv water treatment system fed by a gpv source using … modeling and simulation of a uv water treatment system fed by a gpv source using the bond graph approach riahi said ur-laper, faculty of sciences of tunis university of tunis el manar tunis, tunisia riahi.said@fst.utm.tn naoufel zitouni ur-laper, faculty of sciences of tunis university of tunis el manar tunis, tunisia naoufel_zitouni@yahoo.fr viorel minzu control and electrical engineering department dunarea de jos university galati, romania viorel.minzu@ugal.ro abdelkader mami ur-laper, faculty of sciences of tunis university of tunis el manar tunis, tunisia abdelkader.mami@fst.utm received: 15 february 2022 | revised: 4 march 2022 | accepted: 5 march 2022 abstract-this work presents a simulation model for a uv water treatment system, powered by a photovoltaic generator, which relates the current consumed by the lamp to the uv flux and water quality. the overall system also includes electronic converters, electronic ballast (rlc resonant circuit), a uv lamp (uv irradiation source), and a centrifugal pump. to optimize the power transfer from the pv generator to the ballast and the uv lamp, a maximum power point tracking (mppt) device is used. the overall water treatment system presents a complex model due to its hybrid components. the bond graph tool with a multidisciplinary vocation allows precisely, by its graphic nature, using a unified language, to explicitly display the nature of the power exchanges in the system and facilitate its control. this tool is a solution for non-linear systems that guarantees and facilitates their modeling without difficulties. keywords-bondbraph; uv water treatment system; complex model; photovoltaic generator; centrifugal pump; simulation i. introduction several water resources may be untreated and therefore they can be factors of transmission of diseases. the reuse of wastewater after an adequate treatment by uv radiation, presents a very good solution to solve the problems related to water pollution and constitutes a potential water resource. the majority of the existing uv disinfection systems use low pressure mercury arc lamps as a source of uv radiation that generates short waves in the region of 253,7nm [1-3]. the discharge lamp is placed in a reactor and is surrounded by a quartz tube immersed in a chamber in which the fluid is circulated. it is powered by an energy source such as a photovoltaic generator via an electronic ballast composed of an inverter, a transformer and a resonant circuit (rlc) [4, 5]. a centrifugal motor pump as shown in figure 1 ensures the circulation of water between the two tanks. the physicochemical parameters (ph, temperature, etc.), the applied uv dose, the exposure time, as well as the number and type of microorganisms, are factors that can influence the final water quality. many studies have been developed to improve water treatment systems despite their complexity, especially of the uv lamp model [6-8]. the aim of this study was to build a simulation model for all the components of the complex uv water treatment system shown in figure 2. the bond graph approach is a modeling tool that facilitates the links between the different physical domains (mechanical, hydraulic, electrical) that represent the overall system. a photovoltaic (pv) generator model is presented in the first section along with the mppt control in order to adapt the pv source and the load with a simulation result. fig. 1. structure of the overall uv water treatment system powered by a pv panel. corresponding author: abdelkader mami engineering, technology & applied science research vol. 12, no. 3, 2022, 8559-8566 8560 www.etasr.com said et al.: modeling and simulation of a uv water treatment system fed by a gpv source using … fig. 2. representation of the energy exchanges in the system with different physical fields. ii. modeling of the pv source by the bond graph approach a. the pv generator model in order to power uv water disinfection systems with solar energy in a simple and inexhaustible way, we need to use pv generators. pv panels are characterized by the non-linearity of their output which is influenced by environmental factors (temperature and irradiation). the pv model used has two resistors in series and in shunt as shown in the equivalent electrical diagram in figure 3. fig. 3. equivalent electrical circuit of a single diode pv generator. the simplified equation of the pv current is: 0 ( ) exp 1 s pv ph sh s q v i r i i i i n k n t × + × = − − − × × ×           (1) where ipv is the the output current, i0 the diode inverse saturation current, and rs the series resistor. k is the boltzmann's constant, q is the electronic charge, n is the ideal diode factor (1<n<2) for a unique junction, and t is the functioning temperature. the current through the shunt resistor is given by: ( ) /sh pv pv s shi v i r r= + × (2) the photocurrent generated by the cell depends on the ambient temperature (t) and the solar irradiation (g) and is represented by: ( 298) /1000ph sc ii i k t= + ⋅ − ⋅g (3) b. bond graph model of the photovoltaic generator a simplified model that does not take into account the losses was adopted. this model is called mono-diode coupled to a starting capacitor that is placed in parallel with the photovoltaic generator. the added capacitance represents the capacitance of the pn junction and it depends on the voltage vd. fig. 4. electrical diagram of the pv generator with starting capacity. the bond graph model for the equivalent circuit is presented in figure 5. it contains an element of capacitance, and the element noted as rd is the resistance of the diode. it contains the non-linear characteristic. this allowed us to replace the generator by a modulated flux source sf which plays the role of the modulating signal representing the photovoltaic current iph. this model was simulated by the software 20-sim [6, 9-11]. fig. 5. bond graph of the pv model. to simulate the characteristics of the photovoltaic panel i=f(v) and p=f(v) [18-19], we use the bg model shown in figure 5. in this simulation, the receiver is an initially discharged capacitor. the simulation results are represented in figure 6. fig. 6. simulation of the characteristic curves of the pv system. iii. converters used static converters are mainly made up of semiconductor components that work in switching mode (thyristors, power msfiph 0:vpv c:cp r:rd puissance r1 1:ipv engineering, technology & applied science research vol. 12, no. 3, 2022, 8559-8566 8561 www.etasr.com said et al.: modeling and simulation of a uv water treatment system fed by a gpv source using … transistors, etc.). in our uv system, the converters are placed as follows: a first chopper booster is inserted between the uv lamp and the pv generator, a second chopper devolver is inserted between the motor pump and the pv panel, and a single-phase inverter generates a square voltage. a. dynamic boost converter as the name suggests, this type of static converter amplifies the output voltage relative to the input voltage. in electronic structure, a boost chopper generally has a switch controlled on opening and closing (transistor, igbt) and a diode [14, 15]. (a) (b) fig. 7. boost converter: (a) equivalent model, (b) its bond graph model. b. dynamic buck converter the static converter (dc/dc) used, is most frequently used as a devolving converter, its basic schematic is that of figure 8. a buck converter converts a dc voltage into another dc voltage of lower value [11, 16-18]. (a) (b) fig. 8. buck converter: (a) equivalent model, (b) its bond graph model. c. single inverter the resonant circuit (electronic ballast) requires a square voltage, which is obtained with an inverter, which is a static converter that converts electrical energy from dc to ac. it allows obtaining an alternating voltage adjustable in frequency and in rms value, thus using an appropriate control sequence. fig. 9. equivalent electrical diagram of a single-phase inverter. d. bond graph mppt: perturbation and observation algorithm the perturbation and observation (p&o) method is a widely used approach in mppt research, because it is a simple iterative method. it can track the maximum power point (mpp) even during sudden changes in irradiance and temperature [2, 9, 11, 17, 20]. using the p&o algorithm, a link graph mppt model was developed (figures 11-12). fig. 10. bond graph model of a single inverter. fig. 11. adaptation model of an mppt converter with a pv panel by bond graph. fig. 12. simulation of the p&o control algorithm for different illuminations. iv. bond graph modeling of the electronic ballast and the uv lamp the electronic power supply (electronic ballast) of a uv lamp can be broken down into three parts: the dc/ac converter, which is described above, the transformer, and the resonant circuit. a. the resonant circuit (electronic ballast) a discharge lamp needs sufficient voltage to light up. this lamp uses an electronic ballast capable of creating a high frequency voltage and an increase in the voltage value on the uv lamp for a short time. this overvoltage is obtained by a resonant circuit (rlc). the voltage delivered by the dc/ac converter, feeds a transformer to a resonant system formed by a resistor rr in series with an inductance lr and two capacitors cr1 and cr2 (figure 13) the receiver is a discharge lamp (uv) which is compared to an infinite impedance before start-up and to a low value impedance after start-up [4, 5]. the corresponding bong-raph model is shown in figure 14. 1 2 3 4 5 6 7 8se: ve 1 r:rl i: l tf c r:rc r: r load0 engineering, technology & applied science research vol. 12, no. 3, 2022, 8559-8566 8562 www.etasr.com said et al.: modeling and simulation of a uv water treatment system fed by a gpv source using … fig. 13. equivalent electrical diagram of a uv lamp power supply. fig. 14. bond-graph model of the irradiation system. b. the uv lamp the uv water treatment system consists of a high pressure lamp placed vertically in a quartz sheath to be thermally isolated from the water. this lamp is assembled in a closed reactor. the water circulates in thin layers in the vicinity of the lamp because the uv rays are rapidly absorbed by the water. the disinfection efficiency obtained varies between 90% and 99.99%, depending on the duration of exposure of the water to radiation and the characteristics of the water to be treated. certain electrical circuits generated by electronic ballasts are required to start the discharge lamp, to regulate the lamp cycle, and to control the electrical current. fig. 15. schema of the uv reactor. there are several models based on the current-voltage characteristics of the high-frequency discharge when trying to find a function that describes the relationship between current, voltage, and power consumed by the lamp. the uv lamp has a complicated model, it is in conjunction with an electronic ballast as described in (1): ( ) ( ) ( ) ( ) e ballast ballast lamp di t u t r i t l u t dt = + + (1) the universal lamp model is defined by: ( ) ( ) ( ) lamp lamp i t u t g t = (2) the literature describes the conductance of a discharge lamp by a first-order differential equation, named g-model [1, 21, 22], which is presented as follows: 2 2 n n dg a i b g dt = −∑ (3) where the coefficients α2 and bn can be determined experimentally from the voltage-current characteristics or by physical evaluation. the physical evaluation is possible when n is equal to 2 or 3. in this case, the coefficients have a physical meaning: 2 2 2 2 1 ( ) ( ) dg a i b g t b g t dt = − − (4) the determination of the parameters α2, b1, and b2 is done using an identification approach. according to (4), we developed the bond graph model of the uv lamp. figure 16 exhibits the established model of the uv lamp. fig. 16. bond graph model of the uv lamp. v. bond-graph modeling of the hydraulic system the hydraulic system is a very important part of the water treatment system. it consists of a direct current motor connected to a centrifugal pump. a. modeling of the dc motor the water treatment system has a motor pump to draw contaminated water from the inlet tank as shown in figure 17. the motor pump subsystem must be able to control the flow rate of the contaminated water, which will determine the uv exposure time. equation (5) expresses the latter: exposure /t v q= (5) the values v and q are the volume of the reactor and the flow rate of water respectively. the variation of q determines the possibility to control the exposure time and consequently the uv dose received by the water [6, 10, 11, 23]. the dynamics of the engine [5, 10], are described by: a a a a a b di u r i l k w dt = + + (6) engineering, technology & applied science research vol. 12, no. 3, 2022, 8559-8566 8563 www.etasr.com said et al.: modeling and simulation of a uv water treatment system fed by a gpv source using … m m r dw c j fw c dt = + + (7) the dc motor is modeled in bond-graph by inertial elements i:la and resistive elements r:ra, representing respectively the inductance and the resistance of the armature. a gyrator models the transfer of energy from the electrical part to the mechanical part bk ( a be k w= ). the mechanical losses are modeled in bond graph by an inductive element i:j and a resistive element r:f which indicate respectively the coefficients of inertia and viscous friction of the dc machine. the dc motor drives a centrifugal pump characterized by a rotor shaft γ proportional to the square of speed w ( 2 tk wγ = ). figure 18 presents the bond graph model of a dc motor. fig. 17. schematic representation of the location of a dc motor in the uv water treatment system. fig. 18. bond graph model of a dc motor. b. modeling of the centrifugal pump the water disinfection operation consists of water circulating through a uv reactor. once the pump is running, the rotation of the impeller produces pressure and a speed that determines the flow of the fluid in the hydraulic system [5, 10, 14]. the theoretical head he developed by a centrifugal pump is given by: 2 2 2 2 e w r h g = (8) the pressure developed by the wheel is directly proportional to the angular velocity w. the shaft speed is proportional to the flow rate q. the developed pressure and the transmitted torque have the following expressions: 22 2 2 e ep gh wrρρ= = (9) 2 2 2 et q wrρ = (10) the relationship between the pressure supplied by the pump and the rotation speed, can be modeled in bond-graph by a modulated gyrator element, mgy. the latter transforms the mechanical flow (speed) into hydraulic force (pressure). the pressure losses in the pump are due to the friction between the liquid threads and against the walls of the machine: fp mpt f w= (11) this friction is modeled in bond-graph by a resistive element r:fmp and the moment of inertia of the rotating parts of the pump has the following expression: ip pt dw t j dt = (12) this moment of inertia is modeled in bond-graph by an inertial element i:jpt.the pressure losses in the hydraulic circuit are due to the friction of the flow lines against the walls of the machine. they are modeled by a resistive element r:fξd. the height difference between the two tanks is modeled by a negative force source: ese ghδ= − (13) the associated bond graph model of the centrifugal pump is shown in figure 20. fig. 19. synoptic diagram of a centrifugal pump. fig. 20. bond graph model of the centrifugal pump. for a stationary regime (constant speed), the characteristic of the theoretical head of a pure centrifugal pump in vacuum (isolated from the hydraulic network) can be seen in figure 21. engineering, technology & applied science research vol. 12, no. 3, 2022, 8559-8566 8564 www.etasr.com said et al.: modeling and simulation of a uv water treatment system fed by a gpv source using … fig. 21. he (q) simulation characteristic of a centrifugal pump. vi. global model of a water treatment system by bond graph after having modeled the different elements of the water treatment system and simulated the obtained models, we can deduce the global model (bg) by combining the different models obtained, which is presented in figure 22. fig. 22. global model of the global uv water treatment unit vii. simulation results the uv water treatment system consists of a closed cylindrical stainless steel reactor with an annular cross-section, 70cm in length, 6cm in internal diameter and 2l of useful volume. it is equipped with a single low-pressure mercury discharge lamp with the following characteristics: power 70w, nominal current 0.65a, length 400mm, diameter 15mm, placed in the axis of the irradiation room and protected by a clean quartz sleeve. the lamp is powered by an electronic ballast consisting of a single-phase inverter with transistors producing 25-100khz at its output and a resonant circuit to realize the ignition of the lamp. the disinfection system is also equipped with a motor pump for the suction of contaminated water, a pump to draw contaminated water from the inlet tank, a flow control valve to obtain different flow rates, and a filter to improve the transmittance of the contaminated water. the treated water in this system could be recycled through a recirculation circuit that could allow multiple passes through the irradiation chamber. according to the global model simulation, we obtained the following results: figure 23 shows the output voltage of the single-phase inverter, which converts dc voltage to ac voltage to power the ballast and uv lamp, as they require ac voltage. the voltage and current curves of the uv lamp (discharge lamp) are shown in figures 24 and 25 with the following values: the voltage is approximately 150v and the current 1.42a. the parameters of the uv lamp and the electronic ballast are: a2=93.33, b2=582036.5, b1=994.7, r=0.9ω, c=2.8µf, l=0.16ma. figure 26 describes the evolution of the conductivity g of the uv lamp. fig. 23. simulation of the output voltage of the inverter. fig. 24. the voltage of the uv lamp. fig. 25. the current of the uv lamp. fig. 26. the conductivity of the uv lamp. due to the negative impedance of discharge lamps and the complexity of the analysis, it is difficult to obtain models for the discharge lamps due to their negative impedance and the engineering, technology & applied science research vol. 12, no. 3, 2022, 8559-8566 8565 www.etasr.com said et al.: modeling and simulation of a uv water treatment system fed by a gpv source using … complexity of the physical phenomena that occur inside the discharge tube. discharge lamps can be operated at different frequencies with electronic ballasts. these different operating conditions can affect the behavior of the lamp. generally, the non-linear i-v characteristic of the discharge lamps changes with frequency. figure 27 represents the evolution of the nonlinear obtained i-v characteristic after these simulations. fig. 27. i-v characteristic curve of the uv lamp. the simulation of the continuous motor pump was performed using the buck converter. the motor voltage ua is 24v. figure 28 shows the evolution of the induced current, the motor torque, the rotation speed and the water flow. one can see a normal evolution of the four parameters. fig. 28. evolution of the motor pump's parameters. viii. conclusion this paper proposes link graph models for each subsystem of a uv water treatment unit. the different elements were connected to produce a dynamic model, which was used as the basis for building the simulation model. using the 20-sim software, a general simulation model was proposed. the series of simulations performed proved that the models were realistic and produced useful data. the link graph approach facilitates the connections between the different components of the overall model given the complexity of this unit. future work could use this global model to determine the optimal parameters for all subsystems under given circumstances. the performance index could be the quality of water disinfection. references [1] m. tlili, "conductivity polynomial model parameters identification based on particle swarm optimization," journal of control engineering and applied informatics, vol. 15, no. 4, pp. 58–65, dec. 2013. 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[23] k. ouelhazi, a. ben chaabene, a. sellami, and a. hassen, "multivariable model of an ultraviolet water disinfection system," desalination and water treatment, vol. 67, pp. 89–96, 2017. microsoft word etasr_v13_n4_pp11355-11359 engineering, technology & applied science research vol. 13, no. 4, 2023, 11355-11359 11355 www.etasr.com gupta & kumar: buckling behavior of a functionally graded sandwich plate buckling behavior of a functionally graded sandwich plate anil kumar gupta department of civil engineering, national institute of technology patna, india anilguptakeck@gmail.com (corresponding author) ajay kumar department of civil engineering, national institute of technology delhi, india sajaydce@gmail.com received: 16 may 2023 | revised: 27 may 2023 | accepted: 28 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6059 abstract this research focuses on the buckling behavior of a porous functionally graded (fg) sandwich plate using the sinusoidal shear deformation theory and hyperbolic tangent and secant thickness stretching functions with novel displacement fields. the proposed model assumes a different thickness layer system with fgm on the top and bottom and a ceramic core. hamilton's energy principle is applied to the fgm sandwich plates to understand their buckling behavior. the mesh convergence on finite element (fe) model is carried out, and the accuracy of the results is tested using the existing research. the present model results match reasonably well with the previously published literature. the impact of the transverse shear deformation, plate aspect ratio, size-to-thickness ratio, and volume fraction is investigated for different thickness layer systems. keywords-fg sandwich plate; finite element method; critical buckling load i. introduction composite structures are highly demanding due to mechanical properties such as endurance, light weight, high strength, and stiffness to mass ratios. they are employed in numerous modern engineering applications, including civil construction, vehicles, marine industry, and aerospace applications. understanding the mechanical behavior of composite laminates is essential for the intricate design since composite laminates can be customized to serve the intended purpose while having a very complicated composition due to their layered structure. functionally graded composites are able to carry out contemporary and unique tasks that traditional composite materials are unable to. these sophisticated composite materials, which are manufactured using advanced combinations of metal and ceramic techniques, have microscopically inhomogeneous morphology [1]. exploring optimal materials that fulfil the strength and stability standards over their lifetime is a tough work for an engineer due to the rising demands given by the numerous structural components. composites are increasingly preferred in this context due to the amount of flexibility they provide in terms of product design. high stiffness and strength may be achieved with a minimal weight by using a variety of lamination schemes, fibre orientation, material types, and material combinations. nowadays, numerous types of engineering structures use functionally graded (fg) sandwich plates. in order to achieve improved mechanical characteristics in traditional laminated composite materials, homogeneous elastic laminae are joined to one another. however, a sudden shift in material characteristics at the interface between two materials may result in high interlaminar stresses, which may lead to delamination. the use of fgms, where material characteristics vary continuously, is one method to counteract these negative effects. this can be implemented by varying the volume fraction of the constituent materials progressively, typically along the thickness direction. this reduces interfacerelated problems of composites, resulting in uniform stress distributions. generally, fgms are composed of a composition of ceramic and metal or made up of different materials. the ceramic component in a fgm provides temperature barrier effects and prevents the metal from corrosion and oxidation, while the metallic component toughens and reinforces the fgm [2-4]. due to widespread use of fg sandwich structures, it has become essential to know their responses. shear deformation theories like the first-order shear deformation theory (fsdt) and higher-order shear deformation theory (hsdt) need to be implemented to predict the responses of fg sandwich plates, as the shear deformation effect is more noticeable in thick plates or plates composed of novel materials such as fgm. the fsdt offers good results, but they rely on the shear modification factor, which is challenging to figure out because it involves a number of variables. on the other hand, hsdt doesn't need a shear modification factor, but its equations of motion are more difficult compared to fsdt [5]. from the 3-d equations of elasticity, a 2-d theory of bending engineering, technology & applied science research vol. 13, no. 4, 2023, 11355-11359 11356 www.etasr.com gupta & kumar: buckling behavior of a functionally graded sandwich plate movements of isotropic, elastic plates can be made. like timoshenko's one-dimensional theory of bars, this theory takes into account the effects of rotatory inertia and shear [6]. authors in [7] proposed a mathematical 3d elasticity solution for a sandwich hybrid with a fg core, loaded by a hard sphere indentor in a crosswise direction. on the basis of first order shear deformation theory and nonlinear von karman displacement field with variable thickness under uniform temperature rise, the thermal stability of a sandwich fgm circular plate with variable thickness has been analysed in [8]. the buckling behavior of fgm circular plates with variable thickness under radial compression has been investigated in [9]. under thermal and mechanical loadings, authors in [10] conducted buckling analysis of truncated conical sandwich fgm shells with stiffeners and various material combinations along the thickness supported by pasternak elastic foundations under thermal and mechanical loadings. the four-node quadrilateral element for plates based on third order zigzag theory was improved in [11] and was validated by static and dynamic behavior. the inverse hyperbolic shear deformation theory based on c0 continuity finite element (fe) technique has been proposed for the analysis of sandwich plates and laminated composites in [12]. unified formulation has been extended to fgm plates, and a variable kinematic model taking into account different material laws along the thickness was proposed in [13]. the c0 isoparametric element and moritanaka homogenization technique have been used to conduct static and dynamic analyses on fgm skew plates exposed to mechanical pressure in [14]. the impact of skew angle on the axial stress and deflection has been studied employing the same lagrangian element in combination with higher order shear deformation theory in [15]. the buckling of fgm sandwich plates is analyzed in this study using the equivalent single layer shear deformation theory. in order to take into consideration the shear deformation in the displacement field, a modified hyperbolic function in terms of thickness direction was used. to evaluate the buckling behavior of fgm sandwich plates, an fe model has been created. the c0 fe model was developed based on a new mathematical model to facilitate buckling analysis and was evaluated for convergence. the outcome has been corroborated by previously published research. the buckling behavior has been analyzed using parametric studies to assess the impact of different material layers with various thicknesses by varying size to thickness ratio, power index, and aspect ratio. ii. formulation a. geometry of the fgm sandwich plate the geometrical features of a sandwich plate (with fgm on top and bottom surface and ceramic core) are described in figure 1 with sides a and b and total thickness h. the midplane of the plate is taken as the reference plane (z = 0). b. homogenization of the fg plate the volume fraction function is defined in (1), with the power index (p) and the distance from the mid-plane (z) of the plate. fig. 1. geometry of the fgm sandwich plate. effective material parameters like young’s modulus e�z� and poisson ratio µ�z� can be determined as functions of thickness for different thickness layer systems from mid-plane as follows: v��z� = �� ���� �� (1a) here, z lies between h� and h�. v��z� = 1 (1b) here, z lies between h� and h�. v��z� = ���������� (1c) here, z lies between h� and h�. e�z� = e� + �e� − e� � ∗ v��z� (2a) µ�z� = µ� + �µ� − µ� � ∗ v��z� (2b) where e� , µ� , and e� , µ� represent young’s modulus and poission’s ratio of metal and ceramic, respectively. power index is denoted by p≥ 0, v��z� is the volume fraction function of layer n (n = 1, 2, 3) at thickness z. the suggested hsdt uses the shear deformation function g(z) associated with ψsx and ψsy which is represented in (3), whereas the transverse shear strain distribution along plate thickness, thickness stretching function t(z) associated with φ is expressed in (4) to include the thickness stretching deformation of plate. g�z� = �" sin " � � (3) t�z� = �"� � '1 − tanh� �) − �"� sech� �� (4) in-plane displacements u, v, and transverse displacement w are expressed in (5)-(7) using the shape function g(z) and the thickness stretching function t(z). for the c0 continuity of the fe analysis, out of plane derivatives are complex due to the involvement of the strain with second-order derivatives, but c1 continuity is extremely intricate and difficult to model. therefore, new nodal unknowns are substituted for the out-ofplane derivatives to verify that displacement field variables are engineering, technology & applied science research vol. 13, no. 4, 2023, 11355-11359 11357 www.etasr.com gupta & kumar: buckling behavior of a functionally graded sandwich plate continuous within elements and need the application of penalty approach during fe formulation. u�x, y, z� = u��x, y� − zα12�x, y� − g�z�ψ42�x, y� (5) v�x, y, z� = v��x, y� − zα16�x, y� − g�z�ψ46�x, y� (6) w�x, y, z� = w��x, y� + t�z�φ�x, y� (7) where α12 − 9:92 = 0, α16 − 9:96 = 0. c. kinematics of structure strain–displacement can be derived by differentiating the displacement field as given below: ∈22= 9<=92 − z 9>?@92 − g�z� 9ab@92 ∈66= 9c=96 − z 9>?d96 − g�z� 9abd96 ∈ = 9ef9 φ (8) γ26 = {9<=96 + 9c=92 } − z 9>?@96 + 9>?d92 � − g�z�{9ab@96 + 9abd92 } γ2 = 9: 92 − α12 − 9jf9 ψ42 + t�z� 9k 92 γ6 = 9: 96 − α16 − 9jf9 ψ46 + t�z� 9k 96 d. constitutive relations for the fgm sandwich plate linear constitutive relationship between stresses and strain is given by constitutive matrix. q�� = q�� = q�� = m� �n��µ�o���µ���µ� q�� = q�� = q�� = m� �µ��pµ����µ���µ� qqq = qrr = qss = m� ����pµ� (9) ⎩⎪ ⎨ ⎪⎧ σ22σ66σ τ26τ2 τ6 ⎭⎪ ⎬ ⎪⎫ = ⎣⎢ ⎢⎢ ⎢⎡q�� q�� q�� 0 0 0q�� q�� q�� 0 0 0q�� q�� q�� 0 0 00 0 0 qqq 0 00 0 0 0 qrr 00 0 0 0 0 qss⎦⎥ ⎥⎥ ⎥⎤ ⎩⎪ ⎨ ⎪⎧ ϵ22ϵ66ϵ γ26γ2 γ6 ⎭⎪ ⎬ ⎪⎫ (10) e. governing equation of motion hamilton’s principle derives the equations of motion. u is the strain energy, k is the kinetic energy, and w is the work done by external forces. ∮ δ�u − k − w� ∂ω = 0 (11) the strain energy of fgm sandwich plate is shown in (12): u = �� ∭ ϵlσ ∂x ∂y ∂z = �� ∬ ϵ� l{n zl[qqr]z ∂z}ϵ� ∂x ∂y (12) critical buckling load along the x and y axis is represented by nx and ny, while nxy represents the shear buckling. the total work done by external compressive forces acting on the plate edges is: w = �� ∭ tn2 9:92 � + n6 9:96 � + 2n26 9:92 9:96 w dxdydz (13) the material rigidity matrix [d] is obtained from the constitutive matrix given in (10) and the thickness matrix given in (14). this matrix facilitates the use of the proposed hsdt as an equivalent single layer theory to downscale the 3-d domain to the 2-d domain for the analysis. [z] = ⎣⎢ ⎢⎢⎢ ⎢⎡1 0 0 0 0 z 0 0 0 0 g 0 0 0 0 0 0 00 1 0 0 0 0 z 0 0 0 0 g 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ty 0 00 0 1 0 0 0 0 z 0 0 0 0 g 0 0 0 0 00 0 0 1 0 0 0 0 1 0 0 0 0 gy 0 0 t 00 0 0 0 1 0 0 0 0 1 0 0 0 0 gy 0 0 t ⎦⎥ ⎥⎥⎥ ⎥⎤ (14) [d] = n [z]l {�/� {��/� }qqr~[z] ∂z (15) the geometric rigidity matrix [dg] is obtained by [n]� and thickness coordinate matrix [zb] given in (16): [d�] = n [z1]l}n� ~[z1] {�/� {��/� ∂z (16) where: [n]� = � n2 n26n26 n6 � [z1] = � 10t�z�0 010t�z�� thee displacement in the fe can be represented as the linear combination of node shapes and corresponding shape functions. the principle of virtual work was applied using the mid plane strain vector. the material stiffness matrix and the geometrical stiffness matrix are obtained. the total potential energy for buckling analysis is: π� = �� ∬ ϵ�l[d] ϵ� ∂x ∂y − �� ∬ ϵ1l[d�] ϵ1 ∂x ∂y (17) [k�] = ∬[b�]l[d�][b�] [j] ∂ζ ∂η (18) iii. results and discussion in the current work, buckling analysis on fgm sandwich plate was carried out using fe formulation based on a 9-node isoparametric c0 continuous shape function. a. model convergence and validation based on the suggested innovative hsdt, the governing equations for the fe model which is utilized for the buckling analysis of the fgm sandwich plate are obtained from the principle of virtual work. in-house matlab algorithm for fe formulation was written using the 9-noded lagrangian isoparametric shape functions. using mesh convergence studies, the fe model was evaluated and its performance was assessed. the fe analysis was carried out on a simply supported square fgm sandwich plate. the material properties are shown in table i. to predict the buckling responses of the fgm sandwich plate, we consider the plate subjected to axial in-plane forces. engineering, technology & applied science research vol. 13, no. 4, 2023, 11355-11359 11358 www.etasr.com gupta & kumar: buckling behavior of a functionally graded sandwich plate table i. material properties material poission’s ratio mass density (kg/m 3 ) modulus of elastiity (gpa) al2o3 0.3 2702 70 al 0.3 3800 380 the change in dimensionless critical buckling load with various power law indices, different layers of different thickness types of fgm sandwich and mesh sizes was investigated. the presented numerical solutions are computed using novel theory, and the findings are compared with the existing research. the non-dimensional critical buckling ratio is expressed as: n�� = ���m� �� where n is the buckling load due to external load. from table ii, it can be seen that as power index increases, the nondimensional critical buckling loads for uniaxial and biaxial compression loading for different thickness layer systems decrease. it can be seen that for various layer configurations and for the same boundary condition, non-dimensional critical buckling load decreases with increase in the power index that corresponds to increase in metallic volume fraction. further, it can be seen that the biaxial buckling loads are smaller than the uniaxial buckling loads. for convergence investigations, several mesh sizes have been used, and the results are reported in table ii in terms of non-dimensional critical buckling load. for validation and accuracy, the model's results were compared to the findings of [5]. for a critical buckling load, it has been observed that a mesh size of 9×9 elements can provide sufficient convergence. in table iii, the dimensionless critical buckling load for uniaxial and biaxial compressive loading is presented for various power index and aspect ratios for different thickness layer systems, showing that the decrease in the shorter dimension increases the critical buckling load. the al/al2o3 fgm sandwich plate has been analyzed for buckling with all sides simply-supported (ssss). it has been observed that with a given size-to-thickness (a/h) ratio, a rise in power index results in a gradual decrease in non-dimensional critical buckling load. further, it is also observed that an increase in (a/b) ratio results in an increase in the critical buckling load for a fixed power index. from figure 2, it can be seen that the material variation is continuous within the layers of fgm and core, however, there is a drastic change near the layer interface. table ii. non-dimensional critical buckling loads for various thickness of layer systems for al/al2o3 fgm sandwich plate (a/b=1, a/h=10) p theory ref. uniaxial buckling load biaxial buckling load 1-0-1 2-1-2 1-1-1 2-2-1 1-2-1 1-0-1 2-1-2 1-1-1 2-2-1 1-2-1 0 fsdt [5] 13.0045 13.0045 13.0045 13.0045 13.0045 6.5022 6.5022 6.5022 6.5022 6.5022 present 5×5 13.1092 13.1092 13.1092 13.1092 13.1092 6.5546 6.5546 6.5546 6.5546 6.5546 present 7×7 13.0768 13.0768 13.0768 13.0768 13.0768 6.5384 6.5384 6.5384 6.5384 6.5384 present 9×9 13.0687 13.0687 13.0687 13.0687 13.0687 6.5344 6.5344 6.5344 6.5344 6.5344 0.5 fsdt [5] 7.3634 7.9403 8.4361 8.8095 9.2162 3.6817 3.9702 4.2181 4.4047 4.6081 present 5×5 7.4329 8.0147 8.5142 8.9265 9.2994 3.7165 4.0073 4.2571 4.4632 4.6497 present 7×7 7.4094 7.9894 8.4879 8.8991 9.2717 3.7047 3.9947 4.2439 4.4495 4.6359 present 9×9 7.4034 7.9830 8.4811 8.8921 9.2647 3.7018 3.9916 4.2406 4.4460 4.6323 1 fsdt [5] 5.1648 5.8387 6.4641 6.9485 7.5056 2.5824 2.9193 3.2320 3.4742 3.7528 present 5×5 5.2193 5.8998 6.5306 7.1000 7.5801 2.6097 2.9499 3.2653 3.5500 3.7900 present 7×7 5.2005 5.8785 6.5076 7.0748 7.5485 2.6002 2.9392 3.2538 3.5374 3.7775 present 9×9 5.1956 5.8730 6.5016 7.0683 7.5483 2.6002 2.9365 3.2508 3.5342 3.7742 table iii. non-dimensional critical buckling load for various aspect ratio and power index for various thickness of layer systems for al/al2o3 fgm sandwich plate (a/h = 10) p (a/b) ratio uniaxial buckling load biaxial buckling load 1-0-1 2-1-2 2-1-1 1-1-1 2-2-1 1-2-1 1-0-1 2-1-2 2-1-1 1-1-1 2-2-1 1-2-1 0 1/3 4.1276 4.1276 4.1276 4.1276 4.1276 4.1276 3.7148 3.7148 3.7148 3.7148 3.7148 3.7148 1/2 5.2049 5.2049 5.2049 5.2049 5.2049 5.2049 4.1639 4.1639 4.1639 4.1639 4.1639 4.1639 3/2 28.8668 28.8668 28.8668 28.8668 28.8668 28.8668 10.2921 10.2921 10.2921 10.2921 10.2921 10.2921 2 45.4834 45.4834 45.4834 45.4834 45.4834 45.4834 15.1822 15.1822 15.1822 15.1821 15.1822 15.1821 0.5 1/3 2.3214 2.5035 2.6105 2.6611 2.7934 2.9099 2.0894 2.2533 2.3496 2.3950 2.5144 2.6189 1/2 2.9308 3.1607 3.2941 3.3591 3.5250 3.6726 2.3444 2.5285 2.6352 2.6873 2.8201 2.9381 3/2 16.893 18.2031 18.8385 19.2964 20.1193 20.9776 5.8870 6.3466 6.6030 6.7384 7.0589 7.3506 2 26.8601 28.9383 29.9475 30.6591 31.9572 33.2872 8.7949 9.4791 9.8527 10.0520 10.5227 10.9493 1 1/3 1.6242 1.8360 1.9832 2.0337 2.2171 2.3645 1.4616 1.6525 1.7851 1.8303 1.9952 2.1281 1/2 2.0516 2.3190 2.5018 2.5684 2.7971 2.9855 1.6413 1.8552 2.0015 2.0547 2.2377 2.3884 3/2 12.0322 13.6020 14.4529 15.0143 16.1370 17.3085 4.1485 4.6895 5.0446 5.1874 5.6333 6.0104 2 19.2013 21.7087 23.0957 23.9486 25.7529 27.5610 6.2321 7.0453 7.5701 7.7853 8.4426 8.9974 iv. conclusions the buckling behavior of fgm sandwich plates was carried out using fe formulation based on a 9-node isoparametric c00 continuous shape function from the novel suggested displacement fields with a hybrid hyperbolic tangent and secant function for accounting for the effect of thickness stretching. engineering, technology & applied science research vol. 13, no. 4, 2023, 11355-11359 11359 www.etasr.com gupta & kumar: buckling behavior of a functionally graded sandwich plate −0.5 −0.4 −0.3 −0.2 −0.1 0.0 0.1 0.2 0.3 0.4 0.5 50 100 150 200 250 300 350 400 y o u n g 's m o d u lu s o f e la st ic it y ( g p a ) depth coordinate (z/h) p = 0.2 p = 0.5 p = 1 p = 2 p = 5 p = 10 fig. 2. variation of young’s modulus with thickness coordinates for various values of power index in the 1-1-1 layer system. the performance of the fe model is characterized as quite satisfactory after the comparison with the findings of the existing literature. for the parametric study, the model is transformed for different 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accepted: 18 january 2022 abstractmaximum power point tracking (mppt) is essential for the application of a photovoltaic (pv) energy system in order to extract the maximum possible power under variable conditions of irradiation and temperature. this paper deals with the implementation of different mppt algorithms for a pv array installed for a system connected to the grid: perturb and observe (p&o), fuzzy logic control (flc), cuckoo search (cs), and beta algorithms were simulated in matlab/simulink and the results were analyzed and compared. beta algorithm proved to have greater tracking power, minor power loss, great tracking speed, less time, and less oscillation than the other techniques. keywords-beta algorithm; cuckoo search; fuzzy logic controller; grid; photovoltaic; mppt; p&o; thd i. introduction global increasing energy consumption and inevitable reduction of fossil fuel resources has pushed scientists to find and develop novel renewable energy resources [1, 2]. solar energy is the most abundant renewable energy source [3, 4]. photovoltaic (pv) energy becomes an important alternative as it is ubiquitous, environment friendly, freely available, it has low operational and maintenance costs, and less balance of systems [5]. therefore, the technological innovations with the lower cost of pv modules lead to the implementation of pv grid-connected systems, especially small ones with low voltage (lv), which have gradually emerged [6]. however, the efficiency of a pv system is low, the output characteristics of solar arrays are nonlinear, and they vary with solar irradiance and temperature [7]. in order to make the pv system fully exploited, it must operate at its maximum power point (mpp). there are two categories of maximum power point tracking (mppt) techniques: conventional mppt algorithms which are simple and low-cost, yet they have poor efficiency. the second category consists of the mppt methods based on intelligent control. these methods are complex with high efficiency [8]. many research studies on the mppt techniques have been reported. authors in [9] fixed the duty cycle, in the simplest of methods that does not require any feedback, in which the load impedance is adjusted only once for the mpp and it is not adjusted again. authors in [10], proposed an adaptive reference voltage (arv)-based mppt technique to improve the performance of the constant voltage tracking technique by making it adaptable to weather conditions. constant voltage control can be easily implemented with analog hardware. however, its mppt tracking efficiency is low relative to those of other algorithms [9]. authors in [11] used the simpowersystems platform in matlab to design a pv system and a new gmppt algorithm based on the open circuit voltage. the open circuit voltage method was adapted to a system under shading condition in [12]. this method has high tracking accuracy but does not always track the real peak and instead it causes the system to operate at a point close to the mpp. authors in [13] proposed a hybrid mppt method combined with the conventional short current pulse (scp) mppt method and perturb & observe (p&o) method [14-15]. this algorithm is the most commonly used because of its ease of implementation for standalone pv systems. however, p&o has limitations that reduce its mppt efficiency [16] while it requires complex control circuits [17]. conventional mppt methods are used satisfactorily, but they have the problem of low speed of convergence and high oscillations around the mpp. since the p-v characteristic of a corresponding author: fatima zohra kebbab engineering, technology & applied science research vol. 12, no. 2, 2022, 8228-8235 8229 www.etasr.com kebbab et al.: a comparative analysis of mppt techniques for grid connected pvs pv module is not linear, the conventional mppt control method is not adequate. to resolve this problem, alternative mppt control methods based on intelligent algorithms have been widely proposed and successfully applied .the most known intelligent methods for mppt are fuzzy logic control (flc), artificial neural networks (anns), and meta-heuristic algorithms [18]. authors in [19] proposed anns as a global theoretical approach for predicting and tracking the mpp of solar panels. anns have been extensively used to model the complicated relationship between the inputs and outputs of nonlinear systems [19]. several microcontrollers use flc for mppt. the flc is preferred when the mathematical model of the control plant is difficult to obtain. this technique has been proposed in several research works to achieve the mpp. authors in [20] mentioned that flc can track the mpp quickly while it has better dynamic and steady-state performance. however, the main disadvantages of flc are that the variation of irradiance can cause drift and the implementation is complex. the particle swarm optimization (pso) -based mppt approach has been presented in [21, 22]. in [7], a modified version of pso is developed. the pso is highly potential due to its simple structure, easy implementation, and fast computation capability [23]. the main contribution of this paper is to determine the most efficient method to track the mpp of a grid connected pv system. the proposed methods are the cuckoo search (cs) algorithm [24-27], the beta algorithm [28], p&o method, and flc. ii. model description of the pv module a simple equivalent circuit model for a pv cell is shown in figure 1 [29]. the ideal case is presented by a current source in parallel with a diode, the real case of a pv cell is represented by the insertion of the resistances rs and rsh [30-31]. fig. 1. electric model equivalent of a pv cell. the current of the pv panel is given by [32-33]: i � i� – i �exp .��. �������.� � � 1�– � �� �� � ��� � (1) the current through the diode is given by: i� � i �exp .��. ��������.� � � 1� (2) the solar cell output current is : i � i� – i� – i�� (3) where i is the solar cell current (a), i� is the light generated current (a), i� is the diode saturation current (a), r� is the solar cell series resistance (ω), q is the electron charge (1.6× 10 -19 c), k is the boltzman's constant, t represents the cell temperature (k), v is the solar cell's output voltage (v), and r�� is the solar cell's shunt resistance (ω). in this paper, the solar panel spr-305e-wht-d is considered. the specifications of this solar panel at steady state conditions (stc) of 25 o c and 1000w/m 2 are the parameters used in simulations and are shown in table i [34]. table i. parameters of the considered pv panel [34] information value open circuit voltage 64.2v short circuit current 5.96a voltage at mpp 54.7v current at mpp 5.58a maximum power 305.226w parallel strings 66 series-connected modules per string 55 iii. mppt techniques a. perturbation and observation (p&o) the p&o method is one of the best mppt approaches used to track the mpp in pv panels, combining easy implementation and simplicity of execution [35]. in p&o technique, we introduce a minor -predefined change to perturb the system and consequently cause the power variation of the pv module [30]. the pv output power is measured periodically and is compared with the previous power value [36-37]. if the power output increases, the same process continues, otherwise, the perturbation direction is reversed [36]. b. cuckoo search (cs) the cs algorithm [38] was proposed as an efficient metaheuristic optimization mechanism. this algorithm emulates the behavior of cuckoo birds in their reproduction process [24-25]. the cuckoo bird lays its eggs inside the nests of other birds instead of building its own [24]. it will choose the best nest for her eggs to hatch safely and breed a new generation of cuckoos. in some cases, in order to increase the chance of hatching, the cuckoo bird will make some effort as it lays its eggs strategically in a good position and sometimes drops the eggs of the host birds outside the nest. some cuckoo species even produce eggs similar to the eggs of other bird species [25]. upon hatching, the young cuckoos sometimes destroy the eggs of the host birds to increase the chance of getting more food. in some cases, host birds discover and destroy cuckoo eggs and may abandon their nests [27]. the cs optimization algorithm was developed, to track the mppt of the solar pv. in order to make this algorithm suitable, some simplifications of the actual behavior are needed [39]. this algorithm works based on three rules [40] • each cuckoo bird will only lay one egg in a random host nest. • only the best nest, containing high quality organisms, will transmit the next generation of cuckoo birds. • finally, host networks are considered to have a fixed value. levy flights are used to create new eggs and a step size of the cuckoo is determined with the levy function as follows: engineering, technology & applied science research vol. 12, no. 2, 2022, 8228-8235 8230 www.etasr.com kebbab et al.: a comparative analysis of mppt techniques for grid connected pvs levy β� � l%& , 1 ' β ( 3 (4) where l is the flight length. the optimizing flight size coefficient α is regarded as a fraction of excreted eggs (p+), where p+ ∈ -0,10. c. fuzzy logic controller (flc) the main task of the flc is to reach the mpp. however, the performance of the controller depends principally on human expertise. fuzzy logic can work with imprecise inputs, it does not need the precise mathematical model of the system [41]. e(t) and 12 3� are the flc inputs given by (5) and (6) [42]: e t� � 678 9�%678 9%:��78 9�%�78 9%:� � ∆6 ∆� (5) de t� � e t� � e t � 1� � ∆e (6) where p6� t� and v6� t� are the output power and the voltage of the pv module. the flc output is dd, which is the variable step size of the duty cycle: dd � d t� � d t � 1� (7) in this work, the triangular membership function is chosen for the inputs, due to its simplicity [43]. the proposed control model simulated in matlab/simulink is shown in figure 2. fig. 2. simulink model of the fuzzy logic controller. d. beta method the beta method has been detailed in [44]. in this method, an intermediate variable β is used to track the mpp [45]. the intermediate variable β is given as [29, 46]: β � lna bcdecdf �c h vie (8) c � q/ nsakt� (9) where ipv and vpv are the pv current and voltage, c is the diode constant, q is the electron charge, a is the diode ideality factor, k the boltzmann's constant, t is the temperature of the p-n junction, and ns is the cell number of the pv module. the beta-based mppt algorithm consists in tracking the reference β* that is calculated at the mpp [47]: β∗ � lnabcdrccecdrccf � c h viercc (10) where viercc and iierccare respectively the mpp voltage and current of the pv array at stc. iv. simulation results this paper aims to test the feasibility and effectiveness of the considered mppt methods to track the mpp of a gridconnected pv panel. the simulation of the overall system depicted in figure 3 was carried out in matlab/simulink. the considered mppt methods for this comparative study are: p&o, flc, cs, and beta. the pv array is modeled to have 66 strings and connected to the boost converter that operates with the mppt controller. the linguistic variables in this study are defined as positive big (pb), negative big (nb), and zero (ze). figure 4 presents the grid details connected with the pv. in order to examine the effect of solar irradiation on module characteristic, the temperature of the cells was kept constant at 25 o c. in figures 5 and 6, the obtained i-v and p-v characteristics at different irradiation levels are shown. fig. 3. 100 kw pv grid-connected pv array. engineering, technology & applied science research vol. 12, no. 2, 2022, 8228-8235 8231 www.etasr.com kebbab et al.: a comparative analysis of mppt techniques for grid connected pvs fig. 4. grid details. fig. 5. i-v characteristic of the pv module at constant temperature and variable irradiation level. fig. 6. p-v characteristic of the pv module at constant temperature and variable irradiation level. a dc-dc boost converter is utilized as a powerconditioning unit between the pv module and the grid. the degree of the membership function of the inputs e, de and the output dd is shown in figure 7. the output voltage and current of the converter are converted by a three-phase inverter, to produce ac signals. this pv system is connected to the distribution line via a 100kva transformer. to examine the robustness and the efficacy of the considered techniques in the tracking of mpp and re-tracking with changes in the weather conditions, the temperature of the cells is kept constant at 25°c and the irradiance level changes. sun insulation of 1000w/m² is applied to the pv system in t ϵ [0, 1s]. then, it is changed to 400w/m 2 between 1 and 1.5s. finally it is stepped to 1000w/m 2 between 1.5 and 3s as shown in figure 8. fig. 7. membership function inputs e, de and output dd. fig. 8. irradiation variation. figure 9 shows the output power of the considered methods. in figure 9(a), we see the calculation of the maximum power efficiency (mpe), that presents the main evaluation parameter of the mppt in pv systems, in stc conditions. the mpe measures the percentage of the created power at certain time mentioned to the theoretical maximum created power at the same time. at stc, the mp (maximum power) is 100.7kw. the power achieved by beta, flc, p&o, and cs was: 100.4, 100.3, 100.2, and 100.18kw respectively. the efficiency achieved by beta, flc, p&o, and cs was 99.7%, 99.6%, 99.5%, and 99.48% respectively. we see that beta achieved higher efficiency than the other techniques .we engineering, technology & applied science research vol. 12, no. 2, 2022, 8228-8235 8232 www.etasr.com kebbab et al.: a comparative analysis of mppt techniques for grid connected pvs can clearly note that in a transient state large oscillations can be observed in cs and flc, which cause power loss. (a) (b) fig. 9. pv system’s power output: (a) stc, (b) sudden irradiance change. in order to extent the robustness of the mppt techniques, settling time is an essential tool. the settling time in stc (figure 9(a)) for beta, flc, cs, and p&o is 0.0256s, 0.1614s, 0.2411s, and 0.0914s respectively. so, beta ensures the convergence to the mpp more rapidly. in the zoomed part (1-1.4s) of figure 9(b) the first step change is introduced at 1s. we stepped the irradiance from 1000w/m 2 to 400w/m 2 . the flc and beta reach the mpp without an overshoot in short time, but the cs and p&o reach the mpp with large overshoot. in the interval from 2 to 3s, irradiance changed from 400w/m 2 to 1000w/m 2 . with the cs algorithm, the oscillations around the mpp introduce a power with an average value equal to 98.3kw which creates a static error equal to 1.7kw. these results have confirmed the good performance and the high effectiveness of flc and beta. at t=2.6s, the cs reaches the mpp. cs takes a relatively long time to reach the mpp without an overshoot. p&o presents large oscillations around the mpp. the major inconvenience of p&o algorithm is its poor behavior following a sudden change in irradiance. for the pv voltage (v6�) and the pv current (i6�) shown in figure 10, we observe that in the transient state of pv voltage (v6�), the cs and flc algorithms present large oscillations between t=0 and t=0.2s. in the steady state, flc, cs, and beta are stable, but p&o in the intervals of the change of irradiance, presents large oscillations. figure 11 shows the dc output voltage regulation to connect the pv with the grid. in the zoomed part, with the quick change of irradiance at t = 1 s, beta reached the reference voltage 500vdc quicker than the other algorithms. (a) (b) fig. 10. (a) pv current, (b) pv voltage. fig. 11. the dc output voltage regulation at 500vdc. fig. 12. power injected into the grid. figure 12 shows the power injected into the grid. in the zoomed part (2.8-3s), p&o presents a large oscillation. the power achieved by beta, flc, p&o, and cs is 98.73, 98.72, 98.58, and 98.57kw respectively. this confirms the higher efficacy of the beta algorithm. engineering, technology & applied science research vol. 12, no. 2, 2022, 8228-8235 8233 www.etasr.com kebbab et al.: a comparative analysis of mppt techniques for grid connected pvs (a) (b) (c) (d) fig. 13. ac output current waveform with grid connection, thd performance: (a) p&o, (b) cs, (c) flc, (d) beta. the injected current to the grid has the shape of a sinusoidal wave, as shown in figure 13 that confirms the effectiveness of the considered proposed controllers. to evaluate the quality of the injected current, the fast fourier transform (fft) analysis of the current is also shown in figure 13. all the considered techniques show low thd , within the acceptable limit as per the standards iec 61727, ieee 1547 and ieee 929 [48]. beta and p&o perform better than the other algorithms with thd = 2.13%. v. discussion we note that the beta method has satisfactory application in pv systems but with load resistance. in this paper our model is realized with a 100kw grid-connected pv system. the simulation results showed that the beta method can address the two problems the existing mppt methods face, namely the tradeoff between the steady-state oscillations and dynamic behavior and the tradeoff between high computational load and accuracy, since it shows a fast tracking speed in the transient stage, smaller oscillations in the steady-state and medium complexity of implementation. the performance of the beta method as an mppt technique is evaluated with respect to other known existing techniques, namely p&o [4], which introduces considerable oscillations near the mpp that lead to power losses, the flc [6], and cs algorithm which presented large oscillations around the mpp contrarily to the results presented in [25]. to confirm the efficiency of proposed method, two comparisons were conducted: • power efficiency and settling time: the main evaluation parameters of the mppt in pv systems are power efficiency and settling time. in this paper, the efficacy of the beta technique was proved with efficiency of 99.7% and settling time of 0.0256s • thd comparative study: another criterion taken into account in evaluating the performance of the considered control algorithms is the rate of distortion of the network currents (thd). the results of the fft analysis of the current were compared and validated. vi. conclusion the efficiency of a pv system is an essential indicator for assessing the power of grid-connected pv systems. mppt performance is a key indicator. a mppt algorithm must be used to track the operating point with the highest power output. in this esteem, this paper presented and compared four mppt algorithms: p&o, flc, cs, and beta with regard to the achievement of the mppt and the injection of sinusoidal current to the electric grid. the simulation results showed the superior performance of the beta algorithm in effectively and efficiently following the mpp with minimum oscillations and highest speed, even during a quick change in the solar irradiance. references [1] m. sarvi and a. azadian, "a comprehensive review and classified comparison of mppt algorithms in pv systems," energy systems, nov. 2021, https://doi.org/10.1007/s12667-021-00427-x. fuzzy thd= 2.34% 0 200 400 600 800 1000 frequency (hz) 0 0.5 1 1.5 m a g ( % o f f u n d a m e n ta l) engineering, technology & applied science research vol. 12, no. 2, 2022, 8228-8235 8234 www.etasr.com kebbab et al.: a comparative analysis of mppt techniques for grid connected pvs [2] f. k. abo-elyousr, a. m. abdelshafy, and a. y. abdelaziz, "mpptbased particle swarm and cuckoo search algorithms for pv systems," in modern maximum power point tracking techniques for photovoltaic energy systems, a. m. eltamaly and a. y. abdelaziz, eds. new york, ny, usa: springer, 2020, pp. 379–400. 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[48] s. kumar, c. sethuraman, and g. chandru, "design of control unit for off-grid and grid connected solarwind hybrid system suitable for supplying power to both ac and dc loads," in international conference on recent trends on electronics, information, communication & technology, bangalore, india, aug. 2021, pp. 331– 338, https://doi.org/10.1109/rteict52294.2021.9573541. microsoft word etasr_v11_n6_pp7805-7808 engineering, technology & applied science research vol. 11, no. 6, 2021, 7805-7808 7805 www.etasr.com nguyen et al.: evaluating the possibility of replacing natural fine aggregates in concrete with … evaluating the possibility of replacing natural fine aggregates in concrete with recycled aggregates duy duan nguyen faculty of construction vinh university vinh, vietnam duan468@gmail.com dieu thuy nguyen faculty of construction vinh university vinh, vietnam dieuthuy03@gmail.com thi hao cao faculty of construction vinh university vinh, vietnam haoxd13@gmail.com van tien phan faculty of construction vinh university vinh, vietnam vantienkxd@vinhuni.edu.vn abstract-this paper presents an investigation on the possibility of replacing natural fine aggregates with recycled aggregates in concrete. the studied recycled aggregates were acquired from crushed waste concrete from demolishing works. the rate of replacement of natural fine aggregates was 10%, 20%, and 30% by weight. compressive and flexural tensile strength of concrete incorporating recycled aggregates was investigated at 28 days of curing. the results show that the compressive and flexural strength of concrete is strongly affected by the percentage of recycled aggregates. it has been found that the strength decreases linearly with increasing recycled aggregate content. so, in order to apply recycled waste to concrete as fine aggregates, it is necessary to perform supplement research with appropriate additives to compensate for the loss of compressive and flexural strength. keywords-compressive strength; flexural tensile strength; recycled concrete; fine aggregates i. introduction the use of recycled materials instead of natural sources in concrete has been concerned by various researchers [1-6]. the influence of using recycled waste aggregates instead of natural fine aggregates to the modulus of elasticity, pulse velocity and long-term properties such as drying shrinkage and creep has been investigated in [1]. it has been found that the detrimental effects of using crushed concrete fines in concrete can be mitigated by a partial replacement of crushed concrete fines with pulverized fuel ash [1]. it was found that the rate of replacement of fine aggregates by recycled sources can be up to 10% for producing c30 concrete [2]. by using recycled fine concrete aggregates, the environmental impact and the consumption of natural resources can be significantly reduced. the results in [5] indicate that recycled concrete has a suitable behavior according to the limits indicated by different international codes for structural concrete. the durability of concrete with recycled fine aggregates has also been investigated in [4], in which the recycled fine aggregates proved to be sustainable materials for construction works. the optimum replacement percentage of river sand by recycled fine aggregates was found to be 30%. authors in [5] studied the use of recycled fine aggregates in concrete with durability requirements. different percentages of recycled fine aggregates (0%, 20%, and 30%) were considered and evaluated. it has been found that the compressive strengths of recycled and conventional concrete are similar and the durable behavior of recycled concrete is as good as that of the conventional concrete. many studies on the use of recycled coarse aggregates instead of natural coarse aggregates in concrete have been carried out [2, 6-11]. the effect of the amount of recycled coarse aggregates on the properties of recycled aggregate concrete has been investigated in [11], in which 4 different recycled aggregate concrete types were produced with the same design compressive strength in replacement ratios up to 100%. the influence of the type of recycled aggregates, namely unbound stone, crushed concrete, and crushed brick, to the properties of concrete has been studied in [12]. the results showed that the performance of concrete containing each type of recycled aggregates was largely influenced by the aggregate nature and quality, in addition to the attached mortar content. studies on the use of recycled aggregates in concrete instead of natural coarse aggregates have been carried out by various authors. however, there are only a few published papers on the use of recycled aggregates instead of fine aggregate in concrete. in this paper, the possibility of replacing natural fine aggregates by recycled aggregates in concrete will be evaluated in terms of compressive and flexural strength of concrete. the results will give documented recommendations for further studies. corresponding author: van tien phan engineering, technology & applied science research vol. 11, no. 6, 2021, 7805-7808 7806 www.etasr.com nguyen et al.: evaluating the possibility of replacing natural fine aggregates in concrete with… ii. composition of recycled concrete waste concrete obtained from demolishing works was crushed and then sieved through standard sized sieves to obtain fine recycled aggregates with diameter ranging between 0.14mm and 5mm. the crushed aggregates were soaked in water until saturation, and then they were allowed to dry at room temperature. for evaluating the possibilities of replacing natural fine aggregates with recycled aggregates in concrete, a reference mixture was selected. natural sand was then replaced by recycled aggregates at various rates, namely 10%, 20%, and 30% by weight. after casting into molds, the samples were stored under normal conditions and the experiments were carried out at 28 days of curing. in the compressive strength experiment, normal force was applied on both surfaces of cylindrical concrete specimens with the loading speed set to 0.5kn/s. the maximum compression force was then recorded (figure 1). cylindrical samples sizes d150×h300 were cast and cured in normal conditions before being compressed to determine their compressive strength. the compressive strength of concrete was determined based on the vietnamese standard tcvn 10303:2014. in the flexural bending test, 3 beam specimens with a size of 150×150×600mm were sampled following the standard tcvn 3105:1993, and were left to be cured for 28 days. the flexural strength of concrete beams was determined based on the tcvn 3119:1993 standard. the four-point bending test setup is shown in figure 2. the bending load was continuously increasing at a constant rate equal to 0.6±0.4dan/cm2 for 1s until failure occurred. the replacement rates of recycled aggregates were 0%, 10%, 20% and 30%. mix components for 1m3 of concrete are presented in table i. (a) (b) fig. 1. (a) an in-process experiment (cp20) and (b) the recorded destructive force. (a) (b) fig. 2. flexural experimental set-up. table i. mix contents for 1 m3 of concrete cement (kg) sand (kg) coarse aggregates (kg) water (kg) 292.5 648.3 1216.3 195.0 iii. results and discussion the peak normal load obtained in the compression experiment is shown in table ii. from the value of the destructive force p (kn) of each sample, the compressive strength (mpa) is calculated as follows: the bearing area s is calculated by (1) where r is the sample radius, which is half the sample diameter d = 15cm, so: s=π.r2= π.7.52= 176.71cm2 (1) the compressive strength is then calculated by (2): r=α.p/s (2) where p is the destructive load of the sample, s is the compressive area, α is the coefficient of converting the experimental results when compressing samples with different size from the standard samples (150×150×150mm). with cylinder sample d150×h300, α = 1.2. table ii. compressiv e stren gth experiment results no. replacement rate sample destructive force (kn) compressive strength (mpa) average value (mpa) 1 0 % 295.2 20.04 19.98 2 293.5 19.93 3 294.1 19.97 4 10 % 288.1 19.56 19.36 5 286.2 19.43 6 281.3 19.10 7 20 % 262.1 17.79 17.82 8 259.4 17.61 9 265.8 18.04 10 30 % 251.2 17.05 17.07 11 252.4 17.13 12 250.8 17.03 engineering, technology & applied science research vol. 11, no. 6, 2021, 7805-7808 7807 www.etasr.com nguyen et al.: evaluating the possibility of replacing natural fine aggregates in concrete with… the value of compressive strength of the experimental samples in shown in table ii. it can be observed that the replacement of recycled fine aggregates affects significantly the compressive strength of concrete. the decrease is recorded as 3% at the replacement rate of 10%, 10% at the replacement rate of 20%, and 14% at the replacement rate of 30%. the compressive strength of concrete at various replacement rates of recycled fine aggregate is shown in figure 3. fig. 3. compressive strength of concrete at various replacement rates of natural fine aggregates with recycled fine aggregates. the maximum force achieved in the bending test is the bending load that breaks the specimen. table iii shows the maximum bending force obtained in the flexural bending test. the flexural strength of beam specimens was calculated according to tcvn 3119:1993 by using (3): rfs=ɣ.p.l/(a.b 2) (dan/cm2) (3) where p is the recorded maximum force, l is the span length, a and b are the dimensions of the specimen and ɣ is the coefficient of converting the experimental results when compressing samples of different size from the standard samples. in the present flexural experiment, the beam specimen was cast in standard dimensions, therefore ɣ = 1. it can be seen from figure 4 that the flexural strength of the specimens decreased linearly with increasing recycled aggregates percentage of replacement. table iii. flex ural bendin g experiment results no. replacement rate maximum force (kn) flexural strength (mpa) average value (mpa) 1 0 % 52.03 8.48 8.56 2 53.12 8.66 3 52.37 8.53 4 10 % 52.28 8.52 8.47 5 52.09 8.49 6 51.50 8.39 7 20 % 50.26 8.19 8.27 8 50.96 8.30 9 51.02 8.31 10 30 % 50.12 8.17 8.05 11 49.05 7.99 12 48.98 7.98 fig. 4. flexural strength of concrete at various replacement rates of natural fine aggregates with recycled fine aggregates. the diminution of strength of recycled concrete with partially replacement of recycled aggregates has been reported by numerous authors [2, 3, 7 10, 12]. the present investigation on the influence of recycled fine aggregates on the compressive and flexural strength of concrete indicates that the compressive strength and flexural strength decrease linearly with the increasing content of recycled aggregates. therefore, in order to apply recycled waste to concrete as fine aggregates, it is necessary to perform supplement research with appropriate additives to compensate for the shown above loss of strength. it is also possible to consider reinforcing concrete with fibers at appropriate concentrations. iv. conclusion the current paper presented the results of a research on the compressive and flexural strength of concrete utilizing recycled fine aggregates from demolition works. the rates of replacement of natural aggregate with recycled aggregates were 0%, 10%, 20%, and 30%. the experiments were performed at 28 days of curing. the results show that the compressive strength and flexural strength of concrete are strongly affected by the percentage of recycled aggregates. it has been found that the strength decreases linearly with the increasing percentage of recycled aggregates. additional studies are needed to evaluate more thoroughly the effectiveness of the use of recycled aggregates in concrete. references [1] r. sri ravindrarajah and c. t. tam, "recycling concrete as fine aggregate in concrete," international journal of cement composites and lightweight concrete, vol. 9, no. 4, pp. 235–241, nov. 1987, https://doi.org/10.1016/0262-5075(87)90007-8. [2] v. t. phan and t. h. nguyen, "the influence of fly ash on the compressive strength of recycled concrete utilizing coarse aggregates from demolition works," engineering, technology & applied science research, vol. 11, no. 3, pp. 7107–7110, jun. 2021, https://doi.org/10.48084/etasr.4145. [3] h. yaprak, h. aruntaş, i. demir, o. simsek, and g. durmuş, "effects of the fine recycled concrete aggregates on the concrete properties," international journal of physical sciences, vol. 6, no. 10, pp. 2455– 2461, may 2011. [4] s. k. kirthika and s. k. singh, "durability studies on recycled fine aggregate concrete," construction and building materials, vol. 250, jul. 2020, art. no. 118850, https://doi.org/10.1016/j.conbuildmat.2020. 118850. engineering, technology & applied science research vol. 11, no. 6, 2021, 7805-7808 7808 www.etasr.com nguyen et al.: evaluating the possibility of replacing natural fine aggregates in concrete with… [5] c. j. zega and á. a. di maio, "use of recycled fine aggregate in concretes with durable requirements," waste management, vol. 31, no. 11, pp. 2336–2340, nov. 2011, https://doi.org/10.1016/j.wasman. 2011.06.011. [6] d. v. m. reddy and m. m. s. swaroop, "effect of recycled aggregates on strength and performance of recylced aggregate concrete," e3s web of conferences, vol. 184, 2020, art. no. 01085, https://doi.org/ 10.1051/e3sconf/202018401085. [7] x. h. vu, t. c. vo, and v. t. phan, "study of the compressive strength of concrete with partial replacement of recycled coarse aggregates," engineering, technology & applied science research, vol. 11, no. 3, pp. 7191–7194, jun. 2021, https://doi.org/10.48084/etasr.4162. [8] m. oad, a. h. buller, b. a. memon, and n. a. memon, "impact of long-term loading on reinforced concrete beams made with partial replacement of coarse aggregates with recycled aggregates from old concrete," engineering, technology & applied science research, vol. 9, no. 1, pp. 3818–3821, feb. 2019, https://doi.org/10.48084/etasr.2498. [9] m. f. koondhar, b. a. memon, m. oad, f. a. chandio, and s. a. chandio, "water penetration of concrete made with coarse aggregates from demolishing waste," engineering, technology & applied science research, vol. 10, no. 6, pp. 6445–6449, dec. 2020, https://doi.org/ 10.48084/etasr.3891. [10] l. butler, j. s. west, and s. l. tighe, "effect of recycled concrete coarse aggregate from multiple sources on the hardened properties of concrete with equivalent compressive strength," construction and building materials, vol. 47, pp. 1292–1301, oct. 2013, https://doi.org/ 10.1016/j.conbuildmat.2013.05.074. [11] m. etxeberria, e. vázquez, a. marí, and m. barra, "influence of amount of recycled coarse aggregates and production process on properties of recycled aggregate concrete," cement and concrete research, vol. 37, no. 5, pp. 735–742, may 2007, https://doi.org/10.1016/j.cemconres. 2007.02.002. [12] n. a. abdulla, "effect of recycled coarse aggregate type on concrete," journal of materials in civil engineering, vol. 27, no. 10, oct. 2015, art. no. 04014273, https://doi.org/10.1061/(asce)mt.19435533.0001247. engineering, technology & applied science research vol. 7, no. 4, 2017, 1888-1893 1888 www.etasr.com kanwal et al.: critical factors of e-learning adoption and acceptance in pakistan: a literature review critical factors of e-learning adoption and acceptance in pakistan: a literature review faria kanwal mariam rehman komal bashir uzma qureshi computer science department lahore college for women university lahore, pakistan faria.kanwal@gmail.com computer science department lahore college for women university lahore, pakistan dr.mrehman13@gmail.com computer science department lahore college for women university lahore, pakistan komal.bashir@gmail.com lahore college for women university, lahore, pakistan uzmaqr69@gmail.com abstract—this review paper examines the prior studies on critical factors of e-learning adoption in pakistan. the search terms identified 40 papers reporting 25 conceptual and qualitative and 15 quantitative evidence about the elearning adoption and critical factors that may influence the adoption of e-learning in pakistan. the findings revealed that modern paradigm shift requires the in-depth analysis of government policies, institutional and management role, students and faculty attitude, social norms, cultural values as well as technological advancement. these factors may directly or indirectly affect the intention of students towards e-learning adoption. the lack of quantitative evidences illustrate that policy makers, practitioners and researchers need to pay attention for further research of identifying and analyzing the critical factors which enhances the e-learning adoption in pakistan. keywords-e-learning; adoption; acceptance; success; factors i. introduction e-learning is an amalgamated concept taken from computer science, information technology, education and psychology defined by academics, researchers and practitioners as an information system used to deliver knowledge (in the form of text, audio and video) via intranet, extranet, internet, interactive tv or satellite among learners [1, 2]. in another context, elearning provides and disseminates information used for corporate training such as training in technological skills in order to improve performance within an organization [3]. with the rapid growth of information and communication technologies, e-learning is the most promising medium of learning and teaching in the educational system. the advent of technology in the traditional structure of education has reshaped the teaching and learning paradigm. e-learning is the new paradigm. in the era of knowledge management and dissemination, e-learning has proven to be a cost-effective solution of delivering knowledge irrespective of time and geographical boundaries [4]. in addition, this learning approach has increased the interaction and communication of students not only amongst themselves but also with their instructors as well [5]. as a result, e-learning is growing at an astonishing rate among educational institutions to gain the maximum benefit of this new paradigm [6]. with technological advancements, e-learning is proving to be the most favorable medium of communication and learning irrespective of geographical boundaries. the developed countries showed a significant progress in e-learning adoption and acceptance. although e-learning systems offer great flexibility in learning, teaching and communication, they also present numerous challenges that would significantly affect their continuous use [7]. the basic measure of successful implementation in e-learning systems depends on the adoption, acceptance and continued use [8]. student acceptance and continued use is essential in the implementation of e-learning [8-9]. it should be noted that the dropout rate in developed countries is 20-40% [10-11]. e-learning, in many institutes, is facing numerous challenges like administrative, organizational, technological and human aspects that highly impact the elearning continuous intentions. these challenges must be identified and explored to overcome the failure rate of elearning among students. it is vital to understand the students’ needs, investigate the external factors and encounter hitches that may impact on the adoption, acceptance and intention towards e-learning [12]. in addition, students are unable to take advantage of these systems unless they are willing to use them. the effectiveness and efficiency of e-learning systems depend on students’ attitudes, adoption and acceptance of modern technology [13-16]. therefore, it is essential to explore factors that elucidate students’ acceptance, intention and attitude towards using e-learning systems. prior use of technology, instructor attributes, institutional and management support and environment of e-learning are the frequently discussed critical factors in context of e-learning [17-20]. with the benefits of integrating e-learning in heis, there are numerous limitations to incorporate ict with the traditional learning. poor technology infrastructure, lack of business strategies, students’ frustration against web based education and rapid change in the technology may cause failure to students’ acceptance of technology and technology continuance [12, 21]. engineering, technology & applied science research vol. 7, no. 4, 2017, 1888-1893 1889 www.etasr.com kanwal et al.: critical factors of e-learning adoption and acceptance in pakistan: a literature review the critical success factors are evaluated as external variables in e-learning adoption and acceptance. furthermore, it has been stated that there is no universal model for e-learning adoption [22, 23]. the adoption and acceptance is influenced by the contextual, cultural, social and technological differences of countries [22, 24]. the acceptance and refusal of technology adoption may depend on culturally dependent contextual factors [25]. ii. e-learning status in pakistan the penetration of ict in the educational system has alleviated online learning in developed countries, as they try to cope with the new technology. pakistan is one of the countries trying harder to uplift the education system using modern technologies. the government of pakistan (gop) has amended regulatory settings to encourage growth of the ict by ensuring the availability of internet in the country. the population of pakistan is 170 millions and the adult literacy rate is 58%. in fact, the progress made in the higher education sector of pakistan has not been encouraging for the past few decades. higher education faces numerous problems in this regard. the five year ranking of global competitiveness index (gci) is presented in table i. according to the ranking, higher education & training has achieved a below average score. furthermore, their technology readiness is also below average. basic and higher education access has been continuously defied in the country. basically, education is given low priority with an expenditure of only 2% of the gross domestic product (gdp). table i. gci ranking of pakistan year overall rank/ total economies higher education & training technology readiness rank score (1-7) rank score (1-7) 2011-2012 118/142 112 3.01 115 2.94 2012-2013 124/144 124 2.99 118 2.90 2013-2014 133/148 129 2.76 118 2.90 2014-2015 129/144 127 2.8 114 2.80 2015-2016 122/138 123 2.91 119 2.73 pakistan’s educational facts are poor and e-learning in higher education institutes (heis) remain at the early stages of its development and implementation. in this regard, the gop is trying hard to provide quality education in both urban and rural areas. furthermore, the gop and the ministry of education have invited universities to establish learning management systems. iii. objectives of the study this paper is mainly descriptive in nature, as the authors were interested in identifying the status of e-learning in pakistan, underutilization of modern technologies and the literature gap that exist. thus, by conducting a systematic literature review on e-learning adoption and critical factors of adoption in pakistan, we will contribute to both the policy makers in heis and researchers. the policy makers in heis will be facilitated to unfold the critical success factors. iv. research questions a) e-learning adoption and acceptance in pakistan a questionnaire was used to provide hard evidence to provision the adoption and acceptance of e-learning in pakistan. this review forms on the basis of research carried out in the domain of e-learning concepts, adoption and acceptance predominantly in pakistan. b) critical success factors of e-learning adoption in pakistan the next question arises whether the critical success factors of e-learning adoption and acceptance in pakistan is measured (table ii). table ii. total number of papers in the case of pakistan v. data collection a) database searched this research intends to assess the research published on adoption of e-learning in pakistan and the critical factors that may influence the adoption in pakistan. science direct, emerald, elsevier, ieee, acm and some international and local journals are identified as relevant databases. the databases were searched from 2001 to 2016. b) search terms the search term that was used included terms for e-learning adoption in pakistan and critical success factors of e-learning adoption in pakistan. this search term help to determine the scope of the study since many of studies include e-learning adoption, but more specific criteria “pakistan” was used. we identified the total publications in the specific domain, types of publication (literature review, conceptual and qualitative , quantitative evidences, case study) and types of data analysis techniques used (exploratory factor analysis, confirmatory factor analysis, structural equation modelling). c) selection of papers for inclusion in the review a number of further criteria were specified to select appropriate studies for inclusion in the review. to be included in the review, papers had to refer to (a) e-learning adoption in pakistan and (b) critical success factors of e-learning adoption in pakistan. moreover, 40 papers met with the inclusion criteria and were identified as relevant to the current study. table iii illustrates the databases searched along with the number of papers in the case of pakistan. vi. data analysis a) yearly publications as presented in figure 1, no publication focusing on pakistan was found from 2001-2005. this trend changed in 2006-2010 and 7 publications were found. the trend of elearning in pakistan has noticeably changed for the last six years and the 33 of publication was recorded in 2011-2016. items total number of papers searched total number of papers in case of pakistan a 2840 40 b 1930 25 engineering, technology & applied science research vol. 7, no. 4, 2017, 1888-1893 1890 www.etasr.com kanwal et al.: critical factors of e-learning adoption and acceptance in pakistan: a literature review this increasing trend clearly shows the significance of elearning in pakistan. on the whole this increasing trend in the publications highlights the awareness and importance of this area among the researchers and practitioners. b) types of publication in this section, the authors classify the recorded list of 40 papers based on the publication type. the data presented in figure 2 demonstrate that many of the publications are conceptual and qualitative research papers, followed by the limited number of research papers based on quantitative analysis. the total conceptual and qualitative papers are 25 and the quantitative evidences in this context are 15 in number. this limited number of publications clearly depicts that this growing trend of technology need attention of researchers and practitioners. critical success factors of e-learning adoption should be identified and tested to successfully implement elearning in pakistan. table iv depicts the quantitative evidences in the case of pakistan. table iii. number of papers meeting inclusion criteria database searched total number of papers searched number of papers in case of pakistan science direct 73 1 emerald 6 2 elsevier 25 0 ieee 110 0 acm 127 0 other journals (international & local) 44 37 total 40 fig. 1. total number of publications fig. 2. types of publications vii. discussion e-learning adoption and acceptance, in pakistan is in the rudimentary stages of its development [26-28]. the literature shows that pakistan is also experiencing diverse issues in the successful implementation of e-learning. demographic factors, social factors, non-compliance with the system, infrastructure, and lack of experienced faculty, internet access, cultural and political concerns are the immense hurdles of e-learning implementation in pakistan [22, 29-30]. moreover, the development and implementation faces numerous challenges. the socio-economic situations, technological aptitude, and personality traits of individuals have been identified as great hurdles in e-learning adoption and acceptance. researchers have paid lot of attention in exposing the hurdles of implementing e-learning in pakistan. in [31], authors reported that the gop is overwhelmingly developing and implementing ict infrastructure without evaluating the realistic need and utilization in respective sectors. in the case of pakistan, it is identified that successful integration of ict in heis demands that critical factors should be analyzed and merged into a locally developed model of technology adoption [38]. to investigate the numerous challenges faced by pakistan in the deployment of e-learning systems a research study was conducted in a private university in pakistan to identify the barriers and issues in successful adoption of e-learning [58]. the study concluded that computer access, technical language, and privacy issues are the major challenges. in another study, it was emphasized that hardware and technology support, teachers’ and students’ intention to use e-learning systems, and a knowledge and communication gap among stakeholders (users, developers, and policy makers) may lead to the failure of implementation and policy processes [29]. among all the related concerns, the pre-requisite for policy makers, practitioners, experts, and system developers is to analyze the factors that may significantly affect students’ attitude and positively influence their continued use of elearning systems. furthermore, an investigation found that there is no universal model for e-learning adoption as acceptance and refusal may depend on contextual factors that are culturally dependent. in this study, it was also highlighted that the users’ organizational characteristics, social environment, and ict-policies of pakistan are different from any other country [22]. in addition, the success of e-learning systems does not depend on the availability of technology. the problem arises when the system is not designed from the students’ perspective due to differences in terms of culture and social impact [36]. another study explored how one of the reasons for low adoption and acceptance is poor local research [35]. it is highly necessary to record users’ views and requirements according to the local context for the successful implementation of elearning systems. some experts also highlighted the need to work on the theoretical and conceptual framework of e-learning adoption in the educational sector [59]. moreover, experts identified that understanding and assessment of human requirements in the planning and implementation processes of e-learning are critical for the government and policy makers [34]. another study identified low student motivation, shortage engineering, technology & applied science research vol. 7, no. 4, 2017, 1888-1893 1891 www.etasr.com kanwal et al.: critical factors of e-learning adoption and acceptance in pakistan: a literature review of qualified faculty, lack of educational facilities, and access to higher education as the major problems in pakistan [25]. some of the studies present the quantitative facts in adoption and acceptance of e-learning. authors in [37] investigated the cultural factors, course contents and human-computer interaction. the results revealed that the medium of instruction affects learner outcome whereas computer interaction should be considered while designing the system. table iv. quantitative studies of pakistan reference critical success factors target audience [45]  cultural  power distance  uncertainity avoidance faculty [46]  information quality  system quality  service quality student [47]  synchronous mode  asynchronous mode student [48]  technology quality  usefulness student [49]  cultural  management support  subjective norm  pu & peou faculty [25]  cultural  personal  social  technical  institutions domain experts [50]  categorization of critical factors  software  technical  institutional  cultural  personal faculty [51]  capacity building student employee [52]  social sites used as tool student [53]  learning style  age employee [54]  infrastructure perspective student [53]  learning style employees [55]  compared the traditional learning with e-learning student [56]  e-learning predictors (educational technologies, development and use)  satisfaction, problems and prospects faculty and management [30]  e-learning predictors and use practices faculty and administrator [57]  problems of e-learning academic staff and management in [54], authors investigated the learning objectives and demographic factors on behavior, especially intention towards use, concluded that learning objectives have positive influence on behavior intention through perceived usefulness and perceived ease of use whereas the demographic factors have no influence on behavior intention. moreover, quantitative research concluded that e-learning plays a key role in capacity building and enriches the professional expertise in the specific field of interest [51]. a quantitative investigation found that normative belief, institutes and governments that support perceived usefulness influence behavior intention, whereas government support has no direct impact on behavior intention [49]. viii. conclusion this study provided a systematic literature review and contributed valuable insights into the status of e-learning research regarding pakistan. administrative and organizational support, learner and faculty attitudes, cultural norms (language, religious belief and local culture), social influence, economic concerns and technical factors like organizational infrastructure, content customization, software support, accessibility of hardware and internet are the critical factors of 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agriculture morogoro, tanzania mkwizumh@gmail.com verdiana grace masanja school of computational and communication science and engineering nelson mandela african institution of science and technology arusha, tanzania verdiana.masanja@nm-aist.ac.tz received: 18 january 2022 | revised: 7 february 2022 | accepted: 11 february 2022 abstract-the flow of nanofluids through a porous medium is considered the optimum method for convective heat transfer. in this study, nanofluid flow in a porous pipe with navier slip is investigated. two water-based nanofluids, copper (cu) and alumina (al2o3), were considered. the governing equation is presented and non-dimensionalization has been done for momentum and energy equations, initial and boundary conditions, skin friction, and nusselt number. the governing system was simplified to ordinary differential equations, which were numerically solved and a mathematical model of nanofluid flow was formulated. the results, with regard to variations in various parameters such as temperature, velocity, skin friction, and nusselt number, are presented graphically and discussed. it was found that the velocity during the flow decreases with the increase of the navier slip. keywords-navier slip; skin friction; nanofluid; porous pipe i. introduction flow of a fluid through porous media occurs in many technical fields such as ground water flows, flow through embankment dams, composite-structures (culverts), filtering and waste water treatment. authors in [1] studied the fluid flow in a uniform porous pipe considering suction and injection. they established that changes of velocity and vorticity were great in the boundary layer while outside the boundary layer their variation is low. authors in [2] investigated the flow of nanofluids in porous media and the influence of the flow on heat transfer. it was discovered that porous media and nanofluids can be used to improve heat transmission. although the flowing of fluids through porous media has been a subject of great interest for centuries, however, recently, the movement of nanofluids in porous media has caught a lot of attention especially in cooling systems, filtering systems, heat transfer, diffusion, and osmosis. in 1995, authors in [3] introduced new coolant fluids called nanofluids which, when compared to pure liquids exhibit the following advantages: higher specific surface area, greater dispersion stability with predominantly brownian particle motion, reduced pumping power to obtain an equivalent intensity of thermal transfer, and reduction of the clogging of particles in relation to regular sludge. these advantages favor the miniaturization of the system. authors in [4-6] have established that nanofluids possess variable particle concentrations, including thermal conductivity and adjustable properties to suit various applications and thus significantly improve heat transfer rates. recently, in the field of heat transfer, studies of nanofluid flow in porous media have garnered much interest as a result of their diverse range of uses in high performance insulation, e.g. grain storage, buildings, packed sphere beds, geothermal systems, solar collectors, and underground spread of pollutants [1, 2, 7-11]. skin friction is one form of drag, which happens when the fluid appears to shear around the surface of the wall and thereby it affects the energy expenditure. the performance of a forward moving object or fluid flowing through given media improves when the drag is reduced. authors in [12] established that roughness can cause skin friction inside the pipe or duct or in the boundary layers of the fluid's flow. it was found that systematic roughness can be monitored by knowing which scales of roughness come up with high frictional drag. most studies have considered a no-slip boundary condition at the solid wall. but in reality, this is not quite correct. for example, numerical experiments have indicated that in composite manufacturing processes and in lubrication approximation, the degree of wall slip becomes more important at wall surfaces, which means that micro and nano processes are used in wall slip [13]. navier was the first to mention this ailment in 1827 [14]. his model explains that the tangential celerity or corresponding author: wivina nathan muyungi engineering, technology & applied science research vol. 12, no. 2, 2022, 8342-8348 8343 www.etasr.com muyungi et al.: the effect of navier slip and skin friction on nanofluid flow in a porous pipe boundary slip velocity ���� varies proportionally with the tangential shear stress or shear rate ���� provided that the amount of slip or proportionality coefficient is constant with regard to the boundary flow conditions. this is called slip length ���. slip length is driven by several factors, such as the surface roughness, the strength of the wall-fluid interaction, shear rate, and fluid structure. a non-zero, defined wall slip coefficient would better characterize the state of the wall boundary. authors in [15-17] established that for a wide variety of materials (e.g. polymers and nanofluids), slip exists on solid surfaces. such slip is known as the navier slip. many studies have been carried out on the navier slip. authors in [18] discussed newtonian fluids flowing in an unsteady through a porous cylindrical pipe with slip conditions. they considered flow behavior for two different cases of small suction and small injection, and established that the magnitude of the axial velocity component is directly proportional to the numerical value of the slip parameter. further, it has been observed that for small suction the value of the axial velocity component decreases and it increases when there is a small injection. authors in [19, 20] studied the impact of nanofluid thermal radiation and convection flow due to the cylinder being stretched inside a porous medium, as well as the presence of slip boundary conditions and viscous dissipation. they observed that with a rise in the eckert number, the thermal slip, the radiation parameters, and the nusselt number decrease. in addition, with a rise in the velocity, natural convection and slip parameters are enhanced. studies have established the existence of a close relationship between drag and partial slip parameters. for example, the drag values increase with the increase in the slip parameter [8, 12, 19]. the absolute value of the coefficient of skin friction decreases as heat generation/absorption and thermal radiation increase. also, the overall stress levels are lowered by the regulated level of partial slip. with more attention to nanomaterials, e.g. nanofluids, it is predicted that there will be an increase in the application of partial slip boundary conditions in the future. therefore, the slip at the wall surface is important as it can lead to the improvement of the design and operation of many industrial and engineering devices, for example devices for rheometric measurements, material processing, and fluid transportation [21]. in this paper, a mathematical model is developed and used to study the effect of navier slip and skin friction on nanofluid movement in a porous pipe, which seems to be missing in the literature. ii. mathematical model formulation we consider an unsteady, one dimensional, laminar and incompressible flow through a porous pipe, of cu and al2o3 as nanoparticles in water-based nanofluids. these nanofluids exhibit a high level of catalytic activity consequently, they improve heat performance, and reduce wall temperature disparities. the two nanofluids are considered to be newtonian and they are flowing with uniform velocity �. the partial slip condition on the wall of the porous pipe is assumed to hold. according to newton's law of cooling, the pipe surface exchanges heat with the surrounding environment. the flow problem diagram is expressed in figure 1. fig. 1. the schematic flow of the problem. in figure 1, the nanofluid temperature is denoted by t , and the velocity in the r-direction is given by u. represents the ambient temperature, �� is the dynamic viscosity, �� is the nanofluid thermal conductivity, ��, �, �� are the cylindrical polar coordinates, heat transfer coefficient is denoted by h and � represents the navier slip parameter. the equations governing the flow are: �� �� � 0 (1) ��� � �� ��̅ � � �� �� � ! �" �� � ��� �#� ��# (2) ��$"��� � �% ��̅ � � �% �� � �� �#% ��# � ��� � �� �� & (3) where, '̅ is the time and ( is the nanofluid pressure. the dynamic viscosity of the nanofluid is denoted by ���, ��$"��� is the heat capacity of the nanofluid, and ��� represents its density. the nanofluid constants are defined as given in (4): ��� � �1 ! *��� � *�� +�� � ,-. �/01�-. , ,-.,. � 2,34&,.56&7�,.6,3� 2,34&,.547�,.6,3� , 8 � �/01�3�/01�., (4) ��� � 9. �:67�#.< , ��$"��� � �1 ! *�2�$"5� � *��$"�� where �� and �� respectively are the fluid and solid fraction's reference densities, the thermal conductivities of the solid and fluid volume fractions are represented by � and �, +�� is the thermal diffusivity of the nanofluid, * is the solid volume fraction of nanoparticles, ��$"�� is the heat capacity of the solid and the heat capacity of base fluid is ��$"��. the initial conditions are given in (5) and the boundary conditions are given in (6) and (7). u�r,0� � 0, t�r, 0� � t@ , where 0 d r d a (5) �� �� �� �0,' f�, � !�g�0,' f�, �0,' f� � (6) g�h, '̅� � 0, ! �� �% �� �h, '̅� � i� �h,'̅� ! � (7) table i. nanoparticle and water thermophysical properties physical properties fluid phase (water) cu al2o3 jk(j/kgk) 4179 385 765 l (kg/mn) 997.1 8933 3970 source: [22, 23] engineering, technology & applied science research vol. 12, no. 2, 2022, 8342-8348 8344 www.etasr.com muyungi et al.: the effect of navier slip and skin friction on nanofluid flow in a porous pipe the following are introduced as dimensionless variables and parameters: � � %6%o%p6%o , q = � r , s = � , ' = �̅t. # , u� = 9. /. , vw = r t. , x = " 9.r , y = − �"�� , τ = 2/0153 2/015. , [ = � (8) \$ = r # 01.�%p6%o� , x� = 9.01. ,. , $: = ,34&,.6&7�,.6,3� ,34&,.47�,.6,3� , ]^ = _ ,. , and � = 9. ` substituting the dimensionless quantities from (8) into (2), (3) and (5) (7) results into (9) (13) which form the model equations for this study. �a �� = b :6747/3//. + :�:67�#.<�:6747/3//.� �#a � d# − vw �a �d (9) �e �� = $: : f� �:6747g� �#e �d# + h0 �:67�#.<�:6747g� � �a �d & − vw �e�d (10) q�s,0� = 0, ��s, 0� = 0 (11) �a �d �0,'� = − ` 9. q�0,'�, ��0, '� = 0 (12) q�1, '� = 0, �e�d �1,'� = −i]^��1, '� (13) where vw is the raynolds number, a is the parameter for pressure gradient, x� denotes the prandtl number and ec represents the eckert number. the base fluid and the thermophysical properties of the nanoparticles can be used to derive the values of the parameters $: and 8. the skin friction (j�� and the nusselt number (kg) are crucial for this type of study. they are defined as: j� � gl 9or , kg = ml,.�%l6%o� (14) where no is the heat flux at the pipe wall and 8o is the wall shear stress given by: 8o � !��� �� �� p �q , no = − �� �% �� p �q (15) substituting 8o and no from (15) into (14) and using the dimensionless variables with manipulations results to: j� � ! 1 �1 − *�&.r sq ss at s = 1 (16) kg = $: s� ss iii. numerical procedure the method of lines [24] is a semi-discretization finite difference approach for numerically solving a nonlinear initial boundary value problem (ibvp). we divide the solution region into equal rectangles or meshes. each mesh point specifies the point's position in terms of t and ∆q or ∆s .the horizontal axis represents spatial variables, while the vertical axis represents time variables in this rectangular mesh grid. the method is used to discretize (9) to (13) which results in (21)(24). then, the discretization of the partial differential equations (8) and (9) using second order central finite differences results in ordinary differential equations (21) and (22). ua u� � b :6747/3 /. � : �:67�#.<�:6747/3//.� �avwx6&av4avyx ∆ d# − vw �avwx6avyx&∆d (17) ue u� = $: : z{�:6747g� � evwx6&ev4evyx ∆ d# + h| �:67�#.<�:6747g� � avwx6avyx &∆d & − vw �evwx6evyx&∆d (18) where q}�'� and �}�'� are the approximations of q�s}, '� and ��s},'�. with initial conditions (11) we get (23) and boundary conditions (12) and (13) result in (24). q}�0� = �}�0� = 0, 1 ≤ ^ ≤ k + 1 (19) q} � 6~a# ∆d6~ , *: = 0, q�4: = 1, ��4: = *��1 − i]^∆s� (20) the system of nonlinear ordinary differential equations (17) and (18) with known initial condition (19) and boundary conditions (20) has been solved in matlab. iv. results and discussion water-based nanofluids of two types, cu and al2o3, are considered in this study, while the prandtl number is fixed at 6.2, and the effect of the slip parameter ���, solid volume fraction (*�, reynold number (re), biot number (bi), and pressure gradient (a) on the velocity profile and temperature profile are examined. figure 2 shows that the nanofluid velocity profile of al2o3 is higher than that of cu and this may be attributed to the specific heat capacity of al2o3 being higher than that of cu. also, the density of copper is higher than that of alumina. fig. 2. copper and alumina nanofluid velocity profile. figure 3 depicts the effect of nanoparticle fraction in velocity, demonstrating that as the nanoparticle fraction (*� increases, velocity decreases at the wall compared to the center engineering, technology & applied science research vol. 12, no. 2, 2022, 8342-8348 8345 www.etasr.com muyungi et al.: the effect of navier slip and skin friction on nanofluid flow in a porous pipe of the pipe. this may be due to the fact that the increase of nanoparticle regulates temperature of the fluid and causes the thermal boundary layer's viscosity to increase. also this could be due to the density of the nanofluid. an increase in re leads to a decline in velocity and this may be is caused by the uniform flow of nanofluid as revealed in figure 4. figure 5 displays that velocity decreases with increase in �. this effect may be due to the nanofluid sticking at the wall which lowers the velocity and also due to the high viscosity of the fluid. fig. 3. effect of increasing φ on velocity profiles. fig. 4. effect of increasing re on velocity profiles. fig. 5. effect of increasing λ on velocity profiles. figures 6-9 illustrate the temperature profiles of the nanofluids in the pipe and the impact of various factors on the fluid flow system. the temperature profile decreases as the * increases as shown in figure 6, maybe due to the increase of the density of the nanofluid. figure 7 illustrates the temperature decrease due to the increase of re. when it reaches the wall of the pipe the temperature starts to rise due to the slippery walls. fig. 6. effect of increasing φ on temperature profile. fig. 7. effect of increasing re on temperature profile. fig. 8. effect of increasing a on temperature profile. w w w engineering, technology & applied science research vol. 12, no. 2, 2022, 8342-8348 8346 www.etasr.com muyungi et al.: the effect of navier slip and skin friction on nanofluid flow in a porous pipe in figure 8, as the pressure gradient �y� increases, temperature also increases since the viscosity is reduced. in figure 9, the increase in bi is associated with a reduction in temperature. this could be attributed to the convective cooling at the walls which means that there is heat loss through the wall. as demonstrated in figure 10, copper-water nanofluid skin friction is higher than alumina-water nanofluid skin friction. this difference may be caused by the specific heat capacity of alumina which is lower than that of copper. also alumina-water has a lower velocity gradient near the channel walls than cu-water, hence this is to be expected. fig. 9. effect of increasing bi on temperature profile. fig. 10. effect of increasing φ on the skin friction of cu and al2o3 nanofluids. fig. 11. effect of increasing re on skin friction. in figure 11, the decrease of skin friction with the increase of re may be due to the slip parameter. this result is inconsistent with the results obtained in [5-7]. in figure 12, we see that pressure gradient is inversely proportional to skin friction because the kinetic energy of the fluid is used to overcome the friction of the surface during the flow. this result is consistent with the results obtained in [5]. in figure 13, by means of an increase in re, the nusselt number also increases, since during the flow, there is more heat which is produced due to the increase of speed. the viscosity is also reduced. fig. 12. effect of increase in a on skin friction. fig. 13. effect of increasing re in nusselt number. fig. 14. effect of increasing y on nusselt number. n u engineering, technology & applied science research vol. 12, no. 2, 2022, 8342-8348 8347 www.etasr.com muyungi et al.: the effect of navier slip and skin friction on nanofluid flow in a porous pipe in figure 14, we observe that the nusselt number increases with the increase of pressure gradient since there is more force exerted which cause reduction in viscosity during nanofluid flow. in figure 15, the nusselt number also increases when the biot number increases, maybe due to the reduction in viscosity since the fluid has a higher thermal conductivity. the decrease of nusselt number with increase in slip parameter because of the convective cooling at the wall is presented in figure 16. fig. 15. effect of increasing bi on nusselt number. fig. 16. effect of increasing � on nusselt number v. conclusion the effect of navier slip and skin friction of nanofluid flow in a porous pipe have been investigated in this study. the simplified system of ordinary differential equations is numerically solved with the line method. the following is a list of the findings of the current study: • the velocity and temperature is enhanced by the reynolds number. navier slip parameter causes a decrease of velocity and a rise in biot number coincided with a drop in temperature. • the temperature and velocity of copper-water nanofluid rises faster than that of alumina-water nanofluid. • skin friction is retarded by increasing the reynolds number, so we need to increase the volume of nanoparticles in the base fluid to overcome the increased skin friction. an increase of reynolds number or biot number causes the heat transfer at the wall to increase and the opposite for slip parameter. therefore, near the wall, navier slip reduces friction of the porous pipes, such that the more heat is transferred from the system by non-linear radiation. in a linear thermal distribution, the energy transfer coefficient is higher than in a non-linear thermal distribution. nomenclature ��� nanofluid density (kg.i6n� � dynamic viscosity (kg/m.s) �, kinematic viscosity (m2/s) �� nanofluid thermal conductivity (w/m.k) * concentration of nanoparticles $" specific heat capacity (j/kg.k) � navier slip parameter t nanofluid temperature (k) ambient temperature (k) bi local biot number pr prandtl number ec eckert number a dimensionless pressure gradient j� skin friction coefficient nu nusselt number p pressure acknowledgment the authors acknowledge the support of nelson mandela african institution of science and technology. references [1] m. e. erdogan and c. e. imrak, "on the flow in a uniformly porous pipe," international journal of non-linear mechanics, vol. 43, no. 4, pp. 292–301, feb. 2008, https://doi.org/10.1016/j.ijnonlinmec.2007. 12.006. 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[24] k. w. morton and d. f. mayers, numerical solution of partial differential equations. new york, ny, usa: cambridge university press, 2005. microsoft word etasr_v12_n3_pp8683-8687 engineering, technology & applied science research vol. 12, no. 3, 2022, 8683-8687 8683 www.etasr.com kebbati et al.: memristor, memcapacitor, meminductor: models and experimental circuit emulators memristor, memcapacitor, meminductor: models and experimental circuit emulators youssef kebbati laboratoire de physique et chimie de l’environnement et de l’espace lpc2e, université d’orléans, orléans, france youssef.kebbati@cnrs-orleans.fr pierre-sylvain allaume université d’orléans orléans, france pierre-sylvain.allaume@univ-orleans.fr yacine bennani université saad dahlab blida, algeria bennani.yacine@gmail.com received: 4 march 2022 | revised: 25 march 2022 and 31 march 2022 | accepted: 4 april 2022 abstract-before 1971, the number of passive electrical components was limited to three: resistor, capacitor, and inductor. in 1971, pr. chua predicted the existence of a fourth element, called memristor, since it corresponds to a resistor with memory behavior. several years later, the concept of memory circuit was extended to capacitors and inductors. this paper proposes mathematical models for mem-elements, validated by matlab and experimental circuit emulators for memcapacitor and meminductor. the experimental results show a good fit between theory, ltspice simulations, and emulation circuits. keywords-memristor; memcapacitor; meminductor; models and simulations; experimental emulator i. introduction the memristor, or memory resistor, is a two-terminal passive electronic component. memristor, as a concept, was introduced in 1971 by leon chua [1]. chua defined the behavior of the memristor by a constitutive relationship between flux and charge linkage. however, the concept of memristor did not catch the attention of the scientific community until 2008. the electronic community continued to develop analog and digital circuits without considering the tremendous potential of memristors [2-4]. in fact, hewlett packard (hp) labs manufactured the first memristor component with layers of tio2 between two layers of pt in 2008 [5]. hp also introduced a mathematical model of component operation. the scientific community criticized this model in several points but subsequently the model was widely used [6]. since then, thanks to the memory effect and nonlinear behavior, the memristor found use in various domains, such as neural networks [7–11], programmable analog circuits [12–15], logic gates [16], adaptive filters [17], chaotic circuits [18, 19], and non-volatile memories [20–22]. ii. mathematical models chua, pershin, and di ventra established the electrical relations for memristor, mecapacitor, meminductor as can be seen in [23] and in figure 1 of [24], where the charge (q), the time-integral of the voltage (ϕ), the time-integral of the charge (σ), and the time-integral of the flux (ρ) are visualized. a. memristor models two pairs of equations define the memristor: electrical load control and the magnetic flux control [1, 25]. for electrical load control: ���� = ������ ��� (1) ���� = �����/�� for magnetic flux control: i�t� = w�φ�t� v�t� (2) ���� = �����/�� according to the mathematical relations, the electrical resistance of the memristor is not constant but depends on the current that was previously circulated through the device. in 1976, l. chua introduced dynamic equations to define a memristive system with the property of "pinched hysteresis loop" between current and voltage [25, 26]. according to biolek, this footprint of the memristif is "self-crossing" which corresponds to a cross with coordinates (0:0) [27]. the pinched hysteris loop/self-crossing was extended to memcapacitor and meminductor. the hp model’s is based on the "modulation" of the size of the doping zone w of the memristor between the value ron and roff as a function of the electrical loads (current) that runs through the component. ���� = ���� �1− ����� ! ����" (3) #��� = μ% ���& ���� corresponding author: y. kebbati engineering, technology & applied science research vol. 12, no. 3, 2022, 8683-8687 8684 www.etasr.com kebbati et al.: memristor, memcapacitor, meminductor: models and experimental circuit emulators where m(q) is the instantaneous value of the memristor, w the size of the doped zone, d the total size of the doped zone, and µv the mobility of the electric charge [5, 6]. b. memcapacitor models the memcapacitance is defined with the electrical relation between the time-integral of the charge (σ) and the timeintegral of the voltage (ϕ). it can be either voltage-controlled or charge-controlled depending on its constitutive input variable [25, 28]. in the case of voltage controle, the memcapacitance cm is: '(�)� = *+�,�*, with '( = ./ (4) *+ *0 = ���� then, ���� = *+ *, . *, *0 � '(�)� . ���) c. meminductor models the meminductor represents the link between charge q(t) and the time integral of the flux ρ(t). the mathematical representations of meminductors have two forms: currentcontrolled meminductor or flux-controlled meminductor [22, 25]. thus, the meminductance lm is: 2((q)= *3�4� *4 , � *+ *0 , ⇒ 2((q).di= �� (5) note that, the pinched hysteris loop/self-crossing which corresponds to a cross with coordinates (0 : 0) is footprint of the mem-elements [26, 27]. (a) (b) fig. 1. (a) pinched hysteresis loop appearing between current and voltage for sinusoidal input with frequency f=10hz (green), 50hz (red), (b) variations of memristif values versus voltage. iii. matlab implementation and numerical results a. memristor implementation the model was implemented on matlab. figure 1 shows the pinched hysteresis loop between current and voltage and the variation of memristor versus voltage. for this simulation, the electrical load control was chosen. note that if the frequency increases beyond 100hz, the characteristic becomes a linear line corresponding to ohm's law. b. memcapacitor implementation the model was implemented in matlab and the footprint (pinched hysteresis loop) of the memcapacitor appears under sinusoidal input between voltage and electrical load. figure 2 shows the results. (a) (b) fig. 2. (a) voltage and electric load pinch hysteresis loop, (b) variation of current versus voltage. c. meminductor implementation the model was implemented in matlab and the footprint (pinched hysteresis loop) of meminductor appears under sinusoidal input between flux and current. figure 3 shows the numerical results. iv. experimental circuit emulators to the best of our knowledge, there are no physical implementations of memcapacitor or meminductor circuits. due to this, there has been an emerging research devoted to the development of emulator circuits of these devices during the recent years. in the literature, different approaches have been proposed for the emulation of memcapacitors and m e m ri st o r (ω ) voltage (v) engineering, technology & applied science research vol. 12, no. 3, 2022, 8683-8687 8685 www.etasr.com kebbati et al.: memristor, memcapacitor, meminductor: models and experimental circuit emulators meminductors. most of them are based on memristor component or its circuit emulator [24, 29-32]. in our case, we chose to develop memcapacitor and meminductor circuit emulators that do not require the use of a memristor or its emulator. in fact, our emulators are based on the same design and are able to emulate either a memcapacitor or a meminductor with minimal changes. (a) (b) fig. 3. (a) flux and current pinch hysteresis loop, (b) variation of current versus voltage. the circuit emulators are based on voltage/current converter with operational amplifier. the operating principle of the circuits is based on a second output feedback which is connected to the non-inverting input of the amplifier through the capacitor c2. thus, in both cases, the c2 capacitor provides the memory effect. figures 4-5 show the circuit emulators and transient simulation results from ltspice. the pinched hysteresis appears between the voltage source and the current in c2. the circuit parameters are: • for the memcapacitor emulator c1=c2=50nf, vf=(1v,100hz), vin=(1v,200hz). • for the meminductor emulator l=10mh, c2=50nf, vf=(1v,100hz), vin=(1v,200hz). frequency simulations of the emulator circuits show that they act as filters. the memcapacitor emulator has a high-pass filter behavior and the meminductor emulator acts as a lowpass filter. in the figure 6, the frequency simulation (bode diagram) results can be seen. (a) (b) fig. 4. memcapacitor emulator. (a) (b) fig. 5. meminductor emulator. engineering, technology & applied science research vol. 12, no. 3, 2022, 8683-8687 8686 www.etasr.com kebbati et al.: memristor, memcapacitor, meminductor: models and experimental circuit emulators (a) (b) fig. 6. frequency simulations of emulators: (a) memcapacitor, (b) meminductor. in fact, we can show that the circuit emulators have equivalent circuit filters. these circuits can easily be built from passive elements. figure 7 presents the equivalent circuit filters and bode diagram results. fig. 7. equivalent circuit filters and simulation results. in order to validate the memcapacitor and meminductor emulators, circuit implementations were made. figures 8-9 show the implementation and the experimental responses of the circuits. (a) (c) (b) (d) fig. 8. experimental implementation and results: (a) (b) memcapacitor, (c) (d) meminductor. the obtained results show a good fit between the simulations and the experimental tests. however, during the tests, the memcapacitor and meminductor effects were obtained at lower frequencies than those of the ltspice simulations. we assume that the implementation of emulators on pcb will achieve better results in terms of operating frequency. indeed, some parasitic effects will be reduced. v. conclusion in this paper, the concepts of memory-elements memristor, memcapacitor, and meminductor were presented. after the presentation of the mathematical models describing the behavior of these components, the circuit emulators for memcapacitor and meminductor, based-on operational amplifier voltage/current converter, were shown. the results show a good fit between the experimental tests and theory simulations. references [1] l. chua, "memristor-the missing circuit element," ieee transactions on circuit theory, vol. 18, no. 5, pp. 507–519, sep. 1971, https://doi.org/10.1109/tct.1971.1083337. 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[32] m. d. ventra and y. v. pershin, "on the physical properties of memristive, memcapacitive and meminductive systems," nanotechnology, vol. 24, no. 25, feb. 2013, art. no. 255201, https://doi.org/10.1088/0957-4484/24/25/255201. microsoft word 9-701-ed.doc engineering, technology & applied science research vol. 6, no. 3, 2016, 1018-1022 1018 www.etasr.com miandoab and gharehchopogh: a novel hybrid algorithm for software cost estimation based on … a novel hybrid algorithm for software cost estimation based on cuckoo optimization and k-nearest neighbors algorithms elnaz eskandarian miandoab department of computer engineering, urmia branch, islamic azad university, urmia, iran elnaz_es_m@yahoo.com farhad soleimanian gharehchopogh department of computer engineering, urmia branch, islamic azad university, urmia, iran bonab.farhad@gmail.com abstract—the inherent uncertainty to factors such as technology and creativity in evolving software development is a major challenge for the management of software projects. to address these challenges the project manager, in addition to examining the project progress, may cope with problems such as increased operating costs, lack of resources, and lack of implementation of key activities to better plan the project. software cost estimation (sce) models do not fully cover new approaches. and this lack of coverage is causing problems in the consumer and producer ends. in order to avoid these problems, many methods have already been proposed. model-based methods are the most familiar solving technique. but it should be noted that model-based methods use a single formula and constant values, and these methods are not responsive to the increasing developments in the field of software engineering. accordingly, researchers have tried to solve the problem of sce using machine learning algorithms, data mining algorithms, and artificial neural networks. in this paper, a hybrid algorithm that combines coa-cuckoo optimization and k-nearest neighbors (knn) algorithms is used. the so-called composition algorithm runs on six different data sets and is evaluated based on eight evaluation criteria. the results show an improved accuracy of estimated cost. keywordssoftware cost estimation; cocomo model; coacuckoo optimization algorithm; knn algorithm i. introduction nowadays, software manufacturer organizations are expected to generate computer tools to manipulate and manage usually large amounts of data. the main problem usually observed is the mismatch between the project cost estimation and the sactual cost. in order to reduce this difference, software developers need to collect certain initial information. these socalled information can be classified as follows [1]: • information relating to the capabilities and major and minor objectives of the software. • information relating to the organization that will operate the software. • information relating to the organization that will produce the software. prevalent use of software packages ready in certain parts of software projects reduces the cost of software development. at the same time, new software development processes are presented and manufacturers are trying to adapt to these processes. some of these processes include risk-based and dynamic software processes, new programming languages, software applications for software development as well as commercial software, which improve the quality of software products, reduces production costs, reduces the risk and the produced software life cycle [2]. however, current models of estimating software development cost do not fully cover new approaches. and this lack of coverage causes problems in the consumer and producer ends. ii. previous works with the introduction of machine learning algorithms in the field of software engineering, many researchers have used such algorithms for sce. some of these models can be briefly described as follows: in [3] fuzzy logic was implemented for sce. they introduced cost estimation projects as one of the most important challenges and activities in software development. the researchers used 14 projects included in kemerer projects collections. according to their results, the mean absolute error percentage of relative error and productivity rate improved compared to algorithmic methods. one of the software process criteria having a direct impact on estimated cost is the number of application lines and application thousand-line. in [4], the composition of ant colony optimization algorithm and chaos optimization algorithm was used for sce. the researchers used lorenz mapping to generate random data for the chaos optimization algorithm and for training they used the ant colony algorithm. this composition algorithm was evaluated on nasa 63 data set, and the results showed that the composition of ant colony optimization algorithm and chaos optimization algorithm has a better performance compared to the cocomo model and also has a relative lower error than the cocomo model [4]. the composition of multilayer perceptron networks and cocomo ii is used in [5]. to evaluate the proposed method, 63 cocomo ii software projects have been used. the main objective of this composition is better training of the multilayer engineering, technology & applied science research vol. 6, no. 3, 2016, 1018-1022 1019 www.etasr.com miandoab and gharehchopogh: a novel hybrid algorithm for software cost estimation based on … perceptron. in the composition model, effort factors and scale factors are taught by the intermediate layer and evaluated by the cocomo ii model. the sigmoid function was used as the activation function for the intermediate layer. backpropagation is used for teaching. the data training and testing phases are 80% and 20%, respectively. the experiment results show that the standard error of relative error in the composition model is less than the cocomo ii model. a new methodology for sce based on particle swarm optimization algorithm and fuzzy logic was proposed in [6]. estimation of the software cost depends on the estimation of the size of the project and its parameters. for measurements uncertainty, fuzzy logic is applied and particle swarm optimization is used for parameters. in the proposed method, the triangular membership function is used. evaluation is implemented on nasa63 dataset. the results show that the proposed method has lower error compared to other models. a composition of firefly and genetic algorithms was been proposed in [7]. evaluation is implemented on nasa93 dataset. in the proposed method, the genetic algorithm, via elitism operation, tries to obtain the best answer for effort factors and evaluate the fitness function, and provide the lowest error solution as the final answer. the results show that the average value of the relative error in cocomo model is 58.80, and in genetic and firefly algorithms is 38.31 and 30.34, respectively and in the composition model is 22.53. note that (25) pred on genetic and firefly algorithm models is 77.41 and 80.64 respectively and in the composition model is 88.17. comparisons show that the composition model compared with cocomo model increased the efficiency of the estimated precision about 2.88%. iii. basic concepts a. sce and cocomo ii among the algorithmic models presented for sce, cocomo ii is the most popular. this model provides a basis method to predict the number of people needed per month for software development in the industry. this model can also estimate the development time, the amount of effort required in each software development phase and the required cost [8]. the formulas used are listed in table i. table i. cocomo model formulas formula project type 15 1.05 i i=1 pm=2.4 (size) em⋅ ⋅ organic 15 1.12 i i=1 pm=3 (size) em⋅ ⋅ semi organic 15 1.2 i i=1 pm=3.6 (size) em⋅ ⋅ embedded the “size” parameter is the project’s size in thousands of lines of ksloc code, and the “em” parameter is the effort coefficient b. knn algorithm the knn algorithm was described for the first time in [9]. the selection of k in this method is very crucial. if the value of k is selected too small, the algorithm becomes sensitive to noise. if the value of k is selected too large, the records of other classes may also be included among the nearest neighbors. when k is selected as a large number, it leads to a classification error [10]. the algorithm searches the test space for k samples close to the unknown sample. this closeness is defined by the euclidean distance. then, the label having the majority among k neighbors is given to the unknown sample. c. coa-cuckoo optimization algorithm coa-cuckoo optimization meta-heuristic algorithm was first developed in 2009 [11]. in the first step of the cuckoo algorithm, the first primary settlement sites are produced. in an n-dimensional optimization problem, settlement areas will be an n*1 array, showing the current position of cuckoo living areas. the appropriateness of the current living location is obtained by assessing the utility function at the location. each cuckoo has a specified range for the number of laying eggs. after cuckoo chicks’ growth, theses chicks migrate to other areas for laying eggs and the assumed migration location is also calculated [12]. d. evaluation criteria in sce finally, any research work to determine the accuracy of the work done should be evaluated by a series of criteria. a number of the criteria used to assess sce techniques is shown in table ii [12, 13]. table ii. evaluation criteria criteria name criteria formula mean magnitude error relative (mmer) n i i i=1 i act -est1 mmer= 100 n est ⋅å mean magnitude of relative error (mmre) n i i i=1 i act -est1 mmer= 100 n act ⋅å median magnitude of relative error (mdmre) n i i i=1 i act -est1 mdmre=median( 100) n act ⋅å pred(m) n i=1 1, if mre m1 pred(n)= 0, otherwisen ì £ïïí ïïî å mean squared error (mse) n 2 i i i=1 1 mse= (act -est ) n å root mean squared error (rmse) n 2 i i i=1 1 rmse= (act -est ) n å mean of absolute errors (mae) n i i i=1 1 mae= act -est n å mean absolute percentage error (mape) n i i i=1 i act -est1 mape= 100 n act ⋅å engineering, technology & applied science research vol. 6, no. 3, 2016, 1018-1022 1020 www.etasr.com miandoab and gharehchopogh: a novel hybrid algorithm for software cost estimation based on … in these criteria the “n” variable denotes the total number of data in the data set; the “act” variable represents the real cost; the “est” variable represents the estimated cost; the “i” variable indicates any data index, which ranges from 1 to n. iv. proposed method in the first step of the algorithm, the data is normalized and vague and empty data are deleted. after this stage, a composition algorithm is implemented, and in the first stage of the implementation, the data are classified randomly into two subsets of training and test (20% and 80% respectively). after this initial classification, data in training and testing data set are classified into three different categories using knn based on the features available in the data set, and the training data set is sent to coa-cuckoo algorithm for training. in the first stage of training, the primary parameters of coa-cuckoo optimization algorithm such as the number of initial cuckoo population, the number of algorithm iterations, the minimum and maximum eggs to be laid for each cuckoo, and random variables are initialized. after determining the number of cuckoos, the cuckoos are randomly initialized. upon completion of this stage, cuckoos lay eggs in different nests. at this stage, if alien eggs are identified by an adult cuckoo, these eggs will be destroyed; otherwise, the eggs grow and then are converted to mature cuckoo chicks. after the growth of cuckoos, if the number of cuckoos is greater than the the initial population predetermined, cuckoos that live in the worst place will be lost. after that, the optimal amount of each living location is assessed and the best place is selected. then, the adult cuckoos migrate to places close to this location. it should be noted that the condition of completion of the algorithm is the number of iterations or a minimum value that reaching this minimum value indicates obtaining the goal. in table iii and figure 1, the proposed scheme is shown. as shown in figure 1, after finishing each training phase, the results of this phase are stored, and then are applied as peer to peer test on test data set that is divided into three categories, and finally, the results obtained are displayed in the form of charts and text data. table iii. the outline of the proposed approach inputs: user selected data sets include: factors affecting the estimate and the actual cost of any software project outputs: constant amounts of comoco model and classified data step 1: read the existed data in the dataset step 2: breakdown to training and testing data step 3: classification of training and testing data based on knn step 4: invoking cuckoo optimization algorithm for each class of software step 5: giving the initial value to cuckoo optimization algorithm parameters and constant parameters of comoco model step 6: ovipositing of cuckoos in different nests step 7: killing the alien known eggs step 8: checking the size of cuckoos’ population and in the case of large population, eliminating the worst places of cuckoo residence step 9: checking cuckoo fitness function step 10: finding the best places to grow cuckoos (maximum fitness) step 11: determining cuckoo population and migration to new residential areas step 12: determining the laying radius for each cuckoo step 13: in the case of non-completion algorithm go to the sixth stage step 14: finalizing cuckoo optimization algorithm step 15: save the generated values for fixed parameters of cocomo model (by cuckoo optimization algorithm) and store classified samples fig. 1. the way of performance of the proposed approach v. discussing and evaluating the results the nasa60, nasa63, nasa93, maxwell, kemerer, and miyazaki data sets are used. the results are displayed in tables iv to ix in terms of error rate. for the nasa60 dataset (table iv) the proposed method has acted in all criteria better than comparative approaches. for the nasa63 dataset (table v) the proposed method performs equally to knn for the pred(n) criterion, and better than the cocomo model and knn for the mdmre criterion and worse than the coa-cuckoo optimization algorithm. for the nasa93 dataset (table vi) the proposed method performs equally to knn for the pred(n) evaluation criterion, and better than all comparative algorithms for rest of the criteria. for the maxwell dataset (table vii) the proposed method performs better for all criteria, except for rmse, mse, mae. for these criteria, it has performed better than coa-cuckoo and worse than cocomo model and knn. for the kemerer dataset (table viii) the proposed method has performed better in all criteria, and only in pred(n) criterion has performed equally to coa-cuckoo. for the miyazaki dataset (table ix) the proposed method has performed better in all criteria and only in pred(n) criterion it has performed equally to the knn. engineering, technology & applied science research vol. 6, no. 3, 2016, 1018-1022 1021 www.etasr.com miandoab and gharehchopogh: a novel hybrid algorithm for software cost estimation based on … table iv. evaluation of the proposed method on the nasa60 dataset mmer mmre mdmre rmse mape mae pred(n) mse cocomo ii 19.43 16.09 16.27 92.31 16.09 50.34 0.83 8521.4 knn 16.67 15.52 14.68 83.64 15.52 43.3 0.83 6995.79 cuckoo 14.77 18.6 15.7 83.21 18.6 47.14 0.75 6924.33 proposed method 13.85 14.86 8 67.77 14.86 37.47 0.92 4592.82 table v. evaluation of the proposed method on the nasa63 dataset mmer mmre mdmre rmse mapemae pred(n) mse cocomo ii 19.43 16.09 16.27 92.31 16.09 50.34 0.83 8521.4 knn 16.67 14.52 14.68 81.44 15.16 43.64 0.92 6633.15 cuckoo 15.21 16.76 10.56 99.63 16.76 54.4 0.85 9925.84 proposed method 13.25 12.94 13.75 66.96 12.94 36.49 0.92 4483.69 table vi. evaluation of the proposed method on the nasa93 dataset mmer mmre mdmre rmse mape mae pred(n) mse cocomo ii 23.01 18.23 20.98 77.03 18.23 44.49 0.84 5933.62 knn 21.27 17.24 18.18 70.5 17.24 40.04 0.89 4970.08 cuckoo 15.84 14.87 11.59 51.68 14.87 31.28 0.84 2671.27 proposed method 11.03 11.55 8.69 41.06 11.55 23.77 0.89 1686.23 table vii. evaluation of the proposed method on the maxwell dataset mmer mmre mdmre rmse mape mae pred(n) mse cocomo ii 118.44 43.76 36.58 3809.67 43.76 2603 0.38 145135 knn 118.44 43.76 36.58 3809.67 43.76 2603 0.38 145135 cuckoo 103.81 39.99 34.77 4919.96 39.99 3111.74 0.38 242060 proposed method 91.91 35.82 27.67 4539.28 35.82 2851.59 0.54 206051 table viii. evaluation of the proposed method on the kemerer dataset mmer mmre mdmre rmse mape mae pred(n) mse cocomo ii 118.44 43.76 36.58 3809.67 43.76 2603 0.38 145135 knn 118.44 43.76 36.58 3809.67 43.76 2603 0.38 145135 cuckoo 103.81 39.99 34.77 4919.96 39.99 3111.74 0.38 242060 proposed method 91.91 35.82 27.67 4539.28 35.82 2851.59 0.54 206051 table ix. evaluation of the proposed method on the kemerer dataset mmer mmre mdmre rmse mape mae pred(n) mse cocomo ii 79.23 687.64 626.6 1883.09 687.64 1375.95 0 35460 knn 79.23 687.64 626.6 1883.09 687.64 1375.95 0 35460 cuckoo 57.31 50.98 39.34 260.16 50.67 121.56 0.44 694 proposed method 56.69 49.67 35.61 57.31 49.98 39.34 0.44 676 table x. evaluation of the proposed method on the miyazaki dataset mmer mmre mdmre rmse mape mae pred(n) mse cocomo ii 70.83 272.79 277.48 137.7 272.79 122.16 0 18960.4 knn 70.83 272.79 277.48 137.7 272.79 122.16 0 18960.4 cuckoo 62.95 34.45 42.95 26.45 34.45 21.3 0.4 699.54 proposed method 45.54 30.2 38.64 21.14 30.2 17.33 0.4 447.04 vi. conclusion before presenting the new estimation methods, software projects’ cost estimation process of software projects was done with some simple algorithms. but with the passage of time and presenting new methods in the field of artificial intelligence, many methods have been proposed to solve this problem but none of the proposed methods are able to resolve this issue with one hundred percent accuracy. in this paper, a hybrid of two algorithms of cuckoo optimization and knn was used to solve this problem. this hybrid algorithm was evaluated the 6 different data set and based on eight evaluation criteria that the data set includes: kemerer, maxwell, miyazaki 1, nasa 60, nasa 63, nasa93 and evaluation criteria include: mmer, mmre, mdmre, rmse, mape, mae, pred (n), mse. based on the obtained results, it can be concluded that the proposed method in kemerer, miyazaki1, nasa60, nasa93 datasets outperformed in all criteria better than engineering, technology & applied science research vol. 6, no. 3, 2016, 1018-1022 1022 www.etasr.com miandoab and gharehchopogh: a novel hybrid algorithm for software cost estimation based on … cocomo, knn and cuckoo optimization algorithm but in nasa63 dataset in mdmre criterion and in the maxwell dataset mdmre in the evaluation criteria of mse, mae, mse has not a good performance compared to the comparative algorithms, and its reason can be the lack of consistent data.. references [1] f. s. gharehchopogh, “neural networks application in software cost estimation: a case study”, 2011 ieee international symposium on innovations in intelligent systems and applications, pp. 69-73, istanbul, turkey, june 15-18, 2011 [2] b. boehm, b. clark, e. horowitz, r. shelby, c. westland, “an overview of the cocomo 2.0 software cost model”, software technology conference, 1995 [3] k. parkash, h. mittal, “software cost estimation using fuzzy logic”, acm sigsoft software engineering, vol. 35, no. 1, pp. 1-7, 2010 [4] z. a. dizaji, f. s. gharehchopogh, “a hybrid of ant colony optimization and chaos optimization algorithms approach for software cost estimation”, indian journal of science and technology, vol 8, no. 2, pp. 128–133, 2015 [5] c. s. reddy, p. s. rao, k. raju, v. v. kumari, “a new approach for estimating software effort using rbfn network”, international journal of computer science and network security, vol. 8, no. 7, pp. 237-241, 2008 [6] a. b. krishna, t. k. r. krishna, “fuzzy and swarm intelligence for software effort estimation”, advances in information technology and management, vol. 2, no. 1, pp. 246-250, 2012 [7] i. maleki, l. ebrahimi, f. s. gharehchopogh, “a hybrid approach of firefly and genetic algorithms in software cost estimation”, magnt research report, vol. 2, no. 6, pp. 372-388, 2014 [8] s. sarwar, “proposing effort estimation of cocomo ii through perceptron learning rule”, int. j. comput. appl., vol. 7, no. 1, pp. 22–32, 2013 [9] t. m. cover, p. e. hart, “nearest neighbor pattern classification”, ieee trans. inform. theory, vol. it-13, pp 21-27, 1967 [10] t. bailey, a. k. jain, “a note on distance weighted k-nearest neighbor rules”, ieee trans. systems, man cybernatics, vol. 8, pp. 311-313, 1978 [11] x. s. yang, s. deb, "cuckoo search via levy flights", world congress on nature &biologically inspired computing (nabic2009). ieee publications, pp. 210–214, 2009 [12] r rajabioun, “cuckoo optimization algorithm”, applied soft computing, vol. 11, pp. 5508–5518 , 2011 [13] l. f. capretz, v. marza, “improving effort estimation by voting software estimation models”, advances in software engineering, article id 829725, pp. 1-8, 2009 [14] s. kumari, s. pushkar, “performance analysis of the software cost estimation methods: a review”, international journal of advanced research in computer science and software engineering, vol. 3, no. 7, pp. 229-238, 2013 microsoft word etasr_v12_n4_pp8878-8883 engineering, technology & applied science research vol. 12, no. 4, 2022, 8878-8883 8878 www.etasr.com cuong & khanh: improving the accuracy of surface roughness modeling when milling 3x13 steel improving the accuracy of surface roughness modeling when milling 3x13 steel nguyen van cuong faculty of mechanical engineering university of transport and communications hanoi, vietnam nguyencuong@utc.edu.vn nguyen lam khanh faculty of mechanical engineering university of transport and communications hanoi, vietnam khanh_mxd@utc.edu.vn received: 6 may 2022 | revised: 21 may 2022 | accepted: 22 may 2022 abstract-in this study, a milling experiment was performed, with 3x13 steel selected as the experimental material along with tialn coated inserts. the box-behnken method was used to design the experimental matrix with a total of eighteen experiments. cutting speed, feed amount, and depth of cut were selected as the input parameters. three regression models of surface roughness have been established, one using the experimentally measured surface texture, one using the johnson transform to convert the surface texture data, and one using box-cox transformation to convert the surface texture data. a comparison of the accuracy of the three models was performed. the results show that the model using the box-cox transformation has the highest accuracy, followed by the model using the johnson transformation. in addition, the influence of cutting parameters on surface roughness is also discussed in detail. keywords-milling; 3x13 steel; surface roughness; regression model; johnson transformation; box-cox transformation i. introduction experimental research to build a regression model representing the relationship between the input and the output parameters is a commonly used practice in general and in the research on mechanical machining processes in particular. this method has been used for a long time, but it is still not obsolete because its results can be applied directly in the production process. regression models after being built will be used for many different purposes, such as determining the influence of input parameters on the output parameters, predicting the output from defined values of input parameters, or to determine the value of input parameters that ensure a certain purpose of the output parameters. however, those jobs only achieve high efficiency if the regression model has a high accuracy. the four parameters commonly used to evaluate the accuracy of a regression model include the coefficient of determination r-sq, the coefficient of determination r-sq(adj), the percentage of absolute error (pae), and the mean square error (mse) of the results calculated by the regression model and the experiments [1, 2]. the significance of these coefficients has been discussed in [1-3]. the regression model has high accuracy when the two parameters r-sq and r-sq(adj) are as large as possible, and close to 1, while pae and mse are as small as possible. two data transformations, johnson and box-cox are known for being able to improve the accuracy of the regression model [4, 5, 8]. the johnson transformation has been used to improve the accuracy of the surface roughness model when milling aisi 1045 steel [6]. in this study, the regression model of surface roughness without data transformation has r-sq equal to 0.8571, pae equal to 12.11%, and mse equal to 2.54%. meanwhile, this model using johnson transform has rsq, pae, and mse values of 0.8686, 9.22%, and 2.25% respectively. the box-cox transformation has been used to improve the accuracy of the surface roughness model when centerless grinding of scm435 steel [7]. the value of r-sq in the model without data transformation and in the model using data transformation is 0.7801 and 0.8322 respectively. the pae of the model without data transformation is 17.59%, while it is 13.66% when using the box-cox transformation. the value of mse in the model without data transformation is 5.71% and for the model using data transformation, it is 4.15%. in [9], the box-cox method was also used to improve the accuracy of the surface roughness model when milling aisi 1019 steel. parameters r-sq, r-sq(adj), pae, mse of the model without metric transformation had values of 0.898, 0.8899, 14.2%, and 4.53% respectively, while they were equal to 0.9326, 0.927, 8.7%, and 2.28% in the model using box-cox transformation. both the johnson and the box-cox metric transformations were used to improve the accuracy of the surface roughness regression model when surface grinding 65g steel [10]. in this study, three regression models of surface roughness, namely the model without data transformation, the model using the johnson transformation, and the model using the box-cox transformation were built. the conclusion was that the regression model using the box-cox transformation has the highest accuracy, and the regression model that does not use the data transformation has the lowest accuracy. in [11], both johnson and box-cox metric transformations were used to improve the accuracy of the shear force model when milling scm440 steel. it was found that the two models had similar accuracy, and are more accurate than the model without data transformation. authors in [12] also applied both johnson and box-cox transformations to improve the accuracy of surface roughness model when turning 3x13 steel. it was noted that the surface roughness model using the johnson corresponding author: nguyen van cuong engineering, technology & applied science research vol. 12, no. 4, 2022, 8878-8883 8879 www.etasr.com cuong & khanh: improving the accuracy of surface roughness modeling when milling 3x13 steel transformation had higher accuracy than the model using the box-cox transformation, and the model not using a metric transformation had lower accuracy. both johnson and box-cox metric transformations were applied to improve the accuracy of surface roughness modeling when turning 9xc steel [13]. this study determined that the model that uses the box-cox transformation has the highest accuracy, while the model that does not use the metric transformation has the lowest accuracy. johnson and box-cox transformations have been successful in improving the accuracy of the regression model (mostly the surface roughness model). however, when applying both transformations, it was found that each of them showed different conclusions. for every study that suggests that the johnson transformation is better than the box-cox transformation, there is a study with the opposite conclusion. thus, in order to improve the accuracy of the regression model, it is necessary to use both transformations to determine the regression model with the highest accuracy. 3x13 steel (according to gost standard) is commonly used to make parts in shipbuilding, petroleum, chemical technology, food processing technology, etc. [15]. research on surface roughness when processing this steel or equivalent steels has been carried out in [12-16]. however, up to now, no studies have been found that apply the johnson transformation and (or) the box-cox transformation to improve the accuracy of the surface texture model when milling 3x13 steel. so, in this study, 3x13 steel milling experiments were conducted. two metric transformations, johnson and box-cox were used to improve the accuracy of the surface roughness model. the main purpose of this study is to build a surface roughness model with higher accuracy. ii. milling experiment the 3x13 steel samples used in the experiment are boxshaped steel blocks with dimensions of 70×40×45mm. all six surfaces of the samples were rough milled on prior to testing. a 3-axis cnc milling machine was used for this experiment (figure 1). tialn coated cutting inserts and 42mm diameter tips were used. tialn coated cutting pieces are better than many other cutting inserts such as tin coated chips and ticn coated cutting pieces in improving milling quality and productivity [17]. each of the 4 cutting pieces was used for one test to reduce the error of tool wear to surface roughness. the basic parameters of the cutting piece are: l-type cutting insert, 0.3mm tip radius, 0.8mm back cutting edge length, 3.59mm cutting thickness, and 90 0 main cutting angle [17]. three easily adjustable parameters, namely cutting speed, feed amount, and depth of cut were selected as input parameters for the experimental process. the selected values of the cutoff parameters at each level are shown in table i [17, 18]. the experimental matrix was designed according to the boxbehnken method. this type of design is commonly used to design experimental matrices in optimization research [1, 2]. of course, building a regression function representing each relationship between input and output parameters is the basis for optimization, so in this study, the box-behnken method was also used to design the experimental matrix. with three input parameters, each parameter has three levels of values, so the number of experiments of the experimental matrix is 18, as shown in table ii. surface roughness was measured with an sj-301. the roughness probe has a diameter of 0.005mm, 0.8 is the standard length installed for the gauge. each test specimen was measured at least 3 times to determine the surface roughness as the average of 3 consecutive measurements. in addition, a water-based emulsion solution was used during the experiment, with a flow rate of 12lt/min [12]. table i. input parameters parameter sign unit value at level 1 0 1 cutting velocity vc m/min 168 240 312 feed rate fz mm/tooth 0.075 0.150 0.225 cutting depth ap mm 0.14 0.20 0.26 table ii. experimental matrix and results trial code value real value response vc fz ap vc (m/min) fz (mm/tooth) ap (mm) ra (µµµµm) in experiments after johnson transformation after box-cox transformation 1 0 0 0 240 0.150 0.20 0.99 0.24407 1.02030 2 -1 0 1 168 0.150 0.26 1.14 0.68393 0.76947 3 1 0 -1 312 0.150 0.14 0.75 -1.36782 1.77778 4 0 0 0 240 0.150 0.20 0.96 0.12678 1.08507 5 1 1 0 312 0.225 0.20 1.37 1.11439 0.53279 6 -1 0 -1 168 0.150 0.14 0.92 -0.05376 1.18147 7 0 1 -1 240 0.225 0.14 2.11 1.85155 0.22461 8 1 -1 0 312 0.075 0.20 0.81 -0.78032 1.52416 9 -1 1 0 168 0.225 0.20 1.33 1.05213 0.56532 10 0 0 0 240 0.150 0.20 0.97 0.16740 1.06281 11 0 0 0 240 0.150 0.20 0.92 -0.05376 1.18147 12 -1 -1 0 168 0.075 0.20 0.93 -0.00563 1.15620 13 0 -1 1 240 0.075 0.26 0.81 -0.78032 1.52416 14 1 0 1 312 0.150 0.26 0.69 -1.95000 2.10040 15 0 -1 -1 240 0.075 0.14 0.77 -1.16138 1.68663 16 0 0 0 240 0.150 0.20 0.92 -0.05376 1.18147 17 0 0 0 240 0.150 0.20 1.04 0.41348 0.92456 18 0 1 1 240 0.225 0.26 2.26 1.95000 0.19579 engineering, technology & applied science research vol. 12, no. 4, 2022, 8878-8883 8880 www.etasr.com cuong & khanh: improving the accuracy of surface roughness modeling when milling 3x13 steel fig. 1. cnc milling machine. iii. results and discussion the results of surface roughness measurement (ra) are presented in table ii. table iii presents some parameters obtained when analyzing the experimental results with minitab 16 software, with a chosen significance level of 0.05 [1, 2]. from the results in this table, it can be seen that the feed rate is a parameter that has a great influence on surface texture because the p-value of this quantity is much smaller than the significance level [1]. similarly, the quantity fz 2 also has a significant effect on the surface texture. since the coefficient of the feed rate parameter is positive, it shows that increasing the feed rate increases the surface roughness. as the feed rate increases, the contact time between the work surface and the cutting-edge decreases, reducing the number of times the cutting edge hits the part surface, leading to an increase in surface roughness. on the other hand, when the feed increases, the surface roughness will increase, which is also consistent with the theoretical formula for calculating surface roughness as follows: ra =1000×0.0321× fz 2 /r, where fz is the feed rate and r is the tip radius [19]. cutting speed and depth of cut have little influence on surface texture, because the p-values of these two parameters are 0.335 and 0.662 respectively, which are larger than the significance level. however, the effect of cutting speed on surface roughness is greater than that of the depth of cut. increasing cutting speed reduces surface roughness, while increasing cutting depth increases it. the magnitude of the surface undulation is inversely proportional to the cutting velocity and proportional to the depth of cut [18, 20]. from the data in table iii, the surface roughness model shown in (1) has been built. ��(���.) = 0.9667 − 0.0875 ∙ �� + 0.4687 ∙ �� +0.0436 ∙ �� – 0.2346 ∙ ��� + 0.3779 ∙ ��� + 0.1429 ∙��2 + 0.04 ∙ �� ∙ �� − 0.07 ∙ �� ∙ �� + 0.0275 ∙ �� ∙ �� (1) this model has coefficients r-sq and r-sq(adj) equal to 0.8563 and 0.6945 respectively. the values of these parameters are as close to 1 as possible. the value of the coefficient r-sq can be increased if (1) is supplemented with higher order quantities (larger exponents, for example vc 3 , fz 3 , etc). however, doing so will increase the complexity of the model [1, 2]. only 69.45% of the change in surface roughness is due to the change of input parameters. thus, if model (1) is used to predict surface roughness, the accuracy will be limited. therefore, we need to increase the values of r-sq and r-sq(adj) in the regression model without making the model complicated (without using ternary, quaternary, etc.). two metric transformations, johnson and box-cox, will be used to solve this task. the condition to perform the data transformation according to these two transformations is that the data set must not be distributed according to the normal rules [1, 2]. the distribution rule of surface roughness values while testing is presented in figure 2. this figure is acquired in minitab when determining the distribution rule of surface roughness. each red dot represents the surface roughness value at an experiment. these red dots are located far from the middle line, there are even red dots lying on either side of the two curves on either side. at the same time, the p-value < 0.005, which is much smaller than the significance level. this confirms that the surface roughness datasets are not normally distributed, that is, they are eligible to perform the johnson and box-cox data transformations. table iii. experimental data analysis results coefficients standard error t stat p-value intercept 0.9667 0.0985 9.816 0.000 vc 0.0875 0.0853 1.026 0.335 fz 0.4687 0.0853 5.496 0.001 ap 0.0436 0.0853 0.513 0.622 vc 2 0.2346 0.1155 2.031 0.077 fz 2 0.3779 0.1155 3.273 0.011 ap 2 0.1429 0.1155 1.238 0.251 vc . fz 0.0400 0.1206 0.332 0.749 vc . ap 0.0700 0.1206 0.580 0.578 fz . ap 0.0275 0.1206 0.288 0.825 r-sq = 85.63% r-sq(adj) = 69.45% fig. 2. probability plot of surface roughness (ra). engineering, technology & applied science research vol. 12, no. 4, 2022, 8878-8883 8881 www.etasr.com cuong & khanh: improving the accuracy of surface roughness modeling when milling 3x13 steel minitab is again used to convert data. figure 3 shows the graph of the johnson transformation. the upper left image section is the pre-conversion metric information discussed above. the data set after johnson transformation has also been included in table ii. the lower left part of the figure shows the rule of the data set after the transformation. all the red dots have fit in between the two limiting curves, many of which are already very close to the line, and p-value = 0.587, which is much larger than the significance level. this confirms that the data set after the johnson transformation has a normal distribution. observing the upper right figure also shows that the data set after transformation is distributed according to normal rules. the relationship between the data before and after the johnson transformation is found in the lower right figure (in figure 3). so, a new model of surface roughness has been established as shown in (2). transforming (2) we get the surface roughness model as in (3). this model has coefficients r-sq and r-sq(adj) of 0.8669, 0.7172 respectively. figure 4 shows a graph of the box-cox transformation. the value of the dataset after box-cox transformation has also been included in table ii. the distribution rule of the dataset after box-cox transformation is shown in figure 5. all red dots are located between the two limit curves. the p-value is 0.655, which is much larger than the significance level. that shows that the data set after box-cox transformation is also distributed according to normal rules. since the lambda exponent of the transformation is equal to -2.00 (figure 4), a new model of the surface roughness is established as shown in (4). this model coefficients r-sq and r-sq(adj) of 0.8787 and 0.7422 respectively. −1.35178 + 0.941864 ∙ asinh%%��(&'().) − 0.751544* 0.0906774⁄ * = 0.1407 − 0.5826 ∙ �� + 1.0869 ∙ �� + 0.0794 ∙ �� – 0.4662 ∙ ��� + 0.6707 ∙ ��� − 0.3464 ∙ ��� + 0.2092 ∙ �� ∙ �� − 0.3299 ∙ �� ∙ �� − 0.0707 ∙ �� ∙ �� (2) �� = 0.751544 + 0.0906774 ∙ sinh 1.5846 − 0.6186 ∙ �� + 1.1540 ∙ �� + 0.0843 ∙ ��−0.4950 ∙ ��� + 0.7121 ∙ ��� − 0.3678 ∙ ���+0.2221 ∙ �� ∙ �� − 0.3503 ∙ �� ∙ �� − 0.0751 ∙ �� ∙ �� . (3) fig. 3. johnson transformation for surface roughness (ra). ��(/'�.) = 0 1.0759 + 0.2828 ∙ �� − 0.5466 ∙ �� − 0.0351 ∙ �� + 0.2091 ∙ ���− 0.3404 ∙ ��� + 0.1722 ∙ ��� − 0.1001 ∙ �� ∙ ��+0.1837 ∙ �� ∙ �� + 0.0334 ∙ �� ∙ �� 1 23/5 (4) to compare the three established surface roughness models (1), (3), and (4), it is necessary to first use them to calculate the surface roughness and then compare them with the experimental results. each model was used to calculate the surface roughness with the values of the input parameters as shown in table ii. the results of the surface roughness determination for each experiment using the three models are included in table iv. the surface roughness value when engineering, technology & applied science research vol. 12, no. 4, 2022, 8878-8883 8882 www.etasr.com cuong & khanh: improving the accuracy of surface roughness modeling when milling 3x13 steel calculated by the three models will be compared with the surface roughness obtained from the experiment. pae is calculated according to (5). mse is calculated according to (6). in these two equations, ra(exp.) is the roughness value in the experiment; ra(cal.) is the roughness value when calculating. n is the number of experiments. 678 = 9: ;∑ =>�(?@a.)2>b(cbd.)>b(?@a.) =:ef9 g ∙ 100% (5) ij8 = 9: k∑ l��(���.) − ��(��m.)l�:ef9 n ∙ 100% (6) table v presents some parameters of the 3 surface roughness models. from the data in this table, the models using johnson and box-cox transformations both have values of r-sq and r-sq(adj) larger than the model without a data transformation. the pae and mse of the 2 models using a data transformation are also smaller than those of the model not using any data transformation. thus, the use of a data transformation has improved the accuracy of the model. fig. 4. box-cox transformation for surface roughness (ra). fig. 5. probability plot of surface roughness after box-cox transformation. in table v, both parameters r-sq and r-sq(adj) of the model using box-cox transformation are larger than those in the other two models. the pae and mse parameters of the model using the box-cox transformation are smaller than the other two models. therefore, we can confirm that the surface texture model using the box-cox transformation has the highest accuracy. in contrast, the model that does not use the data transformation has the lowest accuracy. this result is in accordance with the conclusions in [10, 13]. therefore, it can be said that the box-cox transformation is recommended to improve the accuracy of the surface model when milling. table iv. calculated surface roughness trial measured without transformation johnson transformation box-cox transformation 1 0.99 0.9667 0.9634 1.0373 2 1.14 1.0761 1.0114 1.1142 3 0.75 0.8139 0.7858 0.7631 4 0.96 0.9667 0.9634 1.0373 5 1.37 1.5312 1.3341 1.4010 6 0.92 0.8489 0.8454 0.9334 7 2.11 1.8851 1.7297 2.2010 8 0.81 0.5138 0.7339 1.3690 9 1.33 1.6262 2.0451 1.3220 10 0.97 0.9667 0.9634 1.0373 11 0.92 0.9667 0.9634 1.0373 12 0.93 0.7688 0.9422 1.0528 13 0.81 1.0349 0.8491 0.8282 14 0.69 0.7611 0.7367 0.7018 15 0.77 1.0027 0.8109 0.7615 16 0.92 0.9667 0.9634 1.0373 17 1.04 0.9667 0.9634 1.0373 18 2.26 2.0273 1.7480 2.2624 table v. parameters of the calculated surface roughness models surface roghness model r-sq r-sq(adj) pae mse without transformation (1) 0.8563 0.6945 12.20 2.59 using johnson transformation (3) 0.8669 0.7172 9.41 2.36 using box-cox transformation (4) 0.8787 0.7422 8.88 2.10 iv. conclusion from the results of this study, some conclusions when milling 3x13 steel with tialn coated cutting pieces were drawn: • feed rate is a parameter that has a significant influence on surface roughness. as the feed rate increases, the surface roughness increases. the cutting speed and the depth of cut have no significant influence on the surface roughness. • a data set that is not distributed according to the normal rules will be distributed according to the normal rules after performing a transformation using the johnson or box-cox method. • using johnson and box-cox transformations will increase the accuracy of the regression model. in the specific conditions of this study, using the box-cox transformation will build the regression model of the surface texture with the highest accuracy. engineering, technology & applied science research vol. 12, no. 4, 2022, 8878-8883 8883 www.etasr.com cuong & khanh: improving the accuracy of surface roughness modeling when milling 3x13 steel • the use of both transformations, johnson and box-cox, to improve the accuracy of the surface roughness model is not only successfully applied in this study as well as in several other published studies, but also it is a tool that improves the accuracy of the regression model in other cases. acknowledgement this research is funded by the university of transport and communications (utc) under grant number t2022-ck003tđ. references [1] a. dean, d. voss, and d. draguljić, design and analysis of experiments. springer, 2017. 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[20] v. c. nguyen, t. d. nguyen, and d. h. tien, "cutting parameter optimization in finishing milling of ti-6al-4v titanium alloy under mql condition using topsis and anova analysis," engineering, technology & applied science research, vol. 11, no. 11, pp. 6775-6780, 2021, https://doi.org/10.48084/etasr.4015. microsoft word 4-611-ed.doc engineering, technology & applied science research vol. 5, no. 6, 2015, 891-894 891 www.etasr.com sajid et al.: chaotic behavior in flexible assembly lines of manufacturing system chaotic behavior in a flexible assembly line of a manufacturing system mohammad sajid mechanical engineering department college of engineering qassim university buraidah, alqassim, saudi arabia msajid@qec.edu.sa fahad almufadi mechanical engineering department college of engineering qassim university buraidah, alqassim, saudi arabia almufadi@qec.edu.sa mirza jahanzaib mechanical engineering department college of engineering qassim university buraidah, alqassim, saudi arabia mirza@qec.edu.sa abstract—the purpose of the present work is to study the chaotic behavior in a flexible assembly line of a manufacturing system. a flexible assembly line can accommodate a variety of product types. result analysis is performed to obtain time persistent data. the behavior of the system is observed for work-in-process, as assembling systems are sensitive during processing. it is found that the average lyapunov exponent is positive in the considered case, and thus chaotic behavior may be present in flexible assembly lines. keywords-flexible assembly line; chaos; lyapunov exponent i. introduction due to the rapid recent development in assembling technologies and advancement in assembling methods, there is a need to critically investigate, and understand, an assembly system’s environment. the identification and prediction is also a fundamental task, not limited to the field of engineering but in all kinds of other fields as well. during the last few decades, chaos theory has been applied in manufacturing systems and some initial research was carried out to analyze chaotic behavior in [1]. chaos in discrete production systems was investigated in [2] using nonlinear analysis and a dynamical approach was introduced in [3] for modeling and control of production systems, based on nonlinear dynamics theory. it is known that chaos is the phenomena of occurrence of bounded non-periodic evolution in completely deterministic nonlinear dynamical systems with high sensitive dependence on initial conditions. the nonlinearity of a system is considered a necessary condition. sometimes, chaos is called deterministic randomness and is associated with the impediments of forecasting. the chaotic behavior generates a kind of randomness and a loss of information about initial conditions, which might explain somewhat complex behavior in real systems. moreover, a system that is chaotic has a long-term behavior that can be hard to predict or simulate. using chaos theory, it is easier to control more difficult and complicated cases compared to using traditional methods which are being utilized for a long time in manufacturing. alfaro and sepulveda [4] studied the dynamic behavior of a reactive system; a system where there is no determined schedule and the tasks of operations to machines are assigned according to the state of the system. this research was performed using discrete event simulation to represent the system and its analysis was done by using nonlinear dynamical systems theory. further, some significant research works for the chaotic behavior in manufacturing have been conducted in [5-6]. little more extension in this direction is also found for the assessment of fidelity of control-theoretic models of wip in autonomous work systems [7]. furthermore, a nonlinear dynamics approach to model the complexity of a manufacturing system can be found in [8] whereas a nonlinear characterization of the performance of production can be found in [9]. an application of neural networks and vector support machines having a chaotic behavior is given in [10] for the forecasting of the time varying average number of parts in a waiting line of a manufacturing system. the theoretical tool used for quantifying chaotic behavior is the notion of a time series of data for the real system [11]. the analysis of chaotic time series has been reviewed in [12]. the lyapunov exponent is one important tool to define chaos. it is known that a system’s behavior is chaotic if average lyapunov exponent is positive [13]. the lyapunov exponent, for a onedimensional time-series k data, is computed by: 0 1 ln k d k d   (1) where 0 j id x x  , k j k i kd x x   and ix , jx are two close values on the two different time series. in order to detect chaotic behavior in a flexible assembly system, there is a need to describe the assembling process. in this research, work-in-process (wip) of assembling system has been chosen to describe system behavior, as it imposes dynamism if not properly controlled [14]. a real flexible assembly line (with various performance variables) has been analyzed by means of process modeling software and the lyapunov exponent. engineering, technology & applied science research vol. 5, no. 6, 2015, 891-894 892 www.etasr.com sajid et al.: chaotic behavior in flexible assembly lines of manufacturing system ii. methodology several researches have been done on chaos in manufacturing as mentioned in the introduction section, but the fundamental work is credited to taken [15] who detected chaotic behavior in turbulence. the methodology adopted in our case is analyzing the system, obtaining a time series of assembly lines and observing chaotic behavior. the proposed algorithm is presented after reviewing the selection of the tool/technique for analysis. in flexible assembling systems, parts are assembled in a respective station and there exists an interaction of parts with the machines. apart from interaction, dominating relationship also exists in which a change in any parameter in the respective station affects the work in process in the subsequent stations. the system chosen for analysis consists of stations where different parts arrive and are assembled in a series of steps. many approaches can be applied, for example analytic modeling, queuing theory and simulation. the analytical models demand too many assumptions while in queuing theory the estimates of expected value of the inter-arrival time distribution and service-time distribution are not exact. the queuing theory formula does not provide any information on the natural variability (dynamism) in the system [16]. on the other hand, simulation involves modeling of a process or system in such a way that the model mimics the response of the actual system to events that take place over time. a simulation run gives a number of variables in the output, including total production, average waiting time in queue, maximum waiting time in the queue, flow times, work in process, etc. time persistent data of wip is selected for the system. the mathematical form of wip in [14] and calculated as: where mtbf is the mean time between failures, mttr is the mean time to repair, q is the quantity actually produced, 0n is the number of operations in the routing, sut is the setup time, ct is the cycle time per part; not is the non operation time, bq is the batch quantity, n is the number of machines, ws is the shifts per week, sh is the hours in a shift, and pr is the production rate. the following algorithm is proposed for identifying the presence of chaos in a flexible assembly line: (i) finding a time series of the variable to be analyzed and the response obtained from the simulation model. (ii) taking the absolute difference of the series and obtain the logarithm of the difference values. (iii) reconstructing the variables for describing behavior using separation distance plots and measuring the difference for each data values. (iv) estimating the sensitivity by the lyapunov exponent; if it is greater than zero, then chaotic behavior exists in the system. the algorithm is implemented on an assembly system that consists of a series of steps where parts are passed through decision process as described in subsequent section. iii. case of a flexible line (process description) the arriving parts are cast metal bodies that have already been machined to accept electronic parts. there are two parts, a and b, produced in adjacent departments (out of bound for this model). part a arrives in the system with a mean time of 5 minutes. part a is prepared where mating faces of the cases are machined, deburred and cleaned with a combined process time of 6.5 minutes. after the preparation, the work part is transferred to the sealer. the work part b arrives in batches of four units and the time between the arrival of successive batches has a mean of 30 minutes. the batch is separated into four individual units (processed individually) arrived at work part b preparation area. the combined processing time for work unit b preparation is 8.5 minutes after which it is sent to the sealer. at sealer (decision) electronic components are inserted, case is assembled, sealed and then tested. the process time at sealer depends on part type i.e. 3.5 minutes for part a and 5.3 minutes for part b respectively. approximately 90% parts passed the quality test and leave system as ‘yield good’, while 10% parts are sent to the further reworking station. at the rework stage 80% parts passed the quality (decision) and leave system as ‘yield after reworking’ while remaining parts are ‘scrapped’. the process is depicted in figure 1. fig. 1. the process flow of assembly line iv. analysis and graphical display the averaged value data has been used for the analysis. the simulation is run for 480 hours (for warm up) and replicated with different scenarios for ensuring the adequacy of the data. the experimental data is validated and verified and production runs (in simulation) are set for 12000 hours with replications. it can be argued that with finite amounts of data, it is difficult to find a specified line segment in the reconstructed phase space, therefore long range data for the research problem are selected. the parameters of interest which are affecting the performance of the assembly system are wip, number in queue, average time in queue, and utilization. it is pertinent to note that wip is sensitive in assembling process as it directly affects the system and is calculated using (2). the time persistent plots for engineering, technology & applied science research vol. 5, no. 6, 2015, 891-894 893 www.etasr.com sajid et al.: chaotic behavior in flexible assembly lines of manufacturing system the part a are shown in figure 2. the most prominent characteristic of chaos is the unpredictability of the future regardless of deterministic time evolution. there may be an average error when forecasting the response of a future measurement which increases very rapidly with time. this unpredictability is an outcome of the inbuilt instability of the solutions, reflected by what is called sensitive dependence on initial conditions. the time series plot for the situation as given in figure 2 is redrawn from 250 to 350 in figure 3 for part a. it is evident that the two trajectories are separated which shows the divergence of nearby trajectories and it is apparent that lyapunov exponents measure the rate of divergence of initially close trajectories. the separation distance (magnitude of difference) plot is given in figure 4 for the two time series (trajectories) data obtained in figure 2. it is observed that the separation distance between these two trajectories varies irregularly; it indicates the sensitive dependence on initial conditions. the nature of divergence of the nearby trajectories and sensitive dependence on initial condition is quantified and characterized using the lyapunov exponent which is computed by using the algorithm described above. for a deterministic process, the lyapunov exponent has to be a positive finite number and for a linear process, it should be zero. the average lyapunov exponent of experimental data is computed to be 0.0078 as given in fig. 5. the result obtained from the above analysis of the time series data exhibits chaotic behavior since average lyapunov exponent is positive. the small value of average lyapunov exponent shows presence of weak chaos but it proves that chaotic behavior may exist in flexible assembly line manufacturing systems. fig. 2. work in process for part a fig. 3. trajectories of time series data part a fig. 4. separation distance plot for wip part a fig. 5. local lyapunov exponents for wip part a v. conclusion in this work, it is concluded that flexible assembly lines may have a chaotic behavior as very small changes may lead to deviations in performance indicators such as wip. the main interest is focused on the lyapunov exponents since it can be calculated relatively easily and it yields confirmation of the presence of chaos in the observed data. the average lyapunov exponent computed is positive which shows that chaotic behavior occurs in the system. it is recommended that the shop floor management must be careful when carrying out assembling with different scenarios as a chaotic behavior may result from the system. more research work is needed to investigate other similar processes and issues related to control and scheduling. references [1] t. beaumariage, k. kempf, “the nature and origin of chaos in manufacturing systems”, proceedings of the ieee/semi advanced semiconductor manufacturing conference, 169-174, 1994 [2] j. p. m. schmitz, d. a. van beek, j. e. rooda, “chaos in discrete production systems”, journal of manufacturing systems, vol. 21, no. 3, pp. 236-246, 2002 [3] b. scholtz-reiter, m. freitag, a. schmieder, “modelling and control of production systems based on nonlinear dynamics theory”, cirp annals manufacturing technology, vol. 51, no. 1, pp. 375-378, 2002 [4] m. d. alfaro, j. m. sepulveda, “chaotic behavior in manufacturing systems”, international journal of production economics, vol. 101, pp. 150-158, 2006 engineering, technology & applied science research vol. 5, no. 6, 2015, 891-894 894 www.etasr.com sajid et al.: chaotic behavior in flexible assembly lines of manufacturing system [5] n. papakostas, d. mourtzis, “an approach for adaptability modeling in manufacturing analysis using chaotic dynamics”, annals of cirp manufacturing technology, vol. 56, no. 1, pp. 491-494, 2007 [6] h. a. el maragh, m. manns, “transition of interarrival time patterns between automated and manual configurations of assembly systems”, journal of manufacturing systems, vol. 26, no. 1, pp. 1-11, 2007 [7] v. toshniwal, n. duffie, t. jagalski, h. rekersbrink, b. scholz-reiter, “assessment of fidelity of control-theoretic models of wip regulation in networks of autonomous work systems”, cirp annals manufacturing technology, vol. 60, no. 1, pp. 485-488, 2011 [8] n. papakostas, k. efthymiou, d. mourtzis, g. chryssolouris, “modeling the complexity of manufacturing systems using non-linear dynamics approaches”, cirp annals manufacturing technology, vol. 58, no. 1, pp. 437-440, 2009 [9] r. donner, b. scholz-reiter, u. hinrichs, "nonlinear characterization of the performance of production and logistics networks”, journal of manufacturing systems, vol. 27, no. 2, pp. 84-99, 2008 [10] m. d. alfaro, j. .m. sepulveda, j. a. ulloa, “forecasting chaotic series in manufacturing systems by vector support machine regression and neural networks”, int. j. comput. commun. vol. 8, no. 1, pp. 8-17, 2013 [11] a. m. l. jimenez, c. c. m. vara de rey, a. r. g. torres, “effect of parameter calculation in direct estimation of the lyapunov exponent in short time series”, discrete dynamics in nature and society, vol. 7, no. 1, pp. 41-52, 2002 [12] z. liu, “chaotic time series analysis”, mathematical problems in engineering. article id 720190, 31 pages, 2010 [13] r. c. hilborn, chaos and nonlinear dynamics: an introduction for scientists and engineers, 2nd edn, oxford university press, oxford, 2000 [14] j. a. buzacott, j. g. shanthikumar, stochastic models of manufacturing systems, prentice hall, 1993 [15] f. takens, “detecting strange attractors in turbulence” in dynamical systems and turbulence, vol. 898, pp. 366-381, springer verlag, new york, 1981 [16] j. banks, j. s. carson, b. l. nelson, d. m. nicol, discrete event system simulation, 3rd edn, pearson education asia, 2002 engineering, technology & applied science research vol. 7, no. 5, 2017, 1894-1899 1894 www.etasr.com firoozfar et al.: assessing the effects of length, slope and distance between piles on the bearing … assessing the effects of length, slope and distance between piles on the bearing capacity of a pile group under axial loading in granular soil alireza firoozfar civil engineering dpt university of zanjan zanjan, iran firoozfari@ znu.ac.ir arash rostami civil engineering dpt islamic azad university central tehran branch, iran dr.arash.rostami@ gmail.com hamid ghaderi civil engineering dpt islamic azad university maragheh branch maragheh, iran hamid_ghaderi2002@ yahoo.com habib zamani civil engineering dpt university of zanjan zanjan, iran zamanihabibi@ yahoo.com ali rostamkhani civil engineering dpt islamic azad university zanjan branch zanjan, iran alirostamkhan1370@ gmail.com abstract—piles are usually made of steel, concrete, reinforced concrete or wood, used to enhance the ground’s bearing capacity in order to enable the construction of deep foundations, also called pile foundations. however, the exact effect of the complex interaction between the piles and the surrounding soil has not adequately been investigated yet. considering the increased application of the technique recently, further analysis is essential for achieving the highest economic and technical capacity. using fewer piles or shorter piles and allowing greater distances between pile groups, results to reduced construction. however, other restrictions such as high groundwater level, bedrock depth and the limited size of the foundation are also to be considered. the issue of optimal pile layout is further investigated in the current paper employing plaxis, a finite element software, for modeling purposes and considering axial loadings in granular soils. results are shown and further discussed. keywords-pile; group; inclined; bearing capacity; plaxis; model i. introduction the use of piles in foundations is an issue that has gained increased interests recently, and research focuses on piles’ axial or lateral behavior and the effects of intervals in groups, or on the effects of load distribution between the group piles, or lateral displacement of the group and the number of the piles in the groups, or on using inclined piles among pile groups which are under seismic loadings. in [1], authors investigated the effect of increasing the pile inclination angle in earthquake loadings. in [2], authors showed that by increasing the inclination angle of pile groups to a certain amount, displacements and bending moments at junction points of caps to the piles show considerable reduction [2]. in [3], genetic algorithm principals were used to optimize the length, location in the soil, cross section, material, types of installations and functions of the piles in order to reduce construction costs and significant reduction was recorded. in [4], some criteria for lateral bearing capacity of inclined piles were presented and it was concluded that the reason of the differences of lateral loading of positive and negative inclined piles is the reaction amount of mobilized soil on the surface of the earth. thus, for inclined positive piles, soil reaction on the surface ground is zero, while this reaction for negative inclined piles is the maximum amount, and so the material of surface layer has extremely significant effect on loading capacity of inclined piles [4]. in [5], authors experimented on two groups with intervals of 0/9 and 1/2 meters and found that in the larger distances the bearing capacity encounters increase of 1/5 to 2 times [5]. in [6], a few tests with inclined piles in clay soil were conducted. lateral displacement of negative inclined piles under the lateral loads was lower in contrast with positive inclined piles [6]. in [7], authors showed that after the 1995 earthquake in kobe port, quay wall with stands of inclined piles has experienced displacement of about 20 cm without any damage. in [8], numerical methods were employed and it was stated that the coefficient efficiency of the pile groups depends on piles’ spaced intervals and that piles’ coefficient efficiency increases with increasing their intervals. the evidence showed that one of the few walls that remained intact after the earthquake was a composite wall, which was supported by inclined piles, whereas a nearby wall supported on vertical piles was heavily damaged. in [9], authors studied the nonlinear behavior of inclined piles under lateral loads and presented a numerical model with finite elements. the results suggested that negative inclination may result to rapid healing under loading [9]. in [10], authors studied the inclined piles’ behavior under lateral loads and showed that lateral displacement depends on the inclined pile’s angle. in [11], authors showed that the negative inclined piles resistance is more than the resistance of positive inclined piles, under the affection of lateral loads. they also asserted that the lateral displacement of the double pile group consisted of a vertical pile and an inclined pile (positive or negative) is less than the displacement of double vertical pile groups. in [12], authors studied the vertical pile and single inclined pile’s resistance engineering, technology & applied science research vol. 7, no. 5, 2017, 1894-1899 1895 www.etasr.com firoozfar et al.: assessing the effects of length, slope and distance between piles on the bearing … under tensile loads. in these experiments, two piles with two different lengths were evaluated. results showed that the tensile capacity of the piles would decrease with increasing the inclination angle of the pile, however piles inclination angle on the piles’ tensile friction resistance is low. in [13], authors studied the frictional resistance of single verticals and inclined piles. this laboratory research was done on two types of steel piles with diameter of 76 mm and 38 mm, in sand with relative density of 65/3 %. in order to calculate the ultimate strength of the pile, the load deformation curve was plotted, and a point where the slope of the graph charts were changed considered as the final amount of frictional resistance. dividing the final resistance of the pile to the pile length, determined the ultimate amount of frictional resistance of per length unit as fs. with increasing the l/d of the frictional resistance, the length unit of fs increases until the crisis depth and after reaching this depth, increasing the resistance continues too slowly. in addition, by increasing the inclination angle of the vertical pile with friction resistance the unit length decreases. with increasing the inclination angle from zero to 30 degrees, the lateral resistance of the pile would be reduced [13]. ii. modeling and assessing pile group behavior in grangular soil under vertical loads computer modeling was used in order to evaluate the performance of the pile group. the method is that at first a group of 4×4 piles with diameters of 1 meter, length of 8 meters and intervals of 1 meter, placed in sandy soil under vertical load, was modeled by plaxis 3d foundation software. in this study, all the piles were assumed to have a constant diameter of 1 meter. loading on the pile was done according to the wide loading manner. the load was increased gradually until the failure of the soil mass. in this way, the ultimate bearing capacity of the pile group was obtained. then by changing the pile intervals to 1/5 and 2 meters and changing the piles length to 10 and 12 meters, the ultimate loading capacity and logical relation of loading capacity variation in different models were being assessed. then the model with the most loading capacity was selected and the amount of the increase or reduction of the bearing capacity was checked by plaxis 2d, changing the relative angles of the vertical side. plexis 2d was used due to plaxis 3d being unable to correctly model the inclined piles. finally, by evaluating the performance of different arrangements of the piles, the best pattern of pile groups under vertical loads in granular soils was obtained. a. soil characteristics in this study, the soil was of the one layer kind (drainage sand) and the specifications are shown in table i. the thickness of the soil layer was considered as 30 meters and water level was assumed as 13 meters underground. b. characteristics of piles the piles considered in this study were concrete constant piles with diameters of 1 meter and specifications as shown in table ii. concrete pile caps dimensions were 12×12 meters, their thickness was 1 and their specification profile was as the pile’s specifications. in all models, size and thickness of the piles were kept constant and only intervals were changed. confidence coefficient of the ultimate bearing capacity was calculated and assumed to be equal for all models. in all studied models the number of piles were 16 (pile groups of 4×4). also after modeling the mentioned pile group in plaxis, axial loading was applied widely on piles and the load increased until the failure of the soil. then the ultimate bearing capacities of the pile groups were obtained. table i. soil characteristics in modeling the pile groups. dry density γunsat 17.6 kn/m 3 wet density γsat 20 kn/m 3 elasticity module (young) e 19000 kn/m2 poisson ratio v 0.3 adherence c 0 internal friction angle of grains φ 23 degree dilation angle ψ 0 interaction coefficient of soil and concrete rinter 1 lateral pressure of the soil k0 0.6 table ii. piles specifications special weight γunsat 24 kn/m 3 elasticity module (young) e 29.2x106 kn/m2 poisson ratio v 0.15 interaction coefficient of soil and concrete rinter 1 c. assising the effects of different lay outs in these models, piles’ diameters were considered as 1 meter, piles’ length were considered as 8, 10 and 12 meters and piles’ intervals were considered as 1, 1/5 and 2 meters. modeling stills are shown in figure 1. the results are summarized in table iii. by examining the bearing capacity between different pile groups, it was found that the pile groups with 10 meters length show the highest bearing capacity and among them piles with 1/5 meters interval have the highest amount of bearing capacity (figure 2). therefore, examining the ratio between the piles length and intervals showed a logical connection. in models made with 8 and 12 meters, the highest ultimate bearing capacity was in the groups where their ratio of length to interval was 8. fig. 1. pile groups with diameter of 1 meter and length of 8, 10 and 12 meters and intervals of 1, 1/5 and 2 meters. engineering, technology & applied science research vol. 7, no. 5, 2017, 1894-1899 1896 www.etasr.com firoozfar et al.: assessing the effects of length, slope and distance between piles on the bearing … in order to verify this relationship in 10 meters models, a pile group at intervals of 1/25 meters was modeled and the ultimate bearing capacity was acquired. the results showed that in models with 10 meters, the highest bearing capacity is in a model with length to interval ratio of 8. the results of this model’s loading are shown in table iv. in order to verify the ratio of piles’ length with bearing capacity a group of piles with length of 8 meters and intervals of 0/5 meters was considered. after analyzing the results it was found that with increasing the ratio of the length to the interval, the bearing capacity is reduced. therefore in the pile groups with length of 8 meters at different intervals, the highest capacity would be acquired in groups with a ratio of 8. the results of this loading model are shown in table v. figure 3 shows the ultimate bearing capacity changes of pile groups in different intervals of 8, 10, and12 meters which they verify the mentioned relationship. assessing the graphs show that in almost all of the models, the maximum bearing capacity is in ratio of 8, and all figure charts are almost the same. iii. evaluating the effects of slope on ultimate bearing capacity the model which had the largest ultimate bearing capacity on the three dimensional analysis in a 4 row order was modeled with plaxis 2d to calculate the ultimate bearing capacity. then, the angles of lateral piles to vertical piles were varied, and the effects of ultimate bearing capacity of the pile group were checked. the characteristics of the soil, the pile and the pile head is assumed to be as the three dimensional model. in this model, the pile diameter was one meter, the lengths of the piles were 10 meters and the distance between piles was considered as 1/25 meter. the changing angles of lateral piles considered as 0, 15, 30 and 45 degrees. modeling stills are shown in figure 4. results are shown in table vi. table iii. results of loading piles with length of 8,10 and 12 meters and intervals of 1, 1/5 and 2 meters. pile group ratio of the distance to the piles maximum subsidence of the pile group (m) ultimate bearing capacity kn/m2 total stress kn/m shear strain of the soil % shear bulk of the soil % normal effective stress of the pile kn/m length of 8m and distance of 1m 8 1.33 1334 8590 65.11 44.73 639.34 length of 8m and distance of 1.5m 5.33 1.27 1305 9230 54.58 40.47 728.1 length of 8m and distance of 2m 4 1.03 1139 11360 35.70 32.36 677.18 length of 10m and distance of 1m 10 2.31 2088 16160 160.85 79.85 1000 length of 10m and distance of 1.5m 6.67 2.21 2099 17930 123.90 74.99 1100 length of 10m and distance of 2m 5 2.08 1959 15440 74.49 68.98 1130 length of 12m and distance of 1m 12 1.36 1474 12860 91.07 54.83 633.5 length of 12m and distance of 1.5m 8 1.37 1702 18120 83.24 43.18 833.61 length of 12m and distance of 2m 6 1.5 1535 14540 65.39 39.75 665.78 table iv. the results of loading a pile group with length of 10 meters and interval of 1/25 meters ratio of the length to the intervals of the piles maximum subsidence of the pile group m ultimate bearing capacity kn/m2 total stress kn/m shear strain of the soil mass % soil bulk strain % normal effective stress of the piles 8 2.31 2114 16820 91.65 78.70 1080 table v. the results of loading a pile group with lengths of 8 meters and intervals of 0/5 meters ratio of the length to the intervals of the piles maximum subsidence of the pile group m ultimate bearing capacity kn/m2 total stress kn/m shear strain of the soil mass % soil bulk strain % normal effective stress of the piles kn/m 16 1.29 1264 7110 47.47 48.48 629.16 fig. 2. bearing capacity of pile groups shift with 8, 10 and 12 meters and distances of 1, 5.1 and 2 meters. engineering, technology & applied science research vol. 7, no. 5, 2017, 1894-1899 1897 www.etasr.com firoozfar et al.: assessing the effects of length, slope and distance between piles on the bearing … table vi. the results of loading a pile group with inclined lateral piles and angles of 0, 15, 30 and 45 degrees. maximum subsidence of the pile group m ultimate bearing capacity kn/m2 total stress of the pile group kn/m axial force of lateral piles kn/m shear stress of lateral piles kn/m bending moment of lateral piles kn/m axial force of middle piles kn/m shear stress of middle piles kn/m bending moment of middle piles kn/m 0.6 1245 3620 2170 962.17 1560 2090 103.7 262.99 0.86 1860 5390 2460 1780 1560 3440 820.55 1330 2.46 6625 13220 6260 13190 64800 9870 4920 6050 2.32 7645 10330 6880 15910 77000 9690 5610 7570 fig. 3. plot of ultimate bearing capacity of pile groups in different lengths and intervals fig. 4. pile groups with 10 meters length, 1/25 meters of interval and 0, 15, 30, 45 degrees of angles engineering, technology & applied science research vol. 7, no. 5, 2017, 1894-1899 1898 www.etasr.com firoozfar et al.: assessing the effects of length, slope and distance between piles on the bearing … fig. 5. a plot for ultimate bearing capacity results show that with increasing the angles of the lateral piles in contrast with vertical axis, the ultimate bearing capacity of the pile increases dramatically. in the pile groups with 45 degrees of inclination, ultimate bearing capacity reaches its maximum value which is about 6 times the ultimate bearing capacity of lateral vertical piles. also the results showed that the middle piles are more forceful than the lateral piles, but shear stress and bending moment of the lateral piles were much greater compared to the middle piles’. iv. discussion three-dimensional models were built in three groups with lengths of 8, 10 and 12 meters and were loaded under axial loading until the failure of the soil mass. the ultimate bearing capacity of each pile group was acquired. the uploading results are summarized below. a. piles with length of 8 meters four models with intervals of 0/5, 1, 1/5 and 2 meters were considered. by reducing the ratio of length to interval the pile’s ultimate capacity decreased, thus it means by increasing the piles’ intervals, the ultimate bearing capacity would be reduced. the highest bearing capacity of the group obtained at intervals of one meter. also by increasing the piles’ intervals, the amount of groups’ subsidence reduced with regard to reduction in the bearing capacity, which is of course due to the reduction of the applied load. soil’s shear strain and bulk strain are reduced by increasing the piles’ intervals, due to the significant increase in the volume of the soil mass. with an increase in the volume of the soil between the piles, as defined in strain relationship, shear strains and bulk would reduce. b. piles with length of 10 meters four models with intervals of 1, 1/25, 1/5 and 2 meters were constructed in this group. at first hand by reducing the ratio of length to interval from 10 to 8 the pile’s ultimate capacity increased, then by another drop of this ratio, the ultimate bearing capacity was reduced. the highest bearing capacity of the group obtained at intervals of 1/25 meters. it shows that the maximum bearing capacity of the group was obtained at a ratio of 8. also increasing the intervals, group’s subsidence would decrease with reduction in the loading capacity. soil’s shear strain and bulk strain were reduced by increasing the piles’ intervals, due to the significant increase in the volume of the soil mass. c. piles with length of 12 meters three models with intervals of 1, 1/5 and 2 meters were constructed in this group. by reducing the ratio of length to interval from 12 to 8 in this group the pile’s ultimate capacity increased, however by another drop, the ultimate bearing capacity would reduce. the highest bearing capacity of the group was obtained at intervals of 1/5 meters. it shows that the maximum bearing capacity of the group was obtained at a ratio of 8. also, increasing the intervals, group’s subsidence would decrease with a reduction in bearing capacity. soil’s shear strain and bulk strain are reduced by increasing the piles’ intervals. d. 2d model the model with the maximum ultimate bearing capacity from the three-dimensional analysis was selected and modeled as a row of 4 piles in plaxis 2d. then, by varying the angles of the piles, the impact of inclined piles on the bearing capacity of the pile group was investigated. results showed that by increasing the loading angle to the vertical axis, the ultimate bearing capacity dramatically increases. the ultimate bearing capacity reaches its maximum value in the pile group of piles with 45 degrees, which is about 6 times the ultimate bearing capacity of lateral vertical piles. this can be attributed to the fact that when the pile applies upright, the bearing capacity achieves only through the pile toe’s resistance and pile shaft’s resistance. when an inclined pile with length of l was implemented, in addition to the resistance of tip and sidewalls, downward component of the pile’s axial force (from the inclined piles’ share), is equal to l sin α, which applies to the soil beneath the pile. this means that the greater the inclination angle, the greater the force. in other words part of pile’s force transfers to the soil under the pile and so, pile can bear more loads and eventually its bearing capacity increases. v. conclusion the exact layout of piles used in deep foundations has a direct effect on constructional costs. thus, determining an optimal layout is of significant importance. however, a variety of factors are to be considered. 3d and 2d modeling, using engineering, technology & applied science research vol. 7, no. 5, 2017, 1894-1899 1899 www.etasr.com firoozfar et al.: assessing the effects of length, slope and distance between piles on the bearing … finite element software, was employed in this paper to assess different pile layouts on granular soil. different models were employed to investigate the effect of length, slope and distance between piles. the different steps of the analysis are presented and results are further discussed. references [1] r. noorzad, g. r. saghaee, “seismic analysis of inclined micropiles using numerical method”, international foundation congress and equipment expo, orlando, florida, united states, march 15-19, 2009 [2] i. juran, a. benslimane, s. hanna, “engineering analysis of dynamic behavior of micropile systems”, transportation research record: journal of the transportation research board, vol. 1772, pp. 91-106, 2001 [3] b. b. jafar, r. ahmad, “optimize the configuration of piles group with genetic algorithm under asymmetric loading”, 6th national conferences of civil engineering, semnan, iran, 25 april 2011 [4] m. j. tomlinson, j. woodward, pile design and construction practice, 6th edition, crc press, 2014 [5] j. b. kim, r. j. brungraber, “full-scale lateral load tests of pile groups”, asce journal of the geotechnical engineering divission, vol. 102, no. gti, pp. 87-105, 1976 [6] h. niandou, d. breysse, “reliability analysis of a piled raft accounting for soil horizontal variability”, computers and geotechnics, vol. 34, pp. 71–80, 2007 [7] n. gerolymos, a. giannakou, i. anastasopoulos, g. gazetas, “evidence of beneficial role of inclined piles: observations and summary of numerical analyses”, bulletin of earthquake engineering, vol. 6, no. 4, pp. 705-722, 2008 [8] e. m. comodromos, c. t. anagnostopoulos, m. k. georgiadis, “numerical assessment of axial pile group response based on load test”, journal of computers and geotechnics, vol. 30, pp. 505-515, 2003 [9] s. rajashree, t. sitharam, “nonlinear finite-element modeling of batter piles under lateral load”, asce j. geotech. geoenviron. eng., vol. 127, no. 7(604), pp. 604-612, 2001 [10] h. poulos, e. davis, pile foundation analysis and design, john wiley and sons, 1980 [11] g. ranjan, g. ramasamy, r. p. tyagi, “lateral response of batter piles and pile bents in clay,” indian geotech. j., no. 10, no. 2, pp. 135-142, 1980 [12] a. hanna, a. afram, “pullout capacity of single batter piles in sand”, can. geotech. j., vol. 23, no. 3, pp. 387–392, 1986 [13] a. hanna, t. nguyen, “shaft resistance of single vertical and batter piles driven in sand.” asce journal of geotechnical and geoenvironmental engineering, no. 129, pp. 601-607, 2003 engineering, technology & applied science research vol. 8, no. 1, 2018, 2405-2411 2405 ltieswww.etasr.com sarang et al.: a new learning control system for basketball free throws based on real time video … a new learning control system for basketball free throws based on real time video image processing and biofeedback reza sarang m. reza jahed motlagh ali abbaspour tehrani majid pouladian department of electrical and computer engineering science and research branch islamic azad university tehran, iran department of electrical engineering iran university of science and technology tehran, iran department of electrical engineering sharif university of technology tehran, iran department of biomedical engineering science and research branch islamic azad university tehran, iran abstract—shooting free throws plays an important role in basketball. the major problem in performing a correct free throw seems to be inappropriate training. training is performed offline and it is often not that persistent. the aim of this paper is to consciously modify and control the free throw using biofeedback. elbow and shoulder dynamics are calculated by an image processing technique equipped with a video image acquisition system. the proposed setup in this paper, named learning control system, is able to quantify and provide feedback of the above parameters in real time as audio signals. therefore, it yielded to performing a correct learning and conscious control of shooting. experimental results showed improvements in the free throw shooting style including shot pocket and locked position. the mean values of elbow and shoulder angles were controlled approximately on 89o and 26o, for shot pocket and also these angles were tuned approximately on 180o and 47o respectively for the locked position (closed to the desired pattern of the free throw based on valid fiba references). not only the mean values enhanced but also the standard deviations of these angles decreased meaningfully, which shows shooting style convergence and uniformity. also, in training conditions, the average percentage of making successful free throws increased from about 64% to even 87% after using this setup and in competition conditions the average percentage of successful free throws enhanced about 20%, although using the learning control system may not be the only reason for these outcomes. the proposed system is easy to use, inexpensive, portable and real time applicable. keywords-learning; control; free throw; basketball; image processing; biofeedback; shot pocket; locked position i. introduction the shot (including 3-point shot, 2-point shot and free throw) is one of the most important techniques in basketball. these shots have approximately the same dynamics (especially of hands) whereas the easiest way to score is considered the free throw [1]. based on the new basketball rules and the changes in the athlete’s physical conditions from ectomorphy to mesomorphy, contacts and therefore the probability of fouls in a match are increased. on the other hand, increasing the distance of 3-point shots [2] should result in a decreased probability of distant scoring and to an increase of in game playing and to an increase to the number of free throws per game. a free throw is a shot taken from a certain distance while the game has paused as result to a foul. therefore, a high success percentage is expected (notable higher compared to 3point and 2-point shots). however, missed free throws often decide the final outcome of a match. some examples are shown in table i (from matches from the 2008 fiba under-18 asian championship). applying sports engineering methods has resulted in more effective performance in several sports including basketball [4]. computational methods using biofeedback have the potential to improve the free throw dynamics. previous investigations on free throw applied 2d analysis techniques. the study of throw techniques from three different distances led to the conclusion that all of them used the technique of coordination of pushing [5]. it was discovered that good throws presented larger shoulder angle during pushing the ball [6]. these studies mainly focused on identifying kinematic variables related to successful throws and ignored the way they behave when the distance from the basket changes. in [7] authors studied the relationship between selected biomechanical free throw parameters on a sample of basketball players with various capacities. successful free throws are found not to be contingent upon speed, angle or height of the throw and they mostly depend on the precision of the player [8]. in [9], authors compared male and female basketball players in terms of 2 and 3-point jump shots. they reported that joint angles at release have no significant changes for the two groups. in [10] authors found that female players had larger joint range from the time they crouch to the time of release (77.5o) and men had smaller (60.7o). authors in [11] found that the angle of releasing the ball for 3 distances (short range, medium range and long range) from the basket in basketball shooting, is similar and approximately around 49.50±7.13o. in [12], authors studied the relation of kinematics of shooting, the distance to the basket and player position. they found out that as the distance from engineering, technology & applied science research vol. 8, no. 1, 2018, 2405-2411 2406 ltieswww.etasr.com sarang et al.: a new learning control system for basketball free throws based on real time video … the basket increases, players have higher angular velocity because they have higher angular velocities of shoulder flexion and elbow extension, and also the speed of the center of mass in the direction through the basket is higher. in [13], authors assessed the relation between distance, outcome and performance of basketball jump shot, and reported that in close distance, the release angle is higher than in intermediate distance (78.92o to 65.60o). authors in [14] used a model for basketball player arms to estimate angles, velocity and angular velocity of joints at release condition. table i. three under-18 asian championship 2008 matches: final results and free throw statistics.. final result free throw percentage free throw 81 68% 15 of 22 japan 75 39% 7 of 18 s. korea (a) final result free throw percentage free throw 84 65.2% 15 of 23 iran 85 66.7% 20 of 30 philippines (b) final result free throw percentage free throw 106 70.2% 33 of 47 kazakhstan 103 56.8% 21 of 37 lebanon (c) previous works so far have not been combined with computational feedback measurements and instrumentations to amend and control a player’s free throw technique. by this feedback, a correct reference signal as a desired trajectory would be produced and sent to the athlete in real time. after primary training epochs, the athlete would be able to control the movement around the desired trajectory. in fact, measurement (quantitation) and biofeedback have a great role in motor control [15]. biofeedback has wide applications in sports and sports engineering [16, 17]. most of them are in controlling athletes’ psychological parameters [18]. the biofeedback approaches in sports are commonly divided in five groups [19] which are muscular biofeedback (emg) [17, 20], thermal biofeedback [21], electrical dermal activity (eda or gsr) biofeedback [22], eeg biofeedback [22, 23] and cardiovascular biofeedback [24]. these approaches are used to improve the athlete’s performance [25]. biofeedback has also applications in sports learning, training and rehabilitation [26, 27] but it actually has focused on psychological problems. our study is intended in accordance to the biofeedback approach focusing on movement control, so the free throw control system can be categorized in the biofeedback field [16, 28]. this study intends to introduce a new learning control system as training assistance, while trying to show a conjunction between control engineering, video image processing, biofeedback, neuromuscular control system and sports. first, the shooting technique is analyzed by using video image acquisition and processing methods. next, the closed loop system is applied to quantify and feedback the movement parameters as audio signals to subjects via their auditory system. finally, correct learning and conscious shooting control are assessed through the experiments. ii. materials and methods a. participants participants were professional and amateur basketball players of a university basketball team. all participants were at least 19 years old and of varying basketball skill. a set of experiments was made on some famous and national athletes in order to extract their movement patterns and compare it with the desired reference pattern. b. the free throw technique even though participants had basketball-related experience, instructions regarding the correct free throw technique were given before the experiments. they should shot in a plane which is vertical to the ground and is peripheral to the assumed line between eye and the center of the basket (shooting plane). the standard of correct free throw technique was derived from [1, 29]. they were also asked to supervise their hand visually in order not to exit from the shooting plane. however, some effective parameters in shooting can’t be observed visually. one of the most important problems corresponding to shooting is its initial condition named “shot pocket” which consists of the state of elbow and shoulder angles. the elbow and shoulder angles should be approximately 90o and 25o, respectively. generally, if the sp is lower, the ball will be thrown at a lower height. therefore, there will be less chance of making the shot which for a defender will be easier to block or control it. also if a player shoots with the ball in a low pocket, it could be seen that the elbow is inside (medial) or outside (lateral) the center of the ball (usually for younger players with weak arms and a lack of upper body strength). if the elbow is not directly under the center of the ball then this creates inconsistent direction [1]. if the sp is high, the arc and height of the throw will be larger and therefore there will be more chance of making the shot, it will be more difficult to defend but it requires more force. moreover, when the sp is too high the hand and the ball may exit from the adequate field of vision [1]. another important matter in shooting is the final state or “locked position” (lp). τhe final angles of elbow and shoulder must be 180o and 45o, respectively [1]. this occurs simultaneously by the releasing of the ball. in other words, the elbow is completely flat and the arm moves up approximately 20o to 25o. we use this paradigm as a reference or desired trajectory. c. the learning control system this system, firstly measures the effective parameters in shooting e.g. the angles of elbow and shoulder and their dynamics. then simultaneously it sends their feedback to the athlete. these parameters are not recognized by the eye and basically they are not presented to brain consciously and accurately. this system tries to solve it by creating new feedback loops. therefore, we can consider this instrument as a new biofeedback system. figure 1(a) shows the block diagram of this system which will be introduced in parts. figure 1(b) shows the block diagram of athlete’s neuromuscular control system.θ1 and θ2 are elbow and shoulder angles, c1 and c2 are neural motor commands, they show the relations between engineering, technology & applied science research vol. 8, no. 1, 2018, 2405-2411 2407 ltieswww.etasr.com sarang et al.: a new learning control system for basketball free throws based on real time video … external tools and internal subsystems in the athlete’s body and f1 and f2 are frequencies of generated sounds. 1) image acquisition  camera the selected camera is a simple digital camera with pal system, interlaced imaging, fire-wire output for ieee 1394 computer image acquisition port and avi image format with a resolution of 520×780 pixels. by the interlaced imaging system, the camera divides every 40 ms period into two 20 ms segments. in each segment, it captures half of the image as alternate rows, which means two frames instead of one [30]. the image separation in two parts is selection of image matrix rows as alternation. by this method and in case that the marker size is chosen appropriately, it is possible to achieve twice the frame rate (50 fps) resulting in enhanced accuracy. hence for a sampling period of 20 ms and about 180 ms elbow movement duration, the correct sampling rate has been considered sufficiently in the sense of the nyquist criterion [31].  the markers choosing of markers depends on many factors such as the camera type, the motion dynamic and the recording environment. it should be emphasized that this paper introduces an instrument which is very simple, accurate and easy to use. so these markers should be very lightweight, with homogeneous color intensity and easy to distinguish. in this study, the researchers have used active markers.  image import the computer used in this project is a 2 ghz core 2 due cpu laptop with 2 gb ram. since this computer has an ieee 1394 video in port and the related hardware, it can satisfy the conditions of the desired system in order to acquire video images with minimum delay. because of the sampling rate of 25 fps and the avi video image format (576×720 pixels per image or 576×720×3/1024=1215 kb=1.1865 mb), the amount of 29.6625 (1.1865×25) mb per second is needed to be transmitted. so, using a minimum signaling rate of ieee 1394 devices (98.304 mbps for s100 standard), we can import the video images to the computer without any delay. the standard interlaced technique is to transmit the picture in two pieces (or fields), called 2:1 interlaced scanning [30]. in the interlaced scan in each period scanning (40 ms for 25 fps) two images with 20 ms interval are taken instead of one. so, based on interlaced imaging technique 50 images per second will be ready for the video image processing subsystem. fig. 1. the block diagram of learning control system: (a) the block diagram of shooting control system, (b) the block diagram of athlete’s neuromuscular control system. 2) video image processing the processing was performed on images with size of 288x20 pixels. the first part of the algorithm written in matlab, determines the location of the markers based on color image processing [32] and circle detection using hough transform (in offline mode for the algorithm validation) [33]. all marker coordinates are defined toward the origin which is placed on the northwest corner of the image (figure 2). the coordinate axes x and y are represented for the width and height of the image, the vectors m1, m2, and m3 are the marker’s vectors and vectors b and s are representing the effective arms in the movement which are arm and forearm vectors respectively. based on the determined vectors (figure 2) we have: 1 2 3 2,s m m b m m         (1) it can be clearly seen that the angles of elbow and shoulder are just the same as the angles between the vectors s  and b  , and between vector b  and x-axis. so we have: 1 1 1 2 ( . ) sin ( ), . ( . ) sin ( ) . x x x b s b s b s b i b i b i                       (2) where θ1 and θ2 are the angles of elbow and shoulder respectively and ix is the unit vector along x-axis. engineering, technology & applied science research vol. 8, no. 1, 2018, 2405-2411 2408 ltieswww.etasr.com sarang et al.: a new learning control system for basketball free throws based on real time video … the angular velocity and acceleration (for the time ti) are calculated by the use of the approximation equations: 1 1 ( ) ( ) , ( ) ( ) i i i i t t t t t t                        (3) where ω and α are angular velocity and acceleration respectively. the measurement system has a resolution of 0.01o and therefore 0.005o error. fig. 2. the marker’s position on the hand which is identified by three vectors in an assumed plane. 3) conversion of information to audio signals via wireless communication the elbow and shoulder angle information and their acceleration were transformed into audio signals. we used a beep alarm with a smooth frequency (like 500 hz) as discontinuous periodic audio signals. the period of this signal is tuned related to the angle (with a fixed duty cycle). equations (4)-(8) represent the conversion of the motor quantities to proportional audio signals: 1 ( ) re ( . )ih t ct t d (4) 2 ( ) sin(2 )bh t f t (5) ( )i i i it ort f    (6) 1 2( ) ( ) ( )p t h t h t (7) 1 2 1 ( ) n out i ij j t                (8) where h1 and h2 are pulse train and beep signals respectively, fb is the proper frequency for generating the beep alarm, ti is the period of the pulse train signal and is proportional to joint angle or δθi which is the difference between θi and the desired angle (in other words ti is a function of θi), d is the duty cycle of pulse train signal and it must be less than the imaging period and p(t) is the final produced audio signal which is the angle audio feedback. also, τ1, τ2 are the agonist and antagonist muscle torques on hand arms, τ is the consequent torque, j is the inertia of the effective hand arm and α is the angular acceleration (see (3)). moreover, a forced audio feedback can be made through the same method based on the second rule of newton. the torque (force) is relative to the angular acceleration. forced audio feedbacks can be based on appropriate musical notes around the desired force. the produced audio signals were broadcasted through a wireless headphone like fm modulator. 4) the role of neuromuscular control system figure 1(b) shows the block diagram of neuromuscular control system generally in the learning control system and especially in the shooting. figure 3 shows a model of neuromuscular control system in voluntary movements based on feedback error learning approach presented in [32, 34]. the block diagram represents the control system of voluntary movements considering the role of cerebellum as well as the cerebrum as the controllers of motion. according to this model, when the association cortex (assn cx) receives the idea of movement from limbic cortex, it sends the desired movement pattern as θd (which is an expression of the state of limbs) to cerebellum and cerebrum’s motor cortex. here the motor commands ‘t’ related to torques which should be produced in muscles are calculated and then they will be applied by the muscles. the inner sensors namely muscle proprioceptor and joints such as muscle spindles, should measure the actual occurred behavior of limbs ‘θ’. therefore the feedback based movement control can be performed using error signal ( de    ). fig. 3. the block diagram of movement control model consisting of the upper centers (cerebrum and cerebellum) and lower centers (spinal cord and muscles). engineering, technology & applied science research vol. 8, no. 1, 2018, 2405-2411 2409 ltieswww.etasr.com sarang et al.: a new learning control system for basketball free throws based on real time video … on the other hand, the cerebellum makes an inverse model to produce the desired commands. according to this model and some physiological facts, this section receives the desired trajectory ‘θd’ as an input and the motor commands resulted from the cerebrum’s motor cortex, tfb (or, to be more precise, the motor command error (∆t)). tfb is used to correct the model by tuning the weights of neural networks of cerebellum in order to decrease the error. finally, the feedback exits the circuit and the cerebellum learns the inverse model and the system is turned into a feedforward control system [34]. in other words, after correct training and learning and finally gaining the skill, all shots, theoretically, must be successful. the most important matter in the neuromuscular control system effective in shooting is the occurrence of inaccurate or unconscious feedbacks to the brain. in this study, based on physiological facts, we try to modify the existing feedbacks, quantify them, raise awareness about them and design more appropriate feedback paths by a new biofeedback technique. iii. results a. comparison of elbow and shoulder angles before and after applying the learning control system as shown in figure 4, the elbow and shoulder angles are about 100o and 27o in sp deviating from the desired trajectory (especially in elbow) and about 180o and 53o in lp pocket again deviating from the desired trajectory (especially in shoulder). there are some variations even for professional athletes because of bad training. the sp and lp were corrected for all players by using the learning control system. figure 5 displays the elbow and shoulder angles in a free throw by a participant before using the system and figure 6 shows the elbow and shoulder angles after applying it. 0 2 4 6 8 10 12 14 16 18 20 80 100 120 140 160 180 frame number el bo w a ng le 0 2 4 6 8 10 12 14 16 18 20 10 20 30 40 50 60 frame number sh ou ld er a ng le locked position shot poket shot poket locked position fig. 4. the elbow and shoulder angle in a free throw by a famous national player. before using the learning control system the elbow and shoulder angles were calculated as 85.14±11.320 and 35.53±8.650 respectively for sp and 175.45±7.540 and 61.91±11.360 respectively for lp. after using the learning control system, the values measured was 89.32±3.260 and 26.12±2.430 for sp and 180±000 and 46.72±2.650 for lp, for elbow and shoulder angle respectively. these results clearly show the improvement also shown by the decrease in the mean error from the desired trajectory (about 4.1 and 9.4 degrees for sp and 4.5 and 15.2 for lp) and also from the decrease of the deviation from the mean value and consequently show the achieved uniformity in the shooting style (about 8.1 and 6.2 degrees for sp and 7.5 and 8.6 degrees for lp). 1090 1092 1094 1096 1098 1100 1102 1104 1106 1108 80 100 120 140 160 180 frame number el bo w an gl e 1090 1092 1094 1096 1098 1100 1102 1104 1106 1108 40 50 60 70 80 frame number sh ou ld er an gl e shot pocket shot pocket locked position locked position fig. 5. the elbow and shoulder angles in a free throw by a participant before using learning control system. 0 5 10 15 20 25 80 100 120 140 160 180 frame number el bo w a ng le 0 5 10 15 20 25 0 10 20 30 40 50 frame number sh ou ld er a ng le shot pocket shot pocket locked position locked position fig. 6. the elbow and shoulder angle in a free throw which was improved becauseof using the learning control system. b. assessment of performance we applied the learning control system to about 15 players of varying skill. the repetition number depended on the athlete’s level. after necessary repetitions and drills using the setup, an improvement in athletes’ performance was observable. both of sp and lp were corrected towards the desired references. also the percentage of successful free throws increased remarkably. before using this system, in training conditions, the average percentage of making free throws was about 64.4%±8.23 which improved to 87.34%±3.46. also 5 of 15 players were supervised during season matches. in those matches, the average performance engineering, technology & applied science research vol. 8, no. 1, 2018, 2405-2411 2410 ltieswww.etasr.com sarang et al.: a new learning control system for basketball free throws based on real time video … was about 68.4%±3.71 which showed about a 20% improvement from their previous statistics. iv. discussion a. study findings the study has numerically combined dynamic measurements of 15 basketball players with a new shooting control system to consciously amend the free throw technique during training. their elbow and shoulder angles were compared before and after applying the learning control system. both mean value and standard deviation of these angles improved significantly. after training with the learning control system, the elbow and shoulder angles were 89.32±3.26 and 26.12±2.43 respectively for sp and 180±0 and 46.72±2.65 respectively for lp. final mean values are close to the desired pattern (90 and 25 for sp and 180 and 45 for lp), demonstrating the system’s accuracy. also meaningful decrease of the standard deviation from 11.32 and 8.65 to3.26 and 2.43 for sp and from 7.54 and 11.36 to ±0 and 2.65 for lp show player shooting style uniformity and demonstrate the system’s precision. it should be noted that the essential forces when shooting a free throw change based on angular acceleration and could be modified based on acceleration feedbacks. moreover, the players’ performance was also considered. in training condition, the average success of 64.4% of total free throw shooting was improved to 87.34% and the standard deviation significantly decreased about 4.2% (from 7.23 to 3.26). also in competition conditions the average performance showed about 20% improvement. of course many parameters influence the result of a shot (e.g. mental concentration and precision, physical condition, fatigue level, opponent defense and other movement parameters), but especially in free throw most of them are absent or limited because of the static conditions of the shot. moreover, by this system the theory of feedforward control of voluntary skillful movement seems to be confirmed. at first the desired movement pattern is formed in the brain. then neuromuscular control system starts learning by making the correct inverse model of the movement. after sufficient training steps, the brain can control the free throw as an open loop system and after that the feedback is not necessary. based on our knowledge this is the first time that an online, persistent and conscious modifying setup has been combined with dynamic measurements of athletes’ shooting to enable amelioration of free throw as a new biofeedback approach. despite the use of simple and cheap active markers, the common camcorders with an interlaced imaging system, the ordinary laptops and appropriate video image processing algorithms, overall improvement in free throw style was achieved. additionally, in this regard we can say that our setup makes a strong connection between control engineering, real time video image processing, biofeedback and neuromuscular control systems. b. limitations and future trends assuming the hand moves in the shooting plane, 2d images were used whereas actually this movement is not quite 2d and it is needed to process 3d images via at least 2 cameras, though in this work some features (not actual angle) were defined, calculated and applied for all athletes using the same methodology. it is possible to generalize the results and apply them to other types of shooting like 2 and 3 point jump shots, because their dynamic is almost similar to the free throw. besides, by defining and using additional movement features, it is possible to learn and control the shooting skill in a better way. moreover, by making small changes, this system can be used for learning and controlling movements in other sports. v. conclusion 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hopf bifurcation control of subsynchronous resonance utilizing upfc majdi m. alomari mohammad s. widyan mohammed abdul-niby alireza gheitasi electrical engineering dept. the australian college of kuwait, kuwait m.alomari@ack.edu.kw electrical engineering dept. the hashemite university jordan mohammadwidyan@hu.edu.jo electrical engineering dept. the australian college of kuwait, kuwait m.nibi@ack.edu.kw electrical engineering dept. the australian college of kuwait, kuwait a.gheitasi@ack.edu.kw abstract—the use of a unified power flow controller (upfc) to control the bifurcations of a subsynchronous resonance (ssr) in a multi-machine power system is introduced in this study. upfc is one of the flexible ac transmission systems (facts) where a voltage source converter (vsc) is used based on gate-turn-off (gto) thyristor valve technology. furthermore, upfc can be used as a stabilizer by means of a power system stabilizer (pss). the considered system is a modified version of the second system of the ieee second benchmark model of subsynchronous resonance where the upfc is added to its transmission line. the dynamic effects of the machine components on ssr are considered. time domain simulations based on the complete nonlinear dynamical mathematical model are used for numerical simulations. the results in case of including upfc are compared to the case where the transmission line is conventionally compensated (without upfc) where two hopf bifurcations are predicted with unstable operating point at wide range of compensation levels. for upfc systems, it is worth to mention that the operating point of the system never loses stability at all realistic compensation degrees and therefore all power system bifurcations have been eliminated. keywords-hopf bifurcations; subsynchronous resonance; upfc; gto i. introduction series compensation is used in power systems as a valuable technique to effectively increase power transfer capability and improve stability. subsynchronous resonance (ssr) is considered a major drawback of series compensation and can be defined as the electromechanical interaction between electrical resonant circuits of the transmission system and the torsional natural frequencies of the turbine-generator rotor. basically, ssr can cause shaft fatigue as well as damage or failure. the subsynchronous torques on the rotor is an issue of great concern because the turbine-generator shaft has natural modes of oscillation that are typical of any spring-damper-mass system. ssr has been considered intensively since 1970, when a shaft failure took place to its turbine-generator unit in the major transmission network with conventional series compensation in southern california. the bifurcation phenomenon also occurs in power systems. researchers study power system dynamics from the nonlinear dynamics point of view utilizing the modern nonlinear theory (bifurcation theory). bifurcation is defined as a qualitative change in the features of a system, such as the types and number of solutions when a small variation occurs in the parameters of the system. bifurcation theory has been used to show the presence of the dynamic bifurcation (hopf bifurcation) in a single machine infinite bus (smib) power system in the case of neglecting the dynamics of the damper windings and the automatic voltage regulator (avr) of the synchronous generator [1]. the results show that the system operating point losses stability through supercritical hopf bifurcation. bifurcation theory has also been applied on modeling the characteristics of the boardman generator with respect to the north-western american power system and the cholla generator with respect to the sowara station in the usa. the effect of the linear and nonlinear controllers on the bifurcations of ssr of cholla generator is studied in [2]. it is found that the linear controllers increase the compensation level at which ssr occurs while the nonlinear controller does not affect the location and type of the hopf bifurcation. it is also shown that the larger the nonlinear controller gain is, the smaller the amplitude of the limit cycle tends to be. additionally, the bifurcation theory has been applied on the first system of the ieee second benchmark model of ssr where supercritical hopf bifurcation is experienced [3]. a nonlinear controller of the )( 31 3  gk form has been designed where all bifurcations of the system are eliminated at all realistic compensation factors despite the successive interactions of the subsynchronous electrical mode with the three torsional mechanical modes of the first system of the ieee second benchmark model of ssr [4]. the recent improvements of power electronic devices have launched the use of flexible ac transmission system (facts) controllers in power systems. in fact, facts controllers can control the network condition via a very fast approach which in turn can be used to improve the dynamic and steady-state stability of power systems [5]. utilizing facts controllers in power transmission system have led to many applications of these controllers for improving the stability of the existing power network resources as well as providing some operating flexibilities. basically, facts devices have been defined as engineering, technology & applied science research vol. 7, no. 3, 2017, 1588-1594 1589 www.etasr.com alomari et al.: hopf bifurcation control of subsynchronous resonance utilizing upfc “alternating current transmission system incorporating power electronic-based and other static controllers to enhance controllability and increase power transfer capability” [6]. the most familiar and common facts devices are thyristorcontrolled series capacitor (tcsc), static synchronous compensator (statcom), static synchronous series compensator (sssc), static var compensator (svc) and unified power flow controller (upfc) [6 ̶ 7]. technically, each of these devices has specific limitations, characteristics and features. in power systems, upfc is considered as a powerful technique based on economic and technical considerations for controlling active and reactive power flows in a transmission line as well as the bus voltage. in addition, upfc can be used as a stabilizer with the help of the power system stabilizer (pss). controlling the bifurcations of the first system of the ieee second benchmark model using tcsc has been investigated [8]. it is found that the operating point of the system never loses stability at any realistic firing angle and therefore all bifurcations of the system are eliminated at all practical values of series compensation. time domain simulations based on the nonlinear dynamical mathematical model after step reduction in the infinite bus voltage and input power coincide with the results of the bifurcation analysis. the effect of sssc on the bifurcations of the ssr in power system has also been investigated where the effect of replacing the conventional compensation with sssc is highlighted [9]. varying the sssc controller reference voltage changes the compensation degree. the results show that the operating point of the system never loses stability at any realistic compensation degree in case of sssc i.e. all bifurcations of the system have been eliminated. in this paper, the effect of incorporating the second system of the ieee second benchmark model of ssr with upfc on the hopf bifurcation of the system is investigated which is considered as the main contribution of the paper where shunt current and series voltage controllers are considered as controllers for upfc. the paper is constructed in the following manner: section 2 describes the system under study and its nonlinear dynamical mathematical model including the system controllers. in section 3, the model of the upfc with three-level vsc is outlined. numerical simulation results in case of including upfc as compared with the case of conventional compensation without upfc are presented in section 4. finally conclusions are drawn in section 5. ii. system description and mathematical model the system considered in this study is the second system of the ieee second benchmark model of subsynchronous resonance (figure 1) [10]. it is a two-machine infinite-bus (tmib) power system connected to a single seriescompensated transmission line where the terminals of the two generators are connected at the same bus. the capacitive reactance varies in the range of 0 to 100% of the transmission line inductive reactance. upfc is incorporated at the end of the transmission line injecting certain amounts of voltage after the capacitive reactance. fig. 1. electrical system under study (modified version of second system of the ieee second benchmark model of ssr the electro-mechanical systems of the two generators and the data of the electrical and mechanical systems are provided in [10]. each generator is represented in its own rotor frame of reference with the proper transformations as the substitution of the two generators in one equivalent generator will change the resonance characteristics. the electrical system consists of the nonlinear dynamical mathematical model of the two synchronous generators and that of the transmission line in dq stationary reference frame related to the d-axis stator winding, q-axis stator winding, d-axis rotor field winding, q-axis rotor damper winding and d-axis rotor damper winding utilizing park's transformation. each section of the mechanical system of the two generators is represented by second order ordinary differential equation (swing equation) which is presented in state space model as two first order ordinary differential equations. the mathematical model of the electrical and mechanical systems is given in [11]. as a result, this systems can be mathematically represented as a set of first order nonlinear ordinary differential equations with the compensation factor )/( lc xx as a bifurcation parameter. hence, bifurcation theory can be applied to this nonlinear dynamical system which can be written in the following form: );( xf dt dx  (1) engineering, technology & applied science research vol. 7, no. 3, 2017, 1588-1594 1590 www.etasr.com alomari et al.: hopf bifurcation control of subsynchronous resonance utilizing upfc where x is the vector of state variables nxxx ,...,, 21 , n is an integer number representing the number of state variables, f is the field vector and  is the control parameter of the system which is in this study is the transmission line compensation degree. unified power flow controller (upfc) is a facts device utilizing a voltage source converter (vsc). it depends on gateturn-off (gto) thyristor valve technology and can be designed as a coordinated combination of a static synchronous series compensator (sssc) and a static synchronous compensator (statcom), which uses the same technology, coupled through a common dc voltage link [12-22]. upfc is a multifunctional facts controller where its primary duty is to control the power flow [23]. the secondary functions of the upfc are voltage control, transient and steady-state stability improvement and oscillation damping. recently, there is a rising attention in studying upfc which includes its modeling [24], its effect on controlling the power flow [25] and its capability to improve system transient stability [26]. however, so far, little work has been done to investigate the effect of upfc on ssr problems. damping the oscillations of the ieee first benchmark system of ssr using upfc has been examined [27]. a compensator utilizing specific technique based on model control theory with two feedback signals is employed to generate two supplementary damping signals. the two port voltages of upfc are regulated through control of shunt current and series real voltage as shown in figure 2. moreover, it has various operating control modes such as line impedance compensation, voltage and power regulation. the upfc is realized by two three-level 12-pulse voltage source converters (vsc). it consists of a shunt connected voltage source converter (vsc1) and a series connected voltage source converter (vsc2). vsc2 injects a series voltage while vsc1 is controlled to inject reactive current. the series and shunt branches of upfc can generate/absorb reactive power independently and the two branches can exchange active power. the injection of series reactive voltage provides active series compensation while the injection of the shunt reactive current can be controlled to regulate the voltage at the bus where vsc1 is connected. the injection of series real voltage (in-phase with the line current) can be controlled to regulate the reactive power in the line or the voltage at the output port of the upfc. upfc can be viewed as a two port device on a single phase basis [28]. fig. 2. upfc as a two port facts controller iii. mathematical model of upfc and its controllers a. mathematical model of upfc typically, the converter in the power circuit of a upfc is either a multi-pulse or a multi-level configuration. in upfc, it is considered to change the magnitude of ac output voltage of the converter without varying the magnitude of the dc voltage. this can be accomplished by utilizing pulse width modulation (pwm) with two-level topology which demands higher switching frequency and leads to increased losses. the objective can be accomplished by varying dead angle β with fundamental switching frequency of the three-level converter topology [29]. the converters that allow the variation of both magnitude and the phase angle of the converter output voltage are classified as type-1 converters [30]. in this study, a combination of multi-pulse and three-level configuration is used [31]. the three-level converter topology is considered to reduce the harmonic distortion on the aside [5, 29, 32-33]. both the shunt and series branches of the upfc contain 12-pulse converter with three-level poles. a special design of a converter operation by switching functions to improve a complete three-phase model of upfc is considered [31]. upfc can be designed by transforming the three-phase voltages and currents to d-q variables using park’s transformation. this is can be done when switching functions are approximated by their fundamental frequency components neglecting [34]. as shown in figure 2, the resistance and reactance of the interfacing transformer of shunt and series vsc are symbolized as rsh, xsh, rse and xse, respectively. the magnitude control of shunt and series converter output voltages i shv and i sev are accomplished by modulating the conduction period affected by dead angles βsh and βse of individual converters while dc voltage is maintained constant. the shunt converter output voltage ishv can be written as: 2 )( 2 )( shqshd i sh vvv  (2) )sin( 11)(   dcmshd vkv (3) )cos( 11)(   dcmshq vkv (4) where )cos()62(1 shshmk  for a 12-pulse converter, ρsh is the transformation ratio of the interfacing transformer t1 and α is the angle by which the fundamental component of shunt converter output voltage leads the port-1 voltage v1. on the other hand, the series converter output voltage isev can also be written as: 2 )( 2 )( seqsed i se vvv  (5) )sin( 12)(   dcmsed vkv (6) )cos( 12)(   dcmseq vkv (7) engineering, technology & applied science research vol. 7, no. 3, 2017, 1588-1594 1591 www.etasr.com alomari et al.: hopf bifurcation control of subsynchronous resonance utilizing upfc where 2 (2 6 ) cos( ),m se sek p r b= se is the transformation ratio of the interfacing transformer t2 and γ is the angle by which the fundamental component of series converter output voltage leads the port-2 current ι2.the dc side capacitor can be mathematically described as: c b dc c b dc c bcdc b i b i b g dt dv  21  (8) where 1 1 1 , 1 1 ,[ sin( ) cos( ) ],dc m sh d m sh qi k i k iq a q a= + + + ish,d and ish,q are d-q components of the shunt converter current, respectively and: ].)cos()sin([ ,22,222 qmdmdc ikiki   b. shunt current controller the real current drawn by the shunt vsc is controlled by phase angle  and the reactive current by modulating the converter output voltage magnitude which depends on βsh. the dynamical equations of the shunt current control are presented in details in [28]. the schematic representation of type-1 controller for shunt current control is shown in figure 3. in order to keep the port-1 voltage magnitude at the specified value, the reactive current reference of shunt converter can be maintained constant or regulated. fig. 3. type-1 shunt current controller in figure 3, real and reactive currents can be represented as: )cos()sin( 1)(1)()(  shqshdshp iii  (9) )sin()cos( 1)(1)()(  shqshdshr iii  (10) where  and sh are calculated as:           ordshp ordshr v v ),( ),(1tan (11)            dcsh ordshrordshp sh vk vv   2 ),( 2 ),(1cos (12) in the case the shunt vsc is drawing real current and inductive reactive current, (9) and (10) should be positive values. c. series voltage controller figure 4 shows the type-1 controller structure for series converter. the independent injection of real and reactive voltage causes two operating combinations of series converter. the first one is about constant reactive voltage and port-2 voltage control while the second is about constant reactive voltage and constant resistance emulation. the active power can be regulated and/or modulated by controlling series reactive voltage reference [35-37]. on the other hand, the reactive power in the line can be regulated by controlling series real voltage injection and this is equivalent to port-2 voltage control [28]. the voltage at port-2 of the upfc is related to that at port-1 and the voltage injected by series vsc. for simplicity, the series transformer reactance is clubbed with the line impedance. the voltage relation is given by: 2 )(1 2 )(1 2 )(1 2 )(1 2 2 2 22 )()( )()( serrsepp seddseddqd vvvv vvvvvvv   (13) engineering, technology & applied science research vol. 7, no. 3, 2017, 1588-1594 1592 www.etasr.com alomari et al.: hopf bifurcation control of subsynchronous resonance utilizing upfc where vp1 and vr1 are the in-phase and quadrature components of port-1 voltage v1 with respect to port-2 current and vp(se) and vr(se) are the in-phase and quadrature components of isev with respect to port-2 current and can be written as:  cossin )()()( seqsedsep vvv  (14)  sincos )()()( seqsedser vvv  (15) fig. 4. type-1 series voltage controller vp1 and vr1 can be computed from vd1, vq1 and  by assuming vr(se)= vr(se),ref. real voltage vp(se) can be calculated to be injected to obtain desired magnitude of v2 as shown in figure 4. in this case, there are two solutions of vp(se). the solution which has the lower magnitude is chosen. in figure 4, γ and βse are expressed as:           ordsep ordser v v ),( ),(1tan (16)            dcse refserrefsep se vk vv   2 ),( 2 ),(1cos (17) iv. numerical simulations a. system response without upfc this subsection presents the results of the numerical simulations when the power system has no upfc. in this case, the mathematical model of the system is represented by 27 ordinary nonlinear coupled differential equations [11]. the synchronous generators are heavily loaded with an output active power of 0.9 pu and output reactive power of 0.43 pu. the response of the system with 1% initial disturbance on the speed of the generator at μ=0.25 without upfc is shown in figure 5. it can be concluded that the operating point of the system is unstable. figure 6 shows the bifurcation diagram of the power system in this case, which is the steady-state value of the first generator delta angle as function of the compensation degree. two hopf bifurcation points are predicted. the power system has a stable operating point to the left of 1 0.1984h » and to the right of 2 0.8241h » and an unstable operating point between h1 and h2. 0 5 10 15 0.94 0.96 0.98 1 1.02 1.04 time (sec) ro to r sp ee d of th e fi rs t g en er at or ( pu ) first unit 0 5 10 15 0.92 0.94 0.96 0.98 1 1.02 1.04 1.06 time (sec) ro to r sp ee d of th e se co nd g en er at or ( pu ) second unit fig. 5. rotor speed of the generators at μ=0.25 with 1% initial disturbance in rotor speed of the generators (without upfc). the operating point loses stability through subcritical hopf bifurcation at h1. it returns to stability case in a reverse hopf bifurcation at h2. in hopf bifurcation, a pair of complex conjugate eigenvalues of the linearized model around the operating point transversally cross from left to right side of the complex plane or vice versa. the type of the first hopf bifurcation at h1 which decides whether the limit cycles created due to the hopf bifurcation are stable or unstable has been determined numerically by observing the time response of the system after small disturbance slightly before h1. fig. 6. bifurcation diagram showing variation of the first generator rotor angle with the compensation factor (without upfc). figure 7 shows the response of the system with 2% initial disturbance on the speed of the first generator at μ=0.1975, engineering, technology & applied science research vol. 7, no. 3, 2017, 1588-1594 1593 www.etasr.com alomari et al.: hopf bifurcation control of subsynchronous resonance utilizing upfc which is slightly lower than h1. it can be concluded that the system operating point has an unstable behavior. consequently, the type of this hopf bifurcation is subcritical and the periodic solution emerging at the bifurcation point is unstable. 0 2 4 6 8 10 12 14 16 18 20 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 time (sec) ro to r sp ee d of th e fi rs t g en er at or ( pu ) first unit 0 2 4 6 8 10 12 14 16 18 20 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 time (sec) ro to r sp ee d of th e se co nd g en er at or ( pu ) second unit fig. 7. rotor speed of the generators at μ=0.1975 (slightly lower than h1) with 2% initial disturbance in rotor speed of generator (without upfc). b. system response with upfc the system response in case of adding upfc after 2% initial disturbance in generator rotor speed at μ=0.6 is shown in figure 8. in fact, testing of the system at all values of μ shows that the system operating point does not lose stability for all realistic values of compensation factor. hence, the system never experiences any bifurcations for this case. as a result, it can be concluded that upfc has succussed in stabilizing the system operating point at all realistic bifurcation parameters and therefore the hopf bifurcation will never occur for all values of the compensation factor. v. conclusions in this study, a controller is designed and considered for upfc to control bifurcations of subsynchronous resonance in multi-machine power system. the system considered is a modified version of the second system of the ieee second benchmark model of subsynchronous resonance where the compensation degree μ=χc/xl is the bifurcation parameter. upfc is used as a powerful technique based on economic and technical considerations for controlling active and reactive power flows in ac transmission lines as well as controlling the bus voltage. it can also be used to improve the power system stability with the help of the power system stabilizer (pss). when upfc is not included, it is found that as the compensation factor increases the system operating point loses stability through subcritical hopf bifurcation point at relatively early compensation degree before regaining the stability at a very late compensation level in a reverse hopf bifurcation. when upfc is added to the system, the analysis does not predict any bifurcations at all realistic compensation degrees and therefore one can conclude that the upfc and its controllers have succussed in eliminating all bifurcations of the power system at all practical compensation degrees. 0 0.5 1 1.5 2 2.5 3 0.975 0.98 0.985 0.99 0.995 1 1.005 1.01 1.015 1.02 1.025 time (sec) ro to r sp ee d of th e fi rs t g en er at or ( pu ) first unit 0 0.5 1 1.5 2 2.5 3 0.97 0.98 0.99 1 1.01 1.02 1.03 second unit time (sec) ro to r sp ee d of th e se co nd g en er at or ( pu ) fig. 8. rotor speed of the first and second generator at μ= 0.60 with 2% initial disturbance in rotor speed of generator (with upfc controller). references [1] w. zhu, r. r. mohler, r. spce, w. a. mittelstadt, d. maratukulman, “hopf bifurcation in a smib power system with ssr”, ieee trans. on power systems, vol. 11, no. 3, pp. 1579-1584, 1996 [2] a. m. harb, application of bifurcation theory to subsynchronous resonance in power systems, doctoral dissertation, virginia polytechnic institute and state university, usa, 1996 [3] a. m. harb, m. s. widyan, “modern nonlinear theory as applied to ssr of the ieee second benchmark model”, ieee bologna power tech. 2003 conf., bologna, italy, june 23–26, 2003 [4] a. m. harb, m. s. widyan, “chaos and bifurcation control of ssr in the ieee second benchmark model”, chaos, solitons and fractals journal, vol. 21, pp. 537–552, 2004 [5] n.g. hingorani, l. gyugyi, understanding facts, ieee press, new york, 2000. [6] cigre/ieee facts working group, facts overview, ieee power engineering society, no. 95 tp108, 1995 [7] c. a. canizares, “power flow and transient stability models of facts controllers for voltage and angle stability studies”, proceedings of the 2000 ieee/pes winter meeting, singapore, january, 2000 [8] m. s. widyan, “controlling chaos and bifurcations of ssr using tcsc”, international journal of modelling and simulation, vol. 30, no. 3, pp. 308-314, 2010 [9] m. s. widyan, “controlling chaos and bifurcations of smib power system experiencing ssr phenomenon using sssc”, international journal of electrical power and energy systems, vol. 49, pp. 66–75, 2013 [10] ieee ssr working group, “second benchmark model for computer simulation of subsynchronous resonance”, ieee trans. on power apparatus and systems. vol. pas104, no. 5, 1057-1064, 1985 engineering, technology & applied science research vol. 7, no. 3, 2017, 1588-1594 1594 www.etasr.com alomari et al.: hopf bifurcation control of subsynchronous resonance utilizing upfc [11] m. m. alomari, b. s. rodanski, “the effects of machine components on bifurcation and chaos as applied to multi-machine system”, in: topics on chaotic systemsselected papers from chaos 2008 international conference, world scientific publishing co. pte. ltd, 2009. [12] m. l. kothari, n. tambey, “design of upfc controllers for a multimachine system”, ieee pes power systems conference and exposition, usa, october 10-13, 2004 [13] a. ali, a. mehdi, “a multi-objective gravitational search algorithm based approach of power system stability enhancement with upfc”, journal of central south university, vol. 20, no. 6, pp. 1536-1544, 2013 [14] a. kumar, c. sekhar, “congestion management with facts devices in deregulated electricity markets ensuring laudability limit”, international journal of electrical power & energy systems, vol. 46, pp. 258-73, 2013 [15] a. n. hussain, f. malek, m. a. rashid, l. mohamed, i. daut, “upfc device application on power system oscillations to improve the damping performance”, 4th international conference on manufacturing science and engineering, pp. 830-837, china, march 30-31, 2013 [16] a. n. hussain, f. malek, m. a. rashid, l. mohamed, n. a. mohd affendi, “optimal coordinated design of multiple damping controllers based on pss and upfc device to improve dynamic stability in the power system”, mathematical problems in engineering, vol. 2013, pp. 1-15, 2013 [17] a. safari, “pso algorithm for upfc based output feedback damping controller”, international journal of control and automation, vol. 6, no. 1, pp. 33-46, 2013 [18] a. sode-yome, n. mithulananthan, k. y. lee, “comprehensive comparison of facts devices for exclusive loadability enhancement”, ieej transactions on electrical and electronic engineering, vol. 8, no.1, pp. 7-18, 2013 [19] b. gopinath, s. s. kumar, j. michael, “stability improvement in power systems using unified power flow controller (upfc)”, international conference on energy efficient technologies for sustainability, pp. 392-397, 2013 [20] e. gholipour, g. isazadeh, "design of a new adaptive optimal wide area ipfc damping controller in iran transmission network," international journal of electrical power and energy systems, vol. 53, no. 1, pp. 529-539, 2013. [21] i. m. wartana, j. g. singh, w. ongsakul, s. sreedharan, “optimal placement of facts controllers for maximising system loadability by pso”, international journal of power and energy conversion, vol. 4, no. 1, pp. 9-33, 2013 [22] j. khazaie, m. mokhtari, s. badkubi, m. khalilian, d. nazarpour, “subsynchronous resonance mitigation via distributed power flow controller”, international transactions on electrical energy systems, vol. 23, no. 6, pp. 751-766, 2013 [23] l. gyugyo, t. r. rietman, a. edris, c. d. schalider, d. r. torgerson, s. l. williams, “the unified power flow controller: a new approach to power transmission control”, ieee transactions on power delivery, vol. 10, no. 2, pp. 1085-1097, 1995 [24] a. nabavi-niaki, m. r. iravam, “steady-state and dynamic models of unified power flow controller (upfc) for power system studies”, ieee transactions on power systems, vol. 11, no. 4, pp. 1937-1943, 1996 [25] k. s. smith, l. ran, j. penman, “dynamic modeling of a unified power flow controller”, iee proceedings-generation, transmission and distribution, vol. 144, pp. 7-12, 1997 [26] s. limyingcharoen, u. d. annakage, n. c. pahalawaththa, ‘‘effects of unified power flow controllers on transient stability”, iee proceedings-generation, transmission and distribution, vol. 145, pp. 182-188, 1998 [27] w. bo, z. yan, “damping subsynchronous oscillation using upfc a facts device”, proc. int. conf. power system technology, vol. 4, china, october 13-17, 2002 [28] k. r. padiyar, a. m. kulkarni, “control design and simulation of unified power flow controller”, ieee trans. power deliv. vol. 13, no. 4, pp. 1348–1354, 1998. [29] k. sen kalyan, j. stacy eric, , “upfc unified power flow controller: theory, modelling and applications”, ieee trans. power delivery, vol. 13, no. 4, pp. 1453–1460, 1998 [30] m. schauder, “vector analysis and control of advanced static var compensators”, iee proceedings-generation, transmission and distribution, vol. 140, no. 4, pp. 299–306, 1993 [31] k. r. padiyar, n. prabhu, “analysis of subsynchronous resonance with three-level 12-pulse vsc based sssc”, ieee power system stability and control-tencon 2003 conference, pp. 76–80, october 14–17, 2003 [32] r. w. menzis, y. zhuang, “advanced static compensation using a multilevel gto thyristor inverter”, ieee trans. power deliv., vol. 10, no. 2, pp. 732–738, 1995 [33] j. b. ekanayake, n. jenkins, “mathematical models of a three-level advanced static var compensator”, iee proc. generat. transm. distrib. vol. 144, no. 2, pp. 201–206, 1997 [34] k. r. padiyar, power system dynamics stability and control, second ed., b.s. publications, hyderabad, 2002 [35] c. d. schauder, l. gyugyi, m. r. lund, d. m. hamai, t. r. rietman, d. r. torgerson, a. edris, “operation of the unified power flow controller (upfc) under practical constraints”, ieee trans. power deliv., vol. 13, no. 2, pp. 630–639, 1998 [36] b. a. renz, a. s. mehraben, c. schauder, e. stacey, l. kovalsky, l. gyugyi, a. edris, “aep unified power flow controller performance”, ieee trans. power delivery, vol. 14, no. 4, pp. 1374–1381, 1999 [37] k. esakki shenbaga loga, s. umayal, t. c. asha raghavan, “mitigation of subsynchronous resonance in series compensated wind farm using upfc and ann with back propagation algorithm”, international journal of engineering research and general science, vol. 3, no. 2, 2015. authors profile majdi m. alomari (bsc 2001, msc 2004, phd 2011) is an assistant professor in electrical engineering department at the australian college of kuwait. his research interests include: power system analysis, power system stability and control, power system planning, power system protection, power electronics, electrical machines and drives, electric machine design, renewable energy, smart grid, energy planning and policy, control systems, optimal control, nonlinear dynamics, linear system analysis and other related topics. mohammad s. widyan (bsc 2000, msc 2002, phd 2006) is an associate professor in electrical engineering department at the hashemite university. his research interests include: conventional and permanent-magnet electrical machines design, finite element technique, bifurcation theory, nonlinear dynamics and control, subsynchronous resonance in power systems (analysis & control), power system and electrical machine dynamics, renewable and hybrid energy systems (wind and photovoltaic), dynamical analysis of various pv-powered and hybrid electrical systems, simulations of power electronic systems in matlab. mohammed abdul-niby received the b.sc. degree in electrical engineering and msc in electronics and communications from the college of engineering, university of basrah, basrah, iraq and the ph.d degree from the university of surrey, united kingdom in 1998. he is currently an assistant professor at the electrical engineering department, australian college of kuwait, kuwait. he has published in areas of signal processing and electronic circuits. his current research interest include simulation modeling of semiconductor devices, characterization of implanted silicon, and renewable energies. alireza gheitasi (bsc 2002, mengsc 2007, ph.d 2012) has been involved in a number of industrial and research projects since 2008 in new zealand. he is currently working for the australian college of kuwait as a lecturer. his main research interests are power system protection, fault detection and diagnosis and smart grids. microsoft word etasr_7-1_1420-1424.doc engineering, technology & applied science research vol. 7, no. 1, 2017, 1420-1424 1420 www.etasr.com bafghi: clustering of customers based on shopping behavior and employing genetic algorithms clustering of customers based on shopping behavior and employing genetic algorithms elham photoohi bafghi department of computer engineering bafgh branch, islamic azad university bafgh, iran abstract—clustering of customers is a vital case in marketing and customer relationship management. in traditional marketing, a market seller is categorized based on general characteristics like clients’ statistical information and their lifestyle features. however, this method seems unable to cope with today’s challenges. in this paper, we present a method for the classification of customers based on variables such as shopping cases and financial information related to the customers’ interactions. one measure of similarity was defined as clustering and clustering quality function was further defined. genetic algorithms been used to ensure the accuracy of clustering. keywords-classification; customers; shopping; genetic algorithm i. introduction traditional methods of mass marketing are no longer responsive to customers' needs diversity. such diversity must be managed by clustering methods which puts the customers with the same need and similar shopping behavior in the same clusters [1]. using the proper clustering, companies can deliver the customers’ goods, services and specific resources via close relationship. customer clustering is one of the components in modern and successful marketing leading to improved customer relationship management (crm) is [2]. clustering is an important issue in selecting the appropriate variables. clustering variables have two local variables and parameters are based on the product [3]. general variables are included of statistical information (age, gender, etc.), life-style and includes variables based on the buying patterns of customers. different works have been taken in the field of customer clustering based on variables [4, 5]. in a study described in [6], the som (selforganizing map) algorithm and k-means were used for clustering of customers based on public information. in this method, first som helped to determine the number of clusters and then clustering was performed using the k-means. clustering based on general variables is more understandable, but the assumption that the customers have the same statistical information (age, etc.) as well as a similar life style and the same shopping habits, to some extent are doubtful. today, customers can purchase from different parts of the planet, and this makes clustering partly more difficult. on the other hand some information about the local variables may not be provided by the customer. although information may be available they may vary over time. for example, income, marital status, occupation and the similar cases makes the clustering through the use of public variables more doubtful [7]. in this paper we propose a method of clustering of customers based on information about the goods. genetic algorithms were also used in order to enhance the quality of these clusters which also have been used to determine the cluster centers. ii. clustering method based on customer purchases in this section, methods of clustering of customers have been provided by the help of customers' purchase behavior. this method involves pre-processing core, similarity criteria based on purchase, clustering algorithm and the quality function of the cluster. a. data pre-processing the purpose of this selection process is to transform and integrate data from one or more datasets into one data set. suppose ‘i’ as an entire collection of items and t0 a transaction. t0 transaction includes fields such as client id, time of transaction, items purchased and financial information. if idi is the customer id number of ci customer, and itemseti={iia|iia î i} are goods purchased by ci, as well as financial information moneyseti={mia|a=1,…,||itemseti||}, a record of tci=(idi,itemseti,moneyseti) describes ci customer’s behavior based product and which will be displayed. b. criteria of similarity based on purchase after preparing the data, it is necessary to specify the similarity criteria of users or to each other and goods. in this respect, there are two famous criteria of matching coefficient and jaccard's coefficient [8, 9]. but these two criteria are not most appropriate because: • existence of a small number of goods compared to the total of goods in a user set items • inequality of goods (considered equal in the above two methods) • imbalance in the importance of customers for the organization engineering, technology & applied science research vol. 7, no. 1, 2017, 1420-1424 1421 www.etasr.com bafghi: clustering of customers based on shopping behavior and employing genetic algorithms so in this article we have introduced a new similarity measure that has overcome some of these shortcomings. similarity measures presented here considered goods purchased together and the profitability of customers. the criteria of goods purchased together were inspired by the concept of support provided in [10]. suppose supp ({ii, ij)} of transactions involving {ii, ij} is the total transactions: suppose supp({ii,ij)} as the ratio of transactions involving {ii,ij} to the total transactions: 0 000 },{ }),({ t iicontainsttt iisupp ji ji   (1) in the above equation ii,ij î i. it should be noted that if the items are rarely purchased together, support value has a low amount [11] and to solve the problem we use intimacy criteria as follows: }),{()()( }),{( }),({ jiji ji ji iisuppisuppisupp iisup iiint   (2) in the above equation numerical value of int was between 0 and 1. this solves the problem of backup. finally, the proposed formula to measure the similarity of two customers is presented in the following form:               s a t b jb i a s a t b jbibjbia ji mm iiintmm ccsim 1 1 1 1 , ).( (3) c. clustering algorithm based on purchase the proposed purchase algorithm of the customers is based on (3). in the algorithm first customers are classified into k clusters. the value of k can be determined by the help of marketers or the method proposed in this paper (see section 4.2). after determining k, initial cluster centers are chosen from tc records. these centers may also be selected randomly or based on heuristic method (ga). suppose g={cn|n=1,…,k} is a total cluster centers where cn is the center of nth cluster, so that cn î tc. so set(tc-g)={ci|i=1,…,||tc-g||} includes customers not selected as the center of the cluster. then for all customers who are not cluster center, their similarity to all cluster centers are measured and added to the clusters with the maximum similarity to the center. the problem can be seen in the equation below:     gtwherecccsimmax cinisnk .1 (4) after each customer was placed in clusters, cluster centers are calculated again. let ci and cj are two customers in the g n cluster, and the center of gn cluster is equal to cn. in this case priority of ci customer is calculated based on following relationship:      nmgc m i ijgc ji i m m j ccsim ccsim cpio , , ),( ),( )( (5) where cm is the center of gm cluster and   ijgc ji m j ccsim , ),( represents the sum of similarities between the ci customer and other customers in cluster gn. while   nmgc m i m ccsim , ),( represents the sum of similarities between the client ci and the other cluster centers except gn. for all customers existed in a gn cluster, customer is selected as the center of the cluster with the highest priority value. this concept is presented in the following equation:  )(arg icn cpiomaxc ngi (6) after specifying the new centers, algorithm has done a repetition pattern. the algorithm repeats this process until no clustering center change. the overall process of algorithm is shown in figure 1. fig. 1. flowchart of clustering using genetic algorithms d. clustering quality function the purpose of clustering is to maximize the similarity between the centers of the clusters with the cluster's customers as the similarities between the centers of the clusters are engineering, technology & applied science research vol. 7, no. 1, 2017, 1420-1424 1422 www.etasr.com bafghi: clustering of customers based on shopping behavior and employing genetic algorithms minimal. so the quality of clustering based on the following equation can be expressed as:                    k n nm mn nmkmmin k k 1 ,1 1 )(    (7)    n i gc n inn ccsim g ),( 1  (8)    m j gc m jmm ccsim g ),( 1  (9) ),( mnnm ccsim (10) equation (8) considers η n as the average similarity between the center of the cn cluster and existing customers in the cluster gn. equation (9) shows that η m determines the relationship between the average similarity between the center of the cluster cm and existing customers in the cluster gm. equation 10 determines the similarity between cn and cm. using the clustering quality defined in (7), we can define the appropriate value for k in accordance with the following formula:   kmaxk tskss  argˆ (11) in the above equation k value is determined between the lower bound and upper bound of t iii. determining the center of clusters using genetic algorithm genetic algorithms [12] can be used to select primary centers of clusters. a genetic algorithm is an abstract computational models of biological evolution that is used in optimization problems, in which the mutation operation, crossover and production of new population are used. a. encoding the chromosome each chromosome in the genetic algorithm represents a solution to the problem that is investigated. in this studied case, each chromosome represents a set of k centers of initial cluster. if fi is a chromosome, fi=[y1,…,yj,…,yk] where yj is the jth gene and k is the total number of genes (in figure 2). fig. 2. coding of chromosomes b. set values to the initial population let pe represents the population in the eth replication, and 0<=e<=e, where e is the maximum number of times to repeat the genetic algorithm. the number of chromosomes is constant in all occurrences. so pe={fi|i=1,…,l} where fi is the i th chromosome and l is the total number of chromosomes in the population. l number is an even number specified by the user. c. the fitness value of a chromosome fitness value of each chromosome means to determine the suitability of chromosomes in order to survive it. the fitness of each cluster is determined based on the equation 7. so the formula for calculating the fitness of each fi chromosome is calculated as follows: fitness(fi)=ρ(k) , fi=[y1,…,yj,…,yk] (12) in (12) chromosomes existed in the population pe into two categories: good (pebad) and bad (p e good). good chromosomes are the sets of chromosomes with high fitness value and bad chromosomes are the sets of chromosomes with low fitness value as their numbers are equal||pegood||=||p e bad||=i/2. d. production of the new population the purpose of generating new populations is to remove the chromosomes with low fitness value and copy the chromosomes with high fitness value in the new population. so pebad is removed and p e good chromosomes take their place. the higher the fitness value of a chromosome, the higher the probability of selection. the formula for calculating the probability of selection of chromosomes as shown below:   agoodi pgf ii ffitnessfob )(/)(pr (13) the production process of new population has ensured that the new generations are created of the parents with high fitness value. this process is shown in the following figure. fig. 3. the process of creating a new population engineering, technology & applied science research vol. 7, no. 1, 2017, 1420-1424 1423 www.etasr.com bafghi: clustering of customers based on shopping behavior and employing genetic algorithms e. mutate and crossover after generating a new population, mutation and crossover operations are applied over the population. first, a fi chromosome and from pegood and fj from p e bad set are elected. if the genes of fi and fj are not equal, the crossover operation is applied on them. how to crossover them is shown in figure 4. if the two genes are equal, then the gene mutation operation is performed on them. for this purpose, created chromosome is placed instead of one of the two chromosomes. this operation is shown in figure 5. fig. 4. crossover operation fig. 5. mutuation operation iv. results a. assessment of the proposed method in order to evaluate the proposed method, the information collection of shopping store with 9729 customer transaction information relating to 4223 customers and 1560 item were applied. the purpose of the proposed algorithm is that customers in each cluster have the highest similarity with each other. so items purchased by the customer in a cluster are similar. although these items are distinct, customers’ buying patterns are definable by the help of the frequency of each item. this concept is known by the support, as shown in equation 1. to assess this concept, we compared the k-means clustering methods [13] with the proposed method and achieved to the following results. in the results value of the k was set at 30 and calculated the mean support in each cluster of five maximum support besides standard deviation for all items. results of kmeans algorithm and the proposed method are shown in tables i and ii, respectively. the anova test was used to express the differences of obtained results. the test results are shown in table iii. it can be seen that the mean value of support for 5 supported items were significantly higher than the results of kmeans. therefore, it can be argued that in the proposed approach, customers in each cluster have more similar buying pattern than the k-means algorithm. also the standard deviation of proposed method is higher than the k-means which also confirms the previous term. table i. product purchase pattern with the help of k-means method five maximum support values of all items standard deviation of support for all items mean of support for all items mean 5 4 3 2 1 customer’s id 0.0025 0.0063 0.0189 0.0142 0.0189 0.0189 0.0189 0.0236 01 0.0027 0.0063 0.0172 0.0256 0.0156 0.0156 0.0156 0.0208 02 0.0025 0.0047 0.0138 0.0138 0.0138 0.0138 0.0138 0.0138 03 0.0028 0.0056 0.0175 0.0175 0.0175 0.0175 0.0175 0.0175 04 0.0025 0.0054 0.0185 0.0148 0.0148 0.0185 0.0185 0.0259 05 0.0018 0.0035 0.0111 0.0098 0.0098 0.0114 0.0114 0.0131 06 0.0033 0.0084 0.0236 0.0221 0.0221 0.0221 0.0221 0.0294 07 0.0017 0.0035 0.0104 0.0092 0.0107 0.0107 0.0107 0.0107 08 ... ... ... ... ... ... ... ... ... 0.0026 0.0054 0.0175 0.0167 0.0167 0.0167 0.0167 0.0209 28 0.0035 0.0094 0.0244 0.0244 0.0244 0.0244 0.0244 0.0244 29 0.0023 0.0044 0.0152 0.0126 0.0158 0.0158 0.0158 0.0158 30 table ii. product purchase pattern with the help of proposed method five maximum support values of all items standard deviation of support for all items mean of support for all items mean 5 4 3 2 1 customer’s id 0.0058 0.0052 0.0568 0.0381 0.450 0.484 0.0588 0.0934 01 0.0070 0.0060 0.0574 0.0302 0.0302 0.0340 0.0906 0.1019 02 0.0051 0.0050 0.0453 0.0275 0.0275 0.0303 0.0523 0.0799 03 0.0045 0.0040 0.0344 0.0297 0.0297 0.0361 0.0361 0.0403 04 0.0028 0.0061 0.0583 0.0379 0.0455 0.0492 0.0606 0.0985 05 0.0064 0.0052 0.0518 0.0350 0.0420 0.0455 0.0455 0.0909 06 0.0055 0.0042 0.0392 0.0326 0.0350 0.0373 0.0443 0.0466 07 0.0070 0.0039 0.0275 0.0295 0.0385 0.0379 0.0379 0.0463 08 ... ... ... ... ... ... ... ... ... 0.0039 0.0047 0.0463 0.0360 0.0411 0.0411 0.0540 0.0591 28 0.0043 0.0080 0.0759 0.0452 0.0565 0.0621 0.0734 0.1412 29 0.0041 0.0048 0.0400 0.0303 0.0303 0.0379 0.0404 0.0606 30 engineering, technology & applied science research vol. 7, no. 1, 2017, 1420-1424 1424 www.etasr.com bafghi: clustering of customers based on shopping behavior and employing genetic algorithms table iii. evaluation using anova test sum of squares df mean square f-value p-value =5%α variance among groups 1.938*10-2 1 1.938*10-2 variance inside the groups 4.572*10-3 58 mean of 5 maximum supports total variance 2.395*10-2 59 7.883*10-5 245.882 0.000 p<α variance among groups 1.402*10-7 1 1.402*10-7 variance inside the groups 1.113*10-4 58 mean of support for all items total variance 1.114*10-4 59 1.918*10-6 0.073 0.788 p>α variance among groups 1.176*10-4 1 1.176*10-6 variance inside the groups 6.607*10-5 58 standard deviation of support for all items total variance 1.837*10-4 59 1.139*10-6 103.242 0.000 p<α the proposed method has a good convergence rate. as you can see in the following figure, when the replication frequency raised the total similarities between customers, cluster centers was also increased and number of change of cluster centers were also reduced. it was shown after the 9 replications, cluster centers did not change and the algorithm was finished. fig. 6. convergence in proposed method b. evaluating the performance of genetic algorithm as mentioned, the initial cluster centers can be determined randomly or using genetic algorithm. some experiments were taken in order to show the usefulness of genetic algorithms in which the number of clusters was changed from 30 to 80. in the following figure the effectiveness of using genetic algorithms was shown compared to the initial cluster centers randomly. fig. 7. comparison of genetic algorithm and random method v. conclusion mass marketing no longer meets the diverse needs of customers. customer clustering techniques have to be employed so that customers with the same buying patterns are put in a similar cluster. in this paper we presented a method of clustering customers employing genetic algorithms. results are presented and further discussed. as shown, an improved performance is achieved through the discussed technique. references [1] s. dibb, l. simkin, the market segmentation workbook: target marketing for marketing managers, routledge, london, 1996 [2] a. berson, s. smith, k. thearling, building data mining applications for crm, new york: mcgraw-hill, 2000 [3] s. wedel, w. kamakura, market segmentation: conceptual and methodological foundations, boston: kluwer, 1997 [4] t. p. beane, d. m. ennis, “market segmentation: a review”, european journal of marketing, vol. 21, no. 5, pp. 20–42, 1987 [5] k. hammond, a. s. c. ehrenberg, g. j. goodhardt, “market segmentation for competitive brands”, european journal of marketing, vol. 30, no. 12, pp. 39–49, 1996 [6] r. j. kuo, l. m. ho, c. m. hu, “integration of self-organizing feature map and k-means algorithm for market segmentation”, computers and operations research, vol. 29, no. 11, pp. 1475–1493l, 2002 [7] r. g. drozdenko, p. d. drake, optimal database marketing: strategy, development, and data mining, london, sage, 2002 [8] c. d. manning, h. schutze, foundations of statistical natural language processing, cambridge, ma, mit press, 1999 [9] h. c. romesburg, clustering analysis for researchers, belmont lifetime learning publications, 1984 [10] r. agrawal, r. srikant, “fast algorithms for mining association rules”, 20th international conference on very large databases, pp. 487–499, 1994 [11] h. mannila, database methods for data mining, 4th international conference on knowledge discovery and data mining, new york, 1998 [12] j. h. holland, adaptation in natural and artificial systems, ann arbor, mi: the university of michigan press, 1975 [13] j. macqueen, “some methods for classification and analysis of multivariate observations”, 5th conference on mathematical statistics and probability, vol. 1, pp. 281–297, 1967 engineering, technology & applied science research vol. 8, no. 1, 2018, 2361-2366 2361 www.etasr.com lubich: a refinement of the square wave phase noise evaluation a refinement of the square wave phase noise evaluation ludwig lubich technical university of sofia sofia, bulgaria lvl@tu-sofia.bg abstract—oscillators are often followed by square wave forming circuits and frequency dividers. traditionally, the level of the phase noise, transferred from the oscillator outputs to the square waves obtained is calculated ignoring the correlations in the oscillator phase noise spectrum. in this paper, accurate expressions are derived, taking into account the phase noise mechanisms in the oscillators. the phase noise power spectral densities are calculated in both the traditional way and by using the proposed expressions and they are compared. the situations where the proposed expressions can be useful are identified. keywords-phase noise; square wave; frequency divider; oscillator i. introduction a common communication arrangement consists of an oscillator (usually nearly sinusoidal), whose waveform is converted to rectangular by some kind of square wave forming circuit often followed by digital frequency dividers. an important present-day example is the local oscillator frequency synthesis in highly integrated receivers for cognitive and software radio applications where the wide range of frequencies needed is obtained by relatively narrow range plls followed by frequency divider chains [1-3]. the square wave (sw) may not physically exist. for example, in the switching mixers [4], the input rf signal is effectively multiplied by a nearly rectangular waveform even if the mixer is driven by a sine oscillator. usually the power spectral density (psd) of the oscillator phase noise (pn) is known, but the pn of the resulting square wave is what really matters. it is widely agreed [5-8] that the phase noise of the formed square wave, when considered in the time domain, is a sampled version of the oscillator pn, having aliasing as a result. therefore the sw pn spectrum is a sum of frequency translated replicas of the oscillator pn spectrum. the evaluation of square wave’s pn psd by summing up frequency shifted replicas of the oscillator pn psd, tacitly assuming that the oscillator phase noise is uncorrelated in the frequency domain, is widely accepted [5, 6, 8]. such an assumption leads to sufficiently exact results in most cases, but strictly speaking is not correct. if the mechanism of phase noise arising in oscillators is considered, it turns out that the oscillator phase noise is correlated. in this paper, the phase noise psd of square waves obtained from a sine oscillator by edge forming and frequency division is evaluated, taking into account the phase noise model presented in [9, 10]. the investigations are restricted to the phase noise transferred from the oscillator to the sw and do not include the phase noise contribution of the noise sources in the sw forming circuits and dividers themselves. ii. oscillator phase noise real-world oscillations have both amplitude and phase noise. however, the inherent amplitude-limiting mechanisms of the practical oscillators strongly suppress the amplitude noise. therefore the pn is the dominating one [10]. a sinusoidal oscillation with pn can be expressed as     ttfats   02sin , where the excess phase ϕ(t) represents the pn. taking into account that ϕ(t) is small, we obtain:        tfattfats 00 2cos2sin   (1) according to the pn model presented in [10], the excess phase ϕ(t) in an oscillator can be expressed as:        di q t t    0 max 1 (2) where  0 is called impulse sensitivity function (isf) and is a dimensionless, frequencyand amplitude-independent periodic function, qmax is the maximum charge displacement across the capacitor in the oscillator lc tank and i(t) is a noise current injected to the lc tank that can model different noise sources in the oscillator [10]. the isf reflects the sensitivity of the oscillator phase to an impulse injected at phase ω0t. the isf can be approximated by fourier series. multiplying its terms by the noise current in (2) results in frequency translations of the noise spectrum by integer multiples of the oscillation frequency f0. therefore the same components of the original noise i(t) are present at different frequencies in the pn spectrum, thus there are nonzero correlations between the pn spectral components. iii. psd of the square wave phase noise a. phase noise of non-sinusoidal waveforms a non-sinusoidal oscillation is a sum of harmonics, each with its own phase noise sidebands which overlap. it is engineering, technology & applied science research vol. 8, no. 1, 2018, 2361-2366 2362 www.etasr.com lubich: a refinement of the square wave phase noise evaluation impossible to distinguish the phase noise of the fundamental and the phase noise of the other harmonics. but this is not necessary. indeed the total noise psd is what matters. let us consider a periodic non-sinusoidal noiseless waveform  ts . its fundamental is the component of interest and it can be expressed as  tfa w2sin where a denotes its amplitude. if the corresponding noisy waveform can be expressed as        tftatsts w 2cos (3) then, comparing with (1) we can interpret ϕ(t) as phase noise of s(t). b. phase noise after square wave forming although it is intuitively plausible that the square wave forming results in a sampling of the oscillator phase noise in the time domain, it is highly desirable to examine this supposition a bit more rigorously. let us consider a sinusoidal oscillator with an oscillation frequency 0f followed by an sw forming circuit. without loss of generality, a unity oscillation amplitude is assumed. in the general case, a frequency division by a factor d also takes place along with the sw forming. (for sw forming without frequency division d=1). the sw has a frequency of fsw=f0/d and a duty cycle of 21 . (other duty cycles are hardly applicable in wireless communications.) the edges of the sw occur around the time instants 20dtk . the peak-to-peak voltage of the sw is vpp. it is easy to establish that the fundamental amplitude of the sw is ppva 2 . the following assumptions will be adopted: 1. the edge forming of the pulses can be adequately modeled by passing the oscillator sine wave via limiting amplifiers with an unsaturated voltage gain α or −α. 2. the edge duration te of the sw is at least an order of magnitude shorter than the oscillator period. 3. the phase disturbance  tosc at the oscillator output is nearly constant in time intervals    02 ftt osc  . 4. the time extents    02 ftt osc  are orders of magnitude shorter than the edge duration. the first assumption can be replaced by another one: the edge forming circuit has a perfect threshold behavior and the oscillator pn affects the edge positions of the sw instantaneously at the oscillation zero-crossing instants only, shifting the edges by   00 2  dtkosc . then the obtained pn psd of the sw for the frequencies of interest becomes the same as the pn psd obtained here. obviously, the oscillator pn can affect the sw during the edges only. this can be modeled by multiplying the excess phase osc by corresponding time shifted pulses  tp with a unity amplitude and duration te. the oscillator waveform is given by:            tntf tfttftv osc oscosc   0 00 2sin 2cos2sin   (4) let the rising edges of the sw occur when  tvosc rises, i.e. at 0ndtt  where 00 1 ft  is the oscillator period and n is an arbitrary integer. then the falling edges occur at 200 dtndtt  . hence if the frequency division factor d is odd, the falling edges occur when  tvosc falls; if d is even, then the falling edges of the sw also occur when  tvosc rises (figure 1). fig. 1. sine to rectangle conversion for odd and even values of the frequency division ratio d therefore, taking assumption 1 into account, the sw during the k-th edge can be expressed as:      11 kd sw oscv t v t     (5) then the noise during the k-th edge can be expressed as        tntn oscdkk 11  (6) for the k-th edge, taking into account assumption 2, we can approximate the noise term of  tvosc as:         kdoscoscosc ttkdfttn 122cos 00   (7) then after substituting (7) in (6), we obtain:             tttn osckkdoscdkk  111 1   (8) the total noise of the sw can be obtained by summing up the noise of all sw edges, multiplied by the corresponding gating pulses:              k ksw dt ktptntn 2 0 (9) substituting (8) in (9) and taking into account assumption 2, we can express (9) as:       0 cos 2 2 sw sw osc k n t f t t dt p t k               (10) engineering, technology & applied science research vol. 8, no. 1, 2018, 2361-2366 2363 www.etasr.com lubich: a refinement of the square wave phase noise evaluation after inspecting (10) and comparing it with the noise term in (3), we can recognize that the noise of the sw is phase noise only. to obtain the sw excess phase  tsw , we bring (10) to the form      ttfatn swswsw 2cos where ppva 2 is the fundamental amplitude of the sw. then               k osc pp sw dt ktpt v t 22 0   (11) equation (11) shows that in the time domain the sw pn is the oscillator pn non-ideally sampled at a rate of swosc fdf 22  and scaled by magnitude. taking into account assumptions 1 and 2, it can be established that epp tfv 02 . then               k osc e sw dt ktpt t t t 24 00  (12) c. evaluating the square wave phase noise psd the pn psd is found as     t f fs tsw t sw       2 e lim  (13) where  fsw is the fourier transform of  tsw , the subscript τ denotes a truncation to a finite time interval τ and  xe denotes expectation [11]. taking the fourier transform of  tsw , we obtain:          k tswoscsw e tsw kffkfpdt f 22 2 1  (14) where  fp and  tosc f are the fourier transforms of  tp and  tosc , respectively. it can be seen that  tsw f is a sum of replicas of  tosc f shifted by integer multiples of swf2 . assuming that  tosc f is not correlated in the frequency domain, the pn psd can be found as:     2 21 2 2 2 sw sw osc sw ke s p kf s f kf dt            (15) where  fsosc denotes the psd of the oscillator pn. equation (15) expresses the traditional way of evaluating the pn psd. however,  tosc f is correlated. in the oscillator, each component of the spectrum of the original noise i(t) undergoes frequency translations by multiples of 0f , as it was discussed above. in the general case, this includes frequency translations differing by multiples of swf2 from each other. next, the aliasing due to the sampling causes further frequency translations of the oscillator pn spectrum by multiples of swf2 . therefore, each component of the original noise will get to the same frequencies in many (strictly speaking countless) different ways, as illustrated in fig. 2. then the voltages of these replicas of the same noise component should be summed up (instead their powers). in contrast, in (15) only power summations are performed. fig. 2. frequency translations for d=4. for the sake of clarity, only three different ways for only one frequency translation (by 2fsw) are indicated by solid arrows and the magnitude decay caused by the integration is not presented. let us express  tosc f following the oscillator pn model presented in section ii. we will deviate a little from the original designations of [10]: the isf will be an explicit function of the time, periodic in 00 1 ft  and will be designated by γ(t). its fourier transform will be denoted by  f . similarly, the fourier transform of the original noise current i(t) will be denoted by  fi . thus, the phase disturbances are expressed by        di q t t osc    max 1 (16) then, taking fourier transform of (16) and substituting in (14), we obtain:                 k tsw n n sw sw e tsw ndkffic kff kfp dtjq f 2 2 2 4 11 max     (17) where nc  are the complex fourier series coefficients of the isf. the isf can be well approximated by a limited number of fourier series terms, i.e. n can be restricted to a certain range  maxmax , nn . if d is an even number, i.e. 2 ,d d (17) can be expressed as:                k tsw n nn n sw sw e tsw ndkffic kff kfp dtjq f 2 2 2 4 11 max max max     (18) engineering, technology & applied science research vol. 8, no. 1, 2018, 2361-2366 2364 www.etasr.com lubich: a refinement of the square wave phase noise evaluation after making the substitution ndkl  and simplifying we obtain:                  l n nn sw swn tsw e tsw fndlf fndlpc lffi dtjq f max max 2 2 2 4 11 max    (19) the second sum in (19) contains the scaling factors of all original noise spectrum replicas experiencing the same frequency translation. taking into account the roll-off caused by the integration, it can be established that a very good accuracy for the frequency range of interest can be preserved if a constant     etpfp  0 is assumed. then (19) is simplified to:       . 2 2 4 11 max max max         l n nn sw n tsw tsw fndlf c lffi djq f    (20) after substituting (20) in (13) and simplifying, we obtain the psd of the sw pn:           l n nn sw n swisw fndlf c lffsks 2 2 max max 2 2  (21) where is denotes the psd of the original noise  ti and   1max4  dqk  . if 1d , (17) can be expressed as :                                  k m mm tm tm tsw kff fmkfic kff fmkfic j k f max max 0 012 0 02 2 122 2 22    (22) after making the substitution k+m=l, we obtain:                                          l m mm m t l m mm m t tsw fmlf c flfi fmlf c lffi j k f max max max max 0 12 0 0 2 0 2 12 2 2    (23) after substituting (23) in (13) and simplifying we obtain the pn psd:                                            l m mm m i l m mm m i sw fmlf c flfs fmlf c lffs ks 2 0 12 0 2 0 2 0 2 max max max max 2 12 2 2   (24) the splitting of (24) in two terms reflects the obvious fact that the total frequency translation   02 fnk  of the original noise psd can be an even multiple of 0f for even values of n only and an odd multiple of 0f for odd values of n . in a similar way, an expression for sw phase noise psd for arbitrary odd values of d can be derived. it is not shown here, because odd division ratios are rarely used. at this point the psd of  tsw is known. however, we need to know the psd of the pn sidebands around the sw fundamental. the multiplication of the excess phase by the cosine in (3) produces a sum of two pn spectrum replicas shifted by swf and swf , or shifted by swf2 from each other. since the pn has a sampling rate of swf2 , the pn spectrum has a periodicity of swf2 , therefore the two shifted pn spectrum replicas are absolutely identical. hence, its summation results in a doubled noise voltage and thus the resultant psd becomes 4 times higher than sws . iv. simulation results equations (21) and (24) were verified by numerous matlab simulations. the discrepancy between the calculated psd and the simulation results was less than one tenth of a decibel. the use of the approximation   etfp  increased the prediction error to roughly 1 db for relatively long edge durations. it has been observed that when the isf has only a dc component (a purely hypothetical isf), there is no difference between the psd obtained using the proposed expressions and the psd calculated in the traditional way. conversely, when the isf has at least one ac component, the traditional calculation gives nonzero errors. this is in agreement with our theory, because each frequency translation of the original noise happens in a unique way in the first case, while in the second case the original noise undergoes the same frequency translations in two or more different ways. the simulations showed that the error of the traditional calculation reaches a few decibels when the flicker noise corner ff1 of the original noise  ti is higher than several tens of percent of the oscillation frequency. errors of the traditional calculation of up to several decibels were observed when the original noise psd showed steep changes, but this is unlikely for a real-world noise source. it was observed in all simulations that for frequency offsets up to tens of percent of the oscillator frequency the error of the traditional calculation is negligible (below one tenth of a decibel). v. some examples first we will examine a usual case: sw forming with a frequency division ratio of two. the example isf is given by:  tf 02cos21  . the following parameters are chosen: original noise psd of -160 dbm/hz for fff 1 , oscillator frequency 2000 f mhz and maximum charge displacement across the capacitor in the oscillator lc tank 11max 105.1 q c. the flicker noise corner frequency is 101 ff mhz. the flicker noise corners in this and in following examples may seem to be unrealistically high, but in the contemporary nanoscale cmos processes ff1 can be well beyond 1 mhz [12] and can even reach hundreds of megahertz [13, 14]. the pn psds calculated by the proposed expression (21) and obtained by simulation are shown in figure 3. a perfect agreement between the calculated and simulated psd can be seen. the psd calculated in the engineering, technology & applied science research vol. 8, no. 1, 2018, 2361-2366 2365 www.etasr.com lubich: a refinement of the square wave phase noise evaluation traditional way (15) is also shown. practically there is no difference between two calculated psds. in figure 4 the results for 2001 ff mhz are given, with other conditions unchanged. the error of the traditional calculation (15) reaches nearly 2 db for frequency offsets approaching 0f , while the psd calculated by (21) remains close to the simulated psd. however, the pn psd for such offsets is usually well below the thermal noise psd and the total noise will be dominated by the thermal and the device noise of the divider circuits. therefore, the error caused by the simplified calculation will be ultimately negligible again. fig. 3. comparison between the calculated pn psd and the pn psd obtained by simulation for 2000 f mhz, 2d and 10/1 ff mhz. fig. 4. comparison between the calculated pn psd and the pn psd obtained by simulation for 2000 f mhz, 2d and 200/1 ff mhz. let us consider next an example for sw forming without frequency division. the oscillator frequency is 1000 f mhz. the ideal isf [10], i.e.    tft 02cos   , is chosen. the other conditions are the same as in the first example. the calculation and simulation results are given in figure 5. the traditional calculation erroneously predicts a non-existing steep upsurge of the psd when the frequency offset approaches 0f . the error goes beyond 6 db, while the psd calculation according to the proposed formula (24) gives correct results. as in the previous example, the error increases when the flicker noise corner is higher. fig. 5. comparison between the calculated pn psd and the pn psd obtained by simulation for 1000 f mhz, 1d and 10/1 ff mhz. vi. conclusions a faultless calculation of the square wave phase noise psd cannot be performed if the oscillator and sw forming circuits are not considered as one whole. taking into account the phase noise mechanism in the oscillators, expressions for exact calculation of sw phase noise psd were derived. a practically perfect agreement between the calculated and the simulated psds was obtained. however, in most practical cases, especially at relatively low frequency offsets, the error of the widely used simplified calculation is insignificant. the proposed expressions may be useful when the pn psd at large frequency offsets is important and at the same time one or more of the following are present: the psd of the oscillator noise sources is relatively high, the flicker noise corner of the oscillator noise sources is higher than several tenths of the oscillation frequency, there are steep changes in the psd of the oscillator noise sources. in such cases, an accuracy improvement of several decibels can be obtained using the proposed formulas. references [1] h. m. el misilmani, m. y. abou-shahine, y. nasser, k. y. kabalan, “recent advances on radio-frequency design in cognitive radio”, international journal of antennas and propagation, vol. 2016, article id 9878475, 2016 engineering, technology & applied science research vol. 8, no. 1, 2018, 2361-2366 2366 www.etasr.com lubich: a refinement of the square wave phase noise evaluation [2] z. el alaoui ismaili, w. ajib, f. gagnon, f. nabki, “very wide range frequency synthesizer architecture for avionic sdr applications”, ieee international conference on ubiquitous wireless broadband, pp. 1-5, 2015 [3] b. razavi, “challenges in the design of cognitive radios”, ieee custom intergrated circuits conference, pp. 391-398, 2009 [4] b. razavi, rf microelectronics, prentice hall ptr, 2011 [5] c. calosso, e. rubiola, “the sampling theorem in pi and lambda digital frequency dividers”, joint uffc, eftf and pfm symposium, pp. 960-962, 2013 [6] m. apostolidou, p. baltus, c. vaucher, “phase noise in frequency divider circuits”, ieee international symposium on circuits and systems, pp. 2538-2541, 2008 [7] s. levantino, l. romano, s. pellerano, c. samori, a. l. lacaita, “phase noise in digital frequency dividers”, ieee journal of solid-state circuits, vol. 39, no. 5, pp. 775-784, 2004 [8] w. f. egan, “modeling phase noise in frequency dividers”, ieee transactions on ultrasonics, ferroelectrics, and frequency control, vol. 37, no. 4, pp. 307-315, 1990 [9] t. h. lee, a. hajimiri, the design of low noise oscillators, kluwer academic publishers, 2003 [10] t. h. lee, a. hajimiri, “oscillator phase noise: a tutorial”, ieee journal of solid-state circuits, vol. 35, no. 3, pp. 326-336, 2000 [11] д. в. васильев, м. р. витоль, ю. н. горшенков, к. самойло, т. федосова, е. черниговская, радиотехнические цепи и сигналы [radiotechnical circuits and signals], радио и связь, москва, 1982 [in russian] [12] f. pepe, a. bonfanti, s. levantino, c. samori, a. l. lacaita, “suppression of flicker noise up-conversion in a 65-nm cmos vco in the 3.0-to-3.6 ghz band”, ieee journal of solid-state circuits, vol. 48, no. 10, pp. 2375–2389, 2013 [13] i. chlis, d. pepe, d. zito, “analyses and techniques for phase noise reduction in cmos colpitts oscillator topology”, international journal of circuit theory and applications, vol. 44, no. 3, pp. 616–638, 2016 [14] i. chlis, d. pepe, d. zito, “analysis of phase noise in 28 nm cmos lc oscillator differential topologies: armstrong, colpitts, hartley and common-source cross-coupled pair” journal of circuits, systems, and computers, vol. 24, no. 4, pp. 1550052-1 1550052-18, 2015 microsoft word etasr_v12_n1_pp8053-8057 engineering, technology & applied science research vol. 12, no. 1, 2022, 8053-8057 8053 www.etasr.com nahas: a super high gain l-slotted microstrip patch antenna for 5g mobile systems operating at 26 … a super high gain l-slotted microstrip patch antenna for 5g mobile systems operating at 26 and 28 ghz mouaaz nahas department of electrical engineering college of engineering and islamic architecture umm al-qura university makkah, saudi arabia mmnahas@uqu.edu.sa abstract-microstrip patch antennas have been widely investigated and used in modern mobile communication technologies including 5g. previous works in the area demonstrated that such antennas can be designed to operate in the low, mid, and high bands of 5g networks. this paper focuses on high-band millimeter-wave 5g mobile applications. in particular, the proposed microstrip patch antenna was designed to operate at 26 and 28ghz, which are the first introduced and widely used frequency bands of the 5g. this study aims to enhance the gain and other radiation characteristics of the antenna by adding a combination of different slot shapes to a single rectangular patch that is commonly used in other 5g antennas. the results show that an extremely high gain is achieved by inserting two symmetric l-slots and a middle-placed square slot. the dimensions of the slots were simulated and optimized using the cst studio suite simulator. a comparative study was also conducted showing that the proposed antenna features higher gain and directivity and provides very good vswr and efficiency along with a reasonably large enough bandwidth at the two resonance frequencies considered. keywords-5g mobile communications; antennas; gain; microstrip; patch; slot i. introduction low profile, low cost, small size, easy fabrication, and the conformity of microstrip patch antennas have led to their wide adoption in mobile communication systems including mobile phones, radio frequency identification (rfid), global positioning system (gps), and many more applications [1-2]. such antennas also have been recently found very effective in 5g wireless communication devices [3-4]. the millimeterwave (mmwave) band represents a major part of 5g networks. the new mmwave bands allocated for 5g connectivity lie between 24.25–27.5, 27.5–29.5, 37–40, and 64–71ghz [5]. in particular, the first introduced 26 and 28ghz frequency bands are the two most important operating bands for mmwaves used in 5g, as defined by the federal communication commission (fcc) [6-7]. for example, south korea, us, and japan considered the 28ghz band for their first 5g deployments, while europe and china considered the 26ghz band [8]. the availability of mmwave spectrum, especially at 26 and 28ghz, has attracted the interest of various radio technologies, including mobile communication. therefore, these particular frequencies have attracted considerable attention from many researchers working in 5g [7-11]. on the other hand, many researchers focused on improving the radiation characteristics of microstrip patch antennas for 5g applications. a major issue in microstrip antennas is their narrow bandwidth, which can be improved using various methods such as slotted patch, thick substrates, low effective permittivity substrates, incorporating multiple resonances, and optimizing impedance matching [1213]. moreover, the main disadvantages of using mmwaves can be the high path loss, the susceptibility to atmospheric and rain absorption, shadowing by materials or human body, etc., which can all be mitigated by using antennas with high gain and large bandwidth [14]. nevertheless, the narrow bandwidth is not a major issue in 5g as in wireless applications operating at lower frequency bands, instead the achievement of high gain stands as the main challenge, provided that the bandwidth is not severely compromised. the primary goal of this study is to improve the microstrip patch antenna gain for 5g applications working at 26 and 28ghz bands (ka-band). a summary of the key related works in this area follows. in [15], a compact planar inset-fed microstrip antenna was designed at 28ghz and provided 6.83dbi gain. in [4], a tripleband antenna, using low relative permittivity and low thickness substrate, was designed to operate at 24.4, 28, and 38ghz. the gains achieved at these frequencies were 6.65, 7.02, and 5.05dbi respectively. in [16], a dual-band coplanar waveguide (cpw) slot directive antenna was designed to operate at 28 and 38ghz for 5g. the maximum gains achieved for the two bands were 6.6 and 5.6dbi respectively. in [17], a broadband elliptical-shaped slot antenna was designed to cover the 5g band from 20 up to 40ghz, having a maximum gain of 5dbi. in [18], a dual-band planar inverted-f antenna (pifa) with a cpw feeding line was designed. this antenna achieved a bandwidth of 3.34 and 1.395ghz and a gain of 3.75 and 5.06dbi in the 28 and 38ghz bands respectively. in [19], a combined structure was developed, using a microstrip patch corresponding author: mouaaz nahas engineering, technology & applied science research vol. 12, no. 1, 2022, 8053-8057 8054 www.etasr.com nahas: a super high gain l-slotted microstrip patch antenna for 5g mobile systems operating at 26 … radiator and a waveguide aperture, to provide a wide beam and high gain in a particular tilt direction. the maximum achieved gain was 7.41dbi at 28ghz. in [20] a slotted microstrip patch antenna was designed to operate at 28ghz for 5g applications. the design was based on the use of two slots of different shapes placed in the middle of the patch and connected through a narrow short strip. this compact antenna design provided a 6.37dbi gain. in [21], a dual-band (28 and 45ghz) ellipticalslotted circular patch antenna was designed for 5g communications and provided the maximum gain of 7.6dbi at 28ghz. in [22], defected ground structure (dgs) and stub slot configuration were used to design a dual-band (28 and 45ghz) microstrip patch antenna with wide bandwidth and high gain (8.31dbi). further studies that attempted to optimize microstrip patch antennas to operate at 28ghz for 5g communications were presented in [23-24], while the gains they obtained were 7.43 and 9.82dbi respectively. furthermore, many studies focused on the use of microstrip patch arrays to enhance beamforming and directivity, and hence gain, of microstrip patch antennas for 5g applications. in [10], a novel antenna array design, based on using a square patch, an edge-plated air-filled cavity, and an hourglass-shaped aperture-coupled feed, was developed for the global 26 and 28ghz 5g bands. the presented 1×4 antenna array provided a peak gain of 10.1±0.7dbi. many studies considered the design of array-based microstrip patch antennas for the 26ghz [2529] and 28ghz [14, 30-36] 5g bands. among these studies, the maximum gains achieved were 16.4dbi [25] and 19dbi [12] for the 26 and 28ghz bands respectively, which are considered very high. however, in terms of simplicity, such designs might not be the right choice in many cases, since the integration of patch arrays substantially increases the design complexity and the overall size of the antenna. this study aims to design a dual-band single patch microstrip antenna operating at both the 26 and 28ghz mmwave bands of 5g. the slotted patch method is used in an attempt to improve the antenna gain significantly, as well as return loss (reflection coefficient), voltage standing wave ratio (vswr), directivity, and efficiency while maintaining a sufficiently large bandwidth in the two 5g bands considered. ii. antenna design considering that patch antennas are widely used in other shapes [37], the proposed antenna was based on a rectangular patch that has two symmetric back-to-back l-shaped slots and a single square slot placed between them. the antenna was built on a rectangular rogers rt5880 substrate of 20mm length, 16.5mm width, and 0.508mm thickness. the relative dielectric permittivity εr was 2.2, and the loss tangent tan δ was 0.0009. further details on the rt duroid 5880 substrate can be found in [38]. among the various feeding techniques available for microstrip patch antennas, the inset feed was selected to achieve a good impedance matching between the feed line and the patch. the dimensions of the patch were 9.9×9.7mm 2 , fed by a 50ω microstrip line of 0.7mm width and 4.75mm length. table i provides the optimized dimensions of the proposed antenna depicted in figure 1. the values from ll1 up to ws in the table represent the optimized dimensions obtained from a parametric study performed using the sweep option available in the cst studio suite simulator. table i. optimized dimensions of the slotted patch of the proposed antenna dimension lp wp ll1 ll2 wl1 wl2 ls ws value (mm) 9.7 9.9 5.3 1 1.5 0.5 3.95 4.25 fig. 1. geometrical representation of the slotted patch element of the proposed microstrip antenna. iii. simulation results this section provides the simulation results of the designed antenna, using the cst simulation software. table ii shows the detailed results of the radiation parameters chosen in this study to analyze the performance of the developed microstrip patch antenna. these parameters are center frequency (how close it is to the selected band), reflection coefficient (s11), bandwidth, gain, directivity, vswr, and efficiency. the parameters listed in the table are introduced below. the reflection coefficient is most commonly referred to as "return loss" and is calculated in db as: return loss � �20log|�| (1) where γ is the voltage reflection coefficient. as in all other microstrip antenna design studies, the bandwidth was measured at -10db return loss. the gain was measured in dbi (decibels-isotropic) as a reference to an ideal hypothetic isotropic antenna radiating (or receiving) energy equally in all directions. while the gain is the ratio of the radiation intensity in a given direction to the average of total input power, the antenna directivity, in contrast, is the ratio of the peak radiation intensity in a certain direction to the total radiated power [39]. the gain g is related to the directivity d by: � � �� (2) where � is the efficiency factor lying between 0 and 1. for an ideal lossless antenna, � equals to 1 (i.e. 100%). the antenna efficiency is calculated as the ratio of the power radiated from the antenna to the power delivered to it. the higher the efficiency the more reliable and useful the antenna would be, particularly for 5g communications which require high speeds and reliable communication processes. the vswr is a ratio between the maximum and the minimum voltage expressed by: vswr � ���� ���� (3) engineering, technology & applied science research vol. 12, no. 1, 2022, 8053-8057 8055 www.etasr.com nahas: a super high gain l-slotted microstrip patch antenna for 5g mobile systems operating at 26 … vswr measures the impedance mismatch between the feeding system and the antenna [38]. its value must lie between 1 and 2, and the greater match is achieved as this value decreases towards 1. vswr is calculated by [40]: vswr � � |!| �"|!| (4) where γ is calculated as a function of the load (zl) and source impedance (zs) by [40]: � � #$"#% #$ #% (5) table ii. simulation results of the proposed antenna at 26 and 28 ghz frequency (ghz) s11 (db) bw (ghz) relative bw (ghz) gain (dbi) directivity (db) vswr efficiency 25.98 -24.14 0.55 2.12% 8.63 9 1.13 95.89% 28.2 -25.45 1.1 3.93% 11.26 11.8 1.11 95.42% table iii. comparisons of all antennas at the 28 ghz band design gain (dbi) center frequency (ghz) minimum s11 (db) bw (ghz) relative bw (ghz) directivity (dbi) vswr efficiency % other 5g bands (ghz) proposed 11.26 28.2 -25.45 1.1 3.93% 11.8 1.11 95.42% 25.98 [23] 9.82 28.1 -42 1.29 4.61% 1 99.99% [21] 8.31 28 -54 5.13 18.32% 8.35 1 98% 38.5 [20] 7.6 28 -40 1.3 4.64% 7.68 1.01 85.6% 45 [18] 7.41 28 -35 1.5 5.35% [3] 7.02 28.1 -19.3 0.9 3.21% 7.69 1.244 85.5% 24.4, 38 [14] 6.83 28.06 -18.25 1.1 3.93% 1.278 [19] 6.37 28 -40 2.48 8.86% 6.99 1.022 86.73% the results show that the designed antenna provides high performance against all parameters considered in the study. for example, the reflection coefficients at the 26 and 28ghz frequency bands were equal to -24.14 and -25.45db respectively. such extremely low return loss values have a considerable impact on gain and directivity, which both scored very high values. on the other hand, the vswr values in the two frequency bands are very close to 1, indicating a great match between the feeding system and the antenna. moreover, the antenna efficiency exceeded 95% at both considered bands. furthermore, the bandwidth of the proposed antenna in the two frequency bands is acceptable for 5g applications. such moderate bandwidth values are outweighed by the super high gain achieved, which was the main objective of this study. as mentioned above, gain is of a higher priority than bandwidth in developing 5g antennas, given that the bandwidth is kept wide enough to cover 5g services. the high gain values achieved here by a single patch structure might be obtained by using array antenna structures, which in turn compromises the design simplicity and cost-effectiveness. the relative bandwidth in the table was calculated as the ratio of the bandwidth to the center frequency of the band in which the antenna operates (i.e. 26 or 28ghz in this case). a detailed comparison between the proposed antenna results and those achieved in other studies is provided in the next section. figure 2 shows the s11 parameter in db with respect to the operating frequency. the obtained center frequency and bandwidth are annotated on the graph for both considered operating bands. figures 3 and 4 show the radiation pattern and the e-h plane of the proposed antenna at both resonance frequencies. iv. comparison of the proposed antenna with other designs table iii provides a detailed comparison between the proposed antenna and a set of other designs that used a single patch structure and a resonance frequency of 28ghz. it should be noted that all studies on the 26ghz band found in the literature were either based on antenna arrays or not designed for 5g applications (ka-band), hence no comparison for 26ghz antenna designs is provided. the results are arranged in descending order according to the gain value. the best output value of each parameter is highlighted to facilitate the comparison between the various antenna designs. fig. 2. s11 parameter as a function of frequency for the proposed antenna design. fig. 3. the radiation pattern and e-h plane for the proposed antenna at 26ghz. it can be observed that the proposed antenna provided the highest gain and directivity without compromising other parameters, except the bandwidth which was compensated by engineering, technology & applied science research vol. 12, no. 1, 2022, 8053-8057 8056 www.etasr.com nahas: a super high gain l-slotted microstrip patch antenna for 5g mobile systems operating at 26 … the very high gain and directivity. this indicates that the proposed microstrip patch antenna can be a strong candidate for 5g mobile communication devices, especially when simplicity, low cost, and small size are the key design requirements. fig. 4. the radiation pattern and e-h plane for the proposed antenna at 28ghz. v. conclusions in response to the rising need for fast and reliable mobile communication devices, a rectangular slotted microstrip patch antenna was developed for high-band 5g applications. the main goal was to enhance the antenna gain along with other radiation characteristics. the proposed antenna was intentionally designed with a single patch for simplicity and aimed to resonate the antenna at the 26 and 28ghz 5g frequency bands simultaneously. the antenna consisting of double symmetric l-slots and a single square slot placed in the middle provided very good radiation characteristics, especially the peak gain. the antenna gains for the two resonance frequencies were 8.63 and 11.26dbi respectively, which were significantly higher than those achieved in the reviewed literature. the corresponding directivity values for the two considered bands were 9 and 11.8db, and the minimum reflection coefficients obtained were equal to -24.14 and -25.45db respectively. the latter values are far below the -10db return loss at which the bandwidth is usually measured. the bandwidths of the two bands at -10db return loss were equal to 0.55ghz (2.12% fractional bandwidth) and 1.1ghz (3.93% fractional bandwidth) respectively, with a total bandwidth of 1.65ghz covering the 5g spectrum lying between 25 and 29ghz. furthermore, for the 26ghz band, the vswr and efficiency were 1.13 and 95.89% respectively, while for the 28ghz band, the vswr and efficiency were 1.11 and 95.42% respectively. these results proved to be satisfactory when compared to other designs. based on these results and the small dimensions, light weight, and relatively simple design, the proposed microstrip patch antenna can be a suitable choice for the development of 5g mobile communication devices. in the future, we can investigate various combinations of other slot shapes or antenna array structures to further improve the radiation characteristics, particularly bandwidth. acknowledgment the author would like to thank jasim alotaibi, mohammed alreuthe, sanad al-leheani, saleh bazaid, omar bajunduh, mohammed kalil-alrahman, mohammed alshehri, mohammed saif, and akram babsail for their valuable assistance during this study. references [1] m. u. khan, m. s. sharawi, and r. 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[37] m. m. nahas and m. nahas, "bandwidth and efficiency enhancement of rectangular patch antenna for shf applications," engineering, technology & applied science research, vol. 9, no. 6, pp. 4962–4967, dec. 2019, https://doi.org/10.48084/etasr.3014. [38] a. abdelaziz and e. k. i. hamad, "design of a compact high gain microstrip patch antenna for tri-band 5 g wireless communication," frequenz, vol. 73, no. 1–2, pp. 45–52, jan. 2019, https://doi.org/10.1515/freq-2018-0058. [39] r. kazemi, s. yang, s. h. suleiman, and a. e. fathy, "design procedure for compact dual-circularly polarized slotted substrate integrated waveguide antenna arrays," ieee transactions on antennas and propagation, vol. 67, no. 6, pp. 3839–3852, jun. 2019, https://doi.org/10.1109/tap.2019.2905682. [40] a. diggikar, p. chinchpure, c. ingale, and s. jog, "design and development of microstrip patch antenna for gps applications," in 2018 fourth international conference on computing communication control and automation (iccubea), aug. 2018, pp. 1–4, https://doi.org/10.1109/iccubea.2018.8697751. authors profile mouaaz nahas was born in 1977 in the uk. he received a b.sc. degree in electrical engineering from jordan university of science and technology, jordan, in 2001, an m.sc. degree in communications engineering from loughborough university, uk, in 2002, and a ph.d. degree in embedded systems from the university of leicester, uk, in 2009. he is currently an associate professor in the department of electrical engineering at umm alqura university, makkah, saudi arabia. his main research interest is antenna design for modern wireless communication applications. microsoft word etasr_v12_n1_pp8107-8113 engineering, technology & applied science research vol. 12, no. 1, 2022, 8107-8113 8107 www.etasr.com mohammed et al.: an inclusive study on the effect of strain rate on the stress-strain behavior and the … an inclusive study on the effect of strain rate on the stress-strain behavior and the undrained shear strength of clay soils in kombolcha, ethiopia salman mohammed faculty of civil engineering arba minch institute of technology arba minch, ethiopia salmanmohammed872@gmail.com democracy d. dirate faculty of civil engineering arba minch institute of technology arba minch, ethiopia democracy.dilla@amu.edu.et defaru k. dasho faculty of civil engineering arba minch institute of technology arba minch, ethiopia defaru.katise@amu.edu.et ramesh k. verma faculty of civil engineering arba minch institute of technology arba minch, ethiopia vermark42@gmail.com vasudeva r. pampana faculty of civil engineering arba minch institute of technology arba minch, ethiopia vasudevarao_9@yahoo.com ruth b. sangalang faculty of civil engineering arba minch institute of technology arba minch, ethiopia ruthie_sang@yahoo.com abera e. koshuma faculty of hydraulics and water resource engineering arba minch water technology institute arba minch, ethiopia abera.ermias@amu.edu.et abebe t. ayalew faculty of hydraulics and water resource engineering arba minch water technology institute arba minch, ethiopia abebe.temesgen@amu.edu.et abstract-this research aims to study the effect of strain rate on the stress-strain association and shear strength of clay soils in kombolcha, ethiopia. field and laboratory experimentations were conducted on 3 soil samples collected at 4.5m depth, considering the physical and engineering properties of the soil. unconsolidated, undrained triaxial compression tests were performed under confining pressure on the specimens that were axially loaded at a rate of strain varying from 0.38mm/min to 1.14mm/min by taking 2 points above and below 1% of the specimen height. stress-strain relations were developed under the stated different rates of strains to describe their effect. it was revealed that the strain rate effect was observed. by increasing the strain rate shifts the stress-strain curve upward, and the corresponding shear strength of the soil also increased under effective stress. accordingly, the strain rate increased the shear parameters. the average angle of friction increased by 13.43%, 15.08%, 13.18%, and 14.33% when the rate of strain changed from 0.38 to 0.57mm/min, 0.57 to 0.76mm/min, 0.76 to 0.95mm/min, and 0.95 to 1.14mm/min respectively, while the average cohesion increased by 17.67%, 19.52%, 14.87%, and 16.48%. the failure at strain rate 1%/min of sample height (0.76mm/min) was uniformly distributed and there was uniform pore pressure distribution throughout the sample height. the effect is slightly more when the shear strength increased at the left side than at the right side. average shear strength parameters such as cohesion and angle friction were recorded for strain rates from 0.57mm/min to 1.25mm/min specifically for the clay soils found in kombolcha town, ethiopia. keywords-inclusive study; rate; strain; shear; soil i. introduction investigation on the properties of soil is significant in designing and building structures with foundations secured by materials such as soils and/or rocks. soils have a maximum shearing resistance that they can sustain to the applied shear stress, which is a function of the effective normal stress that can determine its magnitude [1]. shearing resistance is developed by friction, interparticle forces, cementation, or bonding at particle contacts, therefore, if the effective normal stress is zero, then the shearing resistance must be zero (unless there is cementation between the particles). if at a point on any plane within a soil mass the shear stress becomes equal to the shear strength of the soil then failure will occur. one of the factors that affect the shear strength of the soil is the strain rate [2]. the strength of saturated clay, as observed in undrained shear tests increases with the increasing strain rate [3-5]. the peak shear resistance increases from slow to fast strain rate. small strains occur from increased strength in terms of effective stress, and large strains from decreased excess pore pressure [6, 7]. increasing the strain rate applied to a saturated soil means larger effective stresses and consequently greater shear resistance [8]. at large strains, the relationship between void ratio and effective stress is strain-rate dependent. as the strain-rate is increased, larger effective stress is required to corresponding author: defaru k.dasho engineering, technology & applied science research vol. 12, no. 1, 2022, 8107-8113 8108 www.etasr.com mohammed et al.: an inclusive study on the effect of strain rate on the stress-strain behavior and the … hold the soil at any given void ratio [9]. at faster strain rates, adjacent soil particles find it more difficult to move relatively, and, unless restrained by increased effective stress, will tend to ride up over one another. the measured pore water pressure is smaller at fast than at slow strain rate. the behavior of the pore pressure following a sudden increase in the strain rate proves that there is fundamentally an inverse relationship between the strain rate and the excess pore pressure [10-12]. the effect of strain rate on the stress-strain relationship and shear strength of clay by conducting a series of triaxial compression tests on remolded soil samples prepared with 38mm diameter and height of twice the diameter was studied in[13-15]. the type of triaxial test employed was consolidated undrained (cu) test with pore pressure measurement and by using different effective consolidation pressures. the specimens were axially loaded at a rate of strain varying from 0.001mm/min to 2mm/min. the results show that the strain rate affects both the stress-strain relationship and the strength of the soil. as the strain rate increases, the strength of the soil also increases, but the strain rate has a more pronounced effect on the cohesion and little effect on the angle of internal friction of the soil [16]. in this research, unconsolidated undrained (uu) triaxial test was used to measure the undrained shear strength of clay soil from kombolcha. the soil in the town is dominantly finegrained, belonging in the clay group. the aim of this research is to set quick and convenient uu shear tests for the clay soils found in the study area and to determine the best strain rate for the elastic and shear strength behaviors of soils [17]. kombolcha is an industrial and grooming town that has seen increase in its infrastructures. the town is found in the eastern part of the amhara region, ethiopia, and is located about 375km north of the state capital, addis ababa, along the road to mekelle and 23km southeast of dessie city. it is situated on the western margin of the main ethiopian rift valley and covers an area of about 120km 2 . soils found in this town belong mostly to the fine-grained clay class [18]. ii. research methodology to achieve the study goals, 8 soil samples were collected from kombolcha at a depth of 4.50m from the ground surface. from the samples, 3 were nominated to represent the other 5 samples according to their physical properties. the remolded clay specimens were prepared and used in the laboratory [19]. the selected samples’ locations are presented in table i. moisture content and field densities of the 3 pits were determined in the field and the samples were transported to the laboratory while they were kept in a plastic bag to prevent moisture loss. the measured amount of the wet soil was put in a conventional oven of 105℃ and kept for 24 hours and was examined to determine its weight loss in order to the determine moisture and density of the collected soils [20]. table i. test pit location and coordinates of the study area pit no. location latitude (dms) longitude (dms) pt-1 kurangoye 11° 5' 27.59" 39° 43' 11.64" pt-2 elkbeye 11° 4' 48.36" 39° 42' 50.76" pt-3 sheshaber 11° 5' 27.59" 39° 42' 35.64" a. soil grain and consistency limit test sieve analysis was performed to determine the distribution of the course, larger-sized particles, and hydrometer test was conducted for 24 hours to determine the distribution of finer particles (less than 0.075mm). two jars with 1000ml capacity were used. a control jar with distilled water and 5g of sodium hexametaphosphate was used as a dispersing agent and the other was a soil sample with distilled water and 5g of dispersing agent. a mechanical stirrer was also used for mixing the soil samples with distilled water and the dispersing agent. soils passing through a 0.425 mm sieve were used to determine the plastic and liquid limits of fine-grained soil. the specimens were soaked for 30 minutes and mixed for 5 minutes [21-23]. b. specific gravity and free swell determination tests the specific gravity of the samples was determined with the help of a pycnometer using a soil sample that passed through the 2mm sieve. the sample was connected to the hydrometer and was oven-dried at 105℃. a minimum soil sample of 20g was used [24]. free swell index is the increase in the volume of soil, without any external constraints, on submergence in water. representative oven-dried soil samples having mass of 10g passing through 0.425 mm sieve were put in 100ml of water in a jar for 24hours. swelling was examined as a percentage of the volume change to the original volume [25 ,26]. c. compaction test laboratory compaction procedures were used to determine the relationship between water content and the dry unit weight of soils. the soil samples were compacted in 3 layers with a 24.4n rammer dropped from a height of 305mm producing a compactive effort of 600 kn-m/m 3 . 8% of 3000g of the test sample were added in mm as the initial water content and 4% water content increments were used to obtain a well-defined maximum dry unit weight. after obtaining the density and moisture of each compacted soil sample, maximum dry density (mdd) and optimum moisture content (omc) were determined from the compaction curve [27,28]. d. consolidation and permeability test this test was performed to determine the magnitude and rate of volume decrease a laterally confined soil specimen undergoes when subjected to different vertical pressures. from the measured data, the consolidation curve (pressure-void ratio relationship) can be plotted. these data are useful in determining the compression index and the recompression index of the soil. besides, the obtained data can also be used to determine the coefficient of consolidation and the coefficient of secondary compression of the soil. tests were carried on the undisturbed samples by pushing the consolidation ring into the ground at a depth of 4.50m during the sample collection. the samples were transported to the laboratory while they were kept in a plastic bag. soil samples with diameter of 63mm and height of 20mm were loaded with pressures from 7kpa to 1600kpa. for each loading the compression was recorded from the dial gauge at intervals of 0.1, 0.25, 0.5, 1, 2, 4, 8, 15, 30, 60, 120, 240, 480, and 1440 minutes for 24 hours. unloading to examine unloading behavior was also done in steps. a total of 3 consolidation tests were run on undisturbed samples and different results were obtained. from the test results of the engineering, technology & applied science research vol. 12, no. 1, 2022, 8107-8113 8109 www.etasr.com mohammed et al.: an inclusive study on the effect of strain rate on the stress-strain behavior and the … consolidation curve (pressure-void ratio relationship), compression index (cc) and expansion index (ce) were determined [29]. the purpose of the permeability test is to determine the permeability (hydraulic conductivity) of the soil by the falling head test method. a representative soil sample that passed through the 4.75mm sieve was collected and compacted at optimum moisture content to achieve maximum dry density in a mold having 10cm diameter and 12.73cm length. after the soil sample was saturated, its permeability was examined by allowing the water to come through it falling from the initial head. the head change and the time taken to the water to come through the sample were recorded until the water begun to flow out of the water bath [30]. e. unconsolidated undrained triaxial compression test in this paper, remolded cylindrical specimens passed through the 2.36mm sieve and having a diameter of 38mm and a length twice the diameter (76mm) were used. all the test samples were compacted within 6 layers in a manner that can represent the site condition of the soil. axial load was applied to produce axial strain at a rate of approximately 1%/min of the specimen height, which is used as a reference rate in this study. the confining pressure was calculated from the unit weight of the soil, the depth where the samples were collected, and by assuming a coefficient of earth pressure at rest to represent the site that was conveniently used as per kombolcha town soils behavior. hence, 5 different strain rates were used, the conventional strain rate of 0.76mm/min and 2 strain rates below and 2 above it. trials were done during the triaxial test for each selected pit sample. the trials were conducted with increasing strain rate of 0.5% (0.38mm/min), 0.75% (0.57mm/min), 1% (0.76mm/min), 1.25% (0.95mm/min) and 1.5% (1.14mm/min) of specimen height with confining pressure of 50kpa, 100kpa, and 150kpa in order to assess the better strain rate for kombolcha clay soils. a failure envelope was used to determine the shear strength parameters of the test samples [31-33]. iii. results and discussion a. soil index and density results as described in table ii, the average moisture content was 31.60%, which lies between stiff and soft clays. table ii. moisture content, bluk and dry density, specific gravity, and atterberg's limit results pit no. location moisture content, % bulk density, g/cc dry density, g/cc liquid limit, (%) plasticity index (pi %) soil class specific gravity, at 20 0 c pt-1 kurangoye 30.12 1.75 1.34 63.68 33.11 ch 2.75 pt-2 elkbeye 29.71 1.85 1.43 56.47 31.50 ch 2.72 pt-3 sheshaber 34.84 1.77 1.31 78.32 44.04 ch 2.76 the ranges for bulk density and dry density are 1.75 to 1.85 and 1.31 to 1.43g/cc respectively, which are within the range of silt or clay. the soil grain size analysis ranges results of the obtained samples are 5.82 to 10.14% sand particles, 25.44 to 32.14% silt, and 57.43 to 67.25% the clay fraction. these results show that clay soil is dominantly found, which was also indicated by the results of atterberg limit results. the liquid limit for these clay soils was found above 50% and a plasticity index of more than 30% was obtained. hence, soils are classified as highly plastic clay (ch) as presented in table ii with an average specific gravity of 2.75. b. compaction and free swell results optimum moisture content (omc, %) and maximum dry density (mdd, g/cc) of the test pits are listed in table ii. they vary from 22.50% to 29.80% and from 1.39g/cc to 1.55g/cc respectively. maximum dry density of the soil for all pits is greater than the in-place dry density of the soil, which shows that it needs densification to attain maximum density and optimum moisture. fig. 1. standard proctor compaction test results for pit one. c. soil free swell, consolidation, and permeability results the results of the free swelling of the study area lie within the range from 49.21 to 60.25%, which describes the medium swelling potential (table iii). the magnitude of the compression index varies between 0.25 and 0.29 whereas the swelling index of the clay soils ranges between 0.0169 and 0.0280. the soils fall within the permeability range of 6.78×10 5 to 8.09×10 -6 cm/s at 20 0 c, which indicates that the area is accumulated by fine soils with low permeability. table iii. compaction properies, coefficient of compression and swelling indeces, and permeability results pit no. free swell, % omc, % mdd (g/cc) compression index, cc swelling index, ce coefficient of permeability at 20 0 c, k(cm/s) pt-1 51.53 27.50 1.46 0.27 0.0178 8.09e-06 pt-2 49.21 22.50 1.55 0.25 0.0169 6.78e-06 pt-3 60.25 29.80 1.39 0.29 0.0280 7.19e-06 d. unconsolidated undrained triaxial compression results the plots of deviatoric stress to axial strain relationship for the same strain rates under different confining pressure for the 3 test pit samples are shown in figure 2. in a similar manner, the stress-strain curves for the not listed strain rates were performed. from these graphs, it was observed that an increase in confining pressure shifts the stressstrain curve upward with different patterns, which illustrate the increase in shear strength up to the failure point. maximum deviatoric stresses at failure for each strain rate were obtained to determine the shear strength parameters called angle of friction and cohesion. engineering, technology & applied science research vol. 12, no. 1, 2022, 8107-8113 8110 www.etasr.com mohammed et al.: an inclusive study on the effect of strain rate on the stress-strain behavior and the … (a) (b) (c) (d) (e) (f) fig. 2. deviatoric stress-strain curves for pt-1 at (a) 0.38, (b) 0.57, pt-2 at (c) 0.57 and (d) 0.76, and pt-3 at (e) 0.95 and (f) 1.14mm/min strain rates under 50, 100, and 150kpa confining pressure. (a) (b) (c) (d) fig. 3. stress strain behavior of the three pits under various strain rates. engineering, technology & applied science research vol. 12, no. 1, 2022, 8107-8113 8111 www.etasr.com mohammed et al.: an inclusive study on the effect of strain rate on the stress-strain behavior and the … plots of the deviatoric stress versus axial strain with the different strain rate and same confining pressure is shown in figure 3. only 4 stress-strain graphs are presented (pit-1 for confining pressure of 50kpa, pit-2 for confining pressure of 100kpa and 150kpa, and pit-3 for confining pressure of 150kpa). by the same fashion, all 3 pit samples' stress-strain graphs were developed for confining pressures of 50kpa, 100kpa, and 150kpa under different strain rates. it was revealed that an increase in the strain rate shifts the stressstrain curve upward, which describes the faster strain rate induced increase in deviatoric stress and failure point of the soil under induced pressure. figure 5 presents the shear strength parameters with the different strain rates for 3 test pit samples. the results were derived from figures 2 and 3. from figure 5, it is observed that the cohesion and the angle of internal friction increase when the strain rate increases. shear parameters angle of friction (∅^0) and cohesion (c in kpa) axes are determined for each stress path at failure strain rates. in a similar way the remaining three samples' determination is done and shear strength parameters are presented in figure 6. the average angle of friction is equal to 6.81 0 and the average cohesion is 13.55kpa under the described strain rates. these results define clay soil behavior. the soils were weak to bear the imposed load from the buildings in kombolcha. (a) (b) (c) fig. 4. normal to shear stress chart at failure and different strain rates for (a) pit-1, (b) pit-2, and (c) pit-3. (a) (b) fig. 5. strain rate effect on: (a) angle of friction and (b) cohesion of soil. (a) (b) fig. 6. increase in soil shear parameters: (a) angle of friction and (b) cohesion. accordingly, at higher strain rates (0.75 to 1.25mm/min) produced in higher undrained shear strength for the clay soil samples, the results show that the failure at the strain rate of 1%/min (0.76mm/min) of sample height is uniformly distributed and there is uniform pore pressure distribution throughout the sample height. it was also shown that the angle of friction and the cohesion of soils are inversely related as indicated in figure 5. as illustrated in figure 6, the strain rate increased the clay soil shear parameters. these shear strength parameters actually indicate properties of clay soils with high plasticity. hence, the average angle of friction increased by 13.43%, 15.08%, 13.18%, and 14.33% at strain rates of 0.38 to 0.57mm/min, 0.57 to 0.76mm/min, 0.76 to 0.95mm/min and 0.95 to 1.14mm/min respectively (figure 6 a)), whereas, the average cohesion increased by 17.67%, 19.52%,14.87% and engineering, technology & applied science research vol. 12, no. 1, 2022, 8107-8113 8112 www.etasr.com mohammed et al.: an inclusive study on the effect of strain rate on the stress-strain behavior and the … 16.48% respectively (figure 6(b)). as indicated in the results of the angle of friction, the change in the strain rate is not significantly affected, but cohesion is slightly more increased with the early strain rates for these soils. the minimum average unconsolidated undrained shear test result for clay soils from kombolcha occurs for the strain rate of 0.76mm/min to 0.95mm/min. iv. conclusions the current study described the soils in kombolcha town as dominantly clay soils. uu triaxial compression tests were performed on the soil at different strain rates. when the strain rate increased, the stress-strain curve moved up and the shear strength also increased. the failure at strain rate 1%/min of sample height is uniformly distributed and there was uniform pore pressure distribution throughout the sample height. the increase in undrained shear strength can be associated with the less excess pore water pressure during shearing at faster rates. test were conducted on the clay soil of komblocha using strain rates ranging from 0.75% (rate of 0.57mm/min) to 1.25% (rate of 0.95mm/min) of specimen height of the remolded samples and the average stress-strain and shear strength behaviors of these samples were studied. acknowledgement the authors would like to express their gratitude to the arba minch university institute of technology for its support during this research activity. references [1] y. wang, j. li, q. jiang, y. huang, and x. li, "experimental study on variation law and mechanism of soil shear strength parameters along the slope," advances in civil engineering, vol. 2019, aug. 2019, art. no. e3586054, https://doi.org/10.1155/2019/3586054. 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[33] m. zhao, g. liu, l. deng, and y. li, "optimizing the compaction characteristics and strength properties of gravelly soils in terms of fine contents," advances in materials science and engineering, vol. 2021, jan. 2021, art. no. e6634237, https://doi.org/10.1155/2021/6634237. microsoft word etasr_v12_n5_pp9155-9159 engineering, technology & applied science research vol. 12, no. 5, 2022, 9155-9159 9155 www.etasr.com mohammed & al-zaidee: deflection reliability analysis for composite steel bridges deflection reliability analysis for composite steel bridges duaa mohammed department of civil engineering college of engineering university of baghdad baghdad, iraq d.rasol1901m@coeng.uobaghdad.edu.iq salah al-zaidee department of civil engineering college of engineering university of baghdad baghdad, iraq salah.r.al.zaidee@coeng.uobaghdad.edu.iq received: 18 june 2022 | revised: 6 july 2022 | accepted: 17 july 2022 abstract-reliability methods offer a very efficient serviceability assessment of structures with randomness due to geometry, material, and loading. al-awsej composite bridge in diyala-iraq with a span of 33.2m has been studied and its deflection reliability index for three lifespans was estimated and compared with the reliability target index. the reliability indices of the bridge have been evaluated through the first-order reliability method (form) and monte carlo simulation (mcs) method. mcs has adopted matlab functions to generate pseudo-random numbers for the considered parameters, but it requires large sample sizes to estimate the small probabilities of failure. that leads to the use of the reduction variance methods such as the importance sampling (is) method. four cases of random loading were included: dead load and three cases of live loads, i.e. uniformly distributed load with knife-edge load, military load, and sidewalk load. some assumptions are needed to assess the system behavior, where the bridge is represented as a parallel system with uncorrelated and perfect correlated girders. the reliability index of the composite bridge in the two cases was investigated for lifespans of 1, 10, and 50 years. for the uncorrelated case, the system shows the reliability index in the range of 5 and 4. in contrast, the correlated case offers a range between 4 and 2. with these assumptions, the results show that no failure occurs, hence the reliability index of the system is still within range of the target. keywords-steel girder bridge; statistical characteristics; form; mcs; importance sampling; parallel system; reliability i. introduction structure design is associated with a substantial level of uncertainty due to the limited information in the estimation of structural parameters. in practice, most structural engineering designs are based on deterministic parameters where structural performance is determined using a deterministic model for simplification and often ignore the variations in material properties, structure geometry, and applied loads. in previous studies, structural reliability methods that rationally evaluate the safety of complex structures or systems with unusual designs have been developed [1]. in this study, these methods will be used to assess the reliability of a bridge by determining the reliability indices of the steel girders considering the bridge is a parallel system and comparing it with target reliability that ensures that structures meet the specified safety level. thus, reliability is an approach to determine the relationship between an element and system reliability [2]. ii. courbon's method of analysis courbon's method is one of the earliest rational analyses of bridges and is very popular due to its simplicity. the reaction factor for individual longitudinal girders is given by [3]: �� = �� �1 + �×�×� ∑ � � �� (1) where �� is the reaction load distribution factor of the girder, p the total concentrated live load on the span, n the number of longitudinal girders, e the eccentricity of live load to the axis of the bridge, and �� is the distance from the girder to the central axis of the bridge. iii. load application the applied loads on the composite bridge have been determined based on the iraqi code specifications. the selfweight of the pavement, deck, sidewalk, supporting girders, and bracing have been determined depending on the crosssection dimensions and material densities. the own weight of the handrail has been estimated based on iraqi standard specifications for road bridges [4]. two cases, namely lane live and military load have been considered and applied according to the iraqi standard. for a span of 33.2m, the lane load has a value of 28.7kn/m per lane with a knife-edge load (kel) of 120kn per lane. the military load consists of 900kn (class 100) tracked vehicles.two tracked vehicles have applied for a carriageway width of 9m [4]. iv. reliability analysis of the system structural reliability analysis is based on the limit state design �(�), where � = (��, ��, . . . , ��) represents the set of random variables that have some statistical information. the limit �(�) = 0 separates the failure domain (�(�) < 0) and the safety domain (�(�) > 0) [7]. the probability of failure can be defined by: corresponding author: duaa mohammed engineering, technology & applied science research vol. 12, no. 5, 2022, 9155-9159 9156 www.etasr.com mohammed & al-zaidee: deflection reliability analysis for composite steel bridges ! = [�(�) ≤ 0] (2) the major source of uncertainty is actions with statistically independent maximums each year. the values of the probability of failure, !% and of the reliability index, '� for each reference period may be estimated using [5]: !% = 1 − (1 − !) )� (3) and '� = −*+�,− !% (4) where * , and *+� are the functions of the standard normal cumulative distribution. the target reliability is a design constraint that ensures that structures meet the specified safety level. table i shows the target values of reliability indices for various limit states and periods [6]. table i. target reliability indices reference period t (years) target reliability index β for serviceability target reliability index β for moment 1 2.9 4.7 10 2.2 4.2 50 1.5 3.8 100 1.1 3.6 200 0.6 3.5 v. reliability analysis methods the evaluation of the failure probability of the structure in a closed-form is difficult and almost impossible. as a result, various analytical and numerical approaches have been developed, e.g. taylor-series-based approaches, such as the first-order reliability method (form), and simulation-based methods, such as monte carlo simulation (mcs). the form approximation approaches are efficient for simple issues with few random variables, but for more complex problems with many random variables, mcs seem to be more reliable [7]. a. first-order reliability method it is possible to expand the original model into an infinite taylor series (ts) around the mean values: �(�) = �(./) + (� − ./ ) 010/ + � � (� − ./ )� 0�1 0/� + ⋯ +� �! (� − ./ )� 0%1 0/% (5) where the function and derivatives are evaluated at ./ . it is common to include only linear terms, assuming that random input variables are independent. a function � (�) of n independent random variables can be approximated by linear terms of the ts, which are [8]: 4(5) ≈ �,./) , ./� , … , ./% (6) and 89:(5) ≈ ∑ ;/ � <10/ � ���=� (7) the limit state function is: (�) = � − >, �, and > both are random variables uncorrelated and assumed to be normally distributed. the reliability index ' is evaluated as a function of mean and standard deviations of resistance � and load > as given by [8]: ' = ?@+?a bc@�dca� (8) b. monte carlo method the failure probability in mcs is the ratio of the number of samples in the failure domain to the total number of samples: ! = �e� = � � ∑ f[�(�) ≤ 0]��=� (9) where the sampling points � are generated according to the probability density function, g! is the number of sampling points such that �(�) ≤ 0, g is the total number of sampling points, �(�) is the limit state, f[�(�)] is an indicator function taking values of unity when are �(�) ≤ 0 and zero otherwise. with increasing n, the accuracy of this estimation improves, and more simulations are needed to predict a smaller failure probability [9]. the required number of trials g of mcs is approximated by: g ≈ (�+�e)(hij �×�e) (10) where kl8 is the coefficient of variation of the response estimates smaller than 0.1 and ! is usually between 10+� to 10+m . the total number required for that simulation is determined by: g ≈ (�+�no�)(n.��×�no�) ≈ 9900 (11) c. importance sampling the main idea of is is to distribute the sampling points in the most important area so that the failure probability evaluation may be completed faster. the failure probability can be estimated as (9) is rewritten as follows: ! = �� ∑ f(�� ) !�(�q) r�(�q) �s=� (12) where the sampling points �s , t = 1, . . . , g are generated according to the distribution ℎ� instead of v� . the effectiveness of is is dependent on choosing an adequate ℎ� (�) so that the probabilistic sampling in (12) may be prioritized for the most important area, resulting in a higher convergence rate. although no overall conclusion has been reached on the best choice of ℎ� (�), it has been suggested that the most probable point (mpp) and its surroundings can be a suitable selection for the most important area [10]. vi. system reliability the system reliability is affected by component reliability and several other parameters, such as the correlation among the component resistances and the system type. structural system reliability is determined by considering the system failure rather than a single component failure [11]. the series system means that the entire system fails. the formula of the failure system for the statistically independent elements is given by: ! = 1 − ∏ (1 − ! )��=� (13) engineering, technology & applied science research vol. 12, no. 5, 2022, 9155-9159 9157 www.etasr.com mohammed & al-zaidee: deflection reliability analysis for composite steel bridges where ! and ! are the probability of failure for the element x and the system respectively. the equation of the system failure for perfectly correlated elements can be defined as: ! = y9�z ! [ (14) a parallel system is an overall system that fails after all its elements have failed. the probability of failure for the entire system when the elements are statistically independent and perfectly correlated respectively is defined as [11]: ! = ∏ ! ��=� (15) ! = yx\z ! [ (16) vii. case study the al-awsej composite bridge is constructed in awsej valley at diyala town in iraq. it has 33.2m length and 14m width and consists of three longitudinal steel girders connected by steel bracings (2l100×10). the i-steel plate girders are nonsymmetrically with an upper flange of 400×30mm and two lower flanges of 510×30mm and 490×30mm respectively. the floor bridge consists of a concrete deck slab with a thickness of 250mm and pavement bitumen of 60mm extending above a carriageway width of 9m, with a 2.5m sidewalk width and handrail of 1m on each side. (a) (b) fig. 1. the composite steel bridge. viii. statistical characteristics of variables in this article, the applied loads, beam span, cross-section dimensions, and modulus of elasticity are considered random variables. the statistical characteristics of these variables have been collected based on previous studies and are summarized in table ii. table ii. statistical characteristics of variables uncertainty mean/nominal cov distribution type weight of the deck slab 1.05 0.10 normal weight of the girder 1.03 0.08 normal weight of the pavement 1.00 0.25 normal weight of the military 1.10 0.18 lognormal uniform distribution with knife-edge live loads 1.10 0.18 lognormal sidewalk live loads 1.10 0.18 lognormal length of the girder 1.00 0.000502 normal width of the flange girder 1.00 0.00403 normal thickness of the flange and web 1.05 0.044 lognormal depth of the web girder 0.996 0.000486 normal modulus of elasticity 0.993 0.034 normal ix. statistical properties for the deflection of girders two methods have been used to analyze the exterior and interior girders: first-order approximation and mcs. a. first-order approximation method the determination of statistical characteristics of girder deflection has been determined due to the uncertainties in the moment of inertia f, span ], modulus of elasticity 4, and loads. self-weight and superimposed loads ^] are considered uncertain due to the randomness in the weight of concrete deck slab, girders, and pavements. randomness in the own weight of bracing, sidewalk, and handrail has been neglected. live load (ll) uncertainties have been considered for the cases of military, sidewalk, uniform distributed, and knife-edge loads. table iii provides the mean and standard deviation of deflection. table iii. statistical characteristics of the girder deflection form loads nominal (mm) mean (mm) standard deviation (mm) cov e x te r io r g ir d e r self-weight and superimposed loads 70.44 70.72 7.10 0.10 military with sidewalk live loads 52.54 56.11 10.48 0.18 uniformly distributed with knife-edge and sidewalk live loads 61.26 65.45 12.22 0.18 in te r io r g ir d e r self-weight and superimposed loads 51.95 51.60 6.50 0.13 military and sidewalk live loads 52.54 56.11 10.48 0.18 uniformly distributed with knife-edge and sidewalk live loads 49.11 52.45 9.80 0.18 b. monte carlo simulation the mcs was utilized for deflection of the exterior and interior girders. a matlab code has been used to generate pseudo-random sampling. six samples, each with a size of 1000, have been generated to include the randomness in the moment of inertia f, the span of the girder ], and the modulus of elasticity 4. engineering, technology & applied science research vol. 12, no. 5, 2022, 9155-9159 9158 www.etasr.com mohammed & al-zaidee: deflection reliability analysis for composite steel bridges fig. 2. deflection sample for the case of dead and superimposed loads. fig. 3. deflection sample for the case of military and sidewalk live loads. fig. 4. deflection sample for the case of uniform lane with knife-edge and sidewalk live loads. three samples have been considered for each of the exterior and interior girders. for each girder, the samples represent the randomness in dead loads, military with sidewalk loads, and uniform lane with knife-edge and sidewalk loads respectively. table iii shows that each random variable has been generated based on preselected statistical parameters and probability density function. the sample data are presented in the histogram figures 2-4, and the statistical characteristics for the deflection of the girders are shown in table iv. table iv. statistical characteristics of the girder deflection mcs loads mean (mm) standard deviation (mm) cov distribution type e x te ri o r g ir d e r self-weight and superimposed loads 70.76 5.74 0.08 normal military and sidewalk live loads 56.59 8.74 0.15 lognormal uniformly distributed with knifeedge and sidewalk live loads 65.37 9.10 0.13 lognormal in te ri o r g ir d e r self-weight and superimposed loads 51.99 4.77 0.09 normal military and sidewalk live loads 56.12 8.21 0.15 lognormal uniformly distributed with knifeedge and sidewalk live loads 52.46 6.71 0.13 lognormal x. reliability analysis for steel girder deflection form and mcs methods have been adopted to estimate the reliability associated with girder deflection. some assumptions have been adopted in the form, assuming all independent variables have a normal distribution. the mean and standard deviation of girders deflection in table iii have been used to evaluate the reliability index ' and the probability of failure, ! by: ' = ∆`aabcdeaf gdh+i(∆)j∆ (17) where ∆kllmnopl� qo� represented a threshold limit of 80mm that was adopted as a camper in the design of the al-awsej bridge case study. table v. reliability index and probability of failure by form loads 1 year 10 years 50 years rs t rs t rs t e x te r io r g ir d e r self-weight and superimposed loads 0.09 1.31 0.63 −0.34 0.99 −2.47 military with sidewalk live loads 0.001 3.09 0.009 2.33 0.048 1.66 uniform distributed with knife edge and sidewalk live loads 0.03 1.89 0.26 0.65 0.77 −0.75 in te r io r g ir d e r self-weight and superimposed loads 6 × 10+m 4.37 6 × 10+v 3.84 0.0003 3.42 military and sidewalk live loads 0.001 3.09 0.009 2.33 0.048 1.66 uniformly distributed with knife edge and sidewalk live loads 0.0001 3.68 0.001 3.04 0.005 2.52 table vi. reliability index and probability of failure by is method loads ws 1 year 10 years 50 years rs t rs t rs t e x te ri o r g ir d e r self-weight and superimposed loads 39 0.039 1.76 0.33 0.44 0.86 −1.09 military and sidewalk live loads ≈0 ≈0 / ≈0 / ≈0 / uniformly distributed with knife edge and sidewalk live loads 9 0.009 2.36 0.09 1.36 0.36 0.35 in te ri o r g ir d e r self-weight and superimposed loads ≈0 / / ≈0 / ≈0 / military and sidewalk live loads ≈0 / / ≈0 / ≈0 / uniformly distributed with knife-edge and sidewalk live loads ≈0 / / ≈0 / ≈0 / regarding the live load deflection, � has been taken as the limit ratio of l/375 according to the american association of state highway and transportation officials (aashto) [12]. in the mcs method, importance sampling techniques have been used to reduce the number of simulations. these methods rely on random sampling from random variable distributions to obtain the response uncertainty and the numerical estimate probability of failure. the assessment of the probability of engineering, technology & applied science research vol. 12, no. 5, 2022, 9155-9159 9159 www.etasr.com mohammed & al-zaidee: deflection reliability analysis for composite steel bridges failure is based on the samples that exceed the threshold limit for girder deflection. the reliability index and probability of failure for exterior and interior girders for the three loading cases and through a lifetime of 1, 10, and 50 years are summarized in tables v and vi. the results show that the firstorder approximate analytical method has the ability to show the values of the probability of small failures, unlike mcs. also, these tables noted that the probability of failure increases with the passage of time thus, the reliability indices of the system decrease. xi. reliability analysis for composite bridge deflection the composite bridge has been simulated as a system of elements (girders). the live load was distributed to the girders through a flexible medium and the deck slab and bracing were represented as the applied load to the girders. in this case, the composite bridge can be considered as a parallel system. hence, the reliability has been estimated with two instances of correlation: uncorrelated and perfect correlated. the composite bridge reliability depended on the probability of failure and the reliability index of the steel girders deflection. the results of mcs show that the probability of failure approaches zero, so the reliability of the parallel system was estimated based on the outcome of form (table vii), which showed that the probability of failure increases with the passage of time, thus the reliability indices of the system decrease. table vii. reliability index and probability of failure for parallel bridge deflection loads one year ten year fifty year rs t rs t rs t uncorrelated, xyz=0 self-weight and superimposed loads 5.42 × 10+~ 5.31 5.42 × 10+� 4.88 2.70 × 10+m 4.55 military and sidewalk live loads 0.1 × 10+~ 5.99 0.1 × 10+� 5.61 0.05 × 10+m 5.33 uniformly distributed with knife-edge and sidewalk live loads 8.41 × 10+~ 5.23 8.41 × 10+� 4.79 4.20 × 10+m 4.45 perfect correlated, xyz=1 self-weight and superimposed loads 6 × 10+m 4.37 6 × 10+v 3.84 0.0003 3.42 military and sidewalk live loads 0.001 3.09 0.009 2.33 0.048 1.66 uniformly distributed with knife edge and sidewalk live loads 0.0001 3.68 0.001 3.09 0.005 2.52 xii. conlcusion a reliability analysis of al-awsej composite bridge has been performed in this paper, considering the randomness in geometry, material, and applied loads. the bridge is located in diyala-iraq and has a span of 33.2m. the main conclusions of the current study are: • the first-order reliability method has estimated two moments (mean and standard deviation) of the girder deflection. at the same time, the mcs method determined four moments (mean, standard deviation, skewness, and peakedness) in addition to the distribution type. • the mcs with is method allowed the generation of 1000 pseudo-random samples instead of a large number of samples to estimate the probability of failure of a girder’s deflection by distributing the failure sampling in the most crucial area. hence, the failure probability evaluation was completed while saving cost and time. • with an increase in the correlation between girders, the reliability decreases and the probability of failure increases. • the reliability index of the deflection with two cases of correlation (uncorrelated and perfect correlated) was greater than the target 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[11] d. m. frangopol, b. m. kozy, b. zhu, and s. sabatino, "bridge system reliability and reliability-based redundancy factors," us department of transportation, federal highway administration, tech report fhwa-hif-19-093, sep. 2019. [12] aashto lrfd bridge design specifications, 8th ed. washington dc, usa: aashto, 2017. microsoft word etasr_v11_n6_pp7757-7762 engineering, technology & applied science research vol. 11, no. 6, 2021, 7757-7762 7757 www.etasr.com aldriwish: a deep learning approach for malware and software piracy threat detection a deep learning approach for malware and software piracy threat detection khalid aldriwish department of computer science college of science and humanities majmaah university majmaah, saudi arabia k.aldriwish@mu.edu.sa abstract-internet of things (iot) -based systems need to be up to date on cybersecurity threats. the security of iot networks is challenged by software piracy and malware attacks, and much important information can be stolen and used for cybercrimes. this paper attempts to improve iot cybersecurity by proposing a combined model based on deep learning to detect malware and software piracy across the iot network. the malware’s model is based on deep convolutional neural networks (dcnns). apart from this, tensorflow deep neural networks (tfdnns) are introduced to detect software piracy threats according to source code plagiarism. the investigation is conducted on the google code jam (gcj) dataset. the conducted experiments prove that the classification performance achieves high accuracy of about 98%. keywords-cybersecurity; malware; software piracy; deep learning; internet of things i. introduction artificial intelligence (ai) approaches are overgrowing through machine learning and deep learning technologies. using ai in applications improves accuracy and efficiency. the ai approach supports innovations in various fields [1-10]. the internet of things (iot), as an interconnection of devicebased sensors through the internet, requests a safety mechanism based on ai methods to prevent attacks and intrusion. iot devices are defined by unique radio frequency identifier (rfid) tags and are connected via nodes. the iot interconnection mechanism ensures distant monitoring and controlling [9]. the iot connectivity is a universal mechanism to support cloud computing, service industries, and innovative applications. with the number of connected devices via the internet exceeding 50 billion by 2021 [10], data security becomes a significant challenge. the iot technology faces a massive amount of data due to the growth of communication networks. attackers benefit from the iot architecture to handle attacks through iot devices. pirated software and malware infection have been used to affect the security of the industrial iot cloud [11]. these methods attempt to reuse source code illegally and to use the system as a regular user. the attacker writes a malware code based on reverse engineering through the logic of the original code [12]. this kind of attack is a severe threat because it allows unlimited downloads of pirated software. this issue is solved by using an intelligent software plagiarism technique that finds the stolen source code in the illegal software. intelligent software plagiarisms are based mainly on test-based analysis and structure. the proposed techniques use many methods: similarity identification, clone detection, software birthmark investigation, and software bug analysis [12]. software plagiarism based on structure technique focuses on the basic structure of the source code, graph behavior, function call graph, and syntax trees. these methods do not catch the attack if another type of programming can preserve the same behavior as the original software. providing secure iot networks is the purpose of many malware detection and intelligent software plagiarism techniques. infecting the privacy of iot nodes, smartphones, and computer systems is the goal of malware attacks. the different ways to detect malware are: statistic identification analysis and dynamic identification analysis. the second one learns malware patterns when the code is executed in real-time. the malware is detected considering function parameters’ exploration, function calls, visual investigation of codes, dataflow, and instruction traces. some detection tools based on the dynamic behavior of malicious codes such as anubis, tt analyzer, and cw sandbox [13] are provided online. these tools, characterized by the monitoring of every dynamic behavior, suffer from the time-consuming issue. statistic methods attempt to capture the layout information without realtime execution. as a statistic method, the signature identification technique detects windows-based malware via specification signatures as opcode frequency, string signature, and control flowgraph. statistic methods are supported by disassembling tools to extract the hidden patterns from binary executables [14]. byte sequence technique is considered a statistic method and removes n-byte sequences from patterns. a. software piracy detection in most software plagiarism cases, the software is written on a single programming language and crackers change the control flow using a similar programming language. authors in [15] proposed a method-based software benchmark to detect threats in java source code. the authors retrieved structural features by extracting the control flow of source codes. then the similarity is computed between benchmarks of two source corresponding author: khalid aldriwish engineering, technology & applied science research vol. 11, no. 6, 2021, 7757-7762 7758 www.etasr.com aldriwish: a deep learning approach for malware and software piracy threat detection codes. authors in [16] attempted to acquire the similarity between codes through a hybrid approach. the compiler level features technique was considered. the authors performed an unsupervised learning approach to detect plagiarism. the proposed method computes the similar functionalities of different sources codes. authors in [17] introduced an approach to achieve the similarity features between c++ and c source codes. the proposed method was based on a source forager search engine to extract features of every code. the control flow of the source code is identified based on the shape functionalities of the code. authors in [18] computed the difference between two source codes using a logic-based approach. the semantics for differences were captured using symbolic execution and preconditions techniques. authors in [19] tried to detect plagiarism related to student’s assignments using the latent semantic analysis (lsa) method. the authors aimed to compare source codes with regard to syntactic structures. this objective was achieved by combining lsa with plagate to identify the similarity. then, the syntax tree detected the syntactic view and the abstract of the source code. authors in [20] attempted to detect similar source code fragments using the parse tree kernel. the authors focused on java files and proved that the achieved results were inaccurate. therefore, a fingerprinting method was proposed instead of the parse tree kernel. authors in [21] introduced a behavioral approach called bplag to detect source code plagiarism. the behavior was extracted using symbolic execution. then, the code was assimilated to a novel graph-based format. the plagiarism was computed according to these graphs. the authors proved that their approach was more accurate and more robust to plagiarism-hiding than 5 source code plagiarism tools. authors in [22] presented a combined approach, using a greedy string tiling and explicit semantic analysis method named esagst. the proposed method supported the detection of source code plagiarism independently from the programming language. the evaluation was conducted using different languages, including java, c++, python, php, and java-script. the results proved the good performance of the esagst approach. b. malware detection malware detection is an open scientific topic. authors in [23] used a machine learning approach to classify worms from the binaries of benign files based on a sequence of variable length instructions. the authors built a dataset including 1330 benign files and 1444 worms. the experimental results achieved a classification accuracy of around 96%. authors in [24] combined the svm-based machine learning and n-opcode sequences to detect malware. the detection process included the critical instruction sequence and cosine similarity. findings demonstrated that similar malware possessed common core signatures. the proposed malware detection method achieved an accuracy around 98%. authors in [25] introduced a method based on the dynamic analysis approach to highlight the limits of the static analysis approach. the author proposed an obfuscation model to execute binary samples and identify significant behavioral features within a virtual machine. the evaluation proved the insufficiency of the static analysis approach in the case the malware is obfuscated. authors in [26] attempted to automate malware detection by identifying abnormal behavior within the program. the proposed idea provides little information about malicious behavior. authors in [27] applied a classification approach based on the clustering method. the aim was to classify malware samples based on behavioral features. the proposed method was added to the anubis system to track malware samples. the tracking report detailed the in-depth activities of the malware samples. authors in [28] aggregated between statistic and dynamic analysis to detect malware accurately. the statistical analysis managed the operational codes based on frequency occurrences. the dynamical analysis executed traces of system calls and executable files. tacking the advantages of each approach, the authors achieved a better result than statistic or dynamic case separately. authors in [29] utilized convolutional neural networks for malware detection. the announced purpose was to reduce time, size, and resource overhead. the proposed method used image-based malware for classification with 98.5% accuracy. authors in [30] tried to detect malware using the image similarity technique. the authors employed benign and vision research lab datasets to evaluate their method. samples from executable files were converted to binary code. in the testing phase, the accuracy reached 98%. authors in [31] established an enhanced method to detect malware variants based on the deep learning approach. the authors intended to obtain high accuracy at a low time cost. the suggested process transformed the malicious code into a grayscale image, then classified samples using the cnn based on significant features. the authors overcame the imbalance of data by applying the bat algorithm. according to the experimental results based on the research lab dataset, the computed accuracy and speed were sufficient. authors in [32] applied a machine learning method with processor core events to detect malware with a hardware event counter to ensure the detection. the purpose was to detect the spectre using on-chip hardware on time. the proposed hardware architecture was based on software agents. to predict malicious activity, the authors used several machine learning classifiers. the predictive results achieved an accurate detection. the current paper's contributions can be summarized as follows: • a deep learning approach based on the tensorflow deep neural network is proposed to detect software piracy through source code plagiarism. • a deep convolutional neural network (dcnn) is proposed to detect malware through binary visualization. • the two models are combined into the same architecture for the iot case. • the proposed architecture is evaluated according to adequate datasets. ii. the proposed architecture figure 1 describes the proposed architecture, which is composed of malware and software piracy detection. cloud data storage faces many kinds of attacks. cyber security threat samples are stored in 4 databases. database 1 contains network traffic data. database 2 stores a list of earlier known malware data. database 3 comprises new signatures and features of engineering, technology & applied science research vol. 11, no. 6, 2021, 7757-7762 7759 www.etasr.com aldriwish: a deep learning approach for malware and software piracy threat detection detected malware. database 4 includes pirated software via iot devices. these databases contain a massive amount of data and request a lot of computational time and cost. firstly, the network traffic data database (d1) transmits raw data to the detection module, which identifies the kind of attack (malware or software piracy). the classification is ensured based on learning signatures stored in databases d2 and d4. fig. 1. the proposed architecture for malware and software piracy. a. software piracy threat detection model the proposed software piracy attack detection is based on deep learning. the detection based on plagiarism methodology is captured through different types of source codes. the pirated version uses the same logic as the original software. once the traffic data are classified as software piracy, the source codes are tokenized to decrease the dimensions of the data. in that step, significant features are extracted using the tensorflow framework. the keras api for deep learning is applied to capture source code plagiarism. the first database (d1) includes the network traffic data collected from google code jam (gcj) database. the d1 data are built from 100 programmers and contain about 400 source code documents. software piracy threat detection is preceded by a preprocessing step. the purpose of this step is to divide the source code into small pieces. then, the semi-code is converted into useful information, and noise is removed. meaningful tokens are obtained during the tokenization step. finally, the contribution of each token is zoomed through a weighting mechanism, see (1), based on the logarithm of term frequency algorithm [33] and the term frequency and inverses document frequency (tfidf). ���,���,�� ����, ��� � ��� ��,�� (1) where t defines the token, doc defines a document, ds represent all the documents used in the dataset, tf defines the term frequency function, and idf defines the inverse document frequency function. deep learning is conducted by tensorflow, which is used for high-level computations. the pirated software is identified through extracted similar codes. a fully connected network with dense layers is utilized for input and output data. the first layer, which contains 100 neurons, receives the data. the second layer is composed of 50 neurons. the third layer consists of 30 neurons. the output variable uses the fourth dense layer to identify the target of the plagiarized code. deep learning is able to solve the overfitting problem using the drop out layer. the pattern is computed based on the rectifier (relu) activation method [34]: ��� �� max �0,� (2) where x defines the input of the equivalent neurons. the multi-class problem is conducted using the sigmoid method defined by: engineering, technology & applied science research vol. 11, no. 6, 2021, 7757-7762 7760 www.etasr.com aldriwish: a deep learning approach for malware and software piracy threat detection ��� � ����� (3) the deep learning approach used to detect software piracy provides the following benefits: (1) the model is trained automatically, (2) the design supports various computational types, (3) services are reliable while updating and extending the model, and (4) the proposed model supports big networks. b. malware threat detection model the proposed malware threat detection model consists of two steps: preprocessing and deep convolutional neural network. raw binary files generate the color images and the problem is becoming an image classification problem. the adopted color system is grayscale, and features are extracted from the color image. a feature reduction method is used to enhance the classification performance. it aims to reduce the feature set. the generation of the color image from a binary file proceeds as follows: (1) generate the hexadecimal strings, (2) divide the hexadecimal strings into a chunk of 8-bit vector, (3) convert each 8-bit vector to a two-dimensional matrix, and (4) plot the two-dimentional space. then, the deep convolutional neural network (dcnn) is utilized to identify the malware. the dcnn receives training images. the convolution layer's purpose is to reduce noise and enhance signal features. it reduces the over-fitting problem. the convolutional layer performs the computations using (4): �� � ��∑ �� ��� ∗ !� � " #� � !∈%& (4) where f defines the activation function, m is the cluster of given maps, #� � presents the bias consistent, and !� � denotes the convolution kernel. the accuracy of the proposed dcnn is improved through the convolutional kernel width. the pooling layer ensures the reduction of the data overhead and selects useful information. it minimizes the consequence of image distortion using (5): �� � ��'��()�� ���* " #� � (5) where pool() ensures the pooling task. the classification of the output of the pooling layer is performed at the fully connected layer. it aims to enhance the model by reducing the over-fitting issue. the noise is removed using filters. then, the training of the proposed dcnn is performed using softmax-cross-entropy loss [35], as defined by: + ,log � �01 ∑ �011 (6) where 23 denotes the rank of the k class. the learning of the parameters attempted to minimize the loss is conducted with the use of the adam optimizer. iii. experimental part a. software piracy detection performance evaluation the evaluation is based on the code similarity between the pirated software and the source software using the gcj dataset [36]. the similarity is checked using codeleaks plagiarism tool [12]. the dataset is proceeded by the preprocessing step to provide the valuable tokens of each source code as root word, stemming, token’s length, and token’s frequency. then, the tfidf and logtf algorithms are applied to conduct token weighting. the accuracy of the classification is improved according to the number of neurons. the evaluation is shown in figure 2 based on validation accuracy, validation loss, and loss. (a) (b) fig. 2. (a) loss and (b) accuracy results for source codes. the loss curves (figure 2) start from 0.75 and follow the same trend until 0.3. a fluctuation can be seen in the loss curve, but both curves are reduced in a similar way. from the accuracy curves, we can see that the proposed software piracy threat detection model achieved an accuracy of about 98%. b. malware detection performance evaluation the proposed model measures the effect of malware image ratios. the image size is taken as 180×180 and 196×196. we used the leopard mobile dataset [37], which is composed of 2486 benign and 14733 malware samples for evaluation. the training phase uses 15219 samples, and the testing phase employs 2000 samples. according to the experiments, the 196×196 dimension reached better accuracy than the 180×180 dimension. therefore, the 196×196 ratio is more suitable for the proposed model. table i highlights the comparison between the different dimensions based on the classification results. the image size of 196×196 achieves 98.12% testing accuracy. the computation time is about 18s. figure 3 presents the performance evaluation related to the 196×196 image size based on training accuracy, training loss, test accuracy, and test loss metrics. a comparison with previous works is presented in table ii. engineering, technology & applied science research vol. 11, no. 6, 2021, 7757-7762 7761 www.etasr.com aldriwish: a deep learning approach for malware and software piracy threat detection table i. classification results ratio precision (%) recall (%) accuracy (%) time (s) 180×180 94.15 94.68 94.47 16s 196×196 98.02 97.88 98.12 18s fig. 3. loss and accuracy results for malware detection. table ii. malware detection approaches comparison ref method year approach accuracy (%) time (s) [38] svm+gist 2017 ml 86.1 46 [39] svm+lbp 2018 ml 78.05 27 [40] svm+clgm 2019 ml 92.06 21 proposed dcnn 2021 dl 98 18 the comparison in table ii proves that the proposed malware threat detection model is more accurate than previous studies that are based only on the machine learning approach. the proposed method requires only 18s of computation time. iv. conclusion recent industrial systems migrate to industrial-based iot to support new network services. many security issues are related to iot networks, especially malware threats and software piracy. accurate cyber security defending iot big data is needed. in this paper, a new security architecture based on the deep learning approach is proposed. the attempt aims to detect malware attacks and pirated software. the proposed approach is a combined methodology to detect threats. a deep learning approach based on the tensorflow deep neural network is introduced to detect software piracy through source code plagiarism. then, a dcnn is utilized to detect malware through binary visualization. the findings prove that the proposed combined approach of dcnn and tfdnn achieves a classification accuracy of about 98%. the results of the proposed approach are better than the results obtained by related works. speeding up the computation time to support real-time systems can be the purpose of future work. this target could be reached by proposing a high-security level hardware accelerator. references [1] j. huang, j. chai, and s. cho, "deep learning in finance and banking: a literature review and classification," frontiers of business research in china, vol. 14, no. 1, jun. 2020, art. no. 13, https://doi.org/10.1186/ s11782-020-00082-6. 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[40] z. cui, l. du, p. wang, x. cai, and w. zhang, "malicious code detection based on cnns and multi-objective algorithm," journal of parallel and distributed computing, vol. 129, pp. 50–58, jul. 2019, https://doi.org/10.1016/j.jpdc.2019.03.010. microsoft word etasr_v12_n5_pp9310-9315 engineering, technology & applied science research vol. 12, no. 5, 2022, 9310-9315 9310 www.etasr.com bikkina & jayasree: development of a wire mesh composite material for aerospace applications development of a wire mesh composite material for aerospace applications siva chakra avinash bikkina department of electrical, electronics and communication engineering, gitam deemed to be university visakhapatnam, india sbikkina@gitam.in pappu v. y. jayasree department of electrical, electronics and communication engineering, gitam deemed to be university visakhapatnam, india jpappu@gitam.edu received: 13 july 2022 | revised: 9 august 2022 | accepted: 14 august 2022 abstract-the electrical conductivity of fiber-reinforced polymers (frps) may be used to reduce the dangers of lightning strikes, radar radiation, and aerial radio frequency transmitters. metal matrix composites (mmcs) were created to guard against electromagnetic interference (emi) in the aircraft's electric and electrical systems. high-intensity radiated field protection (hirfp) aircrafts are required to be manufactured from a metal matrix consisting of al6061, al2o3, and fly ash (fa) to keep up with the ever-increasing needs of industry. the current work considered three mmc combinations. mmc1 is al6061+10% and al2o3+5% fa, mmc2 consists of al6061+15 and al2o3+5% fa, and mmc3 of al6061+20% and al2o3+5% fa. these mmcs made the shielding more effective at different percentages. the material electrical properties were interpreted based on experiments. analytical approaches include the testing of the electrical parameters of materials to measure the shielding effectiveness. the calculated shielding efficiencies mmc1-55.7db, mmc2-57.2db, and mmc3-59.1db allow the composites to be employed in aircrafts. this indicates that, for specific applications like hirfps, the constructed mmcs perform well. keywords-metal matrix composites (mmcs); reinforcement; al2o3; fly ash i. introduction frequent lightning strikes can harm commercial airliners. lightning's high-intensity fields interfere with the electronic devices of the in-built guidance and communication systems [1-2]. the damage caused by lightning to aircrafts varies significantly with altitude and flight duration [3]. with its precise rigidity, strength, and lightweight, frps are ideal for aircraft reinforcement [4]. the materials used in their construction have sufficient mechanical qualities and low energy consumption per unit. however, they have low electrical conductivity, and the electric field cannot travel through it, resulting in delamination and embrittlement when lightning hits an aircraft [5]. aluminum composites have great promise since their fundamental qualities may be enhanced by reinforcing with other materials. metals including titanium, nickel, magnesium, copper, and aluminum have all been utilized to create metal matrix composites. as a result of its low density, high strength, low electrical conductivity, and high reflectivity, aluminum is the material of choice [6]. authors in [7] studied various physical models based on the electrical qualities of lightning strike protection. with its low density, particular corrosion resistance, high strength, and solid electrical qualities, al6061 was developed as an alternative to frps [8]. since many incident em waves are arbitrarily oriented, an evaluation of wire mesh's shielding effectiveness for normal incidence might be generalized to all practical applications. the study is based on tl modelling in the situation of normal incidence. it is an arbitrary perspective because the polarized electric and magnetic fields in this situation are normal or vertical to the plane. the referenced research analyzed the oblique impact of lightning's em waves on aircraft. authors in [9] created a lightning-proof carbon filter epoxy pre-preg laminate with a 55db se. the novelty of the proposed research work is the protection of the electronic components of the aircraft from the lightning strike effect. to protect from this effect, a mmc (al6061) with a variety of al2o3/fa particle reinforced was considered. electrical conductivity, permeability, and permittivity were measured after reinforcing al6061 with varying concentrations of considered and 5% fa. the shielding effectiveness of the composite material was calculated with the tl method. simulations were performed to determine the efficiency of shielding against x-band electromagnetic radiation with oblique incidence. the whole process was well-organized, from the preparation of the materials to the efficiency assessment of the shielding, and to result analysis. ii. utilized materials aluminum oxide (al2o3) has a density of 0.0039kg/cc 3 , and is employed as a reinforcing material because of its high corrosion resistance and high-temperature tolerance. as a result, the al2o3 particles in hybrid composites are also used as load-bearing and electrical conductivity components in metals. al2o3 and al6061 may be used in aircraft design because of their low cost [10-11] fa is a byproduct of coal-fired thermal power plants. in recent decades, carbon fibers have been used as a reinforcing material for aluminum-based metal matrix composites. to prevent al4c3, fa may be used for aluminum metal matrix composites reinforced with silicon carbide (sic) [14]. a corresponding author: siva chakra avinash bikkina engineering, technology & applied science research vol. 12, no. 5, 2022, 9310-9315 9311 www.etasr.com bikkina & jayasree: development of a wire mesh composite material for aerospace applications substance's absorption capacity may be increased to enhance the shielding qualities of the substance. only 5% fa may be utilized in the composite since it affects the material's tensile strength [12-13]. iii. composite material preparation as indicated in figure 1, stir casting was used to add microsized al2o3 and fa to the al6061 metal matrix composite to improve its electrical and mechanical characteristics. a composite is formed when two or more materials are combined, as shown in table i. the fabricated materials made from stir casting are shown in figure 2. stir casting is the most cost-effective technique for synthesizing particle-reinforced composites, and this is how the proposed mmc is made. a furnace, a feeder for reinforcing ingredients, and a stirrer were used in the stir casting process to create the composite. the stirrer comes with a rod and blades for stirring. a resistanceheated muffle furnace was used to heat 1kg of al6061 alloy to 720°c in a ceramic crucible. before casting, the al 6061 alloy was warmed to 600°c to remove any gases and moisture from the reinforcing particles (al2o3 and fa). this prevents temperature drops during the casting process. the stirrer's alumina-coated blades are used to avoid ferrous ions. fig. 1. experimental setup for reinforcement using stir casting. fig. 2. fabricated material from stir casting. fa (5wt%) and varied quantities of al2o3 (5wt%) were used to make the composites described in table i. the liquid composite was mixed with all the reinforcing elements and was then poured into a steel mold warmed to 250°c to prevent condensation from forming. the metal cools in the atmosphere before solidifying. the mold was emptied of the solidified composite. the other specimens were made with the same process but with varied quantities of reinforcing materials. table i. metal matrix representation material and weight percentages combined representation al6061+10% al2o3+5% fa mmc-1 al6061+15% al2o3+5% fa mmc-2 al6061+20% al2o3+5% fa mmc-3 iv. electrical parameter calculation the transmission/reflection method utilized by a e8263b agilent technologies vector network analyzer (vna) was used to determine the permeability (�), permittivity (�), and conductivity (�), of the mmcs (figure 3). in order to create the incident electromagnetic wave, a piece of mmc was put into the waveguide [14-15]. to analyze the electrical properties of the composite, a waveguide measuring 22.86mm × 10.16mm was implanted in the test specimens. the mmc samples utilized in the waveguide are shown in figure 2, and the experimental setup for the transmission/reflection approach is shown in figure 3. we conducted the experiment in the x-band and determined the vna levels for a range of frequencies. the results of the vna are shown in figures 6–9. they provide evidence that μ, σ, and � have a connection to periodicity. it is important to note that the electrical characteristics of mmc vary with its operating frequency. the degree to which a given material may operate as a shield depends on the values of μ, σ, and � in the mmc ratio. fig. 3. transmission/reflection method experimentatal setup. v. theoretical analysis of shielding effectiveness for wire mesh metal matrix composites the shielding efficiency (se) [17] statistic is often used to evaluate a material's shielding capacity. figure 4 shows the mesh surface with an oblique incidence of electromagnetic (em) waves [16]. the mesh surface with an oblique incidence of em wave is shown in figure 4. the ratio of received power before and after shielding is used to quantify em shielding effectiveness. in (1), �� represents the received power before the area was shielded, and �� represents the measured power after the region was shielded. the same approach is used to protect against electric and magnetic fields and is effective in both application circumstances. �� �� 10 log�� ������ (1) engineering, technology & applied science research vol. 12, no. 5, 2022, 9310-9315 9312 www.etasr.com bikkina & jayasree: development of a wire mesh composite material for aerospace applications fig. 4. representation of oblique incidences for wmmmc. simple in design, the wire metal matrix mesh composite (wmmmc) is made up of parallel mmc wires that are equally spaced apart. this means that the effectiveness of wmmmc as a radiation shield depends on parameters such as the distance between the wires, their thickness, the wave's incidence angle, etc. it is possible to increase the se of such a mesh by using additional orthogonal wires to the initial set of wires. electromagnetic shielding effectiveness is examined when mesh apertures are small in contrast to the operating wavelength of the screen. the impedance of a wire-mesh screen sheet is used to measure its impedance [18-19]. when an electromagnetic wave with a relatively low frequency strikes a mesh, a reactive field is formed near the mesh surface. without a screen, this reactive field diminishes exponentially with distance [19]. as can be seen in figure 1 of [22], a mesh with a square aperture length �� and wire radius �� has a shielding efficacy [20-22] that may be defined as: ��� �� � �� � !"# (2) ��% �� & '()* % +,-.% (3) the following calculations show that the transmission coefficients for polarization t1 and t2 represent te and tm modes and can be calculated for a range of frequencies and incidence angles. /� %�0�102 �34�5 �6%�0�102 � 34� 5 (4) /% %�0�702 �34�5 �6%�0�702 �34�5 (5) where . is the incidence angle, calculated from the flat sheet's regular, �4 is the free-space impedance, and ��� and ��% are the eigenvalues of te and tm mesh impedance operators respectively. the sheet inductance "� is calculated from: "� µ2.:�%; ln 1 & = >7?��@� �>� (6) the wire impedance per unit length �� � depends on the resistance per unit length, a� is a time constant and i0 and i1 are first kind bessel functions. �� � �′� cd'�efg.h2.cd'�efg%.h1.cd'�efg (7) �� &10ijk�� l��% /�%� � � � % /%%�m (8) /n4n:o &�� (9) since no noticeable change occurred for the frequencies and structures under examination when the skin effect was included in (7), the dc wire resistance was included as an approximation to the wire impedance (6). consequently, it becomes straightforward to determine the se of a particular mesh (with square openings) under various situations (and in different directions). vi. simulation results a. electrical parameter measurements the connection between an electrical parameter of a composite material and its frequency may be deduced from the vector analyzer’s output considering the electrical characteristics of conductivity, permeability, and permittivity. as a direct result of the material's permeability and permittivity, its electrical properties are intimately linked. the essential portion of the permittivity of lossless materials displays the quantity of stored electrical energy. fig. 5. electrical parameters of pure al6061. fig. 6. electrical parameters of mmc-1. engineering, technology & applied science research vol. 12, no. 5, 2022, 9310-9315 9313 www.etasr.com bikkina & jayasree: development of a wire mesh composite material for aerospace applications fig. 7. electrical parameters of mmc-2. fig. 8. electrical parameters of mmc-3. the imaginary part of permeability is used to quantify the power lost due to magnetic fields, which is crucial for calculating the magnetic energy stored in a material. a vna having a waveguide or coaxial construction and working at 8– 12ghz may be used to assess scattering properties (x-band frequency). to calculate the reflection coefficient equation's value, |s11| and |s21| were plugged into the calculator's bar. the vna results are shown in figures 5-8. b. shielding effectiveness mesearument most electromagnetic signal occurrences on the mesh surface were oblique in practice, as described in the literature. using a range of angles from 0 to 90°, the shielding performance of each composite was evaluated. as the incidence angle increases, so does the shielding, as shown by the relationship between the electromagnetic mesh surface and the incidence angle. the stimulated results of pure al6061 and mmc are represented in figures 9-12. at increasing incidence angles, the shielding efficiency of pure al6061 and composites supported by varying proportions of al2o3 and fa as shown in table ii. se decreases as the incidence angle becomes normal to the mesh material. al2o3 and fa have been used in this study to support al6061 alloys. shielding relies on absorption and reflection for its success. permeability may be used to measure the material's ability to absorb. depending on the conductivity of the substance, the reflectance of the object changes. the material's excellent permeability and conductivity result in high absorption and reflection losses. the composite material's permittivity improves as a result of the al2o3 growing proportion. also, the whole composite's absorption loss rises. for aviation applications of 48.83db, the effective shielding effectiveness is considered adequate [29-30]. the material's excellent permeability and conductivity result in high absorption and reflection losses. the composite's 55.7db shielding value at a 20° angle of incidence aided by al2o3 (10%) and fa (5%) reinforcement resulted in reflection and only absorption from the fa. by increasing the al2o3 and fa content by 15% and 20%, 57.6db and 59.1db increase in shielding value is respectively obtained. the material will no longer be suitable for aviation applications if the percentage exceeds that level. fig. 9. shielding effectiveness of pure al6061. fig. 10. shielding effectiveness of mmc-1. 0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2 frequency in ghz 10 10 -10 0 10 20 30 40 50 60 70 permeability conductivity permitivity engineering, technology & applied science research vol. 12, no. 5, 2022, 9310-9315 9314 www.etasr.com bikkina & jayasree: development of a wire mesh composite material for aerospace applications fig. 11. shielding effectiveness of mmc-2. fig. 12. shielding effectiveness of mmc-3. fig. 13. shielding effectiveness comparison of mmcs with pure al6061. the fa content of all combinations is fixed to 5%. if the concentration is more, the material strength decreases, and the material properties are lost. shielding increases by around 20% for incidence angles of 45°, 60°, 70°, and 85°, but as the incidence angle increases, the values decrease. table ii shows the comparison of the results of the present work with other known works and table iii exhibits the shielding effectiveness of mmcs with different angle of incidences. table ii. comparison of shielding effectiveness values reference material frequncy shielding effectiveness [23] al2o3/fesial/flaky graphite x band 30.4 [24] ti3si(al)c2/al2o3 x band 42.1 [25] al2o3 x band 29-32 present work al6061/ al2o3/fa x band 59.1 table iii. relationship between the shielding properties of various reinforced materials and al6061 composite at various incidence angles incidence angle material 20° 45° 60° 70° 85° pure al6061 32.62 23.48 22.72 17.86 11.77 mmc-1 55.7 39.5 32.8 25.8 24.6 mmc-2 57.6 41 33.1 30.9 26.17 mmc-3 59.1 48.2 37.6 33.8 29.3 vii. conclusion composite materials with strong se are well-known in aerial applications. the wmcs developed in this work will give se up to 59.1db. electromagnetic shielding is evaluated from different perspectives (20°, 45°, 60°, 70°, and 85°). these mmcs have an se of more than 55db. so, these materials are more suitable for protecting aircrafts from lightning strikes. mmcs structure has physical flexibility and less weight, so they are more suited to protect large structures than metal sheets. compared to metal-coated windows, wire mesh screens offer a unique advantage. the proposed wmmmc has lower se than metallic sheets. according to the literature, using a material with a 50db shielding efficiency for aircraft surfaces provides good lightning protection. regarding high-intensity radiation fields, the shielding of prepared compositions may 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[23] l. zhou et al., "dielectric properties and electromagnetic interference shielding effectiveness of al2o3-based composites filled with fesial and flaky graphite," journal of alloys and compounds, vol. 829, jul. 2020, art. no. 154556, https://doi.org/10.1016/j.jallcom.2020.154556. [24] n. dong et al., "fabrication and electromagnetic interference shielding effectiveness of ti3si(al)c2 modified al2o3/sic composites," ceramics international, vol. 42, no. 8, pp. 9448–9454, jun. 2016, https://doi.org/10.1016/j.ceramint.2016.03.001. [25] l. zhu et al., "significantly enhanced electromagnetic interference shielding in al2o3 ceramic composites incorporated with highly aligned non-woven carbon fibers," ceramics international, vol. 45, no. 10, pp. 12672–12676, jul. 2019, https://doi.org/10.1016/j.ceramint.2019.03.079. microsoft word etasr_v11_n6_pp7968-7973 engineering, technology & applied science research vol. 11, no. 6, 2021, 7968-6973 7968 www.etasr.com kazmi et al.: photometric ligature extraction technique for urdu optical character recognition photometric ligature extraction technique for urdu optical character recognition majida kazmi faculty of electrical and computer engineering ned university of engineering and technology karachi, pakistan majidakazmi@neduet.edu.pk fauzia yasir faculty of electrical and computer engineering ned university of engineering and technology karachi, pakistan fyasir@neduet.edu.pk samreen habib neurocomputation lab, ncai ned university of engineering and technology karachi, pakistan habib@cloud.neduet.edu.pk muhammad saad hayat deptartment of electrical engineering ned university of engineering and technology karachi, pakistan hayat@cloud.neduet.edu.pk saad ahmed qazi faculty of electrical and computer engineering neurocomputation lab, ncai ned university of engineering and technology karachi, pakistan saadqazi@neduet.edu.pk abstract-urdu optical character recognition (ocr) based on character level recognition (analytical approach) is less popular as compared to ligature level recognition (holistic approach) due to its added complexity, characters and strokes overlapping. this paper presents a holistic approach urdu ligature extraction technique. the proposed photometric ligature extraction (ple) technique is independent of font size and column layout and is capable to handle non-overlapping and all inter and intra overlapping ligatures. it uses a customized photometric filter along with the application of x-shearing and padding with connected component analysis, to extract complete ligatures instead of extracting primary and secondary ligatures separately. a total of ~ 2,67,800 ligatures were extracted from scanned urdu nastaliq printed text images with an accuracy of 99.4%. thus, the proposed framework outperforms the existing urdu nastaliq text extraction and segmentation algorithms. the proposed ple framework can also be applied to other languages using the nastaliq script style, languages such as arabic, persian, pashto, and sindhi. keywords-ligature; holistic; urdu ocr; nastaliq; photometric filter; urdu printed text images i. introduction ocr technology is used to obtain machine editable text from text images. it allows the digitization of valuable printed and handwritten data covering cultural and historical milestones [1]. the commercial ocr systems that are now available report near to 100% recognition rates for languages using the latin alphabet, such as english, german, and french. arabic and chinese ocr systems are also well-developed. despite the significant research interest in this area, ocr systems for many languages, including urdu, are still in the development stage [2-3]. urdu is pakistan’s official language having a large collection of valuable printed and handwritten data in the form of books, novels, magazines, and newspapers. most of these valuable data are not accessible digitally. the urdu language has 39 basic characters, 28 of which are arabic. it is mostly written in the nastaliq script style, which is a complex calligraphic style, written diagonally from right-to-left with varying inter and intra word spaces, overlapping of characters and strokes, incorrect or filled loops and lack of fixed baseline [4-5] as shown in figure 1. fig. 1. major challenges in nastaliq text: intra overlapping ligatures (red), inter overlapping ligatures(green), false and filled loops (blue) and missing baseline (yellow). urdu ocr is primary composed of five stages: image acquisition, pre-processing, segmentation, classification and recognition, and post-processing [6]. image acquisition collects digital images through camera shots, scanned text images, or corresponding author: majida kazmi engineering, technology & applied science research vol. 11, no. 6, 2021, 7968-6973 7969 www.etasr.com kazmi et al.: photometric ligature extraction technique for urdu optical character recognition generated synthetic images [6]. pre-processing aims to enhance the quality of an acquired image [6]. noise and skew removal, binarization, contrast enhancement, etc. are mainly performed in this step with the use of classic image processing techniques. segmentation decomposes a source image into characters, ligatures, or words [7-8]. this step usually employs projection profile and connected component analysis (cca). classification aims to correctly classify the extracted/segmented features (ligatures, characters, words, etc.). the most common classifier methods are decision tree (dt), statistical classifier (sc), neural networks (nns) [9, 10], hidden markov models (hmms), and support vector machines (svms). finally, post-processing corrects the recognition errors in the obtained text [10]. the techniques used for ocr post-processing include manual error correction, dictionary-based error correction, and context-based error correction [12-13]. among the above stages, segmentation at character, ligature, or word level is the most challenging stage in urdu ocr. based on these levels, urdu ocr can be divided into two categories: analytical approach at character level [14-15] and holistic approach at ligature level [7, 16-17]. the analytical approach segments text at character level either explicitly or implicitly. the explicit segmentation requires an extensive knowledge of characters as it explicitly divides handwritten or printed text into characters. many researchers have adopted the explicit character segmentation [17-21]. on the other hand, implicit segmentation is an integration of the segmentation and recognition processes. successful work has been reported by researchers for implicit segmentation [22-26] due to the smaller number of segments. however, both algorithms require a massive amount of training data for better results. the holistic approach is also referred to as segmentation-free method. it extracts at ligature or word level. groups of isolated (nonjoiner) characters and non-isolated (joiner) characters (figure 2(a)) are termed as ligatures. these ligatures are grouped to form words. ligatures are further classified as primary and secondary ligatures. primary ligatures represent the main body of a word, while dots or diacritic marks are the secondary ligatures (figure 2(b)). (a) (b) fig. 2. word breakdown. (a) ligatures in an example word, (b) ligature components. avoiding character level segmentation has made the holistic method extremely popular [3, 27-32]. authors in [27] followed the projection technique for text line extraction. the main body and diacritics were identified based on the distance between the horizontal base and the average line. the technique was tested on a small data set that was not specific to nastaliq script, consisting of 1050 single characters and ligatures, with 98.86% accuracy. authors in [28] used the horizontal projection technique. cca was applied before text segmentation. the horizontal span of each secondary component on the baseline was calculated for the re-association of diacritics to their respective primary ligature. however, this approach assumed to work on text files instead of text images to extract complete ligatures. similarly, authors in [29] applied the vertical projection profile method for the association of secondary ligatures by calculating the start and end point of diacritics. the proposed method reported 100% and 99% accuracy in baseline identification and ligature extraction respectively on scanned images with 48 font size but this technique ignores intra-overlapping ligatures and is also font size dependent. authors in [3] employed the horizontal projection method along with dilation to merge secondary and primary ligatures before line separation from the image. authors in [30] used only 300 ligature samples to evaluate their proposed method, reporting 91.3% accuracy in segmentation and 78% in diacritics association. authors in [31] proposed an extraction ligature technique based on 6 heuristic conditions reporting an accuracy of 99.02% on 45 images. authors in [32] proposed the line segmentation technique with the connected component analysis method on images to collect width, height and centroids of ligatures reporting 99.80% accuracy. however, this technique does not segment multi-column scripts and overlapped inter and intra ligatures. many recognition techniques carry out separate classifications of primary and secondary components [3, 27-32] to reduce the number of distinct recognizable classes. such techniques face significant challenges in re-associating the secondary components with their primary components to recognize the entire ligature. the complexity at character segmentation has shifted the focus towards the holistic approach, i.e. the recognition of words or ligatures in the text. segmenting text at the character level is more complex than the recognition of words and ligatures due to character overlapping, varying inter and intra word spaces, context sensitivity, different forms of characters according to their position in a word or a ligature, and the cursive script style. the literature review reveals that urdu ocr is an open field for the researcher to design a system capable of incorporating factors such as intra and inter ligature overlapping, multi-column text images with borders, font variation, and mass data of ligatures for classification. an efficient ligature extraction technique for urdu ocr is proposed in this paper. the proposed method is capable to extract complete ligatures efficiently unlike separating primary and secondary components. the proposed technique is independent of font size and column layout, and is capable to handle all overlapping and non-overlapping ligatures by addressing the issue of intra overlapped ligatures as well as the complex association of the secondary components. it extracts complete ligatures, rather than separating primary and secondary components, thus secondary ligatures do not need to reassociate with their primary ligature in the classification and recognition steps. the proposed framework is designed for engineering, technology & applied science research vol. 11, no. 6, 2021, 7968-6973 7970 www.etasr.com kazmi et al.: photometric ligature extraction technique for urdu optical character recognition urdu but is applicable to other languages that follow the nastaliq style, such as arabic, persian, pashto, and sindhi. ii. the proposed methodology the proposed framework for ligature extraction is depicted in figure 3. it consists of 3 steps: image acquisition, image binarization, and ple. urdu printed text images from novels, religious books written in nastaliq style, in single and double columns and varying font sizes were downloaded from different sources [33] and are referred to as iimg. first, the iimg is converted into binarized images ith by using hard thresholding. the resultant ith is a mono-chrome image with white background and black text (figure 4). then, an efficient process of ple is applied on each ith. fig. 3. framework for urdu ligature extraction. a. photometric ligature extraction (ple) the proposed ple used a customized photometric filter which is specifically designed to decompose an image based on the photometric similarity. the stepwise description of ple process follows: • in the first step, ple deploys a photometric filter to extract text lines (llines) from the image (ith). the algorithm in figure 4 demonstrates the working of the photometric filter. this filter scans the binarized image from top to bottom to detect text using the logical and operator. the size of the photometric filter is adjusted with the width (w) of the image as (1xw). the output of the photometric filter is then saved in an array. the resultant array is a stream of zeroes and ones, on which unary and operation is performed to get a single bit value, i.e. 0 or 1. the 0 value indicates the presence of black pixel/s in the row, otherwise the value will be 1. • in the second step, the image llines is first rotated counterclockwise by 90º. the photometric filter is then applied to each line of llines to extract both overlapped and non-overlapped ligatures. • the overlapped ligatures are corrected in this step by applying x-shear transformation and padding simultaneously on each llig to overcome the most challenging issue of inter and intra ligatures overlapping. the output of this step consists of the sheared and padded ligatures lsheared-lig. • in this step, the lsheared-lig images are classified into two classes based on the extent value of the first encountered ligature in image using cca. height, width, centroid, etc. are major properties obtained through the cca method. the developed methodology utilized another component property termed as extent which is defined as the ratio of contour area to the bounding rectangle area. the extent value is a key feature in distinguishing secondary and primary ligatures with 99% accuracy. if the extent value of ligature is less than the hard threshold value, then dilatation operation is carried out on the encountered ligature producing lligs, dilated. this process reduces the distance between the primary and the secondary component of a ligature. • in the last step, the photometric filter is again applied to all dilated and non-dilated ligatures lligs,dilated and lligs,non-dilated to extract complete ligatures as final output lextracted-ligs. fig. 4. the photometric filter algorithm. fig. 5. the result of image binarization (ith) on the input image iimg. engineering, technology & applied science research vol. 11, no. 6, 2021, 7968-6973 7971 www.etasr.com kazmi et al.: photometric ligature extraction technique for urdu optical character recognition b. demonstration of the proposed ple the stepwise demonstration of the proposed ple technique is shown in figure 6. the input of the ple technique is a mono-chrome image with white background and black text (figure 5). (a) (b) (c) (d) (e) fig. 6. ple framework illustration. (a) an extracted line (l line ). (b) segmented ligatures from the sentence in (a). the red encircled ligatures are overlapped. (c) the overlapping issue of ligatures obtained in (b) is resolved by x-shearing of ligatures encircled as green. (d) list of ligatures (lligs,dilated,lligs,non-dilated) after morphological operation (dilation). correctly extracted ligatures (lextracted-ligs) after pf applied on (lligs,dilated,lligs,non-dilated). in the first step, text lines are extracted one by one from the text image by applying the photometric filter (figure 6(a)). in the next step, each extracted line is first rotated counterclockwise and then again passes through the photometric filter to extract both overlapped (marked as red circle) and non-overlapped ligatures (figure 6(b)). the issue of inter and intra overlapping is resolved (see figure 6(c), marked as green circles) by applying x-shearing and padding simultaneously on each ligature. figure 6(d) depicts the list of dilated and non-dilated ligatures. the dilation process reduces the distance between the primary and secondary component of a ligature. finally, the photometric filter is again applied on these ligatures to get the final output as shown in figure 6(e). this step will further enhance the correct separation of ligatures. iii. results and analysis the proposed urdu ligature extraction framework was evaluated on downloaded urdu printed text images. the technique was tested on a total of 600 novel and book images. the working dataset mainly comprised of non-overlapping lines with no boundary across images. first, the photometric filter was applied on the images and extracted lines with an accuracy of 99.6%. a total of 13,200 lines were extracted from 600 images. these lines were then segmented into ligatures. a total of 267,800 ligatures were extracted after the complete execution of all the steps of the proposed ple with an overall accuracy of 99.4%. table i compares the proposed ligature extraction framework with previously reported methods. authors in [27] evaluated their approach on 1050 ligatures with 98.86% accuracy in primary and secondary stroke extraction. authors in [29] achieved 99% accuracy in ligature and diacritics extraction. authors in [30] tested their system on 300 sample images out of which 274 were segmented correctly with 91.3% accuracy. authors in [30] analyzed 45 urdu images to classify and associate the connected components with 99.02% accuracy. authors in [32] used 10,063 text lines to test their algorithm and reported an accuracy of 99.8%. however, as discussed above, due to the limited data set of ligatures, researchers have mostly deployed algorithms on their own datasets to check the accuracy of ligature segmentation/extraction. therefore, the accuracy depends upon the complexity of the text images used for segmentation and reassociation of primary and secondary components. segmentation algorithms achieving segmentation accuracy near 99% apply cca for primary and secondary component segmentation in [28, 31-32] and projection profile method in [3, 27, 29-30] and then reassociate the secondary components. these studies also ignore the extraction of inter overlapped ligatures. the last row of table i presents the findings of the proposed technique. the proposed solution resolved the problem of inter ligature overlapping with an accuracy of 99.4%. however, the efficiency of the proposed method is reduced due to the redundant use of the word . this complete ligature remains unaffected even after x-shearing because the primary component alif " ا " lies in the region of the second main component ‘يک ‘and the diacritics also overlap with the neighboring primary components. it was observed that spacing between diacritics that lie below the main body sometimes leads to incorrect line segmentation. iv. conclusion this paper presented an efficient ligature extraction technique for the extraction of urdu ligatures in nastaliq fonts. the technique used a customized photometric filter along with the application of x-shearing and padding with cca that result in the efficient extraction of overlapped and non-overlapped ligatures. the proposed framework achieves an accuracy of engineering, technology & applied science research vol. 11, no. 6, 2021, 7968-6973 7972 www.etasr.com kazmi et al.: photometric ligature extraction technique for urdu optical character recognition 99.4%. the efficiency of ple technique can be enhanced by overcoming the association of secondary ligatures to respective main component before the extraction of text lines. this work can also be deployed for other nastaliq script-based languages like persian, pashto, saraiki, panjabi, etc.. table i. comparison with relevant holistic approaches work ligature extraction limitations accuracy (%) extracted overlapped ligatures technique result [32] cca separate primary and secondary components declares the secondary ligature as primary ligature when the size exceeds the threshold value 99.8 no [30] pp separate primary and secondary components extracted only 300 ligatures low diacritics association accuracy 91.3 no [31] cca separate primary and secondary components relies on zonal information tested on only 45 images 99.02 no [29] pp separate primary and secondary components cannot extract overlapped ligatures -dependent on font size of 48 99.0 no [27] pp separate primary and secondary components -did not specify the script style -the system was tested on 1050 ligatures 98.86 no [28] cca separate primary and secondary components the proposed method was directly tested on text files 97.4 no proposed ple photometric filter, x-shearing and stretching, cca, and dilation complete ligature extraction uneven baseline recognition -narrow spacing between the ligatures of the word which reduces efficiency 99.4 yes cca: connected component analysis, pp: projection profile references [1] a. wali and s. hussain, "context sensitive shape-substitution in nastaliq writing system: analysis and formulation," 2007, pp. 53–58, https://doi.org/10.1007/978-1-4020-6268-1_10. 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[33] "kutubistan," kutubistan. https://kutubistan.blogspot.com/ (accessed dec. 01, 2021). microsoft word etasr_v12_n4_pp9005-9011 engineering, technology & applied science research vol. 12, no. 4, 2022, 9005-9011 9005 www.etasr.com mazouz et al.: assessing the effect of underground void on strip footing sitting on a reinforced sand … assessing the effect of underground void on strip footing sitting on a reinforced sand slope with numerical modeling badis mazouz department of civil engineering faculty of technology university of batna 2 batna, algeria b.mazouz@univ-batna2.dz tarek mansouri department of civil engineering faculty of technology university of batna 2 batna, algeria t.mansouri@univ-batna2.dz messaoud baazouzi department of civil engineering faculty of technology university of khenchela batna, algeria messaoud.baazouzi@gmail.com khelifa abbeche department of civil engineering faculty of technology university of batna 2 batna, algeria abbechek@yahoo.fr received: 9 june 2022 | revised: 19 june 2022 | accepted: 20 june 2022 abstract-this paper presents the results of the numerical analysis undertaken to investigate the effect of the underground void on the load-bearing capacity of a strip footing placed on an unreinforced and geogrid-reinforced sand slope with a void inside. the failure mechanism of the soil was also investigated. the numerical model was obtained using 2d plane-strain fem analysis (in plaxis software), in which the nonlinear mohrcoulomb model was utilized. the effects of various parameters such as the number of geogrid layers (n), the vertical distance ratio between the top of the cavity from the base of footing (h/b), the horizontal distance of void centerline to the footing center (x/b), on the behavior of footing are studied in this research. the results indicate that there is a critical zone under the footing in which the existence of void has no influence on the bearing capacity and stability of the footing. in addition, the use of geogrid reinforcement reduces the settlement and enhances bearing capacity. finally, the bearing capacity factor and failure mechanism increase with increasing horizontal and vertical void distances ratios (x/b and h/b) and reinforcement layers. keywords-cavity; slope; strip footing; geogrid-reinforced; sand, finite element analysis i. introduction in civil engineering, sometimes buildings and other engineering structures may sit on underground voids. underground cavities that traverse the subsoil can be classified into two types: the ones of artificial origin due to human activity (e.g. installation tunneling, exploitation of underground quarries and mines, gas and water networks creation, etc.) or natural cavities formed by the action of water, which dissolves limestone or gypsum found in subsoil. generally, the existence of underground voids on a foundation can cause large-scale disorders in the constructions, inducing the collapse of structures and the settlement of foundations. there is a vast literature analysis of the carrying capacity and failure mechanisms of foundations resting on unreinforced soil with void through three principal methods: experimental investigations, numerical studies, and theoretical studies [1-5]. the numerical observation of [6] reported that the failure zone has developed considerably toward the void closest to the foundation and does not usually extend other voids. theoretical methods [7] and centrifuge tests [8] have been performed to examine the stability of the void. authors in [9] used a finite element method (fem) to investigate the bearing capacity and the failure mechanism of a strip footing built on double-voids. their results indicate that the mode of failure depends on the size and location of the voids. authors in [10] applied the procedure dlo to analyze the stability of footing situated on cohesive-frictional soil with single and dual square voids. the results implied that the presence of voids has a greater impact on c– φ soil compared to that on non-drained soil. the failure mechanism is related to several soil properties, the placement of voids, and the linear distance between two voids. authors in [11] carried out a series of laboratory loading tests and numerical modeling simulations to investigate the impact of an underground void on the load-settlement behavior of a strip footing. they demonstrated that the fem results are in good agreement with the experimental load-settlement curve. also, the presence of subterrane voids can lead to stress concentrations within the soil, which can cause failure. authors in [12] adopted fem to study the collapse of strip foundations corresponding author: badis mazouz engineering, technology & applied science research vol. 12, no. 4, 2022, 9005-9011 9006 www.etasr.com mazouz et al.: assessing the effect of underground void on strip footing sitting on a reinforced sand … on the sand with single and twin continuous voids. the obtained results are in accordance with the theoretical and numerical solutions available. for over 40 years, due to its relatively ease of use, and small cost, geogrid reinforced soil has been used in a variety of fields of geotechnical engineering [13, 14]. when a foundation is found above the void, one of the possible remedial measures to improve the bearing capacity and reduce the settlement and the performance of footing would be to reinforce the foundation soil with layers of geogrid. with this in mind, some researchers have also studied the behavior of a foundation built on reinforced soil containing the void [15-21]. authors in [22, 23] presented an analytical solution for designing a planar geosynthetic reinforced soil system on a cavity. authors in [24] conducted full-scale model tests on a shallow circular footing placed on geocell-reinforced sand bed overlying a clay bed having a circular void. they found that a substantial improvement of the bearing capacity of the footing can be achieved by providing an adequately sized geocell mattress, over the clay subgrade with the void. they also observed that, in order to have a great impact, the geocell mattress must extend beyond the void at a distance greater than the diameter of the void. authors in [25] developed a laboratory-scale model with the intention of studying the effects of varied parameters on the performance of the strip footing supported by geogridreinforced sand over a void. the investigated parameters included void embedment depths, the number of reinforcement layers, and relative densities. they reported that loading pressure and footing settlement improved significantly with increasing void anchorage depth, number of geogrid layers, and relative soil density. authors in [26] used numerical analysis to investigate the behavior of single and two adjacent strip footings placed on unreinforced/reinforced granular bed overlying clay containing voids. their results show that the proving geogrid reinforcement increases the load carrying capacity of the footing in both cases. the influence of a single void on the bearing capacity is negligible when the void is situated at a critical depth greater than 5b and at a horizontal distance greater than 3b from the center of the footing. the majority of the above mentioned studies focused on foundations resting on a horizontal ground, however, many of these structures are placed above or near slopes. there are some investigations that have been conducted to calculate the ultimate load carrying capacity of strip footings subjected to central loading near reinforced slopes without voids [27-31]. in contrast, strip footings adjacent to reinforced slopes with voids have received little experimental and theoretical/numerical research. therefore, in the present paper, a series of finite element studies were conducted to analyze the bearing capacity behavior of footing on a reinforced sand slope with a single circular void subject to static vertical loading. additionally, the benefits of geogrid-reinforcement application to stabilize strip footing and failure mechanisms of the sand slope were examined under different conditions of the void. to achieve this objective, a total of 80 numerical model tests were conducted with different depth ratios (h/b), horizontal spacing ratios (x/b) and reinforcement layers (n). ii. finite element modeling the finite element software plaxis was used to simulate the footing-void system in both condition unreinforced and geogrid reinforced sand slope. the sand surrounding the void is supposed to follow perfect and elastoplastic behavior law, where the rupture criterion is considered as mohr–coulomb in conjunction with non-associated flow rule, i.e. ψ ≠ φ. the mohr-coulomb model was chosen for its simplicity and the availability of the necessary parameters. the adopted parameters of the analysis are summarized in table i. the foundation was treated as an elastic beam element based on mindlin’s beam theory with significant flexural rigidity (ei) equal to 32,000mpa, poisson’s ratio of 0.2, and normal stiffness (ea) equal to 25kn/m 3 . the void was considered to be circular in form and of diameter equal to the width of the footing. in addition, the void is simulated as a tunnel without a lining. table i. soil parameters parameters name unit sand model type model mohr-coulomb dry density γ����� kn/m 3 16.7 wet density γ��� kn/m 3 19.3 young's modulus eref kpa 1.2 104 poisson's ratio ν kpa 0.30 cohesion c kn/m 3 1 angle of friction φ (°) 38 angle of dilation ψ (°) 6 reinforcement geogrid, which is usually used to increase load bearing capacity, has only one tensile stiffness (ea=30kn). the reinforcement layers were simulated using the elastic geogrid element of plaxis. the interaction between the soil and the geogrid is modeled on both sides through interface elements. the boundary conditions for all the models were chosen such that the vertical boundary is constrained horizontally and free vertically, while the bottom of the numerical model is fully fixed. during the generation of the mesh, 15 triangular plane strain elements were selected to model the soil, while the geogrid was modeled with 5 node elastic elements. the refined mesh option was adopted to guarantee a better representation of the stress field under the base of the foundation, near the crest of the slope, geogrid layers, and the void. the model slope geometry, generated mesh, and boundary conditions are shown in figure 1. fig. 1. the numerical model. the calculation is performed in three phases: the first relates to the formation of the initial stress condition, the second stage deals with building the sand layers by placing the engineering, technology & applied science research vol. 12, no. 4, 2022, 9005-9011 9007 www.etasr.com mazouz et al.: assessing the effect of underground void on strip footing sitting on a reinforced sand … reinforcement elements and creating the void, and the last one is to load the strip footing. it is worth noting that for each analysis, a prescribed footing load was applied in increments, followed by iterative analysis, until failure. in all numerical models, the failure load is determined by the pronounced peaks in the load-displacement curves. iii. validation of the finite element model in order to confirm the numerical model, the slope surface was replaced by a horizontal ground surface. the bearing capacity factor nγ values obtained by the finite element approach were compared with those given in the literature. table ii presents the numerical results for nγ values associated with various friction angles (φ) obtained by different researchers. it is clear that the magnitude of nγ increases with increasing φ. as shown in table ii, the computed values of nγ are significantly lower than the solutions reported in [32], however, they are in good agreement with those reported in [33, 34], with a difference less than 6%. this good agreement can be considered as a validation of the numerical model obtained from this study. table ii. bearing capacity factor nγ φ° current study [32] [33] [34] [35] [36] 25 7.24 9.7 6.76 6.76 10.88 6.74 30 15.47 19.7 15.07 15.67 22.4 15.24 35 31.03 37.5 33.92 37.15 48.03 35.65 iv. test program four series of tests were conducted to analyze the inclusion effect of the geogrid layers on the bearing capacity of shallow foundations supported by sand containing a void near a slope. figure 2 illustrates the different tests conducted in this study with parameter details. in previous studies, several values of µ /b, h/b and l/b were proposed for foundations on geogridreinforced sand, where “µ ” is the distance between the footing bottom and the first geogrid layer (l) the length of the geogrid, (h) is the distance between two geogrid layers, and b is the footing width. fig. 2. geometry parameters. in order to study the best arrangement of geogrid layer inclusions, authors in [37, 38] reported that there are critical values for µ /b, and h/b ranging from 0.3-0.35, beyond which the reinforcement has no effect on the bearing capacity. on the other hand, the optimal value of l/b was 0.35, as determined in [25]. based on these results, the values of µ/b=0.35, h/b=0.35, and l/b=4 were adopted in the current study in order to achieve maximum bearing capacity and reduce the settlement of the footing. each series of tests analyzed the effect of one parameter while the other parameters were held constant. the variable parameters included the number of reinforcement layers (n), the depth between the foundation base and the crest of the cavity (h/d), and the horizontal distance of the void from the foundation centerline (x/b). table iii presents the different numerical programs and their fixed and variable parameters. table iii. numerical programs and parameters test series type of reinforcement variable parameters fixed parameters n x/b h/b 1 unreinforced (without void) 0 µ /b=0.35 h/b=0.35 l/b=4 tg (β)=2/3 2 unreinforced (with void) 0 0 1 2 3 0.5 1 1.5 2 2.5 3 3.5 2 reinforced (without void) 1 2 3 4 reinforced (with void) 1 2 3 0 1 2 3 1.5 2 2.5 3 v. results and discussion a total of 80 model tests in 4 series were conducted on a strip footing constructed on a reinforced sand slope with a void to account for the influence of all the variable parameters. two dimensionless factors are introduced to quantify the influence of the void and reinforcing layers on the bearing capacity in order to establish accurate comparisons between the numerical tests, knowing that authors in [4, 6, 26] also assessed the impact of void and reinforcement soil in terms of reduction factors, not in terms of ultimate bearing capacity. the first parameter is the bearing capacity ratio (ih), which can be given in the form shown in (1). this factor is defined as the ratio of load-bearing capacity of the footing on the unreinforced sand with a void and without void respectively. ih = ��(���� � ����) �(���� ��� ����) (1) the second parameter is used to assess the combined effect of reinforcement layers and the existence of the void on bearing capacity. this parameter is defined as ihr, i.e. the ratio between the load-bearing capacity of the strip footing on the reinforced soil with a void to that of unreinforced soil without one: ihr = ���(���� � ����) �(������� ����) (2) a. effect of geogrid layer to examine the effect of geogrid-reinforcement, the strip footing was placed on the reinforced sand slope with 3 layers of reinforcement (n = 1, 2, and 3). figure 3 represents the variation of the reduction factor ihr with different void embedment depths ratios (h/d = 1.5, 2, 2.5, and 3), when the void is assumed to be located directly below the centerline of engineering, technology & applied science research vol. 12, no. 4, 2022, 9005-9011 9008 www.etasr.com mazouz et al.: assessing the effect of underground void on strip footing sitting on a reinforced sand … the foundation (x/b = 0). it can be observed that the bearing capacity increases due to the provision of the reinforcement layers. in addition, the bearing capacity of the foundation was increased along with the number of layers of geogrid reinforcement. additionally, as the mass of the sand layer above the void increases (increasing h/d), the shear resistance increases. fig. 3. variation of reduction factor ihr at different h/b. therefore, significant stability of the void had been observed. also, the ihr increases, regardless of the number of geogrid-reinforcement layers. figure 3 displays that in the case of reinforced sand when n = 1 and h/d attained a value of 3, the bearing capacity values of the strip footing tended toward the bearing capacity of the strip footing on unreinforced sand without a void. however, with up to two layers of reinforcement, the bearing capacity of strip footing on reinforced sand with a void, is greater than the unreinforced sand's without a void. these results demonstrate the effectiveness of the reinforcement layers in improving the ultimate bearing capacity of strip footings resting on a sand slope with a void. b. effect of void depth the embedment depth of the void from the soil surface is one of the main parameters of soils with a void. figure 4 reveals the variation of reduction factor ih versus depth ratios (h/b) varying from 0.50 to 3.50 with an increment of 0.5. interestingly, it is observed that the value of ih increases continuously with increase in the value of depth ratios h/b up to a reach a limit value at h/b = 3.5, beyond which the reduction factor becomes constant. this limit value is called the critical depth, hcr. at this specified depth. the footing behavior converges to that without void. a similar result was reported in [25]. a significant reduction in the bearing capacity value was observed when the void was located at h/b = 0.5 and 1. this happened because the soil layer above the void was thin and the failure surface gets smaller than the one without a void. therefore, low pressure is necessary for the failure surface to achieve the slope, causing a decrease in bearing capacity. fig. 4. variation of reduction factor ih versus different depth ratios for x/b=0. c. effect of horizontal distance figure 5 reveals the variation of reduction factors ih and ihr, versus depth ratios (h/b), for different horizontal distance ratios (x/b= 0, 1, 2, and 3) and reinforcement layers n=0, 1, 2, 3. (a) (b) fig. 5. variation of ih and ihr versus different depth ratios h/b for varying x/b. engineering, technology & applied science research vol. 12, no. 4, 2022, 9005-9011 9009 www.etasr.com mazouz et al.: assessing the effect of underground void on strip footing sitting on a reinforced sand … (a) (b) (c) (d) fig. 6. failure surface for unreinforced sand slope. as shown in figure 5(a), the reduction factor is affected by the position of the void (x and h). furthermore, the value of bearing capacity increases with increasing depth distance ratios (h/b, x/b) and number of reinforcement layers. it is observed from figure 5 that the maximum reduction on the ihr is noted when x/b = 0 and h/b < 3. for unreinforced sand, if the depth ratio h/b or x/b is greater than 3.5 and 3.0 times the width of the footing respectively, the bearing capacity of the footing does not affect by the presence of the void, while ih is greater than 0.8. for the case of reinforced sand as shown in figure 5(b) when n=3 for different x/b ratios, ihr remains constant and the corresponding value approaches 1.0. in this case, the bearing capacity of the footing is similar to the case without void, while the influence of void becomes insignificant. as reported in [39, 40], this behavior occurs because the maximum extend of the failure zone in cohesionless soil is 3b below the footing and 2.5b on both sides. therefore, the void is located out of the soil shear zone. vi. failure mechanism figure 6 shows the failure surfaces for the strip footing close to the unreinforced sand slope with or without a void. various horizontal spacings between void and footing x/b = 0, 1.0, 2.0, and 3.0 and different embedment depths of void h/b were considered. as shown in figure 6, the failure mechanism depends significantly on the location of the void. when the foundation is situated on an unreinforced sand slope without void, a triangular zone formed under the foundation. the failure surface occurs at the footing side and extends laterally towards the slope, as illustrated in figure 6(a). for the unreinforced sand case with a void, and with depth ratios x/b = 0 and h/b < 3, as can be seen in figure 6(b), the failure surface doesn't form the triangular wedge and the void is located in the shear zone of the failure mechanism. however, the slip surface extends vertically connecting both the edges of the foundation to the upside of the void crest and is appearing smaller than the one in the case without void. on the other hand, if x/b or h/b are above 3 and 3.5 respectively, the void is located out of the rupture zone. in addition, the behavior and failure mechanism are similar to the strip footing on unreinforced sand without a void (see figure 6(c)-(d)). this proves that the void does not affect the load-bearing capacity of strip foundations. vii. conclusion the current numerical study analyzed the effect of underground void on the bearing capacity behavior of strip footing sitting on the crest of unreinforced and geogridreinforced sand slope. the main conclusions of the study are: • it was found that the ultimate bearing capacity depends on the location of the underground void (x/b and h/b) and the number of reinforcement layers. • the presence of voids always reduces the load carrying capacity of the footing in both unreinforced and reinforced cases. • the ultimate bearing capacity increases with distance (x and h). • using geogrid reinforcement increases bearing capacity and reduces the settlement of the strip footing. • the load-bearing capacity of a strip footing increases with increasing number of reinforcing layers. • there is a critical distance (xcr = 3 and hcr = 3.5) beyond which the influence of the underground void on the footing stability is considered to be negligible. • the depth and width of the failure surface increase with increasing vertical and horizontal distance (x and h). engineering, technology & applied science research vol. 12, no. 4, 2022, 9005-9011 9010 www.etasr.com mazouz et al.: assessing the effect of underground void on strip footing sitting on a reinforced sand … references [1] r. l. baus and m. c. wang, "bearing capacity of strip footing above void," journal of geotechnical engineering, vol. 109, no. 1, pp. 1–14, jan. 1983, https://doi.org/10.1061/(asce)0733-9410(1983)109:1(1). 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tiendung@haui.edu.vn abstract-this paper investigates the influence of dry high-speed milling on the surface quality of jis skd61 hard steel, compared to the conventional coolant fluid method. this research was conducted in a super mc 500 high-speed cnc milling machine with a hitachi coated carbide 20mm in diameter. high-speed cutting parameters such as cutting speed v, cutting depth t, and spindle speed s were considered as variants. the experiment was designed based on taguchi's l9. surface quality, including ra and rq, was measured using the mitutoyo surftest sv-210. a mathematical regression model was found for the average values of surface roughness through regression analysis for dry and coolant fluid conditions. the chosen high-speed milling parameters and the respective ra and rq values were obtained by anova. the grey relation scores for wet and dry milling surface quality for cut depth, feed rate, and cutting speed were 0.7527, 0.7869, 0.6302, and 0.8167, 0.7199, 0.6040, respectively. the results showed that the feed rate had the greatest influence on the surface quality during the high-speed coolant milling of hardened steel, while the depth of the cut had the greatest influence on the surface quality during the high-speed dry milling process. keywords-skd61; fgra; surface roughness; high-speed milling i. introduction jis skd61 (or aisi h13) alloy steel is a hot work mold steel, popular for its remarkable toughness, sufficient resistance to high-temperature fatigue, and high rigidity. in general, the manufacturing processes of extrusion die sets, hot forging, and casting dies include roughing, heat treatment, and machine finishing. this process is costly and time-consuming. the increasing pressure in the global economy forces the manufacturers to increase machining productivity while maintaining or improving product quality. the improvement of the cutting productivity and quality of high-speed cutting processes have attracted the attention of many companies and researchers in recent decades. the coolant fluid is essential when milling hardened steel or other difficult-to-machine materials, especially when machining at high speeds. the main effect of a coolant in milling is to reduce temperature and friction, prolong the life of the cutting tool, and improve the machining efficiency and surface quality [1-3]. moreover, a coolant also has anticorrosion and cleaning effects [4, 5]. nowadays, with the continuous development of precision and ultra-precision machining, machined surface integrity is more important than cutting efficiency and tool life, especially for important components such as mold parts working in harsh environments. however, the effect of the coolant fluid on machined surface quality and its performance in the high-speed machining of hardened steels has not been given attention and compared with dry milling under the same machining conditions. the cost of the coolant fluid can increase the total production cost by up to 15% [6]. dry, near-dry, and mql machining processes are viable alternatives to reduce this cost. dry machining is now considered an excellent solution to minimize the negative impacts on human health and the environment. therefore, dry or near-dry machining has attracted considerable interest among manufacturers and researchers [7]. dry milling can offer significant advantages such as reducing pollutants in the air, water, or the earth, having less harmful effects on human health [20], and a significant cost reduction as there is no need to invest in cooling equipment, maintenance, operation, and handling coolant after machining [8, 9]. dry milling processes can be applied to a wide range of materials, such as cast iron, carbon steel, alloy steel, and difficult-to-machine steels [10, 11]. however, in dry milling conditions, due to the large friction between the tool and the workpiece, the cutting temperature increases and causes increased wear of the cutting tool. build of edge also appears more frequently [9], adversely affecting corresponding author: the-hung le engineering, technology & applied science research vol. 12, no. 1, 2022, 8023-8028 8024 www.etasr.com le et al.: surface finish comparison with dry and coolant fluid in high-speed milling of jis sdk61 … the quality of the machined surface. although the further improvement of surface quality and the reduction of tool wear during dry milling has attracted the interest of many researchers, most of them focused on measures to offset the positive effects of lubricants through the optimal selection of cutting parameters, changing the geometry of the cutting tool, choosing the right tool material, improving the machine, etc. however, these studies have not mentioned or compared the main factors that affect surface quality between the wet and dry milling process. this study examined the factors influencing the dry and wet high-speed milling of hardened steel on surface quality under the same machining conditions. fuzzy grey relationship analysis (fgra) was applied to determine the influence of each factor on surface quality in the two different milling environments. based on the experimental results obtained by the taguchi l9 method, the fgra processes were used to evaluate the main factors affecting surface quality. the dry and wet milling comparison provides excellent reference values to be applied to the machining processes and further improve the surface quality of high-speed milling of hardened steel. ii. experimental setup a. the workpiece the skd61 hard steel, used as the workpiece specimen, was prepared in square blocks of 70×40×15mm dimensions. the chemical composition and mechanical properties of jis skd61 mold steel are demonstrated in tables i and ii. table i. chemical composition of jis skd61 hard steel c si mn p s cr mo ni cu v 0.349 0.582 0.720 0.001 0.001 5.59 1.18 0.062 0.036 0.573 table ii. mechanical properties of jis skd61 hard steel properties metric imperial (psi) tensile strength at 20° c 1.200 ÷ 1.590mpa 174.000 ÷ 231.000 tensile strength, yield at 20° c 1.000 ÷ 1.380mpa 145.000 ÷ 200.000 reduction of area at 20° c 50% 50 % modulus of elasticity at 20° c 215 (gpa) 31.200 poisson’s ratio 0.27÷0.30 0.27-0.30 fig. 1. super mc 500 high-speed cnc milling machine. b. machine and cutting tool an mc50 high-speed machine, made by foxconn corporation and a hitachi cutting tool with coated inserts were used for the experiment process (figure 1). c. measurement equipment the surface roughness value for all experiments was determined as the average of three measurements at separate locations in the workpiece specimens using a mitutoyo surftest sv-210. these average values are shown in table iii. iii. applying grey fuzzy relationship analysis gra is an effective statistical method to measure the approximation between objects using the grey relational level. the model has been successfully applied in many different fields [12-14]. the level of information in a gra assists decision-making in difficult situations [15, 16]. an improved version of this method is the fuzzy grey relationship analysis (fgra). this is an approach based on a fuzzy system developed on coefficients and grey relation levels. this model considers all the different criteria, including their importance and the uncertainty about the weights. in this work, fgra was used to evaluate the effects of various factors from the cutting mode parameters on the machined surface quality in both dry and wet milling environments. the steps of the algorithm are described as follows: • step 1: when applying fgra to determine the factors affecting surface quality in wet and dry milling, the reference matrix y is established based on the surface roughness parameters obtained. y(1), y(2),..., y(n) correspond to the surface roughness values obtained by the experiments 1, 2, ..., n. the reference matrix with the surface quality in high-speed milling is described by: � � ���1� ��2�…�� �� (1) the factors investigated in the high-speed milling process include inputs such as cutting speed, feed, wet milling, dry milling, etc. in the experiments. if the number of the investigated factors is m and the number of experiments is n, the comparison matrix is: � � ����⋮�� � � ���1����2�⋯��� ����1����2�⋯��� �⋮ ⋮ ⋮ ⋮���1����2�⋯��� � � (2) • step 2: nondimensionalize original sequences. as the investigated factors (surface roughness) and the reference variables (depth of cut t, feed rate s, cutting speed v) have different dimensions, they must be nondimensionalized by [17]: �����′ � ������������������������������������� (3) • step 3: calculate the cosine value of the fuzzy membership. in this study, the included-angle cosine method was adopted, which is not affected by the linear proportional relationship of the data. the similarity of the two factors engineering, technology & applied science research vol. 12, no. 1, 2022, 8023-8028 8025 www.etasr.com le et al.: surface finish comparison with dry and coolant fluid in high-speed milling of jis sdk61 … was determined by the included-angle cosine of the two factors, which was calculated by [18]: �� � ∑ �������!"#$%∑ ���&!"#$ %∑ ����&!"#$ (4) • step 4: the grey level relationship was calculated by [18]: '� � (.*+,-.*+�!(.*+,-.*��� (5) this variant must be suitable for working conditions and resist any noise signal, as the values of dispersion coefficients may not accurately reflect the relationship between the investigated variants. the dispersion coefficient was calculated by [14]: / � ��.� ∑ ∑ 0�1��� 2 �13���0��4��34� (6) where ∆ is the absolute error's mean. as 5 � ∆∆+,, the resolution factor was obtained as: 7 ∈ 9�5;1,5 = 5�; 5 > �?�1,5 = 5;25�; 5 @ �? (7) if 5 > �?, then l=1.25c. if 5 @ �? then l=1.75c. • step 5: the euclidean distance was used to determine the difference between the comparison and reference matrices and increase the accuracy of the estimation processes. therefore, the weight vector of the different elements in the reference matrix was defined by: w = (w1, w2, … , wj), j = 1, 2, …, n (8) the grey euclidean r2 levels were calculated using [17]: �� � 1 2 2a∑ �bc1 2 '����d����4� (9) • step 6: determine the fuzzy grey points. according to the fuzzy association coefficient, the grey relationship’s level and grey relationship with the fuzzy correlation coefficient of the research variants were calculated by: � � %e$&.e&&� (10) • step 7: ranking. based on the magnitude of the grey relational grade, the impact of the investigated factors was ranked. iv. experimental procedure the experiment was designed based on the taguchi orthogonal array [19] to reduce the number of experiments. two responses, ra and rq, were analyzed simultaneously in both dry and coolant fluid environments. cutting speed v, spindle speed s, and depth of cut t were chosen. table iii shows the high-speed milling parameters and results. v. results and discussion figures 2 and 3 depict a quality comparison of the workpiece surface in wet and dry milling, according to ra and rq, respectively. the results show that the surface quality in dry is lower than in coolant fluid milling with the same cutting parameters. table iii. experimental results no variant code surface quality in flood cooling condition surface quality in dry condition t s v ra (µm) rq (µm) ra (µm) rq (µm) 1 1 1 1 0.382 0.464 0.543 0.615 2 1 2 2 0.714 0.836 1.314 1.525 3 1 3 3 1.492 1.712 1.829 2.290 4 2 1 2 0.827 1.011 0.978 1.117 5 2 2 3 0.405 0.487 0.536 0.622 6 2 3 1 0.56 0.666 1.317 1.557 7 3 1 3 0.848 1.046 1.000 1.204 8 3 2 1 0.521 0.613 0.521 0.616 9 3 3 2 1.010 1.215 1.301 1.588 fig. 2. ra surface roughness comparison in wet and dry milling. fig. 3. rq surface roughness comparison in wet and dry milling. the anova results of the surface quality in wet milling conditions are shown in figure 4. the results show that the smallest s/n ratios were in level 3 for all variables. feed rate s had the smallest s/n ratio (0.31), followed by cutting speed (0.99) and depth of cut (2.15). the anova results in dry milling conditions are shown in figure 5. the results show that feed rate s and cutting speed v had the smallest s/n ratios in level 3 (-3.36, -2.92, respectively). depth of cut t had its smallest s/n ratio in level 1 (-0.78). therefore, there is a significant difference in the anova results between the wet and dry milling processes. the fgra was applied to determine the main factors affecting the surface quality through the following steps: engineering, technology & applied science research vol. 12, no. 1, 2022, 8023-8028 8026 www.etasr.com le et al.: surface finish comparison with dry and coolant fluid in high-speed milling of jis sdk61 … • step 1: the surface quality of different machining conditions had the y(x) and z(y) reference arrays for wet and dry milling, respectively. the depth of cut, feed rate, and cutting speed were y1(x), y2(x), y3(x), and z1(x), z2(x), z3(x) for conventional and dry milling, respectively. the reference and the comparison matrixes are shown in (11) and (12). fg gh���i����i��?�i���i� jk kl � 1 1 1 2 2 2 3 3 31 2 3 1 2 3 1 2 31 2 3 2 3 1 3 1 20.382 0.714 1.492 0.827 0.405 0.56 0.848 0.521 1.010� (11) fg gho��i�o��i�o?�i�o�i� jk kl � 1 1 1 2 2 2 3 3 31 2 3 1 2 3 1 2 31 2 3 2 3 1 3 1 20.543 1.314 1.829 0.978 0.536 1.317 1.000 0.521 1.301� (12) fig. 4. anova results of surface quality in wet milling. fig. 5. anova results of surface quality in dry milling. • step 2: the angular cosine of the fuzzy membership function was obtained by (4). figures 6 and 7 depict the fuzzy membership classes of four surface quality parameters in wet and dry environments. the results showed that in the wet machining process, the change of feed rate was the highest (0.7705), followed by the depth of cut (0.7525) and cutting speed (0. 5413). the analysis results in dry high-speed milling depicted a clear difference, as the depth of cut was kept at the most considerable value (0.8468), followed by the feed rate (0.6748) and cutting speed (0.487). hence, in comparison with wet milling, the feed rate dramatically influenced the surface quality. cutting speed had an almost negligible impact on the surface quality, just as in wet milling. meanwhile, in dry milling, the depth of cut had the most influence on surface quality. • step 3: the grey euclidean relationship levels were calculated using (5) (8) and are depicted in figures 6 and 7. the euclidean grey equivalent ratios of different elements were not much for the wet milling process. but it was still found that the feed rate most influenced the surface quality in wet milling. in dry milling, the depth of cut had the most effect on surface quality. fig. 6. grayscale analysis to surface quality in wet milling. fig. 7. grayscale analysis to surface quality in dry milling • step 4: the fuzzy grey relationship scores of the input variants were obtained by (12) and are illustrated in figures 6 and 7. the results showed a comprehensive way to evaluate the impact of experimental variants on the surface quality in both convenient and dry milling conditions. therefore, the matt grey related scores for wet and dry milling surface quality of the three factors depth of cut t, feed rate s, and cutting speed v were 0.7527, 0.7869, 0.6302, and 0.8167, 0.7199, 0.6040, respectively. hence, the influence of feed rate on the surface quality in the high-speed machining of a difficult-to-cut material in wet milling is the most. by contrast, the depth of cut has the most engineering, technology & applied science research vol. 12, no. 1, 2022, 8023-8028 8027 www.etasr.com le et al.: surface finish comparison with dry and coolant fluid in high-speed milling of jis sdk61 … significant influence on the surface roughness in dry machining, while the cutting speed has an almost negligible effect on the surface quality in both dry and wet milling methods. vi. conclusion this study investigated the high-speed cutting parameters optimization of milling processes in dry and coolant fluid conditions to ensure a satisfactory surface quality. fgra was obtained to analyze the relation among the surface roughness parameters ra, rq, and the cutting parameters cutting speed v, spindle speed s, and depth of cut t. anova was used to determine the model’s adequacy and factor significance. the main results can be summarized as: • the surface quality in high-speed milling of mold steel jis skd61 in dry conditions is lower than in coolant fluid conditions with the same cutting parameters. • the effects of different cutting parameters on the surface roughness in dry and coolant fluid environments differ. cutting speed v had the smallest s/n value at 0.31 and 0.21, respectively. by contrast, the s/n value of the depth of cut t was highest, at 2.51 and -0.78, respectively, followed by the s/n of spindle speed s. • the fgra confirmed that the influence of spindle speed was the most in the coolant fluid high-speed milling of hardened steel. by contrast, the effect of depth of cut on the surface roughness in the dry machining was the most significant. at the same time, both dry and wet conditions showed that the influence of cutting speed was insignificant. acknowledgment the authors highly appreciate hanoi university of industry (https://haui.edu.vn) for supporting the research process. nomenclature x comparison matrix y reference matrix l resolution coefficient, l∈[0,1] ∆min minimum absolute difference, ∆min=min|y(k)-xi(k)| ∆max maximum absolute difference, ∆max=max|y(k)-xi(k)| ∆(k) absolute difference, ∆(k)=|y(k)-xi(k)| ξi relational coefficient r fuzzy grey relational grade r1 fuzzy membership grade r2 euclidean grey relational 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[20] f. siddiqui, m. a. akhund, a. h. memon, a. r. khoso, and h. u. imad, “health and safety issues of industry workmen,” engineering, technology & applied science research, vol. 8, no. 4, pp. 3184–3188, aug. 2018, https://doi.org/10.48084/etasr.2138. authors’ profile the-hung le is a lecturer at hanoi vocational college of high technology. he is a phd candidate in the faculty of mechanical engineering at hanoi university of industry. his research work focuses on the multiple optimizations of high-speed machining process of hardcutting alloy steel. van-bong pham is an associated professor in the manufacturing department, faculty of mechanical engineering, hanoi university of industry. his research work focuses on the multi-optimization of the cutting processes. dung hoang tien is an associated professor in the mechanical technology department, faculty of mechanical engineering, hanoi university of industry. his research work focuses on dynamic machining, modeling and optimization, adaptive machining, am/3d printing technology, and micro-machining. microsoft word etasr_v13_n4_pp11230-11234 engineering, technology & applied science research vol. 13, no. 4, 2023, 11230-11234 11230 www.etasr.com kumar & kumar: bending analysis of steel-concrete composite beams with porosity bending analysis of steel-concrete composite beams with porosity prashant kumar department of civil engineering, national institute of technology patna, india pk0895300@gmail.com (corresponding author) ajay kumar department of civil engineering, national institute of technology delhi, india sajaydce@gmail.com received: 17 may 2023 | revised: 26 may 2023 | accepted: 28 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6050 abstract this study investigated the bending behavior of a simply supported pervious composite beam using the finite element method based on cubic order beam theory. the cubic order axial displacement was assumed and solved using shear stress-free conditions on the extreme surfaces of the composite beam. for simplicity, this study considered one-dimensional axial displacement. three nodded finite elements were assumed, and each node had eight unknowns. shear locking was eliminated in the present model by numerical integration of the stiffness matrix. a uniform porosity distribution was implemented in the upper layer of the composite beam. the damping ratio was also considered for the bending analysis. the accuracy of the present model makes it robust for the analysis of composite beams. keywordsporous concrete; finite element method; bending response; shear interface; shear stress i. introduction lightweight materials with higher strength are always the first choice of engineers. composite materials meet all the criteria for complex construction. over the past forty years, high-temperature resistant, more flexible, high-strength, and cost-effective composite materials have been created for civil engineering, aerospace technology, and the formation of household materials. other applications for these materials include electrical appliances, energy transformation, biomedical engineering, optics, etc. [1-2]. the advantages of these structures are their high strength, improved material properties, and lower weight. functionally graded composites can fulfill current and distinctive functions that traditional composite materials cannot [3]. these are sophisticated composite materials with a microscopically inhomogeneous morphology that are created using powder metallurgy processes from a combination of metal and ceramic. there are fewer stress discontinuities in fg materials because the material characteristics change gradually and smoothly across the thickness, and interlaminar stress discontinuities are removed. knowing the bending, buckling, and free vibration frequencies is vital because structural components made of composite laminates, such as aircraft wings and panels, are regularly subjected to mechanical loads, critical buckling, shocks, and vibrations [4]. the static and dynamic analysis of beams has an exciting history for its development. various beam theories have been developed to get precise and accurate results. the eulerbernoulli beam theory is used to analyze the beam [5]. as the euler-bernoulli beam theory is not enough to analyze a thin beam, the timoshenko beam theory (tbt) has become popular [6-7]. high-order beam theory (hbt) is more accurate than tbt. today, hbt is the first choice for the analysis of beam behavior [8-10]. the strength of a composite material also depends on the type and strength of shear studs used to hold the two elements, so investigation of shear stiffness parameters and inter-layer slip is essential [11-12]. in [13-15], the impact of porosity distribution on the vibrational behavior was investigated. in [16], the dynamic behavior of a beam was examined under various loading conditions using the state-space technique. this study investigated the impact of porosity distribution on the bending of simply supported two-layered sandwich steel-concrete composite beams. the one-dimensional c 0 finite element method was incorporated to model this problem and produce accurate results. the effect of the damping ratio was also calculated. to the best of our knowledge, the present work has not been used in any previous bending analysis study of composite beams. the novelty of the present work is the uniform distribution of porosity provided along the transverse direction of the upper element of the two-layered sandwich composite beam. the formation of voids at the time of modeling is a major issue for every engineer. so, its analysis is useful for future work. engineering, technology & applied science research vol. 13, no. 4, 2023, 11230-11234 11231 www.etasr.com kumar & kumar: bending analysis of steel-concrete composite beams with porosity ii. formulation a. porosity distribution in the upper element porosity is incubated in the concrete element changing the material properties of the simply supported composite beam, such as young’s modulus (e), shear modulus (g), and density of the concrete element. � �� ��� = ��� �1 − � ��� ��� = ��� �1 − � ��� ��� = ��� �1 − ��� � (1) where e is young's modulus, g is the shear modulus, ρ is mass density, and k is the function of porosity. b. mathematical formulation the high-order beam theory was used to solve the cubic order axial displacement equation. figure 1 shows the shear interface of the beam. fig. 1. shear flexible interface of the composite beam. the cubic order axial displacement equation for the upper and lower layer of the beam is written as: ��� � = �1 −�� �� � �� ������ �� �� �� �� (2) where u is the axial displacement equation along the centroidal axis, θ is the bending rotation, ζ and ξ are higher order terms, and i = c, s. the transverse equation of both layers is expressed as: �� ��, �� , � = �! ��, �! , � = ���� = � (3) the partial shear interaction between two layers of the composite beam is modeled by taking distributed shear springs at their interface. interfacial stiffness and shear slip at the interface are used to determine the shear stress at the interface. interfacial slip (s) is calculated as given below, where uc and us are the axial displacements of the upper and lower layer at the interface. " = ��′� − �′! � (4) the axial displacements in (2) are higher-order equations that are concerned with the warping of the transverse sections but do not describe the commonly used displacement parameters adopted in beam theories. so, higher-order terms are eliminated using shear stress-free conditions at the extreme surfaces of the composite beam. the shear stress can be calculated at any point in the upper layer using (2) and (3). �#� � = ��� ��$�� $� = %&'(&)( + &+& , = �−1 2�� 3�� � 1� /�� �� �� &+& 0� (5) where γc is the shear strain and gc is the shear modulus of the porous concrete layer. 1� = %1 − 23�)456(4 7 + 238)956(9 7,, ;� = %23�)456(4 7 − 238)956(9 7,, <� = %−� − 2=)456( 7 + 23�)956(4 7,, >� = − %2�)456( 7 + 2 =)956(47, 1! = %1 − 23�)456?4 7 − 238)956?9 7,, (6) ;! = %23�)456?4 7 + 238)956?9 7,, <! = %−� + 2=)456? 7 + 23�)956?4 7,, >! = %2�)456? 7 − 2 =)956?47,, and @ = a+a the shear stress-free conditions are applied at the top and bottom surface of the beam to find out the displacement equation: ��� � = b1� ;� c� >� d���� �� �� @�� (7) the normal stress and normal strain at any point beam are calculated using the following equation: ef̄hi = �>j �i ek̄hi (8) where σj is the normal stress, τj is the shear stress, ej is the modulus of elasticity, gj is the shear modulus, εj is the normal strain, and γj is the shear strain of the j th layer, and j=c represents the upper layer and j=s represents the lower layer of the two material composite beams. ek̄hi = %ki$i , = � &'l& &'l&)l + &+& m = �n�i ekhi (9) the strain energy can be given as a function of stress and strain using (8) and (9): � = 3� o�ekh̅�� efqh� + ekh̅!� efqh!�r1r� = 3� o�ekh̅�� e>h� ekh� + ekh̅!� e>h! ekh! �r� (10) where: �>�� = o�n����>s���n�� r1� and �>�! = o�n�!� �>s�! �n�! r1! numerical integration was used to evaluate the crosssection rigidity matrix �>�� and �>�!. the stored strain energy was calculated using (4) and distributed shear springs stiffness ks. t = 3� o u! "�r� = 3� o u! ��� − �! �r� (11) engineering, technology & applied science research vol. 13, no. 4, 2023, 11230-11234 11232 www.etasr.com kumar & kumar: bending analysis of steel-concrete composite beams with porosity c. finite element formulation three nodded iso-parametric c 0 elements were selected. this theory assumed eight nodal degrees of freedom to solve the present problem using a one-dimensional finite element approximation. the unknown nodal displacement vector {d} on the middle surface of a typical element is given by: erh = ∑ w� ��, ��. er� h��y3 (12) where ψi is the shape function. the generalized strain vector as a function of the nodal displacement vector {d} can be found by: ekhi = ∑ �z� �er� h��y3 (13) where [pi] is the interpolation function differential operator matrix. the strain vectors were calculated using (11) and (13) as a function of the stiffness matrix [k l ]. t = 3� erh� �[ \ �erh (14) where: �[ \ � = o��z��� �>���zh� + �z�!� �>�! �zh! �r� (15) similarly, the interfacial stiffness and the stiffness due to the penalty function approach were calculated. an element's mass matrix and its geometric stiffness matrix can be found in the same way as the element stiffness matrix calculated above. equations (3) and (12) were used to find the displacement component vector at a point in the beam layer as follows: ] ĵ_ = %�i�, = b ì de^h = b ì d�a�erh (16) where fj is a matrix of order 2×8 which contains the coefficient of displacement component expressed in (16), and [x] is a shape function matrix of order 8×24. the consistent mass matrix of three nodded elements is: �b� = ∭�a�� 2b ì d� �i b ì dr 7 �a�r�. r� (17) free vibration analysis was performed to determine the fundamental natural frequency from: b[d − e�]bd_defh = 0 (18) where ω is the vibration frequency and λ is the eigenvector. the dynamic response of the composite beam was analyzed using the following equation: �[d <d bd � hrrirj k = e l̀ h (19) where, d, ri , and rj are the displacement, velocity, and acceleration vectors. iii. result and discoussion a c 0 finite element method was used to solve the cubicorder axial displacement equation. these equations were solved using fortran. a. comparison study to validate the results, the mid-span deflection of a twolayered simply supported composite beam was compared with a t-cross section, using the results of [16], which used the state-step approach to tackle this problem. table i shows the mid-span deflection of a simply supported composite beam, which varies with its interfacial stiffness. the percentage error mentioned in table i shows the accuracy of the model. table i. variation of mid-span deflection with interlayer shear stiffness. s.n. interfacial shear stiffness (mpa) mid-span deflection (mm) present [16] 1 10 -16 9.7741 9.7224 (0.529) 2 2 8.2072 8.1957 (0.140) b. steel-concrete porous beam this study considered a simply supported composite beam having a porous upper layer. figure 2 shows the cross-section of the beam. a 15 m long simply supported beam was made up of a porous concrete slab and a steel joist. the dimensions of the concrete slab were 2.25×0.15 m 2 . the dimensions of the flange and web of the i-shaped steel joist were 0.1780×013 m 2 and 0.380×0078 m 2 , respectively. the material properties of the upper layer were ec = 13.55 gpa, gc = 6.775 gpa, and ρc = 2396.45 kg/m 3 . similarly, the material properties of the upper layer were es = 200 gpa, gs = 100 gpa, and ρs = 7948.89 kg/m 3 . a 100 kn moving point load is taken for the analysis, moving at a velocity of 16.67 m/s. the interfacial shear stiffness (ks) of the partially composite beam was considered as 100 mpa. fig. 2. cross section of the steel-concrete composite beam. c. porosity and damping effect on mid-span deflection the porosity of the upper layer ranged from 0 to 0.5. the effect of damping ratios on mid-span deflection was observed. this study used a variation of damping ratios from 0% to 10%. figures 3 and 4 show that the deflection of the partial and complete composite beams increased with increasing the porosity of the concrete elements. engineering, technology & applied science research vol. 13, no. 4, 2023, 11230-11234 11233 www.etasr.com kumar & kumar: bending analysis of steel-concrete composite beams with porosity fig. 3. variation of deflection with concrete porosity of partial composite beam. fig. 4. variation of deflection with concrete porosity of complete composite beam. fig. 5. variation of deflection of partial composite beam with damping ratio. fig. 6. variation of deflection of complete composite beam with damping ratio. table ii. variation of deflection with porosity and damping ratio. porosity (e) deflection (mm) partial composite full composite d=0% d=2% d=5% d=10% d=0% d=2% d=5% d=10% 0.00 74.789 73.548 71.974 69.931 54.254 53.248 52.138 50.865 0.10 75.898 74.634 73.028 70.936 55.217 54.310 53.170 51.852 0.20 77.043 75.758 74.121 71.982 56.383 55.454 54.284 52.920 0.30 78.239 76.937 75.270 73.085 57.661 56.709 55.506 54.096 0.40 79.512 78.196 76.499 74.269 59.092 58.114 56.877 55.420 0.50 80.898 79.574 77.847 75.573 60.740 59.733 58.457 56.950 the proposed trend of deflection variation satisfied the mathematical formulation above. the magnitude of the material properties of the concrete element decreases with an increase in porosity, and the stiffness of the element was directly proportional to the material properties. figures 5 and 6 show that the deflection of the partial and complete composite beams decreased with increasing damping ratio, which satisfied the mathematical formulation since the damping effect reduces the load effect. figures 3-6 show that beam deflection varies when the moving load passes from the left to the right support. table ii satisfies the above pattern of beam deflection. this study introduced an innovative investigation of the effect of porosity on the bending behavior of a simply supported sandwich composite beam. porosity in concrete has long been a concern for civil engineers due to its detrimental impact on the strength of concrete elements. in the field of construction, steel-concrete beams are extensively used. therefore, this study is of significant importance as it provides valuable guidance for future composite material research. iv. conclusions a c 0 finite element method was used to solve the cubicorder one-dimensional axial displacement equation. the cubic order shear deformation theory was used to analyze the bending behavior of a simply supported composite beam.  this study took into account the uniform distribution of porosity in the upper layer of the composite, proposing a novel relationship between porosity, damping, and bending.  the deflection of the simply supported composite beam increased with an increase in the porosity of the upper layer of the partial and complete composite beams.  the porosity of the upper layer of the composite beam increased from 0.0 to 0.50, and then the beam deflection increased up to 8% in the case of the partial composite and 12% in the case of the complete composite. engineering, technology & applied science research vol. 13, no. 4, 2023, 11230-11234 11234 www.etasr.com kumar & kumar: bending analysis of steel-concrete composite beams with porosity  the beam deflection in both the partial and complete composite cases decreased with an increase in damping.  the beam deflection decreased by 6.5% in the partial composite and 6% in the complete composite, while the damping increased from 0 to 10 %.  the presented model was more accurate in the prediction of the banding of the composite beam. acknowledgment the authors would like to thank the national institute of technology patna (india) for its financial support. references [1] d. mohammed and s. r. al-zaidee, "deflection reliability analysis for composite steel bridges," engineering, technology & applied science research, vol. 12, no. 5, pp. 9155–9159, 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[16] x. shen, w. chen, y. wu, and r. xu, "dynamic analysis of partialinteraction composite beams," composites science and technology, vol. 71, no. 10, pp. 1286–1294, jul. 2011, https://doi.org/10.1016/j. compscitech.2011.04.013. microsoft word etasr_v12_n3_pp8597-8604 engineering, technology & applied science research vol. 12, no. 3, 2022, 8597-8604 8597 www.etasr.com doan et al.: load-frequency control of three-area interconnected power systems with renewable … load-frequency control of three-area interconnected power systems with renewable energy sources using novel pso~pid-like fuzzy logic controllers diem-vuong doan faculty of control and automation electric power university hanoi, vietnam vuongdd@epu.edu.vn khoat nguyen faculty of control and automation electric power university hanoi, vietnam nkn.research@gmail.com, khoatnn@epu.edu.vn quang-vinh thai institute of information technology vietnam academy of science and technology hanoi, vietnam tqvinh@ioit.ac.vn received: 16 march 2022 | revised: 30 march 2022 | accepted: 4 april 2022 abstract—modern era power systems may include not only traditional primary energy sources like hydro or thermal energy, but also a variety of renewable energy (re) sources such as solar and/or wind power. this leads to the complexity of the electrical networks related to their design and construction as well as system stability and control issues. considered to be one of the most crucial control issues, load frequency control (lfc), must be continuously improved in order to ensure the control goals. for an interconnected power system, the control purposes are to maintain the net frequency at nominal value, e.g. 50 or 60hz as well as to ensure that tie-line power flows are stable at scheduled values. this work proposes a novel lfc strategy applying particle swarm optimization (pso) ~ pid – like fuzzy logic–based controllers. pso is one of the most effective optimization techniques. it is used to optimally determine four scaling factors for each lfc proposed in this study. a three-area power network consisting of a hydraulic station, a non-reheat plant, and a reheat unit along with re sources such as wind and solar power are taken into consideration. the control performance of the proposed control strategy is compared to those of existing controllers, i.e. genetic algorithm (ga), bacteria foraging optimization algorithm (bfoa), fractional order-pid (fpid), and fuzzy logic-based pi controllers for the same interconnected power grid model with various case studies of load changes along with nonlinearities and different re source conditions. simulation results implemented in matlab/simulink demonstrate the feasibility and applicability of the proposed control strategy. keywords-load-frequency control (lfc); pso~pid – like fuzzy logic controller; pid controller; re sources; nonlinearities i. introduction the complexity and vastness of an interconnected power grid with hundreds of parameters needing to be managed have increased the difficulty of network control and stability. it is a fact that one of the most important control problems in power systems is controlling the generation capacity of plants. in [1], the authors proposed an effective integration between an artificial neural network model and a pd-like fuzzy logic inference system to control the frequency in six areas. a controller fuzzy-like pid was designed in [2] to stabilize frequency in an interconnected power system with nonlinearities and uncertainties. controlling the output power of generating sub-stations such that transient difference in frequency of each region and power source variation between interconnected areas remains within the specified limits and ensuring zero-steady state error is called load frequency control (lfc) [3–4]. the purpose of the authors in [5] is to present lfc using a ga-based robust controller in a multi-area interconnected power system with governor uncertainties. in [6], a robust h∞ control technique for an islanded micro-grid in the presence of sudden changes in load conditions was proposed. in [7], the authors proposed the optimal sliding control method h∞ load frequency (smlfc) for power systems with time delay. a fractional order fuzzy pid is used to stabilize the frequency of the four areas in [8]. smart grid is becoming an important issue at present and future power system network configuration [9]. new modern grids provide detailed information about the grid in real-time, corresponding author: khoat nguyen engineering, technology & applied science research vol. 12, no. 3, 2022, 8597-8604 8598 www.etasr.com nguyen et al.: load-frequency control of three-area interconnected power systems with renewable … fast analysis of errors, and the ability to connect a large number of re sources to the electrical system [10]. the rapid development of industry and business has caused a significant shortage of energy available in circumstances of excessive use of fossil fuels [11]. security of sourcing concerns and environmental concerns invested in low-carbon power generation technology consist one of the priorities in the energy program of many countries [12, 13] therefore, re generation is a viable option that will not only meet the growing energy needs, but will also protect the environment [14]. the re source integration poses additional uncertainties and challenges for power systems, since re sources are discontinuous and their locations are geographically dispersed [15]. penetration of different re sources in modern power systems that are interconnected can greatly reduce the inertia of the system. when switching re sources powering multi-area electrical systems using converters/inverters, such power electronic interfaces will reduce the total inertia of the system and the voltage/frequency stability. therefore, a sufficient reduction of inertia will be a major limitation of grid connected re sources. by increasing the penetration of the existing re sources, the inertia of the interconnected power system may not be sufficient, creating dynamical problems for the stability of the system voltage and frequency, and cause negative effects on the stability/resiliency of the power system [16, 17]. if massive wind generation is faltered due to error, it may harm the power system’s operation and lead to load frequency control issues [18]. an interconnected power system with additional re sources is a practical need in modern life, but it reduces the inertia of the system and increases the frequency oscillations of the regions and at the same time increases the power fluctuations on power transmission lines. these include devices with nonlinear system components such as gdb (governor dead band), grc (generation rate constraint), time delay in the system, changes of parameters of the electrical equipment, and varying operating loading conditions. in traditional pid controllers, the controller parameters may not be updated when the system encounters the above problems. therefore, a pso~pid like fuzzy logic – based controller is proposed in this paper to solve the lfc problem. the response results of the system are compared with the results of ga-tuned pi (ga pi) [19], bfoa pi [19], fpid [20], and fuzzy logic based – pi [21] controllers. ii. mathematical modeling of interconnected power systems the interconnected power system with high re sources used in this study can be seen in [22]. the studied system comprises 3 areas that are interconnected by likely short transmission lines, called tie-lines. each interconnected power system consists of several single areas. a single area usually includes a governor, a turbine, a load, and a generator. these elements are connected to be the core of a power plant. a. speed governor governors are units used in power systems to sense the frequency bias caused by the load change and cancel it by varying the inputs of the turbines. a governor can be mathematically modeled as: 1 1 ( ) ( ( ) ( )) 1 p s p s f sg c st rg ∆ = ∆ − + (1) where r is a speed regulation of the governor and tg is the time constant of the speed of the governor. b. turbine types a turbine unit in power systems is used to transform the natural energy, such as the energy from steam or water, into mechanical energy that is supplied to the generator. there are three kinds of commonly used turbines: non-reheat, reheat, and hydraulic turbines, all of which can be modeled by transfer functions. 1) non – reheat turbine non-reheat turbines are first-order units. a time delay, denoted by tch, occurs when switching the valve and turbine torque is produced. the transfer function for the non-reheat turbine is represented as: 1 1 g ( ) ( ) ( ) t g t stch s p s p s = + = (2) 2) reheat turbine reheat turbines are modeled as second-order units, since they have different stages. the transfer function of these turbines is: 1 2 ( ) 1 g ( ) ( ) ( ) t g f t shp rh t t t s t t sch rh ch rh s p s p s + = + + + = (3) where trh and fhp are low pressure reheat time constant and high pressure stage respectively. 3) hydraulic turbine hydraulic turbines are non-minimum phase units due to the water inertia. in the hydraulic turbine, the water pressure response is opposite to the gate position change at first and recovers after the transient response. thus, the transfer function of the hydraulic turbine can be described as: ( 1) (0.5 1) g ( ) ( ) ( ) t g t sw t t sw s p s p s − + = + = (4) for stability concern, a transient droop compensation part in the governor is needed for the hydraulic turbine. the transfer function of the transient droop compensation part is given by: ( 1) ( . . 1) 3 g( ) t sr rt t sr r s + + = (5) where tr, tw, and rt are the reset time of the hyraulic unit and water star time and reset time respectively. c. wind turbine (re source) the wind turbine [23] consists of a turbine-generator shaft mechanism, which is used to convert the rotor rotation into electrical energy. equation (6) represents the mechanical output of the wind turbine: engineering, technology & applied science research vol. 12, no. 3, 2022, 8597-8604 8599 www.etasr.com nguyen et al.: load-frequency control of three-area interconnected power systems with renewable … 31 ( , ) 2 wt p w p ac vρ λ β= (6) where λ, ρ, vw, cp are tip speed ratio, air density factor (kg/cu.m), wind speed (m/s), and power coefficient respectively. for small signal stability of the system, the rate of change of wind power output given in (7) has been considered for assessing the stability of the proposed systems. 5 4 3 2 0, 0, 0, [0.007872 0.23015 1.3256 11.061 102.2 2.33] w cut in w cut out rated w cut out wt w w w w w w v v v v v v v p v else v v v v v − − −  <   >   ≤ ≤≤    ∆ =     −   + +   − + ∆   (7) the first-order transfer function model of the wind turbine is: 1 1 ( ) ( ) wtg wt t swts p s p s = + ∆ ∆ (8) d. solar power (re source) the transfer function model of solar power [24] is: 1 1 ( ) ( ) spv sp t sspv p s p s = + ∆ ∆ (9) e. generator load a generator unit in power systems converts the mechanical power received from the turbine into electrical power. for lfc, we focus on the rotor speed output (frequency of the power systems) of the generator instead of the energy transformation. since electrical power is hard to store in large amounts, balance has to be maintained between the generated power and the load demand. the mathematical model of generator – load is: 1 f( ) ( ( ) ( ))s p s p s t dms d ∆ = ∆ − ∆ + (10) where m is the inertia constant of the generator and d is the load damping constant. figure 1 shows a block diagram of a three-area interconnected power system with re sources and gdb along with grc established in matlab/simulink. the control objectives of the lfc in multi-area interconnected power systems are mainly to control the frequency variation, and tie-line power deviation in the areas towards zero while the system has many nonlinear elements, varying operating load conditions, and different loads in re sources. fig. 1. a three-area interconnected power system model with re sources, gdb, and grc. engineering, technology & applied science research vol. 12, no. 3, 2022, 8597-8604 8600 www.etasr.com nguyen et al.: load-frequency control of three-area interconnected power systems with renewable … iii. design of the pso~pid fuzzy logic controller pso~pid like fuzzy logic – based controllers are applied in each of the three areas. the structure of the proposed controller is shown in figure 2. the error inputs to the controllers are the respective area control errors (acei) as shown in the following equations: ( ) ace 1 1 1 1 e t b f ptie= = ∆ + ∆ (11) ( ) ace 2 2 2 2 e t b f ptie= = ∆ + ∆ (12) ( ) ace 3 3 3 3 e t b f ptie= = ∆ + ∆ (13) k4∫ k2 k1 k3 fuzzy logic architecture e(t) = ace (t) e (t) de (t) de(t) du dt upd-flc(t) upd-flc(t) upi-flc(t) upi-flc(t) upid-flc(t) fig. 2. the proposed structure of the fuzzy – pid controller the pid-like fuzzy logic controller has two inputs: error e(t) and derivative of error de(t). the output of the fuzzy controller u is the control input which must be taken to the governor. each pid-like fuzzy logic controller designed with ace, ∆ace as inputs and u as output has membership functions as illustrated in figures 3 and 4. the fuzzy logic rules are presented in table i. nb ns z ps pb 0-1 0 1-0.5 0.5 1 µ x= ace or ∆ace fig. 3. membership functions of ace and ∆ace. nb ns z ps pb 0-1 0 1-0.5 0.5 1 µ u fig. 4. membership functions of u. table i. the fuzzy rules nb ns z ps pb ace nb nb nb nb ns z ns nb nb ns z ps z ns ns z pb pb ps ns z ps pb pb pb z pb ps pb ps in the design of a modern heuristic optimization based controller, the objective function is first defined based on the desired specifications and constraints. performance criteria usually considered in the control design are the integral of time multiplied absolute error (itae), the integral of squared error (ise), the integral of time multiplied squared error (itse), and the integral of absolute error (iae). in this paper, ise is used as the objective function to optimize , , , 1 2 3 4 k k k k in the pso pid like fuzzy logic – based controller. the optimization technique uses the iate objective function which is depicted in (14): 3 1 2 3 , , 1 ( ) 0 f f f ptie i k i k i k tsim j iate tdt       ∆ + ∆ + ∆ + ∆ ∑  =   ≠  = = ∫ (14) where ∆f1, ∆f2, and ∆f3 are the system frequency deviations, ∆ptie is the incremental change in tie-line power and tsim is the time range of simulation. fig. 5. a typical flowchart of the pso algorithm. engineering, technology & applied science research vol. 12, no. 3, 2022, 8597-8604 8601 www.etasr.com nguyen et al.: load-frequency control of three-area interconnected power systems with renewable … the objective is to minimize the function j during changing conditions of the operating load with re sources and gdb and grc nonlinearities. applying the objective function in (14), an effective optimization method can be used. in this study, the pso [25] technique is chosen. pso is a biological-inspired optimization mechanism. the computational optimization method mimics the activity of finding food of a flock of birds or fish. a typical flowchart of the pso algorithm is illustrated in figure 5. in this study, the pso mechanism is executed with the parameter values indicated in table ii. n, c1, c2, and w are the population size, two acceleration coefficients, and the inertia weight factor of the pso respectively. with these parameters, the pso is able to optimally determine all scaling factors for the pid-like fuzzy logic controllers. case studies of applying this optimization technique are presented below. table ii. pso parameter values parameter n c1 c2 w value 80 3 2.5 0.8 iv. case studies according to the control idea presented above, the pso algorithm is employed to find the optimal coefficients k1, k2, k3, k4 for the pid-based fuzzy logic controller based on the iate objective function indicated in (14). after executing the pso, the optimal coefficients given in table iii were obtained. the proposed controller is compared with ga pi [19], bfoapi [19], fpid [20], and fuzzy pi [210] to verify its quality and feasibility. five different case studies regarding load changes embedded in the 3 areas were considered (table iv). in each simulation scenario of the load variations, the pulse loads in re sources also affect the power network (table iv). the obtained simulation results are shown in figures 6-10 and table v. table iii. optimal fuzzy logic-pid parameters using pso coefficient k1 k2 k3 k4 value 800.91 154.46 624.09 709.43 table iv. simulation case studies case studies step load (pu) random load (pu) pulse load in re sources (pu) case 1 1 2 0.03 3 p p d d p d ∆ =∆ = ∆ = 0.03p p spv wts ∆ =∆ = case 2 1 2 0.05 3 p p d d p d ∆ =∆ = ∆ = 0.03p p spv wts ∆ =∆ = case 3 1 2 0.05 3 p p d d p d ∆ =∆ = ∆ = ∆p =∆p = 0.05 spv wts case 4 0.05 1 2 0.05 3 p p d d p d ∆ =∆ = ∆ = ∆p =∆p = 0.05 spv wts case 5 0.08 1 2 0.08 3 p p d d p d ∆ =∆ = ∆ = ∆p =∆p = 0.05 spv wts (a) (b) (c) fig. 6. dynamic responses (case 1) in the three areas (a) ∆f1, (b) ∆f2, (c) ∆f3. table v. itae objectives of the considered controllers techniques/parameters itae (pu) peak time (s) ∆f1 ∆f2 ∆f3 fpid [19] 68.02 55.25 55.04 59.13 ga pi [8] 67.55 61.16 60.59 60.62 bfoa pi [8] 69.60 60.13 60.34 60.16 fuzzy pi [20] 62.09 60.88 60.09 60.34 proposed 53.17 1.32 1.062 0.71 it can obviously be seen that the proposed pid-like fuzzy logic controller exhibits better control performance than the other controllers [19-21]. major control indexes, such as overshoots and settling times, resulting from the proposed controller outperform the four existing controllers. engineering, technology & applied science research vol. 12, no. 3, 2022, 8597-8604 8602 www.etasr.com nguyen et al.: load-frequency control of three-area interconnected power systems with renewable … (a) (b) (c) fig. 7. dynamic responses (case 2) in the three areas (a) ∆f1, (b) ∆f2, (c) ∆f3. the simulation results shown in figures 6-10 illustrate that the output response of the frequency deviations in the three areas has settling times of about 20 to 30s, the overshoot is very low and frequency oscillation does not exist when using the proposed controller, proving its optimality. it is clear that when different types of load disturbances exist in the system, the undesirable effects will be minimized under the active capability of the proposed controller. in addition, from table v, the minimum itae value is obtained with the proposed controller (itae = 53.17). consequently, much better system performance in terms of minimum peak times in frequency deviations is achieved. it is extremely significant for the control of an interconnected power system with a huge number of electric equipment operating based strongly on the net frequency. the shorter the peak times of the frequency deviation are, the better the obtained control quality of the power network can be. these illustrations demonstrate the applicability of the proposed fuzzy logic control strategy, which outperforms the other controllers in the lfc of an interconnected electric power grid, especially when considering uncertainties, nonlinearities, and re sources. (a) (b) (c) fig. 8. dynamic responses (case 3) in the three areas (a) ∆f1, (b) ∆f2, (c) ∆f3. v. conclusion and future work in this paper, a novel pso~pid-like fuzzy logic – based load-frequency control strategy has been proposed for a three – area interconnected power system with various re sources and grc and gdb nonlinearities. such an electric power grid with time(s) 0 20 40 60 80 100 ∆ f 1 ( h z ) 10 -3 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 fuzzy pso controller ga controller[19] bfoa controller[19] fpid controller[20] fuzzy pi controller [21] engineering, technology & applied science research vol. 12, no. 3, 2022, 8597-8604 8603 www.etasr.com nguyen et al.: load-frequency control of three-area interconnected power systems with renewable … embedded various re sources is highly complicated with different kinds of turbines used for generating stations as well as nonlinear parameters, making the control extremely challenging. it was also demonstrated from the numerical simulation results that the proposed pid-like fuzzy logic lfc controllers applying the pso technique are completely able to solve the lfc problem, outperforming existing solutions. (a) (b) (c) fig. 9. dynamic responses (case 4) in the three areas (a) ∆f1, (b) ∆f2, (c) ∆f3. major control indexes of the proposed system, such as overshoot and settling time, obtained from the proposed lfc strategy were good enough, verifying this control scheme to be feasible and applicable. future work raised from this study will concentrate on stepby-step application of the theoretical control methodology to practical power networks. in this aspect, the effectiveness of the studied intelligent lfc controllers will come to reality. (a) (b) (c) fig. 10. dynamic responses (case 5) in the three areas (a) ∆f1, (b) ∆f2, (c) ∆f3. appendix parameters of the three areas [19] area with non reheat turbine value area with reheat turbine value area with hydraulic turbine value m1 (p.u.s) 10 m2 (p.u.s) 10 tw (s) 1 d1 (p.u./hz) 1 d2 (p.u./hz) 1 tr (s) 5 tch1 (s) 0.3 tch2 (s) 0.3 fhp 0.3 tg1 (s) 0.1 tg2 (s) 0.2 trh (s) 7 r1 (hz/p.u.) 0.05 r2 (hz/p.u.) 0.05 tspv (s) 1.8 b1 (p.u./hz) 21 b2 (p.u./hz) 21 twts (s) 1.5 t1 (p.u./rad.) 22.6 t2 (p.u./rad.) 22.6 engineering, technology & applied science research vol. 12, no. 3, 2022, 8597-8604 8604 www.etasr.com nguyen et al.: load-frequency control of three-area interconnected power systems with renewable … references [1] t.-m.-p. dao, y. wang, and n.-k. nguyen, "novel hybrid loadfrequency controller applying artificial intelligence techniques integrated with superconducting magnetic energy storage devices for an interconnected electric power grid," arabian journal for science and engineering, vol. 41, no. 9, pp. 3309–3320, sep. 2016, https://doi.org/10.1007/s13369-015-1850-3. 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[25] d.-t. nguyen, n.-k. nguyen, h.-l. le, and v.-t. nguyen, "designing pso-based pi-type fuzzy logic controllers: a typical application to load-frequency control strategy of an interconnected hydropower system," in 3rd international conference on automation, control and robots, prague, czech republic, jul. 2019, pp. 61–66, https://doi.org/10.1145/3365265.3365278. microsoft word etasr_v12_n3_pp8482-8487 engineering, technology & applied science research vol. 12, no. 3, 2022, 8482-8487 8482 www.etasr.com martins & romão: the importance of accurate boundary condition in obtaining reliable shearing … the importance of accurate boundary condition in obtaining reliable shearing stresses on a torsional finite element simulation jairo aparecido martins research & development desch north america cambridge, ontario, canada jairo.martins@desch.com estaner claro romão department of environmental engineering lorena school of engineering, university of são paulo lorena, são paulo, brasil estaner23@usp.br received: 21 december 2021 | accepted: 3 january 2022 abstractmany combustion engines and electric motors drive machines or equipment by turning a shaft and thus producing work. as a relevant part of a machine principle, torque transference deserves deep analysis regarding the techniques that determine precisely the finite element (fe) boundary conditions that are to be applied. this work presents a shaft loaded with a torque that causes torsion and results in shear stresses in the shaft material. in this context, when designing and calculating a shaft to transfer torque, virtual analysis like fe analysis (fea) must replicate the reality as accurately as possible. indeed, slight changes in load and constraint in a virtual simulation can produce considerably different shear stresses and unrealistic results. this paper aims to demonstrate how distinct boundary conditions for the same torque transference can result in very different results when a simulation does not comply with reality. the results showed the importance of being very attentive when applying loads and constraints on a shaft under torsion while calculating it via fea. keywords-torsion; numerical simulation; boundary conditions i. introduction finite element analysis (fea) is becoming increasingly popular among design engineers who use it as a product design tool. being safe and cost-efficient, the use of fea as a productdesign tool requires training, practice, and, mainly, experience, which is not present in the undergraduate curricula of mechanical engineering programs due to time constraints [1-4]. among applications and calculations by the tool, there are many books on metallurgy and mechanics that describe many types of loads and boundary conditions to consider, torque being one among them as an important load. authors in [5-7] presented solid concepts and provided examples of real applications for readers. in addition, there are scientific works that calculate and analyze torque for several interesting applications. authors in [8] developed a fea program based on fortran for analyzing working behavior and calculating torque and drag during oil extraction. the values of displacement obtained from the fea model matched those from the analytical model. authors in [9] presented different methods for the calculation of torque as a function of rotation angle in an electrical machine. the results obtained by the distinct methodology were compared with the experimental data, which allowed attaining practical information concerning the advantages and limitations of each method. authors in [10] investigated techniques for the optimal design of permanent magnet motors considering rotation. by applying the optimal design method, the authors reduced about 40% of the volume of the permanent magnet of the ipm motor and about 15% of the torque ripple. this reinforced the idea that most of the fe models should also be evaluated experimentally in order to be calibrated with reality. however, even in a virtual simulation platform, the model has to be as much realistic as possible and should utilize the most accurate and realistic boundary techniques. in this context, authors in [11] studied the simplification of the design geometry in the fea of structural and other continuum problems and concluded that strategies for identifying possible idealizations, controlling their application, and estimating the associated errors appear to be feasible. in particular, authors in [12] assessed the mechanical properties of glass/metal joints. in his study, a finite element method (fem) was implemented to analyze the torsional shear strength test designed for glass-ceramic/steel joints aiming towards solid oxide fuel/electrolysis cell application. the authors concluded that the difference between the analytically derived nominal shear strength, and the real critical shear stress derived via simulation, reduces with decreasing fracture torque. the boundary condition results might end up differently and some of them wrong if the simulation is not as close to reality as it could be. to the best of our knowledge, there are no papers that describe the impacts on the results on fe simulations when torque incurs on different (non-realistic) boundary conditions. many pieces of literature and videos on media teach watchers how to run a fe simulation. however, not always the presentations are correct and precise. for instance, [13-15] described a few boundaries conditions for torque application incompatible with reality and can cause problems in the field. for this reason, this paper aims to demonstrate how distinct boundary conditions for the same corresponding author: estaner claro romão engineering, technology & applied science research vol. 12, no. 3, 2022, 8482-8487 8483 www.etasr.com martins & romão: the importance of accurate boundary condition in obtaining reliable shearing … torque transference can result in expressively distinct results when a simulation does not comply with reality. ii. material and methods this study used classical equations to determine the torque to utilize in the fem as a torsion load. the shaft used on the simulations had one extreme constrained and another one receiving a torsional momentum (torque). to calculate the shearing stresses by numerical simulation, the shaft diameter was kept fixed at 10mm, and the length changed throughout the simulations. in addition, the loading region, where torque incurred, was altered in the simulations, from face to partial body, to whole body, and finally using an arm like if it were a wrench. two opposing torques (t) produce a twisting load along the axis of a circular shaft, resulting in a total shear stress distribution (τ) given by (1) [16]: τ = �.� � (1) where 0 ≤ r ≤ r. r is the distance from the center of the shaft and r is the outside radius, both in mm. since the diameter of the shaft is fixed, therefore r.t is the applied torque (n.mm), τ the shear stress (mpa), and j is the moment of polar inertia (mm 4 ), which is given by (2): � = � � .π. (2) therefore combining (1) to (2) results to: τ = �.� π.�� or = τ .π.� � � (3) assuming a fixed shearing stress of 100mpa as well as a fixed shaft diameter of 10mm, the torque result comes from (3) and is fixed at 19,635n.mm. it is relevant to highlight that since the purpose of the simulation is to apply 19,635n.mm as a total torque, only half of the torque was input on the shaft because the torque reaction generates the whole aimed torque. the fixed torque value was used throughout all simulations when running the fea. in addition, each simulation had the shaft length altered progressively from 10mm to 1,000mm. for numerical simulations autodesk f360 was utilized, considering a linear-elastic analysis and as an output the von mises stress [18-20]. as seen in table i, the same torque was input in four different ways. on the shaft face, along the shaft body, at a particular region, and by applying a vertical force on the arm attached to the shaft. in terms of mesh configuration, the same mesh for all simulations was utilized, which followed a maximum number of mesh refinement of 6, a convergence tolerance of 5%, a portion (40%) of elements to refine it, and an average element size of 10%. table i. boundary conditions for a shaft diameter 10mm loaded with a fixed torque of 9,817.5n.mm. simulation boundaries description shaft 10mm in diameter with length from 10 to 1,000mm. simulation with constraint at back surface and torque applied on shaft face (sf). shaft 10mm in diameter with length from 10 to 1,000mm. simulation with constraint at the back surface and torque applied on shaft whole body (swb). shaft 10mm in diameter with length from 10 to 1,000mm. simulation with constraint at the back surface and a torque applied on a body region of 15mm length (1.5 times the shaft diameter) (spb). shaft 10mm in diameter with length from 10 to 1,000mm. simulation with constraint at the back surface and force applied on a wrench extreme (swr). engineering, technology & applied science research vol. 12, no. 3, 2022, 8482-8487 8484 www.etasr.com martins & romão: the importance of accurate boundary condition in obtaining reliable shearing … iii. results and discussion figures 1 to 4 show the different equivalent stress (von mises) in mpa for the following configurations: shaft with a torque applied at its face (sf), shaft torque body (swb), shaft region (slip body) torque (spb), and force with arm like a wrench (swr). figure 1 shows the maximum stress at the edge of the face where the torque is transmitted, and it reaches 105.1mpa for a shaft length of 60mm (sf). figure 2 shows a von mises stress of 89.08mpa at constraint face. fig. 1. example of a shaft (10mm diameter × 60mm) simulated with a torque applied on the face (sf). swb differed from the sf condition, from 105.1mpa to 89.08mpa. not only the shear stress intensity was different, but also the stress localization. unlike sf, the maximum torque for swb moved to the opposite side from the torque load. figure 3 shows a change in torque from swb to spb. at this case, the maximum shearing stress was seen where the load was applied, and it reached 92.79mpa. when an arm was added (swr), then a force was applied to simulate the torque. the shearing stress reached 107.5mpa and was positioned close to the shaft constraint (figure 4). figure 5 shows the variance of shearing stress for 10mm shaft diameter with a length changing from 10mm to 1,000mm, and affixed torque of 9,817.5n.mm applied on the shaft face (sf). for a short shaft (10mm length), the stress was significantly higher than the calculated value of 100mpa, reaching a peak of 180mpa. the diameter and length for this condition are the same and fixed at 10mm. there is a wide stress variance and up and down change for lengths from 10 to 200mm when the stress decreases and reaches a value close to the calculated value. however, after 200mm length, the measured stress is unstable and has a high standard deviation as seen in table ii and figures 9 and 10. fig. 2. example of a shaft (10mm diameter × 60mm) simulated with a torque applied on the body (swb). fig. 3. example of a shaft (10mm diameter × 60mm) simulated with a torque applied on a region of the body (spb). fig. 4. example of a shaft (10mm diameter × 60mm) simulated with a force applied on arm (swr). moreover, the standard deviation changes, depending on the length. it begins from 28mpa for lengths between 10mm and 100mm and reduces to 14mpa for lengths between 100mm and 300mm and it ends up with 12mpa from lengths between 300mm and 1,000mm. fig. 5. shear stress with a torque applied on shaft face versus different lengths (sf). when stress is applied to the shaft body (swb), it reaches the highest stress level of 102mpa to a length of 10mm (figure engineering, technology & applied science research vol. 12, no. 3, 2022, 8482-8487 8485 www.etasr.com martins & romão: the importance of accurate boundary condition in obtaining reliable shearing … 6), thereafter it drops with length increment, reaching 86mpa when the length is 30mm. soon after this point, the stress starts increasing again and it reaches 95mpa for a length maximum of 1,000mm. the standard deviation changes from 4mpa for lengths between 10mm and 100mm, then it reduces to 1mpa for lengths between 100mm and 300mm and ends up at 1mpa for lengths between 300mm and 1,000mm. fig. 6. shear stress with a torque applied on shaft body versus different lengths (swb). when the torque is loaded on a specific and limited region of the shaft (spb), the stress starts with a high value for a short shaft (103mpa for 10mm length), then it drops to 93mpa, thereon stresses fluctuate up and down and reach 95mpa at 1,000mm length (figure 7). when it comes to standard deviation, it changes from 3mpa for lengths between 10mm and 100mm, then it reduces to 1mpa for lengths between 100mm and 300mm, and ends up at 1mpa for lengths between 300mm and 1,000mm. this presents a quite similar standard deviation when compared with the previous condition (swb). fig. 7. shear stress with a torque applied on shaft specific region versus different length (spb). a distinct behavior from previous situations is verified for a shaft that has an arm with a force-generating a torque (swr) as shown in figure 8. the shearing stress is pretty close to 100mpa as previously calculated analytically, but for 120mm and onwards it raises continually and moderately until 300mm when there is a steep inclination on the graph, demonstrating a mechanical instability. the standard deviation changes from 2mpa for lengths between 10mm and 100mm, then it goes up to 15mpa for lengths between 100mm and 300mm and it steeped up considerably to 89mpa for lengths between 300mm and 1,000mm. this presents the highest instability of all previous conditions. this stability comes from a lack of rigidity of the bar when it gets longer and longer until a point where the combination becomes totally mechanically unstable (uneven). fig. 8. shear stress with a torque applied on shaft by a force applied on an arm (swr). table ii shows the partial calculations of shearing stress averages and standard deviations. it compiles variations of von mises stress average and how data deviation occurs based on standard deviation. the shaft with a torque applied on a specific region showed the closer value to the calculated 100mpa (95mpa) and the lower standard deviation throughout all shaft lengths. in figures 9 and 10, there is a comparison among stresses generated by torques applied on a region of a shaft body. a line at 100mpa is traced to help compare fea to the analytical calculated value. the condition where the torque is applied on the face of the bar (figure 9 left) shows that for short bars, the von mises stress is higher, then it decreases constantly until the length of 1,000mm, which is 100 times the diameter of the shaft. therefore, this condition shows stress values that, when compared with the analytical calculation, do not seem accurate enough or reliable. when the torque is applied on the whole body (figure 9(b)), the von mises values are similar, and close to 90mpa for the full range of lengths with a standard value very low for short shafts as well as for longer bars. this means that the stress value is only 10% lower than the analytical calculated von mises stress. when the torque is applied on a specific region of the bar, established as 1.5 times the shaft diameter (figure 10(a)), the stress values were very close to the analytical calculation and varied from 95 to 96mpa. engineering, technology & applied science research vol. 12, no. 3, 2022, 8482-8487 8486 www.etasr.com martins & romão: the importance of accurate boundary condition in obtaining reliable shearing … table ii. distinct values for each configuration condition von mises stress (mpa) average 10 ≤ l ≤ 100 calculated stress (ττττ) (mpa) stdev 10 ≤ l ≤ 100 von mises stress (mpa) average 100 ≤ l ≤ 300 calculated stress (ττττ) (mpa) stdev 100 ≤ l ≤ 300 von mises (mpa) average 300 ≤ l ≤ 1,000 calculated stress (ττττ) (mpa) stdev 300 ≤ l ≤ 1,000 sf 145 28 125 14 115 12 swb 90 4 91 1 95 1 spb 95 3 94 1 96 1 swr 95 2 117 15 276 89 (a) (b) fig. 9. (a) torques and standard deviation from distinct length intervals for (a) sf, (b) swb. this configuration represents remarkably real conditions seen on machines and equipment where an electrical motor has a coupling assembled on a specific length of the shaft. the final configuration applied a torque indirectly on the shaft by using an arm. at the extreme of the arm, the force that generates the torque was applied. at this case, the value was very close to the analytical one (100mpa analytical value versus 95mpa for simulation) for short shafts smaller than 100mm. for shafts with lengths between 100mm and 300mm the value surpassed the analytical value (117mpa versus 100mpa) and reached 276mpa, which is completely unrealistic. the configurations were ranked comparatively with the analytical calculation. the closer value was verified at the swr condition, to shaft length from 10 to 100mm, presenting a shear stress average of 95mpa and a standard deviation of 2mpa. the second was the spb condition, with also 95mpa for shear stress and a standard deviation of 3mpa. the third condition was swb, with an average of 90mpa and a standard deviation of 4mpa, and the last one was sf with an average of 145mpa and standard deviation of 28mpa, see table ii and figures 9 and 10. (a) (b) fig. 10. torques and standard deviation from distinct length intervals for (a) torque applied on a specific region of the shaft (spb), (b) torque inputted on an arm like a wrench (swr). for shaft's lengths from 100 to 300mm, the sequence changed. the spb condition ranked first with a von mises stress of 94mpa and standard deviation of 1mpa, the second was swb with a von mises stress of 91mpa and standard deviation of 1mpa. swr was the third with a von mises stress of 117mpa and standard deviation of 15mpa, and sf was last exhibiting a von mises stress of 125mpa and standard deviation of 14mpa. for longer lengths (300 to 1,000mm) there was another change in positions. first was spb with a von mises stress of 96mpa and standard deviation of 1mpa, then engineering, technology & applied science research vol. 12, no. 3, 2022, 8482-8487 8487 www.etasr.com martins & romão: the importance of accurate boundary condition in obtaining reliable shearing … swb with a von mises stress of 95mpa and standard deviation of 1mpa. the third was sf with a von mises stress of 115mpa and standard deviation of 12mpa, and swr was last with a von mises stress of 276mpa and standard deviation of 89mpa. iv. conclusions this paper aimed to demonstrate how distinct boundary conditions for the same torque transference could result in different results when a simulation does not comply with reality. the results showed that unrealistic boundary conditions might result in unlikely shearing stresses and depending on the precision aimed, the results can lead to wrong conclusions, sometimes leading to failures. the results reinforced that realistic simulations are compulsory when working with fea, even for a simple load as torsion. for this simulation in particular, the calculation of shearing stresses' averages and standard deviation within intervals helped to define the most appropriate way to apply a torque on a shaft with the presented dimensions. this simplification can lead to wrong conclusions on a system design and generate failure. therefore, close attention and comparison between the simulation and reality are essential in order to produce a successful project. to sum up, many machines and equipment have alternate ways of transferring movement by torsion. it can be by a coupling to transfer torque from an electrical motor to a system or a mechanism lever to produce a parallel actuating system. however, the real matter is that the fea system can provide precise outputs only with precise and realistic inputs (boundary conditions). acknowledgment the authors acknowledge the financial support by capes (process number 23038.000263/2022-19). references [1] p. m. kurowski, "teaching finite element analysis for design engineers," in canadian design engineering network conference, toronto, canada, jul. 2006, pp. 203–234, https://doi.org/10.24908/ pceea.v0i0.3839. 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[20] e. c. romao and l. h. p. de assis, "numerical simulation of 1d unsteady heat conduction-convection in spherical and cylindrical coordinates by fourth-order fdm," engineering, technology & applied science research, vol. 8, no. 1, pp. 2389–2392, feb. 2018, https://doi.org/10.48084/etasr.1724. microsoft word etasr_v12_n5_pp9078-9086 engineering, technology & applied science research vol. 12, no. 5, 2022, 9078-9086 9078 www.etasr.com ghania et al.: α reliability study of renewable energy resources and their integration with utility grids α reliability study of renewable energy resources and their integration with utility grids samy m. ghania university of jeddah saudi arabia, jeddah sghania@uj.edu.sa khaled mahmoud university of jeddah saudi arabia, jeddah mrmahmoud@uj.edu.sa anas m. hashmi university of jeddah saudi arabia, jeddah ahashmi@uj.edu.sa received: 18 may 2022 | revised: 9 june 2022 and 5 july 2022 | accepted: 12 july 2022 abstract-reliability analysis is considered an impressive approach for investigating the planning and design processes of industrial and commercial electrical power distribution systems. reliability analysis is mainly concerned with the analysis of devices and systems whose individual components are prone to failure risk. the demand for renewable energy resources that work in parallel or replace traditional energy resources is significantly increasing. the current research presents the reliability analysis of the ieee 40-bus system integrated with large-scale pv and wind systems. reliability parameters evaluation of power distribution systems will be performed using the zone branch methodology to divide the power system layout into several sections (protected zones). the compensating capacitors will be addressed to clarify their impacts on the system reliability indices. the 40-bus system, known as the ieee standard 493-1997, integrated with large-scale pv and wind is simulated using etap software. the simulation results reveal that the integration of renewable energy resources with the utility grids can improve the reliability indices. these simulation results are consistent with similar works found in literature and some standards in the field of reliability analysis. the integration of power distribution systems with renewable energy resources improves the reliability indices of the distribution grids. keywords-reliability analysis; zone branch methodology; renewable energy resources; high penetration level; impact of compensating capacitors i. introduction the depletion of fossil fuels, their replacement by renewable energy resources, and the global impact on the environment are the main reasons to implement reliable energy resources. the reliability analysis of the power distribution systems integrated with large-scale renewable energy resources is a critical issue. for the last two decades, the pv/solar and wind energy resources have become the main solution to the rapidly increasing energy demand [1]. therefore, the reliability analysis of renewable energy resources is receiving more concern from utility engineers and researchers. reliability analysis approach is used to determine the impact of distribution network components based on their types (overhead lines, cable, transformers, substation, renewable energy resources, etc.) on the system reliability [2, 3]. many researches can be found about the reliability of energy generation systems connected with renewable energy resources [4, 5]. several approaches have been attempted to enhance the renewable energy integration process. distributed generation (dg) and its integration have been investigated to dispatch bidirectional flows [6, 7]. the reliability of any system can be simply defined as the probability that a system can perform its intended function for a specified interval under specified conditions [8-10]. the reliability analysis of electrical power distribution systems integrated with renewable energy resources is performed using mathematical model approaches [11, 12]. these approaches aim to control the consequence of failures and to identify the frequency and their causes. reliability computation mathematical models of the electrical power distribution systems should be developed to include the relationships between different sub systems [13, 14]. there are many approaches that can be implemented to study the reliability of the power distribution systems integrated with renewable energy resources [15, 16]. various approaches such as the optimal location of protective and switching equipment, proper monitoring and maintenance, the use of distributed generation units, electrical energy storage, network automation and smart grid concepts, and preventive and reliability-based maintenance and repairs have been reported [17, 18]. one of the simplest and most practical approaches of reliability studies is sensitivity analysis by which the critical component of the system can be identified [15, 19]. the demand of increased reliability and optimum economic performance of utility grids integrated with renewable energy resources has become very important. recently, concern have been given to the substantial growth in utilizing distributed energy resources. the more the electrical power distribution systems become larger and corresponding author: samy m. ghania engineering, technology & applied science research vol. 12, no. 5, 2022, 9078-9086 9079 www.etasr.com ghania et al.: α reliability study of renewable energy resources and their integration with utility grids interconnected with renewable energy resources, the more complex computational approaches are needed [20, 21]. these approaches should be able to assess the impacts of unreliable protective equipment and protection–coordination schemes on individual load point reliability indices within a given system configuration. one of these approaches is the zone branch methodology that overcomes many limitations and can be applied to a large electrical power distribution system [22, 23]. the main advantage of the zone branch methodology is that it can readily identify faulty protection schemes involving all the components of large electrical power distribution systems and can evaluate load point reliability indices. the current research presents a full simulation of the 40-bus system known as the ieee std. 399-1997 system integrated with large-scale pv and wind systems with capacity up to 3gw. simulations were performed to introduce the reliability concepts and indices of electrical distribution systems integrated with renewable energy resources for the two modes (on and off of the grid) of the system. the reliability evaluation of power distribution systems was performed using the zone branch methodology in which the distribution system is divided into several sections (protected zones). the obtained results will be compared with similar works found in literature and some standards in the field of reliability analysis [24, 25]. the current research could be used by utility engineers that want to estimate the impact of the integrating renewable energy resources on system reliability. moreover, it could be a very powerful planning tool for load scheduling and forecasting in order to meet the increasing demand of electrical energy. ii. reliability indices and zone branch methodology a. reliability main concepts and indices electrical power distribution systems are made up of components or subsystems. each component has its own expected failure rate which is defined as the number of expected failures per unit in a given time interval [26, 27]. the failure rate is evaluated as � � ����: � = �� � �� ���� � ������ �� ������ ��� �� �� ��� (1) as the reliability function is actually a failure density function, the average time for a failure to occur and is known as the mean time to failure (mttf) which is given as [28]: ���� = � � ��� ! ="# $ � (2) the repair time is the time taken to change the unit state from the off state to the on state and it is denoted as mttr. the failure rate is reciprocal of mttf and similarly, the repair rate (r) is equal to the reciprocal of repair time. the percentage of time that the system is functioning is called availability (a), meanwhile its outage of services is the unavailability (%̅) of the system: % = ����� �� �� �� �� ��� �� $ � ��()*# = +��, +��,-+��. (3) %̅ = /0/12 30456 07 077 /89: 8; $ <:15()*# = +��. +��,-+��. (4) for systems that can be treated as a single component with a constant failure rate � and repair rate = the availability is: % = +��,+��,-+��. = > ? > ?> @ = a�-a (5) based on the functionality sequence point of view, the electrical power distribution systems are connected in series, in parallel, or in combinations. each component in a series system has its own failure rate and reliability. the probability of all the components functioning is simply the product of the probabilities of individual components functioning. consequently, if the components have exponential failure probabilities with corresponding failure rates, �$ , �c … … … �� , then the system reliability and the mttf can be presented as: e���� � f!) = e$f!) g ecf!) g … … … . . ge�f!) (6) e���� � = � ��>� g � ��i� g … � ��j� = � ��� (7) �������� � = $ � (8) for the parallel systems, if the q(t) is the probability of failure in a given period, which is considered as the unreliability, then: kf!)���� � = k$f!)g kcf!)g … gk� f!) (9) if all the components have the same q(t), then the system reliability r(t) can be presented as: kf!)���� � = k� f!) (10) ef!)���� � = 1 − kf!)���� � (11) ef!)���� � = 1 − no1 − ���>� pgf1 − ��c� )g … o1 − � ��j� pq (12) if all the components have the same � , then the system reliability and mttf can be expressed as: ef!)���� � = 1 − n1 − � ��� q � (13) ���� = $� + $ c� + $ s� + ⋯ + $ �� (14) reliability evaluation of the electric power distribution systems depends on two basic parameters: load point indices and system reliability indices. the load point indices include the load point failure rate, the average outage time, and the average annual unavailability or outage. load point indices are very important from the customer's viewpoint. system reliability indices are important for system performance. the system reliability indices can be divided into two categories: interruption indices and energy-oriented indices [29, 31]. interruption indices are used to evaluate the average number of sustained interruptions noticed by a customer for long-term sustained interruptions. based on the ieee standard 1366 2012, the four main interruption indices used are: • system average interruption frequency index (saifi) • system average interruption duration index (saidi) • customer average interruption duration index (caidi) • customer total average interruption duration index (ctaidi) engineering, technology & applied science research vol. 12, no. 5, 2022, 9078-9086 9080 www.etasr.com ghania et al.: α reliability study of renewable energy resources and their integration with utility grids saifi indicates the average number of interruptions happened to a customer within one year. it is given by: u%v�v = ∑ x y (15) where ni is the total number of customers interrupted and nt is the total number of customers served. saidi is the most used index to evaluate the system performance through calculating the sustained interruption of each customer in service area during a determined period (minutes or hours) per year and it can be obtained by the following expression [21, 23]: u%vzv = ∑ �x∗ x y (16) where ri is the restoration time for each interruption event. caidi gives the average outage duration that any customer may have exposed. it can be calculated as: \%vzv = ∑ �x∗ x x (17) ctaidi represents the average time the customer spents during interruptions. the value of this index is calculated as: \�%vzv = ∑ �x∗ x]^ (18) where cn is the number of customers interrupted. the average service availability index (asai) is the ratio of the total hours that the service is available during a determined period (usually monthly or yearly) to the total hours of customer demand [24, 26]. %u%v = 1 − �∑ �x∗ x�∗ y � (20) where t is the time under study. energy-oriented indices are very important in evaluating the load in distribution networks. the most important indices are the average load, the expected energy not supplied (eens) index, and the average energy not supplied (aens) index. eens index is used to calculate the total energy generated but not supplied by the system and is calculated by: __`u = ∑ a�f�) ∗ b� (21) where la(i) is the average connected load at point i and ui represents the average annual outage time at the load point i. aens index represents the average value of the energy not supplied by the system corresponding to the total number of customers that are served. %_`u = ∑ cdfx)∗ex x � � (22) loee is used to determine the total expected energy losses (kwh) when the load demand is not satisfied from the generation system [27]. af__ = ∑ �� f_g� < a_z� )��i$ (23) where epi is the generated total energy, ledi is the total load demand, and ei is the unsupported load demand. b. zone branch methodology to evaluate the protection–coordination and reliability characteristics of the electrical power distribution systems, it is essential to divide the electrical power distribution system into protective zones. any protective zone is a part of the power system and can isolate or detach itself automatically or manually from the remaining power system if a fault occurs in any of its links. these protective zones are connected in series or in parallel and each zone is formed by a group of branches. the symbol λ(i,j) represents the failure rate of zone i within the branch j. each zone branch has an isolating device labeled s(i,j) and these isolating devices can be manual or automatic switches, fuses, reclosers, or a relay breaker combination. each isolating device has a probability q(i,j) it will not recognize and isolate any permanent faults of the equipment within its zone the failure rate λ(i,j) of any zone i and branch j is the sum of all the equipment failure rates whose failure will result in the operation of the isolating device of zone i and branch j only. the total failure rate λt(i,j) (f/yr) and the annual downtime λr(i,j) for any zone i and branch j can be calculated as: �� fj, k) = �� + ∑ ev%fl, m) n �opfm)� (24) �� fj, k) = �� n qr ∑ ev%fl, m) n �opfm)� n efl, m) (25) where λs is the failure rate of utility supply or plant supply, rs is the restoration duration of utility supply, z the zone branch number, k the total number of zone branches in system, r(z,k) the repair or switching time of each zone branch, fzb(k) is the failed zone branch array that contains the failure rate of each zone branch k, and ria(z,k) is the recognition and isolation array coefficients. figure 1 presents a simple schematic of the zone branch and the main indices used in the sectionalization process. s(1,1) q (1 ,1 ) λ (1,1) λ (2,1) λ (2,2) λ (2,3) λ (3,1) λ (3,2) λ (3,3) λ (4,1) s (2,1) s (2,2) s (2,3) q ( 2 ,1 ) q ( 2 ,2 ) q ( 2 ,3 ) s (3,1) s (3,2) s (3,3) q ( 3 ,1 ) q ( 3 ,2 ) q ( 3 ,3 ) q ( 4 ,1 ) s (4,1) fig. 1. simple schematic of a branch zone with main parameters. iii. simulated system configuration in this section, the grid system, along with two large-scale renewable energy sources (pv and wind), is simulated using the etap software package. etap is an analytical engineering software package for simulation, design, monitoring, control, operator training, optimizing, and automating power systems. etap can be used to design, analyze, and exchange the system engineering, technology & applied science research vol. 12, no. 5, 2022, 9078-9086 9081 www.etasr.com ghania et al.: α reliability study of renewable energy resources and their integration with utility grids data into many different simulating software packages like pscad to perform electromagnetic transient analysis, such as switching transients, insulation coordination, lightning surges, resonance, etc. the etap interface is a powerful tool needed to be more user-friendly rather than other simulating software packages. etap has impressive capabilities to simulate unlimited number of buses. the selected grid is the 40-bus system, also known as the ieee standard 493-1997 [25], which consists of loads, capacitor banks, transmission lines, and generators. this grid is a 13.8kv (rms line-line) transmission system. zone branch methodology can be applied in many different scenarios by sectionalizing the electrical power system single line diagram. these scenarios are based on the system configurations. table i shows the main reliability data of the grid and the simulated solar and wind farms. the table is truncated to fit and comply with the restrictions and limitations of the paper size and more data can be obtained from the standard. the reliability values given in table i are the design reliability parameters for each piece of equipment and instrument. these values are implemented as the base values for each element in the utility grid. table i. main reliability data of the simulated system main characteristics of the transformers trans. no. rating (mva) λ (failure/year) replace time (h/year) t1 15 0.0153 192 t2 15 0.0153 192 ….. …… …….. ……. t13 3.5 0.0059 79.3 t14 1.5 0.0059 79.3 main characteristics of the motors/generators motor. no. rating (mva) λ (failure/year) replace time (h/year) m1 0.7 0.0824 42.5 m2 0.5 0.0109 18.3 ….. … …. …. m20 1.5 0.0714 75.1 m21 1.75 0.0404 76.0 g 10 0.00536 478.0 main characteristics of the switchgear bus and bus ducts bus bar. no. rating (mva) λ (failure/year) replace time (h/year) 1 0.0034 26.8 2 0.0034 26.8 … …. …. 39 0.001048 11.5 40 0.003601 109.8 main characteristics of each pv and wind system equip. rating (mva) λ (failure/year) replace time (h/year) pv systems 1500 1.254 5 wind turbine 1500 0.02 50 in the current research, 5 different case studies will be implemented, as shown in figure 2. the simplified schematic diagram of the simulated systems connected with the pv and wind systems can be seen in [26]. the pv system consists of 5 sub-farms, 300mw each. meanwhile, the wind system consists of 5 sub-farms, also 300mw each. each pv and wind farm will be connected to the main utility bus labelled by bus number 40 as shown in figure 3. the pv/wind systems are connected to the main supply bus no.40 because of the large scale of the pv and wind systems. the bus no. 40 is the utility bus and the proposed pv and wind system will phase out completely the utility supply. also, based on the limitations of the ieee 40 bus configuration for power capacity and total load flow, the renewable energy systems are connected to bus no. 40. the connected pv and wind farms with different capacities of 300, 600, 900, 1200, and 1500mw respectively are based on the proposed scale by the electric holding company of egypt for two different projects [30, 31]. as the bus no. 40 is the main utility bus, the renewable energy resources will be connected to this bus to work in parallel with the utility grid or phasing out the grid supply. different scenarios for patching of the renewable sources will be simulated to calculate the impacts of connecting different renewable energy resources on the reliability indices. fig. 2. simple schematic of the different case studies. fig. 3. the main zones for the grid model connecting pv and wind systems. figure 3 presents the main zones of the simulated model with connections with pv and wind systems. different scenarios for patching of the renewable sources will be tackled. the main target is to investigate the different impacts on the reliability indices over the different cases of connecting pv and wind systems to the grid. figure 4 presents a simple flowchart for the proposed simulated systems. figure 5 presents a screenshot of the simulated ieee 40 bus system with pv /wind farms using the etap software. engineering, technology & applied science research vol. 12, no. 5, 2022, 9078-9086 9082 www.etasr.com ghania et al.: α reliability study of renewable energy resources and their integration with utility grids start base case utility only constructing the tables of failure rate and repair time information of the power system network topology simulating the power system network using etap/matlab construct zone-branch (from i to n) sections and calculating the reliability parameters i≥ n base case with pv base case with wind base case with pv and wind pv and wind calculating/printing the reliability indices finish no yes fig. 4. flowchart of the proposed approach. iv. simulation results the ieee 40 bus power distribution system was simulated to investigate the reliability indices for different case studies. therefore, each case study was performed to show the impact of connecting pv and wind renewable energy resources to the utility grid on the different reliability indices. the zone branch methodology was used to sectionalize the different protective zones in the simulated system. these protective zones are used to calculate the reliability parameters for all the pieces of equipment included in the zone. the main target is to calculate the failure rate of each zone. for the new added zones of pv and wind systems, the zone failure/repair rates can be calculated by (24) and (25). considering all the components inside the pv system and the circuit breaker, transformer, and busbar systems, the failure rate is: �� f1,2) = �fgt + �quvr. +2\. p + wxrwuq) = 1.254 + 0.0153 + 2 ∗ 0.012 + 0.03 = 1.3233f/yr and the replace time is 76.56h/f. similarly, while considering all the components inside the wind system and the circuit breaker, transformer, and busbar systems �� f1,3) = 0.09f/yr and the replace time is 18.91h/f. based on the different zones shown in figure 3, table ii tabulates the main reliability data of the different zones for the base-case and the different case studies. the renewable energy resources are added as zone (1,2) and zone (1,3) for pv and wind respectively. the failure rates of these two added zones are calculated and added with double-cell borders in table ii. table iii tabulates the different reliability indices for the different case studies while connecting the pv and wind systems with maximum capacity of 1500mw. it can be observed from table iii that when connecting pv and wind systems, the reliability indices are improved, and consequently, the performance of the electrical power distribution systems is improved. this improvement will be reflected to the energy continuity at the customer's side. moreover, focus will be given to the 3 most important indices (eens, aens and loee) while demonstrating the impacts of the compensating capacitors connected as shown in figure 5. the main configuration of the network topology is mentioned in [25]. the main voltage stability indices (reactive and active power, voltage, and power factor) are used to pre-identify the location/size of the capacitor. initially the optimal location depends on the network topology, configurations, loading, etc. in order to overcome this issue, the load flow study is performed using etap to determine the main voltage stability indices at each bus. bus no. 3 is considered the main loading bus and based on the results of the load flow, it is found to have the worst voltage stability indices. so, this bus is connected to the compensating capacitors. the values of 4mvar and 8mvar of the compensating capacitors are proposed after trials to maintain the main targeted voltage stability indices (voltage not less than 98% and power factor not less than 0.9). table ii. failure rate and duration of different zone branches case a: base case (utility only) zone λ (failure/year) interruption (h/year) replace time (h/failure) (1,1) 1.0583 2.16133 2.04226 (2,1) 0.0223 3.32788 149.232 ------------------------- (6,3) 0.1032 8.120 75.339 (6,4) 0.1032 4.2711 41.3869 case b (utility with pv) zone λ (failure/year) interruption (h/year) replace time (h/failure) (1,1) 1.0583 2.16133 2.04226 (1,2) 1.3233 2.752 76.56 (2,1) 0.0223 3.32788 149.232 ------------------------- (6,3) 0.1032 8.120 75.339 (6,4) 0.1032 4.2711 41.3869 case c (utility with wind) zone λ (failure/year) interruption (h/year) replace time (h/failure) (1,1) 1.0583 2.16133 2.04226 (1,3) 0.09 2.3 18.91 (2,1) 0.0223 3.32788 149.232 ------------------------- (6,3) 0.1032 8.120 75.339 (6,4) 0.1032 4.2711 41.3869 case d (utility with pv and wind) zone λ (failure/year) interruption (h/year) replace time (h/failure) (1,1) 1.0583 2.16133 2.04226 (1,2) 1.3233 2.752 76.56 (1,3) 0.09 2.3 18.91 (2,1) 0.0223 3.32788 149.232 ------------------------- (6,3) 0.1032 8.120 75.339 (6,4) 0.1032 4.2711 41.3869 case e (pv and wind without the utility) zone λ (failure/year) interruption (h/year) replace time (h/failure) (1,2) 1.3233 2.752 76.56 (1,3) 0.09 2.3 18.91 (2,1) 0.0223 3.32788 149.232 ------------------------- (6,3) 0.1032 8.120 75.339 (6,4) 0.1032 4.2711 41.3869 engineering, technology & applied science research vol. 12, no. 5, 2022, 9078-9086 9083 www.etasr.com ghania et al.: α reliability study of renewable energy resources and their integration with utility grids fig. 5. screenshot of the simulated ieee 40 bus system with pv and wind farms. table iii. system performance reliability indices indices case a case b case c case e case d saifi 0.1335 0.1348 0.1348 0.1361 0.1373 saidi 9.9537 9.9923 9.9923 10.0309 10.069 caidi 74.569 74.144 74.144 73.727 73.317 asai 0.9989 0.9989 0.9989 0.9989 0.9989 asui 0.00114 0.0011 0.0011 0.00115 0.0011 eens 176.322 177.54 177.54 178.753 179.96 aens 8.3963 8.4542 8.4542 8.512 8.5699 loee 294.21 296.15 296.52 297.13 300.75 the two capacitor banks of 4mvar are considered for the different case studies to show the improvement for reliability indices. figure 6 presents the impact of using 8mvar capacitors on the total energy generated but not supplied by the system (eens) for the different case studies. it can be noted that the eens is improved by about 3%. table iii shows that some reliability indices increase and others decrease with more penetration of pv and wind. the increasing/decreasing level depends on the system engineering, technology & applied science research vol. 12, no. 5, 2022, 9078-9086 9084 www.etasr.com ghania et al.: α reliability study of renewable energy resources and their integration with utility grids configuration and the index definition. for example, the caidi is decreased and this decrease is considered as an improvement based on its meaning and the system's performance is consistent with [35]. figure 7 presents the impact of using 8mvar capacitors on the aens for the different case studies. it can be noted that the aens improved when using the pv and wind systems by about 7%. figure 8 presents the impact of using 8mvar capacitors on loee for the different case studies. it can be noted that, loee is improved by using the pv and wind systems by about 8%. fig. 6. impact of the compensating capacitor on the eens for different case studies. fig. 7. impact of the compensating capacitor on aens for different case studies. fig. 8. impact of the compensating capacitor on the loee for different case studies. to verify and validate the obtained simulated results of the proposed model, they will be compared with the results of similar models found in literature. the reliability and its indices sensitivity analysis has been conducted for ieee 94 – bus and ieee 69– bus with two different techniques [32, 34]. the fault index matrix (fim) technique was implemented in [33], and gaussian distribution and fuzzy technique was used in [34]. eens and saidi reliability indices are shown in table iv for the proposed model and the two studied cases of the literature [33, 34]. the simulated results of the proposed method show reasonable consistency with the two other techniques with minor differences. the differences are less than 10% and mainly come due two the differences in the configuration and the loading conditions. table iv. system performance reliability indices reliability indices proposed model fim [33] fuzzy [34] saidi 10.0309 11.2 11.5 eens 178.753 181.1 187.8 v. conclusions the different reliability indices of the electric power distribution system of ieee 40 bus integrated with large-scale pv and wind renewable energy source systems are elaborated with the use of the etap software. the integration process is simulated for the ieee 40 bus grid with two renewable energy sources consisting of 5 sub-farms of 300mw each. the total capacities of pv and wind systems are 1500mw each. the power distribution system of ieee 40 bus is sectionalized using the zone branch methodology that divides the power system network into several sections (protected zones) in order to calculate the different reliability parameters for the different zones including the new connected pv and wind systems. the reliability indices were evaluated for different case study scenarios. the impact of penetrating pv and wind systems on the reliability indices is demonstrated in this study. furthermore, the impact of connecting the compensating capacitor banks of 2×4mvar on the most important reliability indices (eens, aens, and loee) has been investigated. the reliability indices can be improved by about 8% for integrating pv and wind systems. according to the obtained results, the integration of pv and wind systems into the electric power distribution systems improves their reliability indices. the obtained results have very good consistency and compliance with other research studies and with the standards related to the renewable energy sources. this research can be a pre-design powerful tool for system designers and utility engineers to avoid any maloperation or power discontinuity problems. acknowledgement this work was funded by the university of jeddah, jeddah, saudi arabia, under grant no. 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[35] m. z. kamaruzaman, n. i. a. wahab, and m. n. m. nasir, "reliability assessment of power system with renewable source using etap," in international conference on system modeling & advancement in research trends, moradabad, india, nov. 2018, pp. 236–242, https://doi.org/10.1109/sysmart.2018.8746980. engineering, technology & applied science research vol. 12, no. 5, 2022, 9078-9086 9086 www.etasr.com ghania et al.: α reliability study of renewable energy resources and their integration with utility grids author profiles samy m. ghania was born in egypt, in 1971. he received the b.sc., m.sc., and ph.d. degrees in electrical engineering from the faculty of engineering, benha university, cairo, egypt, in 1995, 2001, and 2005 respectively. in july 2006, he joined the university of waterloo, waterloo, on, canada, as a postdoctoral fellow. he is currently working as a professor of electrical engineering at the university of jeddah, saudi arabia. he has published several papers in international journals and conferences in electrical machines, drives, interference, and electromagnetic simulation, and effects on the human body. he has carried several projects on electrical machine control using micro-controllers, dsp, programmable logic control, and renewable energy resources. his areas of interest include modeling and simulation of electrical machines, drives for electrical vehicles, and its control systems. khaled r. m. mahmoud, is a professor in the mechanical and materials engineering department, college of engineering, university of jeddah, saudi arabia. he received his ph.d. degree from the heinz nixdorf institute, university of paderborn, paderborn, germany in 2005. he has pioneered research in vehicle dynamics and vehicle braking systems and has published more than 35 research articles. he has reviewed several research papers in isi journals, in fields such as energy conversion and management and vehicle dynamics. his current research is on the dynamics of hybrid vehicle systems and internal combustion engines fueled by alternative fuels. anas m. hashmi was born in saudi arabia. he received the b.eng. degree in electrical and electronic engineering with mathematics, the m.sc. degree in electronic and ultrasonic instrumentation, and the ph.d. degree in electrical and electronics engineering from the university of nottingham, u.k. in 2011, 2012, and 2017 respectively. he was with the optics and photonics group, university of nottingham. since 2014, he has been working with the university of jeddah, saudi arabia and he is promoted as the head of electrical and electronic engineering department. he is currently an assistant professor at the university of jeddah. he has published 8 scientific articles. his research interests include the development of inexpensive differential ultrasonic calorimeter for accurate measurement of heat loss in machinery. he received the best paper award at the 2016 ieee international conference for students on applied engineering (icsae'2016). microsoft word etasr_v12_n3_pp8492-8499 engineering, technology & applied science research vol. 12, no. 3, 2022, 8492-8499 8492 www.etasr.com bouzidi et al.: influence of membrane type on some electrical properties of a single microbial fuel cell influence of membrane type on some electrical properties of a single microbial fuel cell hafsa bouzidi lmpmp and lees laboratories faculty of technology ferhat abbas university setif, algeria hafsabouzidi@yahoo.fr lhadi otmani urmes laboratory campus el maabouda ferhat abbas university setif, algeria elhadi_otmani@yahoo.fr rachida doufnoune urmes laboratory campus el maabouda ferhat abbas university setif, algeria doufnoune@yahoo.fr larbi zerroual lmpmp laboratory faculty of technology ferhat abbas university setif, algeria zerroual@yahoo.fr djafer benachour lmpmp laboratory faculty of technology ferhat abbas university setif, algeria bendjafer@univ-setif.dz received: 8 february 2022 | revised: 27 february 2022 | accepted: 14 march 2022 abstract-the effects of different parameters on the electric output of air-cathode microbial fuel cells were investigated in this work. the single microbial fuel cell was equipped by modifying proton exchange membranes (pem). two membrane types were prepared: first by using the combination of poly vinyl alcohol (pva) with polystyrene sulfonate (pssna), while the second membrane was elaborated by mixing poly vinyl chloride (pvc) with methyl tri-octyl ammonium (mtoa) chloride. the pems were incorporated into the air-cathode to form a membrane electrode assembly (mea) to promote electricity generation. pva/pssna and pvc-mtoa membranes were synthesized by solution casting method. fourier transform infrared spectroscopy (ftir), ultraviolet (uv) visible spectroscopy, scanning electronique microscope (sem), differential scanning calorimetry (dsc), and water contact angle (ca) were used as characterization techniques to explore the membrane structure and properties. the performance and the electric capacity of the microbial fuel cell in real time were operated using an external resistance of 5kω. impedance and resistance capacity were determined using the polarization method. it was found that the internal resistance of the pva/pssna and pvc-mtoa membranes were 50 and 350ω respectively. the voltage values at open circuit of the cells using pva/pssna and pvc-mtoa membranes were 600mv and 150mv respectively. the values of power, current, and power density, are quite interesting. cells with pva/pssna and pvc-mtoa membranes gave values of 18.24 and 9.64mw.cm -2 respectively. keywords-pva/pssna; pvc-mtoa; membrane; single microbial fuel cells; renewable energy; wastewater i. introduction human sustainability is determined by deriving factors, among which energy is the most important. during the last decade, fossil fuel commodity has seen a sharp decline because of the harmful effects of fossil fuels on the environment [1]. the problem of pollution pushes the researchers to look for new sources of energy, such as renewable energy [2]. promising results were acquired by different renewable energy sources, such as solar, wind, tidal, geothermal, and biomass. in the last few years, the research into alternative sources of renewable energy has increased exponentially [3]. however, a new source of energy which is sustainable and environmentally stable was needed [4]. wastewater treatment is a new energy technology and a bio-energy source [5-6]. the bio-energy process [7] involves the use of microbes to produce electricity. this technology is considered to have tremendous potential [8]. the bacteria available in a bio-convertible substrate were directly used as a catalyst to convert chemical energy to electricity in [9]. it is known that bacteria can generate electricity from organic waste sources [10]. a renewable process was used to generate energy in the form of electricity, in consistent fresh, resourceful manners, through the use of the microbial fuel cells (mfcs) [11]. it was found that in mfcs, energy can be recovered from wastewater treatment, in fact from a wide range of organic compounds present in wastewater [12]. the mfcs consist of two compartments: anodic and cathodic. mfcs are composed of one anodic chamber filled with wastewater and an air cathodic chamber. the anode compartment includes domestic or industrial wastewater with sludge, and the cathode compartment is either used to remove heavy metals or for denitrification [9]. many mfcs play an important role in producing bio-energy, such as value-added chemicals, via an easy operation, and at low maintenance cost [13]. the removal of organic constituents of wastewater leads corresponding author: djafer benachour engineering, technology & applied science research vol. 12, no. 3, 2022, 8492-8499 8493 www.etasr.com bouzidi et al.: influence of membrane type on some electrical properties of a single microbial fuel cell to the electricity production from the chemical energy stored in chemical bonds [12]. three mechanisms to generate bioelectricity have been proposed: direct electron transport via membrane bound proteins (e.g. cytochromes), conductive nano-wires, and indirect shuttles via redox mediators (e.g. riboflavin) [14]. with regard to the source abundance, high efficiency, and convenient transportation, the most promising energy conversion devices are proton exchange membranes (pems) [15]. pems are the most important factor to transport protons, and nafion membrane has been widely used due to its high conductivity. recently, numerous studies have been conducted to find alternative membranes [16]. desirable pems require excellent characteristics, the most important of which is high and stable proton conductivity [17]. an electron flow through the electrodes producing bioelectricity, has been demonstrated experimentally by the bacterial degradation in wastewater [18]. microbial electricity production offers the possibility of obtaining electrical current from a wide range of soluble or dissolved organic wastes such as artificial, real, and biomass lignocellulosic wastewater [19]. the most important advantages of mfc are wastewater treatment, application of micro-organisms, energy production, and inexpensive biocatalysts [12]. since the production of electricity in mfcs is related to wastewater treatment, it is considered as one of the most attractive energy sources [20]. mfcs are an emerging technology for simultaneous treatment of wastewater and energy recovery [21], following a similar concept to traditional fuel cells [3]. the process of mfcs was based on the generation of bioelectricity, and this method has been leaded by the bio-potential developed between the bacterial metabolic activity and the electron acceptor conditions, separated by a membrane [22]. the use of mfcs is one potential alternative energy source [3]. the reduction of electron acceptors, with electricity, was harvested in a circuit, by the anode which collected organics oxidized by the electrogenic microorganisms and combined with protons to cathode. the electricity generation and stability of mfcs are radically affected by the microbial communities on the electrode surface [23]. mfc operation includes several steps: first, the carbon dioxide is digested from bacteria and the released electrons are transferred to the anode. then, electrical energy is generated via the travel of electrons from the anode in an external circuit. finally, the electrons are taken up by oxygen and hydrogen ions to form water while they are traveling to the cathode to complete the circuit [24]. recently, a suitable secondary stage process to fully recover the energy embedded in the metabolites and improve treatment efficiency, has been proven using mfc technology [25]. in mfc systems, the produced electrons are not directly transferred from bacteria to their electrons acceptor. the transport process is realized over other factors: cathode, anode, resistance, and membrane which transfer protons to the cathode [26-27]. when the mfcs are operated independently of an electrical device and as an integrated part of an electrical grid that controls the fuel cell output, an external resistance is used to dissipate the electrical energy [20]. the separator is an important factor that affects the design of mfcs [28], which is used to separate anode and cathode. the cation exchange membrane (cem) and pem, are investigated as the most important effect in the system: a membrane permits the proton passage and not the substrate, using an organic medium [29-34]. recently, authors in [9] proposed that the factors which can lower the internal resistance in the mfc, should be optimized to obtain the highest values of voltage density and power. most works cited in the literature deal with the use of fuel cells in electrochemical application (batteries), at an industrial scale. in the present work, a new strategy in mfc (single chamber) has been tested using two different pems. combined with a resistance, this separator was based on the order: pva with pssna, and pvc, while the mtoa membrane was synthesized and characterized. the medium contained different organic products and was used as an energy source for the bacteria. lead dioxide (pbo2) was used as the cathode material. ii. materials and methods pva with a molecular weight of 130,000 (99% hydrolyzed powder), pssna powder with a molecular weight of 70,000, glutaraldehyde (gla), pvc powder with a molecular weight of 93.92g/mol, mtoa as ionic liquid with a molecular weight of 404.16g/mol, and tetrahydrofuran (thf) with a molecular weight of 72.10g/mol, which was used as a dissolving agent, were all provided by sigma-aldrich and were used as such without any further purification. figure 1 shows the diagram of the experimental procedure. fig. 1. experimental diagram. a. membrane preparation 1) pva-pssna film preparation as a first step, 1.5g pva were dissolved in deionized water and the obtained solution was stirred at 80°c until the pva particles were completely dissolved. at the same time, the pssna solution was prepared by dissolving 0.6g in deionized water. the obtained mixture was further stirred at room temperature until the stabilization of the solution. as a second step, gla was poured dropwise to the solution and then few drops of hcl solution were added. it is worth noting that a simple pouring of the mixture into a glass sheet with a uniform surface and similar thickness was realized. finally, the thin film was dried at room temperature for a day. engineering, technology & applied science research vol. 12, no. 3, 2022, 8492-8499 8494 www.etasr.com bouzidi et al.: influence of membrane type on some electrical properties of a single microbial fuel cell 2) pvc-mtoa film preparation pvc powder (0.09g) and mtoa (0.21g) were dissolved in thf and stirred until complete dissolution. the obtained viscous solution was poured in a plastic mold (diameter = 2.8cm). after the evaporation of the solvent, the thin film was dried at room temperature. 3) microbial fuel cell configuration and media composition the anodic single chamber is made of glass material with a volume of 250ml (schott duran). the chamber was filled with 200ml of wastewater taken from a water purification station (national office of disinfection-sfiha, setif, algeria), with total sprouts, total coliforms, and fecal coliform. the electrode used in this experiment was a carbon fiber fixed in the cap of the chamber. the cathode is made of 0.6g of pbo2 powder dissolved in 0.5ml ethanol, spread on a piece of stainless steel, left to dry in open air. the voltage open circuit (voc) was measured with a digital multi-meter. the real time voltage values were recorded with an arduino program. the carbon fiber rod in the anodic chamber and the cathode were connected into a recorder by the arduino uno r3 (open-source electronics prototyping platform, italy) and the data were registered on a computer. the medium solution was prepared using different components: nh4cl (1.50gl -1 ), kcl (0.1gl -1 ), na2hpo4 (0.6gl -1 ), acetate (1.36gl -1 ), nahco3 (2.5gl -1 ), cacl2 (0.1gl -1 ), and yeast extract (0.05gl -1 ). these components were dissolved in distilled water and the anodic chamber was filled every week. b. membrane characterization the structure of the thin films was characterized by ftir spectroscopy, the analysis was recorded on a jasco-ir spectrometer. the signal scans of 32 were realized in the 4000400cm -1 wavenumber range at a resolution of 4cm -1 . uv– visible spectroscopy was used to characterize the structure of the thin films; the scan was carried out using a shimadzu uv2401pc uv–visible spectrophotometer in the range of 200– 800nm. the optical absorbance of the obtained membranes was recorded and the energy band gap was evaluated from the uv spectrum. the endothermic and exothermic phenomena change of the physical state of the thin films were determined using a diffraction scanning calorimetric (dsc) ( jupiter ,sta 449 f3), the scan was realized in the temperature range of 35-350°c, with a rate of 10°c/min in open air. the variation in weight loss of the membranes as a function of the temperature was examined by tga analysis, the thermal proprieties were measured using a thermogravimetric analysis (tga perkinelmer) apparatus in which the temperature range was set from 25 to 500°c, with a heating rate of 10°c/min. the surface morphology of the membranes was observed by sem (jeol, jsm 6510 lv) and the analysis was operated at an acceleration voltage of 30kv. water ca measurement was used to determine the hydrophilicity or hydrophobicity character of the prepared membranes. this was done using a ram e-hart ca goniometer/tensiometer. the surface examination was operated at room temperature and with relative humidity of 30 ± 5%. the swelling rate measurements (η) were made through membrane weight, the measurement was based on the calculation of the membrane mass in dry and hydrated state. the swelling rate is expressed as a percentage: � = �������� � ∗ 100 (1) where η is the swelling rate (%), and mf and mi are the final and initial weight of the membrane (g) respectively. c. mfc operation and electrochemical characterization the internal resistance of the membranes was measured with the impedance spectroscopy method. the frequency response analysis (fra) in the beginning and the end (cell discharge) was inspected using a volta-lab instrument pgstat302n, metrohm autolab b.v. the frequencies of the operation were oscillated from 1mhz to 0.01hz with 0.05v amplitude perturbation in 5% of nacl solution. it should be noted that the different measurement steps of impedance and real time operations were operated in nacl and bacterial medium solutions respectively. consequently, the same conditions of mfcs exploited in the impedance measurement were applied. however, nyquist plot was used to determine the internal resistance of the system after applying the electrochemical impedance spectroscopy technique. equation (2) gives the relation between the impedance system and the ionic conductivity: � = �.� (2) where σ is the ionic conductivity (s/cm -1 ), l the thickness (cm), a the cross-section area (cm 2 ) and r the resistance (ω). a nyquist plot was used to determine the internal resistance of the system after applying the electrochemical impedance spectroscopy technique. the membranes were tested in mfcs using wastewater as substrate. a fixed resistance rext of 5kω was used and the result was recorded. a pem was used in mfcs. the charge-discharge cycle with time gives the voltage as a function of current (current density) (v vs. i), and the power (power density) as a function of current density (p vs. i). the power curve was used to determine the internal resistance. it started at open circuit voltage (ocv), the slope is equal to the internal resistance in the case of a linear polarization curve. ����� = ��� − ����� (3) where ecell, i and rint are the voltage of the cell, current density, and internal resistance respectively. iii. results and discussion a. spectroscopic characterization and morphological studies 1) ftir characterization pva-pssna was obtained from the reaction of pvapssna and gla. the ftir spectra confirmed the chemical structure. figure 2 shows the ftir spectra of pva-pssna. the very wide band that appears at 3356cm -1 is related to the stretching vibration of hydroxyl groups of pva chains. the 2931cm -1 band is attributed to alkanes, and ester bands are registered at 1715cm -1 and 1435cm -1 . the symmetric and asymmetric stretching vibrations due to the sulfonic group are located at 1125cm -1 and 1240cm -1 respectively. the broad band at 1125cm -1 indicates the linking of sulfonic anion with phenyl ring. additionally, the aromatic functional groups of pssna engineering, technology & applied science research vol. 12, no. 3, 2022, 8492-8499 8495 www.etasr.com bouzidi et al.: influence of membrane type on some electrical properties of a single microbial fuel cell chain are located at 840cm -1 . in the ftir spectra of pvcmtoa membrane, the band located at 3673cm -1 is associated to a strong free alcohol related to a bond interaction between pvc and mtoa in the presence of the thf as solvent agent. the located bands at 3000-3100cm -1 present an amine deformation of the mtoa. a strong alkane c-h band is situated at 2896cm -1 related to the pvc. the ammonium groups are located at 2400cm -1 . the alkene groups are observed at 2109cm -1 , the band recorded at 965cm -1 confirmed the existence of the alkene. the appearance of a broad absorption band at 1628cm -1 was related to the linked n-h, the bands at 1460cm -1 and 1248 cm -1 indicated the c-h and c-c bonds respectively, an alcohol group was located at 1378cm -1 , and chloroalkane c-cl was located at 723cm -1 [35-36]. fig. 2. ftir spectra of (a) pssna/pva membrane and (b) pvc/mtoa. 2) dsc characterization the dsc thermograms are illustrated on figure 3. fig. 3. dsc curve of (a) the blend pva/pssna, (b) the blend pvc/mtoa. as mentioned above, the mixture was stable and has good miscibility between polymers, thus no visible phase separation between pva and pssna was detected. this confirms the morphology results obtained by sem. in addition, the thermograms revealed a single glass transition temperature (tg) of the blend in the range of 60 to 90°c, which indicates the total miscibility of the polymers. in the dsc curve obtained on pvc/mtoa membrane, a sudden change in heat transfer at 165.5°c is noticed. this may be explained by the irregularly shaped samples, the ionic liquid being more flexible than the pvc, results in a flexible membrane compared to the pva/pssna membrane. the second endothermic peak at 221°c related to the crystalli-zation temperature (tc) corresponds to the side reaction and decomposition of the membrane while the third peak at 245°c corresponds to the melting point temperature. at high temperature all the interactions between the chains are broken. 3) sem characterization sem images of the membranes are presented in figure 4. a micrography of the mixture formed by blending pva, pssna, gla, is also reported in the same figure. (a) (b) (c) (d) fig. 4. (a) sem of the pva/pssna, (b) water ca of pva/pssna, (c) sem of the pvc/mtoa, and (d) water ca of pvc/mtoa. as can be seen in figure 4, no phase separation was observed for the prepared membranes. the pva/pssna presents a good combination between the two polymers and homogenous surface. pvc/mtoa membrane exhibits a smooth and homogeneous nonporous surface too. the obtained membranes are transparent and have good clarity, implying good compatibility between the ionic liquid and the polymer. this leads to more contact area and more compatibility to form a bio-film (in which the ionic charge is produced because it is formed with the bacteria found in the medium). 4) contact angle and swelling rate characterization the hydrophilicity of the membranes was evaluated using the water ca technique. it can be noted that for pva/pssna membrane the values varied from 35.6° to 36.9°, while for pvc/mtoa membrane, the contact angle values varied from 12.3° to 12.7°. the polymers containing sulfonic acid groups engineering, technology & applied science research vol. 12, no. 3, 2022, 8492-8499 8496 www.etasr.com bouzidi et al.: influence of membrane type on some electrical properties of a single microbial fuel cell transport protons via the vehicular mechanism, relying on the presence of water pva/pssna membrane. the water adsorption of the pvc/mtoa membrane is attributed to the ionic liquid group. table i summarizes the ca and the swelling rate values of pva/pssna and pvc/mtoa membranes, it confirms the results observed in figure 4. table i. contact angle and swelling rate values of pva/pssna and pvc/mtoa membranes membrane contact angle (°) swelling rate (%) pva/pssna 35.6-36.9 78.38 pvc/mtoa 12.3-12.7 86.07 the water absorption of the two membranes was studied by immersing the membranes in deionized solution. the weight of the membranes was measured before and after immersion. the membranes show that the water uptake was elevated due to water molecule mobility. the elevated water-uptake improves the swelling rate of pva/pssna (η = 78%) and pvc/mtoa (η = 86%) membranes. the problem encountered is that the membranes never return to their initial states after being immersed in water. consequently, the membranes have a good water uptake, and this will increase the proton conductivity. 5) tga characterization the thermal stability of pva/pssna and pvc/mtoa membranes under nitrogen atmosphere, was evaluated by thermogravimetric analysis. the tga thermograms are presented in figure 5. fig. 5. tga curves of (a) the blend pva/pssna, (b) the blend pvc/mtoa. the thermogram shows a typical three-step degradation of pva/pssna. a small weight loss was observed at about 61°c due to the evaporation of physisorbed water. the second weight loss, which occurred between 217 and 462°c, corresponds to the degradation of pva/pssna. the third weight loss, above 465°c, was due to the decomposition of the backbones of the materials. the curves showed a typical twostep degradation pattern of the pvc/mtoa membrane. no obvious weight loss was observed until 250°c. the weight loss recorded between 253 and 415°c corresponds to the degradation of pvc, whereas the second weight loss in the range 415-495°c is due to the decomposition of mtoa. 6) uv characterization the uv spectra of pva/pssna and pvc/mtoa are presented in figure 6. the main peaks are located at 227193.5nm and are attributed to pva/pssna and pvc/mtoa respectively, which indicates a significant interaction between polymers, while no phase separation was noticed. fig. 6. uv visible spectra of (a) pssna/pva and (b) pvc/mtoa membranes. b. electrochemical monitoring figure 7 shows the nyquist plots for the supported membranes, based on pva/pssna and pvc/mtoa. the values of the internal resistance and the ionic conductivity are given in table ii. the internal resistance values are 54.12 and 350ω for pva/pssna and pvc/mtoa respectively. these values confirm the high conductivity of pva/pssna membrane. table ii. main characteristics of the membranes membrane thickness (µm) area (cm 2 ) internal resistance (ω) ionic conductivity (s cm -1 ) pva/pssna 301 0.785 54.12 1.02*10 -4 pvc/mtoa 230 0.785 350 8.37*10 -6 after the discharge of the cells, it was noticed that the internal resistance was approximately 62ω for the pva/pssna membrane. almost no difference in the internal resistance value before and after the test was detected, while in the case of pvc/mtoa membrane, the internal resistance significantly increased at the end of the test (1200ω). this difference can be related to the membrane aging. the ionic conductivities of the pva/pssna and pvc/mtoa membranes are respectively 1.02×10 -4 and 8.37×10 -6 s/cm. pva/pssna presents higher proton conductivity compared to pvc/mtoa (see table ii). engineering, technology & applied science research vol. 12, no. 3, 2022, 8492-8499 8497 www.etasr.com bouzidi et al.: influence of membrane type on some electrical properties of a single microbial fuel cell (a) (b) (c) (d) fig. 7. frequency response analysis of membranes based on (a,c) pva/pssna and (b,d) pvc/mtoa membranes. table iii. electrical parameters of the membranes external resistance (kω) time (weeks) ocv (mv) maximum power (mw.cm -2 ) maximum voltage (mv) maximum current density (ma.cm -2 ) pva/ pssna 5 1 604 18.24 386.02 0.14 2 377 9.05 278.49 0.09 3 341 6.25 239.78 0.09 4 342 6.98 239.78 0.09 5 300 4.98 205.38 0.08 pvc/ mtoa 5 1 156 1.50 422.58 0.04 2 156 1.55 450.54 0.04 3 198 2.50 212.9 0.05 4 389 9.64 212.9 0.10 5 292 5.26 119.75 0.07 high electron transfer from the anodic chamber to the cathode leads to high current. the anode potential should be low and the cathode potential should be high in order to have a maximum fuel cell performance. the metabolic activities of the biocatalyst and the respective energy dissipation can affect the anode potential. in a biofuel cell, bacteria drain off their electrons to the anode. figure 8 shows the polarization curve of mfcs filled with wastewater. the two curves describe the voltage and power as functions of the current density to identify the maximum output power density of mfcs. the obtained open circuit voltage was 604mv for the pva/pssna and 156mv for pvc/mtoa (table iii). figure 9 shows the polarization curve of mfcs filled with medium. the power and the current density increased after four weeks in the case of the pvc/mtoa membrane but the voltage decreased from the first week. the maximal values were obtained in the second week of using the medium and were 9.64mw/cm 2 power and 0.10ma/cm 2 current density. (a) (b) (c) (d) fig. 8. polarization curves of the mfc using different membranes (in wastewater). fig. 9. polarization curves of the mfc using different membranes (using the medium). regarding the pva/pssna membrane, the maximal values were observed during the first week and they were about 18.24mw/cm 2 power and 0.14ma/cm 2 current density. the cell decreased after that and this decrease of power generation can be related to the structure and to the effect of the internal resistance of the two membranes: the pvc/mtoa membrane is more flexible (from the mechanical point of view) and more 48 50 52 54 56 58 60 0 10 20 30 40 50 z im g ( ωω ωω ) z real (ωωωω) (a) 50 55 60 65 70 0 1 2 3 4 5 6 7 8 (b) z im g ( ωω ωω ) z real (ωωωω) 300 350 400 450 500 0 200 400 600 800 (c) z im g ( ωω ωω ) z real (ωωωω) 0 200 400 600 800 0 200 400 600 800 1000 (d) z im g ( ωω ωω ) z real (ωωωω) -0,02 -0,01 0,00 0,01 150 165 180 195 210 225 240 255 (b) current density (ma.cm -2 ) v o lt a g e ( m v ) -3 -2 -1 0 1 2 p o w er ( m w .c m -2 ) 0,00 0,02 0,04 0,06 0,08 0,10 0 50 100 150 200 250 300 350 400 450 (c) current density (ma.cm -2 ) v o lt a g e ( m v ) 0 2 4 6 8 10 p o w e r (m w .c m -2 ) 0,00 0,02 0,04 0 50 100 150 200 (d) current density (ma.cm -2 ) v o lt a g e ( m v ) 0,0 0,5 1,0 1,5 2,0 2,5 p o w e r ( m w .c m -2 ) 0,06 0,07 0,08 0 50 100 150 (a) current density (ma.cm -2 ) v o lt a g e ( m v ) 1 2 3 4 5 6 7 8 p o w er ( m w .c m -2 ) 0,00 0,02 0,04 0,06 0,08 0,10 0 100 200 300 400 500 (b) current density (ma.cm -2 ) v o lt a g e ( m v ) 0 2 4 6 8 10 p o w e r ( m w .c m -2 ) 0,07 0,08 0 50 100 150 (c) current density (ma.cm -2 ) v o lt a g e ( m v ) 0 1 2 3 4 5 6 7 p o w e r ( m w .m -2 ) 0,00 0,02 0,04 0,06 0,08 0,10 0 100 200 300 400 500 (b) current density (ma.cm -2 ) v o lt a g e ( m v ) 0 2 4 6 8 10 p o w e r ( m w .c m -2 ) 0,5 0,6 0,7 0,8 0 40 80 120 160 (e) current density (ma.cm -2 ) v o lt a g e ( m v ) 0 10 20 30 40 50 60 p o w e r (m w .c m -2 ) 0,040 0,048 0,056 0,064 0,072 0,080 0 20 40 60 80 100 120 140 (f) current density (ma.cm -2 ) v o lt a g e ( m v ) 0 1 2 3 4 5 6 7 p o w er ( m w .c m -2 ) engineering, technology & applied science research vol. 12, no. 3, 2022, 8492-8499 8498 www.etasr.com bouzidi et al.: influence of membrane type on some electrical properties of a single microbial fuel cell resistant (from the electrical point of view) than the pva/pssna membrane. this difference will impact the biofilm formed, while the pva/pssna will be more effective in the electricity generation. accordingly, the electron transfer from the anodic chamber to the cathode decreases according to the bio-film forming the electrical resistances of the electrodes, the membrane internal resistance and electrolyte, the power drops due to the increasing ohmic losses, and the electrode overpotentials to the point where no more power is produced. [37-39]. in a previous similar work [21], the authors used a pvcbased membrane, however the conductivity obtained was not as good as the one obtained in this study for the pvc/mtoa membrane. in addition, we used the ca parameter to evaluate the membrane surface capacity for matter adsorption, which, to the best of our knowledge, is reported for the first time. iv. conclusion in this paper, mfcs were used to directly generate electricity from the oxidation of dissolved organic matter. however, the optimization of mfcs requires more knowledge about the factors that can increase the power output such as the capacity of proton exchange system which can affect the system characteristics, particularly the internal resistance and the external resistance. the power (p) was calculated according to p = iv (i = v/r), where i (a) is the current, v (v) is the voltage, and r (ω) is the resistance. the prepared assisted cross-linked pva-pssna membrane has a good ionic conductivity and a good miscibility and thermal stability. in addition, it exhibits high proton exchange capacity and lower internal resistance, compared to the pvc/mtoa membrane which has a high internal resistance and a long term to discharge. it has also good miscibility, a hydrophilic character, and a good thermal stability. authorship contribution statement the results presented here are part of a ph.d. thesis work. h. bouzidi, as a ph.d. student, conducted most of the experimental and characterization work. l. otmani and r. doufnoune prepared and provided the pva-pssna membrane, l. zerroual (thesis co-advisor) helped in the electrochemical experimental work, while d. benachour (thesis advisor) did the editing. references [1] e. ogungbemi et al., "fuel cell membranes – pros and cons," energy, vol. 172, pp. 155–172, apr. 2019, https://doi.org/10.1016/j.energy. 2019.01.034. 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[39] m. hafani, m. a. chemrak, m. djennad, and d. benachour, "formulation and characterization of a new pet-based membrane for methane gas dehydration," polymer-plastics technology and materials, vol. 60, no. 15, pp. 1605–1619, oct. 2021, https://doi.org/ 10.1080/25740881.2021.1912091. engineering, technology & applied science research vol. 7, no. 5, 2017, 1953-1961 1953 www.etasr.com tabrez et al.: a novel three phase to seven phase conversion technique … a novel three phase to seven phase conversion technique using transformer winding connections m. tabrez electrical engineering dept. indian institute of technology dhanbad, india mdtabrez2008@gmail.com p. k. sadhu electrical engineering dept. indian institute of technology dhanbad, india pradip_sadhu@yahoo.co.in a. iqbal electrical engineering dept. qatar university doha, qatar atif.iqbal@qu.edu.qa abstract-this paper proposes a novel multiphase transformer connection scheme which converts three phase balanced ac input to seven phase balanced ac output. generalized theory to convert a three phase utility supply into any number of phases is presented. based on the proposed generalized principle, a three phase to seven phase power converting transformer design is presented with connection scheme, analysis and simulation and experimental results of the proposed three phase to seven phase conversion transformer. the proposed transformer in this paper is analyzed and compared with the connection scheme for seven phase available in the literature. the connection scheme is found to have higher power density, lower core area and lower core requirement as compared to the available connection scheme of the same rating. impedance mismatching between different phases of the transformer is observed in the three phase to seven phase transformer available in the literature. as this mismatching introduces error in study of per phase equivalent circuit diagrams as well as imbalance in voltage and currents. the present design also addresses the impedance mismatching issue and reduces mismatching in the proposed transformer design. a prototype of the proposed system is developed and waveforms are presented. the proposed design is verified using simulation and validated using experimental approach. keywords-multiphase; seven-phase; transformer connections; high phase order i. introduction multiphase systems are known for reliability, fault tolerance and high power carrying capabilities [1]. there are papers about this application reagarding power generation [2, 3], transmission [4, 5] and utilization [6, 7]. the numerous advantages offered by multiphase systems have attracted researchers’ interest that include higher machine torque density, reduced torque ripples, reduced harmonic currents, better transient and steady-state performance, and more robust control of multiphase based drives. multi-phase ac power is generated from three phase power by two methods. one is by converting three phase ac to a dc power and then converting it back to multiphase ac (i.e. ac-dc-ac). the other one is through multiphase power converting transformers. the second method utilizes transformer winding in a special connection and turns ratios while the first method needs rectifiers and inverters. multiphase is found to produce less ripple with a higher frequency of ripple in an ac-dc rectifier system. thus, 6and 12-phase transformers are designed to feed a multi-pulse rectifier system. recently, 24-phase and 36-phase transformer systems have been proposed for supplying a multi-pulse rectifier system [8-11]. the reason of 6-, 12-, or 24-phase system is that these numbers are multiples of three and designing this type of system is simple and straight forward. as far as odd numbers of phases are concerned, limited literature sources are found. prototypes designed and tested for a three to five phase and three to seven phase power converting transformer are reported in [12-14]. one of which is a scott based three to five phase converting power transformer design [14]. the approach of [14] is extended in this paper for three phase to seven phase transformer. the block diagram of the proposed system is shown in figure 1. the fixed conventional voltage and fixed frequency available three phase ac supply can be transformed into a fixed voltage and fixed frequency seven-phase ac supply. the output, however, may be made variable by inserting the autotransformer either at input or output side. depending on the requirement the input and output can be arranged in the following manner: fig. 1. block diagram of the proposed system 1) input scott, output star 2) input scott, output polygon the primary windings are connected in scott connection to produce a balanced two phase flux in the core of the transformer while secondary side connection is discussed in the following sections iii, a “r”, “y” and “b” represents three phases of input power while a, b1, c,…..g , represents seven phase output voltages with respect to star point. in section ii, phasor approach is presented to explain principle of phase engineering, technology & applied science research vol. 7, no. 5, 2017, 1953-1961 1954 www.etasr.com tabrez et al.: a novel three phase to seven phase conversion technique … conversion of a general three to n phase and derived turns ratios and connection scheme for three to seven phase power conversion from the same theory as given in section i. winding arrangements are presented in section iii. simulation and experimental results, comparison, scope of research and conclusions are presented in sections iv, v and vi, respectively. ii. method and principles of phase conversion a general theory of phase transformation using transformers to convert from m to n number of phases on a klimbed transformer is presented in [15-17]. in this paper the theory of phase transformation is presented by graphical approach using vectors and phasor diagrams of different phases. this approach findings are same the same with that of [15]. it is well known that any odd number of phases m can be converted to (m − 1)/2 decoupled (α, β) planes and one zero sequence, so for three phase balanced phase one can convert it to one decoupled (α, β) plane or in other words, in balanced two phase ac supply. scott connection is the method to implement it. figure 2 shows the phasor diagrams of input and output of the proposed transformer. figure 2(a) is the phasor diagram of the input phase based on scott connection. referring to figure 2, assume the number of turns in the two cores of primary be n1 and n2 in winding ro and yb. and rms voltage of each phase be v. since volts per turn is the same for all three windings (ro, yo and bo) hence, 1 2 2 2 2 r o yo b ov v v n nn               applying geometrical relation to the phasor diagram of figure 2(a), resulting to: 1 2 2 3 2 2 v v v n nn               (1) 2 1 1 1 2 3 n n (2) since winding yb is divided into two parts. hence from (1) and (2), the no of turns for each phase of the input would be in ratios of1:1 / 3 :1 / 3 as tabulated in table i. table i. turns ratios of primary windings windings ratio (% of primary) ro 100% yo 57.78% bo 57.78% referring to figure 3, assume voltage vα and vβ be the outcome of three phase to two phase conversion with a primary scott connection. vα and vβ are voltage induced in winding “ro” and “yb” and have equal rms value as that of supply phase but they are 90 degrees phase apart. the number of turns in winding a1a2 is kept equal to “ro” so voltage induced va in winding a1a2 is the reference voltage and number of turns will be reference for other windings. in terms of magnitude v1=va=vα. also from phasor vβ=j vα. (a) (b) fig. 2. phasor diagram of (a) input voltage and (b) output voltage of the designed transformer fig. 3. phasor diagram of a two phase to n phase conversion let’s assume a phase conversion of two phase to n-number of phases (figure 3). let vi be the i th phasor of an n phases system at an angle iδ and have magnitude v, and δ=2π/n. its projection along axis α and β would be viα and viβ for i th phase. for phasor of ith phase          cos( ) cos( ) cos( ) i i i i v v i v i v a i (3) similarly,          sin( ) sin( ) sin( ) i i i i v v i v i v a i (4) where: i = 0, 1, 2………. (n-1), viα,-projection of i th phasor along x-axis, viβ-projection of i th phasor along y-axis, aα-turns ratio for ith phase along x-axis or with respect to winding on core 1, aβ-turns ratio for i th phase along y-axis or with respect to winding wound on core 2 which produces a flux 90 degrees out of phase with respect to core 1. hence an n phase transformation from a two phase balanced supply could be achieved by employing two core engineering, technology & applied science research vol. 7, no. 5, 2017, 1953-1961 1955 www.etasr.com tabrez et al.: a novel three phase to seven phase conversion technique … transformer with a pulsating flux of 90 degrees out of phase. for n-number of phases, one can get turns ratios of individual windings by varying i from 0 to n-1 and putting δ=2π/n. hence voltage equation and turns ratios can be written in matrix as shown in equations (5) and (6). in matrix form the voltage relationship can be generalized as: 1 2 1 0 cos( ) sin( ) . . . . . . cos( 1) sin( 1) . . . cos( 1) sin( 1) i n v v v v v i i v n n                                                          (5) whereas turns ratios can be generalized as 1 0 cos( ) sin( ) . . . . cos( 1) sin( 1) . . cos( 1) sin( 1) i i n n                              (6) a. three phase to seven phase conversion the matrix in (5) converts to matrix in (7) for a seven phase output. turns ratios can be tabulated from (7) as shown in table ii. aα and aβ represents the turns ratios of the secondary winding with respect to “ro” and “yb” primary windings respectively. 1 0 cos( ) sin( ) cos(2 ) sin(2 ) cos(3 ) sin(3 ) cos(4 ) sin(4 ) cos(5 ) sin(5 ) cos(6 ) sin(6 ) d f a b c e g v v v v v v v v v                                                               (7) positive sign denotes phase voltage addition and negative sign denotes phase voltage subtraction. hence the instantaneous voltage of each phase are described in (8). figure 4 is the graphical and analytical representation that shows how the voltage of each phase in system is made from two phase voltage induced in the windings of each core. proper selection of polarity and voltage ratio (0.623, 0.7818 in this case) creates the desired magnitude and phase difference. though figure 4 shows the waveform of only one output voltage (phase b1) with respect to the star point. the other six phase voltages are created in the same manner. assuming the 7 phasors of the output are balanced as shown in figure 2(b) and based on star or heptagon connection of secondary windings, one can get one phase voltage and three line voltages namely. these voltages are defined here as:  phase voltage: voltages of each phase with respect to neutral/star point “o”. va, vb,vc, vd, ve, vf, vg.  adjacent line voltage: voltage difference of two phases having a phase difference of 51.42degrees, e.g., vab1, vb1c, vcd,vde, vef, vfg, vga  non-adjacent1 line voltage: voltage difference of two phases having a phase difference of 2×51.42 degrees, e.g., vac, vb1d, vce,vdf, veg, vfa, vgb.  non-adjacent2 line voltage: voltage difference of two phasors having a phase difference of 3×51.42 degrees, e.g., vad, vb1e, vcf,vdg, vea, vfb1, vgc 0 0.005 0.01 0.015 0.02 0.025 0.03 -400 -200 0 200 400 times (sec) v o lt ag es ( v o lt s)  max max0.6234 sin 0.7818 sin 2          bv v t v t fig. 4. waveform of output voltage construction from induced winding voltages.       ( ) 0.6234 sin 0.7818 sinmax max 2 2 sinmax 7 0.2225 sin 0.975 sinmax max 2 4 sinmax 7 0.900 sin 0.4338 sinmax max 2 simax v v sin ta v v t v tb v t v v t v tc v t v v t v td v                                                               6 n 7 0.900 sin 0.4338 sinmax max 2 8 sinmax 7 0.2225 sin 0.975 sinmax max 2 10 sinmax 7 0.6234 sin 0.7818 sinmax max 2 max t v v t v te v t v v t v tf v t v v t v tg v                                                               12 sin 7 t       (8) engineering, technology & applied science research vol. 7, no. 5, 2017, 1953-1961 1956 www.etasr.com tabrez et al.: a novel three phase to seven phase conversion technique … table ii. turns ratios of different windings α axis aα β axis aβ a1a2 1 b1b2 +0.6234 b3b4 +0.7818 c1c2 -0.2225 c3c4 +0.9749 d1d2 -0.9009 d3d4 +0.4338 e1e2 -0.9009 e3e4 -0.4338 f1f2 -0.2225 f3f4 -0.9749 g1g2 +0.6234 g3g4 -0.7818 iii. methodology a. connection scheme two separate cores are used where each core contains the primary and secondary coils with the connection and turns ratios shown in figure 5 and table iii. primary terminals are connected via scott connection while the 13 secondary terminals are connected in such a way that the voltages are added or subtracted as in table iv resulting in a seven phase output. the connection scheme of the secondary windings to obtain an output is illustrated in figure 3 and the corresponding phasor diagram is illustrated in figure 2(b). the generation of output phase voltages with requisite phase angles of 51.42 degrees between phases is obtained using appropriate turns ratios, and the governing phasor equations are illustrated in (8). the turns ratios are different in each phase. the choice of turns ratio is the key in creating the required phase displacement in the output phase voltages. the input phases are designated with letters “r” “y”, and “b” and the output are designated as “a”, “b1”, “c”, “d”, “e” “f” and “g” as illustrated in figure 1. the output phase “a” is along the input phase “r”. the output phase “b1” results from the phasor sum of winding voltage “b1b2” and “b3b4”, the output phase “c” is obtained by the phasor sum of winding voltages “c1c2” and “c3c4”. the output phase “d” is obtained by the phasor addition of winding voltages “d1d2” and “d3d4”and the output phase “e” results from the phasor sum of the winding voltages “e1e2” and “e3e4” and so on.                  1 2 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 an a a b n b b b b cn c c c c dn d d d d en e e e e fn f f f f gn g g g g v v v v v v v v v v v v v v v v v v v v in this way, seven phases are obtained. the transformation from three to seven and vice-versa is further obtained by using the relation given in (8). figure 5 shows a labeled diagram of proposed transformer. b. calculation of turns ratios referring to figure 2(a), let the number of turns in the two cores of the primary be n1 and n2 in winding ro and yb and the rms voltage be v. volts per turn is the same on all three windings, hence 2 1 1 2 3( ) 12 and where 2 3 nv v rn r n n    the number of turns would be in the ratios of 1: :r r for the primary winding to produce 2-phase flux. two separate iron cores are designed, one of them carrying one primary (ro) and seven secondary coils, while second core carrying two primary coils connected at point “o” and of equal turns ratios but of .....r r times that of winding “ro” and six secondary coils. the 14 secondary terminals are connected either in star or heptagon arrangement. the connection scheme of secondary windings to obtain star output is illustrated in figure 3 and the corresponding phasor diagram is illustrated in figure 2(b). the generation of output phase voltages with required phase angles of 360/7=51.428 degrees is shown in figure 4. voltage transformation ratio is taken as 1, as an assumption, because the objective is to obtain seven phase balance output. for the secondary step up or step down voltage, a scaling factor would be multiplied to each number of turns as shown in tables ii and iii to get the desired output voltage. the windings arrangements are shown in figure 5. and table iii. fig. 5. winding arrangement of primary and secondary of the transformer engineering, technology & applied science research vol. 7, no. 5, 2017, 1953-1961 1957 www.etasr.com tabrez et al.: a novel three phase to seven phase conversion technique … table iii. turns ratios of secondary windings with respect to primary winding ro α axis turns ratio polarity βaxis turns ratio polarity a1a2 100 + b1b2 62.34 + b3b4 78.18 + c1c2 22.25 c3c4 97.49 + d1d2 90.09 d3d4 43.38 + e1e2 90.09 e3e4 43.38 f1f2 22.25 f3f4 97.49 g1g2 62.34 + g3g4 78.18 the proposed transformer is first simulated through matlab/simulink. from which a prototype is developed based on the presented concept. the waveforms of the output voltage are taken into consideration to validate the design with the following results (figures 7-13). iv. results a. a. simulation results table iv values are taken from table iii. the proposed scheme gives a balanced seven phase output voltage and balanced output current under rl load as shown in figures 713. the designed transformer is simulated and the inbuilt transformer blocks are used to simulate the conceptual design. the simulink model diagram is presented in figure 6. the appropriate turns ratios are set in the dialog box and the simulation is set to run. turns ratios and polarity of winding connection are those shown in table iii. the output is a balanced seven phase supply for a balanced three-phase input (figures 7-8) and an unbalanced output is a seen for an unbalanced three-phase input. three different line voltages can be obtained as shown in section iii. the magnitude and phase angle is shown in table v. the table v results are obtained from simulation but they can be verified from phasor diagram and geometrical analysis. continuous v+v+v+v+v+v+v+v+v+v+rms 1+ 1 +2 2 +3 3 +4 4 +5 5 1+ 1 +2 2 +3 3 +4 4 +5 5 1+ 1 +2 2 +3 3 +4 4 +5 5 +6 6 [ia] [ic] [ib] [c] [b] [a] i+ i+ i+ i+ i+ i+ i+ i+ i+ i+ fig. 6. the simulink model of the proposed system fig. 7. three phase balanced input fig. 8. three phase balanced input current drawn by the transformer from the source. engineering, technology & applied science research vol. 7, no. 5, 2017, 1953-1961 1958 www.etasr.com tabrez et al.: a novel three phase to seven phase conversion technique … table iv. parameters for simulation connection scheme primaryscott connection seconday-heptagon source and load parameter s 10kva v (pri) 220v/ph v (sec) 220v/ph load(7 phase star connected load) r=100ω, l=48mh solver parameters simulation time 0-0.004 sec solver ode45(dormand-prince) type of solver variable step min/max step size auto zero crossing control local settings zero crossing algorithm nonadaptive number of consecutive min steps 1 shape preservation no absolute tolerance auto time tolerance 10*128*eps number of consecutive zero crossings 1000 table v. magnitude and phase angle of different line voltage voltage rms value angle ratio with phase voltage phase voltage 219.65 0.00° 1.00 adjacent line voltage 190.60 -64.26° 0.866 non-adjacent1 line voltage 343.54 -38.63° 1.561 non-adjacent2 line voltage 428.23 -12.89° 1.946 fig. 9. seven phase balanced output current fig. 10. seven phase balanced output phase voltage fig. 11. seven phase adjacent line voltage fig. 12. seven phase non-adjacent1 line voltage fig. 13. seven phase non-adjacent2 line voltage b. experimental results based on the concept developed in sections ii and iii and the scheme of section iv, a prototype transformer is developed. the transformer is of 2 kv a, 220 v/phase, 1:1 transformation ratio. a seven phase resistive and inductive load connected in star is used for electrical loading of the transformer. the transformer primary winding is fed from a three single phase auto transformer to balance the input voltage. the transformer seven-phase output voltages are shown in figure 14. the transformer is tested under balanced condition as well as under unbalanced condition. experimental results are taken on yokogawa four channel digital oscilloscope. due to channel limitations, the wave forms are taken into two separate plots. following steps are taken to get experimental data:  a 100 kva three phase to seven phase converting transformer is designed based on section iii and transformer design procedures.  a prototype is made according to the design.  the primary and secondary windings are left open. engineering, technology & applied science research vol. 7, no. 5, 2017, 1953-1961 1959 www.etasr.com tabrez et al.: a novel three phase to seven phase conversion technique …  the primary and secondary windings are connected later according to figure 5.  an rl load of 25ω and 60mh is connected in heptagon.  the output waveforms are taken using yokogowa 4channel digital oscilloscope. (a) (b) fig. 14. seven phase voltage waveform of experimental results v. discussion the designed transformer has many specific applications in different areas e.g.:  use in power supply for multiphase induction motor or multiphase synchronous motor drive for fixed speed operation.  use in testing of seven-phase machines  use as power transformer and sub-transmission level transformer for multiphase transmission  use in ac-dc converter. high ripple frequency lowers the filter rrequirement. since a transformer act as a two port network, a reverse transformation is also possible. in other words this transformer may be used as a tie between a seven phase generator and three phase grid. furthermore a multiphase transformer can be explored in areas in addition to that mentioned in this paper the presented connection scheme is compared with the scheme reported in [13]. the number of total windings in both schemes is almost the same. a considerable reduction in total volume is obtained in this scheme as the proposed transformer requires only two cores for winding together with a return magnetic path. so the overall volume of proposed transformer is less compared with that of [13] for the same rating. the actual amount of magnetic materials saved and the volume of transformer reduced is a design problem and could be addressed separately. since all seven phases don’t have the same number of windings so, impedance mismatching appears in both schemes. consequently an unbalancing in voltage and current would appear. the unbalancing would be more prominent in case of full-load conditions. the proposed scheme reduces the impedance mismatching. as far as transformer losses are concerned, copper losses are the same but iron losses are reduced because magnetic material requirement is reduced in the proposed design. since three phase input can’t connect in star earthed so zero sequence current won’t flow in case of fault or unbalanced conditions. a detailed comparison of both schemes (proposed and [13]) is show in table vi. table vi. comparison of [13] and the proposed scheme difference in proposed scheme reported scheme in [13] turns ratios effective total windings= 887.46*0.866=769 total winding = 770 primary windings scott-connection star/delta connection secondary windings start or heptagon star or heptagon number of cores 3 2 primary windings ratio 1:0.577:0.577 1:1:1 secondary windings ratio 1:0.6234:0.7818:0.22 25: 0.9749:0.9009:0.4338: 0.9009:0.4338:0.2225: 0.9749: 0.6234: 0.7818 0.1721:1.00:0.1721 : 0.6505:0.6505:0.7854: 0.5010:0.9028:0.3404: 0.5010:0.7854:0.3404: 0.9028 effective res./copper losses(per phase) low high iron losses low high secondary winding impedance ratios 1:1:1:1:1:1:1 1:0.844:0.7327: 0.6741:0.6741: 0.7327:0.844 volume lower higher vi. conclusions in this paper a new transformer connection scheme which converts a three-phase power to a seven-phase output at constant frequency is presented. the connection scheme and the phasor diagram, along with the turns ratios, are illustrated. a general equation of phase transformation from three phase supply to n-phase supply using primary winding scott connection based on vector/graphical approach is given. based on that a connection scheme of three phase to seven phase engineering, technology & applied science research vol. 7, no. 5, 2017, 1953-1961 1960 www.etasr.com tabrez et al.: a novel three phase to seven phase conversion technique … transformer is presented. proposed system is simulated in simulink environment simulation. results show that a balanced seven phase supply could be obtained from a balanced three phase input. the magnetic material requirement in this design is less especially for shell type of transformer as compared to existing approach due to two phase flux. volume required for the same kva rating will be less and power losses are less as well for the proposed scheme. reduced losses obtained by the proposed system make it a more efficient system for phase converting transformer. the implementation of the proposed connection scheme is elaborated using simulation. volume required for the same kva rating comes out to be less. the proposed scheme has the reduced impedance mismatching up to a maximum value of 10% while reported connection scheme [13] has a significant degree of mismatching. hence the proposed transformer is a more efficient and economically viable alternative of the reported three phase to seven phase converting transformer. it is expected that the proposed connection scheme can be used in drives and other multiphase applications like phase converting transformer. the implementation of the proposed connection scheme is elaborated using simulation. volume required for the same kva rating comes out to be less. the proposed scheme has the reduced impedance mismatching up to a maximum value of 10% while reported connection scheme [13] has a significant degree of mismatching. hence the proposed transformer is a more efficient and economically viable alternative of the reported three phase to seven phase converting transformer. it is expected that the proposed connection scheme can be used in drives and other multiphase applications like transmission. although the area of multiphase generation by passive transformation (using transformer) techniques is old, only limited research is done up to date compared to its counter-part: 3-,1phase ac/dc/multiphase ac. most research work available are focused on the phase number in the multiple of three, which opens up a wide window of research therefore there are much more research options for odd number of phases like 5-phase, 7-phase, 11-phase etc. as far as 3-phase to 7-phase conversion is concerned, this paper could be extended for thermal modeling of the transformer. the unbalancing study, threeseven phase conversion and fault studies would be a breakthrough for this transformer study. appendix impedance mismatching calculation from (7), one can show that the turns ratios of different windings placed on the two limb in matrix form are: 1 0 cos( ) sin( ) cos(2 ) sin(2 ) cos(3 ) sin(3 ) cos(4 ) sin(4 ) cos(5 ) sin(5 ) cos(6 ) sin(6 )                                   as explained in section iii.a, the windings of two limbs are connected in series with proper polarity and turns ratios in sin(nδ):cos(nδ) the value of δ=2π/7 and n=0,1,2,3,4,5,6. inductance of a coil is calculated by the following expression 2n a l l   where l = inductance of the coil n = i-th number of turns μ = permeability of the core a = area of the coil l = average length of the coil referring figure 5: the inductance of each phase is sum of inductance of two individual coils. each individual coil having turns ratios proportional to sin(nδ) and cos(nδ) where 2 7    and n varies from 0 to 6. so 2 2 sin cosl n n   1l  for n=0,1,2,3,4,5 and 6 therefore inductance of each phase of secondary will be same. references [1] e. levi, “multiphase electric machines for variable-speed applications”, ieee transactions on industrial electronics, vol. 55, no. 5, pp. 1893– 1909 2008 [2] g. k. singh, k. b. yadav, r. p. saini, “modelling and analysis of multiphase (six-phase) self-excited induction generator”, proc. 8th int. conf. electr. mach. syst., pp. 1922–1927, 2005 [3] g. k. singh, k. b. yadav, r. p sani, “capacitive self-excitation in sixphase induction generator for small hydro power—an experimental investigation”, int. ieee conf. power electron., drives energy syst., new delhi, india, pp. 1-6, 2006 [4] j. r. stewart, d. d. wilson, “high phase order transmissiona feasibility analysis part-ii-over voltages and insulation requirements”, ieee trans. power app. syst., vol. pas-97, no. 6, pp. 2308–2317, 1978 [5] s. n. tewari, g. k. singh, a. b. saroor, “multiphase power transmission research-a survey”, electric power systems research, vol. 24, pp. 207–215, 1992 [6] m. jones, e. levi, “a literature survey of the state-of-the-art in multiphase ac drives”, proc. int. upec, stafford, u.k., pp. 505–510, 2002 [7] e. levi, r. bojoi, f. profumo, h. a. toliyat, s. williamson, “multiphase induction motor drives-a technology status review”, iet electric power applications, vol. 1, no. 4, pp. 489–516, 2007 [8] s. choi, b. s. lee, p. n. enjeti, “new 24-pulse diode rectifier systems for utility interface of high power ac motor drives”, ieee transactions on industry applications, vol. 33, no. 2, pp. 531–541, 1997 [9] v. garg, b. singh, g. bhuvaneswari, “a tapped star connected autotransformer based 24-pulse ac-dc converter for power quality improvement in induction motor drives”, international journal of emerging electric power systems, vol. 7, no. 4, 2006 [10] v. garg, b. singh, g. bhuvaneswari, “a 24 pulse ac-dc converter employing a pulse doubling technique for vector controlled induction engineering, technology & applied science research vol. 7, no. 5, 2017, 1953-1961 1961 www.etasr.com tabrez et al.: a novel three phase to seven phase conversion technique … motor drives”, iete journal of research., vol. 54, no. 4, pp. 314–322, 2008 [11] b. singh, s. gairola, “an autotransformer based 36 pulse controlled acdc converter”, iete journal of research, vol. 54, no. 4, pp. 255–262, 2008 [12] a. iqbal, s. moinuddin, m. rizwan khan, s. m. ahmed, h. abu-rub, “a novel three-phase to five-phase transformation using a special transformer connection”, ieee transactions on power delivery vol. 25, no. 3, pp. 1637–1644, 2010 [13] s. moinoddin, a. iqbal, h. abu-rub, m. rizwan khan, s. moin ahmed, “three-phase to seven-phase power converting transformer”, ieee transactions on energy conversion, vol. 27, no. 3, pp. 757-766, 2012 [14] a. s. abdel-khalik, z. shafik, a. elserougi, s. ahmed, a. massouda, “a static three-phase to five-phase transformer based on scott connection”, electric power systems research, vol. 110, pp. 84–93, 2014 [15] j. e. parton, “a general theory of phase transformation”, 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[16] o. e. gouda, g. m. amer, w. a. a. salem, “a study of k-factor power transformer characteristics by modelling simulation”, engineering, technology & applied science research vol. 1, no. 5, pp. 114-120, 2011 [17] h. fan, j. hu, h. liu, y. yin, m. danikas, “uhf pd experiments on real power transformer and its frequency characteristics results”, engineering, technology & applied science research vol. 6, no. 1, pp. 906-912, 2016 authors profiles md. tabrez received a master and bachelor degree in electrical engineering from aligarh muslim university in 2012 and 2010 respectively. currently he is working as phd research scholar in the electrical engineering department of the indian institute of technology, dhanbad, india. pradip kumar sadhu received the b.e.e. (hons.), m.e.e., and ph.d. (engg.) degrees from jadavpur university, kolkata, india, in 1997, 1999, and 2002, respectively. he is currently an assistant professor in the electrical engineering department, indian school of mines, dhanbad, india. his research interests include power electronics applications, energy efficient devices and drives, and computer-aided power system analysis atif iqbal received the b.sc. and m.sc. degrees in electrical engineering from aligarh muslim university (amu), aligarh, india, in 1991 and 1996, respectively, and the ph.d. degree from liverpool john moore university, liverpool, u.k., in 2006. he has been a lecturer in the department of electrical engineering, amu, since 1991, where he is currently working as an associate. he is on an academic assignment at qatar university, doha, qatar. his main research interests are power electronics and multiphase machine drives. ab pro hu pro dis usu suf sub be sop the pre res bot usi run dom iris at 88. atta pri tru pro [1] sca soc to ind mu 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most gnition f large ns and project ens in system oofing gnition ed iris se the e iris ed iris in [3] rintout pixels uch as rising present cha pos wh cos oph to reco sho pro iris step [6] text dete obf cas thre bein sam at fak from sho tran ava com fig. from feat stoc com dev vol. 8, no. 2, 20 nd srinivas ku spoof jawaharlal neh anged iris text ssibly compro hile colored o smetic reaso hthalmologists correct the e ognition algor own that the ominent and co patterns. dete p toward impr applied fouri tured lenses. the hypothes ection algorit fuscated patter es. in the pro ee databases, ng soft lens a mple images o tvs-fir a pub ke and real ima m both eyes o ows sample i nsparent conta ailable databas mprising of 65 1. row 1: e m atvs-fir data the proposed tures such chasticity of t mputed from veloped appro 018, 2859-2863 umar: feature iris d s. srinivas departmen hru technolog andhra prad samay_ssk2@ ture to the iri omise the ins or textured con ons, it is s to prescribe eye sight. he rithm to find th texture detail ourse and they ection of cont roving reliabil ier transform t sis generated thm has to rns and allow oposed metho one of them b and textured le of the real and blicly availabl ages of iris (8 of 50 subjects mages of the act lens) iris im se [9] acquired 70 iris images ye images with p abase d spoof iris de as intensity the iris texture the gradien oach also exp 3 set fusion for etectio s kumar nt of ece gical universit desh, india @yahoo.com is acquisition stalled iris rec ntact lenses a becoming contact lens f ence it is un he presence of ls in near-inf y will obfuscate act lens presen lity of iris reco to detect the f and tested in first reject th w only the sof od we tested being print att ens cases. fig d fake (printed le database [8 00 from each treated as 10 e real and fa mages of iiitd from 101 su s. print attack, row etection approa distribution, e and edge inf nt of global ploits the textu 2859 spoof iris dete on ty, kakinada system which cognition sys are being wor a practice for medical rea navoidable fo f lens. in [5] i frared imaging e the real or na nce is an impo ognition. auth fake patterns d [7] is that, th he instances ft lens and no the hypothes tack and the o gure 1 shows d) iris images 8]. there are category) cap 0 classes. fig ake (cosmetic d vista, a pub ubjects, 202 cl 2: original eye i ach analyzes i , coarseness formation whi eye image. ural region o ection h can stems. rn for for asons r the it was g are atural ortant hor in due to he iris with o lens is on others some from 1600 ptured gure 2 c and blicly lasses images mage and ich is the of the ent pro app dev att of als tra fro cla sup fea par exp con fig len a. pre the rel and engineerin www.etasr tire eye imag ovide very us proach for sp veloped appro acks, while su soft (transpar so computed ansform. conto om images assification pe pport vector m the rest of th ature set gen rtition and cl perimental re nclusions of th g. 2. row 1: c s images, row 3: fig literature su a detailed esented in [1]. e fake iris patt liable. authors d other quality ng, technology r.com ge using sgl seful descript poof iris detec oach works o ustaining recog rent) lens. in transform do ourlets are su with smooth erformance of machines (svm his paper is st neration is de lassification a esults are pre he proposed m colored contact l images with no l g. 3. proposed urvey survey on i . author in [6] terns due to th s in [10] prov y related meas y & applied sci ldm and g tors. the bloc ction is shown on spoofed im gnition capabi addition to te omain feature uitable for ext h edges an f the algorith ms). tructured as fo escribed. in are presented. esented. in s method are give lens images, row lens from iiitd d d method block d ris recognitio ] used fourier he presence o ved that focus sures can help ience research glrlm which ck diagram o n in figure 3 mages with p ility in the pre extural feature es using cont tracting inform nd contours. hm is tested ollows. in secti section iii d in section iv section v the en. w 2: transparent database. diagram on algorithms r transform to f lens which i s, motion, occ p fake iris dete v suvarchala an h can of our 3. the printed esence es, we tourlet mation the using ion ii, dataset v the e key contact s was detect is less lusion ection. the reco lb atta vec ima mea cha mu algo in [ lb [7] lens entr wor usin a. extr in circ diff met from is n hen and sys thro unw b. par orig rep tem glob 4. t calc gray ima crea from vol. 8, no. 2, 20 nd srinivas ku e effect of both ognition was p p operator an acks in iris re ctor machines ages. in [13], asuring edge aracterization t ulti-scale loca orithm were u [15] applied g p for the detec tested the tran s images using ropy with lbp rks well on pr ng textural and ii. iris pr iris segmenta in any biome raction of diss deciding the cular iris and ferential opera thod proposed m atvs-fir d not possible t nce they cont d glrlm) an tem as ‘fakes ough the seg wrapped and c sgld matrix there are thr rts represent ginal eye imag resents the co mplate. sgld bal descriptor the texture of culating ,(ap ay levels a and age, creating ated, then stat m it and provi energy:  ba p , ( contrast:  ba, correlation: sum of squar 018, 2859-2863 umar: feature s h transparent a presented in [ nd statistical f ecognition in] to train the g , authors det sharpness in through iris-te al binary pat used to classif gaussian smoo ction of textur nsparent conta g modified lb p to detect live rint spoof iris i d contourlet fe reprocessing ation and norm etric system, p similar feature recognition pupil region ator and the iri d in [17]. as so database in [8 to apply cont tain only textu nd subsequentl s’. images with mentation ste contourlet featu x and glrl m ree parts in th the sgldm ge and the grad ontourlet trans features and s derived from f an image is d )b i.e., how fre d b in a stated an sgld ma istical parame de information ba 2),(  bapba 2 ,()( yx ba bapba   , ),( es: variance  a 3 set fusion for and colored co [4, 5, 7]. auth features for id . authors in glcm feature tected textured n the iris im extons and cotterns and a fy textured len othed as well red lens in iris act lens images bp. authors in eness. the me images and iri eatures. g and featur malization preprocessing es from it play rate. in the ns are segmen is region is un ome of the pri 8] failed the se tourlet decom ural features ( ly the images h textured lens ep successfull ures are extrac matrix he feature vec m and glrl dient of eye im sform features glrlm feat m the eye imag described by s equently pixel d spatial relati atrix. once th eters proposed n about the im b) y yx   ba apa , 2 ()(  2860 spoof iris dete ontact lenses o hors in [11] ap dentifying the [12] used su es of textured d contact len mage, iris te -occurrence m adaboost lea ns in [14]. au as sift weig images. autho s as well as co n [16] made u thod proposed is with contact re extraction g of the image ys an essentia current study nted using int nwrapped usin int attacked im egmentation st mposition on t (gradient, sgl are rejected b s and soft lens ly which are cted from them ctor. the first lm parameter mage. the third of normalize tures are low ge shown in f sgld function l pairs with spe ionship occur he sgld matr in [18] are de mage texture. (1) (2) (3) ba ), (4) ection on iris pplied print upport d lens ns by exture matrix. arning uthors ghted ors in olored use of d here t lens n e and l role y, the tegrong the mages tep, it them. ldm by the s pass then m. t two rs of d part ed iris level figure ns by ecific in an rix is erived c. hav of gl dir te num s l g r r wh of d. af ver the ma engineerin www.etasr inverse differ entropy: a  glrl matrix a glrl m ving the same pixels in the lrl matrix, rections having fig. 4. r exture measure let k be the     g rn i n j ipk 1 1 ( where ng is mber of differ short runs em long runs em gray level non run length non run percentage here p is the n one. gradient me one of the m fter gradient im rtical direction e direction of ay be found i ng, technology r.com rence moment log[),( , bap ba  x matrix is a set gray level. th e run. let (p specifying th g the gray leve row 1: sgldm ex es measured fr e number of ru ji ), number of gr rent run length mphasis: rf1 mphasis: 2rf -uniformity: r n-uniformity: e: /1(5 prf  number of runs easure most common u mages have b ns, the pixels w f the gradient in the directio y & applied sci t:  ba p ba, 2)( 1 )],( bap of collinear, he length of th ),( ji be the ( he number of el i and length xample. row 2: g rom the glrl uns. then ray levels in t hs.     g rn i n j j jip k 1 1 2 ),(1 ,( 1 1 21 ip n i n j j k g r     1 1 3     gn i n jk rf 1 1 4    rn j n ik rf ),( 1 1 ) jip n i n j p g r     s if all possibl uses of gradien been computed with the highes become edge on perpendicu ience research bap ),( (5) (6) consecutive he run is the nu thji ),( entry i f primitives h .j glrlm example lm are as follo (7) the image and (8) ), j (9) 2 1 ),(   rn jip (10 2 1 ),(   gn i jip (11 (12 le runs had a l nt is edge dete d in horizonta st gradient val e pixels, and ular to the gr v suvarchala an pixels umber in the of all ows: d nr is 0) ) 2) length ection. al and lues in edges radient dire lens ima sho the pre lim var fig. imag fig. fir r e. effi as a the the pyr poin resp ban coin sign 40× leve com feat mad and sum dete vol. 8, no. 2, 20 nd srinivas ku ection. there i s image from age texture is c own in figure real image i sence of conta mbic and pupil riance and mor 5. row 1: ges. row 2: eye i 6. row 1: g real and fake eye contourlet fe contourlets iciently with li a tool to comp geometrical e double filte ramid (lp) and nt discontinui pectively. hen nk (pdfb). it ncide with lo nificant coeffi ×240 template el and 4 dire mputed for eac ture vector. in de up of sgl d contourlet co mmarizes the ection. 018, 2859-2863 umar: feature s is almost no di m a normal ir course and ran 4. the iris stru is smooth but act lens. the f llary boundari re uniformity a gradient images images with textu gradient images o images eature extract [21] represe ittle redundanc pensate the lim structures tha er bank struc d directional f ities and linki nce the name can be noticed ocation and d icients. once t , it is then dec ections at ii l ch direction a n the proposed ldm, glrlm oefficients of n comparison 3 set fusion for ifference in th ris image but ndom, which d ucture in the s t the additiona fake iris with ies cannot be as shown in fi s of colored, tra ured lens, soft len of real and fake i tion ent the geo cy. contourlet mitation of wa at possess dir cture compris filter bank (df ing them in t pyramidal an d that only tho direction of th the iris image composed in t level. statistic and all are app d method the ir m of original an normalized iri of existing 2861 spoof iris dete e structure of t textured len distinctly appea soft lens imag al edge show print attack (w localized) has igure 5. ansparent and no s and no lens. images. row 2: a ometric struc t transform is f avelets in han rectional mom sing of lapl fb) is used to to linear struc nd directional ose contourlet he image pro is unwrapped to 16 direction cal parameter pended to form ris feature vec nd gradient im is template. ta methods in s ection a soft ns iris ars as e and ws the where s less o lens atvs ctures found ndling ments. lacian catch ctures filter s that oduce d in to ns at i rs are m the ctor is mages able i spoof engineering, technology & applied science research vol. 8, no. 2, 2018, 2859-2863 2862 www.etasr.com suvarchala and srinivas kumar: feature set fusion for spoof iris detection table i. comparison of existing methods in spoof detection method attack nature feature training/testing protocol matching/classifier [11] print spoof statistical features of local and global eye regions atvs-fir: 400 training and 1200 testing neural networks [7] contact lens modified lbp iiit-d: weka classifier [14] contact lens lbp features 300 fake+6000 live irises for training and 300 fake + 4000 live irises for testing adaboost classifier [13] contact lens iris textons and haralick features casia and bath: equal train and test samples svm classifier [19] contact lens scale invariant descriptors iiit-d vista & iiit-d cogent: equal number of training and testing samples svm classifier [16] print spoof entropy with lbp and wp atvs-fir and casia-iris syn databases - [10] print spoof quality related measures and sffs algorithm 200 real images for training and 1400 testing quadratic classifier proposed contact lens and print spoof sgldm, glrlm features and contourlet features atvs-fir: 500 real for training and 1100 for testing svm classifier iii. dataset partition the datasets’ description is given in the table ii. since there are unequal numbers of samples for left and right irises in the iiit-d databases, we considered 5 samples/each class for the experiment. in atvs-fir database 500 samples are used for training and the rest 1100 (300 real + 800 fake) samples are used for testing. the eye image and gradient of the eye image are initially subdivided into blocks sized 80×80 which then form a total of 48 subimages. feature vectors made up of statistical features defined in section ii (b & c) of sgldm and glrlm of subimages are extracted. the size of the textural features will be 1056 (11 features/subimage × 48 subimages × 2 images). contourlet decomposition of the iris template generates 20 subimages. the number of frequency domain features is 220 (11 features × 20 wedges). the final feature vector size is 1276 (1056+220). those fake print attacked images in atvs-fir database which fail the segmentation step, will not have contourlet features but contain only the global textural features. at the end of each feature vector the class name is appended facilitating the supervised learning. table ii. database details database parameter| iiit_d vista iiit-d cogent atvs-fir subjects 101 101 50 categories textured lens soft lens normal textured lens soft lens normal fake real samples/subject left iris=5 right iris=5 left iris =5 right iris=5 left iris=8 right iris=8 classes 606 606 200 total samples 3030 3030 1600 eye image size 640×480 640×480 640×480 train samples 3/class 3/class 5/class (real) test samples 2/class 2/class 3/class (real) + all fake the classification of iris feature vectors is carried out using osusvm package available at [20]. the multiclass svms operated in one-against-all approach are tuned with linear support vector classifier kernel. svms are trained and tested at train sample:test sample ratio of 3:2 for iiitd databases. the classification of normal, soft lens and textured lens iris images in iiit-d vista and cogent databases is conducted separately as well as mixed. the left and right irises are considered as separate classes in all databases. the train:test sample ratio is 5:3 for atvs-fir real database. in this database 500 real iris samples are taken for training and the remaining 1100 (real + fake) samples are considered for testing. iv. results and discussion the experiments are conducted on a pc with pentium i5, 2.67ghz processor and 4gb ram in matlab 11.0 environment. the evaluation of the proposed method is done on atvs-fir, iiit-d vista and iiit-d cogent databases. the performance of the proposed method is appraised in terms of correct classification rate (ccr) and compared with existing methods in table iii. the method proposed in [7], obtained 76.83% and 65.03%. the method described in [19] obtained 89.78% and 83.88% and the proposed method achieved better ccr of 95.63% and 88.83% on iiitd-vista and iiitd-cogent databases respectively. on atvs-fir database the proposed method achieved 100% ccr which is same with [10] and waleed and hanna in [16] but better than chun in [11] which obtained 99.75%. the ccr is less when only either textural or contourlet features are considered but significantly improved when both features are combined. for mixed iiitd database, svms are trained with normal and soft lens iris and tested with all three types including textured lens irises. the obtained results are given in table iv. table iii. %crr comparison of proposed and existing methods database method crr (%) atvs-fir [8] [11] 99.75 [16] 100 [10] 100 proposed 100 iiitd-vista [9] lens* n-n t-t s-s avg** [19] 87.77 98.59 82.99 89.78 [7] 62.10 92.95 75.44 76.83 proposed 97.64 98.85 90.40 95.63 iiitd-cogent [9] lens* n-n t-t s-s avg** [19] 79.80 95.54 76.29 83.88 [7] 65.99 80.81 48.31 65.03 proposed 85.50 96.75 84.24 88.83 note*: n-normal, s-soft lens and t-textured lens. avg**: average engineering, technology & applied science research vol. 8, no. 2, 2018, 2859-2863 2863 www.etasr.com suvarchala and srinivas kumar: feature set fusion for spoof iris detection table iv. performance comparison of different features in % ccr database lens sgldm &glrlm contourlet features feature fusion atvs-fir [8] -98.40 99.25 100 iiitd-vista [9] n-n 94.68 96.56 97.64 t-t 93.65 95.35 98.85 s-s 86.24 87.80 90.40 mixed* 84.52 86.23 89.46 iiitd-cogent [9] n-n 80.40 82.78 85.50 t-t 90.24 93.45 96.75 s-s 79.98 81.25 84.24 mixed* 78.54 80.82 82.66 note: mixed* is trained with normal and soft lens and tested with all 3 types table v. computation time for each block parameter computation time (s) of all databases* image size 640×480 gradient 0.12 sgldm 0.105 glrlm 0.11 preprocessing 0.68 normalization 0.15 contourlet features 0.26 authentication 0.012 total time 1.437 all databases*: atvs-fir, iiitd-vista and iiitd-cogent v. conclusions the method proposed in this paper identifies iris images with soft or textured lens and detects print attacks. the set of features consists of optimized textural and frequency domain descriptors. the print spoof images which fail the segmentation step have their contourlet features null. hence the detection of print attacks is easy during classification. hence the ccr is 100% for atvs-fir database. there is not much difference between normal and soft lens irises. so the classification rate is high with iiitd databases also. the proposed method is well suited for print spoof as well as lens images. acknowledgment the atvs-fir data set is released by the biometric recognition group, uam, madrid, spain and the iiit-d vista and cogent dataset by iiit-delhi, india. references [1] k. w. bowyer, k. hollingsworth, p. j. flynn, “image understanding for iris biometrics: a survey”, computer vision and image understanding, vol. 110, no. 2, pp. 281-307, 2008 [2] unique identification authority of india, role of biometric technology in aadhar enrollment, available at https://pdfs.semanticscholar.org /2db1/e82a61e1b30df3853c429f5a669cdb37c41e.pdf, 2012 [3] j. lee, “spoofing iris recognition technology with pictures”, available at: https://www.biometricupdate.com/201503/spoofing-iris-recognitiontechnology-with-pictures, 2015 [4] j. s. doyle, p. j. flynn, k. w. bowyer, “automated classification of contact lens type in iris images”, 2013 international conference on biometrics (icb), madrid, spain, june 7-13, 2013 [5] n. kohli, d. yadav, m. vatsa, r. singh, “revisiting iris recognition with color cosmetic contact lenses”, 2013 international conference on biometrics (icb), madrid, spain, june 7-13, 2013 [6] j. daugman, “demodulation by complex-valued wavelets for stochastic pattern recognition”, international journal of wavelets, multiresolution and information processing, vol. 1, no. 1, pp. 1–17, 2003 [7] d. yadav, n. kohli, j. s. doyle, r. singh, m. vatsa, k. w. bowyer, “unravelling the effect of textured contact lenses on iris recognition”, ieee transactions on information forensics and security, vol. 9, no. 5, pp. 851-862, 2014 [8] biometric recognition group–atvs, atvs-fir, fake iris images database, available at: https://atvs.ii.uam.es/atvs/fir_db.html [9] image analysis and biometrics lab at in iiit delhi, iiitd contact lens database [10] j. gallaby, j. ortiz-lopez, j. fierrez, j. ortega-garcia, “iris liveness detection based on quality related features”, 5th iapr international conference on biometrics (icb), new delhi, india, pp. 271-276, march 29 april 1, 2012 [11] c.-w. tan, a. kumar, “integrating occular and iris descriptors for fake iris recognition”, 2014 international workshop on biometrics and forensics (iwbf), valletta, malta, march 27-28, 2014 [12] x. he, s. an, p. shi, “statistical texture analysis-based approach for fake iris detection using support vector machines,” lecture notes in computer science, vol. 4642, pp. 540-546, 2007 [13] z. wei, x. qiu, z. sun, t. tan, “counterfeit iris detection based on texture analysis,” 19th international conference on pattern recognition, tampa, usa, december 8-11, 2008 [14] z. he, z. sun, t. tan, z. wei, “efficient iris spoof detection via boosted local binary patterns”, lecture notes in computer science, vol. 5558, pp. 1080-1090, 2009 [15] h. zhang, z. sun, t. tan, “contact lens detection based on weighted lbp”, 20th international conference on pattern recognition, istanbul, turkey, pp. 4279-4282, august 23-26, 2010. [16] w. s. -a. fathy, h. s. ali, “entropy with local binary patterns for efficient iris liveness detection”, in: wireless personal communications, springer science+business media, llc, 2017 [17] j. daugman, “how iris recognition works”, ieee transactions on circuits and systems for videotechnology, vol. 14, no. 1, pp. 21-30, 2004 [18] r. m. haralick, k. shanmugam, i. dinstein, “textural features for image classification”, ieee transactions on systems, man and cybernetics, vol. smc-3, no.6, pp. 610-62, 1973 [19] d. gragnaniello, g. poggi, c. sansone, l. verdoliva, “contact lens detection and classification in iris images through scale invariant descriptor”, 10th international conference on signal-image technology and internet-based systems, marrakech, morocco, november 23-27, 2014 [20] support vector machines toolbox, available at https://sourceforge.net/ projects/svm/ [21] m. n. do, m. vetterli, “the contourlet transform: an efficient directional multiresolution image representation”, ieee transactions on image processing, vol. 14, no. 12, pp. 2091–2106, 2005 engineering, technology & applied science research vol. 7, no. 5, 2017, 1918-1921 1918 www.etasr.com alsaif: highly compact design of trimmed patch with modified partial ground structure … highly compact design of trimmed patch with modified partial ground structure for extreme-wideband systems haitham alsaif electrical engineering department university of hail hail, saudi arabia hal-saif@hotmail.com abstract—–in this paper, a novel highly compact microstrip monopole antenna with adjusted ground plane for ultrawideband (uwb) applications is proposed. the patch antenna is composed of a trimmed radiator and rectangular ground plane with four slots providing relatively extreme wide operating frequency from 2.8 till 16.2 ghz based on -10 db criteria. the high matching impedance in the design results in ultra-wide bandwidth that covers the entire bw allocated by fcc for uwb applications. at the same time, the presented antenna is distinguished by significantly miniaturized structure with total size of 13 mm x 10 mm printed on a substrate material of rogers duriod rt 5880 lz with relative permittivity of εr=1.9 and loss tangent δ of 0.0009. the suggested antenna is appropriate for miniature wireless gadgets. the patch has been investigated, and optimized in terms of operating frequency, impedance matching, radiation characteristics, structure size, and fabrication cost. keywords-compact; planar; antenna; wide operating frequency i. introduction in recent years, ultra-wide band (uwb) wireless technology has remarkable attention because of several significant merits. these applications are able to provide extreme high data rates during their wide operating frequency using low levels of transmitted power. thus, introducing new designs of compact planar uwb patches has played an essential part in gaining high performance features with regard to impedance matching, radiation pattern, and structure size. furthermore, for commercial reasons, these designs should have low fabrication cost minimized and physical size [1, 16]. attributable to these characteristics, printed planar antennas have high attraction for short range communication systems. several uwb monopole designs for instance elliptical shape, u-shape, ring, circular shape, and many others have been suggested and investigated in which the wide operating frequencies are achieved by different forms of radiating structures [2-12]. however, shrinkage in the designs structure sizes is a challenging matter as it is straightly linked to the length of the longest surface current at the lowermost edge of the operating frequency range [13]. most of the formerly proposed ultra-wide patches have comparatively large physical size if not having nonplanar structures while many wireless systems for instance the radio frequency imaging applications necessitate planar structures. this is because miniaturized size antennas are easy to be inserted inside such systems. moreover, numerous published planar uwb antennas’ radiation pattern contain noticeable distortions in over their wide bandwidth. besides, in several monopole designs, the operating frequency does not contain the entire bandwidth from 3.1 ghz to 10.6 ghz assigned by federal communication commission (fcc) for these applications [14]. hence, the key objective of the presented planar design is accomplishing a highly compact monopole and ultra-high impedance bandwidth without any sacrifices in the other parameters characteristics so as to satisfy the main necessities for uwb wireless systems. the proposed antenna is well appropriate for applications of short ranges indoor uwb wireless communications. in the next section, the proposed compact patch is presented with parametric studies in details. ii. proposed monopole structure final geometry and fabricated prototype views of the designed patch are displayed in figure 1 and labelled with dimensions. the patch antenna’s microstrip feeding line has a characteristics impedance of 50 ω and printed on a 0.9 mm thick rogers duriod rt 5880 lz substrate with relative permittivity of εr=1.9 and loss tangent δ of 0.0009. the design has a vitally miniaturized structure with total size of 10 x 13 mm2. therefore, the monopole is more appropriate for small size ultra-wideband devices in addition to economizing space for other wireless system components. the microstrip line that has a length of 6.5 mm and 1.8 mm width feeds the trimmed rectangular radiator as clarified in figure 1. as shown in table i, the partial modified ground plane (3 x 10 mm2) is patched on the rear side of the substrate. the ground carries four i-shape slots that lead to a defected ground structure or dgs. this is in order to improve bandwidth performance and boost the antenna impedance matching. dgs approach has been applied at this antenna in order to increase current path length which results into wider operating frequency whereas the structure is retained very small. table i shows extra information about the design engineering, technology & applied science research vol. 7, no. 5, 2017, 1918-1921 1919 www.etasr.com alsaif: highly compact design of trimmed patch with modified partial ground structure … parameters. the presented planar design has been studied and investigated with industrial simulation code named as computer simulation technology microwave studio or cst. then, it was fabricated and experimentally measured. table i. the proposed uwb monopole parameters in mm dimension l w h wf lf value in mm 13 10 0.9 1.8 6.5 dimension wp ws wg ls lp value in mm 7 2 2 2 3.5 dimension lg lg1 lg2 ws wp value in mm 3 2.8 2.5 2 7 iii. simulation results and experimental parameters narrow bandwidth or single resonant frequency in general is created by the simple patch antennas using a single resonant frequency. thus, having numerous overlapped resonant frequencies will result in ultra-wide bandwidths (uwb). designing uwb patch is based on the concept of forming resonant frequencies overlapping between them, which leads to wide bandwidths [15]. the proposed miniaturized monopole bandwidth contains two interfered resonant frequencies (5.1 and 9.5 ghz), through which an extreme wide operating frequency is modeled as revealed figure 2. the figure shows both simulated and experimentally measured s11 (db) versus frequency (ghz). it can clearly be spotted that the design is illustrious by its ultra-wide operating frequency, that is from 2.8 ghz up to 16.2 ghz based on -10 db standard. both simulated and measured s11 show good agreement and only minor differences due to common reasons such as fabrication tolerance, soldering effects, etc. the parametric and substrate materials studies of the presented design have been performed with respect to bandwidth and s11 parameter as part of the antenna analysis and optimization process. s11 is plotted in figure 3 as a function of operating frequency for some commonly used substrate materials such as polyimide, fr4, and rogers duroid rt5880lz with relative permittivity εr of 3.5, 4.3, and 1.9, respectively. the proposed antenna is characterized by very high impedance matching using rogers duroid rt5880lz which turns into enhanced reflection coefficient and wider bandwidth. this material has the lowest rogers rt dielectric constant with very light weight. moreover, the partial ground plane dimensions were analyzed and investigated. the length (lg) has high effect on the patch results. for this design, it has been found that 3 mm long will introduce low power loss. in other words, that is extreme wide bandwidth and best impedance matching compared to 3.5 mm and 4 mm ground planes long. additionally, the second resonant frequency 9.5 ghz appears noticeably in comparison with the other lengths as demonstrated in figure 4. also, s11 as a function of frequency for the design with and without slots on the partial ground plane are presented in figure 5. using the defected ground structure or dgs technique by placing four i-shape slots improves the bandwidth significantly. besides, microstrip feeding line width parameter plays crucial role in forming the ultra wide bandwidth as revealed in figure 6 which illustrates s11 or reflection coefficient versus frequency for several wf values. after investigation, having feeding line 1.8 mm wide results into very low values of s11 parameter reaches -33 db and high impedance matching. in other words, matching between the radiator and the feeding line translated to more power transferred to the antenna, so the reflected power is reduced to less than -0.1 % whereas the accepted power is more than 99.9% [1]. also, it is observed that wf is inversely related to the bandwidth in this design. in other words, as the feeding line becomes wider, the operating frequency shrink and it may end into a bandwidth not including whole uwb allocated by fcc (3.1ghz to 10.6 ghz). figure 7 displays the normalized radiation pattern to the peak value of the suggested patch monopole 5.1 ghz, and 9.5 ghz. it shows the radiation pattern at the two orthogonal planes, the elevation and azimuth plane (e and h respectively) in polar forms. during the operating frequency, the radiation pattern at the h plane is omni-directional and the e plane is closely in bidirectional form with slight distortion. accordingly, the proposed trimmed patch radiates in an omni-directional pattern which makes it independent of placement position during the complete bandwidth. (a) (b) (c) fig. 1. the final geometry of the proposed design after optimization process: (a) topside view labelled with parameters. (b) backside view labelled with parameters. (c) picture of the fabricated monopole. 2 4 6 8 10 12 14 16 18 -40 -35 -30 -25 -20 -15 -10 -5 frequency in ghz s 11 in d b simulation results experimental measurements fig. 2. simulated and experimentally measured s11(db) versus operating frequency (ghz) iv. conclusion a novel extremely miniaturized planar design is presented for ultra-wideband applications. the patch is miniaturized in structure and has a size of 13 x 10 x 0.9 mm3, with high performance features. the proposed monopole has an outstanding operating frequency that is from 2.8 ghz to 16.2 engineering, technology & applied science research vol. 7, no. 5, 2017, 1918-1921 1920 www.etasr.com alsaif: highly compact design of trimmed patch with modified partial ground structure … ghz which covers beyond the fcc uwb set for such systems. all through the bandwidth, the design radiates in approximate omni-directional pattern; accordingly, the monopole does not depend on the placement direction in the wireless system. in conclusion, the trimmed patch has competitive performance with many other larger size antennas, which makes it more appropriate for exceedingly compact communication systems. fig. 3. s11 (db) as a function of frequency (ghz) using several substrate materials ( polyamide, fr4, and rogers rt 5880lz) fig. 4. the effect of the ground plane length parameter on the reflection coefficient in db fig. 5. the magnitude of s11 in db for the proposed monopole with and without defected ground plane structure (dgs) fig. 6. studying the width parameter of the feeding line (wf) for the presented design -30 -20 -10 0 30 210 60 240 90 270 120 300 150 330 180 0 simulation results experimental measurements -30 -20 -10 0 30 210 60 240 90 270 120 300 150 330 80 0 simulation results experimental measurements (a) -40 -30 -20 -10 0 30 210 60 240 90 270 120 300 150 330 180 0 simulation results experimental measurements -30 -20 -10 0 30 210 60 240 90 270 120 300 150 330 180 0 simulation results experimental measurements (b) fig. 7. the simulated and experimentally measured normalized radiation pattern for e and h planes in polar form at the resonant frequencies (a,b). acknowledgment the author would like to thank the deanship of scientific research at the university of hail in saudi arabia for supporting and funding this project (ba-1512). references [1] h. schantz, the art and science of ultra wideband antennas. norwood, ma: artech house, 2005 w.-k. chen, linear networks and systems, belmont, ca: wadsworth, 1993, pp. 123–135 [2] y. j. ren, k. chang, “ultra-wideband planar elliptical ring antenna”, electronics letters, vol. 42, no. 8, pp. 447–449, apr. 2006 [3] i. k. joon, j. yong, “design of ultra wideband coplanar waveguidefed li-shape planar monopole antennas”, ieee antennas and wireless propagation letters, vol. 6, pp. 383–387, 2007 engineering, technology & applied science research vol. 7, no. 5, 2017, 1918-1921 1921 www.etasr.com alsaif: highly compact design of trimmed patch with modified partial ground structure … [4] a. s. abbosh, m. e. bialkowski, “design of ultra wideband planar monopole antennas of circular and elliptical shape”, ieee transactions on antennas and propagation, vol. 56, no. 1, pp. 17–23, 2007 [5] m. gopikrishna, d. d. krishna, c. k. aanandan, p. mohanan, k. vasudevan, “compact linear tapered slot antenna for uwb applications”, electronics letters, vol. 44, no. 20, pp. 1174–1175, 2008 [6] m. n.moghadasi, h. rousta, b. s. virdee, “compact uwb planar monopole antenna”, ieee antennas and wireless propagation letters, vol. 8, no. 22, pp. 1382–1385, 2009 [7] o. ahmed, a. r. sebak, “a printed monopole antenna with two steps and a circular slot for uwb applications”, ieee antennas and wireless propagation letters, vol. 7, pp. 411–413, 2008 [8] c. deng, y. j. xie, p. li, “cpw-fed planar printed monopole antenna with impedance bandwidth enhanced”, ieee antennas and wireless propagation letters, vol. 8, pp. 1394–1397, 2009 [9] j. liang, l. guo, c. c. chiau, x. chen, c. g. parini, “study of cpw-fed circular disc monopole antenna for ultra wideband applications”, iee proceedings microwaves, antennas and propagation., vol. 152, no. 6, pp. 520–526, 2005 [10] d. t. nguyen, d. h. lee, h. c. park, “very compact printed triple bandnotched uwb antenna with quarter-wavelength slots”, ieee antennas and wireless propagation letters, vol. 11, pp. 411–414, 2012 [11] e. s. angelopoulos, a. z. anastopoulos, d. i. kaklamani, a. a. alexandridis, f. lazarakis, k. dangakis, “circular and elliptical cpwfed slot and microstrip-fed antennas for ultrawideband applications”, ieee antennas and wireless propagation letters, vol. 5, pp. 294–297, 2006 [12] e. ebrahimi, o. litschke, r. baggen, p. s. hall, “isolation enhancement of planar disc antenna and ground plane in uwb applications”, electronics letters, vol. 46, no. 23, pp. 1539–1541, 2010 [13] k. xu, z. zhu, h. li, j. huangfu, c. li, l. ran, “a printed single-layer uwb monopole antenna with extended ground plane stubs”, ieee antennas and wireless propagation letters, vol. 12, pp. 237-240, 2013 [14] federal communication commission, first report and order, revision of part 15 of the commission's rules regarding ultra-wideband transmission system, fcc 02 48, 2002 [15] a. gautam, s. yadav, b. kanaujia, “a cpw fed compact uwb microstrip antenna,” ieee antennas and wireless propagation letters, vol. 12, pp. 151–154, 2013 [16] l. m. devito, “a versatile clock recovery architecture and monolithic implementation” in: b. razavi, monolithic phase-locked loops clock recovery circuits, wiley-ieee press, 1996 microsoft word etasr_v12_n3_pp8555-8558 engineering, technology & applied science research vol. 12, no. 3, 2022, 8555-8558 8555 www.etasr.com al-khazaal & ahmad: a study of the impact of iron content on the thermal response of the spp/fe … a study of the impact of iron content on the thermal response of the spp/fe composites abdulaal z. al-khazaal department of chemical and material engineering northern border university arar, saudi arabia abdulaal.alkhazaal@nbu.edu.sa naveed ahmad department of chemical and material engineering northern border university arar, saudi arabia naveed.ahmad@nbu.edu.sa received: 6 march 2022 | revised: 24 march 2022 | accepted: 29 march 2022 abstract-a set of syndiotactic polypropylene/iron (spp/fe) composite samples were manufactured with the extrusion technique to study the impact of iron content on the thermal behavior of spp/fe composites in the melt phase. the dosage of iron contents varied from 0 to 8%. melting point (tm), crystallization temperature (tc), and thermal degradation temperature (td) were measured by differential scanning calorimetry (dsc) and thermal gravimetric analysis (tga) for each composite sample. thermal temperatures (tm, tc, and td) increased with increasing the iron contents due to the enhancement of the strength and thermal stability of the sample. this investigation is a validated fact that fillers (iron) alter both the macroscopic and microscopic properties of the polymer composites. keywords-thermal properties; dsc; tga; polymer composites; thermal degradation temperature i. introduction polymer composites have become one of the most important manufactured materials and can be industrialized by the incorporation of filler (natural or synthetic) into the polymer to improve its targeted properties [1-5]. polymer composites with different types of fillers and combinations are widely used with improved mechanical, thermal, barrier and fire resistant properties for different applications [6-8]. however, the end desired microstructure and macrostructure properties of polymer composites are greatly dependent on the nature, amount, geometry and interfacial interactions of the components [9]. the thermal properties are highly dependent and sensitive to microstructure properties of polymer and polymer composites [10-14]. therefore, the relationship of the thermal response and microstructure properties is an excellent key in both the process and quality control to realize and develop new materials with the desired properties. thermal properties can be used in the understanding of molecular structure and the link with both microstructure and macrostructure properties [6, 7, 15-18]. some of the recent scientific advances in the iron/polymer and its properties are mentioned below. authors in [19] investigated the thermal properties including thermal conductivity, thermal diffusivity, and specific heat of metal (copper, zinc, iron, and bronze) powderfilled high-density polyethylene composites experimentally in the range of filler content 0-24%. they found a region of low particle content (0-16%), where the particles are embedded homogeneously in the polymer matrix and do not interact with each other. fillers at higher content regions, tend to accumulate and conductive chains result in a quiche enhancement in thermal conductivity. authors in [20] studied the thermomechanical properties of polymer/metal composites. the acrylonitrile butadiene styrene (abs) was used as a matrix and copper and iron particles as fillers. the effect of metal powder was studied to confirm the effects of metal particles on the thermo-mechanical properties of the composites, such as tensile strength and thermal conductivity. it was found that the tensile strength of the composites decreases with increasing loading of the metal particles, while the thermal conductivity of the metal/polymer composite filament was found to improve by increasing metal content. more recently, authors in [21] examined the electrical and thermal conductivity of the ternary epoxy composites (cms) with two-component fillers, multiwall carbon nanotubes (mwcnt)/tio2, and mwcnt/carbonyl iron (fe). both electrical and thermal properties were found sensitive to both fillers. however, mwcnt/tio2 or mwcnt/fe into epoxy supports smaller changes in thermal conductivity as compared to the two-phase mwcnt/epoxy composites. to the best of our knowledge, the understanding of the thermal properties of syndiotactic polypropylene/iron (spp/fe) has not been established by now. thus, in the present work, spp/fe composites with different iron dosages were investigated to study the influence of iron content on the thermal properties of the composites, including melting point temperature (tm), crystallization temperature (tc), and thermal degradation temperature (td). ii. methedology a. experimental work 1) materials polymer composites were prepared using syndiotactic polypropylene (spp) and iron (fe) with content variety as a corresponding author: abdulaal z. al-khazaal engineering, technology & applied science research vol. 12, no. 3, 2022, 8555-8558 8556 www.etasr.com al-khazaal & ahmad: a study of the impact of iron content on the thermal response of the spp/fe … filler. zhongwei industrial co. ltd supplied the polymer with 60% degree of syndiotacticity, and sigma aldrich provided the iron in powder form. five samples were prepared with fe content varying from 0 to 8% with a step size of 2%. 2) preparation of polymer composites the extrusion technique was used to formulate a set of spp/fe composites with different percentages of fe as shown in table i. for each sample, at first the required amount of fe was dried in an oven at 75°c for 24 hours, and then it was accurately weighed. after that, when the extruder reached 250°c, both polypropylene and the required amount of iron entered the extruder for mixing to prepare the composite samples. the size of the prepared polymer-iron composite sample was mechanically reduced to suitable size before completely dried. then, a film of the composite sample was prepared by compression molding at 170°c and 7psi pressure for the duration of 1 hour using hot press. b. analytical work differential scanning calorimetry (dsc) and thermal gravimetric analysis (tga) were conducted to investigate the influence of iron content on the thermal behavior of the spp/fe composites. 1) differential scanning calorimetry the melting temperature (tm) of all samples was determined by dsc using non-isothermal crystallization tests. two main cycles (heating and cooling) were used in this technique. in the heating cycle, the sample having a weight of 4mg was heated up to 200°c at a constant heating rate of 10°c/min. after the melting point peak was obtained, the sample was kept under this annealing process for 5 minutes in order to eliminate the crystallinity and remove thermal history. during the cooling cycle, the dsc temperature was decreased up to -130°c with a cooling rate of -10°c/min. therefore, the peaks of crystallinity and glassy behavior of the composites were observed. evaluations were made using the instrument software ta-60 to estimate the melting temperature (tm) and crystallization temperature (tc) of all the samples. 2) thermal gravimetric analysis thermal degradation temperature (td) shows the maximum temperature at which a polymer is useful. in this investigation, the thermal degradation temperature of all composites was measured using tga. this analysis was conducted by observing the drop in the mass of the composite sample. in the beginning of the analysis, the sample was weighed, and then loaded to the equipment and heated up to 600 o c. during the heating process, the polymer started to burn at a certain temperature where the fall in the mass of samples was observed. the obtained results were analyzed with ta-60 for each sample. iii. results and discussion table i expresses the thermal information of all polymer composites extracted from dsc and tga. the number shown in the sample id represents the percentage of spp and fe in each composite sample. table i. thermal temperatures of the composite samples sample id fe % tc (°c) tm (°c) td (°c) pp-fe-(100-0) 0 113.96 146.72 360 pp-fe-(98-02) 2 114.79 147.86 380 pp-fe-(96-04) 4 115.76 148.62 395 pp-fe-(94-06) 6 116.51 149.71 405 pp-fe-(92-08) 8 117.69 150.62 418 a. the effect of iron content on crystallization temperature dsc determines the heat flow as a function of temperature, which is directly related to the latent heat of crystallization. in dsc measurements, the temperature at the peak of the endothermic heat flow represents the crystallization temperature of the composite sample. fig. 1. figure 1 illustrates the experimental results of dsc related to the crystallization temperature of each sample. figure 2 shows the relation between the crystallization temperatures of a set of composite samples with different fe content. it was found that the increase in fe content increases the crystallization temperature and hence the crystallinity of the composites due to the increase of the crystalline phase. fig. 1. dsc results (tc) of all composite samples. fig. 2. relationship between iron content and crystallization temperature. b. the effect of iron content on melting point temperature the melting point of all the samples was determined from the peak of dsc as displayed in figure 3. 0 2 4 6 8 10 12 100 105 110 115 120 125 130 135 m w temperature (oc) pp-fe-(100-0) pp-fe-(98-02) pp-fe-(96-04) pp-fe-(94-06) pp-fe-(92-08) 113 114 115 116 117 118 0 1 2 3 4 5 6 7 8 9 t c (o c ) fe% engineering, technology & applied science research vol. 12, no. 3, 2022, 8555-8558 8557 www.etasr.com al-khazaal & ahmad: a study of the impact of iron content on the thermal response of the spp/fe … fig. 3. dsc results of all samples showing the melting point peak. the influence of fe content on the melting point of the composites was noted. the melting point was found to increase with the increase in the fe content as illustrated in figure 4. this can be related to the fact that an increase in the fe content increases the adhesive properties of the composites and more energy is required to break the bonds of monomers. in other words, an increase in fe content increases the latent heat of fusion of the composite samples. fig. 4. relationship between the fe content and the melting point of all composite samples. c. the effect of iron content on thermal degradation temperature the td of spp/fe was measured by tga. figure 5 displays that td changes with the fe content of spp/fe composites. td is noted from the dropping point of the mass of the sample (the point at which the mass of the composites starts to drop). this is the maximum point of thermal tolerance of the sample. at this point, irreversible changes occur in the sample. we noted two drops in the mass of spp/fe samples. the first drop occurred at relatively low temperature due to the removal of moisture content from the sample. the second drop occurred at higher temperature, which shows the drop in the mass of the sample. the relationship between thermal degradation temperature and fe content is presented in figure 6. the thermal degradation temperature increases when fe content increases. the thermal degradation can be related to the fact that fe content enhances the thermal stability of the spp/fe composites. td shows the maximum temperature at which a polymer is useful. at higher temperatures, the components of the long chain of the polymer can disrupt (chain scission) and interact with one another (cross-link), thus altering the properties of the polymer. fig. 5. tga results of the composite samples. fig. 6. relationship of fe content and degradation temperature. in the light of the above findings, it is clear that fe as filler alters the thermal properties of spp/fe composites. the same result was found in [17]. the authors found that rheological and thermal properties like melting point vary with varying filler content. to the best of our knowledge, the thermal properties of spp/fe composites have not yet been studied. iv. conclusion thermal properties including melting point, crystallization, and thermal degradation temperatures are used as a tool to predict not only thermal stability, but also other microstructure properties and polymer chain dimensions which affects overall polymer chain dynamics. the iron content alters the thermal properties of the polymer composites and hence the polymer chain dimensions. the experimental results established that thermal measurements performed on spp/fe composites of different iron contents show that melting point, crystallization temperature and thermal degradation temperature significantly depend on the iron loading. in other words, crystallization, melting point, and thermal degradation temperature increase with increase in the iron dosage due to the consequently -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 130 140 150 160 170 180 190 m w temperture (oc) pp-fe-(100-0) pp-fe-(98-02) pp-fe-(96-04) pp-fe-(94-06) pp-fe-(92-08) 146 147 148 149 150 151 0 1 2 3 4 5 6 7 8 9 t m (o c ) fe (%) 0 20 40 60 80 100 120 300 350 400 450 500 w e ig h t (% ) temperature (oc) pp-fe-(100-0) pp-fe-(98-02) pp-fe-(96-04) pp-fe-(94-06) pp-fe-(92-08) 340 360 380 400 420 440 460 0 1 2 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[21] t. a. len, l. l. vovchenko, o. v. turkov, o. v. lozitsky, and l. y. matzui, "electrical and thermal properties of epoxy composites filled with carbon nanotubes and inorganic particles," molecular crystals and liquid crystals, vol. 717, no. 1, pp. 109–120, mar. 2021, https://doi.org/ 10.1080/15421406.2020.1860536. microsoft word etasr_v12_n6_pp9420-9425 engineering, technology & applied science research vol. 12, no. 6, 2022, 9420-9425 9420 www.etasr.com attia & hadji: assessment of the soil structure inertial interaction effect on the behavior coefficient … assessment of the soil structure inertial interaction effect on the behavior coefficient using simplified methods ahmed attia department of civil engineering faculty of sciences and technology ziane achour university djelfa, algeria attia52@yahoo.fr tarek hadji department of civil engineering faculty of sciences and technology ziane achour university djelfa, algeria tarek.hadji@gmail.com received: 18 august 2022 | revised: 29 august 2022 | accepted: 31 august 2022 abstract-this study aims to assess the effect of the soil structure inertial interaction (ssi) on the behavior coefficient (r). for this purpose, r was estimated with and without ssi. the pushover n2 method and its extension ssi-n2 method were applied to the plain reinforced concrete (rc) frame structures. for calculating the ssi effect on r, four shear wave velocities vs, representing rocky soil, firm soil, loose soil, and very loose soil, with three soil damping ratios ζg% for each soil type were considered. the estimated values of r using the n2 method were 4.1, 4.97, 5.75, and 6.96 for rocky soil, firm soil, loose soil, and very loose soil respectively. for the ssi-n2 method, r values were in the range of 3.67-3.97 for rocky soil, 4-4.69 for firm soil, 4.01-5.09 for loose soil, and 4.14-5.81 for very loose soil. in the algerian code, r was kept constant for each soil type, and its value is 3.5 and 5 with and without infill masonry respectively. soil shear wave velocity and the soil damping ratio must be taken into account in calculating r. the redundancy, overstrength, and ductility reduction coefficients were determined by taking into account the ssi. the ssi effect can change the values of r, so it must be taken into account when calculating r. keywords-behavior coefficient; n2 method; ssi-n2 method; rpa 99 v 2003; redundancy; overstrength; ductility i. introduction an earthquake-resistant structure is designed to be subject to structural and non-structural damage during a strong seismic event without sudden collapse. this can be achieved by nonlinear time history analysis [1] which is rather complicated and the responses depend on the registration component. seismic codes have simplified this task by using inelastic response spectra. for this purpose, the elastic response spectra values are divided by the reduction coefficient or behavior coefficient (r) [2-4]. there are also many approaches to assessing inelastic performance using the pushover method [5-7]. the n2 method [8], the displacement coefficient method [9], and the capacity spectrum method [10] are included in many seismic codes (atc40 [11], fema 356 [12], and ec8 [3]). these methods are used in the estimation of the ductility reduction coefficient. the behavior coefficient is also determined by a product of the ductility reduction coefficient, the redundancy coefficient, and the overstrength coefficient [13, 14]. in the algerian seismic code rpa 99 v 2003 [2] and eurocode 8 [3], the behavior coefficient value depends on the typology of structure and the ductility without accounting for overstrength. the ductility reduction coefficient also depends on the interaction between the structure and the soil (ssi). authors in [15] proposed a simplified approach to consider the inertial ssi effects on the ductility reduction coefficient by the combination of the nonlinear replacement oscillator method [16] and the n2 method. in [17], the effect of the height of reinforced concrete (rc) frames on overstrength, redundancy, and ductility response modification coefficients were estimated by the pushover method and nonlinear incremental dynamic analysis. the effect of vertical geometric irregularity on the r values of rc structures with moment resisting frame (mrf) systems was studied in [18]. in this analysis, the capacity spectrum method according to atc 40 was used. in this paper, the behavior coefficient of a 2d rc frame structure is estimated by two simplified methods: the n2 method [8] and the ssi-n2 method [15]. in this study, 4 soil types and 3 soil damping ratios for each soil type were considered when taking into account the soil structure inertial interaction effect on the behavior coefficient value. ii. behavior coefficient in this study, the behavior coefficient is calculated by considering the 3 reduction coefficients (redundancy, ductility, and overstrength), according to [13, 14]: � = �� . ��. �� (1) where rμ, rρ, and rω are ductility, redundancy, and overstrength reduction coefficients. based on the pushover capacity curve in figure 1 of [17], the above coefficients can be expressed as: r = � � , r = � � , and r� = � � (2) corresponding author: tarek hadji engineering, technology & applied science research vol. 12, no. 6, 2022, 9420-9425 9421 www.etasr.com attia & hadji: assessment of the soil structure inertial interaction effect on the behavior coefficient … iii. n2 and ssi-n2 methods the ssi-n2 method is an extension of the n2 method [5] proposed in [15, 19], where the ssi is introduced in the n2 method by using the replacement oscillator concept [16]. the replacement single degree of freedom (sdof) system has the same effective values for the first mode of vibration of the structure (height heff, mass m, lateral stiffness k, and damping c), and 3 degrees of freedom (figure 2). the stiffness ku and kθ, the damping cu and cθ represented in figure 1, were expressed by the impedance function as follows: �� = �� �� (3) �� = �� ������ (4) �� = �� �� (5) �� = �� ������ (6) where vs is the mean shear wave velocity representing the site effects. the quantities �� ,�� , �� , and �� are adimensional parameters that take into account the influence of the excitation frequency on the impedance and ku and kθ represent the static stiffness of a half-space disk and are defined as follows: �� = �� � !�� , �� = � "($ �) !�� (7) &� = 1, �� = )$ (8) &� = 1 − )$ (+,-.) , $/(+, -.), − )"& � 0 (9) �� = )$)� (+, -.) , $/(+,-.), (10) the coefficients a0, b1, b2, and b3 are functions of poisson coefficient ʋ [2], ru, rθ are the equivalent radii of foundation and are expressed as: 1� = 2345 , 1� = 2 674 5 8 , where af and if are the area and inertia moments of the foundation. from the above expressions, the period and the damping ratios of the equivalent system with soil-structure interaction are calculated by the following expressions: 9: = 921 + � < $=� + >, ?44 =ɵ a (11) bc = d,d: , b + <1 + d, d: ,a ef + < d�, d: , e� + dɵ, d: , a e� (12) where heff is the distance from the base to the fundamental mode inertial forces gravity center. 9 = 2h2i jklk , = �m d , b = n �io , p = ∑ pr ∅rtru$ (13) t and ζ are the fundamental mode period and the damping ratios of the equivalent system on a rigid base. mi and ∅r represent the mass and the modal value of the fundamental mode for the floor i, dy and fy represent the yield displacement and the actual strength of the equivalent sdof [8]. v� � = =�i , 9� = �m o� , b� = n� �io� (14) where vu , tu, and ζu represent the natural frequency, the period, and the damping ratios of the equivalent soil structure system where the structure is assumed to be perfectly rigid and the rotation of the foundation is blocked. vɵ � = =ɵi , 9ɵ = �m oɵ , bɵ = nɵ �ioɵ (15) where vɵ, tɵ, and ζɵ represent the natural frequency, the period, and the damping ratios of the equivalent soil structure system where the structure is assumed to be perfectly rigid and the translation of the foundation is blocked. fig. 1. the replacement sdof for ssi. the n2 method was used to determine the ductility μ of the equivalent system (without ssi).to take into account the inelastic interaction effects, an equivalent ductility coefficient is defined according to [13]: [\ = 1 + ([ − 1) d,d: , (16) the strength reduction coefficient proposed in [21] has been used in the case of soil-structure interaction: �:� = ([\ − 1) d:d] + 1 9: ≤ 9n (17) �:� = [\ 9: > 9n (18) the �:� allowed to plot the new demand spectrum (say`9: , bca, sdy `9: , bca), based on the elastic spectrum, and the following relationships: bc-c `9: , bca = dce?`d: ,f: ag:h(d: ) (19) bcjc `9: , bca = d: , 6m, bc-c `9: , bca (20) the displacement demand bcj of the replacement sdof on a flexible base is obtained by the intersection between the new capacity spectrum and the new inelastic demand spectrum ((sa(t, bc), sd(t, bc)). thus the global displacement demand on a flexible base is calculated by the relationship: ij = гbcj where г is the modal participation coefficient. iv. description of the studied rc frame structure the studied 2d rc frame structure is shown in figure 2. the columns and beams are calculated to satisfy the strong column weak beam condition (collapse through global mechanism) according to the algerian code [2]. the design load fd is 300.14kn, calculated with sa/g equal to 0.197 using the inelastic response spectrum (sa/g, t(s)) of the algerian code engineering, technology & applied science research vol. 12, no. 6, 2022, 9420-9425 9422 www.etasr.com attia & hadji: assessment of the soil structure inertial interaction effect on the behavior coefficient … for rocky soil (tc=0.3), where 5% damping ratio and 3.5 behavior coefficient, were considered. the frames were characterized by a span length of 5.5m, 6 spans, inter-story height of 3.0m, and 6 stories. the columns had a rectangular section of 400×300mm 2 ; the beams had a rectangular section of 300×200mm 2 and the reinforcement details are represented in figure 3. the material characteristics are fck = 35mpa, ec = 30gpa for the concrete and fyk = 450mpa, es = 210gpa for the reinforcing bars. the used loads in the pushover analysis and floor masses are presented in figure 3. fig. 2. studied 2d rc frame structure. fig. 3. reinforcement details of the studied structure. the period, the linear displacement shape, and the modal mass participating ratio for the fundamental mode of vibration are t = 1.02s, ø t = [1 , 0.91 , 0.77 , 0.57 , 0.34 , 0.12], and г = 0.795 respectively. v. methodology our study focused on the evaluation of the site effect on the behavior (reduction) coefficient. for this reason, 4 soil types (four shear wave velocities vs) were considered: rocky, firm, loose, and very loose soil (table i). for each soil type, 3 damping soil ratios ζg% had been taken into account: 5%, 10%, and 20% [22]. the lateral load pattern used in the pushover analysis is uniform [16]. the capacity curve is determined by sap 2000 software [12]. the generalized force-deformation curves used in the fema-356 standard were adopted [16]. table i. soil characteristics soil type shear modulus g (kn/m 2 ) poisson coefficient shear wave velocity vs (m/s) rocky soil 648000 0.28 1000 firm soil 180800 0.39 600 loose soil 75000 0.45 300 very loose soil 33500 0.5 150 the elastic response spectrum (sa/g, t(s)) is that of the rpa99 v 2003 seismic code. for each soil type, damping ratio of 5%, peak ground acceleration of 0.5g, and behavior coefficient of 1 were considered (figure 4). fig. 4. the elastic response spectrum for each soil type. ductility μ is estimated by [8]: [ = �� 9 > 9n (21) [ = `�� − 1a d]d + 1 9 ≤ 9n (22) �� = de?dek (23) sae represents the acceleration value corresponding to the period t of the equivalent sdof, in the elastic response spectrum (sa/g, t(s)). the acceleration say is determined by: b-c = lki (24) where fy and m are the actual strength of the equivalent sdof and its mass respectively. vi. results and discussion the pushover curves (base shear versus roof displacement for global structure (f(kn), u(m)), the equivalent model (fy(kn), u(m)), and the bilinear idealization of the equivalent model, are presented in the figure 6 with fy=f/г and u=u/г [5]. the transformation constant (modal participation coefficient ) is г = 1.31 and the equivalent mass amounts to m = 118.58 t. figure 6 shows the pushover curves of the global structure on a fixed base with the necessary forces to calculate the reduction coefficients. fig. 5. pushover curves and bilinear idealization. for each soil type and damping soil ratio, the design strength fd, the first yielding strength f1, and the actual strength fy are shown in figures 7 – 10. fy5, fy10, and fy20 represent the actual strength of the global structure with 5%, 10%, and 20% of the damping soil ratios ζg% respectively. the engineering, technology & applied science research vol. 12, no. 6, 2022, 9420-9425 9423 www.etasr.com attia & hadji: assessment of the soil structure inertial interaction effect on the behavior coefficient … values of the redundancy coefficient (rρ = fy/f1) are in the range 1.05-1.48 and close to rρ = 1.3 prescribed by eurocode 8 [3]. the overstrength coefficient (rω = f1/fd) is 2.1 which is in good agreement with the values found in [23]. the ductility reduction coefficient (rµ = fe/fy) values were determined with the n2 method (without ssi) and the ssi-n2 method (with ssi) (see figure 11). fig. 6. pushover curve of global structure on the fixed base. fig. 7. pushover curve of global structure: rocky soil. fig. 8. pushover curve of global structure: firm soil. fig. 9. pushover curve of global structure: loose soil. fig. 10. pushover curve of global structure: very loose soil. fig. 11. rµ (n2) and rµ ssi (ssi-n2). fig. 12. rρ vs ζg% and soil type. we noted that rµ values with ssi (1.47-1.88) are lower than those estimated without ssi (1.51-2.56). in figures 7-10, fy varies with ζg% and soil type. to clarify this relationship, the variation of the redundancy coefficient (rρ = fy/f1) versus ζg% and soil type is represented in figure 12. this figure shows the decrease of rρ when ζg% is increased in all soil types. indeed, the damping ratio bc of the equivalent system is proportional to ζg% (12), thus the decrease of bc-c `9: , bca. the behavior coefficient, estimated for each soil type with the n2 method, is shown in figure 13. according to rpa 99 v 2003 seismic code, the behavior coefficient in rc frame structure is 3.5 and 5 for infill and without infill masonry respectively. the estimated r values using the n2 method are 4.1, 4.97, 5.75, and 6.96 for rocky soil, firm soil, loose soil, and very loose soil respectively (figure 13). the calculated r values with the ssin2 approach are shown in figure 14 and are in the range 3.673.97 for rocky soil, 4-4.69 for firm soil, 4.01-5.09 for loose soil, and 4.14-5.81 for very loose soil. these values are lower than those of r without ssi (figure 13) and depend on both ζg% and the type of soil (shear wave velocity vs). therefore, damping soil ratios ζg% and soil type should not be neglected when calculating the behavior coefficient r. engineering, technology & applied science research vol. 12, no. 6, 2022, 9420-9425 9424 www.etasr.com attia & hadji: assessment of the soil structure inertial interaction effect on the behavior coefficient … fig. 13. behavior coefficient without ssi (n2). fig. 14. behavior coefficient with ssi (ssi-n2). table ii summarizes the variation in the period t and ductility μ. 9: and [\ are the period and ductility taking into account the ssi. according to (7), when decreasing shear modulus g, ku and kɵ decrease therefore 9: in (11) increase and [\ in (16) increase. table ii. variation of period and ductility vs. shear wave velocity vs soil type t(s) lj(s) μ mn rocky soil 0.66 0.69 1.51 1.47 firm soil 0.66 0.73 1.83 1.68 loose soil 0.66 0.79 2.12 1.79 very loose soil 0.66 0.9 2.65 1.89 the behavior coefficient for the studied frame structure has been estimated by different methods quoted in [24] and shown in table iii. table iii. behavior coefficient with different methods soil type newmark & hall [24] giuffre &giannini [24] krawinkler & nassar [24] rocky soil 1.51 1.57 1.51 firm soil 1.83 1.85 1.80 loose soil 2.12 2.10 2.09 very loose soil 2.07 2.39 2.62 for each soil type, the estimated behavior coefficients r in table iii are close to each other. compared to the r of the algerian code (3.5 and 5), the estimated r using the n2 method or the calculated r using the ssi-n2 method, the r values in table iii are conservative. the mentioned methods in table iii did not take into account the effect of the shear wave velocity and the damping soil ratio on the r value [23]. due to the big difference between the r values calculated by the methods in table iii and the r values calculated by the n2 and ssi-n2 methods, the effect of vs and ζg% on r values cannot be neglected. vii. conclusions in this study, the behavior coefficient r has been estimated with and without soil structure inertial interaction. for this purpose, the pushover n2 method and its extension ssi-n2 method were applied in plan rc frame structures to evaluate the effect of ssi on r value. four shear wave velocities representing rocky, firm, loose, and very loose soil, with three soil damping ratios for each soil type, were considered. the obtained values of r were compared with the values in the algerian code and with those calculated by 3 other methods. based on the obtained results, the following can be concluded: • the n2 simplified method enabled us to estimate the reduction coefficients for each soil type, and thus the behavior coefficients. their values were 4.1, 4.97, 5.75, and 6.96 for the rocky soil, firm soil, loose soil, and very loose soil respectively • the ssi-n2 simplified method allowed us to estimate the reduction coefficients for each soil type and soil damping ζg%. their values were in the range of 3.67-3.97, 4-4.69, 4.01-5.09, and 4.14-5.81 for rocky soil, firm soil, loose soil, and very loose soil respectively. these values are lower than those calculated by the n2 method for each soil type. • the redundancy reduction coefficient increased with decreasing the soil damping ratio. • the ductility reduction coefficient increased with decreasing soil shear wave velocity. • the r values must be calculated while taking into account the shear wave velocity and the soil damping ratio. • the estimated r values without taking into account the ssi effect are conservative. • the n2 and ssi-n2 methods allow us to calculate the behavior coefficient only in buildings where the first mode is predominant and therefore it must be developed to take into account all the modes that have a significant contribution to the response of the building. the effect of torsion also cannot be neglected in the seismic response and therefore on the behavior coefficient, so it must be taken into account in these methods. references [1] g. d. hatzigeorgiou and a. a. liolios, "nonlinear behaviour of rc frames under repeated strong ground motions," soil dynamics and earthquake engineering, vol. 30, no. 10, pp. 1010–1025, oct. 2010, https://doi.org/10.1016/j.soildyn.2010.04.013. 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[24] m. mouzzoun, o. moustachi, and a. taleb, "evaluation du facteur de comportement pour le calcul parasismique des batiments en beton arme (assessment of the behaviour factor for seismic design of reinforced concrete buildings)," journal of materials and environmental science, vol. 4, no. 1, pp. 23–32, 2013. microsoft word etasr_v12_n5_pp9247-9251 engineering, technology & applied science research vol. 12, no. 5, 2022, 9247-9251 9247 www.etasr.com alsuwaiket: feature extraction of eeg signals for seizure detection using machine learning algorthims feature extraction of eeg signals for seizure detection using machine learning algorthims mohammed a. alsuwaiket department of computer science and engineering technology hafar al batin university hafar al batin, saudi arabia malsuwaiket@uhb.edu.sa received: 18 july 2022 | revised: 1 august 2022 | accepted: 2 august 2022 abstract-epilepsy is a central nervous system disorder in which brain activity becomes abnormal and causes periods of unusual behavior and sometimes loss of awareness. epilepsy is a disease that may affect males or females of all ethnic groups and ages. detecting seizures is challenging due to the difference in human behaviors and brain signals. this paper aims to automate the extraction of electroencephalogram (eeg) signals without referring to doctors using two feature extraction methods, namely wavelet packet decomposition (wpd) and genetic algorithm-based frequency-domain feature search (gafds). three machine learning algorithms were applied, namely conventional neural networks (cnns), support vector machine (svm), and random forest (rf) to diagnose epileptic seizures. the results achieved from the classifiers show a higher accuracy rate using cnns as a classifier and gafds as feature extraction reaching 97.93% accuracy while the accuracy rate of the svm and rf was 94.49% and 88.03% respectively. keywords-eeg; cnn; svm; seizure; feature extraction i. introduction epilepsy disorder is considered one of the most common brain diseases. according to the world health organization (who), this disease affects about sixty million people. epilepsy is a brain disorder that causes the recurrent occurrence of epileptic seizures that can cause a possible dangerous lifethreatening situation [1]. brain seizures occur when a temporary and unexpected electrical disruption occurs in the brain along with the discharging of an excessive neuronal apparent in an eeg signal representative of the electrical activity in the brain. eegs are most used in specifying brain disorders and predicting epileptic seizures. epileptic seizure signals can be detected using image scanning of the eeg data, but unfortunately, this commonly requires a few days to collect the data. in addition, it also needs medical experts to study the length of the recorded eeg signals [2]. improving the automated systems that detect seizures will reduce the error that could happen during the data reading process and will decrease the possibility of wrong decisions [3, 4]. recently, other automated seizure detection systems, that use different methods and techniques like machine learning (ml) algorithms, have emerged. the eeg signal has three characteristics that interpret signals as an intricate problem. the first characteristic is the non-stationary and stochastic signal behavior. the main reason for the non-stationary eeg signals is the brain neural activity that might not be in a coherent structure and thus neural charges/discharges of the same fraction of scalp change with different intensity levels over time [5]. the second characteristic is the low signal to noise ratio (snr). eeg signals usually maintain a low snr because electrode conductivity on the scalp is affected by body motion, eye blinking, muscle movement, or other dynamic transitions in the environment. the third characteristic is the non-linearity of the eeg signals. the human brain is a complex system and eeg signals can be seen as a linear model, whereas some researchers have shown that eeg signals fit better in non-linear models [6]. a seizure is a transient extravagant electrical discharge of neurons in the human brain. video monitoring is the most reliable technique for seizure diagnosis [7]. however, eeg signals are used for detection and seizure treatments. also, exploring eeg epileptic records enables neurologists to determine the seizure type and its location in the brain. seizure occurrences in eeg appear as low-frequency abnormal neuronal activities, such as spikes, which might be predominated by high-frequency oscillations and sudden changes in signal amplitude [8]. early seizure detection several hours before its onset is possible by monitoring spike discharge activities and amplitude dynamics of slow waves before seizure occurrences. there are multiple seizure diagnosis tools, such as ct-scan, mri, ultrasound, eeg, and positron emission tomography (pet), where ultrasounds, ct-scan, and mri are too expensive and may not be utilized for extensive assessment. thus, eeg could be one of the most utilized tools to assess epilepsy patients [4]. some researchers tried to detect and select features according to the redundancy and relevancy assessment in seizure monitoring to lower computational complexity. this paper intends to extract the eeg features using two different feature extraction methods and apply two ml algorithms to achieve the best diagnosis of epileptic seizures. the main aim of this paper can be achieved through pre-processing of the corresponding author: mohammed a. alsuwaiket engineering, technology & applied science research vol. 12, no. 5, 2022, 9247-9251 9248 www.etasr.com alsuwaiket: feature extraction of eeg signals for seizure detection using machine learning algorthims eeg signals using different filters, then using two feature extraction methods, namely wpd and gafds to extract the main features from the eeg signal. principal component analysis (pca) method will be used to select the most useful features needed for the classification phase. finally, svm, rf, and cnn ml algorithms will be applied, and the results will be compared in terms of accuracy, speed, and complexity and the best classifier among them will be selected for eeg signal diagnosis. many researchers focused on the use of one classifier with or without the use of any feature extraction methods. furthermore, there is no comprehensive comparison between the used classifiers or feature extraction methods with the evaluation for the running model from run time or performance perspectives. authors in [9, 10] aimed to apply cnns to detect epileptic seizures automatically by utilizing eeg signals to assist neurologists in the diagnostic process. this technique includes creating input data for the cnn model to detect the seizure accurately. the results showed that cnn has the ability to categorize the eeg signals and detect epileptic seizures with high accuracy. the effectiveness of different ml algorithms such as rf, svm, and k-nearest neighbor (k-nn) was tested in [11, 12] to choose the best method with the best performance in detecting epileptic seizures. the ml algorithms were applied to pre-processed data and then to the original dataset. the results showed high accuracy of the rf, svm, and k-nn with values 98.52%, 98.17%, and 96.52% respectively. authors in [13] proposed an automated scheme to identify seizures. they used the svm classifier with a bayesian optimization algorithm to optimize the svm hyper-parameters and integrated the quadratic linear discriminant analysis (qlda) and linear discriminant analysis (lda) to match the findings. the proposed model was tested on a public dataset. the individual level of accuracy of the techniques was 97.05%, 76.41%, and 80.79% for svm, lda, and qlda respectively. epileptic seizure detection was achieved in [14] by applying both extreme gradient boosting (xgboost) and complementary ensemble empirical mode fecomposition (ceemd). two eeg datasets were used to estimate the performance of the suggested model. the results showed that the ceemd-xg boost model is a promising method for epileptic seizure detection. in [15], selection and feature extraction methods were used and ml algorithms were applied to the diagnosis monitoring knowledge system. ii. research methodology the proposed methodology of this paper, as shown in figure 1, starts with the raw data obtained from the eeg dataset. the dataset will be prepared and cleaned by removing the unwanted and noisy data. after that, the data will be ready for the preprocessing phase to be extracted by the proposed feature extraction methods (wpd, gafds). then, the preprocessed data will be passed by the pca feature selection method. finally, the selected features will be applied to the proposed ml algorithms (svm, cnn), and the results will be evaluated and compared. the following sections will go through all the phases mentioned in the proposed methodology in detail. fig. 1. the proposed methodology. iii. eeg dataset description eeg data have been collected from the children’s hospital boston [16], consisting of eeg recordings from pediatric subjects with intractable seizures. recordings, grouped into 23 cases, were collected from 22 subjects (5 males, with ages from 3 to 22 and 17 females, with ages from 1.5 to19). each case in the data files contains between 9 and 40 continuous .edf files from a single subject. in most cases, the .edf files contain 1 hour of digitized eeg signals, although those belonging to some cases are 2 and 4 hours long. occasionally, files in which seizures are recorded are shorter. all signals were sampled at 256 samples per second with 16-bit resolution. most files contain 23 eeg signals (24 or 26 in a few cases). one file in the dataset called recored contains a list of all 664 .edf files included in this collection, and the file records-withseizures lists the 129 of those files that contain one or more seizures. in all, these records include 198 seizures (182 in the original set of 23 cases) [16]. iv. signal preparation and pre-processing in this paper, the preparation phase is used to clean the data by denoising the signals, removing the noise, and selecting the channels and signals that will be used. denoising will be based on signal filters to remove the artifacts and eeg noise from the device and brain signals. the particles are isolated from the signal during the pre-processing phase to observe the artifactfree eeg signals. this method is achieved by filtering the data using the eeg signals acquired from multiple electrodes using a belt pass filter, a common spatial pattern (csp) filter, a broad laplacian filter, and an optimized spatial pattern (osp) filter, which can then be transformed into the surrogate channel. with the use of a finite impulse response (fir) filter, the pure channel data will be small after artifact elimination. in the categorization process, obtaining relevant information is the main issue, and the epilepsy seizure data will be utilized and the whole bio-physical data will be transformed using matlab. engineering, technology & applied science research vol. 12, no. 5, 2022, 9247-9251 9249 www.etasr.com alsuwaiket: feature extraction of eeg signals for seizure detection using machine learning algorthims during the pre-processing phase, the noise will be eliminated from the original signal to acquire the noise-free signal. v. feature extraction feature extraction is a process that removes the corresponding information or functions from the signal to easily explain the features. therefore, the perception of an input signal is a significant operation. the extract of knowledge describes the physiology and pathology of the brain. it includes many variables which involve a huge memory or a strong data processing algorithm [17]. a function extraction method is required for this context to overwhelm these variables or to read the data accurately. the feature collection reduces the dimension of feature space, making it simpler to train and implement results. in this study, two feature extraction methods will be applied to the eeg dataset, wpd and gafds. a. wavelet packet decomposition (wpd) wpd is a wavelet transition under which more filters than other methods are utilized. wavelet packets constitute a peculiar linear wavelet mixture. they form bases that maintain much of their parent wavelets' orthogonality, smoothness, and positions. the linear combination coefficients are determined with a recursive algorithm that allows the study tree's root in each newly computed wavelet packet chain [5]. b. genetic algorithm –based frequency-domain feature search (gafds) the genetic algorithm (ga) uses the chance optimization approach for the analysis and demonstrates global optimization strength. the frequency domain is a coordinate system in signal processing, which defines the frequency characteristics of the signal. a frequency spectrogram represents the relationship between the frequency and the amplitude of the signals, often used for the study of signals. the gafds system adopts ga to look for the proper description of frequency spectrum characteristics [18]. vi. machine learning algorithms supervised ml algorithms are the best classification technique to find whether the data are classified as a seizure or not. in ml, the classification of eeg signals deals with the categorizing a set of classes to which a new reading belongs, based on a training set of eeg feature sets containing occurrences whose class relationship is identified [19]. classification will be done to segment the data that will be tested with obtained data from several classifiers. due to this, it is likely to identify if the information is of seizure or not. svm, rf, and cnns will be implemented in this paper. for software setup, anaconda python 3.7 was used for the experimental work. keras has added due to its success and broad support for various learning styles, design features, and hypermeters. libraries such as panda’s data storage, numpy for multidimensional arrays, and scikit learn for data analysis were enabled. the ml classifiers have been trained, tested, and classified via the sklearn machine libraries. a. support vector machine (svm) svm is an ml technique used for classification and regression. svm is effective in high-dimensional spaces and in cases where the number of dimensions is greater than the number of samples. svm includes a separating hyperplane used to differentiate between the plots or classes. the selection of the hyperplane is done according to the best separating area [20]. the classification method used in svm (figure 2) distinguishes a collection of binary labeled workout data and a maximum distance hyperplane and shows the seizure, nonseizure, and support vector points. the extracted confusion matrix from performing the svm classifier and the comparison of the 2 feature extraction methods can be seen in table i. gafds showed better results with accuracy near 94.5% compared with the wpd which showed a lower accuracy of 92.95%. fig. 2. svm algorithm for eeg data. table i. svm classifier confusion matrix feature extraction number of artifacts accuracy % precision % recall % f1-score % gafds 64,512 94.49 97 98 97 wpd 64,512 92.95 96 97 96 table ii. rf classifier confusion matrix feature extraction number of artifacts accuracy % precision % recall % f1-score % gafds 64,512 88.03 88 98 93 wpd 64,512 87.07 88 97 92 b. random forest (rf) rf is a popular supervised ml technique used in classification and regression problems. it creates decision trees on various instances and takes their vote for classification and average in the case of regression. rf can handle datasets containing continuous variables as in the case of regression and categorical variables as in the case of classification. it performs better in classification problems [21]. with the rf classifier, the data need to be segmented into different sets. we start from calling the sklearn’s ensemble library to call the rf classifier. the function will load the data and split them into training and testing sets. the labeled data will start to train using the maximum iteration number that can be reached. this threshold has been set to 80%. different types of feature extractions have been used to support the classifier. a total of 150 trees, with max depth = 12, and 50 nodes were used. the extracted confusion matrix from the rf classifier and the comparison of the 2 feature extraction methods can be seen in table ii. the engineering, technology & applied science research vol. 12, no. 5, 2022, 9247-9251 9250 www.etasr.com alsuwaiket: feature extraction of eeg signals for seizure detection using machine learning algorthims rf confusion matrix shows the metric values for both feature extraction methods. gafds showed better results with accuracy of 88.03% whereas wpd showed a lower accuracy of 87.07%. c. conventional neural networks (cnns) this paper utilizes a simple cnn to classify epileptic seizures [22, 23]. the diagnosis of epileptic seizure affects the identification and different characteristic of the eeg signals as discussed above. furthermore, it needs a method for classifying epileptic seizures. figure 3 shows the eeg signals classifications using cnn. fig. 3. eeg signal classifications using cnn. table iii shows the cnn parameters that have been used for testing the proposed method. all layers have been chosen based on the dataset size without affecting the performance, run time, and accuracy results. the extracted confusion matrix from the cnn classifier and the comparison of the 2 feature extraction methods can be seen in table iv. the cnn confusion matrix and the used parameters show the metric values for both feature extraction methods used in this paper. gafds showed better accuracy results. table iii. cnn parameters input layer hidden layer neurons epochs output layer based features 10 50 30 based features based features 20 100 30 based features based features 30 150 30 based features based features 40 200 30 based features based features 50 300 30 based features table iv. cnn classifier confusion matrix feature extraction number of artifacts accuracy % precision % recall % f1-score % gafds 10 94.8 97 96 96 20 95.34 97 97 97 30 96.52 97 98 98 40 96.88 97 99 98 50 97.93 97 100 99 wpd 10 94.34 97 95 96 20 95.07 97 96 97 30 95.41 97 97 97 40 96.3 97 98 97 50 97.6 97 99 98 vii. results and evaluation in this paper, eeg signals were used as the data source. the proposed method used and compare different ml techniques. the experiment uses python programming language and an intel i7 processor. the data were split into two sets, the first set (70%) for training and the second (30%) for testing. table v and figure 4 show the obtained results, which show that cnn had the best results for both feature extraction methods, followed by the svm. rf had the lowest accuracy compared with the other ml algorithms in both feature extraction methods. table v. comprehensive results feature extraction number of artifacts accuracy % precision % recall % f1-score % svm gafds 94.49 97 98 97 wpd 92.95 96 97 96 rf gafds 88.03 88 98 93 wpd 87.07 88 97 92 cnn gafds 97.93 97 100 99 wpd 97.6 97 99 98 fig. 4. accuracy results for 70% training and 30% testing of eeg signals. according to the obtained results for classifying eeg data for different size datasets using different ml algorithms, there are considerable differences among the results: some had low and some high accuracy. there are various reasons for such results, such as the use of different eeg data collection and screening methods, the selection of different eeg data features, the use of different eeg data formatting methods, and finally the different classification techniques and their parameters. eeg data classification accuracy is commonly relatively below. the reason behind that is the bulk of noise and artifacts which appear in the eeg signals and are not easy to avoid and hence make their analysis difficult. there are certain methods available to remove the artifacts from the eeg data as discussed above. however, this may cause losing some valuable data and affect the classification accuracy results. viii. conclusions and future work in this paper, different methods of pre-processing for the eeg signals and two feature extraction methods were applied to extract the main features from the eeg signal. pca was used to select the most useful features needed for the classification phase. the goal of this study was to test various ml techniques for the classification of eeg data. three ml algorithms, i.e. svm, rf, and cnn were used in the experiments. the chosen methods were analyzed using eeg data obtained from a children's hospital in boston, including engineering, technology & applied science research vol. 12, no. 5, 2022, 9247-9251 9251 www.etasr.com alsuwaiket: feature extraction of eeg signals for seizure detection using machine learning algorthims eeg reports from children with intractable seizures. the chosen algorithms were built, and the results were compared in terms of accuracy and other evaluation methods, and the best classifier among all methods was selected for eeg signal diagnosis. the cnn gave the best results in eeg data classification with. it should be noted that the findings are fully disparate when it comes to classifying eeg data separately for each subject. this means that the specific participants have major variations. another important finding is that centered brain activities for a particular target will lead to greater accuracy than various brain activities for multiple targets. for future work, the use of other methods such as fuzzy logic [24], decision tree algorithm [25], and other supervised ml methods such as k-nn, naïve bayes, and logistic regression [26-28] is recommended. references 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[28] m. alsuwaiket, a. h. blasi, and r. a. al-msie’deen, "formulating module assessment for improved academic performance predictability in higher education," engineering, technology & applied science research, vol. 9, no. 3, pp. 4287–4291, jun. 2019, https://doi.org/ 10.48084/etasr.2794. microsoft word 6-444-ed.doc engineering, technology & applied science research vol. 4, no. 4, 2014, 686-689 686 www.etasr.com baluch et al.: advanced high strength steel in auto industry: an overview advanced high strength steel in auto industry: an overview nazim baluch school of technology management & logistics cob, universiti utara malaysia nazimbaluch@uum.edu.my zulkifli mohamed udin school of technology management & logistics cob, universiti utara malaysia zulkifli@uum.edu.my che sobry abdullah school of technology management & logistics cob, universiti utara malaysia sobry@uum.edu.my abstract the world’s most common alloy, steel, is the material of choice when it comes to making products as diverse as oil rigs to cars and planes to skyscrapers, simply because of its functionality, adaptability, machine-ability and strength. newly developed grades of advanced high strength steel (ahss) significantly outperform competing materials for current and future automotive applications. this is a direct result of steel’s performance flexibility, as well as of its many benefits including low cost, weight reduction capability, safety attributes, reduced greenhouse gas emissions and superior recyclability. to improve crash worthiness and fuel economy, the automotive industry is, increasingly, using ahss. today, and in the future, automotive manufacturers must reduce the overall weight of their cars. the most cost-efficient way to do this is with ahss. however, there are several parameters that decide which of the ahss types to be used; the most important parameters are derived from the geometrical form of the component and the selection of forming and blanking methods. this paper describes the different types of ahss, highlights their advantages for use in auto metal stampings, and discusses about the new challenges faced by stampers, particularly those serving the automotive industry. keywords: advanced high strength steel; automotive industry; auto metal stampings; ahss i. introduction steel powerfully impacts how all seven billion of us on the planet go about our daily lives, wherever we are. touching every aspect of the way we live, work and play; no other material provides the same unique combination of strength, formability and versatility. steel helps feed and clothe us, provides employment and makes infrastructure, construction and transportation possible; and all this is done sustainably with a recycling rate well above 90 percent. the world’s most common alloy, steel, is the material of choice when it comes to making products as diverse as oil rigs to cars, planes to skyscrapers simply because of its functionality, adaptability, machine-ability and strength [1]. to improve crash worthiness and fuel economy, the automotive industry is, increasingly, using advanced high strength steel (ahss). manufacturers unavoidably have to reduce the overall weight of automotives. the most cost-efficient way to do this is with ahss. however, there are several parameters that decide which ahss type to be used. the most important parameters derive from the selection of forming and blanking methods and from the geometrical form of the component [2]. using ahss offers many environmental advantages. when weight is reduced, a smaller amount of raw material is used and less energy is consumed. at the same time, less energy is needed to transport the steel [2]. ii. ahss exposition the term ahss is generally used for dual phase steels, complex phase steels, trip steels and martensitic steels. it primarily stands for multi-phase steels. the high yield strength micro-alloyed steels also belong to the ahss group. conventional high strength steels are single phase ferritic steels. automotive steels are classified in three designations: metallurgical designation includes low-strength steels, conventional high strength steel, and the newer types of ahss. the second classification method, important to part designers, is the strength of the steel. the third classification method presents various mechanical properties or forming parameters of different steels, such as total elongation, work hardening exponent n, or hole expansion ratio. the metallurgy and processing of ahss grades are somewhat novel compared to conventional steels. their remarkable mechanical properties is the result of their unique processing and structure. all ahss are produced by controlling the cooling rate from the austenite or austenite plus ferrite phase, either on the run-out table of the hot mill (for hotrolled products) or in the cooling section of the continuous annealing furnace (continuously annealed or hot-dip coated products). they are classified into six categories: dual phase (dp) steel, transformation-induced plasticity (trip) steel, complex phase (cp) steel, martensitic (ms) steel, ferriticbainitic (fb) steel and twinning-induced plasticity (twip) steel. the ahss solve two distinct automotive needs by two different groups of steels. the first group, as a class, has higher strength levels with improved formability and crash-energy absorption compared to the current hsla (high strength low alloy) grades. this requirement is fulfilled by the dp and trip grades of steel, which have increased values of the work hardening exponent. the second is to extend the availability of steel in strength ranges above the hsla grades. this area is covered by the cp and ms grades. originally targeted only for chassis, suspension, and body-in-white components, ahss are engineering, technology & applied science research vol. 4, no. 4, 2014, 686-689 687 www.etasr.com baluch et al.: advanced high strength steel in auto industry: an overview now being applied to doors and other body panels. additional steels are designed to meet specific process requirements. these include increased edge stretch flange-ability, strengthening after forming, or increased springback tolerances. by combining a number of different microstructures not traditionally found in conventional hss, a wide range of properties are possible with ahss. this allows steel companies to tailor the processing to meet the ever more focused application requirements demanded by the automotive industry. a. evolving ahss types in response to automotive demands for additional ahss capabilities, steel industry research continues to develop new types of steel [3]. these steels are designed to reduce density, improve strength, and/or increase elongation. for example, nano steels are designed to avoid the low values of edge stretch (local elongation) experienced by dp and trip steels. instead of islands of martensite, the ferrite matrix is strengthened with ultra-fine nano-sized (<10 nm) particles. this is accomplished in hot-rolled high strength steel with a tensile strength around 750 mpa. the resulting steel has a high ys/ts ratio with an excellent balance of total elongation and local elongation (hole expansion ratio). other examples of these developing steels are ultrafine grain, low density, and high young’s modulus steels [3]. b. ahss benefits ahss is most advantageous when used for safety components, structural parts of the car body and the chassis. as a general rule, the weight reduction is about 50 percent, i.e. when compared to mild steel the thickness is halved without sacrificing strength. as a result, ahss has become the material of choice for sill reinforcements, a-pillars, b-pillars, side impact beams, waistline reinforcements, bumpers, roof bows and seats. ahss steel has also been introduced in all other vital areas of the car and many new cars are already composed of 30 to 40 percent ahss. in only a few years, ahss is predicted to make up 40 to 50 percent of the sheet steel used in cars contributing to a 5 percent reduction in total ghg (green house gas) emissions. the advantages of using ahss are evident in all types of cars. small cars benefit from greatly improved crash safety while heavier cars, like suvs, can be made much more fuel efficient. the smooth and cost-efficient transition from mild steels, or conventional high strength steels, to ahss is one of the factors behind the success of ahss within the automotive industry. this is because ahss can be formed and joined in much the same way as milder steel, but with only half the thickness. the cutting and forming of ahss can be done without increased force and common welding and joining techniques can be used with only minor adjustments. even greater benefits can be gained when switching to new forming methods, like roll forming. this process enables the manufacturer to produce complicated profiles in a single run; roll forming can be done with lower tool wear and very tight radii of the profile when using ahss. the advantages of ahss over aluminum are easily summarized: lower cost with the same weight and strength. the ability to form complicated profiles is another of the many benefits offered by ahss compared to aluminum. on beams inside the car, aluminum must be three times the thickness of ahss to provide the same strength. when compared with new materials, such as composites, the cost benefits of using ahss is even more apparent. the automotive industry of today has decided that ahss is superior to aluminum for nearly all applications. c. designing with ahss from a design point of view, ahss is generally a favored solution. however, the high stresses and low thickness puts emphasis on finding a solution that uses the full potential of the material. design challenges can include local buckling effects, loss in stiffness, robustness and fatigue issues. with the right production process and design, it is easy to deal with these challenges. d. the strengths of ahss dual phase and martensitic steels are available with very high initial yield strength. in addition to this initial strength, they also exhibit a pronounced work-hardening when formed, as well as a bake hardening effect from the painting process. typically the work-hardening effect is about 150 mpa at a strain of two percent and the corresponding bake hardening effect another 50 mpa for a typical painting process. in addition to the work and bake hardening effect, ahss exhibits a strain rate hardening effect, i.e. they sustain higher stresses at an increased deformation speed. this effect corresponds to an increase of about 100 mpa for the high strain rates that are involved locally in a car crash. the high strength of ahss is a useful tool to reduce the weight of the body-inwhite (biw), bumpers systems, door side impact beams, seat structures etc. e. optimizing the energy absorption there is a potential to reduce the weight in components, by upgrading the strength of the steel. generally the absorbed energy is proportional to the square of the thickness and linear to the tensile strength of the material. if for instance the tensile strength of the steel is doubled, the thickness and the weight can be reduced by 30 percent, resulting in equivalent energy absorption. one of the main challenges when using ahss for energy absorption by folding is to secure robust behavior. progressive folding gets harder to achieve in axial crushing as the material strength increases and the thickness is reduced. to increase the robustness, an effective pattern of triggers or change of the global geometry can be introduced. f. challenges in forming ahss forming of ahss is not a radical change from forming conventional hss. the major acquisition of new knowledge and experience needed for forming higher strength steels in general increased gradually over the years as ever-increasing strengths became available in the hsla grades. now new demands for improved crash performance and reduced mass and cost, have spawned a new group of steels that improve on engineering, technology & applied science research vol. 4, no. 4, 2014, 686-689 688 www.etasr.com baluch et al.: advanced high strength steel in auto industry: an overview the current conventional base of hss. the improved capabilities the ahss bring to the automotive industry do not bring new forming problems but certainly accentuate problems already existing with the application of any higher strength steel. these concerns include higher loads on presses and tools, greater energy requirements, and increased need for springback compensation and control. in addition, ahss have a greater tendency to wrinkle due to the lack of adequate hold-down and often a reduction in sheet thickness. matching exact mechanical properties of the intended steel grade against the critical forming mode in the stamping not only requires an added level of knowledge by steel suppliers and steel users, but also mandates an increased level of communication between them. new emphasis is being placed on determining specific needs of the stamping, highlighting critical forming modes, and identifying essential mechanical properties. the interaction of all inputs to the forming system means the higher loads and energy needs of ahss also place new requirements on press capacity, tool construction/protection, lubricant capabilities, process design, and maintenance. since many applications of ahss involve load bearing or crash analyses, computerized forming-process development has a special utilization in structural analysis. previously the part and assembly designs were analyzed for static and dynamic capabilities using cad stampings with initial sheet thickness and as-received yield strength. often the tests results from real parts did not agree with the early analyses because real parts were not analyzed. now virtual parts are generated with pointto-point sheet thickness and strength levels nearly identical to those that will be employed when the physical tooling is constructed. deficiencies of the virtual parts can be identified and corrected by tool, process, or even part-design before tool construction has even begun. iii. discussion ahss forming challenges stem mainly from multi-phase structure and complex manufacturing processes, such as determining the material properties with accuracy requires new testing methods, and batch-to-batch inconsistency is common. due to their high strength and low formability early fractures are observed in several forming operations, requiring fracture investigation. larger press capacities are required for forming or blanking and tools wear out quickly. lubricants, tool materials and coatings require careful selection, while larger springback (leading to dimensional inaccuracy) is an important issue requiring additional development and considerations [4]. a. inconsistency of mechanical properties ahss are performance-based steel grades. they are named and marketed according to the metallurgical type (dp, trip, etc.) and their strength. steel producers may achieve the required minimum by various chemical and manufacturing processes; several materials can maintain the minimum strength requirement although their chemical compositions may not be constant. since different mills may have different methods of production, their tensile properties may match while other material parameters such as elongation and weldability may vary [5]. due to the performance based grading, sometimes mills may deliver steels with properties that exceed standard requirements. a stamping company may require an ahss with a minimum strength of 900 mpa. the steel supplier may have a batch that has 1200 mpa strength. technically, the supplier meets the minimum requirement. however, the formability of a stronger metal will be different [4]. b. formability it is well known that ahss grades have different failure mechanisms compared to mild steels and hsla steels. this is mainly caused by local failures which are observed more commonly in forming ahss, due to multi-phase structure and phase changes during deformation. these local failures do not necessarily correlate with n-value, r-value or total elongation [6]. c. lubrication in sheet metal forming lubrication is essential in stamping to avoid metal to metal contact and provide a cooling effect by preventing heat generation and transfer during deformation. friction and lubrication in sheet metal forming are influenced by various parameters such as material properties, surface finish, temperature, sliding velocity, contact pressure, and lubricant characteristics [7, 8]. a good understanding of the parameters that affect friction is essential for selecting lubricants and producing good quality sheet metal parts. in sheet metal forming, the magnitude and distribution of friction affect metal flow, part defects and quality, as well as tool wear and production costs; it is one of the process variables that profoundly affect the quality of stamping sheet materials. using a good lubricant can significantly reduce scrap rate and/or improve the quality of stamping. forming ahss often causes lubricant film break down and galling that increases scrap rates and tool maintenance cost. the increasing use of ahss in new product designs puts higher demands on tool steels and lubricants used in forming and blanking/punching operations. the use of ahss has been steadily increasing in vehicle body constructions to enable improved fuel economy and vehicle safety performance. however, the high press loads required for stamping ahss sheets causes severe chipping and adhesive wear on stamping/blanking die materials [9]. due to the high strength of ahss, more forming loads are required. in many cases, forming loads are further increased on purpose, to reduce springback. due to friction and high cold working, temperatures of tools are higher in forming ahss. there are studies showing that 1200 c temperatures are not uncommon in production conditions. higher contact pressures and higher temperatures in the die-sheet interface are both detrimental for lubricants. lubricant manufacturers recommend high solids polymer (hsp) lubricants or synthetic lubricants with extreme pressure (ep) additives [10]. d. post metal forming operations most of the lubricants are applied on sheet metals before press forming. lubricants also affect post-metal forming operations such as welding, adhesive bonding, and painting. in engineering, technology & applied science research vol. 4, no. 4, 2014, 686-689 689 www.etasr.com baluch et al.: advanced high strength steel in auto industry: an overview addition to their good lubricity, lubricants must be easily removable from the formed panels, because the stamped part has to be completely oil-free for painting. therefore, in selection/evaluation of stamping lubricants, it is necessary to consider advantages and disadvantages of lubricants not only for deep drawing, but also for assembly and painting operations [11]. e. work hardening and springback the work-hardening and springback characteristics of ahss can require stamping operations to boost press tonnage and increase ram dwell time. the resulting increase in friction and associated heat can break down stamping lubricants, deplete their boundary protection and render them ineffective. in these situations, stampers opt for lubricants with extremepressure (ep) additives such as chlorine, sulphur and phosphorous. activated by heat, these additives react with metal to form metallic “salts” with low shear strength. these salts provide an additional yet temporary coating to protect the tools and work piece. as the tool and work piece temperatures increase during deformation, lubricants with ep additive become thinner (low viscosity), may burn. on the other hand, the lubricants with extreme temperature (et) additives become thicker (high viscosity). lubricants with et additives stick to the hot work piece and create a friction-reducing film barrier between the tool and the work piece [12]. dimensional control is extremely important when stamping automotive parts. newer steels exhibit specific stress-strain curves, resulting in unique springback levels and behaviors. springback is the tendency for a material to return to its preformed position and has negative consequences for part dimensions. in order for parts to be manufactured in large volumes, each part must be reproducible hit after hit. researchers must look at how to compensate for springback by examining all the variables in the manufacturing process including tooling, part shape and the machinery itself to ensure volume production repeatability. ahss research has resulted in the development of new steels, like dp 980 and dp 1180 grades. as new steels with differing stress-strain curves enter the manufacturing pipeline, tooling manufacturers need the data to plug into die-design calculations [13]. iv. conclusion the increasing demand for safety in cars necessitates higher strength material to be used in critical safety elements in the car body. a solution to meet these objectives is to use ahss in the car body. a higher strength work material leads to an increased strength of the formed part and less material may be needed to achieve the desired detail strength [14]. newly developed grades of advanced high-strength steel (ahss) significantly outperform competing materials for current and future automotive applications. this is a direct result of steel’s performance flexibility, as well as its many benefits including low cost, weight reduction capabilities, safety attributes, reduced greenhouse gas emissions and superior recyclability [15]. ahss is the most competitive material on the market today. with well proven production processes requiring minimal investments, the higher price of ahss is quickly offset by reduced volumes. one steel grade of ahss replaces several traditional steel grades. the increased use of ahss is leading the way in crash safety. steel is at the core of the green economy. ahss provide an excellent way to reduce weight and improve performance. dual phase and martensitic steels show a good combination of strength, formability and weldability. this, together with the cost-effectiveness of cold forming results in very attractive solutions for body-in-white structural parts, as well as safety parts such as door impact beams, bumper systems and seat structures. references [1] docol, “docol’s advanced high strength steels for the automotive industry”, docol-ssab automotive brochure, 2012 [2] uddeholm-ssab, “tooling solutions for advanced high strength steels–selection guidelines”, ssab swedish steel brochure, 2013 [3] worldautosteels, evolving ahss types,http://www.worldautosteel.org /steel-basics/steel-types/evolving-ahss-types/ [4] m. s. billur, t. altan, “challenges in forming advanced high strength steels”, proceedings of new developments in sheet metal forming, pp. 285-304, 2012 [5] k. s. choi, w. n. liu, m. a. khaleel, “influence of manufacturing processes and microstructures on the performance and manufacturability of advanced high strength steels”, journal of engineering materials and technology, vol. 131, no. 4, pp. 041205-041213, 2009 [6] j. dykeman, d. hoydick, t. link, h. mitsuji, "material property and formability characterization of various types of high strength dual phase steel", sae technical paper 2009-01-0794, 2009 [7] h. kim, h. palaniswamy, t. altan, “investigation of tribological conditions in forming uncoated and galvanized advanced/ultra high strength steels”, cpf, 2, 3/06/01, 2006 [8] n. bay, a. azushima, p. groche, i. ishibashi, m. merklein, m. morishita, t. nakamura, s. scmid, m. yoshida, “environmentally benign tribo-systems for metal forming”, cirp annals-manufacturing technology, vol. 59, no. 2, pp. 760-780, 2010 [9] c. wang, j. chen, z. c. xia, f. ren, “die wear prediction by defining three-stage coefficient k for ahss sheet metal forming process”, the international journal of advanced manufacturing technology, vol. 69, no. 1-4, pp. 797-803, 2013 [10] h. kim, t. altan, q. yan, “evaluation of stamping lubricants in forming advanced high strength steels (ahss) using deep drawing and ironing tests”, journal of materials processing technology , vol. 209, no. 8, pp. 4122–4133, 2009 [11] t. altan, e. tekkaya, sheet metal forming: fundamentals, volume i, asm international, 2012 [12] irmco, “lubricant is lubricant”, irmco brochure 2012 http://www.irmco.com/lib/media/irmco_2012_brochure.pdf [13] l. kren, “hurdles to stamping giga pascal strength steels ahss, metalform”, 2011 http://www.metalformingfacts.com/hurdles-stampinggigapascal-strength-steels.html [14] h. kim, advanced high strength steels (ahss): evaluation of lubricants, tool materials and coatings for reducing galling, lap lambert academic publishing, 2009 [15] steelworks, “steel is the solution to achieve 54.5 mpg by 2025”, http://www.steel.org/en/autosteel_org/web%20root/research/growth %20of%20ahss.aspx microsoft word etasr_v12_n6_pp9579-9583 engineering, technology & applied science research vol. 12, no. 6, 2022, 9579-9583 9579 www.etasr.com lifa et al.: the influence of hot electrons on the calculation of ionization rates the influence of hot electrons on the calculation of ionization rates amal lifa laboratory of operator theory and pde faculty of exact sciences university of el oued el-oued, algeria lifa-amel@univ-eloued.dz samia dilmi laboratory of operator theory and pde faculty of exact sciences university of el oued el-oued, algeria samia-dilmi@univ-eloued.dz salah-eddine bentridi laboratory of energy and smart systems faculty of science and technology university of khemis miliana ain defla, algeria s.bentridi@univ-dbkm.dz received: 28 august 2022 | revised: 12 september 2022 | accepted: 21 september 2022 abstractelectron-impact ionization (eii) is considered one of the most important ionization methods in dynamic systems, in which elements and ions are suddenly exposed to energetic electrons. in many plasma types, it has been observed that some electrons (hot) are governed by a non-maxwellian energy distribution. this study illustrates the effects of a nonmaxwellian distribution on beryllium and be +2 emission lines and their effective ionization rate coefficients. the focus on beryllium as an impacted material by electron flux aimed to evaluate the eii rates for be and generate the corresponding datasets needed for be +2 data analysis. an interaction cross-section was generated using the flexible atomic code (fac) and used in the estimation of the eii distribution energy functions to estimate the ionization rates for a non-maxwellian distribution. the use of nonmaxwellian energy distributions for different fractions of hot electrons showed the sensitivity of these rates to the fraction of hot electrons and the forms of the electron energy distribution. the results were in good agreement with those found in the literature. keywords-electron-impact ionization (eii); fac; distribution function; non-maxwellian distribution; cross-sections i. introduction in plasma physics, considerable efforts are deployed to apprehend the emission of electrons during atomic ionization collisions under experimental and numerical perspectives. electron impact ionization (eii) is important in dynamic systems where ions are immediately exposed to energetic electrons [1]. such incidents may be encountered in solar flares, supernova remnants, and merging clusters of galaxies [2, 3]. eii has attracted considerable interest in the study of the distribution of the charge state of nonthermal electrons in plasma, where the high-energy tail includes a large population of electrons residing above the eii rate. consequently, eii is important to model astrophysical systems including nonthermal distributions [4]. determining the spatial distribution of hot electrons in plasma is very crucial as they affect radiation production, energy balance, and plasma dynamics [5, 6]. these electrons may cause considerable energy losses and negatively impact the plasma's stability and control. in plasma physics and nuclear fusion, non-maxwellian distributions and hot electrons relate to plasma sources and their evolution. besides that, they are necessary to assess the radiative properties of a broad range of plasma sources. beryllium (be) was used in the iter fusion reactor project to cover the inner surface of the first wall as a plasma-facing material because of its unique physical property to contain radiation power and its ability to be less contaminated by plasma with low fuel retention. in this sense, it is very important to obtain accurate collisional data of eii on be. the estimation of coefficient rates is based on analytical concepts developed in previous works and datasets [7]. these studies on hot electrons were related to specific experiments, and the results obtained were restricted to specific types of energy distribution used to characterize these electrons. it should be noticed that rates of collisional ionization, resonant excitation, and radiative recombination present a relative sensitivity with characteristic energy and functional shape of the electron distribution, which may have significant consequences on collisional radiative two-temperature models. these models usually include distributions of hot electrons with much greater energies than the usual transition gaps, where the sensitivity of hot electron effects for both gaussian and maxwellian distributions is observed separately [8]. corresponding author: dilmi samia engineering, technology & applied science research vol. 12, no. 6, 2022, 9579-9583 9580 www.etasr.com lifa et al.: the influence of hot electrons on the calculation of ionization rates in this study, an analytical and numerical investigation on the ionization rates of plasma made from a population of electrons including a non-maxwellian distribution of a given initial velocity, was conducted. the effects of the simultaneous presence of electrons with low and high energies on the calculation of ionization rate coefficients and their energy distribution functions are discussed. this approach aimed to present the influence of hot electrons and investigate the impact of the electron energy distribution functions on the measurement of the ionization rates for be +2 using a nonmaxwellian energy distribution for various hot electron fraction values. the non-maxwellian distribution used gave satisfactory results for larger fractions of hot electrons. this study focused on larger fractions of hot electrons because using a non-maxwellian distribution gives unacceptable results on weak fractions. compared to previous works on neutral helium ionization rates calculated using a non-maxwellian distribution and the power-law distribution functions of electrons [9], this study exhibits a great improvement in the curves obtained, particularly for the maxwellian and power-law distribution functions. ii. theoretical aspect a. ionization cross-sections in laboratory or astrophysical plasma studies, it is very crucial to understand the ionization balance based on the estimation of ionization rates for different ions involved in such plasmas. many analytical and statistical formulas are dedicated to the estimation of ionization rates and the related crosssections. in this way, the lotz formula has been frequently used in plasma-related fields as one of the most suitable empirical formulas to calculate the cross-sections of the ionization rates [10], based on experimental measurements of ionized elements with low z [11, 12]. similarly in [13], the parametric formula initially introduced in [14, 15] was used. recently, dedicated codes were built to calculate the corresponding atomic structure and data related to interaction processes (recombination, ionization, excitation, etc.). therefore, the flexible atomic code (fac) was mainly made to accommodate radiative transformation, direct collisional excitation, and ionization [16]. this robust package was presented in [17] to combine different atomic processes into a common theoretical system and provide a uniform, flexible, and easy-to-use user interface to access all computational tasks. fac was used to calculate the eii cross-section, based on the distorted wave (dw) relativistic approximation and the interpolation-factorization methods [16, 17]. the cross-section of the transition: 2�� → 1�2�� for be was generated using this code on a varying energy range from 0 to 1000ev, as shown in figure 1. the fac code included the dw method and generated cross-section data with a satisfactory level. figure 2 shows the cross-sectional data of the ionization processes, obtained according to the dw method, taking into account the potential felt by the incident electron when approaching the nucleus of the target ion [18]. thus, it was possible to generate the cross-sections needed over a large interval of incident electron energies, starting from the ionization threshold [17]. fig. 1. cross-section of be obtained by fac. fig. 2. cross-section of be+2 obtained by fac. b. the effects of hot electrons on the calculation of ionization rates free electrons in a plasma are characterized by a given energy distribution. the quantity of interest is the ionization rate coefficient per electron impact, obtained by averaging the product of the electron velocity by the corresponding ionization cross-section. in the case of direct ionization, the coefficient of ionization rates is given by [19, 20]: ��� . �� � = � ����������� (1) where v and e are the velocity and energy of the incident electron respectively, σ(ε) represents the impact ionization cross-sections calculated by fac, f(e) is the electron energy distribution function, and e is the energy of the impacting electron. a non-maxwellian distribution function of the energy f(e) was used to calculate the ionization rates by the mean of cross-sections. the produced plasma under low pressure often exhibit a non-maxwellian behavior of electron distributions. such a distribution can be represented by a function of two temperatures corresponding to both hot and cold electron populations. the following non-maxwellian distribution was chosen to study the effects of hot electrons on the ionization rates of be [20]: ��� ��� = �1 − ���� ��� � !"#$ � + ���� �& � ��� � (2) where fhot is the normalized hot electron fraction, fm is the maxwell energy distribution function, and tbulk and thot are the bulk and hot electron temperatures respectively. engineering, technology & applied science research vol. 12, no. 6, 2022, 9579-9583 9581 www.etasr.com lifa et al.: the influence of hot electrons on the calculation of ionization rates by substituting (2) in (1) and including the effective ionization cross sections generated by the fac code for be atoms, it was possible to obtain the ionization rates for different values of hot electron fractions fhot, as shown in figure 3 by plotting the obtained curves representing the variation of the ionization rate coefficients of be using the non-maxwellian distribution. this was carried out for different values of hot electron fractions fhot as a function of the electron temperature t, taken between 1.0 and 10 3 ev, including the results obtained by applying a maxwell distribution for fhot=1. the temperature tbulk was taken equal to an average value of kbtbulk=0.85ev [19]. the fractions of cold electrons are less than those of hot electrons. the rate coefficients at very low temperatures are very sensitive to the cross-section behavior near the threshold and significant discrepancies may be observed between various theoretical calculations and/or empirical scaling. the plane wave of born approximation is not valid at low energies and gives typically lower cross-sections than the dw computation method near the threshold by a factor of 2 [10]. fig. 3. ionization rates of be obtained for a non-maxwellian distribution with different values of hot electrons fraction fhot=0.7, 0.8, 0.9, and 1.0. figure 3 shows that the curves obtained for the various fractions (70%, 80%, 90%) are generally quite close to the plotted for the referential fraction value fhot=1 representing the maxwellian distribution. as a matter of fact, in the case of low temperatures, the ionization rates are very sensitive to the cross-section behavior [21]. there are noticeable differences between theoretical and experimental methods. examining the published results in [10] for comparison, the plotted curves of ionization rates in figure 3 are shifted down from the maxwellian distribution for fhot=1 as the hot electron fraction decreases. this shows a remarkable sensitivity of the ionization rates related to hot electron fractions. c. distribution functions the electron energy distribution is highly important in plasma physics, nuclear fusion reactions, and astrophysics [22]. consequently, collisional-radiative atomic models assessing the effect of a non-maxwellian distribution and hot electrons are extremely important to apprehend the obtained data in atomic physics, such as in spectroscopic analysis to establish the existence and characteristics of the behavior mechanisms of electrons in studied plasmas [23, 24]. dedicated experiments and research on hot electrons provided valuable contributions to build suitable energy distribution functions, as given by the following expressions [20]: maxwellian: �� �', ) � = 2* +,-./ 012 3−' )4 5 (3) gaussian: �6 �', ) � = -.√, 8 � 9):;<9+= -.4 > ? 012 @− <�+�+=�-. > �a (4) powerlaw: �b�', ) � = < c� -.def> '�c; ' ≥ ) (5) where te, ε, ε0 are the energies of electrons corresponding to each distribution, and γ is the decay constant. the energy distribution helps to examine how the used model affects the estimation of the ionization rates for given cross-sections. for plasma described by a single-temperature maxwellian distribution, it is possible to calculate de-excitation and recombination rates with accurate precision, explicitly from the coefficients of collisional excitation and ionization rates. in the case of plasmas with atoms described by nonmaxwellian distributions, the cross-sections related to calculated rates must be integrated through the entire distribution of electron energies. a simple analytical formula could express the associated rate coefficients when using the appropriate approximation of the cross-sections as an energydependent function. this study aims to extend the calculations for plasmas described by a non-maxwellian distribution. plasmas containing a small proportion of hot electrons may be observed in the universe or in the laboratory, and induced plasmas often exhibit non-maxwellian distributions with hot and cold electrons. therefore, using cross-sections generated by the fac, the ionization rates were calculated using different energy distribution functions f(ε). ionization rates were obtained for various values of hot electron fractions fhot by separately substituting fx(ε, τe) from (2) with maxwellian (3), gaussian (4), and power-law (5). iii. results and discussion figures 4 and 5 show the ionization rates for be +2 for different values of hot electron fractions using maxwellian, gaussian, and power-law models in (2). in the case of the maxwellian model shown in figure 4, the values of the coefficient rates increased very rapidly at low temperatures. figure 5 shows the comparison between different distribution functions for a specific value. a good agreement can be observed between the ionization rate curves for hot electron fractions ranging from 1 to 10% over the whole energy range. furthermore, the value of the decay constant γ does not significantly affect the calculation estimation for a given value of the fraction of hot electrons [9]. the relative susceptibility of the ionization rates to the form of the electron energy distribution functions when γ=2 and the hot electron fraction assume high values have significant consequences for engineering, technology & applied science research vol. 12, no. 6, 2022, 9579-9583 9582 www.etasr.com lifa et al.: the influence of hot electrons on the calculation of ionization rates collisional radiative models at two temperatures. when the temperature of electrons increases, the hot electron distribution takes a thermal form with a long tail compared to the maxwellian distribution at thermal equilibrium electron distribution functions over the whole energy range for various values of given hot electron fractions fhot. fig. 4. ionization rates of be+2: coefficient rates obtained for the maxwellian distribution function with various fractions of hot electrons fhot. fig. 5. ionization rates of be+2: coefficient rates obtained for maxwellian, gaussian, and power-law distribution functions with fhot=0.1. fig. 6. ionization rates of be+2: coefficient rates obtained for different power distribution functions with various decay constants: (a) γ=2, (b) γ=3, (c) γ=4 and different hot electron fractions. figure 6 shows the ionization rates of be +2 obtained for different power-law distributions defined by a given decay constant γ. figures 6(a) and (b) show the generated results for both power 2 and 3 models at low temperatures and indicate the presence of susceptibility to the fractions of hot electrons as the value of the constant of decay γ increases. figure 6(c) shows significant variations within the 10-100ev range, where a considerable improvement in curve shape is registered for the power 4 model (γ=4). iv. conclusion this study used the fac code and a non-maxwellian distribution function to calculate the ionization rates and the corresponding cross-sections of be and be +2 . most collisional rates were more sensitive to the hot electron fractions than to the exact functional form of the electron energy distributions. 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[26] s. saxena and l. b. roy, "the effect of geometric parameters on the strength of stone columns," engineering, technology & applied science research, vol. 12, no. 4, pp. 9028–9033, aug. 2022, https://doi.org/10.48084/etasr.5138. microsoft word etasr_v11_n6_pp7824-7835 engineering, technology & applied science research vol. 11, no. 6, 2021, 7824-7835 7824 www.etasr.com alalawi et al.: a survey of the application of artifical intellegence on covid-19 diagnosis and prediction a survey of the application of artifical intellegence on covid-19 diagnosis and prediction hana alalawi computer science department college of computer and information systems umm al-qura university makkah, saudi arabia s44280166@st.uqu.edu.sa manal alsuwat computer science department college of computer and information systems umm al-qura university makkah, saudi arabia s44280158@ st.uqu.edu.sa hosam alhakami computer science department college of computer and information systems umm al-qura university makkah, saudi arabia hhhakam@uqu.edu.sa abstract-the importance of classification algorithms has increased during the recent years. classification is a branch of supervised learning with the goal of predicting class labels categorical of new cases. additionally, with coronavirus (covid-19) propagation since 2019, the world still faces a great challenge in defeating covid-19 even with modern methods and technologies. this paper gives an overview of classification algorithms to provide the readers with an understanding of the concept of the state-of-the-art classification algorithms and their applications used in the covid-19 diagnosis and detection. it also describes some of the research published on classification algorithms, the existing gaps in the research, and future research directions. this article encourages both academics and machine learning learners to further strengthen the basis of classification methods. keywords-artificial intelligence; machine learning; deep learning; classification algorithms; covid-19; medical image introduction i. introduction machine learning is one of the fastest growing fields in artificial intelligence (ai). classification algorithms refer to the problem of predictive modeling, in which the class classification is predicted for a given example of input data. many machine learning algorithms are used. this paper will consider k-nearest neighbor (knn), support vector machine (svm), neural networks (nns), decision tree (dt), logistic regression (lr), and random forest (rf). machine learning is divided into 3 main fields based on the learning style: supervised learning, unsupervised learning, or reinforcement learning. this research will present an overview of the classification algorithms and their application in predicting covid-19 cases, focusing on the strengths and weaknesses of each algorithm. this research surveys the machine learning classification algorithms used to predict and diagnose covid19. ii. covid-19 cases and symptoms coronaviruses are a wide class of virus infections that produce illnesses that range from colds to more serious diseases, like the middle east respiratory syndrome (mers) and severe acute respiratory syndrome (sars). in 2019, in wuhan, china, a new coronavirus was discovered which since then has evolved to a global pandemic status. to diagnose covid-19, quickly and efficiently, screening tools are needed. machine learning algorithms with computer vision systems help diagnose covid-19. this section highlights the research focused on machine learning and classification algorithms for covid-19 diagnosis. a. symptoms of covid-19 according to the world health organization [1], covid19 influences people in various ways. most people who contract it have mild to moderate symptoms and improve without hospitalization. the common characteristic symptoms include high temperature, dry cough, and exhaustion. the less common symptoms are aches, sore throat, diarrhea, conjunctivitis, headaches, loss of sense of taste or smell, rashes, and discoloration of the fingers or toes. the most dangerous symptoms are breathing difficulties or shortness of breath, the losing the ability to speak or move and, chest pain or pressure. b. the way covid-19 spreads individuals can catch covid-19 from other people who have the virus. the disease spreads principally by droplets, which are spread by a person with covid-19 through coughing, sneezing, or talking. if people breathe in these droplets from an infected person, they, too, can become corresponding author: hana alalawi engineering, technology & applied science research vol. 11, no. 6, 2021, 7824-7835 7825 www.etasr.com alalawi et al.: a survey of the application of artifical intellegence on covid-19 diagnosis and prediction infected with covid-19. thus, people should keep at least 1m distance from one another. c. the precautions to stop the spread of covid-19 since december 2019, covid-19 has influenced all countries in the world. as of may 2020, the number of confirmed cases and deaths worldwide has sharply increased [2]. the pandemic has negatively impacted different industries, such as transportation, health services, and tourism. many countries took quick action to stop the spread of the virus, which included awareness campaigns, social distancing, lockdowns, and quarantines, and transferring all work and schooling online. virus researchers and doctors began searching for a cure for the virus. covid-19 is now the most significant cause of mortality in many countries, specifically the united states, spain, italy, china, and iran. figure 1 presents the most recent number of individuals diagnosed with covid-19 around the world, while figure 2 illustrates daily covid-19 deaths per million people. it can be clearly seen that the number of confirmed cases and the number of deaths fluctuate from time to time. fig. 1. confirmed covid-19 cases per million. published online at ourworldindata.org. retrieved from: https://ourworldindata.org/coronavirustesting [3]. during the covid-19 pandemic, in may 2020, authors in [4] provided a pre-tuned boosted rf classification algorithm to help the medical industry overcome the gaps of the traditional healthcare system through applying machine learning algorithms in terms of real-time processing and prediction. authors in [2] used a novel dataset with different algorithms. after comparing the results, the boosted rf classifier was identified as a good model for the problem. it achieved an accuracy of 94% and an f1 score of 0.86. authors in [5] provided a comprehensive survey of various classifications by introducing basic classification algorithms and discussing some of the main classification methods, including bayesian networks, knn classification, rf extrapolation, and svm. they also discussed the problems and potential solutions associated with each. authors in [6] focused on implementing ai and machine learning in healthcare by providing better solutions with a high rate of accuracy to overcome the challenges presented by covid-19. they presented a review of the previous studies that applied ai algorithms and techniques to tackle covid-19, such as support vector regression algorithms, supervised multi-layered classifiers (xgboost), deep learning lstm networks, and regression trees. they presented the results associated with the pros and cons for each suggested model. fig. 2. confirmed covid-19 deaths per million. published online at ourworldindata.org. retrieved from: https://ourworldindata.org/coronavirustesting [3]. early detection of covid-19 is essential. previous studies have shown that in initial covid-19 screenings and in all patient-care environments, blood tests are relatively rapid, cheap, and simple to conduct. authors in [7] analyzed the stateof-the-art covid-19 detection techniques, and clinical data were provided in order to encourage researchers to develop better disease prediction modeling. authors in [8] provided a engineering, technology & applied science research vol. 11, no. 6, 2021, 7824-7835 7826 www.etasr.com alalawi et al.: a survey of the application of artifical intellegence on covid-19 diagnosis and prediction comprehensive overview of the methods used for covid-19 detection as well as a compendium of available open-source datasets related to covid-19. sixty newspaper articles, reports, factsheets, and websites dealing with covid-19 were studied and reviewed. most mathematical models were based on susceptible-infected-recovered (sir) models and susceptible-exposed-infected-removed (seir) models, while convolutional neural networks (cnns) was the main ai implementations used with x-ray and ct images. mathematical modeling and ai have proved to be reliable tools to mitigate this pandemic. iii. research methodology for searching and selecting previous studies, the saudi digital library (sdl), ieee xplore, sciencedirect, google scholar databases were consulted. these databases are considered appropriate for covid-19 prediction and cover the newest literature. the research studies retrieved from these databases are relevant and guaranteed to comprehend the purpose of ai systems in covid-19. the databases were searched in a 2-year period between 2019 and 2021. the following keywords were utilized to direct the process of searching: classification algorithms, classification applications, classification review, machine learning, coronavirus, and covid-19. only modern studies and articles containing relevant information about the application of classification techniques concerning covid-19 were selected and extracted. all publication types that were published in conferences, journals, and review papers were selected. the primary result of the search process identified 47 articles that met the review's eligibility rules, which are the novelty of the paper and the use of ai. after examining the full texts, 40 were selected and 4 articles were excluded because other methods were used in diagnosing covid-19 instead of ai. it is difficult to present a comprehensive review of all machine learning classification methods in one article; consequently, this survey only focused on commonly used classification techniques. iv. classification algorithms classification algorithms are the most widely used techniques in the machine learning field. in general, the models in machine learning are divided into 3 general approaches based on their learning style: supervised learning, unsupervised learning, and reinforcement learning. the classification is a way of learning as the machine learns how to assign the labels to each class of the data. there are several models of classification algorithms, such as lr, dt classifier, svm, nns, knn, and rf. table i shows a quick comparison of all the mentioned classification algorithms in terms of their advantages and disadvantages. a. support vector machine svm classification has become popular due to its impressive performance, which is comparable to the performance of advanced nns trained in complex tasks, using high computing cost algorithms. svms were originally designed as an effective approach for pattern recognition and classification [9]. immediately after their introduction, these algorithms were used for some classification problems and applications, such as speech recognition [10], computer vision, and image processing [11]. the svm algorithm is primarily used for classification techniques. svm generates a hyperplane that separates data into various classes. svm can resolve either linear or non-linear issues. the main objective of the svm is to discover a hyperplane in n-dimensional space (n matches the number of features), which clearly classifies the datasets or points of data. the accuracy of the outcome is directly related to the selected hyperplane. it discovers a plane with the maximum distance among the data points of two classes. the hyperplane is illustrated graphically as a line that divides one class from another. the data points are on different sides of the hyperplane and are assigned to different classes. the hyperplane dimension is dependent on the feature quantity. if the input is two features, then the hyperplane is a line and a 2d plane if the true of input is three. the svm is also utilized in medical diagnosis to detect anomalies and in air quality management systems and financial analyses. b. k-nearest neighbor the knn algorithm supposes that similar objects are close to one another. this algorithm is one of the most powerful supervised classification algorithms. knn classification models are often used for searching the nearest neighbor class to predict the target name or label. the knn is a simple algorithm used to save all available cases and classify new cases according to a measure of similarity, which is measured by a distance function (manhattan, euclidean, minkowski, or hamming). nearest neighbor techniques are categorized as structureless knn techniques and structure-based knn techniques. structure-based knn techniques are based on structures of data, such as the orthogonal structure tree (ost), axis tree, k-d tree, and ball tree. additionally, data and site patterns suggesting suspicious behavior are analyzed by knn algorithms. c. neural networks more accurately artificial neural networks (anns). an ann is a series of neurons associated with synapses that mimic the human brain structure and has several components of processing. the human brain, however, is much more complicated. there are neurons or nodes in a neural network. each of these neurons accepts data, processes them, and transfers them to a different neuron. the various units are communicating by transmitting signals to each other. an ann is constructed as a directed graph with nodes and edges that link the nodes. the edges of each node are the interconnections. nns can essentially be used for any task, from spam filtering to computer vision. they are typically utilized for machine translation, identification of anomalies and risk management, as well as language and face recognition. d. logistic regression lr is a machine-learning algorithm that predicts the likelihood of the response variables by given a set of explanatory independent variables. it is a supervised binary classification algorithm [12]. the response variables are coded as binary values, 0 and 1, and based on the values of the binary target variables, the data will be classified. the lr types are binary or binomial, multinomial, and ordinal. the values of the target variable in the binary lr have two possible types, 0 and engineering, technology & applied science research vol. 11, no. 6, 2021, 7824-7835 7827 www.etasr.com alalawi et al.: a survey of the application of artifical intellegence on covid-19 diagnosis and prediction 1, to represent gender (male and female), success or failure etc. multinomial lr is used when the response variable has an unordered 3 or more possible values to represent the data, such as class types a, b, c, and d. the ordinal lr is the classification in which the response variable has 3 or more ordered values, such as student’s scores (high, middle, and low). the lr algorithm has a solid statistical and mathematical background, but it is sensitive to outliers and prone to multicollinearity. e. decision tree the dt classifier is a supervised machine learning algorithm that builds a tree structure to classify the labeled data based on a condition. the root node is the topmost node in the tree, and the leaf nodes represent the outcomes, where the edges connect the nodes to the leaf nodes. f. random forest rf is a classification and regression model, however, it is usually used in classification problems. it is a combination of random dts selected to find the average of the best predictions [13]. to measure the best separates of the data, the rf uses the most voted class approach to select the best solutions [14]. this algorithm is used in different fields in real life applications, such as gene selection, finance analysis, stock market, ecommerce, and medical diagnoses. table i. advantages and disadvantages of different classification algorithms models advantages disadvantages svm efficient, better accuracy. not biased by outliers. non-overfitting sensitive. problems in selecting the right kernel function. datasets have different results based on the kernel function. not optimal for non-linear situations or problems, not the best option for a huge number of features. knn simple to understand. fast and efficient. sensitive to noise; the k number of neighbors should be picked manually. nn identifies complex associations between independent and reliable variables efficiently. capable of managing noisy data. prone to local minima and overfitting. ann processing is complicated to interpret and demands a long processing time. lr reasonable accuracy for datasets and works perfectly if the data set is separated linearly. cannot solve non-linear problems, since it has a linear decision surface. in real-world situations, linearly separable data are rarely found. sensitive to outliers. dt easily processing large dimension data interpretability works for both linear and nonlinear tasks, with no need for scaling or normalizing features. poor performance, and overfitting can easily occur with very small datasets. rf powerful and accurate. good performance on a variety of problems. no interpretability, overfitting can easily occur. need to choose the number of trees manually. v. applications of classification algorithms in covid-19 detection and diagnosis in coronavirus research, diagnosis is an essential preventive phase because it has a similar appearance to other forms of pneumonia. consequently, the discovery of covid-19 is critically important and vital in its initial stages. different diagnostic methods for covid-19, including a range of techniques of medical imagery, blood tests (cbcs), and pcr, have been suggested. the world health organization states diagnoses of covid-19 disease have to be checked with reverse transcriptase-polymerase chain reaction (rt-pcr) tests [15]. according to the u.s. food and drug administration [39], there are 2 main types of tests that have been used to diagnose the virus, rt-pcr and imaging methods such as xray and ct-scanning [16, 17]. rt-pcr testing, however, takes time and this can be dangerous. for this reason, the initial detection of covid-19 is often first conducted with medical imaging and the rt-pcr test is then carried out. the latest results from radiological imagery indicate that these images provide valuable details on the covid-19 virus. the use of advanced ai technology combined with radiological imaging can be useful to accurately diagnose this disease. x-ray imaging has the benefits of being cheap and of low risk for human health [25, 26]. in an x-ray, it is a relatively complex process to detect covid-19. in these photos, the radiologist should carefully note the very long and problematic spots carrying water and pus. therefore, illnesses such as pulmonary tuberculosis may be erroneously identified by a radiologist or a doctor as covid-19. so, the x-ray method has a big error rate. compute tomography (ct) images are often utilized to detect the virus more precisely. however, ct images are much more costly for patients than x-rays. detecting the effect of different respiratory system diseases such as ards, streptococcus pneumonia, chlamydia pneumonia, cavitating pneumonia, pneumococcal pneumonia, aspiration pneumonia, and covid19 on human lungs by using x-ray imaging techniques can be challenging as these diseases have the same impact on human lungs. in raw chest x-ray (cxr) samples using deep nns, authors in [18] implemented a personalized network (darkcovidnet) for the automatic detection of covid-19. the proposed model provides accurate classifications concerning binary (covid vs. no-findings) and multi-class (covid vs. no-findings vs. pneumonia) classification with outstanding performance precision, 98.08% for binaryand 87.02% for multiclassification. multi-classification demonstrated that the expert system can be applied to assist the radiologists in validating the examination process quickly and accurately. coronavirus causes different symptoms such as cough, fever, dyspnea, musculoskeletal, and anosmia/dysgeusia compared to the common cold, flu, and influenzas [19]. authors in [20] proposed a method for binary classification and multi-classification problems by using deep learning cnn networks for covid-19 detection. the model attains 99.6% accuracy on x-ray images and 71.81% on ct-scan images. engineering, technology & applied science research vol. 11, no. 6, 2021, 7824-7835 7828 www.etasr.com alalawi et al.: a survey of the application of artifical intellegence on covid-19 diagnosis and prediction cnns have been used to classify the images of the patients (covid, normal, and pneumonia classes). the accuracy of the cnn multiclass model with adam, sprop, and sgdm optimizers was 96.4%, 95.4%, and 95.5% respectively. on the other hand, the individual classification accuracy with adam, rmsprop, and sgdm optimizers was 97.7%, 94.8%, and 97.8. authors in [21] proposed a method that used the decompose, transfer, and compose (detrac) technique to predict and classify the chest images of covid-19 patients. detrac deals with image recognition and classification successfully. the authors applied the cnn detrac in an x-ray images dataset gathered from many hospitals around the world. the model was trained in 3 steps: first was the extraction of the deep features of the images. second, the optimization step is done by using stochastic gradient descent (sgd). finally, the images were classified by using the last layer of the detrac network. the model achieved a good performance with 95.12% accuracy, 97.91% sensitivity, and 91.87% specificity. on the other hand, authors in [22] proposed a new deep cnn framework to detect and classify the patient’s x-ray images as positive or negative cases. the proposed framework, covidx-net, includes 7 different cnn layers built by 7 models such as vgg16, inceptionv3, v3, densenet, and google mobilenet to analyze and detect viruses. the covidx-net achieved a good performance in vgg19 and densenet with f1-scores of 0.89 and 0.9, respectively. furthermore, authors in [23] introduced another cnn model to detect the confirmed cases of the coronavirus. authors in [17] used machine-learning for the classification of covid-19 and non-covid lung scan slices with 89.8% classification accuracy. authors in [24] used chest x-ray images for covid19 diagnosis, and their classification accuracy was 99.56% for the disease class. authors in [27] presented an early covid-19 detection using svm. the algorithm has applied to ct of abdominal images. from 150 ct images, 4 various dimensional datasets were generated and 4 different methods were employed for extracting chest ct picture features. then, svm was utilized to distinguish covid-19 patients. during the classification process, 10 times cross-validation was used. the achieved classification accuracy was 99.68%. in coronaviruses detection and prediction, deep learning with a cnn is one of the most accurate solutions. diagnosing the infected patients currently is done by either ct-scan or xray chest imaging. authors in [28] used a dataset provided by the kaggle to develop a covid-19 detector, the dataset contained chest x-ray (cxr) images of covid-19 infected patients and of uninfected people. the proposed cnn-based covid-19 detector was trained on augmented data and achieved high accuracy in the prediction of the patients’ needs in the next 7 days. in addition, the prediction of the number of deaths, new confirmed cases and recovered cases was 94.18%, 99.94%, and 90.29% respectively. implementing the vgg16 cnn in the detector enhanced the model's accuracy. authors in [29] introduced a new open-source network called covidnet. covid-net is a deep cnn to detect the covid-19 positive cases by analyzing cxr images. covidx is the largest open-source dataset of covid-19 patient’s csr images that have been applied to train and assess the suggested covid-net. the model achieved good test accuracy equal to 93.3%. authors in [30] introduced a technique of learning pipeline and multi-view representation of covid-19 classification utilizing different types of features extracted from ct images. 2522 ct images were used (1495 for covid-19 patients, and 1027 for community-acquired pneumonia (cap)). the classification was carried out with different machine learning models, i.e. lr, svm, knn, gaussiannaive-bayes classifier, and nns. the proposed method outperformed the examined machine learning models with accuracy of 95.5%, sensitivity of 96.6%, and specificity of 93.2%. for the selection of features and classification of covid19, authors in [31] suggested two optimization algorithms. there are 3 cascade phases in the proposed structure. initially, features are being extracted using a cnn called alexnet from the ct scans. then, the proposed feature selection algorithm is implemented, a guided whale optimization algorithm (woa) based on stochastic fractal search (sfs). the selected features were then balanced. finally, using voting classification and guided woa based on particle swarm optimization, different classifiers’ predictions were collected to determine the most voted class. for evaluating their proposed model, two data sets were used with positive and negative covid-19 clinical ctimages. the proposed voting classification (pso-guidedwoa) was 99.5%, higher than the other voting classifiers. authors in [32] proposed a new architecture for covid-19 prediction consisting of 3 principal manners: random selection of the region of interest, training of the cnn network to obtain features, and model training on a fully connected network and prediction of various classifiers. this method achieved a classification accuracy of 82.9% utilizing the modified inception (m-inception) deep model developed using ct images. authors in [33] created a large dataset of ct scan and x-ray images from multiple sources and presented two cnn approaches to classify them as having covid-19 or not, which are transfer learning alexnet and a simple cnn architecture. they achieved 98% accuracy via the pre-trained model and 94.1% by using the modified cnn. authors in [34] reviewed the possibility of ml models for diagnosis corona virus using x-ray images. they used lr and cnn and generative adversarial network (gan) for data augmentation in order to overcome the overfitting problem. the model gives 95.2– 97.6% accuracy without pca and 97.6–100% with pca. during the coronavirus period, the collected data were often heterogeneous. their features were categorical and numerical, or specific categorical such as the occurrence of cough, while the numerical features are quantitative, for example the temperature of the body. it is difficult to process these two forms. moreover, this information may be incomplete as certain features have missing values. incompleteness and heterogeneity are major challenges in identifying covid-19 cases for data collected from many people. heterogeneity and missing values are not directly handled by the common classification algorithms. to deal with these two issues, authors in [34] proposed the knn variant (knnv) classification algorithm for incomplete and heterogeneous datasets as tools for detecting covid19 cases accurately and efficiently. the two key concepts of the proposed algorithm are that the parameter k is chosen adaptively and that it calculates the engineering, technology & applied science research vol. 11, no. 6, 2021, 7824-7835 7829 www.etasr.com alalawi et al.: a survey of the application of artifical intellegence on covid-19 diagnosis and prediction distances from other instances in a new way for each case being classified. the datasets were manually generated from a dataset of 68 covid-19 and 62 non-covid-19 cases from the sirm database. flu cases from the influenza research database (ird) were used. then, the 2 datasets were merged and shuffled randomly to obtain an ihc dataset with two subsets: covid-19 and flu. the results indicate that the suggested algorithm outperforms other known algorithms in terms of accuracy, recall, and f score. authors in [35] published the initial research of applying an rf algorithm to determine the covid-19 in clinically available blood test data. the researchers obtained 253 blood samples, including 105 confirmed covid-19 cases, from different hospitals in lanzhou, china. the method uses 11 key features out of the 49 clinical blood indexes that have been derived from the rf algorithm. the trained model, with 11 main features, exhibited 95.12% sensitivity, 96.97% specificity, and an overall 96.95% accuracy. in external blood samples, the algorithm's efficiency was slightly lower, with 95.12% sensitivity, 96.97% specificity, and 95.95% accuracy. the used dataset has a very high positive ratio of 41.5% which can affect performance. moreover, the model in [2] revealed a high positive correlation between the patient's age and gender with the possibility of getting infected by covid-19. authors in [36] introduced a study of analyzing x-ray images of patient's and healthy person's lungs to compare and detect the level of infection on the lungs, and then classify it into level-based effect. because of the complexity and the limited access to x-ray images, complexity-based theory was used to analyze the images. during the covid-19 epidemic, classifying the patients into infected or healthy is critical to prevent the spread of the virus. authors in [37] suggested a technique based on deep learning by utilizing an svm classifier to detect and classify the x-ray images of the patients' lungs as infected or healthy. due to the limitation of diagnostic kits, the diagnosis of the disease has been used by x-ray imaging machines, as they are widely available in clinics and hospitals. the proposed system, based on deep cnns, was used to analyze the x-ray image datasets. the system was trained on two datasets, namely one dataset of positive and one of negative cases. the datasets have been used to extract the images’ features based on deep architectures such as googlenet, resnet50, and inception v3. the combination of the svm classifier, the open-source dataset, and deep feature extraction techniques achieved accuracy of 95.38%. authors in [38] proposed a covid-19 classification by using ct chest images to classify the patients into two groups, +ve (infected) and -ve (not-infected). the model, called multi-objective differential evolution (mode), with cnn has been implemented in a ct-chest images dataset, but the deep cnn showed some hyperparameter-tuning issues. however, the image features have been extracted by implementing many convolutions and the max-pooling layer was used to minimize the spatial size. the suggested model showed a good rate of accuracy, f-measure, and kappa with values of 97.89%, 2.0928%, 1.9276% respectively. authors in [40] introduced a deep learning-based transfer model to diagnose covid-19 cases by using ct-scan and cxr images. the algorithm was trained on 3 datasets. the model showed the detection results faster than the rt-pcr method. in addition, they discovered a pattern between the infected patients with covid-19 and pneumonia. performing an x-ray or ct-scan in an infected lung a shadowy area called ground glass opacity (ggo) will appear. applying deep learning led to fast and efficient detection results. the aim of the model is the binary classification of the chest images in a fast and accurate way. image classification was conducted and 3 experiments were proposed and applied on the dataset. the model achieved accuracy of 95.61%. authors in [7] established a community learning model known as erlx in routine blood tests diagnostics for covid-19. the proposed model used structural diversity by 2 classificatory levels. to improve predictive capabilities, the prediction from the first classification (extra trees, rf, lr) was supplied to the second classifier (xgboost). a series of steps in data preparation were performed using the knn algorithm to control the null values of the data collection. isolation forest (iforest) was used to eliminate outlier data, and smote to equalize data distribution. by comparing the findings with the state-of-the-art studies available for a publicly available dataset from the albert einstein hospital in brazil, the efficacy and reliability of the model for diagnosing covid-19 was demonstrated. ensemble models are more efficient, robust, and flexible since diversity is the fundamental guiding principle for capture underlying training data structure. the ensemble model achieved outstanding performance with an overall accuracy of 99.88%, sensitivity of 98.72%, and specificity of 99.99%. due to the small number of x-rays and ct images with covid-19, training the machine learning and deep network models is extremely difficult. therefore, transfer-learning could be an applicable solution that has been extensively adopted in several latterly submitted covid-19 detection methods. a deep transfer learning-based approach has been suggested in [41] using covid-19, normal, and viral pneumonia cxr images to detect covid-19 pneumonia automatically, using deep cnns. the results show that transfer learning has proven to be successful, robust, and easily deployable for detecting covid-19 with 98% accuracy. however, the conventional transfer-learning system which uses a developed, pre-trained deep network in the images database to transmit the original information might not be an excellent option, since the features of x-rays and ct-image of covid19 are completely different from pictures for other apps. but after this research, researchers gave hope that covid-19 can be recognized from other infections and normal lung conditions by utilizing cxr imaging. authors in [42] report a covid-19 prediction analysis in cxr imagery by applying transfer learning. they compared 4 common deep cnn predictors (resnet18, resnet50, squeezenet, and densenet-161). after training, the models presented an average specificity rate of ~90% and 97.5% sensitivity. authors in [43] suggested a weakly supervised deep-learning technique to detect and identify ct image infection with covid-19 using 3d ct volumes for classification of covid-19 and lesion location. the proposed method can reduce the manual labeling requirements of ct images, but it can still reliably detect infections and draw a distinction between covid-19 and noncovid-19 images. the model achieved 96.2% accuracy, engineering, technology & applied science research vol. 11, no. 6, 2021, 7824-7835 7830 www.etasr.com alalawi et al.: a survey of the application of artifical intellegence on covid-19 diagnosis and prediction 94.5% sensitivity, 95.3% specificity, and an auc value of 0.970. authors in [44, 45] stated that for computerized covid-19 pneumonia detection, ct scans are utilized in deep learning systems. although ct scans contribute more comprehensive information, x-rays are faster, easier to take, less unhealthy, and cheaper. nevertheless, it is extremely hard to effectively train a very deep network because of the scarcity of covid-19 x-rays at that time. the accuracy of their research in covid19 classification exhibited 96% auc, 90% sensitivity, and 96% specificity and 99.6% auc, 98.2% sensitivity, and 92.2% specificity respectively. in terms of analyzing and detecting the radiological images automatically, cnn deep learning techniques are widely used [46]. usually in deep learning techniques, model training is conducted with large datasets, but due to the limitation of the infected x-ray or ct scan images, the network weights have been fine-tuned from pre-trained networks. authors in [47] proposed a classification model to classify the chest ct scan of covid-19 patients as positive (infected) or negative (uninfected). the model was based on deep transfer learning (dtl) with densenet201 and cnn. it had 99.82% training accuracy and the achieved testing and validation accuracies were 96.25% and 97.4% respectively. authors in [48] proposed a deep dt classifier consisting of 3 stages. each dt was trained using a deep learning model with a nn based on a pytorch frame for the detection of covid-19 in chest x-ray images. the average acquired accuracy was 95%. authors in [49] utilized a pretrained densenet121 model for the classification of segmented 3d lung regions. the dataset consisted of 2724 ct scans from 2617 sufferers. lung regions were separated via utilizing the 3d anisotropic hybrid network (ah-net) architecture, achieving 90.8% accuracy, 93% specificity, and 94.9% auc score. the significance of using ai in the medical domain to diagnose and predict diseases is in making several decisions based on big data analysis. authors in [50] suggested a deep learning-based model to predict the coronavirus severity level by using ct scan images of infected patients. the model was trained in 303 chest images and was tested in 105 images, achieving 97.4% training and 81.9% testing accuracy. based on coronavirus confirmed cases, countries have been classified into categories based on the risk rate. authors in [51] proposed an ai-guided method to predict the long-term country-specific risk of covid-19 by the bayesian optimization guided shallow lstm. on average the model showed an accuracy of 77.4%. applying the model during the pandemic posed many challenges such as the limitation of the dataset, data uncertainty, and data confusion. authors in [52] provided a system based on deep learning to covid-19 detection using cnn and convolutional (convlstm) with 100% accuracy and f1 score, while authors in [53] obtained 89.5% accuracy, 88% specificity and 87% sensitivity in ct images. authors in [54] got auc of 99% and recall of 93% in covid-19 diagnosis. authors in [55] used the resnet-50 deep learning model to classify covid-19 in ct scans with 96% auc. authors in [56] identified coronavirus cases rapidly using the restnet-100 cnn along with lr achieving accuracy of 99.15%. authors in [57] proposed covid-19 pneumonia detection using a small number of covid-19 cxr images. they optimized the features using the cnn model convnet with 98.1% accuracy. authors in [58] investigated the performance of knn, dt, nb, svm, and lr to discover covid-19 cases. the results were 93% accuracy for nb and dt, 93.60% for svm, 93.50% for knn, and 92.80% for lr and they concluded that ml methods have an important use in identifying covid-19. authors in [59] proposed a detectionclassification approach to diagnose covid-19 by examining the patients' lungs using ct-scan and x-ray images. their approach was compared with the svm classifier. the comparison was made on the classification accuracy as a performance indicator. the classification–detection model achieved 84% and 75% with cxrs and ct-scans, respectively. table ii provides a summary of all the reviewed studies. vi. covid-19 image datasets ct scanning and x-ray imaging are the most common used techniques in respiratory disease diagnosis. for decades, radiologists and other healthcare professionals have used them. discovering covid-19 early is crucial to prevent its spread by using diagnostic imagery methods. to show the damage of covid-19 on the patient’s lungs, many health and technology centers publish data about covid-19, pneumonia, and acute respiratory distress syndrome. authors in [61] produced the first public dataset of the frontal view of x-ray images. the dataset was collected from different open sources by the university of montreal. it consists of more than 400 ct and xray images of covid-19, sars, mers-cov, varicella, influenza, and herpes patients. the dataset is continuously updated by the newest covid-19 cases through the github link [62]. the dataset in [63] is a public dataset of 5,863 x-ray images categorized into normal/healthy lungs and pneumoniainfected lungs. another dataset of chest x-ray images of covid-19 cases was published in 2020 [64]. the dataset contains x-ray images of covid-19-infected lungs along with normal lungs in addition to viral pneumonia images. it consists of 3,487 images of normal, covid-19, and viral patients. there is also a public dataset available on the kaggle website [65], which contains a mixture of x-ray and ct scan images of patients diagnosed with covid-19. patients' images were extracted from public articles in rsna, radiopaedia, and sirm [66]. chestx-ray8 is a large public database provided in [32]. it consists of frontal-view x-ray images collected from 1992 to 2015. the dataset contains 108,948 images of more than 32,717 patients. images are labeled and divided among 8 common thoracic pathology diseases. authors in [67] produced a publicly available dataset of ct scan images of covid-19 cases. the covid-ct dataset contains 349 ct scans of confirmed cases, which were collected from relative sources, such as medrxiv, nejm, jama, lancet, and biorxiv. the covid-19 ct lung and infection segmentation dataset [68] contains 100 ct images collected from more than 40 patients with covid-19. the covid-19 imaging database is another open-source dataset used by the british society of thoracic imaging [69]. this dataset is used for learning and education purposes and it consists of 59 images of sars-cov2 patients. engineering, technology & applied science research vol. 11, no. 6, 2021, 7824-7835 7831 www.etasr.com alalawi et al.: a survey of the application of artifical intellegence on covid-19 diagnosis and prediction vii. discussion this study focused on the latest studies that used ai applications to confront covid-19. in imaging-based covid19 classification, ai has been successfully applied. however, much work remains to be done. a growing number of different classification and prediction models use ai along with more publicly available datasets. in this paper, many recent research studies were reviewed. these studies involved deep learning and machine learning for covid-19 classification. deep learning approaches, such as cnns, automatically perform the function extraction process. little research, however, has been done on traditional machine learning models, like knn, svm, rf, and dt (see table ii). most of this research used medical images to diagnose covid-19 because they provide more details and depict the diseased areas of the body. the ai-based classification of cxrs has the untapped potential to meet this need. latest research has shown that compared with ct and magnetic resonance imaging (mri), cxr-related diagnosis is the most widely used because of its low cost, short therapy time, and low radiation exposure. however, the reviewed studies that used these images have some weaknesses. some did not involve all age groups or adequately considered the patient's gender. improving upon this can help facilitate the classification process of machine learning models. given the small number of cxr and ct pictures available for covid-19 at that time, the ai models were trained on fewer pictures, which may lead to overfitting in classification models and low accuracy. deep learning models must be based on large datasets to work efficiently. for this reason, some techniques, such as augmentation, have been used to generalize models and to increase the size of the datasets. researchers constantly work to update classification models and to increase their reliability and usefulness in real-life circumstances using the available datasets. in addition, the availability of more and more diversified training images would make the creation of strong and scalable classification models easier. ai-based disease classification can be merged with confirmed lab tests. it would be an excellent suggestion to help diagnose and evaluate recovering/infected patients utilizing fast ai-based tools. deep learning has become the dominant approach for detecting and diagnosing covid-19. the image data in covid-19 applications, however, could be inconsistent and inaccurate, posing a challenge for the creation of an exact segmentation and diagnostic network. for this situation, weakly supervised deep learning approaches may help. some researchers diagnose covid-19 cases employing machine learning methods by utilizing deep learning strategies via selecting the features of the images and obtaining high quality results. finally, all the medical images used in the previous studies were not standardized and from different sources, in addition to the different medical devices that took these pictures. all these factors make a comprehensive comparison difficult. viii. conclusion the negative impact of covid-19 has increased since december 2019. ai methods and applications in the medical fields showed success in fighting the virus. in this paper, an extensive review of the latest studies in covid-19 classification and prediction was presented with a description of the frequently used methods and techniques in disease diagnosis, detection, and prediction. the number of contributions in this field is growing exponentially due to their success in preventing the spread of covid-19. this paper summarized the research papers in classification algorithms and their applications in covid-19 prediction models with a review of the method’s aim in addition to the models’ performance. among the published studies, the use of deep learning in radiology imaging machines improved the models' performance. ix. future directions and challenges the researchers in machine learning –related covid-19 detection may face several challenges, especially when dealing with data provided from different sources and different formats. • large-scale training data are scarce and difficult to get. many deep learning techniques rely on a large dataset to train models, such as medical images to build an automatic system for prediction [70]. due to the rapid explosion of covid-19, the interpretation and labeling of training samples are time-consuming and require expert physicians, which results in insufficient data [71]. • inappropriate data diverse online publications have published incorrect reports concerning covid-19. because of this problem, the use and reliability of ai-based methods have been reduced. • data protection and privacy. to prevent the spread of covid-19 and conduct proper contact tracing, patient's personal information is often collected, such as their identity number, contact information, and medical data. therefore, protecting and maintaining the patient’s privacy during treatment is incredibly important. • incorrect structured and unstructured data. incorrect information in text descriptions and medical images poses a challenge to researchers and machine learning models. a huge amount of data from various sources may be impossible to be used. ai also faces problems, such as dealing with unbalanced datasets, difficulty in screening, triaging patients due to restrictions [72], and social distancing, as well as dealing with poor quality data. regarding future research directions, ai can be used in remote video investigation and consultations, biological research and knowledge of important protein structures and virus sequences, impact assessment of covid-19, drug development, patient contact tracking, as well as diagnosis and treatment of covid-19. engineering, technology & applied science research vol. 11, no. 6, 2021, 7824-7835 7832 www.etasr.com alalawi et al.: a survey of the application of artifical intellegence on covid-19 diagnosis and prediction table ii. summary of the research on covid-19 diagnosis ref. aim methods datasets performance [2] proposed a fine-tuned rf model supported with adaboost algorithm for covid-19 prediction. boosted rf algorithm novel coronavirus 2019 dataset. revealed a high positive correlation between the patient's age and sex with the possibility of getting infected by covid-19. [3] erlx model developed for the detection and classification of covid-19. extra trees, rf, lr, xgboost routine blood examinations of covid19 cases at albert einstein hospital. 99.88% accuracy, 98.72% sensitivity, 99.99% specificity. [4] classifying covid-19 and non-covid classes based on lung ct scans nb, knn, dt, rf, svm ct scans from available datasets, including 500 photos (250 normal and 250 covid-19). accuracy of nb, knn, dt at 80%, of rf at 79%, and of svm at 81% [5] implemented a personalized network (darkcovidnet) for automatic covid-19 detection darknet classifier 127 infected patients, 500 normal cases, and 500 pneumonia frontal x-ray images. 98.08% for binary and 87.02% for multi-class classification accuracy. [6] proposed a method for binary classification and multi-classification problems by using a deep learning cnn network for the identification of covid-19. deep cnn 910 x-rays and ct scans of covid-19. 99% accuracy on x-ray images, and 71% on ct-scan images. [7] used detrac to predict and classify the chest images of covid-19 sufferers detrac with cnn cxr photos from many hospitals worldwide. 95.12% accuracy, 97.91% sensitivity, 91.87% specificity. [8] prediction of patient's images as positive or negative cases. covidx-net deep cnn framework 50 x-ray photos with 25 positive covid-19 confirmed cases. the covidx-net achieved a good performance in vgg19 and densenet including f1-scores of 0.89 and 0.9, respectively. [9] detect the confirmed cases of coronavirus deep cnn with resnet50, resnet101, resnet 152, inception v3, and inceptionresnet v2 dr. joseph cohen open-source dataset and cxr images (pneumonia). accuracy of 96.1%, 99.5, and 99.7 for dataset-1, dataset-2, and dataset-3 respectively. [10] utilizing cnn to diagnose cases of covid19 with chest x-rays xception and resnet50v2-based cnn x-rays datasets of 180 images of covid-19. 99.56% accuracy and 80.53% recall. [11] early covid-19 detection svm 150 ct images for covid-19. 99.68% accuracy. [12] a detector trained on augmented data with high accuracy in the prediction of the patients’ needs in the next 7 days. deep learning cnn covid-19 x-ray images high accuracy of 94.18%, 99.94%, and 90.29% respectively in predicting the number of deaths, newly confirmed cases, and recovered cases. [13] a new open-source network called covidnet to distinguish the covid-19 positive cases by analyzing cxr images. deep cnn covidx is the largest open-source dataset of covid-19 patient’s cxr images. 93.3% accuracy. [14] covid-19 classification based on pipeline and multiview representation learning method. pipeline and multiview representation learning ct images of 1495 covid-19 1027 cap. 95.5% accuracy, 96.6% sensitivity, 93.2% specificity. [15] two optimization algorithms were introduced in order to select and classify features of the covid-19. cnn, guided woa 334 ct images for covid-19 and 794 ct images for non-covid-19. 99.5% accuracy. [16] covid-19 prediction consisting of 3 main processes. cnn ct images of 453 covid-19 cases 82.9% accuracy. [17] knnv classification algorithms for incomplete and heterogeneous datasets as tools for detecting covid19 cases knnv ihc dataset with 68 covid patients and 62 flu patients. all metrics indicate that knnv is much stronger than the relevant algorithms. [18] discover covid-19 from clinically available blood test data rf hospitals, lanzhou, china. 95.12% sensitivity, 96.97% specificity, 96.95% accuracy. [19] suggested a system based on deep cnns to analyze x-ray image datasets. deep cnn one dataset with 25 cases of covid19+ and 25 of covid-19x-ray images and another with 133 crx images as covid-19and 133 as covid-19+. achieved accuracy in terms of testing, f1 score, mcc, and kappa, 95.38%, 95.52%, 91.41%, 90.76 % respectively. [20] classify the patients into +ve (infected) and -ve (not-infected) groups. mode with cnn x-ray and ct scan images accuracy, f-measure, and kappa statistics were 97.89%, 2.0928%, 1.9276% respectively [21] a deep learning-based transfer model to diagnose covid-19 cases. binary classification in a fast and accurate way. deep learning-based transfer model three datasets sars-cov2 ct-scan, crx, and covid-crx 95.61% accuracy. [22] automatic detection of covid-19 pneumonia utilizing dcnns. dcnn 864 covid-19, 1345 pneumonia, and 1341 cxr images. 98% accuracy. [58] building automatic ct picture analysis tools based on ai for coronavirus identification, quantification, and tracking. deep learning ct image datasets, the testing set had 157 international patients 99.6% auc, 98.2% sensitivity, 92.2% specificity. engineering, technology & applied science research vol. 11, no. 6, 2021, 7824-7835 7833 www.etasr.com alalawi et al.: a survey of the application of artifical intellegence on covid-19 diagnosis and prediction [54] a weakly-supervised dl for identifying and classifying covid-19 from ct scans and reduce the requirements of labeling the ct images. weakly-supervised deep learning system using cnn 150 3d chest ct scans of covid-19, cap, and np patients respectively 96.2% accuracy, 94.5% sensitivity, 95.3% specificity, 97.0% auc. [23] covid-19 prediction in cxr imaging using transfer learning. deep transfer learning (cnn) 5,000 cxrs from publicly available datasets specificity rate of ~90% with a sensitivity range of 97.5% [54] a weakly-supervised dl for identifying and classifying covid-19 from ct scans and reduce the requirements of labeling the ct images. weakly-supervised deep learning system using cnn 150 3d chest ct scans of covid-19, cap, and np patients respectively 96.2% accuracy, 94.5% sensitivity, 95.3% specificity, 97.0% auc. [16] a fully automated chest ct framing for detecting covid-19 deep learning 3d chest ct exams acquired from 6 medical centers, consisting of 1296 images of covid-19 patients 96% auc, 90% sensitivity, 96% specificity. [59] a deep learning-based transfer model to diagnose covid-19 cases by utilizing ctscan and x-ray images of the human’s chest. the aim is the binary classification of the chest images in a fast and accurate way. deep learning-based transfer model three datasets sars-cov2 ct-scan, chest x-ray images, and covidcxrs 95.61% accuracy. [60] a covid-19 assessment dt classifier from cxr images. deep learning-based dt classifier cxr 95.0% accuracy. [28] utilized pre-trained model densenet121 to classify the segmented 3d lung regions. ah-net densenet121 ct images of 1029 covid-19 1695 non-covid-19 patients. 0.90% accuracy, 93% specificity, and 94% auc. [62] predict the severity level of coronavirus by using ct scan images of infected patients. deep learning the dataset contains 303 ct-images as a training set and 105 images as testing set. 97.4% training and 81.9% testing accuracy. [43] classify the countries based on the risk rate. ai-guided method with bayesian optimizer covid-19 open-source dataset and weather dataset, the number of cases confirmed, number of cases recovered, and the total number of deaths are included. 77.4% accuracy. [44] create a large dataset and classify covid19 cnn model and pretrained alexnet 170 x-ray images and 361 ct images of covid-19 alexnet =98%, cnn =94.1%. [62] diagnose corona virus with pca. lr, cnn x-ray images. 95.2–97.6% accuracy without pca and 97.6–100% with pca. [63] covid-19 detection lstm and cnn ct and x-ray images 100% for accuracy and f1 score. [64] covid-19 detection deep learning ct images of 259 patients. 89.5% accuracy, 88% specificity, 87% sensitivity. [65] covid-19 diagnosis deep learning-based ct diagnosis ct scans of 88 patients of covid-19, 101 of bacterial pneumonia, 86 healthy persons. auc of 0.99 and recall of 0.93. 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[72] n. k. al-shammari, h. b. almansour, and m. b. syed, "development of an automatic contactless thermometer alert system based on gps and population density," engineering, technology & applied science research, vol. 11, no. 2, pp. 7006–7010, apr. 2021, https://doi.org/ 10.48084/etasr.4103. microsoft word etasr_v12_n2_pp8452-8457 engineering, technology & applied science research vol. 12, no. 2, 2022, 8452-8457 8452 www.etasr.com jamil et al.: design and geometric transformations of koch curve monopole antennas design and geometric transformations of koch curve monopole antennas atif jamil department of computer systems engineering dawood university of engineering & technology karachi, pakistan atif.jamil@duet.edu.pk khalid rafique azad jammu and kashmir information technology board azad jammu & kashmir, pakistan khalidrafiquepk@gmail.com muhammad dawood idrees department of industrial engineering and management dawood university of engineering & technology karachi, pakistan muhammad.dawood@duet.edu.pk abdul sami rajput department of electronic engineering dawood university of engineering & technology karachi, pakistan dr.abdulsami@duet.edu.pk arif abdullah department of electronic engineering dawood university of engineering & technology karachi, pakistan arif.abdullah@duet.edu.pk abdul sattar saand department of electrical engineering quaid-e-awam university of engineering, science and technology, nawabshah, pakistan as-saand@quest.edu.pk received: 19 january 2022 | revised: 1 march 2022 | accepted: 9 march 2022 abstract-in this paper, a modified koch curve monopole antenna is proposed for the dual-band wireless local area network (wlan) and its performance has been compared with the conventional printed koch-curve monopole antenna. both the antennas have been contrived, and their simulated return loss and radiation pattern results have been validated with the measurements. antenna #1 is designed on the geometrical basis of a conventional koch-curve monopole antenna. moreover, the shape of antenna # 1 is bent with a two-step rotation process to yield antenna #2. there are two advantages to this geometrical modification: firstly, the unique rotation in antenna #2 has further increased the mutual coupling between the segments of the koch-curve geometry, and thus improved the impedance matching. secondly, due to its geometric configuration that enhanced its ground plane size, the proposed antenna #2 has been able to demonstrate consistent simulation and measurement results. the compact ground plane in antenna #1 has been identified as the primary reason for the disagreement between the simulated and measured return loss results. the presented antennas have also been studied for the variation of indentation angles: θ=30 and θ=60. keywords-fractal antennas; multiband; geometry; koch monopole; omnidirectional i. introduction the size of the microstrip patch antennas has reduced to a large extent to suit the needs of modern wireless communications requirements. the antenna designers have expanded their horizons to design ultra-portable and multiband antennas, so that they may fit into the chassis of the compact hand-held wireless communication terminals. moreover, the challenge of size reduction has a trade-off with the antenna bandwidth and efficiency [1]. a good antenna design cycle has an emphasis on the optimization of many performance parameters. some of the commonly strived parameters in a good antenna design include frequency tuning, impedance matching, high gain, and better radiation characteristics in the desired bands. many of these antenna parameters are optimized during simulations. fractals have been defined as the geometry possessing the properties of self-similarity. the fractal geometry is nowhere distinguishable at any scale of magnification. the scaled up or scaled down versions of fractal geometry are exactly identical to the original (non-scaled) versions. the fundamental limit on the antenna size has been demonstrated in [1]. the behavior of the koch curve monopole antenna has been discussed, and its relation to the fundamental limit of the small antennas has been presented in [2]. many authors have investigated the behavior of the applied geometrical transformations on koch-curve antenna and its effect on performance parameters [3, 4]. there is some degree of freedom with which one can design kochcurve monopoles. the koch monopole can be bent in particular ways to extend the current path through geometry while shrinking the antenna dimensions. the geometry of the kochcurve monopole antennas can yield the same area as euclidean corresponding author: atif jamil engineering, technology & applied science research vol. 12, no. 2, 2022, 8452-8457 8453 www.etasr.com jamil et al.: design and geometric transformations of koch curve monopole antennas antennas, but the current has an extended path. higher fractal iterations are applied to lower the frequency [5]. however, with the increasing fractal iterations, the overall size of the antenna also increases [6]. it is a well-known fact that the antenna size should be an appropriate fraction of the wavelength. when the antenna size is decreased more than the operating wavelength, the efficiency of the antenna decreases significantly. unlike the euclidean geometries, the occurrences of the multi-band behavior of the fractal antennas are not related to the electrical length, they are rather related to the geometry and the log periodic behavior of the antennas. many fractal geometries have been used in antenna designs, and the relation between the variation of geometrical angles and antenna's performance characteristics has been presented in [7]. such studies show that the change of indentation angle directly affects the input resistance and occurrence of the resonant frequencies. the log periodic behavior of the fractal antennas has been attributed to the factor, by which their geometries are scaled [8, 9]. in fractal antennas, the ratio of the first two resonant frequencies can be controlled by the ratio of the antenna dimensions. many dimensional ratios of the overall radiating structure, including ground plane dimensional ratios and other geometrical variations can change this ratio. in [10], the authors controlled the ratio of the first two frequencies by changing h/w. a compact single probe feed asymmetrical semicircular fractal boundary patch antenna based on his (high impedance surface) is proposed for wide bandwidth at the wi-fi band in [11]. a fractal antenna array for telecommunication applications is presented in [12]. many studies have investigated the measurement-related problems, posed by the electrically small antennas (esas). here, we will limit the scope of the study to the measurement issues related to the small, convoluted shaped antennas. the stringent requirement on the size reduction of modern day antennas has also reduced their ground plane size. the ground plane size in small antennas plays an active role in radiation. certain parameters are affected by the small ground plane size, including a shift in resonant frequencies, impedance mismatch, impedance bandwidth, low gain, low efficiency, and distorted radiation patterns [13, 14]. the effect of the ground plane is also crucial in the design of monopole antennas [15]. this paper presents the results and a discussion on the issues pertinent to the measurement of small antennas, particularly with a small ground plane. the performances of the two designed and developed koch-monopole antennas were compared by the simulation and measurement results. a parametric study has been carried out in order to study the effects of changing the geometrical indentation angles on the shift in resonant frequencies. moreover, a study on the surface current distribution is presented to understand the multiband behavior of both antennas. ii. antenna geometric configuration in this section, two geometric configurations have been realized with two different indentation angles. the indentation angle is an essential element in determining the length of the adjacent segment. the construction of the two antennas is based on iterative transformation. the iteration function system (ifs) [16] offers an integrated platform for the development of fractal geometries including koch curves. in the plane 2 2 :r rω → , the affine transformations are defined as in (1): 1 1 2 2 ex xa b ax t x fc xd ω        = + = +              (1) equation (1) can also be described as: ( ) ( )1 2 1 2, e,x y ax bx cx dx fω = + + + + (2) in (1), the matrix a can be defined as in (3) and the pointx has the coordinates 1x and 2x . the matrix t gives the translation on the plane. the parameters a, b c, d, control the rotation and scaling while the linear translation on the plane is controlled by the parameters e and f. cos sin sin cos a δ θ δ θ δ θ δ θ −  =     (3) in (3), δ is the scaling factor, such that 0 1δ≤ ≤ and θ is the rotation angle. the described geometries in this paper have been scaled by 1 3. for the two cases analyzed in this paper, the angles of rotation are 1 30θ = o and 2 60θ = o . in assumption, if 1 2 3 , , ........ n ω ω ω ω are the set of affine transformations and if the initial geometry is given by a, a new geometry can be constructed by applying a set of transformations to ( )2a . the collective results are expressed by (4). ( ) 1 ( ) n n n w a aω = = u (4) w is the hutchinson operator which determines the looked-for iteration by the repeated application of w to the previous geometry such that if the initial geometry is 0 a then: 1 0 (a )a w= 2 2 (a )a w= ( 1)(a )k ka w −= (5) the method for determination of the geometric structure is to calculate the fractal dimension of a line as a function. two measurement points are taken when associating the fractal with some discrete boxes. these boxes are vital for the calculation of a set of points in a plane. ( ) dn δ δ −= (6) in (6), the ( )n δ is the number of the required boxes. the dimension of a box is defined in (6). equation (6) can be written after taking the logarithm on both sides as in (7): ( ) ( )log logn dδ δ  = −  (7) ( )log 1log n d δ δ   = (8) engineering, technology & applied science research vol. 12, no. 2, 2022, 8452-8457 8454 www.etasr.com jamil et al.: design and geometric transformations of koch curve monopole antennas in (8), the dimension d is the ratio of the newly formed element ( )n δ to the inverse if scaling factor 1δ . (a) (b) (c) (d) (e) (f) fig. 1. iterations of the koch monopole antenna: (a) straight strip, (b) first iteration, (c) second iteration, (d) third iteration, (e) modified koch curve antenna, (f) finalized antenna design. the construction procedure of the antenna #1 and antenna #2 with an indentation angle of � � 30 0 and � � 60 0 is illustrated in figure 1(a)-(b). the design process of geometric transformation starts by taking into account the length of a straight strip of length h. the strip is divided into three equal parts, the middle section is replaced by an equilateral triangle of length 3l . for obtaining the first iteration which is depicted in figure 1(b), (4) can be written as: ( ) ( ) ( ) ( ) ( )1 2 3 4w a a a a aω ω ω ω= u u u (9) the final pattern in figure 1 is obtained by a series of geometric transformations on the shape achieved in the first iteration. the antenna is then rotated by a two-step procedure to reduce its overall length. here, we will focus on tuning the resonant frequencies with modifying indentation angles. the increase in indentation angles increases the length of the subsequent segments and in turn the space occupied by the koch monopole antenna is also enhanced. in this way, the overall area occupied by the radiator is enlarged, and the resonant frequencies can be lowered. figures 2-3 depict the comparison plots of the two indentation angles, � � 30 0 and � � 60 0 for antenna #1 and antenna #2 respectively. it can be noticed that with the decrease of the indentation angle of antenna #1, the input impedance at the resonant bands also changes, accounting for impedance mismatch [3]. with the decrease in indentation angle, similar changes can also be noticed in figure 3. here, the impedance mismatch is somehow better matched than the comparison plot of figure 2. this is mainly due to the enhanced ground plane of the antenna #2. the discussion on the effects of the ground plane on antennas' performance and measurement results are presented in a separate section. in both antennas, the geometrical configuration with higher indentation angle, i.e. � � 60 0 , along with the third iteration, lowered the resonant frequencies to the desired bands. the increase in indentation angles brought the inverted-v arm closer, increasing the capacitance between them. hence, the mutual coupling between the koch-curve member elements is enhanced. as the number of iterations increases, the proportional electrical length is also increased which in turn produces an additional equivalent inductance [7]. fig. 2. antenna #1: effect of the variation of indentation angle on the resonant frequency. fig. 3. antenna #2: effect of the variation of indentation angle on the resonant frequency. fig. 4. photograph of fabricated antenna #1 on substrate (a) top view, (b) bottom view. iii. antenna dimensions the detailed dimensions of the antennas are presented in table i. the parametric study on the role of indentation angles has been carried out through the simulations. all the four geometrical configurations have been simulated. due to the involved cost factor, only the antennas which yielded the optimal results, i.e. antenna #1 and antenna #2 with an � � � 30 0 � � 60 0 � � 30 0 � � 60 0 engineering, technology & applied science research vol. 12, no. 2, 2022, 8452-8457 8455 www.etasr.com jamil et al.: design and geometric transformations of koch curve monopole antennas indentation angle of � � 60 0 were fabricated on fr-4 substrate and were compared with the correspondent simulation results. it can be noticed from table i that the overall dimensions including the ground plane dimensions of antennas #1 and #2 with indentation angles of � � 30 0 and 60 0 are similar. however, due to an increase in the indentation angle, patch dimensions have been enhanced in the third and fourth column of table i. fig. 5. photograph of fabricated antenna #2 on substrate (a) top view, (b) bottom view. table i. various configurations' antenna dimensions configurations antenna #1 � � 30 0 antenna #2 � � 30 0 antenna #1 � � 60 0 antenna #2 � � 60 0 overall dimensions (mm 3 ) 73×16×1.6 55×30×1.6 73×16×1.6 55×30×1.6 patch dimensions (mm 2 ) 49×10.8 37×16.7 49×13 37×28 ground plane dimensions (mm 2 ) 23×16 16×30 23×16 16×30 thickness of copper (µm) 35 35 35 35 dielectric constant 4.34 4.34 4.34 4.34 further discussion in the subsequent sections concentrates mainly on understanding the multiband behavior of the two antennas and the cable effects on the small ground plane size during measurements. it does not include the discussion of the indentation angles. for the mentioned reason we have discarded the antennas with an indentation angle of � � 30 0 from the mentioned investigations. iv. current distribution for studying the multiband behavior of the koch monopole antenna, it is necessary to determine the surface current distribution on the antenna segments. the current allocation of these segments handles radiation from the antenna at any specific frequency. figure 6 depicts the surface current distribution on the surface of antennas #1 and #2. both antennas are placed on the top layer, and the ground plane is located at the bottom layer. the surface current distribution on antenna #1 at 2.45 and 5ghz can be seen in figure 6(a) and 6(b) respectively. figures 6(c) and (d) depict the active segments responsible for radiation from antenna #2 at 2.45 and 5ghz. it is noticed that the radiation on 2.45ghz from antenna #1 is mainly due to the concentration of the surface current vectors in the lower part of the antenna. the radiation at 5ghz from antenna #1 is due to the surface current distribution on the upper and lower sections of the antenna, as illustrated in figure 6(b). the surface currents depicted in figure 6(c) show the λ/4 operation of antenna #2 at 2.45ghz. the operation of antenna #2 on 5ghz is due to the random distribution of surface current vectors on the entire structure, with nulls in between. the ground plane also has a vital role in the construction of small antennas. through current excitation, a monopole antenna ground plane creates another half of the monopole, so that it can act as a dipole antenna. the ground plane plays an active part in the radiation mechanism of small antennas. in this study, the ground plane effect on the performance of both antenna structures is significantly noticed as the height of the ground plane influences the shift in resonant frequencies on both antennas. the excitation of current in both antennas is introduced by a transmission line through a 50ω excitation port. through simulations, the position of placement for both antennas on the ground plane is optimized for achieving good impedance match that results in reduced return loss. fig. 6. current distribution on antenna #1 at (a) 2.45ghz, (b) 5ghz. surface current on antenna #2 at (c) 2.45ghz, (d) 5ghz. v. effects of the ground plane on measurement results both antennas presented in this paper portray good agreement between the simulation and the measurement results. the study presented in this section is primarily an investigation on the ground plane size. the experimental study of antenna #1 showed that the compact and insufficient ground plane is the prime hindrance in achieving measurement results similar to the simulation results. the measurements were carried out on agilent e8363c pna network analyzer. the measurement setup of the pna is matted with a coaxial cable. in small and unbalanced antennas, the cable currents mainly reside on the outer conductor of the cable [11]. the remedy to subside this large current on the outer conductor of the cable is to increase the width of the ground plane, and so the current distributes on it. in antenna #1, due to the geometrical limitations, the ground plane size is limited. in the case of engineering, technology & applied science research vol. 12, no. 2, 2022, 8452-8457 8456 www.etasr.com jamil et al.: design and geometric transformations of koch curve monopole antennas antenna #2, the width of the ground plane was automatically increased as we bend the geometry of koch-monopole antenna. the larger ground plane yielded better measurement result and more comparable with the simulation. realistically, in robust conditions, the antenna measurement is affected by some factors such as coupling with cables, connectors, and fabrication tolerances. the discussion on the ground plane effects is meant to provide insight into the understanding of these factors during measurements. vi. results and discussion it can be noticed from the curves presented in figures 7-8, that both antennas have satisfactory return loss results. the antennas are designed to operate on the wlan frequency bands of 2.45 and 5ghz. the measured s11 plot of antenna #1 shows an impedance bandwidth of 153mhz at -10db scale, around the center frequency of 2.496ghz and a bandwidth of 232mhz around the center frequency of 5.02ghz. for the antenna #2, the measured bandwidth calculated at -10db scale for the 2.45ghz band is 180mhz. the antenna #2 depicts satisfactory return loss measurement performance at the 5ghz band, with a minimum return loss of -24.4db at 4.97 ghz and the calculated impedance bandwidth is 285mhz. the far-field performance of the antennas #1 and #2 has been gauged by the measurement of the e-plane and h-plane patterns at 2.45ghz and 5ghz. the patterns for antenna #1 are presented in figures 9 and 10. frequency (ghz) 2 3 4 5 6 s 1 1 ( d b ) -25 -20 -15 -10 -5 0 simulation measurement fig. 7. antenna# 1: comparison between simulation and measurement s11 results. frequency (ghz) 2 3 4 5 6 s 1 1 ( d b ) -25 -20 -15 -10 -5 0 simulation measurement fig. 8. antenna #2: comparison between simulation and measurement s11 results. figures 11 and 12 show the radiation patterns of the antenna #2. the shape of the plots is mostly symmetric in both e and h fields. in the case of antenna #1, it has been observed that the radiation pattern plot is omnidirectional at 2.45ghz and 5ghz with gains of 4.15dbi at 2.45ghz and 2.57dbi at 5ghz. the far-field radiation pattern of antenna #2 at 2.45ghz depicts that the antenna demonstrates a good omnidirectional h-plane pattern while exhibiting a figure-eight pattern in the eplane. it can be seen from figure 12 that the radiation pattern of antenna #2 has been distorted in e and h planes. due to the bending of antenna #2, this distortion has caused an alteration in current distribution on the antenna structure. the horizontal component of the electric field in antenna #2 is mainly concentrated on the upper and lower sections of the antenna. the horizontal component of the electric field causes a distortion of the radiation pattern at a higher resonant frequency of 5ghz. the simulated directivity gains along the x-y plane are 1.3dbi at 2.45ghz and 4.2dbi at 4.93ghz. fig. 9. measured e-plane pattern of antenna #1 at 2.45 ghz. fig. 10. measured h-plane pattern of antenna #1 at 5ghz.. engineering, technology & applied science research vol. 12, no. 2, 2022, 8452-8457 8457 www.etasr.com jamil et al.: design and geometric transformations of koch curve monopole antennas fig. 11. measured e-plane pattern of antenna #2 at 2.45ghz. fig. 12. measured h-plane pattern of antenna #2 at 5ghz. vii. conclusion in this paper, a technique has been proposed to reduce the size of the conventional koch-curve monopole antenna along with a parametric study on the role of indentation angles. the higher indentation angle along with the higher number of iterations has a great impact on the novel space-filling property of the fractal antennas. moreover, the proposed technique to reduce the antenna size also introduced an additional width to the ground plane of antenna #1. during the process of small antenna designs, most of the designs ignore the effects of the coaxial cable and the connector. cable effects can become the primary reason for the discrepancy between the simulation and the measurement results beside other valid reasons such as fabrication, soldering and measurement tolerances. the increased ground plane width in antenna #2 portrayed better s11 measurement results. the measured e and h-plane radiation pattern results at the resonant frequency of 2.45ghz and 5ghz have been presented for both antennas. the omnidirectional radiation pattern results helped confirm that the designed fractal koch-curves are monopole antennas. references [1] l. j. chu, "physical limitations of omni‐directional antennas," journal of applied physics, vol. 19, no. 12, pp. 1163–1175, dec. 1948, https://doi.org/10.1063/1.1715038. [2] c. p. baliarda, j. romeu, and a. cardama, "the koch monopole: a small fractal antenna," ieee transactions on antennas and propagation, vol. 48, no. 11, pp. 1773–1781, aug. 2000, https://doi.org/10.1109/8.900236. [3] c. puente, j. romeu, r. pous, j. ramis, and a. hijazo, "small but long koch fractal monopole," electronics letters, vol. 34, no. 1, pp. 9–10, jan. 1998, https://doi.org/10.1049/el:19980114. [4] k. j. vinoy, j. k. abraham, and v. k. varadan, "on the relationship between fractal dimension and the performance of multi-resonant dipole antennas using koch curves," ieee transactions on antennas and propagation, vol. 51, no. 9, pp. 2296–2303, sep. 2003, https://doi.org/ 10.1109/tap.2003.816352. [5] s. r. best, "on the performance properties of the koch fractal and other bent wire monopoles," ieee transactions on antennas and propagation, vol. 51, no. 6, pp. 1292–1300, jun. 2003, https://doi.org/ 10.1109/tap.2003.812257. 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[12] c. b. nsir, j. m. ribero, c. boussetta, and a. gharsallah, "design of a 1×2 cpw fractal antenna array on plexiglas substrate with defected ground plane for telecommunication applications," engineering, technology & applied science research, vol. 11, no. 6, pp. 7897–7903, dec. 2021, https://doi.org/10.48084/etasr.4558. [13] m. v. rusu and r. baican, "microwave and millimeter wave technologies," in fractal antenna applications, i. minin, ed. intechopen, 2010, https://doi.org/10.5772/9057. [14] i. t. nassar and t. m. weller, "the ground plane effect of a small meandered line antenna," in wamicon 2011 conference proceedings, clearwater beach, fl, usa, apr. 2011, pp. 1–5, https://doi.org/ 10.1109/wamicon.2011.5872862. [15] h. alsaif, "compact hexagonal monopole antenna for lower 5g bands," engineering, technology & applied science research, vol. 9, no. 3, pp. 4200–4202, jun. 2019, https://doi.org/10.48084/etasr.2714. [16] j. p. gianvittorio and y. rahmat-samii, "fractal antennas: a novel antenna miniaturization technique, and applications," ieee antennas and propagation magazine, vol. 44, no. 1, pp. 20–36, oct. 2002, https://doi.org/10.1109/74.997888. microsoft word etasr_v12_n3_pp8777-8784 engineering, technology & applied science research vol. 12, no. 4, 2022, 8777-8784 8777 www.etasr.com akhtar et al.: a comparative study of the application of glowworm swarm optimization algorithm … a comparative study of the application of glowworm swarm optimization algorithm with other nature-inspired algorithms in the network load balancing problem talha akhtar department of computer science and information technology ned university of engineering & technology karachi, pakistan talhaakhtar@nbp.com.pk najmi ghani haider department of computer science and information technology ned university of engineering & technology karachi, pakistan najmi@neduet.edu.pk shariq mahmood khan department of computer science and information technology ned university of engineering & technology karachi, pakistan shariq@neduet.edu.pk received: 20 april 20222 | revised: 7 may 2022 | accepted: 12 may 2022 abstract-vast amounts of data are transferred through communication networks resulting in node congestion, which varies according to peak usage times. the glowworm swarm optimization (gso) algorithm is inspired by the rummaging and courtship behavior of glowworms. the glow intensity of glowworms is a measure of fitness that attracts other glowworms in its neighborhood. this work applies the gso algorithm to the computer network congestion problem in order to lessen the network burden by shifting loads to the fittest neighborhood nodes, thereby enhancing network performance during peak traffic times, when the response of systems on the network would go down. the proposed solution aims to alleviate the burdened nodes, thereby improving the flow of traffic throughout the network, improving the users’ experience and productivity, and efficiency. in this paper, three swarm algorithms, namely particle swarm optimization (pso), cuckoo search (ck), and gso have been employed to solve the network load balancing problem. the results produced by gso show improvement of 71.17%, 74.14%, and 84.15% in networks consisting of 50, 100, and 200 nodes in peak hour load, while pso shows 13.87%, 11.75%, and 23.72%, and ck 10.61%, 3.19%, and 6%. the results prove the superior performance of gso. keywords-network congestion; load balancing; gso; throughput; swarm intelligence i. introduction the decentralized computer network system is a mixture of heavily and lightly loaded nodes, with the heavily loaded nodes becoming bottlenecks, thereby reducing traffic flow rate, causing system sluggish response on the networks. load balancing addresses this issue to improve the network throughput by routing packets to adjacent edges having lesser traffic load. it enables the reasonable distribution of resources on computer networks and thereby a more efficient utilization of resources. the network burden at an edge depends on the queue of tasks that need to be processed through that node. the queue length is related to the response time of the jobs and is an important indicator of load burden on a computer network [1]. the effectiveness of conventional algorithms for load balancing in computer networks (such as the round robin task scheduler and least connection [2]) will be adversely impacted due to the explosive increase of data coming from mobile devices or tablets. data usage is expected to soon exceed 142 exabyte a month [3]. additionally, it is estimated that there will be 57.7 billion electronic and iot devices linked to the internet by 2023 [4]. all these devices will link to the network via technologies like 2g, 3g, 4g, lte,5g and machine-tomachine (m2m) with wireless options like bluetooth, wi-fi and zig-bee. various approaches have been used to address this problem. the meta-heuristic approach to optimization problems, such as the use of nature-inspired algorithms [5], has attracted the attention of researchers. the term swarm intelligence was introduced by benni and wang in 1989 in the global optimization framework of cellular robotics [6]. swarm intelligence follows the distributed methodology of governing corresponding author: talha akhtar engineering, technology & applied science research vol. 12, no. 4, 2022, 8777-8784 8778 www.etasr.com akhtar et al.: a comparative study of the application of glowworm swarm optimization algorithm … of work in chronological direction. this strategy is motivated from the behavior of ants searching for food in collaboration in appropriate order with nest mates. a swarm is an enormous group of homogeneous agents that are locally interacting among themselves. there is no central control and they are globally distributed in a decentralized manner. the idea of ant colony optimization (aco) algorithm comes from the movement of ants foraging for food and its delivery into the nest [7-9]. the aco is applied for finding the shortest route by emitting chemical substances (pheromones), updating the following path, therefore all ants move like a trail bridge. it is applicable in the travelling salesman problem for calculating the optimal path among different cities. a novel approach of particle swarm optimization (pso) was introduced in 1995 [10, 11] which is inspired from flocks of birds and schools of fish and their social behavior. the pso is used for accessing a target with minimal duration by updating the particle's current velocity and position from its neighborhood. the artificial bee colony (abc) algorithm's [12] inspiration is the behavior of honeybees foraging foods to make honey in a nest. it transfers a message to its nest mate with the help of a wiggle dance. the cuckoo search (ck) algorithm is based on the cuckoo bird’s life and breeding scheme [13]. glowworm swarm optimization (gso) is investigated in this paper with regard to network load balancing. the idea is to mitigate the traffic load burden during peak hours using a meta-heuristic approach about network optimization in iot. due to increasing massive amounts of data traffic on computer network the decentralized approach is attracting the researchers’ attention. the main objective of load balancing method is to allocate the traffic load uniformly dispersed to achieve best performance on homogeneous and heterogeneous data networks. load balancing is used to enhance user fulfillment, better utilization of resources, execution time, and waiting time of task coming from several locations/nodes. to do this, a load balancer needs to be able to predict the load on those edges having lesser amounts of traffic. it can be a static or sequential distribution of tasks among the machines in the neighborhood. one drawback is that all nodes can become overloaded. a dynamic technique in swarm intelligence based approach, such as aco, is one in which data would be segregated on to those nodes that are having the highest amount of pheromone evaporation created as a path. the ants find the shortest route to achieve traffic in minimum amount of time. the honey bee in abc uses another approach to optimize traffic on the optimal path. the main strategy for finding food location, to pass the message to other nest mates is by a waggle dance to find good food sources. in both wired and wireless media, network packets are moved between nodes by routing. routing techniques are of two types: static and dynamic. routing can be based on centralized or decentralized techniques. in the centralized method all nodes are linked into a star configuration [14]. compared to decentralized systems, centralized systems do not require replication. however, the disadvantage is that when the midpoint of a star network is down, the entire network becomes detached. the swarm intelligence algorithms follow the decentralized scheme of operation. the gso algorithm is based on multimodal functions to find a set of local optimal solutions. applying the analogy of glowworm behavior to communication networks, the network traffic can be shifted to neighborhood glowworm nodes having the highest luminance levels [15, 16]. large quantities of data from diverse devices and applications traverse through a network. network optimization has benefits such as faster information rate, information recovery, and elimination of redundant records enabling perceptible improvement in load balancing which plays a crucial role in network performance. the goals of this investigation are: • to reduce the queue length and thereby divert network traffic to adjacent lighter loaded nodes which in turn would improve network performance. • to increase the throughput and decrease response time and delay in network systems through the application of gso. • the comparison of load balancing via gso and other nature-inspired algorithms. load balancing is a mechanism that distributes a fair allocation of resources among the network nodes. load balancing methods can be implemented either in hardware or in software. in hardware balancing, there are four layers in a computer network. switches offer server redundancy and load balancing. software balancing is used to calculate usage and allocate resources. furthermore, load balancing can be static and dynamic. in static load balancing, the predictable load is segregated among nodes which are connected directly or indirectly to the network. dynamic load balancing is used to deal with unpredictable load which can be adjusted on various conditions of homogeneous and heterogeneous data passing through hybrid networks. static load balancing utilizes the surveying strategy (the round robin approach). the technique disperses data sequentially to each designated host, however it can be unbalanced among various virtual machines during data distribution [17]. the dynamic load balancing method is primarily based on the associated task, processing time and computational cost of each server that decide the distribution of information in order to acquire the processing time for the tasks. it will lead to uneven server distribution. it can be classified into several sub groups [18-22]. data traversing through the computer network for choosing the shortest routes is highly beneficial when the data delivery is more important than the overall network lifetime [23]. for minimizing network traffic, uniform load balancing is used to maximize network throughput and reduce queue length [24]. for segregating network traffic, the sub-network load balancing approach, which is constructed on the greedy growing method is developed with strong emphasis on utilizing the on-board batteries of the sensor nodes effectively. it is the best approach for transferring traffic on neighboring nodes [25]. a biased energy and haphazard movement based technique [26] spreads the network traffic among multiple routes in the resource constraint environment. a tree-based load balancing method is introduced, where a leaf of a tree or child node finds one of its parent nodes [27]. the different parameters, i.e. packet delivery, packet loss, and energy engineering, technology & applied science research vol. 12, no. 4, 2022, 8777-8784 8779 www.etasr.com akhtar et al.: a comparative study of the application of glowworm swarm optimization algorithm … consumption are considered when transferring packets from start to end node. a stochastic distributed approach based on node settlement and load optimization approach is proposed in [28] to balance the energy consumption through the network. ii. load balancing performance measures the performance of load balancing is measured by the following parameters: • throughput: the number of packets transferred per unit time span. the performance of computer network is enhanced if throughput is maximized. throughput = ��� ������� ���� (1) • fault tolerance: recovery from state when a process is abnormally disconnected or in failure mode. • migration time: it is the period required to transfer packets from a source node to the destination node. • traffic reduce rate: the traffic rate is calculated as the total reduction in traffic divided by the total data packets transferred from that node multiplied by 100. traffic reduce rate = �������_������ ���� _������� x 100 (2) • response time: the total time-to-live when transferring a packet from one node to another. it is minimized with increase in throughput. response time = ' �(���)(*�� (3) • queue length: the unprocessed tasks are accumulated into a waiting stage. it is processed for decreasing accumulated task to improve response time and maximizing throughput. +,-. = +,-. + 0 ,-. − 23 45 (4) where 0,-. is the predictable amount of requests allocated to server m in t interval, 6μ/9: is the mean of the new arrival request in the time interval that the server is continuously in busy state. iii. glowworm swarm optimization algorithm a glowworm has the ability to spread randomly in a search space. it is attracted to the glowworm with the highest glow intensity in its neighborhood [29]. each glowworm broadcasts its glow intensity and is attracted to its neighbors on the basis of a fitness function. the glowworm moves towards the neighboring glowworm having the most glow intensity. the fitness is proportional to the function being optimized. iv. steps of the glowworm swarm optimization algorithm the steps of gso algorithm are depicted in figure 1. on initialization, all glowworms contain the same amount of luciferin lo. every cycle of the algorithm passes through three stages: luciferin modify stage, association stage, and community array update stage. the luciferin modify stage denotes the function assessment at the glowworm position. every glowworm updates its level from its prior luciferin level: li (t + 1) = (1−ρ) li(t) + γ j (xi (t + 1)) (5) where li(t) denotes the luciferin level of the i th glowworm at time t, ρ represents the luciferin degeneration variable (0 < ρ < 1), γ is the luciferin enhancement variable, and j(xi (t)) denotes the cost of the objective function or the prior level of luciferin of the i th glowworm at time t. initialize n (number of glowworms) stages of glowworm life cycle solve the objective function for updating the luciferin level find glowworm in its neighbourhood calculate the probability and update the movement if iteration is not maximize then repeat cycle no output yes start fig. 1. stages of gso. in the movement period, each glowworm determines the probability to move in the direction where an adjacent glowworm has luciferin quantity greater than its own, so the glowworm would move towards where the intensity of the radiance is the highest. the probability of moving towards a glowworm at the adjacent j th position is given by: ;<= ,>. = ?@,�. a ?b,c. ∑ e∈ gb,c. ?e,c. a ?b,c. (6) where j ∈ ni(t), ni(t) = {j: dij(t) < rid(t) ; h<,>. < h=,>. (t)} at neighborhood of glowworm i in time span t, dij(t) the euclidean distance between glowworms i and j in time span t, and rid(t) indicates the adjacent array related to glowworm i in time span t. so, the glowworm i selects a glowworm j ∈ ni(t) with pij(t). the prototype for the glowworm arrangement [30] is specified as: i<,> + 1. = i<,>. + , jb,c. a j@,c. ||jb,c.a j@,c.|| . (7) where yi(t) ∈ r m is the position of glowworm i in time span t in the m-dimensional real space r m , ||.|| represents the euclidean norm operator and s > 0) is the step size. in the neighborhood range update stage, each glowworm i has a neighborhood in its radial range r i d ( 0 < r i d <= rs), where engineering, technology & applied science research vol. 12, no. 4, 2022, 8777-8784 8780 www.etasr.com akhtar et al.: a comparative study of the application of glowworm swarm optimization algorithm … rs is the glowworm sensor range. each glowworm's neighborhood range is updated as: r i d(t) (t + 1) = min { rs, max { 0, r i d(t) + β (nt−|ni(t)|) } (8) where β is a constant and nt is the number of neighbors. v. multi-modal functions the multi-modal function is a branch of optimization concerned with finding good solutions. it is defined as a function having multiple local optima. a local optimum is a solution which is better than all its neighboring solutions. these functions also have multiple global minima scattered throughout the search space. it is also defined as a statistical distribution of values with multiple peaks. the gso algorithm captures the multiple optima of the multi-modal optimization function [31]. in the context of load balancing on computer networks, the traffic is shifted towards either balanced or under loaded nodes. these problems are introduced for continuous data of equal (balanced nodes) or unequal (under loaded and over loaded nodes) peaks. the cases considered for multi-modal function during peak times of traffic are: unequal peaks, equal peaks, and peaks of concentric circles located at irregular intervals. it is much more helpful to optimize data in computer networks when the response time is increasing with increase in queue length. using the gso algorithm, the network traffic can be shifted towards the path to the fittest neighborhood with the lighter traffic [32]. the problem is to find the local optima having equal and unequal values. the multi-modal function contains maximum and minimum number of traffic during the passage of data [33-35]. fig. 2. gso circle function: each glowworm is attracted to its neighboring glowworm. the multi-modal functions used in gso regions are: (i) rastrigin’s function, (ii) circle function, (iii) equal-peaks-a function, (iv) equal-peaks-b-function, and (v) equal-peaks-cfunction [36]. the circle function is the most appropriate in application to load balancing. the circle function contains multiple concentric circles as the region of local maxima is depicted in figure 2. the concentric circles share the same center point, therefore circular lines of local peaks present an infinite-peak case unlike other multi-modal functions such as rastrigin’s function, two dimension exponential function, and gaussian distribution functions where the peak is located on a single point. the circle function is given as: lm,i', io. = ,i' o + io o.p.or ((sin 2 (50,i' o + io o.p.'))+1.0 (8) vi. experiment this section presents the determination of load burden on computer network and the shifting of load towards neighboring nodes having lesser burden. it studies the performance of gso algorithm and compares it with the performance of other nature-inspired algorithms such as pso and ck. in the designed setup, all devices are connected from any location in a network and transfer data packets over it. the details of all the devices, such as device identification number, device name, and device geographical location is saved on the internet data repository [37]. the test model is depicted in figure 3. data generated b y multip le sources network analyzer t-gso load bala ncer san (central repository load shifting via t-gso load balancer connecting with multiple iot devices virtual machines 1 to m physical ma chines 1 to n in ternet cloud fig. 3. network topology of load balancing using t-gso segregated on three layers. users' requests are coming from a number of iot devices. the requests are segregated onto virtual machines via a load balancer (t-gso) and are finally saved in a central repository. the load is mitigating queue tasks to be fetched on priority basis with increased throughput, thereby minimizing response and latency times. data pass through the gso to find the luciferin level and compute the fitness function given in (4). the glowworms find the fittest neighbor on the basis of probability, so they move data packets towards fittest neighbor, having highest value of fitness function. it selects the network packet and transfers it to the least congested nodes. the parameters of gso, ck, and pso set for the experiment are depicted in tables i-iii. these parameters can be further adjusted for tuning the performance of the system. experiments were conducted for network configurations of 50, 100, and 200 nodes. at the initial stage, data are extracted from a prtg network monitoring tool configured on computer network for visualizing network traffic. the data are uploaded into the data repository. then, the data are subjected to gso, pso, and ck algorithms and the performance is noted. engineering, technology & applied science research vol. 12, no. 4, 2022, 8777-8784 8781 www.etasr.com akhtar et al.: a comparative study of the application of glowworm swarm optimization algorithm … table i. gso variables parameter fixed value ρ rho 0.4 γ ghama 0.6 s sensor 0.03 nt neighborhood nodes 5.00 lo luciferin 5.00 table ii. ck parameters parameter fixed value npar quantity of enhancement 100 varlo minimum value of band -5.0 varhi maximum value of band 5.0 numcuckoos initial quantity 5.0 numnewcuckoos new quantity 0.0 minnumberofeggs least quantity of eggs 2.0 maxnumberofeggs extreme quantity of eggs 4 maxiter highest repetitions 100 knnclusternum quantity of clusters 1 motioncoeff lambda variable, default=2 9 table iii. pso parameters parameter fixed value problem dimensions 2 number of particles 5 inertia weight 0.729 cognitive weight 1.49445 social weight 1.49445 vii. simulation results and discussion the performance results of gso, pso, and ck algorithms in terms of throughput and queue length are presented in this section. figures 4-7 show the results of gso. the result of the comparison of gso with pso and ck algorithms is depicted in figure 8. the behavior of fitness function vs. the number of iterations is given in figure 4. the less loaded node would have a high value of luciferin level, therefore more data packets are delivered through this node. the load balancer routes data traffic towards neighboring nodes having higher luciferin than its level. the euclidean distance should be less than the radial sensor ranges of neighboring glowworm, e.g. from table i, the radial sensor range is 0.22mb/s therefore the highest probability of data packets shifted towards adjacent node (node number 1). the number of iterations was computed for 358 time slots over 50, 100, and 200 nodes, and luciferin level has stabilized at similar levels for all nodes (figure 4) indicating load balanced over the nodes. the comparison of traffic data packets and optimum load (gso-x, gso-y) is depicted for 50, 100 and 200 nodes. the trend shows that the node capacity is maximized which would be segregating a large number of data packets on the virtual machine, therefore the load is mitigated on a neighboring node. the incoming and outgoing data packets are 20mb/s and 13mb/s. the load is optimized by t-gso load balancer executing the iterations, thereby gso-x and gso-y are 16mb/s and 15mb/s in node 1. the proposed t-gso scheme shows improved network throughput during peak traffic for networks of 50, 100, and 200 nodes. (a) (b) (c) fig. 4. fitness function vs. iterations under (a) 50, (b)100, (c) 200 nodes (a) (b) (c) fig. 5. data traffic vs. optimum load under (a) 50, (b) 100, (c) 200 nodes. engineering, technology & applied science research vol. 12, no. 4, 2022, 8777-8784 8782 www.etasr.com akhtar et al.: a comparative study of the application of glowworm swarm optimization algorithm … considering traffic-in and traffic-out, figure 5 shows the traffic at nodes indicated at the start of the gso algorithm. gso-x and gso-y give the resulting position on completion of iterations of gso algorithm. it can be seen that the input traffic at nodes was reduced and the output traffic was increased in the completion of the gso algorithm. furthermore, the number of nodes increased, the resultant load gso-x, gso-y appear more balanced. figure 6 shows queue length vs. iterations. the network performance depends upon important indicators of load balancing, such as the queued tasks that are to be executed on each node. if the queue processes are increased, the network throughput reduces, which may cause request timeout and time delay. queue length is recorded on each node with respect to time. the queue length is reduced with the help of gso algorithm for diverting traffic. the highest value of luciferin level is corresponding with the minimum value of queue length on an adjacent node. the trend shows that the queue task is released when the number of nodes is increased, therefore network load was mitigated on adjacent nodes having maximum value of fitness function. (a) (b) (c) fig. 6. queue length vs. load for: (a) 50, (b) 100, (c) 200 nodes. in gso algorithm, each glowworm finds the optimal path where the glow intensity is maximum. the luciferin level of that node is indirectly proportional to the traffic accumulated on the node. the highest luciferin level on an adjacent node indicates the lowest number of data packets is delivered on every node. in figure 7, at 10pm the luciferin level is 3.1nm and traffic-in and traffic-out are 1.94 and 0.2, which indicates inverse relation between fitness value and data bandwidth. the trend of the plot in figure 7 shows that when the number of nodes increases, the luciferin level is maximized, therefore the load is mitigated on that node. (a) (b) (c) fig. 7. luciferin and data packets accumulated under: (a) 50, (b) 100, (c) 200 nodes. (a) (b) (c) fig. 8. comparison of luciferin and data packets accumulated under: (a) 50, (b) 100, (c) 200 nodes. engineering, technology & applied science research vol. 12, no. 4, 2022, 8777-8784 8783 www.etasr.com akhtar et al.: a comparative study of the application of glowworm swarm optimization algorithm … the performance comparison of gso with pso and ck algorithms for network load balancing is given in figure 8. the results demonstrate the achievement of reducing node traffic in peak network usage periods. the gso gave 71.79%, 61.17%, and 57.17% improved performance on 50 nodes, 74.14%, 70.95%, and 62.38% on 100 nodes, and 84.15%, 78.14%, and 60.42% on 200 nodes respectively, showing its superiority. gso picks the fit neighborhood where the traffic is lighter and forwards traffic to under loaded and normal loaded nodes. the gso algorithm worked as a distributed mechanism by decreasing response time and overhead in addition by increasing throughput to improve the performance. viii. conclusion the explosive growth of data on the internet from the increasing numbers of iot and m2m devices has the impact of diminishing the network performance, efficiency, and data delivery. the results from this work show that nature-inspired meta-heuristic approaches can be applied to the network load balancing problem and model network traffic. gso is a more recent algorithm than pso and ck. from the study of performance comparison of these three nature-inspired algorithms on the basis of node queue length, throughput, and response turnaround time, gso showed better performance over pso and ck. the comparison of gso with pso showed improvement in traffic reduce rate by 13.87%, 11.75%, and 23.72% for 50, 100, and 200 nodes respectively. likewise, in comparison with ck, gso improved the traffic reduce rate by 10.61%, 3.19%, and 6.00% respectively. furthermore, it appears that performance improvement is scaling with increase in nodes. the gso algorithm therefore seems more suited to mitigating the load balancing problem. for future work the following are proposed: • improvement of the gso algorithm through study of different multi-modal functions depending on the basis of network topology. • the multi-modal function parameters would be studied to find setting for optimal performance in different traffic scenarios. • a hybrid model of gso with another optimization algorithm such as the genetic algorithm. acknowledgement the funding agency of the current project is ned university of engineering technology and karachi, pakistan by higher education commission of pakistan. references [1] h. ben alla, s. ben alla, a. touhafi, and a. ezzati, "a novel task scheduling approach based on dynamic queues and hybrid meta-heuristic algorithms for cloud computing environment," cluster computing, vol. 21, no. 4, pp. 1797–1820, dec. 2018, https://doi.org/10.1007/s10586018-2811-x. 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[37] y. verma, "secure system simulation internet of things," ph.d. dissertation, california state university, california, usa, 2016. authors profile talha akhtar received his b.s. and m.s. degrees in computer science & it from ned university in 2002 and 2008 respectively. he is studying as a ph.d. scholar at ned university of engineering and technology. mr. akhtar has 16 year industry experience and 5 years of teaching experience. he has successful completed many projects in the banking sector. the focus of his research lies in the area of swarm intelligence, graph theory and nature inspired algorithms. najmi ghani haider received his phd. degree from brunel university, u.k, in 1989. he has 24 years of experience in the industry and 14 years in academia. he has served as a professor in the department of computer science and information technology, ned university of engineering and technology, karachi, pakistan. his research interests include network and information security and artificial intelligence. shariq mahmood khan received his b.s. and m.s. degrees in computer science from ned university of engineering and technology, pakistan, in 2005 and 2007 respectively. he earned his ph.d. degree from the brunel university london, uk in 2015. he is currently serving as a professor of computer science at ned university. he has authored or coauthored multiple research articles in international journals and conferences. he is a regular reviewer for a number of international journals and serves as the tpc member and reviewer for various international conferences. he also served as the founding conference secretary of the international conference on innovations in computer science & software engineering (iconics). the focus of his research lies in the areas of routing protocol design in mobile and vehicular ad-hoc networks, iot security, and wireless sensor networks. microsoft word 3-644-ed.doc engineering, technology & applied science research vol. 6, no. 3, 2016, 987-992 987 www.etasr.com mansouri and hafedh: torque ripple minimization and performance investigation of … torque ripple minimization and performance investigation of an in-wheel permanent magnet motor ali mansouri ces laboratory engineering school of sfax tunisia ali.mansouri@isetgf.rnu.tn trabelsi hafedh ces laboratory engineering school of sfax tunisia hafedh.trabelsi@enis.rnu.tn abstract—recently, electric vehicle motoring has become a topic of interest, due to the several problems caused by thermal engines such as pollution and high oil prices. thus, electric motors are increasingly applied in vehicle’ applications and relevant research about these motors and their applications has been performed. of particular interest are the improvements regarding torque production capability, the minimization of torque ripple and iron losses. the present work deals with the optimum design and the performance investigation of an outer rotor permanent magnet motor for in-wheel electric vehicle application. at first, and in order to find the optimum motor design, a new based particle-swarm multi-objective optimization procedure is applied. three objective functions are used: efficiency maximization, weight and ripple torque minimization. secondly, the effects of the permanent magnets segmentation, the stator slots opening, and the separation of adjacent magnets by air are outlined. the aim of the paper is the design of a topology with smooth output torque, low ripple torque, low iron losses and mechanical robustness. keywords-permanent magnet motor; optimization; performance; magnets design; ripple torque i. introduction in recent years, permanent magnet machines (pmm) have become widely used in different industrial applications [1-4]. this is essentially due to their miscellaneous advantages: higher efficiency, compact structure, smaller size, lower weight and flexibility of control. depending on the permanent magnets magnetization, three types of machines can be distinguished: the radial flux machine [5], the axial flux [6] and the transverse flux ones [7]. based on the arrangement of the rotor, two configurations may be encountered: the machine with an internal rotor and the machine with external rotor. in our work, the investigated topology is a surface mounted permanent magnet motor with an outer rotor and concentrated windings which is applied for in-wheel electric vehicle. the choice of the outer rotor configuration can be justified by the fact that this machine has a large air gap diameter, allowing a large number of poles. also, because of the fact that it is most suitable for direct integration in the vehicle wheel, making more compact the overall system. further, during the rotor rotation, the centrifugal forces exert a pressure on the permanent magnets, making their detachment more difficult. the magnetic circuit of a permanent magnet motor is very complex, nonlinear and characterized by a high number of parameters making its design a difficult task. in this case, an artificial intelligence technique is used. in the present work, a new based particle swarm optimization (pso) method is applied [8]. an optimized design is selected and studied by means of finite element analysis (fea) tool. then fea results are compared with those obtained by the optimization procedure. in order to reach the best machine performance, the effects of different parameters such as magnets segmentation, slot opening and adjacent magnets separation by air are outlined. ii. studied topology in the present work, the investigated machine topology is a 26 kw, 3-phase, 18-poles, 27 stator slots and concentrated windings synchronous surface-mounted permanent magnet motor with an outer rotor. the stator is made up of laminated iron core and a three phase stator windings. the rotor consists of thin permanent magnets mounted in an iron core. the magnets, alternatively magnetized in a radial direction, produce a magnetic field across the air gap. then, this magnetic field reacts with currents in windings placed in stator slots to produce the output torque. a general layout of the studied machine is illustrated in figure 1. the materials used to define the physical properties of the different regions analyzed by the finite element analysis are as follows: • a linear model of rare earth neodymium-iron-boron (ndfeb) permanent magnet materiel characterized by constants values: the relative permeability μr, the coercive force hc and residual flux density br,. • for iron parts (stator and rotor core), a non-linear laminated iron model (m800-65a). engineering, technology & applied science research vol. 6, no. 3, 2016, 987-992 988 www.etasr.com mansouri and hafedh: torque ripple minimization and performance investigation of … fig. 1. machine layout. iii. artificial intelligent technique and optimization procedure several electric machines optimization techniques have been proposed. from these techniques, we can distinguish, essentially, those based on the genetic and the particle swarm optimization (pso) algorithms which are the two most popular methods in electrical machine design and optimization [9-12]. in this work, we have used an optimization method based on the second algorithm: the speed-constrained multi-objective pso (smpso) algorithm [8]. in cases where the speed is too high, the proposed method enables the generation of new efficient particle locations. other characteristics of the smpso algorithm are: the use of an external archive to save the non-dominated solutions found during the search, and the use of polynomial mutation as a turbulence factor [8]. compared to other multi-objective optimization algorithms, the smpso algorithm performs better in terms of speed convergence to the pareto front, and of quality of the approximations of the found pareto front. in order to find the optimum geometric parameters of the investigated permanent magnet machine, an optimization procedure, based on the pso algorithm, was performed. these design parameters are: the airgap length δ, the rotor inner diameter drint, the magnets height hm, the slot wedge height hsw, the stator teeth width bts, the stator slot height hs, the opening slot factor kopen, the active machine length l, the pole angle α, and the stator inner diameter dsint. these parameters are shown in figure 2. in this paper, and in order to implement the optimization procedure, an analytical model, dealing with the magnetic and electric machine features is required. such model has been developed in previous works [13-14], and it is summarized as follows: • maximum value of the airgap flux density created by the permanent magnets: (1)mm r m r e h b b h m d = + where δe is the effective airgap length and kc is the carter coefficient. • peak air gap flux density: 4 sin (2) 2 pm g m a p b b p æ ö÷ç ÷= ç ÷ç ÷çè ø where pmα is the relative magnet width. • stator tooth flux density: ' (3)s mst fer ts l b b k lb t = where kfer, sτ and l’ are the stacking factor of the stator iron laminations which is taken equal to 0.95, the slot pitch and the iron core length. • stator and rotor yokes flux densities: (4) 2 p g sy sy fer b b h k t = (5) 2 m m ry ry fer b b h k t = where m , hsy, p and hry are respectively is the magnet pitch, the stator yoke height, the pole pitch and the rotor yoke height. • fundamental of the phase electromotive force: ,1 1 'ˆ 2 (6)sexta c g w d l e fn b k p p= where f, nc, dsext, p and kw1 are respectively the electrical frequency, the number of turns of windings of a phase, the stator outer diameter, the pole pairs number and the fill factor. • electromagnetic torque: 2 1̂ 'sin (7) 4 rms g sextt b s d l p b= where sî , β and 1ŝ are respectively the amplitude of the fundamental current of a phase, the electrical angle between the current and the magnet flux vector and the amplitude of the fundamental component of electric loading. • copper losses 23 (8)cu ph php r i= iph is the phase current and phr is the phase resistance. engineering, technology & applied science research vol. 6, no. 3, 2016, 987-992 989 www.etasr.com mansouri and hafedh: torque ripple minimization and performance investigation of … • iron losses: 2 2 2 2 1.5 1.5 (9)6 8.67 h st st st st c st d k fb b f p v k f b b sp æ ö÷ç ÷+ +ç ÷ç ÷=ç ÷ç ÷ç ÷÷çè ø 2 2 2 2 1.5 1.5 (10)6 8.67 h sy sy sy sy c sy d k fb b f p v k f b b sp æ ö÷ç ÷+ +ç ÷ç ÷=ç ÷ç ÷ç ÷÷çè ø 2 2 2 2 1.5 1.5 (11)6 8.67 h ry ry ry sy c ry d k fb b f p v k f b b sp æ ö÷ç ÷+ +ç ÷ç ÷=ç ÷ç ÷ç ÷÷çè ø where pst, psy, pry, kh, β, σ, d, kc, vst, vsy and vry, the stator tooth losses, the stator yoke losses, the rotor yoke losses, the hysteresis coefficient, the steinmetz constant , the iron lamination conductivity, the lamination thickness, the excess losses coefficient, the stator teeth, stator yoke and rotor yoke volumes. fig. 2. machine layout basic machine geometric dimensions. in the present work, three objective functions were carried out; the efficiency maximization, the machine weight and ripple torque minimization: objective_function1=minimum(1) (12)h where η is machine efficiency defined by: (13)out out cu st sy ry p p p p p p h = + + + + pout, pcu, pst, psy, pry are respectively the machine output power, the copper losses, the stator teeth losses, the stator yoke losses and the rotor yoke losses. the second objective function is described by the following equation: objective_function2=minimum( ) (14)weight where “weight” is the total machine weight. the third objective function is the ripple torque minimization: objective_function3 minimum( ) (15)ript= where, trip, is the ripple torque which can be evaluated analytically from the harmonics in the back-emf [15]: ( ) ( ) ( ) ( ) 2 2 7 5 13 11 12 2 19 17 25 23 ˆ ˆ ˆ ˆˆ2 / (16) ˆ ˆ ˆ ˆ rip e e e e t e e e e e + + = + where iê is the amplitude of the i th harmonic component of the back-emf. afterwards, the optimization procedure was implemented and run many times. as first results of the optimization process, we are interested to the pareto fronts, which are illustrated in figures 3-5. from these fronts, the designer should select the points meeting the specific design requirements. all front values are feasible and the choice can be made by considering other features that the motor must have. referring to these figures, we notice the tradeoff between the weight, the efficiency and the ripple torque. thereafter increasing the efficiency, leads to machine weight and ripple torque increase. this is due to the fact that when the weight increases, the machine can be designed with lower magnetic and electric loading. in order to verify the accuracy of the proposed optimization procedure, an optimized topology, whose parameters are given in table i, was selected and analyzed by fea. the obtained results, for the most relevant parameters, are provided in table ii. table i. optimized topology parameters parameter value δ (mm) 1.6 drint (mm) 285.6 hm (mm) 3 hsw (mm) 2.1 bts (mm) 13 kopen 0.5 hs (mm) 35.2 l (mm) 50 α (°) 16 dsint (mm) 183 efficiency (%) 0,981 weight (kg) 31,44 cpu (s) 8.672 trip(%) 37 engineering, technology & applied science research vol. 6, no. 3, 2016, 987-992 990 www.etasr.com mansouri and hafedh: torque ripple minimization and performance investigation of … fig. 3. pareto front for objective functions 1-3 fig. 4. pareto front for objective functions 2-3 fig. 5. pareto front objective functions 1-2 table ii. comparison between fea results and optimization results parameter optimization fea magnet flux density bm (t) 0.7 0.72 airgap flux density bg (t) 0.85 0.91 stator yoke flux density bsy (t) 1.7 1.77 stator teeth flux density bst (t) 2 1.85 rotor yoke flux density bry (t) 1.86 2.1 torque ripple trip (%) 37.5 42 iron losses ( kw) 1.057 1.064 iv. machine performances amelioration a. magnet segmentation effect for the purpose of showing the magnet segmentation effect on the output torque and on the torque ripple, the magnets are divided into segments on the radial direction as illustrated in figure 6. fea computation results of the machine output torque are illustrated in figure 7 and table iii. according to these results, the maximum output torque and the lower ripple torque are provided in the 8 segments-magnets topology. fig. 6. different rotor structures: a: 2 segments, b: 4 segments and c: 8 segments. fig. 7. torque variation for different magnet segmentation numbers engineering, technology & applied science research vol. 6, no. 3, 2016, 987-992 991 www.etasr.com mansouri and hafedh: torque ripple minimization and performance investigation of … table iii. torque ripple versus number of magnets number number of magnets segments torque ripple (%) 1 43 2 44 3 47 4 46 5 43 6 42 7 44 8 40 b. effect of air width between adjacent magnets with the aim of improving the machine performances and reduce the torque ripple, adjacent magnet segments are separated by air as illustrated in figure 8. in this case, the effect of the air width on the machine performance has to be investigated. fea calculation dealing with this parameter are illustrated in figures 9 and 10. based on these figures, it is shown that the output toque increases with the air width until it reaches a maximum value corresponding to an air length equal to 0.45° and after that it decreases. this is due to the fact that on one hand the saturation in the rotor poles increases with the magnet width, and on the other hand, to the increase of the flux linkage between the stator and the rotor when the magnet width increases. referring to figure 7, we can note the decrease of the torque ripple as function of the air width to achieve a minimum value, corresponding to an air length of 0.55°, and then its increase with the same parameter. c. slot opening effect another influent parameter is the stator slot opening. this parameter influences directly the air gap magnetic field in two ways. it deceases the average flux density and it affects the flux density distribution through the air gap. these two effects are illustrated in figure 11 for semi closed and fully opened slots. v. conclusion this paper investigates the optimization and performance investigation of a surface mounted outer rotor and concentrated windings permanent magnet machine designed for in-wheel application. at first, an optimization procedure based on the improved pso multi-objective optimization algorithm was implemented. the goal of this optimization procedure is to find the optimum machine’s geometric parameters providing the maximum efficiency and the minimum weight and ripple torque. afterwards, an optimized topology is selected and analyzed by fea. simulation results illustrates that the results obtained by analytical optimization are in good agreement with those obtained by fea. magnet segmentation, air between adjacent magnet segments width and slot opening effects are investigated with fea. based on the obtained results, it is shown that a higher number of magnet segments leads to higher output torque. it is also shown that the output torque increases with the air between adjacent magnet segments width, until it reaches a maximum value corresponding to a magnet segments width of 0.45°. subsequently, the slotting effect on the airgap flux density is investigated. in this case, it is illustrated that both magnetic flux density average and distribution are influenced by this parameter. fig. 8. topology with air between adjacent magnets. fig. 9. maximum output torque versus air between adjacent magnets width. fig. 10. ripple torque versus air between adjacent magnets width. engineering, technology & applied science research vol. 6, no. 3, 2016, 987-992 992 www.etasr.com mansouri and hafedh: torque ripple minimization and performance investigation of … fig. 11. airgap flux density versus rotor position for semi closed and fully opened slots. references [1] z. q. zhu, d. howe, “electrical machines and drives for electric, hybrid and fuel cell vehicles”, proc. fn the ieee, vol. 95, no. 4, pp. 746–765, 2007 [2] j. wang, k. atallah, z. q. zhu, d. howe, “modular 3-phase permanent magnet brushless machines for in-wheel applications”, ieee t. veh. technol., vol. 57, no. 5, pp. 2714-2720, 2008 [3] y. chen, p. pillay, a. khan, “pm wind generator topologies”, ieee t. ind. appl., vol. 41, no. 6, pp. 619-1626, 2005 [4] x. sun, c. ming, w. hua, l. xu, “optimal design of double layer permanent magnet dual mechanical port machine for wind power application”, ieee t. magn., vol. 45, no. 10, pp. 4613–4616, 2009 [5] f. libert, design, optimization and comparison of permanent magnet motors for a low-speed direct-driven mixer, ph.d. thesis, royal institute of technology, sweden, 2004 [6] l. brooke, protean electric tackles the unsprung-mass ’myth’ of inwheel motors, 2011 sae world congress, usa, 2011 [7] h. weh, “ten years of research in the field of high force densitystransverse flux machines”, in proc. speedam’96, capri, 1996 [8] a. j. nebro, j. j. durillo, j. garcia-nieto, c. a. coello coello, f. luna, e. alba, “smpso: a new pso-based metaheuristic for multi-objective optimization”, ieee 2009 symposium on computational intelligence in multi-criteria decision-making, nashville, tn, usa, 30 march-02 april 2009 [9] r. ilka, a. r. tilaki, h. a. alamdari, r. baghipour, “design optimization of permanent magnet-brushless dc motor using elitist genetic algorithm with minimum loss and maximum power density”, int. j. mecha. elecr. comput. technol., vol. 4, no. 10, pp. 1169-1185 2014 [10] y. ahn, j. park, c. g. lee, j. w. kim, s. y. jung, “novel memetic algorithm implemented with ga (genetic algorithm) and mads (mesh adaptive direct search) for optimal design of electromagnetic system”, ieee t. magn., vol. 46, no. 6, pp. 1982–1985, 2010 [11] v. p. sakthivel, r. bhuvaneswari, s. subramanian, “multi-objective parameter estimation of induction motor using particle swarm optimization”, eng. appl. artif. intel., vol. 23, no. 3, pp. 302–312, 2010 [12] m. ashabani, y. a. r. i. mohamed, “multi-objective shape optimization of segmented pole permanent-magnet synchronous machines with improved torque characteristics”, ieee t. magn., vol. 47, no. 4, pp. 795-804, 2011 [13] a. mansouri, n. smairi, h. trabelsi, “multi-objective optimization of an in-wheel electric vehicle motor”, int. j. app. elect. mech., vol. 50, no. 3, pp. 449-465, 2016 [14] a. mansouri, n. smairi, h. trabelsi, “a new multi-objective optimization procedure based on particle swarm algorithm for optimum design of in-wheel permanent magnet motor”, tur. j. elec. eng. comp. sci. (submitted) [15] s. huang, m. aydin, t. lipo, “comparison of (non-slotted and slotted) surface mounted pm motors and axial flux motors for submarine ship drives,” in proc. of 3rd naval symposium on electrical machines, usa, dec. 4-7, 2000 microsoft word 02-sarode-ed.doc etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 139-143 139 www.etasr.com sarode and deshmukh: image sequence denoising with motion estimation in color image sequences image sequence denoising with motion estimation in color image sequences milindkumar v. sarode assistant professor department of computer science & engineering jawaharlal darda institute of engineering & technology yavatmal, maharashtra state, india. parthmilindsarode@rediffmail.com prashant r. deshmukh professor & head of department of computer science & engineering & it sipna’s college of engineering amravati, maharashtra state, india. prdeshmukh@ieee.org abstract— in this paper, we investigate the denoising of image sequences i.e. video, corrupted with gaussian noise and impulse noise. in relation to single image denoising techniques, denoising of sequences aims to utilize the temporal dimension. this approach gives faster algorithms and better output quality. this paper focuses on the removal of different types of noise introduced in image sequences while transferring through network systems and video acquisition. the approach introduced consists of motion estimation, motion compensation, and filtering of image sequences. most of the estimation approaches proposed deal mainly with monochrome video. the most usual way to apply them in color image sequences is to process each color channel separately. in this paper, we also propose a simple, accompanying method to extract the moving objects. our experimental results on synthetic and natural images verify our arguments. the proposed algorithm’s performance is experimentally compared with a previous method, demonstrating comparable results. keywordsvideo denoising; motion estimation; thresholding; segmentation; image sequence; ps�r. i. introduction denoising of image sequences is one of the critical tasks of image processing and signal processing. there is an affluence of signal image denoising algorithms; a comprehensive review of these techniques can be found in [1-6]. denoising image sequences extends the above operations to handle the sequential dimension. such sequences can be tv broadcast, camcorder files etc. in many cases, one can assume noise, to be an additive zero-mean white gaussian noise or impulse noise or a mixture of both noises. algorithms for the denoising of image sequences aim to remove such type of noise while utilizing both the spatial and temporal domains. denoising of video sequences attracted some attention in the past decade, with various suggested algorithms and principles. a suggested approach that utilizes the temporal redundancy is motion compensation [2, 7-10]. the estimation of motion characteristics within a time-varying scene is a challenging task, required in various types of video applications, such as video coding, object tracking, contentbased video retrieval etc. most of the motion estimation approaches deal only with monochrome images. however, color information is important and color processing is needed especially for new applications. since color images have 3-d pixels, the most straightforward way to apply these approaches to color sequences is to process each color channel separately. a different approach to deal with color, as proposed in [11-14], is to treat color images as vector fields by encoding the channel components on the imaginary parts of hyper complex numbers and specially using the quaternion algebra [15]. in this paper, fourier transformed based approaches [2] are used to deal with color image sequences for motion estimation. the color motion estimation problem is solved and utilized in the frequency domain. then motion compensation and finally filtering of image sequences is applied. each group of three consecutive sequence frames is processed in two steps: i) estimate motion between frames and ii) use motion vectors to get the final denoised current frame. motion trajectories are obtained recursively by region recursive estimation. the proposed approach further computes motion parameters and filter weights by maximizing peak signal to noise ratio. different types of video sequences are used to test the filter performance in terms of visual quality and peak-signal-to-noise ratio (psnr). ii. motion estimation of image sequences in this process, motion vectors that describe the transformation from one 2-d image to another (commonly from adjacent frames in a video sequences) are to be determined. it is an ill-posed problem as the motion is in three dimensions but the images are a projection of the 3-d scene on to a 2-d plane. in this section we consider the problem of determining motion estimates via a fourier transform formulation [16]. consider a sequence 1,,3,2,1,0),,,( −−−−−= kttyxf , where k is the digital image frames of size m x n generated by a stationary camera. assume all frames have a homogeneous background of zero intensity, except a single, 1-pixel object of unit intensity that is moving with constant velocity. for a sequence of k digital images of size m x n, the sum of the weighted projection on to the axis at any integer instant of time is given by: etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 139-143 140 www.etasr.com sarode and deshmukh: image sequence denoising with motion estimation in color image sequences ( ) ∑∑ − = − = ∆∏= 1 0 1 0 2 1 1),,(, m x � y txaj x etyxfatp (1) t = 0, 1, 2, -------, k-1. the sum of the projections on to the y axis is given by: ( ) ∑∑ − = − = ∆∏= 1 0 1 0 2 2 2),,(, � y m x tyaj y etyxfatp (2) t = 0, 1, 2, -------, k-1. where a1, a2 are the positive integer and ∆t is the time interval between frames. the fourier transform of equation (1) is given by: ( ) ∑ − = −= 1 /2 11 1),( 1 , k ot kutj xx eatg k aup π (3) u1= 0, 1, 2, -----k-1 similarly the fourier transform of equation (2) is given by: ( ) ∑ − = −= 1 /2 222 12),( 1 , k ot ktuj yy eatg k aup π (4) u2= 0, 1, 2, -----k-1 the frequency velocity relationship is given by: u1 = a1 v1 (5) u2 = a2 v2 (6) the sign of the x-component of the velocity is obtained by: [ ] nt xe x dt atprd s == 2 1 2 1 ),( and [ ] nt xm x dt atpid s == 2 1 2 2 ),( because px is sinusoidal, it can be shown that xs1 and xs 2 will have the same sign at an arbitrary point in time n, if the velocity component v1 is positive. if either xs1 or xs 2 is zero, we consider the next closest point in time tnt ∆±= . similarly the sign of v2 is to be computed. iii. motion compensation the process of applying the motion vectors to an image to synthesize the transformation to the next image is called motion compensation. the combination of motion estimation and motion compensation is a key part of image restoration and video compression. motion compensation describes a picture in terms of the transformation of a reference frame to the current frame. motion compensation exploits the fact that, often for many frames of a movie, the only difference between one frame and another is the result of either the camera moving or an object in the frame moving. motion compensation is a set of techniques that take advantage of redundancy in consecutive video frames. these techniques are used in video processing applications such as video compression and video stabilization. for both of these applications, motion compensation is a two-step process of detection and compensation. the detection step results in the specification of a motion vector that relates two consecutive video frames. for video restoration, the compensation step involves using the motion vector to predict the current video frame from the previous frame and encoding the prediction residual. for video stabilization, the compensation step involves translating the current frame in the opposite direction of the motion vector to stabilize the video sequence. a. motion compensation in mpeg in mpeg, images are predicted from previous frames (pframes) and future frames (b-frames). b-frames are more complex because the image sequence must be stored out of order, so that future frame is available to generate the bframes. b. block motion compensation in block motion compensation, the frames are partitioned in blocks of pixels. each block is predicted from a block of equal size in the reference frame. iv. filtering technique: the filter proposed order statistic filters are spatial filters whose response is based on ranking the pixels contained in the image area encompassed by the filter [17]. the response of the filter at any point is determined by the ranking result. here a definition of rank-ordered absolute differences statistics [1] is used. if x is the location of pixel and its neighborhood pixels are y and ( )� i ω be the set of points ( ){ }jix ,+ , here ji, should be in between �− and �+ , in a )12()12( +×+ �� neighborhood centered at x for positive and negative integer � . if 2≥� then xx ω=ω0 represents the set of points in a 55× neighborhood of x . for each point y which belongs to x 0ω , the absolute difference in the intensity of the pixel is defined by yxyx iid −=, . after taking all the differences between the neighborhood pixels with centered pixel, choose m smallest values of neighborhood pixels, and then sort these yxd , values in ascending order. thus this statistic gives a measure of how close a pixel value is to its m most similar neighbors. ∑ = = m i i sxr 1 )( (7) where i s is the smallest yx d , of i for y belongs to x 0ω . if 4=m , then )()( 4 xrxr = . etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 139-143 141 www.etasr.com sarode and deshmukh: image sequence denoising with motion estimation in color image sequences the value of )( xr is very simple to introduce into existing filters. a new weighting function is incorporated into bilateral filter to implement trilateral filter. bilateral filters are used to remove gaussian noise. it retains the sharpness of edges. each pixel is replaced by the weighted average of the intensities in the neighborhood. consider x be the position of the pixel, which is under consideration. the weight of y with respect to x is the product of spatial and radiometric components. the weight of spatial component ( i ω ) and the weight of radiometric component ( dω ) are given by                 − − = i xy i e 22 1 σω (8) and 2 2 1         − = d xyd d e σ ω (9) where iσ and dσ controls the behavior of weight. they serve as rough thresholds for identifying spatially or radiometrically close pixels. impulsive weight i ω at point x is defined as; 2 )( 2 1       − = i xr i e σω (10) approximate threshold value is determined by the i σ parameter. for the addition of )(x i ω function into the bilateral filter, we have to determine the strength of radiometric component in the impulse noise. the impulsivity v i of y w.r.t x will be defined as;           −=               + − 2 )()( 4 1 2 1 1),( iv yrxr v eyxi σ (11) the values of ),( yxi v function are 0 and 1. the parameter iv σ is used to control the shape of the overall function. if at least one of x or y is impulsive and has high )( xr value w.r.t iv σ , then 1),( =yxi v and if neither pixel is impulse like then 0),( =yxi v . thus 1),( =yxi v is taken to reduce the impulses. the resulting weight of y w.r.t central pixel x is written as; ),( )(),(),( yxi i c diw vyyxyxf ωωω ∗= (12) where ),(1 yxic v −= and 0=c or 1 . 0=c for impulsive pixel and 1=c for non impulsive pixel. when 0=c , the radiometric threshold becomes very large and thus there are irrelevant radiometric differences. when 1=c , only radiometric weight is used to differentiate pixels, because of high impulsive threshold. in this way a particular weighting function is applied on each pixel. specifically the control parameters iσ and dσ depends on the type of noise added. the values of these parameters are chosen automatically according to the percentage of noise added to the image. the method is applied iteratively to suppress noise, using the output of the previous iteration as the input of the next iteration. for high levels of noise (>30%) applying five to ten iterations, gives better results. v. design and implementation here we describe step-by-step the procedure for the denoising of image sequences. also, we provide experimental results for the method proposed. figure 1 describes the design and implementation process for denoising image sequences. fig. 1. design and implementation of image sequence denoising. this process consists of main four parts: shot detection/segmentation, motion estimation, motion compensation and filtering. each group of three consecutive sequence frames is processed in two steps i) estimate motion between frames and ii) use motion vectors to obtain the denoised current frame. motion parameters and filter weights are to be computed using motion estimation method and proposed filter respectively. here we use various types of video sequences for testing filter performance. etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 139-143 142 www.etasr.com sarode and deshmukh: image sequence denoising with motion estimation in color image sequences algorithm works as below: 1) take an image sequences / video as an input. 2) add variable noise e.g. gaussian / impulse noise. 3) detect shots of image sequences. 4) do motion compensation of the detected shots. 5) compute a representation of the motion fields that best aligns pixels in one frame of the sequence with those in the next. a) image intensity at instant (n-1) = noise free frames at (n-1) + noise sequences at (n-1) b) image intensity at instant (n) = noise free frames at instant (n) + gaussian/impulsive image noise sequences at instant (n). 6) do motion modeling to represent the motion of each region. a) do parameter initialization; i) compute motion vector descriptors from an initial dense motion field. ii) compute global motion attributes using shot detection/segmentation process. iii) compute new motion fields which provides a suitable initialization to optimize a cost function for image reconstruction using motion compensation. b) estimate motion for every moving region. c) estimation of motion needs the segmentation procedure, either prior or simultaneous with the motion estimation step. (i) compute number of pixels in each region (ii) compute entropy of the region in the error image before splitting. (iii) compute entropy of the sub region after splitting. (iv) compute threshold value automatically by calculating variance ( ) ( ) ( ) ( ) iv i i ii i ii threshold value× − × >∑ 7) use/apply described filter in section iv. following are some visual (figure 2 to 8) and quantitative results (table i) to show the performance of the method described in this paper. fig. 2. detection of shots of airplane image sequence fig. 3. detection of shots fig. 4. air plane noisy image gaussian/impulsive fig. 5. air plane denoised image etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 139-143 143 www.etasr.com sarode and deshmukh: image sequence denoising with motion estimation in color image sequences fig. 6. background does not move and it is occluded by the moving image of a boat. (a)–(c) (figure of motion estimation) fig. 7. tennis sequence with noise level 15. left: original frame. middle: noisy frame. right: denoised frame. fig. 8. garden sequence with noise level 20. left: original frame. middle: noisy frame. right: denoised frame. table i. result of the proposed method compared to the results reported in [1] image sequence �oise level results from [1] in db results of proposed method in db difference garden 10 15 20 32.22 29.28 28.08 32.86 30.03 29.10 +0.64 +0.75 +1.04 tenis 10 15 20 33.78 31.65 30.18 34.10 31.86 31.43 +0.32 +0.21 +1.25 salesman 10 15 20 37.95 35.17 33.33 38.18 36.24 33.83 +0.23 +1.07 +0.50 airoplane 10 15 20 not available 33.58 31.09 30.12 /a v. conclusion in this paper, an image sequence denoising algorithm and a motion estimation process is described. many noise removal algorithms, such as bilateral filtering, tend to treat impulse noise as edge pixels, and hence end with unsatisfactory results. in order to process impulse pixels and edge pixels differently, we introduce a new statistic based on rank ordered absolute differences (road) in some neighborhood of a pixel. this statistic represents how impulse-like a particular pixel is in the sense that the larger the impulse, the greater the road value. we then incorporate the road statistic into the bilateral filtering by adding a third component to the weighting function. the new nonlinear filter is called the trilateral filter, whose weighting function contains spatial, radiometric, and impulsive components. the radiometric component combined with the spatial component smooth away gaussian noise and smaller impulse noise, while the impulsive component removes larger impulses. the filter offers a new edge-preserving detail remover that smoothes input towards a piecewise constant gradient approximation. the filter requires only one user specified parameter and is applicable to �-dimensional data. visual and quantitative results shown in this paper are found better than the results of an earlier method. the results obtained are quite promising and illustrate the potential usefulness of this tool in the context of future mpeg-4 and mpeg-7 applications. references [1] m. protter, m. elad, “image sequence denoising via sparse and redundant representations”, ieee transactions on image processing, vol. 18, no. 1, pp. 27-35, 2009. [2] d. s. alexiadis, g. d. sergiadis, “estimation of motions in color image sequences using hypercomplex fourier transforms”, ieee transactions on image processing, vol. 18, no. 1, pp. 168-187, 2009. [3] m. elad, m. aharon, “image denoising via learned dictionaries and sparse representation”, international conference computer vision and pattern recognition, new york, 2006. [4] m. elad, m. aharon, “image denoising via sparse and redundant representation over learned dictionaries”, ieee transactions on image processing, vol. 15, no. 12, pp. 3736–3745, 2006. [5] a. buades, b. coll, j. m. morel, “a review of image denoising algorithms, with a new one”, multiscale modeling & simulation, vol. 4, no. 2, pp. 490–530, 2005. [6] j. portilla, v. strela, m. j. wainwright, e. p. simoncelli, “image denoising using scale mixtures of gaussians in the wavelet domain”, ieee transactions on image processing, vol. 12, no. 11, pp. 1338– 1351, 2003. [7] v. zlokolica, a. pizurica, w. philips, “recursive temporal denoising and motion estimation of video”, int. conf. image processing, singapore, 2004. [8] f. jin, p. fieguth, l. winger, “wavelet video denoising with regularized multiresolution motion estimation”, eurasip journal on applied signal processing, vol. 2, pp. 01–11, 2006. [9] r. dugad, n. ahuja, “video denoising by combining kalman and wiener estimates”, proceeding of international. conference on image processing, japan, 1999. [10] v. zlokolica, a. pizurica, w. philips, “wavelet-domain video denoising based on reliability measures”, ieee transactions on circuits and systems for video technology, vol. 16, no. 8, pp. 993– 1007, 2006. [11] t. a. ell, “hypercomplex spectral transformations”, ph.d. dissertation, univ. minessota, minneapolis, 1992. [12] s. j. sangwine, “fourier transforms of colour images using quaternion or hypercomplex numbers”, electronics letters, vol. 32, pp. 1979– 1980, 1996. [13] s.-c. pei, c.-m. cheng, “a novel block truncation coding of color images by using quaternion-moment preserving principle”, ieee int. symp. circuits and systems, vol. 2, pp. 684–687, atlanta, 1996 [14] t. a. ell, s. j. sangwine, “hypercomplex fourier transforms of color images”, ieee transactions on image processing, vol. 16, no. 1, pp. 22–35, 2007. [15] w. r. hamilton, elements of quaternion, second edition. new york: longmans, green & co., 1901. [16] r. c. gonzalez, r. e. woods, digital image processing, pearson education, second edition, prentice hall, 2005. [17] r. garnet, t. huegerich, c. chui, w. he, “a universal noise removal algorithm with an impulse detector”, ieee transactions on image processing, vol. 14, no. 11, pp. 1747-1754, 2005. microsoft word etasr_v12_n5_pp9108-9112 engineering, technology & applied science research vol. 12, no. 5, 2022, 9108-9112 9108 www.etasr.com ali & albayati: statistical modeling for traffic noise: the case of kirkuk city statistical modeling for traffic noise: the case of kirkuk city sundus shakor ali department of civil engineering college of engineering university of baghdad baghdad, iraq s.albayati1901m@coeng.uobaghdad.edu.iq amjad hamad khalil albayati department of civil engineering college of engineering university of baghdad baghdad, iraq a.khalil@uobaghdad.edu.iq received: 2 july 2022 | revised: 6 july 2022 | accepted: 20 july 2022 abstract-the auditory system can suffer from exposure to loud noise and human health can be affected. traffic noise is a primary contributor to noise pollution. to measure the noise levels, 3 variables were examined at 25 locations. it was found that the main factors that determine the increase in noise level are traffic volume, vehicle speed, and road functional class. the data have been taken during three different periods per day so that they represent and cover the traffic noise of the city during heavy traffic flow conditions. analysis of traffic noise prediction was conducted using a simple linear regression model to accurately predict the equivalent continuous sound level. the difference between the predicted and the measured noise shows that the model's accuracy is 93.93%. the results show the effectiveness of the suggested method and confirm its applicability in developing mitigation plans for both existing and future roadways. to test the effectiveness of the suggested method, the selected location of different road functional classifications of kirkuk city in iraq was studied. it was noticed that in all the selected sites, the noise level was observed to be above the permissible noise standard of the world health organization (who). keywords-noise level; traffic noise; road functionality; traffc volume; speed i. introduction noise is not only hard on our senses [1], our physical and emotional well-being also are also negatively affected [2]. exposure to high noise levels, i.e. over 85dba, for 8 hours or longer may be dangerous [3]. expansion of cities, industries, and facilities put people’s health at risk [4]. generally, noise has significant effects on human health [5]. table i shows the recommended noise level standards for several countries and the world health organization (who) [6]. noise levels in kirkuk city have been reported to be high, therefore, the situation requires evaluation. vehicles are the main source of noise pollution [7]. for reducing the noise pollution caused by transportation in cities, it is necessary to predict traffic noise [810]. research has been conducted to develop a traffic noise model for surat's main arterial road in india and different variables affecting traffic noise were analyzed in [11]. the survey involved 3 arterial roads based on mixed traffic patterns and a variety of land use patterns. the parameters were measured during peak hours. multiple linear regression analysis was utilized and the model showed that the variables had a good relationship to the noise. a comprehensive noise prediction model was developed for 8 significant highways in the indian states of telangana and andhra pradesh in [8]. each highway was measured for 7h each day. the variables include carriage width, traffic volume, and speed. the 15min interval model produced a negative relation against the 1h interval model. a traffic noise model was developed to measure the noise level of collector roads in denpasar city, indonesia in [13]. measurements were conducted from 6:00 a.m. to 6:00 p.m. and 48 sets of data in total were obtained in 15min intervals. it was shown that if all the other variables remain constant, an increase of 100 motorcycles increases traffic noise by approximately 3dba. in [14], the noise level was measured on the asian highway at the golestan national park, iran. for the analysis of independent variables and noise, 76 sampling locations were selected between 0 and 250m from the road. at each sampling station, monitoring was done for one week with 15min periods between 8:00 a.m. and 8:00 p.m. while spss software was used for modeling. a model was developed in [15] to forecast traffic noise on the roadways of the iranian city ahvaz. on 7 roads of the city, 1344 observations were performed at 12 stations. during the model development, out of 15 variables, just 9 independent variables were used. table i. noise level standards noise level standard noise level (dba) day time night time who 55 45 australia 45 35 germany 45 35 korea 50 45 japan 45 35 india 55 45 philippines 50 45 ii. materials and methods to measure traffic noise in kirkuk, 3 features were selected, road functionality, traffic volume, and speed, and their corresponding author: amjad hamad khalil albayati engineering, technology & applied science research vol. 12, no. 5, 2022, 9108-9112 9109 www.etasr.com ali & albayati: statistical modeling for traffic noise: the case of kirkuk city impact on traffic noise was investigated. to measure the noise levels, the 3 variables were examined at 25 locations. at each road, functional classification, traffic volume, and speed survey were conducted and recorded at 15min intervals. figure 1 displays the process for the suggested model starting with data collection using a sound level meter, variable selection analysis, model development, evaluation, and analysis of the findings. the obtained data include 3 variables: f (functional classification of the road), q (traffic volume), and v (average speed of vehicles). statistical analysis was designed to construct a noise level estimation model to highlight the effect of each variable on the noise level. fig. 1. pipeline of the proposed model. iii. traffic noise data the sound level meter (figure 2) was used to measure the sound levels during peak hours. the average of maximum and minimum noise levels was calculated and plotted in a normal graph with respect to time. a tripod supported the device at 1m height and kept it at 6.5m away from the middle lane of the road as depicted in figure 3. fig. 2. the sound level meter. fig. 3. a schematic diagram of the monitored site. iv. site selection kirkuk, located in the north of iraq, was selected as a typical representative modern city to carry out the study on the aspect of traffic noise. kirkuk witnessed extensive urban development over the past decades to become a node for commercial activity characterized by modern and beautiful buildings and modern sites. traffic noise measurements were conducted at 25 locations on the main streets of kirkuk, representing the classes of roads and zone types as shown in figure 4. the data have been taken during 3 different periods of the day so that they may represent and cover the traffic noise of the city during heavy traffic flow conditions. the periods were: 8:00 a.m. to 9:00 a.m. (supposed to be the peak traffic hour density of the day), 1:00 p.m. to 2:00 p.m. (supposed to be the end of the governmental staff working hour), and 6:00 p.m. to 7:00 p.m. (time of the evening marketing). measurements of the traffic count and speed were not taken during holidays [16, 17]. fig. 4. locations of data collection sites on kirkuk city. v. road functional classification (f) the road functional classification of a city is a channel for communication between the city's various parts and with nearby cities and urban areas. factors like traffic volume and average speed are related to functionality. therefore, functionality is associated with traffic noise [18]. the functionality variable was applied and 4 types of roads were considered according to their functionality: highway, arterial, collector, and local road. the highways and arterial roads recorded the highest noise level measurements since they are characterized by very congested traffic volumes and faster speeds. vi. traffic volume (q) the vehicles were counted within each time span of sound level measurement during observation. the traffic count was conducted manually by using a video camera [19] or by utilizing sensors on roads [20]. vii. vehicle speed (v) it is the average measured speed of the cars. vehicle speed can be manually measured by estimating the travel distance of engineering, technology & applied science research vol. 12, no. 5, 2022, 9108-9112 9110 www.etasr.com ali & albayati: statistical modeling for traffic noise: the case of kirkuk city a car per second or by a velocity speed gun [21]. bushnell 101911 (figure 5) was used to detect the spot speed of passing vehicles. the gun was directed at the passing vehicle. the gun was designed to measure the speed in km/h. it delivers signals to moving objects and can detect any object running faster than 20km/h. fig. 5. the bushnell speed gun. viii. noise level descriptor (leq) the traffic noise statistical descriptors used in this study is the equivalent continuous sound level. leq is often used in noise measurements [22]. the dba is the most often used unit for sound measurement. table ιι lists the independent variables (f, q, and v) as well as the measured dependent variable (leq) in relation to the sample values. table ii. dataset sample values f q v leq highway (erbil principal) 1424 80 78.19 arterial (king qazi street) 1309 63 78.86 collector ( university street) 895 53 76.52 local (iskan street) 122 31 68.27 ix. results and discussion as the road type is considered one of the primary noise sources, each road was statistically analyzed for noise response. the analysis revealed that the noise is very dependent on the functional classification of the road, especially the highway and arterial class, since they are designed to accommodate high speeds and are utilized in large-scale movements. there is a relationship between traffic volume and noise [23]. the noise level is more dependent on traffic volume followed by the road functional class. the study investigated the characteristics of traffic noise and found that traffic noise is closely related to traffic volume. the distribution of traffic noise in different regions is determined by the kinds of vehicles in the area and the density of a road network [24]. the speed variable also affects noise levels [25]. reducing speed could decrease noise, moreover, noise reduction is achievable by traffic calming policies because it prevents forceful accelerations [26]. both these claims are accurate in terms of producing sound pressure levels that the vehicles moving at a slower speed would produce less noise. figures 69 show the relationship between each variable and the noise level (the plotted points refer to the average value of multiple readings). fig. 6. noise of the principal road (erbil highway). fig. 7. noise of the arterial road (king qazi street). engineering, technology & applied science research vol. 12, no. 5, 2022, 9108-9112 9111 www.etasr.com ali & albayati: statistical modeling for traffic noise: the case of kirkuk city fig. 8. noise of the collector road (university street). fig. 9. noise of the local road (iskan street). a statistical model was constructed to fit these parameters and connect them to the noise level. simple linear regression was used for formulating the model (using minitab 21) and the output is the following model: noise (dba) = 43.34 + 0.282 v + 0.000690 q + 3.87 f (1) the noise level was reasonably predicted by the model, as shown in figure 11. the model's effectiveness can be seen in the difference between the predicted and the measured noise. plotting was done for the additional statistical indicators which show very good potential for prediction as depicted in figure 12. it demonstrates the reliability of the predicted noise level within a given range. the accuracy of the model is important because it can then be used to plan noise abatement measures. the current study can be further expanded by adding additional features to these 3 variables. fig. 10. scatter of leq dba (measured vs predicted). fig. 11. statistical indicators of the model. engineering, technology & applied science research vol. 12, no. 5, 2022, 9108-9112 9112 www.etasr.com ali & albayati: statistical modeling for traffic noise: the case of kirkuk city x. conclusion analysis of traffic noise prediction is carried out in the present work using a simple linear regression model to precisely predict the equivalent continuous sound level. the suggested method predicts the leq dba at various locations of kirkuk city using 3 independent variables: road functionality, traffic volume, and average vehicle speed as essential features that affect the level of noise. it was confirmed that these 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[26] h. ryu, i. k. park, b. s. chun, and s. i. chang, "spatial statistical analysis of the effects of urban form indicators on road-traffic noise exposure of a city in south korea," applied acoustics, vol. 115, pp. 93– 100, jan. 2017, https://doi.org/10.1016/j.apacoust.2016.08.025. microsoft word etasr_v12_n3_pp8667-8674 engineering, technology & applied science research vol. 12, no. 3, 2022, 8667-8674 8667 www.etasr.com machoke et al.: performance comparison of ensemble learning and supervised algorithms in … performance comparison of ensemble learning and supervised algorithms in classifying multi-label network traffic flow mwita machoke school of computational and communication science and engineering, department of information technology system development and management, nm-aist, arusha, tanzania machokem@nm-aist.ac.tz jimmy mbelwa university of dar es salaam dar es salaam, tanzania jimmymbelwa@gmail.com johnson agbinya school of information technology and engineering melbourne institute of technology melbourne, victoria, australia jagbinya@mit.edu.au anael elikana sam school of computational and communication science and engineering, department of communication science and engineering, nm-aist arusha, tanzania anael.sam@nm-aist.ac.tz received: 16 february 2022 | revised: 21 march 2022 | accepted: 22 march 2022 abstract-network traffic classification is of significant importance. it helps identify network anomalies and assists in taking measures to avoid them. however, classifying network traffic correctly is a challenging task. this study aims to compare ensemble learning methods with normal supervised classification to come up with improved classification methods. three types of network traffic were classified (benign, malicious, and outliers). the data were collected experimentally by using paessler router traffic grapher software and online and were analyzed by r software. the datasets were used to train five supervised models (k-nearest neighbors, mixture discriminant analysis, naïve bayes, c5.0 classification model, and regularized discriminant analysis). the models were trained by 70% of the samples and the rest 30% were used for validation. the same samples were used separately in predicting individual accuracy. the results were compared to the ensemble learning models which were built with the use of the same datasets. among the five supervised classifiers, k-nearest neighbors and c5.0 classification scored the highest accuracy of 0.868 and 0.761. the ensemble learning classifiers bagging (random forest) and boosting (extreme gradient boosting) had accuracy of 0.904 and 0.902 respectively. the results show that the ensemble learning method has higher accuracy compared to the normal supervised classifiers. therefore, it can be used to detect malicious activities in network traffic as well as anomalies with improved accuracy. keywords-ensemble; malicious; anomalies; security i. introduction the rapid development of information and communication technologies (icts) including hardware, the internet, data science techniques, and services such as online transactions, edge, and cloud computing has changed the way many societies communicate, work, and learn [1]. because of the variety of computer software available as well as the growing number of users, large-volume data processing has become more complex. the trends show that an increase in mobile data traffic will exceed zettabyte (200 10 ) by 2025 [2]. the total network traffic pattern has increased exponentially the last few years [3, 4]. furthermore, it has also been reported that such rapid growth in data traffic is likely to cause security breaches, risks, and lowering of network performance, especially in communication network systems [5, 6]. it also provides room for potential demand for re-designing network architectures to overcome security threats [7]. through the use of the internet, there is a possibility of security attacks occurring at any given time in the communication network system including software, hardware, and attached accessories or communication devices. data flows from one point to another as unidirectional packets in internet protocol (ip) communication networks. the flows depend on the hardware performance and network architecture [8]. a flow is a traffic stream with a common set of identifiers that has the same source ip, destination ip, protocol, source, and destination ports [9]. monitoring data traffic in connected devices provides useful information that would be of importance in the timely understanding of the behavior of the flows and in predicting bandwidth usage. monitoring data flows is crucial in that, any denial of service attacks (dos) and other network security threats and vulnerabilities within the network can be easily identified for timely interventions [5, 10-12]. it helps system administrators and security experts to understand and monitor all activities in the given computer network. high online service demand is embedded in our daily life. detecting anomalies in the network can be very difficult [13]. corresponding author: mwita machoke engineering, technology & applied science research vol. 12, no. 3, 2022, 8667-8674 8668 www.etasr.com machoke et al.: performance comparison of ensemble learning and supervised algorithms in … it is very difficult to detect, identify and prevent malicious activities in computer networks, especially in a distributed computing environment. priority is given to the process of identifying the characteristics of applications that generate high traffic due to malicious activities in communicating devices. these facts reveal that network traffic management and monitoring for the smooth running of an information system is a demanding task [14]. hence, in order to avoid the occurrence of such an unpreferred situation in a computer network, highperforming models are needed for both hardware and software solutions, therefore, the study of machine learning (ml) is of importance to supplement both hardware and software-based solutions [15]. ml is the ability of computer algorithms to learn from a large amount of data through experience and provide a predicted output. ml can be applied in different fields such as data science, ict, health care, finance, etc. [16]. there are four types of ml schemes: supervised, semisupervised, unsupervised, and reinforcement learning. they both use classification algorithms. examples of supervised learning classifications algorithms are decision tree (dt), knearest neighbors (k-nn), naïve bayes (nb), and logistic regression [6]. they use labeled training data as input features to generate the output [17]. examples of unsupervised classification algorithms include k-means and hierarchical clustering [18]. they use unlabeled input features to generate the outputs. the supervised learning classification relies on an ensemble learning technique to generate multiple models. ensemble learning technique is a collection of classifiers used to build very sophisticated models with higher accuracy compared to single estimator classifiers [19, 50]. it is a machine learning approach in classifying datasets with high dimensions and its training process is not very complex [12]. its output is based on the training data by aggregating them to generate a strong model. it thus fuses the results from several different models. this improves performance and prediction by stacking different models. there are many studies related to the use of supervised and unsupervised ml in flow-based network traffic classification. for instance, in [20], the authors used ml in the classification of end users’ applications. different methods were used, such as k-nn, random forest (rf), and j48. the k-nn technique provided the best results followed by rf with accuracy of 93.94 % and 90.87% respectively. in [21], the authors compared principal component analysis (pca) with the gaussian nb method. the mean accuracy of pca was about 86% during the validation process in network intrusion detection compared to the 74% of gaussian nb. a comparison study of dt, k-nn, support vector machine (svm), and rf was conducted in [22], resulting in higher accuracy of rf (96.87%) in comparison to the 48.56% of the svm. this study shows that the ensemble learning method rf is very useful in network traffic data analytics compared to other ml techniques. in this study, svm which is a supervised classifier, failed to separate network traffic based on feature classes used. data mining approaches were applied in [18] in finding the dynamic patterns of network traffic. the study applied the clustering method by portioning the data from different domains and characterization the traffic in the time series data set. two feature classes (benign and malicious) were considered. the authors in [23] compared the data mining approach using ml and ensemble learning method to forecast water flow. it was shown that the use of ensemble learning provided the best performance. some of the performance metrics were not generated, for example recall, sensitivity, and kappa. when compared to other supervised algorithms, the use of ensemble learning in evaluating intrusion detection by using different data from network traffic tracing shows an improvement in network traffic classification [19]. the development of network infrastructure hardware has resulted in the use of the deep packet inspection (dpi) method in classifying network attacks and threats. however, this approach needs a lot of memory as well as resources during computation. another weakness of the method is that it is very difficult for database maintenance, especially for zero-day attacks and protocols [24]. in the field of ict, there are three main approaches in classifying network traffic, namely flow, payload-inspection, and port-based methods [25]. regarding the port-based and flow-based classification, it was shown in [26] that port-based classification has higher accuracy. however, ml classification provides both higher accuracy and performance results [27] compared to port and flow-based classifications. based on the above study, this paper aimed at comparing the accuracy and performance of ml approaches. since the focus of the study for this article was to develop a learning classification model that can identify and detect network anomalies with high accuracy, especially zero-day attacks, we opted for supervised learning classification algorithms. the supervised learning classification algorithms provide higher accuracy than the unsupervised ones [24]. there are two types of ensemble learning methods in supervised learning classification [28]: boosting and bootstrap aggregating (bagging), both with a potential of being used in classification and regression. boosting is an ensemble learning method which combines several weak learners to build a strong learner by using supervised classification [29]. bagging methods divide the training data set into small samples for training the models. in tanzania, only a few studies have been conducted on the evaluation of computer system network traffic by using data mining and the ml approach. authors in [30] compared network traffic classification and packet detection, showing that both computational performance and classification accuracy can be used for the management of computer network systems. this article thus aims to compare the performance of ensemble learning techniques (bagging and boosting) with the normal supervised classification algorithms, particularly k-nn, nb, lda, mda, and c5.0. the comparison is focused on three metrics (accuracy, kappa, and logloss). the question is whether using ensemble methods improves the accuracy and value of kappa. to fulfill this objective, we computed model sensitivity and specificity, precision and recall metrics from the models, and generated both positive and negative predictions from the models. this article contributes to the development of models, hardware or software, to detect network traffic anomalies in a much more effective and efficient way. it also engineering, technology & applied science research vol. 12, no. 3, 2022, 8667-8674 8669 www.etasr.com machoke et al.: performance comparison of ensemble learning and supervised algorithms in … contributes to the literature related to the ml approach in the computer network security field. ii. materials and methods a. data capture and classification process this section illustrates the structure of network traffic dataset classification step by step from data capture up to model evaluation as shown in figure 1. fig. 1. diagram illustrating data capture and classification. b. network traffic data collection we set experiments for network traffic data capture by using paessler router traffic grapher (prtg) software and cisco flow software in a cisco 3900 router series hardware. the data captured at this stage were used to test the models. online data donated by mills [31] were downloaded in april 2021 from the kaggle website (www.kaggle.com). these data were used for training the models with the variables shown in table ii. the experiment of the training dataset was set at lancaster university's network address space. the data set contained robust ground truth through the correlation of malicious behavior in the network. the data were then stored in a computer and external hard disks for backup in packet capture (pcap) file format. c. feature selection from datasets in supervised learning, after data capture, the next step is to select features from the data set collected from the network intended for testing the models. we used joy software [32] which is a bsd-licensed libpcap-based software package for extracting features from live network traffic or pcap files. sixteen variables with three feature class labels were generated in comma separated values (csv) and ms excel format (table i). d. data pre-processing data pre-processing was done in r software (version. 4.1.2 named bird hippie) [33] by using rstudio editor integrated development environment (ide) [34]. data pre-processing was performed to transform the data to a useful format for import and manipulation by ml algorithms. a total of 191,223 datasets were extracted, followed by feature selection and were labeled as benign (86,762), malicious (74,110), and outliers (30,351). the pre-processing stage generated 133,971 labeled samples. out of these samples, 70% (n = 93,780) and 30% (n = 40,191) were used for training and model testing respectively. the dataset was then scaled and centered by using median imputation for every variable. table i. description of variables complete name abbreviation average inter packet time avgipt bytes in bytesin bytes out bytesout destination ip address destip destination port number destport entropy entropy number of packets out numpktsout number of packets in numpktsin protocol proto source ip address srcip source port number srcport time end timeend time start timestart total entropy totalentropy duration duration feature class label label e. variable multicollinearity test after the data pre-processing stage, we looked for variable multicollinearity by using the spearman correlation coefficient test [35]. the variance inflation factor (vif) method was applied to detect and remove highly correlated variables based on vif interpretation as shown in table ii. table ii. vif interpretation vif value conclusion vif = 1 not correlated 1 < vif < 6 moderate correlated vif > 6 highly correlated to identify variables to remove or to retain in the model, r software [33] was used and rstudio ide [34]. model development and data analysis were conducted in a laptop with quad intel core i5, 8gb of ram, and 560 ssd running macos big sur. vif is the measure of how the variance is inflated by the correlation of the predictors which leads to the variance increase of predictors [36]. variables with higher correlation were removed from the list while those with vif 1 ≤ vif < 6 were kept for model development as shown in table iii. f. model development models were developed by using the classification and regression training (caret) packages [21] in r software with r programming language. other packages (e.g. ggplot2, randomforest, and xgboost) were used for calculations, data manipulation, and visualization. a total of nine predictors, with three classes, namely benign, malicious, and outlier from engineering, technology & applied science research vol. 12, no. 3, 2022, 8667-8674 8670 www.etasr.com machoke et al.: performance comparison of ensemble learning and supervised algorithms in … 133,971 samples were used. re-sampling was done by using the 10-fold cross-validation method to validate the outcome of the classifier, whereby the classification was repeated once. in this paper, different models were developed by using normal supervised classifications: c5.0, k-nn, mixture discriminant analysis (mda) algorithm, regularized discriminant analysis (rda), and nb. for comparison purposes ensemble learning classifiers, namely rf from boosting techniques and egb from bagging techniques were used as indicated in table iv. table iii. multi-colinearity test variables tolerance vif eigenvalue condition index avgipt 0.998 1.002 3.421 1.000 bytesin 0.660 1.516 1.470 1.525 bytesout 0.351 2.852 1.096 1.767 entropy 0.816 1.225 0.990 1.859 numpktsout 0.300 3.338 0.691 2.224 numpktsin 0.268 3.738 0.645 2.303 totalentropy 0.198 5.051 0.372 3.031 distance 0.807 1.238 0.186 4.292 table iv. classifiers and learning method classifier learning method egb ensemble (boosting) rf ensemble (bagging) c5.0 normal supervised k-nn normal supervised rda normal supervised mda normal supervised nb normal supervised a serial process for rf and egb as sequential and parallel categories of ensemble learning classifiers respectively was completed as indicated in figure 2. rf algorithm depends on aggregating the output from several trees. trees are modified, pruned, and an average of the results and predictions is done by using the estimation of the dependent variables on new observations. the egb a popular ensemble learner’ method which is used in ml with adaboost in dts. it avoids overfitting challenges and its accuracy is higher than adaboost's. fig. 2. flow chart for ensemble learning classifiers. the normal classifiers and learning methods are described below. 1) c5.0 classification model this model is an extension of c4.5 which establishes a dt where every feature is considered during classification [37]. the trees constructed by c50 have high accuracy and a minimum breakdown which makes the classifier reliable and faster. the model is used to handle non-numerical features such as factor, character, etc., therefore, the model was used as a dt classifier or boosted classifier following [38]. in most studies, c5.0 performs higher than cart and c4.5 [39]. 2) k-nearest neighbors algorithm in ml, k-nn is considered as a lazy learning classifier and it is used to classify objects that are closely related in training data samples based on instance learning. it uses similarity and distance between two points and categorizes the dataset based on the distance or similarities from other categories as shown in (1) and figure 2. by calculating the euclidean distance [40], the new class in the figure will belong to class c and not in class b whereas, by using similarities, this occurs when we choose k = 4 as the number of neighbors. alternatively, these can be done by using the euclidean distance as indicated in (1) from p1 to p2. euclidean distance=���2 � �1�� � 2 � 1�� (1) in this study, we used k = 29 because it produced the optimal results for the acquired data. fig. 3. diagram illustrating the k-nn classification technique. 3) mixture discriminant analysis discriminant analysis is used to predict the probability of belonging to a given class (or category) based on one or multiple predictor variables. it works with continuous and/or categorical predictor variables. in mda, each class is assumed to be a gaussian mixture of subclasses. it is the extension of linear discriminant analysis (lda) which can be used as supervised classification. the method is nonparametric because it minimizes within-group variability. lda can be used in multi-class classification methods that follow the gaussian theorem to model classes. in our dataset we had three classes denoted by "p" and our training sample was denoted by (y1……. yn) with classes (w1…… wn), where wi ∈ {1...p}. the prior probability jk of each class follows the gaussian engineering, technology & applied science research vol. 12, no. 3, 2022, 8667-8674 8671 www.etasr.com machoke et al.: performance comparison of ensemble learning and supervised algorithms in … model θ(y |µp, σ). the estimation from the model (� � can be generated mathematically by: � = ∑ ����� � � � ��� (2) where � is the model estimate, p is the number of classes in the data sets, n the number of samples, and z� a constant for normal distribution. 4) regularized discriminant analysis rda uses multivariate means as well as a covariance matrix. the properties are generated from the data and used in the predictions. rda data use gaussian assumptions whereby each variable when plotted is like a bell curve. the model generates variance and means of each class from the data as illustrated in (3): ���� = � � ∑ ������ (3) the variance of the samples was computed using (4): �� ���!� = � �"# ∑ 〖���〗 � ���� & � ��� (4) where n is the number of instances, p the number of classes, x the input values, and np is the number of classes in the instance. for model prediction in rda, we used the classes with the highest probability of the classes (h) with x as input through the bayesian theorem as illustrated in (5): ��' = ℎ |) = �� = #�*�×#�,|*� ∑ -#�.� ×#�,|.�&/012 (5) where p(x|k) is the estimated probability of x belonging to the class k, p(y = k|x = x) is the probability of the class (y = k) given the input data x, and p(k) is the base probability of a given class k. we are considering (y = k). 5) naïve bayes the use of nb classifiers in ml especially in anomaly detection has been widely applied in filtering spam emails. the accuracy of separating spam in the email is limited because its strength depends on the independence between the features [41]. the model also suffers from the heavy overhead computation which makes the mode use more resources during execution [42]. therefore, we used this model with others for comparison due to simplicity and efficiency. nb uses the concept of the bayesian theorem with the assumption of prior knowledge of a given hypothesis to classify features. the theorem state as: ��ℎ|3� = #�4|*�×#�*� #�4� (6) where p(d) is the probability of the data, p(h) is the probability of hypothesis h being true, p(h|d) the posterior probability, p(d|h) the probability of data d given that the hypothesis h was true. likewise, the maximum posterior (map) hypothesis can be calculated by applying (7): 56��ℎ� = max � #�4|*�×#�*� #�4� � (7) 6) model evaluation metrics the proposed classification techniques used two ensemble learning methods versus five normal supervised ml. model accuracy, precision, recall, f1 score metrics were used for model evaluations. recall, f1 score, precision, accuracy can be mathematically computed by using the equations from table v [11, 28]. true positive (tp) occurs when the values of both predicted class and actual class are 1. true negative (tn) occurs when the values of the predicted actual classes are both 0. false negatives (fn) and false positives (fp) occur when the predicted class changes the actual class. table v. model evaluation metrics metrics formula accuracy (tp + tn) / (tp+tn+fp+fn) true positive rate tp / (tp + fn) false positive rate fp / (fp + tn) precision tp / (tp + fp) recall tp / (tp + fn) f1 score 2 precision × recall / (precision + recall) iii. results and discussion the study's main objective was to evaluate the performance of different models in network traffic classifications. to achieve this objective, the current study used ensemble learning methods and normal supervised classifications for comparison. multilabel data features were classified by using different models. the following evaluation metrics were applied for both ensemble and normal supervised learning: accuracy, under the curve (auc), precision, recall, sensitivity, specificity, positive and negative predictions. a. model accuracy 1) normal supervised learning methods results from the five algorithms that were developed before subjecting individual models to ensemble learning techniques showed that k-nn had the highest accuracy followed by c5.0 and mda with accuracy of 0.868, 0.761, and 0.741 respectively. nb classifier scored the lowest accuracy of 0.696 as shown in table vi. these results are in accordance with the findings in [25, 43, 44]. table vi. evaluation metrics of normal supervised learning methods method accuracy kappa k-nn 0.868 0.833 c5.0 0.761 0.585 mda 0.742 0.558 rda 0.738 0.561 nb 0.696 0.491 2) ensemble models results from the two higher-performing ensemble models in higher dimensional dataset techniques showed that rf had higher accuracy compared to egb as presented in table vii. our study is supported by [45], in which ensemble methods (xgb and rf) were used with accuracy of 89.09% and 85.49% engineering, technology & applied science research vol. 12, no. 3, 2022, 8667-8674 8672 www.etasr.com machoke et al.: performance comparison of ensemble learning and supervised algorithms in … respectively. another study that supports our result was [13] as indicated in the comparison in table xiii. table vii. evaluation metrics of ensemble learning methods method accuracy kappa logloss rf (bagging) 0.904 0.841 2.369 egb (boosting) 0.902 0.830 0.223 3) comparison of normal supervised and ensemble models the results from the comparison done after developing the models by using ensemble learning and supervised algorithms revealed that in normal supervised algorithms, k-nn had the highest accuracy as shown in table vi. both the ensemble learning methods had higher accuracy, with rf having the highest. b. evaluation of the normal supervised learning processed by ensemble classifier after processing supervised algorithms by using ensemble learning methods, there was an improvement of accuracy and kappa values as shown in table viii. c5.0 had the highest accuracy (0.902) as compared to the previous accuracy of 0.761 (table v). on the other hand, k-nn also improved with a small margin from 0.868 to 0.898. table viii. accuracy and kappa for normal supervised learning processed by ensemble classifiers normal supervised learning accuracy kappa logloss c5.0 0.902 0.839 0.229 k-nn 0.898 0.832 2.699 rda 0.738 0.561 0.653 mda 0.739 0.560 0.747 nb 0.698 0.470 0.471 c. model auc auc was the highest in egb, followed by c5.0, whereas rda had the least as shown in table ix. the value of f1 score metrics, as the measure of the test’s accuracy, was highest in c50, followed by k-nn and egb. rda scored the least f1 score. table ix. auc and f1 score classifier auc f1-scores egb 0.979 0.865 c5.0 0.978 0.870 rf 0.944 0.854 k-nn 0.916 0.868 nb 0.910 0.521 mda 0.888 0.589 rda 0.863 0.489 d. precision and recall the results showed that egb has the highest precision followed by k-nn and rf, while rda scored the least precision as presented in table x. rf exhibited the highest recall followed by c50 and k-nn, while nb scored the lowest value. table x. precision and recall results classifier precision recall egb 0.906 0.843 k-nn 0.900 0.849 rf 0.900 0.867 c50 0.897 0.865 nb 0.777 0.553 mda 0.670 0.601 rda 0.558 0.593 e. model sensitivity and specificity rf scored the highest sensitivity, followed by c50 and k nn, while nb had the lowest sensitivity as shown in table xi. furthermore, rf attained the highest specificity, followed by knn and egb, while nb scored the lowest. table xi. sensitivity and specificity results classifier sensitivity specificity rf 0.867 0.946 c50 0.865 0.897 k-nn 0.849 0.942 egb 0.843 0.943 mda 0.601 0.859 rda 0.593 0.859 nb 0.553 0.822 f. prediction both positive and negative predictions generated from the models are presented in table xii. egb attained the highest positive prediction followed by rf and k-nn. rda scored the lowest positive prediction. nb scored the highest negative prediction, followed by mda. table xii. positive and negative predictions classifier positive negative egb 0.906 0.954 k-nn 0.900 0.954 rf 0.900 0.955 c50 0.897 0.955 nb 0.777 0.874 mda 0.670 0.883 rda 0.558 0.891 g. discussion the result from this study has been compared with the results from [13] as shown in table xiii and figure 4. the acquired results show that the proposed techniques achieved better accuracy, auc, recall, and precision, but not f1 score. the study which [13] shows that egb, c5.0, and rf had an accuracy of 0.901, 0.886, and 0.885 respectively. the findings of this paper also show an accuracy of 0.902, 0.902, and 0.904 for c5.0, egb, and rf. therefore, our results are higher considering model accuracies. the study conducted in [46] was looking at anomaly detection by using ml techniques by using rf. one of the performance metrics was the accuracy of rf which was 99.7 which is higher compared to this paper results. another study [47] was utilized the rf classifier and scored an accuracy of 0.893, recall 0.890, f1 score of 0.896, and precision of 0.92. in [45], egb obtained the following metrics scores; accuracy of 0.926, precision 0.927, recall 0.926, and engineering, technology & applied science research vol. 12, no. 3, 2022, 8667-8674 8673 www.etasr.com machoke et al.: performance comparison of ensemble learning and supervised algorithms in … f1 score 0.924 which are similar or less than the same respective scores of the current study (table xiii). table xiii. comparison with [13] classifier accuracy auc recall precision f1 score kappa [13] egb 0.901 0.995 0.75 0.901 0.899 0.875 rf 0.885 0.948 0.741 0.882 0.885 0.855 c5.0 0.886 0.985 0.725 0.883 0.884 0.856 k-nn 0.85 0.966 0.675 0.846 0.847 0.811 nb 0.297 0.633 0.128 0.23 0.228 0.096 current study mda 0.739 0.888 0.601 0.67 0.56 0.56 rda 0.742 0.86 0.593 0.558 0.561 0.738 rf 0.904 0.979 0.867 0.9 0.854 0.841 egb 0.902 0.944 0.843 0.906 0.865 0.83 nb 0.698 0.91 0.553 0.777 0.521 0.47 k-nn 0.898 0.916 0.849 0.9 0.868 0.32 c5.0 0.902 0.978 0.865 0.897 0.87 0.839 fig. 4. graphs showing comparisons of this study with others. the results of this paper are also equivalent and sometimes above the results of [48, 49]. one can conclude that the results of the current study are supported by other studies, however, with slight variations in some parameters. iv. conclusion, recommendations, and future work this article presented and compared the results of normal supervised algorithms and ensemble learning techniques, namely rf and egb. the individual classifiers were compared with ensemble learners by using a real experimental dataset with little correlation. the overall accuracy of the ensemble methods was higher than the accuracy of normal classifiers. therefore, we can conclude that the ensemble learning techniques can be used to classify the multilabel network traffic. this study contributes to the knowledge of network traffic classification by using supervised and ensemble learning and multilabel datasets. to the best of our knowledge there are no similar studies regarding the network traffic classification in tanzania. the current study can be extended to new emerging technologies (edge computing, cyber security, e-commerce, fog computing, and distributed databases such as blockchain). also, the use of emerging ml approaches like reinforcement and deep learning could be applied with new experimental datasets. the performance comparison 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[50] d. k. singh and m. shrivastava, "evolutionary algorithm-based feature selection for an intrusion detection system," engineering, technology & applied science research, vol. 11, no. 3, pp. 7130–7134, jun. 2021, https://doi.org/10.48084/etasr.4149. microsoft word etasr_v13_n2_pp10414-10418 engineering, technology & applied science research vol. 13, no. 2, 2023, 10414-10418 10414 www.etasr.com boudina et al.: a comparative analysis of seismic site response in time and frequency domains a comparative analysis of seismic site response in time and frequency domains tounsia boudina architecture department, university of bejaia, algeria tounsia.boudina@univ-bejaia.dz sofiane bounouni architecture department, university of bejaia, algeria sofiane.bounouni@univ-bejaia.dz naas allout civil engineering department, zian achor university, algeria allout.naas@univ-djelfa.dz received: 21 january 2023 | revised: 1 february 2023 | accepted: 4 february 2023 abstract this study aims primarily to perform a comparative analysis of the seismic response of a soil profile, in the time and frequency domains, in order to evaluate the seismic response of soil subjected to seismic excitation. after a few remarks made on the responses given by the linear elasticity method for this type of problem, it was considered necessary to use shake 2000 and plaxis in this study. the obtained results were then compared with those of the available theoretical predictions. rock elasticity, viscous damping and damping by hysteresis, and the nonlinearity of the ground were then taken into account. in addition, comparisons between recorded responses were also conducted. keywords-dynamic analysis; soil damping; finite elements; site response i. introduction dynamic soil-structure interaction (ssi) problems involve determining the reaction of a building under the seismic effect and defined by the free surface of ground without any structure [1]. variations in free surface seismic responses, which are used as the input motion, must satisfy the so-called free-field motion equations which can be obtained from the ground response analysis [2-3]. thus, according to the literature, before studying the soil-structure interaction system, a free field response is required. it should be known that the dynamic finite element analysis can be considered as one of the most comprehensive available tools in geotechnical problems [4]. it is an approach capable of providing insight into the distribution of stresses in soil or the deformations, and the loads applied to structural components that interact with the soil. but, this technique requires the availability of an appropriate soil model, with sufficient information on soil properties, provided by performing different experiments. here, the seismic input motion ought to be appropriately determined. the response of a finite element model [5] is also conditioned by the adjustment of several parameters that affect the sources of energy dissipation in the time domain analysis. furthermore, the amount of damping exhibited by a discrete numerical system can be determined by the proper choice of the constituent model (material damping), the integration scheme of equations, and the boundary conditions (numerical damping). in addition, material damping models the viscous and hysteresis energy dissipation effects in soils. note that the numerical damping appears as a consequence of the numerical algorithm for the dynamic equilibrium solution in the time domain [6]. moreover, the boundary states can influence the numerical model and convey the specific energy of waves outside the time domain [7-8]. in this article, the free field surface is exclusively taken, and the responses provided for different domain analyses are interpreted and compared. ii. profiles of the soil under study for the purposes of this study, it was considered necessary to examine different soil profiles that are characterized by an increasing level of heterogeneity. the soil includes a homogeneous viscoelastic layer (denoted hom profile), a linear elastic layer with increasing stiffness at depth, and finally a non-linear soil layer (denoted sds for stress dependent stiffness profile) [9-10]. a. homogeneous viscoelastic layer the soil stiffness is displayed by a constant value of shear modulus g. in the present case, the homogeneous linear viscoelastic profile is placed on a rigid rock and is then engineering, technology & applied science research vol. 13, no. 2, 2023, 10414-10418 10415 www.etasr.com boudina et al.: a comparative analysis of seismic site response in time and frequency domains examined. the soil profile characteristics are shown in figure 1(a). such a system can be entirely presented through its amplification function a(f). on the other hand, figure 2 shows the graphical representation of the amplification function in relation to frequency, while admitting that the soil layer considered has the adopted characteristics. the two verticals refer to the first and second natural frequencies of the soil profile. (a) (b) (c) fig. 1. soil profiles: (a) physical characterization, (b) shear wave propagation velocity of the profiles, (c) shear modulus of the soil. fig. 2. amplification function of a homogeneous viscoelastic soil layer on a rigid rock. b. stress dependent stiffness layer stiffness is a function of the average effective stress p', and therefore of the depth. a linear relation describes the evolution of the shear modulus g as a function of depth z (m = 1/2): � = � 1 + �� �� = � 1 + �� (1) afterwards, it was decided to adopt a single value for the density �. the velocity of shear wave propagation was then obtained by: �� = �� 1 + �� � = �� 1 + �� � �⁄ (2) where vs0 is the shear wave velocity at the free surface, an a is a coefficient that represents the level of soil heterogeneity c. non-linear layer the average value curves for sand, similar to those proposed in [11], were then considered. figure 3 shows the graphical representations of these curves. it is important to emphasize that the variation of the initial shear modulus according to depth is identical to that of the sds profile. fig. 3. curves representing the adopted shear modulus (solid line) and damping factor (broken line), calculated by hashash's mrdf model. iii. the input signal in numerical calculations, the seismic loading is often imposed as an accelerogram at the base of the geometrical model (the rock). in order to clarify and better understand the impact of the seismic signal on the nonlinear soil response, two acceleration histories were used [12]:  the first signal corresponds to the w-e component of the acceleration recording that was made at the tolmezzo station for the main shock of the friuli earthquake in italy that occurred on may 6, 1976. it is denoted as tmz-270. the data were recorded at a frequency of 200hz, for a whole of 7279 recording points. the peak of horizontal acceleration, even to 0.315g was obtained after t = 3.935s. it is worth noting that most energy is within a frequency range among 0.8 and 5 hertz.  the second signal corresponds to the w-e component of the acceleration recording that was made at the station of kedarra 1 for the main shock of the earthquake that occurred on may 21, 2003, in boumerdès (algeria). the data were recorded at a frequency of 200hz for a total of 7000 recording points. the maximum horizontal acceleration, equal to 0.331g, was reached after t = 7.415 s. (a) (b) fig. 4. tmz-270 seismic input signal: (a) acceleration history, (b) fourier spectrum. (a) (b) fig. 5. keddara-1 seismic input signal: (a) acceleration history, (b) fourier spectrum. engineering, technology & applied science research vol. 13, no. 2, 2023, 10414-10418 10416 www.etasr.com boudina et al.: a comparative analysis of seismic site response in time and frequency domains iv. results and discussion with regard to the soil profile interaction with the acceleration history, different analyses were performed in order to show the influence of some numerical parameters. in the present case, the response found from the hom and the sds profiles are presented. the equivalent linear approach for the time domain analyses with the plaxis code was used [13-14]. the obtained responses were compared with those resulting from the frequency domain analysis, carried out with shake [15]. lastly, comparisons of various calculated soil responses supplied were reviewed and interpreted. a. linear analysis of the hom linear profile linear analysis was carried out in the frequency and time domain. the obtained results were compared with of the homogeneous elastic profile resting on a rigid rock in order to show the effect of the various origins of energy dissipation on the finite element model and to explain the choices made for a good numerical modeling process. the frequency-domain and time-domain responses of linear analyses carried out in shake and plaxis, respectively, are illustrated in figure 6 which depicts the amplification function and the maximum acceleration profiles. (a) (b) fig. 6. comparison between the numerical and the reference solutions: (a) amplification functions, (b) maximum acceleration profiles for tmz-270 input motion. b. linear analysis of the sds profile linear analysis was performed in the frequency domain for tmz-270 and keddara-1 motions in shake software. the obtained responses were used as a basic response for the finite element analysis. the rayleigh coefficients (αr = 1.224, βr = 2.441×10) were determined arbitrarily by selecting the first natural frequency f1 of the layer, and the mean (f2 + f3)/2, of the 2nd and 3rd natural frequencies of the soil [16-17]. numerical damping was assumed to be equal to zero. figure 7 shows specific gaps observed on the amplification functions, around the third natural frequency of the layer. nevertheless, it turned out that there was a good agreement between the maximum acceleration profiles, which proves the effectiveness of the adopted lateral boundary conditions. c. analysis using the equivalent linear approach for the sds profile to simulate the non-linearity of the ground under periodic stress, it was deemed necessary to use the most common method, which in this case is the equivalent linear approach. this method was applied in the shake software. the plaxis software does not allow equivalent linear analysis. in order to carry out an operation, the domain must be separated into sub-layers. a different material is indicated for each sublayer. consequently, the only eventual way out is to first perform equivalent linear analysis with the assistance of shake including an auto-iterative procedure. the output profiles of g(z) and d(z), obtained from shake, determine the plaxis material parameters. the initial shear modulus and damping constant profiles as well as those derived from the shake analysis are plotted in figure 8. the resulting curves represent the data profile for plaxis. thus, the values accepted for the rayleigh damping parameters are clearly reported. (a) (b) (c) fig. 7. comparison between the linear analyses in the frequency domain and time domain of the sds profile: (a) amplification functions, (b) maximum acceleration profiles of tmz-270 seismic motion, (c) maximum acceleration profiles of keddara-1 seismic motion. (a) (b) (c) (d) fig. 8. profiles of the soil parameters adopted by the equivalent linear approach: (a) shear modulus, (b) damping, (c), (d) rayleigh parameters. engineering, technology & applied science research vol. 13, no. 2, 2023, 10414-10418 10417 www.etasr.com boudina et al.: a comparative analysis of seismic site response in time and frequency domains figure 9 presents the responses achieved from the numerical tests of the equivalent linear approach when using the time investigation scheme. in addition, the average constant acceleration and the rayleigh parameters of each sub-layer were evaluated. the 1st and 2nd natural frequencies of the subsoil, as indicated in table i, are considered as the reference frequencies. it should also be noted that the calibration of the analysis parameters in the time domain are based on the results of the frequency domain. note also that the two types of equivalent linear approaches provide the same seismic excitation, particularly with regard to maximum accelerations. table i. reference frequencies for the evaluation of rayleigh numerical damping sds soil layer abbreviation type of analysis f1 (hz) f2 (hz) lin linear 6.48 15,15 lin equi linear equivalent 4.72 16,99 the maximum values of the amplification function determined with finite element software are near to those obtained with the shake, particularly close to the reference frequencies. these responses show that, as indicated, the soil parameters determined for each sub-layer are in accordance with the deformation rate generated by the seismic movement. (a) (b) fig. 9. comparison between the peak acceleration profiles obtained by equivalent linear analysis in the frequency and time domain of the sds profile using (a) tmz-270, (b) keddara-1 seismic motions. d. nonlinear analysis of the sds profile it is recognized that the equivalent linear approach ensures satisfactory results, particularly for the site seismic effect, although this approach is an estimate of real nonlinear treatments. a new approach consists of analyzing the results of a real nonlinear profile, based on numerical integration in the time domain. deepsoil [18] solves 1d problems related to wave propagation in a nonlinear medium. estimates were computed in the time domain, and the constitutive modeling was implemented according to the modified hyperbolic modeling. note that this software was used first to deal with the problem of vertically propagating s-waves in the non-linear sds profile on a hard rock, and then to make a comparison of the obtained responses with those resulting from the equivalent linear model [19-21]. figure 10 presents the peak acceleration profiles and response spectra that were computed by shake and deepsoil, by suggesting the shear modulus and damping constant curves shown in figure 3 for hard rock. (a) (b) fig. 10. comparison between the maximum acceleration profiles obtained by the equivalent linear analyses (shake) and by the non-linear analysis (deepsoil) of the sds profile, using: (a) tmz-270, (b) keddara-1 seismic motions. v. conclusions the findings of this study showed that one-dimensional nonlinear soil response analysis provides a more accurate characterization of true nonlinear soil behavior in comparison with the equivalent linear procedures. however, the use of nonlinear software remains limited, resulting in insufficiently documented and imprecise choice of code application parameters and official procedures of used software. in the current study, linear responses were employed in the frequency domain for the evaluation of energy dissipation sources in association with dynamic finite elements analysis. the calculations carried out using the plaxis indicated that the adopted numerical model was rightly chosen. both were applied for the evaluation with rayleigh damping parameters, while considering numerical dissipation for the time integration scheme, and also for lateral boundary conditions, to minimize the impact due to wave reflection. the obtained results are quite encouraging for using such methods whenever finite element seismic analyses are carried out in various types of geotechnical systems, i.e. retaining walls, tunnels, etc. in finite element software, such as the plaxis, the filtering input for transforming the input motion from the rock outcrop to the interior is not taken into account. besides, the input seismic motion can be simply converted to the outcrop interior with the help of other software (like the shake) and by submitting the filtered signal to the base of the soil profile, in order to simulate an elastic rock using the finite element model. finally, the non-linear behavior of the soil was also examined. the numerical parameters of a two-dimensional soil profile using the finite element method developed in plaxis should be calibrated first using the equivalent linear approach analysis applied in shake. then, the non-linear approach, in deepsoil, followed. the obtained responses were compared with those obtained by the equivalent linear approach. the maximum acceleration values at the surface of the equivalent linear analysis remain higher than those resulting from the nonlinear analysis. this can be attributed to the greater amplification of the soil motion by frequencies near the first frequencies of the seismic excitations used. engineering, technology & applied science research vol. 13, no. 2, 2023, 10414-10418 10418 www.etasr.com boudina et al.: a comparative analysis of seismic site response in time and frequency domains references [1] a. s. jawad and b. s. albusoda, “numerical modeling of a pile group subjected to seismic loading using the hypoplasticity model," engineering, technology & applied science research, vol. 12, no. 6, pp. 9771–9778, dec. 2022, https://doi.org/10.48084/etasr.5351. 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[22] v. c. f. santucci de magistris, and e. bilotta, “comparative study on frequency and time domain analyses for seismic site response," the electronic journal of geotechnical engineering, vol. 15, pp. 1–20, jan. 2010. microsoft word etasr_v13_n2_pp10228-10231 engineering, technology & applied science research vol. 13, no. 2, 2023, 10228-10231 10228 www.etasr.com slimani et al.: adaptive dynamic cutting force control analysis for peripheral milling adaptive dynamic cutting force control analysis for peripheral milling abdesselem slimani mechanical engineering department, faculty of technology, university of batna 2, laboratory lrp, algeria a.slimani@univ-batna2.dz allaoua kherraf mechanical engineering department, faculty of technology, university of batna 2, laboratory lrp, algeria a.kherraf@univ-batna2.dz kamel zidani mechanical engineering department, faculty of technology, university of batna 2, laboratory liecs_ms, algeria k_zidani57@yahoo.fr received:19 december 2022 | revised: 9 january 2023 | accepted: 13 january 2023 abstract the implementation of condition monitoring tools can improve plant availability and lower downtime costs in general. a reliable adaptive control system can prevent machine downtime or undesired situations such as chatter vibration and excessive tool wear, permitting the best utilization of a tool's life. this study used dynamic force analysis to create an adaptive dynamic control system for computer numerical control (cnc) milling to adjust a controlled system for signals from offline measurements that will be processed and supplied back to the machine tool controller to correct cutting parameters. this paper describes a better adaptive control system for peripheral milling with helical end mills based on a dynamic cutting force model. this theoretical model is based on the oblique cutting principle and takes into account the effects of the size of undeformed chip thickness and the effective rake angle. simulation results showed that the enhanced dynamic cutting-force model accurately predicted cutting forces in peripheral milling. keywords-machining process; adaptive control; dynamic force analysis i. introduction peripheral milling operations are widely used in automobile, aerospace, textile machinery, and other manufacturing industries where 2d contour parts, i.e. engine components, cams, etc., are milled using complex end-mills. in recent years, due to the need to improve the dimensional accuracy of the parts, there is a push towards the reduction of the machining errors commonly generated in the milling process. these errors derive from machine tools, cutters, nc programming, and the machining process itself. the errors of the machining process generated in peripheral milling originate from several sources, such as tool deflection, workpiece deflection, tool wear, friction, tool run-out, and chatter vibration. of all these, tool deflection due to cutting force is a major problem for precision machining [1]. an accurate dynamic cutting-force model is vital for the precise prediction of tool and workpiece deflection in peripheral milling. several models based on theoretical assumptions and experimental observations have been developed to predict cutting forces [2]. in [3, 4], an investigation was presented for a tool condition monitoring system which consisted of a fast fourier transform preprocessor for generating features from online acousto-optic emission (aoe) signals to develop a database for appropriate decisions. the drawback of modern computer numerical control (cnc) systems is that the machining parameters, such as feed rate, speed, and depth of cut, are programmed offline [5]. as a result, many cnc systems are inefficient to operate under operating conditions that are far from optimal. to ensure the quality of machining products, reduce machining costs, and increase machining efficiency, it is necessary to adjust the machining parameters in real-time to satisfy the optimal machining conditions at any given time as per modern condition monitoring strategies [6, 7]. the control of cnc machining processes is presently receiving significant attention due to the potential economic benefits associated with automated machining. control techniques that have been developed for machining traditionally require some form of r et r ac te d engineering, technology & applied science research vol. 13, no. 2, 2023, 10228-10231 10229 www.etasr.com slimani et al.: adaptive dynamic cutting force control analysis for peripheral milling parameter adaptation, and the solution to this problem is adaptive control. an adaptive control system was introduced to the cutting process in [8]. the most commonly used systems are model reference adaptive control (mrac) and self-turning regulations (str). in [9], an investigation was presented on an adaptive model reference controller approach, simulating, evaluating, and physically implementing it. continuous monitoring of the machining is necessary for effective automatization where the process takes place without human interference. most frequently, it is materialized by measuring the cutting forces because they contain more information about the process and the tool condition [10-12]. despite the initial difficulties in development, a trend towards equipping the cnc machine with modern adaptive systems can be observed [13-15]. the most commonly used adaptive control (ac) systems use adaptive control constraint (acc), with the constraints being the cutting force, displacement due to vibration, spindle deflection, current, and cutting torque. operating parameters are usually the feed rate, depth of cut, and spindle speed. this study implemented an online adaptive control in conjunction with offline optimization. in this ac system, the feed rate and depth of cut are adjusted online to maintain a constant displacement and cutting force despite variations in cutting conditions. the modern market forces producers to meet the demands of customers, but the accelerating technological progress still makes this goal very difficult to achieve. the manufacturer must provide a product that meets customers' expectations while maintaining a satisfactory price on both sides. manufacturing costs have a key influence on the final price of the product, so it is very important to develop new methods to estimate the manufacturing cost and improve the existing ones. this paper presents an improved dynamic cutting-force model for peripheral milling with helical end mills. the theoretical model was based on the oblique cutting principle and included the size effect of undeformed chip thickness and the influence of the effective rake angle. ii. fundamental principles two basic models are normally used to describe chip formation in metal cutting:  orthogonal cutting, characterized by a normal cutting edge and a chip flow parallel to the direction of tool motion.  oblique cutting, characterized by a cutting face inclined by an angle. a. geometric model of helical end-mill the end mill can be divided into a number of slices along its z-direction, as shown in figure 1 of [16]. within each slice, the cutting action for an individual tooth can be modeled as for single-point oblique cutting, and the tangential and normal cutting forces at any point on the rake face can be obtained from the oblique cutting model. it is important to note that the tangential and normal directions together with chip thickness vary during the formation of a single chip in milling. consequently, a dynamic model must account for these variations in the magnitude and direction of cutting forces. b. cutting-force model the cutting forces acting on the helical flute's rake face depend on the undeformed chip thickness. if dl is a portion of the developed cutting edge of elemental length, then dz may be considered as the width of an elemental oblique tool with inclination angle β [16]: �� = ��. ��� (1) and the differential area of the undeformed chip cross-section: ��� ��� = �� �� ��� = �� �� ���. ��� dl=rd�/sin (2) where ti(i) is the undeformed chip thickness. the differential tangential cutting force of the peripheral milling, as can be seen in figure 1 of [16]: ���� �� � = �� ��� �� � = �� �� �� �� ��� �� (3) where ks is the tangential cutting-force coefficient, which has the same meaning as the total energy per unit volume u. considering the size effect of undeformed chip thickness and the influence of effective rake angle gives: �� = � !1 − $%&$%'( ) ! �'�* +*�) ., (4) where u0 is the initial total cutting energy per unit volume, αe (in degrees) is the effective rake face, αe0 (in degrees) is the initial effective rake angle, and t0 is the initial undeformed chip thickness. to develop the total force applied on the whole cutter, the differential forces are resolved into the feed (y) and normal (x) directions. the differential cutting-force components are just opposite to the corresponding directions of the curvilinear coordinate system (t, r, a). 1) for down-milling ⎩⎪ ⎨ ⎪⎧ ��1 ≈ −�′4� � ��� 0.5�� − 0.25 �89 2 �� +0.5556. �. �89(.= �� �> +?+%��� ≈ �′4� � ��� 0.5556 �89(.= �� − 0.5�� +0.25. �. �89 2 �� �> +?+% (5) because: 0 ≤ � ≤ a, �� = � − ct+ i-1� 2d/m� and 0 ≤ �� ≤ ω �� = ghi !0, -ct+ i-1� ,jk ) (6) �l = g89 !ω, a − ct+ i-1� ,jk ) (7) 2) for up-milling: ⎩⎪ ⎨ ⎪⎧ ��1 ≈ −�′4� � ��� 0.5m� − 0.25 �89 2 m� −0.5556. �. �89(.= m� � n o?o%��� ≈ −�′4� � ��� 0.5556 �89(.= m� + 0.5m� −0.25. �. �89 2 m� � n o?o% (8) also: 0 ≤ � ≤ a, m� =-� + cti-1� 2d/m� and 0 ≤ m� ≤ s gives the extreme values of the parametric angle m� as: r et r ac te d engineering, technology & applied science research vol. 13, no. 2, 2023, 10228-10231 10230 www.etasr.com slimani et al.: adaptive dynamic cutting force control analysis for peripheral milling m� = ghi !0, -a + cti-1� ,jk ) (9) ml = g89 !s, cti-1� ,jk ) (10) summing up the cutting forces acting on all the m helical flutes gives the total force applied on the whole cutter: �1 = ∑ ��1k�u(�� = ∑ ���k�u( iii. estimation of cutting-force coefficients the cutter, workpiece material, and cutting conditions of this study were:  cutter: a single-fluted carbide end-mill with a helix angle β=30°, a rake angle αr =12° and a diameter of 19.06mm.  material properties of the carbide cutter: 90% wc, 10% co, hardness 92 rockwell.  material properties of the titanium alloy: 6% al, 4% v, young’s modulus=110gpa, poisson’s ratio=0.34, tensile strength=900mpa.  cutting parameters: axial depth of cut ba=7.62mm, radial depth of cut d=19.06mm (slotting), =26.45°, ω=π, spindle rotation speed n=500rpm (cutting speed v=498.99 mm.s-1), with a feed rate ranging from 0.0127mm per tooth to 0.2030mm per tooth. iv. results and discussion this section presents the simulation results in matlab for a number of particular examples. figure 1 shows the results of predicting cutting forces for a full immersion up-milling, revealing that when the feed rate is far smaller than the radius of the cutting edge, the ploughing force is dominant and the cutting-force model must be modified. figures 2 and 3 show the results on the influence of the cutting angles, feed per tooth, and cutter radius on the cutting force. the values of the instantaneous predicted forces were found as shown in figure 2 but with different amplitudes. adjusting the initial total cutting energy per unit of volume and the cutting-force ratio to u0=2.109jm -3 , c=0.45, the instantaneous predicted forces were obtained, as shown in figure 3. a comparison of these results with the cutting forces shown in figure 1 shows that there is a very good agreement. figure 3 shows that when the feed rate is greater than 0.0254mm per tooth, the predicted cutting forces are very good approximations of the measured cutting forces, and the improved dynamic cutting-force model can be used to predict the cutting forces. however, when the feed rate is less than 0.0254mm per tooth, the predicted cutting forces are smaller than the measured. this reveals that when the feed rate is far smaller than the radius of the cutting edge, the ploughing force is dominant and the cutting-force model must be modified. v. conclusion the adaptive dynamic cutting force control analysis estimation process in manufacturing is a very important stage of the design construction process, as the decisions made at this stage have a large impact on the product's final price. this study presented a manufacturing adaptive dynamic cutting force control analysis estimation method based on dynamic force analysis. the quality of the results of this method depends on the exponent values. the standard values of exponents are known and described in many publications. these values were compared to values calculated based on a practical simulation of the manufacturing process. the differences between standard and calculated values can be observed. the standard values assigned to the operation should give proper results for every kind of cut type, e.g. rough and finish. values based on simulation results from real situations are specified for every type of cutting process. this approach can improve the results accuracy of the proposed method based on cost similarity, and finally, this method could help in securing the economic profit of the company. fig. 1. predicted cutting forces for a full immersion up-milling test, g = 1, � = 3.51 ∗ 10xyg&z, [\ = 12°, ^_ = 7.62gg, � = 19.06gg, a = 26.45°. this study investigated the size effect of undeformed chip thickness and the influence of the effective rake angle in peripheral milling. verification results showed that the model is suitable for general peripheral milling when the feed rate is greater than the radius of the cutting edge. for fine milling, when the feed rate is less than the radius of the cutting edge, the measured cutting force will be greater than the cutting force predicted by the model. this result shows that the ploughing force is dominant in this condition and the general cutting force model is no longer effective. case studies reveal that the model may be very effective in reducing the surface form error due to tool deflection if flute number, axial depth of cut, and radial depth of cut are selected carefully. r et r ac te d engineering, technology & applied science research vol. 13, no. 2, 2023, 10228-10231 10231 www.etasr.com slimani et al.: adaptive dynamic cutting force control analysis for peripheral milling fig. 2. influence of angle helice (m=1). fig. 3. influence of ft (m=1) references [1] j. w. sutherland and r. e. devor, "an improved method for cutting force and surface error prediction in flexible end milling systems," journal of engineering for industry, vol. 108, no. 4, pp. 269–279, nov. 1986, https://doi.org/10.1115/1.3187077. [2] s. smith and j. tlusty, "an overview of modeling and simulation of the milling process," journal of engineering for industry, vol. 113, no. 2, pp. 169–175, may 1991, https://doi.org/10.1115/1.2899674. [3] b. s. prasad, m. m. m. sarcar, and b. s. ben, "development of a system for monitoring tool condition using acousto-optic emission signal in face turning—an experimental approach," the international journal of advanced manufacturing technology, vol. 51, no. 1, pp. 57–67, nov. 2010, https://doi.org/10.1007/s00170-010-2607-5. [4] b. s. prasad, m. m. m. sarcar, and b. s. ben, "real-time tool condition monitoring of face milling using acousto-optic emission â an experimental approach," international journal of computer applications in technology, vol. 41, no. 3/4, 2011, art. no. 317, https://doi.org/ 10.1504/ijcat.2011.042709. 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[17] h. a. sonawane and s. s. joshi, "analytical modeling of chip geometry and cutting forces in helical ball end milling of superalloy inconel 718," cirp journal of manufacturing science and technology, vol. 3, no. 3, pp. 204–217, jan. 2010, https://doi.org/10.1016/j.cirpj.2010.11.003. r et r ac te d microsoft word etasr_v13_n4_pp11484-11489 engineering, technology & applied science research vol. 13, no. 4, 2023, 11484-11489 11484 www.etasr.com larik et al.: islanding issues, consequences, and a robust detection method for hybrid distributed … islanding issues, consequences, and a robust detection method for hybrid distributed generation based power systems nauman ali larik school of electric power engineering, south china university of technology, china epnauman.ali@mail.scut.edu.cn (corresponding author) meng shi li school of electric power engineering, south china university of technology, china mengshili@scut.edu.cn touqeer ahmed state key laboratory of electrical insulation and power equipment, xi’an jiaotong university, china touqeer.87@gmail.com jawed ahmed jamali school of energy and power engineering, dalian university of technology, china jawedahmed879@gmail.com qing hua wu school of electric power engineering, south china university of technology, china wuqh@scut.edu.cn received: 15 june 2023 | revised: 1 july 2023 | accepted: 9 july 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6120 abstract islanding refers to the situation where a distributed energy resource (der) remains as the sole power supply for a specific section of a power system, even after the main utility grid has been cut off. suitable islanding detection is crucial to maintain the stability and dependability of a power distribution system that includes ders. islanding detection using easy-to-implement passive techniques exhibits a cost-effective response. the purpose of this study was to examine the causes and effects of islanding that a system can experience and propose a passive islanding detection method that uses rocopad. the effectiveness of the proposed method was assessed using a matlab simulink-based power system integrated with multiple distributed generations (dgs). the results showed that the proposed rocopad-based islanding detection provided the best results. evaluation metrics, including detection accuracy, false operation, and detection time, highlighted the effectiveness of the proposed approach. keywords-renewable energy; unintentional islanding; non-detection zone; multiple distributed generation; phase angle difference i. introduction renewable energy generation has seen significant development in recent years due to the exponentially increasing power demand, the sharp increase in the price of oil and natural gas, and environmental concerns [2-4]. the development of renewable energy generation will increase since it reduces global warming, improves public health, and stabilizes energy prices, which is not possible when using fossil fuels with fluctuating prices [5-7]. renewable power sources, such as solar panels, wind turbines, and fuel cells can be used in conjunction with biomass or geothermal energy power plants because they are an economical source of energy that makes a power distribution system more stable and efficient [8]. microgrids facilitate the efficient use of distributed generation (dg) systems that use renewable energy [9]. dg is described as generating capacity that is placed close to the load being served, typically at the client site, and is not produced by central generating stations [10]. in addition to reducing the cost engineering, technology & applied science research vol. 13, no. 4, 2023, 11484-11489 11485 www.etasr.com larik et al.: islanding issues, consequences, and a robust detection method for hybrid distributed … of expansion of the transmission and distribution infrastructure, they decrease power losses, lower peak loads, decrease peak demand, and serve the requirement of a reserve margin [11]. as a result, many electric utilities all over the world have begun connecting distributed energy resources (ders) to distribution networks [12]. however, when ders are integrated into the grid, the distribution network becomes dynamic, raising concerns about electricity quality, reliability, and security [13]. the development of such an energy system has complicated issues, where the subject of its dependability and resilience is in flux [14]. however, renewable energy generation has established itself as the future of the power sector. in a successful system, dgs can keep the load energized totally or partly if the power grid goes down for whatever reason, as shown in figure. 1. this situation is known as islanding [15]. in islanding, the grid loses control over these disconnected loads and generators [16]. islanding identification is one of the biggest problems in modern power systems, which is made more difficult by the fact that many distribution networks already have many dgs. fig. 1. schematic diagram of the island system when a power outage occurs, it is vital to ensure that ders do not continue to energize isolated sections of the grid, as this can pose serious risks, including the potential to harm utility workers who may assume that the grid is de-energized and damage the equipment due to uncontrolled voltage or frequency fluctuations. by implementing effective islanding detection methods to identify islanding quickly, the grid control service can take steps to protect workers, restore power to customers, and prevent damage to the grid, improving the integrity and stability of the overall power system. islanding detection is the process of identifying when a der has disconnected from the main power grid and is operating in an islanded mode [1]. many techniques have been proposed to detect islanding, which can be divided into two groups: remote and local. the difference between local and remote approaches is the necessity of the former for a communication plan [17]. in other words, local systems observe, while remote systems communicate [18]. although remote processes are extremely reliable, they are challenging to implement, since they require direct communication between dgs and utilities via networks like fiber optics and wireless communication. furthermore, real-time implementation of these techniques may be rigid, challenging, and expensive due to the significant penetration of dgs in complex systems [19]. as a result, for ease of use and adaptability, a more affordable local technique is recommended. as suggested by the name, this strategy depends on identifying islanding by identifying changes in particular system characteristics at the dg location. voltage, current, resistance, and harmonic distortion are variables that can be measured [20]. this broad category is further subdivided into passive methods, active methods, and combined methods. multiple characteristics of the system are passively monitored at the point of common coupling (pcc), including voltage, frequency, harmonic distortion, and current, as shown in figure 2. these values change drastically when the distribution system is running in islanded mode. certain thresholds have been established to prevent incorrect identification of other system breakdowns [21]. fig. 2. passive idm working philosophy. active approaches use the dg's response to a small perturbation to detect islanding occurrences. the addition of perturbation after the distribution system has been linked to the grid will result in a little shift in a system parameter. however, the system will recognize islanding if there is a sudden change in the islanded mode's properties [22]. for distributed inverter generation, active strategies predominate. however, the vast majority of active islanding detection methods are often recommended only for nearby and tractable sources. since the ndz of the active methods is less than that of the passive ones, they can detect islanding even when load and generation are in equilibrium. however, the main problem with these strategies is that they typically reduce power quality by introducing disruptions into the system that are unnecessary in typical operating conditions [23]. additionally, active methods take a lot longer time to detect islanding than passive ones. hybrid islanding detection approaches combine the benefits of active and passive. these methods are only used when it is clear that passive approaches cannot differentiate between islanding events [24]. the benefits of these methods are that they generate just a negligible amount of ndz and the system is not subjected to a constant stream of signals. because of this, there is far less power loss. the cost and time required to discover islanding occurrences both increase with this combination [25]. most electrical companies use passive approaches to monitor islanding due to their simple operating principles and their ability to maintain power quality. two common passive methods are voltage under/over and frequency under/over [26]. however, they perform satisfactorily when there is a significant power imbalance but poorly when there is a minor power mismatch. although the frequency change rate in [27] performs better than previous methods, it can be put in engineering, technology & applied science research vol. 13, no. 4, 2023, 11484-11489 11486 www.etasr.com larik et al.: islanding issues, consequences, and a robust detection method for hybrid distributed … danger when active power mismatch approaches less than 15%. thd-based islanding was used in [28], however, occasionally, when there are sudden changes in load, thd exceeds the prespecified threshold, resulting in false tripping. ii. islanding causes and consequences whenever the central utility grid is disconnected from the rest of the system, including a few distributed generation sources and their respective load on the end side, the system is said to be in islanding state. islanding can be intentional, which is created to avoid severe blackouts or to perform maintenance tasks on the grid side. unintentional islanding happens when a der continues to generate electricity, even after a fault or other sudden sort of disturbance which has disconnected the grid from the rest of the network. there are a variety of causes for unintentional islanding. a. unintentional islanding causes  loss of grid connectivity: loss of grid connectivity can occur when there is a fault or failure in the transmission line that joins the main grid to the dispersed generation system. in this case, the isolated area of the distributed generation system may continue to produce power.  faults in the grid: faults in the grid, such as short circuits, broken conductors, or equipment failures, can cause an islanding condition when they disconnect a portion of the grid from the main power system.  human error: if a part of the system is accidentally removed from the main grid, this is an islanding state that can be caused by a human error such as improper switch manipulation.  natural disasters: natural disasters such as earthquakes, hurricanes, or tornadoes can cause an islanding condition if they damage the power system and disconnect a portion of the grid from the main system. b. islanding consequences the integrity of electrical networks is seriously threatened by unintentional islanding, which often results in cascading failures and blackouts. such cascade failures are responsible for several power outages that have occurred worldwide over the past ten years [29]. cascading failure is the process in which one failure could result in subsequent failures of other grid segments. instability in frequency, angle, or voltage may result from a lack of active or reactive power on these haphazard islands. this instability in frequency, angle, or voltage may cause a power quality variation that spreads to another region if it is not well regulated. when islanding occurs, the auto recloser will keep trying to reestablish contact between the island and the power grid. this will result in an asynchronous reconnection between them. this occurs because the phase angles, voltage levels, and frequencies of the two powered systems are not compatible with each other. the impact of this situation on a spinning dg has been well established. the primary mover of the generator could be harmed by the high mechanical torque and currents produced by an out-of-sync closing. if repair personnel are sent to an unmonitored part of the power grid, they may come into contact with live parts of the equipment, which could cause serious injuries or even death. that is the important reason to track down and cut power to any rogue electric island. iii. proposed idm the proposed method uses the rate of change of phase angle difference for efficient islanding detection in multiple dg-based power, as shown in figure 3. with the help of the dg's own current and voltage data, the pad can be determined between the dg and the utility grid. an islanding condition is determined to occur after the pad rate rises above a predetermined threshold. the pad is constantly tracked by the algorithm and compared to a predetermined limit. the program announces an islanding when the pad exceeds the threshold value for a predetermined amount of time and disconnects the dgs from the microgrid. fig. 3. flow chart of the proposed idm. at the dg end, the rocopad algorithm keeps an eye on phasor estimation based on synchronous transformation using the retrieved instantaneous voltage and current signals. the power system signal x(t) with a frequency f is given by: �(�) = ∑ �� �(�� � + ��)∞��� (1) where ak is the amplitude and k is the phase angle of the k-thorder waveform. the d-q transformation is used to convert the three-phase to two-phase: ������ = � �(� �)−�� (� �)−�� (� �)− �(� �)� × � 1 ��� ���0 √!� �√!� " × # �$�%�&' (2) where f0 is the system frequency, which is 50 hz, ω0 equals to 2πf0, ts is the sampling interval, that equals m at the m-th instant. therefore, (2) may be rewritten as: ���(()��(()� = �! �∑ �� �� )2+(,− ).(/0 + 1� 2���−∑ �� �)2+(,− ).(/0 + 1�2��� � (3) the fundamental quantities can be determined by setting k=1. ���(() = 1.5�� �� )2+(− ).(/0 + 1� ���(() = 1.5�� �)2+(− ).(/0 + 1� (4) engineering, technology & applied science research vol. 13, no. 4, 2023, 11484-11489 11487 www.etasr.com larik et al.: islanding issues, consequences, and a robust detection method for hybrid distributed … it is possible to calculate the signal's amplitude (a1), phase (1), and frequency (f) from the d and q values. now, rocopad can be calculated as: 56768�9 = :(;<�;=):> (5) the rocopad relay can detect an islanding condition quickly and accurately. the phase angle difference will be calculated and compared to the cutoff value. with the proper threshold, rocopad is used as a criterion for islanding detection. iv. results and discussion a. test system the proposed method was evaluated using a testing infrastructure, as shown in figure 4. the simulation aimed to model a power system that combines solar power, energy storage, and a diesel generator with the primary electricity grid. this is a popular hybrid power system. the main power grid is the base of the power system and provides power when solar power and energy storage aren't enough. the solar power system consists of pv panels. the energy storage system is made up of batteries that store the extra energy made by the pv panels and release it when the energy demand is higher than what the pv panels can provide. a diesel engine is used as a backup power source if there is not enough power from the pv panels and energy storage. it is also responsible for maintaining the stability of the system during sudden load changes or disturbances. a main circuit breaker was added that disconnects the generator from the grid to achieve an islanding condition. the proposed method was then evaluated in a variety of steady-state load switching, severe fault, and capacitive switching scenarios. fig. 4. schematic diagram of the hybrid power system. b. islanding events the efficiency of the suggested method was measured with a conventional testing setup by generating several islanding situations. since a parallel rlc load has a narrow ndz and is hard to detect with passive islanding detection methods, it was selected as the most difficult scenario. 1) using rlc load to evaluate idm, it is common practice to model the load as an rlc load because rlc loads can pose certain detection difficulties, especially for loads with high-quality factors. to mimic this scenario, a parallel rlc load was connected to the distribution network, which resulted in an islanding event at 0.3 s. figure 5 shows typical results. fig. 5. results during rlc under islanding condition. c. non islanding conditions to test how well the suggested method would work in realworld settings, various events that would not normally constitute an islanding condition, but whose signatures were very similar, were replicated. the proposed solution was tested using load shedding, capacitor switching, and large induction load switching, to ensure that it would not fail in these circumstances. 1) capacitor switching some voltage transients in power networks are caused by capacitor switching, which can degrade the effectiveness of islanding detection approaches. occasionally, they could cause similar signatures in source voltages or currents, which may reduce the accuracy of the proposed approach. to evaluate the viability of the proposed strategy, a capacitor switching scenario at 0.3 s was simulated. figure 6 shows the resultant signals, which occasionally exceed the average levels but fall short of the set threshold. fig. 6. results during capacitive switching for normal conditions. d. load shedding load shedding refers to the intentional and temporary reduction of electrical power to certain areas or customers to prevent a widespread power outage. power flow and system dynamics can abruptly change as a result of load shedding. to identify islanding, the proposed idm method tracks the rate at which power angles vary. if load shedding causes rapid changes in power flow, it can trigger false alarms and lead to incorrect detection of islanding events. a large portion of the load was isolated in the given simulation at 0.3 s to evaluate the load-shedding scenario. figure 7 illustrates the simulation results, showing that although the current decreased and deviated to a great extent, it was within the acceptable threshold. engineering, technology & applied science research vol. 13, no. 4, 2023, 11484-11489 11488 www.etasr.com larik et al.: islanding issues, consequences, and a robust detection method for hybrid distributed … fig. 7. results during load shedding for normal conditions. 1) heavy load switching load change scenarios can affect islanding detection methods, as sudden load changes can result in false alarms or delayed detection of islanding events due to disturbances in power flow, voltage, and frequency. certain load changes can pose a challenge to the sensitivity of the islanding detection method. a load change scenario was simulated to evaluate the effectiveness of the proposed strategy. however, as shown in figure 8, the results do not have a noticeable impact on the detection method. fig. 8. results during load switching for normal condition. table i. comparison of conventional passive idas conventional passive idms detection (time) ndz ouf [30] 200 ms-2 s large ouv [31] 200 ms-2 s large rocop [32] 300 ms large rocof [27] 300 ms small rocofop [33] 100-300 ms small voltage unbalance [34] 400 ms harmonic distortion [28] 200-400 ms large proposed very small v. conclusion effective islanding detection is crucial in ensuring the reliability of power distribution networks that incorporate dg sources. this study investigated the reasons for islanding and the consequences of electrical system islanding events for utilities and their end users. this paper presented a rocopad-based passive islanding detection method that monitors for the aforementioned changes and other indicators of islanding activity. to evaluate the method's success, several dg-based test systems were subjected to extensive simulations. the results demonstrated the effectiveness of the suggested method in detecting islanding events with minimal disturbances. furthermore, the proposed rocopad-based idm not only offered islanding detection based on multiple dg sources, but exhibited high accuracy, short response time, and be cost-effective and robust to variations in power system parameters, such as load conditions, system impedance, and der characteristics. future research should concentrate on the rocopad with other computational methods. artificial intelligence (ai) can be used to improve the accuracy and 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[34] c. li, c. cao, y. cao, y. kuang, l. zeng, and b. fang, "a review of islanding detection methods for microgrid," renewable and sustainable energy reviews, vol. 35, pp. 211–220, jul. 2014, https://doi.org/ 10.1016/j.rser.2014.04.026. microsoft word etasr_v12_n5_pp9166-9171 engineering, technology & applied science research vol. 12, no. 5, 2022, 9166-9171 9166 www.etasr.com sarade & ruikar: development of a wide bandwidth massive eight dissimilar radiating element … development of a wide bandwidth massive eight dissimilar radiating element multiband mimo antenna for mm-wave application shrenik suresh sarade electronics engineering walchand college of engineering sangli, india shreniks2k7@rediffmail.com sachin d. ruikar electronics engineering walchand college of engineering sangli, india sachin.ruikar@walchandsangli.ac.in received: 10 june 2022 | revised: 26 july 2022 | accepted: 28 july 2022 abstract-this paper proposes a massive mimo antenna operating on 6ghz frequency as millimeter-wave. it consists of eight dissimilar-shaped radiating elements. the radiating element of the antenna is designed using square shape with different cut slots. parasitic elements and defected ground structure are introduced for the enhancement of the correlation coefficients and total active reflection coefficients of the mimo antenna. the rectangular shape parasitic elements are placed between the square radiating patches. the ground plane consists of rectangular shape defected ground structures. the antenna is constructed on the fr-4 substrate. parameters such as isolation, cross-correlation, and bandwidth are enhanced. the obtained through simulations antenna parameters values of return loss, isolation, cross-correlation, total active reflection coefficients, and bandwidth are less than -10db, less than -9.30db, less than 0.16, less than 0.00015, and greater than 200mhz respectively. the antenna operates on various bands with fractional bandwidth greater than 3% for a frequency of 6ghz. this antenna is useful for a variety of applications in wireless systems. keywords-mimo; dgs; tarc; cc;ecc i. introduction antennas are a crucial part of communication systems. an antenna is used to transport data from one location to another without interfering with the original signal. as a result, there is a need to build an antenna that meets the requirements of the communication system, such as size, weight, and signal quality. multiple input and multiple output (mimo) antennas play an important role in the antenna field nowadays. multiple antennas may be present at the transmitter and the receiver. the low data rate in single input and single output (siso) system can be improved using an mimo antenna system. the data rate of mimo antenna grows linearly and depends on the number of patches in the antenna. the performance of the mimo antenna differs with return loss, isolation, correlation coefficients, and total active reflection coefficients. in a mimo antenna, multiple radiating patches are positioned on the same substrate in close proximity to one another. the close proximity of the square radiating patches influences the isolation (which becomes high) between the radiating patches and the correlation coefficients become higher. there is a requirement of improvement in antenna's isolation, correlation coefficients, and data rate. to improve isolation and correlation coefficients, several studies employ defective ground structure (dgs), parasitic elements (pes), metamaterials, decoupling structure (ds), and electromagnetic band gap (ebg) approaches. a dgs technique is used to improve isolation. cut slots of various shapes are used in the ground plane [1-6]. to improve isolation, a decoupling structure is constructed that decouples the input of radiating patches from the matching network setup in [7-11]. pes are used to improve the isolation between the patches in [12-17]. from the above literature survey, it can be concluded that there is a requirement to develop a massive mimo antenna that operates on wide bandwidth multiband applications, with better tarc and better cross correlation. a diverse shaped-element gigantic mimo antenna is proposed in this work. it operates at multiband frequency with wide band operation. parasitic elements and a defective ground structure are used to improve antenna parameters such as isolation, cross correlation, and total active reflection coefficients. ii. design of the massive mimo antenna the concept of the mimo antenna is explained above along with the literature survey. in this section, the massive mimo antenna is designed and explained in detail. the designed antenna comprises of 8 square radiating patches with distinct cut slots for the 6ghz frequency, as shown in figure 1. the antenna dimensions are provided in figure 2. the antenna is developed using a fr-4 substrate with 1.6mm height h and 4.4 dielectric constant. the antenna's geometrical structure, i.e. length lre and width wre, was created using the square radiating patch transmission line model [20], which has the dimensions listed in table i, which shows the measurements of 8 radiating elements with varying cut slots. a rectangular cut slot [20] is placed in patch-1 and patch-3, with length c and width d. a similar rectangular cut slot [20] is placed in patches-5, -7, and 8. a square cut slot is placed in patch-6, with both length and corresponding author: shrenik suresh sarade engineering, technology & applied science research vol. 12, no. 5, 2022, 9166-9171 9167 www.etasr.com sarade & ruikar: development of a wide bandwidth massive eight dissimilar radiating element … width c. the cut slot dimensions of the single patch are optimized using the equivalent circuit explained in section iii. inset feed line (ifl) [20] with length c and width d is used to excite the antenna elements (dimensions listed in table i). the antenna's dimensions (fr-4 substrate) which consist of length e and width f of the patch are summarized in table i. the distance between the parasitic elements and the radiating patches is less than half of the wavelength. fig. 1. massive mimo antenna with 8 distinct shaped components with pes and a gds. fig. 2. the dimensions of the developed massive mimo antenna. fig. 3. the ground plane of antenna with dgs. engineering, technology & applied science research vol. 12, no. 5, 2022, 9166-9171 9168 www.etasr.com sarade & ruikar: development of a wide bandwidth massive eight dissimilar radiating element … pes and dgs improve the total active reflection coefficients (tarc), the correlation coefficient (cc), and the envelope correlation coefficient (ecc) values between the radiating elements. table i shows the size of parasitic elements (p1 to p14) [12-17]. as indicated in figure 1, rectangular shaped parasitic elements (pes) are used between the radiating patches. the pes are used to negate parts of the coupled field between the elements because it creates an opposite coupling field, which lessens the original field and hence reduces total coupling on the antenna. the pe structure and the radiating patch are not physically related. figure 3 depicts the antenna's ground plane, while figure 4 depicts its dimensions. table i shows the length d and width c of the dgs in the ground plane. the ground plane is made up of rectangular-dgs cut slots [1-6] that are utilized to improve isolation table i. antenna dimensions sr. no. parameter dimensions (in mm) 1 patch length (lre) a = 11.38 2 patch width (lre) b = 11.38 3 length of ifl d = 6.41 4 width of ifl c= 2.942 5 length of substrate e= 36.522 6 width of substrate f= 80 iii. equivalent circuit model of the antenna in this section, the operation of the single radiating patch of the antenna is explained using the equivalent circuit model. that is applicable to all radiating patches. dgs and pes are used in the development of the gigantic mimo antenna. these two techniques are used to improve the antenna's isolation, tarc, cc, ecc, and bandwidth. the equivalent circuit mathematical model is used to describe how antennas work. the corresponding circuit of a single radiating patch is shown in figure 5. fig. 4. the dimensions of the ground plane of the antenna with dgs. fig. 5. equivalent circuit model for square-radiating patch. as shown in figure 1, the antenna comprises of a square radiating patch with a cut slot. figure 5 is divided into two parts: a square shape circuit with impedance z1 and rectangular cut slot-1 and 2 with impedance z2 and z3. the inductor and capacitor values of the equivalent circuit [21] are used to compute the cut slot dimensions using (1) and (2): g� � �.����� � �1 � 0.04167�k�h���� �� (1) b� � �.����� � �1 � 0.636 ln�k�h���� � (2) where g1 is the resistive value of the circuit, b1 is the capacitive or inductive value of the circuit, w= lre the width of the patch, h the height of the substrate, and k0 constant. because the antenna elements have distinct cut slots, the antenna can function on many frequencies. this antenna's operating concept is similar to that of any other radiating patch, and cut slots are provided according to the desired frequency. iv. result analysis the antenna is simulated using the high frequency structure simulator (hfss). isolation, cc, ecc, tarc, and bandwidth [19] are the performance parameters of the mimo antenna. the 8 radiating patches are arranged in a row (close to each other) which results in high level of isolation among the radiating patch. dgs and pe techniques are employed to improve the isolation between the radiating patches. the rectangular carved slit acts as a dgs in the ground. the dgs alters the properties of the transmission line's inductor and capacitor, resulting in a shift in the antenna's frequency response. a rectangular shaped pe is placed between the radiating elements to improve the antenna's isolation and bandwidth. it prevents the radiating energy passing from one element to the nearby element. the isolation performance between the parameters helps improve cc, ecc, and tarc. the return loss (s11) and the acquired isolation between the remaining elements of patch-1 are shown in figure 6. the antenna operates on 6.2ghz (m1) and 7.1ghz (m3), with less than -17.50db return loss (s11), less than -11.25db isolation (s12 (m2 and m4)), and 347.4mhz (5.79%) bandwidth. the isolation between the remaining patches, s13, s14, s15, s16, s17, and s18 is less than -11.25db (s12). fig. 6. return loss (s11) and isolation of patch-1. the antenna element bandwidth [18-20] is obtained at 10db return loss. the return loss (s22) and the isolation engineering, technology & applied science research vol. 12, no. 5, 2022, 9166-9171 9169 www.etasr.com sarade & ruikar: development of a wide bandwidth massive eight dissimilar radiating element … between the remaining elements of patch-2 are shown in figure 7. it operates on the 5.7ghz, with less than -24.79db return loss (s22 (m1)), less than -11db isolation (s26 (m2)), and 437.3mhz (7.289%) bandwidth. the isolation between the remaining patches such as s21, s23, s24, s25, s27, and s28 is less than -11db (s26). the return loss (s33) and the isolation between the remaining elements of patch-3 are shown in figure 8. it operates on 5.8ghz (m1) and 6.9ghz (m3), with less than 12.50db return loss (s33), less than -11.40db isolation (s34 (m2) and m4)), and 403.32 mhz (6.72%) bandwidth. the isolation between the remaining patches such as s31, s32, s35, s36, s37, and s38 is less than -11.40db (s34). fig. 7. return loss (s22) and isolation of patch-2. fig. 8. return loss (s33) and isolation of patch-3. fig. 9. return loss (s44) and isolation of patch-4. the return loss (s44) and the isolation between the remaining elements of patch-4 are shown in figure 9. it operates on 6.1ghz (m1) and 6.7ghz (m3), with less than 10.25db return loss (s44), less than -9.35 db isolation (s43 (m2 and m4)), and 488mhz (8.146%) bandwidth. the isolation between the remaining patches such as s41, s42, s45, s46, s47, and s48 is less than -9.35 db (s43). the return loss (s55) and the isolation between the remaining elements of patch-5 are shown in figure 10. it resonates on 5.8ghz (m1) and 6.8ghz (m3), with less than 18.50db return loss (s55), less than -9.70db isolation (s51 5.8ghz (m2 and 5.8ghz m4)), and 399mhz (6.65%) bandwidth. the isolation between the remaining patches such as s52, s53, s54, s56, s57, and s58 is less than -11.33db (s51). the return loss (s66) and the isolation between the remaining elements of patch-6 are shown in figure 11. it resonates on 5.8ghz (m1), with less than -20.92db return loss (s66), less than -11.17db isolation (s67 5.8ghz (m2)), and 425.76 mhz (7.096%) bandwidth. the isolation between the remaining patches such as s61, s62, s63, s64, s65, and s68 is less than -11.33db (s67). fig. 10. return loss (s55) and isolation of patch-5. fig. 11. return loss (s66) and isolation of patch-6. fig. 12. return loss (s77) and isolation of patch-7. the return loss (s77 (m1)) and the isolation between the remaining elements of patch-7 are shown in figure 12. it resonates at 5.7ghz, with less than -16.25db return loss (s66), engineering, technology & applied science research vol. 12, no. 5, 2022, 9166-9171 9170 www.etasr.com sarade & ruikar: development of a wide bandwidth massive eight dissimilar radiating element … less than -10.98db isolation (s76 (m2)), and 297mhz (4.95%) bandwidth. the isolation between the remaining patches such as s71, s72, s73, s74, s75, and s78 is less than -11.33db (s76). the return loss (s88) and the isolation between the remaining elements of patch-8 are shown in figure 13. it resonates at 5.8ghz (m1) and 6.8ghz (m3), with less than 20.30db return loss (s88), less than -11.10db isolation (s84 (m2 and m4)), and 379.2mhz (6.32%) bandwidth. the isolation between the remaining patches such as s81, s82, s83, s85, s86, and s87 is less than -11.33db isolation (s84). fig. 13. return loss (s88) and isolation of patch-8. the results of the antenna parameter investigation show that the gain attained is 2.69db, as shown in figure 14. figure 15 shows the antenna radiation pattern. tarc is less than 0.16, cc is less than 0.0122, ecc is less than 0.00015, and dg is near to 9.9985 [20]. fig. 14. gain of the mimo antenna. fig. 15. radiation pattern of the mimo antenna. v. comparison the proposed antenna's parameters are compared with other works in table ii. the comparison shows that the proposed antenna is developed for 8-different shaped radiating elements. it operates on the multiband frequency with a wide bandwidth. table ii. comparison of the proposed antenna with other works ref technique used parameter frequency band and bandwidth radiating patches [1] dgs -10 db rl, -12db isolation single band and narrow band same shape 8-radiating patches [7] dgs -20 db rl, -15db isolation dual band and narrow band same shape 8-radiating patches [12] pe -10 db rl, -10db 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[21] c. a. balanis, antenna theory: analysis and design, 3rd ed. hoboken, n.j, usa: wiley, 2005. microsoft word etasr_v12_n1_pp8075-8079 engineering, technology & applied science research vol. 12, no. 1, 2022, 8075-8079 8075 www.etasr.com abbas & burhan: investigating the causes of poor cost control in iraqi construction projects investigating the causes of poor cost control in iraqi construction projects nagham nawar abbas department of civil engineering university of baghdad baghdad, iraq nagham.nawwar@gmail.com abbas m. burhan department of civil engineering university of baghdad baghdad, iraq abbasm.burhan@coeng.uobaghdad.edu.iq abstract-controlling cost in construction projects is an essential issue. this study investigates the most critical problems that cause weakness in cost control in iraqi construction projects. the quantitative technique was used by conducting a survey directed to professionals who work on construction projects. one hundred and sixty-four questionnaire forms were distributed to private sector companies, government companies, and government institutions, and the responses were subjected to the required statistical analysis. the results indicate that the most influential factors are the weakness in keeping up with the use of modern concepts, methods, and technologies, the delay in receiving the amounts due for work done from the owner, fluctuations in market prices, the lack of knowledge and the inefficient use of currently available tools and technology, and the security situation in the country. the results indicate that the iraqi construction projects suffer from weakness in cost control, which causes them to stop or delay their delivery, and this needs serious and quick solutions. one of the most important solutions is the adoption of modern technologies and their inclusion in the construction sector and the development of special systems for managing costs that are appropriate to the iraqi construction environment. keywords-cost control; construction project; statistical analysis; causes; investigation i. introduction a construction project will be successful if its technical goals are aligned with its budget and the budget is not exceeded. it is difficult to envisage a construction project being completed without cost variances and schedule delays, which may occur at any time during the procedure due to various factors such as poor management, supervision, and control [1]. most construction projects require the completion of a specific set of operations to deliver a specific product. construction projects include new buildings and structures, additions, changes, conversions, expansions, reconstruction, renovations, large replacements, and mechanical and electrical installations. cost and time control is essential in the construction industry [2]. in general, a construction project's success is determined by its ability to fulfill the client's cost, time, safety, resource allocation, and quality objectives. a successful project meets technical goals, stays on schedule, and stays within cost limitations [3]. the construction industry as a whole has been deemed to be underperforming, resulting in an inability to attain effective cost performance. as a result, most building projects have a wide range of costs [4]. one of the most important concerns confronting the construction sector is cost overrun [5]. time and cost overrun are common issues for the majority of construction projects [6, 7]. cost overrun is a common theme in iraq's construction industry. despite the development of many cost control approaches and technologies, the iraqi construction industry has yet to implement them [8]. this research contributes to the identification of the current reality of the iraqi construction sector. ii. design of the questionnaire initially, previous studies were reviewed to collect, organize, and analyze relevant information in a manner appropriate to the intended purpose. after that, this information was subjected to a series of discussions, analyses, and modifications that helped develop a questionnaire. the first page of the questionnaire is a cover containing information related to the research topic. the questionnaire included two parts. the first part includes general information about the concerned entity (such as its type and name) and information about the people who fill out the questionnaire from the target community in the study (specialization, educational qualification, workgroup, and the amount of experience). the second part includes a list of factors that are probable to have a negative impact on the control of the cost of a construction project. this part includes 22 closed questions designed with a five-point likert scale (1: always, 2: frequently, 3: sometimes, 4: scarcely, 5: never). each respondent was asked to assign a degree of measure to each factor based on his/her perceptions about the iraqi construction sector's environment. the most prominent and important problems the process of construction project cost control faces, according to the review of the previous literature and interviews with experts specialized in the field of construction projects, are shown in table i. corresponding author: nagham nawar abbas engineering, technology & applied science research vol. 12, no. 1, 2022, 8075-8079 8076 www.etasr.com abbas & burhan: investigating the causes of poor cost control in iraqi construction projects table i. a review of the issues the construcion project cost control s issue references 1 weakness in keeping up with the use of modern concepts, methods, and technologies [9-12] 2 lack of knowledge and inefficient use of currently available tools and technology [13, 14] 3 failure in the decision-making process due to various reasons [12] 4 poor communication and transfer of information and data between the concerned parties [15] 5 lack of progress in measuring work properly [16] 6 poor planning and scheduling and not dividing work items in a way that helps tracking costs easily [14, 17] 7 unclear contract documents (contracting details, technical specifications, general and special requirements) [17] 8 failure to prepare an appropriate purchase plan [14, 18] 9 fluctuations in market prices [14, 18] 10 involving inexperienced executive staff in terms of cost and low labor productivity [17, 18] 11 low labor productivity [16] 12 changes made by the owner [14, 18, 19] 13 changes resulting from design errors [19] 14 poor management of site data and not accurate documentation [14, 18, 19] 15 delay in receiving the amounts due for work done from the owner [18] 16 excessive waste of materials on the site [19] 17 inaccurate estimation of quantities [14, 20] 18 insufficient information needed to achieve cost control [20] 19 lack of a fixed and specific method in the process of making measurements for real work added during the open survey 20 not clearly specifying the type of data and information required added during the open survey 21 inadequate analysis of cost data to ensure a better benefit in the control process added during the open survey 22 security situation in the country added during the open survey iii. face validity face validity, or content validity is a sort of validity in which diverse aspects, skills, and behaviors are measured appropriately and successfully. the research tools and data may be reviewed by professionals in the field of study to this goal. vague and cryptic questions can be updated, and the difficult items can be reworded based on the reviewers' remarks [21]. since the construction of the scale of measurement items was primarily based on an exhaustive analysis of the literature and detailed reviews by numerous industry experts, professionals, and academics, the content validity of the proposed questionnaire was satisfied in this study. five specialists with more than 10 years of experience in construction projects and with an academic background in questionnaire evaluation were consulted to analyze the questionnaire and make revisions that best match the iraq conditions. iv. pilot study a pilot study is a small experimental attempt or study that applies to a part of the study population whose characteristics are usually similar to those of the study population [22, 23]. according to [24] the pilot research is a test run for the questionnaire, which includes detecting any vague questions, testing the phrasing of questions, testing the data collection technique, etc. the most important challenge that the study faced is the difficulty of communicating with experts directly due to the covid-19 related quarantine, so finishing this stage took a long time. the sample size for the pilot study is preferably between 30 and 50 [25]. in this research, 35 respondents were selected, the questionnaire was distributed to them, and the answers were collected, organized, and prepared for conducting the required statistical tests. the pilot study was applied to respondents with characteristics similar to the total sample, and after ensuring the validity of the research tool, the questionnaire was distributed to the total sample without including the pilot sample. v. pilot study tests (validity and reliability) using a good research tool is one of the most critical factors to reach acceptable and valuable results. according to [26], one of the researcher's key goals is to develop his research tool which should be characterized by three traits, i.e. it should be meaningful, accurate, and efficient. the data collected from the pilot study were subjected to the required tests using the statistical analysis software statistical package for the social sciences (spss) version 26 to verify the extent of validity and reliability. a. statistical validity the validity of an instrument refers to how well it measures what it is supposed to measure [27]. this test is used to find the correlation coefficients between each item in a specific portion and the part as a whole [28]. each of the 22 items of the questionnaire was assigned a different symbol from f1 to f22. table ii shows the results of the internal validity test for the second part of the questionnaire titled possible reasons for poor cost control in construction projects. b. statistical reliability (cronbach's alpha) the value of the cronbach's alpha constant, which ranges from 0 to 1, is an essential technique of calculating reliability. the closer it is to 1, the higher the degree of reliability [29]. table iii shows the classification of reliability according to the value of the cronbach's alpha coefficient. after implementing the cronbach's alpha test, the results were compared with the standard values mentioned in table ii and they were found to be within excellent limits with a value of 0.902 which confirms the reliability of the used questionnaire. engineering, technology & applied science research vol. 12, no. 1, 2022, 8075-8079 8077 www.etasr.com abbas & burhan: investigating the causes of poor cost control in iraqi construction projects table ii. item correlation coefficients item correlation coefficient sig. (2-tailed) f1 0.479** 0.000 f2 0.427** 0.000 f3 0.484** 0.000 f4 0.629** 0.000 f5 0.620** 0.000 f6 0.506** 0.000 f7 0.577** 0.000 f8 0.604** 0.000 f9 0.252** 0.002 f10 0.577** 0.000 f11 0.512** 0.000 f12 0.365** 0.000 f13 0.519** 0.000 f14 0.696** 0.000 f15 0.379** 0.000 f16 0.586** 0.000 f17 0.707** 0.000 f18 0.736** 0.000 f19 0.665** 0.000 f20 0.660** 0.000 f21 0.684** 0.000 f22 0.193* 0.017 correlation is significant at the 0.05 level (2-tailed)٭ correlation is significant at the 0.01 level (2-tailed)٭٭ table iii. reliability cut-off values [30] cronbach's alpha degree of reliability α ≥ 0.9 excellent 0.9 > α ≥ 0.8 good 0.8 > α ≥ 0.7 acceptable 0.7 > α ≥ 0.6 questionable 0.6 > α ≥ 0.5 poor 0.5 > α unacceptable vi. questionnaire distribution convenience sampling was adopted. convenience sampling is a sort of nonprobability sampling in which respondents are chosen because they are "convenient" data sources for researchers [31]. the questionnaire form was distributed to the intended sample, consisting of 180 individuals, and 164 forms were answered (response rate 91%). after checking, 14 forms were found to be incomplete, resulting in a total of (150) forms which were processed. professionals in iraqi construction projects (architects, civil engineers, mechanical engineers, electrical engineers, and other professionals with associated specialty) were included in the research population. the questionnaire was distributed manually in paper form through group interviews with specialists from different workplaces and through an electronic link. questionnaire completion took about 7 to 9 minutes. table iv shows the statistical analysis of the characteristics of the target sample. vii. questionnaire data analysis the quantitative method was used. quantitative data analysis methods can be beneficial to a researcher attempting to extract meaningful conclusions from a vast body of qualitative data. the key advantage is that a quantitative analytical technique allows the separation of many confounding elements that can obfuscate the core qualitative conclusions [32]. table iv. characteristics of the target sample question categories percentage concerned party percentage of respondents contracting companies owner consulting offices 51% 42% 7% respondents' educational level diploma bachelor's degree master's degree ph.d. other 1% 56% 38% 3% 2% respondents specialization architects civil engineers electrical engineers mechanical engineers others 1% 85% 5% 3% 6% current field of respondents designers consultants project managers contractors site engineers others 5% 8% 19% 4% 53% 11% respondents' experience less than 5 years 5-10 years 11-15 years 16-20 years more than 20 years 27% 33% 23% 8% 9% statistical approaches play an essential part in most studies that rely on quantitative data analysis by converting ordinal to numeric data using a rating scale (i.e. the 5-point likert scale). ibm spss was used to analyze the data. the relative importance index (rii) method was employed to determine the respondents' rankings of items/variables. rii can be calculated by: rii = ∑� (�∗ ) (1) rii = �(� )��(��)��(��)��(��)��� �(� ������������) (2) where w is the weight given to each component by the respondents (ranging from 1 to 5), a represents the most significant weight (which equals to 5), and n is the total number of people who took part in the survey. the rii value ranges from 0 to 1 (0 not inclusive). the higher the rii value, the more significant the attribute's impact. rii, on the other hand, does not take into account the relationships between the various elements. table v shows the details of the statistical analysis of the second part of the questionnaire. the results indicated that "weakness in keeping up with the use of modern concepts, methods, and technologies" is the highest cause of weakness to control costs in construction projects according to specialists' point of view with rii=80.00, mean=2.00, sd=0.82. the follow-up and use of the world's continuous development in administrative and technical tools related to project cost management has a significant role in solving most of the problems facing this process and shortening the time for the relevant parties. this study is in agreement with the findings in [9,11]. "delay in receiving the amounts due for work done from the owner" came second with rii=78.81, mean=2.06, sd=0.96. this reason falls outside the control of the implementing party and hinders the good management of project costs, but sometimes this delay may be based on problems or weaknesses in the data provided by the contractor. this result is in agreement with [18]. engineering, technology & applied science research vol. 12, no. 1, 2022, 8075-8079 8078 www.etasr.com abbas & burhan: investigating the causes of poor cost control in iraqi construction projects table v. statistical analysis of the second part of the questionnaire item mean std. deviation rii rank weakness in keeping up with the use of modern concepts, methods, and technologies 2 0.82 80 1 delay in receiving the amounts due for work done from the owner 2.06 0.96 78.81 2 fluctuations in market prices 2.11 0.9 77.88 3 lack of knowledge and inefficient use of currently available tools and technology 2.23 0.85 75.5 4 security situation in the country 2.24 0.91 75.23 5 poor planning and scheduling and not dividing work items in a way that helps tracking costs easily 2.4 1.09 72.05 6 failure in the decision-making process due to various reasons 2.46 0.85 70.86 7 involving inexperienced executive staff in terms of cost and low labor productivity 2.46 0.91 70.73 8 changes made by the owner 2.5 0.91 69.93 9 poor management of site data and not accurate documentation 2.56 1.08 68.74 10 inadequate analysis of cost data to ensure a better benefit in the control process 2.62 0.98 67.68 11 lack of progress in measuring work properly 2.62 1.03 67.68 12 failure to prepare an appropriate purchase plan 2.62 1.06 67.68 13 insufficient information needed to achieve cost control 2.65 0.95 67.02 14 low labor productivity 2.68 0.96 66.49 15 poor communication and transfer of information and data between the concerned parties 2.7 0.99 66.09 16 inaccurate estimation of quantities 2.72 1.04 65.56 17 changes resulting from design errors 2.81 0.93 63.71 18 not clearly specifying the type of data and information required 2.85 0.98 63.05 19 excessive waste of materials on the site 2.89 1.06 62.12 20 unclear contract documents (contracting details, technical specifications, general and special requirements) 3.01 1.1 59.74 21 lack of a fixed and specific method in the process of making measurements for real work 3.05 1.08 59.07 22 the ranked third reason for the poor cost control is "fluctuations in market prices" with rii=77.88, mean=2.11, sd=0.90. it is a problem that frequently occurs in the construction sector in iraq due to the country's fluctuating economic conditions and negatively affects the performance of construction projects. also, this result is in agreement with what was stated in [14, 18]. the fourth reason is "lack of knowledge and inefficient use of currently available tools and technology" (rii=75.50, mean=2.23, sd=0.85). this result is somewhat consistent with the first result, which indicated the weakness of keeping pace with modern technologies, as the current technologies are insufficient and need to be developed. this result is in agreement with [13, 14]. the fifth reason for poor cost control is the "security situation in the country" with rii=75.23, mean=2.24, sd=0.91. this is actually and negatively reflected on the performance of construction projects in general and not only on the cost performance. the top 5 reasons for the poor cost control appear to be reasonable and commensurate with the problems that iraqi building projects face. the two lowest-ranking reasons are "unclear contract documents (contracting details, technical specifications, general and special requirements)" and "lack of a fixed and specific method in the process of making measurements for real work". viii. conclusion according to the opinions of specialists in the field of the iraqi construction sector, construction projects mainly need to develop in the field of knowledge by adopting the most modern, at a global level, techniques in this field to solve multiple problems, including cost overruns. also, there is a need for real solutions related to financing. specifically concerned with addressing the problem of late payments allocated to projects, which impede the progress of projects. on the other hand, there is an urgent need to address the issue of market prices and reduce price fluctuations that occur at various times in the iraqi market and negatively affect the cost of construction projects. cadres of the public and private sectors need continuous education and updating in order to keep pace with the most prominent developments in the field of construction. finally, the general security situation of any country is directly reflected in the performance of its construction projects. the data indicate that cost overruns can be minimized. it is evident from the fact that most of the factors mentioned in each of the problems is caused by human incompetence and therefore can 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[32] a. field, discovering statistics using ibm spss statistics. thousand oaks, ca, usa: sage, 2013. microsoft word etasr_v12_n6_pp9414-9419 engineering, technology & applied science research vol. 12, no. 6, 2022, 9414-9419 9414 www.etasr.com chew hernandez et al.: a user-friendly dynamic reactor simulator built in microsoft excel a user-friendly dynamic reactor simulator built in microsoft excel mario luis chew hernandez industrial engineering department technological institute of superior studies of coacalco coacalco, mexico mario@tesco.edu.mx leopoldo viveros-rosas industrial engineering department technological institute of superior studies of coacalco coacalco, mexico leopoldo@tesco.edu.mx isaac hernandez arrieta industrial engineering department technological institute of superior studies of coacalco studies of coacalco coacalco, mexico isaac.subb@tesco.edu.mx received: 29 june 2022 | revised: 25 july 2022 | accepted: 27 july 2022 abstract-computer plant simulation is being used in all aspects of engineering, through many simulation software packages. however, almost all of them require licenses that must be purchased by engineering colleges intending to use simulation in their teaching. as public educational institutions everywhere are facing a scarcity of economic resources, they can resort to a freeware steady-state plant simulator, however, there is no availability of reliable, free dynamic plant simulators. in addition, published experiences on developing dynamic simulators use programming languages requiring paid licenses (e.g. matlab) and thus have limited relevancy to schools struggling to cut expenses. this article first uses a set of typical college objectives to discuss the advantages of building their own dynamic simulators, and then shows the development of a userfriendly dynamic simulator of a batch reactor constructed entirely within microsoft excel, which, in contrast to the programming languages used in related reports, is already widely used by universities around the world. keywords-batch reactor; dynamic simulation; visual basic i. introduction the typical bachelor chemical engineering degree program includes the subject of computer plant simulation in its last semesters [1]. one of the aims of the subject is that the student becomes familiar with commercial simulators, both dynamic and stationary. while some universities are able to purchase simulator licenses, this is not the case of most public institutions in developing countries, where financial resources are limited. as global trademark agreements have led to the prohibition of using unlicensed software in teaching, some institutions have resorted to free-ware software, of which reliable steady-state process simulators can be found (notably, the cape open simulator [2]). however, no reliable, sufficiently tested, and license-free dynamic simulators are currently at hand. fortunately, the academic staff of most colleges has the skills required to develop and program process simulators containing most of the elements of professional software. this work shows, taking a batch reactor as an example, how such a simulator can be developed using the functionalities included in the widely used microsoft excel program. the use of transient state simulation to promote industrial performance is well documented, both in its discrete-event version [3-5] and in its continuous form. regarding the latter, literary reviews can be found in [6] on the application of neural networks in simulating chemical and biochemical processes and in [7] on the modeling of energy systems. specific applications of simulation can be found in [8] where simulations to optimize plant design with respect to environmental objectives are applied and, more recently, in [9] that pressure dynamics to the simulation of a combined cycle gasification plant are incorporate. authors in [10] simulated a petrochemical wastewater treatment plant, authors in [11] dealt with a desalination plant energized by ocean waves, authors in [12] optimized the drying process of phosphate pellets, authors in [13] emphasized on energy use when studying a benzenetoluene-xylene distillation system, and authors in [14] treated the control of the activated sludge process. regarding the software used to perform the simulations reported in the literature, the usage of simulation environments (e.g. aspen) and high-level programming languages that provide routines facilitating simulation (e.g. matlab) has recently increased, as opposed to the use of general-purpose languages (e.g. c++ or fortran). for example, authors in [15] studied distillation tower sequences with aspen dynamics and matlab simulink, authors in [16] simulated a polymerization reactor using chemcad, and authors in [17] studied a heat corresponding author: mario luis chew hernández engineering, technology & applied science research vol. 12, no. 6, 2022, 9414-9419 9415 www.etasr.com chew hernandez et al.: a user-friendly dynamic reactor simulator built in microsoft excel integrated reactor applying aspen-hysys. authors in [18] used matlab and cosmol multiphysics to simulate heterogeneous catalysis, authors in [19] applied aspen dynamics for studying the control of a combustion system, authors in [20] modeled an activated sludge process using insel, and authors in [21] used aspen and matlab to evaluate a predictive control scheme for co2 absorption plants. didactic applications of dynamic simulations are reported in [22], in which the authors used aspen hysis to train engineers in statistical methods to analyze distillation systems and in [23] where the honeywell unisim design software was applied to simulate an isopropyl alcohol plant and train its operators. instances of reports on the development of process simulators for didactic purposes are found in [24], in which a steady-state free-ware simulator was designed to which third parties could make additions in a "wiki" scheme, called lazarus, running on uml language, and [25, 26] in which educational software was developed to analyze the dynamics of exchanger networks. finally, authors in [27] used an online simulator to train operators to manage overpressures in natural gas systems, authors in [28] built the "labvirtual" platform, with educational material including simulators, and authors in [29] developed a matlab-based dynamic simulator for chemical reactors. previous reports on the development of dynamic simulators for training purposes use either a commercial simulator or an advanced programming language (matlab). however, the usage of such software requires the purchase and continual renovation of licenses. this limits the relevancy of the mentioned approaches to cash-strapped public schools in developing countries, who may find simulators running on easily accessible, universally used programming languages, like the one sketched in [30], far more useful. the current work builds on the latter reference by discussing, from the perspective of institutional objectives, the convenience for schools to build their own simulators, and presenting a complete description of an excel-based dynamic simulator of a batch reactor. the shown simulator contains many of the features offered by professional software (button-based operations, filling the blank inputs, dialogue boxes, etc.). ii. methods this article has two main purposes, for which different methods are applied: • the first is to show, the convenience for colleges on developing their own simulators. this is done through objective analysis [31]: a hierarchy of fundamental objectives is built and the probable impact of the alternative on the objectives is assessed. • the second is to present the dynamic simulator of a batch reactor developed in microsoft excel. iii. results and discussion a. analysis of institutional objectives generally speaking, public education institutions have two conflicting objectives: an academic one, related to the development of professional skills of their students and an economical one, which refers to minimizing cost. this is shown in the structure in figure 1. fig. 1. fundamental objectives hierarchy. when contemplating the purchase of an educational tool, an institution should balance its price and the way it may benefit student formation. this is shown in figure 2, where the objective damaged by the alternative is pointed at by a dotted arrow while that which is benefited by a solid one. fig. 2. purchase impact on objectives. the academic objectives aim for the student to acquire relevant professional skills. this is shown in figure 3, where ci,j denotes skill i of subject j (for example, c1,qg refers to skill 1 of the subject "general chemistry"). figure 3 represents three skills covered in the subject "process simulation": c1,sp, c2,sp, and c3,sp. c3,sp is defines as "the student will use commercial process simulators" [1]. figure 3 breaks down the c3,sp skill into its steady-state simulation element ss part and a dynamic simulation one, dyn. fig. 3. details of academic objectives. engineering, technology & applied science research vol. 12, no. 6, 2022, 9414-9419 9416 www.etasr.com chew hernandez et al.: a user-friendly dynamic reactor simulator built in microsoft excel if a school hasn´t already bought a simulator license, then it views the purchase impact on c3,sp as not worth its cost. for the steady-state simulation part of c3,sp, this is solved by downloading one of the trustable, free-ware stationary plant simulators that can be found on-line. however, as there is no availability of transient state simulators with these qualities, the part of c3,sp dealing with dynamic simulation goes uncovered. nevertheless, if the institution was to build its own dynamic simulator, this deficiency would be corrected (figure 4). fig. 4. institutional options. b. process description the reactor to be simulated is based on the case described in [32], which features a steam heating jacket at temperature ts and a cooling coil. a pair of consecutive reactions occur in the reactor. a b c reaction a→b has a second order kinetics while b→c is a first order reaction and component b is the desired product. the assumptions used in the model are: • the reactor is thermally insulated and perfectly mixed. • the temperature of the water in the coil is described by its average tc value. • condensed steam is disposed at its saturation temperature. • reaction volume v and specific heat capacity cp are constant. • the heat transfer coefficient uj of the heating jacket is constant while the one of the cooling coil uc depends on the fc cooling water flow according to: 8.10 1 4550 11 8.0 += cc fu (1) species and energy balances produce the following three differential equations, which describe reactor dynamics: 2 1 a a dc k c dt = − (2) 2 1 2 b a b dc k c k c dt = − (3) ( ) ( ) ( ) ( )c p cc s p jj b p a p tt vc au tt vc au ck c h ck c h dt dt −− −+ ∆− + ∆− = ρ ρρρ 2 22 1 1 (4) ca and cb are the concentrations of species a and b, (-∆h1) and (-∆h2) the enthalpies of reactions a→b and b→c respectively, ρ and cp are the liquid density and specific heat capacity, and uj and uc are the global heat transfer coefficients of the heating jacket and cooling coil of heat transfer area respectively, aj and ac. reaction constants k1 and k2 and the temperature t are related by:       − = rt e k 1 101 expα (5)       − = rt e k 2 202 expα (6) where e1 and e2 are the reaction activation energies and α10 and α20 their respective frequency factors. when the reactor is in closed-loop operation, the water flow to the cooling coil (fc) and the steam temperature in the heating jacket (ts) are manipulated to control the reactor temperature (t). in order to improve the yield of product b, the temperature set-point (td) may follow a time (t) dependent trajectory [32]. td(t)=54+71×exp(-2.5×10 -3 t) (7) as there are two manipulated variables, ts and fc, and one controlled variable t, the controller adjusts, through a proportional-integral control logic, the value of a parameter u, that linearly sets the value of the manipulated variables between their maximum and minimum values, according to: ts = (ts,max−ts,min)u+ts,min (8) uc = (uc,min−uc,max)u+uc,max (9) the implicit euler method is used to solve the differential equations and a newton-raphson procedure is used to solve the nonlinear algebraic equations in each integration step. c. simulator description the simulator was implemented as an excel macro. it is delivered to the user as an excel file, the opening of which produces figure 5. clicking on the "batch reactor" button displays the user interface (figure 6). at the interface top (figure 7) the simulation time and initial conditions are set: concentrations of a and b and temperature. the final values of these variables will appear in the "final ca", "final cb" and "final t" dialog boxes. the user can propose a step size for the integration (10s is the default value). if the implicit euler method does not converge for this step size, the program reduces it until convergence can be achieved. the step size used is shown the "final step size (h)" box. k1 k2 engineering, technology & applied science research vol. 12, no. 6, 2022, 9414-9419 9417 www.etasr.com chew hernandez et al.: a user-friendly dynamic reactor simulator built in microsoft excel fig. 5. initial screen. fig. 6. user interface. fig. 7. run initial state and parameters. fig. 8. heating/cooling characteristics. the characteristics of the heating/cooling are set to the right of the interface (figure 8). if "adiabatic" is selected, no heat transfer is considered and when "with heat transfer" is chosen, dialog boxes become active so the heat transfer areas per unit volume for the cooling coil and steam jacket are entered. if the "with heat transfer" option is selected, fields become active for the user to specify how the cooling water flow and steam temperature are to be managed. when selecting the "open loop" option, the user must input a value for the water flow and steam temperature, which remains constant throughout the simulation. if the cooling does not begin at time zero, a cooling commencement time can be specified (figure 9). if the "closed loop" option is checked, the user should decide the temperature set point value management scheme: if the option "automatic" is active, the temperature set point follows the time-dependent path of (7). if "manual" is selected, the user inputs the temperature set point. additionally, the proportional gain (kc) and integral reset time (tau) of the temperature controller must be specified. fig. 9. control loop specification. the functionality of the interface (figure 6) is completed by the buttons "close", which closes it, "start simulation", which begins integrating the differential equations, and "details", which displays the problem equations. once "start simulation" is clicked, the interface hides and a progress bar appears (figure 10). the columns a-f of the excel sheet are cleared as the new results will appear there. fig. 10. progress bar. once the simulation is completed, the simulation interface reappears and a dialog box asks if the results are to be graphed engineering, technology & applied science research vol. 12, no. 6, 2022, 9414-9419 9418 www.etasr.com chew hernandez et al.: a user-friendly dynamic reactor simulator built in microsoft excel (figure 11). if "yes" is answered, the results are placed in the spreadsheet, and the graphs are updated with the most recent results (figure 12). if "no" is clicked, the dialog box disappears, and the user can read the final concentrations and temperature in the corresponding dialog boxes. fig. 11. "simulation completed" message. fig. 12. final charts. iv. conclusions as public education institutions receive taxpayer's money, they must use their resources efficiently, minimizing expenses that are perceived as unnecessary. due to this, some institutions have opted not to purchase simulator licenses, thus limiting their students' acquisition of the skills related to the usage of this type of software. as far as the steady-state simulation of chemical processes is concerned, this can be solved by using a simulator downloadable for free, as some of them have been extensively validated. this is not the case, however, for the simulation of processes in a dynamic or transient state, where there are no free simulators that have been sufficiently tested. however, higher education institutions in most countries have the necessary human capacities to produce their own process simulators. this paper argues, based on a set of typical institutional objectives, that this is a convenient alternative for schools, and illustrates how a dynamic simulator developed using the microsoft excel software, an everywhere present tool, looks like. it is hoped that this will encourage more institutions to develop their own dynamic process simulators. the main advantage of the shown simulator is its running on microsoft excel that is already widely used by most engineering faculties in developing countries, and so it can be used without purchasing another license. one of its shortcomings, compared to the most powerful commercial dynamic process simulators available (eg. hysys dynamics), is that it doesn´t show an animation of the real-time behavior of the variables, but rather calculates a response and then plots it. this, however, suffices for tuning of controllers and studying the dynamics of the system when faced with several disturbances, which are some of the main applications of simulation. finally, the presented simulator requires that the version of ms office its run in codifies macros in the visual basic programming language. this does not appear to be a serious limitation, as ms excel has maintained this condition in versions as old as office 95, and new desktop versions of ms office are projected to continue to use visual basic as their macro-programming language for the foreseeable future. however, cloud or web-based versions of excel (eg. in office 365) as well as open versions of office are transitioning to a java-script kind of language for macro programming, and the simulator in its current form cannot be expected to run in these programs. the simulator would need to be re-programmed in said languages, of made to run directly in a visual basic standalone programming suite. the basic simulation functionalities shown here, however, would be maintained in these changed simulator versions. references [1] "licenciaturas," tecnológico nacional de méxico. https://www.tecnm. mx/?vista=licenciaturas. 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[32] a. k. jana, chemical process modelling and computer simulation, 2nd ed. new delhi, india: phi learning pvt ltd., 2011. microsoft word 11-688-ed.doc engineering, technology & applied science research vol. 6, no. 3, 2016, 1029-1034 1029 www.etasr.com shukrie et al.: air distributor designs for fluidized bed combustors: a review air distributor designs for fluidized bed combustors: a review ahmmad shukrie energy sustainability focus group faculty of mechanical engineering universiti malaysia pahang malaysia shukrie@ump.edu.my shahrani anuar energy sustainability focus group faculty of mechanical engineering universiti malaysia pahang malaysia shahrani@ump.edu.my ahmed nurye oumer energy sustainability focus group faculty of mechanical engineering universiti malaysia pahang malaysia nurye@ump.edu.my abstract—fluidized bed combustion (fbc) has been recognized as one of the suitable technologies for converting a wide variety of biomass fuels into energy. one of the key factors affecting the successful operation of fluidized bed combustion is its distributor plate design. therefore, the main purpose of this article is to provide a critical overview of the published studies that are relevant to the characteristics of different fluidized bed air distributor designs. the review of available works display that the type of distributor design significantly affects the operation of the fluidized bed i.e., performance characteristics, fluidization quality, air flow dynamics, solid pattern and mixing caused by the direction of air flow through the distributors. overall it is observed that high pressure drop across the distributor is one of the major draw backs of the current distributor designs. however, fluidization was stable in a fluidized bed operated at a low perforation ratio distributor due to the pressure drop across the distributor, adequate to provide uniform gas distribution. the swirling motion produced by the inclined injection of gas promotes lateral dispersion and significantly improves fluidization quality. lastly, the research gaps are highlighted for future improvement consideration on the development of efficient distributor designs. keywords-fluidized bed combustor; air distributor design; swirling distributor; perforated distributor i. introduction fluidized bed combustion has been recognized as a suitable technology for converting a wide variety of fuels into energy. one of the key features offered by fluidized bed combustion is the reduced emission of so2 and nox. the noxious combustion products released from the combustion of hydrocarbon fuels are captured by the calcined limestone for easy handling and disposal. unlike many others energy conversion technologies such as gasification and pyrolysis, the combustion efficiency in a fluidized bed can reach up to 99% resulted from constant temperature distribution and adequate amount of oxygen supplied [1]. depending on the distributors design in a fluidized bed, different types of particles with different sizes and shapes can be used. for instance, the fluidized bed combustor (figure 1), which consists of the following: combustion chamber, distributor plate, bed pre-heater, gas outlet, and fuel feeding system, uses inert particles, usually alumina and river sands, as its bed materials. the inert materials are preheated to the operating temperature by the pre-heater, and this causes the particles bed to absorb and store high amounts of heat. fluidizing air is passed through the distributor plate, and when the air velocity reaches a particular point on which the gravity, the weight of the particle and the overall weight of the bed are balanced, the bed is suspended and exhibits a fluid-like property. then, the bed is said to be fluidized and the velocity at this particular point is the minimum fluidization velocity. one of the key parameters that affect the successful operation of fluidized beds is the type of the distributor plate. it is known that the efficient and stable operation of a fluidized bed is sensitively controlled by the design of the distributor [2, 3]. the hydrodynamics of flow in the dense phase, quality of gas dispersion, bubble size and its behaviour, gas-solids contacting, gas hold-up, residence time distribution of gas, solid movement and mixing pattern are some of the aspects that are affected by the distributor design [4, 5]. the objective of this paper is to give an overview on past and present works related to the characteristics of different distributor designs in fluidized beds. legend 1 blower 4 pressure tapping 7 screw feeder 2 air plenum chamber 5 bed/combustion chamber 8 cyclone 3 distributor 6 hopper of biomass solid fuel 9 exhaust fig. 1. schematic of fbc. engineering, technology & applied science research vol. 6, no. 3, 2016, 1029-1034 1030 www.etasr.com shukrie et al.: air distributor designs for fluidized bed combustors: a review ii. distributor designs figure 2 summarizes the various types of distributor designs available in the literature. the distributors are grouped based on the direction of air entering into the distributor (normal direction, lateral direction and inclined direction). each distributor’s functionality and its applications are discussed in detail in the following sections. a. normal direction of air entrance a wide range of distributor plates available are designed in such a way that they inject the air into the fluidized bed in a normal direction to the distributor plate. the main types are: (i) perforated plate (ii) sparger and (iii) sintered metal distributors. (i) perforated plate distributor perforated plate distributor consists of holes arranged in either square or triangular pitches that are distributed over the distributor’s area. the percentage opening area, or some might refer it as perforated ratio, is calculated by dividing the total number of holes area over the distributor area. the effect of distributor plates on the distribution of temperature profiles along the axis of the combustion chamber during the combustion of low density rice husk fuels in a fluidized bed was studied in [6]. two different distributors with perforated ratios of 2.6% and 7.6% were tested. the peak temperature points – as an indication for combustion of fuel particles were found at 25 cm and 60 cm above the distributors for 2.6% and 7.6% perforated ratio distributors respectively. the low bulk density of the fuel (rice husks) that prone to float to a certain height resulted to the increment of peak temperature profile in the freeboard area. however, no specific discussion pertaining on the effect of perforated ratio on temperature variation was highlighted by the authors. in [7] the importance of perforated ratios on the distributor and bed pressure drop, solid holdup, and gas-solid behavior was investigated. three different types of perforated distributors having 0.46%, 0.86% and 1.10% perforated ratios were investigated by utilizing the cfd simulation and comparison with experimental and available published data. the results showed that as superficial velocity progressed, the distributor pressure drop increased with decreasing perforated ratio due to increase of airflow resistance. however, solid circulation and gas-solid distribution was recorded more homogenous in the bed of 0.46% perforated ratio than that of 0.86% and 1.10%. the authors concluded that fluidization was more stable in the bed operated in the low perforated ratio distributor due to the pressure drop across the distributor being adequate to provide uniform gas distribution. (ii) sparger various sparger designs are available such as radial pipes and multiple rings [8-11]. air is uniformly distributed to all the holes through the main air inlet or header. comparison between different sparger configurations has been conducted by many researchers to find the optimum sparger type and design. for instance, systematic procedures for the selection of sparger design and type were highlighted in [8]. in that study, a new wheel-type sparger was proposed based on the finding that conventional type spargers provide highly non-uniform flow. more recently, the effect of entrance configurations on the flow field in an industrial fluidized bed reactor were the primary interest of some researchers [5, 12]. the computational fluid dynamics-population balance model (cfd-pbm) coupled model was implemented to investigate the effect of a sparger distributor on reactor performance. comparison of reactor performances in terms of bubble formation and dead zone formation were made with a perforated distributor. the image processing analysis of the bubble phase show that the bubble size distribution in the case of the sparger distributor was more uniform than that of the perforated plate. the cfd-pbm simulation results however showed that dead zones were spotted in the corners of the sparger distributor due to particles clustering. the authors concluded that the perforated distributor was found to be more advantageous than the sparger-type distributor. the jet formation above the perforated distributor due to the restricted air passages provides adequate driving force and thus eliminates the cluster formation, resulting in more heterogeneous flow field and better gas–solid interaction. fig. 2. summary of primary distributor designs available in the literature. engineering, technology & applied science research vol. 6, no. 3, 2016, 1029-1034 1031 www.etasr.com shukrie et al.: air distributor designs for fluidized bed combustors: a review (iii) sintered metal sintered metal distributor (smd) is made from multiple layers of woven wire mesh of comparatively small aperture and high open area ratio compared to perforated-type distributor. the effect of smd with different apertures and open area ratios on the fluidization quality of air dense medium fluidized bed separator was investigated in [2]. five smds of aperture sizes and open area ratios ranging from 5-10 μm and 25-40% were employed in the experiments. results showed that the quality and stability of fluidization over a wide range of air velocity was achieved by using a smaller aperture size of 5 μm smd with a bigger open area ratio of 40% due to the increase of pressure drop. the effect of different smd aperture sizes on the solid flow structure in a bubbling fluidized bed from [13] showed that there exist four solid flow patterns in a bubbling fluidized bed, influenced by the distributor aperture size and the bed aspect ratio (h/d). the solid flow patterns and behaviors were observed by using the positron emission particle tracking (pept) technique. five different aperture sizes: 1μm, 10 μm, 15 μm, 60 μm and 230 μm of open area ratios ranging from 24% to 30% were investigated with 1, 1.5 and 2 bed aspect ratios resulted in more than 25 sets of experiments. poor solid circulation patterns was observed with single unit bed aspect ratio fluidized bed operated with smd of 15, 60 and 230 μm aperture sizes. from the results, it was concluded that the desirable flow patterns in a fluidized bed that were very much related to particles’ kinetic energy were the combination of superficial air velocity, bed aspect ratio and distributor aperture size. b. lateral direction of air entrance some types of distributor plates are designed in such a way that the fluidizing air is injected into the fluidized beds in lateral direction. the main types are: (i) bubble-cap, (ii) nozzles and (ii) multi-vortex type distributors. (i) bubble-cap bubble cap type distributor consists of orifices attached with caps in the upper part of the orifice plate to avoid the accumulation of stationary solids and particles fall back. the fluidizing air is flowing through the holes in a lateral direction beneath the caps in a way that the solid fall through the holes is prevented by high velocity jets. the distributor free open area is low and results in high pressure drop through the distributor. the distributor effect at the bottom region of the fluidized bed during turbulent fluidization was studied in [14]. experimental results by using a bubble cap distributor showed that the axial flow structure at the bottom region of the bubbling fluidized bed was more stable. comparison was made with the perforated plate distributor that showed opposite pressure variation, though both having the same open area ratio and similar distributor pressure drop profile. the possible reason behind this was the jetting effect through the perforated holes and the formation of dead zones through the perforated interstices. the entrainment rate however was found to be higher in the perforated plate distributor than that of the bubble cap distributor given the same superficial velocity when operated at the transition region from bubbling to turbulent fluidization. this indicates that the bubble formation from lateral jets through the bubble cap reduce the entrainment rate compared to the perforated plate. motivated by the fact that none of the literature available pertaining on the performance of the distributors at higher operating temperature, sánchez-prieto et al [15] compared the performance of two types of distributors, bubble cap and perforated distributors up to 300oc operating temperature. considering that both distributors have a similar free open area of 0.8%, distributor pressure drop was found to be higher in the bubble cap distributor measured at ambient and higher operating temperatures due to a lower discharge coefficient compared to that of the perforated plate distributor. at the same air velocity, pressure drops for both distributors were recorded to decrease as the operating temperature increases due to the decrement of gas density. moreover, a new methodology was developed in designing the distributor plate for higher operating temperatures. the parameters that have shown to have significant effect on the distributor performance at higher operating temperatures were the distributor free open area ratio, the bed aspect ratio and the pressure drop ratio. however, no distinctive comparison regarding the effect of distributors on bed behavior particularly on particulate mixing operated at higher operating temperatures was made by the authors. (ii) nozzles the nozzles were either mounted on the distributor plate with inverted ‘l’ shapes or with some inclination angles. the significant difference between nozzles and bubble cap type distributors is that no caps are installed on top of the nozzles and the solely prevention method of particle fall back into the plenum is by the lateral jet flow from the nozzles. horizontal gas dispersion in a bubbling fluidized bed was investigated in [16] by using response surface methodology (rsm). three nozzle distributors with different open area ratios of 1%, 2.5% and 4% were employed in the experiments. three different sizes of glass beads of 360 μm, 460 μm and 545 μm were used as bed materials in a rectangular shaped bubbling fluidized bed. the horizontal gas dispersion was further compared with two other types of distributors; bubble cap and perforated fabricated with the same open area ratios as the nozzle distributor. the coefficient of horizontal dispersion was assigned as an objective function for the three types of distributors and was calculated from tracer concentration. the higher value of coefficient of horizontal dispersion implies better horizontal gas dispersion and thus better mixing. the perforated distributor was recorded to have a low value of dispersion coefficient for all operations. no distinctive difference observed in the dispersion coefficient between the nozzle and the bubble cap distributors at low operating velocity. at higher operating velocities the coefficient of horizontal dispersion for the nozzle type was higher compared to the bubble cap and perforated types. this suggests that the dispersion in the bubbling fluidized bed can be enhanced by increasing the operating velocity. authors concluded that the distributor design was the dominant factor for gas dispersion in the fluidized bed. engineering, technology & applied science research vol. 6, no. 3, 2016, 1029-1034 1032 www.etasr.com shukrie et al.: air distributor designs for fluidized bed combustors: a review computational fluid dynamics (cfd) simulation on the hydrodynamics of the bubbling fluidized bed gasifier with a nozzle-type gas distributor was studied in [17]. two cases of air distribution (one ideal and one realistic) with the nozzletype distributor were considered in their 3d cfd simulations. in the ideal case, uniform gas injection was located at the bottom of the fluidized bed (without considering the individual nozzle distributors). the realistic case, on the other hand, dealt with full scale nozzle geometry. the geometry was further simplified for cfd analysis. significant differences were recorded for the two cases in terms of solid volume fraction (svf), uniformity index (ui) and solid stack volume (ssv). gas flow streamline from cfd simulation showed that the gas flow was more uniform in the ideal case. svf was measured higher in the realistic case due to the non-uniform flow distribution where some dense and stationary solid zones were observed at the bottom zone of the fluidized bed, corners and between nozzle distributors. the ui along the fluidized bed height for the realistic case was lower about 5% than that of the ideal case. the ui of unity represents even solid distribution in a specified surface area. the ssv that measures the dead zones region was found lower in the ideal case. it was shown that the ssv has to be identified and minimized when modeling fluidized-beds with real distributors because it may lead to serious operating problems such as slugging and channeling due to blocking of distributors. modeling the fluidized bed with ideal air entering the system showed significant deviation from the real phenomenon. thus, the actual distributor geometry should be considered in modeling the air distribution in fluidized bed system. (ii) multi-vortex type distributors a novel multi-vortex distributor was introduced in [18] and it consisted of 38 unit of 1/6 inch outside diameter (od) tubes with different orientations arranged in a rectangular pitch. according to the authors, the proposed tubes would theoretically improve the horizontal momentum and eliminate the problem associated with dead zones at the surface of the distributor and at the bottom region of the bed. this would in turn intensify the lateral dispersion and improve mass transfer. the gas dispersion was compared to the conventional perforated plate distributor that consisted of 35 perforated holes of 2 mm internal diameter (id). the conversion efficiency, defined as experimentally measured conversion over the ideal maximum conversion, was used as a comparison parameter. conversion efficiency of unity attributed to better interfacial and axial dispersion. for all inlet velocities, it was found that the multi-vortex distributor improved the conversion effeciencies by 14.75% compared to the perforated plate distributor. an unexpected increase in bubble size however was observed in multi vortex distributor in a factor of 1.4 and 1.5 from visual and pressure fluctuation measurements. the authors argued that the increment of bubble size indicates an increment of mass transfer mechanism which was later associated with an increment of conventional and diffusional components by using multi-vortex distributor. however, no quantification was made by the authors to support the validity of the arguments. c. inclined direction of air entrance the inclined direction of air entering into the fluidized bed at an angle θ produces swirling air motion as a result of velocity u entering the bed which consists of two velocity components: ucosθ which is responsible for fluidization and usinθ that induced swirling air motion inside the fluidized bed. the main types of inclined distributors are: (i) annular inclined blades, and (ii) helical nozzle distributors. (i) annular inclined blades the annular distributor consists of blades arranged at α certain inclination angle. the overlapping length between the blades directs the air at the desired angle. the centrifugal force is a result of a swirling motion of bed material in a circular path which is imparted by the tangential component of air velocity due to the inclined angle of the distributor blades. the original idea of annular inclined blades for fluidized bed can be traced back to [19]. the annular inclined distributor consists of n number of overlapping sector-shaped blades. the performance of the distributor was evaluated as a function of number of blades and fraction free area. comparison was made with the sintered metal distributor by using a heat transfer coefficient between immersed heater and bed materials as an objective parameter. significant improvement of the heat transfer coefficient of the bed materials was achieved by using inclined blades compared to that of the sintered metal distributor at higher operating velocity. changing fraction free area from 1.2% to 4.1% seemed to have no effect on the heat transfer coefficient but changing the number of blades from 24 to 32 units showed a significant effect. moreover, the correlation that governs the heat transfer coefficient and the distributor geometry was developed. following the annular inclined distributor of ouyang and levenspiel, the work of some researchers was devoted to understand the hydrodynamics of swirling fluidized beds [2029]. the annular inclined blades of ouyang and levenspiel was modified into truncated sectors of a circle that resulted in arrangement of blades of annular inclined distributor [22]. varying the distributor angle (sector) from 12o to 15o and 18o was shown to have a significant effect on particle velocity [23]. generally, the particles velocity was reduced by 18% for every 3o angle increment. increment of the distributor angle makes the distributor sector to become wider thus results in higher surface friction due to larger surface area of particles in contact with the distributor sector. the inclined arrangement of blades was shown to move the air radially towards the peripheral of the bed. eventually an insignificant dead-region was created at the center region of fluidized bed that required the installation of a cone. in [20] it was reported that the installation of a central cone reduced the superficial air velocity from the distributor to the free surface of the bed due to the increasing cross section available for air flow. application of annular inclined distributors in the fluidized bed combustion are documented in the works of many researchers [25, 26, 30]. an innovative swirling fluidized bed combustor (sfbc) was used to burn 80 kg/hr rice husk of different moisture contents of 8.4% to 35% and 20%-80% of excess air [26]. the primary air for combustion was supplied through an annular inclined distributor that induced swirling engineering, technology & applied science research vol. 6, no. 3, 2016, 1029-1034 1033 www.etasr.com shukrie et al.: air distributor designs for fluidized bed combustors: a review flow motion in a combustion chamber. constant axial temperature profiles were recorded along the height of sfbc that reflects effectiveness of the combustion by using annular inclined distributor; in contrast to the inconsistent axial temperature profile recorded during the combustion of rice husk in [6] using a perforated plate distributor. it is thus anticipated that the swirling distributor holds promise for industrial fluidized bed applications. (ii) helical nozzle distributors a novel spiral helix nozzle distributor introduced in [31] was shown to induce swirling air motion as the air enters the fluidized bed. the swirling distributor consists of a 5 mm diameter rod with six-turn helical coil attached in a 10 mm diameter nozzle. besides producing a swirling air motion, the functionality of the helix was to retain the particles when the fluidized bed is at a de-fluidized state. the spiral helix nozzle was attached together with 61 perforated holes of 0.4 mm diameter on a 50 mm diameter distributor plate. different case studies were conducted on which the distributors were modified into three configurations: plain nozzle, lowered helix and flush helix. the formation of jets and bubbles from these configurations were observed and recorded by using ultra-fast magnetic resonance imaging (mri). the experimental results indicated that the swirling motion produced by novel helicaltype gas distributors promotes lateral dispersion and significantly improves the fluidization quality compared to a plain nozzle without a spiral. however, the presence of the helical coils in the distributor significantly increases the pressure drop across the distributor. iii. findings and research gaps the critical findings from the literature review are listed below:  1. the major factors which might affect the intensity of mixing include fluidizing velocity, particle size and arrangement of the gas flow through the distributor.  2. the parameters that have shown to have a significant effect on the distributor’s performance at higher operating temperatures were the distributor free open area ratio, the bed aspect ratio and the pressure drop ratio. 3. high pressure drop across the distributor is one of the major draw backs of the current distributor designs.   4. fluidization was more stable in the bed operated in a low perforated ratio distributor due to adequate pressure drop across the distributor to provide uniform gas distribution. 5. the swirling motion produced by inclined injection of gas promotes lateral dispersion and significantly improves the fluidization quality.  it is thus anticipated that the performance of the current fluidized beds can be further improved through the development of new distributor designs. moreover, the swirling motion produced by the inclined injection of air was shown to improve particle mixing. however, the current swirling distributor designs used overlapping blades that limits the application of fluidization only to larger bed size materials. besides, the recent attempt on inducing swirling flow by using helical coil was proven to increase the distributor pressure drop; which is a drawback in the distributor design. the fluidization was found more stable in the bed operated by a perforated distributor due to the adequate pressure drop across the distributor to provide uniform gas distribution. therefore, a new distributor design is in need by integrating the perforated and swirling distributors. considering most of the fluidization processes are operated with pressurized air as a working fluid, attempts have to be made in future studies to investigate the effect of different distributor designs on the hydrodynamics of the fluidized bed operated by a low pressure blower. iv. conclusion overview on past and present works related to the characteristics of different distributor designs in fluidized bed were critically reviewed and discussed in this paper. the parameters that affect the performance of fluidized bed were identified and research gaps pertaining to the distributor designs were highlighted for improvement consideration on future developments of distributor designs for fluidized bed combustors. this review indicated that the efficient operation of a fluidized bed is dependent on distributor performance, which, in turn, is dependent on the design parameters of the distributor. in general, the incorporation of the right distributor design in a fluidization operation would represent inexpensive means to offer better economic and technical performance for future developments of fluidized bed combustors. acknowledgment the authors wish to express their gratitude to the faculty of mechanical engineering and research and innovation department, universiti malaysia pahang for providing the research facilities and supporting the research under university research grant rdu140355 and post graduate research scheme (pgrs) grs140346. references [1] j. han, h. kim, w. minami, t. shimizu, g. wang, "the effect of the particle size of alumina sand on the combustion and emission behavior of cedar pellets in a fluidized bed combustor", bioresour. technol., vol. 99, pp. 3782–37866, 2008 [2] x. yang, y. zhao, z. luo, z. chen, s. song, “effects of sintered metal distributor on fluidization quality of the air dense medium fluidized bed”, min. sci. technol., vol. 21, pp. 681–685, 2011 [3] k. vakhshouri, j. r. grace, “effects of the 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technical education, india mkavitha@jssateb.ac.in (corresponding author) s. akhila b.m.s. college of engineering, india akhilas.ece@bmsce.ac.in anand kannan texas instruments india private ltd, india anandk@ti.com received: 15 december 2022 | revised: 31 december 2022 | accepted: 3 january 2023 abstract the recent developments in biosignal acquisition devices for continuous supervision of cardiovascular signs of high-risk patients require a high-precision and low-power analog front end (afe) circuit. the proposed design adopts continuous-time (ct) sigma-delta modulator (σδm) architecture to achieve high resolution and signal-to-noise and distortion ratio (sinad) requirements. the proposed modulator is a second-order ct-σδm with cascade of integrators feed-forward (ciff) architecture that consists of a ct loop filter, a single-bit quantizer, and a digital-to-analog converter (dac). the use of single-bit quantization in the design reduces circuit complexity and power consumption. to use the designed σδm for measuring ecg signals, a bandwidth (bw) of 150 hz is considered with a sampling frequency (fs) of 153.6khz to achieve an oversampling ratio of 512. the design is simulated in a standard cadence virtuoso eda tool at 180nm cmos technology, operating at 1.8v supply voltage at the block level. the simulation results for the designed modulator show that sinad is 104.5db, the effective number of bits (enob) is 17.06bits, with power consumption of 24µw, and achieves schreier’s figure-of-merit (fom) equal to 172.45db. keywords-sigma delta modulator; continuous-time; quantizer; dac i. introduction innovations in communications and advances in cmos technology along with low power design techniques have given impetus to the research in devices intended for the acquisition of biopotential signals. these signals are very weak, having amplitude and bandwidth ranging from µ v to mv and from dc to a few khz [1]. typical biopotential acquisition systems for acquiring signals such as electroencephalogram (eeg), electromyogram (emg), electro-cardiogram (ecg), electrooculogram (eog), as shown in figure 1, consist of an instrumentation amplifier (ia) to provide adequate gain with low noise, a low-pass filter (lpf) to confine noise bandwidth and an analog-to-digital converter (adc) that interfaces the afe and the digital processing unit. several architectures to design the ia for the afe of a biopotential signal acquisition have been reported using techniques such as three operational amplifiers [2], differential difference amplifier [3], capacitively-coupled chopper [4], and current-balancing ia [5]. all these techniques have their own advantages and limitations. the lpf circuit designed using ota-c continuous-time filtering [6] operates in the sub-threshold region to save power for portable ecg signal detection and a second order lpf [7] is used with low noise and low power for programmable afes. adcs also play a significant role in biosignal acquisition and health monitoring integrated circuits [8]. adcs that are most commonly used for the ecg signal acquisition are successive approximation register (sar) and oversampled adcs. sar adcs have moderate accuracy and excellent power to performance ratio, but low resolution of 8 to 12 bits [9, 10]. higher resolution sar adcs need high engineering, technology & applied science research vol. 13, no. 1, 2023, 10128-10133 10129 www.etasr.com kavitha et al.: design and implementation of a second order continuous-time σδ modulator for ecg … resolution feedback dacs, resulting in increased area and power consumption. σδ adcs are oversampled converters, comprising of either a switched-capacitor (sc) or a continuous-time (ct) σδ modulator. a state-of-the-art sc implementation provides high precision and accuracy but due to switched integrators it suffers from stringent settling and slew requirements that lead to more power consumption [11, 12]. compared to sc, ct architecture consumes less power due to inherent anti-alias filtering that obviates the need for a dedicated analog filter required in the signal acquisition system. in order to attain high resolution, wide dynamic range and low power consumption ctσδms are used with active integrators [13-15]. active rc and gm-c based are the two types of ctσδm structures. this paper discusses the implementation of ctσδm with active rc integrators, summer, quantizer, and resistive dac. the designed modulator exhibits sinad of 104.5db and enob of 17.06bits. the experimental results are aligned with mathematical model and simulations. fig. 1. block diagram of a biopotential acquisition system. ii. design methodology the proposed work uses the top-down hierarchical design of σδm synthesis methodology shown in figure 2. fig. 2. design methodology flow graph. a. modulator specifications for acquiring the ecg signal, the system-level specifications of σδm are set to achieve enob of 16-18 bits, snr > 100db with sampling rate fs of around 150khz and signal bandwidth bw of 150hz. b. architecture selection the design starts with the selection of the noise transfer function (ntf) and the modulator architecture with parameters such as the oversampling ratio (osr) and the order of the modulator (l) and n-bit quantizer. the value of osr or clock rate is constrained by technology node and power consumption, which varies between 8 and 512 [16]. higher order modulators having l > 2 improve the snr significantly, but with an increase in circuit complexity and deterioration of stability. hence, the proposed design aims for a lower order modulator with higher osr. the single-bit quantizer is intrinsically linear without mismatch in the quantization step, whereas the multibit quantizer exhibits mismatched quantization steps but has low in-band quantization noise and allows a more aggressive ntf with higher out-of-band gain (obg), reduced sensitivity to the clock jitter, and lower slew rate requirements from the loop filter [17]. according to the rule-of-thumb [18], for a single-bit quantizer to ensure stability the value of obg must be about 1.5 and for a multibit quantizer between 1.5 to 3.5. higher values of obg cause overloading of the quantizer resulting in modulator instability. c. ntf synthesis σδm employs a ntf implemented using the high-pass butterworth or inverse chebyshev transfer function, having a cut-off frequency located outside the signal band. considering the parameters osr, l, n, obg, optimization value and type of filter, the ntf is determined using schreier’s matlab delta-sigma toolbox [19]. for an ideal l th order system, the ntf is given by (1 − z −1 ) l with all poles located at z = 0 and zeros at z = 1. spreading these zeros within the signal band and moving the poles within the unit circle, significantly improves sqnr and stability. the modulator becomes unstable if system poles move out of the unit circle. d. coefficient generation ntf is realized to obtain ctσδm coefficients for feedback (fb) and feedforward (ff) form topologies. each of them is further distinguished by two different forms to generate four topologies cascade of resonators fb (crfb), cascade of integrators fb (cifb), cascade of resonators ff (crff), and cascade of integrators ff (ciff).the fb structure consists of several dacs that fed back to all the integrator output and does not require a large summer before the quantizer. in ff structure, a single dac is required in the fb path without excess loop delay compensation, which is more area efficient [20]. the other advantage of the ff structure is the reduced output swing of the first integrator. given a certain output range, the first integrator allows a bigger loop gain and hence lower performance requirements on the following stages. however, the ff architecture requires a multi-input adder to sum all the ff branches before the quantizer. in the current work, a ctσδm with ciff architecture is implemented with its state-space representation as shown in figure 3. the ctabcd matrix is given by (1) along with its description in table i. [abcdc] = (1) engineering, technology & applied science research vol. 13, no. 1, 2023, 10128-10133 10130 www.etasr.com kavitha et al.: design and implementation of a second order continuous-time σδ modulator for ecg … ʃ + dac uc x1c ẋ2cẋ1c vc x2c yc ʃ+ fs fig. 3. state-space representation of the ctσδm. table i. description of the abcdc matrix based on (1), the obtained block diagram of the 2 nd order ctσδm with ciff is as illustrated in figure 4. fig. 4. block diagram of the second order ctσδm with ciff. e. system level simulation the behavioral simulation is performed using matlab excluding circuit noise to determine the key parameters and individual block specifications. to use the designed σδm for measuring ecg signals, bandwidth of 150hz is considered with a sampling frequency of 153khz. for osr=512, l=2, n=1, obg=1.5, opt =1, the pole-zero plot by which design stability is verified and the frequency response of ntf is illustrated in figure 5. the pole-zero map of the 2 nd order system has two complex conjugate poles (marked with x) and two zeros (marked with o) at dc that suppress the in-band quantization noise. frequency response shows that the obg is 3.438db (1.5). the resulting ntf is given by: ntf (z) = ������� ����.�� �� .��� (2) the time domain response of σδm with a two-level quantizer is shown in figure 6. for a sinusoidal input, the output is pulse-density modulated. the density of the pulse output waveform varies with input amplitude. the frequency domain response of the designed ctσδm is shown in figure 7 in which the power is maximum at the input frequency of the signal and it clearly exhibits 2 nd order noise-shaping with a slope of 40db/decade. the σδm achieves high resolution by the combination of oversampling and noise shaping. for the designed modulator, the matlab simulation depicts in-band snr of 103.85db at input amplitude of 0.5v with enob of 16.96 bits as shown in figure 7. fig. 5. left: pole-zero plot, right: ntf frequency response. fig. 6. time domain plot of input and output with 2-level quantizer. fig. 7. measured output spectrum. the obtained value of peak snr of 122.7db at -1.7dbfs input signal with dynamic range of 120db is shown in figure 8. the values of in-band snr and enob for different values of osr of 2 nd order ctσδm is shown in figure 9. it’s observed that snr increases with osr at the rate of approximately 13db/octave. matrix & order function representation a l×l loop filter interconnects 0:no fb connection from x1c toẋ1c 0: no fb connection from x2c to ẋ1c 1: x1c directly feeds ẋ2c 0: no fb connection from x2c to ẋ2c b l×l modulator i/p & the f/b dac o/p to the loop filter. 1: fb connection from uc to ẋ1c -1: fb connection from vc to ẋ1c 0: no connection from uc to ẋ2c 0: no fb connection from vc to ẋ2c c 1×l k coefficients, i/p from loop filter to the summer. k1: coefficient value from x1c to yc k2: coefficient value from x2c to yc k1 = 0.6667 k2 = 0.2288 d 1×l excess loop delay 0: no connection from uc to yc 0: no connection from vc to yc engineering, technology & applied science research vol. 13, no. 1, 2023, 10128-10133 10131 www.etasr.com kavitha et al.: design and implementation of a second order continuous-time σδ modulator for ecg … fig. 8. measured snr versus input level. fig. 9. psd of the modulator output with values of snr and enob for different osr values. f. macro model simulation and verification the obtained system-level behavioral model of the σδm architecture that satisfies the required specifications was translated into a macro model consisting of active and passive components in standard cmos technology using cadence spectre. ideal building blocks (clock generator, integrators, quantizer, and dac) [21] were used for validating the design architecture. the schematic of the single-ended 2 nd order ct active rc type σδm is shown in figure 10. fig. 10. schematic of single ended 2nd order ctσδm. the schematic is composed of a single-loop, ciff structure, and single-bit feedback dac. active integrators are used to obtain the low power 2 nd order ct system, veriloga model for a single-bit quantizer, and resistive dac. ideal switch and reset signal are used across the integrator capacitors at the beginning of the simulation. when the reset is high, the switch is shorted and sets the dc voltage on the integrator output. the values of the active rc integrators are calculated by using the sampling frequency fs. the summer circuit is designed using the k-coefficients. the designed values are r1 = r2 =100kω, c1 = c2 = 66.67pf, rf = 100kω, r11 = 150kω, r21 = 437.06kω. the simulation of the designed modulator with macro models is carried out using the components from analoglib and ahdllib of cadence for a signal with input amplitude of 0.25v, 150hz bandwidth, and 153.6khz sampling frequency. the swing of integrators, summer, quantizer, dac before scaling is shown in table ii. before scaling, the integrator outputs were saturated having values more than the supply voltage, hence through scaling the output voltage levels were reduced. g. dynamic range scaling an integrator's output doesn’t respond to changes in its input if it saturates. in order to avoid integrator saturation, the loop filter coefficients were scaled without modifying the loop filter transfer function. this is referred to as dynamic range scaling. the values of active rc integrators are calculated using (3) where fs is the sampling frequency and α and β are scaling coefficients. fs = � � ��� and fs = � � ��� (3) the weighted addition of the integrator outputs is carried out using a summing amplifier. the design of the summing amplifier is calculated using the k-coefficients obtained from table i. k� | = �� � ; r11 = � �� | (4) k� | = �� �� ; r21 = � �� | (5) the lower and upper limits for r and c are set by the matching consideration and thermal noise level that is fixed by the overall dynamic range requirements. table ii shows the value of the output swing across different blocks before and after scaling. it is clear that after scaling the voltage levels are reduced, maintaining the desired snr. the obtained parameter values before and after scaling are shown in table ii. table ii. output values before and after scaling. parameters before scaling after scaling integrator-1 -0.375 to 2.19v 0.46 to 1.34v integrator-2 -0.94 to 2.69v 0.32 to 1.42v summer 0.023 to 1.69v 0.20 to 1.56v quantizer 0 to 1v 0 to 1v dac 0 to 1.8v 0 to 1.8v signal power input -12.04 -12.04 signal power output -17.15 -17.15 sinad input 234.8 234.8 sinad output -13.97 -13.97 sinad 102.02 104.5 enob 16.65 17.06 engineering, technology & applied science research vol. 13, no. 1, 2023, 10128-10133 10132 www.etasr.com kavitha et al.: design and implementation of a second order continuous-time σδ modulator for ecg … iii. second-order ctσδm the proposed modulator is a 2 nd -order ctσδm with ciff architecture that consists of a ct loop filter, single-bit quantizer, and resistive dac as shown in figure 11. fully differential architecture implementation minimizes even-order harmonics and common-mode noise [22]. the circuits implemented with active rc integrators are highly linear, insensitive to parasitics, and simple to design. the first stage processes in-band and dac signal. the designed values of the first stage integrator input resistance r1 and capacitance c1 are 100kω and 161.8pf respectively. in order to reduce power and to enhance the linearity of the modulator, r1 is maximized up to the input-referred thermal noise, pn given by: pn = 8ktbw�r� + r��� � � ���� + � ���,!"� #1 + � ���% �& (6) where k, t, b, rdac, gm,ota represent the boltzmann constant, the absolute temperature, signal bandwidth, feedback dac resistors, and amplifier input transconductance, respectively. the values of the 2 nd stage integrator r2 and c2 are 200kω, 41.89pf, respectively. fig. 11. schematic of the fully differential 2nd-order ctσδm designed with active-rc type. the summing amplifier uses the resistors rf = 80kω, r11 = 61.8kω, r21 = 143.26kω designed using (4) and (5) ff coefficients. switched-resistor feedback dac, rdac, is chosen to be equal to r1 for better matching performance that provides less noise [23] than the current-steering dac. iv. measurement results the presented modulator has been implemented in 180nm cmos technology at 1.8v supply voltage, for applied input of a sinusoidal signal of 45hz with input amplitude of 0.25v and sampling frequency of 153khz achieving osr of 512. for hanning window of 16384-points, the block level simulation depicts sinad of 104.5db with enob of 17.06 with a power consumption of 24µw and achieves schreier’s figure-of-merit of 172.45db. table iii shows the performance comparison of the proposed work with other known methods, showing an increase in the values of sinad and enob. v. conclusion this paper proposes the ctσδm design for the acquisition of ecg signals. the cascade of integrators with ff is opted for the implementation of loop filter, with active-rc integrators and resistive feedback dac that reduces noise and power dissipation. the set target of enob is attained by the systematic coefficient generation using matlab and the loop filter coefficients scaling using the cadence eda tool. the designed modulator implemented in 180nm cmos technology with signal bandwidth of 150hz, high osr of 512 has sinad of 104.5db and enob of 17.06 achieving around 10% increase in comparison with existing techniques. the modulator consumes 24µw power from 1.8v supply and achieves schreier’s fom of 172.45db. table iii. ctσδm performance comparison reference [15] b [24] a [21] a proposed year of publication 2021 2018 2012 technology [nm] 180 180 180 180 bandwidth 2khz 200hz 20khz 150hz osr 256 256 512 512 sinad in db 94.28 96 87.3 104.5 enob * 15.37 16 10 17.06 power 32.34 µw 24µw foms ** 177.9db 172.45db **foms in db = sinad + 10log10 # '()*+,-%, *enob = ./012��.34 4. � , a block-level simulation, b 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[24] n. beigh, a. hamid, f. beigh, and f. ahmad, "2nd order sigma delta modulator design using delta sigma toolbox," asian journal of electrical sciences, vol. 7, no. 2, pp. 41–45, sep. 2018. microsoft word etasr_v13_n1_pp9932-9940 engineering, technology & applied science research vol. 13, no. 1, 2023, 9932-9940 9932 www.etasr.com mas'ud: the combined effect of current boosting and power loss on photovoltaic arrays under … the combined effect of current boosting and power loss on photovoltaic arrays under partial shading conditions abdullahi abubakar mas’ud department of electrical engineering, jubail industrial college, saudi arabia masud_a@rcjy.edu.sa (corresponding author) received: 24 september 2022 | revised: 23 october 2022 | accepted: 25 october 2022 abstract this study proposes a novel technique for improving the performance of photovoltaic (pv) arrays under partial shading conditions (pscs). a 4×4 solar pv array with 16 panels was considered. bridge-linked (bl), total cross-tied (tct), honey comp (hc), one cross-link (ocl), and two cross-link (tcl) were among the topologies of interest. first, the combined effect of connecting switches and partial shading on the pv array was studied. then, the power loss/gain caused by reconfiguring the pv array structure from series-parallel (sp) to other schemes was investigated. finally, a method of boosting current into the pv array is proposed to reduce pscs-related power losses in the connecting switches. the results show that the number of connecting switches in the topology plays an important role in determining power gain or loss at different partial shading levels. tct and hc outperformed the others in terms of power improvement when pscs were considered without current boosting. this is true for different levels of solar irradiation exposure. the sp topology is optimal when the solar irradiation level is greater than 900w/m 2 or less than 200w/m 2 . tct outperformed the others when the current was boosted in the pv array, with a power improvement of 108%, for certain pscs. keywords-partial shading conditions; photovoltaic; total cross-tied; bridge coupled; honeycomp i. introduction it is widely accepted that the global electricity demand is increasing rapidly, but the amount of fossil fuels available for power production is limited [1, 2]. on the other hand, fossil fuel emissions contribute to environmental pollution [3, 4]. as a result, renewable energy sources for power generation are widely advocated. among these, solar photovoltaic (pv) technology has advanced significantly during the recent years [5, 6]. so far, it is one of the most imaginative developments, with the highest probability of dominating the renewable energy (re) market [7]. because of their low maintenance, zero pollution, and low-noise characteristics, pv systems have a wide range of applications, including solar vehicles, streetlights, and other hybrid energy systems [8, 9]. on the other hand, the output characteristics of pv panels are primarily determined by temperature and irradiance, and they are frequently unpredictable [9, 11]. when pv modules experience partial shading, they are not exposed to the same amount of irradiance. this results in inconsistent module characteristics [11]. partial shading conditions (pscs) occur when some modules in a pv array are shaded by trees and buildings and this results in the reduction of the voltage and current of the afflicted panel [12-15]. the panel that generates the least amount of electricity will act as an electrical load drawing energy from the system’s other modules [14, 15], resulting in a decrease in the overall power output. partial shading can be reduced by selecting appropriate pv topologies or physically reconfiguring pv modules, as well as employing maximum power point tracking (mppt) technologies. the most common configurations for pv arrays are honeycomb (hc), series-parallel (sp), total cross-tied (tct), and bridge-link (bl) [20-21]. under various pscs, the tct has the lowest mismatch losses and the highest power output. in [20], it has been shown that the tct configuration does not deliver the maximum power possible when operating in partial shading and the extracted output power can be further increased [20]. several researchers have investigated different techniques to reduce mismatching power losses in pv arrays [5, 17, 2333]. authors in [27] compared large interconnected sp array schemes operating under pscs [27]. these combinations were modeled and analyzed in matlab/simulink, and the results were validated experimentally. the result indicates that the global maximum power point (gmpp) depends on the shading pattern and the architecture of the pv array. authors in [22] developed a modified bypass circuit that effectively finds a compromise between the increased reliability and the increased complexity of the pv array. the results were validated experimentally. the bypass circuit worked well in lowering the hot spot temperature of the cryptic cell below the average engineering, technology & applied science research vol. 13, no. 1, 2023, 9932-9940 9933 www.etasr.com mas'ud: the combined effect of current boosting and power loss on photovoltaic arrays under … temperature of the module without significantly increasing the complexity of the system. genetic algorithm [33], particle swarm optimization [34], mine blast optimization [35], cuckoo search [36], and ant colony optimization [34] are other examples of optimization techniques deployed for minimizing losses under pscs. recently, authors in [23] proposed an improved technique to enhance the performance of the pv array technologies (pvat) under pscs. the study takes into account 8 shading patterns. to combat partial shading, 6 novel pvats based on specific array configurations were presented. the simulation results were compared to those obtained with conventional pvats, and the best topologies for different pscs are determined. the tct typically achieves maximum power extraction from pscs. it also enhanced pvat output power for short and wide psc by 105%. the performance of the tct was enhanced in another investigation employing the minimizing losses technique [25]. different arrangements were introduced by reducing the number of connecting switches. the pv module configuration was altered to generate 5% more power in pscs. if 50% or more of the area was partially shadowed, no reconfiguration was required. when the darkened region was less than 50%, reconfiguration significantly increased power. many studies have developed pv reconfiguration strategies that can reduce the impact of pscs on pv arrays. however, one aspect that has yet to be investigated is the way pv arrays perform under pscs, when both current boosting and switch losses are considered. a pv array reconfiguration, on the other hand, necessitates an increase in the number of switches, resulting in increased switching power loss and the need for more current to be boosted during pscs. therefore, in this paper, a novel strategy for minimizing losses in pv arrays under pscs is presented. the approach involves boosting the current in the partially shaded sections of the pv array. to obtain a more robust result, current losses in connecting switches are also considered. a 4×4 pv array with 4 shading patterns was investigated, and all simulations were performed in matlab/simulink. configurations of interest include sp, tct, hc, bl, ocl, and tcl. ii. materials and methods a. modeling of the pv array the pv cell is the most important part of a pv system because it converts energy from the sun to electricity [38, 40]. the amount of electricity produced by a pv module or cell is primarily determined by temperature and solar irradiation. because of its higher accuracy in obtaining the shunt and series resistances, the single diode model of a pv cell has been used in pv modeling [28, 42]. a pv module is a grouping of pv cells connected in series, whereas a pv array is a grouping of pv modules connected in series or parallel, as well as a slew of others [21, 43]. equation (1) depicts the mathematical representation of the current-voltage (i-v) characteristics for an ideal pv cell model with a terminal current [29].   0 exp 1 s sh pv b sh q v r v r i i i ak t r               (1) where i0 represents the saturation current of the diode, ipv represents the current of the pv, v represents the pv module’s terminal voltage, a represents the identity factor, kb is the boltzmann's constant, q represents the electronic charge, rs represents the series resistance, t represents the junction temperature, and rsh represents the shunt resistance. the 4×4 pv module is designed in matlab/simulink using a single diode pv model. equation (2) describes the i-v characteristics of a pv array composed of np parallel and ns series-connected modules [41]. exp 1 pv p s s s s p p r p sb sh p i i n n n q v r i v r n n i n nak t r n                          (2) where i represents the diode reverse leakage current. the parameters of the 25w blue solaria pv module that was used to model the pv array schemes are listed in table i. table i. parameters for the 25w solari pv module s/no parameters values 1 maximum power of the pv 25w 2 short circuit current of the pv(isc) 1.45a 3 open circuit voltage of the pv (voc) 22.2v 4 current at the maximum power 1.37a 5 the voltage at the maximum power 18.2v 6 the temperature coefficient of voc -0.34%/ oc 7 cells per module 40 8 cells per module 40 9 temperature coefficient of isc 0.041%/ oc 10 rsh 1114.063ω 11 rs 0.9635ω b. proposed pv module configuration to reduce the partial shading impact, pv array arrangement is critical. a proper array arrangement must be adopted to produce the necessary power output improvement from the pv array system. some of the most commonly used pv array configurations in the literature are sp, tct, bl, and hc [42]. among them, the sp (see figure 1(a)) is the most widely used. under the pscs, the sp scheme is the most effective against mismatch power losses in series strings. to minimize mismatch power losses in series strings, alternative tie connections are inserted between the parallel strings of a sp scheme. they are designed in the bl, hc, and tct configurations. figure 1(b) is the bl scheme. the pv modules resemble a bridge rectifier arrangement. one drawback of the bl arrangement is that it performs poorly under pscs. the tct configuration is shown in figure 1(d). to design the tct arrangement, cross ties must be connected between each module in the sp scheme. these cross-links connect the modules in the array arrangement. engineering, technology & applied science research vol. 13, no. 1, 2023, 9932-9940 9934 www.etasr.com mas'ud: the combined effect of current boosting and power loss on photovoltaic arrays under … (a) (b) (c) (d) (e) (f) fig. 1. pv array schemes considered: (a) bp, (b) bl, (c) hc, (d) tct, (e) ocl, (f) tcl. the cross ties help reduce mismatch losses in the shaded module's series string by providing an additional current channel. tct, on the other hand, suffers from high initial installation costs and cable losses due to the extensive interconnections. to reduce these losses, some interconnections can be disabled and set to either hc or bl. in this study, two additional schemes will be considered, i.e. one and two crosslinks in the sp configurations (see figure 1(e)-(f)). previous research did not consider non-ideal switches between crosslinks, particularly during pv shading mitigation using the current boosting method [23]. due to the fact that these switches can result in additional power losses during pscs, the purpose of this study is to examine the possibility of incorporating crosslink switching into the current boosting procedure. in this instance, a more reliable result will be obtained. (a) (b) (c) (d) fig. 2. shading patterns on the pv scheme. cases (a) 1, (b) 2, (c) 3 (d) 4. engineering, technology & applied science research vol. 13, no. 1, 2023, 9932-9940 9935 www.etasr.com mas'ud: the combined effect of current boosting and power loss on photovoltaic arrays under … c. proposed partial shading schemes when pscs occur, portions of the pv array will not receive the required level of irradiance. as a result, the shading scenario is unpredictable. as shown in figure 2, four shading conditions will be considered to analyze the partial shading effect on the 4×4 pv modules:  case 1: a single pv module is shaded.  case 2: two pv modules are shaded.  case 3: four pv modules are shaded  case 4: four pv modules are shaded (diagonally). as previously stated, this study investigates the effects of shading on pv modules at 40°c with varying amounts of irradiance. under the same conditions, when the pv array is uniformly shaded, the irradiance value of all 16 modules is exactly 1000w/m2. solar radiation reduction from 900w/m2 to 100w/m2 will be considered for all pscs. each model ran with a load of 13.2ω. iii. current boosting procedure a current boosting strategy has been proposed in [14] which improves pv power during pscs. however, the current boosting procedure for different schemes has not been well investigated. a more in-depth analysis will be provided in this study. in this study, the current is directly boosted across the partially shaded panel, with a bypass diode connected across all pv modules to provide a low resistance path for the flow of any current, thereby improving the gmpp. although using bypass diodes increases the cost and complexity of any pv array, it can significantly improve power during pscs. previous research has shown that under pscs and with bypass diodes, the gmpp for sp, tct, hc, and bl pv topologies is 21.54%, 52.74%, 16.09%, and 20.78% higher than what it would be in a scheme without bypass diodes [32]. the bypass diodes across a pv panel can cause peaks in the p-v characteristic curve but are not detrimental to the system. in this study, the bypass diode was utilized. figure 3 depicts the current boosting schemes for each of the considered topologies. equation (3) is a generalized equation that shows the current produced by a pv module in a tct architecture [14]. , 1ni ni g stc g i i i d g     (3) where n denotes the number of rows and d the number of pv panels. gstc denotes irradiation at standard temperature conditions, whereas gni denotes irradiation received by a pv panel. ig denotes the maximum current generated by a pv panel under stcs. the total current generated in each row is the sum of the currents generated in each pv module in that row. the mismatch current in the tct topology is the difference between the total current under pscs and the peak value of the current without pscs. the mismatch current will be boosted across the specific row to improve power during the current boosting procedure. the current is boosted across the shaded rows on the tct topology at every instant, based on the partial shading situation, as shown in figure 3. the boosted current scheme cannot be implemented in the other topologies shown in figure 3 (bl, hc, ocl, and tcl). in this case, regardless of the shaded pv panel in the topology, the current will only be boosted at specific locations. this is proposed to comply with circuit theory rules and to avoid boosting current in places where it is not required. because there are fewer interlink connections between neighboring strings in these topologies than in the conventional tct topology, mismatch losses are greater. however, the proposed scheme will only provide the best pv or i-v characteristic curve in tct configuration. (a) (b) (c) (d) fig. 3. current boosting scheme for a tct configuration under pscs. engineering, technology & applied science research vol. 13, no. 1, 2023, 9932-9940 9936 www.etasr.com mas'ud: the combined effect of current boosting and power loss on photovoltaic arrays under … (a) (b) (c) (d) fig. 4. current boosting schemes with connecting switches under pscs: (a) hc, (b) bl, (c) ocl, (d) tcl. iv. result and discussions matlab/simulink was utilized to simulate a 4×4 pv array with 5 different configurations (i.e. sp, bl, hc, tct, ocl, and tcl) and 4 different shading patterns (cases 1-4). first, the combined effect of connecting switches and partial shading on the power output of 5 pv topologies (bl, hc, tct, ocl, and tcl) was investigated. then, the power loss/gain caused by switching from sp to the aforementioned topologies was investigated. a current boosting technique was subsequently used to see if the performance of the pv array had improved. the ultimate goal was to use as few switches as possible in order to minimize switch loss. when partial shading occurs, this approach may be able to produce the best architecture in terms of peak output power. table ii shows a comparison of the proposed and existing pv topologies under 4 distinct pscs. in contrast to the current topology, the proposed method employs the boosting current strategy. table ii. the output power improvement of all schemes under various pscs switch combinations pv shading configuration gmpp(w) total boosted current (a) power improvement (w) existing scheme proposed scheme all switches closed (tct) case 1 266.72 350.21 0.79 84.49 case 2 263.9 344.13 1.64 80.23 case 3 132.11 370.2 5.528 228.09 case 4 259.13 337.32 3.4 78.19 switches 1.3,5,7,9 closed (hc) case 1 266.44 344.45 0.748 78.01 case 2 262.50 337.88 1.562 75.38 case 3 139.23 362.0 5 223 case 4 261.33 335 3.164 73.67 switches 1,5,6,7 closed (bl) case 1 265.99 336.4 0.75 70.41 case 2 263.53 337.60 1.6 74.07 case 3 208.57 356.70 4.432 148.13 case 4 219.76 323 3.68 103.24 switches 1,2 closed (ocl) case 1 274.65 330.33 0.69 55.68 case 2 264.87 340.989 0.77 76.12 case 3 228.20 326.50 1.1 98.3 case 4 212.32 360.17 1.254 147.85 switch 1 closed (tcl) case 1 275.11 328.39 0.66 53.28 case 2 263.91 338.49 0.79 74.6 case 3 228.75 321.93 1.09 93.18 case 4 212.611 357.77 1.16 145.16 first, the shaded pv module is assumed to have a solar irradiation level of 100w/m2, implying very low pv shading. when one of the 16 pv panels is shaded, the hc, tct, and bl configurations suffer more losses than the others, with the tcl arrangement appears to be the most efficient because the shaded pv module is at the end of the topology and the tct has more interconnecting switches than the ocl and tcl. furthermore, in case 1, the more connecting switches there are, the greater the power loss. for case 2, the power loss under pscs appears to be nearly identical for all topologies, with tcl appearing to be the optimum. because the shaded panels are in the upper left quadrant of the array, close to the two connecting switches, current may flow in a different direction during partial shading. case 3 appears to favor ocl and tcl, though bl outperforms tct and hc. this is an indication that the number of connecting switches increased the power loss of the complete system. this conclusion, however, does not apply to all pv shading situations. the tct and hc appear to perform best in case 4, where the shading appears in a diagonal form, demonstrating that the scheme's performance improves with more connecting switches. in general, it appears that the shading pattern in case 3 causes more power loss than the others. figures 5–8 show the percentage of power loss or gain when converting from sp to hc, bl, tct, ocl, and tcl configurations. solar radiation is varied between 900 and 100w/m2, and each shading pattern is investigated. it should be noted that the percentage of power loss/gain for bp is zero in all the figures because it was assumed to be the reference configuration. tct is the best configuration when switching from bp to the others in case 1 (figure 5), followed by hc. at 500w/m2, tct and hc improve power by 3% and 1.8%, respectively. engineering, technology & applied science research vol. 13, no. 1, 2023, 9932-9940 9937 www.etasr.com mas'ud: the combined effect of current boosting and power loss on photovoltaic arrays under … fig. 5. the percentage of power loss/gain when switching from sp to the other configurations in case 1. fig. 6. the percentage of power loss/gain when switching from sp to the other configurations in case 2. fig. 7. the percentage of power loss/gain when switching from sp to the other configurations in case 3. fig. 8. the percentage of power loss/gain when switching from sp to the other configurations in case 4. the solar radiation in the shaded module for case 1 should be between 200 and 700w/m2 for any power improvement in the tct and hc. tct is the best configuration for case 2 (figure 6), followed by tcl. power improvements of 1% have been made. in case 3 (figure 7), when reconfiguring from bp to tct, the tct appears to outperform the others. in this case, however, the hc performs nearly as well as the tct. this performance is only noticeable when the solar radiation on the shaded module exceeds 500w/m2. however, reconfiguration from bp to the other schemes below 500w/m2 results in a power loss of up to 50% for tct and hc and 10% for the bl. as a result, when reconfiguring pv modules under pscs, care must be taken because significant power losses are possible and thus detrimental at certain solar irradiation levels. ιn case 4, the tcl and hc appear to outperform the others at nearly all irradiation levels. as a result, it appears that this is an appropriate scheme for this type of partial shading. it is important to note that the tct can achieve maximum power improvements of 3%, 1%, 35%, and 42% for case 1, case 2, case 3, and case 4 shading configurations, respectively. when the boosted current values in table ii are examined, it is clear that the tct receives more boosted current than the others for all of the pv shading schemes considered. this is because a current is boosted in every row with mismatching power in the tct, whereas in the other cases, a current is boosted in specific rows regardless of shading location. despite the fact that the gmpp value will improve, one major disadvantage of non-uniform current boosting is the formation of numerous peaks in the characteristic curves. tct appears to be the best strategy in terms of power improvement when considering the proposed technique (see figure 9). case 3 shading pattern can improve power by up to 228w. the tct has more interconnecting switches than the others, and the mismatch current is enhanced in each row. figure 9 shows the proposed and existing p-v and i-v curves for tct in each of the 4 partial shading scenarios. the p-v curve of the proposed technique has fewer peaks than the existing technique, with power improvements of 31%, 30%, 108%, and 30.1% for case 1, case 2, case 3, and case 4, respectively. for cases 3 and 4, the proposed technique has one peak, whereas the existing technique has two peaks. engineering, technology & applied science research vol. 13, no. 1, 2023, 9932-9940 9938 www.etasr.com mas'ud: the combined effect of current boosting and power loss on photovoltaic arrays under … (a) (b) (c) (d) fig. 9. i-v curve of the (a) existing pv scheme, (b) proposed tct scheme. p-v curve of the (c) existing pv scheme, (d) proposed p-v scheme. despite a significant power improvement, the number of peaks in cases 1 and 2 is the same for both the existing and proposed techniques. in this study, the p-v and i-v curves for the other switching configurations (bl, hc, ocl, and tcl) were not shown, because the number of peaks does not change even with current boosting, and only power improvement is visible. the current boosting scheme, as described in the literature, cannot be implemented in the sp configuration [14]. according to the results of this study, reconfiguration of the bp scheme under pscs may not be required for certain solar irradiation levels. furthermore, current boosting will result in power gains relative to any of the commonly used pv topologies, i.e. tct, hc, bl, ocl, and tct, and the power loss in the connecting switches plays a significant role in the amount of current boosted during pscs. v. conclusion in this study, the effect of current boosting and power loss caused by connecting switches on the i-v and p-v characteristic curves of a pv array were investigated. matlab/simulink was utilized to simulate 4×4 pv array under various degrees of shade and shading patterns. the shading patterns of 4, 2, and 1 in 16 pv panels were investigated. power loss or gain as a result of reconfiguring pv panels from the bp to other configurations such as bl, tct, hc, ocl, and tcl has been studied in depth. the level of solar irradiation at which the pv array could be reconfigured was also evaluated. the results show that the number of connecting switches in the topology is an important factor in determining power gain/loss at various shading levels. the more connecting switches there are, the more power is lost, and more current is required to compensate for the power mismatch. tct and hc appear to outperform the others in terms of power improvement for the majority of the partial shading scenarios considered without current boosting. this is only true for certain solar irradiation levels. it has also been shown that, under certain shading patterns (case 4, diagonal shading), up to 50% of the power is lost when compared to the bp scheme. in the case of current boosting, tct showed greater power improvement than others because, in tct, current is boosted in every row with power mismatch, whereas in the other cases, current is boosted in specific rows regardless of the shading position. for a specific 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[42] y. j. wang and p. c. hsu, "an investigation on partial shading of pv modules with different connection configurations of pv cells," energy, vol. 36, no. 5, pp. 3069–3078, 2011, https://doi.org/10.1016/j.energy. 2011.02.052. authors profile abdullahi a. masud received his be degree in electrical engineering from ahmadu bello university (abu) in 1999. subsequently, he pursued his master’s degree in the same discipline at abu and graduated in 2003. he has also obtained a phd in electrical engineering in 2013 from the glasgow caledonian university, scotland, uk. in 2002 he became an assistant lecturer in the faculty of engineering at the ahmadu bello university, zaria, nigeria. in 2013 he joined jubail industrial college, saudi arabia, and is currently an associate professor in the department of electrical engineering. he has several publications in high impact factor journals and conference proceedings in high voltage partial discharge and renewable energy. he is a chartered engineer, a member of the iet, and a registered engineer (coren) nigeria. microsoft word etasr_v12_n4_pp8864-8871 engineering, technology & applied science research vol. 12, no. 4, 2022, 8864-8871 8864 www.etasr.com salman et al: enhancing voltage profile and power loss reduction considering distributed … enhancing voltage profile and power loss reduction considering distributed generation (dg) resources muhammad salman school of automation and electrical engineering lanzhou jiaotong university, china salmankhan5780@gmail.com hongsheng su school of automation and electrical engineering lanzhou jiaotong university, china shsen@163.com muhammad aamir aman faculty of electrical engineering university of engineering and technology peshawar, pakistan aamiraman@uetpeshawar.edu.pk yousaf khan faculty of electrical engineering university of engineering and technology peshawar, pakistan yousafkhalil@gmail.com received: 7 may 2022 | revised: 21 may 2022 | accepted: 25 may 2022 abstract-in recent years, distributed generation (dg) has received attention due to its benefits on the distribution network. in this paper, the influence of dg along with several techniques for mitigating the detrimental impact on voltage profile and power losses was examined. the test system of 132 kv residential test feeder was selected, examined, and modeled in the electrical transient analyzer program (etap). various tests were carried out to determine the influence of dg on the distribution network. results were compared with, and with-out dg, taking into account the voltage profile. when injecting dg with unity power factor at different buses in a radial test system, it was discovered that when the right dg size and type is injected at the ideal position, the voltage profile improves while the power losses are reduced. when an un-deterministic dg is injected at multiple points on the test feeder, no improvement in voltage profile was observed. when the cross sectional area of conductors is increased and a dg is injected at optimal locations, a positive impact on voltage profile is observed while a detrimental impact on power losses were also analyzed. these findings may be useful for many distribution firms regarding the future expansion of the power systems and the proliferation of dg. keywords-distributed generation; voltage level; power losses; synchronous and induction generator i. introduction electricity consumption is quickly expanding in all the sectors of global economy. currently, a number of factors are creating significant challenges to the power supply, including pollution, depletion of local energy supplies, and the need to improve the energy infrastructure. promoting the broad use of distributed generation (dg) is a strategy to fulfil the continually expanding demand for power [1]. the government's energy policy aims of reducing emissions, ensuring a dependable energy supply, and promoting competitive markets will all benefit from increased deployment of dg technologies. dg may work as a single construction, such as a home or a firm, or it can be part of a small grid (that is also linked to the larger power distribution network), e.g. at a huge industrial site, military base, or college campus [2, 3]. dg can support the distribution of clean, dependable power to additional consumers while also reduces power losses along the distribution and transmission lines when inserted to the electric utility's lesser voltage distribution lines. some of the benefits of installing dg include increased electric system reliability, improved power quality, reduced system energy loss, and improved voltage profile. dg can work both as conventional energy sources (non-renewable) and non-conventional energy sources (renewable) [4]. wind energy, pv energy, and small hydro energy are the most capable renewable energy resources in dg, while coal, petroleum, and natural gas are all nonrenewable energy sources [5]. nowadays the need for electricity is rapidly rising, while one of the most significant challenges for power and electrical engineers is to produce power from non-conventional energy sources in order to meet the rising demand while minimizing the environmental impact of power generation. however, whenever a new generation is linked with the power distribution system, issues come up because traditional distribution systems were built to run radially, without taking into account the new generation's future integration [6, 7]. using dg is necessary to assure reliable power generation and dropping power losses, while, on the other hand, extensive use of these technologies brings additional challenges to power systems such as voltage regulation, optimal location, and power loss issues [8]. the installation of dg may destabilize the system voltage and create over-voltage and volatility. if management is not appropriately achieved, the inserting of dg may raise the system losses in the distribution network, depending on the network structure, the penetration level, and the nature of dg technology [9, 10]. corresponding author: hongsheng su engineering, technology & applied science research vol. 12, no. 4, 2022, 8864-8871 8865 www.etasr.com salman et al: enhancing voltage profile and power loss reduction considering distributed … in this research paper, various cases are considered in order to see their effect on voltage level and power losses. six-bus bar distribution systems were considered as test cases. they were designed and examined in the electrical transient analyzer program (etap). firstly, results were obtained without the injection of a dg unit. this case is used as a model for the other cases. in the second case, a dg unit (synchronous generator) is injected at busbar-3 and in the third case a dg unit (synchronous generator) is injected at busbar-6. in the fourth case, a dg unit (induction generator/wind generator) is injected at busbar-3 and in the fifth case a dg unit (induction generator/wind generator) is injected at busbar-6. moreover, two more cases were considered as " injecting un-deterministic dg in a distribution system" and "increasing a cross sectional area of the transmission cable". the results were compared in order to determine the best dg size and location. ii. the impact of distribution generation the term "distributed generation" (dg) refers to energy generation close to the point of consumption. because of its good impact on the electrical distribution system, dg has received a lot of attention. dg has the potential to improve grid dependability by lowering transmission losses, providing greater voltage support, and enhancing power quality. because dg uses renewable energy resources, it has lower initial cost and reduces greenhouse gas emissions, resulting in more clean and efficient energy [11]. tiny combustion and micro turbines, micro steam turbines, battery storage, comparatively tiny hydro dams, photovoltaic (pv) panels, wind turbines, power storage systems, and other power generation technologies are being developed or are now in use [12]. distributed resources (drs) can reduce t&d system losses, enhance service performance and stability, improve voltage strength, and reduce t&d system crowding [13]. the connection of dg may vary the voltage level along a feeder by varying the direction and amplitude of actual and reactive power flows. furthermore, the effect of dg on voltage parameters might be positive or negative depending on the distribution network, the distributed generator features, and the dg site. due to the immense injection of active and reactive power, overvoltage may occur when dg units are installed along with power distribution feeders [14, 15]. dg is the best option to satisfy the increasing requirements of power and improve voltage profile. this is dependent on the dg injection site and the kind of dg that is to be inserted in the power system or grid. if a dg is inserted into the power system in an ad hoc manner, voltage profiles may vary [16]. dg has a big impact on power losses as well. dg must be properly coordinated with the distribution system in order to have a positive impact. because dg and its effect on the system are proportional to feeder requirements and ability, the injection of dg into the system should be precisely enhanced to avoid this kind of problems [17]. the dg is a significant standard that has to be examined in order to be able to get a better consistency of the system with reduced losses. dg has negative impact as well: if not injected in a proper way, it may result in power losses [8]. iii. mathematical modeling because of the slow changing nature of power networks, steady state analysis is used. in the steady state, disruptioninduced transients are supposed to be unchanged. the operational technique for the steady state analysis is called power flow analysis. the voltage magnitude and phase angle, as well as the flow of active and reactive power across the network at all buses, may all be found using load flow analysis. the newton-raphson method is discussed below as one of the approaches for solving the power flow equations. the approach begins by solving the issue with only two equations and two variables. after that, the study will be extended to the solution of the load flow equation. consider the following equation for a two-variable function za and zb equal to a constant ca as: f��z�, z� � = c� (1) f��z�, z� � = c� (2) c� = f��z� , z� � = f�� ���� + ∆ ����, z� + ���� � (3) c� = f��z� , z� � = f�� ���� + ∆ ����, z� + ���� � (4) expanding (3) and (4) in taylor’s series we have: c� = f� � ���� + ����� + ∆ ���� ������ � + ∆z� ��� ��� ������� ��� + …(5) c� = f� � ���� + ����� + ∆ ���� ������ � + ∆z� ��� ��� ������� ��� + . .. (6) �c� − f�� ����, �����c� − f�� ����, ������ = � ������ ������������ ������ ! ∆ ����∆ ����" (7) !∆#����∆#����" = j(0) ! ∆ ����∆ ����" (8) for a total of n buses, the intended voltage at any bus a and $% and &% are given as: '� = %()) *+�,-.�/)∗ − ∑ 2�3 '3435% 6 (9) $% − 7&% = �2�� '� + ∑ 2�3 '3435% � (10) $% ,7&% = '� ∗ ∑ 2�3/8435% (11) $%5'� ∗ ∑ 2�3435% '3 (12) &%5 − 9:; <'� ∗ ∑ 2�3 '3435% = (13) the voltage at bus and line entries in polar form is: '�5 |'�| < @�; '3 = |'3 | < @3; 2b3 = |2cd| < e�3 by exchanging these in (11): $% − 7&% = ∑ 2�3 '3 < e�3435% + @3 − @� (14) $%5 ∑ 2�3 '3435% #fg�e�3 + @3 − @� � (15) and: &% 5 − ∑ 2�3 '3435% ghd�e�3 + @3 − @� � (16) now by relating (8) with the power system we have: engineering, technology & applied science research vol. 12, no. 4, 2022, 8864-8871 8866 www.etasr.com salman et al: enhancing voltage profile and power loss reduction considering distributed … ∆#� ��� = ∆$% = $%ijkl − &%mbnl ∆#� ��� = ∆&% = &%ijkl − &%mbnl ∆ � ��� = ∆@� ��� ∆ � = o'� ���o the partial derivative of real and reactive power is contained in the jacobian "j." the following is the fundamental iterative procedure: • start with the previous case's outcome. • calculate the dispersion and stop when the acceptance value's bound exceeds it. • calculate the jacobian's power flow, update the value, and return to the previous step. iv. methodology in this research, different cases were analyzed/investigated. in the first case, the power flow was tested on the test scheme without injecting a dg unit. voltage profile and power losses on each bus bar were monitored. furthermore, synchronous generator and induction generator were injected on two optimum points which were selected by the hit and trial method, which resulted to finding that bus bar 3 and bus bar 6 were suitable for the installation of dg. furthermore, an undeterministic dg was injected and voltage level and power losses were monitored. as a result, disturbance occurred in the overall network. finally, the conductor's cross sectional area was raised, and the influence on voltage profile and power losses was noted. v. test cases a. case-1: without dg unit injection the load flow evaluation of the radial distribution system in case 1 is illustrated in figure 1. fig. 1. without inserting a dg unit. in this case, there is no injecting dg unit and the load demand is met by the electricity grid. this situation is used as a model for future cases. the voltage profile at various buses is displayed. the red color demonstrates critical situation of buses. we can see that bus bars 4, 5, and 6 are in critical situation. table ⅰ shows the power losses at various points of the distribution system. the entire active power losses in this situation are 542.7kw, whereas the total reactive power losses are 1048.6kvar. table i. total power losses without dg injection branch/circuit id losses kw kvar line-1 158.9 31.7 line-2 217.9 32.1 line-3 95.8 14.1 line-4 44.7 6.6 line-5 3.4 0.5 t1 3.3 146.5 t2 2.1 92.4 t3 4.3 192.2 t4 4.1 183.4 t5 3.1 141.1 t6 2.8 110.1 t7 2.4 97.8 total 542.7 1048.6 b. case-2: synchronous generator inserted at bus-3 power flow analysis of case-2 is illustrated in figure 2. during this case, a dg unit is inserted at bus bar 3. a dg unit (synchronous generator) of 2.5mw is attached in the system at bus bar 3 and the load demand is achieved by the electricity grid. the voltage level is enhanced at various buses when linked to the previous case, as illustrated in figure 2. in this case, bus bar 5 and bus bar 6 are in critical state. table ⅱ shows the power losses at various points of the distribution system. the entire active system losses are 376.8kw, whereas the overall reactive system losses are 1025.4kvar. when compared to the previous case the power losses are reduced. fig. 2. a dg unit (synchronous generator) is inserted at bus-3. engineering, technology & applied science research vol. 12, no. 4, 2022, 8864-8871 8867 www.etasr.com salman et al: enhancing voltage profile and power loss reduction considering distributed … table ii. power losses when a synchronous generator is inserted at bus bar 3 branch/circuit id losses kw kvar line-1 155.0 39.2 line-2 108.2 27.4 line-3 68.5 13.0 line-4 22.0 5.6 line-5 1.7 0.4 t1 3.3 146.6 t2 2.0 90.7 t3 4.2 188.4 t4 4.0 178.3 t5 3.0 135.8 t6 2.7 106.1 t7 2.3 93.9 total 376.8 1025.4 c. case-3. synchronous generator inserted at bus-6 the power flow study of case 3 is illustrated in figure 3. a dg unit (synchronous generator) of 2.5mw is inserted in the network at bus bar 6 and the load demand is met by the power grid. fig. 3. a dg unit (synchronous generator) is inserted at bus 6. table iii. power losses when a synchronous generator is inserted at bus bar 6 branch/circuit id losses kw kvar line-1 153.6 38.9 line-2 107.1 27.1 line-3 26.7 11.2 line-4 10.1 5.0 line-5 0.8 0.4 t1 3.3 146.5 t2 2.0 90.7 t3 4.2 188.4 t4 3.9 176.1 t5 3.0 133.4 t6 2.6 104.4 t7 2.3 92.2 total 319.5 1014.2 in this situation, the dg source and the power grid work together to meet the load requirements. the voltage level is enhanced at various buses when compared to the previous case. table ⅲ shows the overall power losses in the distribution network at various locations. the entire active power losses when a synchronous generator unit is inserted at bus bar-6 are 319.5kw, whereas the entire reactive power losses are 1014.2kvar. these losses are decreased when compared to dg unit placed at bus bar-3. d. case-4: induction/wind generator inserted at bus-3 the load flow study of case 4 is shown in figure 4. a dg unit (induction/wind generator) of 2.5mw is linked with the network at bus bar 3 and the load demand is met by the grid. the electricity grid and the dg source work together to meet the load requirements. in this case bus bars 4, 5, and 6 are in critical state. table iv shows the overall power losses in the distribution network at various locations. the entire active power losses are 621.7kw when the 2.5mw induction generator unit is linked at bus 3, whereas the total reactive power losses are 1046.9kvar. compared to the prior examples, the losses are increased. fig. 4. a dg unit (induction/wind generator) is inserted at bus 3. table iv. power losses when induction/wind generator is inserted at bus bar 3 branch/circuit id losses kw kvar line-1 296.6 39.8 line-2 189.2 27.9 line-3 95.0 14.0 line-4 44.3 6.5 line-5 1.7 0.4 t1 3.3 147.8 t2 2.0 91.8 t3 4.2 190.8 t4 4.0 181.9 t5 3.1 140.0 t6 2.7 109.2 t7 2.4 96.8 total 621.7 1046.9 engineering, technology & applied science research vol. 12, no. 4, 2022, 8864-8871 8868 www.etasr.com salman et al: enhancing voltage profile and power loss reduction considering distributed … e. case-5: induction/wind generator inserted at bus-6 the load flow examination of case 5 is illustrated in figure 5. a 2.5mw dg unit (induction/wind generator) is attached to the network at bus bar 6 and the electricity grid and the dg source work together to meet the load demand. table v shows the overall power losses in the distribution network at various locations. the entire active system losses are 445.0kw, whereas the entire reactive system losses are 1012.8kvar. these losses are improved when compared to case 4. fig. 5. a dg unit (induction/wind generator) inserted at bus 6. table v. power losses when induction/wind generator is inserted at bus bar 6 branch/circuit id losses kw kvar line-1 264.5 39.0 line-2 68.7 22.8 line-3 45.3 11.5 line-4 27.1 6.9 line-5 18.2 4.6 t1 3.3 147.6 t2 2.0 90.4 t3 4.2 187.8 t4 3.9 175.2 t5 2.9 132.4 t6 2.6 103.6 t7 2.3 90.9 total 445.0 1012.8 f. case-6: inserting a small un-deterministic dg unit in this situation, a small dg is inserted in the system and its effect on voltage level and power losses are examined. the power flow analysis for this situation is shown in figure 6. the red color indicates the critical state of buses. bus bars 4, 5, and 6 are in critical state. table vi shows the overall power losses in the distribution network at various locations. the entire active power losses in this situation are 518.7kw, while the entire reactive power losses are 1031.5kvar. fig. 6. load flow analysis when inserting un-deterministic dg in the distribution system. table vi. injection of un-deterministic dg in the distribution system branch/circuit id losses kw kvar line-1 274.8 40.5 line-2 97.0 24.6 line-3 82.1 12.1 line-4 29.8 5.7 line-5 13.4 2.0 t1 3.3 148.6 t2 2.0 91.6 t3 4.2 190.3 t4 4.0 179.6 t5 3.0 136.4 t6 2.7 106.6 t7 2.3 93.6 total 518.7 1031.5 g. case-7: increasing the cross sectional area of the conductor in this case, the cross sectional area (csa) of the transmission cable is increased in order to analyze the effect of voltage profile and power losses. by considering the csa of the conductor, its resistance is equal to: r=ρ l / a where ρ is the resistivity, l the length, and a the csa. the above equation shows that csa a is inversely proportional to the resistance r and by increasing the csa, the r will be decreased and maximum current will flow. figure 7 illustrates the findings of the load flow analysis. the power grid and the un-deterministic dg unit meet the load requirements. table vii shows the overall power losses in the distribution network at various locations. the overall active power losses are 426.7kw and the total reactive power losses are 1019.7kvar. comparing with the power losses from the previous situation, we see that the power losses are much improved. engineering, technology & applied science research vol. 12, no. 4, 2022, 8864-8871 8869 www.etasr.com salman et al: enhancing voltage profile and power loss reduction considering distributed … fig. 7. total power losses of the system by increasing the csa of the conductor. table vii. increasing the csa of the onductor branch/circuit id losses kw kvar line-1 270.5 40.0 line-2 95.5 24.2 line-3 23.5 9.9 line-4 11.5 4.8 line-5 3.9 1.6 t1 3.3 148.5 t2 2.0 91.5 t3 4.2 190.2 t4 3.9 177.4 t5 3.0 134.2 t6 2.6 105.0 t7 2.3 92.5 total 426.7 1019.7 vi. result analysis and discussion in this section, the obtained results and voltage profile analysis and power losses analysis from different cases are discussed in detail. a. voltage profile analysis when various kinds of dg units are inserted to the radial distribution network, they have various impacts on the voltage level. the entire results are illustrated in table viii. table viii. radial feeder voltage arrangement bus bar no case (1) case (2) case (3) case (4) case (5) case (6) case (7) 1 11 11 11 11 11 11 11 2 10.81 10.8 10.81 10.75 10.75 10.7 10.71 3 10.51 10.64 10.64 10.56 10.66 10.57 10.58 4 10.31 10.49 10.58 10.36 10.61 10.44 10.53 5 10.17 10.42 10.54 10.22 10.59 10.39 10.5 6 10.13 10.4 10.53 10.19 10.62 10.42 10.5 1) voltage level without dg injection in this case, no dg is inserted. figure 8 illustrates the radial fall in voltage level from the source to the load. the decrease in voltage profile is caused by the impedance of the line. 2) effect on voltage profile when a dg (synchronous generator) is inserted at bus-3 and bus-6 figure 9 shows the voltage level at different bus bars when a synchronous generator is injected at buses 3 and 6. it can be seen that the voltage profile improves when the synchronous generator is injected at bus-6. 3) effect on voltage level when a dg (induction/wind generator) is inserted at bus-3 and bus-6 here, the voltage comparison is made at different bus bars when an induction generator is injected at bus-3 and bus-6. it is shown in figure 10 that the voltage profile is improved when the induction generator is injected at bus-3 and bus-6 as compared to the base case, but when compared to the previous case, the synchronous generator injected at bus 6 gives the best result. fig. 8. voltage level when no dg is injected. fig. 9. voltage profile when a synchronous generator is inserted at bus 3 and bus 6. 4) effect on voltage level when injecting an undeterministic dg unit and increasing the conductor's csa in this case an undeterministic dg unit is injected and the csa of the conductor is increased and its impact on the voltage engineering, technology & applied science research vol. 12, no. 4, 2022, 8864-8871 8870 www.etasr.com salman et al: enhancing voltage profile and power loss reduction considering distributed … level is observed. it is shown that voltage level is improved when the csa of the conductor is increased. the result obtained is shown in figure 11. fig. 10. voltage profile when an induction generator is inserted at bus 3 and bus 6. fig. 11. voltage profile when an un-deterministic dg is inserted and the csa of the conductor is increased. b. power losses analysis when various kinds of dg units are linked to the radial distribution system, different effects on power losses occur. 1) total power losses in the base case in this case, the power losses are observed without injecting a dg unit. the total losses are shown in figure 12. impedances in the lines cause these losses. no dg unit is inserted and all power is supplied by the electrical grid. each cable carries current from the grid to the customer locations, resulting in significant power losses. 2) power losses when a dg (synchronous generator) is inserted at bus 3 and bus 6 figure 13 shows the total power losses in kw when a synchronous generator is inserted at bus 3 and bus 6. it is seen that the power losses are reduced when the generator is injected at bus 6. fig. 12. total power losses of the base case. fig. 13. total power losses when a synchronous generator is inserted at bus 3 and bus 6. 3) power losses when a dg unit (induction/wind generator) is inserted at bus bars 3 and 6 figure 14 shows the total power losses when an induction generator is injected at buses 3 and 6. it is seen that the injection caused increase in power losses due to the absorption of reactive power by the induction generator. fig. 14. total power losses when an induction generator is injected at buses 3 and 6. inserting a synchronous generator at bus 6 has an outstanding result in comparison with the other cases. as a result, injecting a dg unit at an optimal position, such as bus bar 6, and a dg type, such as the synchronous generator, will have positive impact on power losses. 4) power losses when an un-deterministic dg is inserted in the distribution system and the conductor csa is increased in this case, an un-deterministic dg unit is injected and the csa of the conductor is increased and the impact on power engineering, technology & applied science research vol. 12, no. 4, 2022, 8864-8871 8871 www.etasr.com salman et al: enhancing voltage profile and power loss reduction considering distributed … losses is observed. it is seen that the power losses will be reduced when the csa of the conductor is increased. the entire power losses are shown in figure 15. fig. 15. total power losses when an un-deterministic dg is injected and the csa of the conductor is increased. the novelty of this research work is that a real test system of 132kv residential test feeder is modeled in etap. various tests were carried out to determine the influence of dg on the distribution network. various researchers work on ieee builtin systems and very limited work has been conducted by taking or selecting a real test system. dg was injected at multiple points on the test feeder, and improvement in voltage profile and reduction in power losses were observed. these findings will be useful to many distribution firms around the world, and specifically in pakistan, in the future expansion of the power systems and the proliferation of dg. vii. conclusion and future work in this research paper, the effect of dg on voltage level and system losses in a radial test system was observed and different cases were considered. it was concluded that by connecting a synchronous generator at bus 6, the voltage level improved and power losses were reduced the most. attaching an induction/wind generator considering as dg unit close to a load improves the voltage profile, but, due to the immersion of reactive power by the induction generator, the power losses will be increased. moreover, it was concluded that when an undeterministic dg unit is inserted in the distribution system, it will cause disturbance in the whole system. inserting undeterministic dgs has negative effect on the voltage level and power losses. furthermore, it was concluded that by increasing the csa of the conductor, the voltage level can be elevated and power losses can be reduced. the effects of various conventional and non-conventional dg units can be examined more in the future, considering harmonics and reliability. references [1] a. al-sakkaf and m. almuhaini, "power flow analysis of weakly meshed distribution network including dg," engineering, technology & applied science research, vol. 8, no. 5, pp. 3398–3404, oct. 2018, https://doi.org/10.48084/etasr.2277. [2] b. singh and j. sharma, "a review on distributed generation planning," renewable and sustainable energy reviews, vol. 76, pp. 529–544, sep. 2017, https://doi.org/10.1016/j.rser.2017.03.034. [3] s. essallah, a. khedher, and a. bouallegue, "integration of distributed generation in electrical grid: optimal placement and sizing under different load conditions," computers & electrical engineering, vol. 79, oct. 2019, art. no. 106461, https://doi.org/10.1016/j.compeleceng. 2019.106461. [4] m. a. aman, s. ahmad, a. ul asar, and b. noor, "analyzing the diverse impacts of conventional distributed energy resources on distribution system," international journal of advanced computer science and applications, vol. 8, no. 10, pp. 390–396, https://doi.org/10.14569/ijacsa.2017.081051. [5] t. ackermann, g. andersson, and l. söder, "distributed generation: a definition," electric power systems research, vol. 57, no. 3, pp. 195– 204, apr. 2001, https://doi.org/10.1016/s0378-7796(01)00101-8. 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[13] p. de lima vianna, m. sabino viana, g. manassero, and m. e. morales udaeta, "a general analysis of the distributed generation impact on electrical energy planning," in 2018 53rd international universities power engineering conference (upec), glasgow, uk, sep. 2018, pp. 1–6, https://doi.org/10.1109/upec.2018.8542020. [14] c. k. das, o. bass, g. kothapalli, t. s. mahmoud, and d. habibi, "overview of energy storage systems in distribution networks: placement, sizing, operation, and power quality," renewable and sustainable energy reviews, vol. 91, pp. 1205–1230, aug. 2018, https://doi.org/10.1016/j.rser.2018.03.068. [15] m. a. aman, s. ahmad, b. noor, and f. w. karam, "mitigating the adverse impact of un-deterministic distributed generation on a distribution system considering voltage profile," engineering, technology & applied science research, vol. 8, no. 3, pp. 2998–3003, jun. 2018, https://doi.org/10.48084/etasr.2033. 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[17] a. rajendran and k. narayanan, "optimal multiple installation of dg and capacitor for energy loss reduction and loadability enhancement in the radial distribution network using the hybrid wipso–gsa algorithm," international journal of ambient energy, vol. 41, no. 2, pp. 129–141, jan. 2020, https://doi.org/10.1080/01430750.2018.1451371. engineering, technology & applied science research vol. 7, no. 3, 2017, 1600-1604 1600 www.etasr.com narayan et al.: simulative study into the development of a hybrid hvdc system through a comparative… simulative study into the development of a hybrid hvdc system through a comparative research with hvac: a futuristic approach ram s. narayan electrical engineering department national institute of technology, calicut, india shilpa mohan electrical engineering department national institute of technology calicut, india k. sunitha electrical engineering department national institute of technology, calicut, india karakkadsunitha@gmail.com abstract— high voltage direct current transmission (hvdc) is considered a better solution for bulk long distance transmissions. the increased use of hvdc is a result of its advantages over the hvac systems and especially of its fault stability nature. a better solution is proposed by using a voltage source controlled– hvdc as one of the infeed for the multi-infeed hvdc (midc or mi-hvdc) systems. the main advantage with the vsc converter is its flexible power control which enhances the stability of the midc systems. in this paper, the behavior of an hvdc system is compared with that of an hvac during faults. a hybrid hvdc system that includes a lcc as a rectifier unit and a vsc converter as the inverter is being proposed. it is considered suitable for midc systems and particularly for supplying a weak ac system. the performance of the system during steady state and transient conditions for all the proposed topologies including hvdc, hvac and hybrid hvdc are studied in matlab/simulink. all of the proposed control strategies are evaluated via a series of simulation case studies. keywords-high voltage direct current; hvdc; hvac; transmission system; hybrid; fault; transmission; power i. introduction the rally for direct current (dc) transmission, particularly, for long-distance power transport started in 1954 when asea, a predecessor of abb, connected the island of gotland to mainland sweden with high-voltage direct-current (hvdc) lines, even though hvdc transmission was considered as a power transmission option since 1950s [11]. hvdc found to be a seemingly convincing solution to a majority of problems and supported power transmission between asynchronous grids and bulk long distant power transport with reduced losses. the main reason for the wide acceptance of hvdc over hvac systems is due to the unmatchable quality of hvdc systems to operate with flexibility [2]. a non-exhaustive list of advantages of hvdc over hvac are: reduced corona loss, reduced insulation requirement, diminishing voltage drops, economically viable cost of towers, insulators, poles and conductors, and most importantly, the elimination of skin effect [4]. nowadays, a single ac network is housing a large number of high voltage dc transmission links with near electrical proximity. this system of integrating numerous high voltage dc links to feed power into a single ac network at different points is known as “multi-infeed high voltage direct current system” (midc) [1]. a midc system includes either a shared/common ac bus or buses which are in close proximity as shown in figure 1. there exist some practical examples where more than one hvdc transmission are linked towards the very same ac network with close electrical proximity. a very common setting of such a system is the multi-bipole infeed connected to the same place in the network. this will in turn call for mutual interferences between the two inverters which results in the commutation failure. the scenario stands good only if the converters terminate at the same place in the network and rather if they terminate at separate places (by electrically separating the inverters through impedances in the network), then we could always reduce the interaction. the afore said problems in the multi-bipoles ending up at the same place could be safely reduced with the implementation of multi-infeed hvdc systems. these advantages of multi-infeed systems motivated us to propose a hybrid hvdc technology suitable for such systems. fig. 1. mi-hvdc system ii. the effect of fault current in power systems short circuit current (also known as “fault current”) arises as soon as a fault occurs in a power system. fault current is nothing but essentially a massive flow of current through an electric circuit. the effects of short circuit current could be catastrophic mostly damaging the equipment and completely destroying its insulation system. sometimes they may also lead to power surges in the system or even administer an electric shock by charging the device. faults can be classified into engineering, technology & applied science research vol. 7, no. 3, 2017, 1600-1604 1601 www.etasr.com narayan et al.: simulative study into the development of a hybrid hvdc system through a comparative… symmetrical and asymmetrical ones. in symmetrical faults, all the phases are affected with the same magnitude and effect. but in practice only 5% of faults are symmetrical and asymmetrical faults occur in abundance where only one (mostly) or two phases are affected asymmetrically. but the analysis of asymmetrical faults is always a headache due to their misaligned distribution of current among the phases and thereby forcing us to assume equal distribution of currents among all the three phases [7-10]. unbalanced faults can be broadly classified into three common types namely line-to-line, line-to-ground and double-line-to-ground faults. in power systems, generators are encountered with high level fault currents subjecting the generator to experience stress beyond its design limits and eventually a temperature rise. some more direful consequences of fault currents are the sudden loss of loads, fault clearances and unbalanced flux densities distorting the air gap torques. the consequences are not alone related to these electrical stresses but may also create some mechanical unbalances resulting in the amplification of oscillations encountering in the shaft. the main aim behind the reduction of the magnitude of fault currents is not only to counter-effect these dire outcomes of fault currents but also to optimize the size and cost of circuit breakers thereby increasing the flexibility of operation of circuit breakers. there are a lot issues to be concerned in case of a mi-hvdc system. some of the major concerns include huge over-voltages, commutation failure risk, instabilities occurring in voltage and power and ac/dc fault recovery [12]. the above-said problems will get aggregated particularly when mi-hvdc is connected into a weak system. an ac system is considered in terms of a factor called short circuit ratio (scr) which is described in (1), as the ratio of short circuit mva (scmva) of the ac system at the converter terminal ac bus to the rated dc terminal power (pdc). scr=v12/(zs*pdc) (1) a strong system can be defined as a system possessing an scr greater than 3 whereas if scr lies between 2 and 3, the system is moderately strong or weak. the system can be termed to be very weak, if scr is less than 2. it can be seen from the simulation patterns that strong systems tend to be dynamically stable while weaker systems are more prone to the risk of dynamic instability. this could result in huge deflections in voltage and other parameters even for a very small disturbance. the fore-said effect of unstable condition becomes a major concern when lcc based hvdc systems are used. but recent trends are shifting the mi-hvdc systems from using lcc based hvdc systems to vsc-based systems. vsc based hvdc transmission technology is more preferred mainly because of its advantages like independent control of active and reactive power, possibility to invert into a weak or passive ac network, reduced harmonics and good controllability [6]. the demerits of the vsc based hvdc system lies in case of cost and high frequency switching losses which are absent in lcc-hvdc. this results in lesser rating of voltage and power for vsc based hvdc. to overcome these problems faced by vsc based hvdc systems, a hybrid hvdc system can be utilized [1]. the major plus point of a hybrid hvdc system is that it is having the merits of both lcc and vsc based hvdc systems and can eradicate the demerits of both effectively. the lcc system helps in optimizing the cost and the vsc system plays a role in reducing the issues with commutation failures. in this paper a hybrid hvdc system is considered consisting of both lcc and vsc converters, which can be used to integrate with conventional lcc-hvdc inverting into a very weak ac system. the main advantage of hybrid hvdc is in its use in mi-hvdc systems. hybrid systems are preferred for unidirectional power transmission scenarios, like transmitting power to estranged islands and remote load centers, particularly where it is difficult to construct new transmission lines. as like in vsc hvdc systems, here also the control strategies for the rectifier and inverter are preferred and implemented using proportional integral (pi) controllers. iii. simulation a. hvac transmission system a three-phase hvac transmission system is simulated using matlab as in figure 2, transmitting power between two stations through a 300 km pi section line. as part of the compensation requirements, series capacitors are provided to improve the total transmitted power capacity. the series reactance actually decreases the transfer reactance between the buses to which the line is connected and thus increases the maximum power transmission capability. this in turn effects in decreasing the effective reactive power losses [4]. three phase breakers are provided at both ends for protection purposes and the measurements are taken from the buses at both sides. a three-phase series rlc load is also provided at one side for dump loading purposes. a single phase to ground fault have also been simulated at the transmission end of the system for contingency analysis purposes. b. hvdc transmission system the simulation model of a hybrid high-voltage direct current (hvdc) transmission system using a 6-pulse thyristor based universal bridge converter, transmitting power between two stations through a 300 km dc transmission line. a 500 mw (250 kv, 2 ka) dc inter-connection is used for transmitting power from a 315 kv, 5000 mva ac network. the network is simulated as an llr damped equivalent (impedance angle of 80 degrees at 60 hz and 3rd harmonic). the converter transformer and the rectifier are modeled using the already available universal transformer and universal bridge blocks. the converter used here is a 6-pulse rectifier. it is inter-connected using a 300 km distributed parameter line with the help of a 0.5 h smoothing reactor lsr. the main purpose behind using smoothing reactor is to provide protection against intermittent current and fault currents, and also to prevent resonance in the dc circuits [3-5]. in this simulation, the inverter is simulated as a simple dc voltage engineering, technology & applied science research vol. 7, no. 3, 2017, 1600-1604 1602 www.etasr.com narayan et al.: simulative study into the development of a hybrid hvdc system through a comparative… source in series with a diode (for unidirectional conduction) and smoothing reactor lsi. the reactive power required by the converter is provided by a set of filters (c bank plus 5th, 7th and high pass filters; total 320 mvar). the voltages being sent to the synchronized system are filtered using a second order band pass filter. the parameters for both the simulation are kept the same in order to get a more clarified analysis of the system under faulted conditions. a hybrid hvdc system with power rating of 1000 mw and a dc rating of 500 kv is considered here. the other hybrid hvdc system parameters are identical with the cigre hvdc benchmark model. the scr of the combined system of 1300 mw is 1.92 which corresponds to a very weak ac network. a dc link of 300 km length with specified inductance and capacitance values is used in the simulation. the 1000 mw hybrid hvdc system as shown in figure 3 has lcc at the rectifier side and vsc at the inverter side. the ac rms voltage at the rectifier side is same at both the rectifier and inverter sides as 345 kv. the simulations are run for 2 sec, giving ample time for the system to attain its steady state. the control scheme utilized for lcc rectifier of hybrid system is constant current control while dc and ac voltage control used for the vsc inverter of hybrid system. iv. results a. hvac transmission system figure 4 shows the simulation output of hvac transmission system under normal and faulted conditions. the system attains the steady state condition quickly. a dc fault is applied to the system at 0.5 seconds for 0.01 seconds duration. figure 4 shows that the system tries to reach a new steady state condition on the occurrence of a fault in a slow pace and it almost takes 0.5 seconds to arrive at the new steady state position after fault clearance. b. hvdc tranmission system figures 5 and 6 show the simulation output for the hvdc transmission system. figure 7 represents the output of the hvdc system with uncontrolled rectifier without faults under steady state performance. the system reaches a steady state position quickly, taking only 0.1 seconds. the dc side voltages and currents have been held constant using both ac side filters and dc side filters. figure 5 corresponds to the faulted condition performance of hvdc system with thyristor controlled rectifier for a dc side fault. the same fault of 0.01 seconds duration as given to the hvac system was applied to this system also at the same position of 0.5 seconds. the dc side voltage was then suddenly reduced to zero and the dc side current raised anomaly corresponding to the fault. the system reached a new steady state after 0.3 seconds of fault clearance. while observing figures 4-6, we can observe that the hvdc system was affected less severely compared to the hvac system of same specifications under similar conditions. from figure 4, we get a picture about the intensity and impact of the fault current in hvac systems when compared with hvdc system of similar dimensions and specifications. the effect of single-line-to-ground fault is observed at the sending end of voltage and current waveforms of hvac system as they get distorted deviating from its normal position even though the fault occurs at the receiving end. also, this causes a disturbance among the phase angles between the phases. for the same fault condition, sending end voltage and current waveforms of the hvdc transmission system are in approximate proper position. here, the current waveforms seem to be disturbed because of the 6 pulse converter whereas this will not affect the overall performance of the system. c. steady state and three-phase-to-ground fault the proposed hvdc system reaches the stable steady state at 0.5 sec. the dc link voltage and current at inverter side of hvdc attains the standard magnitude at around 0.5 seconds as shown in figures 7 and 8. three-phase-to-ground fault at the rectifier side of the hvdc was simulated during 1.0 sec for a duration of 0.05 sec and the results are depicted as shown in figures 9 and 10. here, a considerable improvement in dc voltage and current transients of the system has been observed, during the fault. there has been an increment of the rectifier alpha order to a maximum value and a decrement in the inverter extinction angle. the system achieves steady state within 0.25 sec after the fault is cleared and the recovery is again fast. the performance of dc side and ac side inverters were almost similar to that of the single phase faults. the severity of fault disturbances were not found to be increased in case of three phase faults, as seen in conventional hvdc systems. v. discussion & conclusion this paper initially performs a ‘fault current’ analysis and a comparison study between hvac and hvdc power transmission systems. the fault analysis was conducted for both hvac and hvdc topologies. the interpretation of the results confirms the reduced fault level and impact in the hvdc system. a hybrid hvdc system consisting of lcc at the rectifier side and an vsc at the inverter side has been proposed for a very weak ac network and validated. the system steady state response and the performance of the system under various faulted conditions were simulated to get a complete picture of its behavior. the system performance under steady state and ac fault conditions were also studied. a conclusion can be drawn that there has been a considerable improvement in the transient performance of the mi-hvdc system under ac fault conditions. this proves the credibility of the hybrid system which utilizes the merits of both lcc and vsc system and seems to be a better solution to mi-hvdc systems inverting into a weak ac network. the dc voltages in this model seem to be distributed unevenly among the hvdc links depending upon the nominal voltages. there had been some ripple observed in the dc side voltages of the system which comes as a result of circulating currents present in the converter, and this can be decreased by utilizing another modulation strategy or by using a huge capacitor across the converter arms. when a single-phase to ground fault has been applied at the rectifier side of the model, harmonic disturbances arise in the voltages and currents due to the unbalance of the fault. the lcc has not suffered from engineering, technology & applied science research vol. 7, no. 3, 2017, 1600-1604 1603 www.etasr.com narayan et al.: simulative study into the development of a hybrid hvdc system through a comparative… failure of commutation in the inverter. a three-phase to ground fault has been applied at the rectifier side of the model. fig. 2. the hvac power transmission system simulink model fig. 3. the hybrid hvdc system simulink model fig. 4. hvac system under normal and faulted condition engineering, technology & applied science research vol. 7, no. 3, 2017, 1600-1604 1604 www.etasr.com narayan et al.: simulative study into the development of a hybrid hvdc system through a comparative… fig. 5. hvdc system with fault fig. 6. hvdc system without fault fig. 7. steady state current and voltage of ac side of hvdc system fig. 8. steady state analysis– dc side waveform fig. 9. three phase fault in hvdc-ac side performance fig. 10. three phase fault – dc side waveforms a considerable improvement in the transient performances of mi-hvdc systems under faulted conditions using hybrid hvdc technology can be observed. the proposed hybrid system provides a good solution for mi-hvdc system inverting into a weak ac network. the simulation studies show that the vsc system makes the conventional lcc system less susceptible to commutation failure. as a part of future work, fault current for all types of symmetric and asymmetric faults in different sections should be analyzed, enabling a complete comparative study of hvac and hvdc grid systems, along with their cost analysis. the developed hybrid model can be further extended to mtdc systems replacing the hybrid hvdc model with independent lcc and vsc hvdc units under different ends. vi. references [1] g. shilpa, p. manohar, “hybrid hvdc system for multi-infeed applications”, 2013 international conference on emerging trends in communication, control, signal processing & computing applications (c2spca), pp. 1 5, india, october 10-11, 2013 [2] m. p. bahrman,b. k. johnson, “the abcs of hvdc transmission technologies”, power and energy magazine, vol. 5, no. 2, pp. 32-44, 2007 [3] y.a. garces, e. a. cano-plata, a. j. ustariz-farfan, “hybrid simulation: an active power filter case study”, revista ingenieria e investigacion, vol. 31, pp 76-80, 2011 engineering, technology & applied science research vol. 7, no. 3, 2017, 1600-1604 1605 www.etasr.com narayan et al.: simulative study into the development of a hybrid hvdc system through a comparative… [4] v. behravesh, n. abbaspour, “new comparison of hvdc and hvac transmission system”, international journal of engineering innovation & research, vol. 1, no. 3, pp. 300-304, 2012 [5] p. fischer, j. pan, k. srivastava, w. wang, c. hong, “case study of a multi-infeed hvdc system”, powercon 2008, new delhi, india, october 12-15, 2008 [6] p.d fischer, g. asplund, e. jansson, “aspects on infeed of multiple hvdc into one ac network”, abb power system, hvdc division, sweden, april 2012 [7] g. asplund, “electric transmission system in change”, key notes, ieee power electronics specialists conference, greece, june, 2008 [8] c. guo, y. zhang, a. m. gole, c. zhao, “analysis of dual-infeed hvdc with lcc-hvdc and vsc-hvdc,” ieee transactions on power electronics, vol. 27, no. 3, pp. 1529-1537, 2012 [9] a.tirupati rao, p. ramana, p. kanata rao, “modeling of cigre hvdc benchmark system in matlab/simulink”, international journal of education and applied research, vol. 4, no. spl-1, pp. 112115, 2014 [10] j. kreusel, “integrated ac/dc transmission systems–benefits of power electronics safety and sustainability of power supply” power system computation conference, uk, july, 2008 [11] o. kotb, a hybrid hvdc transmission system supplying a passive load, m.sc. thesis, department of electrical and computer engineering, oshawa, ontario, canada, 2010 microsoft word etasr_v12_n1_pp8175-8179 engineering, technology & applied science research vol. 12, no. 1, 2022, 8175-8179 8175 www.etasr.com sriputtha et al.: investigation of polycaprolactone/carboxymethyl cellulose scaffolds by mechanical … investigation of polycaprolactone/carboxymethyl cellulose scaffolds by mechanical and thermal analysis noppadol sriputtha department of advanced manufacturing technology faculty of engineering pathumwan institute of technology bangkok, thailand idol7877@gmail.com fasai wiwatwongwana department of advanced manufacturing technology faculty of engineering pathumwan institute of technology bangkok, thailand fasaiw227@gmail.com nattawit promma department of mechanical engineering faculty of engineering chiang mai university chiang mai, thailand nano_504@hotmail.com abstract-the objective of this work was to learn more about three-dimensional porous scaffolds made from biomaterial based on polycaprolactone (pcl) containing different amounts of carboxymethyl cellulose (cmc) nanoparticles. composite material samples containing 0, 2, 6.5, 11, 15.5, and 20% w/w of cmc and pcl/cmc scaffolds were prepared with the use of the salt particle leached technique. the mechanical properties were evaluated with the compressive strength analysis method. the studied temperature range started at very low temperatures and ended at crosslinking temperatures. it was evaluated using the thermal analysis methods of differential scanning calorimetry (dsc) in the range 0ºc-200ºc. the results revealed that the compressive modulus of blended pcl/cmc scaffold was higher than the one of pure pcl scaffold (582.2±106.2 kpa for pure pcl scaffold and 612.2±296 kpa for blended scaffold which contained 20% of cmc). for dsc analysis, in addition to the 15.5% w/w cmc pcl/cmc composite scaffold, other proportions of composite materials showed a decrease in crystallization temperature. the crystallinity of pcl-20% cmc was higher than that of pcl scaffolds. keywords-polycaprolactone; carboxymethyl cellulose; compressive strength; thermal analysis; differential scanning calorimetry i. introduction damage or loss of tissue or a portion of the body is usually one of the most deadly and costly problems in health care [1]. tissue engineering has grown in popularity as a result of the necessity to consider merging or engaging multi-skilled approaches in order to solve this medical problem. medical progress, along with increasing interaction in a range of fields of knowledge such as materials science, biology, engineering, and physics, has produced breakthroughs in the diagnosis, evaluation, and implementation of implant instruments and tissue transplantation. extraction of isolated cells, execution with tissue-persuasion chemicals, and implantation of a cell into a scaffold composite are common approaches for tissue regeneration [3, 4]. in addition, the usage of composite scaffold typically yields more lucrative outcomes [2]. nanotechnology has become one of the world's fastest expanding industrial sectors, influencing a wide range of scientific and technology industries [5]. scaffolds are critical components in tissue engineering. when it comes to choosing scaffolds for tissue engineering however, researchers are usually presented with a confusing number of choices [6]. polymers have been utilized as biomaterials in the manufacturing of medical devices and tissue-engineering scaffolds [7, 8]. the most recent scaffolds mimic biological processes in the extracellular matrix in order to capture the structure and functions of growing tissues and aid cell adhesion, growth, and dispersal [9]. biodegradable polymers such as pcl, plla, plga, etc. are used as scaffolds in tissue engineering to foster cells until they are replaced by the extracellular matrix (ecm) [10-12]. an ideal scaffold should be extremely porous with linked pores, biodegradable, and made of components that are compatible. even though most scaffolds comply with these parameters, their final features are mostly defined by their technique of construction. however, the approach is determined by the goal of the tissue engineering application [13-14]. three-dimensional porous scaffolds can be prepared using a variety of processes, including 3d printing, phase separation, gas-foaming, solvent casting, salt particle leaching, and freeze-drying [15-17]. corresponding author: noppadol sriputtha engineering, technology & applied science research vol. 12, no. 1, 2022, 8175-8179 8176 www.etasr.com sriputtha et al.: investigation of polycaprolactone/carboxymethyl cellulose scaffolds by mechanical … particulate leaching has been employed in tissue engineering since it is one of the simplest methods used to create porous materials using salt. the method of salt leaching is simple and does not need the use of high pressure or expensive equipment [18-20]. controlling of porosity, pore structure, and pore size is as easy as changing the quantity and particle size of salt. in this work, scaffolds were fabricated using the salt particulate leaching method. polycaprolactone (pcl) is a linear aliphatic polyester. it is a hydro-phobic, biocompatible, semi-crystalline, slowly disintegrating polymer which is simple to work with [21-24]. as a result, a pcl composite based material with tunable hydrophilicity is utilized. the changed hydrophilicity was achieved by offering different magnitudes of a highly hydrophilic biocompatible substance, such as carboxymethyl cellulose (cmc) [21]. the current study investigated the properties of porous scaffolds made of pcl and cmc. the morphological, thermal, and mechanical characteristics of pcl/cmc composite material samples containing 0, 2, 6.5, 11, 15.5, and 20% w/w cmc were studied. ii. experimental part a. materials pcl with an average molecular weight (mw) of 45g/mol and melting temperature of 56–64°c, and cmc with a medium viscosity, were acquired from sigma-aldrich, usa. sodium chloride (nacl), which will be used as a porogen, was received from merck kgaa (darmstadt, germany). trifluoroethanol (tfe) from sigma-aldrich was employed as a solvent for these composite polymers. b. scaffold preparation the scaffolds were fabricated using the salt leaching method. a polymer solution was made by combining a pcl pellet with cmc (pcl/cmc), with tfe as a solvent at a concentration of 30% (by mass). the pcl solution contained 3g of pcl and 7g of tfe [25, 26]. the mixture design parameter in the minitab software was used to generate the design of the pcl and blended pcl with cmc mixing formulations, as shown in table i. codes were used to name the materials, with p0 being the pure base material of pcl produced by mixing a pcl pellet and tfe at a 30% concentration (by mass). the salt was mixed into the solution, which is utilized for 24g [27]. the pure pcl p0 sample (6g) was used for comparison. the weight ratios of the p1-p5 samples were 5.88:0.12, 5.61:0.39, 5.34:0.66, 5.07:0.93, and 4.80:1.20 respectively. table i. solution abbreviations and compositions sample pcl % (w/w) cmc % (w/w) p0 100 p1 98 2 p2 93.5 6.5 p3 89 11 p4 84.4 15.5 p5 80 20 c. porous scaffold fabrication in this process, scaffolds were produced by casting a mixture of polymer solution and salt particles. following solvent evaporation, the scaffolds were fractionated in a suitable solvent, allowing particles to be leached off. porous scaffolds were formed when these particles were completely eliminated from the mixture [19]. first, the pcl was melt on a stirrer at 55-65°c and then the tfe solvent was added to make a 30% pcl solution. the cmc was poured, stirred, and mixed into the pcl solution until the solution became homogeneous. the nacl was then stirred into the mixed pcl/cmc solution. the solution was poured into a teflon mold, which produced 20mm edge cube molds. the molds were placed under a ventilation hood overnight to allow the solvent to evaporate. after the solvent evaporated, deionized water was used to leach off the salt particles. the scaffolds were then air dried for two days before being stored in a desiccator. the produced saltleached pcl/cmc scaffolds revealed strongly linked porosity networks. d. morphological characterization optical and electron microscopy were used to examine the morphology of the scaffolds. a coxem model em-30 plus was used with 20kv acceleration voltage. scanning electron microscopy (sem) was utilized as a measurement technique to quantify the average pore size. the average pore size of each component was calculated after measuring at least 20 different pore sizes. the porosity of the scaffold was determined using a specific gravity bottle with ethanol as the fluid in motion, according to the archimedes hypothesis [28-30]. finally, the porosity of a scaffold was determined by: ( ) 2 3 s e 1 3 e (w w w )/ porosity % 100 (w w )/ − − ρ = × − ρ (1) where w1, w2, and w3 represent the weights of specific gravity bottles containing ethanol, both ethanol and scaffold, and a taken out of ethanol-saturated scaffold respectively, ws represents the weight of the scaffold, and ρe represents the ethanol density. e. mechanical testing pcl has been extensively researched in bone tissue engineering. long bones respond better to compression stresses than other types of loads [31]. as a result, it was customary to investigate the compression properties of a material that was intended to be utilized for bone replacement [32-34]. the compressive mechanical properties of scaffolds were tested using a zwick roell universal testing machine. five replicas of scaffolds were cut into rectangular pieces of 10mm length, 10mm width, and around 3mm thickness [31]. the crosshead speed was set at 1mm/min. the compression modulus was computed by taking the first part of the linear segment of the stress–strain curve and dividing it by the initial cross-sectional area. the parameters were computed in accordance with the processes outlined in the astm d3574 standard. f. thermal analysis to investigate the temperature behavior of the pcl/cmc composite scaffold, a differential scanning calorimeter (dsc 3+, mettler toledo, switzerland) was used. the samples were engineering, technology & applied science research vol. 12, no. 1, 2022, 8175-8179 8177 www.etasr.com sriputtha et al.: investigation of polycaprolactone/carboxymethyl cellulose scaffolds by mechanical … around 10mg in weight [4]. all samples were put in a hermetically sealed aluminum pan with a nitrogen flow rate of 50ml/min. the samples were heated for 5min at temperatures ranging from 0 to 200°c before being cooled to 0°c and reheated to 200°c. the ramp rate was 10°c/min during all heating and cooling cycles [35]. iii. results and discussion a. morphological analysis after being coated with gold by an ion-sputter machine. (ion-coater, a coxem spt-20), the porous scaffold was studied for morphological characterization using sem (coxem model em-30 plus) at 20kv. the dimension of the pore size was measured for at least 20 pores [15, 26] and the average pore size was calculated as shown in figure 1. figure 1 shows the p0, p1, p2, p3, p4, and p5 occurring pore diameters of 227.35, 269.48, 348.28, 271.82, and 284.70mm respectively. the average porosity of the pcl (p0) scaffold was 81.44% and the porosities of the blended p1 to p5 scaffolds were 98.70, 98.30, 98.73, 98.06, and 98.88%. the porosity of blended pcl/cmc scaffolds was higher than that of the pure pcl scaffold, which might be due to cmc particles being dispersed throughout the pcl matrix surrounding the scaffold [27]. (a) (b) (c) (d) (e) (f) fig. 1. sem images of pcl and pcl/cmc composite scaffolds, (a) p0, (b) p1, (c) p2, (d) p3, (e) p4, and (f) p5. b. morphological analysis adding cmc loading had a detrimental influence on the mechanical characteristics of the composite scaffolds [36]. as demonstrated in table ii, the compression modulus decreased as the additive concentration of cmc increased. the decreasing of cmc was not significantly different (p >0.05) when compared to p0 scaffold as shown in figure 2 which shows the apparent compressive modulus of pcl and composite scaffolds. p0, p3, p4, and p5 scaffolds demonstrated mechanical behavior with a consistent pattern within each group. p1 and p2 scaffolds, on the other hand, exhibited mechanical behavior with more diversity. the p2 mixture showed the highest compressive modulus which was 789.6kpa, whereas the p3 mixture showed the lowest compressive modulus which was 509kpa. p1, p4, and p5 had compressive moduli of 706, 605.4 and 612.2kpa, respectively. the compression modulus values were compared with the reported results of previous studies. the results obtained in this work for pcl scaffold, as well as the values published in [31] were close to the lower limit of the homogeneous compression modulus range. table ii. compressive modulus of the blended scaffolds scaffolds compressive modulus (kpa) p0 582±106 p1 706±39 p2 789.6±183 p3 509±225 p4 605.4±124 p5 612.2±296 fig. 2. comparison of the compressive modulus of pcl/cmc blended scaffolds. c. differential scanning calorimetry figure 3 shows the dsc results taken during the second heating, and table iii shows the measured parameters. with these data, melting temperature (tm), and melting enthalpy (∆hm) were obtained. crystallinity (xc) was determined using (2). the considered melting enthalpy of the 100% crystalline pcl (∆ho) was 146j/g [37]. m c o h x h ∆ = ∆ (2) the sample p4 showed the greatest peak melting temperature, a melting enthalpy of 83.27j/g, and a crystallinity of 57.0%. other authors discovered that the addition of cmc to plc had no effect on melting temperature [38], however their experiments were restricted to increase of up to 20% by weight of cmc in particular. authors in [2, 21, 31] reported that combining 20% cmc with pcl raised the melting temperature by 1°c. we observed that the 20% cmc scaffold exhibited a consistent melting temperature change of about p0 p1 p2 p3 p4 p5 0 500 1000 1500 2000 sample c o m p re ss iv e m o du lu s (k p a) engineering, technology & applied science research vol. 12, no. 1, 2022, 8175-8179 8178 www.etasr.com sriputtha et al.: investigation of polycaprolactone/carboxymethyl cellulose scaffolds by mechanical … 1°c. it was found that the melting temperature was 68°c with 10% cmc addition [22], and 67.31°c for 11% cmc addition in this investigation. fig. 3. heating dsc scan for pcl and its composite scaffolds. table iii. compressive moduli of the pcl/cmc blended scaffolds samples tm (°°°°c) ∆∆∆∆hm (j/g) xc (%) p0 67.31 59.35 40.65 p1 65.43 57.62 39.46 p2 67.79 23.13 15.84 p3 67.31 23.04 15.78 p4 69.53 83.27 57.03 p5 66.49 81.59 55.88 d. discussion according to the results of these experiments, the pcl/cmc mixture of 93.5/6.5 (p2) combined the maximum compressive modulus with a good porosity value and interconnected porous structures that reacted similarly to other circumstances. the presence of cmc mitigated the degradation temperature and decreased it continuously as the amount of cmc rised. the blended pcl/cmc scaffolds p1-p5 were fabricated using the salt leaching method which could be used for tissue engineering applications. however, the amount of cmc used should be sufficient to alter the hydrophilicity of the scaffold. the melting temperature of p4 was the highest (89.53°c), with a melting enthalpy of 83.27j/g and a crystallinity of 57.03%, whereas the melting temperatures of the other components were quite comparable. this might imply that the addition of mc to the pcl had no influence on the melting temperature. iv. conclusion the salt leaching method was used in this work to effectively fabricate pcl/cmc composite scaffolds. using the solvent cast salt leaching method, it was feasible to create homogeneous pcl/cmc composite scaffolds with efficiently distributed homogenous porous structure. the scaffold from salt leaching with the mixture of pcl-6.5% cmc (p2) ratio showed the greatest compressive modulus, which was 789.6kpa, whereas the combination of pcl-11% cmc (p3) ratio had the lowest compressive modulus, which was 509kpa. the ratios p4 and p5 were lower than p3, but they were higher than the pcl. in summary, adding cmc to pcl can improve the mechanical characteristics of the scaffold. with the exception of the 15.5% w/w cmc, the pcl/cmc composite scaffolds showed decreasing in crystallization temperature, enthalpy of crystallization, melting enthalpy, and crystallinity degree in dsc analysis. in addition, the crystallinity of pcl20% 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[38] e. díaz, j. aresti, and j. león, "evaluation of physicochemical and mechanical properties with the in vitro degradation of pcl/nha/mwcnt composite scaffolds," journal of reinforced plastics and composites, vol. 40, no. 3–4, pp. 134–142, 2021, https://doi.org/10.1177/0731684420943304. microsoft word 451-ce-r1.doc engineering, technology & applied science research vol. 4, no. 4, 2014, 673-676 673 www.etasr.com benaissa et al.: physical and mechanical properties of the muds of the fergoug dam physical and mechanical properties of the muds of the fergoug dam a. benaissa z. aloui m. s. ghembaza h. trouzine y. sebaibi laboratory of civil engineering and environment lgce, university of djilali liabes de sidi bel abbes, algeria assia.benaiss@ gmail.com laboratory of civil engineering and environment lgce, university of djilali liabes de sidi bel abbes, algeria labiodzh@ yahoo.fr laboratory of civil engineering and environment lgce, university of djilali liabes de sidi bel abbes, algeria ghembaza_moulay@ yahoo.fr laboratory of civil engineering and environment lgce, university of djilali liabes de sidi bel abbes, algeria h_trouzine@ yahoo.fr laboratory of civil engineering and environment lgce, university of djilali liabes de sidi bel abbes, algeria sebaibi2004@ yahoo.fr abstract—volumes of dredged sediments are rather considerable and are estimated approximately 600 million m3 per year worldwide. these can represent a very interesting source of raw materials, in particular for a sector consuming aggregates such as civil engineering. the work presented in this article is interested particularly in the valorization of the muds which come from the dam of fergoug (algeria), with an aim of improving their mechanical behavior using binders (cement, lime) in order to use them in road engineering. to this end, we carried out a series of physical, chemical, mechanical and mineralogical analyses presented in this paper. keywordssediments of dredging; valorization; muds; road engineering; stoppings; mechanical behavior i. introduction the recycling and re-use of waste in the field of construction has been an issue of increasing concern in the last years. in algeria, the valorization of waste records a considerable delay, because of the absence of a policy favorable to the development of a waste market. currently, several researchers direct their studies on the valorization of muds with an aim of using them in road engineering, an area calling for the greatest requirement out of materials. for the valorization of muds in this paper, the physicochemical characteristics initially measured (the limits of atterberg, granulometry, the value with the methylene blue, the content of organic matter etc), are given according to french standards. the results obtained can be used to classify the studied sediments. ii. mud characteristics the sediments used in this study come from the fergoug stopping which provides an illustration of the privileged surfaces of deposit of the eroded solid matters. dam fergoug is located at 20 km upstream of perrégaux on the road of mascara in algeria (figure 1a). it is an earth dam of initial capacity (in 1963) of 18 million m3. its capacity fell to 17 million m3 in 4 years, and from 1970 to 1987 the rate of silting was 0.75 m3 per year [1]. currently, the stopping “feeds” only the commune of béthioua and its useful volume of storage reduced dramatically due to the sediment accumulation (figure 1b). fig. 1. (a) the restraint of fergoug dam (b) siltation at the level of the drain from the bottom of the dam a. physical and geotechnical analysis the test sample selection in march 2007 was carried out manually using a shovel within ten meters of the right bank of (a) (b) engineering, technology & applied science research vol. 4, no. 4, 2014, 673-676 674 www.etasr.com benaissa et al.: physical and mechanical properties of the muds of the fergoug dam the stopping. we determined the physical and geotechnical properties of this material. the parameters selected are those defined in [2] and are shown in table i. table i. physical and geotechnical characteristics of the base parameters wl (%) wp (%) ip (%) s(g/cm 3) vb mo %) values (%) 34.28 17.79 16.49 2.50 5.50 4.40 where: wl the liquid limit, wp the plastic limit, ip the index of plasticity, s the voluminal weight of the solid matter constituents, vb the value of blue and mo the organic matter b. chemical and mineralogical analysis the results of the analysis to the diffraction of x-rays made on the mud of fergoug [1], give us an idea on principal crystalline minerals, by the existence of quartz (sio2) with significant, followed peaks of carbonates (calcite (caco3) and (dolomite), and a small quantity of alumina (al2o3) represented in the form of kaolinite (al2o3 2sio2 2h2o). these resulted are confirmed by the chemical analysis, the results of which are shown in table ii. table ii. chemical analysis results characteristic symbol content silica sio2 62.68 lime cao 12.51 magnesia mgo 0.37 alumina al2o3 7.39 oxideof iron fe2o3 0.71 sulphate so3 0.17 chloride cl 00 loss in fire p.f 16.39 total 100 carbonate caco3 22.73 gas carbonic co2 10 water combination h2o 6.39 on the basis of the results of table ii, it is interesting to note that the principal mineralogical components of the mud are silica, followed by carbonates, then lime and finally alumina. silica and alumina are minerals which constitute the structure of clays. the presence of calcium carbonate indicates that the mud belongs to the group of limestones clays. in addition, one notices that the loss on the ignition is rather significant, which proves the existence of organic matter in the mud. iii. results interpretation the results of the geotechnical enables the classification of the material according to french criteria of road engineering, with a proportion of organic matter lower than 10%. from the granulometry point of view, the materials are classified in heading of fine grained soils, noted class a. the subclass can be given according to the argillaceous activity (vb) and of the plastic character; however the parameters obtained can be contradictory. the value with blue and the limits of atterberg make it possible to identify the mud under a2 class. the technical guide for the construction of the embankments and the subgrades indicated that if the index of plasticity (ip) is equal to or higher than 12, it constitutes the identifying information adapted best. so the studied mud of the stopping of fergoug is placed under class a2 [2]. iv. mechanical stabilization by compaction the geotechnical characteristics of our mud remain poor compared to officially accepted road materials. this provide a motivation to improve the mechanical properties of the muds by the addition of lime or cement cpj 42,5. the proctor test is carried out on the grounds obtained for various lime mud and cement mud mixtures with percentages 0, 2, 4, 6 and 8%. the results are given by the curves of compaction with or without treatment in figures 2 and 3. fig. 2. test proctor of the base lime mixture fig. 3. test proctor of the base cement mixture engineering, technology & applied science research vol. 4, no. 4, 2014, 673-676 675 www.etasr.com benaissa et al.: physical and mechanical properties of the muds of the fergoug dam from the results of the curves of the proctor test, we noted that the untreated mud has a maximum dry density of 1.70 with a water content optimal located at approximately 17.73%. after the treatment with lime or cement, one notes a displacement of the proctor optimum towards a lower maximum dry density and a larger water content optimal. these results seem to be in agreement with those reported in [3] and [4]. v. mechanical behavior-the rectilinear shear test the shear tests were carried out with the proctor optimum with various treatments of proportioning of lime and cement. the objective of this part is the determination of the strength to shearing parameters (the friction angle and cohesion). another goal was to see the effect of the addition of the lime and cement chemical agents on the mechanical parameters. results and related values are shown in tables iii and iv. table iii. parameters of the shear strength of mixtures mix +0% lime +2% lime +4% lime + 6% lime + 8% lime c (kpa) 145 154 171,67 214.33 203.33 ϕ (degrees) 22.05 34.21 36.87 35.18 30.33 table iv. parameters of the shear strength of mixtures mix +0% cement +2% cement +4% cement + 6% cement +8% cement c (kpa) 145 221 93,33 156 132 ϕ (degrees) 22.05 27.70 29.03 8.53 28.37 from the results of tables iii and iv, we represented graphically the variations of cohesion c and of the friction angle φ according to the percentage of lime and cement (figures 4-7). vi. discussion we observe on figure 4 that the measurements taken on the base-lime mixtures show an increase in cohesion according to the percentage of lime, with an optimum of the cohesion of 214 kpa and 6% of lime. one notices the same observations for the natural friction angle (figure 5), with an optimum of 29 degree for a percentage of 4% lime. one can note in figures 5 and 6, that the values of cohesion and friction angle are not proportional to the added quantity of cement, thus the behavior of new material is influenced by the chemical reactions intern between various minerals. however, a quantity of cement of 2% clearly improves the cohesion (221 kpa) and the friction angle (27.7 degree). fig. 4. cohesion vs the percentage of lime fig. 5. friction angle vs the percentage of lime fig. 6. cohesion vs the percentage of cement fig. 7. friction angle vs the percentage of cement engineering, technology & applied science research vol. 4, no. 4, 2014, 673-676 676 www.etasr.com benaissa et al.: physical and mechanical properties of the muds of the fergoug dam vii. conclusion the treatment of the sediments with the hydraulic binders (lime and cement) showed clearly that several parameters of formulation influence the mechanical behavior, i.e. the hardening and the state of the treated mud. we notice that there are two kinds of parameters influencing the mechanical behavior of the treated mud; parameters related to the conditions of realization, like the water content, the malaxation and the energy of compaction; and the parameters which must remain in an extremely tight fork to lead to sufficient densities, in order to avoid the permanent deformations at the time of the implementation. other parameters influence the mechanical behavior directly, depending on the nature of the mud. the results of the shear tests show that some compounds can decrease the effectiveness of a treatment but without making the ground inapt for the treatment, such as the presence of organic matter in the ground (weak when expressed as a percentage, just 4.4%). this, involves an embarrassment with respect to any addition and of any malaxation, they slow down the hydration of cement and trap the ions calcium and hydroxide which are responsible for the low mechanical resistances [3], as well as other elements like nitrate, sulphates, phosphate. one can also note that the nature and the proportioning of the treatment used will influence the mechanical behavior. the mud treated with cement shows an anomaly in its behavior. the interpretation of the found values must be the analysis object of the structure (mud+cement). in any event, it is necessary to study the influence and the role of the organic matter present in the construction of structures. the organic compounds strongly interfere with the processes of hydrated or formation of the cementing phases. according to the results obtained, it is significant to note that the 5% lime treatment clearly improves the mechanical parameters of shearing. by comparing our results with those in [5], one notes that the mud treated with 5% lime presents a potential use of the material as a filling. references [1] r. boutin, dragage et rejets en mer : les produits de type vase, presses de l’ecole nationale des ponts et chaussées, paris, 2000 [2] gtr, technical guide for the realization of fill and of the subgrades, booklet i, principles general, 1992 [3] m. boutouil, traitement of the muds of dredging by stabilisation/solidification containing cement and additive, phd thesis, university of le havre, 1998 [4] n. cant, sols treated with lime and the binders hydraulics (contribution to the identification and the analysis disturbing elements of stabilization), phd thesis, school of the mines of alés, 2004 [5] j. bacot, a. kham khoeup, “essais of stabilization muds estuariennes using hydraulic binders in sight of a use in road construction”, insa of rennes, lgcgm–equips geology with the engineer and with environment, department gcu, 2005 microsoft word karakalos 2.doc etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 13-16 13 www.etasr.com karakalos : growth mode study of mgcl2 on au foil … growth mode study of mgcl2 on au foil and si (111) 7x7, under ultra high vacuum by xps stavros karakalos 1, 2 * 1 forth/ice-ht, stadiou str., platani achaias, gr-26504, p.o. box, 1414, patras, greece 2 surface science laboratory, department of chemical engineering, university of patras, university campus, gr-26504, rion, patras, greece abstract the growth mode of mgcl2 on au foil and si (111) 7x7 reconstructed surface under uhv conditions, was investigated by x-ray photoelectron spectroscopy (xps). magnesium chloride grows with the frank-van der merve, (fm) growth mode on the au foil. on si surface there is evidence for the layer by layer growth of mgcl2 but leaving uncovered silicon areas at the first steps of deposition due to the si (111)7x7 surface roughness. keywordsgrowth mode; mgcl2; au foil; si(111)7x7; uhv; xps i. introduction magnesium chloride is one of the most important magnesium compounds as far as industrial applications are concerned. in catalysis, mgcl2 is used in ziegler-natta (zn) catalyst preparation [1]. supported on mgcl2 or on mixed mgcl2/sio2 supports, ziegler-natta catalysts are used for the industrial olefin polymerization and the production of polymers, such as isotactic polypropylene or high density and linear low-density polyethylene. zn catalysts are the best candidates for the low pressure production of linear lowdensity polyethylene and ethylene co-polymers from the gas phase, with improved optical properties in the film form. magni and somorjai [2] studied model ti-based ziegler-natta catalysts prepared by mgcl2 sublimation under ultra high vacuum (uhv) conditions onto a gold foil. surface sensitive spectroscopies comprise the most effective means of investigating the growth mode of mgcl2 on various substrates providing significant information of the surface composition and structure. nevertheless, the study of different mgcl2 interfaces at a molecular level is a particularly difficult task due to the sensitivity of magnesium chloride to oxygen and humidity. furthermore, the poor conductivity of mgcl2 makes surface analysis rather complicated. in the preset work, the growth mode of mgcl2 on au foil and si (111) 7x7 is investigated by x-ray photoelectron spectroscopy (xps). for the purposes of the present study, mgcl2 is applied on these supports by evaporation under uhv conditions. ii. experimental the experiments took place in the surface science laboratory of chemical engineering department of university of patras. for the xps measurements the non-monochromatic mgkα line was used with hν= 1253.6 ev. the hemispherical analyser (leybold ea-11) was working at constant pass energy ep=100 ev. the au foil was subjected to ar + sputtering in order to gain an atomically clean surface. the si(111) single crystal substrate, 10mm x 10mm (mateck), which could be heated up to 1200k, was subjected to cycles of ar + sputtering and annealing at 1200k in order to remove c and o contamination and cooled back to rt with a constant rate of -1k/sec, in order to obtain the 7x7 reconstructed surface which was confirmed by a low energy electron diffraction (leed) image (not shown here). mgcl2 was deposited in ultra high vacuum (uhv) through a magnesium chloride evaporation source, described elsewhere [3]. all depositions were carried out at a source temperature of 795k, while the substrate was held at room temperature. the cl/mg atomic ratio was found to be ~2 indicating that the deposit consists essentially of stoichiometric mgcl2. iii. results and discussion after confirming the atomically clean au surface, a stepwise deposition procedure of mgcl2 took place under uhv, at the constant source temperature of 795k, measuring the deposition time of each step in seconds. after each mgcl2 deposition, three photoelectron peaks were recorded. figure 1 shows the xps spectra of au4f derived from the substrate and mgkll, cl2p coming from the deposit. the au4f core level peak appears at 84.1ev binding energy (be) and it is not shifted after mgcl2 deposition indicating no chemical interaction between the support and the deposit. the mgkll auger photoelectron peak shifts 1.9ev to lower kinetic energy (ke) and the cl2p core level peak shifts 0.63ev to higher be after deposition of the maximum amount of mgcl2 on au foil. etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 13-16 14 www.etasr.com karakalos : growth mode study of mgcl2 on au foil … 9 2 9 0 8 8 8 6 8 4 8 2 8 0 a u 4 f a ft e r m g c l 2 d e p . b in d in g e n e r g y /e v x p s p e a k i n te n s it y / a .u . 2 0 6 2 0 4 2 0 2 2 0 0 1 9 8 1 9 6 c l2 p a f t e r m g c l2 d e p . o n a u b i n d in g e n e r g y / e v x p s p e a k i n te n s it y / a .u . 1 1 6 8 1 1 7 0 1 1 72 1 1 74 1 1 76 1 1 78 1 1 80 1 1 82 1 18 4 1 18 6 k i n e ti c e n e r g y /e v x p s p e a k i n te n s it y / a .u . m g k l l a f te r m g c l2 d e p . o n a u figure 1. xps peak intensity of au4f, mgkll and cl2p spectrum after stepwise mgcl2 deposition on au foil at rt. this is an expected observation [3],[4] due to electrostatic charging of the deposited mgcl2 layer, as mgcl2 is an insulating material. 0 50 100 150 200 250 300 350 400 450 500 550 600 0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,14 0,16 0,18 0,20 0,22 0,24 0,26 0,28 0,30 0,32 4ml 3ml 2ml 1ml a re a c l2 p / a re a a u 4 f t /sec 0 50 100 150 200 250 300 350 400 450 500 550 600 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 t /sec a re a m g k l l / a re a a u 4 f 4ml 3ml 2ml 1ml figure 2. graphical representations of the ratios cl2p/au4f and mgkll/au4f as a function of the mgcl2 deposition time. figure 2 shows the ratio of the intensity of each of the two xps peak of the deposit, divided with the intensity of the au4f of the substrate as a function of the deposition time of each step. it is observed that there is strong indication that mgcl2 follows a layer by layer deposition. the figure shows that the completion of each layer is obvious and this is a frank-van der merve, (fm) growth mode. the same procedure of mgcl2 deposition took place also on si (111) 7x7 substrate. figure 3 shows the xps spectra of si2p derived from the substrate and mgkll, cl2p coming from the deposit. the si2p core level peak appears at 99.5ev be and it is not shifted after mgcl2 deposition indicating that also in this etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 13-16 15 www.etasr.com karakalos : growth mode study of mgcl2 on au foil … case no chemical interaction between the support and the deposit takes place. the mgkll auger photoelectron peak shifts again by 1.9ev to ke and the cl2p core level peak shifts 2.1ev to higher be after deposition of the maximum amount of mgcl2 on si single crystal. these shifts are observed due to electrostatic charging of the deposited mgcl2 layer. 1 0 8 1 0 6 1 0 4 1 0 2 1 0 0 9 8 9 6 9 4 b in d in g e n e r g y /e v x p s p e a k i n te n s it y / a .u . s i 2 p a ft e r m g c l 2 d e p o s i t i o n o n s i (1 1 1 )7 x 7 1 1 7 0 1 1 7 2 1 1 7 4 1 1 7 6 1 1 7 8 1 1 8 0 1 1 8 2 1 1 8 4 1 1 8 6 k in e t ic e n e r g y /e v x p s p e a k i n te n s it y / a .u . m g k l l a ft e r m g c l 2 d e p o s i t i o n o n s i ( 1 1 1 ) 7 x 7 2 0 8 2 0 6 2 0 4 2 0 2 2 0 0 1 9 8 1 9 6 c l 2 p a f te r m g c l2 d e p o s it io n o n s i( 1 1 1 )7 x 7 b in d in g e n e r g y /e v x p s p e a k i n te n s it y / a .u . figure 3. xps peak intensity of si2p, mgkll and cl2p spectrum after stepwise mgcl2 deposition on si (111) 7x7 at rt. figure 4 (a) shows the ratio of the intensity of cl2p photoelectron peak of the deposit, divided with the intensity of the si2p of the substrate as a function of the deposition time of each step. in this case there are no obvious changes in the slope of the line, indicating that there is no layer by layer growth of the deposit. although, fig.4 (b) shows an almost exponential increase of mgkll intensity as a function of deposition time which is characteristic of layer by layer growth of the deposit through the law of beer. this observation could be explained by taking into account that the reconstructed si (111)7x7 surface is a very rough surface 0 200 400 600 800 1000 1200 1400 1600 1800 2000 0 1 2 3 4 5 6 r a ti o c l2 p /s i2 p deposition time /sec 0 200 400 600 800 1000 1200 1400 1600 1800 2000 deposition time /sec p e a k i n te n s it y m g k l l / a .u . figure 4. graphical representations of the ratios cl2p/si2p and mgkll/si2p as a function of the mgcl2 deposition time. etasr engineering, technology & applied science research vol. 1, �o. 1, 2011, 13-16 16 www.etasr.com karakalos : growth mode study of mgcl2 on au foil … figure 5 shows that the well characterized si (111)7x7 surface consists of a large number of si atoms which extrude outside the 1x1 level. this might cause different behavior of the ratio cl2p/si2p as a function of deposition time, even for layer by layer growth of the mgcl2. during the first steps of deposition the layer of mgcl2 may leave uncovered the si atoms which extrude outside the surface. moreover, this surface roughness would not affect the mgkll intensity as a function of deposition time, which should appear as exponential increase for a layer by layer growth following the law of beer. figure 5. representation of the si (111) 7x7 reconstructed surface. iv. conclusions the mgcl2 deposited on the atomically clean au foil surface resulted in a layer by layer growth. no interaction between the deposit and the substrate was observed and the energy shifts of the mgcl2 photoelectron peaks were obvious due to electrostatic charging. similar energy shifts were observed after deposition of mgcl2 on si(111)7x7 due to the insulating nature of the deposit. the growth mode of mgcl2 the si surface indicates the frank-van der merve, (fm) growth mode, but leaving uncovered areas of silicon at the first steps of the deposition. references [1] ep 297 824 a2, shell oil company, invs r.f. job; chem abstr., (1989), 110, 21363h [2] e. magni, g.e. somorjai , surf. sci. 345 (1996) 1-16 [3] s. karakalos, a. siokou, v. dracopoulos, f. sutara, t. skala, m. skoda, s. ladas, k. prince, v. matolin, v. chab, journal of chemical physics 128, (2008),104705 [4] karakalos s., siokou a., sutara f., skala t., vitaliy f., ladas s., k. prince, v. matolin, v. chab, journal of chemical physics 133, (2010), 074701 authors profile stavros karakalos was born in athens in 1979. he received b.s. in physics from the university of ioannina in 2003, msc in material science and technology and ph.d. in chemical engineering – surface science in 2009. presently he is post doctoral researcher at the foundation for research and technology, institute of chemical engineering and high temperature chemical processes in patras, greece. his research interests include the use of a large variety of surface analysis and characterization techniques in order to determine the structure, composition and electronic properties of the outermost atomic layers of solid materials exposed to ultra-high-vacuum or controlled gaseous atmospheres and correlate them with the material behavior in various processes. his main research interests include surface science aspects of heterogeneous catalysis. microsoft word etasr_v12_n5_pp9347-9350 engineering, technology & applied science research vol. 12, no. 5, 2022, 9347-9350 9347 www.etasr.com al-fahdawi et al.: the mechanical properties of ferrocement mortar with waste plastic fibers at … the mechanical properties of ferrocement mortar with waste plastic fibers at elevated temperatures farah a. al-fahdawi department of civil engineering university of anbar anbar, iraq far20e1013@uoanbar.edu.iq abdulkader i. al-hadithi department of civil engineering university of anbar anbar, iraq abdulkader.alhadithi@uoanbar.edu.iq jamal a. al-asafi department of civil engineering university of anbar anbar, iraq jamal.khalaf@uoanbar.edu.iq received: 21 july 2022 | revised: 31 july 2022 | accepted: 10 august 2022 abstract-the main aim of the current research was to investigate the behavior of ferrocement mortar reinforced with waste plastic fibers at elevated temperatures. the use of pet residues in ferrocement mortar at normal temperatures could be a viable option. however, the utilization of pet-containing ferrocement mortar in high-temperature applications requires more research. in this study, one reference mix was made along with 3 other mixes containing polyethylene terephthalate (pet) fiber by volumetric ratios of 0.5, 0.75, and 1%. compressive and flexural strength tests were performed on the samples before and after being exposed to elevated temperatures. each batch of ferrocement mortar samples was heated to the requisite temperature for roughly 60 minutes, then was progressively cooled to room temperature before being tested. the compressive and flexural strengths of some samples were evaluated at room temperature (25°c). other samples were evaluated after being exposed to high temperatures in an electric furnace (100°c, 200°c, 400°c, and 600°c). both compressive and flexural strengths were found to be significantly reduced after being exposed to a temperature greater than 400°c. results proved that the addition of 0.75% pet was determined as the optimum percentage that enhanced the mechanical properties of the produced ferrocement mortar at 25°c. at 200°c, the ferrocement mortar samples retained their original color. as a result of the combustion of pet fibers, black spots formed on the top surfaces of the tested specimens that were heated to 400°c. keywords-elevated temperature; ferrocement mortar; flexural strength; compressive strength; pet; mechanical properties i. introduction ferrocement is a thin water-cement mortar that has been reinforced with close layers. it is considered the best regarding the resistance to compression, tensile strength, and fracture parameters. also it is light weight, easy to operate, and economical. ferrocement technology was introduced in the '70s; damaged parts of concrete structures were reinforced with this mortar [1]. cement mortars are a main component of the construction industry, used in many applications and in the manufacturing of ferrocement elements [2]. the mortar is the resulting material for the proposed mixture (intimate mixture) of sand grains, binder, and water. its properties depend mainly on the nature of the compounds of the binder in it [3]. cement mortar is used as a binder for building units in walls or to protect building surfaces. when making ferrocement, the mortar has a 95% or more effect on the behavior of the final product. ferrocement mortar has practical uses in strengthening concrete structures damaged by loads and stresses. managing waste is a global major challenge, as various human activities result to the production of significant amounts of waste of different kinds [4]. the residues of mineral water bottles and pet beverage containers consist a major source of solid trash. sustainable materials are being developed with economic and environmental benefits in order to reduce pollution, including co2 emissions, and recycle waste by incorporating environmentally friendly materials into civil engineering projects. the use of post-consumer plastics in concrete production is an economical alternative and consumption of resources. the global widespread use of pet as well as the long-term degradation of this plastic type in nature has prompted researchers to investigate pet recycling solutions. the incorporation of plastic waste into concrete to enhance the qualities of hardened concrete and solve the problem of brittleness has garnered considerable research interest. the inclusion of plastic wastes, such as polypropylene fibers, in concrete can prevent cracking and improve the resistance of concrete components to cracking [5]. the usage of hand-cut pet fibers with length of 6cm, width of 1.2cm, and various geometric shapes, increases the strength of hardened concrete [6]. corresponding author: farah a. al-fahdawi engineering, technology & applied science research vol. 12, no. 5, 2022, 9347-9350 9348 www.etasr.com al-fahdawi et al.: the mechanical properties of ferrocement mortar with waste plastic fibers at … when structural elements deteriorate as a result of exposure to high temperatures, the risk of a structure collapsing increases. as a result, the selection of fire-resistant materials to limit heat damage to structural elements is critical. the research on the behavior of concrete at elevated temperatures has showed that elevated temperatures degrade the mechanical characteristics of concretes. the behavior of concrete at high temperatures depends on a few parameters, including the constituents of the materials used for the concrete mixture and the permeability of the concrete [7]. exposure to temperatures above 300°c can drastically reduce the mechanical characteristics of concrete. the calcium hydroxide content of the cement material can be dehydrated at temperatures above 400°c. consequently, the water vaporizes, which causes the physical qualities of concrete to deteriorate [8]. the effect of rising temperatures on the characteristics of strengthened cement mortar by adding waste plastic fibers from soft drink bottle recycling is studied in this paper. these fiber types were added in volumetric proportions (0.5%, 1%, 1.5%, and 2%) and a reference mixture was utilized for comparison. the specimens of cement mortar from each group were heated to the desired temperature before being evaluated. some samples were tested for compressive and flexural strength at room temperature, while others were studied after being exposed to increased temperatures of 100, 200, 400, and 700°c. after exposure to temperatures over 400°c, the compressive and flexural strength values decline significantly [9]. the main objective of this study is to investigate experimentally the effect of high temperatures on the mechanical properties of concrete and the effect of the added fibers to the ferrocement mortar as a solution to increase the resistance and to control cracking during fire exposure. ii. materials a. cement ordinary portland cement (opc) type i with 3.15g/cm 3 specific gravity was used as a binder in all mixes. cement is the most important component in concrete production [10]. the physical properties of opc are shown in table i, according to the iraqi [iqs no.5/ 2019]. table i. physical characteristics of opc physical characteristics test result iqs, no.5/ 2019 fineness using blain method (cm 2 /g) 3344 >2500cm 2 /gm initial setting time (min) 164 >45min final setting time (min) 222 <600min soundness (mm) 1 <10mm b. fine aggregates local sand passing through 2.36mm with specific gravity of 2.65g/cm 3 was used. table ii shows the characteristics of the used sand according to the iraqi specifications [11]. table ii. characteristics of fine aggregates type aggregate sand passing sieve 2.36 specific gravity 2.65 salt content % 0.11 c. water tap water was used to create and cure concrete in this research. d. polyethylene terephthalate (pet) the type of waste plastic considered in this study came from waste plastic soft drink bottles. the waste plastic bottles were sliced to small uniform pieces with an average length equal to 30mm, width equal to about 3mm, and thickness equal to 0.3mm. the density of the waste plastic fibers was 1300kg/m 3 , the aspect ratio was 28, and the tensile strength 103mpa. the volumetric ratios used in this study were 0, 0.5%, 0.75%, and 1%. iii. types of molds a total of 120 cube and prism specimens were cast. the dimensions were 70×70×70mm cubes for compressive strength testing and 40×40×160 mm prisms for flexural strength testing. iv. mix design several experimental mixtures were produced to choose the optimal mixing water ratio by using a mold of mortar 50×50×50mm to determine the compressive strength after 7 days. the chosen design was 1:3:0.45 cement, fine aggregates, and water/cement ratio respectively by weight. the designed strength was 30mpa. v. casting and curing to prevent the mortar from adhering to the inside surfaces of the molds, they were cleaned and pre-coated with coating oil. all the specimens were covered with nylon sheets to avoid water evaporation immediately after the concrete was mixed. the samples were de-molded and immediately submerged in the treatment water basin for 28 days after the nylon sheets were removed. vi. heating process at the age of 28 days, the specimens were withdrawn from the water cure and were left to dry in the laboratory for one day. the concrete specimens were then dried in a vented oven before being exposed to high temperatures. the first group with 24 cube and prism samples (3 samples for each mixture) was assessed and utilized as a comparison standard at room temperature (25°c). in the laboratory furnace, 4 more groups were exposed to temperatures of 100, 200, 400, and 600°c for 1h. after the exposure, the specimens were allowed to cool at room temperature before being tested. vii. testing program a. compressive strength test based on [12], compressive tests on the cubic samples were carried out to find the concrete's compressive strength after 28 water-curing days. all samples were tested in the ele-digital testing compression machine with a maximum capacity of 2000kn at the rate of 3kn/s. three cubes were tested for each case (room temperature, 100°c, 200°c, 400°c, and 600°c) and the average strength was considered. engineering, technology & applied science research vol. 12, no. 5, 2022, 9347-9350 9349 www.etasr.com al-fahdawi et al.: the mechanical properties of ferrocement mortar with waste plastic fibers at … b. flexural strength test flexural strength was measured according to [13]. a machine with a capacity of 5kn was used to determine flexural strength (center-point loading method) on the prismatic samples after 28 water-curing days. three prisms were tested for case and their average strength was considered. viii. results and discussion figure 1 shows the relationship between temperature and compressive strength for all ferrocement mortar mixes. in general, it can be clearly seen that all cement mortar mixes exhibited a loss in compressive strength as temperature increased. as the temperature increases above 400°c there is a major decrease in compressive strength, which can be attributed to the loss of cement paste plasticity at high temperatures [14]. at room temperature (about 25°c), the mixes with vf value equal to 0.75% exhibited higher compressive strength by 17.63% than the reference ferrocement mortar mix. at the same temperature, the mix with vf = 1% had lower compressive strength than the reference mix by 12.28%. that decrease in compressive strength might be caused by the forming of segregations on the mixes containing waste plastic fibers, leading to form stiff bonds about these bulks. also, the plastic fibers reduced the density of cubes, and that leads to a decrease of the compressive strength of the composite [15]. using of waste plastic fiber with vf = 1% increased the porous inside the mortar structure and that reduced the compressive strength. fig. 1. relationship between temperature and compressive strength for all ferrocement mortar mixes. flexural strength results of ferrocement mortar mixtures at the age of 28 days are shown in figure 2, which shows a decrease in flexural strength with the elevation of temperature for all 4 mixes. as the temperature increases above 400°c there is a major decrease in flexural strength. at room temperature, the addition of waste plastic fiber to mixes had a positive effect on flexural strength in compared with the reference mix, in accordance with the findings of [16]. this can be attributed to the increase of homogeneity, the decrease in voids, and the increase of the bond strength between the waste plastic fibers and the other components of concrete mixture. fibers resist the generation of cracks and bridging of these cracks. the test results showed increase in flexural strength by 2.81%, 5.45%, and 1.08% when waste plastic fibers were added by vf equal to 0.5%, 0.75%, 1% respectively. when the volumetric ratio of waste plastic fibers is equal to 1%, the decreasing in flexural strength is still greater than that of the reference mixture. the reason for this is that increasing the volumetric ratios of fiber reduces flexural strength due to the irregular distribution of fibers. the samples (cubes and prisms) which were heated to a temperature equal to 200°c maintained their original color, while in specimens heated to 400°c, black spots appeared on the top surfaces of the cubes due to the burning of pet. at 700°c, the black spots disappeared due to the evaporation of the burned pet residuals and the specimens suffered noticeable color changes with a spalling occurred on the samples surfaces. fig. 2. relationship between temperature and flexural strength for all ferrocement mortar mixes. ix. conclusions the following conclusions could be drawn from the current research work:  the addition of pet fibers is an effective method for recycling plastic waste.  the compressive and flexural strength values of reference cement mortar and mortar containing waste plastic fibers reduced by an amount depending on the value of the exposing temperature.  for specimens evaluated at temperatures up to 200°c, the loss in compressive strength was relatively small.  a severe decrease in the compressive and flexural strength values occurred when the specimens were exposed to temperatures higher than 400°c.  the samples which were heated to temperature equal to 200°c maintained their original color and no apparent visual discoloration occurred in the ferrocement mortar.  due to the combustion of pet fibers, black patches form on the surfaces of mortar cubes and prisms heated to 400°c. engineering, technology & applied science research vol. 12, no. 5, 2022, 9347-9350 9350 www.etasr.com al-fahdawi et al.: the mechanical properties of ferrocement mortar with waste plastic fibers at …  at 700°c the black spots disappear due to the evaporation of the burned pet residuals and the specimens suffered noticeable color changes with a spalling occurring on the sample surfaces. references [1] l. m. jiang, f. h. tang, and m. l. ou, "experimental 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[16] a. a. chyad, "flexural strength and impact behavior of ferrocement members containing waste materials," m.s. thesis, university of anbar, ramadi, iraq, 2021. microsoft word etasr_v12_n2_pp8426-8430 engineering, technology & applied science research vol. 12, no. 2, 2022, 8426-8430 8426 www.etasr.com alrashdi & khan: design and comparative analysis of high speed and low power alu using rca … design and comparative analysis of high speed and low power alu using rca and sklansky adders for high-performance systems ali fraih alrashdi department of electrical engineering university of hail hail, saudi arabia gnem.h2003@gmail.com muhammad imran khan department of electrical engineering university of hail hail, saudi arabia imran@alumni.chalmers.se received: 9 february 2022 | revised: 28 february 2022 | accepted: 1 march 2022 abstract—this study examines how different initial design decisions affect the area, timing, and power of technologymapped designs. asic design flow, tools used during the flow, and the factors to consider to maximize the performance and power ratio are discussed. the alu (arithmetic logic unit) is a fundamental part of all processors. in this study, two alus were implemented using two different types of adder circuits: a ripple carry adder (rca) and a sklansky adder. the cadence eda tools were used for the implementation. a comparative analysis was conducted for the two designed alus in terms of area, power, and timing analysis. the alu design was also used as an example to examine the whole workflow front-end wise by constructing a block schematic and back-end wise by floorplanning, placing, and routing the physical design. keywords-arithmetic logic unit (alu); ripple carry adder; sklansky adder; vhdl i. introduction the basic purpose of this study was to examine the impact of initial design decisions on the area, timing, and power of asic designs and to introduce the asic design flow from the beginning to the end, i.e. from rtl design to floorplanning and layout. the arithmetic logic unit (alu) is a key element of a processor that performs arithmetic and logical operations on binary numbers [1-7]. several 32-bit alus have been designed and coded in vhdl [8-13]. an alu consists of three major parts: adder, logic unit, and shifter. the adder is responsible for the subtraction and addition operations of signed and unsigned numbers. the logic unit is responsible for bitwise logical operations, and the shifter unit is responsible for the arithmetic and logical shift operations, as shown in figure 1 [14-20]. in the first alu design, a ripple carry adder (rca) was used, while in the second one, a prefix tree of sklanskytype adder was used. the adder is a very important component in digital systems, and in the past, much research has been conducted on various adder types to improve their speed and area requirements [21-25]. apart from the adder, both alu types consisted of logical and shifter blocks. the design in figures 1 and 2 has three main blocks: adder/subtractor, bitwise operations, and shifter. the adder block has two different implementations: a ripple carry and a sklansky type. the alu registers in data (a/b), opcode (op), and output were positively edge-triggered. the design was implemented using two approaches. the first approach, shown in figure 2, has all the functional blocks that compute the operations and the mux at the output decides which functional block is connected to the output. the other approach intended to guard the individual functional blocks using a mux after the input registers. this input mux intended that if the opcode is not meant for the particular functional block, it will get all zeroes as data input, reduce the combinatorial switching, and hence decrease power consumption. but then, the first design approach was chosen as including six 32-bit muxes would take up too much area and would probably kill the basic idea of saving power consumption. [25-30]. fig. 1. block diagram of a 32-bit alu ii. simulations and verification after completing the design in vhdl, the functionality of the alu design was verified using a test bench and test vectors. the test bench was also designed in vhdl as a nonsynthesizable code, while the rest of the alu code was synthesizable. the test bench was designed to be able to read the test vectors and send them as input to the 32-bit alu. the test bench compared the outputs received from the alu to the corresponding author: muhammad imran khan engineering, technology & applied science research vol. 12, no. 2, 2022, 8426-8430 8427 www.etasr.com alrashdi & khan: design and comparative analysis of high speed and low power alu using rca … expected outputs. as these test vectors and expected outputs were a design specification, running them on the test bench was a functional verification. functional verification of rca and skl was performed by the cadence simulation tool called ncsim. three different sets of test vectors were used to verify the alus: 1001 random test vectors, 1001 regular test vectors, and 154999 real trace test vectors. these test vectors were not enough to provide the full test coverage, however 268 combinations of test vectors can be a reliable number. fig. 2. specifications of the alu. iii. synthesis after the successful simulation and verification of the design, the next step was to synthesize it. logic synthesis is the process to convert hdl code into rtl netlist in terms of standard cells. a 130nm process technology was used for the standard cell library. the rtl compiler tool generated the netlist at the end of synthesis in the form of verilog code. opening this verilog code revealed that it was an entirely structural code with hardware description in terms of connections between standard cells. after making sure that the alu design was synthesizable, static timing analysis was used to analyze the timing performance of the design without simulating the design. the alu rca design was synthesized using various timing constraints and tables i-ii show the results of those attempts. the rca-based alu did not meet the timing constraint for an 800mhz processor. the best timing was achieved by the rca-based alu at around 2250ps (444 mhz). the critical path of the rca-based alu laid in the rca block for all the above implementations, though the exact path changed as stricter timing constraints were introduced. but for the most part, the path consisted of input carry rippling through the circuit from the lsb to the msb. table i. sta results for alu rca effort time constraint (ps) worst case delay (ps) area of implementation (µm 2 ) low none 4369 12619 medium 2689 2688 12482 medium 1250 2000 13906 medium 2250 2250 13049 the skl based alu was able to meet the timing constraint for an 800mhz processor and was even able to clock up to 1ghz, although it pays in terms of area to reach this frequency. one major difference between the rca and skl designs was in terms of the critical path. for stricter timing constraints, the rca had its critical path lying in the adder block, whereas the skl had it in the shifter block. this is understandable since the sklansky adder is much faster compared to the rcar. examining the 10 worst paths showed that the critical paths for the skl design were evenly distributed between the shifter and adder blocks. [31-35]. table ii. sta results for alu skl effort time constraint (ps) worst case delay (ps) area of implementation (µm 2 ) low none 4528 13960 medium 2500 2480 13283 medium 1250 1250 16069 medium 1000 1000 18185 iv. comparison for both rca and skl adders, the power at 0.1 toggling probability is greater than at 0.02, i.e. power(0.1)>power(0.02). the leakage power is almost the same at different toggling probabilities, but dynamic power increases with an increase in toggling probability, as table iii shows. this makes sense as increasing the toggling probability increases the switching activity of internal nodes and nuts, which results in increased power. skl dissipates less power than rca. the area of implementation depends on the effort used by the rtl compiler and the timing constraints. the structure of skl is more regular compared to rca because skl has an improved structure. the clock capacitance of rca is more than skl. figures 3 and 4 show the area of implementation of the rca and skl alus respectively. fig. 3. alu rca area implementation (µm 2 ). fig. 4. alu skl area implementation (µm 2 ). engineering, technology & applied science research vol. 12, no. 2, 2022, 8426-8430 8428 www.etasr.com alrashdi & khan: design and comparative analysis of high speed and low power alu using rca … figure 5 shows the area of implementation for both alus, while figure 6 shows their power dissipation plots. figure 7 shows a comparison of the efficiency of both alus in terms of power consumed under different timing constraints. rca is more power-efficient than skl. skl increases its power efficiency in lower timing constraints. the choice of the input sequence is very important for power analysis. the input sequence can be chosen from real logic simulations. three value change dump (vcd) files were created for rca, having random, regular, and real trace vectors as sets of input patterns. the vcd file gets real switching information in the power analysis and goes into the rtl compiler. fig. 5. implementation area comparison of rca and skl alus. fig. 6. power dissipation of rca and skl alus using different timing constraints. fig. 7. power comparison between rca and skl alus. table iii. power analysis of skl and rca based on varying toggling probabilities timing constraint (ps) adder type toggling probability leakage power (µw) dynamic power (µw) total power (µw) clock power (µw) clock capacitance (ff) unconstraint rca 0.02 294 1334 1608 104 309.400 unconstraint rca 0.1 294 3892 4186 104 309.400 unconstraint sklansky 0.02 326 1760 2086 176 307.400 2508 sklansky 0.1 326 4322 4648 176 307.400 2508 rca 0.02 346 1873 2219 208 363.000 2508 rca 0.1 346 4695 5041 208 363.000 2508 sklansky 0.02 328 1963 2291 208 310.200 2150 sklansky 0.1 328 4701 5029 208 310.200 2150 rca 0.02 369 2190 2559 293 437.400 2150 rca 0.1 369 5194 5563 293 437.400 1250 sklansky 0.02 350 2857 3207 378 328.100 table iv. power estimation based on test vectors timing constraint (ps) adder type test vector type leakage power (nw) dynamic power (nw) total power (nw) 2508 rca random 346558.721 6983081.572 7329640.292 2508 rca regular 348672.104 36022780.146 3951452.250 2508 rca real trace 351631.026 3954686.641 4306377.667 2508 sklansky random 32364.014 6358256.700 6685620.713 2508 sklansky regular 330858.982 3205877.702 3536070.684 2508 sklansky real trace 340725.210 3516652.143 3857377.353 2150 rca random 370941.482 8473036.411 8843977.893 2150 rca regular 372972.466 4485655.551 4858628.017 2150 rca real trace 373893.091 4747270.943 5121064.034 2150 sklansky random 328880.228 7649393.717 7978273.945 2150 sklansky regular 331153.317 4040497.554 4371650.871 2150 sklansky real trace 335008.116 4308426.483 4643434.599 engineering, technology & applied science research vol. 12, no. 2, 2022, 8426-8430 8429 www.etasr.com alrashdi & khan: design and comparative analysis of high speed and low power alu using rca … table iv indicates that random vectors consume more power while the regular and real trace vectors consume less. the real trace vectors consume a little more power than the regular vectors. the flow for creating a use case power analysis was to synthesize the design with a specified timing constraint and compile cell library files along with the verilog netlist of the synthesis and the testbench. a simulation was then run on a test vector set and signal switching activity was written into a vcd file. this file was compiled by an rtl compiler to obtain "real" switching information in the power analysis [28-30]. comparing the power dissipation from the analyses made with random, regular, and real-trace test vectors showed that the random file is the most power-consuming, while the regular and the real trace are close, and the latter consumed a little more power. random vectors were expected to consume more power. the real trace was expected to be the least powerconsuming set but it seems that the regular set has more regularity and thus less switching than the real trace. power consumption depends on the use of the design. assuming that the design meets the power constraints, when it is only analyzed with a limited and perhaps irrelevant test vector set it can result in faulty conclusions. it is always good if real use cases can be tried, which is not always the case [35-40]. v. place and route finally, the design was examined through the back-end flow using the cadence soc encounter. floorplanning is the first step of the place and route flow. floorplanning means specifying where to place different blocks of the design. in this step, it is important to make a good modular partitioning of the design. also, since the critical path is in the rca block, the maximum area should be provided in terms of utilization percentage. once the floorplanning was complete, the necessary stages of physical design, such as pin placement, power grid routing, standard cell placement, clock tree synthesis, and routing, followed. the next step was the clock tree synthesis (cts) which was optimized in three steps: prects, cts, and post-cts. it is useful to perform a timing analysis between each optimization to see if the timing constraints are met. the actual cts step is like mapping the design to actual cells. the positions of clock buffers and clock tree were checked and it was found that the design had one level of buffers. the timing was checked again after this step but the constraint still wasn't met. the last step of cts, i.e. post-cts optimization, was followed to achieve the optimization based on the existing clock tree. the timing was checked again and it was found to be improved a lot, as the slack time was -0.466, much better than before when it was -2.259. routing and postroute optimization were performed. the clock and reset signals should have the highest priority because they have to be provided to every block in the design and therefore are critical. filler cells were used to fill the gaps and connect them to the power rails. layout verification was performed. four mincut violations were found, which were later removed using the fixmincutvia command. the final timing analysis showed a slack time at -0.395. vi. conclusion an alu design was drawn through the eda flow from the basic idea and block schematic through rtl, verification, and back-end design with place and route. the synthesis results showed that the area of the rca alu changes more rapidly than that of the skl alu because the former has to put more effort to meet the stricter timing constraint at the expense of more area. the skl alu is a fast adder and easily meets the stricter timing constraint without increasing area and power consumption. it was also observed that the rca alu used less area and power compared to the skl alu, so it is better to use it if the timing constraint is not high, as it can be a more efficient design in terms of area and power consumption. furthermore, it was very instructive to see how different initial 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[40] y. choi and e. e. swartzlander, "speculative carry generation with prefix adder," ieee transactions on very large scale integration (vlsi) systems, vol. 16, no. 3, pp. 321–326, mar. 2008, https://doi.org/ 10.1109/tvlsi.2007.915502. microsoft word etasr_v13_n4_pp112290-11297 engineering, technology & applied science research vol. 13, no. 4, 2023, 11290-11297 11290 www.etasr.com ali et al.: numerical modeling of the flow around a cylinder using featool multiphysics numerical modeling of the flow around a cylinder using featool multiphysics binahi m. a. said ali department of water resources engineering, college of engineering, salahaddin university, iraq binahi.saidali@su.edu.krd jehan m. sheikh suleimany department of water resources engineering, college of engineering, salahaddin university, iraq jehanmohammed.sheikhsuleimany@su.edu.krd safa s. ibrahim chemistry department, faculty of science, university of zakho, iraq safa.ibrahim@uoz.edu.krd (corresponding author) received: 17 may 2023 | revised: 8 june 2023 | accepted: 9 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6053 abstract the current study examines the numerical analysis of the laminar flow around a cylinder at various reynolds numbers (0.1, 1.1, 20, 26, 50, 100, and 195). the research found that a steady state can exist for reynolds number values of 0.1, 1.1, 20, and 26. however, the flow pattern becomes unstable at reynolds numbers 50, 100, and 195, leading to the development of the kármán vortex street. the featool multiphysics software in matlab (r2019b) was utilized to numerically solve the steady 2d navierstokes equation. the study compared the estimated drag coefficient to previous experimental and analytical studies in abaqus/cfd. the lift and pressure coefficients were also calculated, and their results were found to be in strong agreement with earlier investigations in terms of predicting pressure and velocity distribution. the analysis provided insight into how the flow field changes with increasing reynolds numbers. keywords-drag coefficient; cylinder; featool multiphysics in matlab (r2019b); ` i. introduction studies on the flow through a cylinder have been extensive in fields such as fluid mechanics, hydraulics, and wind engineering, as it is crucial to comprehend the dynamic forces that are produced by the flow around an object in determining its aerodynamic shape. an effective method for gaining a comprehensive understanding of the flow field is by utilizing computational fluid dynamics (cfd), which is widely employed in design processes [1]. in the field of fluid dynamics, the flow around a cylinder has been a topic of interest for numerous researchers [2-4]. wieselsberger's study [5] verified lamb's empirical formula and provided extensive experimental data for cylinder flow at both low and high reynolds number values. the measurements in [6] on a pressurized wind tunnel show that a large circular cylinder experiences a high reynolds number transition. at reynolds numbers ranging from 10 6 to 10 7 , the drag coefficient initially increases from its low supercritical value. however, at r = 3.5 × 10 6 , it stabilizes at a value of 0.7. additionally, beyond this point, the cylinder exhibits clear vortex shedding with a strouhal number of 0.27. the empirical reynolds number formulas for the drag coefficient at low reynolds numbers were summarized in [7]. authors in [8] used the kpd2 algorithm, an integral method, to determine the boundary layer around a cylinder, correcting distortions in vortex modeling present in earlier versions of the system. authors in [9] performed a numerical investigation of the velocity and pressure around a cylinder in the near field at reynolds numbers 100, 500, and 1000. they used the alternating direction implicit (adi) method to solve the continuity and momentum equations, which describe mass and momentum conservation in the flow field. authors in [10] applied multi-grid methods to investigate flow past a cylinder at reynolds number 200. these techniques were used to address the challenge of accurately simulating unstable incompressible flow. the authors validated their solution by comparing it to both numerical and experimental data. authors in [11] utilized a two-dimensional (2d) numerical approach combining reynolds-averaged navier-stokes (rans) and large eddy simulation (les) to investigate the flow behavior around a cylinder at high reynolds numbers. this approach solves navier-stokes equations in both stable and unstable flow conditions, as suggested in [12]. to test their engineering, technology & applied science research vol. 13, no. 4, 2023, 11290-11297 11291 www.etasr.com ali et al.: numerical modeling of the flow around a cylinder using featool multiphysics method, authors in [11] studied the flow around a cylinder at low reynolds numbers using a finite difference and meshless technique, a widely used method in cfd simulations. authors in [13] employed the finite volume method to analyze the flow through a cylinder in laminar and turbulent regimes by solving the unsteady reynolds-averaged navier-stokes (urans) equations. they used wall interference adjustments to ensure the accuracy of their results in both numerical analysis and experimental investigation. authors in [14] aimed to control the flow around a circular cylinder by introducing artificial roughness to its exterior, both experimentally and numerically. using cfd simulations, the researchers determined the correlation between roughness size and re variations in the re range of 1×10 4 to 2×10 5 in a boundary layer wind tunnel (blwt). the results were compared with previous experimental data and computational simulations. these findings have practical applications in the testing of scale models in low-speed blwts seeking super-critical flow characteristics. authors in [15] performed a numerical investigation of vortex shedding in laminar flow around twodimensional (2d) and three-dimensional (3d) circular cylinders using the finite volume method, a commonly used computational fluid dynamics technique. they controlled the flow around high reynolds number cylinders with surface roughness through analytical and experimental methods. authors in [16] studied the flow around a round cylinder in a planar channel using 2d and 3d direct numerical simulation (dns) techniques. they examined the flow behavior at low reynolds numbers, where vortex shedding was often observed. similarly, authors in [17] carried out numerical simulations to study the flow through a cylinder in the laminar regime. they employed the finite volume method to solve the navier-stokes equations, which describe the conservation of momentum in the flow field. authors in [18] completed a series of fundamental studies on the fluid flow around a circular cylinder placed in a uniform flow using abaqus/cfd, a computeraided engineering (cae) software package. authors in [19] used numerical simulations to study the flow around two oscillating cylinders at a reynolds number of 100. they applied the characteristic-based-split finite element method and mini triangular elements to solve the 2d navierstokes equations using an arbitrary-lagrangian-eulerian formulation. the results showed five flow response states via analysis of lift forces, phase portraits, energy transfer, and flow fields for in-phase oscillation at different frequencies and small amplitudes, using power spectra. authors in [20] carried out experiments on the growth and separation of leading-edge vortices (levs) from a plunging profile in a free-surface water tunnel. the experiments measured the direct force and velocity field at a reynolds number of 10,000, a reduced frequency of 0.25, and a strouhal number of 0.16, using three different leading-edge shapes. the results showed that the shape of the leading edge significantly impacted the formation of the lev and the flow pattern. authors in [21] conducted an experiment to analyze the movement of flow separation points on a circular cylinder at high acceleration rates and reynolds numbers, using hot-film sensors to measure wall shear stress. the results indicated that as a cylinder accelerates, the flow separation point moves quickly, symmetrically, and linearly from 160° to 85° on both sides. it then fluctuates between 75° and 85° during the rest of the acceleration phase. the pattern of separation points is consistent for both acceleration cases when scaled by non-dimensional time. authors in [22] conducted research to analyze the flow patterns around a vertical cylinder that rises above the water surface. they employed both experimental and numerical methods to examine the flow under different velocities, with reynolds and froude numbers ranging from 15,000 to 60,000 and 0.4 to 1.7, respectively. the findings showed a strong correlation between the experimental and numerical results, particularly in terms of the depth of the cavity downstream of the cylinder, the drag coefficient, and the critical velocity. authors in [23] focused on using cfd to examine fluid flow around a cylinder. the ansys fluent cfd software was utilized to simulate the flow in both steady and unsteady regimes for specific values of reynolds number, i.e. 1, 25, 75, and 150. authors in [24] investigated the effect of a cylindrical object on turbulent flow using numerical simulations with featool multiphysics software. the outcome was evaluated on the basis of pressure differential and drag coefficient and a simulation of turbulent flow past a square cylinder was also performed. the goal of the current research is to investigate the effect of changing reynolds number on the flow around a 2d cylinder using featool multiphysics in matlab (r2019b). as parts of this study, the drag coefficient, lift coefficient, and pressure coefficient on the cylinder will be calculated and the simulation results will be presented in the form of velocity and pressure contours. after performing the simulations, a thorough analysis of the output will be conducted for each reynolds number. this configuration allowed the investigation of the influence of the reynolds number on the flow behavior around the cylinder. ii. the suggested approach the cfd data generation process is an essential step in the implementation of deep learning algorithms in computational fluid dynamics. the process typically involves the following steps [23]:  random obstacle generation: the first step is to generate random obstacles using the matlab featool solver. this involves defining the geometry of the obstacles and setting up the simulation environment in the software.  resolution of the navier-stokes equations: the navierstokes equations which describe the behavior of fluid flow, are solved numerically using the immersed method to obtain fluid velocity, pressure, and other flow parameters.  acquisition of cfd fluid fields: the final step is to obtain the cfd fluid fields, including the coordinates (x, y), velocities (u, v), and pressure (p). these fluid fields provide detailed information about the fluid flow patterns and can be used to train deep learning models (figure 1). the following sections present the detailed components of the architecture. engineering, technology & applied science research vol. 13, no. 4, 2023, 11290-11297 11292 www.etasr.com ali et al.: numerical modeling of the flow around a cylinder using featool multiphysics fig. 1. data collection from the cfd solver. a. numerical resolution of the navier–stokes equation the mass and momentum equations for the incompressible 2d navier-stokes system are expressed as follows: � ����� � ��. ∇��� ∇. ���∇� � ∇� � �� � � � � (1) ∇. � � 0 (2) where the velocity field is denoted by u, density is denoted by �, the pressure field is denoted by p, the stress tensor is denoted by � , � � μ/�� is the kinematic viscosity, and body forces (ex. gravity) are denoted by f, whereas in this case the time dependent term can be neglected. the benchmark quantities that should be computed include the pressure difference between the front and rear of the cylinder ∇p = p (0.046,0.05) − p (0.054,0.05), and the coefficients of drag cd and lift cl, defined as: �� � �� !"#$%&' ( , �* � ��+ !"#$%&' ( (3) the drag and lift forces, �, and �, can be computed as �, � . �� /�0�1� /2 34 �35 � �6 7 (4) �� . �� /�0 �1� /2 35 �34 � �6 7 (5) where �8 is the velocity in the tangential direction � � �34 , 35 , 0�� . b. random shape generation the numerical simulations for seven different reynolds numbers (re = 0.1, 1.1, 20, 26, 50, 100, and 195) were performed using the featool multiphysics simulation toolbox in matlab (r2019b), based on previous studies. a rectangular 2d computational domain with a circular cylinder was considered in the numerical domain in the xy plane. figure 3 presents the benchmark problem for stationary and incompressible laminar flow around a cylinder, which was established in a rectangular 2d domain as in [18]. the dimensions of the rectangular 2d domain were set as: the width in the stream direction is 0.2 m and the height perpendicular to flow is 0.1 m. the cylinder has a diameter of 0.008 m and the center point located at (0.05, 0.05) from the inlet, with the computational domain centered around it, as shown in figure 2. c. mesh generation and boundary conditions grid computation and boundary specification are crucial elements in the execution of cfd modeling. in order to analyze the velocities and pressure fields, a structured mesh with triangular elements of varying sizes was employed during preprocessing and deep learning network training. the fluid domain was divided into two sections, where the region close to the cylinder wall was meshed with elements of a size of 0.0002, and the rest of the fluid domain was meshed with elements of a size of 0.002, as depicted in figure 3. consequently, the average number of cells was approximately 35,000. fig. 2. geometry of the flow system. the selection of these element sizes was predicated on the convergence of the drag coefficient, as demonstrated in figure 4. it was established that a reduction in the grid size below 0.002 did not result in significant alterations to the drag coefficient. utilizing a structured mesh with strategically chosen element sizes facilitated an exact and efficient simulation of the fluid flow dynamics surrounding the cylinder. engineering, technology & applied science research vol. 13, no. 4, 2023, 11290-11297 11293 www.etasr.com ali et al.: numerical modeling of the flow around a cylinder using featool multiphysics fig. 3. the structured mesh used to discretize the flow domain around the cylinder, with triangular elements of varying sizes used to capture the complex flow behavior in the boundary layer and far field. fig. 4. variation of the drag coefficient with the size of the grid. the fluid in this simulation was modeled as a viscous laminar flow. to establish the simulation, it was necessary to input the relevant material properties into the software, as indicated in table i. these properties included dynamic viscosity and density, both of which are critical for accurately modeling the flow behavior. for boundary setting, the left side of the 2d domain was the velocity inlet and the right side was the pressure outlet. no-slip conditions were assigned to the surface of the circular cylinder and the top and bottom sides as obstacle walls, as illustrated in figure 5. table i. physical properties of the fluid fluid density 9 (kg/m3) dynamic viscosty, : �;<. =� water 998.2 0.001 fig. 5. boundary specifications for the circulation of water around a cylinder. in the study of the fluctuation of the flow field at various reynolds numbers, the inlet velocity input (with u = u0) had its boundary coefficients adjusted seven times based on the reynolds number through (6)-(8) (v0 was set to 0). the outflow pressure output (p0 = 0) had its boundary coefficient fixed at 0. the walls, with no slip (u = 0), did not have any boundary coefficients. additionally, the boundary conditions were constant, with the density (ρ) set to unity at 998.2, viscosity (miu) at 0.001, and a default value of 0 for the forcing term (f). the velocity fluctuation was analyzed using the maximum velocity >?@5 and the mean velocity >?a@2 , with the reynolds number (re) representing the laminar flow. the details of the boundary conditions used can be seen in table ii. bc � !"#$%&(d (6) >?@5 � e � >?a@2 (7) � � 4g>?@5 h ij4 i' k (8) where u represents the entrance velocity (m/s), and d represents the cylinder diameter (m). table ii. mean velocity for each reynolds number cases re umean (m/s) umax (m/s) case 1 0.1 0.0000125 0.0000188 case 2 1.1 0.0001377 0.0002066 case 3 20 0.0025045 0.0037568 case 4 26 0.0032559 0.0048838 case 5 50 0.0062613 0.0093919 case 6 100 0.0125225 0.0187838 case 7 195 0.0244190 0.0366284 iii. results and discussion a. the drag coefficient the drag coefficient of the flow surrounding the cylinder was determined through a simulation utilizing featool multiphysics in matlab (r2019b) [23-25]. the calculation was performed using the following equations [28, 30, 31]: �� � ��l!"#$%&' ( (9) �� � �m�no�.npqa r.stu� qa (10) �� � p.ve √qa � 1.17 (11) the drag coefficient (cd) and the drag force ( �5 ) were analyzed and compared to previous experimental studies [29] and abaqus/cfd simulations [18] as well as various empirical formulas. the simulation process resulted in a set of reynolds numbers and their corresponding drag coefficients, which were then used to create a drag curve. the drag curve depicts the relationship between the drag coefficient and reynolds number, and can be utilized to anticipate the drag coefficient under varying flow conditions around the cylinder. the examination of the flow around the cylinder typically revealed slightly higher drag coefficients compared to those observed in experimental studies. despite this, the general pattern of the curve was determined to be consistent. as illustrated in figure 6, the drag coefficient drops significantly as the reynolds number increases from 1 to 50. beyond this point, the decline becomes less steep and continues until re = 195. the computational study's results for reynolds numbers from 0.1 to 1.1 were found to be relatively in line with the empirical formula for the clift values, but as the reynolds number increased, the results began to deviate. the discrepancy in drag coefficients between the analysis and experiment might be due to the acceleration in the lateral analysis region. when engineering, technology & applied science research vol. 13, no. 4, 2023, 11290-11297 11294 www.etasr.com ali et al.: numerical modeling of the flow around a cylinder using featool multiphysics compared to the empirical equations that predict the drag coefficient, the solution presented in [30, 31] appears to be the most thorough. b. the lift coefficient the lift coefficients of hydrodynamic forces on the cylinder surface were calculated in [28]: �* � ��z!"#$%&' ( (12) where �* represents the coefficient of lift and �4 represents the y-component of the lift force acting on the surface. the results of the reynolds numbers and their respective lift coefficients can be seen in figure 7. fig. 6. comparison of the drag coefficient as predicted by experimental studies, empirical formulas, and computational simulations, showing the variation of the coefficient with the reynolds number. fig. 7. variation of the lift coefficient with the reynolds number. figure 7 demonstrates that the value of cl was negligible for low reynolds numbers (1 and 26) and became more significant for higher values (50 and 195). this is because the flow around the cylinder becomes increasingly complex and unstable as the reynolds number increases, leading to stronger lift forces. the lift coefficient is not zero due to the existence of the von karman vortex street, which generates lift forces through flow fluctuations and re-circulation around the cylinder. consequently, the lift forces operating in opposite directions in the separation region and following eddies contribute to overall lift variations ranging from negative to positive values for reynolds numbers 50 and 100. a negative lift indicates that the force was directed downwards. when compared to the results obtained using the ansys fluent software [32], it was observed that the shape of the curve was similar in shape. this comparison highlights that the lift coefficients calculated through different methods are in close agreement. c. pressure coefficient the pressure drag is a force that results from the difference in pressure between the front and back of a cylinder. it plays a significant role in determining the overall drag experienced by the cylinder as it moves through the fluid. to understand the pressure drag, the coefficient of pressure (cp) was calculated at various points on the cylinder's surface using the conformal mapping technique, as reported in [33]. �[ � \j\]n/�!^' = 1 − 4_`3 �a (13) where p denoted the pressure on the surface of a cylinder and the inlet pressure and the velocity in the free stream are denoted as �b and v, respectively, both play a role in determining the pressure distribution. the pressure distribution on the cylinder's surface, as a function of the angle measured clockwise from the front stagnation point (0 o -180 o ) is depicted in figure 8. the illustration clearly shows that the pressure on the surface of the cylinder is at its highest near the front edge and becomes negative when the fluid flow reynolds number surpasses 50 at angles ranging from 50 to 18 o . as the reynolds number increases, the minimum of the numerical curves decreases, signifying that the pressure distribution becomes increasingly intricate and diverse as the flow becomes more unstable. the calculated pressure coefficient values were compared to those obtained through comsol simulation, as reported in [33]. it was observed that the shape of the curve was consistent in both results. this comparison indicated a full concurrence between the two outcomes, as depicted in figure 9. fig. 8. at different reynolds numbers, the pressure coefficient from the leading edge to the trailing edge of the cylinder's surface. engineering, technology & applied science research vol. 13, no. 4, 2023, 11290-11297 11295 www.etasr.com ali et al.: numerical modeling of the flow around a cylinder using featool multiphysics fig. 9. at re = 100, the pressure coefficient of the circular cylinder from the leading edge to the trailing edge. d. the velocity contours figure 10 presents a visual representation of the velocity distribution surrounding the cylinder. the figure provides insight into the flow patterns and the movement of the fluid in the vicinity of the cylinder, thereby highlighting the impact of the cylinder on the surrounding flow field. this information can be used to gain a deeper understanding of the hydrodynamic forces acting on the cylinder and how these forces vary with changes in flow velocity and cylinder shape. at low reynolds numbers (re = 0.1 26), the velocity distribution displays a symmetrical pattern around the cylinder, demonstrating the stability and well-behaved nature of the flow. however, as the reynolds number increases to 50 100, the flow becomes increasingly unstable and begins to detach from the surface of the cylinder. this is evidenced by the formation of eddies above and below the cylinder, which are a result of the flow becoming turbulent. as the turbulence intensifies, the wake behind the cylinder expands in length and the velocities above and below the cylinder become mismatched. at the highest reynolds number (re = 195), the flow becomes fully turbulent and the wake behind the cylinder becomes shorter and more energetic. this is due to the increase in the strength of the swirling flow downstream, which results in a reduction in the length of the wake past the cylinder. fig. 10. velocity contours around the cylinder. engineering, technology & applied science research vol. 13, no. 4, 2023, 11290-11297 11296 www.etasr.com ali et al.: numerical modeling of the flow around a cylinder using featool multiphysics fig. 11. pressure distribution around the cylinder. e. the pressure contours figure 11 presents the low and high-pressure distribution surrounding the cylinder. at low reynolds numbers, specifically re = 0.1 and 1.1, the pressure is observed to be high in front of the cylinder, gradually declining as the flow moves across its surface. however, as the reynolds number increases, the position of the low-pressure region shifts and the pressure decreases both above and below the cylinder. the wake trailing behind the cylinder becomes discernible at reynolds numbers 50 and 100, reflecting the presence of flow separation and turbulent eddies. at the maximum reynolds number of 195, the flow is fully turbulent, resulting in an intensified wake behind the cylinder. on the other hand, when the reynolds number is less than 20, the flow is smooth and laminar, as indicated by the low intensity of the wake. when the reynolds number ranges between 26 and 50, two stationary vortices are formed as the flow becomes unstable, which are attached to the top and bottom of the cylinder. as the reynolds number continues to increase within the range of 50 to 195, the vortices that were previously attached to the top and bottom of the cylinder become detached and the vortex street is a distinctive pattern of alternating vortices that are created by the fluid flow past a cylindrical obstacle. iv. conclusion this study focused on analyzing the behavior of the laminar flow around a cylinder at different reynolds numbers to predict steady-state flows in two-dimensional geometries with arbitrary obstacles. the study successfully achieved all its objectives by conducting simulations and drawing several conclusions. firstly, the study found that the reynolds number significantly influenced the fluid flow over a two-dimensional cylinder. the lower reynolds numbers generated minimal or no vortex at the engineering, technology & applied science research vol. 13, no. 4, 2023, 11290-11297 11297 www.etasr.com ali et al.: numerical modeling of the flow around a cylinder using featool multiphysics back of the cylinder, while the higher reynolds numbers resulted in a continuously oscillating vortex called the kármán vortex street. this finding indicates that the fluid flow was unsteady. the computed drag coefficient results were compared with previous research, and were validated, indicating a good agreement. it was found that low reynolds numbers resulted in larger drag coefficients, while high values produced smaller drag coefficients. also, the study computed the lift coefficient and pressure coefficient 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[31] b. r. munson, d. f. young, and t. h. okiishi, fundamentals of fluid mechanics. new york, ny, usa: wiley, 2005. [32] "to simulate flow over a cylinder and explain the phenomenon of karmen vortex street using ansys fluent." https://skilllync.com/student-projects/steady-vs-unsteady-flow-over-a-cylinder59295. [33] t. baracu and r. bosneagu, "numerical analysis of the flow around a cylinder for the perspective of correlations of the drag coefficient of the ship’s hulls," scientific bulletin of naval academy, vol. 22, no. 2, pp. 256–267, 2019, https://doi.org/10.21279/1454-864x-19-i2-031. engineering, technology & applied science research vol. 7, no. 6, 2017, 2251-2255 2251 www.etasr.com asl et al.: a gain programmable analog divider circuit based on a data converter a gain programmable analog divider circuit based on a data converter shahin navabi asl department of electrical engineering damghan branch islamic azad university damghan, iran setare64.navabiasl@gmail.com mahdi tarkhan department of electrical engineering zahedan branch islamic azad university zahedan, iran m.tarkhan@gmail.com mojtaba shokohi nia department of electrical engineering damghan branch islamic azad university damghan, iran mshokohinia@damghaniau.ac.ir abstract—analog dividers are widely used in analog systems. analog realization of such circuits suffer from limited dynamic range and non-linearity issues, therefore, extra circuitry should be required to compensate these types of shortcomings. in this paper a gain controllable, analog divider is proposed based on data converters. our circuit can be implemented both in current and voltage mode by selecting proper architectures. the resolution, power consumption and operation speed can be controlled by proper selecting of components. another advantage of our circuit is its gain programmability. moreover, the gain can be adjusted independently based on the relationship between input signals. our proposed method offers two different gain control abilities, one for situation that the numerator signal is bigger than the denominator, and another gain is applied when the denominator is larger than the numerator. as a result, no extra amplifier is required for signal amplification. moreover, the input and output signal nature can be chosen arbitrarily in this circuit, i.e. input signal may be a voltage signal while the output signal is current. simulation results from spice confirm the proper operation of the circuit. keywords-analog divider; data converter based divider; gain adjustable analog divider; wide dynamic range analog divider; mixed signal divider i. introduction dividers are a basic building block in analog signal processing systems. such a system usually requires high precision dividers to realize modulators, squarers, automatic level controllers, etc. several techniques are proposed in the literature to design dividers in continuous time monolithic circuits from different technologies. cmos dividers are reported both in the strong and weak inversion. strong inversion approaches are very complex in signal interfacing point of view [1-7]. on the other hand, weak inversion circuits are slow [8-13]. some researchers design dividers working in voltage mode, while current mode circuits can achieve lower power consumption, higher dynamic range and linearity. an alternative approach is using switched capacitor technique [14]. authors in [15] proposed a novel method of realization of voltage mode analog multiplier/divider based on the modified cyclic data converter. a current mode multiplier/divider in current mode utilizing data converter techniques is presented in [7]. in this paper, a novel divider circuit is proposed based on data converters. there is a trade-off between speed, power consumption and resolution that can be managed by properly selecting the components used. furthermore, our proposed circuit can produce the output signal with controllable gain. two conditions might occur in dividers, the numerator signal is larger than the denominator‘s and vice versa. the gain of our proposed circuit can be adjusted independently in both conditions via a control signal and hence, offers the maximum level of gain adjustability. ii. proposed circuit suppose x and y are analog signals (current or voltage) and our goal is to produce a signal that is proportional to the division of x and y as follows: y x kz    where x in the numerator, y is the denominator, k is the gain of division and z is the final output. the straightforward solution to realize a divider is to use the analog dividers. however, as it was mentioned earlier, analog dividers have some limitations. another solution is the use of digital signal processor, nevertheless, this method requires two adcs to convert input signals to digital and a dac to produce the analog signal from the division result. our proposed circuit needs only an adc and a dac with similar resolution as depicted in figure 1. the adc sampled and converts the input signal (xnum) based on its reference signal level (xden) and its resolution (n bits) as follows:  2 den num n x x b   where b is an n-bit digital code. applying the digital code to a dac with similar resolution results to producing an analog signal as represented in (3). engineering, technology & applied science research vol. 7, no. 6, 2017, 2251-2255 2252 www.etasr.com asl et al.: a gain programmable analog divider circuit based on a data converter 2 ref out n x x b   solving (2) and (3) we come to (4): num out ref den x x x x    with the quantization error of 1/ 2ndenx  . two situations might occur: numerator is bigger than the denominator and vice versa. they can be considered separately. a. denominator is bigger than the numerator (y>x) in this situation, the output signal resulting from (1) is less than k. figure 2 shows the proposed circuit configuration to produce the output signal in this mode. denominator signal (y) is connected to the reference signal pin of adc (xden) and numerator (x) is connected to the input of the adc (xnum). adc voltage source (k1) is connected to the reference signal of the dac, and the final output is appeared on the output of the dac based on (5). 1 x z k y     since in this mode, x<y, then for fixed k1, the produced output is the scaled version of the desired result. the amplification coefficient can be chosen arbitrarily based on the dynamic range of the dac. therefore, no extra amplification stage is required, and the output dynamic range of the output signal is in the range of [0, k1]. in out ref adc bn … b0 n n out ref dacinxnum xden xref xout fig. 1. the general configuration of our proposed circuit. x zin out ref adc bn … b0 n n out ref dacin y vdc=k1 fig. 2. the configuration of the circuit when x<y. b. numerator is bigger than the denominator (x>y) in this situation, the division result is greater than k. the connectivity diagram of the circuit in this mode is illustrated in figure 3. in this situation, x is used as reference voltage of adc (xden) and y is connected to the input of adc (xnum). equation (6) shows the final output produced by dac.  out ref y x x x    since x>y so the output swings from zero to xref like the first mode. the output signal generated in this mode is the inverse of the desired signal. finding xref from above equation we have:  ref out x x x y     dac produces an analog signal based on its resolution, reference signal and the applied digital code. the digital code is already produced by adc and is constant between cycles. suppose we compare the xout signal with a constant signal (e.g. k2). rising xref gradually from zero, increases the output signal (xout) as well. at the time that the output signal reaches k2, the xref signal has a value proportional to the division result as proved in (8).  2ref x x k y     so the xref is the scaled version of desired output (z). adcs have internal sample and hold that capture the input signal at the specific time produced by a clock generator. then the conversion process is performed on the sampled signal. our proposed circuit is suitable to be used in the sampled analog system in which the output signal is valid in specific time and between time slices, the signal processing is done in internal circuits. therefore, between time steps, the digital code produced by adc would not change. a ramp generator is used to produce the reference signal for dac. it's simply a sawtooth signal generator with reset capability. since the digital code is not changing, increasing the xref signal results in increasing the output of the dac as well. the output signal produced by dac is compared by a constant value (i.e. k2) by a comparator. when the output signal is low, the comparator output is at the low saturation level, too, and the switch is opened. increasing the xref, increases the xout and this process is performed until the positive and negative voltages of comparator become equal. at this time, the comparator output signal flips to high saturation level. consequently, the switch turns on and xref connected to the output pin (z). meanwhile, the ramp generator is being reset in order to start the new cycle, resulting in decreasing xout and turning off the switch. figure 4 depicts the internal structure of the ramp generator. the sawtooth signal is generated by a pmos current source (mp1) and an integrating capacitor (c). nmos switch is connected in parallel to the capacitor in order to discharge it during reset phase. since xclk and enable signals are not allowed to be activated simultaneously, direct current path from vdd to gnd cannot be created, which means no extra static power is dissipated. it is worth mentioning that ramp generator is solely used in second mode where the numerator is bigger than the denominator. using enable signal makes it possible to deactivate the circuit in the first mode. c. complete circuit combining the abovementioned circuits, the final structure of the proposed circuit can be achieved as shown in figure 5. engineering, technology & applied science research vol. 7, no. 6, 2017, 2251-2255 2253 www.etasr.com asl et al.: a gain programmable analog divider circuit based on a data converter this circuit has two signal paths that activate based on the modes describe before. this is done by comparing the numerator and denominator signals. analog multiplexers are used to form the signal path. in figure 5, the input signals are compared by the comparator (comp2) which generates the sel signal. suppose x is greater than y then sel would be at low saturation level results in selecting the zero line of the multiplexers. therefore, y signal is applied to the input and x is applied to the reference of adc. this is the second mode which utilizes the ramp generator. hence the ramp generator is enabled by the sel signal (turning on mp2), and the sawtooth signal (xramp) is applied to the reference of the dac (xref). in this configuration, the xref signal is applied to the output pin through mux4 (z=xref). as it is mentioned earlier, this signal is equal to the division result scaled by k2. if x<y, then sel signal is high and x is applied to the input of the adc and y to its reference pin. the ramp generator disabled (mp2 is off), and the xref is connected to k1 voltage source. in this mode, the output signal generated by dac is connected to output pin (z). data converters are reported in the literature both in current and voltage mode [16-21]. they are designed in a wide variety of methodologies such as: flash, successive approximation, pipeline and sigma delta. the selection of the data converter is based on the nature of input and output signals. while the adc type is determined by the input signal nature, output signal is a criterion for dac selection. since both current and voltage mode data converters work with digital code, using different architectures makes it possible for the designer to manage a trade-off between speed, cost and power consumption based on the desired input and output signal nature. in table i, the different selection guideline is summarized. reset comparator ramp generator vdc=k2 xref xout xclk x in out ref adc bn … b0 n n z out ref daciny fig. 3. circuit diagram in the second mode (x>y). buffercmn1 mp1 enable xclk out bias mp2 fig. 4. internal structure of the ramp generator. enableout xclk ref ref in inout out dac n comp2 k2 m ux 1 m ux 2 ramp generator comp1 adc k1 z sel sel sel sel sel sel xref y x y x x y xramp xout xoutxclk m ux 4 m ux 3 y x 0 00 0 1 1 1 1 fig. 5. the complete structure of the proposed circuit. table i. data converter selection guide input signal output signal adc type dac type voltage voltage voltage mode voltage mode voltage current voltage mode current mode current voltage current mode voltage mode current current current mode current mode iii. simulation results the proposed circuit is simulated in hspice. the generic model of adc and dac with 8-bit resolution is used in the simulation environment. the transient simulation is done in three different conditions. a. state 1 (x<y) in this situation, the signals defined in table ii are applied in the simulation engine as depicted in figure 6. simulation is performed for two different k1 values. in figure 7a the results when k1 is considered to be 1v is depicted. the green curve shows the ideal output while the red one is the result produced by the circuit. the sampling frequency is considered to be 100khz. figure 7b shows the output signal when k1=2v. as it can be seen, the output is doubled when increasing k1 from 1v to 2v. b. state 2 (x>y) in this state, the numerator is fixed at 120mv using a dc source, while a 1khz sine wave with 20mv ac amplitude and 0.1v of dc offset is applied to the denominator input pin as depicted in figure 8a. figure 8b shows the ideal as well as the actual output signal when the sampling frequency is 10khz. the output signal generated by dac (xout) and the comparator output (xclk) are illustrated in figure 8c. when the xref is rising from zero, xout increases as well. this process continues until xout is becoming equal to k2, where the xout has a value equal to the division result. simultaneously, the comparator output flips to high saturation level disabling the ramp generator. halving the k2 signal to 0.5v, halving the final output as well as illustrated in figure 8d. engineering, technology & applied science research vol. 7, no. 6, 2017, 2251-2255 2254 www.etasr.com asl et al.: a gain programmable analog divider circuit based on a data converter x y v (v ) .2 .4 .6 .8 1.0 1.2 1.4 time (us) 0.0 100.0 200.0 300.0 400.0 fig. 6. numerator (green) and denominator (red) signals applied to the circuit in 1st state (x<y) ideal output z v (m v ) -200.0 0.0 200.0 400.0 600.0 800.0 1000 time (us) 0.0 100.0 200.0 300.0 400.0 z ideal output v (v ) -.25 0.0 .25 .5 .75 1.0 1.25 1.5 1.75 2.0 time (us) 0.0 100.0 200.0 300.0 400.0 fig. 7. simulation results in the first state (x<y). ideal (green) and actual (red) result produced when (a) k1=1v and (b) when k1=2v. c. state 3 in the final simulation run, the overall performance of the system is examined using arbitrary input signals as characterized in table iii and plotted in figure 9a. in this situation, both modes are used because sometimes the numerator is bigger than the denominator, and the opposite inother times. figure 9b shows the simulation results with 10khz of sampling frequency. as it is shown when x is greater than y, xout is rising from zero and converges to the output result equal to the sampling time otherwise the output signal is generated by the circuit configuration described in the first mode. table ii. signals used in state-1 simulation signal name signal attribute frequency (khz) amplitude (mv) dc offset (v) numerator (x) 10 200 0.6 denominator (y) 3 200 1 table iii. signals used in state-3 simulation signal name signal attribute frequency (khz) amplitude (mv) dc offset (v) numerator (x) 3 50 0.12 denominator (y) 1 20 0.1 x y v (m v ) 70.0 80.0 90.0 100.0 110.0 120.0 130.0 time (ms) 0.0 .25 .5 .75 1.0 ideal output xref v (v ) -.25 0.0 .25 .5 .75 1.0 1.25 1.5 1.75 2.0 time (ms) 0.0 .25 .5 .75 1.0 xclk ideal xout v (v ) -.25 0.0 .25 .5 .75 1.0 1.25 1.5 1.75 2.0 time (ms) 0.0 .25 .5 .75 1.0 xref ideal out (k2=0.5) v (v ) -.25 0.0 .25 .5 .75 1.0 time (ms) 0.0 .25 .5 .75 1.0 fig. 8. simulation results in 2nd state (x<y). (a) numerator (green) and denominator (red) signal in 2nd state (b) ideal (green) and actual (red) result output signal when k2=1v (c) dac (blue) and comparator (green) output signal generated when k2=1v ideal output (red) signal is also plotted (d) output signal (green) and ideal output (red) when k2=0.5v (d) iv. conclusion in this paper, a novel divider/defuzzifier circuit is presented. using data conversers makes it possible to design a divider with wide dynamic range. the speed, power consumption and dynamic range are limited by the data (a) (b) (a) (b) (c) (d) engineering, technology & applied science research vol. 7, no. 6, 2017, 2251-2255 2255 www.etasr.com asl et al.: a gain programmable analog divider circuit based on a data converter converter specification used. by proper component selection, a designer can manage the trade-off between above-mentioned parameters. the gain of the circuit is controlled by two different dc sources, each of them utilized in specific situation, i.e. when the numerator signal is bigger than the denominator and vice versa. another advantage of our proposed method is that one can use different data converters based on the nature of desired input and output signal. for example, having a voltage mode adc and current mode dac, means the input signals are voltage while the output is a current signal. x y v (m v ) 50.0 75.0 100.0 125.0 150.0 175.0 time (ms) 0.0 .25 .5 .75 1.0 sun jan 1 10:18:08 2017 ideal output v (v ) -.25 0.0 .25 .5 .75 1.0 1.25 1.5 1.75 2.0 time (ms) 0.0 .25 .5 .75 1.0 fig. 9. simulation results in the 3rd state. (a) numerator (red) and denominator (green) signal (b) ideal (red) and actual (green) result output signal when k1=k2=1v. references [1] m. t. abuelma’atti, m. a. alabsi, “a cmos analog cell and its applications in analog signal processing”, international journal of electronics, vol. 93, no. 4, pp. 251-267, 2006 [2] h. asiaban, e. farshidi, “a new true rms-to-dc converter in cmos technology”, international journal of electrical and computer engineering, vol. 71, no. 11, pp. 1592-1595, 2010 [3] k. bult, h. wallinga, “a class of analog cmos circuits based on the square-law characteristic of an mos transistor in saturation”, ieee journal of solid-state circuits, vol. 22, no. 3, pp. 357-365, 1979 [4] m. dei, n. nizza, m. piotto, p. bruschi, “a voltage controlled cmos current divider with linear characteristic”, analog integrated circuits and signal processing, vol. 58, no. 1, pp. 43-47, 2009 [5] c. dualibe, m. verleysen, p. jespers, “two-quadrant cmos analogue divider”, electronic letters, vol. 34, no. 12, pp. 1164–1165, 1998 [6] e. farshidi, h. asiaban, “a new true rms-to-dc converter using updown translinear loop in cmos technology”, analog integrated circuits and signal processing, vol. 70, no. 3, pp. 385-390, 2012 [7] i. baturone, s. sanchez-solano, j. l. huertas, “a cmos current-mode multiplier/divider circuit”, , ieee international symposium on circuits and systems, vol. 1, pp. 520–523, 2002 [8] m. a. al-absi, “low-voltage and low-power cmos current-mode divider and 1/x circuit”, international conference on electronic devices, systems and applications, pp. 245-247, 2010 [9] m. barbaro, g. n. angotzi, “compact, low-power, analogue building blocks derived from mosfets translinear loops”, ieee international conference on electronics, circuits, and systems, pp. 592-595, 2006 [10] c.-c. chang, s.-i. liu, “weak inversion four-quadrant multiplier and two-quadrant divider”, electronic letters, vol. 34, no. 22, pp. 20792080, 1998 [11] a. mahmoudi, a. khoei, k. h. hadidi, “a novel current-mode micropower four quadrant cmos analog multiplier/divider”, ieee conference on electron devices and solid-state circuits, pp. 321-324, 2007 [12] e. rodriguez-villegas, j. alam, “ultra low power four-quadrant multiplier/two-quadrant divider circuit using fgmos”, 49th international midwest symposium on circuits and systems, pp. 64-68, 2006 [13] a. taji, a. khoei, k. hadidi, m. padash, “low-voltage and low-power consumption 0.35um cmos voltage-mode defuzzifier”, international conference on electronic devices, systems, and applications, pp. 161164, 2011 [14] a. cichocki, r. unbehauen, “a novel switched-capacitor four-quadrant analog multiplier-divider and some of its applications”, ieee transactions on instrumentation and measurement, vol. im-35, no. 2, pp. 156-162, 1986 [15] m. s. piedade, a. pinto, “a new multiplier-divider circuit based on switched capacitor data converters”, ieee international symposium on circuits and systems, pp. 2224–2227, 1990 [16] y.-j. chen, k.-h. chang, c.-c. hsieh, “a 2.02–5.16 fj/conversion step 10 bit hybrid coarse-fine sar adc with time-domain quantizer in 90 nm cmos”, ieee journal of solid-state circuits, vol. 51, no. 2, 2016 [17] y. choi, y.-b. kim, i.-s. jung, “a 100ms/s 10-bit split-sar adc with capacitor mismatch compensation using built-in calibration”, ieee 25th north atlantic test workshop, pp. 1-5, 2016 [18] a. elkafrawy, j. anders, m. ortmanns, “a 10-bit 150ms/s current mode sar adc in 90nm cmos”, 11th conference on ph.d. research in microelectronics and electronics, pp. 274-277, 2015 [19] k. ragab, n. sun, “a 1.4mw 8b 350ms/s loop-unrolled sar adc with background offset calibration in 40nm cmos”, 42nd european solid-state circuits conference, pp. 417-420, 2016 [20] y. song, z. xue, y. xie, s. fan, l. geng, “a 0.6-v 10-bit 200-ks/s fully differential sar adc with incremental converting algorithm for energy efficient applications”, ieee transactions on circuits and systems i: regular papers, vol. 63, no. 4, pp. 449-458, 2016 [21] y. tao, y. lian, “a 0.8-v, 1-ms/s, 10-bit sar adc for multi-channel neural recording”, ieee transactions on circuits and systems i: regular papers, vol. 62, no. 2, pp. 366-375, 2015 (a) (b) microsoft word etasr_v13_n1_pp10033-10038 engineering, technology & applied science research vol. 13, no. 1, 2023, 10033-10038 10033 www.etasr.com eisa et al.: study of gamma-ray shielding of two different heavy metals and their combination for cs… study of gamma-ray shielding of two different heavy metals and their combination for cs-137 and co-60 sources mohamed e. m. eisa department of physics, northern border university, saudi arabia | department of physics, sudan university of science and technology, sudan memeisa@yahoo.com (corresponding author) m. d. m. ali department of physics, sudan university of science and technology, sudan mohameddaffallah@yahoo.com mustafa j. abuualreish department of chemistry, northern border university, saudi arabia mustjeed_2008@hotmail.com received: 23 november 2022 | revised: 7 december 2022 | accepted: 12 december 2022 abstract this article presents data collected by measurements of lead (pb) and iron (fe) and their combination as heavy shielding materials. measurements were performed using gamma photon energies of 662, 1173, and 1332kev for the cs-137 and co-60 sources. the theoretical data part was calculated using winxcom, phyx, and py-mlubf software packages. tables and graphs of the photon mass attenuation coefficient (mac), linear attenuation coefficient (lac), half value layer (hvl), tenth value layer (tvl) and mean free path (mfp) are presented for both heavy metals and their combination to study the shielding properties experimentally and theoretically. the results will contribute to the ongoing research as a database for future use. keywords-linear attenuation coefficient; photon mass attenuation coefficient; radiation resistance data; heavy metals; gamma photon energies; gamma radiation properties i. introduction radiation protective shields play many functions, the most important of which is to reduce radiation exposure [1]. radioactivity is common in the rocks and soil, in the water and oceans, and even in our building and home materials [2-4]. with the increasing use of gamma radiation in various applications such as industry, medicine, agriculture, nuclear reactors, and particle accelerators, radiation exposure for longer duration can cause very harmful effects on human health. therefore, the use of shielding becomes paramount [5]. the interaction with gamma radiation photons takes place in various processes like the photoelectric effect, incoherent scattering, coherent scattering, and pair production and depends upon the energy of the photons [6-7]. possible exposure to radiation emitted from radionuclides can occur in houses, offices, and other working places. in order to be able to assess radiological hazard, it is important to study the levels of radiation emitted from these building materials [8]. different radiation shielding materials have been developed in the past. ionizing photons such as x-rays and gamma rays can change the chemical structures of molecules, which may result in biological damages, cellular level mutations, or deterioration of materials [9-10]. protection of biological entities from the harmful effects of radiation exposure is a fundamental requirement in the application of nuclear technology. radiation exposure can be avoided by methods involving time, distance, and shielding, with shielding being the most important method [11-14]. when a gamma-ray beam passes through a sample of thickness x (cm) under narrow beam geometry, the photons are transmitted according to beer-lambert's equation [2, 15, 16]: � = ��� ��� (1) where io and i represent the gamma-ray intensity before and after passing through the sample, respectively, and µ (cm -1 ) is the linear attenuation coefficient (lac) of the sample. engineering, technology & applied science research vol. 13, no. 1, 2023, 10033-10038 10034 www.etasr.com eisa et al.: study of gamma-ray shielding of two different heavy metals and their combination for cs… the lac can be described in terms of the mass attenuation coefficient (mac) as follows [10, 17-19]: µ = µ � µ� (2) where µ� µ (cm 2 g -1 ) is the mac and (g cm-3) is the density of the sample. the mean free path (mfp) (cm) is: mfp= � µ (3) the effectiveness of the shielding capability of a material to a photon can be described by the half value layer (hvl) (cm) [20-21]: hvl= �� (�) µ (4) similarly, the tenth value layer (tvl) (cm) is given by: tvl= �� (��) µ (5) ii. materials and methods measurements were conducted at the irradiation room of the secondary standard dosimetry laboratory of the sudan atomic energy commission (saec) on model ob-85 gamma calibrator manufactured by the buchler gmbh and by using cs-137 and co-60 radioactive sources. experimental measurement tables ii-iv were constructed using a secondary standard ionization chamber which has a volume of 1000cm 3 and displays the radiation dose of the sources and the thicknesses. the ionization chamber was chosen to be the center of a sphere relative to the reference source in a 2m distance from the source to the reference point. the holder of shielding samples was placed close to the ob-85 gamma calibrator. the shielding materials were placed inside the holder one by one. this procedure was followed for all shielding materials [22, 23]. through the measurements the intensity of radiation was recorded, before and after placing the shielding material in the holder. the experimental coefficients were evaluated using gamma energies of 662kev for cs-137 and 1173 and 1332kev for co-60 and the gamma transmission parameters such as the mac, hvl, mfp, and transmission factor were determined and calculated. iii. results density, chemical composition, and concentration of the iron and lead samples and their combination can be seen in table i. table ii-iii present the experimental results of the attenuation coefficients and hvls of fe and pb slabs using different thicknesses and doses of cs-137 and co-60. table iv presents the experimental results of the combination of fe and pb using cs-137 gamma ray. the theoretical coefficient of the two materials and their combination were determined using pymlubf, phy-x, and xcom [24, 26, 28-31] software packages which gave very close results. the results were compared against the experimental findings and gave very good agreement. tables v-vii present the simulation results of fe and pb shielding using py-mlubf [32-33], phy-x and winxcom software. the combination of the two shielding materials, pb and fe, is shown in tables viii and ix. figures 1 and 2 show the relation between hvl and mac vs energy by using py-mlubf for fe. figures 3 and 4 show the relation between hvl and mac vs energy by using py-mlubf for fe and pb calculated by py-mlubf for cs-137. figures 8 and 9 show the relation between the gamma ray shielding factor for fe and pb calculated by py-mlubf for energies of 1173 and 1333kev, respectively for the co-60 source [33]. table i. density and chemical concentration of lead (pb) and iron (fe) samples material lead iron density(g/cm 3 ) 11.34 7.87 concentration(%) sn 0.0023 sb 0.00051 bi 0.0025 as 0.0019 ag 0.00064 cd 0.00006 zn 0.00022 te 0.00026 au 0.00096 in 0.00015 na 0.00028 ca 0.001 pb 99.99 0.006 c 0.062 si 0.035 mn 0.345 cr 0 mo 0.022 ni 0.00029 0 al 0.00039 0.01 cu 0 ti 0 v 0 nb 0 co 0.046 w 0 fe 99.474 table ii. experimental results for fe using cs-137 and co-60 attenuation coefficients and hvl for fe slabs using cs-137 gamma rays with initial dose of 474.76µgy. attenuation coefficients and hvl for fe slabs using co-60 gamma rays with initial dose of 1.906 µgy. thickness (cm) dose (µgy) lac (cm -1 ) mac (cm 2 /g) hvl (cm) dose (µgy) lac (cm -1 ) mac (cm 2 /g) hvl (cm) 0.202 434.58 0.437 0.055 1.583 1.797 0.291 0.037 2.377 0.522 373.03 0.462 0.058 1.500 1.602 0.332 0.042 2.081 1.036 289.54 0.477 0.060 1.451 1.346 0.335 0.042 2.063 1.350 249.21 0.477 0.060 1.451 1.202 0.341 0.043 2.029 engineering, technology & applied science research vol. 13, no. 1, 2023, 10033-10038 10035 www.etasr.com eisa et al.: study of gamma-ray shielding of two different heavy metals and their combination for cs… table iii. experimental results for pb using cs-137 and co-60 attenuation coefficients and hvl for lead slabs using cs-137 gamma rays with initial dose of 474.76µgy. attenuation coefficients and hvl for lead slabs using co-60 gamma rays with initial dose of 1.906 µgy. thickness (cm) dose (µgy) lac (cm -1 ) mac (cm 2 /g) hvl (cm) dose (µgy) lac (cm -1 ) mac (cm 2 /g) hvl (cm) 0.154 400.46 1.105 0.097 0.627 1.744 0.576 0.050 1.211 0.472 274.69 1.159 0.102 0.597 1.428 0.611 0.053 1.132 0.812 190.42 1.125 0.099 0.615 1.169 0.602 0.053 1.151 0.966 164.63 1.096 0.096 0.632 1.079 0.589 0.051 1.176 table iv. experimental results for fe and pb using cs-137 lac and hvl for lead and iron slabs using cs-137 gamma rays with initial dose of 237.74µgy thickness (cm) dose (µgy) experimental results lac µ(cm -1 ) hvl (cm) 0.356 182.72 0.7394 0.937 0.676 157.52 0.608 1.138 0.994 110.09 0.774 0.894 1.014 87.74 0.983 0.705 1.334 76.17 0.853 0.812 1.822 74.86 0.634 1.092 1.848 59.86 0.746 0.928 2.162 51.84 0.704 0.983 table v. results of fe by phy-x and py-mlbuf phy-x(fe) py-mlubf (fe) energy (mev) source mac (cm²/g) lac (1/cm) hvl (cm) tvl (cm) mfp (cm) mac (cm²/g) lac (1/cm) hvl (cm) tvl (cm) mfp (cm) 6.62e-01 cs (137) 0.073 0.578 1.199 3.982 1.729 7.35e-02 5.78e-01 1.1983 3.9806 1.730 8.00e-01 0.067 0.527 1.315 4.368 1.897 6.70e-02 5.27e-01 1.3147 4.3675 1.897 8.26e-01 co (60) 0.066 0.519 1.336 4.437 1.927 1.00e+00 0.060 0.472 1.469 4.881 2.120 6.00e-02 4.72e-01 1.4691 4.8804 2.118 1.17e+00 co (60) 0.055 0.435 1.594 5.295 2.300 5.53e-02 4.35e-01 1.5927 5.2907 2.298 1.33e+00 co (60) 0.052 0.408 1.701 5.650 2.454 5.18e-02 4.08e-01 1.7003 5.6482 2.450 1.50e+00 0.049 0.384 1.804 5.992 2.602 4.88e-02 3.84e-01 1.8037 5.9918 2.604 2.00e+00 0.043 0.336 2.065 6.861 2.980 4.27e-02 3.36e-01 2.0651 6.86 2.976 table vi. results of pb by phy-x and py-mlbuf phy-x(pb) py-mlubf (pb) energy (mev) source mac (cm²/g) lac (1/cm) hvl (cm) tvl (cm) mfp (cm) mac (cm²/g) lac (1/cm) hvl (cm) tvl (cm) mfp (cm) 6.62e-01 cs 137 1.10e-01 1.25e+00 0.5557 1.8459 0.800 1.10e-01 0.110 1.250 0.555 1.843 8.00e-01 8.87e-02 1.01e+00 0.6891 2.2892 0.990 8.87e-02 0.089 1.006 0.689 2.289 1.00e+00 7.10e-02 8.05e-01 0.8607 2.8591 1.2422 7.10e-02 0.071 0.805 0.861 2.859 1.17e+00 co (60) 6.18e-02 7.01e-01 0.9891 3.2856 1.426 6.18e02 0.062 0.700 0.990 3.288 1.33e+00 co (60) 5.61e-02 6.36e-01 1.0896 3.6194 1.572 5.61e-02 0.056 0.636 1.089 3.618 1.50e+00 5.22e-02 5.92e-01 1.1705 3.8884 1.689 5.22e-02 0.052 0.592 1.170 3.888 2.00e+00 4.61e-02 5.22e-01 1.3268 4.4074 1.915 4.61e-02 0.046 0.522 1.327 4.408 table vii. results of fe by winxcom winxcom (fe) photon energy (mev) scattering photoelectric absorption (cm 2 /g) total attenuation coherent (cm 2 /g) incoherent (cm 2 /g) with coherent scattering (cm 2 /g) without coherent scattering (cm 2 /g) 6.620e-01 9.955e-04 7.159e-02 8.713e-04 7.346e-02 7.246e-02 8.000e-01 6.833e-04 6.575e-02 5.650e-04 6.699e-02 6.631e-02 1.000e+00 4.381e-04 5.916e-02 3.514e-04 5.995e-02 5.951e-02 1.022e+00 4.196e-04 5.853e-02 3.335e-04 5.928e-02 5.887e-02 1.173e+00 3.188e-04 5.466e-02 2.524e-04 5.526e-02 5.494e-02 1.250e+00 2.808e-04 5.292e-02 2.256e-04 5.350e-02 5.322e-02 1.332e+00 2.473e-04 5.122e-02 2.014e-04 5.181e-02 5.156e-02 1.500e+00 1.951e-04 4.811e-02 1.627e-04 4.883e-02 4.864e-02 2.000e+00 1.099e-04 4.107e-02 1.003e-04 4.265e-02 4.254e-02 2.000e+00 1.099e-04 4.107e-02 1.003e-04 4.265e-02 4.254e-02 engineering, technology & applied science research vol. 13, no. 1, 2023, 10033-10038 10036 www.etasr.com eisa et al.: study of gamma-ray shielding of two different heavy metals and their combination for cs… table viii. results of the combination of the two shielding materials fe+pb combination, py-mlubf results fe+pb combination, phy-x results energy (mev) source mac (cm²/g) lac (1/cm) hvl (cm) tvl (cm) mfp (cm) mac (cm²/g) lac (1/cm) hvl (cm) tvl (cm) mfp (cm) 6.62e-01 cs(137) 1.10e-01 1.25e+00 0.555 1.845 0.800 0.102 0.984 0.705 2.341 1.017 8.00e-01 8.87e-02 1.01e+00 0.689 2.289 0.990 0.084 0.808 0.858 2.851 1.238 1.00e+00 7.10e-02 8.05e-01 0.860 2.859 1.242 0.069 0.660 1.051 3.491 1.516 1.17e+00 co (60) 6.18e-02 7.01e-01 0.989 3.285 1.426 0.060 0.580 1.195 3.971 1.724 1.33e+00 co (60) 5.61e-02 6.36e-01 1.089 3.619 1.572 0.055 0.530 1.307 4.342 1.886 1.50e+00 5.22e-02 5.92e-01 1.170 3.8884 1.689 0.052 0.495 1.401 4.655 2.022 2.00e+00 4.61e-02 5.22e-01 1.326 4.407 1.915 0.045 0.435 1.592 5.287 2.296 table ix. results of the combination of the two shielding materials by winxcom winxcom (pb+fe) photon energy (mev) scattering photoelectric absorption (cm 2 /g) total attenuation coherent (cm 2 /g) incoherent (cm 2 /g) with coherent scattering (cm 2 /g) without coherent scattering (cm 2 /g) 6.620e-01 3.831e-03 6.586e-02 2.210e-02 9.180e-02 8.796e-02 8.000e-01 2.652e-03 6.056e-02 1.464e-02 7.785e-02 7.519e-02 1.000e+00 1.714e-03 5.454e-02 9.223e-03 6.548e-02 6.377e-02 1.022e+00 1.643e-03 5.399e-02 8.826e-03 6.445e-02 6.281e-02 1.173e+00 1.253e-03 5.044e-02 6.727e-03 5.851e-02 5.725e-02 1.250e+00 1.106e-03 4.884e-02 5.955e-03 5.613e-02 5.502e-02 1.332e+00 9.754e-04 4.728e-02 5.282e-03 5.398e-02 5.301e-02 1.500e+00 7.712e-04 4.443e-02 4.242e-03 5.053e-02 4.976e-02 2.000e+00 4.363e-04 3.795e-02 2.567e-03 4.436e-02 4.392e-02 metals are commonly used in the design of radiation protection systems. lead is dense and can be used against various high-energy applications of radiation. lead possesses specific characteristics, e.g. its hvl increases with increase in energy [34]. to assess the shielding ability of a material, hvl is inversely related to the shielding effectiveness. with the increase in energy, hvl increases, due to the reducing intensity of incident gamma radiation to one half, more target thickness will be required. in iron, the hvl increases slightly. this is attributed to the small decrease in lac with the decrease in iron content (figures 1 and 2). we can see the significant differences in the hvl of fe and pb in figures 1 and 3. the mac of fe and pb can be seen in figures 2 and 4. however, the combination is slightly changed in hvl and mac. gamma ray factor is larger through cs-137 source and it is decreased in co-60. the theoretical and experimental values of mac, hvl, and tvl of gamma energy at 662, 1173 and 1333kev for lead and iron show that there is a good agreement between the theoretical and the experimental values [35]. fig. 1. py-mlubf (fe) hvl vs energy. fig. 2. py-mlubf (fe) mac vs energy. fig. 3. py-mlubf (pb) hvl vs energy. iv. conclusion in this paper, mass attenuation coefficients and half-value layer values have been studied using com, phy-x, and pymlubf. the codes provide quick calculations of gamma-ray engineering, technology & applied science research vol. 13, no. 1, 2023, 10033-10038 10037 www.etasr.com eisa et al.: study of gamma-ray shielding of two different heavy metals and their combination for cs… interaction parameters of the sample for the selected energies. the mac values are found to reduce exponentially with increasing energy, whereas the hvl values are found to increase exponentially and radiation shielding values increase with increasing energy. the theoretical results are in good agreement with the results from the experimental work. fig. 4. py-mlubf (pb) mac vs energy. fig. 5. fe+pb combination hvl vs energy. fig. 6. fe+pb combination mac vs energy. the efficiency of the shielding material depends on its thickness and interaction energy. knowing mac, hvl, tvl, and mfp values may help determine which material reduces the radiation intensity more effectively. the results of this study may 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[35] a. b. aziz, md. f. rahman, and m. m. prodhan, "comparison of lead, copper and aluminium as gamma radiation shielding material through experimental measurements and simulation using mcnp version 4c," international journal of contemporary research and review, vol. 9, no. 8, pp. 20193–20206, aug. 2018, https://doi.org/10.15520/ijcrr/2018/9/ 08/584. microsoft word 14-702-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1187-1194 1187 www.etasr.com faridi masouleh et al.: genetic-firefly hybrid algorithm to find the best data location in a data cube a genetic-firefly hybrid algorithm to find the best data location in a data cube m. faridi masouleh information technology management department science and research branch islamic azad university tehran, iran m.faridi@srbiau.ac.ir m. a. afshar kazemi information technology management department science and research branch islamic azad university tehran, iran m.afsharkazemi@yahoo.com m. alborzi information technology management department science and research branch islamic azad university tehran, iran mahmood_alborzi@yahoo.com a. toloie eshlaghy information technology management department science and research branch islamic azad university tehran, iran toloie@gmail.com abstract—decision-based programs include large-scale complex database queries. if the response time is short, query optimization is critical. users usually observe data as a multidimensional data cube. each data cube cell displays data as an aggregation in which the number of cells depends on the number of other cells in the cube. at any given time, a powerful query optimization method can visualize part of the cells instead of calculating results from raw data. business systems use different approaches and positioning of data in the data cube. in the present study, the data is trained by a neural network and a genetic-firefly hybrid algorithm is proposed for finding the best position for the data in the cube. keywords-database; data cube; genetic algorithm; firefly algorithm; neural network i. introduction business intelligence (bi) is a vast category of methods, applications and technologies of gathering data, accessing information, and analyzing a large amount of data for getting knowledge in the organization to make effective business decisions and made information technology (it) measurements powerful. typical bi technologies include business rule modeling, etl (extraction, transformation and load) tools, data profiling, data warehousing and online analytical processing, and data mining. the focus of bi is to fully utilize massive data to help organizations gain competitive advantages. decision support systems are increasingly used in business. they provide access to data that has been locked in a database and convert it into useful information. many organizations and companies are developing integrated decision support systems known as data warehouses, where users can carry out analysis. as operational databases update the state of their information, data warehouses typically store the history of that information. as a result, data warehouses tend to grow over time. users of decision support systems are generally reluctant to identify behaviors instead of searching for an independent record. queries in a decision support system build aggregation. the size of the data warehouse and complexity of the queries can produce long queries that require much time for completion. this causes delays that are not acceptable in most decision support system environments because it reduces the efficiency of the system. data cube analysis is a powerful tool for analyzing multi-dimensional data. cube analysis allows users to simply explore data by calculating the aggregate size of all possible groups as defined by their new dimensions. a number of techniques have been used to design effective methods to calculate the cube. technically, a cube is a multi-dimensional redundancy plan relationship that calculates all sql-grouped operators and aggregates their results in n-dimensional space to answer olap queries. this aggregation is calculated in derivative summary tables or multi-dimensional arrays and mathematical tools are required to estimate the aggregation sizes. because an aggregation is generally quite large, indexing, which adds redundancy, is deemed necessary to speed up the inquiry [42, 43, 44]. ii. olap online analytical processing (olap) is rooted in systems such as iri express, comshare, and essbage. unlike statistical databases that hold census data and economic information, olap collects everyday commercial transactions data, such as that for sales or health. the main objective of olap is to enable analysts to build a mental image of the underlying data by exploring different perspectives at various stages of generalization and interaction [39]. as a component in decision support systems, olap interacts with other components such as data warehouses and data mining to assist business analysts in the decision-making. data warehouses collect data from multiple data sources, such as transactional databases, across an organization. the data is cleaned and converted to a sustainable format before being collected in the data warehouse. subsets of the data in the warehouse are extracted to meet the specific needs of the organization. unlike transactional databases, where data is continuously updated, the engineering, technology & applied science research vol. 6, no. 5, 2016, 1187-1194 1188 www.etasr.com faridi masouleh et al.: genetic-firefly hybrid algorithm to find the best data location in a data cube data collected in a warehouse updates itself; this is only possible by data sources in cyclic form. olap and data mining both allow analysts to discover knowledge about the data in a warehouse. data mining algorithms automatically generate such knowledge in a pre-defined state, such as by classification or collaborative laws [2, 3]. olap does not produce knowledge directly, but relies on human analysis to interpret the results of the query. olap is more flexible than data mining because analysts can access different patterns and trends rather than a specific set of knowledge. olap and data mining can be combined to enable analysts to obtain data mining results from various sectors of the data and in the generalization stages [9, 39]. in a typical session of olap, analysts count aggregated queries about the underlying data. olap can obtain data in a few seconds, even if the query has a very long record. the results allow analysts to collect large amounts of data to determine general patterns and trends. based on their observations about an exception to a pattern, analysts can collect smaller amounts of data in greater detail to fill in parts. this process can be repeated in different parts of the data using data segmentation until the mental imagery is satisfied. olap system needs are determined in ways such as the fasmi test and codd law. some requirements are unique to olap. to enable olap for an interactive process, the system must first effectively respond to queries. olap often relies on large-scale pre-computing, specialized indexing, and storage to improve performance. in the next step, analysts are allowed to explore the data from different perspectives and stages of generalization to organize and generalize the data into multiple dimensions and hierarchies. the data cube model described below is a popular abstract model for this purpose [9]. the data to be analyzed by olap is collected in the data warehouse using the communication model and are organized using stellar models measuring dimension and other features. each dimension has a table that displays contributions to dimension hierarchically. the table of dimensions could have redundancies which can be eliminated by dividing each dimension into other tables. the result is called a snowflake model. rolap and molap are popular architectures of olap. rolap provides a front tool that translates the multidimensional queries in the corresponding sql queries for processing within a relationship. olap is lightweight and is scalable to large datasets, but its effectiveness is limited because intra-relational optimization methods are not designed for multi-dimensional queries. olap does not rely on the relational model, but focuses on a multi-dimensional view. molap can achieve better performance by visualization and improvement of a multi-dimensional view, although it requires significant storage for visualization and is not always scalable [2, 4, 23]. iii. data cube a data cube is an sql operator that supports olap functions such as histograms and subsidiary operations. histograms are aggregations at the calculation level. even if such tasks are possible using standard sql queries, they become too complicated. the number of sets needed for the number of dimensions is exponential. a complex query could produce results during the explorations of the base table which result in weak performance. because a subtotal of all queries is common for olpa queries, a new operator can be arbitrarily determined to collect subtotals as a data cube. users of the system want the data cube to offer a summary of the data in detail from different aspects. a data cube comprises reciprocal table generalization that occurs in multiple approaches. at first, a data cube is ndimensional. it is divided into eight parts, each of which is called a cube. the first cube is a three-dimensional cube known as the nucleus. the next tuesday cube contains data in which all values are 2d surface values. the next three cubes contain all values and 2d levels. the next three cubes are onedimensional. the last cube has a single value and a dimensionless point [1, 11, 16]. the second generalization approach is the aggregation function. this aggregation will be discussed with sum. in general, any aggregation function can be used with a custom value to build data cubes. this function can be divided into distributive, algebraic, and comprehensive categories. i is a set of values and },...,2,1{)( pnppip  is part of i. the aggregation function of f( ) is distributive if the function of g is }.1:)(({)( nipfgif i  under these circumstances, distributive sum, sount, min, and max are easy to examine. after generalization of function g( ) to one, the vector of m is restored and algebraic aggregation shows characteristics similar to the distributive sample of }1:)(({)( nipfgif i  . the third approach is dimensional hierarchy. for a data cube, each dimension has two stages of weak hierarchy. each dimension can have many features. dimension features can create a weak hierarchical network. features on the base table have lower bounds on the network and all queries have higher bounds. the network structure plays an important role in most data cube approaches [25, 35]. core cube visualization is necessary because this cannot be achieved by calculating other items. if any cube with all values has a value comparable to the core cube, it is not necessary to visualize the core cube because responding to a query using the cube incurs the same cost as the core cube. many greedy algorithms have been proposed to position data in data cube [16, 25]. even if all data cubes must be calculated, the network structure can be used to improve the efficiency of calculations. for example, if calculation is based on ordering records, then core cubes can be ordered in three ways. every choice leads to simplification of the calculation to one cube with all values, because that cube can be calculated without additional ordering, although calculation of the two other cubes will require a core cube to be re-ordered. based on the estimated cost, the algorithms available as the optimal choice for ordering each cube and the choices leading to construction of calculation pipelines again reduce the size of the cube ordered [11, 12, 25]. data warehouse users work in a graphical environment and data is displayed as a data cube in multidimensional form. dimensions are usually 2d or 3d, but higher dimensions can also be generated to increase information exploration. the values in each cell of a data cube contain a measuring value [4, 23, 30, 35]. engineering, technology & applied science research vol. 6, no. 5, 2016, 1187-1194 1189 www.etasr.com faridi masouleh et al.: genetic-firefly hybrid algorithm to find the best data location in a data cube iv. related work effective calculations and multi-dimensional aggregation in a data cube have been studied by many researchers. a data cube has been classified as an aggregation of generalizations by a relational operator based on subsidiary data cubes with distributive, algebraic and comprehensive categories [10]. a greedy algorithm has been developed to provide a partial cube for data cube calculations [35, 36]. a calculation method has been developed based on piece processing to effectively organize large multi-dimensional arrays [32]. several guidelines have been suggested for effective calculation of multidimensional aggregations for rolap servers [31]. a model has been developed based on multi-path array aggregation piece processing for data cube calculations in molap [40]. a method has been also been developed to calculate scattered data cubes [18]. after iceberg queries were developed [25, 26], the buc method, a scalable method with the ability to calculate iceberg cubes head downward, was introduced [16, 17]. the h cube method was also developed for calculating iceberg cubes with complex measurements using h-tree structure [12]. the star cube method was introduced for calculation of an iceberg cube with a dynamic star tree structure [7]. the mm cube is an effective method of calculating the iceberg cube using factorized network space [41]. a shell-piece method based on data cubes is very effective for olpa multi-dimensional data processing [23]. apart from these studies on data cube models, the smart dwarf method has been suggested for the calculation of a declined data cube and is known as the condensed model [38]. calculation of compression data cubes (dwarf cubes) uses a smart cube structure that summarizes the semantics of a data cube [21]. the same method was also developed in a qc tree structure [22]. an aggregation-based approach known as a closed cube or cube c has been developed [8] to close calculation in a closed cube using a new algebraic method of measurement. studies have been conducted on calculations using compressed data cubes by estimation, including the quasi-cubic [6] and the wavelet cube [13] methods. compressed cubes for estimation in continuous dimensions [14] have been applied using the linear logarithm models [5] to a compressed data cube. v. neural network and evolutionary algorithms everything is done in an environment directly or indirectly and is a collection of decisions. it is important at the beginning of a decision to have sufficient knowledge of the issue investigated to make appropriate decisions. evolutionary algorithms have been used to identify environments. in the present paper, two algorithms are used to comprehend the issues to facilitate knowledge [37]. a. neural networks the perceptron network is a well-known neural network and its multilayer state is a widely-used neural network. perceptron networks probably had the greatest effect on early neural networks. the perceptron learning rule is stronger than those such as the hebbian rule. with reasonable assumptions, this method of learning by repetition converges to correct weights. convergence means that network learning leads to estimation of weights that allow it to produce correct output values for each education input pattern and similar patterns. moreover, the performances of neural networks are related to the choice of the neurons count, architecture of networks and learning algorithms [28, 44]. the perceptron learning rule is supervised learning in which a stimulus, response, input, optimal output, pattern, and pattern class are available. learning error occurs; hence, in practice, at each step the learning error must be used to set network parameters such that the learning error becomes less when the same input is applied again. the perceptron learning rule is generated for one-layer neural networks consisting of neurons with a conversion function with a two-value limit threshold [20, 32, 37]. normally, primary perceptrons have three layers: sensory neurons, connecting units, and the response unit forming an approximate retina model. although these networks are only taught weights between the second and third layers, the activation function for each connecting unit is a binary step function with an optional, but fixed, threshold value. the signal sent from the connecting units to the output unit is a binary signal and )( inyfy  is the perceptron output with the activation function:             in in in in yif yif yif yf 1 0 1 )( this function determines the network output in addition to the usual outputs of +1 (belonging to the category or group) and -1 (not belonging to the category or group) and includes the area between θ and –θ in which a decision will not be made [34, 37]. the unit weights connected to the response or output units are set using the perceptron learning rule. in the perceptron training rule, the network computes the output unit response for each input learning vector and then determines whether or not an error has occurred for the model. here, an error occurs when the output calculated by the network does not equal the target value. learning this rule is similar to learning the hebbian rule, except that the weights only alter when the network response for the input contains an error. the perceptron network does not identify the difference between errors when the calculated network output is 0 (area without decision) and the target value is -1 or when the calculated output value is +1 and the target value is -1. the learning rule changes the direction of network weights such that the response becomes equal to the target value. only the weights on the joints of connecting units that send non-zero signals to the output unit will be changed, because these signals have caused the error. in the perceptron training rule, if an error occurs in the training input pattern, the weights vary as: taxoldwneww iii  )()( where t represents the target value as +1 or -1 and a is the learning rate and determines the speed of the weights. in this network, if no error occurs, the weights will not change and training will continue until no further error occurs. engineering, technology & applied science research vol. 6, no. 5, 2016, 1187-1194 1190 www.etasr.com faridi masouleh et al.: genetic-firefly hybrid algorithm to find the best data location in a data cube an optimization algorithm which supplies the best training dataset for appropriate artificial neural networks is proposed in this study like [24,44] that updates weights and bias and the trained net is added as input dataset for genetic algorithm. the perceptron learning rule convergence theorem states that if there are weights that allow the network to produce the correct answer for all training patterns, then the perceptron learning method uses these values when setting weights. this means that the perceptron network will be able to solve the problem or learn the desired categorization. in addition, the network will use these weights several times with a limited number of training repetitions [23, 44]. b. genetic algorithm in genetic algorithms, every solution is displayed as a binary string and the measurement of the related fitness function. a genetic algorithm solves a problem by first randomly generating a population of chromosomes. second, the fitness of each chromosome in the population is assessed and, third, new chromosomes are created by random mating and mutation of some bits. fourth, less fit members are excluded from the current population and, fifth, new chromosomes are evaluated and included in the population. finally, the third to fifth steps are repeated until population convergence occurs, which is also the termination condition. the fitness of the total population increases as the number of people in the population increases; however, the number of fit people, or more fit people, is equal at t and t-1. the population is considered for evolution rather than an individual or components. a set of chromosomes makes up the population. the effect of genetic operators on the population is to form a population with the same number of chromosomes. the fitness function provides an indicator for independent functioning in the work area. fenestration and linear normalization are terms within the fitness function [20, 27, 29, 33, 37]. reproduction takes place in two stages when parental chromosomes are duplicated in bits of a child’s chromosomes and functions alter the chromosomes of each child. the major operators are intersection, mutation, and inverse mutation. intersection is the strongest supporter of genetic algorithms and is usually associated with high probability. mutation is less important than intersection and less likely to occur. as the parameters change and simulation advances, mutation become more important and population change decreases [14]. intersection is the driving force behind a genetic algorithm which uses reproduction. initially, a genetic algorithm uses a random number generator to select a random point in each parent at an intersection where a genetic algorithm occurs [14, 15, 27]. mutation causes searches in untouched spaces and it can be deduced that the most important task of mutation is to avoid convergence to the local optimum. when a member of the new population arises, each gene will mutate if possible. inversion is used in the genetic algorithm because it is biologically plausible. it can be said that in inversion, one chromosome can be selected at any time and then two points are randomly selected and their locations reversed. there are different strategies for selecting people from a population for reproduction. the selection operator selects a number of chromosomes from a population for reproduction and the more fit chromosomes are more likely to be selected [15, 33, 37]. c. firefly algorithm the firefly algorithm is inspired by observation of actual fireflies. fireflies are social insects that live in colonies and their behavior tends toward survival of the colony rather than survival of a small fraction of them. one of the most important and interesting behaviors of fireflies is finding food, especially how to find the shortest path between a food source and their nest. the firefly algorithm is a swarm intelligence method; the difference between this algorithm and fireflies in nature is memory. the most important features of this algorithm are its high convergence speed, flexibility, high error tolerance, and its insensitivity to initial values [15]. the similarity of the data placement in a data cube with a firefly algorithm and the parameters used to select the appropriate position for data and suggest the best location prompted the use of this algorithm in the present study [19]. two very important factors in the firefly algorithm are variation in light intensity and formulation of attractiveness. for simplicity, it is always assumed that the attractiveness of a firefly is determined by its brightness, which is associated with target function coding. for maximum optimization problems, brightness i is selected for fireflies in position )()( xfxi  . β attractiveness is a common point that can be seen by fireflies and there is no difference in distance ijr for fireflies i and j. note that the light intensity decreases as the distance from its own resources increases. in the simplest case, the light intensity of i(r) differs according to inverse square law and is defined as [4, 19]: 2 )( r i ri s where si is the intensity at the source. for a given media, a constant light absorption coefficient is considered with variable γ where the brightness intensity i differs at distance r. this relation is defined as: reii  0 where 0i is the main brightness intensity. to avoid the singularity at r = 0 in relation 2/ ri s , the effect of inverse square law and absorption is gaussian and defined as: 2 0)( reiri  firefly attractiveness develops as intensity that can be observed by fireflies and β attractiveness of fireflies can be defined as: 2 0 re   where 0 attractiveness in r = 0. )1/(1 2r is faster than the power function for calculation and is generally defined as: engineering, technology & applied science research vol. 6, no. 5, 2016, 1187-1194 1191 www.etasr.com faridi masouleh et al.: genetic-firefly hybrid algorithm to find the best data location in a data cube 2 0 1 r     to implement the project, attractiveness function β(r), is assumed to be a uniform reduction function such as: )1(,)( 0   mer mr the distance between two fireflies (or equipment) i and j in ix and jx is similar to a cartesian distance:    d k kjkijiij xxxxr 1 2 ,, )( where kix , is the kth location coordinate component of ix and the ith firefly. in the 2d state, it can be expressed as:    22 jijiij yyxxr  the motion of firefly i is attractive for firefly j as expressed by: iji r ii xxexx ij     )( 2 0 the second part of relation (11) represents the attractiveness of the firefly where α is a random parameter and i î is the vector of random numbers drawn from the gaussian or uniform distribution [15]. to use this algorithm, first an n-member population of fireflies in different locations is randomly generated. all fireflies initially have the same amount of light and with each iteration a light update phase and a location update phase are carried out. the location of the fireflies is the randomly-placed location and the purpose of the light is for best placement of the data. the amount of light for each firefly in each iteration is determined by its location fitness value. the fitness value is the value added to the light in each iteration. firefly light for each update can be expressed as: ))(()1()1()( txjtipt ii   where )(( txj i is the new value of firefly light when used again, )1()1(  tp i is the fitness of firefly i in iteration t of the algorithm and p and  are constants with which to model the gradual decline and its effect on light. relation 13 is used to detect the position of other pieces of data in the neighborhood as:      )( )()( )()( )( tnk ik ij ij i tt tt tp   where )(tni is the set of fireflies in the neighborhood of firefly i at time t. the distance between fireflies i and j at time t uses the euclidean distance )(tdij discrete-time movement of fireflies with probability p is expressed as:              )()( )()( )()1( txtx txtx stxtx ij ij ii where operator ||…|| shows the euclidean norm r, s is its stepsize movement. the term )(txt is an m-dimensional vector of firefly location over time t. a neighbor is assigned to each firefly i in which radial range idr is naturally dynamic. updating of the neighbors is achieved as:  |)(|()(,0max,min{)1( tnntrrtr itidsid   where  is a constant parameter and tn controls the number of neighbors. vi. proposed method in this project, a data set containing information from a printing company was used. this data warehouse contained information such as user name, company id, company name, company address, company phone number, company-enabled state, and company ads. user name, company id, and company name are used as location dimension features. company address, company phone number, company-enabled state, and company ads are used as time dimension features. other pieces of data contain information about orders by these companies, including id, user name, user id advertised, company id, order name, color of ordered item, requested size (x and y), material used for ordered item, order date, enabled or disabled state, confirmed or unconfirmed order state, send order to user, and change of order by user. id, user name, user id advertised, and company id are used as location dimension features. order name, color of ordered item, requested size (x and y), material used for ordered item, order date, enabled or disabled state, confirmed or unconfirmed order state, send order to user, and change of order by user are used as time dimension features. as like [28] we use the genetic algorithms techniques and firefly algorithm to optimize finding best location for data in data cube. the data was to consider being genetic algorithm inputs and the initial population totaled 1000. the initial population of the firefly algorithm was set at 700. the values were inserted experimentally and the population distribution in the environment was very effective because the area was very large. determination of the initial population was based on trial and error. reduction of data size was done using the genetic algorithm and placement improvement was done using the firefly algorithm. the proposed algorithm was written as a pseudo-code. algorithm 1 gives the output (s) set by testing the mlp as input for optimized placement and algorithm 2 receives this input and makes a hybrid genetic-firefly algorithm to find the appropriate place for data in the data cube. engineering, technology & applied science research vol. 6, no. 5, 2016, 1187-1194 1192 www.etasr.com faridi masouleh et al.: genetic-firefly hybrid algorithm to find the best data location in a data cube algorithm 1. mlp for optimizing data place. input: dataset output: (s) 1. define weights and bias for mlp; 2. learn dataset with mlp; 3. if error_occurs in learning of mlp 4. update weights and bias 5. end 6. test dataset with mlp; 7. use output (s) from testing of mlp as input for optimized placement algorithm 2. genetic algorithm and firefly algorithm as a hybrid algorithm for data cube. input: output (s) from mlp (algorithm 1) output: place data in data_cube 1. use the output (s) from testing of mlp as input for optimized placement; 2. initialize the parameters for both genetic and firefly algorithms; 3. generate main_population_size from the dataset for the genetic algorithm; 4. use the fitness function for the genetic algorithm; 5. while generating for genetic from 1 to n do: 6. use genetic fitness function; 7. create new_population; 8. evaluate each individual; 9. while new_population < main_population_size do: 10. select parents from new_population using roulette wheel method; 11. use genetic crossover; 12. use genetic mutation; 13. place offspring into new_population; 14. endwhile 15. main_population_size new_population; 16. lighting from new_generation for new population for firefly generated; 17. define new firefly (component or population) for firefly algorithm; 18. define distance beyond firefly (component or population); 19. lighting for attractiveness of firefly; 20. move firefly (component or population) for attractiveness with light; 21. place data in data_cube 22. endwhile vii. simulation results applying the optimization algorithm to the genetic-firefly hybrid algorithm, the initial population of genetic algorithm totaled 1000 and firefly algorithm totaled 700. user name, company id, and company name are used as location dimension features. company address, company phone number, company-enabled state, and company ads are used as time dimension features. as it shown two dimensions are defined for this simulation; one “location” and the other “time”. simulation was done in a matlab environment using the observational method. at first step weights and bias are defined for multi-layer perceptron and learning with mlp occurred. if errors occurred in learning, weights and bias are updated. at the end in this phase, test dataset are tested. the data was first inserted into the data cube environment sporadically as shown in figure 1. now this phase output is as input for optimized algorithm. parameters for both genetic and firefly algorithms initialize. the mail population size from dataset generate for genetic algorithm. fitness function is used in this level and new population has been created and evaluated. in this part with using “roulette wheel” method, parents from new population are selected. crossover and mutation in genetic algorithm occurs and offspring is placed into new population. the best data position was as shown in figure 2. firefly algorithm applies in new population and generated lighting. distance beyond firefly population is defined. component for attractiveness with light are moved and placed in data cube. figure 3 shows the reduction of dimensions over time determined visually for the operation. viii. conclusion in this study, placement of data in the scalable space of a data cube was done using a hybrid genetic-firefly algorithm. the data was first inserted into the data cube environment sporadically then the best data position was shown and the reduction of dimensions made over time determined visually for the operation. dataset clustering was carried out with the help of a perceptron multi-layer neural network and then the hybrid genetic-firefly algorithm was used for placement to find the best position for the data in the data cube. decision-based programs include large-scale complex database queries. if the response time is short, query optimization is critical. users usually observe data as a multi-dimensional data cube. each data cube cell displays data as an aggregation in which the number of cells depends on the number of other cells in the cube. at any given time, a powerful query optimization method can visualize part of the cells instead of calculating results from raw data. business systems use different approaches and positioning of data in the data cube. in the present study, the data is trained by a neural network and a genetic-firefly hybrid engineering, technology & applied science research vol. 6, no. 5, 2016, 1187-1194 1193 www.etasr.com faridi masouleh et al.: genetic-firefly hybrid algorithm to find the best data location in a data cube algorithm is proposed for finding the best position for the data in the cube. fig. 1. data in data cube. fig. 2. best data position in data cube. fig. 3. visualization of data dimensions for reducing dimensions of data cube. references [1] a. nandi, c. yu, p. bohannon, r. ramakrishnan, “data cube materialization and mining over mapreduce”, ieee transactions on knowledge and data engineering, vol. 24, no. 10, pp. 1747-1759, 2012 [2] h. cheng, y. lu, c. sheu, “an ontology-based business intelligence application in a financial knowledge management system”, expert systems with applications,vol. 36, no. 2, pp. 3614-3622, 2009 [3] l. 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[43] p. k. dey, s. o. ogunlana, “selection and application of risk management tools and techniques for build-operate-transfer projects”, industrial management and data systems, vol. 104, no. 4, pp. 334-346, 2004 [44] j. a. johannessen, b. olsen, b., j. olaisen, “aspects of innovation theory based on knowledge-management”, international journal of information management, vol. 19, no. 2, pp. 121-139, 1999 [45] d. pelusi, r. mascella, “optimal control algorithms for second order systems”, journal of computer science, vol. 9, no. 2, pp. 183-190, 2013 microsoft word etasr_v12_n6_pp9487-9490 engineering, technology & applied science research vol. 12, no. 6, 2022, 9487-9490 9487 www.etasr.com pasha et al.: epenthesis: the movement of the urdu alveolar-fricative sound into the punjabi palatal-… epenthesis: the movement of the urdu alveolarfricative sound into the punjabi palatal-affricate sound ali rizwan pasha riphah institute of language and literature riphah international university lahore, pakistan alirizwanpaxa@gmail.com nadeem abbas department of english linguistics government college university faisalabad, pakistan nadeemnadi57@gmail.com hafiz nauman ahmed riphah institute of language and literature riphah international university lahore, pakistan nauman.ahmed@riphah.edu.pk received: 29 august 2022 | revised: 9 september 2022 | accepted: 11 september 2022 abstract-pakistan is a multilingual country where the urdu language serves as lingua franca. although urdu is the national and official language of pakistan, it bears the status of the second language (l2) in most of the regions due to the dominance of regional languages. the punjabi language is the first language (l1) of the people of punjab. this study intends to investigate the interlanguage influence and extralinguistic factors of phonological variants produced in the process of epenthesis of punjabi palatal-affricate (/dʒ/) with the deletion of urdu alveolarfricative (/z/). the analysis of this study has been conducted using praat software which proved that the native punjabi speakers replace the /z/ sound with the /dʒ/ sound no matter if it occurs at the start, middle, or the end of a word. moreover, this process of epenthesis is the result of the influence of the native language, i.e. punjabi. the outcome of the analysis indicates that the gender and dwelling (urban or rural) of the participants have nothing to do with epenthesis. however, the education of the participants is the main reason for epenthesis. keywords-epenthesis; phonological variant; interlanguage influences; extralinguistic factors i. introduction being the national language of pakistan, urdu serves as lingua franca for all the regions of the country, where regional languages are spoken as the first language (l1), i.e. punjabi in punjab, pashto in khyber pakhtunkhwa, and sindhi in sindh. the relationship of influence between urdu and regional languages is reciprocal, as the medium of instructions at educational institutions of pakistan is urdu [1-3]. as far as punjabi is concerned, it shares a lot of its diction with urdu due to their cultural similarities. in other words, variants of various urdu words are found in punjabi. since several words are the same in urdu and punjabi, the punjabi speakers pronounce these (urdu origin) words with phonological variations due to the influence of their first language. similar to urdu and punjabi, several other languages have influenced each other in many ways, e.g. phonological, orthographic, and accentual variations [4-7]. therefore, many research works have been conducted to analyze the influence of one language on another. authors in [8] investigated the process of phonological variations and the way laterals have been developed in the last three generations of punjabi-english bilinguals residing in the united kingdom. the findings of the study conclude that the speakers of the third generation still have high phonetic distinctions among their punjabi and english as compared to the first and second generation. moreover, the accent of younger speakers (third generation) does not match with the native english speakers, although they have developed a unique accent which is similar to british asian english. authors in [9] analyzed prevocalic /r/ in the non-rhotic expression of english speakers of the uk through articulatory and acoustic data. the data obtained from 24 speakers show that the patterns of lingual variation of rhotic expression is similar to the non-rhotic expression of the english speakers. moreover, the authors suggested that a specific lip posture of anglo-english /r/ is different from /w/ due to their exposure of labiodental variants and the stream of air that maintains a contrast between /r/ and /w/. authors in [10] analyzed the cues which are important to contrast between urdu and hindi laryngeal stops. they argue that murmured and breathy voices are the key features to differentiate among the voiced aspirates in the process of sound production. in other words, the authors found that aspirated sound (breathy voice quality) is sufficient for the identification corresponding author: ali rizwan pasha engineering, technology & applied science research vol. 12, no. 6, 2022, 9487-9490 9488 www.etasr.com pasha et al.: epenthesis: the movement of the urdu alveolar-fricative sound into the punjabi palatal-… of voiced aspirates even if one of the other two key features (prevoicing and aspiration) is missing. authors in [11] argue that the phonemic realization of /r/ in two scottish towns is variable due to various linguistic and sociolinguistic factors [11]. their findings show that the realization of /r/ bears a change from the alveolar tap to the approximant in one of the selected towns whereas the other town shows no variation and thus can be considered as linguistically orthodox. moreover, the variation in the realization of the same phoneme /r/ largely depends upon the phonological environment of the area in which it is spoken. it is evident from the existing literature that few studies draw the comparison of various linguistic and non-linguistic factors of urdu and punjabi. therefore, the current research work analyzes the movement of the urdu alveolar-fricative phoneme (/z/) into the punjabi palatal-affricate phoneme (/dʒ/) using praat software. four different but mutual tokens of urdu and punjabi have been selected for this study to analyze the reciprocal influence of both languages. to ensure the phonological variations, samples have been collected on the basis of literacy, living style, and gender. ii. methodology in this section, the methodology for analyzing the movement of the urdu alveolar-fricative into the punjabi palatal-affricate has been provided in detail. data collection is outlined in subsection a while the detail of the analysis process using praat software is presented in subsection b. a. data collection to investigate interlanguage phonological variation through epenthesis of the punjabi palatal-affricate phoneme (/dʒ/) with the deletion of the urdu alveolar-fricative phoneme (/z/) semantic fields were made for the collection of data from the native punjabi speakers. eight punjabi native speakers have been selected as sample for the purpose of analysis. among the selected punjabi native speakers, 4 were educated and 4 were uneducated. data were recorded using voice recorder without telling the subjects so that the responses may be recorded in natural frequency. the subjects have been kept anonymous. b. analysis process the praat is open-source software that has been widely used by the research community to perform speech analysis in various disciplines [12]. to perform the analysis, the praat software converts the sound file into frames and calculates multiple pitch values within the frame length [13]. therefore, praat has been used to analyze the phonemic movement from alveolar-fricative to palatal-affricate. the key steps we took for the analysis process using praat have been mentioned as follows:  step 1: record the selected words for 4 seconds or longer.  step 2: open the selected sound files in praat and chose "edit" from the main menu.  step 3: select the stable part of the file from the sound editor and extract the stable part to focus on the targeted phonemes.  step 4: activate the pitch, energy, and spectrum functions to complete voice analysis.  step 5: repeat the above-mentioned steps until achieving satisfactory results to perform analysis as fair as possible. in praat, the length of the time interval is measured from the pitch value of a sound when the sound signal is higher than the average sound signal. the range of the pitch is defined between maximum and minimum values of the intensity of the sound signal. iii. results and discussion the simulation results of this study are discussed in this section. the analysis is conducted through different samples and analysis process using praat. the samples include 8 different punjabi native speakers, namely an educated adult male, an uneducated adult male, an educated adult female, an uneducated adult female, an uneducated rural male, an uneducated urban male, an educated rural male, and an educated urban male. z l i: l (a) dʒ l i: l (b) fig. 1. comparison of the pronunciation of the word "zaleel" (dishonored): (a) educated male, (b) uneducated male. the speech samples consist of 4 lexemes, i.e. zaleel (dishonored), namaz (prayer), roza (observing fast), and raza (name). figures 1-4 illustrate the speech analysis of the selected lexemes with the chosen punjabi native speakers. the speech analysis results of "zaleel" and "namaz" are presented in figures 1-2. the comparison of the word "zaleel" in terms of pronunciation by educated and uneducated males has been drawn in figure 1. engineering, technology & applied science research vol. 12, no. 6, 2022, 9487-9490 9489 www.etasr.com pasha et al.: epenthesis: the movement of the urdu alveolar-fricative sound into the punjabi palatal-… n m a: z (a) n m a: dʒ (b) fig. 2. comparison of the pronunciation of the word "namaz" (prayer): (a) educated female, (b) uneducated female. r ɔ: dʒ a: (a) r ɔ: dʒ a: (b) fig. 3. comparison of the pronunciation of the word "roza" (observing fast): (a) uneducated rural male, (b) uneducated urban male. figure 2 shows the comparison of pronunciation of the word "namaz" by educated and uneducated females. figure 1(a) shows that the /z/ phoneme, at the initial position of the word /zli:l/, has been pronounced by an educated male as alveolar-fricative /z/, whereas an uneducated male pronounced the same phoneme as palatal-affricate /dʒ/, as shown in figure 1(b). on the other hand, figure 2 shows the same phoneme at the ending position of the word "namaz" which has been pronounced as alveolar-fricative /z/ by an educated female in figure 2(a) whereas an uneducated female pronounced the same phoneme as palatal-affricate /dʒ/ in figure 2(b). r z a: (a) r z a: (b) fig. 4. comparison of the pronunciation of the word "raza" (name): (a) educated rural male, (b) educated urban male. figures 3-4 present the speech analysis results of the words "roza" and "raza". figure 3 reflects the comparison of the pronunciation of "roza" between uneducated rural and uneducated urban males. figure 3(a) shows that the /z/ phoneme, in the middle of the word /rɔ:za:/, has been pronounced as alveolar-fricative /z/ by an uneducated rural male. on the other hand, an uneducated urban male pronounces the same phoneme as palatal-affricate /dʒ/ as shown in figure 3(b). figure 4 showcases the pronunciation comparison of "raza" between an educated rural male and an educated urban male. the phoneme /z/ is in the middle of the word /rza:/ and has been pronounced by both the participants as a palatalaffricate /z/. pitch is a fundamental acoustic feature for the analysis of the speech process. the pitch of the phoneme /z/ is higher than that of /dʒ/ as shown in figure 1, although both are voiced phonemes. similarly, phoneme /z/ has higher pitch than /dʒ/ as shown in figure 2. the results indicate that the epenthesis of /dʒ/ at the place of /z/ depends on the premise of being educated or not. however, gender is not a decisive factor for this epenthesis. the pitch of the phoneme /dʒ/ in figure 3(a) engineering, technology & applied science research vol. 12, no. 6, 2022, 9487-9490 9490 www.etasr.com pasha et al.: epenthesis: the movement of the urdu alveolar-fricative sound into the punjabi palatal-… and (b) remained almost unchanged, whereas the pitch of phoneme /z/ is higher in figure 4(a) than (b). it can be deduced from the results that the urban or rural setting of the participants has nothing to do with the replacement of /z/ with /dʒ/, but the factor whether the participant is educated or not is the major reason for epenthesis. the educated participants are less likely to accept the influence of native punjabi language, as the medium of instructions at educational institutions is urdu. the spectrograms in figures 1-4 show a very slight difference as alveolar-fricative and palatal-affricate are both voiced phonemes and create more vibration in vocal cords than the voiceless phonemes. iv. conclusion and future work epenthesis is a prominent feature of interlanguage variations. it has been observed from the analysis that the initial, middle, and final position of the urdu alveolar-fricative phoneme (/z/) is always epenthesized by the punjabi palatalaffricate phoneme (/dʒ/), a permanent feature of the phenomenon having only one variable of orthographic knowledge of urdu language. this interlanguage influence of the second language has been developed in the educated native punjabi speakers permanently. therefore, they pronounce /z/, not /dʒ/, however, uneducated native punjabi speakers pronounce it as /dʒ/ because they did not acquire the influence of urdu. in future work, we intend to extend our analysis to the influence of punjabi language on english and arabic using praat and machine learning algorithms. the reciprocal influence of punjabi and urdu can be analyzed at phrase or sentence level. in this way, we plan to analyze the impact of the native language on the national language in terms of phonological variations along with syntactic variations. acknowledgment the authors would like to express their gratitude to the riphah institute of language and literature for providing access to their language lab. references [1] a. korn, "a grammar for balochi: challenges of describing a language that maybe is not one," presented at the 2nd conference "descriptive grammars and typology," paris, france, dec. 2021. 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[13] l. zhang and j. barnden, "affect sensing using linguistic, semantic and cognitive cues in multi-threaded improvisational dialogue," cognitive computation, vol. 4, no. 4, pp. 436–459, dec. 2012, https://doi.org/10.1007/s12559-012-9170-3. authors profile ali rizwan pasha received the ma eltl (english language teaching & linguistics) from the punjab university lahore, pakistan and the mphil english linguistics from the riphah international university, pakistan. his main research interests are phonetics and phonology, second language acquisition and discourse studies. nadeem abbas received the ma english from the university of sargodha, pakistan and the mphil english linguistics from the government college university faisalabad, pakistan. his main research interests are cognitive linguistics, corpus-bases studies and phonotactics. hafiz nauman ahmed received the ma eltl from the punjab university lahore, pakistan and mphil applied linguistics from the university of lahore, pakistan. he has more than six years research experience in discourse studies, second language acquisition, task-based language teaching, phonology and syntax. he is currently working at riphah international university, pakistan as a senior lecturer. microsoft word etasr_v12_n1_pp8039-8044 engineering, technology & applied science research vol. 12, no. 1, 2022, 8039-8044 8039 www.etasr.com biabani & tayyib: a review on the use of machine learning against the covid-19 pandemic a review on the use of machine learning against the covid-19 pandemic sardar asad ali biabani science and technology unit umm al-qura university makkah al-mukarramah, saudi arabia sabiabani@uqu.edu.sa nahla a. tayyib faculty of nursing, deanship of scientific research umm al-qura university makkah al-mukarramah, saudi arabia natayyib@uqu.edu.sa abstract-coronavirus-2019 disease (covid-19) is a contagious respiratory disease that emerged in late 2019 and has been recognized by the world health organization (who) as a global pandemic in early 2020. since then, researchers have been exploring various strategies and techniques to fight against this outbreak. the point when the pandemic appeared was also a period in which machine learning (ml) and deep learning (dl) algorithms were competing with traditional technologies, leading to significant findings in diverse domains. consequently, many researchers employed ml/dl to speed up covid-19 detection, prevention, and treatment. this paper reviews the state-of-the-art ml/dl tools used, thoroughly evaluating these techniques and their impact on the battle against covid-19. this article aims to provide valuable insight to the researchers to assess the use of ml against the covid-19 pandemic. keywords-covid-19; machine learning; deep learning; coronavirus; evaluation; detection; prevention; treatment i. introduction deep learning techniques can be employed in many technical predicaments instead than conventional ones in order to save time and resources. this paper investigates and evaluates the use of machine learning (ml) and deep learning (dl) techniques on the fight against the covid-19 pandemic. we will mainly focus on four states: at first, dl and ml models require a lot of data in their training process to provide accurate predictions. therefore, we begin this study by reporting some covid-19-related datasets used to train ml/dl tools. then, we will investigate the way these tools are employed to prevent the disease, either by tracking the spread of the virus or by helping in the productions of a new vaccine. thirdly, the paper will study the utilization of ml techniques in the discovery phase, presenting the models and algorithms adapted to diagnose and detect the virus. finally, we will examine the same approaches, but this time applied to the drug discovery and treatment of the disease. this paper aims to present a review about the use of ml against covid-19, to evaluate these techniques, and to analyze their effectiveness to counter the pandemic. however, before talking about implementing ml or dl techniques in any given field, essentially, when the models we are dealing with are on supervised learning methods, the fundamental problem to deal with is data. various types of covid-19 datasets available for practitioners and researchers are examined below. a broad range of data was collected and made open during this pandemic. it ranges from classic computerized tomography (ct) scans to x-ray chest (xrc) radiograph images, but one can also find datasets based on text data, video, or sound. authors in [1] collected a dataset of 123 computerized ct scans. this dataset contains not only covid19 but also mers, sars, and ards (other coronaviruses) images. the authors in [2] provide a more extensive dataset of 275 ct scans of covid-19 patients. a familiar and productive technique used to augment data in ml is segmentation. this technique was used in several studies [3] to develop more samples. in addition to segmentation, other studies collected negative covid-19 ct images to combine them with positive cases for binary classification diagnosis models [4-6]. xrc images belong to a different type of data. one of the first efforts to collect an xrc covid-19 dataset was [7]. the authors used a collection of more than 13000 images to train a neural network classification model that achieved 93.11% accuracy. moreover, added preliminaries in the xrc datasets were developed in [1]. this resource framed the basis of many extensions [8-11], whether by appending more images of covid patients, using data augmentation techniques such as segmentation or by adding non-covid-19 images. in addition, an italian hospital provided more than 4700 x-ray images of covid-19 patients [12]. another popular dataset type deals with tracking and visualizing covid-19's new cases and deaths in real-time. the most known dataset of this kind is [13], while [14] was used to predict the pandemic's spread. besides these platforms that offer universal statistics, many country-focused datasets accumulate information about specific countries [15-17]. although these datasets represent limited regions, they generally present richer resources since they consider demographic aspects, travel restrictions, and sometimes even personal data. in [18], the authors presented a collection of covid-19, pneumonia, and healthy videos. a related dataset [19] consolidated data from some hospitals and web resources to present a collection of images and videos of lung ultrasounds. additionally, the coswara ongoing project [20], consists of collecting breathing, cough, and speech sounds from covid-19 patients to build a diagnostic tool. likewise, corresponding author: sardar asad ali biabani engineering, technology & applied science research vol. 12, no. 1, 2022, 8039-8044 8040 www.etasr.com biabani & tayyib: a review on the use of machine learning against the covid-19 pandemic another sound-based south african dataset was erected [21] on cough audio. table i summarizes the cited datasets, the nature of the data they contain, and, more importantly, the number of samples in each one. notably, the big problem in using these datasets to train dl models is that they do not have enough data to predict real-world situations accurately. table i. reviewed covid-19 datasets ref. nature of the data number of samples [1] frontal view x-rays 123 [2] ct scans 275 [3] ct scans 20 cases [4] ct scans 5900 images of 1200 patients [5] ct scans 888 ct scans of 888 subjects [6] ct scans 366,558 ct scan images [7] xrc 13000 images [12] x-ray images 4700 [19] videos 247 the following sections will provide an extensive literature review of the papers that used ml techniques to help the spreading prevention, detection, and treatment of covid-19. ii. ml methods for covid-19 prevention this section will examine the operation of ml techniques in the prevention of the spreading of covid-19. to accomplish this, we will present two effective solutions that have been used in response to the outbreak: vaccines (to reduce the spread of the infection) and spread estimation (to embrace the appropriate restrictions at the right time and place). a. vaccine discovery the invention of a vaccine is arguably the most prolific covid-19 area of research. in fact, given its significance in putting an end to the limitations placed on people (lockdown, festivities, gatherings), the vaccine is the ultimate solution to the covid-19 crisis. unfortunately, the firms that use ml techniques in their vaccine development pipeline publish minimal data, if any [22]. a pioneering effort to use ml in the process of developing an effective covid-19 vaccine was conducted in [23]. the authors trained an xgboost model (a decision-tree-based ensemble ml algorithm) to predict the best candidate protein for the vaccine. their work resulted in 6 potential candidates. the authors adopted an optimized mlbased technique to pick some suitable amino acid fibers to improve the composition of already discovered vaccines [24]. separate studies [25-27] relied on support vector machine (svm) and other ml techniques in the same direction. svm is a supervised learning ml algorithm generally used to classify data by figuring out the best hyper-plane that could separate them with the lowest error rate. the most documented dl-based approach to explore the world of proteins is the alphafold project powered by google deepmind [28, 29]. it focuses on predicting the 3d structure of proteins based on their genetic sequence. during the first months of the pandemic, deepmind published a prediction for many proteins related to sars-cov-2, the virus responsible for covid-19. this work aimed to contribute to the understanding of the functioning of the virus. b. spread estimation the compartmental models are the most used models to forecast the spread of the pandemic [30]. they rely on stochastic frameworks to predict the right actions, decisions, and strategies to perform under any circumstances. in [31], the authors used this method to evaluate the impact of social distancing on the pandemic spread to predict the expected number of infections after the lockdown. a similar approach was used in [32] to predict the outbreak's growth in wuhan, the chinese city where the first covid-19 cases were detected. the main recommendation of this work was that the lockdown and travel restrictions in china would help the control of the spread of the virus in the rest of the world. compartmental models were further used in various studies [33-36] to predict the transmission of covid-19 in japan, egypt, and other countries. researchers used dl [37] and logistic growth [38] models to estimate the spread in china and south korea. a complex approach was used in [39], where the authors used markov chain monte carlo and the number of confirmed deaths and cases to predict the reproduction rate. dl models were also used to predict a condition that refers to rapid breathing associated with covid-19 infections. the authors in [40] relied on a bidirectional gated recurrent unit (gru) model and data coming from smartphones. impressive results were provided by the authors in [41] by training a deep neural network (dnn) on a sizeable real-time dataset collected from smartphones. a long short-term memory (lstm) model was used in [42] to estimate the pandemic spread in canada. the authors in [43] developed a technique that joined lstm and gru to design and train a model to measure the covid-19 release and death cases. table ii sums up the primary discussed studies that used ml/dl tools for covid-19 prevention. table ii. ml studies on the prevention against covid-19 role ref model vaccine discovery [23] xgboost [24] combinational ml system [25, 26] svm [28, 29] dnn spread estimation [31-36] compartmental models [38] logistic growth models [39] markov chain monte carlo [40] bidirectional gru [42] lstm [43] gru + lstm iii. ml methods for covid-19 detection a prominent area where artificial intelligence (ai) methods shined during the coronavirus pandemic is disease diagnosing and detecting. several published papers highlight the use of dl models on covid-19 identification. it is also worth noting that many of the studies we found are on ct chest scans [44]. the authors in [45] used a dl model to perform visual feature extraction from ct chest images. this project aimed to implement a classifier discriminating between covid19 and other pneumonia diseases. the researchers in [46] achieved promising results (86.30% accuracy) when developing a classification model to tackle the same problem. authors in [47] proposed a similar work by implementing a dl engineering, technology & applied science research vol. 12, no. 1, 2022, 8039-8044 8041 www.etasr.com biabani & tayyib: a review on the use of machine learning against the covid-19 pandemic algorithm to detect covid-19 infections through ct segmentation. a robust system was developed in [48], where the authors created and trained a convolutional neural network (cnn) on lung images to detect covid-19 cases. the authors in [8] proposed another cnn model trained on ct chest scans and aimed to distinguish people affected by covid19 from others. authors in [47] took a different approach than we have seen hitherto. they presented an approach based on deep transfer learning to build and train a model to classify chest ct images. moreover, the researchers in [49] opted for transfer learning (tl) to design a classification model to detect patients infected by covid-19 based on their ct chest scans. however, instead of applying the densenet201 pretrained model as the basis of their architecture, the authors proposed the resnet50 model. also, based on ct chest images, the authors of [50] proposed a model based on resnet50 and dpn-92 for classifying infected and non-infected patients. tl was also proposed in [51], where the inception pre-trained model was used to create a diagnosis model. the authors of [52] intended the same goal. however, their approach was slightly different since they trained their model on x-ray images. similarly, the authors in [9] proposed a tl model based on pre-trained models such as vgg19, vgg16, resnet, densenet, and inceptionv3. it should be mentioned that these dnn models are well-known for reaching state-ofthe-art results for many applications, especially in computer vision classification. authors in [53] proposed a new classification model based on the random forest algorithm and x-ray scans from people affected by covid-19 and other lung diseases. an aggregated model was developed in [54], where pre-trained models such as resnet, vgg, and alexnet were used, along with svm. the pre-trained models were used for feature extraction, while the svm model handled the classification. in another direction, some studies were exploring a completely different path to achieve the same goal of detecting covid-19, namely sound-based and video-based techniques. for example, the authors of [18] used videos of healthy people and patients affected by covid-19 and pneumonia. these data then fit a pre-trained model (vgg-16) used in the prediction phase. moreover, authors in [55, 56] shown that respiratory sounds (mainly cough and breathing sounds) could be employed to detect people affected by covid19. the authors of [55] built binary classifiers for distinguishing covid-19 positive patients from other respiratory diseases. figure-1 illustrates the intersections between covid19 and other lung diseases and why it is difficult to distinguish one from the others. iv. ml methods for covid-19 treatment so far, this article explored the use of ml methods in the detection and prevention against covid-19. however, the most straightforward and essential action to fight the outbreak is to assist the affected people to recover. it can eventually be solved by finding drugs that have a practical impact in fighting the new virus. this section will discover how ml models contributed to alleviating this problem and how efficient they were. drug discovery is one of the trickiest and most challenging areas in medicine. furthermore, it is known for taking many years to give valuable results. fig. 1. covid-19 vs. other lung diseases. many researchers have turned their attention towards dl techniques instead of traditional technologies to speed up this process. for instance, the authors in [57, 58] used lstm, cnn, and other dl models in their quest to find acting antivirals among the existing known drugs. several other studies focused on biomedical knowledge graphs (bkgs), a technique used to detect similarities and relationships between drugs, viral proteins, and genes. authors in [59] utilized bkgs to identify a promising treatment for covid-19. authors in [60] used the same technique to describe the relations between gene-disease pairs. the ml model showed relations between the viral protein and some previously known drugs, which led to the prediction of many potential drug candidates that could be effective against covid-19 [61]. similar work has been done in [62], in which the researchers used a dl model to find candidate drugs. a multitask ml model and more than 2000 human proteins were used in [63] to find relations between covid-19 and known drug targets (kdts). the drug representation was extracted in [64] using a deep graph network and known biological interactions. ml and dl techniques were also applied to narrow the possibilities in the molecular docking process, one of the most computationally expensive, yet frequently used techniques in drug design. the authors used a neural network to narrow 3 million candidates to 1000 [65]. a random forest model to identify 187 molecules in the coronavirus s-protein was proposed in [66]. moreover, the ml framework to predict viral protein activities was developed in [67]. the ensemble model used in this framework studied 19 drugs and ranked them based on their capacity to prevent the coronavirus proteases. the authors also used docking to assess critical aptitude. ai was also used to find new chemical compounds. the authors in [65] used the protein homology model along with 28 dl models and reinforcement learning (rl) techniques to evaluate drugs based on some predefined metrics. furthermore, the authors in [68] used rl in their quest to discover new sars drugs. more precisely, they used deep q learning and evaluated the discovered molecules according to 3 predetermined factors. figure-2 summarizes the ml-based initiatives in handling the covid-19 crisis. engineering, technology & applied science research vol. 12, no. 1, 2022, 8039-8044 8042 www.etasr.com biabani & tayyib: a review on the use of machine learning against the covid-19 pandemic fig. 2. ml solutions towards the covid-19 pandemic. v. evaluation and discussion many researchers have used ai as a forefront tool in the fight against covid-19. choosing this technology instead of traditional approaches was driven by the impact that dl techniques have gained during the last decade. this section addresses these contributions evaluates their impact, and presents their limitations. ml and dl approaches have contributed to the findings and improvements in the fight against the pandemic. we presented many examples in this paper to back up this claim. however, our study also shows that ai did not play a game-changing role in this fight. we dedicate this section to present our observations and explain why this is the case. the companies that used ml tools in their research and development process generally publish little relevant information about their findings, particularly in drug discovery and treatment of the disease, although the biggest challenge the development of effective dl solutions faces is the lack of data. dl is known to be more effective when an abundant amount of (useful) data is available. however, as we have seen above, covid-19 datasets are generally composed of a few samples. for instance, we have seen models built upon data collected from only 28 cases. the number of samples is not the only issue with covid-19 datasets. the quality of these samples also raises another challenge. many datasets are being collected from web portals, affecting the quality of images and the information credibility. another issue regarding covid-19 data consists of their non-representativeness. there is a substantial disparity in the number of tests between countries, classes, and cities in the same country, affecting the scaling of the trained models and resulting in inaccurate predictions. the challenge of extracting these samples could explain the lack of quality and quantity of data related to covid-19. besides, one should not forget that we are dealing with personal data, so privacy constraints come into play. one solution that has been used in lots of studies to handle this problem is data augmentation. simultaneously with data augmentation, tl could present a great opportunity using the already available models and data developed for similar medical scenarios. it is essential to note that the dilemma with data issues when using dl models is that we can have a well-trained model that gives high performance in the limited data but fails to scale when new situations arrive. therefore, it is unlikely to get a solution applied in the real world. our study shows that most of the contributions are generally about predicting the spread of the pandemic or detecting the virus. there are relatively few studies in the drug and vaccine discovery area. this is in line with the previous remark about real-world implementations since these areas present a more significant risk and therefore do not allow a margin of error to play with non-scalable and non-precise models. our study also revealed that the primary source of covid-19 data is in the form of images. therefore, cnns constitute the basis for many propositions. there is also the issue regarding privacy protection and the issue of the interpretability of dl models and how much we could trust their predictions in critical situations. table iii exhibits the problems of existing dl/ml approaches when applied to the covid-19 pandemic. table iii. problems with the use of ai regarding covid-19 problem details proposed solutions competition closed models and datasets open-source initiatives data number of samples open-source initiatives data augmentation tl quality of samples non-representativeness model scalability data quantity and quality privacy differential privacy interpretability more research vi. conclusion according to the official public service announcement on coronavirus from the who, covid-19 caused almost 5 million deaths while there are more than 238 million confirmed cases. this enormously heavy toll has generated the commitment of the research and development communities to alleviate this crisis. it turned out that ml and dl tools have been widely used in many applications during the last decade, including healthcare applications [69, 70]. to render valuable guidance to researchers in evaluating the use of ml/dl models against covid-19, this paper studied the available covid-19 datasets, the indispensable fuel for any dl-based approach. then, the article reviewed how ml/dl tools were used in preventing, diagnosing and treating/curing the covid-19 virus. we presented the models that advanced to detect the virus and then find drugs to treat the disease. finally, the last section of the paper is devoted to the thorough evaluation of these techniques, along with a discussion about their effectiveness in fighting covid-19. the results that came from this study reveal that ml/dl techniques are not mature enough to be used in critical situations when people's lives are at stake, mainly due to the scarcity of the required medical data that are needed to train the models. the quality of the available data samples often raises 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a new power control method in dynamic wireless charging systems for electric vehicles. a dualloop controller is proposed to control charging power while the electric vehicle is moving without communication between the transmitting and receiving sides. the output power is estimated through the coupling coefficient estimation. however, the coupling coefficient varies with the position of the vehicle. therefore, this paper also presents an easy-to-do practical estimation method from the transmitting side, in which the coupling coefficient value is continuously updated according to the vehicle's position. as a result, the output power is controlled according to the required level with an error of less than 5%. keywords-electric vehicle; dynamic wireless charging; coupling coefficient estimation; lcc compensation; power control i. introduction the use of electric vehicles (evs) to reduce air pollution is globally rising. much research on evs is performed to make their use more convenient and safer [1-3]. one of the issues of interest to researchers is wireless charging technology for evs [4, 5]. wireless charging eliminates all charging cables, making charging safer and more flexible. currently, dynamic wireless charging (dwc) systems are preferred because evs can be used on the road while charging [6, 7]. therefore, the evs can travel longer distances, the size and weight of the battery can be smaller, and the transportation efficiency is improved [8, 9]. in the dwc systems, output power pulses occur because coupling coefficients vary as the evs move along the transmission lane. moreover, output power sharply drops when the ev moves with lateral misalignment [10, 11]. this problem affects battery life. many studies have been done to reduce the pulse of the output power by coil design [12, 13]. this solution may not be consistent for real evs that have different sizes of receiver coil. in addition, these researches have not addressed the problem of evs moving in lateral misalignment. also, in a dwc system, many evs of different types move and interact with the transmission lane and each ev type requires different levels of charging power [14]. therefore, advanced control methods need to be applied in dwc systems to control the output power. some studies perform power control for evs in a wireless charging system [15]. in these studies, the output power is controlled using dc/dc converters on the receiving side. this solution increases the converters' number as well as increases the loss in the system. this paper proposes a new power control method on the transmitting side without additional dc/dc converters. however, to be able to perform control only at the transmitting side, it is necessary to know the output power on the receiving side. the output power can be known by using the wireless communication network [16]. this solution is not suitable for the dwc system where the evs are always moving in a hard environment. in [17], the transmitting-side inverter is also used to control the output power in dwc systems. this study uses auxiliary coils to detect the position of the ev and determines lateral misalignment to control the output power. this system takes up a lot of space and is expensive. in [18], parameters are estimated based on high-frequency voltage, current, and phase angle measurements. however, the method of measuring these parameters at high frequency is a challenge in practice. in [19], a quadrature transformation algorithm is used to estimate power. this method requires a complex measuring circuit and signal conversion. to solve the above difficulties, the current paper proposes an easy-to-do practical power estimation method based on measuring the resonant current rms value on transmitter coils and inverter input dc power. this new power control method provides stable output power to any ev position and provides multi-level output power for different ev types in the dwc system. ii. the power control problem a. structure of the proposed system the structure of the designed system is shown in figure 1. on the transmitting side, transmitters are designed modular. each module includes a full-bridge inverter that provides power to three transmitting coils through lcc compensation circuits. at the receiving side, the induced ac voltage on the receiving coil is also fed through the lcc compensation circuit to the impedance matching circuit, the battery management converter, and the battery. the transmitting coils are placed under the roadway to form a dwc lane for the evs. in figure 1, at the transmitting side: s1 ~ s4 is the sic mosfet; dc ab u ,u are input and output voltages of the inverter corresponding author: nguyen thi diep engineering, technology & applied science research vol. 12, no. 4, 2022, 9042-9047 9043 www.etasr.com diep & trung: transmitting side power control for dynamic wireless charging system of electric … respectively, fi fr fi fr i r l , l ,c ,c ,c ,c are the inductances, lower branch capacitors, and upper branch capacitors of double lcc compensation circuit respectively, i li i , i are the input current to lcc compensation circuits and the resonant current on the transmitting coils (i=1,2,3) respectively, lr r ab i ,i ,u are the resonant current on the receiving coil, the output current/voltage of the compensation circuit, and i r l ,l are the coil inductances. the issue of switching between modules has not been considered in this paper. proposed transmitting side controller d w c la n e lf1 cf1 c1 l1 i1 il1 lf2 cf2 c2 l2 i2 il2 lf3 cf3 c3 l3 i3 il3 udc a b s1 s3 s4 s2 uab i dc iab lr cr cfr lfri lr ir ub ibrl impedance matching circuit a dwc module zli cin a b u ab battery management converter fig. 1. the structure of the proposed dwc system. b. characteristics of the coupling coefficient according to the ev’s position figure 2 shows the fea simulation model of a design system's magnetic coupler. the design of the transmitter and receiver is described in [20]. it is assumed that during dynamic charging, the transfer distance is always 150mm. receiver's positions in the x and y directions are defined as dx and dy respectively. when the receiver is centered with the first transmitter (t1), dx is zero and dy is zero. figure 3 shows the fea simulation result of the total coupling coefficient. this result is obtained in case dx increases from 0 to 800mm and dy increases from 0 to ±60mm, where the total coupling coefficient of the receiver with the transmitters is performed as follows: 3 1 r ir i k k = =  (1) where ir k is the coupling coefficient of the ith transmitting coil (ti) with the receiving coil (r). the results show that the coupling coefficient ir k is the greatest when the receiving coil is centered with the transmitting coils. the fea simulation result in figure 3 (solid lines) shows that when dy is 0mm (case 1-red line), the average value of the total coupling coefficient is 0.143. when dy is 40mm (case 2blue line), the average value of the total coupling coefficient is 0.111. in case 3 (black line), the dy is 60mm and the average value of the total coupling coefficient is 0.078. these show that during dynamic charging, the total coupling coefficient is varied and is significantly reduced when lateral misalignment increases. fig. 2. the fea model of the proposed magnetic coupler. fig. 3. fea simulation/estimation coupling coefficients result. c. analysis of power control capability the fundamental harmonic approximation method was used to give an equivalent circuit as shown in figure 4. ab u is engineering, technology & applied science research vol. 12, no. 4, 2022, 9042-9047 9044 www.etasr.com diep & trung: transmitting side power control for dynamic wireless charging system of electric … approximated as a sinusoidal source. for simplicity in circuit analysis, the losses on the compensation circuit and inverter are ignored. i r r ,r are the resistances of the transmitting and receiving coils respectively, l r is the equivalent load impedance seen from the impedance matching circuit input to the load, 1 2 3 i l l l l= = = are the transmitting coils which are designed the same, i m is the total mutual inductance of transmitting coil (li) with other transmitting coils ( 3 1 i ij j , j i m m = ≠ =  ), and irm is the mutual inductance of the transmitting coil (li) with the receiving coil (r). uab iab jωm1rilr jωm1ili 0 lf1 cf1 c1 r1 l1 0 jωm2rilr jωm3rilr jωm2ili jωm3ili lf2 cf2 c2 r2 l2 lf3 cf3 c3 0 r3 l3 jωm1ril1 jωm2ril2 jωm3ril3 lr rr cr lfr cfr rl il1 il2 il3 i1 i2 i3 ilr ir zp1 zp2 zp3 zm3 zm2 zm1 zs zl1 zl3 zl3 fig. 4. equivalent resonant circuit. fig. 5. the pwm signals for s1, s2, s3, s4, and voltage waveform. the relationship of compensation circuit parameters is shown in (2) [20]: 2 2 2 2 1 1 1 1 fi fi i i fi i fr fr r r fr c l c ( l l m ) c l c l l ω ω ω ω  =   = − +   =    =   −  (2) ω = 2πfsw the resonant current in transmitting coils is the same and is expressed as [20]: 1 2 3l l l li fi ab i i i i j c u= = = = − ω (3) analyzing the circuit of figure 4 and combining it with (2)(3) the output power can be expressed as: 2 2 2 2 l i r out r li r l fr fr r l l p k i r r l l =   +    ω (4) in designed dwc systems, the resonant frequency is usually kept constant, and the designed parameters of coils and compensation circuits are constant. it is assumed that at the receiving side the equivalent load impedance value is maintained constant and equal to the optimal load value for maximum transfer efficiency. equation (4) shows that if the coupling coefficient ( r k ) is estimated, then the output power could be controlled by regulating the resonant current of transmitting coils ( li i ). further, (3) shows that this resonant current can be controlled by controlling the inverter output voltage value ( ab u ). the output voltage of the inverters is adjusted by the phase-shift method. the signals for s1~s4 and the inverter output voltage waveform are shown in figure 5. the rms of the inverter’s output voltage can be expressed as [21]: 2 2 2 ab dc u u cos α π = (5) from (3), (4), and (5) it is shown that the output power can be adjusted by adjusting the phase-shift angle α. d. estimated output power given the circuit of figure 4 at resonant point, the derivatives of the equations are shown below. the equivalent reflected impedance of transmitting coils to each other is: i li mi i li j m i z j m i = = ω ω ; with i = 1,2,3 (6) the receiving side impedance ( s z ) can be represented by the ratio between the coupled voltage r li j m iω and the receiver resonant current lr i as follows: 1 1 2 2 3 3 3 2 2 1 r l r l r l s lr ir li fri r li r lr lr l j m i j m i j m i z i j m i lj m i r i i r = + + =       = = = +  ω ω ω ω ωω (7) the equivalent reflected impedance of the receiving coil to each transmitting coil can be expressed as: 2 ir lr ir r pi li s j m i m m z i z ω ω = = (8) engineering, technology & applied science research vol. 12, no. 4, 2022, 9042-9047 9045 www.etasr.com diep & trung: transmitting side power control for dynamic wireless charging system of electric … the equivalent impedance of each transmitting coil is calculated as: li i pi i i z r z j l j mω ω= + + + (9) at the resonance condition, the reflected impedance pi z can be calculated as: { } 2 li pi li i i li .rms p z re z r r i = − = − (10) approximately, ignoring the power loss on the inverter, the total impedance reflected from the secondary to the transmitting side is shown in (11): 3 3 1 2 2 1 3 3 li i dc pi i i i li .rms li .rms p p z r r i i = = = − = −   (11) where dc p is the input power of the inverter. from (8) and (11), the coupling coefficient is given by: 2 2 2 1 3 fr dcr r i i r l li .rms l pr k r l l r iω     = + −         (12) when the dwc system is designed, the system parameters, such as coils, compensator, and resonant angular frequency are assumed to be constant. when dc p and li .rms p are measured by sensors, the equivalent load impedance ( l r ) is maintained constant and r k is estimated according to (12). therefore, the output power is estimated according to (4). e. the proposed power controller the block diagram of the proposed power controller is shown in figure 6. pout.ref ili kr.est pout.est i*li α estimate output power (4) power controller current controller estimate coupling coefficient (12) pdc ili idc udc voltage/ current measurement giα(s) fig. 6. power control block diagram. the inner loop is the current loop which is important for the estimated results to have high accuracy. the outer loop is a power control loop according to the load. at the transmitting side, the rms value of resonant current ( li i ) and the value of the inverter input voltage/current ( dc dc u / i ) are measured. then, (12) is used to estimate the coupling coefficient, and (4) is used to estimate the output power. the reference output power ( out .ref p ) is compared with the estimated output power ( out .est p ), then the error is taken to the power controller to determine the referent current value ( li i * ). the error between the referent and the measured current is passed to the current controller. the current controller determines the phase shift angle to control the inverter. iii. simulation and experimental results a simulation model was built on psim simulation software to verify the proposed method. the system parameters are shown in table i. table i. parameters of the dwc system parameter values parameter values out p 1.5kw fil 52.6μh dc u 310v fic 66.5nf ab u 400v 1 c 93.7nf r k 0.14 2 c 123.2nf sw f 85khz 3 c 95nf i l 102μh frl 28.9μh i r 0.13ω frc 120.9nf r l 120μh r c 38.5nf r r 0.115ω fig. 7. simulation characteristic of the output power according to the reference power. fig. 8. the experimental dwc system setup. engineering, technology & applied science research vol. 12, no. 4, 2022, 9042-9047 9046 www.etasr.com diep & trung: transmitting side power control for dynamic wireless charging system of electric … the total coupling coefficient estimation results are shown in figure 3(b) (dot lines). in case 1, dy is 0mm and the average value of the estimated total coupling coefficient (kr.est) is equal to 0.138. in case 2, dy is 40mm and kr.est is equal to 0.108. in case 3, dy is 60mm and kr.est is equal to 0.074. the estimation error is less than 5.3%. figure 7 shows the simulation result of power control when the reference power changes from 0.8kw to 1.2kw. it shows that the value of the estimated power ( out .est p ) and the load power ( out .load p ) grip to the reference value ( out .ref p ) with a response time of 1.1ms and an error of 0.5%. figure 8 shows the experimental model of the proposed dwc system. pe40 ferrite bars were used to increase magnetic conductivity. polypropylene film capacitors were used for their small loss and high ability to withstand high currents at high frequencies. mosfets sic (c3m0280090d) was used for the inverter. stranded wire was used in building the coils. the impedance matching circuit and battery were replaced by an equivalent load. the experimental waveforms when the receiver position dx and dy are zero and 310 dc u v= are presented in figure 9. the results show that the resonant frequency is 85khz and the zvs condition for sic is achieved in both cases of phase shift angle (α) equal to 0 and 60 0 . figure 9(a) shows the resonant current 10 6 li i . a= , output power equal to 1.32kw, and the system efficiency reaching 89.6% in the case of α =0 0 . figure 9(b) shows that when α=60 0 , 9 2 li i . a= , the output power is equal to 1.2kw and the system efficiency reaches 89.2%. fig. 9. experimental waveforms: inverter output voltage/current and resonant currents. the following tests were performed to demonstrate the operation of the dual-loop controller in two cases. the dc voltage ( dc u ) was set to 250v and the equivalent load l r to 53.3ω. in case 1, when the position of the receiver is dx = 0mm to 800mm and dy = 0mm, the required output power changes from 600w to 400w. the experimental results of the reference/ estimation/measured output power, phase shift angle α, the inverter output voltage waveform ( ab u red color), and resonant current ( li i blue color) are presented in figure 10. the results show that the angle α increased from 41.6 to 51.4 0 , li.rms i decreased from 6.34a to 5.21a, and the output power responds to the preset value. in case 2, when the position of the receiver is a lateral misalignment in the y-direction from 0mm to 40mm, the reference output power is 400w. the experimental results are presented in figure 11. in this case, the coupling coefficient reduces, the phase shift angle α decreased from 52.6 to 36.7 0 , the r.m.s value of li i increased from 5.18a to 6.9a, and the output power was constant. fig. 10. experimental results when the reference output power changes from 600w to 400w. fig. 11. experimental results when the reference output power is 400w. these results show that the proposed control method could control the output power with a response time of 0.01s and an error less than 5%. the output power estimation method could continuously estimate the output power. the proposed system responds well when the vehicle speed is below 40km/h. figure 12 shows the system's efficiency experimental result when the engineering, technology & applied science research vol. 12, no. 4, 2022, 9042-9047 9047 www.etasr.com diep & trung: transmitting side power control for dynamic wireless charging system of electric … receiver moves along the transmission lane without any lateral misalignment. the average system efficiency is 80.7%. fig. 12. experimental efficiency characteristics. iv. conclusion this paper proposes a new method of controlling the output power in the dwc system for evs. the transmitting side inverter has been used to control power without using an additional boost/buck 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[21] z. ye, p. k. jain, and p. c. sen, "a full-bridge resonant inverter with modified phase-shift modulation for high-frequency ac power distribution systems," ieee transactions on industrial electronics, vol. 54, no. 5, pp. 2831–2845, jul. 2007, https://doi.org/10.1109/tie. 2007.896030. microsoft word etasr_v12_n3_pp8548-8554 engineering, technology & applied science research vol. 12, no. 3, 2022, 8548-8554 8548 www.etasr.com bella & zohra: application of fminsearch optimization to minimize total maintenance cost with the … application of fminsearch optimization to minimize total maintenance cost with the aim of reducing environmental degradation yasmina bella las laboratory electrical engineering department ferhat abbas sétif university 1 setif, algeria b_yasmina2014@ univ-setif.dz kebbab fatima zohra dachr electrical engineering department ferhat abbas sétif university 1 setif, algeria fatimazohra.kebbab@univ-setif.dz received: 7 march 2022 | revised: 24 march 2022 | accepted: 28 march 2022 abstract-this study examined a production system under deterioration and its impact on the degradation of the environment. the environment degrades as the production system reaches a certain level of deterioration. to reduce environmental degradation, the system's deterioration is monitored through scheduled inspections, after which preventive or corrective actions are taken. to achieve the optimum inspection dates that minimize the average total cost per time unit, the fminsearch algorithm was applied to calculate the optimal inspection dates for two cases of sequential inspection: periodic and aperiodic. to validate the performance of the proposed fminsearch algorithm, simulation results were compared with the nelder-mead method. the comparison results showed the superiority of the fminsearch algorithm in optimizing inspection maintenance dates to reduce the environmental degradation ratio. keywords-environment degradation; fminsearch algorithm optimization; maintenance; nelder-mead; production system i. introduction environmental protection is described by international standards to which manufacturers must comply. the degradation of industrial systems can impact the environment in many ways. for example, the process of meeting energy demands raises concerns about energy sustainability and environmental protection, in conjunction with the market and regulatory requirements [1, 2]. many environmental taxes have been imposed in recent decades all over the world. in the united states, the use of pollution prevention activities has increased significantly in the last two decades. the pollution prevention (p2) program is considered one of the main ways to reduce pollution [3, 4]. to ensure the efficient operation of an industrial system and meet the requirements of the environmental protection standards, inspection and maintenance activities are carried out. inspection aids in controlling the degradation process of a production system and collecting crucial data on its reliability to determine the maintenance measures to be taken. since the difficulties faced in maintenance inspections are attracting a lot of attention in the industry, many inspection strategies have been developed. in [5], the optimal inspection dates and treats for the sequential inspection strategy were calculated, while a similar model was used in [6]. in [7], the same model was proposed with the estimate of the delay of the inspections, integrating the penalty cost in the mathematical model. the optimal inspection period and the maintenance threshold of system degradation were calculated in [8, 9]. a mathematical model was developed in [10] for the overall cost, including the production cost along with the maintenance action cost. this study analyzed an inspection strategy that covers the environmental impact of the degradation of a production system. this strategy decreases degradation through maintenance actions to reduce environmental impact [11-13]. the system under consideration is submissive to continuous growing degradation. in this system, failure is detected only when it occurs, while the level of degradation of the system is only known after periodic or aperiodic sequential inspections. after checking the level of degradation when it exceeds a threshold, preventive actions are planned after a fixed timeframe, while corrective actions are carried out immediately after a system failure [14]. the main task was to minimize environmental degradation by decreasing the overall maintenance cost. the total cost is made up of the cost of corrective and preventive operations and inspection actions and the cost of penalties due to the environmental impact of system degradation. the main contribution of this study is the resolving of the optimization problem based on the fminsearch algorithm. this algorithm is a direct search method to reduce non-linear functions [15-17]. ii. description of the problem a. notations the following notations are used: • ���: the average cost of corrective maintenance. • ���: the average cost per time unit of severe environmental degradation. corresponding author: yasmina bella engineering, technology & applied science research vol. 12, no. 3, 2022, 8548-8554 8549 www.etasr.com bella & zohra: application of fminsearch optimization to minimize total maintenance cost with the … • ����: the average cost of an inspection. • � �: the average cost of preventive maintenance. • � : the timeframe to perform preventive maintenance. • tth: a random elapsed time from when the system degradation began until it reaches the threshold. • �: variable of � on the time axis. • ��: the probability density function of �. • � : a random elapsed time from instant � until failure (lifetime of the system after exceeding the threshold). • �: variable of �, from the instant �. • ��, ��: probability density and distribution function of � respectively. • ����: a random number of examinations during a cycle. • �∗���,��,…���: the vector of examination dates. • trd: a random time of excessive environmental degradation. • tcy: a random cycle time measured between two consecutive maintenance actions: preventive or corrective. • ��� : probability that the cycle will end with corrective maintenance action. • � � : probability that the cycle will end with preventive maintenance action. • ctot: the total cost incurred by maintenance and examination operations and by environmental degradation during a cycle. b. assumptions this study was based on the following assumptions: • after each inspection, two types of action are likely: to leave it as it is or perform preventive maintenance. • corrective maintenance is performed immediately after a system failure. • the inspection actions are assumed to be perfect, i.e. the inspection reveals the actual level of the system’s degradation without error. • corrective and preventive maintenance actions are meant to be perfect. • the durations of inspection and maintenance actions are negligible. • system degradation leads to environmental degradation. • the system only fails if its degradation level exceeds the alarm threshold. such a failure is supposed to be detected automatically (self-declared failure case). • the system works as it should after corrective or preventive maintenance actions. • the costs ���, � � , ���� and ���, with the timeframe � as well as the densities �� and �� are kept in the system’s database. • preventive maintenance action is scheduled after a timeframe � , if the inspection reveals that the level of degradation has exceeded the alarm threshold, as seen in figure 1. any inspections in this interval are canceled. as an example: in the interval [��, �� + � ], the inspections are canceled. fig. 1. evolution of system degradation and distribution of examinations over time. iii. the mathematical model of maintenance cost this section presents the mathematical model of the average total cost per time unit q of maintenance. q is defined as the ratio between the average global cost �� ! � and the average cycle time � �"� [18]: # $ �� ! � / � �"� (1) this cost includes the cost of preventive and corrective actions, the inspection cost, and the penalty cost. in the case of corrective action, the average cost is ���� & ����, while the expression �� � & � �� indicates the average cost in the case of preventive maintenance. ������ is defined as the average number of inspections during the time cycle, and their average cost is given by ���� & ������. � �� � is the average time of the critical environmental degradation and the expression ��� & � �� � corresponds to the penalty cost due to severe environmental degradation. the following formula illustrates the average cost: �� ! � $ ���� & ��� � ' �� � & � �� ' ����� & ������� ' ���� & � ���� (2) this formula uses the proposals developed in [4, 18]. the probability ��� that a time cycle will end with corrective actions is given by: ��� $ ∑ ) ����� ' � * �� �����+�,-,-./��0� (3) the probability that corresponds to the case where the time cycle ends with preventive action is given by: � � $ 1 * ��� (4) the average number ������ of examinations during a time cycle is given by: ������ $ ∑ 2 ���0� ) ����3� * �� �����+� ,-4/5 × ) ���� * �� �����+��,5 (5) engineering, technology & applied science research vol. 12, no. 3, 2022, 8548-8554 8550 www.etasr.com bella & zohra: application of fminsearch optimization to minimize total maintenance cost with the … the average time � 6�� of excessive environmental degradation through a time cycle is given by: � 6�� $ ∑ ) �) 71 * �����8+�������+�,-39:;< 5,-,-./��0� (6) the expression of the numerator of the function presented by (1) is concluded from (2) (6) as: �� ! � $ �= ��� * � �> ∑ ) ��=�� ' � * �>�����+�,-,-./��0� ' � � '���� ∑ 2 ���0� ) ����3� * �������+� ,-4/5 ) ���� * �� �����+��,5 ' ��� ∑ ) �) 71 * �����8+�� �����+� ,-39:;< 5,-,-./��0� (7) the denominator of (1) is given by: � �"� $ ∑ ) � ?-?-./��0� t ' ) 71 * �����8 +� � ?-39:;<a 5 ���t�+t (8) from (7) and (8), the general expression of the mathematical model of the average total cost per time unit of the maintenance function defined by (1) is deduced as: #���� $ bc cc d �= efg < e;g>∑ ) hi=,39:; < >ji� �� k-k-./ l-m/ 3e;g 3n-lo ∑ � �l-m/ ) h�,-4/< �ji� �� k-4/p ) h�,< � ji� �� �kp 3nqi ∑ ) �) 7�<hi�r�8�r� ji� �� k-4st;.u pk-k-./ l-m/ vw ww x ∑ ) y 3) 7�<hi�r�8�r k-4st;.u p z ji� �� k-k-./l-m/ (9) the minimum value of the average total cost per time unit minq(φ) is considered an objective function. the fminsearch optimization was applied to calculate the optimal inspections vector to reduce the environmental degradation ratio and minimize the maintenance cost value q(φ). iv. optimization procedure a periodic and an aperiodic sequential examination plan were applied to solve the problem without any constraint on the examination periods. in the aperiodic plan, the interval between examinations is independent. this problem is a multidimensional nonlinear problem [19]. the mathematical model exposed in section iii was exploited to solve this problem. the objective was to find the optimal examination dates which minimize the average total cost per time unit q(φi) given by (9). the fminsearch algorithm was used to find the minimum of an unconstrained multivariable function using a derivative-free method. this algorithm has been used repeatedly to resolve nonlinear functions and is well known for its robustness and ease of implementation [14]. a. analytical procedure the flowchart shown in figure 2 corresponds to the analytical approach and was developed to determine the optimal sequential examination dates that minimize the average global cost per time unit. at first, the input data: ��, ��, ���, � � , ���, ���� and � are given. afterward, the fminsearch algorithm is applied to calculate the optimal vector of examination dates ( �∗���,��,…��� ). then, the iteration number is tested: if the inequality n>n is unattained, n increases. if it was attained, iterations stop. finally, the solution vector of examination dates �� that match up to the minimum value #���� is selected. fig. 2. pseudo code of the fminsearch algorithm. two techniques were proposed to calculate the optimal inspection dates of the production system: periodic and aperiodic sequential inspection. the results of the fminsearch algorithm were compared to the nelder-mead optimization method [18, 20]. b. numerical applications the above procedure was used to estimate the optimal examination dates. the input data were provided: probability densities�� and��, the costs ���, � � ,���, ���� and time flow � . time was expressed in time units, while cost was expressed in monetary units. λ is the ratio between the mean time � 6�� of severe environmental degradation and the average time � �" � of the time cycle: [ $ \�9]i�\�9f^� (10) therefore: [ $ ∑ ) y) 7�<hi�r�8�r k-4st;.up zk-k-./ ji� �� l-m/ ∑ ) y 3) 7�<hi�r�8�r k-4st;.u p z ji� �� k-k-./l-m/ (11) 1) periodic sequential examination in this case, inspection is performed periodically. the inspection period ∆φ is defined as: ∆ � $ ���� * ���<�� $ ��` , 2 $ 1,2 ..n (12) the probability densities �� and �� correlate jointly to the random variables �" and x. the probability density �� is given by: �� �d� $ �ej√�g `< / hij.klml n (13) with µf = 1100 and o� = 150. the probability density �� is given by: ���d� $ �ep√�g ` </hiq.krmr n h (14) with µg = 130 and og = 40. the average costs are fixed as ��� = 16108, � � = 988, and ���� = 150. ��� and � are introduced as parameters. engineering, technology & applied science research vol. 12, no. 3, 2022, 8548-8554 8551 www.etasr.com bella & zohra: application of fminsearch optimization to minimize total maintenance cost with the … a) application 1: to examine the impact of cost ��� over the cost #� ∆�∗� and the ratio [ , the analytical fminsearch algorithm was implemented in matlab. the delay � was considered negligible, so the preventive operations are executed immediately. the cost #�∆�∗� and the ratio [ are presented intable i. table i. the impact of cost ���over #�∆�∗� and ratio [ with � $ 0, in the case of a periodic inspection strategy tuv ∆w∗ x�yz{|� x�}~v� t��� x�}��� ��∆w∗� �7%8 0 22 3.48 15.02 987.36 726 1.36 2.07 10 19 2.01 8.50 985.53 541.5 1.82 1.57 20 18 2.20 5.97 986.58 486 2.03 1.23 30 15 3.54 3.51 985.50 337.5 2.92 1.04 40 13 2.12 2.53 986.11 253.5 3.89 1.00 50 12 1.62 1.96 987.12 216 4.57 0.91 as shown in table i, when ��� increases, λ decreases, reducing the rate of environmental degradation. � ��� decreases by increasing the penalty cost ���, therefore the rate of environmental deterioration decreases. figure 3 presents the variation of #�∆�∗� as a function of ��� . the results obtained by the fminsearch algorithm show a decrease in the value of #�∆�∗�. this value varies from 55.11% to 2.76% compared to the nelder-mead method. fig. 3. influence of penalty cost ��� over #�∆�∗� in the case of a periodic examination strategy. fig. 4. impact of penalty cost ��� on the ratio [, in the case of periodic examination strategy. figure 4 shows the variations of λ. the fminsearch algorithm gives lower values that vary from 46.37% to 67.38% compared to the nelder-mead, for an increasing value of ���. on the other hand, the ratio λ decreases by increasing the penalty cost, i.e. the degradation of the system as well as that of the environment are reduced. b) application 2 the penalty cost ��� was fixed at 20 monetary units to study the impact of the duration � over #�∆� ∗ � and λ. table ii shows the optimal period between inspections ∆�∗ for different values of the parameter � , by applying the fminsearch algorithm. from table ii, it is noted that for � = 0, λ and #�∆�∗ � have a minimal value of 1.20% and 1.64, respectively. therefore, preventive operations should be carried out as soon as possible, i.e. the delay � , should be minimal. figure 5 presents the variation of the optimal value of the cost #�∆�∗ � as a function of � , the fminsearch algorithm gives better cost optimization for low values of � , (up to 56.50%). table ii. the impact of � over #�∆� ∗� and [ with ��� $ 20, in the case of a periodic examination strategy. }�� ∆w ∗ x�yz{|� x�}~v� t��� x�}��� ��∆w ∗ � �7%8 0 20 2.41 7.2 984 600 1.64 1.20 10 17 1.35 8.97 984.04 433.5 2.27 2.07 20 14 2.75 9.73 987.84 294 3.36 3.31 30 13 2.12 10.74 981.04 253.5 3.89 4.24 40 11 1.23 8.67 987.36 181.5 5.44 4.78 50 10 2.44 6.19 797.04 121.5 6.58 5.10 fig. 5. impact of timeframe � over #�∆�∗�, in the case of periodic examination strategy. fig. 6. influence of timeframe � over λ, in the case of a periodic sequential inspection strategy. engineering, technology & applied science research vol. 12, no. 3, 2022, 8548-8554 8552 www.etasr.com bella & zohra: application of fminsearch optimization to minimize total maintenance cost with the … figure 6 shows that the ratio λ increases with the lengthening of the time to carry out preventive operations. the fminsearch algorithm gives an improved λ compared to the nelder-mead method. 2) aperiodic sequential examination the probability densities �� and �� correspond to the random variables � and x, respectively. it is assumed that each of the two densities follows the weibull law whose scale parameter is expressed in time units, while the form parameter has no unit. the probability density �� is given by: �� ��� $ � �l �l �� �l ��l<� `<� u �l� �l (15) where the scale parameter is �j= 1164 and the shape parameter is �j= 8.7. the probability density ��of the random time � elapsed from the instant � until the occurrence of the failure is given by: ����� $ ��r�r�� r �r��r<� ` <� q�r� �r (16) where the scale parameter is �p=144 and the form parameter is �p=3.6. the average costs are respectively fixed as ���=6180, � �=4170, and ����=492, while ��� and � are introduced as parameters. a) application 3: the effect of ��� on #�� ∗) and [ was examined using the fminsearch algorithm, when � is fixed at zero, i.e. when preventive maintenance actions are not delayed. table iii shows the optimal q for each value of the optimal vector �∗. when ���= 0, #�∆� ∗) has a minimum and [ has a maximum value of 3.23 and 3%, respectively. according to table iii, the increase in the ��� penalty cost induces an increase in the number of inspections. these additional inspections are necessary to detect, as quickly as possible, the exceeding of the degradation threshold to reduce the resulting cost, i.e. the reduction of (���× � �+)). table iii. the impact of penalty cost ��� over # �� ∗) and [, in case of a periodic sequential inspection strategy\ tuv w ∗ ��w∗) �% 0 1.33, 5.99, 48.59 3.23 3.00 10 2.18, 6.15, 10.32, 12.96, 54.21 3.48 2.67 20 2.50, 5.89, 9.40, 15.04, 62.60 3.93 2.40 30 1.32, 4.58, 8.74, 9.24, 23.99, 62.49 4.94 2.22 40 1.32, 3.36, 8.74, 10.24, 24.03, 62.50 5.95 2.20 50 1.40, 4.58, 8.60, 9.80, 25.30, 61.49 6.96 2.17 figure 7 shows the variation of the optimal value of the average total cost per time unit #�∆�∗) according to the penalty cost ��� . the evolution of #�∆� ∗) is directly proportional to the ��� cost. the obtained results show that fminsearch gives a better optimization of the cost #�∆�∗) compared to the nelder-mead algorithm, as there is a decrease in the value of #�∆�∗) up to 30.08%. the variation of the rate of degradation λ as a function of ��� is presented in figure 8. the evolution of the ratio λ is inversely proportional to ���, which implies that excessive environmental degradation is reduced. figure 8 confirms the superiority of the fminsearch algorithm compared to the nelder-mead in minimizing the degradation ratio. the fminsearch algorithm has a maximum reduction of 60.05% compared to the nelder-mead at ���= 0 fig. 7. influence of the penalty cost ���on #�� ∗) in the case of an aperiodic sequential inspection strategy. fig. 8. influence of the penalty cost ��� on degradation rate λ in case of an aperiodic sequential inspection strategy. b) application 4: to evaluate the impact of � over #�� ∗)and λ, the cost ��� was set to 30 currency units, while several values are assigned to the duration � . table iv shows the average total cost per time unit #��∗) with the corresponding ratio λ for each vector �∗. table iv. influence of the duration fp over #�� ∗) and [ in case of an aperiodic sequential examination strategy }�� w ∗ ��w∗) �% 0 2.27, 3.73, 6.41, 7.79, 10.48, 63.39 4.00 2.59 10 4.23, 6.35, 7.56, 19.00, 59.88 5.24 3.53 20 3.43, 5.68, 21.51, 60.97 6.30 4.31 30 3.70, 5.76, 19.18, 56.98 7.32 5.14 40 1.28, 8.37, 54.14 8.38 5.92 50 1.24, 8.79, 55.29 9.36 6.26 according to table iv, in the case where the duration � is set to zero, the ratio λ is minimal and equal to 2.59%, and the optimal value of the average total cost per time unit #��∗) is 4.00. figure 9 shows the optimal value of the average total cost per time unit #��∗) concerning � . the fminsearch [% ] engineering, technology & applied science research vol. 12, no. 3, 2022, 8548-8554 8553 www.etasr.com bella & zohra: application of fminsearch optimization to minimize total maintenance cost with the … algorithm gives a better optimization of the cost, up to 53.04%, for low values of � . figure 10 shows the degradation rate λ as a function of � . the fminsearch algorithm improves the λ up to 53.99% compared to the nelder-mead algorithm. fig. 9. influence of the duration � over #�� ∗) in the case of an aperiodic sequential inspection strategy. fig. 10. influence of the duration � on [ in the case of an aperiodic sequential inspection strategy. v. conclusion this study aimed to maintain a production system whose declining performance causes environmental degradation by applying the fminsearch algorithm to optimize periodic and aperiodic inspection maintenance dates. this method improved the impact of the environmental degradation cost ��� and the duration � on the total average maintenance cost and the ratio of environmental degradation. moreover, the results of this method were compared to those of the nelder-mead method. the simulation results showed the superior performance of the fminsearch algorithm in the optimization of inspection maintenance dates to reduce the ratio of environmental degradation. future work could examine the modification of certain assumptions, such as the duration of inspections and maintenance actions. these hypotheses could enable the study of the production system availability. other optimization methods such as metaheuristics or simulation methods could be applied, while the industrial production could be described with real data. references [1] τ. m. kumar and ν. a. singh, "environmental economic dispatch with the use of particle swarm optimization technique based on space reduction strategy," engineering, technology & applied science research, vol. 9, no. 5, pp. 4605–4611, oct. 2019, https://doi.org/ 10.48084/etasr.2969. [2] k. siderakis, d. pylarinos, e. thalassinakis, i. vitellas, and e. pyrgioti, "pollution maintenance techniques in coastal high voltage installations," engineering, technology & applied science research, vol. 1, no. 1, pp. 1–7, feb. 2011, https://doi.org/10.48084/etasr.6. [3] l. t. m. bui and s. kapon, "the impact of voluntary programs on polluting behavior: evidence from pollution prevention programs and toxic releases," journal of environmental economics and management, vol. 64, no. 1, pp. 31–44, jul. 2012, https://doi.org/10.1016/j.jeem. 2012.01.002. [4] d. r. harrington, "two-stage adoption of different types of pollution prevention (p2) activities," resource and energy economics, vol. 34, no. 3, pp. 349–373, sep. 2012, https://doi.org/10.1016/j.reseneeco. 2012.02.002. [5] y. s. sherif and m. l. smith, "optimal maintenance models for systems subject to failure–a review," naval research logistics quarterly, vol. 28, no. 1, pp. 47–74, 1981, https://doi.org/10.1002/nav.3800280104. [6] l. a. cox jr. and y. qiu, "optimal inspection and repair of renewable coherent systems with independent components and constant failure rates," naval research logistics (nrl), vol. 41, no. 6, pp. 771–788, 1994, https://doi.org/10.1002/1520-6750(199410)41:6<771::aid-nav3 220410607>3.0.co;2-0. [7] a. chelbi and d. ait-kadi, "an optimal inspection strategy for randomly failing equipment," reliability engineering & system safety, vol. 63, no. 2, pp. 127–131, feb. 1999, https://doi.org/10.1016/s09518320(98)00031-3. [8] b. castanier, c. bérenguer, and a. grall, "a sequential condition-based repair/replacement policy with non-periodic inspections for a system subject to continuous wear," applied stochastic models in business and industry, vol. 19, no. 4, pp. 327–347, 2003, https://doi.org/10.1002/ asmb.493. [9] a. mancuso, m. compare, a. salo, and e. zio, "optimal prognostics and health management-driven inspection and maintenance strategies for industrial systems," reliability engineering & system safety, vol. 210, jun. 2021, art. no. 107536, https://doi.org/10.1016/j.ress.2021. 107536. [10] m. sharifi and s. taghipour, "optimal production and maintenance scheduling for a degrading multi-failure modes single-machine production environment," applied soft computing, vol. 106, jul. 2021, art. no. 107312, https://doi.org/10.1016/j.asoc.2021.107312. [11] w. fauriat and e. zio, "optimization of an aperiodic sequential inspection and condition-based maintenance policy driven by value of information," reliability engineering & system safety, vol. 204, dec. 2020, art. no. 107133, https://doi.org/10.1016/j.ress.2020.107133. [12] m. l. neves, l. p. santiago, and c. a. maia, "a condition-based maintenance policy and input parameters estimation for deteriorating systems under periodic inspection," computers & industrial engineering, vol. 61, no. 3, pp. 503–511, oct. 2011, https://doi.org/ 10.1016/j.cie.2011.04.005. [13] o. a. adebimpe, v. oladokun, and o. e. charles-owaba, "preventive maintenance interval prediction: a spare parts inventory cost and lost earning based model," engineering, technology & applied science research, vol. 5, no. 3, pp. 811–817, jun. 2015, https://doi.org/ 10.48084/etasr.565. [14] n. rezg, s. dellagi, and a. khatab, "joint optimization service and maintenance policies under environmental constraints," in joint optimization of maintenance and production policies, london, uk: john wiley & sons, ltd, 2014, pp. 105–130. [15] l. m. rios and n. v. sahinidis, "derivative-free optimization: a review of algorithms and comparison of software implementations," journal of global optimization, vol. 56, no. 3, pp. 1247–1293, jul. 2013, https://doi.org/10.1007/s10898-012-9951-y. engineering, technology & applied science research vol. 12, no. 3, 2022, 8548-8554 8554 www.etasr.com bella & zohra: application of fminsearch optimization to minimize total maintenance cost with the … [16] s. lavania and d. nagaria, "fminsearch optimization based model order reduction," in 2016 second international conference on computational intelligence communication technology (cict), ghaziabad, india, oct. 2016, pp. 568–571, https://doi.org/10.1109/ cict.2016.118. [17] l. wu and q. zhou, "adaptive sequential predictive maintenance policy with nonperiodic inspection for hard failures," quality and reliability engineering international, vol. 37, no. 3, pp. 1173–1185, 2021, https://doi.org/10.1002/qre.2788. [18] h. chouikhi, "optimisation des stratégies de maintenance verte pour les systèmes de production," ph.d. dissertation, université de lorraine, lorraine, france, 2012. [19] s. khouni and k. e. hemsas, "nonlinear system identification using uncoupled state multi-model approach: application to the pcb soldering system," engineering, technology & applied science research, vol. 10, no. 1, pp. 5221–5227, feb. 2020, https://doi.org/ 10.48084/etasr.3247. [20] h. chouikhi, a. khatab, and n. rezg, "a condition-based maintenance policy for a production system under excessive environmental degradation," journal of intelligent manufacturing, vol. 25, no. 4, pp. 727–737, aug. 2014, https://doi.org/10.1007/s10845-012-0715-9. microsoft word etasr_v13_n1_pp10199-10203 engineering, technology & applied science research vol. 13, no. 1, 2023, 10199-10203 10199 www.etasr.com kazem et al.: the impact of operational scenarios and concrete aging factor on the freeboard height … the impact of operational scenarios and concrete aging factor on the freeboard height of an irrigation canal masoud kazem faculty of civil engineering, iran university of science and technology, iran masoud_kazem@cmps2.iust.ac.ir mohammad nazari-sharabian department of mathematics, engineering, and computer science, west virginia state university, usa m.nazari@wvstateu.edu (corresponding author) hossein afzalimehr faculty of civil engineering, iran university of science and technology, iran hafzali@iust.ac.ir nader darban faculty of civil engineering, iran university of science and technology, iran n_darban@cmps2.iust.ac.ir moses karakouzian department of civil and environmental engineering and construction, university of nevada, usa mkar@unlv.nevada.edu received: 21 december 2022 | revised: 8 january 2023 | accepted: 11 january 2023 abstract the prediction of operational freeboard in irrigation canals is a complicated issue, particularly when the cumulative effects of time-dependent factors, such as maloperation and concrete aging, are considered. while most classic approaches consider a fixed freeboard due to uniform flow as a fundamental assumption. τhis study proposes a flowchart considering the effects of nonuniform flow to determine the adequacy of the freeboard of irrigation canals under different conditions, including time-dependent and operational scenarios. the results of this method indicated that the freeboard values obtained by classical methods may not be sufficiently reliable in providing the appropriate level of performance in the operating conditions of agricultural canals. regarding the case study of this paper, an irrigation canal in kurdistaniran, the results showed that the formation of the m1 profile is the most critical scenario and the initial freeboard must be extended by 20cm at a distance of about 2.3km at the end of the canal towards upstream. keywords-freeboard; concrete aging; irrigation canal; operational scenarios i. introduction despite the prevalent traditional methods that are widely used in the initial design phase of irrigation canals, water delivery performance and economically optimal design of canal sections are still hot topics in current engineering works [1-4]. the geometry of the canal section plays a key role in the total cost of an irrigation system. in [5], an optimal parabolic section with a freeboard was proposed to provide optimal flow capacity. however, mathematically designed sections are generally difficult to construct. in addition to the need for specific machinery, such parabolic sections may not perform well in geotechnical stability analysis without a thick concrete lining, especially in large canals. in [6], a power-law section was proposed that had similar disadvantages to the parabolic section. therefore, traditional trapezoidal sections with engineering, technology & applied science research vol. 13, no. 1, 2023, 10199-10203 10200 www.etasr.com kazem et al.: the impact of operational scenarios and concrete aging factor on the freeboard height … concrete lining are still the most common sections in many irrigation systems. a trapezoidal section is an optimal choice in the design phase, not only compared to curved sections, but to other simple geometries. in [7], triangular, rectangular, and trapezoidal sections were compared, concluding that the optimal trapezoidal section has the lowest seepage loss and cross-sectional area among the three optimal sections. consequently, practical approaches to refine the design procedure of trapezoidal sections can help engineers to consider various affecting factors which are usually ignored in the initial design phases. in general, canal lining and banks are extended above a canal's normal water surface as a safety measure to protect the conveyance system from overtopping. freeboard in a canal provides a water surface higher than normal, which may be caused by sedimentation in the canal, temporary maloperation of the canal system, excess flows caused by storm runoff entering the canal through drain inlets, additional water depth resulting from a higher friction coefficient than used in the design, and waves produced by wind or surges which accompany sudden changes in flow. in the initial design phase, the freeboard height is generally recommended to be 1/6 of the total depth in uniform flow conditions [8]. figure 1 illustrates the freeboard of an irrigation canal. however, as a prevalent issue, overestimating or underestimating the freeboard can increase construction and operational costs [9, 10]. an overestimated freeboard can also increase the water loss in an irrigation canal, particularly in the compacted earth lining [11, 12]. on the other hand, underestimation of the freeboard can lead to difficulties in the operation or even to catastrophes in some cases [13-15]. the efficiency of the freeboard critically depends on the precise estimation of canal roughness. the effect of concrete aging on manning's roughness coefficient (n) has always been a controversial issue. an uncertain assumption for this factor not only causes problems such as overflow, but also can disturb the controllability of an automated irrigation canal [16]. although engineering codes recommend a standard range of 0.012-0.017 for manning's n, there is evidence that the value could be increased to 0.023 in aged concrete-lined canals [17]. increasing roughness can occur at a higher rate in smaller canals compared to large ones. fig. 1. freeboard in a typical irrigation canal. to increase the efficiency of water transport in irrigation canals, engineers offer slight modifications in the design phase that can influence construction prices and long-term maintenance costs. there is not a certain rule to guide water authorities in selecting the best option, and the selection procedure is performed case by case. on the other hand, it must be well thought-out that in many water transport projects, such as the studied case, the initial investment and construction costs are covered by governmental budgets while the operational costs rely on the stakeholders' payments, and most of them use leased facilities and cannot handle high costs of major rehabilitation for many years. this view is also amplified when considering that this project aims to improve the economy of a relatively poor region on the aging issue and the effectiveness of the freeboard depends on the appropriate prediction of operational scenarios. most operational canals are designed based on a normal flow regime and predefined demand scenarios. therefore, they would transfer the design flow plus a fixed freeboard to cover up fluctuations and waves. however, in constant geometric and roughness conditions, any change in demand nodes would disturb the water surface profile. therefore, this factor plays an important role in the fundamental hydraulic analysis that determines the crest level of emergency spillways or the installation level of automated intake gates and is rarely considered in determining the general freeboard. the operational flow regime variation is more critical in long canals with multi-demand points, because of the effects of back-water and slight steepness in long distances in addition to the multi-stakeholders policies. in [18], it was shown that the conventional freeboard design did not suit a long-distance water transfer project [18]. there are also examples of aged canals, such as the chashma right bank canal in pakistan, where the freeboard, adequate for the normal operational flow regime, could be over-stressed under specific flow conditions [19-22]. therefore, unforeseen operational conditions must be considered for each irrigation canal. as there is no common rule for generally addressing this issue, it should be investigated case by case. the current study investigated the following questions:  to what extent a constant freeboard height calculated using classic approaches is reliable under different operational and time-dependent scenarios?  how can some modifications help engineers to evaluate the freeboard height by considering operational and timedependent scenarios? ii. case study the garan water transport canal is part of an extensive irrigation project in the kurdistan region, west iran, next to the international borderline with iraq. having a length of 17km, the garan agro-industrial water transport system consists of a concrete-lined trapezoidal canal that conveys approximately 44 mcm of water annually. according to the design data, the maximum flow from the dam intake is 7m 3 /s. however, after supplying a pumping station, the flow decreases to 5m 3 /s in the mpc2 canal, as shown in figure 2, before arriving at a reversesiphon pipeline. the main subject of this case study was the evaluation of the adequacy of the freeboard, as there are extreme operational scenarios in emergency conditions. figure 3 shows the studied part of the canal and the control sill at the endpoint, which warrants a minimum water level for industrial demands upstream during winter when the irrigation demand is zero. the mpc2 canal was designed later and despite the supposition for the garan canal, where manning's roughness is engineering, technology & applied science research vol. 13, no. 1, 2023, 10199-10203 10201 www.etasr.com kazem et al.: the impact of operational scenarios and concrete aging factor on the freeboard height … 0.015, its roughness was assumed to be 0.016 in the design phase. during the construction phase, a design review was considered to evaluate the effects of different roughness coefficients assigned to these two canals. an optional retarder sill is planned at the endpoint of the garan canal to maintain a minimum water level during winter to supply the constant industrial demand when there is no irrigation demand and the mpc2 canal must be shut down. this obstruction will create an m1 g.v.f flow profile towards the upstream that will raise the water level. however, there is a question to what extent it would affect the upstream. in addition, particular operational scenarios were considered to evaluate the capacity of the canal with different roughness values by considering the concrete aging effects. based on a flowchart developed, shown in figure 4, the surface profile of the water was determined using the g.v.f equations. this profile was then compared to the canal geometry, and the freeboard was increased accordingly in critical regions. fig. 2. aerial view of the garan irrigation canal and the location of the garan dam and the mpc2 canal. fig. 3. the profile and cross-sections of the garan and mpc2 irrigation canals in the attentive region. iii. methodology and calculations this study considered the change in roughness and the shutdown/running of the pumping station as the main factors to derive the critical scenarios shown in table i. the g.v.f equation was used to develop the water surface profile: �� �� � ����� ��� � (1) where so is the bottom slope which is positive in the downward direction, sf is the friction slope which is positive in the downward direction, y is the water depth measured from the canal bed to the water surface, x is the longitudinal distance measured along the canal from the endpoint toward upstream, and fr is the froude number. the friction slope was approximated using manning’s equation: �� � � � �� � � (2) where sf is the friction slope which is positive in the downward direction, n is manning's roughness coefficient, v is the crosssectional mean velocity, φ is a constant equal to 1.49 for english units and 1.00 for si units, and r is the hydraulic radius. fig. 4. determination of the ogee discharge coefficient and the g.v.f boundary condition flowchart. table i. operation and aging scenarios scenario no. canal roughness pumping station condition garan mpc2 1 0.011 0.011 running 2 0.014 0.014 running 3 0.015 0.016 running 4 0.017 0.017 running 5 0.011 0.011 shut down 6 0.014 0.014 shut down 7 0.015 0.016 shut down 8 0.017 0.017 shut down a variety of mathematical techniques can be applied in a traditional method to generate the results [23]. in this case, due to the effect of the ogee weir, the boundary condition of the g.v.f equation had to be determined carefully. the effect of downstream conditions on weir function was determined by the ogee spillway discharge coefficient diagram recommended in [8]. consequently, a flowchart was developed to perform the engineering, technology & applied science research vol. 13, no. 1, 2023, 10199-10203 10202 www.etasr.com kazem et al.: the impact of operational scenarios and concrete aging factor on the freeboard height … calculations considering the effects of different scenarios, as shown in figure 4. the final goal was to evaluate the performance of the canal and its freeboard upstream of the ogee sill. table ii presents the results and figure 5 illustrates the water surface profiles generated by g.v.f for each scenario. according to the diagram, for the worst-case scenario (no. 8), a freeboard extension must be installed throughout the entire length of the canal. for scenarios 6 and 7, the water surface level never exceeds the berm level upstream of the pumping station. however, the desirable freeboard was not achievable for the entire length of the canal. for scenario 5, a minimum of 20cm freeboard was attainable if the berm level increased for 2,300m of the canal length from the sill, upward to the pumping station. in the other group of scenarios, where the pumping station was assumed to be operational, the current berm level was sufficient. however, for scenario 4, the aging effect would cause the maximum freeboard not to exceed 17cm. as an outcome of this calculation, the water surface profile converged to the normal water level in a shorter distance when the roughness increased. however, the final water level was higher. table ii. results of freeboard extension scenario no. q (cms) garan roughness mpc2 roughness freeboard extension span (m) 1 5 0.011 0.011 120 2 5 0.014 0.014 180 3 5 0.015 0.016 300 4 5 0.017 0.017 960 5 7 0.011 0.011 2,300 6 7 0.014 0.014 up to the pumping station 7 7 0.015 0.016 up to the pumping station 8 7 0.017 0.017 the entire canal fig. 5. g.v.f water surface profile for the garan canal. note scenario 5 where a freeboard extension is needed for a length of 2300m. iv. discussion many challenging factors influence the hydraulic geometry of canals, including roughness, discharge coefficients, and the application of g.v.f. although these factors have been used in many studies, the results show that there is no unique and theoretical method to solve the challenges of canal design. this calls for more empirical data to apply to specific sites. any change in the estimation of the roughness coefficient influences the energy slope estimation, and any change in the discharge coefficient affects the velocity estimation. consequently, the changes in these coefficients affect the water surface determination when applying (2). the effect of climate change (including changes in rainfall and evaporation), drought, and economic considerations force the designers to work on practical methods for canal restoration and modify the inputs in the g.v.f equation. one suitable and easy approach to canal design is to modify inputs including freeboard and hydraulic coefficients based on specific regional considerations. figure 4 presents a practical approach to obtaining suitable results in irrigation canals. v. conclusions relying on the classic approaches to determine the freeboard height can lead to technical difficulties in multiple irrigation canals, particularly when there is a large gap between the demands during various seasons. in addition to the classic approaches followed in the initial design phase, operational scenarios must be considered through more sophisticated approaches. this study proposed a flowchart to determine the adequacy of the freeboard of a particular irrigation canal in different scenarios. the freeboard of the garan canal was designed using the conventional approach that considers normal water level as the basic water surface profile. however, the results showed that there is a need for freeboard extension up to 20cm for a distance of about 2.3 kilometers from the next-added sill towards the upstream in a moderate scenario. the pessimistic scenarios indicated that a freeboard extension must be installed for the entire length of the canal. this output emphasizes the fact that the initial assumption about the freeboard and the conventional design approach must be revised. the sill and aging effects could influence the freeboard, which could be sufficient for the normal range of variation, but could be over-stressed under specific operation sets. the results of this study indicate that engineers should use the freeboard values obtained by traditional methods with more caution. in this regard, the development and use of methods such as the proposed algorithm can help engineers make the necessary revisions. references [1] a. r. vatankhah, "normal depth and wetted perimeter in general powerlaw channels," flow measurement and instrumentation, vol. 64, pp. 234–241, dec. 2018, https://doi.org/10.1016/j.flowmeasinst.2018. 11.003. 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[23] c. d. jan, "basic equations for the gradually-varied flow," in gradually-varied flow profiles in open channels: analytical solutions by using gaussian hypergeometric function, c. d. jan, ed. berlin, heidelberg: springer, 2014, pp. 1–20. microsoft word etasr_v12_n5_pp9097-9101 engineering, technology & applied science research vol. 12, no. 5, 2022, 9097-9101 9097 www.etasr.com radhi & burhan: non-profit organization project selection process using the hygiene method of … non-profit organization project selection process using the hygiene method of multi-criteria decision making ahmed reyadh radhi college of engineering al musaib university of babylon and college of engineering, university of baghdad iraq ahmedrr989@gmail.com abbas m. burhan civil engineering department college of engineering university of baghdad baghdad, iraq abbasm.burhan@coeng.uobaghdad.edu.iq received: 4 july 2022 | revised: 14 july 2022 | accepted: 16 july 2022 abstract-with the fast increase in technological development and society's needs, using multi-criteria decision making (mcdm) as a solution to tackle problems faced during a project's life cycle in different engineering fields gains interest. the use of artificial intelligence gave new opportunities to deal with problems faced during the optimization of unknown or known solutions and methods. even more, the application of optimized solutions can be developed or modified by using different optimization approaches and methods. this paper proposes a model for the project selection process for non-profit organizations that have a limited budget and social factors strictly related to the selection process. this method is based on mcdm and takes into consideration criterion weights and experts' evaluation of projects according to the selection criteria using the hygiene method consisting of two stages, fuzzy logic, and topsis. keywords-multi criteria decision making; topsis; fuzzy logic; project selection; decision making; optimization i. introduction mcdm can be considered as an applicable solution to overcome the constraints raised and need to be optimized in different engineering fields. some optimization methods discussed in published papers are: analytical network process (anp), visekriterijumska optimizacija i kompromisno resenje (vikor), artificial neural networks (anns), analytical hierarchy process (ahp), preference ranking organization method for enrichment of evaluations (promethee), and the technique of order preference by similarity to ideal solution (topsis). this paper introduces a hygiene method for the project selection process of non-profit organizations. most papers related to project selection depend mainly on economic measures (numerical) neglecting the social factors that affect the selection process. ii. multi criteria decision making application a. civil engineering promethee and ahp ranking proposals were used at the project construction sector and 7 critical paths of project were examined with triangular fuzzy numbers to evaluate path selection criteria in [1]. vikor approach was also used to detect the critical path. in addition, fuzzy analytical network process was adopted in [2] in order to find activities' priority and correlation. a methodology named construction method selection model (cmsm) was introduced in [3], which consists of two main stages to assess and select the prefabrication construction method for projects. at first, the strategic stage, using simple multi-attribute rating technique (smart) resulted to 4 main attributes (project characteristics, market attribute, site conditions, and local regulations) and 12 sub – attributes with higher relative weights to project characteristics sub – attributes. the main objective of this stage was to assess the feasibility of the prefabrication process through the mentioned attributes. the second stage is the tactical stage, in which multi-attribute utility theory (maut) is used to evaluate the uncertainty associated with the project prefabrication ability taking sustainability performance into consideration. a guidance method was proposed in [4] for engineering designers to select sustainable building materials depending on two main issues: evaluation criteria and stakeholder’s requirements. the evaluation criteria were recognized using the sustainable triple bottom line (tbl) method and the impact of each factor was determined by experts before applying the data to the fuzzy extended ahp (feahp) to get the final results. the sustainable assessment depends on 3 major categories: environmental, social-economic, and technical. more than 20 sub categories were directly responsible for the material evaluation process. the researchers used varimax rotation to reveal the correlation between the observed and latent criteria [4]. ambiguities associated with project selection were studied using fuzzy topsis (ftopsis) in [5] to support contractors to choose the best project for bidding according to their abilities and the project requirements. this method is considered one of the multi attribute decision making methods corresponding author: ahmed reyadh radhi engineering, technology & applied science research vol. 12, no. 5, 2022, 9097-9101 9098 www.etasr.com radhi & burhan: non-profit organization project selection process using the hygiene method of … that give an acceptable representation to real world problems. the research uses triangular fuzzy number to represent verbal factors. the best alternative selection process was examined in [6] by project evaluation and selecting the best projects using additive ratio assessment (aras) and ahp. ahp was used to build and assess the selection process structure and assign weights to the selection criteria while aras performed project ranking. this method cannot deal with qualitative criteria unless they are evaluated on a numerical scale. authors in [7] discuss the assessment of infrastructure design methods by embracing the monte carlo optimization multi attribute selection model. one of the main ruling factors of the process is the epistemic uncertainty risk that differs from each method to another. authors in [8] described mcdm methods in relevance to their usage fields and their contribution in maintenance management. ahp was adopted in [9] to design a dynamic decision model for inspecting and maintaining reinforced concrete structures. the model aims to select the best alternative by pair-wise comparison between the criteria with global priority vector instead of depending on experts’ opinions. b. environmental engineering environmental engineering has its share of using artificial intelligence. topsis and anp were used in [10] to analyze the construction methods in accordance to the productivity aspect. the main analyzing factors are management, materials, costs, time, human force, environmental sustainability, planning, and architectural design with overall 24 sub-factors. the impact of factors is examined by the decision making trial and evaluation laboratory method (dematel). construction and demolition waste were optimized using a proposed methodology to support decision makers in [11]. the methodology consists of 3 main stages: at first, an index system is established depending on technical, financial, environmental, and social attributes. the second stage is the evaluation framework with experts' opinions through a multi criteria decision framework using the trapezoidal fuzzy numbers (trfn), interval numbers, and triangular fuzzy numbers (tfn). the next stage is examining the correlation between the criteria using the anp to detect the main and sub criteria in order to use the fuzzy multi-attributive border approximation area comparison (mabac) method as a final ranking tool. fuzzy anp (fanp) was exploited in [12] to build a methodology for sustainable project selection depending on criteria defined by experts' opinions. a multi criteria optimization procedure was introduced in [18] to develop and evaluate 5 renewable energy scenarios. promethee method was used taking into consideration the evaluation criteria and their weights. the simos method was used for weight determination. c. transportation engineering authors in [13] considered the problems related to the transportation sector problem solution optimization. they introduced an assessment for technologies used in 6 public transportation fare collection methods. the authors used were agrepref as an mcdm method to evaluate the methods according to 6 criteria (operation costs, safety, speed, demand of applications, multipurpose, simplicity and comfort). the public transportation project selection problem in istanbul city brought in the spotlight the use of optimization solutions [14]. a mathematical model was built in [14] by integer linear programming with ibm ilog cplex 12.6.2 program. the selection process depended on selection constraints which are budget, travel time, station number accessed, and travel distance. the model's objective function looked to maximize the benefits from project proposals. the review in [15] worked with more than 50 papers from 1982 to 2019 and summarized the alternative multi criteria transport project evaluation methods instead of cost effective analysis. d. geotechnical engineering geotechnical engineering tends to use the particle swarm optimization (pso) method due to the nonlinear behavior of the considered variables. authors in [16] wrote a review paper on the use of pso in various geotechnical engineering aspects. pso was used in [17] to solve geotechnical difficulties related to slope stability, retaining wall, and shallow footings. iii. the proposed model project selection is a very complex process. one of the most common goals is optimizing resource utilization. this process may be easier for private and marketing companies which use economic measures to evaluate the proposed project in addition to risk management taking into consideration organization resources. for government organizations, the social aspect enters as an active factor. social goals and similar criteria are judged by experts or decision makers. for better understanding of the project selection process, some abbreviations need to be defined: pi: the proposed project (p1, p2,…., pi) crj: selection criteria (cr1, cr2,…,crj) xij: project evaluation according to the criteria e: no. of experts (1, 2, …, e) the proposed model uses trapezoidal fuzzy number to evaluate the qualitative criterion shown in figure 1. the fuzzy number is calculated according to (1). the values of verbal evaluations responding to each trapezoidal fuzzy number are stated in table i. xij = (fije, gije, lije, mije) μ�x� = ⎩⎪⎪ ⎨ ⎪⎪⎧ 0 x < t�� � ���� � �� t� ≤ x ≤ t� 1 t� ≤ x ≤ t� � � ���� � �� t� ≤ x ≤ t� 0 x < t� (1) fig. 1. trapezoidal fuzzy numbers. engineering, technology & applied science research vol. 12, no. 5, 2022, 9097-9101 9099 www.etasr.com radhi & burhan: non-profit organization project selection process using the hygiene method of … table i. linguistic evaluation qualitative evaluation fuzzy number value very low (vl) (1, 1, 1.2, 2.8) low (l) (1.2, 2.8, 3.2, 4.8) medium (m) (3.2, 4.8, 5.2, 6.8) high (h) (5.2, 6.8, 7.2, 8.8) very high (vh) (7.2, 8.8, 9, 9) each project evaluation provided by individual experts is multiplied by its own criteria weights. in order to aggregate experts’ opinion regarding the proposed projects with respect to the selection process, criterion aggregating of fuzzy numbers needs to be performed according to the following equations: x�ije = �fije, gije, lije, mije� fij = min (fije) (3) g%& = �' ∑ g%&''')� (4) l%& = �' ∑ l%&**')� (5) mij = max (mije) (6) the selection criteria can be categorized into benefit criteria (maximum value is preferred) or cost criteria (minimum value is preferred) according to the criteria category normalization equations. if the criterion is a benefit criterion we have: x�ij = ( +,-./0..,, 2,-./0..,-, 3,-./0..,, .,-./0..,-� (7) if it is a cost criterion: x�ij = (.%4.+,-.,, .%4.+,-3,, .%4.+,-2,, .%4.+,-+,� (8) the next step is performing defuzzification for the input values using the middle of maxima that will used at the second stage of optimization process matrix according to (9): µ�,= 6.,�+,7 63,-�2,-7� (9) the vector normalization deals with the input criteria according to (10). x8%& = �,-9∑ 6�,7�,,:�� (10) the resulting matrix will be the normalized decision matrix (ndm). ndm will be multiplied by criteria weights to determine the weighted ndm (wndm) as shown in (11). ndm = ⎣⎢ ⎢⎡ x8�� x8�� ⋯ x8�&x8�� x8�� ⋯ x8�&⋮ ⋮ … ⋮x8%� x8%� … x8%& ⎦⎥ ⎥⎤ x8f%& = x8%& × wi (11) wndm = ⎣⎢ ⎢⎡ w�x8�� w�x8�� ⋯ w&x8�&w�x8�� w�x8�� ⋯ w&x8 �&⋮ ⋮ ⋯ ⋮w�x8%� w�x8%� … w&x8 %& ⎦⎥ ⎥⎤ the next step is detecting the best and worst ideal values for each criterion according to its behavior, either it is a cost criterion, where minimum value is preferred or a benefit criterion where maximum value is preferred, in order to find the euclidean distance from the proposed solution to the best and worst ideal solutions using (12) and (13) respectively. d%k = 9∑ 6x8f%& − x%&k7� %%)�� (12) d%� = 9∑ 6x8f%& − x%&�7�%%)�� (13) the distance between the proposed solution and the ideal best and worst solutions will be calculated by (14): di = m�x� − x��� + �y� − y��� + �z� − z���� (14) the performance score function that will rank the proposed projects is shown in (15) pi = r,sr,t k r,s (15) iv. an illustrative example in this example, we consider a group of 6 projects with an expert committee consisting of 3 experts. projects will be evaluated regarding 5 criteria which are the quantitative criteria cr1 (project cost) and cr2 (number of beneficiaries) and the qualitative criteria cr3 (organization staff expert), cr4 (project legal constraints), and cr5 (project meets end-user requirements). the owner organization has the expert weights and the weights regarding the quantitative criteria as shown in tables ii and iii. the expert evaluations according to the qualitative criteria are shown in table iv. table ii. expert weights expert weight e1 high e2 very high e3 high table iii. quantitative criteria cr1 cr2 projects cost benefit p1 1,125,000,000 2000000 p2 4,300,000,000 265000 p3 1,050,000,000 140000 p4 4,400,000,000 1170000 p5 4,700,000,000 180000 p6 450,000,000 1200000 table iv. experts evaluations on qualitative criteria expert 1 expert2 expert3 cr3 cr4 cr5 cr3 cr4 cr5 cr3 cr4 cr5 p1 m l h vh h m l m h p2 h h vl vl h h h vl l p3 vl vh m l vh l h h vl p4 vl h vl vl vh h vl h vl p5 l vh h h l vh m m m p6 vl l m vh m vl h vh l engineering, technology & applied science research vol. 12, no. 5, 2022, 9097-9101 9100 www.etasr.com radhi & burhan: non-profit organization project selection process using the hygiene method of … the experts’ evaluations for criteria weights are aggregated and normalized using trapezoidal fuzzy numbers in order to be transformed to crisp value taking into consideration the relative importance of expert weights shown in table v. all the outputs will be used as input to topsis. the calculation steps and their results are shown in tables vi-x. table v. criteria evaluation criterion e1 e2 e3 crisp % cr1 vh vh h 24% cr2 h vh h 22% cr3 m h m 17% cr4 h h m 19% cr5 h m h 18% table vi. qualitative criteria fuzzy output project cr3 cr4 cr5 benefit cost benefit p1 0.4869 0.4698 0.3852 p2 0.4819 0.4740 0.4899 p3 0.4914 0.3489 0.4866 p4 0.4344 0.3522 0.4854 p5 0.4896 0.4572 0.4260 p6 0.4905 0.4684 0.4779 table vii. normalized matrix cr1 cr2 cr3 cr4 cr5 p1 0.1423 0.7597 0.4145 0.4440 0.3417 p2 0.5439 0.1007 0.4103 0.4480 0.4346 p3 0.1328 0.0532 0.4183 0.3297 0.4317 p4 0.5565 0.4444 0.3698 0.3328 0.4306 p5 0.5945 0.0684 0.4168 0.4321 0.3779 p6 0.0569 0.4558 0.4176 0.4427 0.4240 table viii. weighted normalized matrix cr1 cr2 cr3 cr4 cr5 p1 0.0341 0.1698 0.0698 0.0827 0.0623 p2 0.1303 0.0225 0.0691 0.0834 0.0792 p3 0.0318 0.0119 0.0705 0.0614 0.0787 p4 0.1334 0.0993 0.0623 0.0620 0.0785 p5 0.1425 0.0153 0.0702 0.0804 0.0689 p6 0.0136 0.1019 0.0703 0.0824 0.0773 table ix. ideal best and worst solutions cr1 cr2 cr3 cr4 cr5 v0.1425 0.0119 0.0623 0.0834 0.0623 v+ 0.0136 0.1698 0.0705 0.0614 0.0792 table x. performance and project ranking s s + pi ranking p1 0.1917 0.0340 0.8492 1 p2 0.0243 0.1892 0.1140 5 p3 0.1143 0.1589 0.4183 3 p4 0.0919 0.1392 0.3978 4 p5 0.0112 0.2023 0.0527 6 p6 0.1581 0.0711 0.6897 2 v. conclusion mcdm methods have the advance of a methodology that tackles problems characterized by multi variable conditions, factors, and constraints. even more, the high level of work and research continuously develops many algorithms, and optimization methods. the of fuzzy logic, genetic algorithms, and real life phenomena simulations like ant colony optimization, grey wolf optimization, particle swarm optimization, etc. enriched the optimization approach. these methods lead to deep learning and machine learning 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[27] a. daghouri, k. mansouri, and m. qbadou, "enhanced model for evaluating information system success: determining critical criteria," engineering, technology & applied science research, vol. 8, no. 4, pp. 3194–3198, aug. 2018, https://doi.org/10.48084/etasr.2148. microsoft word 10-692.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1089-1092 1089 www.etasr.com aminallah and habibi : exploitation of nanoindentation and statistical tools to investigate the behavior … exploitation of nanoindentation and statistical tools to investigate the behavior of materials laid aminallah dept of mechanics, mustapha stambouli university faculty of science and technology mascara 29000, algeria abdaminn@yahoo.fr samir habibi dept of mechanics, mustapha stambouli university faculty of science and technology mascara 29000, algeria habibismr@yahoo.com abstract—the determination of the performance of materials requires the characterization of materials at scales: macro, micro and nanoscale. among the most common experimental methods one can find the instrumented indentation test for determining the contact stiffness and contact depth and analyzing the characteristic curve by nanoindentation load on the penetration of the indentor. through statistical processing of the experimental results, the rigidity of contact on the contact depth is investigated, depending on the indentation load, for bronze, brass and copper. a mathematical model is adopted to describe the polynomial regression by the method of least squares growth rigidity with one or more geometric parameters representative of the size of the footprint. this study allows us to identify factors that influence the rigidity of the materials examined and the sensitivity of the used indenters. keywords-nanoindentation; modeling; power law; contact stiffness; contact depth i. introduction the instrumented indentation test is used to record the displacement of the indenter during the whole cycle of loading and unloading [1]. analysis of the unloading curve leads to a contact depth value. the basic idea behind this methodology dates back to late 19th century but it the mathematical were laid the past few decades. this article is devoted to the analysis of results on various materials chosen according to the objective sought. the main objective remains to better understand and better explain the phenomena involved in the indentation. experimental indentation tests were conducted on films of bronze, copper and brass deposited on glass slides using a nanoindentor instrumented mct (instrument csm2107). for each sample, at least 20 tests were carried out with maximum load of 20 mn to 3000 mn. the indentation tests were performed with a vickers indenter. the load is applied at a rate of 40 mn/min. the maximum load is maintained for 15 seconds and then gradually withdraws at a speed of 40 mn/min. all curves penetration strength results are exported and processed using matlab to calculate the mechanical properties of material studied by different methods [2-4]. the end of each penetration defects were evaluated using an electron microscope field emission scanning hitachi s-type 4300 se/n. the measures are estimated at 150 nm for the vickers indenter [5]. ii. results and discussion a. analysis of the load-displacement curve in an instrumented indentation test, the indent diamond is pressed to the sample surface corresponding to a maximum load value at a given depth. simultaneously the load and the displacement of the indenter is recorded and key locations are considered. hmax is the maximum depth reached, hf the residual depth after withdrawal of the indentor and * n c s k h is the contact depth used in calculating the hardness [1]. calculating hc, wherein a parameter ε is introduced to take into account the deformations of the indenter impression [8] (deflection of the sink-in surfaces) is expressed by the following relationship: m a x m a x .  u c s p h h                       (1) to treat the results the model of [3] was applied and the calculated values are shown in figure 1. fig. 1. results rigidities contact vs contact depths by vickers nanoindentation. engineering, technology & applied science research vol. 6, no. 4, 2016, 1089-1092 1090 www.etasr.com aminallah and habibi : exploitation of nanoindentation and statistical tools to investigate the behavior … b. mathematical modeling of materials we carried out a mathematical modeling of the three materials studied, using two indenters with different geometries: a vickers pyramid and a spherical. using the power law * n c s k h , we expressed the rigidity of contact s, of the three materials depending on the contact depth of the indentor hc. the experimental results of the vickers nanoindentation tests are shown in figure 2 relating to the 21 tests considered. the curve shows good reproducibility. following the polynomial regression by the method of least squares, we determine the expressions of s vs hc for all three materials. we determine the values of k and n for the three materials for the case of vickers indenter, using the least squares method, as shown in table i. for the case of spherical indenter, we adopt the same approach for the three materials examined, (figure 2). the calculated values of k and n are shown in table ii. table i. the determination of the coefficients k and n power law vickers indentation reference material k n r2 1 bronze 0.0004 1.1229 0.9788 2 copper 0.0074 0.7227 0.9331 3 brass 0.0005 1.0685 0.9761 table ii. determining coefficients k and n power law spherical indentation reference material k n r2 1 bronze 0.076 0.5991 0.9764 2 copper 0.2124 0.3766 0.7227 3 brass 0.3049 0.2699 0.8593 fig. 2. results rigidities contact vs contact depths by spherical nanoindentation. c. discussion a cloud of high density points such as the three characteristic curves merge and converge contact rigidities is evident. s is recognized in the interval [0, 2] corresponding to depths of contact between [500, 2500]. however, point (2, 2500) is an inflection point of the three characteristic curves, from which it is noted that: 4.10-4∙hc 1.1229>5∙10-4∙hc 1.0685>>74∙10-4∙hc 0.7227. hence, s1> s3> s2, namely bronze contact stiffness is greater than the brass for a lower penetration, except that the brass can reach smax>18mn/nm for high tees penetration of the order of 20000 nm and the stiffness of the brass is much greater than that of copper. this means that bronze and brass are stiffer and more ductile copper. the models obtained in the case of vickers indenter, is acceptable such as r2≈94%÷98%, and tend to the perfect model. in the case of vickers indenter k=0.0004÷0.0074 and n =0.7227÷1.1229, where the existence of an inverse relationship between k and n for each examined material. it is also shown that 760∙10-4∙hc 0.5991>>2124∙10-4∙hc 0.3766>3049∙10-4∙hc 0.2699 hence s1>>s2>s3. but only r 2 bronze enables the reproducibility of the experiment. by cons, r2 of copper and brass is not statistically significant to allow repeatability of experiments and thus, is not predictive. in all cases, the bronze has the best rigidity of contact, whether for vickers indenter or spherical. but his modeling shows that the constant k for vickers cases: kv=(1/190)∙ks (ks: for the spherical case); however, the exponent of the power law nv=1.8743∙ns. this explains the effect of the geometrical correlation factor between the two types of geometry indenters. d. expression of k and n according to the indentation loading we would like to assign a mathematical formulation of k and n varying in ascending order the maximum load pmax for each indentation test, as indicated by the following graphs (figures 3-6). a relatively similar mechanical behavior of both materials bronze and brass so that a convergence in the charging interval [0, 3000] mn is recognized at the loading point 3000 mn when k1=k3=0.00075 and a tendency to very close up 10000 mn curve with a spread of k<0.0008. however, copper adopts a behavior quite different insofar as the trend of the curve believes in a very narrow range of around [0, 2250] mn with a peak of the constant k in [0, 0005] with the exception of two focal points recorded on the first k1=k2=400 and the second k3=k2=800 in a reduced interval [0, 900] mn. it is shown that the coefficient n is a special strain hardening coefficient varies in the range of [0.95, 1.15]. the coefficients of bronze and brass namely n1=n3=1.05 for a load 3750 mn. and a tendency of relatively constant curve with a reduced gap of n<0.1 in the range [3000, 10000] mn. against by an inversely proportional relationship is found between n and pmax for copper and a sudden drop of n from [1.75, 10000] for a varying indentation load of [0, 10000] mn. further, it seems that there is a proportional relationship between k1 and k2 vs pmax, namely that for bronze gentle growth is noticed between (49.2, 0.00006) and the maximum point (10023.19, 0.0010). but for copper indentation loading effect on the coefficient k is very pronounced, in so far as there is a peak (10023.19, 0.0074). k1=k2=0.00045 for a loading 184.07mn and a critical load point for copper since he believes engineering, technology & applied science research vol. 6, no. 4, 2016, 1089-1092 1091 www.etasr.com aminallah and habibi : exploitation of nanoindentation and statistical tools to investigate the behavior … abruptly. finally the existence of an inverse relationship between n1 and n2 vs pmax and n1=n2=1.25 for a maximum indentation load equal to 127.56 mn is evident. on the other hand, n for brass develops sensitivity to the intensity of the load, since noticed a proportional relationship between the n3 vs pmax. table iii summarizes the results obtained by nanoindentation of the three materials, expressing k and n vs pmax. modeling coefficients and exponents of the power law of the three materials studied as a function of the variation of the indenting force to the residual imprint of the specimens are summarized in table iii. fig. 3. relationship of k as a function of the maximum indentation load. fig. 4. relation of n as a function of the maximum indentation load. fig. 5. the coefficients k of the power law vs the indentation loading. fig. 6. factors n power law vs the indentation loading. table iii. expressions of k and n vs max f reference material k n 1 bronze 2e-05.pmax 0.4748 1.6609.pmax -0.061 2 copper 2e-08.pmax 1.5753 3.5179.pmax -0.192 3 brass 0.0036.pmax -0.19 0.7552.pmax 0.0351 iii. conclusion the use of statistical methods and the least squares method, allowed the characterization of three nonferrous materials: bronze, brass and copper. using mathematical tools, the power law of the mechanical behavior of the reviewed materials by instrumented nanoindentation was investigated. the rigidity of the contact material essentially depends on the following factors: the nature of the material, the type of nanoindentor geometry and the intensity of the indentation force applied to the imprint. the power law also allows the modeling of its coefficients and exponents treated as stiffness coefficients and the hardening respectively, which are sensitive to the intensity of the load by nanoindentation. the nature of the material also influences the sensitivity, i.e. the chemical composition of different materials examined. acknowledgments the authors wishes to thank professor noureddine benseddiq for having offered the opportunity to realize indentation tests polytechnic iut of lille1/ france. the authors gratefully acknowledges professor didier chicot advice for relevance and quality of leadership within the iut polytechnic in the research laboratory of lille1 / france. references [1] s. habibi, a. ziadi, a. megueni, “modeling a small punch testing device”, eng. technol. appl. sci. res., vol. 4, no. 2, pp. 612-617, 2014 [2] w. c. oliver, g. m. pharr, “an improved technique for determining hardness and elastic modulus using load and displacement sensing indentation measurements”, j. mat. res., vol. 7, no. 6, pp. 1564-1583, 1992 [3] a. h. w. ngan, h. t. wang, b. tang, k. y. sze, “correcting power-law viscoelastic effects in elastic modulus measurement using depth-sensing indentation”, int. j. solids. struct., vol. 42, no. 5-6, pp. 1831-1846, 2005 [4] d. chicot, f. roudet, v. lepingle, g. louis, “strain gradient plasticity tostudy hardness behaviour of magnetite (fe3o4) under multicyclic indentation”, j. mater. res., vol. 4, no. 3, pp. 749-759, 2009 engineering, technology & applied science research vol. 6, no. 4, 2016, 1089-1092 1092 www.etasr.com aminallah and habibi : exploitation of nanoindentation and statistical tools to investigate the behavior … [5] m. r. van landingham, “review of instrumented indentation”, j. res. nat. inst. stand. techn., vol. 108, pp. 249-265, 2003. [6] j. m. antunes, j. v. fernandes, l. f. menezes, b. m. chaparro, “a new approach for reverse analyses in depth-sensing indentation using numerical simulation”, acta. mater., vol. 55, pp. 69-81, 2007 [7] t. c. ovaert, b. r. kim, j. wang, “multi-parameter models of the viscoelastic/plastic mechanical properties of coatings via combined nanoindentation and non-linear finite element modeling”, prog. org. coat., no. 47, pp. 312-323, 2003 [8] y. t. cheng, c. m. cheng, “scaling, dimensional analysis, and indentation measurements”, mater. sci. eng. r., vol. 44, pp. 91-149, 2004 [9] g. kermouche, j.l. loubet, j.m. bergheau, “extraction of stress-strain curves of elastic-viscoplastic solids using conical/pyramidal indentation testing with application to polymers”, mech. mater., vol. 40, pp. 271283, 2008 [10] l. anand, n. m. ames, “on modeling the micro-indentation response of an amorphous polymer”, int. j. plast., vol. 22, pp. 1123-1170, 2006 [11] o. sahin, o. uzun, u. kolemen, n. ucar, “analysis of ise in dynamic hardness measurements of β-sn single crystals using a depth-sensing indentation technique”, mater. charact., vol. 59, pp. 729-736, 2008 [12] g. m. pharr, a. bolshakov, “understanding nanoindentation unloading curves”, j. mater. res., vol. 17, no. 10, pp. 2660-2671, 2002 microsoft word 7-648-ed.doc engineering, technology & applied science research vol. 6, no. 2, 2016, 956-963 956 www.etasr.com haider et al.: a novel efficient sine wave inverter with custom programmed pwm and intelligent control a novel efficient sine wave inverter with custom programmed pwm and intelligent control ali shahbaz haider ee dept., ciit wah, pakistan alishahbaz@ ciitwah.edu.pk ali naz ee dept., ciit wah, pakistan a.naz23@ gmail.com faiza akhter ee dept., ciit wah, pakistan fakhter92@ gmail.com wardah azhar ee dept., ciit wah, pakistan wrdhaz94@ gmail.com rashid mehmood ee dept., ciit wah, pakistan rashedm92@ gmail.com abstract—this article presents an efficient design of a pure sine wave inverter which results in an electronic design with reduced losses. the proposed design incorporates the generation of custom programmed pulse width modulation (cppwm) waveforms; the gate drive signals that are customized for the harmonic elimination from the output voltage, maximizing the fundamental component and resulting in an efficient electronic circuit design as compared to the traditional techniques in terms of the switching losses and the filtering energy losses. the cppwm signals are digitally programmed in a micro-controller. the inverter realization is followed by an intelligent compensator design for the regulation of output voltage amplitude. the proposed algorithm self-adjusts its parameters in response to the load current and voltage amplitude variations hence resulting in an improved performance. the simulation results of the control algorithm are presented. the experimental validation of the theoretically investigated controller is also presented by implementing a discrete time realization of the control algorithm using digital controller interfaced in real time with matlab®/simulink®. the hardware results are elucidated. the feasibility of the proposed controller is theoretically and experimentally verified by its efficiency compared to the classical techniques, the available tunable parameters in the controller structure and the immense flexibility in the attainable closed loop dynamics. keywords-intelligent compensator; customized programmed pwm; rapid control prototyping; pure sine wave inverter; isolation power supplies; digital controller; intelligent controller i. introduction a switch-mode-dc-to-ac inverters are fundamental to motor drives and uninterruptible power supply circuits. their significance is well manifested by their key importance in the modern era applications like grid tied inverters, the balance of system (bos) solar inverters, induction heating coil inverters, high-voltage direct current (hvdc) station inverters etc.[1]. there are various types of inverter implementation topologies and gate drive mechanism in practice these days. the most familiar form is the pulse width modulation (pwm) inverter. the availability of the cheap, fast and reliable digital microprocessors has increased the domain of application for the pwm inverters owing to the advent of digital pulse width modulated (dpwm) drive techniques, in contrast to the classic methods that rely heavily on analog electronics for instance classical sinusoidal pwm (spwm) scheme. various different techniques have been proposed for gate drive and inverter implementation topologies with the objectives of achieving increased power efficiency and reduced harmonic loss [2], for instance, the performance analysis of different control strategies in a z-source inverter in investigated in [3]. a threephase three-level voltage source inverter with a three-phase two-level inverter as a main circuit is presented in [4]. the performance of random pwm controlled converters is analyzed in [5]. the programmed pwm (ppwm) techniques to eliminate harmonics have been evaluated in [6]. however, a clear power efficiency comparison of ppwm techniques with traditional techniques like the spwm technique is not explicitly present in the literature. the digital modules that are used to generate ppwm waveforms are programmable hence, they provide extra degrees of freedom that are not possible with conventional analog methods. these programmable processors enable us to generate “customized” pwm waveforms that may optimize the performance indexes such as the current and the voltage selective harmonics elimination or minimization. it, in turn, gives us control on the torque harmonics and the speed ripples. the harmonic loss can also be minimized. we regard such waveforms as custom programmed pwm (cppwm). we have designed a power efficient sine wave inverter for which we have addressed the problem of cppwm signals generation. these signals are optimized for the particular harmonic content minimization and the fundamental component maximization. the results are subsequently compared with the results of spwm technique for power efficiency. the inverter design is followed by regulation of the output voltage amplitude in response to the source voltage fluctuations and the output current variations resulting from the electrical or electromechanical load variations. there are various feedback control laws that are proposed and tested in the literature, for instance, the direct power control method is presented in [7]. a deadbeat control for three phase pwm inverter using fpga engineering, technology & applied science research vol. 6, no. 2, 2016, 956-963 957 www.etasr.com haider et al.: a novel efficient sine wave inverter with custom programmed pwm and intelligent control based hardware controller is discussed in [8]. an easy, simple, and flexible control scheme for a three-phase grid-tie inverter system is presented in [9]. a variable gain pi controller is implemented in [10]. a direct torque control scheme is presented in [11]. although these techniques fulfill well the objectives that are present in the respective article, however, we propose the intelligent controller scheme of figure 1. by introducing an element of the environment (load etc.) and systems’ parameter (current, voltages, frequency, faults etc.) monitoring, our algorithm adjusts its parameter to make the system behave as desired. the parameter adjustments capability is implemented by a multi-dimensional look-up-table (lut) and an if-then-else conditional statement algorithm. this compensation scheme is intuitive, easy to be programmed in the eeprom for execution by the digital processors, provides flexibility in the control of system behavior and resulted in excellent system transient performance. fig. 1. the schematic block diagram of a general intelligent controller. ii. an overview of proposed inverter system the schematic diagram of the proposed inverter system is shown in figure 2. a dc-to-ac inverter is driven by a cppwm module that is interfaced with a pc unit in the rapid control prototyping (rcp) mode. this mode enables us to monitor and update system parameters during real-time operation of the plant. the inverter drives an electrical or electromechanical load. the dc supply is provided to the inverter from a variable dc supply system, which is implemented by controlled rectification of mains ac supply and low-pass filtering. the sensors are used in the system to monitor currents and voltages at various nodes and branches in the system. an intelligent controller monitors the data from these sensors and controls the dc voltage level to regulate the inverter output voltage. a supervisory pc-unit in rcp mode is interfaced in realtime with an ni® data-acquisition-card (daq), and two atmel® sam3x8e arm crotex-m3 core digital boards. the daq is used for data monitoring from the sensor board. this sensor board comprises of potential transformers (pt) for voltage sensing, hall-effect sensors for current sensing and signal conditioning network. an induction motor acts as a variable electromechanical load. a tachometer is used to measure the speed of this motor. the controlled variable dc power supply comprises of a controlled thyristor full bridge converter followed by a capacitor bank for removing ripples from rectified output. one of the two digital boards is used to generate the thyristor firing signal. the other digital board is used to generate cppwm signals to drive the mosfet board and transformer assembly for dc to ac inversion. the output of the inverter is low pass filtered and drives the electromechanical load. the hardware experimental setup is shown in figure 4. fig. 2. the schematic block diagram of the proposed inverter system. fig. 3. the hardware experimental setup. iii. the custom programmed pwm generation problem a typical cppwm waveform is shown in figure 4. it has quarter wave symmetry hence the waveform generation problem is formulated for the interval / 2[0, ] . this interval is broken down into n points at the angles i such that starting from an initial waveform value of 0, waveform toggles at point until we reach at / 2 , hence these angular variables i are pulse toggling angles such that, 1 0 , [1, ] (1) 2 k k k n p b b +< < î<  engineering, technology & applied science research vol. 6, no. 2, 2016, 956-963 958 www.etasr.com haider et al.: a novel efficient sine wave inverter with custom programmed pwm and intelligent control we want a customized waveform of figure 4 such that the amplitude of its fundamental component is maximized and the amplitudes of subsequent selective harmonics are minimized. fig. 4. a general cppwm waveform demonstrating the pulse toggle angles βi’s and the quarter wave symmetry. the cppwm generation problem boils down to the problem of determination of angular variables under the constraints of maximization of fundamental amplitude and elimination of subsequent selective harmonics from the fourier contents of cppwm. this is an optimization problem. to eliminate m harmonics and to control the amplitude of fundamental, we must have 1n m  angular variables resulting equations are nonlinear transcendental with a nonunique solution. since the ccpwm waveform has quarter symmetry and it is an odd function so it has only odd harmonics [12] given by, ( ) ( ) { }1 1 4 cos , 1, 3, 5,1 (2) n k n k k b n n n b p + = = î-å   we select to maximize the fundamental 1 b and to eliminate first consecutive 7 odd harmonics hence, we have 7m and 8n  in (2). the corresponding optimization problem can be formularized as, ( ) ( ) 1 8 1 1 4 max cos1 (3) k k k b b b p + = = -å  subjected to equality and inequality constraints,  ( ) ( ) { } 8 1 1 4 cos 0 (4) 0 2 3, 5, 7, 9, 11, 13,15 1 n k k k k b n n n b p p b + = = = < < î -å  these equality constraints in (4) can be written in the matrix notation as .m 0 now considering the defining    . .c cos the matrix m is given by (5). the optimization problem formulated for cppwm generation is solved using the optimization toolbox of matlab™. the resulting values of the cppwm waveform toggle angles are given in table i.  table i. cppwm waveform pulse toggle angles i pwm waveform toggle angles values (deg) toggle time (msec) 1   13.8055 0.7670 2   21.3150 1.1842 3   27.9059 1.5503 4   58.4557 3.2475 5   63.9416 3.5523 6   75.9398 4.2189 7   85.0347 4.7242 8   89.7661 4.9870 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 c(3β ) -c(3β ) c(3β ) -c(3β ) c(3β ) -c(3β ) c(3β ) -c(3β ) c(5β ) -c(5β ) c(5β ) -c(5β ) c(5β ) -c(5β ) c(5β ) -c(5β ) c(7β ) -c(7β ) c(7β ) -c(7β ) c(7β ) -c(7β ) c(7β ) -c(7β ) c(9β ) -c(9β ) c(9β ) -c(9β ) c(9β ) -c(9β ) c(9β 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 ) -c(9β ) c(11β ) -c(11β ) c(11β ) -c(11β ) c(11β ) -c(11β ) c(11β ) -c(11β ) c(13β ) -c(13β ) c(13β ) -c(13β ) c(13β ) -c(13β ) c(13β ) -c(13β ) c(15β ) -c(15β ) c(15β ) -c(15β ) c(15β ) -c(15β ) c(15β ) -c(15β ) é ê ê ê ê ê ê ê ê ê ê ë (5) ù ú ú ú ú ú ú ú ú ú ú ê ú ê ú ê úû using (2) the normalized harmonic amplitude can be expressed by (6). ( ) ( ) { } 1 1 1 1 cos 4 1, 3, 5, (6) n kn bn k p k b h n v n n b p + = = = î æ ö÷ç ÷ç ÷è ø å   figure 5 shows the comparison of harmonics contents from (6) for cppwm and spwm with frequency modulation ratio 40fm  and amplitude modulation ratio 0.8am  [1]. this comparison plot is further explored in section iv. fig. 5. comparison of harmonic contents of ccpwm scheme and spwm scheme. engineering, technology & applied science research vol. 6, no. 2, 2016, 956-963 959 www.etasr.com haider et al.: a novel efficient sine wave inverter with custom programmed pwm and intelligent control iv. the power efficiency considerations for cppwm scheme a. the runnig switching energy loss (rsel) the instantaneous switching power loss ( ) s p t for a typical mosfet is plotted in figure 8 for a resistive load oi and the drain voltage d v . the turn on time ( )c ont and turn off time ( )c offt for a typical mosfet are given by (7) and (8). ( ) ( ) (7) c on delay on rise t t t   ( ) ( ) (8) c off delay off fall t t t   the parameters rise time riset , fall time fallt , on delay time delay( )ont and off delay time delay( )offt in (7)-(8) can be determined from the manufacturer’s datasheet for a particular mosfet unit. fig. 6. demonstration of mosfet switching power losses. the running switching energy loss (rsel) is defined in (9) as a comparison criteria for energy and power efficiency of different pwm schemes. 0 ( ) ( ) ( ) ( ) ( ) ( ) 1 1 ( ) ( ) 2 2 (9) t s on off d o c on d o c off rsel e t p t d n t e n t e n t v i t n t v i t t     = = + = + ò  in (9) ( )n t and ( )n t are the number of positive edges and the number of negative edges in the pwm waveform from time 0 to t respectively. one and offe are the areas of shaded regions in figure 8. noting the fact that typically (on) ( )c c off ct t t  , we can recast (9) to describe the normalized rsel ( )nrsele t in (10).  the plot for comparison of ( )nrsele t for spwm and cppwm schemes is shown in figure 8. a reduction of nearly 58% in switching losses is clearly visible. ( ) ( ) ( ) ( ) (10) 0.5 s d o c nrsel e t e t n t n t v i t   = = +  fig. 7. comparison of the normalized rsel for the spwm and cppwm schemes over one cycle of the waveform. b. the receding harmonic energy loss(rhel) the receding harmonic energy loss (rhel) is defined in (11) as a comparison criteria for energy and power efficiency of different pwm schemes. ( )2[ ] [ ] (11) n i n i xxh k n e n h k = = å  the physical interpretation of [ ]hx ie n is that it is a measure of the sum of energy of fourier components in the discrete interval [ , ] i n n n . the plot of (11) for the spwm and cppwm schemes for 161n  is shown in figure 8. fig. 8. plot of the receding harmonic energy loss (rhel) for the harmonic contents of spwm and ccpwm schemes; a manifestation of filtering energy loss. if a filter is chosen with a cutoff frequency 10 20( , ), f fc f f fî where ff is the fundamental frequency, then it is evident from figure 8 that by using cppwm scheme there is nearly 83% reduction in the energy engineering, technology & applied science research vol. 6, no. 2, 2016, 956-963 960 www.etasr.com haider et al.: a novel efficient sine wave inverter with custom programmed pwm and intelligent control consumed by the low-pass filter that will not be able to reach the load and hence a significant reduction in the filtering energy loss. v. intelligent compensator for output voltage regulation the implementation of the feedback mechanism for output voltage regulation in response to the variations of load current and voltage is shown in figure 9. fig. 9. simulink model of the single phase sine wave inverter with the voltage regulation feedback mechanism. the ac-to-ac converter block in figure 9 consists of the two dotted boundary modules in figure 2, namely variable dc supply and dc-to-ac inverter. its expanded view is shown in figure 10. fig. 10. expanded view of the ac-to-ac subsystem. the thyristor gate drive subsystem produces firing pulses for the controlled full bridge thyristor circuit. it takes the firing angle command in degrees as an input from the controller block. figure 11 shows the inverter topology that been implemented to eliminated the need of multiple isolation power supplies in contrast to the half bridge and the full bridge inverter topologies [1]. the cppwm sequence shown in figure 4 is broken down into two sequences to drive mosfets in the two branch inverter topology of figure 11. these two sequences are shown in figure 12. a single isolation power supply for the gate drive of mosfet board is needed. the cutoff frequency for the low pass filter in figure 9 is set at 500hz. a variable electromechanical load subsystem is designed to test the control algorithm against load variations in the simulation. the control law subsystem in figure 9 is shown expanded in figure 13. it monitors the rms value of load voltage error and load current and produces the firing angle as its output to adjust the variable dc power supply output that in turn drives mosfet board and connected with it the transformer unit. the intelligence in the control law has been implemented using a cascade of two parts. the first part consists of a 2-dimensional look up table (2d-lut) followed by the second part with consists of if-then-else conditional algorithm. fig. 11. two branch inverter topology. fig. 12. decomposition of cppwm sequence into two unipolar waveforms for the single phase inverter. fig. 13. expanded view of the control law subsystem. engineering, technology & applied science research vol. 6, no. 2, 2016, 956-963 961 www.etasr.com haider et al.: a novel efficient sine wave inverter with custom programmed pwm and intelligent control the lut part makes a decision on the value of the variable [ ] lut u n on the basis of rms load voltage error [ ]rms errorv n and load current [ ].li n the variable [ ] lut u n represents proposed change to be made in the value of the firing angle [ ]u n . the lut values are online tuned in matlab using rapid control prototyping (rcp) mode of operation. the selection of the value of [ ] lut u n by lut is represented by the surface-mesh plot in figure 14. fig. 14. surface (mesh) based depiction of the proposed 2-d lut data. the second part of the intelligent control law takes in the value of the incremental variable [ ] lut u n and [ ]rms errorv n , and makes decision on the value of the variable [ ]satu n that is the firing angle in radian. the flow chart of this conditional algorithm is shown in figure 15. fig. 15. flow chart based explanation of the functionality of code-basedalgorithm (cba) block. the max and min values in the flowchart are online tuned using rcp mode of operation of the system. these values are given by, min max min max5, 5, 0, u 0.98 (12)e e u      the implementation of a three-phase inverter system supplying a star connected electrical load is shown in figure 16. the cppwm signals for inverter unit 2 and unit 3 are simply 120o and 240o phase shifted (time delayed) versions of sequences shown in figure 12 respectively. fig. 16. extension of the single phase inverter to the three phase implementation vi. results figure 17 shows the step response of the variable dc power supply module output voltage for two different output load current conditions. the responses are stable and have settled down in 1sec with the overshoot or undershoot not greater than 12%. fig. 17. step responses of dc voltage for the two different output load current conditions. engineering, technology & applied science research vol. 6, no. 2, 2016, 956-963 962 www.etasr.com haider et al.: a novel efficient sine wave inverter with custom programmed pwm and intelligent control figure 18 shows the step response of the variable dc power supply module output current. the response is stable and has settled down in 0.5 sec with an overshoot of 4%. figure 19 shows the step response of rms value of the load voltage for two different output load current conditions. the responses are stable and have settled down in less than 1sec time within a settling band of 5% and the overshoot or undershoot not greater than 7%. fig. 18. step response for the variable dc power supply output current. fig. 19. simulation step responses for the load voltage rms value for two different output load current conditions. figure 20 shows the step response of rms value of the load current for two different output electrical conditions. the responses are stable and have settled down in less than 5 sec. fig. 20. simulation responses for the load current rms value: step responses for the two different output electrical load conditions. figure 21 shows the experimental step response of the instantaneous value of the load voltage. the response is stable and has settled down in less than 0.65 sec time within a settling band of 5% and the overshoot less than 6%. figure 22 shows the experimental step response of the instantaneous value of the load current. the response is stable and has settled down in less than 3.5 sec time within a settling band of 5%. fig. 21. experimental responses for the instantaneous load voltage. fig. 22. experimental responses for the instantaneous load current. vii. discussion and conclusion a power efficient inverter system with intelligent controller algorithm to regulate the output voltage in response to load and input variations has been presented. a custom programmed pwm scheme has been implemented with an objective of optimal selective harmonic elimination and maximization of the fundamental. as compared with a special case of spwm our results show a promising 58% reduction in switching losses and about 83% reduction in the filtering energy loss. analysis can be further extended for comparison with the spwm scheme with different amplitude and frequency modulation ratios and the other pwm schemes like vector-space pwm. an inverter electronic topology has been implemented that does not require multiple isolation power supplies for the gate drive. an intelligent controller scheme has been implemented. the voltage regulation results are satisfactory and system withstands load variations and various disturbances within admissible stability and performance margins. engineering, technology & applied science research vol. 6, no. 2, 2016, 956-963 963 www.etasr.com haider et al.: a novel efficient sine wave inverter with custom programmed pwm and intelligent control references [1] n. mohan, t. m. underland, w. p. robbins, power electronics: converters, applications, and design, wiley, 2003 [2] n. z. yahaya , k. m. begam , m. awan, “comparative assessment of gate drive control schemes in high frequency converter”, engineering, technology & applied science research, vol. 1, no. 4, pp. 76-83, 2011 [3] b. nayak, s. s. dash, “performance analysis of different control strategies in a z-source inverter”, engineering, technology & applied science research, vol. 3, no. 2, pp. 391-395, 2013 [4] m. ahmed, s. mekhilef, "a three-phase three-level voltage source inverter with a three-phase two-level inverter as a main circuit", iet conference on power electronics, machines and drives, vol. 4. no. 15 pp. 640-644, 2008 [5] r. jadeja, a.d ved, s. k. chauhan, “an investigation on the performance of random pwm controlled converters”, engineering, technology & applied science research, vol. 5, no. 6, pp. 876-884, 2015 [6] p. n. enjeti, p. d. ziogas, j. f. lindsay, "programmed pwm techniques to eliminate harmonics a critical evaluation", conference record of industry applications society annual meeting, ieee, pp. 418-430 vol. 1, no. 19, 1988 [7] t. a. trivedi , r. jadeja , p. bhatt, “a review on direct power control for applications to grid connected pwm converters”, engineering, technology & applied science research, vol. 5, no. 4, pp. 841-849, 2015 [8] t. ide, t. yokoyama, "a study of deadbeat control for three phase pwm inverter using fpga based hardware controller", ieee power electronics specialists conference, vol. 1, no. 13, pp. 50-53, 2004 [9] s. park, j. lai, w. lee, “an easy, simple, and flexible control scheme for a three-phase grid-tie inverter system”, ieee energy conversion congress and exposition, no. 12, pp. 599-603, 2010 [10] t. m. chikouche , a. mezouar , t. terras, s. hadjeri, “variable gain pi controller design for speed control of a doubly fed induction motor”, engineering, technology & applied science research, vol. 3, no. 3, pp. 433-439, 2013 [11] m. k. sahu, a. k. panda, b. p. panigrahi ,“direct torque control for three-level neutral point clamped inverter-fed induction motor drive”, engineering, technology & applied science research, vol. 2, no. 2, pp. 201-208, 2012 [12] v. francesco, i. luigi, dynamics and control of switched electronic systems, springer, 2012 microsoft word etasr_v13_n4_pp11426-11431 engineering, technology & applied science research vol. 13, no. 4, 2023, 11426-11431 11426 www.etasr.com adware & chandrakar: a hybrid approach with statcom to enhance grid power quality associated… a hybrid approach with statcom to enhance grid power quality associated with wind farms ramchandra adware department of electrical engineering, g. h. raisoni college of engineering nagpur, india ramchandra.adware@raisoni.net (corresponding author) vinod chandrakar department of electrical engineering, g. h. raisoni college of engineering nagpur, india v12k5c63@gmail.com received: 16 june 2023 | revised: 30 june 2023 | accepted: 6 july 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6125 abstract the growing use of renewable energy sources in the production of electric power has certain adverse effects on power quality. a compensation system includes some additional devices, such as capacitors, compensators, or reactive power injection devices. facts devices, such as the static var compensator (svc), dynamic voltage restorer (dvr), and unified power quality conditioner (upqc), have become popular as power electronics become more sophisticated. this study investigated the properties of three significant compensating devices: svc, statcom with pi controller, and a hybrid statcom with a harmonic filter. common power quality concerns, such as voltage sags and swells and the percentage of total harmonic distortion (tdh), were taken into account during the initial modeling and performance analysis of the proposed system. the overall results showed that the proposed hybrid statcom system enhanced the power quality in wind energy systems more than the other two systems. keywords-harmonic filter; hybrid statcom; total harmonic distortions; voltage sag/swell; voltage flickers i. introduction power quality problems, such as harmonic distortion, unstable voltage from sags and surges, and unreliable operation, are among the most critical problems in a power system [1-2]. wind energy generating systems (wegs) with double-fed ig have become popular in power generation because they are cost-effective and can operate at variable speeds with constant frequency [3-5]. however, this is not always the case, as wind power is often located far from the point of common coupling (pcc), also known as load bus, and its end users. when a pcc has a multi-terminal load (mtl) tied to a wind farm, power quality problems such as frequency fluctuations and voltage sag/swell can occur, necessitating the use of shunt compensation [6-7]. voltage flicker is a phenomenon in which the frequency abruptly varies from the rated frequency for a brief period due to load switching and the integration of compensatory devices [8-10]. due to this, the voltage stability is affected along with the pcc's demand for reactive power [11-13]. voltage collapse results from a voltage sag that lasts a long time, and harmonics can be introduced into the system if voltage swell or flickers last for a long time. the fault current generated by sag/swelling or flickers will also affect the pcc's switch gears and protection system [5, 10, 12, 14-15]. power quality issues can be handled by integrating svc and statcom with a wind farm connected by a transmission line [16-17]. a hybrid structure was introduced to improve statcom operation performance while using active power filters (apfs) and passive power filters (ppfs) with lower current ratings [5, 7]. on the other hand, hybrid structures only perform well when subjected to inductive loads and are not good when subjected to capacitive loads [12]. however, due to the higher cost of apf with a multilevel structure, they do not apply to high-voltage transmission lines [18]. many studies investigated reactive power compensation for the stability of a power system [14]. improving voltage regulation and voltage stability with shunt facts devices is comparable to using svc or statcom [8, 11, 18-19]. the most common application for svc and statcom based on pi can be found in the industry [4]. the performance of statcom and svc is affected as a result of the pi gains kp and ki remaining constant and unchanged, regardless of the operating conditions the system experiences [15]. ann-based svc and statcom, among other fuzzy and diverse computer-based topologies, are better suited to replace pi [5]. however, the real-time implementation with the grid and its integration with the power system requires precise and timeconsuming commissioning and testing, creating a very complex engineering, technology & applied science research vol. 13, no. 4, 2023, 11426-11431 11427 www.etasr.com adware & chandrakar: a hybrid approach with statcom to enhance grid power quality associated… system to analyze and control under unforeseen transient conditions [14, 20]. very few studies addressed these difficulties, particularly when there are power quality issues. this study investigated a harmonic filter tuned with statcom, modeled in matlab-simulink, to address the above issues with the following objectives:  modeling and design of a three-phase harmonic filter with statcom.  using the three-phase harmonic filter to successfully mitigate the harmonic signal from the given power compensated from statcom.  comprehensive analysis of different power quality issues with the proposed compensator. ii. proposed power system with wind farm matlab-simulink simulations were carried out to evaluate the efficacy of the proposed model and examine the shunt compensator with svc, statcom with pi, and hybrid statcom with a harmonic filter. the proposed test system included two generators, 500 kv 3000 mva and 500 kv 2500 mva, coupled to three buses, designated b1, b2, and b3, as illustrated in figure 1. bus b3 is where the multiterminal load system with a 6000 mw load and a 9 mw wind generator are connected. concerns about power quality were taken into account whenever pcc or load bus b3 connects a wind farm. power quality analysis was carried out during the time that load bus b3 was connected to an mtl load with a wind generator. fig. 1. test system with the proposed strategy. shunt compensators are used more frequently in power systems because of their ability to quickly compensate for power loss while requiring little maintenance. svc, as shown in figure 2, is a shunt compensator that dynamically creates static reactive var power to modify reactive impedance in a network and change the characteristics of a transmission line. fig. 2. test system with svc. adjusting the output of the converter in statcom, as depicted in figure 3, reactive power can be transferred from the converter into the grid. fig. 3. test system with statcom. a. test system with the proposed statcom as shown in figure 4, the simulated system used three different types of compensators: svc, statcom, and hybrid statcom. the proposed hybrid statcom was a combination of an active inverter part with a dc link in conjunction with a customized three-phase c-type high-pass harmonic filter connected in line with the inverter part. fig. 4. hybrid statcom. figure 5 shows a statcom submodel in the phasor model, which was designed in matlab-simulink using simscape in the simpowersystem toolbox. the statcom submodel consists of a power component model, measurement system, statcom control block, converter output voltage calculation, and dc-link voltage calculation. the power components model consists of the connection between statcom with the grid at bus 2, the measurement system that continuously measures grid voltage, id and iq currents with phase angle theta, as well as a reactive power component. the statcom control block continuously monitors the measured values of the system parameters and compares them with the ac output voltage and the dc link voltage of statcom. the shunt converter output voltage computation block generates a control signal to control similarly the dc link voltage computation block and the input dc voltage to the active converter part. after obtaining the control parameter from statcom, the control signals are fed from the power modeling block through a three-phase harmonic filter via output signals a, b, and c. high-pass filters are used to filter high-order harmonics and are responsible for the filtration of a engineering, technology & applied science research vol. 13, no. 4, 2023, 11426-11431 11428 www.etasr.com adware & chandrakar: a hybrid approach with statcom to enhance grid power quality associated… wide spectrum of frequency ranges. a specific type of highpass filter, known as a c-type high-pass filter, was used. this filter was used to both provide reactive power and prevent parallel resonances. it is also possible to filter the low-order harmonics, such as the third harmonic, while at the same time ensuring that there are no losses at the fundamental frequency. fig. 5. harmonic filter in phase with the statcom. iii. power quality investigation this section describes the performance analysis of the proposed hybrid statcom and its effectiveness compared to a similar system consisting of svc or statcom. the effects of voltage sag, swell, voltage distortions, and harmonics were investigated in the respective systems connected to mtl and a 9 mw wind farm. all performance parameters were examined for three different instances: 1-before fault, 2-during fault, and 3-after fault. a. voltage sag simulation result a voltage drop is a common and serious issue that can occur in transmission line systems as a result of system faults, a sudden increase in load, or the start of powerful motors. near bus b1, the line-to-line ground fault depicted in figure 6 has a duration of 0.2 to 0.3 s, a fault resistance of 80 ω, and a ground resistance of 0.001 ω. svc, statcom with pi, and hybrid statcom with a harmonic filter are shown in the figure, illustrating their respective voltage sag calculations. pcc is equipped with svc, statcom with pi, and statcom with a harmonic filter. table i shows the four parameters examined on the dynamic behavior of the system. understanding the effect of transient voltage sag on voltage stability requires testing the pcc rms voltage with and without a compensator and measuring active, reactive, and harmonic influences before, during, and after a fault occurs. the voltage on the load bus rises in proportion to the reactive power it draws, so compensating for this consumption requires using facts controllers. a line-to-line short circuit was simulated on generator bus b1 to examine voltage sag. after a short circuit occurs in a system without a compensator, as shown in figure 7, the rms voltage drops to 0.64 p.u. but is kept at 0.77 p.u. by the svc and pi controllers, 0.84 p.u. by the statcom pi controller, and 0.86 p.u. by the proposed hybrid statcom controller. fig. 6. test system with ll fault. table i. voltage sag parameter no compensator pi-svc pistatcom hybrid statcom rms voltage (pu) 1 0.70 0.88 0.94 0.96 2 0.64 0.77 0.84 0.86 3 0.70 0.88 0.94 0.96 active power (watt) 1 825 1040 1100 1130 2 540 640 670 680 3 825 1040 1100 1130 reactive power (var) 1 324 -170 -300 -335 2 35 -310 -470 -500 3 326 -170 -300 -335 % thd 484.96 412.43 320.61 283.08 fig. 7. rms voltage during l-l fault. fig. 8. active power during a voltage sag. fig. 9. reactive power during a voltage sag. statcom efficiently preserves active power in the event of a fault. while the system requires around 35 var of power engineering, technology & applied science research vol. 13, no. 4, 2023, 11426-11431 11429 www.etasr.com adware & chandrakar: a hybrid approach with statcom to enhance grid power quality associated… during faults without a compensator, svc provides 310 var, statcom with pi provides 470, and a hybrid statcom provides around 500 var, as shown in figure 9. the proposed compensation was used by statcom to return the system voltage to normal. the installed capacity of the svc prevents voltage recovery in this case. b. voltage swell simulation result the proposed mtl load system with wind farm featured a parallel load with 500 mw of active power, 100 var of inductive reactive power, and 100 var of capacitive reactive power to produce a voltage swell. the three-phase circuit breaker shown in figure 10 was responsible for creating the voltage swell test system. table ii shows the results of the proposed system, which consists of statcom with a harmonic filter, statcom, and svc with pi control. fig. 10. the proposed system with a sudden load off. table ii. voltage swell parameter no compensator pi-svc pistatcom hybrid statcom rms voltage (pu) 1 0.64 0.78 0.86 0.88 2 0.7 0.88 0.94 0.96 3 0.64 0.78 0.86 0.88 active power (watt) 1 765 944 1040 1062 2 825 1040 1105 1130 3 765 944 1040 1062 reactive power (var) 1 400 -80 -220 -250 2 325 -170 -297 -335 3 400 -80 -220 -250 % thd 484.96 485.68 448.51 406.57 figures 11-13 show the evaluation of the test system with and without compensation, examining the effects of various compensators while accounting for a brief voltage surge that lasts between 0.2 and 0.3 s. as seen in table ii, without statcom, electrical mode instability occurs when a load is suddenly removed from bus b3 as the rms voltage was 0.7 p.u. the rms voltage improved to 0.88 with svc, up to 0.94 with statcom, and up to 0.96 with the proposed hybrid statcom with a harmonic filter. during load off, the active and reactive power were respectively 825 w and 325 var without a compensator, 1040 w and -170 var with svc, 1105 w and -297 var with statcom, and 1130w and -335 var using the proposed hybrid statcom with a harmonic filter. as can be seen, the proposed hybrid model provided the best results. fig. 11. vrms during a sudden load off. fig. 12. active power during a sudden load off. fig. 13. reactive power during a sudden load off. c. voltage flickers voltage flickers and voltage distortion are the most common power system problems. as seen in figure 14, capacitor banks were connected to bus b3 by a switch to simulate voltage distortion or flickering. capacitor banks were used as shunt compensators with the load bus to regulate reactive power fluctuations. each on/off cycle of capacitor banks distorts the load voltage at the bus. voltage flickers or distortion occur on the bus when a capacitor operates during steady-state operation or when load compensation is needed. these phenomena were examined at pcc with and without a compensator, as well as with the suggested hybrid statcom. fig. 14. test system with a switching capacitor. table iii shows how different compensators affect transmission line performance characteristics during different transient events. with the help of the proposed hybrid statcom, the rms voltage at the pcc can be raised to a maximum of 0.97 p.u, near 1 p.u, as shown in figures 15-17. engineering, technology & applied science research vol. 13, no. 4, 2023, 11426-11431 11430 www.etasr.com adware & chandrakar: a hybrid approach with statcom to enhance grid power quality associated… the proposed hybrid statcom with harmonic filter outperformed pi-based svc and statcom in simulations measuring active and reactive power transmission. table iii also shows that the proposed controller improved thd by 2025%. fig. 15. rms voltage during capacitor switching. fig. 16. active power during capacitor switching. fig. 17. reactive power with capacitor switching. table iii. voltage flickers parameter no compensator pi-svc pistatcom hybrid statcom rms voltage (pu) 1 0.71 0.88 0.95 0.96 2 0.72 0.90 0.96 0.97 3 0.71 0.88 0.95 0.96 active power (watt) 1 826 1040 1106 1130 2 878 1104 1166 1177 3 826 1040 1106 1130 reactive power (var) 1 324 -170 -298 -335 2 311 -270 -400 -420 3 326 -171 -299 -335 % thd 484.96 485.55 418.53 323.02 iv. discussion the paper presented a novel hybrid strategy for statcom using a harmonic filter and compared it with a pi-based svc and statcom shunt compensator. most power industries rely on svc and statcom built on the pi platform. the performance of statcom and svc was negatively affected as a result of the inability of the pi gains kp and ki to adapt to changing system operating conditions. one of the distinctive features of this hybrid statcom is the three-phase harmonics filter, which lowers the harmonic component produced by the active inverter component of the statcom during compensation, and thereby increases the range of compensation. very few studies have focused on harmonic filters and shunt facts devices to improve power quality. v. conclusion this study carried out a comprehensive analysis of the proposed hybrid statcom with a harmonic filter controller for power quality issues under different transient conditions in matlab-simulink. the simulation results showed that statcom and svc using a pi controller can effectively lower voltage sag/swell. simulations of the same system showed that combining a hybrid controller based on a harmonic filter with statcom improved performance. the proposed hybrid statcom had rms voltage values that were significantly more consistent during voltage sags, voltage surges, and switching of capacitor banks compared to svc, statcom with pi, and a system without a compensator. the harmonic filter-based statcom immediately provided the system with reactive power during sudden transients. the proposed hybrid statcom produced a remarkably stable voltage profile, with only minor transient overshoots caused by sudden events, such as the removal of a heavy load or capacitor switching. moreover, the proposed hybrid statcom showed fewer distortions in load voltage, line active power, and reactive power. the simulation results showed that voltage ripple and distortion can be reduced by 5-10% and 10-20%, respectively, with the proposed hybrid statcom. the proposed controller can reduce thd by approximately 20-25% compared to a system with a pi controller. references [1] o. p. bharti, r. k. saket, and s. k. nagar, "controller design of dfig based wind turbine by using evolutionary soft computational techniques," engineering, technology & applied science research, vol. 7, no. 3, pp. 1732–1736, jun. 2017, https://doi.org/10.48084/ etasr.1231. 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[20] v. p. rajderkar and v. k. chandrakar, "design coordination of a fuzzy-based unified power flow controller with hybrid energy storage for enriching power system dynamics," engineering, technology & applied science research, vol. 13, no. 1, pp. 10027– 10032, feb. 2023, https://doi.org/10.48084/etasr.5508. microsoft word etasr_v12_n4_pp8928-8935 engineering, technology & applied science research vol. 12, no. 4, 2022, 8928-8935 8928 www.etasr.com abbas & abbas: the taguchi approach in studying and optimizing the electro-fenton oxidation to … the taguchi approach in studying and optimizing the electro-fenton oxidation to reduce organic contaminants in refinery wastewater using novel electrodes rowaida n. abbas chemical engineering department university of baghdad baghdad, iraq rowida.abbas1307d@coeng.uobaghdad.edu.iq ammar s. abbas chemical engineering department university of baghdad baghdad, iraq ammarabbas@coeng.uobaghdad.edu.iq received: 18 may 2022 | revised: 1 june 2022 | accepted: 4 june 2022 abstract-this study investigated the degradation of organic pollutants using an advanced electrochemical oxidation technique in a batch reactor cell consisting of a graphite anode, modified by electrodeposition of pbo2, and a graphene-modified carbon fiber cathode. the experiment was designed by the taguchi design approach with an orthogonal array of l18 to study and optimize the degradation of chemical oxygen demand (cod) by the electro-fenton oxidation process. four process parameters, current density (cd), temperature, fe 2+ concentration, and time were measured at different levels. the impact of each factor was analyzed by analysis of variance (anova). furthermore, a linear model analysis was applied for the signal-to-noise (s/n) ratio and mean values, obtaining the optimal conditions. the most significant parameter of the cod removal efficiency was time, and the least one was temperature. keywords-organic pollutants; taguchi; electro-fenton; cod removal i. introduction wastewater from the oil industry is frequently produced and discharged into the main water bodies, causing severe environmental issues. the amount and characteristics of pollutants in oil refinery wastewater depend on the type of oil being processed, the plant configuration, the operation procedures, and the type of processing units [1]. pollutants in refinery wastewater often consist of free hydrocarbons, suspended solids, and inorganic matter, with a high concentration of salts, sulfides, ammonia, organic carbon, phenol, benzene, heavy metals, nutrient grease, and chemical additives [2, 3]. phenol is the most produced contaminant in the refinery industry, which pollutes surface and ground water and causes harmful effects on human health [4-7]. phenol and its derivatives are highly soluble in water, so they can be present in a wide range of water concentrations, from a few milligrams to high concentrations that reach 7000mg/l, whereas refineries contribute approximately 6-500mg/l. phenolic compounds persist in water or transform various reactions such as chlorination and methylation into more harmful and toxic materials than phenol itself, such as chlorophenols and cresols [8]. phenol is classified as one of the most harmful pollutants by the environmental protection agency (epa) and the european agency (ea) and is toxic to humans and the environment [9]. phenol can poison humans when ingested, inhaled, or in contact with the skin. phenol vapors cause severe irritation to the eyes and mucous. other severe symptoms caused by exposure to phenol include fatigue, headache, loss of consciousness, nausea, and vomiting. exposure to phenol for a long time can change blood pressure and damage the liver, kidneys, and the nervous system [10, 11]. phenol and phenolic compounds can be treated using several methods such as adsorption [12], biological treatments [13], coagulation/flocculation [14], chemical oxidation [15], ion exchange [16], and electrochemical oxidation processes [17]. adsorption is limited by the adsorbers, as they cannot be easily renewable and need regeneration after a period of use, and the pollutant is not converted to less hazardous materials as it is concentrated and transferred to a vapor or an organic phase [18]. biological treatment was related to many problems that concern the operating conditions, including providing a suitable environment for microorganisms, the low settle capacity of the sludge due to the low ratio of food to microorganisms, the formation of polymers consisting of lipids, proteins, and carbohydrates that negatively affect the settlement of the sludge, and the poisoning of microorganisms due to toxic compounds that require very long times for acclimatization and start-up [19, 20]. coagulation requires the junction of nonreusable chemicals such as coagulants, flocculants, and aid chemicals and requires physical and chemical monitoring of the affluent. the volume of sludge generated increases, as well as the need for management and the cost of treated contaminates [14, 20-21]. chemical oxidation, such as simple oxidation, ozonation, and hypochlorite treatment, requires completed physical and chemical treatments. still, these corresponding author: ammar s. abbas engineering, technology & applied science research vol. 12, no. 4, 2022, 8928-8935 8929 www.etasr.com abbas & abbas: the taguchi approach in studying and optimizing the electro-fenton oxidation to … processes require chemicals, thereby, production, transportation, and management of the necessary oxidants for the pre-treatment step. the type of oxidant directly affects the efficiency of the process. the creation of intermediates that may be more toxic than the treated substance has a limited effect on chemical oxygen demand, aromatic compounds, and volatile substances, especially when using hypochlorite, and the formation of sludge [15, 22]. ion exchange technology needs a high initial cost of the selective resin, maintenance cost, time-consuming regeneration, and large equipment if there is a large volume of wastewater to be treated. beads are easily fouled by organic matter that requires a physicochemical pre-treatment to remove these pollutants, which is not effective for organic target pollutants [16]. at this time, electrochemical treatment is one of the cleanest and most eco-friendly methods used as an alternative to other treatment processes for environmental protection. electrochemical technology is a most promising one for the treatment of organic pollutants in refinery wastewater. it includes electrocoagulation-electroflotation, anodic oxidation, electrochemical reduction, and advanced electrochemical oxidation [23-24]. electrochemical methods do not need to add a lot of chemical reagents because the leading reagent used is the electron, which is considered a clean reagent. these processes can also remove contaminants from even a massive quantity of different phases of polluted streams and require lower temperature and pressure than other non-electrochemical processes. many electrochemical processes have high selectivity, which prevents the formation of unwanted byproducts because the applied potential can be controlled, which helps attacking specific bonds. the chemical substances added in electrochemical processes are small and safe. electrochemical methods operate flexibly and their control processes, and equipment, are simple and inexpensive [17, 2425]. electrochemical oxidation processes are popular for treating organic pollutants in refinery wastewater and are classified into direct and indirect. direct oxidation occurs on the surface of the anode electrode, and indirect oxidation uses an oxidizing mediator that forces organic matter to contribute to the oxidation reaction, such as hypochlorite [26], chlorine [27], and hydrogen peroxide (h2o2) [28]. the electro-fenton oxidation process is an indirect advanced oxidation process that uses the electrogenerated hydroxyl radical (•oh) on the surface of electrodes, which has a high oxidation capacity in the oxidation of organic substances [29]. in the electro-fenton oxidation process, ferrous ion (fe2+) is added externally, and h2o2 is generated electrochemically in-situ on specific electrodes that have appropriate cathodic potential by a twoelectron reduction of oxygen [30]: �� + 2�� + 2� � → ���� (1) the electricity used in electro-fenton oxidation processes is clean and contamination-free, so these processes are ecofriendly and do not generate secondary pollutants. •oh is generated in the solution by using fe2+ as a catalyst which attacks the organic contaminants [30]: �� �� + ���� + �� → �� ��+•�� + ��� (2) • �� + �� → �• + ��� (3) the fe3+ ion produced in (2) can transform to fe2+ by a one-electron reduction reaction [30]: 3 2 fe e fe + − + + → (4) the electrode material is an important factor that affects the performance of the electro-fenton oxidation because it affects selectivity, efficiency, mechanism, and the products of the oxidation process [2, 31]. so, when choosing the electrode, material-specific properties must consider its electrical conductivity, selectivity, catalytic activity, cost, lifetime, and oxygen overvoltage [31]. the effect of the cathodic reaction on the efficiency of the overall oxidation process is also taken into account [31, 32]. carbon electrodes are widely used as anodes and cathodes in electro-fenton processes. they have high surface, high porosity, corrosion resistance, and offer lowpressure drops compared to other materials because they have a large space. examples of these electrodes are graphite [33-35], reticulated vitreous carbon [36], activated carbon fibers [37], and carbon nanotubes [38]. this study uses the taguchi approach to investigate the electro-fenton oxidation process of organic pollutants in refinery wastewater. the process was carried out in a batch reactor cell consisting of a graphite anode modified by electrodeposition of a pbo2 film on its surface and a carbon-fiber cathode modified by graphene. different operating conditions were used in the oxidation process, and the effect of these parameters on the cod removal was also studied. ii. experimental work a. taguchi experimental design the taguchi experimental design was used to examine the effect of several factors on the response characteristics with a minimum number of experiments using the orthogonal array technique. the studied parameters were three operating temperatures (15, 25, and 35°c), three current densities (2, 5, and 8ma/cm2), three concentrations of fe2+ (0.1, 0.2, and 0.4mm), and 6h of electrolysis. three levels were investigated for each current density, temperature, and fe2+ concentration, and six levels of time, as shown in table i. table i. control parameters and levels control parameters levels temperature (°c) 15, 25, 35 current density (ma/cm2) 2, 5, 8 fe2+ concentration(mm) 0.1, 0.2, 0.4 time (h) 1, 2, 3, 4, 5, 6 table ii presents the orthogonal array layout of l18 (3 3×61) used in this study. the notation 33 denotes 3 parameters studied on 3 different levels, and 61 represents one of the parameters investigated on 6 levels. taguchi parameter design identifies the best-operating levels that lead to high cod removal. it was investigated which factors had the most and least significant effects on the efficiency of the process. a mathematical relation between the process parameters and the output was employed using regression analysis. engineering, technology & applied science research vol. 12, no. 4, 2022, 8928-8935 8930 www.etasr.com abbas & abbas: the taguchi approach in studying and optimizing the electro-fenton oxidation to … table ii. layout of l18 (33×61) experimental design no time (h) cd (ma/cm 2 ) t, ( ° c) fe 2+ (mm) 1 1 2 15 0.1 2 1 5 25 0.2 3 1 8 35 0.4 4 2 2 15 0.2 5 2 5 25 0.4 6 2 8 35 0.1 7 3 2 25 0.1 8 3 5 35 0.2 9 3 8 15 0.4 10 4 2 35 0.4 11 4 5 15 0.1 12 4 8 25 0.2 13 5 2 25 0.4 14 5 5 35 0.1 15 5 8 15 0.2 16 6 2 35 0.2 17 6 5 15 0.4 18 6 8 25 0.1 b. electro-fenton oxidation process the aqueous solution was prepared to simulate the organic pollutants of the al-dora refinery wastewater (350ppm cod). the electro-fenton oxidation process was used to treat the phenolic compound, carried out in an open undivided cell equipped with an anode and cathode having a distance of 3cm between them. the volume of the treated solution was 0.4l. the process used pbo2 deposit on graphite as an anode and carbon fiber modified by graphene as a cathode. a rotation of 200rpm was achieved in the treated solution using a magnetic stirrer with a heating plate (labinco, model l-81). compressed air was bubbled into the treated solution at 1l/min flow rate using an electromagnetic air pump (aco-001). the electrolysis process for the treated solution was carried out at three different operating temperatures (15, 25, 35°c ± 1°c). the ph of the treated solution was adjusted to 3 by adding 1m h2so4 to maximize h2o2 production. the experiments were carried out by applying different cd 2, 5, and 8ma/cm2 using a dc power supply (korad ka3005d). feso4· 7h2o was added externally as a catalyst with different concentrations of 0.1, 0.2, and 0.4mm. sodium sulfate (na2so4) was used as a supporting electrolyte with a concentration of 0.05m to improve the conductivity of the solution. electrolysis was carried out for up to 6h, and samples were collected after each 1h to check the degradation efficiency by cod analysis. cod removal (%) was calculated with: cod removal,%= cod�cod� ���� × 100 (1) codo and codt were the initial and the cod concentration at time t in (mg/l) respectively. iii. results and discussion a. taguchi design analysis for cod removal the effect of the most influencing parameters on the removal of organic pollutants was investigated by applying the taguchi experimental design (ted). the process operating parameters of the l18 (3 3×61) orthogonal array were specified. the phenol and cod removal by the electro-fenton oxidation process calculated from (5) are shown in table iii. table iii. ted of l18 (33×61) orthogonal array no. time (h) cd (ma/cm 2 ) temp. ( ° c) fe (mm) cod removal (%) s/n 1 1 2 15 0.1 33.52 30.51 2 1 5 25 0.2 43.62 32.79 3 1 8 35 0.4 51.78 34.28 4 2 2 15 0.2 48.32 33.68 5 2 5 25 0.4 57.32 35.17 6 2 8 35 0.1 52.34 34.38 7 3 2 25 0.1 50.87 34.13 8 3 5 35 0.2 67.81 36.63 9 3 8 15 0.4 68.75 36.75 10 4 2 35 0.4 73.64 37.34 11 4 5 15 0.1 60.87 35.69 12 4 8 25 0.2 69.78 36.87 13 5 2 25 0.4 75.41 37.55 14 5 5 35 0.1 73.65 37.34 15 5 8 15 0.2 79.36 38.00 16 6 2 35 0.2 82.32 38.31 17 6 5 15 0.4 82.89 38.37 18 6 8 25 0.1 84.72 38.56 the experimental data were analyzed using minitab 19. the taguchi method uses a signal-to-noise ratio (s/n) to evaluate the optimum removal conditions and determine the response variation of the mean value that causes experimental noise. it uses it to recognize the levels of controlling factors that minimize the response variance from noise factors. the quantitative measure s/n refers to the mean of the output value (desired value) to the standard deviation of the output value (undesired value) [39-40]. s/n can be divided into three categories: smaller the better (stb), nominal the better (ntb), and larger the better (ltb). the type of s/n was chosen depending on the goal of the experimental process and the desired process quality characteristics. the ltb s/n was selected to maximize the phenol and cod removal efficiency. the ltb response can be evaluated by the standard formula for this type of characteristic [4144]: � ���� = −10 log ! " ∑ ! $%& ' " �(! (2) where i is trail number, yij represents the response of the measured value for the i-th trial and the j-th run, and n is the number of replications for the experimental combination. in general, the highest s/n value is preferable. figure 1 shows a plot of s/n against cd, t, fe2+, and t. figure 2 shows the main effects graph for the means and represents the relationship between the operating parameter under study and the response obtained. the results plotted in figures 1 and 2 are shown in tables iv and v respectively, showing the effect of each operating parameter on cod removal. the ranks in these tables are based on delta statistics. the delta statistic equals to the difference between each factor's highest and lowest average. the highest delta value was assigned to rank 1, followed by rank 2 for the second-highest delta value, and so on [45]. the delta values in tables iv and v indicate that the time of the experiment had the most significant effect on the cod removal. the second parameter that influenced cod removal was fe2+ concentration, followed by current density, while temperature had the lowest impact on cod removal. engineering, technology & applied science research vol. 12, no. 4, 2022, 8928-8935 8931 www.etasr.com abbas & abbas: the taguchi approach in studying and optimizing the electro-fenton oxidation to … fig. 1. main effects plot for s/n. fig. 2. main effects plot for means. table iv. response of s/n for cod removal level time (h) cd (ma/cm 2 ) temp. ( ° c) fe (mm) 1 32.53 35.25 35.50 35.10 2 34.41 36.00 35.85 36.05 3 35.83 36.47 36.38 36.58 4 36.63 5 37.63 6 38.41 delta 5.89 1.22 0.88 1.48 rank 1 3 4 2 table v. response of means for cod removal level time (h) cd (ma/cm 2 ) temp. ( ° c) fe (mm) 1 42.97 60.68 62.28 59.33 2 52.66 64.36 63.62 65.20 3 62.48 67.79 66.92 68.30 4 68.10 5 76.14 6 83.31 delta 40.34 7.11 4.64 8.97 rank 1 3 4 2 b. analysis of variance for means and s/n ratio the orthogonal array in the taguchi experiments contributes to each process parameter in the process response. anova is used to show which parameters have the most significant effect on the process and find the percentage contribution of each parameter to the change in the value of the dependent parameter [46]. the order of significance of the process variables can be easily identified by anova because it is possible to calculate the source of the variation during the process [47]. the anova table involves the degree of freedom (df), the sequential sum of squares (seq ss), the adjusted sum of squares (adj ss), the adjusted mean of squares (adj ms), f-value, and p-value. these terms are defined in many handbooks as statistical expressions and are studied and analyzed with experimental designs. these factors showed the importance of each parameter on the process performance [48]. a small variation in any process variable with an excellent percent contribution will greatly influence the process performance. a portion of the total variance detected in the experiment for each effecting parameter is the percent contribution. so, the factor of the greater value of percentage contribution contributes more than other factors to the process's final results [49]. tables vi and vii show that the highest sum of squares (ss) value went to time t, which had the most significant effect on cod removal. these tables also showed that the statistical significance of the mentioned factors is as follows: fe2+, cd, and t based on p-values. time is the most significant factor in phenol and cod removal, having 5 degrees of freedom. the least important factor in the processes is t, and the degree of freedom for the cd, t, and fe2+ variables is 2. in general, when f is greater than 4, the change in the parameter studied significantly affects the process performance [40]. it is clear that all factors, time, current density, ferrous ion concentration, and temperature, significantly affect the removal of cod by the electro-fenton oxidation process since the f values are greater than 4. table vi. anova for s/n of cod removal source df seq ss adj ss adj ms f p time 5 70.3327 70.332 14.066 104.65 0.000 cd 2 4.5298 4.5298 2.2649 16.85 0.003 temp 2 2.3735 2.3735 1.1868 8.83 0.016 fe 2+ 2 6.7040 6.7040 3.3520 24.94 0.001 residual error 6 0.8065 0.8065 0.1344 ---- total 17 84.746 -------- table vii. anova for means of cod source df seq ss adj ss adj ms f p time 5 3328.85 3328.85 665.771 84.30 0.000 cd 2 151.65 151.65 75.824 9.60 0.013 temp 2 68.42 68.42 34.208 4.33 0.069 fe 2+ 2 249.09 249.09 124.546 15.77 0.004 residual error 6 47.38 47.38 7.897 ---- total 17 47.38 ----------- moreover, the significance of process factors using a pvalue indicates that when the p-value is less than 0.05, the process parameter significantly affects the quality characteristic [40]. therefore, time is the most significant parameter, followed by fe2+ concentration and current density, while the temperature is the least important parameter of cod removal. the adequacy of the model results can be evaluated using engineering, technology & applied science research vol. 12, no. 4, 2022, 8928-8935 8932 www.etasr.com abbas & abbas: the taguchi approach in studying and optimizing the electro-fenton oxidation to … random and normally distributed residual plots, such as histogram of residuals, normal probability, residual fit, and residual order. figure 3 depicts the residual plots for cod removal. the following should be noted: • histograms showed that data have no outliers and are not skewed. • normal probability plots showed that data are distributed normally, factors employ the response, and there are no outliers. • residuals versus order showed that there are methodical influences in the data because of the time or the order of collection data. • residuals versus fitted data showed that there is constant variance and the relationships are nonlinear. in the ideal case, the data points should randomly drop around the zero line. fig. 3. residual plots of cod removal. c. multiple regression model and optimization the equation that describes the multiple regression model for cod removal was: cod = 11.08 + 7.936x1 + 1.185x2 + 0.2319x3 − 144.2x4� (7) where x1 is the time of experiment (h), x2 is cd (ma/cm2), x3 is temperature (ᵒc), and x4 is fe2+ (mm). the squared value of the correlation coefficient (r2) for the predicted equation was 98.07%. all four factors affected the efficiency of cod removal. the most influential parameter was time, followed by fe2+concentration and current density, while the temperature was the least effective parameter. table viii shows the highest possible cod removal obtained from the optimization of (7). the optimal cod values ranged between 78.34-94.02%. the highest optimal value of cod removal agrees with the findings obtained from the s/n and means analysis results. the selected operating parameters to examine their effects were temperature = 35 ᵒc, fe2+ = 0.4mm, cd = 8ma/cm2, and t = 6h. the regression equation (7) was utilized to observe the effect of the process variables on cod removal by the electro-fenton oxidation process. table viii. optimal cod removal and operating parameters time (h) cd (ma/cm 2 ) temp. (ᵒc) fe 2+ (mm) cod removal (%) 5 8 15 0.2 78.34 6 8 25 0.1 82.72 6 2 35 0.2 83.80 6 5 15 0.4 85.81 6 8 35 0.4 94.02 d. the impact of operating parameters on cod removal the effect of current density on cod removal from simulated wastewater was studied using the electro-fenton oxidation process at 35ᵒc temperature, 0.4mm fe2+ concentration, supporting electrolyte consisting of 50mm sodium sulfate (na2so3), solution ph at 3, and applied cd ranging from 2 to 8ma/cm2. 1) the effect of current density figure 4 shows the effect of current density (cd) on the removal of cod. the removal of cod was 86.9, 89.28, 91.65, and 94.02% at 2, 4, 6, and 8ma/cm2 respectively, after 6h of electrolysis. increasing cd from 2 to 8ma/cm2 improved the rate of degradation of organic pollutants. organic degradation increased with cd due to an increase in the amount of h2o2 generated electrochemically by electrolysis. when the amount of hydrogen peroxide increases, •oh increases enough to react with the organic pollutants that existed in the treated solution, minimizing cod values [50, 42]. the obtained results agree with other works that treated organic wastewater using the electro-fenton oxidation process [2, 51-53]. fig. 4. effect of applied current density on cod removal from phenolic wastewater, temperature=35ᵒc, fe2+=0.4mm, na2so3=50 mm, ph=3. 2) the effect of fe 2+ concentration fe2+ added to the system was externally considered an important parameter that influences the performance of the electro-fenton oxidation process. the reaction rate increased with increasing concentration of fe2+ up to a limiting value. increasing the concentration above this value decreased organic engineering, technology & applied science research vol. 12, no. 4, 2022, 8928-8935 8933 www.etasr.com abbas & abbas: the taguchi approach in studying and optimizing the electro-fenton oxidation to … degradation due to scavenging reactions [53, 54]. figure 5 shows that the removal of cod was 81.03, 85.05, 90.92, and 94.02% at 0.05, 0.1, 0.2 and 0.4mm fe2+ respectively. increasing fe2+ leads to increased organic degradation because of the increased amount of produced •oh radicals [55]. the results showed that ferrous ion concentration greatly affected the removal, especially on cod, which proved that the electrofenton oxidation process was largely influenced by the reaction conditions in the bulk solution between fe2+ and h2o2, not by the electrochemical reactions on the electrode surface [56]. the results obtained agree with [56], who reached a cod removal efficiency of 95.9% using 0.7mm feso4 concentration and 25ma/cm2 cd. fig. 5. effect of fe2+ concentration on cod removal from phenolic wastewater, temperature=35ᵒc, cd=8ma/cm2, na2so3=50mm, ph=3. 3) the effect of temperature sometimes, a temperature increase would lead to an increase in the degradation performance. choosing an optimum temperature is essential because a further increase in temperature is not needed and depends on the system. figure 6 presents the effect of temperature on the removal of cod and shows that it was 89.38, 91.70, and 94.02% at 15, 25, and 35ᵒc. increasing the process temperature leads to a slight increase in the degradation of the organic pollutants by the electro-fenton oxidation process because raising the temperature promotes the generation of fe2+ [57]. the obtained results agree with the temperature behavior reported in [58, 59], who found that the increase in temperature affects relatively low the organic degradation of the electro-fenton oxidation process compared to other factors. furthermore, many studies noticed that the best range of operating temperature is 25-35ᵒc because lower or higher temperatures have a negative impact on removal efficiency. a lower temperature causes a slower initial kinetic process and reduces the degradation performance and reaction rate. higher temperatures negatively influence the removal of organic contaminants because, at these temperatures, the electrogenerated h2o2 is dropped due to the decrease in the dissolved oxygen concentration. furthermore, at high temperatures, h2o2 decays rapidly and decomposes into less reactive water and oxygen [58, 59]. fig. 6. effect of operating temperature on cod removal from phenolic wastewater, cd=8ma/cm2, fe2+=0.4mm, na2so3=50 mm, ph=3. iv. conclusion a taguchi experimental design was achieved using the l18 orthogonal array technique. the effect of the variable parameters on the removal of cod was studied by choosing four factors: cd, t, fe2+, and t. the optimum conditions was obtained from a linear model analysis for the s/n ratios and means. the optimum operating conditions for the removal of cod were temperature of 35°c, current density of 8ma/cm2, fe2+ concentration of 0.4mm, and 6h electrolysis duration. the removal of cod under optimal operating conditions was 94.02%. the time of process variable had the most significant effect on cod reduction efficiency, and the temperature had the 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[59] f. c. moreira, r. a. r. boaventura, e. brillas, and v. j. p. vilar, "electrochemical advanced oxidation processes: a review on their application to synthetic and real wastewaters," applied catalysis b: environmental, vol. 202, pp. 217–261, mar. 2017, https://doi.org/ 10.1016/j.apcatb.2016.08.037. microsoft word etasr_v12_n2_pp8273-8277 engineering, technology & applied science research vol. 12, no. 2, 2022, 8273-8277 8273 www.etasr.com ronoh et al.: human-wildlife conflict early warning system using the internet of things and short … human-wildlife conflict early warning system using the internet of things and short message service emmanuel kipchumba ronoh school of computational and communication science and engineering nelson mandela african institution of science and technology arusha, tanzania erono20@gmail.com silas mirau school of computational and communication science and engineering nelson mandela african institution of science and technology arusha, tanzania silas.mirau@nm-aist.ac.tz mussa ally dida school of computational and communication science and engineering nelson mandela african institution of science and technology arusha, tanzania mussa.ally@nm-aist.ac.tz received: 23 december 2021 | revised: 12 january 2022 | accepted: 18 january 2022 abstract-human-wildlife conflict (hwc) is an important challenge to communities living in areas bordering wildlife game parks and reserves. it is more evident in the united republic of tanzania, whose economy depends on wildlife tourism. this paper proposes a low-cost and low-power early warning system using the internet of things (iot) and short message service (sms) to support hwc respond teams in mitigating these challenges. the system comprises three primary units: sensing, processing, and alerting. the sensing unit consists of a passive infrared (pir) sensor, a global positioning system (gps), and a raspberry pi camera. the pir sensor detects the proximity of the animal using the heat signature, gps senses and records the current location, while the raspberry pi camera has the primary purpose of taking a picture after the pir sensor detects the proximity of the animal. the processing unit with a raspberry microcomputer performs data processing and image inferencing using the you only look once (yolo) algorithm. last is the alerting unit, which includes a global system for mobile (gsm) communications module for sending sms messages to the human-wildlife conflict response team and the nearer community response team leader whenever wild animals are spotted near the park’s border. the system detects, identifies, and reports the detected wild animals. the gprs provides internet connectivity to support data collection, storage, and monitoring in the cloud. keywords-camera trap; edge machine learning; raspberry pi; human-wildlife conflict; early warning system i. introduction human-wildlife conflict (hwc) is an interaction between humans and wild animals with negative consequences. the typical results of the conflicts include crop damage, and injuries or deaths of livestock, humans, and endangered wildlife species [1]. hwc is caused primarily by the human population increase, which causes loss of wildlife habitats due to the pressure to increase agricultural land [2]. hwc is a serious issue in tanzania and has been rising over the years. the hwc data in tanzania from the wildlife division have shown a rising trend, as shown in table i. table i. hwc statistics in tanzania [22] year deaths permanent injuries temporary injuries licestock deaths crop damage (acres) 2012-13 69 23 38 46 1518 2013-14 61 31 49 93 4046 2014-15 59 20 41 107 6786 2015-16 102 20 78 64 8924 2016-17 132 30 54 130 4567 2017-18 380 20 29 149 5016 2018-19 266 60 149 203 10547 total 1069 204 438 792 41404 like most economies in sub-saharan africa, the tanzanian economy majorly relies on agriculture and wildlife tourism, which contribute to the gdp about 30% and 17% percent. moreover, tourism is the main contributor of foreign currency, therefore, it is an important sector of the economy [3]. the government of the united republic of tanzania has adopted some strategies to mitigate hwc by getting real-time information about hwc. for example, collaring utilizes the iot to geo-fence movement of large body species, such as elephants, known for causing hwc or endangered species being poached. another method is using hotline numbers to report hwc incidences. these methods have significantly corresponding author: emmanuel ronoh engineering, technology & applied science research vol. 12, no. 2, 2022, 8273-8277 8274 www.etasr.com ronoh et al.: human-wildlife conflict early warning system using the internet of things and short … improved the efficiency in handling hwc. however, continuous monitoring of wildlife using collaring has been proven to be expensive to install and operate due to its networking requirements and the equipment’s initial cost, especially in remote areas with poor network coverage and low population density [4], while a hotline system utilizes a reactive approach, hence there is a need for a cheaper and proactive approach. therefore, a low-cost camera trap was developed. camera traps have gained popularity in wildlife monitoring and surveys because of their efficiency in collecting wildlife images without monitoring [5, 6]. they need slight improvements, such as the ability to use microcomputers which support machine learning algorithms to support early warning systems. the phone use has become essential, even for for pastoral communities, therefore such a system could be used by the locals [7]. different researches have tried to come with different early warning systems. authors in [8] developed an early warning system using motion detectors and passive infrared sensors to detect wildlife and notify residents through loudspeakers and mobile apps. however, the system is not suitable for the human-wildlife response teams in tanzania who need wildlife identification to determine the method of responding. authors in [9] developed a camera trap system that used a pc for image inferencing. however, it needs bandwidth to transmit a lot of data between the end node device and the pc, hence it requires more power to perform inferencing. authors in [10] developed a machine learning model that accurately identified elephants with accuracy up to 94%. the system used a convolution neural network to develop its model. authors in [11] developed a seismic sensor system as an early warning system to detect and report elephants. ii. materials and methods a. case study the studied area was the ngorongoro conservation area and the tarangire national park. these parks were chosen because they receive significant complaints concerning hwc. b. data collection the equired images to develop the machine learning model were collected by taking pictures in the parks, while other photos were borrowed from the tarangire national park authorities. three hundred images of each species were gathered. all the images were preprocessed by labelling, rescaling, and augmenting. each image was labelled correspondingly to the 6 classes of considered animals: elephant, lion, leopard, zebra, buffalo, and rhino and their localization in the image. c. image preprocessing the images were scaled to 214×214 before being fed to the model. augmentation is a technique used to generate new images by a random transformation of existing data. it decreases the chances of overfitting. augmentation can increase data up to 50 times. d. deep learning computer vision is an important field of study in artificial intelligence that enables computers to detect and identify objects. object detection methods are usually three-stage processes: proposed region selection in the image using bounding boxes, feature extraction, and then the trained classifier is used to perform classification. the basic approaches to machine learning in images are traditional machine learning and deep learning. deep learning has better performance than machine learning when a lot of data and many parameters are involved. a convolutional neural network (cnn) is a powerful data mining algorithm used in deep learning classification problems because it has higher accuracy with large datasets [12]. object detection in cnn is divided into region-based detection and regression object detection methods. region-based detection algorithms perform better in object detection accuracy, but have slow operation. these algorithms are region-based convolutional neural network (rcnn), fast region-based convolutional neural network (fast rcnn), and faster region-based convolutional neural network (faster rcnn). on the other hand, the regression object detection methods generate a region proposal network and then classify the region simultaneously producing results faster than the region-based detection. these methods are single-shot detectors (ssd) and you only look once (yolo). the yolo [13] algorithm is faster than ssd in object detection. moreover, it can detect small objects accurately, it is therefore suitable to our scenarios due to the microcomputer usage in which the results are required promptly to reduce the power consumption of the camera trap. e. proposed model the yolo detector usually divides the image into grids and then performs prediction to get the location of the object. the next step is intersection-over-union to predict the bounding box to find the truth box. finally, the bounding box’s threshold is determined to obtain the final results. the architecture used is darknet-53. the training was done using a batch size of 512, relu activation, and 40 epochs. the size of the input image is 214×214×3 pixels and after 3 pooling and 6 convolutions, the size is shrunk to 21×21×128 pixels for the output feature maps. further convolutions produce a 1×1×4096 neuron [14]. the proposed model achieved training accuracy of 90% and validation accuracy of 78%, as shown in figures 1-2. f. the tinyml model the collected images were converted into a matrix in the edge impulse graphical processing unit (gpu) server. all photos were annotated with their respective labels. label mapping was done to detect an object from the annotated images. the label mapping was transformed to the tensorflow file format of the trained model to produce an interface graph that would classify pictures. the graph was converted into a tensorflow lite file that the python program would infer from when detecting objects in the images [15]. g. system architecture and design the system architecture has 3 major units: sensing, processing, and alerting. the system block diagram is shown in figure 3. 1) sensing unit engineering, technology & applied science research vol. 12, no. 2, 2022, 8273-8277 8275 www.etasr.com ronoh et al.: human-wildlife conflict early warning system using the internet of things and short … the main sensing unit consists of a passive infrared (pir) sensor, a raspberry pi camera, and a gps module. the pir sensor is used to detect the presence of wildlife in its proximity using its heat signatures [16] to perform its role, therefore it can work under all light conditions [17]. the raspberry pi camera [18] is used to take the picture after its activation following the presence of wildlife. the gps module is used to accurately determine the device’s current location using gps coordinates [19]. fig. 1. taining and validation accuracy. fig. 2. training and validation loss. fig. 3. system block diagram. 2) the processing unit a raspberry pi equipped with the yolo model was used to analyze the image taken by the camera and to detect and identify wildlife. the raspberry pi used is a low-power consuming microcontroller [20]. the reason for choosing the raspberry pi was its low power consumption for its reasonable processing speed. 3) alerting after wildlife classification and identification, sms messages were sent containing the google map location link of the wildlife along with the name of the animal to the relevant personnel. the link is used to visualize the location of the wildlife identified [21]. h. system configuration the system components were configured to the raspberry pi development board. all the components were connected to the raspberry pi. i. programming tools the system was developed in python to control all sensing units and the alerting unit. the processing unit processes data using the yolo model packaged into the tensorflow lite file. after object detection and identification, the alerting unit sends the data to the intended destination. figure 4 shows the flowchart of the steps of the proposed model. fig. 4. system flowchart. j. testing 1) model testing the yolo model was tested using the park data and achieved 98% detection accuracy as shown in table ii. engineering, technology & applied science research vol. 12, no. 2, 2022, 8273-8277 8276 www.etasr.com ronoh et al.: human-wildlife conflict early warning system using the internet of things and short … table ii. model testing confusion matrix result table 2) system testing the system testing was done in the lab. the system was tested by directing the camera to a picture of a wild animal on the screen and then swapping it with different pictures of objects and animals. the system identified the animals and uploaded data to the cloud. iii. results and discussion the results presented here show the work from testing the camera trap. the camera was developed using a raspberry pi microcomputer, a pir sensor, a gps module, a raspberry pi camera, and a gsm module. the prototype of the system is shown in figure 5. the sensing units include the pir sensor that activates the camera when it detects the proximity of an animal from its heat signature. after the picture is taken, the image is sent to the model packaged into the tensorflow file to perform inference to detect and identify the animal in the picture. if the animal is identified, an sms is sent to the listed numbers belonging to the hwc response team and the community human-wildlife response group. the model was able to detect and identify wildlife with good accuracy. it detected different species as shown in figures 6 and 7. fig. 5. system prototype. it was observed that when the object was placed at a close distance from the camera, it was accurately identified. however, if it was placed too far or too near, the system tended to misidentify the animal or even not identify it at all. the recipient of the sms message is determined based on the species of the identified animal. if the wild animal is dangerous, a message is sent to both the community response team leader and the hwc response team. if it cannot cause hwc, but is an endangered wild animal, a message is sent to the hwc response team only, while if the wild animal cannot cause hwc and it is not a endangered one, no message is sent. the sms contains the name of the species of the wild animal and the google map link location of the wild animal. fig. 6. buffalo detection. fig. 7. elephant detection. fig. 8. a received notification message. a web-based system was developed with the primary purpose of monitoring and managing data from the sensor nodes. it is accessible by a web browser. park rangers and park managers are the only people allowed to use the system to access the park’s wildlife spotting data from the database. the system works best if the camera traps are placed at a distance of 40 meters apart to ensure their efficiency. this distance is the combination of the efficiency of the pir sensor and camera distance of focus that come into play. in our case study area, it is best to place the cameras in places with weak fences and near areas with high human population to reduce the cost of the whole project. a. discussion the conducted experiments in selected places proved that the system can monitor the movement of wildlife and rapidly report the identified dangerous or endangered wildlife species. buffalo elephant leopard lion rhino zebra uncertain buffalo 100 0 0 0 0 0 0 elephant 1.7 94.8 0 0 3.4 0 0 leopard 0 0 100 0 0 0 0 lion 0 0 0 100 0 0 0 rhino 0 3.1 0 0 95.3 0 1.6 zebra 0 1.1 0 0 0 98.9 0 f1 score 0.99 0.95 1.00 1.00 0.96 0.99 engineering, technology & applied science research vol. 12, no. 2, 2022, 8273-8277 8277 www.etasr.com ronoh et al.: human-wildlife conflict early warning system using the internet of things and short … the processed data were sent to the server for visualization and tracking was conducetd by using a web application dashboard. iv. conclusion and recommendations the proposed low-cost early warning system was developed to report incidents that may cause hwc using sms. it is suitable for use by the park and community hwc response team members living in hwc-prone areas. this system can support the rangers patrolling the parks by providing insightful information about wild animal locations fast. the 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[22] mnrt (2020), national human-wildlife conflict management strategy 2020-2024. united republic of tanzania: ministry of natural resources and tourism, 2020. authors profile emmanuel ronoh is an msc candidate in embedded and mobile system specializing in embedded systems at the nelson mandela african institution of science and technology. mussa ally is a senior lecturer at the nelson mandela african institution of science and technology. silas mirau is a senior lecturer at the nelson mandela african institution of science and technology. microsoft word etasr_v13_n2_pp10453-10459 engineering, technology & applied science research vol. 13, no. 2, 2023, 10453-10459 10453 www.etasr.com alkhliwi: huffman encoding with white tailed eagle algorithm-based image steganography technique huffman encoding with white tailed eagle algorithm-based image steganography technique sultan alkhliwi department of computer science, faculty of science, northern border university, saudi arabia salkhliwi@nbu.edu.sa (corresponding author) received: 18 november 2022 | revised: 3 december 2022 | accepted: 15 february 2023 abstract since the internet is a medium for transporting sensitive data, the privacy of the message transported has become a major concern. image steganography has become a prominent tool for hiding data to ensure privacy during transfer. an efficient steganography system is essential to accomplish the best embedding capacity and maintain the other parameters at a satisfying level. image encryption systems provide a secure and flexible system to maintain the privacy of image conversion and storage in the transmission system. many existing image steganography methods can be attacked by various techniques, or do not support many image formats for embedding. to resolve these shortcomings, this study presents the huffman encoding with white tailed eagle algorithm-based image steganography (hewtea-is) technique, aiming to achieve secrecy with no compromise in image quality. the hewtea-is method uses discrete wavelet transform (dwt) for the decomposition of images into different subbands, and huffman encoding to determine the embedding bits on the decomposed blocks and offer an additional layer of security. moreover, the wtea resolves the problem of imperceptibility by identifying the optimal probable position in the cover image for embedding secret bits. the proposed algorithm was simulated and examined in terms of different measures, and an extensive experimental analysis ensured that it is superior to other methods in several aspects. keywords-image steganography; embedding process; huffman encoding; image decomposition; security i. introduction steganography is the procedure for embedding secret or confidential data in cover media such as video, text, image, and audio files. cover mediums with a higher level of redundancy are more suitable for steganography [1, 2]. a digital image can be used as a cover medium to transmit confidential data embedded in the least significant bit (lsb) of a pixel. steganography can be utilized to securely transmit and store data and can have other applications, such as content authentication, copyright protection, and data integrity assurance [3]. various data-hiding methods have been explored and several valuable steganographic methods have been proposed to improve security and protect data against unauthorized access [4, 5]. in information-hiding mechanisms, the three quality parameters considered are robustness, capacity, and imperceptibility [6]. these parameters are very important in image steganography. robustness determines the degree of security from hackers or eavesdroppers during data transmission, imperceptibility means that the hidden information and the original cover image are indistinct, and capacity defines the amount of hidden data or image size that is transferred [7-10]. an image steganography method is generally assessed from five different aspects: computational costs, perceptual transparency (visual quality), temper resistance, payload (embedding) capacity, and security. visual quality is regarded as good whenever the variance between the stego and the original image can be invisible to the human vision system (hvs) [11]. the embedding capacity is determined by the volume of data hidden in the cover images and can be measured by bits per pixel (bpp). a high payload permits a high confidential data insertion into the host images. security is the capacity of a mechanism to protect confidential data from any intruder. image steganography can provide superior imperceptibility and payload [12]. steganography methods having less distorted stego images are much more secure compared to others with more distortion, as they do not allure the attention of an intruder [13-15]. an ideal steganographic method must have a large embedding capacity and outstanding visual quality. but, as visual quality can be the inverse proportion of embedding capability, increasing one variable results in massive compromise on the other. in [16], a higher-capacity image steganography method was introduced utilizing ga. this method used lsb replacement steganography to embed confidential data. but confidential engineering, technology & applied science research vol. 13, no. 2, 2023, 10453-10459 10454 www.etasr.com alkhliwi: huffman encoding with white tailed eagle algorithm-based image steganography technique data can be modified and rearranged by previously encoding them in the lsbs of cover imageries. the variables utilized for rearranging and modifying the confidential data could be managed by the ga. a unique idea named flexible chromosomes was presented, which permitted ga to interpret chromosome values in distinct techniques. ga tried to discover the optimal variable values that have a high visual quality in the stego images. in [17], an image steganography method related to integer wavelet transform (iwt) was presented. using iwt, the cover image was converted to suppress the confidential message into the hl, hh, and lh frequency bands of the cover image. according to their most significant bits (msbs), the coefficients of these bands were labeled into 6 classes. all coefficients from various bands belonging to the same class were gathered. the embedding procedure was initiated from the highest class by supervising the coefficients to match the secret message size. in [18], an image steganography method was presented that used lsb and secret map methods by implementing 3d chaotic maps, such as 3d logistic and chebyshev maps, to improve security. this approach utilized the idea of performing random insertion and choosing a pixel from a host image. in [19], a novel hybrid technique named compressed encrypted data embedding (cede) was presented. in this method, the confidential data were initially compressed with the lempel-ziv-welch (lzw) compressing method. the compressed secret data were encoded using advanced encryption standard (aes) symmetric block ciphers. in the final stage, the encoded data were encoded into 512×512 pixel images. the encoded and compressed secret data bits were split into sets of two bits, and the cover image pixels were also ordered in four pairs. in [20], a steganography method was presented that utilized chaos theory and pso targeting to identify the optimal pixel in the cover image to hide confidential data while maintaining the prominence of the resulting stego images. to enhance embedding capacity, the secret and host images could be split into blocks that stored a suitable amount of secret bits. in [21], a dl-related steganography method was presented, using a deep supervised edge detector and cnn to retain more edge pixels than traditional edge-detection methods. the cover images were preprocessed by masking the latter 5 bits of all pixels, and the edge detector was used to obtain a grayscale edge map. in [22], emphasis was placed on improving the secret-sharing approach to enhance security along with simplicity and fast computation. this study solved certain published flaws in the share reconstruction stage by suggesting a new distribution method to increase security and authenticity. the current study proposes huffman encoding with white tailed eagle algorithm for image steganography (hewteais). this method uses the discrete wavelet transform (dwt) to decompose images into different subbands, huffman encoding to determine the embedding bits on the decomposed blocks and offer an additional layer of security, and white tailed eagle algorithm (wtea) to resolve the problem of imperceptibility by identifying the optimal probable position in the cover image to embed secret bits. the proposed method was simulated and examined with various measures. ii. proposed model the proposed hewtea-is method aims to achieve secrecy without compromising image quality. the hewteais method encompasses different subprocesses, namely dwtbased image decomposition, embedding, huffman encoding, wtea-based pixel selection, and extraction. a. image decomposition the cover image is decomposed into different subbands. wavelet transforms (wt) can be used to identify individual locations in host images to hide confidential data [23]. these regions of the host image that are minimum sensible to hvs are recognized as frequency bands. the hidden data in these bands do not degrade the quality of the visual image significantly. these bands continuously comprise data on texture, edge, and sharp transitions of images. the haar dwt coefficient was calculated horizontally and vertically. in horizontal, an image was decomposed to high-(h) and low‐ (l) frequency bands, where l was computed by taking the average of 2 sequential pixels horizontally, and h by taking the variance between them. in vertical, l and h were again decomposed into 4 distinct subbands using high-low (hl), low-low (ll), high-high (hh), and low-high (lh) by taking the average and the variance between two vertically sequential pixels. the superior magnitudes of the wavelet coefficient show the most important data of the images. the magnitudes of the ll coefficients were superior to the other subbands (hh, lh, and hl) and comprise the smooth and plane region of an image that is extremely sensitive to human eyes. thus, embedding even little data into the ll subbands results in maximum distortion. the other three subbands comprise edge details and sharp transitions in images. so, the data should be embedded in these three subbands. the haar dwt coefficient was computed using pairwise average and variance as shown in (1) and (2): ��,� = ���, ���, � �� ; ��,� = ��,���� − ��,�� (1) the inverse of haar dwt was computed by: ��,�� = ��,� + � , � ; ��,���� = ��,� − � , � (2) at this point, ��,�� , ��,���� are the sequential pixel values of cover images. b. embedding process normally, the wtea begins the search with an arbitrarily selected initial population. using a fitness function, these randomly generated solutions are evaluated throughout iterations and are enhanced via a set of formulas until an ending condition is met. however, despite the differences between population‐based methods, this technique shares baseline data. in this study, the search procedure was divided into exploration and exploitation stages [24]. exploration includes searching the region for an open location that is farther from the existing location. the exploration phase takes place when a metaheuristic algorithm tries to find a better area. at the same time, exploitation explores the near‐optimum point, focusing on the neighborhood of high-quality answers inside the search space. executing exploration alone might lead to a engineering, technology & applied science research vol. 13, no. 2, 2023, 10453-10459 10455 www.etasr.com alkhliwi: huffman encoding with white tailed eagle algorithm-based image steganography technique novel location with a poor degree of precision, while exploitation increases the risk of getting trapped in local optima. several studies emphasized the importance of balancing exploitation and exploration in metaheuristic algorithms. consequently, it is crucial to achieving an accurate balance between these two phases. this study used two different stages to carry out efficient exploitation and exploration. the wtea step‐by‐step method can be described as:  step 1 population initialization: wtea, begins the investigation via a set of randomly produced components (a set of eagles with a random location): �� = ��� + ���� × � �� − ��! �; " = 1,2, … , & (3) where ei is the location of the i-th eagle, ubi and lbi are the lower and upper boundaries, respectively, and rand represents a random number within [0,1].  step 2 population assessment: in this stage, the randomly generated solution is evaluated through a fitness function, and the eagle with optimal fitness value is selected as ebest.  step 3 searching phase (exploration): white-tailed eagles search for prey within the search region they have chosen and move in diverse directions to accelerate their hunt. this process explores different regions using its randomized operator. every eagle collaborates with the best and randomly interacts with others to upgrade the location. figure 1 shows the steps involved in wtea. this behavior is determined by: �� '( + 1) = *�� '() + 2 × �� × ��+ '() − �'()� ", �� < 0.5�� '() + 2 × �� × 1�2345'() − �! '()6 ", �� ≥ 0.5 (4) where ei(t) is the location of i-th eagle in the search space at iteration t, ebest is the location of the better eagle (adjacent to the prey), and r1 and r2 are random numbers within [0,1].  step 4 improving phase (exploitation): every eagle gets knowledge from the best candidate in the population. to improve the quality of the wtea solution, every eagle interacts with the better eagle of the swarm ebest, which has the highest influence on others to discover the prey: �� '( + 1) = ���� × �2345'() + ���� × ��2345 '() − �� '()� (5)  step 5 movement limitation: in all iterations, wtea alters the distance every eagle moves through every dimension of the scratch region. equations (4) and (5) show that eagle movement is a stochastic parameter and could allow the eagle to follow a large distance. consequently, to accomplish this oscillation and prevent the eagle divergence, any eagle that goes beyond the search space limit would be reproduced based on: �� = 8��� ", �� ≤ ��� �� ", �� ≥ ���! otherwise (6) this model is used to select the best pixels to hide private information [25]. the optimum location is found by using the wtea approach that implements initialization by arbitrarily choosing particles and later searching for the better fit by upgrading each particle position. initially, the population is chosen at random, and the location is upgraded through the objective function. next, the better solution gets recognized to embed information. the original cover image is considered as o with m×n dimensions. usually, the image can be described by a spatial representation. dwt is applied to convert them into a frequency domain. then, the image undergoes sampling and decomposition to provide a higher degree of robustness as: bc�c�cdcef = �gh'c) (7) where o1 represents the coefficient of the lower frequency band and comprises each substantial data of the image, o2, o3, and o4 indicate the higher‐frequency bands and represent data such as edges of the image. the o1 band is carefully chosen for additional processing and the coefficient is extracted as: bc�ii c�ij c�ji c�jj f = �gh'c�) (8) where c�ii indicates the low-frequency subband, and c�ij , c�ji , and c�jj denote the high-frequency subbands of o1. then, the stego image is created by: k�∗! = k�! + ��� × mno5 � (9) where dj indicates the secret textual information, and popt is the optimal location for embedding the information. inverse dwt is executed to characterize the image after data hiding: c�∗∗ = p�gh'c�∗iic�∗ijc�∗ji c�∗jj ) (10) the embedded secret information with the adapted band is: c∗∗ = p�gh'c�∗∗c�cdce) (11) fig. 1. steps involved in wtea c. huffman encoding huffman coding is a lossless data compression technique. its objective is to allocate parameter-length code to input characters, as the length of the assigned code depends on the engineering, technology & applied science research vol. 13, no. 2, 2023, 10453-10459 10456 www.etasr.com alkhliwi: huffman encoding with white tailed eagle algorithm-based image steganography technique frequency of the characters [26]. the more common character gets a smaller code, and the less common character gets a larger one. the parameter length code assigned to each input character is a prefix code, which implies that a code is assigned so that it is not the prefix assigned to any other. huffman coding ensures that there is no ambiguity while decoding the bit stream. 1. generate a leaf node for all input characters and construct a minimum heap of each leaf node. 2. for the minimum heap, obtain the topmost two nodes (n1 and n2) with the least frequency. 3. generate a novel internal node n3 with a frequency equivalent to the sum of frequencies of nodes n1 and n2. make n1 the left and n2 the right child of n3. a new node n3 is added to the minimum heap. 4. repeat steps 2 and 3 until the minimum heap has a single node. d. extraction process the objective is to successfully extract the secret messages from the input stego images on the receiver. the stego image undergoes dwt to transform it from spatial to frequency representation. the stego images are indicated as o **r : bc�∗∗q c�∗∗q cd∗∗qce∗∗q f = �gh'c∗∗q) (12) the modified band is c�∗∗q, therefore the coefficient of the sub‐ band is: rs�iit∗ c�ijt∗ 0�jit∗ c�jjt∗ u = �gh'c�∗∗q ) (13) next, match the secret key and once it matches, the original secret message is extracted. wtea is applied to locate the position of hidden information, and huffman decoding is applied to extract the secret message. thus, the stego image is attained in binary format. when the secret keys don’t match, an encrypted image is received. the encrypted images are produced for adding another level of security to the system. iii. results and discussion this section examines the security performance of the hewtea-is algorithm on several images from the usc-sipi repository [27]. the experimental values were assessed under varying message sizes (ms).table i shows a result analysis of the hewtea-is method under variable message sizes and images. the hewtea-is model showed a good performance in all images. figure 3 provides the results of the hewtea-is method with different message sizes using image 1. in this image, the hewtea-is method gained an average mse of 0.00012, an average psnr of 126.36db, an average ber of 0.033, and an average ssim of 0.9993. figures 4, 5, and 6 show the results of the hewtea-is method with different message sizes in images 2 and 3. in these images, the hewtea-is system achieved average mse of 0.00011, 0.00013, and 0.00012, average psnr of 127.05, 126.18, and 126.94db, average ber of 0.035, 0.0034, and 0.032, and average ssim of 0.9995, 0.9994, and 0.9995, respectively. table i. results analysis of hewtea-is approach with distinct images and measures images message size (kb) mse psnr (db) ber ssim image 1 50 0.00012 126.55 0.028 0.9992 100 0.00011 127.30 0.035 0.9993 150 0.00014 125.21 0.031 0.9995 200 0.00015 124.61 0.042 0.9991 250 0.00010 128.13 0.031 0.9994 average 0.00012 126.36 0.033 0.9993 image 2 50 0.00011 127.30 0.038 0.9994 100 0.00010 128.13 0.034 0.9992 150 0.00014 125.21 0.038 0.9998 200 0.00011 127.30 0.029 0.9995 250 0.00011 127.30 0.036 0.9996 average 0.00011 127.05 0.035 0.9995 image 3 50 0.00011 127.30 0.039 0.9991 100 0.00015 124.61 0.037 0.9998 150 0.00013 125.85 0.032 0.9997 200 0.00011 127.30 0.030 0.9992 250 0.00013 125.85 0.034 0.9992 average 0.00013 126.18 0.034 0.9994 image 4 50 0.00010 128.13 0.032 0.9998 100 0.00015 124.61 0.029 0.9992 150 0.00011 127.30 0.034 0.9997 200 0.00012 126.55 0.031 0.9994 250 0.00010 128.13 0.036 0.9992 average 0.00012 126.94 0.032 0.9995 fig. 2. classification analysis of the hewtea-is algorithm in image 1: (a) mse, (b) psnr, (c) ber, (d) ssim. table ii shows the comparative results of the hewtea-is with other recent methods, and figure 7 shows a visual psnr analysis of hewtea-is with them. the hewtea-is achieved the highest psnr value of 126.634db, hpso and huffman-pso models had close psnr values, while the psodwt and pso algorithms had the least psnr values. figure 8 shows a comparative ssim investigation of the hewtea-is. the hewtea-is had the highest ssim of 0.9994, the hpso and huffman-pso algorithms had close ssim values, while pso-dwt and pso had the least ssim. engineering, technology & applied science research vol. 13, no. 2, 2023, 10453-10459 10457 www.etasr.com alkhliwi: huffman encoding with white tailed eagle algorithm-based image steganography technique fig. 3. classification analysis of the hewtea-is algorithm in image 2: (a) mse, (b) psnr, (c) ber, (d) ssim. fig. 4. classification analysis of the hewtea-is algorithm in image 3: (a) mse, (b) psnr, (c) ber, (d) ssim. fig. 5. classification analysis of the hewtea-is algorithm in image 4: (a) mse, (b) psnr, (c) ber, (d) ssim. table ii. comparison of hewtea-is with other methods methods mse psnr (db) ber ssim hewtea-is 0.00012 126.634 0.0338 0.9994 pso 4.26800 35.526 0.0520 0.9597 hpso 0.00200 102.110 0.0492 0.9857 pso-dwt 0.73000 50.864 0.0498 0.9764 huffman-pso 0.00020 122.110 0.0413 0.9935 fig. 6. psnr analysis of the hewtea-is with recent methods. fig. 7. ssim analysis of the hewtea-is with other methods. figure 9 shows a detailed ber comparison of the hewtea-is. the hewtea-is had the least ber of 0.0338, while pso, hpso, pso-dwt, and huffman-pso had increased ber of 0.0520, 0.0492, 0.0498, and 0.0413, respectively. these results affirmed the superiority of the hewtea-is method. fig. 8. ber analysis of the hewtea-is with other methods. engineering, technology & applied science research vol. 13, no. 2, 2023, 10453-10459 10458 www.etasr.com alkhliwi: huffman encoding with white tailed eagle algorithm-based image steganography technique iv. conclusion this study presented the novel huffman encoding with white tailed eagle algorithm for image steganography (hewtea-is) with the purpose of achieving secrecy without compromising image quality. the proposed method used discrete wavelet transform (dwt) for the decomposition of images into different subbands, huffman encoding to determine the embedding bits on the decomposed blocks and offer an additional layer of security, and wtea to resolve the problem of imperceptibility by identifying the optimal positions in the cover images for embedding secret bits. the proposed method was experimentally analyzed and compared to other recent methods in several aspects, showing its superiority. in the future, the hewtea-is can be extended to audio messages. references [1] b. lakshmi sirisha and b. chandra mohan, "review on spatial domain image steganography techniques," journal of discrete mathematical sciences and cryptography, vol. 24, no. 6, pp. 1873–1883, aug. 2021, https://doi.org/10.1080/09720529.2021.1962025. 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[26] g. p. pandey, "implementation of dna cryptography in cloud computing and using huffman algorithm, socket programming and new approach to secure cloud data." rochester, ny, aug. 07, 2019, https://doi.org/10.2139/ssrn.3501494. [27] "sipi image database." https://sipi.usc.edu/database/database.php. engineering, technology & applied science research vol. 13, no. 2, 2023, 10453-10459 10459 www.etasr.com alkhliwi: huffman encoding with white tailed eagle algorithm-based image steganography technique authors profile sultan alkhliwi received his b.e. degree from the northern border university in 2008. he received an m.sc. and ph.d. from the university of manchesteru.k in 2013 and 2018, respectively. currently, he works as an assistant professor in computer science department, faculty of science, northern border university, saudi arabia. his research interests include multi-hop communication networks, cryptography, network security, and information security. microsoft word etasr_v12_n6_pp9570-9578 engineering, technology & applied science research vol. 12, no. 6, 2022, 9570-9578 9570 www.etasr.com amraoui & saadi: a novel approach on speaker gender identification and verification using dwt … a novel approach on speaker gender identification and verification using dwt first level energy and zero crossing abdelkader amraoui laboratory of applied automation and industrial diagnostics, faculty of sciences and technology, ziane achour university of djelfa, djelfa, algeria kader2717@yahoo.fr slami saadi department of computer sciences, faculty of exact sciences and informatics, ziane achour university of djelfa, djelfa, algeria s.saadi@univ-djelfa.dz received: 18 august 2022 | revised: 3 september 2022 | accepted: 5 september 2022 abstract-the aim of this work is to find a new criterion for determining a range of values in order to determine the gender of a speaker. the use of the discrete wavelet transform (dwt) of the daubechies db7 parent wavelet and the computation of the zero crossing energy from the first level of the dwt was followed by computation of the values of the criterion for both genders and comparison with the value of the speech basic frequency for both genders for the same sign or sentence. the standard has a limited range of values close to the basic frequency range of the same speaker through which we can determine gender. this criterion has been tested on several men and women databases with different repeated sentences for the same person or for both genders and it gives acceptable results that can be worked on. keywords-speaker gender; dwt; energy; zero crossing i. introduction the difference in the linguistic characteristics of humans is characterized by the variance in frequencies of the two genders. generally, the frequencies of women are smaller than those of men. usually, the sound consists of vibrations with different lengths and heights. as the human ear cannot hear all the vibrations, some of them are audible, i.e. from 20hz to 20khz, and some are inaudible. frequencies smaller than 20hz are inaudible and frequencies larger than 20khz are inaudible and painful to the human ear. of course, as we get older, the limit of hearing drops, sometimes to 17khz [1]. the speech signal is non-stationary, complex, and variable with time [2]. in addition, the highest frequency of the speech signal is in the order of 5khz. the operations done on this signal, such as sampling, require frequencies according to shannon’s law that the sampling frequency is more than twice the frequency of the original signal under study. many research works have formerly addressed the study and determination of the range of f0 values [3], which dealt with extracting the basic frequency in the domains of time and frequency as well as wavelets. in addition, some research works deal with a comparison between estimation methods for computing the fundamental for a newborn. in [2], the authors presented techniques for determining the frequency position in time. other research works [4-6] were interested by this subject, on which researches are still developing since it is not possible to confirm definitively the criterion that determines the gender of the speaker according to the basic frequency domain. authors in [7] present an efficient approach for automatic speaker identification based on cepstral features, the normalized pitch frequency (npf) with discrete cosine transform (dct) and wavelet de-noising pre-processing. on the other hand, wavelet based features in combination with spectral-subtraction (ss) were proposed in [8] for speaker identification in clean and noisy environment. using neural networks for speech recognition tasks, where words are constructed from sequential individual and text-independent sound segments was addressed in [9] for speaker identification. to reduce memory utilization for speaker audio segment identification, authors in [10] proposed a new on line speaker identifier model using short input audio segments. extracting features from raw speech that captures the unique characteristics of each speaker is accomplished by the filter bank-based mel frequency cepstral coefficients (mfcc) approach [11] using discrete wavelet transform (dwt). the average framing linear prediction coding (aflpc) technique combined with wavelet transform for text-independent speaker identification systems was presented in [12]. extracting features from raw speech that capture the unique characteristics of a particular individual using wavelet packet transform (wpt) is presented in [13]. authors in [14] identify speakers basing on cepstral feature strategy and the npf as a new feature, for enhancing accuracy using neural networks (nn). a motivating application of speech signals identification, for the detection of people with heart failure by glottal features, was presented in [15]. a robust feature extraction method for a real-time speech recognition hardware system was presented in [16]. in the current work, a novel approach for speaker gender identification and verification is introduced. this new criterion is based on dwt and the intersections with zero of the dwt first level for both genders with comparison to speech fundamental frequency. the simulation results prove that the proposed approach enhances the performance of speaker corresponding author: slami saadi engineering, technology & applied science research vol. 12, no. 6, 2022, 9570-9578 9571 www.etasr.com amraoui & saadi: a novel approach on speaker gender identification and verification using dwt … identification, especially with the dwt and the de-noising preprocessing step. ii. speech signal characteristics the speech signal is an audio carrier of complex and diverse information and has features such as the fundamental frequency characteristic, which is often denoted by f0. other characteristics are the energy and the frequency spectrum [17]. the vibration or the cycle of opening/closing of the vocal cords represents f0. this frequency characterizes only the voiced segments and evolves slowly over time [17]. the speaker frequency varies according to age and gender. it extends approximately from 60hz to 150hz for men and from 150hz to 450hz for women. the fundamental frequency extraction is not an easy task since the periodicity of vibration of the vocal cords is not always perfect [6]. the amplitude of the speech signal changes significantly over time and in the audible speech. this amplitude is much greater than in the inaudible speech and reflects to us the energy changes in the signal. one of the characteristics of the speech signal is the energy feature, usually symbolized by e, computed according to (2). this energy is very high in audible sounds compared to inaudible sounds in which the energy is weak [18]. e� � ∑ �x�n �� � � (1) according to the scheme shown in figure 1, we symbolize the standard called wavelet energy rate (wer), which is applied to the first dwt level of the speech signal under study. this signal is a spoken sentence by some speakers of different genders containing repeated and different sentences. these are samples taken from a database that was prepared specifically for this study: videos of sentences in mp4 format were taken from people of both genders. these videos are downloaded and the spoken sentences were converted to wav format. each sentence was sampled separately according to the sampling frequency fe =11025hz, which is a frequency greater than double the frequency of the speech signal (5khz) on the basis of shannon's law. iii. filtering the filtering step is accomplished through a mathematical transformation applied on the speech signal under study using a low pass filter with cutoff frequency f� � 600hz. this low pass filter reduces the signal high frequency to �10log10 (2)db in the order of -3db, which means decreasing the signal output energy to the 71% of the original speech signal [19]. among the most widely used filters are the butterworth linear filters, which are similar in shape with a difference in the cut-off frequency range. this filter has the largest amplitude and is more stable with frequency in the pass range and in the transition region with moderate reduction and is selected based on amplitude accuracy [20]. the filter order represents the number of columns in the filter pass region. for example, a filter of order n has a reduction rate of 6×n db/decade to 20×n/decade. when n=8 its reduction is 48db/ decade [20]. fig. 1. general scheme. fig. 2. filtered speech signal. iv. discrete wavelet transform dwt is based on sub-band coding, and developed after that to be a technique similar to sub-band coding called hierarchical coding [21]. it is identified by the following relationship [22]: x����n� � x�n� ∗ h�n� � ∑ x�k� ∗ h�n � k� � �� � (2) dwt analyzes the original signal x(n) in different frequency bands with different degrees of accuracy by evaluating the signal into approximate and detailed coefficients where the approximate coefficients have the highest amplitude, the lowest frequencies, and possess most of the energy. the components of the highest frequencies are mixed with the noise existing in the original signal. engineering, technology & applied science research vol. 12, no. 6, 2022, 9570-9578 9572 www.etasr.com amraoui & saadi: a novel approach on speaker gender identification and verification using dwt … (a) (b) fig. 3. first level signal dwt decomposition after filtering. (a) approximation part a1 of speech signal, (b) detail part of speech signal d1. as previously mentioned, the dwt uses digital filtering techniques, in which the signal to be analyzed passes through filters with different cut-off frequencies at different scales. the original signal is divided into details coefficients and approximation coefficients, which are often denoted by ak and dk respectively, where d denotes the detailed coefficients and a denotes the approximate coefficients, while k denotes the analytical level. the two parameters are the result of the convolution of the original signal x(n) with the pass filter, meaning that the approximate parameters are the result of the low pass filter convolution with the original signal and the detailed parameters are the convolution of the high pass filter with the original signal [24]. a1 � ∑ x�k y�2n � k���� � (3) d1 � ∑ x�k z�2n � k�∞�� ∞ (4) in the waveform analysis, the signal is analyzed and synthesized according to stages starting from dividing the signal x(n) to the end of the required level and rebuilding it from the last level we stopped to the end of the first level from which we started. for example, if the original signal x(n) contains 512 samples and a frequency from 0 to π, then each of the approximate and detailed coefficients in the first level has 256 samples and one half(1/2) the frequency of the signal, i.e. π/2, and in the second level there are 128 samples and the half frequency of the signal level, i.e. f = π/4 or ¼ of the original signal frequency for both approximate and detailed parameters. as mentioned above, the wavelet transform has more flexibility in designing the pulse shape and less sensitivity to signal distortion. the dwt analyzes the original signal x(n) in different frequency bands with different degrees of accuracy by analyzing the signal into approximate coefficients and detailed coefficients. the approximate coefficients have the highest amplitude and components of low frequencies and possess most of the signal energy. it is known that the speech signal is continuous and the fundamental frequency of a man’s voice is around 50hz (with period t = 20ms) whereas the f0 of a woman’s voice is near 180hz, with a period t = 250ms. also, the basic frequency for the voice of a woman and of a man rises to 500hz and to 200hz respectively. v. intersections with zero intersections with zero is the number of the times the signal x(n) passes through zero in a certain period of time. it is an indication of the frequency at which the energy is concentrated in the signal spectrum, as the energy is concentrated at low frequencies in audible speech, while in inaudible speech most of it is found in high frequencies. from this, the highest number of intersections with zero is at high frequencies and the lowest is at low frequencies [18]. we can say that the intersection of the signal with zero has a strong relationship with the distribution of energy with frequency. the number of intersections with zero is computed for the signal according to [25]: npz = ��� ∑ |sgn�x(n)� − sgn�x(n − 1)�|� ���* (5) sgn�x(n)� = + +1x(n) ≥ 0 −1x(n) < 0 (6) vi. the proposed wavelet energy rate (wer) the wer criterion is calculated according to (7). this new criterion allows us to determine the gender of the speaker based on the studied values. wer is the quotient of the energy ea1 obtained from the approximation coefficient of the first level of the dwt applied on the signal x(n) according to (8) divided by npz: wer = 234�56 × tpz (7) e9� = ∑ �a1(n) �� �� (8) where a� is the dwt first level, ea1 the dwt first signal approximation of coefficients energy, npz the dwt first level signal approximation of coefficient intersections with zero, and tpz the intersection ratio with zero for the original signal. the value of the wer criterion is distributed over a defined range from 50 to 180hz for men and from 180 to 500hz for women. these values are similar to the fundamental frequency of the speech signal f0, which determines the gender of the speaker as a first process, before identifying the speaking person by comparison with other values in our previously prepared database. vii. used computation tools ιn our investigation, we used kvideo downloader4 program to download english learning videos in mp4 format 0 0.5 1 1.5 2 2.5 x 10 4 -8 -6 -4 -2 0 2 4 6 8 x 10 -4 0 0.5 1 1.5 2 2.5 x 10 4 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 engineering, technology & applied science research vol. 12, no. 6, 2022, 9570-9578 9573 www.etasr.com amraoui & saadi: a novel approach on speaker gender identification and verification using dwt … from an internet database. then, these clips were converted to wav format using on line covertio and on line cloud convert. the obtained signal was sampled into some specific sentences using the audacity program by a sampling frequency fe=11025hz to be analyzed and studied by the matlab a13 toolbox on a compute with the following specifications: pc acer based on x67, processor: intel® core™ i3-2348m, cpu: n2.30ghz, version smbios 2.7, operating system: windows 10 viii. experimental results through the obtained experimental results presented below, the developed approaches were applied on some different repeated sentences from male and female speakers. we run 200 experiments on the speech signal to extract about 4500 different values, after filtering the speech signal with a butterworth filter of degree n=8 and sampling frequency fe=11025hz. this signal was analyzed to the first level by dwt seventh partition (db7). the number of intersections with zero to be multiplied by the ratio of the original signal intersections with zero, according to (7) and (8) are shown in table i. through tables i and ii, it was found that the energy of the original signal has different values in the two genders. the energy of the original signal for men is much greater than for women and this happens for the same repeated sentence, several different sentences for the same woman or the same man, or using the same sentence for several women and several men, as shown in figure 9. e:; ≫ e:= (9) where e:; is the energy of the original signal for men and e:= the energy of the original signal for women. table i. a sentence repeated for the same person and for several people (4 women and 3 men) a sentence repeated for the same person and for several people (4 women and 3 men) "do you speak english" signal sample number energy signal energy >?@ zcn signal abc?@ abd?@ women woman a 601 22243 879380 28077000 1268 4405.3 0.0570 woman a 602 21060 833610 25851000 1224 4282.3 0.0581 woman b 201 12487 271940 9406900 740 2623.8 0.0592 woman b 203 12820 275960 10579000 811 2874.1 0.0632 woman d 301 12449 1795300 9581200 768 2701.7 0.0617 woman d 302 12793 2313000 10444000 815 2885.4 0.0637 woman m 1000 15493 577710 11501000 723 2600.5 0.0467 woman m 1003 15988 583980 12943000 795 2833.3 0.0497 men man b 101 13292 5851300 6844900 526 1790.1 0.0396 man b 102 13667 6016100 7346700 538 1864.2 0.0394 man k 100 11341 317560 4442000 391 1371.3 0.0345 man w 400 11685 773940 4254200 364 1285.6 0.0311 man w 401 11638 425690 4075200 354 1245.3 0.0304 fig. 4. man b101 speech signal analysis (original, filtered, dwt decomposed, and energy spectrum), sentence: "do you speak english"? 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -1 0 1 time(s) a m p li tu d e wav b 101 for a man voice original signal 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -1 0 1 time(s) a m p li tu d e wav b 101 for a man voice filtered signal 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -2 -1 0 1 time(s) a m p li tu d e wav b 101 for a man voice nv1 wavelet db7 0 2000 4000 6000 8000 10000 12000 14000 0 0.5 1 1.5 wav b 101 for a man voice energie engineering, technology & applied science research vol. 12, no. 6, 2022, 9570-9578 9574 www.etasr.com amraoui & saadi: a novel approach on speaker gender identification and verification using dwt … fig. 5. woman b601 speech signal analysis (original, filtered, dwt decomposed, and energy spectrum), sentence: "do you speak english"? fig. 6. woman b201 speech signal analysis (original, filtered, dwt decomposed, and energy spectrum), sentence: "do you speak english"? 0 0.5 1 1.5 2 2.5 -0.5 0 0.5 time(s) a m p li tu d e wav a601 for a woman voice original signal 0 0.5 1 1.5 2 2.5 -0.5 0 0.5 time(s) a m p li tu d e wav a601 for a woman voice filtered signal 0 0.5 1 1.5 2 2.5 -0.5 0 0.5 time(s) a m p li tu d e wav a601 for a woman voice nv1 wavelet db7 0 0.5 1 1.5 2 2.5 x 10 4 0 0.05 0.1 wav a601 for a woman voice energie 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -0.5 0 0.5 time(s) a m p li tu d e wav b 201 for a woman voice original signal 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -0.2 0 0.2 time(s) a m p li tu d e wav b 201 for a woman voice filtered signal 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -0.5 0 0.5 time(s) a m p li tu d e wav b 201 for a woman voice nv1 wavelet db7 0 2000 4000 6000 8000 10000 12000 14000 0 0.05 0.1 wav b 201 for a woman voice energie engineering, technology & applied science research vol. 12, no. 6, 2022, 9570-9578 9575 www.etasr.com amraoui & saadi: a novel approach on speaker gender identification and verification using dwt … fig. 7. comparison between woman a601 and woman b201 speech signal analysis (original, filtered, dwt decomposed, and energy spectrum), sentence: "do you speak english"? fig. 8. comparison between woman b201 and man b101 speech signal analysis (original, filtered, dwt decomposed, and energy spectrum), sentence: "do you speak english"? in the approximate coefficient a1 signal, in the first level of the dwt, we find that the energy ea1 for women is greater than the energy for men and this is for the same repeated sentence or several different sentences for the same woman or the same man as shown in tables i and ii and figure 10, or for a repetitive sentence or several different sentences for several women and several men: e9�; ≫ e9�= (10) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -0.5 0 0.5 time(s) a m p li tu d e wav b 201 for a woman voice original signal 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -0.2 0 0.2 time(s) a m p li tu d e wav b 201 for a woman voice filtered signal 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -0.5 0 0.5 time(s) a m p li tu d e wav b 201 for a woman voice nv1 wavelet db7 0 2000 4000 6000 8000 10000 12000 14000 0 0.05 0.1 woman a 601 wav b 201 for a woman voice energie 0 0.5 1 1.5 2 2.5 -0.5 0 0.5 time(s) a m p li tu d e wav a601 for a woman voice original signal 0 0.5 1 1.5 2 2.5 -0.5 0 0.5 time(s) a m p li tu d e wav a601 for a woman voice filtered signal 0 0.5 1 1.5 2 2.5 -0.5 0 0.5 time(s) a m p li tu d e wav a601 for a woman voice nv1 wavelet db7 0 0.5 1 1.5 2 2.5 x 10 4 0 0.05 0.1 wav a601 for a woman voice energie 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -0.5 0 0.5 time(s) a m p li tu d e wav b 201 for a woman voice original signal 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -0.2 0 0.2 time(s) a m p li tu d e wav b 201 for a woman voice filtered signal 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -0.5 0 0.5 time(s) a m p li tu d e wav b 201 for a woman voice nv1 wavelet db7 0 2000 4000 6000 8000 10000 12000 14000 0 0.05 0.1 man b 101 wav b 201 for a woman voice energie 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -1 0 1 time(s) a m p li tu d e wav b 101 for a man voice original signal 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -1 0 1 time(s) a m p li tu d e wav b 101 for a man voice filtered signal 0 0.2 0.4 0.6 0.8 1 1.2 1.4 -2 0 2 time(s) a m p li tu d e wav b 101 for a man voice nv1 wavelet db7 0 2000 4000 6000 8000 10000 12000 14000 0 1 2 wav b 101 for a man voice energie engineering, technology & applied science research vol. 12, no. 6, 2022, 9570-9578 9576 www.etasr.com amraoui & saadi: a novel approach on speaker gender identification and verification using dwt … where e9�; e9�= represent the energy of the approximate coefficient a1 for men and women respectively. fig. 9. comparison of the signal energy between a man and a woman. fig. 10. comparison of the energy of the dwt first level signal between a man and a woman. it is noticeable that the number of intersections with zero (zero crossing number-zcn) in the original signal differs for the two genders with diverse values. the zcn of the original signal for men is much greater than for women, and for the same repeated sentence, several different sentences for the same woman or the same man, and for several different sentences and several men/women as shown in tables i-ii and figure 11. npz:= ≫ npz:; (11) where npz:; is the intersection of the original signal with zero for men and npz:= for women. fig. 11. zcn comparison of for the signal between a man and a woman. fig. 12. zcn comparison of in the dwt first level for the signals of a man and a moman. on the other hand, for the approximate coefficient a1 signal in the first level of the dwt, we find that the zero crossing npza1f and the zero crossing ratio (zcr) for women is greater than that for men, for the same repeated sentence, several different sentences for the same woman, or for a repeated sentence or for different sentences for a number of men and women, as shown in tables i-ii and figure 12. through figure13, we conclude that the crossing ratio with zero for the same level is greater for women than for men. npz9�= ≫ npz9�; (12) where efgh�i and efgh�j represent the crossing with zero of a1 signal for men and women respectively. fig. 13. comparison of zcr in the dwt first level for the signal of a man and a woman. table ii. wer comparison for men and women signal sample number energy signal energy signal kh� lmnh� lmoh� wer 4 women and 2 men with the same sentence: "do you speak english"? repeated 3 times woman a 601 22243 879380 28077000 4405.3 0.0570 363.3295 woman a 602 21060 833610 25851000 4282.3 0.0581 350.8538 woman b 201 12487 271940 9406900 2623.8 0.0592 212.4698 woman b 202 12645 274830 9855600 2715.3 0.0606 219.8762 woman d 301 12449 1795300 9581200 2701.7 0.0617 218.7851 woman d 302 12793 2313000 10444000 2885.4 0.0637 230.6052 woman m1000 15493 577710 11501000 2600.5 0.0467 206.3805 woman m1003 15988 583980 12943000 2833.3 0.0497 227.1477 man b 101 13292 5851300 6844900 1790.1 0.0396 151.3138 man b 104 13666 6009400 7216300 1827.3 0.0391 154.3159 man k 100 11341 317560 4442000 1373.3 0.0345 111.5123 man w 400 11685 773940 4254200 1285.6 0.0311 103.0833 man w 401 11638 425690 4075200 1245.3 0.0304 99.5563 4 women with the same sentence: "see you later" woman a 2001 13595 420980 12289000 3129.3 0.0664 260.8490 woman b 2003 9503 311870 6561400 2401.4 0.0721 197.2349 woman d 402 5277 5571700 1748100 1171.4 0.0627 93.6040 woman m 3002 10365 322280 5379100 1826.2 0.0506 149.1963 man c201 12686 5501500 7000400 1923.6 0.0436 158.6357 women and men with different sentences woman a 401 20629 699960 24785000 4187.6 0.0583 345.1550 woman a 901 12242 306010 9660000 2726 0.0649 230.1245 woman a 803 9077 237420 5131100 1984.3 0.0622 160.9541 woman a 202 13809 374400 12119000 3059.5 0.0632 250.4241 woman a 101 12444 388450 10553000 2946.0 0.0676 242.3755 woman b 402 12880 486000 8577500 2319.3 0.0497 183.7694 woman b 501 8002 132600 5120800 2172.6 0.0813 191.7493 woman b 802 20612 662150 23670000 3982.7 0.0552 328.4199 woman b 901 11119 258280 7549900 2346.7 0.0620 199.6459 womanb 3003 13112 247580 11385000 3006.3 0.0665 251.8563 woman d 502 10428 2916500 7576900 2519.8 0.0696 209.3417 woman d 202 11089 1078200 7591400 2390.4 0.0617 195.8928 woman d 001 12320 1556200 9288400 2666.1 0.0613 213.5040 man b 501 13160 2597500 8359000 2153.7 0.0487 189.0446 man b 904 10492 2106500 3325500 1081.8 0.0299 92.0017 man b 144 11025 2578600 5503800 1718.6 0.0455 145.8184 man b1004 10227 2481400 4480800 1520.2 0.0434 127.9606 man b193 10998 2365600 5382100 1678.9 0.0446 143.1177 man x102 8405 391600 5291400 2182.7 0.0748 181.4226 man x 100 14152 1428800 13458000 3296.2 0.0668 272.9188 man c100 11710 2518300 3975700 1196.7 0.0292 97.0313 engineering, technology & applied science research vol. 12, no. 6, 2022, 9570-9578 9577 www.etasr.com amraoui & saadi: a novel approach on speaker gender identification and verification using dwt … fig. 14. comparison of wer for different speakers of both sexes. the values shown in table ii give us the wer values for the studied speech signals x(n). the signal is a repeated sentence for the same woman or the same man, the same sentence for several men and several women, or a speech signal containing different sentences for several men and several women, as shown in figure 14. a comparison of these values in relation to the range of the fundamental frequency f0 values in recently published research works was made. the result is that the wer criterion provides values approximately close to the values of f0 for speakers of different sentences and gender. accordingly, we can through wer specify values in a range from 50 to 180hz for male speakers and values in a range from 180 to 504hz for female speakers, which are almost similar to the range of fundamental frequency values which determine the speaker gender according to the value of his/her fundamental frequency using different methods. the direct computational speed of the wer is a faster and easier way to determine the gender of a speaker. table ii illustrates the comparison between wer values and figure 14 shows their progress. after this stage, which determines the gender of the speaker, the next stage of verifying the speaker is followed by reference to our stored database, according to the comparison process based on a suitable algorithm to authenticate and confirm the speaker as shown by the flowchart in the general scheme of figure 1. ix. conclusion in speech investigation, gender identification is usually performed by extracting the information from the speech signals. in this paper, we propose a novel criterion for determining the speaker gender by defining a range of sampled values using the discrete wavelet transform (dwt), and computing the energy in addition to the intersections with zero (zcr) of the first level dwt followed by estimating the introduced criterion (wer) values for both genders. comparison was made with the value of the speech fundamental frequency for speakers of both sexes. the proposed criterion was tested on a large database prepared for this research, containing many repeated sentences from the same person and from persons of both sexes and gives acceptable results, proving its suitability for speaker gender identification. acknowledgment the authors would like to thank the laadi research laboratory for the technical support. references [1] l. jeancolas, "détection précoce de la maladie de parkinson par l’analyse de la voix et corrélations avec la neuroimagerie," ph.d. dissertation, paris-saclay university, paris, france, 2019. 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[25] k. tajane, r. pitale, and j. umale, "review paper :comparative analysis of mother wavelet functions with the ecg signals," international journal of engineering research and applications, vol. 4, no. 1, pp. 38–41, jan. 2014. microsoft word etasr_v12_n2_pp8366-8373 engineering, technology & applied science research vol. 12, no. 2, 2022, 8366-8373 8366 www.etasr.com bhalekar & bedekar: d-cnn: a new model for generating image captions with text extraction using … d-cnn: a new model for generating image captions with text extraction using deep learning for visually challenged individuals madhuri bhalekar school of computer engineering and technology mit world peace university pune, india madhuri.bhalekar@mitwpu.edu.in mangesh bedekar school of computer engineering and technology mit world peace university pune, india mangesh.bedekar@mitwpu.edu.in received: 24 january 2022 | revised: 14 february 2022 | accepted: 22 february 2022 abstract-automatically describing the information of an image using properly constructed sentences is a tricky task in any language. however, it has the potential to have a significant effect by enabling visually challenged individuals to better understand their surroundings. this paper proposes an image captioning system that generates detailed captions and extracts text from an image, if any, and uses it as a part of the caption to provide a more precise description of the image. to extract the image features, the proposed model uses convolutional neural networks (cnns) followed by long short-term memory (lstm) that generates corresponding sentences based on the learned image features. further, using the text extraction module, the extracted text (if any) is included in the image description and the captions are presented in audio form. publicly available benchmark datasets for image captioning like ms coco, flickr-8k, flickr-30k have a variety of images, but they hardly have images that contain textual information. these datasets are not sufficient for the proposed model and this has resulted in the creation of a new image caption dataset that contains images with textual content. with the newly created dataset, comparative analysis of the experimental results is performed on the proposed model and the existing pre-trained model. the obtained experimental results show that the proposed model is equally effective as the existing one in subtitle image captioning models and provides more insights about the image by performing text extraction. keywords-image captioning; text extraction; convolutional model; long short-term memory; deep learning i. introduction image captioning is one of the numerous computer vision tasks that have been aided by deep learning. image captioning is helpful to annotate objects which might be overlooked by a human observer. it can be useful when images are extremely cluttered and it is difficult to recognize objects in them. currently, the majority of research is done with image description, which can be extended on scene comprehension through images and videos. with domain-specific image captioning datasets (such as sports, night vision images, forest animal images, etc.) we can further improve the accuracy of a captioning system. in the existing available research, the textual part present in an image is not considered while generating its caption. considering this research gap, the objective of the proposed system is to generate a new image captioning dataset and to perform more prescribed image captioning with text extraction from the image and including the extracted text in generated captions. the proposed system can be deployed as a mobile application where the user takes a photograph as an input image and the system generates the description of the image. this will be helpful as a smart assistant for children and especially for visually challenged people. the proposed system can also be deployed on robots to help them understand their surroundings. it can be used even in an application to identify famous objects for a tourist who goes without a tour guide. the user can capture the monument or artifact in his mobile phone camera and the application displays relevant information in the form of text. ii. related work μany different architectures have been proposed for generating captions for a given image. authors in [1] presented an image captioning system that takes advantage of image and sentence parallel structures. it also introduces scene-specific contexts, resulting in a novel model. for an input image, it finds visual regions and generates words for these regions, and performs alignment between visual regions and words. the attention model aligns words and regions very well. authors in [2] proposed a two-stage image captioning module which consists of detectors. a collection of attribute classifiers is applied to each candidate object region and the sentences are constructed using a conditional random field (crf) to predict labelling for an input image. for experimentation they used the uiuc pascal dataset. this approach can be further extended to accommodate more general image contents, such as actions and scenes, and can also be used to describe video content. in [3], the authors proposed a system in which region-wise natural language descriptions of the images are generated. the suggested model is a novel combination of cnns applied on images and bidirectional recurrent neural networks (brnns) corresponding author: madhuri bhalekar engineering, technology & applied science research vol. 12, no. 2, 2022, 8366-8373 8367 www.etasr.com bhalekar & bedekar: d-cnn: a new model for generating image captions with text extraction using … applied on text and the alignment of these two models is described as the multimodal recurrent neural network architecture. a region convolutional neural network (rcnn) is used to recognize items in each image. this approach is made up of two different models. one approach is to utilize a multimodal embedding to match word samples with the visual regions they describe, and then use the correlation as training data for a multimodal recurrent neural network model, to learn to produce the samples. the system can be further improved by creating a single model which can be trained with the image annotation dataset to region-level annotations. authors in [4] presented an architecture with a linguistic model and a multimodal part. a deep cnn extracts the image features. a one-layer representation connects the language model and the deep cnn in the multimodal component. a perplexity-based cost function is used to learn the m-rnn model. the errors are propagated backwards through the three sections of the m-rnn model, updating the model parameters. the m-rnn architecture performs three tasks: i) sentence creation, ii) sentence retrieval (finding the most appropriate sentences for a given image), and iii) image retrieval. this technique can also be expanded to include more complicated image features and a more complex language model. in [5], a generative model based on the deep recurrent architecture is proposed. this research combines vision deep cnn with language generating rnn to generate natural sentences that describe an image. given the training image, the model is trained to maximize the probability of the desired description sentence. this model is referred to as the google nic (neural image caption) generator. to produce descriptions from images, the authors propose a neural and probabilistic framework. the proposed model is quite accurate. however, the problem of how to use unsupervised data to improve the image description is not solved and is discussed in the proposed method. in [6], the bi-directional mapping between images and their sentence-based descriptions is proposed. an rnn is the key component of the approach, as it attempts to dynamically construct a visual representation of the scene. on its own, the representation learns to remember long-term visual notions. the model has the ability of producing unique captions and reconstructing visual features from an image description. for learning, the back propagation through time (bptt) algorithm is used. the rnn model works in both directions. as a result, it is possible to derive image features from sentences as well as sentences from image features. long-term interactions can be learned by the model. it would be interesting to replace the proposed rnns with long shortterm memory (lstm) models to learn a bi-directional model as the authors had not examined the usage of lstm models that have proven the ability to learn long-term notions. the proposed method in [7] employs an attention-based model which is capable to describe the image content. it has an encoder-decoder form, in which a cnn is used as an encoder to extract a set of feature vectors, and the lstm network is used as a decoder. the authors presented two different processes for the attention model: stochastic and deterministic attention. both models can pay attention to important parts of an image while producing a caption, and the output is more interpretable as a result of the attention mechanism. authors in [8] used pre-trained cnn models vgg16 and resnet-101 and the experimental results on flickr8k dataset were tested and compared. in [9], for the classification task a small portion of the training images were labeled. the purpose is to predict the class label of test images which are not having tags. when paired with visual characteristics, tags provide a suitable feature that further improves the performance of classification. it uses the multiple kernel learning (mkl) framework which provides a semi-supervised learning strategy for using the information contained in the tags linked with unlabeled images. for classification of leaf diseases, the hybrid deep learning approach gives better performance [10]. in [11], authors presented a deep learning approach for the early detection of banana diseases, which can be deployed on a mobile system. along with this, authors in [12, 13] presented their work on object detection methods. in [12], the authors used a binary mask which is created around the object to identify the borders of the image. the binary mask is applied in both vertical and horizontal fashions to identify the borders of the image. after that, a refinement process is applied and repeated until the classification is as precise as possible. as a result, the basic strategy is to use the entire image as an input and perform localization using a deep neural network (dnn). the dnn localizer is used on a small set of big windows for precision localization. this approach has some computational cost during training because each object type and mask type must be trained separately. authors in [13] propose a special formulation for multiple instance learning (mil) for object detection. the mil optimization problem is modified into a convex problem and is addressed using stochastic gradient descent (sgd). relaxed multiple instance (rmi) svm can be used to solve various recognition problems, such as visual tracking, image classification, and object detection. the experimental results show that rmi-svm outperforms other known mil benchmark methods. iii. the proposed system model after analyzing the existing systems, we have identified some of the research gaps. the current research work is done mostly with generic image datasets, with domain-specific image captioning datasets we can further improve the accuracy of a captioning system. in the existing available research, attention on textual part present in image is missing while generating the captions from an image. considering these research gaps, the main objective of the proposed system is to generate a new image captioning dataset and further to perform more prescribed image captioning with text extraction from the image and include the extracted text in the generated captions. the overall system flow of the proposed model is presented in in figure 1. a. dataset creation (phase i) in the first phase, we have created a new image captioning dataset, in which images with textual information are included. it builds on [14] to understand the dataset creation model for image captioning task in which the authors have created and presented the microsoft coco dataset. considering this benchmark dataset for image captioning, we have created the image dataset of mit world peace university campus vicinity engineering, technology & applied science research vol. 12, no. 2, 2022, 8366-8373 8368 www.etasr.com bhalekar & bedekar: d-cnn: a new model for generating image captions with text extraction using … consisting of 1500 images which are labeled. these labels talk about the significant objects present in the image. for extracting the text information, we have considered images which contained textual information. validation on images is done while creating the new dataset. the images should provide a good representation of the classes which can further help the classification process, diverse images must be collected to have proper training on the dataset in order to avoid the problem of over fitting or under fitting during training. along with the image files, the new dataset also contains relevant caption files (in csv and json format) which are further used in generating the natural language description of the image. further, the model was trained and validated with the cnn architecture. this allows the system to predict multiple significant objects present in the input image and will generate an appropriate description using natural language processing. this dataset is used in phases ii and iii as shown in figure 2 which represents the phase wise working of the proposed model for image captioning with text extraction. fig. 1. overall system flow of the proposed architecture. fig. 2. overview of the proposed model. fig. 3. proposed d-cnn model followed by lstm for image feature extraction. b. image feature extractor with the proposed cnn model (part of phase ii) cnn works fantastically in computer vision tasks such as recognizing different objects present in an image. it consists of multiple layers of a cnn architecture [24]. the relu layer serves as an activation function, maintaining non-linearity which passes through each layer of the network. the fully connected layer allows performing the classification task. in the proposed model we used three convolution layers which allow seeing specific features using filters. the convolutional layers consist of 32, 64, and 124 filters followed by the max pooling layer which reduces the sample size of the extracted feature map which makes processing faster as it reduces the number of parameters from processing. the pooling layer provides the pooled feature map. we propose the enhanced deep cnn (d-cnn) model for image feature extraction followed with lstm as shown in figure 3. while creating the proposed optimized enhanced d-cnn model we performed optimization and took into consideration different parameters like the number of convolutional layers, flatten layers, and dense layers, the number and size of filters, engineering, technology & applied science research vol. 12, no. 2, 2022, 8366-8373 8369 www.etasr.com bhalekar & bedekar: d-cnn: a new model for generating image captions with text extraction using … optimizer type, learning rate, number of epochs, batch size, etc. based on this experimentation, the different hyper parameters used in model training are presented in table i. we tuned the model with different values of batch size, number of epochs, and different types of optimizers such as stochastic gradient descent (sgd), adam optimizer, and root means square propagation (rmsprop) optimizer. after analyzing the obtained results, we selected the sgd optimizer which updates the weight and bias parameters to get the minimum loss/error while training the cnn as shown in (1) and (2) where w represents the weight and b represents the bias value. from the obtained loss value, we calculate the partial derivative of loss and then adjust the weight to reduce the error. �=�−�������� � �∗(�� ��/��) (1) ∑ = −=∂∂ n i eoutputvalupredictedactualnwloss 1 )(/1/q )/(* blosstelearningrabb ∂∂−= (2) ∑ = −=∂∂ n i valueoutputpredictedactualnbloss 1 )(/1/q sgd gradient measures how much the output of a function changes if there is a change in input value. gradient is the slope of function in which a higher value indicates that the model learns faster and a lower value with almost zero slope indicates that the model stopped learning. after analyzing the obtained results, the hyper parameters for the proposed model were selected: batch size 64, number of epochs 60, and sgd optimizer. the results of hyper-parameter tuning for the proposed model are shown in table i. table i. hyper parameter tuning for the proposed model batch size no. of epochs used optimizer’s used sgd adam rmsprop 32 20 78.12 75.30 75.90 40 79.33 78.08 77.53 60 79.86 78.66 79.19 100 79.81 78.93 79.27 64 20 79.36 78.77 79.85 40 79.28 78.90 79.49 60 79.96 79.85 74.40 100 79.72 77.29 77.38 selected hyper parameters for the proposed model: batch size 64, 60 epochs, sgd optimizer. the obtained training and validation accuracy was 86.30% and 74.56%, due to the over fitting problem. to avoid the over fitting problem, initially we used the dropout method which is a regularization technique. using the dropout normalization, the system achieved 85.28% training accuracy and 83.02% validation accuracy. to improve the performance of the proposed model, the model was trained with dropout and batch normalization and 87.43% training accuracy and 86.30% validation accuracy were achieved. the results of cross entropy loss and classification accuracy with dropout and batch normalization are shown in figure 4. the training loss and validation loss, after training the model and tuning the hyper parameters, are shown in figure 5. figure 6 shows the accuracy during training and validation. the optimized parameters for the proposed d-cnn model are shown in table ii. table ii. optimized parameters of the proposed model parameters learning rate regularization method training time/ epoch training accuracy validation accuracy 6,237,936 0.01 8.345 sec 86.30% 74.56% 6,237,936 0.01 dropout 8.4532 sec 85.28% 83.02% 6,328,816 0.01 dropout and batch normalization 9.4787 sec 87.43% 86.30% selected hyper parameters for the proposed model: batch size 64, 60 epochs, sgd optimizer. fig. 4. cross entropy loss and classification accuracy with dropout and batch normalization. fig. 5. loss plot during training and validation. fig. 6. accuracy plot during training and validation. engineering, technology & applied science research vol. 12, no. 2, 2022, 8366-8373 8370 www.etasr.com bhalekar & bedekar: d-cnn: a new model for generating image captions with text extraction using … c. caption generation using the lstm model ((phase ii) after obtaining the extracted image features, the next step is to use vector to sequence representation with the lstm model [15, 16] to generate the caption for the image as shown in figure 7 and the lstm structure as shown in figure 8. lstm consists of forget gate ft, input gate it, output gate ot with one cell state co with each gate having different weight vectors wc, wi, wo, wf. sigmoid activation function is used in lstm. the computations are presented in the following equations [15, 16]: forget gate: ft = σ(wf st-1 + wf xt) (3) input gate: it = σ(wi st-1 + wi xt) (4) output gate: ot = σ(wo st-1 + wo xt) (5) the intermediate cell state is: ct = tanh(wc st-1 + wc xt) (6) the value for the input gate is obtained using the sigmoid activation function. after that, the intermediate cell ct is obtained using the tanh activation as shown in (6). similarly, the calculation of forget gate is done and its multiplication with old state co is performed and by adding these we get the new cell state c1. finally the new state s1 is generated by using output gate and the cell state. fig. 7. image vector to sequence the representation using the lstm model. fig. 8. structure of lstm. using the proposed model with lstm, the generated captions for an input image given from the new dataset are shown in figure 9. for evaluating the results of caption generation of the proposed model, comparative analysis of the existing approach was conducted, i.e. vgg with lstm and inception v3 model on flickr-8k dataset and the new dataset. d. caption generation with text extraction (phase iii) along with identifying different objects in the image, textual information present in the image is also important. this textual information can give more information about the image, like image background. extracting the text from an image and including it in the generated image caption gives more details about the image. this approach is missing in the existing systems. in the proposed model, we present image caption generation along with text extraction. the pre-processing on the input image is carried out, the original image is converted to grayscale, and then otsu’s threshold method is used which produces a single intensity threshold that divides pixels into foreground and background. then, dilation is applied on the threshold image, which is a mathematical morphological operation to find the contours as shown in figure 10. fig. 9. result of image captioning using the proposed model. fig. 10. text extraction. after looping through the contours, the rectangular part is cropped and passed to the optical character recognition (ocr) system [17] for text extraction. with the deep learning approach, text is extracted with better accuracy [25]. figure 10 shows some sample results of text extraction. the performance evaluation of text extraction is measured with precision and recall metrics [18]. a sample of precision and recall calculation follows. system summary: there is plotted plant reference summary: there is potted plant in garden engineering, technology & applied science research vol. 12, no. 2, 2022, 8366-8373 8371 www.etasr.com bhalekar & bedekar: d-cnn: a new model for generating image captions with text extraction using … recall = number of overlapping words/total words in reference summary: (4/6=0.6) precision = number of overlapping words/total words in system summary: (4/4=1) the results of precision and recall computations are shown in figure 11 and the average result is summarized in table iii. fig. 11. results of precision-recall computations for text extraction. table iii. text extraction evaluation metric used recall precision obtained result 0.75 0.86 iv. results for evaluating the quality of the text of generated captions of the proposed system the utilized performance metrics are blue score [19], meteor, cider [20] which measures how much the machine generated output is closer to the human generated output, i.e. how similar is the candidate text to the reference text. it normally ranges between 0 and 1. fig. 12. result of image captioning without text extraction. figures 12-13 show some results of image captioning without the text extraction module and table iv shows the results of image captioning with the text extraction module using the proposed system, which is able to generate a more detailed description of the image. in order to check the performance of the proposed image captioning model, it was trained on flickr-8k [21] dataset. table v shows the performance of the proposed model for image captioning (without text extraction) on flickr-8k. the obtained results exhibit a satisfactory performance. comparative analysis of existing architectures like vgg-16 [22], inception v3 [23], and the proposed model for image captioning (without the text extraction module) on the new dataset is shown in table vi. it is seen that the proposed system outperforms the existing methods with improved bleu score and meteor score and also has an accuracy that reaches 87% for caption generation without text. fig. 13. results of image captioning without text extraction. table iv. image captioning with text extraction results input image validation of the proposed model predicted caption is: there is a poster on the wall extracted text: madhuri a. bhalekar assistant professor generated captions is: there is a poster on the wall and the extracted text is madhuri a. bhalekar assistant professor predicted caption is: there is a poster extracted text: maeer’s maharashrta institute of technology, pune 17/01/20008 generated captions is: there is a poster and the text extracted is maeer’s maharashrta institute of technology, pune 17/01/20008 table v. performance comparison of vgg-lstm and the proposed model for image captioning without text extraction dataset architecture evaluation metrics bleu-1 bleu-2 bleu-3 bleu-4 meteor [21] vgg with lstm [22] 0.647 0.459 0.318 0.216 0.201 proposed model 0.495 0.352 0.276 0.201 0.425 engineering, technology & applied science research vol. 12, no. 2, 2022, 8366-8373 8372 www.etasr.com bhalekar & bedekar: d-cnn: a new model for generating image captions with text extraction using … the result of performance evaluation for caption generation with text extraction model is shown in table vii. we see that the proposed model was an accuracy that reaches 83%, thus providing more information about the image. further, the generated captions can be presented in audio form. also, the model can be deployed on smart glass which will be useful for visually challenged individuals and can be used as a navigation system. table vi. comparative analysis of existing architectures and of the proposed model for image captioning without text extraction dataset architecture evaluation metrics bleu-1 bleu-2 bleu-3 bleu-4 meteor our new dataset vgg with lstm [22] 0.644 0.522 0.441 0.374 0.644 inception v3 model [23] 0.534 0.452 0.343 0.253 0.534 proposed 0.879 0.752 0.743 0.678 0.653 table vii. evaluation of the proposed model for image captioning with text extraction dataset architecture evaluation metrics bleu-1 bleu-2 bleu-3 bleu-4 meteor our new dataset proposed model with lstm 0.832 0.645 0.672 0.611 0.589 v. conclusion and future work this paper reviewed various methodologies used for image captioning from the domain of machine learning and neural networks. various methodologies were analyzed for feature extraction, classification, and caption generation. a new dataset was implemented which trained further the proposed deep cnn model. the paper also analyzed text extraction from the image and included the extracted text as a part of the generated image captions. extracting the text from an image and including it in the image caption gives more details about the image. the proposed system outperforms the existing methods with the curated new dataset and also gives satisfactory performance on the benchmark flickr8k dataset. considering the recent advances in image captioning systems, generating more accurate image captioning and image description is still an open problem. automatic image captioning will continue to be a major research topic for a while, due to the advancement of deep learning-based network architectures. further, fine tuning the hyper-parameters of the proposed model can give better results. there is a huge impact of image captioning in many social relevance applications such as video surveillance, navigation for visually challenged individuals, online education systems, medical assistance, and many more which add significant value in our daily lives. acknowledgment the authors would like to thank the authorities of mit world peace university for permitting and becoming a vital part of the new dataset and for supporting this research. references [1] k. fu, j. jin, r. cui, f. sha, and c. zhang, "aligning where to see and what to tell: image captioning with region-based attention 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[25] b. ahmed, g. ali, a. hussain, a. baseer, and j. ahmed, "analysis of text feature extractors using deep learning on fake news," engineering, technology & applied science research, vol. 11, no. 2, pp. 7001–7005, apr. 2021, https://doi.org/10.48084/etasr.4069. authors profile madhuri bhalekar is a ph.d. research scholar in the school of computer engineering & technology, mit world peace university, pune, india. she is currently working as an assistant professor in the school of computer engineering & technology, mit world peace university, pune, india. her research interests include image processing, computer vision, and natural language processing. orcid id: 0000-0003-1863-5293. mangesh bedekar is currently working as a professor in the school of computer engineering and technology at mit world peace university, pune, india. he received his m.sc. and ph.d. from bits palani, rajasthan, india. he is a member of csi, iste, iet, and acm. his primary research interests include web data mining, web personalization, user interface design, user interface improvements, browser customization, affective computing, information cisualization, computer vision, and natural language processing. orcid id: 0000-0003-4461-9641 microsoft word etasr_v13_n2_pp10425-10431 engineering, technology & applied science research vol. 13, no. 2, 2023, 10425-10431 10425 www.etasr.com milu et al.: improvement of classification accuracy of four-class voluntary-imagery fnirs signals … improvement of classification accuracy of fourclass voluntary-imagery fnirs signals using convolutional neural networks md. mahmudul haque milu department of biomedical engineering, jashore university of science and technology (just), bangladesh mahmudhmilu@gmail.com md. asadur rahman department of biomedical engineering, military institute of science and technology (mist), bangladesh bmeasadur@gmail.com mohd abdur rashid department of eee, noakhali science and technology university, bangladesh | division of electronics and informatics, gunma university, japan marashid.eee@nstu.edu.bd (corresponding author) anna kuwana division of electronics and informatics, gunma university, japan kuwana.anna@gunma-u.ac.jp haruo kobayashi division of electronics and informatics, gunma university, japan koba@gunma-u.ac.jp received: 23 january 2023 | revised: 6 february 2023 | accepted: 8 february 2023 abstract multiclass functional near-infrared spectroscopy (fnirs) signal classification has become a convenient way for optical brain-computer interface. fnirs signal classification with high accuracy is a challenging assignment while the signals are produced by means of voluntary and imagery movements of the same limb. since the activation in time and space of voluntary and imagery movement show a similar pattern, the classification accuracy by the conventional shallow classifiers cannot reach an acceptable range. this paper proposes an accuracy improvement approach with the use of convolutional neural networks (cnns). in this work, voluntary and imagery hand movements (left hand and right hand) were performed by several participants. these four-class signals were acquired utilizing fnirs devices. the signals were separated based on the tasks and filtered. with manual feature extraction, the signals were classified by support vector machine and linear discriminant analysis. the automatic feature extraction and classification mechanism of the cnn were applied to the fnirs signals. from the results, it was found that cnn improves the classification accuracy to an acceptable range, which has not been achieved by any convolutional network. keywords-fnirs; voluntary and imagery fnirs signal; classification accuracy; conventional classifiers; convolutional neural network (cnn) i. introduction brain-computer interface (bci) is a remarkable notion of current neuro-computational research that offers the scope to control the computer with brain commands. research and development regarding bci can strongly contribute to neuroprosthetics applications [1-2]. a brain-controlled computer needs to read the brain functionalities properly. the brain engineering, technology & applied science research vol. 13, no. 2, 2023, 10425-10431 10426 www.etasr.com milu et al.: improvement of classification accuracy of four-class voluntary-imagery fnirs signals … functionalities can be assessed by both invasive and noninvasive procedures with non-invasive procedures being the primary choice of modern bci [3]. electroencephalography (eeg) and magneto-encephalography (meg) are well-known noninvasive methods based on electric impulsive signals of the brain. due to some questionable features like noise sensitivity, poor spatial resolution, and motion sensitivity, these modalities should be replaced by some newer ones [4-5]. to meet the challenge of overcoming the previous limitations, functional near-infrared spectroscopy (fnirs) is a widely used noninvasive optical modality that can measure functional neuro-activations based on the hemodynamics of the brain tissue [6-7]. although this modality is comparatively slower than the eeg and meg regarding the brain response, due to very high spatial resolution and robust activation level, fnirs gets significant importance in bci research and applications [8-10]. for bci the brain is to be stimulated externally or internally, with procedures termed as stimuli. most of the stimuli are provided to the brain in bci research by imagery or voluntary motor actions [11]. these movementrelated functions of the brain correlate with the motor cortex which is located in the frontal lobe of the brain. there are several research works related to movement-related (either voluntary or imagery) hemodynamics classifications for bci applications. the activation patterns of the voluntary and imagery movement-based stimuli are widely examined in [12-15]. these studies suggested that several areas in the motor cortex and some prefrontal cortex become active due to movement execution and imagination. voluntary and imagery movementrelated tasks were not classified by machine learning algorithms. in [16], the two-class problems of imagery left and right-hand wrists movement were classified with the linear discriminant analysis (lda) method. three classes of bci were studied in [17], with two classes being motor imagery tasks. voluntary movement-related tasks of the left and right hand were classified in [18] from the fnirs signals of optimally selected channels. multiple motor imagery tasks (movements of the left hand, right hand, left foot, and right foot) were classified in [19]. in these works, authors classified either the voluntary or imagery movement-related fnirs signals. to the best of our knowledge, no work classified fnirs signals regarding both voluntary and imagery movement stimuli. this is a challenge for the researchers to find the voluntary and imagery movement related fnirs signal, simultaneously, because the activation area of the voluntary and imagery movement by an organ is the same in the brain [13] and their activation strengths are alike. this is a challenge for signal classification at high classification accuracy that was considered to be solved in this work. in this work, both voluntary and imagery movement fnirs signals were classified separately utilizing linear discriminant analysis (lda) and support vector machines (svm). we found satisfactory results for two class voluntary and two class motor imagery fnirs signals. additionally, we made it a fourclass problem adding the voluntary and imagery fnirs signals together and thereafter we classified the signal utilizing the same procedure applied with lda and svm. in this approach, the classification accuracy was only 55-65%. this is a great barrier to implementing neuro-rehabilitate prosthetics where several events occur and the classification must be accurate and precise. to improve the classification accuracy for such a problem, we deployed a convolutional neural network (cnn) which has an automatic feature extraction capability. since the fnirs signals are of multiple channels, the time series data of the change in the concentration of oxidized hemoglobin (hbo2) and deoxidized hemoglobin (dhb) are used to prepare twodimensional data. these data were used to prepare topographic images of the hemodynamic activations and are fed to the proposed cnn structure. our proposed cnn method can classify the 4-class fnirs signal with 86.14% (on average) accuracy which is a significant improvement. therefore, the contribution of this research work can be summarized as:  developing a shallow deep neural network to classify multiple class fnirs signals with high accuracy.  proposing a method for effective bci for same limb voluntary-imagery fnirs signal classification in subject dependent and independent approach. ii. materials and methods a. dataset the dataset used in this research is available in [20], and was collected with permission from the authors. according to the description given in [20], the participants were healthy. in their experiment, four types of tasks were performed by the subjects: left hand (lh) movement, right-hand (rh) movement, imagery left-hand (ilh) movement, and imagery right-hand (irh) movement. therefore, the subjects performed two voluntaries and two imagery hand movement tasks in different sessions. in each trial, a subject performed a 10second task of two different movements with 20 seconds of rest after each task. at first, 20 seconds passed at the resting condition to correct the baseline values of the data. a 10second task followed. this task might be lh or ilh. this was followed by another 20-second resting period, which was followed by another 10 second task which was either rh or irh. this trial was repeatedly performed. each subject performed 5 trials in each session. as a whole, sixteen (16) sessions (8 voluntary and 8 imagery) were performed by every participant in a total of 40 trials of each task. eventually, 40 trials of 4-class data were acquired from every subject. the fnirs data were acquired using fnir devices [21], which have 4 nir sources and 10 detectors. the optode of this device covers 16 channels. the device provides a measure of continuous real-time concentration change in the values for hbo2 and hb. the cognitive optical brain imaging (cobi) studio software was used to log the fnirs data in computer memory [22]. b. methods in this section, all the data processing steps from signal acquisition to event classification for the performance test are explained. after designing the data acquisition protocol, data from prefrontal hemodynamics were collected. then, in order to reduce dimensions, data compression using principle component analysis (pca) was applied. after that, the engineering, technology & applied science research vol. 13, no. 2, 2023, 10425-10431 10427 www.etasr.com milu et al.: improvement of classification accuracy of four-class voluntary-imagery fnirs signals … baseline of fnirs data was corrected. as a part of the preprocessing, these data were filtered. then the data were separated into some sequential events and some prominent features were extracted. using these features, classification accuracy was calculated. the main steps of the proposed data processing methods for the fnirs data classification are presented briefly in figure 1. the figure is mainly focused on the conventional data classification technique. the steps are also described concisely with technical details in this subsection. feature extraction and classification procedure by cnn are also discussed in order to clarify how this proposed method customized the cnn structure for achieving the objectives of the proposed method. fig. 1. block diagram of the total signal processing steps to create a machine learning-based predictive model and the accuracy of the testing data. 1) data compression since the data were acquired with 16 channels, the processing could face the issue of high dimensionality. to check the actual dimensions, the data were transformed by pca and it was found that the actual dimension of the data was 4 instead of 16. the result of pca is shown in figure 2 with a similar channel number of ilk dimension. the resulting 4 dimensions are termed as left lateral (ll: channel 1, 2, 3, 4), left medial (lm: channel 5, 6, 7, 8), right medial (rm: channel 9, 10, 11, 12), and right lateral (rl: 13, 14, 15, 16). the signals having the same dimension were averaged. therefore, the 16-channel configuration becomes compressed from i×16 to i×4. this compression helps reduce the feature dimension, which is very important for achieving high classification accuracy in the machine learning approach. 2) filtering and baseline correction since fnirs electrodes collect data from the human body, the signal is full of artifacts and noises. so, removing different types of noises is the first step of data processing. the fnirs data can be affected by three types of noise [23]. these are motion artifacts, physiological signals, such as heart rate and respiration, and instrument and environment-related noises. motion artifacts occur due to head movement and it results in fnirs detectors shifting and losing contact with the skin exposing them to ambient light or light emitted directly from the fnirs source. these types of motion artifacts can be easily recognized because they cause sudden, large spikes in the raw fnirs data. rapid head movements can cause the blood to move toward or away from the area that is being monitored, rapidly increasing or decreasing blood volume. as the dynamics of this type of motion artifacts are slower than led pop, they can be confused with the actual hemodynamic response due to brain activation. physiological signals such as heart rate (over 0.5hz) and respiration (over 0.2hz) are at higher frequency ranges than hemodynamic responses, thus they should also be eliminated. so the raw fnirs signals were filtered by a savitzky-golay filter of the 3rd order with 21 frame length (equivalent to 0.1hz cut-off fir low pass filter in 2hz fnirs signal) [10]. the raw noisy and filtered data of fnirs are shown in figure 3. then, the data were separated in each trial. every trial of the fnirs data was corrected by subtracting the baseline from the original signal. the baseline was calculated by averaging the data of the first task. fig. 2. principle component 1 vs. component 2 presents the actual signal dimensions in eigenspace. fig. 3. the raw fnirs signal with physiological artifacts and the filtered signal after the savitzky-golay filtering technique. 3) feature extraction when the input data are too large to be processed and are suspected to be redundant, then they can be transformed into a reduced set of features. analyzing a large number of input variables requires a large amount of memory and computation power. it also over-fits the classification algorithms. the selected features are expected to contain the relevant information from the input data so that the desired task can be performed by using this reduced representation instead of the s ig n a l a m p li tu d e i n m ic ro m o le /l it e r engineering, technology & applied science research vol. 13, no. 2, 2023, 10425-10431 10428 www.etasr.com milu et al.: improvement of classification accuracy of four-class voluntary-imagery fnirs signals … complete initial data. in this study, mean, slope, standard deviation, and skewness were extracted as the dominant features. since the fnirs signal does not exhibit complexity like eeg, meg, or fmri, simple time domain features are enough to represent the signal characteristics [23]. in this experiment, we have worked with the above features. before training the machine learning-based network, all the values of the training features were normalized between 0 and 1. minmax min'       (1) where ' are the feature values that are rescaled between 0 and 1. on the other hand, n r  are the actual values of the features. the maximum and minimum values of the features are presented as max and min respectively. 4) classification methods classification is the process of predicting the class of given data points. classes are sometimes called targets. classification predictive modeling is an important task of approximating a mapping function from input variables to discrete output variables. a training process continues until the model achieves the desired level of accuracy on the training data for the svmand lda-based predictive models. since the machine learning models (svm and lda) gave lower accuracy in multiclass (4class classification) problems, cnn (a deep neural network) is applied. c. deep neural network-based classification a deep neural network needs no extracted features because it extracts features from its own. a cnn is one of the best formats of deep neural networks. in this work, cnn is utilized for fnirs data classification. since the feature extraction and classification process are included in the cnn structure, it is very important to prepare the input layer and output layer of cnn. the fnirs data preparation to run the cnn and the structure of the proposed cnn layers are described briefly below. 1) input preparation cnn is applied when the inputs are images or a twodimensional matrix. when the computer sees an image, it will see an array of pixel values depending on the dimension of images. the image dimension is 32×32. so it will see an array of 32×32×3 numbers for rgb values and 32×32×1 for grayscale images. each of these numbers is given a value from 0 to 255 that describes the pixel intensity at that point. cnn consists of convolutional, nonlinear, pooling, and fully connected layers. in convolutional layers, a convolutional filter whose width is equal to the dimension of the input and kernel size is convolved with the input data. to build the feature map, the output of the convolutional layer is converted by an activation function similar to anns'. after each convolutional layer, additional subsampling operations such as max-pooling and softmax are performed to enhance the performance [2425]. as with anns, hyper-parameters such as learning rate, batch size, and the number of epochs should be investigated for the cnn to improve its classification performance. 2) structure of the cnn layers in this research, at first any two events: motor imagery hand movement or motor execution hand movements were classified by two shallow neural networks (svm and lda), with satisfactory accuracy. but when the 4-event classification was performed, the accuracy became very low, which means shallow neural networks like svm and lda cannot be utilized for more than 2-class events. to improve this result, the cnn algorithm is proposed. a general structure of a cnn is given in figure 4 including its main layers. fig. 4. layers (convolutional, relu, pooling, and fully connected) of a cnn. deep learning is a class of machine learning algorithms that uses a cascade of multiple layers of nonlinear processing units for feature extraction and transformation. a cnn is highly capable of automatically learning appropriate features from the input data by optimizing the weight parameters of each filter, using forward and backward propagation to minimize classification errors. a) convolution layer the convolution layer is the first layer to extract features from an input image (as given in figure 4). convolution preserves the relationship between pixels by learning the image features using small squares of input data. it is a mathematical operation that takes two inputs, the image matrix and a filter or kernel. consider the dimension of an image matrix is dwh  and the filter's is h wf f d  . so, the output of the matrix dimension is ( 1) ( 1) 1h wh f w f      . a very important note is that the depth of the filter should be the same as the depth of the input image. so for a 5×5×3 image, the dimension of the filter is 5×5×3. starting from the first position of the input image, the filter is sliding or convolving around the input image, it is multiplying the values in the filter with the original pixel values of the original image. the method used in this work to prepare the input images from the data (hbo2 and hb) is illustrated in figure 5. the way convolutional filters worked on the images is shown in figure 6. this multiplication is all summed up and a single number will be found. it should be remembered that this single number is only for when the filter is on the starting corner of the input image. this process is repeatedly performed for every location of the image. engineering, technology & applied science research vol. 13, no. 2, 2023, 10425-10431 10429 www.etasr.com milu et al.: improvement of classification accuracy of four-class voluntary-imagery fnirs signals … fig. 5. the input data consisting of the concentration changes of hbo2 (red) and hb (blue) overall channels. a convolutional filter runs through the input data along the vertical axis. b) relu layer relu (rectified linear unit) layer induces nonlinearity in the values of the incoming layer. the relu function only passes the values x which are greater than zero:       0 0 0 )( xif xifx xf (2) other functions are also used to increase nonlinearity, for example f(x) = tanh(x), f(x) = |tanh(x)|, and the sigmoid function 1 ( ) 1 x f x e   . relu is often preferred to other functions because it trains the neural network several times faster without a significant penalty to generalization accuracy. c) pooling layer this layer reduces the number of parameters if the images are too large. spatial pooling is also called downsampling and reduces the dimensionality of each map, but retains the important information. spatial pooling can be of different types: max pooling, average pooling, and sum pooling. in this work, the max pooling layer is used. d) fully connected layer this layer takes the output of the convolution, relu, and pooling layers as input. with the fully connected layers, we combine these features to create a model. finally, we have an activation function such as softmax or sigmoid to classify the outputs. e) cross validation k-fold cross-validation is used to estimate the classification performance of the predictive model. the first step in this process is to divide the data into k folds, where each fold contains an identical amount of input data. οne fold is used as a test dataset, while the remaining folds are used as training sets. afterward, a classification procedure is applied to the selected test and training sets. this process is performed for each of the k folds. in this study, 5-fold cross-validation was performed. the parameters of different layers and the structure of the proposed cnn are summarized in table i. table i. cnn layer parameters parameters value matrix input layer 384×384 convolution layer 1 2, 8 max-pooling layer 1 2 (pool size) convolution layer 2 4, 16 max-pooling layer 2 2 (pool size) fully connected layer 4 learning rate 0.01 epoch 15 validation frequency 3 iii. results and discussion the activation due to imagery movement planning occurs in the prefrontal cortex which can be measured by the increased concentration of hbo2. for the left-hand and right-hand imagery movement planning, the activation level is found to be increased in the concentration of hbo2 in the right hemisphere and left hemisphere, respectively. since 4 different portions are selected to observe the actual concentration change in hbo2 of lh and rh movement planning. the variation of hbo2 concentration in the ll, lm, rm, and rl portions of the prefrontal cortex due to planning movements of lh and rh of a randomly selected subject is presented in figures 6 and 7. (a) (b) fig. 6. comparison of the concentration changes in hbo2 between lh and rh movement planning in (a) ll and (b) lm portion of the prefrontal cortex. (a) (b) fig. 7. comparison of the concentration changes in hbo2 between lh and rh movement planning in (a) rm and (b) rl portion of the prefrontal cortex. it is easily observable from figures 6 and 7 that all the proposed portions of the prefrontal cortex exhibit significant variations in the concentration of hbo2. engineering, technology & applied science research vol. 13, no. 2, 2023, 10425-10431 10430 www.etasr.com milu et al.: improvement of classification accuracy of four-class voluntary-imagery fnirs signals … fig. 8. training and validation progress with loss reduction process in cnn. fig. 9. classification accuracy comparison of svm, lda, and cnn. table ii. classification accuracy of lda and svm for 2-class and 4-class fnirs signal sub svm classification accuracy (%) lda classification accuracy (%) svm 4-class classification accuracy (%) lda 4-class classification accuracy (%) lh vs rh ilh vs irh lh vs rh ilh vs irh 1 80 77.5 90 81.5 45.45 47.5 2 83.5 80 92.5 82 52.27 45 3 78 69.5 78 69.5 50 45 4 80 72 85 73.5 54.54 55 5 83.5 81.5 88.5 80 52.27 52.5 as a result, all these portions should have to be taken into account as a significant source to discriminate the imagery activities. accordingly, features were extracted from the fnir signals of ll, lm, rm, and rl. the features were used to train svm and lda separately to check the feature-dependent accuracy of the predictive model. several time domain features like variance, total summation, and kurtosis did not return good classification accuracy except mean and slope. the classification accuracies for two classes by svm and lda were satisfactory. but for 4 classes, the classification accuracy was very low. the results are given in table ii. therefore, cnn was applied in order to improve the classification accuracy for the 4-class problem. the training progress of cnn is shown in figure 8. here, both training accuracy and loss are shown graphically for a randomly chosen subject. the classification accuracy of the applied cnn is presented in figure 9 along with the results of svm and lda. from the results given in figure 9, it was found that the classification accuracy of cnn for the 4-class fnirs signal is way more satisfactory than the results of lda and svm. iv. conclusion this research work investigates how cnn can enhance the classification accuracy with data of more than two classes when the svm and lda classification accuracy is very low. the results show that for ilh, irh, lh, and rh on five subjects, the cnn-based scheme provides 86.24% (on average) accuracy, whereas, in the case of svm and lda, the average classification accuracy is 50.9% and 49%, respectively. in the case of subject-independent data, cnn shows 83.33% accuracy. this result revealed that cnn can lead to the practical development of a bci system. since classification accuracy is the most essential factor to design a practical bci device, we will try to explore further improvements in the accuracy of fnirs-based bci by implementing several deep learning-based algorithms. we can also try to merge some other modalities with fnirs and check whether this process provides better accuracy or not. acknowledgment the authors acknowledge the partial financial support provided by the department of biomedical engineering, mist, dhaka-1216, bangladesh. references [1] s. ajami, a. mahnam, and v. abootalebi, "development of a practical high frequency brain–computer interface based on steady-state visual evoked potentials using a single channel of eeg," biocybernetics and biomedical engineering, vol. 38, no. 1, pp. 106–114, jan. 2018, https://doi.org/10.1016/j.bbe.2017.10.004. 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[25] s. nuanmeesri, "a hybrid deep learning and optimized machine learning approach for rose leaf disease classification," engineering, technology & applied science research, vol. 11, no. 5, pp. 7678–7683, oct. 2021, https://doi.org/10.48084/etasr.4455. microsoft word etasr_v12_n3_pp8675-8682 engineering, technology & applied science research vol. 12, no. 3, 2022, 8675-8682 8675 www.etasr.com naghel et al.: household waste management challenges household waste management challenges the case of m’sila, algeria mostepha naghel city, environment, society, and sustainable development laboratory university of biskra, algeria mostepha.naghel@univ-msila.dz abdallah farhi design and modeling laboratory of architectural and urban forms and atmospheres university of biskra, algeria a.farhi@univ-biskra.dz ali redjem city, environment, society and sustainable development laboratory university of m'sila, algeria ali.redjem@univ-msila.dz received: 16 march 2022 | revised: 9 april 2022 | accepted: 14 april 2022 abstract-household waste and uncontrolled urbanization management are considered major problems in african countries. in the hodna region, the phenomenon seems to be more important in urban centers because of the huge amount of household waste generated by domestic and commercial activities. in most algerian cities, solid waste is piled up in huge quantities in dumps and is dumped indiscriminately in waterways and public spaces. uncontrolled urbanization, industrial development, and the evolution of lifestyle lead to increased production of waste, whereas the waste management techniques used in urban areas should be reconsidered. from this perspective, this paper studies and analyses in a spatio-temporal approach, the practices of household waste management in the city of m’sila in order to evaluate the state of such management and identify the key elements of integrated planning of waste management. keywords-m’sila; household waste; environment; urbanization; living environment i. introduction all algerian cities are undergoing an accelerated urbanization process [1]. the strong demographic growth and the economic, social, and political upheavals directly impact the constantly increasing volume of household waste produced daily [2]. these problems common to all the algerian cities, are characterized by uncontrolled urbanization, i.e. poor functioning of public services following a strong urbanization (organized or informal) consuming space, and with the lack of materials and human means, this leads to difficulties of waste management (transport, collection, elimination) [1, 5]. the authorities have difficulty in containing and eliminating waste, as evidenced by the spectacle of garbage covering the roadsides and the piling up of waste in illegal dumps [4]. according to a survey conducted by the ministry of land management and environment services, more than 3000 illegal dumps have been identified. waste management remains one of the weak stages of algeria’s urban management and urban services [5, 6]. all urban actors must be involved, first the population, then the municipality, and finally the state to solve the waste problem. however, when it comes to the environment, specifically waste management, it is a matter of using existing management methods and responding to increasingly complex issues by constantly reinventing them. in addition, there are limitations to the national waste disposal policy. this policy remains fundamentally archaic and is characterized by the inefficiency of public intervention [6]. indeed, the operational strategy of waste management is limited only to the collection, transport, and dumping. so far, this strategy lacks any complementary disposal and treatment structure [6]. the material and human resources of collection companies must be adapted to the rate of population growth. it is necessary to organize landfills in order to overcome the problem of saturation, and finally, it is necessary to revalorize the waste for possible reuse [7]. the research that has been done so far on household waste in m’sila remains insufficient. generally speaking, the available literature on household waste focuses on the technical and organizational aspects of the public waste service and the threats posed by waste. however, there are themes in recovery/recycling that need to be explored in greater depth in order to understand better the multiple facets of waste in m’sila. thus, this paper presents an inventory of waste management in m’sila. in particular, this study aims to contribute to the problem of solid waste management for better strategies to fight against insalubrity in urban areas [8]. ii. waste definition according to the algerian regulations waste consists of three main categories [8, 14-15]: household and similar waste, special waste (industrial, agricultural, care, services, etc.), and inert waste. the definition of the different types of waste and treatment methods may vary from one country to another [8]. according to the regulations in force, household waste is defined by article 2 of decree no. 84-378 of december 15, 1984, setting the conditions for corresponding author: mostepha naghel engineering, technology & applied science research vol. 12, no. 3, 2022, 8675-8682 8676 www.etasr.com naghel et al.: household waste management challenges cleaning and removing household waste, which are domestic waste and assimilable by nature volume. it is in particular: • industrial or collective household waste. • products resulting from cleaning such as sweeping, sewer cleaning. • bulky waste, bulky objects, scrap metal, rubble, etc. • anatomical or infectious waste from hospitals, chemical or other care facilities. • slaughterhouse waste and offal. • commercial waste, packaging, and other residues generated by commercial activities. fig. 1. location of the city of m’sila in its regional context. iii. sources and methods the methodology adopted is based on literature research and field surveys. the documentary literature review allowed us to consult memoirs, books, theses, and articles in libraries and on the internet. it allowed us to have information concerning the urban dynamics and the waste management plan. the field observation allowed us to discover the garbage deposits, the state of the environment, the infrastructures, and the urban space’s evolution. simple field observation indicates a low collection rate of 152 tons/inhabitant of solid waste produced in the commune of m’sila [26]. the questionnaire was administered on 3 samples in 3 different sectors (collective housing, individual housing "allotment", and traditional housing). in addition to the residential areas, there are also predominantly commercial areas. the method of the household waste characterization was carried out in applying the sampling protocol in respect of the standards nf x30-408 and nf x30413 relating to the characterization of waste (sampling and sorting). carademe is the new guide introduced by ademe (french environment and energy management agency) for local campaigns of household waste characterization [11-13]. a. the study area a medium-sized city, m’sila is located on the northern edge of the steppe of the hodna region. it is located 250km from the capital algiers, covering an area of 233km2 having 224,991 inhabitants [27]. it is characterized by a strategic geographical position. crossed by the rn40 (connecting m’sila to batna, biskra, and setif), the rn60 (connecting m’sila to algiers), and the rn45 (connecting m’sila to bordjbou-arreridj and bou-saada), it is an ideal crossroads connecting the north of the country to the south and the east to the west. it is limited, in the north by the commune of el ache (wilaya of bordjbou-arreridj), in the south by the commune of ouled madhi, in the east by the commune of metarfa, and in the west by the commune of ouled mansour. b. situation of waste management in algeria in algeria, waste management is carried out by public service, the national program for the integrated management of household waste (programme national pour la gestion intégrée des déchets ménagers, progdem), and by the national waste agency (agence nationale des déchets, and) created by executive decree no. 02-175 of may 20, 2002 [9]. the ngos working in algeria on the management of dsu are grouped in an association called coordination des entreprises de gestion des déchets (ceged). the public administration supports the ceged’s actions, which requires inhabitants to join to get rid of dsu [6, 9]. since the johannesburg summit in 2002, algeria has intensified its environmental protection and sustainable development actions, thus giving a prominent place to social and ecological aspects in its choice of society model. the algerian government has implemented a national strategy for the environment and a national action plan for the environment and sustainable development (stratégie nationale de l’environnement et un plan national d’actions pour l’environnement et le développement durable, pnae-dd) which: • involves all the ministries and decentralized services, local authorities, and civil society, whose role is to be a force for proposals; • aims to integrate environmental sustainability into the country’s development strategy (to induce sustainable growth and reduce poverty); • puts in place effective public policies to address the environmental externalities of growth connected to activities increasingly initiated by the private sector. this strategy, whose main objectives are: improving health and quality of life, conserving and improving the productivity of natural capital, reducing economic losses and improving competitiveness, and protecting the regional and global environment, has resulted in: the development of the legislative and regulatory framework, institutional capacity building, and the introduction of economic and financial instruments, and the mobilization of significant investments, through the start-up of the first environmental projects, to halt the degradation of the environment and even reverse certain negative trends observed. the law 01-19 of december 12, 2001, relating to the management, the control, and the elimination of waste constitutes in this respect the starting point and the reference of this new strategy. thus, two particular programs which constitute the continuation of this law are carried out and have obtained encouraging results: • progdem (national program of municipal waste management). engineering, technology & applied science research vol. 12, no. 3, 2022, 8675-8682 8677 www.etasr.com naghel et al.: household waste management challenges • pnagdes (plan national de gestion des déchets spéciaux, national plan for special waste management). these programs are characterized in particular by the elaboration, in collaboration with the authorities and local communities, of master plans of integrated management and treatment of waste, and the realization of concrete projects and adapted to the local specificities, like the realization of the technical landfill centers (centres d’enfouissement technique, cet). c. evaluation of the household waste management process waste management in all its ramifications is simply a planned system to effectively control the generation, storage, collection, transportation, treatment, and disposal of waste. waste management is an important element of environmental protection. its purpose is to provide a hygienic, economical, and efficient solid waste storage, collection, transportation, and treatment or disposal without polluting the atmosphere, soil, or water. the various stages of solid waste management, from generation to sanitary disposal, are considered a solid waste chain. so, the solid waste chain is the pathway through the solid waste from generation to the point of final disposal [3, 5-6]. d. current household waste management in m’sila municipal waste management is generally organized in 3 sectors [8]: the public sector, which has responsibility for monitoring and enforcing the provisions of certain urban services including solid waste management, the formal private sector engaged in waste management, including collection and recycling, and the informal private sector engaged in the reuse of certain types of waste [10, 21, 23]. 1) public sector a) at the national level the ministry of land management and environment (mate) has primary the responsibility for national environmental policy. it was created at the end of the 1980s with a name that varied over time. in the 1970s, the environmental task was attached to the ministry of hydraulics and then to the secretariat of state for forestry. the law on waste management, control, and disposal provides for the creation of three intermediate national bodies: • and was created by executive decree no. 02-175 of may 20, 2002, and placed under the supervision of the mate. it provides an adequate instrument to assist local authorities in implementing the national waste policy. • the national observatory for the environment and sustainable development (observatoire national de l’environnement et du développement durable, onedd) was created on april 3, 2002. it is a public establishment of an industrial and commercial nature (epic), with legal personality and financial autonomy. • the national conservatory for environmental training (conservatoire national des formations à l’environnement, cnfe) was created in august 2002. it has the status of epic and has two main missions: the training of various public or private actors in the field of the environment, and environmental education for the public, especially schools. b) at the regional level at the regional level, the local public service of waste management is under the responsibility of: • the regional environmental inspectorates (inspections régionales de l’environnement) are decentralized bodies of the state, founded by the decree no. 88-227 of november 5, 1988 [29]. they were created on the power, organization, and functioning of the bodies of inspectors responsible for environmental protection. the mission of these inspectorates is to ensure compliance with the legislation and regulations in environmental protection to note and investigate violations in this area. at the level of the wilayas, the state has created decentralized services in charge of the environment. • the wilaya environmental departments (directions de l’environnement de wilaya, dew), were created by the executive decree no. 96-60 of january 27, 1996 [30], and succeeded the 15 wilaya environmental inspectorates. the wilaya directorates have 3 main areas of activity: coordination, control, and information. coordination requires good communication and organization between the bodies of the state, the wilayas, and the communes to establish an environmental protection program for the entire territory and take measures to prevent all forms of environmental degradation (pollution, nuisances, soil erosion, etc.). c) at the local level the local level in this study refers to two structures responsible for local waste services: the communes and the groupings of communes. article 7 of the communal code provides that the commune is responsible for preserving hygiene and public health, particularly the evacuation and treatment of wastewater and household waste. 2) private sector private sector participation in solid waste management in algeria is very limited. the 2001 law made municipal waste management public service available to private investment and concessions to promote this participation. 3) informal sector the third sector involved in waste recovery in algeria is the informal sector, which constitutes an important economic activity. it is relatively structured in two dimensions: the first is vertical from the recovery in garbage cans and landfills to the recycling industry, and the second is horizontal and based on channels by the type of recovered waste (paper, plastic, metals). this sector allows to: • valorize a large amount of waste, • reduce transportation and collection costs for communities, • provide income to many people, • increase the capacity of landfills, engineering, technology & applied science research vol. 12, no. 3, 2022, 8675-8682 8678 www.etasr.com naghel et al.: household waste management challenges • ensure the raw material for some companies, • situation of the pre-collection of waste. iv. mode of collection, delimitation, and waste treatment is provided mainly by the cet of m’sila. the management of household waste has two essential stages: removal and elimination. the removal of waste includes the pre-collection and the collection itself. the elimination refers to landfills and burials in pits. a. collection and pre-collection 1) pre-collection the concept of pre-collection implies all operations that precede the actual collection of waste. it aims to collect, gather, and store waste by the inhabitants of a dwelling, building, housing, or company, then deposit them in places dedicated to waste. in algeria, it takes various forms according to the type of housing and the accessibility of the equipment: • the metal boxes: the pre-collection by the box is more used at the level of local center agglomeration (agglomeration centre local, acl) and secondary agglomerations (agglomerations secondaires, as). these are metal caissons with a capacity of 2 to 2.7t installed in housing estates, districts, and in front of establishments that are major waste generators. the frequency of removal of these boxes varies between 2 to 3 times per week. • the hard niches: are designed in the form of a construction delimited by a low masonry wall surrounding a base in hard material. the low wall has an opening allowing the deposit of waste by the users and their removal by the waste collectors. they are generally implanted in the villages without any preliminary study, with no protection against the attraction of various animals, and without any measure of treatment of leachates. • individual garbage cans: these are individual plastic garbage cans. this method of pre-collection is used more by the inhabitants of city centers and shopkeepers. the waste is put in these garbage cans, which the residents take back once emptied by the collection service. • plastic bags: this type of pre-collection is the most common in the city centers and individual housing estates. before the collection trucks pass by, the residents deposit their waste in bags or cardboard boxes in front of their homes or on the sidewalks of the streets, in the form of piles that the apc truck collects for the public dump. fig. 2. pre-collection of waste. 2) collection the collection operation is located at the heart of the waste management process. it is a public order operation that falls within the framework of protecting the population’s health and ensuring a better quality of life. it consists of the collection and grouping of waste for transportation. at present, there are two methods of removal in algeria: (1) door to door, in which the collection service ensures a regular passage for the waste evacuation, (2) involuntary contribution, in which the generator ensures the waste transfer towards a point of regrouping so that they are transported by the service in charge of the operation towards a place of elimination or treatment. this collection mode is very suitable for the selective sorting operation [31]. fig. 3. means of transporting waste to the landfill. b. waste disposal in algeria, municipal solid waste management services have traditionally focused on "cleaning" only, with little attention paid to waste disposal resources. this had significant negative economic, environmental, and social impacts and the household waste sector was experiencing difficulties in almost all areas. 1) dumping sites in algeria, the elimination of household and similar waste by the setting in wild dumps is the most used mode, with a rate of 87%. despite an environmental policy and regulations on waste disposal, such waste is constantly increasing. according to a survey conducted by the mate services, more than 3000 illegal dumps have been identified in the 48 wilayas with an area of about 4552.5ha. an almost similar geographical location characterizes the majority of these dumps. 2) technical landfills since 2001, the algerian government has chosen to eliminate urban waste by burying it in landfills and has launched an ambitious program of technical landfills throughout the country. one of the objectives of progdem is to abandon the traditional method of waste disposal by landfilling [27]. fig. 4. burial and sorting of waste at the cet of m’sila. engineering, technology & applied science research vol. 12, no. 3, 2022, 8675-8682 8679 www.etasr.com naghel et al.: household waste management challenges v. evolution of the population of m’sila as a factor generating household waste recent research has shown that the population grows by more than 30% annually in developing countries. this growth is most evident in urban areas, accompanied by increased waste generation [11, 24-25]. the waste problem is getting worse every year as the population increases. table i shows a significant evolution of the amount of waste in the commune of m’sila. the amount of solid waste generated is equivalent to 85 t/d [26], which requires considerable efforts from the public authorities. this continuous increase in quantity can be explained by the population growth, the lack of recycling infrastructure, the failing collection system, and finally, the change in the socio-economic behavior of households where the standard of living has become acceptable even though the purchasing power has been decreasing in recent years. this evolution is also very remarkable according to the urban structure: • the quantities of waste produced by collective housing are greater than those of individual housing. • the collection systems used to receive these quantities of waste also differ according to the types of housing (for collective housing: there are boxes used for 500, 600, etc. houses). table i. evolution of the quantity of waste generated in m’sila [27] year 2008 2009 2010 2011 2012 2013 2014 2015 2016 number of inhabitants 161647 167480 175080 183803 194735 203822 214661 216788 224991 quantity (t/year) 15621 18934 20688 33318 37280 46428 53274 55393 57902 vi. management system-the collection of household waste in m’sila the management of household waste in the city is a complex problem that the municipality must face in order to better protect the environment and the public health. however, this management requires the participation of all the city actors (social, economic, administrative). the collection is one of the main operations of waste management and forms the cornerstone of the whole operation. it requires material and human means to evacuate the waste from the city. a. sector delimitation according to the various formal interviews carried out on several occasions with the services concerned and [31], we were able to know that to collect the waste of the city of m’sila, the technical service of the municipality has delimited 19 sectors of intervention based on two criteria: • existing material and human resources. • structural roads of the city. b. existing material and human resources 1) material resources the means implemented for the disposal of the city’s household waste are wheeled collection vehicles and fixed collection means (caissons). the wheeled collection vehicles are: • 19 tipper trucks, • 8 regular dump trucks, • 2 dumpers, • 3 agricultural tractors, • 2 bulls and chargers, • 1 amp truck. for the rolling collection means mobilized for this operation, we noted that: • some non-specialized collection vehicles directly affect the organization of the collection. • there often temporary breakdowns. • the number of specialized collection vehicles (tippers) represents the 15% of the total number of vehicles in the municipal fleet. the breakdowns of these means are explained by this low percentage and the age of the existing vehicles (14 and 20 years). suppose we allocate the vehicles according to the number of inhabitants of m’sila. in that case, it can be noted that each specialized vehicle for 10,000 inhabitants is higher than the national average (1 vehicle/7500 inhabitants), while the international average is 1 vehicle/4000 inhabitants. therefore, the fleet of vehicles of the municipality shows a deficit of 4 to 5 vehicles to ensure a regular and average organization in terms of waste collection of the city and following financial means there are two types of caissons: • 3.5-ton boxes, • 2.5-ton boxes, • 240l and 120l wheeled bins. the boxes are intended for collective housing and city facilities (hospitals, universities, etc.). 2) human resources currently, the commune of m’sila mobilizes for the collection of household waste of the city, a workforce of 70 workers including: • 19 drivers, • 44 waste collectors, • 16 sweepers, • the rest are agents of different categories (office, sorting, press, security), • additional agents of private companies. engineering, technology & applied science research vol. 12, no. 3, 2022, 8675-8682 8680 www.etasr.com naghel et al.: household waste management challenges this workforce represents 1 employee for every 2500 inhabitants, which is much higher than the national average of 1 employee/1500 inhabitants, so the human resources show a deficit of 36 workers (waste collectors and sweepers). we note that the staff has no training in the field and that many waste collectors and sweepers are illiterate. vii. quantity of waste generated in m’sila from 2011 to 2016, the amount of waste generated by the city has increased continuously. the annual production of the accumulation has increased from 33318 t/year to 57902 t/year [26, 27] (table i), which is equivalent to an annual growth rate of 11%. if this growth rate continues, by the end of 2025, the quantity will reach 83795.97 t/year. the average waste quantity per capita ratio is 0.8kg/capita/day. this ratio is 0.41kg/capita/day in the slum areas and 1.23kg/capita/day in the residential areas. the ratio for the areas is higher than the estimated average for the major metropolitan areas of developing countries. algeria’s average annual per capita rate increased from 202kg in 1980 to 360kg in 2006. in urban areas, the ratio is 0.7kg/inhabitant/day. this correspondence of weight between m’sila and the rest of the country’s cities is mainly related to the composition, which is in the majority made of fermentable but also of the low rate of humidity of the region. indeed, the city of m’sila is under the influence of a dry semi-arid climate. it receives low rainfall, which is the case for the whole country. the latter influences the waste and makes it more or less light, especially as it is composed of 74.5% of organic matter [26]. viii. composition of household waste in m’sila the study of waste composition is an essential step for good management. authors in [32, 33] cite several reasons for this, including the need to estimate the number of materials produced, identify the source of generation, facilitate the design of treatment equipment, define the physical, chemical, and thermal properties of waste, and ensure compliance with legislations. the waste of the city m’sila is composed of 74.5% of biodegradable materials, 33.1% of recyclable materials (paper, cardboard, plastic, glass, and metals), and 17% of inert materials in the form of construction debris. if we proceed to a finer classification, we obtain 13categories in compliance with the nf x30-408 standards: putrescible waste (fermentable), plastic, metals, glass, paper, cardboard, textiles, sanitary textiles, combustible, composites, incombustible (inert), hazardous waste, fines (sand and ash). however, the content of waste varies according to the standard of living of the populations of the areas (table ii). a typological study allows us to classify the habitat in three categories: • high standard of living settlements (generally in housing estates) where households have substantial financial resources enabling them to consume manufactured goods. these are populations belonging to the upper socioprofessional class. a relatively high rate 76.2% of putrescible waste is composed essentially of organic matter despite the low concentration of its population. • medium standing habitats where households with a medium standard of living reside (these are the inhabitants of collective housing), which partly explains the rate (75.3%) of putrescible waste composed essentially of organic matter; this is certainly due to the high concentration of population, translated by the important quantity of waste generated by the inhabitants of this sector whose collective housing is predominant. • low standard of living habitats of economic, evolutionary, and spontaneous type, highly populated with very little infrastructure (traditional or precarious habitat). there, the rate of putrescible waste is 75.9%, which corresponds to the lifestyles and standards of living of the inhabitants. to these habitat zones, it is necessary to add those of the commercial and business centers and the industrial zones that have a rate of 70.8%. the rate of cardboard and paper is the highest (13.7%) against 5.3% in the collective habitat, 5.2% in the individual, and 3.6% in the precarious one, because of the packaging activities of consumable products. the waste can be grouped into 2 main categories according to the composition obtained: household waste produced by households of different types on the one hand and waste from industrial and commercial areas on the other. this differentiation of the residential regions from industrial and commercial sites allows better waste management planning, especially for a possible recycling program. table ii. physical composition of household waste by type of habitat and activity in m’sila in 2016 [26] materials sector 8 (cet) mostly collective housing (%) sector 2 (apc) mostly individual housing (%) sector 4 (cet) mostly precarious housing (%) sector 1 (apc) mostly commercial use (%) putrescible waste 76.2 75.3 75.9 70.8 papers 3.7 3.2 1.9 3.9 cardboard 1.6 2.0 1.7 9.8 textile 0.1 0.2 0.4 0.2 sanitary textile 1.5 1.2 1.2 1.3 plastics 6.6 8.5 6.6 6.4 fuels 0.8 1.3 1.4 1.1 glass 0.9 0.5 0.6 0.6 composites 0.1 0.7 1.3 0.6 metals 0.2 0.1 1.9 0.2 fuels 1.7 0.9 1.3 1.5 hazardous waste 0.1 0.8 0.9 0.7 fines ≤ 20 mm 6.5 5.3 4.9 2.9 total 100% 100% 100% 100% a. physical characteristics the physical waste composition is largely determined by the nature of the products, the packaging, and the consumption practices of the population. knowing the waste composition is essential because it allows determining waste management methods and promoting treatment and recovery channels [13, 23]. the sampling results (table iii) allowed us to collect essential information to identify the waste. this sampling shows that the composition of household waste is very diverse. the composition of household waste during the random sampling of the 19 sectors of m’sila and the random selection of the contents of the weighing of a quantity of 10kgs of each engineering, technology & applied science research vol. 12, no. 3, 2022, 8675-8682 8681 www.etasr.com naghel et al.: household waste management challenges sector allowed us to note that 74.8% of the waste is organic materials. the remaining 25.2% are distributed mainly on plastics, paper, and cardboard. their percentages are higher than those of the metal and the glass. the share of paper and cardboard remains dominant due to collecting part of the waste from commercial activities such as packaging with household waste. b. chemical characteristics several studies have focused on waste chemical characterization. some aim to evaluate the polluting potential of these wastes [13] or demonstrate harmful effects on human health and the environment. table iv gives examples of the elemental chemical composition of the waste in m’sila. control of the nature and the volume of solid household waste produced in m’sila is necessary for better waste management. also, the determination of the production of the different waste elements aims to facilitate the choice of the technology for the recovery of the pre-collected waste and support the development of the recovery and recycling channels. table iv indicates the chemical composition of the household waste in m’sila. table iii. composition of household waste in m’sila (20112016) [26] category subcategories % % putrescible waste food waste/green waste 74.5 74.8 other putrescible waste 0.2 paper newspapers/recyclable papers 1.4 3.3 other 1.9 cardboard flat cardboard packaging 0.1 2.9 corrugated packaging 2.2 other 0.6 textiles textiles 0.5 0.5 sanitary textiles sanitary textiles 1.3 1.6 plastic flexible plastics 4.2 6.3 recyclable bottles/flasks 1.1 other 1.0 fuel unclassified fuels 1.1 1.1 glass recyclable glass 0.2 0.3 other 0.1 composites food cartons 0.2 0.7 other 0.5 metals ferrous metals 0.1 0.6 non-ferrous metals 0.2 other metals 0.3 fuel unclassified fuels 1.8 1.8 hazardous waste household hazardous waste 0.6 0.6 fines fine less than 20mm 5.5 5.5 total 100 100 table iv. chemical characteristics of household waste [34] features values density 0.28 humidity level 60% carbon to nitrogen ratio 38 calorific value 1000kcal/g ix. conclusion household waste management is a daily and very concrete problem for which local authorities and city residents have often believed it to be simple and linear: collect and dump. instead, it has become more complex with the demographic and spatial growth of cities, changes in nutrition habits, and new environmental challenges to the point of surprising urban actors. seasonal results show that organic matter increases to more than 77% in summer, which is justified by the consumption of fruits and vegetables. in comparison, paper and cardboard drop to 3.5% in periods of high vacations. it can also be noted that the volumes of waste and the composition are not the same in each group of households. they depend on the standard of living, habits, and morals of the population to which we can add that the production of waste tends to increase with the standard of living. for example, residential areas differ from other areas. the current situation of household waste management in the city of m’sila highlights that the latter has difficulty in assuming the management of its waste, and this occurs due to the following reasons: • the lack of material and human resources. • organizational issues. • the lack of training of the staff in charge of these tasks is also a hindrance to good management of household 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[34] compendium of regulatory texts, on environmental protection. m’sila, algeria: mate, 2016. microsoft word 536-1458-1-sm-ed.doc engineering, technology & applied science research vol. 5, no. 2, 2015, 775-780 775 www.etasr.com abdelkarim et al.: volume resistivity and mechanical behavior of epoxy nanocomposite materials volume resistivity and mechanical behavior of epoxy nanocomposite materials mohamed f. abdelkarim electrical p/m dept., faculty of engineering, new cairo academy, egypt mohamed_abdalrehim@yahoo.com loai s. nasrat electrical p/m dept., faculty of engineering, aswan university, egypt loaisaad@yahoo.com salem m. elkhodary electrical p/m dept. faculty of engineering, ain shams university, egypt drsalem@tedata.net.eg abdelmohymen m. soliman electrical p/m dept. faculty of engineering, ain shams university, egypt abdelmohymen_soliman@eng.asu.edu.eg amer m. hassan electrical p/m dept. faculty of engineering, ain shams university, egypt amrmohamedhassan@yahoo.com samia h. mansour polymers & pigments dept. national research center, egypt s.mansour26@hotmail.com abstract-electrical and mechanical properties of polymer composite materials are investigated through the determination of resistivity and hardness for composites samples. epoxy composite samples have been prepared with different concentrations of certain inorganic fillers such as; titanium dioxide (tio2) and silica (sio2), of various size (micro, nano and hybrid) to study the electrical and mechanical behavior. the volume resistivity reaches 3.23×1014 ohm.cm for the micro silica composite. surface of composite material has been mechanically examined by hardness test. the results show that the resistivity of microcomposites and nanocmposites are increased with the decrease of filler concentration. but the resistivity of hybrid composites is increased with the increase of filler concentration. maximum hardness value was obtained from hybrid silica composite with 0.1% filler concentration. keywords: volume resistivity; polymer composite materials; micro-nano-hybrid filler; hardnes i. introduction during the last years, alternative materials (instead of porcelain and glass) for outdoor insulation have been used. the new polymer materials are presently very widely used for outdoor insulation applications. polymer materials such as silicone rubber and epoxy composites are used in outdoor insulators. the maintenance of polymer insulators is easy at the electrical site within small period. due to the high surface areas of the nano fillers and their molecular-level interactions with the polymer chains, there is a great interest in nanocomposites due to significant scientific questions relating to interfacial chemistry and physics as well as their greatly enhanced practical properties [1]. the incorporation of nanoparticles such as al2o3, tio2, and sio2 into a polymer matrix can lead to a simultaneous improvement of different material properties [24]. especially toughness and stiffness of the nanocomposite can be enhanced at the same time, which is not possible for conventional composites with micro or even macro scale fillers to the same degree and for the same low filler contents [5, 6]. due to the high specific surface (relation of the surface to the mass) that mainly distinguishes nanoparticles from microparticles, their insertion into matrix materials can provide completely new properties compared to conventional composite materials [7–10]. in order to develop a new insulation material for heavy electric equipment, epoxy/microand nanocomposites (emnc) were prepared by mixing micro-sized silica with nano-sized layered silicate [11]. epoxy resin is one of the most commonly used thermosetting materials in high voltage apparatus as insulation, due to its excellent mechanical, electrical properties and chemical stability. in recent years, the nano reinforced epoxy resin has attracted a wide interest as it significantly enhances the epoxy’s properties. researches on nano reinforced epoxy resin composites are being carried out ceaselessly. research has shown that the epoxy/nanocomposites demonstrate some advantages in both mechanical and dielectric properties, compared to pure resin system and epoxy with micrometer-size fillers [12]. hardness, a measure of a material’s resistance to localized plastic deformation (e.g., a small dent or a scratch), is considered an important mechanical property. early hardness tests were based on natural minerals with a scale constructed solely on the ability of one material to scratch another that was softer [13]. an analytical relation between hardness and effective strain is established on a metal during cold working. this way, its hardness can be determined from numerically obtained plastic strains without producing the part and following astm2240 d [14]. in this study, volume resistivity and hardness properties have been measured for different epoxy composite samples using micro, nano and hybrid titanium dioxide and silica fillers. ii. expermintal set-up and techniques a. material specimen epoxy package contains two free liquid solvent component resins. component a is a medium viscosity liquid (epoxy resin) and component b (hardener) is a difunctional primary amine. the used fillers are titanium dioxide (tio2) and silica (sio2) in engineering, technology & applied science research vol. 5, no. 2, 2015, 775-780 776 www.etasr.com abdelkarim et al.: volume resistivity and mechanical behavior of epoxy nanocomposite materials micro and nano size. the micro size range is less than 20 μm and the nano size particles are less than 100 nm. a mixture of the two components, a and b in the ratio of (3:1 wt. /wt. %) were blended thoroughly using a magnetic stirrer for 3 minutes. the mixture was degassed under vacuum to remove air bubbles, and then poured into a plastic mold. curing occurred after 24 hours at room temperature (25˚c ±1). the sample is stable to machine after 7 days. epoxy composites were prepared by mixing different ratios (0.1 up to 7 wt. % by weight) of titanium dioxide (tio2) and silica (sio2) as fillers, in micro and nano size with epoxy/hardener mixture [15]. also epoxy composites were prepared from hybrid fillers (different types and concentration of titanium dioxide (tio2) and silica (sio2)). the prepared samples were molded in disc shapes. the disc specimen is coded in table i and table ii due to the type, size and concentration of the added filler. the titanium dioxide and silica filler has different size in micro (m), nano (n) and hybrid (m/n) and also concentration as shown in tables i and ii. table i. code of epoxy composite samples at different type and concentration of fillers. table ii. code of hybrid composite samples at different type and concentration of fillers. filler type filler size and concentration wt% tio2/ sio2 tio2 sio2 nano 0.05/nano 0.05 tin/sin(0.1) nano 0.375/nano 0.375 tin/sin(0.75) micro 0.05/nano 0.05 tim/sin(0.1) tim/n (0.1) si m/n (0.1) micro 0.375/nano 0.375 tim/sin(0.75) tim/n(0.75) si m/n (0.75) nano 0.05/micro 0.05 tin/sim(0.1) nano 0.375/micro 0.375 tin/sim(0.75) micro 0.05/micro 0.05 tim/sim(0.1) micro 0.375/micro 0.375 tim/sim(0.75} the samples dimensions were limited and chosen due to the limitations of the capabilities of available measuring devices in the high voltage laboratory. the dimension of each disc specimen is 50×2 mm for resistivity test and 50×6 mm for hardness test. b. test apparatus resistivity test is applied on disc samples for measuring the volume resistivity indirectly using a resistance tester (high voltage insulation tester) and a circular ring electrode, (figure 1) [16, 17]. fig.1. high voltage insulation tester hardness test measure the ability to resist plastic deformation by penetration. this test is based on measuring the penetration of a specified type of indenter when forced into the specimen under specified conditions. the test was performed according to astm d 2240 standards using hardness tester (zwick 3150, germany) (figure 2) [18]. fig.2. hardness tester c. measurement and uncertainty the result of a measurement is only an approximation or estimate of the true value of the specific quantity measured. the sources of uncertainty in the results of a measurement can be affected by many factors as following: • reference standards and measurement equipment • measurement setup • measurement process • environmental conditions misreading of instrument results, incorrect adjustments, using the wrong instrument, errors in recording calibration data, and computational errors are also common uncertainty factors. all of these errors can be avoided with proper training and attention to detail [19]. the uncertainty of measurement associated with the input estimates is evaluated according to either a “type a” or a “type b” method of evaluation. the “type a” evaluation of filler type filler concentratio n (wt. %) micro tio2 nano tio2 micro sio2 nano sio2 0.1 tim0.1 tin0.1 sim0.1 sin0.1 0.25 tim0.25 tin0.25 sim0.25 sin0.25 0.5 tim0.5 tin0.5 sim0.5 sin0.5 0.75 tim0.75 tin0.75 sim0.75 sin0.75 1 tim1 tin1 sim1 sin1 3 tim3 tin3 sim3 sin3 5 tim5 tin5 sim5 sin5 7 tim7 tin7 sim7 sin7 engineering, technology & applied science research vol. 5, no. 2, 2015, 775-780 777 www.etasr.com abdelkarim et al.: volume resistivity and mechanical behavior of epoxy nanocomposite materials standard uncertainty is the method of evaluating the uncertainty by the statistical analysis of a series of observations. the “type b” evaluation of standard uncertainty is the method of evaluating the uncertainty by means other than the statistical analysis of a series of observations [20]. in this case the input estimate xi is usually the arithmetic mean or the average of the individual observed values that is given by: , 1 1 (1) n i i k k x x x n = = = å ( ) ( ) ( ) (2)ii s x u x s x n = = where: 2 , 1 1 ( ) ( ( ) ) (3) 1 n ii i k k s x x x n = = å when the number of repeated measurements is low (n<10), type a evaluation of standard uncertainty is used as expressed in (2). it should be multiplied by the student, s factor (t) which is selected due to number of samples n for a required confidence level p. ( ) ( ) ( ) (4)iii s x u x t s x t n = ⋅ = ⋅ if the probability distribution is characterized by the measurement result y and its combined standard uncertainty u(y) is approximately normal (gaussian), and u(y) is a reliable estimate of the standard deviation of y, then the interval [yu(y)] to [y+u(y)] is expected to encompass approximately 95% of the distribution of values [21]. although the combined standard uncertainty u(y) is used to express the uncertainty of many measurement results, for some commercial, industrial and regulatory applications (e.g., when helth and safety are concerned), what is often required is a measure of uncertainty that defines an interval about the measurement result y within which the value of the measured y can be confidently asserted to lie. the measure of uncertainty intended to meet this requirement is termed expanded uncertainty, suggested symbol u, is obtained by multiplying u(y) by a coverage factor (k). ( ) (5)u k u y= ⋅ it is confidently believed that y is greater than or equal to [y-u] and is less than or equal to [y+u], which is commonly written as [y=y±u]. in general, the value of the coverage factor k is chosen on the basis of the desired level of confidence to be associated with the interval defined by the equation (5) [21]. iii. results and discussion a. electrical resistivity of epoxy composites at different type for micro and nano fillers. the addition of an inorganic filler to epoxy means that the ionic particle increases in the polymeric composites. if the bond between the particle of filler and epoxy resin is weak, the ionic particle will be liberated at increasing the filler concentration. when filler concentration increases, the resistivity will be decreased for epoxy composites. the electrical conductivity of composites made of a conductive phase dispersed in an insulating matrix critically depends on the filler loading [22]. the resistivity test is considered nondestructive because the specimen is tested by passing current through the sample using dc high voltage supply. the color of all samples under investigation remains the same and there is no change to be found regarding the exterior surface after the test (figure 3). the resistivity is measured for composite samples which have micro, nano or hybrid filler (figure 4). the epoxy composite with 0.1% micro silica filler records maximum resistivity at 3.23×1014 ohm.cm. the resistivity for micro titanium composite is 1.3 times the resistivity of micro silica composite at 3% filler concentration. epoxy composite loaded with 0.1% micro filler is larger than epoxy which records 2.75×1014 ohm.cm (figure 4). tim0.1 tin0.1 sim0.1 sin0.1 tim/n (0.1) fig.3. the specimens at different type and size of filler fig.4. electrical resistivity of micro composite loaded with different type and filler concentration. for epoxy loaded with filler concentration larger than 3%, the resistivity for nanocomposite with titanium oxide is larger than the resistivity of microcomposite for the same filler as shown in figure 5 due to distributed nano filler uniformly in epoxy matrix at preparation but the micro filler particle is accumulated with other particles when filler concentration increase. the behavior of resistivity for nanocomposites depends on the physical interaction between the epoxy and filler. the micro particle filler is concentrated with other particles in the mixture which gives bad filler distribution. on the other hand the distribution of nano filler in composite is uniformly distributed. nanocomposites have good insulation properties comparing with microcomposites due to the material resistivity of titanium oxide and silica as fillers. engineering, technology & applied science research vol. 5, no. 2, 2015, 775-780 778 www.etasr.com abdelkarim et al.: volume resistivity and mechanical behavior of epoxy nanocomposite materials fig.5. electrical resistivity of epoxy composite filled with titanium dioxide at different size and concentration. nanocomposites resistivity has maximum value at wide range of filler concentration comparing with microcomposites (figure 6). this is referring to the chemical structure of composites. the resistivity of nano silica composite is decreased by 24.37% when the filler increase from 1% up to 5% due to the percolation theory of material. percolation point illustrates the characteristic of epoxy composites at increasing the filler which leads to transform the material from insulator to conductive. the sharp decreasing of resistivity for micro silica composite is referring to increase filler up to critical concentration which is called the percolation threshold point. fig.6. electrical resistivity of epoxy composite filled with silica at different size and concentration. b. application of uncertainty concept in the resistivity test and hardness test. the resistivity test is applied for polymer composites to evaluate the electrical property of composite materials and the hardness test is employed on polymer composites to illustrate the mechanical behavior of composites. the electrical test and mechanical test are repeated on four samples which have the same content. the uncertainty concept is used to detect the error in reading and how this result to be applicable and error within range. the error u is calculated with (1)-(5). if the number of similar samples (n) is equal to four and also student factor →k, the coverage factor (k) will be 3.18 at confidence level 95%. table iii illustrates the final results in error calculation in value and percentage. there is four samples with the same chemical feature, the resistivity ρ for this samples represent the mean advised value for this type and also has error u in form ρ=ρ±u(ρ). the hardness for composite samples is detected through the mean advised value for this type in addition to error u in form hardness= hardness ±u (hardness). for uncertainty principle, the suggested confidence level in 95% is suitable with the final results in error at range 5%. the calculated error is detected under uncertainty concept and in range for resistivity and hardness test. c. electrical resistivity for epoxy composites at different type and size for hybrid fillers. the electrical behavior for epoxy hybrid composites depends on the added filler. therefore the filler contains two types with different particle size (hybrid filler). the main purpose of filler addition is the improvement of electrical performance and mechanical feature. the resistivity of composite with hybrid filler is maximized comparing with nano and micro composite. figure 7 illustrates that the maximum resistivity will be detected for composites with 0.1% hybrid filler from mixing of micro titanium dioxide and nano silica by 50:50 weight. the filler which is added to composite contains two different materials (titanium dioxide and silica) in micro size or in nano size. if this hybrid filler concentration increases, the resistivity will be decreased at any size of filler as shown in figure 8. the hybrid filler used contains two different particle sizes for same silica material. the resistivity of hybrid composite is shown in figure 9. if this filler concentration increases, the resistivity will decay. fig.7. electrical resistivity of hybrid composite with two different materials and size at various filler concentration. fig.8. electrical resistivity of hybrid composite with two different materials at same particle size engineering, technology & applied science research vol. 5, no. 2, 2015, 775-780 779 www.etasr.com abdelkarim et al.: volume resistivity and mechanical behavior of epoxy nanocomposite materials fig.9. electrical resistivity of hybrid composite with two materials at same type and various particle sizes. d. effect of filler type and size on the hardness of epoxy composites. mechanical properties are detected by static mechanical tests and dynamic mechanical analysis. one of the important tests in static analysis is hardness test. hardness is indicated by a static indentation test which means that a ball, cone, or pyramid is forced into the surface of the metal being tested. the relationship of load to the area or depth of indentation is the measure of hardness, such as in brinell, knoop, rockwell, and vickers hardness tests. when the indentation is small, material hardness will be large. hardness is a mechanical property, which can be dramatically changed by processing and heat treatment [23]. hardness test is applied on the samples according to the astm d 2240 standard. hardness of composite samples is measured by a digital hardness tester which is used to determine the hardness of soft plastic and epoxy is found on scale shore d [16]. the hardness test is applied on four samples with the same content to achieve minimum error in results and get good practical results at scale shore d. the hardness results are shown in tables iii and iv. micro composites have hardness larger than the nano composites. epoxy filled with micro titanium and silica filler records maximum hardness at 85.3% and 86.7% shore d scales respectively (table iii). the average of hardness is considered for four samples with the same content and error percentage due to uncertainty concept within maximum error at 6.29%. hybrid silica composite which contain different filler size in micro and nano has maximum hardness at 87.43% and is larger than hybrid composite (tim/sin (0.1)) with 2.76% only at shore d scale. iv. conclusion micro filler is added to epoxy with minimum concentration 0.1% in order to get maximum resistivity at 3.23 × 1014 ω.cm and other hand, hybrid composites which contains mixture from nano titanium and nano silica filler with 0.1% concentration has at 3.35×1014 ω.cm. the resistivity of epoxy composites decrease if the filler concentration increases regardless of filler size and concentration due to percolation theory. hardness of hybrid composite material is more strength than microcomposite and nanocomposite. hybrid silica composite using 0.1% mixture of micro and nano size gave maximum hardness at 87.43% shore d. table iii. the calculation of different filler concentration. table iv. the calculation of uncertainty forhybrid epoxy composites references [1] x. fan, l. lin, p. b. messersmith, “surface-initiated polymerization from tio2 nanoparticle surfaces through a biomimetic initiator: a new route toward polymer–matrix nanocomposites", composites science and technology, vol. 66, no. 9, pp. 1195–1201, 2006 [2] b. wetzel, p. rosso, f. haupert, k. friedrich., “epoxy nanocompositesfracture and toughening mechanisms”, engineering fracture mechanics., vol. 73, no. 16, pp. 2375–2398, 2006 [3] a chatterjee, m. s. islam., “fabrication and characterization of tio2 epoxy nanocomposite”, materials science and engineering: a, vol. 487, no. 1-2, pp. 574–585, 2008 [4] t. mahrholz, j. stängle, m. sinapius, “quantitation of the reinforcement effect of silica nanoparticles in epoxy resins used in liquid composite composites using titanium filler composites using silica filler sample hardness % u % sample hardness % u % epoxy 78.5 1.97 tim0.1 79.2 0.58 sim0.1 80.3 3.16 tim0.25 79.8 2.06 sim0.25 82.2 0.84 tim0.5 85.3 6.08 sim0.5 83.1 1.84 tim0.75 82.7 1.91 sim0.75 86.7 2.61 tim1 82.3 1.98 sim1 86.7 1.11 tim3 79.2 4.32 sim3 84.7 1.27 tim5 80.2 2.66 sim5 84.8 1.28 tim7 83.1 3.42 sim7 84.8 1.35 tin0.1 75.9 2.10 sin0.1 86.15 4.04 tin0.25 78.2 2.39 sin0.25 84.35 4.54 tin0.5 77.4 2.24 sin0.5 85.35 3.74 tin0.75 78.2 1.66 sin0.75 85.15 2.03 tin1 78.4 5.12 sin1 78.83 3.42 tin3 84 6.00 sin3 77.55 6.20 tin5 81.2 1.78 sin5 81.75 3.29 tin7 81.1 3.73 sin7 83.30 5.44 samples hardness% u% tin/sin(0.1) 81.60 6.29 tin/sin(0.75) 76.13 3.45 tim/sin(0.1) 85.08 2.03 tim/sin(0.75) 76.38 3.55 tin/sim(0.1) 80.93 1.73 tin/sim(0.75) 76.13 4.16 tim/sim(0.1) 82.45 1.71 tim/sim(0.75} 75.08 2.47 tim/n (0.1) 78.53 3.63 tim/n(0.75) 82.58 6.23 si m/n (0.1) 87.43 1.01 si m/n (0.75) 77.83 1.31 engineering, technology & applied science research vol. 5, no. 2, 2015, 775-780 780 www.etasr.com abdelkarim et al.: volume resistivity and mechanical behavior of epoxy nanocomposite materials moulding processes”, composites part a: applied science and manufacturing, vol. 40, no. 3, pp. 235–243, 2009 [5] b. wetzel, f. haupert, m. q. zhang, “epoxy nanocomposites with high mechanical and tribological performance”, composites science and technology, vol. 63, no. 14, pp. 2055–2067, 2003 [6] j. cho, m. s. joshi, c. t. sun, “effect of inclusion size on mechanical properties of polymeric composites with micro and nano particles”, composites science and technology, vol. 66, no. 13, pp. 1941–1952, 2006 [7] r. a. vaia, t. b. tolle, g. f. schmitt, d. imeson, r. j. jones, “nanoscience and nanotechnology: materials revolution for the 21st century”, sampe journal, vol. 37, pp. 4–31, 2001 [8] e.t. thostenson, c. li, t. w. chou, “nanocomposites in context”, composites science and technology, vol. 65, no. 3-4, pp. 491–516, 2005 [9] b. wetzel, f. haupert, k. friedrich, m. q. zhang, m .z. rong, “impact and wear resistance of polymer nanocomposites at low filler content”, polymer engineering & science, vol. 42, no. 9, pp. 1919–1927, 2002 [10] b. bittmann, f. haupert, a. k. schlarb, “preparation of tio2/epoxy nanocomposites by ultrasonic dispersion and their structure property relationship”, ultrasonics sonochemistry, vol. 18, no. 1, pp. 120–126, 2011 [11] j. j. park, c. h. lee, j. y. lee, h. d. kim, “preparation of epoxy/micro and nanocomposites by electric field dispersion process and its mechanical and electrical properties”, ieee transactions on dielectrics and electrical insulation, vol. 18, no. 3, pp. 667-674, 2011 [12] q. wang, g. chen, a. s. alghamdi, “influence of nanofillers on electrical characteristics of epoxy resins insulation”, 10th ieee international conference on solid dielectrics solid dielectrics (icsd), potsdam, germany, july 4-9, 2010 [13] w. d. callister jr., d. g. rethwisch, fundamentals of materials science and engineering, 5th edition,, john wiley & sons, inc., 2000 [14] f. o. sonmez, a. demir, “analytical relations between hardness and strain for cold formed parts”, journal of materials processing technology, vol. 186, no. 1-3, pp. 163–173, 2007 [15] m. f. abdelkarim, l. s. nasrat, s. m. elkhodary, a. m. soliman, a. m. hassan, s.h. mansour, “effect of nano fillers on electrical performance of epoxy composite insulators”, international journal of engineering and technical research, vol. 2, no. 7, pp. 60-65, 2014 [16] kyoritsu electrical instruments works, ltd., http://www.kew-ltd.cp.jp. [17] instruction manawal 4-range high voltage insulation resistance tester, model 3125, http://www.kew-ltd.cp.jp [18] zwick materials testing, zwick 3140 digital shore hardness testers/densimeters, www.zwick.com [19] e. brown, “understanding and expressing measurement uncertainty associated with dc and low frequency metrology”, quality systems lab boca raton, fl 33487 [20] european co-operation for accreditation, evaluation of the uncertainty of measurement in calibration, ea-4/02 m, 2013. [21] k. birch, measurement good practice guide no. 36: estimating uncertainties in testing, british measurement and testing association, crown, 2003 [22] n. grossiord, j. loos, l. van laake, m. maugey, c. zakri, c. e. koning, and a. j. hart, "high-conductivity polymer nanocomposites obtained by tailoring the characteristics of carbon nanotube fillers'', advanced function material, vol. 18, pp. 3226–323, 2008 [23] h. chandler, introduction to hardness testing, 2nd edition, 06671g, 1999 microsoft word etasr_v12_n4_pp8967-8971 engineering, technology & applied science research vol. 12, no. 4, 2022, 8967-8971 8967 www.etasr.com priyadarsini et al.: controller design for the pitch control of an autonomous underwater vehicle controller design for the pitch control of an autonomous underwater vehicle linkan priyadarsini school of electrical engineering kiit deemed to be university bhubaneswar, india linkanpriyadarsini88@gmail.com shubhasri kundu school of electrical engineering kiit deemed to be university bhubaneswar, india shubhasri.kundufel@kiit.ac.in manoj kumar maharana school of electrical engineering kiit deemed to be university bhubaneswar, india mkmfel@kiit.ac.in bibhu prasad ganthia department of electrical engineering igit, sarang dhenkanal, odisha, india bibhuganthia@igitsarang.ac.in received: 8 may 2022 | revised: 29 may 2022 | accepted: 4 june 2022 abstract-in recent years, the autonomous underwater vehicle (auv) has found its application in a large number of areas, especially in the ocean environment. but due to its highly nonlinear nature with six degrees of freedom and the presence of hydrodynamic forces, the equations for auv control become complex and difficult to design. hence, in order to overcome this complexity and non-linearity, a reduced-order subsystem is derived for controlling the pitch. linear quadratic regulator (lqr) and fractional order pid (fopid) techniques have been applied for determining the controller for better performance of pitch control in the presence of disturbance. keywords-autonomous underwater vehicle (auv); imc-pid; lqr; fopid i. introduction an auv is an automatic submersible vehicle that can function in the absence of real time controller, without any human interference [1]. the presence of nonlinearity in the vehicle dynamics makes difficult to apply linear controller to the auvs and the complexity in the dynamics of auvs makes the design of its controller difficult. due to the presence of high non-linearity, time-varying characteristics, unpredictable hydraulic coefficients, and the interference caused by sea currents and waves, the dynamics of the auv become quite complex. the design of a controller for auv is a challenging task as the complexity in design basically lies in finding the hydrodynamic parameters and the non-linearity in the dynamics of the vehicle [2]. in order to control the pitch of auv many methods have been proposed. the lqr-based controller has been designed for the derived divine plane model of auv and the performance is analyzed with matlab/simulink in [3, 4]. the current paper, gives a detailed study of the particle swarm optimization (pso) algorithm used to optimize the fractional order pid (fopid) controller for obtaining a fast and robust response for the pitch control of an auv [1, 5]. the parameters obtained using the pso-based fopid will be utilized for obtaining the response for pitch angle. the response of the pso based fopid controller is compared with the response of imc-pid and lqr controllers. with the help of the response, rise time, settling time, overshoot and integral of time absolute error (itae) can be computed. itae has been considered as the objective function [6, 7]. ii. modeling of the auv the mathematical modelling of an auv requires the study of its kinematics and dynamics. the geometrical aspect describes the kinematics, while the dynamics of the vehicle describe and analyze the forces that cause motion [8]. to identify the location and direction of the auv, the differential equation of the vehicle's 6-dof (degrees of freedom) motion must be solved [9]. the positional and translational motion along x, y and z axes is represented using flow, amplitude, and heave [9] respectively, while the orientation and rotational motion are described with the help of roll, pitch, and yaw [1, 11, 12] a. vehicle kinematics a two-coordinate frame has been used to analyze a vehicle path with 6 dofs [13]. because it is attached to the vehicle, the moving reference frame is known as a body-fixed reference frame [13, 14]. an inertial frame is used to describe the trajectory of the body-fixed frame. with the body-fixed frame, we can characterize the vehicle's linear and angular velocities, whereas the inertial frame describes its position and orientation [1]. six-dof vehicle motion can be represented in a generic sense by the following vectors [14]: corresponding author: bibhu prasad ganthia engineering, technology & applied science research vol. 12, no. 4, 2022, 8967-8971 8968 www.etasr.com priyadarsini et al.: controller design for the pitch control of an autonomous underwater vehicle � � �������� (1) � � � �� (2) � � � �� (3) where �� � � �� � is the position vector, �� � � ���� the euler angle vector, � � � � �� the uniform speed vector [3], � � � ��� � the rotational speed vector, � � � ���� represents the direction of the forces, and � � � ��� � is the moments vector. table i. motion of the auv dofs motion forces and moments velocity [10] position and euler angles [10] 1 surge x u x 2 sway y υ y 3 heave z w z 4 roll k p φ 5 pitch m q θ 6 yaw n r ψ the euler angle transformation �� � !��" , where !��" is the jacobian matrix, represents plotting among the two coordinate systems [14]. b. vehicle dynamics the vehicle dynamics consist of translational as well as rotational motion [3, 8]. the equation for the translatory movement of the vehicle is: #! $ % & ∗ $ % &� ∗ �( % & ∗ !& ∗ �( "" � )$� (4) and the rotational movement of the vehicle is: *$&� % & ∗ !*$&" % #�( ∗ ! $ % & ∗� $" � #$ (5) by employing newton's and euler's equations and ignoring surge, sway, heave, and yaw, the equation of pitch control can be expressed as [8, 15]: *+ �� % ,*. */ 0�� . !�� % ��"*12 % !�� . ��"*/-% !�� . �� "*+/% #3�( !�� . �� % 4�". ( !4� . �� % ��"5 � � (6) */ �� % !*+ . *"�� . !�� % ��"*1/ % !�� . ��"*+-% !�� . ��"*/-% #3 ( !�� . 4� % ��". �( !�� . �� % �"5 � � (7) assuming the velocity of the heave is very small and can be neglected, the state space equation of the system will be [16]: �*/ . �6 0 00 1 00 0 1� � �� ��� �+ � .�6 0 �9 �0 0 ��.1 0 0 � � � �� = � �:;00 � (8) the transfer function for the pitch control can be obtained from the matrix representation as: <9 !=" = 9!;":>!;" � ?@>abc?d ;ef ?@>abc?d;f ?gabc?d (9) the transfer function for the auv can be obtained considering the following data: fin lift (�:;) = -1575.9kg.m2/s, */ = 469kg/m2, added mass �6 = -458 kg.m2, hydrostatic �9 = 13719.6kg.m 2 /s 2 , and takes the following form: <9 !=" � f�.i�i$.$$jj;ek$.l$j;k� (11) iii. conctroller design in this section, we will go over the designs of various controllers that will be used to control the pitch of the auv. it is necessary for the controller to be observable in all the states in order to be used effectively. a. imc-pid controller the internal model controller (imc) is composed of a constant controller q(s) and the plant model, where g(s) is the model of the plant. it is equipped with an inbuilt filter controller f(s). q(s) and f(s) are corrected by increasing the robustness of the filter, which is achieved by selecting the filter parameter appropriately [2]. figure 1 gives a representation of an imc structure. the controller is given by: mn !=" � 6!;"�f(o!;"6!;" (12) fig. 1. imc structure. b. linear quadratic regulator (lqr) controller the advantage of using lqr is that it provides practical feedback gain [3]. conventional controllers have a drawback as they result in higher overshoot and due to the lack of proper tuning, often the controller is not optimal [17]. the state space model of the system is given by [3]: �� � p� % q� (13) the lqr design method consists of designing the gain factor k, i.e. a state feedback. the objective function j is taken in such a way that its minimization makes the system stable [3]: engineering, technology & applied science research vol. 12, no. 4, 2022, 8967-8971 8969 www.etasr.com priyadarsini et al.: controller design for the pitch control of an autonomous underwater vehicle � r !� s t� % �s u�"vwx$ (14) q and r represent symmetrical diagonal matrices that decide the weight factors [3]: q, r ≥ 0 (15) the main aim of the lqr controller is to give optimal feedback gain as described below [3]: � � .�� (16) the feedback gain (k) can be calculated using the matrix algebraic riccati equation (mare) [3] as follows: � � .ufs qs y� (17) � � .ufs qs y (18) fig. 2. lqr structure. c. fractional order pid controller [18] podlubny proposed the fractional order pid controller in 1997 [19], and since then, it has become widely used. it should be noted that the order of the integrator and differentiator in fopid is different from the order of the integrator and differentiator in the typical pid controller. both the integrator and the differentiator should be in the correct order [18, 20]. the transfer function of a pid controller of this type is: <:z !=" � �[ % \]^_ % �` ab (19) fig. 3. fopid structure. authors in [5] proposed the particle swarm optimization (pso) technique, in which a swarm is represented by m particles. these particles are described by two variables, x and v, representing the position and its corresponding velocity in the search space. the pso algorithm is given in figure 3. the algorithm starts with randomly initializing the particles and updating their position and velocity values until an optimized value is obtained [1]. the updated equation for position and velocity for the swarm in the search space is given by: �c !w % 1" = �c!w" + c!w + 1" (20) c!w + 1" = & c!w" + d�∅�fgc!w" − �c!w"h + d�∅�fm!w" − �c!w"h (21) itae has been considered as the objective function and is given by: *ipj = r w|l!w"|vw x $ (22) fig. 4. flowchart of the pso algorithm. with the help of pso, it is possible to optimize the parameters of the fopid controller. the initial population is assumed to be 100 and the number of iterations is calculated to be 50. iv. results and discussion a. simulation of pitch control for auv the step response for the pitch control of the auv using imc-pid, lqr-pid, and fopid is shown in figure 5. the performance comparison of the three controllers is shown in table ii. table ii. parameter index of step for pitch subsystem method over-shoot (%) mn(s) mo(s) mp(s) itae imc-pid 30.8 0.896 18.3 2.05 4.068 lqr 5.27 0.532 7.39 1.07 3.79 fopid 3.55 0.0129 0.0558 0.031 2.867 b. simulation of pitch control for auv in the presence of disturbance the response of the pitch subsystem using imc-pid, lqr and fopid in the presence of sinusoidal disturbance is illustrated in figure 6. engineering, technology & applied science research vol. 12, no. 4, 2022, 8967-8971 8970 www.etasr.com priyadarsini et al.: controller design for the pitch control of an autonomous underwater vehicle fig. 5. step response of the pitch subsystem via fopid, optimal pid, and imc-pid. fig. 6. response of the pitch subsystem via fopid, optimal pid, and imc-pid in the presence of disturbance. table iii. parameter index for the response of the pitch subsystem in the presence of disturbance method over-shoot (%) mn(s) mo(s) mp(s) itae imc-pid 32.33 2.236 36.66 4.579 11.642 lqr 5.96 1.601 10.96 1.015 10.978 fopid 4.62 0.9720 0.0558 0.626 10.447 v. conclusion this study presents a pid control technique for auv pitch subsystems that is of fractional order. when compared to optimum pid and imc-pid, this technique has significantly shorter settling time, rising time, peak time, and overshoot. it demonstrates an increase in the quickness of response in the presence of a disruption. it is obvious from the simulations that the performance of the proposed fopid is superior to that of the optimum controller and the imc. references [1] y. liu, j. zhang, and s. wang, "optimization design based on pso 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[16] w. doyle, "magnetization reversal in films with biaxial anisotropy," ieee transactions on magnetics, vol. 2, no. 2, pp. 68–73, jun. 1966, https://doi.org/10.1109/tmag.1966.1065802. [17] s. w. jun, d. w. kim, and h. j. lee, "design of t-s fuzzy-model-based controller for depth control of autonomous underwater vehicles with parametric uncertainties," in 2011 11th international conference on control, automation and systems, gyeonggi-do, korea (south), jul. 2011, pp. 1682–1684. engineering, technology & applied science research vol. 12, no. 4, 2022, 8967-8971 8971 www.etasr.com priyadarsini et al.: controller design for the pitch control of an autonomous underwater vehicle [18] s. d. joshi and d. b. talange, "integer & fractional order pid controller for fractional order subsystems of auv," in 2013 ieee symposium on industrial electronics & applications, kuching, malaysia, sep. 2013, pp. 21–26, https://doi.org/10.1109/isiea.2013. 6738961. [19] i. podlubny, "fractional-order systems and y*qrb controllers," ieee transactions on automatic control, vol. 44, no. 1, pp. 208–214, jan. 1999, https://doi.org/10.1109/9.739144. [20] n. wang, j. wang, z. li, x. tang, and d. hou, "fractional-order pid control strategy on hydraulic-loading system of typical electromechanical platform," sensors, vol. 18, no. 9, sep. 2018, art. no. 3024, https://doi.org/10.3390/s18093024. authors profile linkan priyadarshini is working as a phd research scholar in the school of electrical engineering at kiit deemed to be university, bhubaneswar, odisha, india. her research area is under water vehicle design. shubhasri kundu is an assistant professor in the school of electrical engineering at kiit deemed to be university, bhubaneswar, india. manoj kumar maharana is an associate professor in the school of electrical engineering at kiit deemed to be university, bhubaneswar, india. bibhu prasad ganthia is an assistant professor in the department of electrical engineering, igit, sarang, dhenkanal, odisha, india. microsoft word etasr_v12_n6_pp9503-9509 engineering, technology & applied science research vol. 12, no. 6, 2022, 9503-9509 9503 www.etasr.com husain et al.: a study of one-dimensional weak shock propagation under the action of axial and … a study of one-dimensional weak shock propagation under the action of axial and azimuthal magnetic field: an analytical approach akmal husain department of mathematics, school of engineering university of petroleum and energy studies dehradun, india akmal.h04@gmail.com s. a. haider department of mathematics shia p. g. college lucknow, india aftabhaidershiapgc2019@gmail.com v. k. singh department of applied sciences institute of engineering and technology lucknow, india singhvijaikrishna9@gmail.com received: 22 august 2022 | revised: 9 september 2022 | accepted: 12 september 2022 abstract-the present paper presents an analytical study of the one-dimensional weak shock wave problem in a perfect gas under the action of a generalized magnetic field subjected to weak shock jump conditions (r-h conditions). the magnetic field is considered axial and azimuthal in cylindrically symmetric configuration. by considering a straightforward analytical approach, an explicit solution exhibiting time-space dependency for gas-dynamical flow parameters and total energy (generated during the propagation of the weak shock from the center of the explosion) has been obtained under the significant influence of generalized magnetic fields (axial and azimuthal) and the results are analyzed graphically. from the outcome, it is worth noticing that for an increasing value of mach number under the generalized magnetic field, the decay process of physical parameters (density, pressure, and magnetic pressure) is a bit slower, whereas the velocity profile and total energy increase rapidly with respect to time. moreover, for increasing values of shock-cowling number the total energy grows rapidly with respect to time. keywords-weak shock waves; analytical solution; rankine hugoniot conditions; magnetogasdynamics i. introduction in general, the complex physical phenomena occurring in nature are non-linear and are described by mathematical models in the form of non-linear partial differential equations (npdes). during the last few decades such nonlinear mathematical models are getting a vital role in the fields of natural, engineering, and medical sciences such as plasma physics, solid-state physics, fluid mechanics, optical fibers, geophysics, biomechanics, etc. and many efforts have been made for confronting the exact and numerical solutions of such physical systems [1-6]. due to the high complexity, finding the exact (closed form) solution of such realistic models is thus a challenging and rigorous task because it comprises many physical and natural intricacies and only in certain cases can we explicitly unravel the solutions. mathematically, the nonlinear wave (shock wave) propagation phenomenon is formulated as a quasilinear hyperbolic system of partial differential equations. the shock wave occurs in gaseous media by a dynamical mechanism in which an immense amount of energy is abruptly released over a small interval of time during the propagation of wave discontinuity, e.g. prolonged rapid electrical discharges in the air such as thunder-strokes, explosions of long thin wires, etc. it is well known that shock processes usually occur due to the high temperature in which the gas ionizes, so the effect of the magnetic field also becomes significant. the understanding of the influence of the magnetic field on wave propagation phenomenon and the resulting flow field is of great importance as it involves many applications in the field of space science research, atmospheric sciences, nuclear sciences, etc. the study of shock wave propagation under the action of a magnetic field for a perfect gas are important for the interpretation of the phenomena encountered in astrophysics from the theoretical and experimental points of view, as the ideal magnetogasdynamic flow involves a plasma in which the diffusion effects are negligible. many researchers [7-11] have worked to better understand the magnetic field effects on the dynamics of shock waves. in keeping with [7-11], authors in [12] discussed the self-similar solution of the blast wave problem with identical geometry under constant axial current. authors in [13] studied one dimensional steady flow of a perfect gas and reported the first corresponding author: akmal husain engineering, technology & applied science research vol. 12, no. 6, 2022, 9503-9509 9504 www.etasr.com husain et al.: a study of one-dimensional weak shock propagation under the action of axial and … complete explicit shock solution in the aligned field magnetogasdynamics. in [14], the authors considered spherical shock propagation in a magnetized medium and found that the model has some limitations on real flare produced shocks, taking into account isothermal flow conditions in planar and identical geometry. authors in [15] reported the existence of self-similar solutions for blast waves and observed that the magnetic field effects play a significant role in the theory of blast waves. authors in [16] used the asymptotic approach and analyzed the decay behavior of sawtooth profile for planar and cylindrical gas dynamical flows headed by weak wave front under the action of axial magnetic field. authors in [17] studied the evolution and formation of the 1-dimensional magnetohydrodynamic shock wave in the approximation of the low plasma-to-magnetic pressure ratio and obtained an analytical expression for shock formation. a detailed theoretical, experimental, and computational review on magneto aerodynamics was presented in [18] and the features of shock structure in the presence of magnetic field were discussed. within the above mentioned framework, several investigations have been recently performed for finding the analytical solution of ideal mhd equations. authors in [19] obtained a particular solution of strong discontinuity waves in ideal magneto-gasdynamic flow via lie group transformation analysis and studied the effect of the applied magnetic field on the evolutionary behavior of reflected and transmitted waves which arises when a magnet-acoustic wave collides with a shock. the methodology proposed in [20, 21] gave the precise solution of the shock wave problem involving strong discontinuities in magneto-gas-dynamic regime. the convergence of the shock wave in the cylindrical symmetry was investigated in [22] and rendered analytical asymptotic results on the shock trajectory for small radii. by using the method of generalized wavefront expansion, authors in [23] derived nonlinear coupled evolution equations and assessed how the magnetic field, either axial or azimuthal, influences the formation of weak shock waves in an ideal gas. authors in [24] presented the numerical description of the flow field in magnetogasdynamics and analyzed that the presence of magnetic field suppresses the instabilities in the point explosion problem. authors in [25] reported an approximate analytical solution for propagation of cylindrical shock waves in isothermal flow conditions with azimuthal magnetic field. authors in [26] initiated the analysis of weak shock propagation in a simplified van der waals gas influenced by thermal radiation under optically thin limit. authors in [27] studied the strong explosion problem in perfect gasdynamics with magnetic field effects using power series solution and recovered the result described by [28] in the absence of magnetic field. recently, authors in [29] scrutinized the point explosion problem in perfect magneto-gasdynamic flow on stellar surface and reported an explicit exact solution of fluid characteristics (density, velocity, and pressure) which expounds time-position dependence. authors in [30] highlighted the impact of dust-laden particles on the evolution of magnetic shock waves and analyzed the behavior of half n-wave. authors in [31, 32] solved the riemann problem for the hyperbolic system of conservation laws and examined the study of discontinuous solutions in non-ideal material media. in this article, our goal is to construct a closed-form solution (which exhibits a space-time dependence) to the weak shock wave problem in an ideal gas for cylindrically symmetric flow under the influence of axial and azimuthal magnetic fields (modelled in the form of shock-cowling number, �� = 2ℎ� ��� �⁄ ) and to investigate how the magnetic field and the mach number affect the thermodynamic flow characteristics. it has been assumed that the mass density distribution obeys a power law of the radial distance from the centre of explosion. furthermore, we derived an analytical expression for the total energy of the weak shock wave, influenced by the magnetic field. the way the behavior of physical parameters such as density, velocity, pressure, magnetic pressure and energy is affected by the mach number and the presence of magnetic field, is also assessed. ii. mathematical model of the problem to outline the approach, we consider a basic set of governing conservation equations, consisting one-dimensional compressible cylindrically symmetric unsteady adiabatic motion of a perfect gas under the influence of magnetic field in which viscous stress is negligible. mathematically, this system of euler’s equations corresponding to mass balance, momentum balance, energy and magnetic pressure balance in non-conservative form is given by [33-35]: � + �� + �� + ��� ⁄ � = 0 (1) ��� + �� � + � + ℎ + �2�ℎ ⁄ � = 0 (2) � + �� + �� ��� + �� ⁄ �� = 0 (3) ℎ + �ℎ + 2ℎ�� + ��1 − �� � ⁄ �� = 0 (4) in the above equations, ∈ ℝ and � > 0 stand for the spatial and time variables, �� , �� refers to the mass density, �� , �� is the pressure, �� , �� is the flow velocity, ℎ the magnetic pressure defined as ℎ = � � 2⁄ with � as the magnetic permeability, and is the transverse magnetic field. the entity c accounts for the equilibrium speed of sound and is defined as � � = γ� �⁄ where γ = "# "$ �1 < γ < 2�⁄ is the adiabatic exponent and thermodynamic constants "# and "$ denote the specific heat of the gas at constant pressure and at constant volume respectively. here and hereafter nonnumeric subscripts with respect to physical characteristics indicate partial differentiation unless stated otherwise. the constant � = 0 exhibits the axial magnetic field and � = 1 the azimuthal magnetic field. for motion in ideal gasdynamic medium, the governing dynamical equations (1)-(4) are supplemented with the following constitutive relation (or equation of state): � = �'( �5� where ' is the specific gas constant and ( is the temperature. let ℛ = ℛ��� be the shock-location at time � moving with the shock speed � = +ℛ+ into the medium immediately ahead of the shock given by �� = 0 , �� = constant, �� = ��� � and ℎ� = ℎ�� �, where the thermodynamic profiles with subscript 0 express the values in the pre-shock region. it has been also assumed here that weak shock propagation obeys a power engineering, technology & applied science research vol. 12, no. 6, 2022, 9503-9509 9505 www.etasr.com husain et al.: a study of one-dimensional weak shock propagation under the action of axial and … law �� = �� ℛ , , in which the density of the pre-shock (undisturbed) region �� varies with respect to the shock radius. here, �� is a dimensional constant and , a constant. the value of constant , is to be determined in the ongoing analysis. it is well known that the energy produced during the propagation of a weak shock wave in any gas medium is equal to the sum of the kinetic energy and internal energy of the gas and is a constant. the balance equation for the total energy -. in an ideal magneto-gas-dynamic flow is given by: -. = / 01� �� + 1�231� 4#5 − #6567 + 485 − 865679 � ℛ� : (6) in view of the relation / 556ℛ� : = ℛ ; � obtained from lagrangian equation of continuity, �6� yields the following expression for total energy: -. = / 05=;� + #�231� + ℎ9 ℛ� : − #6 ℛ ; ��231� − 86ℛ ; � (7) iii. formulation of shock-jump conditions at the outset, for the formulation of shock-jump conditions, we recast the fundamental set of balance equations (1) – (4) in conservation form which yields: � + ���� = −��� ⁄ � (8) ���� + ���� + � + ℎ� = −���� ⁄ � − �2�ℎ ⁄ � (9) 45=;� + #>�231�8�231� 7 + 4 2#= �231� + 5= ?>@=8 � 7 = 2#= �132� − 5=?>@8=� (10) 4ℎa;7 + 4�ℎ a;7 = bℎ a;�� − 1�� c d (11) the rankine-hugoniot conditions across the shock front that connects the flow ahead and behind the shock waves can be derived from (8)-(11) and are given by: �� − ���� = ��� − ��� (12) ���� + � + ℎ� − ����� � + �� + ℎ�� = ���� − ����� (13) 42#=231 + 5= ? >@=8 � 7 − 42#6=6231 + 56 =6 ?>@=686 � 7 = � 045=;� + #>8�231��231� 7 − 456=6 ; � + #6>86�231��231� 79 (14) 4�ℎa;7 − 4��ℎ�a;7 = � 4ℎa; − ℎ�a;7 (15) substituting the values of flow profiles from (12), (13), and (15) in (14� yields the following cubic equation in terms of density profile �� , ��: �γ − 2���� ��f + ��2�� + ����� �� + ���γ − 1�g�� γ��� − γ�γ + 1������g� = 0 (16) where g = � ��⁄ represents the mach number with �� = �γ�� ��⁄ �1 �⁄ and �� = 2ℎ� ��� �⁄ denotes the shock cowling number. on solving the cubic equation (16), one obtains the values of the thermo-dynamical characteristics �, �, and ℎ in terms of the density parameter �. thus, (16) along with (12), (13), and (15) allow us to obtain the rankine-hugoniot jump conditions as follows: � = 2>1231 b1 + ��231�i;d 31 �� (17) � = �2>1 41 − 1i;7 � (18) � = j�b13 kla;km;d2>1 + n6ob231> ;m;d ;3�2>1�;p �b231> ;m;d ; q ��� � (19) ℎ = n6�2>1�;�b231> ;m;d; ��� � (20) iv. derivation of the analytical solution to the weak shock wave problem in this section we shall derive an exact solution of compressible eulerian equations (1)-(4) governing the onedimensional unsteady propagation of weak shock waves in generalized magnetogasdynamics by using an analytical approach proposed in [6]. in order to find an exact solution, subject to the rankine-hugoniot’s ratios (17)-(20), we establish an expression immediately behind the shock front for the physical characteristics of pressure and magnetic pressure of the flow, in terms of the other thermo-dynamical variables, density and flow velocity, given as: � = @�231�;b13 kla;km;d>n6�2>1�o�231�;3�2>1�;b1> ;�kla� am;d l;p r�231�413 am;7 ;b1> ;�kla� am;d la ��� (21) ℎ = n6�2>1�?b1> ;�kla� am;d la r�231�413 am;7 ; ��� (22) an inspection of (21) and (22) leads the eulerian nonlinear system (2)-(4) to the following form: � + ==s�1>ℱ�la − =5u5ℱ la + = ; j �vn64231> ; m;7 la r�2>1�l?413 am;7 ; − ℱq = 0 (23) where ℱ = @b13�kla�;k am;d>n6�2>1�rb231> ;m;dla413 am;7; and: � + ��w + �231�� � 4�w + =w7 = 0 (24) � + ��w + =� 0�w + �13�v�=w 9 = 0 (25) plugging (23) and (24) and performing some algebraic manipulations, we get the resulting equation as: x��� = ����3ℒ�� �ℳ3ℒ (26) where x(t) denotes the single function of time and the values of the constants ℒ and ℳ are given as: ℒ = �231��ℱ and ℳ = 2� n6�2>1�?b1> ;�kla� am;d la r�231�413 am;7 ;ℱ engineering, technology & applied science research vol. 12, no. 6, 2022, 9503-9509 9506 www.etasr.com husain et al.: a study of one-dimensional weak shock propagation under the action of axial and … using (26) and after some analytical steps, the massbalance equation (1) of the compressible euler system is eventually recast in the following form: ��3ℒ� = � + �1 − ℒ�� − �ℒ − ℳ + 1� = − 1x +x+ = 0 (27) on solving (24) and (27) we have: � = 1�ℒ2>ℳ3��ℒ>2�� x +x+ (28) by substituting the value of flow velocity from (28) in (27) and after simplification we have: x��� = x����3[ (29) where [ = ��ℒ>2�3ℒ23ℳ2 and x� is an arbitrary constant. on using the rankine-hugoniot jump boundary conditions (17) and (18), we obtain explicit expressions for the radius of shock front ℛ and constant , as: ℛ = ��� �k\a� ;k4al am;7 (30) , = �2]i;31^��3�ℒ>[��>��ℒ3ℳ 3���2>1�i;�2>1�i; (31) eventually, in reference of jump conditions (17)-(20), the analytical solution of the flow-field variables to the weak shock wave problem modelled in the prior section is given as: � = x��γ��3ℒ � �;ℒlℳl;� ��ℒ\[�l; (32) � = ��ℒ�132�>2��>ℒ�3ℳ�2����ℒ>2�3ℒ��>2�3ℳ� w (33) � = x6� �;ℒlℳ ⎣⎢ ⎢⎢ ⎢⎡413 kla;km;7> al �k\a�; 4kla\ ;m;7 ; b�c6�k\a��la ⎦⎥ ⎥⎥ ⎥⎤ ��2�ℒ � ��ℒ\[�413 am;7 ;4231> ;m;7 la (34) ℎ = x6n6� �;ℒlℳ4231> ;m;7 la r�2� ℒ � ��ℒ\[��2>1�l?413 am;7 ; (35) by applying the values of the physical flow parameters from (32)-(35), the explicit cumbersome solution for total energy -. is given as: -. = λ. ��� �k\a�m;�;�ℒ\a�lℳ�l;k�ℒ\[�]m;la^ ;k]m;la^ (36) where: λ = x6 ⎣⎢ ⎢⎢ ⎢⎢ ⎢⎡ c6�k\a�?hkla\ ;m;i >@413 am;7 ;3 ;�k\a�h a;k�kla� am;\c6b i �;�ℒ\a�lℳ�lahkla\ ;m;i la >bhal �kla�;k am;i\c6�k\a�jal�k\a�;hkla\ ;m;i l;k ha\ ;�kla� am;i la ⎦⎥ ⎥⎥ ⎥⎥ ⎥⎤ r���ℒ>1�3ℳ��2�ℒ 413 am;7 ; v. results and discussion the formulation of precise (closed form) and analytical solutions is of utmost importance in the field of natural and engineering sciences as these solutions are very helpful to understand and classify the involved physical phenomena. the expressions (32)-(36) depict explicitly the analytical solution of physical flow characteristics (such as density, velocity, pressure, and magnetic pressure) and total energy, to the cylindrical symmetric weak shock wave problem in an ideal supersonic magnetogasdynamic flow. it should be noted that the exact solutions obtained for the density, pressure, and magnetic pressure flow are greatly affected by the generalized magnetic field and shock mach number. however, velocity profile and shock radius remain unchanged under the influence of the magnetic field, whereas the effect of shock mach number appears significantly. figures 1-3 illustrate the behavior of flow characteristics density, pressure and magnetic pressure, for the propagation of cylindrical weak shock wave in azimuthal magnetic field with the variation in mach number g with respect to time �. the values of the constants utilized for numerical computation have been taken as: x� = 1, γ =1.67, and ��=0.05. for the sake of convenience, the effect of magnetic field h has been entered through shock-cowling number ��. fig. 1. dispersal of density profile with time at various values of mach number. fig. 2. dispersal of pressure profile with time at various values of mach number. engineering, technology & applied science research vol. 12, no. 6, 2022, 9503-9509 9507 www.etasr.com husain et al.: a study of one-dimensional weak shock propagation under the action of axial and … fig. 3. dispersal of pressure profile with time at various values of mach number. from figures 1-3, it is evident that for increasing value of shock-mach number, the decay process of physical parameters (density, velocity, and pressure) gets a bit slower with respect to time. further, it is observed that for the case of axial magnetic field �� = 0� , and various values of the ratio of specific heats �γ� , the behavior of density, pressure and magnetic pressure remains unchanged, however, for smaller values of shock-cowling number, the discussed flow profiles decay rapidly with respect to time as compared to larger values of �� which closely coincide with the results obtained in [36, 37] for non-magnetic flow. figure 4 exhibits the behavior of velocity profile for cylindrical weak shock wave in ideal magneto-gas-dynamic flow with the variation in m with respect to �. it is observed that when increasing the value of m, the velocity profile of the cylindrical weak shock waves at the shock front under the influence of the magnetic field increases rapidly with time. additionally we perceive that as compared to γ = 1.67, the fluid velocity characteristics enhances faster for the adibatic index γ = 1.4. figures 5 and 6 demonstrate the behavior of the energy carried by the cylindrical weak shock wave in magnetogas-dynamic regime with respect to � for varying values of mach number and shock-cowling number respectively. fig. 4. dispersal of velocity profile with time at various values of mach number. fig. 5. dispersal of total energy with time at various values of mach number. fig. 6. dispersal of total energy with time at various values of shockcowling number. it is evident from figure 5 that when the value of m increases, the energy of the cylindrical weak shock waves under the influence of the magnetic field increases much faster with time. moreover, it can be noted, that for the case of axial magnetic field �� = 0� , the values of the total energy with respect to time for varying m get a bit slower as compared to the azimuthal magnetic field �� = 1� , which confirms the experimental considerations. in figure 6, the behavior produced due to the varying shock-cowling number reveals that increasing the values of �� causes a rapid upsurge in the total energy with respect to time. furthermore, it should be noted, that for the case of axial magnetic field, for increasing values of ��, the values of the total energy with respect to time are much closer, which means that the effect of azimuthal magnetic field has a more considerable impact on the behavior of energy with respect to time. vi. conclusion in the present work, we performed an analytical investigation of the problem of propagation of quasi-onedimensional unsteady state compressible non-viscous adiabatic cylindrical weak shock wave in a perfect gas-dynamical regime, under the influence of axial and azimuthal magnetic fields. for this purpose, the simple and efficient analytical technique proposed in [20] has been used and the exact engineering, technology & applied science research vol. 12, no. 6, 2022, 9503-9509 9508 www.etasr.com husain et al.: a study of one-dimensional weak shock propagation under the action of axial and … solutions for the physical flow characteristics, such as density, velocity, pressure, and magnetic pressure, were obtained in the form of space-coordinates and time relations. also, the cumbersome expression for total energy (i.e. the sum of kinetic and potential energy) carried by weak shock flow in the considered plasma influenced with magnetic field (axial and azimuthal) having dependency of space-time is determined. to describe the effect of mach number and magnetic field (modeled in the form of the shock-cowling number) on flowfield characteristics and total energy carried are graphically presented. all the computations for this purpose have been done with the computational software package mathematica 9.0. since the shock proliferation processes are associated with a high-temperature gas dynamics phenomenon, thermal radiation has a significant impact on the wave phenomenon due to its coupling with the magnetic field and its various applications in terms of theoretical and industrial aspects. in addition, for such physical processes, the consideration that the medium is perfect is no longer valid. therefore, an analytical investigation of the current study into realistic gas-dynamic regimes, and thermal radiation effects, is a potentially interesting area for future work. based on the results of the present study, the following conclusions are made:  for increasing value of shock-mach number, the decay process of physical parameters (flow velocity, density, and pressure) gets a bit slower with respect to time for a fixed value of �� , which clearly resembles the pattern of nonmagnetic flow.  an increase in the value of mach number causes a rapid increase to the flow velocity of weakly nonlinear waves with respect to time. consequently, we perceive that as compared to the specific heat ratio γ =1.67, the velocity characteristics grows faster for the adibatic index γ =1.4.  the total energy of the cylindrical weak shock waves under the influence of the azimuthal magnetic field increases much faster with respect to time for an increasing value of mach number. however, as compared to the azimuthal magnetic field �� = 1�, in the of the axial magnetic field �� = 0�, the total energy with respect to time enhances a bit slower for varying 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abstract-cardiovascular or heart diseases consist a global major health concern. cardiovascular diseases have the highest mortality rate worldwide, and the death rate increases with age, but an accurate prognosis at an early stage may increase the chances of surviving. in this paper, a combined approach, based on machine learning (ml) with an optimization method for the prediction of heart diseases is proposed. for this, the improved auto categorical particle swarm optimization (iacpso) method was utilized to pick an optimum set of features, while ml methods were used for data categorization. three heart disease datasets were taken from the uci ml library for testing: cleveland, statlog, and hungarian. the proposed model was assessed for different performance parameters. the results indicated that, with 98% accuracy, logistic regression (lr) and support vector machine by grid search (svmgs) performed better for the statlog, svmgs outperformed on the cleveland, while the lr, random forest (rf), support vector machine (svm), and svmgs performed better with 97% accuracy on the hungarian dataset. the outcomes were improved by 3 to 33% in terms of performance parameters when ml was applied with iacpso. keywords-svmgs; iacpso; knn; lr i. introduction globally, many people suffer from heart diseases [1]. in 1990, there were 24 million fatalities related to heart disease in the united states, by 2010 that number had risen to 38 million, a 59% increase [2]. according to current forecasts, india will have the world's highest prevalence of cardiovascular diseases and will soon overtake the rest of the world [3]. heart disorders are responsible for almost 4 million fatalities in europe and 1.9 million deaths in the eu [4]. in africa, heart diseases are the leading cause of death among persons over the age of 35 [5]. massive quantities of data on heart illnesses are collected from hospitals all around the world, which can be used manually to quantify disease rates. however, the data so far have not been efficiently translated to correlate with disease risk and symptoms [6]. cardiovascular disorder is accompanied by common symptoms of chest tightness, loss of body strength, and swollen legs [7]. health history examination, clinical test reports, and associated symptoms are usually used by the doctors for diagnosis. but the obtained results by this method are not always accurate, whereas they are costly and difficult to computationally analyze [8]. researchers have tried to come up with an efficient technique to detect heart diseases since the current diagnostic approaches for heart disease are not very effective in identifying the early stages [9]. it has been reported from different methodological approaches that a combination of ml and optimization methods may be effective in predicting early-stages of heart diseases [10]. appropriate data are needed for training and testing in ml predictive models. we can increase the performance of ml algorithms by optimal dataset balancing for training and testing [11]. feature selection is capable of reducing dimensionality, increasing efficiency, and enhancing classification accuracy [12-14]. the data comprising several dimensions may create trouble in feature selection. according to [15-18], classification and clustering methods of ml were proven to be more effective in terms of accuracy rates. several feature selection evaluation metrics were investigated in [19], to improve the computational efficiency of ml algorithms as well as to discuss the unexpected problems of feature selection. various data mining and combinations of data mining with optimization algorithms have been proposed as a means of detecting heart diseases. ant colony optimization (aco) was applied to select an effective subset from a large training set with improved accuracy in [20]. in [21], a combination of optimization and data mining was proposed, based on glowworm swarm optimization (gso) with k-means to improve the accuracy of image classification. for omics data corresponding author: animesh kumar dubey engineering, technology & applied science research vol. 12, no. 3, 2022, 8567-8573 8568 www.etasr.com dubey et a.: an improved auto categorical pso with ml for heart disease prediction classification, a particle swarm optimization (pso)-based model was developed in [22] and claimed good accuracy. in [23], a hybrid structure, based on pso and grid search was proposed to predict heart diseases with 95.95% accuracy. authors in [24], suggested a combined approach of pso with support vector machine (svm) and convolutional neural networks (cnns). the highest accuracy, 98%, was achieved by pso with cnn. in [25], the performance of swarm optimization algorithms artificial bee colony (abc), pso, and aco to an artificial neural network (ann) was studied, and pso was determined to be the most effective. a hhybrid genetic algorithm (hga) with k-means was implemented in [26] for classifying and predicting heart diseases with 94.06% accuracy. in [27], anns with pca and pso were used to predict cardiac diseases, with an accuracy of 98%. in [28], pso algorithm was proposed for dimension reduction, and several classification methods were used to diagnose heart diseases. utilizing the dataset from the uci library, naïve bayes (nb), decision tree (dt), and k-nearest neighbour (knn) models were applied in [29] to predict heart diseases. in [30], pso with feedforward backpropagation ann were implemented to diagnose heart diseases, and achieved 91.94% accuracy. nb with a genetic algorithm (ga) were used to eliminate unnecessary information in [31] achieving high accuracy. to deal with the issues related to overfitting and underfitting, as well as selecting attributes, a deep ann was implemented in [32], and the achieved precision was 93.33%. similarly, random search algorithm (rsa) for feature selection and random forest (rf) for classification were used in [33]. several dt-based methods along with pso were used in [34], to identify heart disease occurrence and the highest precision was obtained using a bagged tree with pso. svm with a multiclass approach of ml was applied in [35], to detect apple fruit diseases. in [36], crow search with deep learning method were used for the prediction of parkinson’s disease with 96% accuracy. for the detection of various plant diseases, ml algorithms were used in [37]. various unsupervised learning and optimization methods were used in [38-40] for the prediction of heart diseases. most researchers used supervised and unsupervised ml methods and swarm intelligence-based optimization methods such as aco, gso, pso, etc., in conjunction with ml. but their approaches were not stable in handling real-time situations. hence, there is a need for an automated approach, which can generate the optimal solution based on the current situation. the present research work proposes a combined approach, including ml algorithms with optimization to predict heart diseases. ml methods, such as logistic regression (lr), dt, svm, svm by grid search (svmgs), rf, knn, and nb, are used, and the improved auto categorical pso (iacpso) method is applied for selecting an optimized set of features. the major objectives of this research are: • for pso, to create an automated approach to the selection of the optimal value of control parameters at each iteration. • to analyze the impact of ml algorithms on different performance parameters in the prediction of cardiovascular diseases. • to evaluate the combined impact of ml algorithms with optimization for heart disease prediction. ii. materials and methods three heart disease datasets were taken from the uci ml library for testing: cleveland, statlog, and hungarian [41]. the datasets consist of a total of 76 attributes, but only 14 relevant attributes including the attributes preferred in most published experiments [42]. predicted trait values were represented by a and p indicating the absence and presence of heart disease respectively. ml algorithms such as lr [43, 44], dt [45, 46], rf [47], knn [48], svm [49, 50], and nb [45, 48], were used for prediction and analysis. iacpso was used to select an optimal set of features. a. iacpso pso is a search-based stochastic optimization technique based on population. the particles, which are potential solutions in pso, follow the current optimum particles through the problem space [51]. the performance of pso depends on three control parameters which are the inertial weight (w), the acceleration coefficients (c1 and c2), and random numbers (r1 and r2) [52]. the inertial weight is used for maintaining the effect of convergence and diversity. a large value of w indicates better global exploration, while a small value works on exploitation. unbalanced values containing the parameters can hurt the results, such that if we take low values for c1, it tends to acquire a smooth particle trajectory and abrupt movements. similarly, if c1 is much greater than c2, it tends to excessive wander and cause premature convergence [53]. large inertial weight tends to global search ability and small inertial weight leads to increase in local search power. by dynamic changing w, the acceleration coefficients, efficiently explore the search space [52]. therefore, in the proposed iacpso, the control parameters are updated automatically based on the number of particles as well as balancing them at each iteration. the steps included in iacpso are given below: step i: initialize the particle size (p0, p1, p2, ………., pn) in the d-dimensional space. step ii: initialize the velocity �� �(0), where x ∈ {p0, p1, p2, ………., pn}, d ∈ {0, 1, …., d}. calculate the velocity of a particle at the mth iteration by using (1): �� �(�) = �� �(� −1) +ø����(�)− �� �(� − 1)�+ ø� ��(�)− �� �(� − 1)� (1) where w is the inertial weight, ø� =r1c1 (local accelerations), ø�= r2c2 (global accelerations), c1 and c2 are the acceleration coefficient, and r1 and r2 are random numbers. �� � is the position of the particles, ��(�) and �(�) are the local and global best positions. for each iteration, control parameter values have been chosen automatically on the basis of the number of swarm particles (n), which are given in (2-5). for the value of ø� and ø� , generate the n/8 random number between 0 to 2 for the selection of c1 and c2. �� = {�� �,�� �,�� �,…. . . ,�� ! " where 0 ≤ �� ≤ 2} (2) engineering, technology & applied science research vol. 12, no. 3, 2022, 8567-8573 8569 www.etasr.com dubey et a.: an improved auto categorical pso with ml for heart disease prediction c2 = {�� �,���,���,…. . . ,�� !" where 0 ' �� ' 2) (3) ø� = ∑ �� !"+,� .-� (4) ø� =∑ �� !"+,� .-� (5) then, as per (6), divide the value of ø� and ø� into three categories: low (l), mid (m), and high (h). ø�,ø� . l, if �0 ' c�,c� ' 0.8� m, else if �0.9 ' c�,c� ' 1.2� h, else �1.3 ' c�,c� ' 2� (6) similarly, for the value of w, select three values between 0.4 and 0.9 and categorize those into l, m and h, in which l is close to 0.4, m is nearer to the mean of the other two values, and h is close to 0.9. for each iteration select the value of w as per the following conditions: (i) if (ø� & ø� ∈ l) then consider w = h (value) (ii) if (ø� & ø� ∈ m) then consider w = m (value) (iii) if (ø� & ø� ∈ h) then consider w = l (value) so, the updated velocity at each iteration is: �� �(�) = (�,:,;������� 1� ∑ �� !"+,� .-������������� � 1�� ∑ �� !"+,� .-� ����� � ������1�� (7) step iii: calculate position of the particles, given in (8): �� �(�)= �� �(� −1�+ ���(�) (8) by using (8), we get n/8 number of positions for each particle, then we proceed to step iv. step iv: calculate the current fitness function ɣ(�). based on the n/8 position of particles, calculate the fitness function, given in (9) and (10), and choose the best one based on minimization or maximization. ��(�) = ��(�=) : ɣ���(�=)� = >?@ >abcdedf ɣ���(g)� (9) �(�) = ��h(�) : ɣ���h(�)� = min/maxcd�d+ ɣ������� (10) step v: on the basis of the fitness value, update ��(�) and �(�). iii. experimental results and analysis figure 1 shows the flow chart of the suggested methodology. cleveland, statlog, and hungarian datasets of heart diseases were considered for the evaluation of the proposed approach. experiments were run using an x64-based processor with windows 10 os and an intel (r) core (tm) i57200 cpu @ 2.50ghz. the analysis and visual presentation were done using python and java7. the experimental results and analysis on heart diseases datasets, based on ml algorithms like lr, svm, dt, svmgs, rf, nb, and knn and the iacpso optimization method are reported. fig. 1. flowchart of the proposed methodology. a. result analysis based on ml algorithms we assessed the effectiveness of the ml models by using parameters such as accuracy (ac), precision (pr), matthews correlation coefficient (mcc), sensitivity (sv), and f-score (fs) [11]. table i presents the ac, pr, sv, fs, and mcc values, where pr, sv, and fs were either a or p. here, 25% of the data were used for testing and the rest for training. for knn, the considered values of k were 11, 17, and 15 for cleveland, statlog, and hungarian datasets respectively. according to the comparative analysis shown in figure 2, svmgs outperformed the other methods in all aspects and achieved accuracy of 89% for cleveland and hungarian datasets, while for statlog dataset, nb and lr showed better accuracy of 91%. fig. 2. comparative analysis of ml algorithms in terms of ac, average pr, and average sv. b. result analysis based on iacpso with ml methods iacpso was used for feature selection. the selection of features depend upon their ranks, their values are either 0 or 1, with 0 representing the rejection of a feature and 1 representing its selection. the number of features represents the solution size for each data set. for the optimization process, the selected features along with the performance of the classifier were taken into account. the fitness function was αc(e)+β (|sf|)/(|tf|) (11) where c(e) is the misclassification rate, |sf| shows the number of the selected features, |tf| represents the total features in the data set, and α belongs to [1,0], β = (1-α). the value of α and β were taken from [54, 55]. for experimentation, the parameters values are: population size=12, number of iterations=100, dimension=7, w= 0.4 to 0.9 and c1 and c2= 0 to 2. engineering, technology & applied science research vol. 12, no. 3, 2022, 8567-8573 8570 www.etasr.com dubey et a.: an improved auto categorical pso with ml for heart disease prediction table i. evaluation results based on the performance parameters of the ml methods classification methods lr dt rf svm svmgs knn nb cleveland dataset ac 0.87 0.82 0.87 0.87 0.89 0.76 0.87 pr a 0.86 0.76 0.89 0.86 0.89 0.77 0.84 p 0.88 0.89 0.85 0.88 0.88 0.74 0.90 sv a 0.86 0.90 0.83 0.86 0.86 0.69 0.90 p 0.88 0.75 0.91 0.88 0.91 0.81 0.84 fs a 0.86 0.83 0.86 0.86 0.88 0.73 0.87 p 0.88 0.81 0.88 0.88 0.89 0.78 0.87 mcc 0.74 0.65 0.71 0.74 0.77 0.51 0.74 statlog dataset ac 0.91 0.83 0.89 0.87 0.89 0.76 0.91 pr a 0.89 0.82 0.86 0.88 0.85 0.81 0.89 p 0.94 0.88 0.94 0.85 1.00 0.68 0.94 sv a 0.97 0.94 0.97 0.91 1.00 0.79 0.97 p 0.81 0.67 0.76 0.81 0.71 0.71 0.81 fs a 0.93 0.87 0.91 0.90 0.92 0.80 0.93 p 0.87 0.76 0.84 0.83 0.83 0.70 0.87 mcc 0.81 0.65 0.61 0.73 0.78 0.50 0.81 hungarian dataset ac 0.88 0.82 0.86 0.87 0.89 0.77 0.88 pr a 0.87 0.77 0.88 0.85 0.90 0.77 0.85 p 0.88 0.88 0.85 0.89 0.87 0.75 0.91 sv a 0.87 0.89 0.82 0.85 0.86 0.70 0.91 p 0.88 0.75 0.90 0.89 0.91 0.82 0.85 fs a 0.87 0.83 0.85 0.85 0.88 0.74 0.88 p 0.88 0.81 0.88 0.89 0.89 0.78 0.87 mcc 0.77 0.65 0.69 0.74 0.77 0.53 0.76 table ii. accuracy obtained based on ml methods with iacpso ml methods with iacpso lr+iac pso dt+ia cpso rf+ia cpso svm+iacp so svmgs+iac pso knn+iacps o nb+iac pso cleveland ac 0.96 0.92 0.97 0.97 0.98 0.92 0.92 pr a 0.97 0.90 0.98 0.98 0.98 0.92 0.93 p 0.96 0.95 0.96 0.96 0.95 0.91 0.92 sv a 0.97 0.96 0.97 0.97 0.96 0.90 0.94 p 0.96 0.91 0.98 0.98 0.96 0.91 0.90 fs a 0.98 0.95 0.99 0.99 0.97 0.90 0.90 p 0.95 0.90 0.95 0.95 0.96 0.94 0.91 mcc 0.89 0.83 0.90 0.90 0.90 0.84 0.83 statlog ac 0.98 0.93 0.97 0.97 0.98 0.92 0.94 pr a 0.99 0.94 0.97 0.97 0.98 0.91 0.91 p 0.98 0.97 0.98 0.98 1.00 0.93 0.98 sv a 0.99 0.98 0.98 0.98 1.00 0.92 0.98 p 0.95 0.90 0.97 0.97 0.96 0.93 0.87 fs a 0.98 0.98 0.98 0.98 0.97 0.91 0.94 p 0.99 0.94 0.97 0.97 0.96 0.88 0.90 mcc 0.95 0.83 0.89 0.89 0.90 0.81 0.85 hungarian ac 0.97 0.93 0.97 0.97 0.97 0.91 0.92 pr a 0.96 0.91 0.96 0.96 0.98 0.90 0.91 p 0.99 0.94 0.99 0.99 0.95 0.91 0.93 sv a 0.98 0.94 0.96 0.96 1.00 0.91 0.94 p 0.97 0.92 0.99 0.99 0.94 0.90 0.90 fs a 0.99 0.93 0.98 0.98 0.98 0.89 0.91 p 0.96 0.93 0.97 0.97 0.95 0.89 0.91 mcc 0.92 0.82 0.88 0.88 0.90 0.80 0.82 the percentage of data based on misclassification rates (shown in figure 3) were considered for the experiment. based on the iacpso, only 7 of the 14 features were chosen for testing, which were thalassemia, chest pain, number of major vessels, st anxiety exercise-induced relative to rest, exerciseinduced angina, maximal heart rate achieved, and exerciseinduced angina. table ii presents the ac, pr, sv, fs, and mcc values, based on the combined performance of ml methods and iacpso. with 98% accuracy, svmgs outperformed the other methods in the cleveland dataset. svmgs and lr with 98% accuracy outscored rf, dt, knn, nb, and svm on the statlog dataset. lr, rf, svm, and svmgs with a 97% accuracy outperformed knn, nb and dt on the hungarian dataset. for cleveland, with an optimal set of features, the highest mcc was achieved by svmgs, svm, and rf, while lr did better in terms of mcc in statlog and hungarian. figure 4 compares the ml algorithms with iacpso results based on ac, average pr, and sv. for the engineering, technology & applied science research vol. 12, no. 3, 2022, 8567-8573 8571 www.etasr.com dubey et a.: an improved auto categorical pso with ml for heart disease prediction cleveland dataset, lr, rf, svm, and svmgs performed better in terms of average pr, rf and svm in terms of average sv. lr and svmgs achieved the highest average pr of 99%, whereas the highest average sv was achieved by rf, svm, and svmgs for the statlog dataset. regarding the hungarian dataset, lr, rf, and svm, with 98% of average pr and sv, performed better than dt, svmgs, knn, and nb. with 97%, lr, rf, svm, and svmgs outperformed in terms of ac. fig. 3. comparison of the misclassification rates of ml algorithms. iv. discussion the performance of ml algorithms with and without optimization was examined in this paper. an optimization algorithm (iacpso) was used for the selection of features to improve accuracy in less time, using the optimum value of the acceleration coefficients in each iteration. in addition, these values were also linked to the graded inertial load, to balance exploration and exploitation. table iii compares the results, based on ml techniques with and without optimization. figure 5 shows the improvement rates of performance parameters when combined approach (ml algorithms + iacpso) were used. outcomes were improved by 3 to 33% in terms of performance parameters when ml was applied with iacpso. as per table iii and figure 5, the major findings were as follows: • when lr was applied separately, the achieved ac was 87% (cleveland), 91% (statlog), and 88% (hungarian) but in the combined methodology of lr with iacpso, the ac increased by 9% for cleveland and hungarian and 7% for statlog. • when the dt was applied separately, ac was 82% for cleveland and hungarian, and 83% for statlog, but in the combined methodology of dt with the iacpso, the ac increased by 10% for cleveland and statlog and 11% for hungarian. • in the case of rf with iacpso, ac was 10%, 8%, and 11% higher for cleveland, statlog, and hungarian than for separately applied rf. • for svm, the obtained ac with the iacpso in cleveland, statlog and hungarian was 97%, which was 10% higher than when using only svm. there was an increase in ac of 1% in cleveland and statlog when iacpso was used with svmgs. • for knn with iacpso, an increase of 16% in ac occurred for cleveland and statlog. a large difference was found in the improvement percentage in the value of mcc, being 33% in cleveland, 31% in statlog, and 27% in hungarian. • for nb, improvement after iacpso was 3 to 5% in terms of ac, pr, sv, and fs. for all the aspects of performance used in the currrent research, ml methods with iacpso were proven to be superior. ml algorithms were used for the classification and iacpso method was applied for the selection of effective features. this type of combined approach gave better models for the early prediction of cardiovascular diseases. fig. 4. comparison of ml methods with iacpso in terms of ac, average pr, and average sv. table iii. result comparison of ml methods with and without iacpso datasets cleveland statlog hungarian ml methods ac pr sv fs mcc ac pr sv fs mcc ac pr sv fs mcc lr 87 87 87 87 74 91 92 89 90 81 88 88 88 88 77 lr+iacpso 96 97 97 97 89 98 99 97 99 95 97 98 98 98 92 dt 82 83 83 82 65 83 85 81 82 65 82 83 82 82 65 dt+iacpso 92 93 94 93 83 93 96 94 96 83 93 93 94 93 92 rf 87 87 87 87 71 89 90 87 88 61 86 87 86 87 69 rf+iacpso 97 97 98 97 90 97 98 98 98 89 97 98 98 98 88 svm 87 87 87 87 74 87 87 86 87 73 87 87 87 87 74 svm+iacpso 97 97 98 97 90 97 98 98 98 89 97 98 98 98 88 svmgs 89 89 89 89 77 89 93 86 88 78 89 89 89 89 77 svmgs+iacpso 98 97 96 97 90 98 99 98 97 90 97 97 97 97 90 knn 76 76 75 76 51 76 73 75 75 50 77 76 76 76 53 knn+iacpso 92 92 91 92 84 92 92 93 90 81 91 91 91 89 80 nb 87 87 87 87 74 91 92 89 90 81 88 88 88 88 76 nb+iacpso 92 93 92 91 83 94 95 94 92 85 92 92 92 91 82 engineering, technology & applied science research vol. 12, no. 3, 2022, 8567-8573 8572 www.etasr.com dubey et a.: an improved auto categorical pso with ml for heart disease prediction fig. 5. improved performance rates of ml algorithms due to iacpso. v. conclusion in this paper, a combined approach, based on ml algorithms and optimization is proposed to predict heart diseases at an early stage using the history of the patients. ml algorithms, such as dt, lr, svm, svmgs, nb, knn, and rf were used and iacpso was used for optimization. in iacpso, the optimum value of control parameters was used, which helped in proper 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[55] e. emary, h. m. zawbaa, and a. e. hassanien, "binary grey wolf optimization approaches for feature selection," neurocomputing, vol. 172, pp. 371–381, jan. 2016, https://doi.org/10.1016/j.neucom. 2015.06.083. microsoft word etasr_v11_n6_pp7917-7921 engineering, technology & applied science research vol. 11, no. 6, 2021, 7917-7921 7917 www.etasr.com diffellah et al.: removal of multiplicative gamma noise from images via srad model amelioration removal of multiplicative gamma noise from images via srad model amelioration nacira diffellah electronics department eta laboratory mohamed el bachir el ibrahimi university bordj bou arréridj, algeria diffellahn@gmail.com rabah hamdini automatics department set laboratory saad dahlab university blida, algeria hamdinirabah@gmail.com tewfik bekkouche electromecanics department eta laboratory mohamed el bachir el ibrahimi university bordj bou arréridj, algeria bekkou66@hotmail.com abstract-in this paper, an improved speckle reducing anisotropic diffusion (srad), destined to remove multiplicative gamma noise applied to different images is proposed. the basic idea is to divide the image into several riddled areas and then calculate the equivalent number of look (enl) of each region. the largest value of the enl is the best optimal homogeneous region of the image. this optimal choice allows us to solve the major problem of the srad algorithm articulated around a visual choice of the homogeneous region which is not satisfactory and causes non-uniformity in this area. to give more validity to the proposed method, several experimentations were conducted using different kinds of images and were approved by some quantitative metrics like psnr, snr, vsnr, and ssim. the computer simulation results confirm the efficiency of the proposed method which outperformances the classical srad method. keywords-multiplicative gamma noise; srad; enl; optimal homogeneous zone; speckle noise i. introduction images are not immune to contamination by noise that can degrade their visual quality. to deal with this problem, image denoising is the recommended solution. in this context, several restoration filtering algorithms have emerged. these algorithms are based on a variety of denoising techniques [1-8]. the noise in turn is divided into several forms. in this paper, we consider the gamma multiplicative noise. among the existing techniques, we cite those that are based on anisotropic diffusion. authors in [1] proposed an algorithm called srad, which consists in exploiting the instantaneous coefficient of variation which is a function of local gradient magnitude, and laplacian operators. however, this method gave good performance in terms of the quality of the restored images, but has the disadvantage of the choice of the homogeneous area determined by a simple subjective visual choice. srad [12] needs to know a homogeneous region in the processed image. although it is not difficult for a user to select a homogeneous region in the image, it is non-trivial for a machine to do that. to remedy this problem an improved method, based on the calculation of the enl [2], is proposed in this paper, which allows us to analytically determine the optimal homogeneous zone for any image type. once this area is determined, we apply the srad algorithm itself, through simulations carried out on a set of images of different types. the obtained results confirmed the superiority of the proposed over the original srad method using several metrics such as: peak signal to noise ratio (psnr) [6], signal to noise ratio (snr) [9], visual signal-to-boise ratio (vsnr) [10], and structure similarity index method (ssim) [13]. ii. the speckle noise model multiplicative noise [5, 13] is generally more difficult to remove than additive noise [3]. the model is given by: ( ) ( ) ( ), , ,f i j u i j i j= ×η (1) where the speckle image f is the product of the original image u and the non-gaussian noise η. the indices i, j represent the spatial position over the image. in most applications involving multiplicative noise, the noise content is assumed to be stationary with unitary mean and unknown variance σ 2 . the probability density function (pdf) of erlang (gamma) noise is given as [4]: ( ) ( ) 1 ; , x k k k x e p x k k − − = γ θ θ (2) corresponding author: nacira diffellah engineering, technology & applied science research vol. 11, no. 6, 2021, 7917-7921 7918 www.etasr.com diffellah et al.: removal of multiplicative gamma noise from images via srad model amelioration for x > 0 and k > 0, θ > 0 where κ is the number of looks of the image (i.e. the number of independent values averaged) and ( )γ � is the classical gamma function. x k= ⋅θ is the mean and 2 2 k= ⋅σ θ is the variance. in this work, we assume that the images are corrupted by gamma distributed noise: ( ) 1 ~ k k k e k − − γ η η η θ (3) iii. the speckle reducing fast variational restoration method we consider an image f that corresponds to an unknown ground truth image u perturbed with a speckle multiplicative noise η. the objective is to denoise the available image f and recover an image as close as possible to u according to (1). the srad algorithm [1] for the speckle noise reduction in images is summarized as follows: • let u be the original image which is normalized on [0,1]. define the smoothing time step and choose the homogeneous region within the original image. • compute the speckle scale from the delimited homogenous region which is depended on its variance and mean. • compute the laplacian approximation of the image depending on the nearest-neighbor difference. compute the nearest-neighbor difference. • compute the diffusion coefficient based on the instantaneous coefficient of variation. • compute the divergence by which we can update the srad function. iv. the proposed method the enl is used to evaluate the speckle noise reduction performance of the homogeneous regions in the image. the enl is defined as: 2 2 u u enl = ∂ µ (4) where u µ and n∂ are the estimated mean and standard deviation of the image. larger enl values indicate excellent speckle noise removal ability. enl is a well-known and effective metric for evaluating the regularization effectiveness on homogeneous areas. the proposed method is summarized in a process of 6 steps: • obtain the degraded image f from an imaging system which is the product of the true intensity u and draws from a gamma distribution. • calculate the different evaluation metrics between the original and noisy images. • divide the noisy image into several overlapping regions according to the value of d. the total number of regions is equal to: ( ) 2 2 1n d= − , where d is an integer ≠ 0. • calculate the enl for each region using (4) and choose the greatest value of enl which corresponds to the most homogeneous region. • determine the coordinates of the previous optimal zone which has the greatest value of enl. then, apply the srad algorithm with the purpose to find the restored image. • calculate the metrics between the original image and the restored image and compare the obtained results, before and after restoration. v. simulation results and discussion in this section, we will compare and discuss the results of the proposed method. the implementation has been tested against a set of images consisting of: • image 1: "image union" [14] with a size of 1024×999 pixels by kevin dooley is licensed with cc by 2.0 [15]. • image 2: "first nac image obtained in mercury orbit" [16] with a size of 1024×1020 by nasa goddard photo and video, which is also licensed under cc by 2.0. • image 3: "transportation_airplane_on_lake" [17] with a size of 1289×1024. this image was acquired from wikipedia. it was marked as public domain or cc0 and is free to use. the images were corrupted with gamma multiplicative noise having 1 mean and different standard deviation of 4%, 10%, 20%, and 60%. in tables i-iii we summarize the simulation results for a sample of given values. figures 1-3 are composed of: • the illustration of the position of the homogeneous zone within the noised image, automatically determinated by the enl metric. • the number of the homogeneous zone, its coordinates as well as the value of the enl which is estimated to be the largest by the proposed algorithm. • the original and the restored images. • in addition, in order to validate the illustration of these figures, we also supported the assessment of our approach by all the metrics used. tables i-iii summarize the results obtained concerning the different metrics used, namely psnr, snr, vsnr, and ssim applied to the original and the noisy images and the real and restored images, by varying each time the number of looks k = 4, k = 10, k = 20, and k = 60. in tables i-iii, we clearly notice that the metrics of the proposed method are significantly better than those of the original srad method for different noise levels, for the three images used in this paper. engineering, technology & applied science research vol. 11, no. 6, 2021, 7917-7921 7919 www.etasr.com diffellah et al.: removal of multiplicative gamma noise from images via srad model amelioration (a) noisy k = 20 region [333.8000 800.2000 51.2000 49.9500], d=20 psnr=21.0963db, snr=9.0602, vsnr=29.9563db, ssim=0.9514 (b) k= 20, enl= 471.0219, number=1262 (c) original (d) restored psnr=26.5126db, snr=13.7435, vsnr= 30.8696db, sim=0.9470 fig. 1. results of image 1. table i. psnr, snr, vsnr, and ssim of noisy and despeckled image 1 with different levels of k psnr snr vsnr ssim k=4 15.1109 3.5008 26.4856 0.8231 proposed 20.7247 7.3498 26.1100 0.8760 srad 18.8231 4.7549 26.1531 0.8270 k=10 17.6972 5.8270 27.9382 0.9040 proposed 24.1607 11.3095 26.4329 0.9271 srad 23.5171 10.5614 26.0267 0.9195 k=20 21.0963 9.0602 29.9563 0.9514 proposed 26.5126 13.7435 30.8696 0.9470 srad 23.5093 10.5496 29.9626 0.9193 k=60 32.8812 20.7208 33.5205 0.9955 proposed 28.4062 15.9718 28.3802 0.9643 srad 26.4717 13.7056 26.0019 0.9464 (a) noisy k = 20, d = 15 region [786.0667 35.0000 68.2667 68.0000] psnr=20.0851db, snr=0.4349, vsnr=10.5243 d8, ssim0=0.8115 (b) enl= 83.4313, number=53 (c) original (d) restored psnr=24.9378db, snr=3.5459 vsnr=12.4653, ssim=0.8247 fig. 2. results of image 2. table ii. psnr, snr, vsnr, and ssim of noisy and despeckled image 2 with different levels of k psnr snr vsnr ssim k=4 13.9953 -4.5188 5.7907 0.6204 proposed 19.5193 1.2013 11.9192 0.7196 srad 16.7190 -0.0049 11.5444 0.6345 k=10 16.6044 -2.6240 7.5992 0.7688 proposed 22.9478 2.6145 12.3695 0.7944 srad 19.0560 0.9626 11.8564 0.7070 k=20 20.0851 0.4349 10.5243 0.8115 proposed 24.9378 3.5459 12.4653 0.8247 srad 21.3566 1.9513 12.1517 0.7625 k=60 31.7254 11.7804 19.5227 0.9907 proposed 27.3115 5.9811 14.1275 0.8929 srad 24.8388 3.3729 12.2072 0.8147 1262 471.0219 zone number e n l enl best value of enl 53 83.4313 zone number e n l enl best value of enl engineering, technology & applied science research vol. 11, no. 6, 2021, 7917-7921 7920 www.etasr.com diffellah et al.: removal of multiplicative gamma noise from images via srad model amelioration (a) noisy k = 20, d = 15 region [419.9250 717.8000 64.4500 51.2000] psnr=16.5447db, snr=2.3706, vsnr=12.1235d8, ssim0=0.72320 (b) enl= 4332.8337, number=1106 (c) original (d) restored psnr=25.6970db, snr=11.4072 vsnr=16.4865, ssim=0.8497 fig. 3. results of image 3. table iii. psnr, snr, vsnr, and ssim of noisy and despeckled image 3 with different levels of k psnr snr vsnr ssim k=4 10.5052 -2.6031 7.9086 0.4547 proposed 16.8892 5.9958 16.0305 0.7133 srad 15.3289 6.3297 15.3680 0.7065 k=10 13.0901 -0.6873 9.5656 0.5802 proposed 21.6008 9.0109 16.2655 0.7940 srad 18.6167 9.4196 15.7187 0.7807 k=20 16.5447 2.3706 12.1235 0.7232 proposed 25.6970 11.4072 16.4865 0.8497 srad 22.2708 11.6397 16.0748 0.8280 k=60 28.2317 13.7751 17.4724 0.9661 proposed 29.3506 14.8891 16.9263 0.9056 srad 29.2033 14.5952 15.9009 0.8875 vi. conclusion in this paper, an efficient approach for image denoising when the image is corrupted by gamma multiplicative noise was presented. the proposed approach is based on the application of the enl metric which consists of dividing the image successively in overlapping regions and then calculate automatically the largest value of enl. the proposed method was applied to three different images and gave better and more satisfactory results than the classical srad algorithm. in the future, we plan to work on image denoising in the field of deep learning and compare it with the method presented in the current paper. acknowledgements the authors would like to thank the general directorate for scientific research and technological development of the algerian republic and the eta laboratory of bordj bou arreridj university. references [1] y. yu and s. t. acton, "speckle reducing anisotropic diffusion," ieee transactions on image processing, vol. 11, no. 11, pp. 1260–1270, nov. 2002, https://doi.org/10.1109/tip.2002.804276. [2] s. n. anfinsen, a. p. doulgeris, and t. eltoft, "estimation of the equivalent number of looks in polarimetric synthetic aperture radar imagery," ieee transactions on geoscience and remote sensing, vol. 47, no. 11, pp. 3795–3809, nov. 2009, https://doi.org/10.1109/ tgrs.2009.2019269. [3] k. kim, s. jung, and j.-h. kim, "adaptive speckle filtering for real-time computing in low earth orbit satellite synthetic aperture radar," ict express, vol. 7, no. 2, pp. 187–190, jun. 2021, https://doi.org/10.1016/ j.icte.2021.02.003. [4] d. k. nirmala, "a brief study on the various noise models in digital image processing," international journal of emerging technologies in engineering research, vol. 5, no. 10, pp. 17–23, oct. 2017. [5] n. diffellah, z. e. baarir, f. derraz, and a. taleb-ahmed, "a global variational filter for restoring noised images with gamma multiplicative noise," engineering, technology & applied science research, vol. 9, no. 3, pp. 4188–4195, jun. 2019, https://doi.org/ 10.48084/etasr.2737. [6] a. horé and d. ziou, "image quality metrics: psnr vs. ssim," in 2010 20th international conference on pattern recognition, istanbul, turkey, aug. 2010, pp. 2366–2369, https://doi.org/10.1109/icpr.2010.579. [7] m. v. sarode and p. r. deshmukh, "image sequence denoising with motion estimation in color image sequences," engineering, technology & applied science research, vol. 1, no. 6, pp. 139–143, dec. 2011, https://doi.org/10.48084/etasr.54. 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[11] z. wang, a. c. bovik, h. r. sheikh, and e. p. simoncelli, "image quality assessment: from error visibility to structural similarity," ieee transactions on image processing, vol. 13, no. 4, pp. 600–612, apr. 2004, https://doi.org/10.1109/tip.2003.819861. [12] a. siddig, z. guo, z. zhou, and b. wu, "an image denoising model based on a fourth-order nonlinear partial differential equation," computers & mathematics with applications, vol. 76, no. 5, pp. 1056– 1074, sep. 2018, https://doi.org/10.1016/j.camwa.2018.05.040. [13] r. chan, h. yang, and t. zeng, "a two-stage image segmentation method for blurry images with poisson or multiplicative gamma 1106 4332.8337 zone number e n l enl best value of enl engineering, technology & applied science research vol. 11, no. 6, 2021, 7917-7921 7921 www.etasr.com diffellah et al.: removal of multiplicative gamma noise from images via srad model amelioration noise," siam journal on imaging sciences, vol. 7, no. 1, pp. 98–127, jan. 2014, https://doi.org/10.1137/130920241. [14] k. dooley, image union. 2017. [15] "attribution 2.0 generic — cc by 2.0," creative commons. https://creativecommons.org/licenses/by/2.0/ (accessed nov. 16, 2021). [16] nasa goddard space flight center, first nac image obtained in mercury orbit. 2011. [17] "transportation airplane on lake." https://free-images.com/display/ transportation_airplane_on_lake.html (accessed nov. 16, 2021). microsoft word etasr_v13_n2_pp10407-10413 engineering, technology & applied science research vol. 13, no. 2, 2023, 10407-10413 10407 www.etasr.com quaisie et al.: the effect of cavitation water jet shock as a newly technology on micro-forming process the effect of cavitation water jet shock as a newly technology on micro-forming process james kwasi quaisie welding and fabrication engineering department, faculty of engineering, tamale technical university, ghana jkquaisie@tatu.edu.gh (corresponding author) philip yamba mechanical engineering department, faculty of engineering, tamale technical university, ghana pyamba@tatu.edu.gh vitus mwinteribo tabie mechanical engineering department, faculty of engineering, dr. hila liman technical university, ghana tabieson@yahoo.com joseph sekyi-ansah department of mechanical engineering, takoradi technical university, ghana josephsekyiansah1981@gmail.com anthony akayeti mechanical engineering department, faculty of engineering, tamale technical university, ghana aanthony@tatu.edu.gh abdul-hamid mohammed welding and fabrication engineering department, faculty of engineering, tamale technical university, ghana zuuham78@gmail.com received: 22 december 2022 | revised: 11 january 2023 | accepted: 15 january 2023 abstract this article proposes a novel technology called water jet cavitation shock micro-forming to fabricate micro-features on 304 stainless steel foils with a thickness of 100µm, using a cavitation nozzle with an incident pressure of 8 to 20mpa. this study investigated the surface morphology of the formed part, the influence of incident pressure, target distance, and impact time on the forming depth, and an analysis of the punching phenomenon of the formed components. the experimental results after the water jet cavitation shocking indicated that the surface morphology of the formed part of the 304 stainless foil sample had good quality and no conventional defects such as die scratches and cracks. furthermore, when the incident pressure was 20mpa, the height of the uniform-shaped spherical cap exceeded 262µm. the forming depth increased with increasing incident pressure and impact time. under an incident pressure of 20mpa, with the increase of target distance, the average depth of the formed part increased at first and then decreased. finally, the analysis of the blanking phenomenon indicated that when the incident pressure increased to 30mpa, the workpiece was completely blanked. this is mainly because, under this incident pressure, the shockwave pressure generated by the collapse of the bubble deforms the workpiece beyond the stress limit of the material itself. keywords-novel technology; cavitation nozzle; incident pressure; surface morphology; shockwave engineering, technology & applied science research vol. 13, no. 2, 2023, 10407-10413 10408 www.etasr.com quaisie et al.: the effect of cavitation water jet shock as a newly technology on micro-forming process i. introduction water jet technology is a cold working method that has been applied to a variety of industries, including civil engineering, architecture, and manufacturing. in this technology, water is discharged from nozzles under big pressure. this technology has been used to investigate water jet flows and develop new usages [1]. cavitating jet in air [2], multifunction cavitation [3-6], and water jet cavitation (wjc) [7, 8] are some of the available water jet processing methods. this study investigated wjc technology, which involves processing a workpiece surface using a high-speed underwater cavitation jet in a water-filled tank. the impact pressure slightly deforms the material surface layer plastically by generating a restraining force between the lower layers and the surface and causes a peening (forming) effect that increases the pits' depth hardness near the surface and applies compressive residual stress. many studies have investigated micro forming using various forms of applications for plastic deformation of metal foil. in [9], a study was conducted on a metallic foil using a micro-energy ultraviolet pulse laser shock for micro-pattern transfer. the experimental results indicated that the depth of the micropattern increased with increasing single pulse energy and the ratio of overlap in a certain range. this revealed that the depth formed of aluminum foil printed on a #400 mold was greater than that in #1000 and more sensitive to the pulse energy and the rate of overlap. in [10], a novel laser shock technology was also used to study the deformation behavior of pure copper foil. the results showed that after each shock, the formed area increased, and, at the same time, the undeformed area decreased until it disappeared. the power density of the laser can be applied to improve the accuracy dimension, surface roughness, and micro-hardness of micro-parts. the impact of the base metal surface roughness and the spread behavior of the bag-8 was studied in [11], and the optimum surface roughness found in rz was 0.92 [12]. in [13], the degradation of the micro-mold surface was investigated using laser dynamics in forming and its effects on the material. the experimental results showed the avoidance of growth, coalescence, and nucleation under repeated shock loading form surface degradation on micro-mold. laser shock waves can be used for micro-coining to replicate features on the metal surface. in [14], laser shock hydraulic forming was proved to have a good matching influence and can prevent or even suppress copper foil springback, which is appropriate for forming features of the large-region array. in [15], the punch force behavior was investigated during the micro v-bending of the copper foil. the results indicated that the free-bending and the coin-bending stages were part of the punch force profile. the application of laser technology has been studied extensively and has become more mature and applied to many processes, such as laser welding, laser shock peening, and laser shock forming [16-17]. to the best of our knowledge, there are no reports of metal foil micro-forming using water jet cavitation shock. this paper introduces a new process technology called cavitation water jet shock micro-forming. this process has the advantages of being low-cost, having good processing flexibility, and dramatically improving formability. the versatility and low cost of water-jet cavitation technology make it superior to conventional microforming such as laser micro-forming, which is more expensive, requires high-skill labor, etc. additionally, as the interface between fabrication tools and the work components is liquidto-solid, the manufacturing friction is reduced, negating the need for lubrication during the forming process. this study aims to demonstrate the feasibility of this process. water jet cavitation shock micro-forming is based on high-pressure shocks as a source for the forming energy created through the collapse of cavitation bubbles. during this process, a highspeed jet of water is injected into a water-filled chamber, and cavitation occurs in the shear layer around the jet. this type of jet is called a cavitation shock water jet. during the process, cavitation bubbles are generated by injecting high-speed water through a nozzle into a chamber filled with water. the cavitation bubbles periodically flow out from the nozzle and spread over the surface of the material to be processed, using the cavitation bubbles generated in the jets as the driving force, and applying high-pressure shock generated by the collapse of the bubbles [18, 19]. in the process of acting on the surface of the material, high-pressure shock waves propagate into the interior of the metal foil. this study investigated the cavitating water jet shock micro-forming technique to examine the processing parameters on the surface morphology of the formed part, the effect of incident pressure, impact time, and target on forming depth, and analyze the blanking phenomenon using 304 stainless steel foil. ii. forming mechanism and its apparatus as illustrated in figure 1, the typical application of the water jet cavitation shock micro-forming system is mainly composed of a jet-generating device and a forming device. the incident pressure drives the flow of water at a high speed through the cavitation nozzle, aggregation occurs when there is a large number of cavitation nuclei, the low-pressure region inside and outside the cavitation nozzle develops, and finally, the high-velocity liquid flow forms cavitation bubble groups. adjusting the standoff distance, when the cavitation bubble groups approach the surface of the sample, the environmental pressure around the cavitation bubble groups is suddenly increased due to the huge turbulent pressure pulsation causing the collapse of the cavitation bubble groups and releasing the high-pressure shocks (cavitation bubbles collapse impact loads) at the moment of collapse [20, 21]. these high-pressure shocks act on the surface of the material and propagate into its interior, while, due to the high concentration of energy [22-24], they are confined to a very small area, and when the peak value of the collapse pressure exceeds the hugoniot elastic limit (hel) of the material, the metal foil is yielded and plastically deformed. the peak stress of the shock wave decreases as the shock wave propagates deeper into the metal foil. the plastic deformation of the metal foil continues until the peak stress falls below the dynamic yield strength. since the loading direction is downward and the metal foil is free at the bottom side, the metal foil will bend downward and fill the die. the forming device is installed on the platform. the quality of the initial interface between the metal foil and the micro-die engineering, technology & applied science research vol. 13, no. 2, 2023, 10407-10413 10409 www.etasr.com quaisie et al.: the effect of cavitation water jet shock as a newly technology on micro-forming process is very crucial, so the two surfaces should be attached and bonded to each other. the forming device consists of a locking block, mask, seal ring, metal foils, and micro-die. at the initial stage, the foil was placed on the top of the die, completely covering its openings. the metallic foil flatness should be guaranteed during the process. next, the mask is placed on the foil and the micro-die had the same axial hole at the center. finally, the initial contact between the foil and the micro-die is very important, therefore, the two surfaces were firmly locked by a locking block to prevent material wrinkling. in addition, a seal ring was also applied between the foil and the mask to ensure effective sealing. fig. 1. (a) the formation system of water jets cavitation shock microforming and (b) forming device. iii. materials and methods a. material this study used 304 stainless steel foils due to their technical and economic advantages, as they are widely used in a variety of industrial applications, especially in the manufacture of micro-device components. these steel foils have good processing properties, high durability, good thermal conductivity, high temperature, corrosion resistance, good workability, need little maintenance, are nonmagnetic, are easy to weld and shape, and are completely recyclable (100%). tables i and ii show the chemical composition and the mechanical properties of the 304 stainless steel, respectively. the 304 stainless steel foil samples having 100μm thickness were cut into 50×50mm square specimens. the square samples were cleaned from dirt with anhydrous alcohol and the residual liquid was wiped off the surface. table i. chemical composition of 304 stainless steel element c mn p s si cr ni wt (%) ≤ 0.8 ≤ 2.0 ≤ 0.045 ≤ 0.03 ≤ 1.0 ≤ 18.0 ≤ 8.0 table ii. mechanical properties of 304 stainless steel elastic modulus (gpa) poisson ratio yield strength (mpa) tensile strength (mpa) extension rate (%) 194 0.3 ≥ 205 ≥ 520 ≤ 40 b. experimental setup figure 2(a) shows a schematic diagram of the experimental setup of the water jet cavitation shock micro-forming equipment used for the process. tap water was stored for at least 24 hours before the experimental test in a large tank of 2.5×2×1.5m at a room temperature of 25±2°c. a transparent water tank with a square horizontal cross-sectional area of 500×500×900mm was used to carry out the experiments. for transparent flow purposes, the tank was made of acrylic resin. the nozzle used in this experiment was designed regarding the angular nozzle for producing the periodic behavior of the jets of cavitation as shown in figure 2(b) [25]. the nozzle was fixed in water at room temperature. the pumped water was discharged at an incident pressure of 8-20mpa. the throat nozzle diameter was 1.5mm and the throat length l was 12mm with an expansion angle θ of 30°. the optimal nozzle size ratio was d:l=1:8 [26]. the distance between the sample workpiece was 120mm. inside the test cell, the sample was placed perpendicularly to the cavitating jets. the axial distance sl between the micro-die cavity and the jet axis was fixed at 10mm (the eccentricity sl was 10mm). pressure was attached to the nozzle through the inflow hole. a duration time of 120s was selected for this experiment with incident pressures of 8, 12, 16, and 20mpa. according to (1), the cavitation number is a measure of the flow's resistance to cavitation and is roughly equal to the ratio of the incident (upstream) to downstream pressures. � � �� �� (1) in this instance, p1 denotes the incident pressure and p2 denotes the downstream pressure. incident pressure is one of the crucial factors in the process of water-jet cavitation shock micro-forming. the downstream pressure p2 was maintained at 0.1mpa, while the incident pressure p1 was set to 8, 12, 16, and 20mpa [19], resulting in cavitation numbers of 0.0125, 0.0083, 0.0063, and 0.005, respectively. fig. 2. (a) experimental system of water jets cavitation shock microforming, (b) nozzle geometry diagram. c. forming device according to figure 3, the forming tool includes a locking block, mask, seal ring, workpiece, and micro-die. the top of the die was covered with foil, totally enclosing the die apertures, assuring it was flat. the mask was then positioned on the foil with the identical axial hole in the center as the microdie. the initial interface between the foil and the micro-die is engineering, technology & applied science research vol. 13, no. 2, 2023, 10407-10413 10410 www.etasr.com quaisie et al.: the effect of cavitation water jet shock as a newly technology on micro-forming process particularly important for preventing material wrinkling, hence, the two surfaces should be firmly linked to one another by a locking block. in addition, a seal ring was placed between the mask and the foil to provide an efficient seal. fig. 3. the forming device. iv. results and discussion this section presents the results of the surface morphology of the formed part, the influence of incident pressure on forming depth, the influence of impact time on forming depth, the effect of target distance on forming depth, and an analysis of the punching phenomenon. a. surface morphology of formed part in the process of metal foil micro-forming, a good forming effect can be obtained by selecting the appropriate process parameters [27]. a 304 stainless steel foil with a size of 50×50mm was selected for micro-forming experiments. figure 4 shows the 304 stainless steel foil at incident pressure of 20mpa, target distance of 120mm, impact time of 2min, and eccentricity of 14mm. figure 4(a) shows that the finished surface of the 304 stainless steel foil-formed parts was better than the surrounding unformed parts and had better outline shape and surface quality. in addition, it was observed that the edge of the formed part had no wrinkles, fractures, or other phenomena, indicating a better surface quality than the traditional micro-forming method [28]. fig. 4. (a) micro-formed sample, (b) 3d surface morphology of formed parts, and (c) section profile curve of formed parts. figure 4(b) shows that the 304 stainless steel foil obtained a good geometric shape during this forming process. the center area of the formed part has the darkest color, indicating that a strong plastic deformation occurred during the process. around it, the color gradually becomes lighter and the amount of deformation gradually decreases. figure 4(c) shows the typical cross-sectional profile curve of the micro-formed part. its cross-sectional shape is like a "spherical coronal cone" with a diameter of 1.2mm. in addition, the cross-sectional curve of the formed part had a smooth profile, without abrupt changes, and a good forming effect, which indicates that the material flows into the die uniformly during the forming process. the maximum forming depth of the formed part was 268.9μm. b. effect of incident pressure on forming depth in the experiment of cavitation water jet shock metal foil micro-forming, the forming depth of the foil can be an evaluation index of its forming quality. the incident pressure is one of the key parameters of the cavitation water jet shock micro-forming experiment, so it is necessary to analyze its effect on the deformation of the foil. to make the test results comparable, the other process parameters were fixed and only incident pressure was adjusted to 8, 12, 16, and 20mpa. the target distance was 120mm, the impact time was also 2min, and the eccentricity was 14mm. the results showed that when the incident pressure was 8, 12, 16, and 20mpa, the corresponding average forming depths were 89.2, 145.9, 169.9, and 226.6μm, respectively. figure 5 shows the variation in the forming depth. this indicates that the plastic deformation of the 304 stainless steel foil increased non-linearly with incident pressure [29]. the forming depth improved at a decreasing rate when the incident pressures increased from 8 to 16mpa and increased sharply when the incident pressures changed from 16 to 20mpa. this could be attributed to the following reasons:  when the incident pressure is less than 16mpa, the cavitation bubbles mostly collapse before reaching the material surface under the standoff distance of 120mm, hence, the shock energy was relatively low and the improvement of the forming depth was not high. although the cavitation bubbles have a larger size and collapse on the material surface, they produce greater shock energy which increases the forming depth sharply when the incident pressure increased to 20mpa.  the dynamic yield limit of the material increases due to the residual stress and the hardened effect during the shockforming process. therefore, a stronger force is needed to produce continued deformation. c. effect of target distance on forming depth incident pressure was set to 20mpa, impact time was set to 2min, and eccentricity to 14mm and the influence of target distance (80, 100, 120, and 140mm) on the forming depth was studied. the depth was measured and its average value was calculated. figure 6 shows the average depth curve of 304 stainless steel foil-formed parts at different target distances. under an incident pressure of 20mpa, with increasing target distance, the average depth of the formed part increases first and then decreases. when the target distance was 120mm, the average depth of the formed part was the largest, reaching 226.6μm. this was mainly due to the increase in the target distance that increased the shockwave pressure acting on the workpiece surface. however, with an increasing target engineering, technology & applied science research vol. 13, no. 2, 2023, 10407-10413 10411 www.etasr.com quaisie et al.: the effect of cavitation water jet shock as a newly technology on micro-forming process distance, most of the cavitation bubbles collapse before reaching the surface of the workpiece, so the impact energy was relatively low as the depth increased. fig. 5. the maximum depth with different incident pressures. fig. 6. the average depth depending on different target distances. d. effect of impact time on forming depth to investigate the influence of impact time on the forming depth of the 304 stainless steel foil, the incident pressure was 8, 12, 16, and 20 mpa, the target distance was 120mm, the eccentricity was fixed at 14mm, and the impact time was 40, 80, 120, and 160s, respectively. figure 7 shows that under the same incident pressure (8 mpa), the average forming depth of the formed part increased nonlinearly with increasing impact time. with an incident pressure of 8mpa, when the impact time increased from 40 to 160s, the forming depth increased from 40.4μm to 116.1μm, which is almost three times the initial value. however, with increasing time, the growth rate of forming depth gradually decreased. when the incident pressure increased from 12 to 16mpa, the change in the average forming depth followed the same trend. in addition, when the incident pressure was 20mpa, forming depth increased from 91.8μm at 40s impact time to 252.7μm at 160s, which is also approximately a three-time increase. these results show that the incident pressure and the impact time directly determine the forming effect of the metal foil. in addition, it was found that in the subsequent impact process of the cavitation water jet, the growth rate of the forming depth of the material gradually reduced. this can be attributed to the fact that as the entire forming device was placed in water, the forming depth also increased with increasing impact time. furthermore, since it is difficult to achieve complete sealing, a small amount of tap water will flow into the pit, thereby gradually reducing the impact effect. fig. 7. the average forming depth depending on different impact times. e. analysis of the blanking phenomenon in the micro-forming process of metal foil impact by cavitation water jet, the analysis of the causes of material failure and the mechanism behind it helps to understand the impact process conditions and improve the forming quality of the material. in high-speed impact, the material is damaged by crack initiation and propagation, but when cavitation collapses, shockwave and inertia act on the target and at the same time a variety of damages such as adiabatic shear instability, breakage, and spallation would also occur. when the target distance was 120mm, the eccentricity was 14mm, and the incident pressure exceeded a certain value, the foil had a severe shear effect and a cut-off at the edge of the die. figure 8 shows the blanking effect of the 304 stainless steel foil under an incident pressure of 30mpa. fig. 8. the morphology of punched hole at the bottom: (a) front, and (b) reverse side. figure 9 shows an sem image of the back of the punched round hole under the corresponding conditions. when the incident pressure increased to 30mpa, the workpiece was engineering, technology & applied science research vol. 13, no. 2, 2023, 10407-10413 10412 www.etasr.com quaisie et al.: the effect of cavitation water jet shock as a newly technology on micro-forming process completely blanked. this is mainly because, under this incident pressure, the shockwave pressure generated by the collapse of the bubble deforms the workpiece beyond the limit stress of the material itself. at the edge of the cavity, the stress value was obtained, which completely exceeds the shear fracture limit of the cavity, leading to the fracture of the material and the complete blanking process. fig. 9. sem for punched bottom circle: (a) whole view, and (b) local magnification view. v. conclusion this study conducted experiments using a cavitation water jet shock micro-forming on a 304 stainless steel foil. the single characteristic micro-forming experiments were carried out, and the impact micro-forming law of the cavitation water jet was analyzed and studied from the aspects of incident pressure, target distance, impact time, and 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[29] l. saidi, s. mekroussi, s. kherris, d. zebbar, and b. mébarki, "a numerical investigation of the free flow in a square porous cavity with non-uniform heating on the lower wall," engineering, technology & applied science research, vol. 12, no. 1, pp. 7982–7987, feb. 2022, https://doi.org/10.48084/etasr.4604. microsoft word etasr_v12_n6_pp9747-9751 engineering, technology & applied science research vol. 12, no. 6, 2022, 9747-9751 9747 www.etasr.com zisopol et al.: compression behavior of fff printed parts obtained by varying layer height and infill … compression behavior of fff printed parts obtained by varying layer height and infill percentage dragos gabriel zisopol mechanical engineering petroleum – gas university ploiesti, romania zisopol@zisopol.ro ion nae mechanical engineering petroleum – gas university ploiesti, romania inae@upg-ploiesti.ro alexandra-ileana portoaca mechanical engineering petroleum – gas university ploiesti, romania alexandra.portoaca@upg-ploiesti.ro received: 1 january 2022 | revised: 2 february 2022 | accepted: 3 march 2022 abstract-in this research, two polymeric materials, pla(polylactic acid) and abs (acrylonitrile butadiene styrene) were used to 3d print compression samples at 3 layer heights (0.10, 0.15, and 0.20mm) with 3 infill percentages (50%, 75%, 100%). in order to determine the material's behavior under applied crushing loads, 135 samples were fabricated and tested. the built compression pla specimens were subjected to common annealing treatment just above glass transition temperature and it was proved that the set of 45 samples exhibited higher resistance to the compressive load applied to the material before fracturing by an average of 9.20%. keywords-3d printing; annealing; compressive test; postporcessing treatments i. introduction additive manufacturing has a wide range of applications and the advantage of specific application tailored part fabrication. the most common additive layer by layer technology is fff (fused filament fabrication), which consists in successively depositing filaments layer by layer. in order to meet the physical and mechanical requirements various additive manufacturing processes have been developed and a wide variety of materials have been used and studied with emphasis on compression tests (niti shape memory alloys processed via the laser-based directed energy deposition technique [1], fiber-reinforced pla/tpu (thermoplastic polyurethane) [2], polymeric materials [3, 4], ni-rich niti alloys [5], pa-12 nylons produced by multi-jet fusion technology [6]). regarding tension or compression loading, significant functional risks are generated by the microstructure of 3d printed materials, characterized by an important degree of anisotropy [1]. however, industrial manufacturing processes aim to eliminate waste and to obtain higher stress, flexibility, and energy absorption. so, besides considering full volume structures, recent researchers make reference on lattice structures [6-9]. additive manufacturing offers the opportunity to design and create various configurations of lattice structures by controlling relative densities, material components, and microstructure [6, 7, 10]. similar to subtractive technologies [11-13], several post treatments can be applied to additive manufactured parts depending on the processes used, with the aim to partially reduce porosity and relief internal stress. in this context, the present paper presents compression test results also on a set of pla samples subjected to thermal treatment [1, 6] that consists in heating materials at a temperature between the glass transition and melting point temperature and by slow cooling in the oven. ii. materials and methods a. parameter set up significant 3d printing parameters have been analyzed in the recent scientific literature:  raster orientation and printing speed [14],  layer height and infill percentage [15-18],  building orientation: flat, on edge, and upright oriented [19, 20]. for this research, the considered parameters were the layer height and the infill percentage, their values are shown in table i. the material specifications were provided through manufacturers' data sheets and are also depicted in table i. in this experimental study, the samples were fabricated with three infill percentages, i.e. 50%, 75%, 100% and in order to asset the mechanical characteristics (table ii), compressive tests were conducted made on both considered materials (pla and abs). for pla polymer heat treatment was experimented in order to compare the compressive stress values. the annealing corresponding author: alexandra-ileana portoaca engineering, technology & applied science research vol. 12, no. 6, 2022, 9747-9751 9748 www.etasr.com zisopol et al.: compression behavior of fff printed parts obtained by varying layer height and infill … treatment for pla consisted in maintaining a temperature of 75 0 c for a period of 3h, succeeded by slow cooling in the oven. b. sample preparation a raise e2 3d printer was used to fabricate the samples with a volume capacity of 330×240×240mm. the design of the samples, later converted in stl format, was drawn in solid edge software [21] and the slicing parameters, such as internal structure pattern, infill percentage, and layer thickness were adjusted in the idea maker software. samples were x-z orientated and printed with a bed platform for better adhesion to the printing table as shown in figure 1. table i. printed sample characteristics parameters material specifications pla abs nozzle diameter 0.40mm 0.40mm build orientation flat flat top solid layers 4 layers 4 layers bottom solid layers 4 layers 4 layers outline/perimeters shell 3 outlines 3 outlines internal fill pattern lines lines external fill pattern rectilinear rectilinear internal infill angle offsets 45°-135° 45°-135° extruder temperature 210°c 240°c heated bed temperature 60°c 110°c default printing speed 70mm/s 45mm/s cooling fans on on filament diameter 1.75mm 1.75mm filament density 1.24g/cm3 1.04g/cm3 table ii. 3d printed infill parameters constant parameters variable parameters materials building orientation x, y layer hight (hsmm) infill procentage (pu-%) abs pla as pla an extrusion temperature (te) samples bed temperature (tp) 0.10 50 75 100 15 15 15 speed (vp) 0.15 15 15 15 filling model 0,20 15 15 15 (a) (b) fig. 1. sample pictures: (a) as built pla, (b) annealed pla. the samples were tested on a zwick roell universal machine to obtain their compressive stress values. the preload was 20n and the test speed was 10mm/min, according to plastics — determination of compressive properties, iso 604:2002(e) [21]. c. compressive test sets of 5 specimens were printed for each of the characteristics considered in the current study, as can be seen in figure 2. the compression tests were done at the liea laboratory, within isim timișoara, on a mu 400kn testing machine, type zd 40/90. fig. 2. geometrical features of the compressive test samples. iii. results and discussion a. results values and averages of compressive stress are depicted in tables iii-v for each combination of layer height and infill percentage for the as built pla. table iii. compressive stress test values of as built pla for 0.10 thickness layer infill, % compressive stress, mpa sample 1 2 3 4 5 average 50% 34 35 34 35 35 34.6 75% 48 48 47 46 46 47 100% 64 62 66 67 98 71.4 table iv. compressive stress test values of as built pla for 0.15 thickness layer infill, % compressive stress, mpa sample 1 2 3 4 5 average 50% 32 33 31 32 31 31.80 75% 45 45 47 46 45 45.6 100% 65 63 63 63 61 63 table v. compressive stress test values of as built pla for 0.20 thickness layer infill, % compressive stress, mpa sample 1 2 3 4 5 average 50% 30 30 32 32 29 30.6 75% 43 43 44 43 43 43.2 100% 59 59 60 59 61 59.6 as can be seen in tables vi-viii, the compressive stress values of the annealed tested samples are higher, which reveals that annealing has a positive effect in the microstructure of the material, by releasing internal stress and decreasing the porosity of the parts obtained by 3d printing. the thermal annealing post-process technique applied for improving properties of polymer extrusion-based parts has been intensively studied recently [1, 5, 6]. engineering, technology & applied science research vol. 12, no. 6, 2022, 9747-9751 9749 www.etasr.com zisopol et al.: compression behavior of fff printed parts obtained by varying layer height and infill … table vi. compressive stress test values of annealed pla for 0.10 thickness layer infill, % compressive stress, mpa sample 1 2 3 4 5 average 50% 39 38 29 39 38 36.6 75% 52 50 52 51 52 51.4 100% 67 67 69 67 66 67.2 table vii. compressive stress test values of annealed pla for 0.15 thickness layer infill, % compressive stress, mpa sample 1 2 3 4 5 average 50% 35 36 37 36 37 36.2 75% 53 52 52 51 51 51.8 100% 71 72 71 71 71 71.2 table viii. compressive stress test values of annealed pla for 0.20 thickness layer infill, % compressive stress, mpa sample 1 2 3 4 5 average 50% 37 33 34 35 34 34.6 75% 47 47 47 48 48 47.4 100% 69 65 64 64 65 65.4 table ix. compressive stress test values of abs for 0.10 thickness layer infill, % compressive stress, mpa sample 1 2 3 4 5 average 50% 21 22 21 22 23 21.8 75% 60 50 31 55 52 49.6 100% 61 60 63 61 62 61.4 table x. compressive stress test values of abs for 0.15 thickness layer infill, % compressive stress, mpa sample 1 2 3 4 5 average 50% 26 26 27 22 24 25 75% 42 42 46 43 47 44 100% 68 62 33 60 54 55.4 table xi. compressive stress test values of abs for 0.20 thickness layer infill, % compressive stress, mpa sample 1 2 3 4 5 average 50% 31 31 27 31 23 28.6 75% 26 26 45 25 44 33.2 100% 66 18 60 61 60 53 similar average compression stress results with [20] were obtained for 50% infill: 34.67mpa and 43.67mpa and for 100% infill: 71mpa and 93.34mpa. values and averages of compressive stress for abs samples are depicted in tables ixxi for each combination of layer height and infill percentage studied in this research. as shown in [23], compressive stress values are scattered due to the variation of the process parameters like orientation, layer thickness, raster angle, raster width, and air gap with an average of 14.63mpa comparable with 50% average abs values 21.8mpa. significant influences regarding the infill percentage can be noticed in the drawn stress-strain curves of as built pla, annealed pla, and abs sample. as assumed, 100% infill percentage samples have the greatest resistance to compressive stress. fig. 3. compressive stress variation of 0.10 layer thickness of as built pla. fig. 4. compressive stress variation of 0.10 layer thickness of annealed pla. fig. 5. compressive stress variation of 0.15 layer thickness of as built pla. as can be seen in figures 3-8 the curves of the annealed set of samples have clearly higher compressive stress supported in the case of failure. the percentage of the average increase in compressive stress of the thermal treated pla with 0.10mm layer thickness is 3.70%, for the 0.15mm layer thickness the average increase is 13.39%, and for the 0.20mm layer thickness the increase is 10.49%. it is noted that the compressive strength values of the annealed pla are higher than those of plain pla (tables iii-viii). this can be explained by the influence of the annealing treatment that led to the homogenization of the structure and the increase of the adhesion of the deposited layers. engineering, technology & applied science research vol. 12, no. 6, 2022, 9747-9751 9750 www.etasr.com zisopol et al.: compression behavior of fff printed parts obtained by varying layer height and infill … analyzing the force-deformation diagrams (figures 3-11) obtained by the test machine following the compression load, the following areas of the load-specific curve can be observed:  a linear zone characteristic of the behavior of the material in the elastic domain.  a convex curve which corresponds to the yield strength.  a constant level which corresponds to the flow zone at which the force remains relatively constant, the deformation increasing significantly. fig. 6. compressive stress variation of 0.15 layer thickness of annealed pla. fig. 7. compressive stress variation of 0.20 layer thickness of as built pla. fig. 8. compressive stress variation of 0.20 layer thickness of annealed pla. after a slight increase in the compression force, the breaking phenomenon occurs (cracks appear in the material structure). this is marked on machine-drawn diagrams by a peak. then a decrease in force with a minimum is noted on the diagram after which the force increases significantly. this growth is probably produced due to the compaction of the material after the cracks appear. regarding the abs material, similar results are revealed in figures 9-11. also, the infill percentage has a great emphasis in the character of the stressstrain curves. the curves for abs with 0.10 layer thickness reveal more instable graphics than the other layer thickness samples, that can be the result of a more brittle behavior also noticed in the tensile behavior studied in [15-18, 24, 25]. fig. 9. compressive stress variation of 0.10 layer thickness abs. fig. 10. compressive stress variation of 0.15 layer thickness abs. fig. 11. compressive stress variation of 0.20 layer thickness abs. b. disscusion this paper aims to highlight the variation of mechanical characteristics (compressive stress) of annealed pla 3d and abs, with different parameters of the printing process. the general mechanical properties of plastics have been introduced to facilitate comparison with other classes of materials or with the same materials but having different chemical compositions. the study presents the experimentally determined values for the compression test of abs and two types of pla. the initial mechanical characteristics of the tested materials correspond to the specifications of the filament manufacturers (pla-raise and abs-verbatim) shown in table i. engineering, technology & applied science research vol. 12, no. 6, 2022, 9747-9751 9751 www.etasr.com zisopol et al.: compression behavior of fff printed parts obtained by varying layer height and infill … the research plan consisted in fabricating the samples on a raise e2 3d printer. the considered variable research parameters were infill degree (50, 75, 100%) and layer thickness (0.10, 0.15, 0.20mm). the samples were compression tested on a zwick roell universal machine. the preload was 20n, and the test was performed at a speed of 10mm/min, according to iso 604:2002(e) determination of compression properties. the shape of the researched samples is parallelepiped (figure 2), having a square cross-section of 10×10mm and 20 mm height. due to the elasticity of the researched materials, it was adopted that the length (height) of the test piece should be twice the side of the square. iv. conclusions in the case of a plastic material that does not yield in compression by a break (crack), the compressive strength is arbitrary, depending on the degree of distortion that is considered to indicate complete failure of the material. situations may arise where plastic specimens will continue to deform in compression until they are reduced to a flat disk, the (nominal) compressive stress increasing steadily, without any well-defined material cracking. for this research, the failure criterion was considered the appearance of cracks on the surface of the studied specimen. according to the experimental research carried out, for one type of material (pla, abs) if the thickness of the deposited layer is kept constant with the increase of the degree of filling, the magnitude of the compression stresses increased (tables iii-v). this can be explained by the higher rigidity of the structure formed by 3d printing. to sum up, for each material type (pla, abs) and at the same degree of filling, the increase in the thickness of the deposited layer leads to a decrease of the magnitude of the compressive stress (tables iii-v). this can be explained by cracking at the level of the structural blocks, having a height equal to the thickness of the deposited layer. references [1] b. a. bimber, r. f. hamilton, j. keist, and t. a. palmer, "anisotropic microstructure and superelasticity of additive manufactured niti alloy bulk builds using laser directed energy deposition," materials science and engineering: a, vol. 674, pp. 125–134, sep. 2016, https://doi.org/ 10.1016/j.msea.2016.07.059. 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[18] d. g. zisopol, a. i. portoaca, i. nae, and i. ramadan, "a comparative analysis of the mechanical properties of annealed pla," engineering, technology & applied science research, vol. 12, no. 4, pp. 8978–8981, aug. 2022, https://doi.org/10.48084/etasr.5123. [19] j. m. chacón, m. a. caminero, e. garcía-plaza, and p. j. núñez, "additive manufacturing of pla structures using fused deposition modelling: effect of process parameters on mechanical properties and their optimal selection," materials & design, vol. 124, pp. 143–157, jun. 2017, https://doi.org/10.1016/j.matdes.2017.03.065. [20] z. mehdiyev, c. felhő, and k. p. zoltán, "investigation on 3d printing parameters of pla polymers for gear applications," in vehicle and automotive engineering 4, 2023, pp. 654–664, https://doi.org/10.1007/ 978-3-031-15211-5_55. [21] iso 604:2002 plastics — determination of compressive properties. iso, 2002. [22] "3d cad design software | solidworks." https://www.solidworks. com/. 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[25] d. g. zisopol, d. v. iacob, and a. i. portoaca, "a theoreticalexperimental study of the influence of fdm parameters on pla spur gear stiffness," engineering, technology & applied science research, vol. 12, no. 5, pp. 9329–9335, oct. 2022, https://doi.org/10.48084/ etasr.5183. microsoft word etasr_v12_n4_pp9063-9070 engineering, technology & applied science research vol. 12, no. 4, 2022, 9063-9070 9063 www.etasr.com ibrahim & abdulkareem: pressure drop in horizontal two-phase flow pressure drop in horizontal two-phase flow safa subhi ibrahim petroleum engineering department university of zakho zakho city, kurdistan region-iraq safa.ibrahim@uoz.edu.krd lokman aziz abdulkareem petroleum engineering department university of zakho zakho city, kurdistan region-iraq lokman.abdulkareem@uoz.edu.krd received: 25 june 2022 | revised: 12 july 2022 | accepted: 12 july 2022 abstract-in an artificial environment, the most important key in the process equipment design is determining gas-liquid two-phase flow frictional pressure drop of pipes. to achieve this, an experimental investigation was carried out in this study to analyze the pressure drops of air-water two-phase flow in a 30mm internal diameter horizontal pipe with a length of 6m at different flow conditions. the study was carried out at 20c o using tap water and air. to cover the slug flow pattern, the volumetric flow rate of water varied from 30 to 80 lpm, and the volumetric flow rate of air from 40 to 200 lpm. pressure transmitters were used to measure pressure at four different points along the test section, each 2m apart. the results of the experiments were compared to 8 models using 3 distinct methods: mean absolute percentage error (mape), relative performance factor (rpf), and the percentage of data included in the range of the 30% error band. all methods produced similar results, with the sunmishima model being the most accurate. keywords-two-phase flow; frictional pressure drop; slug experimental model; horizontal flow; homogenous and separated flow model i. introduction many industrial applications, such as heat exchangers, pipeline network systems, refrigeration and heat pumps, thermal energy plants, environmental control, life-support systems, and fuel cells rely on the measurement of pressure drop in two phases [1, 2]. furthermore, the pressure drop is essential because the co-current flow of liquid and gas causes design and operational problems due to the formation of various types of two-phase flow patterns. in these cases, estimating pressure drop helps the piping designer in determining the optimal line size and designing a better piping system [3-5]. during the past 60 years, investigators have been researching two-phase frictional pressure drop. a comprehensive theoretical and experimental research was carried out and various relationships were proposed in [6]. for estimating the frictional pressure drop in horizontal and vertical pipes, there are two types of models: homogeneous and separated flow models. in homogeneous flow, the two phases are considered to be intimately mixed with no relative motion between them, either locally or overall [6]. thome suggested utilizing the homogeneous model for mass fluxes more than 2000kg/m 2 s at high-reduced pressures and higher mass velocities [7]. the separated flow, on the other hand, recognizes that the two phases can exist separately, each flowing through its own pipe, with the assumption that the velocity of each phase is constant in the zone occupied by the phase [8-14]. some researchers assessed a few correlations using limited experimental data. authors in [15] used r134a, r123, r402a, r404a, and r502 evaporation data in two horizontal pipes with 10.92 and 12.0mm id (inner diameter), with mass flux ranging from 100 to 500kg/m 2 s and vapor quality ranging from 0.04 to 1.0, to evaluate 7 models. overall, authors in [16, 17] proposed the most accurate predictors, with the one in [10] being the third-best prediction. authors in [18] validated 15 equations based on experimental data of r410a convective boiling in two pipes of 1.5 and 3mm id, with inlet saturation temperature of 10 o c, mass flux of 300 to 600kg/m 2 s, and heat flux of 10 to 40kw/m 2 . they discovered that a homogeneous approach could accurately predict frictional pressure drop. authors in [19] compared 11 correlations to empirical observations of r123, r134a, r22, r236ea, r245fa, r404a, r407c, r410a, r507, co2, water, and air, with hydraulic diameters ranging from 0.506 to 12mm, rel ranging from 10 to 37,000, and reg ranging from 3×10 5 to 4×10 5 . the results showed that the correlations in [8, 12, 20, 21] performed similarly in the viscous region, while the muller-steinhagen and heck [17] correlation performed best in the turbulent region. authors in [21] tested 10 correlations against a variety of experimental data sets using a separated flow approach. according to the results, the correlations of [21] had the highest accuracy. authors in [22, 23] studied the possibility of calculating two-phase frictional pressure drop in microgravity using normal gravity two-phase frictional pressure drop correlations. microgravity experimental data were compared to 23 two-phase frictional pressure drop correlations. the above evaluations based on normal gravity experimental data produced inconsistencies. τhe homogeneous model [18, 24, 21], the chen et al. correlation [23], and the zhang et al. formula [21] have been proposed, whereas authors in [15, 19, 25] suggested the muller-steinhagen and heck [17] correlation as the best prediction. the effects of fluid refrigerant and channel geometry on the frictional pressure drop during twophase flow of r134a, r1234ze(e), r1234yf and r600a in a horizontal tube with mass velocities varying between 100 and 1600kg/m 2 s, saturation temperatures of 31 and 41°c and vapor corresponding author: safa subhi ibrahim engineering, technology & applied science research vol. 12, no. 4, 2022, 9063-9070 9064 www.etasr.com ibrahim & abdulkareem: pressure drop in horizontal two-phase flow quality from 0.05 to 0.95 was investigated in [26]. they concluded that the new method accurately predicted the database, predicting 89% of the results within an error band ±20%. authors in [27] studied experimentally the pressure drop of evaporative propane with mass flux of 360 to 915kg/m 2 s and vapor quality of 0 to 1.0 in microchannel with 500μm diameter and 0.5m length. authors in [28] conducted an experimental analysis of the frictional pressure drop in a plate heat exchanger using the working fluid r-1233zd(e). according to the experimental findings, the frictional pressure drop increases with increasing mass flux and mean vapor quality while it decreases with increasing saturation pressure. the experimental results led to the development of correlations for the friction factor of r1233zd(e) in plate heat exchangers. the new correlation of the friction pressure drop and mixture viscosity for two phase flow in homogenous approach modeling was developed in [1] and was compared to 846 experimental data of friction pressure drop that were collected from previous studies. the experimental data including various working fluids such as r1234ze(e), r32, r-600a r717, r134a, r410a and carbon dioxide (co2) at various hydraulic ids and mass flux. the discovered mean absolute relative deviation (mard) was 30%. these new correlations of two-phase flow pressure drop were used to predict the experiment measurements of pressure drop on circular pipes, minichannels, and micro-channels. the experimental data used for their evaluations were rare, which could be the root cause of the inconsistency. furthermore, the number of correlations examined in each paper was limited to no more than 15 in total. a complete evaluation is therefore necessary. this article has conducted a review of the literature on two-phase frictional pressure drop correlations for homogeneous and separated flows for finding an optimal model for experimental data. ii. pressure drop in horizontal two-phase flow two-phase pressure drop predicting methods in horizontal pipes are discussed in this article. the sum of the static pressure drop (elevation head) ∆������� , momentum pressure drop (acceleration) ∆����� , and frictional pressure drop ∆� ��� is the total measured pressure drop ∆������ of a fluid in a horizontal two-phase flow pipe [7]: ∆������ = ∆������� + ∆����� + ∆� ��� (1) the gravitational pressure drop ∆������� in a horizontal pipe is zero, and the quality is constant throughout the pipe (as a result, in adiabatic flow, the acceleration term appears to have no effect on the pressure drop and can be ignored). only the frictional pressure drop was studied. the following two classic models are used for two-phase flows. a. homogeneous flow model because gas and liquid have similar velocities in the homogeneous flow model, the frictional pressure drop for twophase flow can be rewritten as [29]: (����)��,��� = (� ���������� )��,��� (2) where ��� is the friction factor for smooth pipe based on petukhov correlation (where: ��� = (0.79 ln !��−1.64)−2) [23], "�� is the two-phase mass flux (kg/m2s), d is the diameter of the pipe (m), #�� is the two-phase flow density (kg/m3), and !�� is the two-phase flow reynolds number. the values of #�� and !�� are calculated as [1]: #�� = ( %�& + '(%�) )(' (3) !�� = ����*�� (4) where: +�� = ( %*& + '(%*) )(' (5) where +�� , +� , and +, are the dynamic viscosities of twophase, liquid, and gas (kg/ms) respectively [30], x is the air mass quality, and #, and #� are the densities of gas and liquid phases (kg/m 3 ) respectively. according to the homogeneous flow, the correlations of frictional pressure drop are: mcadams [30] and chen et al [13]. table i contains more information. table i. homogeneous correlations reference correlations [30] (2) [13] (-.-/)�� = ω�� (-.-/)��,��� where ω�� parameter depends on bond number bo: ω�� = 1 1.2 − 0.9 exp (−;<) ;< < 2.5 1 + ?!��@.�exp (;<@.a) − 0.9 exp(−;<) ;< ≥ 2.5 in which, ;< = ,(�)(�&)(�/�)�d and ?!�� = ���� �e��� where g is the gravity acceleration (m/s 2 ), wetp is the two-phase weber no. (-), and σ is the surface tension of water (n/m). b. separated flow model this model is based on the use of the two-phase friction multiplier f�� , where the subscript i can be l, g, lo, or go indicating liquid, gas, liquid-only, or gas-only respectively. the separated flow is divided into two branches: 1) liquid and gas frictional multipliers (∅�� and ∅,� ) two-phase friction multiplier method depends on liquid (f��) and gas (f,�). the frictional multiplier is the ratio of the two-phase frictional pressure drop to the single-phase frictional pressure drop as follows [9]: f�� = (����)�� (����)�h (6) where: i����j� = � k�k���k (7) where the subscript i can be l or g denoting liquid or gas respectively, (����)� is the single-phase frictional pressure drop (kpa/m), �� is the friction factor, and "� is the actual mass flux (kg/m 2 s). based on [23], the friction factor of liquid and gas for a smooth pipe can be calculated as: engineering, technology & applied science research vol. 12, no. 4, 2022, 9063-9070 9065 www.etasr.com ibrahim & abdulkareem: pressure drop in horizontal two-phase flow �� = 0.25 lm<n o 'p@.aqr�ks.tuuvw − 'p�.xxr�k yz (� (8) and the !� values for each phase can be calculated as [1]: !� = �k�*k (9) authors in [8] discovered that [�� and [,� are functions of the dimensionless variable \ in the following way [8]: \ = ] (��/��))(��/��)& (10) where \ is the lockhart-martinelli parameter. many other researchers’ studies and correlations were inspired by this model. according to the separated flow model, the frictional pressure drop correlations are: chisholm [31], and sunmishima [19]. table ii contains additional information. table ii. the separated correlations: liquid and gas frictional multipliers ([�� and [,� ). reference correlations [31] ^_̀ = a + bc + ac` c gas liquid 20 12 10 5 turbulent turbulent laminar laminar turbulent laminar turbulent laminar [19] for viscous flow: b = 26 o1 + !�1000y [1 − exp o −0.1530.8 + 0.27ijy] where la is the laplace number, for turbulent flow: [�� = 1 + lmn.nt + 'm�, where: o = 1.79 ir�&r�) j@.p ]'(mm , !, = "�� qr/+,, js !� = "�� (1 − q)r/+� 2) liquid-only and gas-only frictional multipliers (f��� and f,�� ) the frictional multipliers in this case are defined as the ratio of the two-phase frictional pressure gradient over the pressure gradient that would arise if the phase flowed alone in the pipe to the total mass flux of the two-phase flow [31]: f�� = (����)�� (����)�h (11) where the subscript i can be lo, or go indicating liquid-only, or gas-only respectively. the single-phase frictional pressure drop is computed as follows: (����)� = � k������k (12) in this case, the fang et al. correlation (8) was used to calculate the friction factor. table iii displays the frictional pressure drop correlations for this method. table iii. the separated correlations: liquid-only and gasonly frictional multipliers (φuv� and φwv� ). reference correlations [9] [��� = 1 + (x� − 1){b[(1 − q)]@.{|p + q'.|p where: x� = (-.-/),� (-.-/)��} ~� 0 < x < 9.5, ; = 1 55 "�� @.p⁄ "�� ≥ 19002400 500 < "�� < 19004.8 "�� ≤ 500 ~� 9.5 < x < 28, ; = �520 x"��@.p⁄ "�� ≤ 60021/y "�� > 600 if y > 28, b = 15000/y�g��@.p [10] for viscous flow: [��� = (1 − q)� + q � �#� �,�#,��� � + 3.24q @.|{(1 − q)@.��p����@.pp?!��@.@ap where: � = o �)�&y @.q' i*&*) j@.'q (1 − +_n/+_m )@.|, and, ���="��� nr#���h [16] [��� = 1 + (-.-/)� [� #�#,� o +,+� y @.�p − 1] where: (����)� = �� [q + 4(q'.{ − q'@�� @.p)], �� = 11 ���� ≥ 1���@.a + 0.0055[ln ( 1����)]� ���� < 1, and ���� = "��� nr#�⁄ [17] [��� = x�qa + (1 − q)'/a[1 + 2q(x� − 1)] iii. experimental setup and measurements the specially designed system was constructed to measure pressure drop in two-phase slug flow in a horizontal pipe. the two-phase air-water system was designed and built-up in the multi-phase laboratory of the petroleum engineering department, college of engineering, university of zakho. the system's main components were the air and water supply systems, a two-phase mixer, a visual horizontal test section, pressure transmitters, and facility instrumentation. the airwater flow loop system scheme is illustrated in figure 1. the fluids in this system were air and water. a shimge centrifugal water pump with a head of 22.5m and 600 lpm capacity was utilized to circulate water from a water storage tank to feed the test section via a water rotameter. the water rotameter was controlled by two ball valves and had a range of 20 to 150 lpm with an accuracy of ±4%. they were both used to control the amount of flow that entered the test section, passed through a horizontal pipe, and then to a separator/first tank. in the separator tank, the air was released into the atmosphere via the separator tank’s top, and the liquid settled under gravity and flowed through the bottom to return to the second tank. the water was stored in the two tanks that were linked together with pvc pipe. the first tank housed the return water from the test section, while the second tank, with a capacity of 426l, was used to feed the system via a pvc pipe connected to the pump. the second tank's function was to keep air bubbles and debris from transferring from the tank to the pump and to control the pump's excess flow. engineering, technology & applied science research vol. 12, no. 4, 2022, 9063-9070 9066 www.etasr.com ibrahim & abdulkareem: pressure drop in horizontal two-phase flow fig. 1. the schematic diagram of the experimental facility. meanwhile, the compressor supplied air to the loop, which was controlled by an air filter regulator with 0-11 bar range. an air rotameter with a measuring range of 40 to 400lpm and accuracy of ±4% was utilized to measure the air flow rate. at the t-junction at the test section’s entrance, air and water were mixed. water from the pump was fed into the mixer from one side, while compressed air was charged into the mixer via a 6mm diameter flexible hose parallel to the main flow. to distribute the air in the water stream, a mixer was also used. the designs of [23, 33] were used in the mixing section. the mixer section was constructed of a 6mm stainless steel pipe and was installed in the water stream using a plastic t-junction and a compression fitting. the stainless-steel pipe was soldered to prevent air flow from the end. sixty holes with 1.3cm spacing and varying diameters were drilled in 15 columns around the stainless-steel pipe over a length of 25cm (3 rows of 1mm, 4 rows of 2 mm, and 8 rows of 3 mm). to prevent water from entering the air flow, the size of the holes was decreased through the internal tube. the testing section was divided into 3 parts. each part was constructed from the acrylic pipe with a visual thickness of 5mm, a length of 2m, and an id of 30mm. each of the 3 parts of the test section was connected using flange connections. the total length of the test section was 6m. the flanges were mounted on fixed rigid steel frames to ensure long-term support and safe operation. moreover, 4 different pressure transmitters from the wiki company with a range of 0-2bar were fixed to the top of the test section pipe by brass pipe fittings and installed to measure the pressure difference along the test section. figure 2 depicts the experimental setup. the strategy employed at the start of each run was to start with a fixed water discharge flow rate and gradually increase the air flow rate until slug flow appeared, then increase the water flow rate and repeat the previous steps. the baker flow pattern map was used to determine experimental settings for the air-water flow rates [34]. these experimental conditions were scripted in matlab (r2017b). the result is shown in figure 3. the water and air flow rates were 30 to 80 lpm and 40 to 200 lpm respectively. the system’s 4-channel voltage reader was utilized to read transient pressures from the pressure transmitter to a pc. the optimum time for all variable test requirements to exclude the influent effect on the flow was 30s. the experiments were conducted at a pressure of 1bar and a temperature of 20 o c. all the experimental operating conditions are displayed in table iv. fig. 2. the experimental setup. engineering, technology & applied science research vol. 12, no. 4, 2022, 9063-9070 9067 www.etasr.com ibrahim & abdulkareem: pressure drop in horizontal two-phase flow fig. 3. flow pattern map produced by matlab (r2017b) based on the experimental operating conditions. iv. results and discussion statistical analysis was performed on the results of the twophase pressure drop models to determine the best model among the 8 considered models. the results are shown in table v. the analytic parameters are included in the following equations [35]: !� = ∆�k ��)(∆�k ���∆�k ��� (13) �' = '@@� ∑ !����' (14) �� = '@@� ∑ |!� |���' (15) �a = ∑ ](�k(�n) � �(' ���' (16) �p = '� ∑ !����' (17) �p = '� ∑ |!� |���' (18) �x = ∑ ](�k(��) � �(' ���' (19) e1 is the mean percentage error (mpe), e2 is the mean absolute percentage error (mape), e3 is the standard deviation percentage, e4 is the mean error, e5 is the mean absolute error, and e6 is the standard deviation. according to table v, the mape values for [13] and [30] were 18.54% and 29.15% respectively, for the homogeneous model, while for separated models, the model of [19] with 17.54% gives the least amount of mape, followed by the models of [17] with 28.53%, [9] with 28.99%, [10] with 35.14%, [16] with 41.70%, and [31] with 41.9%. it can be concluded that, out of the 8 models tested, the sun-mishima model [19] predicts the two-phase pressure drop with greater accuracy. the relative performance factor (rpf) used to identify the best model is [36]: rpf = |�n|(|�n¢k£||�n¢��|(|�n¢k£| + |��|(|��¢k£||��¢��|(|��¢k£| + |�¤|(|�¤¢k£||�¤¢��|(|�¤¢k£| +|��|(|��¢k£||��¢��|(|��¢k£| + |�w|(|�w¢k£||�w¢��|(|�w¢k£| + |�v|(|�v¢k£||�v¢��|(|�v¢k£| (20) for predicting two-phase pressure drop, the model with the least amount of rpf is the best, and the model with the most amount of rpf is the worst. in this method, [13] with 0.47 rpf value for homogeneous models and [19] with 0.76 rpf value for separated models produce the most accurate results, as displayed in table v. the third method investigates whether the data points fall within ±30% of the error band and the results are depicted in table vi and figures 4-9. the model of [13] results showed that most data points were within ±30% error band for homogeneous models. for the separated model, the models of [19] displayed the highest percentage of data with 88.9% of data within ±30% of the error band as illustrated in the figures 4-9. these results differ from previous results, but the sunmishima [19] model provides the best predictions of two-phase pressure drop models in each method. table iv. experimental operating conditions fluids temperature (c o ) gas flow rate (lpm) water flow rate (lpm) pressure (bar) data rerecording time no. of tests air-water 20 o 40, 60, 80, 100, 120, 140, 160, 180, and 200 30, 40, 50, 60, 70, and 80 0-1 30s 54 table v. error results for each model reference mpe (e1%) mape (e2%) standard deviation percentage (e3) mean error (e4) mean absolute error (e5) standard deviation (e6) rpf [30] -25.99 29.15 190.83 -0.26 0.29 1.07 2.95 [13] -5.73 18.54 42.05 -0.06 0.19 1.23 0.47 [31] 41.61 41.90 305.57 0.42 0.42 1.88 5.74 [19] 9.64 17.54 70.82 0.10 0.18 1.30 0.76 [9] -21.73 28.99 159.60 -0.22 0.29 1.45 2.78 [10] 31.08 35.14 228.26 0.31 0.35 2.36 4.57 [16] -41.21 41.70 302.64 -0.41 0.42 0.51 4.95 [17] -23.40 28.53 171.85 -0.23 0.29 1.23 2.77 e-min 5.726 17.544 42.047 0.057 0.175 0.506 e-max 41.612 41.895 305.571 0.416 0.419 2.362 table vi. data point percentage within the ±30% error band model [30] [13] [31] [19] [9] [10] [16] [17] ±30% 50 88.9 55.6 88.9 51.9 68.5 0.0 59.3 engineering, technology & applied science research vol. 12, no. 4, 2022, 9063-9070 9068 www.etasr.com ibrahim & abdulkareem: pressure drop in horizontal two-phase flow fig. 4. comparison of the experimental data with the mcadams [30] and chen et. al [13] correlations. fig. 5. comparison of the experimental data with the chisholm [31] and sun-mishima [19] correlations. fig. 6. comparison of the experimental data with the chisholm [9] correlation. fig. 7. comparison of the experimental data with the friedel correlation [10]. fig. 8. comparison of the experimental data with the grounerud correlation [16]. fig. 9. comparison of the experimental data with the muller-steinhangen and heck correlation [17]. engineering, technology & applied science research vol. 12, no. 4, 2022, 9063-9070 9069 www.etasr.com ibrahim & abdulkareem: pressure drop in horizontal two-phase flow v. conclusion the current work evaluated 8 models based on experimental data of air-water flow that were chosen to rely on baker map in a horizontal test section 6m long and with 30mm id, and with discharge flow rates for water and air ranging from 30 to 80 lpm and 40 to 80 lpm respectively. four pressure transmitters were used to measure the pressure along the test section, with a 30s ideal measurement period. the 54 experimental data points were compared to 8 well-known pressure drop models using a variety of methods. some key findings of the current study are: • mape was used to compare the experimental results to previous correlations. the sun-mishima model was found to be the best, with 17.54%, while the müller-steinhagen and heck, chisholm, friedel, and gronnerud models produce acceptable results. chisholm is the least accurate model, with 41.9% accuracy. • the results of the rpf comparison show that the outcomes were identical to the results of mape. the sun-mishima model had the highest rpf of 0.76, while the chisholm model had the lowest. • to evaluate these models, the percentage of data that falls within ±30% of the error band was used. the results of this method differ slightly from those of the previous methods, but ultimately, the sun-mishima model was again the 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[36] m. mirzania, "investigation and modelling of pressure drop for twophase flow in wells and inclined pipes," tarbiat modares university, iran, 2005. microsoft word etasr_v12_n1_pp8029-8032 engineering, technology & applied science research vol. 12, no. 1, 2022, 8029-8032 8029 www.etasr.com amouri & fawzi: the effect of different curing temperatures on the properties of geopolymer … the effect of different curing temperatures on the properties of geopolymer reinforced with micro steel fibers mohammed shaker amouri department of civil engineering university of baghdad baghdad, iraq mohammed.amori2001m@coeng.uobaghdad.edu.iq nada mahdi fawzi department of civil engineering university of baghdad baghdad, iraq nada.aljalawi@coeng.uobaghdad.edu.iq abstract-in this study, geopolymer mortar was designed in various experimental combinations employing 1% micro steel fibers and was subjected to different temperatures, according to the prior works of other researchers. the geopolymer mortar was developed using a variety of sustainable material proportions (fly ash and slag) to examine the influence of fibers on its strength. the fly ash weight percentage was 50%, 60%, and 70% by slag weight to study its effect on the geopolymer mortar's properties. the optimal ratio produced the most significant results when mixed at a 50:50 ratio of fly ash and slag with 1% micro steel fibers at curing temperature 240 o c for 4 hours through two days. the compressive strength of the geopolymer mortar increased by 11%, 11.5%, and 14% after 3, 7, and 28 days when utilizing fibers. the result shows that fly ash with a ratio of 50% by weight of slag improved the compressive strength of the mixture. it was discovered that a combination with 50% of the weight of fly ash with micro steel fibers, when treated at 240 o c for curing age of 3, 7, and 28 days, had a flexural resistance rate of 28%, 30%, 33% higher than a mixture without fibers. keywords-sustainable material; geopolymer mortar; fly ash; ground granulated blast furnace; slag i. introduction the primary binder used in concrete production is ordinary portland cement (opc). the environmental concerns surrounding the manufacturing of opc are well-known. furthermore, the amount of energy needed to manufacture only steel and aluminum is equal to that necessary to build opc [1]. cement production varies widely due to differences in the availability of raw materials [2]. sustainable materials are being developed to limit the emission of co2 from the cement industry and help recycle the industrial waste by incorporating environmentally friendly materials into civil engineering project [3]. many cement composites may be found in addition to regular concrete. various byproducts may be employed to produce blended cement classified as supplementary cementitious materials, such as ggbfs, fly ash (fa), and silica fume (sf) [4]. fa and slag waste from thermal power plants pose a severe environmental hazard if not treated and repurposed. since the fa from thermal power plants is buried, it does long-term damage to the environment by polluting the groundwater and harming the farmlands [5]. the byproduct of combustion is a fine powder. a significant amount of this garbage is produced every year, creating a substantial environmental threat. pozzolanic (siliceous and aluminous) materials may be utilized to minimize waste to some degree [6]. in 1978, the term "geopolymer" was developed to designate a group of mineral binders having a similar chemical makeup to zeolites. on the other hand, geopolymers use polycondensation of silica and alumina precursors instead of traditional portland/pozzolanic cement to form the matrix. geopolymers are mainly composed of source materials and alkaline liquids. alumino-silicate-based raw materials with high silicon (si) and aluminum (al) content should be used. byproducts like fa and sf may be added to the mix. as opposed to other alumino-silicate compounds, geopolymers are a unique creation (e.g. alumino-silicate gels, glasses, and zeolites). geopolymerization produces higher concentration of solids than alumino-silicate gels or zeolite synthesis [7]. geopolymer concrete, made from fa and slag, is an excellent alternative to conventional concrete because it is more environmentally friendly and has diverse ingredients and qualities [8]. therefore, in this paper, the effect of different proportions of fa by weight of slag with deferent curing temperatures is studied. ii. experimental setup a. fly ash the acquired fa is a fine, glassy powder produced by coal combustion throughout the generation of electrical energy at the isken-ment-turkey power station. the chemical composition of the fa used in this research is shown in table i. b. slag the slag utilized in this study complied with astm c618 [8] requirements, as shown in table ii. corresponding author: mohammed shaker amouri engineering, technology & applied science research vol. 12, no. 1, 2022, 8029-8032 8030 www.etasr.com amouri & fawzi: the effect of different curing temperatures on the properties of geopolymer … table i. fly ash chemical composition (astm c618) requirements [9] content % oxide sum of value more than 70% 5.35 fe2 o3 17.59 al2 o3 65.63 sio2 max. 5% 0.21 so3 -0.84 mgo -0.98 cao max. 6% 2.76 l.o. i -2.33 k2o -1.36 na2o table ii. ggbfs chemical composition oxide content % (astm c618) requirements [9] fe2 o3 0.35 sum of value more than 70% al2 o3 25.53 sio2 45.88 so3 4.98 max. 5% mgo 4.95 - cao 37.21 - l.o. i 3.89 max. 6% k2o 2.10 - na2o 0.96 - table iii. physical characteristics of the fine aggregates sieve size, mm cumulative percentage pass iqs (45-1984), zone 2 10 100 100 4.750 91 90-100 2.360 80 75-100 1.180 71 55-90 0.60 53 35-59 0.30 22 8-30 0.150 7 0-10 table iv. mechanical properties of micro steel fibers according to the manufacturer properties micro steel fibers tensile strength (mpa) 2600 diameter (mm) 0.2 density(kg/m 3 ) 7800 length (mm) 13 aspect ratio 65 modulus of elasticity (gpa) 250 c. sodium hydroxide commercially available naoh flakes have a 98% purity. naoh is used to make geopolymer mortar solutions. naoh is made by melting caustic soda flakes with water. based on the ratio of the soda flakes added to the water, different molar concentrations may be obtained. d. sodium silicate the concentration of na2sio3 is determined by the ratio of na2o to sio2 and h2o. the na2sio3 used in this formulation was produced in the united arab emirates. e. water distilled water was used to dissolve the caustic soda flakes to make the naoh solution. tab water was added to the geopolymer mix to improve workability. it conforms to iqs 1703 [10]. f. fine aggregates this research used natural sand from the al-ekhadir (karbala city) area as fine aggregates. it belongs to zone 2 and complies with the physical and chemical characteristics of the iraqi standard requirements iqs (no.45/1984) [11] as shown in table iii. g. micro steel fibers table iv shows the properties of the micro steel fibers utilized in this research. h. superplasticizer a high range water reducer (superplasticizer) based on modified sulfonated naphthalene formaldehyde condensate was used to improve the geopolymer mortar's workability. it confirmed to astm c494 [17]. iii. geopolymer manufacturing a. alkaline solution preparation the sodium hydroxide molar concentration was set to 12 molars when making the geopolymer mortar in this experiment. the sodium silicate-to-sodium hydroxide ratio was set at 2:1, and the solution-to-cementitious-material ratio was set at 0.45. table v shows the sodium hydroxide flakes weight. table v. amount of solid naoh for 1kg of solution at specified molarity and weight concentration [1, 12] molarity (mole/l) naoh concentration (w/w%) weight of naoh flakes (g) weight of water (g) 8 26.2 262 738 10 31.4 314 686 12 36.2 362 638 14 40.4 404 596 16 44 440 560 b. mixing the day before it was utilized, the alkaline liquid was produced and then mixed with the superplasticizer before the mixing procedure. the dry components (ggbs, fa, fibers, and sand) were first incorporated by hand for about 2 minutes before the alkaline liquid and superplasticizer were combined at a 75% concentration. after 5 minutes of mixing, the mixture was left for roughly 15 seconds before the remaining 25% of the mixed alkaline liquid was added and then it was recombined for another 5 minutes. approximately 10 to 15 minutes of mixing time were required to achieve homogeneity as shown in table vi. table vi. mix design of 1m 3 geopolymer mortar micro steel % naoh sodium silicate solution fa slag fa/slag ratio water * fine aggregates mix 112.5 225 375 375 0.5:0.5 75 1400 g1 1 112.5 225 375 375 0.5:0.5 75 1400 g2 112.5 225 300 450 0.6:0.4 75 1400 g3 1 112.5 225 300 450 0.6:0.4 75 1400 g4 112.5 225 225 525 0.7:0.3 75 1400 g5 1 112.5 225 225 525 0.7:0.3 75 1400 g6 weight in kg/m 3 engineering, technology & applied science research vol. 12, no. 1, 2022, 8029-8032 8031 www.etasr.com amouri & fawzi: the effect of different curing temperatures on the properties of geopolymer … iv. results and discussion mortar testing was carried out in accordance with astm: c109-2 [13]. since compressive strength is an essential feature of concrete mixtures or mortar, regular patterns in standard specifications are highly reliant on compressive strength at 3,7, and 28 days of curing age, with varying curing temperature. the test was performed on 50×50×50 mm cubic test samples as shown in table vii and figures1-2. table vii. compressive strength test results compressive strength result (mpa) mix curing age of testing (days) 28 7 3 240ºc 160ºc 80ºc 240ºc 160ºc 80ºc 240ºc 160ºc 80ºc 54.42 48.25 43.53 51.33 46.18 42.60 49.82 45.06 41.73 g1 62.23 53.31 48.44 57.21 51.11 46.88 55.63 50.81 45.36 g2 45.12 43.48 36.63 41.81 39.77 33.66 38.32 36.89 32.06 g3 48.31 46.87 42.86 46.43 44.27 41.88 44.51 42.64 40.04 g4 41.50 39.45 34.69 38.01 37.20 32.85 36.1 34.29 30.50 g5 44.32 43.52 41.72 43.64 40.64 39.92 41.9 38.20 36.29 g6 the increase of the proportion of the replacement of fa with ggbfs giving optimal compressive strength was at 50% fa and 50% slag (g1) with an additional 1% of fibers (g2) at 3,7, and 28 days. this conclusion is in accordance with the findings in [14]. the compressive strength of geopolymer mortars increases by increasing curing temperatures from 80 o c to 160 o c and 240 o c. that conclusion is in accordance with the findings in [15]. the results of g1, g3, and g5 show increases in compressive strength with the increasing percentage of ggbfs, compared with g1 at 240 o c and 28 days of curing as shown in figure 3. fig. 1. compressive strength of geopolymer mortar at 28 days with curing temperatures. fig. 2. geopolymer mortar cubes. fig. 3. relationship between compressive strength and ggbfs. flexural strength testing is a method of determining the way materials respond to basic beam loading. the test was carried out according to astm c 293m-16 [16]. cubic 50×50×50 mm specimens were used in this test with different curing ages (3, 7, 28 days). the result is shown in table viii. the optimal proportion mix was g1 (50% fa : 50% slag) and g2 (50% fa : 50% slag : 1%fiber). table viii. flexural strength results flexural strength result (mpa) mix curing age of testing (days) with 240ºc 28 7 3 5.7 5.3 5.12 g1 7.61 6.9 6.57 g2 fig. 4. flexural strength of geopolymer mortar at 240 o c curing temperature. table viii and figure 4 indicate that increased compressive strength leads to increased flexural strength, which is clearly shown by the experimental results of these two properties. this study found that at 3, 7, and 28 days of curing age, the flexural strength of geopolymer mortar supplemented with micro steel fibers was increased by 28%, 30%, and 33% compared with the mixture without fiber at the same temperature of 240 o c, which is the ideal dry heat curing temperature for fly ash-slag blends with a 50:50 weight ratio. however, the introduction of fibers in concrete increased the capacity to regulate fracture propagation, transforming the brittle cementitious material into a ductile composite. these results are in accordance with the findings in [18]. engineering, technology & applied science research vol. 12, no. 1, 2022, 8029-8032 8032 www.etasr.com amouri & fawzi: the effect of different curing temperatures on the properties of geopolymer … fig. 5. geopolymer prisms during curing. v. conclusion the main conclusions according to the results of the current study on geopolymer mortar are: • geopolymer is an ecologically acceptable substitute for opc in structural applications. • fa and slag-based geopolymer mortar are preferable to conventional concrete because of their sustainable ingredients and improved characteristics. • best geopolymer mortar qualities may be achieved by adding 1% by volume micro steel fibers to the mixture. • the additional micro steel fibers in geopolymer mortar increase strength by 10%, improving bond strength. • the optimum strength of geopolymer mortar was acquired with proportions of 50% of fa: 50% of ggbfs with 1% of micro steel fibers (mix g2). • the addition of ggbfs to geopolymer concrete as an alternative to fa improved compressive strength in mixtures g2, g4, and g6 with ratios of 11%, 8.5%, and 5% respectively, with 240 o c curing temperature at 28 days. • geopolymer mortar can develop high early strength by using high curing temperatures. • by increasing temperatures of curing age from 80 o c to 240 o c, the compressive strength increased by about 25% without fibers and 28.5% with micro steel fibers (at 28 days). • the flexural strength increased by 28%, 30%, and 33% by additional micro steel fiber for 3, 7, 28 days of curing respectively. references [1] d. hardjito and b. rangan, "development and properties of lowcalcium fly ash based geopolymer concrete," curtin university of technology, perth, australia, research report gc 1, 2005. [2] m. s. imbabi, c. carrigan, and s. mckenna, "trends and developments in green cement and concrete technology," international journal of sustainable built environment, vol. 1, no. 2, pp. 194–216, dec. 2012, https://doi.org/10.1016/j.ijsbe.2013.05.001. [3] z. f. muhsin and n. m. fawzi, "effect of fly ash on some properties of reactive powder concrete," journal of engineering, vol. 27, no. 11, pp. 32–46, nov. 2021, https://doi.org/10.31026/j.eng.2021.11.03. [4] a. sicakova, e. kardosova, and m. spak, "perlite application and performance comparison to conventional additives in blended cement," engineering, technology & applied science research, vol. 10, no. 3, pp. 5613–5618, jun. 2020, https://doi.org/10.48084/etasr.3487. [5] v. t. phan and t. h. nguyen, "the influence of fly ash on the compressive strength of recycled concrete utilizing coarse aggregates from demolition works," engineering, technology & applied science research, vol. 11, no. 3, pp. 7107–7110, jun. 2021, https://doi.org/10.48084/etasr.4145. [6] s. a. chandio, b. a. memon, m. oad, f. a. chandio, and m. u. memon, "effect of fly ash on the compressive strength of green concrete," engineering, technology & applied science research, vol. 10, no. 3, pp. 5728–5731, jun. 2020, https://doi.org/10.48084/etasr.3499. [7] j. l. provis and j. s. j. van deventer, eds., geopolymers: structures, processing, properties and industrial applications, 1st ed. oxford : boca raton, fl, usa: woodhead publishing, 2009. [8] s. s. hussein and n. m. fawzi, "influence of using various percentages of slag on mechanical properties of fly ash-based geopolymer concrete," journal of engineering, vol. 27, no. 10, pp. 50–67, oct. 2021, https://doi.org/10.31026/j.eng.2021.10.04. [9] astm c618-19: standard specification for coal fly ash and raw or calcined natural pozzolan for use in concrete. astm international, 2019. [10] iraqi standard specification no 1703: water used in concrete. baghdad, iraq, 2000. [11] iraqi standard specification no 45, "aggregates from natural sources for concrete and building construction. baghdad, iraq, 1984. [12] b. rangan, "fly ash-based geopolymer concrete," in proceedings of the international workshop on geopolymer cement and concrete, dec. 2010, pp. 68–106. [13] astm c109/c109m-20: standard test method for compressive strength of hydraulic cement mortars (using 2-in. or [50-mm] cube specimens). astm international, 2020. [14] m. albitar, m. s. mohamed ali, p. visintin, and m. drechsler, "effect of granulated lead smelter slag on strength of fly ash-based geopolymer concrete," construction and building materials, vol. 83, pp. 128–135, may 2015, https://doi.org/10.1016/j.conbuildmat.2015.03.009. [15] a. a. adam and x. x. x. horianto, "the effect of temperature and duration of curing on the strength of fly ash based geopolymer mortar," procedia engineering, vol. 95, pp. 410–414, jan. 2014, https://doi.org/10.1016/j.proeng.2014.12.199. [16] astm c293/c293m-16: standard test method for flexural strength of concrete (using simple beam with center-point loading). astm international, 2016. [17] astm c 494/c 494m – 05a: standard specification for chemical admixtures for concrete. astm international, 2005. [18] p. zhang, j. wang, q. li, j. wan, and y. ling, "mechanical and fracture properties of steel fiber-reinforced geopolymer concrete," science and engineering of composite materials, vol. 28, no. 1, pp. 299–313, jan. 2021, https://doi.org/10.1515/secm-2021-0030. microsoft word etasr_v12_n2_pp8458-8462 engineering, technology & applied science research vol. 12, no. 2, 2022, 8458-8462 8458 www.etasr.com hang et al.: stochastic buckling analysis of non-uniform columns using stochastic finite elements … stochastic buckling analysis of non-uniform columns using stochastic finite elements with discretization random field by the point method do thi hang university of transport and communications hanoi, vietnam hangdo@utc.edu.vn nguyen xuan tung university of transport and communications hanoi, vietnam ngxuantung@utc.edu.vn dao ngoc tien hanoi architectural university hanoi, vietnam tiendn@hau.edu.vn received: 9 february 2022 | revised: 9 march 2022 | accepted: 10 march 2022 abstract-this study examined the discretization random field of the elastic modulus by a point method to develop a stochastic finite element method for the stochastic buckling of a nonuniform column. the formulation of stochastic analysis of a nonuniform column was constructed using the perturbation method in conjunction with the finite element method. the spectral representation was used to generate a random field to employ the monte carlo simulation for validation with a stochastic finite element approach. the results of the stochastic buckling problem of non-uniform columns with the random field of elastic modulus by comparing the first-order perturbation technique were in good agreement with those obtained from the monte carlo simulation. the numerical results showed that the response of the coefficient of variation of critical loads increased when the ratio of the correlation distance of the random field increased. keywords-non-uniform column; buckling; stochastic fem; spectral representation; random field i. introduction science and technology revolution has produced many high-strength and lightweight materials used in a variety of slender structures such as steel structures [1-7] and functionally graded beams [8]. the problem of stability calculation of these structures is very important, e.g. in a steel truss bridge with many slender compression members. in many cases, column or tower structures are designed with variable cross-sections to match the bearing characteristics of the structure and save materials. many studies have examined the stability of bars with variable cross-section and many basic problems on the stability of bars with variable cross-section were presented in [9-12]. in addition, many researchers studied the stability of the replacement with a changing cross-section with different forms, calculated by different methods. in [13], a polynomial series approximation was used to solve the problem of column stability with variable cross-sections subjected to axial forces. in [14], the column was calculated with a cross-sectional variation of the ladder using the rayleigh-ritz method. in [15], the stability of a column of the variable cross-section with elastic connections was calculated by approximating the stability differential equation. in [9], the stability of reinforced concrete columns with elastic connections was studied. an exact solution for some types of columns with variable crosssections with elastic connections under distributed axial forces was presented in [16]. in addition to analytical methods with exact solutions, some studies used finite element methods. in [17], the stability of a bar with variable cross-section was studied using the galerkin finite element method. in [18], the stability calculation of columns with stepped and cracked cross-sections was studied using the finite element method. in [19], a finite element model of circular concrete-filled steel circular-tube columns was studied under axial compression loading. however, these studies were limited to deterministic problems. in most practical engineering, structure analysis ignores the random heterogeneity of materials. for the advanced analysis of structures, a probabilistic model is needed to consider random variables, random fields of geometry, and material properties of structures. several methods for random field discretization were developed for stochastic finite element methods, such as the integration point method [20, 21], the nodal point method [22, 23], and the local averaging method [24]. in [25], a stochastic finite element method was presented using the weighted integration approach to analyze the static behavior of non-uniform columns. in [26], a semi-analytical method was applied to investigate the buckling of composite beam-columns with random elastic stiffness and geometric properties. in [27], the free vibration of functionally graded beams was examined using a stochastic perturbation-based corresponding author: nguyen xuan tung engineering, technology & applied science research vol. 12, no. 2, 2022, 8458-8462 8459 www.etasr.com hang et al.: stochastic buckling analysis of non-uniform columns using stochastic finite elements … finite element method. the random finite element method was improved for the seismic analysis of gravity dams in [28]. in [29, 30], a probabilistic problem was developed for the seismic analysis of cabinet facilities in nuclear power plants and soil properties. in this study, a stochastic finite element model was built for the buckling of the non-uniform column with the random field of elastic modulus. ii. the finite element model of the non-uniform column consider a non-uniform column with the coordinate system (x, z) as shown in figure 1: fig. 1. model of non-uniform columns the column element is assumed to have two degrees of freedom, one rotation and one translation, at each end. the location and positive directions of these displacements in a typical linearly tapered column element are shown in figure 2, where le is the length of the element, e and i are the area and inertia moment of the cross-section column. the depths of the cross-sections at the smaller and larger end of the column are denoted as h2 and h1, respectively. the longitudinal axis of the element lies along the x-axis. the element was assumed to have two degrees of freedom at each end: a transverse deflection u1, u3, and an angle of rotation of slope u2, u4. fig. 2. model of a non-uniform finite element. the displacement field is approximated by the shape function as: �� = ��� �� �� � � ������� = �� ���� (1) where � = ��� �� �� � �, and �� is the shape function of the i-th degree of freedom, and the hermite polynomial functions [31] are: �� = 1 − 3 � ���� + 2 � ���� �� = � �1 − 2 ��� + � ���� � �� = 3 � ���� − 2 � ���� � = � �− ��� + ����� � (2) the deformation potential of the column is: �� = �� � !"�# $%�&�% �� '� (���) (3) the potential energy of load is: *� = − +� � $%&�%� '� (���) (4) the cross-section moment of inertia in the element is approximated by linear interpolation: "�#!�"�# = "�#!�� $1 − ���' + "�#!�� ��� (1) the random field of elastic modulus is assumed as: "�# = )�1 + ,"�# (2) where e0, r(z) are the mean elastic modulus and a onedimensional gaussian random field with a mean equal to zero respectively. the form of the autocorrelation function of random field r(x) is: -".# = � � ,"�#,"� + .#/�"�, � + ., .#(,"�#(,"� + .#∞1∞∞1∞ (7) the random field elastic modulus requires discretization to random variables for the governing equation of buckling problem by finite element formulation. fig. 3. average model for approximating random field of elastic modulus. ei0 h 0 h1 h p l z u 1 u 2 u 3 u 4 h1 h2 w e (e) ei1 ei2 ei e1 e2 e3 en e ei e(z) e1 e2 e3 en engineering, technology & applied science research vol. 12, no. 2, 2022, 8458-8462 8460 www.etasr.com hang et al.: stochastic buckling analysis of non-uniform columns using stochastic finite elements … by averaging random variables within the element as illustrated in figure 3, the random field of the elastic modulus in the element is calculated as: ,̄ = 34 53� 5⋯5378 = ) 91 + 3453� 5⋯5378 : (8) taking the variation with respect to q, the resulting equation [32] is obtained for the buckling of the column: ;�< − =�< >?��� = 0 (9) [k] and [m] denote the assembled and global stiffness respectively of the cross-section column and λi denotes the critical load. the stiffness matrix [k]e is defined as: �< � = ) 91 + 3453�5⋯5378 : × × bc cc cc de"f4� 5f�� #��� f4� 5�f����� − e"f4� 5f�� #��� �f4� 5 f������f4� 5f���� − f4� 5�f����� f4� 5f����e"f4�5f�� #��� − �f4� 5 f�����ghi. f4� 5�f���� kl ll ll m (10) the geometric stiffness matrix is defined as: �< >� = n bc cc cc d eo�� ��) − eo�� ��)��o�� − ��) − ��)��eo�� − ��)sym ��o�� kl ll ll m (3) iii. formulation of the stochastic finite element method using the perturbation technique for the buckling of the column the governing equation of the buckling problem in (9) includes random variables and can be perturbed concerning the mean of the random variables as follows: s �< ) + ∑ u�v u3w ,�x3�y� −$=) + ∑ uzu3w ,�x3�y� ' �< > [ \�) + ∑ u]u3w ,�x3�y� ^ = 0 (12) solving the stochastic equation (12), the zeroth-order and the first-order solutions can be obtained as: zeroth-order: ;�< ) − =)�< > ?��)� = 0 (4) and first-order: ;�< ) − =) �< > ? \ u]u3w^ = − $u�v u3w − uzu3w �< > ' ��)� (14) premultiplication of (14) by \�) + ∑ u]u3w ,�x3�y� ^_gives: \�) + ∑ u]u3w ,�x3�y� ^_ × × \�< ) + ∑ u�v u3w ,�x3�y� − $=) + ∑ uzu3w ,�x3�y� ' �< >^ × \�) + ∑ u]u3w ,�x3�y� ^ = 0 (15) solving (15) using the orthonormal property, the first-order partial derivatives of critical load respect random variable is given by: uzu3w ≈ �]a �wb c�d cew �]a��]a�wb�f �]a� (16) the mean of the critical load given solved by the first-order perturbation solutions is: μz = � \$=) + ∑ hzh3w ,�x3�y� ' − =)^ i",� #(,�j1j = =) (17) the variance of the critical load is solved by the first-order perturbation solution as follows: *k,z = � � \$=) + ∑ uzu3w ,�x3�y� ' − =)^ ×l× �=) + ∑ uzu3m ,nx3ny� � − =)o ×× /�;,�, ,n , ,n − ,� ?(,� (,n ∞1∞∞1∞ = ∑ ∑ \ uzu3w uzu3w -".#^x3ny�x3�y� (18) where r(τ) denotes the autocorrelation function of the random field, and the relative distance vector is defined as τ=rj-ri. the autocorrelation function was assumed in the form: -".# = q� rsi $− t�%�' (19) where σ, d are the coefficient of variation (cov) and the correlation distance of the random field of elastic modulus respectively. the response variability can be represented using the cov defined as: uv* = wxy3z||z| (20) iv. examples a. validation of the finite element approach for deterministic analysis the buckling non-uniform column in figure 1 was considered to validate the proposed finite element for the nonuniform column with the moment of inertia as a formulation: !"�# = }fa� \√2 − �� ;√2 − 1?^� (21) the analytical solutions of the column were given by [9] with a critical load factor m=2.023: n�3 = 2.023 }fa� � (22) where the critical load factor m is given by: i = +�e� �}fa (5) engineering, technology & applied science research vol. 12, no. 2, 2022, 8458-8462 8461 www.etasr.com hang et al.: stochastic buckling analysis of non-uniform columns using stochastic finite elements … fig. 4. comparison of critical load factor between analytical and finite element method. fig. 5. error depending on mesh refinement. as shown in figure 4, the finite element agreed with the analytical solution if a reasonable number of finite elements was used in the model (approximately more than 10 finite elements). the convergence features of the proposed finite element are shown in figure 5. the discrepancies between the analytical and finite element solutions of the critical load factor tend rapidly to zero as the mesh is refined. b. response variability of critical load due to the randomness of elastic modulus a scheme of monte carlo simulation (mcs) was employed to validate the response variability of critical loads of the nonuniform columns. mcs repeats the deterministic analysis on a set of samples of the random field of the elastic modulus. using the spectral representation proposed in [33], the numerical generation of the homogeneous univariate random field r(z), with zero mean in one dimension, can be generated via the summation formula of cosine functions as follows: ,"�# = √2 ∑ �� ���"�� � � �� #x1��y) �� � w2g33 "���#�� �� � �] � , �� � ���, � � 0,1,2, . . . , � � 1 (24) where, �], g33 are the upper cut-off frequency and the power spectral density functio, respectively. the stochastic buckling of linearly tapered cantilever columns with a concrete rectangular cross-section was considered, as shown in figure 6. the mean modulus of elasticity of the column was assumed to be 33.10 3 mpa. the geometric dimensions of the example cross-section columns were: h0 =1m, h1 =0.5 m, h=12m, and b=0.6m. fig. 6. linearly tapered cantilever columns with a concrete rectangular cross-section. fig. 7. effects of the correlation distance d on the different standard deviation σ of the critical load. figure 7 shows the comparison of the effect of the correlation distance d of the random field on the variability of the critical load of the proposed formulation with the mcs, for the same cases of the stochastic finite element method. the results of the mcs with 10,000 samples, presented by the dashed-dotted line, denote the corresponding cov of the random field of elastic modulus 0.1 and 0.2. as shown in figure 6, the response variability of a critical load is converging to cov of the random field of the elastic modulus, as the correlation distance tends to move to infinity in both analysis schemes. as can be observed, the increasing rate of the correlation distances is accelerated with an increase in the coefficient of variation of the random field. v. conclusion the paper presented a perturbation technique in conjugation with finite element analysis that was successfully developed for the stochastic buckling problem of non-uniform columns with a random field of elastic modulus. mcs was performed employing 10,000 random samples to simulate the validity of the proposed first-order perturbation solution of the stochastic finite element method. the efficacy of the first-order b h cross-section p h 0 h 1 h engineering, technology & applied science research vol. 12, no. 2, 2022, 8458-8462 8462 www.etasr.com hang et al.: stochastic buckling analysis of non-uniform columns using stochastic finite elements … perturbation method was verified using a homogeneous gaussian random field by the stochastic finite element method and was in perfect agreement with the mcs, where the correlation distance was as high as 5. the effect of the correlation distance on the response cov of a critical load was obvious, and the response cov increased when correlation distances increased. acknowledgment this research is funded by the 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[32] t. j. r. hughes, the finite element method: linear static and dynamic finite element analysis. new york, ny, usa: dover publications, 2012. [33] m. shinozuka and g. deodatis, "simulation of stochastic processes by spectral representation," applied mechanics reviews, vol. 44, no. 4, pp. 191–204, apr. 1991, https://doi.org/10.1115/1.3119501. microsoft word etasr_v12_n6_pp9697-9702 engineering, technology & applied science research vol. 12, no. 6, 2022, 9697-9702 9697 www.etasr.com benaouda & benaouda: an original approach for translating grafcet into c/unix code for validation … an original approach for translating grafcet into c/unix code for validation purposes nacera benaouda department of computer science ferhat abbas university setif i setif, algeria nacbenaouda@univ-setif.dz abdelhafid benaouda department of computer science ferhat abbas university setif i setif, algeria ahbenaouda@univ-setif.dz received: 19 september 2022 | revised: 3 october 2022 | accepted: 6 october 2022 abstract-this paper proposes an approach to simulate the function of the control part of a grafcet model, translating it into c code in a unix environment. first, the grafcet/c generation schemes are established. the grafcet model, described in graphic or text form, is transformed in an internal form and then to c code by a generation algorithm based on the previously found diagrams. the result is a program that simulates the operation of the automation in question and makes it possible to validate the functional specifications of sequential automation. this validation can be used for educational purposes, such as the learning of the grafcet formalism, or corrective or evolutionary maintenance. once the configuration, testing, and validation of the program are complete, it is possible to implement the object code on the microcontroller of the control system. keywords-c/unix; grafcet; process; sequential automation i. introduction equipment manufacturers and automation engineers responsible for automated industrial installations should master the programs that drive their installations to perform preventive [1, 2], corrective, adaptive, and evolutionary maintenance tasks [3]. these programs are often outsourced, use a variety of libraries, and depend not only on the problem to be solved but also on the past of their provider. grafcet [4, 5] is a graphic formalism for describing automatisms, accepted by mechanical automation engineers who consider it to represent the right level of specification without much complexity. in an automated system, the control part is the image of the operative part that represents the automated machine. simulation and validation of the operation of an automated system are necessary before its implementation in the actual installation. simulating the operation of grafcet is equivalent to translating it into appropriate languages, which generate programs with the same semantics. these programs have shown their usefulness for maintenance or educational purposes. this study chose c/unix as the target language and system for the grafcet translation. this choice was motivated by two reasons; the c language extended by the unix libraries has all the necessary tools for the translation of grafcet, and the required hardware and software configuration for the application is very simple, just a personal computer with a linux distribution. ii. related work several studies achieved to formalize grafcet. in [6], grafcet translation schemes were designed in the occam2 language, which is executable on transputers, exploiting the possibilities of expressions of parallel tasks offered in occam2 to express the respective representation in grafcet. the resulting program could run on a parallel machine and simulate the actual operation of an automated system. this work could obtain the equivalent occam2 program from a grafcet in graphical or textual form. being a parallel language, occam2 possesses the necessary tools to translate grafcet, but the resulting program can only be exploited if a parallel machine existed. since parallel machines are only available in certain research laboratories or specific industrial settings, such a program may have limited use. in [7], a semi-coarse ontology was defined and tested by integrating it into an existing educational tool to teach grafcet for use in programmable logic controllers. this ontology was owl (web ontology language) dl based, a specific decidable fragment of firstorder logic applied to owl markup language. the objective of this method was to complement previous studies and promote this type of technique in the formalization of grafcet. the advantages of ontologies are numerous, as they make collaboration and sharing of knowledge easier, provide better reliability, and assure to handle automatically any input change without having to recompile the processing code. this approach was validated according to two criteria, accuracy and completeness. a new vision was adopted in [8], by proposing a systematic implementation of the control software in iec 61499. this constituted a key advantage over previous grafcet implementations because it allowed engineers to implement models distributed over several devices and also kept the initial centralized design. iec 61499 has all the translation tools for most of the grafcet elements. this work made it possible to systematically translate grafcet and introduced several translation models. the disadvantages of this method lied in the fact that it was not possible to model the structuring mechanisms such as fences or forcing steps, and the macrossteps that could be implemented were limited to simple sequences. corresponding author: nacera benaouda engineering, technology & applied science research vol. 12, no. 6, 2022, 9697-9702 9698 www.etasr.com benaouda & benaouda: an original approach for translating grafcet into c/unix code for validation … iii. motivation for choosing c language grafcet is a logical automatism description formalism that allows expressing competing processes. a language to translate grafcet has to preferably be parallel [6] and/or real-time. the duration of the task's installation or its switching time is decisive in choosing such a language. c and unix [9] were chosen due to their portability, universality, and control by most computer scientists. its disadvantage lies in the fact that unix is not quite real-time, because its slow temporal primitives were defined according to the only problems of the timeshare. c language is a high-level machine-oriented language (hlmol) that allows defining bit-close fields, and expanded by unix libraries can provide the illusion of simultaneous execution of tasks on uniprocessor machines, as shown by functions such as fork, wait, sleep, kill [9]. pipes are the main means of communication between unix processes [9]. several synchronization means are available in unix. this study used the wait function, which is the most basic mean of synchronization and can be used to synchronize a parent process on the termination of its children. time management was carried out using the sleep() function, as the call to the sleep(n) function suspends the calling process for n seconds. since the seconds are not useful for many real-time scenarios, the macro tempo() was used to allow timers in microseconds: #define tempo(n){ clock_t reveil = clock()+n; while(clock()<reveil) sleep(0); }/*n in microseconds */ so, sleep(1) is equivalent to tempo(1000000). these timers were used in processes running in parallel and can limit the waiting time for certain events. iv. simulation system description two subsystems constitute the simulation system [10]:  grafcet entry: this subsystem offers two possibilities: o graphical input: based on a graphical editor, allows any grafcet to be entered graphically and outputs its image data structure. o text entry: rarely used in practice, except for maintenance purposes. it allows to enter the grafcet as text, so requires a text analyzer that outputs the same data structure as the graphical editor.  translation of the grafcet: this subsystem exploits the data structure from the entry and translates it into c. two steps are possible: o interpreter/simulator: a program that executes step-bystep the appropriate c sequences according to the data structure. o generator: a program that creates a complete c code of all the grafcet. executing this code is the simulation of the automatism described by the grafcet, as long as this code is not configured according to real i/o. in both cases, translation requires defining the grafcet/c generation schemes. v. grafcet/c translation schemes the definition of the translation schemes from grafcet to c consists of finding for each grafcet basic element a program scheme in c which has the same semantics. the elements of grafcet are: simple transition, divergences (and, or), convergences (and, or), the stage, and the macro stage [10]. a. preliminary study [10] let's consider the following scenario:  a rotating bar at a position x, y of the screen successive display in x, y of characters -, /, |, \, -, /, …)  in case of no overflows, pressing the arrow keys causes the bar to move down, left, right, and up respectively.  if limits are exceeded, the above characters produce an audible signal, and the bar keeps rotating in the same place.  pressing the character "q" stops the scenario.  pressing any other character is ineffective. figure 1 shows the grafcet of the above scenario. fig. 1. grafcet associated with the rotating bar scenario. let eb and tb be the stages and transitions of the rotating bar branch, and el and tl be the stages and transitions of the reading characters branch. stages e0: initial stage, beginning of the program. eb1: rotating bar. eb2: end of the rotating bar process. eb3: test of the character read in the pipe. eb4: audible alarm. eb5: moving the bar. eb6: rest (sleep). el1: read and test the read character. el2: sending a kill and exit. el3: write ↓, ←, →, ↑ in the pipe. el4: rest (sleep). s: end of the scenario. transitions t1: pressing any key to start both processes. tb1: reception of a kill signal. tb2: read ↓, ←, →, ↑ in the pipe. tb4: overcoming limits. tb5: no overflows. tb6: = 1; tb7 = 1 tl2: read ↓, ←, → or ↑ from the keyboard. tl3: reading of the 'q' character of the keyboard. tl4 = 1; tl5 = 1; tlf = 1. engineering, technology & applied science research vol. 12, no. 6, 2022, 9697-9702 9699 www.etasr.com benaouda & benaouda: an original approach for translating grafcet into c/unix code for validation … b. principles of the image program once the program is launched, two processes are created and launched simultaneously (proc1, proc2). proc1 is a standalone process associated with the rotating bar, while proc2 is associated with its movement and is under external influence. at some point, the two processes must act simultaneously on the coordinates x, y of the bar. a first solution is to create a critical section within each process to achieve mutual exclusion of both accesses [8]. a second solution would be to allow effective access to a single process, such as proc1, which will rotate and move the bar, proc2 reads the arrow characters, considered as the move commands of the bar, and sends them through a pipe to proc1 to use them to move the bar in the desired direction. the end of the scenario will take place when proc2 reads the "q" key. table i shows the general processing algorithms of proc1 and proc2. this program, modeled in grafcet, is the basis to deduce the basic translation schemes from grafcet into c. these schemes were extended for industrial processes where the system entries can be numerous, simultaneous, and real-time. therefore, push buttons and sensors were integrated. table i. parallel running of proc1 and proc2 proc1 proc2 at each position of the bar: display the bar look in p[0] if a character is placed in the pipe. if yes the character is stored in cc1 and tested. if exceeding the limits, warning sound, otherwise move in the desired direction. rotation of the bar. reads a cc character from the keyboard and test it. if cc ='q' then sends a sigkill to proc1 then exit. if cc ="↓", "←", "→" or "↑" then places cc in the inlet p[1] of the pipe; if cc is other, ignore cc. c. grafcet-c translation schemes a simple transition is an external event that can arise at any time from a sensor, button, etc. three cases exist to simulate it: keyboard, order box, and always concurrent. keyboard input can be given as a simple scheme: cc=getch() in case of an order box, let boitcom be the port address of the command box, reading 8 to 16 digital inputs. by assimilating all the bits to zero in the absence of an entry, the scheme could be the following: while(!(*boitcom)) sleep(0); these diagrams are taken up and developed when a configuration language would cover the essential cases concerning the real-time management of arbitrary devices, which will be part of a realistic simulation. meanwhile, the input from the control box can be simulated by programming the keys of the keyboard, associating a sequence of bits: for i=1,…,7, command[0],…, command[7], command[i]=1 when the receptivity i is true, and command[i]=0 when no receptivity is true. in an always occurrent case, t=1, which means that the sum of the internal and external receptivity conditions is 1. in this case, a comment is generated (/* t=1 */). 1) divergences  and divergence: while(!t) sleep(0); rep=forkn(tab_fonc,nproc,tab_pid); rep1=wait(&status); while((rep1 !=-1) wait(&status); where tab_fonc is an array of pointers to functions performed in the context of each process, nproc is the number of the created processes, tab_pid is the pid chard of the created processes, and tab_fonc[i] is the pointer to the function executed by the process with the pid_tab_pid[i]. forkn() details can be found in [9].  or divergence: the exclusive or divergence is given by: while(!t1&&!t2&&!t3... &&!tn)sleep(0); switch(transition){ case t1 : p1(); case t2 : p2(); . . . case tn : pn(); } where pi() is the procedure executed for the transition ti and there is no priming of new paths. inclusive or is given by: while(!t1&& !t2&&... && !tn) sleep(0); if(t1) p1(); if(t2) p2(); … if(tn) pn(); /* the creative process enters the zombie state */ rep1=wait(&status); while (rep1 !=-1) wait(&status); where pi() is the process creation procedure i. there is a boot of new paths. two images are likely in the classical case of an input form: a general but expensive image (competition diagram), or an effective image applicable under certain conditions. in the case of an effective image, the alternative scheme is applicable if and only if the transitions are disjoined two by two. the evaluation of this question in a generator is the subject of a decision procedure, which in case of difficulties may substitute, the absolute criterion above, one or more sufficient conditions easier to evaluate. for example, if two transitions occur as products of elementary conditions, they are disjoint if the same condition is present in the two transitions in opposite forms, such that: t1 = x y z and t2 = x y z. in the case of expectations with time-out, there is divergence with two issues, one of which carries the receptivity "event" and the other a receptivity "time limit". since this can only be performed in excess, it is normal to consider the two as disjoint (in case of conjunction, the event is considered to have happened after the prescribed duration). the quality of the decision procedure thus directly governs the quality of the code, which may be inaccurate, correct but heavy, correct and effective, and even optimal for a perfect decision procedure. on the other hand, the generation with divergences must agree with the generation with convergences. engineering, technology & applied science research vol. 12, no. 6, 2022, 9697-9702 9700 www.etasr.com benaouda & benaouda: an original approach for translating grafcet into c/unix code for validation … 2) convergences  and convergence: two cases arise: if pi has the same divergence as the origin, the synchronization is performed by wait(), while if they don't have the same origin, synchronization is mandatory. for each father process, synchro is a global variable. initially, synchro is the number of incoming branches. once it finishes, each process simulating an incoming branch must access synchro and decrement it. when synchro becomes null, it implies the end of all branches. as the access to synchro may be simultaneous, it must therefore be a critical section within each process, using either semaphores or locks [11]. this study used a method of choosing a process, called the coordinator, and took the one that simulates the most left incoming branch. when it finishes, the coordinator performs the following algorithm. /* scheme associated with coordinator*/ /*only the coordinator accesses synchro*/ int rep ; char cc ; ... /* as soon as it finishes, it decrements synchro */ synchro-; while(1){ cc = ' '; dup(tube1[1]); close(tube1[1]); read(tube1[0],cc,1); if (cc=='f') synchro--; ... cc=' '; dup(tuben[1]); close(tuben[1]); read(tuben[0],cc,1); if (cc=='f') synchro--; }/* finwhile */ /* synchro=0, le process p0 kills all the other processes and makes an exit */ rep=kill(pid1, sigkill); rep=kill(pid2, sigkill); ... rep=kill(pidn, sigkill); exit(); once it finishes, each other process associated with other branches should perform the following algorithm: /* let's suppose the process number i, other than the coordinator, sends the character 'f' in the pipe */ dup(tubei[0]); close(tubei[0]); write(tubei[1],'f',1); /* infinite loop as wait */ for( ; ;) sleep(0);  or convergence: exclusive or comes down to the simple transition, while inclusive or is discussed in the same way as the and convergence. 3) the stages it executes within a process, and can be simulated by a message specifying it, possibly a time-dependent timer associated with it, encapsulated in an enn() procedure: void enn() printf("etape %d",num_etape); tempo(duree) ; 4) the macro stage the macro stage is translated using a procedure that is an image similar to the main program because it is a sub-grafcet and militates a recursive generation. 5) forcing the diagrams can be implemented in the case where the automatism is modeled by a single grafcet, which is a single connected component. they can be extended by adding the associated macros in the case of forcing or applied in the case of a hierarchy of grafcets. the forcing function is an action of macro stage m. this is then called macroaction, and is a procedure using another grafcet (slave). the functions associated with forcing operations are summarized below:  freezing: this operation consists of sending the signal sigstop to the active stages of the given grafcet. void suspendre(g){ int i, rep ; i=1 ; while (i<= nbactif){ rep=kill((pid[i],sigstop); i++ ; } //nbactif = number of active stages //pid : table of active pid  disabling the slave grafcet: this operation is associated with a deactivate() procedure which consists of sending a sigkill signal to the active processes in the slave grafcet given by g.  put in initial situation: this procedure consists of calling a subroutine that is analogous to the main program. this is similar to using the macro stage in the case of the normal operation of automation.  put in any situation: two cases may arise, reactivate a previously suspended grafcet, which would consist of sending the sigcont signal to the suspended process, or activate certain stages of the grafcet in question where it would be necessary to put to true their input receptivities and launch the functions associated with them. vi. necessary configuration for the system the implementation of this system requires:  a unix or linux or any multitasking system.  a graphic screen for entering the grafcet.  a keyboard as input device and, if possible, a box of commands.  effectors: leds, bulbs, effectors. the screen is divided into two windows. the first window (fen1) is used to draw the currently active grafcet (command part), while the second (fen2) is specific to the messages that illustrate the actions carried out by the operative part. initially, engineering, technology & applied science research vol. 12, no. 6, 2022, 9697-9702 9701 www.etasr.com benaouda & benaouda: an original approach for translating grafcet into c/unix code for validation … the grafcet is animated from the initial situation. the arrival of the transitions from the keyboard or the control box causes the evolution of the grafcet, i.e. activation of the new stage or stages (following the transition), and deactivation of the stage or stages. active stages will be highlighted in fen1, showing their associated messages in fen2. the command box allows making several entries at once, a case that can be tested for or divergences and transitions whose branches run in parallel. figure 2 shows a grafcet and the corresponding c program. fig. 2. from grafcet to c code. vii. application figures 3 and 4 show two industrial grafcet examples that were used to validate the proposed method. the principle of validation of a grafcet has two phases: static validation, respecting the conditions of good form, and dynamic validation of the execution. a. grafcet good form conditions a grafcet is:  except: if for any situation accessible from e0, no step is reactivated.  living: if for any accessible situation from e0, a crossing sequence of any transition exists.  clean: if for any situation accessible for e0, there is a crossing sequence leading to e0. b. importance of the preceding properties for the grafcet evolution if the grafcet is safe, no step is reactivated during its possible evolutions. reactivation is dangerous and can lead to errors. a living grafcet will never block and will never find inert steps or transitions (unactivated steps, unsensitized transitions) at a certain stage of the evolution. if a grafcet is clean, this implies possible re-initiation. this is a very important phenomenon for automation, as the initial step is considered a resting stage. the proposed method assumes:  transitions from the keyboard or the control box are always occurring (= 1), simulating well external or internal events.  simple steps: the considered grafcet can easily be assimilated to the complete grafcet that takes into account any type of transition or step. this method is effective for grafcet validation. the grafcet shown in figure 3 is not safe because there is a reactivation of step 2, in the case of crossing transition 5. the proposed method indicates it by a message and rejects it when meeting again step 2 within the normal operating cycle. fig. 3. industrial grafcet example1. fig. 4. industrial grafcet example2. in figure 4, transitions 2 and 3, are or divergences. if they occur together, the or of this divergence is inclusive and the grafcet is clean, alive, and safe. if they do not occur together, the or is exclusive, and one branch will be executed, but arriving at the and convergence, transition 5 can be crossed only if steps 4 and 5 are both active and the transition is equal engineering, technology & applied science research vol. 12, no. 6, 2022, 9697-9702 9702 www.etasr.com benaouda & benaouda: an original approach for translating grafcet into c/unix code for validation … to 1, which is not the case if the or is exclusive. the proposed program reports a blockage in this case. c. compatibility of simultaneous actions and correlation of stages and receptivity a subsystem displaying the steps and associated actions would allow the user to know if the steps that have run simultaneously correspond to compatible actions, after observing the execution of the grafcet. for example, two pumps, one operating while the other is at rest, should never appear together in two simultaneous actions in a grafcet. similarly, the action-receptivity correlation can be checked by consulting the transitions and the associated receptivity conditions (the symbol table contains all the information relating to the steps and transitions). d. search of cycles in principle, a cycle exists, outside the normal operating cycle, if there is a reactivation of at least one previous step. the proposed algorithm, as designed, rejects the grafcet as soon as a previously activated stage is reactivated. a cycle within the normal cycle of operation can have dangerous consequences. viii. conclusion the proposed algorithm allows to translate a large number of grafcets by compositions of the most elementary elements. on a practical level, this study created a grafcet library of translation diagrams. this library was tested on several examples, is independent of the assumed internal form, takes into account the automatisms described by a single grafcet, and can be extended to explicit macros and procedures relating to forcing processing used in the case of a grafcets hierarchy. a program was developed that requires to start from a graphic editor or specialized analyzers to enter the grafcet in an internal form to produce a c code whose execution will behave according to the entered grafcet. automatic production of the c code is based on the elementary translation schemes described. as a second step, after the test, validation, and configuration of the algorithm and the program, the object code can be implemented on the microcontroller of the actual control system, in particular explaining everything related to the execution configuration. the advantage of the proposed algorithm is that it can be widely used because it requires a simple hardware and software configuration as a microcomputer equipped with the linux operating system is more than enough. compared to other works, the proposed method can simulate any type of grafcet and the various forcing treatments, and it presents precision and exhaustiveness. the only downside of the proposed method is that unix is not quite real-time, but this approach can be assumed as complete by staying at the simulation stage. future work would focus on translating grafcet into promela/spin. acknowledgment this paper pays tribute to mr. louis frécon, who was a professor at insa/lyon, and passed away on november 11, 2018, for his contribution during the realization of this work. references [1] o. a. adebimpe, v. oladokun, and o. e. charles-owaba, "preventive maintenance interval prediction: a spare parts inventory cost and lost earning based model," engineering, technology & applied science research, vol. 5, no. 3, pp. 811–817, jun. 2015, https://doi.org/ 10.48084/etasr.565. 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[11] m. raynal, concurrent programming: algorithms, principles, and foundations. springer, 2013. microsoft word 11-703-ed.doc engineering, technology & applied science research vol. 6, no. 6, 2016, 1264-1268 1264 www.etasr.com al-mufadi et al.: influence of γ-irradiation on the structural properties of indium monoselenide crystals influence of γ-irradiation on the structural properties of indium monoselenide crystals f. a. al-mufadi a. el-taher g. a. gamal college of engineering alqassim university saudi arabia almufadi@qec.edu.sa physics dept, faculty of science, al-azher university, assuit branch, egypt atef_eltaher@hotmail.com physics dept, south valley university, egypt and college of engineering, alqassim university, saudi arabia profdrgamal@qec.edu.sa abstract—indium monoselenide (inse) which is a layered semiconductor whose energy gap is 1.24 ev has received attention because of its potential applications in optoelectronic devices. in the present work n-type inse crystals were grown by a special modification of the vertical bridgman technique. x-ray diffraction (xrd) patterns showed that all samples were single phased inse. the crystals were irradiated with 100 500 kgy to reveal the influence of irradiation on the structural properties of the samples. detailed structural analysis was done by scherrerr’s procedures, x-ray peak broadening and williamson–hall plot methods to evaluate the crystalline sizes and lattice strain. also from the relations between the irradiation dose and the deformation of the lattice parameters we could investigate and discuss the mutation of the dislocation density, grain size, microstrain and crystallinity of the grown crystals. striking results are found due to irradiation in the present study for the first time. keywords-crystallite size; dislocation; inse crystals; micro strain; radiation effects; xrd analysis i. introduction binary chalcogenide compounds of iii–vi semiconductor like inse, inte, and ins have experienced great developments in the last few decades. among them inse is the most studied both experimentally and theoretically. inse is a layered semiconductor whose energy gap is 1.24 ev [1, 2] and has ntype conductivity [3]. lnse is formed by "bidimensional" layers stacked with se-ln-ln-se sequence. each layer is bounded to its neighbor by van der waals bonds. so cleavage occurs perpendicularly to the caxis. literature survey revealed that it is one of the most suitable compounds of semiconductors for optoelectronic and photovoltaic applications [4]. this semiconductor has been used to design technologically many devices, such as solar energy converters, infrared detectors, optical fibers, solar elements and other photoelectric sensors [5]. it has been reported that the photoconductive response is mostly in the visible region [6]. also from literatures one can conclude that the results concerning the structure and physical properties of lnse are often contradictory and it depends on the perfection of the grown crystals [7]. it is an established fact that these discrepancies are the consequence of the poor quality of the grown crystals [8]. it has been found that the efficiency of inse solid state devices is limited by the defects which are created during crystal growth [9]. also similarly to other crystals, the preparation method plays a very important role with regard to the structural properties. some researchers intend to add excess of in because it enables the growth of easily cleavable layered crystals. this is why we introduced a modification to the vertical bridgman technique in order to obtain high quality crystals because of these modifications. in fact a perfect crystal would extend in all directions to infinity, so no crystals are perfect due to their finite size of the products. this deviation from perfect crystallinity leads to a broadening of the x-ray diffraction peaks. the two main properties extracted from peak width analysis are (a) crystallite size and (b) lattice strain. crystallite size is a measure of the size of a coherently diffracting domain [10]. so the current research is an attempt to find the effect of irradiation on the quality of the grown crystals. another reason encouraged us to undertake such study where inse crystals may suffer from radiation damage as pre-mentioned above during the review applications or even it is a candidate under development for the next generation of high-energy physics experiments. generally since the main goal of the present study is to estimate the structural properties of the crystals and their relations under the influence of the γirradiation doses, we did apply x-ray profile analysis as a simple and powerful tool for this purpose [11]. ii. experimental technique a. crystal growth stoichiometric proportions of indium and selenium was used to produce inse crystals. the charge elements were: in (6n pure), and se (5n pure) as obtained from aldrich. the starting materials were placed in a sealed evacuated silica tube (~10-6torr). for growing single crystals of inse a new method, which is illustrated in figure1, was used. this technique is very simple but it enabled us to obtain crystals of high quality. this engineering, technology & applied science research vol. 6, no. 6, 2016, 1264-1268 1265 www.etasr.com al-mufadi et al.: influence of γ-irradiation on the structural properties of indium monoselenide crystals is because of the absence of motor vibrations. details of this technique have already been published [12]. among the advantages of this method is that the growth rate can be controlled easily. the ampoule is moved downward in the thermal gradient of 40°c/cm, between the temperatures of 750 and 250°c, with a speed of 3 mm/h. prior to the growth process, the in and se charge was slowly heated up to 750oc and maintained at this temperature for 12 hours to ensure melting and complete the reaction. during the growth process the tube with its charge were held at 660oc (according to the phase diagram [13]).the grown crystals were identified by means of x-ray diffraction since it is an established fact that the x-ray diffraction is a good tool for verifying crystals. also the lattice parameters, grain size, strain and dislocation density of a given material can be determined by using x-ray investigations [11]. the conformation of the product crystal showed that it is single phase with a monoclinic structure (c2/m (12)) and the unit cell parameters obtained are the same as reported earlier [13].the samples were irradiated with γ-rays obtained from cells available at king saud university. the average dose rate from the cell was 1 gy/s.the doses were adjusted to be 100 kgy (for about 1day), 300 kgy (for about 4 days) and 500kgy (for about 6 days). fig. 1. method for growth of single crystals of indium monoselenide b. x – ray diffraction technique the x–ray diffractograms were measured with scan speed 2 deg/min (continuous scan mode) at ambient temperature with a goniometer type ultima iv. the instrument is equipped with a copper anode generating ni filtered cukα radiation (λ=1.5406 ao, 40 kv, 40 ma, backmonochromator). the equipment was used in a θ-2θ geometry in the range between 10 and 80o with a divergence slit of 2/3 deg. in the present work, we will show how we can utilize the x–ray pattern for determination of many important parameters. it must be mentioned that background subtraction and ka2 elimination were done before the peak search work. iii. results & discussion the measurement of structural parameters by means of xray diffraction is of great interest from both experimental and theoretical point of view. the direction of the reflection beams is determined entirely by geometry of the lattice which in turn is governed by the orientation and spacing of the crystalline planes. if for crystal of symmetry the given size of the structure cell a, b and c, the angle at which the beam diffraction from the crystal plane (hkl) can easily be calculated from the interplanar spacing relationships. a. xrd analysis the measurement of structural parameters by means of xray diffraction has therefore of many advantages over the other techniques. for example it does not require time for sample preparation (tinning) and image analyzing. utilization of the xray diffraction has been done to reveal the influence of irradiation on the crystal structure of the grown inse crystals. figure 2 shows the powder diffractogram of the inse sample. in this figure, we can see strong bragg peaks of x-ray diffraction pattern which indicate that the sample is crystalline. no other or foreign peaks were detected. the intense peaks in the patterns prove the high crystallinity of the products. the relative intensities of the reflection peaks in all patterns agree well with the xrd pattern of bulk inse. also the effect of irradiation on inse structure is present in xrd charts. this can be observed as a change in the peak intensities. the variations of the intensities of the main peaks is due to that localized variations in intensity within any individual diffracted spot arise from structural non-uniformity in the lattice planes causing the spot, and this forms the basis for the x-ray topographic technique. this topographic contrast arises from differences in the intensity of the diffracted beam as a function of position inside the crystal. so this change, simply, is a function of crystallinity. on the other hand, with increasing irradiation doses from 100 to 300 and 300 to 500 kgy, the crystallinity of the products was changed. in this work, it is desired to establish the extent to which the irradiation treatment plays a significant role in improvement of the crystal quality. 300 kgy shows the preferable dose that can be used in this respect where at 500kgy the peak intensity is no longer high. now if the crystallite is strained then the d spacing will be changed; a compressive stress would make the d-spacing smaller (and a tensile stress would make the d spacing larger), say reducing a given spacing d to d−δd. then by bragg's law the position of the peak will increase from 2θ to 2(θ + δθ). if every crystallite in the sample was strained (compressed) by the same amount it would result in a peak shift from (2θ) to 2(θ + δθ). based on the above facts and regarding to figure 2 we concluded the following: 1. all the three patterns prove that the crystal, understudy, is confirmed as inse monoclinic if compared to data and the d spaces of [13]. 2. under the influence of irradiation the peaks shift upward. since the peak height depends on the crystal quality, so it is easy to conclude that irradiation improves the crystallinity and hence the crystal quality. 3. in spite of the observable broadening, the peak positions are the same for the different irradiation doses. this indicates that the compressive stress is excluded. 4. irradiation improves the crystallinity and the crystal quality but until a certain limit. this is concluded where peaks started to decrease above 300 kgy. engineering, technology & applied science research vol. 6, no. 6, 2016, 1264-1268 1266 www.etasr.com al-mufadi et al.: influence of γ-irradiation on the structural properties of indium monoselenide crystals b. determination of crystal lattice parameters the direction of the reflection beams is determined entirely by geometry of the lattice which in turn governed by the orientation and spacing of the crystalline planes. if for crystal of symmetry the given size of the structure cell a, b and c, the angle at which the beam diffraction from the crystal plane (hkl) can easily be calculated from the inter-planar spacing relationships. we did so and the obtained data were used to identify the product crystal. moreover with the aid of bragg’s law: nλ=2dsinθ we calculated, by computational treatments, structure cell a, b and c substantially free from experimental error by using the extrapolation function f (θ). fig. 2. x-ray charts of inse crystals at 100, 300 and 500 kgy fig. 3. relation between the lattice parameters a,b and c and the extrapolation function f (θ) for inse crystals at 100, 300 and 500 kgy from the values of d-spaces, for different reflection planes, we calculated the lattice parameters of the monoclinic inse according to the following equation [14]: 2 2 2 2 2 2 2 2 2 2 hkl h k l (2 h l cos β)1 = sin β + + sin β (1) d a b c (a csin β) é ù é ù é ù é ùê ú ê ú ê ú ê úê ú ê ú ê ú ê úë ûê ú ë û ë ûë û where d is interplanar spacing, h,k and l are miller's indices and a,b and c are the lattice parameters. it is observed in fig.2 that peak broadenings occurred. this is regarded as a result of: (a) crystallite size and (b) lattice strain. for more utilization of figure 2, we shall digress with a discussion on the width of the main peak in the three cases. the pre-mentioned three cases correspond to the three crystals as irradiated with 100, 300 and 500 kgy. in order to obtain the lattice parameters a, b and c of the monoclinic inse substantially free from experimental error, one should plot the apparent values of a, band c respectively against the corresponding values of the famous extrapolation function f (θ) which is [15]: 2 2cos θ cos θ f(θ)= + sinθ θ (2) figure 3 shows the relation between the lattice parameters a, b and c vs f(θ). the interception of the extrapolation of straight line with y-axis gives the value of the lattice parameters a,b and c accurately. the results of lattice parameters as estimated from figure 3 are shown in table i. table i. results of lattice parameters as estimated from fig 3 lattice parameter ao values in [13]ao dose a b c a b c (100 kgy) 11.582 4.138 4.548 (300 kgy) 11.581 4.137 4.548 (500 kgy) 11.585 4.139 4.549 11.74 4.11 4.61 the data appeared in table i and figure 3 leads to the following comments: 1. results of a, b and c support that the crystal is monoclinic. 2. generally all the lattice parameters are influenced by the exposure of irradiation 3. careful look at the estimated values compared to those reported in [13] leads to conclude that generally a and c values are always less than those of the standards, while b values are higher than the reported standards. 4. from the results and calculations we concluded that the expansion rate of b values is less than the shrinkage rate in a and c values. accordingly, the unit cell volume decreases under the influence of the radiation doses i.e. radiation cause shrinkage. however as concluded from preivous section, tensile stress is excluded. 5. the lowest unit cell volume value was observed at 300 kgy. 6. the fluctuation in the lattice parameters under the different irradiation doses, as observed in figure 3, may be attributed to the variation occurred in the quality and/or the lattice imperfections of the crystals due to irradiation [16]. engineering, technology & applied science research vol. 6, no. 6, 2016, 1264-1268 1267 www.etasr.com al-mufadi et al.: influence of γ-irradiation on the structural properties of indium monoselenide crystals 7. the calculated shrinkage is not the same in all cases of radiation. the greatest shrinkage is observed at 300 kgy, while the least effect is occurred at 500 kgy. c determination of crystallite size in (3) by substituting the values of γ (the full width at half maximum) and the values of the main peak we can obtain the value dvol (crystal size) .this quantity is important because it is proportional to lvol (the column lengths). the primarily obtained column lengths of an ensemble of particles can be transformed into average grain sizes if all the crystallites in the sample have roughly the same shape [17]. the standard assumption is a spherical shape, then: dvol = 4/3lvol this is why we computed dvol and lvol as shown in table ii. from the scherer’s equation [18]: vol 0.94λ γ= (3) d cosθ we can obtain the crystallite size (dvol), and hence (lvol),for the monoclinic inse crystals at the different conditions understudy .the results are as follows: table ii. results for monoclinic inse crystals at different conditions dose lvol dvol 100 kgy 38.534 51.38 300 kgy 51.120 68.16 500 kgy 37.571 50.10 in spite of scherer’s formula beina an approximation, it is observed that the values of dvol and hence lvo are inversely proportional to the unit cell volumes that estimated in previous section. also the williamson-hall equation can be given as [19]: vol 0.94λ γcosθ= +4 ε sinθ (4) d where γ is the full width at half-maximum of x–ray peak at diffraction angel θ. we utilized williamsonhall relation because it takes into account that the total width of the x-ray diffraction peak is due to both size and strain effects. for the separation, the different dependence is helpful: the size broadening is proportional to cos-1θ and the strain broadening is proportional to tanθ. accordingly from plotting the relation between γcosθ and sinθ, we can get from the intercept the value of dvol and from the slope the value of the microstrain. this is done in figure 4 regarding to williamson-hall relation. from the figure and the results we can conclude the listed data as shown in τable ιιι. as for the obtained results in table iii, the following comments can be made: 1. both dvol and lvol are influenced by the irradiation. 2. both dvol and lvol have the highest values when the crystals are irradiate to 100 kgy while the lowest are corresponding to300 kgy. 3. the above result is acceptable if we consider the peak broadening appeared in figure 2. again xrd peaks are broadened by small crystallite size and lattice distortion caused by lattice dislocations. 4. generally the values of crystallite size calculated by scherrer’s method are less than that obtained by williamson-hall method. this difference is attributed to the strain value and confirms that the role of strain is important. 5. this difference should be considered in the calculation of crystalline size. thus, calculations by using the scherrer’s method without considering strain may yield inaccurate results. table iii. results dose lvol (nm) dvol (nm) microstrain dislocation density (m2) 100 kgy 186.14 248.19 0.0017 5.57 x 1010 300 kgy 47.00 62.67 0.0003 1.88 x 109 500 kgy 63.49 84.66 0.0014 3.8 x 1010 0.1 0.2 0.3 0.4 0.5 0.6 0.7 -2 0 2 4 6 8 10 inse 100 kgy sin () -2 0 2 4 6 8 inse 300 kgy  c os ( ) ( x1 03 ) -2 0 2 4 6 8 10 inse 500 kgy fig. 4. γcosθ as a function of sinθ d determination of the microstrain and the dislocation density as it is mentioned williamson hall technique takes into account both size and strain effects. the formula which is between γcosθ and sinθ is a liner relationship as predicted. from the intercept of the linear we had above the crystal size. the slope of the fitted line provides the micro-strain. the average dislocation density er can be determined from the following equation [20]: engineering, technology & applied science research vol. 6, no. 6, 2016, 1264-1268 1268 www.etasr.com al-mufadi et al.: influence of γ-irradiation on the structural properties of indium monoselenide crystals 2 2 eε =(πab /2)r c (5) where (b2/2) is the burgers vector, a is a constant defined by the effective outer cut-off radius of dislocations re and c is the contrast factor. the results of the microstrain and the dislocation density are listed in table iii. the results reveal the following: 1. both values of the microstrain and the dislocation density are influenced by the irradiation. 2. both the microstrain and the dislocation density behave in the same manner. 3. they reach the maximum values at irradiation of 500 kgy while the lowest values are observed at 300 kgy. 4. from the dislocation density relations, the average distance between the adjacent dislocations lc (as appeared in the previous table) can be checked simply as cl =1/ ρ (6) iv. conclusion inse crystals were grown by a special modification of the vertical bridgman technique. via x-ray diffraction examinations it was indicated that the grown samples are crystalline inse in their monoclinic form. the crystals were irradiated with 100 500 kgy. the crystallite size and lattice strain were estimated from broadening of xrd peaks by using scherrer and williamson-hall methods. a lot of structural work was done. the basic conclusions are as follows: 1. as the crystals are irradiated: the crystallinity, lattice parameter a, b and c, crystal size, the column length, microstrain and dislocation density are influenced by the exposure of irradiation. 2. irradiation improves the crystallinity and the crystal quality but until a certain limit (300 kgy). x-ray peak positions are the same at the different irradiation doses. this indicates that the compressive stress is excluded. 3. the unit cell volume decreases under the influence of the radiation doses exposure i.e. radiation cause shrinkage. however as concluded from section iii.b tensile stress is excluded. 4. since both values of the microstrain and the dislocation density are influenced by the irradiation, this was utilized to interpret the reason irradiation improves the crystal quality by dislocation reduction which causes unit cell shrinkage. 5. generally the values of crystallite size calculated by the scherrer method are lower than the ones obtained by the williamson-hall method. this is a minor result if compared to previous work that was already published for other compounds [21]. however similar situations have been reported [22]. references [1] t. iishii, “high quality single crystal growth of layered inse semiconductor by bridgman technique”, journal of crystal growth, vol 89, pp. 459-462, 1988 [2] r. triboulet, c. levy-clement, b. theys, “growth of inse single crystals by the travelling heater method”, journal of crystal growth,vol. 79, pp. 984-989, 1986 [3] a. segura, f. pomer, a. cantarero, “electron scattering mechanisms in n-type indium selenide”, phys. rev., vol. b29,pp. 5708, 1984 [4] s. shigetomi, h. ohkubo, “annealing behaviour of optical properties and structure of r.f-sputteredinse films”, thin solid films, vol. 199, pp. 215 -222, 1991 [5] j. hossain, m. d. julkarnain, k. s. sharif, k. a. khan, “preparation and properties of indium selenide (inse) thin films for selective surface applications”, journal of physical science and application, vol.1, pp. 37-43, 2011. [6] a. a. darwish, m. m. el-nahass, m. h. bahlol, “structural and electrical studies on nanostructured inse thin films”, applied surface science,vol. 276, pp. 210–216, 2013 [7] a. cttevy, a. kuhn, m. s. marlin, “large inse monocrystals grown from a non-stoichiometric melt”, journal of crystal growth, vol. 38 pp. 118-122, 1977 [8] s. hirohata, j. s. moodera, g. p. berera, “structural and electrical properties of inse polycrystalline films and diode fabrication”, thin solid films, vol. 510, pp. 247–250, 2006 [9] c. d. e. blasi, g. hicocci, s. mongelli a.tepore, f. zuanni, “growth and characterization of high quality inse single crystals”, materials chemistry and physics, vol. 9, pp. 55-64, 1983 [10] s. vives, e. gaffet, c. meunier, “x-ray diffraction line profile analysis of iron ball milled powders”, materials science and engineering, vol. 66, no. a3, pp . 229–238, 2004 [11] v. d. mote, y. purushotham, b. n. dole , “williamson-hall analysis in estimation of latticestrain in nanometer-sized zno particles”, journal of theoretical and applied physics, vol. 6, pp. 1-8 , 2012 [12] g. a. gamal, m. abou zied, a. a. ebnalwaled, “the electronic properties of the red ptype tl2s5 single crystals”, chinese physics letters,vol. 22, pp. 6, 2005 [13] k. cenzual, l. m. gelalo, e. parthe “inorganic structure types with revised space group”, acta cryst., vol. b47, pp. 433-439, 1991 [14] s. q. xiao, a. h. gleiter, “nanocrystalline titanium aluminide”, acta metall. mater., vol. 42, pp. 25352545, 1994 [15] r. a. varin, j. bystrzycki, a. calka, “processing and fabrication of advanced materials”, intermetallics, vol. 7, pp. 917, 1999 [16] c. castro ribeiro, i. gibson, m. adolfo barbosa, “the uptake of titanium ions by hydroxyapatite particles—structural changes and possible mechanisms”, biomaterials, vol. 27, no. 1,pp. 749-176, 2006 [17] c. e. krill, r. birringer, “crystallite size distribution and dislocation structure determined by diffraction profile analysis” philos. mag., vol. 77, pp. 621,1998 [18] p. scherrer, “determining the size and the internal structure of colloidal particles by means of x-rays”, nachr. ges. wiss. göttingen.,vol. 26, pp. 98, 1918 [19] g. k. williamson, w. h. hall, “cold-worked iron and molybdenum”, acta met.,vol. 1, pp. 22-28, 1953 [20] m. wilkens, “the determination of density and distribution of dislocations in deformed single crystals from broadened x-ray diffraction profiles”, physica status solidi a, vol 2, no. 2,pp. 359-370, 1970 [21] g. a. gamal, f. a. al-mufadi, a. h. said, “effect of iron additives on the microstructure of hydroxyapatite”, engineering, technology & applied science research,vol. 3, no. 6, pp. 532-539, 2013 [22] v. d. mote, y. purushotham, b. n. dole, “williamson-hall analysis in estimation of latticestrain in nanometer-sized zno particles”, journal of theoretical and applied physics, vol. 6, pp. 1-8, 2012 microsoft word etasr_v13_n2_pp10595-10600 engineering, technology & applied science research vol. 13, no. 2, 2023, 10595-10600 10595 www.etasr.com alghamdi & bishta: preliminary site investigation based on rgb electromagnetic energy of landsat-7 … preliminary site investigation based on rgb electromagnetic energy of landsat-7 images in wadi fayidah, saudi arabia mohammed a. m. alghamdi faculty of earth sciences, king abdulaziz university, jeddah, saudi arabia mmushrif@kau.edu.sa (corresponding author) adel zein e. a. bishta faculty of earth sciences, king abdulaziz university, jeddah, saudi arabia abishta@kau.edu.sa received: 21 february 2023 | revised: 11 march 2023 | accepted: 16 march 2023 abstract in this paper, geostatistical analysis of digital image processing data efficiently contributed to the preliminary site investigation and geotechnical mapping of wadi fayidah, saudi arabia. 3d modeling, clustering, and chart pattern changes were used to analyze the spectral electromagnetic energy reflected values in red, green, and blue (rgb) ranges on false color composite landsat-7 images. therefore, from upstream to downstream, a series of measurements were carried out on a 70km dendritic drainage pattern at 78 stations. wadi fayidah was found to have a dominant structural lineament of 56° to 84°. furthermore, as a preliminary engineering geology mapping, wadi fayidah has 9 lithofacies that may differ in engineering geological properties. keywords-structural lineaments; lithofacies; statistical analysis; image processing i. introduction site investigation is an essential step in any engineering project in order to identify and quantify ground conditions affecting a structure's viability, design, or construction. as a preliminary site investigation tool, remote sensing aims to acquire a general engineering geological understanding of the project area or site. hence, it gathers information about lithology, structure, and geomorphology without physical contact [1]. remote sensing and digital image processing techniques are essential in mineral and groundwater exploration, lithological discrimination, and structural mapping [2]. remote sensing, high-resolution imagery, and gis have become essential tools for locating and selecting the best sites of mineral deposits by detecting the locations of alteration zones [3]. the mineral deposits usually occur along or are adjacent to the geologic structures and alteration mapping, as mineral deposits are commonly associated with hydrothermal alteration of the surrounding rocks [4-5]. image processing of digital data has been used for lithological and structural interpretation [6-11]. authors in [12] used remote sensing techniques for geological mapping. authors in [13] utilized landsat images to assess construction materials, while authors in [14] employed statistics and enhanced rgb images in surface water interpretation. the differences in soil color from an rgb camera were investigated at different distances, times, and illumination levels obtained from loam soil over four weeks of data acquisition [15]. authors in [16] studied munsell's soft color and soil reflectance in the visible spectral bands of landsat mss and tm data. rgb values appear to be strongly correlated with the soil reflectance measured in the corresponding spectral bands of landsat sensors. as a different approach for a preliminary site investigation of wadi fayidah, this work uses geostatistical analysis such as 3d modeling, clustering, and phenomena chart tracking of landsat-7 etm+ (enhanced thematic mapper plus) digital satellite data. consequently, this study aims to achieve a method of interpreting drainage patterns, structural lineaments, and lithofacies. the aim is to produce an engineering specialpurposed geological map. ii. geological setting wadi fayidah is located in the northern makah region, between latitudes 21 o 50' and 21 o 59'n and longitudes 39 o 20' and 39 o 55 e (figure 1). the investigated area belongs to the arabian shield, shielded by precambrian metasediments and metavolcanics. these rocks are covered by quaternary sediments and intruded by dioritic rocks. it is a basin among the deformed, weakly metamorphosed, post-amalgamation volcano-sedimentary sequence in the arabian shield, saudi arabia [17]. engineering, technology & applied science research vol. 13, no. 2, 2023, 10595-10600 10596 www.etasr.com alghamdi & bishta: preliminary site investigation based on rgb electromagnetic energy of landsat-7 … fig. 1. location map. according to [18], the geology of wadi fayidah falls into four groups: (1) proterozoic crystalline basement, (2) tertiary sedimentary rocks, (3) tertiary volcanic rocks, and (4) quaternary sediments. the proterozoic basement comprises volcanic and volcano-sedimentary formations of various ages and compositions, intruded by plutons of diverse composition but with strong granodiorite affinities. tertiary sedimentary rocks consist of shumaysi, khulays, and khulaysiyah [18, 20] and hammar formation [21]. it comprises tertiary clastic and carbonates rocks that crop out over a minimal area. however, they are thought to underlie the quaternary sediments and late tertiary basalts in much of wadi as sukkah (as suqah), wadi al aghran, and the coastal plain [21]. the shumaysi to ubhur formations has been tilted, faulted, and linked to the significant red sea rifting [21]. iii. methodology the multispectral digital satellite data of landsat-7 etm+ were downloaded from the usgs website. they were radiometric and geometrically corrected to utm 37n (wgs84 datum) by the usgs eros center. this information is used for regional geotechnical surveys of the study area. advanced remote sensing software such as erdas imagine and pci geomatica provide various image-processing techniques such as geometric correction and image enhancement. this study uses digital image processing techniques with the statistical analysis of digital satellite data. a geometric correction has been applied to the data because geometric errors are caused by the sensor or scanner's geometry, the earth's curvature and rotation, etc. [22]. these data (landsat-7 etm+) comprise bands b1-b3 (visible rays), bands b4, b5, and b7 (infrared rays), band b6 (thermal rays), and a panchromatic band (b8). these bands are of 30m spatial resolution except band 6 (60m) and band 8 (15m). in addition, to make the processed images interpretable, histogram equalization and smooth filtering were applied [22]. the geostatistical analysis of the extracted lineaments, visible green enhancement band (eg), and the digital number (dn) values of rgb pixels (landsat etm+ bands 7, 4, 2, in red, green, and blue, respectively), along wadi fayidah, are summarized in the flow-chart approach shown in figure 2. eg 3d clustering distance clustering preliminary engineering geology map rgblineaments length trend clustering lithofacies zones structure zones wadi fayidah landsat image data geostatistics zonation mapping geomorphology imagery fig. 2. graphical abstract of the workflow. landsat-7 etm+ digital data were processed to yield a false-color composite (fcc) image on a scale of 1:100000. the best band combination obtained for this fcc image consists of etm band 7 (swir), band 4 (nir), and band 2 (visible green) in rgb, based on the selection of the most significant variance bands with the minor correlation. in addition, it shows a regional view of the study area, the main rock units, and wadies. the landsat images cover a large area (185 by 170km) and illustrate its regional geology and topography. extraction of lineaments from the digital landsat data is carried out to show the structural analysis of the wadi fayidah area. it is also very useful in the seismic and risk of landslide evaluation [22]. lineaments usually reflect linear structural features in the rocks or artificial features like roads or buildings. lineament extraction is usually carried out by using digital data of satellite either manually [23-24] or automatically [25-26]. the automatic lineament extraction technique is applied in this work to interpret and extract the structural lineaments from the digital spot-5 data of the study area. iv. results seventy-eight stations were placed at spaced distances (about 70km long) with the wadi fayidah. these stations begin at the highest valley (upstream) on the east and end at the mouth of the wadi (downstream) on the west (figure 3). the statistical analysis of the relationship between interfaces, distance separations, and frequencies (the total number of stations in each distance) was carried out. figure 4 shows the normal distribution of a histogram of the relationships between the distance separations between stations and their frequencies. each station has taken various measurements, such as location coordinates and rgb spectral values of landsat color composite images for raw and enhancement data in the three bands (bands 7, 4, and 2, in red, green, and blue). in addition, rock type, geomorphological type, and the trends and lengths of the structural lineaments were also taken at each station (figure 5). table i describes the lithologic unit types in the 78 stations along wadi fayiddah. the symbols and descriptions of the lithologic units with their codes (arranged from 1-the oldest rock units to 23-the youngest rock units) are also listed. engineering, technology & applied science research vol. 13, no. 2, 2023, 10595-10600 10597 www.etasr.com alghamdi & bishta: preliminary site investigation based on rgb electromagnetic energy of landsat-7 … fig. 3. locations of the 78 stations along wadi fayidah, on false color composite landsat image. fig. 4. frequencies of the distance separations between stations. fig. 5. some rgb data acquired from the landsat image on the 78 stations along wadi fayidah. table i. lithological unit types of the 78 stations along wadi fayidah station no. rock type symbol code description 1-5 ibmv-p€ 2 meta-andesitic to metabasaltic 6-8 todr-p€ 11 tonalite 9-11 gr-p€ 13 granite 12-14 gdmo-p€ 12 granodiorite 15-18 mdgb-p€ 1 metadiorite and gabbro 19-32 todr-p€ 11 tonalite 33-35 sscg-t 15 sandstone and conglomerate 36 ss-t 16 sandstone and oolitic iron ore 37 sscg-t 15 sandstone and conglomerate 38-51 ibvs-p€s 3 samran group, volcanosedimentary rocks 52-54 sscg-t 15 sandstone and conglomerate 55 ibvs-p€s 3 samran group, volcanosedimentary rocks 56, 57 gv-q 22 gravel 58, 59 sscg-t 15 sandstone and conglomerate 60 gv-q 22 gravel 61 to 78 clss-t 14 clay, sandstone and tuff v. analysis and discussion the study area's landsat-7 color composite images (bands 7, 4, 2 in rgb) were processed. the study area is dissected by some significant wadies running from the east to the west, as shown in figure 6. fig. 6. false color composite landsat-7 etm+ image, showing wadi fayidah area. a. drainage the image processing technique was applied to extract a subset of the false color composite landsat image for the exact boundary of wadi fayidah basin, as shown in figure 7. fig. 7. false color composite landsat-7 etm+ image of wadi fayidah basin. figure 8 shows the dendritic drainage pattern of wadi fayidah as interpreted from the fcc landsat-7 etm+ image in figure 7. the wadi fayidah is one of the longest, more than 70km long, wadies in the area. a dendritic drainage pattern that looks like the branching pattern of tree roots develops in regions underlain by homogeneous material. the availability of this pattern reflects the similarity of resistance to weathering, so there is no apparent control over the direction the tributaries take. fig. 8. the dendritic drainage pattern of wadi fayidah. b. lithofacies as illustrated in figure 5, numerous variables were measured at the 78 stations for classification purposes. the statistical analysis was performed in three steps. 1) step-1: 3d visual rgb clustering figure 9 shows the 3d layout of the raw data's red, green, and blue bands. the plotting indicates that the data can be engineering, technology & applied science research vol. 13, no. 2, 2023, 10595-10600 10598 www.etasr.com alghamdi & bishta: preliminary site investigation based on rgb electromagnetic energy of landsat-7 … categorized into two groups. the stations of the first category were clogged on the map with yellow color (figure 10). in addition, it was observed that stations located close to each other, are classified as one zone with the same lithofacies properties. therefore, the study area can be categorized into two zones with different lithological properties. fig. 9. two views of the same 3-d plot showing two rgb clusters (a and b). fig. 10. the first cluster of 3d rgb stations (yellow color). 2) step-2: eg (enhancement green) fluctuation the eg spectrum was selected to reflect the highest intensity and reflectance compared to other spectra. based on the different properties from one location to another, the change in eg values is shown in figure 11. it offers three distinct clusters. these categories are discriminated in the profile and satellite image as zone-i, zone-ii, and zone-iii (figure 12). fig. 11. eg profile through distance, along wadi fayidah. 3) step-3: eg and 3d_rgb merging after merging the rgb clusters and the eg zones, wadi fayidah can be categorized into 7 zones. each zone depicts different lithofacies, which may reflect different engineering properties. alternatively, this classification will organize the sampling area rather than reducing or expanding it. fig. 12. zones of eg fluctuation (blue, red, and green ellipses). c. lineaments automatic lineament extraction was carried out from the digital data of fcc landsat image of wadi fayidah basin. visual editing was done to delete the false lines (not structural lines) for the extracted lineaments to construct the wadi fayidah basin's structural lineaments, as shown in figure 13. it was interpreted from a false color composite landsat-7 etm+ image. fig. 13. structural lineament map of wadi fayidah area. figure 14 illustrates the relationship between the structural lineaments (frequency) and trend ranges. it concludes that wadi fayidah's dominant structure tends to be between 56° and 84°. the relationships between the directions of the lineament's structure (x-axis) and their lengths (y-axis) are shown in figure 15, which reflects the availability of two lineament clusters. fig. 14. histogram of the predominant structural lineaments trend. engineering, technology & applied science research vol. 13, no. 2, 2023, 10595-10600 10599 www.etasr.com alghamdi & bishta: preliminary site investigation based on rgb electromagnetic energy of landsat-7 … fig. 15. structural lineament evaluation of wadi fayidah. both clusters offer a positive relationship between length and direction. however, the first cluster, which covers fewer stations, shows more significant lengths than the second one. otherwise, the trends in the first cluster are limited compared to the second cluster. the second cluster covers most stations in wadi fayidah. it has shorter lengths, with greater directions than the first one. generally, the second cluster trend is predominant in the wadi fayidah. the relationship between the length and azimuth of the structural lineaments is positive. from a geology engineering point of view, keeping the construction far from the structure locations and short length of constructions walls or foundation perpendicular to lineament trends is recommended. circular or curved design may also be recommended for equality stress distribution. in a lineament structure of about 200m long, the study area can reflect two zones, as sown in figure 15. the remaining shorter lineaments will cover the other stations. so, if these 2 zones are added to the previous 7 zones, we get 9 engineering geological zones (figure 16). fig. 16. zones of the study area. d. engineering geological mapping to ensure that the approach used in this document is practical, the analysis and interpretation of the landsat images were compared with the geological map of [21]. it was found that the 9 zones explored through this research match the changes in rock types of [21]. table ii summarizes the lithofacies and structure length of each zone. consequently, an engineering geological map was introduced (figure 17). previous works, such as the applicability of landsat-8 and regression analysis in developing models for estimating water quality parameters explored in [14], did not utilize the beneficial approach used in the current research, i.e. the rgb spectral value characterization of landsat etm+ data and the clustering method in the 3-d plot of the rgb data, to classify and identify the spectral enhanced data into different zones. the current study produced an engineering geological map with 9 lithofacy zones in wadi fayidah. to the best of our knowledge, the technique of rgb electromagnetic energy processing is presented in this study for the first time. table ii. lithological unit types of the 9zones along wadi fayidah zone no. stations (st.) no of st. rock type structure symbol code description length zone-1 1-8 9 ibmv-p€ todr-p€ 2 meta-andesitic to metabasaltic tonalite ≥ 200 m zone-2 9-16 8 gdmo-p€ gr-p€ 12 granodiorite granite ≤ 200 m zone-3 17-32 16 todr-p€ 11 tonalite ≤ 200 m zone-4 33-39 7 sscg-t sssh-t 15 sandstone and conglomerate ≥ 200 m zone-5 40-51 12 ibvs-p€s 3 samran group, volcanosedimen tary rocks ≤ 200 m zone-6 52-56 5 sscg-t 15 sandstone and conglomerate ≤ 200 m zone-7 57-59 3 gdma-p ss-t granodiorite sandstone and oolitic iron ore ≤ 200 m zone-8 60-64 5 clss-t 14 clay, sandstone and tuff ≤ 200 m zone-9 65-78 14 clss-t 14 clay, sandstone and tuff ≤ 200 m fig. 17. engineering geological map showing the 9 lithofacy zones of wadi fayidah (a) landsat image view, (b) clear view. vi. conclusion based on landsat-7 rgb electromagnetic energy and statistical data analysis, wadi fayidah has been primarily investigated for engineering geological purposes in this paper. the resulting conclusions of the current research are: engineering, technology & applied science research vol. 13, no. 2, 2023, 10595-10600 10600 www.etasr.com alghamdi & bishta: preliminary site investigation based on rgb electromagnetic energy of landsat-7 …  with a length of 70km from upstream to downstream, wadi faydah is classified as a dendritic drainage pattern that reflects the similarity of resistance to weathering for the subsurface.  the primary trend of the lineament structure of wadi fayidah ranges between 56° and 84°.  based on geology, structural lineaments, and rgb analysis, wadi fayidah is classified into 9 different lithofacies.  for more emphasis on validity and reliability, applying the geostatistical analysis approach to rgb data in other studies is recommended. references [1] l. g. de vallejo and m. ferrer, geological engineering. london, uk: crc press, 2011. 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[26] n. vassilas, s. perantonis, e. charou, t. tsenoglou, m. stefouli, and s. varoufakis, "delineation of lineaments from satellite data based on efficient neural network and pattern recognition techniques," in 2nd hellenic conf. on ai, setn-2002, 11-12 april 2002, thessaloniki, greece, proceedings, companion volume, apr. 2022, pp. 355–366. microsoft word etasr_v13_n3_pp10828-10833 engineering, technology & applied science research vol. 13, no. 3, 2023, 10828-10833 10828 www.etasr.com nguyen et al.: preparation, characterization, and antibacterial activity of silver nanoparticle … preparation, characterization, and antibacterial activity of silver nanoparticle-decorated ordered mesoporous carbon dung van nguyen faculty of chemical engineering, ho chi minh city university of technology (hcmut), vnu-hcm, ho chi minh city, vietnam nvdung@hcmut.edu.vn (corresponding author) duong thuy nguyen faculty of chemical engineering, ho chi minh city university of technology (hcmut), vnu-hcm, ho chi minh city, vietnam ntduong49@gmail.com vi le tuong tran faculty of chemical engineering, ho chi minh city university of technology (hcmut), vnu-hcm, ho chi minh city, vietnam vi.tranhoak19@hcmut.edu.vn khang dinh vo faculty of chemical engineering, ho chi minh city university of technology (hcmut), vnu-hcm, ho chi minh city, vietnam khang.vocek19@hcmut.edu.vn long quang nguyen faculty of chemical engineering, ho chi minh city university of technology (hcmut), vnu-hcm, ho chi minh city, vietnam nqlong@hcmut.edu.vn received: 14 february 2023 | revised: 16 march 2023 and 23 april 2023 | accepted: 24 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5782 abstract in this study, ordered mesoporous carbon (omc) was prepared using resol as a carbon precursor and f127 as a soft template. small-angle x-ray diffraction (xrd), transmission electron microscopy (tem) images, and nitrogen adsorption and desorption isotherms revealed that omc possessed ordered hexagonal mesostructures (p6m) with an ordered pore size of 3.2nm, a high specific surface area (sbet) of 539m 2 /g, and a large total pore volume (vtotal) of 0.44cm 3 /g. subsequently, silver nanoparticles synthesized from an aqueous agno3 solution using glucose as a reducing agent and starch as a stabilizing agent were decorated on omc, producing ag/omc. xrd analysis revealed that the composite contained silver crystals. in addition, the content and size of silver nanoparticles in ag/omc were 0.71wt% (aas) and around 25-50nm (tem), respectively. due to the surface cover of silver nanoparticles, sbet and vtotal of ag/omc slightly decreased to 417m 2 /g and 0.38cm 3 /g, respectively. both agar and broth dilution techniques were used to evaluate the antibacterial activity of the material against staphylococcus aureus. ag/omc with a minimum inhibitory concentration (mic) of 25.0μg/ml is a potential candidate for use against staphylococcus aureus. keywords-mesoporous carbon; soft template; silver nanoparticles; green synthesis; antibacterial activity; staphylococcus aureus engineering, technology & applied science research vol. 13, no. 3, 2023, 10828-10833 10829 www.etasr.com nguyen et al.: preparation, characterization, and antibacterial activity of silver nanoparticle … i. introduction over the past few decades, nanomaterials, which exhibit unique nanoscale properties compared to their bulk composition, have propelled research in numerous fields [1-3]. advances in nanoparticle production in a variety of sizes and shapes have facilitated the expansion of their applications [46]. due to their outstanding physical, chemical, and biological properties, silver nanoparticles have been intensively studied for various uses, such as antibacterial agents, imaging probes, reduction catalysts, and oxidation catalysts [7-9]. to prepare silver nanoparticles, chemical reduction techniques are commonly and extensively used [10], which involve the use of reducing agents like sodium borohydride, hydrazine, and citrate to convert silver ions into silver nanoparticles. these methods provide multiple advantages, including a high yield of silver nanoparticles and the ability to control the size and shape of the nanoparticles. however, the use of toxic chemicals is a significant obstacle. to overcome that problem, different green methods have been explored. glucose and starch are recognized as natural, renewable, non-toxic, and inexpensive agents [11-12]. glucose can replace traditional reducing agents, while starch molecules can act as stabilizing agents by adsorbing onto the surface of nanoparticles, preventing their aggregation. as a result, the combination of glucose and starch offers a green and sustainable approach for the preparation of silver nanoparticles with controlled size and shape. however, silver nanoparticles with high surface energy tend to aggregate [13]. as a result, the peculiar properties of these nanoparticles can be drastically diminished during use [14]. to address this issue, silver nanoparticles should be stabilized on appropriate supports to prevent their aggregation [15-16]. in recent years, ordered mesoporous carbon (omc) with pore diameters ranging from 2 to 50nm has garnered considerable interest due to its higher specific surface area, larger pore volume, electrical and thermal conductivity, chemical inertness, good thermomechanical stability, and various oxygen-containing functional groups [17-18]. therefore, omc has been applied in numerous fields, such as adsorption, catalyst support, hydrogen storage, carbon dioxide capture, lithium batteries, electrochemical sensors, electrochemical capacitors, and drug delivery [19-22]. commonly, omc can be fabricated by nanocasting using ordered mesoporous silica as a hard template. this method yields omc with a high specific surface area and a large pore volume [23]. nevertheless, this process requires the preparation of ordered mesoporous silica in the first step but sacrifices it in a later step [24]. furthermore, the removal of this template has the potential to damage the surface of the omc and cause environmental pollution [25]. in general, this method has the drawbacks of being expensive, complicated, and difficult to scale up [26]. a cost-effective and eco-friendly soft-template method was developed to address the limitations of existing technologies. self-assembly of block copolymers is the basis for omc production [27]. carbon precursors (e.g. resol, phenolic resin) are self-assembled into supramolecular aggregates with block copolymers (acting as soft templates, e.g. f127, p123) [28-30]. the mixture is then thermopolymerized to give a cross-linked composite, the template is removed, and carbonization occurs. resol is a common carbon source for this approach due to its moderate weight and size and its moveability in surfactant environments [23, 31]. f127 has advantages as a versatile and widely used soft template for the preparation of mesoporous materials, including high porosity, tunability, thermal stability, biocompatibility, and ease of use [32-33]. moreover, f127 can be decomposed easily at low temperatures (e.g. 350°c), while resol is more stable [30]. the template can be removed to leave mesopores. the complete carbonization of resol to obtain the final omc framework can be conducted at high temperatures (e.g. 600°c). several studies have reported the dispersion of silver nanoparticles on mesoporous carbon supports. in [34], silverdecorated mesoporous carbons (cmk-3 type, hard template) were prepared to promote wound healing. in [35], the softtemplate method and tetraethyl orthosilicate were used to create mesoporous carbons containing embedded silver nanoparticles. in [36], a silver nanoparticle-omc composite was prepared using f127 as a soft template and phenolformaldehyde resin as a carbon source, and then applied it to a lithium-ion battery. in [37], a soft template was used to synthesize ordered mesoporous silver nanoparticle/carbon composites for the catalytic reduction of 4-nitrophenol. in general, the use of softtemplated omc as a support for silver nanoparticles has been rarely reported in the literature. hence, this research was carried out to investigate the feasibility of incorporating silver nanoparticles and omc. omc was first fabricated with f127 as a soft template and resol as the carbon source. the omc surface was then coated with silver nanoparticles, and the resulting composite was tested for its potential as an antibacterial agent. ii. experimental procedure phenol (≥99.0%), formaldehyde (37.0-40.0%), agno3 (99.8%), and hcl (36.0-38.0%) were purchased from xilong scientific co., ltd. f127, starch, glucose, and ethanol (99.5%) were obtained from basf, merk, guangdong guanghua sci-tech co. and vn-chemsol co., respectively. all chemicals were used as received without any further purification. resol was produced from phenol and formaldehyde. in a spherical flask, 9.35ml of liquid phenol was magnetically swirled with 1.75ml of a naoh solution (20wt%). after adding 16.0ml of formaldehyde dropwise, the mixture was agitated continuously for 1 hour at 70°c. after completion of the reaction, the liquid was chilled to room temperature, and the ph was adjusted to approximately 7.0 by adding a 0.6m hcl solution. the water was then vacuumed out at 50°c. the resulting resol was redissolved in ethanol to generate a resol solution (20 wt%), while sodium chloride was separated as a precipitate. omc was synthesized from resol as a carbon source and f127 as a soft template. at the beginning, 1.00g of f127 was dissolved in 10.0g of ethanol. following this, 5.00g of resol solution (20 wt%) were added. after 60 minutes of stirring, the solvent was separated within 24 hours by evaporation at room temperature. the solid was then crushed into a fine powder and placed in a tube furnace with a constant nitrogen flow rate of 70ml/min. pyrolysis was performed in two consecutive steps: the sample was heated to 350°c at a rate of 2°c/minute and kept at that temperature for 3 hours. then, it was heated to engineering, technology & applied science research vol. 13, no. 3, 2023, 10828-10833 10830 www.etasr.com nguyen et al.: preparation, characterization, and antibacterial activity of silver nanoparticle … 600°c at a rate of 5°c/minute and the final temperature was kept for 3 hours. then, the prepared omc sample was stored in a plastic bag for further use. ag/omc was prepared by dispersing a colloidal sol of ag nanoparticles on omc. at first, a mixture of 1.50ml of agno3 (0.100m), 3.00ml of glucose (0.100m), and 90ml of starch solution (0.17 wt%) was heated and stirred at 70°c. after 15 hours of heating and stirring, the sample was collected to determine the formation of ag nanoparticles using a uv-vis spectrometer (spectronic genesys 2 pc), and then 1.60g of omc was added to the colloid. the mixture was stirred for 30 minutes and then sonicated. lastly, the sample was centrifuged, rinsed with distilled water and ethanol, and oven-dried at 60°c for 4 hours. x-ray diffraction (xrd) measurements were performed on a bruker axs d8 diffractometer with cu-kα radiation (40kv, 20ma). the morphologies of omc and ag/omc were observed on a jeol jem-1400 (100kv) instrument. nitrogen adsorption and desorption isotherms were conducted on a quantachrome autosorb-1 system. samples were degassed at 300°c for 5 hours. total pore volume (vtotal) was calculated at a relative pressure (p/po) of 0.995. the brunauer-emmett-teller equation was used to determine the specific surface area (sbet). the average pore size (daverage) was obtained from 4vtotal/sbet. the ag content in ag/omc was analyzed with a shimadzu aa6650 atomic absorption spectrophotometer (aas). the antibacterial activity of ag/omc was investigated on staphylococcus aureus using two methods: agar dilution and broth dilution. for the agar dilution method, the bacterial strains were grown in luria-bertani (lb) medium (peptone 10g/l, yeast extract 5g/l, and nacl 10g/l) until a density of 10 8 cfu/ml was reached (optical density of 0.5 at 600nm). the suspension was then diluted 10 times to obtain a density of 10 7 cfu/ml. the bacteria were inoculated on agar plates with different ag/omc concentrations. regarding the broth dilution method, 2ml of lb medium, 100µ l of bacteria, and different ag/omc concentrations were added into the test tubes. the mixture was shaken at 200rpm and 37°c. for both methods, bacterial growth and minimum inhibitory concentration (mic) were observed in 24 hours. iii. results and discussion small-angle xrd was used to determine the mesoporous structure of omc, as shown in figure 1. several reflections were found in omc. these reflections at 2θ=0.42, 0.66, and 0.82° correspond to the 10, 11, and 20 planes of the hexagonal (p6m) structure [21-22]. in addition, the high intensities of these peaks suggest that the mesoporous structure is relatively uniform. the tem images shown in figure 5(a) reveal that omc had a well-ordered mesoporous system with trenches running along the plane (110). compared with [21-22], this morphology of omc is fairly similar to that of fdu-15 and other 2d hexagonal (p6m) mesoporous materials. figure 2 depicts the nitrogen adsorption and desorption isotherms of omc. as p/po increased from 0.01 to 0.71, the adsorbed volume gradually increased, indicating that omc contained both micropores and mesopores. next, the adsorbed volume increased very slightly and nearly reached equilibrium at p/po, going from 0.71 to 0.99, suggesting that omc lacked macropores. notably, a hysteresis loop was long at p/po between 0.15-0.71 and wide at p/po between 0.36-0.62. this hysteresis loop might belong to type iv, according to the iupac classification [38]. additionally, the shape of the hysteresis loop may be associated with a particular porous structure. this one might be of the h1 type, which represents uniform, open-ended cylinder pores in a 2-d hexagonal structure [39-41]. the bjh pore size distribution shows that omc had relatively uniform mesopores at 3.2nm and certain micropores, possibly in the mesopore walls. table i also shows that omc possessed a high sbet=539m 2 /g and a large vtotal=0.44cm 3 /g. fig. 1. small angle x-ray diffraction of omc. (a) (b) fig. 2. (a) nitrogen adsorption and desorption isotherms and (b) bjh pore size distribution of omc. table i. properties of omc and ag/omc sample sbet (m 2 /g) vtotal (cm 3 /g) dpore (nm) daverage (nm) ag (wt%) omc 539 0.44 3.2 3.3 ag/omc 417 0.38 3.6 0.71 engineering, technology & applied science research vol. 13, no. 3, 2023, 10828-10833 10831 www.etasr.com nguyen et al.: preparation, characterization, and antibacterial activity of silver nanoparticle … the surface plasmon resonance of the silver nanoparticles allowed the exploration of their formation using uv-vis absorption in the 350-625nm range, as shown in figure 3. colloidal silver had a broad absorption band centered at approximately 418nm and a light yellow color. these observations demonstrated the successful generation of silver nanoparticles. moreover, the broadband signal revealed a high polydispersity of silver nanoparticles in size and shape. the detailed morphology of the silver nanoparticles was observed together with omc in the ag/omc sample. fig. 3. uv-vis spectroscopy of silver nanoparticle suspension and its yellow color. figure 4 shows the xrd pattern of ag/omc to determine its crystal phases. face-centered cubic silver planes (111), (200), and (220) were represented by distinct peaks at 2= 38.3, 44.5, and 64.2 o , respectively (jcpds card no. 04-0783). consequently, only silver nanocrystals were found on omc. theoretically, based on the amounts of agno3 and omc used, the maximum amount of ag in ag/omc was calculated to be 1.01wt%. the aas results, however, indicate that the silver content was only 0.71wt%. as a result, approximately 70% of the silver was coated on the surface of the omc, and the remainder was possibly removed during cleaning. fig. 4. x-ray diffraction of ag/omc. fig. 5. tem images of (a) omc and (b) ag/omg figure 5 shows tem images of omc and ag/omc samples. compared to omc, the presence of dark spots in the ag/omc showed the morphology of silver nanoparticles. in general, a wide size range of 20-50nm was observed for silver nanoparticles of various shapes. as only 0.71wt% of the silver nanoparticles were loaded on the omc surface, their density was relatively low. therefore, the stripe-like structure of the omc was still exposed. in addition, sbet and vtotal of ag/omc were 417m 2 /g and 0.38cm 3 /g, respectively, which were slightly lower than those of omc. these decreases were not significant, since silver nanoparticles could have low surface coverage. thus, the porosity of omc could be advantageous. staphylococcus aureus was used to assess the antibacterial activity of ag/omc using both agar and broth dilution methods. figure 6 and table ii show that the bacteria were not found on agar plates at ag/omc concentrations of 25.0 and 50.0μg/ml. certain bacteria growths were observed at low ag/omc concentrations of 0.10-12.5μg/ml. therefore, the mic for ag/omc was 25.0μg/ml. figure 7 and table iii engineering, technology & applied science research vol. 13, no. 3, 2023, 10828-10833 10832 www.etasr.com nguyen et al.: preparation, characterization, and antibacterial activity of silver nanoparticle … show the results of the broth method. after 24 hours of shaking, the bacteria still caused turbidity in tubes 4-10, showing that they survived at low ag/omc concentrations of 0.20-12.5μg/ml. the antibacterial ability of ag/omc became effective at higher concentrations of 25.0, 50.0, and 100μg/ml. the mixtures in tubes 1, 2, and 3 were transparent, showing that staphylococcus aureus could not grow. hence, both methods resulted in similar mics of 25.0μg/ml. the antibacterial ability of ag/omc (0.71wt% ag) against staphylococcus aureus was generally comparable to those of ag/activated carbon (0.92wt% ag, 10μg/ml) [42], ag/carbon dots (5.4wt% c and 94.6wt% ag, 20μg/ml) [43], and better than silver nanoparticles prepared by different routes (a broad range of 0.25-430μg/ml) [44]. the dispersion of silver nanoparticles on omc could prevent their ability to agglomerate, possibly resulting in their enhanced antibacterial activity. fig. 6. experimental image of the agar dilution method. table ii. results of agar dilution method control concentration (μg/ml) 50.0 25.0 12.5 6.25 3.13 1.56 0.78 0.39 0.20 0.10 c 1 2 3 4 5 6 7 8 9 10 + + + + + + + + + fig. 7. experimental image of the broth dilution method. table iii. results of broth dilution method control concentration (g/ml) 100 50.0 25.0 12.5 6.25 3.13 1.56 0.78 0.39 0.20 c 1 2 3 4 5 6 7 8 9 10 + + + + + + + + iv. conclusion this study successfully fabricated silver nanoparticlecoated ordered mesoporous carbon. at first, resol was used to synthesize omc using f127 as a soft template. omc was composed of a mesoporous p6m structure with a typical pore size of 3.2nm, sbet=539m 2 /g, and vtotal=0.44cm 3 /g. the surface of omc was then decorated with silver nanoparticles prepared from agno3 using glucose as a reducing agent and starch as a stabilizing agent. tem images showed that silver 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[44] e. o. mikhailova, "silver nanoparticles: mechanism of action and probable bio-application," journal of functional biomaterials, vol. 11, no. 4, dec. 2020, art. no. 84, https://doi.org/10.3390/jfb11040084. microsoft word etasr_v12_n3_pp8646-8651 engineering, technology & applied science research vol. 12, no. 3, 2022, 8646-8651 8646 www.etasr.com pahadasingh et al.: jaya algorithm-optimized load frequency control of a four-area … jaya algorithm-optimized load frequency control of a four-area interconnected power system tuning using pid controller sunita pahadasingh school of electrical engineering kalinga institute of industrial technology deemed to be university, bhubaneswar, odisha, india spahadasingh@gmail.com chitralekha jena school of electrical engineering kalinga institute of industrial technology deemed to be university, bhubaneswar, odisha, india chitralekha.jenafel@kiit.ac.in chinmoy kumar panigrahi school of electrical engineering kalinga institute of industrial technology deemed to be university, bhubaneswar, odisha, india panigrahichinmoy@gmail.com bibhu prasad ganthia electrical engineering department indira gandhi institute of technology sarang, odisha, india jb.bibhu@gmail.com received: 8 march 2022 | revised: 26 march 2022 and 30 march 2022 | accepted:1 april 2022 abstract-this study examined the design of a load frequency control (lfc) component in a four-area interconnected power system. lfc maintains the frequency of a power system within a prescribed limit. various controllers for the lfc of a power system have been proposed. the pid controller is a classical approach to lfc. a pid controller that uses a filter in the derivative part amplifies and smooths out the high-frequency noise. the selection of the appropriate optimization method to tune controller gains plays a vital role for lfc. in this work, the pid controller was optimized using the particle swarm optimization (pso) and the jaya optimization methods and was simulated in matlab-simulink. after studying and comparing the results, it was concluded that the pid controller using the jaya algorithm provided better lfc in terms of system settling time, overshoot, undershoot, and performance index compared to other optimization methods. keywords-load frequency control; agc; tie line; pidn; pso; jaya i. introduction an electric power system is a sequential arrangement of components to generate, transmit, distribute, and utilize power while continuously protecting it [1]. a power system has two important parameters that need to be constantly monitored and corrected: voltage and frequency. a generator generates power at some voltage and frequency, and these parameters should be controlled when there is a mismatch between active or reactive power generation and demand [2]. there are basically two methods to perform such control. when the active power demand is not equal to the active power generation, the frequency should be controlled, and when the reactive power demand is not equal to the reactive power generation, the voltage should be controlled [3]. control of voltage and frequency can be performed in two ways, which are the primary and secondary control mechanisms. the primary control mechanism examines the aspects of generation, as generation remains constant most of the time while demand varies [5]. in the primary control mechanism, the automatic generation control (agc) has to match the demand by varying the generation. but in emergency conditions, where it is not possible to control generations, the load should be controlled, which is known as the load side management [6]. agc can control voltage as well as frequency, i.e. load frequency control plus excitation control [7]. in agc, there is a generator that generates active power �� and reactive power �� . the generator gets input power from a turbine, and the turbine gets input power from the boiler [8]. while the steam comes from the boiler, there is a governor valve placed in the boiler to control the steam. when the active power is delivered to the bus, there is a comparator that receives and senses the frequency �� coming from the generator [9]. the comparator has a reference frequency ����, which has to be maintained, and if there is any difference between �� and ����, there will be an error �� which will be operated by the generator valve. this whole closed loop is the lfc [10]. ii. interconnected system the operation of more than one interconnected areas is known as an interconnected system or power pool or pool operation [12]. under normal operating conditions, each control area carries its own load and each control area adopts beneficial regulating and control strategies. these are two basic operating principles of a multi-control area system [11]. unlike a small system, where a sudden change in load causes a large corresponding author: bibhu prasad ganthia engineering, technology & applied science research vol. 12, no. 3, 2022, 8646-8651 8647 www.etasr.com pahadasingh et al.: jaya algorithm-optimized load frequency control of a four-area … frequency drop and could result in a system blackout, the interconnected systems don’t have these problems. in an interconnected power system, a sudden change in load causes a large frequency drop [13]. peak demands occur at various hours of the day in various areas of an interconnected system, so the ratio of peak to average load is smaller than that of an individual load. a control area in an interconnected system is characterized by the same frequency throughout, and the frequency deviations in different areas are represented as ∆ 1, ∆ 2, ∆ 3,… in an interconnected system, each area has a generator, a speed governing system, and a turbine. each area has three inputs, i.e. the controller input ( ∆���� ), load distribution ∆���, and tie-line power error (∆����� [14]. each area has two outputs, which are the generator frequency (∆ ) and the area control error (ace), which is the signal fed into the integrator: ��� � �∆ � ∆���� (1) where b is the frequency bias parameter. fig. 1. simulation model of four area power system. iii. pid controller with derivative filter when an interconnected or micro-grid power system is subjected to a change, it is very crucial to adjust the gain parameters of the pid controller [15]. as the pid controller often ignores the noise and non-linear effects, most of the time it does not work properly in practical problems. for this reason, a first-order filter is put on the derivative term to tune it [16], as it reduces the high-frequency noise and smoothes it out, so chattering due to noise does not occur and the derivative will not reduce the high-frequency noise [17]. the transfer function of the pid controller with derivative filter (pidn) is given as: � ���� � �� � �� � � � � � � ! " # ! $ � (2) fig. 2. simulink model of pidn controller. iv. particle swarm optimization method in pso, a particle is each member of a population, called a swarm. each particle has a velocity in a given direction [18], similar to the speed of a bird in the direction of food. each particle searches for the optimal value by an updating generation (iteration). in each iteration, every particle is updated by following the two best values. the best one is the best solution (fitness), while the second best is tracked by the pso optimizer. after finding the two best values, the velocity and position have to be updated for each particle, using: %� �#� � %� � � &� � ∗ ( (3) &)#� � � *&) � � +�,� %�-.(� � / %� �� � +0,0 1�-.(� � / %� �� (4) where xbest is the best particle position and gbest is the best global position. the best global position is the main strategy that all birds follow because this is the position of the bird closest to the food. the parameter w is the inertia weight. this is the main key factor, as it has the major role to change the position of each particle in the search space, from the previous position to a new one by updating velocity. +�, +0 are two positive constants, and ,�, ,0 are two random parameters within [0, 1]. the current position can be updated by adding the velocity v to the old position: �,-.-2( � 345 73.8(832� &-43+8(9 &� (5) the main aim of the pso algorithm is to follow the bird which is closest to the food. its main steps are given below: • step 1: initialize the parameters and the population. at first, initialize the position %� and velocity &� randomly for each particle. • step 2: compute the fitness value � %� �� of each particle, and choose the particle with the best fitness value gbest. engineering, technology & applied science research vol. 12, no. 3, 2022, 8646-8651 8648 www.etasr.com pahadasingh et al.: jaya algorithm-optimized load frequency control of a four-area … • step 3: update the position and velocity of each particle, by (3) and (4). • step 4: check again the fitness value � %� �� and then find again the best global gbest. • step 5: update ( � ( � 1. • step 6: the output comes as gbest and %� � fig. 3. flowchart of pso algorithm. v. jaya optimization technique jaya is a specific parameter-less algorithm. this algorithm was formulated to solve various constrained or unconstrained optimization problems. its concept is based on the fact that the solution for a given particular problem should move towards its best solution, as its major objective is victory, meaning that it should avoid the worst solution [19, 20]. jaya has some control parameters, such as population size and the number of generations. however, unlike other algorithms, jaya does not have any specific parameters. for example in pso, the inertia coefficient w and +�, +0, ,�, and ,0 have to be updated. but in the case of the jaya algorithm, such specific parameters are not required to obtain the optimal solution. the terms used in the jaya algorithm are iteration, design variable, candidate solution, best and worst values for the solution, modified solution, and update solution. the jaya algorithm can be described as follows: • let � %� be the objective function • minimize/maximize � %�: 4� : %; : <;, j=1,2,3…m • at any iteration t, assume there are m design variables and n candidate solutions. • for n values, o � %�=-.( is the best value of � %� o � %�*3,.( is the worst value of � %� • the fitness value can be computed from 2 >?. • @;,) is the value of the j th variable for the k th candidate. • @;,) � is the value of the variable during the t iteration. • @b��� is the best value of the variable. • @cd��� is the worst value of the variable. • the position update equation is given by: @e�c � @;,) � ,� @b��� / |@;,)|� / ,0 @cd��� / |@;,)|� • @e�c is the updated value of the variable @;,). • ,�, ,0 are two random numbers between 0 to 1. • ,� @b��� / |@;,)|� is the tendency of the solution to move closer to the best solution. • /,0 @cd��� / |@;,)|� is the tendency of the solution to avoid the worst solution. • concerning the t iteration: @e�c � � @;,) � � ,� @b��� � / |@;,) � |� / ,0 @b��� � / |@;,) � |� • now, a greedy selection has to be made, by comparing the obtained solution with the previous one, to check whether the obtained solution is better or not. • for minimization, if �e�c g �dh update the solution, otherwise not. • for maximization, if �dh g �e�c update the solution, otherwise not. • �e�c � � %e�c� is the fitness value at %e�c, and �� is the previous fitness value at %�. for minimization, if �e�c g �� then replace %� with %e�c and �� with �e�c . for maximization, if �e�c i fk then replace %�with %e�c and �� with �e�c. • the algorithm stops when the number of iterations reaches its maximum value. engineering, technology & applied science research vol. 12, no. 3, 2022, 8646-8651 8649 www.etasr.com pahadasingh et al.: jaya algorithm-optimized load frequency control of a four-area … fig. 4. flowchart of the jaya algorithm. vi. simulink results figure 5 shows the four-area model with a pid controller. figure 6 represents the jaya optimization in pid controller gain for the frequency control in each area of the agc. figure 7 represents the jaya optimization in pidn controller gain for the frequency control in each area of the agc. the controller block tuned the gains for the optimized data set for the jaya algorithm and the frequency of each area of the agc controlled concerning the demand of the grid. the deviation in frequency and the corresponding tie-line power were investigated. the value of the proportional, integral, and derivative constants, the derivative filter, and an objective function were obtained after optimizing using the pso and then the jaya methods. the efficacy of the jaya-based pid controller with the derivative filter was shown by comparing it with the pso simulation result. the changes in frequency and the corresponding tie-line deviations under load disturbance of 0.1p.u in four areas are shown in figures 8-11, for jaya, pso, and ga methods. the jaya method minimized the error during the controller objective function operation in the system model of agc. fig. 5. four area model with pid controller. fig. 6. jaya optimization with pid controller. fig. 7. pidn controller block for frequency control in agc. fig. 8. frequency response of area 1 using pid controller engineering, technology & applied science research vol. 12, no. 3, 2022, 8646-8651 8650 www.etasr.com pahadasingh et al.: jaya algorithm-optimized load frequency control of a four-area … fig. 9. frequency response of area 2 using pid controller. fig. 10. frequency response of area 3 using pid controller. fig. 11. frequency response of area 4 using pid controller. table i. tuned pid controller gains controller gains pso jaya kp1 0.0112 0.0218 ki1 6.5402 2.7319 kd1 3.7943 4.7272 itae1 4.7943 4.7272 kp2 0.2176 0.2762 ki2 3.2531 2.4062 kd2 5.7291 5.4251 itae2 5.7291 5.4251 kp3 0.0221 0.2373 ki3 4.6011 2.1165 kd3 4.1982 3.4231 itae3 4.1982 3.4231 kp4 0.0262 0.0254 ki4 4.7198 2.3068 kd4 3.6846 3.3076 itae4 3.6846 3.3076 vii. discussion from figures 8-11, it is clear that the settling time for the jaya optimization method is faster than for ga and pso optimizations. the frequency variation is less by 18-20% when using the proposed controller method. the gains were limited by the optimization method and the errors were reduced by 8% for area 1, and 11% for area 2. the frequency deviation error was reduced by 4% in area 3 and 6% in area 4. the pidcontrolled jaya optimization method improved the transient stability of the multi-area system by 14% of rated values. viii. conclusion this study used a pso and a jaya optimized pid controller in a four-area power system. the proposed method was compared to traditional control algorithms. a pid controller was used to examine the results of the proposed method. simulations were carried out in matlab-simulink. it was observed that the jaya tuned pid controller exhibited better performance than pso and ga in terms of settling time, peak overshoot, and undershoot. thus, the jaya-based pid controller helped maximize the power quality of the agc. further analysis of this topic can be carried out using different optimization methods. different controllers, like the fractional order proportional derivative controllers (pidn) (fopid), and fopid (1+pi) can be tested for improved alfc in a power system. appendix f = 50hz, b1 = b2 = b3 = b4 = 0.425pu mw/hz, pr = 1,000mw (rating), pl=1,500mw (nominal loading), r1 = r2 = r3 = r4 = 2.4hz/p.u. mw, �l� = �l0 = �lm = �ln =0.08, �o� =�o0 =�om =�on =0.03, ��� = ��0 = ��m =��n =20, k=-1, ��0=�0m=�mn=�n�=0.545. references [1] r. shankar, s. r. pradhan, k. chatterjee, and r. mandal, "a comprehensive state of the art literature survey on lfc mechanism for power system," renewable and sustainable energy reviews, vol. 76, pp. 1185–1207, sep. 2017, 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[16] t. lachumanan, r. singh, m. i. shapiai, and t. j. s. anand, "analysis of a multilevel voltage-based coordinating controller for solar-wind energy generator: a simulation, development and validation approach," engineering, technology & applied science research, vol. 11, no. 6, pp. 7793–7799, dec. 2021, https://doi.org/10.48084/etasr. 4489. [17] c. l. wadhwa, electrical power system, 7th edition. new delhi, india: new age international, 2017. [18] h. saarat, power system analysis. new delhi, india: wcb mcgrawhill, 1999. [19] b. p. ganthia, a. pritam, k. rout, s. singhsamant, and j. nayak, "study of agc in two-area hydro-thermal power system," in advances in power systems and energy management: etaeere-2016, a. garg, a. k. bhoi, p. sanjeevikumar, and k. k. kamani, eds. singapore: springer, 2018, pp. 393–401. [20] a. pritam, s. sahu, s. d. rout, s. ganthia, and b. p. ganthia, "automatic generation control study in two area reheat thermal power system," iop conference series: materials science and engineering, vol. 225, dec. 2017, art. no. 012223, https://doi.org/ 10.1088/1757-899x/225/1/012223. authors profile sunita pahadasingh is working on her ph.d. in the school of electrical engineering, kalinga institute of industrial technology, bhubaneswar, odisha, india. her research area is agc smart grids. chitralekha jena, is an assistant professor in the school of electrical engineering, kalinga institute of industrial technology, bhubaneswar, odisha, india. chinmoay kumar panigrahi, is a professor in the school of electrical engineering, kalinga institute of industrial technology, bhubaneswar, odisha, india. bibhu prasad ganthia is an assistant professor in the department of electrical engineering, indira gandhi institute of technology, sarang, dhenkanal, odisha, india. his research areas include renewable energy systems and power system control. microsoft word etasr_v12_n5_pp9178-9185 engineering, technology & applied science research vol. 12, no. 5, 2022, 9178-9185 9178 www.etasr.com gopan k & shree: implementation of a high power quality bldc motor drive using bridgeless dc to … implementation of a high power quality bldc motor drive using bridgeless dc to dc converter with fuzzy logic controller vishnu gopan k. department of electrical and electronics engineering coimbatore institute of technology, coimbatore tamil nadu, india gopan1vishnu@gmail.com j. devi shree department of electrical and electronics engineering coimbatore institute of technology, coimbatore tamil nadu, india devishreecit@gmail.com received: 20 july 2022 | revised: 28 july 2022 | accepted: 29 july 2022 abstract-electric motor drives based on electronic power converters having good power quality parameters are getting huge acceptance. conventional diode bridge rectifier (dbr) and dc to dc converter-based methods have become obsolete, as they provide low power quality indices which hamper the supply by introducing current harmonics and conduction losses. although there are many developments in motors and control strategies, the risk and complexity of such drives become bottlenecks in implementation. this study implemented a drive scheme with a brushless dc motor. the new improved bridgeless topology was modified with an advanced fuzzy logic controller to further improve its power quality and performance. due to low power, a high-speed application of brush less (bldc) motor was selected for the drive scheme. this combination could achieve almost unity power factor (upf) and significantly improve control compared to conventional topologies. a circuitwise analysis was conducted to design the converter's components. the modifications were elaborated through mathematical expressions, and the parameters of power quality were analyzed and validated. keywords-brush-less direct current motor (bldc); diode bridge rectifier (dbr); high-frequency transformer (hft); total harmonic distortion (thd); discontinuous inductor current mode (dicm); bridgeless dual cuk (bdc); fuzzy logic controller (flc); unity power factor (upf) i. introduction the need for quality ac supplies and their efficiency is becoming a primary concern in modern power electronics [1], especially in the development of various dc-dc and ac-dc converters. this paper discusses dc-dc converters, as they are more flexible and versatile in terms of power quality and efficiency. improved power quality is mandatory for electrical equipment nowadays by the international power quality (pq) standard iec 61000-3-2. this standard also stipulates high power factor and low total harmonic distortion (thd) of the ac main current for class-a applications (<600w, <16a) [2]. due to their advantages of high efficiency, high flux density per unit volume, low maintenance requirement, low emi problems, high ruggedness, and a wide range of speed control, brush-less dc (bldc) motors are recommended for many lowand medium-power drive applications [3]. bldc motors are used in numerous areas such as household applications [4], transportation (hybrid vehicles) [5], aerospace [6], heating, etc. this study implemented and evaluated a variety of power electronic circuits to drive a bldc motor. an ac supply is essential for domestic loads. conventionally, a diode bridge rectifier (dbr), followed by a filter capacitor is used for the generation of a dc supply. today, many applications continue to use them due to their simplicity of construction and costeffective production. the high value of the filter capacitor draws a high non-sinusoidal current from the supply. in addition, dbrs with their inherent flaw of high conduction losses reduce the efficiency of converter circuits, and increased harmonic levels cause a rise in the thd levels between 4565% [7]. many power factor correction (pfc) converters have been developed to reduce the thd levels to permissible limits and improve the power factor of the supply, and most of them serve their purpose on their performance levels. therefore, more reliable drive control is performed through the control of the dc link voltage by controlling the switches on the pfc converter side [8]. to implement such a control, the converter has to be chosen from an array of dc-dc converters divided into isolated or nonisolated and bridged or bridgeless topologies [9, 10]. moreover, it has to be decided in which mode the converter should operate to achieve unity power factor (upf). this study selected a cuk converter, after examining various topologies with different types of loads and applications of pfc converters, intending to improve the power quality of ac to dc conversion. this study also presents the bridgeless topology with a proposed modification. additionally, a fuzzy logic-based advanced linguistic controller was implemented for the bridgeless topology to further enhance the performance of the converter and improve power quality at the main supply. the simulated results along with their mathematical validation, were used to analyze the improvements. performance analysis and input power quality corresponding author: vishnu gopan k. engineering, technology & applied science research vol. 12, no. 5, 2022, 9178-9185 9179 www.etasr.com gopan k & shree: implementation of a high power quality bldc motor drive using bridgeless dc to … of the operation of the converter were used to conduct the harmonic analysis of the topology. as there are many speed control drive schemes for various applications, this study allowed the operation of a motor drive with quick response and very low speed variations from the reference value. moreover, the incorporation of flc into a bridgeless configuration further improved performance and power quality. ii. configuration for speed control, the selection of the front-end converter and its operation configuration are equally important to achieve a high power factor at the supply mains. the cuk converter was selected due to its many advantages [12]. there are multiple approaches for the conversion of ac input to variable dc for the drive scheme. a dbr followed by a high dc link capacitor was used, which due to its high losses was replaced by "dbr-power factor correction (pfc)" converter configuration. in such circuits, the speed control of the drive can be achieved in several ways. one way is to control the switching of the 6 individual switches of the motor-end voltage source inverter (vsi). due to the increased number of control switches and the high frequency of motor operation, it is not preferred due to high switching losses [8]. another solution could be a pfc converter to control the dc link voltage. the pfc converter can be controlled by 2 methods: a voltage follower or a current multiplier method [13]. these methods depend on which mode the pfc converters operate. this study discussed the 2 modes of operation and attempted to compare their results with the bridgeless topology. pid controllers were used for the three types of converters, using a linearized modeling technique to standardize the results. in the voltage follower approach [13], the converter operates in dcm and is further divided into dicm and dvcm where the respective inductor currents or capacitive voltages become discontinuous during a switching period of the converter switch [13]. the advantage of this mode is that it requires only one sensor for control. the need for 2 voltage sensors and 1 current sensor makes this multiplier method more complex [13]. in this configuration, the converter operates in ccm and ensures more robust control [14]. the configuration consists of a dbr followed by a power factor correction cuk converter designed to operate in ccm operation. the dc output of the converter is fed to the input side of the voltage source inverter that controls the speed of the bldc motor. even though both configurations have their advantages, the main drawback of lack of isolation between the highand lowfrequency switching parts hampers the smooth operation by introducing harmonics in the circuit. this reduces the converter's efficiency and the purported operation in power factor correction. the proposed configuration, shown in figure 1, resolves this inherent problem by providing high-frequency isolation [9]. this is done by providing 2 high-frequency transformers (hft) in the respective positive and negative side converters of the modified cuk converter topology. the modification of the proposed converter eliminates the need for a dbr and avoids any conduction losses. the converter operates in dicm, where the current through the output side inductor becomes discontinuous over a switching period. three converters were constructed and analyzed in matlab 2018 and their performance was compared during changes in speed conditions. fig. 1. proposed isolated coupled cuk converter-fed bldc motor drive iii. operation of the configuration the input side dbr was eliminated in the proposed converter-fed bldc motor drive. this was achieved by incorporating another cuk converter in parallel with the existing one so that one works in the positive half-cycle and the other in the negative half-cycle of the supply, by implementing a zero-crossing detector on the input side. another major advantage of this method was that the ac input and the output side bldc motor drive were completely isolated with the help of an hft. hence, the speed control of the drive was hasslefree and the amount of noise present in the control signals could also be reduced. the converter was designed in such a way that the current through the output inductors lo1 and lo2 becomes discontinuous over a switching period in either half cycle of the input supply, as shown in figure 2. therefore, the converter operated in discontinuous inductor current mode engineering, technology & applied science research vol. 12, no. 5, 2022, 9178-9185 9180 www.etasr.com gopan k & shree: implementation of a high power quality bldc motor drive using bridgeless dc to … (dicm) [15]. even though there are many categories of discontinuous conduction modes, such as dicm on input, dicm on output, and dcvm [16], applying dicm on the output side inductor was simpler and lowered harmonics. several advantages can be gained by operating the rectifier in dicm, such as a natural near-unity power factor and at zero current the power switches are turned on and the output diodes are turned off. (a) (b) (c) (d) fig. 2. operating modes of the proposed converter at different intervals of the switching period during the positive half cycle: (a) switch closed, (b) switch open – inductor discharging, (c) switch closed – inductor fully discharged, and (d) associated waveforms. in the first mode, switch sw1 is turned on and the inductors li1, lo1, and magnetizing inductance lm1 start charging. the capacitor ci1 charges lm1, and co1 delivers dc link voltage. in the second mode, the switch is being turned off, inductors li1 and lo1 discharge thereby charging ci1 and co1, and the magnetizing inductance lm1 discharges through cd. in the third mode, the output side inductor lo1 is completely discharged and the input inductor li1 and the magnetizing inductance of hft lm1 continue to discharge. figure 3 shows the negative half operation of the converter. the converter operates in such a way that the input side energy storage components remain in non-conducting mode and the output side components remain non-discharged. the converter is designed so that the positive sinusoidal input from the ac supply at the fundamental frequency of 50hz is split into a large number of cycles of operation of the upper cuk converter switch. (a) (b) (c) (d) fig. 3. operating modes of the proposed converter at different intervals of switching period during the negative half cycle: (a) switch closed, (b) switch open – inductor discharging, (c) switch closed – inductor fully discharged, and (d) associated waveforms. a. motor speed control an electronic commutation of the bldc motor includes the proper switching of the voltage source inverter (vsi) to engineering, technology & applied science research vol. 12, no. 5, 2022, 9178-9185 9181 www.etasr.com gopan k & shree: implementation of a high power quality bldc motor drive using bridgeless dc to … draw a symmetrical dc from the dc link capacitor for 120° [17] and placed symmetrically at the center of the back electromotive force (emf) of each phase. a hall-effect position sensor was used to sense the rotor position on a span of 60°; which is required for the electronic commutation of the bldc motor [18]. the front-end converter was controlled by feeding back the dc voltage. the control scheme was comprised of feedback dc voltage, reference voltage generator, and pwm generator. the reference voltage was obtained by multiplying the reference speed by the motor speed constant kv: ��� ∗ � �� . this reference voltage was compared with the actual dc link value of the converter and the error was used for pwm generation in 3 different ways for the front-end converter switches to obtain speed control [19]. table i illustrates the switching signals to be sent to the phase 3 vsi. the controller logic was designed to send the on pulses to the respective switches following the rotor position in a single direction. table i. switching states for the vsi angular placement state of switches t1 t2 t3 t4 t5 t6 na 0 0 0 0 0 0 0-60 0 0 0 1 1 0 60–120 0 1 1 0 0 0 120–180 0 1 0 0 1 0 180–240 1 0 0 0 0 1 240–300 1 0 0 1 0 0 300–360 0 0 1 0 0 1 na 0 0 0 0 0 0 iv. design the basic cuk converter is shown in figure 4. fig. 4. cuk converter circuit. for this cuk converter, the output equation is given as [21]: vdc= d 1-d vin in the case of the shown converter topology, the negative output at the output changes to a positive value by interchanging the terminals. in this type of arrangement, the average ac voltage applied across the input side can be obtained as: ��� �� � |�� ��� ��| � �230√2 ��� 340��� (1) using the following parameter values: vmin=100v, vmax=200v, vsmin=170v, vsmax=270v, pmax=250w, and pmin=125w. the selected switching frequency fs was 20khz for the operation of all 3 converters. a. design of the bdc converter the output voltage is obtained as [21]: ��� � ������ � !�� ��� (2) transformer ratio, ������ was taken as 0.5. let d(t) be the instantaneous value of the duty ratio, then we have [16]: " �� � #$%&�� ��' (#)* +�,#$% � #$%&�� ��' (∗|#)* -�� .+�|,#$% (3) instantaneous power is given by: /� � 0 1234#$%_234 ��� 6 (4) 1) inductor design [20]: 7� � 7�8 � #)* +�.� +�9:)* +�;< � 9.;< & #<� 1) ( & #$% �#)* +�,#$%( (5) where η is the input current ripple, which was taken as 50%, and n is the turns ratio of the hft, taken as 1:2. 7= � 7=8 � &#< � 1) ( #$% 8#)* +�;< & #$% �#)* +�,#$%( (6) both equations are used under the assumption that pi=pi-max and vin= √2 vs_min.the value of the input side inductor was 7mh. the value of the output side inductor was obtained as 1.502mh for vdc=200v, and 0.546mh for vdc=100v, so a value lower than 0.546mh should be chosen. the selected value selected was 0.1mh. the magnetizing inductances are [16]: 7� � 7�8 � &#< � 1) ( >.;< & #$% �#)* +�,#$%( (7) where ς is the permitted ripple current on the output side, taken as 50%, were obtained as 7mh. 2) capacitor design ?� � ?�8 � �.1)@.√8#<.;<. �√8#<,#$%� (8) where ci1=ci2=220nf. ?= � ?=8 � 1)a.#$%.;< �√8#<,#$%� (9) where co1=co2=2.2μf. the output side dc link capacitor was given as: ?� � :$%8.b#$% � & 1) #$%( 8..c.#$%� (10) where k is the input side ripple voltage (25%), x is the ripple voltage at the converter side (10%), and ρ=δvdc is the permitted output ripple (5%). the obtained value of cd was 1000μf. 3) filter design a low pass lc filter was used to avoid higher order harmonics in the supply system. the maximum value of the filter's capacitance was given by [13]: engineering, technology & applied science research vol. 12, no. 5, 2022, 9178-9185 9182 www.etasr.com gopan k & shree: implementation of a high power quality bldc motor drive using bridgeless dc to … cmax= im ωlv m tan θ = √2 pmax / vs ωl√2 vs tan θ (11) where θ is the displacement angle between the fundamental value of supply voltage and supply current, taken as 2°. the maximum value of the filter capacitor was calculated using (11) at 574.4nf and was selected as 330nf. this value was selected for all 3 configurations as there is no variation in input voltage, and the capacitor always acts across one-half of the input supply at any given time. the value of the filter inductor was designed by considering the source impedance ls as 4-5% of the base impedance. hence, the additional value of required inductance was given as: 7; � 7def + 7=> 7def = 7; − 7 7def = j k� ;l��m − 0.025 & .o( & #<� 1p ( (12) where fc is the cut-off frequency, selected such that fl<fc<fs. therefore, fc was taken as fs/10. hence, the value of filter inductance was calculated using (20) as 3.77mh. table ii shows the motor operation details of the proposed topology. table ii. motor specifications number of poles 4 rated power 251.32 w dc rated voltage 200v rated torque 1.2nm rated speed 2000rpm back emf constant, kb 78v/krpm torque constant, kt 0.74nm/a per phase resistance 14.56ω per phase inductance 25.71mh moment of inertia, j 1.3×10 −4 kgm 2 v. fuzzy logic controller the conventional pid controller has the inherent flaw of the limitation of operation range as it can only be tuned for a particular range or input-output combinations. the flc [22], which uses linguistic variables to specify the wide range of inputs as its membership functions (mfs) can solve this problem of the pid controller and can operate effectively under the complete specified range of the dc voltage of the converter. the voltage range is split into segments and each segment is provided as a mf for the reference voltage and the actual output variables. these variables are considered the input variables of the flc. table iii and figures 5 and 6 illustrate the association of mfs to the two inputs to the flc. from the inputs, flc calculates the error and, based on the rule base shown in table iv, it provides the apt duty ratio of the switching pulse, which is to be given to the converter switches. duty ratios, ranging from 0 to 0.5, are divided into flc mfs for the defuzzified output variable, as shown in figure 7. table v shows the fuzzy rule base defined for the flc [23]. the selection of an appropriate output for the converter pulse duty ratio is decided on the error between the reference and the actual dc output voltage of the converter. the weightage and the point of selection of the exact value are decided based on the centroid method of flc. fig. 5. input 1 (ref. voltage) membership functions. fig. 6. input 2 (actual voltage) membership functions. fig. 7. de-fuzzified output (duty ratio output) membership functions. table iii. flc input mfs and range mf range of voltage l5 -20 to 20 l4 0 to 40 l3 20 to 60 l2 40 to 80 l1 60 to 100 m 80 to 120 h1 100 to 140 h2 120 to 160 h3 140 to 180 h4 160 to 200 h5 180 to 220 table iv. fuzzy rule base input 1 mfs in p u t 2 m f s l5 l4 l3 l2 l1 m h1 h2 h3 h4 h5 l5 zer zer zer zer zer zer zer zer zer zer zer l4 l2 l3 l3 l4 l4 zer zer zer zer zer zer l3 l2 l2 l2 l2 l4 l4 l4 l4 l4 l4 zer l2 l1 l1 l1 l1 l2 l3 l4 l3 l4 l4 l4 l1 mid mid l1 l1 l1 l1 l2 l2 l4 l3 l4 m h1 h1 h1 h1 h1 mid l1 l1 l1 l2 l3 h1 h1 h1 h1 h1 h1 h2 mid l1 l1 l1 l2 h2 h1 h1 h1 h1 h1 h2 h2 mid mid l1 l1 h3 h2 h2 h1 h1 h1 h1 h1 h2 h1 mid l1 h4 h2 h2 h2 h2 h2 h2 h2 h2 h2 h1 mid h5 h2 h2 h2 h2 h2 h2 h2 h2 h2 h1 h1 vi. results and discussion the complete simulation schematics of the bridgeless dual cuk converter controlled by the flc are shown in figure 8. as can be noted, the bdc cuk converter has a significant advantage over the conventional bridge-type converters. the flc converter performs efficiently with a fast response to inputs and gives good power quality indices. figure 10 shows its output voltage response. as the flc is mainly employed to improve power quality, the input side power quality parameters are very important. engineering, technology & applied science research vol. 12, no. 5, 2022, 9178-9185 9183 www.etasr.com gopan k & shree: implementation of a high power quality bldc motor drive using bridgeless dc to … fig. 8. simulation diagram of the bdc converter with flc. figure 9 shows the pure sinusoidal waveform of the supply current in the flc-based converter compared to the partially sinusoidal current profile in the pid controller one. fig. 9. rotor speed, source voltage, source current, input inductor current, and output inductor current. fig. 10. rotor speed output for the step reference voltage input. a. thd analysis the harmonic content in the supply current can be determined by finding the thd value. this value was computed taking into account the percentage values of individual harmonic current components for the fundamental value. also, some dc components may be present in the circuit due to switching losses or emi, which should also be considered. by default, it was assumed to be 1%, unless it is present significantly. thd is the ratio of the root mean square sum of the individual harmonic components to the fundamental value. either the percentile or the actual value of harmonics can be used. this study used harmonics as the percentage of the fundamental. thd %�� u i22+i32+ i42+…+in2 �i12 z100 %�+dc component %� (13) the dc component was not present in the harmonic analysis, so it was assumed to be 1%. from table v we get: thd %�= uab.82+1.22+ 0.82+c.d2 + 0.32+ 0.22+ 0.152 + 0.12+ 0.152e 100 2 ×100 thd(%) was 4.58%, which is close to the simulated value (3.98%). the analysis of the thd content on the supply current, shown in figure 11, shows that the bdc converter with advanced flc significantly improved the power quality of the input supply. it can be noted that the thd levels significantly dropped to 3.98% compared to conventional converter topologies [10]. table v. current harmonics in bdc converter with fuzzy logic controller harmonic order value (% of fundamental) 3 3.2 5 1.2 7 0.8 9 0.6 11 0.3 13 0.2 15 0.15 17 0.1 19 0.15 dc component 1% b. power factor the bdc topology achieved a very high power factor, almost close to unity (0.99), compared to the other two conventional topologies with pfs of 0.95 and 0.97 respectively [10], as shown in figure 12. compared to conventional topologies, the proposed bdc scheme has the advantage of a engineering, technology & applied science research vol. 12, no. 5, 2022, 9178-9185 9184 www.etasr.com gopan k & shree: implementation of a high power quality bldc motor drive using bridgeless dc to … wide operating range because of the reduced stress on the operating components. due to the single half-cycle specific operation of the converter, the bdc method used relatively fewer components at a time with minimal power rating. fig. 11. thd analysis. fig. 12. results of power factor analysis. c. efficiency the performance of the three converters was examined to analyze their operation efficiency. as the vsi-fed bldc motor part is the same for the three converters, the back end of the pfc converter was used to calculate the output power. figure 13 shows that due to the absence of a current controller and the inherent conduction loss of the rectifier diodes, the overall efficiency was very low, ranging from 42.7% to an underwhelming 62.7%, even at the motor-rated voltage. the current multiplier method, due to the incorporation of the current controller and amidst the heavy conduction loss in the dbr, controlled the power loss and presented a much more efficient operation. the efficiency values were 51% at 40v dc and ranged to a maximum of 73.2% at the rated motor voltage of 200v dc. the proposed design rectified the issues of the previous topologies. the conduction loss is not a concern, as the dbr was eliminated, and the converter operation used a single sensor control for the same reason. the dcm operation resulted in a better power factor, and the power transfer was smooth due to the coupled configuration of the cuk converter. the efficiency of the converter was in the range of 88.7-96.1% at the rated motor voltage. moreover, the life of the switching components can be extended because of the reduced transient time when the converter switches are subjected to switching stress due to the single half-cycle operation of each converter. fig. 13. comparison of converter efficiency. vii. conclusion the power quality of a new bldc motor-based speed control drive was analyzed and the results showed that the proposed design attained significantly better power quality parameters compared to the conventional topologies [10]. the power factor and thd of conventional cuk and proposed bridgeless dual cuk converter topologies were analyzed using the simulated results for varying input conditions. the proposed method was portrayed to assert the merits of the bdc converter in attaining a power factor nearly unity for the drive. the fuzzy logic controller-based control strategy of the converter enhanced the performance of the modified cuk converter and helped to achieve a very low thd value. the method was simulated using matlab 2018 based on varying input conditions. the analysis proved experimentally that the bdc design was more efficient and the flc-based bdc converter was the most efficient among other topologies and is suitable for modern variable speed electric drives that employ bldc motors. the reduction of current sensors, one-cycle operation, and low current stress on the power electronic switches make it suitable for long-duration operation. therefore, this topology is a notable choice for high-power motor drive schemes used in household and industrial equipment. references [1] v. v. prabhakaran and a. singh, "enhancing power quality in pvsofc microgrids using improved particle swarm optimization," engineering, technology & applied science research, vol. 9, no. 5, pp. 4616–4622, oct. 2019, https://doi.org/10.48084/etasr.2963. 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[14] l. kathi, a. ayachit, d. k. saini, a. chadha, and m. k. kazimierczuk, "open-loop small-signal modeling of cuk dc-dc converter in ccm by circuit-averaging technique," in 2018 ieee texas power and energy conference (tpec), college station, tx, usa, oct. 2018, https://doi.org/10.1109/tpec.2018.8312045. [15] s. buso, g. spiazzi, and d. tagliavia, "simplified control technique for high-power-factor flyback cuk and sepic rectifiers operating in ccm," ieee transactions on industry applications, vol. 36, no. 5, pp. 1413– 1418, sep. 2000, https://doi.org/10.1109/28.871291. [16] v. vlatkovic, d. borojevic, and f. c. lee, "input filter design for power factor correction circuits," ieee transactions on power electronics, vol. 11, no. 1, pp. 199–205, jan. 1996, https://doi.org/10.1109/63. 484433. [17] kanaiya g bhatt and yogesh parmar, "implementation of brushless dc motor speed control on stm32f407 cortex m4," international journal of engineering trends and technology ijett, vol. 53, no. 3, pp. 118– 123, nov. 2017, https://doi.org/10.14445/22315381/ijett-v53p221. [18] jagraj singh and manpreet singh, "comparison and analysis of differenttechniques for speed control of brushlessdc motor using matlab simulink," international journal of engineering trends and technology ijett, vol. 38, no. 7, pp. 373–379, aug. 2016, https://doi.org/10.14445/22315381/ijett-v38p267. [19] p. yadav, r. poola, and k. najumudeen, "high dynamic performance of a bldc motor with a front end converter using an fpga based controller for electric vehicle application," turkish journal of electrical engineering and computer sciences, vol. 24, no. 3, pp. 1636–1651, jan. 2016, https://doi.org/10.3906/elk-1401-289. [20] k. gunasekaran and s. v. thazhathu, "improved resettable integrator control for a bridgeless interleaved ac/dc converter," turkish journal of electrical engineering and computer sciences, vol. 25, no. 5, pp. 3578–3590, jan. 2017, https://doi.org/10.3906/elk-1512-86. [21] muhammad h. rashid, power electronics: circuits, devices, and applications, second edition. englewood cliffs, nj, usa: prentice hall, 1993. [22] o. a. heubo-kwegna, "fuzzy logic versus classical logic: an example in multiplicative ideal theory," advances in fuzzy systems, vol. 2016, dec. 2016, art. no. e3839265, https://doi.org/10.1155/ 2016/3839265. [23] r. o. reddy, s. kautish, v. p. reddy, n. s. yadav, m. m. alanazi, and a. w. mohamed, "effects of integrated fuzzy logic pid controller on satellite antenna tracking system," computational intelligence and neuroscience, vol. 2022, mar. 2022, art. no. e7417298, https://doi.org/ 10.1155/2022/7417298. microsoft word etasr_v13_n1_pp10158-10164 engineering, technology & applied science research vol. 13, no. 1, 2023, 10158-10164 10158 www.etasr.com saoudi et al.: processor-in-the-loop validation of an observer current-based dead-beat control for a … processor-in-the-loop validation of an observer current-based dead-beat control for a single-phase ups inverter mohammed saoudi laboratory of electrical engineering (lge), university of m’sila, algeria mohammed.saoudi@univ-msila.dz (corresponding author) hani benguesmia laboratory of electrical engineering (lge), university of m’sila, algeria | department of electrical engineering, faculty of technology, university of m’sila, algeria hani.benguesmia@univ-msila.dz aissa chouder laboratory of electrical engineering (lge), university of m’sila, algeria | department of electrical engineering, faculty of technology, university of m’sila, algeria aissa.chouder@ univ-msila.dz received: 25 november 2022 | revised: 29 december 2022 | accepted: 3 january 2023 abstract this paper presents a dead-beat control algorithm for uninterruptible power supply (ups) applications of single-phase inverters. the proposed control method requires the measurement of capacitor current and output voltage in order to keep the output voltage sinusoidal ensuring high dynamic performance even under load changes. the dead-beat controller optimizes the behavior of the system by eliminating the error between the output and the reference voltage without increasing the number of current sensors, which are costly, and eliminates load voltage distortions and restores the system state in the event of external shutdown-loop road interference. in this paper, we propose a capacitor current estimation based on the luenberger observer. processor-in-the-loop (pil) is a test method that allows us to create and evaluate controllers by running built-in c code on the dsp scheduled for the controller during simulated psim power phase control. it can be seen that the simulation results match the pil test results, which proves the validity of the proposed controller. keywords-dead-beat control; single-phase inverter; pwm; luenberger observer; pil; dsp; ccs i. introduction using the output lc filter to control the inverters is important in applications such as distributed generation, renewable energy-based island applications, and uninterruptible power supplies (upss) [1-3], where high quality voltage is required. the main control objective of ups is to adjust the output voltage in the presence of parameter uncertainty and disturbance, and its characteristics depend on the quality of the output voltage. disturbances from various loads, uncertainty due to inductive loads, non-linear loads, and model mismatches can lead to poor output voltage tracking and high total harmonic distortion (thd). the effects of noise and uncertainty must be minimized to achieve excellent voltage performance. any ups system has two operating modes: backup mode and bypass mode. ideally, a ups should be able to deliver a regulated sinusoidal output voltage with low thd during the two modes and includes a dead-beat controller [410]. in [6, 11], the dead-beat controller is used with the disturbance observer for proper response and robust controlled performance. in [12-14], the pwm technique using a modified dead-beat controller is explained clearly, but the pwm pattern in the presence of load uncertainty is not detailed. in [15], the dead-beat control for power converters using fractional-order time delay compensation is defined as an effective and powerful delay compensation approach that has been applied in various control systems. in [16-21], single-phase inverter's deadbeat-based proportional-integral (pi) controller was proposed and comparisons with conventional control techniques were made. however, the implementation of the deadbeat controller is very complicated, and due to the engineering, technology & applied science research vol. 13, no. 1, 2023, 10158-10164 10159 www.etasr.com saoudi et al.: processor-in-the-loop validation of an observer current-based dead-beat control for a … difficulty of its design, it is not suited for low cost implementations. however, the technique uses relatively higher energy losses. the main purpose of control is to obtain a nearly sinusoidal output voltage across the output capacitor of the lc filter. dead-beat control is the most attractive control method in discrete time systems because it can reduce the error between the reference and measured values as long as the number of samples goes to infinity and the error goes to zero, giving the inverter a fast dynamic response. the inverter's output voltage is achieved with very low thd. dead-beat control is sensitive to variations of the filter parameters, even when the load fluctuates. the proposed dead-beat control system can work stably when the load variation is within the allowable range. in order to decrease the number of sensors, an observer to estimate the capacitor current is proposed. however, conventional dead-beat controllers suffer from two delays, the first is inherent to the dead-beat control algorithm and causes a steady-state error [12], and the second arises when the psim simulates the algorithm after ccs builds it and installs it on a dsp-based platform. it has an impact on the system's stability and causes ripples and phase shifts in the output current. the dead-beat response has some advantages:  zero steady-state error.  shortest rise time.  minimum settling period.  an over/undershoot of less than 2%.  very high control signal output [16]. ii. system description the proposed single-phase inverter is shown in figure 1 and consists of an h-bridge inverter connected to the load through lc filtering. insulated gate bipolar transistors (igbts) are chosen as the switching elements to perform energy transfer and power conversion. lc filters are used to filter higher harmonics before the load. the capacitor voltage and current are generated by the luenberger observer. this system performs better with imbalanced loads and is more adaptable when it comes to working conditions. fig. 1. basic scheme of the proposed system. iii. the considered system the single-phase inverter consists of two arms in a halfbridge. if the power switches s1 and s'1 are supposed to be perfect (and are negligible), the system (source-inverter-filtercharge) is then represented by the second-order linear model of figure 2. fig. 2. basic scheme of the proposed system. this system's representation in state space is given by: ( ) ( ) ( )x t ax t bu t ɺ (1) where 1 2 ( ) ( ) ( ) x t x t x t        . ( )x t is the state vector, such that: 1 2 ( ) ( ) ( ) ( ) c c x t v t x t v t    ɺ (2) according to the second-order linear model of the halfbridge inverter, applying the laws of kirchhoff and calculating the matrices a and b, we get: int ( ) ( ) ( )l cv t v t v t  (3) int ( ) ( ) ( ) ( )c c c l v t l c v t v t v t r   ɺɺ ɺ (4) by (4) we have: 1 2 2 int 2 1 ( ) ( ) 1 1 1 ( ) ( ) ( ) ( ) ( )c x t x t x t v t v t x t x t lc rc lc        ɺ ɺ ɺɺ (5) so: 0 1 1 1a lc rc          and 0 1b lc          . figure 3 shows the waveforms of  invv t during a sampling period te, where invv is the output voltage of the inverter and has two values, +e and –e. engineering, technology & applied science research vol. 13, no. 1, 2023, 10158-10164 10160 www.etasr.com saoudi et al.: processor-in-the-loop validation of an observer current-based dead-beat control for a … fig. 3. two-level pwm pattern. the discrete-time system equation of the two-lever switching patterns is [14]:   0 0 int ( ) exp ( ) ( ) exp ( ) ( ) x t a t t x t a t b v d         (6) thus, the discrete state equation from t0 to t1and t2 to t3 is: int [ ( 1) ] exp ( ) exp ( ), ( ) ( ) 2 e e e x k t at x k t a be t k e t k v               (7) we will find from (8) the value of the duration δt that we must apply at all times to generate the control signals of the switches. δt(k) equals to the pulse-width in the k th sampling interval. assuming 2t lc , the exponential quantities in (7) are approximated using the power series expansion: 11 12 21 22 2 2 2 2 2 2 2 exp[ ] 1 2 2 1 1 1 1 ( ) 22 k k a at t t t lc rc a t t t lc rc lcrlc r c                              (8) in order to improve this problem, a predictive dead-beat control method is proposed, in which the control input at the k th sampling time is predicted by using the system values at the (k-1) th sampling time. pwm modulation signal, i.e. the reference output voltage of the inverter, calculated by the reference voltage vref, the actual capacitor current ci , and the output load voltage of the inverter vch at the (k-1) th sampling time calculated with the reference voltage can be described as: 11 12 1 21 22 2 ( 1) ( ) ( ) g x k x k e t k g                    (9) the first line of (9) gives us the recurrent expression of the sampled output voltage: 11 1 12 2 1 1 ( ( 1) )reft v k x x g e       (10) iv. state observer in the control system, observers can replace sensors. we can't estimate the state variables for which the observer is utilized. for the proposed control, capacitor current measurement is necessary and the principle of the observer is combining the feedback signal measured with the known components of the control system. the plant's behavior may be predicted with more precision than when the feedback signal is used alone. the observer augments the sensor output and provides a feedback signal to the control laws, as shown in figure 4. fig. 4. diagram of an observer. a. designing the state observer to introduce an observer to the system presented by (9), the system must be observable. for a system to be observable, it is sufficient that the size of the rows of the observability matrix o is equal to the number of state variables n. hence the observability matrix is: 11 12 1 0c o ca              (11)   2rang o n  , verified condition. b. the observer model the state representation for a linear discrete system is: ( 1) ( ) ( ) ( ) ( ) k k k x k a x k b u k sys y k c x k       (12) where  11 12 1 21 22 2 , , 1 0k k k g a b c g                   . the state vector of the system x(k), is reconstructed using an observer whose dynamic equation, based on luenberger’s method, is expressed as: ˆ ( 1) ( ) ( ) ( ( ) ( ) ) ( ) ( ) k k k k x k a x k b u k h y k y k y k c x k       ⌢ ⌢ ⌢ ⌢ (13) where u(k) is defined as input,  y k⌢ is the estimated output, hk is the observer’s gain, and  x k ⌢ is the estimated state vector. engineering, technology & applied science research vol. 13, no. 1, 2023, 10158-10164 10161 www.etasr.com saoudi et al.: processor-in-the-loop validation of an observer current-based dead-beat control for a … the error ( ) ( ) ( )e k x k x k  ⌢ must converge to zero for all values of k for the observer to be stable. when the observer error satisfies the equation ( 1) ( . ) ( )k k ke k a h c e k   , then ( . )k k ka h c has its eigenvalue i inside the unit circle. the determination of this matrix means that |λi=1….n| < 1. the choice of the eigenvalues must be such that the module is lower than 1 in order to ensure stability, the real part is closer to z = 0 to ensure a faster real part, and the imaginary part is faster if the angle to the real axis increases, but it should not be very close to the unit circle because otherwise the pole will be more resonant. therefore λ1 and λ2 are chosen as: 1 2 0.1 0.1 0.1 0.1 j j        (14) by calculating the determinant of the matrix ( )k k kz i a h c  and by identification on the polynomial 1 2( )( )z z   we can find h1 and h2: 1 2det ( ) ( )( )k k kz i a h c z z      (15) the components of kh are given by:   1 11 22 1 2 2 1 2 22 22 1 2 21 12 1 ( ) h h                         (16) v. simulation study simulations and tests can be used to determine the performance of the above suggested control technique using the dsp f28335 to implant the control algorithm in the digital circuit and igbt switching devices for the single phase inverter. the inverter's switching frequency is set to 10khz, and the algorithm's sample period is set to 0.0001s. the inverter's design parameters are given in table i. table i. parameters of the inverter parameter value rated output voltage vc 220v dc link voltage e 400v filter inductance l 2mh resistance r 20ω filter capacitor c 20uf sampling frequency fs 10khz the system's simulation results are presented with and without the presence of the observer, in order to show the role played by the latter in replenishing the vc voltage as well as to ensure a good release of the disturbance when connecting charges occur. vi. pil implementation the dsp is connected to the computer with a usb cable, which is the hardware configuration required for pil simulation as shown in figure 9. (a) (b) (c) fig. 5. simulation of a deadbeat control with a psim observer. (a) lyanberger observatory, (b) reference tension, (c) dead-beat control. fig. 6. simulation result of the system without an observer. fig. 7. current observer of the capacitor. 0 0.02 0.04 0.06 0.08 0.1 time (s) 0 -200 -400 200 400 vc_ref vc 0 0.02 0.04 0.06 0.08 0.1 time (s) 0 -5 -10 5 10 15 20 ic_obs engineering, technology & applied science research vol. 13, no. 1, 2023, 10158-10164 10162 www.etasr.com saoudi et al.: processor-in-the-loop validation of an observer current-based dead-beat control for a … fig. 8. tension estimation with the reference tension. fig. 9. pil of dead-beat control whit observer. figure 10 shows a simulated block diagram with the pil structure developed by psim in order to achieve safe and rapid prototyping. the control blocks (dead-beat) have been deleted and the creator code ccs has been added instead. this block uses the uart communication protocol to establish communication between the psim software and the fa28253. the inverter output voltage vc values, which are input from the contact block, are supplied to the microcontroller at each step of the psim. the microcontroller gets the switching data (t1, t2, t3, and t4) of the inverter control, which is the output of the contact block. the cooperative effort between fa28253 and psim is built using this structure. (a) (b) fig. 10. pil simulation of deadbeat control whit observer. a. linear load with r=20ω figure 11 shows the simulation result of the deadbeat control with linear load equal to 20ω. a current sensor and the observer’s current are used to show the effect of load variation, nonlinear load, and purely inductive load on the controller. we start with preliminary tests to show the robustness of the linear overload command. purely sinusoidal current and voltage are applied, the current being phase shifted 90 o ahead. the error of the current and voltage between the measurement system and the estimation is close to zero, the feedback fault of the measured voltage is controlled by the observer and is injected in the current observer. (a) (b) (c) (d) fig. 11. pil simulation of dead-beat control with observer: (a) current ic (measured and observed), (b) error current, (c) voltage vc (reference and observed), (d) voltage error. b. linear load r=20ω with increasing load up to 100% the pil simulation of dead-beat control with increasing load up to 100% is presented in figure 12. according to the obtained results, figure 12 shows the pil results for output voltage and current under a resistive load, at t = 0.045s. when the load is increased to 100%, we observe a voltage loss, which the control quickly recovers. in addition, the current is controlled relatively well, so it can be concluded that the controller is good. 0 0.02 0.04 0.06 0.08 0.1 time (s) 0 -200 -400 200 400 vc_ref vc_obs 0.01 0.02 0.03 0.04 0.05 time (s) 0 -5 5 10 15 ic_mes ic_obs 0 0.01 0.02 0.03 0.04 0.05 time (s) 0 -2 -4 -6 -8 -10 -12 2 vc_mes-vc_obs 0 0.01 0.02 0.03 0.04 0.05 time (s) 0 -200 -400 200 400 vc_ref vc_obs 0 0.01 0.02 0.03 0.04 0.05 time (s) 0 -2 -4 -6 -8 -10 -12 2 vc_mes-vc_obs engineering, technology & applied science research vol. 13, no. 1, 2023, 10158-10164 10163 www.etasr.com saoudi et al.: processor-in-the-loop validation of an observer current-based dead-beat control for a … (a) (b) fig. 12. pil simulation of dead-beat control with increasing load up to 100%, equal to r=40ω: (a) current ic (measured and observed), (b) voltage vc (reference and observed). c. nonlinear load diode bridge with r=20ω and c=30μf in parallel the proposed controller was then tested using a distorting load (a diode bridge with a capacitive filter of 30µf and a resistive load of 20ω). the output voltage remains sinusoidal, but the capacitor current waveform deviates from the ideal sinusoidal waveform, as seen in figure 13. (a) (b) fig. 13. pil simulation of dead-beat control with nonlinear load diode bridge with r=20ω and c=30uf on parallel: (a) current ic (measured and observed), (b) voltage vc (reference and observed). according to the obtained results, the sudden connection of a nonlinear load has caused a distortion in the output current. however, the proposed controller has eliminated this distortion in the voltage. d. purely inductive load l=0.10h figure 14 presents the pil simulation of dead-beat control with purely inductive load of l=0.10h. figure 14 shows the pil results for the output voltage and current for a purely inductive load. (a) (b) fig. 14. pil simulation of dead-beat control with purely inductive load l=0.10h: (a) current ic (measured and observed), (b) voltage vc (reference and observed). we observe a voltage loss, which the control quickly recovers, but the capacitor current waveform deviates from the ideal sinusoidal waveform. vii. conclusion in this work, a dead-beat control scheme for a single-phase inverter with an observer is described. the feasibility of the proposed controller with an observer has been demonstrated by simulations and was implemented in a processor in the pil loop. the results showed that the proposed scheme achieves good voltage regulation with linear and nonlinear loads. the proposed controller does not have any parameters that can be changed, it needs a model of the system to calculate the controlled variables, allowing fast dynamic response of voltage control. it has been proved that the use of an observer allows a better estimation of the unknown capacitor current. dead-beat control serves a different approach for the control of power converters, considering the discrete nature of the converters and the microprocessors used for control. moreover, the high calculation power of the current existing dsps makes this method very attractive for controlling power converters. since the dead-beat controlled system's efficiency is successfully proved, the next steps are to study the dead-beat control of a grid-connected inverter, the islanded operation of an inverter, and the application of the proposed control to other inverter structures. references [1] j. m. carrasco et al., "power-electronic systems for the grid integration of renewable energy sources: a survey," ieee transactions on industrial electronics, vol. 53, no. 4, pp. 1002–1016, jun. 2006, https://doi.org/10.1109/tie.2006.878356. 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[18] s. bayhan, h. komurcugil, and i. s. bayram, "deadbeat control of a three-phase t-type inverter with output lc filter for ups applications," in 2021 ieee 30th international symposium on industrial electronics (isie), kyoto, japan, jun. 2021, https://doi.org/ 10.1109/isie45552.2021.9576216. [19] w. yao, j. cui, and w. yao, "single-phase inverter deadbeat control with one-carrier-period lag," electronics, vol. 9, no. 1, jan. 2020, art. no. 154, https://doi.org/10.3390/electronics9010154. [20] w. guo, s. duan, k. xuejuan, y. kang, and j. chen, "a modified deadbeat control for single-phase voltage-source pwm inverters based on asymmetric regular sample," in 2001 ieee 32nd annual power electronics specialists conference (ieee cat. no.01ch37230), vancouver, bc, canada, jun. 2001, vol. 2, pp. 962–967 vol.2, https://doi.org/10.1109/pesc.2001.954244. [21] a. s. haider, a. naz, f. akhter, w. azhar, and r. mehmood, "a novel efficient sine wave inverter with custom programmed pwm and intelligent control," engineering, technology & applied science research, vol. 6, no. 2, pp. 956–963, apr. 2016, https://doi.org/ 10.48084/etasr.648. microsoft word 8-649-ed.doc engineering, technology & applied science research vol. 6, no. 3, 2016, 1013-1017 1013 www.etasr.com saqer and barhoom: steganography and hiding data by indicators-based lsb using a secret key steganography and hiding data with indicators-based lsb using a secret key wesam saqer faculty of information technology islamic university of gaza gaza, palestine wesam.sqr@gmail.com tawfiq barhoom faculty of information technology islamic university of gaza gaza, palestine tbarhoom@iugaza.com abstract—steganography is the field of science concerned with hiding secret data inside other innocent-looking data, called the container, carrier or cover, in a way that no one apart from the meant parties can suspect the existence of the secret data. there are many algorithms and techniques of concealing data. each of which has its own way of hiding and its own advantages and limitations. in our research we introduce a new algorithm of hiding data. the algorithm uses the same technique used by the least significant bit (lsb) algorithm which is embedding secret data in the least significant bit(s) of the bytes of the carrier. it differs from the lsb algorithm in that it does not embed the bytes of the cover data sequentially but it embeds into one bit or two bits at once. actually it depends on indicators to determine where and how many bits to embed at a time. these indicators are two bits of each cover byte after the least two significant bits. the advantage of this algorithm over the lsb algorithm is the randomness used to confuse intruders as it does not use fixed sequential bytes and it does not always embed one bit at a time. this aims to increase the security of the technique. also, the amount of cover data consumed is less because it sometimes embeds two bits at once. keywords-steganography; steganographic; least significant bit; lsb; data hiding; data concealing; data covering i. introduction the idea of hiding secret data is not new, but after the extreme development of the information technology field, steganography became widely used in digital fields and its techniques are developed more and more day by day. steganography is a branch of the information security field. another field of information security is cryptography. steganography and cryptography are somehow related as they both intend to protect information from unauthorized parties. the main difference between them is that steganography is concerned with hiding data and hiding the existence of the data, where cryptography is concerned with transforming data into a not understood form [1-4]. so steganography is concerned with not detecting secret data whereas cryptography is concerned with not revealing the visible secret data by altering the structure of the data itself [5, 6]. of course, they can be combined to make data more secure. data can be encrypted (cryptography) and then be hidden within a carrier (steganography) to provide another layer of protection [4]. steganography may also be used for watermarking to protect the ownership of copyrighted products [5]. the key purpose of every new steganography technique is to enhance the security or the capacity. security is enhanced by enhancing the imperceptibility or the robustness. imperceptibility depends on the quality of the resulting stegoobject to be as the original by avoiding making noticeable changes to the cover object [2, 3]. robustness depends on making the algorithm withstand against steganalysis and attacks [6]. as an example, one of the ways to hide data is just to append its bytes after the bytes of the container file then simply pack all these bytes in one individual file. however this approach has a very big defect which is the size of the result file. this is the sum of the sizes of both the secret and the carrier, which may arouse suspicion if the final size is too large. a lot of algorithms and techniques have been developed in this scope. some depend on the nature of the carrier such as the algorithms which hide into photos, audios or other [1, 7], and some can be used with different types of carriers. the carrier of the secret data can be any of many kinds of mediums, like image, audio, video, text and even network protocols [1-3, 7]. so steganography can be categorized according to the cover medium. there is image steganography, which is the most used, audio, video and even network steganography [2]. in our work we focus on developing a new algorithm that can be used with several types of cover mediums, because it depends on the least significant bit (lsb) which can be used with several types. steganography can also be categorized into three types which are pure steganography, secret key steganography and public key steganography [1]. ii. least significant bit this work uses the same principle with a famous algorithm called least significant bit (lsb). in the lsb algorithm secret data is hidden in the least bit of each byte of the container data. a byte consists of eight bits. lsb takes replaces the least bit of a series of eight bytes of the cover medium with the secret bits. consequently every secret byte consumes eight cover bytes to get embedded into [2]. an example is shown in figure 1. the 01101010 byte is hidden using the lsb algorithm. engineering, technology & applied science research vol. 6, no. 3, 2016, 1013-1017 1014 www.etasr.com saqer and barhoom: steganography and hiding data by indicators-based lsb using a secret key fig. 1. data hiding using lsb there are several advantages for this algorithm. first it doesn’t affect the size of the cover data because it does not increase or decrease the number of the cover data bytes. it just replaces some of the cover data bits with secret bits without affecting the size. it does not make noticeable changes to the cover data and this is according to two factors. firstly the change occurs in the least bit (rightmost) which has the least weight between all the bits in a byte. simply if the value of this bit is changed, the value of the byte is changed only by 1 increasingly or decreasingly as shown in figure 1 at byte 3 and 2. this amount of change is neither noticeable by human eye nor ear. secondly some of the bits are replaced with its same value as shown in figure 1 above, for example byte 7. thus, on average, half of the cover bits are modified using the maximum cover size [2, 4, 6]. so, if we hide some data into, for example, an image the change would not be detectable by human eye [2]. on the other the hand this algorithm has two disadvantages, it consumes a big amount of bytes to embed a small amount into, as for each secret byte it needs 8 cover bytes, but this disadvantage is not that severe. one just needs to hide secret data into a suitable-sized cover. further, secret data can be compressed. the next issue is that the mechanism of hiding is simple, so it is easy to detect (and be “broken”) [2]. we addressed the simplicity issue in this work by making the process of determining the bytes to contain the data involve randomness. also the proposed algorithm hides two bits sometimes and one bit other times, and this reduces the amount of cover bytes needed by 25% and increases the complexity of the hiding process. iii. related work a. image steganography image steganography techniques can be applied in the image domain and transform domain [2, 6, 7]. at image domain we can use bmp and gif, and at transform domain we can use jpg images to hide the data [2, 7]. other techniques as spread spectrum and patchwork are used too for hiding inside images [2, 6]. lsb is more suitable for bmp, png and gif [5, 8], but gif needs extra care when it is used for hiding data [6, 8]. also images with a large size, as bmp, are relatively uncommon on the internet, so using such images would attract attention during transmission [4]. a good choice is to use gif and many steganography experts recommend using gray-scale images because the shades change very gradually from byte to byte [4]. many approaches to enhance lsb-based image steganography have been proposed. in [9], using a secret key to decide the appropriate positions within the image to hide data into was proposed. this would make it difficult to retrieve the hidden data in absence of the secret key. the bits were also hidden inside only green or blue pixels, so the modification of the cover image is less than modifying all of the bytes and that increases the quality of the stego-image. in [10], the rc4 algorithm, which uses a stego-key to randomize the embedding of the secret data over the entire cover image, was applied. this approach makes it hard to retrieve the data without having the stego-key. a bit-inversion technique to improve the stego image quality was also introduced in [10]. in [11], lsb was used to hide the data depending on a filtering based algorithm. this filtering requires finding out which pixels are greater in number, the lighter or darker pixels, by checking the 3 msbs of the pixels. the embedding is done in the dominant area. they also proposed to encrypt the data using ase before the embedding process. b. image steganography audio and video is considered good carriers because of redundancy [12]. many researchers used the lsb modification technique with improvement to hide data inside audio mediums. in [12] two techniques were introduced. the first is bit selection which is used to select the cover bits within a sample. the second is sample selection which is used to determine the cover samples. these techniques add randomness and confusion to the hiding process to increase the security. c. video steganography video is a combination of images and audio, so both image steganography and audio steganography can be used. it has much capacity and it is hard to detect small changes in the whole video stream [13]. lsb is an efficient method for video steganography. in [14], a new method that according to a function was introduced that assigns a frame of the cover video to be the index frame. this frame is used to locate the frames that would contain the secret data. d. network steganography some techniques of hiding use the network protocol functions associated with the osi layers to hide the secret data into. these protocols such as arp, tcp, udp or icmp protocols, referred to as carrier-protocols [15]. iv. indicators-based lsb in this approach of concealing data the secret data bits are hidden inside the least one or two bits but this process is done depending on indicators. we use an indicator to determine the byte into which the secret bit(s) are embedded and another indicator to determine how many bits are embedded at a time. engineering, technology & applied science research vol. 6, no. 3, 2016, 1013-1017 1015 www.etasr.com saqer and barhoom: steganography and hiding data by indicators-based lsb using a secret key the indicator is a fixed bit in every byte of the cover bytes other than the least two bits, because the least two bits are used to contain the secret data. let’s assume the indicator which tells us where to embed is the fourth bit (the bit with index 3 from the right). according to the indicator bit value we determine the byte to hide our secret data into. if the value of the indicator bit value is zero, our current secret bit(s) will be embedded into some byte of the previous bytes before the indicator byte itself (the byte that we do the embedding operation according to its indicator bits values), and if the value of the indicator bit is 1, our current secret bit(s) will be embedded into exactly the next byte after the indicator byte. through the hiding process the fourth bit of every byte of the cover data is scanned to identify where the current secret bit(s) of the secret data should be hidden. this procedure is done starting from the second byte as an indicator to ensure that there is a previous byte, and the final indicator byte is the one before the last byte of the cover data to ensure there is a next byte. when the hiding process is directed to embed into the next byte according to the value of the indicator, the embedding is done into exactly the next byte after the indicator byte. but when the embedding is aimed to be done into the previous byte, the previous byte is not always the byte exactly before the indicator byte. most times, it precedes the indicator byte by a random number of bytes. in the beginning of the hiding process, the first byte is the previous byte and the second byte is the indicator byte. as long as the indicator bytes hide into the next byte, the first byte stays the previous. when an indicator decides to hide into the previous byte, that previous byte will be hidden into, and the next unused byte will be the previous byte. simply in the beginning of the hiding process the first indicator is the second byte (byte with index 1). the previous byte is the first byte (byte with index 0), which can be called current-previous. also, the byte that will be the previous byte after using the current-previous byte should be determined. this byte is called the next-previous and at the beginning of the process it is the second byte, just like the indicator. now as long as every indicator byte is hiding into the next byte, the current-previous and the next-previous never change. when some indicator byte decides to hide into the previous byte, the embedding is done into the current-previous, then the currentprevious moves to the next-previous and the next-previous moves to the next byte after the indicator byte. that means every time after embedding is done into the current-previous, the next-previous becomes the current-previous and the next byte after the indicator byte becomes the next-previous. finally the indicator just steps ahead one byte and so on. because we use indicators to identify the byte to hide into, this procedure increases the randomness and confusion of the hiding process, because we sometimes embed into the previous byte and other times into the next byte. and since the previous byte is not fixed for every indicator byte, extra randomness and confusion are added to the process. so this approach makes the process of retrieving the hidden data more complex which increases the security, and this is the main aim of the proposed approach. also through the hiding process, not always only one bit at a time is embedded (one or two bits may be embedded). this is done depending on another indicator of the indicator byte. again let’s assume the indicator bit which tells us how many secret bits to embed at a time is the third bit (the bit with the index of 2 from the right). if the value of the indicator is 0, we embed only one bit, and if it is one, we embed two bits into the cover byte. this operation adds more randomness and confusion to the hiding process because the amount of the embedded bits is not fixed, so we can’t identify the number of embedded bits into each byte without checking the indicator. on the other hand this operation increases the capacity of the hiding process over the normal lsb which embed only one bit at a time and this is another advantage besides increasing the randomness and confusion. hiding two bits at once causes change to the byte value, but this change ranges from 0 to 3 at maximum, which is a very small change and is not noticeable by the human eye or ear. so, all bytes of the cover data are scanned and the values of the indicator bits (the fourth and the third bits) in every byte are checked. the fourth bit is the indicator that determines where to hide. if its value is zero, then hiding is done into some previous byte, and if it is one, into exactly the next byte after the indicator byte. the third bit is the indicator that tells us how many bits to hide. if its value is zero, then only one bit is hid, and if it is one, two bits are hid. so, according to the indicator we sometimes hide into the previous and other times into the next. the previous is not fixed since it is not always the byte exactly before the indicator byte, it could be any one of the bytes before the indicator byte. according to another indicator we sometimes hide one bit and other times we hide two bits. figure 2 shows the flow chart of the hiding process. all of these factors increase the randomness and confusion of the hiding process, which makes it hard to retrieve the secret data by unauthorized parties. suppose we want to hide the following bits 11101100, 01100110 into the below series of bytes using indicators-based lsb algorithm as shown in figure 3. the hiding process is not done sequentially like plain lsb. the secret bits are hidden into cover bytes randomly depending on the values of the indicator bits of the cover bytes. as shown in figure 3, the order of the cover bytes that were embedded into is 0, 3, 4, 1, 2, 5, 8, 6, 10, 7 and the amount of embedded bits in the same order is 1, 1, 2, 2, 1, 1, 2, 2, 2, 2. here we can realize that the hiding process is not sequential unlike normal lsb approach and some bytes contain only one secret bit and others contain two bits. v. indicators-based lsb with secret key to make the algorithm more robust and secure, a secret key is used through the hiding process. the secret key is a series of bits which can be represented with one dimensional circular array (so any size can be used). at each cycle of the hiding process, the position indicator bit, which is used for deciding the byte into which the secret bit is embedded, is xored with the current bit of the secret key. if the resulting value is zero, then a byte is chosen for hiding. otherwise, the next byte is chosen. also, the amount indicator bit, used to decide the number of bits to be emdedded, is xored with the next bit of the secret key, and if the result is zero then one bit is hidden (otherwise two). this way, security is further increased. engineering, technology & applied science research vol. 6, no. 3, 2016, 1013-1017 1016 www.etasr.com saqer and barhoom: steganography and hiding data by indicators-based lsb using a secret key fig. 2. the hiding flow chart, pi : position indicator, ai : amount indicator vi. experiment and results this approach was implemented and tested on photos and audios without any noticeable or detectable distortion. this is because the approach uses the lsb technique for hiding data, and this technique does not make any noticeable modification in the carrier medium. a carrier image before and after the hiding process is shown in figure 4 whereas the corresponding histograms are shown in figure 5. the approach was also applied on an audio file. figure 6 shows the audio waveform before and after the process. fig. 3. data hiding using indicator-based lsb fig. 4. the cover image before (up) and afetr (down) the hiding process engineering, technology & applied science research vol. 6, no. 3, 2016, 1013-1017 1017 www.etasr.com saqer and barhoom: steganography and hiding data by indicators-based lsb using a secret key fig. 5. the cover image histogram before (left) and after (right) the hiding process fig. 6. the cover wave form before (up) and after (down) the hiding process vii. conclusion as the development of information and communication technologies are increasingly growing day by day, the need to protect private information is also growing. a branch of information security concerned with hiding secret data called steganography has surfaced and a lot of approaches have been proposed. in our work, we introduced a new approach of data hiding based on the lsb technique with the additional advantage, compared to plain lsb, that it adds much randomness and confusion to the data hiding process which makes it harder for unauthorized parties to detect and retrieve the hidden data. this is accomplished by not employing sequential hiding. the proposed algorithm also shows increased capacity compared to plain lsb as it sometimes hides two bits at once. viii. references [1] b. dunbar, “a detailed look at steganographic techniques and their use in an open-systems environment”, sans institute, vol. 2002, pp. 1-9, 2002 [2] t. morkel, j. h. eloff, m. s. olivier, “an overview of image steganography”, issa, pp. 1-11, 2005 [3] r. krenn, “steganography and steganalysis”, available at http://www.krenn.nl/univ/cry/steg/article.pdf [4] n. f. johnson, s. jajodia, “exploring steganography: seeing the unseen”, computer, vol. 31, no. 2, pp. 26-34, 1998 [5] k. thangadurai, g. sudha devi, “an analysis of lsb based image steganography techniques”, international conference on computer communication and informatics (iccci), pp. 1-4, india, january 3-5, 2014 [6] h. wang, s. wang, “cyber warfare: steganography vs. steganalysis”, communications of the acm, vol. 47, no. 10, pp. 76-82, 2004 [7] j. silman, “steganography and steganalysis: an overview”, sans institute, available at https://www.researchgate.net/publication/ 242743284_steganography_and_steganalysis_an_overview [8] d. neeta, k. snehal, d. jacobs, “implementation of lsb steganography and its evaluation for various bits”, 1st international conference on digital information management, pp. 173-178, portugal, september 1921, 2006 [9] s. m. karim, m. s. rahman, m. i. hossain, “a new approach for lsb based image steganography using secret key”, 14th international conference on computer and information technology (iccit), pp. 286291, bangladesh, december 22-24, 2014 [10] n. akhtar, p. johri, s. khan, “enhancing the security and quality of lsb based image steganography”, 5th international conference on computational intelligence and communication networks (cicn), pp. 385-390, india, september 27-29, 2013 [11] m. r. islam, a. siddiqa, m. p. uddin, a. k. mandal, m. d. hossain, “an efficient filtering based approach improving lsb image steganography using status bit along with aes cryptography”, 3rd international conference on informatics, electronics & vision (iciev), pp. 1-6, bangladesh, may 23-24, 2014 [12] m. asad, j. gilani, a. khalid, “an enhanced least significant bit modification technique for audio steganography”, international conference on computer networks and information technology (iccnit), pp. 143-147, pakistan, july 11-13, 2011 [13] p. yadav, n. mishra, s. sharma, “a secure video steganography with encryption based on lsb technique”, ieee international conference on computational intelligence and computing research (iccic), pp. 1-5, india, december 26-28, 2013 [14] r. balaji, g. naveen, “secure data transmission using video steganography”, ieee international conference on electro/information technology (eit), pp. 1-5, usa, may 15-17, 2011 [15] j. lubacz, w. mazurczyk, k. szczypiorski, “principles and overview of network steganography”, ieee communications magazine,vol. 52, no. 5, pp. 225-229, 2014 microsoft word etasr_v12_n3_pp8760-8764 engineering, technology & applied science research vol. 12, no. 3, 2022, 8760-8764 8760 www.etasr.com hameurlaine et al.: design of protection strategies and performance analysis of an hvdc link … design of protection strategies and performance analysis of an hvdc link during multiple disturbances abdelhadi hameurlaine department of electrical engineering university of djelfa djelfa, algeria elhadi06@gmail.com haouari sayah intelligent control and electrical power system laboratory university of sidi bel-abbes sidi bel-abbes, algeria housayah@yahoo.fr larbi boukezzi materials science and informatics laboratory (msil) university of djelfa djelfa, algeria larbiboukezzi@gmail.com received: 20 april 2022 | revised: 9 may 2022 | accepted: 13 may 2022 abstractin high voltage direct current (hvdc) transmission system applications, the control and protection system plays an essential role in the overall performance. this paper aims to give solutions to some performance problems that can occur in the hvdc link. in this paper, ways to mitigate this serious malfunction of the commutation failure process in the operation of hvdc converters are studied and protection functions like the commutation failure prevention (cfprev) have been used. furthermore, hvdc transmission systems are vulnerable to dc faults and its protection becomes ever more important with the fast growth in the number of installations. in this context, the dc fault protection function is one of the most important challenges to the development of hvdc transmission systems. the dynamics of the studied power system including the hvdc link are thoroughly investigated in this paper through various simulation scenarios. keywords-commutation failure; control strategies; protection functions; hvdc; faults; performance i. introduction high voltage direct current (hvdc) transmission systems are an excellent asset in modern power systems, mainly for their ability to overcome problems of ac transmission, such as the interconnection of asynchronous grids, stability of long transmission lines, and use of long cables for power transmission [1-4]. due to environmental, technical, and economical reasons [2-6], the hvdc system is a mature technology but it has certain constraints such as the risk of commutation failures [3]. commutation failures following ac system disturbances may occur in hvdc systems, especially in the inverter station. this fault is the result of the failure to complete commutation before the commutation voltage reverses its polarity [5]. furthermore, faults in the dc transmission system, which are generally pole-to-ground faults, block power transfer and are not likely to be of much significance unless voltage reduction occurs [7]. the objective of the current paper is to demonstrate ways to to improve hvdc system performance, especially during large disturbances, such as three-phase faults on the ac side of the inverter and dc line faults at the rectifier side. therefore, in this paper, the dc fault protection (dcprot) is inserted to detect faults on the line and take the necessary actions to clear them [8]. the protective function commutation failure prevention (cfprev) is used in the inverter [9]. the control subsystem mitigates commutation failures due to ac voltage dips. finally, in order to improve the dynamic performance of the proposed controller and protection devices, various simulation scenarios are tested. the main conclusion is that the reliability of an hvdc link depends on control and on the protection system. ii. system modeling and control in order to define the needs in terms of control and protection, the first step is to develop a model for the hvdc transmission system. hvdc systems traditionally use the fixed-parameter pi controller to control the dc line current and excitation angle [10], where the rectifier station controls the dc current through the firing angle (α) and the inverter controls voltage through the extinction angle (γ). in general, a typical basic monopolar hvdc system can be configured as shown in figure 1 [11], where the schematic diagram and the equivalent circuit are shown in (a) and (b) respectively [12]. corresponding author: hameurlaineabdelhadi engineering, technology & applied science research vol. 12, no. 3, 2022, 8760-8764 8761 www.etasr.com hameurlaine et al.: design of protection strategies and performance analysis of an hvdc link … (a) (b) fig. 1. hvdc transmission link: (a) schematic diagram, (b) equivalent circuit. the direct current can be expressed using the equivalent circuits as [13]: cos cos0 0v vd r d i i d r r rcr cil α γ− = + − (1) where rcr and rci are the equivalent commutating resistances for rectifier and inverter respectively, and rl is the line resistance. both impedances are nonlinear and are not pure resistive, referred from converter side ac systems. 3 r lcr cω π = and l l lcr co c= = (2) where vd0r and vd0i are the ideal no-load rectifier and inverter voltages respectively, referred from converter side ac systems. therefore, the direct voltage vd at any point on the line and the direct current id can be controlled by controlling the internal terminal voltages: vd0r cosa and vd0i cosγ. these two voltages can be controlled by controlling the firing instant of the thyristor or through the tap changing of the converter transformer. another important control function is implemented to change the reference current according to the value of the dc voltage. this control, named voltage dependent current order limiter (vdcol) [9], automatically reduces the reference current set point when dc voltage decreases during a dc line fault or a severe ac fault. reducing the reference currents also reduces the reactive power demand on the ac system, helping to recover from fault. iii. concepts of the proposed protection in this section, we insert two different protection devices associated with the proposed control strategy to improve the dynamic performance of an hvdc system. the first one, at the rectifier, is the dc fault protection (dcprot) to detect and remove faults in the dc line. the second protection function is the commutation failure prevention (cfprev) at the inverter, which controls subsystem commutation failures due to ac voltage dips. in this context, the expected behavior in steady state and stability problems are discussed in order to define the needs in terms of control and protection. moreover, the reliability of the hvdc control system depends on the regulators, but also on the protection sub-functions [14]. the actions that are taken by device protection systems when faults or dysfunctions occur are shown. to evaluate the performance of the proposed protection, simulation results are presented. a. dc protection function the protection is active in the rectifier. it will detect a fault on the dc side and will force the delay angle into the inverter region in order to extinguish the fault current [15]. the fault detection on the dc line is based on the drop in the line to ground voltage. the normal voltage polarity of the line is a parameter as well as the reference level of the fault detection. delay time is used in the detection to discriminate between a line fault and other disturbances resulting in low dc voltage. a delay time of 200ms is allowed, after the dc system start-up, before activating the detection logic to make sure that the normal operating dc voltage is established. also, an external signal generated by another protective detection will trigger a forced alpha during an adjustable interval sufficient to allow the deionization of the fault path prior to the re-application of voltage. b. commutation failure prevention function the objective of this device is to develop a control and protection strategy to accommodate large disturbances when an hvdc system is connected to a weak ac system [16]. this phenomenon is the result of the failure to complete commutation before the commutation voltage reverses its polarity, taking into account the need for sufficient extinction time for de-ionization and to re-establish the blocking ability. the protective function, used in the inverter, mitigates commutation failures due to ac voltage dips. after fault detection (three-phase or one-phase) an angle value is sent to the converter control in order to be deducted from the maximum delay angle limit. commutation failure is the most common disoperation of an inverter due to the minimum limit on extinction angle gamma [17]. this puts a limit to the maximum firing angle for a successful inverter operation, as shown by the following equation: 0180 ( )α β γ= − + (3) a signal transmitted to the vdcol indicates the detection of a commutation failure, as this vdcol function prevents the detection of commutation failure by the cfprev module, the vdcol transiently reduces the current in order to prevent the converter from excessive current [18]. to detect three-phase faults abc-αβ transformation is used where, uα and uβ may be expressed by: 1 (2 ) 3 3 ( ) 3 u u u ua cb u u ucb α β = − − = −      (4) the clark transformation [19] is used for three-phase fault detection and zero-sequence voltage evaluation. the engineering, technology & applied science research vol. 12, no. 3, 2022, 8760-8764 8762 www.etasr.com hameurlaine et al.: design of protection strategies and performance analysis of an hvdc link … detection is based on instantaneous values, which ensure fast reaction of the control system when an ac fault occurs. iv. system study the hvdc system simulated in this study, is modeled based on the cigre hvdc benchmark system [20], as shown in figure 2. the system is monopolar with a 12-pulse converter. the rectifier is connected to the strong ac system with a short circuit ratio (scr) of 5. the inverter is connected to the weak ac system with a scr of 2.5. fig. 2. basic configuration of the hvdc transmission system. the model description follows [20]. the ac side of the hvdc system consists of a supply network, filters, and converter transformers. the ac supply network is modeled by a thevenin equivalent with equivalent source impedance [22]. the filters are added to absorb the harmonics generated by the converter and to supply the reactive power needed by the converter. the dc side of each converter consists of a smoothing reactor. the dc transmission line connected to each converter station is represented by a t network. the 12-pulse converter station is configured by two universal bridge blocks in series. the universal bridge block implements a universal three-phase power converter that consists of up to six power switches connected in a bridge configuration[23]. the system parameters of the hvdc system are given in table i. table i. hvdc system parameters parameter value ac side 1 ac side 2 dc side ac voltage 500 kv 345 kv ---- reactive power 5000 mva 10000 mva ---- frequency 60hz 50hz ---- dc voltage --------500 kv dc current --------2 ka active power --------1000 mw dc cable length --------300 km smoothing reactors --------0.5 h v. simulation results and analysis in this section the behavior of the hvdc transmission system is analyzed. in order to test the controllers and the proposed protection functions, two different scenarios will be simulated in order to analyze the dynamic performance. during the first scenario, a dc line fault on the rectifier side is applied to observe the dc fault protection action. in the second one, a three-phase-to-ground fault on the ac side of the inverter is studied to evaluate cfprev control. in both scenarios, the waveforms for electrical quantities like dc voltage, dc current, and firing delay angle α are presented and analyzed during the application of faults, at rectifier and inverter side, and finally, the corresponding inverter side ac voltage and ac current waveforms are shown. a. first scenario:dc system faults the scenario is shown in figure 3. this fault is applied at t= 0.7s for a duration of 50ms. the dc current increases quickly until 2.22p.u., and it is cancelled at the inverter side. (a) (b) (c) fig. 3. dc fault on the rectifier side. the dc voltage falls to zero at the rectifier. this dc voltage drop is seen by the vdcol through dc fault protection. the vdcol reduces the reference current to 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 time (s) v d ( p u ) 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 -0.5 0 0.5 1 1.5 2 2.5 time (s) id & i d re f (p u ) id & i d re f (p u ) id & i d re f (p u ) id & i d re f (p u ) id idref 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 0 50 100 150 200 time(s) a lp h a (d e g ) 166 deg engineering, technology & applied science research vol. 12, no. 3, 2022, 8760-8764 8763 www.etasr.com hameurlaine et al.: design of protection strategies and performance analysis of an hvdc link … 0.28p.u. at the rectifier. a dc current still continues circulating in the fault. at t=0.78s, the rectifier firing angle α is forced to be 166º by the dc protection function after detecting a low dc voltage. in this situation the rectifier operates in inverter mode. the dc line voltage becomes negative and the energy stored in the line is returned to the ac system. then α is released at t=0.83s and the dc voltage and the current recover in approximately 0.5s. b. second scenario: ac system faults three-phase-to-ground fault is applied at the ac side of the inverter at t=0.7s and is cleared at t=0.75s. figure 4 shows the inverter side, the dc voltage, dc current and firing delay angle during the fault. the oscillation of the dc voltage and current waveform are primarily caused by the controller action. (a) (b) (c) fig. 4. three-phase-to-ground ac fault on the inverter side. the dc voltage at the inverter drops and the dc current increases rapidly to 2.22p.u. on the inverter side. when the fault is cleared at t=0.8s, the control function (vdcol) operates and reduces the reference current to 0.3p.u.. the system recovers in approximately 0.35s after fault clearing. during the fault period, the dc voltage oscillates around zero due to the commutation failure on the inverter side. the control scheme provides smoother operation of the converter firing angles, which is shown in waveform firing angle. furthermore, figure 5(a)-(b) shows the phase ac voltage and ac current waveforms at the inverter side, for a threephase-to-ground fault. the ac fault does not affect the rectifier side ac system because the rectifier is connected to a strong ac system. the ac voltage becomes nearly zero, after the fault is cleared, the inverter side ac voltage increased to 1.53p.u.. the ac currents at the inverter shows minor disturbance and high amplitude fault current flows with oscillations. (a) (b) fig. 5. voltage and current responses under three phase to ground fault at the inverter. vi. conclusions this paper focuses mainly on the hvdc performance assessment dynamic state under various scenarios. first, the dynamic response of the hvdc system is analyzed under unbalanced grid conditions. in a typical hvdc link, the rectifier station controls the dc current through the firing angle and the inverter station controls voltage through the extinction angle. the faults associated with an hvdc system are cleared through the action of protection devices. the protection devices thus play a vital role in the satisfactory operation of the hvdc systems. simulation results show clearly that the reliability of an hvdc control system does not depend only on the 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 -1.5 -1 -0.5 0 0.5 1 1.5 time (s) v d & v d r e f (p u ) vd vdref 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 -0.5 0 0.5 1 1.5 2 2.5 time (s) id & i d r e f (p u ) id idref 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 110 115 120 125 130 135 140 145 150 155 time (s) a lp h a ( d e g ) 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 -2 -1.5 -1 -0.5 0 0.5 1 1.5 time (s) v a b c ( p u ) -1.53pu 1.23pu 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 -20 -15 -10 -5 0 5 10 15 20 time (s) i a b c ( p u / 1 0 0 m v a ) engineering, technology & applied science research vol. 12, no. 3, 2022, 8760-8764 8764 www.etasr.com hameurlaine et al.: design of protection strategies and performance analysis of an hvdc link … controller, but also on protection functions. in this paper, the actions that are taken by some hvdc link protection systems when faults or dysfunctions occur are presented. the obtained results demonstrate that the dc fault line is eliminated by the rectifier operation in inverter mode through the increase of its firing angle to ensure the extinction of the residual current. this necessary action, is ensured by the dc protection device. for three-phase faults, the commutation failure prevention greatly reduces the risk of repeated commutation failures. finally, from the simulation results, it can be seen that the system works stably with the purposed protection devices and the fixed parameter pi controller applied to an hvdc system. the protection devices implemented in this paper showed good performance under various scenarios. however, more extensive studies can be conducted in the future. future work should explore other possibilities and routes in which this paper could lead to. the main perspectives should include: • the development of a voltage source converter (vsc), with the insertion of these protection devices applied to the conventional hvdc link. • protection and implementation of nonlinear control algorithms for vsc-hvdc systems. appendix abbreviations ac alternating current dc direct current dcprot direct current fault protection cfprev commutation failure prevention hvdc high voltage direct current vdcol voltage dependent current order limiter references [1] j. arrillaga, n. r. watson, and y. h. liu, flexible power transmission: the hvdc options, 1st ed. chichester, uk; hoboken, nj, usa: wiley, 2007. 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[23] s. dey and t. bhattacharya, "a transformerless dc–dc modular multilevel converter for hybrid interconnections in hvdc," ieee transactions on industrial electronics, vol. 68, no. 7, pp. 5527–5536, jul. 2021, https://doi.org/10.1109/tie.2020.2994889. microsoft word 9-694.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1084-1088 1084 www.etasr.com zneit: on-line handwriting signature verification based on using extreme points extraction on-line handwriting signature verification based on using extreme points extraction dr. rushdi saleem abu zneit bau, fet, computer engineering amman, jordan zneit_rush@hotmail.com abstract—this paper presents a method for on-line handwriting signature verification (hsv) using extreme points matching (epm). epm does not use direct computation of curve’s curvature thus it does not expect smoothness in the analyzing process of the trajectory. in the proposed method the curve’s form is described by a small set of extreme points and the method thus seems more precise. furthermore, it provides an effective preprocessing of the curve and can be utilized in one-to-many pattern matching in a restricted access systems. keywordsline signature verification; hsv; trajectory; extreme points; hand writing; curvature i. introduction signatures are used legally and financially for identity verification in case of official certificates, contracts, credit cards and checks. signature verification remains an open challenge as it cannot be considered just as a combination of characters. automatic signature verification has received extensive research interests in pattern recognition. signature verification methods are classified [5-6, 8, 12-13] to offline (static) and online (dynamic). in offline methods, signatures are recorded as images, scanned into computers and processed using offline verification stages. offline signature verification uses static features like shape, style variation, distortion, rotation variation, etc. online methods, uses dynamic features such as pressure, velocity, stroke length, pen up/down time, etc. and the shape of the signature [12]. one of the key requirements of a signature verification system can be achieved with greater precision in the online signature verification due to the availability of dynamic information system. the intensive developing in computer technology provides the capability to analyze the dynamic drawing motion of handwriting signature as they are written. a special graphical pad provides the ability to trace the hand angle and the motion and pressure of the pen. a hand pad together with an instructed pen [5-6, 8, 13] or a video camera [12] may be used to obtain the online information of pen tip (position, speed, and pressure), therefore, the input may be considered as a sequence of features. online signature verification has been shown to achieve much higher verification rate than offline verification [5-8, 12-15]. state-ofthe-art of online methods achieve error rates (eers) ranging from 2% to 5% [5-6, 8, 12-13], while the eers of offline verification are as high as 10%-30% [7, 12]. this difference is largely due to the availability of dynamic information in online methods [5, 14-15]. hence, the matching and annotation problems for 2dimensional images are more difficult in signature verification and more time consuming than those for 1-dimensional sequences. although online verification methods outperform offline ones, their use of special devices for recording the pentip trajectory increases their system cost and brings constraints on their applications. however, in some applications such as check transaction and document verification, offline signature is obligatory. in [16], an identification and verification of signatures method is proposed, it is a scale and rotation invariant technique that involves the extraction of rotation invariant sub uniform as a feature vector from the 12 blocks within an image, and it is a combination of chi square distance and linear support vector machine. this paper focuses on online signature verification and on the preprocessing step of curves of online hsv by extracting the extreme points of the curves in signature. hsv has been used earlier in the field of criminal investigations and the start of active research in the field of hsv is established in [1]. ii. problem formulation in online hvs a set of parametrical sequence given curve  ( ), ( ), 0,g x t y t t t is considered. informations included in this timing sequence reflect the dynamic motion of hand muscles and can be used as personal biometrical characteristics. this paper proposes a method that gives the ability to input handwriting signatures to the signature verification system and then the system finds the matching signature from its database and performs the identification. this method of biometrical identification has great functionality and a wide area of implementations. to solve the problem of finding matches from a database, the description of the dynamic curve by a vector of extreme points is proposed. the dynamic curves are parameterized by timing and trajectory as shown in: engineering, technology & applied science research vol. 6, no. 4, 2016, 1084-1088 1085 www.etasr.com zneit: on-line handwriting signature verification based on using extreme points extraction 1g s    (1) equation 1 describes motion with constant speed through trajectory which is also applicable for offline parameterization given the following condition: 2 2 1 g g s s       (2) equation 2 describes the constancy of the parallelogram area constructed on the vectors g s   and boundary 2 2 g s   , where s is calculated by [3]: 1 2 3 2 0 t g g s s       (3) dynamic curves include information such as pen dynamic motion and timing sequence of points that form the trajectory. to solve the problem of identification (searching etalon), this paper focuses only on the shape of the curve, therefore, the parameterization through the curve is described as:   : ( ), ( ), 0, gg x s y s s s (4) where the parameter s is calculated by: 0 ( ) t g s t d     (5) given that the rounding pen speed is lower than the speed of the straight movements, it is noticed that dynamic hand motion (the speed of writing curves) is tightly close to trajectory's shape. there are different signature elements that may complicate the authentication. in [3], some signature verification methods only considered the shape of the trajectory and ignored time parameterizations and some other parameters such as the pressure of pens and the slope hand. in this paper, only the time parameterizations are ignored as in [2]. iii. comparisons of the trajectories based on extreme points dynamic curves recognition is very close to the continuous human speech recognition. the data derived from the graphic digitizer is similar to a sound signal. as with phoneme speech recognition, objects of handwriting recognition (letters and symbols) are clearly defined. the shape of handwritten signs depends on their position in the word, which is conceptually close to the variation of phonemes in the pronunciation of words depending on their entourage. all these allowed the adaptation of developed methods from the field of speech recognition to the field of handwriting text recognition [4, 5]. however, direct application of these techniques to cursive text recognition is associated with certain difficulties of finding diacritical signs [6]. at the same time, the words in the written language can quite often easily be separated from one another, unlike the sounds in continuous speech. the main methods of handwritten signature recognizing is a statistical approach based on hidden markov models, an approach using neural networks, and the comparison of dynamic curves by dynamical transformation of these curves in timescale (dynamic time warping (dtw)). depending on the principles of the trajectories mapping, there are various methods of dtw: symmetric dynamic time warping [7], continuous dynamic time warping [8], piecewise aggregate approximation dynamic time warping [9] and iterative deepening dynamic time warping [10]. in most studies [11, 12], trajectory comparisons are exposed to all points of the trajectory. however, it was noted that the dtw method has two major drawbacks [13]: high computational cost and bringing spurious signatures and conform them with the reference signature. to eliminate these drawbacks, a method of comparing the signature based on finding a match between extreme points (extreme points warping (ewp)) was introduced. many researchers [13, 14] represented the input signal as a series of “peaks” and “valleys” since such a conformity approach [14] needs to find the matching between the points of the same type which significantly accelerate the comparison process. on the basis of the samples of 25 users’ signatures, in [13] empirical assumptions were made that there are three types of errors of comparisons: missing segment at the beginning of a signature, missing segment at the end of a random pair of peek and valley (ripples) with a little difference in height. to exclude from consideration these points, a heuristic rule is introduced: a point is marked as extreme, if the two following conditions are performed at the same time: ,o or h d h  where r is the height difference between successive "valley" and "peak»; d is the drop in height between a "peak" and the subsequent "valley»; ho is a threshold (one pixel). the resulting extreme points are compared by dynamic programming [13, 14]. a direct move diagram when a path from (i, j) point can be extended to one of three points (i+1, j+1), (i+1, j+3), (i+3, j+1) which gives the minimum penalty of inconsistency. straight pass allows to find the difference between two curves, the sequence of points (i, j) defines the path in which each point is a locally-optimal match between the ith point and its reference (reference points are numbered on the x-axis) and the jth point of the sample (points of sample are numbered on the y-axis). the rules of possible continuation of the path followed by from the fact of interleaving extremes, wherein, an extension is selected, which gives minimum penalty for discrepancy. at the end of the count the table’s upper right corner contains the measure of the difference between the two curves. if necessary, the backward pass by using an existing path allows finding the best match of two curves. this paper proposes an improved version of finding the extreme points [13, 14]. the proposed method takes in consideration some of the characteristics of a handwriting signature as well as the accumulation of errors during the comparison process of successive chords formed by the corresponding extreme points. engineering, technology & applied science research vol. 6, no. 4, 2016, 1084-1088 1086 www.etasr.com zneit: on-line handwriting signature verification based on using extreme points extraction iv. methodology and results a. method many handwritten signature verifiers are based on the procedure of finding characteristics or extreme points. in earlier handwritten signature verification methods, points are manually selected, then the coordinates of these points are entered to computers for processing. however, the usage of touch panels and graphical tablets automates this process. however, the concern is to find the most informative points on the curve and those with a value greater than the threshold curvature. the calculation of the curvature of differential geometry requires the existence of second derivation with respect to the time, which puts a limit on the smoothness of the investigated trajectory. therefore, the curvature is determined by the velocity of the pen using the first derivation as the correlated value [8] at the same time, 15-18% of the average velocity of writing is selected using the threshold value and replacing the limit 0lim sc s          , where δα is a change in the angle of the slope of the tangent for the part of trajectory from s to δs. the curvature of the trajectory in the i-th point is the set of points 2 1 1 2, , , ,i i i i ip p p p p    determined by the angle between two vectors 2 ,i ip p  and 2,i ip p  . as a variant, it is possible to replace the function of the curvature by its discrete analog time-series of angle change [14]. in this paper, extreme point’s definitions that are slightly different from the terminology in the previous section are introduced: 1 vertical extremum is a point    * *,x t y t , for which:   *| 0t t y t t     2 horizontal extremum is a point    * *,x t y t , for which:   *| 0t t x t t     each vertical exremum defines a local maximum or minimum in the trajectory. the extreme points that respect to curvature, have a local curvature of the trajectory which is larger than the threshold value. it may be argued, that the above described methods of finding the extreme points are not always optimal, and thus ineffective. however, those vertical and horizontal extremes are closer to the curvature’s extreme points. at the same time, incorrect threshold setting for the specific given signature may miss the important points that are not having a large curvature. figure 1 shows an example of two english letters “l” with different shapes of trajectory. when skipping the point which characterizes the convexity of the pull-down section, the first letter may be erroneously classified as the letter "e". the developed method for finding the extreme points allows tracking changes of the trajectories. this is particularly important in recognition of handwritten letters and words, for example, when the user enters a graphical text on handheld computers. fig. 1. english letter “l”. in figure 2, a "skeleton" representation of the same letter is obtained by connecting extreme points, it is clear that all the necessary information about the structure of the letters have been preserved and assigned to a smaller number of points. figure 3 shows the steps that must be performed to obtain the set of extreme points. firstly, the original trajectory is smoothed and interpolated (re-sampled) to obtain an equidistant curve. it is known that noise due to digitizing and trembling of the pen points is distributed along the trajectory, as a result, it is desirable to implement a smoothing process on the curve. in this paper, a simple and an effective smoothing method is implemented to the coordinates of adjacent points. compared to gaussian smoothing, the implemented smoothing method has a lower computational cost. the implemented smoothing method is based on the following equations that are separately implemented for each of the coordinates:        0.25 1 0.5 0.25 1smoothedx i x i x i x i            0.25 1 0.5 0.25 1smoothedy i y i y i y i     (6) fig. 2. example of finding extreme points. fig. 3. steps of searching extreme points. engineering, technology & applied science research vol. 6, no. 4, 2016, 1084-1088 1087 www.etasr.com zneit: on-line handwriting signature verification based on using extreme points extraction the resulting representation of the curve is used to find the critical points. it should be noted that the term "critical point" refers to the pre-found extreme points, as then some of these points will be filtered. unlike [5], this paper does not exclude endpoints with a small drop in height, however, such points form a so-called "plateau" (see figure 4). after smoothing and resampling, finding the critical points step takes place. the critical points that are important in this step are: the endpoints of the curve segments, vertical and horizontal extremes, the boundary points of the vertical plateau, and the point of inflection. for finding the vertical extremes, a simple heuristic is applied: point pi is the extreme point if the following condition is true:   1 1 0y y y yi i i ip p p p    if for some thi point the above equation drawn to zero, and the coordinates of three consecutive points do not match, a point was added to the set as a boundary point of the plateau. similarly, there were also horizontal extremes (critical point). since special attention was paid to the speed and efficiency of the algorithm. for infliction points we analyze the sign of vector product of 2 2sgn i i i ip p p p     the last expression in this case can be replaced by a simplified coordinate entry to the flat case:      2 2 2 2sgn x x y y y y x xi i i i i i i ip p p p p p p p          (7) fig. 4. the horizontal plateau so, after we finish this step:  we obtain a set of critical points, which, strictly speaking, are redundant. depending on the parameters of the program the number of points obtained in the 2-2.5 times higher than the finally found amount of the extreme points.  the next step is to remove the extra points, and the addition of new ones, that more accurately characterize the shape of the trajectory. particularly, all the inflection points must be deleted, because usually they are located in the middle of the "straight" section, which reduces their informative value. instead of that, the set of extreme points, conventionally called the curvature extremes are added, although the curvature value at these points cannot be very large. the basis of the filtering procedure supposed the following mere: in horizontal plateau, critical points are the features of the plateau. here we consider that quantities 1 1 y y y y prev i i next i idy p p and dy p p     , where i th point belong to the plateau if and only if 0 0prev nextdy or dy  . suppose that for the sequential viewing points on the curve for ith point 0,nextdy  then for the point i+1 0predy  , which means that ith and (i+1)th points belong to the same plateau. the above allows to formulate selection rules for the plateau points pmax and pmin where pmin means that the point may be a local minimum and pmax means that the point may be a local maximum. in this notation, figure 4 presents variant plateau    max max min min, ,p p and p p . if we denote by the letter v the vertical extremum, and the letter c the extremum of the curvature, the selection rules are written in the following form:                         max max max min min max max max min min min min max max min 1 : , , ; 2 : , , , , , , ; 3 : , , mirule p p v or p p v if the size of plateau less than threshold value rule p p c v c or p p c v c if the size of plateau greater than threshold value rule p p or p p if the s                min max max min ; 4 : , , , , ; ize of plateau less than threshold value rule p p c c or p p c c if the size of plateau greater than threshold value   similar rules can be formulated for the case of horizontal extremums. the algorithm is based on the comparison of the curves on the idea of finding matching between the vertical extreme points. the algorithm is based on local features of the curve, which can minimize the loss of important information. in figure 5 an example of a signature for which the generated view is not accurate because boundary point of the horizontal t-stroke does not indicate the presence of extreme vertical or plateau is shown (although this is not the fault of the program). it happened due to trembling in the exercise of that stroke, and due consideration that specified the local neighborhoods of the critical points. but this can lead to an error, since the matching algorithm used is focused on locating (finding) pairs of vertical extremes of the opposite type. in order to avoid unexpected errors, the last stage of the process of marking up of the signature by using extreme points is the secretion of horizontal portions. at this stage the final horizontal strokes are marked if they are presented in the signature. fig. 5. example signature with horizontal stroke. b. experiment results the proposed on-line signature verification system was applied to 200 genuine signatures from 50 users, 150 skilled forgeries from 75 forgers and 150 random signatures. table i shows the on-line signature verification results for the proposed method. we used two parameters to evaluate the performance of signature verification systems, namely: false acceptance rate (far) and false reject rate (frr). as it can be seen from table i the performance for the genuine signatures was far=0.5%. for skilled forgeries and random forgeries: frr=4% and 0% respectively. comparing these results with the other methods of verification in the literature, our proposed engineering, technology & applied science research vol. 6, no. 4, 2016, 1084-1088 1088 www.etasr.com zneit: on-line handwriting signature verification based on using extreme points extraction method seems more accurate and it highly succeeded in verifying the online signatures. table i. results type of signature tested accepted rejected genuine signatures 200 199 1 skilled forgeries 150 6 144 random forgeries 150 0 150 v. conclusion in this paper, a method for efficient on-line signature verification is proposed, so as to increase security in access control and financial transactions. in this proposed method, finding the extreme points is used to speed up the comparison of the dynamic curves. in contrast to the existing alternative approaches, the proposed algorithm takes into account the particular shape of the trajectory. moreover, the acceptance rate for genuine signatures and the rejection rate for forgeries are found high enough. compared to other signature verification algorithms, the proposed method seems more accurate and efficient. references [1] r. plamondon, g. lorette, “automatic signature verification and writer identification – the state of the art”, pattern recognition, vol. 22, no. 2, pp. 107–131, 1989 [2] m. e. munich, p. perona, “visual signature verification using affine arclength” conference on computer vision and pattern recognition cvpr, pp. 2180-2186, 1999 [3] v. s. nalwa, “automatic on-line signature verification”, proceedings of the ieee, vol. 85, no. 2, pp. 215-239, 1997 [4] t. starner, j. makhoul, r. schwartz, g. chou, “on-line cursive handwriting recognition using speech recognition methods”, ieee conference on acoustics, speech, and signal processing, vol. 5, pp. 125-128, 1994 [5] l. yang, b. k. widjaja, r. prasad, “application of hidden markov models for signature verification”, pattern recognition, vol. 28, no.2, pp. 161-170, 1995 [6] g. seni, j. seybold, “diacritical processing for unconstrained on-line handwriting recognition using forward search”, international journal on document analysis and recognition, vol. 2, no. 1, pp. 24-29, 1999 [7] t. hastie, e. kishon, “a model for signature verification”, ieee international conference on decision aiding for complex systems, pp. 191-196, 1991 [8] m. e. munich, p. perona, “continuous dynamic time warping for translation-invariant curve alignment with applications to signature verification”, 7th ieee international conference on computer vision, vol. 1, pp. 108-115, 1999 [9] e. keogh, m. pazzani, “scaling up dynamic time warping for datamining applications”, 6th acm sigkdd international conference on knowledge discovery and data mining, pp. 285-289, 2000 [10] s. chu, e. keogh, d. hart, m. pazzani, “iterative deepening dynamic time warping for time series” ieee international conference on data mining, maebashi city, japan, 2002 [11] a. k. jain, f. d. griess, s. d. connell, “on-line signature verification”, pattern recognition, vol. 35, no. 12, pp. 2963–2972, 2002 [12] s. d. connell, a. k. jain, “template-based online character recognition”, pattern recognition, vol. 34, no. 1, pp.1-14, 2001 [13] f. hao, c. w. chan, “online signature verification using a new extreme points warping technique”, pattern recognition letters, vol. 24, no. 16, pp. 2943-2951, 2003 [14] x. li, m. parizeau, r. plamondon, “detection of extreme points of online handwritten scripts”, progress in handwriting recognition, world scientific, 1997 [15] r. c. sonawane, m. e. patil, “an effective stroke feature selection method for online signature verification”, 3rd international conference on computing communication & networking technologies (icccnt), pp. 1-6, coimbatore, india, july 26-28, 2012 [16] s. singh, a. kaur, “off-line signature verification using sub uniform local binary patterns and support vector machine”, international conference on chemical engineering & advanced computational technologies (icceact’2014), pretoria, south africa, nov. 24-25, 2014 microsoft word etasr_v12_n6_pp9523-9526 engineering, technology & applied science research vol. 12, no. 6, 2022, 9523-9526 9523 www.etasr.com nguyen et al.: time-dependent reliability assessment of a continuous i-shaped steel beam … time-dependent reliability assessment of a continuous i-shaped steel beam considering corrosion effects sy-minh nguyen dpt. of engineering and technology ha tinh university ha tinh city, vietnam minh.nguyensy@htu.edu.vn van-long phan department of civil engineering vinh university vinh, vietnam vanlong.kxd@vinhuni.edu.vn ngoc-long tran department of civil engineering vinh university vinh, vietnam longtn@vinhuni.edu.vn xuan-hieu nguyen department of civil engineering vinh university vinh, vietnam xuanhieu.kxd@vinhuni.edu.vn trong-ha nguyen department of civil engineering vinh university vinh, vietnam trongha@vinhuni.edu.vn received: 19 august 2022 | revised: 7 september 2022 | accepted: 8 september 2022 abstract-among other fields, climate change has a great influence on metal corrosion that reduces the durability and reliability of steel structures. a time-dependent reliability analysis includes time-dependent climate scenarios and deterioration processes as well as random variables, material properties, and dimensions. the extent of corrosion damage is calculated by tracking the evolution of the corrosion process using monte carlo simulations. the current paper presents a time-dependent reliability assessment of a continuous i-shaped steel beam, considering the corrosion effects of climate change in vietnam. the results showed that the safety probability of a continuous steel beam considering metal corrosion from the pristine to 100 years reduces from 96.77% to 63.08%. these findings can be used to assess and provide a cost-technical analysis of climate adaptation measures. keywords-time-dependent reliability; continuous i-shaped steel beam; corrosion damage; monte carlo simulation i. introduction continuous steel beams that contain two or more spans are typically used in steel frame buildings and bridges. the design of continuous beams not only ensures the strength condition but also minimizes their weight and material costs. a steel beam can be influenced in the long term by corrosion, leading to an acceleration of structural deterioration. therefore, a timedependent reliability assessment of continuous steel beams is very important, especially in the context of climate change. the assessment of the reliability and durability of steel structures for metal corrosion attracted the interest of many studies. the structural reliability of ships, offshore structures, and pipelines takes into account essential theoretical concepts and realistic data [1]. an investigation of corrosion behavior was conducted on a scale of 1:5 of a transport container sunk in a seabed [2]. evaluations and surveys on structural reliability considering metal corrosion in steel frame structures and steel-concrete composite beams were conducted in [3-6]. meanwhile, an assessment process was proposed to consider the effects of climate change on the atmospheric corrosion rate of steel structures, taking into account changes in ambient temperature, carbon dioxide, relative humidity, wind, precipitation, and pollution [7]. however, the structural reliability and durability of continuous i-shaped steel beams with corrosion damage have not been assessed so far. this study aimed to evaluate the time-dependent reliability of continuous i-shaped steel beams, considering the effects of corrosion based on a climate change scenario. the climate change scenario was assumed from 2020 to 2120 with time of wetness (tow), sulfur dioxide (so2), chlorides (cl), and temperature (t) as input parameters, and adopted the corrosion model proposed in [8]. the timedependent reliability assessment was a combination of the monte carlo (mc) simulation and the finite element method (fem), estimating the corrosion loss of the cross-section of a steel beam. the computations were conducted in matlab. the numerical results of the corrosion reliability and durability behaviors were determined for exposure times of 10 to 100 years. ii. theoretical background a. climate change scenario this study considered a climate change scenario that included tow, so2, cl, and t as input parameters [9]. their ranges were as follows:  445.40 ≤ tow ≤ 518.80 h/year corresponding author: trong-ha nguyen engineering, technology & applied science research vol. 12, no. 6, 2022, 9523-9526 9524 www.etasr.com nguyen et al.: time-dependent reliability assessment of a continuous i-shaped steel beam …  80.00 ≤ so2 ≤ 98.26 g/m 3  25.85 ≤ cl ≤ 36.78 g/m 2 /day  25.53 ≤ t ≤ 28.10 o c. figure 1 shows the curves of the environmental parameters, each one corresponding to a scenario of climate change. fig. 1. climate change scenarios assumed from 2020 to 2120. b. atmospheric corrosion rate model metal atmospheric corrosion is a complex process and depends on a large number of interacting environmental factors. the atmospheric corrosion of carbon steel in various environments was intensively studied and proposed in [8]. this study adopted this corrosion model to evaluate the reliability of the structures. the following model was used to estimate corrosion loss: �(�) = �. � � �� �� . 1 + ������ �� . 1 + � ��� �� � �( � �) (1) where d(t) is the corrosion depth in μm, t is the exposure time in years, tow is the time of wetness in h/year, [so2] is the sulfur dioxide concentration in g/m 3 , [cl] is the chloride deposition rate in g/m 2 /day, t is the avenge temperature in o c, t0 is an empirical coefficient, and a, b, c, d, e, f, g, h, j are numerical values, which can be found in [8]. c. nominal and distributions of material properties the nominals and distributions of material properties were based on [10], while the cross-sections and loadings were adopted from [11]. d. safety condition of the continuous steel beam the safety condition of the continuous steel beam was based on the eurocode design of steel buildings ec3-1-1 [12]. the safety condition is given by: �( ) = ⎩⎪ ⎪⎪ ⎨ ⎪⎪⎪ ⎧% &'(&),+( − 1,0. /0 ≤ 0 23 &4,'(&56,4.+(7 8 + 3 &9,'(&56,9.+(7 : − 1,0; /0 ≤ 0 % <'(<),+( − 1,0. /0 ≤ 0 2 =>�,? − @ab�cdb � e4fg� − h?,i,jk ; /0 ≤ 0 (2) e. monte carlo simulation the mc simulation method is based on the use of pseudorandom numbers and the law of large numbers to assess the reliability of any system. if the safe domain is defined by the condition f(x)>0, where x is a random vector containing all input random variables, the unsafe probability of the system is determined by: me = n oe(p)qrsp(t)�t = uvoe(p)qrw (3) where if(x)<0 is the indicator function, defined by oe(p)qr = x1 if s(x) < 0 0 if s(x) ≥ 0 (4) according to the theory of statistics, if there are n realizations of the random vector x by propagating the randomness, a sample of n realizations of the indicator function can be obtained. the expected value of the indicator function can be approximately determined by taking the mean of the sample, as expressed in: m̑e = uvoe(p)qrw = /] ∑ oe(p)qr_]_`/ (5) 2020 2030 2050 2070 2120 years 20 25 30 35 40 climate change scenarios year 2020 2020 2030 2050 2070 2120 years 420 440 460 480 500 520 climate change scenarios year 2020 engineering, technology & applied science research vol. 12, no. 6, 2022, 9523-9526 9525 www.etasr.com nguyen et al.: time-dependent reliability assessment of a continuous i-shaped steel beam … a 95% confidence interval for the estimation was defined in [13] as: m̑e %1 − 1.96c/dȇf]ȇf . ≤ me ≤ m̑e %1 + 1.96c/dȇf]ȇf . (6) reliability assessment was evaluated using mc simulations in matlab. the verification of the matlab code has already been presented in [3, 4, 14-16]. iii. time-dependent reliability combining fem, metal corrosion modeling, and monte carlo simulation the computational program for the reliability assessment of the continuous steel beam was developed using fem, the corrosion model with input parameters based on the climate change scenario, and the mc simulations. a. convergence of the monte carlo simulation at pristine a continuous i-shaped steel beam with 3-spans was examined, having the geometry of structure and cross-section as shown in figure 2. the nominal values and distributions of the random variables are shown in table i. the nominal values and the distributions of the material properties were adopted from [10], while the cross-sectional dimensions and applied load were adopted from [11]. reliability assessment was applied in pristine conditions (t = 0 years). figure 3 shows the convergence tests of the mc simulations at the design time (t = 0) for the continuous steel beam. the convergence test of the continuous steel beam was achieved after 2340 samplings in 28.5min, and the safety probability of the structure was up to 96.77%. the test was conducted using an intel® core™ i73930 cpu at 3.20-4.20hz. this result also shows that although there was a safety factor of 1.15 in the analysis, the reliability of the structure was only ps = 96.77%, because of the randomness of input parameters. thus, the assessment of the structure’s reliability is necessary, especially considering the metal corrosion over time. fig. 2. continuous i-shaped steel beam with 3-spans. table i. statistic properties of random variables for reliability assessment properties variables nominal mean/ nominal cov distribution ref. geometric l 6000 (cm) deterministic material fy 248.0 (gpa) 1.10 0.06 lognormal [11] e 200.0 (gpa) 1.10 0.06 lognormal [11] g 81.0 (gpa) 1.10 0.06 lognormal [11] loading dl* 50.0 (kn/m2) 1.05 0.10 normal [10] ll* 30.5 (kn/m2) 1.05 0.10 normal [10] crosssection beam b 200.0 (mm) 1.00 0.05 normal [10] h 480.0 (mm) 1.00 0.05 normal [10] tf 20.0 (mm) 1.00 0.05 normal [10] tw 10.0 (mm) 1.00 0.05 normal [10] fig. 3. convergence of the safety probability (above) and failure probability (below) in the monte carlo simulation of the continuous steel beam at the design time (t = 0). b. effect of metal corrosion on the safety probability the reliability assessment of the continuous steel beam was carried out for different corrosion durations of 10, 20, 50, and 100 years. the summary of the safety probability in the monte carlo simulation of the continuous steel beam, considering its metal corrosion, is shown in table ii and figure 4. table ii. safety probability of the continuous steel beam from 0 to 100 years years 0 10 20 50 100 safety probability (%) 96.77 81.44 75.91 68.61 63.08 fig. 4. reliability decline of the continuous steel beam in 0-100 years. x x y t f t f h b tw cross-section dl+ll l l l y = -0.1832x + 79.777 r² = 0.9049 0 10 20 30 40 50 60 70 80 90 0 20 40 60 80 100 s a fe ty p ro b a b il it y p s ( % ) years engineering, technology & applied science research vol. 12, no. 6, 2022, 9523-9526 9526 www.etasr.com nguyen et al.: time-dependent reliability assessment of a continuous i-shaped steel beam … table ii and figure 4 show that the safety probability of the continuous steel beam, considering metal corrosion from the pristine to 100 years using mc simulation, reduced from 96.77% to 63.08%. in other words, the safe probability after 10, 20, 50, and 100 years of corrosion reduced by 15.33%, 20.86%, 28.16%, and 33.69% respectively. it should be noted that the used convergence criteria of 1.5% justify the confidence of the estimated reliability. iv. conclusion this study evaluated the time-dependent reliability of a continuous i-shaped steel beam, considering the influence of metal corrosion. the numerical results were based on the corrosion model with input parameters from the climate change scenario and monte carlo simulation. in the structural reliability assessment, a wide range of corrosive exposure times from 10 to 100 years was considered. the findings of this study can be summarized as follows:  a climate change scenario in vietnam from 2020 to 2120 was considered in the structural reliability assessment of a continuous i-shaped steel beam.  a computational program was developed in matlab to assess the time-dependent reliability of a continuous ishaped steel beam, considering corrosion effects.  the safety probability of the continuous i-shaped steel beam, considering the metal corrosion from pristine to 100 years, reduced from 96.77% to 63.08%. references [1] r. e. melchers, "the effect of corrosion on the structural reliability of steel offshore structures," corrosion science, vol. 47, no. 10, pp. 2391– 2410, oct. 2005, https://doi.org/10.1016/j.corsci.2005.04.004. [2] a. kosaki, "the corrosion behavior of one-fifth scale lid models of transport cask submerged in sea bottom," corrosion science, vol. 47, no. 10, pp. 2361–2376, oct. 2005, https://doi.org/10.1016/j.corsci.2004. 10.015. [3] t. h. nguyen and d. d. nguyen, "reliability assessment of steelconcrete composite beams considering metal corrosion effects," advances in civil engineering, vol. 2020, dec. 2020, art. no. 8817809, https://doi.org/10.1155/2020/8817809. [4] m. rohani, g. shafabakhsh, a. haddad, and e. asnaashari, "sensitivity analysis of workspace conflicts according to changing geometric conditions," engineering, technology & applied science research, vol. 7, no. 1, pp. 1429–1435, feb. 2017, https://doi.org/10.48084/etasr.1012. [5] n. l. tran and t. h. nguyen, "reliability assessment of steel plane frame’s buckling strength considering semi-rigid connections," engineering, technology & applied science research, vol. 10, no. 1, pp. 5099–5103, feb. 2020, https://doi.org/10.48084/etasr.3231. [6] τ. η. nguyen, "global sensitivity analysis of in-plane elastic buckling of steel arches," engineering, technology & applied science research, vol. 10, no. 6, pp. 6476–6480, dec. 2020, https://doi.org/ 10.48084/etasr.3833. [7] m. n. nguyen, x. wang, and r. h. leicester, "an assessment of climate change effects on atmospheric corrosion rates of steel structures," corrosion engineering, science and technology, vol. 48, no. 5, pp. 359–369, aug. 2013, https://doi.org/10.1179/1743278213y.000000 0087. [8] d. e. klinesmith, r. h. mccuen, and p. albrecht, "effect of environmental conditions on corrosion rates," journal of materials in civil engineering, vol. 19, no. 2, pp. 121–129, feb. 2007, https://doi.org/10.1061/(asce)0899-1561(2007)19:2(121). [9] "viet nam: environment and climate change assessment," asian development bank, mandaluyong, philippines, 2013. [10] b. ellingwood, j. g. macgregor, t. v. galambos, and c. a. cornell, "probability based load criteria: load factors and load combinations," journal of the structural division, vol. 108, no. 5, pp. 978–997, may 1982, https://doi.org/10.1061/jsdeag.0005959. [11] m. f. bartlett, "updating standard shape material properties database for design and reliability," engineering journal-american institure of steel construction, vol. 40, pp. 2–14, 2003. [12] "design of steel structures part 1.4: general rules supplementary rules for stainless steels.," european committee for standardization, cen brussels, env 1993-1-4, 1996. [13] m. lemaire, a. chateauneuf, and j. c. mitteau, fiabilité des structures: couplage mécano-fiabiliste statique. paris: hermes-lavoisier, 2005. [14] n.-l. tran, t.-h. nguyen, and v.-p. phan, "reliability assessment of buckling strength for battened built-up columns steel considering shear deformations," iop conference series: materials science and engineering, vol. 869, no. 5, mar. 2020, art. no. 052041, https://doi.org/10.1088/1757-899x/869/5/052041. [15] d. x. hung and n. t. ha, "assessment reliability of plan frame in the buckling condition using stochastic finite element method," journal of science and technology in civil engineering, vol. 10, no. 2, pp. 23–30, mar. 2016. [16] n. ha t, "reliability assessment of frame steel considering semi-rigid connections," journal of materials and engineering structures « jmes », vol. 6, no. 1, pp. 119–126, mar. 2019. microsoft word etasr_v12_n3_pp8701-8706 engineering, technology & applied science research vol. 12, no. 3, 2022, 8701-8706 8701 www.etasr.com fahim et al.: the behavior of rc beams retrofitted with carbon fiber reinforced polymers (cfrp) the behavior of rc beams retrofitted with carbon fiber reinforced polymers (cfrp) muhammad fahim civil engineering department university of engineering and technology, peshawar peshawar, pakistan drmfahim@uetpeshawar.edu.pk fakhere alam civil engineering department university of engineering and technology, peshawar peshawar, pakistan falam.ms20nice@student.nust.edu.pk hazrat khan civil engineering department university of engineering and technology, peshawar peshawar, pakistan hazkhan.pg19mce@student.nust.edu.pk inzimam ul haq civil engineering department university of engineering and technology, peshawar peshawar, pakistan inzimamul.haq2@students.uettaxila.edu.pk shahid ullah civil engineering department university of engineering and technology, peshawar peshawar, pakistan shahid.ullah@uetpeshawar.edu.pk saeed zaman civil engineering department university of engineering and technology, peshawar peshawar, pakistan saeed.zaman79@gmail.com received: 17 march 2022 | revised: 5 april 2022 | accepted: 7 april 2022 abstractthe need for the introduction of economical and quicker retrofitting techniques is increasing due to the ever-aging infrastructure and damages produced by major catastrophic events around the world. the application of carbon fiber reinforced polymers (cfrps) for strengthening and retrofitting of reinforced concrete structures is gaining popularity due to its higher strength, lightweight, durability, corrosion resistance, and aesthetic value. this study presents the results of two strengthened and two retrofitted beams in comparison to control specimens. two specimens were strengthened and two were retrofitted by attaching cfrp (sika carbo-dur s812 or sikawrap 230c) to the tension side of the beams using high strength epoxy. the results show that one cfrp strip/wrap simply attached at the tension side can help the damaged beam regain/pass the original strength. all specimens fail due to debonding of cfrp from the concrete surface emphasizing the need for efficient anchorage systems. among the four patterns adopted, cfrp strips along with u-shaped anchorages at the ends provided the highest strength enhancement of 17.36%. keywords-cfrp; strengthening; retrofitting; reinforced concrete beams; debonding i. introduction collapse and cracking of structural elements of buildings, bridges, or other structures take place due to poor construction practices, use of low quality materials, inappropriate design of elements, and application of unexpected external loads that have not been considered during the design. retrofitting is defined as the strengthening intervention that is able to restore an acceptable level of safety against such actions [1]. the terms retrofitting and strengthening are generally used interchangeably. however, more precisely, the term rehabilitation is used when a structure is strengthened before an earthquake or other damaging phenomena whereas strengthening of damaged structures is called retrofitting [2]. carbon fiber reinforced polymer (cfrp) is made of two components, carbon fiber and resin and is used extensively for the retrofitting of reinforced concrete structures. it has the desirable properties of higher strength, light weight, durability, electrical and corrosive resistance, and good aesthetic appearance. the base material (poly acrylonitrile-pan) of cfrp has higher molecular orientation [3]. in 1977, because of its higher stiffness and high strength-to-weight ratio, cfrps were used in the casing of aircrafts. in 1980, cfrps were used as a reinforcement material in reinforced concrete beams. ever since their first use in the construction industry, cfrp retrofitted members have been extensively investigated, both experimentally and numerically. authors in [4] compiled a database of 127 beam specimens from the literature which were externally bonded with cfrp and gfrp sheets to increase the flexure capacity and were tested under 4-point loading. about one third of the tested specimens with external reinforcement demonstrated strength increase of 50% or more in combination with considerable deflection capacity. authors in [5] used three different reinforcement ratios of cfrp and concluded that with corresponding author: muhammad fahim engineering, technology & applied science research vol. 12, no. 3, 2022, 8701-8706 8702 www.etasr.com fahim et al.: the behavior of rc beams retrofitted with carbon fiber reinforced polymers (cfrp) the increase in reinforcing ratios in beams, their load carrying capacity increased. authors in [6] carried out an experimental study of rc beams to investigate the behavior of structurally damaged full-scale rc beams retrofitted with cfrp laminates. the increase in maximum load value of the specimens was between 7% and 33% for retrofitting in flexure. the main failure mode found was plate debonding which reduced the efficiency of retrofitting. authors in [7] performed experimental and numerical studies of cfrp retrofitted beams and concluded that the strength of rc beams with single layers of cfrp was enhanced from 18 to 20% and for double layers from 40 to 45%. the deflection of rc retrofitted beams was also decreased by about 80% that of control beams. authors in [8] studied the flexure behavior of corroded reinforced concrete beams strengthened with cfrp and found 30 to 50% increase in capacity along with improvement in stiffness. cfrp has also been used in other rc components and under different loading conditions. for example, t-beams [9], columns [10], shear walls [11], and joints [12]. similarly, various rc components retrofitted with cfrp were investigated under various loading conditions, e.g. under torsion [13], impact loading [14], and under fire exposure [15]. in many practical situations, adopting a comprehensive retrofitting scheme is not feasible due to financial, time, or execution constraints. therefore, the main objective of this study is to investigate the effect of simple retrofitting schemes on the flexural behavior of reinforced beams. two specimens were strengthened and two were retrofitted by attaching cfrp (sika carbo-dur s812 or sika-wrap 230c) to the tension side of the beams using high strength epoxy. in addition, one strengthened and one retorfitted beam had u-shaped anchorages of the same sika-wrap 230c. the results are discussed and recommendations are presented in the subsequent sections. ii. experimental study a. materials concrete with a specified compressive strength of 4,000 psi was used for casting the beam specimens. the average compressive strength of the companion cylinders tested in accordance with astm c-39 as shown in figure 1 was found to be 3,940 psi. fig. 1. concrete cylinder test setup. astm a615 grade 60 steel (1/2in diameter bars) was used for tension reinforcement and grade 40 steel (3/8in diameter bars) was used for transverse reinforcement as well as compression hangers. the average yield strength was found to be 59.94ksi and 52.28ksi for grade 60 and grade 40 steel respectively. sika carbodur s812 cfrp strips and sikawrap 230c wraps/sheets were used for strengthening and retrofitting the beam specimens. these conform to astm d7205/d7205m-06 [16]. the properties of cfrp strips and wraps as provided by the manufacturer are given in table i. table i. cfrp properties cfrp type thickness (in.) width (in) tensile strength (ksi) modulus of elasticity (ksi) sika carbodur s812 0.047 3.15 400 23.2 × 10 3 sikawrap 230c 0.0052 6 460 31.9 × 10 3 high strength epoxy sikadur 30 [17] was used for attaching cfrp strips with the concrete surface. similarly, for bonding the cfrp wraps to the concrete surface, sikadur 330 [18] adhesive was used. both types of epoxy are two-component thixotropic [17] epoxy including resin and filler designed for use at normal temperature. they conform to astm c-881 [19] and aashto m-235 [20] specifications. b. test specimens five beams of 7ft length were casted and tested under 4point (pure bending) loading. the dimensions and reinforcement details of the specimens are shown in table i. two beams were strengthened with cfrp before the application of any load whereas two beams were first tested to cracking moment and then retrofitted before testing again to collapse load. two patterns were used for cfrp application, the first pattern consisted of a 3.15in wide and 0.0394in thick strip with 5in wide u-shaped anchorages at the ends as shown in figure 3. the second pattern consisted of a 6in wide and 0.0052in thick wrap without any anchorage as shown in figure 4. in both cases the cfrp was applied on the tension side in the middle half of the span. each pattern was applied to one strengthened and one retrofitted beam. fig. 2. cross section details of the specimens. engineering, technology & applied science research vol. 12, no. 3, 2022, 8701-8706 8703 www.etasr.com fahim et al.: the behavior of rc beams retrofitted with carbon fiber reinforced polymers (cfrp) fig. 3. first pattern of cfrp for beam specimens. fig. 4. second pattern of cfrp for beam specimens. c. test setup the beams were tested under 4-point loading (pure bending) as shown in figure 5. the deflection was recorded using a ucam-70a data logger. fig. 5. schematic of the test setup. iii. results and discussion a. failure pattern the failure patters of the four strengthened/retrofitted specimens are shown in figures 6-9. the predominant failure was due to the debonding of cfrp from the concrete surface. the higher flexural stresses in the middle half of the beams caused tensile cracks which were widened with the increase in the applied load. at the location of these cracks, concentrated stresses weaken the bond between cfrp and concrete and eventually lead to the complete debonding of cfrp from the surface. failure immediately follows after the debonding. the specimens without any anchorages (specimens b4 and b6) experienced even more pronounced debonding as shown in figures 7 and 9. the simple u-shaped anchorages (without any mechanical anchors) provided in the specimens b3 and b5 has a significant impact in reducing the crack widths and delaying debonding as shown in figures 6 and 8. (a) (b) fig. 6. final failure pattern of specimen b3. b. load vs displacement relationships figures 10 and 11 show the load vs mid-span deflection of control and strengthened beams with cfrp strips and wraps. the strengthened beams are in fact the control beams after they were tested to their ultimate capacity and were strengthened with cfrp before being tested again. it can be seen that the beams strengthened with cfrp strips regain/crossed their original strength but the beams strengthened with cfrp wraps fell slightly short of their original strength. in both cases, the strengthened specimens had larger ultimate displacement. however, reduced stiffness was observed in strengthened beams, especially the specimen with cfrp wraps. however, the final displacement recorded was much higher than that of both control specimens. it must be noted that the cfrp strip used in the specimen b3 was anchored by applying u-shaped wraps at both ends as shown in figure 6. the effect of this anchorage can be noted by comparing figures 10 and 11 as both ultimate load and displacement are higher for specimen b3 than for specimen b4. engineering, technology & applied science research vol. 12, no. 3, 2022, 8701-8706 8704 www.etasr.com fahim et al.: the behavior of rc beams retrofitted with carbon fiber reinforced polymers (cfrp) (a) (b) fig. 7. final failure pattern of specimen b4. (a) (b) fig. 8. final failure pattern of specimen b5. figures 12 and 13 show the load vs mid-span deflection of control and retrofitted beams with cfrp strips and wraps. the cfrp strip in beam b5 was anchored at the end using a ushaped shear wrap as shown in figure 8. this beam achieved the highest ultimate strength and the recorded displacement at failure was also the highest among all specimens. retrofitted beam b6 reached the strength level of control specimen b2 but it was less than control specimen's b1. (a) (b) fig. 9. final failure pattern of specimen b6. fig. 10. load vs displacement relationships of control specimens and a specimen strengthened with cfrp strips. fig. 11. load vs displacement relationships of control specimens and a specimen strengthened with cfrp strips. engineering, technology & applied science research vol. 12, no. 3, 2022, 8701-8706 8705 www.etasr.com fahim et al.: the behavior of rc beams retrofitted with carbon fiber reinforced polymers (cfrp) fig. 12. load vs displacement relationships of control specimens and a specimen retrofitted with cfrp strips. fig. 13. load vs displacement relationships of control specimens and a specimen retrofitted with cfrp wraps. table ii shows the maximum load, the corresponding displacement, and the final load and displacement values for all specimens. the highest load and displacement capacity were observed for specimen b5 which was retrofitted with cfrp strips along with u-shaped anchorages. one of the most important characteristics observed for the strengthened and retrofitted beams was their ability to withstand inelastic deformations. this manifests an increased ductility of the beams which is highly desirable in earthquake resistant structures. table ii. summary of the test results of beam specimens specimen maximum load and corresponding displacement final load displacement debonding load (kn) pmax (kn) ∆max (mm) pf (kn) ∆f (mm) b1 121.11 13.76 118.65 14.21 - b2 105.07 11.19 100.26 14.40 - b3 117.61 12.03 101.09 32.71 113.74 b4 99.33 14.65 89.60 20.68 96.08 b5 132.71 29.10 125.21 41.09 131.36 b6 105.54 30.86 92.18 33.69 100.97 iv. conclusions this study investigated the effect of cfrp retrofitted on the flexural behavior of reinforced concrete beams. six specimens were tested, two control beams, two beams strengthened with cfrp after testing to ultimate capacity, and two beams were retrofitted with cfrp before they were exposed to any loading. the following conclusions can be drawn from the results obtained in the study: • a simple strip/wrap of cfrp applied at the critical locations can help damaged structural components regain their original (pre-loading) strength. all four specimens in this study regained/crossed the strength of control specimens with the application of a single cfrp strip/wrap in the middle half span on the tension side. • the study demonstrates the common failure pattern in cfrp retrofitted beams is the debonding of cfrp from the concrete surface. effective anchorage systems can greatly enhance the capacity of retrofitted rc structures by delaying the debonding process and stressing the cfrp to higher levels. • the highest strength achieved in this study for a retrofitted beam is 17.36% higher the average strength of control specimens. this is an encouraging sign for the use of cfrp in retrofitting and strengthening of existing old or damaged rc structures. the application is quick, simple and doesn’t involve high skilled labor. references [1] a. costa, a. arêde, and h. varum, eds., strengthening and retrofitting of existing structures, 1st ed. new york, ny, usa: springer, 2017. [2] m. ashraf, "development of low-cost and efficient retrofitting technique for unreinforced masonry buildings," ph.d. dissertation, university of engineering and technology, peshawar, pakistan, 2010. [3] "carbon fiber reinforced polymer (cfrp) uses and properties," essaycompany. https://www.essaycompany.com/essays/chemistry/ carbon-fiber-reinforced-polymer-cfrp-5854 (accessed apr. 27, 2022). [4] j. f. bonacci and m. maalej, "behavioral trends of rc beams strengthened with externally bonded frp," journal of composites for construction, vol. 5, no. 2, pp. 102–113, may 2001, https://doi.org/ 10.1061/(asce)1090-0268(2001)5:2(102). [5] m. r. esfahani, m. r. kianoush, and a. r. tajari, "flexural behaviour of reinforced concrete beams strengthened by cfrp sheets," engineering structures, vol. 29, no. 10, pp. 2428–2444, oct. 2007, https://doi.org/10.1016/j.engstruct.2006.12.008. [6] y. t. obaidat, s. heyden, and o. dahlblom, "the effect of cfrp and cfrp/concrete interface models when modelling retrofitted rc beams with fem," composite structures, vol. 92, no. 6, pp. 1391–1398, may 2010, https://doi.org/10.1016/j.compstruct.2009.11.008. [7] p. alagusundaramoorthy, i. e. harik, and c. c. choo, "flexural behavior of r/c beams strengthened with carbon fiber reinforced polymer sheets or fabric," journal of composites for construction, vol. 7, no. 4, pp. 292–301, nov. 2003, https://doi.org/10.1061/(asce)10900268(2003)7:4(292). [8] s. linwang, c. jian, c. qingjun, l. guobao, and z. juan, "investigation on the flexural behavior of corroded concrete beams repaired by cfrp sheet under different corrosion levels," the open civil engineering journal, vol. 10, no. 1, sep. 2016, https://doi.org/10.2174/1874149501610010598. [9] a. bennitz, j. w. schmidt, j. nilimaa, b. taljsten, p. goltermann, and d. l. ravn, "reinforced concrete t-beams externally prestressed with unbonded carbon fiber-reinforced polymer tendons," structural journal, vol. 109, no. 4, pp. 521–530, jul. 2012, https://doi.org/ 10.14359/51683871. [10] j. a. o. barros, r. k. varma, j. m. sena-cruz, and a. f. m. azevedo, "near surface mounted cfrp strips for the flexural strengthening of rc columns: experimental and numerical research," engineering structures, engineering, technology & applied science research vol. 12, no. 3, 2022, 8701-8706 8706 www.etasr.com fahim et al.: the behavior of rc beams retrofitted with carbon fiber reinforced polymers (cfrp) vol. 30, no. 12, pp. 3412–3425, dec. 2008, https://doi.org/10.1016/ j.engstruct.2008.05.019. [11] n. askarizadeh and m. r. mohammadizadeh, "numerical analysis of carbon fiber reinforced plastic (cfrp) shear walls and steel strips under cyclic loads using finite element method," engineering, technology & applied science research, vol. 7, no. 6, pp. 2147–2155, dec. 2017, https://doi.org/10.48084/etasr.1279. [12] w. t. lee, y. j. chiou, and m. h. shih, "reinforced concrete beam– column joint strengthened with carbon fiber reinforced polymer," composite structures, vol. 92, no. 1, pp. 48–60, jan. 2010, https://doi.org/10.1016/j.compstruct.2009.06.011. [13] g. al-bayati, r. al-mahaidi, and r. kalfat, "experimental investigation into the use of nsm frp to increase the torsional resistance of rc beams using epoxy resins and cement-based adhesives," construction and building materials, vol. 124, pp. 1153–1164, oct. 2016, https://doi.org/10.1016/j.conbuildmat.2016.08.095. [14] j. abd and i. k. ahmed, "the effect of low velocity impact loading on self-compacting concrete reinforced with carbon fiber reinforced polymers," engineering, technology & applied science research, vol. 11, no. 5, pp. 7689–7694, oct. 2021, https://doi.org/10.48084/etasr.4419. [15] h. a. al-baghdadi and a. sabah, "behavior of rc beams strengthened with nsm-cfrp strips subjected to fire exposure: a numerical study," engineering, technology & applied science research, vol. 11, no. 6, pp. 7782–7787, dec. 2021, https://doi.org/10.48084/etasr.4493. [16] d. p. abrams and n. shah, "cyclic load testing of unreinforced masonry walls," illinois university at urbana advanced construction technology center, urbana, il, usa, 92-26-10, dec. 1992. [17] "sikadur®-30," sika. https://gbr.sika.com/en/construction/structuralstrengthening/adhesives-and-bonding/structural-adhesives/sikadur30.html (accessed apr. 27, 2022). [18] "sikadur®-330," sika. https://gbr.sika.com/en/construction/structuralstrengthening/adhesives-and-bonding/structural-adhesives/sikadur330.html (accessed apr. 27, 2022). [19] g. magenes and g. m. calvi, "cyclic behavior of brick masonry walls," in earthquake engineering, tenth world conference, rotterdam, netherlands, 1992. [20] aashto m 235m/m 235-13 (2018): standard specification for epoxy resin adhesives (astm designation: c 881-10). american association of state and highway transportation officials, 2013. microsoft word etasr_v13_n1_pp10027-10032 engineering, technology & applied science research vol. 13, no. 1, 2023, 10027-10032 10027 www.etasr.com rajderkar & chandrakar: design coordination of a fuzzy-based unified power flow controller with … design coordination of a fuzzy-based unified power flow controller with hybrid energy storage for enriching power system dynamics vedashree p. rajderkar department of electrical engineering, g h raisoni college of engineering, india vedashree.rajderkar@raisoni.net (corresponding author) vinod k. chandrakar department of electrical engineering, g h raisoni college of engineering, india vinod.chandrakar@raisoni.net received: 21 november 2022 | revised: 5 december 2022 | accepted: 7 december 2022 abstract in power networks, operation planning has become necessary due to the continuously increased load demand. the unified power flow controller (upfc) controls the power flow through the network and improves the dynamics of the power system. in this paper, the design application of the coordination of a fuzzy-based upfc with hybrid energy storage has been proposed to enrich the system's dynamic performance during abnormal conditions and improve the hybrid energy storage performance during transients when the dc link voltage is insufficient to meet the converter voltage demand. the hybrid energy storage consists of a supercapacitor and a battery connected across the upfc vdc shunt capacitor. the proposed system to improve the upfc performance during large disturbances on a multi-machine system was designed and tested in matlab/simulink. keywords-fuzzy logic; upfc; hybrid energy storage; super capacitor; battery; dynamic stability i. introduction in modern power networks, the interconnected transmissions have to limit the challenges on stability, security, and control operation of the power system in order to operate the transmission network below its thermal capability. when transferring power at a high voltage level, a power system's transient stability refers to its capacity to keep equipment running synchronously in the face of significant disturbances [1]. flexible ac transmission system (facts) controllers are utilized in power transmission systems to increase the stability of the electrical network. the most adaptable facts device is the upfc. the upfc's main duty is to regulate the flow of both reactive and actual power by providing a voltage to the line. voltage control, improved transient stability and damping oscillation are the secondary functions of the upfc [2]. in the upfc design, the shunt converter's primary job is to generate or absorb active power from the line, much like a shunt compensator. the dc link capacitor can be charged by the shunt converter, which also uses it to power the series converter. any losses and useful power utilized or supplied by the series branch must be compensated by a shunt branch. if the power balance is not maintained, voltage cannot remain constant. the active power can have a closed channel via the converter but the reactive power cannot due to the associated dc link capacitor between the two converters. during small transients, the dc bus compensates for the converter losses in the upfc by charging or discharging operations [3]. the energy in the dc bus cannot be suppressed during large transient oscillations without degrading the dc voltage. in order to reduce oscillations without impacting the effect of dc link voltage, it is desirable to interchange real power with the storage device when using a fully discharged hybrid energy storage system with a back to back dc-dc converter [4-5]. to offer a significant amount of short-term actual power exchange, a shunt with a dc bus capacitor and a hybrid energy storage device are used. the components of a upfc with hybrid energy storage are coordinated by using fuzzy logic to improve the transient stability of the system. authors in [1] introduce the pole-shifting controller-based csc-statcom, which is intended to improve the transient stability of a two-area network. in order to boost oscillation damping capabilities, a damping stabilizer based on pss is being used. however, they are unable to confirm how well the fuzzy-based upfc with hybrid energy storage will operate in a dynamic environment. the way a coordinated upfc based on fuzzy logic affects the flow of actual power was evaluated in both normal and abnormal circumstances in [2]. the performance of the hybrid energy storage is not a metric in this case. the statcom can be used along with battery energy storage with the performance engineering, technology & applied science research vol. 13, no. 1, 2023, 10027-10032 10028 www.etasr.com rajderkar & chandrakar: design coordination of a fuzzy-based unified power flow controller with … indices technique for improved power situation when using various power controllers [3]. due to the additional control freedom, the facts/bess has greater flexibility and damping capabilities than the standard facts. however, the use of fuzzy-based hybrid energy storage in conjunction with the upfc for dynamic performance was not tried. authors in [4] offer a new approach of decreasing the error by the coupling of a neuro-fuzzy scheme with the pi controller for boosting transient stability. however, the damping capability of the hybrid energy storage was not tested. the first swing stability problem is dampened by the upfc utilizing a local measurement approach. the use of hybrid energy storage in conjunction with the fuzzy-based upfc to maintain the necessary dc bus voltage to transfer real power across converters during an interruption was not demonstrated [5]. authors in [6] present an innovative, best-practice fuzzy pid controller based on upfc, its gains are increased when the time-weighted absolute error integral is taken into consideration by the pso-gwo method. low frequency oscillations in the power system have been reduced with the proposed controller, but the impact of storage with upfc was not covered. in [2], a fuzzy logic technique was used to increase a power network's transient stability. the unified power flow controller has three synchronized control inputs. however, how well the fuzzy-based upfc works with storage hasn't been tested. authors in [7] examined quadrature voltage control and in-phase voltage control as fuzzy logic-based upfc solutions for enhancing power system transient stability utilizing the energy function method. however, the compatibility of fuzzy-based upfc with storage was not examined. in order to improve the transient stability for upfc, the authors in [8] looked towards designing a neuro-fuzzy controller, although the fuzzy-based upfc with storage was not investigated. for improving transient stability, rbfnbased upfc performance was reported in [9], but upfc with storage was not considered. for improving transient stability, rbfn based upfc performance was reported in [10]. many researchers presented combinations of fuzzy-based upfcs [1113]. however, they did not focus on the effects of the hybrid energy storage during abnormal conditions [14-16]. the above mentioned authors did not covered in depth the hybrid energy storage, which consists of a supercapacitor with lithium-ion batteries connected across the vdc of the upfc, during large sudden disturbances in a power network. hybrid energy enhances the upfc primary function of power flow and the secondary function of oscillation damping. the pi-based upfc has limitations under various system conditions in large nonlinear systems. the fuzzy-based upfc replaced the pi with significant improvement of performance. in this study, we present the design of a fuzzy inference for series and shunt voltage source converter (vsc)-based upfc controller to improve the transient performance of upfc, which is comparable with the pi-based upfc. the transient performance of the upfc was enhanced during sudden large disturbances in the power network by connecting hybrid storage across vdc. according to the simulation results, the coordination of the fuzzy-based upfc combined with the hybrid energy storage will function better in enhancing the dynamics under significant disturbances in the network. the improved upfc performance has led to an improvement in system performance. matlab was used to test the proposed fuzzy-based upfc design with hybrid energy storage in a multi-machine scenario. ii. the proposed model the power network used in this paper is a multi-machine system with upfc in combination with hybrid energy storage during abnormal condition as shown in figure 1. generator g1 represents dynamic sources, while generators g2 and g3 provide static sources. two six-pulse converters linked to a common capacitor make up the power injection model of the upfc. the upfc shunt converter regulates the useful power insertion from the shunt converter to the power network by controlling the dc bus voltage across the capacitor. in contrast, a vsc that is connected in series can inject a voltage at the line frequency that has a controlled magnitude and phase angle. as a result, the vsc connected in series receives a very less amount of useful power from the transmission system to change the injected series voltage. a back-to-back dc-dc converter is used to create a shunt connection between the dc bus of the upfc device and the hybrid energy storage, as shown in figure 1. in order to enhance the dynamic stability of the power network, the upfc device often generates or absorbs reactive power. when the dc bus capacitor is unable to support the upfc during a transient circumstance, the hybrid energy storage offers its energy storage to the upfc [17, 18]. the converters' ability to exchange real power is required anytime. when there are disturbances, it can maintain a balance in the power transmission between generation and demand without violating the stability limit. while the upfchybrid energy storage is connected between bus b1 and b2, a 3-phase short circuit fault occurs near bus b1 for durations of 0.3s and 0.2s. the following equation describes the generator dynamics: � ����� � = �� − � (1) where pm is turbine power, pe is output electrical power, m is the inertia constant, and δ is the torque angle. the fundamental p and q equations are: � = �� ���� sin � + ��� � � � �� − ���� sin 2� (2) � = ���� �� cos � + � � � ��� − � �� � !"#�� − ����� (3) the upfc equations are: � = �$�%x sin � + �'(�% x sin(� + *) (4) � = �$ �%x (cos � − 1) + �'(�% x cos(� + *) (5) when * = 90/ − �. the hybrid energy storage consisting of a super capacitor and a battery is demonstrated in figure 2. engineering, technology & applied science research vol. 13, no. 1, 2023, 10027-10032 10029 www.etasr.com rajderkar & chandrakar: design coordination of a fuzzy-based unified power flow controller with … g3 500kv, 9000 mva g1 13.8kv, 1000 mva 13.8kv/500kv 1000mva b1 500 kv b2 500 kv b3 500 kv b4 500kv g2 500 kv, 6500 mva l1 3000mw l 2 9500mw 3ϕ fault 75km 180km dc link series transformer upfc sh transformer 255km dc -dc converter hybrid energy storage vsc2vsc 1 sw fig. 1. system model with combination of upfc and hybrid energy storage. fig. 2. hybrid energy storage. the supercapacitor output voltage is expressed as: 01 = 2'34�252( 6678$ + �2(2'9: ; sinh=� > 34 25 2(�8$?@9:667a b c01 ∙ "01 (6) where �: is the electric charge, ef is the number of series supercapacitors, np the number of parallel supercapacitors, r the ideal gas constant, t the operating temperature, d the molecular radius, ne the number of layers of electrodes, ai the interfacial area between the electrodes and the electrolyte, c the molar concentration, and f the faraday's constant. the super capacitor energy is directly proportional to the dc voltage and its capacitance is [17]: g01 � �� h 01� (7) the maximum power of the super capacitor is: ��ij � �kl � m9(� (8) where req is the equivalent resistance. the stored energy in a battery depends on the stored charge and its voltage. the operating power of a battery is represented by: p =vi= (e-ir) i= ei-i2r (9) the following equations are used in the lithium-ion battery model: a) model for discharge (i* > 0) n�) "o, " ∗, "+ � gr s. 33=u� . " ∗ s. 3 3=u� . "o � v. wxy ) z. "o) (10) b) model for charge (i* < 0) n�) "o, " ∗, "+ � gr s. 3u�[/.�3 . " ∗ s. 3 3=u� . "o � v. wxy ) z. "o+ (11) where a is the exponential voltage, b is the exponential capacity, e0 is the constant voltage, k is the polarization constant, i* is the low-frequency current dynamics, i is the battery current, and q is the maximum battery capacity. the hybrid energy storage voltage and the steady state dc bus voltage are related through the duty cycle d, which can be modified in such a way that it will helps damp power oscillations as: �a � \�=\ ]�0 (12) a. fuzzy logic-based upfc in comparison to the traditional control strategy, the advantage of the fuzzy logic technique is that it does not need exact quantitative values for the control inputs and system variables. fuzzy logic controllers are more adaptable and work without the need for a mathematical description of the power network. the fuzzy logic approach is a good and effective method for regulating a upfc. b. fuzzy-based shunt voltage regulator of the vsc the input to the fuzzy logic controller consists of vref and vmes. the process of fuzzification entails mapping the input variables onto linguistically fuzzy variables. there is a distinct membership function for each fuzzy variable. the inputs are fuzzy-set using 3 trapezoid-shaped membership functions. the voltage regulator is achieved by adjusting the difference of vref and vmes which is the input to the fuzzy logic as shown in figure 3. on the basis of fuzzed linguistic features, control judgments are made. inference entails guidelines for selecting which outputs to employ. the input variables of the fuzzy coordination controller of the shunt voltage regulator consist of 3 fuzzy variables and 9 fuzzy rules to control the shunt current. fig. 3. fuzzy-based shunt voltage regulator of vsc. table i shows the input output mapping of the fuzzy rulebased system. the mamdani inference system produces linguistic variables as its output. they need to be quantitatively translated into the output. the fuzzy controller employs the centroid approach. c. fuzzy-based series current regulator of the vsc using a current regulator, the line currents are forced to match the corresponding reference values in order to control the useful and reactive power flow in the line. each fuzzy variable has a different membership function. for input and engineering, technology & applied science research vol. 13, no. 1, 2023, 10027-10032 10030 www.etasr.com rajderkar & chandrakar: design coordination of a fuzzy-based unified power flow controller with … output, trapezoidal membership functions were chosen. as shown in figure 4, the fuzzy control produces the series injected voltage in collaboration with 2 separate pi controllers. a collection of basic membership functions is produced using the current. nine concepts are used by the fuzzy coordination controller to control series voltage. a time-based pulse in a model of all-systems has a defuzzifier as its final state. table i. input-output mapping of the shunt vsc vm v ref s_vm m_vm l_vm s_v ref s_o/p m_o/p l_o/p m_v ref m_o/p m_o/p l_o/p l_v ref l_o/p l_o/p l_o/p fig. 4. series current regulator of vsc with fuzzy logic. the design of the series current regulator for the fuzzy inference system of the vsc is shown in tables ii and iii. table ii. series current regulator signal id inference system coordination for vsc id id ref s_id m_id l_id s_idref s_o/p m_o/p l_o/p m_idref m_o/p m_o/p l_o/p l_idref l_o/p l_o/p l_o/p table iii. coordinated series current regulator signal iq of the vsc inference system iq iq ref s_iq m_iq l_iq s_iq ref s_o/p m_o/p l_o/p m_iq ref m_o/p m_o/p l_o/p l_iq ref l_o/p l_o/p l_o/p iii. simulation results the digital simulation of the hybrid energy storage with fuzzy logic-based upfc was carried out in a multi-machine system in matlab when a 3-phase fault occurs at the sending end of the transmission lines near bus b1. the aim is to enhance the power system dynamic performance as well as to check the secondary function of upfc to damp out the oscillations during abnormal conditions. the design coordinated action of the fuzzy-based upfc with hybrid energy storage improves the damping performance of the system and reduces the dynamics. figure 5 demonstrates how the fuzzy-based upfc with hybrid energy storage reduces the power fluctuations in the rotor speed of the generator g1 in all the considered scenarios during fault durations. the system with the fuzzy-based upfc and the hybrid energy storage is superior than without upfc, with pi-upfc, and with fuzzy logic-based upfc. it significantly improves the dynamic performance of the system. the proposed fuzzy-based upfc with hybrid energy storage was tested in a multi-machine system for fault durations of 0.2 and 0.3s. the terminal voltage of the generator g1 is shown in figure 6. the results indicate that the proposed fuzzy controller has satisfactory operation over the pi-based controller and gets better enrichment in the dynamic performance of the system. the fuzzy-based upfc with hybrid energy storage stables the generator g1 terminal voltage waveform in minimum number of cycles. (a) (b) fig. 5. speed of rotor at g1 without upfc, with upfc based on pi, with fuzzy logic-based upfc, and with fuzzy logic-based upfc and hybrid energy storage during (a) a 0.2s fault and (b) a 0.3s fault. figure 7 shows that the initial swing is suppressed under post fault conditions. the flow of real power with the fuzzybased upfc with hybrid energy storage indicates that it increases the power handling capability of the upfc during transient conditions when the dc link capacitor is inadequate to exchange the real power between the converters. figure 8 indicates that the fuzzy-based upfc with hybrid energy storage provides reactive power support during large disturbances to maintain the dc link voltage between the converters and also helps maintain voltage profile after clearing the fault. engineering, technology & applied science research vol. 13, no. 1, 2023, 10027-10032 10031 www.etasr.com rajderkar & chandrakar: design coordination of a fuzzy-based unified power flow controller with … (a) (b) fig. 6. g1 terminal voltage without upfc, with upfc based on pi, with fuzzy logic-based upfc, and with fuzzy logic-based upfc and hybrid energy storage during (a) a 0.2s fault and (b) a 0.3s fault. (a) (b) fig. 7. bus b2 real power voltage without upfc, with upfc based on pi, with fuzzy logic-based upfc, and with fuzzy logic-based upfc and hybrid energy storage during (a) a 0.2s fault and (b) a 0.3s fault (a) (b) fig. 8. bus b2 reactive power voltage without upfc, with upfc based on pi, with fuzzy logic-based upfc, and with fuzzy logic-based upfc and hybrid energy storage during (a) a 0.2s fault and (b) a 0.3s fault iv. discussion rotor speed damping varies from 13s without upfc to 7.5s with the fuzzy-based upfc with hybrid energy storage for the fault duration of 0.2s. therefore, settling time reduces by 42.3%. similarly, for 0.3s fault duration, the settling time of the rotor speed without upfc is 9.5s which reduces to 5.5s with the fuzzy-based upfc with hybrid energy storage (38.7% reduction). these values indicate the significant dynamic performance of the fuzzy-based upfc with hybrid energy storage for improving the dynamic stability of the system. the primary function of the upfc is to regulate the terminal voltage which is enhanced by the fuzzy-based upfc with hybrid energy storage. the basic function of the upfc is to control real and reactive power under abnormal condition, something that has been significantly achieved with the proposed controller. the proposed hybrid energy storage with upfc improves the fundamental performance of the upfc during sudden large disturbances hence the system dynamic stability is improved. v. conclusion in this paper, a fuzzy-based upfc with hybrid energy storage is proposed to enrich the power system dynamics. the engineering, technology & applied science research vol. 13, no. 1, 2023, 10027-10032 10032 www.etasr.com rajderkar & chandrakar: design coordination of a fuzzy-based unified power flow controller with … design objectives are to maximize the power flow and to minimize the oscillation damping during large disturbances in a multi-machine system. the simulation results illustrate that the combination of the fuzzy-based upfc with the hybrid energy storage meets the design objectives and demonstrate the robustness of the fuzzy logic controller over the pi controller. due to the hybrid energy storage application during large disturbances with duration of 0.2s and 0.3s, the real power support from vdc to the system increases and helps oscillation damping. the fuzzy inference is designed to coordinate the pi controller with the storage device. the overall performance of the upfc during disturbance conditions has been significantly improved. references [1] s. gupta and r. tripathi, "two-area power system stability improvement using a robust controller-based csc-statcom," acta polytechnica hungarica, vol. 11, no. 7, pp. 135–155, jan. 2014. 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[18] v. p. rajderkar and v. k. chandrakar, "enhancement of power system security by fuzzy based unified power flow controller," in 2022 2nd international conference on intelligent technologies (conit), hubli, india, jun. 2022, https://doi.org/10.1109/conit55038.2022.9847699. microsoft word etasr_v12_n5_pp9160-9165 engineering, technology & applied science research vol. 12, no. 5, 2022, 9160-9165 9160 www.etasr.com vu et al.: correlation analysis of earthquake intensity measures and engineering demand parameters … correlation analysis of earthquake intensity measures and engineering demand parameters of reactor containment structure xuan-hung vu department of civil engineering, vinh university vinh, vietnam vxhlkc@gmail.com thanh-tung thi nguyen department of civil engineering, vinh university vinh, vietnam ntttung@gmail.com van-long phan department of civil engineering, vinh university vinh, vietnam phanlongkxd@vinhuni.edu.vn duy-duan nguyen department of civil engineering, vinh university vinh, vietnam duyduankxd@vinhuni.edu.vn received: 4 july 2022 | revised: 24 july 2022 | accepted: 25 july 2022 abstract-this study aims to analyze the correlation between earthquake intensity measures (ims) and seismic responses of a reactor containment building in an apr-1400 nuclear power plant. a total of 20 ims were employed to develop seismic demand regression models (sdrms), which show the relationship between ims and engineering demand parameters. a numerical model of the structure was constructed using the lumped-mass stick model (lmsm) in sap2000. additionally, a three-dimensional finite element model was developed to validate the simplified lmsm approach. a set of 90 ground motion records was used to perform a time-history analysis, where the motions cover a wide range of amplitude, intensity, epicenter distance, significant duration, and frequency of earthquakes. engineering demand parameters were monitored in terms of floor accelerations and displacements. consequently, strongly correlated ims were identified based on the evaluation of sdrms using four statistical indicators: coefficient of determination, standard deviation, practicality, and proficiency. the results showed that the strongest ims were sa(t1), sv(t1), and sd(t1) followed by asi, epa, pga, and a95. on the other hand, the weakly correlated ims were pgd, drms, sed, vrms, pgv, hi, vsi, and smv. keywords-reactor containment structure; earthquake intensity measure; seismic demand regression model; floor acceleration; floor displacement i. introduction currently, seismic design codes and guidelines use peak ground acceleration (pga) and spectral acceleration (sa) as intensity measures. these parameters are widely employed to evaluate the probabilistic seismic damage of structures. however, each structure has specific characteristics, such as structural dimensions, material properties, and details. therefore, the correlation between seismic structural responses and earthquake intensity measures may differ for different structure types. numerous studies evaluated the correlation between seismic intensity measures (ims) and responses of different structures such as buildings [1-6], bridges [7-12], intake tanks [13], chimneys [14], and underground structures [15-17]. these studies concluded that pga and sa were not the optimal parameters to evaluate seismic responses and fragility analyses of structures. there is a need to systematically identify efficient earthquake ims for seismic risk analysis of nuclear power plants (npps), where the reactor containment building is one of the crucial structures. some studies investigated the interrelation of the responses of npp structures and earthquake ims. in [23], the correlation coefficients between typical ims and seismic fragility of the canada deuterium uranium reactor building were determined, pointing out that spectral acceleration sa(t1) and spectral displacement at the fundamental period sd(t1) are the most correlated ims. in [24], time-history analysis was performed to recognize the strongly correlated earthquake ims with the structural responses of base-isolated nuclear power plant structures, considering the high-frequency content of earthquakes. as a result, pga, a95, and sustained maximum acceleration (sma) had the largest correlation with structural behaviors subjected to low-frequency earthquakes. meanwhile, specific energy density (sed), characteristic intensity (ic), and arias intensity (ia) were the strongest ims under highfrequency ground motions. however, a systematic study on the correlation analysis between seismic ims and structural behaviors of the 1400 npp containment structure has not been performed. since this structure is designed according to the us nuclear regulation commission 1.60 (nrc 1.60) with pga=0.3g, a selection of large ground motions is required, where the mean spectrum matches the design. moreover, a simplified numerical model called the lumped mass stick model (lmsm) and a full three-dimensional corresponding author: duy-duan nguyen engineering, technology & applied science research vol. 12, no. 5, 2022, 9160-9165 9161 www.etasr.com vu et al.: correlation analysis of earthquake intensity measures and engineering demand parameters … finite element model (3d fem) have been used to evaluate nuclear structures [18]. however, since 3d fem takes a long time for time-history analysis and occupies a large amount of memory, lmsm is preferred. several studies demonstrated that lmsm was capable of evaluating fragility analyses of npp structures [19-22]. this study conducted a correlation analysis between ims and engineering demand parameters (edps) of reactor containment structures. a total of 20 ims were considered to establish seismic demand regression models representing the relationship between ims and edps. a numerical model of the containment structure was developed using the simplified lmsm in sap2000. additionally, a solidbased 3d fem was built to validate the lmsm. a set of 90 seismic ground motion records was selected for time-history analysis. the edps were measured in terms of floor accelerations and displacements. four statistical properties were used to evaluate the efficiency of seismic demand regression models, including coefficient of determination (r2), standard deviation, practicality, and proficiency. ii. earthquake intensity measures and input ground motions this study selected 20 ims to develop the seismic demand regression models, as shown in table i. these ims were classified in by amplitude, frequency, intensity, and energy. table i. considered earthquake intensity measures no earthquake ims formula unit ref. 1 peak ground acceleration pga = max |a(t)| g 2 peak ground velocity pgv = max |v(t)| m/s 3 peak ground displacement pgd = max |d(t)| m 4 root-mean-square of acceleration ���� = � �� � �(�)��� � g [25] 5 root-mean-square of velocity ���� = � �� � �(�)��� � m/s [25] 6 root-mean-square of displacement ���� = � �� � �(�)��� � m [25] 7 arias intensity �� = ��� � �(�)��� � m/s [26] 8 characteristic intensity �� = (���� )�/������ m1.5/s2.5 [27] 9 specific energy density sed = !(�)�"�� # m2/s 10 cumulative absolute velocity cav = |%(�)|"�� # m/s [28] 11 acceleration spectrum intensity asi = &� '( =#.*#.� 0.05, ./". g*s [29] 12 velocity spectrum intensity vsi= &� '( =�.*#.� 0.05, ./". m [29] 13 housner spectrum intensity hi = 0&� '( =�.*#.� 0.05, ./". m [30] 14 sustained maximum acceleration sma = the 3rd of pga g [31] 15 sustained maximum velocity smv = the 3rd of pgv m/s [31] 16 effective peak acceleration epa= �1�2(34�.56�.7(89#.#*))�.* g [28] 17 spectral acceleration at t1 &� (.�) g [32] 18 spectral velocity at t1 &� (.�) m/s 19 spectral displacement at t1 &� (.�) m 20 a95 parameter a95 = 0.764 ��#.:�; g [33] a group of 90 ground motion records was selected from worldwide earthquakes provided by the peer center, considering a wide range of amplitude, magnitude, epicentral distance, duration, fundamental period, and frequency. figure 1 shows the response spectra of the 90 motion records. it should be noted that the mean spectrum of these motions is close to the design response spectrum of the us nrc 1.60 [34]. fig. 1. response spectra of 90 motion records. iii. finite element model of containment structure the reactor containment structure in the advanced power reactor 1400 (apr-1400) npp was employed to develop the modeling. this structure is made of reinforced concrete with a cylinder and a top dome. the diameter and height of the cylinder are 47m and 54m respectively. the thickness of the rc cylinder wall is 1.22m. the radius and thickness of the dome are 23.2m and 1.07m respectively. figure 2 shows the structural dimensions of the containment structure. fig. 2. configurations of the containment structure. since the containment structure is a vertically symmetric cantilever column, its fem can be developed using the simplified lmsm. this numerical model was based on beam elements with nodal masses assigned at the nodes of the elements. the model consisted of 14 beam elements, where their length was determined based on the change of vertical stiffness of the structure and the location where secondary systems are connected to the containment structure. the lumped masses and structural section properties of elements were calculated based on the real cross-section of the structure [35]. the lmsm of the containment structure was constructed in sap2000, a commercial structural analysis program. figure 3(a) shows the lmsm of the containment structure in sap2000 and table ii shows the material properties. 0 0.5 1 1.5 2 2.5 3 0.1 1 10 100 s p ec tr al a cc el er at io n ( g ) frequency (hz) average spectrum nrc 1.6 spectrum 1.22 m 22.8 m 1.07 m 5 4 m 2 3 .5 m 1.22 m reinforcement details d18 @300 1.22 m d18 @300 engineering, technology & applied science research vol. 12, no. 5, 2022, 9160-9165 9162 www.etasr.com vu et al.: correlation analysis of earthquake intensity measures and engineering demand parameters … 3d fem is known to be the most accurate numerical approach and was used to validate the simplified lmsm. in this study, 3d fem was developed using solid elements in ansys. the structural model was meshed into 13,571 prism elements, after conducting a sensitivity meshing analysis as shown in figure 3(b). the elastic modulus of the material was 30,500mpa, poisson’s ratio was 0.17, and volumetric density was 24.0kn/m3. (a) lmsm (b) 3d fem fig. 3. finite element models. table ii. material properties used in lmsm model elastic modulus (kn/m 2 ) volumetric density (kn/m 3 ) poisson’s ratio containment structure 3.05e+07 0.00 0.170 iv. seismic responses of the containment structure a series of linear time-history analyses was performed since the stiffness of the containment structure was very high and was expected to behave elastically under earthquakes. acceleration records were imposed on the horizontal direction, and the effects of vertical motion were neglected. the edps (seismic responses) of the structure were quantified in terms of floor accelerations and displacements. these parameters are commonly used in structural and earthquake engineering analyses [36-38]. figure 4 displays the time-history responses of the containment structure at the top and middle nodes using lmsm and 3d fem, showing that the results of the two models are highly compatible. figure 5 shows the floor response spectra (frs) at different elevations of the structure, which also implies that lmsm results are very close to 3d fem and highlights the capability of the former to perform a seismic time-history analysis of the npp structure. v. seismic demand regression model the seismic demand regression model (sdrm) has been widely used to represent the relationship between earthquake ims and edps. this model was also applied to seismic designs according to the probabilistic approach [6, 39]. the popular expression of sdrm is [7, 10, 40]: &< = % × (�>)? (1) where sd is the mean seismic response of the structure, a and b are regression coefficients, and im is the intensity measure considered. equation (1) can be also written as: @a(&< ) = @a(%) + c × @a(�>) (2) fig. 4. time-history responses of the structure subjected to the 1940 el centro earthquake. fig. 5. frs at different elevations of the structure under the 1940 el centro earthquake. a total of 40 sdrms of the structure were constructed for 20 ims and edps. optimal ims were evaluated using four statistical indicators: coefficient of determination (r2), efficiency (standard deviation), practicality, and proficiency. it should be noted that r2 represents the percentage of data closest to the regression line, and a higher r2 value indicates a more optimal sdrm. on the contrary, efficiency denotes the scattering (standard deviation) of sdrm, and smaller efficiency indicates more optimal sdrms. it practicality indicates the slope of the regression line, and smaller practicality means more correlated im. similarly, proficiency represents the balance between efficiency and practicality, and smaller proficiency means a more proficient sdrm. figure 6 shows the sdrms for floor displacement for the 20 ims. the results demonstrate that the ims corresponding to sdrms with the highest r2 values and having the smallest scattering were: sa(t1), sv(t1), sd(t1), asi, epa, pga, and a95. displacement-based regression models using sa(t1), sv(t1), and sd(t1) had r 2 greater than 0.95. similarly, r2 values were also greater than 0.85 in acceleration-based regression models using sa(t1), sv(t1), sd(t1). the trend of sdrms was similar for both using floor displacement and acceleration as edps. overall, a high correlation was observed for acceleration-based ims, attributed to the large mass and stiffness of the investigated structure, so it was sensitive to acceleration rather than velocity and displacement [24]. moreover, sa(t1), sv(t1), sd(t1) had the strongest correlation with edps since they combine the earthquake characteristic and structural property (i.e. the fundamental period t1). -20 -15 -10 -5 0 5 10 15 0 10 20 30 40 d is p la ce m en t (m m ) time (s) lmsm 3d fem top node -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 0 10 20 30 40 a cc el er at io n (g ) time (s) lmsm 3d fem top node -10 -8 -6 -4 -2 0 2 4 6 8 0 10 20 30 40 d is p la c em en t (m m ) time (s) lmsm 3d fem middle node -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0 10 20 30 40 a cc el er at io n (g ) time (s) lmsm 3d fem middle node 0 2 4 6 8 10 1 10 100 a cc el er at io n (g ) frequency (hz) top node lmsm 3d fem 0 2 4 6 8 10 1 10 100 a cc el er at io n (g ) frequency (hz) middle node lmsm 3d fem engineering, technology & applied science research vol. 12, no. 5, 2022, 9160-9165 9163 www.etasr.com vu et al.: correlation analysis of earthquake intensity measures and engineering demand parameters … fig. 6. sdrms concerning floor displacement for 20 ims. figure 7 summarizes four statistical indicators (r2, efficiency, practicality, and proficiency), which were calculated based on sdrms that combined 20 ims and two edps. the results showed that the trend in each indicator was similar for the acceleration and displacement responses. it was also found that sdrms using sa(sa(t1), sv(t1), sd(t1) had the smallest efficiency and proficiency and the largest r2 and practicality. the following-up ims were asi, epa, pga, and a95. in other words, these ims were strongly correlated with edps (i.e. seismic responses) of the npp structure. by contrast, pgd, drms, sed, vrms, pgv, hi, vsi, and smv are weakly correlated with edps of the containment structure. these findings emphasize that it is necessary to select strong correlation ims to evaluate the seismic performance of containment structures. fig. 7. calculated statistical parameters of sdrms. y = 0.8721x + 3.7995 r² = 0.7662 1 2 3 4 5 -3 -2 -1 0 1 ln (e d p ) ln(pga) y = 0.4986x + 3.4106 r² = 0.3796 1 2 3 4 5 -3 -2 -1 0 1 ln (e d p ) ln(pgv) y = 0.172x + 3.2978 r² = 0.0772 1 2 3 4 5 -5 -4 -3 -2 -1 0 1 ln (e d p ) ln(pgd) y = 0.8524x + 5.5014 r² = 0.6396 1 2 3 4 5 -5 -4 -3 -2 -1 ln (e d p ) ln(arms) y = 0.3843x + 3.9891 r² = 0.2297 1 2 3 4 5 -5 -4 -3 -2 -1 ln (e d p ) ln(vrms) y = 0.1088x + 3.3267 r² = 0.0323 1 2 3 4 5 -6 -5 -4 -3 -2 -1 0 ln (e d p ) ln(drms) y = 0.4362x + 2.7896 r² = 0.6226 1 2 3 4 5 -3 -2 -1 0 1 2 3 ln (e d p ) ln(ia) y = 0.6005x + 4.5592 r² = 0.6539 1 2 3 4 5 -5 -4 -3 -2 -1 0 ln (e d p ) ln(ic) y = 0.1666x + 3.2494 r² = 0.187 1 2 3 4 5 -6 -5 -4 -3 -2 -1 0 1 2 3 ln (e d p ) ln(sed) y = 0.5569x + 1.7109 r² = 0.3061 1 2 3 4 5 1 2 3 4 ln (e d p ) ln(cav) y = 0.9801x + 4.1101 r² = 0.8746 1 2 3 4 5 -3 -2 -1 0 1 ln (e d p ) ln(asi) y = 0.5519x + 2.7691 r² = 0.445 1 2 3 4 5 -2 -1 0 1 2 ln (e d p ) ln(vsi) y = 0.485x + 2.8386 r² = 0.3765 1 2 3 4 5 -2 -1 0 1 2 ln (e d p ) ln(hi) y = 0.8434x + 4.0894 r² = 0.6986 1 2 3 4 5 -3 -2 -1 0 ln (e d p ) ln(sma) y = 0.5326x + 3.6857 r² = 0.3536 1 2 3 4 5 -4 -3 -2 -1 0 ln (e d p ) ln(smv) y = 0.8891x + 3.8372 r² = 0.7853 1 2 3 4 5 -3 -2 -1 0 1 ln (e d p ) ln(epa) y = 0.8674x + 3.8076 r² = 0.7648 1 2 3 4 5 -3 -2 -1 0 1 ln (e d p ) ln(a95) y = 0.9979x + 3.1674 r² = 0.9982 1 2 3 4 5 -2 -1 0 1 2 ln (e d p ) ln(sa(t1)) y = 0.9433x 0.2184 r² = 0.957 1 2 3 4 5 1 2 3 4 5 6 ln (e d p ) ln(sv(t1)) y = 1.0011x + 2.6516 r² = 0.9987 1 2 3 4 5 -2 -1 0 1 2 ln (e d p ) ln(sd(t1)) 0 0.2 0.4 0.6 0.8 1 1.2 r 2 va lu e intensity measure max acceleration max displacement 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 e ff ic ie nc y (σ d |i m ) intensity measure max acceleration max displacement 0 0.2 0.4 0.6 0.8 1 1.2 p ra ct ic al it y (b ) intensity measure max acceleration max displacement 0 5 10 15 20 25 p ro fi ci en cy ( ξ ) intensity measure max acceleration max displacement engineering, technology & applied science research vol. 12, no. 5, 2022, 9160-9165 9164 www.etasr.com vu et al.: correlation analysis of earthquake intensity measures and engineering demand parameters … vi. conclusion this study examined the correlation between earthquake ims and edps of the containment structure of an apr-1400 npp. numerical modeling was developed using lmsm and validated using a 3d fem. a set of 90 ground motion records and 20 typical ims were considered in time-history and correlation analyses. the correlation of ims with edps was evaluated using statistical indicators. based on the numerical results, the following conclusions can be drawn: • lmsm is reliable for performing time-history analysis of containment structures in npps. • the strongest correlated ims with edps of the containment structure were sa(t1), sv(t1), sd(t1), followed by asi, epa, pga, and a95. • the weakest correlated ims with edps of the containment structure were pgd, drms, and sed, followed by vrms, pgv, hi, vsi, and smv. • it is necessary to select strongly correlated ims to evaluate the seismic performance and fragility of npp containment structures. references [1] a. elenas and k. meskouris, "correlation 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[40] c. a. cornell, f. jalayer, r. o. hamburger, and d. a. foutch, "probabilistic basis for 2000 sac federal emergency management agency steel moment frame guidelines," journal of structural engineering, vol. 128, no. 4, pp. 526–533, apr. 2002, https://doi.org/ 10.1061/(asce)0733-9445(2002)128:4(526). microsoft word etasr_v12_n5_pp9172-9177 engineering, technology & applied science research vol. 12, no. 5, 2022, 9172-9177 9172 www.etasr.com tomer & gandhi: an enhanced software framework for improving qos in iot an enhanced software framework for improving qos in iot uma tomer faculty of computer applications manav rachna international institute of research and studies, faridabad haryana, india uma.tomer@gmail.com parul gandhi faculty of computer applications manav rachna international institute of research and studies, faridabad haryana, india parul.fca@mriu.edu.in received: 20 may 2022 | revised: 25 june 2022 | accepted: 1 july 2022 abstract-internet of things (iot) and artificial intelligence (ai) with its subcomponents are the latest emerging technologies that make our daily lives easier. quality of service (qos) plays a very important role in iot due to the large number of interconnected nodes. qos is inversely dependent on the node count, i.e. the increment of nodes causes hampering to qos, as increasing the number of nodes increases the number of requests to the iot server. an enhanced framework is strongly needed to control qos in iot applications. this study proposes and implements an enhanced framework using matlab, to control the number of requests. the proposed model can improve qos parameters like throughput, latency, and packet loss by reducing the number of requests generated by the end nodes without compromising the services to the end user. the results showed that qos parameters improved in terms of throughput by 5-10%, packet loss by up to 6%, and packet latency by 4%. this model can also be tested in hardware and may provide a better qos solution. keywords-qos; packet loss; latency; throughput; qol; poe i. introduction technology is transforming daily life and the world is getting more and more digitized, as objects are interconnected to the internet to provide. digital applications exploit networks, wireless sensors, wireless local area networks (wlans), and the internet to improve their performance. everything related to iot can be considered as an edge node that helps in sensing, measuring, and interpreting data, and therefore requires good internet connectivity [1-5]. the huge number of complex interactions between devices in edge nodes causes difficulties in achieving dynamic qos requirements. serviceoriented iot is based on dynamic services for various applications and software tools to process and monitor parameters. this technology faces many challenges such as power consumption, lack of compliance, botnet attack, realtime sensing, and failure of components [1]. various architectures have been proposed for traditional networks, but the existing traditional qos attributes are inappropriate, and more qos attributes should be considered to include energy consumption, information accuracy, better utilization of the network, and iot coverage [6]. to overcome these problems, a new qos model is required to improve and balance data accuracy and the quality of the data delivered to the sensors [6]. the accuracy of the information is the key to closing the gap between sensor data and the actual world [6]. iot technology faces challenges such as standardization, cyber security, and energy management [6-8]. these problems motivated researchers to examine new iot architectures for qos, considering traditional and special attributes such as accuracy, energy consumption, and network optimization. this study proposes a three-layer architecture, i.e. sensor, network, and architecture, to achieve adequate performance depending on the demanded service. the building management system (bms) is responsible for automatic regulation, control, and maintenance of predefined parameters to control functionality. it improves the quality of life (qol) by improving the management system including transportation, smart grids, traffic lights, surveillance, and smart services. iot-based systems can support these requirements easily by using power over ethernet (poe), which offers an opportunity to revolutionize these devices. a survey study showed that buildings are responsible for consuming around 40% of the total energy consumption, but the bms is increasing rapidly due to iot applications. this study aims to: • investigate and analyze the main parameters that are vital for improving the performance of iot qos. • propose a framework to improve certain parameters of the iot network, such as latency, throughput, and packet loss. • propose a novel algorithm to reduce the number of requests generated by iot end-nodes and hence reduce the load of the iot server. ii. related works although qos for traditional networks has been explored a lot, the research on service-oriented iot was comparatively less. a three-layered architecture was proposed for serviceoriented iot in [1], including the application, network, and sensing layers, to optimize scheduling performance and minimize resource costs. the application layer was used to explore optimal qos-aware services using component services. corresponding author: uma tomer engineering, technology & applied science research vol. 12, no. 5, 2022, 9172-9177 9173 www.etasr.com tomer & gandhi: an enhanced software framework for improving qos in iot the network layer was used to deal with the scheduling of heterogeneous network environments. the sensing layer was used to deal with information acquisition and resource allocation. edge computing improved the user experience by bringing computing resources closer to the location where iot produces data [7]. iot users face qos hindrances for the isolated execution of their applications. the skillful pairing of cloudlets to iot applications is the primary task to resolve qos constraints. a bilateral solution for edge services was proposed in [7], taking into account the demands of qos in terms of service response time and establishing the dynamic pricing of the edge service rooted in the motives of cloudlets, iot users, and the system. the existing energy management mechanism fails to estimate real-time computation and the mobility of batterypowered iot [8]. this study presented real-time computations under qos constraints for battery applications and proposed a mobility-aware network for lifetime maximization. this was performed in two stages, online and offline. the online stage included a time-efficient qos for the execution of a task to the frequently changing qos requirements, while optimal mobility maximized network lifetime in the offline stage. a qosconstrained iot system operating with finite block length (fbl) codes was proposed in [9] to support low latency communications, studied the arrival model and the deadline limit, and presented a qos-constrained throughput expression. this study proposed an optimal power control algorithm to maximize throughput while guaranteeing a certain reliability target. despite the enormous attempts in standardization to reach the full potential of iot, many challenges still exist. in [10], the qos parameters and metrics were highlighted to improve an iot device, considering qos metrics such as throughput, delay, and packet loss. as multimedia services demand equalized qos, they can use quality of experience (qoe) to dynamically assign resources [11]. this study determined various methods to enhance qoe and presented a mathematical model to meet the desired qos. as qos factors have a strong influence on qoe, iot services were examined by equating three fundamental metrics of qos: small loss, latency, and jitter [12]. these studies show that there is room for further improvement in the qos of iot. as iot applications are vital in different parts of life, such as health monitoring [13, 14] or intrusion detection [15], there is still a need to improve existing algorithms and improve the throughput, latency, packet loss, and performance of the iot server by reducing the number of packets. iii. performance parameters for qos of iot iot is expanding rapidly in wireless communications [16]. cisco proposed a standard iot framework having 7 iot levels, distributed in 3 computational layers: edge-side, server/cloudside, and user-side layer. these computational layers transform real-world data into application visions. the edge-side layer consists of 3 different levels in the framework: edge nodes, communication, and edge computing. edge nodes provide the intelligence to sense, measure, and connect the internet gateway to the cloud [18]. iot information communication technology (ict) transfers information human to human, human to things, and things to things [19]. edge-computing is an emerging model that extends the cloud and its services to the edge of the network [20]. the server/cloud-side layer embeds data accumulation and abstraction, requiring high computational power, transmission cost, and delay [16]. to address the needs of non-real-time applications, real-time data is acquired in the data aggregation stage, which determines whether the data is relevant or not for the required application. the data abstraction stage conducts data preparation for the consumer application. the user-side layer consists of users and centers. the performance parameters of qos in iot are latency, accuracy, and packet error rate (per). latency is a measure of delay. in networking, latency is the measurement of data transmission to the target. in [21], the latencies of 3 amazon web service (aws)_ regions east-1, east-2, and west-2, and three azure areas west, central, and east were examined. to handle the latency of iot instruments, it was noted that the aggregated processing latency in aws was more than in azure. the average latency was 45, 49, and 46ms for aws east-1, east-2, and west-2 respectively, while 14, 12, and 4ms were the latencies for azure west, central, and east respectively. in [22], the analytical and downlink latency was compared, deriving expressions and highlighting performance tradeoffs in channel scheduling. the simulator was developed in matlab and it was observed that it had a latency of 10ms. accuracy measures how close the displayed measurement is to the actual value of a signal. a framework was proposed in [23] to evaluate the accuracy by estimating the number of disk i/o per process. it was implemented with the inu emulator in matlab by fixing 2 parameters: n as the number of buckets in the bucket array, and m as the number of buckets in each bucket subarray. three simulations were performed for t= 1, 5, and 10 minutes, and n and m were observed to be 20 and 5 respectively, to achieve accuracy. piggybacking was used in [24] to improve accuracy. a comparison of the shewhart and least mean square (lms) methods was performed for datatransmission reduction of the two datasets. for the indoor scenario, the numbers of transmissions were 408 and 58 for lms and shewhart respectively. for the outdoor scenario, the number of transmissions was 682 for lms and 201 for shewhart. during the measurements, it was observed that the current consumption increased with the increase in piggyback, and the battery life reduced. per is used to test the access terminal's receiver performance. a newscast approach was proposed in [25], using a moving average along with a network of devices to survey the per of the current frame. this process can increase the probability of data renewal by providing the aimed number of encrypted yield packets to meet the number of required packets for appropriate data decoding and recovery. when using the legacy procedure, the data recovery probability strongly decreases accompanying the increase in packet inaccuracy. the packet error probability was between 0.1 and 0.3, and the per was 0.012 for the legacy and 0.015 for the proposed model. per in wireless sensor network (wsn) for heating, ventilation, and air conditioning (hvac) systems was engineering, technology & applied science research vol. 12, no. 5, 2022, 9172-9177 9174 www.etasr.com tomer & gandhi: an enhanced software framework for improving qos in iot investigated in [26]. per data were captured for 1 month. temperature and humidity were collected and packet loss percentage was reported. the data were split into 3 classes: temperature and moisture (class 1), neighbor node id along with the number of hops (class 2), amount of packets and small rebroadcast counts (class 3). it was noticed that impenetrable node classification regionally can considerably reduce packet drain. the packet loss ratio of class 1 was higher compared to the other two classes, possibly due to the large size of the packets. it was also deduced that a network could be simulated to decrease the leap counts by balancing the optimum count of nodes and separation. iv. proposed framework an iot network consists of a large number of interconnected devices. some interconnections are based on local networking, and some of them require an internet connection. the qos of the iot is based on the requests generated per unit of time for a particular iot platform. an iot platform can use bluetooth, wifi, zigbee [27], or satellite networks [28]. figure 1 shows the conventional and the proposed architecture of the iot layer and the generation of a request to the iot server. if the number of requests for a particular application can be reduced, then the qos can be enhanced. there are many iot platforms available on the market that focus on enhancing the devices to be served. the mutual benefit of an iot hardware manufacturer and an iot platform developer is that the more devices demanded, the more profit can be earned. but there is a very good scope for enhancing the qos of a particular server by reducing its load. fig. 1. (a) conventional and (b) proposed iot framework. the proposed framework is based on a bms application. increasing the number of iot devices requires a greater number of iot devices connected to the iot cloud, increasing the load of the server and compromising qos as a greater number of requests is generated. figure 1(a) shows the conventional approach of an iot framework where both the user and the edge side layer generate requests to access the internet. this may be to access the devices, log data to the cloud, etc. this generates a higher number of requests to the iot service provider. figure 1(b) shows the proposed approach of the iot framework, which is based on user requirements. there are many tasks where the user is near to the edge side layer, so he can directly access the data from the edge side layer. in such cases, low-distance wireless communication can help a lot. wifi, bluetooth, and zigbee are some of the protocols which can be accessed locally, so some requests generated by this model could be handled locally by the user. this approach can significantly enhance the qos by decreasing the load over the iot service platform. figure 1(b) also shows that the number of requests generated by the edge side layer can also decrease due to the direct access to the user. figure 2 shows the flowchart of the request generation and handling using the proposed iot architecture. users and devices generate requests in the application and session layers. the application and edge-side layers will check whether it is necessary to send these requests to the cloud server or not. after examining the type of request, if the request can be handled locally, then the network conditions will be checked. if the deployed network has some local networking with lan wifi, bluetooth, or zigbee, then the request will be checked and forwarded to the deployed network. such requests can be handled locally, and there is no need to send them to the iot platform server. if the request is not local, then the iot platform has to be accessed. the same procedure must be followed if the network does not exhibit any local networking. fig. 2. flowchart of the proposed iot framework. v. simulation results a simulation model was created to examine the proposed architecture. the numbers of requests generated by the userside layer and the edge-side nodes were combined for the iot service platform, and it was assumed that the number of service requests generated per node per unit of time was between 1 and 10, 30, and 50. in this scenario, the number of iot nodes increases as time increases, and the load over the number of requests generated per unit of time can be formulated as: � � ∑ ���� � ��� �� (1) where r(i) is the number of requests generated by the i-node at any time t. figure 3 shows the number of requests generated at any time t in a stochastic nature. the graph also shows that the number of requests continuously increases for an increasing number of iot nodes. the number of requests was considered stochastic due to their random nature. as figure 4 shows, applying the proposed method decreased the total number of requests. this was due to bypassing some user requests directly to the edge side layer. figures 3 and 4 show that requests may proceed to 4500 requests per time unit using the conventional framework and a maximum of 2600 requests per time unit using the proposed method. engineering, technology & applied science research vol. 12, no. 5, 2022, 9172-9177 9175 www.etasr.com tomer & gandhi: an enhanced software framework for improving qos in iot fig. 3. request generation by a conventional network of 100 nodes. fig. 4. request generation by the proposed network of 100 nodes. a test environment was built in matlab to validate and justify the proposed method, considering a wi-fi network. this network requires a wi-fi access point (ap) and a station point (sta). a 12-node ap and a 24-node sta model were considered and used for the development of a wi-fi-enabled iot model for a bms application. some network parameters were considered to examine the load sharing of the server. the iot servers were accessed by the ap, which was responsible for sending and receiving data from the stas to the server and vice versa. figure 5 shows the throughput of 12 aps in the proposed and conventional approaches. the number of requests generated by the stas was taken in two domains. in the first domain, the requests were forwarded to aps directly without using any filtration process, and in the second, the requests were forwarded to aps with the intelligent queuing process. this process followed the algorithm shown in figure 3 to separate the server-oriented and local requests. figure 5 shows that the throughput of the ap improved significantly in each node, increasing the quality of the network. figures 6 and 7 show the packet loss and the average packet latency of stas for both methods, considering again 24 stas. fig. 5. throughput of conventional and proposed scheme. fig. 6. packet loss for conventional and proposed frameworks. engineering, technology & applied science research vol. 12, no. 5, 2022, 9172-9177 9176 www.etasr.com tomer & gandhi: an enhanced software framework for improving qos in iot fig. 7. average packet latency for proposed and conventional schemes. figure 5 shows the reduction in packet loss for each node that functions as an sta. stas are nodes that have some sensors, and may connect directly with the user based on the request type. conventionally, each sta is supposed to provide and receive data from the server, and any request generated by the user or the sta pings the server and increases its load and packet latency. the proposed method reduced the number of requests to the server, and thus reduced the packet loss on each node. figure 7 shows the average packet latency for the proposed and the conventional method. average packet latency also decreased using the proposed algorithm, due to the smaller number of requests to the server. packet latency is directly proportional to the number of requests generated by each sta. the number of requests generated for any iot platform using the conventional approach increases significantly with the number of nodes, lowering the qos parameters of the iot network. as the increasing number of nodes in an iot platform can’t be controlled, the proposed approach can suit many applications. the proposed algorithm helps to lower the requests without limiting the number of nodes, and hence it can be very useful. future work could investigate an ai-based intelligent approach to control the number of requests to the server at the device level. the nature of such a modification should have a very small memory footprint because of limited resources. vi. conclusion enhancing qos without compromising the number of nodes is a challenge for iot applications and the research society. the most important qos parameters of an iot network, i.e. packet loss, throughput, and latency, are directly proportional to the number of packets generated by the network. an intelligent model was proposed and investigated to reduce the requests to the server from the nodes. this model recognized requests that can be handled locally or should be forwarded to the server. the packet loss, throughput, and packet latency of the proposed model were examined using matlab. the results showed that the proposed method minimized the number of requests by almost half on average of the conventional model. this enhanced the throughput of the networks by around 510%, depending on the number of nodes, and decreased the average packet latency by 4%. the average packet loss also decreased by around 3-6%. dividing the number of requests to those to be handled locally and by the server can become smarter using ai and machine learning algorithms, which could be future work. ai and machine learning algorithms can drastically enhance the proposed 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[28] j. zhou, x. gong, l. sun, y. xie, and x. yan, "adaptive routing strategy based on improved double q-learning for satellite internet of things," security and communication networks, vol. 2021, apr. 2021, art. no. e5530023, https://doi.org/10.1155/2021/5530023. microsoft word etasr_v13_n1_pp10151-10157 engineering, technology & applied science research vol. 13, no. 1, 2023, 10151-10157 10151 www.etasr.com ayari: on the efficiency of the advanced twa approach to the 60-ghz microstrip antenna analysis … on the efficiency of the advanced twa approach to the 60-ghz microstrip antenna analysis for 5g wireless communication systems mohamed ayari faculty of computing and information technology, northern border university, saudi arabia | syscom laboratory, national engineering school of tunis, university of tunis el-manar, tunisia mohamed.ayari@nbu.edu.sa (corresponding author) received: 21 december 2022 | revised: 5 january 2023 | accepted: 7 january 2023 abstract the bandwidth demand in mobile wireless applications has grown at an astounding rate due to the fast evolution of technology, spurring the antenna design fields. the approaches associated with realizing antenna structure at mm-wave frequency bands for future 5g cellular devices present advantages and disadvantages. this paper exhibits a fast and original approach based on the transverse wave formulation called-up advanced transverse wave approach (atwa). a compact 5g patch antenna is designed, measured, simulated, and analyzed in the context of unlicensed mm-wave ism-band applications. compared to recently published works, the obtained result analysis proves the efficiency of the proposed method in terms of calculation accuracy, computational efficiency, and peak memory usage and the overall good performance of the proposed antenna. keywords-5g antennas; advanced transverse wave approach; calculation accuracy, mm-wave analysis i. introduction nowadays, much research is directed at the fifth-generation mobile communications system (5g). soon the traffic volume will be 1000 times over than the last decade with low cost and minimum power consumption, data rate communication will exceed 10gbps making it 100 times faster than 4g, simultaneous connection of a large number of terminals will be available to support the future spread of m2m communications and internet of things (iot), all thanks to the 5g technology. undoubtedly, there are many challenges in this context, among them is to design, treat, and simulate mm-wave antennas used in 5g wireless in an effective way. numerous recent scientific works have concentrated on the design and mm-wave investigation of 5g antennas with diverse size, from compact to large, either 2d or 3d [1-3]. besides, 5g antenna shapes (i.e. circular, elliptical, rectangular, hexagonal, cross, etc.) [4-7] are considered as a significant parameter in the analysis process to achieve or not good quality in terms of performance and costeffectiveness. in wireless communication systems, small patch antennas play an important role in the gain and bandwidth improvements due to features such as multiband properties, low profile topology and cost, good gain, and easy fabrication [8-10]. several publications have been reported in this context. for instance, a compact size dual band patch antenna functioning at 10.15ghz and 28ghz for 5g mobile communications has been designed and studied in [11]. in [12], the authors presented a new capacitive coupled patch antenna array operating at the frequency band of 24-28ghz providing 360° coverage for 5g based smartphone services. in [13], a patch slotted antenna using fr4 substrate with the size of 18×18×1.6mm 3 providing at 10.15ghz a gain of 4.46db and one of 6.6db at 28ghz was reported in [14] using a small antenna with coplanar feeding for a rogers rt5880 substrate and 5×5×0.254mm 3 size. such antennas present low radiation efficiency, low gain, and some intricacy in the fabrication process. the mm-wave phased array 5g antenna which is running in the frequency range of 25 to 40ghz has been designed and analyzed in the context of multiple-input multiple-output (mimo) applications. the increased demand of frequency allocation coerced the federal communication committee (fcc) to boost more than 18ghz of spectrum surrounding the mm-wave frequencies [15, 43] in order to enhance the development and scientific research in 5g technology. however, the 57-71ghz interval which is the unlicensed frequency band according to fcc covers an important set of applications, such as wigig [16], a new technology derived from wi-fi but supporting faster wireless transfer speed than wifi. so, many recent publications have engineering, technology & applied science research vol. 13, no. 1, 2023, 10151-10157 10152 www.etasr.com ayari: on the efficiency of the advanced twa approach to the 60-ghz microstrip antenna analysis … been reported in the context of analysis and design of 5g antennas used for wigig applications. in [17], a stacked circular patch antenna with monopole type pattern was developed for 60ghz wpan application. a 60ghz microstrip patch antenna was investigated in [18] based on different dielectric materials to prove their impact on antenna operation. in [19], the authors proved the efficiency of a 60ghz virtual loop antenna built on low resistivity silicon substrate. these antennas have been fabricated and designed in different shapes, such as rectangular, circular, helical [20], double f-slot [21], double u-slot [22], t-slot [23], eand h-slots [24]. moreover, the feasibility of 5g connectivity beyond 70ghz was demonstrated using an experimental prototype in [25]. the investigation and analysis of mm-wave 5g antenna based on numerical methods is an unprecedented and great challenge in the full-wave electromagnetic (em) simulation sphere. numerical em methods belong to the core of the mm-wave analysis of 5g planar structures such as the method of moments (mom) [26], or its alternative fast multipole method (fmm) [27], and the full spectrum method named partial element equivalent circuit (peec)[28] for solving integral equations of em waves. in the same vein, finite element method (fem)[29], finite difference time domain (fdtd) method [30], and finite integration technique (fit) [31] belong to differential equation solvers. these numerical methods necessitate a significant amount in memory and processor power as well as high accuracy in features and design for full-wave and mm-wave analysis of planar structures employed in wireless systems [32]. in the area of wireless applications, the advanced transverse wave approach (atwa) developed by our research team has significant benefits over previous numerical em approaches in terms of speed, compactness, and memory consumption. to this purpose, we adapt and refine our atwa approach to work with mm-wave 5g antenna simulations, and we tested its efficiency and stability in this setting. in line with the above mentioned works, an appropriate 5g antenna was considered and designed to validate our approach in the context of mm-wave 5g applications and offer the possibility to investigate smart and powerful antennas for the next generation of innovative wireless technology. in the following, we present and develop our numerical em method –advanced transverse wave approach– in the context of mm-wave applications. ii. atwa: theoretical background for most practical interest problems pertaining to em radiation and scattering, an analytic solution of integral equations formulating the problem cannot be found. therefore, researchers tend to utilize computational techniques to obtain a solution. we briefly present in this section the mathematical background and the theoretical foundation of the numerical em method atwa as well as its main characteristics and strong points. the two-dimensional transverse wave approach – a fast numerical method based on an iterative process– has several potentialities that set it apart from other computational em approaches. there are no matrix inversion calculations in the twa process, no constraints are required on the component forms, no numerical instabilities frequently arising from large matrices can be found, and the convergence is guaranteed independently of the interfaces of studied planar structures. in the following, we present a small theoretical background of our em-approach 2d-atwa for mmwave analysis of planar structures. the general integral relation linking the electric field to current density and considering the boundary and edge conditions on sub-domains characterizing the air-dielectric interface � can be written as follows: �(�, �) = (�, �, �� , �� )�(��, ��) �� ��� (1) where (�, �, ��, �� ) denotes the dyadic green’s function [33]. referring to the wave concept already investigated and developed in [36], the general equation linking the transverse electric field et to the transverse magnetic field ht can be expressed as: ��,� = (4��� )������,� + (−1)���� ��,� � (2) where τ is a boolean parameter referring to the wave nature (i.e. τ=0 for incident wave (w=a) and τ=1 for reflected wave (w=b)), the superscript t refers to the tangential components, and ��� stands for the wave impedance of the homogeneous isotropic region i ∈ {1,2} given by: ��� = � × "#$% &$%' ( ) *' (3) where � is the intrinsic impedance of free space defined as: � = 120or 377ω (4) where &$% , #$%, denote the relative permittivity (capacitivity) and relative permeability (inductivity) of the medium i and the vector jt is defined from the tangential magnetic field ht phased by π/2 from v which denotes the outgoing normal vector oriented towards region i. it can be written as: �� = .� × � (5) overall, both incident (a) and reflected (b) waves can be associated through the following relation: /0 = 123 in modal domain3 = 450 + 3(�) in spatial domain (6) where 3(�)represents the general excitation wave on the source. moreover, shifting from spatial to modal spaces is guaranteed by the transitional spectral space. in fact, at the discontinuity interface, the two-dimensional fast fourier transform (2d-fft) or the two-dimensional non-uniform fast fourier transform (2d-nufft) [37-38] for uniform and non-uniform distribution, respectively, are intercepted in the transition between the spatial and spectral domains in order to accelerate the iterative process. the change from spectral to modal spaces can be ensured by the rotation of angle 6, given by: 6 = 789:;(<=>? <@>?' ) (7) engineering, technology & applied science research vol. 13, no. 1, 2023, 10151-10157 10153 www.etasr.com ayari: on the efficiency of the advanced twa approach to the 60-ghz microstrip antenna analysis … undoubtedly, the passing from modal to spatial domains is achieved by the inverse 2d-fft or 2d-nufft as a first step and the rotation of angle−6 as the next step. the round trip from these spaces is repeated until the system’s convergence. the 2d-twa can be accelerated by applying the anisotropic mesh technique [39] which calls the 2d-nufft to manage precisely the non-uniform discretization. memory and computational complexity for both the forward and backward of the atwa process is guaranteed at o(b� cd;b� ) time, where b� represents the meshing density applied to the structure to be analyzed, whereas the overall computational complexity of iterative solvers is o(b *), the same with mom and fem-based solvers [40]. table i recapitulates the iterative process of the atwa approach, highlighting at each step the computational effort and the total time efficiency. table i. iterative process and computational effort of atwa step description complexity init computation of spectral-modal transition, reflection, and diffraction coefficients. input complex vectors of bilateral excitation source (incident and reflected waves at t=0) b00 and a0=0. e(fg) 1 application of 2d-fft/2d-nufft at iteration k. e(fg hijfg) 2 application of modal transform at iteration k. e(fg) 3 application of reflection operator at iteration k+1. e(fg) 4 application of the inverse modal transform at iteration k+1. e(fg) 5 application of the inverse of 2d-fft/2dnufft at iteration k+1 e(fg hijfg) 6 application of diffraction operator at iteration k+1. e(fg) 7 compute current density, electric field, and input impedance zin at iteration k+1. e(fg) 8 test the convergence of zin at iteration k+1. if zin converges, then keep all em quantities else goto step 1. e(fklm) (b�no ≪ b� : total number of pixels on the subdomain source) iii. antenna design for 5g the new 5g demand can open prospects for miscellaneous new applications and the design process can be evolved taking into consideration these requirements. against this background, a 5g small patch antenna fed by a microstrip line has been designed in the context of wireless applications (figure 1). such an antenna can enhance the radiation directivity and be used to fix and relay signals around obstacles in the context of ism-band applications. the proposed planar structure is composed by an lp×wp radiating patch printed upon an ls×ps×hs substrate with rogers 5880. rt/duroid 5880 laminate is considered as a judicious choice and a perfect substrate, since it is isotropic and characterized by the lowest electrical loss for reinforced polytetrafluoroethylene (ptfe) [34], uniform electrical properties over frequency, low moisture absorption, and excellent chemical resistance. this substrate is more convenient to mm-wave applications, military radar systems, commercial airline broadband, and missile guidance systems. fig. 1. the proposed 5g small patch antenna fed by microstrip line. table ii. geometric simulation parameters of the proposed 5g-antenna meshing resolution 512×512 box dimensions (mm) qr = 8.192 �r = 8.192 patch length cs = 2.912 = 182 pixels width ts = 3.2 = 200 pixels microstrip line (mm) co) = 2.56 = 160 pixels co* = 0.96 = 60 pixels cou = 1.12=70 pixels to = 0.736=46 pixels u-slot simensions (mm) cv = 1.12 = 70 pixels tv = 1.024 = 64 pixels width wx (mm) ty = 0.192 = 12 pixels source dimensions (mm) cz = 0.736 = 46 pixels tz = 1.792 = 112 pixels form factor of source cz tz' = 0.41 substrate thickness [ = 130μm type: rogers rt/duroid height h = 0.5mm in order to enhance the capacitance inhibiting the probe inductance which causes an expansion of the impedance bandwidth, the u-slot has been loaded on the patch. the u-slot technique has been applied in many recent 5g structures [15, 35] showing adeptness in wideband notion. the design parameters are detailed in table ii. iv. simulation results and discussion this section provides a concise and precise description of the experimental results, their interpretation, and the conclusions that can be drawn. in order to validate our numerical method in the em simulation space of 5g antennas, we investigate the proposed planar structure shown in figure 1 by analyzing the s11 parameter and comparing it with the results obtained in the literature. the simulation investigation was carried out by our em simulator based on the atwa method and developed in c++ environment. the modeling simulation constraints are given in table iii. the advanced twa approach gives certain significant potentialities to the iterative scheme. it detaches the continuities relations defining the boundary conditions from the integral one, taking into consideration the half-spaces describing the different metallic interfaces identifying the proposed structure. one of these potentialities are the above mentioned heaviside functions associated to the 5g-antenna (i.e. sub-domains: metallic .\]^_ = `a , dielectric .\]^_ = engineering, technology & applied science research vol. 13, no. 1, 2023, 10151-10157 10154 www.etasr.com ayari: on the efficiency of the advanced twa approach to the 60-ghz microstrip antenna analysis … bc , source .\]^_ = 49a , and surface impedance .\]^_ =dzv$e ). the reflection coefficient or insertion parameter s11 is considered as the standard parameter for antennas. it quantifies the power reflected from the antenna and identifies the different resonance frequencies. the simulation result as depicted in figure 2 shows the evolution of the s11 of our proposed antenna. table iii. modeling simulation parameters of the proposed 5g-antenna modeling parameters description nature of box periodic walls type of polarization bilateral in x-direction number of iterations nghij = 500 value of surface impedance �� = 0 (surface impedance subdomain is equivalent to metallic sub-domain) permittivity of regions &$� = 1 &$� = 2.2 waveband k>�? = 50ghz k>l= = 70ghz 4:am_k$o = 0.5ghz height ℎ� ℎ� = 0 (monolayer) fig. 2. evolution of s11 coefficient. two bands have been detected at [57.62, 63.32] ghz and [64.29, 66.05] ghz, where the resonance frequencies are respectively depicted at 60.47ghz and 65.17ghz. the return losses are correspondingly -37.83db and -12.44db. the fractional bandwidths (fbws) [36] are consequently 9.43% for the first and 2.7% for the second band of the proposed 5gantenna. the voltage standing wave ratio (vswr) is deduced at 1.0260db for the 60ghz band which is considered as a good impedance for 5g wireless systems. the presence of double resonances is due to the u-slot loaded on the patch antenna that it is warranted by simulation result based on 2datwa. table iii illustrates the comparison between the proposed 5g antenna and other known antennas. it is noticed that the three selected reference 60ghz antennas are simulated using the finite-element method (fem)-based frequency domain solver (fds) of cst microwave technology [41] and the fem based highfrequency structure simulator (hfss) of ansys [24, 42]. besides, different simulation results of the proposed antenna based on our atwa method are successfully presented such as the evolution of the impedance as a function of frequency (figure 3), making evident the stability of the system around the resonance frequency, the 3d-radiation pattern (figure 4), the azimuth pattern (figure 5), and the elevation pattern (figure 6) at 60ghz proving the high and accurate radiation directivity and gain of the proposed 5g antenna. fig. 3. evolution of the impedance as a function of frequency. fig. 4. radiation pattern at 60ghz. overall, the obtained simulation results are in good agreement with the results of [24, 41, 42], with some preferences of our system in terms of size, multi-band notion, and impedance bandwidth. the computational statistics in terms of memory and cpu time for these simulations, using an intel® core™ i7-10875h processor with 8 cores based on the comet lake architecture, are given in table iv. the peak memory usage and total calculation time are significantly reduced in comparison with the other fem-based solvers with the same computing resources. this proves the feasibility, plausibility, and em-validity of our approach in 5g antenna simulations along with its accuracy and numerical stability in the compilation process. in addition, considering the above mentioned features as the efficiency of the amt technique presented by our approach (atwa), a good workspace can be opened to investigate miniaturized and sensible structures used for new 5g wireless technologies. 45 50 55 60 65 70 75 80 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 frq(ghz) r e fl e c ti o n c o e ff ic ie n t (d b ) s11 parameter simulated ref [23] ref [35] measured engineering, technology & applied science research vol. 13, no. 1, 2023, 10151-10157 10155 www.etasr.com ayari: on the efficiency of the advanced twa approach to the 60-ghz microstrip antenna analysis … table iv. comparison between the proposed 5g-antenna and reference antennas antenna parameter proposed [24] [41] [42] substrate rt/duroid 5880 rt/duroid 5880 rt/duroid 5880 rt/duroid 5880 shape-slot u-slot e and h slots u-slot u-slot size (mm 2 ) 8.192×8.192 8×8 7.5×9.5 7.5×9.5 simulator own simulator hfss fds hfss numerical em method atwa fem fem fem return loss (db) -37.83 -40.99 -37.5 -29.36 single/multiband double band single band double band single band impedance bandwidth (db) 4)) ≤ −10 4)) ≤ −10 4)) ≤ −15 4)) ≤ −15 vswr at 60ghz band (db) 1.0260 1.0186 1.0270 1.038 peak memory usage/gb 6.96 9.53 11.41 10.31 fig. 5. azimuth pattern at 60ghz. fig. 6. elevation pattern at 60ghz. v. conclusions in this paper, a brief theoretical background and the mathematical foundations of our two-dimensional advanced transverse wave approach (2d-atwa) has been presented and developed for mm-wave applications. a 5g small patch antenna with u-slot fed by microstrip line was presented and effectively designed taking into account the presence of the ushaped slot etched in the radiating patch and the isotropic substrate rt/duroid 5880. the obtained simulations were validated, evaluated, and compared to various 60ghz reference antennas already simulated and investigated using the finite element method-based frequency domain 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[43] s. ahmad et al., "design of a tri-band wearable antenna for millimeter-wave 5g applications," sensors, vol. 22, no. 20, jan. 2022, art. no. 8012, https://doi.org/10.3390/s22208012. author profile mohamed ayari –received the dipl.-ing., m.s., and ph.d. degrees in telecommunications in 2003, 2004, and 2009, respectively, from the national engineering school of tunis (enit), tunisia, in collaboration with the national polytechnic institute of toulouse, france, and virginia tech, usa. he has been teaching at several universities since 2003. he has been a permanent research member at the 6'com laboratory at enit from 2003. in 2005, he joined rcem-inc. in toulouse, france. since 2010, he has been a tenure-track associate professor at the national engineering school of carthage (enicar), carthage university, tunisia. in 2015, he joined the it department of the faculty of computing and information technology, northern border university (nbu), kingdom of saudi arabia, as an assistant professor. his current research interests are electromagnetic (em) fields, numerical em methods, and computer-aided design of microwave circuits and antennas. his research interests also include information security, image processing and wireless applications. microsoft word etasr_v12_n2_pp8463-8466 engineering, technology & applied science research vol. 12, no. 2, 2022, 8463-8466 8463 www.etasr.com amouri & fawzi: the mechanical properties of fly ash and slag geopolymer mortar with micro steel … the mechanical properties of fly ash and slag geopolymer mortar with micro steel fibers mohammed shaker amouri department of civil engineering university of baghdad baghdad, iraq mohammed.amori2001m@coeng.uobaghdad.edu.iq nada mahdi fawzi department of civil engineering university of baghdad baghdad, iraq nada.aljalawi@coeng.uobaghdad.edu.iq received: 18 february 2022 | revised: 28 february 2022 | accepted: 4 march 2022 abstract-in this study, experimental mortar combinations with 1% micro steel fibers, were examined to create geopolymer mortars. to test the effect of the fibers on the mortar's resistance, the geopolymer mortar was designed with various proportions of more environmentally friendly materials fly ash and slag. the percentage of fly ash by weight was 50, 60, and 70% of the slag. the best results were obtained when a 50:50 ratio of fly ash and slag were mixed with 1% micro steel fibers. the results showed that the mixtures containing fibers performed better in the considered tests (toughness index, ductility index, and resilience index). in the impact resistance test, the mixture contained 50% fly ash by weight of the slag with a temperature of 240°c and a curing period of 28 days, with and without micro steel fibers. water absorption test results and void content increased when adding micro steel fibers after 7 and 28 days of curing at 24°c. keywords-fly ash; slag; alkaline solution; geopolymer mortar i. introduction the most common kind of cement used in the production of concrete is the ordinary portland cement (opc). many environmental concerns have long been related to the production of opc. due to the amount of limestone calcination and the necessary burning of fossil fuels, the amount of carbon dioxide produced during the manufacturing of opc is around one ton for every metric ton of produced opc. the construction of opc requires the same amount of energy as manufacturing steel and aluminum [1]. to reduce the amount of co2 emitted by cement factories and aid the recycling of industrial waste, environmentally friendly materials were developed for use in civil engineering projects [2]. cement composites are a viable alternative to traditional forms of concrete. additional cementitious materials, such as ggbfs, fly ash, and sf, can be used in the production of blended cement [3]. waste from thermal power plants, such as fly ash and slag, can constitute an environmental threat if not properly handled and reused. in the long run, the fly ash from thermal power plants contaminates groundwater sources and damages croplands, causing long-term environmental impact, while the by-product of combustion is a powdery substance [4]. fly ash is produced in large quantities each year, posing a threat to the ecosystem. some pozzolanic waste materials (siliceous and aluminous) may be reduced [5]. geopolymers are a category of mineral binders that have a chemical composition similar to that of zeolites. the polycondensation of silicate and alumina precursors, rather than standard portland/pozzolanic cement, is used in geopolymers to build the matrix and increase strength. source materials and alkaline liquids make up the majority of geopolymers. silicon (si) and aluminum (al)-rich aluminosilicate raw materials are recommended. fly ash and silica fume, for example, are by-product minerals that can be used in the mix. geopolymers are distinct from conventional aluminosilicate compounds (e.g. aluminosilicate gels, glasses, and zeolites). geopolymerization contains more solids than zeolite synthesis or alumino-silicate gel [6]. since fly ash and slag are used to make geopolymer concrete, it is a more ecologically friendly and diversified alternative to ordinary concrete [7]. ii. experimental setup a. fly ash the fly ash produced at the isken-ment power plant in turkey can be described as a fine, glassy powder that results from coal burning. table i shows the chemical composition of the fly ash used in this study. b. slag according to table ii, the slag used in this study met the astm c618 standards [8]. c. sodium hydroxide naoh flakes, which are readily accessible in the market, are 99.8% pure. solids should be dissolved in filtered water to produce a concentrated solution. geopolymer mortar solutions are made using sodium hydroxide (naoh). caustic soda flakes were melted with water to produce naoh. a variety of molar concentrations can be achieved by altering the amounts of caustic soda flakes in the water. d. sodium silicate the ratio of na2o to sio2 and h2o determines the concentration of na2sio3. na2sio3 was produced in the united arab emirates. corresponding author: mohammed shaker amouri engineering, technology & applied science research vol. 12, no. 2, 2022, 8463-8466 8464 www.etasr.com amouri & fawzi: the mechanical properties of fly ash and slag geopolymer mortar with micro steel … table i. chemical composition of fly ash astm c618 requirements [8] contents (%) oxide sum more than 70% 5.35 fe2 o3 17.59 al2 o3 65.63 sio2 max. 5% 0.21 so3 -0.84 mgo -0.98 cao max. 6% 2.76 l.o. i -2.33 k2o -1.36 na2o table ii. chemical composition of ggbfs oxide contents (%) (astm c618) requirements [8] fe2 o3 0.35 sum more than 70% al2 o3 25.53 sio2 45.88 so3 4.98 max. 5% mgo 4.95 - cao 37.21 - l.o. i 3.89 max. 6% k2o 2.10 - na2o 0.96 - e. water the naoh solution was produced by dissolving caustic soda flakes in distilled water. to facilitate mixing, tap water was included in the geopolymer mix, compliant with the iqs 1703 [9]. f. fine aggregates the fine aggregates came from the al-ekhadir karbala city region and met the iraqi standard iqs no.45/1984 for physical and chemical properties [10], as shown in table iii. the fineness modulus was 2.76. g. micro steel fibers table iv shows the properties of micro steel fibers. h. superplasticizer using a modified sulfonated naphthalene formaldehyde condensate (superplasticizer), the geopolymer mortar's workability was improved to meet astm c494 standards [11]. table iii. physical characteristics of the fine aggregates sieve size ( mm) cumulative percentage pass iqs (45-1984), zone2 [10] 10 100 100 4.750 91 90-100 2.360 80 75-100 1.180 71 55-90 0.60 53 35-59 0.30 22 8-30 0.150 7 0-10 table iv. micro steel fiber mechanical properties (according to manufacturer) properties micro steel fibers tensile strength (mpa) 2600 diameter (mm) 0.2 density(kg/m3) 7800 length (mm) 13 aspect ratio 65 modulus of elasticity (gpa) 250 iii. manufacturing geopolymer a. preparation of alcaline solution when producing the geopolymer mortar for this experiment, the naoh molar concentration was fixed to 12 molars. solubility was determined by adjusting the sodium silicate/sodium hydroxide ratio to 2:1 and the solution/cementitious-materials ratio to 45%. the weight of the naoh flake is shown in table v. table v. amount of naoh solids for 1kg of solution at specified molarity and weight concentration [1,12] molarity (mole/l) naoh weight concentration (w/w%) weight of naoh flakes (g) weight of water (g) 8 26.2 262 738 10 31.4 314 686 12 36.2 362 638 14 40.4 404 596 16 44 440 560 b. mixing before use, the alkaline liquid was prepared the day before and was then combined with a superplasticizer. to begin, the dry ingredients (ggbs, fly ash, fiber, and sand) were mixed by hand for approximately 2 minutes before the alkaline liquid and superplasticizer were added at a 75% concentration, and the mixing process was performed a second time. finally, after another 5 minutes of mixing, the mixture was allowed to sit for about 15s before being blended with the remaining 25% of the mixed alkaline liquid. table vi shows the homogeneity achieved after 10 to 15 minutes of mixing. table vi. mix design of geopolymer mortar for 1m 3 , weight in kg/m 3 micro steel % naoh sodium silicate solution fly ash slarg fa / slag ratio water * fine agg. mix 112.5 225 375 375 0.5:0.5 75 1400 g1 1 112.5 225 375 375 0.5:0.5 75 1400 g2 112.5 225 300 450 0.6:0.4 75 1400 g3 1 112.5 225 300 450 0.6:0.4 75 1400 g4 112.5 225 225 525 0.7:0.3 75 1400 g5 1 112.5 225 225 525 0.7:0.3 75 1400 g6 iv. results and discussion these tests were carried out according to the astm c642 [13]. the results measured density, absorption percentage, and void content of hardened g1 and g2 mixtures at 7 and 28-day intervals with heat curing at 80,160, and 240 o c. in this test, fracture pieces of concrete mortar were used, and each portion was free of fractures or fractured edges. each test used an average of three specimens. the results for 7 and 28 days of curing at 240 o c are shown in tables vii, viii, and ix and figures 1, 2, and 3. table vii. bulk density of mixes g1 and g2 mix type density, kg/m 3 at seven days/240 o c at 28 days/240 o c g1 2437 2463 g2 2456 2503 engineering, technology & applied science research vol. 12, no. 2, 2022, 8463-8466 8465 www.etasr.com amouri & fawzi: the mechanical properties of fly ash and slag geopolymer mortar with micro steel … the dry density at 28 days was greater than in 7 days, as it increased from 0.07% to 1.6%. the geopolymerization process continuity and the development of microstructure were linked to this rise in density over time. the results comply with [14], showing that the inclusion of micro steel fiber (g2) enhanced the dry density compared to specimens without fibers (g1). fig. 1. the bulk density of g1 and g2 mixes. table viii. water absorption results of mixes g1 and g2 mix type water absorption % at seven days/240 o c at 28 days/240 o c g1 4.38 3.89 g2 4.45 3.93 as the results show, the improved microstructure of the geopolymer mortar and the increased product properties with rising temperatures and curing age led to decreased amount of water that all mixtures can absorb with time but increased with additional fiber due to the generation of voids around the fibers. the increase was about 1.6% and 1% compared with the mixture without fibers for 7 and 28 days of curing, respectively. fig. 2. water absorption of g1 and g2 mixes. table ix. void content of g1 and g2 mix type void content % 7 days/240°c 28 days/240°c g1 9.45 7.85 g2 9.51 7.93 table ix shows the void content of g1 and g2 mixtures at 28 days of curing at 240 o c. the void content of all mixtures decreased with aging. a continuous geopolymerization process enhances the microstructure and generates a denser geopolymer mortar. for all mixtures, the void content decreased with time and increased with additional fibers. the variation between g1 and g2 was 0.6% and 1% for 7 and 28 days of curing respectively. the load-deflection curve test was performed by calculating the area under the curve, where a hydraulic device and a measurement deflection carried out the loading by a dial gauge with 0.01mm accuracy. it was used with a prism with dimensions 50×50×250mm, as shown in figure 4. fig. 3. void content % of g1 and g2 mixes. fig. 4. testing the load-deflection curves. the ends were placed on simple support with a space of 200mm to extract the toughness index, ductility index, and resilience. tables x, xi, and xii show the results of toughness index, ductility index, resilience at 3, 7, and 28 days, respectively, at the curing temperature of 240 o c. table x. flexural strength test results at 3 days samples load at failure (kn) deflection at failure (mm) toughness index ductility index resilience (kn.mm) g1-1 1.705 0.99 1.15 1.52 0.16 g1-2 g2-1 1.94 0.77 4.35 3.88 3.91 g2-2 fig. 5. load deflection curve at three days. table xi. flexural strength text result at 7 days samples load at failure (kn) deflection at failure (mm) toughness index ductility index resilience (kn.mm) g1-1 1.76 0.86 1.20 1.59 0.23 g1-2 g2-1 1.84 1.62 4.43 4 3.98 g2-2 the most significant results of reinforced geopolymer mortar can be based on the mechanical ductility property of pulling and breaking the reinforcement. on this basis, the engineering, technology & applied science research vol. 12, no. 2, 2022, 8463-8466 8466 www.etasr.com amouri & fawzi: the mechanical properties of fly ash and slag geopolymer mortar with micro steel … excellent adhesion between the bonding material and the reinforcement increases the friction resistance of the common interface between them. fig. 6. load deflection curve at seven days table xii. flexural strength test results at 28 days samples load at failure (kn) deflection at failure (mm) toughness index ductility index resilience (kn.mm) g1-1 1.89 0.98 1.19 1.52 0.16 g1-2 g2-1 2.18 0.77 5.88 5.63 4.97 g2-2 fig. 7. load deflection curve at 28 days. figures 5-7 show that the black line drops suddenly, opposite of the red line, because the addition of micro steel fibers with uniform random distribution in the mortar increases the resistance of the first crack of the mortar, especially when the reinforcing fibers prevent the expansion of these cracks with high energy absorption when withdrawn from the cracked cement mortar mass, which makes the reinforced specimens with these fibers of high strength and resistance. fig. 8. geopolymer prisms while testing. v. conclusions • geopolymers are an ecologically acceptable substitute for opc in structural applications [15]. • water absorption and void content increased by adding micro steel fibers at 240 o c at 7 and 28 days of curing, which is considered an indication of durability. • for the mixes g1 and g2 with curing temperature of 240 o c, the results of the density test showed increasing values with additional micro steel fibers while decreasing values with curing age. • toughness index, ductility index, and resilience increased by adding micro steel fibers for all mixes. references [1] d. hardjito and b. v. rangan, "development and properties of lowcalcium fly ash-based geopolymer concrete," curtin university of technology, perth, australia, 2005. [2] z. f. muhsin and n. m. fawzi, "effect of fly ash on some properties of reactive powder concrete," journal of engineering, vol. 27, no. 11, pp. 32–46, nov. 2021, https://doi.org/10.31026/j.eng.2021.11.03. [3] a. sicakova, e. kardosova, and m. spak, "perlite application and performance comparison to conventional additives in blended cement," engineering, technology & applied science research, vol. 10, no. 3, pp. 5613–5618, jun. 2020, https://doi.org/10.48084/etasr.3487. [4] v. t. phan and t. h. nguyen, "the influence of fly ash on the compressive strength of recycled concrete utilizing coarse aggregates from demolition works," engineering, technology & applied science research, vol. 11, no. 3, pp. 7107–7110, jun. 2021, https://doi.org/10.48084/etasr.4145. [5] s. a. chandio, b. a. memon, m. oad, f. a. chandio, and m. u. memon, "effect of fly ash on the compressive strength of green concrete," engineering, technology & applied science research, vol. 10, no. 3, pp. 5728–5731, jun. 2020, https://doi.org/10.48084/etasr.3499. [6] j. l. provis and j. s. j. van deventer, geopolymers: structures, processing, properties and industrial applications. cambridge, uk: woodhead publishing, 2009. [7] s. s. hussein and n. m. fawzi, "influence of using various percentages of slag on mechanical properties of fly ash-based geopolymer concrete," journal of engineering, vol. 27, no. 10, pp. 50–67, oct. 2021, https://doi.org/10.31026/j.eng.2021.10.04. [8] "standard specification for coal fly ash and raw or calcined natural pozzolan for use in concrete," american society for testing and materials, standard astm c618-15, 2015. [9] "used water in concrete," iraqi standard specification, no. 1703, 2018. [10] "aggregate from natural sources for concrete and construction," iraqi standard specification, no. 45, 1984. [11] "standard specification for chemical admixtures for concrete," american society for testing and materials, standard astm c494m05a, 2005. [12] b. v. rangan, "fly ash-based geopolymer concrete," in proceedings of the international workshop on geopolymer cement and concrete, mumbai, india, dec. 2010, pp. 68–106. [13] "standard test method for density, absorption, and voids in hardened concrete," american society for testing and materials, standard c64213, 2013. [14] m. olivia and h. r. nikraz, "strength and water penetrability of fly ash geopolymer concrete," arpn journal of engineering and applied sciences, vol. 6, no. 7, pp. 70–78, jul. 2011. [15] m. s. amouri and n. m. fawzi, "the effect of different curing temperatures on the properties of geopolymer reinforced with micro steel fibers", engineering, technology & applied science research, vol. 12, no. 1, pp. 8029–8032, feb. 2022, https://doi.org/10.48084/ etasr.4629. microsoft word etasr_v12_n4_pp8916-8921 engineering, technology & applied science research vol. 12, no. 4, 2022, 8916-8921 8916 www.etasr.com khadhraoui et al.: energy management of a hybrid electric vehicle energy management of a hybrid electric vehicle ahmed khadhraoui analysis and treatment of electrical and energy signals and systems (atssee) laboratory faculty of sciences of tunis tunis el-manar university, tunisia ahmed.khadhraoui@fst.utm.tn tarek selmi analysis and treatment of electrical and energy signals and systems (atssee) laboratory faculty of sciences of tunis tunis el-manar university, tunisia t.selmi@issatkr.u-kairouan.tn adnen cherif analysis and treatment of electrical and energy signals and systems (atssee) laboratory faculty of sciences of tunis tunis el-manar university, tunisia adnen2fr@yahoo.fr received: 9 may 2022 | revised: 31 may 2022 | accepted: 4 june 2022 abstract-electric vehicles (evs) are becoming more popular and gaining attention due to a combination of factors such as falling prices and increasing environmental awareness. evs fall into several categories related to energy production and storage. standard developed, tested, and commercialized ev technologies include fuel cell electric vehicles (fcevs), all electric vehicles (aevs), also known as battery electric vehicles (bevs), plug-in hybrid electric vehicles (phevs), hybrid electric vehicles (hevs), and flexible fuel vehicles (ffvs). still, the advantages of fcevs are relatively small compared to other autonomous and refueling technologies. considering the above aspects, this work presents a matlab/simulink model of an fcev’s behavior and opportunities. keywords-fuel cell; electric vehicle; ems; solar energy; pem; matlab; dynamic-modeling i. introduction nowadays, the gases emitted by fossil fuel-based vehicles are seriously threatening the environment and directly impact climate [1, 2]. global warming and climate change are amplified by pollution due to the extensive burn of diesel by diesel-based vehicles [3, 4]. it has been reported that transportation is the origin of 24% of co2 emissions worldwide [5]. even worse, in 2020, the european environment agency suggested that about 27% of co2 is emitted by the transport sector, while more than 70% of emissions are mainly caused by vehicles [5]. from the 1970s, fossil fuel combustion increased the emission of co2, co, so2, and no by 90% to reach 36.1gt in 2014 [6]. for this reason the petroleum cars represent one of the most important sources of pollution to the environment [7]. moreover, this type of car is witnessing an increasing demand from citizens. with this development, research and studies on clean energy have multiplied. these factors, aim to reduce pollution and encourage people to use electric vehicles (evs) [8]. the standard ev utilizes one energy source, however it is not profitable in return. so, it has been upgraded by adding a second source with an energy management system (ems). the complex setup and behavior of the multi-source hybrid power system puts additional requirements on the operation of the ems. regardless of the design of the power system, the ems manages the power flow of the transducer in real time to achieve the control goal [9]. therefore, the optimal control algorithm used in the driving cycle can be used as a representative research program for energy management technology. ems was selected as a potential research problem in industry and academia [10]. in the evaluation of the existing literature, there are many classifications of energy management methods. emss are classified into three types according to their optimization strategy: rule-based, local, and global. in [11], the authors outline the ems of plug-in hybrid evs. the classification of energy management is discussed, including rule-based and optimization-based control systems. in [12], the authors compare the advantages and disadvantages of each technique. finally, many aspects of real-time implementation (for example, computational burden and optimization) are discussed. in [13], the authors examine and show various classifications of hybrid evs that use hydraulic driveclassifying and internet-related technologies. with the advancement of its technology and machine learning methods (such as adaptability and real-time execution) [14], a new ems is being created to meet the increasing performance requirements. however, a complete evaluation of emss is needed to better grasp the current technology and future research work. unlike previous ems studies, this one includes a complex ranking system. there are two types of offline ems: one based on global improvement and one based on regulations [15]. instant improvement, predictive improvement, and learning-based corresponding author: ahmed khadhraoui engineering, technology & applied science research vol. 12, no. 4, 2022, 8916-8921 8917 www.etasr.com khadhraoui et al.: energy management of a hybrid electric vehicle improvement are three types of online environmental management systems [16]. since the proposed technology contains various methods for solution goals, optimization, and real-time implementation, a thorough review of the literature is conducted. the concepts, advantages and disadvantages of each technology are compared, and the design and operational characteristics of the proposed scheme are highlighted [17]. finally, the development of a new ems and recent literature highlight the important prospects for macromolecules. the hybrid part on a vehicle is the application of two energy sources. the proton exchange membrane fuel cell (pemfc) [18] is the best type for the ev due to its high efficiency and fast response rate with back up source (super-capacitor (sc)) [19]. the addition of photovoltaic (pv) energy will reduce the consummation of hydrogen up to 40% [20]. the current article describes a realistic environmental management system for the pvfcev. the proposed method was developed in response to various constraints, including energy requirements and subsystems. unlike previous papers, it avoids clustering (on/off) and global/local optimization, which may be deceptive due to algorithm modification and implementation assumptions. instead, each algorithm is presented and reviewed individually, emphasizing its advantages and limitations, as well as alternative technologies to compensate for them. ii. the system description of the pvfcev the pvfcev consists of a pemfc stack, hydrogen tank, a super-capacitor (sc), a pv array as a secondary power source, ems, and an electric motor with driveline. the model description is shown in figure 1. fig. 1. schematic of the pvfcev. the fc system is the principal energy source. the details of the fc used on the simulink model are shown in table i. table i. the details of the fc parameter value number of cells 65 nominal power 4.2 kw nominal voltage 45 v peak power 6 kw fuel supply pressure 1.5 bar the sc has high power density and fast response. it gives power in the acceleration phase and is recharged by the excess energy generated by regenerative braking and the pv array. the main parameters of the sc source and the pv array are shown in table ii and iii. table ii. super-capacitor main parameters parameter value rated capacitance 15.6 f rated voltage 291 v initial voltage 270 v number of series capacitors 105 current prior open circuit 10 a soc start 80% table iii. the parameters of the pv array parameter value number of cells per module 72 max power per module 250 w nominal voltage 50 v circuit current 6.3 a fuel supply pressure 1.5 bar number of series-connected module 2 the permanent magnet synchronous motor (pmsm) was chosen thanks to its high operating efficiency and reliability. the ems monitors the working status of the system, including pv array power, sc soc, and the required power, to determine the power of the fc and the torque of the motor. the vehicle is subjected to several forces, where some of their vectors lead to the traction force (figure 2). fig. 2. the ttractive forces on the vehicle. the ��� traction force is needed to overcome the resistance to advance and accelerate the vehicle. it is written in the form of: ��� = ����� + � + ������ + ��� (1) thus, according to newton’s second law, the acceleration can be expressed by. = ����(���������������� ) �� (2) ����� is the aerodynamic force (n): ����� = � � ��� ! " � (3) engineering, technology & applied science research vol. 12, no. 4, 2022, 8916-8921 8918 www.etasr.com khadhraoui et al.: energy management of a hybrid electric vehicle ��� is the rolling force: ��� = #$��� (4) �%���� is the resistance force of hill climb: �%���� = #$ sin()) (5) table iv shows the hybrid ev’s parameters. table iv. parameters of the vehicle parameter value vehicle mass 1400 kg gravity 9.8 m/s 2 air density 1.18 kg/m 3 road angle 0.5 degrees air drag 0.38 iii. the energy management system the ems is based on the output of the soc of the sc, the pv and the power demanded from the electric motor as shown in the figure 3. fig. 3. the scheme of the ems: pv, fc, sc, and ev. the position of the pedal determines the power needed from the motor. to determine the powers of the sc and the fc, the fc power is selected as the principal control variable of the controller. from figure 3, the bus capacitive energy of ems (**+, ) is: *-./ = 0�1 + 023 + 0/1 − 015 (6) the fc stack and the pv are generators (06�7 ): 06�7 = 0�1 + 023 (7) by combination (6) and (7) we get: *-./ = 06�7 + 0/1 − 015 (8) the generators' power is: 06�7 = *-./ − 0/1 + 015 (9) general, the pv panel cannot be fast in terms of electricity production. for this case, the fc power compensates the lack of energy as given in (10): 0�1 _��! = 06�7 − 023 (10) moreover, we made a fuzzy algorithm with 3 inputs (cycle, ppv, and psc) and the output is the 0�1 _��! as shown in figure 4. figures 4, 5, 6, and 7) represent the input and the output of the fuzzy algorithm according to 45 rules. fig. 4. input parameter pv. fig. 5. input parameter soc. fig. 6. input parameter power demand. fig. 7. output parameter fc. the pedal determines the power demanded for a specific torque. the pedal represents the brake and the accelerator. the pressure ratio on the pedal is present in the testing model in the simulation. in the fuzzy system, the power is between 0 and 1. the fuzzy set for the pv are low, middle, and high to represent the intensity of the solar radiation. the fuzzy set for the soc of sc are low, middle, and high to represent the radio of the residual capacity. the power demand is split into five levels, from very small (vs) to very large (vl) after passing small (s), middle (mid), and large (l). finally, the fuzzy set of the fc has 6 levels: zero (ze), vs, s, m, l, and vl. the rules of the fuzzy reasoning are presented in table v. the algorithm was developed in matlab. the em of the pv array is controlled by the perturb and observation (p&o) algorithm. figure 8, presents the flowchart of the ems algorithm for the pv. this method gives excellent results among different mppt techniques. engineering, technology & applied science research vol. 12, no. 4, 2022, 8916-8921 8919 www.etasr.com khadhraoui et al.: energy management of a hybrid electric vehicle table v. fuzzy reasoning rules inp 9:;<= inp soc inp pv vs s m l vl low low vs m l l vl low middle vs s m l vl low high vs s m m l middle low ze vs s m l middle middle ze vs s m m middle high ze ze vs s m high low ze ze vs vs s high middle ze ze ze vs s high high ze ze ze ze vs fig. 8. flowchart of the p&o algorithm. iv. results and discussion in order to validate the proposed ems, the pvfcev mode was simulated in matlab/simulink. we started testing the model with the following cycle of pedal positions: • time ∈ [0. . .2s] stop: the pedal is at 0% • time ∈ [3s. . .6s] acceleration: the pedal is at 80% • time ∈ [7s . . . 17s] stability: the pedal is at 70% • time ∈ [18s . . . 27s] apply the brakes: the pedal is at 75 % • time ∈ [28s . . . 30s] system shutdown figure 9 shows the results of model under the following conditions: 500w/m 2 solar radiance, 25 0 c temperature, and 80% soc of the super-capacity. the soc of the sc is high with medium radiation, the sc acts as the principal source on the [2s... 6s] period, according to the faster response of the sc compared to the fc. however, the sc is in the recharging mode during [0...2s] and when the vehicle stops. the power of the sc during [0..2s] is negative and this action means that the pv array is charging the sc. the fc started to produce power at the 3rd second. when the fc power tries to become stable, the sc powers down and starts to recharge during [6...7s]. the period os [6s….7s] represents the change of acceleration from 80% to 70%. fig. 9. simulation results of the vehicle for 500w/m2 solar radiation. the fc becomes the principal source in [8s…17s]. the fc power is the same as the motor power according to the stability of the system in that duration. after that, the fc power becomes zero and the power of the motor becomes negative due to the baking during [18s...27s]. at this time, the engine is trying as a primary source to recharge the sc. at the end, the vehicle stops and the power of the system is zero. the nedc (new european driving cycle) is one of the cycles used to measure the degree of performance of the vehicle engines and energy economy. this cycle is divided in two parts: the first part is represented from 0s to 800s (urban driving cycle) and the second part from 800 s to 1200s (extra urban driving cycle) in figure 10. the demand power (015 ) of the vehicle when the path traveled corresponds to the nedc speed profile is given by figure 11. 015 = 0�1 + 023 + 0/1 (11) fig. 10. profile of vehicle speed (nedc). fig. 11. demand power. engineering, technology & applied science research vol. 12, no. 4, 2022, 8916-8921 8920 www.etasr.com khadhraoui et al.: energy management of a hybrid electric vehicle the power delivery of the vehicle (pch), the fc power, and the sc power are shown in figure 12. we can see that the power profile of the fc depends on the fuzzy rules applied and the power profile requested. this allows meeting the demands of the vehicle while ensuring an energy exchange between the fc and sc during the traction phase, precisely, for the calls of low power and when the soc of the sc has low values. in this case, the fc allows, at the same time, satisfying the demand of the vehicle and charging the pack of scs. the gap between the power supplied by the fc and that required by the traction system is used to ensure the loading phase of the storage system. the sc load reached a high value during the fc stress period up to t = 965s. this is explained by the use of the sc during the braking phases most of the time. thereafter, the soc value decreases during the interval up to t=1170s when it is solicited from the fc. when the vehicle is in acceleration mode and the sc soc is average, the sc shoulders the fc to provide the required power. the fc provides the power required charging the sc during the acceleration mode and when the soc of the sc is low. in this case, the sc can easily recover from the braking energy. fig. 12. power elements. v. conclusions this paper presents the technical results of pvfcev via a mathematic model with a fuzzy algorithm designed for it. the ems of the vehicle using the power of the pv, the demand power and the soc of an sc as input parameters. the output of the ems is the reference power of the fc. the use of the sc contributed to improving the vehicle’s effectiveness in the acceleration phase, similar to previous research that remained in the use of the battery despite its poor efficacy. the ems was validated by the simulation results. in order to get good results, the simulation started by the cycle of pedal position as a first step and the nedc driving cycle was considered in the next phase. the proposed ems operated efficiently and robustly under rapid changes in power demand, changes in solar power, and different levels of sc soc. in future work, we will focus on the design and implementation of experiments to validate the proposed pvfchev and its ems. the pvfcev physical model in this work helps to facilitate the design of the experimental setup, as real physical component models are used. references [1] m. a. hannan, m. 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[15] s. khan, a. ahmad, f. ahmad, m. shafaati shemami, m. saad alam, and s. khateeb, "a comprehensive review on solar powered electric vehicle charging system," smart science, vol. 6, no. 1, pp. 54–79, jan. 2018, https://doi.org/10.1080/23080477.2017.1419054. [16] m. e. bendib and a. mekias, "solar panel and wireless power transmission system as a smart grid for electric vehicles," engineering, technology & applied science research, vol. 10, no. 3, pp. 5683–5688, jun. 2020, https://doi.org/10.48084/etasr.3473. [17] h. peng, j. li, l. löwenstein, and k. hameyer, "a scalable, causal, adaptive energy management strategy based on optimal control theory engineering, technology & applied science research vol. 12, no. 4, 2022, 8916-8921 8921 www.etasr.com khadhraoui et al.: energy management of a hybrid electric vehicle for a fuel cell hybrid railway vehicle," applied energy, vol. 267, jun. 2020, art. no. 114987, https://doi.org/10.1016/j.apenergy.2020.114987. 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[20] r. shirwani, s. gulzar, m. asim, m. umair, and m. a. al-rashid, "control of vehicular emission using innovative energy solutions comprising of hydrogen for transportation sector in pakistan: a case study of lahore city," international journal of hydrogen energy, vol. 45, no. 32, pp. 16287–16297, jun. 2020, https://doi.org/10.1016/ j.ijhydene.2019.02.173. microsoft word etasr_v13_n2_pp10316-10321 engineering, technology & applied science research vol. 13, no. 2, 2023, 10316-10321 10316 www.etasr.com abdullah & hatem: alternative construction using bim in old educational buildings alternative construction using bim in old educational buildings case study: the deanship building of the materials engineering department, university of technology, iraq oday hammody abdullah department of civil engineering, university of baghdad, iraq 10984@uotechnology.edu.iq (corresponding author) wadhah amer hatem middle technical university, iraq | baquba technical institute, iraq wadhah1970wadhah@gmail.com received: 3 october 2022 | revised: 24 december 2022 | accepted: 31 december 2022 abstract the current study analyzes historic educational buildings to discover the optimum combination of improvements for optimal energy cost. the analysis was conducted using bim technology and associated programs such as auto desk revit 2020 and auto desk insight 360 to determine the optimal strategies by which the most applicable alternative construction materials and procedures are considered to obtain environmentally and economically sustainable old educational buildings. the analysis showed that several approaches may reduce the cost of electrical energy usage and generator fuel in aged schools. optimal changes lead to such reductions. altering wall and roof materials minimizes electrical energy usage. the findings reveal that altering the lighting efficiency (0.3 w/sf) in the best way decreases the cost of electrical energy consumption by about 65,575,500 iraqi dinars (id), and reduces the cost of fuel energy consumption by approximately 510,000 id. keywords-bim; historic buildings; construction projects; sustainable design; energy efficiency; autodesk insight 360 cloud i. introduction given the importance of the energy industry and the occurring economic downturn in iraq, the goal of this research is to look into the possibility of using environmentally friendly alternatives in old buildings, like schools, in order to cut down the amount of money these buildings spend on electricity and generator fuel. building information modeling (bim) capabilities will be used to construct and maintain schemes that are grounded in reality via the 3d visualization of the structures. this will replace any schemes that are either missing or have not been fully explained. rivet 2020 and autodesk insight 360 cloud were utilized in order to conduct an analysis of a wide variety of sustainable design options. ii. literature review construction projects are dissimilar in size, type, location, site conditions, inputs and outputs, something that makes each project unique and consequently the standardization of construction processes becomes extensively difficult and risky [1]. the construction industry is one of the most important industries, as it plays a significant part in the provision of buildings, public institutions, and infrastructure, as well as in the alleviation of poverty. [2]. technology is the use of scientific effects for practical purposes. the word "technology" can also mean a group of tools and techniques that work together, like those used in construction [3]. the capacity of anything to be utilized without entirely depleting it or deteriorating is one definition of sustainability. another definition is the capacity of something to continue existing or functioning for a significant amount of time [4]. different kinds of goods, stakeholders, processes, and working conditions set the construction business apart from others [5]. a sustainable building is one that generates stakeholder value and contributes to the well-being of present and future generations by minimizing its environmental impact over the course of its entire lifespan. this is done by making the most of the building's economic value and improving human, natural, manufactured, and financial capital [6]. bim [7] is an approach that is enabled by information technology (it), and it requires applying and maintaining an integral digital representation of all building information in the form of a data repository throughout the various phases of a project's engineering, technology & applied science research vol. 13, no. 2, 2023, 10316-10321 10317 www.etasr.com abdullah & hatem: alternative construction using bim in old educational buildings lifecycle [7]. the term bim refers to a system that encompasses everything having to do with the various phases of a building project. it's a central repository of project information where stakeholders may access financial details [8]. bim is a system that looks at every part of a construction project and uses the information to help make better decisions at every stage [9]. to increase the level of performance in a construction project throughout its life cycle, bim is a complete and coherent system for all parts of the project. this system includes a set of effective rules, processes, and computer applications [8]. implementing and maintaining an integrated digital representation of information across several project phases is a part of this [10]. bim is a useful tool for simulating the conditions of a construction site in a virtual setting, where potential dangers can be found and fixed before they become big problems [11]. construction of a green building is an ongoing process that begins with careful preplanning and continues long after the construction completion. the primary goal of most green construction projects is to reduce the building's energy consumption. the two main approaches to lowering energy use are active and passive design techniques [5]. a green building is one that uses sustainable methods in its planning, construction, and day-to-day operations to lessen or get rid of the impact the building has on its surroundings and the people who live there [12]. sharing ideas and traditions makes people's lives more interesting and opens their minds to new things. sharing cultural heritage also helps strengthen economies and communities [13]. the majority of the energy used currently by homes goes toward heating. the effects of electrical power use are expanding in commercial and industrial structures. lighting, ventilation, and air conditioning, along with use-specific gadgets like computers and manufacturing gear, all account for a significant portion of an industrial facility's total energy consumption. this is especially true for newly built structures, since their heating needs are far less than those of older structures. powering electronics, such as refrigerators and washing machines, use a lot of electricity. in places where heating is more important, like in the climate of central europe, there are clear seasonal differences in how much energy the buildings use [14]. since far-off energy and fresh-water sources would necessitate more energy for transferring electricity and water into cities, minimizing the demand for natural resources and limiting natural resource consumption is the primary challenge in the development of green buildings. to lower the ever-increasing energy demand, it is important to use new building system designs and renewable energy sources when possible [15]. a building is considered energy-efficient if its design and construction result in a considerable decrease in the amount of energy required for its operation and maintenance. every facet of a building's development is attended to from the very beginning of each project by a dedicated staff. people who will be working and living in the building are parts of the team, along with architects, engineers, developers, owners, and, the future tenants. they collaborate to establish targets for resource conservation, productivity, and innovative space use. buildings that use a collaborative strategy may be up to 70% more efficient than traditional commercial buildings [16]. a net zero or zero energy building (zeb) is a residential or commercial building with greatly reduced energy needs through efficiency gains such that the balance of energy needs can be supplied by renewable technologies. energy efficiency in buildings means using less electricity, gas, and other fossil fuels. this is done by using high-performance equipment, appliances, products, and design strategies to reduce and control how much electricity is used [6]. the research on the utilization of building energy (building energy efficiency) also defined as greening or modernizing of a building (building retrofit), or the process of modifying the structure of the building referring to changes that increase its energy efficiency [17]. one of the most energy demanding sectors in modern agriculture, the greenhouse industry is in definite need of energy consumption reduction [18]. energy consumption in new commercial buildings may be reduced by 20% – 30% on average, and by over 40% for particular building types and locations, with the help of conventional energy efficiency technologies like thermal insulation, low-emissivity windows, window overhangs, and day lighting controls. increasing a building's energy efficiency might raise the initial expenses, but the money saved on energy bills over the building's useful life can more than make up for it. one of the biggest advantages of sustainable design over traditional building methods is that it saves money on energy costs over the whole life of a building [5]. the energy consumption in the residential sector is very complex due to the large variety of construction types, sizes, thermal envelope materials, and the very wide variety of occupant behavior [19]. according to green globes, energy consumption is the single most influential factor in determining a building's overall sustainability. as such, it is given the most weight in green globes' three rating systems for buildings: existing building (eb), new construction (nc), and sustainable interiors (si) [20]. most of a building's electricity bill goes toward running the air conditioner and lights. the energy requirements of a building can be drastically reduced through the use of passive design optimization in conjunction with building system optimization. bim software can help architects, engineers, and building owners evaluate different design options and their effects on energy consumption, day lighting, thermal comfort, etc. [21]. creating energy by burning fossil fuels results in the emissions of carbon dioxide. by cutting down the energy use, we may lessen that impact on the environment and cut down the human-caused causes of global warming, as well as the pollution that causes heat waves and other urban problems [22]. iii. research methodology the study strategy is mostly made up of two parts that are based on previous studies about bim technology and take into account different ways to control how much energy a building uses. a. part one (theoretical study) relevant literature, including theses, books, journals, and websites was reviewed. b. part two (practical study) by examining the building in autodesk insight 360 cloud, a feature included in revit 2020, sustainable design solutions engineering, technology & applied science research vol. 13, no. 2, 2023, 10316-10321 10318 www.etasr.com abdullah & hatem: alternative construction using bim in old educational buildings were assessed. this study includes an energy audit that is completed in line with ashrae 90.1. the process used to conduct this analysis is outlined below.  autodesk revit 2020 was used to create a threedimensional building information model for the project.  we made sure that each of the rooms has enough space.  the energy settings changed and some information was provided, such as the location of the project and the kind of project it will be.  energy analysis was conducted in the cloud with insight 360 by using rivet 2020 to create an energy model and selecting the optimization panel.  an investigation on the amount of energy that was used was conducted, with the findings being shown in the cloud by autodesk insight 360.  the research results gave information about the different aspects of different design options and how those options affect the total amount of energy used (eui).  using the cloud-based version of autodesk insight 360, the various ways in which energy efficiency may be improved via sustainable design were demonstrated and compared. the results of the investigation were based on net-zero scenarios. iv. case study the deanship building of the materials engineering department of the university of technology was the case study. the department was established in 1999/2000, and the first b.sc. group graduated in 2002/2003. in the department, evening classes first began in 2000/2001. the deanship building is one of technology university's instructional buildings. this building has 4 levels and occupies a total area of 3368m 2 . the segment building is made up of two structures joined together by a bridge. fig. 1. the case study building. a. creating the 3d visualization for the case study visualization is a technique that is used to the benefit of the client in order to acquire knowledge of the construction projects, and this is something that can be readily done when applying bim. the usual techniques involve the preparation of drawings in just two dimensions, which the clients may find difficult to grasp due to the fact that it is hard to generate a realistic mental picture of the complicated projects based simply on the drawings alone. with the help of autodesk revit 2020, the researchers were able to make a picture of the case study. fig. 2. rendering of a case study in revit 2020. v. findings and discussion the findings of this study are derived from the energy settings in revit 2020 and the scenario that was chosen from autodesk insight 360 on the web. figure 2 depicts the case study model that was carried out in the insight 360 cloud. the results showed the following: a. roof construction green roofs provide a number of advantages, including shielding a building from uv radiation and temperature extremes and reducing the amount of heat that escapes and enters the structure. roof construction demonstrates the overall resistance of roofs to heat gains and losses. this study compares and contrasts different ways to insulate a building and how well they reduce the amount of energy used. figure 3 and table i show that roof construction-r 10.25-inch sip has fewer costs (electrical and fuel) than the other types of thermal insulation. r-value is a measure of the insulation used. table i. annual costs of various roof construction types roof construction electric ($) fuel ($) uninsulated 228711 4568 r10 227492 4522 r19 227361 4547 r38 227310 4535 r60 227300 4572 r 10.25inch sip 227267 4520 r15 227347 4542 engineering, technology & applied science research vol. 13, no. 2, 2023, 10316-10321 10319 www.etasr.com abdullah & hatem: alternative construction using bim in old educational buildings fig. 3. roof construction. b. infiltration holes in the building envelope are a common cause of unintended air flow into or out of climate-controlled spaces. figure 4 and table ii shows that infiltration ach-2.0 has fewer costs of electricity, fuel, and energy than the other types of infiltration ratings. fig. 4. infiltration. table ii. annual costs of various infiltration types infiltration electric ($) fuel ($) 0.17 ach 227078 4530 0.4 ach 226997 4540 0.8 ach 226792 4553 1.2 ach 226609 4559 1.6 ach 226419 4571 2.0 ach 226365 4529 c. lighting control system this improvement included the installation of a regulation system for the building's lights, which combined presence detectors with twilight sensors in order to reduce the amount of electricity that was used. it's a typical occupancy sensor system that changes the lighting depending on how much daylight is available. in addition to day lighting apertures like skylights and windows, a day lighting management system often incorporates a lighting control system that is sensitive to the presence of daylight. when daylight alone provides enough light, this method may reduce the amount of electricity needed for electric lighting. this lighting system is able to recognize when a certain area is unoccupied and alter the level of illumination accordingly. occupancy sensors are used in this process. the lights will either gradually dim or turn off completely in order to reduce cost. another benefit is that it makes it easy to have the lights turn on automatically when the device detects people, which could also make the area safer. figure 5 and table iii show that the occupancy control system has fewer costs (electrical, fuel, energy) than the other types of lighting control systems for buildings. fig. 5. day lighting and occupancy controls. table iii. annual costs of various day lighting and occupancy control types day lighting and occupancy electric ($) fuel ($) none 226997 4540 daylighting control 226997 4540 occupancy control 219687 4517 daylighting and occupancy control 219689 4519 d. lighting efficiency lighting efficiency provides information on the power consumption as well as the average internal heat gain and power consumption of electric lighting per unit of floor area. in addition, it is a representation of the amount of electricity used. figure 6 and table iv show that a lighting efficiency system of -0.3w/sf has the lowest cost (electric, fuel, and energy) than the other considered types of lighting efficiency systems. engineering, technology & applied science research vol. 13, no. 2, 2023, 10316-10321 10320 www.etasr.com abdullah & hatem: alternative construction using bim in old educational buildings fig. 6. lighting εfficiency. table iv. annual costs of various lighting efficiency types lighting efficiency electric ($) fuel ($) 0.3 w/sf 183228 4496 0.7 w/sf 190027 4587 1.1 w/sf 196789 4507 1.5 w/sf 203557 4505 1.9 w/sf 210262 4498 e. energy operating schedule this study highlights the many different operating schedules that may be used in buildings, as well as the degree to which different operational schedules can affect energy consumption and the intensity of energy use. figure 7 and table v show that the (12/5) operating schedule has less cost (electric, fuel, energy) than the other types of operating schedule systems (12 means that there are 12 working hours in total every day, while 5 means that there are 5 working days in total). fig. 7. operating schedule. table v. annual costs of various operating schedule types operating schedule electric ($) fuel ($) 24/7 319692 11251 12/7 277194 7351 12/6 264673 6636 12/5 235477 6631 vi. energy simulation after the 3d bim model has been finished in revit 2020, it was transferred to green building studio (gbs) by using the green building xml (gbxml). this allowed coming up with different design options and give information about how much energy and water are being used efficiently. gbxml is an open schema that was developed to make simpler for engineering analysis tools to utilize bim to access building data. the file was imported from the website of autodesk green building studio (the gbs cloud). table vi. annual cost savings alternative type alternative name annual electric cost of the alternative (id) annual electric cost savings (id) annual fuel of alternative (id) annual fuel cost saving (id) annual energy cost saving (id) roof construction r 10.25inch sip 226267* 1500 = 340,900,500 678* 1500 = 1,017,000 4520* 1500 = 6,780,000 316* 1500 = 474,000 1,491,000 infiltration 2.0 ach 226365* 1500 = 339,547,500 580* 1500 = 870,000 4529* 1500 = 6,793,500 307* 1500 = 460,500 1,330,500 lighting efficiency 0.3 w/sf 183228* 1500 = 274,842,000 183228* 1500 = 65,575,500 4496* 1500 = 6,744,000 340* 1500 = 510,000 66,085,500 day lighting and occupancy occupancy controls 219687* 1500 = 329,530,500 7258* 1500 = 10,887,000 4517* 1500 = 6,775,500 319* 1500 = 478,500 11,365,500 operating schedule 12/5 225477* 1500 = 353,210,500 1468* 1500 = 2,202,000 4631* 1500 = 9,946,500 205* 1500 = 307,500 2,509,500 *1500 represents the factor of converting the id to $ engineering, technology & applied science research vol. 13, no. 2, 2023, 10316-10321 10321 www.etasr.com abdullah & hatem: alternative construction using bim in old educational buildings vii. create design alternatives gbs allows producing a variety of design options that have the potential to enhance the building's overall energy performance. many different options, which are provided by gbs, were chosen based on an analysis by autodesk insight 360 and their impact on the amount of energy used and the amount of carbon emissions produced by the case study. some of these options are orientation, window ratio, window shades, lighting control for the hvac system, type of window glass, and type of wall. equations (1)-(2) will be used to compute the yearly energy savings. annual electric cost saving (id/year) = annual electric cost of βuilding – annual electric cost of αlternative (researcher) (1) annual fuel cost saving (id/year) = annual fuel cost of the βuilding – annual fuel cost of αlternative (researcher) (2) for example, the current yearly cost of electricity was 340,422,000 id and the annual cost of fuel was 7,254,000 id (maintenance division / university of technology). table vi illustrates the annual cost savings for fuel and electricity. viii. conclusions this article gave a summary of the procedure that was used to establish a set of assessment criteria for historical structures. these criteria were utilized in the evaluation of historical and archaeological buildings. by using modern research methods, the authors of this study are making an effort to define relevant instruments and procedures that may be of assistance in the energy management. the main conclusions from the current research are:  bim is a very useful tool for a wide range of assessments, each of which helps find new ways to improve the energy efficiency of a project.  lighting efficiency of 0.3 w/sf has the greatest annual electric cost saving of 65,575,500 id and infiltration of 2.0 ach has the lowest with 870,000 id.  lighting efficiency of 0.3 w/sf has the greatest annual fuel cost saving of 510,000 id and 12/5 operating schedule has the lowest annual fuel cost savings with 307,500 id.  the results indicate that there is a clear difference between the estimated and the actual consumption of electricity and fuel energy. this is shown by the fact that there is a plain separation between the two. based on these results, it seems that using bim during the design stage is a great way to figure out how well a building uses energy. references [1] k. m. m. el-dash, o. m. o. ramadan, and w. m. m. a. youssef, "duration prediction models for construction projects in middle east,” engineering, technology & applied science research, vol. 9, no. 2, pp. 3924–3932, apr. 2019, https://doi.org/10.48084/etasr.2531. [2] hatem khaleefah al-ageeli and abdul salam j. ali alzobaee, "critical success factors in construction projects (governmental projects as a case study),” journal of engineering, vol. 22, no. 3, pp. 129–147, mar. 2016. [3] h. seaton, the construction technology handbook: making sense of artificial intelligence and beyond, 1st ed. hoboken, nj, usa: wiley, 2021. [4] r. a. altalebi and i. al-bazzaz, "similarity and difference between sustainable and green architecture (a comparative study),” journal of engineering, vol. 24, no. 12, pp. 21–42, dec. 2018, https://doi.org/ 10.31026/j.eng.2018.12.10. [5] v. tam and k. le, sustainable construction technologies 1st ed. butterworth-heinemann, 2019. [6] construction specifications institute, the csi sustainable design and construction practice guide, 1st ed. hoboken, nj, usa: wiley, 2013. 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[10] f. m. kareem, a. m. abd, and r. n. zehawi, "utilize bim technology for achiveing sustainable passengers terminal in baghdad international airport,” diyala journal of engineering sciences, vol. 14, no. 4, pp. 62– 78, dec. 2021, https://doi.org/10.24237/djes.2021.14406. [11] w. a. hatem, a. m. abd, and n. n. abbas, "motivation factors for adopting building information modeling (bim) in iraq,” engineering, technology & applied science research, vol. 8, no. 2, pp. 2668–2672, apr. 2018, https://doi.org/10.48084/etasr.1860. [12] i. m. chethana illankoon, v. v. tam, and k. le, life-cycle cost models for green buildings, 1st ed. butterworth-heinemann, 2020. [13] j. e. anderson, c. bucher, b. briseghella, x. ruan, and t. zordan, eds., sustainable structural engineering. zürich: international association for bridge and structural engineering, 2015. [14] k. voss and e. musall, net zero energy buildings: international projects of carbon neutrality in buildings, 1st ed. munich, germany: detail, 2013. [15] t. schröpfer, dense + green: innovative building types for sustainable urban architecture. birkhäuser, 2015, https://doi.org/10.1515/9783038210146. [16] c. j. schexnayder and c. m. fiori, handbook for building construction: administration, materials, design, and safety, 1st ed. new york, ny, usa: mcgraw hill, 2021. [17] s. j. n. al-khafaji and g. m. i. a. r. kamoona, "greening existing buildings in contemporary iraqi urban reality/ virtual model,” journal of engineering, vol. 21, no. 11, pp. 1–21, nov. 2015. [18] a. belkadi, d. mezghani, and a. mami, "energy design and optimization of a greenhouse: a heating, cooling and lighting study,” engineering, technology & applied science research, vol. 9, no. 3, pp. 4235–4242, jun. 2019, https://doi.org/10.48084/etasr.2787. [19] a. zerroug and e. dzelzitis, "a study of modeling techniques of building energy consumption,” engineering, technology & applied science research, vol. 10, no. 1, pp. 5191–5194, feb. 2020, https://doi.org/10.48084/etasr.3257. [20] p. andrasik, leed lab: a model for sustainable design education. routledge, 2021. [21] v. yellamraju, leed-new construction project management, 1st ed. new york, ny, usa: mcgraw hill, 2010. [22] a. athienitis and w. o’brien, eds., modeling, design, and optimization of net-zero energy buildings. hoboken new jersey, usa: wiley, 2015. microsoft word etasr_v12_n1_pp8080-8084 engineering, technology & applied science research vol. 12, no. 1, 2022, 8080-8084 8080 www.etasr.com khameesa & altaay: evaluating the efficiency of finance methods in residential complex projects … evaluating the efficiency of finance methods in residential complex projects in iraq alaa s. khameesa department of civil engineering university of baghdad baghdad, iraq dr.alaa@bauc14.edu.iq meervat r. altaay department of civil engineering university of baghdad baghdad, iraq abstract-financial funding of a construction firm plays an important role in all aspects of the process development. it has been noted that financial crises have a direct impact on the construction industry. the iraqi government, whether locally or globally, has faced a severe shortage of financing which has resulted in incomplete projects. due to the financial crisis that iraq went through which led to the suspension of many residential complex projects and the difficulty of the use of public financing methods, we researched the private financing (publicprivate partnership) methods instead of public financing methods in residential complex projects implementation. this study verified the financial problems and the factors that relate to the possibility of their occurrence with the use of a questionnaire that was designed and distributed to professionals in the field. arbitration of the questionnaire, pilot study, questionnaire distribution, and statistical tests were conducted. the t-test (paired samples t-test) was used to find out if there are differences between the public and private financing methods. the results showed that the private financing (public-private partnership) methods, under the current conditions in iraq, are better than the public financing methods. keywords-finance methods; residential complex projects; paired samples t-test; iraq i. introduction many previous studies have criticized the public financing methods. their issues include the completion of the project on time, the completion within budget, delay in payment of contractor entitlements, clear roles and responsibilities for project participants, errors and inconsistencies in the contract document, etc. the concept of public-private partnership (ppp) is relatively new to residential complex projects for the iraqi government since the construction of residential complexes is the responsibility of the iraqi government which uses public financing methods. due to the high cost of residential complex projects in recent years, ppp schemes have become popular in the global construction market. by implementing them, governments are able to put projects on the right track without worrying themselves too much about raising funds [1]. ppp can be defined as the contractual agreements between a private party and a part (or all) of the government. under this contract, the private party agrees to perform certain functions or activities which are considered a public responsibility.[2]. a ppp project includes many important contractual arrangements between the participants. it is a complex network of relationships that includes multiple parties and their formal relationships are defined by contracts. the basic rationale for establishing partnerships is that both public and private sectors have unique characteristics that provide them with advantages in specific aspects of the service or project delivery. the most successful partnership arrangements are built on the strengths of both sectors to establish complementary relationships [3]. the concept of ppp has been around for centuries in europe and the united states while it has been a recent development in other parts of the world. ppp as a concept originated in the uk and its early development was primarily driven by the need for new investments and financing possibilities to provide and deliver public sector assets and services [4]. common reasons for the discontinuation of projects are insufficient project preparation, inadequate funding, lack of administrative/legal procedures, inflation, variance in project scope, political factors, client's death, conflicts, and incompetence of the project manager. in addition, the lack of strong government control and monitoring management is a key factor contributing to the causes of discontinuation projects [5]. table i represents a set of success and failure factors in the use of financing methods collected from previous studies. ii. questionnaire design all necessary information was collected, reviewed, and formalized based on literature review, personal observations, and interviews with experts in the topic. a. part i (general information) this part contains general information about the participant (name, age, gender, ministry name, and sector of work), as well as classifications of educational qualifications, specializations, employment positions, and work experience. b. part ii (evaluating the efficiency of public financing) this section contains a list of 32 factors that can occur when using public funding related to project completion in time, cost, quality, quality of communication between project parties, experience and skill needs, government guarantee, and quality of service. regulatory and legal framework, capital strength, project financing, ability of the contractor to deal with corresponding author: alaa s. khameesa engineering, technology & applied science research vol. 12, no. 1, 2022, 8080-8084 8081 www.etasr.com khameesa & altaay: evaluating the efficiency of finance methods in residential complex projects … a large number of projects at the same time, etc. it was constructed using the 5-point likert scale (very high, high, medium, week, very week) design [18]. the respondents answered based on their experience. table i. project success and failure factors most important factors ref. competition and innovation improved operation and maintenance quality the government is able to focus on core public sector responsibilities [7] financial and capital strength technical ability personnel reserve project management capacity ability of communication [10] favorable legal and political support financial allocations are available favorable social support economic viability reliable contractual arrangement government guarantee and experience [8] avoid claims and consequent disputes avoid cost and time overruns consider concurrent delays project progress can be efficiently tracked throughout the project lifecycle [6] appropriate concessionaire contracts and agreements clear definition of project scope and documentation the roles and responsibilities are clear accelerated permitting and approvals appropriate risk distribution [12] appropriate risk distribution and risk sharing competition and innovation commitment of public and private sector thorough and realistic cost and benefit assessment feasibility of technical project good governance favorable legal framework [13] on time financing public organizations' cooperation commitment quality of team intercommunication [15] public awareness and support public safety a multidisciplinary and multinational team quality control and supervision financial market availability appropriate project identification [17] adequate funding throughout the project multidisciplinary/competent project team contractor’s good combination of expertise of design and techniques of building strong design of contractor and construction management capability comprehensive contract documentation contract form and contract period [14] quality improvement shorter project durations reduction of long term projects [16] shortest construction and concession period most cost-effective and innovative solution safest for construction strongest financial commitment [11] legal and economic framework can be developed. political stability-opposed/support right project can be selected feasibility study financial capability compatibility/complimentary skills [3] c. part iii (evaluating the efficiency of private financing ppp) this part contains a list of 32 factors that can occur when using ppp related to completion of projects in cost, time, quality. appropriate risk distribution and risk sharing, quality of communication between parties of project, skill needs and experience. a comprehensive cost-benefit assessment with good project cost, experienced management, skilled and multidisciplinary staff, speed in permits and approvals, project financing, ability of the contractor to deal with a large number of projects at the same time, etc. it also was created with the use of the pentatonic scale design [18]. iii. questionnaire arbitration questionnaire arbitration is a good approach for professionals to see if the questionnaire is measuring what they want to measure [19]. according to the arbitration, the questionnaire was submitted to a group of contracting experts in funding of residential complexes projects. the previously developed questionnaire was presented to them, their comments and recommendations were taken into account, and the amendments they mentioned were approved. iv. pilot study before collecting the final data from the entire sampled population, a pilot study was conducted. the pilot study is a trail run for the questionnaire, which includes checking the wordings of questions, clarifying ambiguous questions, and evaluating the techniques that were utilized to collect the data [20]. the study's main purpose is to identify obstacles and concerns that are more ambiguous than others, allowing remedial actions to be taken and the testing process to be improved. the sample size of the pilot study should range from 30 to 50 respondents .the sample size of the current study was 40. v. statistical validity of the pilot study according to [21], validity refers to how well an instrument measures what it is designed to measure. validity has many different aspects and methods of evaluation. there are two statistical tests that should be performed, namely internal validity and external validity (figure 1). they are used to ensure the questionnaire's validity. the tests of statistical validity were conducted with the data obtained from the pilot study. the tests included in the statistical validity of the pilot study were conducted with ibm spss v.26. fig. 1. statistical validity tests of the pilot study. engineering, technology & applied science research vol. 12, no. 1, 2022, 8080-8084 8082 www.etasr.com khameesa & altaay: evaluating the efficiency of finance methods in residential complex projects … a. internal validity the questionnaire's internal validity is the first statistical test used to determine its validity. it is done by computing the correlation coefficients between each item in one field and the entire field [22]. table ii shows the results. table ii. spearman's rho correlation for evaluating the efficiency of public finance in pilot data s p e a r m a n 's r h o item correlation coefficient sig. (2tailed) item correlation coefficient sig. (2tailed) pf 1 0.619** 0.000 pf17 0.685** 0.000 pf 2 0.605** 0.000 pf 18 0.705** 0.000 pf 3 0.624** 0.000 pf 19 0.403** 0.000 pf 4 -0.159* 0.044 pf 20 0.161* 0.042 pf 5 -0.175* 0.027 pf 21 0.650** 0.000 pf 6 0.183* 0.021 pf 22 0.649** 0.000 pf 7 0.301** 0.000 pf 23 0.554** 0.000 pf 8 0.380** 0.000 pf 24 0.665** 0.000 pf 9 0.411** 0.000 pf 25 -0.469** 0.000 pf 10 0.567** 0.000 pf 26 0.676** 0.000 pf 11 0.563** 0.000 pf 27 -0.240** 0.002 pf 12 0.568** 0.000 pf 28 0.613** 0.000 pf 13 0.643** 0.000 pf 29 0.648** 0.000 pf 14 0.703** 0.000 pf 30 0.544** 0.000 pf 15 0.508** 0.000 pf 31 0.561** 0.000 pf 16 0.609** 0.000 pf 32 0.634** 0.000 *correlation is significant at the 0.05 level (2-tailed) correlation is significant at the 0.01 level (2-tailed)٭٭ the correlation coefficients ranged from 0.159 to 0.705, and the p-values were all less than 0.05, indicating that all items are consistent and have the validity to measure what they were put up to measure. table iii shows the values of the spearman correlation coefficient for the evaluation of the efficiency of private financing (ppp). table iii. spearman's rho correlation for evaluating the efficiency of ppp in pilot data s p e a r m a n 's r h o item correlation coefficient sig. (2tailed) item correlation coefficient sig. (2tailed) ppf 1 0.744** 0.000 ppf 17 0.778** 0.000 ppf 2 0.695** 0.000 ppf 18 0.729** 0.000 ppf 3 0.741** 0.000 ppf 19 0.441** 0.000 ppf 4 -0.289** 0.000 ppf 20 -0.198* 0.012 ppf 5 -0.248** 0.002 ppf 21 0.698** 0.000 ppf 6 0.292** 0.000 ppf 22 0.725** 0.000 ppf 7 -0.165* 0.037 ppf 23 0.673** 0.000 ppf 8 0.544** 0.000 ppf 24 0.765** 0.000 ppf 9 0.565** 0.000 ppf 25 -0.441** 0.000 ppf 10 0.748** 0.000 ppf 26 0.779** 0.000 ppf 11 0.722** 0.000 ppf 27 -0.405** 0.000 ppf 12 0.792** 0.000 ppf 28 0.705** 0.000 ppf 13 0.763** 0.000 ppf 29 0.733** 0.000 ppf 14 0.752** 0.000 ppf 30 0.570** 0.000 ppf 15 0.669** 0.000 ppf 31 0.719** 0.000 ppf 16 0.731** 0.000 ppf 32 0.675** 0.000 *correlation is significant at the 0.05 level (2-tailed) correlation is significant at the 0.01 level (2-tailed)٭٭ the correlation coefficients ranged from 0.165 to 0.792, and the p-values were all less than 0.05, indicating that all items are consistent and have the required validity b. structural validity the structural validity was calculated by computing the correlation between a particular part of the questionnaire and the questionnaire as a whole [22]. table iv shows the correlation coefficient between each field and the other fields of the questionnaire. table iv. spearman's rho correlation coefficient between the questionnaire’s parts s p e a r m a n 's r h o part correlation coefficient sig. (2tailed) evaluating the efficiency of public finance 0.782** 0.000 evaluate the efficiency of ppp 0.881** 0.000 *correlation is significant at the 0.05 level (2-tailed) correlation is significant at the 0.01 level (2-tailed)٭٭ the correlation coefficients ranged from 0.782 to 0.881, and the p-values were all less than 0.05, indicating that all items are consistent and have the required validity. vi. statistical reliability of the pilot study a. cronbach'salpha model one of the most widely used indicators of reliability analysis is cronbach's alpha. the questionnaire's reliability was calculated using cronbach's alpha coefficient for each field and for the whole questionnaire. cronbach's alpha coefficient value lies between 0.0 and +1.0. a greater value indicates a higher degree of internal consistency [23]. table v shows the classification for the degree of reliability according to the value of the cronbach's alpha coefficient. table v. reliability cutoff values [21, 23] cronbach's alpha degree of reliability α ≥ 0.9 excellent 0.9 > α ≥ 0.8 good 0.8 > α ≥ 0.7 acceptable 0.7 > α ≥ 0.6 questionable 0.6 > α ≥ 0.5 poor 0.5 > α unacceptable τhe findings were found to be within acceptable limits. this result verifies the questionnaire's dependability. the cronbach's alpha values are shown in table vi. table vi. values of cronbach's alpha reliability value of α part good 0.885 evaluating the efficiency of public finance excellent 0.908 evaluate the efficiency of ppp vii. questionnaire data analysis the questionnaire data were analyzed using a series of quantitative statistical techniques to obtain a thorough view of the opinions received from the iraqi experience regarding to the subject of financing residential complexes. these statistical techniques will be explained below. descriptive statistics is a statistical tool for summarizing, organizing, and simplifying data. the following descriptive statistics were used. engineering, technology & applied science research vol. 12, no. 1, 2022, 8080-8084 8083 www.etasr.com khameesa & altaay: evaluating the efficiency of finance methods in residential complex projects … a. central tendency measurement a measure of central tendency (also known as a central location measure) is a summary measure that aims to describe a whole set of data with a single value that denotes the middle or center of its distribution. b. t-test (paired samples t-test) once the subjects being tested are the same, a paired samples t-test is performed because the two mean scores cannot be independent of each other [24-26]. in testing these samples, we analyzed the data by using the spss 26.0's paired samples t-test. the hypotheses can be expressed in two forms that are mathematically comparable and express the same idea. (h0: µ1 = µ2) means that the paired populations are equal. (h1: µ1 ≠µ2) means that the paired population are not equal. or: (h0: µ1 µ2 = 0) means that the difference between the paired population is equal to zero. (h1: µ1 µ2 ≠ 0) means that the difference between the paired populations is not zero. where µ1 is the mean of the population of variable 1, and µ2 is the mean of the population of variable 2. the data were processed with the spss 26.0. the result of the paired samples t-test can be seen in table vii. table vii. result from the paired samples t-test paired sample statistics mean n std. deviation std. error mean pair 1 private financing 101.03 160 15.773 1.247 public financing 95.01 160 13.539 1.070 paired samples test m e a n s td . d e v ia tio n s td . e r r o r m e a n l o w e r u p p e r t d f s ig . 2 -ta ile d pair 1 private financing – public financing 6 .0 2 5 1 4 .2 0 1 1 .1 2 3 3 .8 0 8 8 .2 4 2 5 .3 6 7 1 5 9 0 .0 0 0 the hypothesis states that the effectiveness of the first method is equal to that of the second. since the average effectiveness of the second method is higher than the first method's, the second method is considered better. viii. conclusion in this study, the factors that evaluate the efficiency of public and private financing were collected from previous studies and an open questionnaire survey. the study population was relevant to the subject and the questionnaire was designed and arbitrated by experts. statistical methods were used in data analysis such as descriptive statistics and t-test. since the average effectiveness of the second method is higher compared to the first method, the second method is considered better. we can conclude that ppp methods are more efficient than public financing methods regarding the construction of residential complex projects in iraq. references [1] o. al-juboori, "conditions for applying public private partnership ppp in iraq infrastructure projects successfully," ph.d. dissertation, technische universitat munchen, munchen, germany, 2015. 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[23] p. julie, spss survival manual, 5th ed. new york, ny, usa: mcgrawhill, 2013. [24] j. larson-hall, a guide to doing statistics in second language research using spss and r, 2nd ed. new york, ny, usa: routledge, 2015. [25] a. zhang, advanced analysis of gene expression microarray data. singapore, singapore: world scientific, 2006. [26] n. carbonara, n. costantino, and r. pellegrino, "an empirical study of risks in ppp: the case of the motorway sector," in second international conference on public-private partnerships, austin, texas, may 2015, pp. 473–485, https://doi.org/10.1061/9780784480267.037. microsoft word etasr_v13_n4_pp11497-11504 engineering, technology & applied science research vol. 13, no. 4, 2023, 11497-11504 11497 www.etasr.com hussain et al.: a finite element approach to evaluate and predict the shear capacity of steel … a finite element approach to evaluate and predict the shear capacity of steel fiberreinforced concrete beams laith n. hussain civil engineering department, university of technology, iraq bce.20.74@grad.uotechnology.edu.iq mohammed j. hamood civil engineering department, university of technology, iraq 40040@uotechnology.edu.iq ehsan a. al-shaarbaf civil engineering department, al-esraa university college, iraq ishaarbaf@esraa.edu.iq received: 19 may 2023 | revised: 13 june 2023 | accepted: 26 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6054 abstract adding steel fibers to a concrete matrix enhances the shear capacity of reinforced concrete beams. a comprehensive understanding of this phenomenon is essential to evaluate engineering designs accurately. the shear capacity of steel fiber reinforced concrete (sfrc) beams is affected by many parameters, such as the ratio of the shear span to the effective depth of the sfrc beam, the compressive strength of concrete, the longitudinal reinforcement ratio, volume fraction, aspect ratio, and the type of fibers. therefore, to cover the influence of these parameters on the shear capacity of sfrc beams, 91 beams from previous studies, divided into 10 groups, were considered in the current study. two approaches have been used to predict the shear capacity of sfrc beams. the first approach used 7 predicting equations derived from previous studies and the second one used finite element analysis (ansys software) to simulate the 91 beams. despite the many approaches to simulate the structure elements, there is no reliable approach able to simulate satisfactorily 91 sfrc beams as this study does. the log file of ansys software was used to simulate and calculate the shear strength capacity of the beams. the results show a reasonable agreement with the experimental tests. the extracted results were much closer and more realistic than those obtained by the predicting equations. also, the χ factor (squared value of experimental shear capacity to the predicted shear capacity) of the ansys software results is 97%, while the closest proposed equation gives 91%. keywords-fibers; experimental shear capacity; ansys; predicting shear equation i. introduction poor toughness of high-strength concrete can be overcome with the addition of short discontinuous fibers. fibers control the propagation of cracks and limit the crack width. the high elastic modulus of steel fibers also enhances concrete's flexural toughness and ductility. the participation of steel fibers can be seen mainly after matrix cracking in concrete. however, adding steel fibers at high dosages has a prospective impediment in terms of poor workability and growth cost. in addition, the increased stiffness of steel fibers and micro-defects such as voids and honeycombs may form during placing due to inadequate consolidation at the low workability stage [1, 2]. a compromise of the concrete mixture properties to gain good fresh concrete properties (in reduced early-age cracking and workability) and the toughness of hardened concrete can be reached by adding two different fiber types, which can function individually at different volume fractions to yield optimum performance. the addition of steel fibers to the concrete matrix results in excellent fresh concrete properties and deducts micro cracks [3]. the hybrid combination of metallic and nonmetallic fibers can offer potential advantages in improving concrete properties and reducing the cost of concrete production. when the volume fraction of the fibers is increased, it results in denser and more uniform distribution of the fibers throughout the concrete, reducing shrinkage cracks and improving concrete post-crack strength. in addition, it is essential to have a combination of low and high-modulus fibers to arrest the micro and macro cracks, respectively. another engineering, technology & applied science research vol. 13, no. 4, 2023, 11497-11504 11498 www.etasr.com hussain et al.: a finite element approach to evaluate and predict the shear capacity of steel … ffiffiffi beneficial variety of threads is that of long and short fibers. using different lengths of fibers would control different scales of cracking [4-7]. there are many challenges when conducting finite element analysis for many beams or for beams of complicated geometry [8-10]. the nonlinear finite element technique was utilized in this work to predict the shear capacity of 91 sfrc beams and evaluate the accuracy of the proposed equations by previous studies to calculate the shear capacity sfrc beams [11-13]. a new nonlinear finite element approach was built in ansys software to model the selected data involving sfrc beams with different parameters such as the ratio of shear span to the effective depth of the sfrc beam, compressive strength of concrete, longitudinal reinforcement ratio, volume fraction, aspect ratio, and type of used fibers [14-16]. according to the experimental work, concentrated load was applied in different shear spans. one support prevents the movement in the x and z directions and the translation in the y direction acted as a pin support. the second support prevents the movement in the x direction and prevents the translation in the y direction to act as roller support. table i. the considered shear strength equations for sfrc beams ref. shear strength expression [17] �� = �� ��( /�)�/� bd, where k = 2/3, fct is the frc split cylinder strength,and a is the shear span. if fct is unknown, it can be taken as ��� = 0.79��′� (���). [18] �� = {[0.16 �� ′� + 17.2 (� /�)] + "�# }% , where v and m are the shear and moment capacity at critical section, and σtu is the frc post crack tensile stress. for beams with a/d ≥ 2 subjected to a concentrated load placed at a distance a from support, �/� = (�&�'/� )— = � − where mmax is the moment at the section the concentrated load is applied. for specimen tested in [17] the σtu values used for all specimens was calculated as, σtu = 0.41τ f, where fibre-matrix bond τ was taken as 0.68 �� ′�, as recommended in [20] and + = (,�/-�) ��⁄ �, where ,�, -�, and �� are the length, the diameter, and the volume fraction the used fiber, respectively, and df = 1 for the hooked steel fibers. [19] �� = {/[0′� 12� � + 3′4( /�)] + 5%}% , where e = 1.0 for a/d > 2.8 and e = 2.8 d/a when a/d ≤ 2.8, ρ is the ratio of longtudinal reinforcement, 0′ = 0.24,,b' = 80 mpa, f spf c = [f cuf /(20 —√+)] + b + c √+,where �789 is the frc cube strength, b = 0.7 mpa, c = 1 mpa, and vb = 0.41τ f, where τ is the fiber interficil bond assumed as 4.15 mpa. [20] vn = (2.11p3 ��′�+7f)[4( /�)�/:]bd, where a/d ≥2.5. [21] vn = [0.167/ + 0.25+] ��′�% , where e = 1.0 for a/d > 2.5 and e = 2.5d/a when a/d ≤ 2.5. [22] vn = {3.7/�=>?�@/: [4( /�)�/:] + 0.85a }% , where e = 1.0 for a/d > 3.4 and e = 3.4d/a when a/d ≤ 3.4. �=>? � = [��#? /(20 — √+)] + 3 + b +, where fcuf is the frc cube strength, b = 0.7 mpa, and c = 1 mpa/ vb = 0.41τ f, where τ = fibre-matrix interfacial bond,assumed equal to 4.15 mpa. [23] �c = (0.11� d� e� �% + ("� )fgh%( �)�i��� where (σk)lmn= @op.qars � , c = @op.tu?v�ar � note: concrete cylinder test � d� was assumed as 0.8 times the concrete cube strength fcuf . ii. methodology the methodology used in this study was carried out by ansys software based on the validation of the 7 equations presented in table i [17-23]. a new approach will be adopted to simulate this vast amount of data. this approach will use the log file (figure 5) to simulate and apply all the variables of the selected sfrc beams. these variables are: the ratio of shear span to the effective depth of the sfrc beam, compressive strength, longitudinal reinforcement ratio, volume fraction, aspect ratio, type of fiber. iii. equations for the shear strength capacity of sfrc beams several studies proposed equations that describe the shear capacity of sfrc beams. however, data analysis of previous studies indicates that the behavior of the sfrc beams remains a complicated issue. therefore, all the suggested calculation methods for a shear load capacity of the beams are separated into the following three elements: (1) shear strength of the member without shear reinforcement which is found in the compression zone, longitudinal reinforcement, aggregate interlock (2) contribution of shear reinforcement, (3) contribution of steel fibers. table i presents the most successful proposed equations that calculate the ultimate shear strength of sfrc beams without transverse reinforcement. iv. material mechanical properties a. concrete in order to obtain an accurate finite element analysis, defining the modulus of elasticity, compressive behavior, and tension behavior of sfrc are essential. therefore, this study extracted the stress-strain curves in tension and compression for the selected sfrc beams using the most famous available relationships for two types of fibers because the selected data involve straight and hooked-end steel fibers. furthermore, an excel sheet was prepared to predict the stress-strain curve for all simulated models. 1) the behavior of the sfrc (straight fibers) in compression the contribution of steel fibers becomes more obvious after cracking. so the consequences of adding steel fibers appear clearly in the compressive behavior in the stress-strain curve of the sfrc beams. volume fraction, geometry, and bond characteristics of steel fibers affect the compression behavior of the stress-strain curve. this contribution depends on the ability of concrete matrix with steel fibers to develop pull-out strength as the fibers provide crack-bridging function which allows to transverse the stress across the cracks and to arrest crack growth for already developed cracks [24-26]. however, the compressive strength is slightly increased when the matrix contains a low volume fraction of steel fibers. authors in [27] proposed a formula to simulate the compressive stress-strain curve of concrete with straight steel fibers: "� = ��.wx y1 − z1 − [\[\].^_` @a (1) where εco.cf is the strain value of the sfrc at the ultimate compressive stress. the first stage of the curve is assumed to engineering, technology & applied science research vol. 13, no. 4, 2023, 11497-11504 11499 www.etasr.com hussain et al.: a finite element approach to evaluate and predict the shear capacity of steel … remain linear until 85% of fc.sf. the other parameters corresponding to this point are calculated using the following expressions: strength value is: fc.sf = fc(0.2315f + 1) (2) strain at ultimate strength, εco.sf: εco.sf = εco(0.95f + 1) (3) ultimate strain: εcu.sf = εco.sf(1.40f + 1) (4) where the fc is the cylinder compressive strength of concrete without steel fibers, εco is the maximum strain, usually assumed as 0.002. f is the fiber factor that depends on the geometry shape of the added steel fibers in the sfrc mixture, f=βvsf(lsf/dsf), where β is the bond factor, equal to 0.5 for round shape, 0.75 for hooked, crimped, and undulated shapes, and 1.0 for indented shape, the vsf, lsf, and dsf are the volume fraction, length, and diameter of the steel fibers, respectively. 2) the behavior of the sfrc (hooked end fibers) in compression using a high volume fraction of straight steel fibers results in workability difficulties. therefore hooked end steel fibers have been used in many studies because this fiber geometry provides more pull-out resistance between the steel fibers and the matrix, which leads to obtaining better properties of sfrc by using fewer steel fibers to satisfy the workability requirements. the compressive behavior of the sfrc beams is significantly affected by the hooked end type. adding hookedend steel fibers to a concrete matrix enhances the deformation capability of the post-peak more than the straight type. authors in [28] proposed an equation describing the compressive behavior of hooked-end sfrc. bc = d0.0003�? efgf + 0.0018h ��dp.�@ (5) i� = d−367�? efgf + 5520h ��dp.�� (6) �� = ��d y j([\ []⁄ )jk�l([\ [])⁄ ma (7) 0 = 3 = � �kd f\vn]o\h �ip b� bc 1.0kq⁄ (8) 0 = 1 + 0.723 d�? efgfh kp.tt@ for b� bc > 1.0⁄ (9) 3 = z?\vup` p.pv� w1 + 0.882 d�? efgfh kp.tt@x 0 ky in (6) for b� bc > 1.0⁄ (10) b. tensile behavior of the sfrc many analytical stress-strain expressions have been derived from previous studies to identify and determine the sfrc behavior during tension. in this research, a smeared crack method that has previously been adopted in many studies has been used in this study to extract the behavior of sfrc concrete under tension for the selected data. the total tensile strain, εt, is the sum of an elastic, εt,el, and a fracture component, εt,fr, that can be estimated based on the following: εt = εt,el + εt,fr (11) εt,el = σt / et,sf (12) εt,fr = wt /lfr,sf (13) where σt is the tensile stress of sfrc, et,sf. is the modulus of elasticity under the tension of sfrc, wt is the crack width, and lfr,sf is the length of the sfrc. although the previous equations will produce the stressstrain curve for both hardening and softening regions for sfrc under compression and tension stresses, it is important to explain that the ansys software deals only with the hardening region in the stress-strain curve, either in compression or tension (red and blue colored region in figure 1) and the softening part after the colored region will not be considered, according to the fact that the ansys does not need more than one point to identify the tensile stress-strain curve (table ii). the hardening region in the tensile stress-strain curve of concrete shows linear behavior under the tension stress for a low dosage of steel fibers is used because the addition of high dosage leads to high residual stress of bending or direct tensile stress tests. also, the effect of added steel fibers to concrete appears after the cracking of the concrete matrix [29]. in contrast, regarding the compression stress-strain of concrete, there are two regions to identify the compression behavior of concrete. fig. 1. the modified region of concrete stress-strain curve in ansys. the region beyond the elastic limit in the compressive stress-strain curve represents the first point to be entered in ansys, and the last point is the maximum compressive stress. therefore an excel sheet was prepared to identify and select the intended part from the compressive stress-strain curve to model the sfrc beams, see figure 2. c. steel rebars steel rebars are assumed to be bilinear isotropic in this study. their elastic modulus of elasticity is 200000 mpa and poisson's ratio is 0.3. the bilinear model requires the yield stress (fy), and in some beams, the hardening modulus of steel rebars has to be defined [30, 31]. engineering, technology & applied science research vol. 13, no. 4, 2023, 11497-11504 11500 www.etasr.com hussain et al.: a finite element approach to evaluate and predict the shear capacity of steel … fig. 2. the compressive stress-strain curves of sfrc beams. d. steel bearing plate steel plates are usually placed at support locations of the tested beams and under two point loads in the finite element models to provide the stress distribution over the support areas and prevent a local failure of the model. the modulus of elasticity for the steel is 200000 mpa and poisson's ratio is 0.3. v. material modeling in ansys a. concrete the solid element solid65 is used to model the concrete in ansys. this element has 8 nodes with 3 degrees of freedom for each node in x, y, and z directions. the element is capable of plastic deformation and cracking in 3 orthogonal directions. b. steel rebar for the steel reinforcement rebars, the beam element 188 was used between two nodes. this element provides an easier and more accurate change of area steel. c. steel plates steel plates were modeled by using element soild185. this element is defined by 8 nodes with three 3 of freedom. d. simulation by log file feature of ansys authors in [11] used the classical approach. in this study, using the log file of ansys provides many benefits in the studies with many parameters and variables, since one log file can simulate and modify all physical and mechanical properties. for example, the selected 91 sfrc beams of the current study were simulated by one log file involving all their parameters and variables that could be processed by a text editor and new command lines could be added to describe the input information. however, using finite element software with vast data in high definition has many challenges. therefore, in terms of compaction, the log file was considered as the best approach to simulate the beams in this study. also, this file involves all records of the commands and steps used during the simulation. furthermore, since the log file is written in text format, it is easy to transfer from one machine to another and use it to solve errors and do further analysis. table ii contains all the required information, such as the physical and material properties of the selected data. these data have been modeled to correspond to one log file, as this log file involves all physical properties of bearing steel plates, steel rebars, and boundary conditions of the sfrc beam. as shown in figure 3, changing model geometry is effortless when we depend on these features. for example, the geometry of selected data, such as beam dimensions and rebar's radius of any selected beam are reachable without creating a new job as in conventional simulation approaches. the figure also explains the lines in the log file responsible for modifying the other physical properties, such as the modulus of elasticity, poisson's ratio, etc. for control mesh size in a regular geometry, the manual meshing of a block has been used. however, cutting the line of entities of the solid in 3 dimensions is more practical than applying distance, so it computes element edges in 3 dimensions by these cut lines. this method is used because the dimensions of the beams in the selected data are different and error messages will appear. engineering, technology & applied science research vol. 13, no. 4, 2023, 11497-11504 11501 www.etasr.com hussain et al.: a finite element approach to evaluate and predict the shear capacity of steel … fig. 3. the log file. (a) (b) fig. 4. (a) assembly of concrete, steel rebar and bearing plates, (b) crack pattern. figure 4 shows the finite element representation for sfrc concrete and steel reinforcement simulation of the selected beams. all elements had a mesh of the same size therefore every used material shares the same node. the boundary conditions are represented as hinge and roller support. these supports have been simulated by an individual line of nodes created on a steel plate located under the applied load points and support zones. in hinge support, the selected nodes were constrained for ux, uy, and uz displacement, while in the roller support, the selected nodes were constrained in uy and uz displacement. the steel plates were used for a better distribution of the stresses in the applied load points and support areas. the intelligent method of meshing was used to mesh the entire model entities. hexahedral elements were used. vi. comparison among the proposed shear equations a total 91 concrete sfrc beams were analyzed in ansys program. many researchers have proposed analytical equations to calculate the ultimate shear capacity of sfrc beams based on the results of experimental investigations. the performance and accuracy of the extracted results of ansys need to be evaluated with the results of experimental tests and the proposed equations of table i. most proposed equations comprise the term fibre factor f, which collects the effect of the fiber aspect ratio a and volume fraction vf on the shear strength of sfrc beams. the accuracy of the extracted results from the used equations was compared based on descriptive statistical analysis. two statistical parameters were used in the comparison: (a) χ factor, which is the inverse of the slope of a linear least-square regression of the experimental work (vexp) versus the calculated shear strength (vcal) predicted either by formula or finite element analysis and (b) absolute error (ae), which is calculated by (7): ae = |}. ~��k|}. ��~ |}. ~�� (7) where �#. ��> is the experimental ultimate shear capacity (kn), and �#. >�� is the predicted shear strength (kn). according to the analysis results of figure 5, the χ value of [23] was the closest result to the experimental value among the seven equations, while [17] gave the furthest. conversely, the χ value of [22] and ansys is 0.91 and 98, respectively. the predicted shear strength capacity values for the sfrc beams along with the ansys results of this study are listed in table ii. the results of ansys are more close to the experimental results because the finite element theory can estimate the load failure capacity for any failure. a good agreement was found between the derived shear equations and ansys software results of shear strengths for the tested beams. the ae factors of the closest of the considered equations and ansys software shear are 45and 34, respectively. vii. conclusions the main conclusions derived from the obtained results of the current study are:  adding steel fibers to normal concrete causes dramatic changes in the behavior of the stress-strain curve, therefore, shear capacity will withstand a considerable change. however, this change depends on the aspect ratio and volume fraction of the steel fibers.  the equation from [22] that predicts shear capacity gives the closest results to the experimental χ while the equation from [17] predicted the furthest value.  the contribution of steel fibers on the shear strength capacity of sfrc beams by fibres bridging diagonal cracks can be reasonably estimated for beams along the compression and tension zone while neglecting the contribution of aggregate interlock and steel reinforcement. engineering, technology & applied science research vol. 13, no. 4, 2023, 11497-11504 11502 www.etasr.com hussain et al.: a finite element approach to evaluate and predict the shear capacity of steel … table ii. comparison of the experimental and the derived shear capacity equations with ansys beam bw mm h mm d mm a/d ρ % vf % f 'c' mpa vu, exp (kn) vu, pre (kn) ���.��� − ��. �����.��� ��. ����� (kn) ���.��� − ��.��������� a2 152 229 197 2.8 1.3 — 24.2 44.192 18.12 6 14 46.3 5 a3 152 229 197 3.6 1.3 — 24.2 38.299 20.30 6 24 41.2 8 a4 152 229 197 4.4 1.3 — 24.2 33.88 22.36 6 19 36 6 b2 152 229 197 2.8 1.3 0.50 29.1 51.69 44.97 3 6 61.54 19 b3 152 229 197 3.6 1.3 0.50 29.1 45.229 47.49 1 3 52.17 15 c2 152 229 197 2.8 1.3 0.750 29.9 60.582 53.31 3 3 66.1 9 c6 152 229 197 2.8 2.0 0.750 29.9 65.495 54.36 3 2 69.9 7 e2 152 229 197 2.8 1.3 0.750 20.6 44.849 45.75 1 0 42.6 5 e3 152 229 197 2.8 2.0 0.750 20.6 59.799 49.63 3 1 63.53 6 f3 152 229 197 2.8 2.0 0.750 33.4 86.527 61.43 6 8 91.1 5 2/0.5/2.5 152 254 221 2.5 1.2 0.51 34.0 58.762 50.54 3 8 53.18 9 2/0/3.5 152 254 221 3.5 1.2 — 34.0 39.175 18.80 6 5 42.17 8 4/0.5/2.5 152 254 221 2.5 2.4 0.51 34.0 62.679 50.77 4 0 66.11 5 4/0.5/3.5 152 254 221 3.5 2.4 0.51 34.0 48.968 51.91 5 4 51.33 5 4/0/3.5 152 254 221 3.5 2.4 — 34.0 35.257 16.92 1 5 35.43 0 4/1.0/2.5 152 254 221 2.5 2.4 0.51 34.0 82.267 67.46 2 0 81.51 1 4/1.0/3.5 152 254 221 3.5 2.4 0.51 34.0 66.597 68.59 7 3 43.96 34 — 127 229 203 3.0 2.2 — 17.8 42.42 19.94 2 4 36.44 14 — 127 229 203 3.0 2.2 0.50 22.7 78.613 56.60 6 18 85.53 9 — 127 229 203 3.0 2.2 0.50 26.0 78.875 58.37 3 2 74.07 6 hsfrc1 127 254 225 2.9 3.6 0.50 68.9 156.55 100.19 6 20 74.86 7 hsfrc2 127 254 225 2.9 3.6 0.50 68.9 156.55 100.19 6 19 77.66 21 hsfrc3 127 254 225 2.9 2.2 0.50 68.9 99.62 80.69 3 3 77.19 23 1 type a 200 250 180 3.3 4.5 — 68.9 212.16 106.08 2 45 200.9 5 5 type a 200 250 180 3.3 4.5 0.70 68.9 251.01 148.10 7 41 266 6 6 type a 200 250 180 3.3 4.5 0.70 68.9 262.96 160.41 7 39 272.3 4 1 type b 200 300 235 2.8 4.3 — 68.9 280.89 112.36 2 43 288 3 3 type b 200 300 235 2.8 4.3 0.60 68.9 308.2 172.59 6 35 311.4 1 1 type c 200 500 410 2.9 3.0 — 68.9 176.97 70.79 3 6 191.54 8 7 type c 200 500 410 2.9 3.0 0.70 68.9 265.45 177.85 2 4 255.1 11 8 type c 200 500 410 2.9 3.0 0.70 68.9 313.1 194.12 6 4 310.7 1 9 type c 200 500 410 2.9 3.0 0.70 68.4 339.09 213.63 6 3 349.6 6 10 type c 200 500 410 2.9 3.0 0.70 68.9 292.68 201.95 3 5 300.1 11 4 type d 300 700 570 3.0 2.9 0.70 68.4 509.13 381.85 1 5 525.9 9 fhb1-3 127 254 213 3.0 1.5 — 62.6 68.489 28.77 6 22 81.8 19 fhb1-4 127 254 213 4.0 1.5 — 62.6 53.507 29.96 6 20 62.6 17 fnb2-3 127 254 213 3.0 1.5 0.80 30.8 69.058 49.72 2 13 77.1 12 1.2/1 200 300 260 3.5 3.6 — 44.0 89.682 43.94 3 5 96.4 7 1.2/3 200 300 260 3.5 3.6 0.90 43.7 120.31 99.86 3 3 133 11 1.2/4 200 300 260 3.5 3.6 0.90 48.3 155.4 122.76 6 3 163.78 5 2.3/1 200 300 262 2.5 1.2 — 40.1 79.637 27.08 3 14 70.3 12 2.3/3 200 300 262 2.5 1.2 0.90 38.7 107.57 91.44 1 0 111.31 22 2.4/1 200 300 260 2.5 1.8 — 40.1 118.54 42.68 6 8 119.3 1 2.4/3 200 300 260 2.5 1.8 0.90 38.7 142.33 99.63 2 6 155.6 9 2.6/1 200 300 260 4.0 1.8 — 40.8 76.394 43.54 6 7 77 3 2.6/3 200 300 260 4.0 1.8 0.90 40.3 115.54 112.07 6 1 113.9 1 20 × 30-plain-1 200 300 260 3.5 2.8 — 32.1 58.923 28.87 1 1 61.3 4 20 × 30-sfrc-1 200 300 260 3.5 2.8 0.90 37.7 111.75 96.10 3 1 109.1 17 20 × 45-sfrc-1 200 450 410 3.3 3.1 0.90 37.7 146.01 137.25 1 3 144.6 1 20 × 60-plain-1 200 600 540 3.5 2.7 — 32.1 110.14 53.97 5 5 123.5 12 t 10 × 50-sfrc-1 200 500 460 3.4 2.8 0.90 37.7 169.46 155.911 2 179.5 6 t 15 × 50-sfrc-1 200 500 460 3.4 2.8 0.90 37.7 265.5 196.472 1 274 7 t 15 × 75-sfrc-1 200 500 460 3.4 2.8 0.90 37.7 259.85 194.882 15 265.9 14 t 15 × 100-plain-1 200 500 460 3.4 2.8 — 32.1 151.16 74.076 11 144.3 5 t15 × 100-sfrc-1 200 500 460 3.4 2.8 0.90 37.7 242.9 184.602 10 234.6 3 20 × 30-sfrc-2 200 300 260 3.5 2.8 0.90 38.8 132.8 106.24 2 5 131 16 20 × 50-sfrc-2 200 500 460 3.4 2.4 0.90 38.8 149 149.00 7 0 157.7 6 20 × 60-sfrc-2 200 600 540 3.5 2.7 0.90 38.8 222 195.36 3 2 234 5 t 10 × 50-sfrc-2 200 500 460 3.4 2.8 0.90 38.8 154.73 148.547 4 147.5 5 t 15 × 50-sfrc-2 200 500 460 3.4 2.8 0.90 38.8 160.46 150.831 3 161.1 0 t 23 × 50-sfrc-2 200 500 460 3.4 2.8 0.90 38.8 252.15 189.112 12 277 10 a00 150 249 218 2.8 1.9 — 41.2 39.88 15.15 1 2 33.8 15 a10 150 249 218 2.8 1.9 0.51 40.9 96.198 73.11 6 3 104.9 9 a20 150 249 218 2.8 1.9 0.51 43.2 103.16 89.75 5 2 111.77 8 b18-0a 152 457 381 3.4 2.7 — 42.8 64.408 30.27 5 2 64.9 1 b18-0b 152 457 381 3.4 2.7 — 42.8 64.408 30.27 5 1 66.3 3 b18-1a 152 457 381 3.4 2.0 0.55 44.8 170.55 131.33 2 12 183.32 7 b18-1b 152 457 381 3.4 2.0 0.55 44.8 158.92 125.55 2 6 167.3 5 b18-2a 152 457 381 3.5 2.0 0.55 38.1 175.16 136.62 2,6,7 22 171.6 2 b18-2b 152 457 381 3.5 2.0 0.55 38.1 178.73 137.62 2,6,7 23 176.8 1 b18-2c 152 457 381 3.5 2.7 0.55 38.1 200.18 148.13 6,7 26 221.1 10 b18-2d 152 457 381 3.5 2.7 0.55 38.1 146.56 124.58 6 1 16.8 10 engineering, technology & applied science research vol. 13, no. 4, 2023, 11497-11504 11503 www.etasr.com hussain et al.: a finite element approach to evaluate and predict the shear capacity of steel … beam bw mm h mm d mm a/d ρ % vf % f 'c' mpa vu, exp (kn) vu, pre (kn) ���.��� − ��. �����.��� ��. ����� (kn) ���.��� − ��.��������� b18-3a 152 457 381 3.4 2.7 0.55 31.0 148.32 126.07 4 4 149.1 1 b18-3b 152 457 381 3.4 2.7 0.55 31.0 196.69 149.48 3 14 207.2 7 b18-3c 152 457 381 3.4 2.7 0.55 44.9 190.15 146.41 3,6 5 201.8 6 b18-3d 152 457 381 3.4 2.7 0.55 44.9 190.15 146.41 6 4 201.6 6 b18-5a 152 457 381 3.4 2.7 0.75 49.2 170.61 133.07 1 1 177.4 10 b18-5b 152 457 381 3.4 2.7 0.75 49.2 219.35 155.74 6 16 213.6 3 b18-7a 152 457 381 3.4 2.0 0.38 43.3 190.54 139.09 2 23 178.5 6 b18-7b 152 457 381 3.4 2.0 0.38 43.3 186.73 138.18 6 21 174.8 6 b27-1a 203 686 610 3.5 2.1 0.55 50.8 361.86 278.63 6 347.5 4 b27-1b 203 686 610 3.5 2.1 0.55 50.8 335.38 268.31 2 2 350 7 b27-2a 203 686 610 3.5 2.1 0.75 28.7 344.96 269.07 3,6 18 533.8 8 b27-2b 203 686 610 3.5 2.1 0.75 28.7 338.33 267.28 6 16 330.3 2 b27-3a 203 686 610 3.5 1.6 0.55 42.3 338.26 270.60 2 8 330 2 b27-3b 203 686 610 3.5 1.6 0.55 42.3 346.31 273.58 10 334.76 3 b27-4a 203 686 610 3.5 1.6 0.75 29.6 262.75 231.22 2,3,6 2 275.5 5 b27-4b 203 686 610 3.5 1.6 0.75 29.6 222.32 217.88 3 1 231.2 4 b27-5 203 686 610 3.5 2.1 0.55 44.4 429.06 326.09 3,6 16 457.3 7 b27-6 203 686 610 3.5 2.1 0.75 42.8 421.26 324.37 1 2 440.4 5 b27-7 203 686 610 3.5 1.6 — 37.0 158.18 77.51 6 2 169.3 7 1 [19]; 2 [18]; 3 [20]; 4 [21]; 5 [22]; 6 [23]; and 7 [24] fig. 5. χ factor value (r-squared value of experimental shear to predicted shear) of the selected data.  the results obtained from ansys were more correlated to the more reliable experimental results. therefore the modeling made with ansys can reduce cost and save time. also, the errors that can be made in the design stage or wrong material selection can be prevented, therefore, this method can guide further experimental studies.  this approach of simulations in ansys allows the simulation of many sfrc beams, therefore the predicted equations of shear capacity will be more accurate than the derived experimental or analytical equations.  this approach provides the ability to derive the most accurate equation to predict the shear capacity of the sfrc beams, as it is easy to modify the physical properties of sfrc in the text lines of the log file, to simulate a large number of sfrc beams not involved in the experimental work.  finally, this method will allow studying the effect of more variables that had not been discussed in precious studies and derive more accurate equations to determine either shear or flexural capacity. references [1] aci committee 544, aci prc-544.5-10: report on the physical properties and durability of fiber-reinforced concrete. american concrete institute, 2010. engineering, technology & applied science research vol. 13, no. 4, 2023, 11497-11504 11504 www.etasr.com hussain et al.: a finite element approach to evaluate and predict the shear capacity of steel … [2] aci committee 544, aci prc-544.4-18: guide to design with fiberreinforced concrete. american concrete institute, 2018. 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[37] k. h. tan, k. murugappan, and p. paramasivam, "shear behavior of steel fiber reinforced concrete beams," aci structural journal, vol. 90, no. 1, pp. 3–11, feb. 1993. microsoft word etasr_v13_n1_pp10073-10077 engineering, technology & applied science research vol. 13, no. 1, 2023, 10073-10077 10073 www.etasr.com leulmi: a comparative numerical study between minorant functions and line search methods in … a comparative numerical study between minorant functions and line search methods in penalty methods for linear optimization assma leulmi department of mathematics, ferhat abbas university setif-1, algeria as_smaleulmi@yahoo.fr (corresponding author) received: 16 november 2022 | revised: 27 november 2022 | accepted: 2 december 2022 abstract the aim of this paper is to present a comparative numerical study between the minorant functions and line search methods in computing the step size in the penalty method for linear optimization. the minorant functions were confirmed by many interesting numerical experimentations to be more beneficial than the classical line search methods. keywords-linear optimization; penalty methods; line search; minorant function i. introduction optimization is an especially interesting topic in data science. linear optimization (lo) or linear programming (lp) problems form an important class of optimization problems, aiming to find the feasible region and optimize the solution in order to have the highest or lowest value of a function. it is now well established as an important and very active branch of applied mathematics. the wide applicability of lo models and its richness as a mathematical theory that underlines these models and the methods developed to solve them have been the driving forces behind the rapid and continuing evolution of the subject. the template is general enough to express many different problems in engineering, industry, commerce, economics, business administration, physical sciences, and mathematics, or in any other area where decisions (in a board sense) must be taken in some complex (or conflicting) situation that can be represented by a mathematical model. there are two classes of methods for the resolution of lo problems, simplex method and interior point methods. in this study, we are interested in interior point methods. these are efficient methods developed to solve lo and np problems. several algorithms have been proposed to solve lo problems. some fundamental classes of interior point methods are the affine method, the projective method with the potential reduction of karmarkar and its alternatives [5, 9], central trajectory methods, and penalty/barrier methods [6, 13]. our work is based on the latter type of interior point methods for solving lo problems. in this paper, we propose a logarithmic barrier interiorpoint method for solving lo problems. in fact, the main difficulty to be anticipated in establishing iterations in such a method will come from the determination and computation of the step-size. the aim of this paper is to present a comparative numerical study between the line search methods and the minorant function to compute the step-size along the direction in barrier logarithmic methods. ii. problem formulation we consider the following lo problem � min� �� � � � ≥ �, � ∈ �� . (1) where ∈ ��×� , such that ���� = � < �, � ∈ �� and � ∈ �� . the problem (1) is the dual of the following linear program: � max � � ! � ! = �! ∈ �� , ! ≥ 0. (2) the problem (1) can be written in the following standard form: $ min� �� � � � − � = & � ∈ �� , & ∈ �� , & ≥ 0. (3) one of the advantages of problem (1) with respect to its dual problem (2) is that the variable of the objective function is a vector instead of a matrix. furthermore, under certain convenient hypothesis, the resolution of problem (1) is equivalent to (2) in the sense that the optimal solution of one of the two problems can be reduced directly from the other through the application of the theorem of the sladeness complementary [15]. in the rest of the paper, the following are denoted: engineering, technology & applied science research vol. 13, no. 1, 2023, 10073-10077 10074 www.etasr.com leulmi: a comparative numerical study between minorant functions and line search methods in …  ' = {� ∈ �� ∶ � � − � ≥ 0}, the set of feasible solutions of (1).  '+ = {� ∈ �� ∶ � � − � > 0} , the set of strictly feasible solutions of (1).  = {! ∈ �� ∶ ! = �, ! ≥ 0}, the set of feasible solutions of (2).  -+ = {! ∈ �� ∶ ! = �, ! > 0}, the set of strictly feasible solutions of (2). let ., / ∈ �� . 0heir scalar product is defined by: 〈., /〉 = .� / = ∑ .4 /4�456 we suppose that the sets '+ and -+ are not empty. a. the perturbed problem of (1) problem (1) is approximated by the following perturbed problem: �min� 78 (�)� ∈ �� . (4) where 9 > 0 is the the penalty parameter and 78 is the barrier function defined by: 78 (�) = ��� � + �9 ln9 − 9ln ∑ 〈<4 , � � − �〉�456 if � � − � > 0+∞ if not where (<6, <a, … , <� ) is the canonical base in �� . we are interested in solving the problem (4). the idea of this new approach consists to introduce one original process to calculate the step-size based on minorant functions. the main advantage of (4) resides in the strict convexity of its objective function and its feasible domain. consequently, the conditions of optimality are necessary and sufficient. this fosters theoretical and numerical studies of the problem. in the next section, the existence and uniqueness of the optimal solution of (4) is proved and we show its convergence to (1), in particular the behavior of its optimal value and its primal solutions when 9 → 0, then lim8→d �8 =� ∗ is an optimal solution of (1). in section iii, we propose an interior point algorithm based on the newton's approach which allows us to solve the nonlinear system resulting from the optimality conditions. the iteration of this algorithm is of descent type, defined by: �fg6 = �f + hf if , where dk is the descent direction and αk is the step-size. also, we present different steps-sizes by minimizing a minorant function which approximates the one-dimensional function j(hf ) = minkld 7(� + hi). the last section is dedicated to the presentation of comparative numerical tests to illustrate the effectiveness of our approach and to determine the most efficient algorithm. the main advantage of (4) resides in the strict convexity of its objective function and its feasible domain. consequently, the conditions of optimality are necessary and sufficient. this fosters theoretical and numerical studies of the problem. before this, it is necessary to show that (4) has at least an optimal solution. b. convergence of the perturbed problem firstly, we give the following definition: definition: let 7 be a function defined from �� to � ∪ {∞}. 7 is called inf-compact if for all 9 > 0, the set '8 (7) = {� ∈ �� ∶ 7(�) ≤ 9} is compact, which comes in particular to say that its cone of recession is reduced to zero. to prove that (4) has an optimal solution, we show that 78 is inf-compact. for that, it is enough to prove that the cone of recession '+ pq78 rst = ui ∈ �� ∶ q78 rs(i) ≤ 0v, is reduced to the origin, i.e. pq78 rs(i) ≤ 0t ⇒ (d = 0), where q78 rs is defined by: q78 rs(i) = limk→gs 7y(� + hi) − 7y(�)h = �� i. this needs the following proposition: proposition: i = 0 whenever �� i ≤ 0 and � i ∈ '+. then, the problem (4) has an optimal solution. we know that the hessian matrix z = ∇a7y(�) is positive definite, then the problem (4) is strictly convex, and if it has an optimal solution, then it is unique. we have: 78 (�) = �� � + �9 ln9 − 9ln \〈<4 , � � − �〉 � 456 then: ]78 (�) = � − 9 ∑ ^_`〈_`,^a�bc〉�456 and: ]a78 (�) = 9 ∑ ^_`(^_`)a〈_`,^a�bc〉d�456 as 78 is inf-compact and strictly convex, therefore the problem (4) admits a unique optimal solution. we denote by �(9) or �8 the unique optimal solution of (4). c. convergence of the perturbed problem to the initial problem for � ∈ '+, let's introduce the symmetrical definite positive matrix e4 of rank �, f = 1, … , � and the lower triangular matrix g, such that e4 = <4 ( <4 )� = gg� , which implies that z is a positive definite matrix. in what follows, we will be interested in the behavior of the optimal value and the optimal solution �(9) of problem (4). proposition: for 9 > 0, let �8 an optimal solution of the problem (4) then there is an optimal solution of (1) � ∈ ', such that, lim8→d �8 = �. remark: we know that if one of the problems (1) and (2) has an optimal solution, and the values of their objective functions are equal and finite, the other problem has an optimal solution. engineering, technology & applied science research vol. 13, no. 1, 2023, 10073-10077 10075 www.etasr.com leulmi: a comparative numerical study between minorant functions and line search methods in … iii. resolution of the perturbed problem in this part, we are interested in the numerical solution of problem (4). we use a logarithmic barrier interior point method. this method types are based on the optimality conditions which are necessary and sufficient, and consist of constructing a sequence of iterate �fg6 = �f + hf if , where �8 is an optimal solution of (4) if it satisfies the following condition: ∇78 q�8 r = 0 (5) to solve (5) we use the newton's approach which means to find in each iteration a vector �8f + if checking the following linear system: zf if = −]78 q�8f r. (6) as zf = ] a78 q�8f r is a symmetric positive definite matrix, the cholesky methods and the conjugate gradient methods are the best convenient for solving (6). to ensure the convergence of the algorithm towards an optimal solution � ∗ of (4), it should be made sure that all the iterations �8f + if remain strictly feasible. for that, we introduce a step-size hf checking the condition: � q�8f + hf if r − � > 0 a. effectual computation of the step size there are two main techniques used for computing the displacement step hf. 1) line search these methods try out a sequence of candidate values of hf, stopping to accept one of these values when some conditions are satisfied. an ideal choice of the step-size is the global minimization of the one-dimensional function j(∙) defined by: j(hf ) = minkld 7(� + hi) the most used line search methods are wolfe, goldstein— armijo, fibonacci, etc. unfortunately, these methods have big computational cost. 2) principle of approximate function a minorant function ij must be close to: i(h) = 68 k78 (� + hi) − 78 (�)l which must give the mink ij (h) in m0, hno by a simple and easy manner, which permits the computation of the step-size at each iteration in a relatively short time and with a smaller number of instructions in contrast to line search technique. authors in [12] gave a simple form for the function, which is presented in the following proposition: proposition [12]: let hn = &.p{h: 1 + r4 h} with r4 = 〈_`,^as〉〈_`,^a�bc〉 , ∀f = 1, … , �. for all h ∈ m0, hno, the following function i(h) is well defined: i(h) = �(∑ r4�456 )h − ‖r‖ah − ∑ ln(1 + r4 h)�456 such that, i(h)verifies the following properties: ‖r‖a = �(r̅a + wxa) = iyy(0) = −iy(0), i(0) = 0 b. minorant function authors in [10] proposed 3 minorant functions in 2019. in this paper, we are interested in their best minorant function defined as: ij6(h) = zh − (� − 1) ln(1 + {h) − ln(1 + |h) with: z = �r̅ − ‖r‖a { = r̅ − }~√�b6| = r̅ + wx √� − 1. in addition, they proved that the minorant function ij6 is defined and convex on m0, hno, i(h) > ij6(h) ( ij6 minorant function on m0, hno ), and the function ij6 verifies the following properties: ‖r‖a = �(r̅a + wxa) = ij yy(0) = −ij y(0), ij (0) = 0 the minimum of ij6 is obtained in h�4 = h��� , such that, ij6y(0) = 0. we are then coming back to solve the second order following equation: h a − 2�h + � = 0, with: � = 6a p�� − 6� − 6�t and � = b‖x‖d��� the roots of this equation are of the type h� = � ± √�a − �. let's take one root of the two that belong to m0, hnm. thus, the h� is explicitly computed, then, we consider it belongs to the interval (0, hn − �) and i′ (h) < 0, with � > 0 being a fixed precision. remark: the calculation of h� is performed by a dichotomous procedure, in the cases where h�4 ∉ (0, hn − �), and iy(h) > 0, as follows: put h = 0 and � = hn − � while |� − �| > 10b� . if i p�g�a t < 0 , then � = �g�a . else � = �g�a , so h� = �. this calculation guarantees a better approximation of the minimizer of ij ′ (h) while remaining in the domain of i. proposition [10]: let �fg6 and �f be two strictly feasible solutions of (4) obtained respectively at the � + 1 and � iterations, so we have 78 (�fg6) < 78 (�f ). iv. algorithm description and numerical results in this section, we present the algorithm of our approach to obtain an optimal solution �̅ to problem (1) and some numerical tests. a. the αlgorithm in this section, we present the algorithm of our approach to obtain an optimal solution �̅ to the problem (1). for simplicity, we consider �f instead of �8f and � instead of �8 . engineering, technology & applied science research vol. 13, no. 1, 2023, 10073-10077 10076 www.etasr.com leulmi: a comparative numerical study between minorant functions and line search methods in … begin algorithm initialization �d is a strictly feasible solution of (1), id ∈ �� and � > 0 is a given precision. iteration while |�� if | > � do solve the system zf if = −]78 q�8f r. compute the step-size using the strategy of minorant function or line search method. take the new iterate �fg6 = �f + hf if . take � = � + 1. end while end algorithm this approach tries to reduce the number of iterations and the time of calculation. some examples are presented below. b. numerical results to measure the numerical performance of the proposed methods, we present a numerical comparison of the results obtained by the proposed algorithm using the minorant function given in [10] to compute the step-size and those obtained by using the line search wolfe's method. we use examples with fixed and variable sizes to carry out the numerical tests. the following examples are taken from the literature [1, 4, 8] and were implemented in matlab. we took � = 1.0< − 006. in the result table:  (size) represents the size of the example.  (itrat) represents the number of iterations necessary to obtain an optimal solution.  (time) represents the time of computation in seconds (s).  (mf st) represents the strategy that uses minorant function.  (lr st) represents the strategy that uses wolfe's line search. recall that the considered problem (1) is: � min� ��� � � ≥ �, � ∈ �� we note that the matrices used in the numerical tests are full matrices. 1) examples with fixed size example 01: = �2 3 1 23 0 −2 1� , � = �20� and � = m4 1 2 0o�  the initial strictly feasible point is � d = m1 1.5 1 1o� .  the optimal solution is � d = m0 0.67 0 0o� . example 02: = �2 1 0 −1 0 00 0 1 0 1 −11 1 1 1 1 1 � , � = � 001� and � = m3 −1 1 0 0 0o�  the initial strictly feasible point is � d = m1 1 2o� .  the optimal solution is � ∗ = m0.5 0.0713 0.5o�. example 03: = �1 −1 1 1 0 01 1 0 0 1 02 2 1 0 0 1� , � = � 624� and � = m4 −2 −2 0 0 0o�  the initial strictly feasible point is � d = m0.5 1 1o� .  the optimal solution is � d = m0 0 0o� . example 04: , 100000541232 010000221112 001000512010 000100143354 000010310135 000001113401                           a � = m1 4 4 5 7 5o� � = m−4 −5 −1 −3 5 −8 0 0 0 0 0 0o�  the initial strictly feasible point is: � d = m−2 4 1 1 1 1o�  the optimal solution is � ∗ = m0.5 1.5 0 0 1.5 0o� example 05: �4 = 10�, f = 1, … ,5, � = m1 1 1 1 1 1 1 1 1 1 0 0 0 0 0o�  the initial strictly feasible point is � d = m1 1 1 1 1o�  the optimal solution is � d = m0 0 0.0888 0 0.0078o� the results of the last examples are given in table i. table i. examples with fixed size size mf st ls st itrat time itrat time 2 × 4 5 0.032 13 0.130 3 × 6 6 0.044 33 0.128 3 × 6 7 0.051 34 0.132 6 × 12 9 0.055 34 0.306 5 × 15 8 0.048 22 0.170 a  1 2 3 4 5 5 4 3 2 1 1 0 0 0 0 6 7 8 9 10 5 2 8 3 1 0 1 0 0 0 11 12 13 14 15 6 7 80 90 10 0 0 1 0 0 1 10 20 30 40 50 60 80 90 10 0 0 0 1 0 3 9 27 60 45 60 75 8 9 46 0 0 0 0 1 = engineering, technology & applied science research vol. 13, no. 1, 2023, 10073-10077 10077 www.etasr.com leulmi: a comparative numerical study between minorant functions and line search methods in … 2) example with variable size � = 2�, for f, � = 1, … , �, mf, �o = 0 if f ≠ � or (f + 1) ≠ � mf, �o = mf, f + �o = 1, �mfo = 2.  the initial strictly feasible point is � d = m1 1 … 1o� .  the optimal solution is � ∗ = m0 0 … 0o� . table ii resumes the obtained results. table ii. examples with fixed size size mf st ls st itrat time itrat time 50 × 100 1 0.031 49 8.5512 100 × 200 1 0.053 50 32.6145 200 × 400 2 0.088 51 91.6524 400 × 800 3 0.096 52 161.4374 500 × 1000 3 0.12 52 411.8901 v. conclusion the conducted numerical study clearly shows that the strategy of the minorant function seems to be more efficient than that of the line search in time and number of iterations. our future work will consider further improving the computational time of the logarithmic barrier algorithm by proposing another, better, approximate function. but the extensions would be envisaged to the nonlinear, and not necessarily relevant to the lo problem. references [1] m. achache, "a polynomial-time weighted path-following 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[12] h. mansouri and m. zangiabadi, "an adaptive infeasible interior-point algorithm with full-newton step for linear optimization," optimization, vol. 62, no. 2, pp. 285–297, feb. 2013, https://doi.org/10.1080/ 02331934.2011.611881. [13] m. r. rezoug, m. benaouadj, d. taibi, and r. chenni, "a new optimization approach for a solar tracker based on an inertial measurement unit," engineering, technology & applied science research, vol. 11, no. 5, pp. 7542–7550, oct. 2021, https://doi.org/ 10.48084/etasr.4330. [14] h. wolkowicz and g. p. h. styan, "bounds for eigenvalues using traces," linear algebra and its applications, vol. 29, pp. 471–506, feb. 1980, https://doi.org/10.1016/0024-3795(80)90258-x. [15] j. f. bonnans, j. c. gilbert, c. lemaréchal, and c. a. sagastizábal, numerical optimization: theoretical and practical aspects (universitext). berlin, heidelberg, germany: springer-verlag, 2006. [16] r. t. rockafellar, convex analysis: (pms-28), vol. 30. princeton, nj, usa: princeton university press, 1970. microsoft word etasr_v12_n5_pp9092-9096 engineering, technology & applied science research vol. 12, no. 5, 2022, 9092-9096 9092 www.etasr.com nguyen et al.: the influence of nearand far-field earthquakes on the seismic performance of … the influence of nearand far-field earthquakes on the seismic performance of base-isolated nuclear power plant structures van-binh tran faculty of engineering and technology ha tinh university ha tinh, vietnam binh.tranvan@htu.edu.vn sy-minh nguyen faculty of engineering and technology ha tinh university ha tinh, vietnam minh.nguyensy@htu.edu.vn tien-hong nguyen department of civil engineering vinh university vinh, vietnam tienhongkxd@vinhuni.edu.vn van-hoa nguyen department of civil engineering vinh university vinh, vietnam vanhoakxd@vinhuni.edu.vn thi thuy-huong doan department of civil engineering vinh university vinh, vietnam doanhuongdhv@gmail.com duy-duan nguyen department of civil engineering vinh university vinh, vietnam duyduankxd@vinhuni.edu.vn received: 25 june 2022 | revised: 14 july 2022 | accepted: 16 july 2022 abstract-this study aims to investigate the influence of nearand far-field earthquakes on the seismic performance of base-isolated nuclear power plant (npp) structures. two earthquake motion groups of near-field and far-field characteristics are selected for fragility evaluation analysis. a base-isolated advanced reactor power 1400 (apr-1400) is employed for numerical analysis. a set of fragility curves are derived for various limit states based on the maximum likelihood estimation. the limit states are defined in terms of lead rubber bearing (lrb) deformation capacity. the numerical results reveal that the median maximum deformations of lrbs were smaller for far-field ground motions than for near-field motions. also, the comparison of fragility curves demonstrates that the probability of failure of baseisolated npp structures is higher for near-field ground motions than far-field motions. it is crucial to select earthquake ground motions with both nearand far-field motions for the seismic evaluation of npp structures. keywords-near-field earthquake; far-field earthquake; lrb; fragility analysis; nuclear power plant structure; lumped mass stick model i. introduction the near-field strong ground motion consists of complex characteristics, mainly affected by the fault rupture velocity, the length of fault rupture, sliding direction, and other factors. those characteristics can cause significant damage to structures during an earthquake. the influence of near-field earthquakes on the response of civil engineering structures has been numerously investigated in [1-7]. some of the nuclear power plants (npps) in korea are located near fault ruptures. after the 2016 gyeongju and 2017 pohang earthquakes, the seismic safety of npp structures is getting more and more attention. seismic analyses and fragility evaluations of npp structures were implemented in [8-16]. among that, remarkably, authors in [9-10] developed the seismic fragility curves of a nonisolated candu type npp containment building for near-field ground motions based on the displacements obtained from the nonlinear time history analyses. authors in [17] assessed the safety implication of near-field earthquakes on npp structures designed according to the north american codes. they concluded that the near-field motion effects were not so damaging to the containment which is a relatively stiff structure. however, the effects of near-field forwarddirectivity, fling-step, and far-field motions on seismic fragility curves of base-isolated npp structure were not evaluated. the purpose of this study is to develop seismic fragility curves of a base-isolated apr-1400 npp structure considering the influence of nearand far-field ground motions. for nearfield earthquakes, two typical characteristics, forwarddirectivity and fling-step are accounted for in fragility analyses. the limit states are defined based on the shear strain capacity of lead rubber bearings (lrbs). a set of fragility curves for limit states are generated using the maximum likelihood estimation. the influence of earthquake groups on fragility curves is also examined. ii. input ground motions near-field earthquakes contain a large portion of fault energy in the form of pulses [2]. pulses can normally be recognized through acceleration, velocity, and displacement time histories. two typical effects in near-field ground motions are forward-directivity and fling-step phenomena. forward directivity occurs where the fault rupture propagates with a velocity close to the shear-wave velocity. this is accompanied corresponding author: duy-duan nguyen engineering, technology & applied science research vol. 12, no. 5, 2022, 9092-9096 9093 www.etasr.com nguyen et al.: the influence of nearand far-field earthquakes on the seismic performance of … by generating long-period, short-duration, and large-amplitude pulses in the velocity time histories. displacement associated with such a shear-wave velocity is largest in the fault-normal direction for strike-slip faults [1, 3]. on the other hand, fling step effect produces the evolution of residual ground displacement due to the tectonic deformation associated with the rupture mechanism. this is generally characterized by a unidirectional high amplitude velocity pulse and a monotonic step in the displacement time history [2]. figure 1 illustrates the time-history traces of nearand far-field earthquakes. a high-velocity pulse can be seen in the 1979 imperial valley earthquake. for the 1971 san fernando earthquake, i.e. a farfield motion, no high pulses existed in the time histories. it should be noted that if a motion record has an epicentral distance less than 12km, it is considered as a near-field earthquake, otherwise it is considered a far-field motion [18]. in this study, two different groups of ground motions classified into near-field and ordinary far-field types were considered. for each group, 20 motion records were involved for fragility analysis. all used records were adopted from the peer center database. figure 2 shows the response spectra of ground motions in three groups. the thick curve indicates the mean spectrum. (a) (a) fig. 1. example of time-history traces of (a) nearand (b) far-field earthquakes. fig. 2. spectral accelerations of input ground motions. iii. structural modeling in this study, the advanced power reactor 1400 (apr-1400) developed by korea electric power corporation, was employed for numerical analysis. we focused our modeling on the reactor containment building (rcb), the internal structure (is), and the auxiliary building (ab). the finite element model (fem) of the base-isolated npp structure was developed using the lumped-mass stick model (lmsm) in sap2000 [19]. the masses and equivalent section properties were calculated based on the designed cross sections of the structures. the structures were modeled in terms of elastic beam elements. furthermore, elastic shell elements were applied for the base-mat. the lumped masses were assigned to the associated element nodes. figure 3(a) shows the fem of the base-isolated npp structures and the mechanical properties of lrbs. for the base isolation system, 486 lrbs were installed under the base-mat to enhance the seismic performance of the npp structures. figure 3(b) illustrates the bilinear shear force-deformation model of lrbs due to shear forces. the bilinear model of lrb was assumed to be a parallelogram. therefore, the values of qd, fy, ku, and kd in the negative direction are equal to those in the positive. the mechanical properties of lrbs are also described in figure 3(b). the results of eigenvalue analysis are presented in figure 4. the result is consistent with the findings in [20-21]. (a) (b) fig. 3. fem of base-isolated npp structures and bilinear model of lrbs: (a) lmsm of base-isolated npp structures, (b) arrangement and properties of lrbs. mode 1, t1 = 0.477 sec mode 2, t2 = 0.477 sec mode 3, t3 = 0.709 sec mode 4, t4 = 3.786 sec fig. 4. vibration mode shapes of base-isolated npp structures. -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0 10 20 30 40 a c c e le ra ti o n ( g ) time (s) imperial valley 1979 -0.2 -0.1 0 0.1 0.2 0 10 20 30 a c c e le ra ti o n ( g ) time (s) san fernando 1971 0 1 2 3 0 1 2 3 s p e c tr a l a c c ( g ) period (sec) mean spectrum near-field motions 0 0.5 1 1.5 0 1 2 3 s p e c tr a l a c c ( g ) period (sec) mean spectrum far-field motions engineering, technology & applied science research vol. 12, no. 5, 2022, 9092-9096 9094 www.etasr.com nguyen et al.: the influence of nearand far-field earthquakes on the seismic performance of … iv. response of npp structures and fragility ananlysis a series of time-history analyses were performed. all ground motions were imposed on the npp models in the horizontal direction. to evaluate the fragility of the baseisolated npp structure, the hypothesis that lrb is the critical element was made. the superstructures are expected to vibrate within an elastic range during earthquakes. it is common to quantify the lateral displacement or/and acceleration responses of structures subjected to earthquakes [22-24]. therefore, the seismic response of the base-isolated model is obtained in terms of the shear deformation behavior of lrbs. figure 5 shows an example of the behavior of lrb during different types of earthquakes (i.e. nearand far-field motions) with a specified level pga = 0.4g. it can be found that the deformation responses of lrbs due to near-field earthquakes are significantly larger than that under the far-field motion. figure 6 shows the maximum lateral deformation of lrbs in various levels of pga under different earthquake groups. the thick lines represent the mean results. because of the pulse characteristic, the mean values of deformation of lrbs under near-field earthquakes are higher than those due to ordinary far-field earthquakes. fig. 5. hysteretic behavior of lrb under earthquakes with pga = 0.4g. fig. 6. incremental displacements of lrb with pga under nearand farfield earthquakes. for developing fragility curves, a set of limit states should be pre-defined according to the damage levels of the components. this study used three defined limit states, namely slight, moderate, and extensive. these limit states were determined based on the shear strain of lrb. the shear strain (γ) is expressed by the ratio of the maximum lateral deformation (∆) and the height of lrb (h). according to recent experimental studies [29-34], the lrb can reach an ultimate capacity of beyond 400% shear strain. we adopted these results to define three limit states, if the shear strain exceeds 100% (i.e. ∆ ≥ 40cm) the slight limit state (ls1) is specified. if the shear strain goes beyond 200% (i.e. ∆ ≥ 80cm) and 300% (i.e. ∆ ≥ 120cm) the moderate (ls2) and extensive (ls3) limit states are respectively established. among several methods to develop seismic fragility curves, the maximum likelihood estimation (mle) approach [25] was used in this study. in this approach, the fragility function is assumed as a log-normal cumulative distribution function (cdf) expressed by: ����� = φ� ��/ �� �� � (1) where � is the earthquake intensity, namely pga in this study, �� and �� are the median and the log-standard deviations of the log-normal cdf, and φ�−� is the standard normal cdf. in (1), the subscript � indicates the �-th limit state when more than one limit state is considered. in the mle, �� and �� are determined by maximizing the likelihood function. this function is defined by: � = ∏ �����������1 − ��������������� � (2) where ����� increases when damage occurs and 1 − �����, the probability of not experiencing a damage, increases when damage does not occur for an earthquake intensity ��. ! is the number of ground motions considered and "� is a bernoulli random variable that indicates whether the structure is damaged or not where 0 indicates no damage and 1 indicates damage. �� and �� are determined so that (2) is maximized with respect to �� and �� as follows: #$ # � = #$#�� = 0, � = 1,⋯,!()�)* (3) where !()�)* is the number of limit states. fragility curves of base-isolated npp structures were developed for the 3 limit states considering the three groups of ground motions. figure 7 shows the fragility curves for the 3 limit states with different earthquake groups. it can be observed that the base-isolated npp structure might behave as without damage if the level of pga less than 0.6g, which is significantly higher than the operational basis earthquake design level of apr-1400 npp structures. additionally, the isolated structure suffered no damage within pga 0.8g of farfield earthquakes. fig. 7. seismic fragility curves of base-isolated npp structures subjected to nearand far-field earthquakes figure 8 shows the comparison of fragility curves for the three groups of earthquakes. it can be observed that the structural model under near-field motions is more vulnerable than that due to far-field earthquakes. this can be attributed to the obvious reason that the deformation of lrbs produced by near-field motions is higher than that under far-field motions. -3000 -2000 -1000 0 1000 2000 3000 -400 -200 0 200 400 s h e a r fo rc e ( k n ) deformation (mm) near-field eq. -3000 -2000 -1000 0 1000 2000 3000 -400 -200 0 200 400 s h e a r fo rc e ( k n ) deformation (mm) far-field eq. 0 500 1000 1500 2000 0 0.4 0.8 1.2 1.6 2 d e fo rm . o f l r b ( m m ) pga (g) near-field earthquake 0 500 1000 1500 2000 0 0.4 0.8 1.2 1.6 2 d e fo rm . o f l r b ( m m ) pga (g) far-field earthquake 0 0.2 0.4 0.6 0.8 1 0.0 0.4 0.8 1.2 1.6 2.0 p ro b a b il it y o f d a m a g e pga (g) ls1 ls2 ls3 near-field earthquake 0 0.2 0.4 0.6 0.8 1 0.0 0.4 0.8 1.2 1.6 2.0 p ro b a b il it y o f d a m a g e pga (g) ls1 ls2 ls3 far-field earthquake engineering, technology & applied science research vol. 12, no. 5, 2022, 9092-9096 9095 www.etasr.com nguyen et al.: the influence of nearand far-field earthquakes on the seismic performance of … fig. 8. comparison of fragility curves of base-isolated npp structures in different defined limit states. v. conclusions in this study, seismic fragility curves of the base-isolated apr1400 npp structures were derived for different limit states based on the maximum likelihood estimation. the influence of near-field and far-field ground motions was considered. based on the numerical results, the following conclusions are drawn. • the maximum deformations of lrbs were shown to be smaller for far-field earthquakes than for near-field ground motions. this is due to the high-amplitude pulse effect of near-field motions. • the probability of failure of base-isolated npp structures is significantly higher for near-field ground motions compared to that for far-field earthquakes. • the npp model has not suffered any damage within pga 0.6g, which is higher than the safe shutdown earthquake design level of apr-1400 npp structures. • it is crucial to select earthquake ground motions with both nearand far-field motions for the seismic evaluation of npp structures. references [1] e. kalkan and s. k. kunnath, "effects of fling step and forward directivity on seismic response of buildings," earthquake spectra, vol. 22, no. 2, pp. 367–390, may 2006, https://doi.org/10.1193/1.2192560. 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institute, university of mustapha benboulaid batna 2, algeria f.tebbi@univ-batna2.dz received: 16 december 2022 | revised: 29 december 2022 and 6 january 2023 | accepted: 7 january 2023 abstract in the present study, flood frequency analysis (ffa) is performed on the daily inflows of a reservoir dam taken as a case study. the peaks-over-threshold (pot) approach was adopted. a comparison between the default generalized pareto distribution and the best distribution fitted to the data has been carried out. after the risk analysis, the reliability of the structure decreases to 25.60% for the chosen threshold values if the best distribution is adopted instead of the default fit. keywords-flood frequency analysis; peaks-over-threshold; generalized pareto distribution; best fit; risk analysis i. introduction flood frequency analysis (ffa) [1, 2] plays a major role in the design of hydraulic structures because it affects both safety and cost of the structure. the principal objective of ffa is to construct a relationship between the flood magnitude and the return period by the estimation of the probability of exceedance [3]. hydrologists generally apply two types of approaches to perform ffa, annual maximum (am) and peaks-over-threshold (pot), also called partial duration series approach. the am series approach is the most used method in ffa due to its simplicity in the sampling process [4, 5]. it uses only one maximum discharge value from each year. however, defining the samples in such a way eliminates a large portion of the data and results in loss of useful information, e.g. the second highest flow data in a year (which could be higher than many data points in the am series) is not selected [4, 5]. the pot approach consists in retaining all peak values that are above a certain level usually called the threshold. the pot approach is more useful to the analysis of extreme values. the main advantage of the pot approach is that it allows the selection of an enriched series of events to be considered as floods [7] and controls the number of flood occurrences to be used in the analysis, unlike the am approach which includes only one event per year. authors in [7] prepared a guide for the use of the pot approach. authors in [6] indicate that the pot method can provide adequate and comparable estimates of nyear discharges for more stations with short temporal coverage. authors in [8] reviewed recent advances in the pot approach from a statistical perspective. authors in [4] reported that the pot method has better results than the am method after comparing the results of both methods for data from the litija 1 gauging station on the sava river in slovenia. authors in [5] reviewed and summarized the current status of the pot model and identified the difficulties in applying it in ffa. ensuring the independence of the data series and choosing an appropriate threshold value are two of the main difficulties associated with the pot approach [4]. the threshold should be high enough to maintain the assumption of flood independence, but should not be so high as to increase the variance by reducing the number engineering, technology & applied science research vol. 13, no. 1, 2023, 10175-10180 10176 www.etasr.com krimil et al.: best fit versus default distribution and the impact on the reliability over the design … of events needed for flood analysis [9]. therefore, the selection of an appropriate threshold is the subject of several studies and many methods, either graphical or analytical, have been reported. graphical methods are widely used [10]. there are several probability distributions for modeling flood extreme events, the selection of the best fit distribution and the associated parameter estimation is an important step in ffa [11]. generalized pareto distribution (gpd) is broadly used to model extreme floods over a threshold and the distribution of pot can be approximated by the gpd [12]. the annual number of events above the threshold can be approximated by either poisson or negative binomial distributions [13, 14]. in the current study, the ffa method, applied to the daily inflows of the koudiat medouar reservoir and the pot approach are adopted. several additional distributions are tested to find the best one that fits the data. a risk analysis is then conducted. ii. study area located 7km north-east of timgad and 35km from batna, the koudiet medouar dam was built in 1994 on the oued rebôa. it has a height of 48m. the reservoir is a part of the great strategic hydraulic complex beni haroun transfer, with a capacity of 70 million m 3 . it supplies drinking and irrigation water to several towns. figure 1 shows the koudiat medouar reservoir location. fig. 1. location of the koudiat medouar reservoir. iii. methodology ffa is a statistical method that consists of studying past events and characteristics of a given process (hydrological or other) to define the probability of future occurrence by a probability distribution using the am or pot series. the pot approach consists in the constitution of a series of data by extracting the values superior to a well determined threshold. the selection of an appropriate threshold value is an important phase, mean residual life plot (mrlp) and the stability graph of the parameters are recommended in [15]. the threshold value is chosen upon a certain stability of the scale and shape graphs. threshold is taken at the tail of the mrlp when the function of the mean value begins to be almost linear. the pot flood series are adjusted by the distribution of gpd [16]. the adjustment of excesses above a threshold according to the gpd model hypothesis must be ensured by two discrete distributions, poisson or negative binomial. the main step in the application of the pot method is the choice of the threshold. indeed, selecting a very high threshold has the effect of decreasing the size of the series and thus increasing the sampling uncertainties. the number of maximums per year (nmpy ≈1) subsequently gives a very short am series [17]. on the other hand, a threshold that is too low (nmpy ≥ 6) gives series artificially enriched with information but one will be confronted on the problem of obtaining dependent series. therefore, a trade-off must be found between acquiring information and obtaining independent series (figure 2). however, there is no universal criterion for identifying such a threshold value [18]. in this paper, we focus on the following criteria for threshold selection:  mrlps.  the stability of scale and modified shape graphs.  fixing the nmpy. once the preselection has been performed according to the above criteria, the basic hypothesis tests of ffa, i.e. homogeneity, independence, and stationarity, must be verified. to verify these hypotheses, three non-parametric statistical tests are used: [19] to verify the independence, [20, 21] to verify whether the data come from the same distribution or not, and [22, 23] to verify the stationarity of the data. fig. 2. methodology chart. a. model fitting several types of distribution are used to estimate flow extremes. the reasons for the operational use of a particular distribution type in many countries are often subjective or historical [24]. table i illustrates the probability distributions mostly used to fit inflows. the choice of the appropriate estimator is one of the most important issues in ffa [25, 28]. the most commonly used are: the method of moments (mom), the method of l-moments (ml), and the maximum likelihood estimation (mle). the ml is more used in statistical hydrology for estimating various hydrometeorological variables [29, 30]. the objective of the ffa is to find reliable estimates of quantiles that will help us in the design of structures. after the selection of the thresholds, and defining the best fit, the quantiles are evaluated for a return period of 100 years. engineering, technology & applied science research vol. 13, no. 1, 2023, 10175-10180 10177 www.etasr.com krimil et al.: best fit versus default distribution and the impact on the reliability over the design … table i. usual probability distributions functions distribution pdf normal 2 2 1 2 1 ),;(              x exf log normal    20 /ln 2 1 0 0 2)( 1 ),,;(       xx e xx xxf gumbel                       0exp exp )( 0 xx e xf xx pearson 3                           x e x xf 1 1 ),,;( generalized extreme value                              1 1 1 )(1exp1 1 ),,;( xxxf generalized pareto distribution                                             0,exp 1 0,1 1 ),,;( 1 1           x x xf kappa   hxfxkhxf          1 1 1 1 )( )( 1),,,;(     , where h x hhxf 1 1 )( 11),,,;(                   α: scale parameter, μ: location parameter, κ: shape parameter, γ: second scale parameter, h: second shape parameter, γ( ): gamma function, f( ): cumulative distribution function b. risk analysis water-control design requires the consideration of risk [31]. risk and reliability analysis have great importance when it comes to natural phenomena such as floods. risk analysis of future events requires a probabilistic approach [32]. this natural hydrological risk can be calculated using the following equations: at least once in years 1 ( ) 1 (1 ) n t np x x t     (1)  ntxxpr )(11  (2) where: 1 ( )tp x x t   (3) 1 1 1 n r t         (4) where n is the expected life of the structure (in our case n=50 years), t is the return period (usually the life expectancy of a hydraulic structure is 100 years), and �� is the probability that an event � ≥ �� will occur at least once in n years. the reliability re is defined by: re = 100 − �� (5) iv. results and discussion a. data description the used database in this study was collected from the national agency for dams and transfer (anbt). daily inflows of koudiat medouar reservoir spanning the period from 2004 to 2019 were calculated according to the following water balance equation: inflow= (� − �� ) + (��� + ��� + ��� + ��� + ��� + ���) (6) where inflow is the daily inflow, ���i and ���� represent the initial and the volume in the reservoir, dev is the daily evaporated volume, dws the daily volume allocated to water supply, drv the daily volume allocated to irrigation, dsv the daily spilled volume, �fv the daily flashed volume, and dlv is the daily leakage volume. daily inflows are not normally distributed. the box plot in figure 3 shows that two values 117.608m 3 /s and 110.915m 3 /s appear as outliers, but in fact they are real occurred events. figure 4 shows the interannual variations of daily inflows at the koudiat medouar reservoir. even if the stability of scale and shape parameters are confirmed (figure 5), it is important to verify the hypothesis tests (homogeneity, independence, and stationarity). between the thresholds of 5m 3 /s and 11m 3 /s, even with that of 14m 3 /s, the tests were not verified. engineering, technology & applied science research vol. 13, no. 1, 2023, 10175-10180 10178 www.etasr.com krimil et al.: best fit versus default distribution and the impact on the reliability over the design … fig. 3. daily inflows description of koudiat medouar reservoir. fig. 4. time series of the daily inflows at koudiat medouar reservoir (2004-2019). fig. 5. mean residual life plot for the daily inflows of the koudiat medouar reservoir. this led us to keep only the values of 12, 13, and 15m 3 /s respectively (table ii). using the r code rstudio [33] and for the previously chosen thresholds, we tested whether the different distributions fit. the results show that gpd distribution is not the best fit for 12m 3 /s and 13m 3 /s threshold (figure 6). the threshold of 15m 3 /s just ensures an exceedance number of 2 per year, for this purpose, this threshold is presented as a limit of choice beyond which we find the statistical situation of the am. for thresholds below 12m 3 /s, the opposite situation arises: these are samples artificially enriched in size with a greater chance of losing the satisfaction of the hypothesis tests, in particular the homogeneity and the randomness required for any reliable frequency analysis without statistical violation (table iii). the frequency distribution results are shown in figure 6. table ii. statistical parameters corresponding to pot time series statistic u=12m 3 /s u=13m 3 /s u=15m 3 /s sample size 50 40 31 min 12.08 13.12 15.22 1 st quantile 13.34 15.31 19.85 median 17.06 22.41 27.67 mean 26.81 30.40 35.20 3 rd quantile 30.27 37.26 43.42 max 117.60 117.60 117.60 wald-wolfowitz p-value 0.086 0.337 0.137 wilcoxon-mannwhitney p-value 0.851 0.814 0.759 mann-kendal p-value 0.536 0.954 0.838 table iii. estimated quantiles for return period t=100 years threshold type of fit distribution quantiles (m 3 /s) rmse (m 3 /s) u =12m 3 /s best fit pearson 3 159.285 0.024 default fit gpd 211.924 0.049 u =13m 3 /s best fit kappa 169.318 0.026 default fit gpd 190.416 0.037 u =15m 3 /s best fit = default fit gpd 174.899 0.028 the frequency distribution results are shown in figure 6. the plots indicate that the pearson 3 (rmse=0.024) and kappa (rmse=0.026) distributions are the best fit for u = 12 and 13m 3 /s, respectively. using (4) and (5), the risk reliability is calculated for a return period of 100 years and is presented for best fit and gpd distribution results. the quantile corresponding to 100 years return period for pearson 3 distribution is equivalent to a 48 years return period of the gpd for the 12m 3 /s threshold. respectively, quantile corresponding to 100 years return period for kappa distribution is equivalent to a return period of 70 years of the gpd fit for the 13m 3 /s threshold (table iv). by selecting the best fit, the reliability of the structure decreases by 25.60% and 11.80% for thresholds of 12m 3 /s and 13m 3 /s, respectively, compared to the default fit. quantile pearson 3= 159.285m 3 /s for t=100 years, corresponding to t=48 years quantile in gpd (reliability=-25.60%) and quantile kappa= 169.318m 3 /s for t=100 years in gpd corresponding to t=70 years (reliability=-11.80%). we note that when the reliability decreases, the risk increases, so we have under dimensioned hydraulic structures. engineering, technology & applied science research vol. 13, no. 1, 2023, 10175-10180 10179 www.etasr.com krimil et al.: best fit versus default distribution and the impact on the reliability over the design … fig. 6. probability density function of best and default fit for the selected thresholds. table iv. risk reliability pearson 3 gpd u (m 3 /s) 12 return period (t) 100 48 risk (for n=50 years) 39.50% 65.10% reliability 60.50% 34.90% 13 kappa gpd return period (t) 100 70 risk (for n=50 years) 39.50% 51.30% reliability 60.50% 48.70% v. conclusion this article presents high flood analysis in relation to the data from daily inflows of the koudiat medouar reservoir for the period from 2004 to 2019. ffa was carried out with the pot series. one of the main disadvantages concerning the pot approach is the selection of the threshold value. in ffa, choosing a very high threshold number of maximums per year (nmpy ≈1), has the effect of decreasing the size of the series and therefore increasing the sampling uncertainty which subsequently gives a very short series. on the other hand, a too small threshold gives series artificially enriched information (nmpy ≥ 6). for this reason, we have retained only the series of 2 to 4 max per year. after the verification of the basic hypothesis tests, the thresholds retained were 12, 13, and 15m 3 /s. in this study, the gpd distribution is not systematically the best fit of the daily inflows. the study showed that the pearson 3 and kappa distributions are better suited than gpd 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[33] r core team, r: a language and environment for statistical computing. vienna, austria: r foundation for statistical computing, 2018. microsoft word etasr_v12_n6_pp9692-9696 engineering, technology & applied science research vol. 12, no. 6, 2022, 9692-9696 9692 www.etasr.com salahaldeen & al-hadithi: the effect of adding eps on the hardened properties……. the effect of adding expanded polystyrene beads (eps) on the hardened properties of concrete aya sabah salahaldeen department of civil engineer university of baghdad baghdad, iraq aya.arif2001m@coeng.uobaghdad.edu.iq abdulkader ismail al-hadithi department of civil engineer university of anbar ramadi, iraq abdulkader.alhadithi@uoanbar.edu.iq received: 21 august 2022 | revised: 9 september 2022 | accepted: 10 september 2022 abstract-this study investigated the possibility of producing lightweight concrete using expanded polystyrene beads (eps), using one reference and five light concrete mixes by replacing coarse aggregates with eps grains in five volumetric ratios: 20, 40, 60, 80, and 100%. the properties of hardened concrete of all mixed specimens, such as compressive strength, flexural strength, and density, were evaluated. the results showed that the addition of eps caused an apparent reduction in the mechanical properties of concrete. the compressive strength at 28 days of curing ranged from 13.6 to 1.96mpa, while the rupture modulus ranged from 2.26 to 0mpa. adding eps grains as coarse aggregates led to a decrease in the concrete's weight. replacing the coarse aggregates with eps grains resulted in lightweight concrete with a density of 1086.5kg/m 3 . keywords-lightweight concrete (lwc); coarse aggregates; expanded polystyrene beads (eps); properties of hardened concrete i. introduction concrete is an artificial material used to construct various civil engineering structures [1]. concrete is the most commonly used substance in construction and can be used as stand alone mass concrete, reinforced concrete, or prestressed concrete when combined with steel [2]. for every ton of cement produced, one ton of carbon dioxide (co2) is emitted into the atmosphere. cement manufacturing is responsible for 5% of anthropogenic co2 emissions [3]. cement production produces a significant amount of co2 and requires a large amount of energy during the manufacturing process. given that pakistan is already facing an energy crisis, the high energy consumption in cement production puts additional pressure on its energy sector. as a result, the price of cement is rising daily. furthermore, waste disposal and the restoration of concrete components after demolition have negative environmental consequences. as a result, the use of this waste reduces cement manufacturing and energy consumption while also helping protect the environment [4]. one of the drawbacks of traditional concrete is its high self-weight. the density of regular concrete ranges between 2200 and 2600kg/m 3 making it an uneconomical structural material. several attempts have been made in the past to reduce the self-weight of concrete to increase its efficiency. lightweight concrete (lwc) is a type of concrete with a density ranging from 300 to 1850kg/m 3 [5]. since lwc was first used approximately two thousand years ago, several lighter structures were built, particularly in the mediterranean region. the three most important structures built during the roman empire are the colosseum, the port of cosa, and the pantheon dome [6]. the use of lwc in buildings, structural and non-structural, as construction material must have specific characteristics that meet the requirements of strength and performance for the application. before using any material in construction, there is a need to study its mechanical properties to determine its suitability [7]. due to its low density, which offers tremendous benefits by reducing the cross sections of the components, there is an increase in the demand for lwcs in many modern architectural constructions [7]. there are two categories of lightweight aggregates: natural, such as diatomite, volcanic cinders, etc., and industrial such as expanded shale, clay, and slate. polystyrene is an industrial material with a density less than 300kg/m 3 and no absorption properties [8-9]. polystyrene has a closed cell structure, is stable, has low density, and is not absorbent or hydrophobic [10-11]. concrete can be used for all parts of a building (structural and non-structural) as a very lightweight material by altering the percentage ratio of its aggregates [12-13]. unlike lightweight industrial aggregates, polystyrene is commercially available everywhere. most polystyrene manufacturing facilities are located in europe and russia [14]. the effects of adding eps to cement mortar and concrete have not been extensively studied. this addition leads to a decrease in the density and mechanical properties of both cement mortar and concrete [15-16]. ultra-high-performance concrete and eps beads composite sandwich plates were investigated in [17], examining the use of these sandwich plates in high-rise structures. because of their low density and high compressibility, eps beads are frequently used as filling materials in earthquake buffers [18-20]. this study aimed to investigate the production of lwc using eps as coarse aggregate, carrying out several tests to examine the effect of adding eps as coarse aggregate with different volume percentages on the properties of the new lwc. corresponding author: aya sabah salahaldeen engineering, technology & applied science research vol. 12, no. 6, 2022, 9692-9696 9693 www.etasr.com salahaldeen & al-hadithi: the effect of adding eps on the hardened properties……. ii. experimental setup a. cement all specimens were cast using ordinary portland cement (opc) type i throughout the experiment. this kind of cement complies with the iraqi specification 5/2019 [19]. table i shows its physical attributes and chemical composition. b. fine aggregates sand from the al-ekhadir area (karbala city) was used as fine aggregates, as shown in figure 1. this sand is classified as zone 2 and meets the physical and chemical requirements of the iraqi standard 45/1984 [20], as shown in table ii. fig. 1. fine aggregates (left) and coarse aggregates (right). c. coarse aggregates natural gravel from the al-nibaee region with a nominal aggregate size of 5-10mm, shown in figure 1, was used as coarse aggregates in all mixes. table iii shows that the physical and chemical parameters of the coarse aggregates comply to the iraqi standard 45/1984 [20]. d. water potable (tap) water, obtained from the laboratory, was used for mixing and curing. this water meets the requirements of the iraqi standard 1703 [21]. e. expanded polystyrene beads (eps) this study used spherical-shaped eps beads with a maximum nominal size of 10mm to replace coarse aggregates. table iv depicts the gradient and physical properties of eps beads, shown in figure 2. fig. 2. expanded polystyrene beads (eps). f. superplasticizer (sp) a superplasticizer called sika viscocrete 5930, which complies with the astm c494 type g [22] criteria, was used in the adjusted mixes, and table v shows its features. table i. physical and chemical composition of cement physical properties test result limits of iqs 5/2019 [19] setting time: -initial setting (min) -final setting (hrs.) 106 4.83 45 min 00 hrs. max comp. str. (mpa): 2-days 28-days 11.25 33.31 min. 10 min. 32.5 chemical properties oxide composition result limits of iqs 5/2019 [19] (����) 21.62 no limited (�����) 5.94 no limited (� ���) 3.32 no limited (cao) 61.55 no limited l.s.f. % 0.86 no limited (mgo) 2.85 max. 5 sulfate (so3 %) max c�a<5% not applicable 2.5 c�a >5% 2.25 2.8 (l.o.i.) 1.07 max. 4 (i.r.) 0.88 max. 5 (c�s) 35.11 no limited (c�s) 35.07 no limited (c�a) 10.13 no limited (c af) 10.09 no limited table ii. fine aggregates sieve analysis limits of [20] (zone 2) passing % sieve size (mm) 100 100 10 90-100 92 4.75 75-100 85 2.63 55-90 56 1.18 35-59 42 0.6 8-30 13 0.3 0-10 5 0.15 physical and chemical properties limits of iraqi standards test results physical characteristics ----2.5 specific gravity 0.5% (max) 0.4% (so3 %) ----0.7% absorption (%) table iii. coarse aggregate's properties sieve size (mm) test results limits of [20] 14 100 90-100 10 75.1 50-85 5 1.2 0-10 2.36 -no limited so�% content 0.092 max. 0.1% table iv. sieve analysis and properties of eps sieve size passing % astm c330 12.5mm 100 100 9.5mm 91 80-100 4.75mm 6.5 5-40 2.36mm 1.5 0-20 specific gravity -- water absorption 0 - maximum particle size (mm) 10 - table v. properties of superplasticizer [23] density 1.08 kg/l ph 8.0 ±1.0 chloride content nil (en934-2) engineering, technology & applied science research vol. 12, no. 6, 2022, 9692-9696 9694 www.etasr.com salahaldeen & al-hadithi: the effect of adding eps on the hardened properties……. iii. molds, mixing, and casting three 100×100×400mm prism samples were produced for each group of 7, 14, and 28 days of curing to test the flexural strength and three 100×100×100mm cube samples with ages 7, 14, and 28 days were constructed to test compressive strength. before placing the materials, the internal surface of the mixer was cleaned and wet. to ensure even dispersion of the polystyrene, the raw materials were first thoroughly combined and dried for about 3 minutes. afterward, water was gradually added while mixing to produce a smooth and flowing liquid. the mixing process was extended for 3 minutes to create a uniform and consistent concrete. this process was performed in the concrete laboratory of baghdad university's college of engineering. all concretes were blended using a planetary mixer, shown in fig. 4. the mixture was poured into oiled molds, which were then vibrated on a vibrating table for 1 minute to improve compaction and reduce air bubbles. the samples were demolded after 24 hours and placed in water for curing before testing. fig. 3. mixing of concrete. iv. concrete mix this study used 1 reference and 5 different concrete mixes to create the samples. concrete was produced with a water/cement ratio of 0.45 and a coarse aggregate ratio of 1:1.6:3.12, by weight, of opc. table vi shows the details of the samples. table vi. mix of 1m3 of concrete mix code r e20% e40% e60% e80% e100% cement (kg/��) 401 401 401 401 401 401 sp (kg/��) 1.2 1.2 1.2 1.2 1.2 1.2 fine aggregates (kg/��) 643 643 643 643 643 643 coarse aggregates (kg/��) 1254 1002 753 501 250 0 eps (kg/��) 0 2 4 6 8 10 water (kg/��) 180 180 180 180 180 180 v. test results and discussion a. density the quantity and density of lightweight aggregates are two of the most crucial elements in regulating a variety of physical properties in lwc. due to the low density of polystyrene, the density of lwc falls as polystyrene volume increases [24-25]. table vii shows the densities of the samples and figure 4 shows their density variation with age. table vii. density test results mix code 7 days 14 days 28 days r 2550 2573 2589 e20% 2266 2283 2295 e40% 1944 1975 1984.5 e60% 1615 1627 1635 e80% 1356.5 1400 1422.5 e100% 1035 1055.5 1086.5 fig. 4. variation of density with age b. compressive strength according to figure 5, the compressive strength gets stronger with curing time. this rise is the result of the cement hydration process becoming more advanced with time. figure 6 and table viii both provide a comparison of the compressive strengths of several specimens at 7, 14, and 28 days of age. table viii. compressive strength test results mix code 7 days 14 days 28 days r 25.7 33.11 42.4 e20% 9.67 10.12 13.6 e40% 6.04 9.29 10.88 e60% 3.47 3.62 4.08 e80% 3.42 3.62 3.86 e100% 1.36 1.81 1.96 fig. 5. variations of compressive strength with age per sample. figure 6 shows that the concrete containing eps had a decrease in compressive strength when the p/agg ratio reached 20% or higher. as eps increased, the compressive strength decreased. in the case of higher-density concrete mixes, those that contained less polystyrene typically had higher strengths, but compressive strength decreased when the polyester content was greater than 80% of the aggregate. this is because the polystyrene fills in the gaps left by the absence of coarse aggregates. in addition, the compressive strength of engineering, technology & applied science research vol. 12, no. 6, 2022, 9692-9696 9695 www.etasr.com salahaldeen & al-hadithi: the effect of adding eps on the hardened properties……. polystyrene is lower than that of coarse aggregates. similar to the conventional concrete, it is evident that strength declines as polystyrene content increases. figure 6 shows the variation in compressive strength per sample and figure 7 shows the compressive strength test procedure. fig. 6. variation of compressive strength with polystyrene content %. fig. 7. compressive strength test. c. flexural strength figure 8 shows that all prisms made of concrete mixtures exhibited a steady increase in flexural strength over time. figure 8 and table ix show a comparison of the variance in flexural strength values with different polystyrene content percentages at 7, 14, and 28 days of age. fig. 8. variation of flexural strength with age. table ix. results of flexural strength tests mix code 7 days 14 days 28 days r 3.72 3.85 6.01 e20% 1.13 1.52 2.26 e40% 1.71 2.09 3.43 e60% 0.73 0.93 1.09 e80% 0.28 0.36 0.42 e100% 0 0 0 figure 9 shows the change in flexural strength after 7, 14, and 28 days, and figure 10 shows the flexural strength test procedure. figure 9 shows that the flexural strength of concrete containing polystyrene decreased when the p/agg ratio was 20% or higher. this could be because lower-density concrete has lower flexural strength as it contains higher amounts of polystyrene. figure 9 illustrates how higher-density concrete mixes with lower amounts of polystyrene typically had a higher flexural strength. however, flexural strength decreased when polyester content was greater than 80% of the aggregates. this is because polystyrene fills in the gaps left by the absence of coarse aggregates and has lower flexural strength than coarse aggregates. fig. 9. variation of flexural strength with polystyrene content %. fig. 10. flexural strength test. vi. conclusion this study investigated the compressive and flexural strengths of concrete with various proportions of eps beads replacing coarse aggregates. the results showed that:  as the polystyrene/aggregate ratio increases, lightweight concrete's compressive strength decreases. engineering, technology & applied science research vol. 12, no. 6, 2022, 9692-9696 9696 www.etasr.com salahaldeen & al-hadithi: the effect of adding eps on the hardened properties…….  as the polystyrene/aggregate ratio increases, the density of the lightweight concrete mixes decreases. the lowest density value was 1086.5 kg/m 3 for the total replacement of coarse aggregate with polystyrene (100%).  as the polystyrene/aggregate ratio increases, the flexural strength of the lightweight concrete mixes decreases. the lowest value of flexural strength was 0mpa for total replacement of coarse aggregates with polystyrene (100%). finally, recycling waste materials can help create new and environmentally friendly lightweight concrete for specific purposes. references [1] n. bheel, a. s. memon, i. a. khaskheli, n. m. talpur, s. m. talpur, and m. a. 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[29] d. saradhi babu, k. ganesh babu, and t. h. wee, "properties of lightweight expanded polystyrene aggregate concretes containing fly ash," cement and concrete research, vol. 35, no. 6, pp. 1218–1223, jun. 2005, https://doi.org/10.1016/j.cemconres.2004.11.015. microsoft word etasr_v12_n3_pp8500-8505 engineering, technology & applied science research vol. 12, no. 3, 2022, 8500-8505 8500 www.etasr.com dagsa et al.: development of an automated ticketing and tracking system for the monitoring of … development of an automated ticketing and tracking system for the monitoring of surface mine hauling operations lovely mae dagsa smart mines research project caraga state university butuan city, philippines lmdagsa@carsu.edu.ph alexander t. demetillo smart mines research project caraga state university butuan city, philippines atdemetillo@carsu.edu.ph alfred dennis b. balamad smart mines research project caraga state university butuan city, philippines densvanz13@gmail.com edgardo ricardo b. sajonia jr. smart mines research project caraga state university butuan city, philippines ebsajonia@carsu.edu.ph gerome l. amper smart mines research project caraga state university butuan city, philippines glamper@carsu.edu.ph marie claire o. virtudazo smart mines research project caraga state university butuan city, philippines mcovirtudazo@carsu.edu.ph received: 9 february 2022 | revised: 18 february 2022 | accepted: 23 march 2022 abstract-telematics systems that integrate wireless communications and automation for equipment tracking and trip monitoring in mining operations have an advanced impact on the operational efficiency and optimization of the mine's asset inventory. in this study, a system was developed for solution in a mining area with low mobile network signal coverage and no internet service available to monitor and analyze the actual utilization executed by heavy equipment using microcontrollers with communication capabilities (gsm/gprs, wifi, and bluetooth) and sensor modules for fuel monitoring and location tracking. open-source software was utilized, such as php framework and mysql, to provide a fast and real-time display of daily mine operations. the study provides an online tracking and ticketing system on mine hauling vehicles, introducing a costefficient, reliable, interactive platform for web-based monitoring and real-time telematics. the data acquired in real-time provide significant information which will allow innovative equipment optimization. keywords-telematics; microcontrollers; gsm; gprs; wifi; php; mysql; tracking and ticketing system; web-based monitoring i. introduction by allowing the extraction of important information from industrial processes, the industrial revolution, which includes automation, information, and communication technology, can improve production and commercial processes. due to the infrastructural limitations in communication, data management, storage, and information exchange, the mining industry is rather traditional and slow to change [1]. the hauling system has been a mainstay of the mining industry for many years. while machines have increased in size and scale and automation has become an important development, there have been few innovations to the actual load and haul process [2]. most recent efforts focused on using robotics and automation to assist the extraction and transport of minerals and ore [3]. trip analysis in mining hauling operations can lead to a series of important analytics applications for asset managers. analyzing trip data helps fleet managers and dispatchers understand and estimate asset utilization, route deviation, and eta (estimated time of arrival). this system is extremely crucial when making production decisions and adjustments to improve the efficiency and use of equipment. implementing good monitoring systems plays a vital role in achieving this. nowadays, the competitive global economy is forcing mining companies worldwide to modernize their operations through increased mechanization, automation, and monitoring [4–8]. historically in fleet management, trips are logged manually or semi-automatically, whereas using gps-based data to infer trips provides an automated approach to trip management and analysis [9–11]. this system alleviates the labor of manual recording and avoids the possibility of unauthorized or misreported trips, and improves the accuracy of actual trip data. one of the most common asset tracking technologies is an embedded gps receiver and other sensors to track a movable asset such as a trailer, which connects with a central data server via satellite or cellular communications. every telematics communication typically contains location data, vehicle identity information, timestamps, and an event code [12]. monitoring systems implemented in various fields utilize different technologies like unmanned vehicles, gsm, iot, and wsn to retrieve information from the monitored equipment or area [13–17, 21-22]. however, in mining area settings where corresponding author: lovely mae dagsa engineering, technology & applied science research vol. 12, no. 3, 2022, 8500-8505 8501 www.etasr.com dagsa et al.: development of an automated ticketing and tracking system for the monitoring of … mobile network connection and internet coverage are difficult to acquire, it is necessary to implement a one-of-a-kind data transfer system. this study developed such a system to solve the transmission problem and to monitor and analyze the actual utilization executed by the mining company’s heavy equipment, by using microcontrollers with wireless communication capabilities (gsm/gprs, wifi, and bluetooth) and sensor modules for fuel monitoring and location tracking. open-source software, such as php framework and mysql database, was utilized to provide a fast and real-time display of daily mine operations. the study provides an online tracking and ticketing system of mine hauling vehicles, introducing a cost-efficient, reliable, and interactive platform for web-based monitoring and real-time telematics [18–20]. this system is specially tailored for the mining industry and their environmental conditions. measures are made in order to accommodate areas with low mobile network and internet coverage. unlike other tracking systems [23-27], this tracker module is integrated in the mining industry process, and the data it sends include some mining hauling operation parameters. this helps smoothen out their operations in terms of equipment monitoring and management. table i shows the differences of the proposed method and the current process used by this project’s partner mining company. table i. proposed system vs current company operations parameter proposed method status quo vehicle status check status/location instantly check status at the end of day, no location tracking checker transaction wireless transmission, automatic data transfer to server paper transactions, data is manually encoded to the server at the end of day data summary view data in the web anytime of the day view data in excel after they are manually encoded after shift (end of day) ii. system architecture/methodology and flowchart figure 1 indicates the system overview of the study. the details of the system components are shown in figure 2 and are analyzed below. fig. 1. system overview. • loading station: in this station, the dump truck (dt) is being loaded with ore in the mine yard. the installed tracker module in the dt is started. dt location and fuel status are always periodically sent to the cloud every 30s for the whole duration of the trip. this module uses gsm/gprs communication to send all the data acquired by the dt module to the cloud. if a mobile network signal is not available, the tracker module can save all the acquired data and send them when it acquires a signal later on the trip. • checker station: after ore loading, the equipment, specifically the dump truck, passes through a checker station. there, checker personnel create a trip ticket or delivery receipt (mdr) to track the ore's trip. trip ticket data are sent back to the dt module to the cloud since checker stations don't have mobile network signals or internet connections. the dt module will send the mdr information once it acquires a mobile network signal later on the trip. • receiver station: in this station, the equipment, specifically the dt, arrives at the stockyard where the ore is expected to be delivered. receiving personnel send the destination information to the dt module. the dt module then sends it to the cloud. this process completes one trip data and can be viewed on a web application. fig. 2. system architecture and flow. iii. hardware, software, and system integration a. hardware design the tracker module design for this system used methods slightly different from the existing technologies [10-13]. this tracker module sends the location and status of the monitored vehicle and carries essential operations' data generated during the trip. table ii shows the comparison of the proposed system with the existing tracker modules [23-27]. the proposed system includes fuel monitoring and integration to smartphones in order to add additional information like vehicle status and driver info. also, the proposed system is specially tailored for engineering, technology & applied science research vol. 12, no. 3, 2022, 8500-8505 8502 www.etasr.com dagsa et al.: development of an automated ticketing and tracking system for the monitoring of … mining industry conditions in the philippines, where mobile network coverage is very low. also, this tracker module is integrated in the mining industry process, and the data it sends include some mining hauling operation parameters. fig. 3. tracker module. table ii. proposed tracker vs existing tracker modules parameters proposed existing tracker modules gsm/gprs transmission existing existing gps module existing existing smartphone integration existing none sd card backup existing existing fuel monitoring existing none web integration existing existing two interconnected esp32 modules with sim800l, a fuel sensor, and a micro sd module make up the primary tracker module. a processor unit, short-range wireless communication technology (wifi and bluetooth), and a cellular network unit make up the esp32 module (sim800l). the two esp32 modules are connected in a serial communication protocol. the first esp32 module will receive the external data from other modules such as the checker module, weighbridge, and receiver modules through wireless communication and then send them to the second esp32 module through serial communication. the second esp32 module, which is equipped with the sim800l(gsm/gprs) module, will send the received data to the cloud. the tracker module is also equipped with a fuel sensor port, which receives the fuel level data of the vehicle. the system also has three indicator leds that help the user identify the device's working status. the first led is the power led, which lights up when the system is turned on and has performed all needed initializations, the second is the bluetooth led, which lights up when the module is connected to an external device, and the third is the receive data indicator, which lights up when external data are received. three switches were also installed in the module. the first switch is the main switch, which is responsible for turning the device 'on' and 'off,' the second switch is the reset which can be used to reset the device when restarts are needed, and the third is the toggle switch which is used to tell the device to receive external data. an sd card module can also be found in the system. it serves as a temporary data storage device while the data are not yet sent to the server. the data on the sd card are erased once a transmission confirmation is received. if the transmission is not successful, the sd card retains the data until the module acquires signal to resend them. the sd card is not manually erased since it will not be full from the stored data. a li-ion battery was used as the system's power supply, which was also partnered with a charging module that controls the system's charging and discharging and protects the battery from overvoltage and undervoltage situations. the modules will be tapped directly into the vehicle’s internal power supply. the batteries in this case will act as backup every time the vehicle is turned off, so the tracking may continue. when the vehicle is turned on again, the batteries are automatically recharged. with the battery’s capacity of 13.3wh, and 1.3w average power consumption of the tracker, the battery can last up to 10hrs, until the vehicle is needed to be turned on again to charge it. since the vehicles are used daily in day and night shifts, there is only little time that the battery is being used, only during transition of drivers and maintenance after shift. a shock-proof rubber was also used in the enclosure to protect the modules from possible external vibrations. the dimensions of this module are 10cm×7cm×4cm. fig. 4. checker module. the checker module consists of two interconnected esp32 modules with sim800l and a micro sd module. the two esp32 modules are connected in a serial communication protocol. the first esp32 module will receive the data from an external device with a user interface to create the trip ticket through bluetooth communication and then send it to the second esp32 module through serial communication. the checker application has the interface for the checker personnel to enter additional information for the trip (e.g. source of material, destination, shift, department, ore composition, etc.). the app has the ability to check the authenticity of the user checking the current trip. the checker personnel are registered in a database, and the checker app is being synced into that database in order to get the list of the valid personnel. the app then checks the person who is logged-in in the app if he/she is in the list before he/she can proceed with the transactions. the second esp32 module transmits the received data to the tracker module through wifi communication. the system has two indicator leds that help the user identify the device's working status. the first is the power led which lights up when the system is turned on and has performed all needed initializations and the second is the bluetooth led, which lights up when the module is connected to an external device. two switches are also installed in the module. the first is the main switch, which is responsible for turning the device 'on' and 'off' and the engineering, technology & applied science research vol. 12, no. 3, 2022, 8500-8505 8503 www.etasr.com dagsa et al.: development of an automated ticketing and tracking system for the monitoring of … second switch is the reset which can be used to reset the device. an sd card module is also installed. this system serves as temporary data storage while the data are not yet forwarded to the tracker module. like the tracker module, the data on the sd card are also being erased once a transmission confirmation is received to avoid data overflow. a li-ion battery was used as the system's power supply, which was also partnered with a charging module that controls the system's charging and discharging and protects the battery from overvoltage and undervoltage. the checker station is expected to also have a stand-alone solar station to accommodate the module’s charging. like the tracker module, a shock-proof rubber was also used in the enclosure to protect the modules from external vibrations. the dimensions of this module are 10cm×7cm×4cm. b. software • arduino ide 1.8: an open-source software platform used to write programs, while programs can be uploaded directly to the board. this ide is compatible with esp32 microcontroller chips and is used to compile and upload programs to an onboard microcontroller unit in the system. • php 7.2 and mysql 5.5: the system utilized open-source software such as php scripting language towards the web development of the study and mysql database to display the data acquired by the modules during operations. iv. results and discussion the full system was tested for 10 days straight, and the testing gathered over 4300 lines of raw data. the system enabled quick tracking/monitoring of the equipment used during hauling operations. the biggest benefit from the system was the easy access in monitoring by the management, which allowed them to have production data in their operations in contradiction to their old methods. in their old method, they were only able to check their production data at the end of the day, which limits them to make adjustments in their operations mid-day. being able to monitor data so close to real time helped them improve efficiency and optimize their operations. fig. 5. system testing. this system also reduced paper usage, which is responsible for a good amount of their budget. implementing this system would provide savings to the company in terms of operation cost in the long run. figure 5 shows the tracker module interacting with the developed android app, which provides the necessary data needed for monitoring. the tracker module sends parameters like the equipment id, operator id, department, mdr, status, location, speed, and fuel level and the sensor sends the data. the location sent by the tracker was validated by comparing the values to the readings of garmin oregon 750 during field testing. the raw data were received by a web server (figure 6), which displays the data in tabular form for easy reviewing. the web server also processes the data and translates the latitude and longitude data into actual map locations (figure 7). fig. 6. monitoring data display on the web. fig. 7. map showing actual track traversed by the equipment. fig. 8. checker app sending data to the checker module. figure 8 shows the checker app interacting with the checker module. the checker app and module together send the mdr data to the tracker module consisting of parameters like shift engineering, technology & applied science research vol. 12, no. 3, 2022, 8500-8505 8504 www.etasr.com dagsa et al.: development of an automated ticketing and tracking system for the monitoring of … schedule, activity, ore type, source, destination, distance traveled, fuel consumed, and other mining operation-related parameters. the mdr data are being recorded on the server (figure 9) and can be tracked if the trips are already completed or still on pending status. the reliability assessment of the data transmission aspect of this research was done by comparing the raw data logs shown in figure 10 and 11 received from the modules to the data being displayed in the server. the data sent by the modules were sampled periodically and compared to the current display on the web. fig. 9. tabular display of the checker data (trip tickets) on the web. fig. 10. sample raw data logs from the checker module. fig. 11. sample raw data logs from the tracker module v. conclusion and future work in this research, an automated ticketing and tracking system for mining industry applications was developed. the system was able to monitor pieces of equipment even in areas with low mobile network coverage and no available internet connection. based on the results, the system showed a big contribution in making the daily operations of mining industries more efficient by providing real-time monitoring and ticketing tools that can be used in process decisionand adjustmentmaking during operations. the system was able to improve the company's data transfer, from the end-of-day status to real-time. it was also able to provide faster ticket issuance, improve the safety of the personnel since the operations are done wirelessly, and save on the cost of paper used on the tickets. eventually, using this automation system will lead to more efficient daily operations, thus potentially increasing the overall output and profitability of the company. therefore, the proponents highly recommend this project to the mining industries in the philippines, which are still using manual ticketing systems and no equipment monitoring, especially those located in low mobile network coverage areas. however, the required personnel responsible for the maintenance and operation for its sustainability in a full-time basis are needed to be trained. moreover, for future work, the researchers recommend looking for a cheaper alternative in data sending technology since gsm load is relatively expensive in the philippines. acknowledgment the authors wish to acknowledge the support and funding of the department of science and technology philippine council for industry, energy, and emerging technology research and development (dost-pcieerd). this project is under the collaborative r&d to leverage philippine economy (cradle) science for change 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[27] v. callegari, "gps receiver comprising a data link via gprs and/or umts," ep2023155a1, feb. 11, 2009. microsoft word etasr_v12_n5_pp9395-9399 engineering, technology & applied science research vol. 12, no. 5, 2022, 9395-9399 9395 www.etasr.com rehman et al.: prediction of the stress wave amplification factor of a spherical blast source using … prediction of the stress wave amplification factor of a spherical blast source using numerical simulations jawad ur rehman department of civil and environmental engineering hanyang university seoul, south korea jawad640@hanynag.ac.kr can-ngon nguyen department of civil engineering vinh university vinh, vietnam ngon_nguyencan@yahoo.com tuan-anh nguyen department of civil engineering vinh university vinh, vietnam anhhandico52@gmail.com trong-cuong vo department of civil engineering vinh university vinh, vietnam cuongvqc@gmail.com trong-kien nguyen department of civil engineering vinh university vinh, vietnam nguyentrongkien82@gmail.com van-quang nguyen department of civil engineering vinh university vinh, vietnam nguyenvanquang240484@gmail.com received: 2 august 2022 | revised: 25 august 2022 | accepted: 27 august 2022 abstract-a typical blast wave attenuation curve presents a relationship between peak particle velocity (ppv) at the surface of a geologic profile and distance. as the stress wave is amplified at the free-field boundary, the attenuation curve at the surface is always larger than the within media profile curve. measurements are made at the rock's surface and test blasts are always conducted to ensure the safety of underground existing structures. in order to design underground blasting, the recorded ppvs are then reduced by a factor of 2. in this paper, particle velocity amplification was studied by using numerical simulation, and the difference between ppv at the surface and within media profiles is quantified. the amplification factor depends upon source depth, incidence angle, and poisson’s ratio of the media. it is calculated as the ratio of the magnitude of ppv at the surface of the media to the within media profile. according to the parametric study, the amplification factor for a uniform medium increases with increasing source depth, while the amplification factor decreases with increasing poisson’s ratio. considering a three-layer model with a source depth of 30m, the amplification factor is high for low incident angles and low for higher incident angles. the range varies between 1.5 to 2.1. keywords-free surface; numerical simulation; underground blasting; wave amplification; wave attenuation i. introduction blasting is one of the most extensively utilized methods for extracting rock in mining and construction operations and the most cost-effective excavation method [1]. the appropriate design of blasts and the management and prediction of blast consequences importance is increasing as the magnitude of these operations grows [2, 3]. the majority of the explosive energy is utilized in the crushing and fracturing of the rock mass. when blasting energy is transferred to the rock mass, it might cause damage to the surrounding rock in the form of undesired fractures. many researchers have contributed to the development of the blast vibration safety criterion, and several criteria or prediction models have been proposed to assess the structural stability of diverse constructions [4, 5]. peak particle velocity (ppv) is the most extensively used indicator for evaluating blast-induced damage. ppvs are widely assumed to be determinable in empirical models based on the maximum charge per delay, distance from the blasting source, and site coefficients. the scaled distance concept proposed by the united states bureau of mines (usbm) [6] is the most acceptable vibration prediction equation. it takes into account the quantity of explosive energy in shock and seismic waves, as well as distance effects. test blasts are usually conducted to record surface ppvs, and an attenuation curve is then corresponding author: van-quang nguyen engineering, technology & applied science research vol. 12, no. 5, 2022, 9395-9399 9396 www.etasr.com rehman et al.: prediction of the stress wave amplification factor of a spherical blast source using … developed by conducting regression analysis. the scaled distance (sd) is calculated by taking the distance between the source and measurement locations and dividing it by the maximum charge per delay: sd � �√� (1) where r is the distance between the charge and monitoring station and w is the maximum charge weight per delay. the usbm predictor equation for the estimation of the peak particle velocity is: ��� � �� � (2) where k and n are the site and geological constant factors respectively. the ground transmission factor, or constant k, is influenced by the confinement of the charge, and the local geology. higher values of k denote either well-coupled explosives or a mass of rock that is relatively large and fracture-free. the quality of the rock mass affects the constant n, which indicates the impact of attenuation with distance. lower values of n indicate more competent rock mass with less fracturing, whereas higher values of n indicate poorer quality rock mass that attenuates vibration energy more quickly and within a shorter distance from the charge. test blasts are usually conducted to record surface ppvs, and an attenuation curve is then developed by regression analysis. artificial intelligence (ai) techniques like artificial neural networks (anns) and particle swarm optimization (pso) have been utilized in mining and civil engineering during the last few years to forecast the ppv based on total charge, distance, maximum charge per delay, frequency, and blasting parameters [7, 8]. previously, the wave amplification effect studies mainly focused on earthquakes [9-14] and the amplification effect for the blast source has not been studied extensively. this paper uses numerical simulations to study the amplification factors using a spherical blast source. ii. numerical modeling in the present study, numerical analysis is carried out using flac 2d version 7.0 [15]. an axisymmetric model with a spherical blast source and a quad mesh with a mesh size of 0.05m is used. the blast-induced fracture zone is described as a spherical cavity with a radius of 0.5m. the half-space was modeled as an elastic material. the computational model and boundary conditions are shown in figure 1. the reflected wave created at the upper boundary travels to the side wall and the lower end as it propagates in the radial direction with vertical and horizontal velocity components. therefore, viscous dampers are installed in two directions, at the side wall and at the bottom to absorb the impact of vibrations, as suggested in [16]. the modelling strategy used in this paper is as follows: first, a geometric model of the rock mass is created and a behavioural model and material properties are applied. then, a mesh is generated, boundary conditions and viscous boundaries are applied, and finally, a blast load is applied. the explosion depths employed were 10, 20, and 30m. the computational domain has a 70m lateral dimension. the blast load was applied to the cavity surface in the normal direction as a pressure-time history. fig. 1. the computational model. to verify the numerical model, the results of the dynamic analysis for the undamped case are compared to the closedform solution in [17]. to solve the spherical charge blasting vibration problem, the authors in [17] simplified the cavityblasting pressure. the solution showed that the spherical blasting generates only p waves, and an elastic velocity equation for the spherical blasting vibration was later obtained as follows: v r, τ̄ � � �� f τ̄ � � � �� � q τ̄ (3) where v is the velocity induced by the blast source, a is the source cavity, r is the distance from the measured point to the charge centre, f(τ), q(τ) are time history functions of the wave at r, and � is the dimensionless time. f τ̄ � c �� !�"̄� , q τ̄ � c � ! �"̄ (4) where c is the wave velocity and ϕ1 is the displacement potential function: #$ � %&'()*�) +��̄ � 2 *!) *�) � %.' /̄ 0 %.) /̄ 1 *!)2*�)3) 456 78 �̄ � 9 � $2*�) 6:; 78 �̄ � 9 <= where: >? � @ab � c ? � � �̄ � �d � �%c? � ? c78 � $%�e !/� $%e g8 � $%�e $%e g? � c ? gh$8 � c ? gi � g  h�8 � � c ? � � 7i� 0 gi � g � 9 � *!)3)  time-varying blast pressure is applied to the wall of an equivalent cavity using the following formulation [17]: � d � �k d �%lm (4) where p(t) and p0 denote time-varying blast pressure and initial detonation pressure respectively, t represents time, n is an integer, and β denotes decay of the pressure pulse. figure 2 engineering, technology & applied science research vol. 12, no. 5, 2022, 9395-9399 9397 www.etasr.com rehman et al.: prediction of the stress wave amplification factor of a spherical blast source using … shows a blast pressure profile calculated using ( � d � �k d �%lm ). fig. 2. pressure time history applied to the wall of an equivalent cavity. the velocity-time history estimated from the numerical simulation and the equation from [17] for the undamped medium is shown in figure 3. the shear wave was fixed to 2309m/s, with a poisson ratio of 0.25, whereas unit weight was set at 24.5kn/m 3 . the selected loading pressure was 1gpa. n and β were set to 1 and 2000 respectively. the blast equivalent cavity was assumed as 0.5m. it is shown that the numerical model correctly predicts the wave attenuation, providing results that are almost identical to the analytical solution. a parametric study is conducted to study the influence of effective parameters on wave amplification at the surface. these parameters include source depth, angle of incidence, and poisson’s ratio. first, a homogeneous rock mass is modeled and then layered model with weathered rock at the surface, followed by soft rock, and then hard rock mass is considered. fig. 3. comparison of the numerical simulation with a closed-form solution. iii. results and discussion blast-induced vibrations are usually recorded in the form of ppv at the surfaces. surface vibrations are always higher than within profiles [18]. table i shows the mechanical properties of the rock mass [19]. the attenuation of ppv for surface and within profiles for the depth of 30m with poisson’s ratio of 0.25 is shown in figure 4. the calculated ppv at the surface is almost two times the one within profiles. table i. mechanical properties of the rock mass [19] rock type shear velocity (m/s) unit weight (kn/m 3 ) poisson ratio hard rock 2500 25 0.25 2000 1500 soft rock 1200 23 0.27 1000 800 weathered rock 650 21 0.3 500 150 fig. 4. comparison of ppv within profile and surface for homogenous media. to study the amplification factor in detail, three source depths of 10, 20, and 30m from the surface are considered. three poisson’s ratios of 0.20, 0.25, and 0.30 are selected. for uniform homogeneous rock mass, figure 5(a) shows the results of poisson’s ratio of 0.20, for the three depths. the amplification factor at high angles is 1.8, whereas at lower angles it increases up to 2. a source at greater depth shows an amplification factor near to 2 at 10° to 50°. for poisson’s ratio of 0.25, at high angles the amplification factor in figure 5(b) is 1.7 and at lower angles it is 2. the amplification factor for poisson’s ratio of 0.30 in figure 5(c) is 1.5 at higher angles and 1.9 at lower angles. low poisson’s ratio has amplification from near 1.8 to 2.1, whereas higher poisson’s ratio shows less amplification factor and gradually increases for lower angles up to 1.9. until now, the rock mass was considered homogenous, however, in the real field, it is inhomogeneous. for this purpose, a three-layer model is developed: near the surface the rock mass consists of soft rock, followed by weathered rock, and the lower most part consists of hard rock. figure 6 shows the computational model for inhomogeneous rock mass. the attenuated ppv at 30m depth is shown in figure 7. the amplification factor at smaller distances, i.e. at lower incident angles, is more than 2, whereas at greater distances, i.e. at higher incident angles, the amplification factor is 1.5. to further get a clear view, figure 8 shows the amplification factor engineering, technology & applied science research vol. 12, no. 5, 2022, 9395-9399 9398 www.etasr.com rehman et al.: prediction of the stress wave amplification factor of a spherical blast source using … at 30m depth, which shows high amplification factor for low incident angles. the amplification factor decreases for higher angles. fig. 5. amplification factor for homogeneous rock: (a) υ = 0.20, (b) υ = 0.25, (c) υ = 0.30. fig. 6. a computational model for inhomogeneous rock mass. the results show that the inhomogeneity of rock mass plays a vital role in wave amplification. amplification factors for different sites will be different based upon rock mass strata. many studies [20] assume an amplification factor of 2 for homogenous rock mass using a spherical blast source. a numerical simulation is suggested for finding amplification factors for the specific site. this study is limited to spherical blast sources. in the field, cylindrical blast sources are utilized. future research will include a complete parametric investigation employing a cylindrical blast source. fig. 7. comparison of ppv of within profile and surface for inhomogeneous rock mass. fig. 8. amplification factor for inhomogeneous rock mass iv. conclusions this paper presented a numerical analysis-based amplification factor for a spherical blast source. the velocity amplification factor is defined as the ratio of wave amplitude at the free field boundary to the incident wave amplitude. poisson’s ratio, source depth, angle of incidence, and geological characteristic of a specific site are the main factors that affected the velocity amplification. the results show that the amplification factor varies between 1.5 to 2.1. as a consequence, velocity amplification phenomena should be taken into account while assessing underground damage. it is recommended to utilize numerical analysis to predict site-specific amplification factor, which can improve design procedures and help engineers predict the inner profile attenuation curves for controlling damage to the surrounding rock mass. references [1] i. a. onederra, j. k. furtney, e. sellers, and s. iverson, "modelling blast induced damage from a fully coupled explosive charge," international journal of rock mechanics and mining sciences, vol. 58, pp. 73–84, feb. 2013, https://doi.org/10.1016/j.ijrmms.2012.10.004. engineering, technology & applied science research vol. 12, no. 5, 2022, 9395-9399 9399 www.etasr.com rehman et al.: prediction of the stress wave amplification factor of a spherical blast source using … [2] l. malmgren, d. saiang, j. töyrä, and a. bodare, "the 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[3] d. saiang and e. nordlund, "numerical analyses of the influence of blast-induced damaged rock around shallow tunnels in brittle rock," rock mechanics and rock engineering, vol. 42, no. 3, pp. 421–448, jun. 2009, https://doi.org/10.1007/s00603-008-0013-1. [4] j.-h. shin, h.-g. moon, and s.-e. chae, "effect of blast-induced vibration on existing tunnels in soft rocks," tunnelling and underground space technology, vol. 26, no. 1, pp. 51–61, jan. 2011, https://doi.org/10.1016/j.tust.2010.05.004. [5] p. pal roy, "vibration control in an opencast mine based on improved blast vibration predictors," mining science and technology, vol. 12, no. 2, pp. 157–165, mar. 1991, https://doi.org/10.1016/0167-9031(91) 91642-u. [6] w. i. duvall and d. e. fogelson, ri 5968 review of criteria for estimating damage to residences from blasting vibrations ? summary and conclusions. washington dc, usa: united stated department of the interior, 1962. [7] d. j. armaghani, m. hajihassani, e. t. mohamad, a. marto, and s. a. noorani, "blasting-induced flyrock and ground vibration prediction through an expert artificial neural network based on particle swarm optimization," arabian journal of geosciences, vol. 7, no. 12, pp. 5383– 5396, dec. 2014, https://doi.org/10.1007/s12517-013-1174-0. [8] d. j. armaghani, e. momeni, s. v. a. n. k. abad, and m. khandelwal, "feasibility of anfis model for prediction of ground vibrations resulting from quarry blasting," environmental earth sciences, vol. 74, no. 4, pp. 2845–2860, aug. 2015, https://doi.org/10.1007/s12665-0154305-y. [9] m. aaqib, d. park, m. b. adeel, y. m. a. hashash, and o. ilhan, "simulation-based site amplification model for shallow bedrock sites in korea," earthquake spectra, vol. 37, no. 3, pp. 1900–1930, aug. 2021, https://doi.org/10.1177/8755293020981984. [10] m. aaqib, d. park, y.-g. lee, and u. pervaiz, "development of site classification system and seismic site coefficients for korea," journal of earthquake engineering, oct. 2021, https://doi.org/10.1080/ 13632469.2021.1990164. [11] y. lee, h.-s. kim, m. i. khalid, y. lee, and d. park, "effect of nonlinear soil model on seismic response of slopes composed of granular soil," advances in civil engineering, vol. 2020, nov. 2020, art. no. e8890247, https://doi.org/10.1155/2020/8890247. [12] t. nagao, "seismic amplification by deep subsurface and proposal of a new proxy," engineering, technology & applied science research, vol. 10, no. 1, pp. 5157–5163, feb. 2020, https://doi.org/10.48084/etasr. 3276. [13] t. nagao, "maximum credible earthquake ground motions with focus on site amplification due to deep subsurface," engineering, technology & applied science research, vol. 11, no. 2, pp. 6873–6881, apr. 2021, https://doi.org/10.48084/etasr.3991. [14] t. nagao, "variation evaluation of path characteristic and site amplification factor of earthquake ground motion at four sites in central japan," engineering, technology & applied science research, vol. 11, no. 5, pp. 7658–7664, oct. 2021, https://doi.org/10.48084/ etasr.4405. [15] "flac (fast lagrangian analysis of continua) version 220," itasca consulting group, inc., minneapolis, mn (usa)) nuclear regulatory commission, washington, dc (usa), report nureg/cr--5430vol.3, 1989. [16] j. lysmer and r. l. kuhlemeyer, "finite dynamic model for infinite media," journal of the engineering mechanics division, vol. 95, no. 4, pp. 859–877, aug. 1969, https://doi.org/10.1061/jmcea3.0001144. [17] j. jiang, d. p. blair, and g. r. baird, "dynamic response of an elastic and viscoelastic full-space to a spherical source," international journal for numerical and analytical methods in geomechanics, vol. 19, no. 3, pp. 181–193, 1995, https://doi.org/10.1002/nag.1610190303. [18] j.-k. ahn and d. park, "prediction of near-field wave attenuation due to a spherical blast source," rock mechanics and rock engineering, vol. 50, no. 11, pp. 3085–3099, nov. 2017, https://doi.org/10.1007/ s00603-017-1274-3. [19] j.-k. ahn, d. park, and j.-k. yoo, "estimation of damping ratio of rock mass for numerical simulation of blast induced vibration propagation," japanese geotechnical society special publication, vol. 2, no. 45, pp. 1589–1592, 2016, https://doi.org/10.3208/jgssp.kor-34. [20] p. zhang, e. nordlund, g. swan, and c. yi, "velocity amplification of seismic waves through parallel fractures near a free surface in fractured rock: a theoretical study," rock mechanics and rock engineering, vol. 52, no. 1, pp. 199–213, jan. 2019, https://doi.org/ 10.1007/s00603-018-1589-8. microsoft word etasr_v13_n1_pp10045-10050 engineering, technology & applied science research vol. 13, no. 1, 2023, 10045-10050 10045 www.etasr.com baazi: aquifer vulnerability assessment by drastic and si methods: the case study of guelma plain … aquifer vulnerability assessment by drastic and si methods: the case study of guelma plain, northeast algeria houria baazi natural hazards and territory planning laboratory (lrnat), institute of earth sciences and universe, geography and territory planning department, university of batna 2, algeria h.baazi@univ-batna2.dz (corresponding author) received:27 november 2022 | revised: 9 december 2022 | accepted: 18 december 2022 abstract guelma plain, located in northern algeria, contains an alluvial nappe that provides economic opportunities such as industrial and agricultural employment. in guelma, the pressure of anthropogenic origin is combined with unfavorable climatological conditions that expose it to environmental and social risks. the current study aims to assess the level of groundwater vulnerability to pollution using two methods, drastic and si. these are coupled with the arc gis software in order to carry out the mapping. from south to north, several levels of vulnerability have been identified, from low to high. the result comparison allows us to conclude that the si method is the most appropriate for assessing the vulnerability to pollution of the study region's wetlands. the result of this study can be used as a decisionsupport tool for the management and protection of the quality of water resources in the guelma plain. keywords-guelma; groundwater; nappe; vulnerability; pollution; drastic; si i. introduction water is one of the most important ecosystem, climate, and social components [1, 2]. water in sufficient quantity and of acceptable quality is a fundamental necessity, but maintaining its quality is challenging [3]. groundwater is severely overexploited because it is the main source of water for drinking, domestic, industrial purposes, and livestock operations, and it is in a critical state based on quantitative and qualitative evaluations [4-6]. surface and ground water are the main resources of drinkable water, since the 97.5% of the total water on the globe is saline. civilizations have long promoted an understanding of the need of protecting water resources. technical methods are crucial for conserving these resources. these tools are based on evaluations of the sensitivity and susceptibility of water to pollution, as well as a compilation of maps that clearly delineate zones of sensitivity and vulnerability at various levels. the drop in groundwater level and ensuing rise in susceptibility are caused by human and agricultural activities. this study sought to ascertain guelma alluvial plain's sensitivity to groundwater pollution using the following vulnerability methods: the general drastic [7] approach and the si [8] method combined with gis. in order to establish measures to conserve these resources and prevent the loss of this wealth, the created maps of groundwater pollution sensitivity using various methodologies help us better pinpoint the location of polluted areas. ii. study area the wilaya of guelma is located in the north-east of the country. it is limited by the wilaya of annaba in the north, el tarf in the north east, skikda in the north-west, souk ahras and oum el-bouaghi in the south east, and finally constantine in the west. it is a part of the maghreb chain of eastern algeria [9] and extends between 7° and 7°30' east and between 36° and 36°30' north, having between 180 and 250m altitude [10]. this area is characterized by subtropical climate. the rainy season lasts from october until may, with an annual precipitation that doesn’t surpass 550mm and with sparse vegetation. in addition, the annual average value of temperature is 17.75°c, and the monthly temperatures variate between a minimum of 9.72°c and a maximum 26.76°c. it is surrounded by various thrust sheets, giving rise to the current mountains [9, 11-13]: mahouna (1411m) to the south, haouara (1292m) to the north, and débar (1060m) to the north-west [10]. the reliefs are made up of allochthonous lands belonging mainly to the tellian domain made up of meso-cenozoic marls and carbonates [14]. iii. geological and hydrogeological settings the geology of guelma region consists of three major sets: pre-aquifer, a mio-pliocene set (continental, from guelma basin), and a recent set (pliocene and quaternary). guelma engineering, technology & applied science research vol. 13, no. 1, 2023, 10045-10050 10046 www.etasr.com baazi: aquifer vulnerability assessment by drastic and si methods: the case study of guelma plain … region includes djebel debagh neritic domain, heliopolis, and guelma south. this jurassic-cretaceous carbonate facies unit, which is more or less karstified, is overlain by several thrust layers and subjected to significant tectonic events. along its course between nador and medjez amar, the seybouse wadi has deposited alluvium [9]. the center of the plain represents a zone of collapse filled with miocene (clay and gypsum marl) and quaternary (terraces of heterogeneous alluvium) deposits (figure 2) [10]. these permeable alluviums are nourished by the infiltration waters of the rains and the lateral contributions of the seybouse wadi's watershed. there are three distinct terrace levels (low, medium, and high) [10]. fig. 1. study area. fig. 2. hydrogeological section in the guelma north-south plain. iv. materials and methods a. application of the drastic and si methods the drastic index was developed by the us environmental protection agency as a standardized approach for measuring how sensitive groundwater is to pollution [6]. drastic can be utilized by people with a wide range of backgrounds and degrees of competence due to its simplicity [6]. drastic evaluates groundwater vulnerability by incorporating 7 physical and hydrogeological parameters: depth of water (d), net recharge (r), aquifer media (a), soil media (s), topography (t), vadose zone impact (i), and hydraulic conductivity are the (c) parameters. for convenience of use, they have been organized to form the abbreviation drastic. the drastic factors are measurable parameters for which data is generally available from a number of sources without extensive investigation. the susceptibility index (si) is a modification of the drastic approach for determining aquifer sensitivity to disperse agricultural pollution. depth to water, net recharge, aquifer medium, topography, and land use are the 5 parameters involved. it differs from drastic in that it includes the land-use factor while excluding the soil media, vadose zone, and aquifer. land use is a critical and influential factor in groundwater contamination caused by anthropogenic activities such as agricultural land use which can negatively impact groundwater through the application of fertilizers, pesticides, and industrial land use, which can negatively impact groundwater through the disposal of chemical compounds into water bodies and landfills [11]. table i. ratings and weights of the drastic method parameters [7] d (m) weight evaluation 0-1.5 5 10 1.5-4.5 9 4.5-9 7 9-15 5 15-22.5 3 22.5-30 2 > 30 1 a weight evaluation karst limestone 3 10 sand and gravel 8 solid sandstone 6 altered metamorphic 4 metamorphic 3 metamorphic 1 sand and fine gravel 5 t ( slope %.) weight evaluation 0-2 1 10 2-6 9 6-12 5 12-18 3 > 18 1 c (m/s) weight evaluation > 9.4×10-4 3 10 4.9×10 -4 9.4×10 -4 8 32.9×10 -54.7×10 -4 6 14.7×10 -532.9×10 -5 4 4.7×10 -5 -14.7×10 -5 2 4.7×10 -7 4.7× 10 -5 1 r (mm) weight rayting >25.5 4 9 25.517.5 8 17.5-10 6 10-5 3 5-0 1 s weight rayting thin or absent 2 10 sands 9 sandy loam 6 silt 4 silty loam 3 clays 1 i weight reyting karstic limestone 5 10 sand and gravel 9 sand and gravel with silt and clay 8 sandstone 6 limestone 6 silt and clay 1 engineering, technology & applied science research vol. 13, no. 1, 2023, 10045-10050 10047 www.etasr.com baazi: aquifer vulnerability assessment by drastic and si methods: the case study of guelma plain … for each used models we have applied the following formulas:  drastic: id = d� × d� + r� × r� + a�a� + s� × s� + t� × t� + i�i� + c × c� (1) where d: depth, r: net recharge; a: aquifer media, s: soil media, t: topography, i: unsaturated zone; c: hydraulic conductivity, and the subscripts r and w are the corresponding rating and weights, respectively:  si: i� = d × d� + r × r� + a × a� + s × s� + t × t� + lu × lu� (2) where d, r, a, s, t, and lu are the parameters of the si method, p the weight of the parameter, and c the associated score. the land cover parameter (lu) was obtained by processing the sentinel satellite image taken in july 2020. this image was used to establish the land cover map of the study area. tables iiii are used to elaborate the maps of the parameters of the drastic and si methods. table ii. weights assigned to the si method parameters [8] n° parameters weight 1 d: depth 0.186 2 r: net recharge 0.212 3 a: aquifer media 0.259 4 t: topography 0.121 5 lu: land use 0.222 table iii. vulnerability assessment criteria of the drastic and si methods [7,12,13,8] vulnerability index drastic si very low < 80 -- low 180-120 <45 moderate 121-160 45-64 high 161-200 65-85 very high >200 >85 b. elaboration of maps of the specific parameters of the vulnerability of the aquifer in order to use the drastic and the si methods, the following steps must be followed:  data collection  data digitization  calculation of scores (score × weight)  assignment of scores  classification and reclassification of the 7 specific parameters of the groundwater  map development for each specific parameter of the tablecloth on raster mode  calculation of the global vulnerability index by the sum of the 7 raster maps of the specific parameters of the vulnerability of the tablecloth  classification and development of the final vulnerability map fig. 3. map spatial distribution of depth to water. fig. 4. spatial distribution of net recharge. fig. 5. spatial distribution of aquifer materials. engineering, technology & applied science research vol. 13, no. 1, 2023, 10045-10050 10048 www.etasr.com baazi: aquifer vulnerability assessment by drastic and si methods: the case study of guelma plain … fig. 6. slope spatial repair. fig. 7. spatial distribution of soil type in the region. fig. 8. distribution of values of the nature of the vadose zone index. v. results and discussion a. synthesis map by the drastic method the application of the drastic method at the guelma plain has allowed the realization of the vulnerability map of figure 11, from which we can distinguish three classes of different degrees of vulnerability. we notice that the areas of low vulnerability are encountered in the southeast of the plain. this can be explained by the nature of the soil that is characterized by a fine texture and the slope that varies from medium to strong. similarly, the areas of medium vulnerability are located in the center of the plain to the south, more precisely in the southeast or at the wastewater discharges (drainage of wastewater by the various tributaries of oued seybouse) and at the level of settlements which contain a large number of boreholes for agricultural development. fig. 9. distribution of hydraulic conductivity values. fig. 10. land cover map. fig. 11. aquifer vulnerability map (drastic method). engineering, technology & applied science research vol. 13, no. 1, 2023, 10045-10050 10049 www.etasr.com baazi: aquifer vulnerability assessment by drastic and si methods: the case study of guelma plain … the area of high vulnerability is noticed at the north-east and north-south edges, which can be explained by the drainage of wastewater by the main wadi (seybouse) interrupted by a site of medium vulnerability. this elevation is explained by the gravelly nature of the soil of the vadose zone, the materials of the aquifer which are very permeable, and the urban discharges. b. synthesis map by the si method the application of the si method at the guelma plain has allowed the realization of the vulnerability map of figure 12, from which we can again distinguish three different classes of degrees of vulnerability. the areas of low vulnerability are distributed throughout the plain but the large area of this class is located in the south, affirming the result found in the case of the drastic method, which is explained by the nature of the soil at an important depth that can reach 25m. a sector of medium vulnerability is distributed all over the plain, where the wastewater discharges are located and at the level of the agglomerations. the area of high vulnerability is mainly noticed all along the wadi seybouse (drainage of wastewater by oued seybouse) and even in the center going south, where there is the presence of an unauthorized dump site and in the industrial area between oued skhoun and oued maiz. fig. 12. aquifer vulnerability map (si method). vi. conclusion surface and ground water are the main resources of drinkable water [14]. with the ever-increasing demand for water and the increasing lack and deterioration of water quality, the need for vulnerability mapping methods is necessary. due to the large number of methods in use, it is essential to recognize which ones are the most reliable and effective. the plain of guelma is made up of agricultural land that is irrigated from the seybouse wadi, which is the receiving medium for all the urban and industrial wastewater from the city of guelma and its agglomerations. the contamination of the plain's groundwater has been brought to light by this study. in order to achieve this goal, the application of the drastic and si methods allowed the vulnerability assessment of the pollution of the guelma alluvial groundwater. this vulnerability increases from the center of the plain to the northern edges and especially along the oued seybouse and its tributaries (oued maiz, oued zimba, chaabet maamora). the distribution of pollution sources has induced this growth. the analysis of the two vulnerability maps resulting from the application of these methods revealed three distinct classes of low, medium, and high vulnerability. although the two vulnerability maps are relatively close, the vulnerability map made from the si method reflects more the reality of the groundwater pollution of the guelma plain, which can be explained by the high vulnerability area located in the southern part (presence of an industrial area and an unauthorized dump site). as the 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[20] n. kumar, a. a. mahessar, s. a. memon, k. ansari, and a. l. qureshi, "impact assessment of groundwater quality using wqi and geospatial tools: a case study of islamkot, tharparkar, pakistan," engineering, technology & applied science research, vol. 10, no. 1, pp. 5288–5294, feb. 2020, https://doi.org/10.48084/etasr.3289. microsoft word etasr_v13_n2_pp10338-10346 engineering, technology & applied science research vol. 13, no. 2, 2023, 10338-10346 10338 www.etasr.com duarte de souza et al.: maize yield prediction using artificial neural networks based on a trial … maize yield prediction using artificial neural networks based on a trial network dataset paulo vitor duarte de souza campus santa helena, universidade tecnologica federal do parana, brazil victorduart366@gmail.com leiliane pereira de rezende campus santa helena, universidade tecnologica federal do parana, brazil rezende@utfpr.edu.br aildson pereira duarte centro de graos e fibras, instituto agronomico de campinas, brazil duarteaildson@hotmail.com glauco vieira miranda campus santa helena, universidade tecnologica federal do parana, brazil glaucovmiranda@utfpr.edu.br (corresponding author) received: 6 january 2023 | revised: 17 january 2023 | accepted: 20 january 2023 abstract the prediction of grain yield is important for sowing, cultivar positioning, crop management, and public policy. this study aims to predict maize productivity by applying an artificial neural network and by building models of multilayer perceptrons (mlps) using public data and maize experimental networks. the dataset included parameters of climate, soil water balance, and agronomic characteristics from maize hybrids of an experimental network of two agricultural years. the climatic and soil balance water parameters were divided according to the maize plant development stages. six databases were obtained by combining the imputation of missing data with the agronomic characteristics of the maize hybrids, the climatic parameters/soil water balance, and the complete database with both. hyper parameterization of the models was obtained using gridsearch and k-fold cross-validation. the models with imputation were more accurate than those without it. the model with climate data/soil water balance and the complete model with imputation presented the smallest errors of 71 kg ha −1 . in all the models, cultivars, locations, and their interactions were important, and different climatic conditions had the greatest weight in predicting productivity. it was concluded that the mlp models performed adequately and captured the non-linear effects of the interaction between the environment and maize hybrids. climatic and soil balance water parameters at different stages of maize plant development explain the productivity of maize hybrids more than the agronomic characteristics of the cultivars. keywords-artificial neural networks; deep learning; multilayer perceptron; agricultular productivity i. introduction interpretation of the genotype x environment interaction is essential to increase productivity with the positioning of the cultivar in the microregion and its predictability of performance according to the sowing date [1]. traditionally, analysis methods of the genotype x environment interaction have been used for the positioning of cultivars, however, the interpretations obtained after obtaining data and generalizations about the environment do not allow the application or extrapolation of results for all regions [2-3]. however, when the environments are well characterized, conclusions on cultivar performance are extrapolatable, as used nitrogen levels in rice [4] or used water deficit environments in maize [5]. the simulation models of plant growth in response to climate, soil, and cultivars allow identifying the best sowing times, which are made available annually for different cultures and locations, such as the agricultural zoning of climatic risk, and have helped brazilian farmers in all grain-producing locations [6-7]. however, even with agricultural risk zoning, weather conditions are unpredictable, and productivity losses are common in different regions, locations, and years when this engineering, technology & applied science research vol. 13, no. 2, 2023, 10338-10346 10339 www.etasr.com duarte de souza et al.: maize yield prediction using artificial neural networks based on a trial … information is not available in real time. production losses caused by drought in the paraná-la plata basin, brazil, have reduced soybean and maize production and affected global and south american agricultural markets during the past ten years, with the 2020-2021 drought imposing a 2.6% reduction in the cereal harvest compared to the previous year [8]. the multilayer perceptron (mlp) is an artificial neural network (ann) that can be used for productivity estimates. it uses the factors that affect productivity as an implicit function of the network input. mlps have been successful in creating predictive models using plant development parameters, soil characteristics, management, climatic conditions, and geographic positions with a small mean error for yield prediction [9-11]. the predicting maize productivity using ann can generate information for public policy on the production and supply of this important crop for local and national food security. the prediction can also generate realtime information for managing corn crops to increase productivity and sustainability. anns are being applied with different models or architectures to solve common problems in plant breeding and genotype x environment interactions and other agriculture situations. this can be observed when determining drought tolerance indices for durum wheat and identifying their efficiency in relation to other methods [12], parents for crossings in breeding programs [13] and, selected soybean plants in segregating populations of different maturity groups [14]. a machine learning approach was used in the automatic irrigation system based on humidity and temperature in the soil in [15]. the deep convolutional neural network architecture is very efficient to identify plants in the different stages including seedling of weed plants [16]. in addition, the estimate of maize productivity as a function of leaf chlorophyll content, measured in three stages of plant development, was determined by an arn-mlp and was adequate, considering that in the stage of development of the plant with six leaves (v6), it explained 50% or more of maize productivity data [17]. in turn, arabica coffee production was predicted to meet the market demand using anns with data on productivity, rainfall, relative humidity, and minimum and maximum temperatures. an adequate prediction accuracy was obtained with an r 2 of 0.8524 and rmse (root-mean-square deviation) of 0.0784 tons, demonstrating the potential of anns in determining the yield of the coffee cherry [18]. therefore, the objective of this study was to predict maize productivity by applying anns and building mlp models while using public data and maize experimental networks. ii. material and methods the variables for the analysis in this study were divided into agronomic, climatic, and soil water balance parameters. the agronomic characteristics of maize hybrids were obtained from the performance of maize hybrids at the second season, with 38 hybrids in 2018 and 32 hybrids in 2019 in 9 locations and 4 replications/locations in the bernardino de campos, capão bonito, cândido mota, cruzália, ibirarema, manduri, maracaí, palmital, and pedrinhas paulista in the middle region of the paranapanema valley, state of são paulo [19-21]. the agronomic characteristics evaluated were plant height, ear height, the ratio between ear height and plant height, the number of lodged plants, number of broken plants, number of days to flowering, plant population, productivity, grain moisture at harvest, and ear index per plant. the daily climate parameters were total precipitation, maximum, average, and minimum temperatures, average atmospheric pressure, average dew point temperature, average and minimum relative humidity, average wind speed, and maximum wind gust. the daily soil water balance variables included water storage, actual evapotranspiration, soil water deficit, soil water surplus, and evapotranspiration. total precipitation, water storage, and water surplus in the soil were considered at the cumulative sum of each plant development stage. the average for each period was considered for the other climate and water balance variables. daily climatic and soil water balance data were obtained from automatic stations (ourinhos a716, itapeva a714, avaré 725) at the national institute of meteorology (inmet), which provides a variety of daily meteorological data on a platform [22]. as the inmet does not have meteorological stations in some municipalities, it was necessary to consider data from the nearest stations, covering distances from 27 to 95km. water balance variables were subdivided according to the growth and developmental stages of the maize plant. the developmental stages of the maize were plant emergence (ve), 4 leaves with a visible leaf collar (v4), 8 leaves with a visible leaf collar (v8), tasseling (vt), silk and blister (r1 and r2), milky and dough grains (r3 and r4), dent grains (r5), and physiological maturity (r6). the cultivars had the same 120-day cycle, and the stages were considered with the same periods for all cultivars. the days for each stage were ve from the emergence to the 10 th day, v4 from the 11 th to the 40 th day, v8 from the 41 st to the 50 th day, vt from the 51 st to the 60 th day, r1 and r2 from the 61 st to the 75 th day, r3 and r4 from the 76 th to the 90 th day, r5 from the 91 st to the 105 th day, and r6 from the 106 th to the 120 th day. the database was processed before the effective implementation of the models and comprised up to 2392 data from 17 experiments on the performance of maize hybrids at the second season in 2018 and 2019. the necessary procedures for data preparation were the imputation of missing data, coding of categorical variables, and normalization (figure 1). the database contained missing data on flowering and grain moisture, representing 6% of the total database. the iterative imputation algorithm was used to impute these data, and the necessary parameterization for the execution of the iterative imputation was the neural network's own mlp with a δmin of 0.1. the parameter δmin defines the number of iterations performed by the iterative imputation and the minimum acceptable error in relation to previous iterations. the regressor defined for the predictions in the mlp with the hyperparameters for data imputation had three hidden layers, 64 neurons per layer, the relu (rectified linear unit) activation function in the hidden layer, 300 epochs, adam optimizer, 0.001 rate learning curve, mse (mean squared error) cost function, and the glorot normal-weight initialization method. this regressor was chosen based on the engineering, technology & applied science research vol. 13, no. 2, 2023, 10338-10346 10340 www.etasr.com duarte de souza et al.: maize yield prediction using artificial neural networks based on a trial … ability of anns to capture nonlinear relationships between data [23]. the dataset was divided into two groups: one with all variables with complete data and the other with only variables with missing values. therefore, two mlp models were built to estimate the variables of both sets using the same hyperparameters. for model training, each dataset was partitioned into training and testing sets. the training set had 80% of the examples, and the test set had the 20%. after inputting the data, transformations were applied to the categorical variables, cultivars, and years. the codification adopted transformed them as a function of annual productivity, given the variable of interest: 1 1 r i year i location p p l    (1) where l is the number of observations carried out in the r th location, pi is the i th productivity of the location, and pyear is the average of the observations made. 1 1 a s j year j year p p a    (2) where a is the number of observations carried out in the s th year, and pj is the j th productivity of the year. ck = pk − plocation (3) 1 1 e e k k cultivar c e    (4) where pk is the k th observation of the productivity of cultivar ck, plocation is the average productivity of a given location and, e is the number of observations of the cultivar, and ck is the k th difference between pk and plocation. in all the above equations, the categorical variables are functions of the observed average productivity, allowing the attribution of an evaluation to these variables. in the normalization procedure, the network input dataset was normalized by minmax scaling. the dataset was separated into 3 distinct bases: agronomic characteristics, climatic/water balance parameters, and complete with all variables with or without missing data imputations. in addition, 6 network models were implemented for the same purpose, with the task of predicting productivity as the model output. the necessary hyper parameterization in the 6 models was defined using grid search and k-fold cross-validation to find a set of hyperparameters with the smallest error in the cost function. for this purpose, a set of hyperparameters was previously considered to be tested by grid search and evaluated by k-fold cross-validation. k = 5 was considered for k-fold crossvalidation, which is one of the values commonly used in the literature [24]. the input hyperparameters for gridsearch were 3 hidden layers with 32, 64, and 128 neurons per layer, the relu activation function in the hidden layer, 300, 600, and 900 epochs, the adam optimizer, learning rates of 0.005, 0.003, and 0.001, the mse cost function, and the glorot normal weight initialization method. fig. 1. the proposed methodology. the mlp experiments were performed on the services provided by google research, google collaboratory, or colab, which is a host of services based on the jupyter notebook, where it is possible to interactively execute codes in the python language, in addition to having a set of tools for the development of deep learning models [25-26]. six models were constructed using tensorflow and keras [27-28]. the k-fold cross-validation used in model validation matched that of the machine learning library scikit-learn, which has a set of tools for developing machine learning models [23]. the shapley additive explanations (shap) method was applied so that the model with the best performance could be interpreted agronomically [29]. iii. results the hyperparameters of the models without imputation, with the lowest rmse among the 142 models trained using grid search and k-fold cross-validation, are listed in table i. the agr_m model required a greater number of layers and a larger batch size than the cli_m and cop_m models, demonstrating a greater requirement of hyperparameters for model adjustment. a hidden search is computationally expensive, which makes it impossible to apply the method to a large number of hyperparameters [30]. therefore, there is a possibility that the hyperparameters are not the global optimum but local optima due to the small set of hyperparameters. however, the use of the grid search is justified by its computational cost [30]. the learning curves of the agr_m, cli_m, and cop_m models with mse show concise training without much variation between training and validation and without overfitting to training data, with training time up to 1000 epochs (figure 2). in the cli_m model, closer values were obtained between the training and validation sets, as can be observed in the distance between the training and validation curves. in addition, there was variation at the beginning of the adjustment of the models, which is evidenced by the epochs where the adjustments of the functions began, remaining below 100 epochs for agr_m and cop_m, and close to 250 for cli_m. the possible causes for this are the hyperparameters used in the models, such as the batch size, number of layers, and database. the cop_m model presented an intermediate distance between the training and validation cost functions. engineering, technology & applied science research vol. 13, no. 2, 2023, 10338-10346 10341 www.etasr.com duarte de souza et al.: maize yield prediction using artificial neural networks based on a trial … this occurred when the data of agronomic characteristics were included, bringing data variation to the adjustment of the functions. however, they lose the advantage of the greater adjustment of the climatic data of the cli_m model. in the model validation dataset, the agr_m obtained the highest rmse (201 kg ha −1 ) and the cli_m model had the lowest rmse (191 kg ha −1 ), demonstrating the best fit in relation to the first (table ii). model-associated errors (mse) were relatively similar, with a tendency to be greater in the agr_m model than in the others, demonstrating the lowest fit and highest hyper parameterization of the ann. based on pearson's correlation statistics, all models obtained similar values close to 1. in the training dataset, the agr_m model presented the lowest rmse and mse values, characterizing its better performance in the adjustment in relation to the other two models that were very similar, with the smallest variation of the dataset. in turn, this situation is reversed, in validation, when the agr_m model presented the highest rmse and mse values. table i. hyperparameters of models with lower errors by grid search and k-fold crossvalidation with (i) and without (m) imputation for predicting grain yield (kg.ha−1) hyper parameters agr _m cli _m cop _m agri _i cli _i cop _i hidden layers 2 1 1 2 1 1 neurons 64 64 64 128 128 64 epochs 1000 1000 1000 1000 600 1000 batch size 128 32 64 128 32 64 learning rate 0.001 0.001 0.001 0.005 0.001 0.001 fig. 2. cost function (mse) training and k-fold cross-validation without data imputation for agr_i, cli_i and cop_i models. when imputing the missing data in the base, another set of hyperparameters was needed to reach the local optimum when submitted to grid search (table ii). this indicates that the missing data complement new standards for the adjustment of the models and that each one of them was changed differently with a greater number of hidden layers, neurons/layer, epochs, and batch size for agr_i, a smaller number of layers, batch size, epochs, and larger neurons/layer for cli_i, and fewer hidden layers and neurons/layer for cop_i among the 142 models trained by grid search and k-fold validation (table i). the changes between the non-imputed and imputed models were in the number of neurons, epochs, batch size, and learning rate, requiring a new ann architecture. considering that each neuron corresponds to a hyperplane, a greater number of 128 neurons for the agr_i and cop_i models is necessary to properly separate the instance space. only cop_i remained with the same number of neurons as the models without data imputation, characterizing the explanation of model adjustment using climate variables. to predict the behavior of parents for breeding programs, the architecture of the ann was optimized using 3 layers: the first with 64 neurons, the second with 32 neurons, and the third with 16 neurons, with the relu activating function having the highest accuracy of prediction [13]. the learning rate of agr_i was 0.005, demonstrating that the model was "stuck" in poor locations with a lower learning rate. only cli_i managed to converge in a smaller number of epochs, and 600 epochs reinforced the quality of the climate data for predicting productivity with the imputed data. the impact of data imputation on model training showed that the mse in 1000 epochs was lower than that of the models without data imputation for agr_m and cop_m (table i). however, the training was less consistent, as can be seen by the requirement for a greater number of epochs to start the adjustment of the imputed models agr_i, cli_i, and cop_i compared to the non-imputed models agr_m, cli_m, and cop_m (figures 2 and 3). one possible reason for this is that imputation increases data variability. table ii. metrics of models with and without imputation for predicting grain yield (kg.ha −1 ) metrics agr _m cli _m cop _m agr _i cli _i cop _i rmse validation 201 191 197 80 71 74 mse validation 414 365 390 87 60 60 correlation validation 0.99 0.99 0.99 1 1 1 r 2 (%) validation 0.9875 0.9819 0.9842 0.9978 0.9975 0.9983 rmse training 162 177 172 49 75 69 mse training 264 315 295 25 56 48 correlation training 1 0.99 0.99 1 1 1 r 2 (%) training 0.9912 0.9890 0.9907 0.9994 0.9986 0.9987 the curves of the models with imputation show that cli_i training and validation are closer than those of agr_i and cop_i (figure 3). in addition, the number of epochs needed to converge was smaller, so, it can be inferred from this model, with or without imputation of data, that climate explains the behavior of productivity. the imputed model that obtained the lowest rmse was cli_i with 71 kg.ha −1 , demonstrating an adequate fit with an error of just over one bag of maize per hectare (table ii). it is also possible to notice that the training and validation errors are similar, demonstrating that the model engineering, technology & applied science research vol. 13, no. 2, 2023, 10338-10346 10342 www.etasr.com duarte de souza et al.: maize yield prediction using artificial neural networks based on a trial … can generalize productivity prediction. however, agr_i obtained the highest validation rmse (80 kg ha −1 ), which allows adjusting the model to the training examples. the cop_i model obtained a validation rmse of 74 kg ha −1 . however, it tended to increase the error (mse) during training. in all models, there was a high correlation, with no significant differences with the models without data imputation. the agr_i model, when compared to the agr_m model, showed more overfitting to the training data (figures 1 and 2). like agr_m, the agr i model presents the same situation as the agronomic characteristics, which are not sufficient to explain productivity. this suggests that more agronomic traits are needed to increase grain yield prediction and that climate variables are fundamental for hybrid yield estimation. this can be confirmed by the cop_i and cop_m models, which consider all variables in the database; therefore, the training and validation curves are closer to each other. fig. 3. cost function (mse) training and k-fold cross-validation validation with data imputation for agr_i, cli_i and cop_i models. based on the metrics of the models, the imputation of data obtained superior performance compared to the base with missing data. the models with imputation presented rmse up to 3 times lower than those without, which suggests that the problem in question requires a reasonable amount of data so that the performance of the ann is increasing, but due to database reduction and imputation, the mlp models are adequate. the models with and without imputation obtained an rmse very close to 1% and 3% of grain yield which is considered very good. in the syngenta crop challenge 2018, with a productivity data set of 2,267 maize hybrids in 2,247 locations between 2008 and 2016, the of [10] was considered one of the best, with an rmse of 12% of the average yield using forecast weather data. using another strategy, maize yield prediction was performed with machine learning with different models, and the best of them, stacked lasso, presented a mean bias error (mbe) of 53 kg/ha and a relative rmse (rrmse) of 9.5% [32]. for the soybean crop, annual productivity was predicted in the region of the brazilian states of maranhão, tocantins, piauí, and bahia as a function of monthly climate variables (air temperature, precipitation, and global radiation) and water balance components (cultivation evapotranspiration, storage, actual cultivation evapotranspiration, water deficiency, and surplus) during plant development through a deep artificial neural network [33] with a dataset size of 920 examples, the obtained rmse was 167.85 kg.ha −1 . the unprecedented differential in the strategy of using climatic variables subdivided into maize plant development stages that are differentially sensitive to water stress was assertive. this can be the main reason why, even with a smaller database, the rmse of the models was smaller than that found in the literature. despite the generalization of the positioning of cultivars by different methodologies, either the traditional methods of adaptability and stability or ann models, the germplasm of the species must have a genetic response to the common stress in the region, as verified by the authors in [34, 35], who identified maize cultivars with different responses to nitrogen. authors in [36] identified the response of maize cultivars as a function of organic fertilization, and in [37] identified different responses of maize cultivars to irrigation with saline water. therefore, without genetic control of tolerance or resistance to stress, the differences between cultivars do not affect productivity, and it is simply dependent on the environment, being high when this is favorable. however, when tolerance or resistance to stress has genetic control, the environment with or without the presence of stress does not affect the productivity of the cultivar, as it is due to its genes. due to the importance of the cultivar in the models, it can be stated that there are differences between the cultivars how they interact with the environment. mlp models with different precisions do not allow us to identify which agronomic or climatic variables are the most important for predicting productivity. this can be achieved with shap analysis applied to the cop_i model, identifying the variables with the greatest impact on the model (figure 4). the most important variables were the cultivar, the average productivity of the cultivars/site, and the site itself (edaphic conditions), which is consistent with the agronomic explanation of the productivity of the cultivar, the physical and climatic environment, and the interaction of the cultivar with the environment [38]. the cultivar defines the productive potential of the environment and its limitations in certain environments. the adaptation of cultivars to the environment is related to their genetic adaptation to the soil, water regime, plant development cycle, absorption and use of nutrients, and tolerance to insects, pests, and diseases [39]. cultivar, productivity/location (prod_local), and location had the greatest impact on the output of the variable in the cop_i model. the prod_local defines the average productivity that can be obtained in a given location, showing the effect of the climate× soil×cultivar interaction. the local variable defines the edaphic conditions, latitude, and altitude of the environment. this means that the model was able to capture edaphic effects on productivity and the interaction between the cultivar and the environment. the environment, represented by the effect of climate and local conditions, is an important factor that can vary over time, and edaphic conditions are fixed between harvests [38]. eph (ear/plant height) ratio is an important characteristic of grain yield and is directly related to plant lodging, which directly interferes with harvesting when engineering, technology & applied science research vol. 13, no. 2, 2023, 10338-10346 10343 www.etasr.com duarte de souza et al.: maize yield prediction using artificial neural networks based on a trial … performed mechanically. however, it should be considered that the agronomic characteristics present genetic correlations, which are determinants in the expression of the phenotype when evaluated under a certain stress, which is also a cause of productivity [40]. in the results found, the evaluated agronomic characteristics and the cultivars were presented in a similar way, not being related to the climatic variables that explain productivity. relative humidity (rh), excess precipitation in the soil (ep), eph ratio, total daily precipitation (tp), minimum daily temperature (mt), soil water storage (ws), deficit precipitation in the soil (dp), wind with maximum daily gust (wg), evapotranspiration (ev), emergence (ve), forth leaf (v4), eighth leaf (v8), tassel (vt), silk and blister (r1_r2), physiological maturity (r6). fig. 4. average impact of the variables on the output of the cop_i model. in the emergency stage, only the relative air humidity (hr_ve) is important. the emergence of seedlings and their establishment provide the formation of a stand, which is the main component that explains productivity and is affected by hr_ve. relative air humidity plays an important role in plant transpiration and soil evaporation, making plants more sensitive to a lack of precipitation [41]. in the vegetative phase, during the fourth-leaf stage, only excess precipitation (ps_v4) was highlighted, and in the eighth-leaf stage, the total daily precipitation (pt_v8), minimum daily temperature (mt_v8), water storage (ws_v8), and precipitation deficit (pd_v8) were highlighted. mt_v8 and ps_v4 act together in plant growth and development, where the number of plants per hectare and plant height is defined. relative air humidity plays an important role in plant transpiration and soil evaporation, rendering the lack of precipitation more sensitive [41]. the minimum daily temperature is an important factor for the metabolism of corn and the entire c4 plant, inhibiting the rubisco enzyme that affects carbohydrate production, which is closely related to productivity [42]. the variables ps_v4, pt_v8, ws-v8, and pd_v8 related to precipitation are fundamental for the development of the plant and the prediction of productivity, requiring 3–4 mm in the initial stages of the corn plant and reaching the need close to 6-8 mm being the main parameters associated with the limitation of grain yield [43]. in tasseling, relative air humidity (ah_t), wind with maximum daily gust (wg_t), and precipitation deficit (pd_t) were important. the variable ah_t during this phase can affect grain production by reducing plant fertility in dry environments typical of the second crop sowing in february in são paulo state, brazil [44-45]. wind gusts can damage maize plant leaves, break plant culms, or bed down plants, causing a direct loss of harvest [46]. these results are consistent in predicting the performance of maize productivity and temperature in the flowering phase, and the frequency and the amount of water received during the vegetative phase, and grain filling were identified as the main environmental factors [47]. the lack of precipitation is considered the most important environmental parameter in bolting, delaying the coincidence of receptivity between male and female flowers and preventing fertilization [44, 48]. in the reproductive phase, in the silk and blister stage, relative humidity (rh_r1_r22), water storage (ws_r1_r22), and evapotranspiration (ev_r1_r22) were important. at the physiological maturity stage, total daily precipitation (tp_r6), minimum daily temperature (mt_r6), and excess precipitation (ep_r6) were important for predicting the model in the final stage of maturation and were related to plant physiology at this stage. this is justified by the intense water, thermal, and relative humidity requirements of the air at the beginning of filling and grain formation of the corn plant. note that the 30 days referring to the reproductive stages r3 to r5 did not influence productivity prediction. different climatic and water balance variables had different impacts on the stages of maize plant development, indicating that the partitioning of these variables must be carried out to increase the accuracy of the models. iv. discussion the different ann architectures of the models demonstrate a greater need for data or hyper parameterization for the agr_m model than for the other models due to the greater number of hidden layers and batch size. the cli_m model had the lowest data requirement for productivity prediction, characterizing the importance of environmental data in relation to hybrids when they were evaluated in groups with the same cycle. however, all three models without imputation showed good error estimates with values around 200 kg.ha -1 , which is considered small in yields that reach at least 6000 kg.ha -1 , representing only 3%. the agr_m, cli_m, and cop_m models with 3 hidden layers did not obtain optimal hyperparameters defined by the grid search and k-fold cross-validation in the databases without data imputation. only the models with 1 or 2 hidden layers obtained optimal hyperparameters, and therefore, the models with 3 layers were discarded. this may have occurred because the model tended to overfit the training data. the agr_m model required a larger batch size than the other two models for more consistent training, because the agronomic characteristics of the hybrids, such as the same cycle, height of plants and spikes, and grain productivity, are similar or very close, because brazilian legislation requires that the new cultivars must be at least equal to those on the market in terms of productivity, even though the germplasms that originated from different hybrids have some similarity between the companies. therefore, the agronomic characteristics of the hybrids do not concisely explain the different yields between engineering, technology & applied science research vol. 13, no. 2, 2023, 10338-10346 10344 www.etasr.com duarte de souza et al.: maize yield prediction using artificial neural networks based on a trial … the environments since none of the hybrids capitalized on the genotype×environment interaction between the evaluated microregions. this similarity between the hybrids required different batch sizes of the cli_m and cop_m models for adjustment. the mlp-ann models with imputation (i) showed lower errors than the models without imputation (m), lower ann architecture requirements, and even fewer epochs. the set of routines for maize hybrid evaluation is more suitable for use in mlp-ann models when data imputation is applied. different architectures of the mlp-ann models with smaller batch sizes, layers, or epochs occur for the cli_m and cli-i models. they also present the smallest errors and converge in models more assertively even with climate data from distant meteorological stations, from 27 to 100 km. this characterizes the robustness of the mlp-rna models and the importance of climate data in predicting productivity in relation to the agronomic data of hybrids that present significant differences in their productivity [17, 18]. the agr_m and agr_i models that are based only on the agronomic data of corn hybrids require a greater process capacity and more complex models with larger batch sizes, layers, and times. the agr_i model had the lowest precision (0.005) among all models. the accuracy of the models characterizes their adequacy. it was also found that, in several scientific publications in experiments evaluating the productivity of maize hybrids, the coefficients of variation were equal to or less than 12%, which can characterize minimal significant differences between the hybrids than 600 kg.ha -1 , considering yields from 5 ton.ha -1 . significant differences between corn hybrids in experiments as to their yields were detected when their differences were greater than 12%, as verified in 143 experiments in 15 years of publications with the maize crop for the grain yield, in which the average coefficient of variation was 11.87% [49]. when dealing with both agronomic and climatic characteristics, the cop_m and cop_i models bring to their iterations the difficulties encountered with the agr models. however, with data imputation, the agr_i model presents an mse close to the cop_i's but requires a greater number of epochs. the low rmse values can be explained by the methodology used to evaluate the climatic data in the different stages of plant development, which were strategically correct and possibly the cause of the success of the arn used. this was confirmed by the importance of different climatic parameters and water balance as variables of importance in the construction of the model. this also allows the model to be used in advance according to the stages of development of the plant, allowing for more assertive decision-making in different scenarios and moments of the crop. therefore, those in charge of the crop can obtain new information at the time of sowing and at the time of cultural practices and fertilization during the vegetative phase, where it is still possible to manage the crops when they are not irrigated. when crops are irrigated, it is possible to manage the application throughout the plant's development, especially at the most critical times, such as grain filling. the models can detect the non-linear effects between climate, soils, and genotypes, especially when climate information is included in the model or when they are sufficient to predict grain yield, even with several hybrids that have the same cycle. the results of the models are adequate, even considering the limited amount of data analyzed on the anns and their application in the processes of the improvement programs without the need for modifications in the processes. the ann models can identify important variables during the development stage of the plant, and it is observed that climatic and water balance variables are important. the water balance variables are important at all the stages of maize plant development and demonstrate the availability of water that is stored in the soil and that can be used by the plant, being the main environmental parameter limiting productivity [48]. new environmental parameters can be incorporated into the ann models, further increasing their accuracy. an ann based on a graph-based framework developed by graph neural network-recurrent neural network (gnn-rnn), using geospatial and temporal information to predict crop productivity was proposed in [11]. v. conclusion  the implemented anns managed to extract a pattern in the data even if the locations of the experiments and cultivars were different, which shows the capacity of the anns in the generalization of productivity prediction.  the ann models are well suited for predicting corn yield and present concise training, even with a limitation in the amount of data, when exclusively using the agronomic characteristics of the hybrids. this limitation is overcome when climatic data are incorporated into the model 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[49] r. fritsche-neto, r. a. vieira, c. a. scapim, g. v. miranda, and l. m. rezende, "updating the ranking of the coefficients of variation from maize experiments," acta scientiarum. agronomy, vol. 34, pp. 99–101, mar. 2012, https://doi.org/10.4025/actasciagron.v34i1.13115. microsoft word 535-ed.doc engineering, technology & applied science research vol. 5, no. 2, 2015, 781-789 781 www.etasr.com fernandes: value analysis, going into a further dimension value analysis going into a further dimension manuel t. fernandes caam – corporate academy for advanced management (by gestão total) samora correia, portugal mtf@gestaototal.com abstract—value analysis (va), as it was originally conceived, was defined and applied as a cost cutting tool, in order to make products more competitive. that short scope was early identified as limiting further developments and applications of the concept, by its initial pathfinder, if no extra effort was made to take the concept into other levels of management and, consequently, of business. the many different and alternative applications of the concept and of its original methodology have taken many professional practitioners and scholars to theorize and apply new concepts and methods. we can find a tremendous number of different learning exercises and theoretical evolution from that work, but that has not yet answered many aspirations regarding the initial concept of value and value analysis. this paper aims at bringing a new and more comprehensive understanding to professional practitioners, scholars, trainers and students, about some major concepts and applied methodologies in the disciplines of value management (vm), value analysis (va) and value engineering (ve). keywords – value; value analysis; function; function analysis; value management i. introduction there is a wide view among professional practitioners and scholars of the application of some managerial tools in the field of value management (vm). this is part of the concept of value analysis (va) in itself, which leaves the application of the methodologies up to individual criteria with enough freedom for its adaptation to contexts and objectives. despite the benefits of such freedom in the application of the methods and tools in the disciplines of value management, value analysis, and functional analysis (fa), such “liberty” has led to settled variations in the practice of some of those methods. this reality can be found in many papers presented in different professional conferences across continents and in some existing literature, especially in given examples of real applications. although most professional practitioners can differentiate and understand such subtle or evident divergences in practices, new comers to the discipline of value management may find it difficult to comprehend how such divergences can exist. this opens the discussion about the desired standard application of some methods, which this paper aims to touch. my individual practice and the observation of other professionals’ practices in many documented applications have helped me develop my own methodologies in my value management entrepreneurial and consulting activities. that will be explored in this article. ii. concepts and literature review the following literature review of concepts is restricted to the disciplines of value management, value analysis and value engineering (ve). as most literature repeats the same ideas and definitions in a very short range of variations, this review will focus on the best known and disseminated texts. in the same way, this literature review will only focus on aspects that are relevant to the purpose of this article, leaving out many issues related to the methodologies around value analysis, and therefore subjected to the readers own research in order to complete the full vision of the entire subject. a. the concept of value miles [1], the main pathfinder of value analysis, had in his day questioned the future application of the concept in business: “the basic question is: what do we really have in value analysis? what we have is a tremendous problemsolving system.” (p.69). in miles’s opinion, value had to go on a new and different path in supporting business development, rather than keeping its action, as at the time, exclusively in the field of “cost reduction”. he continued on his new vision for value analysis: “it becomes essential that we in value analysis work to help modify the management of areas into which the work will go. at the same time, we must further change our approaches in value analysis so that we are modifying the seed and the soil together without taking the strength out of the problem-solving approach” (p.70). this would mean, at that time, going one dimension further ahead in value analyses. many other professional practitioners and scholars have brought this issue up to the public and professional level, including into the standardization arena. before going any further in pursuit of how value analysis has evolved or is yet evolving, we need to understand what value is or may be. generally, value is understood as expressing the worth of something. but a closer look into the existing literature can reveal different types of value, as jensen [2] has identified: (i) economic value – or value as exchange; (ii) use value – or value as utility; (iii) cultural value – or value as meaning and sign; and, (iv) perception value – or value as experience. cross-disciplinary research proves those findings. to smith [3] any “good” had two different meanings, one expressing the utility of the same particular object, “value in use”, and the other, the power that the possession of the object conveys to engineering, technology & applied science research vol. 5, no. 2, 2015, 781-789 782 www.etasr.com fernandes: value analysis, going into a further dimension purchase other goods, “value in exchange”. [aristotle (384-322 b.c.) was the first to differentiate between a use value and an exchange value of goods. (politics, book i.)]. according to kopytoff [4], this is what defines a “commodity”: “an item with use value that also has exchange value” (p. 64). the consumer or user is at the center of this inter-relation of different types of value in the same good, leading value to be understood as a perception function, represented by the equation “customer perceived value=perceived benefits/perceived sacrifice”, as referred by ravald and gronroos [5]. another way to view the issue, supported by anderson, narus and kumar [6], is that “customer perceived value=customer benefits–customer sacrifices”, arguing that this is easier to be understood by individuals and businesses. we should note that perceived value differs from “desired value”, where the last represents what the customer wants to happen and the first represents what the customer has obtained or that it has happened. according to flint, woodruff and gardial [7], desire value can take two aspects: value in use and possession value. clawson and vinson [8] argue that, in order to investigate consumer’s product valuation, it is necessary to integrate cultural values, personal values, consumption values, and product benefits. to engel, blackwell and miniard [9], cultural values are related to how cultural, social and familial environments affect the formation and development of individual beliefs, also called “society core values”, which are implanted naturally through socialization and education. personal values are the individuals’ beliefs about what is desirable for themselves, therefore self-centered, deriving from and modified through personal, social, and cultural learning (clawson and vinson, op. cit.). rokeach [10] divides “human values” into two types: terminal (or end-state), beliefs about goals that people strive for, like self-fulfillment and enjoyment in life, and instrumental (or means), beliefs about desirable ways to attain those terminal values, like owning a luxury car or going to an entertainment event. personal values correspond to terminal values, while instrumental values are comparable to values of desirable “activities”. according to sheth, newman and gross [11], people achieve personal values, or goals, through actions or activities, such as social interaction, economic exchange, possession, and consumption. consumption values refer to subjective beliefs about desirable manners to attain personal values, therefore being instrumental in nature. to hooley and saunders, product benefits refer to what customers benefit from buying, using or consuming a product [12]. in the customers’ perspective, product benefits are not the same as product attributes, as argued by day [13] and by peter and olson [14]). in a competitive market, products have many attributes such as features, durability, quality, style, symbolism and related services, in addition to the basic provided benefits. i will return to the issue of benefits later on. according to boztepe [15], value can be something assigned by the user, being independent of the product’s physical qualities, or embedded in the object and recognized by the user. this leads to the view of a philosophical branch concerned with the theory of value, known as axiology, which posits a bipolar distinction between objectivism (utilitarian or instrumental use of a particular solution as a means to a specific end) and subjectivism (emotional appreciation of the consumption), as argued by hartman [16]. positioning value as inherent to an object, prior to any subject interaction or evaluation, is an objectivist view. on the other hand, if it is the user understanding that prevails, including many other factors under consideration, it can be seen as a subjectivist view. this dichotomy between objectivism and subjectivism views leads to a discussion between tangible or intangible, use or emotion, and utility or esteem, which i will address later, together with the issue of measuring value. this continued “consumer perspective” creates a need to understand consumers in a much wider extension. one of the many ways to understand users’ needs, as consumers, is studying their specific functional and emotional needs and, consequently, transforming those into product attributes or functionalities [17]. value analysis contributes to that understanding through a process of functional analysis and function costing [18], determining the relation between the satisfaction of needs and wants and the resources utilized, being this relationship called “value”. according to the european norm en 1325:2014 [19] value is the “measure which expresses how well an organization, project, or product satisfies stakeholders’ needs in relation to the resources consumed”. on the other hand, according to the save international value standard [20] value is “defined as a fair return or equivalent in goods, services or money for something exchanged. value is commonly represented by the relationship: valuefunction/resources”. both versions of the same concept of value were initially mostly based on the satisfaction of the user’s needs, but it has been developing into the concept that value also speaks to all other stakeholders in the same manner, as expressed in the value management handbook [21] and the european norm en 12973:2000 [22]. integrating all previous views and trying to encompass all possible situations of value applicability, i came to the definition of value as “the relationship between the output(s) and/or outcome(s) [expected benefits] provided by a thing or event, to an individual person or group of people, and the effort [potential sacrifice] consumed to acquire, use or make it happen” [23]. i will come to this later, to explain the rational behind this conclusion. if we consider that all stakeholders have some kind of interest in a product and in its life cycle, that opens an opportunity to determine who out of the same stakeholders will be affected positively (positive value) and who may be impacted negatively (negative value) by the value subject. in the same fashion, different stakeholders may take advantages and benefits from some attributes or functions of the product and its life cycle in utility (tangible/use value) or emotional terms (intangible/esteem value). these wider visions of what value is or may be take us to a new journey into the discipline of value analysis, as we need to contemplate all of those variations of value in our analytical process. as mentioned before, value is generally understood as the result of a transaction between two parties, where the equation engineering, technology & applied science research vol. 5, no. 2, 2015, 781-789 783 www.etasr.com fernandes: value analysis, going into a further dimension “value=benefit/sacrifice” is mostly taken into account. benefits may respond to requirements (needs or wants). benefits can be positive, subjected to being expressed as gain, or negative, therefore expressed as a loss or damage, and, consequently, linked to risk. lay [24] proposes a typology of benefits related to products that consumers may derive from possession or consumption, including eight generic product benefits: functional, social, affective, epistemic, aesthetic, hedonistic, situational, and holistic. (i) functional benefits are related to a product’s capacity for functional, utilitarian, or physical performance, deriving from tangible and concrete attributes that consumers may experience when using or consuming a product. (ii) social benefits are perceptual benefits related to a product’s association with social class, social status, or specific social group. (iii) affective benefits refer to the perceptual benefits deriving from a product’s capacity to enhance feelings or affective states, associated with cultural-ethnic meanings or personal idiosyncratic meanings, tastes and memories. (iv) epistemic benefits are the benefits acquired from a product’s capacity to satisfy curiosity, provide novelty, and meet a desire for knowledge. (v) aesthetic benefits are the benefits acquired from a product’s capacity to present a sense of beauty or to enhance personal expression. (vi) hedonic benefits are the benefits acquired from a product’s capacity to meet a need of enjoyment, fun, pleasure, or distraction from work or anxiety. (vii) situational benefits are the benefits acquired from a product’s capacity to meet situational needs and specific situations, measured on the profile of a particular consumption circumstance. (viii) holistic benefits are the perceptual benefits acquired from the complementarities, coherence, compatibility, and consistency in a product constellation as a whole. still according to lay [24], customers’ evaluation of a product purchase begins from their perceived product benefits based on their terminal personal values and instrumental consumption values. against the cost-and-benefit principle, which states that customers evaluate benefits against cost, lay [24] proposes that customers’ evaluation is based on three major inputs: “perceived product benefits”, “perceived logistic benefits” and “perceived costs”. value is, therefore, extended to a multidimensional level. benefits are what consumers and users take out of product attributes, and attributes are representations of functions. functions deliver value of any of the types identified before. all those are expressed by the voice of the consumer (customer). the subject of the voice of the consumer is very important in the study of value, if one wants to evaluate the same value in an accurate manner. many other value management tools such as quality function deployment (qfd), use the voice of the customer to determine the desired value to be delivered [25]. the voice of the consumer reaches special relevance when determining the demanding importance of the attributes of a product, as argued by zaltman and coulter [26] and hauser [27]. in the opposite way, the voice of the consumer can be used to identify problems and dissatisfaction [28]. all these issues will be brought into play in this article, as new elements to be taken into consideration when i present my method to perform functional analysis. that is part of my work in developing an approach in accordance with miles’s [1] desire in taking value analysis into a further dimension. b. the concept of function the european norm en 1325:2014 [19] defines function as the “effect of a product or of one of its constituents”. the standard notes that: (i) “functions should be expressed in an abstract form, free of technical solutions”; and, (ii) “functions may describe what a product or its component parts must do (meet customer requirements) or what product or component parts actually do or achieve”. according to save [29] “a function is that which makes an item or service work or sell— in other words, an item’s function is why the customer buys the product or service. an item, including structures and services, is a means to the end of providing a function, not the end itself”. rich and holweg [30] argue that a “function can be defined as the use demanded of a part of a product and the esteem value that it provides. these functions therefore make the product work effectively or contribute to the ‘saleability’ of the product”. not being too far apart from one another, these views demonstrate the importance of understanding functions in products (goods or services). product functions are, in fact, what deliver outputs and outcomes to users and other interested parties. if a product does not perform any function, it is of no use and, therefore, of no value whatsoever. we may find different actors, or interested parties, involved and with interests in a given subject of value, represented by a product (good or service) or not (event), and that will lead us to identify a variety of functions related to those. the european norm en 1325:2014 [19] identifies some different types of functions of interest to this paper: (i) “user related function – effect expected from a product, or performed by it, in order to meet a part of the need of a definite user”. this type of function represents what the product does or delivers and can be of use or esteem, being this the unique interest that users and the market may have in the product; (ii) “product related function – impact of the product, what the product does, and the effect of a constituent or the effect between constituents of the product for the purpose of performing user related functions that might be either necessary or unnecessary, desirable or undesirable”. this type of function represents how the product delivers the user related function (use or esteem), and it can be related to the technology applied to produce the desired result or effect; (iii) “unnecessary function function that does not contribute to the satisfaction of the need of a user, and so has no positive contribution to the value of the product”; (iv) “undesirable function function which has an adverse effect for the user, sustainability or the environment. it has a negative contribution to the value of the product”. this type of function generally represents the unanticipated result of the technical choices or the result of waste; (v) “basic function need which must be (or is) fulfilled in full”; (vi) “primary function high level function which communicates the functional purpose of the product”; (vii) “secondary function function which contributes to the fulfillment of a primary function”; (viii) “supporting function function which engineering, technology & applied science research vol. 5, no. 2, 2015, 781-789 784 www.etasr.com fernandes: value analysis, going into a further dimension maintains the conditions for the fulfillment of several primary functions”. this type of function may be associated with organizational support and brand perception that may be outside the scope of a specific value management study or value management program. save [29] classifies functions as: (i) “basic function the primary purpose(s) for which the item or service was designed when it is operating in its normally prescribed manner. this function must be accomplished to meet the purpose of the product, structure, or service.” a product (good or service) may have more than one basic function. some professional practitioners may call it “primary” function; (ii) “secondary functions are ones that support the basic function (and, hence, are sometimes referred to as “support functions”). they result from a specific design approach to achieve the basic function. if the design changes, the need for existing secondary functions may be modified or even eliminated”. some professional practitioners may break secondary functions into a subclassification of “required”, “aesthetic”, and “unwanted”. the differences in nomenclature used by the two parties are not relevant to the exercise of value analysis per se. despite the fact that americans and europeans currently use different terminologies, the semantics remain the same and there are no major obstacles for a clear understanding between the parties. since the very beginning of the value analysis discipline, and as defined by save [29] and accepted by all other professional and scholar players, a function “is always expressed by a verb and noun”, and it “must be expressed in a measurable parameter in order to obtain a value for it later in the analysis. nouns may be either measurable or non measurable. non measurable nouns must be explained so that they may be translated into a measurable element and later evaluated”. active verbs, denoting action, instead of passive verbs, are preferable in the description of the functions. despite the advisable use of two words, a verb and a noun, to describe a function, extra description should be provided in order to give full meaning to the narrative. the description used has to be as clear as possible in order to avoid misunderstandings and confusion in future utilization of such narrative. c. the concept of function analysis the function analysis is the “process that describes the functions and their relationships, which are systematically characterized, classified and evaluated” [19]. there are two approaches to function analysis: (i) the functional need analysis (or external function analysis), related to use or esteem functions; and, (ii) the technical function analysis (or internal function analysis) related to product functions. there are several methods of performing a function analysis exercise, supported by different tools, in order to identify, classify and evaluate functions. the simpler methods are the “natural or intuitive search” of functions and the “random function identification”, supported by exercises of brainstorming. the “function tree diagram” method (also known as “value tree diagram”), the method of “interaction with external environment” (also known as the roseta method) and the “functional analysis system technique” (fast), are used for more complex value subjects analysis. as this article is not aiming at doing any comparison of function analysis methods, like the ones just mentioned above which are well documented in existing literature, it is appropriate to leave this issue for later discussion when i revise some concepts in the discipline of value analysis. nevertheless, all methods identified aim at evaluating the importance of each individual function in order to compare its relative importance against its relative cost, as we will see next. d. the concept of function cost the european norm en 1325:2014 [19] defines function cost as the “whole of the expenditure forecast or incurred for including a function in a va subject”. the standard also notes that: “before design or re-design, the function cost is a target or a limit: the expenditure which is granted for including that function. after development or implementation, the function cost is the cost which has been effectively incurred”. save [29] refers that “it is the cost function relationship that often vividly illustrates where unnecessary costs exist within the study project”. according to almost every existing scholar and professional literature and training program, the process of function costing can be divided in four phases: (i) identification of all components that are or will be part of the value subject. components of a value subject can be parts (composed of materials, labor and other costs) and services (composed of activities and other costs related to the utilization of equipments and others); (ii) calculation of the cost of every component (parts and services) of the value subject. this costing exercise must be as extensive as possible, including all possible elements of cost; (iii) assignment of existing or future relationships between each function and each component. one component may be assigned to one or more functions and vice versa; and, (iv) assignments of corresponding cost to each function based upon the assigned relationship with components (parts or services). according to one initial definition of value, the cost of each function is essential to determine the value of the same function: value=function/cost. however, as this cost may not include all possible sacrifices that a given user or any other interested party may have to deliver in order to make full use of the value subject (product), the concept has been adapted, transforming cost into resources used. despite such a theoretical change being accepted by almost every professional practitioner and scholar, the observance of common practices shows that in most instances, the quantification of resources used is limited to the monetary costs of components (parts and services), determined by the economical value (monetary value) of raw materials or equivalent, plus labor, and plus direct and indirect costs, mostly determined at the production stage. that observance leads to questioning the accuracy of the method applied in such fashion. this will be brought up again during the next discussion on revising some concepts. engineering, technology & applied science research vol. 5, no. 2, 2015, 781-789 785 www.etasr.com fernandes: value analysis, going into a further dimension iii. revising some concepts in my recent entrepreneurial and professional experience, i have come to use a well-defined set of self-created concepts and definitions related to value analysis and extended to value management. they took form along many years of activity and research and are mainly the result of revising existing concepts and definitions according to my learning and practical experience. some of that work is reflected next. a. value if one needs to understand what value is, one has to go back to nature to under the phenomenon. if we consider that in the universe the total quantity of existing energy is a constant, despite the various forms that energy may have, the total “value” of that same energy also remains constant. therefore, any mutation in the energy form, like solid changing into liquid, does not affect the total value, as there is no loss of energy in such mutation. consequently, the universe and nature in its basic form do not use or apply the concept of value, at least not as implicitly defined by the equation “value=benefits/sacrifice”. however, any form of existing life on earth seems to understand and apply the above principle of value. any tree, being placed between dry and wet land, directs its roots mainly towards where the water is, reducing the effort of sending roots all around in full length. animals only fight for food when the reward is higher than the effort (sacrifice) spent to get it. humans do the same, even at the sub-conscious level, when making the least important decision in their lives. it seems that “value” is in any decision making process. i argue that, based on such evidences, “value is the absolute criteria used in any decision making process, based on the relationship between expected benefits versus potential sacrifice to be made”. therefore, in terms of the disciplines of value management and value analysis, “value is the relationship between the output(s) and/or outcome(s) [expected benefits] provided by a thing or event, to an individual person or group of people, and the effort [potential sacrifice] consumed to acquire, use or make it happen” [23], as previously stated. this conceptualization still maintains value as the result or expression of a measurement, staying in accordance with existing accepted definitions. b. attributes an attribute is a permanent or timely condition of a solution (product) to some consumer need. an attribute is not defined by any action in particular, like functions, but rather by a given status quo that is intrinsic to the solution/product. attributes are properties, predicates, features, dimensions, characteristics or even independent variables, depending on the context that defines the product. an attribute is not necessarily defined by a verb, but if so, it is likely to be a passive one such as to be, to have, to cost, to give, to enhance, or to seem. starting from the concept that consumers or users understand value as represented by the equation “value=benefits/sacrifice”, we may accept that attributes can be related to benefits and to sacrifices. attributes that are benefits may be “resistance”, “duration”, “design”, “accessibility”, “taste”, “sound” or “pleasure”. attributes that are sacrifices may be “cost”, “assemblage”, “transportation”, “storage”, “disposure”, or “displeasure”. however, some of these attributes, depending on the context, can transform from benefit into sacrifice, like sound that becomes loud noise, or from sacrifice into benefit, like making the assemblage of a product that becomes pleasant entertainment. a color, like (being) blue, is an attribute. this can be a benefit to some or a sacrifice to others, depending on the context and of what one does with that attribute. we also need to bring into play other conditional factors of value to understand attributes. before, we identified four types of value: economic value; use value; cultural value; and perception value. economic value is mostly related to (monetary) costs, therefore a sacrifice, from a purchaser point of view, but it can be seen as a benefit if the cost, or price, represents accumulation of value of some kind to the holder. economic value can also be a benefit to the seller if a thing is sold at a profit. therefore, economic value is related to different and almost all attributes, being at the same time a benefit and a sacrifice, depending on the standing point of each interested party. perception value, like economic value, also very much depends on the standing point of each interested party and can be simultaneously a benefit or a sacrifice to different interested parties. these two types of value are very much diffused in any set of attributes of a solution (product) and they can transform into any of the next types of value that we will see next, as they lose their own independent definition in the context of attributes. use value is connected to most attributes in a solution (product). consumers or users, and any other interested party, perceive the value of a solution based on the use value that it may deliver. in other words, the utility of the solution is fundamental for the existence of value in it. a product with no utility has no use value or no “value” at all, for this matter. the level of use of a product, expressed in its set of “utility attributes”, may affect the economical value or the perception value of the whole product. the utilities of a product are, most of the time, benefits to some interested parties, mainly consumers or users, but can also be a sacrifice in some contexts to other interested parties. therefore, we may find that utility attributes can be benefits or sacrifice, and that must be clearly identified in any value analysis exercise. cultural value may be connected to some attributes of a solution (product). consumers and users, or any other interested party, may find cultural value in some attributes of a product. a given design style applied to a product may provide it with cultural value. the cultural value is mostly felt at the emotional level or sphere of any consumer or user, or of any other interested party. the level of cultural value in a product, expressed by “emotional attributes”, may affect the economic value or the perception value of the same product. in conclusion, we may find some attributes in a product that are benefits to someone, and other attributes that are sacrifices to the same person or to somebody else. at the same time, those attributes can be of utility or emotional. engineering, technology & applied science research vol. 5, no. 2, 2015, 781-789 786 www.etasr.com fernandes: value analysis, going into a further dimension attributes are what the consumer or user, or any other interested party, sees in a solution (product) to solve a need. in order to deliver the desired solution to a need, the product must perform some functions. this logical path connects attributes to functions. i will discuss this issue next. c. functions starting from the attribute side of a solution (product), and taking for good that there are some direct connections between attributes and functions, we can rapidly arrive at the functions that are representations of the former. if we consider the utility attributes, then we must find a service function that performs in such a way that the need implicitly connected to the attribute is conveniently answered. i call this the “use related function”. the same happens if we consider an emotional attribute, where some service function must provide the required answer to some need. in this case, i call it “esteem service function”. however, if on the one hand a utility attribute is answered mostly by a use service function, on the other hand, an emotional attribute can, and is likely to be answered by both types of service function – use service functions and esteem service function. occasionally, an esteem service function may turn into a utility attribute. the use service function provides some tangible answer, measurable and predictable. the esteem service function provides some intangible answer, very difficult, if not impossible to measure and unpredictable. continuing from the service functions point of view of a solution (product), and taking for good what literature refers, we can arrive at another level of functions that answer the first. these are the product related functions, also known as internal or secondary functions. following the same rational previously used, a use service function must be connected or answered by one or more product functions, which i call “hard-product/technical function” as most answers are given through a technological solution. an esteem service function, following the same logic, should be answered by one or more product functions, which, in this case, i call “soft-product/cultural function”, as the answers are provided through human actions, with or without the support of technology, that induce human behavior as part of a given culture. however, esteem service functions may also be connected to hard-product/technical functions, as used service function may be connected to soft-product/cultural function, and that will affect function cost, as we will discuss later. summarizing, we may establish connections between attributes and service functions, and between service functions and product functions, as in figure 1. examples of these types of attributes and functions will be provided ahead. fig. 1. connections between attributes and functions d. function analysis i have been using, for a while now, a combination of techniques to execute functional analysis. the first step is defining, with the organization sponsoring the project, the composition of the working team in such a manner that the team includes someone representing each and every interested parties, taking into special consideration the consumer’s voice, who must represent the needs and wants of consumers and users. this is, anyway, a step taken by everybody working in functional analysis. then, i start, with the project team, by identifying all potential interested parties in the value subject under study, even if not represented in the project team. that covers all entities, internal and external to the organization or holder of the value subject, under study. to find all interested parties, we ask four questions: (i) who interacts directly with the value subject?; (ii) who reaps benefits from the value subject?; (iii) who can be affected negatively by the value subject?; and, who has to provide effort (sacrifice) for the value subject to exist? for that purpose, i use an adaptation of allee’s value network methodology [31]. once all the interested parties are identified, the team identifies the potential transactions that may occur between those entities. transactions are understood as an exchange, in one or both directions, between two or more entities. transactions can be tangible if they are measurable, like transacting products, money, services, data or information, or intangible if they are not measurable, like transacting behaviors (i.e. misuse of an equipment, avoidance to use a product, or referring a service to someone else) and feelings (i.e. happiness, trustfulness, or confidence). the next step is identifying all interactions that the entities (interested parties) may have with the value subject. for this purpose, three questions are asked: (i) what are the direct interactions between each interested party and the value subject?; (ii) what are the interactions between the value subject and any other system or sub-system?; and, (iii) what are the interactions between the value subject and the environment (the whole physical context). this follows the “roseta” method previously identified. the questions are mainly placed in reference to all identified transactions. normally, this exercise uncovers other transactions not considered until that point in time. out of each transaction, tangible or intangible, and related interactions, the team identifies corresponding attributes that may be considered by each of the interested parties in their own judgment in classifying the value subject (product). after listing all transactions, related interactions, and consequent attributes, the team identifies the needed corresponding service functions that answer those. at the same time and for each service function identified, either use service functions or esteem service functions, the team identifies the needed corresponding product function or functions, hardproduct/technical functions or soft-product/cultural functions, respectively. in order to follow the logic flow, from transactions, at one end, to product functions, at the other end, the team always has to ask the question “how”, as following: – (i) question: how is engineering, technology & applied science research vol. 5, no. 2, 2015, 781-789 787 www.etasr.com fernandes: value analysis, going into a further dimension such transaction solved? answer: by such interaction; (ii) question: how is such interaction answered? answer: by such attribute; (iii) question: how is such attribute answered? answer: by such service function; (iv) question: how is such service function answered? answer: by such product function. this technique follows the previously mentioned fast method. we can also use the “why” question to validate the sense and correctness of the answer to the “how” question, but inverting the direction of the flow. we should note that this process of questioning and answering is very dynamic and often we can work with multiple transactions, interactions, attributes, service functions and product functions at one time. when the full exercise is completed and all service functions are identified, isolated, and validated, the project team connects them to the identified interested parties, following the value creation stream flow by this order: (i) who has to provide the function; (ii) who is served by the function. this provides a view of the relevance and level of interest of each interested party. for better visualization of such relevance and level of interest, the team builds a pyramid with all interested parties. at the top of the pyramid is the last interested party or parties to be served by a service function, normally the user. at the bottom of the pyramid are all interested parties that have to provide functions to others, normally the manufacturer or service provider. then, two exercises of relative importance evaluation must be performed: (i) an exercise with all the identified service functions, taking into consideration the relevant participation or level of interest of each identified interested party, and (ii) one individual exercise by an interested party, only including the service functions related to the same interested party. as a note of precaution, the team must make sure that only service functions are included in the exercise of measuring the relative importance. the inclusion, in this relative importance evaluation, of attributes or product functions, to be compared with service functions, completely destroys the accuracy of the evaluation. e. function cost the function cost exercise can be of some complexity in some cases, when a deeper understanding of the “real cost” is required. we must keep in mind that we are not looking only at the monetary cost of functions but also at all other resources used or applied to obtain those functions. in my activities, i take the project team to do the service function costing in two stages: (i) the cost of a service function (use or esteem) is in the product functions (technical or cultural) that provide answer to the former. the hardproduct/technical functions are provided by the application of some kind of technology, through the utilization of components: parts – material, labor and other direct and indirect costs like r&d or design; and, services – storage, shipping, installation, advertising or guaranty, therefore subject to monetary costing. then, the cost of each component (part or service) is proportionally assigned to the service functions to which the hard-product/technical function is related. this first stage of monetary costing of all hard-product/technical functions is calculated according to the costs of the holder of the study (i.e. manufacturer); (ii) using the previously established use service functions cost, there is a need to adjust it to each individual interested party, taking into consideration the extra resources applied or used by the same interested party, if we want to do a comparison of the relative importance with the relative cost of service functions by each individual interested party. these costs may be related to shipping, storage, assemblage, distribution, communication and others within the exclusive relationship to each of the individual interested parties. this exercise will calculate costs for components (parts and services) that may be assigned, according to their contribution, to the corresponding use service functions and esteem service functions. the cost of the handle (component) of a kettle (value subject) may be assigned exclusively to a use service function (facilitate pouring water) if it only has that purpose (utility attribute), or it can also be assigned to an esteem service function (providing sign) if it is made of some noble material (gold plated), or in case it also has a special uniqueness meaning (emotional attribute). the soft-product/cultural function cost calculation was left out of the above exercise description because that needs a special narrative. normally, a soft-product/cultural function is associated with the brand name of the product and the pride or other feelings that users may have in using it, or the confidence that the brand transmits to users. but it can also be associated with some design style, artistic connection, compliancy assurance and novelty. all those sources for any softproduct/cultural function are intangible, which makes these functions impossible or almost impossible to be a cost. in some cases, the project team establishes a cost for those “cultural” sources that can be imputed to the value subject. using the above example of the kettle, the design style of the handle and its authorship may induce some extra esteem value to the product (enhance collection), which is impossible to cost in accordance with any economic monetary term, therefore a “value” has to be put on it as representing the extra value that the feature adds to the value subject. f. new practice the introduction of the concepts of tangible and intangible transactions and utility and emotional attributes are new and unexpected for many professional practitioners and scholars. the introduction of such concepts in my professional practice are due to the necessity of bringing a better understanding of needs to all interested parties, and of expressing functions in a common day-to-day language understandable to most people, mainly for consumers and users. the tangible and intangible transactions extracted from the value network exercise are the expression of implicit needs of each and all interested parties. this exercise avoids the potential missing of interested parties and needs that normally are not expressed in brainstorming exercises. the utility and emotional attributes are the expression of the use and esteem service functions of any product. the wording of attributes is used to reach consumers and users in engineering, technology & applied science research vol. 5, no. 2, 2015, 781-789 788 www.etasr.com fernandes: value analysis, going into a further dimension clearer and more understandable marketing and communicational activities. the attributes description is mostly used in marketing activities, reaching the target in their language terms, therefore easier to be understood and assimilated. this is one of the most appreciated results that participants take out of value analysis exercises, according to my experience. the recent work led me to standardize the value study process, as shown in figure 2. fig. 2. value study process flow iv. conclusions going back to miles’s [1] initial question: “what do we really have in value analyses?”, we may conclude that it goes far beyond the simple “cost cutting” objective that served the creation of value analysis. in fact, value has a major and vaster scope of application than the simple cost cutting exercise that is still used in many cases. value is strategic to every business: either they produce or sell commodities or premium products. in the first case, even if the importance of costs cutting is unavoidable, there is much more to consider, like identifying the value of the product for each interested party and work improvements from that status quo position. in the case of premium products, their value is based on the intangibilities that are attached to them by many different emotional attributes and esteem functions. and that brings value into a different and further dimension. this article, reflecting my professional work, is part of an ongoing challenge since i was once questioned “if value is so important, why isn’t the value management methodology used by everyone in business?”. despite the work already developed and the conclusions extracted, there is still a great need for further practice in the utilization of the concepts and methods explored in this article. professional practitioners and scholars must apply, evaluate and discuss this issue further, in the same fashion that i have done, or in any other manner, always keeping in mind that we need to progress in the development of value analysis in order to answer the miles’s initial inevitable question. references [1] l. d. miles, “the challenge that lies ahead”, value engineering, vol. 2, no. 2, pp. 69-70, 1969 [2] p. a. jensen, “value concepts and value based collaboration in building projects”, cib w096 architectural management: 'special meeting' on designing value: new directions in architectural management of the cibw096 architectural management, technical university of denmark, lyngby, pp.3-10, 2005 [3] a. smith, “an inquiry into the nature and causes of the wealth of nations”, e-book published online in www.political-economy.com, 1776 [4] i. kopytoff, “the cultural biography of things: commoditization as process” in: the social life of things, appadurai, a. ed., cambridge university press, cambridge, pp.64-94, 1986 [5] a. raval, c. gronroos, “the value concept and relationship marketing” , european journal of marketing, pp.19-30, 1996 [6] j. c. anderson, j. a. narus, n. kumar, value merchants: demonstrating and documenting superior value in business markets, harvard business school press, boston, 2007 [7] d. j. flint, s. woodruff, s. f. gardial, “customer value change in industrial marketing relationships”, industrial marketing management, vol. 26, no. 2, pp. 163-175, 1997 [8] c. j. clawson, d. e. vinson, “human values: a historical and interdisciplinary analysis”, advances in consumer research, vol. 5, pp. 472-477, association for consumer research, provo, ut, 1978 [9] j. f. engel, r. d. blackwell, p. w. miniard, consumer behavior and marketing strategy, 6th ed., dryden press, chicago, il, 1990 [10] m. rokeach, the nature of human values, free press, new york, ny, 1973 [11] j. n. sheth, b. i. newman, b. l. gross, “why we buy what we buy: a theory of consumption values”, journal of business research, vol. 22, no. 2, pp.159-170, 1991 [12] g. j. hooley, j. saunders, competitive positioning: the key to marketing strategy, prentice hall, new york, ny, 1993 [13] g. s. day, market driven strategy, free press, new york, ny, 1990 [14] j. p. peter, j. c. olson, consumer behavior and marketing strategy, (2nd ed.), irwin, homewood, il, 1990 [15] s. boztepe, “user value: competing theories and models”, international journal of design, vol. 1, no. 2, pp. 55-63, 2007 [16] r. s. hartman, the structure of value: foundations of a scientific axiology, southern illinois press, carbondale, il, 1967 [17] m. t. fernandes, “business strategic model”, international journal of innovation, management and technology, vol. 2, no. 4, pp. 301-308, 2011 [18] l. d. miles, techniques of value analysis and engineering, mcgraw hill, new your, ny, 1972 [19] european committee for standardization, value management– vocabulary–terms and definitions, en 1325:2014 european committee for standardization, brussels, 2014. [20] save, value standard and body of knowledge, save international, 2007. engineering, technology & applied science research vol. 5, no. 2, 2015, 781-789 789 www.etasr.com fernandes: value analysis, going into a further dimension [21] value management handbook, european commission dg xiii l-2920, luxembourg, 1995. [22] european committee for standardization, value management, en 12973:2000 european committee for standardization, brussels, 2000. [23] m. t. fernandes, “innovation: technological and cultural construct model”, international journal of economics, finance and management, vol. 3, no. 7, pp. 351-370, 2014 [24] a. w. lay, “consumer values, product benefits and customer value: a consumption behavior approach”, advances in consumer research, vol. 22, no. 1, pp. 381-388, 1995 [25] a. griffin, j. r. hauser, “the voice of the customer”, marketing science, vol. 12, no. 1, 1993 [26] g. zaltman, r. h. coulter, “seeing the voice of the customer: metaphorbased advertising research”, journal of advertising research, vol. 35, no. 4, pp. 35-51, 1995. [27] j. r. hauser, note on the voice of the customer, mit, cambridge, ma, 2008 [28] s. u. kucuk, “consumer exit, voice, and power on the internet”, journal of research for consumers, no. 15, pp. 1-13, 2008 [29] save, monograph–function: definition and analysis, save international, 1998. [30] n. rich, m. holweh, “value analysis / value engineering”, report produced for the ec funded project “innoregio: dissemination of innovation and knowledge management techniques”, lean enterprise research centre, cardiff, u.k., 2000 [31] v. allee, “the value evolution: addressing larger implications of an intellectual capital and intangibles perspective”, journal of intellectual capital, vol. 1, no. 1, pp.17-32, 2000 authors profile manuel t. fernandes is a private researcher in the disciplines of value and innovation. as a result of his research he has published several books and academic and professional articles. he has developed some managing models, such as “value based strategy” (map), “value based innovation” (vbi), and “economic value return” (evr), comprising a full assessment and a dynamic graphic software application, applied professionally in over two hundred companies. his last research work was focused on the processes of value creation and innovation, resulting in the development of analitical models in the realm of “tangible and intangible value” and “technological and cultural innovation”. manuel t. fernandes is a bm, mba, and a qualified tvm (trainer in value management) and pvm (professional in value management). microsoft word aien-64-218-1-sm-ed.doc etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 126-132 126 www.etasr.com aien et al: probabilistic load flow considering wind generation uncertainty probabilistic load flow considering wind generation uncertainty morteza aien electrical engineering dpt sharif university of technology tehran, iran morteza_aien@yahoo.com reza ramezani electrical engineering dpt sharif university of technology tehran, iran rezaramezani65@gmail.com s. mohsen ghavami shahid bahonar copper industries (sbci) kerman, iran mohsen.ghavami270@gmail.com abstract— renewable energy sources, such as wind, solar and hydro, are increasingly incorporated into power grids, as a direct consequence of energy and environmental issues. these types of energies are variable and intermittent by nature and their exploitation introduces uncertainties into the power grid. therefore, probabilistic analysis of the system performance is of significant interest. this paper describes a new approach to probabilistic load flow (plf) by modifying the two point estimation method (2pem) to cover some drawbacks of other currently used methods. the proposed method is examined using two case studies, the ieee 9-bus and the ieee 57-bus test systems. in order to justify the effectiveness of the method, numerical comparison with monte carlo simulation (mcs) method is presented. simulation results indicate that the proposed method significantly reduces the computational burden while maintaining a high level of accuracy. moreover, that the unsymmetrical 2pem has a higher level of accuracy than the symmetrical 2pem with equal computing burden, when the probability density function (pdf) of uncertain variables is asymmetric. keywordsprobabilistic load flow; two point estimation method; uncertainty; wind turbine generator (wtg). nomenclature the notation used throughout the paper is stated below for quick reference. c the weibull scale factor [ sm / ]. h the nonlinear function that relates y to x , here, the lf problem. k the weibull shape factor. )( ' 3 kxm 3th moment of the kx pdf.. n the number of uncertain variables. 1,kp the weight associated to 1,kε . 2,kp the weight associated to 2,kε . p the wind turbine generator (wtg) output power [ mw ]. dp the demand active power [ pu ]. dgp the distributed active power generation [ pu ]. d ip the active power demanded at bus i [ ..up ]. g ip the active power generation at bus i [ ..up ]. net ip the net active power injection at bus i [ ..up ]. rp the wtg rated power [ mw ]. slackp the power generated by the slack bus [ pu ]. dq the demand reactive power [ pu ]. dgq the distributed reactive power generation [ pu ]. net iq the net reactive power injection at bus i [ ..up ]. ijs the power transmitted between buses i and j [ pu ]. v the wind speed [ sec/m ]. v the bus voltage magnitude vector [ pu ]. iv the magnitude of voltage at bus i [ ..up ]. iv the wind turbine generator (wtg) cutin speed [ sec/m ]. rv the wtg rated speed [ sec/m ]. ov the wtg cutout speed [ sec/m ]. x the uncertain input variable. y the uncertain output variable. ijy the admittance magnitude between buses i and j [ ..up ]. δ the bus voltage angle [ rad ]. iδ the bus voltage angle [ .rad ]. ijθ the angle of ijy [ .rad ]. 1,kε the location of concentration for variable number k above the mean, nk ,...,2,1= . 2,kε the location of concentration for variable number k below the mean, nk ,...,2,1= . µ mean value of the x kx,µ the mean of kx σ standard deviation of the x kx,σ the standard deviation of kx etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 126-132 127 www.etasr.com aien et al: probabilistic load flow considering wind generation uncertainty i. introduction a. motivation computation of power flow in the electric power system is one of the major requirements that power system designers face. deterministic load flow requires specific values for loads, unit’s generation and network conditions. as the power industry is being restructured and new technologies develop more and more uncertainties are introduced. these uncertainties mainly stem from bus loads and changes in the network’s configuration and power supplies. recently, attention is particularly focused in the increasing penetration of renewable energy sources in power systems. the introduced uncertainties inevitably result to errors in the deterministic load flow (lf) solutions. in order to cope with the increased uncertainties imposed to power systems, probabilistic tools are employed to predict the state of the system at any time instant. in system planning, it is desired to assess bus voltages and line flows for a range of load and generation conditions. executing the lf for every possible or probable combination of bus loads and generating unit’s conditions is completely impractical because of the extremely large computational burden required. performing plf study gives system planning engineers a better feel of system conditions and can provide increased assurance regarding investment planning [1]. b. literature review and paper contribution several methods of analysis for engineering systems under uncertainty have been employed. to account for power system uncertainties, probabilistic techniques have been used since the early seventies [1], when the uncertainty in system demand was first considered. the monte carlo simulation (mcs) technique has been employed to solve the plf problem by repeated simulations and provided considerably accurate results with the drawback of very large computation time [2]. an approach based on the application of the combined cumulant and gramcharlier expansion theory in the plf problem has been followed in [3, 4]. the method has also been used in ac-plf to compute the load flow of power system containing wind farms [5] and to obtain the pdf of transmission line flows [3]. fast fourier transforms (fft) and a discrete frequency domain convolution technique have been applied to reduce the computation time in [6]. a fuzzy concept to consider the wind generation uncertainties in the plf problem has been employed in [7]. a two point estimation method (2pem) has been applied to cope with uncertainties in engineering systems in [8, 9] and a point estimation method (pem) has been used for plf evaluation, taking into account the uncertainties of bus injections and line parameters in [10]. in this paper, a new method for plf study is proposed, by adapting the 2pem to the plf problem, taking into account the uncertainties of load, wind power generation and a simple branch outage. different scenarios are defined and the obtained results are discussed for each case study. in order to justify the effectiveness of the method, the obtained results are compared with those of mcs in terms of accuracy and computational burden. c. paper organization section ii formulates the lf and the plf problem. section iii introduces different plf methods. section iv describes the adaptation of the plf methods to power systems. section v reports results concerning two detailed case studies. section vi presents a comparison of the results. section vii closes the paper, providing concluding remarks. the appendix clarifies technical details about the wind turbines used. ii. load flow (lf) problem lf computation is one of the most essential tasks in electric power systems. to handle this task successfully, the set of system state variables which contains the bus voltage magnitude and angles have to be known. having this set of variables, every output variable can be calculated. the below section formulates the lf problem. a. load flow formulation the lf problem is solved to obtain the power system state variables. the lf problem has been formulated in several technical references and will not be discussed at length here. however, it should be recalled that it can be formulated as follows: ∑∑ −= d d i g g i net i ppp (1) ∑∑ −= d d i g g i net i qqq (2) )cos( 1 ijjij + j iji net i vyvp b θδδ −−= ∑ = (3) )sin( 1 ijjij + j iji net i vyvq b θδδ −−= ∑ = (4) b. plf formulation power system has an uncertain nature. this causes power system analysis tools to be inaccurate when deterministic data are used, since the state of the system is changing instantaneously. this is why probabilistic data are used. the plf problem is formulated as: )( xhy = (5) the input vector x can be written as: ,...],,[ , dgdgdd qpqpx = (6) and the output vector y can be written as: ...],,,,[ slackij psvy δ= (7) iii. plf methods several methods for plf study have been developed. theses methods fall in two basic groups: simulation methods like mcs and analytical methods like 2pem. etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 126-132 128 www.etasr.com aien et al: probabilistic load flow considering wind generation uncertainty a. monte carlo simulation method mcs is a technique that involves using random numbers and probabilities to solve a probabilistic problem. it is a method for iteratively evaluating a deterministic model using sets of random numbers as inputs. this method is often used when the model is complex, nonlinear, or involves more than just a couple of uncertain parameters [11]. a simulation can typically involve over 10000 evaluations of the model, a task which in the past was only practical using super computers. although the mcs method is able to provide accurate results, the computation is significantly time-consuming; therefore, it is not suitable for real time applications. b. two point estimate method in order to account for uncertainties in the plf, a 2pem [8], which is basically a variation of the original point estimate method (pem) described in [9, 10], is used to decompose (5) into several sub-problems by taking only two deterministic values of each uncertain variable placed on both sides of the corresponding mean value. the deterministic lf is then ran twice for each uncertain variable, once for the value below the mean, and once for the value above the mean, with other variables kept at their means. these two points may be symmetric about the mean or not. both possible point locations are investigated in this paper and simulation results are compared. in plf studies it is desired to find the distribution function of output variables. therefore, it is necessary to calculate the expected value and the standard deviation of the output variables using proper methods, such as 2pem. the procedure of this method with symmetrical location of two sampling points is as follows [12]: step 1: determine the number of uncertain variables. step 2: set 0)( =ye and 0)( 2 =ye . step 3: set 1=k . step 4: determine 1,kε , 2,kε , 1,kp and 2,kp . nk =1,ε (8) nk −=2,ε (9) n pp kk 1 2,1, == (10) step 5: determine the two concentrations 1,kχ and 2,kχ . kxkkxk ,1,,1, σεµχ += (11) kxkkxk ,2,,2, σεµχ += (12) step 6: run the deterministic lf for both concentrations ikx , using ],...,,...,,[ ,,2,1, nxikxxx µχµµ= , 2,1=i . step 7: calculate )(ye and )( 2 ye ∑∑ = = ≅ n k i nxikxxik hpye 1 2 1 ,,2,1,, ])),...,,...,,([()( µχµµ (13) ∑∑ = = ≅ n k i nxikxxik hpye 1 2 1 2 ,,2,1,, 2 )]),...,,...,,([()( µχµµ (14) step 8: calculate the mean and the standard deviation of the output variable. )(yey =µ (15) )()( 22 yeyey −=σ (16) it is obvious that the heart of the suggested method lies in how to produce appropriate samples having enough information about the pdf of input variables. in the case of unsymmetrical probability distributions for the input variables, the equations for the location of each point are [12]: 23,3, 1, ) 2 ( 2 kk k n λλ ε ++= , nk ,...,2,1= (17) 23,3, 2, ) 2 ( 2 kk k n λλ ε +−= , nk ,...,2,1= (18) k k k n p ς ε 2, 1, −= (19) k k k n p ς ε 1, 2, = (20) 2 3, )2/(2 kk n λς += , nk ,...,2,1= (21) 1)( 1 2,1, =+∑ = n k kk pp (22) n pp kk 1 2,1, =+ (23) 3 , ' 3 3, )( kx k k xm σ λ = (24) it is notable that for symmetric probability distributions, in which skewness and as a result 3,kλ equals to zero, (17)-(20) convert to (8)-(10). finally, the first three moments can then be approximated by: ∑∑ = = ≅ n k i nxikxxik hpye 1 2 1 ,,2,1,, ])),...,,...,,([()( µχµµ (25) ∑∑ = = ≅ n k i nxikxxik hpye 1 2 1 2 ,,2,1,, 2 )]),...,,...,,([()( µχµµ (26) ∑∑ = = ≅ n k i nxikxxik hpye 1 2 1 3 ,,2,1,, 3 )]),...,,...,,([()( µχµµ (27) iv. adaptation of the plf methods to the power system for probabilistic modeling, the uncertain variables must be specified first. the next step is uncertainty modeling and the final step is evaluating the output variable statistics. the uncertain parameters related to the power system include generation, load, and network topology. this paper mostly focuses on the load, wind power generation and simple network configuration uncertainties. the load in each bus is modeled with a normal pdf with µ equal to the base load and σ equal to %5± of the base load. the normal pdf can be stated as (28). etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 126-132 129 www.etasr.com aien et al: probabilistic load flow considering wind generation uncertainty ])( 2 1 [ 2 2 1 )( σ µ σπ − − = x exf (28) the wind speed is modeled with weibull pdf given by: ])([ 1 )()( k c v k e c v c k vf − − = (29) it is assumed that in each region, the pdf of wind speed is known, therefore, the transformation of wind speed to wind turbine output power is given by: 0=p , ivv ≤ or ovv > ir i r vv vv pp − − = , oi vvv << (30) rpp = , oi vvv << the system loads are modeled as pq buses with specified real and reactive load demand and the wind farm output power is modeled as negative load. for simple modeling of the network topology, some transmission lines have been assumed to have a specific forced outage rate (for). the overall procedure of plf evaluation is as follows: in each iteration, the quantity of uncertain input parameters is obtained, the lf problem is executed and the output variables are stored. finally, the statistics of the uncertain output variables are calculated using (13)-(16) or other appropriate equations such as (31)-(32) depending on the method used. v. case studies to justify the effectiveness of the proposed method, two case studies are employed, a 9-bus, and a 57-bus standard system, and the obtained results are compared with those obtained by mcs. the proposed method was implemented on a dell inspiron 1420 system with a 2-ghz processor and 2-gb of ram using matlab optimization toolbox. a. case study 1 this case study is the ieee 9-bus system with base power, base voltage, and total active and reactive demand equal to 100mva, 345kv, 315mw and 115mvar, respectively. the single line diagram of this network is illustrated in figure 1. in this case, bus 7 is assumed to have a wind farm whose detailed information is attached in the appendix. in this case, the point of interest is to investigate on the total active losses [mw], 76→p (power from bus6 to bus 7 [mw]) and 87→p (power from bus 7 to bus 8 [mw]). in the plf study, it is desired to assess the contribution of each uncertainty on the output variables uncertainty. to do this, four scenarios are defined: scenario 1: the load is assumed fixed and active power generation of the wind farm is considered as an uncertain variable. scenario 2: in this scenario, besides the wind farm output power uncertainty, the load is also assumed as another uncertain variable. scenario 3: in addition to uncertainties of scenario 2, in the third scenario the lines between buses 6, 7 and buses 7, 8 are assumed to have for=0.05. it must be noted that these lines connect bus 7, in which the wind farm is placed, to the other buses. scenario 4: in addition to the assumptions of the third scenario, the reactive power consumption of wind farm is also considered with a power factor equal to 0.85lag. table i outlines the summary of the assumptions for each scenario. it is noteworthy that there is a base scenario in which none of the uncertainties mentioned above exist. in table i, y and n denote yes or no, respectively. fig. 1. single line diagram of 9-bus test system. table i. summary of different scenarios scenarios wi6d ge6. u6cert. load u6cert. lines for wi6d farm q co6sum. base n n n n no.1 y n n n no.2 y y n n no.3 y y y n no.4 y y y y in the msc method, the statistics of output variables can be obtained using (31) (32). ∑ = = + i imcs x + 1 1 µ (31) ∑ = −= + i mcsimcs x + 1 2 )( 1 µσ (32) etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 126-132 130 www.etasr.com aien et al: probabilistic load flow considering wind generation uncertainty where n is the number of mcs samples, which in this study is set to 3000 samples and x is the output variable. table ii shows the results for different scenarios in this case study. in table ii, the std denotes the standard deviation of the output variable. the obtained results indicate that as the network uncertainty increases, the std of output variables increases. the std represents the degree of uncertainty for each variable. increasing the input variables uncertainty increases the output variables uncertainty. std is largest in the last scenario since this scenario has most uncertainty. the contents of table ii indicate that in this case, it is mostly the network configuration that affects the line flows, followed by the wind farm output power and load uncertainty. figures 2-6 show results using the theory of normal distribution function. the uncertainty can be better described by using the cumulative density function (cdf) concept. figures 5 and 6 portray the cdf of some output variables. as uncertainty increases, the slope of the cdf decreases as shown in figure 5 and 6. figure 5 shows that the unsymmetrical 2pem has a higher level of accuracy compared to the symmetrical 2pem. it is also shown that in scenario 4, which has the most uncertainties, the cdf slope is smaller. the power transmitted from bus 6 to bus 7 in scenarios 3 and 4 may have reverse direction due to network configuration and wind generation uncertainties as shown in figure 2. as shown in figure 4, in case of total losses, the probabilities of being greater than 5 mw in all scenarios are 0.7635, 0.72, 0.629, and 0.633, respectively. table iii compares the obtained results for scenario 2. b. case study 2 this case is the ieee 57-bus standard system with base mva, base kv, total active and reactive load equal to 100mva, 345kv, 1250.8mw and 336.4mvar, respectively. in this case, bus 8 is assumed to have a wind farm that its detailed information is attached in the appendix. in this case study, scenario 4 which has the most uncertainty is evaluated by different methods and the obtained results are given in table iv. figure 7 shows the comparison of the cdf for total active losses obtained by different methods for this case study. table ii. mean and std of output variables in different scenarios by mcs –case1 scenarios base 6o.1 6o.2 6o.3 6o.4 mean active losses 4.955 5.1097 5.1473 5.4388 5.5809 std active losses 0 0.1523 0.2501 1.3251 1.7072 mean p6-7 24.11 22.098 22.092 22.017 24.804 std p6-7 0 1.906 3.0916 15.186 18.161 mean p7-8 -75.99 -73.753 -73.725 -72.929 -70.722 std p7-8 0 2.123 3.4935 14.889 17.612 fig. 2. the pdf of active power between buses 6 and 7case1 . fig. 3. the pdf of active power between buses 8 and 7case1. fig. 4. the cdf of total active losses in different scenarioscase1 etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 126-132 131 www.etasr.com aien et al: probabilistic load flow considering wind generation uncertainty fig. 5. the cdf of total active losses obtained by all methodscase1. fig. 6. cdf of active power between buses 8 and 7-case1. fig. 7. the cdf of total active losses obtained by all methods-case2. table iii. comparison of the resultscase1 table iv. comparison of the resultscase2 vi. comparison of the results the intention at this point is to interrogate the accuracy of the obtained results by 2pem; the mean and the standard deviation of results obtained by the 2pem are compared with the corresponding values obtained by the mcs, which is considered accurate. the errors for the mean and standard deviation of output variable are respectively defined as: 100)( 2 × − = mcs pemmcs µ µµ ε µ (33) 100)( 2 × − = mcs pemmcs σ σσ εσ (34) table v indicates that the 2pem can decrease the run time severely and still maintain a high level of accuracy. the time efficiency of the 2pem is decreased as the number of uncertain variables increases, because the deterministic lf is ran twice for each uncertain variable, once for the value below the mean, and once for the value above the mean, with other variables kept at their means. therefore, the 2pem run time is proportional to the number of uncertain variables. table v. comparison of accuracy and computational efforts of different methods case study method ru6 time[s] µε [%] σε [%] mcs 9.864 0 0 2pems 0.18 1.9 9.68 case 1 2pemu 0.188 0.038 0.76 mcs 28.76 0 0 2pems 0.884 0.194 2.89 case 2 2pemu 0.884 0.181 0.716 vii. conclusions the incorporation of renewable energy sources into power systems is constantly increasing, as a result of energy and environmental concerns. renewable energy sources are variable and intermittent and introduce uncertainties into power systems. probabilistic methods are employed in order to analyze these uncertainties. in this paper, the two point estimation method is proposed for probabilistic load flow study. comparison of the results obtained by utilizing two methods mea6 of the losses std of the losses mcs 5.1473 0.2501 2pems 5.2452 0.2743 2pemu 5.1453 0.252 methods mea6 of the losses std of the losses mcs 27.8841 2.01 2pems 27.83 2.052 2pemu 27.8336 2.0244 etasr engineering, technology & applied science research vol. 1, �o. 5, 2011, 126-132 132 www.etasr.com aien et al: probabilistic load flow considering wind generation uncertainty different methods indicates that the two point estimation method shows a similar level of accuracy and a smaller computational burden compared to the monte carlo simulation method. results also indicate that the unsymmetrical two point estimation method shows a higher level of accuracy compared to the symmetrical one, with equal computing effort. the time efficiency of the two point estimation method is decreased with the increase of the number of uncertain variables since the run time for this method is proportional to the number of uncertain variables. appendix the detailed technical data about used wtgs and wind speed data is given in table vi. table vi. wind farm information parameters value no. of wtgs 25 rp [mw] 0.6 vr [m/s] 15 vi [m/s] 3 vo [m/s] 25 c[m/s] 6.7703 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[12] g. verbic, c. a. canizares, “probabilistic optimal power flow in electricity markets based on a two-point estimate method”, ieee trans. power syst., vol. 21, no. 4, pp. 1883 –1893, 2006. microsoft word etasr_v13_n1_pp10170-10174 engineering, technology & applied science research vol. 13, no. 1, 2023, 10170-10174 10170 www.etasr.com sreenatha & mallikarjuna: a fault diagnosis technique for wind turbine gearbox: an approach … a fault diagnosis technique for wind turbine gearbox: an approach using optimized blstm neural network with undercomplete autoencoder m. sreenatha jss academy of technical education, india sreenath.jssate@gmail.com (corresponding author) p. b. mallikarjuna jss academy of technical education, india pbmalli2020@gmail.com received: 21 december 2022 | revised: 3 january 2023 and 7 january 2023 | accepted: 9 january 2023 abstract the gearbox is one of the critical components of a wind turbine. proactive maintenance of wind turbine gearboxes is crucial to decrease maintenance and operational costs and the long downtime of the complete system. as the gearbox is a significant part of the wind turbine, a fault in the gearbox leads to the breakdown of the wind turbine system. hence, it is important to study and analyze the faults in wind turbine gearbox systems. in this article, a neural network-based model, a bidirectional long short-term memory (blstm) fused with an autoencoder is intended to categorize the condition of the gearbox into good or bad (broken tooth) condition. feature learning and reduction are achieved extensively through the autoencoder. this improves the performance of the blstm model regarding time complexity and classification accuracy. this model has been applied with time series vibration data of the gearbox in a wind turbine system. the suggested model's performance is analyzed using an openly available wind turbine gearbox vibration dataset. the result showed that blstm accuracy with an under-complete autoencoder is highly robust and appropriate for the health monitoring of wind turbine gearbox systems using time series data. also, in order to illustrate the advantage of the projected model for fault analysis and diagnosis in wind turbine gearbox, the throughput or time complexity of training and testing of the split dataset is compared with the conventional blstm model. keywords-autoencoder; bidirectional long short-term memory; fault detection; vibration data; wind turbine gearbox i. introduction wind energy is very popular, since it is form of clean energy. for the effective production of wind energy, the wind turbines must be maintained with less downtime. gearbox failure directly impacts the reliability of the gearbox in the wind turbine. the operation and the cost towards the maintenance of wind turbines installed at remote locations is around 15–35% of the installation cost. around 80% of this is spent on unplanned maintenance issues resulting from defects in the wind turbine's various components [1]. wind turbine fault analysis and diagnosis are usually performed manually from individuals with a high level of technical expertise. this method is inefficient and incapable of meeting the needs of wind farm operations and maintenance. it also leads to production loss due to the prolonged unavailability of the energy production system and requires a large number of fault diagnosis analysts. the increase in demand for wind energy needs reliable wind farms. to reach the demands, the design of low-cost advanced proactive intelligent fault detection systems is crucial for better performance. the gearbox is one of the most vital and frequently worn parts of the mechanical rotatory system of a wind turbine. wind turbine gearbox failure diagnosis is critical in mechanical rotating systems, and unpredicted breakdown of this component results in prolonged system downtime. wind turbine energy production unit maintenance and operating may determine whether the system is cost-efficient or not. therefore, an intelligent and proactive fault detection system, which reduces the downtime of the wind turbine energy production system, is essential, since it reduces the number of skilled professionals required for maintenance. an expert system enables timely intervention and engineering, technology & applied science research vol. 13, no. 1, 2023, 10170-10174 10171 www.etasr.com sreenatha & mallikarjuna: a fault diagnosis technique for wind turbine gearbox: an approach … early warnings and hence reduces production loss due to prolonged unavailability. as a result, a smart system for condition monitoring of wind turbines improves the reliability by reducing downtime significantly. in the current work, the proposed hybrid bidirectional long short-term memory (blstm) model with an autoencoder achieves an accuracy of 98.68% in wind turbine gearbox healthiness classification and improves the performance by 71.73% in testing and 65.61% in training when compared with the original blstm model. in the next section, various efforts to diagnose and analyze wind turbine gearboxes are discussed. ii. related work a few efforts have been made to use traditional machine learning algorithms to classify the healthiness of the gearbox. the time-domain sequence approximate entropy (apen) adaptive strategy, a wavelet packet transform (wpt) filter, and a cross-validated particle swarm optimized (cpso) kernel extreme learning machine were used to develop gearbox fault analysis models in [1]. the discrete wavelet transformation (dwt) was used to compute wavelet coefficients for vibration signals obtained from wind turbines. wavelet coefficients are applied to phase space reconstruction (psr) and singular value decomposition to extract fault attributes in [2]. the supervisory control and data acquisition (scada) process delivers the most frequently used input data for wind turbine anomaly detection [4]. by reducing the feature dimension of the time-series data, dynamic principal component analysis (dpca) was used to identify faults in the gearbox of wind turbines in [5]. to extract gearbox vibration features from oscillated vibration signals of gearbox fault diagnosis, a method combining the empirical mode decomposition (emd) and time synchronous averaging (tsa) was used in [6]. to detect anomalies in the wind turbine gearbox, twin support vector machine (twsvm) and an adaptive threshold were used in [7]. to extract features from three-axial vibration data for fault diagnosis of a wind turbine gearbox, a deep enhanced fusion network (defn) was used in [8]. the deep joint variational autoencoder method was used in conjunction with wind farm supervisory control and data acquisition to diagnose faults in the wind turbine gearbox in [9]. by decomposing vibration signals with a wavelet packet, a fast deep graph convolutional network model was used to analyze the wind turbine gearbox in [10]. the fused vibration signals were classified with a multiclass svm model in [11]. electrical signals from generator terminals were used to find faults in the gearbox of the wind turbine in [12]. using fault features of convolution channels and frequency bands of wavelet coefficients, the residual network can be used to identify a fault in the gearbox of a wind turbine [13]. the methods of convolutional neural networks and isolation forests were applied to classify the health of the gearbox of a wind turbine in [14]. the neighborhood component analysis technique for best feature collection was used to evaluate the healthiness of wind turbine gearboxes in [15]. the remaining useful life of a wind turbine gearbox and its failure can be predicted using machine learning methods such as artificial neural networks, svm, and logistic regression [16]. cnn is used for feature extraction and representation, and lstm is used to learn the latent time series relationship between features in various periods of time [17]. an optimized lstm neural network with cosine loss was used to analyze wind turbine gearbox faults in [17]. the cos-lstm networks were analyzed using the wavelet energy entropy and energy sequence features of the vibration signals in [18]. the traditional lstm model was improved using multiple swarm intelligence models for classifying failures in the wind turbine gearbox using vibration signal data acquired from the faulty gearbox in [19]. the simulated annealing (sa) algorithm was used to optimize the vibration of the powertrain system in [21]. to analyze the functional schemes of the selected gears, the method for trying to generate a mechanism of kinematics equations for signal dependency graphs was used in [22]. industrial bearing, fault detection, and isolation using time frequency domain has been applied and compared with the theoretical results in [23]. the following are the main contributions of the current article:  design of a gearbox diagnostic model using an undercomplete autoencoder and the blstm deep learning model.  analysis of vibration data collected through sensors.  comparison of the proposed model's training and testing times to those of the conventional blstm model. iii. proposed model the projected model was created on undercomplete autoencoder along with a blstm-based hybrid model to diagnose and classify wind turbine gearbox health conditions. the undercomplete autoencoder and blstm architectures are described below. a. undercomplete autoencoder autoencoders are unsupervised learning methods used for representation learning. the neural network architecture denotes autoencoders to impose a bottleneck in the neural network, resulting in a compressed feature representation of the original input. autoencoders contain four layers, namely input layer, hidden layer, bottleneck layer, and output layer. the objective of autoencoders is to minimize the number of nodes located in the hidden layer in order to reduce the information flow through the neural network. an autoencoder model discovers the most important characteristics of the input data. the compressed and essential features are extracted at the bottleneck layer in order to recreate the original data with minimal loss. the number of neurons in the hidden layer is lesser than the number of neurons in the input layer. the bottleneck layer contains fewer nodes than the hidden layer. the reduced features are extracted from the bottleneck layer. b. bidirectional lstm the bidirectional lstm recurrent neural network is made up of lstm cells, which are memory blocks with a hidden unit. such states have the responsibility to transfer immediately preceding time step data in the network from the input state to the next cell. these cells are made up of input, forget, and output gates. the forget gate forgets irrelevant information, the input gate updates new information, and the output gate passes the updated information to the next cell. engineering, technology & applied science research vol. 13, no. 1, 2023, 10170-10174 10172 www.etasr.com sreenatha & mallikarjuna: a fault diagnosis technique for wind turbine gearbox: an approach … c. design figure 1 depicts the construction of an autoencoder with a blstm-based model. to design the proposed model for time series gearbox vibration data analysis, input samples of 3600 (1600×2) with a sample size of 500 time steps were fed to the undercomplete autoencoder. the output of the encoder tapped at the bottleneck has reduced features and contains 350 time steps in each sample. the compressed data are loaded into the blstm model, which is trained for 500 epochs. to achieve better results, the model employs the rmsprop optimizer and the sigmoid perceptron at the output layer. the metrics are recorded and discussed below. fig. 1. proposed autoencoder and blstm-based model. iv. experimentation and results the developed autoencoder and blstm-based model were tested on experimental data collected in a publicly available wind turbine gearbox vibration dataset [20]. spectra quest's gearbox fault diagnostics simulator was used to generate vibration data for two conditions of the gearbox, one for good health and the other for a broken tooth, and both were subjected to bearing capacity ranging from 0% to 90%. four sensor nodes were positioned in 4 different locations on the body of the gearbox. the dataset contains 10 samples with different loads of wind turbine gearbox vibration data in good and bad conditions. the dataset was created with a 30hz frequency for a total of 6.9s. each sample was collected at a rate of 12,800 time steps/s. a total of 69s (6.9×10) for data generation for a broken tooth or bad condition and data generation for a healthy condition was considered. table i shows the raw recorded data. table i. wind turbine gearbox vibration dataset wind turbine gearbox condition number of samples time steps per second time steps per sample good 10 12800 88320 bad (broken tooth) 10 each sample is made up of 88320 time steps. because the time series sequence is too long, the data have been divided into subsamples of 500 time steps. as a result, 176 samples from each sample of length 88320 time steps were derived by considering 500 time steps for each individual sample. as a result, we acquired 1760 (176×10) good-condition gearbox samples and 1760 (176×10) bad-condition gearbox samples. the derived dataset contains 3520 samples, as shown in table ii. the purpose of choosing 500 as the subsample's time step is to facilitate experiments, however the size of the sample set can vary. we chose 3200 sample data at random from a total of 3520 for experiments. table ii. generated wind turbine gearbox vibration dataset wind turbine gearbox condition number of samples total number of samples good 1760 3520 bad 1760 to collect vibration data, 4 sensors were placed on the body of the gearbox in 4 different directions. table iii displays the accuracy, precision, recall, f1-score, training time (time taken to train a total 80% of the 3200 (i.e. 2560) training samples, and testing or execution time (time taken to test a total of 640 testing samples (20% of 3200)). it is tested with data frequency (dataset sample size in time steps) equal to 500 time steps and a trained dataset with 500 epochs. the results were captured on a machine with the following architecture: gpu: nvidia-smi 460.32.03, cuda version:11.2, tensor core gpu: a100-sxm4-40gb with a runtime memory of 89.6gb. table iii. performance of the blstm model sensor precision recall f1-score training time (s) testing time (s) classification accuracy s-1 0.9875 0.9783 0.9828 8697.74 9.76 98.28% s-2 0.9838 0.8892 0.9341 8121.10 8.17 93.28% s-3 0.6451 0.8695 0.8480 8722.22 13.30 78.12% s-4 0.9062 0.6904 0.7837 8200.48 19.03 75.00% table iv. performance of the undercomplete autoencoder with the blstm model tested with vibration data from sensor-1 no. of time steps tapped at the bottleneck precision recall f1-score training time (s) testing time (s) classification accuracy 50 0.9617 0.9123 0.9364 1175.35 2.16 93.59% 100 0.9593 0.8924 0.9246 1334.07 2.68 92.19% 150 0.9693 0.9080 0.9376 1776.15 2.70 93.44% 200 0.9660 0.9260 0.9456 1997.61 2.61 94.38% 250 0.9670 0.9376 0.9571 2188.04 2.31 95.12% 300 0.9793 0.9776 0.9421 2792.95 2.46 96.53% 350 0.9895 0.9783 0.9857 2991.74 2.76 98.68% engineering, technology & applied science research vol. 13, no. 1, 2023, 10170-10174 10173 www.etasr.com sreenatha & mallikarjuna: a fault diagnosis technique for wind turbine gearbox: an approach … since the classification accuracy using sensor-1 and sensor-2 vibration data is optimum, the significance of sensor3 and sensor-4 vibration data analysis has less importance. hence, the diagnosis of the gearbox fault can be achieved with an exemption of sensor-3 and sensor-4 vibration data as these two sensors yield less accuracy. hence, the proposed model was tested only on sensor-1 vibration data. table iv shows different test cases with varied numbers of features extracted at the bottleneck layer of the autoencoder with data frequency equal to 500 (number of time steps in each sample), tested with sensor-1 vibration data. the results clearly show that at the bottleneck output of 350 time steps outperforms the model with respect to accuracy and training and testing times. fig. 2. roc curve for vibration data from sensor-1 with 80-20% split ratio blstm model. fig. 3. roc curve for vibration data from sensor-2 with 80-20% split ratio blstm model. the proposed method outperforms the bltsm algorithm model in classification accuracy, training time, and testing time. based on the experimental observations; the results indicate that the gearbox fault vibration data features can be learned to improve the generalization and the model's accuracy by fusing the undercomplete autoencoder and blstm models. however, the result comparison in tables v-vi shows that the proposed model achieves 98.68% accuracy with reduced features (350 time steps) in the samples, and the performance is increased by 71.73% in testing time and 65.61% in training time when compared to the blstm model. as a result, the fused model of autoencoder with blstm outperforms the conventional blstm. fig. 4. roc curve for vibration data from sensor-3 with 80-20% split ratio blstm model. fig. 5. roc curve for vibration data from sensor-4 with 80-20% split ratio blstm model. table v. performance comparison of the proposed model with blstm sensor conventional blstm model with 500 time steps per sample training time (s) testing time (s) classification accuracy s-1 8697.74 9.76 98.28% undercomplete autoencoder with blstm model with 350 time steps per sample training time (s) testing time (s) classification accuracy s-1 2991.74 2.76 98.68% table vi. gearbox health diagnosis method comparison ref. method accuracy [2] wpt-pso-kelm 94.17% [18] cos-lstm 98.55% with 550 samples [19] lstm with firefly, cuckoo, pso and aco and relu activation function 87.5% [5] support vector machine model used to detect and isolate gear faults. it performs better than the dynamic principle component analysis (dpca) using mlp 91.24% [24] a technique for feature extraction based on cnn and lstm for categorization was used to estimate gearbox faults using a better prediction method based on the early fusion of multisource sensing data 97.9% proposed undercomplete autoencoder with blstm 98.68% engineering, technology & applied science research vol. 13, no. 1, 2023, 10170-10174 10174 www.etasr.com sreenatha & mallikarjuna: a fault diagnosis technique for wind turbine gearbox: an approach … fig. 6. performance of the undercomplete autoencoder with blstm. v. conclusion this article provides the analysis of wind turbine gearbox vibration data for fault classification. the proposed hybrid model, combines the bidirectional lstm neural network algorithm with the undercomplete autoencoder and is used for wind turbine gearbox fault detection and diagnosis. the experimental results demonstrate that the suggested model gives an accuracy of 98.68% in wind turbine gearbox fault classification and improves the performance by 71.73% in the dataset testing samples and 65.61% in the dataset training samples, when compared to the traditional bidirectional lstm model. with respect to testing and training time, as well as classification accuracy, the proposed model outperforms the known models that was compared with. acknowledgment the authors would like to thank dr. yogesh pandya, symbiosis university of applied sciences, indore for his help and for providing the dataset for public access. references [1] m. ruiz et al., "wind turbine fault detection and classification by means of image texture analysis," mechanical systems and signal processing, vol. 107, pp. 149–167, jul. 2018, https://doi.org/10.1016/j.ymssp. 2017.12.035. 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[24] h. habbouche, t. benkedjouh, y. amirat, and m. benbouzid, "gearbox failure diagnosis using a multisensor data-fusion machine-learningbased approach," entropy, vol. 23, no. 6, jun. 2021, art. no. 697, https://doi.org/10.3390/e23060697. microsoft word etasr_v12_n5_pp9276-9281 engineering, technology & applied science research vol. 12, no. 5, 2022, 9276-9281 9276 www.etasr.com hussein & abdul rasoul: steel fiber addition in eco-friendly zero-cement concrete: proportions and … steel fiber addition in eco-friendly zero-cement concrete: proportions and properties ali n. hussein department of civil engineering university of kerbala kerbala iraq ali.naser@s.uokerbala.edu.iq zainab m. r. abdul rasoul department of civil engineering university of kerbala kerbala iraq zainabm@uokerbala.edu.iq aymen j. alsaad department of civil engineering university of kerbala kerbala iraq aymen.alsaad@uokerbala.edu.iq received: 4 july 2022 | revised: 20 july 2022 | accepted: 23 july 2022 abstract-the main objective of this paper is to study the behavior of eco-friendly zero-cement concrete, its proportions, and its properties. the experimental program involves casting and testing many specimens divided into three main groups according to the percentage of added steel fibers in order to investigate the effect of steel fibers on the density, compressive strength, modulus of elasticity, and splitting tensile strength of concrete. the experimental outcomes indicated that the percentage of steel fibers has a small impact on the dry density: adding 0.5% and 1% of steel fibers increased the dry density by about 0.9% and 1.6% respectively. the percentage of steel fibers has an important impact on the compressive strength: after 28 days, steel fibers increased the compressive strength by about 4.9% and 12.8% for added steel fiber percentages of 0.5% and 1%. also, the results indicated that steel fiber had an important impact on the splitting tensile strength in concrete after 28 days of curing: adding 0.5% and 1% steel fibers increased the splitting tensile strength by about 11.8%and 23.2% respectively. finally, adding steel fibers has an impact on the modulus of elasticity: after 28 days, adding 0.5% and 1% steel fibers improved the modulus of elasticity approximately by 1.7% and 5%. keywords-eco-friendly concrete; pozzolime concrete; steel fibers; mechanical properties i. introduction global attention in eco-friendly and sustainable building materials has increased over the last decades and new constructional adhesives to replace conventional cement are researched. researchers are being urged to investigate alternatives, such as the reinstitution of lime pozzolanic systems. lime might be considered an ecologically friendly binder due to its low energy needs, limited co2 emissions during production, and carbonation-induced co2 uptake through setting [1]. lime natural pozzolans are ancient building materials that were utilized in the process of building using masonry. the use of lime natural pozzolanic materials had ceased to exist due to the development of inorganic bindings due to their sluggish setting and hardening. after the discovery of portland cement in the nineteenth century, the use of natural pozzolan-lime binding materials decreased considerably. the environmental repercussions of the portland cement production process have increased interest in limenatural pozzolan cement during the last 50 years [2]. kadum [3], created pozzolime, a unique, sustainable binder composed of hydrated-lime, silica fumes, and fly ashes. many studies have shown that the addition of fibers, especially steel fibers, to concrete can reduce the requirement for conventional reinforcement in certain circumstances. steel fibers increase the post-cracking tension response and cracking control qualities of reinforced concrete [4]. utilizing deformed fibers, like those that are hooked, corrugated, or twisted, can further boost the mechanical strength of composite materials. reportedly, deformed steel fibers give 3 to 7 times the fiber-matrix binding strength of straight fibers. several factors, including fiber shape, fiber length, and curing conditions, influence the degree to which mechanical properties are enhanced [5]. fibers are typically added to fiber-reinforced cementitious composites (frccs) in order to restrict the volumetric ratio of the mix to 3% in order to address mixing and casting issues such as fiber floating and balling. pozzolans are natural or man-made materials that are not cementitious on their own but, because they are made of aluminosilicates, they create hydraulic cement when mixed with lime hydrates. authors in [6] investigated the viability of employing pozzolans derived from natural sources in algeria. this pozzolanic material is seldom used in concrete, so its features have not been thoroughly examined. to learn more about the effectiveness of pozzolan concrete, 6 concrete mixes were tested: one with portland cement (as a reference), and 5 corresponding author: ali n. hussein engineering, technology & applied science research vol. 12, no. 5, 2022, 9276-9281 9277 www.etasr.com hussein & abdul rasoul: steel fiber addition in eco-friendly zero-cement concrete: proportions and … with 10, 20, 30, 40, and 50% pozzolan substitution of cement. to make lightweight aggregate concrete, shattered pozzolan was used as the lightweight aggregates (la), and fine sand was added to all mixes (lac). workability and density of fresh concrete mixes were evaluated. the compressive strength, splitting tensile strength, and flexural strength of hardened concrete samples were measured after 3, 7, 28, 90, and 365 days. all the concrete mixes had a constant cementitious material concentration of 400kg/m 3 . the findings of this experiment indicated that the inclusion of pozzolan at 20% of the weight of cement results in the greatest gain in strength among the evaluated mixes. the experimental results of [7-12] showed that the addition of fly ash particles had little effect on the mechanical properties of normal concrete, while steel fibers had the greatest effect. the highest increase was reported in compressive and flexural strength. ii. experimental work a. materials 1) hydrated lime in pozzolime concrete compositions, hydrated lime is utilized. the main component of hydrated lime is calcium hydroxide (ca(oh)2). the utilized hydrated lime was manufactured at a lime factory in karbala and conforms to the iraqi standard iqs no. 807 /2004 [13]. table i displays the chemical analyses, chemical composition, and physical properties. table i. chemical and physical test values of hydrated lime* c h e m ic a l a n a ly si s components results % limits iqs no. 807 cao + mgo 73.1 min. 65% sio2 2.28 al2o3 1.08 fe2o3 0.23 mgo 0.46 5% max. fe2o3+al2o3+ sio2 3.60 5% max. so3 0.2 loss on ignition 22.8 ca(oh)2 92.49 85% min cao % activity 70.12 p h y si c a l te st co2 % 2.27 5% max. residue on 90µ m 2.2 10% max. slaking time 24 min fineness m 2 /kg 361 * the tests were carried out in karbala plant for cement and lime 2) cement this study utilized portland cement, since it is readily accessible on the market. the used cement was utilized in the production of earlier concrete mixtures. the chemical and physical characteristics agree to the limitations of iraqi standard no.5/1984 type v [14] (see tables ii and iii). 3) fine aggregates local fine sand complying to zone two of the iqs no. 45 was utilized as fa [15]. according to the findings, the fa satisfies the grading requirements of this standard. table ii. chemical composition and main compounds of sulfate-resisting portland cement* oxides composition content % limits of iraqi standard no.5/1984 cao 62.15 -- sio2 19.88 -- al2o3 3.5 -- fe2o3 4.7 -- mgo 3.23 < 5.00 so3 1.84 < 2.50 na2o 0.26 k2o 0.51 l.o.i. 1.25 < 4.00 insoluble residue 0.80 < 1.5 lime saturation factor 0.928 0.66-1.02 main compounds (bogue's equations) c3s 54.51 -- c2s 18.77 -- c3a 1.51 < 3.50 c4af 14.14 -- * chemical analysis wase carried out in the karbala laboratory table iii. physical properties of cement physical properties test results limits of iraqi standard no.5/1984 surface area (blaine) m 2 /kg 282 ≥ 250 setting time (vicat) initial setting, hrs: min 3:51 ≥ 45 min final setting, hrs: min 6:20 ≤ 10 hrs compressive strength, mpa 3 days 23.7 ≥ 15.00 7 days 27.9 ≥ 23.00 soundness (autoclave) % 0.13 ≤ 0.8 4) coarse aggregates all mixtures contained local river gravel broken to a maximum size of 12.50mm as coarse aggregates (ca). the grading of ca corresponds to the iraqi standard iqs no.45/ 1984 [15]. the ca properties were determined at the karbala construction laboratory. table iv. chemical analysis of silica fume* no. components silica fume % astm c1240 limitations 1 cao 1.22 sio2 91.05 ≥ 85 al2o3 0.018 fe2o3 0.012 mgo 0.01 so3 0.225 na2o 0.205 k2o 0.155 loss on ignition 2.975 ≤ 6 moisture content 0.68 ≤ 3 2 activity index with portland cement at 7 days 132.4 ≥ 105 percentage retained on 45µm (no. 325) sieve, max, % 7 ≤ 10 surface area (blaine) m 2 /kg 20000 ≥ 15000 *the tests was carrying by the manufacturer engineering, technology & applied science research vol. 12, no. 5, 2022, 9276-9281 9278 www.etasr.com hussein & abdul rasoul: steel fiber addition in eco-friendly zero-cement concrete: proportions and … 5) silica fume silica fume is a by-product of the production of silicon composites in electrical arched furnaces and may be utilized as a cementitious additive to improve the performance of concrete [16]. densified micro-silica fume from mega-add mc (d) type was utilized in this study. its pozzolanic activity index is 132.4% after 7 days. table iv displays the chemical and particular surface of the utilized silica fume, which conforms to astm c1240 [17]. 6) high-range water reducing admixture as shown in table v, this additive belongs to the 3rd generation of superplasticizers. the admixture satisfies the standards of astm c 494 type g [18]. table v. technical description of the additive* chemical base polycarboxylic ether based appearance/color amber homogenous liquid density 1.082 1.142 kg/liter, at 20°c chlorine content% < 0.1 alkaline content% < 3 recommended dosage (0.5 1.5) of binder weight % *manufacturer data sheet 7) water tap water was utilized for mixing and curing. the molten salts comprise fewer than one thousand parts per million. distilled water was utilized for concrete mixing and curing. 8) steel fibers micro-steel fibers of the rc 59/13 bn type, with low carbon content, and with both straight ends were utilized. the fibers have a length of 13mm, diameter of 0.22mm, aspect ratio of 59, tensile strength of 2850mpa, and density of 7.85g/cm 3 . b. mix proportion authors in [3] have invented a sustainable binder known as pozzolime. this binder consists of hydrated-lime, silica-fume; and does not include portland cement. table vi displays the proportions chosen for two pozzolime mixtures, mix1 and mix2, based on the work of [3]. using a small quantity of cement in mix2 hastened setting time. firstly, 6 cubes were tested for compressive strength (fcu) for each mix, and the results show that the value of fcu for mix2 was 15.4 and 18.3mpa for age of 7 and 14 days respectively, while the fcu for mix1 was 16.6 and 18.6mpa respectively. so, mix1 was chosen for the rest of the experimental work. table vi. pozzolime concrete mix proportions and properties mixing materials hydrate lime (kg/m 3 ) cement (kg/m 3 ) silica fume (kg/m 3 ) fa (kg/m 3 ) ca (kg/m 3 ) w/b ratio by wt. hrwr by wt. of cement (%) slump mm compressive strength, 28 days (mp)a mix1 225 225 625 945 0.45 2.9 100 24.3 mix2 310 25* 110 600 940 0.5 2.5 115 23.8 * for accelerated setting time c. casting and curing of specimens all steel molds (cylinders and cubes) were cleaned and their inside was completely lubricated to prevent the concrete from adhering to the molds after setting. the concrete was poured in two layers before being compacted with a tamping rod or vibrating machine to exclude as much air as possible [19-21]. the samples' top surfaces were then troweled, and in order to avoid the loss of mixing water and moisture from the top surface and plastic shrinkage breaking, they were protected with polythene sheets for 24 hours. fig. 1. the tested specimens. the samples were then demolded and completely submerged in tap water until testing time. the curing schedule for pervious concrete was 7 and 28 days of water curing. figure 1 shows the tested specimens. control specimens were also used in this research, so the total samples used were 9 cubes (10×10×10cm) for the density test, 27 cubes (10×10×10cm) for the compressive strength test, 27 cylinders (30×15cm) for the splitting tensile strength test, and 27 cylinders (30×15cm) for the modulus of elasticity test. iii. results and discussion a. dry density concrete's dry density following astm c138 [22] was determined using a cylinder mold. the specimens were evaluated after 28 days of water curing. the density of hardened concrete was determined using the subsequent procedures: γdry = wdry / vol (1) where γdry is the dry density (kg/m 3 ), wdry the oven-dry mass (kg), and vol the volume of the specimens (m 3 ). b. compressive strength compressive strength testing was determined in accordance with the bs en 12390.0 [23] using a standard hydraulic digit ele machine of 2000kn capacity at a loading rate of about 0.30mpa/s. at each test, the average value of 3 tested cubes was determined. the tests on pozzolime concrete were conducted after 7 and 28 days of curing. engineering, technology & applied science research vol. 12, no. 5, 2022, 9276-9281 9279 www.etasr.com hussein & abdul rasoul: steel fiber addition in eco-friendly zero-cement concrete: proportions and … c. splitting tensile strength (fct) splitting tensile strength tests were based on astm c 496/c496m-(2011) [24]. a hydraulic digital testing ele machine of 2000kn capacity was used to load the cylinders constantly up to failure at a loading rate of 2.2kn/sec. the mean splitting tensile strength was calculated using the average of 3 cylinders. d. modulus of elasticity (ec) the modulus of elasticity of concrete (ec) was tested using 3 concrete cylinders in accordance with astm c-469-(2002), [25]. ec is calculated from the stress-strain diagram using a compress meter gauge with a length of 20cm and an accuracy of 0.001mm. the load was applied at a steady rate up to 40% of the maximum load. all laboratory tests values for concrete mix1 are shown in tables vii and viii. table vii. test results of concrete mix1 property steel fibers (%) density (kg/m 3 ) increase in density (%) fresh density 0 2283 ref. fresh density 0.5 2288 0.2 fresh density 1 2292 0.4 dry density 0 2250 ref. dry density 0.5 2270 0.9 dry density 1 2285 1.6 oven density 0 2150 ref. oven density 0.5 2200 2.3 oven density 1 2225 3.5 table vii indicates that the steel fiber percentage has a small effect on the fresh density: the increase of the percentage increased the fresh density by about 0.2, and 0.4% for added steel fiber percentage of 0.5 and 1% with respect to the reference specimens. also, the steel fiber percentage has a small impact on dry density. steel fibers increased dry density by about 0.9 and 1.6% for 0.5 and 1% added steel fiber percentage. steel fibers had a higher impact on the oven density: steel fibers increased the oven density by about 2.3 and 3.5% for 0.5 and 1% added steel fiber percentage. figure 2 shows the impact of steel fiber percentage on concrete density. fig. 2. the impact of steel fiber percentage on concrete density. table vii indicates that the steel fiber percentage has an important impact on compressive strength: steel fibers increased compressive strength by about 2.4 and 16.3% when 0.5 and 1% steel fibers were added at curing age of 7 days. this is comparable to [7], which shows that the percentage of 2% steel fibers increased the compressive strength by about 10.8%. adding steel fibers increased the compressive strength by about 4.1, and 37.6% for 0.5 and 1% steel fiber addition at 14 days. at 28 days, the respective increase percentages were 4.9 and 12.8%. figure 3 shows the effect of steel fiber percentage on concrete compressive strength at various ages. table viii. results of laboratory tests for concrete mix1 property steel fiber (%) result (mpa) increase (%) fcu, 7 days 0 16.6 ref. 0.5 17 2.4 1 19.3 16.3 fcu, 14 days 0 18.6 ref. 0.5 22.7 4.1 1 25.6 37.6 fcu, 14 days 0 24.3 ref. 0.5 25.5 4.9 1 27.4 12.8 fct, 7 days 0 2.11 ref. fct, 14 days 0.5 2.36 11.8 fct, 28 days 1 2.6 23.2 ec, 7 days 0 23800 ref. ec, 14 days 0.5 24200 1.7 ec, 28 days 1 25000 5 fig. 3. the impact of steel fiber percentage on concrete compressive strength at various ages. also, table viii indicates that the steel fiber percentage has a significant impact on splitting tensile strength (fct) for 28 days curing age. steel fiber 0.5 and 1% addition increased fct by about 11.8 and 23.2%. finally, the addition of steel fibers has an impact on ec after 28 days of curing. steel fiber 0.5 and 1% addition increased ec by about 1.7 and 5%. iv. parametric study figures 4, 5, 6, and 7 indicate the impact of steel fiber percentage on density, compressive strength, splitting tensile strength, and modulus of elasticity respectively. the relation between the steel fibers percentage and splitting tensile strength was linear, while the relation between steel fiber percentage and compressive strength and modulus of elasticity was nonlinear for specimens cured for 28 days. engineering, technology & applied science research vol. 12, no. 5, 2022, 9276-9281 9280 www.etasr.com hussein & abdul rasoul: steel fiber addition in eco-friendly zero-cement concrete: proportions and … fig. 4. impact of steel fiber percentage on density. fig. 5. impact of steel fiber percentage on compressive strength. fig. 6. impact of steel fiber percentage on splitting tensile strength after 28 days of curing. fig. 7. effect of steel fiber percentage on the modulus of elasticity after 28 days of curing. v. conclusions • steel fiber percentage had a minor influence on fresh density. adding 0.50 and 1.0% steel fiber to the reference specimen enhanced the fresh density by 0.2% and 0.4% respectively. • steel fiber percentage had a marginal impact on dry density. adding 0.5 and 1.0% steel fibers to the reference specimen raised the dry density by 0.9% and 1.6% respectively. • steel fiber percentage had a larger influence on oven density. adding 0.5 and 1% steel fibers raised oven density by 2.3% and 3.5% respectively. • steel fiber percentage had an important impact on compressive strength. adding 0.50 and 1.0% steel fibers increased compressive strength by 2.4% and 16.3% respectively, after 7 days of curing. adding 0.50 and 1.0% steel fibers increased compressive strength by 4.1% and 37.6% at 14 days and 4.9% and 12.8% at 28 days. • steel fiber percentage had a substantial influence on splitting tensile strength at 28 days. adding 0.50 and 1.0% steel fibers enhanced splitting tensile strength by 11.8% and 23.2% respectively. • steel fiber percentage affects the modulus of elasticity at 28 days. adding 0.50 and 1.0% steel fibers increased the modulus of elasticity by 1.7% and 5% respectively.. vi. recommendations for future work • studying eco-friendly zero-cement concrete proportions and properties under the effects of high-temperature. • studying slurry infiltrated fiber concrete (sifcon) proportions and properties under the effects of hightemperature. references [1] a. j. alsaad, t. s. al-attar, and b. s. al-shathr, "utilization of mineral sequestration for co2 capturing in car parks and tunnels," engineering and technology journal, vol. 38, no. 5, pp. 728–737, may 2020, https://doi.org/10.30684/etj.v38i5a.594. 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[17] astm c1240-20 : standard specification for silica fume used in cementitious mixtures. astm international, 2020. [18] astm c494/c494m-13: standard specification for chemical admixtures for concrete. astm international, 2013. [19] a. m. al-hilali, a. f. izzet, and n. oukaili, "static shear strength of a non-prismatic beam with transverse openings," engineering, technology & applied science research, vol. 12, no. 2, pp. 8349–8353, apr. 2022, https://doi.org/10.48084/etasr.4789. [20] b. f. abdulkareem, a. f. izzet, and n. oukaili, "post-fire behavior of non-prismatic beams with multiple rectangular openings monotonically loaded," engineering, technology & applied science research, vol. 11, no. 6, pp. 7763–7769, dec. 2021, https://doi.org/ 10.48084/etasr.4488. [21] h. m. hekmet and a. f. izzet, "performance of segmental postτensioned concrete beams exposed to high fire temperature," engineering, technology & applied science research, vol. 9, no. 4, pp. 4440–4447, aug. 2019, https://doi.org/10.48084/etasr.2864. [22] astm c138/c138m-17a: standard test method for density (unit weight), yield, and air content (gravimetric) of concrete. astm international, 2017. [23] bs en 12390-3:2019 tc: testing hardened concrete compressive strength of test specimens. bsi, 2019. [24] astm c496/c496m-17 : standard test method for splitting tensile strength of cylindrical concrete specimens. astm international, 2017. [25] astm c469/c469m-14: standard test method for static modulus of elasticity and poisson’s ratio of concrete in compression. astm international, 2014. microsoft word etasr_v12_n3_pp8605-8610 engineering, technology & applied science research vol. 12, no. 3, 2022, 8605-8610 8605 www.etasr.com espina et al.: the optimal high heating value of the torrefied coconut shells the optimal high heating value of the torrefied coconut shells randell u. espina school of engineering and architecture ateneo de davao university davao city, philippines ruespina@addu.edu.ph renyl b. barroca school of engineering and architecture ateneo de davao university davao city, philippines rbbarroca@addu.edu.ph michael lochinvar s. abundo nanyang technological university singapore mlsabundo@gmail.com received: 21 march 2022 | revised: 31 march 2022 | accepted: 4 april 2022 abstractcoconut is a biomass resource that is abundant in tropical countries. in 2020, the philippines planted 347 million coconut trees that produced 14.7 million tons of coconuts. the coconut shells (endocarp) are considered a waste material, which comprise 15.18% of each fruit and account for 2.2 million tons. the calorific value of raw coconut shells is 30.79mj/kg. when torrefied at 275°c for 30 minutes holding time, the calorific value reached the optimal of 34.37mj/kg, representing an increase of 11.64%. the mass yield (my) was 90.10% and the energy density was 111.64%, resulting in an energy yield of 100.59%. keywords-coconut; shells; torrefaction; downdraft; gasifier; gasification; gas synthesis i. introduction herbaceous and woody biomasses are used as feedstocks for biomass power plants to produce electricity. biomass has the potential to replace fossil fuels as a way of fuel-switching to protect the environment [1]. the philippines, with a total forest land of 15,805,325 hectares [2], is home to various naturally grown trees, such as the industrial tree plantation species (itps) like the paraserianthes falcataria [3], coconut, and agricultural products, like bananas, abaca, corn, rice, sugarcane, pineapple, and many others [4, 5]. in 2020, the philippines produced 820 thousand cubic meters of logs [2] and 66.30 million tons (mt) of various agricultural products and falcata. rice contributed by 19.29 mt, corn by 8.12 mt, sugarcane by 24.40 mt, and coconut by 14.49 mt [5]. the coconut tree, which is considered a woody biomass, grows throughout the humid areas of the tropics. each tree can have an average of 70 nuts and a maximum of 150 nuts every year, and the shell of each fruit accounts for 15.18% of its mass [6]. in 2020, 14.49 mt of coconut fruits were harvested [4, 5] thus producing about 2.20 mt of coconut shells. these coconut shells are also used as activated carbon furniture. they are typically used for cooking briquettes, either as coconut choir with high flexural strength [7] or other biomass feedstock. coconut trees are widely grown and owned by big companies, individuals, or villagers. there are various methods of changing the thermochemical properties of coconut shells like torrefaction, carbonization, pyrolysis, and combustion [8]. torrefaction is a burning or combusting process where the raw biomass is heated up at a modest temperature from 200°c to 300°c to dry it or convert it to a coal-like material which eventually improves its properties as a biofuel [9]. moreover, exposing the materials to a moderately high temperature at an expanded holding time enhances their calorific value [10]. biomass gasification power system (bgps), is a known and efficient biomass power technology [8]. biomass gasification is claimed to produce fewer greenhouse gases since it recaptures carbon dioxide and reuses other hazardous gases [8, 11]. the energy conversion efficiency of any biomass power technology depends mainly on the characteristics of the biomass feedstock, especially on its calorific value or high heating value (hhv) [8, 12]. hhv can be quantified through proximate analysis where the moisture content (%mc), the volatile matter (%vm), the ash content (ash), and the fixed carbon (%fc) are measured or with the use of a bomb calorimeter. the calorific value can also be calculated through ultimate analysis using the assessed carbon (c), hydrogen (h), nitrogen (n), oxygen (o), and sulfur (s). torrefied coconut shells (tcs) are not extensively studied for energy production. in [10], the tcs's hhv increased from 18.94mj/kg to 31.23mj/kg at 250°c, with 30 minutes of holding time, and a size of 15mm×15mm. this indicates that the torrefaction procedure increased the hhv of coconut shells by 64.89%. also, authors in [13] showed that the hhv of torrefied coconut leaves improved significantly from 17.95mj/kg (air-dried) to 27.78mj/kg (torrefied at 295°c), a 54.76% increase. however, despite the demonstrated improved properties of the tcs, the energy density, mass yield, and corresponding author: randell u. espina engineering, technology & applied science research vol. 12, no. 3, 2022, 8605-8610 8606 www.etasr.com espina et al.: the optimal high heating value of the torrefied coconut shells energy yield of the biomass gasification power system utilizing tcs as biomass feedstock is not yet well supported. to determine if there is an improvement to the calorific value of the coconut shells that are torrefied, the study performed torrefaction to improve the coconut shells' thermochemical properties. torrefaction is heating without air using a temperature from 200°c to 300°c, while pyrolysis uses heating temperature above 300°c without the presence of air [8, 14, 15]. the study torrefied the coconut shells using an electric furnace/oven and set the temperatures at 200°c, 225°c, 250°c, 275°c, and 300°c, and holding times of 10, 20, and 30 minutes. before torrefaction, the coconut shells were ground at an average size of 25mm×25mm. ii. materials and methods the study used an experimental research design where the calorific value or hhv of the tcs was determined using proximate and ultimate analyses. the hhv using proximate analysis was compared to the hhv using ultimate analysis. figure 1 shows the experimental setup of the torrefaction of the coconut shells. a series of experiments and tests was conducted to determine the impact of torrefaction on the coconut shells' mass yield, energy density, and energy yield when exposed to varying temperatures and residence time. ensuring the integrity of the experimental results, the samples were sent to the davao analytical laboratory for elemental analysis. using a crusher, 15kg of raw coconut shells were ground at approximately 25mm×25mm (see figure 2). the selected ground coconut shells weighing 1,000 ±0.5%g were placed in a pan for heating at an electric furnace. for each test, the furnace was set to 200°c, 225°c, 250°c, 275°c, and 300°c, for cooking or holding time of 10, 20, and 30min for every temperature setting. fig. 1. torrefaction experimental setup. fig. 2. torrefied coconut shells. after heating, the tcs weighing 500±0.5%g were placed in cellophane and were sealed (figure 3). for elemental analysis, 16 samples were sent to the davao analytical laboratory, an accredited analytical lab in davao city, philippines. the analytical test results for 1 raw and 15 torrefied shells were considered. the resulting %mc, %vm, %fc, %ash, and s were used in determining the high heating values and applied in assessing h, c, n, and o. fig. 3. sealed torrefied coconut shells. iii. result analysis a. proximate analysis results the proximate analysis determines the %mc, %ash, %vm, and %fc of any biomass feedstock [8]. the davao analytical laboratory uses the astm d1762-84 standard test method for chemical analysis of biomasses to determine %mc, %ash, %vm, and %fc [16] and gravimetry to determine the s content of tcs. hhv is the amount of heat released per unit mass of any fuel. to find the calorific value or the hhv, the equation: hhv = 354.3× %fc + 170.8 × %vm (1) introduced in [17] was used. the result falls not more than 2% relatively to the measured heating values of any biomass feedstock using the bomb calorimeter. additionally, the calculation can be cross-checked using [18, 19]: hhv = 0.1846 × %vm + 0.3525 × %fc (2) table i displays the proximate analyses of the 16 samples, including the hhv. it can be seen that the coconut shells with the lowest hhv are the raw coconut shells (rcs). table i. proximate analysis type, temp (°c), time (min) %mc %ash %vm %fc hhv (mj/kg) bcs 0, 0 11.90 0.88 0.63 86.60 30.790 tcs 200, 10 7.40 0.06 3.40 89.10 32.150 tcs 200, 20 6.80 0.54 3.30 89.30 32.200 tcs 200, 30 6.60 1.70 2.40 89.30 32.050 tcs 225, 10 7.60 0.76 3.10 88.50 31.890 tcs 225, 20 6.50 1.50 6.30 86.70 31.790 tcs225. 30 7.20 0.44 6.20 86.20 31.600 tcs 250, 10 8.00 0.97 5.00 86.00 31.320 tcs 250, 20 4.80 0.43 6.40 88.40 32.410 tcs 250, 30 3.60 1.80 9.90 84.70 31.700 tcs 275, 10 7.50 0.10 6.30 86.10 31.580 tcs 275, 20 5.00 0.20 4.40 90.40 32.780 tcs 275, 30 2.00 0.60 0.66 96.70 34.370 tcs 300, 10 4.70 0.95 2.00 92.40 33.080 tcs 300, 20 2.40 2.80 8.20 86.60 32.080 tcs 300, 30 1.10 0.81 14.20 83.90 32.150 as shown in figure 4, the optimal hhv is at the temperature of 275°c for holding time of 30min, where the magnitude reached 34.37mj/kg. at 300°c and holding time of 10min, hhv reduced to 33.08mj/kg, or by 3.75%. relatively engineering, technology & applied science research vol. 12, no. 3, 2022, 8605-8610 8607 www.etasr.com espina et al.: the optimal high heating value of the torrefied coconut shells to the rcs, the increase was about 11.63%. in [10], the hhv increased by 51.65% when the coconut shells were torrefied at 250°c for a holding time of 15min. several studies claim that the torrefaction process improves the hhv of biomass feedstock [20]. fig. 4. hhv of coconut shells. figure 5 compares the hhv of coconut shells torrefied at various temperature levels and holding times. at a temperature of 275°c and holding time of 30min, the maximum hhv of 34.37mj/kg was achieved. fig. 5. torrefied coconut shells proximate analysis. b. ultimate analysis results the ultimate analysis determines carbon (%c), hydrogen (%h), nitrogen (%n), sulfur (%s), and oxygen (%o) [21]. hhv can be measured using the bomb calorimeter or can be calculated using various correlational equations. in the proximate analysis, the value of hhv was determined with an equation using %vm and %fc. for ultimate analysis, the equation [22, 23]: hhv = 0.341 × %c + 1.322 × %h + 0.0686 × %s – 0.12 × %o + % × n – 0.0153 × %ash (3) was used. this equation differs from that of [17], since it uses the results of the ultimate analysis parameters and %ash from the proximate analysis. note that the calorific value of the biomass is highly dependent on %c and %h. the davao analytical laboratory and other chemical analytical laboratories do not offer ultimate analysis services, hence correlation equations were used. to determine the %c, the equation espoused by [24, 25] was used: %c = 2.1877 × hhv + 5.9068 (4) for the determination of the %h, the equation supported by [19] was used: %h = 0.059 × %fc + 0.060 × %vm + 0.010 × %ash (5) the equation introduced in [26] can be used also to determine %h: %h = ((3.55 × %c – 232) × %c – hhv + 131 × %n + 20600) / (2230 – 51.2 × %c) kj/kg (6) regarding the %n determination, the equation introduced in [27] was used: %n = 2.6116 × hhv – 1.1092 × %c + 6.3884 × %s (7) though these equations may introduce a minute deviation to the measured values, they are widely used in biomass elemental analyses [19, 20]. table ii lists the ultimate analysis and the hhvs for the rcs and tcs. temperature and residence time affect the calorific value of the biomass [28]. at 275°c and holding time of 30min, the hhv of the tcs increased to 34.37mj/kg. moreover, syngas is highly dependent on h2 and co content [28]. table ii. coconut shells ultimate analysis type, temp (°c), time (min) c (%) h (%) n (%) s (%) o (%) hhvult (mj /kg) hhvprox (mj /kg) bcs 0, 0 73.3 5.2 0.8 0.3 19.7 30.18 30.79 tcs 200, 10 76.2 5.5 0.5 0.2 17.6 31.60 32.15 tcs 200, 20 76.4 5.5 0.6 0.2 16.8 31.88 32.20 tcs 200, 30 76.0 5.4 0.7 0.2 15.9 31.90 32.05 tcs 225, 10 75.7 5.4 0.4 0.2 17.6 31.29 31.89 tcs 225, 20 75.5 5.5 0.9 0.2 16.4 31.90 31.79 tcs 225. 30 75.0 5.5 0.9 0.3 17.9 31.56 31.60 tcs 250, 10 74.4 5.4 0.7 0.2 18.3 30.95 31.32 tcs 250, 20 76.8 5.6 0.9 0.2 16.0 32.61 32.41 tcs 250, 30 75.3 5.6 0.8 0.2 16.3 31.89 31.70 tcs 275, 10 75.0 5.5 0.8 0.2 16.8 30.84 31.58 tcs 275, 20 77.6 5.6 1.0 0.2 13.8 32.51 32.78 tcs 275, 30 81.1 5.8 1.3 0.2 9.8 35.00 34.37 tcs 300, 10 78.3 5.6 1.0 0.2 13.1 32.85 33.08 tcs 300, 20 76.1 5.6 0.9 0.2 15.4 31.98 32.08 tcs 300, 30 76.2 5.8 0.9 0.2 15.1 32.48 32.15 milne’s [27] equation was used for ultimate analysis, while the cordero's [17] for proximate analysis. figure 6 shows the graphs and the variation of the hhv using the milne's equation: hhv = 0.341 × %c + 1.322 × %h + 0.0686 × %s – 0.12 × %o + % × n – 0.0153 × %ash (8) engineering, technology & applied science research vol. 12, no. 3, 2022, 8605-8610 8608 www.etasr.com espina et al.: the optimal high heating value of the torrefied coconut shells and provides identical value with: hhv = 354.3 × %fc + 170.8 × %vm (9) introduced in [17]. note that the optimal hhv for the two equations is at 275°c and 30min. the mean difference on the hhv using the two equations is only ±0.52% or the mean absolute error (mae) was 0.3388. fig. 6. hhv ultimate vs. hhv proximate. c. mass yields, energy densities, and energy yields with the hhv known, mass yield (my), energy density (ed), and energy yield (ey %) can be determined. my gauges the amount of the torrefaction process. it provides the portion of the mass retained in the biomass after torrefaction [21]. it is the mass produced as a result of the processing of the biomass and is expressed as the ratio between the mass of the torrefied biomass (mtorr) to the mass of the raw biomass (mraw) or (mtorr/mraw) × 100%. ed is the amount or quantity of energy stored in a given biomass, which is expressed mathematically as the proportion between the hhv of the torrefied biomass (hhvtorr) to the hhv of the raw biomass (hhvraw) or (hhvtorr/hhvraw) [8]. ey is the quantity of energy essentially collected from the biomass. it is expressed as the product of the ed and the my or my × (hhvtorr/hhvraw) × 100%. though torrefaction causes some losses, it makes biomass to be utilized effectively, especially in energy systems. this loss in energy can be quantified by the ey [30]. table iii shows the coconut shells' my, ed, and ey. on average, each sample weighed 500±0.5%g. after torrefaction, the weight of each sample was reduced by an average of 6.27% and the average moisture content was 5.82%. figure 7 shows the graphical presentations of my, ed, and ey. as the temperature and holding time increase, the my, the ratio between the mass of the tcs and the mass of the rcs, reduce. this is true, since the mass of the tcs becomes lower than the mass of the rcs as the exposure to a high temperature is lengthened. the process also reduces the %mc. moreover, the ratio between the tcs and the rcs hhv increases while the my decreases. this increase in the ed is a proof that the calorific value of the coconut shells increases at a reduced moisture content of the biomass. table iii. mass yield, energy density, and energy yield type, temp (°c), time (min) mass (torr) (g) mass (dry) (g) hhv (mj/kg) my (%) ed (%) ey (%) bcs 0, 0 500.0 440.5 30.8 tcs 200, 10 477.5 442.2 32.2 95.5 104.4 99.7 tcs 200, 20 474.5 442.2 32.2 94.9 104.6 99.3 tcs 200, 30 473.5 442.3 32.1 94.7 104.1 98.6 tcs 225, 10 478.5 442.1 31.9 95.7 103.6 99.1 tcs 225, 20 473.0 442.3 31.8 94.6 103.3 97.7 tcs225. 30 476.5 442.2 31.6 95.3 102.6 97.8 tcs 250, 10 480.5 442.1 31.3 96.1 101.7 97.8 tcs 250, 20 464.5 442.2 32.4 92.9 105.3 97.8 tcs 250, 30 458.5 442.0 31.7 91.7 103.0 94.4 tcs 275, 10 478.0 442.2 31.6 95.6 102.6 98.1 tcs 275, 20 465.5 442.2 32.8 93.1 106.5 99.1 tcs 275, 30 450.5 441.5 34.4 90.1 111.6 100.6 tcs 300, 10 464.0 442.2 33.1 92.8 107.4 99.7 tcs 300, 20 452.5 441.6 32.1 90.5 104.2 94.3 tcs 300, 30 446.0 441.1 32.2 89.2 104.4 93.1 average 469.6 441.9 32.1 93.5 104.6 97.8 std. dev. 11.3 0.3 0.8 2.3 2.5 2.2 the product of the my and the ed or the ratio between the products of the mass and hhv of the tcs and rcs is the ey. ideally, the value of the ey should be greater than 1 (100%). at a temperature of 275°c and resident time of 30min, the ey reached 100.59%. this indicates that the torrefaction process improved the value of biomass. fig. 7. mass yield, energy density, and energy yield. d. summary 1) proximate and ultimate analysis forest and agricultural resources can be used to produce electricity. one of the available resources is the coconut shell, made at 2.2 mt per year in the philippines [4, 5, 31]. its hhv was investigated for the possible use of coconut shells to produce electricity. to improve the hhv of any biomass resource, torrefaction (200°c to 300°c) is a good choice [20]. coconut shells were torrefied at 200, 225, 250, 275, and 300°c with residence times of 10, 20, and 30min. tcs were sent to an accredited analytical laboratory for proximate analysis. they determined %mc, %vm, %ash, and %fc using the standard test method for chemical analysis of wood charcoal and other biomasses [8, 16]. the sulfur content (%s) was analyzed using gravimetric analysis. using (9) [17], the hhvprox of 15 engineering, technology & applied science research vol. 12, no. 3, 2022, 8605-8610 8609 www.etasr.com espina et al.: the optimal high heating value of the torrefied coconut shells torrefied shells, including the rcs, were determined. the optimal hhv of 34.37mj/kg was found for shells torrefied at 275°c for 30min. for the ultimate analysis wherein %c, %h, %n, %s, and %o [21], various known equations were used. though these equations introduced minor deviations to the measured values, they are widely used in the elemental analyses of biomass and other feedstocks [19, 20]. table iv lists the equations used in solving the hhv using ultimate analytical elements. table iv. ultimate analysis equations element equation reference %c (4) [24, 25] %h (5) [19] %n (7) [27] %s laboratory test results gravimetric %ash laboratory test results astm d1762-84 %o %o = 100% %c %h %n %s %ash [32] the hhvulti (ultimate analysis) was found using (3) [22, 23]. comparing the hhvprox and hhvulti, the mae was ±0.3388. 2) mass yield, energy density, and energy yield on average, the my, the ratio between the hhvtorr and the hhvraw, was 93.51%, this is what remains in tcs after torrefaction [21]. the higher the temperature and the residence time, the higher the reduction in mass hence reducing the my. ed, i.e. the ratio between the hhvtorr and the hhvraw, is 104.61%. higher ratio would mean that the tcs had increased their hhv by an immense amount. ey, i.e. the product of the my and the ed, was 97.83%. this is the amount of energy that can be potentially collected from the tcs. at the temperature of 275°c and residence time of 30min, the my was 90.10%, and the ed was 111.64% resulting in an ey of 100.59%. iv. conclusion biomass is a non-fossilized, biodegradable organic substance that can be utilized to supplement other renewable energy technologies and replace fossil fuels. coconut is woody biomass that grows in abundance in the tropics and is a good alternative energy resource. ground coconut shells (25mm×25mm) were torrefied to increase their hhv. at 275°c and 30min residence time, the optimal hhv of 34.37mj/kg was achieved. this suggests an hhv 11.63% higher than the rcs's hhv of 30.79mj/kg. this result supports the findings of [10, 13]. the computed calorific value or hhv can be determined with high certainty utilizing a combination of laboratory analyses using established test procedures for chemical analysis and correlative equations developed and extensively used. since the tcs achieved optimal hhv, they reached an ey of 100.59%. ey is the product of the my at 90.10% and the ed at 111.64%. acknowledgment this work was supported financially by the ateneo de davao university, the office of the president, and the university research council. this project is a part of the biomass gasification power system program of the school of engineering and architecture of the ateneo de davao university. references [1] i. naim and t. mahara, "fuel substitution for energy saving: a case study of foundry plant," engineering, technology & applied science research, vol. 8, no. 5, pp. 3439–3444, oct. 2018, https://doi.org/ 10.48084/etasr.2298. 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[32] s. h. solangi, a. q. jakhrani, k. c. mukwana, a. r. jatoi, and m. r. luhur, "investigation of quantity, quality and energy content of indigenous sugarcane trash in naoshehro feroze district, sindh," engineering, technology & applied science research, vol. 8, no. 6, pp. 3609–3613, dec. 2018, https://doi.org/10.48084/etasr.2411. microsoft word etasr_v13_n3_pp10622-10629 engineering, technology & applied science research vol. 13, no. 3, 2023, 10622-10629 10622 www.etasr.com nguyen et al.: an application of analytic network process (anp) to assess critical risks of bridge … an application of analytic network process (anp) to assess critical risks of bridge projects in the mekong delta region minh duc nguyen faculty of transport economics, ho chi minh city university of transport, vietnam duc.nguyen@ut.edu.vn (corresponding author) phu quang tran faculty of transport economics, ho chi minh city university of transport, vietnam phu.tran@ut.edu.vn hoang ba nguyen faculty of transportation engineering, ho chi minh city university of transport, vietnam hoangnb@hcmutrans.edu.vn received: 21 february 2023 | revised: 9 march 2023 | accepted: 17 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5802 abstract risk management is one of the critical factors contributing to infrastructure project success. risk assessment enables both practitioners and decision-makers to identify and analyze potential risks and quantify risk impacts on project performance in terms of time, cost, and quality. even though many studies attempt to investigate the risk of construction projects with the consideration of technical, organizational, and legal aspects, only a few studies deeply focus on identifying the critical risks of bridge projects with the examination of climate change impact. the current study concentrates on analyzing risks in bridge construction projects in the mekong delta region which has been significantly affected by climate change. an intensive review of previous publications and technical project reports from 2010 to 2021 was conducted to identify the list of potential risks and interviews and discussions with engineers and managers involved in bridge projects were carried out to identify critical risks of bridge projects. analytic network process (anp) method was introduced to evaluate the impact of such risks on the performance of bridge project implementation. the initial results of this study provide a holistic picture of risk management for bridge projects with the consideration of climate change impact. the findings can help the involved parties including owners, contractors, and project managers to assess particular risks and scheme backup plans to mitigate project delays and cost overruns. keywords-risk assessment; risk management; bridge projects; mekong delta i. introduction risk is defined as a positive or negative deviation of a variable from its expected value and is commonly understood as a loss [1]. due to potential risks, bridge construction projects often fail to achieve their time, quality, budget and operation goals [2]. risk management plays a vital role in minimizing the negative consequences of unexpected events on the bridge project performance. however, risk management for bridge construction projects is a challenging process with the involvement of uncertainty factors from policy, society, economy, environment, finance, and technology [3]. even though many studies have attempted to investigate the separate risks of bridge construction projects, only a few studies provide a holistic picture of risk management regarding bridge construction projects. particularly very few scholars focus on assessing the potential risks of bridge projects in the context of developing countries. thus, a case study in vietnam with the consideration of bridge projects in the mekong delta region is carefully examined in this paper. the selected case study, the mekong delta region, encompasses a large portion of southwestern vietnam, with an area over 40,500km 2 , which has a large number of ongoing bridge projects [4]. bridge construction projects in this area play a vital role in connecting the southern areas of vietnam, and improving the agricultural trading capacity which directly contributes to the local economic growth [5]. risk management for bridge projects in the mekong delta is considered monumental in ensuring the success of strategic connection goals of local governments. in practice, conventional studies on risk assessment in technical and organizational terms have been carried out, but there is a engineering, technology & applied science research vol. 13, no. 3, 2023, 10622-10629 10623 www.etasr.com nguyen et al.: an application of analytic network process (anp) to assess critical risks of bridge … lack of studies concentrating on potential risks caused by climate change. therefore, in this paper, we aim to provide a holistic picture of risk management by considering potential risks caused by climate change. the analytic network process (anp) is a promising approach [6] that was selected to identify critical risk factors and assess the impacts of risk on project objectives including time, cost, quality, and operation. ii. risk identification a. literature review in this study, a mini scoping technique was applied for searching articles. the scopus database was selected for searching with the use of the combination of keywords: construction projects and bridge projects and risk management or risk identification or risk assessment within a specific period from 2000 to 2020. the initial search resulted in 192 articles related to construction project risk management. next, we focused on the risks of bridge projects to eliminate some articles and a shortlist of 52 articles was produced. further, our research team carefully read the titles and abstracts and skimmed the whole content of the studies and finally, 28 of 52 publications were selected for analysis. b. documentation review the mekong delta region in vietnam is one of the affected places by climate change [1]. the implementation of bridge projects in this region suffers from many difficulties and potentially contains significant risks in comparison with bridge construction conditions in other regions in vietnam. in this study, we carefully examined the documentation of real bridge projects in the mekong delta region during the period from 2000 to 2020. as a result, 30 typical projects were selected to clarify practical risks which were used to compare to risks identified from the literature. c. risk identification results through the survey of literature review along with the project documentation review, a list of critical risk factors was identified and is presented in table i. these risk factors were classified into the following groups: political and legal risks, social risks, technical risks, economic risks, environmental risks, and financial and commercial risks. iii. application of analytic network process (anp) to assess critical risks a. analytic network process model anp is widely used for multi-criteria-decision-making [52]. anp is a multi-criteria theory of measurement used to derive relative priority scales of absolute numbers from individual judgments that also belong to the fundamental scale of absolute numbers [53]. the judgments in the anp model show the relative impact of one of two elements over the other in a pairwise comparison process on a third element in the system [53]. in anp, pairwise comparisons of the elements in each level are conducted with respect to their relative importance towards their control criterion. table i. risk factors in bridge construction projects in the mekong delta region no code risks references i pl political and legal risks pl1 changes in the state organization [2-11] pl2 political interference [2-5, 12, 13] pl3 legal procedures are complicated and unclear [3, 9, 14-18] pl4 changes in legal documents and regulations [3, 8, 9, 16-18] pl5 corruption of officials [3, 17, 19, 20] ii so social risks so1 difficulty in ground clearance [6, 9, 15, 21-25] so2 compensation cost [23-25] so3 opposition of the community [6, 9, 15, 21, 22] so4 disputes in projects [26-29] so5 security at the construction site [26, 28, 29] so6 local resident consensus [19, 30-33] iii te technical risks te1 lack of management method [29, 23] te2 errors in defining project scope [4, 7, 14, 29, 35] te3 incomplete and inaccurate survey and experimental data [4, 16, 36, 37] te4 inappropriate project approaches [9, 10, 21, 37-39] te5 errors in design appraisal and estimation [13, 40] te6 non-compliance with construction standards [4, 7, 14, 29, 41] te7 changing design and technical plans [4, 17, 18] te8 supply delays [10, 37-39] te9 unsuitable construction organization [8, 14, 21, 37] te10 machinery breakdown [8, 14, 17, 22, 36, 39] te11 capacity of contractors, supervision consultants [8, 10, 15, 37, 38, 42, 43] iv ec economic risks ec1 inflation [3, 36] ec2 interest rates change [3, 4, 43, 44] ec3 economic policy [3, 4, 9, 10, 37, 44] ec4 currency exchange rate changes [3, 6, 22, 36] ec5 economic depression [3, 4, 9, 10, 37, 43, 44] ec6 fuel/material prices change [13, 45] ec7 macroeconomics [3, 4, 9, 10, 37, 43, 44] ec8 the market changes [21, 39, 46] v en environment risks en1 unstable geology [6, 9, 15, 21, 22, 47-49] en2 sea level rise [10, 14, 21, 43, 50] en3 erosion [10, 14, 21, 50] en4 changes in rainy season, rainfall [2, 7, 10, 14, 21, 43, 50] en5 temperature change [2, 7, 10, 14, 21, 43, 50] en6 saltwater intrusion en7 storms [6, 8, 50] en8 floods [6, 8, 50] vi fc financial and commercial risks fc1 project funding [6, 22, 51] fc2 the ability to attract finance for the project [6, 22, 51] fc3 financial capacity of the contractor [8, 14, 22] fc4 weak financial management [4, 16, 21, 46] fc5 disrupted commercial activities [14, 20, 24, 25, 30] fc6 compensation for accidents [2, 22] fc7 weak contract management [10, 14, 15, 21, 22] fc8 weak cost management [5, 18, 21, 50] fc9 exceeded estimated cost [5, 17, 18, 21, 20] engineering, technology & applied science research vol. 13, no. 3, 2023, 10622-10629 10624 www.etasr.com nguyen et al.: an application of analytic network process (anp) to assess critical risks of bridge … once the pairwise comparisons are completed for the whole network, the vectors corresponding to the maximum eigenvalues of the constructed matrices are computed and a priority vector is obtained. the outcome of the comparison process is used in the development of the unweighted matrix, weighted matrix, and limit matrix. the super matrices’ outcome of anp is used to assess the priority of risk groups as in figure 1. the goal of the anp model in this study is to assess the priority of risks with the consideration of successful criteria of a bridge project. in the literature, there are common perspectives on success criteria for a construction project, as is clearly shown in table ii. fig. 1. the anp model assesses the priority of risks. table ii. summary of success criteria no success criteria reference 1 cost, time, performance, satisfaction, operation, effectiveness [54] 2 cost, time, technical requirements, customer satisfaction, operation [55] 3 time performance, cost performance, quality performance, health, safety and environment (hse), client satisfaction [56] 4 cost, time, meeting the technical specifications, customer satisfaction, stakeholder satisfaction, operation [57] 5 cost, time, quality, scope, customer satisfaction, safety, team satisfaction, shareholder satisfaction [58] conventionally, successful criteria for a construction project often include time, cost, and quality. however, the efficiency of operating bridge projects is a major concern. thus, we decided to select 4 main successful criteria, i.e. quality, cost, time, and operation to assess the priority of risks to ensure comprehensive risk assessment. in addition, the alternatives in the anp model are 6 main risk groups (figure 1) consisting of political and legal risks (pl), social risks (so), technical risks (te), economic risks (ec), environmental risks (en), and financial and commercial risks (fc). b. questionnaire survey the identification of risk factors obtained in the literature review and documentation review (table i) was used to design a questionnaire survey. the survey was then carried out to collect data from project stakeholders including project owners, project managers, contractors, sub-contractors and consultants who have been involved in the bridge construction projects in the mekong delta region. the respondents were asked to rate the impact level of critical risks on project cost, time, quality, and operation on the scale shown in table iii. table iii. score of importance score importance score importance score importance 1 extremely low importance 4 moderately low importance 7 high importance 2 very low importance 5 moderate importance 8 very high importance 3 low importance 6 moderately high importance 9 extremely high importance iv. research results a. questionnare participants a total of 170 survey questionnaires were sent to experts in the bridge construction field. face-to-face and online modes were used to survey. we received 88 full responses, accounting for around 53% of the total number of target participants. most respondents have more than 5-year experience, and particularly more than 32% of respondents have more than 10-year experience in the construction industry domain. fig. 2. stakeholder percentages fig. 3. expert experience percentages. engineering, technology & applied science research vol. 13, no. 3, 2023, 10622-10629 10625 www.etasr.com nguyen et al.: an application of analytic network process (anp) to assess critical risks of bridge … b. impact risk level rating by msi (mean score of importance) results six main groups and 47 associated risk factors were assessed by experts through the questionnaire survey. the experts participating in the survey were asked to rate the importance of the risk prioritization with the consideration of four main project objectives: quality cost, time, and operation. the final results are shown in tables iv-xi. table iv. importance of the criteria through msi criteria min score max score average score ranking importance of quality 7 9 8.44 1 importance of cost 6 9 7.64 3 importance of time 6 9 7.57 4 importance of operation 7 9 8.07 2 table v. importance of risk groups risk groups importance average score ranking quality cost time operation pl 4.78 5.94 6.78 6.38 5.97 5 so 4.17 5.50 6.50 6.22 5.59 6 te 7.28 6.83 7.16 7.11 7.09 1 ec 5.84 6.78 6.17 6.61 6.35 3 en 6.00 6.33 6.22 7.22 6.44 2 fc 5.72 6.83 6.17 6.11 6.20 4 table vi. importance of risk factors in political and legal groups risk factors the importance for average score ranking quality cost time operation pl1 5.11 5.44 5.33 4.72 5.15 5 pl2 5.28 5.72 5.33 5.44 5.44 4 pl3 5.78 7.17 7.00 6.33 6.57 1 pl4 6.06 6.94 6.78 6.27 6.51 2 pl5 6.11 6.78 5.94 5.77 6.15 3 table vii. importance of risk factors in social group risk factors the importance for average score ranking quality cost time operation so1 6.00 7.89 7.83 6.77 7.12 1 so2 5.67 7.50 7.39 6.77 6.83 2 so3 5.39 6.28 6.83 6.22 6.18 3 so4 4.94 5.89 6.94 6.05 5.96 5 so5 4.83 5.56 5.78 5.83 5.50 6 so6 4.94 6.83 6.39 6.50 6.17 4 table viii. importance of risk factors in technical group risk factors the importance for average score ranking quality cost time operation te1 5.67 6.22 6.00 7.00 6.22 8 te2 7.39 6.50 6.67 7.11 6.92 5 te3 6.89 6.33 6.33 7.05 6.65 7 te4 7.56 6.39 6.72 7.27 6.99 4 te5 7.78 6.56 6.56 7.27 7.04 3 te6 6.83 6.28 6.89 6.72 6.68 6 te7 6.00 6.11 6.28 5.77 6.04 9 te8 7.22 6.39 6.50 6.50 6.65 7 te9 6.39 5.67 5.72 5.94 5.93 10 te10 7.50 7.44 7.33 7.00 7.32 1 te11 7.17 7.17 7.11 6.94 7.10 2 table ix. importance of risk factors in economic group risk factors the importance for average score ranking quality cost time operation ec1 5.11 6.39 5.89 5.66 5.76 2 ec2 4.89 6.11 5.89 5.61 5.63 4 ec3 4.89 5.83 6.11 5.66 5.62 5 ec4 4.83 5.56 5.44 5.50 5.33 8 ec5 5.06 6.11 5.61 5.50 5.57 6 ec6 6.11 7.22 6.89 5.72 6.49 1 ec7 5.00 6.22 5.83 5.83 5.72 3 ec8 4.78 6.11 5.56 5.72 5.54 7 table x. importance of risk factors in environmental group risk factors the importance for average score ranking quality cost time operation en1 6.94 6.72 6.17 6.27 6.53 1 en2 4.94 6.11 5.33 4.94 5.33 2 en3 4.94 6.17 5.44 4.77 5.33 2 en4 5.22 5.67 5.44 4.77 5.28 3 en5 4.83 5.06 4.83 4.61 4.83 7 en6 4.89 5.33 4.94 4.61 4.94 5 en7 5.00 5.00 4.83 4.72 4.89 6 en8 5.17 5.22 5.39 4.72 5.13 4 table xi. importance of risk factors in financial and commercial groups risk factors the importance for average score ranking quality cost time operation fc1 5.83 7.28 7.00 6.22 6.58 1 fc2 5.28 6.78 6.39 5.61 6.02 7 fc3 6.22 7.33 7.00 5.66 6.55 2 fc4 6.00 6.78 6.61 5.77 6.29 4 fc5 5.22 5.28 5.67 5.33 5.38 9 fc6 5.22 5.78 5.56 5.22 5.45 8 fc7 6.17 6.78 6.22 6.05 6.31 3 fc8 6.00 6.44 6.06 6.00 6.13 5 fc9 5.61 6.50 6.28 5.83 6.06 6 the presented survey results helped us to assess the importance level of the risks on specific groups. however, this approach does not accurately reflect the interaction of risks within the whole project. in order to clarify the impact among criteria and risks, the anp model was applied to overcome obstacles. c. analytic network process rating of the impact level of risks the purpose of applying the anp model is to evaluate the priority of the risk groups and risk factors through the calculation of the risk priority index (rpi). this is a method of ranking all risks while taking into account their importance to all considered criteria. based on the survey results of experts, the msi has been determined. in addition, along with the opinions of experts in the group discussion, a pairwise comparison matrix for each model will be established which is scored by a pairwise table [53]. 1) criteria priority to assess risk priority considering the main criteria, a sub model was established and is depicted in figure 4. engineering, technology & applied science research vol. 13, no. 3, 2023, 10622-10629 10626 www.etasr.com nguyen et al.: an application of analytic network process (anp) to assess critical risks of bridge … table xii. pairwise table level of importance pairwise comparison score 1: equally important 1:1 2: equally important to moderate 2:1, 3:2, 4:3, 5:4, 6:5, 7:6, 8:7, 9:8 3: moderately important 3:1, 4:2, 5:3, 6:4, 7:5, 8:6, 9:7 4: moderately important to slightly more important 4:1, 5:2, 6:3, 7:4, 8:5, 9:6 5: slightly more important 5:1, 6:2, 7:3, 8:4, 9:5 6: slightly important to very important 6:1, 7:2, 8:3, 9:4 7: very important 7:1, 8:2, 9:3 8: very important to extremely important 8:1, 9:2 9: extremely important 9:1 fig. 4. sub model for assessing the priority of criteria. through the use of super decision software, the unweighted super matrix, the weighted super matrix, and the limit matrix of bridge project criteria were calculated and are presented in tables xiii-xv. table xiii. unweighted super matrix considering the four main criteria cluster quality cost time operation priority value 0.400 0.00 0.259 0.310 0.167 0.200 0.310 0.412 0.000 0.333 0.000 0.195 0.327 0.493 0.333 0.400 0.493 0.00 0.195 0.167 table xiv. weighted super matrix considering the four main criteria cluster quality cost time operation priority value 0.400 0.00 0.259 0.310 0.167 0.200 0.310 0.412 0.000 0.333 0.000 0.195 0.327 0.493 0.333 0.400 0.493 0.00 0.195 0.167 table xv. limit matrix considering the four main criteria cluster quality cost time operation priority value 0.243 0.243 0.243 0.243 0.243 0.236 0.236 0.236 0.236 0.236 0.252 0.252 0.252 0.252 0.252 0.267 0.267 0.267 0.267 0.267 the normalized priority value (npv), total priority value (tpv), and ideal priority value (ipv) of criteria were calculated and can be seen in table xvi. table xvi. criteria priority criteria tpv npv ipv ranking (r) quality 0.333 0.333 1.000 1 cost 0.167 0.167 0.500 2 time 0.167 0.167 0.500 2 operation 0.333 0.333 1.000 1 2) risk group priority the 6 risk groups of bridge construction projects are political and legal risks (pl); social risks (so); technical risks (te); economic risks (ec); environmental risks (en); financial and commercial risks (fc). the model in figure 1 could be used to assess the priority of the risk groups. through the use of super decision software, the unweighted super matrix, the weighted super matrix, and the limit matrix of the bridge project criteria were calculated and are shown in tables xvii-xix. table xvii. unweighted super matrix for risk groups nodes ec en fc pl so te cost operation quality time a lt e r n a ti v e s ec 0.000 0.206 0.183 0.252 0.219 0.186 0.222 0.166 0.176 0.100 en 0.201 0.000 0.252 0.100 0.136 0.312 0.111 0.223 0.176 0.200 fc 0.180 0.162 0.000 0.190 0.252 0.121 0.222 0.125 0.176 0.100 pl 0.222 0.182 0.177 0.000 0.205 0.190 0.111 0.152 0.097 0.200 so 0.171 0.249 0.186 0.271 0.000 0.191 0.111 0.111 0.060 0.200 te 0.226 0.200 0.201 0.186 0.187 0.000 0.222 0.223 0.315 0.200 c r it e r ia cost 0.250 0.250 0.250 0.250 0.250 0.250 0.000 0.000 0.000 0.000 operation 0.250 0.250 0.250 0.250 0.250 0.250 0.000 0.000 0.000 0.000 quality 0.250 0.250 0.250 0.250 0.250 0.250 0.000 0.000 0.000 0.000 time 0.250 0.250 0.250 0.250 0.250 0.250 0.000 0.000 0.000 0.000 table xviii. weighted super matrix for risk groups nodes ec en fc pl so te cost operation quality time a lt e r n a ti v e s ec 0.000 0.103 0.092 0.126 0.110 0.093 0.222 0.166 0.176 0.100 en 0.100 0.000 0.126 0.050 0.068 0.156 0.111 0.223 0.176 0.200 fc 0.090 0.081 0.000 0.095 0.126 0.061 0.222 0.125 0.176 0.100 pl 0.111 0.091 0.089 0.000 0.103 0.095 0.111 0.152 0.097 0.200 so 0.086 0.125 0.093 0.136 0.000 0.095 0.111 0.111 0.060 0.200 te 0.113 0.100 0.101 0.093 0.094 0.000 0.222 0.223 0.315 0.200 c r it e r ia cost 0.125 0.125 0.125 0.125 0.125 0.125 0.000 0.000 0.000 0.000 operation 0.125 0.125 0.125 0.125 0.125 0.125 0.000 0.000 0.000 0.000 quality 0.125 0.125 0.125 0.125 0.125 0.125 0.000 0.000 0.000 0.000 time 0.125 0.125 0.125 0.125 0.125 0.125 0.000 0.000 0.000 0.000 engineering, technology & applied science research vol. 13, no. 3, 2023, 10622-10629 10627 www.etasr.com nguyen et al.: an application of analytic network process (anp) to assess critical risks of bridge … table xix. limit matrix for risk groups nodes ec en fc pl so te cost operation quality time a lt e r n a ti v e s ec 0.113 0.113 0.113 0.113 0.113 0.113 0.113 0.113 0.113 0.113 en 0.116 0.116 0.116 0.116 0.116 0.116 0.116 0.116 0.116 0.116 fc 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 pl 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 so 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 te 0.134 0.134 0.134 0.134 0.134 0.134 0.134 0.134 0.134 0.134 c r it e r ia cost 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 operation 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 quality 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 time 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 the npv, tpv, and ipv of risk groups were calculated and are shown in table xx. table xx. priority of risk groups risk group tpv npv ipv r ec 0.16942 0.16942 0.845723 3 en 0.174148 0.174148 0.869325 2 fc 0.152897 0.152897 0.763242 4 pl 0.152674 0.152674 0.76213 4 so 0.150537 0.150537 0.751463 5 te 0.200325 0.200325 1 1 v. discussion a. criteria priority through the anp, this study ranked the risk priority with the consideration of the main assessment criteria of a bridge construction project. quality and operation are the most important criteria with a priority value of 0.333 for both. in addition, cost and time had equal importance with a score of 0.167. b. risk group priority the technical risk group is the most critical in a bridge construction project in the mekong delta region. this group has significant impacts on the quality, cost, time and operation of projects. the results are similar with the ones of [9, 36, 37]. the results revealed that technical risk is always the first risk priority for construction project management. the environmental risk group ranks second among risk groups. this result can be explained by the geographic features of the mekong delta region which was significantly influenced by climate change in recent years. the third-ranking group is the economic risk. this group consists of 8 risk factors, in which "fuel/material prices change" is assessed as the most important factor. in fact, the main material prices for bridge construction projects have increased dramatically over the years. for instance, the steel price went up around 40% in one year and the cement price jumped up by approximately 90.000vnd (3.94$) per ton compared to the price in 2020. consequently, bridge projects suffered cost overrun, which this is the main cause leading to project delays. finally, while political and legal risks and financial and commercial risks are ranked equally, the social risk is considered as having less impact on the bridge construction projects in the mekong delta region. this shows that the vietnam government has provided a sustainable political environment and mainly facilitated consistent policy for construction industry development. the findings of this study are in accordance with the results of recent studies [59-61] and provide insight for policy makers in establishing risk mitigation strategies for large-scale bridge projects. vi. conclusion in this paper, we identified 47 potential risk factors with the focus on bridge construction projects in the mekong delta region. such risk factors have been categorized into 6 main groups for assessment, including political and legal (pl), social (so), technical (te), economic (ec), environmental (en), and financial and commercial (fc). by reviewing the importance of the risk-given groups with the consideration of 4 main criteria (quality, cost, time, and operation) along with practical surveys to collect expert opinions, the priority of risk groups had been determined. the te group was ranked at the highest level (ipv = 1) which potentially has the most significant impact on the performance of bridge construction projects. the en group was ranked at the second-highest level (ipv = 0.8693), which reflects the risk consequences of the climate change on the bridge projects carried out in the mekong delta region. in addition, the ec group was also ranked in the top three, which indicates that economic risks have potential influences on the project’s success. the results of this study can enhance project managers to have a backup plan which can mitigate potential risks in the implementation of bridge construction projects in the mekong delta region. moreover, the 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[61] p. t. nguyen and p. c. nguyen, "risk management in engineering and construction: a case study in design-build projects in vietnam," engineering, technology & applied science research, vol. 10, no. 1, pp. 5237–5241, feb. 2020, https://doi.org/10.48084/etasr.3286. microsoft word etasr_v13_n3_pp10861-10869 engineering, technology & applied science research vol. 13, no. 3, 2023, 10861-10869 10861 www.etasr.com kassem et al.: solar-powered solutions for the water and energy shortage problem: the case study of … solar-powered solutions for the water and energy shortage problem: the case study of nahr el bared, lebanon youssef kassem department of mechanical engineering, engineering faculty, near east university, cyprus | energy, environment, and water research center, near east university, cyprus yousseuf.kassem@neu.edu.tr (corresponding author) huseyin gokcekus department of civil engineering, civil and environmental engineering faculty, near east university, cyprus | energy, environment, and water research center, near east university, cyprus huseyin.gokcekus@neu.edu.tr ismail ataher ab albakoush department of environmental education and management, ataturk faculty of education, near east university, cyprus 20215636 @std.neu.edu.tr kareemah sh. basheer abdullah department of environmental education and management, ataturk faculty of education, near east university, cyprus 20215634 @std.neu.edu.tr received: 17 march 2023 | revised: 2 april 2023 | accepted: 10 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5858 abstract solar power is an effective way to reduce the dependency on conventional fuels and mitigate the water and energy shortage issue. the main aim of the current paper is to assess and compare the techno-economic feasibility of rooftop grid-connected photovoltaic energy systems for generating electricity and generating drinkable water in nahr el bared, lebanon. to this aim, the present paper first reviews previous scientific studies associated with the water resources and energy situation to summarize the current status in lebanon. according to this review, lebanon's water resources are highly polluted, domestic and industrial sewage is largely untreated, and intolerable agricultural practices further exacerbate the situation. furthermore, population and economic growth and the continuous utilization of old power plants have led to an increase in the number of hours of power outages in the country. accordingly, the proposed project aims to evaluate the viability of using solar energy as an alternative solution to the shortage of water and energy in the country. secondly, the techno-economic performance of the proposed system in the selected region was evaluated based on the variations in financial parameters using retscreen experts software. the results demonstrate that 11770–13451kwh/yr could be generated from the solar system, which can help reduce the energy shortage and generate drinkable water. furthermore, the investment was found to be economically viable and attractive for investors. this paper concludes that solar energy can be able to solve the energy shortage of electricity, reduce the country's electricity costs, and produce freshwater for drinking and domestic use in the country. keywords-lebanon; solar energy potential; grid-connected; small-scale; retscreen software i. introduction recently, renewable energies, including solar and wind energy, have increased their contribution in power generation worldwide. the use of renewable energy sources is imperative nowadays, due to the scarcity of fossil fuel resources in developing countries, specifically lebanon. the generation of electricity from renewable energy sources will be an essential engineering, technology & applied science research vol. 13, no. 3, 2023, 10861-10869 10862 www.etasr.com kassem et al.: solar-powered solutions for the water and energy shortage problem: the case study of … part of lebanon’s future development. solar energy has been widely utilized globally to generate electricity and reduce greenhouse gas (ghg) emissions. it is a clean energy, an inexhaustible and environmentally friendly energy source. authors in [1] found that solar power will reduce the emissions of about 69-100 million tons of co2, 68-99 thousand tons of nox, and 126-184 thousand tons of so2 by 2030. authors in [2] concluded that solar energy has a significant potential to meet the world's electricity requirements in the future. authors in [3] concluded that solar energy technologies have an essential role in reducing energy-related emissions. photovoltaic (pv) solar panels produce electrical power directly from the sunlight. it is a considerable power source to meet the demand for electricity in developing countries [4]. additionally, it is utilized as an alternative source to meet the energy required for desalination plants [5]. in general, pv power systems are classified into two types (on-grid and offgrid pv systems). the on-grid pv system significantly reduces costs by eliminating the need for battery storage [6]. also, it helps reduce the consumption of fossil fuels in the country. additionally, the small-scale grid-connected pv system can help customers earn money using their grid-connected rooftop pv systems because they purchase much less electricity [7]. a. water resources in lebanon generally, the main water resources of lebanon are surface water (49%), which is mostly supplied by rivers (46%), surface storage water such as dams and lakes (3%), and groundwater (51%) [8]. in lebanon, there are 40 rivers of which 16 are permanent [8, 9]. the total flow of the rivers is found to be in the range of 2151-3900 mcm/yr with most of the flow occurring from january to may [8, 9]. three water basins alone represent approximately 44% of the country's area: the litani (2140km 2 ), the orontes (1720km 2 ), and the hasbani (680km 2 ). on the other hand, lebanon has many coastal rivers that originate from mount lebanon and flow into the mediterranean sea [10]. rivers and springs are greatly affected by the annual variation in precipitation. according to the united nations development program in 2014, the annual rainfall is within the range of 7.8-11.9 billion m 3 of which between 4.1 and 6.6 billion m 3 is groundwater recharge. the annual rainfall is within the range of 600-1100mm in the coastal regions and rises to more than 1400mm in higher altitudes [11]. the average rainfall and the exposed geological formations with major karstic features and fractures make the stratified environment and water permeability distinctive. renewable water is a major source of groundwater [12]. groundwater reserves generally consist of leakages of the rainwater that result from the melting of snow [13]. the layers that prevent or semi-prevent leakage and runoff play the main role in seizing groundwater reserves and directing them inside the stores [8]. however, groundwater makes up nearly 50% of the water supply. this has affected the management of groundwater and its quality. according to the ministry of energy and water in 2014, the number of public wells extracting groundwater is about 1325 of which 943 are operational. it has also been reported that about 46% of the wells drain unspecified aquifers, 33% drain the sannine-maameltain aquifer, and 9% drain the kesrouane jurassic aquifer [14]. the volume of water extracted from public wells is estimated at 270 mcm/yr. moreover, the registered well number with the ministry of energy and water reached 20537 in 2012. it is expected that the total number of wells is within the range of 55000-60000 distributed over the country. the volume extracted from groundwater resources through public and private wells is estimated to be about 700 mcm [14]. moreover, water sources in lebanon have been exposed to all kinds of pollution due to the absence of sewage networks in most of the areas, the lack of maintenance and monitoring, and not linking sewage networks to refining stations [8]. generally, domestic sewage, solid waste, and pollution from industrial facilities, health care facilities, tourism, and quarries along with agricultural waste are considered the main sources of pollution for surface and groundwater in the country [15]. these different types of pollutants lead to water contamination such as microbiological contamination, heavy metals (copper, zinc, strontium, chromium, and nickel), or increased levels of concentration of nutrients in the surface water [8, 15]. additionally, the coastal area is also widely affected by pollution and the discharge of untreated wastewater and solid waste [15, 16]. it has been found that the total domestic wastewater generated which is discharged into the sea through offshore flow points, is about 65%. moreover, due to over-abstraction and anthropogenic pollution, the quality of groundwater is deteriorating [8]. also, over-abstraction especially in the coastal regions has led to seawater intrusion, which affects the groundwater quality. additionally, nitrate pollution is considered a major threat to groundwater resources in agricultural areas. furthermore, by considering the karstic nature of groundwater aquifers, domestic wastewater is the main cause of bacterial pollution (mainly coliform bacteria) [17, 18]. b. the energy situation in lebanon the main electrical energy sources are fossil fuels (97%) and hydropower (3%). the total capacity of thermal plants and hydropower plants is 2368mw and 252mw, respectively. due to the population growth and rising people living standards, the energy demand has increased. lebanon's need for electric energy is estimated to be about 3562mw according to the ministry of energy and water in 2019. lebanon has been suffering for at least 3 decades from an escalating problem in the electricity sector. the power outage periods in all the cities of the country have increased to 6-14 hours per day. thus, diesel generators are distributed around the country to supply the population's energy consumption demands [19-21]. with these sources, co2 emissions have increased over the years. additionally, electricity generation that comes from these sources contributes about 83% of total co2 emissions [20, 22]. thus, the use of renewable energy sources, such as solar energy, will reduce the ghg emissions and the dependence on fossil fuels. according to the world bank group (global solar atlas), the specific photovoltaic power output is within the range of 3.99-5.30kwh/kwp. moreover, lebanon receives approximately 300h/yr of sunshine. the average sunshine hours in lebanon range from 8h to 9h. lebanon has high insulation on a horizontal surface ranging between 16.51mj/m 2 and 20.71mj/m2. therefore, it is essential to increase the access to electricity in the country with a particular focus on utilizing engineering, technology & applied science research vol. 13, no. 3, 2023, 10861-10869 10863 www.etasr.com kassem et al.: solar-powered solutions for the water and energy shortage problem: the case study of … solar resources. authors in [23] found that the county has a great chance of utilizing solar power in order to reduce its dependency on fossil fuels. additionally, installing a solar system in the country is technically reliable due to the high value of average daily radiation on the horizontal surface [24] recently, several studies have investigated the potential of utilizing renewable energy, mainly solar, in the country [2433]. few studies have focused on the evaluation of the solar potential in lebanon. for instance, authors in [29] investigated the techno-economic feasibility of small-scale grid-connected rooftop solar projects with various sun-tracking systems and pv technologies. the findings demonstrated that the proposed pv system could provide enough electricity to satisfy the demand and hence reduce the nation's current electricity shortage. authors in [25] described the utilization of a hybrid pv-diesel system to cool a tertiary building in beirut during the summer. the results indicated that a pv-diesel system can provide 260kw of power throughout the year. authors in [28] developed a gis model to locate the optimal location for a solar power plant in lebanon. the results showed that the optimum locations (amioun, bterram, and kfaraakka) with an area of 2.8km 2 can provide 50% of the north’s power needs. authors in [31] provided the footprint and solar rooftop potential maps using deep learning-based instance segmentation. they concluded that lebanon has a total rooftop solar capacity of about 28.1twh/year, which is about twice the electricity needed by the country in 2019. authors in [21] assessed the feasibility of a 100mw grid-connected pv plant in the rayak region, lebanon. the results showed that the amount of electricity generation from pv systems (1.47gwh) could help solve the electricity crisis in the country. based on prior scientific research findings [24-33], the results indicated that (1) the country has a huge concentrating solar power that would be able to meet the maximum energy demand, (2) solar pv systems will have significant socio-economic benefits and assist the sustainability of solar power generation in the country, and (3) the solar power systems will employ 100% renewable energy, resulting in zero carbon emissions in the future. c. solar desalination unit one major global problem is the increasing demand for drinking water. seawater/brackish water desalination units are considered an alternative way to solve the problem of freshwater supply. in general, desalination is the process of purifying water and removing excess salinity and minerals from it through several processes [34, 35]. desalination processes are categorized into two main categories: thermal processes and membrane processes. according to [36], the most widely utilized and reliable technology process is reverse osmosis (ro), which has also been utilized as an alternative source of clean water production [35, 36]. generally, the desalination processes require a significant amount of energy. therefore, renewable energy, particularly solar energy, is a viable alternative as a clean energy source to operate desalination plants and reduce fossil fuel dependency and the cost of clean water production. many researchers have investigated the potential of renewable energy in terms of wind and solar energy. for instance, authors in [37] utilized wind energy potential as an energy source for an ro desalination plant in spain. authors in [38] evaluated the feasibility of solar energy projects to supply the required power for seawater desalination in algeria. moreover, several studies investigated the feasibility of gridconnected solar plants as an energy source for desalination plants [35, 38-41]. authors in [35] investigated the economic viability of small-scale grid-connected pv systems with various sun-tracking systems as clean energy for brackish water desalination units in northern cyprus. the grid-connected pv system was used as a power source for a 2500m 3 /d saltwater ro desalination plant [38]. authors in [39] analyzed gridconnected pv/wind projects as power sources for ro and multiple-effect distillation plants. authors in [40] proposed a new strategy for grid-connected seawater reverse osmosis focused on energy cost reduction. authors in [41] evaluated the potential of solar energy and designed a solar-powered seawater ro desalination plant for gaza strip. d. research οbjectives lebanon is facing an energy deficiency and some of its regions are still not electrified, particularly in rural areas. the energy supply and demand are very large. besides, the poor economy does not allow importing fossil fuels on a large scale. consequently, the potential of renewable energy resources can be utilized to electrify off-grid areas, specifically rural areas, or on-grid in urban locations for reducing the consumption of fossil fuels and environmental pollution. lebanon is known to have a good potential for solar energy and the potential of solar energy for solving the electricity and water crisis in the country has been evaluated in a few studies. thus, there is no doubt that a comprehensive economic and environmental study must be conducted to obtain results that can serve as a roadmap for investing in solar energy in the country. besides, it has been indicated that grid-connected solar power systems are an alternative solution for the electricity crisis, one that reduces carbon emissions and mitigates power shortage. consequently, it can be concluded that the small-scale solar systems in the country can not only bridge the energy gap but also reduce the environmental pollution impact. the current research is a first attempt to examine the viability of small-scale solar energy systems in lebanon from a strategic viewpoint to address the country's electricity shortage and generate freshwater for household consumption. this paper presents a methodology to accurately evaluate the technoeconomic and environmental sustainability of rooftop pv systems in nahr el bared, lebanon. a typical household was selected for this region to create a load profile according to the monthly electricity bills and reduce the groundwater salinity using ro desalination. the techno-economic feasibilities for the rooftop solar systems at the selected location were developed for various policy scenarios using the retscreen experts software. ii. materials and methods a. study area nahr el-bared is located in the northern part of lebanon with a population of about 30000. the mean maximum and engineering, technology & applied science research vol. 13, no. 3, 2023, 10861-10869 10864 www.etasr.com kassem et al.: solar-powered solutions for the water and energy shortage problem: the case study of … minimum elevations are 27m and 12m above sea level, respectively. nahr el-bared camp is separated into two camps: the old camp (78m 2 average apartment area and 360000m 2 total built residential area) and the new camp (150m 2 average household area and 300000m 2 total constructed household area). nahr el-bared is facing a water crisis due to the shortage of electricity and seawater intrusion. according to the institute for palestinian studies, about 60% of drinking water is salty in most regions in the selected area. moreover, the large number of private wells, which are located along the coastline, is a major cause of seawater intrusion according to the institute for palestinian studies. recently, the level of salinity has increased to 90% of the public and private wells extracting groundwater, which forced the residents to buy freshwater from internal refineries' water trucks to fill the water storage tanks. this has given rise to serious problems due to the cost of water from these sources (the price of 1m 3 varies from 2 usd to 4 usd, which depends on the locations in the region) and the shortage of electricity. moreover, power outages in the selected location are considered one of the most difficult situations by the residents, as the hours of feeding from the electricity company do not exceed 3 to 4 per day b. on-grid photovoltaic system grid-connected pv systems consist of pv panels that supply the required power during the day and are connected to the local electrical grid to generate power at night. moreover, the excess power from the pv system is fed back to the grid when the power generated is more than the load required [42]. in general, the grid-connected pv system consists of solar panels, inverters, a power-conditioning unit, and gridconnection equipment. to get more power from the pv arrays, the pv panels should have high cell efficiency and a high operating temperature. generally, the inverter is one of the most important components of a grid-connected system because it converts direct current (dc) to alternating current (ac). in addition, electricity meters are utilized to read the flow of electricity to and from the grid. recently, on-grid pv systems have attracted substantial attention due to the advantages of their compatibility with the electricity grid. in this system, the output power of the pv system is connected directly to the grid and the household. the electric energy produced by the pv system can cover the energy demand of the household. when the produced energy by the pv system is high, the remaining energy can be fed into the grid through an electric meter. this system comprises pv panels, which absorb sunlight and produce direct current, an inverter, a distribution controller, and load as shown in figure 1. generally, it is necessary to estimate the optimal sizing of grid-connected pv systems as the first step to meet the energy demand of the household. according to [43], the amount of output energy by the pv system (epv) should be greater than the amount of electricity taken from the grid (egrid) as shown in (1). in this case, the energy demand of the household can be shared between the pv system and the electric grid. the generated energy from the pv system is utilized to cover the household/building instantaneous electricity load and the surplus energy is injected into the grid. ��� > ����� (1) the maximum power ( �� ) of the developed on-grid solar pv system can be estimated as a function of global solar radiation ( �� ) in kwh/m 2 /d, solar radiation at standard test conditions ( � ) in kw/m 2 , pv derating factor ( ��� ), daily power consumption (��� ) of the household in kwh/d, and the inverter yield (���� ), as in (2) [44]: �� = ��� �� ����� !�"# (2) fig. 1. components of an on-grid pv system. c. energy required for an ro desalination plant the power needed for a ro plant should be calculated to assess its energetic requirements and integrate it with the renewable energy system. the power needed to desalinate the water (i.e. push water through membranes mechanically) as well as the electricity needed to pump the feed water to the plant and the treated water into the water system are all taken into account when calculating the overall power requirement of an ro plant. the major source of water for the desalination plant is the saline groundwater from the coastal aquifer. according to [45, 46], the energy needs for an ro desalination plant can be calculated using by: $ = %��∙' �() (3) where $ is the power requirement of the ro in kw, *+$ is the capacity factor of the plant, , is the flow rate for the feed water in m 3 /h, and -�* is the specific energy consumption of desalination in kwh/m 3 . d. retscreen expert software retscreen expert is a clean energy management tool developed by the canadian government. it is a decision support tool utilized to determine the potential of energy, costs, savings, ghg emission reduction, and economic viability [47, 48]. retscreen is commonly employed to explore the engineering, technology & applied science research vol. 13, no. 3, 2023, 10861-10869 10865 www.etasr.com kassem et al.: solar-powered solutions for the water and energy shortage problem: the case study of … feasibility of grid-connected wind and pv power systems. for instance, authors in [48] used retscreen to evaluate the techno-economic feasibility of a grid-connected pv system in nigeria. authors in [49] utilized it to investigate the potential of pv systems for electricity generation in various locations in libya. authors in [50] evaluated the cost-benefit of a 100mw solar pv installation in pakistan using retscreen. iii. results and discussion the mean monthly energy demand for the selected household is illustrated in figure 2. the energy demand data were collected during 2012-2021. it is found that the energy demand is within the range of 210-309kwh with an average value of 250kwh. the highest and lowest value of energy demand is recorded in december and july, respectively. fig. 2. monthly mean energy demand for the selected household during 2012-2021. fig. 3. monthly average daily global radiation on a horizontal surface and a 34° tilted plane. according to [51], the influence of the tilt angle on the solar electricity generation can be considered a minor effect when compared to the natural variation. the tilted and azimuth angles were chosen based on the highest value of solar irradiance and electricity exported to the grid. the monthly average daily global radiation on a horizontal surface and global radiation on a horizontal surface and a 34° tilted plane are illustrated in figure 3 for the selected location. june and december are the periods with the highest and lowest solar radiation. the minimum and maximum tilted solar radiation were found to be 3.9kw/m 2 /d and 7.2 5.57kw/m 2 /d. the power requirement of the brackish water ro is calculated to estimate its energetic needs in order to estimate the capacity of the pv system. in this research, the total power demand of the ro plant is calculated using by (3). the desalination capacity factor and specific energy consumption of desalination are assumed based on [48, 52, 53]. table i lists the parameters needed for the calculation of the power requirements of the ro. table i. parameters for estimating the power requirement of the ro parameters value desalination capacity factor [%] 95 specific energy consumption of desalination [kwh/m3] 1.5 flow rate of the feed water [m3/h] 0.5 and 1 power requirement [kw] 1 and 2 moreover, using (2), the maximum power of the pv system is found to be 6kw based on the minimum value of solar radiation. thus, the total capacity of the pv system is estimated to be 7kw and 8kw, which depends on the power requirement of the ro desalination unit (table i). the required area for the proposed systems is estimated to be within the range of 3337m 2 . in this study, the solar module jkm545m-72hl4-tv with a capacity of 545w and efficiency of 21.13%, manufactured by jinko solar, is used. output ac power, dcac conversion efficiency, and capital cost of the inverter are the main factors to select a suitable inverter. ost 6000tl-d1 and ost 3000tl-s1 solar inverter with a capacity of 6kw and 3kw were selected. a. technical viability the performance of pv systems in terms of pv output and capacity factor depends on the orientation angles. thus, the electricity exported to the grid (eeg) and capacity factor (cf) were estimated at a tilted angle of 34° and azimuth angle of 0° for the selected location. it should be noted that fixed-tilt mounting systems are simpler, cheaper, and require less maintenance compared to tracking systems. the mean monthly value of eeg for all the considered pv systems is shown in figure 4. it is observed that the eeg is within the range of 676.55-1161.75kwh and 773.20-1327.71kwh for pv systems with a capacity of 7kw and 8kw, respectively. the lowest and highest values of eeg are recorded in december and july, respectively. fig. 4. monthly average value of eeg on a 34° tilted plane for the proposed pv systems. moreover, the monthly average electricity produced by the pv system and the electrical energy purchased from the grid is illustrated in figure 5. it is found that the pv systems cover the household load and ro brackish groundwater desalination unit. the installation of the pv systems can solve the electricity crisis and produce freshwater for drinking and domestic use. engineering, technology & applied science research vol. 13, no. 3, 2023, 10861-10869 10866 www.etasr.com kassem et al.: solar-powered solutions for the water and energy shortage problem: the case study of … the annual value of eeg of the proposed system is 11769.99kwh and 13451.42kwh for a system with capacity of 7kw and 8kw, respectively. the cf of the proposed systems is 19.19%. this result can be supported by previous studies. for instance, authors in [48] found that the cf value of their proposed pv plants varied from 20.40% to 21.70%. authors in [54] found that the cf values of 10mw grid-connected pv systems are within the range of 20.08-25.07%. authors in [55] found that the proposed pv projects in oman have a cf ranging from 16% to 23%. according to [56], the value of cf for grid-connected pv systems with various sun-tracking techniques fell between 17.54 and 27.42%. as a result, the current study's value for each site is compatible with the acceptable values. consequently, it is technically feasible to construct a rooftop pv system that is connected to the local power grid. (a) (b) fig. 5. monthly average electric production of (a) 7kw and (b) 8kv pv systems. b. economic sustainability to determine if the project is viable and sustainable economically, an economic study is vital. thus, the technoeconomic feasibility for rooftop pv systems at the selected location was evaluated for different values of electricity export rate (0.03-0.12usd/kwh in the step of 0.03usd/kwh) and discount rate (0% and 5.4%) to explore the possible variations in the results. the values of the used financial input parameters, namely inflation rate (2.9%), reinvestment rate (9%), project life (25 years), debt ratio (70%), debt interest rate (0%), and debt payment period (20 years), were assumed based on previous studies. based on these input parameters, npv, alcs, sp, ep, lcoe, and the internal rate of return (irr) were estimated by retscreen. table ii summarizes the cost of the proposed system. moreover, the cost of the final desalinated water is listed in table iii. it should be noted that the pv module and inverter were selected from a list of efficient pv modules and inverters which are currently available in the market. the cost of the small-scale ro brackish groundwater desalination unit (0.5m 3 /h and 1m 3 /h) can be found in the literature. the initial investment cost of the proposed system is 6507 usd and 10482 usd for a pv system with a capacity of 7kw and 8kw, respectively. the npv was determined for each location and each value of the electricity export rate (eer) is tabulated in table iii. it is found that the value of npv for each value of eer is positive, which indicated that the project is potentially feasible [57, 58]. besides, it is noticed that there is a strong correlation between npv and eer. moreover, irr is estimated to evaluate the economic viability of the project [48, 57]. the irr provides the true return of interest generated by the equity over the life of the project [47]. the results showed that increasing the rate of exporting electricity led to an increase in the value of irr. in addition, it is observed that the value of irr gotten for the three locations is higher than the required rate of return of the project. alcs is calculated by using npv, discount rate, and project lifetime. it is found that alcs is within the range of 274.0-2571.1 usd/year for pv systems with a capacity of 7kw and 93.4-2773.5 usd/year for pv systems with a capacity of 8kw, as shown in table iii. table ii. costs of the pv project and the ro desalination unit parameter unit value pv module cost usd/w 0.3 lifetime of the pv module year 25 cost of a 6kw inverter usd 450 cost of a 3kw inverter usd 250 miscellaneous/contingency fund % of the total initial cost 3 installation and spare parts % of the total initial cost 8.6 feasibility study, development, and engineering cost % of the total initial cost 0.6 lifetime of inverter year 10 inverter replacement periodic cost every 10 years investment cost of a 7kw pv system usd 3366 investment cost of a 8kw pv system usd 5273 investment cost of brackish groundwater desalination unit (0.5m3/h) usd 3141 investment cost of brackish groundwater desalination unit (1m3/h) usd 6282 furthermore, the economic viability of a project is estimated by determining the payback period, which indicates the time required to recover the initial investments, with net positive income [47, 48]. table iii lists the payback period including ep and sp for all selected locations. it is found that the ep is within the range of 1.50-15.8 years. the developed pv project with 7kw technology has the lowest value of ep. the proposed project with 8kw has the longest sp (7.2-28.6) compared to the other project (4.6-18.4 years). the results reveal that the increase in eer will lead to a decrease in ep and sp. the results demonstrate that the sp value exceeds the lifetime of the project (25 years) when eer is equal to 0.03 usd/kwh, especially for the project of 8kw. this indicates that installing pv projects at the selected locations is not economically viable when eer is equal to 0.03 usd/kwh. additionally, the value of b-c, which is utilized to determine engineering, technology & applied science research vol. 13, no. 3, 2023, 10861-10869 10867 www.etasr.com kassem et al.: solar-powered solutions for the water and energy shortage problem: the case study of … the cash flow generated viability, is higher than 1 as shown in table iii. these findings indicate the feasibility of the projects [59]. c. climate co-benefit assessment in addition to economic feasibility, an estimate of the environmental benefits in terms of reducing ghg emission of the proposed system would be attractive. the climate cobenefits in terms of ghg emission reduction were calculated using retscreen and are listed in table iv in multiple equivalent formats. the results indicate that a large amount of co2 emissions can be avoided by implementing the developed pv project in each location. it should be noted that the total amount of co2 emission reduction for each location is determined based on the electricity generated annually [56]. the annual ghg emission reduction is 8.32 tco2 for the 7kw pv system and 9.51 tco2 for the 8kw pv system, as shown in table iv. table iii. economic performance of developed pv projects for the selected location pv capacity parameters case#1 case#2 case#3 case#4 case#5 case#6 case#7 case#8 7 kw electricity export rate [usd/kwh] 0.03 0.06 0.09 0.12 0.03 0.06 0.09 0.12 discount rate [%] 5.4 5.4 5.4 5.4 0.0 0.0 0.0 0.0 pre-tax irr-equity 14.7 33.0 51.5 70.2 14.7 33.0 51.5 70.2 pre-tax irr-assets 4.4 12.5 18.8 24.7 4.4 12.5 18.8 24.7 simple payback [year] 18.4 9.2 6.1 4.6 18.4 9.2 6.1 4.6 equity payback [year] 8.7 3.5 2.1 1.5 8.7 3.5 2.1 1.5 net present value (npv) [usd] 3712.1 12117.0 20521.9 28926.8 11193.0 28888.1 46583.1 64278.2 annual life cycle savings [usd/year] 274.0 894.5 1515.0 2135.5 447.7 1155.5 1863.3 2571.1 benefit-cost (b-c) ratio 2.9 7.2 11.5 15.8 6.7 15.8 24.9 34.0 debt service coverage 1.6 3.3 4.9 6.5 1.6 3.3 4.9 6.5 energy production cost [usd/kwh] 0.0294 0.0294 0.0294 0.0294 0.0221 0.0221 0.0221 0.0221 8 kw electricity export rate [usd/kwh] 0.03 0.06 0.09 0.12 0.03 0.06 0.09 0.12 discount rate [%] 5.4 5.4 5.4 5.4 0.0 0.0 0.0 0.0 pre-tax irr-equity 7.4 20.1 31.8 43.6 7.4 20.1 31.8 43.6 pre-tax irr-assets 2.9 8.0 10.3 11.9 2.9 8.0 10.3 11.9 simple payback [year] 28.6 14.3 9.5 7.2 28.6 14.3 9.5 7.2 equity payback [year] 15.8 6.2 3.6 2.5 15.8 6.2 3.6 2.5 net present value (npv) [usd] 1265.7 10871.4 20477.0 30082.6 8667.9 28890.8 49113.7 69336.6 annual life cycle savings [usd/year] 93.4 802.6 1511.7 2220.8 346.7 1155.6 1964.5 2773.5 benefit-cost (b-c) ratio 1.4 4.1 6.9 9.7 3.5 9.3 15.2 21.0 debt service coverage 1.0 2.1 3.1 4.2 1.0 2.1 3.1 4.2 energy production cost [usd/kwh] 0.0458 0.0458 0.0458 0.0458 0.0344 0.0344 0.0344 0.0344 table iv. ghg emission reduction (tco2) annual ghg emission reduction [tco2] equivalent to pv capacity 7 kw 8 kw gross annual ghg emission reduction 8.32 9.51 care and light trucks not used 1.52 1.74 liters of gasoline not consumed 3575.18 4085.92 barrels of crude oil not consumed 19.35 22.11 people reducing energy use by 20% 8.32 9.51 acres of forest absorbing carbon 1.89 2.16 hectares of forest absorbing carbon 0.77 0.87 tons of waste recycled 2.87 3.28 iv. conclusions and future work population growth and energy demand have prompted governments and researchers to find alternative energy sources. solar-powered energy has received the most attention among the alternative energy sources due to its environmentally friendly nature. in this paper, the use of solar energy as an alternative source for generating electricity and drinking water was investigated. accordingly, this paper first reviewed the literature on water resources and the energy situation in the country to offer persuasive suggestions for policymakers to consider solar energy as an energy source in the future. the result showed that the use of solar energy can help the country reduce its dependence on fossil fuels and generate electricity at a low cost as well as produce freshwater using small units of ro brackish groundwater desalination. a household was selected to determine the energy demands according to the monthly electricity bills in addition to the energy required for ro desalination to assess the pv system's capacity. then, the techno-economic feasibility of rooftop grid-connected pv systems was investigated. the results demonstrated that rooftop grid-connected pv systems are technically, economically, and environmentally feasible for the selected region. hence, solar energy can be an alternative energy source to solve the water and energy shortage in the country. future work is needed to address the profit from the use of the photovoltaic system, which largely depends on the tariffs for the region and the possibility of connecting a given power to the grid about the quality of electricity, voltage 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https://doi.org/10.48084/etasr.5787 abstract the increasing use of e-commerce websites and social networks is continually generating an immense amount of data in various forms, such as text, images or sounds, videos, etc. sentiment analysis (sa) in online product reviews is a method of identifying the overall sentiment of customers about a specific product or service. this study used natural language processing (nlp) and machine learning (ml) algorithms to identify and extract opinions and emotions expressed in text. online reviews are often written in informal language, slang, and dialects, making it difficult for ml models to accurately classify sentiments. in addition, the use of misspelled words or incorrect grammar can further complicate the analysis. the recent developments of deep learning (dl) models can be used for the accurate classification of sentiments. this paper presents an adaptive particle grey wolf optimizer with deep learning based sentiment analysis (apgwo-dlsa) method to accurately classify sentiments in product reviews. initially, data pre-processing was performed to improve the quality of the product reviews using the word2vec embedding process. for sentiment classification, the proposed method used a deep belief network (dbn) model. finally, the hyperparameter tuning of the dbn was performed using the apgwo algorithm. an extensive experimental analysis demonstrated the improved results of apgwo-dlsa over other methods, showing a maximum accuracy of 94.77% and 85.31% on the cell phones and accessories (cpaa) and amazon products (ap) datasets. keywords-sentiment analysis; online product reviews; machine learning; deep learning; natural language processing i. introduction sentiment analysis (sa) uses machine learning (ml) and natural language processing (nlp) methods to extract and identify subjective data from text [1]. it is useful to understand the sentiments of product reviews since they allow companies to know the overall satisfaction of users [2]. sa regulates the insolence of a writer or a speaker regarding the contextual polarity, a specific topic, or some particular event, discussion, etc. the indispensable task of sa is to identify the polarity of the text at a document or sentence level [3]. the rise in internet use has enabled all users to share their views using various platforms [4]. sa assists to examine such opinioned data and deriving certain significant insights which could be helpful for others to make decisions [5]. social networking sites generate various kinds of data such as sports, products, movies, healthcare, hotel, and news and articles reviews. many sa algorithms have been proposed, using computational linguistic methods or ml [6], such as support vector machines (svms), naive bayes (nb), and maximum entropy [7]. ml methods show much better efficiency than computational linguistic methods. as deep learning (dl) presents notable results for a variety of nlp problems, it has attracted the interest of researchers [8], and several dl methods have been used, such as dcnn, cnn, deep restricted boltzmann machine (rbm), deep neural networks (dnns), etc. [9]. however, reviews or sentences stating various aspects related to complicated sentiments are not treated very well by these methods. similarly, complete sa evaluation using ml has not offered efficient training time and better accuracy [10]. several methods have been proposed to conduct sa using dl, and the best method depends on the specific needs of the application. although several approaches have been proposed for sentiment classification, there is still a need to improve their performance. due to the continuous expansion of the dl models, the parameter count increases, leading to overfitting of engineering, technology & applied science research vol. 13, no. 3, 2023, 10989-10993 10990 www.etasr.com elangovan & subedha: adaptive particle grey wolf optimizer with deep learning-based sentiment … the model. as the manual selection of hyperparameters is a laborious task, it is useful to use evolution algorithms. this study developed an adaptive particle grey wolf optimizer with dl-driven sa (apgwo-dlsa) model to accurately classify sentiments on online product reviews. for sentiment classification, the proposed apgwo-dlsa model used a deep belief network (dbn). the hyperparameter tuning of the dbn was performed using the apgwo approach. a wide range of simulations was carried out to demonstrate the improved performance of the apgwo-dlsa model. ii. related works in [11], a novel word representative method was presented, that incorporated the contribution of a sentiment dataset into the standard tf-idf method and produced weighted word vectors. this weighted word vector can be input to bidirectional lstm (blstm) to efficiently capture contextual datasets. the sentiment tendency of a comment can be gained using ffnn classifiers. in a similar condition, the sa approach was compared to nb, cnn, lstm, and rnn sa methods. in [12], a graph convolution network was presented with an external knowledge model (ek-gcn). in [13], a particular order of pre-processing stages was presented to enrich the sa performance of an ann, since typically, the weights of the ann are arbitrarily initialized (r-ann) and may not provide a favorable result. in [14], a new cognitive computing method used big data analysis tools for sa and pre-processing to eliminate unnecessary words. in [15], the performance of companies was investigated using dl and ml, showing how ai can improve business procedures and results using sa. this study examined all aspects of ai in the business domain with its benefits in enhancing business performance. in [16], dl was used to analyze the sentiments of pets. iii. the proposed model this study presents the apgwo-dlsa method for sentiment classification on online product reviews. the apgwo-dlsa method includes data preprocessing, word2vec word embedding, dbn classification, and apgwobased parameter tuning. figure 1 illustrates the entire workflow of the apgwo-dlsa method. a. data preprocessing initially, data pre-processing was performed to improve the importance of product reviews. data analysis requires data preprocessing to eliminate redundancies and improve the learning method of the classification model and accuracy [17]. redundant data represent any information that contributes minimal or none to predicting a targeted class, but it increases the feature vector size and presents redundant computation complexity. subsequently, the accuracy of a classifier model is degraded if improper or no pre-processing is performed before encoding. this study used python's nlp toolkit to preprocess the data. at first, the text was transformed into lowercase, and then punctuation, links, and html tags were discarded. then, lemmatization and stemming approaches were implemented to clean the stopwords, and finally, the text was detached.  change to lowercase: the text was converted to lowercase. the model considers lowand upper-case words as distinct, influencing the classification performance and the training process.  removal of punctuation, url links, numbers, and tags: they do not contribute to the classifier accuracy since they provide no further meaning for the learning model and increase feature space. thus, eliminating them aids in decreasing the feature space.  lemmatization and stemming: the objective of this step is to minimize inflectional forms and occasionally derivative relevant forms of the word to the typical baseline.  removal of stopwords: stopwords are often used words that provide no valuable data. fig. 1. working process of the apgwo-dlsa method. b. word embedding the word2vec model was used for the word embedding process. word2vec is a popular word embedding algorithm that maps word types that have the same meaning and are closer to each other [18]. this method uses 2 approaches; the former is the skip-gram approach that accepts the center word as input, transfers it to the embedded layer, and later predicts the context word in a small dataset. the other approach is the continuous bow (cbow) approach, which uses contextual words as input, transfers them to the embedding layer, and forecasts the center or the original word. cbow works very fast and offers a good representation of the most common word. c. sentiment classification the apgwo-dlsa used the dbn model to classify sentiments. dbn uses the structure blocks of rbm and several rbm approaches [19]. rbm with a single hidden layer may not be effective for extracting features from data. the feature learned and then trained in an rbm network is used as input to distinct rbm networks. therefore, the last rbm network learns features of the whole trained method and extracts the features from the input data. back-propagation (bp) is frequently used to train a typical ann with a huge number of engineering, technology & applied science research vol. 13, no. 3, 2023, 10989-10993 10991 www.etasr.com elangovan & subedha: adaptive particle grey wolf optimizer with deep learning-based sentiment … model parameters. this can be achieved more efficiently using the pre‐training method. the pre‐ training method in a dbn is a procedure of greedy layer‐wise and alternative sampling. after the unsupervised pre‐processing from the greedy layerwise procedure, h k (x) refers to the representation of abstracts x in the k layer. to achieve optimum distinctive performance, the labeled data were used to correct the parameter space w. this was developed by including a final layer of variables prepared by the chosen label samples in the trained database. this optimizer method is signified by the subsequent equation: ��ℎ� ���, �� = ∑ ∑ �� ������ �ℎ� ���� � ×�� � (1) where t is the loss function. the squared error function has been generally exploited in bp, and the loss function was: � = ℎ� ��� � × �� (2) d. hyperparameter tuning apgwo is considered a hyperparameter optimizer of the dbn model. eberhart and kennedy presented a pso model on the herd prey hunting approach from the environment, where all the animals in a pack are aware of their position relative to the food and the position adjacent to it [20]. this study proposed a pso technique to solve optimization problems. the two basic features of pso are the present element position x and the velocity v. simultaneously, the fitness function (ff) computes the fitness values for all parts. at the same time as the departure, the position of all the elements is stated at random. every feature is influenced by two position parameters: pbest and gbest. the pso element navigates the problem space with subsequent attributes that are present. afterward, all steps, the velocity, and the position of all components can be defined by the following equations: ����� = � ∗ ��� + ��� ∗ � !" ∗ �#$%&'�� − ��� � + �)� ∗� !" ∗ �*+%&' − ��� � (3) ����� = ��� + ��� (4) the values of c1 and c2 are generally stated as constants in pso for balancing the exploration phase, most probably to c1=c2=1 or c1=c2=2. during all the iterations, the equation is used for changing the acceleration coefficients. equations (5) and (6) define these novel coefficients: ��, = 1.2 − 0�12 3 � 0�4567�� (5) �), = 0.5 + 0�12 3 � 0�4567�� (6) where t is the iteration, k is the coefficient, and f is the global optimum fitness of swarms. the values 0.5 and 1.2 are chosen by empirical analysis. the instance of the inertia equation is: �� = �: �;'%� − '� ∗ <=>? a<=bc d>?efgh + �ij! (7) the sigmoid function is: �� k ��� = &j* l�� ���m = ���6nopq�r� (8) the development of the particle's positions is determined by: �� �' + 1� = s1, j� �� < &j* l�� �' + 1�m0� u'ℎ%��j&% (9) where the ij parameter is a value from 0 to 1. during the pso execution, some gwo iteration rounds reproduce the possibility of mutations that resolve the result in hybrid variation. the possibility of mutations was fixed at 0.1. the internal round can be only activated sometimes, as these values were smaller to make sure that the solution quality was unaffected. the primary and final weights can be represented by w_max and w_min, and this study used fixed values of 0.9 and 0.2, respectively. the purpose for reducing the ff is: ij!j:jv% w × x� + �1 − w� × yz (10) where eτ signifies the validation set rate of errors, a=0.9, and s and l represent the count of the selected features and the entire count of features, respectively. an effort is developed to concurrently optimize this ff and decrease the count of chosen features to improve validation accuracy. the optimization focuses on improving validation accuracy once the a value was higher. the fitness value can be computed by the apgwo algorithm by: [j'!%&& = max �_� (11) _ = `a`a�ba (12) where tp and fp signify the true and false positives. iv. results and discussion the apgwo-dlsa model was developed and executed using python 3.6.5 on an i5-8600k/16gb ram/geforce 1050ti 4gb pc. the sa effectiveness of the apgwo-dlsa method was examined on two datasets: cell phones and accessories (cpaa) and amazon products (ap), as shown in table i. figure 2 shows the confusion matrix created by the apgwo-dlsa model on the two datasets. the results showed that the apgwo-dlsa model accurately determined two kinds of sentiments. for instance, with 70% trs in the cpaa dataset, the apgwo-dlsa model recognized 61410 positive samples and 7256 negatives. meanwhile, with 30% tss in the cpaa dataset, the apgwo-dlsa model recognized 26327 positive samples and 3120 negatives. eventually, with 70% trs in the ap dataset, the apgwo-dlsa model recognized 9189 positive samples and 361 negatives. finally, with 30% tss in the ap dataset, the apgwo-dlsa method recognized 3936 positive samples and 169 negatives. table i. dataset details class no. of instances cpaa ap positive 88516 13251 negative 11484 749 total 100000 14000 table ii shows the sa results of the apgwo-dlsa method on the cpaa dataset, demonstrating that it distinguished positive and negative data instances. with 70% trs, the apgwo-dlsa model achieved average accuy, precn, recal, fscore, and mcc of 94.77%, 95.75%, 94.77%, engineering, technology & applied science research vol. 13, no. 3, 2023, 10989-10993 10992 www.etasr.com elangovan & subedha: adaptive particle grey wolf optimizer with deep learning-based sentiment … 95.25%, and 90.52%, respectively. additionally, with 30% trs, the apgwo-dlsa method achieved average accuy, precn, recal, fscore, and mcc of 94.65%, 96.20%, 94.65%, 95.41%, and 90.84%, respectively. fig. 2. confusion matrices: (a-b) cpaa dataset on trs/tss of 70:30; (c-d) ap dataset on trs/tss of 70:30. table ii. sa results of the apgwo-dlsa model on the cpaa dataset class accuracybal precn recal fscore mcc training phase (70%) positive 99.08 98.77 99.08 98.93 90.52 negative 90.46 92.73 90.46 91.58 90.52 average 94.77 95.75 94.77 95.25 90.52 testing phase (30%) positive 99.21 98.71 99.21 98.96 90.84 negative 90.10 93.69 90.10 91.86 90.84 average 94.65 96.20 94.65 95.41 90.84 table iii. sa results of the apgwo-dlsa model on the ap dataset class accuracybal precn recal fscore mcc training phase (70%) positive 98.93 98.38 98.93 98.66 73.06 negative 70.51 78.48 70.51 74.28 73.06 average 84.72 88.43 84.72 86.47 73.06 testing phase (30%) positive 99.32 98.30 99.32 98.81 77.26 negative 71.31 86.22 71.31 78.06 77.26 average 85.31 92.26 85.31 88.43 77.26 table iii shows the overall sa results of the apgwodlsa method on the ap dataset, demonstrating that the model distinguished positive and negative samples proficiently. for example, with 70% trs, the apgwo-dlsa method achieved average accuy, precn, recal, fscore, and mcc of 84.72%, 88.43%, 84.72%, 86.47%, and 73.06%, respectively. furthermore, with 30% of tss, the apgwo-dlsa model achieved average accuy, precn, recal, fscore, and mcc of 85.31%, 92.26%, 85.31%, 88.43%, and 77.26%, respectively. figure 3 displays the accuracy and loss curves examination of the apgwo-dlsa method on the cpaa and ap datasets. fig. 3. accuracy and loss (a-b) on the cpaa dataset, (c-d) on the ap dataset. table iv shows the comparative sa results of the apgwo-dlsa with existing models in the cpaa dataset [21], demonstrating its superior performance. the apgwodlsa model reached the highest accuy of 94.77%, while the xgboost, rf, svm, gradient boosting, nb, and dl models reached 91.60%, 91.38%, 90.16%, 89.74%, 91.01%, and 90.85%, respectively. simultaneously, the apgwo-dlsa model had a higher fscore of 95.25%, while the xgboost, rf, svm, gradient boosting, nb, and dl achieved 91.89%, 91.79%, 89.81%, 90.49%, 91.64%, and 89.88%, respectively. table iv. comparative analysis of apgwo-dlsa with other models on the cpaa dataset methods accuracy f-score apgwo-dlsa 94.77 95.25 xg boost 91.60 91.89 random forest 91.38 91.79 svm 90.16 89.81 gradient boosting 89.74 90.49 naïve bayes 91.01 91.64 dl model 90.85 89.88 table v compares the sa results of the apgwo-dlsa with existing models on the ap dataset. the results show that the apgwo-dlsa model achieved the best performance. the apgwo-dlsa model achieved the highest accuy of 85.31%, while the xgboost, rf, svm, gradient boosting, nb, and dl models achieved 80.63%, 83.23%, 83.02%, 81.49%, 81.38%, and 80.93%, respectively. similarly, it can be noticed that the apgwo-dlsa model reached the highest fscore of 88.43%, while the xgboost, rf, svm, gradient boosting, nb, and dl engineering, technology & applied science research vol. 13, no. 3, 2023, 10989-10993 10993 www.etasr.com elangovan & subedha: adaptive particle grey wolf optimizer with deep learning-based sentiment … methods achieved 82.24%, 83.42%, 84.25%, 83.94%, 84.80%, and 84.36%, respectively. these results highlight the enhanced sa results of the proposed apgwo-dlsa method table v. comparative analysis of apgwo-dlsa with other models on the ap dataset methods accuracy f-score apgwo-dlsa 85.31 88.43 xg boost 80.63 82.24 random forest 83.23 83.42 svm 83.02 84.25 gradient boosting 81.49 83.94 naïve bayes 81.38 84.80 dl model 80.93 84.36 v. conclusion this paper presented the apgwo-dlsa method for accurate sentiment classification in online product reviews. this model invokes data preprocessing with word2vec word embedding process, uses the dbn model for sentiment classification, and selects the hyperparameters of the dbn model. the proposed model was tested in two product review datasets and its were compared with the results of other methods. the comparative analysis results showed that apgwo-dlsa achieved optimum accuracy of 94.77% and 85.31% on the cpaa and ap datasets, respectively. in the future, an advanced dl classification model can be developed to further improve the apgwo-dlsa model. references [1] r. s. jagdale, v. s. shirsat, and s. n. deshmukh, "sentiment analysis on product reviews using machine learning techniques," in cognitive informatics and soft computing, singapore, 2019, pp. 639–647, https://doi.org/10.1007/978-981-13-0617-4_61. 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india pragnesh.bhatt@ee.charsuat.ac.in abstract—the direct power control strategy has become popular as an alternative to the conventional vector oriented control strategy for grid connected pwm converters. in this paper, direct power control as applied to various applications of grid connected converters is reviewed. the direct power control for pwm rectifiers, grid connected dc/ac inverters applications such as renewable energy sources interface, active power filters, doubly fed induction generators and ac-dc-ac converters are discussed. control strategies such as look-up table based control, predictive control, virtual flux dpc, model based dpc and dpc-space vector modulation are critically reviewed. the effects of various key parameters such as selection of switching vector, sampling time, hysteresis band and grid interfacing on performance of direct power controlled converters are presented. keywords-direct power control; power conversion; pulse width modulation converters; space vector pulse width modulation i. introduction power electronics has emerged with strong merits of power processing and control of key parameters in the field of power system. traditionally, grid connected converters are designed with either uncontrolled rectifiers or controlled converters followed or preceded by strong dc links due to robustness, cost-effectiveness and ease of implementation. over the years, it has been observed that these systems are responsible for grid pollution. strict regulations have been imposed on users of such systems especially when the grid is referred as ‘weak’ [1] which applies to all applications such as switch mode power supplies, ups, adjustable speed drives, renewable energy sources interface and furnaces. to meet the above requirements, pwm converters were introduced due to their advantages of nearly sinusoidal current, unity power factor and better dc link voltage regulation. it is worth noting that these objectives are more or less same in all the grid connected systems whereas slightly differs in certain applications e.g. in active power filters in terms of output current references [2]. due to better dynamic response and close tracking to the reference, hysteresis current controlled pwm has been very popular though alternative techniques have also been suggested. in such cases, the control strategy used is based on grid voltage vector information and output currents are decomposed into currents responsible for active and reactive powers [3]. the major disadvantages of these schemes are: variable switching frequency, increased power losses, dependency on system parameters, and tuning of inner current control loops. to obtain better dynamic response in the drive, a scalar control technique called direct torque control abbreviated as dtc was proposed in [4] where torque and flux are treated as two variables of control and an appropriate switching vector is selected to obtain the desired operation [5]. considering grid connected converters, direct power control technique [6] was proposed by the same authors, which is still considered a benchmark work for grid connected converters applications. direct power control (dpc) technique is based on p-q theory [2] where instantaneous power errors of active and reactive power components are kept within a fixed hysteresis band to provide reference values of powers. a lookup table is developed based on the effect of a particular space vector on the variation of power [6-13]. alternatively, model based space vector selection [14-16] and predictive control [17-19] have also been suggested. the method has several advantages over conventional control techniques.  no precise information of grid voltage is required. a binary word determines position of voltage vector.  appropriate switching states that results in minimal commutation of converters switches can be selected  the method works equally well for sinusoidal as well as non-sinusoidal supply voltages. due to benefits mentioned above, direct power control has gained attention of many researchers. however, a clear engineering, technology & applied science research vol. 5, no. 4, 2015, 841-849 842 www.etasr.com trivedi et al.: a review on direct power control for applications to grid connected pwm converters approach of direct power control for specific applications still requires further investigation in order to improve performance. in the present paper, an attempt has been made to review the applications of direct power control for grid connected pwm converters. the paper is organized in five sections. in section ii, the principle of dpc is explained in detail. applications of dpc to various grid connected pwm rectifier, dc-ac converters, active power filter, ac-dc-ac converters are discussed in section iii. the control of doubly fed induction generator (dfig) using dpc is also discussed. section iv gives the classification of direct power control technique and discusses the major improvements achieved. section v highlights the key issues to be considered for the development of direct power control. conclusion and demerits are discussed in section-vi. ii. the basic rinciple of direct power control conventionally, grid connected converters are controlled using hysteresis current controlled pwm [3, 7,8] where the current error space phasor is treated as a control variable. whenever actual current deviates from the reference current, a switch of respective phase is turned on/off depending on the instantaneous value of current error. for grid connected converters, kvl yields: s s s c di v r i l v dt    (1) where s v is grid voltage vector, i is current vector and c v is converters voltage vector. the grid voltage vector is denoted as j t s mv v e  (2) where ω is the angular velocity of the grid voltage vector. in contrast, converters voltage occupies fixed states depending on switching combinations. for two level inverters, there are eight switching states. the hexagonal plane can be divided into either 6 or 12 sectors. hence, converters voltage vector is given by, 2 4 3 3 1 2 3 2 3 j j c dcv v s s e s e           (3) where s1, s2 and s3 are switching states of upper switch of pwm converter (1 or 0) and vdc is dc link voltage. the difference of voltage (vs vc) results in current error [9] . the actual current space phasor is given as *i i i  (4) where i is current error space phasor and it must be controlled in appropriate hysteresis band to obtain reference current. the control of current error space phasor has following limitations:  to obtain desired active and reactive power for converters, accurate information of voltage magnitude as well as phase are required.  the switching state of converters depends on instantaneous value of current error which often results in non-optimal voltage vector selection.  expensive current control algorithm has to be incorporated in order to limit switching frequency of converter and to generate appropriate current references. to overcome the above limitations, a direct power control algorithm was first proposed in [6]. in this section, the dpc algorithm is elaborated in order to understand and optimize the performance of grid connected pwm converters. for grid connected converters with voltage vs and current i, instantaneous complex power is given by, ˆss v i (5) where î = complex conjugate of line current vector. differentiating (5), we get ˆ ˆ s s dvds di v i dt dt dt   (6) differentiation of current is obtained from eq.(1) whereas differentiation of grid voltage is given by j ts m dv j v e dt  (7) from (5) and (6), variation in power is calculated from,  ( ) ˆs s c s s v v vds j iv dt l     (8)  21 s s c s ds v v v j s dt l    (9) since (9) is processed using digital computers/ dsps, differentiation of apparent power results in power variation whereas time differentiation is replaced by fixed sample time ts which may be generated using timers/external interrupts. the final equation for complex power variation is written as,  21 s s c s s s s v v v t j st l     (10) the active and reactive powers are calculated as, engineering, technology & applied science research vol. 5, no. 4, 2015, 841-849 843 www.etasr.com trivedi et al.: a review on direct power control for applications to grid connected pwm converters re( ) im( ) p s q s       (11) substituting the values of the grid voltage vector as well as the converter voltage vector into (10) and (11) yields the power variation rates for state vectors in respective sectors. from (8)(10), the following observations are made for the successful implementation of direct power control algorithm:  if control is to be done based on one state vector for one sample time only then the sample time ts must be small enough to calculate variation in power. large values of ts may result in deviation from the reference resulting in large power variations [11]. as a consequence, more harmonics/thds are introduced into the system which is highly undesirable.  large value of inductance is essential to keep variation of power within acceptable limits.  application of state vector and its effect also depends upon instantaneous power requirement. such a study has already been carried out in [11-13] . iii. applications of dpc algorithm a grid connected pwm converter can be considered as a dual of inverter fed induction motor (ac motor) drive where the grid voltage vector is similar to the back emf of the induction motor and the application of appropriate switching states lead to the control of the desired quantities. hence, all the major advancements that have been reported in the control of induction motors can be implemented, with exact dual quantity, for pwm converters. direct power control of pwm rectifiers was first proposed keeping such a view in mind. a. pwm rectifier three phase pwm rectifier as a front end converter is the most sought application in applied dpc literature. in pwm rectifiers, sinusoidal line current and unity power factor, which are the main objectives, can be directly obtained if reference active power pref is maintained equal to the power consumed in the load. this reference active power pref is a dc quantity and the reference reactive power qref is set to 0. any change in demand of power will be immediately reflected in reference power value pref to obtain an excellent dynamic response from the converter. in [6], the requirement for voltage sensors has been eliminated using direct power control so that power errors are maintained in prescribed limits. switching states are selected from the look-up table and grid voltage is estimated. the scheme has severe drawbacks of very high sampling frequency requirements (111 khz) as well as dependency on the inductance value to obtain instantaneous grid voltages. despite of these limitations, this control strategy has shown an excellent dynamic behaviour and hence considered as a benchmark work for dpc. to eliminate the need of estimation of voltage based on instantaneous power values, a new technique which was based on estimation of voltage from virtual-flux concept was implemented [14]. as mentioned above, voltage imposed by the line in combination with the acside inductors can be assumed to be quantities related to induction motor (or ac motor) and hence the technique is named virtual-flux direct power control. it is interesting to note that the equations of active and reactive powers of pwm converters in arbitrary reference frame are similar to the equations for power in the virtual ac motor. in another approach [12], errors of active power and reactive power are considered as output regulation subspaces (ors) and the required voltage vector is calculated from the information of the grid voltage vector. the method still requires measurement of voltage, increasing the cost but it delivers unity power factor and lower thd under distorted or unbalanced supply. also, wide variation in dc link voltage can be obtained with the method. it still requires however a look-up table for vector selection. since the classical look-up table method does not guarantee superior performance with parameter variation, model based direct power control for pwm rectifier was investigated in [13]. this concept leads to accurate information of desired voltage vectors in given conditions because of an adaptive control law. even though solutions mentioned above can achieve good steady state and dynamic response with simplicity in terms of implementation, they suffer from the following disadvantages:  variable switching frequency [14]  requirement of fast and accurate microprocessor and a/d converters [6, 14] space vector modulation schemes have been applied to reduce variation in switching frequency and obtain constant switching frequency. a simple method based on virtual flux estimator concept and space vector modulation is implemented in [15] where active and reactive power errors are fed to pi controllers (which act as natural low pass filter) instead of hysteresis controller and reference voltage vector generated is realized using the space vector modulation method to obtain the desired active and reactive power. since virtual flux estimator itself acts as a low pass filter, the method works satisfactorily under sinusoidal as well as distorted supply voltages. similar to this, constant switching frequency can be obtained using duty cycle control [16,17] where active vector is applied for a fraction of the duty period and null vector for the rest of the duration. although implementation is based on modulation of the vector for a given duty cycle, different methods have been proposed to calculate applied vector and time duration [10,16-18]. since the method is increasingly becoming popular, a task force was initiated by ieee on dynamic average modelling of dpc based pwm rectifiers [19]. the classification of control methods for pwm rectifiers is given in section iv. b. renewable energy sources most of the renewable energy sources in grids employ pwm inverters since available power is in the form of dc e.g solar, fuel cell. this power is transferred to the grid by means of a three phase line. the key parameters of the control scheme of such interface are voltage and frequency control and engineering, technology & applied science research vol. 5, no. 4, 2015, 841-849 844 www.etasr.com trivedi et al.: a review on direct power control for applications to grid connected pwm converters islanding operation [11]. direct power control can be effectively applied to the above control schemes. all the schemes of dpc of pwm converters are equally applicable to dc/ac inverter with the implications of output power limits which must be defined properly. in [20], authors use dpc algorithm for grid connected dc/ac converters for medium power application which is the often case with distributed generation. due to spread spectrum of the method, a new lcl filter [20] design approach is adopted to reduce large filtering inductance requirements. a predictive control strategy based on dpc of dc/ac inverter is implemented [21, 22] to reduce commutations and to achieve desired power level with space vector modulation. c. active power filters an active power filter is a special case of grid connected dc/ac inverter in which reference powers and reactive powers differ from all other applications. the common techniques available in literature are based on current control [2,7] and hence suffer from the same disadvantages mentioned for pwm converters. an optimal table is proposed in [23] for active filtering applications. the method is based on variation of hysteresis band to obtain regulation in switching frequency. also, the method is applicable to ideal source voltages only. for unbalanced and distorted conditions, the method is implemented in [24] through the concept of high selectivity filter (hsf). using the idea of virtual flux, pwm rectifier having active filtering function is implemented using the concept of dpc [25]. in this paper, combination of uncontrolled and pwm converter are used to control multidrive systems. using dpc, pwm converter provides compensating current for other uncontrolled converters resulting in reduction of overall thd in the system. similarly, dpc is also applied to multilevel inverter based active power filters [26, 27]. in addition, techniques mentioned in [10, 20, 21, 22] are equally effective for such applications. a careful investigation of direct power control to active power filter applications can further improve the performance. d. doubly fed induction generator (dfig) for grid connected applications for wind turbine generating systems, dfigs have become very popular because of their numerous advantages [28]. vector control or direct torque control techniques are applied to dfig system to obtain the desired performance. however, the control of dfigs is very complicated due to involvement of stator and rotor parameters, indirect control based on voltages and expensive current controllers. any deviation of the parameter in control loop can further deteriorate the performance. direct power control, can take advantage of its simplicity to control power fed to the grid. active and reactive power calculations in dfigs are done based on stator and rotor flux values. virtual stator flux estimator is used [29] to select an optimal vector from the table. a dpc with constant switching frequency [30] gives satisfactory performance for large power (2 mw) dfig independent of parameter variations. an algorithm called dpc+ is reported in [31] based on dpc under small variation in voltages. a discrete space vector modulation control is applied in [32] to reduce power ripples and current harmonics with constant operating switching frequency. the objectives of sinusoidal current with variation in steady state values of voltages and decoupled control of active power and reactive power with reduced ripples and good dynamic performance are yet to be investigated. several attempts have been made towards this objective [28, 31, 33, 34]. e. ac-dc-ac (back to back) converters in medium power drives, ups and other application where dc-ac inverter is preceded by pwm ac-dc converter, the direct power control algorithm is applicable for both the inverter as well as the converters side. one such application of voltage source ac-dc-ac converter is mentioned in [35]. the reference power is calculated based on commanded current values, whereas current reference can be calculated based on any control technique of the drive. a unique approach of dpc of rectifier and dtc of inverter fed induction motor drive is employed in [36]. in all such applications, it is assumed that, * rec invp p (11) in addition, direct power control is also applied to facts devices. a series converters control for multilevel inverter is discussed in [37, 38] which is further improved in [27] with sliding mode control. all the applications discussed so far applies two level or multilevel inverter topology based on vsi [38, 39]. for application involving ac-ac interaction, dpc has also been investigated for matrix converters based unified power flow controllers [40, 41]. iv. control strategies the performance of dpc to any application largely depends upon the selection of the control strategy. the different control strategies are investigated based on certain objectives. a. look-up table (lut) approach a basic approach in direct power control algorithm is to select appropriate inverter voltage vectors based on instantaneous power errors. based on instantaneous power errors and hysteresis band limits, there are four possible combinations with each having its own physical significance. for example, when dp>0 and dq>0 (active and reactive power are more than reference values), converters/inverter should act in capacitive effect as sources of reactive power reducing instantaneous reactive power requirement and supplying instantaneous active power to the grid. several alternative look up tables are proposed for optimal switching for respective applications such as grid connected inverter [42], active power filter [23], pwm converters [10,16], and ac-dc-ac converters [35] which are basically based on the technique proposed in [6]. all the lut based schemes suffer from disadvantages such as variable switching frequency resulting in wide current spectrum and introduction of lower order harmonics in line currents, high sampling frequency and steady state errors. engineering, technology & applied science research vol. 5, no. 4, 2015, 841-849 845 www.etasr.com trivedi et al.: a review on direct power control for applications to grid connected pwm converters b. model based dpc in a model based technique [13], output control vector applied to the converters is derived as a function of input control parameter using an adaptive control law. the method is an extension of the ors concept [12] and applies few steps to decide reference vector for given active and reactive power errors.  the reference vector for which active and reactive power errors ( p and q ) are zero is treated as equilibrium point in α-β plane [12].  based on the equilibrium point, selection area is defined using binary word.  an output control vector that compensates for given active and reactive power is determined and applied using pwm or svm. due to control over power errors, smoothening inductor value is decreased. moreover, the method is based on adaptive control law and is immune to parameter variations. c. virtual flux dpc to eliminate the requirement of line voltage sensors, estimation of voltage can be performed [6] leading to a technique called virtual flux direct power control [14, 43] (vf-dpc) where it is assumed that virtual flux (of virtual ac motor) is responsible for line voltage being induced. from line current measurement and current switching state, a virtual flux vector is calculated from, s s c di v v l dt   (13) s s c di v l dt dt            (14) using torque equations of ac motor, the instantaneous powers are computed as ( ) ( ) s ss s s s s s p i i q i i                  (15) . the method still uses look-up table for selection and application of voltage vector and hence results in variable switching frequency. due to natural low pass filter characteristics, the method works satisfactorily under distorted line voltages whereas sampling frequency is lower than classical dpc approach. d. model based dpc in a model based technique [13], output control vector applied to the converters is derived as a function of input control parameter using an adaptive control law. the method is an extension of ors concept [12] and applies few steps to decide reference vector for given active and reactive power errors.  the reference vector for which active and reactive power errors ( p and q ) are zero is treated as equilibrium point in α-β plane [12].  based on the equilibrium point, selection area is defined using binary word.  an output control vector that compensates for given active and reactive power is determined and applied using pwm or svm. due to control over power errors, smoothening inductor value is decreased. moreover, the method is based on adaptive control law and is immune to parameter variations. e. predictive algorithm the principle of predictive algorithm of dpc uses information regarding the grid voltage vector and the variations in power due to the application of converters voltage for the given sample time. the equation below shows the basic principle on which predictive algorithm is applied. 1 1 ( 1) ( ) ( 1) ( ) n n n i n n n i dp p k p k t dt dq q k q k t dt           (16) where n dp dt and n dq dt are active and reactive power variations, respectively, due to respective voltage vector and tn is fraction of sample time ts for which the voltage vector is applied. using the least square optimization technique, the time duration for kth control period are calculated such that 2 2 [ ( 1)] [ ( 1)]p k q k       (17) is minimum. depending upon the number of voltage vector applied in (15), the scheme is referred as two voltage vector sequence [22] or three voltage vector sequence [21]. a predictive dpc based on svm is proposed in [17]. dpc combined with svm leading to robust control of grid connected inverter for distributed generation has proven to have high speed and accuracy having low steady state errors [44]. compared to other methods, predictive algorithm has less sampling frequency [10], constant switching frequency [17, 21, 22, 45] and minimum switching losses [21,46]. f. space vector modulation to limit switching frequency variations and reduce the number of commutations in converters, desired voltage vector is synthesized using svm. the method is mostly used in conjunction with the above methods or any other method. in model based dpc, synthesis of calculated voltage vector is an example of svm. the method is applied in [10, 17, 45] for predictive algorithm, whereas virtual flux dpc based svm is discussed in [15]. engineering, technology & applied science research vol. 5, no. 4, 2015, 841-849 846 www.etasr.com trivedi et al.: a review on direct power control for applications to grid connected pwm converters it should be noted that although the above methods are commonly found in literature, other techniques such as sliding mode control [34, 47], and fuzzy control [48] are also referred to provide comparable performance for given applications. v. key issues of direct power control there are many key issues or factors which affect the performance of the direct power control algorithm: selection of switching vector from the table/ on line calculation, effect of sample time, determination of hysteresis band and grid interfacing are of utmost importance and are further elaborated in this section. a. selection of switching vector direct power control uses bang-bang type of controller where appropriate switching vector is selected for the given sample time. the selection may be done using either look up table; model based control, predictive control. it is essential to understand the effect of state vector on the power variation. to simplify the understanding of phenomena, it is assumed that line voltage drop across the impedance is negligible and that the boundary of the hexagon is sufficient to accommodate infinite power throughout the operation. the tip of the voltage vector is assumed to be the equilibrium point of the state vectors dp and dq in the pq plane and the variation of power due to application of voltage vector is obtained. the attempts to optimize the selection of switching state depending upon type of the application are widely reported in [6, 16, 23, 49]. the major observations can be summarized as follows:  when the grid voltage vector is in sector-i, application of vector v2 results in an increase of both active and reactive power. on the other hand, application of voltage vector v1 results in an increase of active power and decrease of reactive power.  application of voltage vector other than v1 and v2 results in decrease of active power which needs to be analyzed very carefully. it has been found that application of null vectors v0 (000), v7 (111) results in medium reduction of active power [10] and reduction in number of commutation of switches.  reactive power variations are sinusoidal function of the angle between the voltage space vector and the grid voltage vector i.e. a positive angle results in an increase in reactive power and a negative angle results in a decrease in reactive power. table i shows such a selection of voltage vector for respective error in kth sector while referring to 6sector approach. table i. selection of state vector in kth sector dp>0, dq>0 vk+3 dp>0, dq<0 vk-1 dp<0, dq>0 vk+1 dp<0, dq<0 vk b. effect of sample time the method being a digital control, works on fixed sample time. sample time of the system plays a crucial role in implementation since too large sample times reduce the performance of the system whereas too small sample times increase the burden on the controller. normally, a look up table based approach requires high sampling frequency of the order of 50-100 khz [6, 14, 23, 49]. this necessitates microprocessor and a/d system with higher speeds. since the technique is mainly applied to grid connected systems with medium and large power ratings, the cost of such high speed system is not considered as constraint. the use of the model based technique or space vector modulation, further reduces sampling frequency requirement. in modulator based technique, where multiple converter voltage vectors are used to meet reference power requirement, sampling frequency is twice that of the switching frequency [21, 50]. when duty cycle control based techniques are used [16] , sampling frequency can be further reduced to 20 khz. c. determination of hysteresis band in look-up table approach, vector selection from the table depends upon the pre-determined hysteresis band. a fixed hysteresis band of ±4-5% is usually set [10] to obtain satisfactory performance. the set hysteresis band of active and reactive power also depends upon accuracy and resolution of adcs as well as sample time of the system. since these variations are different for selected converter voltage vectors, they must be treated separately and are discussed below.  active power: for grid voltage vector in kth sector, only the nearest two active vectors in the sector are responsible for the increase of active power whereas all other vectors (six vectors) are responsible for the decrease in active power. this variation is a function of angle between the grid voltage vector and the inverter state vector and hence becomes unequal in magnitude. this may lead to large switching frequency variation and poor control over reference power quantity. in such case, there are two approaches to reduce the variation of active power. one being the application of active vector for a fraction of time period and null vector in rest of the period using duty cycle control as in [15, 16, 50]. another is to change the symmetry of hysteresis band in positive and negative direction such that frequency variation is limited to acceptable limits.  reactive power: the reactive power limit follows the same criteria of the hysteresis band. but the reactive power variation is equally spaced in all sectors. for example, three active vectors produce position variations whereas the remaining three active vectors produce negative power variations. also, reactive power control is always considered a secondary function (except in case of active power filter or facts) and hence limits are simplified and are symmetrical. depending upon the magnitude of variation, the vectors are also divided among small, medium and large groups. engineering, technology & applied science research vol. 5, no. 4, 2015, 841-849 847 www.etasr.com trivedi et al.: a review on direct power control for applications to grid connected pwm converters d. grid interfacing there are two aspects of grid interfacing while applying any control strategy for grid connected converters (or inverter).  passive filter (l or lc) for interfacing  determination of grid voltage vector position. to eliminate switching ripples of current and/or voltage as a consequence of operation of pwm converters, appropriate values of inductances and capacitances must be connected at the point of coupling. in dpc, high gain of controller necessitates the use of inductors with high value [13]. thus, overall cost, size and weight of the system are increased. additionally, due to the wide spectrum of frequency in current waveform, it becomes difficult to decide the optimum value of passive filters. the possible remedies are:  reduction of variation in switching frequency or adopt constant switching frequency technique discussed above  design a suitable lcl filter [20] for grid connected systems. in contrast to, voltage oriented control method where the determination of absolute position of grid voltage vector is necessary, direct power control method requires position of the grid voltage vector in particular sector of α-β plane. based on the sector number, voltage vector of converters is selected. the sector pertaining to the grid voltage vector can be decided from their magnitudes [6, 23, 35], using virtual flux vector [14, 15, 18, 25, 31] or using conventional phase locked loops. it is obvious that magnitude based determination of sector cannot work satisfactorily when line voltages are unbalanced or distorted. virtual flux based technique has shown satisfactory performance under all these conditions due to its ability to act as low pass filter. the review of dpc techniques for various application related to grid connected pwm converters are tabulated in table ii for quick reference. table ii. review of dpc techniques for various applications dpc technique pwm rectifier renewable energy sources active power filter doubly fed induction generator ac-dc-ac converters look up table √ √ √ √ √ model based √ √ virtual flux dpc √ √ √ √ predictive control √ √ √ space vector modulation √ √ √ vi. conclusion direct power control of the grid connected pwm applications such as pwm rectifier, grid connection of renewable energy sources, active power filter, upfc, ac-dc-ac converters and doubly fed induction generators (dfig), are reviewed in this paper. the method is reported to have excellent dynamic performance, higher efficiency and easy implementation. due to the high gain of the controller, it poses several challenges in terms of variation in switching frequency, high sampling frequency, accurate estimation of voltage vector and reduced power ripples. various methods have been proposed to meet the above challenges and 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shielding effectiveness; transverse electric polarization; transverse magnetic polarization; four-layered head model i. introduction mobile handsets [1-3] are used worldwide, but their introduction brought unforeseen adverse effects. these mobile handsets emit rf energy, a kind of non-ionizing electromagnetic radiation that severely affects human head tissues during their usage. more power in the form of biogenic magnetite crystals gets deposited in the human brain at higher frequencies. the brain is a target organ for em radiation, and the different received dosage is categorized into ionizing and non-ionizing radiation [4]. the fifth generation (5g) technology features high cell density and higher data transmission rates. the frequency bands 5g mobile communication uses are below 6ghz, and known as the sub-6 ghz band and fr-2 [5]. the amount of radiation emerging from a handset and entering the brain layer is estimated using the specific absorption rate (sar) parameter [6-7]. the dependent parameters of sar are the conductivity ( � ), the mass density of human head tissues (�), and the tissue incident electric field (e). from the icnirp guidelines [8], the permissible sar is around 2w/kg. hence, any mobile handset causing sar more than the allowable is unauthorized for usage. embodying a transparent shield material [9] with conductive coating helps reducing sar. after incorporating a shield, the shield performance is estimated using a parameter called shielding effectiveness (se). this parameter depends on the calculated total transmission coefficient (ttc) using the corresponding author: sai spandana pudipeddi engineering, technology & applied science research vol. 12, no. 4, 2022, 8954-8959 8955 www.etasr.com pudipeddi et al.: polarization effect assessment of sub-6 ghz frequencies on adult and child … transmission line method (tlm) for two planar four-layered head models representing humans of different age. the incoming em radiation can be incident at any arbitrary angle. the calculation of sar for the head models includes both te and tm polarization of the incident em wave. mobile phone antenna performance and design are not examined in the current work. all sar calculations are evaluated considering a planar four-layered head model. the planar head model in figure 1 has four layers, namely skin, fat, bone, and brain. the considered parameters are electrical conductivity (�), relative permittivity (�� ) and relative permeability (�� �. (a) (b) fig. 1. a 4-layered planar human (adult/child) head model with pet shield and cu coating. (a) parallel polarization, (b) perpendicular polarization of the em wave incident on the shield surface transmitted through the head tissues. many researchers have worked on estimating and reducing the sar absorbed by human adult and child head models at various mobile frequencies. authors in [10] studied the mutual effect of interaction between mobile phones and the human head with the fdtd method to find the sar distribution in the head near the hand-held receiver. the mobile frequencies used are 900mhz and 1800mhz. maximum 1g and 10g averaged sar using the fdtd method were calculated in adult and child scaled head models in [11] at gsm 900mhz and 1800mhz. the effect of a plane wave that is obliquely incident on a six-layered head structure at 900mhz and 1800mhz was analyzed mathematically by deriving the exact formula for the electric field. the sar distribution concerning various distances between the source and head model is plotted and compared in [12]. authors in [13] studied the sar distributions and temperature elevation with fdtd modeling of mobile phones and wlan networks when a plane wave is excited with an obliquely incident wave in a head model of six layers. sar and temperature rise are calculated and studied for each head layer at 900mhz, 1800mhz, and 2400mhz at parallel and perpendicular polarization. authors in [14] investigated the relationship between peak sar and temperature elevation averaged over 10g of human head tissues in head models in the 1 to 300ghz range. the novelty of the proposed work is the numerical and mathematical evaluation of sar by utilizing the tlm taking shield parameters such as se of different planar-aged human head models with no shield condition and with the mesh coated thin film as a laminated shield. the sar estimation and reduction using the transparent mesh coated film is not available in literature for mobile phone applications up to 5g frequencies. the novelty of the current work is the study of the theoretical analysis of sar with the usage of a transparent metal mesh of minimum thickness with the tlm. ii. analysis of shielding effectiveness of human head a. shielding material and parameters of mesh a shield is required to control the radiation from the handset and its design should be able to control the sar imposed on the planar four-layered human head. this can be achieved by designing a transparent laminated shield, i.e. coating a polymer film coated with a conductive film. in the current work, the considered polymer is polyethylene terephthalate (pet), and the conductive coating is copper (cu). the combination forms a laminated mesh. the material parameters of thickness, conductivity, relative permittivity, and relative permeability are included, whereas the mesh parameters, as shown in figure 2, are mesh spacing and width [15]. the mesh spacing and the mesh width are used to find the cu-mesh impedance [16]. the parameters involved in the impedance equation are: � �� ���� �� � ����� �� (1) ���� �� �������� �� �� � ∗ ! "# (2) ���� �� $ !% &'()*+( , -# ! ./ ∗ �0 (3) equations (1)-(3) are used in the impedance calculation of coating film used in the analysis of the ttc from which the shielding effectiveness is derived. the shield on which the coating film is embedded is the polymer pet and its properties are shown in table i. the impedance of the pet shield can be calculated from [17]. therefore, the impedances of the films are calculated from (1)-(3), which help in determining the ttc. it is also necessary to resolve the tissue impedance of the human models, as described. table i. parameters of the shielding material material pet film cu mesh film thickness 100 μm 100 nm conductivity (s/m) 7.80e-13 5.96e+07 relative permittivity 3.4 1 relative permeability 1 1 mesh spacing not applicable 300 μm mesh width not applicable 15 μm b. human head models and tissue parameters in the current work, a planar four-layered head model of the adult/child human head is considered. the model properties differ significantly in their water content and tissue thickness. the tissues include the skin, fat, bone, and brain. these tissues vary in thicknesses, as shown in table ii. however, their properties vary with the operating frequency of the mobile phone device (1 ). the electrical conductivities (� ), relative permittivities (�� ), and also the relative permeabilities (�� ) of the tissues change with frequency. but since all the tissues are biological, all the relative permeabilities are equal to unity. engineering, technology & applied science research vol. 12, no. 4, 2022, 8954-8959 8956 www.etasr.com pudipeddi et al.: polarization effect assessment of sub-6 ghz frequencies on adult and child … also, the impedances of the tissues depend on the operating frequency. the tissue impedance is generally given by �234k for skin, fat, and bone with (4) as the corresponding equation for impedance calculation: �234 )1 � ��7-89:;<�9:; (4) from (4), the corresponding tissue relative permeability and conductivity at the mobile phone operating frequency are found by substituting all tissue impedances. fig. 2. mesh parameters of a copper coating film. table ii. tissue thickness of head models [18-19] tissue tissue thickness (mm) adult head child head skin 1 1 fat 2 0.5 bone 7 6.5 brain 70.5 62.3 table iii. electrical conductivity and permittivity of tissues with frequency frequency (ghz) head tissue electrical conductivity (s/m) relative permittivity 3.6 skin 2.085 36.92 fat 0.161 5.1641 bone 0.637 10.74 brain 2.724 47.159 4.5 skin 2.687 36.18 fat 0.212 5.0766 bone 0.844 10.28 brain 3.58 45.862 c. effect of polarization on the impedance of shield medium and tissues electromagnetic radiation can be incident over a wide range of the angle (=). in the case of a te/tm polarized wave, the impedances of the shield or any medium or tissue are altered by a ratio of >?* =. the angle of incidence (=) would range for all acute angles (0° to 90°)—the polarization effect results in different transmission coefficients than the ones considered without polarization. therefore, a variation is introduced in the se of the head, and the sar is absorbed. the interpretation of sar considering the aoi of em wave for polarization and head models is considered. irrespective of medium or tissues, the impedance variation with polarization is: @234 a9:;bc� d )1?� ef� (5) @234 �234 ∗ >?* = )1?� eg� (6) d. se and sar calculations using the transmission line method during the estimation of sar, its relatively dependent parameter se needs to be calculated. se can be calculated by determining the corresponding ttc (e) of the wave radiated by the tlm. the reflection coefficients at the interfaces of the tissues are calculated by taking the impedances introduced by them under te and tm polarization. once the total transmission coefficient is calculated through the tlm, the se can be determined [20-21]. hf)ij� = −20'?m�0)e� (7) e = n ∏ p)1 − q234r �"s9:;t9:; �ur �s9:;t9:;vcw 3xy3zw (8) e = n ∏ p)1 − q234r �"s9:;t9:; �ur �s9:;t9:;vcw 3x[\] (9) the step-by-step numerical procedure to evaluate the sar absorbed into human head is: step 1: the mathematical finding of the transmission coefficient t without shield and with the pet/cu coated laminated mesh as shield is obtained from (8) and (9). k ranges from pet shield and cu mesh coat to brain layer. q234 gives the reflection coefficient at the interface of the layered medium, ^234 is the respective propagation constant of the layered medium, and '234 is the thickness of each medium. step 2: the se of any barrier in terms of electric field e is: hf = 20 log�0 , \b \� . (10) step 3: the incident electric field )fz � from (10) is obtained from the power density incident on the head from the guidelines issued by icnirp [8] which is 40w/m 2 for frequency greater than 2ghz. step 4: the transmitted electric field (fc ) into the brain can be determined from the shielding effectiveness of the human head models without shield and with the pet and cu laminated mesh. step 5: equations (7) and (11) are necessary for sar calculation, and thus, (8) and (9) give the variation of sar with polarization for both head models. hde = �\� f g (11) iii. results and discussion from (8), the se from the tlm varies according to the aoi range from 0° to 90° for both te and tm polarizations. the results are obtained by simulations in matlab. the variations with aoi are plotted and compared. the se and sar calculations with changing operating frequency are listed in tables iv and vi. engineering, technology & applied science research vol. 12, no. 4, 2022, 8954-8959 8957 www.etasr.com pudipeddi et al.: polarization effect assessment of sub-6 ghz frequencies on adult and child … table iv. shielding effectiveness of human head models in variation with angle of incidence at two sub6 ghz frequencies frequency (ghz) shielding effectiveness (se in db) aoi (degrees) 4-layer adult head model 4-layer child head model without shield with pet/cu laminated shield without shield with pet/cu laminated shield te polarization tm polarization te polarization tm polarization te polarization tm polarization te polarization tm polarization 3.6 0 9.83 9.83 68.75 68.75 2.46 2.46 61.34 61.34 30 9.62 10.08 70.26 67.28 2.21 2.74 62.80 59.92 45 9.35 10.48 72.45 65.26 1.90 3.20 64.92 57.98 60 9 11.33 76.41 61.96 1.48 4.16 68.76 54.78 89 8.13 31.80 127.74 36.61 0.41 25.15 119.98 29.96 4.5 0 12.30 12.30 70.87 70.87 4.72 4.72 63.02 63.02 30 12.12 12.51 72.49 69.29 4.52 4.95 64.59 61.49 45 11.91 12.84 74.85 67.14 4.27 5.32 66.89 59.40 60 11.61 13.56 79.14 63.63 3.93 6.12 71.08 56.00 89 10.90 32.69 132.24 37.55 3.08 25.55 124.37 30.40 table v. result comparison frequency range (mhz) sar assessment technique obtained sar absorption values (w/kg) head model reference 900, 1800 finite-difference timedomain (fdtd) 0.037 adult [11] 900, 1800 fdtd 0.42 at te polarization, 0.83 at tm polarization adult [12] 900, 1800, 2400 fdtd 1.8 at te polarization, 2 at tm polarization adult [13] 3600, 4500 tlm 1.51e-06 at te and 5.38e-05 for tm polarizations for adult model with laminated shield and 9.42e-06 for te and 3.03e-04 for tm polarizations for child model with laminated shield. adult and child current work table vi. sar absorbed by brain in both head models in te and tm polarization at two sub-6 ghz frequencies frequency (ghz) sar (w/kg) aoi (degrees) 4-layer adult head model 4-layer child head model without shield with pet/cu laminated shield without shield with pet/cu laminated shield te polarization tm polarization te polarization tm polarization te polarization tm polarization te polarization tm polarization 3.6 0 12.71 12.71 1.63e-05 1.63e-05 66.68 66.68 8.63e-05 8.63e-05 30 13.34 12 1.15e-05 2.29e-05 70.63 62.52 6.17e-05 1.20e-05 45 14.2 10.95 6.95e-06 3.64e-05 75.86 56.23 3.78e-05 1.87e-04 60 15.39 9 2.79e-06 7.79e-05 83.56 45.08 1.56e-05 3.91e-04 89 18.81 0.08 2.06e-11 0.027 106.91 0.36 1.18e-10 0.12 4.5 0 7.3 7.3 1.02e-05 1.02e-05 40.73 40.73 6.03e-05 6.03e-05 30 7.61 6.97 7.00e-06 1.46e-05 42.69 38.64 4.20e-05 8.57e-05 45 8 6.45 4.06e-06 2.40e-05 45.21 35.45 2.47e-05 1.38e-04 60 8.56 5.46 1.51e-06 5.38e-05 48.86 29.53 9.42e-06 3.03e-04 89 10.1 0.07 7.41e-12 2.18e-02 59.38 0.34 4.41e-11 1.10e-01 fig. 3. se plot of the head without shield and pet-cu mesh laminated shield (ls) for aoi in the 4-layered adult head at 3.6ghz fixed-mobile frequency for te and tm polarization. in figures 3 and 4, the comparison of the se variation with the operating frequency for a four-layered adult head is made. it is observed that at 3.6ghz, the se values for te polarization appear to be constant. however, they decrease drastically without the shield. with the shield, the se values increased sharply from 30° to 89°. in the case of tm polarization without a shield, the se values increased symmetrically about te polarized se values from 72° to 89°. however, it can be seen that the se values with shield at tm polarization abruptly decrease from 30° to 89°. at 4.5ghz, the phenomenon remains the same, but the difference is that at 4.5ghz, the se values are higher than at 3.6ghz. figures 5 and 6 compare the se variation with the operating frequency of the mobile phone for the four-layered child head. at 3.6ghz, the se values for te polarization appear constant, but they decreased drastically without the engineering, technology & applied science research vol. 12, no. 4, 2022, 8954-8959 8958 www.etasr.com pudipeddi et al.: polarization effect assessment of sub-6 ghz frequencies on adult and child … shield, while they increased with the shield. in the case of tm polarization and without a shield, the se values increased symmetrically about the te polarized se values. we see that the se values with the shield are more significant than those without it. moreover, the se values in the model of the child head are always less than in the adult head model. fig. 4. se plot of the head without shield and pet-cu mesh ls for aoi in the 4-layered adult head at 4.5ghz fixed-mobile frequency for te and tm polarization. fig. 5. se plot of the head without shield and pet-cu mesh ls vs angle of incidence in the 4-layered child head model at 3.6ghz fixed-mobile frequency for te and tm polarization. fig. 6. se plot of the head without shield and with pet-cu mesh ls vs angle of incidence in the 4-layered child head model at 4.5ghz fixed-mobile frequency for te and tm polarization. from figures 3-6, for te polarization with pet and cu shield, the se started to increase sharply at 35°, and for tm polarization, it abruptly decreased from 35° to 89°. the values of se of head variation for particular angles of incidence of em waves are listed in table iv, and their corresponding sar values in table vi. it is observed from table v that with an increase in the se of the four-layered adult/child head with frequency, the sar absorbed by the brain consistently decreased to a negligible level much lesser than the prescribed sar limit. the comparison of the results of the proposed method with the existing results is exhibited in table v. iv. conclusion the current paper compares the effect on human head models of the penetration of rf em radiation for varying aoi from the sub-6 ghz operating frequency mobile phone. in te and tm polarization, the sar of the child model without a shield dominated over the adult model without a shield. when using a pet with a cu laminated shield mounted on the front part of the mobile handset, the sar is decreased in both models. based on the operating mid-band 5g mobile smartphones and the incident angle polarization, the sar variations are observed in both the head models without and with the laminated shield. in contrast, at the same operating frequency, for te polarization, the sar absorbed by the brain of the child model without a shield varied from 40.73 to 50.38w/kg for 0° to 89° angle of incidence variation. in contrast, the sar decreased from 6e-05 to 4.41e-11w/kg with the pet and cu lamination in te polarization. for tm polarization and the same child head model, operating frequency, and aoi variation, the sar decreased from 40.73 to 0.34w/kg, and with pet cu mesh, it increased from 6.03e-05 to 0.11w/kg. also, the minimum absorbed sar was found at 4.5ghz for the adult head model in te polarization at 89°, and the maximum absorbed sar by the brain tissue was observed at 3.6ghz in the child head model in te polarization at 89°. therefore, the adult model absorbed more negligible radiation than the child head model with the pet/cu mesh. however, compared to sar without the laminated shield in a child's head, incorporating pet and cu-based transparent film in the mobile handset has considerably decreased the sar absorbed by the brain. references [1] d. t. t. my, h. n. b. phuong, t. t. huong, and b. t. m. tu, "design of a four-element array antenna for 5g cellular wireless networks," engineering, technology & applied science research, vol. 10, no. 5, pp. 6259–6263, oct. 2020, https://doi.org/10.48084/etasr.3771. 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[11] m. martinez-burdalo, a. martin, m. anguiano, and r. villar, "comparison of fdtd-calculated specific absorption rate in adults and children when using a mobile phone at 900 and 1800 mhz," physics in medicine and biology, vol. 49, no. 2, pp. 345–354, jan. 2004, https://doi.org/10.1088/0031-9155/49/2/011. [12] a. a. omar, q. m. bashayreh, and a. m. al-shamali, "investigation of the effect of obliquely incident plane wave on a human head at 900 and 1800 mhz," international journal of rf and microwave computeraided engineering, vol. 20, no. 2, pp. 133–140, 2010, https://doi.org/ 10.1002/mmce.20402. [13] a. i. sabbah, n. i. dib, and and m. a. al-nimr, "sar and temperature elevation in a multi-layered human head model due to an obliquely incident plane wave," progress in electromagnetics research m, vol. 13, pp. 95–108, 2010, https://doi.org/10.2528/pierm10051502. 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[21] p. k. dutta, p. v. y. jayasree, and v. s. s. n. s. baba, "sar reduction in the modelled human head for the mobile phone using different material shields," human-centric computing and information sciences, vol. 6, no. 1, apr. 2016, art. no. 3, https://doi.org/10.1186/s13673-0160059-0. microsoft word etasr_v12_n4_pp8896-8900 engineering, technology & applied science research vol. 12, no. 4, 2022, 8896-8900 8896 www.etasr.com ternane et al.: regression modeling and process analysis of resistance spot welding on dissimilar … regression modeling and process analysis of resistance spot welding on dissimilar steel sheets fouad ternane department of mechanical engineering is2m laboratory, university of aboubekr belkaid tlemcen, algeria fouadsciences@yahoo.fr mustapha benachour department of mechanical engineering is2m laboratory, university of aboubekr belkaid tlemcen, algeria bmf_12002@yahoo.fr fethi sebaa department of mechanical engineering is2m laboratory, university of aboubekr belkaid tlemcen, algeria sebaafethi@yahoo.fr nadjia benachour department of mechanical engineering is2m laboratory, university of aboubekr belkaid tlemcen, algeria nbenachour2005@yahoo.fr received: 10 may 2022 | revised: 27 may 2022 | accepted: 28 may 2022 abstract-the resistance spot welding process is used to weld dissimilar materials. dissimilar joining is formed by two 2mm thick sheet metals of 304l austenitic stainless steel and galvanized steel. this study investigates the effects of welding parameters such as welding current, welding time, and welding force. the welding time and the welding force were, respectively, in the range of 10-13 cycles and 7-8bar, while the welding current was in the range of 10–16ka. tensile tests were applied to determine the resistance parameters of dissimilar joining. the experimental results showed that increasing the welding current increased the tensile shear stress of the weld coupon. regression analysis was carried out to determine the significance of the process parameters by using the coupled of the full factorial experimental design with statistical and graphical analysis of the results. furthermore, analysis of variance was used to determine the optimal parameters and combinations to achieve the highest strength level. keywords-resistance spot welding; dissimilar joining; stainless steel & galvanized steel; welding parameters; regression model; tensile shear stress i. introduction resistance spot welding (rsw) is the main welding process used in the manufacturing industry, especially in the manufacturing of automobile truck cabins, rail vehicles, motorcycles, and home appliances such as refrigerators. for example, there are 3000 to 12000 spot welds in a car [1, 2]. the majority of the research investigations in spot welding has been carried out on the joining of homogeneous materials [3-6]. currently, research in different industries is directed towards the reduction of co2 emissions. the combination of heterogeneous materials is necessary to reduce the weight of the structures and co2 emissions [7-9]. engineers are increasingly looking to join different material types ensuring good mechanical strength, corrosion resistance, and sealing function [10, 11]. rsw of dissimilar materials was investigated in [10], finding that the lap shear strength depends on the strength and thickness of the non-stainless steels. a failure in dissimilar joining is called a plug failure. the properties of rsw of dissimilar stainless steel lap joints were studied in [12], where the weld quality of dissimilar joints was linked to their tensile-shear strength. the welding current was the main governing factor that affected the tensileshear strength of the rsw specimens. the current contribution of the weld was approximately 67% compared to weld time and applied load. as the weld current increases, the size of the weld nugget also increases. the mechanical performance of dissimilar stainless steel and carbon steel depends on the size of the fusion zone on the carbon steel side, where the pullout failure location of the carbon and stainless steel joint was in the base metal (bm) of the carbon steel side [11]. tensile-shear properties and types of fracture of rsw joints were examined in [1], showing that increasing the weld time increased the tensile shear load-bearing capacity. pullout and tearing failures are identified depending on the dissimilar joints (back hardening steel/304 stainless steel and back hardening steel/interstitial steel). pullout and interfacial failure modes were observed in several studies of homogeneous and inhomogeneous rsw of stainless steel and low carbon steel [11, 13-18]. the effects of welding current and welding process on residual stress distributions for dissimilar welded joints between stainless steel 316l and ferritic steel were investigated in [19], which have been used for lifetime assessment and failure mode predictions of the welded joints. several studies have been conducted to optimize the welding parameters [22-24]. factorial analysis was applied to investigate the effect of feed water temperature, flow rate, and corresponding author: fouad ternane engineering, technology & applied science research vol. 12, no. 4, 2022, 8896-8900 8897 www.etasr.com ternane et al.: regression modeling and process analysis of resistance spot welding on dissimilar … radiator dimension on the total heat transfer coefficient and entropy generation in the panel radiator [22]. the effect of welding parameters on the tensile strength of rsw of the 5052al alloy using a factorial design was studied in [25]. the effects of rsw process parameters and their interactions were studied in [26] using a non-linear regression model. this paper presents an experimental study on determining the effect of the rsw parameters on the tensile-shear strength of dissimilar joints of stainless steel 304l with galvanized steel z275. linear regression, variance analysis, and a mathematical model were applied to evaluate the effects of the rsw parameters and some combinations on tensile-shear stress. ii. experimental procedures this study used 304l stainless steel (ss) and z275 galvanized steel (gs), each having a thickness of 2mm. the chemical compositions of the steels are given in table i. the dimensions of the tensile specimens were 85mm length and 30mm width, as shown in figure 1. the total length of the rsw welded specimen was 140 mm. table i. chemical composition of the welding materials element c si mn p s cr ni ss 304l 0.03 1.0 2.0 0.045 0.015 0.1 0.03 gs z275 0.12 0.50 0.60 0.10 0.045 / / fig. 1. dimensions of the tensile test specimens. the samples were welded by a tecna art 8201n rsw machine. welding was performed using a water-cooled electrode with a hemispherical active face. the electrode in the cuni2be alloy had 6.0mm in contact surface according to: � ������ 2� � 3 (1) where d is the active diameter and e is the sheet thickness in mm. iii. welding parameters determination the welding parameters were determined from previous research and the weldability of materials, depending on the nature of the base materials and thickness [20]. the welding current varied from 10ka to 16ka, the welding time increased from 10 to 13 cycles, and two values of the electrode force (7 and 8bar) were also applied. the distribution of the values of the three parameters was carried out with a factorial plan to ensure the union of all the values. table ii shows the combination of the welding parameters and the number of trials for each factor. the mechanical properties of joining ss 304l and gs z275 materials are given in table iii. table ii. factors of welding parameters factor levels values i (ka) 5 10; 12; 14; 15; 16 t (cycles) 3 10; 11; 13 f (bar) 2 7; 8 table iii. mechanical properties of 304l sl and z275 gs materials e (gpa) ��mpa) uts (mpa) a% hrb ss 304 l 190 336 655 43.2 60 gs z275 200 266 330 22.0 / iv. results and discussion a linear regression model was proposed to relate the tensile-shear strength of the rsw joints to welding current i, welding time t, and welding force f. minitab 19 was used for regression analysis. as a result, a mathematical model was developed for the influence of the three welding parameters on tensile-shear stress, described as: � � � �1�1 � �2�2 � �3�3 � �11�1�1 � �23�2�3 (2) the regression equation between the welding parameters i, t, and f and tensile-shear strength was: ������� �ℎ��� ������ ����� �343 � 33,2 ! � 35,4 � � 47,4 $ � 0,767 !² � 4,58 � ∗ $ (3) table iv shows the results of tensile-shear stress with the parameters of each test. table iv. experimental data for tensile-shear stress trial order i (ka) t (cycles) f (bar) tensile shear stress (mpa) 1 10 10 7 292.01 2 10 10 8 265.07 3 10 11 7 279.15 4 10 11 8 271.81 5 10 13 7 303.64 6 10 13 8 276.71 7 12 10 7 287.72 8 12 10 8 320.17 9 12 11 7 309.15 10 12 11 8 319.56 11 12 13 7 314.66 12 12 13 8 280.99 13 14 10 7 348.94 14 14 10 8 342.21 15 14 11 7 335.48 16 14 11 8 331.19 17 14 13 7 346.49 18 14 13 8 352.00 19 15 10 7 348.33 20 15 10 8 355.07 21 15 11 7 353.23 22 15 11 8 350.78 23 15 13 7 355.07 24 15 13 8 350.17 25 16 10 7 363.02 26 16 10 8 355.07 27 16 11 7 344.66 28 16 11 8 348.33 29 16 13 7 363.02 30 16 13 8 356.90 engineering, technology & applied science research vol. 12, no. 4, 2022, 8896-8900 8898 www.etasr.com ternane et al.: regression modeling and process analysis of resistance spot welding on dissimilar … table v illustrates the results of the analysis of variance with some interactions between the three welding parameters. the data show that the main effects of the welding current are relevant for the maximum load. since the p-value of welding current is inferior to the significance level established at a 5% probability level (p<0.05), the interaction between welding time and electrode force cannot be considered significant. this table also shows other adequacy measures: r²=88.96%, adjusted r²=86.66%, and predicted r²=81.59%. since they are all very close to 0.9, they indicate a suitable model. table v. analysis of variance source df adj. ss adj. ms f.value p.value regression 5 25237.7 5047.5 38.68 0.000 i 1 632.6 632.6 4.85 0.038 t 1 258.8 258.8 1.98 0.172 f 1 201.3 201.3 1.54 0.226 i*i 1 228.4 228.4 1.75 0.198 t*f 1 245.0 245.0 1.88 0.183 error 24 3132.0 130.5 total 29 28369.7 r²= 88.96% adjusted r² = 86.66% predicted r² = 81.59% it is necessary to compare the tensile shear stress values estimated by the model equations (2), (3) with the values obtained as a result of experimental calculations. the residuals consist of the difference between the data and the model data. a comparison of the estimated and experimental data for tensile shear stress is shown in figure 2 [26, 27]. according to figure 2, a good agreement was observed between the mathematical model obtained for the tensile-shear stress and the experimental data, and residuals fall relatively along a straight line. consequently, the normal distribution assumption was considered satisfied. fig. 2. normal probability plot of residuals. figure 3 is a residual versus observation order graph showing that all residual points are spread within the lower and upper bounds without evident patterns, confirming the assumption that the residuals have a regular variance. as a result, all diagnostic plots denote that all the necessary anova assumptions are satisfied. fig. 3. residuals versus observation order. as shown in figure 4, all residual points are dispersed within the lower and upper bounds, showing no pattern. this graph denotes that the independence assumption is also satisfied. the histogram shown in figure 5 forms a normal curve equally distributed around zero, showing that the normality assumption is more than likely true. fig. 4. residuals versus fits plots. fig. 5. histogram of residuals. as shown in figure 6, a pareto diagram provides statistical information on the effects of input variables, factors or welding parameters in this case, on tensile shear stress. it is observed that the welding current factor has a relevant impact on the engineering, technology & applied science research vol. 12, no. 4, 2022, 8896-8900 8899 www.etasr.com ternane et al.: regression modeling and process analysis of resistance spot welding on dissimilar … tensile-shear stress because it occurs outside the dotted line at 2.064. the other parameters and interactions have a meaningless or less impact relative to the welding current. it is important to know the effect levels of welding parameters on tensile-shear stress. using this information, one could choose which parameter is more important for perfect welding joining [22, 28]. fig. 6. pareto chart of normalized effects. these factors can be classified in decreasing order: welding time, welding time electrode force interaction, welding current, welding current interaction, and welding force. this result can be further supported by taking into account the main effects and interaction graphs, as shown in figures 7 and 8 respectively. figure 7 shows a graphical representation of the primary effects of the factors examined for the spot weld regarding tensile-shear stress. according to the graph, it can be concluded that the impact of a factor is directly linked to the slope and length of the line in the graphic. the greater the slope is, the higher the influence on the average maximum load increase will be when varying levels from low to high. according to figure 7, the welding current has a significant impact on tensile-shear stress due to the higher slope, while welding time is less sensitive to the variability in tensile-shear stress compared to welding current. on the other hand, welding force has less effect on tensile shear stress. fig. 7. main effects plot for tensile shear stress (mpa). figure 8 shows the main effect graph for tensile-shear stress. the three two-factor interaction graphs denote a powerful interaction between welding current and welding time, and welding current and welding force. tensile-shear stress reaches its highest when welding current and welding time are kept at a high level, but welding force is at a low level, 16ka, 13cycles, and 7bar respectively. similarly, tensile-shear stress reaches its minimum when welding current and welding time are both at low levels, but electrode force maintains a high level, i.e. 10ka, 10cycles, and 8bar respectively. fig. 8. interaction plot for tensile shear stress (mpa) v. conclusion this paper presented a linear regression analysis used to investigate the effect of rsw parameters on the tensile-shear stress of dissimilar joints from experimental results. based on this investigation, the following conclusions can be drawn: • the regression analysis showed that there is a linear relationship between welding parameters (welding current, welding time, and electrode force) and the tensile-shear strength of the rsw joints. • according to the p-values and the pareto chart, the welding current had the highest impact on tensile-shear stress compared to welding time, welding force, and other combinations. • the welding process and the effects of parameters and interactions between them on tensile-shear strength can be analyzed based on regression models of the welding process on two heterogeneous sheets, stainless steel and galvanized steel, with a thickness of 2mm which can make it to be an assistant reference for the welding process. • the optimal parameters that gave a higher tensile-shear strength were higher welding current (16ka) and welding time (13cycles) and lower welding force (7bar). acknowledgment the authors gratefully acknowledge the technical support and welding specimens from the soremep society in tlemcen. engineering, technology & applied science research vol. 12, no. 4, 2022, 8896-8900 8900 www.etasr.com ternane et al.: regression modeling and process analysis of resistance spot welding on dissimilar 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vietnam hieu.dotrong@hust.edu.vn received: 5 august 2022 | revised: 23 august 2022 | accepted: 24 august 2022 abstract-the input shaping technique is widely used as feedforward control for vibration suppression of flexible dynamic systems. the main disadvantage of the input shaping technique is the increasing system time response since the input shaper contains time delay parts. however, with the same reference input, the actuator effort in the case of using an input shaper is smaller than the one in the case without an input shaper. thus, it is possible to decrease the system response time by designing the feedback controller to maximize the actuator effort. this paper proposes a design approach to design the proportional-derivative (pd) controller for position control of the actuator so that the settling time of the flexible system with input shaper is minimized. the actuator system with a pd controller is equivalent to a critically damped system, and the condition for the controller gains is established. in addition, the settling time and actuator effort with shaped step input are calculated. the controller gains can be determined by solving the settling time optimization problem with the actuator effort constraint. the effectiveness of the proposed approach is verified via experiments with an overhead crane model. keywords-flexible system; input shaping;pd controller; settling time optimization; overhead crane i. introduction the vibration of flexible dynamic systems such as live load and flexible beam systems [1-3] and flexible robot manipulator and cranes [4-12] often causes a decrease in operation speed and accuracy. due to sensor noise and unmodeled flexible dynamic problems, vibration suppression control using feedback control has often substantial limitations [4-7]. openloop control is effective and widely used for the vibration suppression control of flexible machines. if the vibration dynamics are known with some confidence, then several techniques for modifying commands can suppress the system's vibration [8-13]. among them, input shaping [13], which convolves a sequence of impulses with the command signal, is one of the most attractive techniques. various improvements and applications of input shaping have been reported [14, 15]. the input shaping technique has also been used along with feedback control to optimize the system performance [16-24]. in [16-18], the concurrent design of the proportional-derivative (pd) controller and input shaping was considered. the pd controller parameters were chosen to fasten the feedback system response, and the input shaping was designed to eliminate the natural vibration frequency of the pd feedback control system. the same idea was deployed in [19] for the combination of input shaping technique and a linear quadratic regulator (lqr) feedback control system. these works only considered the single mode vibration. the design technique was proposed for a feedback control system with multi-mode vibration in [20-21]. the vibration model uncertainty was also considered when combining input shaping and feedback controller [22-24]. the above mentioned studies used input shaping that eliminates the vibration of the feedback system to optimize the system performance, not to suppress the vibration of a flexible system. in general, the vibration suppression control of a flexible dynamic system includes a feedback control part for actuator position control and a feed-forward control part for vibration control, as shown in figure 1. when using an input shaper (is) as feed-forward control, the is only depends on the vibration model, not the feedback system. the feedback control is usually designed independently with the feed-forward controller. this design method is simple but does not optimize the system performance. corresponding author: minh-duc duong engineering, technology & applied science research vol. 12, no. 5, 2022, 9388-9394 9389 www.etasr.com duong et al.: settling time optimization of a critically damped system with input shaping for … fig. 1. feed-forward control structure for vibration suppression control. since the is includes time delay parts that slow down the system, various efforts have been made to shorten the delay, see [14] for more details. however, most of them have not considered combining a feedback controller to reduce the system response. in this paper, a design technique to optimize the time performance of the system with the is is proposed. at first, the is is designed using the vibration’s parameters. next, the pd controller is chosen to minimize settling time while keeping the actuator effort within the acceptable range. for this purpose, design techniques such as the one in [16] can be applied. however, that technique can only be applied to an under-damped feedback system. in many applications, the under-damped system is not expected since the existence of overshoot may cause limit excess. thus, in this paper, we consider a design technique for a critically damped system. the pd feedback controller is designed to optimize the settling time, in consideration that the is has been added to shape the input. the actuator effort is used as a design constraint. the settling time and actuator effort calculation are established such that the optimization problem can be easily solved by an optimization toolbox. ii. input shaping method input preshaping [13] is a feed-forward control technique for vibration suppression. the idea of input preshaping method is to cancel the vibration of an impulse input by generating another impulse that causes the inverse phase vibration with the first one. let’s consider a simple vibratory system that can be expressed as second order system as following: �� � �������� � �02�2�2.�0 0.���02 (1) where ��is the undamped natural frequency, � is the damping ratio of the system, y(s) and v(s) are the laplace transforms of output y(t) and input v(t) respectively. if an impulse input with amplitude �� is put into the system at time �� , then the output response y(t) is calculated as: ���� � �� . sin��. � � �� � (2) where �� � �� . ������� � ������!�!"�, � � ���1 $ � % , and �� � ���1 $ � %��. in order to suppress the vibration caused by the impulse, we consider applying a second impulse to the system. then the response of two impulses is calculated as: � � ��. sin��. � � ��� � �%. sin��. � � �%� (3) using the trigonometric relation, we can obtain: � � �. sin��. � � �!& � (4) where: '� � (����)*�� � �%�)*�%�% � ��� +,��� � �%+,��%�%�!& � tan�� / 012�34150�2�34�016724150�6724�8 by setting the response of two impulses equal to zero after applying the last impulse, we can easily obtain (supposing that the time of applying the first impulse is �� � 0 and the impulse amplitude are normalized �� � �% � 1): 9���� : � ; ��5< <�5<0 ∆� > (5) where ' ? � $a.b(1$b2∆� � a�0.√1$b2 . the two-impulse shaper is called the zero vibration (zv) shaper. in general, if we apply n impulses with amplitude �� and at time �� (i = 1, …, n), then the response of n impulses is calculated as: � � ∑ �� ���e�f� � ∑ �� . sin��. � � �� �e� (6) where g� � (�∑ �� �)*��e�f� �% � �∑ �� +,���e�f� �%�!& � tan�� h∑ 0"2�34"i"j1∑ 0"6724"i"j1 k by setting the amplitude and its derivative equal to zero after applying the last impulse, we can obtain the result for 3 impulses (n=3) as follows: 9���� : � ; ���5<�� %<��5<�� < � ��5<��0 ∆� 2δ� > (7) the three-impulse shaper or zero vibration derivative (zvd) shaper is more robust than the zv shaper. more results can be seen in [14, 15]. by convolving the reference input and the above impulse series, the vibration can be suppressed. this paper will apply vibration suppression control using input preshaping with two and three impulses. it is noted that the response of the system with input preshaping is slower than that without input preshaping. the delay time is ∆t with zv and 2∆t with zvd input preshaping. iii. controller design in a flexible system, the actuator, such as an electrical motor, is controlled by a motor driver under velocity control mode. the actuator then can be modeled as follows: m�2�n�2� � gp��� � <q�rq25��2 (8) where ?6 is the gain and s6 is time constant of the system, u(s) and x(s) are the laplace transforms of control voltage input u(t) and actuator position x(t) respectively. the system structure is shown in figure 2, where gpd(s) is the transfer function of the feedback controller, gp(s) is the transfer function of the plant (actuator and driver). the is includes n impulses designed based on the flexible system’s vibration frequency and damping. we consider the system step engineering, technology & applied science research vol. 12, no. 5, 2022, 9388-9394 9390 www.etasr.com duong et al.: settling time optimization of a critically damped system with input shaping for … input to design the pd controller for position control. system response and settling time are calculated. in addition, the actuator effort is also determined. then the settling time optimization with actuator effort constraint can be established, and the selection of pd controller parameters can be made by solving this optimization problem. fig. 2. input shaper – pd feedback control structure. a. system output response the pd controller can be described by the following transfer function: �tu��� � ?u � � ?t (9) where ?t v 0 is the proportional gain and ?u v 0 is the derivative gain. then, the transfer function of the closed-loop system is: �wx � �y�zb�y�zb�1 � ?+?bs+ ��?+?zs+�2�?+?z�1s+ ��?+?zs+ (10) by setting: ?+?bs+ � [ and <q<\rq � ] we have: �wx � [��]�2�[s+�1s+ ��] � ^���_��� (11) because the underdamped system is not expected, the denominator of gcl(s) must have negative real roots. in addition, we require minimum response time. thus, the denominator should have double negative roots. the condition for being double root is: /[s+�12s+ 82 � n ⇔ /?+?b�12s+ 82 � ?+?zs+ (12) now, we introduce an input step with magnitude l into the system at time t0, b��� � cd ef�g2 , the response of the feedback system is: ^��� � cd ef�g2 h25e2�5ijqk1jq 25e (13) thus, the response of the system with single step input can be expressed as: l��� � c.hm� n� $ � �m�!�!�� � o�o $ ���� $ ��� �m�!�!��p (14) where o � h.rq5�%rq and � � eh. since the overshoot is not expected to appear, x(t) must be a non-decreasing or non-increasing function in the region � v ��. thus, the root �q of equation lr ��� � 0 must be outside the region � v �� , or �q s �� . solving the equation lr ��� � 0 we obtain �q � �� � mm�t. thus: �q s �� ⟺ mm�t s 0 ⇔ o s � ⟺ <v�rq s ?t (15) from the system response with single step input (14), the response of the system with convolved step command after step k is: ���� � chm� w� ∑ x�xyf� $ � ∑ x� �mz!�!{|xyf� �o�o $ �� ∑ x� z� $ �y | �mz!�!{|xyf� } (16) since hm� � � 1, the response y(t) can be rewritten as: ���� � l ∑ xyxyf� $ l ∑ xy �mz!�!{|xyf� � x�[ $ o� ∑ xy z� $ �y | �mz!�!{|xyf� (17) b. settling time settling time is a primary concern for most industrial applications. the faster the settling time, the higher throughput and accuracy are. the system is defined to be settled when the output response falls below a certain percentage (usually 5% or 2%) of the step magnitude. the settling time is the required time for the output curve to reach and stay within a range of a certain percentage (usually 5% or 2%) of the final value. in this paper, we use the range of 5% to calculate settling time. we can describe the definition of settling time ts as the following conditions: 1 $ ��!�c � 0.05, ∀� v �2 (18) 1 $ ��!g�c � 0.05 (19) it is obvious that settling time is determined after the final step. thus, the output y(t) to calculate settling time is the output with n steps. since ∑ x�3yf� � 1 , and substituting (17) into (19), we have: 1 $ ��!g�c � ∑ xy �mz!g�!{|eyf� $ �[ $ o� ∑ xy z�2 $ �y | �mz!g�!{|eyf� � 0.05 (20a) moreover, since �2 � �3 , it can make the approximation �mz!g�!{| ≅ 0 and z�2 $ �y | �mz!g�!{| ≅ 0 with j < n. then (20a) becomes: x3 n �m(!g�!�) $ ([ $ o)(�2 $ �3) �m(!g�!�)p � 0.05 (20b) using the lambert w function w(z) (i.e. � � �(�) �(�)) [25], the settling time ts can be determined as: �2 � �3 � �h�m $ � m �( �.��m.d � ie� m(h�m) ) (21) c. actuator effort with reference input as step input, we are also interested in the actuator effort when designing the controller. according to figure 2, with the input r(s), the actuator effort can be determined as: �(s) � ������.��5� . r(s) � 2(rq25�)(<q<v25<q<\) rq.2�5(<q<v5�)25<q<\ . b(�) (22) engineering, technology & applied science research vol. 12, no. 5, 2022, 9388-9394 9391 www.etasr.com duong et al.: settling time optimization of a critically damped system with input shaping for … if the input r(t) is the step input with magnitude l at the time t0, b(�) � cd ef�g 2 , then: �(s) � x �!�2 (rq25�)(<q<v25<q<\)rq.2�5(<q<v5�)25<q<\ (23) the actuator effort can be calculated as: �(�) � l <\rq�<q<v�rq n �m(!�!�) � (�� $ o)(� $ ��) �m(!�!�)p (24) where �� � <\�<q<\.<vrq<\�<q<v� . then, the actuator effort with convolved step command after step k is: �(�) � <\rq�<q<v � rq × ∑ xy w �mz!�!�| � (�� $ o)z� $ ��| �mz!�!�|}xyf� (25) the actuator effort u(t) can be represented as the form: �(�) � zx �m! � �x � �m! (26) where: zx � <\rq�<q<v � rq ∑ xy n1 $ (�� $ o)�y p m!{xyf� �x � <\rq�<q<v � rq ∑ xy (�� $ o) m!{xyf� to find the maximum value of u(t), we solve the equation: �r (�) � �($ozx � �x )$o�x �� �m! � 0 (27) thus, the maximum value of u(t) can be obtained at time: �x� � ���mt�m�� (28) it is noted that we can only consider u(t) after step k, and u(t) is decreased when t > tku. therefore, the maximum value of actuator effort ukmax is calculated as: �x�m� � � zx �m!� � �x �x �m!� if �x� � �x zx �m!�� � �x �x� �m!�� if �x� � �x (29) to guarantee that u(t) is within the allowable actuator effort range, the following constraint is required after the step corresponding to each impulse: �x�m� � ��m� for all k = 1, …, n (30) where ��m� is the maximum allowable actuator effort. d. controller designing the designing process of actuator position control using a pd controller and vibration suppression control using input shaping for a flexible dynamic system is: step 1: determine the system vibration parameters, including natural vibration frequency and damping factor. step 2: choose the appropriate input preshaping techniques such as zv, zvd, etc. see [14, 15] for more details about is techniques. step 3: choose the pd controller parameters ?t and ?u to minimize the system settling time by solving the following optimization problem: minimizing (21) with constraints (12), (15), and (30). iv. application to overhead crane figure 3 describes the overhead crane. in this figure, x is the cart’s position, l is the rope length, m is the load mass, m is the cart mass, and   is the angle between the rope and the vertical axis (y axis). according to [26], the overhead crane linearized model can be described as: ¡� � ([ � ¢)l£ � ¤� lr � ¢¥ £ (31) $l£ � ¥ £ � ¤¦  r � §  (32) where ¤� and ¤¦ are the equivalent viscous damping of the cart and the load respectively. it can be seen that (31) describes the relation between the input force and the cart’s position. the load angle plays the role of disturbance. equation (32) describes the effect of the cart’s motion to the vibration of the load. fig. 3. overhead crane model. in practice, the cart is controlled by a motor with a driver. that can allow us to control the velocity of the cart. therefore, to control the cart’s position, we use the motor model with a driver instead of (31). the cart plays the role of an actuator in a flexible system and has (8) as the transfer function. the control of the overhead crane is to move the load to the desired position while suppressing the load vibration. to control the cart’s position precisely, a pd controller is used. in addition, to suppress the load vibration, input preshaping is applied. the actual experiments are conducted with the overhead crane model shown in figure 4. the vibration model can be calculated from (32), however, the model’s parameters may not be precise. thus, we measured the sway angle and identified the natural vibration frequency and damping factor. the experiment parameters are shown in table i. table i. experiment parameters parameter values ?6 4 s6 0.2 �� 4.45 rad/s � 0.007 g 9.81 m/s 2 umax 10 v engineering, technology & applied science research vol. 12, no. 5, 2022, 9388-9394 9392 www.etasr.com duong et al.: settling time optimization of a critically damped system with input shaping for … fig. 4. experimental crane system. then, two types of input shaping including zv and zvd can be designed using (5) for zv and (7) for zvd. using the designed iss, the pd controllers that optimize the settling time were calculated. we call them optimized pd-zv and optimized pd-zvd. in addition, the pd controller that optimizes the settling time of the feedback system using step input only and with the same constraint is also calculated. we call it optimized pd without is. the iss (5) and (7) are then applied to the optimized pd without is. we call them zv-optimized pd and zvd-optimized pd without is. the results are shown in table ii. fig. 5. cart’s position in three cases: optimized pd without is, zvoptimized pd without is, and optimized pd-zv. fig. 6. actuator effort in three cases: optimized pd without is, zvoptimized pd without is, and optimized pd-zv. fig. 7. sway angle in three cases: optimized pd without is, zv-optimized pd without is, and optimized pd-zv. fig. 8. cart’s position in three cases: optimized pd without is, zvdoptimized pd without is, and optimized pd-zvd. fig. 9. actuator effort in three cases: optimized pd without is, zvdoptimized pd without is, and optimized pd-zvd. fig. 10. sway angle in three cases: optimized pd without is, zvdoptimized pd without is, and optimized pd-zvd. 0 1 2 3 4 5 6 7 8 9 time (s) 0 5 10 15 20 25 30 35 c a r t' s p o si ti o n ( c m ) optimized pd without is zvoptimized pd without is optimized pd-zv a c tu a to r e ff o r t (v ) 0 1 2 3 4 5 6 7 8 9 time (s) -10 -5 0 5 10 s w a y a n g le ( d e g r e e ) optimized pd without is optimized pd-zv zv-optimized pd without is 0 1 2 3 4 5 6 7 8 9 time (s) 0 5 10 15 20 25 30 35 c a r t' s p o si ti o n ( c m ) optimized pd without is zvd-optimized pd without is optimized pd-zvd a c tu a to r e ff o r t (v ) s w a y a n g le ( d e g r e e ) engineering, technology & applied science research vol. 12, no. 5, 2022, 9388-9394 9393 www.etasr.com duong et al.: settling time optimization of a critically damped system with input shaping for … table ii. controller parameters and settling time parameter values optimized pd without is optimized pd-zv optimized pd-zvd ?t 0.325 0.52 0.59 ?u 0.01 0.07 0.09 settling time (s) 2.66 using zv: 3.18 using zvd: 3.67 2.27 2.64 the experimental results are shown in figure 5-9. it is clear that zv and zvd can suppress the payload vibration significantly. in the case of optimized pd without is, the settling time is 2.66s. but when the is is applied to the vibration suppression control, the settling time increases to 3.18s for zv shaper and 3.67s for zvd shaper. in addition, the actuator effort also reduces from 10v in the case of optimized pd without is to 6.80v and 5.90v when applying zv and zvd shapers respectively. therefore, we should design the pd controller inconsideration of using is at the system input. at a result, the actuator effort is larger but still in the required limit, and the system moves faster with settling time only 2.27s for zv and 2.64s for zvd shapers. it is also found that in the case of optimized pd-zv the settling time is smaller than the one in the case of zvoptimized pd without is, but the residual vibration magnitude is larger. the reason for this is the difference between the actual vibration frequency and the designed vibration frequency and the effect of the feedback system to the response of the is shaper. this can be improved by using zvd shaper. it is clear that in the case of optimized pd-zvd the settling time is smaller than the one in the case of zvd-optimized pd without is, and the residual vibration magnitude is almost the same. v. conclusions the current paper proposes a design process for the pd controller of the actuator in a flexible system that uses input shaper for vibration suppression control. the controller gains are chosen such that the feedback system is of the critically damped type and system’s settling time is minimized while keeping the actuator effort constraint. the experiments with overhead crane model show the effectiveness of the proposed designing process. the settling time is reduced, in comparison to the case of the optimizing pd controller without considering the use of the input shaper. in the future, a designing tool will be developed to apply the proposed designing process for a real flexible system. in addition, the designing process for the system with time varying vibration frequency is also considered. acknowledgment the paper is supported by the hanoi university of science and technology project t2021-pc-002. references [1] i. esen and m. a. koç, "dynamic response of a 120 mm 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[26] d. qian and j. yi, hierarchical sliding mode control for underactuated cranes. berlin, heidelberg: springer, 2015. microsoft word 3-485.doc engineering, technology & applied science research vol. 4, no. 6, 2014, 724-727 724 www.etasr.com okeyinka and idowu: assessment of the suitability of paper waste as an engineering material assessment of the suitability of paper waste as an engineering material oriyomi m. okeyinka oluwatobi j. idowu department of civil engineering, faculty of technology, university of ibadan ibadan, nigeria oriyomiokeyinka@yahoo.com department of civil engineering, faculty of technology, university of ibadan ibadan, nigeria idowuoluwatobijohn@yahoo.com abstract—this research work investigates the potential applicability of waste paper in the production of ceiling boards with focus on achieving: environmental sustainability, safe disposal of waste paper and more cost effective production of materials. the main view was to provide an alternative to the conventional asbestos ceiling boards that are costly and also pose health risks. three mix designs were formulated and used for the casting (1:1, 1:1.5 and 1:2), varying in regards of the weight of the waste paper components. caco3 was added to the mix as an additive as well as starch bond glue to aid binding. laboratory experiments were conducted to determine the properties and suitability of the produced boards. properties such as water absorption, abrasion, compressive strength, flexural strength and ultimate loads were considered for comparison. the boards with 1:1 mix ratio displayed the best results of the test properties hence, its mechanized manufacturing was recommended. keywordswaste paper; ceiling board; compressive strenght; water absorption. i. introduction managing waste is one of the greatest challenges for human societies, as various human activities result to the production of significant amounts of waste of different kinds. the term waste describes the unneeded byproducts (materials) produced during the production of a certain product or the product itself after a certain time span. waste has usually nothing to contribute to the environment other than pollution. the reuse of waste materials is a waste minimization strategy which includes reclaiming activities [1, 2]. waste materials can be used directly or recycled to produce the same or another product. this has the benefit of not only reducing the amount of waste material but can also provide significant cost reduction for the production of new materials [3-4]. solid waste is of most interest is, as it is the most frequently occurring of all waste types as it occurs from individual or domestic, industrial and agricultural activities. especially domestic wastes tend to pile up and their management is a task of significant importance for advanced cultures. recycling is a good approach to waste reduction, but it has been reported that during recycling, a 40% of the wastes to be recycled are proved to be non-recyclable, (i.e. a lot of these wastes still remain in the waste stream) [3]. in an attempt to counter this problem, waste is adopted as raw materials for the production of other materials. paper seems to be the most common as it is involved in many areas such as stationeries, cartons for packaging, disseminating news to people and many more. paper is an example of valuable materials that can be recycled. disposable paper available in abundance throughout the world is composed mainly of short, natural, cellulose fibers and is already used in many local raw materials. waste paper comes from various sources such as newspapers, office and printing papers etc. each has a different type of fiber quality, and mixing all these papers of different qualities will reduce the purity of the highest quality fiber. the quality of the waste determines the end quality of the recycled paper. therefore, an investigation concerning the potential of the different re-pulped waste paper types as construction materials is essential in order to gain an insight into their behavior and properties [5]. various researchers have shown that waste paper may be useful in construction materials such as concrete, solid blocks and ceiling boards and also can act as insulators in buildings. a hollow concrete block using recycled paper waste has been constructed and the result was similar to using expanded slate as an aggregate [6]. the response of recycled paper waste concrete has been studied in [7] and concluded that it has much softer response to higher damping and energy absorption. the eco-friendly parameter was underlined in [8]. the use of waste paper as constituent materials in plastering mortar was considered in [9] and it was shown that it enables the utilization of non-polluting technology with low energy consumption. therefore, the use of waste paper in building materials could solve problems concerning the quality and affordability of building materials and simultaneously ameliorate the associated environmental concerns. this paper targets at producing ceiling boards with waste newspaper. the mix ratio are presented along with the integrity of the final product, considering various different parameters. engineering, technology & applied science research vol. 4, no. 6, 2014, 724-727 725 www.etasr.com okeyinka and idowu: assessment of the suitability of paper waste as an engineering material ii. experimental procedure a. materials the materials used for the experimentation include waste newspaper, cement, gum and caco3. the cement used was an ordinary portland cement (elephant cement) produced by the west african portland cement ewekoro, and certified by the british standard specification (bs 12) [10]. old newspapers newsprint were obtained from large offices, hotels and nearby markets. these papers are with organic composition greater than 95% and inorganic composition of less than 5%. it was soaked in water for softening and was ground thoroughly to form paper slurry with little water present. the caco3 used was finely ground with equivalent particle sizes smaller than 2 mm. it was mixed with water and the undissolved part of it was removed. b. preparation and casting of board the shredded newspapers were soaked into hot water for two days to allow for adequate softening and thereafter grounded thoroughly to form a slurry. this ground paper material was dewatered with the use of a hydraulic jack. it was left for a day (24 hrs) for proper dewatering. three replicates of the boards were produced, at 1:1, 1:1.5 and 1:2, cement paper ratio respectively. on each replicate sample, constant quantities of caco3 and gum were added without varying. the watercement ratio used was 1.0:0.50 and 150 g of caco3 and 150 g of starch was used for each of the samples. then the materials were poured and thoroughly mixed together and then poured into the formwork of dimension 400 mm x 400 mm x15 mm, where adequate compaction and smoothening was ensured. the formworks were removed after 24hrs and the boards were cured for 14 days to attain the necessary strength. the necessary tests were thereafter conducted. c. test procedures tests which considered abrasion, flexural and compressive strength, water absorption rate, density, modulus of elasticity, modulus of rupture were carried out on the boards and the procedures used are described below. 1) abrassion test for the purpose of this test, a dried sample of the board was weighed (w1). a hard shoe brush was used to rub against the two surfaces of the board. 50 strokes of forward and backward movements each were made against the surfaces. the flaked particles from the surfaces were collected and weighed. the flaked board was also weighed (w2). this procedure was repeated for nine more samples. flaking concentration (fc) was determined using the expression in (1): 1 2 1 w -w fc= w (1) 2) flexural and compressive strength test these tests were conducted at the federal institute of industrial research, oshodi (fiiro) in lagos state of nigeria. they were carried out using a testometric machine .the flexural test shows the ability of the boards to resist shearing; the maximum force that can cause the board to fail flexurally was recorded and plotted against the deflection. the compressive test shows the ability of the boards to resist compression. the load intensity was increased gradually and the responding compressions of the boards at each load variation were noted. 3) water absorption rate test the dry boards were weighed and immersed in water for 24 hours. they were allowed to surface-dry then weighed. water absorption was calculated using: s d d (w -w ) p= 100 (%) w ⋅ (2) where p is the percentage water absorption, ws is the weight of the surface-dry sample and wd is the weight of dry sample 4) modulus of elasticity this is the measure of resistance of the board to bending or flexure, (it is related to the stiffness of the board).this was calculated on the boards from the data supplied in the flexural test by using the formula: 3 23 p l moe= 648 i δ ⋅ ⋅ ⋅ ⋅ (3) where p=the applied load or force on the board, l= length of the board; i=moment of inertia=bh3/12 where b and h are the width and thickness of the board respectively and δ= deflection on the board. 5) modulus of rupture this is to determine the peak load the board can carry, it is calculated with the formula p l c mor= 6 l ⋅ ⋅ (4) all parameters remain the same as above and c=half thickness of the board iii. result and discussions a. properties of the board the results of compressive strength test, flaking/abrasion, water absorption and density check conducted on the board samples are summarized and presented in table i and figures 1-3 1) density the average densities of the boards are presented in table i. mix 1:2 was found to be the densest of the board samples. this can be attributed to the quantity of waste paper it contains. the volume of each of the test board sample was 2.25 x 10-4 m3 calculated from the product of the length, width and thickness which are 150 mm, 150 mm and 15 mm respectively. 2) compressive strength the result here shows that the compressive strength increases with the increase in cement content. increase in proportion of paper pulp to cement leads to brittleness. engineering, technology & applied science research vol. 4, no. 6, 2014, 724-727 726 www.etasr.com okeyinka and idowu: assessment of the suitability of paper waste as an engineering material 3) flaking/abrassion the mean values of the abrasion obtained from the experimental board samples ranged from 0.69% to 1.23%. this shows that the ceiling boards with the higher quantity of newspaper pulp are prone to flaking. 4) water absorption out of the three samples tested for water absorption, it was found that sample a with the mix ratio of 1:1 absorbed the least quantity of water and its percentage water absorptivity was 17% unlike samples b and c of mix ratio 1:1.5 and 1:2 respectively which in turn showed a percentage water absorptivity to be 19.8% and 30.7% respectively. based on the results shown, it is noted that the mixing proportion has significant effect on the water absorption. this shows that more water is absorbed with increasing quantity of paper pulp. hence, there is a need for pretreatment of paper to be used in ceiling boards in order to to reduce its affinity for water. table i. properties of the board produced from three different mixes s a m p le s m ix es d en si ty (k g /m 3 ) c o m p re ss iv e s tr en g th (n /m m 2 ) f la k in g / a b ra ss io n (% ) w a te r a b so rp ti o n (% ) a 1:1 91.11 13.50 0.69 17.00 b 1:1.5 147.56 9.00 1.11 19.80 c 1:2 184.89 7.59 1.23 30.70 fig. 1. compressive strength of boards made with different cement/paper mix ratios fig. 2. flaking/abrasion properties of boards made with different cement/ paper mix ratios. fig. 3. water absorption properties of boards made with different cement/ paper mix ratios. b. mechanical properties of the board the mechanical properties in terms of flexural strength, mor and moe are summarized in table ii. figure 4 shows the load deflection curve for the three board samples. 1) flexural strength the highest flexural strength value 0.31 n/mm2 was achieved on the board sample with mix ratio 1:1. other values are 0.25 n/mm2 and 0.18 n/mm2 for samples produced from mixes 1:1.5 and 1:2 respectively. it was found that sample a failed on the application of more than 15 n load, sample b failed after the load applied was more than 10 n and sample c failed on the application of load more than 6 n. fig. 4. load deflection curves for boards made with different cement/paper mix ratio. 2) modulus of elasticity and modulus of rupture the results of the flexural strength test were used to compute both the moe and the mor of the boards. having obtain the thickness, h of the board= 15 mm, length of the samples=150 mm, c= half of thickness= h/2=7.5 mm, width, b of the samples=100 mm. hence i=bh3/12=28125 mm4. therefore, from the values of mor and moe presented in table ii, it can be seen that the maximum mor is 0.1 n/mm2 which is satisfactory with the astm 208-72 requirement of not exceeding 2 n/mm2. engineering, technology & applied science research vol. 4, no. 6, 2014, 724-727 727 www.etasr.com okeyinka and idowu: assessment of the suitability of paper waste as an engineering material table ii. summary of flexural strength and mechanical properties of the boards mix 1:1 mix 1:1.5 mix 1:2 load (n) deflection (mm) mor (n/mm2) moe (n/mm2) deflection (mm) mor (n/mm2) moe (n/mm2) deflection (mm) mor (n/mm2) moe (n/mm2) 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1 0.01 0.01 0.43 0.06 0.01 0.07 0.07 0.08 0.06 2 0.03 0.02 0.43 0.11 0.13 0.08 0.11 0.01 0.08 4 0.07 0.03 0.30 0.15 0.03 0.11 0.15 0.03 0.11 6 0.12 0.05 0.25 0.19 0.04 0.14 0.18 0.04 0.14 8 0.17 0.06 0.23 0.23 0.05 0.15 failure 10 0.23 0.07 0.20 0.25 0.07 0.17 13 0.27 0.09 0.20 failure 15 0.31 0.1 0.20 17 failure iv. conclusions based on the results of this work, the following conclusions can be drawn:  old newsprint paper fibers had significant effects on the mechanical and physical properties of the composites.  as the paper fiber content is increased, significant increase in water absorption occurs.  the optimum condition was obtained at cement paper ratio 1:1. further increase in paper fiber content results in lower strength properties  however, the result of mor was satisfactory based on the astm 208-72 standard requirement.  the use of caco3 also contributes to less water absorption. the overall water absorption of the three samples, appears to be lower compared to boards made with other admixtures in previous research. references [1] h. s. peavy, d. r rowe, g. tchobanoglou, environmental engineering, mcgraw-hill, 1984 [2] r. l. schroeder, “the use of recycled materials in highway construction”, public roads, vol. 58, no. 2, 1994, available at: https://www.fhwa.dot.gov/publications/publicroads/94fall/p94au32.cfm [3] vicroads, “recycled materials in pavement construction”, 2014 [4] a. o. ibhadode, environmental pollution: causes, effects and solutions, ambik press, nigeria, 2004 [5] v. sangrutsamee, panya srichandr, nuchthana poolthong, “re-pulped waste paper–based composite building materials with low thermal conductivity”, journal of asian architecture and building engineering, vol. 11, pp. 147-151, 2012 [6] s. modry, “use of waste paper as a constituent of concrete” in recovery and recycling of paper international symposium, thomas telford publishing, united kingdom, pp. 77-80, 2001 [7] j. d. decard, r. p. west, s. j. prichard, “the impact response of recycled paper waste concrete”, in recovery and recycling of paper international symposium, thomas telford publishing, united kingdom, pp. 81-92, 2001 [8] j. s. manuel, “how do paper houses stack up?”, journal on environmental health perspective, vol. 3, no. 110, p. 126, 2002 [9] c. aciu, d. a. ilutiu-varvara, n. cobirzan, a. balog, “recycling of paper waste in the composition of plastering mortars”, procedia technology, vol. 12, pp. 295-300, 2014 [10] british standard institute, specification for portland cement, 1991 [11] b. c. tobias, “fabrication and performance of natural fiber-reinforced composite materials”, 35th international sampe symposium, pp. 970978, 1990 appendix symbols meaning moe modulus of elasticity mor modulus of rupture p applied load or force acting on the board h thickness of board samples p percentage water absorption l length of board samples b width of board samples i moment of inertia c half of thickness of board samples δ deflection of board samples w1 weight of dry board samples w2 weight of flaked board samples ws weight of surface dried board samples wd weight of dry board samples microsoft word etasr_v13_n1_pp10209-10216 engineering, technology & applied science research vol. 13, no. 1, 2023, 10209-10216 10209 www.etasr.com djeffal & belkacemi: slope reliability analysis in locating and observing the direction of failure … slope reliability analysis in locating and observing the direction of failure propagation houcine djeffal tissemsilt university, algeria | ecole nationale polytechnique, algeria houcine.djeffal@yahoo.com (corresponding author) smain belkacemi ecole nationale polytechnique, algeria smain.belkacemi@g.enp.edu.dz received: 22 november 2022 | revised: 5 december 2022 | accepted: 12 december 2022 abstract slope stability analysis is traditionally carried out with the ultimate equilibrium methods. in these approaches, the global assessment of slope stability is obtained through the evaluation of the factor of safety. the strength parameters that allow the evaluation of resistant forces along the hypothetical slip surface are considered unique and constant. the shape of the stress-strain curve of the soil may substantially affect the stability of the soil mass over, particularly in the case of the potential of a progressive failure. as a part of this work, the influence of uncertainties on the peak and post-peak strength parameters and the impact of a progressive failure on the failure probability of a hypothetical slip surface are discussed. the conventional method of morgenstern-price of slope stability analysis consisted of locating the critical slip surface by evaluating the minimum factor of safety. the probability of failure was estimated using three different techniques, i.e. form, fosm, and monte carlo simulation. this study improved the assessment of the impact of progressive failure on the risk of slope failure. the reliability analysis of slices allowed for locating the failure area and observing the direction of failure propagation. keywords-limiting equilibrium; slope stability; slip surface; progressive failure; uncertainties; reliability index i. introduction slope failure has become one of the most important problems in geotechnical engineering. the limit equilibrium method is commonly used in slope stability analysis due to its simplicity and high efficiency. the assumptions and simplifications of conventional limit equilibrium slope stability methods may not be sufficient to represent the behavior of complex slope problems. since this method is a statically indeterminate problem, assumptions on the inter-slice shear forces are employed to render the problem statically determinate. the classical limit equilibrium method only considers the ultimate limit state of the slope and provides no information on the development of progressive failure [1]. some researchers [1-3] extended the limit equilibrium method to analyze the stability of strain-softening slopes, and assumed that the soil strength decreases directly to the residual value from the peak value. with the recent advancements in computational approaches, it is possible to model slope stability problems more realistically by adopting numerical simulation methods [4-6]. due to depositional and post-depositional processes, soil characteristics such as density, mineral composition, moisture content, stress history, and shear strength change geographically. in addition, there are other factors, including the insufficient number of samples and measurement errors, which make more difficult to determine the soil properties precisely. in practice, measurements are taken only at selected locations, and thus, the soil properties are known only at these locations and can therefore be considered as random quantities. then, utilizing their correlation structures, soil characteristics may be efficiently described in terms of their spatial variations [7, 8]. true security is unknown because the simplifications of these methods take into account neither the variability of soil strength nor the role of the deformation behavior of the mass of slip soil. the progressive failure mechanism is also dominant for the slope stability, because the interfaces between components in slopes exhibit strain-softening behavior [7]. the shape of the stress-strain curve of the soil may substantially affect the stability of the soil mass over, particularly in the case of a potential progressive failure. the many sources of uncertainty that emerge in these types of problems are systematically evaluated using a reliability approach to a slope stability analysis that takes into account the spatially correlated soil variables. measurement errors and bias that often occur during soil investigations are now incorporated into the engineering, technology & applied science research vol. 13, no. 1, 2023, 10209-10216 10210 www.etasr.com djeffal & belkacemi: slope reliability analysis in locating and observing the direction of failure … probabilistic model of soil properties in addition to the spatial variability and the effects of spatial averaging. probabilistic methods are increasingly recognized as a useful tool to explicitly consider the effect of uncertainties on slope stability assessment. many methods regarding slope reliability analysis have been developed [8-13]. such approaches allow the engineers to better understand and quantify the risks. in order to analyze slope stability, the current research suggests integrating several mechanical methodologies with reliability analysis methods. this paper examines the issue of slope stability in a probabilistic framework and aims to quantify the influence of uncertainties of strength parameters, and the incidence of progressive failure on stability. the analysis employed the morgenstern-price slope stability deterministic approach. probabilistic methods form (first order reliability method), fosm (first order second moment), and the monte carlo simulation (mcs) technique were used to perform slope reliability analysis at different uncertainty levels of the basic parameters. ii. reliability index and probability of failure soils are heterogeneous materials, created by complex geological processes. their properties change from one point to another. due to the uncertainty inherent spatial variability, and the limited information available, soil properties can be considered as random variables. the probability theory provides a mathematical framework for quantifying uncertainty. the probabilistic approach is based on a deterministic model, in which the various uncertain parameters are modeled as random variables x = [x1, x2, x3, ..., xn]. considering the simple case of a resistance r subjected to an s, consisting of independent random variables or dependent and distributed according to given laws of probability, the failure probability free operation, reliability, is equal to the probability of occurrence of the event r ≥ s. r and s are characterized by their first moments, i.e. r and s, r and s, respectively [14]. a widely accepted and simple definition of the reliability index is the ratio of the expected safety margin to the standard deviation of the performance function. several numerical methods have been developed for estimating the statistical moments of a performance function dependent on multiple random variables. for practical purposes, the two important statistical moments to be estimated are the expected value and the variance (square of standard deviation) [14-21]. the fundamental problem of reliability theory lies on the calculation of the integral multiple of probability to estimate the probability of failure pf: ( ) 0 [ ( ) 0] ( )f g x p p g x f x dx      (1) where g(x) is the performance function associated with an operating rule, the relation g(x) = 0 constitutes the state limit. various solution methods have been proposed to estimate pf and the reliability index. among the most widely used methods are fosm, form, and mcs [14, 15]. iii. slope stability analysis once the geometry and conditions of the basement of a slope were determined, slope stability can be assessed. the main objectives of slope stability analysis include the assessment of rupture risk, through the calculation of the overall safety factor for a slope and the locations along the potential slip surface areas with high potential rupture [16]. there are several methods of slope stability analysis, based on the calculation of the limit equilibrium. most of these methods use a technique called slices. in these methods, the safety factor is calculated using one or more equations of static equilibrium applied to the soil mass. the limit equilibrium methods need first to define the surface for which the safety factor will be evaluated. the safety coefficient calculations are repeated for a sufficient number of slip surfaces arbitrarily selected to locate the surface having the minimum safety factor. the slip surface shape depends on the geometry, stratigraphy of the problem, physical characteristics, and capabilities of the analytical method used. forms of the slip surface may be circular or noncircular. the methods of static equilibrium decompose the soil mass above the sliding surface, in a finite number of slices. the analysis problem of slope stability is statically indeterminate. the various limit equilibrium methods use different assumptions or constraints to remove the indeterminacy. iv. progressive failure since the sixties, several authors have observed that the failure of slopes is a consequence of the development of large shear stresses well before the start of the failure, eventually leading to what is called the progressive failure [16-18]. more recently, many authors confirm that the rupture of the slopes is often a progressive nature [22]. the analysis of slope stability is often associated with the stress-strain curve of the soil for very large deformation which mobilizes a residual strength. if the material, along with a sliding surface, is best represented by a stress-strain curve having a peak, it will be impossible to engage the same shear strength on the entire surface. after the mobilization of the shear strength available to the peak, the mobilized shear strength decreases and tends towards the peak with shear strength increasing ground deformation. for simplicity, we assume that the strength reduction, the peak to residual, is instantaneous (figure 1). fig. 1. stress-strain curve used in the model. assessing the reliability of a slope in a progressive failure is a difficult task. when the shear strength mobilized locally engineering, technology & applied science research vol. 13, no. 1, 2023, 10209-10216 10211 www.etasr.com djeffal & belkacemi: slope reliability analysis in locating and observing the direction of failure … corresponds to the maximum shear strength of the soil, there is a failure due to local stress concentrations likely to spread. the differential shear force is systematically transferred to the neighboring elements. v. progressive failure probability the slope stability problem can be considered as a system with multiple slip surfaces. the failure probability of the critical slip surface is considered as an estimate of the failure probability of the system. this approach assumes that the failure probabilities along the different slide surfaces are strongly correlated [23, 24]. the common approach in the probabilistic analysis is to locate the critical surface and then calculate the failure probability corresponding to this surface. however, the surface having a minimum safety factor may not be the surface of maximum failure probability [25]. the critical surface probability is associated with the highest failure probability or the lowest reliability [24, 26-29]. a model based on the bivariate failure probability of successive slices was presented in [17, 18]. this model has been developed to include the gradual overall probability by considering the slope of the spread out along the entire sliding surface. fracture propagation is only a consequence of the interdependence of different age breakdowns of a sliding surface. the bivariant calculated probabilities relate to progressive successive events. this probability depends on the order in which the various tranches occur in sequence during the rupture propagation. a. the proposed model the proposed model treats the probabilistic progressive failure of a slope based on conditional probabilistic calculations of failure. the formulation of the statistical parameters of the safety factor, and in particular the correlation coefficient between the performance functions gi and gi-1 of slices i and  i-1, is laborious. extending the problem to 4 strength parameters (cp, p), (cr, r), representing respectively the peak and the residual (post-peak) state, and their spatial variability is particularly cumbersome. obviously, it is desirable to have a simpler model, in which complex calculations involving such correlations and joint probabilities of events are not required. the performance function gi of a slice i is defined as the safety margin calculated assuming that the shear strength has reached the maximum peak: ( )i p i ig r s  (2) the performance function gj* of progressive failure is defined as the conditional safety margin related to failure propagation until the j th slice of the slip surface: (3) where (rp)j is the shear strength of the slice j in peak, (rr)1,j-1 is the sum of the residual shear resistance of units 1 to (j-1), sj is the shear stress of slice j, s1,j is the sum of shear stresses along the slices 1 to j. b. progressive failure probability let as assume fj as the conditional event for failure, the mobilization of peak strength, developed at the slice j, given that the (j-1) previous installments mobilize the peak strength after the residual strength. the conditional event fj is expressed by �� = ��� ∗ < 0 . ej is the event of progressive failure of slices 1 to j in the order listed and about 1 to j represents the order of reaching the breaking of each slice. the probability that the failure develops gradually from slice 1 to slice j is a conditional probability. if we consider the situation in which the failure is propagated to the jth slice, this occurs only if the slices 1 to (j-1) are beyond the post-peak, this particular situation allows to write: 1 / 1j jp f f    (4) knowing that: 1 1 / j j j j j p f f p f f p f            (5) 1 1 1 / j j j j j p f f p f f p f             (6) equations (4)-(6) are used to acquire (7): 1 1 / j j j j p f p f f p f            (7) hence: 1 1 j j j j p f p e p e p f              (8) failure propagation, based on conditional events, is a process in which a number of slices are already at the state of failure, having a failure probability that should be considered equal to unity. the likelihood of progressive failure of the system composed of n slices knowing that the first j slices are already beyond the state of failure is: �� ������ = ���|�� = �� = ⋯ = �� = 1�� (9) hence: �� ������ = ��� ����⁄ � ����� ����⁄ � ����� ����⁄ � …. ����� ��⁄ � (10) calculations are performed in 3 distinct stages. in the first step, successive calculations of the probability or reliability index of the performance function gi of each slice are made. after evaluating the failure probability of each slice, the direction of the rupture propagation is identified. a new index j is used to order the slices in descending order of failure probability of the slice. in the second stage, the calculation of conditional probabilities p[fj /fj-1] and the probabilities p[ej] is performed. the final step in the simulation of the probability of progressive failure of the system composed of n slices, considering that for an increasing proportion, defined by a number of slices, the previously located surface potential shift, occurs beyond the peak strength and thereby engages only a residual strength.    * 1,1, 1j p r jjjg r r s   engineering, technology & applied science research vol. 13, no. 1, 2023, 10209-10216 10212 www.etasr.com djeffal & belkacemi: slope reliability analysis in locating and observing the direction of failure … vi. illustrative example the evaluation of the reliability index of slopes, taking into account the progressive failure, is made in two stages. in the first step, the limit equilibrium method of morgenstern-price is used to locate the critical slip surface. the geometrical parameters are assumed deterministic and their average values are shown in table i. in the second step, a probabilistic analysis of the critical slip surfaces is carried out by means of physical models of the objective function for each of the developed considered deterministic methods. the analysis is made by taking into account the variation of the strength parameters and includes the impact of a progressive failure through an evolution of strength parameters of their initial values (cp,p) at their peak to residual values (cr,r). the probabilistic methods form, fosm, and mcs were used. the parameters considered as random variables in the reliability analysis of slopes are shown in table i. the change in the reliability index or the failure probability as a function of the variation coefficient of random variables is obtained while keeping the average random variables constant, and setting the coefficients of change in the other random variables at an arbitrary fixed value of 30%, and by changing the value of the variation coefficient of the variable into account. random variable distributions are considered either normal or lognormal. strength parameters to peak and post-peak are either independent or negatively correlated with a correlation coefficient ρ = -0.5. table i. parameters and mean values considered in the slope stability analysis parameter symbol variable mean value cohesion term in peak cp random 20kn/m 2 friction angle in peak øp random 25° cohesion term in post-peak cr random 10kn/m 2 friction angle in post-peak ør random 10° weight γ deterministic 18kn/m3 slope angle β deterministic 26.56° slope height h deterministic 20m fig. 2. the critical slip surface morgenstern-price method. a. deterministic analysis of slope stability the results of the deterministic study of the slope stability obtained by morgenstern-price method are represented below. the equilibrium of forces and moments is examined for each slice and the whole system, by dividing the soil mass into 250 slices. the critical slip surface is shown in figure 2. the results of the deterministic analysis of slope stability have yielded a value of safety factor fs = 2.01. b. probabilistic analysis of slope stability the results of the reliability analysis of each slice are shown in figures 3-8. these figures show, for each value of the variation coefficient of strength parameters, variations in the reliability index of each slice of the system depending on the physical number of slices and the number of slices ordered in ascending order of reliability index. the main results are: fig. 3. variation of the reliability index of the slice as a function of the physical number of the slice (normal distribution of independent random variables). variation coefficient of the cohesion terms in peak cov = 10%. fig. 4. variation of the reliability index of the slice as a function of the physical number of the slice (normal distribution of independent random variables). variation coefficient of the cohesion terms in peak cov = 30%.  the change in the shape of the reliability index as a function of the physical number of slices can locate the first slice passed in the failure state. it corresponds to the slice of the least reliability index.  the change of the reliability index takes place simultaneously in both directions, relative to the first phase triggering failure.  a strong decrease in the reliability index of slices is observed for high variation coefficients of strength parameters in post-peak. this decrease reflects the high sensitivity of the reliability index of a slice to the strength parameters in post-peak relatively to peak strength parameters. engineering, technology & applied science research vol. 13, no. 1, 2023, 10209-10216 10213 www.etasr.com djeffal & belkacemi: slope reliability analysis in locating and observing the direction of failure …  taking into account the correlation between the strength parameters results in an increase in the reliability index of slices. this increase is more sensitive to low variation coefficients.  for all cases considered, the form, fosm and mcs methods give very similar results, regardless of the distribution type of random variables, normal or lognormal, and regardless of the correlation matrix considered. fig. 5. variation of the reliability index of the slice as a function of the physical number of the slice (normal distribution of independent random variables). variation coefficient of the cohesion terms in peak cov = 10%. fig. 6. variation of the reliability index of the slice as a function of the physical number of the slice (normal distribution of independent random variables). variation coefficient of the cohesion terms in peak cov = 30%. fig. 7. variation of the reliability index of the slice as a function of the physical number of the slice (normal distribution of independent random variables). variation coefficient of the cohesion terms in post-peak cov = 10%. fig. 8. variation of the reliability index of the slice as a function of the physical number of the slice (normal distribution of independent random variables). variation coefficient of the cohesion terms in post-peak cov = 30%. fig. 9. variation of the progressive failure probability of the system as a function of the number of slices past failure state (normal distribution of independent random variables). variation coefficient of the cohesion term in peak cov = 10%. fig. 10. variation of the progressive failure probability of the system as a function of the number of slices past failure state (normal distribution of independent random variables). variation coefficient of the cohesion term in peak cov = 30%. the probabilistic analysis results of the progressive failure of the system are shown in figures 9-14. these figures show, for each value of the variation coefficient of strength parameters peak or post-peak changes in the failure probability of the system based on the number of slices past at failure state. the main derived results are: engineering, technology & applied science research vol. 13, no. 1, 2023, 10209-10216 10214 www.etasr.com djeffal & belkacemi: slope reliability analysis in locating and observing the direction of failure … fig. 11. variation of the progressive failure probability of the system as a function of the number of slices past failure state (normal distribution of independent random variables). variation coefficient of the cohesion term in peak cov = 10%. fig. 12. variation of the progressive failure probability of the system as a function of the number of slices past failure state (normal distribution of independent random variables). variation coefficient of the cohesion term in peak cov = 30%. fig. 13. variation of the progressive failure probability of the system as a function of the number of slices past failure state (normal distribution of independent random variables). variation coefficient of the cohesion term in post-peak cov = 10%.  for all the considered cases, fosm and mcs give very similar results, regardless of the type of distribution of the random variables.  the failure probabilities of the system obtained by the reliability methods fosm and mcs differ from those obtained by form, and they become similar when over 90% of the slices of the system are under the condition of failure.  the inclusion of a negative correlation between the strength parameters in probabilistic analysis, results in a decrease in the failure probability of the system. fig. 14. variation of the progressive failure probability of the system as a function of the number of slices past failure state (normal distribution of independent random variables). variation coefficient of the cohesion term in post-peak cov = 30%. the results of the system reliability analysis are shown in figures 15-20. these figures show, for each strength parameter of the limit state function, changes in the reliability index of the system depending on variation coefficient. the main derived results are:  the reliability index is strongly dependent on the strength parameters in post-peak relative to the peak strength parameters, regardless of the type of distribution of the random variables and regardless of the considered correlation matrix. fig. 15. variation of the reliability index of the system as a function of the variation coefficient of the cohesion terms in peak. independent random variables. engineering, technology & applied science research vol. 13, no. 1, 2023, 10209-10216 10215 www.etasr.com djeffal & belkacemi: slope reliability analysis in locating and observing the direction of failure … fig. 16. variation of the reliability index of the system as a function of the variation coefficient of the cohesion terms in peak. negatively correlated random variables. fig. 17. variation of the reliability index of the system as a function of the variation coefficient of the cohesion terms in post-peak. independent random variables. fig. 18. variation of the reliability index of the system as a function of the variation coefficient of the cohesion terms in post-peak. negatively correlated random variables.  in post peak, the cohesion term has a strong influence on the reliability index of the system with respect to the friction angle.  the distribution of strength parameters has a strong influence on the reliability index.  for all the considered cases, fosm and mcs give very similar results, regardless of the distribution of the random variables.  the reliability index of the system obtained by fosm and mcs differs from that obtained by form. fig. 19. variation of the reliability index of the system as a function of the variation coefficient of the cohesion terms in post-peak. independent random variables. fig. 20. variation of the reliability index of the system as a function of the variation coefficient of the cohesion terms in post-peak. negatively correlated random variables. conclusion the study of reliability analysis of slope stability has, in the case of a progressive failure, to assess the effects of the uncertainties of strength parameters and the reliability index. the main conclusions from this paper are:  the traditional design of slopes that uses safety factors can be misleading. the slopes designed with large safety factors are not exempt from failure risk.  reliability analysis provides a logical framework to introduce uncertainties in the design process and improve the perception of risk in traditional design methods.  the limit state function considered in the probabilistic analysis of slope stability depends more on post-peak strength parameters that in peak strength parameters.  the integration of the residual strength parameters of (cr, r) in the proposed model has better simulation results than the progressive failure process of slopes. engineering, technology & applied science research vol. 13, no. 1, 2023, 10209-10216 10216 www.etasr.com djeffal & belkacemi: slope reliability analysis in locating and observing the direction of failure …  the reliability analysis of slices allowed locating the area triggering a failure and observing the direction of failure propagation.  the existence of a subsystem which limits the evaluation of the system behavior to that of the subsystem.  the residual strength parameters of the soil are the most dominant variables and the order of influence of the other variables depends on the choice of distribution.  the monte carlo simulation method is simple and robust, but requires a large number of simulations.  the 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[29] s. s. kar and l. b. roy, "probabilistic based reliability slope stability analysis using fosm, form, and mcs," engineering, technology & applied science research, vol. 12, no. 2, pp. 8236–8240, apr. 2022, https://doi.org/10.48084/etasr.4689. microsoft word etasr_v12_n4_pp8837-8842 engineering, technology & applied science research vol. 12, no. 4, 2022, 8837-8842 8837 www.etasr.com kumar et al.: gis-based analysis of a rainwater harvesting system in the multipurpose hall of quaid-… gis-based analysis of a rainwater harvesting system in the multipurpose hall of quaid-e-awam university of engineering, science, and technology vijay kumar environment engineering department quest, nawabshah, pakistan vk141994@gmail.com kishan chand mukwana environment engineering department quest, nawabshah, pakistan kcmukwana@quest.edu.pk abdul rehman jatoi environment engineering department quest, nawabshah, pakistan arjatoi@quest.edu.pk mahdi hassan energy system engineering department quest, nawabshah, pakistan engrmahdi@gmail.com abdul qayoom jakhrani environment engineering department quest, nawabshah, pakistan aqunimas@hotmail.com asif ali siyal environment engineering department quest, nawabshah, pakistan asifsiyal2007@quest.edu.pk khaleeque u. zaman environment engineering department quest, nawabshah, pakistan khaleeque20@gmail.com love kumar institute of food and agricultural sciences, west florida research and education center, university of florida, gainesville, fl, usa lovekumar@ufl.edu received: 19 april 2022 | revised: 18 may 2022 | accepted: 21 may 2022 abstract-drinking water availability has become a major issue. rainwater harvesting systems (rhss) amass and store rainwater for future use. in pakistan, drinking water availability has become a major issue. rainwater can be used as a constant alternative to clean water resources. google earth pro (gep) is utilized in this paper to select suitable locations for the installation of rhss. the decision must not be too excessive, must fit in buildings that have small available space, and must cover the needs of bigger buildings. the required capacity for an rhs to cope with an unusually high water shortage in the study area was calculated using gep and arcgis. the total estimated amount of rainwater harvesting potential during the average annual monsoon period from 2012 to 2021 is 1064.056 m 3 from the 13452.05 m 2 available area from rooftops and plain surfaces. the capacity of storage containers is primarily based on day-today spills and breadth. keyword-rainwater harvesting system; argis; pakistan meteorological department (pmd); google earth pro; potential demand of water i. introduction a rainwater harvesting system (rhs) is an adaptation to climate change that helps improving local livelihoods and conserve water that can be used for future use [1]. in nawabshah, there is a frightening decline of the available drinking water, making the saving of water essential in order to overcome the present and forthcoming water crisis [2]. a large number of countries rely on rhss for conserving water due to urbanization and imprudent extraction of drinking water from aquifers [3]. rainwater harvesting (rwh) can be defined as catching and storing the excess seasonal runoff and diverting it for domestic and agricultural purposes. this activity has been developed for use in arid and semi-arid regions, in rural or urban settings, and can be used as a primary or secondary water supply [4]. rwh is not a new technique. humans have been harvesting rainwater for drinking and non-drinking purposes for more than 4000 years [5]. in many places, rooftop rainwater collection is still used to supply water demands. rainwater can corresponding author: mahdi hassan engineering, technology & applied science research vol. 12, no. 4, 2022, 8837-8842 8838 www.etasr.com kumar et al.: gis-based analysis of a rainwater harvesting system in the multipurpose hall of quaid-… be captured as a means of preventing flooding roadways, recharging aquifers, increasing water tables, and meeting the requirements of the growing population [6, 7]. compared with most unprotected ordinary water sources, drinking rainwater from well-maintained roof catchment typically represents a substantial enchantment [8]. rhss add safety to the city water supply system in the event of unexpected failures [2, 9]. the main purpose of this study is to determine the possibility of rainwater collection for storage and use at household level. this strategy is advantageous for minimizing groundwater overuse and conserving it, particularly in nawabshah, where there will be a water-scarcity in the coming years. therefore, this research study entails a thorough examination of the necessity for and application of rainwater collection in the quest nawabshah multipurpose hall. for the rwh analysis, the geographical information system (arcgis) and google earth pro (gep) tools were used. this research work suggests steps to be taken at a local level to deal with the issue of water shortage in communities and at the individual level. a. general aspects of rainwater harvesting the rhs mounted to collect rainwater from the roof areas of the three dormitories would be ample for the flushing consumption as 2831m 3 of water that can be amassed annually with a reliability of 93% [9]. the volume of rainwater that can be gathered from a roof, is based on its measurement and texture. the catchment floor will have an effect on the rainwater via the contaminants that might be present on the surface [10, 11]. furthermore, the groundwater will be recharged with the aid of rwh [8]. some details about filters used in rhss, calculations, and the set up price are discussed in [11, 12], where, additionally, the calculation and format of the rwh device was introduced and price analysis was given. rainfall of high quality via water treatment technologies, such as photovoltaic collector disinfection, is needed to minimize health risks. the manageable of rwh structures on lowering runoff goes with the flow height for households in southern italy, and simulation outcomes exhibit that, with the aid of the usage of tank-based rhss, there is a top-notch discount in runoff peak, between 30% and 65%, depending on the dimensions of rainwater tanks [13]. a linear programming method for a single residential housing unit to decide the topquality rainwater storage tank volume for rwh and storage was established in [14]. a lifecycle cost-benefit model and a nonlinear metaheuristic algorithm to optimize rhss was presented in [15]. furthermore, an optimization-based model for the utilization, storage, and distribution of rainwater aiming for cost-efficiency and water saving was proposed in [16]. an analyzed model was used in [17]. this model can analyze the most useful graph variables, price, and overall environmental performance of rhss, and make comparisons with other models, such as the aqua cycle and the rain cycle. b. potential of rainwater harvesting rwh is the collection of rainwater which can be used for irrigation or to replenish groundwater supplies [12, 15, 18, 19, 22]. as the demand for water for industrial and household usage continues to rise, rwh is becoming increasingly important [19]. it is considered to be a low-cost and a better option than other strategies for increasing water supply in the near future. due to the frightening decline of the water table in nawabshah, conserving water is essential to deal with the existing and upcoming water crisis [15, 18]. it is possible to define rwh as capturing and storing seasonal excess runoff and diverting it for domestic and agricultural use. creating a rainwater collection system is a simple method for conserving rainwater for future use. the majority of global population will be affected by the global water crisis by 2025 [18]. rwh has become a necessity in the current arid climate. currently, rwh is an easy solution to unregulated urbanization and rising water demand. rwh is a concept for conserving fresh water and using it for potable and nonpotable applications that has been proven practicable and practical all over the world. it can also be used in nawabshah to replace the city's diminishing water table, which is quickly dwindling. c. treatment techniques for rainwater harvesting the fundamental categories are heat and uv-based methods, chemical treatment procedures, and bodily elimination operations [19]. moreover, rwh structures intended for potable use must be screened, settled, filtered, and disinfected before use [20]. the utilization of satellite images and gis data for particular land-cover classification of rooftops is extremely important for superior city runoff simulation and estimation of the feasibility of rainwater storage and harvesting systems [21]. the reliability of rwh structures for exclusive situations below the local weather conditions is primarily based on the water balance model to find out the most effective rainwater storage tank extent of the rwh structures serving a common six-member family [22, 23]. a daily water stability model of the overall performance of rwh structures under climate change was established in [18]. the set-up of rwh structures comes collectively with a number of direct and indirect fees and benefits [24]. mass stability methodology, ripple sketch method, analytical approach, and the sequent height algorithm were used to determine the extent of water. the analytical hierarchy process (ahp) was utilized to determine which rwh technique was the best for the considered area. ahp can be an effective tool for assessing rwh procedures and structures [25]. microfinance institutions may play an important role in the spread of domestic rhss. ii. methodology a. description of the study area the study area, as shown in figure 1, using an arcgis map of the rooftop and the plain surface area surrounding the multipurpose hall building of the quaid-e-awam university of engineering, science, and technology (quest), nawabshah, is located on the outskirts of the city, near the airport road, at latitude 26°14′9.38′′n and longitude 68°23′24.24′′e. the total area of the multipurpose hall building is 11,453.403ft 2 , while the total area of the university is 457 acres on both sides of the main sakrand road. b. rainfall data collection the pakistan meteorological department (pmd) in nawabshah collected precipitation data for the city of nawabshah for 10 years (2012-2021) [26, 27]. in our study engineering, technology & applied science research vol. 12, no. 4, 2022, 8837-8842 8839 www.etasr.com kumar et al.: gis-based analysis of a rainwater harvesting system in the multipurpose hall of quaid-… area there is not a particular rain gauge station. so, precipitation data from the pmd station at the airplane terminal of nawabshah (opnh-417490) were utilized to assess the water volume. only the monsoon period is considered in this study. as presented in table i, the annual monsoon rainfall data (2012 to 2021) and the minimum to maximum total monsoon rainfall data for the last 10 years are noted as 179.07, 277.3, 284.61, and 389.43mm in the months of june, september, july, and august respectively. minimum to maximum average rainfall data are 17.90, 27.73, 28.46, and 38.9mm in june, september, july, and august respectively as shown in figure 2. the maximum annual monsoon precipitation occurred in 2019, which was 274.90mm. the average annual monsoon precipitation within the period of 2012 to 2021 was 277.3mm. the minimum annual monsoon precipitation happened in 2018 and was 4.42mm. fig. 1. study area (arcgis map). table i. annual monsoon rainfall data of nawabshah (2012 to 2021) year monthly data total (mm) june july august september 2012 0.00 0.00 15.20 163.50 178.70 2013 19.00 7.50 39.00 3.50 69.00 2014 0.00 0.00 11.20 0.00 11.20 2015 37.20 69.00 0.00 0.00 106.20 2016 58.00 4.00 63.20 0.00 125.20 2017 58.86 33.17 65.71 4.40 162.15 2018 0.01 1.71 2.70 0.00 4.42 2019 0.00 152.20 41.70 81.00 274.90 2020 0.00 1.03 150.72 12.90 164.65 2021 6.00 16.00 0.00 12.00 34.00 average (mm) 17.90 28.46 38.9 27.73 total (mm) 179.07 284.61 389.43 277.3 c. catchment area a catchment area is a surface, of any kind, where rainwater can be collected. the rooftop surface and plain surface area are catchment regions that get precipitation. the catchment area of the multipurpose hall building and its surroundings is estimated. this estimation was done physically with the assistance of a measuring tape. the equation for spillover catchment region estimations is : plain surface area = total surrounding surface area – area of multipurpose hall and total grass area (1) d. runoff coefficient cr the runoff coefficient is a proportion of the amount of precipitation and the rate of spillover. there are certain factors that are determined by taking into account that not all rainwater can be collected. in some cases, there is a constant loss of overflow from the catchment area due to vanishing or holding at a superficial level. the runoff coefficient is calculated using: t r r v v c = (2) where vr and vt are the runoff volume and the total precipitation volume on a superficial level. the calculated factors of runoff coefficients for several forms of catchments are given in table ii. table ii. runoff coefficients for different catchment area types cr factor catchment type 0.7 to 0.9 corrugated-metal sheets 0.8 to 0.9 tiles 0.5 to 0.6 brick concrete 0.6 to 0.8 concrete 0.2 to 0.5 rocky natural catchments 0.0 to 0.3 soil on slopes less than 10% 0.05 to 0.10 green area e. rainwater harvesting potential in a particular area, the whole amount of water that was mainly received as rainfall is the rainwater endowment. the amount of rainwater that is commendably harvestable is the rwh potential. the rwh potential for the study area is estimated with (3): r s r a c= × × (3) where s, r, a, and cr are the runoff potential of rainwater harvesting (m 3 ), the average annual rainfall (m), the area of the catchment (m 2 ), and the runoff coefficient (%) respectively. f. weekly discharge and volume of storage tank calculation the volume of the storage tank is calculated based on the expected discharge. catchment area and weekly rainfall are used to calculate weekly discharge. monsoon weekly rainfall will be calculated by multiplying the daily monsoon rainfall with 7. the daily monsoon rainfall is calculated by dividing the maximum average annual monsoon rainfall by 122 as there are 122 days in the monsoon period every year (june, july, august, and september). the maximum average monsoon rainfall is 274.90mm which occurred in 2019. as a safety precaution, the tank should be built larger than the storage volume required. engineering, technology & applied science research vol. 12, no. 4, 2022, 8837-8842 8840 www.etasr.com kumar et al.: gis-based analysis of a rainwater harvesting system in the multipurpose hall of quaid-… g. specifications of the rainwater harvesting treatment system rainwater is collected in drain pipes on the roofs of buildings. after that, the rainwater is filtered to make it safe to drink. a first rain separator, or first flush, can be used to remove most pollutants from the rain water before it enters the filter. rainwater can be collected and stored in one or more connected tanks, either below or above the ground. rainwater is either pumped to an internal holding tank or delivered directly where it is needed on demand. figure 2 shows the diagram of the multipurpse hall building's rooftop rhs. fig. 2. diagram of the rooftop rhs. iii. results and discussion a. digitization of rooftop and plain surface area with google earth pro the rooftop and the plain surface area of the surroundings of the multipurpose hall building were digitized in google earth pro (gep) using the available polygon tool. rwh is an attractive source of drinking water in urban areas due to the scarcity of conventional sources and their limited capacity [9]. in water-scarce areas, the system could be used to secure water demand locally and commercially. when the water quality parameters are met, rainwater harvested from rooftops could be used as supply water [10, 11]. the surface areas of rooftops (1642.130m 2 ) and the total plain surface (11788.989m 2 ) were digitized in gep, they were saved as kml files and are shown in figures 3 and 4. b. calculation of the the rooftop and plain surface area using arcgis the saved kml files were imported into arcgis as layers. the kml layers have been converted to shape files because each shape file coordinate system has been changed to a projected coordinate system that is actually separate for each country (epsg: 32644-wgs 84/utm zone 43n) to calculate the areas of digitized rooftops and plains with the help of an available geometry calculation tool (figure 5). figure 5 shows the projected shape file in arcgis, as well as the digitized rooftop and plain surface area catchment shape files. fig. 3. rooftop and plain surface area digitized with (gep). fig. 4. the shape files of the projected coordinates in arcgis. fig. 5. calculation of the areas of digitized rooftop and plain surface catchments using arcgis. c. estimated rooftop and plain surface rwh potential table iii shows the estimated average monsoon annual runoff from 2012 to 2021 from the rooftop of the multipurpose hall and the plain surface area surroundings. the maximum average annual monsoon runoff was 932.509m 3 , collected from the plain surface area surroundings of the multipurpose hall. the minimum average monsoon runoff was 129.892m 3 , collected from the rooftop of the multipurpose hall building. engineering, technology & applied science research vol. 12, no. 4, 2022, 8837-8842 8841 www.etasr.com kumar et al.: gis-based analysis of a rainwater harvesting system in the multipurpose hall of quaid-… table iii. estimated rainwater harvesting potential of the study area (2012 to 2021) catchment type runoff (m³/year) average annual monsoon rainfall (m) cr area (m²) rooftop 129.892 0.113 0.7 1642.130 plain surface 932.509 0.113 0.7 11788.989 total 1062.401 13431.119 d. estimated rwh potential (runoff) on a yearly basis figure 6 shows the results of the estimated rwh potential (runoff) from the study area on a yearly basis. the maximum estimated amount of runoff water that could be collected from the rooftop and the plain surface area is 2584.550m 3 during 2019 and the minimum estimated amount of runoff water was 41.367m 3 during the year 2018. arcmap 10.4.1 was used to calculate the rwh potential for the roofs of buildings. it is also proposed to use the rwh model at the household level with its utilities. uncontrolled urban sprawl, rapid population growth, and uncontrolled immigration contributed to extensive groundwater extraction. therefore, in addition to other sources such as rooftops, roadways provide a significant opportunity for rainwater harvesting as a viable solution to urban flooding. fig. 6. comparison of the estimated annual monsoon runoff from the study area. e. estimated weekly discharge and volume of storage tank table iv shows that a weekly monsoon discharge of 210.868m 3 from the rooftop and the plain surface area can be obtained. a tank size of 330m 3 per week is required for this discharge. table iv. estimated monsoon weekly discharge and the required volume of the storage tank catchment type weekly discharge (m 3 ) volume of storage tank per week (m 3 ) rooftop 25.781 40 plain surface 185.087 288 total 210.868 330 iv. conclusion an analysis was made in this study to determine whether rooftop and plain surface rwh can meet the general water demands in the study area. gep was used for digitizing and arcgis was used to calculate the rooftop and the plain surface areas surrounding the multipurpose hall. the total estimated amount of rwh potential during an average annual monsoon period (2012 to 2021) is 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[26] n. k. bhatti, s. r. samo, m. a. keerio, a. ali, and a. a. ansari, "an analysis of diurnal air temperature range change and its components in shaheed benazir abad sindh," stavební obzor civil engineering journal, vol. 28, no. 2, pp. 176–187, 2019, https://doi.org/ 10.14311/cej.2019.02.0015. [27] s. r. samo, n. bhatti, a. saand, m. a. keerio, and d. k. bangwar, "temporal analysis of temperature and precipitation trends in shaheed benazir abad sindh, pakistan," engineering, technology & applied science research, vol. 7, no. 6, pp. 2171–2176, dec. 2017, https://doi.org/10.48084/etasr.1388. microsoft word etasr_v12_n6_pp9483-9486 engineering, technology & applied science research vol. 12, no. 6, 2022, 9483-9486 9483 www.etasr.com benabdallah & boudour: smart collection of waste bread in algeria using the internet of things smart collection of waste bread in algeria using the internet of things ahcene youcef benabdallah laboratory of embedded systems badji mokhtar university annaba, algeria benabdallah.ahcene@gmail.com rachid boudour laboratory of embedded systems badji mokhtar university annaba, algeria racboudour@yahoo.fr received: 23 august 2022 | revised: 9 september 2022 | accepted: 12 september 2022 abstract-algerians are among the largest consumers of bread throughout the year and produce large amounts of bread waste. as bread is made from imported wheat, these losses on currency are a heavy loss for the national economy. to minimize these losses, algeria needs to encourage the recycling of stale bread to minimize the cost of importing soft wheat and valorize it for farmers. this paper presents a framework based on the internet of things (iot) to monitor and collect waste bread from recycling bins. this system could assist small and medium enterprises (smes) in algeria in bread waste collection, by monitoring the level of filling of the outdoor waste bins. the proposed system's architecture used a mega 2560 microcontroller, hc-sr04 ultrasonic sensors, and sim 808/900 modules. keywords-waste bread; recycling; smart city; iot; arduino i. introduction algerian consumers are among the people who consume the most bread throughout the year. university restaurants, hospitals, and school canteens are considered the largest waste cells that affect daily bread consumption. the absence of consumption culture increases bread waste, causing problems for poultry farmers, livestock, and garbage management. the waste of bread made with imported wheat in foreign currency is a serious loss to the national economy [1]. algeria should promote the recycling of stale bread to minimize these economic losses. the recycling process is based on several steps starting with the collection of waste through its sorting and processing to the marketing of the recycled products. the collecting operations of each country are carried out in different ways, according to their level of civism and industrialization. waste collection in developed countries is performed in a selective way called "selective sorting", while this operation is performed manually in underdeveloped countries by people or employees while sorting the waste by nature according to the demand [2, 3]. today, the world is witnessing an increasing use of the internet of things (iot) which uses devices that collect massive amounts of data and attracts the interest of both academia and industry [4]. the enhanced capability of applications, cloud services, and databases to communicate with iot devices produces a vast number of new interconnections between current and new systems. iot devices are expected to reduce the cost of waste collection using the information exchanged among bins, containers, and trucks [5]. this study aims to investigate the recycling and recovery of waste bread by reviewing iot techniques for the smart collection of stale bread systems and proposes an efficient management method to improve the collection systems in the source area, which is the most important stage of waste management, and can lead to a reduction in the bill for importing soft wheat and animal food products. ii. materials and methods a. bread waste situation the algerian ministry of commerce revealed that during the period between april 13 and 24, 2021, only the first 12 days of ramadan, 535 tons of bread (2,139,884 breads) equivalent to 45 tons/day (178,323 breads) were wasted at national level, with a financial value estimated at 20 million algerian dinars [6]. official statistics show that an average of 2.7 million breads are not consumed daily. the financial value of the wasted quantities was estimated by the ministry of commerce at 20 million algerian dinars, which represents more than 1.5 million algerian dinars per day. table i presents the provinces that recorded the highest rate of waste bread. table i. highest rates of waste bread nο province quantity of breads(units) 1 blida 321,924 2 bechar 161,648 3 tlemcen 150,696 4 djelfa 139,364 5 annaba 118,680 6 tebessa 115,152 7 oran 108,200 moreover, algeria imports large quantities of soft wheat to ensure the production of flour destined for bakeries. table ii illustrates a yearly account of soft wheat imports. on the other hand, there is the problem of covering the food needs of farms (bovine/ovine and poultry), whose numbers are large and their corresponding author: ahcene youcef benabdallah engineering, technology & applied science research vol. 12, no. 6, 2022, 9483-9486 9484 www.etasr.com benabdallah & boudour: smart collection of waste bread in algeria using the internet of things annual import bills for corn, soya, and are increasing. the collection and processing of stale bread can be a solution to this problem by using automatic recovery solutions and resulting in environmental protection and sustainable development. some waste collection establishments sort bread from other waste to restore and sell it to cattle and poultry breeders. table ii. cost of imported soft wheat year quantity (tons) cost of imported soft wheat (billion $) 2017 6,832,777 1.4 2018 7,179,399 1.6 2019 5,800,844 1.3 b. methodological approach the rapid evolution of technology has led to the development of increasingly complex systems, capable of processing information flows of diverse nature and origin and whose access must remain nevertheless simple and fast [7]. the proposed system could assist algerian smes in collecting waste bread by monitoring the fullness status of outdoor bins with a list of requirements. several studies examined the domain of smart waste management (household/solid) using different materials and techniques [8-17]. in this context, this study adopted an appropriate approach to the specificity of the product, stale bread, the area, and the country. the solution framework is based on wireless sensor nodes connected to the intelligent bins manager with a monitoring station by sending the bins filling level status for analysis and control of waste. this solution involves the following features:  optimal fill level setting: this allows the user or system operator to specify the fill level they consider optimal. exceeding this limit will result in notifications for collection.  check bin status: this allows a user to view at any time the fill level of a bin using a web application.  notifications: this feature allows the users to be notified whenever the fill level exceeds the specified optimum levels.  reports: this feature allows the system to generate reports when needed. after successful installation and login, the user can request the system to display the status of a bin from a web application. this request should trigger actions to check the bin filling level and pass the values through an arduino microcontroller to the user's device browser. the user must register and then log in to interact with the system. using smart bins and iot, data should be collected and presented in a meaningful way to waste managers, as described in the proposed conceptual iot infrastructure model. figure 1 shows the flowchart of the proposed approach after starting the system and connecting composites. the iot infrastructure model works in the following manner: 1. citizens fill the smart bins. 2. the filling height is measured with an ultrasonic sensor. 3. the height is transmitted to the cloud via sms or wifi or a hybrid system with a gsm module. 4. the server receives the data. 5. a notification for a transporter is sent. 6. the bin is emptied. 7. the transporter goes to the sorting and grouping center. 8. the bread is unloaded and the stock status is changed. 9. the stock status is transmitted to the system to notify recyclers. fig. 1. architecture of the proposed system. fig. 2. the smart bin. an ultrasonic sensor, a gsm module sim808/sim 900 mhz quad-band, and an arduino uno microcontroller should be installed on the upper part or the bin cover, as shown in figure 2. the system would be active when the garbage is in a closed position and the ultrasonic sensor should detect any changes in the height of the garbage volume. the data of the garbage height are then processed by the arduino uno microcontroller mega 2560 and then sent to a firebase real-time database using the http protocol and the gprs network via engineering, technology & applied science research vol. 12, no. 6, 2022, 9483-9486 9485 www.etasr.com benabdallah & boudour: smart collection of waste bread in algeria using the internet of things the gsm sim808/sim 900 module [18]. to enable wireless connectivity and sensing capabilities, a microcontroller was installed in each collection box. figures 3 and 4 show the three main components. the ultrasonic sensor is capable of determining the level of the collection box. the arduino board supplies power for the ultrasonic sensor and allows for a customized program to control the sensor and the wi-fi module. the ultrasonic sensor will then operate and scan for any changes in the level of the collection box. fig. 3. arduino uno (mega 2560) connected with the hc-sr04 ultrasonic sensor. the wi-fi module board connects the arduino board with the wi-fi network and the database server to store the measured waste level via the ultrasonic sensor. (a) (b) fig. 4. (a) module sim 808, (b) module sim 900. following the collection, the products are sent to a sorting facility where they would be sorted mechanically to optimize the operations of transformation. this operation can also be completed by manual sorting using a conveyor belt. once the operation of sorting is finished, the waste is ready to be integrated into the transformation operation by factories that will transform it into ready-to-use materials. fig. 5. transportation to the regional recycling center. iii. results and discussion the proposed system was designed to assist algerian smes in collecting waste bread by monitoring the filling status of outdoor recycle bins. iot devices are expected to reduce the cost of waste collection by using the information exchanged between bins, containers, and trucks. these devices enable automation and accelerate the identification of waste for processing. as there are no similar studies on using iot for smart collection of stale bread, the proposed system was compared with studies on recycling other products. this study utilized the same communication technologies with [5, 6, 17] for solid and [10-16, 18] for household waste. the architecture design adopted a model that responds to:  the specificity of the product: to avoid the high cost of the system as the main objective was to recycle at a lower cost.  the specificity of the region and the lack of internet connection in some collection sites: this was accomplished by a hybrid architecture using a sim 808 reader for sending sms and sim 900 which supports gprs internet connection. the proposed architecture can be implemented in a metropolitan area. the main advantage of this system is that it is very independent and transparent. instead of using gsm and gprs modules, the server could directly send the messages and the hardcoded coordinates. this could reduce the working and maintenance cost of these embedded bins. iv. conclusion this paper discussed a smart collection system of waste bread in algeria, proposing a solid waste monitoring system. a framework based on iot and arduino was presented for collecting waste bread from the bins to the recycling establishment. the system was designed to assist algerian smes to collect waste bread by monitoring the fullness status of outdoor bins. this system's features are: engineering, technology & applied science research vol. 12, no. 6, 2022, 9483-9486 9486 www.etasr.com benabdallah & boudour: smart collection of waste bread in algeria using the internet of things  it can monitor the fill level in a short time.  it can notify the persons in charge simply and with good interactivity.  it is a secure system with access restrictions.  it can provide usage reports the level of waste in each bin is monitored and transmitted to a central management platform and can be accessed remotely to check and perform the collection process in any web browser. in future work, the proposed architecture will be extended to other actions that could encourage and promote the collection of waste bread by integrating them into the system platform. references [1] m. hocine and l. sebbache, "la ressource alimentaire pain et ses deshets a l’ aune de l’intelligence territoriale par ‘economie sociale et circulaire’. cas d’el-harrach dans la banliere est algeroise," revue d’economie & de gestion, vol. 2, no. 2, pp. 114–123, 2018. [2] k. louisa, "economic advantages of the recycling business," the journal of research and scientific studies, vol. 16, no. 1, pp. 513–231, 2022. [3] m. naghel, a. farhi, and a. redjem, "household waste management challenges: the case of m’sila, algeria," engineering, technology & applied science research, vol. 12, no. 3, pp. 8675–8682, jun. 2022, https://doi.org/10.48084/etasr.4925. [4] s. benkhaled, m. hemam, m. djezzar, and m. maimour, "an ontology – based contextual approach for cross-domain applications in internet of things," informatica, vol. 46, no. 5, mar. 2022, https://doi.org/ 10.31449/inf.v46i5.3627. [5] k. pardini, j. j. p. c. rodrigues, s. a. kozlov, n. kumar, and v. furtado, "iot-based solid waste management solutions: a survey," journal of sensor and actuator networks, vol. 8, no. 1, mar. 2019, https://doi.org/10.3390/jsan8010005. [6] "ministry of trade algeria." https://www.commerce.gov.dz/en/. 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[18] k. d. kang, h. kang, i. m. s. k. ilankoon, and c. y. chong, "electronic waste collection systems using internet of things (iot): household electronic waste management in malaysia," journal of cleaner production, vol. 252, apr. 2020, art. no. 119801, https://doi.org/10.1016/j.jclepro.2019.119801. microsoft word 6-695-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1139-1148 1139 www.etasr.com mohamadian and khanzade: a five-level current-source inverter for grid-connected or high-power… a five-level current-source inverter for gridconnected or high-power three-phase wound-field synchronous motor drives sobhan mohamadian school of engineering damghan university damghan, iran s_mohamadian@iust.ac.ir mohammad hosein khanzade department of fava engineering imam hossein comprehensive university tehran, iran mhokhanzade@gmail.com abstract—simple converter structure, inherent short-circuit protection and regenerative capability are the most important advantages of current-source inverters (csi’s) which have made them suitable for medium-voltage high-power drives. usually in grid-connected gas turbine generators or pumped storage hydro power plants, efficient and reliable current-source loadcommutated inverters (lci’s) with thyristor switches are employed. also, this type of csi is widely used in very large drives with power ratings of tens of megawatts to supply woundfield synchronous motors (wfsm’s). however, lci’s suffer from some disadvantages such as large torque pulsations, poor power factor, and start-up criticalities. in this paper, a novel multilevelbased csi is proposed. the proposed converter consists of one lci and one csi bridge with self-turn-off switches along with a voltage clamping circuit. the csi switches are forced commutated; hence, a voltage clamping circuit is employed to limit voltage spikes caused by current variations in inductive paths during commutation transients. drastic reduction in harmonic distortion of stator current and improved fundamental power factor are achieved by the proposed topology. in addition, torque pulsations are reduced remarkably for normal and starting operating conditions. comprehensive analysis of the proposed structure is presented and the design of converter components is elaborated. keywords-current-source inverter (csi); five-level current waveform; load-commutated inverter (lci); voltage clamping circuit; wound-field synchronous motor (wfsm) drive i. introduction in industrial current-source inverter (csi)-fed drives, selfturn-off power devices such as gate turn-off thyristors (gto’s) or insulated gate bipolar transistors (igbt’s) are switched by pulsed-width modulation (pwm) schemes such as trapezoidal pwm (tpwm), selective harmonic elimination (she) and space vector modulation (svm) to attenuate the low-frequency harmonic components of the machine stator current [1]1-3]. in these structures, a three-phase capacitor bank is mandatory at the csi output to absorb the high-voltage spikes produced due to the switching of the current in inductive paths. the capacitor bank also serves as a filter for high-frequency current harmonics created by the pwm switching. however, this capacitor bank has some drawbacks such as the possibility of the resonance risk between output capacitors and machine magnetizing inductance at the fundamental frequency or machine leakage inductance at higher harmonic orders [4]. thus, the capacitor bank must be designed so that the lowest harmonic order of the stator current is much higher than the resonance frequency. accordingly, the bank size will typically range between 0.3 per unit (pu) to 0.5 pu for switching frequencies of approximately 400 hz [1]. furthermore, the effect of the capacitor bank on the motor current and air-gap flux specifically at high operating speeds must be taken into account in the control system so as to get adequate response and avoid instability of the drive at transients [5]. in addition to these disadvantages, for some high-power applications (usually higher than 10 megawatts [6]) using pwm switching is not usual in csi-fed drives since the converter efficiency is reduced due to the switching and conduction losses of the self-turn-off power devices. therefore, load-commutated inverter (lci)-fed wound-field synchronous motor (wfsm) drives are the preferred choice in this power range because of the higher efficiency and reliability of the converter. also, the initial investment cost of the converter is low due to the inexpensive silicon-controlled rectifier (scr) devices [1]. in these drives, wfsm operates at over-exciting mode resulting in natural commutation of the thyristors [7]. therefore, there is no need for capacitor banks. lci-fed drives are widely used in high-power applications specifically in pumped-storage power plants and girdconnected synchronous machines for star-up purposes [8, 9]. due to the great increase in social electricity consumption level and the proliferation of the capacity of nuclear power and renewable energy resources, it was expected that the capacity of pumped-storage power plants would gain more than 200 gw worldwide by 2014 [10, 11]. there is also a great trend in utilizing lci’s for driving high-power compressors used for liquefying natural gas, pumps, fans [12-14], grinding mills in mining applications [15] and ship propulsion systems [1]. engineering, technology & applied science research vol. 6, no. 5, 2016, 1139-1148 1140 www.etasr.com mohamadian and khanzade: a five-level current-source inverter for grid-connected or high-power… however, the quasi-square waveform of the stator phase current of these drives is a major problem. this waveform is rich in low order harmonics, specifically 5th and 7th orders, which result in large torque pulsations and increased winding and iron losses. the torque ripples can interact with the torsional natural frequencies (tnf’s) of the mechanical system and lead to accelerated shaft fatigue, lifetime reduction, gearbox damage, and system failures [12-14]. the most common method to reduce the torque pulsations is to use dual threephase wfsm in which each three-phase winding set of the machine is independently supplied from a three-phase lci [6, 16]. in this configuration, the 6th order of the electromagnetic torque is cancelled out. although, this solution is not always possible, e.g. it does not cover the cases where lci’s are utilized to feed grid-connected (three-phase) generators for start-up before synchronization or in pumped storage hydro power plants [7]. another solution is to use multi-pulse converters. in these structures, two series or paralleled 6-pulse (three-phase) lci’s are connected to a three-phase threewinding phase-shifting transformer feeding a three-phase wfsm to eliminate the 6th order harmonic of the torque. however, the transformer is bulky and expensive and increases system losses [17]. on the other hand, recent development in in high-power semiconductor devices such as igbt’s has drawn the attention to use voltage-source inverters (vsi’s) in these applications. in [11], a multilevel cascaded h-bridge (chb) vsi is used for the start-up of synchronous motor in a pumped storage power station. in this configuration the harmonic distortion of the stator current is improved remarkably, however, the volume of the converter is increased since there are nine power cells connected in series each phase. another problem regarding to lci-fed wfsm drives is the start-up operating conditions. at standstill or low speeds, the generated back electro-motive forces (emf’s) of the machine are not large enough to turn off thyristors and the load commutation process, as will be explained in iii.a, is not accomplished. to cope with this problem, dc-link pulsing method is generally used [7, 18]. in this method, the dc-link current is forced to zero by the operation of the rectifier at the commutation instants. therefore, the previous conducting thyristors in the lci is turned off since its current reaches below the holding current [19, 20]. after a short interval, the next incoming thyristor is fired and the dc-link current is again built up to its reference value by the rectifier. however, this method produces high torque ripples. in this paper, a novel multi-objective structure for lci-fed three-phase wfsm’s is proposed based on the five-level current-source configuration. in addition to several advantages related to high-power multilevel converters such as reduction of the voltage and current stresses of the switching devices and lower harmonic distortion of the load current [21][21], the machine fundamental power factor is improved significantly. furthermore, the start-up criticalities of the lci-fed wfsm drives are removed with the proposed structure. ii. structure of the proposed five-level converter the proposed five-level converter is shown in figure 1 and consists of two converters (that supply the main power of wfsm): an lci with thyristors t1-t6 and a csi with self-turnoff power devices s1-s6. in csi-fed wfsm drives, each motor phase can be modeled as a sinusoidal back emf in series with the commutation inductance, lc, which is approximately equal to (lʺd+lʺq)/2 [19], as shown in figure 1. lʺd and lʺq are the machine sub-transient inductances along rotor d and q axes, respectively. it should be mentioned that stator resistances are neglected in this circuit. fig. 1. proposed five-level csi for wfsm drives. both converters are switched at the machine fundamental frequency. since the csi switches are forced-commutated, the variation rate of current in machine inductances must be limited at the commutation transients. on the other hand, the capacitor bank cannot be utilized because its size would be very large due to the low switching frequency of the converters. in this paper, a voltage clamping circuit is used to inhibit voltage spikes. voltage clamping circuits usually consist of a diode rectifier to transfer the reactive energy of the machine to an electrolytic capacitor at the commutation intervals [21]. in order to avoid the continuous increment of the capacitor voltage, an energy recovery circuit such as a dc/dc chopper or an inverter is used to pump the capacitor energy into the dc-link or ac-grid, respectively [21]. in this paper, a voltage-source inverter (vsi) is utilized with six self-turn-off devices k1-k6 and six free-wheeling diodes d1-d6 as shown in figure 1. the same vsi is introduced in [22] to reduce voltage spikes in a thyristor-based csi-fed induction motor drive. in [22], the vsi is employed for two main tasks: 1) forced-commutation of the thyristors and 2) clamping the voltage spikes. while, the vsi in the proposed multilevel converter serves only as the voltage clamping circuit during commutation transients and thyristors are turned off naturally. for this reason, as will be explained in section iii.b, the conduction states of the switches in the proposed multilevel are different and simpler than those presented in [22]. iii. operation principles of the proposed five-level converter the desired stator phase current waveform, e.g. ia(t) in figure 1, of the proposed five-level converter is shown in figure 2a. this waveform results from the summation of two quasi-square waveforms, i.e. ilcia(t) and icsia(t), at node a engineering, technology & applied science research vol. 6, no. 5, 2016, 1139-1148 1141 www.etasr.com mohamadian and khanzade: a five-level current-source inverter for grid-connected or high-power… (figure 1). as in the case of conventional lci’s, ilcia(t) and icsia(t) have a pulse-width of 120 electrical degrees in each half cycle and ilcia(t) leads icsia(t) by 30̊. the resultant waveform of ia(t)=ilcia(t)+icsia(t) has five levels of 0, idc/2 and idc. the phase displacement between ilcia and icsia, i.e. ∆t where  is the motor speed in electrical rad/sec, is set to 30̊ so as to minimize the thd of ia as shown in figure 2b. according to this figure, the amplitude of the 5th and 7th harmonic components of the desired phase current is equal to 5.36% and 3.83% of the fundamental for ∆t=30̊, respectively, while they would be 20% and 14.35% if the usual lci topology with quasi square-wave currents were employed. a. operation principles of lci the switching pattern for the lci thyristors is shown in figure 3. since the thyristors of the lci are naturally commutated, currents ilcia(t), ilcib(t) and ilcic(t) must lead the phase voltages ea(t), eb(t) and ec(t) with a minimum angle of lcimin=µ+tq [19], where µ is the commutation angle and tq is thyristors turn-off time. considering phase ‘a’ as an illustration, practically negative and positive zero-crossing instants of eac(t) are used as the reference for firing t1 and t4, respectively. thus defining  as the firing angle, t1 will be fired at point a in figure 2a and the commutation interval ‘1’, shown in figure 3, is started. conduction of t1 produces a short-circuit loop between the incoming phase ‘a’ and the outgoing phase ‘c’ as shown in figure 4 in which eac(t) drives ilcic(t) to decrease from idc/2 to 0 and ilcia(t) to increase from 0 to idc/2. the current variations are almost linear since the stator phase resistances are practically negligible. the commutation phenomenon lasts for µ electrical degrees. consequently, the current in t5 is diminished to zero and the commutation interval is finished. after commutation, the voltage across t5 (eac(t) in this case) must be negative for a time interval of at least equal to tq in order to be able to withstand positive voltages [20]. usually in high-power lci-fed drives the maximum firing angle is set to 150̊ to avoid commutation failure. in this case, the fundamental component of the current leads stator phase voltage by lci =30̊. it should be mentioned that in a conventional three-phase three-level lci (with levels of 0, +idc and -idc in the output waveform of phase current), the fundamental power factor angle, lci, is equal to . at higher loading conditions, the firing angle is lower than 150̊ which can be translated into a relatively high reactive power. b. operation principles of csi and vsi the switching instants and sequences for s1-s6 are the same as t1-t6 except for a 30̊ displacement as shown in figure 5. for instance, s1 must be switched on at point b (figure 2a) which is 30̊ later than the firing instant of t1. contrary to the situation explained for lci at point a, the voltage eac(t) might be positive at point b and, consequently, the current in phase ‘c’ cannot be naturally commutated to phase ‘a’ by switching of s1. therefore, an external negative and positive voltage must be applied to phases ‘c’ and ‘a’, respectively, to force ic(t) to decrease from idc/2 to 0 and ia(t) increase from idc/2 to idc. in this way, the currents in the outgoing and incoming phases should not abruptly change in order to limit the voltage spikes over the machine inductances. the external voltage source can be a dc capacitor which is applied by proper switching of vsi at commutation instants. fig. 2. (a) ilcia(t), icsia(t) and ia(t) waveforms and their corresponding fundamentals and wfsm phase and line voltages, (b) 5th and 7th harmonic amplitudes (relative to fundamental) and thd for the phase current ia as a function of ∆t. fig. 3. switching pattern of lci.  corresponds to point a in figure 2a fig. 4. the loop created by the simultaneous conduction of t1 and t5 (commutation interval ‘1’ in figure 3) and (b) current variations. engineering, technology & applied science research vol. 6, no. 5, 2016, 1139-1148 1142 www.etasr.com mohamadian and khanzade: a five-level current-source inverter for grid-connected or high-power… fig. 5. switching pattern of csi and vsi devices. +/6 corresponds to point b in figure 2a. fig. 6. csi and vsi equivalent circuits for: (a) normal conduction before commutation between phases ‘a’ and ‘c’ starts, (b) mode 1, (c) mode 2 and (d) mode 3. fig. 7. waveforms related to commutation between phases ‘a’ and ‘c’, (a) icsia and icsic, (b) d1 and d2 currents and -icap, (c) vcap. in order to explain the operation of csi and vsi at commutation instants, consider switches s5 and s6 of the csi and t1 and t6 of the lci are conducting with the equivalent circuit shown in figure 6a and s1 is switched on at t=t0 (point b in figure 2a). thanks to the symmetrical operation of the circuit, we confine our analysis to one sixth of a cycle which can be divided into three operating modes. the equivalent circuits of these three modes and their corresponding waveforms are shown in figs. 6 and 7, respectively. in the following subsections, details are given on how forced commutation is obtained in the csi bridge using the vsi. the description includes mathematical details which are however required to obtain some practical dimensioning rules regarding capacitors cdc as well as vsi switches k1-k6 and d1d6. 1) mode 1 (t0<t<t0+s5, s6, k1 and k2 are conducting at t=t0, k1 and k2 are also switched on in addition to s1. according to the equivalent circuit of this interval shown in figure 6b and assuming that cdc is initially charged to vc0, capacitor voltage drives ic and icsic (ic=icsic) to decrease and ia and icsia (icsia=ia-ilcia) to increase (see figure 7a). since the command pulse is not removed from the gate of s5, the capacitor negative voltage prevents s1 to conduct. in this period, cdc is discharged (icap<0) via k1 and k2 as shown in figure 7c. by applying kirchhoff’s voltage law (kvl) in the loop shown in figure 6b, one can write: dt di lee dt di ldti c vv ccca a c t cap dc ccap   0 1 0 (1) and: 2 dc acsiavsiavsiccap ca dcbca i iiiii dt di dt di iiii   (2) in the above equations, )sin(2)( tetea  and )34sin(2)(   tetec where e and  are the rms value of the machine back emf’s and machine speed in electrical rad/sec, respectively. replacing (2) into (1) and making its derivative yields:   2 ) 3 sin(6 2 2 2 2 dc dc dcac dca a dcc i tec i dt eed ci dt id cl       (3) since the inductance current and capacitor voltage cannot go any discontinuity, their value must be equal for t=t0 and t=t0 +. thus, ia is equal to idc/2 for t=t0 +. also, cdc is charged to vc0 at t=t0 and, consequently, the initial condition for the derivative of ia is obtained according to (1) as:   )4( 2 ) 3 cos(6 2 00 0 0 0 c c c ttcac tt a l tev l eev dt di          according to these initial conditions, the final expression: engineering, technology & applied science research vol. 6, no. 5, 2016, 1139-1148 1143 www.etasr.com mohamadian and khanzade: a five-level current-source inverter for grid-connected or high-power… for ia(t) in (3) is:     )5())(cos( 2 ))(sin( 2 ) 3 cos(6 ) 3 sin())(sin() 3 cos( ))(cos() 3 sin( 1 6 0 0 00 00 002 tt itt l tev tttt ttt ec ti dc c c dc a                               where, dcc cl21 . if the variations of ia(t) during this mode occurs rapidly in relation to the rate of variations of the back emf’s, the expression ec(t)-ea(t) in (1) and (3) can be treated as a constant equal to its value at t=t0. therefore, (3) is simplified as: 2 2 2 2 dc a a dcc i i dt id cl  (6) and the simplified expression for ia during this mode is determined as:   2 ))(sin( 2 ) 3 cos(6 0 00 dc c c a i tt l tev ti         (7) this period ends at t=t0+where, t0+is considered as the instant in which ia(t) is increased to 3idc/4 and ic(t) is decreased to about idc/4. in other words, approximately half of the energy stored in phase ‘c’ inductance in addition to a fraction of energy stored in cdc are transformed to phase ‘a’ to increase its current from idc/2 to 3idc/4. 2) mode 2 (t0+<t<t0+2s1, s6, d1 and d2 are conducting at t=t0+, k1, k2 and s5 are switched off and s1 which has received its gating pulse at t=t0 can now conduct. the equivalent circuit for this interval is shown in figure 6c. in this period, diodes d1 and d2 produce a free-wheeling path to avoid discontinuity in current ia and ic as shown in figure 7b. therefore, the remaining phase ‘c’ inductive energy is gradually discharged into phase ‘a’ and cdc and increases ia and vcap as shown in figs. 7a and 7c. since the operation of the circuit is repeated every one-sixth of the motor operating frequency, vcap and ia reach vc0 and idc, respectively, at the end of this period. similar to mode 1, kvl equation of (1) holds also for this mode. the only difference is in the vsi currents direction. according to the equivalent circuit shown in figure 6c, one can write: dcaccsicvsicvsiacap ca dcbca iiiiiii dt di dt di iiii   (8) replacing (8) into (1) and making its derivative yields:   dcdc dc ac dca c dcc itec i dt eed ci dt id cl     ) 3 sin(6 2 2 2   (9) for simplicity, we can assume that the ia increment from 3idc/4 to idc in mode 2 takes the same time as its increment from idc/2 to 3idc/4 in mode 1. therefore, (9) can be solved as in (10) knowing that ia is equal to 3idc/4 at t=t0+ and idc at t=t0+2.       )10())2(sin( )sin(4 ) 3 sin( 1 6 ))(sin() 3 )2(sin( ))2(sin() 3 )(sin( 1 6 )sin( 1 02 00 002 dc dcdc dc a itt i t ec ttt ttt ec ti                             similar to (6), ec(t)-ea(t) can be considered as constant during mode 2 and ia in (10) can be simplified as:   dcdca i tti ti     )sin( ))2(sin( 4 0   (11) at t=t0+2,the voltage across cdc is equal to vc0 for reasons of symmetry accordingly, vcap has the following relation by writing kvl in the loop shown in figure 6c. 022 00 2 cttca a cttcap vee dt di lv          (12) therefore the expression for vc0 can be achieved by making derivative of (11) and replacing that into (12): ) 3 )2(cos(6 )sin(4 2 00         te il v dccc (13) 3) mode 3 (t0+2<t<t0+/3s1 and s6 are conducting commutation transient in the csi ends when ivsia and ivsic diminish to zero and the conducting diodes d1 and d2 turn off. the equivalent circuit for this mode is shown in figure 6d. thus, all the switches in the vsi will be in the off state until the next commutation between phases ‘b’ and ‘c’ in which s6 is turned off and s2 is turned on. iv. design considerations of the device components in this section, dimensioning of the vsi components is explained by taking a high-power wfsm, with the specifications listed in table i, as the load. this machine will be later utilized for simulation studies. starting from vc0 which is an important factor in dimensioning and cost of the dc-link capacitor, this value is a function of different parameters such as e, idc, , cdc and as indicated in (13). however, parameters e, idc and  in (13) can be extracted according to the different loading conditions of the machine as explained in [23] in which field-oriented control (foc) in stator flux reference frame is applied. among cdc and , only  can be controlled by the vsi. hence, we first keep cdc equal to a typical value such as 500 engineering, technology & applied science research vol. 6, no. 5, 2016, 1139-1148 1144 www.etasr.com mohamadian and khanzade: a five-level current-source inverter for grid-connected or high-power… f to study the effect of  on vc0. in figure 8, vc0 is plotted as a function of under different operating conditions, i.e. different values of idc, using (13). it is obvious from figure 8 that for shorter time duration , vc0 rises significantly. for instance, for rated loads where idc is around 1400 a, vc0 reaches to about 3000 v for  equal to 10 sec. as illustrated in figure 6 for the equivalent circuits of commutation intervals in csi, vc0 is superimposed across load terminals during commutation and is applied across the vsi switches during the non-commutating intervals. therefore,  must be set to higher values, e.g. higher than 50 sec, so that to have reasonable values for vc0. on the other hand, increasing  results in a longer conduction period for the vsi devices. as an example, in (14), the equation for the current flowing in k1 is given. in this equation, it is assumed that the current in k1 is linearly increased from 0 to idc/4 during the first commutation interval (+/6<t<+/6+) when turning s1 on and during the sixth commutation interval (+11/6<t<+11/6+) when turning s4 off (see figure 5).                otherwise ttttttt i ttttt i i dc dc k 0 3535 4 4 000 000 1   (14) where, t is the period of the motor quantities, i.e. voltages and currents. thus, the rms and average values of the current flowing in the vsi switches can be found according to (14) as in (15).   t i dti t i dc t kkrms  62 1 2 1     t i dti t i dc t kkave  4 1 1   (15) on the other hand, the dc-link current, idc/2, flows in the main switches (t1-t6 and s1-s6) for an interval of t/3 during a period. consequently, the rms and average values of the current in the main switches can be simply found equal to idc /(2 3 ) and idc/6, respectively. thus, ikrms and ikave can be normalized to those of the main ones as in (15). in figures 9a and 9b, iknrms and iknave are plotted, respectively, as a function of for different values of motor speed (=2/t). figure 9 shows that as increases the current rating of switches also increases. however, it can be seen that totally the current ratings of the vsi switches are small compared to those of the main switches. for instance, for motor rated speed (628 rad/sec or 100 hz) ikrms and ikave are around 5 and 1.1 percent of the rated current of the main switches, respectively, for  equal to 100 sec. the design criteria for the dc capacitor size cdc is the permissible voltage variations vdc=vc0-vc1 shown in figure 7c. vc1 in figure 7c is obtained as follows by replacing t=t0+ in (1) and using (2) as: ti t i i dc dc knrms 2 32 62    ; ti t i i dc dc kave   2 3 6 4  (16) substituting (7) into (16), vc1 will be equal to        0 21 ttca a cc ee dt di lv (17) in figure 10, vr is plotted as a function of cdc for different loading conditions. in this figure, cdc is ranged from 100 f to 1000 f and also a fixed value of 70 sec is considered for. according to figure 10, the dc voltage ripple is in an acceptable range for a wide variety of capacitor sizes and it reaches below 5 percent for cdc higher than 500 f. the highest ripple is 8.8 percent of vc0 for cdc equal to 100 f under the light load conditions. furthermore, cdc can affect the value of vc0 according to (13). in figure 11, vc0 is plotted as a function of cdc for the rated machine speed and current. it can be seen from this figure that vc0 decreases, but not significantly, as cdc is increased. to sum up, vc0 totally decreases as the time duration and cdc are increased. on the other hand, the devices current ratings increase as is increased. therefore, a simple compromise must be made in order to have the best dimensioning for the vsi components according to the load conditions. as mentioned previously, the only factor controlled by the vsi switching is the time duration. thus, this value can be treated as a proper constant, e.g. 70 sec for the machine and load specifications stated in table i, under different operating conditions. the ripple factor, vr , is determined in terms of the voltage variations vdc and vc0 as [22]: 0c dc r v v v   (18) table i. characteristic data of the wfsm. apparent power 1000 (kva) q-axis magnetizing inductance, lmq, 0.53 (mh) line-to-line voltage 570 (v) d-axis magnetizing inductance, lmd, 0.632 (mh) line current 1034 (a) *d-axis damper leakage inductance, llkd, 0.015 (mh) frequency 100 (hz) *q-axis damper leakage inductance, llkq, 0.024 (mh) number of poles 4 *field leakage inductance, llf, 0.050 (mh) stator leakage inductance, lls, 0.07 (mh) commutation inductance, lc, 0.087 (mh) * rotor quantities are referred to the stator. engineering, technology & applied science research vol. 6, no. 5, 2016, 1139-1148 1145 www.etasr.com mohamadian and khanzade: a five-level current-source inverter for grid-connected or high-power… fig. 8. vc0 as a function of  under different operating conditions (cdc=500 f). fig. 9. current ratings of vsi switches as a function of  for different motor speeds (cdc= 500 f) , (a) iknrms and (b) iknave. fig. 10. dc capacitor voltage ripples as a function of cdc (=70 sec). fig. 11. vc0 as a function of cdc (=70 sec) for rated operating condition. v. simulation results in this section, dynamic model of the wfsm with the specifications highlighted in table i in rotor d-q reference frame is implemented in matlab/simulink software [24] and the proposed five-level csi is utilized to drive the machine. the results are compared with those of a three-level counterpart. foc in stator flux reference frame [23] is also used as the drive strategy. in the simulations, cdc andare considered equal to 500 f and 70 sec, respectively. also, the dc-link inductance, ldc in figure 1, is equal to 20 mh. this section is divided into two subsections. in the first subsection, the results are shown for normal operating conditions and in the second part, the performance of the proposed inverter is studied during starting of the machine which can be an important issue in the case of conventional lci-fed wfsm drives. a. normal operatind condition in figure 12, machine stator phase ‘a’ current and voltage waveforms are shown when the machine is supplied from the proposed converter scheme and running at the speed of 2100 rpm (70 hz). the firing angle of the thyristors is set to 165̊. in the resultant five-level waveform of the current, the phase shift between fundamental components of phase current and voltage,  in figure 2, is equal to /12. therefore, unity power factor operation (upf) for the fundamental components of the stator phase current and voltage is almost achieved that can be also concluded from figure 12. from figure 12, two types of distortion are observable in the stator phase voltage: voltage notches which are due to the load commutation in lci and voltage spikes which are produced during the commutation instants in csi. the depth and duration of the voltage notches depend upon thyristors firing angle,  in figure 2, dc-link current, idc/2, commutation inductance, lc, motor speed, , and back emf. in addition to these parameters, voltage spikes are also affected by the time duration. as  increases the current variation rate and, consequently, the voltage spikes are decreased at the cost of increased vsi rating. dc capacitor voltage, vcap, is shown in figure 13. it is evident from the figure that ripple factor, vr, is limited to less than 3 percent by using a capacitance of 500 f. on the other hand, the drive system is simulated under the same conditions, i.e. same motor speed and load torque, in which wfsm is being fed from the conventional three-phase lci. the motor phase current and voltage waveforms are shown in figure 14; where, the maximum allowable firing angle, , for the thyristors is equal to 157̊ for safe commutation. this means that lci (figure 2) is equal to 23̊ which is much higher than  (figure 2) equal to zero in the case of five-level converter. thus, one can expect lower field current and, consequently, lower field losses in the proposed drive. this fact is shown in figure 15 where the field current waveforms for both converters are compared. furthermore, fast fourier transform (fft) analysis of the current waveforms shows that the current thd is remarkably decreased for five-level converter. in table ii, the amplitude of the current dominant harmonic components is normalized to the amplitude of the fundamental component for both five-level (figure 12) and three-level (figure 14) current waveforms. according to table ii, the fifth and seventh harmonic components are reduced significantly for the proposed converter. these harmonic components are mostly responsible for the machine large electromagnetic torque pulsations featuring six times the operating frequency. in figure 16, machine electromagnetic torque is depicted for both five-level engineering, technology & applied science research vol. 6, no. 5, 2016, 1139-1148 1146 www.etasr.com mohamadian and khanzade: a five-level current-source inverter for grid-connected or high-power… and three-level stator current waveforms. this figure indicates that lower level of current harmonic distortion yields in lower torque pulsations in the case of proposed drive. fig. 12. stator phase ‘a’ current and voltage waveforms when the machine is supplied from the five-level current-source inverter (=2100 rpm, idc/2=445 a, cdc=500 f and =70 sec). fig. 13. vcap in the proposed five-level current-source inverter (=2100 rpm, idc/2=445 a, cdc=500 f and =70 sec). b. start-up dc-link pulsing method is widely used in industrial lcifed wfsm drives such as gas turbine starters [7] to control the machine during starting as well as at low-speed operation (≤10%). however this method generates pulsating current and torque with a reduced average torque. on the contrary, the proposed converter is also beneficial in start-up and at lowspeed operation of the machine. for these conditions, the firing pulses are not released for thyristors in lci and the csi and voltage clamping vsi (figure 1) are switched according to the procedure explained in subsection iii.b. consequently a threelevel current waveform is available for the stator phase currents. in figure 17, simulation result for the stator phase current is shown when the machine is fed from the csi and running at the speed of 90 rpm (0.03 pu). for comparison, figure 18 shows the simulation result in which the machine is supplied from lci and dc-link pulsing method is utilized for the same loading conditions. the interruptions in the stator phase current are due to the zero intervals in the dc-link current which must be applied every sixty electrical degrees, because the commutation are taken place every one-sixth of the period (see figure 3). these interruptions reduce the active power for the same dc-link current, idc, comparing to the case in which the machine is fed from the csi. thus, the output of the speed controller, idcref, will be higher in the dc-link pulsing method for the same load torque. also, the interruptions produce notches in the electromagnetic torque which can be detrimental for mechanical parts specifically for the drives with intermittent startings. in figure 19, the resultant torque waveforms are shown for both cases. a much smoother torque for low-speed operation is observable from the proposed drive scheme. fig. 14. stator phase ‘a’ current and voltage waveforms when the machine is supplied from the conventional three-level lci (=2100 rpm, idc=850 a). fig. 15. field current of wfsm (=2100 rpm). fig. 16. electromagnetic torque of wfsm (=2100 rpm). table ii. phase current fundamental, afi , and harmonic components as a percentage of afi for the proposed csi and conventional lci (=2100 rpm). iaf (a) ia5 (%) ia7 (%) ia11 (%) ia13 (%) thd (%) five-level csi 953 8.35 0.34 6.97 6.12 14.11 conventional lci 931 18.22 11.88 5.57 3.81 23 vi. discussions and comparison with other multilevel csi structures so far, several multilevel csi configurations are presented in literature for motor drive applications, most of them utilizing pwm techniques as their switching strategy. on the other hand, to the best of authors’ knowledge, there is only [25] that has focused on the multilevel csi-fed induction motor drive in which the power electronic devices are switched at the machine working frequency. in [25], a multilevel current waveform is obtained for the machine stator current by adding the output currents of one lci and one csi. a three-phase capacitor bank is considered at the machine terminals to generate the leading power factor for the natural commutation of the lci switches. on the other hand, in order to minimize the size of the capacitor bank a phase-shift of 60 degrees is computed to be considered between the lci and csi output currents. with this phase-shift, a four-level current waveform is obtained with a thd of approximately 24% (see figure 2b) while it is around 10% in the proposed five-level csi (it should be mentioned that in figure 2b only the 5th and the 7th harmonic components engineering, technology & applied science research vol. 6, no. 5, 2016, 1139-1148 1147 www.etasr.com mohamadian and khanzade: a five-level current-source inverter for grid-connected or high-power… are taken into account and the dc-link current is assumed to be smooth). despite several advantages of the proposed multilevel csi configuration in the wfsm drive system, there are few limitations regarding the vsi switches. although the current rating of the vsi switches is much lower than that of the csi and the lci switches, the vsi devices conduct the dc-link current during the commutation periods of csi. thus, attention is required to select the devices which can tolerate surge currents equal to the dc-link current value at rated operating conditions. fig. 17. stator phase current when the machine is supplied from csi and lci is turned off during start-up or low-speed operating conditions (f = 3 hz, idcref=38 a, cdc=500 f, =70 sec). fig. 18. stator phase current when the machine is supplied lci and dc-link pulsing method is applied (f = 3hz, idcref=48). fig. 19. machine electromagnetic torque (f = 3hz). vii. conclusion this paper proposes to add a csi, which is switched at machine operating frequency, to the conventional three-phase lci’s to improve the characteristics and performance of the high-power lci-fed wfsm drives. to avoid large voltage spikes at the commutation instants, a voltage clamping circuit is used. accordingly, a five-level waveform for the output current is acquired. lower harmonic distortion of the output current results in lower torque pulsations and lower harmonic losses of the windings comparing with the conventional lci’s. also, the air-gap flux will be less distorted which yields in lower iron losses. furthermore, unity power factor operation is achieved for a wide range of machine speed, thus, decreasing the field current and its consequent losses. moreover, torque notches produced by the dc-link pulsing method at start-up and at low speeds are removed by the introduced converter. references [1] b. wu, j. pontt, j. rodríguez, s. bernet, s. kouro, “current-source converter and cycloconverter topologies for industrial medium-voltage drives”, ieee trans. ind. electron., vol. 55, no. 7, pp. 2786–2797, 2008 [2] q. wei, b. wu, d. xu, n. r. zargari, “a natural-sampling-based svm scheme for current source converter with superior low-order harmonics performance”, ieee trans. power electron., vol. 31, no. 9, pp. 61446154, 2016 [3] y. zhang, y. w. li, “investigation and suppression of 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[25] s. kwak, h. a. toliyat, “multilevel converter topology using two types of current-source inverters”, ieee trans. ind. appl., vol. 42, no. 6, pp. 1558-1564, 2006 microsoft word etasr_v13_n4_pp11387-11392 engineering, technology & applied science research vol. 13, no. 4, 2023, 11387-11393 11387 www.etasr.com zahid & al-zaidee: validated finite element modeling of lightweight concrete floors stiffened … validated finite element modeling of lightweight concrete floors stiffened and strengthened with frp manar zahid department of civil engineering, college of engineering, university of baghdad, iraq manar.ali2001m@coeng.uobaghdad.edu.iq (corresponding author) salah al-zaidee department of civil engineering, college of engineering, university of baghdad, iraq salah.r.al.zaidee@coeng.uobaghdad.edu.iq received: 22 may 2023 | revised: 9 june 2023 | accepted: 16 june 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.6055 abstract the main challenge in designing light-weight concrete (lwc) is to adapt most of the design, production, and execution rules from normal-weight concrete. carbon fiber-reinforced polymer (cfrp) composites provide strength and stiffness to the composite system. this study investigated the stiffness of an lwc flat slab with cfrp when subjected to human-induced vibration. this was determined by finding the natural frequency of the slab and comparing it with the acceleration limit ratio (human perception of vibration) of 0.5% g. in most cases, vibration characteristics are examined using commercial software based on finite element analysis (fea) methods that are powerful tools, but the user needs to understand the underlying assumptions and methods implemented, especially for reinforced concrete floor systems where inherent attributes, such as cracking, play an important role in the determination of vibration characteristics. this study used abaqus cae. the main idea of this study was that such software cannot detect the behavior of cracks in structures over the years and the effect on frequencies, as stiffness depends on the modulus of elasticity and not on the moment of inertia. therefore, the natural frequency equation has a component that constantly accounts for the level of cracking on concrete slabs. this component was theoretically determined with detailed calculations that are not provided in the design guide for vibrations of reinforced concrete floor systems. then, the constant that accounts for the level of cracking k1 was multiplied by the modulus of elasticity e and substituted in the latter's place in abaqus to ensure the right behavior of the slab with and without cfrp. this study also investigated the properties of cfrp and how to represent it in the abaqus. the numerical results showed good agreement with fea and the acceptance criteria for walking excitations increased when using cfrp on a floor system. keywords-light weight concrete; validation; frp; floor stiffness i. introduction since the 1990s, engineers and researchers have been aware of the advantages of combining concrete with frp materials, as concrete aids in compressive resistance and stability and fiber reinforced polymers (frps) provide tensile resistance [1]. this study considered a slab with and without frp stiffening. a preliminary finite element model (fem) was prepared for the slab considered but with normal-weight concrete in the design guide for vibrations of reinforced concrete floor systems [2]. this model was validated by comparing its results with the semi-empirical results of [2]. subsequently, the validated model was adopted to show how light-weight concrete (lwc) and cfrp affect the vibrational aspects of the slab. there are many advantages to having low density, as it helps reduce dead load, increases building progress, and reduces transportation and handling costs [3]. also, by reducing the cross sections of the components, there is an increase in the demand for lwcs in many modern architectural constructions [4]. figure 1 shows the flat plate reinforced concrete system considered in this study. for validation purposes, the indicated dimensions were the metric equivalent of the corresponding customary united states dimensions in [2]. the design guide for vibrations of reinforced concrete floor systems was written with two objectives. it aimed to support structural engineers in selecting a suitable reinforced concrete floor system subjected to human-induced vibration and to present simplified approaches on estimating the vibration characteristics of reinforced concrete floor systems that can be used to evaluate whether the anticipated vibration is acceptable or not, by computing the natural frequency and comparing it with the ratio aspects. engineering, technology & applied science research vol. 13, no. 4, 2023, 11387-11393 11388 www.etasr.com zahid & al-zaidee: validated finite element modeling of lightweight concrete floors stiffened … (a) (b) (c) (d) fig. 1. flat plate system details: (a) 3d view, (b) top view, (c) longitudinal section, (d) cross section. the peak acceleration as a fraction of the acceleration of gravity ap/g is less than or equal to the acceleration limit a0/g for the appropriate occupancy, as shown in (1) and (2), respectively. the natural frequency is the quantity of the floor system's response to the sources that can cause vibration and is related to how occupants will perceive such vibrations. many methods and resources are available to determine this property. �� � ���� � � �� � �� �� � ���������� � �⁄ (1) �� � � ����� .�"#$� %& ' �° � (2) service bending moments were taken from table v from the guide of normal weight concrete [2]. a. finite element analysis fem is useful in providing the overall performance of structurally reinforced concrete. it also provides a reasonable prediction of the loading capacity and crack formation, but realistic fracture conditions, such as crack patterns, are difficult to obtain [5]. the three-dimensional finite element analysis (fea) of the flat plate system can be achieved using abaqus [6], as it is one of the leading finite element packages, notwithstanding the quality of the pre and postprocessing capabilities. abaqus consists of abaqus standard and abaqus explicit for dynamic analysis. abaqus cae (complete abaqus environment) is used for data input for fea and allows monitoring and viewing of the results through an input file prepared with a text editor. b. walking-induced vibration of flat plate system there are important requirements in designing building structures related to people's sensitivity to a vibration that is the comfort of building occupants and safe building conditions. the dynamic response of a building loaded with dynamic loads requires finding the response. one of the responses is that human activities such as walking or jumping can cause strength much greater than their body weight [7]. c. upgrading the flexural capacity of slabs the main cause of damage is that the flexural capacity cannot meet the demand. fiber-reinforced plastics (sheets or laminates) are externally attached to the slab at the top or bottom surface (positive or negative bending moment demand). such a scheme was used to upgrade the seismic capacity of the slabs of a four-story r/c building built in 1933, subjected to the 1995 earthquake in kozani, greece [8]. vibration measurement has been proven to be promising in structural health monitoring (shm). this scheme is used to study the behavior of structures, such as vibrations and damage, by evaluating the natural frequency and other dynamic parameters [7] using the properties of the model of table vi after converting the units to n/mm and assuming the length of the column to be 3 m, as shown in figure 2. ii. carbon fiber reinforcement polymer a. overview carbon fibers, also called graphite fibers, are lightweight and strong fibers with excellent chemical resistance. they dominate the aerospace market and are considered an orthotropic material [9]. cfrp composites are extremely stiff and brittle and susceptible to galvanic corrosion. their use in field applications has grown since the late 1980s due to their low cost and importance in strengthening improperly or insufficiently designed structural elements, especially in seismic areas [10]. the use of cfrp strengthening techniques improves the stiffness and flexural strength of rc members and reduces crack spacing and crack width [11]. b. orthotropic material an orthotropic material has three planes of symmetry, as shown in figure 2, which coincide with the coordinate planes. engineering, technology & applied science research vol. 13, no. 4, 2023, 11387-11393 11389 www.etasr.com zahid & al-zaidee: validated finite element modeling of lightweight concrete floors stiffened … a unidirectional fiber-reinforced composite can be considered orthotropic. one plane of symmetry is perpendicular to the fiber direction, and the other two can be any pair of planes parallel to the fiber direction and orthogonal among themselves. only nine constants are required to describe an orthotropic material: e1, e2, e3, g12, g13, g23, v12, v13, and v23 [9]. fig. 2. orthotropic material. c. mechanical properties the modulus of elasticity value of carbon fibers is approximately 240 gpa [8]. based on modulus and strength, carbon fibers can be divided into [8]:  ultra-high-modulus (uhm) for > 450 gpa  high-modulus (hm) between 350-450 gpa  intermediate-modulus (im) between 200-350 gpa  super high-tensile (sht) for tensile strength > 4.5 gpa in the mechanics of materials, both fibers and matrix are assumed to be isotropic. isotropic material stiffness is completely represented by two properties: modulus of elasticity and poisson's ratio. using micromechanics, the combination of two isotropic materials, fiber and matrix, is represented as an equivalent, homogeneous, and anisotropic material [9]. the stiffness of the equivalent material is represented by five elastic properties: e1 is the modulus of elasticity in the fiber direction, e2 is the modulus of elasticity in the direction transverse to the fibers, g12 is the in-plane shear modulus, g23 is the out-ofplane shear modulus, and v12 is the in-plane poisson's ratio. table i. material properties of the lamina [13]. e1 e2 e3 g12 g13 g23 v12 v13 v23 131.9 9.51 9.43 5.27 7.03 3.39 0.326 0.341 0.485 in general, all types of frp exhibit high tensile strength and low density and are non-corrosive [12]. cfrp composites are very durable, have excellent fatigue properties, and can withstand most environmental conditions. many challenges prevent the additional growth of the frp market. some of these challenges are the brittle failure of frp-strengthened rc structures due to sudden failure modes such as frp rupture or debonding, deterioration of the mechanical properties due to harsh environmental conditions such as wet-dry cycles and freeze-thaw conditions, reduction in strength due to the effects of improper installation procedures, and lack of agreement among debonding behavior and bond length models [10]. iii. values in abaqus a. part module three main parts were defined for the concrete, longitudinal rebars, and cfrp: solid extrusion, wire planar, and shell planer, respectively. b. property module three sections were defined, where solid and homogeneous were defined and assigned to the concrete mass and two truss sections were defined and assigned to the longitudinal rebars and stirrups. for concrete, the values of young's modulus and poisson's ratio of 6713.8 and 0.2 were inserted, respectively. the e with the effect of crack was: )* � +� × -*�.� × 0.0431�* = 0.54 × 1440�.� × 0.043 × √28 = 6713.8 :;< table ii shows the values inserted for cfrp. table ii. values inserted for cfrp e1 e2 nu12 g12 g13 g23 170000 9000 0.34 4800 4800 4500 iv. steel reinforcement of slab the maximum spacing of the main bar of the slab must be at least 300 mm or three times the effective depth, and the maximum spacing of the distribution bar of the slab must be at least 450 mm or five times the effective depth. meanwhile: )��=*>?@= a=b>ℎ = 150 − 20�*e@=f� − g102 h �f=?i. � = 125jj therefore, the spacing used was 300 mm in two ways. v. dynamic loads generated by human activities the dynamic loads generated by human activities can be grouped into two types according to the person-structure interaction. the first is when there is a loss of contact with the structure, such as running and jumping, and the second is when there is no loss of contact with the structure, such as walking. a human being produces a dynamic load during walking or running that can be represented by a force that varies in time with components in three directions: vertical, lateral, and frontal. the vertical component is the most investigated because it presents greater amplitudes compared to the others. this dynamic force is produced by the acceleration and deceleration of the body mass. for walking, its frequency range has been stated to be between 1.6 and 2.4 hz. although there has not been the same comprehensive investigation for running or jumping activities, the typical frequency range for running is considered 2.0 to 3.5 hz while for jumping it is 1.8 to 3.4 hz [1]. people are exposed daily to vibrations on floor slabs or on footbridges caused by different sources of excitation. the evaluation of human sensitivity to these vibrations involves psychological and physical aspects. human-induced vibrations can cause serviceability problems and discomfort to users. the main factors that influence human sensitivity are position, such as standing, sitting, or lying, and the type of activity that engineering, technology & applied science research vol. 13, no. 4, 2023, 11387-11393 11390 www.etasr.com zahid & al-zaidee: validated finite element modeling of lightweight concrete floors stiffened … depends on age, gender, mood, vibration frequency, displacement amplitudes, damping, and finally the acceleration of dynamic excitation [1]. the natural frequency of two-way reinforced concrete floor systems can be obtained using some fundamental concepts in plate theory. the simplifying assumptions made in the following discussion enable the natural frequency to be determined straightforwardly and consistently for all two-way systems [2]. assume that a reinforced concrete flat plate or a voided slab system can be modeled as a rectangular, isotropic plate where the primary vertical deflection is due to flexure. since the slab is supported only by columns, it is free to deflect at any point except at the locations of the columns, where it is generally assumed that vertical displacements are negligible and that rotations are not restricted. equation (1) can be used to determine the natural frequency fi, which applies to rectangular plates with corner supports. �� = ���� � � �� � �� ������������� � �⁄ (1) where h is the total thickness of the flat plate or voided slab, γ is the mass per unit area of the plate, v is the poisson's ratio, l1 is the longest of the two center-to-center span lengths of the plate panel, and n?2 is a function of the panel aspect ratio l1/l2. table iii shows the values of n?2 for the fundamental mode of vibration. in [13-15] there are values of this parameter for other modes and panel aspect ratios. table iii. values of n�� for a corner-supported, rectangular plate [2]. l1/l2 opq 1.0 7.12 1.5 8.92 2.0 9.29 the constant k2 accounts for the effect of rigidity at the joint between the slab and the columns, which are cast monolithically in typical reinforced concrete structures. column size has a direct impact on joint rigidity: the larger the column size, the greater the slab stiffness and fundamental frequency. instead of a more exact analysis, the following are approximate values of k2 that can be used in (1) and are based on column size c1 [16]: +� = r1.9 �ef *� ≤ 24 ?i.2.1 �ef *� > 24 ?i (3) where the constant k1 accounts for the level of cracking in the concrete slab and can be determined by dividing the effective moment of inertia ie by the gross moment of inertia ig. when k1 is less than 1.0, the stiffness of the slab is less than the gross stiffness, and the natural frequency of the system is reduced [2]. for a flat plate, ie for a panel is approximated by adding the average ie of the column strip in one direction to the average ie of the middle strip in the orthogonal direction. the average ie for the column and middle strips is used to take into account positive and negative regions in the strips. the following equation is applicable for square panels that have both ends continuous [17]: u@=f<v= w� = 0.7wx + 0.15�w�� + w�� � (4) where im refers to ie at the midspan section and ie1 and ie2 refer to ie at the end sections of the panel [2]. for a rectangular panels system, ie for a panel is approximated by taking the average of the average ie values in the column strips (cs) and middle strips (ms) in both the x and y directions: w � z[\ ]�� ^�_� = `ab �c deab fc ghe`ab �c geab fc dh� (5) in (4), the effective moment of inertia ie can be determined for sections with relatively low reinforcement ratios. the contribution of shrinkage restraint to cracking should also be considered in such systems. to account for this effect, the use of a two-thirds factor applied to mcr was recommended in [18], which is equivalent to using a reduced modulus of rupture �\ = 5.01� ij , while in [19] it was proposed using �\ = 4.01� ij to determine ie. w � = a�k ��lm�kmn o � p��q�kqr s ≤ w� (6) a reduced modulus of rupture �\ = 4.5n1�*′ was adopted for vibration analysis in [2] for flat plate and voided slab systems. a. flat plate system walking excitation an existing flat floor system residential building will be converted into an office building. the vibration of the system was evaluated assuming normal occupancy of the office. table iv shows the design data. it was also assumed that the office space will have some non-structural components [2]. notice that wc = 1440 kg/m 3 for lwc. table iv. design data [2] concrete compressive strength f’c= 4,000 psi f’c= 28mpa density w = 150 pcf reinforcing steel yield strength fy=60,000 psi fy = 412mpa loads superimposed dead load = 20 psf live load (design) = 65 psf (includes partition) live load (vibration) = 11 psf spans typical bay: 25'–0"×20'-0 7620×6096mm members sizes slab thickness hi= 9.5" hs = 240mm columns 22"×22" 560×560mm b. determination of concrete properties the modulus of elasticity is determined as: )i = ui�.� 331 �′i (7) avi<j?* )* = 1.2)* :ewxy<f f<>?e i = c�.� � = 29000000/2138400 = 13.6 c. determination of the bending moments at the critical sections for a typical interior bay since the limitations of aci 13.6.1 are satisfied, the direct design method can be used in the bending moment determination at the critical negative and positive sections in the column and middle strips along the span. the bending moments are determined by calculating the total static moment in each direction and then applying the appropriate coefficients given in aci 13.6.3. table v gives a summary of the service engineering, technology & applied science research vol. 13, no. 4, 2023, 11387-11393 11391 www.etasr.com zahid & al-zaidee: validated finite element modeling of lightweight concrete floors stiffened … bending moments. it was assumed that the 25-foot span is in the north-south direction [2]. fig. 3. dimensions of cs and ms. table v. service bending moments (ft-kips) [2] north-south east-west column strip middle strip column strip middle strip negative d 91.2 29.8 70.1 22.9 l 42.7 14.0 32.9 10.7 positive d 39.1 26.1 30.1 20.0 l 18.3 12.2 14.1 9.4 d. determination of the required flexural reinforcement table vi shows the required flexural reinforcement. the provided area of steel is set equal to the minimum area of steel where required and the sections in all cases are tension controlled [2]. table vi. required flexural reinforcement (in2) [2] north-south east-west column strip middle strip column strip middle strip negative 5.39 2.05 4.15 3.08 positive 2.31 2.05 2.05 3.08 e. determination of the effective moments of inertia ie and the crack coefficient k1. the effective moment of inertia of the column and middle strips is determined using (7). for this floor system with rectangular panels, ie for the panel is determined by (4), where the average of the average ie values in the column strips (cs) and middle strips (ms) in both directions are used. detailed calculations are provided below for the section containing the negative flexural reinforcement in a column strip in the northsouth design strip. calculations for the other sections are similar [2]. for a column strip width of 10 ft, the section properties yt and ig are 4.75 in and 8574 in 4 , respectively. ie can be determined by: <� = i[ {x_ |]\�^ &�}]�_~c (8) +w = 1�}��e����� (9) wi\ = ��[ {x_ |]\�^ &�}]���} � � + iu��w − +w�� (10) :i\ = zkar�� (11) w� = a�k ��lm�kmn o � p��q�kqr s ≤ w� = ���� ��l ��.���.�� ��.�o ����� ���"��� = 3160 in� (12) similarly, ie = 2071 in. 4 for the positive section in this column strip. using (5), the average ie for this column strip in the north-south direction is ie|cs,n-s = (0.7×2071) + 0.15 (2×3160) = 2398 in. 4. the average ie for the middle strip in the north-south direction and the column and middle strips in the east-west direction are determined by (7) similarly: ie|ms,n-s = 3126 in. 4 , ie|cs,e-w = 2546 in. 4 , and ie|ms,e-w = 12861 in. 4 . the effective moment of the panel is determined by (6) as ie/panel = 10466 in. 4 . the gross moment of inertia of the panel is averaged in the same way as the effective moment of inertia: w�|��� = w�|i|,��� + w�|x|,��� = 17148 ?i.� w�| �� = w�|i|, �� + w�|x|, �� = 21435 ?i.� w � ^�_� ⁄ = 19292 ?i.� the constant k1 accounts for the level of cracking in the slab and is determined by dividing the effective moment of inertia of the panel by the gross moment of inertia of the panel +� = ���������� = 0.54. f. determination of the natural frequency. the fundamental frequency for a flat plate floor system is estimated by (1). the quantities in this equation that have not been previously determined are as follows [2]:  k2 = 1.9, since the column is less than 24 in.  n�� = 8.02 by linear interpolation from table iii for l1/l2 = 1.25.  mass = 1587.7 lb  γ = 3.175 slugs/ft 2 therefore, �� � �.� × �.�� � × ��� � �.��×��������� ×��.�/���� ��×�.�������.��� � � �⁄ � 5.83 hz. for comparison purposes, an fea was performed to determine fi for this flat plate system. using the nonlinear option which includes the effects due to cracking, fi was found to be 8.7 hz with a crack coefficient equal to 0.71. the crack coefficient was determined by dividing the maximum deflection obtained from the elastic analysis by the deflection from the inelastic analysis of the system. thus, the simplified method yielded a conservative estimate for fi, approximately a 10% difference [2]. engineering, technology & applied science research vol. 13, no. 4, 2023, 11387-11393 11392 www.etasr.com zahid & al-zaidee: validated finite element modeling of lightweight concrete floors stiffened … vi. results and discussion according to (2), a floor system is satisfactory if the peak acceleration as a fraction of the acceleration of gravity ap/g is less than or equal to the acceleration limit a0/g for the appropriate occupancy [2]. for an office occupancy, the damping ratio β can be taken as 0.03 for offices that have some nonstructural components but no full-height partitions. thus, �� � � ����� .�"×".��� �.�� ×����� � 0.0055 for fi calculations without cfrp, and �� � � ��� �� .�"×�.��� �.�� ×����� � 0.00487 for fi from abaqus with cfrp. fig. 4. fi calculation with cfrp fig. 5. fi calculation without cfrp. vii. conclusion after detailed calculations for the natural frequency according to [1], it was cleared that the natural frequency of the lwc flat plate without frp is higher than the frequency applied due to human activities, while for walking excitations, ap is approximately equal to 0.55% of g. this acceleration is more than the acceleration limit a0, which is equal to 0.50% of g for office occupancies [2]. on the other hand, the natural frequency of an lwc flat plate with cfrp in fem is 0.487%. therefore, this flat plate system is satisfactory for walking excitations (human perception of vibration) only with cfrp, which is useful in increasing the stiffness and strength of concrete structures. it should be noticed that this lwc satisfied the strength limits even without frp. references [1] p. junges, h. l. l. rovere, and r. c. de a. pinto, "vibration analysis of a composite concrete/gfrp slab induced by human activities," journal of composites science, vol. 1, no. 2, dec. 2017, art. no. 11, https://doi.org/10.3390/jcs1020011. 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[20] "c331/c331m standard specification for lightweight aggregates for concrete masonry units," american society for testing and materials, west conshohocken, pa, usa, standard astm c331/c331m, 2017. microsoft word etasr_v13_n1_pp10192-10198 engineering, technology & applied science research vol. 13, no. 1, 2023, 10192-10198 10192 www.etasr.com reffad et al.: a dynamic adaptive bio-inspired multi-agent system for healthcare task deployment a dynamic adaptive bio-inspired multi-agent system for healthcare task deployment hamza reffad lrsd, faculty of technology, technology department, university ferhat abbas sétif 1, algeria hamza.reffad@univ-setif.dz (corresponding author) adel alti lrsd, faculty of sciences, computer science department, university ferhat abbas sétif 1, algeria alti.adel@univ-setif.dz ahmed almuhirat department of management information systems, college of business & economics, qassim university, saudi arabia a.almuhirat@qu.edu.sa received: 16 december 2022 | revised: 30 december 2022 | accepted: 3 january 2023 abstract the use of the internet of things (iot) in healthcare is increasing significantly, bringing high-quality health services, but it still generates massive data with massive energy consumption. due to the limited resources of fog servers and their impact on limiting the time needed for health data analysis tasks, the need to handle this problem in a fast way has become a necessity. to address this issue, many optimization and iot-based approaches have been proposed. in this paper, a dynamic and adaptive healthcare service deployment controller using hybrid bio-inspired multi-agents is proposed. this method offers optimal energy costs and maintains the highest possible performance for fog cloud computing. at first, igwo (improved grey wolf optimization) is used to initialize the deployment process using the nearest available fog servers. then, an efficient energy-saving task deployment was achieved through particle swarm optimization (pso) to reduce energy consumption, increase rewards across multiple fog servers, and improve task deployment. finally, to ensure continuous control of underloaded and overloaded servers, the neighborhood multi-agent coordination model is developed to manage healthcare services between the fog servers. the developed approach is implemented in the ifogsim simulator and various evaluation metrics are used to evaluate the effectiveness of the suggested approach. the simulation outcome proved that the suggested technique provides has better performance than other existing approaches. keywords-iot; multi-agent; energy consumption; pso; grey wolf optimization; fog-cloud i. introduction we live in the era of the digital healthcare revolution. every day, healthcare organizations generate billions of gigabytes of data from various sources of information such as medical sensors (iot), social networks, telemedicine, etc. for this reason, data production and energy consumption are growing dramatically [1]. for example, a smart hospital consists of different actors (i.e. physicians, patients, and nurses) with various smart devices (i.e. smartphones, tablets), exchanging different health-related data (temperature and humidity levels, user glucose, user movement state, etc.), analysis results, and technical reports throughout various health services. due to the explosion of services and massive energy consumption, the need to handle a large number of healthcare services and minimize their energy consumption increases sharply. nowadays, most developers focus on improving healthcare task scheduling with optimum cost and reduced execution time. interesting service configurations have been produced, satisfying the user requirements, but without considering the change of their needs and the incoming loads of applications on the limited resources of devices. on the other hand, a great deal of data is collected through many different devices (wearables, medical/vital monitors, smartphones, etc.) and their heterogeneity is related to the type of data (text, video, image, sound) or the type of service such as healthcare services (glucose level, heart beating, etc.), spatiotemporal services (location, time, etc.), and social services (facebook, twitter, etc.). all these factors make service management more complex, and their placement is certainly very difficult [2]. thus, many researchers work on service placement through a deployment component called service controller. they aim to deploy service on external data engineering, technology & applied science research vol. 13, no. 1, 2023, 10192-10198 10193 www.etasr.com reffad et al.: a dynamic adaptive bio-inspired multi-agent system for healthcare task deployment centers, build deployment scripts, and dynamically deploy it to the desired data centers [3]. cloud computing is an interesting solution to efficiently deploy large candidate services. it allows interconnecting and integrating iot devices and fogs according to the current services and users’ needs. besides, it is essential to know that the deployment of service is not a standardized solution. it can vary according to specific needs [4]. for this reason, service controllers must use advanced and intelligent techniques to deploy large candidates of services. in recent years, several approaches for efficient service deployment have been proposed and are generally classified into 3 main categories [519]: (1) green iot approaches [5-9], (2) optimization approaches [11-14], and (3) hybrid approaches combining mobile devices, fog, and cloud optimization techniques [1519]. authors in [8] presented a new model called health-fog based on deep learning for saving energy on the fog and the cloud while the data are processed and transmitted from the fog to the cloud. authors in [15] introduced a microservice-based system for industrial internet of things (iiot) in distributed fog cloud environments. authors in [19] introduced a new priority traffic-conscious task placement algorithm that aimed to reduce the energy use of incoming iot traffic servers. these techniques do not react to frequent moving scenarios of the users and none of them could get an optimum consensus between energy saving, processing load, computational cost, and fast waiting time. the most striking case is the health mobile applications where the mobility causes them to lose valuable time in providing accurate diagnosis results to their patients. there is a high computing required to select the right server to deploy services dynamically. in the current work, a novel bio-inspired adaptive and dynamic multi-agent system for providing optimal deployment of healthcare services and applications under context changes (e.g. user’s location, workload, bandwidth, reduced total time of execution) is presented. it enables much less deployment cost of health services in an optimal and context-aware fog cloud design and ensures effective solutions to deploy complex services by subdividing them into smaller ones. the main contributions of the current paper are:  providing an optimal deployment map for incoming loads of healthcare applications using a hybrid bio-inspired system by combining the improved grey wolf optimization (igwo) and particle swarm optimization (pso) in iot fog-cloud systems.  developing an adaptive and dynamic multi-agent-based controller that offers redeployment map for the ongoing needs of various users to the corresponding neighboring fog servers while minimizing energy consumption and waiting time, maximizing the gain of service.  evaluation of the proposed approach on the real healthcare data set of qassim hospital in terms of energy consumption and execution time using the ifogsim simulator. ii. the case study: qassim smart hospital qassim hospital consists of many floors. each floor consists of many patient rooms and a fog server. each room is equipped with sensors (e.g. ip cameras). any patient can be equipped with biosensors (glucose meter, heart tracking, smart bracelet, and gps) that monitor medical data. the monitored information covers patient identifier, glucose level, temperature, patient location, etc. the monitored information is collected in a gateway. the aggregated context health data of the patient in a given room are transmitted to the fog server and the cloud controller for data analysis and storage. the local fog server triggers an immediate response to the device that gives an order to release some quantity of the drug in the body of a patient. the iot healthcare application consists of connected iot and various health tasks. each task is defined by arrival time, priority, deadline, service time, and requested resources. connected things are constantly consuming energy and sending huge data flows. this leads to low latency and consumer pressure on the amount of data flow on the fog and the internet. whether for patient healthcare, examinations or treatments, or hospitalization, an optimized task deployment approach of data collected by increasingly smart sensors can shed new light, improve flows, and reduce energy consumption. this case study raises several needs: (1) ensuring an optimal deployment map for incoming loads of healthcare applications and (2) determining their (re-) deployment into fog-cloud systems while reducing energy consumption and minimizing waiting time. iii. the proposed approach to develop an efficient and effective task deployment approach that can provide minimum energy costs and maximum benefits for users (i.e. patients, medical personnel, and administrators), we propose a new adaptive and dynamic system based on bio-inspired and cooperative agents with capacities like mobility, scalability, and efficiency. figure 1 shows an overview of the proposed approach. our goal is to ensure the coordination between the different agents of the healthcare system to determine the nearest best fog server between all feasible servers and select the server with the lowest processing load, waiting tasks, and energy consumption. fig. 1. an overview of the proposed approach. engineering, technology & applied science research vol. 13, no. 1, 2023, 10192-10198 10194 www.etasr.com reffad et al.: a dynamic adaptive bio-inspired multi-agent system for healthcare task deployment the proposed approach consists of 3 static agents (interact agent, deployer agent, and execution agent) and two mobile agents (monitor agent and bio-research agent) that interact and cooperate for realizing the deployment process. when a user sends a request, it consists of an application deployment to interact agent who plays the role of a mediator. bio-research agent is a mobile bio-inspired agent that is able to migrate to fog servers to look for the requested deployment application. the bio-research agent searches for local fog servers able to make partial or full deployment of the requested application. the bio-research agent gives all the possible solutions and sends its result to the deployer agent. the deployer agent selects the best solution (a single fog server or a set of fog servers). various politics based on weights (user’s location, cpu load, energy-saving, high bandwidth) are used. once the deployment map has been generated and the application has been deployed, the deployment results are sent back to the user. if the bio-research agent does not find any solution on local fogs, it sends requests to the deployer agent to deploy tasks involved in the application on cloud servers. the monitor agent is responsible for handling the environment context during the execution of tasks such as changes of users’ needs and incoming new urgent tasks. if it is about a single fog server, it is going to move and if it is about more than one fog servers, it clones himself, moves towards one fog server, and sends its clones to the other fog servers. the context execution parameters (cpu load, current bandwidth) will be transmitted to the deployer agent. the deployer agent selects the best fog server and generates the re-deployment map. fig. 2. the multi-agent functional model of ad-gwopso. a. problem formulation the problem consists of finding out an optimal deployment of iot applications on iot-fog-cloud infrastructure for minimizing energy consumption while maximizing the benefits of users (i.e. response time, reliability, and security). we consider three hierarchical levels of fog infrastructure ℐ consisting of � physical nodes. the iot layer (level 0) regroups a set of � smart devices, sensors, actuators, mobile devices, and edge devices. the fog computing layer (level 1) is a set of ℱ fog servers and getaways. the cloud computing layer (level 2) consists of a set of � large-scale data centers. the physical network is denoted as �ℐ = (�, ℰ) which consists of a set of nodes (i.e. servers) � and a set of edges ℰ. each edge ℯ�,� represents a link between a server � and a server � . each node �� (1≤ � ≤ � ) is localized by a position (x�� , y�� ). a node �� has a queue �� defined by the occupation rate �� and maximum size ���_�� . each node �� has a current workload ���� ! . "��� !# , denotes the power consumed by the server �� in the active state and "��� !�$%& denotes the power consumed in the idle state. '��� represents the available bandwidth and ()�� the data transferred (throughput) between servers � and � . the energy bandwidth consumed between servers � and � in their active state is "��*+# , and the energy bandwidth consumed between � and � in the idle state is "��*+�$%& . to solve the problem, we use a four step approach. at first, we sort all tasks by priority. a task is designed with a name and its priority value. then, we initiate and sort all possible solutions (i.e. servers’ nodes) by their weights based on the user’s location and resource availability. thirdly, we lunch a bio-inspired search algorithm that gives all possible server chains providing the deployment. the best solution is based on the weight (cpu charge, energy-saving, low bandwidth, and security) of each deployment. finally, we ensure an automated task transfer between neighboring nodes for incoming loads of applications. the problem is formalized as follows:  the set , = {./ , .0, … , .2 } of 4 users. each user ,� requests the deployment of the application �� and broadcasts his current location is (x5� , y5� ).  each task 6� (1 ≤ � ≤ m) can be deployed to a device :; (� = 1, 2, … =) by the projection > ∶ t � , → : . this projection is called the deployment map.  ((�� ab is the time taken by a server �� to perform a task t� . equation (1) calculates the euclidian distance separating the person’s location from � servers of deployment map >: d��6(>) = ∑ fg�h − ��� j 0 + glh − l�� j 0m�n/ (1) where �h , lh are the current location coordinates of the user u and ��� ,l�� are the coordinates of the fog server �� . fogs with the shortest distance closer to a person’s current device tend to be selected as best fogs by minimizing d��6(>). the best fog has the smallest distance from the person. equation (2) calculates the total consumed computing energy "� ! of the deployment map: engineering, technology & applied science research vol. 13, no. 1, 2023, 10192-10198 10195 www.etasr.com reffad et al.: a dynamic adaptive bio-inspired multi-agent system for healthcare task deployment "� ! (>) = ∑ ���� ! × "��� !# + g1 − ���� ! j ×��∈q "��� !�$%& (2) by reducing "� ! , lower computing energy fogs tend to be chosen as the best deployment maps. equation (3) calculates the total consumed network energy to transfer r tasks between fogs of deployment map >: "*+ (>) = ∑ ()�� × "��*+# + g'��� − ()�� j × "��*+�$%&(�,�)∈ℰ (3) equation (4) calculates the total network energy consumption, the total cpu power consumption applied to the fog servers for the task requests on deployment map: stutvwx = "� ! (>) + "*+ (ρ) (4) equation (5) is used to minimize the waiting time of the performed task. sz[ = (z\�[ = ∑ (�� )m�n/ (5) where �� is the occupancy rate of fog �. equation (6) is used to maximize the reward time of the servers: s]^_` = abcd^be� = ∑ rewards × elm×nno�p m�n/ (6) where q is the discount rate, ranging between 0 and 1. our goal is to establish an objective function (s) such that: (1) the total energy is minimized, (2) the global occupation rate of a person’s tasks is minimized, and (3) the global gain of the fog server is maximized. from such a perspective, we define the objective function as follows: s = zr#�s×tuvwx z&s&yrz×t{x{|u} ~z���&×t�p (7) where �tutvw� �[�mt , and �w\�u are the weights associated with the objectives energy, time, and gain, respectively. all are normalized in [0, 1]. the higher the weight value, the more important this criterion is. the objective function is customizable according to the different customer needs. b. the dynamic adaptative service placement algorithm  solutions coding: each solution is represented by an array of n fog servers.  generate the initial population based on igwo: gwo [20] is the most well-known optimization approach, and is used to generate the initial population (i.e. list of fog servers). the wolf agent moves towards the nearest server and provides information on server cpu load, available storage, and bandwidth communication. the best list of servers is assigned a high number of particles according to its objective functions whereas a good server has a higher fitness value than a bad one. we build the vector � = [�/, , … , �u, where �� = !� y � s��� !� y is used to allocate particles for each server and ,�v is the utility of the given fog server � based on r attributes that describe the fog. the number of particles for all services is the total number of particles multiplied by their normalized weight to better valorize the suitable server and the fitness of each particle is evaluated according to (7) of their related energy, time, and gain functions.  fitness evaluation: from the initial particles' position that defines the service placement map, a particle changes iteratively from one map to another with respect to velocity. the velocity is defined between two maps: the local best map (pbest) and the global best map (gbest). fog servers with the best score (lowest energy consumption, lowest occupation rate, and highest rewards by server) are assigned a high-priority value.  optimal deployment map generation. the system generates an optimal deployment map to those selected fog servers.  copy deployment map and service execution. the generated deployment map in the previous phase will be copied to fog servers and deploy services. fig. 3. multi-agent functional model of the dynamic adaptive igwopso. when unpredicted events occur, such as patient mobility or low latency on the fog server, the service controller will be switched to the adaptive mode, and the neighboring multi-agent technique is employed to tackle such events. each service controller agent ��_:� has a set of neighboring agents ��_:��. the agent ��_:� of server :� selects the best neighbors engineering, technology & applied science research vol. 13, no. 1, 2023, 10192-10198 10196 www.etasr.com reffad et al.: a dynamic adaptive bio-inspired multi-agent system for healthcare task deployment depending on occupancy rate, processing load, and transmission consumption energy. it checks the occupation rate � from a queue of the fog server :� , and if it is greater than a threshold (� then selects the tasks that are going to be transferred. the selection of a task is based on the type of task and the requested resources. a deployment request is created and sent to every neighbor. everyone can accept or reject the request according to its occupation rate and processing load. the list of neighbors will be sorted by their queue size, available computing resources, and bandwidth. the controller transfers the requested tasks to the top ranked neighbors. iv. experimental results and discussion the developed approach was implemented in eclipse using ifogsim [21]. the number of rejected/waited tasks is used to assess the efficiency of the proposed approach. various evaluation metrics were considered, including the number of rejected tasks, the number of waiting tasks, and the average makespan. the number of fog servers is 10 and the size of the waiting queue is 10. we simulated and compared different priority strategies: (1) shortest arrival time (p-sat) which selects the task with high priority and the shortest arrival time and (2) least requested resources (p-lrr) that selects the task with high priority and the fewest requested resources. a. evaluation of average makespan figure 4 shows the average makespan time (ms) of the existing approaches (p-spt, p-lrr), and the proposed approach with varying number of tasks. we can see that the proposed approach demonstrated optimum makespan compared to p-spt and p-lpr due to the optimal deployment time using igwo-pso with a good energy saving while exploiting performance metrics. b. evaluating the number of rejected and waited tasks figure 5 shows the performance of the proposed approach with varying number of tasks from 87 to 2697. the number of rejected and waited tasks is computed for different numbers of tasks and different algorithms (p-sat, p-lrr and proposed approach). the proposed approach obtained the optimum number of rejected tasks and the optimum number of waiting tasks for all the number of task values, due to the pre-selection of the best servers using igwo and applying an adaptive task transfer to neighboring fog servers with a good server utility while exploiting performance metrics. fig. 4. the average makespan of the proposed and exisitng approaches. c. evaluation of energy consumption to evaluate the energy consumption of our approach, we measure the average bandwidth/processing energy consumption of the proposed approach in cloud + fog and fog only. the proposed approach in fog environments is better in terms of bandwidth and processing energy consumption compared to the same approach in fog + cloud environments (figure 6). d. discussion in this paper, a dynamic and fast-to-deploy ds-igwopso is proposed, one that ensures dynamic task deployment and applies a transfer to neighboring fog servers. compared to other popular deployment algorithms (p-spt and p-lrr), dsigwopso demanded less bandwidth and processing energy to deploy tasks. it also reduces the makespan average on varying number of tasks. to have igwopso with its best performance, the neighbor selection should be based on the optimization of occupation rate and waiting time. however, it still depends on the number of requests to ensure optimal computational time. fig. 5. performance comparison. engineering, technology & applied science research vol. 13, no. 1, 2023, 10192-10198 10197 www.etasr.com reffad et al.: a dynamic adaptive bio-inspired multi-agent system for healthcare task deployment fig. 6. bandwith and processing energy consumption of the proposed approach in fog and fog+cloud. v. conclusion an adaptive and dynamic bio-inspired multi-agent approach for deploying healthcare tasks in iot-fog-cloud environments was developed and presented in this paper. hybrid particle swarm and grey wolf optimizers were utilized for the determination of a set of optimal hosts when deploying health services to optimize deployment cost and improve response time at run-time. the approach is based on neighboring agents for ensuring the continued functioning of health services by using both service priority and high servers' resource of availability. the approach was evaluated by deploying different types of tasks. the evaluation of the obtained results was achieved through well-known metrics such as waiting tasks and average makespan time. the results show that the proposed approach is economic in 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bellabed.faris@univ-jijel.dz received: 4 october 2022 | revised: 22 october 2022 and 25 october 2022 | accepted: 27 october 2022 abstract-for the prediction of the shear strength of reinforced soil many approaches are utilized which are complex and they depend on laboratory tests and several parameters. in this study, we aim to investigate and compare the ability of the gray and ohashi (go) model and artificial neural networks (anns) to predict the shear strength of reinforced soil. to achieve this objective, this work was divided into two parts. in the first part and in order to evaluate the impact of different fiber reinforcing parameters on the behavior of the soil, many direct shear experiments were carried out. the results revealed a significant improvement in shear strength values with fiber reinforcement. the increase in shear strength is a function of the fiber length, proportion, and direction. in the second part, we used the results of our experimental study to develop the ann model. the obtained results agree reasonably well with the experiment ones, with very acceptable error (rmse =1.714, mae=5.981, r 2 = 0.960, and e = -1.601%). the comparative study showed that the ann model was more accurate and statistically more stable than the go model, and the ann model took all the conditions of the reinforced soil into one equation. on the other hand, the go model does not take reinforcement failure and uses several equations. keywords-shear strength; reinforced soil; natural fibers; gray & ohashi model; artificial neural networks i. introduction soil instability can be dangerous and destructive. soil reinforcement takes into consideration several factors, such as the reinforcement's form, texture, and rigidity [1], its costeffectiveness, and its environmental friendliness [2-3]. in this work, we used soil reinforced by natural fibers. the prediction of its shear strength is necessary in order to study the soil behavior [1]. different methods for estimating shear strength in soils have occurred, generally based on variable theories such as force equilibrium [1, 4-5], statistical analysis [6-7], the approach of superposition of the effects of soil and fibers [8-9], and the energy dissipation approach [10-13]. gray and ohashi (go) [1] suggested that with the addition of discrete fibers, physical and mechanical properties increase, and post-peak strength loss decreases. based on the force equilibrium approach, the go model established the shear strength of fiberreinforced soil ( ��� ) as a combination of shear strength increment (∆s) and unreinforced soil shear strength ( ��� ) parameters. the behavior of composite soils is complex since it depends on laboratory tests and many parameters [14]. in this regard, artificial intelligence methods such as the anns are promising and can be applied for the development of an approximate function that determines the shear strength under various conditions, considering the complexity of the approach models and the high cost of empirical experiments. during the recent years, the increased use of anns to tackle different engineering challenges has become popular in the domains of electronics [15-16], geophysics [17], hydraulics [18], etc. anns are used less in geotechnical engineering than in other domains even though there is success in solving such problems (e.g. prediction of pile deflection [19], bearing capacity of foundations [20], seismic deformation of rooted slopes [21], etc.). the purpose of the current article is to investigate and compare the ability of the go model and anns to predict the shear strength of soil reinforced with natural fibers. the results of the experimental program were utilized to develop the database used in the creation of the ann structure. this research was carried out at the laboratory of civil and environmental engineering (lgce) of the university of jijel. corresponding author: leila arabet engineering, technology & applied science research vol. 12, no. 6, 2022, 9795-9801 9796 www.etasr.com arabet et al.: a comparative study of reinforced soil shear strength prediction by the analytical … ii. experimental study a. materials figure 1 presents the particle size analysis (according to nf p 94-056 and nf p 94-057). table i describes the physical properties of the studied soil. the soil class is "sm" according to the lpc code. alfa fiber "esparto grass" was used as reinforcement. table ii describes its mechanical properties. fig. 1. grain size distribution of the studied soil. table i. soil geotechnical characteristics property value code sand equivalent es (%) 34 nf p 18-598 water content (%) 25.85 nf p 94-050 liquid limit (%) 8.27 nf p 94-051 plastic limit (%) 1,00 nf p 94-051 plasticity index (%) 7,27 nf p 94-051 initial void ratio 0.521 methylene blue index (%) 0.215 nf p 94-068 wet density (kn/m 3 ) 19 nf p 94-054 specific gravity gs 2.65 nf p 94-049 table ii. mechanical properties of fibers used [22] property σ (gpa) ε (%) e (gpa) average value 63.83 3.12 2.05 standard deviation 16.80 0.63 0.77 coefficient of variance 26.31 20.12 37.55 b. experimental procedure direct shear tests were conducted to a strainless metal box of a squared section of 6×6 cm 2 and 3cm high (according to nf p 94-071-1). the samples were prepared in undrained conditions and under normal stresses of 100, 200, and 300kpa (with 0.02mm/s loading velocity). firstly, each sample was mixed with a constant fiber length of 1cm. after that, we added different fiber ratios ρf from 0 to 1% by weight of dry soil with a step of 0.25%, in different directions (horizontal, vertical, and inclined at 45°). then, each sample was mixed with a constant fiber ratio. then, we added different fiber lengths lf from 1 to 2.5cm, with an increment step of 0.5cm) in different directions (figure 2). fig. 2. specimen preparation in the inclined direction of the alfa fibers. c. experimental results 1) variation in fiber ratio from table iii, we can see that there is an improvement in shear strength relatively to the increase in reinforcements up to an optimum value. above that, ��� decreases. these findings are consistent with those of [1, 14]. the average relative error (1) between the experimental results and the predicted results of shear strength from the go model varies from 2.32 to 18.68%. the results show acceptable agreement between these two values. e (%) = �� ∑ ��� (������������)���� (�������) ��� (������������) ������ (%) (1) table iii. obtained results in different orientations of the fibers direction fiber (%) τff (kpa) experimental τff (kpa) go model [1] observation σn = 100kpa σn = 200kpa σn = 300kpa σn = 100kpa σn = 200kpa σn = 300kpa unreinforced 0.00 52.22 124 160.77 vertical 0.25 65.85 170.97 177.91 70.78 121.17 182.04 e = 2.89 % 0.50 60.20 111.07 191.41 73.24 137.86 198.54 0.75 89.27 187.37 267.82 80.67 141.60 205.69 1.00 79.94 142.75 205.70 101.18 170.60 238.12 inclined 0.25 79.30 136.00 192.65 62.14 117.63 172.87 e = 5.22 % 0.50 73.04 123.32 170.68 68.56 126.37 183.36 0.75 69.50 111.32 170.22 75.42 131.78 190.15 1.00 65.56 111.56 164.5 78.81 141.25 195.58 horizontal 0.25 78.32 152.5 214.04 59.57 114.25 169.74 e = -18.68 % 0.50 71.49 134.61 246.57 61.36 116.62 171.76 0.75 71.43 170.10 211.28 63.06 120.55 174.79 1.00 76.25 134.72 215.47 64.72 123.19 183.76 0,01 0,1 1 0 20 40 60 80 100 p e rc e n ta g e f in e r (% ) particale size (mm) engineering, technology & applied science research vol. 12, no. 6, 2022, 9795-9801 9797 www.etasr.com arabet et al.: a comparative study of reinforced soil shear strength prediction by the analytical … 2) variation of fiber length the unreinforced soil's shear strength improves in each direction and is limited by the optimum fiber length (table iv). the fiber direction changes the peak fiber length. this can be caused by the variation in the tensile fiber stress for each direction. the average relative error between the experimental results and the predicted results from the go model of shear strength varies from 18.16 to -7.56%. the results show acceptable agreement between these two values. in the vertical direction and at a length of 2.5cm, we observed a higher value of the error (= 59.69%). in this case, and during the test, we observed failure in the fibers. this inaccuracy can be explained by the fact that the go model does not account for the plasticity of fibers. table iv. obtained results in different fiber orientations of different lengths direction fiber (cm) τff (kpa) experimental τff (kpa) gray & ohashi observation σn = 100kpa σn = 200kpa σn = 300kpa σn = 100kpa σn = 200kpa σn = 300kpa unreinforced 0.00 52.22 124 160.77 vertical 1.00 65.85 170.97 177.91 70.78 121.17 182.05 e = 18.16 % 1.50 63.50 128.30 174.90 76.46 139.04 199.44 2.00 67.38 134.37 180.54 79.10 151.97 216.92 2.50 59.92 109.91 166.51 95.68 164.96 223.16 inclined 1.00 79.30 123.32 170.68 62.14 117.37 172.49 e = -15.43 % 1.50 74.25 145.80 196.04 65.23 123.18 179.23 2.00 85.10 160.30 211.60 69.79 126.11 182.03 2.50 89.45 148.48 293.25 70.52 128.92 187.92 horizontal 1.00 78.32 152.50 214.04 59.57 114.25 169.74 e = -7.56 % 1.50 68.87 161.30 207.22 60.49 115.25 171.13 2.00 58.32 115.30 161.37 61.56 117.01 171.58 2.50 54.25 129.05 162.60 68.00 117.39 174.68 iii. artificial neural networks many studies have been conducted on the influence of ann parameters, especially the activation function, on the ann performance to assure good model generalization [2324]. that is why in the current study, we used the growing technique [25]. the growing approach starts with a simple construction and then adds neurons and hidden layers until the performance is satisfactory. as a result, a huge number of simulations were run to determine the best ann model design. for this, various ann structures were trained with a different set of activation functions, numbers of hidden layers, and hidden neurons. for the learning algorithm, we used levenberg-marquardt (lm) back-propagation, which is the most commonly used for supervised learning [26]. a. architecture of the neural network the dataset that is utilized to create the neural network model is the product of the previous experiments. of the 75 data samples, 70% are used for the training, and the algorithm to compute the validation error used the rest of the data. in this research, the model's inputs are the unreinforced soil's shear strength (��� ), the mobilized tensile strength of fibers (�� ), the fiber ratio (ρf), the fiber length (lf), and the angle of shear distortion (θ). according to experimental and theoretical studies, these input parameters are the most influential on the shear strength of reinforced soil [1], which is the output of our model (see figure 3). as we mentioned above, we trained various architectures with different activation functions to obtain an optimum ann model. in this study, sigmoid, tangent hyperbolic, and linear activation functions through one, two, three, and four-hidden layers with a different number of neurons were investigated. the growing technique is the method employed in this study to determine the ideal architecture for a neural network model. as a result, we assume a certain number of hidden layers and neurons at every layer. then, we calculate the performance criteria (rmse, mae, and r 2 ) given by (2)-(4). if these are very satisfactory, it means that the chosen architecture is performing well. otherwise, we change the number of hidden layers and neurons until performance criteria are satisfactory. fig. 3. the basic structure of the proposed ann model. r! = 1 − $ ∑ %���_'(���� (������������)) *+, ∑ (��� (������������)�-./(��� (������������))*+, 0 (2) mae = �� ∑ 3���_4� − ��� (567589:5;<=>)3���� (3) rmse = @�� ∑ a���_4� − ��� (567589:5;<=>)b !�� (4) where �cc_de and �cc (experimental) are the predicted and the target values of shear strength of reinforced soil respectively. b. application of the neural network many simulations were carried out to find the best ann model. we started with a simple structure and neurons and engineering, technology & applied science research vol. 12, no. 6, 2022, 9795-9801 9798 www.etasr.com arabet et al.: a comparative study of reinforced soil shear strength prediction by the analytical … hidden layers were added with various activation functions until the performance was adequate. table v presents the architecture of the created mlps. the best obtained models for each combination using different numbers of neurons are indicated. c. results and discussion table vi shows the rmse, mae, and r 2 considering the training dataset, testing dataset, and all datasets in each best ann model. the last model (a15), which consists of 57 neurons and 4 hidden layers, performs best (see figure 4). for a1, a2, and a11 models, the training was good but not enough to ensure good generalization ability. by considering the rmse, mae, and r 2 of models a7, a8, and a9, it can be concluded that the sigmoid transfer function in the output layer performs worse than other transfer functions. table v. different architectures of mlp models ann modes number of hidden layers number of neurons in hidden layers activation function best ann model input output a1 1 1 to 30 sigmoid linear 24 a2 1 1 to 30 tangent hyperbolic linear 12 a3 1 1 to 30 linear linear 29 a4 1 1 to 30 tangent hyperbolic tangent hyperbolic 2 a5 1 1 to 30 linear tangent hyperbolic 29 a6 1 1 to 30 sigmoid tangent hyperbolic 30 a7 1 1 to 30 sigmoid sigmoid 25 a8 1 1 to 30 tangent hyperbolic sigmoid 25 a9 1 1 to 30 linear sigmoid 6 a10 2 1 to 30 1 to 30 tangent hyperbolic tangent hyperbolic tangent hyperbolic 3 19 a11 2 1 to 30 1 to 30 tangent hyperbolic tangent hyperbolic linear 4 9 a12 2 1 to 30 1 to 30 linear linear linear 8 11 a13 2 1 to 30 1 to 30 linear linear tangent hyperbolic 81 a14 3 1 to 30 1 to 30 1 to 30 linear linear linear linear 3 9 6 a15 4 1 to 30 1 to 30 1 to 30 1 to 30 tangent hyperbolic linear linear linear linear 12 10 – 25 10 table vi. prediction performance of different ann models rmse training mae training rmse testing mae testing rmse mae e % r 2 training r 2 testing r 2 a1 0.081 3.080 72.053 21.741 5.382 10.596 -3.664 0.992 0.820 0.886 a2 6.286 11.303 18.713 19.196 0.602 13.715 -0.253 0.938 0.827 0.900 a3 0.013 15.561 3.220 19.006 0.242 16.949 2.235 0.851 0.797 0.832 a4 0.002 33.104 4.506 38.780 0.293 34.839 11.550 0.339 0.262 0.318 a5 9.707 17.560 23.161 20.371 0.555 18.419 4.079 0.827 0.821 0.819 a6 63.194 16.608 24.453 28.551 4.613 20.257 0.287 0.903 0.492 0.757 a7 259.847 51.872 202.907 56.492 38.738 53.284 54.801 0.141 0.115 0.108 a8 321.020 46.351 231.911 53.502 46.635 48.536 58.461 0.554 0.344 0.501 a9 352.123 52.086 125.542 45.105 42.760 50.258 56.758 0.407 0.139 0.297 a10 38.635 25.309 59.366 21.533 7.662 24.155 -3.500 0.634 0.833 0.684 a11 8.993 10.752 23.499 23.085 0.648 14.520 1.090 0.938 0.748 0.879 a12 0.039 13.916 70.602 23.188 4.595 16.749 -0.645 0.894 0.802 0.833 a13 18.476 17.295 17.734 21.041 2.970 18.439 6.193 0.851 0.731 0.817 a14 15.639 18.039 18.039 21.197 16.069 0.155 17.437 0.806 0.892 0.836 a15 6.004 2.080 35.422 14.848 1.714 5.981 -1.601 0.998 0.891 0.960 fig. 4. the architecture of the optimal ann model (a15). engineering, technology & applied science research vol. 12, no. 6, 2022, 9795-9801 9799 www.etasr.com arabet et al.: a comparative study of reinforced soil shear strength prediction by the analytical … equations (5)-(9) are used to predict the shear strength of the reinforced soil: ���_4� = dpeqrst. avw�x. y�x + [�\b (5) ]y�x^ = dpeqrst. (vw�_. y�_ + [�x) (6) ]y�_^ = dpeqrst. (vw�!. y�! + [�_) (7) ]y�!^ = dpeqrst. (vw��. y�� + [�!) (8) ]y�� ^ = `atbsc. (dw� . d + [��) (9) where p is the matrix of inputs, iw9. p is the weight matrix, representing the connection of the weights between the input layer neurons and the first hidden layer neurons, vw�� is the weight matrix representing the connection of the weights between the first and the second hidden layer neurons, vw�! is the weight matrix representing the connection of the weights between the second and the third hidden layer neuron, vw�_ is the weight matrix representing the connection of the weights between the third and the fourth hidden layer neurons, vw�x is the weight matrix representing the connection of the weights between the fourth hidden layer neurons and the output neurons, [��, [�!, [�_, [�x and [�\ are the bias vectors of the first, second, third, and fourth hidden layer neurons, and the bias vector of the output layer respectively, dpeqrst(g) = g , and tatbsc(t) = !�hi j*+ − 1. fig. 5. correlation results analysis of the model using the training data set. fig. 6. correlation results analysis of the model using the testing data set. figures 5 and 6 illustrate the training and testing data correlation between the target and predicted shear strength of reinforced soil using the optimal ann model (a15). the values of rmse (6.004), mae (2.080), and r 2 (0.998) indicate that the target and predicted values for the training dataset are quite close. the testing dataset's rmse (35.422), mae (14.848), and r 2 (0.891) values are adequate proof that the proposed ann model is the most reliable approach. because the shear strength of the reported instances in the dataset is different, we plotted the measured and estimated shear strength in figure 7 against each other for all given cases. as shown in this figure, the overall agreement between the predicted values obtained by the approximated function developed in this study and the values of the experimental model is indeed good, which is confirmed by the low values of rmse (1.714), mae (5.981), r 2 ( 0.960), and the relative average error value (e = -1.601%). table vii presents the comparison between the go model and the developed ann model of this study. the different performance values (rmse, mae, r 2 , and e) obtained by the two models show that the optimum ann model estimates the shear strength of reinforced soil more precisely than the go model. table vii. comparison between the performance values obtained by the go model and the developed ann model gray and ohashi model ann developed model rmse mae r 2 e (%) rmse mae r 2 e (%) vertical 31.93 26.00 0.680 10.53 1.714 5.981 0.960 -1.601 inclined 28.44 20.50 0.732 -5.10 horizontal 30.81 24.91 0.719 -13.12 engineering, technology & applied science research vol. 12, no. 6, 2022, 9795-9801 9800 www.etasr.com arabet et al.: a comparative study of reinforced soil shear strength prediction by the analytical … fig. 7. comparison of all experimental and predicted shear strengths evaluated by the ann model of this study. iv. conclusion an ann model was built in this paper to predict the behavior of reinforced soil. the experimental results of the shear strength of reinforced soil was compared with the predicted results from the go model and the ann model. a parametric study to explain the impact of various factors on the behavior of reinforced soil was conducted. the main conclusions of this study are:  the improvement of the shear strength of reinforced soil is not only influenced by the fiber length and ratio, but also by their direction.  the fiber direction changes the optimal fiber ratio and the optimal fiber length. this can be due to the variation in fiber tensile stress for each direction.  from the experimental study, the go model does not take into account the plasticity of fibers.  the shear strength of unreinforced soil (��� ), the mobilized tensile strength of fibers (�� ), the fiber ratios (ρf), the fiber length (lf), and the angle of shear distortion (k) are the major factors influencing the behavior of reinforced soil, according to the parametric study and the theoretical analysis.  the excellent agreement between the predictions of the optimal ann model and the laboratory shear tests suggests that the developed model can quickly and conveniently predict the shear strength of reinforced soil for different values of reinforced parameters, which was confirmed by the values of rmse (1.714), mae (5.981), r 2 (0.960), and e (-1.601%).  the developed optimal ann model predicts the shear strength of reinforced soil more precisely than the go model. moreover, the go model is based on many equations and it doesn't take into consideration the case of the fiber failure. instead, the proposed ann model considers all conditions in one equation with minimal error and the best correlation. therefore, the ann model developed in this study is a robust and efficient alternative. references [1] d. h. gray and h. ohashi, "mechanics of fiber reinforcement in sand," journal of geotechnical engineering, 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[26] j. j. jeremiah, s. j. abbey, c. a. booth, and a. kashyap, "results of application of artificial neural networks in predicting geo-mechanical properties of stabilised clays—a review," geotechnics, vol. 1, no. 1, pp. 147–171, sep. 2021, https://doi.org/10.3390/geotechnics1010008. microsoft word 5-655-ed.doc engineering, technology & applied science research vol. 6, no. 3, 2016, 1000-1005 1000 www.etasr.com adebayo: brittleness and packing density effects on blast-hole cuttings yield of selected rocks brittleness and packing density effects on blast-hole cuttings yield of selected rocks b. adebayo department of mining engineering federal university of technology, akure, futa akure, nigeria baayoakinola@googlemail.com abstract—this paper evaluates brittleness and packing density to analysis their effects on blast-hole cutting yield for three selected rocks in nigeria. brittleness test (s20) was carried out in accordance with norwegian soil and rock engineering and the brittleness index (bi) for the selected rocks were estimated. the packing density determined from the photomicrograph of the rock samples. the grain size of 45 blast-holes drill cuttings collected from three selected while drilling of these rocks were determined using standard method of america society for testing and materials (astm) d 2487. the brittleness values are 50%, 44% and 42% for micro granite, porphyritic granite and medium biotite granite respectively. the result of bi varied from 10.32 – 11.59 and they are rated as moderately brittle rocks. the values of packing density varied from 92.20 – 94.55%, 91.00 92.96% and 92.92 – 94.96% for all the rocks. the maximum weights of blast-hole particle size retained at 75 µm are 106.00g, 103.28 g and 99.76 g for medium biotite granite, micro granite and porhyritic granite respectively. packing density values have correlation to some extent with (s20) values hence, this influence the yield of blast-hole cuttings as drilling progresses. the minimum weight of blast-hole cuttings particle size retained at 150 µm agrees with brittleness index classification for micro granite. keywords-blast-hole; cuttings; yield; brittle; index; density i. introduction generally a natural rock mass is non-homogenous and full of unfavorable geological structures such as joints and cracks [1]. chaput [2]; nicodeme [3] and richard [4] were of the view that if depth of cut is shallow, ductile mode will dominate and the cutting will behave like grinding. the possibility is very high that when the depth of cut is deep, brittle failure may dominate since rocks generally are brittle. pozin et al. [5] identified that rock brittleness is employed in two different ways: measure of energy consumption in the process of rock cutting/ drilling or as a physical measure of rock strength. however, cigla et al. [6] regarded brittleness as rock property when mechanical forces an excavator are in operation. altindag [7] and copur, et al. [8] found that increase in the rock brittleness is accompanied by a higher specific energy of cutting which is an indication of low cutting efficiency. goktan and yilmaz [9] concluded that an increase in rock brittleness is accompanied by an increase in the cutting efficiency this contrary to the conclusions reached previously others. these researchers described brittleness index (bi) as (brittleness ratio, the brittleness coefficient or the ductility number). in addition, it is the ratio of uniaxial compressive strength to tensile strength. hucka, and das, [10] stated that with higher brittleness the following occurred: cracks formation as indentation, elongation values are low, fracture failure, fines formation, coupled with higher ratio of compressive strength to tensile strength. this is commonly used parameters to quantify the brittleness of rocks. blast-hole cuttings are generated at the bit-rock contact interface and these cuttings are progressively generated as the makes contact with new rock surface. opafunso and adebayo [11] described blast-hole cuttings are debris, chippings or caving flushed by compressed air rock is attacked mechanically. adequate flushing of the blast-hole cuttings while drilling will ensure that as the bit advanced into the rock a new surface is contacted by the bit for fresh debris to be produced. gokhale [12] was of the view that if the percentage of the annular space is less than 17% then for every 1% reduction in this percentage the bailing velocity must be increased by 2% and this may reduced the rate at which the cuttings are flushed out of the blast-hole. the other factors that may affect size distribution yield of the blast-hole cuttings are packing of the individual grains that make up the rock, type bit (sharpened, dull and worn buttons). erosy and waller [13] explained that textural characteristics refer to the geometrical features of rock particles and identified that matrix (packing density) is one of the textural properties of rock. they concluded that textural characteristics will go a long way to determine the mechanical behavior of rocks. adebayo and akande [14] correlated selected textural properties (quartz proportion, silica content, average grain size, porosity and packing density) with penetration and found that these have strong relation with penetration rate. rock is one of the material where brittle failure dominates [15]. more importantly, it appears that the relation between rock brittleness and particle size distribution of blast-hole cuttings has not been fully established. relatively, little published materials are available on the relation among rock brittleness, packing density and particle size distribution, hence, all these will be the focus of this paper. engineering, technology & applied science research vol. 6, no. 3, 2016, 1000-1005 1001 www.etasr.com adebayo: brittleness and packing density effects on blast-hole cuttings yield of selected rocks ii. experimental methods a. determination of brittleness value (s20) the brittleness test is basically an aggregate impact test and this was conducted in accordance with the norwegian soil and rock engineering association (borg, 1988). in addition s20 is defined as the percentage of material that passes the 11.2 mm sieve after 20 drops of 14 kg weight. b. determination of brittleness index the brittle index was determined as the ratio of uniaxial compressive strength to tensile the expressed in (1). s ucs bi= (1) t where bi is the brittleness index, ucs is the uniaxial compressive strength and ts is the tensile strength. table i. rock brittleness classification (after aftes, 2003) class brittleness index (bi) description 1 > 25 very brittle 2 15 < bi < 25 brittle 3 10 < bi < 15 moderately brittle 4 bi < 10 low brittle c. determiantion of packing density the packing densities for the samples were determined using (2) proposed by kahn, (1956). length of grains along traverse pd= (2) length of traverse å where, pd is the packing density (%) iii. results and discussion table ii presents brittleness values (s20) for the three selected rocks. the brittleness values are 50%, 44% and 42% for micro granite, porphyritic granite and medium biotite granite respectively. these values are evaluated as the percentage of a pre-sieved fraction that passes through the finer sieve after 20 impacts. this revealed that more than 50% of the particle sizes pass through the finest sieve size and could be considered as the most easily broken rock to smaller fragment among the three selected rocks. mediun biotite-granite is the least brittle while micro granite is the most brittle as presented in table ii. table iii presents rock properties and brittleness index for the three selected rocks. the uniaxial compressive strength, tensile strength and brittleness index (bi) varied for 90.30 – 120.86 mpa, 8.25 10.43 mpa and 10.32 – 11.59 respectively for the selected rocks. also, the brittleness index of micro granite is the highest make it to be the most brittle this agrees with (s20) brittleness value. in addition, this is not the case for porphyritic granite and medium boitite granite where bi rate medium biotite granite to be more brittle than porphyritic granite. the reason may that the grain size ranges that make up the rocks are marginal as well as the bonds holding the grains together as shown by the tensile strength values for the rocks in table iii and all the rocks are moderately brittle. table iv presents packing densities for the selected rocks. the values of packing density varied from 92.20 – 94.55%, 91.00 -92.96% and 92.92 – 94.96% for micro granite, porphyritic granite and medium biotite granite respectively. medium biotite granite has the most closely packed grains. table ii. brittleness value (s20) of the selected rocks table iii. rock properties and brittleness index for the selected rocks rock name ucs (mpa) tensile strength ts (mpa) bi descript. micro granite 120.86 10.43 11.59 moderately brittle porphy. granite 96.42 9.34 10.32 moderately brittle medium biotitegranite 90.30 8.25 10.95 moderately brittle table iv. packing densities for the selected rocks rock type pd (%) 1 pd (%) 2 pd (%) 3 pd (%) 4 pd (%) 5 micro granite 92.98 93.77 93.00 94.55 92.20 porphyritic granite 91.93 91.02 92.96 92.40 91.00 medium biotite granite 92.92 93.45 93.62 94.96 93.70 tables v – vii present descriptive statistics for packing density, weight of blast-hole cuttings retained at 75 µm and weight of blast-hole cuttings retained at 150 µm respectively. the maximum packing density values are 94.96%, 94.55% and 92.96 % for medium biotite granite, micro granite and porphyritic granite respectively and this has correlation with (s20) value but true to some extent for brittleness index. the maximum weights of blast-hole particle size retained at 75 µm are 106.00g, 103.28 g and 99.76 g for medium biotite granite, micro granite and porhyritic granite respectively. this revealed that the packing density has slight effect on the mechanical fragmentation of the rock. the minimum weights of blast-hole particle size retained at 150 µm are 36 g, 27.68 g and 26.88 g for micro granite, medium biotite granite and porhyritic granite respectively and agrees with brittleness index classification that micro granite has most brittle response to larger fragments blast-hole cutting. the standard deviation and coefficient of variation were calculated as well summarized in tables v-vii. the coefficient of variation describes the variability of the results. this is defined as the ratio between standard deviation of a group of test values and the population in percentage. the coefficient of variation for packing density between micro granite and porphyritic granite are a bit close, therefore their rock name brittleness value (s20) (%) micro granite 50.0 porphyritic granite 44.0 medium biotite-granite 42.0 engineering, technology & applied science research vol. 6, no. 3, 2016, 1000-1005 1002 www.etasr.com adebayo: brittleness and packing density effects on blast-hole cuttings yield of selected rocks strength properties may be closely related. porphyritic granite and medium biotite granite have closer values of coefficient of variation for weight of particle size retained on 75 µm sieve size. this may be the reason behind the interchange of brittleness classification with (bi) and (s20). the coefficient of variation for weight of blast-hole cuttings retained on 150 µm varied from 9.2% for micro granite to 23.79% for porphyritic granite. table v. statistics for packing density of the selected rocks rock name n rang min max mean std. d cov m. granite 5 2.35 92.20 94.55 93.30 0.89 0.95 p. granite 5 1.96 91.0 92.96 91.86 0.86 0.94 m.b granite 5 2.04 92.9 94.96 93.73 0.75 0.80 table vi. statistics for weight blast-holes particle size retained at 75 µm for selected rocks rock name n rang min max mean std. d cov m. granite 15 40.60 62.68 103.28 91.56 14.2 15.56 p. granite 15 43.16 56.60 99.76 83.07 14.8 17.83 m.b granite 15 42.40 63.60 106.00 89.06 15.5 17.39 table vii. statistics for weight blast-holes particle size retained at 150 µm for selected rocks rock name n rang min max mean std. d cov m. granite 15 12.9 36.00 48.96 45.3 4.2 9.27 p. granite 15 33.1 26.88 60.00 49.4 11.8 23.79 m.b. granite 15 32.4 27.68 60.16 50.1 11.5 22.92 figures 1, 2 and 3 present weight retained against mean sieve size of blast-hole cuttings for micro granite, porphyritic granite and medium biotite granite respectively while drilling through fifteen blast-holes. the weight of the blast-hole cuttings retained on 850 µm decreases while the retained on 75 µm increases as the drilling operation progresses from blasthole 1 to blast-hole 15. this trend was observed in all the selected rocks and may also be a measure of the brittleness of the rock since smaller particle sizes are generated as drilling progresses. iv. conclusion in order to able to gain a better understanding of the mechanical fragmentation processes and select rock drill bit for a particular rock type, there is the need to analyze rock properties. however, there are different methods for evaluating brittleness and two of the methods were adopted for this work. brittleness and packing density were related to degree of blasthole cutting yield. the following were found: the brittleness index of micro granite is the highest which makes it to be the most brittle this agrees with (s20) brittleness value. all the selected rocks belong to moderately brittle class this in line with aftes (2003) rating. the maximum weights of blast-hole particle size retained at 75 µm are 106.00 g, 103.28 g and 99.76 g for medium biotite granite, micro granite and porhyritic granite respectively. this revealed that the packing density has a slight effect on the mechanical fragmentation of rocks. the minimum weights of blast-hole particle size retained at 150 µm varied from 36 g for micro granite to 26.88 g for porhyritic granite and this agrees with brittleness index classification that micro granite has most brittle response to larger fragments of blast-hole cuttings. porphyritic granite and medium biotite granite have closer values of coefficient of variation for weight of particle size retained on 75 µm sieve size. this may be the reason behind the interchange of brittleness classification with (bi) and (s20).the coefficient of variation for packing density between micro granite and porphyritic granite are a bit close, therefore their strength properties may be closely related. acknowledgment the author would like to acknowledge the administration and technical personnel of piccolo, and agi, quarries, nigeria for providing enabling environment for acquisition of data for this research work. references [1] r. e. goodmman, methods of geological engineering in discontinuous rock, wiley, new york, 1976 [2] e. j. chaput, observation and analysis of hard rocks cutting failure mechanisms using pdc cutter, ph.d. thesis, imperial college, london, 1991 [3] p. nicodeme, transition between ductile and brittle mode in rock cutting, rapport de stage d’ option scientifique, ecole polytechnique, 1997 [4] t. richard, determination f rock strength from cutting test, ms thesis, university of minnesota, 1999 [5] e. z. pozin, v. z. melamed, s. m. azovtseva, “towards a method of quantitative assessment of the cuttability of coals”, soviet min. sci., vol. 15, 1979, pp. 573–581, 1979 [6] m. cigla, s. yagiz, l. ozdemir, “application of tunnel boring machines in underground mine development”, 17th international mining congress and exhibition of turkey, ankara, turkey, 2001, pp. 155–164, 2001 [7] r altindag, “correlation of specific energy with rock brittleness concepts on rock cutting”, the journal of the south african institute of mining and metallurgy, vol. 103, no. 3, pp. 163–171, 2003 [8] h. copur, n. bilgin, h. tuncdemir, c. balci, “a set of indices based on indentation tests for assessment of rock cutting performance and rock properties”, the journal of the south african institute of mining and metallurgy, vol. 103, no. 9, pp. 589–600, 2003 [9] r. m. goktan, n. g. yilmaz, “a new methodology for the analysis of the relationship between rock brittleness index and drag pick cutting efficiency”, the journal of the south african institute of mining and metallurgy, vol. 105, pp. 727 – 734, 2005 [10] v. hucka, b. das, “brittleness determination of rocks by different methods”, int. j. rock mech. min. sci. and geomech. abstr., vol. 11, pp. 389–392, 1974 [11] z. o. opafunso, b. adebayo, “blast-hole cuttings: an indicator of drill bit wear in quarries”, european journal of scientific research, vol. 20, no. 4, pp. 721-736, 2008 [12] b.v. gokhale, “flushing of blast-hole”, http://rockproducts.com, pp 1-4, 2004 [13] a. erosy, m. d. waller, “textural characteristics of rocks”, in: engineering geology, elsevier, netherlands, pp. 123136, 1995 [14] b. adebayo, j. m. akande, “textural properties of rock for penetration rate prediction”, daffodil international university journal of science and technology, vol. 6, no. 1, pp 1-8, 2011 [15] g. e. andreev, brittle failure of rock materials. balkema/rotterdam, 1995 engineering, technology & applied science research vol. 6, no. 3, 2016, 1000-1005 1003 www.etasr.com adebayo: brittleness and packing density effects on blast-hole cuttings yield of selected rocks [16] a. borg, hard rock tunnelling boring in norway, in: norwegian tunnelling today, norwegian soil and roc engineering association, publication no. 5, tapir publisher, trondheim, pp. 109 – 112, 1988 [17] aftes, guidelines for characterization of rock masses useful for the design and the construction of underground structures, tunnels et ouvrages souterrains, no. 177, mail / juin, 2003, p. 49, 2003 [18] j. s. kahn, “the analysis and distribution of the properties of packing density and size sediments”, journal of geology, vol. 64, pp 385-395, 1956 fig. 1. weight retained against mean sieve size of blast-hole cuttings micro granite engineering, technology & applied science research vol. 6, no. 3, 2016, 1000-1005 1004 www.etasr.com adebayo: brittleness and packing density effects on blast-hole cuttings yield of selected rocks fig. 2. weight retained against mean sieve size of blast-hole cuttings for porphyritic granit engineering, technology & applied science research vol. 6, no. 3, 2016, 1000-1005 1005 www.etasr.com adebayo: brittleness and packing density effects on blast-hole cuttings yield of selected rocks fig. 3. weight retained against mean sieve size of blast-hole cuttings for medium biotite-granite microsoft word etasr_v12_n5_pp9265-9269 engineering, technology & applied science research vol. 12, no. 5, 2022, 9265-9269 9265 www.etasr.com kamal & abbas: langmuir-hinshelwood-hougen-watson heterogeneous kinetics model for the … langmuir-hinshelwood-hougen-watson heterogeneous kinetics model for the description of fe (ii) ion exchange on na-x zeolite sanarya k. kamal chemical engineering department college of engineering university of baghdad baghdad, iraq sanarya.kamal1507d@coeng.uobaghdad.edu.iq ammar s. abbas chemical engineering department college of engineering university of baghdad baghdad, iraq ammarabbas@coeng.uobaghdad.edu.iq received: 26 june 2022 | revised: 14 july 2022 | accepted: 29 july 2022 abstract-this study aimed to investigate the kinetics of the anion exchange step of ferrous ions with na-x zeolite in a temperature range of 20 and 80°c for a period of up to 8 hours. a ferrous sulfate heptahydrate solution was used as a ferrous ion source to exchange with the sodium of the na-x zeolite. the results showed a change in the physical appearance of the zeolite with the progress of the ion exchange process. the catalyst color was observed with the progress of the ion exchange time and changed from yellow to brown. the ferrous ion exchanged contents increased with temperature and reached 0.519 at 80°c after 8 hours. a kinetic model based on the langmuir-hinshelwoodhougen-watson model was suggested and developed to describe the ion-exchange process. the proposed model was solved numerically, and the results indicated its ability to describe the experimental results with high correlation coefficients. finally, the activation energy for the forward reaction was 31590.7j/mole compared to 28105.5j/mole for the backward, and the frequency factors for the forward and backward reactions were investigated. keywords-fe exchanged; na-x zeolite; ion exchange; anion capacity i. introduction zeolites are microporous, crystalline aluminosilicates with a unique mix of physical and chemical properties that make them excellent for a wide range of uses in industry [1-3], agriculture, medicine [4], and environmental pollution cleanup [5]. na-x zeolites are synthetic zeolites that have been used and investigated in industrial chemicals as ion exchangers, sorbents [5, 6], and catalysts [7] due to their significant void volume of 50% of the frame structure, their ion exchange capacity, shape selectivity, and solid acid sites [8, 9]. the structure of na-x zeolites is a faujasite framework with a cage made up na86[(alo2)86(sio2)106].h2o with a ratio of 1-1.5 joined together by bridging oxygen atoms resulting in a 12-ring pore opening and 3-dimensional channel system [10]. the negative charges of alo4 units are balanced by sodium cations (na + ) which are exchanged by other cations such as co 2+ , cu 2+ , zn +2 , and cr +3 ions in the solution [11, 12]. because of the destruction of the zeolite framework, the exchange capacity of na-x zeolites makes them particularly effective adsorbents or catalysts. metal-containing zeolites are especially appealing [13]. iron-containing zeolites can be used as heterogeneous fenton or photo-fenton catalysts [14] and utilized to remove organic pollutants in water treatment plants [15, 16]. transition metal-containing zeolites are manufactured using a variety of methods including: (i) ion exchange from aqueous solution [11, 17, 18] or solid-state reaction [19], (ii) hydrothermal synthesis [20], and (iii) adsorption and decomposition of volatile organometallic compounds [21, 22]. ion exchange from an aqueous solution is frequently used to introduce transition metal ions into na-x zeolites. the mechanics and outcomes are not always straightforward. transition metal ions may usually replace only a portion of the original cations, which are mainly sodium ions [23]. ferrous ions (fe (ii)), which are frequently introduced into na-x zeolites by ion exchange, can coordinate with oxygen atoms more selectively than filling the shell cations and have easy access to other oxidation states [24], so their introduction into zeolites leads to new mechanisms for their function as sorbents [14] and catalysts [25]. however, because ion exchange is reversible, once adsorbed nuclides in water are exchanged by other cations (na + , ca 2+ , mg 2+ , etc.) [26]. this research aimed to study the effect of temperature and time on the fe (ii) exchange process with na on the x zeolite. a heterogeneous kinetics model was developed to describe the exchange process based on the heterogeneous langmuirhinshelwood-hougen-watson (lhhw) approach. ii. experimental process the zeolite used was the type na-x zeolite (commercial grain, si/al ratio 1.75, pore volume 0.2733cm 3 /g, surface area 450m 2 /g, initial na=14.719%), which was crushed and then sieved with 200 mesh strainers to homogenize its size. 40g of zeolite were weighed and then washed with distilled water. afterward, they were washed with deionized water at various corresponding author: ammar s. abbas engineering, technology & applied science research vol. 12, no. 5, 2022, 9265-9269 9266 www.etasr.com kamal & abbas: langmuir-hinshelwood-hougen-watson heterogeneous kinetics model for the … times, the na-x zeolite was filtered by filter paper (chm f1002 filter paper,150mm, penetration range (7-8µ m)), went through a buckner funnel, a vacuum pump, and then was dried at 60 o c overnight in an oven (memmert, sigma, england uk). na-x was mashed by crushing until powder again. the activation process was carried out using a 0.1n chloride acid solution (36.5% hcl, usa) to clean the pore surface of zeolite and remove impurities. the cleaning hcl acid solution was mixed with na-x zeolite in a 10:1 ratio (v/w ratio) and stirred with a hot plate magnetic stirrer (thermo fisher scientific inc, usa) for 1 hour at 250rpm at 25°c [27]. the hcl solution was separated from the na-x zeolite using filter paper, washed with distilled water, and stopped until a neutral ph=7 was obtained. the activated na-x zeolite was dried at 60°c overnight. the calcination of the cleaning na-x zeolite samples was obtained at 550°c for 3 hours with a furnace (carbonite, sigma, england uk). after cooling, the samples were stored in a desiccator to prevent water absorption. then, na-x zeolite containing a high sodium weight percentage (14.719%) was exposed to an ion exchange procedure with ferrous sulfate heptahydrate (feso4∙7h2o, india) to replace the sodium from na-x zeolite. this procedure was carried out in beakers with a volume of 0.5lt, under controlled temperatures (20, 40, 60, and 80°c) and were stirred again. 5g of dried na-x zeolite were added to 100ml of a 0.319m solution and maintained at the required temperature with constant stirring at 300rpm for 8 hours. subsequently, exchanged na-x zeolite samples were taken from the ion-exchanged solution and filtered, washed several times with distilled water to remove the fe (ii) that was not exchanged, and taken to an oven to dry at 60°c overnight. the samples were calcined in a furnace at 550°c for 3 hours, and were left to cool inside desiccator until they reached room temperature. the concentration of fe (ii) in the exchange solution was measured using atomic absorption spectrophotometry (varianaa240fs, australia), and the amount of exchange fe (ii) was determined. the atomic absorption spectrophotometry was tested at north gas company (ministry of oil, iraq). iii. results and discussion the ion exchange reaction was carried out between na-x zeolite and ferrous sulfate solution with a stoichiometric amount of fe/na at different temperatures for a processing time up to 8 hours. at first, the color of the catalyst was observed with the progression of the ion exchange process. a darker yellowish-brown product was generally obtained with increasing ion-exchange time and processing temperature. figure 1 depicts three zeolites: original na-x zeolite, activated na-x zeolite, and x zeolite after fe (ii) ions were exchanged for 8 hours at 80°c. the color change of the treated zeolite indicated that fe-13x was formed. (a) (b) (c) fig. 1. color of (a) na-x zeolite, (b) na-x activated, and (c) modified fe-13x for 8 hours at 80°c. the amount of fe (ii) conversion versus time and temperature by ion exchange reaction is shown in figure 2. figure 2 shows that the fe (ii) ion exchange (conversion) increased with the reaction time and temperature, and the results showed a rapid increase during the first 0.25h, after which the conversion increased slowly and reached a similar to the equilibrium state at the end of the studied time. the conversion accelerated with the reaction time as the temperature increased. the conversion was 0.179 after 0.25h of reaction at 20°c, whereas it was 0.415 after the same period at 80°c, while the higher required value of fe (ii) conversion was 0.519 obtained after 8h of ion exchange at 80°c. these results agree with the cobalt exchange on na-x zeolite previously found in [28]. fig. 2. fe (ii) conversion on the na-x zeolite versus time at different temperatures. langmuir-hinshelwood-hougen-watson (lhhw) kinetics model assumes that before the surface reaction, the fe (ii) is adsorbed onto the catalyst surface. the final stage of the mechanism involves the desorption of na ions. the surface reaction (1) was assumed to be the rate-controlling step, and the lhhw kinetics model performing the ion exchange can be written as (2) (11). �������� � � ���������  ����′  ⇄ � ������ ��� ��������� (1) ������� � �� !�����!"�#$� � %&� !'"���!��#$�( (2) the adsorbed phase concentrations can be written as: !����� � )����!����!* (3) c,-.�/ � k,-.�c,-.�c1 (4) substituting these values in (3) and (4) into (2) gives: engineering, technology & applied science research vol. 12, no. 5, 2022, 9265-9269 9267 www.etasr.com kamal & abbas: langmuir-hinshelwood-hougen-watson heterogeneous kinetics model for the … ������� � �� 2)����!����!*)"�#$!"�#$!* � 1)� )'"��!'"��!*)��#$!��#$!*4 (5) now, !����5 � !����� !'"��� !* (6) which can be simplified into: !����5 � !*�)����!���� )'"��!'"�� 1� (7) finally, solving for cv gives: !* � 678��59&78��678���&:;<�6:;<��%= (8) by substituting and simplifying, this can be rewritten as: ������� � �>)����)'"���!�����? @ a78��a;<bcd:;<� # a:;<�a78bcd�d78��%�&78��678���&:;<�6:;<�e (9) )� � 6:;<��678��� � ����′ (10) ) � &78��&:;<� . )� (11) where cfe+2 is the concentration of fe (ii) in the solution, cna-x is the concentration of the catalyst na-x zeolite, czna+ is the concentration of na + in the solution, cfe-x is the concentration of fe exchanged on the zeolite, ks is the forward surface reaction rate constant, ks’ is the backward surface reaction constant, ks is the equilibrium constant for exchange surface reaction, and kfe and kna are the equilibrium constants for fe (ii), and na + respectively. the correlation coefficient (r 2 ) is presented in (12): g� � �∑ �78��8ij#�78��8ijkkkkkkkkkkkkkk(lmno ��78��p<q#�78��p<qkkkkkkkkkkkkk���∑ �78��8ij#�78��8ijkkkkkkkkkkkkkk(lmno �×∑ 9�78��p<q#�78��p<qkkkkkkkkkkkkk=lmno � (12) where rfe +2 exp is the experimental reaction rate, rfe +2 cal is the calculated reaction rate from the model, and (¯ ) represents average value. the kinetics equation was solved numerically using the damped least-squares method with the levenbergmarquardt algorithm by finding the reaction rate constant and the values of the equilibrium constants at each temperature, which gives a reaction rate approximating the experimental reaction speed, which was obtained by maximizing the r 2 value (12) at each temperature. figure 3 shows the relationship between the reaction rate values calculated from the model and the experimental values. figure 3 also shows that the model rate values were slightly higher than the experimental rates at low reaction rate values, but in general, the model excellently described the experimental results with a high r 2 . fig. 3. relation between the experimental and model rates. the results of the model solution, including the values of the reaction rate and the equilibrium constants, and the values of r 2 for each temperature, are summarized in table i. as can be noted, the values of ks, ks’, and ks increased with the temperature of the ion exchange process. the increase in the values of ks, ks’, and ks with increasing temperature and the values of ks remaining higher than the values of ks’ indicated that the reaction of ion exchange of fe (ii) with sodium improved with increasing temperature. the results of the model solution also showed that the values of kfe and kna lowered with the increase in temperature, indicating that the quantities at the catalyst surface of these two substances decrease with temperature rise. table i. reaction rate constant vs different temperatures temperature, °c ks, 1/liter.mmol.h ks ks', 1/liter.mmol.h kfe kna 20 10.1997 1.1318 9.0119 59.9865 1.8494 40 63.5805 1.2086 52.607 21.3015 1.6658 60 84.7414 1.2661 66.931 5.4395 1.3750 80 100.6624 1.4658 68.674 4.3195 1.2513 activation energies and frequency pre-exponential factors were calculated for both the forward and backward reaction constants (ks, or ks’) using the arrhenius equation [29]. the linear form of the arrhenius equation is: st� �u� � st� v� � wxy (13) where ki is the rate constant (ks, or ks’), t is the absolute temperature in kelvin, a is the pre-exponential factor for the chemical reaction, e is the reaction activation energy, and r is the general gas constant. figure 4 shows the linear form of the arrhenius equation, and the activation energy and frequency factor values were calculated for each of the forward and the back reactions of the ion exchange process. the activation energies were 31590.7j/mole for the forward reaction and 28105.5j/mole for the backward. the value of the frequency factor for the forward reaction was higher than for engineering, technology & applied science research vol. 12, no. 5, 2022, 9265-9269 9268 www.etasr.com kamal & abbas: langmuir-hinshelwood-hougen-watson heterogeneous kinetics model for the … the backward (6596171.7 versus 1418343.2). the large value of the activation energy of the forward reaction relative to the backward supports the fact that the ion exchange process improves with increasing temperature, which was experimentally observed. fig. 4. arrhenius plot of fe exchange kinetics. iv. conclusion the fe (ii) exchanged na-x zeolite was prepared by the ion exchange method from a feso4.7h2o solution. the catalyst color changed from yellow to dark brown with the ion exchange progress and increased temperature. the fe (ii) exchanged contents increased with temperature and reached 0.519 at 80°c after 8 hours. an lhhw heterogeneous kinetics model was developed and used to describe the ion-exchange experimental data. the results indicated the ability of the model to describe the experimental results with high correlation coefficients. in general, the values of the reaction constant and reaction equilibrium constant increased with temperature, while the equilibrium 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[29] o. levenspiel, chemical reaction engineering. new york, ny, usa: john wiley & sons, 1998. microsoft word etasr_v12_n5_pp9404-9408 engineering, technology & applied science research vol. 12, no. 5, 2022, 9404-9408 9404 www.etasr.com said: visitors’ knowledge, awareness, and perception (kap) of climate change in mashar national … visitors’ knowledge, awareness, and perception (kap) of climate change in mashar national park, hail-saudi arabia mohamed ahmed said architectural engineering department, college of engineering, university of hail, hail, saudi arabia and department of architecture and planning, college of architecture and planning, sudan university of science and technology, khartoum, sudan mo.said@uoh.edu.sa received: 3 august 2022 | revised: 22 august 2022 | accepted: 28 august 2022 abstract-this paper assesses the knowledge, awareness, and perception (kap) of climate change among the visitors of mashar national park, hail, saudi arabia. empirically, it has been established that climate change has an impact not only on the cultural and natural heritage but also on the visitor traffic patterns in national parks. the objectives guiding the study center on the identification of the level of knowledge and the investigation of the perception of park visitors regarding climate change. in the hail region, which is in the kingdom of saudi arabia's north central region, the average temperature ranges from 39°f to 103°f and is infrequently lower than 31°f or higher than 108°f. this kap research adopted quantitative methods using a questionnaire survey for data collection. a total of 120 park visitors were purposively sampled for the study. it was concluded that the visitors in al-mashar park are not fully prepared to mitigate the impact of climate change even though hail is undoubtedly experiencing climate variability. according to the study's findings, recommendations were made to maintain the park and provide opportunities for managing the park in a way that would allow it to better adapt to the effects of climate change, maintain effective resource management, and improve tourist satisfaction. keywords-climate change; knowledge; park visitors; perception i. introduction climate change is a phenomenon that has been identified by numerous academic fields and authorities. the intergovernmental panel on climate change, defined climate change as a shift in the condition of the climate that may be identified and measured by changes in the mean and/or variation of its parameters [1]. extreme weather conditions, including those related to temperature, wind, rainfall, and humidity, may come from climate change, which has been ongoing for decades [2]. variable consequences of climate change affect the environment, human health, agriculture, and transport. climate change has resulted, among others, in heat waves and wildfires. according to [3], climate change refers to changes in the typical meteorological occurrences as well as their extremes, timing, and spatial distribution that express as hot or chilly, dry or moist, snowfall or winds, floods, or thunderstorm tracks, and increasing temperatures, as well as water currents or upwelling. climate change is a proven tendency toward extremes in the global climate, independent of underlying reason [3]. as a result, in order to discuss climate crisis, the indicators in issue must be quantifiable and show extreme behavior, i.e. a trend that deviates from the usual. extreme temperatures (ets) have a negative influence on socioeconomic events and human health in middle eastern countries [4]. with regard to local climate change, saudi arabia, the largest nation in the middle east, has seen a number of et occurrences and their aftereffects. for instance, on june 22, 2010, jeddah city experienced summertime high of 52°c [5]. several communities lost power as a result of the country's 8 power stations being forced to shut down due to the high temperature. due to the tremendous negative effects of ets, it is crucial for every region and nation to conduct thorough investigations of temperature extremes utilizing current records. this is crucial for saudi arabia, in which the semiarid and arid environment is dominant [6]. the two basic factors that trigger climate change are aspects related to biogeography, such as natural forces and factors that are caused by human activity, or anthropogenic influences. climate changes may result from human actions that lessen the amount of carbon that is absorbed from the atmosphere [7]. deforestation, farming methods, and other detrimental changes in land use are a few examples of these actions. growing population, rapid urbanization, and the lack of land use planning, in addition to the effects of changing temperatures, precipitation, wind, and solar radiation, continue to contribute to the degradation of the environment and water supplies [8]. in addition, industrialization, gas flaring, and forest burning contribute to the release of significant quantities of greenhouse gases into the atmosphere, which contributes to climate change. researchers have cautioned that changes in climatic factors could affect the ability of mountain tributaries to store snow and ice. the shift in seasonality could impede agricultural corresponding author: mohamed ahmed said engineering, technology & applied science research vol. 12, no. 5, 2022, 9404-9408 9405 www.etasr.com said: visitors’ knowledge, awareness, and perception (kap) of climate change in mashar national … development, including future hydrological installation planning and operation [9]. parks and protected areas are a germane context to investigate the perceptions of climate change because some visitors interact with climate-influenced resources and often notice climate-related biophysical impacts [9, 10]. conversely, many impacts (e.g. increased temperatures, decreased water in the soil, species migration) from a changing climate remain relatively unnoticeable in heavily developed metropolitan areas where the 80% of u.s. citizens reside [11]. therefore, parks and other nature-based areas provide unique opportunities to experience, notice, and respond to climate change impacts, which are perhaps much less apparent in the metropolitan built environment. national parks' ecological and cultural resources, as well as visitor patterns, will surely be impacted by climate change. with further global warming, it's conceivable that the places, times, and the number of people who visit parks will change. for instance, visitors may avoid the hottest months in low-latitude parks, whereas the season for visiting northern parks may last for several extra weeks or months. several environmental and social elements will determine whether park visitors monitor climate change and alter their behavior. however, a crucial first step for park management and surrounding communities to predict, plan for, and actively influence future attendance is recognizing likely change in visits based on past records and anticipated trends of change in temperature [12]. according to a un habitat report, cities cover 2% of the earth’s surface — yet, as hubs of social and economic activity, they consume about 78%of the world’s energy. and cities produce, on average, more than 60% of the co2 emissions and greenhouse gases that give rise to global warming and climate change. clearly however, the impact of climate change affects urban and rural dwellers alike — and saudi arabia has been experiencing it for at least during the last decade. with dry climatic conditions, its ecosystems are sensitive, water resources are limited, and agricultural fields are vulnerable to environmental transitions. the 2007 intergovernmental panel on climate change report showed that climate change has caused worldwide changes in precipitation levels, and that these have manifested in saudi arabia as increased levels of rainfall. in the major cities of the country, this increased rainfall, coupled with the presence of unplanned settlements, has led to increased hazards such as flash floods [13]. the physical infrastructure, natural ecosystem, cultural resources, visitor experience, and other intrinsic values of parks are at risk from the effects of climate change [14]. impacts from localized changes in climate may influence the quality of visitors’ experience and, therefore, visitors’ perceptions of climate change are a concern for resource professionals who manage nature-based leisure services [15, 16]. several studies show that climate related factors are important considerations for visitors making travel related decisions [17-21]. for example, it was found that certain climate variables, such as rain, storms, and higher humidity are likely to negatively influence travel decisions, in addition to higher temperatures alone, which are not always perceived as negative. similar researches [20, 21] all found that seasonality, extreme weather events, and annual climate variability impact visitor decisions. further, increased temperatures and changes in precipitation impact recreation opportunities and particularly the activities highly reliant on weather conditions [22, 23]. further, visitor experiences can also be impacted by climatic condition changes that result in loss or relocation of native species, introduction of invasive species, alteration of vegetation patterns, reduced availability of water, and increase in the frequency, severity, and size of wildfires [24]. according to [25], climate change is modifying species distribution, which makes conservation efforts more challenging. according to [16], measurable plant and animal responses to recent climate change within national parks have already been documented. as such, the management may need to alter practices and policies regarding allowable activities to accommodate changing species distributions and invasive species. in addition, the frequency and intensity of extreme weather events can impact the park resources and animal habitats [26-28]. the public's knowledge, understanding, and perception of climate change must be assessed in order to successfully implement sustainable environmental practices. the kap strategy of this study is therefore very helpful. kap research techniques are used to discover what people understand, believe, and act regarding a specific topic [29]. in light of this, research was conducted to determine the kap of park visitors in mashar national park regarding climate change. ii. aims and objectives the dominant rationale behind this kap survey is to address the gaps in climate change knowledge, awareness and perception among park visitors in al-mashar national park. this would be achieved through the objectives guiding the current study, which are: • to identify the level of knowledge of visitors regarding climate change in al-mashar national park. • to determine the awareness of visitors on climate change in al-mashar national park. • to investigate the perception of visitors regarding climate change in al-mashar national park. iii. materials and methods a. study area the hail region is situated in the northernmost region of saudi arabia. the area is 118,232km 2 in size. the only important city in the area is ha'il (hael), which is situated in the region's center. it is roughly 600km from riyadh, 450km from madinah, and 650km from tabuk, and has good connectivity to other regional centers. due to its elevation of 915m above sea level, ha'il experiences a mild climate. ha'il's geographic location offers a number of benefits, including a moderate climate and picturesque mountain and desert landscapes [12]. in ha'il, the winters are chilly, dry, windy, and mainly clear while the summers are lengthy, scorching, desert, and clear. the average annual temperature ranges from 39 to 103 o f, rarely falling below 31 or rising over 108 [22]. early may through early july and early september through midengineering, technology & applied science research vol. 12, no. 5, 2022, 9404-9408 9406 www.etasr.com said: visitors’ knowledge, awareness, and perception (kap) of climate change in mashar national … october are the ideal seasons to visit ha'il for hot-weather activities, according to the beach/pool score [13]. fig. 1. mashar national park. b. methodology this research uses a social constructionist approach to examine subjective meanings, experiences, and behaviors of visitors related to global standards of climate change. this kap research adopted the quantitative method using a questionnaire survey for data collection. there were 4 sections in the questionnaire. information on the sociodemographic characteristics of park visitors was presented in section a and sections b, c, and d consisted of questions regarding the knowledge, attitudes, and perceptions relating to climate change respectively. the content was validated to make sure that the items measured the things they were meant to measure. quantitative data analysis was done using spss software and was further presented and interpreted using frequency distribution tables and narratives were scripted to discuss the findings. iv. results and discussion a. visitors knowledge on climate change table i presents whether the visitors are informed of climate change as a concept. we see that the majority of 108 (90%) visitors claim to know what climate change is while 12 (10%) were not informed about climate change. table ii presents the sources of knowledge on climate change. table iii presents the visitors’ perception on the types of change in climate change. it should be noted that the majority of the respondents is aware of at least one major change in weather patterns due to climate change, but a significant minority (22.8%) claims to be unaware or uninformed. table i. being informed about climate change informed frequency percentage yes 108 90% no 12 10% table ii. sources of knowledge on climate change sources frequency percentage newspapers 25 15.4% radio 19 11.7% television 32 19.7% health workers 9 5.5% teachers 51 31.4% family members 13 8.3% religious leaders 10 6.2% others 3 1.8% table iii. climate change acknowledged types change frequency percentage excessive temperature 41 26.7% excessive cold 19 9.8% alteration in the rainfall pattern 42 27.4% recurring cyclones or tides 3 1.9% periodic floods 10 6.5% logging in water 7 4.5% unaware or uninformed 35 22.8% table iv. causes of climate change causes frequency percentage deforestation 45 29.4% industrial effluents 21 13.7% population growth 19 12.4% automobiles' dark exhaust smoke 15 9.8% high carbon emissions from developed nations 17 12.5% rapid urbanization and lifestyle changes 7 4.5% astrophysical event (polar wander) 3 1.9% unaware or uninformed 26 16.9% table iv presents visitors’ perception of the causes of climate change. b. visitors awareness on climate change table v presents how often visitors are getting informed on climate change. we can see that the majority is informed either frequently or very frequently. table vi presents the sources of information on climate change. it should be noted that the majority does not mention mass media as the source of information. engineering, technology & applied science research vol. 12, no. 5, 2022, 9404-9408 9407 www.etasr.com said: visitors’ knowledge, awareness, and perception (kap) of climate change in mashar national … table v. frequency of awareness of climate change frequency level frequency percentage very frequently 41 34.1% frequently 35 29.1% occasionally 16 13.3% rarely 11 9.1% very rarely 7 5.8% never 10 8.3% table vi. source of information on climate change source frequency percentage scientist 44 36.6% teacher 40 33.4% neighbour/friend 6 5% mass media 30 25% c. visitors perception on climate change table vii presents visitor’s perception of climate change while table viii presents the component of climate change felt the most by the respondents the majority of which reported temperature change as the most vivid climate change indicator. table vii. perceptions on climate change agree undecided disagree perception frequency % frequency % frequency % rainfall pattern is changing 90 78 10 10.3 20 16.6 timing of the rainfall is changing 70 58.8 8 6.6 42 33 the amount of rainfall is changing 80 66.6 4 3.3 36 30 the intensity of rainfall is changing 66 55 23 19.1 31 25.8 summer temperature is changing 60 50 15 12.5 45 37.5 hot waves are changing 90 75.1 8 6.6 22 18.3 cold waves are changing 70 58.3 20 16.6 30 25.1 winter temperature is changing 77 64.1 19 15.8 24 20.1 the overall annual temperature is changing 88 73.3 12 10 20 16.6 hail-storm event frequency is changing 100 83.3 0 0 20 16.6 thunderstorm and lightening event frequency is changing 60 50 40 33.3 20 16.6 wind velocity is changing 85 70.8 17 14.1 18 15 table viii. components of climate change felt the most component frequency percentage temperature 71 59.1% rainfall 32 26.6% wind 10 8.3% hail-storm 3 2.5% lightening 4 3.3% table ix. behaviors exhibited to reduce the impact of climate change felt the most behaviour frequency percentage reducing energy consumption 15 11.8% reducing water consumption 16 12.5% waste recycling 19 14.9% reducing consumption of disposable items 17 13.3% buying environmentally friendly products 12 10% installing renewable energy equipment, e.g. solar panels 8 6.2% none 17 13.3% don’t know/don’t understand 23 18.1% table ix presents the behaviors reported by the visitors on what they do to reduce the impact of climate change. it should be noticed that the majority already does something regarding climate change in their everyday life, but a significant minority of 23 (18.1%) visitors don’t know/understand the habits to be exhibited in order to reduce the impact of climate change. v. discussion this research has made it clear that visitors to al-mashar national park feel responsible for the protection of the park but are not fully equipped with the necessary technical know-how in terms of capacity on issues surrounding climate change in their region. it is also evident that the research subjects, i.e the al-mashar national park visitors, want to learn more about climate change and the actions they can take to mitigate its effects on these treasured landscapes. furthermore, with proper education and access to varying information sources about climate change, visitors can become important advocates in the need to respond to climate change, within the parks and their communities. vi. conclusion and recommendations since climate change is a complicated topic that is frequently met with skepticism, there is a need for convincing evidence to prove its truth. the findings of this study prove that, despite the fact that saudi arabia is clearly experiencing climate variability, visitors to al-mashar park are not adequately equipped to lessen the effects of climate change. the administration of protected areas, visitor traffic, and regional economics are all expected to be impacted in a complicated and cascading manner by a changing climate. recognizing the strong correlation between visitation and climate allows for future planning and has two main effects on the management of protected areas and municipal services: travel patterns will change [14] and services and facilities will need to adapt to changing needs. to adjust to the changing conditions, which are a result of climate change, involves minimizing harm and seizing advantageous chances [15]. in the future, it might be necessary for the administration of almashar national park to balance the benefits of shifting engineering, technology & applied science research vol. 12, no. 5, 2022, 9404-9408 9408 www.etasr.com said: visitors’ knowledge, awareness, and perception (kap) of climate change in mashar national … visiting patterns with the negative effects of both too few and too many people attend (either not enough tourists to support local businesses and far too many tourists that interfere with recreational fun), e.g. by increased recreation and education opportunities and visitation during shoulder seasons. changes in the environment as well as modifications in visitor usage and preference patterns are predicted to occur in the ensuing decades. protected places and their surrounding communities, like al-mashar national park, will need to adapt to the opportunities provided by changing visitors, and they may be able to take use of them. globally comparable historical weather data and future estimates are available, however the availability and methodology of visitation data in different protected areas varies greatly. al-mashar national park management can increase tourist satisfaction and combine it with increased efforts to measure human visitation trends. the current analysis can be followed by additional studies into relatively brief visitation patterns and other drivers of visitation in order to help 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[29] "the kap survey model (knowledge, attitudes, and practices)," spring. https://www.spring-nutrition.org/publications/tool-summaries/ kap-survey-model-knowledge-attitudes-and-practices. microsoft word etasr_v12_n3_pp8617-8627 engineering, technology & applied science research vol. 12, no. 3, 2022, 8617-8627 8617 www.etasr.com moustafa et al.: detecting mineral resources and suggesting a physical concentration flowsheet … detecting mineral resources and suggesting a physical concentration flowsheet for economic minerals at the northern border region of saudi arabia mohamed i. moustafa engineering college northern border university arar, saudi arabia ismail2251962@yahoo.com mohammed a. tashkandi engineering college northern border university arar, saudi arabia mohammd.tashkandi@nbu.edu.sa anas m. el-sherif engineering college northern border university arar, saudi arabia anas.alshareef2@nbu.edu.sa received: 8 march 2022 | revised: 28 march 2022 | accepted:5 april 2022 abstract-there is a limited number of studies on sand deposit resources of saudi arabia, which cover nearly the one-third of the area of the country, whereas most of these studies deal with the environmental rather than the mineralogical or mining aspects. in this paper, and in the effort to detect the mineral resources of the northern border region, the surficial wadi sediments along the ar'ar-sakaka road are studied. the deposits of several wadies (al aqra, shiban al hanzaliyat, and arar) are mixed. the sediments of the collected samples are investigated to determine definite areas characterized by a relatively higher content of heavy minerals and a relatively lower content of carbonate minerals that are also friable enough to be investigated by some of the available physical concentration techniques. a large quantity of the surficial deposits, weighing 4.69 tons was collected from the stretch at the investigated area which is 3km long and 1.5km wide. evaluation of the heavy minerals content, their types, and their ability for concentration and separation, was conducted. a suggested physical concentration flowsheet was concluded for concentrating and separating the contained economic minerals. the average heavy mineral content is 1.55 wt% and the identified economic minerals are magnetite, ilmenite, hematite, goethite, zircon, rutile, anatase, monazite, and xenotime. the other contained heavy minerals include monoclinic pyroxenes (diopside, and augite), monoclinic amphibole (winchite), and muscovite mica. dolomite and calcite carbonate are also contained. the concluding results ensure that magnetite, zircon, tio2 minerals, and monazite are mineable for separation in individual mineral concentrates. most of the detected economic minerals are recorded in the area for the first time. monazite, xenotime, and zircon are responsible for some recorded radioactivity in the area. keywords-wet gravity concentration; high intensity magnetic separation; heavy liquid separation; x-ray diffraction; scanning electron microscope i. introduction the sedimentary cover of the kingdom of saudi arabia contains many resources of economic importance such as phosphorous and aluminum. the precambrian rocks of saudi arabia are highly dissected by dry valleys that are filled by a wide variety of stream sediments. a thorough survey of the relevant literature indicates that there are no published studies on the economics of stream deposits in saudi arabia except for construction materials [1]. transported (allochthonous) sediments of economic interest are usually referred to by geologist as placer deposits. the fluvial process (river transport) is effective in liberating and transporting gold as well as many heavy minerals and may concentrate them to economic grade [2-4]. wadi arar is one of several main wadies in the northern border region of saudi arabia [5]. the mineralogical investigation of the surfacial sediments of wadi arar reflects the occurrence of some important economic minerals of iron and titanium. in fact, most of friable sand sediments, either placer beach sand, placer sand dunes, stream or wadi sediments, are sources of various economic minerals. it is important to detect the mineral resources of the northen border region, which is a wide area of almost 112,000km 2 . the investigation will start by covering the deposits along the area located to the right of the high way between arar and sakaka. at the end of this area, the deposits corresponding author: mohamed i. moustafa engineering, technology & applied science research vol. 12, no. 3, 2022, 8617-8627 8618 www.etasr.com moustafa et al.: detecting mineral resources and suggesting a physical concentration flowsheet … of several wadies (al aqra, shiban al hanzaliyat and arar wadies) are met and mixed. therefore, relatively larger amounts of sediments are noticed in the area. however, the amount of materials transported from each wadi may depend on several variables such as the flow type and the sediment load [6]. hence, the occurrence of various heavy minerals is expected and some of them may be of economic interest. the determination of the types and contents of the associated economic minerals of these deposits and their mineability for some physical concentration techniques are the main subject of the current study. ii. studied area and sampling techniques a. the studied area the studied area consists of friable sediments, mainly sand, carbonates, and silt. it is located to the right along the high way between arar and sakaka, 12km from arar, northern border region, until 10km before talat ammar, al gouf region, a distance of about 40km. twenty two samples were taken from the top surfacial meter of the deposits along a perpendicular profile, in a distance of 250m to the right of the high way. one sample was taken for each two successive kilometers. also, about 4.69 tons of the surfacial friable sediments were collected from the area located 14km before talaat ammar and extending towards sakaka. the area is about 3km along the high way and has a width of 1.5km to the right of the road (figure 1). the average depth of the taken sediments ranges between 20 and 30cm. fig. 1. the northern border region and the location of the studied area, at the right of the road from arar to talaat ammar. b. sampling techniques several techniques and instruments were used in the mineralogical investigation and the physical concentration of the collected samples. they include the following: • an oven for drying. • screening using a 2mm and/or 500µ size aperture screen to remove trash and/or large sediment fragments. • a jones riffle splitter to obtain representative samples of various weights. • a mechanical shaker and a set of standard sieves, with size apertures of 50, 3, 2, 1, 0.5, 0.25, 0.125, 0.063, and 0.045mm, at a definite adjustment of operating conditions to study the size distribution of the collected samples. • heavy liquid separation technique using bromoform (with 2.89gm/cm 3 density), separating funnels, glass funnels, fast filtration papers, glass rods, holders, and acetone. • a binocular microscope for investigating the mineral components of the various samples and also for counting the detected heavy mineral grains. • the outotec laboratory high intensity induced roll magnetic separator, model: mih (13) 111-5 physep-inc usa for the differentiation of the different heavy and economic minerals into magnetic and non-magnetic mineral fractions. the separator is adjusted at definite parameters of operating conditions: air gab, feeding rate, rotor speed, and definite splitter position adjustment between the two obtained magnetic and non–magnetic fractions, using definite ampere values. • a half-size shaking table to investigate the wet gravity concentration of the various economic and heavy minerals at a definite adjustment of operating conditions of feeding rate, feeding pulp density, washing water, and stroke frequency. the recommended deck side slope is in the range of 8-12mm/m and the stroke length is 16mm. • x-ray diffraction (xrd): philips x-ray generator (pw 3710/31) with automatic sample changer (pw 1775, 21 position) using scintillation counter, cu-target tube and ni filter at 40kv and 30ma was used. this instrument is connected with a computer system using the x40 diffraction program and astm cards for mineral identification. • the environmental scanning electron microscope (esem): highly purified picked mineral grains representing the different heavy minerals were examined by a philips esem model xl 30 equipped with an energy dispersive x-ray unit (edx). esem and edx analyses were used to investigate the morphological and chemical characteristics of the examined mineral grains. iii. the importance of titanium and zirconium minerals ilmenite is mainly used for the manufacture of titanium dioxide white pigment which is the whitest of all white pigments known today. this pigment is more stable, being entirely unaffected by acids or alkalis that dissolve and destroy other whites. it has the good ability to maintain its visual appearance for a considerable period of time and is stable up to 1800°c. rutile is mainly used in the manufacture of arcwelding electrodes, and for the production of titanium dioxide electrodes and is used as a coating material in ship-building and other structural steel for which there is a growing demand [7]. titanium forms extremely hard metallic compounds with carbon, silicon, nitrogen, and boron. these are used as tips for cutting tools and in abrasive stones and wheels. titanium engineering, technology & applied science research vol. 12, no. 3, 2022, 8617-8627 8619 www.etasr.com moustafa et al.: detecting mineral resources and suggesting a physical concentration flowsheet … dioxide is used as an opacifier in porcelain enamels on steel sheet for refrigerators, sanitaryware, etc. ceramic titanates are used in the electric industry. ilmenite and rutile are now extensively used in the paint industry as well as in rubber, plastic, paper, textile, and ceramic industries [8-9]. the three principal zircon-based industries are refractories, foundries, and ceramics. zircon sand is used in molds and shall cores, while it is becoming important to the foundry market. due to its chemical inertness, good heat conductivity, high specific gravity, low expansion, good resistance to abrasion, high melting point, and size stability upon heating up to l,750°c, zircon is an outstanding refractory mineral. another traditional usage is in the ceramic industry, where the finely milled material is applied to glazes and its high refractive index is utilized to good effect for pacification purposes [10]. zirconium offers excellent corrosion resistance and, consequently, is widely used in chemical process equipment, reactor vessels, and aerospace engineering. in particular, in the nuclear industry, zirconium in the form of zircaloy has yet to find a competitor as a cladding and structural material in watercooled, pressurized, and boiling water type nuclear reactors [9]. iv. results and discussion a. treatment of the collected samples for each of the 22 collected samples, the used mineralogical analysis procedure program was: • drying of the collected individual samples at 110 o c for 1h. • screening with a 2mm aperture screen to remove the oversize wt% (table i). • each sample was split to obtain a relatively smaller representative sample of suitable weight. • using the relatively smaller representative sample, the slime wt% content was determined using the decantation method. the decantation was repeated several times until the decanted water became clear from any suspended particles. the residue of sediments was dried and weighed. the wt% of slime content was calculated (table i). • each deslimed original sample was subjected to a process of wet gravity concentration to obtain a bulk first tabled concentrate containing most of the contained economic minerals and a considerable portion of other heavy minerals. the grade of the obtained bulk concentrate was low while the recovery for most of the individual economic minerals is very high. the obtained individual tabled concentrates of the treated 22 samples range between 5.6 and 22 wt% (table i). • screening process with a 500µ size aperture screen was carried out for each individual bulk tabled concentrate to remove some of the oversized calcareous fragments which can affect the feeding rate during the magnetic separation. the wt% of the obtained oversize fraction was calculated (table i). • for each obtained undersize fraction (-500µ), the process of magnetic separation was carried out using successive current values of 0.05, 0.6, and 1.5a. the weight % for each obtained fraction was calculated (table i). • for each obtained individual non-magnetic fraction at 1.5a, wet gravity concentration process was carried out to obtain a second tabled concentrate for each sample. this fraction would contain most of zircon and tio2 minerals (rutile and anatase). • for each obtained second tabled concentrate, the process of heavy liquid separation using bromoform (2.89g/cm 3 ) was carried out. • mineral identification and counting: each of the obtained bromoform heavy liquid fractions was investigated under the microscope. a definite representative number of grains, ranging between 750 and 1,000, for each individual heavy fraction were detected and counted (table i). the grain size of the mineral grains must be considered during the microscopic counting. the weight percent of each mineral in every fraction was calculated using the equation of [11]. due to the investigation of several samples in wadi arar [5], it is known that magnetite is the essential economic mineral in the area, while ilmenite and goethite are considered minor ones. so, it is better to depend on the contents of magnetite, zircon, and rutile in evaluating the investigated samples. hence, both the obtained magnetic fractions, at 0.05a which contains most of the magnetite content, and the nonmagnetic fraction at 1.5a which contains most of zircon and rutile contents, can be used to choose the most suitable sediment region for carrying out the physical concentration experiments. however, both the other two magnetic fractions obtained at 0.6 and 1.5a are composed mainly of pyroxenes, amphiboles, and minor ilmenite, goethite and monazite. then, the region at the end of the investigated area is considered to be the relatively more enriched with economic minerals (table i). it also contains a relatively lower content of the calcareous fragments and the most friable sediment grains. this is why the relatively larger bulk sample was collected from this region. b. the physical concentration of the bulk large sample for the collected larger sample of 4.69 tons, the following steps were carried out: 1) determination of the +2 mm oversize fraction a representative sample of 2kg was taken from the collected bulk raw sediments. screening was carried out for the sample using an aperture screen of 2mm. the trash oversize fraction was calculated as 1.93 wt%. 2) determination of the grain size distribution a considerable representative sample was taken from the obtained undersize fraction (-2mm) and was treated using the mechanical shaker and a set of sieves with screen aperture sizes of 1, 0.5, 0.25, 0.125, and 0.075mm. taking into consideration the obtained +2mm oversize fraction into calculation, the various grain size classes are given in table ii. engineering, technology & applied science research vol. 12, no. 3, 2022, 8617-8627 8620 www.etasr.com moustafa et al.: detecting mineral resources and suggesting a physical concentration flowsheet … table i. different mineralogical treatments and components of the investigated collected raw samples. m=magnetic and nm=nonmagnetic fractions, fr=fraction and conc.=concentrate s a m p le + 2 m m % s li m e % f ir s t ta b le d t a il in g % f ir s t ta b le d c o n c . % distribution of the magnetic fractions of the first tabled concentrate % distribution of the various obtained tabled fractions of the 1.5a nonmagnetic fr % original heavy frs original mineral composition contents of the heavy fractions, % +500µ 0.05am 0.6am 1.5am 1.5am second tabled tailing second tabled conc. z ir c o n r u ti le p y r o x e n e s c a r b o n a te s 1 7.7 2.1 68.2 22 5.46 0.41 1.15 1.59 13.39 11.10 2.3 0.103 0.046 0.026 0.025 0.006 2 23.9 5.8 60.4 9.9 2.82 0.08 0.66 1.07 5.26 3.94 1.3 0.057 0.027 0.012 0.014 0.004 3 15.1 1.7 72.5 10.7 3.90 0.24 0.37 0.46 5.73 4.57 1.2 0.049 0.023 0.010 0.010 0.005 4 8.5 2 79.2 10.3 3.22 0.32 0.48 0.49 5.80 4.39 1.4 0.064 0.032 0.013 0.015 0.004 5 15.3 0.9 76.3 7.5 1.95 0.39 0.51 0.41 4.25 3.71 0.5 0.016 0.006 0.003 0.004 0.003 6 13.5 1.7 76.8 8 1.74 0.20 0.32 0.44 5.29 4.16 1.1 0.032 0.015 0.007 0.006 0.004 7 32 1.3 54.8 11.9 5.09 0.18 0.35 0.53 5.75 4.53 1.2 0.053 0.023 0.011 0.016 0.003 8 2.3 1.8 82.9 13 2.27 0.39 0.63 0.50 9.21 6.95 2.3 0.097 0.048 0.029 0.014 0.006 9 19.6 1.5 70.9 8 2.54 0.29 0.44 0.42 4.31 3.54 0.8 0.021 0.011 0.004 0.003 0.002 10 8.5 1.4 81.6 8.5 2.24 0.36 0.51 0.49 4.90 3.63 1.3 0.036 0.017 0.008 0.009 0.003 11 4.5 0.7 82.1 12.7 3.58 0.30 0.49 0.62 7.71 5.78 1.9 0.064 0.023 0.011 0.022 0.008 12 3.7 1.4 81.9 13 2.56 0.40 0.59 0.68 8.78 6.64 2.1 0.069 0.035 0.018 0.014 0.003 13 8.2 1.6 78.2 12 1.58 0.33 0.56 0.61 8.91 6.56 2.4 0.071 0.035 0.014 0.015 0.006 14 10.3 1.2 76.6 11.9 3.10 0.45 0.79 0.77 6.78 5.36 1.4 0.053 0.028 0.010 0.011 0.003 15 5.6 1.9 81 11.5 3.08 0.38 0.59 0.51 6.95 5.04 1.9 0.117 0.052 0.024 0.033 0.007 16 1.8 2.2 87.5 8.5 2.18 0.33 0.46 0.43 5.11 4.14 1.0 0.078 0.035 0.016 0.023 0.004 17 2.6 1.8 84.9 10.7 2.38 0.33 0.55 0.55 6.91 5.01 1.9 0.136 0.061 0.027 0.036 0.012 18 0.8 1.5 84 13.7 2.47 0.70 1.19 0.96 8.38 6.54 1.8 0.143 0.071 0.019 0.043 0.010 19 0 1.8 90.3 7.9 1.82 0.35 0.61 0.55 4.56 3.65 0.9 0.100 0.055 0.020 0.017 0.007 20 5.1 1.9 82.1 10.9 2.16 0.40 0.65 0.60 7.09 5.80 1.3 0.085 0.045 0.018 0.017 0.005 21 0.1 1.6 92.7 5.6 1.82 0.20 0.29 0.28 3.00 2.50 0.5 0.044 0.021 0.009 0.011 0.003 22 11.2 1.7 78.4 8.7 2.19 0.25 0.46 0.41 5.39 4.54 0.8 0.079 0.040 0.016 0.016 0.008 3) determination of slime content a relatively smaller representative sample was taken from the obtained under-size fraction (-2mm) to determine the slime content (-63µ) of the investigated raw sediments. the process of decantation was carried out for the sample. the residue of sediments was dried and weighed. the calculated slime content is 2 wt% (figure 2). table ii. various grain size classes of the studied raw sediments items grain size classes, mm distribution of grain size of raw sediments, wt% 1 + 2 1.93 2 + 1 0.34 3 + 0.5 3.79 4 + 0.25 34.81 5 + 0.125 39.80 6 + 0.075 14.68 7 0.075 4.65 total % 100 4) heavy mineral separation with bromoform heavy liquid several relatively smaller representative samples were taken from the obtained deslimed fraction. the process of heavy liquid separation using bromoform was carried out for 3 of these representative samples. their weight ranged between 30 and 38g. the heavy mineral content was determined by taking the average of the individually obtained heavy bromoform fractions. the determined heavy mineral content of the investigated original raw sediments is 1.55 wt%. 5) wet gravity concentration a representative technological sample weighing 1290kg was taken from the bulk collected raw sediments (figure 3(1)) of the area under investigation. the undersize sediment fraction (-2mm sized grains) was subjected to a rougher wet gravity concentration using the shaking table. several circuits of wet gravity concentration by shaking table were carried out (figure 2). a) rougher wet gravity concentration several authors explained the operation principles of shaking tables [12-15]. several representative raw sand samples were treated individually at different feeding rates, feed pulp densities, and washing water. each time, a definite sample weight of about 100kg was dried using sunlight and screened using a 2mm aperture screen to remove the oversize fraction (+2mm), and was then subjected to a rougher stage of wet gravity concentration by shaking table (figure 3(2)). the feeding rate ranged between 80 and 140kg, the feed pulp density ranged between 10 and 19 wt% while the used washing water ranged between 1.4 and 3.2l/m. engineering, technology & applied science research vol. 12, no. 3, 2022, 8617-8627 8621 www.etasr.com moustafa et al.: detecting mineral resources and suggesting a physical concentration flowsheet … fig. 2. a simplified flowsheet showing the different treatment stages of the studied sediments to obtain the various economic mineral concentrate fractions. the following parameters represent the concluded optimum adjustment of operating conditions: feeding rate 100kg/h, feeding pulp density 14 wt%, washing water 2.2l/min, stroke length 12mm, and stroke frequency 300rpm, while suitable longitudinal and side slope values were used. the obtained rougher tabled concentrate (c1) weighs 136.79kg and contains 8.15 wt% heavy minerals (hm). the middling (m1) weighs 197.32kg and contains 2.85 hm. the tailings (t1) weighs 955.9kg, and contains 0.4 wt% hm (table iii). these three obtained tabled fractions represent 10.6, 15.3, and 74.1 wt% of the original raw sediments respectively. the obtained rougher tailings were discarded (figure 2). for a treated sample with feeding rate of 115kg/h, feed pulp density of 19 wt% and washing water of 1.4 l/min, the obtained tabled tailing (t1a) represents 78 wt% of the treated feed and contains 1 wt% heavy minerals. for another treated sample, with 140kg/h feeding rate, 11 wt% feed pulp density, and 3.1 l/min washing water, the obtained tailings (t1b) represent 81 wt% of the treated feed but contain 0.67 wt% hm. it is obvious that both the used feeding rates and feed pulp densities are very important in the recovery of the hm inside the tabled concentrate and lowering their loss in the tabled tailing fraction. b) cleaner wet gravity concentration the three shaking table parameters: feeding rate, feed pulp density, and washing water were recorded to obtain the suitable adjustment of operating conditions. the feeding rate ranged between 40 and 50kg/h, the feed pulp density ranged between 6-10 wt%, and the washing water between 1.65 and 2.75 l/min. using several adjustments of the operating conditions, c1 and c2 were mixed and treated on several batches by shaking table (figure 3(3)), and finally three fractions were obtained. the final obtained tabled concentrate c3 weighs 33.87kg and contains 30.44 wt% hm. the final obtained tabled middling m3 weighs 48.8kg and contains 4.66 wt% hm. the final obtained tabled tailings (t3) weighs 77.53 wt%, and contains 1.25 wt% hm table iii. these three fractions represent 21.14, 30.46, and 48.4 wt% of the treated feed respectively. on using the most effective adjustment of operating conditions as 50kg/h engineering, technology & applied science research vol. 12, no. 3, 2022, 8617-8627 8622 www.etasr.com moustafa et al.: detecting mineral resources and suggesting a physical concentration flowsheet … feeding rate, 7.5 wt% feed pulp density, and 2.5 l/min washing water, the obtained tabled tailing (t3a) represents 71 wt% of the treated feed and contains 0.75 wt% of heavy minerals. fig. 3. the various treated fractions using the wet gravity concentration by shaking table and the different obtained magnetic and nonmagnetic fractions: (1) the collected raw sand, (2) the rougher tabling of raw sand, (3) the cleaner tabling of the obtained two tabled concentrates, (4) the scavenger tabling the obtained tabled middling (m1), (5) the scavenger tabling of the obtained two tabled middlings (m1 and m2), (6) the tabling of the non magnetic fraction containing zircon and rutile, (7) the obtained nonmagnetic fraction at 1.5a, (8) the obtained magnetic fraction at 0.05a, (9) the obtained magnetic fraction at 0.3a, (10) the obtained magnetic fraction at 0.6a, and (11) the obtained magnetic fraction at 1.5a. table iii. obtained tabled fractions with their symbols, weights, heavy bromoform fractions, and corresponding original contents item deparated fraction heavy content, % original heavy content, % 1 deslimed raw sediments 1.61 1.55 2 rougher concentrate 8.15 0.84 3 rougher middling 2.85 0.43 4 rougher tailings 0.40 0.29 5 scavenger concentrate 10.00 0.18 6 scavenger middling 3.43 0.08 7 scavenger tailings 1.51 0.16 8 cleaner concentrate 30.44 0.80 9 cleaner middling 4.66 0.18 10 cleaner tailings 1.25 0.075 11 concentrate of m2+m3 15.13 0.102 12 tailings of m2+m3 2.83 0.154 13 concentrate of t2+t3 10.24 0.046 14 tailings of t2+t3 1.18 0.197 15 non-magnetic fraction of back magnetic separation 6.09 0.089 16 tabled non-magnetic tailings 0.96 0.021 17 tabled non-magnetic zircon and rutile concentrate fraction 30.00 0.08 18 bulk magnetic fraction of back magnetic separation 70.00 0.81 it was noticed that some of the relatively larger composite grains of grain sizes smaller than 2mm and larger than 0.6mm were increased and were collected within the tabled concentrate (c3). these composite grains were most probably composed of calcareous and sand materials. they were noticed with c1 and c2 but with relatively lower contents. screening using an aperture screen of 0.6mm was carried out for the obtained c3 concentrate. an oversize (+0.6mm) fraction weighing 4.06kg was obtained (figure 2). however, these composite grains are not too hard and can be effectively diminished in size using one or two stages of attritioning process at the top of the flowsheet of figure 2. in this case, the process of the non-economic screening stage using a 0.6mm aperture screen can be neglected. c) scavenger wet gravity concentration the obtained tabled rougher middling (m1) was treated with the shaking table (figure 3(4)), and 3 tabled fractions were obtained. the tabled concentrate (c2) weighs 23.41kg and contains 10 wt% hm, the tabled middling (m2) weighs 29.98kg and contains 3.43 wt% hm, and the tabled tailings (t2) weighs 143.93kg and contains 1.51 wt% hm (table iii). these three obtained fractions represent 11.86, 15.19, and 72.94 wt% of the treated rougher middling respectively. the parameters of the shaking table were: 75kg/h feeding rate, 13 wt% feed pulp density, 2.1 l/min and washing water. d) wet gravity concentration of the obtained middling and tailings fractions both m2 and m3 middling fractions were mixed and treated by the shaking table (figure 3(5)) to obtain two fractions: the tabled concentrate (cm2m3) and the tabled tailings (tm2m3). the used shaking table parameters are: 60kg/h feeding rate, 10 wt% feed pulp density, and 1.6 l/min washing water. also, both t2 and t3 tailings fractions were mixed and treated by the shaking table to obtain two fractions: the tabled concentrate (ct2t3) and the tabled tailings (tt2t3). the used shaking table parameters are: 100kg/h feeding rate, 12 wt% feed pulp density, and 2.2 l/min washing water. e) magnetic separation and fractionation to obtain most of the magnetic economic minerals, the process of magnetic separation is suggested due to the scarcity of water in the region. more than 25 wt% of the weight of the obtained final concentrates c3, cm2m3 and ct2t3 are magnetic minerals. most operating conditions for magnetic separators are explained in [16-17] in order to obtain the most magnetic minerals in only one magnetic fraction of a relatively smaller weight and using only one stage of dry magnetic separation. more efficient wet high intensity magnetic separation can be carried out only for such obtained small magnetic fractions, at various successive current values. the used operating conditions for the first dry magnetic separation and the fractionated dry magnetic separation are: 10kg/h feeding rate, 140rpm magnetic drum speed, 2mm air gap, and 2a current for the first magnetic separation and are 0.05, 0.3, 0.6 and 1.5 for the successive four current values for the second magnetic separation circuit (figure 2). engineering, technology & applied science research vol. 12, no. 3, 2022, 8617-8627 8623 www.etasr.com moustafa et al.: detecting mineral resources and suggesting a physical concentration flowsheet … f) cleaning wet gravity concentration of zircon and rutile minerals fraction a bulk non-magnetic fraction is obtained by mixing the nonmagnetic fraction obtained from the c3 tabled concentrate at 2a with the non-magnetic fraction of the magnetic separation at 2a of the mixed cm2m3 and ct2t3 tabled fractions in addition to the obtained non-magnetic fraction at 1.5a due to the magnetic separation of the obtained bulk magnetic fraction (figure 2). finally, the obtained bulk nonmagnetic fraction weighs 31.42kg and contains 4.08 wt% hm (table iii). most magnetite and goethite were separated and contained in the obtained magnetic fractions. the majority of zircon and rutile mineral grains were contained in the obtained non-magnetic fraction at 1.5a. the specific gravity of zircon mineral grains is 4.6 and that of rutile is 4.2, while most of the associated gangue mineral grains have specific gravities ranging between 3.4 and 2.65. then, a circuit of wet gravity concentration using shaking tables (figure 3(6)) was carried out for the aforementioned bulk non-magnetic fraction. two tabled fractions were obtained, the tabled concentrate, weighing 3.37kg and containing 30 wt% hm and the tabled tailings, weighing 28.05kg and containing 0.96 wt% hm (table iii). the obtained tabled middlings are recycled with the treated feed. the used shaking table parameters are feeding rate of 40kg/hour, feed pulp density of 5 wt%, and washing water of 2.75 l/min. the mineral composition of the heavy bromoform fractions of the different obtained tabled fractions in addition to the deslimed original raw sand sample are given in table iv. using the same stages of concentration and separation of the flowsheet of figure 2, another sample of 3400kg of the investigated sediments was treated and finally 49.73kg were obtained as bulk magnetic fraction. due to the back magnetic separation at 2a, two non-magnetic fractions were obtained at 2 and 1.5a weighing 152.43kg and 7.52kg respectively. the bulk magnetic fraction (49.73kg) was treated through four successive stages of magnetic separation at four different successive current values: 0.05, 0.3, 0.6, and 1.5a. the non-magnetic fraction of the magnetic separation stage at 0.05a is considered the feed of the second magnetic separation stage at 0.3a. the nonmagnetic fraction of the last separation stage is the feed of the third magnetic separation stage at 0.6a where the obtained nonmagnetic fraction is the feed of the final four magnetic separation stage at 1.5a. table iv. heavy and economic mineral contents of the obtained various tabled fractions with their corresponding contents of the heavy bromoform fraction (h br fr) weight percentages fractions heavy fractions %. mineral components of heavy fractions % carbonates pyroxenes goethite ilmenite rutile zircon monazite magnetite quartz t1 0.40 1.41 86.49 12.08 0.00 0.00 0.00 0.00 0.00 0.00 t1a 1.00 3.10 71.00 6.40 0.00 0.00 0.00 0.00 19.5 0.00 t1b 0.67 1.40 91.90 6.70 0.00 0.00 0.00 0.00 0.00 0.00 t2 1.51 1.82 91.30 4.07 0.00 1.74 1.09 0.00 0.00 0.00 t3 1.25 0.78 92.70 3.72 0.00 3.45 0.00 0.00 0.00 0.00 t3a 0.75 1.90 94.2 3.20 0.00 0.00 0.00 0.00 0.00 0.00 t4 0.96 1.38 93.11 4.02 0.00 1.48 0.00 0.00 0.00 0.00 m1 2.85 1.64 86.83 3.24 3.83 1.30 1.53 0.00 1.66 0.00 m2 3.43 0.98 91.52 4.89 0.55 0.98 1.08 0.00 0.00 0.00 m3 4.66 0.41 90.04 5.96 0.46 1.03 1.58 0.51 0.00 0.00 cm2m3 15.13 0.60 78.50 13.10 1.30 2.50 3.30 0.70 0.00 0.00 tm2m3 2.83 0.60 98.40 0.70 0.00 0.00 0.20 0.10 0.00 0.00 ct2t3 10.20 1.40 77.30 11.30 0.00 5.00 4.30 0.80 0.00 0.00 tt2t3 1.20 1.50 94.80 2.30 0.00 1.60 0.00 0.00 0.00 0.00 c1 8.15 0.816 35.651 11.531 13.69 3.10 7.50 3.03 24.68 0.00 c2 10.00 1.688 80.870 1.80 8.62 1.09 2.18 0.00 3.76 0.00 c3 nm 6.09 1.01 13.32 0.00 0.00 23.29 62.38 0.00 0.00 0.00 deslimed raw sand 1.61 1.150 59.054 9.371 8.46 2.03 4.48 1.64 13.82 0.00 light br. fr. of raw sand 8.50 0.00 0.00 0.00 0.00 0.00 0.00 0.00 91.50 finally, another four successive magnetic fractions were obtained: at 0.05a, weighing 12.67kg, at 0.3a, weighing 7.58kg, at 0.6a, weighing 12.86kg, and at 1.5a, weighing 9.10kg. the obtained non-magnetic fraction at 1.5a weighs 7.52kg. the final obtained non-magnetic fraction at 1.5a was mixed with the non-magnetic fraction at 2a and a bulk nonmagnetic fraction of 159.95kg was obtained and was subjected to wet gravity concentration using the available half-size shaking table. the final tabled zircon and rutile fractions weighing 7.67kg and containing 35 wt% zircon and rutile were obtained. each obtained magnetic fraction was mixed with the corresponding obtained one of the treated 1290kg sample (see the flowsheet in figure 2) along with the two obtained zircon and rutile fractions of the two treated samples, weighing 1290 and 3400kg, and the following obtained five concentrate fractions were obtained: the tabled zircon and rutile fraction, weighing 11.04kg (figure 3(7)), the magnetic fraction at 0.05a, weighing 17.04kg (figure 3(8)), the magnetic fraction at 0.3a, weighing 9.58kg (figure 3(9)), the magnetic fraction at 0.6a, weighing 16.89kg (figure 3(10)), and the magnetic fraction at 1.5a, weighing 11.59kg (figure 3(11)). c. the mineralogical investigation most of the detected heavy and economic minerals are concentrated in relatively finer grain sizes. almost all of them are present in the undersize fraction of a screen with an aperture of 0.5mm. most previous studies ensured that heavy minerals are highly concentrated in the relatively finer grain size classes [18-19]. engineering, technology & applied science research vol. 12, no. 3, 2022, 8617-8627 8624 www.etasr.com moustafa et al.: detecting mineral resources and suggesting a physical concentration flowsheet … fig. 4. xrd patterns of the different separated fractions: (1) ferromagnetic fraction separated at 0.05a, (2) magnetic fraction separated at 0.3a, (3) magnetic fraction separated at 0.6a, (4) magnetic fraction separated at 1.5a, (5) heavy bromoform fraction obtained from the separated tabled nonmagnetic fraction at 1.5a. m=magnetite, i=ilmenite, h=hematite, mo=monazite, g=goethite, q=quartz, d=diopside, fd=ferrian diopside, a=augite, do=dolomite, w=winchite, c=calcite, ch=chlorite, z=zircon, r=rutile, and an=anatase. it was noticed that a considerable portion of quartz grains, present particularly in the finer grain sizes, are stained with reddish to pink materials in addition to the presence of inclusions of opaque inclusions. therefore, the quartz grains are met in most obtained magnetic fractions, either at 0.05, 0.6, or 1.5a. the heavy silicate minerals are relatively coarser than most economic minerals grains. the grains are subrounded, rounded to well rounded, elongated more than spherical with highly pitted surfaces. many of their grains are locked or stained with magnetite fragments or inclusions. they have different color shades of dark green, green, brown, yellowish to brownish green or colorless. the grains are translucent to opaque. according to the xrd identification, their majority are monoclinic pyroxenes of augite and diopside in addition to minor winchite (monoclinic amphiboles). most of the magnetite grains are iron black and have a chain structure which is characteristic for the ferromagnetic grains of high magnetic susceptibilities. most of the grains have relatively finer grain sizes, they are angular to subangular or subrounded and spherical. many of the grains have cubic octahedron crystals. several grains are stained or locked with small parts of silicate minerals, most probably ferrian diopside. the identified xrd pattern of a sample of the obtained 0.05a magnetic fraction is given in figure 4(1). the presence of ilmenite and hematite in subordinate contents is noticed. the essential line of ferrian diopside is also given in the pattern. the identified mineral patterns of magnetite, ilmenite, and hematite are in accordance with the astm cards 86-1355, 89-2811, and 130534 respectively. it seems that individual ferriilmenite grains or ilmenite exsolved intergrowth with magnetite are present, in addition to the martitization of some magnetite grains it was noticed that for most of the obtained magnetic fractions of various different samples of the same studied area, the same mineral can be identified by more than one astm cards. for example, magnetite can be identified with the astm cards no. 86-1355, 086-1340, 75-1609, or 19-629. this may reflect the diversity of magnetite grains with respect to the source area, grain mineral chemistry, exsolution, inclusions or also the types of associated minerals in the identified sample. the edx analysis of an area of a sample from the obtained magnetite fraction at 0.05a is shown in figure 5(1). both k and al are related to the presence of minor muscovite in the ferromagnetic fraction. fig. 5. edx chemical analyses of the different obtained economic minerals: (1) an area chemical analysis of the ferromagnetic fraction separated at 0.05a, (2) a spot chemical analysis of a hematite grain separated at 0.3a, (3) a spot chemical analysis of an ilmenite grain separated at 0.3a, (4) a spot chemical analysis of a most probably chromspinel grain separated at 0.3a. engineering, technology & applied science research vol. 12, no. 3, 2022, 8617-8627 8625 www.etasr.com moustafa et al.: detecting mineral resources and suggesting a physical concentration flowsheet … the detected ilmenite grains are angular to subangular of grey color with bluish tints. the xrd pattern of a sample of the obtained magnetic fraction at 0.3a is shown in figure 4(2). the fraction is composed mainly of quartz, diopside, augite, ilmenite, and hematite, in accordance with the astm cards 89-8936, 082-0460, 24-0203, 003-0781, and 013-0534. minor portions of winchite, chlorite, and kaolinite are also noticed in the pattern. the edx analyses of a hematite and ilmenite individual grains in the obtained fraction are shown in figure 5(2)-(3). the edx analysis of one of the detected grains identified under the binocular microscope as pyroxene, gives the chemical analysis of most probably cr-spinel (figure 5(4)). in the obtained magnetic fraction at 0.6a, monazite and goethite are detected. most of monazite grains are rounded to well rounded, of yellowish to pale yellowish color and have relatively finer grain sizes. the xrd pattern of the fraction reflects its composition of quartz, diopside, goethite, and monazite (figure 4(3)), in accordance with the astm cards 79-1906, 71-1494, 17-0536, and 11-556. the edx analysis of two individual grains, one for monazite and one for xenotime are shown in figure 6(1)-(2). in fact, the second grain was thought to be monazite or magnetic zircon. it is well rounded elongated, colorless with pale yellowish tint color. the chemical analysis of the first monazite grain reflects the composition of rare earth elements, essentially ce, la, nd, pr, sm, and gd, phosphate in addition to ca, th, and u silicates. also, fe, al, mg and k are recorded. fig. 6. edx chemical analyses of the different obtained economic minerals: (1) spot chemical analysis of a monazite grain separated at 0.3a, (2) spot chemical analysis of a xenotime grain separated at 0.3a, (3) spot chemical analysis of a zircon grain separated as nonmagnetic at 1.5a, and (4) spot chemical analysis of a rutile grain separated as non-magnetic at 1.5a. it is known that th and u are incorporated by two exchange mechanisms in monazite and xenotime [20-27]: the brabantite exchange: (th, u) 4+ + ca 2+ = 2ree 3+ and the huttonite exchange: (th, u) 4+ + si 4+ = ree 3+ + p 5+ . it is obvious that the detected monazite is not homogeneous but contains exsolved intergrown with both huttonite and brabantite. the chemical analysis of xenotime reflects the composition of y, p and some heavy rare earths: er and yb. due to the presence of these radioactive minerals, the water quality index (wqi) and the irrigation water quality (iwq) of the groundwater in the area can help us determine the quality and drinkability of this water [28-29]. the xrd pattern of a representative sample of the magnetic fraction obtained at 1.5a gives the mineral composition of ferrian diopside, quartz, goethite, dolomite and winchite (figure 4(4)). these minerals are in accordance with the astm cards 83-0102, 78-2315, 08-0097, 34-0517, and 020-1390. the goethite grains are minor in the fraction, and have brownish, reddish, yellowish to grayish opaque color. the xrd pattern of the heavy bromoform fraction of the tabled non-magnetic fraction at 1.5a reflects the composition of zircon, rutile, anatase in addition to diopside and calcite (figure 4(5)), in accordance with the astm cards 81-0588, 72, 1148, 02-0387, 75-1092, and 5-586. the edx analysis of two individual grains, one for zircon and the one for rutile are shown in figure 6(3)-(4). the majority of zircon grains are prismatic, elongated, and spherical. the grains are mainly colorless with a considerable number stained with pink material. the majority of rutile grains have black, brown, red to dark-red colors. the grains are mainly elongated subangular to subrounded in shapes. several grains are very fine acicular prismatic. the detected anatase grains are bluish in color, relatively coarser than rutile. virtually, it is the first time such a study is applied to the fraiable sediments of the northern border region for economic mineral identification and their mineability of concentration and separation. the presence of zircon and rutile was ensured in addition to the other iron-bearing minerals. the suggested separation flowsheet of the different recorded economic minerals will be a guide for their industrial exploitation. in fact, there are no previous similar works, neither for economic mineral identification nor for their separation, except that of [5] for economic mineral identification of one of the wadies extended in the present area where the concluded content of total economic minerals was very low and most of the studied sediment locations were inside the arar city. also, not all the recorded minerals in the present study were detected in [5]. v. conclusions the detected heavy and economic minerals were recorded for the first time in the studied area. most of the recorded heavy minerals are totally concentrated in relatively fine grain sizes, finer than 500µ. on the other hand, the majority of the detected economic minerals have grain sizes finer than 250µ. the calculated original heavy mineral content equals to 1.55 wt%. the majority of heavy minerals are monoclinic pyroxene, mainly augite and diopside, in addition to minor monoclinic amphibole, mainly winchite. the identified economic minerals are magnetite (fe3o4), ilmenite (fetio3), goethite (feooh), zircon (zrsio4), rutile (tio2), anatase (tio2), monazite [(ce, la, nd)po4], and xenotime (ypo4). the detected monazite is not homogeneous, it contains exsolved intergrowths of huttonite and brabantite in addition to several other light rare earth elements. the detected xenotime contains the heavy rare earth elements er and yb. hematite (fe2o3) is also recorded engineering, technology & applied science research vol. 12, no. 3, 2022, 8617-8627 8626 www.etasr.com moustafa et al.: detecting mineral resources and suggesting a physical concentration flowsheet … but it may be composite with the martitite magnetite or with the ferriilmenite. the calculated original grades of the detected economic minerals are 0.21 wt% magnetite, 0.15 wt% goethite, 0.13 wt% ilmenite, 0.07 wt% zircon, 0.03 wt% rutile, and 0.025 wt% monazite. anatase is included within rutile content while xenotime is included within monazite content. most of these economic minerals can be easily concentrated and separated in acceptable grades and recoveries. the magnetite can be obtained inside an individual magnetic ferromagnetic fraction using the available dry magnetic separator. on using a wet low intensity magnetic separator, the grade of the obtained concentrate can be increased through one or two stages of separation. most of zircon and rutile mineral content is obtained in an individual non-magnetic fraction. the associated minerals have specific gravities ranging between 3.4 and 2.65. both these two economic mineral concentrates can be easily upgraded using the wet gravity concentration by spirals and then subjected to a circuit of the high tension electrostatic separation, where finally rutile is obtained as conductor while zircon is obtained as non-conductor. most of the contained ilmenite is obtained in a definite magnetic fraction associated with pyroxenes, amphiboles, and quartz. then, using both of the wet gravity concentration and/or rare earth roll magnetic separation, ilmenite can be obtained in an individual concentrate. goethite and monazite are obtained inside a magnetic fraction by a relatively greater magnetic field. they are associated with pyroxenes and quartz. then, using wet gravity concentration and electrostatic separation, goethite can be obtained as conductor while monazite is obtained as nonconductor. as a final conclusion, the presence of zircon, monazite, and xenotime in association with the iron-containing minerals in addition to the major quartz mineral grains, which are stained/coated with iron oxides may lead to the absorption of some radioactive elements on the grain surfaces of the associated minerals. if these three radioactive minerals are represented in relatively higher percentages in some locations, care must be taken in using the most upper surfacial deposits in building or agriculture. acknowledgement the authors wish to acknowledge the approval and the support of this research study by the grant no. if_2020_4448 from the deanship of scientific research in northern border university (n.b.u.), arar, kingdom of saudi arabia. references [1] a. m. al-safarjalani, placer gold deposits in the hofuf formation the eastern province of saudi arabia. al-ahsa, saudi arabia: king faisal university, 2004. 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[26] a.-m. seydoux-guillaume, r. wirth, w. heinrich, and j.-m. montel, "experimental determination of thorium partitioning between monazite and xenotime using analytical electron microscopy and x-ray diffraction rietveld analysis," european journal of mineralogy, vol. 14, no. 5, pp. 869–878, sep. 2002, https://doi.org/10.1127/0935-1221/2002/00140869. [27] m. i. moustafa, "chemistry and origin of enigmatic monazite and chevkinite/perrierite in the egyptian black beach sand," resource geology, vol. 60, no. 3, pp. 271–287, 2010, https://doi.org/10.1111/ j.1751-3928.2010.00132.x. [28] k. praveen and l. b. roy, "assessment of groundwater quality using water quality indices: a case study of paliganj distributary, bihar, india," engineering, technology & applied science research, vol. 12, no. 1, pp. 8199–8203, feb. 2022, https://doi.org/10.48084/etasr.4696. [29] n. kumar, a. a. mahessar, s. a. memon, k. ansari, and a. l. qureshi, "impact assessment of groundwater quality using wqi and geospatial tools: a case study of islamkot, tharparkar, pakistan," engineering, technology & applied science research, vol. 10, no. 1, pp. 5288–5294, feb. 2020, https://doi.org/10.48084/etasr.3289. microsoft word etasr_v13_n1_pp10005-10013 engineering, technology & applied science research vol. 13, no. 1, 2023, 10005-10013 10005 www.etasr.com malaoui et al.: geotechnical characterization of phosphate mining waste materials for use in ... geotechnical characterization of phosphate mining waste materials for use in pavement construction rachidamalaoui environmental laboratory, civil engineering dpt, echahid cheikh larbi tebessi university, algeria rachida.malaoui@univ-tebessa.dz (corresponding author) el haddi harkati mining laboratory, civil engineering dpt, echahid cheikh larbi tebessi university, algeria harkati.elhaddi@gmail.com mohamed redha soltani mining laboratory, civil engineering dpt, echahid cheikh larbi tebessi university, algeria msoltani.mohamedredha@univ-tebessa.dz adel djellali environmental laboratory, civil engineering dpt, echahid cheikh larbi tebessi university, algeria adel.djellali@univ-tebessa.dz abderraouf soukeur laboratory of hydrometallurgy and inorganic molecular chemistry, faculty of chemistry, university of science and technology houari boumediene, algeria abderraoufsoukeur@gmail.com rabah kechiched underground reservoirs laboratory: oil, gas, and aquifers, kasdi merbah ouargla university, algeria rabeh21@yahoo.fr received: 16 november 2022 | revised: 7 december 2022 | accepted: 9 december 2022 abstract waste rock materials are becoming widely used in road pavement and building constructions in many countries. in this work, experimental laboratory tests were carried out on the waste rock produced from the extraction of the phosphate in the kef-essenoun mine, to study the performance of road pavement foundations built with these types of material. two types of waste, namely phosphatic limestone (type 1) and limestone (type 2), were initially tested to determine the most suitable one to be used in pavement structures. the characterization tests showed that the presence of carbonate-fluorapatite and carbonatefluorapatite, and calcite, dolomite, and quartz are predominant in phosphatic limestone and limestone, respectively. the los angeles abrasion (la) and micro-deval (md) values range from 59.9% to 90.4% and 42.05% to 86.31% for phosphatic limestone and from 43.64% to 95.88% and 38.25% to 75% for limestone. the cbr values of type 1 and type 2 waste were found to be 10.5% and 18.7% respectively. the results show that these materials, classified as b42ts and b42s respectively, could be used cautiously in capping layers and pavement backfilling materials. furthermore, they must be treated with a hydraulic binder such as cement in order to improve their physical and mechanical properties. keywords-characterization; mine waste; phosphatic limestone; limestone; road construction; kef-essenoun engineering, technology & applied science research vol. 13, no. 1, 2023, 10005-10013 10006 www.etasr.com malaoui et al.: geotechnical characterization of phosphate mining waste materials for use in ... i. introduction road infrastructure projects require large quantities of materials. the growing demand for aggregates in the civil construction sector has become more pronounced in recent years as cities grow more and more. the use of unusual industrial mining products in road construction can contribute to the conservation of non-renewable natural resources and minimize the waste quantities produced by mining industries [1]. such large amounts of waste, resulting from mining operations, have led to the awareness regarding their impact on environment, ecology, and geotechnical side. the release of toxic components from heavy metals and acid mine drainage are examples of such effects. underground water contamination, large amounts of space of exploitable natural land, instability of the waste storage zone, and dust cloud generation are some examples of such effects. there are numerous economic and ecological gains in the exploitation of alternative materials for the road construction sector. when waste materials with adequate properties are used, it is possible to reduce energy consumption, transport distances, and extraction costs [2]. for several decades the reuse of waste materials as construction materials has been studied in depth, e.g. mine tailings [1-3], recycled construction and demolition wastes used in road construction, embankments and concrete [4-7], coal mining waste [8-9], plastic and rubber waste in flexible and rigid pavements, ferrocement mortar [10-12], steel slag and glass as secondary aggregates in asphalt mixtures [1315], tungsten mining waste [16], marine sediments [17], bottom ash and fly ash in geotechnical engineering [18], iron and gold mining waste [19], and red mud and lime [20]. in addition, pozzolanic materials such as cement, lime, fly ash, cement kiln dust, and ordinary portland cement have been used to stabilize some tailings materials for construction purposes [21-23]. algeria has a large reserve of phosphate [24]. about 41ha of land are currently under exploitation in kef-essenoun. the current removal mining rate is 2.8 million tons of ore with a stripping ratio of approximately 2.2 which produces annually 10 million tons of waste that must be removed and disposed of. the accumulation for several decades of waste rock from openpit phosphate mines and upgrading processes poses serious environmental, ecological, and health problems in the surrounding areas [25]. these types of waste are unsafe to humans, animals, and vegetation. they pollute the air, the surrounding soil, and contaminate the groundwater. the main objective of this research consists in suggesting a reusing solution in order to reduce the negative impact of rock waste on the environment. reusing consists of finding a new use for available waste materials with adequate acceptable properties in their current form in order to ovoid disposal on landfills. as reported in [26-31], those materials (phosphate tailings) could be widely used in building and road construction. the proposed reusing approach should be integrated in the algerian road guide. it is worth noting that studies on phosphate mining waste in algeria are rare, thus, chemical, mineralogical, physical, and geotechnical characterizations of mining waste from kef-essenoun phosphate mine were investigated in this study. ii. general setting the kef-essenoun phosphate mine (34.726784 e, 7.895978 n) is located on the southern flank of djebel onk cretaceous anticline in the eastern saharan atlas [32]. it is situated 7km southeast of bir el ater city (tebessa, northeast algeria) and about 21km to the algerian-tunisian border [33]. the study site extends approximately to 250ha and belongs to the djebel onk mining basin which represents the occidental part of gafsa-metaloui-onk basin containing many phosphorite layers deposited from late cretaceous to early eocene [32-34]. although this lateral continuity, the kefessenoun deposit displays substantial differences to the gafsa metlaoui basin, especially with regard to the lithology and the succession particularly in the phosphorite formation [35-36]. in the kefessenoun deposit, the sedimentary lithologies consist of ~ 500m thick succession of upper cretaceous (maastrichtian) to middle eocene (lutetian) age where upper thanetian phosphorite layer is mined for phosphate raw material [32-37]. mine waste rock from kef-essenoun mine (figure 1) consists of soil and rock excavated during the mining operations after the commercially recoverable part has been recovered. these waste rocks are unloaded and accumulated in huge quantities. between 2006 and 2017, the estimated quantity of waste rock produced is approximately 5.5 to 18.5mt/yr. this quantity will increase to more than 18mt/yr in the future (figure 2). fig. 1. phosphate mine waste hips nearby the mining site. fig. 2. estimated quantities of waste rock from kef-essenoun [38]. engineering, technology & applied science research vol. 13, no. 1, 2023, 10005-10013 10007 www.etasr.com malaoui et al.: geotechnical characterization of phosphate mining waste materials for use in ... fig. 3. tailings of kef essenoun mine: (a) phosphatic limestone, (b) limestone. those amounts of waste can be utilized in the field of pavement construction. the reuse of mine tailings for subgrade and foundation layers is a relatively new approach in algeria. the lack of fundamental knowledge about their behavior limits their reuse. therefore, and in order to examine the various aspects concerning the possibility of using this mining waste in road engineering, complete characterization is necessary. the objective of this experimental study is to make a geotechnical characterization of the two recycled mining materials of kefessenoun. in this research, the studied materials are phosphatic limestone (type 1) and limestone (type 2) (figure 3). iii. experimental program and test procedures a. initial testing and study material selection the mining waste samples used in this research were collected from different locations of stacked tailings located in the surroundings of the kef-essenoun mine. the waste consists mainly of phosphatic limestone and limestone. these materials were brined to the laboratory in order to describe their mineralogical, chemical, physical, and mechanical properties. b. chemical and mineralogical characteristics the analysis of the major elements was conducted by the algerian phosphate company somiphos using colorimetric, gravimetric, volumetric, ionometric, and spectrophotometric by atomic absorption spectrometry (aas) analytical methods. the phosphate ore tailings of crystalline phases were performed by x-ray diffraction, (xrd). diffraction patterns were made with a panalytical x’pert pro diffractometer equipped with a conventional x-ray (cu kα radiation, running at 40kv and 30ma) with detection in the 2θ range of 10-90°. c. physical and mechanical parameters of waste materials the main physical and mechanical characteristics of the studied waste samples are shown in table i. using oven drying at 105°c (+/5°c), the measured initial water content was about 4.62% and 8.54% for phosphatic limestone and limestone, respectively (nf p94-050). the following parameters were measured:  specific gravity was measured with a nf p94-054 pycnometer.  clay fraction activity was measured by methylene blue test (nf p 94-068).  liquid and plastic limits (nf p94-051).  particle size distribution was measured according to nf p 94-056.  modified proctor (nf-p 94-093).  california bearing capacity (nf-p94-078).  los angeles, micro-deval, and friability (p 18-573, p 18572, p18-576).  unconfined compressive strength procedure nf p98-230-3. the test particle size consists of a representative sample of soil passing through superposed sieves with openings from 50mm to 0.08mm. figure 4 shows the particle size distribution curves of the samples. the samples were classified according to the modified lpc classification system. according to the particle size curve, the percentages of cobbles, gravel, sand, silt, and clay in phosphatic limestone and limestone were 51%, 29%, 17.28%, and 2.72%, and 27.5%,29%, 40.23%, and 3.27%, respectively. the coefficients of uniformity (cu) and curvature (cc) obtained for phosphatic limestone and limestone were 69.44, 17.85, and 0.36, 4.11, respectively. based on the unified soil classification system, both sample types were classified as well-graded gravel (gm). the particle size distribution and gradation characteristics of the tested samples are shown in table i. fig. 4. particle size distribution curves of phosphatic limestone and limestone waste. d. soil classification based on the technical guidelines of embankment and capping layer construction (gtr), the tailing materials belong to the b class of sand and gravel soils with fines. depending on the nature of these materials, their class is b4. they have a passing percentage less than 12% and less than 70% from the of 80μm and 2mm sieves, respectively. there is no grain-size over 50mm. the methyl blue absorption value is more than 0.2. md coefficient and la coefficient are greater than 45. these types of materials are sensitive to water due to the existence of plastic fines and contain a large proportion of coarse particles, so they are generally pervious. the waste materials are classified as: b42ts (very dry) for type 1 and b42s (dry) for type 2 as can be shown in figure 5. engineering, technology & applied science research vol. 13, no. 1, 2023, 10005-10013 10008 www.etasr.com malaoui et al.: geotechnical characterization of phosphate mining waste materials for use in ... table i. physico-mechnical parameters of waste materials properties of mine railing unit type1 type2 moisture content % 4.62 8.54 ph 6.8 7.8 geotechnical properties—natural parameters grain size distribution color grayish beige shape angular angular particle size distribution silt and clay % 2.78 3.27 sand 17.28 40.23 gravel 29.00 29.00 cobbles 51.00 27.50 coefficient of uniformity (cu = d60/d10) 69.44 17.85 coefficient of gradation 0.36 4.11 cc = (d30)2/(d10 × d60) group symbol lpc gm gm optimum moisture content (wopt) 12.30 14.15 maximum dry density dmax kn/m 3 1.85 2.00 unsoaked cbr % 24.724 36.675 soaked cbr 10.548 18.293 free swelling 0.303 0.308 liquid limit (ll) 30.88 33.41 plastic limit (pl) not measured 23.805 plasticity index (pi) 9.6 methylene blue value (mbv) g/100g 0.83 1 carbonate content % 54 88 organic matter < 1 < 1 sand equivalent (se) 22.22 12.82 specific gravity kn/m3 2.737 2.631 apparent specific gravity 1.434 1.328 los angeles abrasion test 4/6.3 6.3/10 10/14 % % 82.9 75.5 72.2 95.88 59.36 43.64 10/25 16/31 25/50 68.8 59.9 90.4 43.74 88.3 84.4 micro deval and deval test 4/6.3 6.3/10 10/14 % 82.6 86.31 81.96 64 73 75 25/50 42.05 38.25 sand friability coefficient 32 31 material classification b42 ts b42 s unconfined compressive strength (ucs) after: 24 hours kn/m2 182 520 14 days 683 2671 28 days 715 2807 note: d10, d30 and d60 represent the percentage of soil particles that are smaller than 10, 30, and 60%, respectively table ii. chemical composition of the phosphatic limestone (type 1) and limestone (type 2) waste major elements (wt %) trace elements (ppm) p2o5 so3 co2 cao al2o3 mgo fe2o3 sio2 na2o k2o loi f h2o corg pb zn cu type1 0.40 0.72 0.02 37.84 0.70 4.66 0.35 10.40 0.42 0.04 18.80 2.05 1.54 0.22 30 60 2.50 type2 0.89 0.03 39.06 49.77 0.25 5.24 0.26 2.30 0.09 0.01 40.70 0.40 0.72 0.02 30 32.5 3.00 iv. results and discussion a. chemical and mineralogical 1) x-ray diffraction (xrd) the xrd pattern of the two samples is illustrated in figure 6. it shows the presence of the apatite mineral class with variable substitution rates of co� �� ,f� and oh� , including carbonate-fluorapatite [ca10(po4)5co3f1.5(oh)0.5], fluorapatite [ca5(po4)3f], carbonate-apatite [ca10(po4)6], carbonatehydroxyapatite [ca10(po4)3(co3)3(oh)2], hydroxyapatite [ca5(po4)3(oh)], and hydrated phosphate, but the gangue elements are basically represented by calcite [caco3], quartz [sio2], dolomite [camg(co3)2], and gypsum [caso4] [39-40]. carbonate-fluorapatite is the dominant phase indexed in a hexagonal symmetry (sg: p63/m) according to the astm xrd data reference 98-003-4653 [41]. however, limestone is richer than phosphatic limestone in calcite, quartz, and dolomite. 2) chemical analysis the chemical analysis results of the two phosphate waste types is presented in table ii. the results show a high percentage of major elements cao, sio2, and mgo for type 1 engineering, technology & applied science research vol. 13, no. 1, 2023, 10005-10013 10009 www.etasr.com malaoui et al.: geotechnical characterization of phosphate mining waste materials for use in ... and cao, mgo, and sio2 for type 2. however, type 1 has higher concentrations of p2o5. the chemical composition confirms that the mineral composition of phosphatic limestone and limestone contains four main minerals: carbonatefluorapatite, calcite, dolomite, and quartz. the results are in agreement with the findings of [25, 34-43]. fig. 5. classification of studied waste samples: a: fine soil, b: sandy and gravely soil with fine particles, and d: soil insensitive to water. (a) (b) fig. 6. xrd analysis of kef-essenoun mine waste: (a) phosphatic limestone, (b) limestone. b. basic characteristics the waste materials used in this study were grayish and beige in color for type 1 and type 2 respectively, with dry moisture content due to the arid climate of the region. the ph values of the tailings are 6.8 and 7.8, indicating basic ph. the specific gravity of limestone is lower than that of phosphatic limestone due to the presence of p2o5 in the latter. the phosphatic limestone sample is non-plastic, and thus, the measurement of the plastic limit and index was avoided. however, the limestone sample has a plasticity index (pi) of 9.6% which was validated by the methylene blue test. c. mechanical behavior of the materials 1) compaction characteristics the results of compaction tests of the waste materials, in terms of dry density and measured water contents, are given in figure 7. (a) (b) fig. 7. corresponding modified proctor compaction curves for mine wastes of (a) phosphatic limestone, (b) limestone. the 85% and 100% saturation curves are also shown. the results indicate that the limestone waste provides the highest mdd of 2.00g/cm 3 and omc of 14.15%. generally, the compaction characteristics depend on both the grain size distribution and the specific gravity of the materials. in this case, the presence of cenospheres (hollow particles of large size) is the main cause for the lower density of the phosphatic limestone samples. engineering, technology & applied science research vol. 13, no. 1, 2023, 10005-10013 10010 www.etasr.com malaoui et al.: geotechnical characterization of phosphate mining waste materials for use in ... 2) california bearing ratio (cbr) figure 8 shows the values of both unsoaked cbr and soaked cbr after 4 days of curing in water related to the mdd. it can be observed that the cbr values of the two types of samples increase as the mdd increases. it is also noticed that the phosphatic limestone waste gives a value of soaked cbr of 10.5%, indicating medium bearing capacity material, while the obtained value of soaked cbr of 18.7% of limestone indicates that it can be used as an appropriate material for the foundation layers of pavements. the fsi of samples obtained for type 1 and type 2 samples are 0.303% and 0.308%, respectively. these results show that these waste materials are not expansive (is 2720 (part xl)). fig. 8. cbr values related to mdd. 3) los angeles and micro-deval the variation of la and md values is shown in table i. the la values range from 59.9% to 90.4% for phosphatic limestone and from 43.64% to 95.88% for limestone for all the considered granular classes. the results indicate that limestone waste gives more suitable values, but these waste materials are unsuitable for pavement constructions. the values of la and md tests of materials have to be less than 45%. sand friability (fs) coefficient is an indicator to assess the resistance of untreated sandy materials used for pavement subgrade to traffic loading. the fs values of the samples are 32% and 31% for type 1 and 2 materials, respectively. the recommended limit for this use is fs ≤ 60. 4) unconfined compressive strength (ucs) the ucs of the mining waste samples was tested after 1, 14, and 28 days of curing as shown in figure 9. it is well known that the materials gain in strength overtime and the magnitude of compressive strength increased with increasing mdd of the compacted granular material. it was also shown that the compressive strength of limestone at 28 days is 3.9 times larger than that of the phosphatic limestone. on the other hand, the mechanical characteristics do not deteriorate with time. the limestone closes the interior ports by cementing the grains (lime reacts strongly with water and compaction energy), favored by the plasticity of the compacted material. in this case, limestone and rock behave similarly and the compressive resistance increases over time. furthermore, the phosphatic limestone does not cement during compaction due to the absence of plasticity and the presence of a large content of friable phosphate, which explains its lower mechanical resistance. fig. 9. ucs of samples cured for 1, 14, and 28 days. v. possibility of using waste materials in road construction for the road material field the general rating of the mining wastes as sub-grade materials ranges from fair to poor. the phosphatic limestone waste is considered a water-sensitive material, found in a very dry hydrous state (ts) and is not normally reusable in the embankment construction or capping layer, but in certain cases, its humidification can be considered to bring it to the s (dry) or m (normal) state. the use of limestone waste material could be allowed in road construction with treatment by hydraulic binders. this treatment requires prior measurement of their mechanical strength. for compaction procedure, the very dry soil is considered as being impossible to compact properly by standard methods. in both dry (s) and very dry (ts) states, those soils are not easy to compact to form stable fill structures. the catalog of the national agency for technical control of public works algerian for new pavement design [44], requires the use of well-graded (gw) materials with pi less than 10% and la less than 40% in the base layer. the findings indicate that waste rock materials, which are categorized as b42ts and b42s, respectively, should be used with caution as backfill and capping materials for road paving. they need to be treated with a hydraulic binder, such as cement, to increase their mechanical and physical qualities, raising their classes as a result. increasing the mechanical properties of the tailing materials to be used as pavement sub-base materials will be cost effective and ecologically friendly since it will result in thinner sub-base layers and will maybe reduce the thickness of the pavement layer. in this case, stabilization is the best choice. as the mine is expanded, the waste piles created by its exploitation will ultimately result in great environmental and ecological issues. from the economic and environmental perspectives, the reuses of such waste are beneficial. 10 15 20 25 30 35 40 20 unsoaked cbr phosphatic limestone d r y d e n si ty c b r (% ) limestone mdd soaked cbr 18 engineering, technology & applied science research vol. 13, no. 1, 2023, 10005-10013 10011 www.etasr.com malaoui et al.: geotechnical characterization of phosphate mining waste materials for use in ... vi. conclusions the management of tailings and waste from mines and quarries is an essential requirement to limit their environmental, ecological, and geotechnical impacts. in the current research work, a characterization of two tailings from the kef-essenoun mine (phosphatic limestone and limestone) was investigated in order to allow reusing these materials in pavement foundations. the main findings of this investigation can be summarized as follows:  the waste materials contain mainly cao, sio2, and mgo. the phosphatic limestone has a much higher concentration of p2o5 (22.66 wt%) than limestone (0.89 wt%). in terms of trace elements, very low concentrations of pb, zn, and cu were detected. the mineralogical composition of the two phosphate wastes contains four main minerals: carbonatefluorapatite, calcite, dolomite, and quartz.  the materials are well-graded gravel containing all grain sizes from cobbles down to clay. the particles were of angular shape with very low plasticity index. they have no grains larger than 50mm, a passing proportion from of 80μm sieve less than 12%, and less than 70% for the 2mm sieve.  the los angeles and micro-deval coefficients of the studied materials exceeded 45%, and they are classified as b42ts (phosphatic limestone) and b42s (limestone).  from the points of mechanical behavior and applicability in road construction, the values of cbr and ucs, increase with mdd and the ucs increases with curing age.  the mechanical performance of limestone waste is more appropriate than phosphatic limestone's, and is governed essentially by the phosphate content (p2o5 wt%). the mechanical proprieties are improved with higher phosphate content. the phosphatic limestone presents low plasticity and a larger proportion of friable phosphate which lead to less material compaction.  in terms of environmental impact, the efficient reuse of mining waste in the road sector field helps reduce the production of waste, thereby minimizing the environmental damage and ensuring sustainable construction. both waste materials considered in this study could be used in pavement structure construction provided that they are treated with hydraulic binders. based on this study, the presented methodology could constitute a starting point for the investigation of the reuse of the mining waste of kef-essenoun mine in the field of road construction. vii. declarations a. author contributions rachida malaoui conducted all the physical and geotechnical characterization tests, investigation, formal analysis, and the writing of the original draft. abderraouf soukeur interpreted the chemical and mineralogical characterizations. the geological part was conducted by rabah kechiched. the interpretation of the results and the writing of the paper were done by rachida malaoui, adel djellali, and abderraouf soukeur. el haddi harkati and mohamed redha soltani were responsible for conceptualization, supervision, writing, reviewing, editing, and funding acquisition. b. funding this work is funded by the environmental laboratory under the grant no. a01l05un120120210001. acknowledgment the authors are grateful to the national company of phosphate somiphos for providing samples and filed assistance. we would also like to thank the staff of the civil engineering laboratory of larbi tebessi university. we thank warmly mr. malik atout for his help in 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[44] cttp, catalogue de dimensionnement des chaussees neuves. algiers, algeria: organisme national de controle technique des travaux publics, 2001. microsoft word 3-622-ed.doc engineering, technology & applied science research vol. 6, no. 1, 2016, 913-916 913 www.etasr.com ahmed et al.: penetration evaluation of explosively formed projectiles through air and water… penetration evaluation of explosively formed projectiles through air and water using insensitive munition: simulative and experimental studies mukhtar ahmed school of chemical and materials engineering national university of science and technology islamabad, pakistan mukhtar@scme.nust.edu.pk abdul qadeer malik school of chemical and materials engineering national university of science and technology islamabad, pakistan aqmalik46@yahoo.com shakeel abbas rofi school of chemical and materials engineering national university of science and technology islamabad, pakistan shakeelabbas@hotmail.com zheng xiang huang school of mechanical engineering nanjing university of science and technology nanjing, china huangyue@njust.edu.cn abstract—the process of formation, flying, penetration of explosively-formed projectiles (efp) and the effect of water on performance of the charge for underwater applications is simulated by ansysis autodyn 2d-hydro code. the main objective of an explosively formed projectile designed for underwater applications is to disintegrate the target at longer standoff distances. in this paper we have simulated the explosively formed projectile from ofhc-copper liner for 1200 conical angle. the affect of water on the penetration of efp is determined by simulations from ansysis autodyn 2-d hydrocode and by varying depth of water from 1cd-5cd. the depth of penetration against steel target is measured experimentally. flash x-ray radiography (fxr) is used to capture efp jet formation and its penetration against target is measured by depth of penetration experiments. simulation results are compared with experimental results. the difference in simulated and experimental results for depth of penetration is about 7 mm, which lies within favorable range of error. the jet formation captured from fxr is quite clear and jet velocity determined from flash x-ray radiography is the same as the ones obtained by using other high explosives. therefore, it is indicated that insensitive munition (8701) can be utilized instead of polymer bonded explosives (pbx) for air and underwater environments with great reliability and without any hazard. keywords-explosively formed projectiles; liner; jet formation; jet penetration; depth of penetration. i. introduction explosively formed projectiles have become the most lethal device to defeat armor, masonry and other underwater moving objects including ships and submarine vehicles. in order to accomplish the objective, the efp must be aerodynamically stable, so as to hit the target with small velocity decay rate and with small angle. in the last few decades, efforts have been made to optimize the liner shape and initiation mechanism of efp’s which affect the formation and penetration properties of efp [1-3]. the formation of efp is a complex process involving high pressure and high temperature. in this work efp jet is formed in air. to examine the effect of water on the velocity and penetration of the efp, water with varying depths is introduced after the jet has traversed into air for 3cd. experimental results for 120o angle are compared with simulated results. flash x-ray radiography is used to capture the images of jet formation. the cross-sectional view of the charge without casing with conical angle 120o and geometry of the model used for simulation is shown in figure 1. fig. 1. cross-sectional view of the standard shaped ii. dimensions and material model the shapes of the liner and charge are shown in figure 1. the shape of the liner is conical. the diameter of the liner is 54 mm. charge diameter is kept 60 mm for convenience. the length of charge is 84 mm for numerical simulations. the explosive, air, water and liner are meshed with 0.2 mm along xaxis. along y-axis for 0-20 mm the mesh size is 0.2 and for 20-40 mm the mesh size is 0.4. the euler solver is used to model the explosive liner and air. the target is modeled using lagrange solver. to avoid the interaction problem with euler and lagrange solver, euler/lagrange coupling method is used. point detonation method is chosen for initiation of the charge. the materials models of air, charge, liner and target are described in table i. the material parameters of 8701 explosive, ofhccopper liner and target, steel-45 are listed in tables ii, iii and iv respectively. liner explosive engineering, technology & applied science research vol. 6, no. 1, 2016, 913-916 914 www.etasr.com ahmed et al.: penetration evaluation of explosively formed projectiles through air and water… the jwl equation of state is used to describe the detonation of efp charge, which in generalized form is given below: v e e vr be vr ap vrvr                21 21 11 table i. material models part name material equation of state strength model explosive 8701 jwl none liner cu-ofhc gruneisen steinburg guinan air air ideal gas none target steel-45 shock johnson cook water water shock none table ii. jwl parameters of 8701 ρ[g/cm3] 1.695 d 8.425e+3 a 8.544e+08 b 2.049e+0724 r1 4.6 r2 1.35 ω 0.25 e 9.5e+06 table iii. shock parameters for ofhc-copper (liner) ρ[g/cm3] g c1[km/sec] c2 s1 s2 8.93 2.02 3.94 0.0 1.489 0.0 table iv. material parameters for steel-45 (target) ρ[g/cm3] g c1[km/sec] c2 s1 s2 7.83 2.17 4.56 0.0 1.33 0.0 iii. simulation of penetration performance of efp (jet formation and penetration) for penetration against rocks and other armor piercing applications the jet with larger diameter is essential to obtain the better penetration depth. also the efp jet must be stable and with minimum velocity gradients to avoid the jet break up while approaching the target surface [6]. the jet formation for liner angle 120 at time t= 0, 20, 40, 60 and 72 microseconds (μsec) is shown in figure 2. the target is made of steel -45 with a width of 100 mm. the penetration picture for explosively formed projectile for 1200 conical liner after 250μsec traversing through 3cd air and 3cd water against steel target obtained from simulation code is shown in figure 3. iv. simulation results the kinetic energy behavior of the efp jet emerged from conical liner angle 1200 is predicted. the jet formation is accomplished in air. the effect of water depth on kinetic energy of the jet during penetration through water for a standoff distance of 1-charge diameter (1cd) to 5-charge diameter (5cd) and steel target is determined using 2dhydrocode. by taking time along x-axis and kinetic energy along y-axis, it is observed from simulation that when water depth increases, the kinetic energy decay rate is slow. this is also clear from figure 4. t= 0μsec t= 20μse t= 40μsec t= 60μsec t= 72μsec fig. 2. jet formation at different time steps fig. 3. numerical simulation of the jet penetration against steel target. fig. 4. kinetic energy behavior of the copper liner during jet formation and penetration engineering, technology & applied science research vol. 6, no. 1, 2016, 913-916 915 www.etasr.com ahmed et al.: penetration evaluation of explosively formed projectiles through air and water… v. experimental setup a. flash x-ray radiography (fxr) setup to radiograph the efp jet formation, the fxr experiment method was used. the efp charge and other armor were hanged by a cotton rope. passive detonation technology was utilized in the experiments to visualize the jet deformation accurately and to avoid the discrepancies attributable to detonator. the pictorial representation of the fxr setup is shown in figure 5. two 450 kv flash x-ray tubes were installed for registration of the jet after interaction. the protected cassette films were positioned to capture the fragments after interaction. the schematic of the fxr setup is shown in figure 6. fig. 5. image of the experimental test setup with vertically hanging shaped charges. fig. 6. schematic of the test set up of 60 mm shaped charge in front of double flash x-ray tube. b. jet formation and jet velocity calculation through fxr. the jet tip and tail velocities are measured simultaneously measured using a multi channel flash x-ray system. the exposures obtained from x-ray at 30 µsec and 50 µsec after ignition are shown in figure 7. the x-ray exposure magnification is 2.0. the jet tip velocity obtained from x-ray exposure is 4.614 km/sec. in the experiments, the distance from the first marked line on x photographic plate to the ground is 137mm and the distance from the second marked line on x photographic plate to the ground is 120mm. l1=142 mm, l2=83 mm, l3=149 mm, l4=88 mm. 1 1 2 a l k l l   142 0.631 142 83    3 3 4 149 0.6287 149 88 b l k l l      fig. 7. (a) jet formation at 30 micro-seconds (b)jet formation at 50 micro-seconds c. depth of penetration setup the penetration performance of the explosively formed projectiles is determined by its penetration against target made of 45-steel. the charge is placed at a standoff distance of 3cd air and 3cd water from the target. the target is made of three cylindrical blocks having 100 mm height and 100 mm diameter. the experimental set up for the depth of penetration before experiment is shown in the figure 8. 4 221.15 0.6287 74.09 0.6311 92.28mms      5 4 92.28 4614.0m/s 50 30 s v t       (a) (b) engineering, technology & applied science research vol. 6, no. 1, 2016, 913-916 916 www.etasr.com ahmed et al.: penetration evaluation of explosively formed projectiles through air and water… fig. 8. (a) efp change at rest (b) steel target with 3cd water (c) setup for dop experiment d. depth of penetration (dop) results the penetration produced by the jet after initiation and interaction with the steel target is shown if figure 9. fig. 9. efp jet effect on the 45-steel target vi. conclusions simulations were carried out to predict the effect of water on the kinetic energy and penetration of explosively formed projectiles in underwater environments. jet velocity of the efp has been calculated via the flash x-ray technique, a high speed diagnostic technique used to record micro-second phenomena. the penetration performance is determined through dop experiments against steel targets. the depth of penetration measured from simulation and experiments are 79 mm and 72 mm respectively which shows a variations of about 7 mm, which is an within an acceptable range. from this comparison we can conclude that simulation and experimental are in reasonable agreement. this comparison also shows that from simulation we can predict the performance of efps against underwater targets very effectively. the insensitive material (8701-explosive) has been used first time as the energetic material for the underwater application. this material can be utilized well in naval and other underwater applications. acknowledgment the authors are thankful to “key laboratory of fundamental sciences for national defence", nanjing university of science and technology nanjing, jiangso, china, for providing experimental facility. references [1] t. h. bouet, p. tarayre, j. p. guillon, “study of a multi-point ignition efp”, 15th international symposium on ballistics, pp. 159-166, israel, 1995 [2] d. bender, b. chhouk, r. fong, b. rice, e. volkmann, “explosively formed penetrators (efp) with canted fins”, 19th international symposium on ballistics, pp. 755-761, switzerland, 2001 [3] c. yu, q. d. dong, c. w. sun, y. j. tong, c. l. yan, f. b. li, “the experimental studies of explosively formed projectile with star shaped tail”, explosive shock waves, vol. 23, no. 6, pp. 561-564, 2003 [4] j. carleone, d. bender, “a unique method of providing an explosively formed projectile with fins”, 17th international symposium on ballistics, pp. 55–62, midrand, south africa, 1998 [5] w. jun, l. jingbo, d. yixin, “experimental and numerical study on the flight and penetration properties of explosively-formed projectile”, international journal of impact engineering, vol. 34, pp. 1147–1162, 2007 [6] c. yu, t. yanjin, y. chengli, f. li, y. gui, z. ming, w. bingren, x. panhai, l. li, “applied research of shaped charge technology”, international journal of impact engineering, vol. 23, no. 1, pp. 981988, 1999 (a) (b) (c) microsoft word etasr_v13_n3_pp10721-10724 engineering, technology & applied science research vol. 13, no. 3, 2023, 10721-10724 10721 www.etasr.com lakshmi & sharma: dc-38ghz nonuniform distributed amplifier design with gate and drain line … dc-38ghz nonuniform distributed amplifier design with gate and drain line optimization using 0.1µm gaas phemt technology balla lakshmi department of electrical, electronics and communication engineering, gitam (deemed to be university), india ballalakshmi79@gmail.com (corresponding author) gollakota venkata krishna sharma department of electrical, electronics and communication engineering, gitam (deemed to be university), india gvks007@gmail.com received: 18 march 2023 | revised: 4 april 2023 | accepted: 5 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5859 abstract this paper presents an optimized three-cell nonuniform distributed amplifier (nuda) suitable for optoelectronic drivers in the q band. this is the first nuda of darlington topology designed with the 0.1µm gaas phemt process with a transition frequency ft of 130ghz. gate microstrip line sections, drain microstrip line sections, and active device sizes were optimized to obtain high gain and large bandwidth from a monolithic microwave integrated circuit (mmic) distributed amplifier (da). this paper presents two nuda designs with different topologies. the first was designed with a three-stage common source (cs) topology that enhanced the bandwidth up to 34ghz with a gain greater than 8db, and the second was designed with two darlington stages and one cs stage that enhanced the bandwidth up to 38ghz with a gain greater than 8db. the bandwidth enhancement of nuda with the darlington topology was compared and verified with the nuda of common source topologies. keywords-monolithic microwave integrated circuit (mmic); distributed amplifier (da); pseudomorphic high electron mobility transistor (phemt); gallium arsenide (gaas); optimization; nonuniform distributed amplifier (nuda) i. introduction the demand for wideband applications in the crowded lower k and ka bands has forced designers to choose the q band for modern wideband designs. distributed amplifier (da) design is the best choice for wide bandwidth applications like optical drivers [1]. das were designed at first with vacuum tube technology. later on, mmic das were designed with the mesfet technology. with high electron mobility and high transition frequency features of gaas, inp hemt technologies dominated the da designs in the 90s. the first da designs were uniform in nature and all gate and drain transmission line sections had the same inductance values [2]. later, using optimization, nonuniform distributed amplifiers were implemented by varying the parameters of the distributed amplifiers [3]. the common source [4-5] and cascode [6-8] topologies are the most commonly used in da design. in [5], a uniform da design used a gain control switch and 8 gan hemt cells of cs topology to obtain 8±1.5db gain. as cascode topologies are very sensitive, they need an extra stability network. in [6], a 5-cell cascode topology da with a stability network obtained a gain of 11.23db and a bandwidth of 10mhz-22ghz. in [7], a 6-cell cascode da topology with dual gate device mode obtained a dc-33ghz bandwidth with a gain of 10.6db. another 6 cell cascode da topology [8] with a series r and c network at the device gate obtained a dc40ghz bandwidth with a gain of 12db. however, the first proposed da design with cs topology without any additional network obtained competitive gain and bandwidth with the minimal number of 3 cells only. the proposed design also offers the highest transition frequency (ft). the second proposed da design used the darlington topology [9] to enhance bandwidth. the darlington triplet offers 3 times the transition frequency ft of a single hemt and handles high current and high frequencies. the high transition frequency plays a significant role in improving the bandwidth of da. in both proposed designs, nonuniform design using gate optimization and drain microstrip lines were carried out with gaas phemt technology, where all gate and drain microstrip line sections had different inductance values. this design drives the perception of nuda using gaas phemt in mmwave applications [10-12]. proper selection of the active engineering, technology & applied science research vol. 13, no. 3, 2023, 10721-10724 10722 www.etasr.com lakshmi & sharma: dc-38ghz nonuniform distributed amplifier design with gate and drain line … device, gate and drain line optimization, and active device size balance the tradeoff between gain and bandwidth. the pp1010 gaas phemt was selected as the active device for this design. simulations of this design were carried out with a 100nm gate length gaas phemt technology on 2mil (50μm) substrate thickness to achieve high gain. the high transition frequency ft of 130ghz and the optimized size of the active device had significant contributions in achieving high bandwidth and gain. ii. 0.1µ m gaas phemt mmic technology the pp1010 gaas phemt used in the da design has a gate length of 0.1µm generated using the e-beam process with a substrate thickness of 2mil. the t-gates are generated using the electron-beam lithographic process. the ingaas channel has a pinch-off voltage of -0.95v at id=1ma/mm and can be operated up to a maximum drain bias of 4v. the device is passivated using nitride and can be used as a dielectric for 400pf/mm 2 metal insulator metal (mim) capacitors. these passive components support the mmic fabrication process. two thick metals with an air bridge are used as interconnection. the highest transconductance (gm) of the device is 725ms/mm at vds=1.5v and the maximum drain current id is 760ma/mm at vgs=−0.5v. at peak transconductance, vgs is −0.28v. the device has a maximum gate-to-drain breakdown voltage of 9.6v. the device's maximum oscillation frequency (fmax) is 180ghz at vds=1.5v. the device's transition frequency is 130ghz at vds=1.5v. table i shows all the features of the 0.1µm gaas phemt. table i. features of the 0.1µm gaas phemt feature value 1 gate length 0.1µ m 2 pinch off voltage -0.95v 3 breakdown vdg 9.6v 4 idss 520ma/mm 5 maximum gm 725ms/mm 6 idmax 760ma/mm 7 ft 130ghz 8 fmax 180ghz 9 mim capacitor 400pf/mm 10 tfr resistor 50ohm/square 11 epi resistor 135ohm/square fig. 1. cross section of the pp1010 gaas phemt. iii. circuit and design a. 3-cell nuda design with cs topology figure 2 shows a simplified schematic of the 3-cell nuda with cs topology. each cell was implemented with the win semiconductor pp1010 phemt process on 0.1µ m gaas substrate. all cells were connected in a cs configuration. all gates were connected with microstrip lines. similarly, the drains were interconnected with microstrip lines from one cell to another. supplied with a gate bias of -0.35v, provided a drain bias of 1v and a quiescent drain current idss of 63.9ma. fig. 2. cell architecture of the distributed amplifier. as the number of cascaded cells increases, the gain should increase, but this is not the case for the da because as the number of cells increases, the voltage wave gets more attenuated as it travels through the transmission line and the gain reduces. therefore, the optimum of 4 cells [13] were needed in this design to achieve a greater than 8db gain. the optimized lengths of the gate transmission line sections were tx l1=100.053µ m, tx l2=327.455µm, tx l3=147.222µ m, tx l4=537.156µ m and the optimized lengths of drain transmission line sections were tx l5=533.489µm, tx l6=255.256µm, tx l7=1036.54µm, and tx l8=912.267µm. in addition to optimizing drain and gate transmission lines, the proper selection of device size plays a vital role in achieving a high gain. the gain was reduced for device sizes larger than 4×50µm. similarly, the optimal bias of vgs=-0.5v and vds=1.5v is needed to achieve a better tradeoff between gain and bandwidth. the amplifier design was perceptively optimized to achieve optimal performance while maintaining the required gain and bandwidth. b. 3-cell nuda design with darlington topology in order to enhance bandwidth, the first and second cells used the triple darlington topology and the third cell used the cs topology, as shown in figure 3. the triple darlington topology offers 3 times the transition frequency (ft) of a single transistor [14]. ��,� ≅ 3.05 �� (1) therefore, it handles high current and high gain at higher frequencies, compared to the cs stage, is very popular for broadband amplifiers, and extends bandwidth to microwave frequencies. the optimal sizes of m1 and m2 were 4×50µ m and 4×25µm for m3. in the triple darlington topology, the condition w1,w2=2w3, provides a wide bandwidth compared to other width choices for hemts. the optimized lengths of the gate transmission line sections were tx l1=80µm, tx l2=261.826µm, tx l3=117.716µ m, and tx l4=531.156µ m, while the optimized lengths of drain transmission line sections were tx l5=426.246µ m, tx l6=203.944µm, tx l7=828.174µm, and tx l8=728.882µm. a better tradeoff engineering, technology & applied science research vol. 13, no. 3, 2023, 10721-10724 10723 www.etasr.com lakshmi & sharma: dc-38ghz nonuniform distributed amplifier design with gate and drain line … between gain and bandwidth was obtained at biasing values of vgs=-0.35v and vds=5v. fig. 3. cell architecture of the distributed amplifier. iv. results and discussion the inductive lengths of the gate and drain were adjusted iteratively until a maximum gain of 11db was achieved. figures 4-6 show the simulated s parameters for both nuda designs. to compensate for the condition cgs>cds, the drain line lengths were larger than the gate line lengths to achieve phase matching between the gate and drain lines. simulations proved that the optimization of the gate and drain lengths played a crucial role in obtaining high gain and bandwidth. figure 4 shows the simulated s parameters of nuda with the cs topology. a gain greater than 8db was obtained over the dc-34 ghz bandwidth range. the input and output return losses (iorl) were better than -5db. fig. 4. s parameters of nuda with cs topology. the s21 for both 3 and 4 cells was plotted to verify the optimal number of cells, as shown in figure 5. from the s21 curve, it can be observed that 3 is the optimal number of cells. figure 6 shows the simulated s parameters of nuda with the darlington topology. it can be observed that a gain greater than 8db can be obtained over the dc-38ghz bandwidth. therefore, bandwidth improved with darlington topology compared to the cs. the input and output losses were better than -5db. figures 7 and 8 show the layouts of nuda with cs and darlington topologies, respectively. fig. 5. s21 comparison for 3 and 4 nuda cells. fig. 6. s parameters of nuda with darlington topology. fig. 7. the layout of nuda with cs topology. fig. 8. the layout of nuda with darlington topology. em simulations were carried out using keysight’s em solver momentum microwave. the em model was created for the entire design except for the active device. the em model was imported, and a co-simulation was performed. table ii compares the proposed nuda with other similar works, where [6-8] used the cascode topology with gaas hemt technology. engineering, technology & applied science research vol. 13, no. 3, 2023, 10721-10724 10724 www.etasr.com lakshmi & sharma: dc-38ghz nonuniform distributed amplifier design with gate and drain line … the proposed design obtained a bandwidth better than [6-7,9]. the da with the darlington topology using the cmos technology [9] obtained a bandwidth of 0.5-23ghz. the proposed design using the gaas phemt technology with the darlington topology improved the bandwidth to dc-38ghz. compared to cmos with darlington topology [9], the proposed design obtained a wider bandwidth. to the best of our knowledge, this is the first da of darlington topology designed with 0.1µm gaas phemt process. table ii. comparison with other studies ref. technology topology bandwidth (ghz) gain (db) power (mw) 2021 [6] gaas cascode 0.01-22 11.5 125.89 2013 [7] 0.5 µ m gaas e/d hemt cascode dc-33 10.6 62 2018 [8] 0.15 µ m gaas phemt cascode dc-40 13 550 2022 [5] 0.13 µm gan hemt cs 1-42 8 707.94 2012 [9] 0.18 µ m cmos darlington 0.5-23 10 150 this work 0.1 µ m gaas phemt cs dc-34 8-12 319.5 this work 0.1 µ m gaas phemt darlington dc-38 8-12 236.5 all the previously mentioned studies used 5 or 6 cells to obtain a bandwidth around 38ghz and a gain around 8db. the studies with cascoded topologies used extra stability networks at the gate of active devices. however, the proposed designs with proper gate and drain line optimization along with a high transition frequency of 130ghz offered by the win pp1010 gaas hemt succeeded in obtaining competitive bandwidth and gain with a minimum circuitry, as they used only 3 cells. to the best of our knowledge, no nuda design of darlington topology with 0.1µm gaas hemt has ever been proposed, and the proposed design in this paper is the first of its kind. v. conclusions this paper presented two nonuniform distributed amplifier designs using the 0.1 µm gaas phemt process. the cs topology succeeded in obtaining a bandwidth of dc-34ghz with a gain greater than 8db. the simulation results showed that the darlington topology achieved a bandwidth of dc38ghz with a gain greater than 8db. the obtained input and output return losses were better than -5db. the power consumption of nuda with cs topology was 319mw and 236.5mw for the darlington topology. both topologies obtained competitive results using the minimum number of three cells of 0.1µ m gaas phemt. references [1] j. shohat, i. d. robertson, and s. j. nightingale, "10-gb/s driver amplifier using a tapered gate line for improved input matching," ieee transactions on microwave theory and techniques, vol. 53, no. 10, pp. 3115–3120, jul. 2005, https://doi.org/10.1109/tmtt.2005.855119. [2] y. ayasli, r. l. mozzi, j. l. vorhaus, l. d. reynolds, and r. a. pucel, "a monolithic gaas 1-13-ghz traveling-wave amplifier," ieee transactions on microwave theory and techniques, vol. 30, no. 7, pp. 976–981, apr. 1982, https://doi.org/10.1109/tmtt.1982.1131186. [3] b. m. green, s. lee, k. chu, k. j. webb, and l. f. eastman, "high efficiency monolithic gallium nitride distributed amplifier," ieee microwave and guided wave letters, vol. 10, no. 7, pp. 270–272, jul. 2000, https://doi.org/10.1109/75.856985. [4] m. roberg, m. pilla, s. schafer, t. r. mya kywe, r. flynt, and n. chu, "a compact 10w 2-20 ghz gan mmic power amplifier using a decade bandwidth output impedance transformer," in 2020 ieee/mtt-s international microwave symposium (ims), los angeles, ca, usa, dec. 2020, pp. 261–264, https://doi.org/10.1109/ims30576. 2020.9223951. [5] z. hu, q. zhang, and k. ma, "a 1–42 ghz gan distributed amplifier with adjustable gain by voltage-controlled switch," ieee microwave and wireless components letters, vol. 32, no. 4, pp. 339–342, apr. 2022, https://doi.org/10.1109/lmwc.2021.3123947. [6] a. a. babenko, g. lasser, and z. popović, "0.01–22-ghz feedbackstabilized single-supply gaas cascode distributed amplifiers," ieee microwave and wireless components letters, vol. 31, no. 12, pp. 1291– 1294, sep. 2021, https://doi.org/10.1109/lmwc.2021.3111133. [7] s. h. chen, c. c. shen, s. h. weng, y. c. liu, h. y. chang, and y. c. wang, "design of a dc-33 ghz cascode distributed amplifier using dual-gate device in 0.5-μm gaas e/d-mode hemt process," in 2013 asia-pacific microwave conference proceedings (apmc), seoul, south korea, aug. 2013, pp. 728–730, https://doi.org/10.1109/apmc.2013. 6694911. [8] l. diego, b. haentjcns, c. a. mjema, i. barrutia, a. herrera, and y. haentjens, "a dc to 40 ghz, high linearity monolithic gaas distributed amplifier with low dc power consumption as a high bitrate pre-driver," in 2018 48th european microwave conference (eumc), madrid, spain, sep. 2018, pp. 1517–1520, https://doi.org/ 10.23919/eumc.2018.8541690. [9] m. drakaki, s. siskos, and a. hatzopoulos, "a 0.5–20ghz bandwidth enhanced distributed amplifier," microelectronic engineering, vol. 90, pp. 26–28, feb. 2012, https://doi.org/10.1016/j.mee.2011.04.031. [10] d. t. t. my, h. n. b. phuong, t. t. huong, and b. t. m. tu, "a magneto-electric dipole antenna array for millimeter wave applications," engineering, technology & applied science research, vol. 10, no. 4, pp. 6057–6061, aug. 2020, https://doi.org/10.48084/ etasr.3710. [11] z. a. shamsan, m. alammar, a. alharthy, a. aldahmash, k. a. alsnaie, and a. m. al-hetar, "micrometer and millimeter wave p-to-p links under dust storm effects in arid climates," engineering, technology & applied science research, vol. 9, no. 4, pp. 4520–4524, aug. 2019, https://doi.org/10.48084/etasr.2972. [12] h. alsaif, "extreme wide band mimo antenna system for fifth generation wireless systems," engineering, technology & applied science research, vol. 10, no. 2, pp. 5492–5495, apr. 2020, https://doi.org/10.48084/etasr.3413. [13] d. m. pozar, microwave engineering. hoboken, nj, usa: john wiley & sons, 2011. [14] g. nikandish and a. medi, "design and analysis of broadband darlington amplifiers with bandwidth enhancement in gaas phemt technology," ieee transactions on microwave theory and techniques, vol. 62, no. 8, pp. 1705–1715, dec. 2014, https://doi.org/10.1109/ tmtt.2014.2328972. authors' profile balla lakshmi received her b.tech. in electronics and communication engineering from the vignan’s institute of information technology, ap, india in 2011 and m. tech. from the gitam university during 2011–2013. she has a teaching experience of two years during 2013–2015. currently, she is a ph.d. candidate at gitam university. her research interests include rf integrated circuit design. gollakota venkata krishna sharma obtained his ph.d. and master’s degree from the andhra university and the indian institute of science bangalore, india, respectively. he is a professor in the department of e.e.c.e, gitam university, visakhapatnam, india. his research interests include radar signal processing, rf integrated circuit design, and vlsi signal processing. microsoft word etasr_v13_n2_pp10217-10221 engineering, technology & applied science research vol. 13, no. 2, 2023, 10217-10221 10217 www.etasr.com arya: optimization of a perovskite-based multilayer microwave absorber using an equivalent circuit … optimization of a perovskite-based multilayer microwave absorber using an equivalent circuit model aayushi arya department of electrical engineering, indian institute of technology hyderabad, india aayushi.arya1993@gmail.com (corresponding author) received: 22 december 2022 | revised: 7 january 2023 | accepted: 15 january 2023 abstract in this paper, the optimization of a perovskite-based multi-layer microwave absorber is performed to find an optimized value of the impedance step gradient from the refractive index of the constitutive layers. the optimization presented is unique as it is based on maximizing the dissipation and attenuation ability of the absorber along with a constraint of providing an efficient reflection loss in the absorber. this type of approach ensures the maximum absorption rate of the incident em waves as the penetrating waves get fully dissipated. objective and constraint functions are derived from the equivalent circuit model of the multi-layer absorber. the equivalent circuit model is formed using the inductive and capacitive effects across the dielectric and magnetic properties of the constitutive layers. the three layers are composed of perovskite materials with different refractive indexes such that the top layer serves as an impedancematching layer followed by an alternate dielectric and magnetic layer. it is further shown how the capacitive and inductive losses are dominant over each other in the alternate lossy layers. empirical relations are used to tabulate the refractive index of a range of perovskite compounds from which suitable combinations can be selected as per the obtained value of the step gradient function. the current work presents a simplistic method to design multi-layer microwave absorbers with different material combinations that are beneficial to the practical applications of microwave absorbers. keywords-multi layer microwave absorber; equivalent circuit model; perovskite; refractive index i. introduction multilayer structures form an important part in the field of microwave absorption. while single layer absorbers may be sufficient for absorber coatings, in applications where heavy exposure of em radiation is to be absorbed, multilayer absorbers are more efficient [1]. researchers have used optimization-based approaches like genetic algorithm (ga), particle swarm optimization (pso), and other evolutionary algorithms to design multilayer absorbers using chew’s recursive formula [2-3]. however, the recursive formula used in the above algorithms presents a limitation on the analysis of the individual layers in the multilayer design. carbon-based absorbers recursive formula was commonly used as the changes in the properties of each layer are marginal and the configuration of each layer is the same with the difference being only in the volume of fillers used. now, with researchers relying more on the inorganic materials to be used as microwave absorbers, the analysis and modeling theories of multilayer absorbers should be adapted and usually, more prominently used in frequency selective surfaces equivalent circuit models, can help in designing much simplistic models for the optimization of multilayer absorbers [4-5]. in this work, an attempt has been made to analyze and optimize the design of multilayer absorbers. the optimization is done by developing an equivalent circuit model for a threelayer perovskite-based multilayer design. the model takes into account the capacitive and the inductive losses in the alternate dielectric and magnetic layers of the absorber and includes the characteristics and properties of the individual layers. supporting theories have been provided to understand the role of each layer and the loss mechanism occurring at the alternate layers of the absorber. in the current work, an equivalent circuit model for multilayer absorber is formed by including the dissipation properties of each layer. the reason for choosing perovskite for the absorber design is its inherited dielectric and magnetic properties that can be tuned easily by just changing the composition of the oxide [6]. hence, in this work an optimized design of a three-layer microwave absorber is presented with different perovskite oxide combination for the individual layers. ii. equivalent circuit model perovskite oxides are inorganic compounds with a basic composition of abo3 type where a and b are cations and o is oxygen. in microwave absorbing perovskite composites, engineering, technology & applied science research vol. 13, no. 2, 2023, 10217-10221 10218 www.etasr.com arya: optimization of a perovskite-based multilayer microwave absorber using an equivalent circuit … permittivity and permeability depend on the composition of the perovskite compound, the creation of defects, oxygen vacancies, and influence of cations on the boundary material [7-8]. fig. 1. polarization and charge distribution in perovskite composite. permittivity and permeability of a perovskite are affected by different properties of the composite [9]. as shown in figure 1, the permittivity of perovskites is determined mainly by the nature and amount of polarization occurring across the individual unit cell. dipole and interfacial polarizations contribute mainly to the permittivity. these can be easily induced in a composite structure by using functionally active and oxygen interactive binding materials along with the perovskite filler. graphene and reduced graphene oxide form one such example [10]. the interaction between the oxygen in the unit cell and the functional group of the binding material creates vacancies and defects thereby increasing the overall permittivity. similarly, for induced permeability, charge distribution across the b-o-b bond of perovskite plays an important role. in the b-o-b bond of the perovskite p-orbital of oxygen overlaps with the d-orbital of the b cation on both sides, such that the bond is split to an upper and lower energy orbital. if the charge distribution is such that one of the upper energy levels is half filled for one b-o bond while the other on the opposite side is empty, magnetic dipoles get induced across the perovskite unit cell [11-13]. this charge distribution is also affected by the boundary material used in the composite. based on the above explanation, it can be concluded that permittivity and permeability show trade off characteristics in magnetic and dielectric perovskite composites. theoretically, this can be understood by considering that in order to have a higher permittivity, the interaction of the oxygen anion with the binding material must increase to create higher polarization. this in turn will weaken the b-o-b bond leading to lower the magnetic charge interaction across the b-o-b bonds decreasing permeability. hence, in lieu of the above theory presented, maximum amount of dissipation losses can be obtained if separate layers for dielectric and magnetic losses can be combined alternately in multilayer absorbers with the top layer serving as an impedance matching layer to minimize the reflection loss. this will not only provide the required reflection loss, but also an efficient dissipation mechanism. using alternate layers of dielectric and magnetic compounds can also reduce the risk of interference when using microwave absorbers in practical applications with devices that are dielectric or magnetic. in order to formulate an objective function, the equivalent circuit model of figure 2 is presented, which is based on the dissipation theory explained above. two objective functions are formulated: one for the overall reflection loss and another for the net dissipation in the absorber. in figure 2, the first layer provides the impedance matching, with the input impedance of the layer matched with the free space impedance to allow the maximum amount of microwaves to penetrate across the composite with reflection loss less or equal to -20db as per industrial standards. below the top layer, there are the dielectric and magnetic dissipation layers represented as lumped capacitor and inductor respectively. in the dielectric layer, dissipation occurs via the formation of dielectric dipoles across the layer [14]. the dipoles are aligned in such a way that the upper layer intersection is positively charged, while the lower is negatively charged and can be shown as a lumped capacitor in the circuit model. the incident microwave charge is stored and dissipated across this capacitor. the third layer is magnetic with the dissipation occurring due to the formation of magnetic dipoles across the layer [15]. the magnetic dipoles are aligned in such a way that the magnetic lines generated due to the dipoles are directed towards the negative intersection of the capacitive layer. the current direction across the layer falls along the negative x axis. thus the impedance in the magnetic layer is represented as negative induction. fig. 2. equivalent circuit model of the multilayer microwave absorber. iii. objective functions the objective functions for the multilayer absorber are formulated to find an optimized value of the step gradient by which the refractive index of the consequent layers must increase from the top layer. let � be the value of the step gradient and � be the value of the refractive index of the top layer. � and � are assumed to be the lumped inductance and capacitance of the magnetic and dielectric layer of the absorber composite given by [16]: engineering, technology & applied science research vol. 13, no. 2, 2023, 10217-10221 10219 www.etasr.com arya: optimization of a perovskite-based multilayer microwave absorber using an equivalent circuit … � = � � and � = � (1) where � is the characteristic impedance of the absorber and � is the input impedance of the absorber. the attenuation constant � of the absorber composite is given by: � = � � � � � (2) where � � represents the imaginary part of the conductance in the equivalent circuit model. the conductance �� can be presented in terms of � and � as: �� = ����� + ��� (3) where � is the angular frequency. with f=2.54×109hz, the angular frequency is given by ω=2πf=1.59×10 10 /rad/s. combining (1)-(3), the following equation is obtained: �� = �1 + ������ (4) substituting l, c from the above equations, (5) is obtained: �� = √� = �. � (5) where � is the refractive index value of the absorber composite and z is the step gradient value, which is the input variable in the presented model. now reversing f1 for minimization, the objective function is given by: !�. �� = −�1 + ������ (6) for the second objective function, reflection loss (rl) coefficient for the absorber composite is considered [17]: #� = $�%&��'�%&(�'$ (7) the input impedance of the absorber can be written as: �)* = � +,�ℎ .√ /0�12 3 4 (8) �5 is the characteristic impedance of free space. for an efficient amount of absorption in the absorber, the characteristic impedance of the microwave absorber � must be such that rl must not be less than -20db. to obtain the above value, � must be related to �5 as [18]: � = 1.22�5 (9) similarly, to optimize the function for reflection loss in terms of the refractive index, thickness is considered constant to simplify the objective function with: 7 = 28� (10) substituting (8)-(10) in (7) and assuming tanhx≈x for small values of x, the function f2 for optimizing the rl coefficient can be written as: �� = �.��9*�� �.��9*(� (11) �� represents the reflection coefficient of the absorber which depends on the required rl of the absorber as: �� = �:;< �: (12) solving (12) for the rl range from -20 to -60db, the constraint equality for �� function comes out to be: 0.1 < �� < 0.7 (13) iv. dataset the dataset for the refractive index of various perovskite oxides is created using an empirical relation between the spatial energy parameter, pseudo lattice constant, and the refractive index of the perovskite oxide. the spatial energy parameter depends on the polarization ability of the elements and the refractive index of the compound. further, the polarization ability of a perovskite oxide is affected by all its compositional elements. hence, the effective spatial energy is the sum of the individual polarization energy. the refractive index can be empirically calculated from the effective spatial energy and the lattice constant of the compound as follows: �� = � × . 9 �4 (14) the lattice constant of the perovskite oxide is taken from [19] and the polarization energy parameter from [18]. ab� ,abc ,ab5 represent the polarization energy parameter in ev of cations a and b and oxygen as anion respectively. ∑ab is the effective spatial energy parameter, d5 is the pseudo cubic lattice constant in å and n is the calculated refractive index. table i provides the above parameters for different perovskite compounds. v. optimization-multi objective pso in the current study, multi-objective optimization is used for optimizing the step gradient for the refractive index value of the microwave absorber composite. in the presented model �� is minimized, while �� is optimized using the equality constraint. for carrying out the optimization, the object oriented framework is used involving the nsga-ii evolutionary algorithm. nsga-ii has the advantage of providing fast computations and a non-dominated solution set. it is one of the most popularly used gas which uses the fitness value or the rank of an individual along with the assigned crowded distance to sort out individuals from consecutive generations. it uses the binary crossover operator for mutation and offspring generation. the algorithmic parameters used in the current study are an initial population of 50, 10 offspring in each generation, and termination at the 40 th generation. the algorithm is repeated for an initial refractive index range of 1.6 to 2.3. the coding was executed using python in a pc with intel(r) core(tm) i5-8265u (cpu 1.60ghz) processor with 8gb ram. vi. results using the step gradient value and the refractive index value of the top layer, the refractive indices for each layer can be determined as shown above. suitable compounds as per the calculated values, having the same refractive index value, are picked from table i. table ii shows the step gradient value obtained for each refractive index value along with possible multi-layer combinations matched from the data in table i. engineering, technology & applied science research vol. 13, no. 2, 2023, 10217-10221 10220 www.etasr.com arya: optimization of a perovskite-based multilayer microwave absorber using an equivalent circuit … table i. spatial energy parameter and refractive indices of various perovskite oxides compound fgh fgi fgj kj lfg m bafeo3 0.271 1.285 6.287 4.102 7.843 1.91 bamoo3 0.271 0.619 6.287 4.177 7.177 1.72 banbo3 0.271 0.562 6.287 4.212 7.12 1.69 basno3 0.271 1.393 6.287 4.223 7.951 1.88 baho3 0.271 6.728 6.287 4.246 13.286 3.13 bazro3 0.271 0.507 6.287 4.258 7.065 1.66 bairo3 0.271 10.411 6.287 4.148 16.969 4.09 bapbo3 0.271 0.867 6.287 4.322 7.425 1.72 batbo3 0.271 2.848 6.287 4.304 9.406 2.19 bapro3 0.271 0.82 6.287 4.408 7.378 1.67 baceo3 0.271 0.607 6.287 4.432 7.165 1.62 batio3 0.271 0.889 6.287 4.125 7.447 1.81 baruo3 0.271 0.743 6.287 4.42 7.301 1.65 srmno3 0.413 1.174 6.287 3.841 7.874 2.05 srvo3 0.413 0.966 6.287 3.899 7.666 1.97 srfeo3 0.413 1.285 6.287 3.905 7.985 2.04 srtio3 0.413 0.889 6.287 3.928 7.589 1.93 srtco3 0.413 0.679 6.287 3.975 7.379 1.86 srmoo3 0.413 0.619 6.287 3.98 7.319 1.84 srnbo3 0.413 0.562 6.287 4.015 7.262 1.81 srsno3 0.413 1.393 6.287 4.027 8.093 2.01 srhfo3 0.413 6.728 6.287 4.05 13.428 3.32 srtbo3 0.413 2.848 6.287 4.108 9.548 2.32 srcoo3 0.413 1.402 6.287 3.841 8.102 2.11 srzro3 0.413 0.501 6.287 4.061 7.201 1.77 srruo3 0.413 0.743 6.287 4.015 7.443 1.85 cavo3 0.727 0.966 6.287 3.784 7.98 2.11 cazro3 0.727 6.728 6.287 3.934 13.742 3.49 cahfo3 0.727 0.507 6.287 3.946 7.521 1.91 caruo3 0.727 0.743 6.287 3.899 7.757 1.99 casno3 0.727 1.393 6.287 3.911 8.407 2.15 catio3 0.727 0.889 6.287 3.813 7.903 2.07 eutio3 2.036 0.889 6.287 3.801 9.212 2.42 eualo3 2.036 1.767 6.287 3.643 10.09 2.77 eucro3 2.036 1.067 6.287 3.736 9.39 2.51 eufeo3 2.036 1.285 6.287 3.771 9.608 2.55 eugao3 2.036 1.821 6.287 3.742 10.144 2.71 euino3 2.036 1.062 6.287 3.593 9.385 2.61 cealo3 0.607 1.767 6.287 3.771 8.661 2.3 gdalo3 2.426 1.767 6.287 3.631 10.48 2.89 gdcro3 2.426 1.067 6.287 3.725 9.78 2.63 gdfeo3 2.426 1.285 6.287 3.76 9.998 2.66 laalo3 0.418 1.767 6.287 3.795 8.472 2.23 lacro3 0.418 1.067 6.287 3.888 7.772 2 lafeo3 0.418 1.285 6.287 3.923 7.99 2.04 lagao3 0.418 1.821 6.287 3.894 8.526 2.19 larho3 0.418 0.799 6.287 3.947 7.504 1.9 latio3 0.418 0.889 6.287 3.953 7.594 1.92 lavo3 0.418 0.966 6.287 3.917 7.671 1.96 laino3 0.418 1.062 6.287 4.105 7.767 1.89 ndalo3 1.074 1.767 6.287 3.689 9.128 2.47 ndgao3 1.074 1.821 6.287 3.789 9.182 2.42 ndino3 1.074 1.062 6.287 3.999 8.423 2.11 ndcoo3 1.074 1.402 6.287 3.701 8.763 2.37 ndcro3 1.074 1.067 6.287 3.783 8.428 2.23 ndfeo3 1.074 1.285 6.287 3.818 8.646 2.26 ndmno3 1.074 1.174 6.287 3.818 8.535 2.24 pralo3 0.82 1.767 6.287 3.725 8.874 2.38 prcro3 0.82 1.067 6.287 3.818 8.174 2.14 prfeo3 0.82 1.285 6.287 3.853 8.392 2.18 prgao3 0.82 1.821 6.287 3.824 8.928 2.33 prmno3 0.82 1.174 6.287 3.853 8.281 2.15 prvo3 0.82 0.966 6.287 3.847 8.073 2.1 smalo3 1.681 1.767 6.287 3.654 9.735 2.66 smcoo3 1.681 1.402 6.287 3.666 9.37 2.56 smvo3 1.681 0.966 6.287 3.777 8.934 2.37 smfeo3 1.681 1.285 6.287 3.783 9.253 2.45 yalo3 0.455 1.767 6.287 3.608 8.509 2.36 ycro3 0.455 1.067 6.287 3.701 7.809 2.11 yfeo3 0.455 1.285 6.287 3.736 8.027 2.15 table ii. suggested compound layers as per the obtained step gradient values refractive index n step gradient value z suggested compound layers 1.6 2.9 baceo3 cahfo3 bahfo3 1.7 2.8 bapbo3 eutio3 srhfo3 1.8 2.6 srnbo3 srtbo3 gdalo3 1.9 2.5 srtio3 ndgao3 gdalo3 2 2.3 lacro3 cealo3 gdcro3 2.1 2.2 cavo3 cealo3 eufeo3 2.2 2.1 laalo3 prgao3 smvo3 2.3 2 srto3 prgao3 cealo3 vii. conclusion the present work emphasizes on the importance of the use of materials' intrinsic electromagnetic properties in the designing of multilayer microwave absorbers. the provided theoretical framework gives a picture of the way the internal phenomenon of absorption and dissipation in absorbers can affect the output performance parameters. this understanding helps in building mathematical relations and functions which serve as building blocks to advanced computation procedures such as the used optimization. moreover, the provided database from which perovskite compounds can be selected based on their refractive indices gives a wide range of options for 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[19] a. s. verma and v. k. jindal, "lattice constant of cubic perovskites," journal of alloys and compounds, vol. 485, no. 1, pp. 514–518, oct. 2009, https://doi.org/10.1016/j.jallcom.2009.06.001. microsoft word etasr_v12_n6_pp9709-9714 engineering, technology & applied science research vol. 12, no. 6, 2022, 9709-9714 9709 www.etasr.com ali et al.: effectiveness of eps bead size and cement proportions on the strength and deformation of … effectiveness of eps bead size and cement proportions on the strength and deformation of light-weighted soil sharafat ali college of civil engineering and architecture, henan university of technology, henan, china sharafat@stu.haut.edu.cn feng yong college of civil engineering and architecture, henan university of technology, henan, china fengyong@haut.edu.cn amjad hussain bhutto department of civil engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan amjadbhutto62@gmail.com farhad jamil college of civil engineering and architecture, henan university of technology, henan, china jaamfarhad@gmail.com jam shahzaib khan department of civil engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan jskhan@quest.edu.pk riaz bhanbhro department of civil engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan riaz@quest.edu.pk received: 22 september 2022 | revised: 3 october 2022 | accepted: 7 october 2022 abstract-the current study investigates the deformation and strength of light-weighted soil (lws) comprised of silt, expanded polystyrene (eps) beads, cement, and water. the eps bead sizes employed in this study are 4, 5, and 6mm in diameter with densities of 0.011, 0.009, and 0.006g/cm 3 and cement concentrations of 10% and 15%. the effects of different eps bead sizes and cement proportions on the mechanical properties (strength and deformation) of lws are evaluated by unconfined compression strength (ucs) tests. the findings show that the eps bead sizes significantly impact the strength and deformations of the lws. the smaller the eps bead size, the higher the observed strength, but, on the other hand, bigger eps bead sizes have lower strength and higher ductility. it was also revealed that the strength of lsw is entirely dependent on the cement concentration. high cement content in the lws has more strength and brittleness, but it is more prone to deformation. the cost can be decreased by increasing the eps bead size, and thus the prescription of mixed soil can be enhanced. the use of eps beads with a diameter of 4-6mm is recommended in the construction process, especially in backfill for retaining walls. each eps bead size provides advantages in different context, depending on engineering applications and field conditions. keywords-strength and deformation; expanded polystyrene beads; unconfined compression test; cement i. introduction light-weighted soil (lws) comprises of silt, eps beads, cement, and water and it has lower density than the ordinary soil. lws has good independence, hardness, flowability, strength, ductility, heat resistance, and water resistance. the disposal of eps is a problem that many cities face. on its own, eps does not harm or contaminate the soil, but because it takes hundreds of years to break down, it takes up too much space in landfills and reduces the usable area. its lightweight nature and low density have impeded efforts to recycle eps. lightweight fill materials are utilized in a variety of ways. they can be used as fill over poor soils, backfill for retaining walls to minimize lateral loads, fill materials for slopes to decrease driving forces, and seismic buffers, among other applications. these solutions have tremendous engineering merits and can significantly cut project costs. authors in [1] simulated the mechanical properties of mixed lws using indoor tests and abaqus finite element software and assessed its strength characteristics and deformation law. authors in [2] reported that when the size of eps particles was in the range of 1–5 mm, the permeability of the water increased as the eps particle size rose, while the ucs of spherical eps 1–3mm particles was higher than that of fractured and flaky eps particles [2]. eps soil combinations' compressive strength, unit weight, permeability, dynamic properties, creep qualities, and water absorption properties were examined in [3]. authors in [4] reported that when the size of the eps beads increases, the unconfined compressive strength of lws is reduced. to reduce project expenses, the impact of eps beads with a particle size bigger than 3mm on the shear strength of lws was explored in [5]. the stresscorresponding author: sharafat ali engineering, technology & applied science research vol. 12, no. 6, 2022, 9709-9714 9710 www.etasr.com ali et al.: effectiveness of eps bead size and cement proportions on the strength and deformation of … strain properties of eps sand mixture specimens were investigated using consolidated drained (cd) triaxle compression trials, and it was revealed that increasing eps content resulted in lower shear strength and increased volumetric strain [6]. authors in [7] reported that the compressive strength of lws decreases as the eps increases. furthermore, increasing the amount of eps particles lowers the strength of lws [7, 8]. the deformation of lws is quick at the top of the sample and progressively declines to the bottom, according to the cyclic loading test and abaqus simulations of different blends of eps and silty soil under varying confining pressure and cement contents [9, 10]. when the cement mixing ratio is increased, the mixed soil shear strength characteristics are comparable to those of general soil laboratory uniaxial and triaxle compression tests used to determine the relationship between stress and strain strengths. the triaxle test findings demonstrate that mixed soil's shear strength characteristics are very similar to ordinary soil only when the cement mixture is high [8]. authors in [11] studied lightweight fill's unconfined compressive and shear strength and stiffness with regard to the cement-to-soil ratio. the compression strength of a lightweight blend is reduced by the formation of eps particles. the most likely explanation is that the enlarged eps beads have taken the place of the hydrate. in terms of composition, the porosity of the light mixture increases and the strength decreases as the percentage of light particles grows. when the cement percentage is reduced, the lightweight's compressive strength with various eps sections varies only slightly [12]. authors in [13] conducted triaxle and direct shear tests to investigate the shear strength characteristics. the soil friction angle was enhanced by combining 1mm eps beads with fly ash. the effect of various eps geofoam densities and geofoam cell heights on the compressive strength was studied in [14, 15]. the density of eps geofoam improves its compressive strength, whereas the compressive strength of eps geofoam falls along with the cell height [16]. light materials, such as eps particles, are frequently used for mixing in a variety of earthworks in order to minimize the composite weight and reduce self-weight [15, 16]. the addition of cement solidification improves the engineering characteristics of waste soil, and the lightweight treatment reduces embankment settling [17, 18]. additionally, the mechanical constitutive model of the lightweight mixture may be developed, and engineering applications can employ the calculated strengths and deformation of these lightweight additions [15, 21–24]. eps is a type of plastic foam with several features, including light weight, pressure resistance, durability, and thermal insulation. it may be used to make lws and is frequently employed in engineering constructions [20, 21]. strength and deformability features are essential engineering properties of solidified soil as filling soil. thus, focus is given on studying the basic mechanisms of artificially modified soil, such as compression deformability and shear strength. many studies on lws with eps diameters up to 3mm have been reported, however, the mechanical properties of the mixed soil with eps with diameters bigger than 3mm mixed with silty soil have yet to be thoroughly investigated. in the current investigation, laboratory experiments were conducted on silty soil mixed with different sizes of eps beads and cement proportions. this study aimed to discover silty soil blends with various eps bead sizes employed in civil engineering applications such as backfilling. ii. materials and methods a. silty soil silt soil was collected from the yellow river beach, which is adjacent to zhengzhou city, henan province, china, as shown in figure 1(a). the particles have a light-yellow color and uniform shape, as shown in figure 1(b). the index characteristics and the gradation of silty soil are shown in tables ii and iii. all particles passed through us standard sieve no. 40 (425μm). a total of 89.69% of the particles passed through the no. 200 (0.075mm) sieve. the gradation curve of silty soil is shown in figure 1(c). according to the unified soil classification system (uscs), this silt is classified as high plasticity silt (mh). its liquid limit is 52.63, which is greater than 50%, and the plasticity index (ip) is 22.31 (greater than 7), and lies below the a-line in the plasticity chart. (a) (b) (c) fig. 1. (a) yellow river sample collection site, (b) collected sample (silty soil), (c) grain size distribution curve. engineering, technology & applied science research vol. 12, no. 6, 2022, 9709-9714 9711 www.etasr.com ali et al.: effectiveness of eps bead size and cement proportions on the strength and deformation of … b. eps beads lightweight eps insulation is created from solid polystyrene particles. polystyrene, which makes up 90 to 96% of its makeup, is the main gradient. three different sizes of eps beads, i.e. 4, 5, and 6mm, were employed in this study. the beads are round and white. table i displays the densities and sizes of the eps beads. in [22] images of the eps beads taken using scanning electron microscopy (sem) can be seen. table i. size of eps beads and densities size of eps beads (mm) density (g/cm 3 ) 4mm 0.011 5mm 0.009 6mm 0.006 c. ordinary portland cement (opc) the curing agent used in this experiment is 32.5 composite opc, which has a consistent quality, high strength, and quicksetting characteristics. d. sample preparation and mixed ratio the silty soil samples were first dried for 24h at 105°c in an oven. the following day, the dried samples were taken from the oven and were spread in a tray. they were carefully broken into pieces with a rubber hammer so that the structure of the silty soil could not be destroyed. then, the pieces passed through a sieve and debris and unwanted materials were removed. then, the cement was mixed into the dry silty soil. the silty soil's and cement's particles sizes are similar. ordinary tap water was poured into the silt cement powder and they were mixed properly with a spatula for 2min until the admixture became homogenous. eps beads of different sizes were put into the cement silt slurry and the admixture was mixed again for 5min. the mixture became non-homogenous because eps beads are bigger than silt and cement particles [22]. the mixture was then sampled and the light-weighted samples were left for curing for 28 days. the specimens were ready for testing after the curing period. the mixing ratios are shown in table iv. table ii. index properties of silty soil properties values density (g/cm 3 ) 1.49 specific gravity gs 2.72 water content ω 99.5 liquid limit wl 52.63 plastic limit wp 30.32 plasticity index ip 22.31 liquidity index il 3.10 volumetric weight (r/kn/m 3 ) 14.90 pore ratio (e) 2.64 table iii. sieve analysis particle percentage (%) 0.425-0.18mm 0.18-0.15mm 0.15-0.075mm 0.075-0.001mm 1.76 3.19 5.36 89.69 e. test plan the ucs is commonly used in engineering applications and tests. different mixing ratios were chosen and 3 samples were made for each mixing ratio. the sample size dimensions for the ucs test were 40mm diameter and 80mm height, with applied loading pressures of different stresses. the impact of several parameters on the deformation and strength of silt lws were investigated, including eps particle size, cement blending ratios, and eps content. the ultimate axial strength without lateral pressure resistance was measured using unconfined compressive strength. a dial gauge and a proving ring are typically employed to check the compressive strength, as shown in figure 2(a). the ucs test was performed, and the test technique was controlled by strain. the device can directly detect the stress and determine the strain based on the sample's height change. the axial stress and strain data were obtained for 2 cement mixing ratios (10% and 15%) and the effect of eps bead diameter on lws's deformation and strength properties was examined. (a) (b) fig. 2. (a) view of the large-size unconfined compression test apparatus, (b) specimen after the test. iii. results and discussion a. the effects of cement and eps bead size on stress and strain curves of light-weighted soil the stress-strain curves of samples with various eps bead sizes are shown in figures 3-4. the stress-strain curve swings to the right and downward with increasing cement and eps content. this demonstrates that the production of lws follows a distinct pattern. the samples with 4mm eps bead, 15% cement content, and 1% eps content had more strength and lower ductility than the samples with 5mm and 6mm eps bead size with the same percentage of cement and eps. besides, eps beads of bigger sizes have lower shear strength and higher ductility. when the mixing ratio is 15% and 10% cement, and engineering, technology & applied science research vol. 12, no. 6, 2022, 9709-9714 9712 www.etasr.com ali et al.: effectiveness of eps bead size and cement proportions on the strength and deformation of … 1% and 2% eps, the density of 4mm is higher than that of other eps beads. due to the small size of the sample, the eps beads and silty particles have close contact with each other, which enhances shear strength. on the other hand, the tiny holes in the eps beads of 4mm particles make movement more difficult. when the shear stress exceeds the sample's strength, the 4mm samples are easily destroyed quickly due to energy dissipation, which explains the sample's reduced ductility. furthermore, when the size and composition of eps beads grow more significant, the strength falls, and the ductility increases. moreover, when eps, a material with lower strength and better ductility, substitutes silty soil in blends, the strength and ductility of the eps-silt blends drop. another factor contributing to the weakening of eps-silty blends is the failure of eps beads to connect with soil particles. the stress-strain relationship curve comprises three phases. before reaching the yield stress, the early load period expands with the strain, stress rises, and the stress-strain relationship gets closer to a linear connection. the linear relationship demonstrates that samples in an elastic state with no discernible breaks can theoretically be restored. as the load increases in the material plastic yield stage, new cracks are formed, and the existing cracks are improved. the strain growth rate is greater than the stress growth rate as the soil shrinks and expands. the stress-strain relationship fits the curve, and the stress rises to its maximum value. the third step is the fracture stage, in which the stress lowers dramatically, and the curve's slope becomes negative. stress-strain curves of different eps bead sizes and cement mixing are shown in figures 3-5. table iv. mixing ratios specimen serial number cement content (ac) % eps content (ae)% eps beads water content curing time lws 1 10% 10% 10% 1%, 2% 1%, 2% 1%, 2% 4mm 5mm 6mm 40 40 40 28 lws 2 15% 15% 15% 1%, 2% 1%, 2% 1%, 2% 4mm 5mm 6mm 40 40 40 28 silt 99.5 28 b. ucs of lws and eps bead size the ucs comparison for different eps particle sizes is shown in figure 5. the ucs for the 4mm group is larger for a given additive content than it is for the other eps bead sizes. it is evident that when the eps particle size increases, the ucs of eps-silty blends diminishes. for instance, the ucs of the 4, 5, and 6mm groups is 550.30kpa, 320.51kpa, and 221.41kpa respectively, when the eps content is 1% and the cement percentage is 15%. as a result, samples with 4mm eps particle size should have a denser microstructure than samples with other eps sizes, resulting in increased strength. furthermore, the ucs difference between the 5mm and 6mm groups is less than that between the 4mm and 5mm groups. the soil structure of the 4mm group is smaller due to the relatively tinier particle size. the soil particles in the 5mm and 6mm groups cannot be closely mixed with the eps particles because the eps particles are substantially more significant than the soil particles. furthermore, the eps with particle sizes of 5 and 6mm had the most significant specific surface area and smooth surface, which reduced the effects of occlusion between soil particles, resulting in the weakest strength of all groups. the cost can be reduced by increasing the eps size. structural strength and prices drop as the eps size increases. to reduce cost, practical projects should employ eps beads with a diameter of 4-6mm, and material prescription can be adjusted. c. deformation of lws with different cement proportions and eps bead sizes lws's confined stress-strain curve is comparable to other traditional soils. as the load and the size of the eps beads grow larger, the modulus of deformation increases. the rate of development of light soil increased slowly at first and steadily dropped as stress increased, forming a curved dome shape. the turning point of the curve represents the strength of soil, particularly its ultimate strength. (a) (b) fig. 3. 15% cement mixed with (a) 1% (b) 2% eps content. the bigger the eps particle size, the lower the strength of the mix. the strength of a mixed soil containing a significant amount of cement is superior to that of a mixed soil containing less cement. the lws's strength was improved however, if the stress exceeds the mixed soil's strength, the mixed soil's structure will eventually disintegrate and collapse. the ratio of engineering, technology & applied science research vol. 12, no. 6, 2022, 9709-9714 9713 www.etasr.com ali et al.: effectiveness of eps bead size and cement proportions on the strength and deformation of … eps particle volume deformation to the total volumetric deformation decreased as the eps particle size rose from 4 to 6mm, due to the fact that when eps particle size increases, fewer eps particles are incorporated into the system as a whole, which lowers the eps particle deformation ratio. (a) (b) fig. 4. 10% cement mixed with (a) 1%, (b) 2% eps content. the number of eps particles in a structure significantly impacts structural deformation. with more eps content in the sample, the particular surface area grows greater, reducing the sample's consolidation strength. under different stress conditions, increased eps sizes dramatically increase soil deformation. the structural deformation of lightweight silt soil is significantly affected by the added eps particles. the experiment revealed that the added eps particles of various sizes significantly impact the silt lws's shear strength and deformation characteristics. the strength and deformation variation characteristics of lws with varied eps bead sizes are diverse. for instance, the samples with 15% cement and 1% eps contents of 4mm size have the highest shear strength and the lowest ductility. on the other hand, the samples with 10% cement and 2% eps of 6mm have the lowest shear strength and the highest ductility as shown in figures 3 and 4, and they all display multi-stage changes. the failure strain value increased dramatically as the size and quantity of the eps particle content increased, the plastic zone expanded, but the strength decreased. additionally, the changing rate of stress intensity decreased as the eps size increased, resulting in the extension of the elastoplastic range. (a) (b) fig. 5. unconfined compressive strength and eps beads size of (a) 15% and (b) 10% cement with 1% and 2% eps content. according to the analysis of figures 3-5, cement concentration has little impact on the failure strain of light silt soil, and the strain value difference between them at different mixing ratios is small. as a result, the effect of cement amount on the strain value of light silt soil can be ignored within a limited range of cement contents. the strength of the cementation created between the eps particles and the consolidated soil in the lightweight silt soil is quite robust under high cement content conditions. moreover, when the stress level rises, a brittle fracture is more likely to occur. iv. conclusions unconfined compressive strength (ucs) test was utilized in this study to investigate the strength and deformation characteristics of light weighted soil (lws) comprised of eps beads of various sizes, silty soil, cement, and water. from the experimental results, the following conclusions can be drawn:  as the eps particle size rises, the strength of lws does not. eps beads easily adhere to silty particles to create an elastic body in the case of 4mm eps size because there are more pores between the particles and they are closer in size. the silty particles and eps beads are in close contact due to their small diameter, thus increasing shear strength.  the engineering features of eps-silty blends, such as ductility and deformation, increase with high loads and eps engineering, technology & applied science research vol. 12, no. 6, 2022, 9709-9714 9714 www.etasr.com ali et al.: effectiveness of eps bead size and cement proportions on the strength and deformation of … size. when the eps particle size approaches 6mm, the ucs results drop. the ucs of eps-silt mixes with 4mm eps size is greater than all the other groups for a given additive concentration, but their ductility is lower.  the dome shape of lws has confined stress-strain relation curves that differ from typically modified silt, indicating that lws is structural soil. when stress is less than strength, very minor deformation occurs. however, the soil structure rapidly degrades and collapses when stress exceeds strength.  the cost can be reduced by using higher eps bead size. strength and price drop as the eps size increases. to save money, practical projects like wall retaining should employ eps beads with a diameter of 4 to 6mm, while material prescription can be adjusted. references [1] w. q. dai, x. chen, and h. q. zhang, "experiment and numerical simulation of dynamic behavior for cohesive soils," journal of jilin university, vol. 38, pp. 831–836, 2008. 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[24] x. ni, z. wu, w. zhang, k. lu, y. ding, and s. mao, "energy utilization of building insulation waste expanded polystyrene: pyrolysis kinetic estimation by a new comprehensive method," polymers, vol. 12, no. 8, aug. 2020, art. no. 1744, https://doi.org/ 10.3390/polym12081744. microsoft word etasr_v13_n1_pp10186-10191 engineering, technology & applied science research vol. 13, no. 1, 2023, 10186-10191 10186 www.etasr.com aloui et al.: towards an iot approach for smart waste management based on context ontology … towards an iot approach for smart waste management based on context ontology: a case study nadia aloui department of software engineering, college of computer sciences and engineering, university of jeddah, saudi arabia | sfax university, tunisia naaloui@uj.edu.sa wafa almukadi department of software engineering, college of computer sciences and engineering, university of jeddah, saudi arabia wsalmukadi@uj.edu.sa aymen belghith college of computing and informatics, saudi electronic university, saudi arabia a.belghith@seu.edu.sa (corresponding author) received: 28 november 2022 | revised: 10 december 2022 | accepted: 12 december 2022 abstract nowadays, waste management faces the challenge of providing effective and efficient solutions for waste collection, disposal, and recycling while respecting health and environmental standards. this challenge also includes the lack of understanding of the diverse factors that influence the various stages of waste management, inefficient route planning, insufficient resources, etc. faster collection, management, and processing of waste are possible with smart containers and iot technologies allowing waste real-time data provision. thus, this research proposes a waste management system based on generic and comprehensive generic context ontology and smart containers. the context ontology is conceived to solve the limits and the insufficiencies of waste management by covering all the waste facets for all the stakeholders, optimizing, analyzing, and reusing the waste data and conditions. for given smart container and waste management context, we need to have a global view of the relevant contextual data according to a unified model such as the waste environment data, the waste activity context, the waste computing context, the user context, the collaboration context, etc. one significant advantage of our system is that it provides a unified model for waste management contextual data that could be reused for other waste management systems covering all the properties of this domain. the proposed solution implements an intelligent and adaptive iot system for waste management according to different waste contexts, waste objectives, and waste activities. the proposed system has been successfully tested under different scenarios in jeddah city municipality. keywords-smart waste management; waste context ontology; iot; smart container i. introduction waste management, from generation to disposal, is one of the biggest challenges that municipal organizations face today. due to the growth in waste, containers positioned around cities in open spaces are overflowing, putting the citizens in an unhygienic environment. the implementation of smart waste management systems remains in an embryonic stage, something that is expected to change with urban development, similarly to other engineered systems [1]. to overcome this, a smart waste management system is proposed, based on smart containers that enable context-specific waste management via a general exhaustive context ontology. real-time monitoring through smart devices or containers is furthering the digital era of waste management by enhancing transparency, dependability, agility, security, resilience, connectivity, and sustainability of waste chains. the proposed system, based on smart containers and general context ontology, is leading the way in developing smart context-based waste management systems, increasing the quality of life today and assuring a greener world for future generations. the adaptation of a system context can take many aspects, such as behavior, engineering, technology & applied science research vol. 13, no. 1, 2023, 10186-10191 10187 www.etasr.com aloui et al.: towards an iot approach for smart waste management based on context ontology … content, or presentation adaptation. in this approach, focus is given on the adaptation of a smart waste management system to different waste contexts of different stakeholders. it is possible to manage the waste process situations in different contexts, i.e. the waste management domain, waste objectives, and waste activities, such as waste generation, collection, transformation, segregation, cleaning, etc. the proposed solution implements an intelligent and adaptive system for waste management according to the context and the different objectives according to various stakeholders. the main contributions of this paper are:  a unique way to combine two technologies, namely iot and ontological engineering, ensuring an optimal and general based context in the waste management field.  an architectural development process of the smart garbage box and the process of complete waste management in addition to the objectives, activities, reuse, and intelligent learning of the waste management system, as well as a smart way to monitor waste in real time. ii. literature review waste management stakeholders looking for a real-time monitoring, smart, and adaptive solution, will eventually have to use smart containers that are permanently equipped with iot devices. in this section, a brief overview of smart containers and smart devices is presented. a. the impact of smart containers and iot on waste management it is worth noting that technological iot advancements [2] are a key part of the waste problem that we face in industrial processes. fortunately, technological advancements also provide innovative solutions that can help us meet such challenges when they emerge. iot is completely changing the game regarding industrial waste management best practices. firstly, by using iot services and solutions, we can significantly improve the efficacy of waste collection and recycling. we can automate, improve, and interpret the entire waste management process in new ways while reducing cost. smart containers save time and effort [3], as operators know the number of containers that must be collected per day and the number of trucks that go to collect containers, in addition to saving time in classifying waste by type, making it easier for workers to send them to the competent authorities for recycling. the main benefit of iot is the ability to collect huge amounts of data and update them in real time utilizing costeffective sensors. these inexpensive sensors, recording and monitoring equipment, send all their data to the cloud for storage and review. then, ai models can analyze the data and draw actionable conclusions. in a series of case studies, we'll look at how companies in the food, agriculture, transportation, and energy sectors have implemented smart waste management. b. related work the literature includes a variety of waste managementrelated research initiatives. through a design that uses solar energy to feed the system and sensors to keep track of how much waste has been gathered inside the enclosure, authors in [3] introduce the idea of intelligent disposal. if necessary, the container can compress the waste, reducing its volume up to 10 times, even before it is collected. the waste monitoring solution sensoneo [4] combines smart sensors, a smart waste management system, and a citizen app. smart sensors use ultrasound technology to measure the filling levels in boxes and containers several times a day and send data to the waste management system. it divides the container into several sections. authors in [5] offer a novel method of implementing an integrated sensing system, which automates the solid waste management process, using cloud technology and mobile appbased monitoring. the suggested smart trash can is built on ultrasonic sensors and a variety of gas sensors. authors in [6] suggest an iot-based smart waste management system that aids surveying the estimation of garbage in trash cans and then transmits data through the internet to a server. a specific suggestion focusing on the intelligent container was originally made in [7]. in order to prevent trash disposal outside the container, the authors suggest a method in which monitoring takes place both inside and outside the compartment with the help of infrared sensors. the system in [8] includes a method for monitoring dumpsters around-the-clock. a smart and wellorganized mechanism is in place here for selective clearing. the level of waste in the dumpster is determined using the ultrasonic sensor. c. comparison of smart containers/waste management systems to make the system innovative and optimized, a comparison research based on a variety of criteria has been conducted (table i). the primary factors considered in this study are the detection of container fullness, and the used technologies. table i. comparison between the proposed system and other, known, systems criteria reference [3] [4] [5] [6] [7] [8] proposed intelligent route planning   x x x   container fullness        used technologies solar energy and sensors iot cloud technology and mobile app iot infrared sensors iot and cloud iot and ontological engineering includes smart bin   x     recycling and disposal x x x x    full waste management process x  x x x   context awareness x x x x  x  context model x x x x x x  engineering, technology & applied science research vol. 13, no. 1, 2023, 10186-10191 10188 www.etasr.com aloui et al.: towards an iot approach for smart waste management based on context ontology … there are many waste classification techniques currently available, but many of them require human intervention. if a fully automatic system is deployed in a company, it will be a win-win situation for government, companies, and industry. the majority of the research discussed here focuses on the collection system when discussing waste management and doesn’t give interest to the whole process of waste management. previous studies did not take into account the waste management context, objectives, and activities according to the whole waste management process and all the waste management factors. they are not based on context models specific and exhaustive for the waste management field. it is assumed that the best waste management approach has to be based on context and reuse. thus, the services offered for waste management will be more adapted, optimized and context aware. the proposed system in this research takes into account the contributions in the literature and covers their limits. d. context and context-awareness of ubiquitous and smart systems context is all that surrounds and gives a meaning to something [9, 10]. a definition of context cannot be given without taking into account the element concerned by the context. this definition shows that the context must be external to the element related to this context. in the field of ubiquitous computing (computing pervasive), context is any information that can be used to characterize the situation of an entity. an entity is a person, place, or object that is considered relevant to the interaction between a user and an application, including the user and applications themselves [11-14]. there are mainly two types of context [16]. the first one is active context use (automatically adapting the application's behavior in accordance with the state of the context) and the second one is passive context use (visualizing the state of the context for the user or saving this state for its future use). in the literature, many definitions of context-awareness have been proposed. authors in [16] consider contextawareness as the set of context-aware applications. another definition given in [10] specifies that a system is considered as context-aware, if it uses the context to give pertinent information or a service to a user, knowing that the relevance depends on the user's activity. furthermore, context-awareness emerged in the fields of mobile and pervasive computing as a technique to design applications with a conscience of the environment, to ensure high level of autonomy and flexibility. the context-awareness or the conscience of the context is known under other synonyms like adaptive or reactivate [17]. in order to model the smart container context, we use the concept of ontology, which provides an explicit specification of a conceptualization and an important step for reuse [18-20]. moreover, "an ontology is expressed in language (representation) based on a theory (semantics) that guarantees the properties of the ontology in terms of consensus, consistency, reuse, and sharing." [21]. the proposed generic context ontology will be able to guarantee unified, coherent, shared, and reused smart containers management in different contexts. iii. proposed generic context ontology for smart waste management there are several methods for developing ontologies (topdown, bottom-up, and combined). to design the context ontology for waste management, we adopt the iterative method recommended in [22]. a. field and scope of the ontology we proceed to the ontology development process by defining its domain and scope. indeed, ontology is the structured study of a specific field [23], which is accomplished by answering the following questions: what domain will the ontology cover? what are the objectives of ontology creation? who will utilize the ontology? our ontology field is the waste management context-based iot of all actors. our context ontology therefore includes concepts related to the waste management activity through smart containers. this ontology is designed to integrate both the active and passive context (smart container context). moreover, our ontology is not intended to be used by a human, but by the different components of context management to provide a better iot waste management in the city in a given context. b. generic context ontology a current representation of the context object is available for waste management via smart containers according to the generic context ontology. by using this context model, the system can become aware of the current situation and adapt its services for various stakeholders in response to environmental changes. to give the waste management system exact values for these attributes, this generic ontology identifies the characteristics of the current context. these attributes are used to specify the smart container's contextual aspect in an active waste management situation and to adapt the content to that context and the current waste management activity and objective. we offer a general context model based on the different state-of-the-art models, and its attributes are organized into six facets: 1) the actor context all participants in a waste management environment are referred to as actors. we define the identifier and the actor as the two elements that constitute the actor context aspect. the first element uniquely identifies the actor's smart containers for waste management environments. the second element is utilized to link the waste management purpose and action to the actor who used, will use, or reuse the smart container in another waste management context. 2) the waste activity context waste management domain, waste management activity, waste activity objective, generation, collection, transformation, segregation, cleaning, and the collaborative waste activities are the elements the waste activity context. 3) the waste environment context the environment context of a smart container waste management situation is described by a variety of factors that affect waste, including time, place, temperature, humidity, engineering, technology & applied science research vol. 13, no. 1, 2023, 10186-10191 10189 www.etasr.com aloui et al.: towards an iot approach for smart waste management based on context ontology … weather conditions, level, type, status, priority, classification and duration of waste, etc. 4) the waste computing context this aspect of context describes the equipment and tools the actor used to carry out his waste management task, including hardware, waste management platform, organizer, and operating system. 5) the waste reuse context two elements constitute the reuse context: the reuse identifier, which determines how much waste may be reused in each smart container, and the reuse percentage, which increases the value and effectiveness of waste management. 6) the context of waste management objectives the waste management objectives facet can be specified through the waste management platform or environment using the context-specific waste management objective aspect. knowledge of waste management objective, objective type, and waste management evaluation are the parts of the process. iv. proposed approach for smart waste management based on smart containers traditional containers that have been fitted with electronics to allow them to detect, interact, and communicate are known as smart containers. the additional electronics allow for tracking and monitoring of a container as well as the circumstances surrounding the management and transportation of the container's waste. the smart container can be made to exchange physical information close to real-time, including location, door opening and closing events, shocks and vibrations, temperature, humidity, and any other pertinent physical factors (figure 1). fig. 1. the proposed approach for smart waste management. in order to achieve shared visibility amongst diverse stakeholders during the whole smart container journey, the smart container serves as the common data source. in order to clarify the roles and responsibilities of each actor in the waste management chain and to improve collaboration and coordination among stakeholders some essential tasks must be accomplished: (i) shared visibility, (ii) assessing the activities involved for the purpose and determining the type, nature, and estimated volumes of waste to be generated, (iii) identifying any potential environmental impact from the generation of waste at the site, and (iv) recommending appropriate waste handling and disposal measures/routings in accordance with the current legislative and administrative requirements. it is suggested that smart containers could be integrated with other technological advancements to benefit the waste management, trade, and transportation communities even more. v. a case study of the proposed smart waste management system a. study area the study case chosen for developing this waste management system based on smart containers and context model is the municipality of jeddah. for the development of the smart waste management system, the work was divided into the following stages. b. functional and non-functional requirements the functional requirements outline the tasks that the suggested solution must complete in order to function and the non-functional requirements are those aspects of the system that are visible as it is being used. the required specifications are:  the administrator can: 1. edit the existing containers in the system 2. establish the waste collection plan according to the waste management activities. 3. select the best route to collect containers and send information to the collector. 4. track smart containers and trucks locations. 5. view the full container status and context features affecting the waste management activities. 6. view most frequently utilized portion in each container, the full section, the most used section, the total number of containers that have been collected and the section percentage.  the collector can: 1. collect containers that change color on the map. 2. view the location of smart containers. 3. collect containers according to smart containers priority and waste management activities and objectives  the jeddah municipality can: 1. create waste collection report in a daily and or monthly basis according to different waste activity objectives such as waste generation, collection, transformation, segregation, etc. engineering, technology & applied science research vol. 13, no. 1, 2023, 10186-10191 10190 www.etasr.com aloui et al.: towards an iot approach for smart waste management based on context ontology … 2. generate peak day and time of waste collection and prevent waste risks. c. hardware components this section represents the hardware used throughout the implementation of the smart container for waste management. we used neo-6m gps to detect the location, an inductive sensor to detect metal, an ultrasonic sensor to detect the level of trash, an esp8266 nodemcu to connect with the firebase, an arduino uno to do programming over the other products, etc. d. prototype figure 2 depicts the view of the finalized hardware prototype of the smart container of the waste management system. fig. 2. smart container prototype. e. interface the smart waste management system based on smart containers has been implemented by the students of the college of computer science and engineering of jeddah university. screenshots of the user interface are exhibited below. figure 3, the system displays several optimal paths and the best path is indicated as the "best choice", and the administrator will determine the path that suits him. fig. 3. choose optimal path page. as can be seen in figure 4, the waste management system users have access to improved visibility identifying the waste inbound flow to optimize waste management and react to unexpected risks. in figure 5, the administrator must be able to see if the waste in the section has the same type for example. a warning sign will appear if there are different types of waste in a section. the percentage and quantity of each type also appear. the smart sensors and iot technologies utilized in this waste management system that gathers and tracks real-time data allow the administrator to, dispose of, reduce, reuse, and prevent waste collecting peaks (figure 6). (a) (b) fig. 4. (a) container data in real time, (b) truck tracking. (a) (b) fig. 5. containted types of waste, (b) peak time and waste risk. fig. 6. waste management report and statistics. vi. conclusion and future work the context ontology is opening up a variety of data sources that could give the waste management system a context-aware picture. any documentation of the contextual information contained in a container is helpful to the coordination and predictability assuring quality and optimizing engineering, technology & applied science research vol. 13, no. 1, 2023, 10186-10191 10191 www.etasr.com aloui et al.: towards an iot approach for smart waste management based on context ontology … waste management. it is possible to predict when a container will be ready for the next operation and effectively manage risk in accordance with the waste management process by simply being aware of the status of a specific container, its contents, all relevant contextual information, and the waste management objective at a given time. as a perspective of this work, we suggest the use of deep learning methods as an intelligent way to classify waste through image classification. machine learning algorithms can be very beneficial in the waste management data analytics in order to take the best decisions and optimize smart waste management. acknowledgment the authors would like to thank aizah alsomai, njoud barayan, raghad alghamdi, shroug alzhrani for their contribution in implementing the case study application of smart waste management during their senior project. references [1] d. m. s. h. dissanayaka and s. vasanthapriyan, "smart solid waste management — a scientific literature review," the journal of solid waste technology and management, vol. 46, no. 4, pp. 606–619, nov. 2020, https://doi.org/10.5276/jswtm/2020.606. 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[18] t. chaari and f. laforest, "l’adaptation dans les systèmes d’information sensibles au contexte d’utilisation: approche et modèles," presented at the conférence génie électrique et informatique (gei’2005), sousse, tunisia, mar. 2005, pp. 56–61. [19] t. r. gruber, "toward principles for the design of ontologies used for knowledge sharing?," international journal of human-computer studies, vol. 43, no. 5, pp. 907–928, nov. 1995, https://doi.org/ 10.1006/ijhc.1995.1081. [20] s. r. mashwani and s. khusro, "the design and development of a semantic file system ontology," engineering, technology & applied science research, vol. 8, no. 2, pp. 2827–2833, apr. 2018, https://doi.org/10.48084/etasr.1898. [21] c. roche, "terminologie et ontologie," langages, no. 157, pp. 48–62, 2005. [22] n. f. noy et al., "protégé-2000: an open-source ontology-development and knowledge-acquisition environment," amia annual symposium proceedings, 2003. [23] b. heydari and m. aajami, "providing a new model for discovering cloud services based on ontology," engineering, technology & applied science research, vol. 7, no. 6, pp. 2268–2272, dec. 2017, https://doi.org/10.48084/etasr.1577. microsoft word etasr_v12_n6_pp9614-9631 engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9614 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … some mineralogical characteristics of the egyptian black sand beach ilmenite part i: homogeneous ilmenite and titanhematite-ferriilmenite grains mohamed ismail moustafa northern border university, saudi arabia and nuclear materials authority, cairo, egypt ismail2251962@yahoo.com received: 30 august 2022 | revised: 15 september 2022 | accepted: 17 september 2022 abstract-the high-grade egyptian beach ilmenite concentrate contains various mineral textures in addition to the main homogeneous ilmenite grains (63%), which may contain solid solutions of geikielite (mgtio3) and pyrophanite (mntio3) mineral components. few homogeneous ferriilmenite grains (2%) associated with the concentrated ilmenite grains are detected. the contents of fe2o3, mgo, al2o3, and cr2o3 in the ferriilmenite grains range between 7.3% and 22.8%, 3.4% and 6.6%, 0.2% and 0.7%, and 0% and 1.2% respectively. the detected hematite-ilmenite exsolved intergrowths (21.4%) have titanhematite exsolutions of different shapes, sizes, and orientations. they occupy 5%-40% of the whole intergrowth and may show one or two distinct generations. in some ferriilmenite components, mno ranges between 1.5% and 8.6%. the cr2o3 and al2o3 contents range between 0% and 1.2% and 0% and 3.2% respectively. they are mostly between 0% and 0.1% for either of the ferriilmenite components, while relatively greater content is present in the titanhematite components. in some grains, the titanhematite exsolution bodies are replaced by goethite or hydrated iron oxides. in others, the ferriilmenite intergrowth may be partially or completely altered into leucoxene. some minor composite grains are detected in the concentrate, where each grain consists of two parts, one part is titanhematite-ferrimenite and the other is ferriilmenitetitanhematite. the titanhematite exsolved components have relatively lower tio2 content (5.8%-23.8%). both mgo and mno are positively correlated with feo rather than fe2o3. the presence of sphene in the obtained ilmenite concentrate may be responsible for the recorded amounts of sio2 and cao. the cr2o3 content is relatively much higher in sphene spots than in ilmenite spots, ensuring that cr2o3 neither follows tio2 nor feo. the nature of the problem of the relatively lower ti content and the relatively higher fe and cr contents of the obtained ilmenite concentrates is the target of the article. the problem is related to the mineralogy of ilmenite or to the used physical concentration flowsheet of the separated concentrate and the ability to improve the ilmenite concentrate’s specifications. it is concluded that although the homogeneous ilmenite is characterized by low cr2o3 content, some of the other exsolved texture components, e.g. titanhematite and sphene, have relatively higher cr2o3, in addition to fe2o3, sio2, or cao. they can negatively affect the marketable specifications of the separated egyptian black sand ilmenite concentrate. keywords-beach ilmenite; geikielite; pyrophanite; ferriilmenite; titanhematite; egypt i. introduction the egyptian black sand contains huge reserves of 6 common economic minerals, i.e. ilmenite, magnetite, garnet, zircon, rutile, and monazite in descending order of abundance. the egyptian black sand is present either as beach sands (figure 1, (1)), or coastal sand dunes. the egyptian black sand minerals are derived originally from the disintegration of rocks, they are carried by the nile waters, and are deposited after the river meets the mediterranean sea. the egyptian black sand is considered in general as recent to pleistocene in age [1]. the deposit mainly contains the 6 above mentioned minerals. they are associated with quartz and green silicates (amphiboles and pyroxenes). traces of cassiterite, gold, and pb, zn, hg, ag, th, u, nb, ta, and pt minerals have also been detected [2-4]. along the north coast of egypt, in areas characterized by extensive beach erosion, east and west of the rosetta estuary, some surfacially highly concentrated black sands are found parallel to the shoreline. they form narrow patches with lengths that rarely attain 1km and widths ranging from a few up to 60m [2]. however, the original amount of materials transported by the river may be related to several variables such as the flow type and the sediment load [5]. ilmenite (fetio3) is the most abundant titanium mineral. the main source of ilmenite, rutile and leucoxene, are the sand type placer deposits found at or near the coast. ilmenite also occurs in massive rock formations in the form of titaniferous iron ores, associated with hematite and magnetite [6]. ilmenite and rutile are used for the manufacture of titanium dioxide white pigment which is the whitest and most stable of all known white pigments, being entirely unaffected by acids or alkalies that dissolve and destroy other whites. it has the good ability to maintain its visual appearance for a considerable period of time. it is stable up to 1800°c. ilmenite is also used for the production of metallic titanium which is characterized by high strength in relation to its density, the ability to retain its properties from -300°f to 1000°f, and its excellent corrosion resistance. titanium forms extremely hard metallic compounds corresponding author: mohamed ismail moustafa engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9615 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … with carbon, silicon, nitrogen, and boron. they are used as tips for cutting tools and in abrasive stones and wheels [6-7]. the majority of the mineralogical features of the egyptian beach ilmenite can be seen in [2, 8-16]. many authors have reported the relatively lower tio2 content and the relatively higher fe2o3 and cr2o3 contents, while others reported the diversity of the mineralogical textures inside ilmenite grains. however, the ilmenit content of the egyptian black sand ranges from less than 1% in the raw beach sand up to more than 50% in the naturally highly concentrated surfacial black sands. most of the obtained egyptian beach ilmenite concentrates are characterized by a relatively lower tio2 content (44-46% of ilmenite's beach sand and 46-49 wt% of ilmenite's sand dunes) and relatively greater cr2o3 content (0.1-0.4%). also, they have a relatively lower fe 2+ /fe 3+ ratio and relatively higher mgo and mno contents. the ilmenite ore of abu ghalaga mine, south eastern desert of egypt, occurs as massive-type interlayer gabbroic rocks [17]. the massive ilmenite ores are considered the second major type of fe-ti oxide mineral ores in egypt. authors in [18] explained that abu ghalaga ilmenite ore is not found as homogeneous grains but it is mainly hematite-ilmenite exsolution texture containing 36.78% tio2, 25.85% feo, 29.86% fe2o3, and 4.46% sio2 along with other minor oxides of mg, mn, cr, and p. abu ghalaqa and korabkanci, south eastern desert of egypt, are considered two promising areas of fe–ti massive ore deposits [19]. the separation of ilmenite and other economic mineral concentrates from the egyptian beach sand and other deposits are explained in [2-3, 20]. the majority of ilmenite mineral varieties are contained in the obtained highly purified concentrates using wet gravity concentration and magnetic and high tension electrostatic separation techniques. these varieties are characterized by strongly to moderate magnetic susceptibilities. except of magnetite, some minor ilmenite varieties associated with hematite, chromite, and definite magnetic leucoxene varieties are separated in definite magnetic fractions characterized by magnetic susceptibilities ranging from the ferromagnetic to the weakly paramagnetic [2]. the problem of relatively higher cr2o3 and fe2o3 contents in the egyptian beach ilmenite concentrate is the subject of this article. the mineralogical characters of some different ilmenite grains will be investigated. it is necessary to detect if the problem of the high chromium and ferric iron contents in the obtained beach ilmenite concentrates is related to the used ore dressing techniques, or related to the mineralogical features of the obtained ilmenite concentrate. answering this question can lead to the improvement of the chemical specifications and the economic marketability of the egyptian beach ilmenite. lowering the chromium content of the obtained concentrate can improve its use in the white pigment industry. ii. materials and methods a bulk sample weighing about 1000 tons was collected from the surfacial naturally highly concentrated beach black sands (figure 1, (2)), at the mediterranean coast, 7km east of rosetta estuary (figure 1, (1)). the sample represents the raw sand in a 2km stretch with varying width of a few up to 20m. the sands were manually scraped from the mantle to a depth ranging between 10 and 30cm. using the difference in physical characters between the various economic minerals, the collected surfacial naturally highly concentrated beach raw sands were processed in the plant at abu khashaba site (figure 1, (3)), using the following equipment: fulland halfsize wilfley shaking tables for wet-gravity concentration, carpco (hp 167) high-tension roll-type electrostatic separator for electrostatic separation, reading cross–belts magnetic separator, and the carpco (mih 13-231-100) industrial high intensity induced roll dry magnetic separator for magnetic separation. finally, a bulk conductor ilmenite fraction was obtained and subjected to the refining magnetic stage using the reading cross-belt magnetic separator, where an ilmenite concentrate assaying 99.5% ilmenite grains was obtained. four polished sections were prepared from 4 small representative samples and were studied under the reflected microscope and cameca sx-100 microprobe instrument. they were taken from the obtained final ilmenite concentrate (including 2 obtained magnetic fractions of the separator), a representative sample of the obtained ferromagnetic fraction, a representative sample of all the other obtained magnetic fractions of the separator, and, finally, a representative sample of the obtained non magnetic fraction of the separator. fig. 1. (1) distribution of the egyptian black sand showing the location of the surfacial naturally highly concentrated beach black sand 7 km to the east of rosetta estuary, abu khashaba. (2) the collected bulk sample of the surfacial beach black sand, dried by sunlight. (3) a part of the physical concentration plant at abu khashaba showing the fulland half-size wilfley shaking tables and the two r cross belt magnetic separators. engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9616 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … the investigation of the different ilmenite grains was carried out by a cameca sx-100 electron microprobe analyzer (empa), from the institute of mineralogy and crystal chemistry, stuttgart university, germany. the microprobe instrument is equipped with 3 wavelength dispersive spectrometers (wds) and an energy dispersive spectrometer (eds). the whole surface of the polished sections was examined by back scattered electron (bse) images, so that ilmenite grains with 10m size or even smaller could be detected. the analytical conditions were 15kv accelerating voltage, 15na electron current, 180s counting time for each analyzed spot, and 1 to 4m diameter of the focused electron beam. the following standards were used: diopside for mg and ca, albite for na, corundum for al, orthoclase for si and k, rutile for ti, rhodonite for mn, fe2o3 for fe, cr2o3 for cr, v for v, and sphalerite for zn. k lines were used for the element analysis. also, a binocular microscope, a reflectedlight polarizing microscope, sample splitters, and various containers were utilized. iii. calculation a. calculation of the fe 3+ content and the molecular formula of the studied ilmenite grains in the current paper, using the formula of [21], a constructed ilmenite formula in microsoft excel was used for the calculation of the fe 3+ content and the molecular formula of of ilmenite mineral component of the studied individual ilmenite grains. b. calculation of different mineral components of the analyzed spots composed mainly of ferriilmenite and/or titanhematite with or without individual tio2 (rutile) most of the analyzed spots of the grains were subjected to one of the following calculation methods to determine the different mineral fraction components of each analyzed spot. 1) the first method (m1) in this method, the adopted ilmenite excel formula was carried out for each analyzed spot to calculate feo % and fe2o3 %. if the sum of cations is less than 2, then all iron content must be considered as feo, completely contained within the calculated ilmenite fraction component. the calculated iron fraction as feo % (cal) is used to calculate the corresponding content of ilmenite fraction (fetio3), and its corresponding content of tio2 wt% as follows: ilmenite mineral fraction = feo % (cal) × 2.112, included tio2 % = feo % (cal) × 1.112 or = ilmenite mineral fraction (cal)/1.9. these values are concluded from (1): feo + tio2 = fetio3 (ilmenite) (1) then: 71.85 g feo + 79.87 g tio2 = 151.72 g fetio3 or: 47.36 % feo + 52.64 % tio2 = 100 % ilmenite in ilmenite we have: tio2/feo = 1.112, ilmenite/feo = 2.112, and ilmenite/tio2 = 1.9. the calculated fe2o3 % of the analyzed spot will be considered as hematite mineral component %. the mgo % and mno % contents of the analyzed spot are used for the calculation of the corresponding contents of individual geikielite (mgtio3) and pyrophanite (mntio3) mineral components and also their corresponding individual contained tio2 %. the calculation of these values depends on the following equations: mgo + tio2 = mgtio3 (geikielite) (2) then: 40.31 g mgo + 79.87 g tio2 = 120.18 g geikielite or: 33.54 % mgo + 66.46 % tio2 = 100 % geikielite mno + tio2 = mntio3 (pyrophanite) (3) then: 70.94 g mno + 79.87 g tio2 = 150.81 g pyrophanite or: 47.04 % mno + 52.96 % tio2 = 100 % pyrophanite hence, in geikielite, tio2/mgo = 1.982, geikielite/mgo = 2.982, and geikielite/tio2 = 1.51. in pyrophanite, tio2/mno = 1.126, pyrophanite/mno = 2.126, and pyrophanite/tio2 = 1.89. the remaining individual tio2 % (rutile) component can be calculated by subtracting the sum percentages of tio2 contained in the calculated ilmenite, geikielite, and pyrophanite individual mineral components from the bulk analyzed tio2 % of the analyzed spot. all the calculated contents of the mineral fractions inside the analyzed spot are added to obtain the total sums. if the calculated individual tio2 % has a negative value, the contained tio2 in the calculated three mineral fractions is higher than the actual bulk analyzed tio2 % of the spot. there are four reasons for this: at first, there are other analyzed oxides that must be considered and added with the analyzed tio2 % of the spot to be included within the bulk tio2 content of the spot. also, there are some values of the analyzed oxides feo, mgo, mno, not included in their corresponding calculated mineral components. the third reason is that some analyzed oxides are impurities such as sio2 cao, which cannot be neglected and the other analyzed oxides must be corrected. the fourth reason is that it is obvious that the content of individual tio2 content of the analyzed spot is negligible. however, if the obtained individual tio2 % values are equal to – 0.01 down to – 0.05 or even –0.1, these values may be due to the rounding to two decimal places for most of the treated oxides. τhese negative values can be neglected and the content of individual tio2 is considered as zero. however, in the case of obtained negative values, the second method of calculation is recommended. 2) the second method (m2) in this method (m2), we act directly to the analyzed oxides of the detected spot, and the adopted ilmenite excel formula is not applied. the contents of ilmenite mineral fractions are calculated directly from the analyzed tio2 % and not from the calculated feo %. this method of calculation includes the following steps: engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9617 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … the calculation of the geikielite mineral content from the analyzed mgo % of the spot, the calculation of pyrophanite mineral content from the analyzed mno % of the spot, and the calculation of the remaining tio2 % (r tio2) is conducted as follows: r tio2 = the analyzed tio2 of the spot [tio2 contained in geikielite + tio2 contained in pyrophanite] (4) then, r tio2 = tio2 of the spot – [mgo % × 1.982 + mno % × 1.126]. if the result of the last equation equals to zero or a negligible negative value, then there is no ilmenite in the analyzed spot. in the case of the presence of excess tio2, then: ilmenite mineral fraction = r tio2 × 1.9 (5) the feo % contained in the calculated ilmenite is calculated as follows: feo % contained in ilmenite = calculated ilmenite % / 2.112 (6) r feo of the analyzed spot = the analyzed feo % of the spot – the calculated ilmenite % / 2.112 (7) if the analyzed tio2 % of the spot is completely entering in the calculated ilmenite fraction, and there is no hematite fraction in the analyzed spot, then the contained feo % of the calculated ilmenite fraction will be exactly equal to the analyzed one. if the result of (7) has a positive value, then there is a content of fe2o3 fraction in the analyzed spot, equal to r feo × 1.1113. both the analyzed contents of cr2o3 and al2o3 of the spot are added with the calculated fe2o3 % and are considered to represent the present hematite fraction of the analyzed spot. the v2o3 content is not added to the content of the hematite because it was noticed that v2o3 may follow fe2o3 and sometimes tio2. finally, the sum for all the determined mineral fractions was calculated. 3) the third method (m3) this method of calculation is used with analyzed spots composed mainly of ferriforous rutile. it is a modified form of m2, where all the analyzed feo % is completely considered as representative of the hematite mineral fraction. both analyzed mgo % and mno % are used to calculate the corresponding individual mineral fractions of geikielite and pyrophanite respectively. the remaining tio2 % after subtracting the tio2 contents included within both geikielite and pyrophanite mineral fractions from the bulk analyzed sample of the spot is considered to represent the individual tio2 phase in the analyzed spot. in summary, the first method (m1) of calculation is used when there is a definite amount of individual tio2 and the adopted ilmenite program must be used in this method to determine the contents of feo and fe2o3. m2 is used when there is no an individual content of tio2 while m3 is used when there is no ilmenite mineral fraction. in the two last methods, the application of the adopted ilmenite program is not required and we act directly with the the original analyses of detected oxides. iv. results a. general the investigation of the different mineral textures in the obtained ilmenite concentrate and the other obtained magnetic fractions reflects that, except magnetite, the naturally highly concentrated surfacial black sands contain 42.65% different ilmenite mineral varieties and 2.51% other opaques, mainly hematite and chromite, in a total of 45.16%. it also contains 1.85% of completely altered ilmenite varieties, 1.48% magnetic and 0.37% non magnetic highly leucoxenated grains [2]. various mineral textures were detected under the microscope. their content percentages and their chemical compositions were calculated and investigated. 48 analyzed spots within 7 grains of homogeneous ilmenite that have mg content relatively higher than mn have been investigated. 26 analyzed spots within 5 homogeneous ferriilmenite grains with relatively higher mg than mn content were detected. another 51 analyzed spots contained within 6 grains of homogeneous ilmenite have relatively higher mn content. 82 other analyzed spots within 7 grains of titanhematite-ferriilmenite exsolved intergrowth and 2 composite grains consisting of 2 parts of titanhematite-ferriilmenite and ferriilmenite-titanhematite exsolved intergrowths. the corresponding different mineral component fractions of the inhomogeneous spots of the last 82 analyzed spots were also calculated. finally, 17 analyzed spots within 3 grains of partially altered ilmenite into sphene were also investigated. the analyzed oxides of the detected spots include tio2, feo, fe2o3, cr2o3, mno, mgo, al2o3, v2o3, zno, sio2, and cao. the ilmenite molecular formula of homogeneous ilmenite spots and various mineral component fractions of the inhomogeneous analyzed spots were calculated. b. microscopic investigation the homogeneous ilmenite includes grains that appear completely homogeneous under the reflected light microscope. the majority of the grains are elongated to globular, with tabular and rod-shaped not being uncommon (figures 2-3). their color is dull grey with distinct brownish tint. some grains have a characteristic reddish or pinkish brown tint. others have relatively darker brown colors. the majority of ilmenite grains have strong pleochroism from light to a relatively darker brown color. under crossed nicols, the homogenous ilmenite grains have strong anisotropism and change from bright, relatively lighter, brown to dull, relatively darker, brown colors. inner reflections are generally absent. lamellar twining is sometimes observed where twin lamellae exist in one direction along the rhombohedral 1011 planes. the relative darkness or lightness of brown colors for some of ilmenite grains may be related to the presence of either geikielite (mgtio3) or pyrophanite (mntio3) in solid solutions with ilmenite. the ilmenite grains which probably contain geikielite solid solution, show darker color, lower reflectivity, and a reddish brown internal reflection, when compared to normal ilmenite [9]. on the other hand, pyrophanite resembles ilmenite, but shows lower reflectivity, less brown color, less strong bireflectance, anisotropism, and often beautiful reddish internal reflections [22]. some rare ilmenite grains were found to be composed of several aggregates in the form of more or less idiomorphic grains, with intergranular films of transparent spinel granules. engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9618 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … when rotating the stage of the microscope, the aggregates show irregular boundaries and different positions in relation to their reflection pleochroism. however, the aggregates and their boundaries are more pronounced under the crossed nicols due to the different positions of their distinct anisotropy. this feature may be the result of deformation and recrystallization of the ilmenite during metamorphism accompanied by the migration of spinel to the grain borders [23]. homogeneous ferriilmenite grains (figure 2 (8)-(12)), were detected to have paler colors and relatively higher reflectivities with very light brownish tints than the normal ilmenite. the grains are ferromagnetic or strongly paramagnetic with relatively stronger mass-magnetic susceptibilities than the majority of homogenous ilmenite or titanhematite-ferriilmenite exsolved grains. most of the grains are even lighter than titanomagnetite grains. the majority of homogeneous ferriilmenite grains have weak reflection pleochroism while under crossed nicols they have strong and distinct anisotropism. these ferriilmenite grains are the result of a considerable amount of fe2o3 in the solid solution. some of the ferromagnetic and strongly paramagnetic ferriilmenite grains were found to contain exsolution bodies of titanhematite with their long axes parallel to each other and to the (0001) direction of ilmenite. however, such exsolutions do not exceed 10 to 15% of the whole intergrowth and are particularly found as fine seriate exsolution lamellae. the hematite-ilmenite exsolution intergrowth texture is called hemoilmenite where microintergrowths of titanhematite or ilmenohematite are enclosed in the ferrian ilmenite [24]. in a considerable number of the titanhematite-ferriilmenite exsolved intergrown grains, most of the oriented titanhematite exsolution bodies are replaced by goethite or limonite while the host ferriilmenite remains unchanged (figure 4 (1)). some of the replaced titanhematite exsolution bodies give grey material with distinct anisotropism and obvious bluish tint relatively much lighter under the reflected light. sometimes brownish yellow internal reflection colors are observed. this material is certainly goethite. sometimes, some positions in the exsolved titanhematite lamellae seem to be altered to fine grained goethite or to fine aggregates of hydrated iron oxides which are dark in color, nearly isotropic and showing yellow to yellowish brown internal reflections. in this intergrowth, the titanhematite exsolutions show different shapes, sizes, and orientations in the different titanhematite-ferriilmenite grains. in most of them, the exsolution bodies of titanhematite occur in ferriilmenite with their long axes parallel to each other and to the (0001) direction of the ilmenite, showing only one generation of exsolved titanhematite (figure 4, (2)-(4)). some show 2 distinct generations of exsolutions. the exsolution bodies of the first generation, relatively coarser, contain fine seriate exsolutions of ferriilmenite parallel to the (0001) direction of titanhematite. the second generation, on the other hand, is relatively finer and generally parallel to the first titanhematite generation bodies and to the (0001) direction of the ferriilmenite. the titanhematite may be also found as banded or rectilinear exsolution intergrowths traversing the whole ilmenite grain. other grains contain lensoid to elongated broad blades of exsolved intergrowths of titanhematite alternating with broad plates of the host ferriilmenite. in these two last cases, both titanhematite and ferriilmenite exhibit swarms of oriented fine seriate exsolution bodies (figure 4, (5)-(6)). v. discussion a. homogeneous ilmenite (63%) and homogeneous ferriilmenite (2%) the homogeneous ilmenite represents the major component of the obtained ilmenite concentrate. it was found out that the investigated homogeneous grains contain both mg and mn in their chemical composition. some of these grains have more mg content than mn, some the opposite. 1) homogeneous ilmenite and ferriilmenite with more mg than mn content according to [25-26], mg-ilmenites (picroilmenites) indicate derivation of magmas from subcontinental mantle lithosphere. authors in [27] explained that higher mg concentrations are typically associated with more primary ilmenite grains almost 45-55 wt% tio2, while authors in [28] explained that mg-rich ilmenite is typical of mafic igneous rocks. however, the nile river drainage has various rock types and hence, various types of ilmenite grains. some of the investigated homogeneous ilmenite grains contain much more mgo than mno. the 12 grains of figure 2 (table i), are examples of these grains. grains (1)-(7) are detected in the obtained final ilmenite concentrate. in spot 1 (figure 2(1), table i), an inclusion of sio2 (18.82%) is associated with ilmenite. neglecting the sio2 content and the recalculation of the analyzed spots by multiplying by [100/(100-18.82)], spot 1 gives a well-defined ilmenite chemical formula (table i). the other analyzed spots are ilmenite with a slight content of dissolved fe2o3. spots 1-12 of grain (2) are ilmenite with definite dissolved fe2o3. the iron content of spots 13 and 14 is totally ferrous, the sums of cations are 2 and 1.97 respectively. in comparing these 2 spots with the other analyzed spots of the grain, it is obvious that most of their ferric iron content is leached out and some molecular water is included within their pores. the sums of total oxides are 95.4% and 92.6% respectively. these 2 spots contain also considerable amounts of molecular water. grains (3)-(4) are ilmenite with some mixed fe2o3 content as solid solutions. in the grains (1)-(4), the contents of mixed fe2o3 ranges are 4.73-7.60%, 3.885.66%, 4.28-6.03%, and 3.85-4.32% respectively. in grain (5), spots 1 and 7 are beside or inside a crack of the grain. hence, their lower sum of total oxides. in this grain, the fe2o3 content ranges between 2.58 (spot 7) and 7.58 (spot 1). both spots may contain considerable amounts of molecular water. grains (6)(7) are ilmenite with some mixed fe2o3 content ranging between 3.71 and 6.01%. spot 8 of grain (6) is found to be leached ilmenite. a constructed excel forumla was used for the identification and calculation of the leached ilmenite. 2) homogeneous ferriilmenite ferriilmenite grains (8)-(12) of figure 2 (table i) were detected within the ferromagnetic fraction associated with magnetite and titanomagnetite grains and contain relatively higher contents of mixed fe2o3, which are 22.47-22.81%, 7.338.72%, 21.01-22.05%, 14.52-15.25%, and 9.4-14.64% respectively. engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9619 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … fig. 2. bse images of the homogeneous ilmenite grains: (1)-(7), have more mg than mn content. (8)-(12) are homogeneous ferriilmenite grains. however, mgo and al2o3 contents are also relatively higher in these grains, ranging between 3.38-3.57 % and 0.20.25% in grain (8), 3.81-4.05% and 0.21-0.28% in grain (9), 4.38-4.65% and 0.35-0.40% in grain (10), 5.41-5.56% and 0.39-0.46% in grain (11), and 4.57-6.6% and 0.23-0.65% in grain (12) respectively. also, the cr2o3 content in these grains is relatively higher, especially in grain (11). it ranges between 1.04 and 1.21% in grain (11), while it ranges between 0 and 0.31% in the other 4 grains. comparing these grains with the last 7 grains ensures that al2o3 follows fe2o3. the content of al2o3 increases as the contents of fe2o3 increases. 3) homogeneous ilmenite with more mn than mg content mn-rich ilmenite tends to be abundant in peraluminous granite and metapelite, and is thus characteristic of ilmenite with abundant unoriented quartz inclusions [28]. the values for mno in ilmenite from jacupiranga cabonatite, brazil, range between 2.2 and 3.5% with one sample having 7.9% [29-30]. the mno content of ilmenite from chhatrapur coast, odisha, india, varies from 0.125 to 0.579% while the mgo content varies from 0.069 to 1.357%, indicating a solid solution series between ilmenite, pyrophanite, and geikielite [31]. in coexisting magnetite and ilmenite, mgo and mno partition preferentially into ilmenite. mgo shows a regular pattern of distribution between them, whereas mno is distributed irregularly [32]. another type of ilmenite grains in the final obtained ilmenite concentrate is detected where the mn content is larger than the mgo. these grains are shown in figure 3, table ii as follows: in grain (1), most of the analyzed iron content is ferrous iron. spot 1 is in a crack while spot 10 is leached ilmenite. grain (2) is ilmenite with minor fe2o3 content in spots 1-3. the iron content of spots 3-5 is mainly ferrous iron. in grain (3), the analyzed iron content of all the analyzed spots is ferrous iron. in grain (4), ilmenite is mixed with 3.03-4.96% fe2o3 content. in grains (5) and (6), the content of mno is relatively higher and ranges between 2.67 and 3.46% for (5) and 4.52 and 6.09% for (6). their cr2o3 content is negligible. the content of mixed fe2o3 in these 2 grains is relatively higher, ranging between 14.9 and 18.01% in (5) and 3.41 and 10.22% in (6). the content of al2o3 is not positively correlated with the content of fe2o3 in the analyzed spots. also, in grain (6), the comparison of spots 1, 3, 5, and 9 with the others reveals that ilmenite is altered in these 4 spots into individual phases of tio2 and fe2o3 where some of the fe2o3 content is leached out. in spot 1, some of the sio2 content is mixed where a relatively lower content of tio2 wt% is recorded. due to the presence of these 4 spots on the edge of the grain, the process of alteration is relatively higher. hence, there are appreciable contents of molecular water inside them (table ii). b. hematite-ilmenite exsolution intergrowth (21.4%) the most common exsolved intergrowth type in the examined ilmenite grains is the titanhematite-ferriilmenite exsolved intergrowths. the same was also reported in [8, 33]. similar textures of titanhematite exsolution bodies were found in [34], showing that in the majority of grains, the hematite occupies about 20 to 25% of the intergrowth. it was also shown that very coarse intergrowths are occassionally observed where the hematite occupies about 30-35% of the whole intergrowth. on the other hand, the percentage of the titanhematite intergrowths in ilmenite does not exceed 5% in some mineral deposits of um rus area, eastern desert, egypt [35]. fig. 3. bse images of homogeneous ilmenite grains with more mn than mg content. engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9620 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … table i. microprobe chemical analysis and corresponding molecular formulae of the analyzed spots for homogeneous ilmenite grains with a relatively higher mg content, grains (1)-(7) and ferriilmenite grains (8)-(12) of figure 2 g r a in s s p o ts s io 2 m g o m n o c a o z n o f e o a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l s io 2 m g o m n o c a o z n o f e o f e 2 o 3 a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l f e f e r r o u s f e f e r r ic o th e r c a ti o n s t i o fig. 2 (1) 1 18.82 0.70 0.46 0.26 0.05 39.61 0.06 0.36 0.08 40.17 100.56 18.82 0.70 0.46 0.26 0.05 56.56 18.84 0.06 0.36 0.08 40.17 98.68 1.12 -0.34 0.47 0.72 3 1 0.00 0.86 0.57 0.32 0.06 48.72 0.07 0.44 0.10 49.41 100.55 0.00 0.86 0.57 0.32 0.06 41.88 7.60 0.07 0.44 0.10 49.41 101.31 0.87 0.14 0.07 0.92 3 2 0.00 1.19 0.60 0.00 0.03 47.67 0.03 0.42 0.01 50.33 100.29 0.00 1.19 0.60 0.00 0.03 42.52 5.73 0.03 0.42 0.01 50.33 100.86 0.88 0.11 0.07 0.94 3 3 0.00 1.19 0.67 0.01 0.00 48.00 0.01 0.42 0.00 50.60 100.90 0.00 1.19 0.67 0.01 0.00 42.71 5.89 0.01 0.42 0.00 50.60 101.49 0.88 0.11 0.07 0.94 3 4 0.00 1.16 0.57 0.01 0.00 48.15 0.00 0.45 0.00 50.82 101.17 0.00 1.16 0.57 0.01 0.00 43.06 5.66 0.00 0.45 0.00 50.82 101.73 0.89 0.11 0.06 0.94 3 5 0.00 1.26 0.59 0.02 0.00 47.18 0.02 0.45 0.00 50.90 100.42 0.00 1.26 0.59 0.02 0.00 42.92 4.73 0.02 0.45 0.00 50.90 100.89 0.89 0.09 0.07 0.95 3 fig. 2 (2) 1 0.00 1.12 0.52 0.03 0.14 46.13 0.00 0.45 0.01 48.61 97.02 0.00 1.12 0.52 0.03 0.14 41.03 5.66 0.00 0.45 0.01 48.61 97.58 0.88 0.11 0.07 0.94 3 2 0.00 1.13 0.42 0.01 0.02 46.30 0.00 0.48 0.02 48.58 96.96 0.00 1.13 0.42 0.01 0.02 41.23 5.63 0.00 0.48 0.02 48.58 97.52 0.89 0.11 0.06 0.94 3 3 0.00 1.18 0.43 0.00 0.00 45.74 0.01 0.40 0.00 48.97 96.73 0.00 1.18 0.43 0.00 0.00 41.52 4.69 0.01 0.40 0.00 48.97 97.20 0.90 0.09 0.06 0.95 3 4 0.00 1.17 0.48 0.01 0.07 46.00 0.00 0.45 0.04 48.97 97.20 0.00 1.17 0.48 0.01 0.07 41.40 5.11 0.00 0.45 0.04 48.97 97.70 0.89 0.10 0.07 0.95 3 5 0.00 1.13 0.47 0.04 0.04 45.55 0.00 0.46 0.03 49.00 96.72 0.00 1.13 0.47 0.04 0.04 41.51 4.49 0.00 0.46 0.03 49.00 97.17 0.90 0.09 0.07 0.95 3 6 0.02 1.11 0.50 0.00 0.06 45.91 0.02 0.40 0.02 49.02 97.06 0.02 1.11 0.50 0.00 0.06 41.58 4.81 0.02 0.40 0.02 49.02 97.54 0.89 0.09 0.07 0.95 3 7 0.00 1.16 0.40 0.00 0.00 45.41 0.00 0.40 0.04 49.09 96.49 0.00 1.16 0.40 0.00 0.00 41.69 4.13 0.00 0.40 0.04 49.09 96.90 0.90 0.08 0.06 0.96 3 8 0.00 1.22 0.44 0.01 0.00 45.58 0.00 0.44 0.02 49.17 96.89 0.00 1.22 0.44 0.01 0.00 41.60 4.42 0.00 0.44 0.02 49.17 97.32 0.90 0.09 0.07 0.95 3 9 0.00 1.06 0.46 0.00 0.00 45.51 0.00 0.45 0.05 49.22 96.76 0.00 1.06 0.46 0.00 0.00 41.92 3.99 0.00 0.45 0.05 49.22 97.15 0.91 0.08 0.06 0.96 3 10 0.00 1.21 0.47 0.00 0.05 46.22 0.00 0.39 0.00 49.42 97.76 0.00 1.21 0.47 0.00 0.05 41.79 4.92 0.00 0.39 0.00 49.42 98.25 0.89 0.09 0.07 0.95 3 11 0.00 1.19 0.53 0.02 0.03 45.45 0.00 0.38 0.01 49.46 97.07 0.00 1.19 0.53 0.02 0.03 41.79 4.07 0.00 0.38 0.01 49.46 97.48 0.90 0.08 0.07 0.96 3 12 0.00 1.25 0.46 0.00 0.01 45.47 0.01 0.46 0.03 49.68 97.37 0.00 1.25 0.46 0.00 0.01 41.98 3.88 0.01 0.46 0.03 49.68 97.75 0.90 0.07 0.07 0.96 3 13 0.00 1.34 0.44 0.00 0.01 42.31 0.01 0.47 0.02 50.78 95.37 0.00 1.34 0.44 0.00 0.01 42.31 0.00 0.01 0.47 0.02 50.78 95.37 0.93 0.00 0.07 1.00 3 14 0.03 0.99 0.44 0.04 0.06 39.75 0.01 0.37 0.04 50.88 92.59 0.03 0.99 0.44 0.04 0.06 39.75 0.00 0.01 0.37 0.04 50.88 92.59 0.90 0.00 0.06 1.04 3 fig. 2 (3) 1 0.00 1.40 0.62 0.00 0.09 47.63 0.03 0.37 0.00 50.48 100.63 0.00 1.40 0.62 0.00 0.09 42.21 6.03 0.03 0.37 0.00 50.48 101.24 0.87 0.11 0.08 0.94 3 2 0.00 1.28 0.56 0.00 0.02 46.97 0.00 0.47 0.03 50.60 99.94 0.00 1.28 0.56 0.00 0.02 42.64 4.81 0.00 0.47 0.03 50.60 100.42 0.89 0.09 0.07 0.95 3 3 0.00 1.30 0.54 0.01 0.04 47.06 0.01 0.45 0.03 50.64 100.09 0.00 1.30 0.54 0.01 0.04 42.65 4.91 0.01 0.45 0.03 50.64 100.58 0.89 0.09 0.07 0.95 3 4 0.00 1.31 0.56 0.03 0.00 47.38 0.04 0.42 0.02 50.91 100.66 0.00 1.31 0.56 0.03 0.00 42.86 5.02 0.04 0.42 0.02 50.91 101.16 0.89 0.09 0.07 0.95 3 5 0.00 1.25 0.52 0.00 0.15 46.86 0.00 0.44 0.01 51.00 100.22 0.00 1.25 0.52 0.00 0.15 43.00 4.28 0.00 0.44 0.01 51.00 100.65 0.90 0.08 0.07 0.96 3 6 0.00 1.36 0.64 0.01 0.12 46.74 0.00 0.38 0.09 51.05 100.39 0.00 1.36 0.64 0.01 0.12 42.72 4.46 0.00 0.38 0.09 51.05 100.84 0.89 0.08 0.08 0.95 3 7 0.00 1.32 0.54 0.01 0.02 47.73 0.01 0.41 0.03 51.33 101.40 0.00 1.32 0.54 0.01 0.02 43.26 4.97 0.01 0.41 0.03 51.33 101.90 0.89 0.09 0.07 0.95 3 fig. 2 (4) 1 0.00 1.32 0.43 0.00 0.06 45.34 0.03 0.47 0.00 49.24 96.88 0.00 1.32 0.43 0.00 0.06 41.46 4.32 0.03 0.47 0.00 49.24 97.31 0.89 0.08 0.07 0.95 3 2 0.00 1.41 0.49 0.00 0.08 44.84 0.00 0.53 0.00 49.41 96.75 0.00 1.41 0.49 0.00 0.08 41.36 3.86 0.00 0.53 0.00 49.41 97.14 0.89 0.07 0.08 0.96 3 3 0.00 1.40 0.45 0.00 0.05 44.92 0.02 0.51 0.02 49.42 96.78 0.00 1.40 0.45 0.00 0.05 41.45 3.85 0.02 0.51 0.02 49.42 97.16 0.89 0.07 0.08 0.96 3 4 0.00 1.37 0.47 0.02 0.06 44.94 0.03 0.47 0.01 49.44 96.81 0.00 1.37 0.47 0.02 0.06 41.48 3.85 0.03 0.47 0.01 49.44 97.19 0.89 0.07 0.08 0.96 3 5 0.00 1.40 0.45 0.01 0.05 45.48 0.04 0.44 0.00 49.93 97.80 0.00 1.40 0.45 0.01 0.05 41.91 3.97 0.04 0.44 0.00 49.93 98.19 0.89 0.08 0.08 0.96 3 fig. 2 (5) 1 0.06 0.64 0.47 0.01 0.00 46.44 0.00 0.42 0.00 45.77 93.82 0.06 0.64 0.47 0.01 0.00 39.61 7.58 0.00 0.42 0.00 45.77 94.57 0.88 0.15 0.05 0.92 3 2 0.00 1.24 0.42 0.02 0.07 46.84 0.05 0.48 0.01 48.83 97.95 0.00 1.24 0.42 0.02 0.07 41.20 6.27 0.05 0.48 0.01 48.83 98.58 0.88 0.12 0.07 0.93 3 3 0.00 1.21 0.43 0.02 0.00 47.19 0.04 0.46 0.00 48.89 98.24 0.00 1.21 0.43 0.02 0.00 41.35 6.49 0.04 0.46 0.00 48.89 98.88 0.88 0.12 0.07 0.93 3 4 0.00 1.28 0.44 0.00 0.00 46.41 0.02 0.42 0.00 49.01 97.58 0.00 1.28 0.44 0.00 0.00 41.36 5.61 0.02 0.42 0.00 49.01 98.14 0.88 0.11 0.07 0.94 3 5 0.01 1.32 0.53 0.00 0.02 46.18 0.02 0.47 0.03 49.40 97.98 0.01 1.32 0.53 0.00 0.02 41.53 5.17 0.02 0.47 0.03 49.40 98.50 0.88 0.10 0.07 0.95 3 6 0.00 1.28 0.48 0.00 0.04 46.31 0.02 0.39 0.05 49.74 98.32 0.00 1.28 0.48 0.00 0.04 41.94 4.85 0.02 0.39 0.05 49.74 98.80 0.89 0.09 0.07 0.95 3 7 0.07 1.06 0.42 0.02 0.04 41.66 0.02 0.41 0.03 46.29 90.03 0.07 1.06 0.42 0.02 0.04 39.34 2.58 0.02 0.41 0.03 46.29 90.28 0.91 0.05 0.07 0.97 3 fig. 2 (6) 1 0.00 1.63 0.54 0.02 0.10 45.60 0.00 0.53 0.01 49.28 97.70 0.00 1.63 0.54 0.02 0.10 40.76 5.37 0.00 0.53 0.01 49.28 98.24 0.87 0.10 0.09 0.94 3 2 0.00 1.65 0.49 0.01 0.03 45.67 0.02 0.54 0.02 49.45 97.88 0.00 1.65 0.49 0.01 0.03 41.01 5.18 0.02 0.54 0.02 49.45 98.39 0.87 0.10 0.09 0.94 3 3 0.00 1.61 0.48 0.00 0.12 45.32 0.03 0.52 0.02 49.84 97.93 0.00 1.61 0.48 0.00 0.12 41.37 4.38 0.03 0.52 0.02 49.84 98.37 0.88 0.08 0.09 0.95 3 4 0.00 1.62 0.58 0.00 0.02 45.31 0.03 0.50 0.00 49.87 97.93 0.00 1.62 0.58 0.00 0.02 41.37 4.38 0.03 0.50 0.00 49.87 98.37 0.88 0.08 0.09 0.95 3 5 0.00 1.65 0.53 0.03 0.15 45.44 0.04 0.53 0.04 49.92 98.33 0.00 1.65 0.53 0.03 0.15 41.26 4.64 0.04 0.53 0.04 49.92 98.79 0.87 0.09 0.09 0.95 3 6 0.00 1.59 0.47 0.02 0.06 45.70 0.03 0.47 0.01 50.00 98.35 0.00 1.59 0.47 0.02 0.06 41.60 4.56 0.03 0.47 0.01 50.00 98.80 0.88 0.09 0.08 0.95 3 7 0.00 1.54 0.53 0.02 0.00 45.12 0.07 0.49 0.00 50.12 97.90 0.00 1.54 0.53 0.02 0.00 41.78 3.71 0.07 0.49 0.00 50.12 98.27 0.89 0.07 0.08 0.96 3 8 1.29 0.24 1.05 0.11 0.08 31.44 1.18 0.44 0.06 57.95 93.83 fig. 2 (7) 1 0.00 3.01 0.51 0.01 0.14 43.85 0.13 0.45 0.03 49.42 97.54 0.00 3.01 0.51 0.01 0.14 38.44 6.01 0.13 0.45 0.03 49.42 98.13 0.81 0.11 0.14 0.94 3 2 0.00 3.07 0.53 0.03 0.01 43.89 0.09 0.51 0.04 49.90 98.07 0.00 3.07 0.53 0.03 0.01 38.83 5.62 0.09 0.51 0.04 49.90 98.63 0.81 0.11 0.14 0.94 3 fig. 2 (8) 1 0.00 3.39 1.01 0.02 0.02 50.67 0.22 0.33 0.10 41.49 97.24 0.00 3.39 1.01 0.02 0.02 30.22 22.72 0.22 0.33 0.10 41.49 99.51 0.63 0.43 0.18 0.78 3 2 0.00 3.39 1.00 0.01 0.05 50.94 0.21 0.28 0.00 41.72 97.60 0.00 3.39 1.00 0.01 0.05 30.43 22.79 0.21 0.28 0.00 41.72 99.87 0.63 0.43 0.17 0.78 3 3 0.00 3.50 1.02 0.02 0.11 50.69 0.25 0.31 0.01 41.74 97.65 0.00 3.50 1.02 0.02 0.11 30.16 22.81 0.25 0.31 0.01 41.74 99.93 0.63 0.43 0.18 0.78 3 4 0.00 3.48 1.05 0.02 0.09 50.68 0.25 0.29 0.03 41.89 97.76 0.00 3.48 1.05 0.02 0.09 30.32 22.62 0.25 0.29 0.03 41.89 100.02 0.63 0.42 0.18 0.78 3 5 0.00 3.50 1.05 0.01 0.11 50.84 0.23 0.36 0.00 41.99 98.09 0.00 3.50 1.05 0.01 0.11 30.36 22.75 0.23 0.36 0.00 41.99 100.36 0.63 0.42 0.18 0.78 3 6 0.00 3.57 1.00 0.00 0.09 50.68 0.23 0.23 0.10 42.06 97.96 0.00 3.57 1.00 0.00 0.09 30.39 22.54 0.23 0.23 0.10 42.06 100.21 0.63 0.42 0.18 0.78 3 7 0.00 3.38 1.07 0.00 0.06 50.92 0.20 0.25 0.00 42.08 97.96 0.00 3.38 1.07 0.00 0.06 30.69 22.47 0.20 0.25 0.00 42.08 100.21 0.64 0.42 0.17 0.78 3 fig. 2 (9) 1 0.00 4.05 0.54 0.03 0.10 44.45 0.28 0.61 0.08 49.45 99.58 0.00 4.05 0.54 0.03 0.10 36.60 8.72 0.28 0.61 0.08 49.45 100.45 0.75 0.16 0.19 0.91 3 2 0.00 3.81 0.46 0.02 0.01 44.50 0.21 0.64 0.06 50.24 99.95 0.00 3.81 0.46 0.02 0.01 37.90 7.33 0.21 0.64 0.06 50.24 100.68 0.77 0.13 0.17 0.92 3 3 0.00 4.03 0.58 0.01 0.08 45.06 0.23 0.61 0.11 50.29 101.00 0.00 4.03 0.58 0.01 0.08 37.39 8.52 0.23 0.61 0.11 50.29 101.85 0.75 0.15 0.18 0.91 3 engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9621 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … g r a in s s p o ts s io 2 m g o m n o c a o z n o f e o a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l s io 2 m g o m n o c a o z n o f e o f e 2 o 3 a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l f e f e r r o u s f e f e r r ic o th e r c a ti o n s t i o fig. 2 (10) 1 0.00 4.38 0.35 0.00 0.00 49.44 0.18 0.47 0.19 42.85 97.86 0.00 4.38 0.35 0.00 0.00 30.39 21.16 0.18 0.47 0.19 42.85 99.97 0.63 0.39 0.20 0.79 3 2 0.00 4.51 0.37 0.01 0.04 49.76 0.26 0.50 0.11 42.88 98.43 0.00 4.51 0.37 0.01 0.04 30.13 21.81 0.26 0.50 0.11 42.88 100.61 0.62 0.40 0.21 0.79 3 3 0.00 4.62 0.37 0.00 0.00 49.45 0.20 0.49 0.17 42.92 98.23 0.00 4.62 0.37 0.00 0.00 30.00 21.62 0.20 0.49 0.17 42.92 100.39 0.61 0.40 0.21 0.79 3 4 0.00 4.65 0.37 0.00 0.12 49.71 0.22 0.47 0.17 42.94 98.64 0.00 4.65 0.37 0.00 0.12 29.86 22.05 0.22 0.47 0.17 42.94 100.85 0.61 0.40 0.21 0.79 3 5 0.00 4.45 0.40 0.01 0.00 49.54 0.19 0.51 0.17 43.01 98.27 0.00 4.45 0.40 0.01 0.00 30.35 21.32 0.19 0.51 0.17 43.01 100.40 0.62 0.39 0.20 0.79 3 6 0.00 4.46 0.35 0.01 0.20 49.21 0.21 0.46 0.15 43.13 98.18 0.00 4.46 0.35 0.01 0.20 30.30 21.01 0.21 0.46 0.15 43.13 100.28 0.62 0.39 0.21 0.80 3 fig. 2 (11) 1 0.00 5.46 0.34 0.01 0.13 43.43 0.44 0.60 1.08 44.65 96.13 0.00 5.46 0.34 0.01 0.13 29.97 14.95 0.44 0.60 1.08 44.65 97.62 0.62 0.28 0.27 0.84 3 2 0.00 5.41 0.37 0.00 0.01 43.40 0.45 0.59 1.04 44.66 95.92 0.00 5.41 0.37 0.00 0.01 30.14 14.73 0.45 0.59 1.04 44.66 97.39 0.63 0.28 0.27 0.84 3 3 0.00 5.53 0.41 0.02 0.00 43.66 0.44 0.58 1.05 44.72 96.40 0.00 5.53 0.41 0.02 0.00 29.93 15.25 0.44 0.58 1.05 44.72 97.92 0.62 0.28 0.27 0.84 3 4 0.00 5.56 0.38 0.02 0.12 42.96 0.46 0.61 1.16 44.82 96.07 0.00 5.56 0.38 0.02 0.12 29.90 14.52 0.46 0.61 1.16 44.82 97.52 0.62 0.27 0.28 0.84 3 5 0.01 5.45 0.42 0.00 0.13 43.49 0.39 0.50 1.21 44.90 96.50 0.01 5.45 0.42 0.00 0.13 30.15 14.82 0.39 0.50 1.21 44.90 97.98 0.63 0.28 0.27 0.84 3 fig. 2 (12) 1 0.07 4.99 0.44 0.00 0.06 44.07 0.57 0.46 0.26 46.65 97.58 0.07 4.99 0.44 0.00 0.06 32.65 12.68 0.57 0.46 0.26 46.65 98.84 0.67 0.24 0.24 0.87 3 2 0.00 6.01 0.41 0.01 0.02 44.18 0.41 0.47 0.19 46.86 98.54 0.00 6.01 0.41 0.01 0.02 31.00 14.65 0.41 0.47 0.19 46.86 100.01 0.63 0.27 0.26 0.85 3 3 0.00 6.60 0.48 0.01 0.15 43.23 0.23 0.48 0.25 47.19 98.62 0.00 6.60 0.48 0.01 0.15 30.06 14.63 0.23 0.48 0.25 47.19 100.08 0.61 0.27 0.28 0.86 3 4 0.00 4.66 0.42 0.00 0.02 43.83 0.61 0.60 0.24 47.65 98.02 0.00 4.66 0.42 0.00 0.02 34.12 10.79 0.61 0.60 0.24 47.65 99.10 0.70 0.20 0.22 0.88 3 5 0.10 4.57 0.41 0.02 0.05 42.85 0.65 0.56 0.31 47.69 97.21 0.10 4.57 0.41 0.02 0.05 34.39 9.40 0.65 0.56 0.31 47.69 98.15 0.71 0.18 0.22 0.89 3 however, in studying the egyptian beach ilmenite of rosetta and damietta, the size and amount of the titanhematite exsolutions vary. sometimes they are coarse, carrying fine exsolutions of ferriilmenite and forming up to 50% of the intergrowth. occasionally they are too fine to be identified except under high magnification, and form less than 5% of the intergrowth [9]. in the present study, in most of the investigated titanhematite-ferriilmenite exsolution intergrowths, the exsolved titanhematite bodies occupy a minimum of 5% and up to 40% of the whole intergrowth. the majority of the grains exhibiting this intergrowth type have titanhematite exsolution bodies occupying about 10 20% of the whole intergrowth. in some titanhematite-feiriilmenite exsolved intergrown grains, the ferriilmenite component may be altered into rutile and hematite (figure 4 (5)-(6) and figure 5 (7)). the alteration of ilmenite to rutile and hematite is generally attributed to oxidation [34]. authors in [36] demonstrated experimentally that on heating pure ilmenite in air at 730 o c, it was completely oxidized into rutile and hematite with a very minor amount of brookite, but on further heating to 900 o c, a mixture of rutile and pseudobrookite was formed. similar textures have been described from highly metamorphosed epidiorite from assynt [37]. subgraphic intergrowth of rutile and hematite with a thin outer rim of unaltered homogeneous ilmenite of abu ghalaga ilmenite ore was described in [34] in the investigated samples, the ferriilmenite lamellae were found to be occasionally either partially or completely altered into rutile and hematite. in the concentrate under examination, some minor composite grains were detected, each of them consisting of two components. the first component is titanhematite bodies in ferriilmenite, whereas the second is feirilmenite in titanhematite (figure 5 (8)-(9)). several interpretations have been given to explain the different types of the titanhematite-ferriilmenite exsolution intergrowths [9, 22, 38]. authors in [36] found that at normal temperatures, ferriilmenites with 18% fe203 and titanhemtites with 10% tio2 in solid solution exist in nature. according to [39], the unmixing of ilmenite and hematite from their solid solution takes place in two stages, the smaller bodies representing a "generation ii" of exsolution formed at lower temperatures whereas the earlier and relatively coarser ones were termed as "generation i". according to [39], a gap in the miscibility range between fe2o3 and fetio3 originates below 600 o c, in which the solid solution splits into fe2o3 bearing ilmenite and fetio3 bearing hematite. with further temperature fall, the dissolving power of fe2o3 in fetio3 and of fetio3 in fe2o3 decreases intermittently and second generation exsolution discs are formed. fig. 4. bse images of various detected titanhematites-ferriilmenites exsolved intergrowth grains. the size of the exsolutions and the composition of the two components of the intergrowth depends on the rate of cooling, the original composition of the solid solution and the presence or absence of foreign oxides, such as mgo, mno and al2o3 [36]. the irregularity of some exsolution bodies indicates that they have grown in situ, by absorbing exsolution hematite in adjacent ferriilmenite [40]. many of the larger exsolution lamellae are observed to have coalesced and are frequently irregular. some of the coarse titanhematite exsolution bodies have a narrow rim of homogeneous ilmenite and seem to have grown in situ by diffusion [34]. in the present work, most of the observations given by [34, 40] were also detected. however, there are some reasons to accept the suggestion of the two generations given by [39] rather than others. these are : engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9622 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite …  some host ferriilmenite grains contain only one generation of the oriented titanhematite exsolutions.  some host ferriilmenite grains contain fine titanhematite exsolution bodies irregularly distributed without definite orientation.  the presence of the composite grains is considered the most important factor to accept the suggestion of [39]. in these grains, any individual component, either of the ferriilmenite host or of the titanhematite host, could be itself considered as a first generation of exsolution due to the unmixing of 2 solid solutions, 1 of them composed mainly of ferriilmenite and the other mainly of titanhematite, derived from an original single solution. the relative percentages of the obtained 2 solid solutions are related to the concentrations of their corresponding essential components in the original solid solution, the temperature, and the rate of cooling. at a relatively lower temperature and definite rate of cooling, each individual component (e.g. ferriilmenite) exsolves some or most of the miscible hematite inside it. the same process could also occur for the second individual component, the titanhematite, where some or most of the miscible ilmenites are exsolved with the result of a second generation, in relation to the whole composite grain, of relatively much smaller exsolution bodies in each individual component. fig. 5. bse images of detected titanhematites-ferriilmenites exsolved intergrowth grains. in grain (7), the ferriilmenite component is altered into rutile and hematite. composite grains (8)-(9) consist of two components, one being ferriilmenitetitanhematite and the other titanhematite-ferriilmenite. after investigating the results of microprobe analysis of the various detected grains of hematite–ilmenite exsolution intergrowths contained in figures 4-5, the following remarks can be noted. in figure 4 (1) (tables iii-iv), spots 1-4 have considerable amounts of feo oxidized into fe2o3 which is partially leached and the remaining may have changed into goethite and/or hydrated iron oxides (table iii). in these spots, the sio2, al2o3, and cao contents are relatively higher. these impurity oxides may be phases carrying molecular and/or structural water, or they are associated with the molecular water necessary for the process of oxidation and hydroxylation of ferrous iron to ferric iron. so, the loaded impurity oxides are precipitated inside fissures. when this process of entering molecular water is repeated, bearing for these impurity oxides into fissures, an enrichment of the 3 impurity oxides occurs. spots 6-9 and 11 are ferriilmenites where the fe2o3 content ranges between 6.87 and 8.96% while the tio2 content ranges between 47.43 and 47.95%. in spots 5, 10, 12, and 13 some of of fe2o3 content is lost from the ferriilmenite component adjacent to the altered titanhematite component. their areas contain voids and molecular and/or structural water. hence, the fe2o3 content is decreased from 5% in spot 5 to 1.07% in spot 13. on the other hand, the content of tio2 is increased from 47.13% in spot 5 to 49.63% in spot 13, while the content of feo is increased from 38.01% in spot 5 to 40.78% in spot 13. in grain (2) of figure 4, spots 1, 2 are titanhematite. the fe2o3 content ranges between 55.47 and 60.21%, the tio2 content ranges between 19.22 and 22.4%, and the feo content ranges between 14.18 and 16.69%. spots 3-8 are ferriilmenite. the fe2o3 content ranges between 6.09 and 8.54%. when comparing the contents of al2o3, v2o3, and cr2o3 of spots 1, 2 with those of spots 3-8, it is obvious that these oxides are correlated positively with fe2o3 rather than with tio2. mno and mgo are correlated positively with feo and fe2o3, but both favor feo rather than fe2o3. spots 1-3 of grain (3) of figure 4 are titanhematite with a maximum value of tio2 equal to 30.88%, which corresponds to 26.46% of feo in spot 3. spots 4-8 are almost ilmenites. the fe2o3 content in these spots ranges between only 0.02 and 0.54%. when comparing the mgo and mno contents of spots 1-3 with those of spots 48, it is obvious that they follow iron (fe 2+ , fe 3+ ), but much more fe 2+ than fe 3+ . on the other hand, both cr 3+ and v 3+ follow fe 3+ more than fe 2+ or ti 4+ . spots 1-4 in grain (4), are titanhematite. the maximum value of tio2 is 16.34% which is correlated to the 13.71% of feo. spots 6-10 are ferriilmenite, with fe2o3 ranging between 0.47 and 2.36%. when comparing the mno, mgo, and cr2o3 contents of spots 1-4 to spots 5-10, it is notable that mno and mgo follow fe 2+ rather than fe 3+ , while cr2o3 follows fe 3+ rather than fe 2+ . spot 5 is in a crack, with most fe2o3 being leached out while the sio2 content is enriched. in this spot, there is a considerable amount of molecular and/or structural water and all the remaining iron is ferrous iron. spots 1-3 of grain (5), (figure 4, tables iii-iv) are titanhematite, containing small bodies of exsolved ilmenite. in these spots, it is obvious that the content of cr2o3 is relatively higher, reflecting the positive correlation between cr2o3 and fe2o3. spots 4-9 are ferriilmenite and spots 5-9 altered to rutile and hematite with a considerable amount of molecular water, especially spots 6, 7. spots 10-13 are ferriilmenite. in these spots, mgo and mno are positively correlated with feo, while cr2o3 seems to vary inversely with feo. cr2o3 follows fe2o3 rather than feo. comparing the contents of v2o5 in these 4 spots with those of the spots 1-4 or 5-9 reflects the positive correlation between v 3+ with either fe 3+ and/or ti 4+ rather than fe 2+ . therefore, v2o3 content is relatively higher in spots 1-4 which have relatively higher fe2o3 content and also are relatively higher in spots 5-9 which have relatively higher tio2 content (table iii). in spots 14 and 15, some of the fe2o3 associated with the ferriilmenite leached, resulting to increased tio2 content in these spots. engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9623 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … table ii. microprobe chemical analyses and corresponding molecular formulae of the analyzed spots of homogeneous ilmenite grains with a relatively higher mn content. grains (1)-(6) of figure 3 g r a in s s p o ts s io 2 m g o m n o c a o z n o f e o a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l s io 2 m g o m n o c a o z n o f e o f e 2 o 3 a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l f e r r o u s f e f e r r ic f e o th e r c a ti o n s t i o fig. 3 (1) 1 1.00 0.06 0.40 0.13 0.06 41.84 0.00 0.32 0.04 50.10 93.95 1.00 0.06 0.40 0.13 0.06 41.80 0.00 0.00 0.32 0.04 50.10 93.95 0.94 0.00 0.05 1.01 3 2 0.00 0.16 0.45 0.01 0.05 45.04 0.00 0.33 0.01 52.19 98.22 0.00 0.16 0.45 0.01 0.05 45.00 0.00 0.00 0.33 0.01 52.19 98.22 0.97 0.00 0.02 1.01 3 3 0.00 0.15 0.44 0.00 0.10 45.53 0.00 0.31 0.03 52.27 98.83 0.00 0.15 0.44 0.00 0.10 45.53 0.00 0.00 0.31 0.03 52.27 98.83 0.98 0.00 0.02 1.00 3 4 0.00 0.15 0.45 0.00 0.03 45.20 0.00 0.38 0.04 52.30 98.56 0.00 0.15 0.45 0.00 0.03 45.20 0.00 0.00 0.38 0.04 52.30 98.56 0.97 0.00 0.02 1.01 3 5 0.00 0.12 0.50 0.02 0.06 45.22 0.00 0.33 0.05 52.31 98.60 0.00 0.12 0.50 0.02 0.06 45.22 0.00 0.00 0.33 0.05 52.31 98.60 0.97 0.00 0.02 1.01 3 6 0.00 0.16 0.47 0.01 0.06 45.53 0.00 0.44 0.01 52.36 99.04 0.00 0.16 0.47 0.01 0.06 45.53 0.00 0.00 0.44 0.01 52.36 99.04 0.97 0.00 0.03 1.00 3 7 0.00 0.13 0.48 0.02 0.13 45.65 0.00 0.39 0.02 52.61 99.43 0.00 0.13 0.48 0.02 0.13 45.65 0.00 0.00 0.39 0.02 52.61 99.43 0.97 0.00 0.03 1.00 3 8 0.00 0.13 0.42 0.00 0.05 45.04 0.00 0.36 0.01 52.66 98.68 0.00 0.13 0.42 0.00 0.05 45.04 0.00 0.00 0.36 0.01 52.66 98.68 0.97 0.00 0.02 1.01 3 9 0.00 0.14 0.51 0.00 0.04 44.53 0.00 0.39 0.08 52.68 98.37 0.00 0.14 0.51 0.00 0.04 44.53 0.00 0.00 0.39 0.08 52.68 98.37 0.96 0.00 0.03 1.02 3 10 0.05 0.15 0.36 0.07 0.00 35.24 0.02 0.42 0.03 57.14 93.50 fig. 3 (2) 1 0.00 0.11 0.82 0.03 0.00 46.14 0.00 0.38 0.00 50.80 98.27 0.00 0.11 0.82 0.03 0.00 44.64 1.66 0.00 0.38 0.00 50.80 98.43 0.96 0.03 0.03 0.98 3 2 0.00 0.06 0.87 0.02 0.04 46.03 0.00 0.39 0.04 50.83 98.28 0.00 0.06 0.87 0.02 0.04 44.67 1.51 0.00 0.39 0.04 50.83 98.43 0.96 0.03 0.03 0.98 3 3 0.02 0.11 0.94 0.01 0.04 46.28 0.00 0.31 0.03 50.97 98.70 0.02 0.11 0.94 0.01 0.04 44.67 1.79 0.00 0.31 0.03 50.97 98.88 0.95 0.03 0.03 0.98 3 4 0.00 0.08 0.82 0.00 0.05 45.50 0.00 0.47 0.02 51.11 98.04 0.00 0.08 0.82 0.00 0.05 44.97 0.59 0.00 0.47 0.02 51.11 98.10 0.97 0.01 0.03 0.99 3 5 0.00 0.08 0.79 0.01 0.00 45.17 0.00 0.35 0.06 51.19 97.66 0.00 0.08 0.79 0.01 0.00 45.09 0.09 0.00 0.35 0.06 51.19 97.66 0.97 0.00 0.03 0.99 3 6 0.20 0.04 0.87 0.02 0.00 45.54 0.00 0.41 0.02 51.32 98.42 0.20 0.04 0.87 0.02 0.00 45.43 0.12 0.00 0.41 0.02 51.32 98.42 0.97 0.00 0.03 0.99 3 fig. 3 (3) 1 0.00 0.14 1.28 0.01 0.09 43.55 0.00 0.42 0.00 52.56 98.04 0.00 0.14 1.28 0.01 0.09 43.55 0.00 0.00 0.42 0.00 52.56 98.04 0.93 0.00 0.04 1.02 3 2 0.00 0.09 1.10 0.01 0.07 44.01 0.00 0.34 0.00 52.66 98.26 0.00 0.09 1.10 0.01 0.07 44.01 0.00 0.00 0.34 0.00 52.66 98.26 0.96 0.00 0.04 1.02 3 3 0.00 0.09 1.23 0.00 0.08 44.74 0.00 0.32 0.00 52.76 99.23 0.00 0.09 1.23 0.00 0.08 44.74 0.00 0.00 0.32 0.00 52.76 99.23 0.95 0.00 0.04 1.01 3 4 0.00 0.10 1.15 0.01 0.02 43.57 0.00 0.33 0.02 52.81 98.01 0.00 0.10 1.15 0.01 0.02 43.57 0.00 0.00 0.33 0.02 52.81 98.01 0.93 0.00 0.04 1.02 3 5 0.00 0.12 1.01 0.00 0.11 43.03 0.00 0.38 0.01 52.85 97.51 0.00 0.12 1.01 0.00 0.11 43.03 0.00 0.00 0.38 0.01 52.85 97.51 0.93 0.00 0.04 1.03 3 6 0.01 0.11 1.01 0.01 0.05 43.61 0.00 0.36 0.03 52.89 98.08 0.01 0.11 1.01 0.01 0.05 43.61 0.00 0.00 0.36 0.03 52.89 98.08 0.94 0.00 0.04 1.02 3 7 0.00 0.14 1.26 0.00 0.00 43.17 0.00 0.34 0.00 52.93 97.84 0.00 0.14 1.26 0.00 0.00 43.17 0.00 0.00 0.34 0.00 52.93 97.84 0.94 0.00 0.04 1.03 3 8 0.00 0.13 1.18 0.00 0.14 43.89 0.00 0.34 0.00 52.96 98.63 0.00 0.13 1.18 0.00 0.14 43.89 0.00 0.00 0.34 0.00 52.96 98.63 0.94 0.00 0.04 1.02 3 9 0.00 0.14 1.15 0.00 0.17 43.74 0.00 0.38 0.03 52.98 98.60 0.00 0.14 1.15 0.00 0.17 43.74 0.00 0.00 0.38 0.03 52.98 98.60 0.94 0.00 0.04 1.02 3 10 0.00 0.15 1.14 0.00 0.10 42.88 0.00 0.44 0.03 53.03 97.77 0.00 0.15 1.14 0.00 0.10 42.88 0.00 0.00 0.44 0.03 53.03 97.77 0.93 0.00 0.04 1.03 3 11 0.00 0.17 1.15 0.01 0.13 43.16 0.00 0.40 0.00 53.10 98.12 0.00 0.17 1.15 0.01 0.13 43.16 0.00 0.00 0.40 0.00 53.10 98.12 0.93 0.00 0.04 1.03 3 12 0.00 0.15 1.28 0.01 0.03 43.16 0.00 0.36 0.04 53.14 98.18 0.00 0.15 1.28 0.01 0.03 43.16 0.00 0.00 0.36 0.04 53.14 98.18 0.92 0.00 0.04 1.03 3 13 0.00 0.15 1.26 0.02 0.03 42.91 0.00 0.39 0.00 53.21 97.97 0.00 0.15 1.26 0.02 0.03 42.91 0.00 0.00 0.39 0.00 53.21 97.97 0.93 0.00 0.04 1.03 3 fig. 3 (4) 1 0.00 0.34 1.60 0.06 0.00 45.75 0.00 0.34 0.01 48.49 96.60 0.00 0.34 1.60 0.06 0.00 41.33 4.91 0.00 0.34 0.01 48.49 97.09 0.90 0.10 0.06 0.95 3 2 0.00 0.26 1.69 0.07 0.05 45.86 0.00 0.30 0.00 48.79 97.02 0.00 0.26 1.69 0.07 0.05 41.60 4.74 0.00 0.30 0.00 48.79 97.49 0.90 0.09 0.06 0.95 3 3 0.00 0.39 1.59 0.00 0.00 46.19 0.00 0.34 0.00 49.00 97.51 0.00 0.39 1.59 0.00 0.00 41.78 4.90 0.00 0.34 0.00 49.00 97.99 0.90 0.09 0.06 0.95 3 4 0.00 0.35 1.70 0.01 0.03 46.18 0.00 0.29 0.00 49.03 97.59 0.00 0.35 1.70 0.01 0.03 41.71 4.96 0.00 0.29 0.00 49.03 98.08 0.90 0.10 0.06 0.95 3 5 0.00 0.38 1.49 0.00 0.00 46.30 0.00 0.37 0.00 49.13 97.67 0.00 0.38 1.49 0.00 0.00 42.01 4.77 0.00 0.37 0.00 49.13 98.14 0.90 0.09 0.06 0.95 3 6 0.00 0.36 1.68 0.03 0.05 45.04 0.00 0.36 0.00 49.72 97.23 0.00 0.36 1.68 0.03 0.05 42.31 3.03 0.00 0.36 0.00 49.72 97.53 0.91 0.06 0.06 0.97 3 fig. 3 (5) 1 0.00 2.44 3.11 0.00 0.12 46.52 0.00 0.28 0.00 42.53 95.00 0.00 2.44 3.11 0.00 0.12 30.66 17.62 0.00 0.28 0.00 42.53 96.76 0.66 0.34 0.18 0.83 3 2 0.00 2.48 3.27 0.00 0.25 46.50 0.00 0.32 0.00 42.54 95.36 0.00 2.48 3.27 0.00 0.25 30.31 17.98 0.00 0.32 0.00 42.54 97.15 0.65 0.35 0.19 0.82 3 3 0.00 2.37 3.07 0.00 0.22 45.87 0.00 0.29 0.02 42.57 94.41 0.00 2.37 3.07 0.00 0.22 30.78 16.77 0.00 0.29 0.02 42.57 96.09 0.67 0.33 0.18 0.83 3 4 0.00 2.37 3.46 0.00 0.06 46.62 0.00 0.33 0.00 42.61 95.45 0.00 2.37 3.46 0.00 0.06 30.56 17.85 0.00 0.33 0.00 42.61 97.23 0.66 0.35 0.18 0.82 3 5 0.00 2.43 3.12 0.00 0.18 45.97 0.00 0.30 0.05 42.64 94.70 0.00 2.43 3.12 0.00 0.18 30.70 16.97 0.00 0.30 0.05 42.64 96.39 0.66 0.33 0.18 0.83 3 6 0.00 2.52 3.27 0.00 0.18 46.71 0.02 0.32 0.02 42.75 95.80 0.00 2.52 3.27 0.00 0.18 30.51 18.01 0.02 0.32 0.02 42.75 97.59 0.65 0.35 0.19 0.82 3 7 0.00 1.87 2.67 0.00 0.14 46.41 0.00 0.39 0.00 43.53 95.01 0.00 1.87 2.67 0.00 0.14 32.99 14.90 0.00 0.39 0.00 43.53 96.49 0.72 0.29 0.15 0.85 3 fig. 3 (6) 1 2.39 0.19 5.42 0.15 0.15 39.95 0.09 0.49 0.06 42.76 91.65 2.39 0.19 5.42 0.15 0.15 35.18 5.30 0.09 0.49 0.06 42.76 92.18 0.80 0.11 0.22 0.87 3 2 0.86 0.07 5.51 0.11 0.10 44.59 0.03 0.50 0.09 45.14 96.99 0.86 0.07 5.51 0.11 0.10 35.70 9.87 0.03 0.50 0.09 45.14 97.98 0.77 0.19 0.17 0.88 3 3 0.50 0.16 5.88 0.09 0.01 39.15 0.02 0.42 0.08 45.67 91.96 0.50 0.16 5.88 0.09 0.01 35.32 4.25 0.02 0.42 0.08 45.67 92.39 0.81 0.09 0.17 0.94 3 4 0.21 0.04 6.09 0.15 0.03 44.47 0.06 0.41 0.02 46.12 97.60 0.21 0.04 6.09 0.15 0.03 35.27 10.22 0.06 0.41 0.02 46.12 98.62 0.76 0.20 0.16 0.89 3 5 0.42 0.10 6.09 0.08 0.08 39.21 0.02 0.45 0.00 46.20 92.65 0.42 0.10 6.09 0.08 0.08 35.54 4.08 0.02 0.45 0.00 46.20 93.06 0.81 0.08 0.17 0.94 3 6 0.00 0.09 5.18 0.01 0.07 46.06 0.05 0.48 0.02 47.09 99.06 0.00 0.09 5.18 0.01 0.07 36.88 10.20 0.05 0.48 0.02 47.09 100.07 0.78 0.19 0.13 0.90 3 7 0.00 0.09 4.53 0.00 0.05 46.42 0.09 0.52 0.05 47.15 98.89 0.00 0.09 4.53 0.00 0.05 37.63 9.77 0.09 0.52 0.05 47.15 99.87 0.80 0.19 0.12 0.90 3 8 0.00 0.11 4.52 0.01 0.00 46.26 0.08 0.49 0.00 47.18 98.65 0.00 0.11 4.52 0.01 0.00 37.65 9.57 0.08 0.49 0.00 47.18 99.61 0.80 0.18 0.12 0.90 3 9 0.33 0.07 5.18 0.08 0.01 40.65 0.01 0.44 0.02 47.43 94.22 0.33 0.07 5.18 0.08 0.01 37.58 3.41 0.01 0.44 0.02 47.43 94.56 0.84 0.07 0.14 0.95 3 spots 1-5 of grain (6) of figure 4 (tables iii, iv), are titanhematite. spot 6 is titanhematite where a considerable amount of fe2o3 is leached, resulting in the enrichment of tio2. in this spot, there is also a considerable amount of molecular water (table iii). spots 7-8 are ferriilmenite associated with pyrophanite (mntio3) in solid solution. the mno content ranges between 6.36 and 6.64%. spots 9-13 are ilmenite altered to rutile and hematite. the tio2 content ranges between 57.6 and 93.87%, while the fe2o3 content ranges between 41.14 and 4.86%. as the fe2o3 content decreases, the tio2 content increases and the sum of total analyzed oxides is around 100%. from the mno content in these 5 spots, it is engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9624 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … obvious that most iron is ferric iron. also, the back scattered electron image of grain (6) reflects that most of titanhematite associated with tio2 is leached out lefting voids of various sizes. spots 1-5 of grain (7), of figure 5 (tables iii, iv), are titanhematite with tio2 content ranging between 11.5 and 23.84%. comparing the values of feo with tio2 in spots 1-3 with those of spots 4-5 reflects that there is also an individual phase of tio2 in spots 4-5 associated with hematite and ilmenite in the titanhematite. spots 6-8 are ferriilmenite associated with pyrophanite in solid solution. maximum mno content (8.58%) occurs in spot 8. spots 9-10 are rutile and hematite where some of fe2o3 is leached out, especially from spot 10. it is obvious from the investigation of spot 6 of grain (6) of figure 4 and spot 10 of grain (7) of figure 5, that the leaching mechanism of fe2o3 is related to the activity of molecular water which seems to be either associated with dissolved silica or the water molecules or hydroxyl anions complexed with silica and each time the associated sio2 after losing its water content is precipitated in the cracks or pores and finally enriched (sio2 content equals to 9.17% in spot 10 of grain (7)). some minor composite grains were detected, each of them composed of two parts. the first part is titanhematite exsolution bodies in ferriilmenite and the second part is feirilmenite exsolution in titanhematite. the contact between the two parts may be curved, irregular, or perfectly straight. in the majority of the composite grains, the part of the exsolved titanhematite in the host ferriilmenite is the essential one, and may represent up to 80% of the composite grain. on the other hand, in a few grains the part of exsolved ferriilmenite in the host titanhematite is the essential one and represents up to 60% of the composite grain. the composite grain (8) of figure 5 (tables iii, iv) consists of 2 parts, the first part is relatively larger and consists of a ferriilmenite-titanhematite component, while the second part is relatively smaller and consists of a titanhematite-ferriilmenite component. spots 1-2 are almost similar titanhematites, although they are not in the same part of the grain. spots 3-5 are ferriilmenite. also, with the exception of spot 4 in the ferriilmenite-titanhematite part and spots 3-5 in the titanhematite-ferriilmenite part, their chemical composition is almost the same. the result of the comparison of the chemical composition of titanhematite (spots 1, 2) and ferriilmenite (spots 3-5) is that mgo, mno, and zno follow feo and hence, are mixed with ilmenite rather than with hematite. however, cr2o3, v2o3, and al2o3 follow fe 3+ rather than fe 2+ . grain (9) of figure 5 (tables iii, iv), consists of 2 parts. the first part is relatively larger and consists of a ferriilmenitetitanhematite component while the other part consists of a titanhematite-ferriilmenite component. spots 1-5 are titanhematite inside a major ferriilmenite component. the tio2 content ranges between 9.02 and 17.5%. in these spots, the v2o3 content is relatively greater, which may reflect that v2o3 follows fe2o3 rather than tio2 or feo. also, the mgo and mno content of spots 1-5 indicates that they follow feo rather than fe2o3. spots 6-7 are pseudorutile (psr) associated with definite amounts of structural and/or molecular water (table iii). the sums of total analyzed oxides after applying an adopted excel psr formula for the two spots are 95.13 and 96%. the 2 major oxides, tio2 and fe2o3 of each spot, are recalculated by multiplying with 100/95.13 for spot 6 and with 100/96 for spot 7, which gives the following results: 60.38% tio2 and 38.31% fe2o3 for spot 6 and 61.01% tio2 and 36.9% fe2o3 for spot 7. spots 8-9 are leached pseudorutile (lpsr) of various phases. in spots 8-9, the alteration mechanism is different than in spots 6-7, where the calculated structural water by the adopted excel program is incorrect and/or some of the analyzed tio2 and/or fe2o3 is not included in the lpsr chemical formula. spots 10-17 are ferriilmenite with some dissolved individual tio2 phase especially in the spots 14-17. the mno and mgo contents in ferriilmenite (spots 10-17) indicate that both oxides follow feo rather than fe2o3. comparing the contents of v2o3 and cr2o3 of titanhematite (spots 1-5) and ferriilmenite (spots 10-17), clearly shows that both oxides follow fe2o3 rather than feo. comparing the v2o3 content in all the analyzed spots of grain (9) reflects that v2o3 follows fe2o3 in spots 1-5 and tio2 in spots 10-17 (table iii). fig. 6. partially altered ilmenite grain textures: (1) titanhematiteferriilmenite exsolution intergrowth with most of the oriented exsolved titanhematite replaced by goethite or limonitic material. reflected light, ×100. (2) skeletal ilmenite grain with micropores arranged in a crystallographic orientation, indicating leaching out of hematite exsolution lamellae. reflected light, ×100. (3) subgraphic intergrowth of titanhematite and ferriilmenite components with isotropic leucoxenated material along the periphery of the grain and invading its inner part. reflected light, ×100. (4) two partially leucoxenated grains: the left grain shows an isotropic leucoxenated rim (black) completely surrounding the core of titanhematite-ferriilmenite subgraphic intergrowth. the right grain is an ilmenite grain (light grey) containing considerable leucoxenated areas (black) initiated on ilmenite parts originally replaced by sphene (dark grey). reflected light, ×100. c. partially altered ilmenite (7.3%) 1) leached titanhematite component (1.5%) in a considerable number of the titanhematite-ferriilmenite exsolution intergrowthed grains, the host ferriilmenite contains micropores arranged in a crystallographic orientation pattern indicating the leaching out of hematite exsolution lamellae (figure 6(1)-(2)). the size and shape of these micropores are related to those of the preexisting replaced hematite. the same texture was detected and the grains were called skeletal ilmenite grains [41] or pitted ilmenite [12]. the tendency of the hematite bodies to be more susceptable to this type of alteration than the ilmenite host is probably due to the fact that the free ferric oxide of hematite can be more easily hydrated than the ferrous oxide combined in the ilmenite structure. however, the original grain sizes may affect their rate of alteration [42]. engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9625 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … table iii. microprobe chemical analysιs and corresponding molecular formulae of the analyzed spots of the titanhematiteferriilmenite grains of figure 4(1)-(6) and figure 5(7)-(9) g r a in s s p o ts s io 2 m g o m n o c a o z n o f e o a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l s io 2 m g o m n o c a o z n o f e o f e 2 o 3 a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l f e r r o u s f e f e r r ic f e o th e r c a ti o n s t i o fig. 4 (1) 1 3.09 2.30 0.40 0.12 0.07 42.05 0.59 0.54 0.04 39.59 88.79 3.09 2.30 0.40 0.12 0.07 34.59 8.28 0.59 0.54 0.04 39.59 89.62 0.79 0.17 0.23 0.81 3 2 3.46 2.20 0.35 0.70 0.22 40.52 0.82 0.60 0.02 41.27 90.15 3.46 2.20 0.35 0.70 0.22 35.90 5.13 0.82 0.60 0.02 41.27 90.66 0.81 0.10 0.26 0.84 3 3 1.82 2.34 0.43 0.16 0.07 40.89 0.92 0.60 0.00 41.74 88.96 1.82 2.34 0.43 0.16 0.07 34.85 6.71 0.92 0.60 0.00 41.74 89.63 0.80 0.14 0.21 0.86 3 4 3.69 2.73 0.44 0.08 0.08 39.89 1.33 0.58 0.02 43.73 92.58 3.69 2.73 0.44 0.08 0.08 38.26 1.81 1.33 0.58 0.02 43.73 92.75 0.84 0.04 0.27 0.86 3 5 0.12 2.33 0.33 0.02 0.02 42.51 0.06 0.51 0.06 47.13 93.09 0.12 2.33 0.33 0.02 0.02 38.01 5.00 0.06 0.51 0.06 47.13 93.58 0.84 0.10 0.12 0.94 3 6 0.17 2.42 0.40 0.02 0.03 44.27 0.10 0.55 0.03 47.43 95.44 0.17 2.42 0.40 0.02 0.03 38.09 6.87 0.10 0.55 0.03 47.43 96.12 0.82 0.13 0.13 0.92 3 7 0.00 2.57 0.43 0.03 0.13 45.63 0.06 0.56 0.00 47.51 96.93 0.00 2.57 0.43 0.03 0.13 37.57 8.96 0.06 0.56 0.00 47.51 97.82 0.80 0.17 0.13 0.91 3 8 0.00 2.54 0.41 0.02 0.09 45.37 0.04 0.62 0.03 47.82 96.93 0.00 2.54 0.41 0.02 0.09 37.98 8.21 0.04 0.62 0.03 47.82 97.75 0.81 0.16 0.12 0.91 3 9 0.00 2.52 0.38 0.05 0.06 46.01 0.09 0.55 0.00 47.88 97.54 0.00 2.52 0.38 0.05 0.06 38.07 8.82 0.09 0.55 0.00 47.88 98.41 0.80 0.17 0.12 0.91 3 10 0.15 2.11 0.38 0.02 0.00 41.83 0.05 0.54 0.02 47.89 92.98 0.15 2.11 0.38 0.02 0.00 39.07 3.06 0.05 0.54 0.02 47.89 93.28 0.87 0.06 0.11 0.96 3 11 0.00 2.52 0.47 0.00 0.07 45.77 0.08 0.60 0.01 47.95 97.49 0.00 2.52 0.47 0.00 0.07 38.10 8.53 0.08 0.60 0.01 47.95 98.34 0.80 0.16 0.12 0.91 3 12 0.10 2.25 0.37 0.05 0.03 42.26 0.07 0.56 0.00 48.78 94.47 0.10 2.25 0.37 0.05 0.03 39.54 3.03 0.07 0.56 0.00 48.78 94.77 0.87 0.06 0.12 0.96 3 13 0.16 2.01 0.36 0.06 0.04 41.75 0.07 0.58 0.02 49.63 94.68 0.16 2.01 0.36 0.06 0.04 40.78 1.07 0.07 0.58 0.02 49.63 94.78 0.89 0.02 0.11 0.98 3 fig. 4 (2) 1 0.02 1.26 0.51 0.00 0.42 68.37 3.15 1.25 1.17 19.22 95.38 0.02 1.26 0.51 0.00 0.42 14.18 60.21 3.15 1.25 1.17 19.22 101.40 0.30 1.13 0.26 0.36 3 2 0.02 1.51 0.44 0.03 0.35 66.62 2.99 1.18 1.06 22.40 96.59 0.02 1.51 0.44 0.03 0.35 16.69 55.47 2.99 1.18 1.06 22.40 102.13 0.35 1.03 0.25 0.42 3 3 0.12 4.61 0.49 0.06 0.00 42.27 0.08 0.51 0.08 48.32 96.52 0.12 4.61 0.49 0.06 0.00 34.83 8.27 0.08 0.51 0.08 48.32 97.35 0.73 0.16 0.21 0.91 3 4 0.20 4.26 0.54 0.09 0.08 43.38 0.12 0.49 0.10 48.66 97.91 0.20 4.26 0.54 0.09 0.08 35.69 8.54 0.12 0.49 0.10 48.66 98.76 0.74 0.16 0.20 0.91 3 5 0.00 3.66 0.56 0.03 0.06 44.59 0.13 0.50 0.11 50.34 99.99 0.00 3.66 0.56 0.03 0.06 38.11 7.20 0.13 0.50 0.11 50.34 100.71 0.78 0.13 0.17 0.93 3 6 0.00 3.59 0.61 0.02 0.08 44.09 0.11 0.58 0.15 50.45 99.67 0.00 3.59 0.61 0.02 0.08 38.26 6.47 0.11 0.58 0.15 50.45 100.32 0.79 0.12 0.17 0.93 3 7 0.00 3.54 0.62 0.03 0.01 44.59 0.14 0.51 0.15 51.24 100.82 0.00 3.54 0.62 0.03 0.01 39.11 6.09 0.14 0.51 0.15 51.24 101.42 0.79 0.11 0.16 0.94 3 8 0.00 3.74 0.55 0.01 0.00 44.74 0.09 0.56 0.13 51.34 101.15 0.00 3.74 0.55 0.01 0.00 38.96 6.42 0.09 0.56 0.13 51.34 101.79 0.79 0.12 0.17 0.93 3 fig. 4 (3) 1 0.00 0.08 0.71 0.00 0.00 76.60 0.00 0.47 0.06 19.12 97.04 0.00 0.08 0.71 0.00 0.00 16.34 66.95 0.00 0.47 0.06 19.12 103.73 0.34 1.27 0.04 0.36 3 2 0.00 0.08 0.71 0.00 0.00 75.41 0.00 0.44 0.07 20.94 97.64 0.00 0.08 0.71 0.00 0.00 17.99 63.79 0.00 0.44 0.07 20.94 104.01 0.38 1.20 0.03 0.39 3 3 0.00 0.08 1.12 0.00 0.04 65.65 0.00 0.45 0.04 30.88 98.25 0.00 0.08 1.12 0.00 0.04 26.46 43.53 0.00 0.45 0.04 30.88 102.60 0.56 0.82 0.04 0.58 3 4 0.00 0.12 1.89 0.01 0.00 45.03 0.00 0.35 0.00 51.92 99.31 0.00 0.12 1.89 0.01 0.00 44.56 0.51 0.00 0.35 0.00 51.92 99.36 0.95 0.01 0.05 0.99 3 5 0.00 0.13 1.66 0.00 0.02 45.49 0.00 0.32 0.00 52.17 99.80 0.00 0.13 1.66 0.00 0.02 45.01 0.54 0.00 0.32 0.00 52.17 99.85 0.95 0.01 0.05 0.99 3 6 0.00 0.17 1.86 0.01 0.10 44.76 0.00 0.42 0.01 52.20 99.52 0.00 0.17 1.86 0.01 0.10 44.69 0.08 0.00 0.42 0.01 52.20 99.52 0.95 0.00 0.06 0.99 3 7 0.00 0.15 1.85 0.03 0.00 45.22 0.00 0.39 0.00 52.24 99.88 0.00 0.15 1.85 0.03 0.00 44.81 0.45 0.00 0.39 0.00 52.24 99.92 0.95 0.01 0.05 0.99 3 8 0.00 0.11 1.73 0.00 0.00 45.20 0.00 0.37 0.01 52.40 99.84 0.00 0.11 1.73 0.00 0.00 45.18 0.02 0.00 0.37 0.01 52.40 99.84 0.95 0.00 0.05 1.00 3 fig. 4 (4) 1 0.00 0.05 0.32 0.00 0.00 78.78 0.00 0.39 0.12 10.26 89.92 0.00 0.05 0.32 0.00 0.00 8.82 77.72 0.00 0.39 0.12 10.26 97.68 0.20 1.57 0.03 0.21 3 2 0.00 0.04 0.36 0.02 0.00 78.08 0.00 0.39 0.08 10.62 89.59 0.00 0.04 0.36 0.02 0.00 9.09 76.65 0.00 0.39 0.08 10.62 97.25 0.21 1.56 0.03 0.22 3 3 0.00 0.06 0.54 0.01 0.00 75.91 0.00 0.36 0.10 13.07 90.04 0.00 0.06 0.54 0.01 0.00 11.10 72.00 0.00 0.36 0.10 13.07 97.24 0.25 1.46 0.03 0.26 3 4 0.00 0.05 0.85 0.02 0.02 73.16 0.00 0.35 0.08 16.34 90.87 0.00 0.05 0.85 0.02 0.02 13.71 66.06 0.00 0.35 0.08 16.34 97.47 0.31 1.33 0.04 0.33 3 5 0.88 0.23 3.42 0.07 0.05 39.16 0.00 0.33 0.02 49.60 93.76 0.88 0.23 3.42 0.07 0.05 39.16 0.00 0.33 0.02 49.60 93.76 98.10 0.88 0.00 0.12 1.00 3 6 0.00 0.28 3.50 0.00 0.00 43.23 0.00 0.34 0.00 50.18 97.53 0.00 0.28 3.50 0.00 0.00 41.10 2.36 0.00 0.34 0.00 50.18 97.76 0.89 0.05 0.09 0.97 3 7 0.00 0.33 3.57 0.02 0.02 42.83 0.00 0.34 0.03 50.53 97.66 0.00 0.33 3.57 0.02 0.02 41.23 1.77 0.00 0.34 0.03 50.53 97.83 0.89 0.03 0.10 0.98 3 8 0.00 0.35 3.58 0.04 0.21 42.79 0.00 0.32 0.01 50.54 97.83 0.00 0.35 3.58 0.04 0.21 40.98 2.01 0.00 0.32 0.01 50.54 98.03 0.88 0.04 0.10 0.98 3 9 0.00 0.32 3.66 0.00 0.06 43.11 0.00 0.28 0.01 50.57 98.01 0.00 0.32 3.66 0.00 0.06 41.16 2.17 0.00 0.28 0.01 50.57 98.23 0.88 0.04 0.10 0.98 3 10 0.00 0.24 3.69 0.00 0.00 42.39 0.00 0.33 0.07 51.29 98.02 0.00 0.24 3.69 0.00 0.00 41.97 0.47 0.00 0.33 0.07 51.29 98.07 0.90 0.01 0.10 0.99 3 fig. 4 (5) 1 0.00 0.01 0.44 0.00 0.01 76.67 0.00 0.66 0.51 12.71 91.01 0.00 0.01 0.44 0.00 0.01 10.97 72.99 0.00 0.66 0.51 12.71 98.30 0.24 1.47 0.05 0.25 3 2 0.00 0.05 0.49 0.01 0.14 76.30 0.00 0.56 0.44 12.73 90.73 0.00 0.05 0.49 0.01 0.14 10.72 72.86 0.00 0.56 0.44 12.73 98.00 0.24 1.47 0.05 0.26 3 3 0.00 0.01 0.22 0.03 0.00 69.14 0.00 0.69 0.47 19.58 90.12 0.00 0.01 0.22 0.03 0.00 17.35 57.53 0.00 0.69 0.47 19.58 95.87 0.39 1.18 0.04 0.40 3 4 0.00 0.00 0.06 0.03 0.00 59.61 0.00 0.63 0.48 32.00 92.81 0.00 0.00 0.06 0.03 0.00 28.69 34.36 0.00 0.63 0.48 32.00 96.25 0.64 0.69 0.03 0.64 3 10 0.09 0.00 0.91 0.11 0.00 45.55 0.00 0.40 0.08 45.55 92.68 0.09 0.00 0.91 0.11 0.00 40.02 6.15 0.00 0.40 0.08 45.55 93.29 0.91 0.13 0.04 0.93 3 11 0.05 0.11 6.22 0.06 0.11 43.81 0.00 0.34 0.08 46.29 97.05 0.05 0.11 6.22 0.06 0.11 35.04 9.73 0.00 0.34 0.08 46.29 98.02 0.76 0.19 0.16 0.90 3 12 0.00 0.48 3.50 0.11 0.03 45.42 0.00 0.34 0.05 47.63 97.55 0.00 0.48 3.50 0.11 0.03 38.28 7.92 0.00 0.34 0.05 47.63 98.34 0.82 0.15 0.11 0.92 3 13 0.00 0.47 4.19 0.00 0.08 44.11 0.00 0.41 0.05 48.27 97.58 0.00 0.47 4.19 0.00 0.08 38.27 6.49 0.00 0.41 0.05 48.27 98.23 0.82 0.13 0.12 0.93 3 14 0.00 0.07 0.35 0.01 0.00 41.87 0.00 0.47 0.11 48.99 91.87 0.00 0.07 0.35 0.01 0.00 41.87 0.00 0.00 0.47 0.11 48.99 91.87 0.96 0.00 0.02 1.01 3 15 0.02 0.34 2.20 0.05 0.03 38.35 0.00 0.46 0.16 51.28 92.87 0.02 0.34 2.20 0.05 0.03 38.35 0.00 0.00 0.46 0.16 51.28 92.87 0.88 0.00 0.08 1.05 3 fig. 4 (6) 1 0.00 0.00 0.02 0.01 0.03 90.33 0.00 0.15 0.03 5.81 96.38 0.00 0.00 0.02 0.01 0.03 5.18 94.61 0.00 0.15 0.03 5.81 105.83 0.11 1.78 0.01 0.11 3 2 0.03 0.00 0.26 0.01 0.06 85.87 0.00 0.13 0.07 7.90 94.32 0.03 0.00 0.26 0.01 0.06 6.81 87.84 0.00 0.13 0.07 7.90 103.10 0.15 1.69 0.02 0.15 3 3 0.00 0.03 0.42 0.01 0.03 80.20 0.00 0.39 0.06 12.99 94.11 0.00 0.03 0.42 0.01 0.03 11.17 76.69 0.00 0.39 0.06 12.99 101.78 0.24 1.49 0.03 0.25 3 4 0.00 0.03 0.57 0.00 0.00 79.06 0.00 0.43 0.12 13.66 93.86 0.00 0.03 0.57 0.00 0.00 11.65 74.89 0.00 0.43 0.12 13.66 101.34 0.25 1.46 0.03 0.27 3 5 0.00 0.01 0.66 0.00 0.07 79.62 0.00 0.49 0.10 13.69 94.64 0.00 0.01 0.66 0.00 0.07 11.57 75.60 0.00 0.49 0.10 13.69 102.19 0.25 1.46 0.04 0.26 3 6 3.31 0.17 0.34 0.12 0.07 44.02 0.02 0.45 0.10 40.11 88.72 3.31 0.17 0.34 0.12 0.07 39.19 5.37 0.02 0.45 0.10 40.11 89.26 0.92 0.11 0.13 0.84 3 7 0.04 0.09 6.64 0.09 0.01 42.75 0.00 0.33 0.01 47.33 97.28 0.04 0.09 6.64 0.09 0.01 35.61 7.93 0.00 0.33 0.01 47.33 98.07 0.77 0.15 0.16 0.92 3 8 0.00 0.04 6.36 0.01 0.10 44.81 0.00 0.37 0.02 48.46 100.17 0.00 0.04 6.36 0.01 0.10 36.98 8.70 0.00 0.37 0.02 48.46 101.04 0.78 0.16 0.15 0.91 3 engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9626 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … g r a in s s p o ts s io 2 m g o m n o c a o z n o f e o a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l s io 2 m g o m n o c a o z n o f e o f e 2 o 3 a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l f e r r o u s f e f e r r ic f e o th e r c a ti o n s t i o fig. 5 (7) 1 0.00 0.05 0.45 0.00 0.03 79.16 0.00 0.39 0.05 11.50 91.63 0.00 0.05 0.45 0.00 0.03 9.78 77.08 0.00 0.39 0.05 11.50 99.33 0.22 1.53 0.03 0.23 3 2 0.00 0.03 0.30 0.00 0.00 80.31 0.00 0.12 0.01 12.83 93.60 0.00 0.03 0.30 0.00 0.00 11.17 76.82 0.00 0.12 0.01 12.83 101.28 0.24 1.50 0.01 0.25 3 3 0.00 0.00 0.36 0.01 0.07 77.86 0.00 0.40 0.08 13.78 92.56 0.00 0.00 0.36 0.01 0.07 11.95 73.22 0.00 0.40 0.08 13.78 99.87 0.26 1.45 0.03 0.27 3 4 0.00 0.14 1.88 0.00 0.00 66.77 0.00 0.10 0.04 23.12 92.05 0.00 0.14 1.88 0.00 0.00 18.64 53.48 0.00 0.10 0.04 23.12 97.40 0.41 1.07 0.06 0.46 3 5 0.00 0.17 1.85 0.02 0.00 66.19 0.00 0.20 0.06 23.84 92.33 0.00 0.17 1.85 0.02 0.00 19.26 52.14 0.00 0.20 0.06 23.84 97.54 0.43 1.04 0.07 0.48 3 6 0.00 0.10 1.62 0.00 0.00 49.21 0.00 0.29 0.02 46.69 97.94 0.00 0.10 1.62 0.00 0.00 40.18 10.03 0.00 0.29 0.02 46.69 98.94 0.86 0.19 0.05 0.90 3 7 0.00 0.12 1.50 0.01 0.02 49.51 0.00 0.28 0.02 47.06 98.52 0.00 0.12 1.50 0.01 0.02 40.58 9.92 0.00 0.28 0.02 47.06 99.51 0.86 0.19 0.04 0.90 3 8 0.00 0.54 8.58 0.01 0.06 38.84 0.00 0.25 0.03 48.79 97.10 0.00 0.54 8.58 0.01 0.06 34.17 5.19 0.00 0.25 0.03 48.79 97.61 0.74 0.10 0.22 0.95 3 fig. 5 (8) 1 0.00 0.09 0.04 0.02 0.00 78.46 0.13 0.68 0.10 12.41 91.92 0.00 0.09 0.04 0.02 0.00 10.95 75.00 0.13 0.68 0.10 12.41 99.41 0.24 1.49 0.03 0.25 3 2 0.00 0.12 0.03 0.00 0.00 77.42 0.10 0.73 0.09 12.89 91.38 0.00 0.12 0.03 0.00 0.00 11.36 73.39 0.10 0.73 0.09 12.89 98.71 0.25 1.47 0.03 0.26 3 3 0.00 0.70 0.37 0.00 0.08 50.94 0.01 0.39 0.03 45.14 97.64 0.00 0.70 0.37 0.00 0.08 38.92 13.35 0.01 0.39 0.03 45.14 98.97 0.83 0.26 0.05 0.87 3 4 0.00 0.72 0.33 0.00 0.03 49.66 0.00 0.42 0.06 46.67 97.88 0.00 0.72 0.33 0.00 0.03 40.34 10.35 0.00 0.42 0.06 46.67 98.91 0.86 0.20 0.05 0.90 3 5 0.00 0.74 0.34 0.01 0.00 48.66 0.00 0.40 0.01 47.35 97.51 0.00 0.74 0.34 0.01 0.00 40.91 8.60 0.00 0.40 0.01 47.35 98.37 0.88 0.17 0.05 0.91 3 fig. 5 (9) 1 0.00 0.03 0.21 0.00 0.00 80.08 0.00 0.59 0.09 9.02 90.03 0.00 0.03 0.21 0.00 0.00 7.84 80.26 0.00 0.59 0.09 9.02 98.05 0.18 1.62 0.03 0.18 3 2 0.00 0.03 0.14 0.01 0.00 79.79 0.00 0.61 0.05 9.81 90.44 0.00 0.03 0.14 0.01 0.00 8.61 79.08 0.00 0.61 0.05 9.81 98.34 0.19 1.59 0.03 0.20 3 3 0.00 0.01 0.19 0.01 0.11 79.14 0.00 0.58 0.06 9.98 90.09 0.00 0.01 0.19 0.01 0.11 8.66 78.31 0.00 0.58 0.06 9.98 97.91 0.19 1.58 0.03 0.20 3 4 0.00 0.05 0.19 0.00 0.00 78.47 0.00 0.51 0.08 11.84 91.14 0.00 0.05 0.19 0.00 0.00 10.37 75.66 0.00 0.51 0.08 11.84 98.70 0.23 1.51 0.03 0.24 3 5 0.00 0.04 0.82 0.00 0.00 73.87 0.00 0.49 0.00 17.50 92.72 0.00 0.04 0.82 0.00 0.00 14.85 65.58 0.00 0.49 0.00 17.50 99.27 0.33 1.30 0.04 0.35 3 10 0.00 0.18 1.65 0.02 0.00 51.63 0.00 0.39 0.05 42.63 96.55 0.00 0.18 1.65 0.02 0.00 36.33 17.00 0.00 0.39 0.05 42.63 98.25 0.79 0.33 0.06 0.83 3 11 0.00 0.17 2.86 0.00 0.02 47.83 0.00 0.32 0.03 45.61 96.84 0.00 0.17 2.86 0.00 0.02 37.82 11.13 0.00 0.32 0.03 45.61 97.95 0.82 0.22 0.08 0.89 3 12 0.00 0.22 1.86 0.00 0.02 48.59 0.00 0.43 0.03 46.78 97.93 0.00 0.22 1.86 0.00 0.02 39.78 9.79 0.00 0.43 0.03 46.78 98.91 0.85 0.19 0.06 0.90 3 13 0.00 0.23 1.91 0.00 0.08 46.77 0.00 0.36 0.02 47.61 96.99 0.00 0.23 1.91 0.00 0.08 40.42 7.05 0.00 0.36 0.02 47.61 97.69 0.88 0.14 0.06 0.93 3 14 0.00 0.19 1.94 0.01 0.10 46.57 0.00 0.40 0.00 48.60 97.81 0.00 0.19 1.94 0.01 0.10 41.32 5.83 0.00 0.40 0.00 48.60 98.39 0.89 0.11 0.06 0.94 3 15 0.00 0.19 1.83 0.00 0.09 45.95 0.00 0.37 0.03 48.78 97.26 0.00 0.19 1.83 0.00 0.09 41.60 4.83 0.00 0.37 0.03 48.78 97.74 0.90 0.09 0.06 0.95 3 16 0.00 0.17 1.97 0.00 0.14 45.70 0.00 0.41 0.00 49.38 97.77 0.00 0.17 1.97 0.00 0.14 42.00 4.11 0.00 0.41 0.00 49.38 98.17 0.90 0.08 0.06 0.96 3 17 0.00 0.17 2.22 0.00 0.00 45.52 0.00 0.31 0.04 49.82 98.08 0.00 0.17 2.22 0.00 0.00 42.26 3.62 0.00 0.31 0.04 49.82 98.44 0.91 0.07 0.06 0.96 3 2) partially leucoxenated ilmenite (4.6%) some of ilmenite grains showed patchy intergrowths of altered and unaltered ilmenite. it is likely that some of these grains were originally composed of subgraphic intergrowth of titanhematite and ferriilmenite as the major component. patches of isotropic leucoxenated material formed along the periphery of the grain and are invading its inner part (figure 6(3)). the zones of leucoxene invasion seem to have been relatively richer in the titanhematite component. the leucoxenated areas have dark brown colors under the reflected light. between crossed nicols they have yellow and yellowish red internal reflections, most probably due to microcrystalline rutile. in other grains, a leucoxenated rim is completely surrounding the core of titanhematite-ferriilmenite subgraphic intergrowth (figure 6(4)). the unaltered component of the grains is only ilmenite, containing parts of preexisting sphene and hence most of the leucoxenated areas seem to have initiated on ilmenite parts which were originally replaced by sphene (figure 6(4)). we think that in case of partially leucoxenated grains, the unaltered component is prefered to be inhomogenous ilmenite. furthermore, such partial leucoxenated zones have occured at low temperatures similar to those prevailing during weathering, transportation, deposition, and/or post-deposition processes affecting placer deposits. the majority of homogeneous ilmenite grains seem to be more stable and resistant to such partial leucoxenation. the process of ilmenite alteration into different varieties of leucoxene, passing with leached ilmenite, pseudorutile, leached pseudorutile, and even secondary rutile will be explained in another article, so it will not be not explained in detail here. fig. 7. bse images of 3 different partially altered ilmenite grains into sphene. 3) sphene-ilmenite intergrowth (1.2%) some ilmenite grains were detected to have altered and been replaced by sphene. some grains were detected to be of fresh ilmenite cores completely surrounded by a sphene rim (figure 7). engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9627 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … table iv. calculated mineral component fractions included within each microprobe analyzed spot of the grains of figures 4-5 g r a in s s p o ts s io 2 m g o m n o c a o z n o f e o f e 2 o 3 a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l m e th o d g e k p y r il m h r t o ta l fig. 4 (1) 1 3.09 2.30 0.40 0.12 0.07 34.59 8.28 0.59 0.54 0.04 39.59 89.62 m2 6.86 0.85 65.74 12.76 0.00 86.21 2 3.46 2.20 0.35 0.70 0.22 35.90 5.13 0.82 0.60 0.02 41.27 90.66 m2 6.57 0.73 69.40 9.35 0.00 86.06 3 1.82 2.34 0.43 0.16 0.07 34.85 6.71 0.92 0.60 0.00 41.74 89.63 m2 6.97 0.92 69.61 9.73 0.00 87.23 4 3.69 2.73 0.44 0.08 0.08 38.26 1.81 1.33 0.58 0.02 43.73 92.75 m2 8.15 0.93 71.89 7.85 0.00 88.82 5 0.12 2.33 0.33 0.02 0.02 38.01 5.00 0.06 0.51 0.06 47.13 93.58 m2 6.94 0.71 80.10 5.21 0.00 92.96 6 0.17 2.42 0.40 0.02 0.03 38.09 6.87 0.10 0.55 0.03 47.43 96.12 m2 7.22 0.86 80.17 7.15 0.00 95.39 7 0.00 2.57 0.43 0.03 0.13 37.57 8.96 0.06 0.56 0.00 47.51 97.82 m1 7.67 0.91 79.35 9.02 0.19 97.14 8 0.00 2.54 0.41 0.02 0.09 37.98 8.21 0.04 0.62 0.03 47.82 97.75 m1 7.57 0.88 80.21 8.28 0.13 97.06 9 0.00 2.52 0.38 0.05 0.06 38.07 8.82 0.09 0.55 0.00 47.88 98.41 m1 7.53 0.80 80.41 8.91 0.15 97.79 10 0.15 2.11 0.38 0.02 0.00 39.07 3.06 0.05 0.54 0.02 47.89 93.28 m2 6.30 0.80 82.25 3.28 0.00 92.62 11 0.00 2.52 0.47 0.00 0.07 38.10 8.53 0.08 0.60 0.01 47.95 98.34 m1 7.53 1.00 80.46 8.62 0.09 97.70 12 0.10 2.25 0.37 0.05 0.03 39.54 3.03 0.07 0.56 0.00 48.78 94.77 m2 6.69 0.79 83.46 3.12 0.00 94.07 13 0.16 2.01 0.36 0.06 0.04 40.78 1.07 0.07 0.58 0.02 49.63 94.78 m2 5.99 0.77 85.99 1.24 0.00 93.99 fig. 4 (2) 1 0.02 1.26 0.51 0.00 0.42 14.18 60.21 3.15 1.25 1.17 19.22 101.40 m1 3.74 1.09 29.95 64.53 0.40 99.72 2 0.02 1.51 0.44 0.03 0.35 16.69 55.47 2.99 1.18 1.06 22.40 102.13 m1 4.51 0.94 35.25 59.51 0.37 100.58 3 0.12 4.61 0.49 0.06 0.00 34.83 8.27 0.08 0.51 0.08 48.32 97.35 m2 13.74 1.04 73.48 8.46 0.00 96.72 4 0.20 4.26 0.54 0.09 0.08 35.69 8.54 0.12 0.49 0.10 48.66 98.76 m2 12.71 1.14 75.31 8.80 0.00 97.97 5 0.00 3.66 0.56 0.03 0.06 38.11 7.20 0.13 0.50 0.11 50.34 100.71 m1 10.92 1.19 80.49 7.45 0.12 100.17 6 0.00 3.59 0.61 0.02 0.08 38.26 6.47 0.11 0.58 0.15 50.45 100.32 m1 10.71 1.29 80.81 6.73 0.13 99.69 7 0.00 3.54 0.62 0.03 0.01 39.11 6.09 0.14 0.51 0.15 51.24 101.42 m1 10.56 1.31 82.60 6.37 0.07 100.92 8 0.00 3.74 0.55 0.01 0.00 38.96 6.42 0.09 0.56 0.13 51.34 101.79 m1 11.14 1.17 82.27 6.65 0.04 101.27 fig. 4 (3) 1 0.00 0.08 0.71 0.00 0.00 16.34 66.95 0.00 0.47 0.06 19.12 103.73 m1 0.22 1.52 34.51 67.01 0.00 103.26 2 0.00 0.08 0.71 0.00 0.00 17.99 63.79 0.00 0.44 0.07 20.94 104.01 m1 0.23 1.50 37.99 63.86 0.00 103.58 3 0.00 0.08 1.12 0.00 0.04 26.46 43.53 0.00 0.45 0.04 30.88 102.60 m1 0.23 2.39 55.89 43.57 0.05 102.13 4 0.00 0.12 1.89 0.01 0.00 44.56 0.51 0.00 0.35 0.00 51.92 99.36 m1 0.35 4.01 94.12 0.51 0.02 99.02 5 0.00 0.13 1.66 0.00 0.02 45.01 0.54 0.00 0.32 0.00 52.17 99.85 m1 0.38 3.53 95.05 0.54 0.02 99.53 6 0.00 0.17 1.86 0.01 0.10 44.69 0.08 0.00 0.42 0.01 52.20 99.52 m1 0.50 3.95 94.39 0.09 0.11 99.03 7 0.00 0.15 1.85 0.03 0.00 44.81 0.45 0.00 0.39 0.00 52.24 99.92 m1 0.44 3.94 94.64 0.45 0.05 99.52 8 0.00 0.11 1.73 0.00 0.00 45.18 0.02 0.00 0.37 0.01 52.40 99.84 m1 0.34 3.68 95.43 0.03 0.00 99.49 fig. 4 (4) 1 0.00 0.05 0.32 0.00 0.00 8.82 77.72 0.00 0.39 0.12 10.26 97.68 m1 0.14 0.68 18.63 77.84 0.01 97.29 2 0.00 0.04 0.36 0.02 0.00 9.09 76.65 0.00 0.39 0.08 10.62 97.25 m1 0.10 0.77 19.21 76.73 0.03 96.84 3 0.00 0.06 0.54 0.01 0.00 11.10 72.00 0.00 0.36 0.10 13.07 97.24 m1 0.16 1.14 23.45 72.11 0.01 96.88 4 0.00 0.05 0.85 0.02 0.02 13.71 66.06 0.00 0.35 0.08 16.34 97.47 m1 0.14 1.81 28.95 66.13 0.05 97.08 5 0.88 0.23 3.42 0.07 0.05 39.20 0.00 0.00 0.33 0.02 49.60 93.48 m1 0.69 7.28 82.79 0.02 1.72 92.50 6 0.00 0.28 3.50 0.00 0.00 41.10 2.36 0.00 0.34 0.00 50.18 97.76 m1 0.83 7.43 86.80 2.37 0.01 97.45 7 0.00 0.33 3.57 0.02 0.02 41.23 1.77 0.00 0.34 0.03 50.53 97.83 m1 0.97 7.59 87.07 1.80 0.04 97.48 8 0.00 0.35 3.58 0.04 0.21 40.98 2.01 0.00 0.32 0.01 50.54 98.03 m1 1.04 7.62 86.55 2.02 0.26 97.49 9 0.00 0.32 3.66 0.00 0.06 41.16 2.17 0.00 0.28 0.01 50.57 98.23 m1 0.96 7.79 86.92 2.18 0.06 97.91 10 0.00 0.24 3.69 0.00 0.00 41.97 0.47 0.00 0.33 0.07 51.29 98.07 m1 0.73 7.85 88.63 0.54 0.01 97.76 fig. 4 (5) 1 0.00 0.01 0.44 0.00 0.01 10.97 72.99 0.00 0.66 0.51 12.71 98.30 m1 0.02 0.92 23.17 73.50 0.01 97.63 2 0.00 0.05 0.49 0.01 0.14 10.72 72.86 0.00 0.56 0.44 12.73 98.00 m1 0.15 1.05 22.64 73.30 0.15 97.30 3 0.00 0.01 0.22 0.03 0.00 17.35 57.53 0.00 0.69 0.47 19.58 95.87 m1 0.01 0.47 36.64 58.00 0.04 95.17 4 0.00 0.00 0.06 0.03 0.00 28.69 34.36 0.00 0.63 0.48 32.00 96.25 m1 0.00 0.13 60.59 34.83 0.05 95.59 5 0.03 0.05 0.15 0.06 0.05 29.98 0.00 0.00 0.67 0.29 65.39 96.68 m3 0.15 0.32 0.00 33.61 65.12 99.20 6 0.00 0.06 0.18 0.03 0.04 20.14 0.00 0.00 0.60 0.11 72.53 93.69 m3 0.19 0.39 0.00 22.49 72.20 95.27 7 0.00 0.02 0.15 0.01 0.00 18.16 0.00 0.00 0.69 0.14 74.65 93.82 m3 0.04 0.32 0.00 20.32 74.45 95.14 8 0.02 0.02 0.19 0.02 0.00 18.20 0.00 0.00 0.60 0.02 76.26 95.32 m3 0.05 0.40 0.00 20.25 76.01 96.71 9 0.00 0.04 0.09 0.01 0.00 5.37 0.00 0.00 0.87 0.09 93.43 99.89 m3 0.11 0.18 0.00 6.05 93.27 99.61 10 0.09 0.00 0.91 0.11 0.00 40.02 6.15 0.00 0.40 0.08 45.55 93.29 m1 0.00 1.93 84.51 6.22 0.04 92.71 11 0.05 0.11 6.22 0.06 0.11 35.04 9.73 0.00 0.34 0.08 46.29 98.02 m1 0.33 13.21 74.01 9.81 0.13 97.49 12 0.00 0.48 3.50 0.11 0.03 38.28 7.92 0.00 0.34 0.05 47.63 98.34 m1 1.43 7.44 80.86 7.97 0.19 97.89 13 0.00 0.47 4.19 0.00 0.08 38.27 6.49 0.00 0.41 0.05 48.27 98.23 m1 1.40 8.90 80.83 6.54 0.09 97.76 14 0.00 0.07 0.35 0.01 0.00 41.90 0.00 0.00 0.47 0.11 48.99 91.67 m1 0.20 0.74 88.49 0.11 1.89 91.44 15 0.02 0.34 2.20 0.05 0.03 38.30 0.00 0.00 0.46 0.16 51.28 92.33 m1 1.00 4.67 80.89 0.16 5.57 92.29 fig. 4 (6) 1 0.00 0.00 0.02 0.01 0.03 5.18 94.61 0.00 0.15 0.03 5.81 105.83 m1 0.01 0.04 10.93 94.64 0.04 105.65 2 0.03 0.00 0.26 0.01 0.06 6.81 87.84 0.00 0.13 0.07 7.90 103.10 m1 0.01 0.54 14.38 87.90 0.04 102.88 3 0.00 0.03 0.42 0.01 0.03 11.17 76.69 0.00 0.39 0.06 12.99 101.78 m1 0.08 0.89 23.60 76.74 0.05 101.36 4 0.00 0.03 0.57 0.00 0.00 11.65 74.89 0.00 0.43 0.12 13.66 101.34 m1 0.10 1.21 24.61 75.01 0.00 100.92 5 0.00 0.01 0.66 0.00 0.07 11.57 75.60 0.00 0.49 0.10 13.69 102.19 m1 0.04 1.40 24.43 75.70 0.07 101.64 6 3.31 0.17 0.34 0.12 0.07 39.19 5.37 0.02 0.45 0.10 40.11 89.26 m2 0.50 0.72 74.86 9.66 0.00 85.74 7 0.04 0.09 6.64 0.09 0.01 35.61 7.93 0.00 0.33 0.01 47.33 98.07 m1 0.27 14.11 75.21 7.94 0.10 97.63 engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9628 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … g r a in s s p o ts s io 2 m g o m n o c a o z n o f e o f e 2 o 3 a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l m e th o d g e k p y r il m h r t o ta l fig. 4 (6) 8 0.00 0.04 6.36 0.01 0.10 36.98 8.70 0.00 0.37 0.02 48.46 101.04 m1 0.11 13.53 78.10 8.72 0.12 100.58 9 0.00 0.00 0.31 0.03 0.00 37.02 0.00 0.00 0.43 0.02 57.60 95.40 m3 0.01 0.65 0.00 41.16 57.25 99.06 10 0.00 0.03 0.14 0.02 0.01 22.82 0.00 0.00 0.56 0.04 74.81 98.42 m3 0.08 0.29 0.00 25.41 74.60 100.38 11 0.00 0.02 0.03 0.00 0.05 12.45 0.00 0.00 0.64 0.01 86.25 99.45 m3 0.07 0.06 0.00 13.85 86.17 100.15 12 0.00 0.00 0.00 0.01 0.00 5.84 0.00 0.00 0.64 0.00 93.48 99.97 m3 0.00 0.00 0.00 6.49 93.48 99.97 13 0.07 0.00 0.02 0.03 0.00 4.37 0.00 0.00 0.67 0.01 93.87 99.04 m3 0.00 0.03 0.00 4.87 93.86 98.76 fig. 5 (7) 1 0.00 0.05 0.45 0.00 0.03 9.78 77.08 0.00 0.39 0.05 11.50 99.33 m1 0.16 0.95 20.66 77.13 0.03 98.92 2 0.00 0.03 0.30 0.00 0.00 11.17 76.82 0.00 0.12 0.01 12.83 101.28 m1 0.10 0.64 23.59 76.82 0.01 101.16 3 0.00 0.00 0.36 0.01 0.07 11.95 73.22 0.00 0.40 0.08 13.78 99.87 m1 0.00 0.77 25.24 73.30 0.09 99.40 4 0.00 0.14 1.88 0.00 0.00 18.64 53.48 0.00 0.10 0.04 23.12 97.40 m1 0.43 4.00 39.36 53.52 0.00 97.31 5 0.00 0.17 1.85 0.02 0.00 19.26 52.14 0.00 0.20 0.06 23.84 97.54 m1 0.50 3.93 40.68 52.20 0.03 97.33 6 0.00 0.10 1.62 0.00 0.00 40.18 10.03 0.00 0.29 0.02 46.69 98.94 m1 0.29 3.44 84.87 10.05 0.01 98.66 7 0.00 0.12 1.50 0.01 0.02 40.58 9.92 0.00 0.28 0.02 47.06 99.51 m1 0.35 3.20 85.70 9.94 0.03 99.22 8 0.00 0.54 8.58 0.01 0.06 34.17 5.19 0.00 0.25 0.03 48.79 97.61 m1 1.62 18.23 72.17 5.22 0.08 97.33 9 0.00 0.06 0.14 0.00 0.07 32.64 0.00 0.00 0.37 0.00 59.82 93.10 m3 0.18 0.30 0.00 36.27 59.54 96.29 10 9.17 0.52 0.51 0.21 0.08 10.16 0.00 1.36 0.43 0.00 69.65 92.10 m3 1.54 1.09 0.00 12.65 68.06 83.34 fig. 5 (8) 1 0.00 0.09 0.04 0.02 0.00 10.95 75.00 0.13 0.68 0.10 12.41 99.41 m1 0.25 0.09 23.12 75.24 0.03 98.72 2 0.00 0.12 0.03 0.00 0.00 11.36 73.39 0.10 0.73 0.09 12.89 98.71 m1 0.35 0.06 23.99 73.59 0.00 97.99 3 0.00 0.70 0.37 0.00 0.08 38.92 13.35 0.01 0.39 0.03 45.14 98.97 m1 2.07 0.78 82.21 13.38 0.08 98.53 4 0.00 0.72 0.33 0.00 0.03 40.34 10.35 0.00 0.42 0.06 46.67 98.91 m1 2.15 0.70 85.20 10.41 0.03 98.49 5 0.00 0.74 0.34 0.01 0.00 40.91 8.60 0.00 0.40 0.01 47.35 98.37 m1 2.22 0.72 86.41 8.62 0.02 97.98 fig. 5 (9) 1 0.00 0.03 0.21 0.00 0.00 7.84 80.26 0.00 0.59 0.09 9.02 98.05 m1 0.10 0.44 16.56 80.36 0.01 97.46 2 0.00 0.03 0.14 0.01 0.00 8.61 79.08 0.00 0.61 0.05 9.81 98.34 m1 0.10 0.30 18.18 79.13 0.02 97.72 3 0.00 0.01 0.19 0.01 0.11 8.66 78.31 0.00 0.58 0.06 9.98 97.91 m1 0.02 0.40 18.29 78.36 0.13 97.20 4 0.00 0.05 0.19 0.00 0.00 10.37 75.66 0.00 0.51 0.08 11.84 98.70 m1 0.15 0.41 21.90 75.74 0.00 98.20 5 0.00 0.04 0.82 0.00 0.00 14.85 65.58 0.00 0.49 0.00 17.50 99.27 m1 0.10 1.74 31.36 65.58 0.00 98.78 6 0.00 0.23 0.17 0.02 0.00 32.80 0.00 0.00 0.45 0.06 57.45 91.18 7 0.00 0.21 0.42 0.02 0.06 31.86 0.00 0.00 0.43 0.02 58.55 91.58 8 0.00 0.34 0.18 0.03 0.02 21.06 0.00 0.00 0.52 0.01 71.88 94.03 9 0.00 0.26 0.16 0.00 0.00 12.39 0.00 0.00 0.62 0.01 82.73 96.16 10 0.00 0.18 1.65 0.02 0.00 36.33 17.00 0.00 0.39 0.05 42.63 98.25 m1 0.53 3.50 76.73 17.06 0.03 97.86 11 0.00 0.17 2.86 0.00 0.02 37.82 11.13 0.00 0.32 0.03 45.61 97.95 m1 0.50 6.07 79.87 11.15 0.03 97.63 12 0.00 0.22 1.86 0.00 0.02 39.78 9.79 0.00 0.43 0.03 46.78 98.91 m1 0.65 3.96 84.02 9.82 0.02 98.48 13 0.00 0.23 1.91 0.00 0.08 40.42 7.05 0.00 0.36 0.02 47.61 97.69 m1 0.68 4.05 85.37 7.08 0.09 97.27 14 0.00 0.19 1.94 0.01 0.10 41.32 5.83 0.00 0.40 0.00 48.60 98.39 m1 0.55 4.13 87.27 5.83 0.11 97.90 15 0.00 0.19 1.83 0.00 0.09 41.60 4.83 0.00 0.37 0.03 48.78 97.74 m1 0.57 3.90 87.86 4.86 0.10 97.29 16 0.00 0.17 1.97 0.00 0.14 42.00 4.11 0.00 0.41 0.00 49.38 98.17 m1 0.50 4.19 88.70 4.11 0.14 97.65 17 0.00 0.17 2.22 0.00 0.00 42.26 3.62 0.00 0.31 0.04 49.82 98.44 m1 0.52 4.71 89.26 3.66 0.01 98.15 table v. microprobe chemical analysis of the spots of some detected partially altered ilmenite grains of figure 7. the calculated molecular formulae are given for the spots composed essentially of ilmenite; spot 2 of (1), spots 1, 4 of (2) and spots 8-10 of (3). spot 11 of (3) is leached ilmenite while the other remaining spots are sphene g r a in s s p o ts s io 2 m g o m n o c a o z n o f e o a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l s io 2 m g o m n o c a o z n f e o f e 2 o 3 a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l f e r r o u s f e f e r r ic f e o th e r c a ti o n s t i o fig. 7 (1) 1 30.67 0.00 0.12 28.50 0.01 1.26 0.85 0.39 0.00 37.67 99.48 2 0.00 0.06 2.00 0.25 0.00 44.42 0.00 0.58 0.00 51.29 98.61 0.00 0.06 2.00 0.25 0.00 43.68 0.82 0.00 0.58 0.00 51.29 98.69 0.93 0.02 0.06 0.99 3 fig. 7 (2) 1 0.00 0.01 0.15 0.05 0.00 81.87 0.00 0.53 0.06 8.34 91.01 0.00 0.01 0.15 0.05 0.00 7.26 82.89 0.00 0.53 0.06 8.34 99.28 0.16 1.65 0.02 0.17 3 2 30.73 0.00 0.08 28.58 0.00 0.63 1.01 0.31 0.00 38.03 99.38 3 30.76 0.00 0.15 28.82 0.00 0.99 0.93 0.26 0.04 38.29 100.24 4 0.00 0.20 3.40 0.17 0.00 43.94 0.00 0.43 0.00 50.48 98.63 0.00 0.20 3.40 0.17 0.00 41.39 2.84 0.00 0.43 0.00 50.48 98.91 0.88 0.05 0.10 0.97 3 fig. 7 (3) 1 30.11 0.00 0.07 28.41 0.98 0.83 0.23 38.77 99.41 2 30.26 0.00 0.04 28.08 0.94 0.22 0.47 39.33 99.32 3 30.38 0.00 0.00 28.50 0.28 0.62 0.16 39.71 99.65 4 30.46 0.00 0.00 28.75 0.41 0.54 0.13 39.91 100.21 5 30.15 0.00 0.01 28.54 0.54 0.56 0.23 39.93 99.96 6 30.19 0.03 0.00 28.60 0.26 0.46 0.10 40.06 99.70 7 30.28 0.00 0.04 28.74 0.26 0.76 0.09 40.10 100.27 8 0.35 0.17 8.68 0.80 34.89 0.00 0.05 53.10 98.04 0.35 0.17 8.68 0.80 0.00 38.78 0.00 0.00 0.00 0.05 53.10 97.68 0.84 0.00 0.22 1.02 3 9 0.05 0.19 11.19 1.07 34.40 0.00 0.02 53.34 100.26 0.05 0.19 11.19 1.07 0.00 38.23 0.00 0.00 0.00 0.02 53.34 100.19 0.72 0.00 0.27 1.00 3 10 0.02 0.20 10.13 0.74 35.72 0.00 0.04 53.54 100.39 0.02 0.20 10.13 0.74 0.00 39.67 0.00 0.00 0.00 0.04 53.54 100.29 0.74 0.00 0.24 1.01 3 11 0.05 0.19 5.71 0.76 30.88 0.00 0.05 58.44 96.07 engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9629 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … furthermore, some grains were found to be partially replaced by sphene where half of the grain is fresh ilmenite and the rest is replaced by sphene. the complete absence of cavities or cracks between ilmenite and sphene indicates that the replacement process took place volume by volume [12]. according to [23], sphene is developed by magmatic resorption or hydrothermal action. under the reflected light, the sphene is light grey with a reflectivity much lower than that of ilmenite, but somewhat higher than that of the gangue silicate minerals. in fact, its reflectivity is somewhat similar to that of cassiterite or zircon. under crossed nicols, sphene exhibits an obvious anisotropism. however, its abundant white or slightly greyish white internal reflections may mask it. some of the grains composed of ilmenite associated with sphene are detected in figure 7 (1)-(3). spots 1 in grain (1), 2-3 in grain (2), and 1-7 in grain (3) are sphene substituting ilmenite (figure 7, table v). spot 11 in grain (3) is leached ilmenite having the chemical composition of fe 2+ (0.12%), fe 3+ (1.64%), other cations (0.41%), ti3, and o9. the losed iron cations are equal to 0.82 and the sum of total oxides is 99.28%. spot 2 of grain (1) consists of 92.29% ilmenite, 4.25% pyrophanite, 0.80% hematite, 0.30% geikielite, and 0.38% rutile. spots 1, 4 of grain (2) (figure 7), are titanhematiteferriilmenite exsolved intergrowths surrounded by sphene (spots 2-3). spot 1 is titanhematite having mno content similar to spot 3 of the sphene. in spot 1, it is obvious that v 3+ follows fe 3+ rather than fe 2+ , while mn 2+ follows fe 2+ rather than fe 3+ . the spot is composed of 83% hematite, 15.42% ilmenite, 0.43% pyrophanite, and 0.04% rutile. spot 4 is ferriilmenite with a relatively higher mno content (3.4%). the spot consists of 87.44% ilmenite, 7.23% pyrophanite, 2.8% hematite, 0.6% geikielite, and 0.27% rutile. spots 8-10 in grain (3) seem to be ilmenite with relatively higher mno content (table v). this grain may indicate that both feo and mno are replaced by sio2 and cao while the tio2 content remains stable to form sphene replacing ilmenite. the comparison of mno content of spot 11 with the mno content of spots 8-10 reflects that mno is lost during the early stages of ilmenite alteration during the leaching of fe 3+ . also, it is detected that the cr2o3 content is relatively much higher in the sphene spots than in ilmenite spots which ensures that cr2o3 does not follow tio2 content. these 3 last grains reflect the association of some ilmenite grains within the obtained final ilmenite concentrate with the sphene which may responsible for the increment of the sio2 and cao content of the concentrate. also, the ilmenite component associated to or replaced by sphene is characteristic with a relatively higher content of pyrophanite and hence mno. vi. conclusion the obtained egyptian beach ilmenite concentrate from east rosetta area contains several mineral textures. the homogeneous ilmenite represents 63wt% of the detected ilmenite varieties. some of the homogeneous ilmenite grains are characterized by more mgo than mno content, while the opposite occurs in the other grains. the reason for this is the presence of geikielite and pyrophanite solid solutions in different contents. in the homogeneous ilmenite grains the contents of mgo and mno range between 0.0 and 3.1wt% and 0.4 and 6.1wt% respectively. some of the detected homogeneous ferriilmenite grains are associated with the bulk ilmenite grains (2wt%). the included dissolved fe2o3 ranges between 7.3 and 22.8wt%. their mgo, al2o3, and cr2o3 contents are relatively higher. the detected hematite-ilmenite exsolved intergrowth represents 21.4wt%, and may show 1 or 2 distinct generations of exsolutions. some minor composite grains are detected in the concentrate under examination. each of them consists of two parts, one of them is titanhematite-ferriilmenite and the other ferriilmenite-titanhematite. the fe2o3 contents of the ferriilmenite exsolved intergrowth of the different hematiteilmenite grains varies and ranges between 0.02 and 17wt%. in some ferriilmenite components, the mno ranges between 1.5 and 8.6wt%. in the composite ilmenite-hematite grains, the content of both mno and mgo is relatively lower and can be also distributed homogeneously through the analyzed spots. in the titanhematite components, the tio2 content ranges between 5.8 and 23.8wt%. the tio2 content rarely attains relatively greater value, 30.88wt%, where an individual amount of tio2 is postulated to occur with the ilmenite component within the titanhematite. the content of the associated mno is relatively lower, i.e. 0.3-1.9wt%, in comparison with those of the ferriilmenite bodies. it is very low in the titanhematite of the detected composite grains. the solubility of mno with ilmenite seems to be a relatively greater than with hematite. both mgo and mno are positively correlated with feo rather than fe2o3. it was also detected that v2o3 follows tio2 in spots of ferriilmenite and fe2o3 rather than tio2 or feo in spots of titanhematite. in the investigated hematite-ilmenite exsolved intergrowthed grains, the cr2o3 and al2o3 contents of all the analyzed spots for the 2 exsolved components range between 0 and 1.2wt% and 0 and 3.2wt% respectively. relatively greater content is present in the titanhematite components. in some titanhematite components, it was detected that the mechanism of leaching fe2o3 is associated with the presence of molecular water which seems to be recycled and the associated sio2 and/or al2o3 are enriched and finally precipitated inside spots and cracks. generally, it was noticed that the presence of molecular water is important in the alteration process of ilmenite or some associated silicate mineral impurities. the partially altered ilmenite grains represent 7.34wt% and contain a relatively higher mno content in their ilmenite components. the presence of sphene in the obtained ilmenite concentrate may be responsible for the recorded amounts of sio2 and cao and maybe for some of the recorded cr2o3 content. as a final conclusion it is obvious that a considerable number of ilmenite grains contained in the final obtained highpurity ilmenite concentrate (more than 99wt% ilmenite) have exsolved intergrowthed components containing relatively higher quantities of fe2o3, cr2o3, sio2, and cao. these intergrowths may be responsible for the relatively higher values of the recorded impurity oxides and hence the relatively lower tio2 and higher fe2o3 and cr2o3 content, for most of the obtained egyptian beach ilmenite concentrates. magnetic separation treatment, grain size differentiation, or both, of the engineering, technology & applied science research vol. 12, no. 6, 2022, 9614-9631 9630 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite … obtained ilmenite concentrate may improve the marketable specifications of the obtained ilmenite concentrate. acknowledgement the author wishes to express his appreciation to the deputyship for research & innovation, ministry of education, saudi arabia for funding this research work. references [1] e. m. el shazly, "classification of egyptian 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copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5665 abstract in this paper, a simple and effective solution is proposed to accurately estimate the complex relative permittivity of individual layers and multilayers of dielectric material samples from the s-parameters measured by two waveguide cells having equal or different lengths filled with the same vacuum/empty material without having to calibrate before performing experiments. the measurement system is set up by modeling using the computer simulation technology (cst) software. in the modeling, a single layer/multilayer material sample is placed in the x-band rectangular waveguide and it has two ports used for the electromagnetic wave supply and measurement of s-parameters. from the s-parameters measured, the complex relative permittivity of individual layers and the multilayers of the material samples are estimated by the proposed method. the known single-layer and multilayer materials such as garlock, bakelite, and teflon have different dielectric constants and thicknesses. the results show that the complex relative permittivity of the samples matches the measured and calculated values of s-parameters in the frequency range of 8.2ghz to 12.4ghz. keywords-complex relative permittivity; multilayer dielectric material; finite integration technique i. introduction multilayer dielectric material substrates are used in many practical applications, especially in high-speed circuits, such as the microwave integrated circuits (mics) [1, 2], monolithic microwave integrated circuits (mmic) [3-6], and wireless systems applications [7, 8]. the exact knowledge of the individual layers in the multilayer substrate permittivity characterization is of great importance for mic and mmic design. the multilayer material is formed by composite materials and has new properties that could not be found in the individual layers. for the measurement of the electric properties over a wide frequency range, the waveguide method is one of the most popular methods to determine the permittivity of multilayer dielectric substrates [9-14]. in the waveguide measurement method, a sample of the composite multilayer substrate is placed in a waveguide and two port sparameters are measured using a vector network analyzer. this nondestructive method is based on the reflection coefficient and transmission coefficient measurement from which the complex permittivity (εr) or the permeability (μr) of the materials can be determined. in addition, the sample preparation requirements are minimal, and the electric properties can be measured over a wide frequency range. however, the waveguide method is the same as the free space or transmission line method, which are less accurate due to the unavoidable measurement errors. although there are calibration standards, such as the short-open-load-through (solt) [15-20], the through-reflect-line (trl) [21-24], and the multiline trl [25-28], that should be performed before the experiments, these methods experience their own respective defects, such as the requirement of multi-measurement cells, or the presence of the air gap effect. this paper proposes a new approach to estimate the complex relative dielectric based on only one measurement of the s-parameters of the sample to eliminate the defects mentioned above by assuming the waveguide cell with the length l is determined to be filled with empty air inside (εr ≈ 1.0-j0.0) as a layer of dielectric material. the proposed method can eliminate the air gap between the waveguide and the surface of the material sample because the air layer in the engineering, technology & applied science research vol. 13, no. 3, 2023, 10664-10669 10665 www.etasr.com ho & le: accurate estimation without calibration of the complex relative permittivity of multilayer … waveguide reaching the surface of the sample is considered to be an air dielectric layer. ii. proposed model analysis the proposed non-calibrated model to accurately estimate the complex relative permittivity of a multilayer dielectric material based on the finite integration technique is illustrated in figure 1. in the proposed model, between the two waveguide cells, the dielectric material layers have thickness d with an empty air region with length l. the analytical electromagnetic method [11] is used to determine the s11 and s21 parameters of the multilayer dielectric material sample placed in the two ports of the rectangular waveguide as shown in figure 1. in figure 1, the two waveguide cells are filled with the same vacuum/empty material and are defined as layer#1 and layer#n with parameters (εr0, μr0), and the multilayer substrate consists of layer#2 to layer#n-1, where the m th layer has parameters (εrm, μrm), with n >=3. they are located between the transverse planes at z = zn-1 and z = zn. fig. 1. geometry of the multilayer dielectric material sample placed in the two ports of the rectangular waveguide for the estimation of s11 and s21. a. calculating procedure of the s11 and s21 parameters to determine the s11 and s21 components of 2-port parameters, it is assumed that the te10 mode of unit amplitude is incident on the interface at z = 0 from the region z ≤ 0. if et0, et1, et2, ..., etn are the transverse electric fields on the interfaces at z = z0 = 0, z1, z2, ..., zn, respectively, then the transverse electric fields in the various regions of the waveguide are obtained as: 1) for z ≤ 0: 0 0 0 0 0 0 0 0 sin( ) * i j z t i i i z e = -2je z e e ds e e              � � � � � (1) 0 0 0 0 0 0 0 0 0 0 0 cos( ) * i j z t i i i i z h = 2y h z e e ds y h e              � �� � � (2) 2) for zn-1 ≤ z ≤ zn:   1 2 0 1 sin n n n in i i e e e = e z            � � � � (1) where:    1 1 ( 1) sin * n n n i n t n i z z e = z z e e ds      � � �   2 1sin * n n n i n tn i z z e = z z e e ds     � � �   1 2 0 sin nn n n i in i i h h h = y h j            � � �� (4) where:    1 1 ( 1) cos * n n n i n t n i z z h = z z e e ds      � � �   2 1cos * n n n i n tn i z z h = z z e e ds     � � � 3) for z ≥ zn: 1 ( ) 1 0 * n i n n j z z n tn i i i z z e = e e ds e e                  � � � � (5)  11 1 0 * n i n n j z zn n tn i i i i z z h = e e ds y h e                  �� � � (6) 4) for z = 0,       1 1 10 0 1 0 0 01 0 1 1 11 0 1 cos 2 * sin * sin n n i i i t i i i z zi i t i i i z zi y h = y y e e ds h j y e e ds h j                                 � �� � �� � (7) 5) for z = zn:         1 1 ( 1) 0 1 1 1 1 0 1 1 ( 1)1 0 1 0 * sin cos( ) cos( ) + sin sin * + * sin n n n n i i t n in i z zi n n n n ni n i n i i in n i i n i n n i i tn i t n in iz z z zi n y h = e e ds j h y y j j y h e e ds e e ds j                                         � � � � � � � � � (8) 6) for the interface located at z = zn:     1 ( 1) 0 1 0 0 * sin cos( ) + sin * n n n i i t n in i z zi n n n ni n i i in i i n tn i z z y h = e e ds j h y y j e e ds                          � � � � � � (9) the obtained transverse electric fields over the interfaces are: x y z port #2 port #1 transmitted wave incident wave reflected wave layer#2 layer#3 layer#4 layer#1 layer#n-1 layer#n z0 z1z2z3 z4 zn-2 zn-1 zn engineering, technology & applied science research vol. 13, no. 3, 2023, 10664-10669 10666 www.etasr.com ho & le: accurate estimation without calibration of the complex relative permittivity of multilayer … 0 1 0 0 1 1 0 0 0 0 , , ,.... n n j j t j j t j j j j j j tn nj j tn nj j j j e t e e t e e t e e t e             � � � � � � � � (10) where t0j, t1j, ..., tnj are the complex unknown coefficients. using the galerkin’s procedure, the complex amplitudes t0j, j = 1, 2, 3, …, j0, t1j, j = 1, 2, 3, …, j1, tnj, j = 1, 2, 3, …, jn are all zero due to the orthogonal nature of vector modal functions. the solution of (n + 1) gives an estimate of the complex amplitudes t00, t10, t20, tn0 from which s11 and s12 are determined as: 0 0 11 00 21 0 1 and n j z ns t s t e    (11) b. calculation procedure of s22 and s12 parameters the s22 and s12 parameters can be determined by following the procedure used for the estimation of s11 and s21, and reverse the locations of the layers as illustrated in figure 2. fig. 2. geometry of the multilayer dielectric material sample placed in the two ports of the rectangular waveguide for the estimation of s22 and s12. iii. complex permittivity estimation results a. estimation of s-parameters in this section, the properties of the individual layers of the dielectric material and of the empty layers are assumed to be known, the s-parameters for various material layers are computed from the theory as a functions frequency and are compared with the simulated s-parameters. the s-parameter simulations of both proposed models in figures 1 and 2 were performed using the commercial 3-d full electromagnetic simulation software cst microwave studio. figure 3 is based on the finite integration technique. fig. 3. material layers with thickness d between two identical waveguide cells with an empty air region between them. in figure 3, the thickness d of the dielectric samples is assumed to be known, whereas the sample is placed between two identical waveguide cells with length l = 15mm and the empty air region with electric properties εr = 1.0. b. empty garlock empty in this case, a single garlock layer with thickness d = 1.7mm and εr = 7.5 j0.001 is shown in figure 4(a). the simulation results and the calculation of the s-parameters of the sample are shown in figure 4(b)-(c). the results show that the simulated and calculated values of the s-parameters are almost similar in the frequency range from 8.2ghz to 12.4ghz. (a) (b) (c) fig. 4. (a) garlock layer with d = 1.7mm between two identical waveguide cells with an empty air region between them with length l = 15mm, (b) real and (c) imaginary part of the simulated and calculated sparameters of the empty garlock empty layers. c. empty bakelite teflon empty the considered composite sample consists of bakelite and teflon layers. the composite slab is formed by placing the bakelite layer with d1 = 3.3mm, εr = 3.76 j0.001 and the teflon layer with d2 = 6.35mm, εr = 2.03 j0.001 shown in figure 5(a). the simulation and calculation results of the sparameters of the sample are shown in figure 5(b)-(c). the results show that the s-parameters simulated and calculated values agree well in the frequency range of 8.2ghz to 12.4ghz. x y z port #2 port #1 transmitted wave incident wave reflected wave layer#n-1 layer#n-2 layer#n-3 layer#n layer#2 layer#1 z0 z1 z2z3 z4 zn-2 zn-1 zn engineering, technology & applied science research vol. 13, no. 3, 2023, 10664-10669 10667 www.etasr.com ho & le: accurate estimation without calibration of the complex relative permittivity of multilayer … (a) (b) (c) fig. 5. (a) bakelite and teflon layers with thickness d1 = 3.3mm and d2 = 6.35mm between two identical waveguide cells with an empty air region of length l = 15mm, (b) real and (c) imaginary parts of the simulated and calculated s-parameters of empty bakelite teflon empty dielectric layers. d. empty garlock bakelite teflon empty: the composite sample considered consists of garlock, bakelite, and teflon layers. the composite slab is formed by placing the garlock layer with d1 = 1.7mm, εr = 7.5 j0.001, the bakelite layer with d2 = 3.3mm, εr = 3.76 j0.001, and the teflon layer with d3 = 6.35mm, εr = 2.03 j0.001 shown in figure 6(a). the simulation and calculation results of the sparameters of the sample are shown in figure 6(b)-(c). the results show that the simulated and calculated values are in excellent agreement in the frequency range of 8.2ghz to 12.4ghz. e. estimation of complex permittivity in this section, the simulated and calculated s-parameters of dielectric material samples, consisting of single or multilayer samples are used to estimate the complex permittivity based on the objective function and the matlab code from [11]. the results of the complex relative permittivity estimation of singlelayer dielectric (garlock), two-layer composite dielectric (bakelite teflon), and three-layer composite dielectric (garlock bakelite teflon) are shown in figure 7, 8, and 9, respectively. (a) (b) (c) fig. 6. (a) garlock, bakelite and teflon layers with thickness d1 = 1.7mm, d2 = 3.3mmn and d3 = 6.35mm between two identical waveguide cells with an empty air region with length l = 15mm, (b) real and parts of the simulated and calculated s-parameters of empty garlock bakelite teflon empty dielectric layers. fig. 7. relative permittivity (real and imaginary) of garlock material estimated using simulated and calculated s-parameters. fig. 8. relative permittivity (real and imaginary) of bakelite teflon material estimated using simulated and calculated s-parameters. engineering, technology & applied science research vol. 13, no. 3, 2023, 10664-10669 10668 www.etasr.com ho & le: accurate estimation without calibration of the complex relative permittivity of multilayer … fig. 9. relative permittivity (real and imaginary) of garlock bakelite teflon material estimated using simulated and calculated s-parameters. fig. 10. the root mean square error of the complex relative permittivity between calculation and simulation. the estimated results in figures 7-10 show that that the error in the complex relative dielectric estimation from sparameters simulated by the proposed waveguide calibration technique is extremely small or negligible in the frequency range of 8.2ghz to 12.4ghz. iv. discussion in this paper, a solution to eliminate the free space of the waveguide based on an improved measurement model and estimation algorithm is proposed. the novelty of the proposed model in comparison with the model in [11] is that there is no need to calibrate the waveguide when making the actual measurements because, in this study, the free space inside the waveguide is considered a layer of the dielectric material. however, the simulation test results show that the correctness of this solution is very satisfactory. in the future, we will continue to test this proposal by experimental measurements. v. conclusion a simple and effective solution to estimate the complex relative permittivity of single and multi-layered dielectric material samples using waveguide measurements is proposed in this paper. the proposed system consists of modeling the sparameters measurement using cst software combined with matlab. this estimation method is verified based on the complex relative permittivity estimation in the 8.2-12.4ghz frequency range of the reference composite samples garlock, bakelite, and teflon, with known thicknesses. the results show that the simulated and ideal values of the complex relative permittivity of the samples presented an excellent agreement in the entire x-band without having to calibrate the waveguide cell before performing the experiments. the proposed method eliminates the effects of systematic errors of the calibrated experiment setup and thus can afford high measurement accuracy. therefore, the proposed method is great for accurately estimating the complex relative permittivity of singleand multi-layered dielectric material samples. acknowledgment this work was supported by the faculty of electronics and telecommunications, electric power university (epu), hanoi, vietnam. references [1] l. maloratsky, passive rf and microwave integrated circuits, 1st edition. amsterdam, netherlands: newnes, 2003. 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[28] y. rolain, m. ishteva, e. van nechel, and f. ferranti, "a tensor-based extension for the multi-line trl calibration," ieee transactions on microwave theory and techniques, vol. 64, no. 7, pp. 2121–2128, jul. 2016, https://doi.org/10.1109/tmtt.2016.2565474. microsoft word etasr_v12_n4_pp8990-8995 engineering, technology & applied science research vol. 12, no. 4, 2022, 8990-8995 8990 www.etasr.com loquero et al.: cyananobot: miniaturized boat-assisted data acquisition for automated cyanide … cyananobot: miniaturized boat-assisted data acquisition for automated cyanide monitoring in wastewater using optical nano-sensors jorich s. loquero cyananobot research project caraga state university butuan city, philippines jorichloq@gmail.com alexander t. demetillo ctr. for ren. energy, automn, & fab. techs, caraga state university butuan city, philippines atdemetillo@carsu.edu.ph ian benedict pongcol cyananobot research project caraga state university butuan city, philippines ianbenedict.pongcol@gmail.com jamiela m. sakuddin cyananobot research project caraga state university butuan city, philippines jsakuddin@gmail.com ronieto n. mendoza ctr. for ren. energy, automn, & fab. techs, caraga state university butuan city, philippines ronmendoza.ece@gmail.com rudolph joshua u. candare cyananobot research project caraga state university butuan city, philippines rucandare@carsu.edu.ph ydron paul c. amarga cyananobot research project caraga state university butuan city, philippines ydron.paul@gmail.com gerome l. amper cyananobot research project caraga state university butuan city, philippines glamper@carsu.edu.ph rey y. capangpangan college of science and environment mindanao state university naawan, philippines reycapangpangan@gmail.com received: 11 may 2022 | revised: 4 june 2022 | accepted: 6 june 2022 abstract-cyanide contamination in water and wastewater is ubiquitous, particularly in gold mining industries, where cyanide is commonly used to extract gold. it is constantly being monitored by collecting samples which are analyzed in the laboratory using traditional cyanide analysis, which requires complicated instrumentation, skilled analysts, and expensive equipment. using the gold nanoparticle (aunp)-decorated paper-based sensor employing whatman filter paper (wfp) as a substrate, an automated process for cyanide monitoring with the aid of an assembled and improvised remotely controlled miniature boat was developed. the technology is equipped with a filtration system with automated water sample collection and preparation with an automatic paper sensor dispenser. images of the collected wastewater samples are taken at different time intervals and are analyzed on their respective color spaces based on 8 mathematical models, each predicting the cyanide level of the water sample. the predictions are compared to the actual ionselective electrode (ise) measurement, and root mean square error (rmse) values were calculated. the predictions at 165s using the hue, saturation, value (hsv) color space exhibited the highest r 2 of 0.85 and the lowest rmse of 3.80 parts per million (ppm) with an average error of 3.40ppm. the predictions are sent to a database using global system for mobile communications (gsm). the results suggest that the cyananobot technology facilitates fast analysis time, circumvents the frequent instrument calibration, reduces operating costs, minimizes exposure to toxic cyanide-containing samples, and reduces person-to-person interaction. keywords-cyanide; gold nanoparticle (aunps)-decorated paper-based sensor; remote-controlled boat; automated cyanide monitoring; image processing; gsm i. introduction issues of cyanide contamination in water and wastewater are ubiquitous, mainly in gold mining industries, where cyanide is commonly used to extract gold [1]. typically, cyanide mining waste materials are contained in the tailings pond, where necessary treatment is done [2]. monitoring the free cyanide concentration is conducted by collecting water samples and analyzing them in the laboratory using optical methods, electrochemical methods, mass spectrometry, gas chromatography, titrimetric methods, or amperometric procedures [3-5]. all these methods require skilled personnel to do the analysis on-site, however, restricted by the new normal brought by the covid-19 pandemic, automation of this process in the mining industry is deemed necessary. likewise, the conventional cyanide analysis, which requires additional sample preparation, apart from sample collection, needs to be revitalized using a sensitive, low-cost, and fast analysis using a paper-based nano-sensor [6]. corresponding author: jorich s. loquero engineering, technology & applied science research vol. 12, no. 4, 2022, 8990-8995 8991 www.etasr.com loquero et al.: cyananobot: miniaturized boat-assisted data acquisition for automated cyanide … reliable cyanide detection was demonstrated by using the developed gold nanoparticle (aunp)-decorated paper-based sensor using wfp. the sensor can give semi-quantitative detection as low as 0.05ppm, causing discoloration of the sensor from reddish-purple to white due to the formation of the water-soluble gold-cyano complex, which is known to be dependent on the amount of cnin the sample [7]. smartphones to capture images and analyze the chemical concentration [8-11], a paper-based sensing chip [12] and electrochemical sensor [13] have been used to quantify the color changes of paper sensors. this research seeks to automate cyanide monitoring of wastewater in a mining site using the developed whatman filter papergold nanoparticles (wfp-aunps) sensor from on-site wastewater sample collection and preparation. automated cn detection is conducted using the wfp-aunps sensor through digital image-based colorimetry, subsequent collection and analysis of data, and data storage. consoleoperated software and computer vision algorithms were introduced to provide a qualitative, quantitative, and reproducible readout at a low cost for flexibility and an easy quantification system. also, an internet of things (iot)-based system was employed to transmit the acquired cyanide concentration data, other water parameters, and location, offering advantages over traditional methods [14-18]. the module was assembled in an improvised miniature boat that can be controlled remotely to traverse from one monitoring point to another within the sampling site. this remote access capability saves operating time and resources. the waterproof casing of the boat protects the assembly from external disturbances such as rain and winds. this study enables a more feasible and faster analysis, decreased human exposure and labor risk, and improves working efficiency. ii. system μodel figure 1 indicates the system overview of the study. the system architecture shows the details of the system components and operation. fig. 1. system οverview. iii. μethodology and flowchart this section presents the workflow and procedures conducted in the study, as shown in figure 2. boat navigation and movement to predetermined sampling sites are conducted with a remote-control system. the user handles the transmitter, and the receiver is placed on the boat. when the boat arrives at the site where the user wants to test, the user flips a switch that triggers the start of the sensor module. the location coordinates are also sent to the microprocessor. the sensor module is responsible for the automated cyanide level testing process. it uses a microprocessor that is serially connected to a microcontroller that controls water sampling, water preparation, water dispensing, triggering the analyzer module, data transmission, and water discharge, in that order, through a plurality of pumps and motors, a camera, and a gsm module. the sensor module and analyzer module comprise the sensing system. fig. 2. system architecture and flow. iv. hardware, software, and system integration a. navigation system the miniature boat was shaped into a monohull structure using 1-inch styrofoam frames, smoothed and coated with glazing putty, fiber cloth, and body filler. the mini-boat was tested for its buoyancy and its navigational control. the buoyancy test was conducted in a private beach resort by gradually adding loads to the boat. the navigation system used is an fs-i6 2.4ghz 6-channel rc transmitter as its controller bind with an fs-i6 2.4ghz 6-channel receiver. the receiver was connected to two 150a brushless waterproof electronic speed controllers (escs) that control two brushless motors, each attached with motor thrusters at different channels. another receiver channel was connected to the microcontroller of the sensor module to trigger the automated cyanide level testing at the chosen sample site. engineering, technology & applied science research vol. 12, no. 4, 2022, 8990-8995 8992 www.etasr.com loquero et al.: cyananobot: miniaturized boat-assisted data acquisition for automated cyanide … b. sensor module the sensor module was framed to maximize space while using local materials. its layout is shown in figure 3. when the microprocessor of the sensor module, a raspberry pi 4, receives the trigger signal from the navigation system, the microprocessor sends a trigger signal serially to the arduino mega 2560 microcontroller. the microcontroller then starts the automated cyanide level testing process. a 3d printed built-in filtration module placed on the rear of the boat, fully submerged to the water source during testing, is connected to the water sampling system and contains a peristaltic pump and a beaker, through a silicon tube, as shown in figure 4. after priming the tube, the pump then dispenses 50ml of water sample to the beaker. fig. 3. layout of the sensor module. fig. 4. front view of the sensor module. the ph of the collected water sample is then measured. as the previous laboratory ph test result on the water sample indicated a ph level below 11 and the minimum ph level required for cyanide testing is 11, a consistent volume of 1.5ml of sodium hydroxide (naoh) is added to the water sample. the solution was mixed with the water sample by pumping air using a diaphragm pump. the slider system in figure 4 is a rack and pinion attached to a platform and a ball-bearing slider controlled by the stepper motor in figure 2. figure 5 shows the slider system’s positions at different stages in the testing process. first, the slider system retracts to the position shown in figure 5(a), aligning the oblong-shaped hole in the platform to the paper sensor holder cartridge. the paper sensor holder cartridge contains two stacks of paper sensor holders, cylinders trimmed by a spherical cap, as shown in figure 6, with circular aunps-integrated paper sensors in each holder. the paper sensor holders are 3d printed using black polyethylene terephthalate glycol (petg) to capture the edges of the paper sensors better as it turns white. these are stored in a cartridge with 3 segments, 2 are stacked with paper sensor holders, and the middle segment contains no paper sensor holders but has a hole in the base, as shown in figure 7. the cartridge also has a servo motor attached with a semicircle wiper with a hole that can fit a paper sensor holder. as the wiper moves from left to right and vice versa, a single paper sensor holder falls into the wiper hole and gets pushed into the hole on the base of the middle segment of the cartridge. the hole is aligned to the hole in the platform in a position demonstrated in figure 5(a). with a paper sensor holder, the platform is positioned as illustrated in figure 5(b). a silicon tube connected to the dispensing peristaltic dispenses 1ml of the prepared water sample to the paper sensor holder. (a) (b) (c) (d) fig. 5. the slider system positioned at different stages in testing. (a) platform aligned cartridge, (b) platform at dispensing tube, (c) platform at imaging station, (d) platform at dispensing area. fig. 6. a paper sensor holder. fig. 7. paper sensor holder cartridge. the platform moves into the position shown in figure 5(c). the image acquisition chamber in figure 3 is spray-painted with black paint to block the ambient light that might affect the lighting during the data gathering from entering the box. since the box was completely black and dark, a led light strip with engineering, technology & applied science research vol. 12, no. 4, 2022, 8990-8995 8993 www.etasr.com loquero et al.: cyananobot: miniaturized boat-assisted data acquisition for automated cyanide … a diffuser was installed inside the box to ensure consistent lighting during the data gathering process. these light sources are turned on before the platform arrives at the spot aligned to the camera. temperature and humidity are also recorded and trigger the analyzer module. after receiving the predicted cyanide level, the light source is turned off and the data acquired from the process (cyanide level, ph, temperature, humidity, and location coordinates) are saved in the internal storage of the microprocessor and sent through sms and to the iot analytics platform thingspeak. a line graph is shown for each parameter, with each point showing the value and the time the value was received. the platform moves into a position described in figure 5(d), where the paper sensor holders and water are dispensed. another pump pumps the water from the discharging container back to the water source. the user then moves to the next sampling site. before the 50ml water sample is collected at the second site, the tubes and beakers are rinsed by repeatedly intaking and discharging water from the water source 3 times. this is done by introducing the water from the second site to the sensor module. c. analyzer module an algorithm was designed to predict the cyanide level using images taken of the paper sensor at specific time intervals. figure 8 shows the algorithm. fig. 8. analyzer module algorithm. eight mathematical models were tested in this study. each model has a specific time interval and color space. the model names are 135sec_hsv, 165sec_hsv, 195sec_hsv, 240sec_hsv, 270sec_lab, 315sec_hsv, 555sec_hsv, and 555sec_lab. a reference image was taken immediately as the paper sensor holder was pushed to the image acquisition chamber. this reference image was used for all models. at the time specified by the model name, an image will be taken and stored in the internal storage of the raspberry pi 4. a total of 8 images were captured, including the reference image, as the last two models use the same time interval. the stored images were used by a circle detection algorithm. this python script detects a paper sensor in the picture after applying a mask on the image using circle hough transform. the circle was then cropped, and the region of interest (roi) was identified. an example is shown in figure 9. (a) (b) (c) fig. 9. detection of paper sensors in the image. (a) raw image, (b) binary mask, (c) the masked image. each paper sensor image’s mean pixel intensity (mpi) was extracted in different color spaces. the extracted values for the images taken after the time duration in specific color space were then subtracted with the reference image’s mpi in the same color space. the resulting value shows the change of mpi of the paper sensor after the time interval. the 8 mpi values were then fit to their corresponding mathematical model resulting in a prediction of the cyanide level of the water sample. the predictions were then sent to the microprocessor of the sensor module for storage and sending. the predicted cyanide level was also compared to the actual cyanide concentration measured using an ion-selective electrode (ise). v. results and discussion a. navigation system the navigation system was tested in a pool near the campus. the boat's buoyancy was tested by gradually adding load while the boat was afloat. about 80kg can be safely carried by the boat. fig. 10. buoyancy and stability test of the mini-boat. engineering, technology & applied science research vol. 12, no. 4, 2022, 8990-8995 8994 www.etasr.com loquero et al.: cyananobot: miniaturized boat-assisted data acquisition for automated cyanide … the remote-control system was also tested in the private pool. the boat was smoothly navigated with the controls. the expected speed power from the motors was delivered. overall, the remote-control testing has been successful, particularly the differential method. for two consecutive weeks, the team conducted the actual testing in a mining tailing pond. the boat floated adequately with all the loads (batteries, sensor system, and other electronic devices.). the transmitter used was the fsi6 transmitter, a 2.4ghz radio system with 6 channels. ch 1 and 2 were dedicated to the two motors, while ch 6 was set for the toggle switch to trigger the sensing system. the remote control controlled the boat smoothly for a distance of 50m-100m. fig. 11. navigation system actual testing in a mining tailing pond. b. sensing system the cyananobot system was deployed for the actual testing. the system was tested many times in a day, repeatedly conducting water sample collection, water sample preparation, image capturing, paper sensor detection, color extraction, cyanide concentration prediction, water sample discharge, and data transmission. the 8 mathematical models were used to identify the time intervals that needed to be taken. after this, the paper sensor responses were detected and their color values were extracted. then, using the image, the model, and the features needed in the model, the cyanide concentration was predicted using the model and the result was compared with the actual concentration measured with an ise. a total of 18 samples were collected on-site. figure 12 shows the quantile-quantile (q-q) plots of the two best models and their respective r2. the predictions at 165s using the hsv color space exhibited the highest r2 of 0.85 and the lowest rmse of 3.80ppm with an average error of 3.40ppm. this model also showed the lowest prediction error, with the true value at 31.5ppm and its prediction at 31.4ppm. however, its maximum error is 5.9ppm. the model for 195s in hsv has the second-highest r2 of 0.67 but its rmse is 6.41ppm. the 240s model using the hsv color space exhibited the highest rmse of 26.97ppm. the current study has lower r2 than the results of the reviewed literature, but the conducted tests concerned larger cyanide concentration values (12.6ppm to 41.1ppm) compared to studies that detected 0ppm to 1ppm with rmse of 0.06ppm [10], 0 parts per billion (ppb) to 4ppb [11], and 0ppm to 20ppm [12]. figure 13 shows the visualization of the transmitted data in thingspeak. fig. 12. q-q plot of two models during on-site testing. fig. 13. data visualization in thingspeak. vi. conclusion and future work in this study, a boat-assisted cyanide monitoring device focused on the use of aunps-integrated paper sensors through digital colorimetry was developed. the boat was successfully built, it is well-balanced and spacious. the remote-control system has been successfully installed in the system. regarding the sensing system, it is effectively working with the automated procedures of intake, discharge, dispensing, imaging, detection, extraction, and sending of the acquired data. based on the results of the models, the image taken at 165s in the hsv color space is the most promising in predicting the cyanide concentration of the water sample on-site as only one model engineering, technology & applied science research vol. 12, no. 4, 2022, 8990-8995 8995 www.etasr.com loquero et al.: cyananobot: miniaturized boat-assisted data acquisition for automated cyanide … will be chosen for the final deployment. this time interval, 165s, against other model time intervals, such as 315 and 555s, is favorable as the image of the paper sensor can be taken at a lesser time reducing the risk of sample degradation and lessening the idle time of the bot in the sampling site. instead of manually retrieving water samples and testing cyanide concentration using ise, the bot can reduce person-to-person interaction, reduce testing time, avoid frequent calibration of the electrodes, and reduce operating costs as paper sensors are inexpensive. however, trained personnel are highly necessary for using and maintaining the system. for future work, more tests for the model at a broader range of concentration are recommended along with other possible methods of acquiring color intensities of the paper sensors instead of a camera, consideration for confounding factors in the model, and implementing an autonomous navigation system. acknowledgment the authors would like to thank the science for change program of the department of science and technology (s4cpdost) for the funding support for this project, the partner industry apex mining co. inc. (amci), for their invaluable support and shared knowledge in forming the concepts and theories of this project, and the caraga state university-main campus. references [1] b. c. nyamunda, "water quality," in water quality, h. tutu, ed. intechopen, 2017. [2] d. stapper, k. dales, p. velasquez, and s. keane, "best management practices for cyanide use in the smallscale gold mining sector," planetgold programme, 2021. [3] j. ma and p. k. dasgupta, "recent developments in cyanide detection: a review," analytica chimica acta, vol. 673, no. 2, pp. 117–125, jul. 2010, https://doi.org/10.1016/j.aca.2010.05.042. [4] c. anning, j. wang, p. chen, i. batmunkh, and x. lyu, "determination and detoxification of cyanide in gold mine tailings: a review," waste management & research, vol. 37, no. 11, pp. 1117–1126, nov. 2019, https://doi.org/10.1177/0734242x19876691. 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[9] l. lvova et al., "smartphone coupled with a paper-based optode: towards a selective cyanide detection," journal of porphyrins and phthalocyanines, vol. 24, no. 05n07, pp. 964–972, may 2020, https://doi.org/10.1142/s1088424620500091. [10] m. cherbuin, f. zelder, and w. karlen, "quantifying cyanide in water and foodstuff using corrin-based cyanokit technologies and a smartphone," analyst, vol. 144, no. 1, pp. 130–136, dec. 2018, https://doi.org/10.1039/c8an01059e. [11] m. l. firdaus et al., "smartphone coupled with a paper-based colorimetric device for sensitive and portable mercury ion sensing," chemosensors, vol. 7, no. 2, jun. 2019, art. no. 25, https://doi.org/ 10.3390/chemosensors7020025. [12] h. singh, g. singh, d. k. mahajan, n. kaur, and n. singh, "a low-cost device for rapid ‘color to concentration’ quantification of cyanide in real samples using paper-based sensing chip," sensors and actuators b: chemical, vol. 322, nov. 2020, art. no. 128622, https://doi.org/ 10.1016/j.snb.2020.128622. [13] s. smith et al., "development of paper-based electrochemical sensors for water quality monitoring," in fourth conference on sensors, mems, and electro-optic systems, skukuza, south africa, feb. 2017, pp. 110– 115, https://doi.org/10.1117/12.2244290. [14] a. t. demetillo, r. y. capangpangan, m. c. bonotan, j. p. b. lagare, and e. b. taboada, "real-time detection of cyanide in surface water and its automated data acquisition and dissemination system," nature environment and pollution technology, vol. 19, no. 1, pp. 395–402, 2020. [15] n. geetha, "iot based smart water quality monitoring system," international journal of nonlinear analysis and applications, vol. 12, special issue, pp. 1665–1671, jan. 2021, https://doi.org/10.22075/ijnaa. 2021.5853. [16] s. zafar, g. miraj, r. baloch, d. murtaza, and k. arshad, "an iot based real-time environmental monitoring system using arduino and cloud service," engineering, technology & applied science research, vol. 8, no. 4, pp. 3238–3242, aug. 2018, https://doi.org/10.48084/ etasr.2144. [17] a. t. demetillo and e. b. taboada, "real-time water quality monitoring for small aquatic area using unmanned surface vehicle," engineering, technology & applied science research, vol. 9, no. 2, pp. 3959–3964, apr. 2019, https://doi.org/10.48084/etasr.2661. [18] r. govindarajan, s. meikandasivam, and d. vijayakumar, "performance analysis of smart energy monitoring systems in real-time," engineering, technology & applied science research, vol. 10, no. 3, pp. 5808–5813, jun. 2020, https://doi.org/10.48084/etasr.3566. microsoft word etasr_v13_n3_pp10685-10690 engineering, technology & applied science research vol. 13, no. 3, 2023, 10685-10690 10685 www.etasr.com ivanova: damage detection in free–free glass fiber fabric composite beams by measuring flexural … damage detection in free–free glass fiber fabric composite beams by measuring flexural and longitudinal vibrations yonka ivanova faculty of physics, sofia university st. kliment ohridski, bulgaria | institute of mechanics, bulgarian academy of sciences, bulgaria yonivan@phys.uni-sofia.bg (corresponding author) received: 16 february 2023 | revised: 6 march 2023 | accepted: 8 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5788 abstract this paper presents the experimental investigation results of the use of the vibration method by impulse excitation of free flexural and longitudinal vibrations of composite materials. the purpose of the study is to establish the sensitivity of the method used for defect detection and localization. to realize the objective, rectangular notch-type defects were simulated at different distances and depths. the influence of the location and depth of the artificial cracks on the dynamic properties of the beams was investigated by measuring the natural frequencies of flexural and longitudinal vibrations. the conducted experiments show a change in the dynamic characteristics of the beam depending on the dimensions and location of the defects. keywords-glass fiber composite (gfc); impulse excitation; free–free beam; flexural vibration; longitudinal vibration; natural frequencies; damage detection i. introduction natural frequency-based methods are some of the most studied methods for detecting delamination and cracks in composite structures by determining their modal shapes and natural frequencies [1-6]. chronological reviews of frequency methods for damage detection in structures were conducted in [1, 3, 6]. the great advantage of using frequency-based methods is that they are easy to implement in practice. the limitations of their use are that in some cases the changes in frequency are very small and may not be registered due to errors or deficiencies in the measuring equipment. additionally, changes in the mass of the structure under study or measurement temperatures can introduce uncertainty into the measured frequency changes [1]. frequency analysis of composite materials with defects has been developed by many researchers [9-12] who concluded that the natural frequency of the beam changes in the presence of a defect. experimental and simulation studies to determine the frequency characteristics and dynamic behavior of composites are published in [12-16, 18]. the effects of fiber orientation, fiber type, measurement method, and matrix materials on the dynamic properties of composites were investigated in [8, 14, 17]. frequency analysis of composite plates was conducted in [12-14]. the presence of a defect leads to a local reduction in the stiffness of the structure, resulting in changes in the dynamic properties, alteration of the natural frequencies, modal shapes, and an increase in the damping decrement [1-3, 18]. from the reviewed literature, it is seen that a reliable indicator for the detection of defects or damage obtained in service is the change in resonant frequencies. however, unlike modal shape-based methods, identification of the location of the damage is not easily achieved when using frequency measurements. many authors have studied different types of cracks [15, 16]. important factors influencing fracture behavior and mechanisms are fracture depth and length [4, 19]. impulse excitation is a popular technique for the diagnosis of various materials [20]. in [21], it is shown that the shape of the impactor head is an essential parameter on the low-velocity impact. the damage occurring in the composite plates is illustrated and analyzed for hemispherical and flat head shape hammer [21]. the earliest research on the subject analyzed natural frequencies; however, due to measurement errors and noise, natural frequencies in such mode shapes are not sensitive to structural damage [1, 6, 11]. other approaches have been developed to investigate and detect cracks in various composite materials by ultrasonic methods [22-24]. in [25], an approximate analytical method for damage detection in free–free axial vibrations was proposed. the method is based on the measurement of axial natural frequencies, which are global parameters and can be easily measured from any point on the structure. in the same work, the variation of the first two natural frequencies was used to identify the crack location and size. other studies present an analysis of the application of different vibrations for the identification of cracks in metallic materials, but no experimental results are found [26]. engineering, technology & applied science research vol. 13, no. 3, 2023, 10685-10690 10686 www.etasr.com ivanova: damage detection in free–free glass fiber fabric composite beams by measuring flexural … the purpose of the current study is to investigate the effect of cracks on the natural frequencies of excited bending and axial vibrations of gfc beams. the first natural frequencies of out-of-plane and in-plane flexural vibrations as well as the longitudinal vibrations are used to characterize a single beam with defects. the influence of the location and depth of artificial cracks is also investigated. ii. materials and methods a. materials a glass fiber fabric composite plate with a thickness of 5mm was considered in this study. the plate was manufactured by hot pressing the glass cloth layers, impregnated with thermo-reactive phenolic and epoxy type resins. the obtained glass fiber volume fraction was 50%. a sufficient number of beam-type specimens were cut from the composite slab with dimensions l=0.25m length, b=0.025m width and h=0.005m thickness. the threads of the glass fabric are parallel and respectively perpendicular to the x-axis (figure 1). fig. 1. specimen with an artificial rectangular channel type crack. to establish the sensitivity of the impulse excitation vibration method for defect detection, rectangular notch type defects were simulated at different distances from the edge of the specimens (xi), namely on 0.1l and 0.2l, 0.3l, and 0.5l. the slits are transverse, located perpendicular to the stacked layers of glazing. the simulated channels have different depths equal to 0.2h, 0.4h, 0.6h, and, in some cases, 0.8h. a schematic of the samples with the artificial defects is given in figure 1. a sufficient number of specimens were made and examined to investigate the location of the artificial defects at a fixed defect depth. b. methods 1) free flexural vibrations according to the euler-bernoulli theory, in flexural vibrations of a beam of constant cross section and thickness, there are innumerable natural frequencies, which are determined by: �� = � ��� �� � � ( ) �� (1) where a is the cross section of the beam, jy(z) is the moment of inertia, a characteristic of the cross section, ρ is the density of the material, and e is the modulus of elasticity of the composite material. for n=1, 2, 3, 4… the natural frequencies depend on the initial conditions, i.e. the way the oscillations are excited, as well as on the boundary conditions. at n = 1 the beam bends one half wave, at n = 2 there are 2 half waves and so on. for the fundamental frequency realization at first mode (n=1), the nodal points are located at 0.224l from each end of the beam, with the anti-nodes in the center and at each end. the first natural frequency of the two free ends of the beam can be written as [27]: �� = ��� � ��.��� �� � � � ( ) �� (2) the area of cross-section a is 1.25×10 -4 m 2 . the moment of inertia is jy = 2.58×10 -10 m 4 . the density is ρ = 1823kg/m 3 and the modulus of elasticity is e = 2.45×10 10 pa. a schematic of the experimental setup for the free flexural vibration test is given in figure 2. a pulse excitation in the middle of the specimen was used to excite bending oscillations in the specimen using a rubber mallet with flat shape. a superlux ecm-999 type microphone located at the edge of the specimen was used to record the mechanical oscillations. a computer, a pc usb 16-bit two-channel sound card 20hz ~20khz, and a real time acoustic analyzer data logger was used for registration, recording, and subsequent signal processing. fig. 2. schematic of the experimental setup for the free flexural vibration mode test: 1 –rubber mallet, 2 – microphone, 3 real time acoustic analyzer, 4 – computer. to realize "out-of-plane" bending, in which the direction of displacement is perpendicular to the large plane of the specimen, the diagram of suspension is shown in figure 3(a). the scheme given in figure 3(b) is used to excite the in-plane oscillations. the microphone is placed close to the specimen above the anti-node point. (a) (b) fig. 3. schematic representation of the beam attachment for the excitation of free flexural vibration. (a) out of plane flexure mode, (b) in-plane flexure mode, 1 impulse point, 2 microphone point. 2) free longitudinal vibrations the equation of the motion of euler-bernoulli for longitudinal vibration is given by [25, 27]: ��� �� � = �� �� ��� (3) where u is the longitudinal displacement of the current section dx of the beam during oscillations and �� = � �⁄ is the velocity of propagation the longitudinal elastic wave. equation (3) is solved by the standard method of separation of variables. the first natural resonant frequency of longitudinal vibrations is obtained by: engineering, technology & applied science research vol. 13, no. 3, 2023, 10685-10690 10687 www.etasr.com ivanova: damage detection in free–free glass fiber fabric composite beams by measuring flexural … � = !�� � � � (4) where k is a natural integer. the free longitudinal vibration test setup is shown in figure 4. each specimen is held by its center and struck with a plastic hammer at the edge. to analyze the acoustic response of the sample, the microphone was positioned on the opposite side of the sample. subsequently, the corresponding vibrating sounds were recorded and analyzed by fourier transform. fig. 4. longitudinal free vibration test setup. 3) experimental procedure twelve tests were performed on undamaged beams and the same number was conducted on damaged beams. table i presents the failure scenarios, which include 4 different crack locations and 3 crack depth levels at each location. the following procedure was used for the experiments: the specimen was lightly struck in the center. the test was recorded and repeated 5 times. the readings of the resonant frequency were recorded and the average value was taken. the acoustic signals were recorded and processed by signal processing methods (fourier transform) to identify the values of the natural frequencies. they were measured for all undamaged free beams in out-of-plane and in-plane flexural and longitudinal vibration modes. a cut was then introduced into each beam at a controlled distance and depth and the natural frequencies were measured. the signals obtained from the defective and intact beams were compared in both time and spectrum. in addition, tests were made for notches in the middle of the beam with a depth of 80% of thickness. iii. results and discussion the damage induces a local reduction in stiffness, which determines changes in dynamic behavior. this is reflected by shifting of the natural frequencies. the change of the first resonant frequency in flexural and longitudinal vibrations in the presence of a defect can be noted by the parameter ∆f: ∆� = #$%,о($%,)#$%,* , % (5) where ��,о is the first natural frequency of an intact beam and ��,, is the natural frequency of a beam with a crack. the results of the experiments for out of plane flexure mode vibrations of gfc beams are presented in table i. the relative first natural frequency ��,, /��,. and the relative frequency shift ∆f in the defective beams listed in the table. it can be seen that when the depth of the crack increases, the first resonant frequency changes significantly, especially at depth a=0.6h. table i. results of out-plane flexure mode vibrations of gfc beams description of samples dimensionless location x/l dimensionless depth a/h /0,1//0,2 ∆/, % intact beam 0 0 1 0 damaged beam 0.1 0.2 0.998 0.23 damaged beam 0.1 0.4 0.997 0.31 damaged beam 0.1 0.6 0.993 0.7 intact beam 0 0 1 0 damaged beam 0.2 0.2 0.990 0.96 damaged beam 0.2 0.4 0.981 1.92 damaged beam 0.2 0.6 0.952 4.81 intact beam 0 0 1 0 damaged beam 0.3 0.2 0.981 1.87 damaged beam 0.3 0.4 0.990 2.80 damaged beam 0.3 0.6 0.972 11.22 intact beam 0 0 1 0 damaged beam 0.5 0.2 0.972 2.80 damaged beam 0.5 0.4 0.971 5.61 damaged beam 0.5 0.6 0.921 13.08 figures 5 and 6 show the first resonance frequencies obtained during the out-of-plane bending vibrations for intact specimens and for beams with defects located at distances x equal to 0.1l, 0.2l, 0.3l, and 0.5l at different crack depths. it can be noticed that the presence of a defect leads to a decrease in the natural frequencies. (a) (b) fig. 5. first natural frequency of flexure vibration test for intact and damaged beams. (a) notches located at 0.1l with different depths 0.2h 0.4h, 0.6h. (b) notches located at 0.2l with different depths 0.2h 0.4h, 0.6h. (a) (b) fig. 6. first natural frequency of flexure vibration test for intact and damaged beams. (a) notches located at 0.3l with different depths 0.2h 0.4h, 0.6h. (b) notches located at 0.5l with different depths 0.2h 0.4h, 0.6h. as the distance to the notch increases, a larger shift of the first resonant frequency is observed. at a defect distance of engineering, technology & applied science research vol. 13, no. 3, 2023, 10685-10690 10688 www.etasr.com ivanova: damage detection in free–free glass fiber fabric composite beams by measuring flexural … 25mm, i.e. x=0.1l and a depth of 1mm, the changes in resonance frequency are very small and below 1%. at x=0.2l, the frequency shift reaches about 2%. the most significant changes in the first resonant frequency are obtained at a notch in the middle of the composite beams. at a crack depth of 3mm, the frequency shift reaches 14%. additionally, a beam with a depth a=0.8h was investigated. the results show a relative change of about 64%. the results of the in-plane flexure tests are shown in table ii and figure 7. (a) (b) fig. 7. first resonance frequency for in-plane flexure vibration. (a) defect location x/l=0.3, defect depths a/h =0.2, 0.4, and 0.6. (b) defect location x/l=0.5, defect depths a/h =0.2, 0.4, 0.6, and 0.8. the relative shift of the first resonant frequency is not noticeable at defect location x/l= 0.1. as the x/l parameter increases, the frequency decreases and reaches 6% for the deepest crack. figure 7 shows the frequency characteristics for slits at distances x=0.3l and 0.5l. table ii. results of in-plane flexure mode vibrations of gfc beams description of samples dimensionless location x/l dimensionless depth a/h /0,1//0,2 ∆/, % intact beam 0 0 1 0 damaged beam 0.1 0.2 0.999 0.069 damaged beam 0.1 0.4 0.998 0.188 damaged beam 0.1 0.6 0.996 0.390 intact beam 0 0 1 0 damaged beam 0.2 0.2 0.998 0.205 damaged beam 0.2 0.4 0.992 0.820 damaged beam 0.2 0.6 0.988 1.230 intact beam 0 0 1 0 damaged beam 0.3 0.2 0.998 0.206 damaged beam 0.3 0.4 0.990 1.029 damaged beam 0.3 0.6 0.959 4.116 intact beam 0 0 1 0 damaged beam 0.5 0.2 0.992 0.793 damaged beam 0.5 0.4 0.976 2.381 damaged beam 0.5 0.6 0.940 5.952 the results of the longitudinal vibration mode tests are shown in table iii and figure 8. the frequency changes for dimensionless damage location equal to 0.5 and dimensionless depths of 0.6 and 0.8 are about 11% and 26%. if the impulse impact energy is evaluated, it can be concluded that at such small impulse energy the stresses and strains are very small. for this reason, a significant reduction in resonance frequency is recorded when the material thickness at the defect site is at least 5 times smaller than the specimen thickness. (a) (b) fig. 8. first resonance frequencies of longitudinal tests. (a) x/l=0.3 and defect depths 0.2h, 0.4h, and 0.6h. (b) x/l=0.5 and defect depths 0.2h, 0.4h, 0.6h, and 0.8h.. table iii. results of longitudinal vibration tests of gfc beams description of samples dimensionless location x/l dimensionless depth a/h /0,1//0,2 ∆/, % intact beam 0 0 1 0 damaged beam 0.1 0.2 1 0.005 damaged beam 0.1 0.4 1 0.040 damaged beam 0.1 0.6 0.99 0.079 intact beam 0 0 1 1 damaged beam 0.2 0.2 0.998 0.237 damaged beam 0.2 0.4 0.992 0.513 damaged beam 0.2 0.6 0.988 0.908 intact beam 0 0 1 1 damaged beam 0.3 0.2 0.996 0.395 damaged beam 0.3 0.4 0.988 1.202 damaged beam 0.3 0.6 0.942 5.757 intact beam 0 0 1 1 damaged beam 0.5 0.2 0.984 1.641 damaged beam 0.5 0.4 0.961 3.886 damaged beam 0.5 0.6 0.890 10.978 another phenomenon that is evident in the frequency response function of damaged beams is the appearance of double peaks as shown in figure 9. double peaks indicate two resonances that are close. this phenomenon is called "breathing" [28]. it shows up as an irregular "broken peak" on the frequency response. breathing causes variations in local stiffness which is time, frequency, and amplitude-dependent. fig. 9. the "broken peak" phenomenon in frequency response function. engineering, technology & applied science research vol. 13, no. 3, 2023, 10685-10690 10689 www.etasr.com ivanova: damage detection in free–free glass fiber fabric composite beams by measuring flexural … figure 10 presents the effect of defect position and depth on the resonance frequency for flexure and longitudinal vibrations. maximum values of the ∆f are obtained at the deepest crack (a=0.6h), located at a distance of x=0.5l. the frequency shifts are 13%, 6%, and 11% for the out-of-plane, in-plane and longitudinal mode vibrations, respectively. (a) (b) (c) fig. 10. effect of defect location on frequency shift: (a) out-of-plane flexure mode, (b) in-plane flexure mode, (c) longitudinal mode. iv. discussion the effect of the crack on the resonant frequency is revealed differently in the oscillation modes and depends on the attachment of the beam as well as the shape, location, and depth of the crack. for transverse cracks with a specific beam location, increasing depth leads to a decrease in frequency. a crack of a certain depth and width causes different frequency changes in the experimental modes of vibrations, depending on the location of the crack. the current study confirms the opinion expressed in [18] that there are certain places where the damage hardly changes the frequency and they are close to the nodal lines. when the crack does not result in energy loss, the natural frequency in this mode of vibration is not affected. if the crack is located in places where the curvature of the modal shape has maximum values, the largest changes in frequency are obtained. the best crack detection sensitivity is obtained in tests when the crack is in the middle of the beam with out-ofplane flexure oscillations. the contribution of the current study is the conduction of a new systematic experimental study of the damage resistance of widely used composite materials. the novelty of the investigation is the use of a combination of bending and longitudinal vibration modes that should give more accurate results in the preliminary assessment of defect areas. new data have been obtained for the studied materials, which in principle confirm the studied references [1-4, 15, 18]. v. conclusions in this work, the capabilities of the vibration method for identifying defects in glass fiber fabric composite beams have been investigated and verified. the results showed a change in the dynamic performance of the composite beams depending on the size and location of the defects. the shift of the first natural frequency to lower values in the presence of defects was recorded for both flexure and longitudinal vibrations. the cracks in the middle of the specimens show the most significant shift of the frequency peaks in both tests. the relative change of the first resonance frequency was used as the damage parameter. the largest frequency shifts were recorded by outof-plane flexure, which were about 13%, and the smallest were from in-plane bending vibrations, which were 6%. in all cases, the crack depth significantly changed the structure and dynamic properties of the composite specimens. unusual nonlinearities in the frequency response functions were found such as broken or doubled asymmetric peaks, which were are typical of cracked elements. important parameters of the impact events are the peak impact forces and bending, the duration of the impact event, the stresses and strains and the shape of the contact zone [21], which need to be additionally analyzed. further research should be performed to quantify the defect position by modal shape analysis and to investigate other types of defects and the anisotropy caused by the location of glass layers in composite beams. acknowledgment this work has been accomplished with the financial support by the grant no bg05m2op001-1.002-0011-c02 financed by the science and education for smart growth operational program (2014-2020) and co-financed by the european union through the european structural and investment funds. references [1] d. caicedo, l. a. lara-valencia, j. brito, d. caicedo, l. a. laravalencia, and j. brito, "frequency-based methods for the detection of damage in structures: a chronological review," dyna, vol. 88, no. 218, pp. 203–211, sep. 2021, https://doi.org/10.15446/dyna.v88n218.91693. 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technology hanoi, vietnam phuong.vuhoang@hust.edu.vn received: 22 march 2022 | revised: 7 april 2022 and 14 april 2022 | accepted: 17 april 2022 abstract-this paper presents the drive control of a permanent magnet synchronous motor (pmsm) fed by a multi-level inverter for electric vehicle application. in particular, the advantage of torque mobilization of the pmsm engine has been selected for the electric drive of electric cars. in addition, to improve the transmission quality of electric vehicles to ensure requirements, the t-type three-level inverter will be proposed in the control structure of electric vehicles. moreover, the challenge of torque entails determining the appropriate physical qualities. therefore, the design of an active damping and current controller to provide rapid and precise torque response to the induced torsional moment was also conducted. finally, the results of plecs simulations prove the correctness of the theoretical research. the simulation results demonstrate the research theory. keywords-multilevel inverter; t-type inverter; pmsm; active damping; electric vehicles; foc i. introduction electric vehicles have been around for a long time, but their use has grown enormously over the last few years. many electric car applications that solve energy and pollution problems have been developed, put into commercial production, and used in practice [1]. electric cars have the advantages of electric motors, such as the ability to quickly and accurately generate torque, whereas torque control is also realized [2]. however, electric cars still have limitations such as long charging time, inflexibility, and high cost. regarding the outstanding advantages of electric cars, in terms of high performance and environmental friendliness, and considering the efforts to find solutions to reduce battery charging time, lead to the complete replacement of cars powered by internal combustion engines by electric vehicles in the future [3]. scientists have studied technological issues inside electric cars to develop solutions to improve electric vehicles' quality of motion, energy, and performance. according to [4, 5] the structure of an electric car normally includes components such as electric motor, controller, inverter, battery, charging port, powertrain, battery, etc. as shown in figure 1. fig. 1. the structure of a normal electric car. in the longitudinal traction structure of figure 1, we consider some problems with improving the transmission quality of electric cars to ensure requirements, so there is a need to pay attention to the following: firstly, electric motors have outstanding advantages in terms of controllability, allowing the use of advanced control methods to control the motor, thereby improving the kinematics of the car. therefore, the issue of selecting the engine most suitable for electric car transmission has always been considered by many scientists and automobile companies. corresponding author: vo thanh ha engineering, technology & applied science research vol. 12, no. 3, 2022, 8658-8666 8659 www.etasr.com giang et al.: drive control of a permanent magnet synchronous motor fed by a multi-level inverter … some motors have been used for electric cars, such as dc motors, which have the advantage of being easy to control. the disadvantage of this type of motors is the need for manifolds and brushes. it has a low lifespan, requires regular maintenance, and is unsuitable for hot, humid, and dusty conditions. as semiconductor valve technology, microprocessors and control techniques develop strongly and dc motors have been gradually replaced by other types of motors [6]. the brushless dc motor (bldc) is a type of permanent magnet synchronous motor with trapezoidal reactance. the bldc motor has the same mechanical characteristics, power density, high torque capacity, and high efficiency as a dc motor. the main disadvantage of the bldc motor is the significant torque undulation [7-9]. ac motors, such as squirrel-cage rotor (im) asynchronous motors, have the advantages of low cost, typical use, and ease of manufacture. it is possible to implement advanced vector control algorithms for im engines with the current technology, meeting the necessary technological requirements. the disadvantage of the im motor is its low efficiency, especially in light load mode [6]. the pmsm can be considered the most suitable motor for electric vehicle application with a high-efficiency large torque capacity, while it can be controlled with good quality. in particular, the interior permanent magnet synchronous motor (ipmsm) has many advantages, suitable for electric cars [10]. the magnetic motor has benefits such as high efficiency, sizeable power-tosize ratio, high power density, long life, small moment of inertia, wide operating speed range, large amount of torque/current, and low noise stability. therefore, magnetic motors have been promised to be widely used in transmission systems with high-quality speed regulation, such as electric vehicle robots [6, 11]. however, the cost is high and control is complicated. based on the characteristics of electric motors used for electric cars, in this paper we will consider pmsms. secondly, the inverter converts the dc voltage from the battery into the ac voltage to power the motor. the inverter is a virtual device, contributing to the improvement of the transmission quality to ensure the required specifications. therefore, the choice of the suitable inverter for this drive system is also a problem considered by many scientists [12]. it was found that multi-level inverters have advantages over twolevel inverters [13]. based on the current scientific research, it has been discovered that in the control structure of traction power transmission systems, 2-level voltage source inverters with power circuits including six semiconductor valves and the svm pulse width modulation (pwm) technique are often used. however, a multi-level inverter has more advantages than a two-level inverter for reducing thd [14]. acroding to [15], the 3-phase current has a conventional sinusoidal shape with total harmonic distortion (thd) equal to 7.53%, while the 2level inverters have thd equal to 11.39%. in addition, the multi-level inverter comprises semiconductor valves and a dc voltage source, and the output voltage is in the form of wavelengths [16]. therefore, the output voltage of a multi-level inverter may be made sinusoidal with low thd by increasing the number of voltage levels. this paper used -a three-level ttype inverter fed by a pmsm motor in an electric vehicle to improve fast and accurate torque response. thirdly, the torque of the motor shaft tm is the control input variable, and the angular velocity ω of the wheel is the control lever output. when the motor speed changes, the anti-slip is controlled by changing the magnitude of the torque tm. on the other hand, the motor shaft end torque is linearly dependent on the current flowing in the motor. therefore, to adjust the torque tm, we control the starter motor's stator current. the set value of the stator current flowing in the primary engine is the required current proportional to the pedal angle. in addition, due to their structural characteristics, the electric vehicles are prone to small fluctuations during the entry/exit of the accelerator pedal, the resonant frequency of the controller, and during acceleration. this means that the signal to set the motor speed is affected by this oscillation. at the same time, the control object (wheel) does not consider the jerking phenomenon (ts×kgear = 0), so the difference between the price-setting value and feedback will cause recoil. if not rectified and extinguished, this recoil can cause discomfort to the occupants in the vehicle [17, 18]. ii. mathematical model and control of the electric car power system a. mathematical model of the pmsm synchronous motor according to [19], the dq coordinate system to have the system of equations of pmsm motor is : sd sd sd s sd e sq sq sq sq sq s sq e sd sd e f di u l r i l i dt di u l r i l i dt ω ω ω ψ  = + −= + −= + −= + −   = + + += + + += + + += + + +  (1) the equation for calculating the torque of the motor is: ( )3 2 m p f sq sd sq sd sq t p i l l i iψ = + −  (2) the torque of the motor consists of two components: the main component f sq iψ and the reactive component due to the difference sd sq l l− . when building a control system, we need to control the stator current vector is such that the vertical current vector is perpendicular to the polar flux and there is no magnetizing current component, but only a torque generating current component or 0sdi = . the equation describing the motor torque is: 3 2 t p i m p f sq ψ= (3) b. mathematical model of the electric vehicle 1) description of the gearbox and the wheel system the gearbox model shows the angular speed and torque relationships according to the gear ratio 1 gear k p . m gear h h m gear t k t kω ω =  = w w (4) engineering, technology & applied science research vol. 12, no. 3, 2022, 8658-8666 8660 www.etasr.com giang et al.: drive control of a permanent magnet synchronous motor fed by a multi-level inverter … where m t is motor torque, wh t the torque acting on the wheel, with wi h t t= , j is the moment of inertia of the motor. the equation of newton's second law in the rotation of the motor is: m em h d t t j dt ω − = w (5) the drive wheel model is described by: h h h h l t h v r t t f r ω=  = = w w w w w (6) when the wheel rests on the road surface with force n and is driven by a torque twh, the vehicle will act on the road surface with a force f, and, respectively, the road surface will act against the vehicle with a force of the same value in the opposite direction as ft. in this case, ft is the frictional force and is the useful force component that causes the vehicle to move at speed vx. . . t v f m g µ= (7) where µ is the grip coefficient. m t m ω wh t w h ω r arge k fig. 2. description of the gearbox and the wheel system. w h t ω r ω f t wh v wh w h fig. 3. drive wheel model. 2) equation of motion of the vehicle and external force components applying newton's second law to the components of the external force acting on the body of the vehicle, we have: . .sin( )ev v t aero roll v dv m f f f m g dt α= − − − (8) air resistance: ( )2 2 d f aero ev wind c a f v v ρ = + (9) in some cases, or in simulations, we can consider wind speed 0 ind v = w . rolling resistance exists in the case of an underinflated tire: roll r zy f f f= (10) cos( ) zy v f m g α= (11) . . . m t m ω wh t wh ω r . arge k wh ω n f ft x v fig. 4. transmission system, wheels, and the acting forces. c. mathematical model of electric vehicle powertrain the model can be seen in figure 5, where tm is the driving part created by the engine and acting on the electric vehicle, j1, j2 are the moments of inertia of the motor and the load, and ��,��� are motor speed and load. fig. 5. the structure of the electric vehicle model. the response on the engine side represents the mechanical system (axle stiffness, damping) and the body model. therefore, it is necessary to have a mathematical relationship between these two components in the electric vehicle system. the model of the system when considering shaft stiffness and damping is: engineering, technology & applied science research vol. 12, no. 3, 2022, 8658-8666 8661 www.etasr.com giang et al.: drive control of a permanent magnet synchronous motor fed by a multi-level inverter … . 1 . w2 w m m gear s h s h sd sd sd s sd e sq sq sq sq sq s sq e sd sd e f j t k t j t t di u l r i l i dt di u l r i l i dt ω ω ω ω ω ψ  = −  = −   = + −   = + + + (12) . . w ss s s s s gear m h t k b k θ θ θ ω ω  = +   = − (13) the mathematical model of the mechanical transmission system from the engine to the wheel hub is shown in figure 6. from figure 6, it is found that: • combined with the model above, we will observe the vehicle's speed and ft's traction force. • this model can be used to design an active damping unit. the parameter of interest is the speed of the motor shaft. fig. 6. mathematical model of the mechanical transmission system from the engine to the wheel hub. d. active damping controller design [20] changing the torque will have a difference between the motor and load angles, leading to oscillation or jerking due to uncontrollable torsion angles. in addition, a sudden step-change in motor torque leads to inertial instability of the motor. this recoil effect occurs due to the excitation of the natural frequency of the powertrain. this excitation is caused by a sudden change in the amount of torque applied, given by: 0 ar 2 s ge m k f k jπ = (14) where ks is the stiffness coefficient of the shaft, jm corresponds to the rotor inertia of the motor, and kgear to the gear ratio of the gearbox. a practical solution to reduce powertrain oscillation is to actively control the torque set on the pmsm (reference torque tref), which needs to be increased gradually by subtracting an amount of torque tdp (calculated from torsion angle and oscillation speed active damping controller) with this method, the rotor speed is measured and fed to an external speed control loop. motor dynamics and the wheel k noise reft dpt mω fig. 7. the control structure of the anti-shock controller. in figure 7, k is the active damping controller that needs to be designed. compared with the kinematics of the electric vehicle, the motor can be considered the first-order inertia. therefore, the parameters included in the active damping unit can be estimated through the abovementioned models. besides, through the mechanical system, the inertial component is added to the motor shaft to change the natural frequency of vibration and the factors that cause the recoil effect. the structure of the active damping controller is shown in figure 8. fig. 8. active damping controller structure. the inertia of the mechanical system and the electric vehicle is converted to the motor shaft. for the mass of the car acting on the wheel, the vehicle's inertia on the wheel's axis is calculated and then divided by kgear in order to be converted to the engine shaft. 2 a 1 1 _ ( _ )* _ tot l ev wheel radius j j j j ev mass gear ratio   = + = +     (15) a set signal that is the speed affected by the jerking phenomenon and the control object does not consider the cause of the jerk . 0 s gear t k = . the difference between the set value and the feedback is that the cause of the draw through the controller will calculate the torque causing the pull. combined with the set torque, it will calculate the correct torque that the motor needs not to jerk. when the difference between the set value and the feedback is zero or td =0, respectively, there is no longer a component causing the jerking. the inertia component of the motor is minimal compared to the inertia of the whole team, so we consider it total ev j j= . the closed engineering, technology & applied science research vol. 12, no. 3, 2022, 8658-8666 8662 www.etasr.com giang et al.: drive control of a permanent magnet synchronous motor fed by a multi-level inverter … transfer function from the above model is synthesized to determine the set parameter pi. equation (16) can express the available transfer function: 2 2 ( 1) ( 1)1 1 (1 ). . p i i h p i ev i ev k t s t s g k k t s j s t j s s + + = + = = (16) with p i ev k k t j = . the closed transfer function is: 2 2 2 2 ( 1) . (1 ) ( 1)1 (1 ) 1 . i h i i k ih i i t s k g k t s kt s ksg t sg s k t s s kt s k k s + + + = = = = ++ + + + ++ (17) according to the standard form of the quadratic function, it has the form: ( ) 2 2 2 2. . . 2. . . n n k n n s g s s s ω ξ ω ω ξ ω ω + = + + w w w w w w (18) where wn ω is the natural frequency of oscillation of the pi controller with kp and ti as follows: w w 2 w 2. . . . p n ev p i n ev i k j k k j t ξ ω ω =   = =  (19) according to the documentation, we chose w 0.71ξ = (corresponds to overshoot 5%), 1 s t s= . 0.71 4 w nw w s t ξ ω ξ =   = ∗ (20) e. stator curent controller design [18, 21] the design of the torque controller for pmsm motors becomes vital in high-efficiency applications. the design process for synthesizing and implementing current drivers for pmsm motors is the same as for current controllers in asynchronous motor drives. to design a torque controller for a pmsm motor, it is necessary to understand the interaction of the motor, inverter, and current controller. consider the gain of the inverter as kr, and the time constant of the inverter as tr, half the pwm carrier frequency duration. if the desired performance of the current control loop is the same as that of the system, then we have a first-order hysteresis step: 1 d i id i k sti ∗ = + (21) the current loop circuit is: { } (1 ) (1 ) (1 ) (1 )(1 ) q a t m q c a r m r a b a m i k k t s i h k k st st k k st st ∗ + = + + + + + + (22) where: 1 a s k r = ; q a s l t r = ; m r i k b = ; m i j t b = ; b t m afk k k λ= the current transfer function is rewritten as: 2 1 2 ( )s ( )s ( )s s (1 )(1 ) q a t m q a b m a t m c m af r m b i k k t i k k t k k t h t t k t k st st ∗ = + + +   ≅   + +  (23) with 1 2 m t t tp p and based on further estimates, 2 2 (1 )st st+ ≅ then the transfer function of the current loop is given by: (1 s ) q i iq i k ti ∗ ≅= + (24) where: 1 2 ;m r i i b t k k t t t k = = (25) iii. svm modulation of the 3-level t-type inverter the 3-phase design of a 3-level t-type inverter is shown in figure 9 [16]. the 3-level t-type inverter works on 2 dc capacitors to divide the input voltage into two components and create a virtual neutral point. properly adjusting and switching semiconductor valves will give a wire voltage in 5 levels: , / 2, / 2,dc dc dc dcv v v v− − + + . thus, the output phase voltage has the form of 3 levels: / 2,0, / 2dc dcv v− + . fig. 9. three-phase t-type inverter structure. a. pulse width modulation svm according to [16], pwm svm is performed according to the following calculation steps: 1) step 1: locate the reference vector the number of sectors s (s = i, ii, ···, vi) is determined by table i. table i. locating the hexagons z1x.z1y < 0 z1x.z1y ≥ 0 z2x.z2y < 0 z2x.z2y ≥≥≥≥ 0 z1x<0 z1x≥≥≥≥0 z3x<0 z3x≥0 z2x<0 z2x≥0 sec iii sec vi sec v sec ii sec iv sec i engineering, technology & applied science research vol. 12, no. 3, 2022, 8658-8666 8663 www.etasr.com giang et al.: drive control of a permanent magnet synchronous motor fed by a multi-level inverter … 2) step 2: determine the duty cycle in this step, the three nearest vectors are determined, based on the three vertices of the modulation triangle, by calculating the duty cycle of the three most similar defined vectors, and by choosing the switching states of the semiconductor valves. with the assumption shown in figure 10, the sum of the output voltage vector is as follows: the vector is represented by the vectors in (27): ( )1 1 2 3v 1 p p pg h g hm m m m= − − + + r r r r (27) ( ) ( ) ( )2 4 3 21 1 1g gh hv m m p m p m p= + − + − + − r r r r (28) 0 mg m h z1y z1x 2 p(kg+1,kh) rrrr 1 v rrrr 2 v rrrr 4 p(kg+1,kh+1) rrrr3 p(kg,kh+1) rrrr 1 p(kg,kh) rrrr fig. 10. synthesizing the output voltage vector from the 3 vectors of the sub-triangle. the coefficients mg and mh are determined as: 1 1 1 1 1 1 g x x x g h y y y h m z z z k m z z z k  = −   = −    = − = −   (29) with 1 1 g x h yk z , k z =   =    . 3) step 3: determine the switching state if taking coordinates ka = k, the coefficient k must satisfy this condition: m 1 m 1k 2 2 − − − ≤ ≤ . the coordinates of the state vector in (a, b, c) coordinate system are given by: 1 1 1 1 1 an x bn x y cn x y k k k k k k k k k k k        ≈ = −          − −    (30) b. algorithm to balance voltage on two dc capacitors using the svm modulation dc voltage unbalance will degrade the inverter output voltage harmonic quality and this is not allowable. therefore, dealing with this problem is necessary for multi-level inverters in general and t-type inverters in particular. the implementation steps are: • step 1: measure the voltages on the capacitor udc1, udc2. • step 2: compare the voltage on the two capacitors • step 3: if udc1 > udc2, discharge voltage on capacitor c1, and charge capacitor c2. • step 4: if udc2 > udc1, then discharge the voltage on the capacitor c2 and at the same time charge the capacitor c2. iv. simulation results based on the pmsm motor modeling, load, active damping controller, torque, and voltage svm pulse modulation for the t-type 3-level inverter are simulated. the plecs simulation of the structure of drive control of a pmsm motor fed by a threelevel t-type inverter for electric vehicles application shown in figure 11. a. simulation results of the t-type inverter based on the above, an electric car control structure powered by a 3-level t-type inverter was built and simulations were conducted with a 3-level t-type inverter and engine parameters. a 3-level t-type inverter was simulated with a resistive load to evaluate the power circuit structure and svm modulation of the system's 3-level t-type inverter. the results of the 3-phase voltage and stator current response, are shown in figures 12-14. fig. 11. the structure of drive control of a pmsm motor fed by a 3-level t-type inverter for electric vehicle application. engineering, technology & applied science research vol. 12, no. 3, 2022, 8658-8666 8664 www.etasr.com giang et al.: drive control of a permanent magnet synchronous motor fed by a multi-level inverter … fig. 12. three phase voltage response. fig. 13. three-phase voltage response. fig. 14. three-phase current response. through the simulation results of figures 12-14, it is found that the output voltage response of the t-type inverter has the form of 3 levels, with amplitude of 350v. phase voltage response is sinusoidal, and thd harmonic distortion is small (thd is 2.88, 1.52, and 2.16 for phase a, b, and c respectively). fig. 15. dc voltage response on 2 capacitors. the simulation results in figure15, show that the dc voltage on the two capacitors is not significantly different with the largest difference ∆vcmax = 3v (0.6%), proving that the balancing algorithm works effectively. b. simulation results of the active damping controller the structure in the plecs simulation of the active damping controller is shown in figure 16. fig. 16. active damping controller structure. to evaluate the effectiveness of the active damping control design for the permanent magnet synchronous motor drive system fed by a 3-level t-type inverter for electric cars, the following simulation scenario was considered: • at time t = 0s, the torque was put equal to 100nm, after 2s it changed to -100nm, and at t = 5s to 100nm. • simulation was held in the case with not a shock absorber. the setting torque is in the form of step (step) and the setting torque is in the form of oscillation generated by the recoil controller. fig. 17. torque response to shock absorber oscillation. through the simulation results in figure 17, it was found that with the design of the anti-shock controller, the torque response set value for the transmission system was built in accordance with the physical properties. c. simulation results of the torque controller to evaluate the efficiency of the torque control design for the permanent magnet synchronous motor drive system fed by a 3-level t-type inverter for electric cars, the following simulation scenario was implemented: • simulation of an electric car powertrain with a physical model using 3-level t-type inverter with an active damping kit. vc 1 vc 2 δ vcmax engineering, technology & applied science research vol. 12, no. 3, 2022, 8658-8666 8665 www.etasr.com giang et al.: drive control of a permanent magnet synchronous motor fed by a multi-level inverter … • at time t = 0s, the torque was put equal to 100nm, after 2s it changed to -100nm, and at t = 5s to 100nm. the stator current response (isq), torque, wheel speed, motor, triple voltage, and thd can be seen in figures 18-20. through the results of figure 19, it is found that the real stator current response isq is close to the set value, but there is still over-correction at the time of transition (speed increase and decrease). fig. 18. current response isq. fig. 19. torque response. the applied torque response has the correct form for the system physics (small oscillations). this proves that the antishock has been promoted. besides, the torque response has the same form as the current isq, the real torque closely follows the set torque including the oscillation. however, the torque response still has over-correction at acceleration and deceleration times, 20% torque pulsation exists, as shown in figure 20. in addition, it can be seen that the motor speed response still has a large adjustment at the transient time and the setting time is not fast. through the simulation results in figure 21, it is found that the output voltage response of the ttype inverter has a 3-level form when the powering pmsm motor drive system used for electric cars has a 3-level form, with a boundary degree 350v. three-phase voltage response is sinusoidal, and thd is small (3.36, 1.92, and 2.88 for phase a, b, and c respectively). fig. 20. motor speed response. fig. 21. phase voltage response. v. conclusion in this paper, the svm spatial voltage vector modulation for a three-level t-type inverter was implemented and simulated, giving 3-phase voltage and stator current response with minor harmonic distortion. in addition, active damping and torque controllers were designed. the active damping controller has been promoted with the same torque response form as the stator current. the actual torque closely follows the set torque, including the oscillation. however, these controllers use a pi controller, so the torque, stator current, and speed responses still suffer from over-throttling, and the timing set is not fast. therefore, the future research will focus on improving the above responses according to the requirements by using nonlinear control methods and combining state variable observers such as tires and road surfaces. engineering, technology & applied science research vol. 12, no. 3, 2022, 8658-8666 8666 www.etasr.com giang et al.: drive control of a permanent magnet synchronous motor fed by a multi-level inverter … references [1] k. bimbraw, "autonomous cars: 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[21] a. zahedmanesh, k. m. muttaqi, and d. sutanto, "coordinated charging control of electric vehicles while improving power quality in power grids using a hierarchical decision-making approach," ieee transactions on vehicular technology, vol. 69, no. 11, pp. 12585– 12596, aug. 2020, https://doi.org/10.1109/tvt.2020.3025809. microsoft word etasr_v12_n5_pp9102-9107 engineering, technology & applied science research vol. 12, no. 5, 2022, 9102-9107 9102 www.etasr.com kumar et al.: autonomous navigation and real time mapping using ultrasonic sensors in nao … autonomous navigation and real time mapping using ultrasonic sensors in nao humanoid robot suresh kumar department of computer systems engineering sukkur iba university sukkur, pakistan suresh@iba-suk.edu.pk abdul baseer buriro department of electrical engineering sukkur iba university sukkur, pakistan abdul.baseer@iba-suk.edu.pk malak majeedullah department of electrical engineering sukkur iba university sukkur, pakistan malakmajeedullah.be17@iba-suk.edu.pk rohibullah department of electrical engineering sukkur iba university sukkur, pakistan rohibullah.be17@iba-suk.edu.pk received: 5 july 2022 | revised: 18 july 2022 | accepted: 20 july 2022 abstract-mapping is an essential and basic requirement for a mobile robot in order to be able to navigate autonomously. this paper proposes a solution for autonomous navigation and realtime mapping using the virtual humanoid robot called nao. the robot navigates through its environment using ultrasonic sensors only and develops a 2-d map of the environment. for implementation and testing, the webots simulator was used. it provides real-time values, modification and designing of the 3-d world arena, and plugins for other parameters control. we test autonomous navigation in differently shaped environments. the proposed mathematical algorithm allows the autonomous navigation of the robot and calculates the position of the robot and the obstacles (if any). the results indicate that the algorithm can localize the robot within the environment whereas the accuracy in localization can be increased by adding a control constant to the orientation of the robot. the results demonstrate that the algorithm is more effective in the rectangular arena than in the triangular and pentagon arenas. keywords-robotics; mapping; humanoid; navigation i. introduction humans can navigate through unknown areas while avoiding collisions with other humans or objects. we are, also, capable to develop maps in our cognition of the known areas, which help us navigate. if we want robots to navigate around the world as humans do, then they must be capable of autonomous navigation, avoid unnecessary contacts with objects or humans, and develop maps. for navigation in outdoor environment, mobile robots are preferred. however, humanoid robots, due to their symmetrical structure to human beings, are preferred for indoor environments. this structure eliminates many singularity constraints and enables the robots to act in an environment designed specifically for humans [1]. in other words, one can say that humanoid robots can take the place of humans in many workspaces as these days robots are performing very well in assisting humans in health, education, research, etc. [2]. for a humanoid robot to perform a task successfully in a real-world environment, stable dynamic biped locomotion is required [3]. also, in order to work efficiently, a robot must know about its environment through maps, its own and obstacles' location in the environment. however, due to limited sensing capabilities, it is challenging for a robot to localize itself and detect obstacles in its environment. gps has been used to determine the location of the robot, however, the gps does not work in indoor environments or produces an error in location due to the absence of line of sight or reflected signal [4]. furthermore, other sensors are required to detect the objects/obstacles in the environment. by adding more and more sensors, the complexity of the algorithms increases, adding delay in real-time response during navigation. in this paper, we propose an algorithm for obstacle detection and autonomous navigation and mapping of a humanoid robot by using ultrasonic sensors. for this purpose, we used a virtual humanoid, the nao robot, for our experiments [5]. nao is a humanoid robot with 25 degrees of freedom, dual vision cameras, force sensors on its feet, touch sensors in the head and arms and a pair of ultrasonic sensors on its chest. apart from that, the robot has internal temperature and position sensors to detect joint motors’ temperature and joint positions. the official vendor of the robot provides a simulator, choregraphe, for the robot. however, for the experiments, we have used a third-party open-source simulator, webots [6]. in comparison to choregraphe, webots provides extra features such as adding obstacles in the environment and tracking the odometry of the robot. the simulator also contains motion libraries to access robot joints and move them through high-level commands. during the motion, the motion library of the robot also controls physical the stability of the robot, thus, the robot does not fall corresponding author: suresh kumar engineering, technology & applied science research vol. 12, no. 5, 2022, 9102-9107 9103 www.etasr.com kumar et al.: autonomous navigation and real time mapping using ultrasonic sensors in nao … while walking. the robot can be programmed to reach a specific point in its environment by walking, in its frame of reference [7]. the purpose of this study is to propose a mathematical algorithm for the nao robot to detect objects using ultrasonic sensors and localize the detected objects in the environment and localize itself using odometry. furthermore, the algorithm creates a 2-d map of the space/environment in which the robot navigates. ii. literature review different researchers have worked on the mapping of nao humanoid robots using the fusion of the different sensors, i.e. ir sensors, rgb camera, tactile sensors, and ultrasonic sensors [8]. authors in [9] proposed a method for autonomous navigation of the nao robot using a fusion of visual and robot odometry. their approach improves robot pose estimation using the fusion of odometry compared to robot odometry. however, fusion makes the algorithm computational expensive. furthermore, the experiment was conducted in a rectangular environment where the robot followed a predefined path, either straight or l-shaped, only, thus limiting the environment and walking length and direction. authors in [10] demonstrated the navigation of indoor environment by nao robot using robot’s odometry. they used the vision of the robot only to confirm the target position and adjust in pose at any other location than the target position. the robot was tasked to reach for a door that contains a specific symbol. the robot navigates straight using odometry until it reaches the target. although the experiment was performed using a real robot, however, it was performed in a controlled environment where no active object was present. this limits the capability of the algorithm to navigate and map in an environment with active objects present. authors in [11] proposed a fuzzy logic-based obstacle avoidance algorithm for the virtual nao robot. the algorithm decides the orientation and walking speed of the robot based on the data from ultrasonic sensors. they performed the experiment using a virtual robot in webots simulator, as we do in this study. however, the scope of their study is limited to obstacle avoidance only, whereas our study focuses on autonomous navigation 2-d mapping, which contains obstacle avoidance as a part of the algorithm. apart from humanoid robots, mobile robots also have been used for testing algorithms for autonomous navigation and obstacle avoidance. authors in [12] designed a fuzzy logic control system to steer a mobile robot for autonomous navigation and obstacle avoidance. however, they considered a simple two-wheeled mobile robot, which reduces the complexity of motion. furthermore, the authors used simulated sensors to detect the position and angle of the obstacles with respect to the robot. the above-mentioned studies either use a fusion of multiple sensors [9, 10] or limited scope of the robot is considered using ultrasonic sensors [11, 12]. furthermore, using multiple sensors increases the complexity in getting data and computational cost. also, dependency on many sensors can cause failure while performing a task, whereas the battery life is affected adversely [13]. iii. methodology two ultrasonic sensors, along with the ultrasonic transmitters, are placed on the chest of the robot. the sensors are in a distance of 0.0832m (8.32cm) apart from each other. each sensor is able to detect 40khz frequency with an effective cone angle of 60o and range from 0.25m to 2.55m [8]. the simulated robot is able to detect any object within this cone angle and range. it returns the distance of the object from the sensors, irrespective of its position. if there is no object within the range and cone angle, then the simulator returns the maximum distance, i.e. 2.55m. since the two ultrasonic sensors return the distance from the object, thus it is challenging to locate the object within the space. the proposed autonomous navigation algorithm lets robots make movements autonomously based on the sensor data. if the sensors detect any object at distance less than 0.8m, then the robot makes a turn, otherwise, it makes a forward move. the robot makes a left or right turn if an object is at a distance less than 0.8m on either the right or the left side respectively. if both sensors detect an object at a distance less than 0.8m then the robot makes a u-turn, i.e., a 180o turn. the distance, 0.8m, is selected for the robot's safety purpose as it should not strike the object while extending its arms. figure 1 shows the flow diagram of the autonomous navigation. fig. 1. flow diagram of the autonomous navigation. in order to locate the object, we assume that both sensors detect the same object at the same distance. in figure 2, considering "o" as the object position, with respect to the center of the robot, l and r are the distance between the object and the robot detected by the sensors on either side and "d" is the distance between the object "o" and centre of the robot is given by (1): engineering, technology & applied science research vol. 12, no. 5, 2022, 9102-9107 9104 www.etasr.com kumar et al.: autonomous navigation and real time mapping using ultrasonic sensors in nao … 2 2 2 2 0.0416 0.0416 2 l r l r d l d r d d d = − = − + = (1) where dl, dr the object's distance from the left and right sensor and d the object's distance from the robot. the constant, 0.0416, in (1) is the distance (in meters) from the center of the robot to the center of the ultrasonic sensor on either side of the chest. in order to locate the object on the map, we need to consider the current position of the robot and its distance from the object. it should be noted that the robot is initially placed along the x-axis and z-axis is on its left side whereas the y-axis is perpendicular to the robot. in order to determine the position of the detected object, we use the distance calculated by both sensors and then add it to the existing position of the robot. the group (2) of equations provides the calculation details. 0 0 0 0 cos( ) cos( ) sin( ) sin( ) ( ) ( ) x x l x x r z z l z z r x x x z z z ol r d r or r d r ol r d r or r d r o average ol or o average ol or = + = + = + = + = + = + (2) where olx, orx the object's x coordinates with respect to sensors, olz, orz the object's z coordinates with respect to sensors, rx, rz, ro the robot's x, z coordinates, initially 0, and ox and oz the object's x, z coordinates. fig. 2. object localization using ultrasonic sensors. the calculation is only made when the object is at a distance less than 0.8m. objects beyond this range are ignored. for an object to be considered in the map, it must be detected by both sensors and ignored if detected by a single sensor. a nearby object is likely to be detected by both sensors. in order to calculate the position of the object, we must know the current position of the robot. the robot's new x and z coordinates after making a motion, i.e. one step, left turn, right turn, or u-turn are given by: 0( ) cos( )x x sr r s r θ= + + (3α) 0( ) sin( )z z sr r s r θ= + + (3b) where ss is the step size of the robot and θ the current angle, +ve for left anf –ve for right. the position of a robot in its environment's cartesian system is usually expressed in the position coordinates (x,y), and the orientation θ [14]. initially, the robot's orientation and position in x and z (instead of y here) are 0. we conducted an experiment for calculating the step size and the angle of the robot when it walks straight or makes a turn as we observed deviation from the gps position provided by the simulator and the actual location of the robot in the environment. we experimentally found the step size and effective angle of the ultrasonic sensors for the calculations in our algorithm. iv. experiments and results in order to observe the robot's motion and behavior in the simulation, we controlled the robot manually by sending commands through a keyboard. first, we calculated the deviation in forwarding motion as mentioned in [10], hence, we designed an arena without boundary walls and obstacles, and allowed the robot to move straight forward on the x-axis only. after running the simulation for 150 steps, we observed that the robot did not follow the straight line but deviated from the desired path and the average deviation was 0.1856o per step. the deviation was calculated by taking the difference between the initial value of the inertial unit, yaw, and the final value. the deviation did not form a regular pattern but was random at every stage. one can get a different deviation value by running the simulation for more than 150 steps. a. step size experiment the distance covered by the robot depends on the step size of the robot. we did an experiment to calculate the step size, which is mentioned in the reference manual as 0.088m. while performing the step size experiment, the initial coordinates were noted down, and then we sent the move forward command through the keyboard and noted down the final coordinates. the change in the distance gives us the step size of the robot and was found to be 0.086553m per step. the average of 150 steps was found to be 0.088m as claimed by the reference manual of the robot. b. rotation angle experiment nao robot can make a turn on either its left or right side depending upon the information received from the sensors. these turns are made using specific motion files designed by the developer in which the joints and their values, which are changed during the turn, are defined. in this experiment, we only considered 3 angles for the turns: 60o turn to the left side, 60o turn to the right side and 180o turn to the right side. the deviation in the 180o rotation was found to be 12o, which means the robot rotates by 192.56o rather than 180o while making a u-turn. for 60o rotation, the deviation was found to be 3o in both left and right turns. the rotation performed was at 57o rather than 60 degrees. the deviations can be observed in figure 3. we tested the algorithm for autonomous navigation, localization and 2-d mapping in 3 different arenas. in the experiments, the robot position provided by the simulator gps and the object position, set by the user, were considered ground truths. the graphs were plotted with calculated positions against the ground truths. the autonomous navigation was limited to 150 steps. the measurements on axes in all the figures are given in meters. engineering, technology & applied science research vol. 12, no. 5, 2022, 9102-9107 9105 www.etasr.com kumar et al.: autonomous navigation and real time mapping using ultrasonic sensors in nao … fig. 3. deviation in the angle while making turns. c. rectangular arena the rectangular arena was created with four walls, whereas the height of the walls was kept the same to that of the robot. the arena is 2.5m×2.5m area in size. the robot started from different points, i.e. the upper right corner, the lower left corner, and the center to observe if there were any changes. no significant change was observed in the results, thus we considered the center point as the starting point of the navigation. figure 4 shows the simulated rectangular arena and the robot. the results of autonomous navigation and localization are plotted in figure 5. the grey color shows the calculated path using the proposed algorithm and the red color path shows the simulator's gps path followed by the robot. the green color represents the wall bounding the robot in the rectangular arena and the blue points on the map show the parts of the wall detected by the ultrasonic sensors of the robot as objects and plotted on the map with respect to the robot’s position using the proposed algorithm. it is evident that the robot's position and orientation are very accurate while moving in a straight direction. however, a deviation can be seen after the robot is taking turns. this confirms the results shown in figure 3. we found that the deviation varies in each turn. in order to remove this error, we calculated an average of the deviations of the turns the robot made during the 150 steps. the results improved after considering this offset in turns, as shown in figure 6. fig. 4. the robot in the simulated rectangular arena. fig. 5. autonomous navigation in a rectangular arena. fig. 6. autonomous navigation after adding an offset. fig. 7. autonomous navigation in the triangular arena. d. triangular arena the experiment was repeated for the same number of steps in a triangular arena. the arena's area size was kept almost the same as that of the rectangular in the previous experiment. engineering, technology & applied science research vol. 12, no. 5, 2022, 9102-9107 9106 www.etasr.com kumar et al.: autonomous navigation and real time mapping using ultrasonic sensors in nao … figure 7 shows the results obtained while navigating through the triangular arena. figure 7 shows that the calculated path and gps path of the robot has no change while moving in a straight direction. however, again, deviation occurred when the robot made turns. e. pentagon arena the arena of the third experiment was pentagon-shaped. in this arena, the robot was also allowed to autonomously navigate up to 150 steps in total. the results are shown in figure 8. fig. 8. autonomous navigation in the pentagon arena. again, it is evident that the paths calculated through the algorithm and provided by the gps are almost the same. however, deviation can again be observed after the robot takes a turn. the deviation kept increasing as the robot took more turns. f. adding a kalman filter the kalman filter is a generic algorithm that is used to estimate a system variable while observing the measurement over time [15]. it is simple, consumes very small computational power, and is used with inaccurate or noisy measurements to estimate the state of that variable or another unobservant variable with greater accuracy. as the nao robot moves, it encounters some deviations which do not form a regular pattern and hence in the long run will produce more deviations against the gps values. we used a simple kalman filter for one dimension which is very effective in computational cost and does not need any memory except the previous state. fig. 9. autonomous navigation using the kalman filter. the modified algorithm, with the kalman filter, was tested in the rectangular arena. figure 9 shows the results of this experiment. ιt is evident that the position calculation is not improved significantly after using the kalman filter. v. conclusion using the webots simulator, we designed a 2-d real-time mapping for a virtual nao humanoid robot in different arenas using only ultrasonic sensors. all the graphs were plotted while the robot was navigating autonomously through the arena and were updated after each step. the results show that our algorithm is very simple in its calculations, yet it determines a more accurate position than the one provided by the gps position of the simulator. some deviation occurred in the position and orientation of the robot from the gps values as the robot made turns. in figure 3, we demonstrated that the robot is unable to make the turn at an exact angle and hence deviation is produced from the expected position. the results demonstrate that the algorithm is able to localize the robot and obstacles in the environment while autonomously navigating through it. this localization is more accurate in the rectangular arena than in the triangular and pentagon arenas, maybe due to the acute angles and more angles in triangular and pentagon arenas respectively. however, further experiments may need to be conducted to build concrete reasoning. we used the kalman filter for one dimension variable to improve the results. however, it was evident that the filter did not significantly improve the results. the reason behind the negligible improvement from the kalman filter is possibly the very small deviation in the calculated path compared to the simulator's gps path. furthermore, our experiment was limited to 150 steps. the filter may be effective for a higher number of steps. anyhow, we do not consider the kalman effective in our case. knowing the exact position of a robot, obstacles, computational cost, backup, and battery life are crucial for a robot to work in any environment. hence we used only one sensor, the ultrasonic sensor, thus reducing computational cost and increasing battery life. this algorithm can also work as a backup if other sensors, such as the camera, fail. in the future, the work can be extended to improve the robot positioning further by improving the kalman filter and its gain. furthermore, the study will be extended to perform the experiments with real robots. references [1] k. p. tee, r. yan, y. chua, and z. huang, "singularity-robust modular inverse kinematics for robotic gesture imitation," in 2010 ieee international conference on robotics and biomimetics, tianjin, china, sep. 2010, pp. 920–925, https://doi.org/10.1109/robio.2010.5723449. 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[15] j. humpherys, p. redd, and j. west, "a fresh look at the kalman filter," siam review, vol. 54, no. 4, pp. 801–823, jan. 2012, https://doi.org/10.1137/100799666. microsoft word etasr_v12_n6_pp9409-9413 engineering, technology & applied science research vol. 12, no. 6, 2022, 9409-9413 9409 www.etasr.com ho et al.: application of neural networks for the estimation of the shear strength of circular rc … application of neural networks for the estimation of the shear strength of circular rc columns viet-chuong ho department of civil engineering vinh university vinh, vietnam vietchuongxd@vinhuni.edu.vn tien-hong nguyen department of civil engineering vinh university vinh, vietnam tienhongkxd@vinhuni.edu.vn thi-quynh nguyen department of civil engineering vinh university vinh, vietnam quynhkxd@vinhuni.edu.vn duy-duan nguyen department of civil engineering vinh university vinh, vietnam duyduankxd@vinhuni.edu.vn received: 5 august 2022 | revised: 21 august 2022 | accepted: 26 august 2022 abstract-this study aims to develop artificial neural networks (anns) for predicting the shear strength of circular reinforced concrete (rc) columns. a set of 156 experimental data samples of various circular rc columns were utilized to establish the ann model. the performance results of the ann model show that it predicts the shear strength of circular rc columns accurately with a high coefficient of determination (0.99) and a small root-mean-square error (4.6kn). the result comparison reveals that the proposed ann model can predict the shear strength of the columns more accurately than the existing equations. moreover, an ann-based formula is proposed to explicitly calculate the shear strength of the columns. additionally, a practical graphical user interface (gui) tool is developed for facilitating the practical design process of the circular rc columns. keywords-artificial neural networks; circular reinforced concrete column; graphical user interface; shear strength i. introduction circular reinforced concrete (rc) columns have been widely used in civil engineering structures. shear strength is one of the most critical values considered in the design process. estimation of this parameter can be performed by experiments or design code provisions. however, experimental tests require time-consuming implementations and are costly. moreover, many studies pointed out that the current design code equations in calculating the shear strength of rc columns may give a large dispersion compared to the experimental results [1-4]. therefore, it is necessary to develop soft-computing models, which ensure the accuracy demands and have less modeling effort and cost. machine learning (ml) models have been extensively applied for various engineering problems since they possess great advantages such as computational efficiency and sufficient consideration of uncertainties [5-14]. numerous studies utilized ml techniques to estimate the responses of rc structures and elements [15-22]. specifically, ml models have been used to predict the shear strength of rectangular rc columns in [4, 23]. additionally, several studies have carried out data-driven models to estimate the shear strength of circular rc columns [1-3, 23]. authors in [1] collected 47 experimental datasets to develop anns for calculating the shear strength of rc columns. they highlighted that the ann model obtained better results compared to the design codes. authors in [2] developed the gene expression programming (gep) and particle swarm optimization (pso) models to predict the shear strength of short circular rc columns with 200 numerical data sets. the results revealed that those ml techniques outperformed other design code formulas. recently, a set of linear and nonlinear equations, based on regression analysis, were proposed in [23] for the estimation of the maximum shear strength of circular rc columns. previous studies mostly proposed ml models for calculating the shear strength of circular rc columns. however, the previous models were not transferred to practical tools, which can be used in design problems. designers and analysts have difficulty in applying those soft-computing models. additionally, the influence of the input variables on the predicted shear strength was not investigated. so far, only the proposed equation of [23] can be practical in the design purpose. in this study, we aim to develop a gui to simplify the calculation procedure of the shear strength of circular rc columns. for that, anns are constructed based on 156 experimental data samples of rc columns. moreover, an ann-based formula for shear strength calculation of the column is proposed in the present study. ii. dataset to construct the neural network model, 156 experimental data samples of circular rc columns were collected from the literature [24]. nine input parameters, including geometric dimensions, reinforcing bar details, material properties, and axial load, need to be provided to predict the shear strength of corresponding author: duy-duan nguyen engineering, technology & applied science research vol. 12, no. 6, 2022, 9409-9413 9410 www.etasr.com ho et al.: application of neural networks for the estimation of the shear strength of circular rc … the columns. geometric dimensions comprise the height of the column (l), the diameter of the cross − section (d). reinforcement details include the longitudinal reinforcement ratio (�� ), the transversal reinforcing bar ratio (�� ), and the spacing of the transversal reinforcements (s). material properties are the yield strength of the longitudinal (��� ) and transversal (���) reinforcing bars and the compressive strength of concrete (�� ). the axial load ( ) is also considered. fig. 1. distributions of the dataset. the distributions of input parameters of the dataset are shown in figure 1. the statistical properties of the experimental results are described in table i. in this table, the 9 input variables to consider in performing ann models are numbered from x1 to x9. iii. existing equations for shear strength of circular rc columns in this study, we employed 5 typical equations, which were proposed in [25-29] for calculating the shear strength of circular rc columns, as expressed in table ii. table i. statistical properties of input variables of the dataset input variable � (mm) (x1) l (mm) (x2) � (%) (x3) � (%) (x4) � (mm) (x5) �� (mpa) (x6) ��� (mpa) (x7) ��� (mpa) (x8) � (kn) (x9) min 152 250 0.46 0.10 9 19 294 207 0.0 mean 402 1429 2.69 1.03 61 37 420 430 736 max 1520 9140 5.58 4.27 305 90 565 1000 6770 sd 175 1234 1.03 0.73 40 15 57 135 1010 cov 0.44 0.86 0.38 0.70 0.65 0.39 0.14 0.31 1.37 sd: standard deviation; cov: coefficient of variation table ii. circular rc columns shear strength equations no. reference expression eq. 1 aci 318 [25] �� = �� + �� �� = 0.166 �1 + ���.� !" #$%�� �� = &'()&*� ; $ is the effective depth of cross section; $ = 0.8# ,is the gross section of the columns. ,�. is the transversal reinforcement area (1) 2 ascheim and moehle [26] �/ = �� + �� �� = 0.3 �1 + ���.� !" 0.8,-%�� 1 = 23µ� , µ is the displacement ductility �� = &'()&*� 567(�9:); $ = 0.8# (2) 3 biskinis et al. [27] �� = �; + 1(�� + �� ) �� = 0.16<=>?0.5; 100�� b∙ c1 − 0.16<de f5; =$ gh ,� %�� �� = ,�.i ($ − $′)��� �; = k3l/m min ( ; 0.55,� �� ) > is the neutral axis depth, $′ is the depth of the compression reinforcement layer; 1 = 1~0.75 �st µ < 1~6 ,� is the concrete area of cross section. (3) 4 moehle et al. [28] �2 = 1(�� + �� ) 1 = 0.7 � 1.15 − 0.075µ � 1.0 �� = 0.5%�� vw1 + �9.xy(z[ !\ f,k] g �� = �/ &'()^k � cot(459); # = # − 2�dseft (4) 5 priestley et al. [29] �x = �� + �� + �; �� = 0.8,-1%�� 1 = 0.29 for µ < 2 1 = 0.29 − 0.12(µ − 2) for 2 < µ < 4 1 = 0.10 for µ > 4 �� = �/ &'()&k � cot(309); �; = k3�/m (5) engineering, technology & applied science research vol. 12, no. 6, 2022, 9409-9413 9411 www.etasr.com ho et al.: application of neural networks for the estimation of the shear strength of circular rc … iv. performance of the neural network model the ann model was used for predicting the shear strength of circular rc columns. an ann model contains three layers: • the input layer, where input parameters are entered. • hidden layer(s). • the utput layer, where the predicting result is obtained. to perform the ann algorithm, the following processes are required. • firstly, the input data are provided to the input layer, the signals are transferred through the connections, from one node (neuron) to another in the network. this procedure is called the forward pass. • secondly, after obtaining the output from the forward pass, it is required to evaluate this output by comparing it with the target using the mean squared error (mse). • thirdly, the network adjusts its weighted values according to a learning rule and using the error. successively iterative adjustments will cause the network to produce the output, which is increasingly close to the target. after enough iterations, the training can be stopped based upon certain criteria. fig. 2. structure of the proposed neural network. figure 2 shows the structure of the ann model, in which 9 variables are defined for the input layer, while 5 neurons are selected for the hidden layer. the predicted shear strength is the output variable of the network. the iteration for optimizing the network and choosing the optimal model is shown in figure 3. it demonstrates that after 9 epochs the process is converged and the mse value is 0.0003462, highlighting a very small error. figure 4 shows the performance of the ann model with all data used. the difference between the test data and the predicted values is trivial, mostly less than 2%. this result implies that the ann model predicted well the shear strength of the circular rc column. fig. 3. selection of the best ann model. fig. 4. performance of all data. various architectures were tried, in which the training ratio changed from 0.6 to 0.85 and the number of hidden layers varied from 1 to 20. as a result, the best ann architecture with the highest value of coefficient of determination (r 2 ) and the lowest value of root-mean-square error (rmse) in training, testing, and validating phase was chosen. this ann model comprises training ratio of 0.75, testing and validating ratios of 0.125, and 5 neurons in the hidden layer. in the current study, we used 3 statistical parameters, which are i/, ijkl, and =20 − de$f>, to evaluate the performance of ann model. the definitions of these indicators are expressed by following equations: i/ = 1 − �∑ (.n3on)pqnrs∑ (.n3ot)pqnrs " (6) ijkl = yf �ug ∑ (vw − sw )/uwx� (7) =20 − de$f> = y/9u (8) where vw and sw represent the target and output of d.z data point, respectively, s̅ is the mean of output data samples, | is the total number of the dataset, and e20 is the number of data statisfying 0.8 � } ~���~���^nz'} � 1.2, in which ��l; and �;��*w�. are the shear strengths obtained from experiments and predictions respectively. table iii shows the statistical parameters of the performance of the ann model. it is found that the r 2 values are very high (i.e. 0.99) and the rmse is very small. additionally, the =20 − de$f>, which represents whether the x1 x2 x3 x4 x5 x6 d h1 h2 h3 h4 v n input layer hidden layer output layer vmax x7 x8 x9 l ρl s fc' fyl p ρs fys h5 feed forward back propagation engineering, technology & applied science research vol. 12, no. 6, 2022, 9409-9413 9412 www.etasr.com ho et al.: application of neural networks for the estimation of the shear strength of circular rc … samples fit the predicted values considering a deviation of ±20% compared with the test results, are close to unity. these results emphasize that the ann model performed very well. a comparison of shear strength between the predicted models (i.e. the 5 existing equations and the ann model) is illustrated in figure 5. it can be observed that the scattering of the regression obtained from the ann model is significantly smaller than that from the other models. this highlights that the developed ann model outperformed the other existing models which were based on design codes and previous studies. table iii. ann performance statistical properties phase r 2 rmse (kn) a20-index training 0.9980 5.490 0.9828 testing 0.9917 6.026 1.0000 validation 0.9807 1.862 1.0000 all data 0.9949 4.596 0.9872 we also developed a gui in matlab to facilitate the prediction of the shear strength of circular rc columns, as shown in figure 6. nine input parameters need to be provided. the shear strength of the column is readily obtained by clicking the start predict button after filling the inputs. it spends a few seconds to achieve the predictive results. the gui tool is provided freely at https://github.com/duyduan1304/gui_cirrc columns. v. ann-based formula and gui for calculating shear strength of circular rc columns to apply the proposed ann model in the design practice, a convenient tool needs to be established. an ann-based formula is proposed, in which the 9 input parameters are considered, as shown in (9) and (10). �maxpredict = 263.10�(�maxu + 1) + 14.00 (9) �maxu = ℎ9 + ∑ ℎw �wxwx� (10) where �w = v=eℎ(dw9 + dw��� + dw/�/+. . . +dw� ��) , and ℎ9,ℎw , and dw� (j = 1÷9) are coefficients. since the equation is based on the ann model, the accuracy is already verified in the previous section. the coefficients of (10) are provided in table iv. fig. 5. comparison between the predictive models and the test results. table iv. coefficients of (10) � �� ��� ��� ��� ��� ��� ��� ��� ��� ��� ��� 0 -0.4004 1 -2.0669 -0.5781 1.6751 1.6594 -0.1383 -0.3201 -0.3521 0.4429 -0.0890 -0.2107 0.8183 2 0.7730 0.0411 4.5936 -3.0741 0.4458 -0.4895 0.5590 1.0053 -1.0579 -1.5919 -0.6568 3 1.2947 -0.4285 -2.9629 3.2788 0.0685 -0.3139 0.7816 0.7325 -0.1291 -0.2473 -1.0247 4 0.2651 0.9082 4.1902 0.1640 0.4885 0.6303 0.1474 0.7892 1.3074 -0.6409 -0.4272 5 -3.4530 -0.1804 1.6534 -2.3002 -0.6223 0.5371 -2.2544 -2.1388 -1.3028 -0.3572 1.6519 fig. 6. gui for calculating the shear strength of circular rc columns. vi. conclusions a practical ann model was developed to calculate the shear strength of circular rc columns using 156 experiment data samples. the performance result of the proposed model was compared to that of 5 published models. the main conclusions of this study are. • the proposed ann model outperforms the existing equations in calculating the shear strength of circular rc columns. the performance of the model is verified using i/ , ijkl , and =20 − de$f> values with respect to the predict-to-test strength ratio. 0 200 400 600 800 1000 0 200 400 600 800 1000 v c a lc u la te (k n ) v test (kn) aci 318 (2014) 0 200 400 600 800 1000 0 200 400 600 800 1000 v c a lc u la te (k n ) v test (kn) ascheim & moehle (1992) 0 200 400 600 800 1000 0 200 400 600 800 1000 v c a lc u la te (k n ) v test (kn) biskinis et al. (2004) 0 200 400 600 800 1000 0 200 400 600 800 1000 v c a lc u la te (k n ) v test (kn) moehle et al. (2002) 0 200 400 600 800 1000 0 200 400 600 800 1000 v c a lc u la te (k n ) v test (kn) priestley et al. (1994) ann model aci 318 [25] ascheim and moehle [26] biskinis et al. [27] moehle et al. [28] priestley et al. 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[29] m. j. n. priestley, r. verma, and y. xiao, "seismic shear strength of reinforced concrete columns," journal of structural engineering, vol. 120, no. 8, pp. 2310–2329, aug. 1994, https://doi.org/10.1061/ (asce)0733-9445(1994)120:8(2310). microsoft word etasr_v12_n6_pp9464-9470 engineering, technology & applied science research vol. 12, no. 6, 2022, 9464-9470 9464 www.etasr.com kundur & mallikarjuna: deep convolutional neural network architecture for plant seedling … deep convolutional neural network architecture for plant seedling classification niranjan c. kundur department of computer science and engineering jss academy of technical education bengaluru, india niranjanckundur@jssateb.ac.in p. b. mallikarjuna department of computer science and engineering jss academy of technical education bengaluru, india putaplar@gmail.com received: 23 august 2022 | revised: 4 september 2022 | accepted: 6 september 2022 abstract-weed control is essential in agriculture since weeds reduce yields, increase production cost, impede harvesting, and degrade product quality. as a result, it is indeed critical to recognize weeds early in their vegetation cycle to evade negative impacts to crop growth. earlier traditional methods used machine learning to determine crops along with weed species, but they had issues with weed detection efficiency at early growth stages. the current work proposes the implementation of a deep learning method that provides accurate results for precise weed recognition. two different deep convolution neural networks have been used for our classification framework, namely efficient net b2 and efficient net b4. the plant seedlings dataset is utilized to investigate the proposed work. the evaluation metrics average accuracy, precision, recall, and f1-score were used. the findings demonstrate that the proposed approach is capable of differentiating between 12 species of a plant seedling dataset which contains 3 crops and 9 weeds. the average classification accuracy and f1 score are 99.00% for our efficient net b4 model and 97.00% for the efficient net b2. in addition, the proposed efficient net-b4 model performance is compared to the one of existing models on the plant seedlings dataset and the results showed that the proposed model efficient net b4 has superior performance. we intend to detect diseases in the identified plant species in our future research. keywords-deep learning; efficient net; machine learning; plant seedling classification; weed recognition; deep convolutional neural networks i. introduction weed control is one of the most challenging aspects of precision farming. weeds harm the plant seedlings and take up the space and nutrients required for the crops reducing crop growth, while exercising herbicides over the crops would spoil the unexpected crops. it is important to identify plant seedlings because doing so can aid in identifying various plant species. when using machine learning algorithms to monitor plant state and even model climate change, a thorough knowledge of appearances, leaflet, and leaf classes in addition to the complete plant is crucial. weed control should begin as soon as crop germination is complete. as a result, optimal weed control is recommended during the seedling stage. automated plant seedling classification using machine learning methods has emerged as an important and encouraging field of research for enhancing agricultural results. modern academics have developed numerous agricultural applications using cuttingedge deep learning algorithms. at the early stages of growth the weeds and crops look similar in appearances when the images of plant seedlings are collected during various lighting conditions, the cnn methods achieved high classification performance. the goal of the current research is to develop a model for a crop-weed discrimination system that employs deep convolution neural networks (cnns) to classify 12 crops and weed plant species. a generic image database with plant seedling classification benchmarks was acquired with the use of a conditional camera. the dataset consists of 12 species at early growth stages [1]. authors in [2] implemented techniques using binary image conversion and svm to differentiate between crop and weed and obtained an accuracy of around 50%. a review work was done in [3] in the introduction of artificial intelligence for crop and weed management. authors in [4] used deep learning architectures, namely resnet, vgg16, and inceptionv3 for banana disease detection. authors in [5] utilized prediction models on cnn, svm, and knn for apple classification and recognition. authors in [6] conducted research regarding plant image classification tasks, for instance classifying maize plants and weeds by utilizing segmented images at initial stages of growth, with a training accuracy of 97.00%. image processing and identification have been the subjects of [7-8]. weed identification is challenging to ambiguous crop constraints and differing rocky or sandy identities, and long established classification techniques are most likely to fail in this task [9]. authors in [10] proposed a classification model for plant seedlings. the authors attempted to improve classification efficiency by combining seedling and individual leaf classification. bayes belief integration was used for classification design. a deep encoder-decoder cnn was updated with a 14channel image containing vegetation index values for segmentation to solve crop-weed classification consisting of sugar beet plants and weeds in [11]. in [12], a cnn network was able to determine unsupervised feature characterizations from 44 different plant species with high accuracy. in [13], instance segmentation was utilized to identify crops and weeds. corresponding author: niranjan c. kundur engineering, technology & applied science research vol. 12, no. 6, 2022, 9464-9470 9465 www.etasr.com kundur & mallikarjuna: deep convolutional neural network architecture for plant seedling … the authors were able to classify crops and weeds with an accuracy of 60%. for a large dataset to obtain good accuracy we need graphical processing units, in addition, during the training operation, continuous modifications of the training parameters are needed in order to obtain a balanced output [14]. an image classifier model using deep cnns was used to determine the accuracy of cnn, svm, and knn in [15]. author in [16] proposed a cnn framework for classifying plant seedlings. the main topic of the endeavor involves classifying young plant seedlings using a cnn while monitoring accuracy and precision metrics. a hybrid architecture using alex net and vgg net was implemented to determine the model accuracy and f1 score for a plant seedlings dataset with 94.38% average accuracy. in [17], in order to classify images of crop and weed seedlings, 5 pretrained convolution network techniques were used, i.e. resnet50, xception, mobilenetv2, vgg16, and vgg19. resnet50 architecture produced the best results scoring 95.23% testing accuracy [17]. weeds and crops were classified using residual network 101 in [18], obtaining an overall accuracy rate of 98.47% on the validation set and 96.04% on the test set. cnn frameworks for plant seedlings classification by using resnet50v2, mobilenetv2, and efficient net b0 architectures were implemented in [19]. the efficient net b0 method provided an average f1-score of 96.26% and an accuracy of 96.52%. a limitation of this work is that the authors would have added more layers by increasing depth or resolution to obtain maximum accuracy. in this paper, a novel method that fully trains a network is presented. the proposed efficient net b4 model is used to provide better accuracy for image classification by compound scaling the dimension of network width, depth and resolution. for this experiment, we have used an i7 processor with nvidia rtx 3080 ti gpu and other supporting frameworks such as keras and tensor flow for the classification and analysis of the images of plant seedlings. ii. materials and methods a. dataset the plant seedling dataset for training, validation, and testing is described in this section. the dataset was obtained from computer vision and biosystems signal processing group, aarhus university, an open-source website which contains plant seedling images. the dataset contains 5541 plant seedling images, namely 833 test images, 833 validation images, and 3875 training images were acquired, each representing a different stage of growth for all the 12 considered species [1, 19]. b. dataset distribution the plant seedling dataset is split into 3 sections: testing (15%), validation (15%), and training (70%). the testing set is used in evaluating the performance of the trained model. we made sure that testing and validation sets had no duplicates. the plant seedling dataset distribution is displayed in table i and the test set of 12 plant seedling species is shown in figure 1. table i. plant seedling dataset with class wise distribution class species training validation testing total 1 black grass 217 46 46 309 2 charlock 316 68 68 452 3 cleavers 235 50 50 335 4 chickweed 497 108 108 713 5 common wheat 177 38 38 253 6 fat hen 376 81 81 538 7 loose silky-bent 532 115 115 762 8 maize 179 39 39 257 9 scentless mayweed 425 91 91 607 10 shepherd's purse 192 41 41 274 11 small-flowered cranesbill 404 87 87 578 12 sugar beet 325 69 69 463 total images 3875 833 833 5541 fig. 1. test set of the 12 plant seedling species. c. test data set the motivation of our research work was to investigate the efficient net [19, 27] architecture because this model outperforms other cnn models in terms of accuracy and efficiency. the efficient net model has received little attention when considering datasets of plant seedlings. in this paper, a new mobile-size baseline is established. efficient net, compound scaling, and neural architecture are used. efficient models introduced a new baseline network (b0-b7) to provide better accuracy for image classification by compound scaling size (e.g. depth, width, and resolution) of the network by having a balanced output for the above parameters. a compound scaling technique is suggested in [19] that consistently scales width, depth, and resolution according to a set of guiding principles. they suggest the following formula: �. �. �. ��. � � ≈ 2 � ≥ 1, � ≥ 1, � ≥ 1 where depth: = � �, width: � = �� , resolution: � = � � , � is a user-defined coefficient that regulates the resources (e.g. flops, or floating point operations) available for model scaling, and α, β, γ allocate resources according to depth, width, and resolution. a convolution operation uses a certain amount of flops in relation to , � � and � �. in the equation above, engineering, technology & applied science research vol. 12, no. 6, 2022, 9464-9470 9466 www.etasr.com kundur & mallikarjuna: deep convolutional neural network architecture for plant seedling … this information is reflected. for each new �, the number of required flops increases by 2�. the authors scaled it up using the following method starting with efficientnet-b0:  fix � � 1 . we assume that the resource is twice as available at any given scaling step as it was at the one before.  perform a quick grid search across α, β, and γ to ensure that the restriction in the above equation is not violated.  the authors discovered that the values α=1.2, β=1.1, and γ=1.15 perform optimally.  fix α, β, and γ, then scale up the efficientnet-b0 with various � to get recent scaled networks, i.e. efficient net b0-b7 [27]. table ii. modifications in νetwork αrchitecture layer (type) output shape parameters efficient νet β4 (functional) (none,7,7,1792) 17673823 global_max_pooling2d_5 (global max pooling2d) (none,1792) 0 flatten_6(flatten) (none,1792) 0 dense_12(dense) (none,1024) 1836032 batch_normalization_4 (batch normalization) (none,1024) 4096 dropout_5(dropout) (none,1024) 0 dense_13(dense) (none,512) 524800 batch_normalization_5 (batch normalization) (none,512) 2048 dropout_6(dropout) (none,512) 0 dense_14(dense) (none,128) 65664 batch_normalization_6 (batch normalization) (none,128) 512 dropout_7(dropout) (none,128) 0 dense_15(dense) (none,12) 1548 total parameters 20,108,523 trainable parameters 3,237,772 nontrainable parameters 16,870,751 d. the proposed methodology in the proposed methodology, the first step is to obtain a plant seedling data set. once we acquire the image dataset, the next step is to pre-process the raw images in order to keep only relevant information. the preprocessing steps consist of resizing the image into 380×380 resolution for efficient net b4 and 280×280 resolution for efficient net b2 model, sharpening the image to highlight fine details by removing blurring and highlighting edges, and applying segmentation to the objects of interest, which are the leaves of the plant, and finally applying masking. after preprocessing we split the dataset into training, validation, and testing parts with ratio of 70:15:15 and passed it into a custom designed model using the efficient net b4 as the base model. the modified efficient net b4 can be used in many different ways:  training the whole efficient net architecture.  applying transfer learning paradigm to extract features from the pre-trained efficient net on plant seedling dataset.  applying the transfer learning paradigm along with finetuning of the architecture by adding a few more layers like pooling, flattening, and normalization followed by a few dense layers and a final layer with softmax activation function. fig. 2. the proposed methodology. e. pipeline for image-processing for training, each image in the plant seedlings dataset was scaled to 380×380 (resolution scaling) for efficient net b4 and 280×280 for efficient net b2. we synthetically increased the dataset size by using image augmentation through rotating, zooming, and horizontal and vertical flipping. gaussian filter was first used to smooth the image. as can be seen, the background of the plant images has numerous pointless rockformed borders. because these edges would only provide background noise, we converted the values of the discontinuous pixels into continuous ones. our next step was to identify the relevant information in the image and remove any unnecessary background. to classify an object, a binary image that we wish to represent must be created. we will just need to look at the beneficial object's shape, making the classification procedure considerably simpler. to accomplish this, we converted the rgb image to the much more useful hsv format, which makes it much easier to discriminate between colors. there is now no overlap because the object can be easily distinguished from the background, but still there is some noise and flaws in the image, so as a follow-up, we slightly eroded it. we rescaled all images, created a mask for every image and then applied segmentation on each sample. each image in the dataset was subjected to the processing pipe line by a function that we defined which outputs the processed dataset. figure 3 shows the pre-processed images of the training model. fig. 3. pre-processed images of plant seedlings. engineering, technology & applied science research vol. 12, no. 6, 2022, 9464-9470 9467 www.etasr.com kundur & mallikarjuna: deep convolutional neural network architecture for plant seedling … f. transfer learning in order to complete tasks that are related to one another, transfer learning is another used high-level concept. we could not directly apply the pre-trained weights for interpretation and expect excellent performance due to the different fields of the dataset images. as a result, we carried out refinement to customize towards the original domain of the images. for an efficient net b4 model, few more layers were added and minor parameter adjustments to the trained model were made in this step. there are numerous approaches to fine tuning. these incorporate the use of a pre-trained design for feature extractors out of which features were fed to each classifier, for fine adjustment to all or a few parameters at the last number of layers in the pre-trained modeling. iii. implementation we cover the implementation and training of efficient net b4 and efficient net b2 in this section to ensure reproducibility. a. learning rate change the learning rate is classified by the best significant hyperparameters to obtain quick and reliable training for neural networks. a large range of the loss gradient is applied to the latest parameters in order to alter them in the orientation of the reduced loss. in order to do this, the network's learning rate was linearly increased in a certain range of values after each network had been trained for a few epochs. we observed the change in validation loss by decreasing the learning rate from 0.01 to 0.001. after this change, the validation loss is considerable. the final plot of the validation loss against epoch is displayed in figure 4. b. fine tuning efficient net b2 all layers in the efficient net b2 were trained using gradient updates and a learning rate of 0.001. we applied stochastic gradient descent optimizer for custom dense layers and a default decay rate for this implementation. c. fine tuning efficient net b4 since training was unstable, we have added a few more layers for efficient net b4. based on multiple runs with hyper parameter tuning as well as grid search techniques, we found the best parameters suitable for our problem for efficient net b4 architecture with a learning rate of 0.001, rho value of 0.9, epsilon of 1e-08 and default decay values. we applied adam optimizer for the custom dense layers. d. performance evaluation metrics the effectiveness of any classification model cannot be assessed with common criteria. the performance metrics considered for each model are accuracy, precision, recall, f1 score, support, and confusion matrices. e. confusion matrix the confusion matrix provides details about the classifier's errors, including the kinds of errors that are occurring. the performance of a classification model's predicting power was compiled in an n×n table (n represents the number of classes). it is a matrix that shows the relationship between the model's categorization and its real label (predicted label). a correct estimation of an image's class is referred to as a true positive (tp). when the model suggests an image's class incorrectly, it produces a false positive (fp). whenever the model correctly estimates a negative class of the image, it produces a true negative (tn). false negative (fn) will occur when it incorrectly predicts a negative class of an image. the accuracy score is applied to assess our model's performance wherein tpc, fpc and fnc signify true positives, false positives and false negatives. pc indicates a class' specific precision metric that says, out of all points that are predicted to be positive, how many are actually positive. rc represents a class specific recall metric that says, out of all positive points, how many are actually positive. n represents the overall collection of images, whereas nc denotes the overall collection of images of class c and c denotes the overall collection with regard to classes. s denotes the mean of average weighted (f1) over all cross validation folds. p� = ��� ������� (1) r� = ��� ������� (2) f�,� = 2 ���� ����� (3) !"#$%&'($) *+�, = ∑ ./ . . +�,0 0 01� (4) 2 = � .3456 ∑ !"#$%&'($) *+�, .3456 %1� (5) iv. results and discussion we used (1) to (4) to evaluate the performance. the topmost validation accuracy obtained on efficient net b4 model is 99% whereas for efficient net b2 is 97%. figures 4 and 5 show the accuracy and loss curves of training and validation sets for efficient net b4 and efficient net b2 respectively. fig. 4. efficient net b4 model performance. engineering, technology & applied science research vol. 12, no. 6, 2022, 9464-9470 9468 www.etasr.com kundur & mallikarjuna: deep convolutional neural network architecture for plant seedling … fig. 5. efficient net b2 model performance. (a) (b) fig. 6. plant seedlings classification report of (a) efficient net b4 and (b) efficient net b2 on the test data set. the performance metrics on the test dataset for precision, recall, f1-score, and support are depicted in figure 6. the average weighted accuracy of the efficient b4 model is 99% whereas the efficient net b2 model has 97%. for efficient net b4, classes black grass and loose silky bent have f1-score equal to 0.88 and 0.95. for the remaining plant species the f1score is 1 indicating that all the plants are correctly classified. for the efficient net b2 model, classes black grass, common wheat, fat-hen, loose silky bent, and sugar beet have f1-score of 0.85, 0.88, 0.98, 0.94, and 0.97 while the remaining plant species are correctly classified. figures 7 and 8 demonstrate the confusion matrix for the test data set in support of the 12-class configuration of the plant seedlings dataset during testing. the plant seedling dataset consists of 12 species representing 12 rows and 12 columns of the matrix, which analyzes correct classification using 833 test images. in the confusion matrix, the rows indicate the current classification, while the columns indicate the predicted score. from the confusion matrix of the efficient net b4 model we can infer that 6 images of black grass and 5 images of loose silky bent are misclassified while the remaining plant species are predicted correctly. for the efficient net b2 model, 5 images of black-grass, 4 images of common wheat, 6 images of loose silky bent, and 4 images of sugar beet are incorrectly classified and the remaining are classified correctly. the conclusion is that the efficient net b4 model performed better than the b2 model. fig. 7. confusion matrix of the plant seedling test dataset of efficient net b4. fig. 8. confusion matrix of the plant seedling test dataset of efficient net b2. loss engineering, technology & applied science research vol. 12, no. 6, 2022, 9464-9470 9469 www.etasr.com kundur & mallikarjuna: deep convolutional neural network architecture for plant seedling … the proposed efficient net b2 and efficient net b4 methods were compared with existing methods [16-19] for the plant seedlings dataset and the results are shown in table iii. we can see that the proposed efficient net b4 method outperforms the latest competitive approaches in terms of accuracy and f1-score. table iii. method comparison on the plant seedling dataset ref. method accuracy (%) f1-score (%) [16] alexnet + vggnet 94.38 93.57 [17] resnet 50 95.23 95.00 [18] residual network 101 98.47 95.72 [19] efficient net b0 96.52 96.26 proposed efficient net b2 97.00 97.00 efficient net b4 99.00 99.00 figure 9 depicts examples of charlock and sugar beet images of the test set that are correctly classified with the proposed efficient net b4 model. (a) (b) fig. 9. correctly classified charlock and sugar-beet images. figure 10 depicts loose silky-bent and black-grass, images which are misclassified plant seedling images of weed species, because they almost look similar. black grass class contains 6 images and loose silky bent class contains 5 images which are misclassified. (a) (b) fig. 10. incorrectly classified loose silky bent and black grass images. v. conclusion in this paper, deep convolution neural networks were investigated for identifying plant species at early growth stages. the proposed efficient net b4 model for plant seedling classification dataset which contains 12 species of crops and weed achieved a high level of accuracy and average f1-score rate, precision, and recall of 99.00%. when compared with other known methods, the proposed model shows a significant increase in accuracy in the considered plant seedlings dataset. nevertheless, throughout our investigations, we discovered that images from two specific groups, black-grass and loose silkybent, had been incorrectly classified. there are some limitations in distinguishing crops and weeds during the seedling stage: (a) image resolution is insufficient to allow differentiation among susceptible soil, plant seedlings, and weeds, (b) there are spectral and apparent similarities in the initial stages, as there is a competition among weeds and useful crops, and (c) the detection method and the soil background reflectance overlap. the proposed model can be further extended and improved with the use of a larger dataset. references [1] t. m. giselsson, r. n. jorgensen, p. k. jensen, m. dyrmann, and h. s. midtiby, "a public image database for benchmark of plant seedling classification algorithms." arxiv, nov. 15, 2017, https://doi.org/ 10.48550/arxiv.1711.05458. 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and electrical engineering university of transport and communications hanoi, vietnam vothanhha.ktd@utc.edu.vn received: 20 april 2022 | revised: 7 may 2022 and 24 may 2022 | accepted: 8 june 2022 abstract-this article presents a slotless self-bearing motor (ssbm) with a six-phase coil stator instead of an iron core. the rotor consists of a permanent magnet and an encased iron yoke. the magnetic forces caused by the interplay between the stator currents and the magnetic field govern the rotational speed and radial position of the rotor. an ssbm mathematical model and its control method are also included in this study. this motor is controlled by field-oriented control. theoretical analysis of magnetic force and moment characteristics is performed, and a control approach is provided. sliding-mode control is a control technique that is simple, and effective and is used to assist the control system in approaching the reference value. it is also widely utilized to control the position and speed of the motor. the findings were constructed and validated using experimentconfirmed analytical data to prove the proposed control strategy. keywords-foc; slotless self-bearing motor; sliding mode control; pi; pid i. introduction the quality of a powertrain depends on the engine. creating a transmission system capable of smooth speed change with a wide adjustment range and high accuracy of the adjustment quantity in static mode is necessary to create a working area with negligible error. working with any transition process must achieve increased stability, and the system must be able to respond quickly to adjustment requirements [1-3]. all these make more stringent the requirements on powertrains. also, special needs for intelligent and fast control in synchronous motors will be significantly enhanced. conventional motor structures have been greatly improved. however, there are still disadvantages of an engine with a steel core, such as the existence of pulsating torque and low operating frequency [35]. so, the steel coreless self-lifting motor is a significant invention that minimizes the frictional force between the rotating shaft in the machine part, helping the effortless movement for better performance in motion applications of engineering disciplines [6-8]. brushless motors have many advantages such as high speed, fast acceleration, and constant torque (figure 1) and higher continuity, low noise, and less electromagnetic interference (figure 2) [9-11]. fig. 1. comparison of the engine structure with and without steel core. the cogging torque can be reduced by improving the stator grooves and the magnet pole exerts. a 6-phase coreless steel lifter motor comprises of a cylindrical two-pole magnet, a surrounding iron shell, a rotating shaft, and an aluminum base that connects the engine's components. the distance of the air gap between the magnet and the iron case remains constant to ensure a stable magnetic field of the magnet pole. as a result, the magnetic lines of force leaving the surface of interest tend to rotate towards the south pole. in other words, the magnetic lines of the staff will come out perpendicular to the tangent at that point, creating an even distribution of the magnetic field between the rotor and the stator. in addition, in this motor, the increase in the number of teeth on the stator makes for more interaction, and they create pairs of forces that cancel each other, thereby also reducing the cogging torque [11-13]. the ssbm in the experimental set motors is shown in figure 3. corresponding author: vo thanh ha engineering, technology & applied science research vol. 12, no. 4, 2022, 8942-8948 8943 www.etasr.com nhan et al.: an experimental study on the control of slotless self-bearing motor using nonlinear … (a) (b) fig. 2. torque comparison of two types of motors: (a) motor with steel core, (b) motor without steel core. fig. 3. the ssbm in the experimental set motors. this motor creates torque [14-16] and lift will be done by giving the supplied current. thus, lorentz force is generated. according to newton's theorem, since the coil is at rest, the reaction forces acting on the motor rotor have opposite directions. this force consists of two components, one that generates lift and the other that creates rotor torque. when any current (positive or negative) is applied to a phase, a pair of forces is generated whose direction depends on its position relatively to the rotor. thus, the torque and lift can be controlled by varying the amplitude and phase of the current in the stator. consequently, the construction of the controller is required to improve system quality. a pi controller handles speed control, whereas a pid handles displacement position control [17-23]. the actual speed is close to the reference value and reacts effectively. when there is a load torque, the controller boosts or cuts the current to help minimize the divergence. the phase stator currents take on a sinusoidal shape following the speed change. in addition, the actual speed is responsive and close to the reference value. the controller boosts or reduces the current to minimize divergence when a load torque is present. as a result, the phase stator currents take on a sinusoidal shape when the speed changes. on the other hand, the total rotor displacements jump from 0s to 0.1s. this signifies that the rotor is still centered in the stator. as a result, the controller promptly corrects the align deviation when applying external pressures. however, the rotor's speed and displacement overshoot during the transition point. consequently, it has been reported that a sliding mode control (smc) system could be used to improve control quality. smc is a control method that forces the system's trajectory onto the sliding surface using a high-speed switching control rule. sliding-mode control is widely used in practical applications [24-27], because of its benefits, such as ease of implementation, finite-time convergence, excellent dynamic responsiveness, and robustness against parameter variations and disturbances. furthermore, the stability of sliding-mode control may offer flawless tracking even when parameters or model errors are present, based on the design of a bearingless motor's smc and dq axis current regulation [28-34]. consequently, this ssbm outperforms the pid controller in position and speed control. thus, the sliding-mode control will be chosen to design this motor's speed and position controller. ii. mathematical model the stator currents are supplied as [17]: , b,e c,f cos( ) sin( ) cos( ) cos( 2 / 3) sin( 2 / 3) cos( / 3) cos( 4 / 3) sin( 4 / 3) cos( 2 / 3) a d d q m m d q m m d q m m i i i a i i i a i i i a ψ ψ φ ψ π ψ π φ π ψ π ψ π φ π  = + ± = − + − ± +  = − + − ± + (1) where id is the direct axis current, iq is the quadrate axis current, ψ is the angular position of the rotor, am is the amplitude of the motor current, and m φ is its phase. we combine (1) with the stator winding properties to calculate the total force acting on the rotor and the generated torque. the rotating torque and bearing forces in case of turns are: { } { } 0 0 0 0 0 sin( / 4) sin(2 ) cos(2 ) cos(2 ) sin(2 ) nm m m m x nb b d q y nb b d q k k a f k k i i f k k i i τ φ ψ θ π θ θ θ θ  = − + + =− −  = + (2) where τ is the rotating torque, x f and y f are bearing forces, b is the amplitude of the magnetic flux density, lp is the length of the parallel part of the winding, lt is the length of the serial part of the winding, n is the total number of turns, and θ0 is the angular position of the +a-phase winding. it must be an odd number so that the wires do not overlap. from (2), the mathematical model of the ssbm is completely constructed with force and torque equations. next, the control system for the ssbm will be designed. engineering, technology & applied science research vol. 12, no. 4, 2022, 8942-8948 8944 www.etasr.com nhan et al.: an experimental study on the control of slotless self-bearing motor using nonlinear … 8(6 3 2 ) 3 2 12 3 ( 1) 1 2 cos 2 cos 2 2 cos 3 3 2 3 1 2 cos 2 2 cos 4 2 cos ( 1) 3 3 3 m p t b p t nm nb k l l rb k l l b n k n n n k n n n n π π π π π π π π  −  =− +      =− +         −    = + + + +                         = + + + + −               ⋯ ⋯     (3) iii. designing the control system a. control structure when the angular position of the rotor can be obtained, the stator current can be calculated by (1) and the force and torque by (2). the θ0 is the angular position of the +a-phase winding so if the +a-phase coincides with the x-axis then θ0=0. φm is the phase of the torque current and depends on control strategy. to conduct the clear control algorithm, we can assume that 0 0θ = and 4 m π φ ψ= + or 0 4 2 m π π φ ψ θ− + + = . then, (2) becomes: nm m m x nb b q y nb b d k k a f k k i f k k i τ = =  = (4) it is easy to see that the rotating torque is produced by am and the bearing force is produced by id and iq. therefore, the rotating torque can be controlled by am and the bearing force by id and iq. on the other hand, the two components, force and torque, are mathematically independent from each other, thus, the control structure is introduced as shown in figure 3. the smc is used for both the speed control and the displacement position control. smc is a well-known powerful control scheme which has been successfully and widely applied for both linear and nonlinear systems. in this study, the linear sliding mode which uses the linear sliding surface has been used to design the speed and position controller. settings: t n m m k k k= and fx fy nb bk k k k= = , and (4) becomes: t m x fx q y fy d k a f k i f k i τ = =  = (5) the dynamic equation of the rotor is: l d t j dt ω τ− = (6) l f f m a− = (7) where m is the weight of the rotor, a is the acceleration of the rotor, tl is the load torque and fl is the load force. b. designing the position controller assuming the effect of load torque and load force are the same as external disturbances, the mathematical model of the motor can be expressed as [17]: fx q fy d t m k x i m k y i m k a j ω  = =  = ii ii i (8) the parameters of the two equations that generate the bearing force are the same. thus, a sliding controller for both positions along the x and y axes is designed. the settings in the model in (8) are: , , fx fy f d f d q f q k k k u k i u k i m m = = = = (9) we suppose that the controlled object is only a double integral 1/s 2 , the smc is used for calculating parameters ud and uq and then we return to calculate the current parameters id and iq. the controlled object 2 1 / s is expressed as follows: 2 xdx udt   =    and 1y x= (10) where 1 2 x x x   =     is the state vector, y is the output signal and d q u u u= = is the control input. the most commonly used sliding surface is the linear sliding surface which is: 1 0 1 2 ( )s e a e e= + and 1 2 de e dt = (11) where e1 is the position error and a0 is a positive design parameter chosen such that the polynomial 0 ( )p s a s= + is a hurwitz polynomial which has real parts of the roots smaller than zero. to guarantee the stability of the system, the lyapunov stability theory is used. the lyapunov function has the form of: 2 1 1 1 ( ) 2 v s s= (12) then, the control design task becomes to make 1 ( ) 0v s • < in the neighborhood of the equilibrium. thus, we have: 1 1 1 1 1 ( ) 0 0 sgn( (e)) 0 dv s ds ds s s dt dt dt < ⇔ < ⇔ < (13) on the other hand: engineering, technology & applied science research vol. 12, no. 4, 2022, 8942-8948 8945 www.etasr.com nhan et al.: an experimental study on the control of slotless self-bearing motor using nonlinear … 1 1 2 1 0 0 ds de de de a a u dt dt dt dt = + = − (14) thus, (13) becomes: 1 0 1 ( ) sgn( (e)) 0 de a u s dt − < (15) 11 0 1 0 ( ) 0 0 ( ) 0 if s ede a u if s edt < >⇔ − = > < (16) 1 0 1 1 0 1 ( ) 0 ( ) 0 de a if s e dt u de a if s e dt > >⇔ = < < (17) choosing the control input u: 1 0 0 1 0 sgn( (e)) 0 de u a k s k dt = + ∀ > (18) from (9) and (18), the currents id and iq are calculated as: 1 0 0 1 0 0 sgn( (e)) , 0 d q f l de a k s dt i i k a k f f ma + = = ∀ > − = (19) thus, (19) is the smc used for the position controller. next, the speed controller is calculated correspondingly, but it has a difference from the reference signal. c. designing the speed controller it is similar to the position controller, with settings [17]: t t k k j ω = and t mu k aω ω= (20) the controlled object is still a double integral 21 / s , but the feedback signal is state variable, thus, the sliding surface is chosen as: 1 0 1 2 0 1 s (e) de b e e b e dt ω ω ω ω ω = + = + (21) where e2ω is the speed error and b0 is a positive design parameter. similar to the position controller, we have: s 0 sgn( ( )) 0 ds ds s e dt dt ω ω ω ω < ⇔ < (22) 1 0 1 0 ( ) 0 ( ) 0 de b if s e dt u de b if s e dt ω ω ω ω ω  > > ⇔ =   < <  (23) choosing the control input uω as: 1 0 .sgn( ( )), c 0 de u b c s e dt ω ω = + ∀ > (24) from (20) and (23), the current am is calculated as: 1 0 0 . sg n ( ( )) , 0 m t d e b c s e d t a b c k ω ω ω + = ∀ > (25) thus, (25) is the smc which is used for the speed controller. the control system was designed from (19) and (24). however, to reduce the chattering due to the sgn( )s function, the sign function is replaced by the sat( )s function, which is defined as follows: sgn( ) | | sat( ) | | s if s s s if s ε ε ε >  =  ≤  (26) where ε is the boundary layer thickness. however, although the sliding mode can be guaranteed outside the ε , it cannot be guaranteed inside it. this replacement can cause trajectory errors. to reduce both chattered phenomenon and trajectory error, a saturation-integral relay function (satpi) is proposed which is defined as: 0 sgn( ) | | satpi( ) ( ). | | t i t s if s s s k s t dt if s ε ε ε >  =  + ≤   (27) where ki is positive integral coefficient, t0 is the time when the system state starts to reach ε . iv. experiments and results a. setup the entire experimental table is shown in figure 4. control desk software was used to simulate models, build user interfaces, display process variables on screen, performing controller tuning, and monitoring objects. table i presents the motors and the smc controller parameters. table i. simulation parameters motor parameters symbol value motor weight m 0.4 kg rotor radius r 0.022 m stator radius r 0.027 m flux maximum of the rotor b 0.59 t length of the parallel part lp 0.008 m length of the serial part lt 0.006 m the total number of turns n 55 controller parameters symbol value current-torque coefficient km -9.7x10 -4 current-torque coefficient knm 52.5 current-force coefficient kb -0.0277 current-force coefficient knb 45.49 position controller parameter a0 150 position controller parameter k0 100 speed controller parameter b0 92 speed controller parameter c 56 engineering, technology & applied science research vol. 12, no. 4, 2022, 8942-8948 8946 www.etasr.com nhan et al.: an experimental study on the control of slotless self-bearing motor using nonlinear … fig. 4. images of the experimental version. b. results the first tested controller was the position controller. the initial position of the rotor is x = 0.5mm, y = 0.5mm. at 0.8s the position controller was activated. the results are shown in figure 5. at this point, the rotor position was brought back to the equilibrium position after only 0.12s, the currents id and iq changed respectively and were limited from -1a to 1a. after the position controller worked, the motor was brought to the balance position. next, the rotor shaft was aligned with the origin, increasing the motor speed from 0 to 4500rpm. the results of the speed test response and change of rotor position are shown in figure 6. the position response in the x and y axes has a slight fluctuation, but with minimal value. the most significant position deviation is only 0.1mm, thereby showing that the position controller works well even when the engine is running—motion at high speed. (a) (b) fig. 5. experimental results of the position controller. (a) x, y axis position response (mm), (b) id,iq current responses. (a) (b) fig. 6. position response when speed changes. (a) x, y axis position response (mm), (b) speed change from 0 to 4500rpm. the line red is the reference response, and the black line is the real response. fig. 7. response to position and speed in the presence of applied resistance. to demonstrate that the position controller and speed controller work independently when the motor is operating at 4000rpm, a sufficient force is applied in both x and y axes of the engine. the actual speed response is close to the set speed response, without overturning, and the time it takes to set the speed is short (t=2s). at this point, the position error occurs, and immediately after that, the position controller suppresses the error and returns to 0rpm. the motor speed does not change, showing that speed and position controllers operate independently. figure 8 shows the results of testing the rotor's trajectory at rotational speeds of 2000rpm and 4000rpm. again, the maximum orbital deviation is approximately 0.12mm, and the engine operates stably. figure 9 depicts the position deviation trajectory of the rotor along with the axis ox (e1x) and its derivative. figure 9(a) shows the position error trajectory when the position controller starts to operate. at this time, the position error moves from 0.5mm to 0mm. figure 9(b) shows that when the position controller is active, and the motor is stationary, the position error is approximately 0mm. figure 9(c) shows the position deviation trajectory at 4000rpm. the maximum deviation amplitude is approximately 0.125mm. this value is relatively small, so we can say that the position controller is working correctly. engineering, technology & applied science research vol. 12, no. 4, 2022, 8942-8948 8947 www.etasr.com nhan et al.: an experimental study on the control of slotless self-bearing motor using nonlinear … (a) (b) fig. 8. response to position and speed in the presence of applied resistance: (a) 2000rpm, (b) 4000rpm. (a) (b) (c) fig. 9. the trajectory of the rotor position deviation along the x axis: (a) initial starting position of controller response, (b) position response when the motor is stationary, (c) position response at 4000rpm. (a) (b) fig. 10. experimental results of the speed controller: (a) speed response, (b) current response. finally, the response of the speed controller, with increasing and decreasing speed of the motor, is tested. at 1s, the motor speed increased from 0rpm to 2000rpm, and at 6s, it reversed to -2000rpm. the corresponding am current and the speed responses were checked (am current is limited from -1a to 1a). the motor speed increases from 0 to 2000rpm after 0.5s and reverses after about 1s. the experimental results in figure 10 show that the system works stably, and that the position and speed controllers work well. however, there are still errors and incompleteness as in the simulation, but the deviation is not too much. they are enough for the controller to be used to control the motor and they verify that the motor model is almost as accurate as the experimental. v. conclusion this article presents a detailed speed and position control design using smc for ssbms. the experimental results reliably verify the effectiveness of the proposed control method. in addition, it is shown that this motor is able to run stably at a considerable high-speed range with a small position error. therefore, this research is a reasonable basis for controlling ssbms with neural networks and fuzzy or artificial intelligence combined with state observers and tests in the future. acknowledgment the authors would like to thank the institute for control engineering and automation of hanoi university of science and technology for their assistance. references [1] y. okada, k. dejima, and t. ohishi, "analysis and comparison of pm synchronous motor and induction motor type magnetic bearings," ieee transactions on industry applications, vol. 31, no. 5, pp. 1047–1053, sep. 1995, https://doi.org/10.1109/28.464518. engineering, technology & applied science research vol. 12, no. 4, 2022, 8942-8948 8948 www.etasr.com nhan et al.: an experimental study on the control of slotless self-bearing motor using nonlinear … [2] z. ren and l. s. stephens, "closed-loop performance of a six degree-offreedom precision magnetic actuator," ieee/asme transactions on mechatronics, vol. 10, no. 6, pp. 666–674, sep. 2005, https://doi.org/ 10.1109/tmech.2005.859823. 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[34] m. a. khlifi, m. b. slimene, a. alradedi, and s. a. ahmadi, "investigation of a leakage reactance brushless dc motor for dc air conditioning compressor," engineering, technology & applied science research, vol. 12, no. 2, pp. 8316–8320, apr. 2022, https://doi.org/ 10.48084/etasr.4762. microsoft word etasr_v12_n3_pp8512-8519 engineering, technology & applied science research vol. 12, no. 3, 2022, 8512-8519 8512 www.etasr.com le et al.: optimization of load ranking and load shedding in a power system using the improved … optimization of load ranking and load shedding in a power system using the improved ahp algorithm trong nghia le electrical and electronics department hcmc university of technology and education ho chi minh city, vietnam trongnghia@hcmute.edu.vn minh vu nguyen hoang urban engineering department hcmc university of architecture ho chi minh city, vietnam vu.nguyenhoangminh@uah.edu.vn thai an nguyen electrical and electronics department cao thang technical college ho chi minh city, vietnam nguyenthaian@caothang.edu.vn trieu tan phung electrical and electronics department cao thang technical college ho chi minh city, vietnam phungtrieutan@caothang.edu.vn buu dao phan electrical and electronics department hcmc university of technology and education ho chi minh city, vietnam 2180602@student.hcmute.edu.vn received: 21 february 2022 | revised: 12 march 2022 | accepted: 20 march 2022 abstract-this paper proposes a method of load ranking and load shedding in a power system based on the calculation of the priority weighting continuity of the power supply of loads and the improved ahp algorithm. the proposed method applies the theories of covariance between objects, correlation, and fuzzy preference to develop a fuzzy preference correlation matrix based on the percentage of vital load, semi vital load, and non-vital load at each load bus. this matrix replaces the judgment matrix of the traditional ahp algorithm to form the criteria layers and scheme layers of the problem. the priority weighting continuity of the power supply of loads is continuously calculated and updated according to the load profile and is used to distribute the load shedding power to each load bus. this distribution optimizes the objective function and maximizes the load benefits, thereby minimizing the damages due to load shedding. the traditional ahp method and the proposed method are applied to the ieee 30 bus system and the result comparison demonstrates the effectiveness of the proposed method. keywords-optimal load shedding; load ranking; ahp; improved ahp; correlation i. introduction load shedding often occurs in order to optimize the operation, in a case of emergency, or due to power shortage of the power system. there are many studies interested in the problem of load shedding in a power system [1-3], however, to the best of our knowledge, the economic loss of load shedding has not yet been taken into account. to ensure the initiative in planned load break or optimal load shedding without unduly affecting the interests of customers and electricity suppliers in the competitive electricity market, the loads of the system are required to be classified and ranked according to priorities in the power supply continuity. there are many studies on load classification and ranking [4, 5]. a microgrid system constantly evaluates and prioritizes the loads in the system to propose load management strategies to control the power generation dispatch of the power sources in the system. in [6], loads are classified into three types and are considered as schedulable variables based on their characteristics and importance. thereby, the microgrid optimization reduces the operating costs of the system. the methods used to classify loads in the power system suggest the use of isodata algorithm to classify customers based on information supplied by the customers and load profile [7]. in [8], the authors propose a model of load classification according to a five-stage process developed on the summary and analysis of studies on load classification in a smart grid environment. a classification method based on fuzzy c-means (fcm) is presented. in [9], the authors show how to extract characteristic attributes of the frequency domain (cafds) and use these cafds to form a hierarchy of load profiles that can be used as system framework for load classification of customers. the ranking of load shedding is applied quite commonly. in [10], the authors propose load shedding based on the ahp corresponding author: trong nghia le engineering, technology & applied science research vol. 12, no. 3, 2022, 8512-8519 8513 www.etasr.com le et al.: optimization of load ranking and load shedding in a power system using the improved … method to stabilize the voltage of the power system. thus, a simple and flexible load shedding model can be developed. this method is based on the assessment of experts from different backgrounds, so it is subjective. in [11], a method for load shedding based on priority demand is proposed with a combination of wind power. higher priority loads are connected to a wind power source that protects them from shedding under emergency conditions. this is done by realtime monitoring of the power system accompanied by shedding of lower priority loads. in [12], the authors propose the development of a load shedding strategy based on load priority. thereby, loads with high priority demand will be connected to an emergency power source and at the same time, loads with lower priority demand will be shed. in this paper, a method of load ranking and shedding in the system based on the improved ahp algorithm to calculate the power supply priority weighting of loads is proposed. this calculation is consistent with the actual load classification, allowing the system operator to be proactive in planned load shedding or load shedding due to system failure. in addition, this method eliminates the expert factor in traditional ahp calculation and incorporates economic conditions. the load shedding strategy of the proposed method is objective, helping to reduce the shedding power and to minimize the damage to the system and the customers while it optimizes the objective function and load benefits. ii. priority ranking of power supply continuity loads based on the improved ahp algorithm priority ranking of loads in the power system is important in ensuring the reliability of the power supply for the loads that are considered important and are highly ranked in the system. the loads in the power system are classified in three types by their priority level: type 1 (vital load or priority load type 1), type 2 (semi-vital load or priority load type 2), and type 3 (non-vital load or priority load type 3) [13, 14]. type 1 load is a type of load that is continuously power supplied, and in case of power failure, it will cause extremely serious consequences. this type of load includes mines, hospitals, loads of steelworks, blast furnaces, etc. in addition, it also disrupts order and affects international politics, such as loads of embassies, public cultural works, etc. type 2 load is a type of load that, if the power is lost, will cause economic losses such as production shortage, increase of by-products, waste of work, etc. type 3 load is a type of load that allows power outage, which are civil works, welfare works, and residential areas. in the grid diagrams, the load buses usually have high capacity. the case of feeder lines including only one priority load type is quite rare. these loads will be actually collected and from there the percentage of each type of loads on those feeder lines will be summarized. from the power percentages of these loads, an improved ahp method based on statistical math, pearson correlation math, and spearman correlation will be applied to calculate the optimal weights of each respective load bus. from this result, we can rank priority loads that need to be power supplied uninterruptedly and the load power that needs to be shed at each bus when there are many priority loads. the improved ahp method applied in this paper is a combination of the traditional ahp method and fuzzy preference relation theory. based on the percentage of priority load types at each load bus, the theory of variance and covariance is applied to calculate the quantitative value and develop a judgment matrix according to the pairs of load type criteria: type 1 load, type 2 load, and type 3 load of the criteria layer. from this judgment matrix, the weights of each load type in the criteria layer are determined. the value of variance between elements of each type of load of each criterion is used to develop a fuzzy preference correlation matrix. this matrix is used to replace the judgment matrix of the scheme layer to calculate the weights of the loads of each type. the weights of the criteria layer and the scheme layer are combined to get the power supply continuity priority weighting of each load. the process of calculating the power supply continuity priority weighting and distributing load shedding power of the proposed method is shown in figure 1. fig. 1. the process of calculating the power supply continuity priority weighting and distributing load shedding power. the process of calculating the priority weighting continuity of power supply includes the following steps: • develop a hierarchical model of the ahp algorithm, in which the criteria layer includes the load types and the scheme layer includes loads in the power system. the hierarchical model of the ahp algorithm to calculate the power supply continuity priority weighting of loads is presented in figure 2. • calculate the weights of the criteria layer. • calculate the weights of the scheme layer. • calculate the combined weights. details of the process of calculating the weights of the criteria layer and the scheme layer are presented below. engineering, technology & applied science research vol. 12, no. 3, 2022, 8512-8519 8514 www.etasr.com le et al.: optimization of load ranking and load shedding in a power system using the improved … fig. 2. the hierarchical model of the improved ahp algorithm to calculate the power supply continuity priority weighting of the loads. a. calculating the weights of the criteria layer the criteria layer of the model of the calculation of the power supply continuity priority weighting represents the load types in the system. the percentages of the load types of each load show the importance of those loads. the process of calculating the weights of the criteria layer is shown in figure 1 and is in accordance with the following steps: 1) step 1: set up the covariance matrix between the criteria the covariance of the criteria is calculated to form the covariance matrix. the criteria of this problem are the load types (vital load, semi vital load, non-vital load) in the power system. the covariance matrix of the criteria i ε and j ε is expressed as ijε [15]. the model of the steps of calculating the criteria weights is shown in figure 2. the covariance matrix between the criteria has the following form: 11 12 1 21 22 2 1 2 n n n n nn ε ε ε ε ε ε ε ε ε ε      =       l l m m m m l (1) where the main diagonal elements are calculated using the variance of the criterion data: ( )22ii 1 1 n i i x x n ε σ = = = −∑ (2) and the remaining elements are calculated using the covariance between the criteria. when the covariance between the two criteria is negative, its absolute value will be taken and the values of these elements are symmetric to each other through the main diagonal. ( ) ( )( ) , ij i 1 j 1 , n i x j y i j cov x y x µ y µ n ε ε = = = = − −∑ (3) 2) step 2: set up the relative covariance matrix the relative covariance matrix β is obtained by transforming the covariance matrix ε, dividing each covariance column ijε by the covariance iiε . the advantage of this transformation is that a matrix whose main diagonal factor is 1 will be gotten. the obtained matrix has the following form: 12 1 21 2 1 2 1 1 1 n n n n β β β β β β β      =       l l m m m m l (4) 3) step 3: set up the correlation matrix between the criteria the correlation matrix α shows the relation between the criteria. the elements in the correlation matrix are called relation coefficients and have the form of (5) [16]. these values are obtained from the values of the elements of the matrix β. , ij ij ij ji β α β β = × 1 ji ij β β = (5) from (5), the correlation matrix between the criteria has the form of (6): 1 12 1 1 21 2 1 1 2 n n n n α α α α α α α       =         l l m m m m l (6) 4) step 4: calculate the weights of the criteria layer after having the correlation matrixα , the root method will be used to calculate the weights of criteria layer [17]. ( ) 1 n i ij j a α = =∏ (i = 1,2,3, …n) (7) * ( ) ( ) n i iw a= (8) * i w will be normalized and the results of the weights of the criteria are calculated by: * ( ) ( ) * ( 1 ) i c i i n i w w w = = ∑ (9) 5) step 5: check the consistency of the correlation matrix the consistency of the correlation matrix will be checked by calculating the consistency ratio (cr) [17]. a correlation matrix will be called the most consistent matrix when cr < 0.1. cr is calculated by: ci cr ri = (10) with: 1 max n ci n λ − = − (11) where λmax is the maximal eigenvalue of the correlation matrix and is determined by: engineering, technology & applied science research vol. 12, no. 3, 2022, 8512-8519 8515 www.etasr.com le et al.: optimization of load ranking and load shedding in a power system using the improved … ( ) max 1 ( ) ( )n j i i w nw α λ = = ∑ , j =1,…,n (12) where ( ) i wα represents the ith component of the vector wα in the correlation matrix α . b. calculate the weights of the scheme layer the scheme layer of the model represents the relationship between loads in the same criterion. subjectivity in decision making is a problem that needs to be minimized, and fuzzy preference theory is applied to solve this problem [15-16]. the process of calculating the weights of the scheme layer is shown in figure 1 and is described below. 1) step 1: calculate the variance vi is the variance between attributes of n-1 objects in a criterion, excluding the i th object. the variance between attributes in the entire set of criteria is used to calculate the elements of the fuzzy preference relation matrix. vi is calculated according to: 21 1 with 1 n j j i x x v j i n − − =  −    = ≠ − ∑ (13) where xj is the value of the j th object in a criterion, �̅ is the corresponding sample mean of the criterion, and n is the size of the sample of the criterion. 2) step 2: develop the fuzzy preference matrix the pij elements in the fuzzy preference matrix p are determined based on the variance of the object attribute, which is calculated by (14) and (15): i ij i j v p v v = + (14) 1ji ijp p= − (15) where [ ], 1 i j n∈ , the higher the pij value, the greater the priority for the i th object. the diagonal elements have a value of 0.5. based on the calculation of variance, the fuzzy preference matrix is easier to be calculated and the result is unique and certain. the fuzzy preference matrix p has the form of (16): 12 1 21 2 1 0.5 0 0 2 .5 .5 p p n p p np p p n n       =         l l m m m m l (16) 3) step 3: develop the fuzzy preference relation consistency matrix the weights of the scheme layer will be calculated based on the consistency matrix p , which is used to replace the pairwise comparison matrix between the attributes of a criterion and the attributes of another criterion. the elements of the consistency matrix p are established based on (17): ( ) ( ) 1 1 0.5 n ik ij ikn n j n n p p p n× = ×    = + −     ∑ (17) the value of the element of the consistency matrix p represents the level of importance between the schemes. if 0.5ijp > , xi will be more important than xj, if 0.5ijp < , then xj is more important than xi, and if 0.5ijp = , xi is as important as xj. according to the above calculation, the main diagonal of the consistency matrix will be 0.5. 4) step 4: calculate the weights of the scheme layer the weights of the scheme layer are calculated based on the pros and cons of the scheme. the values of this level use the values of the elements in the consistency matrix p . equation (18) is applied to calculate them: ij 1 0.5 e or0 therwis i j i j x x r x x >    = =      (18) where rij is the priority index in the comparison between the scheme xi and the scheme xj. the priority index ri of the scheme xi in the set of scheme x is calculated by: 1 n i ij j r r = =∑ (19) the weights of the scheme layer wp(j) are calculated based on the priority indexes ri for the scheme xi in the set of scheme x and are determined by: [ ] 1 ( ) 1 i i p n i j r j n r w = = ∈ ∑ (20) based on this weight calculation method, it is possible to determine the weights of the scheme layer by solving the fuzzy preference consistency of the relation of alternatives of the matrix p. c. calculate the combined weights based on the calculation results of the weights of the criteria layer and the scheme layer, the aggregate priority weight of the power supply continuity , w l ij of each li is calculated by (21): [ ], ( ) , ( 1 ) , 1 n l ij p j i j c i w i j nw w = = × ∈∑ (21) the shedding power at the buses is calculated according to: engineering, technology & applied science research vol. 12, no. 3, 2022, 8512-8519 8516 www.etasr.com le et al.: optimization of load ranking and load shedding in a power system using the improved … , , , , , , , , 1 . .k i k i k k k k i t shed l t shed l t shed t shed tn i t i k p k p p k = = = ∑ (22) where , ,i ks h ed l t p is the shedding power of the i th load bus (mw), at the k th time stage (with k=1÷6), , kshed t p is the total load shedding power of the system (mw) at the k th time stage, , ,i kshed l t k is the load shedding weight of the i th load bus at the k th time stage, and ,il k p is the load power li at the k th time stage. , ki t k is calculated by: ,, , , 1 1l,ij . 1 i k i l kl ij i t n n l k i i pw k p w= = = ∑ ∑ (23) the distribution of shedding power to the load buses must satisfy the following constraints: first, the smaller the priority weight of the power supply continuity of the load bus, the greater the shedding power and vice versa. in this regard, it should be noted that it is not possible to shed the entire power of the low-priority load buses as to ensure background or base loads and high-priority loads (vital loads) at these load buses. second, the shedding power at the load buses , ,i ks h ed l t p is not allowed to be greater than the power of the load bus at the k th time stage, , , ,i k ished l t l k p p< . iii. objective function benefit function the objective function for load shedding using the traditional ahp method is [17]: , 1 . . n i l ij ij ik i h vw x = =∑ (24) where xik is the decision variable (equals to 0 or 1) on load bus i at the k th time stage [17], ij v is the independent load value (or cost) in a specific load bus i at the k th time stage ($/kw or $/mw), and ,wl ij is the aggregate priority weight of the power supply continuity. ,l ijw , ijv are definite numbers, so the hi function will reach its maximum value when all ikx are equal to 1. decision variable xij equals to 1 if the load demand is satisfied, otherwise it is equal to 0. in this paper, we propose a method to calculate the objective and benefit functions for load shedding using the improved ahp method presented in equations (25) and (26): , , , 1 ) . .(1 i k n i l ij ij shed i l tkh vw = = −∑ (25) benefit = , , 1 , ).( i ki n ij l k e i sh d l tv p p = −∑ (26) iv. case study and simulation results the ieee 30 bus system is used for calculations according to the proposed method. the parameters of the system, the capacity of the generators, and the daily load data, including the independent load value/cost at each load site are listed in [17]. suppose generator g1 is out of service. the total source power is only 225.0mw. this results in limited power supply at some time stages. the total system generation resources pg and load demands pl can be seen in [17]. the results of collecting information about power and power percentage of vital load, semi vital load, and non-vital load at each load bus are presented in table i. implementing the steps of the improved ahp algorithm to determine the priority weights of the load buses in the system, serves as the basis for load shedding. the loads with low priority factors will be prioritized for shedding in order to minimize the damage caused by power outages. table i. percentage load types of the system load buses load li load name vital load (%) semi vital load (%) non vital load (%) variance vi of li in vital load criteria semi vital load criteria non vital load criteria l1 pd2 0.124 0.342 0.534 0.0047 0.0011 0.0024 l2 pd3 0.127 0.346 0.527 0.0047 0.0011 0.0024 l3 pd4 0.131 0.332 0.537 0.0048 0.0011 0.0024 l4 pd6 0.132 0.348 0.52 0.0048 0.0011 0.0025 l5 pd7 0.133 0.328 0.539 0.0048 0.0011 0.0024 l6 pd8 0.134 0.338 0.528 0.0048 0.0011 0.0024 l7 pd10 0.135 0.344 0.521 0.0048 0.0011 0.0025 l8 pd12 0.138 0.324 0.538 0.0048 0.0011 0.0024 l9 pd14 0.136 0.326 0.538 0.0048 0.0011 0.0024 l10 pd15 0.137 0.313 0.55 0.0048 0.0011 0.0023 l11 pd16 0.242 0.289 0.469 0.0050 0.0011 0.0025 l12 pd17 0.246 0.268 0.486 0.0049 0.0011 0.0025 l13 pd18 0.25 0.256 0.494 0.0049 0.0010 0.0025 l14 pd19 0.252 0.274 0.474 0.0049 0.0011 0.0025 l15 pd20 0.258 0.254 0.488 0.0049 0.0010 0.0025 l16 pd21 0.267 0.282 0.451 0.0048 0.0011 0.0024 l17 pd23 0.276 0.258 0.466 0.0048 0.0010 0.0025 l18 pd24 0.279 0.292 0.429 0.0047 0.0011 0.0023 l19 pd26 0.291 0.276 0.433 0.0046 0.0011 0.0023 l20 pd29 0.294 0.28 0.426 0.0046 0.0011 0.0023 l21 pd30 0.298 0.342 0.36 0.0046 0.0011 0.0016 from the percentages of vital load, semi vital load, and non-vital load at the load buses in the system, the theory of section ii is applied to calculate the weights of each criteria layer. the matrices , ,ε β α are calculated by (1), (4), and (6) and are presented as follows: 0.0048 0.0018 0.0030 0.0018 0.0011 0.0007 0.0030 0.0007 0.0024 ε    =      1.0000 1.6026 1.2756 0.3649 1.0000 0. 00.6351 00.60 6 26 275 1.00 β    =      engineering, technology & applied science research vol. 12, no. 3, 2022, 8512-8519 8517 www.etasr.com le et al.: optimization of load ranking and load shedding in a power system using the improved … 1.0000 2.0957 1.4172 0.4772 1.0000 0.7056 1.000 0.6762 1.4788 0 α    =      from the correlation matrix between the criteria α and by applying (7), (8), and (9) we get the weights of the criteria layer. the results are presented in table ii. table ii. equivalent parameters of wind power plant vital load semi vital load non-vital load ( )c iw 0.4581 0.2186 0.3233 applying (12) results to max 3λ = , and by (11) and (10) we get calculate ci=0 and cr=0. this shows the high consistency of the correlation matrix. after calculating the weights of the criteria layer, the theory to calculate the weights of the scheme layer is applied. applying (13) in combination with the data of the percentage of the load type, we get the variances of the characteristics which are shown in table i. the elements in the fuzzy preference relation matrix p and the fuzzy preference consistency matrix �� are calculated by (14), (15) and (17). applying (18) and (19) allows us to calculate the priority index rij of the scheme layers. the results are presented in table iii. table iii. priority index ri of the schemes in the p matrices and weights of the scheme layer load li ri of 1p ri of 2p ri of 3p wp(j) of vital load wp(j) of semi vital load wp(j) of nonvital load l1 3.5 8.5 9.5 0.0159 0.0385 0.0431 l2 4.5 4.5 12.5 0.0204 0.0204 0.0567 l3 6.5 10.5 9.5 0.0295 0.0476 0.0431 l4 8.5 3.5 14.5 0.0385 0.0159 0.0658 l5 9.5 15.5 5.5 0.0431 0.0703 0.0249 l6 10.5 10.5 10.5 0.0476 0.0476 0.0476 l7 11.5 6.5 13.5 0.0522 0.0295 0.0612 l8 14.5 17.5 7 0.0658 0.0794 0.0317 l9 12.5 16.5 7 0.0567 0.0748 0.0317 l10 13.5 20.5 3.5 0.0612 0.0930 0.0159 l11 20.5 18.5 16.5 0.0930 0.0839 0.0748 l12 19.5 6.5 18.5 0.0884 0.0295 0.0839 l13 18.5 1.5 19.5 0.0839 0.0068 0.0884 l14 17.5 10.5 17.5 0.0794 0.0476 0.0794 l15 16.5 0.5 20.5 0.0748 0.0023 0.0930 l16 15.5 14.5 10.5 0.0703 0.0658 0.0476 l17 7.5 2.5 15.5 0.0340 0.0113 0.0703 l18 5.5 19.5 2.5 0.0249 0.0884 0.0113 l19 2.5 11.5 4.5 0.0113 0.0522 0.0204 l20 1.5 13.5 1.5 0.0068 0.0612 0.0068 l21 0.5 7.5 0.5 0.0023 0.0340 0.0023 1 n i i r =∑ 220.5 220.5 220.5 the weights of the scheme layer are calculated based on the priority index ri. applying (20) calculates the weights of the scheme layer. the results are presented in table iii. the hierarchical model showing the results of the weights of the criteria layer and the scheme layer is presented in figure 3. fig. 3. weights of the criteria and the scheme layers in the ieee 30 bus system hierarchy. after obtaining the weights of the criteria layer (table ii) and the weights of the scheme layer (table iii), we apply (21) to calculate the power supply continuity aggregate priority weights of the load buses. the results of calculating and load ranking are presented in table iv. based on the load ranking results the higher ,wl ij the load has, the more important it is and the later its order for load shedding is. the more heavily weighted the load, the smaller the power shedding ratio and vice versa. equation (22) is applied to calculate the power shedding distribution at the load buses. the values of the objective function hi and the benefit function are calculated by (25) and (26). the results are presented in table iv. the comparison results between the ahp and the improved ahp methods are presented in table v. the comparison results show that the engineering, technology & applied science research vol. 12, no. 3, 2022, 8512-8519 8518 www.etasr.com le et al.: optimization of load ranking and load shedding in a power system using the improved … improved ahp approach is truly optimal. it not only has maximal load benefits and reduces the total load shedding, but also considers the percentages of vital load, semi vital load, and non-vital load of the load buses. for example, the improved ahp method has the total load shedding power increased from 10.48% to 69.54% corresponding to time stages of t2-t6. meanwhile, the objective function of the improved ahp method increases from 48.81% to 52.67% and the load benefits also increase from 229$ to 1466$. that shows that the improved ahp method is better than the ahp method. v. discussion in the improved ahp method, the correlation matrix α replaces the pairwise judgment matrix of the traditional ahp method. the elements of the correlation matrix are inversely symmetric across the main diagonal line, just like in the judgment matrix of the traditional ahp method. however, for the improved ahp method, these values are derived from statistical and correlation mathematical processing based on the input as a percentage of the priority load types at each load bus. therefore, this matrix is objective and reliable. meanwhile, in the traditional ahp method, these values are obtained from the subjective opinions of experts. when implementing load shedding in the traditional ahp method, the entire loads are shed [17]. this is difficult to do in practice because base loads or very important loads must be maintained. meanwhile, the improved ahp method, based on the percentages of vital load, semi vital load, and non-vital load as the basis for the application of statistical and correlation math based on the ahp algorithm hierarchical model to calculate power supply continuity weights, is feasible and practical. therefore, if the data collection system of system parameters can satisfy the continuity, this method will be very effective. it ensures less load shedding power while ensuring a higher objective function and higher load benefits compared to the traditional ahp method. table iv. power supply continuity priority weights and load bus ranking load li power supply continuity priority weight of load buses ( l,ijw ) rank vij ($/kw) i 1shed,l ,t p at t1 0.00h – 4.00h (mw) i 2shed,l ,t p at t2 4.01h – 8.00h (mw) i 3shed,l ,t p at t3 8.01h – 12.00h (mw) i 4shed,l ,t p at t4 12.01h – 16.00h (mw) i 5shed,l ,t p at t5 16.01h – 20.00h (mw) i 6shed,l ,t p at t6 20.01h – 24.00h (mw) l1 0.029626441 18 300 0 3.003446 5.828059 3.726798 3.003446 0.209771 l2 0.032136639 17 300 0 0.344511 0.668509 0.450038 0.344511 0.024062 l3 0.037842291 15 300 0 0.825931 1.640064 1.101938 0.825931 0.059031 l4 0.042388041 13 280 0 9.112701 17.68281 11.3498 9.112701 0.636461 l5 0.043168144 12 280 0 2.165763 4.202572 2.823654 2.165763 0.151264 l6 0.047619048 11 300 0 2.583331 5.012845 3.249887 2.583331 0.180428 l7 0.050129246 10 300 0 0.474435 0.92062 0.618553 0.474435 0.033136 l8 0.057738432 7 280 0 0.795413 1.543465 1.037034 0.795413 0.055554 l9 0.05259167 9 280 0 0.483408 0.938034 0.630253 0.483408 0.033763 l10 0.053503791 8 245 0 0.628447 1.219475 0.81935 0.628447 0.043893 l11 0.085123456 1 220 0 0.1686 0.327162 0.220146 0.1686 0.011776 l12 0.074080937 2 280 0 0.498168 0.966673 0.649495 0.498168 0.034794 l13 0.068512253 4 220 0 0.187533 0.371643 0.249702 0.187533 0.013377 l14 0.072425184 3 245 0 0.544156 1.043705 0.70164 0.544156 0.037566 l15 0.064831551 5 280 0 0.139148 0.27001 0.181416 0.139148 0.009719 l16 0.061973073 6 280 0 1.157909 2.246874 1.510099 1.157909 0.080872 l17 0.040785013 14 220 0 0.315025 0.6243 0.419459 0.315025 0.022471 l18 0.034424924 16 220 0 1.036301 2.010898 1.351913 1.036301 0.072379 l19 0.023192711 19 300 0 0.618808 1.200771 0.807996 0.618808 0.04322 l20 0.018699685 20 220 0 0.52628 1.021223 0.686147 0.52628 0.036757 l21 0.00920747 21 245 0 4.720686 9.160291 6.15468 4.720686 0.329708 total 1.00 0 30.33 58.9 38.74 30.33 2.12 table v. summary and comparison of ahp and improved ahp (iahp) load shedding methods for the ieee 30-bus system methods ahp iahp ahp iahp ahp iahp ahp iahp ahp iahp ahp iahp time stage t1 t1 t2 t2 t3 t3 t4 t4 t5 t5 t6 t6 max. system generation (mw) 225.0 225.0 225.0 225.0 225.0 225.0 225.0 225.0 225.0 225.0 225.0 225.0 system demands (mw) 198.69 198.69 255.33 255.33 283.9 283.9 263.74 263.74 255.33 255.33 227.12 227.12 committed loads (mw) 198.69 198.69 213.8 225.0 218.1 225.0 219.93 225.0 213.8 225.0 220.16 225.0 total load shedding (mw) 0.0 0.0 41.53 30.33 65.80 58.9 43.81 38.74 41.53 30.33 6.96 2.12 hi 130.87 254.2 123.87 254.2 120.32 254.2 123.87 254.2 123.87 254.2 130.10 254.2 benefit (×10 3 )$ 55058 55058 60979 62445 62306 62535 62717 62425 60979 62445 61406 62356 engineering, technology & applied science research vol. 12, no. 3, 2022, 8512-8519 8519 www.etasr.com le et al.: optimization of load ranking and load shedding in a power system using the improved … in addition, in this paper, we propose (25) to compare the value of hi function with (24). from there, the advantages of the proposed load shedding distribution method can be seen more clearly. in (24), the entire load at bus i at the k th time stage is cut (xik = 0) and does not consider the ratio of vital, semi-vital, and non vital loads. however, in (25), we do not cut the entire load i, we only cut a part of the load i based on the , ,i kshed l t k weight. , ,i kshed l t k has been calculated by (22) – (23). vi. conclusion the calculation of the power supply continuity priority weighting of each load bus by applying the theory of covariance and forming the criteria and scheme layers was conducted in this paper. the calculation of the power supply continuity priority weighting of each load bus by applying the theory of covariance and forming the criteria and scheme layers of the problem avoids the un-objectiveness of experts’ opinions and gets consistent results, thus overcoming the disadvantages of the traditional ahp method. besides, it supports the ranking of the load buses and distributes the shedding power in the power system in a more optimized way. the objective function and the benefits are better than those of the traditional ahp method. the results of load bus prioritization can serve to set the priority of power cut of load shedding relays or planned power cuts in case of long-term power shortage or load shedding in emergency situations. in further work, more consideration should be given to the continuous variation over time of the percentage of each load type and possible combinations of constraints: the cost of power failure, the cost of fines for power failure, and the load cost for a more optimal distribution of load shedding. acknowledgment this work belongs to the project grant no: 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[17] j. zhu, "optimal load shedding," in optimization of power system operation, ieee, 2015, pp. 437–482, https://doi.org/10.1002/ 9781118887004.ch11. microsoft word etasr_v13_n1_pp9899-9905 engineering, technology & applied science research vol. 13, no. 1, 2023, 9899-9905 9899 www.etasr.com tedjari & abbaoui: space syntax for evaluating attractivity and visit frequency space syntax for evaluating attractivity and visit frequency a comparative study of two public squares of downtown setif (algeria) abdelmalek farouk tedjari habitat and environment laboratory, ferhat abbas university, algeria fatedjari@univ-setif.dz (corresponding author) messaoud abbaoui habitat and environment laboratory, ferhat abbas university, algeria messaoud.abbaoui@univ-setif.dz received: 27 october 2022 | revised: 16 november 2022 | accepted: 19 november 2022 abstract the current study uses the space syntax innovative method for determining the causes of the attractivity and visit frequency gap between two open public spaces of downtown setif (algeria): sahat el istiklal square and masjid ibn badis square. a design drawn from a map coming from the national institute of cartography and teledetection (algeria) is chosen for the configurative analysis carried out by space syntax through the depthmap software. visibility graph analysis (vga) superimposed with the pedestrian real flow permits the visual integration of the analysis of each square. the analysis revealed relevant gaps in the syntactic measure values obtained for each square emphasizing their positive aspects and specific problems. space syntax allows the extension of the initial discussion about public squares in urban environments and to work out causality relationships between spatial configuration and human behavior. keywords-space syntax; special configuration; public square; attractivity; visit frequency i. introduction public squares reflect the identity and culture of a city and are parts of its image and prestige. there is a growing demand to increase the entertainment, conviviality, and social interaction of city residents since the laws no. 2006-06 of 20 february 2006 were promulgated, and the amelioration of the the quality of the urban living environment became a priority for the algerian state [1]. this social aspect is not a priority for the local authorities, which focus more on the development advantages. so, starting from the principle that public squares are optimally central sociability places we considered the case study of two squares of downtown setif: sahal el istiklal and masjid ibn badis squares, which have a gap of attractivity and visit frequency. the current studies about the urban open space widely focus on the qualitative aspect and few studies concern the quantitative perspective. thus, a space syntax-based study intends to quantitatively determine the essential causes of the inequality of attractivity and visit frequency between the two squares. in this way, we consider the accessibility to a place and the visibility degrees of its design as the indices determining social interactions and hence attractivity and visit frequency. a clear comprehension of the relationship between the spatial configuration and popularity of a place is a must for better designs [2]. previous researches focused on the social logic specific to the space, which impacts human behavior, using accessibility and visibility notions [3]. authors in [4] define spatial configuration as the simultaneous relationship set existing between the parts and which design the whole, concluding that the spatial shape must be seen as a factor which contributes to the formation of the integration and segregation models in cities. accessibility is the movement potentiality from one place to another or from a point to another. the event is perceived in the form of time, distance, and cost [5, 6]. space syntax theory presents three interaction forms between persons and space to observe movement, interactions with people, and watching the function of a visual field [7]. moreover, while the visual potentialities are biological or technical, the choice modalities of what is seen or unseen depend on the social dimension [8]. for quantitatively apprehending the attractivity and visit frequency gap between the two considered urban squares, configurative analysis was carried out by space syntax through the depthmap software. it carries out axial integration studies (global (r=n) and local (r=3)) for describing visual move axes engineering, technology & applied science research vol. 13, no. 1, 2023, 9899-9905 9900 www.etasr.com tedjari & abbaoui: space syntax for evaluating attractivity and visit frequency and the visibility graph analysis (vga) for the evaluation of the integration and visual permeability levels. the results of the current research may contribute to innovative proposals for better designs in the development and planning of the urban open spaces. fig. 1. the location of the study area in the city of setif (original image © the national institute of cartography and remote sensing). ii. methodology a. context and case study downtown setif is an ex-nihilo creation of the french army [9]. setif is an eastern city located at 300km from algiers and at a height of 1100m in the algerian highlands. two central historical places, in a distance of 265m, are the object of the current study. fig. 2. location of sahal el istiklal and masjid ibn badis in downtown setif. (image © 2022 maxar technology, google earth, processed by the authors). sahal el istiklal square (figure 3a–c) is the first big historical square of downtown setif, created in 1845 at the western entry of the city. it is distinguished by its location at the intersection of two big historical axes structuring the ancient downtown. its shape results from the enlargement of 8 may 1945 street constituting a 70m sided square, whose center contains a fountain monument surrounded by 4 high trees shading its space. its framework contains al atik mosque, two hotels, an administrative building, and other housing buildings with a commercial ground floor (cafeterias, restaurants and shops...) and in the upper floor some flats and professional spaces (physicians, lawyers, architects, etc.). after the works due to the tramway crossing in 2018, the square became a space reserved to pedestrians and so preventing the access to vehicles. the ground floor is paved with concrete elements and abounds in unified urban furniture with many public benches, flowers trays, and huge umbrellas. the ibn badis mosque square (figure 3b–d) is a historical square of the city, erected far from the big traffic, reinforcing its quiet space pattern [10]. it is located in the eastern side of ben boulaid street, it is 22m wide and is used as a jewelry and craft commerce point. it is the result of the removal of two urban meshes, which replaced two blocks in the european district [11]. this gives a large space in the form of a rectangle whose length and width are 135 and 62m, respectively. this square is framed by communal schools and housing buildings with a ground floor limited to some small retail shops (shoes, one café, and two groceries) and some professionals at the upper floor. after the independence, during the period 19621970, this square has known important modifications: the church became a mosque, the square space has been enclosed and finished as a garden, and a simple stele has replaced the memorial decorating the middle of the square. the urban furniture is almost absent in the square, except some benches and street lamps inside its garden. fig. 3. a, c: the sahal el istiklal square, b, d: the ibn badis mosque square, (images a, b © 2022 maxar technology, google earth, processed by the authors). a. analysis method as said above, public squares in urban environments are the study object of this research. the analysis of the attractivity engineering, technology & applied science research vol. 13, no. 1, 2023, 9899-9905 9901 www.etasr.com tedjari & abbaoui: space syntax for evaluating attractivity and visit frequency and the visit frequency in the considered urban punctualities of downtown setif is based on space syntax as a method and theory developed by the space syntax laboratory (ssl) in the seventies. space syntax can be summed up as a reflection on the rules and the principles of the urban organization and is based on the elements of configuration aspects, which compound the space as social behavior influencers while focusing on the questions linked to the persons' movement. in order to quantitatively explore the correlation between the spatial configuration and a social variable and using the tools given by space syntax, we focused on the fundamental variable of the number of persons crossing the square (pedestrian flow) considered as the real factor of attractivity and visit frequency. the person movement is figured from the axial map describing the mobility system of a given space. through its decomposition in axes we can draw the traffic movement of open spaces of urban meshes [12]. a sketch drawn from the map given by the national institute of cartography and teledetection (algeria) is chosen for the syntactic study because it contains the whole historical downtown of setif (urban colonial nucleus) and its two central historical squares as study topics. its design will be completed by satellite photos from google earth which show the current places' state. concerning the design of each square used for the visual analysis, it is reconstituted from the above design and from the surveys carried out on the field. a contour in dotted blue line drawn on the surrounding walls prints of the ancient city indicates the limits of the study area. the study limit of the visual integration of each square is represented by the square space, the peripheral buildings, and its accessing streets. the design of each square will be drawn with autocad. the global map of the whole study area and the partial maps of the public squares will be changed in dxf format then reproduced by the depthmap software. after the evaluation of the syntactic properties and the calculation of the measures of the global (r=n) and local (r=3) integration plus the visual integration. depthmap automatically assigns a series of colors with different shades: blue for the low values, yellow and green for the medium values, and red for the high values. the axial map of the pedestrian traffic follows the pedestrians' walking which access the squares while the axial lines apply the rule of the longest and the less numerous. in the used method, the pedestrian flows systems are compounded of more or less accessible roads, which are then interpreted in function of their depth. the more accessible axes are qualified as less deep and integrated while the less accessible as deep and segregated. in theory, the most integrated lines are supposed to have a maximal flow of persons and so a greater attractivity and visit frequency. a space is considered as integrated if it tends to bring to it the other system spaces [13]. the axial map of the pedestrian traffic allowed us to compare the two squares with the medium value of the integration of all the axial elements of the global and local integration and the intelligibility of the urban system of the historical center could determine the role of each square in the urban system. in parallel, the values of the visual integration superimposed to the in situ observation (pedestrian real flow) allow us to compare the two squares and to explain the gap of the attractivity and visit frequency values. fig. 4. plan delimiting the study area and the two study squares. (original image © the national institute of cartography and remote sensing. processed by the authors). b. field investigation: counting and following up the pedestrian real flow we are interested in the transit functions and the pedestrian follow up in order to measure the attractivity and the visit frequency of the considered squares. the pedestrian real flow has been counted from the numerical data and the statistical surveys. the used method is based on manual counting, which is preferable to the automatic counting [14]. it consists in counting and following up of the pedestrian flow carried out on each public square in the same time. this method can be based on the geographical information system (gis) for exploring researches in the urban development fields [15]. the counting and following up were carried out by architecture master students. they worked as operators and were pre-trained about the counting program objectives, the data collection process, and the way of using the collect form and the follow up plans. each operator had a chronometer and prepared investigation forms, containing all the information about the counting places and the pedestrians (hour, date, observator, direction, gender and age). moreover, a detailed sketch of the square was given to help situate the pedestrian flow. this was necessary for the accuracy of the results during the data interpretation. standing at the access of the streets serving each square, one or two operators-in function of the importance of the way carried out the counting of the persons entering the square and reported on the form the visually surveyed data. persons leaving the square were not counted. then, a sample of persons, determined from the counting results was followed from their entrance to the square until leaving it. the field visits and the counting development were carried out during the period between may and june 2020. for each counting the interval was not more than five minutes and ran during the working days of the week (sunday and monday) and the weekends (friday and saturday). the timing periods corresponded to rush hours: from 7.30 to 8.30 am and 5.30 to engineering, technology & applied science research vol. 13, no. 1, 2023, 9899-9905 9902 www.etasr.com tedjari & abbaoui: space syntax for evaluating attractivity and visit frequency 6.30 pm and between 8 to 9 pm. the counting results appear in table i. the plans of the moves are exhibited by lines of different thicknesses and colors on plans containing all the ways converging to the square, which can be taken by pedestrians. iii. result analysis, and discussion a. results, analysis, and discussion of the axial map the axial integration map of figure 5 obtained from the pedestrian flow shows a color difference of the axial lines of the most integrated to the system public square, which appears in dominant red color and the most segregated square in axial line mainly in blue tones. it also shows the analysis results of the global integration (hh) at the radius n and the local integration at radius 3, for the description of the move axes which intend to explore the most localized organizations like central public squares in the city. this axial map showcases the evident inequality in the integration values of the pedestrian traffic which crosses each square. so, sahat el istiklal square presents the highest local and global integration values (from 1.75889 to 6.05969) with maximum red colors lines. at the opposite, ibn badis mosque square presents a predominance of less high axial lines (from 2.48420 to 4.04988) with a blue tone primacy. it is relevant to notice in the urban system of the historical center the pertinence of important streets as integration axes of the pedestrian traffic serving each square. so, the map in figure 5 shows that abane ramdane street and 8 may 1945 street which intersect in sahat el istiklal square, present the highest integration values (5.91332 and 6.06208) while ben boulaid street adjacent to the western side of the ibn badis mosque square displays the less high integration value (4.20904). the streets' layout near each square influences the animation and their syntactic values. so we can deduce that the environment may have more effect on the square congestion than the square design itself. fig. 5. results of the axial pedestrian map analysis. so, 8 may 1945 street being a highly integrated move axe, strongly impacts the peripheral sides of the square, especially the emergence of connection places, and the attractivity of the commercial areas located in the building ground floors framing the square, which then become multiplicator spaces of attractivity and frequent visit. the fountain monument site, with its high trees shading its space at the axes intersection, presents the highest integration value. thus, this is a highly integrated connection space and an attractivity element giving sahat el istiklal square a good animation and a good user's frequent visit and permitting great mobility and a better access from its western entry. on the other hand, the wall enclosing the garden in the middle of the ibn badis mosque square, constitutes a barrier and a repulsive element for the pedestrians, preventing any movement. if we put in correlation the global spatial integration and the connectivity of the map axes of the historic center urban network under a dispersion diagram form, we obtain an intelligibility value of r²=0,893. this very high second degree measure shows that these two squares belong to a very intelligible urban system and defines the integration level of each square [17]. this can be demonstrated by the visibility of the historic center urban system and by the role of each square in terms of attractivity and frequent visit. table i. values of visual integration values of visual integration sahat el istiklal masjid ibn badis minimum 5.18850 5.6545 average 21.8004 11.1485 maximum 36.8479 18.4607 table ii. counts of the persons coming from the streets serving the square every 5 minutes sahat el istiklal masjid ibn badis p e o p le / 5 m in u te s street 1 328 108 street 2 281 46 street 3 29 58 street 4 53 28 street 5 14 64 street 6 8 45 total 713 349 observation very animated segregated fig. 6. intelligibility diagram of the historic center of setif city. b. results, analysis, and discussion of the visual integration this part of the study deals with the square analysis compared to its own space. the visibility graph analysis (vga) maps present a chromatic differentiation of the visibility spaces from the most visually integrated spaces -in redto the most visually segregated spaces, in blue. it shows the results of the visual integration analysis (hh) for the evaluation of the integration levels indicating the places with more or less big visual eventuality. the observation of the pedestrian flow concerned a sample of 500 persons coming from the streets of surrounding neighborhoods and entering the engineering, technology & applied science research vol. 13, no. 1, 2023, 9899-9905 9903 www.etasr.com tedjari & abbaoui: space syntax for evaluating attractivity and visit frequency square. the results of the visual integration of the syntactic study in table ii are compared to those of the counting and followed by the real move of the persons in the square. from the results of the pedestrian counting, it appears that greater pedestrian number passes from sahat el istiklal square, which makes it a very animated and visited space compared to the ibn badis mosque square. ibn badis mosque square was at first a church and had been designed as a quiet place. the counting results of table ii are in congruence with the visual integration values of table i. the results of the comparison between the diagrams of the pedestrians real movement and the visual integration plus the square spatial configuration, show that the visual integration values are related with both the pedestrian movement and the spatial configuration as analyzed by the space syntax method (figures 7, 8). actually, the fact that sahat el istiklal square has been designed to be at the exact place of the enlargement of the most integrated axe of the urban system (8 may 1945 street), enhances its attractivity and fluidity. the fountain monument and the dominant building (the mosque) as attractive elements are located at the eastern and western entry of the square. so, they permit good animation, balancing of the syntactic values of the walk in the middle of the square and all along its perimeter with an expressive reduction of the values around the fountain. these attractive elements of the square are positioned in the visibility axe of the most integrated move. the maximal values of the visual integration in table i confirm that sahat el istiklal square offers good visibility and permits to clearly distinguish the borders of the peripheral convex buildings facilitating the interaction. in the visual integration map, the fountain monument erected on a stone pedestal and surrounded by four trees shading its space is considered as a barrier to the square visibility and has very low visual integration values (from 5.572 to 1.4654). concerning ibn badis mosque square, due to its location adjacent to the eastern side of the ben boulaid street, it cannot capture the pedestrian flow coming from this axe and presents low visual integration values. the building dominating the square was originally designed to be located in the visibility axes of the person movement and represented one of the most beautiful urban paintings decorating setif city [18]. the central area of sahat el istiklal square concentrates the highest visual integration value (36.8479), gradually regressing as we approach the periphery of the buildings surrounding the square (figure 7). the central area is the most visible area from which we can visually dominate the rest of the square, which makes it the most potential animated and visited space. on the other hand, for ibn badis mosque square, the buildings located in the square perimeter display low visual integration (9.09819), due to the construction of the garden enclosure wall. it contains a great number of high trees all around the square center constituting a physical barrier preventing continuity in visual integration. moreover, in spite of the low visibility dominating this square, some parts inside the garden or at the mosque entry present moderately high integration values, and other parts situated at the intersection of the streets leading to the square present high values, which could imply a real possibility of animation. in the urban system of the historic center, each square is identified by its diversity and its functions which give vitality to urban life [19]. so the commercial frame gives sahat el istiklal square a role of very animated and visited space, while the ibn badis mosque square is limited to some modest shops and is a very little attractive and less visited space. these in situ observation results are in correlation with the counting values of the pedestrian move (table ii). fig. 7. juxtaposition of the pedestrian movement scheme and the visual integration plan in sahat el istiklal square. iv. conclusion the spatial arrangement of downtown setif city has a rectangular shape laying out ways on which the public squares are distributed. the methodology used for the comparative study of the two central squares, as spatial models through the space syntax method, focused on the study of supposed persons' flows as a necessary factor for real attractivity and visit frequency estimation. this permits to quantitatively estimate the attractivity and visit frequency differences for a future development of the squares. other researches in the space syntax field, in different urban contexts, proved that the spatial integration level is a revelator of the pedestrian urban mobility. the inequalities in attractivity and visit frequency perceived in each square are the consequence of the configuration and the urban role originally devoted to each one. engineering, technology & applied science research vol. 13, no. 1, 2023, 9899-9905 9904 www.etasr.com tedjari & abbaoui: space syntax for evaluating attractivity and visit frequency fig. 8. juxtaposition of the pedestrian movement scheme and the visual integration plan in masdjid ibn badis square. so, sahat el istiklal square is destined to become the most animated and visited urban space of the city due to its design, location, and the number of shops surrounding its space. it has been designed in order to be the anchor link of the two most animated historical and commercial axes of the city. the syntactic measures confirm that the two axes, abane ramdane street and 8 may 1945 street are very integrated in the axial integration r=n of the global system. thus, the square is highly visually and globally integrated and its attractiveness and visiting space are perfectly adapted to the pedestrians' mobility. concerning ibn badis mosque square, even though it is situated in the eastern side of ben boulaid street, it cannot catch its animated flow. this square has been created only for serving its dominant building (sainte monique, church now ibn badis mosque). actually, it was intended to be used as a quiet space, situated apart from the great traffic and with a limited number of surrounding shops. the syntactic results prove that this square owns the lowest visual and global integration values. its few attractive spaces seem more adapted to a mechanical traffic. this animation and frequent visit gap does not absolutely constitute a factor proving the success of the first square compared to the second one. actually, each one finds its originality in the social economic and political role assigned in the urban system of the center of setif city. the obtained results show that the connection to sahat el istiklal square is essentially assured by the square size, the peripheral buildings, the dominant building (the mosque), the monument and the urban context, which fully participate to its attractivity. concerning the connection to ibn badis mosque square, it is more assured by the indoor spaces of the dominant equipment and the schools surrounding the square. this square remains segregated and less visited, especially in the night when the stores and schools are closed. the development of downtown setif goes through the increase of the global and visual integration values of the squares in the urban global context. space syntax, through depthmap software, allowed us to demonstrate the attractivity and traffic inequalities. it allowed to extend the debate initiated about public squares in urban environments and to lay down causality relationships between spatial configuration and human behavior in order to contribute to the elaboration of innovating recommendations. acknowledgements the authors would like to thank the habitat and environment laboratory of ferhat abbas university for its contribution to this research. references [1] i. kaouche and a. boussoualim, "à la recherche des qualités du vécu des espaces publics ; cas des places publiques en algérie," courrier du savoir, no. 20, pp. 109–118, dec. 2015. [2] f. fareh and d. alkama, "the effect of spatial configuration on the movement distribution behavior: the case study of constantine old town (algeria)," engineering, technology & applied science research, vol. 12, no. 5, pp. 9136–9141, oct. 2022, https://doi.org/10.48084/ etasr.5169. [3] a. rahmane and m. abbaoui, "the architectural genotype approach in contemporary housing (1995 to 2010): the case study of setif, algeria," engineering, technology & applied science research, vol. 11, no. 1, pp. 6810–6818, feb. 2021, https://doi.org/10.48084/etasr.4006. [4] b. hillier and l. vaughan, "the city as one thing," progress in planning, vol. 67, no. 3, pp. 205–240, apr. 2007. [5] c. cauvin, h. reymond, and r. kleinschmager, l’espace géographique des villes. pour une synergie multistrates. paris, france: economica, 1998. [6] p. merlin, méthodes quantitatives et espace urbain. paris, france: persée portail des revues scientifiques en shs, 1974. [7] b. hillier, space is the machine: a configurational theory of architecture. createspace independent publishing platform, 2015. [8] j.-n. tardy, "visibilité, invisibilité. voir, faire voir, dissimuler," hypothèses, vol. 10, no. 1, pp. 15–24, 2007, https://doi.org/10.3917/ hyp.061.0015. [9] a. prenant, "facteurs du peuplement d’une ville de l’algérie intérieure : sétif," annales de géographie, vol. 62, no. 334, pp. 434–451, 1953, https://doi.org/10.3406/geo.1953.13052. [10] a. picard, "lotissements et colonisation : algérie, 1830-1970," villes en parallèle, vol. 14, no. 1, pp. 214–237, 1989, https://doi.org/10.3406/ vilpa.1989.1062. [11] a. camborieux, sétif et sa région : essai de monographie historique, géographique et économique. 1978. 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[16] a. hallil and a. redjem, "assessment of urban vulnerability to flooding using multi-criteria analysis: the case study of el bayadh city, algeria," engineering, technology & applied science research, vol. 12, no. 2, pp. 8467–8472, apr. 2022, https://doi.org/10.48084/etasr. 4828. [17] a. r. bouzgarrou, "analyse des formes morpho-fonctionnelles urbaines: mise en place d’un indicateur de mutations paysagères de la ville de monastir entre 1956 et 2013," ph.d. dissertation, l’universite de bretagne occidentale, loire, france, 2019. [18] r. unwin, étude pratique des plans de villes. introduction à l’art de dessiner les plans d’aménagement et d’extension. paris, france: éditions parenthèses, 1981. [19] j. jacobs, the death and life of great american cities. new york, ny, usa: vintage, 1992. microsoft word etasr_v12_n5_pp9336-9341 engineering, technology & applied science research vol. 12, no. 5, 2022, 9336-9341 9336 www.etasr.com abdulghafoor & al-baghdadi: static and dynamic behavior of circularized reinforced concrete … static and dynamic behavior of circularized reinforced concrete columns strengthened with hybrid cfrp zena h. abdulghafoor department of civil engineering university of baghdad baghdad, iraq z.abdulghafar1901m@coeng.uobaghdad.edu.iq hayder a. al-baghdadi department of civil engineering university of baghdad baghdad, iraq baghdadi.hayder@coeng.uobaghdad.edu.iq received: 26 june 2022 | revised: 14 july 2022 and 5 august 2022 | accepted: 14 august 2022 abstract-in this study, three strengthening techniques, nearsurface mounted nsm-crfp, nsm-cfrp with externally bonding eb-cfrp, and hybrid cfrp with circularization were studied to increase the seismic performance of existing rc slender columns under lateral loads. experimentally, 1:3 scale rc models were studied and subjected to both lateral static load and seismic excitation. in the dynamic test, a model was subjected to el centro 1940 ns earthquake excitation by using a shaking table. according to the test results, the strengthening techniques showed a significant increase in load carrying capacity, of about 86.6%, and 46.6%, for circularization and nsm-cfrp respectively, of the reference unstrengthened columns. on the other hand, columns strengthened with hybrid nsm-cfrp and eb-cfrp showed a different failure mode. dynamically, the lateral drift was decreased by about 75%, 47%, and 49% for earthquake amplitudes of 0.05g, 0.15g, and 0.32g respectively. finally, it was concluded, depending on the static and dynamic analyses, that the circularization process showed a significant increase in lateral load-bearing capacity. keywords-circularization; strengthening; cfrp; nsm; dynamic; slender column i. introduction most structures in iraq were built exclusively for gravity loads only, posing a significant problem when minimizing earthquake hazards is concerned. improved design standards and procedures can keep the damage to newer buildings to a manageable level in the event of a moderate to severe earthquake [1]. in this work, three strengthening techniques, externally bonding eb-cfrp, near-surface mounted nsmcrfp, and hybrid cfrp with circularization were studied to increase the seismic performance of existing rc slender columns under lateral loads. after reviewing the literature regarding the cfrp strengthening techniques, and to the best of our knowledge, there is no previous work that studied the strengthening of slender columns under seismic excitation with the use of a circularization technique. therefore, the main aims of this study are: (i) to understand the behavior of several types of strengthened reinforced concrete (rc) slender columns being subjected to different amplitudes of the el-centro 1940 earthquake, and (ii) assessing the efficacy of the strengthening techniques after exposure to seismic excitation. prior to the '70s, the majority of structures were built to withstand gravity stresses. while these structures did well under such pressures, their performance under seismic loads was doubtful. due to the ever-aging infrastructure and losses caused by significant catastrophic events worldwide, there is an increasing demand for the introduction of inexpensive and speedier retrofitting approaches. due to their increased strength, light weight, durability, corrosion resistance, and aesthetic appeal, carbon fiber reinforced polymers (cfrps) are being used more and more for strengthening and retrofitting rc structures [3]. many strengthening techniques have been developed and used to repair and rehabilitate earthquake-damaged and seismically deficient structures. the identification of an effective rehabilitation method is directly related to the outcome of a seismic evaluation of the structure and is based on the consideration of many factors, including the type of structure, its rehabilitation objective, strengthening scheme effectiveness, constructability, and cost. it is possible to employ frp materials and systems to enhance the overall seismic performance of a structure by modifying individual components. there are many advantages of using frp reinforcement strengthening to effectively decrease brittle failure mechanisms at the component level. shear failure of unconfined beam-column junctions, shear failure of beams, columns, or both, and lap splice failure are all possible. frp strengthening may also be used to raise the inelastic rotational capacity of reinforced concrete members, as well as:  to increase the flexural capacity of rc members and prevent flexural steel bars from buckling.  to improve the overall behavior of reinforced concrete structures exposed to seismic events by increasing the structure's global displacement and energy dissipation capabilities. corresponding author: zena h. abdulghafoor engineering, technology & applied science research vol. 12, no. 5, 2022, 9336-9341 9337 www.etasr.com abdulghafoor & al-baghdadi: static and dynamic behavior of circularized reinforced concrete … frp shear strengthening and confinement have a minor impact on the structure's stiffness or mass. a reevaluation of the seismic demand after strengthening is usually not necessary in such circumstances. frp strengthening of local components may be combined with other typical global upgrading approaches when structural stiffness has to be enhanced [4]. many columns have a rectangular or square cross-section because it is simpler and less expensive to construct. some columns have non-regular cross-sections, such as hexagons and other shapes. as a consequence, the goal of this research is to investigate the process of converting existing non-circular columns to circular ones and then wrapping the changed circular elements with sheet reinforcement. modifying rectangular or square members into circular columns may be done in various ways. these approaches may essentially be divided into two categories  a circular mold is used to encircle the non-circular compression element. after that, a rich concrete mix is poured to fill the gaps between the mold and the noncircular compression parts.  to generate a circular cross-section, adhesives are used to adhere previously cast and cured concrete segments to the faces of the non-circular compression component (or column) [5]. furthermore, authors in [6] found that using the circularization technique to change the form of square (noncircular) compression members to a circular shape eliminates stress concentration zones that appear at the corners of externally constrained square compression members. ii. experimental procedure a. methodolgy in the experimental work, 8 square concrete columns were casted for laboratory experiments with length and width of 130×130mm and height of 1500mm. the experimental tests are categorized into two main groups, each group with 4 columns (figure 1):  4 specimens were tested statically.  4 specimens were tested dynamically. all column specimens were designed with a normal concrete strength of �� = 30mpa. for the circularization process, plain concrete was used with concrete strength of �� = 30mpa. b. concrete casting self-compacting concrete (scc) with a compressive strength of 30mpa was used to cast the square columns due to the small cross-section of the column and the difficulty of using a vibration [7]. scc is more workable and its production makes less noise [8]. figure 5 shows the models after casting. table i lists the details of the concrete mix. fig. 1. experimental matrix. table i. details of mix design materials final mix (kg, m 3 ) cement: sand: gravel (ratio by weight) 1:1.25:1.25 water/cementitious materials ratio 0.4125 water 165 cement 400 sand 500 gravel 500 viscocrete 5930 iq 8 ml / kg of cement rapid-1 2.6ml / kg of cement c. strengthening methods 1) nsm cfrp strengthening method the grooves were formed by a diamond blade cutter. the groove size is about 10mm in depth and 5mm in width. the longitudinal distance of the groove is 1250mm with an embedded length of 300mm, so the grooves were extended below the top face of the foundation block by 300mm by drilling holes along the grooves at the foundation, and the spacing between the two grooves was 30mm. the dimensions of the grooves were calculated according to aci-440.2r-17. figures 2-4 show the columns' specifications. the grooves were filled with the adhesive material, sikadur 30lp, after mixing the epoxy adhesive according to supplier recommendations; components a (white) and b (black) were mixed in (3:1) proportion with an electric mixer until the color became a uniform grey. the cfrp strip was inserted into the middle of the groove and was pressed gently so that it was completely covered by epoxy, and then the surface was leveled and pressed well by hand [9]. finally, the columns were cured for 7 days according to the product datasheet before being tested to achieve the maximum strengthening level, as shown in figure 6. engineering, technology & applied science research vol. 12, no. 5, 2022, 9336-9341 9338 www.etasr.com abdulghafoor & al-baghdadi: static and dynamic behavior of circularized reinforced concrete … fig. 2. the column models. all dimensions in mm. fig. 3. the column sections. all dimensions in mm. fig. 4. groove details. all dimensions in mm. fig. 5. the column models after casting. fig. 6. nsm-cfrp technique procedure. 2) strengthening technique with circularization cylindrical formworks were used to change the shape of the square columns from a square cross-sectional into a circular cross-sectional shape. the molds had dimensions of 20cm diameter and 150cm height. for this study, the direct circularization method was used. in this method, the square columns were cast first. after sufficient time had passed, the cylindrical molds were put outside the square columns to perform the shape modification process. finally, it should be noted that, like the square members, the casting of circularization concrete was done vertically. the advantage of applying the direct circularization method is that the surface of final circularized columns is almost a perfect cylinder with no discontinuities or distortions. square columns that are circularized by the direct circularization method are shown in figure 7. fig. 7. circularization and cfrp-eb technique. 3) strengthening with external confinement technique the dry layup technique was used to wrap the columns using epoxy resin. first, the epoxy resin (sikadur 330) was prepared by mixing the two components of the product, a and b, in 1:4 proportions. after putting components a and b of the epoxy in one container following the proportions recommended by the product datasheet, slow mixing rate was applied by hand with a spatula. when applying the epoxy resin to the surface, the resin was spread evenly throughout the model’s surface with a tiny brush. after that, one layer of cfrp was applied to the specimens' surface. a small, serrated roller was utilized to ensure good resin impregnation inside the cfrp layer and to prevent any air bubbles from forming or get trapped inside the epoxy. furthermore, the development engineering, technology & applied science research vol. 12, no. 5, 2022, 9336-9341 9339 www.etasr.com abdulghafoor & al-baghdadi: static and dynamic behavior of circularized reinforced concrete … length for cfrp wraps is mandated by aci-440.2r-17, and is equal to 73mm [10]. a 100mm overlap was adopted for every single layer to ensure more confinement effectiveness. they were additionally arranged around the specimens like hoops. in order to prevent any air bubbles from being caught, the serrated roller spun in the fibers’ direction, the eb process is shown in figure 7. additionally, according to the product datasheet, it should be noted that cfrp wraps were left for 7 days to develop full bonding strength [11]. figure 8 shows the final shape of the models. fig. 8. final shape of column models. iii. static test to study the performance of the rc columns before and after strengthening, all columns, which included 1 column reference column and 3 strengthened columns, were loaded up to failure by applying incremental monotonic static load horizontally over the tipping point of the column where the steel cap was put to prevent local crushing. the load was measured by the testing machine's load cell, and displacement data were recorded by an lvdt placed in the free end of the column. all specimens were tested in the structural laboratory of the department of civil engineering, university of baghdad. fig. 9. static test. for each specimen, the base was screwed on all sides with a steel plate which was fixed on the frame floor by welding to avoid uplifting. an electric control jack applied the lateral load with a capacity of 40kn, which was connected to a load cell with a 200kn capacity. figure 9 shows the static test. a. static results table ii lists the results of the models after being subjected to static lateral force. figures 10-11 show the loaddisplacement curve of the models and the comparison with the reference model. table ii. static test results column code ultimate load pu (kn) load pu (kn) at 60mm δu (mm) % increase in load at 60mm r 4.11 3.15 124 / n 4.67 4.62 72.9 46.6 n-c 3.66 3.42 203.8 8.57 n-ci-c 6.52 5.88 100.5 86.6 fig. 10. load displacement of models. fig. 11. load displacement of models at 60mm displacement. b. static test results and discussion table ii and figures 10-11 lead to the conclusion that a major increase in the load-bearing capacity was detected by the column n-ci-c due to the circularization technique that provided more rigidity in comparison to the column r. column n also showed a significant increase in the loadbearing capacity but less than column n-ci-c. in contrast, the column n-c showed a different failure mode, in which it doesn’t increase the load-bearing capacity. figure 11 shows the load displacement of the models for 60mm displacement due to the serviceability limit [12]. engineering, technology & applied science research vol. 12, no. 5, 2022, 9336-9341 9340 www.etasr.com abdulghafoor & al-baghdadi: static and dynamic behavior of circularized reinforced concrete … iv. dynamic test one column from each group was tested using the shaking table developed in [13], utilizing the time history analysis method to simulate the seismic excitation. two lvdts were put at the top and the base of the columns to assess the displacement after the seismic excitation with 3 amplitudes, 0.05g, 0.15g, and 0.32g, to study the behavior of the columns that were strengthened with different techniques, as shown in figure 12, in this study, an additional mass was used to similitude the loads subjected to the column, so it was assumed that the load on the prototype is 2543kg, and the weight of the mass model is 282.6kg, according to [14]. for mass similitude, additional weight was added in the form of steel plates at the free end of the column models, which were made up for the weight deficiency of 22mm thickness and 15kg weight each. fig. 12. dynamic test. 1) dynamic test results and discussions table iii lists the results of the 4 models after being subjected to el centro seismic excitation. each column was subjected to three amplitudes, 0.05g, 0.15g, and 0.32g. figures 13 to 21 show the displacement-time curve of all models and the comparison with the reference model. fig. 13. time-displacement of r and n models with 0.05g excitation. fig. 14. time-displacement of r and n models with 0.15g excitation. fig. 15. time-displacement of r and n models with 0.32g excitation. fig. 16. time-displacement of r and n-c models with 0.05g excitation. fig. 17. time-displacement of r and n-c models with 0.15g excitation. fig. 18. time-displacement of r and n-c models with 0.32g excitation. fig. 19. time-displacement of r and n-ci-c models with 0.05g excitation. engineering, technology & applied science research vol. 12, no. 5, 2022, 9336-9341 9341 www.etasr.com abdulghafoor & al-baghdadi: static and dynamic behavior of circularized reinforced concrete … fig. 20. time-displacement of r and n-ci-c models with 0.15g excitation. fig. 21. time-displacement of r and n-ci-c models with 0.32g excitation. table iii. dynamic test results column code earthquake amplitude (g) absolute displacement (mm) relative displacement (mm) max. min. max. min. r 0.05 7.607 -4.685 2.059 -2.289 0.15 22.69 -15.12 5.127 -5.968 0.32 48.96 -33.41 5.801 -7.821 n 0.05 6.909 -4.621 0.973 -0.911 0.15 21.08 -13.51 2.233 -3.882 0.32 44.33 -30.31 3.901 -6.019 n-c 0.05 7.384 -5.117 0.924 -1.807 0.15 24.4 -14.93 3.912 -3.187 0.32 43.9 -28.9 4.115 -6.501 n-ci-c 0.05 7.352 -4.8 0.413 -0.551 0.15 22.63 -14.8 3.11 -2.54 0.32 46.05 -32.3 2.322 -3.924 table iii and figures 13-21 showed that a major reduction in the displacement was detected by the column n-ci-c due to the circularization technique that provided more rigidity compared to the column r. column n also showed a significant reduction in the displacement, but less than n-cic. in contrast, the column n-c showed a different failure mode, which doesn’t enhance the dynamic response. v. conclusions in this study, the behavior of slender columns strengthened with strengthening techniques was studied. two approaches were adopted. in the dynamic test approach, a column model was subjected to el centro 1940 ns earthquake excitation by using a shaking table. in the static test approach, a column model was subjected to a lateral load and tested up to failure. depending on the experimental test results the main conclusions can be summarized as: in the static test, the strengthening techniques showed significant increase in load carrying capacity, of about 86.6%, and 46.6%, for circularization with nsm-cfrp and nsmcfrp respectively, of the reference unstrengthened columns. in the dynamic test, columns that were strengthened with hybrid nsm-cfrp and eb-cfrp showed a different failure mode. dynamically, the lateral drift was decreased by about 75%, 47%, and 49% for earthquake amplitudes of 0.05g, 0.15g, and 0.32g respectively. the circularization process effectively avoided stress concentration zones that would otherwise occur when a noncircular column was wrapped in cfrp. as a result, the loadcarrying capacity and dynamic response improved. acknowledgment the authors wish to thank the department of civil engineering at the university of baghdad for their assistance. references [1] seismic evaluation and retrofit of existing buildings. american society of civil engineers, 2014. [2] m. saadi and d. yahiaoui, "the effectiveness of retrofitting rc frames with a combination of different techniques," engineering, technology & applied science research, vol. 12, no. 3, pp. 8723– 8727, jun. 2022, https://doi.org/10.48084/etasr.4979. [3] m. fahim, f. alam, h. khan, i. u. haq, s. ullah, and s. zaman, "the behavior of rc beams retrofitted with carbon fiber reinforced polymers (cfrp)," engineering, technology & applied science research, vol. 12, no. 3, pp. 8701–8706, jun. 2022, https://doi.org/ 10.48084/etasr.4926. [4] k. soudki and t. alkhrdaji, "guide for the design and construction of externally bonded frp systems for strengthening concrete structures (aci 440.2r-02)," in structures congress 2005, apr. 2012, https://doi.org/10.1061/40753(171)159. [5] v. l. doan, "behaviour of shape-modified columns confined with carbon fibre-reinforced polymer under eccentric loading," m.s. thesis, university of wollongong, wollongong , australia, 2013. [6] z. yan, "shape modification of rectangular columns confined with frp composites," ph.d. dissertation, university of utah, salt lake city, ut, usa, 2005. [7] m. nuruzzaman, j. o. camargo casimiro, and p. k. sarker, "fresh and hardened properties of high strength self-compacting concrete using by-product ferronickel slag fine aggregate," journal of building engineering, vol. 32, nov. 2020, art. no. 101686, https://doi.org/ 10.1016/j.jobe.2020.101686. [8] j. abd and i. k. ahmed, "the effect of low velocity impact loading on self-compacting concrete reinforced with carbon fiber reinforced polymers," engineering, technology & applied science research, vol. 11, no. 5, pp. 7689–7694, oct. 2021, https://doi.org/ 10.48084/etasr.4419. [9] c. maheswaran, s. prakash shanmugam, v. mahadik, and a. sharma, "experimental and numerical studies on effectiveness of hybrid frp strengthening on behavior of rc columns under high eccentric compression," journal of bridge engineering, vol. 24, no. 6, jun. 2019, https://doi.org/10.1061/(asce)be.1943-5592.0001420. [10] r. abokwiek, "strengthening of reinforced concrete columns using composite of near surface mounted cfrp strips and fabric," m.s. thesis, american university of sharjah, sharjah, united arab emirates, 2016. [11] ü. karagöz işleyen and h. i̇. kesik, "experimental and numerical analysis of compression and bending strength of old wood reinforced with cfrp strips," structures, vol. 33, pp. 259–271, oct. 2021, https://doi.org/10.1016/j.istruc.2021.04.070. [12] asce 7 standard. asce, 2016. [13] h. al-baghdadi, "nonlinear dynamic response of reinforced concrete buildings to skew seismic excitation," ph.d. dissertation, university of baghdad, baghdad, iraq, 2014. [14] h. harris and g. m. sabnis, structural modeling and experimental techniques, 2nd ed. boca raton, fl, usa: crc press, 1999. microsoft word etasr_v13_n4_pp11106-11111 engineering, technology & applied science research vol. 13, no. 4, 2023, 11106-11111 11106 www.etasr.com alzahougi et al.: an optimization study on resistance spot welding of dp600 sheet steel via … an optimization study on resistance spot welding of dp600 sheet steel via experiment and statistical analysis abdulkarim alzahougi department of mechanical engineering, faculty of engineering, karabuk university, türkiye aalzahougi@yahoo.com bilge demir department of mechanical engineering, faculty of engineering, karabuk university, türkiye bdemir@karabuk.edu.tr muhammed elitas department of mechanical engineering, faculty of engineering, bilecik şeyh edebali university, türkiye muhammed.elitas@bilecik.edu.tr (corresponding author) received: 22 february 2023 | revised: 20 march 2023 | accepted: 29 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5804 abstract resistance spot welding (rsw) is widely used in many automotive, boiler, and ship manufacturing industries. therefore, the optimization and effectiveness of the rsw process are very useful and costefficient processes in addition to improving weld quality. this study used various welding parameters to investigate the optimization of the rsw process of advanced high strength steel (ahss). rsw was carried out using different welding times, currents, and electrode pressure values. microstructural analysis, nugget formation, and tensile shear test were performed on samples. this study applied the taguchi method and anova to set up the welding process and optimize its results. microstructural characterization showed that the weld nugget microstructures had a high-volume fraction of martensite. using the minitab software, taguchi (doe) and anova on the tensile shear test results showed that welding current is more effective than clamping pressure on the tensile shear load-bearing capacity (tlbc). however, clamping pressure affects the weld current effects on weld performance. additionally, the tlbc of rsw samples increases, whereas increasing the clamping pressure leads to a decrease in tlbc and nugget dimensions. consequently, a detailed analysis of the rsw coefficients and their effects led to optimized results. keywords-ahss; resistance spot welding; tensile shear load bearing capacity; optimization i. introduction the main objectives of the automotive industry are increased safety, reduced fuel consumption and weight, and improved comfort [1-2]. advanced high-strength steel (ahss) is the most suitable material for these purposes. ahss is mostly joined with the rsw method, which has many advantages [3-4]. for this reason, academic and industrial research focuses on it [5-8]. in addition, many materials have been successfully welded and studied in detail on rsw so far [9-13]. optimization is one of the most beneficial approaches to match the operational plan requirements of any engineering field, such as maximizing rsw process conditions and minimizing consumption, waste, and costs [14]. from the perspective of rsw, the optimum parameters provide ideal electricity consumption and nugget geometry conditions, resulting in minimum pressing force, electrode wear, excellent heat retention, and better mechanical properties [15]. the primary reason minimum temperatures are important is that excessive heat in the rsw weld zone has detrimental effects on electrode and material properties and energy losses [16]. in addition, increased power consumption causes environmental concerns and increased carbon emissions and poses serious economic and technological problems [17]. several studies focused on the optimization of rsw. in [18], finite element analysis was used, while in [14] statistical analysis was applied. the importance of electrode pressure, electrode diameter, welding current, and welding time were highlighted in [15] but didn't mention tensile shear loadbearing capacity (tlbc) decreasing via increasing the weld engineering, technology & applied science research vol. 13, no. 4, 2023, 11106-11111 11107 www.etasr.com alzahougi et al.: an optimization study on resistance spot welding of dp600 sheet steel via … electrode clamping (ewc) pressure. however, this study reported that electrode pressure was the second most effective parameter after weld current. in [19], it was shown that welding time had a more significant effect on weld strength at low currents than at high currents, but there was no mention of ewc pressure. in [20] the mechanical properties of rsw on dp600-dp1000 sheet steels were studied, and in [6] the effects of welding time and electrode pressure on mechanical properties were investigated. in [21], the optimization of process parameters on the tensile shear strength was investigated in rsw steels. in all these studies, there are differences in the materials used and the results. this study aimed to examine whether these differences arise from differences in practical applications to clear the effect of ewc on weld properties. although many studies investigated the effect of rsw parameters on the mechanical properties of advanced sheet steel junctions, only a few studied the effects of electrode pressure, welding time, and welding current simultaneously [22-24]. furthermore, optimization is rarely seen in these studies. this study used cost-effective optimization, the taguchi method, and anova to describe the effect of electrode pressure under different welding currents and time conditions in rsw. ii. experimental and optimization studies commercial dp600 steel sheet in 250×250×1mm dimensions was supplied from tofaş otomotiv inc. in bursa, türkiye, and table i shows its chemical composition. table i. dp600 steel's chemical composition (wt.%) c mn si cr al ni s v fe 0.078 1.92 0.264 0.177 0.11 0.021 0.006 0.004 97.472 figure 1 shows the dimensions and the overlapping position of the rsw instance as a drawing, carried out according to en iso 14273. fig. 1. the geometry of the overlapped sample of the dp600 sheet steel. the size of the rsw overlapping samples was 170mm. table ii shows the different rsw parameters of the experiments. the rsw machine was ac and pneumatically controlled. before welding, the surfaces of the test pieces were cleaned with methyl alcohol. conical cu-cr alloy electrodes with an 8mm contact diameter were used in the welding process. these cross-section profiles of the rsw joint samples were prepared for optical microscopy microstructure analysis by applying standard metallographic procedures, such as grinding, polishing, and etching with a 2% nital solution. table ii. rsw welding parameters electrode clamping pressure (bar) welding current (ka) welding time (s) 3.5 4, 6 & 8 0.3 & 0.5 4.5 4, 6 & 8 0.3 & 0.5 5.5 4, 6 & 8 0.3 & 0.5 a crosshead speed of 2 mm/min was applied in tensile shear tests, in the scope of din en iso 14272, using a shimadzu ags-x universal tensile test machine having 100 kn loading capacity. the rsw parameters were adjusted using the taguchi method, as: �27�3��; �� ���: 2; ����: 27 tensile-shear strength values were evaluated using the taguchi method. the signal-to-noise ratio (s/n) is a measure of robustness, which can be used to identify the control factor settings that minimize the effect of noise on the response. s/n was calculated for each factor level combination. the formula for the larger-is-better s/n is shown in (1) [25]: �/� = −10 × log �∑ �1 !��/�⁄ � (1) where y represents the given factor level combination and n is the number of responses in the combination. the significance of the rsw parameters was adjusted by performing an anova of the pull-cut results. anova is a statistical process that can be implemented in the results of rsw samples to show the contribution of each variable in the rsw process according to a certain confidence level. different orthogonal arrays are available depending on the number and degree of process parameters. the analysis was achieved by choosing the correct orthogonal sequence for the current process. iii. results and discussion a. microstructure figure 2 shows an example of the rsw nuggets and microstructures formed at minimum weld current and weld pressure of 4 ka and 3.5 bar, respectively. the weld nugget contains heat affected zone (haz), melting, and temperature zones exceeding ac3. as shown in figure 2, the weld metal structure is composed of a martensite phase, residual maybe 29%, excluding austenite detection as it requires a detailed study. the rsw center can heat up to approximately 1900 °c during the process, but this is local heating. the farther away from the weld center, the lower the temperature. in this way, a temperature gradient is formed from the center of the weld to the base metal. a weld zone is formed as metal melts and solidifies (fusion) in a region defined as nugget, haz, and base metal regions. thus, rsw forms three different zones in the weld areas. the austenite forming in the weld metal and haz during rapid cooling by electrode water transforms to martensite, but this depends on the hardenability properties of the materials. due to the high hardenability of general ahss, dual-phase steel is like the one in this study, and martensite formation can easily be observed. engineering, technology & applied science research vol. 13, no. 4, 2023, 11106-11111 11108 www.etasr.com alzahougi et al.: an optimization study on resistance spot welding of dp600 sheet steel via … haz can be divided into martensite and dual-phase zones. in the first region, during rsw, the temperature is between the melting point and the a3 temperatures, thus, austenite was formed. on the other hand, at temperatures between a3 and a1 terminal arrest, austenite transforms into ferrite. in both the austenite and ferrite phases, there is a two-phase change amount according to the top and holding times. consequently, two zones of austenites transform to martensite during cooling after the rws cuts off the electricity. these structures can be seen clearly in figure 2. according to [26-27], the heterogeneous microstructures formed by the rsw process could be explained this way. in addition, the columnar structures elongate in a direction parallel to the electrode force. it could be estimated that the microstructure was more heterogeneous in haz than in the weld nugget. the grains of the superheated central zone mainly contain coarse martensite [27-29]. according to [27, 30], this is due to the high hardenability of dp steels, primarily due to high mn and other alloying elements, despite the low carbon ratio. moreover, this hardenability strictly depends on external cooling conditions. in force applications, the damage of rsw welded joints of dp steels mainly occurs in the softening zone under the tempering effect in the haz or the base material bordering this zone. this issue is more sensitive, especially in high-carbon and highstrength dp steels. fig. 2. macrostructure and microstructure of dp600 rsw sample welded with 4 ka 3.5 bar: a) base metal (bm), b) fusion zone (fz), c) heat affected zone (haz). b. nugget formation previous studies have experimentally investigated nugget formation throughout the rsw. weld strength is the most important feature that determines the weld quality of rsw specimens, which largely depends on the geometry and dimensions of the nuggets [31]. therefore, it is essential to understand the geometry and dimensions of the nuggets [3, 3234]. table ⅲ shows the results. the most oversized nugget diameter was obtained at 8.25 mm, and this result can be accepted for the base metal in the scope of the 5√ rule, where t is the thickness of the material [27]. different studies have reported different ranges for nugget diameter. nugget diameter was in the range of 6.35-8.95 mm in [35], approximately in the range of 3-8 mm in [36], approximately 7.0 mm in [37], 2.977.14 mm in [16], and 4.8-5.58 mm in [38]. compatible values could be observed when comparing these results with the ones of this study. on the other hand, differences in the results can be attributed to welding parameters, electrode tip type, electrode tip diameters, and so on. furthermore, nugget formation depends on welding time, welding current, other periods, welding pressure, and cooling phenomenon [3, 32]. according to [3], rsw nugget formation can be studied in three phases: recovery and progression, growth, and reaching equilibrium. during the rapid, typically shorter than one cycle, development phase, nugget forms due to the metal melting on the metal resistance. the nugget overmagnifies its grade faults during development, occurring over 0.04-0.08 s. eventually, nugget development completes after about 0.08 s [39]. the weld current and time increase the dimensions of the nugget caused by increasing weld heat input [3, 38, 40]. however, increasing the electrode clamping pressure reduces electrical resistance. thus, the heat generated at the interface is reduced, resulting in a smaller nugget size [3, 31, 40]. table iii shows that the diameter of the nugget increases with increasing current and decreases with increasing electrode clamping pressure. table iii also shows that an increase in time increases both the penetration rate of the welding and the diameters of the nugget at a constant electrode pressure and increased welding current. therefore, it could be deduced that the nugget fusion zone size increases with the highest load, indentation ratio, and failure force. in [41], it was reported that there is an essential relationship between weld nugget dimensions, tensile shear load-bearing capacity, and tensile fracture energy. table iii. change of nugget with different welding parameters electrode clamping pressure (bar) welding current (ka) nugget diameter (mm) 0.5s 0.3s 3.5 4 5.52 4.62 6 6.15 5.87 8 8.25 7.67 4.5 4 4.85 4.08 6 5.73 5.52 8 7.80 7.55 5.5 4 4.45 3.82 6 5.64 5.24 8 7.50 7.31 c. tlbc vs weld current via electrode clamping pressure figure 3 shows the results of the tensile shear tests. in general, increasing the electrode clamping pressure decreased the tlbc value for both weld time group samples. for example, samples with 4 ka weld current and 0.5 s weld time indicated that tlbc decreases by 0.0178 when the electrode's clamping pressure increases from 3.5 to 4.5 bar. tlbc decreases by 0.052 when electrode clamping pressure increases from 3.5 to 5.5 bar. furthermore, when the electrode clamping pressure increases from 4.5 to 5.5 bar, the tlbc decreases by 0.0033. a similar trend is also noticed when using 6 ka weld current and 0.5 s weld time. moreover, the tlbc values of 0.3 s weld time samples have more gaps than the 0.5 s weld time samples. however, increasing the weld current also increased the gap between the highest and lowest tlbc values, according to the weld current and electrode clamping pressures. in addition, 8 ka with a 3.5 bar provided the optimal value for 0.5 s samples. in [1, 11, 42-43], it was noticed that an increase engineering, technology & applied science research vol. 13, no. 4, 2023, 11106-11111 11109 www.etasr.com alzahougi et al.: an optimization study on resistance spot welding of dp600 sheet steel via … in welding current increased tlbc for rsw of various metals. the highest tlbc values obtained at 8 ka 3.5 bar in the literature were 17.76 [16], 16.67 [35], and 13.69 kn [36]. the highest tlbc value was reported in [16] for similar weld current and electrode pressure values for dp600. therefore, the differences observed in the maximum tlbc values can be attributed to differences in the chemical composition of the steel samples and their sheet thickness. in that respect, this study's tlbc values could be seen as being close to [16]. a) b) fig. 3. current influence on tensile shear load-bearing capacity in different parameters at a) 0.3 s and b) 0.5 s welding time. d. taguchi analysis for tlbc the optimum joint values were determined for the maximum tensile shear strength. depending on the experiments, the 8 ka 0.5 s 3.5 bar set of values achieved the optimum results. in [38], weld time was found to influence tlbc due to the joule effect. if weld time increases, the tlbc of the specimen increases due to the increased nugget diameter. table ⅳ and figure 4 demonstrate the results of the taguchi analysis. the optimal value of s/n was 22.69 for force level 1. the taguchi method results from minitab were compatible with the experimental results. the optimal s/n values obtained from other studies were 16.18 for force level 2 [21], 16.70 for force level 2 [14], and 9.37 and 19.53 for force level 2 and 1 and 2 mm thickness, respectively [15]. this study obtained higher s/n ratios than the others examined. higher s/n values are known to define control factor settings that minimize the effects of noise factors. table iv. response analysis for s/n ratios level f i 1 22.69 22.08 2 22.46 22.26 3 21.98 22.78 fig. 4. the main response effects plot of parameters for s/n. fig. 5. interaction of the effect of force and current on s/n. table v. influence of parameters on s/n force current tlbc s/n ratio 3.5 4 12.979 22.271 3.5 6 13.316 22.495 3.5 8 14.583 23.272 4.5 4 12.772 22.119 4.5 6 13.074 22.323 4.5 8 13.999 22.922 5.5 4 12.351 21.834 5.5 6 12.498 21.937 5.5 8 12.779 22.139 the left side of figure 5 demonstrates the inverse correlation between force and s/n. table v shows that the highest s/n value was 23.272 at 3.5 bar – 8 ka and decreased with increasing force to more than 3.5 bar at constant current. the right side of figure 5 shows the effect of welding current on the s/n. when the welding current increases, the s/n ratio increases at a fixed clamping pressure. however, in [14] the highest value was 18.77, in [21] the highest value was 18.46, and in [15] the highest values were 11.43 and 20.56 for 1 and 2 mm thickness, respectively. therefore, this study achieved higher s/n results than the reviewed studies. higher than best (hb) includes tlbc and nugget diameter with higher values. lower than best (lb) concerns haz, for which a lower value is preferred [15]. as seen in table ⅴ, s/n was found to be maximum at maximum tensile strength, and the minimum value of s/n was 21.834 at 4 ka welding current and 5.5 bar. while the tensile shear is minimal, the s/n varies according to the parameters, is directly proportional to the engineering, technology & applied science research vol. 13, no. 4, 2023, 11106-11111 11110 www.etasr.com alzahougi et al.: an optimization study on resistance spot welding of dp600 sheet steel via … welding current, and reverses with the clamping pressure after 3.5 bar. e. anova for tlbc as shown in table ⅵ, tlbc results for current welding parameters are more effective than clamping pressure. in [44], the taguchi method indicated that in order of importance, preheat welding current, preheat welding time, hold time, welding current, and welding time were the key parameters that affected the tensile shear strength. according to anova in [21], the effective parameters for tensile shear strength were welding current, welding time, electrode pressure, and electrode tip diameter. the welding current was the most important factor affecting the tensile strength (68.93%), while the welding time was the second (18.66%). in [14], welding current contributed the most (53.57%), while hold time showed less effect on tensile shear strength. in [15], the welding current was also the most important factor affecting the tensile strength (57.80% for 1 mm and 40.56% for 2 mm of sheet thickness), while the electrode force was the second most important factor (29.22% for 1 mm and 35.42% for 2 mm of sheet thickness). therefore, the most important parameter affecting tlbc is the welding current. figure 6 shows the anova results of tlbc for welding current and clamping pressure. the maximum values were obtained at 3.5 bar – 8 ka, and the minimum at 5.5 bar – 4 ka. table vi. anova for tensile shear source df seq ss adj ss force 2 1.84620 1.84710 current 2 1.91440 1.91530 total 8 4.16374 4.16464 fig. 6. anova for tensile shear. iv. conclusion the following results can be drawn from this study:  while rsw nugget size and s/n ratio are directly proportional to the welding current and time, they are inversely proportional to the clamping pressure, according to both experimental and statistical analysis.  tlbc increased in direct proportion to the weld nugget size. the best values of tlbc were estimated for different values of welding parameters and were 8 ka 3.5 bar.  the maximum s/n values for tlbc were 22.69 at force level 1 and 22.78 at 8 ka. the maximum and minimum interaction effect values were 23.272 and 21.834 at clamping pressure and welding current of 3.5 and 5.5 bar and 8 and 4 ka, 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[44] r. neystani, b. beidokhti, and m. amelzadeh, "fabrication of dissimilar fe-cu-c powder metallurgy compact/steel joint using the optimized resistance spot welding," journal of manufacturing processes, vol. 43, pp. 200–206, jul. 2019, https://doi.org/10.1016/j.jmapro.2019.05.014. microsoft word etasr_v13_n3_pp10936-10940 engineering, technology & applied science research vol. 13, no. 3, 2023, 10936-10940 10936 www.etasr.com nimmakayala & vemuri: analysis of ionospheric scintillations using gps and navic combined … analysis of ionospheric scintillations using gps and navic combined constellation shiva kumar nimmakayala department of eece, gitam school of technology, gitam deemed to be university, india 121960402502@gitam.in (corresponding author) bala sai srilatha indira dutt vemuri department of eece, gitam school of technology, gitam deemed to be university, india svemuri@gitam.in received: 17 march 2023 | revised: 19 april 2023 | accepted: 21 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5863 abstract the disturbances and irregularities in the ionosphere are the primarily recognized ramifications of space weather called scintillations. irregularities in the electron densities are the source of the ionospheric scintillations. this article investigates the ionospheric scintillations, which are predominant in the transequatorial and equatorial regions. based on the data from a multi-constellation global navigation satellite systems (gnss) receiver at the chaitanya bharathi institute of technology hyderabad, the relationship between the amplitude scintillation index s4 and the rate of change of total electron content (roti) is examined. the correlation coefficient between s4 and roti is demonstrated in this article. the outcome validates the usefulness of the roti in identifying the scintillations. keywords-ionospheric scintillations; rate of change of total electron content; amplitude scintillation index; global navigation satellite system (gnss) i. introduction the advancement of the global navigation satellite system (gnss), which encompasses glonass, gps, beido, galileo, and numerous regional navigation systems, directed advanced steps in the earth’s atmosphere research [1]. the space-based investigation of the gnss signals is one of best enforced ways to investigate the ionosphere [2]. the space weather trans-ionospheric signals can undergo expeditious variations and disturbances both in amplitude and phase when they pass through indiscriminate electron density irregularities which are present in the ionosphere [3-4]. this anomaly is generally referred to as ionospheric scintillations. the temporal and spatial status of the ionospheric scintillations depends on geographical and geophysical locations, the time of the day, and season [5-6]. the ionospheric scintillations are the major sources of degradation of the vhf band and c band signals, immensely effecting navigation and communication systems [7]. hence, it is vital to investigate and analyze them. the gnss signals are considered a robust tool to investigate the total electron content (tec) and the existence of ionospheric scintillations [8]. phase and amplitude scintillations are both ionosphere irregularities. ii. gnss data collection for this analysis, the data of the multi constellation gnss receiver of chaitanya bharati institute of technology, which is located in hyderabad, during the period from 2020-06-07 to 2020-06-13 were taken into account. the considered parameters are time, prn (pseudo random number) of the satellite, carrier to noise values of the received signal, and the ionospheric delay of the received signal. to reduce complexity, only the results of 2020-06-07 are shown in this paper. iii. methodoly the ionospheric irregularities and scintillations can be investigated in two ways when using gnss signals. the first of these methods uses carrier to noise (� ��⁄ ) ratio to calculate the amplitude scintillation index s� [9] and the second one uses ionospheric delay to calculate the rate of change of tec index (roti) which is the replacement index of s� [10]. the current work is based on the multi-step interpretation and processing of the l (1575.42mhz), l� (1176.45mhz), and s (2492.028mhz) gnss signals corresponding to gps and navic satellite constellations. in the first method, the amplitude scintillation index s� is calculated as the ratio of the standard deviation to the mean value of the averaged � ��⁄ [9]. the effectiveness of the amplitude scintillations index is divided into 3 categories which are week scintillations when s� is less than 0.3, moderate scintillations when s� ranges between 0.3 and 0.6, and strong scintillations when s� is above 0.6 [11]. the amplitude scintillations are calculated as follows: �� = 〈�� �〉�〈��〉� 〈��〉� (1) engineering, technology & applied science research vol. 13, no. 3, 2023, 10936-10940 10937 www.etasr.com nimmakayala & vemuri: analysis of ionospheric scintillations using gps and navic combined … where si is the intensity of the received trans-ionospheric signal. the s� value is computed using the signals received on the l (1575.42mhz), l� (1176.45mhz) and s (2492.028mhz) frequencies for a week-long data from 202006-07 to 2020-06-13. the second method is to calculate the roti using the delay due to ionosphere in the received signals [12]. the ionospheric delay is computed by: �����= ��.� �� *tec (2) where tec indicates the total electron content on the frequency of the received trans-ionospheric signal and ����� is the ionospheric delay of the received signal. tec is used to describe all the electrons that are present along the path from the satellite to the receiver [12-13]. the tec is expressed below and is measured in tecu: 1 tecu = 10 � e/m! (3) tec = �"#$% ∗�� ��.� (4) the rate of change of tec (rot) is calculated at regular intervals by (5): rot = '()*+�'()*,-+ .*�.*, (5) where b specifies the epoch time and a specifies the noticeable satellite. roti is calculated by the standard deviation of rot: roti = /〈rot!〉 3 〈rot〉! (6) the effectiveness of roti is divided into three categories: it is fragile when the roti index ranges between 0.25 and 0.5, modest when the roti index ranges between 0.5 and 1, and vigorous when the roti index is above 1 [14-15]. roti was calculated for signals received on l , l�, and s frequencies for a weak long data from 2020-06-07 to 2020-06-13. to observe the correlation between roti and s� , the covariance and standard deviation of s� and roti are computed [16] by: 41�5 = 〈s�!〉 3 〈s�〉! (7) 416�'� = /〈roti!〉 3 〈roti〉! (8) the covariance of s� and roti is: � 6�'��5 = ∑ 9:5�:5 ;;;;)9<=>?�<=>?;;;;;;;;) @ @� (9) where a�b is the mean of �� and roti;;;;;;; is the mean of roti. the correlation coefficient is a measure of the correlation between roti and s� methods which is expressed by c 6�'��5 , and it is given as: c 6�'� �5 = ϲ-efghi5 j efghj i5 (10) where ϲ16�'��5 specifies the covariance of s� and roti . the flowchart of the followed methodology is shown in figure 1. fig. 1. flowchart of the methodology. iv. results and discussion the pseudo range measurements data of multi-constellation gnss receiver, which were sampled every 1s, are considered for computation and analysis of amplitude scintillations, rot, and roti. figure 2 specifies s� for all the available satellites on 2020-06-07 for the l1 frequency. the highest scintillations are observed from the satellite prn 9. therefore, the values of s� and roti are compared to the prn 9 values. fig. 2. s� index on 2020-06-07 for the l1 frequency. figure 3 shows the comparison plot for s� and roti for the prn-9, which exhibits maximum scintillations. figure 4 shows the correlation between roti and s�. the x axis specifies the epoch time for every hour and the y axis the correlation coefficient between s� and roti. the highest correlation coefficient is 1 and the minimum is higher than the cutoff level. as a result, the correlation coefficient is robust due to the persistent link between roti and s�. figure 5 depicts the comparison of s� for all the available navic satellites on 2020-06-07 for the l5 frequency. the maximum observed s� index is 0.0205 for ir-02, which is an indication of no scintillations on 2020-06-07 for the l5 frequency. the highest s� values are observed in the ir-02 satellite. therefore, the values of s� and roti are compared to the ir-02 values. engineering, technology & applied science research vol. 13, no. 3, 2023, 10936-10940 10938 www.etasr.com nimmakayala & vemuri: analysis of ionospheric scintillations using gps and navic combined … fig. 3. comparison of �� and roti on 2020-06-07 for prn-9 (l1 frequency). fig. 4. correlation of of s� and roti on 2020-06-07 for prn-9 (l1 frequency). fig. 5. s4 amplitute variations on 2020-06-07 for l5 frequency. fig. 6. comparison of s� and roti on 2020-06-07 for ir-02 (l5 frequency). in figure 6, the maximum s� index value of 0.0078 and the maximum roti index value of 0.1911 are observed. from these, it can be concluded that no scintillations are observed on the l5 frequency for ir-02. figure 7 shows the correlation between s� and roti. the maximum correlation of 1 is observed many times, which is an indicative of the similarity between s� and roti. figure 8 shows the s� variations of all visible navic satellites on 2020-06-07 for the � frequency. the maximum observed s� index is 0.0294 for ir-02, which is an indication of no scintillations there on 2020-06-07 for the s frequency. the highest s4 values are observed in the ir-02 satellite. therefore, all s� and roti values are compared with the ones of the ir-02 satellite. fig. 7. correlation of s� and roti on 2020-06-07 for ir-02 (l5 frequency). fig. 8. s4 amplitute variations on 2020-06-07 for s1 frequency. fig. 9. comparison of s4 and roti on 2020-06-07 for ir-02 (s1 frequency). figure 9 shows that the maximum s� index value is 0.0078 and the maximum roti index value is 0.1911. from this it can engineering, technology & applied science research vol. 13, no. 3, 2023, 10936-10940 10939 www.etasr.com nimmakayala & vemuri: analysis of ionospheric scintillations using gps and navic combined … be concluded that no scintillations are observed on the s frequency for ir-02. figure 10 shows the correlation between s4 and roti for navic satellite ir-02 on 2020-06-07 on the s frequency. maximum correlation is observed many times, which indicates that roti can be considered as an alternative metric for the s� index. figure 11 shows the skyplot of all the visible gps and navic satellites at 15:00hrs of 2020-06-07 for the igs (international gnss service) station which is located at hyderabad (lat/long:17.417 0 n/78.551 0 e). fig. 10. correlation of s4 and roti on 2020-06-07 for ir-02 (s1 frequency). fig. 11. sky plot of visible satellites at 15:00 hrs on 2020-06-07. v. conclusions in this article, the analysis of gnss trans-ionospheric signals for a typical day (2020-06-07) is presented. in order to identify the ionospheric perturbations, the amplitude of the scintillations s�, the rate of the change of total electron content (rot), and its index (roti) are computed on l1, l5, and s frequencies using gps and navic combined constellation. based on the correlation coefficient, maximum similarity between the s� and roti is observed, and, thus, roti can be considered as an alternative index for the investigation of the amplitude scintillations. it is also observed that the ionospheric scintillations are robust only on l1 frequency of the gnss trans-ionospheric signals and no 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[16] x. luo, s. gu, y. lou, l. cai, and z. liu, "amplitude scintillation index derived from c/n0 measurements released by common geodetic gnss receivers operating at 1 hz," journal of geodesy, vol. 94, no. 2, feb. 2020, art. no. 27, https://doi.org/10.1007/s00190-020-01359-7. microsoft word etasr_v13_n1_pp9893-9898 engineering, technology & applied science research vol. 13, no. 1, 2023, 9893-9898 9893 www.etasr.com sarade & ruikar: development of a uwb multiband mimo antenna with enhanced isolation and … development of two uwb multiband mimo antennas with enhanced isolation and crosscorrelation shrenik sarade electronics engineering department, walchand college of engineering, india shreniks2k7@rediffmail.com (corresponding author) sachin ruikar electronics engineering department, walchand college of engineering, india sachin.ruikar@walchandsangli.ac.in received: 17 october 2022 | revised: 4 november 2022 and 17 november 2022 | accepted: 19 november 2022 abstract an ultra-wide band (uwb) mimo antenna working at millimeter-wave is proposed in this research. it is composed of eight radiating elements with various shapes. it is designed with a rectangular structure and various carved slots. the carved slots are used to increase the antenna's bandwidth. the antenna's radiating elements are placed near one another, and thus, isolation is widespread. in order to improve the isolation of the mimo antenna, parasitic elements and a defective ground structure are used. antenna parameters such as correlation coefficient (cc), envelope correlation coefficient (ecc), diversity gain (dg), and total active reflection coefficient (tarc) depend on the isolation. parasitic elements with a rectangular form are positioned between the radiating patches. rectangular-shaped ground structures with defects comprise the ground plane. an fr-4 substrate is used to fabricate the antenna. the analysis of the antenna shows that there is less than -14db return loss, less than -40db isolation, less than 0.0010 crosscorrelation, less than 0.10 tarc, and higher than 500mhz bandwidth. the antenna uses a fractional bandwidth higher than 35% (uwb) for the 6ghz frequency and operates on a variety of bands. this antenna is suitable for many different wireless system applications. keywords-mimo; uwb;dgs; tarc; cc; ecc; dg i. introduction modern antenna technology relies heavily on multiple input-multiple output (mimo) antennas with several antennas in both transmitter and receiver. mimo antenna systems increase the poor data rate of the single input-single output (siso) system. depending on the number of patches in the antenna, the data rate of the mimo antenna increases linearly. return loss, isolation, correlation coefficient (cc), and total active reflection coefficient (tarc) represent a mimo antenna's performance. multiple radiating patches are arranged on the same substrate in a mimo antenna [1]. the radiating elements are positioned near one another. the isolation and the cc are influenced by the close proximity of the rectangular radiating patches. the data rate is reduced by the isolation. the isolation, cc, and data rate of the antennas all need to be improved. various techniques, such as defective ground structure (dgs), parasitic elements (pes), metamaterials, decoupling structures (dss), and electromagnetic band gap (ebg) are used to increase isolation and cc. in the ground plane, carved holes of different shapes are employed in dgs methods [2-7]. in order to promote isolation, a decoupling structure is built that isolates the input of the radiating patches from the corresponding network arrangement in [8-12]. to increase the isolation between the patches, parasitic components are utilized in [13–18]. using the literature mentioned above, it is necessary to create a mimo antenna that operates on a multiband application with an ultra-wide bandwidth, improved tarc, and better cross correlation. in previous works, the same shaped radiating elements were used to design an mimo antenna, whereas the cross correlation (cc and ecc) between the radiating elements was high. in this study, a 2-mimo antenna with a variety of shapes is proposed. the antenna is developed using radiating elements of different shapes. the designed antenna operates on a multiband and its bandwidth is uwb. for bandwidth improvement, a rectangular shaped cut slot is introduced between the radiating elements of the antenna. the isolation between the radiating elements is improved using dgs and pes. antenna parameters such as isolation, cross correlation (cc and ecc), and tarc depend on isolation. engineering, technology & applied science research vol. 13, no. 1, 2023, 9893-9898 9894 www.etasr.com sarade & ruikar: development of a uwb multiband mimo antenna with enhanced isolation and … the novelty of the current work is that the radiating elements are developed in different shapes, the rectangular shaped dgs cut slot and pes are designed for the improvement of isolation, cc, ecc, tarc, and dg. for the improvement of the bandwidth, different rectangular cut slots are designed and introduced in the radiating elements. ii. design of a massive mimo antenna using defective ground structure (dgs) in this section, the design of the massive mimo antenna is explained in detail. the designed antenna comprises 8 rectangular radiating patches with distinct cut slots for the 6ghz frequency with the antenna dimensions, as shown in figure 1. the antenna is analyzed and fabricated using an fr-4 substrate with 1.6mm height (h) and 4.4 dielectric constant. the radiating element's geometrical features, such as length (lp) and width (wp) have been created using the rectangular radiating patch transmission line model [21-23] (table i). table i shows the measurements of the 8 radiating elements with varying cut slots. a rectangular cut slot [21-22] is placed in the radiating elements p1 to p8. patch 1 has rectangular cut slots-1 and 2 (cs-1 and 2). patches 2, 3, and 7 have the rectangular cut slot-2. cut slot-3 is placed in patches 6 and 8. in patch 4, rectangular cut slot-1 is introduced. patch 5 introduces rectangular cut slots-1 and 3 (cs-1 and 3). the radiating elements of the antenna are excited using an inset feed line (ifl) [21-22]. the fabricated antenna structure is shown in figure 3. the antenna is fabricated on the fr-4 substrate. the radiating elements of the antenna are placed close to each other. therefore, the isolation between the radiating elements is high. isolation of the antenna affects the performance parameters of the antenna [21-22]. fig. 1. the dimensions of a developed massive mimo antenna (top side). fig. 2. the dimensions of a ground plane (back side) of the antenna. engineering, technology & applied science research vol. 13, no. 1, 2023, 9893-9898 9895 www.etasr.com sarade & ruikar: development of a uwb multiband mimo antenna with enhanced isolation and … fig. 3. fabricated top side of a massive mimo antenna. table i. mimo antenna dimensions parameter dimensions (mm) patch length (lp) 11.38 patch width (wp) 15.21 width of ifl n = 6.41 length of ifl m= 2.942 width of cut slot-1 n = 6.41 length of cut slot-1 m= 2.942 width of cut slot-2 m= 2.942 length of cut slot-2 n = 6.41 width of cut slot-3 k = 12.69 length of cut slot-3 m= 2.942 length of a substrate lg= 32.58 width of a substrate wg = 74 length of a dgs cut slot a = 5.884 width of a dgs cut slot b = 6.38 fig. 4. fabricated back side (ground plane) of a massive mimo antenna. hence, there is a requirement to improve the isolation between the radiating elements. for isolation improvement, the dgs cut slots g1 to g8 [2-7] are introduced in the ground plane as shown in figure 2, whereas the fabrication of the ground plane is shown in figure 4. the dimensions of the ground plane with dgs are shown in table i. the result analysis of the antenna (for radiating elements-1 and 4) is shown in figures 5 and 6. the antenna parameters are tested in the vector network analyser (vna). the analysis shows -14.40db return loss and -42.72db isolation have been measured in the -6db line of return loss. at the -6db line of return loss, the antenna operates on the frequency band of 0.33ghz-7.5ghz. this antenna is operated on uwb. the voltage standing wave ratio (vswr) is illustrated in figure 7. the vswr for the antenna is less than 3.65db. fig. 5. result of return loss s11 and isolation. fig. 6. result of return loss s44 and isolation. fig. 7. vswr of radiating elements of the antenna. fig. 8. radiation pattern of the antenna. engineering, technology & applied science research vol. 13, no. 1, 2023, 9893-9898 9896 www.etasr.com sarade & ruikar: development of a uwb multiband mimo antenna with enhanced isolation and … figure 8 shows the radiation pattern for the gain of the antenna. the gains g1, g2 and g3 of the antenna are measured at ɸ=0 0 , ɸ=90 0 and ɸ=180 0 , respectively. the obtained gain of the antenna is 1.54db. the antenna parameters, such as tarc, cc, ecc, and dg depend on the return loss and isolation [2122]. the analysis of the antenna shows cc less than 0.153, ecc less than 0.0237, tarc less than 0.137 (-8.63db), and 9.99 dg. iii. design of the massive mimo antenna using parasitic elements in this section, the massive mimo antenna is designed using pes for the frequency of 6ghz as shown in figure 10. it consists of 8 radiating elements (patch 1 to 8), which are designed using a rectangular shaped transmission line model [21-23]. radiating elements 2, 4, 7, and 8 have rectangular cut slots. the radiating elements are placed close to each other and the isolation between them is high. for the isolation enhancement between the radiating elements, rectangular shaped pes (p1 to p14) are placed among them [21-23]. the dimensions of the antenna are shown in figure 9 and table ii. the pes are used to negate parts of the coupled field between the radiating elements because they create the opposite coupling field, which lessens the original field and hence reduces the total coupling on the antenna. the pe structure and the radiating patch are not physically related [22]. figure 9 exhibits the fabricated antenna (top side). this antenna is fabricated on the fr-4 substrate which has a 4.4 dielectric constant and 1.6mm height. the fabricated ground plane (back side) of the antenna is shown in figure 11. the ground plane has 36.522mm length (lsub) and 90mm width (wsub). the result analysis of the antenna (for radiating elements-2 and 6) is shown in figures 12 and 13. the antenna parameters are tested in the vna. the measured return loss and isolation in the -6db line of return loss are -13.96db and -46.46db, respectively. at the -6db line of return loss, the antenna operates on two frequency bands, namely, 0.82-1.76ghz and 3.03-7.5ghz. this antenna operates on uwb. figure 14 shows the radiation pattern of the gains of the antenna. the gains g1, g2 and g3 of the antenna are measured at ɸ=0 0 , ɸ=90 0 , and ɸ=180 0 , respectively. the obtained gain of the antenna is 2.73db. the ecc is less than 0.001, cc is less than 0.01, dg is close to 10, and tarc is less than 0.015 (-8.23db) [21-23]. table ii. dimensions of a massive mimo antenna using pes parameter dimensions (mm) patch length (lrrp) 11.34 patch width (wrrp) 15.234 width of ifl b = 6.41 length of ifl a= 2.942 width of cut slot b = 6.41 length of cut slot a= 2.942 pe width (p1 to p10) d= 2.942 pe length (p1 to p10) c= 11.34 pe width (p11 to p14) e= 15.234 pe length (p11 to p14) d= 2.942 length of substrate lsub= 36.522 width of substrate wsub = 90 fig. 9. the fabricated mimo antenna (top side). fig. 10. dimensions of the massive mimo antenna using pes. engineering, technology & applied science research vol. 13, no. 1, 2023, 9893-9898 9897 www.etasr.com sarade & ruikar: development of a uwb multiband mimo antenna with enhanced isolation and … fig. 11. the fabricated mimo antenna (back side-ground plane). fig. 12. result analysis of return loss s22 and isolation. fig. 13. return loss s66 and isolation. fig. 14. radiation pattern of the antenna. iv. antenna performance comparison the major contribution of the designed antenna is the different-shaped radiating elements. the antenna parameters are enhanced using two different techniques, namely, dgs and pes. the designed antenna can operate on various uwb applications. the analysis shows that the cross correlation and tarc are better than the ones reported in previous research works. the comparison of the proposed antenna parameters with the other research works is shown in table iii. the proposed antenna is developed with 8 differently shaped radiating elements. it operates on a multiband frequency with a wide bandwidth. table iii. comparison of the proposed work with other works ref method parameter values frequency band and bandwidth radiating patches [2] dgs -10 db rl, -12db isolation single band and narrow band 8 same shaped radiating patches [8] ds -20 db rl, -15db isolation dual band and narrow band 8 same shaped radiating patches [13] pe -10 db rl, -10db isolation dual band and wide band 8 same shaped radiating patches proposed (section ii) dgs -14.40 db rl, -42.72db isolation 0.33-7.5ghz and uwb with better cross correlation 8 radiating patches of different shapes proposed (section iii) pe -13.96 db rl, -46.46db isolation 0.82-1.76ghz and 3.03-7.5ghz and uwb with better cross correlation 8 radiating patches of different shapes v. conclusion in this paper, two mimo antennas were designed. first, an antenna was developed using the dgs technique. the isolation, cc, ecc, tarc, dg, and channel capacity of the antenna were enhanced with the use of dgs. the dgs cut slots were introduced in the ground plane of the antenna. the analysis shows -14.40db return loss and -42.72db isolation measured in the -6db line of return loss. at that line, the antenna operates on the frequency band of 0.33-7.5ghz. this antenna is operated on multiband applications with ultra-wide bandwidth. another antenna was developed using pes. the antenna parameters cc, isolation, ecc, tarc, dg, and channel capacity were enhanced. the pes were placed between the radiating elements. the analysis shows -13.96 db return loss and -46.46db isolation measured in the -6db line of return loss, in which the antenna operates on two frequency bands, namely 0.82-1.76ghz and 3.03-7.5ghz. references [1] z. a. shamsan, "statistical analysis of 5g channel propagation using mimo and massive mimo technologies," engineering, technology & applied science research, vol. 11, no. 4, pp. 7417–7423, aug. 2021, https://doi.org/10.48084/etasr.4264. 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[20] p. bora, p. pokkunuri, and b. t. p. madhav, "the design of closed square rr loaded 2-port mimo for dual band applications," engineering, technology & applied science research, vol. 12, no. 2, pp. 8382–8387, apr. 2022, https://doi.org/10.48084/etasr.4760. [21] s. s. sarade and s. d. ruikar, "a different shaped radiating element wide band multi-band massive mimo antenna for 5g/wlan applications with enhanced correlation coefficient," iop conference series: materials science and engineering, vol. 1187, no. 1, jun. 2021, art. no. 012017, https://doi.org/10.1088/1757-899x/1187/1/012017. [22] s. sarade and s. r. ruikar, "development of a wide bandwidth massive eight dissimilar radiating element multiband mimo antenna for mm-wave application," engineering, technology & applied science research, vol. 12, no. 5, pp. 9166–9171, oct. 2022, https://doi.org/10.48084/etasr.5133. [23] c. a. balanis, antenna theory: analysis and design, 3rd ed. hoboken, nj, usa: wiley, 2005. authors profile shrenik sarade has received the degree in electronics engineering from pvpit, budhagaon, sangli, under the aegis of shivaji university, kolhapur, in 2007. he has received the postgraduate degree in electronics engineering from tkiet, warananagar, shivaji university, and kolhapur, india in 2014. he is pursuing his phd in electronics engineering under wce, sangli, affiliated to shivaji university, kolhapur. sachin ruikar has received the degree in electronics and telecommunication from gce, aurangabad, in 1998. he has received a postgraduate degree in electronics and telecommunication engineering from coep, pune university, india in 2002. he has completed his phd in electronics in the shri guru gobind singh institute of engineering technology, srtmu nanded, in 2013. presently, he is working as an associate professor in electronics engineering at wce, sangli, india. his research interests include image denoising with wavelet transforms, image fusion, image painting, and image superresolution microsoft word 13-696.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1103-1108 1103 www.etasr.com dragan et al.: a comparative analysis between optimized and baseline high pressure compressor stages a comparative analysis between optimized and baseline high pressure compressor stages using tridimensional computational fluid dynamics valeriu dragan computational fluid dynamics department nrdi comoti bucharest, romania valeriu.dragan@comoti.ro ion malael computational fluid dynamics department nrdi comoti bucharest, romania ion.malael@comoti.ro bogdan gherman computational fluid dynamics department nrdi comoti bucharest, romania bogdan.gherman@comoti.ro abstract—re-vamping of industrial turbo-machinery is commonplace in the oil and gas industry in applications where subterranean combustion is used for oil extraction. the current case study refers to such an industrial compressor re-vamping, using a state of the art 3d fully viscous cfd methodology coupled with artificial neural networks (anns) and genetic algorithms (ga). the ann is used to establish correlations within a database of cfd simulations of geometrical variations of the original rotor and the ga uses those correlations to estimate an optimum. the estimate is then tested with the same cfd method and the results are fed back into the database, increasing the accuracy of the ann correlations. the process is reiterated until the optimum estimated by the ga is confirmed with the cfd simulations. the resulting geometry is superior to the original in terms of efficiency and pressure ratio as well as the range of stabile operation, as confirmed by the successful implementation in the field. in this paper we present an analysis of why the optimized geometry achieves superior performances to the original one. further work will present comparison between the detailed experimental data and cfd. keywords-optimization; cfd; turbomachinery; centrifugal compressor; artifficial neural network; genetic algorithm i. introduction current competiveness requirements in the turbo-machinery industry call for increased operational qualities of the final product. using modern cfd methods, a tailored made solution, which considers more than one criteria, can be obtained and solution customization can be obtained. this paper presents a re-vamping, optimization case study for a high pressure compressor stage used in the petrol industry. the design theme demanded for a 10 percent increase in mass flow as well as an increase in the isentropic efficiency while maintaining the same outlet diameter, height and rotor aspect ratio. from the start this will imply that the flow coefficient will be increased and that the specific wheel speed is decreased, making it less optimal according to traditional design theories. since neither the slip factor nor the jet-wake paradigms allow the design of such a stage, unless the models incorporate more elaborate stochastic models, the case study must be carried out using fully viscous numerical simulations. in this particular case, the optimization study was carried out in two steps, firstly using an in-house goal driven method and finally the numeca design 3d commercial package. in the first re-vamping stage, both the rotor and stator were reshaped using conventional 2d methods coupled with the inhouse stochastic correlations. this process of the stage redesign also incorporates a primary optimization of the two blade rows. version 15 (v15) represents the preliminary result of the re -vamping with the euler in-house code [1]. intuitively, in designing v15 two key aspects were targeted, namely maintaining the specific speed at the highest possible value while preventing flow separation and, secondly, diminishing the machine mach number – which was thought as a source of loss. both those targets were proven to be misguided since v25 actually has a higher machine mach number and a lower specific speed. paradoxically it seems that minimizing and maximizing isolated parameters does not lead to the absolute maximum in overall performance. although fast in terms of convergence, the in-house code cannot account for various details such as viscous heating of the fluid or boundary layer separation due to curvature effects. hence the resulting model cannot be considered the peak in terms of performance attainable. in order to quantify these effects, the geometry was tested using the fine/turbo numerical solver using a fully structured mesh and the k-ω sst model with curvature compensation. the turbulence model has been chosen over other possible candidates since it is traditionally considered to blend the accuracy of the kω model proposed by wilcox, in the boundary layer, with the stability of the k-ε models in the far field region. also, the spalartallmaras model was considered in the early stages of the design but it was abandoned in favor of the sst model due to the latter's reliability and validation [2]. a multi-grid method was employed to stabilize the model, increasing the refinement of the mesh as the intermediate solutions were reached. the numerical scheme used is second order upwind and the cfl number of 1. in order to account engineering, technology & applied science research vol. 6, no. 4, 2016, 1103-1108 1104 www.etasr.com dragan et al.: a comparative analysis between optimized and baseline high pressure compressor stages more accurately for the aerodynamic effects during the compression process, a realistic model of air was used [3]. because of the possibility that the grid itself can influence the results one way or the other, a preliminary screening was carried out on the v15 design. in this screening a number of meshes, increasing in size were used, while maintaining the same y+ distribution through controlling the first cell size. results show that for the parameters of interest, i.e. pressure ratio and isentropic efficiency, a mesh of ~2.9 e6 cells produced virtually identical results as the finest mesh tested, but at only a fraction of the computational cost. table i synthesizes the relevant results for the grid sensitivity tests. table i. grid sensitivity tests for the relevant parameters (the baseline version) grid number of cells wall cell press. ratio isentropic efficiency coarse 1341280 1e-3 2.25 82.7 [%] intermediate 2143870 1e-3 2.21 82.5 [%] fine 2925115 1e-3 2.15 82.2 [%] finest 3739729 1e-3 2.15 82.1 [%] the overall simulation technique is in line with the recommendations in the referenced literature and those of the software producer. various studies exist in the literature to quantify uncertainty of this methodology [4, 5] but all agree that typically errors lye between 3-5% [6] in most global parameters which has been confirmed to be the case here as well. in the final design stage only the rotor geometry was varied, maintaining the same geometry of the diffuser blades. results of the newly re-vamped compressor stage prove an increase of overall isentropic efficiency from ~80% to 82.2% and, after further optimization using cfd, from 82.2% to 85.35%. for the cfd simulations, the k-omega sst model was used. the final design optimization yielded a slight increase in total pressure ratio and decreasing the outlet total temperature. improved loading distribution on the rotor is apparent since the axial camber line has reduced back-sweep, increasing the load in that region, while in the radial part, where diffusion typically occurs, the loading is maintained constant. in the two steps of design, the backsweep angle distribution is visible along the entire camberline, particularly in the outermost radial region. after detailed comparative analysis of the optimized geometries it becomes apparent that the camber beta angle influences the entire flow structure, especially the secondary flow types such as the over-the-tip flow and boundary layer flow in the outermost radial region. an interesting observation regarding the final cfd optimization is that, although the overall efficiency is increased, the actual rotor efficiency decreases. this proves that the overall performance of turbo-machineries is holistic. in other words, there is an optimal way to spread both loading and losses across the stage. an inference is that focusing the optimization on any of the components without observing the overall implications may be misleading. hence, even if the user assigns degrees of freedom to one component (rotor or stator), the whole stage must be simulated in order to see the global effects. furthermore, if the stages of a turbo-machine are coupled aerodynamically, they must be included in the simulation as well. the results were applied to the re-vamping of a fully functioning compressor and performed as expected. the industrial compressor re-vamping described in this paper refers only to the fourth, high pressure (hp) stage of machinery used in the oil industry. since one of the requirements was to keep as much elements as possible from the original machine, the design space was limited to blade setting angles, while maintaining the same rotor height and diameters. another restriction was the wheel speed which was low, due to technological reasons, even for the original mass flow and pressure ratio. in the first stage of the re-vamping, through flow methods [1, 7] and in-house correlations were used to achieve an improvement of 2.2% in isentropic efficiency and reaching the targeted pressure ratio of 2:1. in order to maintain the robustness of the rotor, only the hub and shroud airfoils were varied and the leading and trailing edges were maintained linear and with no lean. a previous case study [8] has shown that this sort of parametric model allows high isentropic efficiencies to be reached, of above 94% per rotor. ii. the cfd optimization setup a parametric model first had to be fitted over the predesigned geometry, establishing the method by which the blades and end-walls are described in three dimensional space by the geometry generator. based on this, a combined set of 200 individual, slightly varied geometries, was generated with the latin hypercube sampling method [9, 10], and meshed using a user-defined blocking structure. after insuring that the mesh quality is satisfactory for the individuals, the full viscous computational fluid dynamic simulations were carried out using the baseline results as initial conditions. variations on the rotor geometry were considered in this case. the relevant flow characteristics were then assessed and interpreted by an artificial neural network which approximated correlations between them and the geometrical characteristics of the individuals. further, based on these assumed correlations, an optimal geometry, which is in fact a minimization of the imposed penalty function, is predicted and cfd tested using the same initial conditions as in the case of each individual in the database. since the correlations are typically less than perfect, the per-se optimization is an iterative process, requiring that the cfd data acquired in each optimization step to be added to the database in order to be fed back into the correlation approximation loop. in this case after 20 optimal design loop iterations, the correlation accuracy, compared to the cfd results, became sufficient for the process to be considered converged, as seen in figure 1. as presented in [11] the ann is used to approximate the various influences of the geometrical parameters on the penalty function which needs to be minimized. the ann is comprised of elementary processing units, or nodes, which are arranged into layers and connected with different weighs in order to create a parallel topology. two layers were used, one layer for input and one for output layer. the elements of the input vectors are connected to the nodes of the input layer through a weight matrix. nodes sum the weighted inputs and bias to generate individual scalar outputs which are then processed through a sigmoidal transfer function to the output layer. the engineering, technology & applied science research vol. 6, no. 4, 2016, 1103-1108 1105 www.etasr.com dragan et al.: a comparative analysis between optimized and baseline high pressure compressor stages ann is "trained", using the databases available from the previous cfd simulations, by finding connection weight matrices and bias to make up the output vector. although typically there needs to be a separate database of cfd runs, which would be used to test the accuracy of the ann, in this case we generate this database in the form of design loop iterations which are iteratively added to the existing database and the ann is re-trained. numeca's design 3d uses the learning by back-propagation of the errors algorithm to train the neural network which initializes the training process with small random values for the weight and bias factors. after this, the input vector is fed into the network input and the signal is propagated to the output layer. the resulting output vector is then compared to the desired output vector and the error between them is backpropagated until the error is minimized through adjustments made in the connection weights. these weights are factored by a learning rate coefficient, which in our case has the value of 0.5. the momentum coefficient, with the value 0.8, is set up in order to speed up the convergence of the training process. also a decay factor may be used in order to avoid exaggerated weight values whish could saturate the sigmoid function, however in this particular case the decay factor was set to 0. other implementations of the same methodology are presented in [12, 13]. since the design requirements held more than one criterion, the process was continued for 10 more individuals. this was done in order to compare the “optimal" candidates which, having the same penalty function score, are most convenient for the user's needs. it needs to be said that this last step is not a necessity, since weights can be added to any of the criteria used for the penalty function. however in practice, it is difficult for the weights to be set a priori so that they completely cover all cases especially for new compressors, since the user doesn't have accurate correlations between the geometry and the flow parameters. figure 2 shows the meshed geometry of a flow channel for the redesigned baseline. fig. 1. the ann approximation of the objective function vs its actual value computed using 3d cfd fig. 2. the meshed geometry of a flow channel for the re-designed baseline and optimized rotor (top) and y+ distribution (bottom) iii. results and discussions in order to make sense of the resulting optimized geometry, both global parameters and flow field analysis were considered. table ii presents a few of the typical turbo machinery parameters calculated for all three cases after the rotor and after the stator. efficiencies are presented in histogram form in order to provide an easy graphical comparison between cases. one quick observation is that the optimized rotor, v25, has the highest machine mach number, lowest specific speed and lowest flow coefficient. this may appear as a paradox since most of global parameters correlations [14-19] with the polytropic efficiency suggest the opposite, i.e. higher specific speeds and flow coefficients. however, the machine at hand has a pre-determined rotor aspect ratio and outlet, hence it cannot be fairly compared with designers specifications and/or rules of thumb. the cordier diagram [20] suggests that for the aspect ratio of this particular rotor, the specific speed at which it should be operated is low, which is confirmed by the optimization design. it needs to be said that, a further optimization can be achieved by completely re-designing the stage in keeping with the general correlations of [14-19], however this paper only refers to the re-vamping results within the design space. also from table ii, as well as the histogram below, it can be seen that the pressure ratio of v25 is higher than the other designs, providing a better safety margin in order to compensate the intercooler and pipe total pressure losses. from table iii, two aspects can be inferred namely that the absolute flow angle, which gives the stator vane incidence, is significantly changed. a second relevant aspect is that the slip factor paradigm only applies, in an approximate manner, to the design point of the rotor. note that the baseline rotor is functioning at off design point, hence having lower efficiency than its design point. although the isentropic efficiency is engineering, technology & applied science research vol. 6, no. 4, 2016, 1103-1108 1106 www.etasr.com dragan et al.: a comparative analysis between optimized and baseline high pressure compressor stages lower on the optimized rotor, the stage efficiency is significantly higher, in spite of the fact that the stator remains unchanged. a simple observation is that the optimized rotor is better suited to the stator. however a more detailed analysis reveals that the polytropic efficiency of v25 is unequivocally higher than that of v15. since polytropic efficiency only accounts for the aerodynamic losses not the thermodynamic losses one might conclude that there is an apparent "barrier" due to the thermodynamic losses. this is because the task the stage must perform is not tailored to the original design i.e. wheel diameters and speed. figures 3 to 6 demonstrate different aspects of the design. fig. 3. the total to total pressure ratios of the three designs fig. 4. (a) total to total isentropic and polytropic efficiency of the rotors and (b) total to total isentropic and polytropic efficiency of the stages fig. 5. entropy [j/(kg*k)] field distribution for the v15 design (left) and v25 (right) fig. 6. relative mach number field for the v15 design (left) and v25 (right) table ii. global parameters of the revamping designs vs the baseline off design point (rotor only) name machine mach no. specific speed c1/ u2 w_in/ w_out w_out [m/s] bsl. 0.67 0.51 0.32 1.62 226.60 v25 0.695 0.437 0.282 1.12 160.57 v15 0.659 0.479 0.285 1.22 176.61 table iii. mass averaged flow parameters (rotor only) name vthroughflow [m/s] vtangential [m/s] absolute flow angle [°] slip cfd slip wiesner v25 73.2 235.2 72.7 0.852 0.878 v15 78.2 220.1 70.5 0.813 0.868 bsl. 137.4 202.9 59.15 0.62 0.86 an entropy distribution study shows the differences between the two designs, v15 and v25, particularly in the stator region. figure 7 reveals that the rotor of v25 produces more entropy than v15, however the stator performs significantly better. this can be explained by looking at figure 6 where the relative mach number is depicted. since the stator is identical in both cases, the improvement must be attributed to the better flow angle matching, the higher throughflow velocity and the more homogenous mach number distribution at the rotor outlet. fig. 7. entropy [j/(kg*k)] field distribution at 10% span, for the v15 design (left) and v25 (right) flow field analysis near the rotor-stator interface provides further indications that the details of the flow patterns that occur in the two stage designs, v15 and v25 are more favorable to the latter. due to the high loading of the radial section of the blade, a recirculation bubble is created which leads to aerodynamic losses. as seen in figure 8, this recirculation bubble forming near the tip of the rotor is eliminated by the new rotor. improved angles of incidence for the stator vanes were also obtained, an average of 2.5 degrees difference between v25 and v15. also, due to the higher absolute velocity magnitude, the machinery reynolds number engineering, technology & applied science research vol. 6, no. 4, 2016, 1103-1108 1107 www.etasr.com dragan et al.: a comparative analysis between optimized and baseline high pressure compressor stages is higher which leads to better attachment of the flow to the stator vanes and improved diffusion efficiency [21]. field plots showing enthalpy reveal that the outlet distribution is more uniform in v25 than in v15 which indicate that the losses, especially near the hub, are reduced. secondary flow is also improved at the rotor outlet, in the vaneless diffuser region since the circulation necessary to compensate the through flow circulation is lower – since the through flow has lower velocity. figure 9 depicts the baseline and optimized rotor mesh as well as the cad and finished part. fig. 8. stream vectors in the vaneless diffuser of v25 (top) and v15 (bottom) fig. 9. the baseline (v15) and optimized (v25) rotor mesh (top), v25 cad and finished part (bottom) iv. conclusions a re-vamping and reconfiguration of an industrial hp centrifugal compressor stage was performed, using a parametric model and a combination of artificial neural networks and genetic algorithm. the design theme was to optimize the rotor geometry so that the match with the stator leads to increased stage performance and efficiency. by comparing the polytropic against the isentropic efficiencies, an apparent plateau was obtained regarding the rotor maximum efficiency. this is attributed to the mismatching of the current task (mass flow and pressure ratio) and the original diameter, wheel speed and rotor length, as confirmed by the specific speed and flow coefficient. compared to the initial re-vamped v15 version, the v25 design obtained higher pressure ratio and improved stage isentropic efficiency. this is due to improved blade loading and lower aerodynamic losses. as shown, in v25 the rotor efficiency is influenced more heavily by the thermodynamic losses and less by aerodynamic friction with the walls as indicated by the high polytropic efficiency. further improvements may be achieved by optimizing the rotor-stator together. segregated optimization has proved futile, which leads to the conclusion that the holistic interactions between the components of the stage have a significant impact on the overall results. a final remark is that although the diffuser is the region where all losses are accounted for, at least some of the aerodynamic losses from a rotor can be hidden if the polytropic efficiency is not compared to the isentropic efficiency. nomenclature ann artificial neural network cfd computational fluid dynamics cfl courant friedrichs lewy coefficient ga genetic algorithm sstshear stress transport y+ dimensionless wall distance k turbulent kinetic energy ε turbulent kinetic energy dissipation ω turbulent kinetic energy specific dissipation references [1] m. l. niculescu, v. silivestru, g. vizitiu, s. danaila, c. berbente, “theoretical and numerical investigation of centrifugal and mixed compressor impellers”, 8th international symposium on experimental and computational aerothermodynamics of internal flows, lyon, july, 2007 [2] l. h. jawada, s. abdullah, r. zulkifli, w. m. f. w. mahmood, “numerical study on the effect of interaction vaned diffuser with impeller on the performance of a modified centrifugal compressor”, journal of mechanics, vol. 30, no. 2, pp. 113-121, 2014 [3] numeca fine™/turbo v9.0, flow integrated environment theoretical manual [4] d. wunsch, c. hirsch, r. nigro, g. coussement, “quantification of combined operational and geometrical uncertainties in turbo-machinery design”, asme proceedings, multidisciplinary design approaches, optimization and uncertainty quantification [5] c. hirsch, c. dinescu, “uncertainty quantification and non-deterministic methodologies for cfd based design-the nodesim-cfd project”, 7th european symposium on aerothermodynamics, brugge, belgium, 2011 [6] f. montomoli, m. carnevale, a. d' ammaro, m. massini, s. salvadori, “limitations in turbomachinery cfd”, in springer briefs in applied sciences and technology, pp. 21-32, 2015 [7] m. r. galvas, fortran program for predicting off-design performance of centrifugal compressors, nasa tn d-7487, 1973 [8] v. dragan, “aerodynamic reconfiguration and multicriterial optimization of centrifugal compressors–a case study”, incas bulletin, vol. 6, no. 4, pp. 41 – 49, 2014 engineering, technology & applied science research vol. 6, no. 4, 2016, 1103-1108 1108 www.etasr.com dragan et al.: a comparative analysis between optimized and baseline high pressure compressor stages [9] b. tang, “orthogonal array-based latin hypercubes”, journal of the american statistical association, vol. 88, no. 424, pp. 1392–1397, 1993 [10] m. rajabi, b. ataie-ashtiani, h. janssen, “efficiency enhancement of optimized latin hypercube sampling strategies: application to monte carlo uncertainty analysis and meta-modeling”, advances in water resources, vol. 76, pp. 127–139, 2015 [11] fine™/design3d v9.0 optimization kernel user manual [12] a. demeulenaere, a. purwanto, a. ligout, f. visser, “design and optimization of an industrial pump: application of genetic algorithms and neural network”, asme fluids engineering division summer meeting, paper no. fedsm2005-77487, pp. 1519-1527, houston, tx, usa,vol. 1, june 19–23, 2005 [13] s. derakhshan, a. mostafavi, “optimization of gamm francis turbine runner”, international journal of mechanical, aerospace, industrial, mechatronic and manufacturing engineering, vol. 5, no. 11, pp. 21392145, 2011 [14] m. v. casey, c. j. robinson, “a method to estimate the performance of a centrifugal compressor stage”, j. turbomach., vol. 135, no. 2, paper no: turbo-11-1200, 2012 [15] c. rodgers, “the efficiencies of single-stage centrifugal compressors for aircraft applications”, international gas turbine and aeroengine congress and exposition orlando, usa, june 3-6, 1991 [16] c. xu, r. s. amano, “empirical design considerations for industrial centrifugal compressors”, international journal of rotating machinery, vol. 2012, article id: 184061, 2012 [17] r. h. aungier, centrifugal compressors: a strategy for aerodynamic design and analysis, asme press, new york, 2000 [18] w. al-busaidi, p. pilidis, “a new method for reliable performance prediction of multi-stage industrial centrifugal compressors based on stage stacking technique: part ii–new integrated model verification”, applied thermal engineering, vol. 90, pp. 927–936, 2015 [19] m. nili-ahmadabadi, m. durali, a. hajilouy, “a novel aerodynamic design method for centrifugal compressor impeller”, journal of applied fluid mechanics, vol. 7, no. 2, pp. 329-344, 2014 [20] p. epple, f. durst, a. delgado, “a theoretical derivation of the cordier diagram for turbomachines”, proceedings of the institution of mechanical engineers, part c: journal of mechanical engineering science, vol. 225, pp. 354-368, february 1, 2011 [21] c. weigel, c. l, ball, “reynolds number effect on overall performance of a 10.8 centimeter (4.25 in) sweptback-bladed centrifugal compressor”, nasa tn d-6640, 1972 authors profile valeriu dragan obtained his ph.d. in 2012 from the politehnica university of bucharest in the field of supercirculation aerodynamics. since then he joined the cfd department of the national research and development institute for gas turbines comoti where he specialized in centrifugal compressor design and optimization for both industrial and aeronautical applications. ion malael obtained his ph.d. in 2013 from the politehnica university of bucharest in the field of flow control with applications to turbomachineries. since 2009 he has worked as a scientific researcher with the nrdi comoti in a variety of cfd applications, ranging from wind turbines, cryogenic pumps to screw compressors. bogdan gherman obtained his ph.d. in 2013 from the politehnica university of bucharest, following a 3 year long study stage at the lund university, sweeden in the field of computational aero-thermodynamics with combustion. since 2005 he has been leading the cfd department of nrdi comoti, in both national and european projects dealing with applications such as jet pumps or supersonic combustion chambers. microsoft word etasr_v12_n4_pp8996-9004 engineering, technology & applied science research vol. 12, no. 4, 2022, 8996-9004 8996 www.etasr.com kechiche et al.: a power-aware real-time system for multi-video treatment on fpga with dynamic … a power-aware real-time system for multi-video treatment on fpga with dynamic partial reconfiguration and voltage scaling lilia kechiche department of science and technology taif university saudi arabia l.kechiche@gmail.com mehdi jemai laboratory of electronics and microelectronics university of monastir monastir, tunisia jmehdie@gmail.com lamjed touil laboratory of electronics and microelectronics university of monastir monastir, tunisia lamjedtl@yahoo.fr bouraoui ouni networked objects control and communications systems lab, university of sousse sousse, tunisia ouni_bouraoui@yahoo.fr received: 21 may 2022 | revised: 10 june 2022 | accepted: 13 june 2022 abstract-as the energy consumption is an evaluating factor for system-on-chip (soc) design, this paper presents a poweraware architecture for a real-time multi-video system on fpga. this architecture aims to optimize power consumption for a multi-video system on arm-based architectures. the proposed architecture uses dynamic reconfiguration and voltage scaling to create a power-aware system for real-time multi-video processing with minimal power dissipation. dynamic partial reconfiguration was used to optimize the utilization of resources and reduce dynamic power consumption. voltage scaling was also used to optimize dynamic power consumption, by configuring the blocks to use the minimum necessary voltage for normal operating conditions. the proposed architecture focused on the zynq platform. the results showed power savings of up to 70% concerning performance and real-time constraints. keywords-power consumption; zynq; arm a9; dynamic partial reconfiguration; voltage scaling i. introduction embedded real-time video applications are widely spread in many systems and have important applications in various domains such as segmentation [1, 2], object tracking [3], visual detection and matching [4], motion estimation [5], etc. these systems are generally executed in an embedded environment and are subjected to many constraints such as power consumption, time, and resources. as the market requires these systems to have high performance at a low cost, designers have to propose new architectures to meet different requirements. many dedicated technologies and methods have been proposed to develop and implement highquality real-time applications and optimized systems. the proposed technologies range from specific processors like general purpose processors (gpps), graphics processing units (gpus), and digital signal processors (dsps) to parallel architectures like application-specific integrated circuits (asics) or even programmable logic devices (fpgas). today, fpgas are being increasingly used to build complex video processing applications. they provide realtime performance that is difficult to achieve with gpp or dsp [6-8] while limiting the extensive design work required for asics. furthermore, fpgas provide the ability to implement highly parallel architectures due to the huge number of programmable logic available on the chip [9]. one of the major problems with fpga implementations compared to asic solutions is power consumption, which is a limiting factor [10]. therefore, more efforts are spent to propose a design with low-power dissipation. since fpgas are cmos-transistors, power consumption can be divided into two main types: static power and dynamic power. static power is dissipated when the circuit is in a quiescent state caused by leakage currents of the cmos transistor. these currents are the sub-threshold leakage current, the gate leakage current, and the junction leakage current [11]. dynamic power consumption is given by: �� = α. c. v � . f (1) where c is the capacitance, α is the charging rate depending on clock frequency, v is voltage supply, and f is the clock frequency. this power is highly related to technology and has become a concern with modern fpgas implemented in 24nm [12-14]. to reduce power consumption, the principal causes of power dissipation have to be investigated during all steps of the design process, from the algorithmic level down to the corresponding author: lilia kechiche engineering, technology & applied science research vol. 12, no. 4, 2022, 8996-9004 8997 www.etasr.com kechiche et al.: a power-aware real-time system for multi-video treatment on fpga with dynamic … transistor level, considering the latest low-power technology methods at all the design levels. this paper proposes a power-aware hardware architecture for real-time multi-video processing, using dynamic reconfiguration and voltage scaling to optimize the power consumption of a multi-video system. this method was applied to a high-performance video system of 1920×1080 pixels at 60fps. ii. fpga power reduction most modern fpga boards are computing platforms that include programmable hardware elements, memory resources, configurable i/o, embedded processors, and even embedded operating systems. hardware (hw) and software (sw) functionalities allow the combination of hardware's performance and software's flexibility. this combination of performance and flexibility comes at the cost of high power consumption, which is the main limit of fpga platforms. to overcome this limit, new methods to optimize power consumption are investigated. the proposed methods explore all abstraction levels of the design process, from the system level to the circuit level and the technological level. some works used hw/sw partitioning to propose optimal systems with low power consumption as power-aware decisions at a very early stage of the design process [15-17]. hw/sw partitioning is the problem of assigning application tasks to the existing computational cores under defined constraints such as area and power. it is formalized as an optimization problem aiming to minimize an objective function under defined constraints. in [15], an algorithm was proposed for hw/sw partitioning to find the best tradeoff between power and latency, modeling the application as a data flow graph and computing the latency and power consumption for every proposed partitioning. this algorithm performed a heuristic search for the best solution that respected the defined constraints. in [17], a data flow graph based on the bee colony algorithm was proposed to solve the optimization problem of hw/sw partitioning under time and power constraints. the heuristic algorithm treated the optimization problem as np-hard, and the exact resolution may take a much longer time. to adjust the constraints according to the user's requirements, weighting coefficients were added to the constraints to specify which of the two conflicting terms is more important for the final partitioning result. other studies examined methods at the architecture level, like dynamic voltage scaling (dvs) and dynamic frequency scaling (dfs). dvs, dfs, or even dynamic voltage and frequency scaling (dvfs) were first proposed to reduce the power consumption of microprocessors [18-20] and, as they were successful, they were generalized and used on fpgas [21-22]. in [18], a method for static timing analysis in dynamic scheduling schemes was proposed. a safe timing analysis was proposed for systems with off-chip memories where memory latency did not scale with processor frequency. this method, called 'frequency-aware', replaced the worst-case execution time (wcet) [23] obtained by static-timing analysis. it expressed wcet bounds with frequency-sensitive parameters, where cycles were interpreted in terms of processor frequency and memory accesses were expressed in terms of the memory latency overhead. the new proposed wcet was determined on-the-fly for a given frequency. the problem of real-time systems with time-critical applications was addressed in [19]. a new algorithm was proposed for dfs, applied directly to the scheduler to modify task management. at first, a static frequency was assigned to every task, which was the lowest possible frequency that allowed the scheduler to meet the deadlines for a given task set. if a task was completed before the worst-case specification, the frequency was re-computed using the latest information. the new value was used until the release of the task for a future invocation. therefore, the utilization was recomputed at every new scheduling time using the real computed time for accomplished tasks and the specified worst-case for the others. this method allowed a 20-40% power reduction. a dvfs technique for non-real-time applications was proposed in [20], where the main idea was to lower the cpu frequency when accessing off-chip peripherals. the temporal distribution of onand off-chip workloads was computed with different scenarios to determine the cpu frequency during idle periods. the energy savings were up to 70%, with a variable performance penalty depending on the saving value. two methods for dvs on commercial fpgas were presented in [21, 22]. in [21], a circuit was used to measure the logic delay, which would be used by the voltage controller block to dynamically adjust the supply voltage using a closed loop. the voltage controller was an external module implemented on a pc. experimental results using a xilinx virtex xcv300e fpga were presented, and power savings were 4-54%. although the study noted that implementing the voltage controller as an internal module is a way for better resource utilization, giving results and statistics based on an external module is disputable since it may lack precision and can cause delay violations or more resource consumption. iii. real-time video processing and architecture a. real-time video processing real-time video processing plays a key role in industrial systems and is expanded to many fields. real-time video processing systems process large amounts of image data in a short time. the purpose varies from a simple display to the extraction of useful information for intelligent scene analysis. digital videos are data-intensive and resource-demanding multidimensional signals, as they need an important amount of resources for computations and memory operations. a typical video system consists of a video source, internal processing, and destination, as shown in figure 1. the video processing module is traditionally classified into three levels: low, intermediate, and high. each level differs from the others in input/output format and processing type. for example, the low-level takes an image and produces an output image, while the high-level takes image attributes as input and makes high-level interpretation to produce a knowledge-based control as output. engineering, technology & applied science research vol. 12, no. 4, 2022, 8996-9004 8998 www.etasr.com kechiche et al.: a power-aware real-time system for multi-video treatment on fpga with dynamic … fig. 1. video processing system. a common concern in real-time video processing systems is how to deal with large amounts of data. this pushes designers to search for a suitable architecture that guarantees the required performance with the worst-case latency to ensure no frame drops. this remains a challenging task, especially for embedded systems that have limited resources and power supply. the architecture has to allow parallel treatments, as it is hard to perform such a large data treatment serially. the best solution often comes with a combination of hardware and software approaches. the hardware offers high performance using parallelism, and the software guarantees flexibility. fortunately, modern fpga devices are characterized by sufficient logic resources and high operating frequencies for video processing. b. hardware and software architecture for real-time multi-video processing the design of a real-time system for multi-video processing is a demanding task. in addition to the constraints discussed above, constraints such as available resources and memory access management are added to the problem. the design of multi-video architecture needs to answer the following demands: • achieve the performance required by different parallel and communicating blocks. blocks concerning video processing systems are subjected to timing constraints for high-bandwidth and data-intensive operations with the need to access the memory at the video rate. • extend it when needed. the extension is the ability to add new video processing chains or blocks or the limit of available resources. • obtain an optimal use of available resources. system partitioning between hard and soft resources allows getting the high performance of hw and the flexibility of sw. in addition to the previous requirements, which are in direct relation to the system and platform, power consumption is another constraint that has to be considered, as battery life has become the main factor in the evaluation of embedded systems. the choice of the appropriate target platform is very essential for real-time systems. of the existing fpga platforms, many are appropriate for video processing with real-time constraints, as they can work at a frequency that can exceed 150mhz, and as a result, can support hd resolutions. in addition, fpga vendors have incorporated various hardware and software ip cores that can be used for different functions needed in video processing, like timing generation and rgb conversions. fig. 2. general architecture for multi-video processing on fpga. figure 2 shows the general architecture for multi-video processing using hw and sw available in the fpga. the hw or programmable logic (pl) is used to implement videorelated blocks like video-in, video processing sub-systems, and video-out. the sw or processing system (ps) contains the application processing unit (apu), which is responsible for system-level control registers, dma controllers, and the accelerator coherency port (acp). the memory interface allows the ps and pl blocks to access the memory. the utilization of ps and pl to implement video processing modules is performed according to the available resources, performance constraints, power constraints, and other issues like flexibility and time to market. this study used a zynq zc 702 based xilinx evaluation kit as a target platform. this kit includes sw, hw, and ip components that facilitate the development of custom video applications. the apu contains two arm cortex-a9 processors sharing a 512kb l2 cache, which can be used for dual-core or single-core devices. each processor is a lowpower, high-performance core with a 32kb l1 cache for instruction and data. the axi protocol [24] defines 3 types of interfaces: axi4 for high-performance memory-mapped requirements, axi4-lite for low-throughput memory-mapped communications, and axi4-stream for high-speed streaming data. these application domains make the protocol indispensable for every real-time video system. the axi interconnect, axi3, and axi video dma ip cores can form the basis of video systems capable of handling video frame buffers and giving access to a shared ddr3 sdram. this design utilized the axi4, axi3, axi4-lite, and axi4stream interfaces. the accelerator coherency port (acp) is used to communicate the pl with the apu, as it is an axi interface that allows the pl to implement an axi master to access the l2 [25-27]. the axi video direct memory access (vdma) core implements a video-optimized direct memory access engine with a frame buffer. the axi vdma core transfers video data to and from memory under dynamic software control. figure 3 shows the block diagram of the implemented design with the interface connection. the processor can access the pl using the axi3 master generalpurpose (gp) 32-bit interfaces. the zynq zc702 has 4 axi_hp interfaces, which allow pl to access ddr memory through high-bandwidth data path bus masters. engineering, technology & applied science research vol. 12, no. 4, 2022, 8996-9004 8999 www.etasr.com kechiche et al.: a power-aware real-time system for multi-video treatment on fpga with dynamic … iv. dynamic partial reconfiguration for power reduction the dynamic partial reconfiguration (dpr) offers a way to optimize the dynamic power consumption by enabling the usage of temporarily shared resources on the fpga among different processing functions in a time-multiplexed manner. hence, dpr enables better resource utilization and efficiency. the dpr results in a partial bitstream loaded onto the fpga, targeting a fixed part of its area. figure 3 shows the general architecture of multi-video processing. fixed areas are predefined during hw design and are called the reconfiguration partition (rp). fig. 3. general dpr architecture for multi-video processing. v. dynamic partial reconfiguration for real-time multi-video processing real-time multi-video processing is a demanding task in terms of performance, resource utilization, and power consumption. the target architecture was composed of the ps part, which allows communication with the dr, and the pl parts where the video-related blocks are implemented. a multi-video architecture is defined as a system with n video inputs, where n is limited by the resource constraints of the target platform. in this case, n=4 since the target zynq platform has 4 hp ports that allow high performance communication with ddr, as shown in figure 4. a dpr-based architecture was proposed to optimize resources and power. dpr, also known as active partial reconfiguration, allows changing a part of the device while other blocks are running. while the fpga is executing different blocks, the partial data will be sent to be configured. there are two ways for dpr [28], known as difference based partial reconfiguration (dbpr) and module based partial reconfiguration (mbpr). dbpr is used when a small change is made to the design. it is especially useful when changing look-up table (lut) equations or dedicated memory block content. mbpr uses modular design concepts to reconfigure large logic blocks. mbpr was used to implement the dpr on the target platform, defining two different parts: static modules and dynamic or reconfigurable modules (rms). the static module is the part of the design that remains in operation during the pr process. the dynamic modules are the parts of the design that can be swapped in and out of the device on the fly, where multiple rms can be defined for a specific region. fig. 4. real-time multi-video processing. figure 5 shows the proposed architecture with both static and dynamic parts. ps and the multi-display present the static part while the dynamic part contains the pl. fig. 5. the proposed architecture with rdp. vi. voltage scaling dvs is the process of varying the voltage of a target block at run-time. as voltage is directly related to power consumption [1], reducing it allows for a quadric reduction of power consumption. the following definitions must be considered to use dvs in a target fpga [29]: • the processing strength of a device is the ability and degree of variation in the attributes of the integrated transistors. there are three classes: weak, nominal, and strong. a weak device can operate with the lowest acceptable frequency at nominal voltages. strong devices can run at faster frequencies than required at nominal voltages and can function at voltages lower than nominal at the minimum specified frequency. • the voltage domain is defined as the group of modules sharing the same power supply voltage for the core logic of each device. engineering, technology & applied science research vol. 12, no. 4, 2022, 8996-9004 9000 www.etasr.com kechiche et al.: a power-aware real-time system for multi-video treatment on fpga with dynamic … • the operating performance point is the voltage required for every device to operate at the desired processor clocking frequency. for example, for the processing system ddr i/o supply voltage, the minimum value is 1.14v and the maximum is 1.89v [30]. • the critical path of a system is defined as the longest path to achieve the execution of a program from the source to the sink of a data flow graph. this information is used to track the critical tasks when scaling voltage and frequency to ensure the performance of the system. to implement dvs on a specific platform for a defined system, information about the operating voltage of each block must be accessible at runtime. this information can be obtained in two different ways: • dynamic analysis of the behavior of the system at runtime requires real-time access to the working blocks on the pl side. this can be done with additional modules implemented in pl or ps. this method requires extra resources to gather information at run-time. • static analysis of the system behavior using different test scenarios. the obtained test results can be used with the information provided by the manufacturer to make design decisions for frequency and voltage scaling. this study followed the second method to perform dvs and dfs at runtime. let vmin_x be the minimum voltage required for block x to operate in normal conditions and under which the system fails. these values are a characteristic of hardware blocks, fixed at the time of device manufacturing. let vop_x be the operating voltage of block x. the algorithm used to scale voltage is shown in figure 6, where st is a float representing the step of incrementing and decrementing the voltage. inputs : vmin_x, , vop_x, st; begin identify voltage bounds for the target block; do vop = vop st ; test performance; if test failed vop = vop + st; break; end if while (vop > vmin_x) end fig. 6. voltage scaling algorithm. in the zc702 board, power is supplied to the components through several independent rails using programmable power regulators (ucd9248) and a power management bus (pmbus) compliant system controller from texas instruments. pmbus is an open standard protocol that defines communication with power converters and allows to write and read power, current, and voltage information. the processors can access the pmbus using a 1-to-8 i2c switch. zynq-zc7020 is divided into several power domains, as shown in figure 7. these power domains are generated by 6 regulators that generate different voltages required by the zynq and the onboard components. the supplied voltage and currents are continuously measured and monitored by three ucd9248 power controllers available on the zc702 board. in this work, scaling the voltage of hard blocks was performed using the pmbus protocol, which simplifies communication with power converters as it allows the device's sw or hw to access a manageable power supply [31, 32]. optimal operating voltages were calculated using the algorithm shown in figure 6. then, the system was configured only one time with these values at every start. the configuration and implementation of the proposed algorithm were carried out by the processor through soft code. fig. 7. zynq power domains [31]. vii. implementation and results the proposed architecture was prototyped on the zynq zc702 evaluation board, which provides a hardware environment for developing and evaluating designs targeting the zynq xc7z020 device. zc702 includes 1gb ddr3 component memory, 128mb quad spi flash memory, usb 2.0, secure digital (sd) connector, hdmi codec, i2c bus, 2 uart interfaces, and other features. this section provides experimental results and shows the benefits of the proposed design in power reduction. a performance comparison was also held to verify the performance of the whole system. a. hardware and software architecture the target system was designed using the vivado design suite. this design suite can accelerate design implementation with place and route tools that analytically optimize for multiple and concurrent design metrics, such as timing and power. vivado gives the ability to analyze the design at each design stage, allowing for modifications in the design process. it also provides timing and power estimations after synthesis, placement, or routing. the following blocks were used to implement the hardware architecture: • the processing system was used to initialize blocks and master memory access. the frequency and voltage scaling modules were also implemented in the processing system. • the axi interconnects were responsible for handling information to and from the processing system. • the axi performance monitor was used for different statistics with the axi protocol interfaces. it was used for transactions, external system events, and performance measurement for axi4, axi3, axi4-stream, and axi4lite interfaces and captured real-time performance metrics engineering, technology & applied science research vol. 12, no. 4, 2022, 8996-9004 9001 www.etasr.com kechiche et al.: a power-aware real-time system for multi-video treatment on fpga with dynamic … for throughput and latency. the performance monitor ip was used to perform real-time profiling using the sdk. • the video pipeline contains video direct memory access (vdma), which is a soft ip core that provides high bandwidth for direct access to the memory using axi4stream video peripherals. the axi4-lite slave interface was used to perform initialization, registers, and status. • the video-related blocks are standard blocks used in a video chain to transfer the video stream after the necessary conversions. the rgb to ycrcb module converts the design pixels from the rgb encoding used by the axi4-stream to the 16-bit yuv 4:4:4 signal format. the chroma resampler block had the output of the rgb to ycrcb as input. its role was to convert the input signals to yuv 4:2:2 required by the hdmi output. the software part running on the ps was built using the xilinx software development kit (sdk). the software part running on the arm processor with a standalone operating system had the role of hardware control. b. partial dynamic reconfiguration results figure 8 shows the resource results without (a) and with pdr (b). figure 9 shows the occupation of the resources on the target platform without (a) and with dpr (b). the figures show an improvement in the used resources, which lowered power consumption. fig. 8. resource utilization. c. voltage scaling results the voltage scaling method was implemented as software code running on the processor. communication with the voltage rails was performed using the i2c bus. to avoid unnecessary additional resources, the optimal values were computed using excessive test scenarios. this analysis defined the optimal values that would be used by the system without the need to collect them at run-time using additional resources. the dvs method requires knowledge of the voltage limits of different blocks. table ii shows the maximum and minimum recommended operating voltage values for some blocks of the zc702 device [30]. fig. 9. resource occupation. table i. voltage recommended values for some blocks of the target zynq zc702 device blocks description minimum operating voltage (v) typical operating voltage (v) maximum operating voltage (v) vccpint ps internal supply voltage 0.95 1 1.05 vccint pl internal supply voltage 0.95 1 1.05 vccpaux ps auxiliary supply voltage 1.71 1.80 1.89 vccaux pl auxiliary supply voltage 1.71 1.80 1.89 vccbram pl block ram supply voltage 0.95 1.00 1.05 although voltage can reach more inferior values than those indicated in the safety bounds, for example, vccpint minimal value can reach 0.5v [30], the safe functioning of the device outside the indicated bounds is not tested. it is indicated that exposure to maximum values for extended periods could affect the device's reliability [30]. figure 10 shows the voltage scaling results of some vcc rails. every figure shows the power margin for every chosen value. for example, for the vccint rail, when the minimum operating value is chosen (0.95), the power consumption of this block varies between 22 and 31mw. engineering, technology & applied science research vol. 12, no. 4, 2022, 8996-9004 9002 www.etasr.com kechiche et al.: a power-aware real-time system for multi-video treatment on fpga with dynamic … fig. 10. voltage scaling results on different rails. figure 11 shows the time needed by the rail to reach the target voltage value. this figure shows the case of two rails with different typical voltage values. for both rails, the typical functioning voltage was attended after 5ms. fig. 11. voltage configuration time. d. frequency scaling and design performance frequency scaling is the concept of varying the operating frequencies of blocks at run-time according to the target architecture. there are two frequencies: the frequency of the pl blocks and the frequency of the ps. an analysis of the functioning of the system was performed to study the possibility of applying frequency scaling, using the system performance analysis (spa) toolbox. this toolbox was used to explore the performance of hw and sw at an early stage in the target system. observing system performance in critical stages helped make the right optimization decisions and refine system performance without degradation. the spa software metrics included cpu utilization, instructions per cycle, l1 data cache access, miss rate, write and read stall cycles per instruction, and other metrics. the hardware metrics were available using the axi performance monitor core, designed to measure the real-time performance of the connected axi interfaces, including axi read and write transactions, throughput, bandwidth, and others. this work used cpu utilization and axi read latency and throughput metrics. figure 12 shows the cpu utilization rate of the proposed realtime architecture. only one core was used. the graph shows that the utilization ranged between 91% and 100%. these results show that applying dfs on one processor executing a real-time video system does not allow a noticeable optimization, as the cpu utilization is usually at its maximum level. fig. 12. cpu utilization. figure 13 shows the read transactions and latency cycles of the ports hp0 (slot 0) and gp0 (slot 1). fig. 13. performance metrics at runtime. e. comparison with other works to the best of our knowledge, this is the first work to bring together dpr and voltage scaling. this section limits the discussion and comparison with works that used frequency and voltage scaling, as these two methods allow the reduction of the biggest part of power consumption (60%). voltage and frequency scaling of commercial fpgas was implemented in several studies using different methods. the proposed method was compared with two existing main methods that focused on the frequency and voltage of commercial 28nm fpgas. the first study used voltage and frequency scaling [34], while in [35], voltage, frequency, and logic scaling were used to optimize power consumption. the voltage scaling unit was identical to the one used in [34]. the frequency-scaling unit used a rom containing the configuration parameters used by the mmcm to generate the clock for the user logic. the frequency decreased continually at run-time and stopped when a value was detected that could cause timing violations. compared to those studies, this study used voltage scaling in addition to the dpr. authors in [34, 35] collected information like frequency and voltage of functioning blocks at run-time and scaled them accordingly. collecting information at run-time results in extra resources and additional complexity. these works applied the proposed engineering, technology & applied science research vol. 12, no. 4, 2022, 8996-9004 9003 www.etasr.com kechiche et al.: a power-aware real-time system for multi-video treatment on fpga with dynamic … methods to power consuming and speed testing modules (pcastms). these pcastms were proposed with different numbers of modules occupyινγ different percentages of the device. for voltage scaling, the voltage values were tested under the recommended values in the datasheet. testing with values below the recommended minimum can give more power savings of up to 60% [36], but with doubtful safety for long-term function with real-time constraints. this study exploited the fact that since the different execution scenarios are known in advance, the collection of information was performed at the design level using tests and timing analysis to determine the optimal operating points. implementing the proposed method requires only an i2c ip core and is of low complexity. additionally, scaling the voltage many times at runtime is not useful as it results in power and heat dissipation while accessing the power rails. it is more efficient to configure the device blocks with the optimal voltage at the start. table iii shows a comparison between [34, 35] and this study. according to the results obtained, the proposed method presents up to 70% power savings with an improvement of 5% compared to the other studies. table ii. comparison with other works additional resources frequency scaling method voltage scaling method test method power achievements [34] microblaze, picoblaze, i2c, ip core, dual-port ram i2c communication with si570 oscillator i2c communication with pmbus random functions with different sizes up to 64.98%, (using voltage and frequency scaling) [35] microblaze, i2c, ip core dual-port ram rom configuration of mmcm, rom i2c communication with pmbus random functions with different sizes up to 60% (using frequency, voltage, and logic scaling) this study i2c ip core none soft configuration of pmbus real-time video application with real-time constraints up to 70% (voltage scaling and pdr) viii. conclusion the design of an optimized system is very challenging due to the complexity of a soc design. power consumption has become a struggle with the increasing consumers’ demands and the saturation due to moore’s law. designers have to find new solutions to reduce power consumption. this study proposed a design method that brings together partial reconfiguration and voltage scaling. these methods were used to design a real-time multi-video processing system, implemented on a zynq zc702 board with an arm 9 target processor. the proposed method ισ general and can be applied to other real-time systems. compared to existing works, the proposed design allowed up to 70% power savings with minimal additional resources. future work should examine the application of other methods like clock gating and their integration in the design of real-time 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[36] m. hosseinabady and j. l. nunez-yanez, "run-time power gating in hybrid arm-fpga devices," in 2014 24th international conference on field programmable logic and applications (fpl), munich, germany, sep. 2014, pp. 1–6, https://doi.org/10.1109/fpl.2014. 6927503. microsoft word etasr_v12_n6_pp9458-9463 engineering, technology & applied science research vol. 12, no. 6, 2022, 9458-9463 9458 www.etasr.com bui: the application of lqg balanced truncation algorithm to the digital filter design problem the application of lqg balanced truncation algorithm to the digital filter design problem huy hai bui faculty of electronic enginering technology university of economics technology for industries hanoi, vietnam bhhai@uneti.edu.vn received: 5 august 2022 | revised: 29 august 2022 | accepted: 30 august 2022 abstract-this paper presents a method for using a model reduction algorithm to design low-order digital filters. designing an iir digital filter that meets the specifications often leads to a high-order digital filter. to reduce the computation time and increase the response rate of the filter, we need to reduce the order of the high-order digital filter. applying the lqg balanced truncation algorithm to reduce the demand for high-order digital filters shows that low-order filters can completely replace highorder digital filters. the simulation results show that the use of the lqg balanced truncation algorithm in order to reduce the filter order is correct and efficient. keywords-model order reduction algorithm; lqg balanced truncation algorithm; digital filter i. introduction a filter is a circuit that removes or "filters out" a specified range of frequencies. in other words, it decomposes the spectrum of the signal into frequency components that will pass and frequency components that will be suppressed. analog filters use analog electronic circuits made up of components such as resistors, capacitors, and optical amplifiers to produce the required filtering effect. a digital filter uses a digital processor to perform numerical calculations on the sampled values of the signal [1-7]. the processor can be a generalpurpose computer such as a pc or a dedicated dsp (digital signal processor) chip. we know that during digital signal processing, the bandwidth of the frequency band can be varied as filters will suppress unwanted frequency components and the bandwidth of the processed signal will decrease and we can reduce the sampling frequency to match the signal's spectral width, which will reduce the number of computations in the digital filter. compared with analog filters, digital filters have the following advantages: it is easy to change the filter structure without affecting the hardware, they are easy to design, deploy, and test, digital filters are extremely stable with time and temperature, they have high signal processing flexibility, and they can handle both low-pass and high-pass filtering accurately [1-2]. due to the superior properties of digital filters, the application of digital filters is increasingly being expanded in the fields of telecommunications, speech processing, image processing, antenna systems, digital audio engineering, and multiplexing systems. filter design involves constructing a filter transfer function that satisfies a given frequency response. to design a digital filter, there are two basic ways:  method 1: design an analog filter that satisfies the given requirements and then apply the equivalent transformation to form a digital filter.  method 2: apply computer-aided optimization methods to determine whether a digital filter satisfies the requirements. of these two designs, the first is commonly applied due to its ease of implementation. the second method is highly complex, so it is rarely used. to design an analog filter, it is necessary to solve two problems: the first is to determine the main requirements of the filter to be designed. the second is to determine whether the filter is designed to be fir (finiteimpulse response) or iir (infinite-impulse response.)  design of the fir filter: the output is the impulse response vector h = [h0, h1, h2, …. ,hn].  design an iir filter: the output is the coefficient vectors of the numerator and denominator of the transfer function b = [b0, b1, …, bn] and a = [ 1, a1, a2, …, an]. the fir filter has the advantage of a stable, linear phase characteristic. its disadvantage is that when a large frequency response is desired, the large filter length n increases computational cost. the iir filter has the advantages of low computational cost and efficient implementation in cascade of 2 nd -order circuits. the disadvantages of the iir filter are that there is instability due to the quantization of the coefficients which can push the poles outside the unit circle and that it is not possible to achieve linear phase over the entire nyquist interval. fir response models are preferred over iir models in practical applications such as signal processing [1, 2], telecommunications [8], and control systems [9-11]. however, the iir model often arises from signal and system modeling and controller and filter design [1, 2, 11], so it is still used in corresponding author: bui huy hai engineering, technology & applied science research vol. 12, no. 6, 2022, 9458-9463 9459 www.etasr.com bui: the application of lqg balanced truncation algorithm to the digital filter design problem practice. since the fir model is more popular than the iir model, efficient methods are often used to approximate the iir model using the fir model. the iir model approximation problem can be stated as follows: given an iir model  zg , which is a stable rational transfer function, find   1 10 1 1... m m z t t z t z       t such that the norm ,f which is the transfer function error      z z z f g t , is minimized, choosing which standard to evaluate the error due to the requirements of each problem. due to the existence of an approximation problem in the design of iir filters, they are usually of high order. high-order filters will lead to many disadvantages in the process of using filters, so in the filter design process, it is necessary to apply model reduction methods to reduce the order of high-order filters. the problem of model order reduction can be stated as follows: consider a linear, continuous, time-invariant parameter system with many inputs and many outputs, described in state space by the following system of equations:    x ax bu y cx ɺ (1) in which x  rn, u  rp, y  rq, a  rnxn, b  rnxp, and c  r qxn . the goal of the order reduction problem for the model described by the system of (1) is to find the model described by the system of equations: r r r r r r r    x a x b u y c x ɺ (2) where xr  r r , u  rp, yrr q , ar  r rxr , br  r rxp , and cr  r qxr , with r  n so that the model described by the system of (2) can replace the model described by the system of (1), and at the same time satisfy some of the following requirements:  the order reduction error is small and can be evaluated.  the order reduction algorithm needs to calculate efficiently and stability.  the order reduction algorithm can be performed automatically based on the formula for calculating the upper bound of the order reduction error.  important properties of the root system, such as stability and passivity, should be preserved in a reduced order system.  it must be suitable for each specific requirement of each order reduction problem. over the years, hundreds of studies have been published that dealt with solving the problem of order reduction of highorder models. most of them focused on solving the problem of order reduction for linear systems. depending on the properties of the original system that need to be preserved in the order reduction system, there are many different order reduction methods. however, they can be classified based on the following basic techniques:  singular perturbations analysis (spa) [12].  modal analysis (ma) [13-16].  singular value decomposition (svd) analysis [19].  moment matching (mm or krylov methods) [17].  combined svd and mm [18]. among the above order reduction techniques, we pay the most attention to the group of methods based on svd analysis and information from the single hankel values of the system. the most important proposal of this group of methods is the balanced truncation method [20]. the balanced truncation method is implemented by applying the equivalence condition to the simultaneous diagonalization of the control and observed gramian matrix of the system. through the process of diagonalizing two gramian matrices, it is possible to convert the original model represented in any basis system into an equivalent system representing the coordinate system in internal equilibrium space. from that equilibrium space, the low-order model can be found by removing the eigenvalues that contribute little to the relationship between the input and the output of the system, as well as the states that are less controlled and observed. the balanced truncation method was further developed in [21], and the relationship with hankel's norm was determined in [22, 23]. in addition to the balanced truncation method, the svd-based method has a number of other methods such as the stochastic balancing method [24], [25], the lqg balancing truncation algorithm [26], etc. each order model reduction algorithm has its advantages and disadvantages and should be used for appropriate cases. in this paper, we are most interested in the lqg balancing truncation algorithm [26] and use it to reduce the high-order filter. ii. the lqg balanced truncation algorithm given a linear, continuous, time-invariant parameter system with many inputs and outputs, described in state space by (1) and according to the balanced truncation algorithm, to determine the transition matrix t , we need to determine the control grammian matrix and the observed gramian matrix by solving a system of lyapunov equations. however, the condition for the system of lyapunov equations to have a solution is that the original system (1) must be stable. if the original system (1) is unstable, we cannot solve the system of lyapunov equations. to solve this problem, the lqg balanced truncation algorithm [26] proposes to calculate the controllable gramian matrix and the observable gramian matrix of the unstable system through an extended riccati system of equations. once the control and observation gramian has been determined, it becomes possible to determine the transition matrix t . the detailed content of the lqg balanced truncation algorithm [26] is as follows: input: the sytem  , , a b c is described in (1) (unstable system). engineering, technology & applied science research vol. 12, no. 6, 2022, 9458-9463 9460 www.etasr.com bui: the application of lqg balanced truncation algorithm to the digital filter design problem step 1: calculate the control gramian matrix p and the observed gramian matrix q according to the extended riccati system of equations as follows: ' ' ' ' 0 ' ' ' 0         ap pa pc c p bb a q qa qbb q c c step 2: determine the triangular matrix on r by cholesky analysis of the controlled gramian matrix: tp rr step 3. use matrix r to calculate svd analysis of control gramian matrix as follows: t trqr uλv step 4: calculate matrix 1/ 2l v . step 5: calculate the non-singular matrix 1 -1/2 l t t r u . step 6: calculate    1 1, , , ,  a b c t at t b ct . step 7: choose r such that r < n, where r is the order of the reduced system. represent  , , a b c in block form as follows:  11 12 1 1 2 21 22 2 , ,               a a b a b c c c a a b where x x x 11 1 1 , , r r r p q r r r r  a b c . output: reduced system  11 1 1, , a b c . iii. reducing the order of the digital filter consider a iir digital filter with a transfer function in the form of h(z) in (3) and the general structure of a laddered iir filter [1-2]:   1 0 1 1 1 0 1 1 ... ... n n n n n n n n b z b z b z b z a z a z a z a              h (3) in [27], the authors have determined the transfer function model of the 6 th -order iir digital filter as follows:       z z z  a h b with:     3 5 4 3 2 6 5 4 2 0.1242 0.1581 0.5273 0.2154 0.0647 0.6889 1.095 1.299 1.113 0.4261.028 0.6043 z z z z z z z z z z zz z            a b the 6 th -order iir digital filter has a non-minimum phase form and has a polarity very close to the unit circle in the zplane. therefore, it is prone to digital errors and is not suitable for performing digital signal processing (dsp). at the same time, the order of the digital filter is high, so when used in practice, there will be many disadvantages. to overcome this implementation difficulty, we need to reduce the order of the irr digital filter. to do so, we convert the 6 th -order digital filter to the form of linear analog filter through the transformation 1z s  . the obtained result is:       s s s  c h d with:     5 4 3 2 6 5 4 3 2 0.1242 0.4629 0.0823 1.504 1.959 1.401 4.905 10.82 13.13 9.533 3.834 0.9407 s s s s s s s s s s s s s              c d performing order reduction of the 6th-order digital filter according to the steps of the lqg balanced truncation algorithm [26], the results are: step 1: the control gramian matrix p and the observed gramian matrix q have the following form: 0.1607 0.0009 -0.2016 -0.0036 0.0943 -0.0013 0.0009 0.4125 0.0118 -0.4250 -0.0607 0.0813 -0.2016 0.0118 0.8439 0.0004 -0.8583 -0.0320 -0.0036 -0.4250 0.0004 p 0.8738 0.1547 -0.3196 0.0943 -0.0607 -0.8583 0.1547 1.8095 0.1140 -0.0013 0.0813 -0.0320 -0.3196 0.1140 0.3995 0.3205 0.4039 0.4465 0.52                    q 28 0.3373 0.3733 0.4039 0.5175 0.5839 0.6999 0.4634 0.5471 0.4465 0.5839 0.6753 0.8327 0.5671 0.7160 0.5228 0.6999 0.8327 1.0586 0.7419 0.9968 0.3373 0.4634 0.5671 0.7419 0.5336 0.7543 0.3733 0.5471 0.7160 0.9968 0.7543 1.1679                    step 2-4: the matrices ,r u , and l have the following form: 0.4008 0.0023 -0.5030 -0.0089 0.2353 -0.0033 0 0.6423 0.0202 -0.6616 -0.0954 0.1266 0 0 0.7685 0.0121 -0.9604 -0.0471 0 0 r 0 0.6602 0.1596 -0.3563 0 0 0 0 0.8929 0.1551 0 0 0 0 0 0.4798           -0.0412 0.0204 -0.5517 -0.7850 0.1946 -0.1985 -0.1800 -0.1740 -0.2263 -0.1283 -0.8878 0.2855 -0.1460 -0.6028 -0.4883 0.4562 0.0765 -0.4037 0.3772 -0.7024         u 0.1683 -0.2285 0.2089 0.4900 0.7612 -0.0154 0.1140 -0.0702 -0.3421 -0.5342 0.4720 0.3352 -0.6038 0.3195 0.0868 0.43669 1.0691 0 0 0 0 0 0 0.355 0 0 0 0 0 0 0                    l .0109 0 0 0 0 0 0 0.0078 0 0 0 0 0 0 0.0065 0 0 0 0 0 0 0.0001                    engineering, technology & applied science research vol. 12, no. 6, 2022, 9458-9463 9461 www.etasr.com bui: the application of lqg balanced truncation algorithm to the digital filter design problem step 5: the non-singular matrix t has the form: 0.4244 0.5900 0.7316 0.9695 0.7049 1.0172 -0.5988 -0.6398 -0.5389 -0.3893 -0.0826 0.4162 -0.2020 -0.0591 -0.0283 -0.0529 0.0361 -0.1311 -0.1191 -0.0274 0.0346 t 0.0053 -0.0172 0.0589 0.0182 -0.0757 -0.0336 0.0415 -0.0335 0.0146 -0.0203 0.0185 -0.0160 0.0158 -0.0084 0.0101                    step 6: the system is in equilibrium equivalent form: 0.0120 0.4910 0.0785 0.0465 0.0073 0.0081 0.4910 0.4415 0.3529 0.2060 0.0301 0.0343 0.0785 0.3529 1.8800 1.2871 0.8508 0.3832 0.0465 0.2060 1.2871 a 0.9049 1.6577 0.3143 -0.0073 0.0301 0.8508 1.6577 0.0255 0.0558 0.0081 0.0343 0.3832 0.3143 0.0558 -1.6653 0.4244 -0.5988 -0.2020 -0.1191 0.018                    b   2 -0.0203 0.4244 0.5988 0.2020 0.1191 0.0182 0.0203                    c the results of the order reduction of the digital filter are shown in table i. table i. result of order reduction of the 6th order filter order hr(s) r h h 5 4 3 2 5 4 3 2 0.1238 0.2611 0.405 0.7221 0.8147 3.24 5.188 4.469 1.952 0.5468 s s s s s s s s s           9.7456.10 -4 4 3 2 4 3 2 0.1235 0.2711 1.003 0.01749 3.214 1.635 0.7117 0.01141 s s s s s s s         0.0437 3 2 3 2 0.1376 0.08334 0.6907 2.309 1.161 0.4662 s s s s s       0.0266 2 2 8 -0.1784 s + 0.3335 0.4294 0.235s s  0.0904 the step response and the bode response are two basic responses that evaluate the quality of the filter. therefore, we will use them to evaluate the quality of the low-order digital filter. the step response and bode response of the low-order digital filters are shown in figures 1-4. we can see that the step response of the 5 th -order digital filter coincides with the step response of the 6 th order digital filter (figure 1). in figure 2 we see that the step response of the 3 rd -order digital filter almost coincides with the step response of the 6 th -order digital filter and the step response of the 4 th -order digital filter has a small deviation from the step response of the 6 th -order digital filter. the step response of the 2 nd -order digital filter has a large deviation from the step response of the 6 th -order digital filter. figure 4 shows the bode response of the 5 th -order digital filter. it is noted that the 4 th -order digital filter completely coincides with the bode response of the 6 th -order digital filter. fig. 1. step response of 5thand 6th-order digital filters. fig. 2. step response of 6th-, 4th-, 3rd-, and 2nd-order digital filters. fig. 3. bode response of the 6th-, 5th-, and 4th-order digital filters. in figure 4, we see that:  in the frequency range  < 9.37rad/s, the frequency amplitude response of the 3 rd -order digital filter coincides with the frequency amplitude response of the 6 th -order digital filter.  in the frequency range  > 9.37rad/s, the frequency amplitude response of the 3 rd -order digital filter has a small deviation from the frequency amplitude response of the 6 th order digital filter. engineering, technology & applied science research vol. 12, no. 6, 2022, 9458-9463 9462 www.etasr.com bui: the application of lqg balanced truncation algorithm to the digital filter design problem fig. 4. bode response of the 6th-, 3rd-, and 2nd-order digital filters.  in the frequency range  < 2.07rad/s and  > 12.5rad/s, the frequency phase response of the 3 rd -order digital filter coincides with the frequency phase response of the 6 th -order digital filter.  in the frequency range 2.07rad/s <  < 12.5rad/s, the frequency phase response of the 3 rd -order digital filter has a small deviation from the frequency phase response of the 6 th -order digital filter.  in the frequency range  < 2.7rad/s, the frequency amplitude response of the 2 nd -order digital filter coincides with the frequency amplitude response of the 6 th -order digital filter.  in the frequency range  > 2.7rad/s, the frequency response of the 2 nd -order digital filter has a large deviation from the frequency response of the 6 th -order digital filter.  in the frequency range  < 1.33rad/s and ω > 29.8rad/s, the frequency phase response of the 2 nd -order digital filter coincides with the frequency phase response of the 6 th -order digital filter.  in the frequency range of 1.33rad/s <  < 29.8rad/s, the frequency phase response of the 2 nd -order digital filter has a large deviation from the frequency phase response of the 6 th -order digital filter. comment: if minimum order reduction error is desired, the 5 th -order digital filter can be used instead of the 6 th -order digital filter. if we want a low-order digital filter with the smallest order, but with quality almost equivalent to that of a 6 th -order digital filter, we can choose a 3 rd -order digital filter to replace the 6th order digital filter. the novelty of the current paper is that the lqg algorithm has been used to determine a low-order filter that can replace the high-order filter. the paper has evaluated the error of order reduction according to both the formula for evaluating the order reduction error and the error on step response characteristics and bode response characteristics. in [27], the author does not specify the order of the order reduction system, only focuses on converting the filter from iir form to fir form by order reduction algorithms and then evaluates the limit of order reduction error at some frequencies. in the future, we will evaluate the order reduction error at frequency points to compare the obtained results with the results in [27]. iv. conclusion digital filters have many advantages, so they are widely used in technical fields. the most common digital filter design method is usually to design first an analog filter and then convert it to digital filter form. digital irr filters often arise in engineering problems, so they are increasingly utilized and studied in research. the design of digital irr filters often has to apply approximation methods, so the resulting filter is often of high order. to make the digital irr filter simple and low in computational cost, we need to apply model order reduction algorithms to reduce the order of the high-order irr filter. this article has applied the lqg balanced truncation algorithm to reduce the order of a 6 th -order digital filter. the results of comparison and evaluation of low-order filters show that the resulting 5 th -order digital filter can replace the 6 th -order digital filter without any change in filter quality. also, a 3 rd -order digital filter can be used instead of a 6 th -order digital filter if it is accepted that the quality of the low-order filter is only approximately that of the 6 th -order filter. the simulation results show the correctness of the filter order reduction results using the lqg balanced truncation algorithm. references [1] s. k. mitra, digital signal processing : a 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[27] l. chai, j. zhang, c. zhang, and e. mosca, "hankel-norm approximation of iir by fir models: a constructive method," ieee transactions on circuits and systems i: regular papers, vol. 55, no. 2, pp. 586–598, mar. 2008, https://doi.org/10.1109/tcsi.2007.913615. microsoft word etasr_v13_n1_pp10204-10208 engineering, technology & applied science research vol. 13, no. 1, 2023, 10204-10208 10204 www.etasr.com neeti & singh: groundwater quality assessment and health risks from fluoride in jamui, bihar groundwater quality assessment and health risks from fluoride in jamui, bihar krishna neeti department of civil engineering, national institute of technology patna, india krishnan.phd19.ce@nitp.ac.in reena singh department of civil engineering, national institute of technology patna, india reena@nitp.ac.in (corresponding author) received: 17 december 2022 | revised: 9 january 2023 | accepted: 11 january 2023 abstract this study aimed to determine the fluoride concentration in drinking water and assess its health risks by analyzing 12 physicochemical parameters, including fluoride, ph, ec, tds, chloride, carbonate and bicarbonate (alkalinity), sulfate, nitrate, calcium, and magnesium hardness. correlation analysis, wqi, and hra were used to determine whether groundwater in the study area was suitable for drinking. correlation analysis showed that fluoride was negatively correlated with ec (-0.649), co3 2 (-0.855) and positively correlated with mg 2+ (+0.559). all water samples exceeded the permissible fluoride limits according to bis (is 10500:2012). the wqi for all water samples was more than 100, indicating that the water was not suitable for drinking. health risk assessment was also performed to determine the risks of non-carcinogenic diseases. the hazard index (hi) was determined as greater than 1. the hi ranged from 1.275 to 3.346 for adult men, 1.431 to 3.954 for adult women, and 1.986 to 5.4864 for children. fluoride concentrations in drinking water pose a greater health risk to children than to adults. the fluoride level in drinking water is an essential parameter that must be monitored as a preventive measure against dental and skeletal fluorosis. keywords-groundwater; fluoride; correlation analysis; health risks i. introduction a healthy lifestyle requires clean and safe water, as poor water quality causes health problems and social difficulties. in certain parts of the world, access to clean drinking water is difficult due to economic, environmental, and budgetary constraints [1, 2]. many countries prioritize providing safe drinking water, but undeveloped and many developing countries cannot meet regulatory drinking water requirements [3-5]. clean water services are not even accessible to 783 million people, according to the world health organization (who). more than half of humanity is expected to suffer from a drinking water crisis by 2025 [6]. drinkable freshwater consumed is more often derived from groundwater than surface water due to the higher microbiological activity of the latter [7]. however, several geological processes increase groundwater contamination [8]. it is common for rural water sources to be contaminated by illegally discharged industrial, agricultural, and urban effluents. these contaminated water bodies harm humans and aquatic life [9, 10], and several efforts are being made to improve the quality of drinking water. the burden of waterborne diseases from consuming contaminated water is measurable and considerable [11], and it negatively affects society on an economic level [12]. many studies have shown that fluoride, nitrate, and arsenic ions adversely affect living organisms [13]. the presence of excessive levels of fluoride in drinking water (>1mg/l) has raised concerns about public health and has been associated with several harmful health effects [4, 14-18]. when people drink excessive amounts of fluoride in water, they are more likely to have fluorosis, which can range from dental (1.54.0mg/l) to severe (>10mg/l), depending on the amount of f consumed [5-6, 18-19]. some areas have significant levels of f in their groundwater due to natural sources present in those areas, making drinking water enriched with geogenic f ions [20]. in sedimentary and igneous rocks, fluoride exists naturally in the minerals sellaite (mgf2), cryolite (na2alf6), fluorite (caf2), and fluorapatite (ca5(po4)3f) [21]. few countries have established allowed limits for fluoride in drinking water in cooperation with the who to reduce overexposure to f . fluorosis poses a significant risk to approximately 200 million people worldwide [22]. engineering, technology & applied science research vol. 13, no. 1, 2023, 10204-10208 10205 www.etasr.com neeti & singh: groundwater quality assessment and health risks from fluoride in jamui, bihar ii. study area the bihar, jamui district, located at latitude 24 o 55'n and longitude 86 o 13'e, was selected as the study area, while most of the district has hilly topography. table i shows the geographical sampling locations. table i. locations of geographical sampling sampling locations latitude longitude harna (s1) 86.41 24.7593 bishanpur (s2) 86.316 24.984 nargango (s3) 86.3544 24.7454 jokatia (s4) 86.3544 24.7454 lalmatia (s5) 86.3 24.9829 chandrasekhar nagar (s6) 86.3553 24.8916 primary school chooljeevan tola (s7) 86.38 24.8 bhadwaria (s8) 86.4624 24.7635 prakash nagar (s9) 86.388 24.8141 panch pahari (s10) 86.3362 24.7469 nabinagar (s11) 86.1572 25.0292 malaypur (s12) 86.2625 24.9717 majhwe (s13) iii. materials and methods a. sample collection the samples were collected in may-june 2022. a total of 13 groundwater samples were collected from 13 different sampling locations, as shown in table i, according to the apha (2005) guidelines. the water samples were collected after pumping for 10 to 15 minutes to eliminate stagnant water. each water sample was collected in a 1l pre-cleaned plastic bottle and stored at 40°c in a dark box. the store box was carried to the laboratory for further analysis. b. water analysis the apha (2005) protocol was followed for all procedures. a portable water analyzer-371 (systronics india ltd.) was used to evaluate ph, tds, and ec at the sampling locations. the argentometric method was used to determine chloride levels. the fluoride concentration was measured using spadns. the concentrations of nitrate and sulfate were determined using ultraviolet (uv) spectrophotometry. calcium, magnesium, carbonate, and bicarbonate (alkalinity) concentrations were measured using titration. c. water quality index (wqi) calculation the water quality index (wqi) was established to evaluate groundwater suitability for drinking [32]. table ii shows the wqi ratings. table ii. water quality index ratings water quality index water quality status 0-25 excellent 26-50 good 51-75 poor 76-100 very poor >100 unsuitable for consumption d. calculating health risk assessment (hra) the united states environmental protection agency (us epa) developed an approach to evaluate the risk to human health, which has since been extensively used [23-25]. the hra is an essential reference for conserving and managing a groundwater environment [25-27]. water and air are the primary sources of health risks for humans. this study focused on drinking water consumption as a primary route, using f to compute hra and noncarcinogenic risks by: �������� = � ×��×��×�� ��×�� (1) where intakeoral (mg/kg/day) is the average daily exposure dosage by groundwater consumption, cw is the amount of a specific contaminant (fluoride) present in groundwater (mg/l), ir is the intake rate for groundwater (ir=1.5l/day for adult men/women and 0.7l/day for children), ef is the exposure frequency (365days/year), ed is the exposure duration (ed=30 years for adults and 12 years for children) obtained from epa, bw is the average body weight (55kg and 65kg for women and men, respectively, and 18.5kg for children) [29], and at is the average exposure time (4380 days for children and 10950 days for adults). the hazard quotient (hq) was applied to evaluate the fluoride risk as: ���� = ��� ���� ! �"��� ! (2) where hqoral and rfdoral are the hazard quotients and reference doses for noncarcinogenic pollutants through drinking water intake, and the oral reference doses of f − were obtained from the epa as 0.04mg/kg/day. an hqoral greater than 1 is considered a noncarcinogenic risk, while hqoral equal to 1 is considered safe. iv. results and discussion a. physicochemical analysis for drinking water table iii shows the statistical analysis of the physicochemical parameters and a comparison with bis (is 1050:2012). table iii. physicochemical parameters analysed statistically variable unit minimum maximum mean stddev bis acceptable f mg/l 2.100 5.800 3.483 1.266 1 ph 7.590 8.570 8.167 0.290 6.5–8.5 ec µs/cm 200.000 1850.000 723.077 460.351 tds mg/l 125.000 920.000 601.538 279.385 500 ca 2+ mg/l 0.180 60.000 20.960 20.853 75 mg 2+ mg/l 3.510 47.500 17.368 15.236 30 cl mg/l 7.560 350.800 107.152 82.175 250 hco3 mg/l 115.340 460.600 316.306 103.397 co3 2 mg/l 1.500 8.000 6.310 1.788 so4 2 mg/l 5.550 75.500 34.981 25.336 200 no3 mg/l 7.550 36.850 16.390 7.949 45 b. analysis of water quality index (wqi) figure 2 shows the wqi of the sampling locations. as can be seen, the water quality rating of all sampling locations was greater than 100, showing that the drinking water at the selected locations was not suitable for consumption. the fluoride was mainly responsible for the higher value of wqi. engineering, technology & applied science research vol. 13, no. 1, 2023, 10204-10208 10206 www.etasr.com neeti & singh: groundwater quality assessment and health risks from fluoride in jamui, bihar fig. 1. fluoride concentrations in the study area. fig. 2. wqi of the sampling locations c. correlation analysis a correlation analysis measures and establishes the relationship between two factors [30]. a value less than 0.5 indicates a low correlation, 0.5 indicates a fair correlation, and greater than 0.5 indicates a very high correlation. pearson's correlation coefficient reveals the essential connection between the unique variables obtained in the non-parametric form [31]. an inducement of zero demonstrates no relationship between the two variables, while a correlation coefficient of +1 or -1 indicates a strong correlation. figure 3 shows the association between fluoride and the other water quality measures of the current study. correlation analysis showed that fluoride was negatively and strongly correlated with ca 2+ (-0.649) and co3 2 (-0.855) and positively with mg 2+ (0.559). fig. 3. fluoride correlation with the physicochemical parameters. d. analysis of hra the population studied was classified into two groups:  children, aged between 2-16 years. data from 50 children were collected.  adults, male or female, aged over 16 years. data from 40 males and 25 females were collected. fluoride concentrations in drinking water pose a greater health risk to children than adults. the hazard index (hi) ranged from 1.275 to 3.346 for adult men, 1.431-3.954 for adult women, and 1.986-5.4864 for children. table iv shows the noncarcinogenic risk for the sample in the study region. fig. 4. hazard index of males, females, and children. table iv. noncarcinogenic risk for males, females, and children in the study region cw fluoride intakeoral (male) intakeoral (female) intakeoral (child) hqoral (male) hqoral (female) hqoral (child) 2.1 0.121153846 0.057273 0.079459 3.028846154 1.431818182 1.986486486 2.21 0.051 0.060273 0.083622 1.275 1.506818182 2.090540541 2.4 0.055384615 0.065455 0.090811 1.384615385 1.636363636 2.27027027 2.7 0.062307692 0.073636 0.102162 1.557692308 1.840909091 2.554054054 2.9 0.066923077 0.079091 0.10973 1.673076923 1.977272727 2.743243243 3 0.069230769 0.081818 0.113514 1.730769231 2.045454545 2.837837838 3.08 0.071076923 0.084 0.116541 1.776923077 2.1 2.913513514 3.35 0.077307692 0.091364 0.126757 1.932692308 2.284090909 3.168918919 3.34 0.077076923 0.091091 0.126378 1.926923077 2.277272727 3.159459459 3.5 0.080769231 0.095455 0.132432 2.019230769 2.386363636 3.310810811 5.3 0.122307692 0.144545 0.200541 3.057692308 3.613636364 5.013513514 5.6 0.129230769 0.152727 0.211892 3.230769231 3.818181818 5.297297297 5.8 0.133846154 0.158182 0.219459 3.346153846 3.954545455 5.486486486 v. conclusion this study investigated the fluoride contamination of groundwater samples in the jamui district of bihar, india, and examined the relationship between fluoride contamination and other water quality measures. the observed physicochemical data were compared with the bureau of indian standards (bis) limits, and it was found that fluoride exceeded the allowed limits. the fluoride was the leading cause of contamination in the selected area, responsible for a higher value of wqi. that engineering, technology & applied science research vol. 13, no. 1, 2023, 10204-10208 10207 www.etasr.com neeti & singh: groundwater quality assessment and health risks from fluoride in jamui, bihar indicates that drinking water at the selected locations is not suitable for consumption. therefore, appropriate filtration units should be installed in hand pumps to remove the excess fluoride. correlation analysis showed that fluoride is strongly negatively correlated with ca 2+ (-0.649) and co3 2 (-0.855) and positively with mg 2+ (0.559). regression analysis showed that fluoride has a decreasing trend with calcium and carbonate and an increasing trend with magnesium. drinking water containing fluoride causes greater health risks in children than in adults, according to published risk assessments for human health. the range of possible values for the hazard index (hi) for adult men ranged from 1.275 to 3.346, for adult females from 1.431 to 3.954, and for children from 1.986 to 5.4864. in the study area, children are more susceptible to health risks than adults due to the highly polluted drinking water with high fluoride levels. references [1] s. ahmad, r. singh, t. arfin, and k. neeti, "fluoride contamination, consequences and 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[32] r. m. brown, n. i. mcclelland, r. a. deininger, and m. f. o’connor, "a water quality index — crashing the psychological barrier," in indicators of environmental quality, boston, ma, usa, 1972, pp. 173– 182, https://doi.org/10.1007/978-1-4684-2856-8_15. microsoft word 6-656-ed.doc engineering, technology & applied science research vol. 6, no. 3, 2016, 1006-1009 1006 www.etasr.com fellaou and bounahmidi: mass balance reconciliation for bilinear systems: a case study … mass balance reconciliation for bilinear systems: a case study of a raw mill separator in a typical moroccan cement plant s. fellaou laboratory for analysis and synthesis of industrial processes (laspi), university mohammed v agdal rabat, mohammadia school of engineers, rabat, morocco soukaina.fellaou@research.emi.ac.ma t. bounahmidi laboratory for analysis and synthesis of industrial processes (laspi), university mohammed v agdal rabat, morocco and euro-mediterranean university of fez, fez, morocco tbounahmidi@gmail.com abstract—stream flow rates and their several compositions are measured in a typical cement raw mill separator. in order to simultaneously reconcile flow and composition measurements in this circuit, the component mass balances was included as constraints which contain the products of flow rate and composition variables in the data reconciliation problem. in this paper, the effectiveness of simultaneous procedures for bilinear data reconciliation is established, the numerical problem constraints were coded in matlab and a mass balance model is built. moreover, based on the difference between the measured and reconciled data it was found that it performs optimally. keywords-mass balance; data reconciliation; bilinear system; cement industry. i. introduction process variables are measured for control purposes and also for economic evaluation and optimization purposes. the estimation of true conditions of process states can impact in different ways to the efficiency of the process. from a statistical point of view, the method that adequately supports data quality improvement is data reconciliation, which can be employed to adjust the entire data set to fit the system constraints [1] i.e. to fulfill the process model. nowadays, the data reconciliation technique has been applied to many different industrial areas such as mineral industry processes, chemical production plants, and nuclear power plants [2]. however it has not yet been commonly used in the moroccan industry. the purpose of this paper is to gather a full understanding of how data reconciliation can be investigated in a satisfactory manner for cement manufacturing process performance evaluation, to present what the most likely state of the system is and to verify the acceptability and the accuracy of measurements. in a processing plant, the total mass entering and leaving any portion of it must obey the mass conservation constraints. since these constraints covered the case of multicomponent balances, the term bilinear data reconciliation is consequently used. this procedure contributes to the improvement of the process data quality which is the basis for process control, production accounting goals, as well as optimization. a vast amount of literature is available in the field of data reconciliation. in 1961, kuehn and davidson [3] were the first to publish an analysis of data reconciliation in the process industry. they solved a linear data reconciliation problem where the process was in steady state with all variables measured. a subsequent publication [4] defined the concepts of observability and redundancy and worked out many of the basic ideas in the field. in [5] it was found that the base method requires a process system in steady state conditions. in recent years, many industrial application of data reconciliation are related in scientific papers involving various processing industries [6-11]. in the same vein, sufficient breadth in software packages supporting data reconciliation are available and allows to manage the operations of different processes (datacon, sigmafine, vali, recon, ebsilon validate, datrec, dval, inlibra). ii. motivation and problem statement the cement industry is responsible for around 33.3 per cent of industrial energy consumption in morocco. it has been remarked as an intensive consumer of natural raw materials, fossil fuels and a major source of pollutants as well. thus, evaluating and maintaining the manufacturing process close to an optimum performance in this industry is has become a necessity. with the purpose of evaluating their performance and determining current efficiencies, balances for cement process must be performed and this cannot be achieved unless the process is first defined and measured. the primary focus of process evaluation is usually equipment specification. in fact, the question of sufficiency of information to make the material balance is answered by the degree of freedom analysis [12]. thus, to make sure that the number of variables and equations are in balance prior to attempting optimal solution. after fixing the degree of required knowledge of the process, the balances which are defined by the measured data, should have been extensive enough to more than satisfy the balance equations [13]. however, due to random and systematic errors, most plant systems face information redundancy in the measurement, in the sense that the system amount of available data exceeds the minimum amount necessary for a unique determination of the independent variables that determine the plant model engineering, technology & applied science research vol. 6, no. 3, 2016, 1006-1009 1007 www.etasr.com fellaou and bounahmidi: mass balance reconciliation for bilinear systems: a case study … which yield a negative value for the number of degrees of freedom. once the process constraints are created, all available or redundant measured variables must first be assigned to the model streams and units together with their respective measurement uncertainties [14]. additionally, the key variables in a cement processing unit are usually flow rates and material chemical compositions. their reconciliation with the laws of mass conservation throughout the system is essential and can be used to ensure consistent product quality. the applicability of the data reconciliation approach is confirmed through an industrial case study of a redundant typical mill/separator circuit, as shown in figure 1. the process for raw meal production requires tube mill as the main machine for grinding and a separator for splitting the material from the grinding mill (f1) into a fine (f3) and coarse fraction (f2), the corresponding measurements data yi is given in table i. material input are limestone, silica stone, clay, cooper slag and the product (f3) is raw meal. material balances are fundamental to the control of processing, particularly in the control of yields of the products. equilibrium of the material balance equations consists of estimating the true quantities that they should be consistent. the process studied has one inlet stream and two outlet streams. initially, mass flow rate and composition of every stream are assumed to be directly measured. according to the law of conservation of matter for the circuit studied, the mass going into the separator must balance with mass coming out. the measurement values are assumed to give an image of the process steady-state behavior. hence, the constraints of mass conservation are written in the form: f1,1+f2,1-f3,1=0 (...) f1,11+f2,11-f3,11=0 fi,j=fjwi,j where fi is the vector of the measured flow rates and wi,j are the composition vectors. the verification whether measured data (given in table i) satisfy the balance equation, indicates that the above equation is not fulfilled. this means that the material input and output of the unit do not balance, so data reconciliation is necessary to derive estimates of the flows that satisfy the above flow balances. table i. bilinear data reconciliation results of raw mill/separator circuit stream components variables raw measurement (kg/h) standard deviation of measured value (kg/h) reconciled measurement (kg/h) standard deviation of reconciled value (kg/h) adjustment (kg/h) total feed f1 300940 140 300520 300530 301360 43 -410 sio2 w1, 1 0,135 0,014 0,093 0,1467 0,177 0,0102 0,0117 al2o3 w1, 2 0,033 0,009 0,006 0,0350 0,06 0,0018 0,0020 fe2o3 w1, 3 0,0211 0,0015 0,0166 0,0213 0,0256 0,0011 0,0002 cao w1, 4 0,4343 0,0249 0,3596 0,4705 0,509 0,0104 0,0362 mgo w1, 5 0,0125 0,0006 0,0107 0,0125 0,0143 0,0006 0,0000 so3 w1, 6 0,0016 0,0002 0,001 0,0017 0,0022 0,0002 0,0001 k2o w1, 7 0,0052 0,0007 0,0031 0,0051 0,0073 0,0004 -0,0001 tio2 w1, 8 0,0022 0,0003 0,0013 0,0023 0,0031 0,0002 0,0001 p2o5 w1, 9 0,0016 0,0002 0,001 0,0016 0,0022 0,0002 0,0000 mno w1, 10 0,0007 0,0001 0,0004 0,0007 0,001 0,0001 0,0000 loi w1, 11 0,3528 0,0056 0,336 0,3518 0,3696 0,0000 -0,0010 separator rejects f2 170290 37 170179 170320 170401 36 30 sio2 w2, 1 0,137 0,038 0,023 0,1498 0,251 0,0189 0,0128 al2o3 w2, 2 0,035 0,001 0,032 0,0350 0,038 0,0010 0,0000 fe2o3 w2, 3 0,0213 0,0019 0,0156 0,0210 0,027 0,0016 -0,0003 cao w2, 4 0,4338 0,0576 0,261 0,4661 0,6066 0,0190 0,0323 mgo w2, 5 0,0121 0,003 0,0031 0,0124 0,0211 0,0017 0,0003 so3 w2, 6 0,0057 0,0016 0,0009 0,0005 0,0105 0,0007 -0,0052 k2o w2, 7 0,005 0,0008 0,0026 0,0051 0,0074 0,0007 0,0001 tio2 w2, 8 0,0024 0,0003 0,0015 0,0024 0,0033 0,0003 0,0000 p2o5 w2, 9 0,0016 0,0003 0,0007 0,0016 0,0025 0,0003 0,0000 mno w2, 10 0,0005 0,0001 0,0002 0,0005 0,0008 0,0001 0,0000 loi w2, 11 0,3516 0,0229 0,2829 0,3517 0,4203 0,0000 0,0001 final product f3 130200 26 130122 130210 130278 26 10 sio2 w3, 1 0,136 0,013 0,097 0,1427 0,175 0,0118 0,0067 al2o3 w3, 2 0,034 0,004 0,022 0,0349 0,046 0,0039 0,0009 fe2o3 w3, 3 0,0224 0,0024 0,0152 0,0218 0,0296 0,0021 -0,0006 cao w3, 4 0,432 0,033 0,333 0,4762 0,531 0,0125 0,0442 mgo w3, 5 0,0123 0,0024 0,0051 0,0126 0,0195 0,0021 0,0003 so3 w3, 6 0,005 0,001 0,002 0,0034 0,008 0,0009 -0,0016 k2o w3, 7 0,0052 0,0006 0,0034 0,0052 0,007 0,0006 0,0000 tio2 w3, 8 0,0022 0,0004 0,001 0,0022 0,0034 0,0004 0,0000 p2o5 w3, 9 0,0015 0,0004 0,0003 0,0015 0,0027 0,0003 0,0000 mno w3, 10 0,0008 0,0002 0,0002 0,0009 0,0014 0,0002 0,0001 loi w3, 11 0,3519 0,0112 0,3183 0,352 0,3855 0,0000 0,0001 engineering, technology & applied science research vol. 6, no. 3, 2016, 1006-1009 1008 www.etasr.com fellaou and bounahmidi: mass balance reconciliation for bilinear systems: a case study … fig. 1. schematic diagram of a typical cement raw mill/separator circuit iii. data reconciliation for bilinear systems a. steady-state linear data reconciliation steady-state mass balance process variables are related by mass conservation laws. although in the presence of measurement errors the balance equations are not satisfied exactly [16]. in such cases the number of balance equations in the system is greater than the number of unknown variables to calculate, some system measurements are then said to be redundant. moreover, it is highly improbable that data will be fully consistent from the viewpoint material balance since they are by definition individual normally distributed around a mean value. in other words, it is impossible to calculate the unknown so that the material balances are respected. in this context, for measurement adjustment, data reconciliation technique applies a correction to each measurement to force the estimated values to exactly obey the balance equations. in other words, it is devoted to determine the most likely process state with the smallest possible uncertainties. in this paper, the redundant measurements were exploited through the lagrange multiplier method to improve the quality of available measures so that all the mass balance constraints are met simultaneously by the adjusted values. the reconciliation problem is thus a constrained optimization problem with the objective function given by : * 2 * i i i 2i i (y -y ) minimize y [ ] (1) σ å subject to * i ay 0 (2)= the parameters involved in bilinear data reconciliation are: 2 i σ the variance associated with the measurement, yi the vector of measurements (flow rate and composition variables), * i y the vector of reconciled measurement (flow rate and composition variables), and a represents the incidence matrix. the standard deviation of the measurements plays an essential role in the data reconciliation problem. an estimate of standard deviation can be obtained by using a simple standard deviation based on the number of measurements taken. the formula for the standard deviation σ of a measurement y is given by 2 1n 2 i=1 1 σ=( (y -y) ) (3) ν-1 iå where σ is the estimated value of standard deviation, yi is the ith measurement and y is the arithmetic average of n observations of the same variable. the analytical solution (1) is expressed explicitly [15] as: * t t -1 i iy =(i-va (ava ) a)y (4) where v is the variance matrix for each of the measurements that contain information about the correlation between them. the constraint matrix, a, is obtained based on the process connectivity information. furthermore, the data reconciliation procedure for the adjustment of the measurements to close the bilinear system constraints is reduced to a linear data reconciliation problem and the quadratic function (4) calculation is done using matlab to give the reconciled values of the inlet and outlet mass flow rate and composition of every stream which are more correctly reflect the actual current performance of the unit than those obtained just from raw measurements. b. accuracy indication this section covers the verifications actions to take after the reconciliation process to ensure that the reconciled values lie in an acceptable range. specifically, the accuracy of the measured datum is expressed in terms of the confidence level of its uncertainty [13]. which indicate how the measurements are adjusted. in bilinear constraint cases in which the objective is to simultaneously reconcile flow rates and compositions measurements, such as the ones presented here, with real industrial data, the level of uncertainty related to the stream component flow rates is compared with a quality indicator to evaluate the overall consistency of the measurements and the reliability of each individual reconciled measurement. the comparison of each of these estimated values with the coverage factor at the prescribed level of confidence are analyzed to determine if the resulting estimates fall within a confidence interval, say within * i iy ±u interval (99,7% confidence interval). for 99,7% confidence the coverage factor is 3 and iu can be expressed in terms of iσ as follows : i iu =3σ (5) table i shows the balance in each node before and after reconciliation as well as the standard deviation of measurements adjustments for every variable. the comparison of the standard deviations of the raw measurements and reconciled values of the circuit show that the reconciled data is more accurate than the raw data. in addition to this, from the same table, we can observe that the measurement adjustments for all the flows fall in the confidence interval and a drastic improvement of the process performance evaluation is usually brought on by the reconciled data. iv. results and discussion in this paper, the process of data reconciliation is discussed, and a procedure is suggested regarding how to obtain reliable data sets in an efficient way. the measurements of the feed, separator rejects, and product, f2, f2, 1, f2, 2 …. f2, 11 raw mill separator raw f3, f3, 1, f3, 2 ….. f3, 11 f1, f1, 1, f1, 2 …. f1, 11 engineering, technology & applied science research vol. 6, no. 3, 2016, 1006-1009 1009 www.etasr.com fellaou and bounahmidi: mass balance reconciliation for bilinear systems: a case study … along with their compositions as well as reconciled values are investigated. when using reconciled values, it can be easily verified that while the measured values do not satisfy the flow balances, the reconciled flows satisfy them. moreover, the results presented for the application of the bilinear data reconciliation method to the typical cement raw mill/separator circuit showed that the proposed technique slightly improves the quality of flow data and the differences between the measured and estimated flows, also referred to as adjustments, is performed optimally. also, the current operated point is within the normal operating area and assigns a quality to each individual measurement. v. conclusion in order to assess the validity of the mass balance of the unit studied, data adjustment is accomplished through bilinear data reconciliation technique and contributed to obtain statistically consistent data and estimate operating criteria. the result obtained has an important practical significance as it allows reconciled variables to be calculated with consistently high precision and provides consistent variables that can be used to determine the typical mill/separator circuit with the objective of calculating its efficiency and improved driving system. acknowledgements the authors gratefully acknowledge the support of engineers of the selected cement factory for providing the necessary facilities support to undertake the above work. references [1] a. spindler, “structural redundancy of data from wastewater treatment systems. determination of individual balance equations”, water res., vol. 57, pp. 193–201, 2014 [2] c. karlsson, tools for reconciliation of measurement data for processes at steady-state, mälardalen university, 2004 [3] h. davidson, d. r. kuehn, “computer control ii: mathematics of control”, chem. eng. prog., vol. 57, no. 6, pp. 1653-1672, 1961 [4] v. václavek, studies on system engineering. iii: optimal choice of the balance measurements in complicated chemical systems, chemical engineering science, vol. 24, no. 6, pp. 947-955, 1969 [5] r. s. h. mah, chemical process structures and information flows, elsevier, 1990 [6] h. s. yi, h. shin, j. h. kim, c. han, “industrial application of gross error estimation and data reconciliation to by production gases in iron and steel making plants”, in international conference on control, automation and systems, muju resort, jeonbuk, korea, 2001 [7] m. j. bagajewicz, e. cabrera, “data reconciliation in gas pipeline systems”, ind. eng. chem. res., vol. 42, no. 22, pp. 5596–5606, 2003 [8] d. özyurt, r. pike, “theory and practice of simultaneous data reconciliation and gross error detection for chemical processes”, comput. chem. eng., vol. 28, pp. 381–402, 2004 [9] m . schladt, b . hu, “soft-sensors based on nonlinear steady-state data reconciliation in the process industry”, chem. eng. process., vol. 46, no. 11, pp. 1107–1115, 2007 [10] m. f. martins, c. amaro, l. s. souza, r. kalid, a. kiperstok, “new objective function for data reconciliation in water balance from industrial processes”, j. clean. prod., vol. 18, no. 12, pp. 1184–1189, 2010 [11] x. jiang, p. liu, z. li, “a data reconciliation based approach to accuracy,” vol. 35, no. 2003, pp. 1213–1218, 2013. [12] a. e. morris, g. geiger, h. alan, handbook on material and energy balance calculations in materials processing third edition, nj, usa: john wiley & sons, inc, 2011 [13] c. maurice. fuerstenau and n. kenneth and han, principles of mineral processing. usa, 2009 [14] m. langenstein, j. jansky, “process data reconciliation in nuclear power plants”, process data, vol. 2, pp. 1–9, 2003 [15] j. ragot, m. aubrun, m. darrouach, “equilibrage de bilan matière méthodes et exemples minéralurgiques”, control comput., vol. 11, pp. 50–59, 1983 [16] j. romagnoli, m. c. sánchez, data processing and reconciliation for chemical process operations, academic press, san diego, 2000 microsoft word 03-odedairo-ed.doc etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 144-150 144 www.etasr.com odedairo and oladokun: relevance and applicability of multi-objective resource constrained… relevance and applicability of multi-objective resource constrained project scheduling problem review article babatunde omoniyi odedairo department of project management technology bells university of technology (but) ota, nigeria tundeodedairo@hotmail.co.uk victor oladokun department of industrial and production engineering university of ibadan (ui) ibadan, nigeria victordokun@yahoo.com abstract-— resource-constrained project scheduling problem (rcpsp) is a �on polynomial (�p) hard optimization problem that considers how to assign activities to available resources in order to meet predefined objectives. the problem is usually characterized by precedence relationship between activities with limited capacity of renewable resources. in an environment where resources are limited, projects still have to be finished on time, within the approved budget and in accordance with the preset specifications. inherently, these tend to make rcpsp, a multi-objective problem. however, it has been treated as a single objective problem with project makespan often recognized as the most relevant objective. as a result of not understanding the multi-objective dimension of some projects, where these objectives need to be simultaneously considered, distraction and conflict of interest have ultimately lead to abandoned or totally failed projects. the aim of this article is to holistically review the relevance and applicability of multi-objective performance dimension of rcpsp in an environment where optimal use of limited resources is important. keywords: project management; scheduling; resourceconstrained project scheduling problem; multi-objective; performance measure. i. introduction a recurring problem in project management involves the allocation of scarce resources to individual activities comprising the project. the international standard organisation (iso)-8402 [1] defined the term “project” as “a unique process, consisting of a set of coordinated and controlled activities with start and finish dates, undertaken to achieve an objective conforming to specific requirements including constraints of time, cost and resources”. the project management institute (pmi) in their project management body of knowledge (pmbok, 2008) [2] defined the term “project” as “a temporary endeavor undertaken to create a unique product, service, or result”. however, no single definition of the term will meet or suit all cases. all projects have several attributes in common, namely: objective, uniqueness, complexity, temporary nature and uncertainty. in project-based management, the performance measure is usually centered on effective utilization of time, cost and resources required for a given scope of work. project management involves planning, scheduling, monitoring and control of project activities to achieve project objectives. project scheduling deals with defining which activities are to be performed at a particular time. sule [3] observed that scheduling involves the arrangement of activities to meet certain requirements, constraints, or objectives. in essence, scheduling is an optimization problem which primarily involves the allocation of resources (machines) to a number of tasks (jobs) such that one or more optimization criteria are met. in scheduling, the resources are characterized in terms of their qualitative and quantitative capacities. this means that resources are described by their type and number. the task is described in terms of its resource requirement, duration, start and finish time. the scheduling objective represents the measure of performance. the growing research effort in scheduling has led to a wide variety of problem types and the introduction of a classification scheme. graham et al (1979) referenced by leung [4] introduced the classification for machine scheduling problems which comprises of three fields α β γ . the α field specifies the machine environment. the β field provides details of the task and resource characteristics. the γ field denotes the optimality criteria (performance measures) and often contains a single objective. demeulemeester and herroelen [5] extending this classification to project scheduling, proposed a similar scheme. the aim is to allow a concise taxonomy of the project scheduling field. the project scheduling problem is characterized by precedence relationship between activities or jobs and the sequence of tasks is typically predetermined with an unlimited number of resources. this problem of scheduling project activities led to the discovery of the critical path method (cpm) and the project evaluation and review technique (pert) in 1959. these techniques are based on the use of a network or graphical model that deals with time element of the schedule known as activity scheduling. the two methods assume the availability of all required resources (i.e. resourceetasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 144-150 145 www.etasr.com odedairo and oladokun: relevance and applicability of multi-objective resource constrained… unconstrained schedule) for a set of precedence-constrained activities in a deterministic environment. this can be denoted as shown in “(1)” where p represents unlimited resources, n is the number of jobs or tasks and the objective is to minimize the completion time or makespan ( )m a xc [6]: max( , ) (1)p n precconst c∞ in project execution, the resources required can be human, machine, financial, material, etc. however, the availability of these resources is a major problem because it may be limited or constrained to a certain limit. therefore, the use of cpm and pert in situations where resources are limited becomes too idealistic for most real life problems of scarce resources. hence, the problem of scheduling project network under resource constraint known as resource constrained project scheduling (rcpsp) emerged. in reality, there are projects which are resource constrained but have to be strictly finished on time (time-related objective), within approved budget (cost-related objective) and in accordance with the preset specifications (quality-related objective). for example, a small and medium enterprise contemplating on introducing advanced manufacturing technologies (amt) in order to ensure high product quality and low product cost. thomas et al [7] identified lack of clear guidance and project management knowledge as the major contributor for not embarking on such project. although, other problems confronting small enterprises have been identified to include improvement in business quality, cost, time, quick return on investment, staff training and sticking to goals [8]. another example is the construction of a residential building by a low income earner in which time, cost and quality objectives are ranked equally. the resource constrained project scheduling is a problem for most project managers because virtually all organizations use their project schedule not only as a tool to manage their project, but also as a basis on which to deliver project objectives to clients. as a result of not understanding the multiobjective dimension of some projects, conflict of interest between project managers and project stakeholders have ultimately lead to abandoned and failed projects. this is because project stakeholders tend to measure the performance and success of their project using the original schedule submitted during the bidding process. viana and pinho de sousa [9] considered the rcpsp to be inherently a multi-objective problem thou it has been treated as a single objective problem. based on this observation, we found that there is no article in literature focusing on the relevance and benefits of multi-objective rcpsp. therefore, the aim of this work is to holistically review the relevance and applicability of single and multi-objective performance dimension of rcpsp. special emphasis will be given to the application project management tools and techniques in nigeria and sub-saharan africa. this paper is organized as follows: section two reviews the theoretical framework of rcpsp, the various optimality criteria and possible combination of project objectives. section three considers the algorithms for solving single and multi-objective rcpsp. section four considers project management in nigeria. section five concludes. ii. literature review the rcpsp is a classical problem in operation research with broad applicability in project management. the problem was first identified by pritsker et al. [10]. pinedo [6] described the problem as: max , (2)m n precconst c where m represent limited resources, n is the number of jobs or tasks, precconst identify the precedence relationship between tasks and the objective ( )m a xc is to minimize the completion time or makespan. kolisch and hartman [11] denoted the rcpsp as: max m,1 / cpm / c (3) this means activities with finishstart precedence relationship and zero time lags have to be scheduled on m renewable resource types such that the maximal completion time of all activities ( )m a xc is minimized. blazewicz et al. [12] further described the rcpsp as a generalization of the job shop scheduling problem that belongs to the class of nonpolynomial hard type optimization problems (np-hard). in general term, the rcpsp considers the limited capacity of resources and how to assign job/ activities to resources in order to meet predefined objectives. the problem is characterized by scheduling project activities subject to precedence and resource constraints. usually, the resource constraints impose a limit on resource usage in one or more time periods of the project execution. as far as the resource categories are concerned, three types of resources are identified: renewable resources, which are renewed from period to period (e.g., machines available per day); non-renewable resources, these resources are available on a total project basis (e.g., money and energy) and doubly –constrained resources, which share the characteristics of renewable and non renewable resources [5]. the resource constrained project scheduling problem (rcpsp) can be stated thus: a project is represented by acyclic graph where nodes represent the activities and arcs represent the finish-start precedence relationship with zero time lag. let j denotes a set of activities ( jobs) to be scheduled where j = {i,….n} with k ={ i,….k} set of renewable resources types. the activities which are numbered from i to n mark the initial and final activity of the project and are assigned dummy status. the activities are constrained as follows: • the precedence constraint forces each activity j to be scheduled after all the preceding activities to j are completed. etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 144-150 146 www.etasr.com odedairo and oladokun: relevance and applicability of multi-objective resource constrained… • executing the activities requires resources with limited capacities the following parameters are characteristics of the rcpsp as shown in table 1. table i. characteristics of rcpsp parameter definition remark ,j kr ,i kr ,n kr activity j requires r units of resource type k resource usage at the start of project resource usage at the end of project k k∈ ,i kr = ,n kr =0 dj id nd jf ( )a t duration of activity j duration for project start duration for project end finish time of activity j set of activities being processed at time instant t id = nd =0 id , nd are dummy activities non-preemptable, deterministic k kr resource type k limited capacity of resource k at any point in time renewable type non-negative from the parameter identified above, the conceptual model of single objective rcpsp is described in “(4)” [13]: , objective function: (4) subject to (constraints) : (1, ) ; 0 ( n j k k min f fn dn fi n j r r k k t j a t ≥ ∈ ≤ ∈ ≥∑ ∈ ) 0 1 .. if j n= = … the objective function is to minimize the finish time of activity n. the first constraint effects the precedence relations between activities; the second constraint limits the resource type k demand by the activities being processed at time t to the capacity available. the last constraint assign a zero completion time to the start activity that is dummy. a. project scheduling objectives the γ field in the project scheduling classification denotes the optimality criteria. this field often contains a single objective. these objectives are the criteria by which the performance of a solution procedure can be measured. oyetunji [14] commented on the little study carried out so far on scheduling objectives. this is because scheduling objectives is complex, conflicting in nature and most times it is difficult to adequately state these objectives [15,16]. the possible combination of time, cost and quality based scheduling objective is a good example of the conflicting nature of scheduling objective. the performance measure can either be regular or nonregular. common examples of regular objectives include the makespan, lateness, tardiness, no of tardy jobs while nonregular objectives include the net present value (npv),earliness penalty and weighted earliness-tardiness. mellor [17] referenced by oyetunji [14] identifies beenhakker (1963) as the only author that highlighted about 27 distinct scheduling goals. for the project scheduling problem, demeulemeester & herroelen [5] identified some common performance measure and their component as discussed in table 2. b. components of resources in project scheduling there are projects where time, cost and quality are equally weighed. in such situation, the “cpm thinking” is weakened and project managers will have to think in terms of a mix of objectives. the multi-objective thinking in rcpsp allows for overall consideration of all constraints found relevant for the successful execution of a project. also, in an environment where resources are limited, a multi-objective approach will have less total cost than independently considering individual constraints [18]. usually, the integrated model developed from a multi-objective approach will be harder than the problems from a single objective approach. dodin and elimam [18] identified components of resources available in project scheduling as shown in table 3. etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 144-150 147 www.etasr.com odedairo and oladokun: relevance and applicability of multi-objective resource constrained… table ii. performance measures and their components performance type components remarks max cγ = minimise the project makespan fγ = minimise the average flow time over all subprojects or activities max lγ = minimise the project lateness max tγ = minimise the project tardiness early / tardyγ = minimise the weighted earliness – tardiness of the project time t nγ = minimise the number of tardy activities . sq devγ = ∑ minimise the sum of the squared deviations of the resource requirements from the average. jumpγ = ∑ minimise the weighted jumps in resource usage for all resource types over all time periods. . abs devγ = ∑ minimise the sum of the absolute deviations of the resource requirements from the average. avγ = minimise the resource availability in order to meet project deadline resources racγ = minimise the resource availability costs i.e. the weighted availability of each resource type. cost npvγ = determine the complete time/cost trade-off curve quality qγ = maximize quality by minimizing both estimated rework times and costs table iii. components of resources in project scheduling resources components material planning ordering cost holding cost of material holding cost completed activities consumption rate per period purchase price and quantity discount human resources selection and cost of the desired skill level overtime and regular cost cost of temporary hires or consultants needed for the project transition cost between activities and between projects equipment planning set up cost buy or lease options overall and per period availability impact of activity duration on equipment cost transition cost between activities and projects c. single objective rcpsp the performance measure of rcpsp common in literature is the completion time or makespan. the makespan usually represent various concerns on accomplishing deadlines and maximizing the customer service. minimizing project duration ensures that resources (machine, equipments, manpower, etc) for project activities are released promptly thereby making them available for use by other projects in the future. also, it reduces the risk of violating a deadline and generates timely incoming cash flows. viana and pinho de sousa [9] addressed the makespan as a “global measure”. goldratt (1997) cited by demeulemeester and herroelen [5] commented that delays in project delivery are heavily penalized than budget overruns. hewlett-packard, for example, studied a high-growth market and found that if a new product innovation project would be getting to market six months later than originally scheduled, profits would reduce by 33%. but if going over the budget by 50% during the product development to ensure that the project was completed on time, profits would be reduced by 4% [19]. a critical look at this example shows that it violated the characteristics of a resource constrained project scheduling. this is evident by the willingness to overrun project cost by 50%. this reduces the problem to a cpm-case where resources are assumed to be unlimited. thou, in project execution, budget overruns are clearly visible and attributable. this is an explicit choice of top management to speed up project delivery (by approving overtime, purchase of extra resources, etc). d. multi objective rcpsp the multiobjective rcpsp (morcpsp) usually contains not a single solution that minimizes all the objectives simultaneously. the aim is then to find a set of solutions where at least one of the objectives is better than the others: the nondominated (pareto of efficient) set [9]. in this case, one solution ( ) ( ) ( ) ( )k k dominates if and y x f y f x k f y f x≤ ∀ ≠ such that if there is no other feasible solution that dominates x, the solution x is nondominated. the multiobjective combinatorial optimization can be formulated as follows: etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 144-150 148 www.etasr.com odedairo and oladokun: relevance and applicability of multi-objective resource constrained… ( ) [ ] 1 ,..........., 0 ( ) k t 1 .. min ( ) { ( ) ( )}, ( ) (5) subject to : where is a vector 1 x , which represents the vector of binary decision variables the space of f k k xn f x f x f x f x c x x d c n x x d = …… = ∈ = easible solutions in literature, some notable references were found for biobjective case of rcpsp. al-fawzan and haouari [20] addressed the issue of a bi-objective rcpsp. they considered the objectives of the robustness maximization along with the makespan minimization. abbasi et al. [21] addressed biobjective resource constrained project scheduling to minimize the makespan and to maximize the robustness aiming at the float time maximization in order to make scheduling more reliable. kazemi and tavakkoli-moghaddam [22] considered a bi-objective multi-mode resource constrained project scheduling problem with positive and negative cash flows. their first objective is maximization of the net present value (npv) and the second is to minimize the makespan and floating time (i.e. maximization of robustness). the net present value (npv) analysis in project management is used among others to determine whether a project should be selected and in the planning and scheduling of projects with long durations [18]. the npv analysis is also useful for cross-borders projects. for multi-objective rcpsp, viana and pinho de sousa [9] considered three objectives in their model: to minimize the makespan, minimize the mean weighted lateness of activities and minimize the sum of the violation of resource availability. also, for the multidimensional rcpsp, dodin & eliman [18] proposed the integration of the components of time, cost and quality on what they called the “totally optimized project system (tops)”. the tops can be stated a follows: “determine the start and finish time of project activities (including duration), the material ordering and inventory policies, and the allocation of human resources and equipment to these activities in order to minimize the total cost of the project or to optimize other selected measures of performance”. they argued that their integrated project scheduling problem will have less total cost than independently considering this objective in a single objective problem. a critical look at tops shows that the authors did not consider the impact of limited resources as clearly identified in rcpsp. a consideration of the trinature of project objective (time, cost and quality) allows for a multi dimension approach to achieving the overall objective where resources are limited. despite the various works dealing with multiobjective resource-constrained project scheduling problems; ballestin & blanco [23] revealed that there is no theoretical study in the literature that establishes the fundamentals for correct algorithm development for the multi-objective rcpsp. another gap in multiobjective rcpsp is lack of studies focusing on the development of solution procedures for problem with more than two objectives where the composite objective is a combination of different objective functions (regular and non-regular performance measures). this is an area where the authors are currently working on. iii. solution techniques for single and multi objective rcpsp due to the increased interest in the rcpsp over the past decade, a vast amount of literature has appeared on different algorithms for solving both single and multiobjective problem types. for the single objective type, focus on the project duration minimization has led to the development of various exact methods and (meta-) heuristic procedures. exact methods (or optimizing algorithms) return a provable optimal solution, whereas heuristic methods return a “good” solution that does not necessarily need to be an optimal solution. exact methods are guaranteed to find a solution if it exists, and typically provide some indication if no solution can be found. while exact solution methods are able to solve smaller problems, they typically take too long (i.e. mostly non-polynomial time) when the problem size grows or when additional constraints are added. hence, exact methods only suit small-scale problems and are not utilized for practical applications. akbari et al [24] identified exact methods proposed by mingozzi et al. (1998), specher (2000) and stork & uetz (2005) as the most represented exact methods. in solving the rcpsp, when the number of activities is large and the planning horizon is long, the rcpsp is usually solved using heuristics and metaheuristics, which can provide relative effective solutions. heuristic methods typically require far less time and / or space than exact methods. the heuristics specify how to make a decision given a particular situation and contains rules for deciding which action to take. heuristics in scheduling are often referred to as scheduling rules or dispatch rules. the definition of these rules is often quite complex, and most are tailored for a specific type of problem with a very specific set of constraints and assumptions. most of the heuristics methods used for solving resourceconstrained project scheduling problems either belongs to the class of priority rule based methods or to the class of metaheuristics based approach [25]. many metaheuristics methods, such as genetic algorithms (ga), simulated annealing (sa), tabu search (ts), scatter search, electromagnetism (em), immune algorithm (ia) , filter and fan (ff) , particle swarm optimization (pso) and ant colony optimization (aco), have been proposed and applied to solve the rcpsp [24, 25]. akbari et al [24] identified authors that exploited the advantages of two or methods to design a hybrid algorithm for better performance. notably are angel (tseng & chen, 2006), acoss (chen et al., 2010), neurogenetic (agrawal et al., 2010), scatter search –fbi (debles et al., 2006), and hybrid – ga (valls et al., 2008). oyetunji [14] identified three approaches for solving bicriteria problems. these are: pareto-optimal, hierarchical and simultaneous minimization approaches. the pareto-optimal approach involves finding the set of all pareto-optimal schedules. the hierarchical minimization involves ranking the criteria in order of importance. the simultaneous approach etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 144-150 149 www.etasr.com odedairo and oladokun: relevance and applicability of multi-objective resource constrained… aggregates the two criteria into a single objective. it is worthy to note that multi-objective metaheuristics versions of genetic algorithms (ga), simulated annealing (sa) and taboo search (ts) have been developed. viana and pinho de sousa [9] applied the multiobjective metaheuristics version of simulated annealing and taboo search to solve a multi objective rcpsp. their results reveal that a multiobjective approach is reliable and efficient way of solving rcpsp. this is because it enables the development of scheduling model which is flexible and reveals reality. ulungu (1994) referenced by viana and pinho de sousa [9] commented that “the adaptation of metaheuristics to a multiobjective environment is certainly one of the more promising research directions”. iv. project management in nigeria project management allows the organization and integration of resources to achieve a specific goal within a designated time frame. successful project management delivers the agreed outcome within an agreed quality, without overrunning its budget and delivery duration and crucially, achieving for the organization the benefit for which the benefit for which the investment in the project was made. most developing nations of the world quest for economic development; this is evident in the commitment of governments in developing countries to withdraw from direct provision of infrastructures and the consequent emergence of public-private partnerships (ppp). as a result, nigeria and many countries world-wide have adopted a project delivery approach wherein government agencies can act as enablers to private sector driven investment projects. the aim is to embark on a number of infrastructural projects that will deliver integrated social, economic, and environmental benefits. a number of projects being delivered through publicprivate partnership (ppp) in two states (lagos and ogun) in nigeria are identified in table three. project management tools and techniques were being used in the implementation of these projects. this information is obtained from random selection of economic bulletins made generally available to the public by the federal government. majority of these projects started in 2008 and their current status is shown in table 4. in nigeria, we can make the following general observations about projects: • a majority of public, individual and public-private projects run beyond their budgets and due-dates. • the public-private partnership (ppp) often face cutoff of funding from foreign partners if the project progress is not completed on time. • resources are limited and optimal use of available resources is prevalent. • a presidential projects assessment committee (ppas) submitted a report in may, 2011 which identifies 11,886 ongoing and abandoned federal capital projects that will require n7.78 trillion naira ($49.6 billion dollars) [26]. all the identified projects are estimated to be completed in eight years. the committee identified lack of direction in project management as one of numerous problems. this had lead to dotting the landscape in various parts of the country with uncompleted projects. • predominant use of gantt chart (based on cpm) for project scheduling. from the above mentioned characteristics of project management in nigeria, the resource constrained project scheduling problem fits into the nigeria case. table iv. example of ppps in two states in nigeria collaborators title focus current status oau/nuc/une sco partnership workshop workshop on strengthening the capacities of universities in science and technology policy and innovation mgt training and capacity building in progress ogun/ondo state government, chevron, shell and british gas development of olokola liquefied natural gas (oklng) oil and gas development in progress change of democratic government that initiated the project afc, ogunondo state government seaport development seaport development abandoned change of democratic government that initiated the project consortium company and ogun state government agro cargo airport development airport construction and management change of democratic government that initiated the project abandoned lagos state government and consortium of banks concession of lekkiajah expressway road / highway construction completed lagos state government and consortium of banks concession of ojoo – badagry expressway road / highway construction in progress guangdong company and ogun state government igbesaogun state free trade zone development free trade zone development in progress no clear direction ipem, ogunondo state government olokola free trade zone infrastructure development and free trade zone in progress, change of democratic government that initiated the project, no clear direction ministry of transport, nigeria and chinese construction company (ccc) lagos – kano railway development transportation development in progress etasr engineering, technology & applied science research vol. 1, �o. 6, 2011, 144-150 150 www.etasr.com odedairo and oladokun: relevance and applicability of multi-objective resource constrained… v. conclusion in this paper, we review the project scheduling problem. the review emphasizes the resource constrained project scheduling problem (rcpsp). we confirmed that the most common performance measure of rcpsp in literature focuses on minimizing the makespan. we emphasized that there are situations where individual or corporate projects with limited resources have to be finished on time, within the approved budget and in accordance with the preset specifications. in such situations, the cpm logic (assuming the existence of unlimited resources) is weak. in practice, project managers tend to think in terms of a mix of objectives. this tends to make single objective approaches in rcpsp generally idealistic. this is not saying that early research focusing on single objective are irrelevant; such studies had tremendously helped to gain more insight into understanding and solving multi-objective rcpsp. we identified few research gaps in the study of multi-objective rcpsp. we identified that there are no solution procedures for solving the multi-objective rcpsp where the composite objective is a combination of regular and non regular objective function. this is an area we are currently working on. also, the study highlighted different algorithms so far developed for solving single and multi –objective rcpsp. we highlighted the characteristics of project management in nigeria and identified gaps. in summary, the multi-objective approach in practical situations was found to be the natural way of solving rcpsp. references [1] international standards organisation (iso) /cd 8402-1, quality concepts and technology part1: generic terms and definitions, international organization for standardization, 1990 [2] project management institute (pmi), a guide to the project management book of knowledge, project management institute, newton square, pa, 2008 [3] d.r sule, industrial scheduling. pws publishing company, boston, ma, 1997 [4] j leung, ( ed), handbook of scheduling: algorithm models and performance, crc press llc; florida. 2004 [5] e. l. demeulemeester, w. s. herroelen, project scheduling: a research handbook, kluwer academic publisher; boston. 2002 [6] m. pinedo, scheduling: theory, algorithms and systems, springer, new york, third edition, 2008 [7] a. thomas, r. barton, p. byard “technology implementation in manufacturing smes: a model for change”. i*proms virtual international conference on intelligent production machines and systems, 2007 [8] a. gunasekaran, l. forker, b. kobu “improving operations performance in a small company: a case study” international journal of operations & productions management, vol. 20, no. 3, pp. 316-335, 2000 [9] a. viana, j sousa, “using metaheuristics in multiobjective resource constrained project scheduling” european journal of operational research , 120, pp. 359374, 2000 [10] a. pritsker, b. allan. l.j watters, p.m wolfe, “multiproject scheduling with limited resources: a zero-one programming approach”, management science, vol. 16, pp.93-108, 1969 [11] s. hartmann, r. kolisch “experimental evaluation of state–of–the–art heuristics for the resource–constrained project scheduling problem”, european journal of operational research, vol. 127, pp. 394–407, 2000 [12] j. blazewicz, j. k. lenstra, k. rinnooy, “scheduling subject to resource constraints: classification and complexity”, discrete applied mathematics, vol. 5, pp. 11-24, 1983 [13] n. christofides, j. m. alvarez-valdes j. m. tamarit, “project scheduling with resource constraints: a branch and bound approach”, european journal of operational research, vol. 29, pp.262-273, 1987 [14] e. o. oyetunji, “some common performance measures in scheduling problems: review article”, research journal of applied sciences, engineering and technology, vol. 1, no. 2, pp. 6-9, 2009 [15] s. french, sequencing and scheduling, ellis horwood limited, 1982 [16] j. albert, l. c. rabelo, survey of job shop scheduling techniques, nistir, national institute of standards and technology, gaithersbury, md, 1998 [17] p. mellor, “review of job shop scheduling”, operations research, vol. 17, no. 2, pp. 161-171, 1966 [18] b. dodin, a. a. elimam, “project management: challenges and opportunities”, available online: www.mes.eg.net/ acrobat_files /1_2pdf: accessed–june 4th,2011 [19] r. suri, quick response manufacturing: a companywide approach to reducing lead times, productivity press , 1998 [20] m. a al-fawzan, m. haouari, “a bi-objective model for robust resource-constrained project scheduling, international journal of production economics”, vol. 96, pp.175 -187, 2005 [21] b. abbasi, s. h. shadrokh, j. arkat, “bi-objective resource-constrained project scheduling with robustness and makespan criteria”, applied mathematics and computation, vol. 180, pp. 146-152, 2006 [22] f. kazemi, r. tavakkoli-moghaddam, “solving a multi-objective multi-mode resource-constrained project scheduling problem with particle swarm optimization”, international journal of academic research, vol. 3, pp. 103-110, 2011 [23] f. ballestin, r. blanco, “theoretical and practical fundamentals for multi-objective optimization in rcpsp, journal of computers and operation research, vol. 38, no. 1, pp. 51-62, 2011 [24] r. akbari, v. zeighami, k. ziarati, “artificial bee colony for resource constrained project scheduling problem”, international journal of industrial engineering computations, vol. 2, pp. 45-60, 2011 [25] a. sprecher, resource-constrained project scheduling: exact methods for the multi-mode case”. lecture notes in economics and mathematical systems, vol. 409, 1994 [26] “jonathan worries over n7trillion uncompleted projects”, thisday newspaper, friday, june 3rd, 2011. available online: thisdaylive.com/articles/jonathan-worries-over n7tr-uncompletedprojects/92555/ : accessed–june 4th,2011mallat, a wavelet tour of signal processing, academic press, 1999 microsoft word etasr_v13_n1_pp10165-10169 engineering, technology & applied science research vol. 13, no. 1, 2023, 10165-10169 10165 www.etasr.com helis et al.: behavior of a circular footing resting on sand reinforced with geogrid and grid-anchor behavior of a circular footing resting on sand reinforced with geogrid and grid anchors rima helis lgc-roi civil engineering laboratory, department of civil engineering, faculty of technology, university of batna 2, algeria helis.r@univ-setif.dz (corresponding author) tarek mansouri lgc-roi civil engineering laboratory, department of civil engineering, faculty of technology, university of batna 2, algeria t.mansouri@univ-batna2.dz khelifa abbeche lgc-roi civil engineering laboratory, department of civil engineering, faculty of technology, university of batna 2, algeria k.abbeche@univ-batna2.dz received: 23 december 2022 | revised: 3 january 2023 | accepted: 7 january 2023 abstract this study used finite element analysis to investigate the influence of using two reinforcing systems, the geogrid and the grid anchor, on the bearing capacity of a circular footing resting on sand. the parameters studied were the effect of the number of reinforcement layers (n), the depth ratio of the topmost layer of reinforcement (u/d), the vertical spacing ratio between consecutive layers (h/d), and the effect of reinforcement length (l). the results showed that the reinforcement layout had a very significant effect on the behavior of the reinforced sand foundation. the maximum bearing capacity for single-layer inclusion was obtained when reinforcement was placed at a depth of u/d=0.42. bearing capacity was also found to improve when increasing the number of reinforcement layers from 1 to 3. additionally, the analysis showed that the sand reinforced by grid anchors performed better than that reinforced by geogrid. finally, an improvement in load capacity was obtained by increasing the length of the inclusions, and the optimal length of the reinforcements was determined at 5d for both inclusions. keywords-geogid; grid anchor; finite element analysis; circular footing; sand i. introduction geosynthetic reinforcing techniques is used to reinforce shallow foundations, improve bearing capacity, and reduce soil settlement below the foundation. several studies investigated the bearing capacity of geosynthetic reinforced foundation soils using experimental, analytical, and numerical methods. one of the first experimental studies to analyze the bearing capacity of reinforced soils with metal strips was presented in [1-2]. since then, many studies investigated the improvement of the loadbearing capacity of shallow foundations supported by sand and reinforced with different materials, such as metal strips and metal bars [3-5], rope fibers [6], geotextile [7], and geocells [810]. in addition, considerable studies were conducted to evaluate the bearing capacity of the reinforced soil by geogrid [11-18]. these studies confirmed the beneficial effect of reinforcement on improving the bearing capacity and reducing the settlement of footing. more recently, the use of geogrid in geotechnical engineering applications was considerably increased due to advantages such as cost reduction, simplicity, and ease of construction [19-20]. laboratory scale model tests on a circular embedded footing supported on geogridreinforced sand beds were presented in [21], reporting an increase in ultimate bearing capacity with the embedding depth ratio of the foundation. in [22], the behavior of circular footing on sand was studied, showing that bearing capacity increased when the number of reinforcement layers increased if the reinforcements were placed within a range of effective depths. this study also showed that increasing the stiffness of the reinforcement did not always have a better effect on bearing capacity. a numerical study was conducted in [23] using finite element analysis to investigate the behavior of circular footing resting over reinforced sand, showing that the depth of the top layer plays an important role in the behavior of the reinforced engineering, technology & applied science research vol. 13, no. 1, 2023, 10165-10169 10166 www.etasr.com helis et al.: behavior of a circular footing resting on sand reinforced with geogrid and grid-anchor soil, and reporting that the optimum depth of the top layer was 0.19 times the diameter of the footing. in [24], a small-scale laboratory model test was carried out on two closely spaced interfering footings resting on the surface of unreinforced and geogrid-reinforced sand bed, finding that the optimal depth of the geogrid layer for both interfering and isolated footings was one-third of the footing width. therefore, footing interference had negligible or no effect on the optimum depth of the reinforcement layer for a single-layered reinforced sand bed. in [25], resting on a semi-infinite layer of reinforced sand with geotextiles was used to experimentally study the behavior of circular footings. furthermore, analytical and numerical analyses were carried out to predict load-settlement behavior and compare them with the experimental observations. in [26], model plate load tests were conducted on various types of sand beds reinforced with geogrid, showing that substantial improvement in the load-settlement behavior can be obtained by increasing the number of geogrid layers (n) and decreasing the spacing between them. it was also shown that the load improvement ratio for the reinforced coarse sand was higher than that of the reinforced fine and medium sand. in [27], the behavior of geosynthetic-reinforced sandy soil foundations was investigated using laboratory model tests, showing that the settlement can be reduced by 20% at all footing pressure levels with two or more layers of geogrid. in [28], the upper bound theorem of limit analysis was used in conjunction with finite elements and linear optimization to determine the bearing capacity of a circular foundation embedded with horizontal layers of circular geogrid sheets. the optimal diameter and the critical positions of the reinforcement layers were established to achieve maximum bearing capacity, and a marked improvement in the bearing capacity was evident in the case of using two layers of reinforcement rather than a single. a laboratory model test of a surface strip footing on reinforced sand beds was presented in [29] to investigate the effects of reinforcement length with various types and numbers of reinforcements. an experimental study was conducted in [30] to assess the influence of the geogrid extension and embedment depth below strip footing rested on fine loose sand. in [31], a regression model was developed to determine the bearing capacity of a circular foundation supported on sand reinforced with geogrid. the results showed that the parameters studied had a significant influence on the performance of the footing in terms of bearing capacity. in [32-33], the bearing capacity of a strip footing subjected to inclined load and resting over a geogrid-reinforced sand bed was studied experimentally and numerically, showing that the footing performance could be substantially improved by including layers of geogrid, leading to an economic design of the footing. the effects of load eccentricity and inclination on the ultimate bearing capacity of shallow rectangular foundations placed over geogrid sand were studied in [34], finding that multiple geogrid-reinforced layers increased the ultimate bearing capacity by 75%. in [35], a strip foundation in weak soil was replaced with a granular trench and reinforced with geogrid, showing that the bearing capacity of a strip foundation could be significantly improved by replacing sand with granular materials up to 3 times. in addition, it was shown that placing the geogrid in the trench indicated a rise in the bearing capacity ratio. a new generation of reinforcement named grid-anchor was introduced in [36-37], showing its effect on the increase of bearing capacity of the foundation. this study aims to evaluate the performance of using ordinary geogrid and grid anchor reinforcement in increasing the bearing capacity and reducing the settlement. to achieve this objective, a numerical model was determined using the plaxis finite element software to investigate the bearing capacity of a circular footing resting over reinforced sand. different parameters that affect the behavior of the reinforcement sand layer are discussed. ii. finite element modeling the plaxis software was utilized to perform a numerical finite element analysis by simulating a circular footing resting on sand reinforced by two reinforcement systems, geogrid (gg) and grid anchors (ga). also, an axisymmetric analysis was performed. for all models, the boundary conditions in displacements were similar, such that the bottom boundary was assumed to be fixed and the vertical boundaries were constrained in motion in the horizontal direction. however, sand's behavior was supposed to be elastic and perfectly plastic, the mohr-coulomb rupture criterion was used, and the nonassociated flow rule was considered. a rigid circular footing with a 12cm diameter was simulated by applying a uniform downward displacement on the surface of the sandy soil. table i shows the properties of the sand adopted in the model. fifteen triangular plane strain elements were selected to model the soil, while the gg reinforcement was simulated with 5 node elastic elements. the ga was modeled using the fixedend anchor option. table ii shows the physical and mechanical properties of gg and ga. the mesh refinement was adopted in the vicinity of the loading area around the foundation and gg layers to improve the accuracy of the numerical results. table i. soil parameters physical and mechanical property value maximum unit weight (kn/m 3 ) 16.4 minimum unit weight (kn/m 3 ) 14.4 maximum void ratio 0.890 minimum void ratio 0.658 specific gravity 2.72 coefficient of uniformity 2.36 coefficient of curvature 1.01 classification sp cohesion (kn/m 2 ) 0 internal friction angle 39˚ table ii. physical and mechanical properties of geogrid and anchors description geogrid ce 131 polymer high-density polyethylene form sheet color black mesh aperture size 27×27mm mesh thickness 5.2mm structural weight (+5%) 660g/m 2 elastic normal stiffness of geogrid 28.0kn/m ea axial stiffness of anchors 0.18kn length of anchors (mm) 50mm engineering, technology & applied science research vol. 13, no. 1, 2023, 10165-10169 10167 www.etasr.com helis et al.: behavior of a circular footing resting on sand reinforced with geogrid and grid-anchor figure 1 shows the prototype soil model with two systems of reinforcement, finite element mesh, and boundary conditions. fig. 1. the numerical model. iii. results and discussion numerical tests were carried out to study the effects of inclusion reinforcement elements on a circular footing, constructed on unreinforced and multi-layered reinforced sand beds, and investigate the improvement of bearing capacity. a non-dimensional factor called the bearing capacity ratio (bcr) was considered, defined as the ratio of the reinforced soil bearing capacity to the unreinforced soil: bcr= �� �� (1) where qr and qu are the bearing capacity values for reinforced and unreinforced soil foundations, respectively. a. effect of reinforcement’s top spacing a numerical study was carried out to investigate the effect of the depth of the first reinforcing layer from the footing on the bearing capacity for different depth ratio values (u/d) with a single reinforcement layer in each reinforcing system, gg and ga. figure 2 shows the variation of the bcr of the soil versus the different reinforcement depth ratios u/d. in the case of gg, as the depth ratio u/d increases from 0.2 to 0.42, the bcr also increases. however, between 0.42 and 0.8, a clear reduction in the bcr was found for both gg and ga. fig. 2. variation of bcr with depth ratio in single-layer reinforced sand. similar results were found in [31], where there is no increase in soil carrying capacity that exceeded u/d>0.75. hence, the optimal value of the depth ratio was obtained when the reinforcement was placed at u/d equal to 0.42 in both systems. therefore, it can be concluded that the results obtained for gg reinforcement are in good agreement with [38]. figure 2 also shows that the effect of the presence of ga reinforcement on the bearing capacity of the circular footing on sand becomes important compared to those obtained by gg. in addition, a considerable improvement of about 52% was observed for the anchorage of the grids. b. effect of vertical spacing of reinforcement layers this study aims to investigate the effect of the spacing between the reinforcing elements on the performance of reinforced sand under the circular footing. the gg and ga layers were tested with a top layer spacing at 0.42d and varied vertical spacing between the layers. figure 3 shows the variation of the bcr with the vertical spacing ratio (h/b). the results showed that for gg reinforcement, the bcr increased to a maximum value at h/d=0.3d, but the ga had a critical value at u=0.42d. then, a remarkable decrease was observed for both reinforcements until 0.6d. beyond this value, bcr seems to stabilize, showing that adding inclusions is insignificant in this region. the trend of the curves is similar to that of [38]. furthermore, in [28-31] it was shown that the increase in bcr was obtained when the vertical spacing between the reinforcement layers was between 0.25 and 0.40d, which justifies the present case study. therefore, the variation in amplitudes and the modest divergence can be attributed to the adapted reinforcement pattern. fig. 3. variation of bcr with the vertical spacing ratio of reinforced sand. c. effect of the number of reinforcing layers α series of numerical tests were conducted to study the influence of the variation of the number of reinforcement elements (n) on the behavior of a circular footing on reinforced sand. the depth of the first layer (u) was taken equal to 0.42d, while the vertical distance between the reinforcement layers (h) was equal to 0.3d for the gg and 0.42d for the ga. figure 4 shows the variation of the bcr as a function of the number of reinforcement elements n. it can be observed that the increase in the bcr results from a considerable increase in the reinforcement elements up to an optimum value n=3, and a slight increase is observed over that. this confirms the findings engineering, technology & applied science research vol. 13, no. 1, 2023, 10165-10169 10168 www.etasr.com helis et al.: behavior of a circular footing resting on sand reinforced with geogrid and grid-anchor of several studies [22-34, 37] that showed that increasing the number of reinforcement layers beyond a certain number would not increase the bcr. fig. 4. variation of bcr with the number of reinforcement layers. d. effect of the length of reinforcement a circular foundation resting on sand was studied by keeping the number of geogrid layers n to 1 and depth of reinforcement at the optimal 0.42d, while the length of the reinforcement layer (l) varied between 4d, 4.5d, 5d, and 6d to investigate its effect on bcr. figure 5 illustrates the variation of bcr with the different reinforcement length ratios (l/d). fig. 5. variation of bcr with the reinforcement layer's length. as can be observed, bcr increases linearly with reinforcement length up to l/d=5, while reinforcement length beyond this value is ineffective on bcr for both reinforcement types. therefore, the optimal length of reinforcement is obtained at 5 times the length of the footing, as in [39]. iv. conclusion this study caused finite element analysis to assess the behavior of a circular footing constructed on unreinforced and reinforced sand soil, drawing the following conclusions:  an increase in bearing capacity was obtained when the depth of the first reinforcing layer to the footing diameter was equal to 0.42. this was considered an optimal depth of the top reinforcement layer from the bottom of the footing.  a visible reduction was noted in the bearing capacity beyond 0.42d for both types of reinforcement.  the effect of reinforcement cannot be seen when the installation depth is deeper than a certain depth (u/d≥0.80).  there is an optimal value for the vertical spacing of the reinforcement layer where the bcr was the highest. this optimal value was found to 0.3d for geogrid and 0.42d for grid anchors.  the bearing capacity of reinforced soil increases with increasing the number of layers. in this study, the optimal number of layers obtained was 3 in both reinforcement types.  the analysis clearly showed that using the grid anchor system reinforcement of circular footing on a sand bed causes a significant increase in the bearing capacity in comparison with the ordinary geogrid.  an improvement in the load capacity was obtained by increasing the length of the inclusions. the optimal length of the reinforcements was determined at 5d for both inclusions. references [1] j. binquet and k. l. lee, "bearing capacity tests on reinforced earth slabs," journal of the geotechnical engineering division, vol. 101, no. 12, pp. 1241–1255, dec. 1975, https://doi.org/10.1061/ajgeb6. 0000219. 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[39] k. m. lee, v. r. manjunath, and d. m. dewaikar, "numerical and model studies of strip footing supported by a reinforced granular fill soft soil system," canadian geotechnical journal, vol. 36, no. 5, pp. 793–806, nov. 1999, https://doi.org/10.1139/t99-053. microsoft word 4-625-ed.doc engineering, technology & applied science research vol. 6, no. 3, 2016, 993-999 993 www.etasr.com okolnishnikov et al.: simulating the various subsystems of a coal mine simulating the various subsystems of a coal mine victor okolnishnikov siberian branch of the russian academy of sciences design technological institute of digital techniques novosibirsk, russia okoln@mail.ru sergey rudometov siberian branch of the russian academy of sciences design technological institute of digital techniques novosibirsk, russia rsw@academ.org sergey zhuravlev siberian branch of the russian academy of sciences design technological institute of digital techniques novosibirsk, russia s-zhur@yandex.ru abstract—a set of simulation models of various subsystems of a coal mine was developed with the help of a new visual interactive simulation system of technological processes. this paper contains a brief description of this simulation system and its possibilities. the main possibilities provided by the simulation system are: the quick construction of models from library elements, 3d representation, and the communication of models with actual control systems. these simulation models were developed for the simulation of various subsystems of a coal mine: underground conveyor network subsystems, pumping subsystems and coal face subsystems. these simulation models were developed with the goal to be used as a quality and reliability assurance tool for new process control systems in coal mining. keywords-coal mining; simulation system; visual interactive simulation; hardware-in-the-loop i. introduction one of the future developments of simulation is to create very detailed simulation models with wide application “from the box”, with the minimum involvement of simulationists and the maximum involvement of field engineers. especially in underground mining, it is frequently reported that resources become less available, and harder to be extracted. the technologies of coal mining are well-known. today mine uses mining machinery for mining, transportation, roof support, etc. key topics of interest are the detailed description of machines’ functionality, the definition of the exact additional machines that may be required, the calculation of the “total cost ownership” of machines, the comparison of the use of big universal machines to the use of more smaller and specialized ones and ultimate product cost definition. these tasks can be solved through the use of computer-based simulation of the coal mining process. these simulation tasks are known as “what-if” ones. the main issue with that particular mining is that it is effective in terms of minimum costs and maximum productivity only if it is planned correctly. usually a big scheme layout contains various components from different vendors interconnected. that makes it hard or, even, impossible to predict the exact effectiveness. this situation gets worse if there is also a requirement to create new components. due to the importance of these problems, there is a large number of papers on the use of simulation in the development and optimization of coal mining systems [1-8]. there is also a large number of simulation tools, both universal simulation systems and specialized systems, and packages for the simulation of coal mining systems. while lots of simulation tools solve the “what-if” problem, there is significantly less such tools that allow building integrated simulation for mines hardware development. a number of models for various technologies of coal mining were developed with the help of a developed simulation system. these models are used for the developing of process control systems for underground coal mines in kuznetsk coal basin (russia, western siberia). the models include both “what-if” tasks and development of hardware for control systems. ii. technologies of coal mining there are several well-known technologies of coal mining. a. longwall mining longwall mining system is a highly-automated, very powerful and productive way to mine. it is most-widely applied around the world. its main advantage is that it leaves almost no product inside mines. but it is limited with the depth of the mine (measured from the surface). also it is applied in relatively flat areas of coal, from 0.8 up to 10 meters high, from 150 to 450 meters face, and up to 4 kilometers in depth. a basic longwall system consists (at least) of an armored face conveyor (afc), a shearer and roof support sections. the afc is connected to an outbound belt conveyor. the shearer cuts the product from coal seam face, in a series of passes along the afc. the afc delivers products to the belt conveyor. the roof support moves itself and the afc, pushing it (and itself) forward with hydraulics. one of the problems of longwall mining is roof caving. this can lead to serious environmental problems. another problem is that longwall requires significant amount of work to be done before its massive equipment is installed in production. this work must be planned as well. one more problem includes a functioning of specialized signaling tools and control systems that monitor marsh gas level, dust level and ventilation facilities. if any of the engineering, technology & applied science research vol. 6, no. 3, 2016, 993-999 994 www.etasr.com okolnishnikov et al.: simulating the various subsystems of a coal mine monitored parameters exceed certain save values, the mining usually stops. the reason is usually not obvious for personnel in mines (gas has no smell, dust does not look dangerous) and it can result in turning off the monitoring systems by mine personnel in order to increase the mining. simulation can help decide the sufficient levels of ventilation that guarantee safe and efficiency. b. highwall mining in case when it is impossible to use longwall, a relatively new technology can be applied, named highwall. this is a shearer tool, mounted on the top of the chain of special sections. these sections can be updated to each other, making a long (up to 300 meters) support chain for a shearer. each section can transport the product developed by the shearer to the end of a sections chain. the shearer and the chain of sections cut the product (coal) from the very thin and curved seams. this is the main advantage of the highwall technology. c. coal mining of flat-laying coal seam this approach uses a number of front-cutting mining machines that cut a coal on a special scheme, and a number of self-moving wagons that move a coal from mining machines to the storage area. it solves the same problem as highwall mining, but requires no specialized equipment. also this approach can be used in deep mining. iii. the simulation system the visual interactive manufacturing and transportation simulation system (mtss) has been developed at the design technological institute of digital techniques of siberian branch of the russian academy of sciences (dtidt) [9, 10]. it is a process-oriented discrete simulation system intended to aim the development and execution of models of technological processes. mtss is a set of interfaces for creating elementary models and for forming complex models. the elementary models are ready-to-use submodels of an equipment unit with capability of low-level control. a model in mtss is created by graphical connection of images of elementary models. the elementary model consists of the following parts:  two-dimensional and three-dimensional graphic images.  input and output parameters.  functionality algorithm describing dependence between parameters.  states which the elementary model can reach during the simulation process.  control commands defining switching process between elementary models states. mtss is also a tool for simulating complex models. statistics are also available as a short overview when model runs, and more statistics are available after model completion. this simulation system is effective in providing an easy-to-use tool for the rapid creation of simulation models by mining engineers. usually field engineers do not have enough expertise in software simulation but they are capable to connect correctly elementary models to create the required topology. mtss uses 2d for the graphical editor and 2d and 3d for the visualization of the running model. such approach seems more natural for mining engineers, when all installations and machines appear first on 2d plans. 3d is more useful for visualizing complex vertical movement. process control systems often have two levels: the low level of equipment and simple control logic and the upper level of complex control of production. therefore one of the distinguishing features of mtss is a separation of the logic of simulation model into two parts: low-level logic and upper level logic. such separation allows us not only to correspond to the usual structure of the process control systems but to use such models for embedding them into actual process control systems in the following ways: to emulate equipment, to simulate upper level logic and to send commands to actual process control system for debugging and testing. this separation into upper and lower logics also allows organizing a switch between various implementations of the decomposition. further, it allows coexisting simulation of upper level logic and a proxy that allows communicating with the upper level logic of actual process control system. the coal mining model can communicate with a new process control system developed in dtidt, to be a source of input signals, emulate equipment, test actual control program with simultaneous visualization of overall process of mining. this allows debugging and tuning of a new process control system in accordance with the behavior of the simulated system, even simulating various accidents. this allows minimizing time and costs on site for commissioning. iv. simulation of underground conveyor network after mining, products are transported by the net of conveyors to the enterprise storage. a fragment of the conveyor network model is shown in figure 1. the conveyor network model consists of elementary models of belt conveyors and bunkers and requires a simulation model of power supply to function. elementary model of belt conveyor is built with the simulation of functionality of its components, such as: structure and belt, drive station, control equipment. the developed model can provide technological processes, control algorithms and the simulation of real information and control signals for the process control system. the main parameters for elementary model of belt conveyor are the following:  position in space.  conveyor maximum load.  drive parameters (amount of motors, capacity, etc.).  state (accelerates, work, decelerate, and stop).  set of analog (belt speed, energy consumption, etc.) and discrete parameters (inspection of tape returns, cable-role switch, etc). this parameters value is defined from em simulation data.  some service parameters and etc. engineering, technology & applied science research vol. 6, no. 3, 2016, 993-999 995 www.etasr.com okolnishnikov et al.: simulating the various subsystems of a coal mine with the help of conveyor network model the following problems for the actual process control system were solved:  centralized turning on of conveyors in the direction opposite to a coal flow.  turning on of a conveyor after the achievement of required speed of a previous conveyor.  turning on of conveyors in defined operating mode.  regulation of the speed of a conveyor belt depending on coal size.  emergency turning off of a whole conveyor network by turning off of all conveyors simultaneously (halt of the conveyor network, for example, if a methane level is high).  optimizing of the energy consumption (lowering of energy consumption needed by conveyor network to work).  creation of tools to train the coal mining personnel. fig. 1. the fragment of the model of conveyor network. v. simulation of pumping subsystem a fragment of the model of the pumping subsystem is shown in figure 2. this subsystem refers to mine safety systems. it averts mine flood. pumping subsystem model consists of pumps, tubes, tanks, water flows and requires elements of the electricity subsystem. pumping simulation is based on two parts: fluid distribution and energy consumption simulation. the simulation model of this subsystem provides technological and underground water pumping out processes and energy consumption simulation. the main settings are the following: pump efficiency, tube throughput, pump energy consumption, tanks capacity, and etc. the following problems were solved with the help of the model of pumping subsystem:  pumps centralized turning on.  pump turning on in according with selected control mode.  selection of optimized control mode for pumps. vi. simulation of coal mining in various types of coal seams a specialized library of simulation models of mining machines for coal mining was developed. this library is a part of mtss and its prime goal is to simulate interactively and visualize various aspects of coal mining in flat-lying coal seam. the library consists of new elementary models of:  highwall mining system.  longwall mining system.  coal seam.  mining machines.  self-moving coal wagon.  storage area. the library contains also a simulation model of a flat-lying coal seam. this model is a source of the product in a simulation engineering, technology & applied science research vol. 6, no. 3, 2016, 993-999 996 www.etasr.com okolnishnikov et al.: simulating the various subsystems of a coal mine model, while storage area is a consumer of a product. the product itself is coal. these new components can communicate with existing libraries of mtss [11-13] which simulate mines subsystems like:  belt conveyor subsystem.  power supply subsystem.  ventilation subsystem. a simulation model of coal mining subsystem in a flatlying coal seam was developed using the library of mining machines. figure 3 contains a sample layout in the simulation model of the flat-lying coal seam (2d and 3d view combined in different views). the simulation model built from the content of the library will simulate the movement of all mobile objects of the model. both 2d (top view) and 3d visualization are available. statistical data are also collected. fig. 2. the fragment of the model of pumping subsystem. fig. 3. the simulation model of coal mining in flat-lying coal seam (4 mining machines and 4 self-moving coal wagons). figure 4 shows a sample layout in another simulation model of the flat-lying coal seam. the main window consists of 6 areas: (1) 2d top view. it contains: main mine, side mines. the origin coordinates is at the left top corner of this view. (2) 3d view. on figure 4 there is a view from point 3. (3) point of view for the 3d. (4) parameters of a simulation model. (5) specialized view for fast navigation in simulation model. (6) settings for the time start, time end and current model time. engineering, technology & applied science research vol. 6, no. 3, 2016, 993-999 997 www.etasr.com okolnishnikov et al.: simulating the various subsystems of a coal mine fig. 4. the main window of mtss system while running of simulation model of coal mining in flat-lying coal seam. the model was created to visualize a new technology of coal-mining in flat-lying coal seam. this simulation model also allows receiving statistical results for usage of this technology. as patent describes, mining is done by frontal winning machine, paired with self-moving coal wagons. patent describes the directions of cut of a flat-lying coal seam for the frontal winning machine. simulation model of this process allows visualizing the process described. for detailed simulation of longwall mining system we finished with next decomposition:  armored face conveyor (afc).  shearer.  roof support sections. simulation model for longwall mining system can function if it is connected (in terms of mtss) with the belt conveyor simulation model. also this model requires a power supply chain, that means it will require a wire and power transformer facility model “connected” to it (in terms of mtss). the goal of creation of simulation of longwall mining system is:  to create a smart, real-looking mines simulation system. our organization is not in charge for the control systems for longwall automation, therefore the primary goal is to provide a simulation model that ensures efficient production.  to investigate the possible pitfalls and bottlenecks of using different longwall configurations for different coal layers. in other words, to do simulation research of longwall system itself, detached from the rest of the mine simulation system. the algorithm for longwall mining system simulation was done closer to the control algorithms of the real longwall mining system. today our simulation contains one-way and two-way shearing (besides there are more shearing techniques combined from these two). figure 5 shows the simplest two-way shearing. in this case, shearer will mine the product while it moves in both directions. roof support section will move itself forward (and afc too) each time the shearer passed it. then it will advance the simulation to the time defined, and then simulate the roof support sections movement. the amount of mined product will be moved to the afc that will deliver it to the connected belt conveyor. task will repeat these steps until the “done” or “postpone” conditions are achieved. task is “done” when shearer reaches the end of an afc line. task is “postponed” when belt conveyor is overloaded and cannot accept the next portion of product or gas level is not safe. during any of these steps, the simulation model of flatlying coal seam simulates roof fall (behind the roof support) and gas level increasing. also ventilation simulated in a simple manner (remove gas from working area, with some defined speed). one-way shearing is to shear the product only in one direction. after the shearing path is over, the shearer will be engineering, technology & applied science research vol. 6, no. 3, 2016, 993-999 998 www.etasr.com okolnishnikov et al.: simulating the various subsystems of a coal mine returned to its starting position, and only then all roof supports advanced to the new position simultaneously. fig. 5. the longwall shearer and roof support in two-way shearing. in most cases, there is no need to simulate in details any technology like longwall or flat-lying coal mining, if it is used just as a source of a product for belt conveyor system, for example. all that is really needed in such cases are:  to define that longwall or flat-lying coal mining is a source of a product for a big mining system like conveyor.  to determine the performance of the longwall coal mining during some time period (working day, 8-hours time interval, 1-hour time interval). note that emergency stops (like gas or coal dust) are already included in this statistical data. the goals of simulation are:  to predict how longwall or flat-lying coal seam mining automation will behave in details (i.e. movement of its parts depending on various situations in mines).  to make a detailed visualization of mining process.  to define how this mining will impact to the overall performance of the mines.  to define scenarios of broken or temporarily inaccessible parts interactively [14]. the achievement of these goals requires a detailed decomposition of common longwall (or highwall) mining system and a detailed visualization of all its parts. figure 6 shows the hardware installation for the real “hardware-in-the-loop” with the combined model and the real control hardware for managing one of the belt conveyors presented in the model. the other conveyors are managed by simulation programs for these belt conveyors simulation models. vii. conclusion detailed simulation of longwall system, connected with detailed simulation of flat-lying coal seam (or multiple flatlying coal seams), will allow the creation of models that will not only predict the behavior of big underground mining systems, but also the simulation of land subsidence while using longwall, especially with very heavy longwall systems that can cut 10-meters-high coal seams. the mtss simulation system can be used not only for simulation of existing coal mining techniques but also for perspective robotized techniques. the library of elements is still growing. it provides the capability to create detailed simulation models of underground mining facilities, including belt conveyor systems, power supply, ventilation, and various coal face models. such simulation models can be used both in solving “what-if” tasks and in hardware development for control systems. fig. 6. belt conveyor controlling hardware connected to the simulation model of whole mines factory. references [1] j. r. sturgul, “modelling and 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simulation system”, patent fap sb ras, novosibirsk, russia, 2011, url: http://fap.sbras.ru/node/2325 (in russian) [11] v. okolnishnikov, “development of process control systems with the use of emulation models”, international journal of mathematics and computers in simulation, vol. 5, no. 6, pp. 553–560, 2011 [12] v. okolnishnikov, s. rudometov, s. zhuravlev, “simulation environment for development of automated process control system in coal mining”, 2013 international conference on systems, control, signal processing and informatics (scsi 2013), rhodes island, greece, pp. 285–288, 2013 [13] v. okolnishnikov, s. rudometov, s. zhuravlev, “simulation environment for development of automated process control system in coal mining”, international journal of systems applications, engineering & development, vol. 7, no. 5, pp. 255–262, 2013 [14] a. cirulis, e. ginters, “training scenario operations realization in virtual reality environment”, 13th wseas international conference on automatic control, modelling & simulation, canary islands, spain, pp. 39–44, 2011 microsoft word etasr_v12_n6_pp9661-9664 engineering, technology & applied science research vol. 12, no. 6, 2022, 9661-9664 9661 www.etasr.com almashhadani & al-sherrawi: effect change concrete slab layer thickness on rigid pavement effect change concrete slab layer thickness on rigid pavement g. a. almashhadani department of civil engineering university of baghdad baghdad, iraq g.almashhadani1901m@coeng.uobaghdad.edu.iq mohannad h. al-sherrawi department of civil engineering university of baghdad baghdad, iraq dr.mohannad.alsherrawi@coeng.uobaghdad.edu.iq received: 23 august 2022 | revised: 16 september 2022 and 25 september 2022 | accepted: 26 september 2022 abstract-years of research have been devoted to developing a tool to model and analyze the behavior of rigid pavements. a major component of the new design approaches is the threedimensional finite element method (fem), which caused a breakthrough in rigid pavement analysis. the current study used fem to analyze a rigid pavement composed of a concrete slab layer and a subgrade. the impact of the depth of the concrete slab layer on vertical stresses and displacements was studied with the abaqus software. three different thicknesses were chosen, 20, 25, and 28cm, while the thickness of the remaining paving layers remained unchanged. according to the study results, the top of the concrete slab layer had an increase in stress of approximately 88% when its thickness increased from 20 to 28cm, whereas the top of the subgrade layer had a decrease of about 21% in stress. the change in vertical stress at the top of the subgrade layer was 46% for a thickness of 20-25cm and 14.8% for 25-28cm. the percent of the reduction in vertical stress at the top of the concrete slab layer was 13.2% and 1.8% for thicknesses of 20-25 and 25-28cm respectively. vertical displacement in the middle of the horizontal distance under the tire print was reduced by 14%, 12%, and 24% when the concrete slab layer increased from 20 to 25, from 25 to 28, and from 20 to 28cm respectively. keywords-rigid pavement; abaqus; concrete slab thickness; finite element method i. introduction rigid pavements are complicated structural systems made up of a variety of concrete slabs connected by longitudinal and transverse joints that may or may not contain dowel bars. many design approaches to determine required pavement thicknesses have been established [1]. analytical solutions developed from closed-form formulas to complicated derivations can be used to determine stress and strain on rigid pavements. finite element (fe) modeling is useful to simulate the structural reaction of pavements under the influence of various loading conditions and is effective in solving partial and integral differential equations [2-4]. fem was developed as a numerical approach to solve numerous engineering and applied science issues [5]. many techniques with various computational costs may be implemented in abaqus, a software widely used for fem analysis [6], as it can solve problems with static, harmonic, and transient dynamic loading as well as thermal gradient conditions in two and three dimensions [7]. linear and nonlinear elastic, viscoelastic, plastic, and modified elastic materials can be represented. several studies used three-dimensional (3d) fe models to investigate the behavior of rigid pavements. various fe models have been proposed to analyze the behavior of concrete pavement systems. in [8], the tension in rigid runway pavement was studied showing that wider wheel arrangements cause less stress by aircraft load. computational modeling of a rigid pavement with load applied to the slab's edge was conducted in [1] using fem. there were no significant variations in stresses at the research control point between modeling a system with three slabs with dowels and modeling an isolated slab for slab sizes frequently used in basic concrete pavements (l≥3.5m). an analysis of a dowel-jointed concrete pavement using a 3d fe model was carried out in [9], observing that voids beneath the joint increased the vertical displacement of the concrete slab and vertical stress at the concrete/dowel bar interface, potentially leading to concrete crushing and dowel loosening. in [2], abaqus was used to investigate the pavement response under the effect of some model parameters, and a comparison with field measurements confirmed the findings. the stress and strains on the concrete slabs were found to minimize by increasing the thickness of the slab. stress reduction is especially noticeable in the joints. in [11], abaqus was employed to model rigid pavements and investigate how varied pavement layer thicknesses, such as base course material and slab thickness, affected the critical pavement reactions. ii. materials and methods a. pavement model this study modeled the concrete slab and subgrade using a 3d fe mesh. a conventional pavement section was used, consisting of a concrete slab and a subgrade, to investigate the effect of the thickness of the concrete slab layer on the performance of the rigid pavement layers, with a fixed subgrade depth thickness. the geometries and the mechanical properties of the materials examined were the elastic modulus e and poisson's ratio ν. the data of the adopted model were: corresponding author: ghfran a.almashhadani engineering, technology & applied science research vol. x, no. x, 20xx, pp 9662 www.etasr.com do not alter header & footer. they will be completed during editing  concrete slab layer of 4.50×5.00m, h=200mm  ec=26000mpa, ν=0.17  subgrade of 4.50×5.00m, h=3.00m.  e=34mpa, ν=0.35 figure 1 shows the geometrical model. table i. layer thicknesses layer layer name thickness case 1 case 2 case 3 1 concrete slab 180 mm 200 mm 250 mm 2 subgrade 3 m 3 m 3 m fig. 1. 3-d model, geometry. b. mesh size distribution in the model the mesh size was optimized to achieve a balance between computation time and calculation stability [4]. a fine mesh of 10×10cm was required in the concrete slab. however, a somewhat coarse mesh of 30×30cm was chosen for the soil foundation, without affecting the accuracy of the stress and displacement predictions. figure 2 shows the model's fe mesh. fig. 2. mesh size distribution for the model. c. boundary conditions the boundary conditions were chosen to be as close as possible to the actual boundary conditions. the peripheric and bottom limitations were defined using the boundary conditions. for boundary conditions, the lower surfaces were considered completely fixed against all degrees of freedom [10]. for all pavement geometry models, the edges can move in the vertical (z) direction. no movement was considered in the horizontal directions for the four sides of the model during fem analysis. figure 3 shows these boundary conditions. fig. 3. the boundary conditions of the model. d. load representation the load was characterized as static, which is the most favorable state for calculating stresses, and the equivalent contact area was used in the load configuration, which is a common technique of representing pavement loads [3]. the single axle, with a single wheel, and a 690kpa pressure of the tire was adopted in the analysis. the use of a square footprint resulted in an improved agreement with fe meshing. figure 4 shows the wheel load configurations, and table ii presents footprint dimensions. fig. 4. wheel load configurations. table ii. footprint dimensions [3] wheel load dimensions "b" (mm) single wheel load (sal) 332 e. interaction modeling techniques interactions between contact surfaces were established in the fe model. the interactions had many features that are necessary for the solution's appropriate convergence and were determined by the physical relationship between its components [3]. iii. results and discussion the distributions of stresses and displacements were studied to properly exploit and develop the results of 3d modeling. figure 5 shows the collected results of stresses and their vertical distribution from the fe model analysis used in this study for case 1, while figure 6 shows the vertical displacement distribution within the pavement layers. figures 7-10 show the collected results of stresses and vertical displacement distribution within pavement layers for cases 2 and 3. engineering, technology & applied science research vol. x, no. x, 20xx, pp 9663 www.etasr.com do not alter header & footer. they will be completed during editing fig. 5. stress distribution within pavement layers, case 1. fig. 6. vertical displacement distribution within pavement layers, case 1. fig. 7. stress distribution within pavement layers, case 2. fig. 8. vertical displacement distribution within pavement layers, case 2. table iii shows the values of vertical stresses (σ33) in the pavement system when applying a pressure of 690kpa. in case 1, vertical stress of 519kpa was concentrated on the top of the concrete slab layer under the tire print, which is about 75% of the applied pressure. this was reduced to 190kpa at the top of the subgrade layer, which is about 28% of the applied pressure. in case 2, vertical stress increased to 598kpa at the top of the concrete slab layer, which is approximately 87% of the applied pressure, and reduced to 163kpa at the top of the subgrade layer, which is approximately 24% of the applied pressure. in case 3, vertical stress increased to 610kpa and 150kpa at the top of the concrete slab and subgrade layers (approximately 88% and 22% of the applied pressure) respectively. fig. 9. stress distribution within pavement layers, case 3. fig. 10. vertical displacement distribution within pavement layers, case 3. table iii. stress levels between the interfaced layers layer name vertical stress (σ33), pa case 1 case 2 case 3 top of concrete slab layer 519652 598887 610052 top of subgrade 190376 163143 150807 the results of this study indicate that the stress levels at the top of the concrete slab layer increased by approximately 88% when the thickness of this layer increased from 20 to 28cm, while the stress levels at the top of the subgrade layer reduced by approximately 21%. figure 11 illustrates how the stress level increased with the increasing thickness of the concrete slab layer. additionally, as the thickness of the concrete slab layer increases, the vertical stresses below the tire print at shallow depths vary slightly. however, at large horizontal distances and depths, the variation is negligible. figure 12 shows the vertical displacement along with the horizontal distance for all cases on top of the concrete slab layer under the center of the inner wheel. the vertical displacement in the middle of the horizontal distance under the engineering, technology & applied science research vol. x, no. x, 20xx, pp 9664 www.etasr.com do not alter header & footer. they will be completed during editing tire print decreased by 14%, 12%, and 24% when the concrete slab layer increased from 20 to 25cm, 25 to 28cm, and 20 to 28cm respectively. however, the vertical displacement at the edge of the concrete slab layer increased by about 26% when the thickness of this layer increased from 20 to 28 cm. fig. 11. vertical stress vs depth. fig. 12. vertical displacement on the top of the concrete slab layer. iv. conclusion the main conclusions drawn from on the results of this study are:  the percentage of deformation in the middle of the horizontal distance under the tire print decreases by 14%, 12%, and 24% as the thickness increases from 20 to 25cm, 25 to 28cm, and 20 to 28cm respectively. this indicates that the concrete slab layer is mainly responsible for this reduction in deformation in the pavement structure.  for concrete slab layer thicknesses of 20, 25, and 28cm, the vertical stress at the top of the concrete slab layer is 519, 598, and 610kpa respectively, and it reduces to 190, 163, and 150kpa on the top of the subgrade layer, which is equivalent to approximately 28%, 24%, and 22% of the applied stress at the top. since the stresses in the layer under the concrete slab layer decrease as the thickness of the concrete slab layer increases, the stresses above the subgrade therefore decrease.  the maximum value of vertical stress is 610.052pa at the top of the concrete slab layer when the concrete slab layer is 28cm, while the minimum vertical stress is 100.152 at the top of the subgrade layer when the concrete slab layer is 25cm.  the analysis clearly shows that the vertical stress at the top of the concrete slab layer increases as the vertical depth of the concrete slab layer increases. references [1] f. m. h. lópez, e. t. piusseaut, e. a. r. veliz, and c. a. r. morfa, "3d-fe of jointed plain concrete pavement over continuum elastic foundation to obtain the edge stress," revista de la construcción journal of construction, vol. 19, no. 1, pp. 5–18, apr. 2020, https://doi.org/10.7764/rdlc.19.1.5-18. [2] m. zokaei, m. fakhri, and s. rahiminezhad, "a parametric study of jointed plain concrete pavement using finite element modeling," modern applied science, vol. 11, no. 11, pp. 75–84, oct. 2017, https://doi.org/10.5539/mas.v11n11p75. [3] y. h. huang, pavement analysis and design, 2nd ed. upper saddle river, nj, usa: pearson education, 2004. [4] m. zdiri, n. abriak, j. neji, and m. b. ouezdou, "modelling of the stresses and strains distribution in an rcc pavement using the computer code ‘abaqus,’" electronic journal of structural engineering, vol. 9, pp. 37–44, jun. 2009, https://doi.org/ 10.56748/ejse.9116. [5] a. s. mahdi and s. d. mohammed, "experimental and numerical analysis of bubbles distribution influence in bubbledeck slab under harmonic load effect," engineering, technology & applied science research, vol. 11, no. 1, pp. 6645–6649, feb. 2021, https://doi.org/ 10.48084/etasr.3963. [6] a. a. abdulhussein and m. h. al-sherrawi, "experimental and numerical analysis of the punching shear resistance strengthening of concrete flat plates by steel collars," engineering, technology & applied science research, vol. 11, no. 6, pp. 7853–7860, dec. 2021, https://doi.org/10.48084/etasr.4497. [7] w. uddin, r. m. hackett, a. joseph, z. pan, and a. b. crawley, "threedimensional finite-element analysis of jointed concrete pavement with discontinuities," transportation research record, vol. 1482, pp. 26–32, 1995. [8] m. r. k. manesh, m. m. s. babaki, a. p. tavandasthi, "examining the effect of weight and the arrangement of aircrafts’ wheels on rollercompacted concrete (rcc) pavement design of runways using finite element method," current world environment, vol. 10, special issue 1, apr. 2015. [9] sii, how bing (perry), "three-dimensional finite element analysis of concrete pavement on weak foundation," ph.d. dissertation, griffith university, queensland, australia, 2015. [10] m. a. s. hadi and m. h. al-sherrawi, "the influence of base layer thickness in flexible pavements," engineering, technology & applied science research, vol. 11, no. 6, pp. 7904–7909, dec. 2021, https://doi.org/10.48084/etasr.4573. [11] m. rahman and n. murshed, "sensitivity of rigid pavement responses to pavement layer thickness due to wheel load: a nonlinear finite element study," trends in transport engineering and applications, vol. 1, no. 1, pp. 1–10, 2014. microsoft word 4-494.doc engineering, technology & applied science research vol. 4, no. 5, 2014, 706-710 706 www.etasr.com chan and yong: comparing the thixotropic and lightly solidified hardening behavior… comparing the thixotropic and lightly solidified hardening behavior of a dredged marine clay chee-ming chan faculty of engineering technology universiti tun hussein onn malaysia batu pahat, malaysia chan@uthm.edu.my hui-yen yong faculty of civil & environmental engineering universiti tun hussein onn malaysia batu pahat, malaysia hui_yen_90@hotmail.com abstract— when a soil is disturbed upon remolding, it may lose part or all of its strength. as time passes, the structural arrangement of the soil particles would be restored to a stable form and the soil would regain hardness under constant volume and water content. the process is known as “thixotropic hardening”. on another note, dredged marine soils of the finegrained type can be reused as a backfill material instead of being disposed to the open sea. the rest period required for the relocated soil to regain strength and stiffness, i.e. thixotropic hardening, needs to be estimated precisely. for this purpose, a study on the phenomena of strength and stiffness gain by a dredged marine clay was carried out. the strength and stiffness improvement with time was measured using the vane shear and fall cone tests respectively. the clay was remolded at different water contents in multiples of the soil’s liquid limit (ll), namely 0.75ll, 1.00ll and 1.25ll, in order to evaluate the effect of initial water content on thixotropic hardening. a separate series of samples were prepared with light solidification using cement, to examine the possibilities of enhancing the soil’s improvement in a shorter rest period. the results showed the dredged marine clay can potentially be used as a backfill material for reclamation works, with lower initial water content and light solidification contributing to accelerated better performance. keywordsthixotropic hardening; light solidification; dredged marine clay; undrained shear strength; cone penetration i. introduction dredging activities in shipping channels generate huge amount of dredged marine sediments (dms). usually, dredging activities are carried out for the maintenance of navigation channels or the deepening of existing port facilities to cope with large ships [1]. the most widely practiced dms management solution is to dispose the material to open sea, especially for dms with are of fine-grained nature (i.e. clay and silt), which have poor engineering properties and limited usage. however, the disposal of dms in the water could contaminate it and endanger the marine ecosystem, leading to potentially long term, irreversible environmental problems. hence it is crucial to review and develop a beneficial reuse for dms, in place of indiscriminate disposal. similarly to the mechanism of secondary compression (postconsolidation hardening process), dms regains strength and hardness under constant volume and water content by thixotropic hardening. this is attributed to the rearrangement of the soil particles to a more stable state. dms can be potentially reused as a backfill material for reclamation work, assuming that thixotropic hardening contributes to the eventual strength and stiffness gain. as reported in [2], there is some marked improvement in the material when left to rest for certain periods. in addition, the present study also explores the possibilities of shortening the rest period for the strength and stiffness gain of the dms by employing light solidification with small dosages of cement. note that the role of cement in the study was mainly to accelerate the thixotropic hardening process and not for solidification purposes. work pertaining to the solidification of soft soil deposits can be found in the literature, where some of the more recent ones include [3-5]. as it is time-dependent, thixotropic hardening is also known as a kinetic process involving the time effect on the soil’s structural destruction / formation mechanisms [6]. continuous viscosity decrease with time when flow is applied to a previously at-rest sample and it would meet a subsequent recovery when the flow is discontinued [7]. it has also been reported that the effect of thixotropy increases when the soil is within the range of the liquid and plastic limits [2]. beyond the liquid limit, thixotropic behavior was found to diminish as the water content rises. this is in line with observations made in [8], although it has also been reported that thixotropic effect can be low or negligible at or close to the soil’s plastic limit [9]. this suggests the initial water content has a significant effect on the thixotropy phenomenon. the soil could undergo full or partial recovery of strength and stiffness, depending on the material’s inherent properties and characteristics. besides, the process is reversible upon remolding and resting, and vice versa [10]. an understanding of the soil’s behavior in regaining timedependent strength and stiffness is necessary to introduce dms as a potential backfill material, particularly in terms of the rest period. areas of applications include eroded shoreline rehabilitation, reclamation, construction of road embankments, creation of elevated grounds and other civil engineering projects [11]. for instance, as illustrated in figure 1, dms reclamation along shorelines to cope with rising sea levels. as additional time means extra costs in construction businesses, engineering, technology & applied science research vol. 4, no. 5, 2014, 706-710 707 www.etasr.com chan and yong: comparing the thixotropic and lightly solidified hardening behavior… practitioners would need to be convinced of the payoff from using a ‘greener’ material without losing out on the time factor. this paper describes an investigation on the matter with a dredged marine clay retrieved from the malaysian waters. an additional set of tests were also conducted on the sample lightly solidified with small dosages of cement (i.e. <10 %), to ascertain the possibilities of shortened rest period. ii. materials and methods a. remoulding of dredged marine clay the dms sample was obtained from a dredged site in the waters of melaka, a historical city of malaysia. key properties of the sample are summarized in table i. note that the natural water content of the sample was higher than its liquid limit. however, in order to examine the thixotropic effect at different water contents, the soil was remolded at three water contents in multiples of the liquid limit (ll), i.e. 0.75ll, 1.00ll and 1.25ll. the soil was semi-dried in a pan over a portable stove, where the heating process was carefully controlled and monitored with regular measurement of the water content. the remolded soil was next poured into a plastic mold of 9.5cm x 30cm x 11cm dimension (figure 2). the mixture was placed in 4 layers. for each layer, the mold was lightly tapped on the bench to remove any entrapped air from the partially liquefied material. the soil bed was kept at 60 mm thick, with each layer’s thickness measuring approximately 15 mm. the layer thickness was used as guide in maintaining the volume of the soil bed in each sample prepared. a separate set of soil bed was prepared similarly at 1.25ll water content, but with the addition of 2-8% of cement (as per dry mass of soil). the small cement dosages added were, as mentioned earlier, to gain insights to the possibilities of hastening the strength and stiffness gain within a shorter rest period. the percentage range of chemical contents in the cement is given in table ii. measurements with the laboratory vane shear and cone penetrometer were then carried out on the samples over a 7-day period, at intervals of 0, 0.5, 1, 2, 4, 8, 24, 48, 96 and 168 hours. table i. physico-chemical properties of dredged sample material properties value oxide element content (%) particle size distribution, % cao2 0.10 sand 9% sio2 57.10 silt 18% al2o3 21.50 clay 69% fe2o3 7.63 atterberg limit, % k2o 3.04 liquid limit 54.20% cl 2.27 plastic limit 30.72% mgo 2.17 plasticity index 23.48% cao 1.98 so3 1.36 natural moisture content (%) 103.44% na2o 1.34 classification of soil ch tio2 1.05 specific gravity, gs 2.53 table ii. limits of chemical contents in cement chemical compound content (%) cao 60-67 sio2 17-25 al2o3 3-8 fe2o3 0.5-0.6 mgo 0.1-0.4 na2o,k2o 0.2-1.3 so3 1-3 fig. 1. using dms as a backfill material in countering rising sea level fig. 2. remolded soil bed with grids marked out for the measurements b. laboratory vane shear test the increase in shear strength by thixotropic hardening was determined by laboratory vane shear test (figure 3a), according to bs1377 [12]. laboratory vane shear test was considered most appropriate since the soil sample was classified as cohesive soil of fine-grained type with very low strength. a standard 12.7 mm wide and 12.7 mm long vane was used in the test. the most appropriate torsion spring was chosen based on the maximum stress each torsion spring can sustain. torque was applied to the vane by rotation at 10° per minute. the minimum centre-to-centre distance for each test point was kept at about 35 mm to minimize disturbance from the adjacent, previous test point. the undrained shear strength (cu) can then be calculated by (1): ) 3 ( 2 2 dhd t cu + = p where t is the measured torque at peak, d is the vane diameter, and h is the vane height. engineering, technology & applied science research vol. 4, no. 5, 2014, 706-710 708 www.etasr.com chan and yong: comparing the thixotropic and lightly solidified hardening behavior… c. fall cone test the fall cone test (figure 3b) was conducted to measure the shear resistance developed from the improved stiffness of the soil with time. the test was performed according to bs1377 [12], with omissions of the plotting and calculations, as normally carried out if the test was intended for measuring liquid limit. the cone (80 g with an apex angle of 30°) was first placed just above the soil’s surface, then dropped under its own weight for 5 seconds before the reading was taken. the cone penetration depth would decrease with time as soil’s stiffness increased, i.e. resistance against the cone penetration would be gained over time. as such, it follows that the cone penetration depth can be related with the undrained shear strength of the soil, as strength and stiffness are known to rise in tandem [13]. fig. 3. (a) vane shear and (b) fall cone tests iii. results and discussions a. undrained shear strength of dms figure 4 shows the undrained shear strength for the dms samples at different water contents. it is apparent that samples 1.00ll and 1.25ll underwent negligible strength improvement over the 1-week period. compared to sample 0.75ll, the initial strength recorded was about 1.5-4 times that of the other two samples. the subsequent rise in strength was charted markedly over 48 hours, before the strength gain reached a relative plateau. this indicates that for this particular dms, an initial water content lower than the liquid limit is necessary to enable thixotropic hardening to take place. at water contents beyond the liquid limit, the soil would be too liquefied and susceptible to flocculation, resulting in repulsion of the soil particles in the water-logged matrix instead of settling down to a more rigid structure. the cone penetration depth vs time elapsed plots are shown in figure 5. all samples underwent a similar rate of penetration in the first 8 hours, though in comparison, the readings for sample 1.25ll seemed to record less dramatic change with time (i.e. more gentle gradient of the initial rise of the plot). sample 1.25ll also reached a plateau later than the other two samples. however note that the initial penetration was far higher for sample 1.25ll, which was approximately twice that of the other samples. besides, both samples 1.00ll and 0.75ll demonstrated slight reduction in the penetration depth after 8 hours of time lapse. sample 1.25ll took a longer time to gain resistance against the cone penetration, i.e. plateau was attained at about 36 hours. b. cone penetration depth in general the cone penetration rate corresponded with the strength gain rate, but the major departure of sample 0.75ll in terms of strength (figure 4) was not observed in the fall cone test. indeed, samples 1.00ll and 1.25ll were remarkably close in terms of the cone penetration rate (figure 5). this suggests limitation of the sensitivity of the fall cone test, as well as possible bleeding in the high water content soils resulting in weakened upper layer of the soil bed. fig. 4. variation in shear strength developed from thixotropic hardening fig. 5. variation in cone penetration depth developed from thixotropic hardening c. comparison between natural and lightly solidified dms figure 6 shows the combined undrained shear strength plots of the natural dms and lightly solidified samples. it can be seen that the strength of the lightly solidified samples with 68% cement increased dramatically. on the other hand, cement addition of less than 5% did not seem to contribute much to the strength improvement, even after the prolonged rest period of a week. clearly the efficacy of light solidification was overwhelmed by the excessive water content present in the soil, (a) (b) engineering, technology & applied science research vol. 4, no. 5, 2014, 706-710 709 www.etasr.com chan and yong: comparing the thixotropic and lightly solidified hardening behavior… as is evidential in the low lying plots even below that of sample 0.75ll. the cement dosage was inadequate to induce solidification of the wet soil. this suggests a threshold cement dosage for meaningful strength gain. besides, the rising trends of samples 1.25ll (6% cement) and (8% cement) underline the benefits of continuous strength gain of the dms, despite the high initial water content. taking into account the time factor, and comparing the plots of samples with 6-8% cement addition, the strength gain rate was dependent on the amount of cement added. this is highlighted by the significant early strength gain recorded by sample 1.25ll (8% cement) within the first 24 hours, before the transition to a more gentle rise in strength. the sample with 6% cement addition had a less remarkable strength gain rate in the first 48 hours, after which a sharp rise was observed till approximately 100 hours. the strength gain rate then declined and returned to approximately the same rate as in the initial stage. gradient indicators (triangles with dashed lines) are included in figure 6 next to the 6% cement plot to illustrate the different strength gain rates. such variations in the rate of improvement was not observed in the sample with 8% cement addition. fig. 6. comparison of variation in undrained shear strength of untreated dms with cement treated dms with time the combined cone penetration depth plots are shown in figure 7. the resistance against cone penetration was best achieved by the samples with 6-8% cement addition, which is in line with the strength gain plots in figure 6. the hardening effect for samples with 1-4% cement addition which was otherwise not captured in the strength plots was obvious (figure 7). note the 2% cement and 4% cement plots lying very close to 1.25ll and 1.00ll respectively, after 48 hours. this could be explained by the limited solidification efficacy of 2% cement addition to the soil. the 4% cement sample, however, was effectively solidified to attain the same stiffness gained by the soil at lower initial water content, i.e. 1.00ll. these results point to the contribution of cement addition in shortening the improvement rate of the dms. the delayed hardening effect of the 6% cement sample was not observed in figure 7, where both 6% and 8% cement samples showed similar improvement rate. nonetheless the eventual stabilization of the cone penetration resistance rate was similar to those seen in the strength plots. the continuous hardening effect was absent in the cone penetration plots too, with all samples recording plateaus after 48 hours. this is perhaps an indicator of the limitations of the fall cone test in assessing the strength and stiffness gain in dms, with or without light solidification. fig. 7. comparison of variation in cone penetration depth of untreated dms with cement treated dms with time iv. conclusions the main conclusions are as follows: 1. the strength and cone penetration resistance improvement rate of the samples follow the ascending order of 0.75ll>1.00ll>1.25ll, indicating the setbacks of high initial water contents on the rest period. 2. the fall cone method seemed less sensitive to the rather small improved structure of the soil with time, which could be attributed to a weakened upper layer of the soil bed due to bleeding. 3. light solidification was effective with a minimum cement dosage of 6%. the strength as well as the strength gain rate both improved markedly, and showed signs of prolonged improvement beyond 7 days. 4. the fall cone test was able to capture the distinction between the solidification efficacy with 2-4% cement, but was insensitive to the continuous hardening effect post 48 hours. 5. overall, small cement dosages (i.e. >6 % in this case) were sufficient to shorten the rest period of the dms. in fact, it was found to contribute to prolonged improvement of the soil too. references [1] w. s. w. salim, w. s., n. a. m. noor, s. f. sadikon, m. f. arshad, n. wahid, s. m. salleh, “the preliminary investigation on the dredged marine sediment of kuala perlis as a potential brick material”, 5th international conference on environmental and computer science (icecs2012), pp. 25-29, thailand, 2012 [2] s. seng, h. tanaka, “properties of very soft clays: a study of thixotropic hardening and behavior under low consolidation pressure”, soils and foundations, vol. 52, no. 2, pp. 335-345, 2012 [3] s. horpibulsuk, w. phojan, a. suddeepong, a. chinkulkijniwat, m. d. liu, “strength development in blended cement admixed saline clay”, applied clay science, vol. 55, pp. 44-52, 2012 engineering, technology & applied science research vol. 4, no. 5, 2014, 706-710 710 www.etasr.com chan and yong: comparing the thixotropic and lightly solidified hardening behavior… [4] n. c. consoli, l. festugato, c. g. da rocha, r. c. cruz, “key parameters for strength control of rammed sand-cement mixtures: influence of types of portland cement”, construction and building materials, vol. 49, pp. 591-597, 2013 [5] c. m. chan, “influence of mix uniformity on the induced solidification of dredged marine clay”, environmental earth sciences, vol. 71, no. 3, pp. 1061-1071, 2014 [6] a. y. malkin, “non-newtonian viscosity in steady-state shear flows”, journal of non-newtonian fluid mechanics, vol. 192, pp. 48-65, 2013 [7] j. mewis, n. j. wagner, “thixotropy”, advances in colloid and interface science, vol. 147-148, pp. 214-227, 2009 [8] a. w. skempton, r. d. northey, “sensitivity of clays”, geotechnique, vol. 3, no. 1, pp. 40-51, 1952 [9] h. b. seed, c. k. chan, “thixotropic characteristics of compacted clays”, asce journal of soil mechanics and foundation engineering, vol. 83(sm4), pp. 1427-1435, 1957 [10] m. d. braja, fundamentals of geotechnical engineering. cengage learning, uk, 2013 [11] c. m. chan, a. shamsuddin, “sustainable geo-materials from agricultural and geo-wastes: reborn and viva!”, australian journal of basic and applied research, vol. 7, no. 11, pp. 87-103, 2013 [12] british standard institution, british standard bs 1377-1: methods of test for soils for civil engineering purposes. london, uk, 1990 [13] h. tanaka, h. hirabayashi, m. tatsuya, k. hiroaki, “use of fall cone test as measurement of shear strength for soft clay materials”, soils and foundations, vol. 52, no. 4, pp. 590-599, 2012 microsoft word etasr_v13_n2_pp10447-10452 engineering, technology & applied science research vol. 13, no. 2, 2023, 10447-10452 10447 www.etasr.com nguyen et al.: multiple response prediction and optimization in thin-walled milling of 6061 … multiple response prediction and optimization in thin-walled milling of 6061 aluminum alloy van que nguyen faculty of mechanical engineering, hanoi university of industry, vietnam nguyenvanque@haui.edu.vn hoang tien dung faculty of mechanical engineering, hanoi university of industry, vietnam tiendung@haui.edu.vn van thien nguyen personnel and administrative department, hanoi university of industry, vietnam nguyenvanthien@haui.edu.vn van dong pham department of science and technology, hanoi university of industry, vietnam nguyenvanthien@haui.edu.vn van canh nguyen faculty of mechanical engineering, hanoi university of industry, vietnam nguyenvancanh@haui.edu.vn (corresponding author) received: 10 january 2023 | revised: 4 february 2023 | accepted: 15 february 2023 abstract in this study, the multi-objective optimization method for thin-wall milling of 6061 aluminum alloy is addressed. the technological parameters including the cutting speed vc, the feed of tooth fz, and the width of cut ar are considered input variables, while the manufacturing responses are surface roughness ra, production rate mrr, and flatness deviation fl. the goal is to find the optimum cutting parameters to minimize ra and fl and maximize mrr, at the same time. to solve this problem, the desirability function approach was used based on taguchi orthogonal array. twenty-seven experiments were conducted and the measured data were collected. the mathematical regression models for responses ra, mrr, and fl were then generated and evaluated by using the analysis of variance method. then, the multiple objective optimization problems were solved by using the desirability function approach. the optimum cutting parameters set are vc=120m/min, fz=0.06mm, and ar=0.13131mm, corresponding to ra=0.1613µm, mrr=17197.45cm 3 /min, and fl=0.0995mm. keywords-thin-walled milling; multiple objective optimization; desirable function approach; taguchi method; 6061 aluminum alloy i. introduction the 6061 alloy is an important product line in aluminum manufactured products [1]. aluminum and its alloys rank second (after steel) in use as structural metals [2], due to properties that make them suitable for many different uses [3]. some of the important properties of 6061 alloy are its light weight, high strength, good chemical corrosion resistance, and good weldability [4]. therefore, 6061 alloy is often used in the transportation industry (e.g. in auto parts, motorcycles, cycle frames, and motorcycle frames) and especially in the marine or aerospace industry [5]. the development of the aviation engineering, technology & applied science research vol. 13, no. 2, 2023, 10447-10452 10448 www.etasr.com nguyen et al.: multiple response prediction and optimization in thin-walled milling of 6061 … industry has led to an increasing demand for aluminum alloy machining, in which the milling of thin-walled parts plays a particularly important role [6]. however, the manufacturing of thin-walled parts is complicated by the possibility of deformation during the machining process [7]. thin-walled products are often difficult to cut due to the complex dynamics involved. during the cutting process, the cutting dynamics for the products varies however it is invariant for the machine tool [8]. on another hand, permanent deformation of the structure can occur and this can cause a proportion of rejected products [9]. in the demand of the growing global market for aluminum alloy thin-walled products, there are several studies focused on optimizing the structure to improve the surface roughness, the load capacity, and the durability of the thin-walled components by reducing deformation and vibration during the cutting process [7]. μany studies have been carried out to improve the economic and technical efficiency of thin-walled processing. authors in [10] developed an analytical approach to investigate the dynamic chip thickness variation in the thin-walled milling process. a general model of the removal volume is calculated by considering the individual axial depth of cut, the radial depth of cut, and the circumferential cross-section of the tool radius contact for each tool step performed. authors in [6] presented a technique to improve the surface quality and production rate in the thin-walled milling process. the results show that double-side milling leads to reduce about 50% in cutting time and a decline in the surface roughness and flatness deviation of the milling products, simultaneously. the quality of thin-walled products when machined can also be improved by selecting and using the right jigs and fixtures [11]. finding suitable cutting parameters can also reduce vibration, thereby reducing deformation during milling. this can be solved through experimentation [12, 13], or mathematical modelling [14]. authors in [8] present a methodology of performing the optimization of the entire cutting process for thin-walled parts based on the relatively changing kinematics of the machining system. according to the comparison between the dynamics of the machine tool and the variable thickness part, the critical thickness is investigated by an iterative algorithm. this method can be used for many other machining processes. there are many other studies on machining thin-walled parts in general, and aluminum alloys in particular. these studies can be applied to improve the quality of processed products in practice. however, due to the increasing competitive pressure from the global market, the manufacturers not only have to improve the quality of processing but at the same time have to increase machining productivity and tool life. those are scientific multi-objective optimization problems and multiple criteria decision-making (mcdm) methods such as the technique for order of preference by similarity to ideal solution (topsis) and multi-objective optimization on the basis of ratio analysis (moora) have been introduced to face them [15-19]. they are often applied due to their simplicity. however, these methods have a common disadvantage, which is the optimal value set is one of the experimental values. this means that these techniques select one of the data sets that have been used, and in many cases, they are not the best [18-20]. with the development of computers, many new algorithms have been researched and applied, e.g. anfis [21], desirability function approach (dfa) [22], etc. many publications have demonstrated the effectiveness of these methods in comparison with mcdm. in this study, dfa and minitab computed software were applied to solve the multiobjective optimization problem at hand. the research aims to find the optimal cutting parameters set to simultaneously maximize the machining productivity mrr, and minimize the roughness ra and flatness deviation fl. a. materials and methods b. 6061 aluminum alloy as mentioned above, 6061 aluminum alloy was selected because it is largely used. all the specimen workpieces were milled with dimensions of 100×50×10mm 3 . the chemical composition and mechanical properties of the workpieces are shown in tables i and ii [23]. the experiments were conducted on a dmu50 cnc machine. to perform thin-walled milling operations, a 3-flute square namely yg alu cutter e5d70100 (15329040k) was used (figure 1). the taguchi orthogonal array was applied to reduce the number of experiments but still ensure reliability in the predictive analysis, with the number of input variables being 3, the number of levels for each variable being 3, and the number of experiments to be performed being 27. the values of the input variables corresponding to the levels are depicted in table iii. the range of the cutting parameters is chosen based on the cutting tool manufacturer’s recommendations. table i. chemical composition of 6061 alloy al (%) mg (%) si (%) cu (%) cr (%) others (%) 97.9 1 0.60 0.28 0.20 0.02 table ii. the mechanical properties of 6061 alloy tensile strength 310mpa yield strength 276mpa shear strength 207mpa fatigue strength 96.5mpa elastic modulus 68.9gpa poisson's ratio 0.33 elongation 12-17% hardness 95 hb table iii. input variable levels parameters symbol unit level -1 0 1 cutting speed vc m/min 120 150 180 feed rate fz mm/tooth 0.04 0.05 0.06 width of cut ar mm 0.8 1.0 1.2 c. experimental data acquisition the experimental set up is shown in figure 2. in this work, 3 thin-walled cutting responses, including the surface roughness ra, material removal rate mrr, and flatness deviation fl are optimized simultaneously by applying the desirable function approach (dfa). based on the en iso 4287 standard, surface roughness ra is calculated by: engineering, technology & applied science research vol. 13, no. 2, 2023, 10447-10452 10449 www.etasr.com nguyen et al.: multiple response prediction and optimization in thin-walled milling of 6061 … ��� = ���� ��� ���� ���� ��� � (1) ��� = ���� ��� ���� ���� ��� � (2) �� = ��� ���� (3) where rax is the arithmetical mean roughness in the x-direction and ray is the mean roughness depth in the y-direction. fig. 1. the experimental setup. fig. 2. a1: negative local flatness deviation, a2: positive local flatness deviation, 1: least squares reference plane (stn p cen iso/ts 12781-1: 2008). (a) (b) fig. 3. measurement systems. (a) renishaw equator 300 cmm highspeed comparative gauge system, (b) non-contact flatness deviation measurement system. table iv. experimental results run vc m/min fz mm/ ar mm ra µm mrr mm 3 /min fl mm 1 120 0.04 0.8 0.228 8025.48 -0.031 2 120 0.05 1 0.128 14331.21 -0.060 3 120 0.06 1.2 0.152 20636.94 -0.044 4 150 0.04 0.8 0.294 10031.85 0.100 5 150 0.05 1 0.274 17914.01 0.063 6 150 0.06 1.2 0.345 25796.18 0.131 7 180 0.04 0.8 0.157 11369.43 -0.015 8 180 0.05 1 0.170 20302.55 -0.045 9 180 0.06 1.2 0.271 29235.67 0.039 10 180 0.04 1 0.150 16242.04 0.050 11 180 0.05 1.2 0.205 24363.06 0.085 12 180 0.06 0.8 0.206 17054.14 0.029 13 120 0.04 1 0.190 11464.97 0.033 14 120 0.05 1.2 0.172 17197.45 0.048 15 120 0.06 0.8 0.170 12038.22 -0.023 16 150 0.04 1 0.275 14331.21 0.085 17 150 0.05 1.2 0.300 21496.82 0.192 18 150 0.06 0.8 0.300 15047.77 0.130 19 150 0.04 1.2 0.292 17197.45 0.368 20 150 0.05 0.8 0.279 12539.81 0.058 21 150 0.06 1 0.309 21496.82 0.055 22 180 0.04 1.2 0.175 19490.45 0.253 23 180 0.05 0.8 0.163 14211.78 -0.050 24 180 0.06 1 0.227 24363.06 -0.046 25 120 0.04 1.2 0.196 13757.96 0.234 26 120 0.05 0.8 0.181 10031.85 -0.084 27 120 0.06 1 0.161 17197.45 -0.099 in this experiment, the surface roughness value of each experiment was measured 3 times on a renishaw equator 300 cmm high-speed comparative gauge system (figure 3) according to the en iso 4287 standard. the flatness deviation (fl, mm) is measured using a non-contact measurement system (figure 3). according to stn p cen iso/ts 12781-2: 2008 standard, the flatness zone was divided into negative and positive (figure 2) local zones based on the least squares reference plane, which is a plane such that the sum of the squares of the local flatness deviations is minimum. the measured results are summarized in table iv. the material removal rate-mrr (mm 3 /min) of each experiment is calculated by: ��� = �� × �� × � × � × �� (4) where ap is the depth of cut (mm). in this experimental work, ap=10mm for all runs. ar is the width of cut (mm), n is the number of cut flutes (n=3), s is the spindle speed (rpm), and fz is the feed of tooth (mm/tooth). the matrix of the experiment design with the input factors and the response data is presented in table iv. these data were utilized to develop the regression models for ra, mrr, and fl. d. the optimization problem the machining parameters, i.e. cutting speed vc, feed rate fz, and width of cut ar, and their corresponding levels are listed in table iii. the target of this research is to decrease the flatness deviation fl and improve the mrr concerning the predefined ra. consequently, the optimizing issue can be described as (5): engineering, technology & applied science research vol. 13, no. 2, 2023, 10447-10452 10450 www.etasr.com nguyen et al.: multiple response prediction and optimization in thin-walled milling of 6061 … find x={vc, fz, ar} to minimize {ra; fl}, and maximize mrr subjected to 120 ≤ vc ≤ 180 (m/min); 0.04 ≤ fz ≤0.06 (mm/tooth) and 0.8 ≤ ar ≤ 1.2 (mm) (5) to solve this multi-object problem, the dfa was adopted. the desirability package contains s3 classes to optimize multiple variables simultaneously using the dfa of harrington [24-26] (1965) with the functions described in [24, 25]. basically, the method is to translate the functions to a common scale ([0, 1]), combine them using the geometric mean and optimize the overall index. for each function r, an individual "desirability" function is constructed to be high when fr(x) is at the desired level (such as maximum, minimum, or target) and low when the fr(x) is at an unwanted level value. authors in [27] proposed three forms of these functions, corresponding to the type of optimization goal. to maximize fr(x), ����� , ������ are obtained for maximization and minimization purposes, while ��!��"�! represents for the best solution. ����� = # 0 if �� '() < +,-.'�)/01/0 23 if + ≤ �� '() ≤ 51 if �� '() > 5 (6) ����� = # 0 if �� '() > 5,-.'�)/10/1 23 if + ≤ �� '() ≤ 51 if �� '() < + (7) ��!��"�! = ⎩⎪⎨ ⎪⎧ ,-.'�)/0!</0 23= if + ≤ �� '() ≤ >?,-.'�)/1!</1 23� if >? ≤ �� '() ≤ 50 otherwise (8) ii. results and discussion a. regression models the regression models for ra, mrr, and fl were generated using minitab software. equations (9)-(11) show the fully developed regression models. �� = −1.609 + 0.04550no − 38.20�� − 1.066�� −0.000188no� + 173.9��� + 0.2767��� + 0.1307no �� +0.002964no . �� + 2.53�� �� (9) mrr = 16932 − 115.4no − 338641�� − 17516�� −0.0000no� + 0.0000��� + 0.0000��� + 2309no �� +119.43no . �� + 340318�� �� (10) vw = −2.390 + 0.05237no − 33.26�� − 1.267�� −0.000188no� + 465.7��� + 1.470��� + 0.0490no �� +0.00407no . �� − 26.42�� �� (11) to assess the adequacy of these models, analysis of variance (anova) was adopted. the anova was conducted with 95% of confidence and 5% significance. the anova results for the predictive models are presented in tables v-vii. the coefficients of mathematical regression models, including "r 2 ", "adjusted r 2 ," and "predicted r 2 ," reveal the accuracy of the developed models. in this work, the values of "r 2 ", "adjusted r 2 ," and "predicted r 2 ," for ra, mrr, and fl the are fluctuated in the range of [96.66%, 99.93%], [94.89%, 99.89%], and [89.78%, 99.76%] mean a good fitting between the experimental and the predicted values. hence, it is concluded that the developed models of ra, mrr, and fl can be used for predicting the optimal process parameters. table v. anova for the predictive models of ra term df adj ss adj ms f-value p-value regression 9 0.102879 0.011431 54.64 0 vc 1 0.039154 0.039154 187.14 0 fz 1 0.006102 0.006102 29.16 0 ar 1 0.003528 0.003528 16.86 0.001 vc*vc 1 0.079044 0.079044 377.8 0 fz*fz 1 0.001814 0.001814 8.67 0.009 ar*ar 1 0.001452 0.001452 6.94 0.017 vc*fz 1 0.012573 0.012573 60.09 0 vc*ar 1 0.004044 0.004044 19.33 0 fz*ar 1 0.000413 0.000413 1.97 0.178 error 17 0.003557 0.000209 total 26 0.106436 "r 2 "=96.66%, "adjusted r 2 "=94.89% and "predicted r 2 "=89.78% table vi. anova for the predictive models of mrr term df adj ss adj ms f-value p-value regression 9 728005304 80889478 2553.25 0 vc 1 199266 199266 6.29 0.023 fz 1 720212 720212 22.73 0 ar 1 1209228 1209228 38.17 0 vc*vc 1 1999162 1999162 63.1 0 fz*fz 1 0 0 0 1 ar*ar 1 4602114 4602114 145.26 0 vc*fz 1 3998324 3998324 126.21 0 vc*ar 1 6685664 6685664 211.03 0 fz*ar 1 9204227 9204227 290.53 0 error 17 538577 31681 total 26 728543881 "r 2 "=99.93%, "adjusted r 2 "=99.89% and "predicted r 2 "=99.76% table vii. anova for the predictive models of fl term df adj ss adj ms f-value p-value regression 9 0.315328 0.035036 97.42 0 vc 1 0.058999 0.058999 164.04 0 fz 1 0.002633 0.002633 7.32 0.015 ar 1 0.006217 0.006217 17.28 0.001 vc*vc 1 0.08127 0.08127 225.96 0 fz*fz 1 0.013011 0.013011 36.17 0 ar*ar 1 0.03372 0.03372 93.75 0 vc*fz 1 0.001546 0.001546 4.3 0.054 vc*ar 1 0.000111 0.000111 0.31 0.585 fz*ar 1 0.054928 0.054928 152.72 0 error 17 0.006114 0.00036 total 26 0.321442 "r 2 "= 98.10%, "adjusted r 2 "=97.09% and "predicted r 2 "=96.09% b. multiple objective optimization results as mentioned above, the dfa was adopted for solving the multiple objective problem (figure 4). the composite desire values (d) corresponding to 27 experiments were computed using the minitab 19 software with the constrain from (5). the results are shown in table viii. engineering, technology & applied science research vol. 13, no. 2, 2023, 10447-10452 10451 www.etasr.com nguyen et al.: multiple response prediction and optimization in thin-walled milling of 6061 … (a) hold value: ar=1 hold value: fz=0.05 hold value: vc=150 (b) hold value: ar=1 hold value: fz=0.05 hold value: vc=150 (c) hold value: ar=1 hold value: fz=0.05 hold value: vc=150 fig. 4. surface plot of (a) fl, (b) ra, (c) mrr vs vc, fz, ar. table viii. composite desirability value (d) solution vc fz ar fl fit mrr fit ra fit d 1 120 0.060 1.131 -0.07 19829.00 0.145 0.769 2 120 0.060 1.180 -0.04 20596.40 0.149 0.763 3 120 0.060 1.199 -0.03 20866.70 0.151 0.758 4 120 0.060 1.200 -0.03 20879.10 0.151 0.757 5 180 0.058 1.052 -0.04 24881.10 0.223 0.718 6 180 0.060 1.034 -0.04 25165.70 0.233 0.699 7 180 0.060 1.012 -0.04 24533.80 0.230 0.698 8 180 0.060 1.137 0.00 27867.10 0.255 0.662 the higher the value of d, the more optimal the experiment is. in this study, the optimal parameter set vc = 120m/min, fz = 0.06mm, ar = 1.13131mm correspond to ra = 0.144601µm, mrr = 19829cm 3 /min, and fl = -0.00699460mm. comparing the optimization results with the resurged results shown in table i, it is easy to see that the optimization results are quite close to the experiment number 27. however, the difference is that the predicted ar value is larger than the selected ar value, at 1mm and 1.131mm, respectively. this increase in the width of the cut led to an increase in production rate by about 15.30%, from 17197.45 to 19829cm 3 /min. at the same time, the surface roughness value ra decreased by 13.10%, from 0.1613 to 0.1446µm and the fl also decreased by -0.07mm, a decrease of 29.65%. the results of this study show the advantages of dfa in comparison with dcdm. the disadvantage of dcdm is that the optimal parameter set is calculated, ranked, and selected from one of the experimental runs, in this case, experiment number 27. with the dfa method, the optimal parameters do not necessarily coincide with the selected parameters. the comparison results are clearly depicted in table ix. table ix. optimization result comparison cutting parameters responses vc (m/min) fz (mm) ar (mm) ra (µm) mrr (cm3/min) fl (mm) actual value 120 0.06 1 0.1613 17197.45 -0.0995 predicted value 120 0.060 1.131 0.145 19829.00 -0.07 comparison 13.10% 15.30% 29.65% iii. conclusion due to the increasing competitive pressure from the global market, the need to maintain or increase product quality while simultaneously increasing productivity is important. this is a multi-objective optimization problem. in this article, the multiple objective optimization issue in thin-walled milling of 6061 aluminum alloy for reducing flatness deviation fl and surface roughness ra while improving production rate mmr simultaneously, has been addressed. predictive mathematical regression models of the three responses have been developed to model the highly non-linear relations between the cutting parameters (i.e. vc, fz, and ar) and the machining responses. the desirability function approach (dfa) was employed to engineering, technology & applied science research vol. 13, no. 2, 2023, 10447-10452 10452 www.etasr.com nguyen et al.: multiple response prediction and optimization in thin-walled milling of 6061 … generate the optimum parameters. the main results of this work can be concluded, as follows: the "r 2 ", "adjust-r 2 " and "predicted-r 2 " of ra, mrr, and fl fluctuated around 90-99%, illustrating the good relationship between cutting parameters and response. hence, these mathematical regression models could be applied in the actual manufacturing process to predict the cutting parameters set corresponding to the desired response. the obtained optimal cutting parameters set of thin-walled milling of 6061 aluminum alloy processes is (vc=120m/min, fz=0.06mm, and ar=1.13434mm), corresponding to the ra, mrr, and fl values of 0.14269µm, 19614.6mm 3 /min, and -0.0653mm, respectively. the findings in this research work can contribute to a broader understanding of aluminum alloy thin-walled milling and can be extended to research with other materials and machining processes. in future works, other cutting parameters such as tool nose radius, tool coaching material, lubrication method, number of inserts, number of flutes, and other responses including cutting force, cutting variation, tool wear, and tool life will be taken into consideration. acknowledgment this research is supported by the hanoi university of industry (haui). references [1] d. carou and j. p. davis, eds., machining of light alloys: aluminum, titanium, and 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24 may 2022 | accepted: 4 june 2022 abstract-biological brain signals may be used to identify emotions in a variety of ways, with accuracy depended on the methods used for signal processing, feature extraction, feature selection, and classification. the major goal of the current work was to use an adaptive channel selection and classification strategy to improve the effectiveness of emotion detection utilizing brain signals. using different features picked by feature fusion approaches, the accuracy of existing classification models' emotion detection is assessed. statistical modeling is used to determine time-domain and frequency-domain properties. multiclass classification accuracy is examined using neural networks (nns), lasso regression, k-nearest neighbors (knn), support vector machine (svm), and random forest (rf). after performing hyperparameter tuning, a remarkable increase in accuracy is achieved using lasso regression, while rf performed well for all the feature sets. 78.02% and 76.77% accuracy were achieved for a small and noisy 24 feature dataset by lasso regression and rf respectively whereas 76.54% accuracy is achieved by lasso regression with the backward elimination wrapper method. keywords-feature fusion; dnn; lasso regression i. introduction emotion detection is a part of artificial intelligence. it is a multidisciplinary area where the major fields involved are medical signal processing, artificial intelligence, machine learning, and brain-computer interfacing. it presents a collection of emotion recognition study scenarios in the following domains: software engineering, website personalization, education, gaming, and medicine. efforts have been made in recent decades to create new methodologies and techniques for emotion identification. researchers are increasingly interested in detecting human emotions via biological brain signals [1]. researchers have been interested in inventing apps that would allow two individuals to communicate without really interacting. electroencephalography (eeg) headsets are accessible on the market and are inexpensive, allowing the study in this field without having to use complicated brain interfaces. eeg is a reliable and affordable way to measure brain activity. to achieve the criteria of a brain-computer interface (bci), emotion recognition using eeg data requires a sequence of operations to be performed, e.g. removing artifacts from the eeg data, extracting temporal or spectral information from the time or frequency domain of the eeg signal, and finally developing a multi-class classification strategy [2]. the main problem is that the extracted characteristics are calculated using the entire recorded eeg signal sample, which frequently contains incorrect information. as a result, supplementary procedures like choosing electrodes that show a big shift in brain activity during emotional states to accurately identify emotional states and conspicuous feature selection for a more precise conclusion are becoming increasingly critical. experiments demonstrate that including these procedures expands the number of possibilities for testing the system's correctness. in the current study, a multimodal technique is employed to assess system accuracy. techniques such as feature selection and feature fusion are employed [3]. ii. related work earlier research focused on either building feature extraction techniques or evaluating multiple classification models for reliable emotion detection on databases such as deap and seed [1]. it is used to extract characteristics that are constant across all participants from a collection of eeg channels. nns and svm models are extensively used for classification and prediction. knn is the most popular algorithm for testing emotional signals. in the studies mentioned below, work has been done on existing databases. these databases record emotional signals in a controlled environment for a predetermined length of time. it is, however, impossible to record all of the signals in a set time frame. the brain's functioning is complicated and varies from person to person as well as from one emotional state to another. each corresponding author: nisha vishnnupant kimmatkar engineering, technology & applied science research vol. 12, no. 4, 2022, 9012-9017 9013 www.etasr.com kimmatkar & vijaya babu: human emotion detection with electroencephalography signals and … participant has a varied excitation time interval for each emotion. hence the real study of emotional signals acquired in the natural world is envisaged, with a primary focus on large applications [3]. in table i the reviewed related work is summarized. work on self-created databases is required in the current context. in applications such as bci for mentally challenged persons and paralyzed people who can't convey their emotions through words, signals must be collected in the real world rather than in a controlled setting. as a result, research on selfcreated databases including signals acquired in the natural world is expected. a self-created database is employed in this research investigation. the following part discusses the database construction process. to increase accuracy, the feature fusion approach is applied. for accuracy testing, a multimodal approach for multiclass classification is adopted. table i. related work summary reference no. of channels feature extraction algorithm classification models accuracy(%) [4] 10 dwt, principle component analysis svm 91.1 [5] 32 minimum redundancy maximum eelevance (mrmr) svm & rf 60 [6] 5 time-frequency domain features dst 81.64 [7] 32 entropy, time and frequency domain features ann 93.75 [8] 3 probability distribution for wavelet packet coefficients svm 70.5 [9] 32 spectral features dbn 79.2 [10] 32 fusing of 6 statistical features svm 81.87 [11] 14 gabor function and wavelet transform ann 64.87 [11] 10 wtwavelet transform knn 84: arousal, 86:valence [12] adaptive kolmogorov-smirnov (k-s) test svm 80.4: arousal, 71.16: valence [13] adaptive feature fusionstatistical, wavelet energy, wavelet entropy svm, knn, qda 83.8 [1] adaptive ztwbes rnn 89.33 ann: artificial neural network, dwt: discrete wavelet transform, rf: random forest, qda: quadratic discriminant analysis, ztwbes: zero-time windowing based epoch estimation iii. the proposed system the emotive epoc 14 channel headset was utilized for data collection. the experiment used a 120-emotion-signal database that was self-created, with 30 signals from each of the four considered classes (angry, calm, happy, and sad). with proper coverage and electrode configuration, it is possible to rebuild a source model of all-important brain regions and understand how they interact. the sensors are made up of saline-soaked felt pads. in figure 1 the proposed system is shown. the first step is signal acquisition and database creation. fig. 1. the proposed system. a. database creation healthy individuals were chosen based on their willingness to participate, whereas intellectually disabled subjects were picked with their parent's permission. the emotive epoc 14 channel eeg headset is simple to use and comfortable to wear. the training data collection included 22 healthy volunteers (15 females, 7 males) ranging in age from 12 to 70 years old (mean = 35.55, sd = 16.97). prior to their participation, each subject signed an informed consent form. one of the participants suffers from mild autism. she can communicate and convey basic emotions. a total of 120 emotional signals were recorded. each emotion class has 30 emotion signals, which were stored in the emotive cloud and could be used at a later time. participants were given auditory stimuli to choose from in order to generate a calm feeling. anger is elicited by the use of a visual stimulus. self-thoughts are also used to evoke emotion in subjects. some of our former events are strongly embedded in our minds, and revisiting them might elicit the same sort of powerful feeling. thoughts have been found to be a very effective sort of stimulus for producing emotions. a single adc technique and sequential sampling were employed. the rate of sampling was 2048 internal down sampled to 128 fs. the dimension of each recorded file is 41* number of samples * 60s). the files were edited and only the 14 electrode data were saved in .csv format. the dimension of the database is 120*[128*60]*[14]. the dataset comprised of 120 files and 30 emotion signals of each emotion type (angry, calm, happy, and sad). [128*60] rows signals were recorded for 1min at 128 fs, [14]col represents the e1.lectrodes. the signals were preprocessed using filtering. ica is a technique for separating data artifacts (since they are usually independent of each other) [3]. statistical modeling [5] was used to extract 24 characteristics from the database. the feature set's dimensions are 120*24. variance, mean, standard deviation kurtosis, ieeg, skewness eeg synchronization mav (mean absolute value), modified mav type 1, modified mav type 2, simple square integral (ssi), eeg-veeg variance root mean square (rms), absolute standard deviation difference mean2 (dastd), pxx with autoregression, waveform length (wl), band power, engineering, technology & applied science research vol. 12, no. 4, 2022, 9012-9017 9014 www.etasr.com kimmatkar & vijaya babu: human emotion detection with electroencephalography signals and … max pow, max pow index, harmonic distortion, hilbert parameter, power spectral density (psd) [14] characteristics were considered. figure 1 depicts the followed multimodal method. b. feature fusion for feature selection classification models were utilized to assess the accuracy of emotion recognition, with feature selection and feature fusion strategies discussed. 14 * samples wrtr captured in 1 minute and (128*60) feature set file is used. feature selection is done by using filter method, wrapper method, and the embedded method. feature fusion is used on the reduced feature set and tested for rf, knn, svm, dnn, and lasso regression models [15]. for feature selection, filter and wrapper methods were used. as a result, these methods generate a reduced feature set. fig. 2. correlation matrix. 1) filter method this approach filters unnecessary features and selects only a subset of important features. after choosing the characteristics, the model is produced. filtering is done with the pearson correlation matrix. the reduced notable feature set is created using the steps described below. step 1: create a heatmap with pearson correlations for all 24 features. step 2: examine the relationship between the independent variables and the output variable label. step 3: choose characteristics that have a 0.4 or higher correlation with the output variable. the correlation coefficient ranges from -1 to +1. dastd and wl characteristics have pearson correlation coefficients of 0.46 and 0.54 respectively. 2) wrapper method it is a repeated procedure. it requires one machine learning method, which is used as an estimation criterion. based on performance, features might be added or eliminated. this approach is more computationally expensive than the filter method, but it is more accurate. recursive feature elimination and backward elimination are utilized. 3) backward elimination the model is fed with all the potential characteristics. the model is tested every time it is used. worst-performing features are deleted one by one until the model's overall performance is within a reasonable range. by verifying the pvalue, the features are eliminated. if the calculated pvalue is more than 0.05, the feature is excluded from consideration. for linear regression, engineering, technology & applied science research vol. 12, no. 4, 2022, 9012-9017 9015 www.etasr.com kimmatkar & vijaya babu: human emotion detection with electroencephalography signals and … an ols (ordinary least squares) model is utilized. the selected features are: 'mean', 'var', 'skew', 'mav', 'veeg', 'dastd', 'ha', 'hc', 'bandpower']. 4) recursive feature elimination it ranks the features using an accuracy feature ranking approach. the model is created using all 24 characteristics. with 24 features, the linear regression model is utilized. it ranks all the variables from most important to the least. true represents a relevant feature and false represents an irrelevant aspect in the output. the model's accuracy is computed repeatedly for each feature. the optimum amount of characteristics with the best accuracy is chosen. it is done by looping through all the features from 1 to 24, and then selecting the one with the best accuracy. a) feature ranking • optimum number of features: 10 • score with 9 features: 0.54 • index (['stddev', 'var', 'mav', 'veeg', 'rms', 'dastd', 'ha', 'band power', 'hilbert', 'psd'] b) feature fusion the output of the feature selection step is a reduced feature set. in this step, 3 reduced feature sets are created and used to test system performance. the system is trained using a reduced feature set and then accuracy is tested for different classification models [4]. c. multimodal approach the classification algorithms used for testing the accuracy of the feature set [7] are: knn, svm, rf, lasso regression, and multiclass classification using neural networks (dnn) [1]. 1) knn knn is a supervised machine learning algorithm, also known as the lazy learner or non-parametric learning method. it uses feature similarity to forecast the values of new data points, which means a new data point will be assigned a value based on how closely it resembles the points in the training set [4]. it is great for nonlinear data since it makes no assumptions about the data, and it is also great for small datasets [16]. 2) svm the purpose of the svm is to find a hyperplane that differentiates data points in an n-dimensional space. the number of features determines the hyperplane's size. it works well when there is a clear demarcation between the dimensions and when the number of samples is larger than the number of dimensions [9]. when the data set contains additional noise, such as overlapping target classes, it performs poorly [17]. 3) rf it creates decision trees from several samples, using the majority vote for classification and the average for regression. this method employs a meta-approach and is based on ensemble learning. it aims to improve forecast accuracy by merging predictions from various models. it associates decision tree predictions and chooses the best prediction among them. 4) lasso regression it is based on the concepts of shrinkage and l1 regularization, and it employs a procedure in which data values are reduced toward the central tendency and a penalty proportional to the absolute size of coefficients is applied. this regularization results in sparse models with a few coefficients. lasso regression helps feature selection by reducing the magnitude of λ to zero if required. the output depends on the value of λ. the followed algorithmic steps are described below: • importing data set • preprocessing: • making a distinction between dependent and target variables. • fitting the model • model predictions • check the initial score of r square and perform hyperparameter tuning if necessary. after performing hyperparameter tuning, a remarkable increase in accuracy is observed. the hyper parameters are: param = {'alpha': [.00001,0.0001,0.001,0.01,0.1], 'fit_intercept': [true,false], 'normalize': [true,false], 'positive': [true,false], 'selection': ['cyclic','random']}. the best found hyperparameters are: {'alpha': 0.01, 'fit_intercept': true, 'normalize': false, 'positive': false, 'selection': 'random'}. after adjusting the alpha parameter and using the best parameters, the accuracy of the model increased remarkably to 78.02, which is the highest among all the models. d. dnn: multiclass classification using neural networks a) encode the variable output there are 4 alternative numerical values in the output variable. when implementing nns to represent multi-class classification issues, the output attribute must be reshaped from a vector of values for each class. each class's value will be represented in the matrix as a boolean type. this is referred to as "one-hot encoding." it is the process of converting category variables into dummy variables [18]. b) create the neural network model wrapper classes are used to define nns. a rectifier activation function was used in the hidden layer. the output layer must produce 4 output values, 1 for each class, using onehot encoding. the highest output value is used to determine the class. table ii summarizes the network structure of this simple one-layer nn. the softmax activation function is employed in the output layer. the output values are between 0 and 1 and may be used to calculate the expected probability. categorical cross-entropy [10] and adam gradient descent optimization with a logarithmic loss function [19] were used. multi-class cross-entropy loss and leibler kullback divergence loss are used in multi-class classification problems. the default loss function is cross-entropy. in this, each class is given a distinct integer value, which is the preferred loss function under the maximum likelihood inference paradigm. the loss function should be estimated initially and adjusted if necessary. engineering, technology & applied science research vol. 12, no. 4, 2022, 9012-9017 9016 www.etasr.com kimmatkar & vijaya babu: human emotion detection with electroencephalography signals and … table ii. neural network topology feature set feature extraction method topology of layers in dnn 24 feature set actual feature set 24 total inputs → [48 hidden nodes] → 4 outputs accurate24_rf_ fm.csv extracted features after filter method 2 total inputs → [4 hidden nodes] → 4 outputs accurate24rf_ wm_bel.csv extracted features after wrapper method backword elimination 10 total inputs → [20 hidden nodes] → 4 outputs accurate24_rf_ rfe.csv extracted features after wrapper method recursive feature elimination 10 total inputs → [20 hidden nodes] → 4 outputs the average difference between the actual and the anticipated probability distributions is calculated via crossentropy for all classes [20]. a measure of how dissimilar one probability distribution is from another is the leibler kullback divergence. it determines the wasted data (in bits) when the anticipated probability distribution is used to approach the desired target probability distribution. in the training phase, the number of epochs passed was 200, and the batch size was 5 [10]. using the 10-fold cross-technique, the model was evaluated on the dataset, a process that takes around 10s to be concluded, and it provided an object that specifies the assessment of the 10 built models for each of the dataset splits. iv. discussion in this study, features are produced using the feature fusion approach, and multiple classification models are used after parameters are adjusted to attain maximum accuracy. the goal of this research is to get the maximum accuracy possible for the multiclass classification issue with tiny and noisy data sets. for this sort of database, the lasso regression and rf algorithms appear to perform better. table iii. accuracy comparison feature selection method feature fusion dnn lasso regression knn svm rf 24 feature set 'mean', 'std', 'var', 'skew', 'kurtosis', 'ieeg', 'mav', 'mav10, 'mav20, 'ssi', 'veeg', 'rms', 'dastd', 'areg_pxx', 'ha', 'hm', 'hc', 'wl', 'bandpower', 'perodogram1 (maxpow)', 'perodogram2 (max pow index)', 'envelope (harmonic dis)', 'hilbert', 'psd' [3] 29.17 78.02 33.33 44 72.66 filter method wl , dastd 31.67 51.19 63 19.4 66.6 wl 31.67 51.89 63 0 68.44 wrapper method: backward elimination 'mean', 'var', 'skew', 'mav', 'veeg', 'dastd', 'ha', 'hc', 'bandpower','psd' 30.83 76.54 36 25 64.58 wrapper method: rfe 'stddev', 'var', 'mav', 'veeg', 'rms', 'dastd', 'ha', 'bandpower', 'hilbert', 'psd' 15.83 63.46 36 19.4 67.47 fig. 3. the accuracy plot. in table ιιι, the comparison of the accuracy using feature fusion and the multimodal approaches for multiclass classification is presented. in this research study, 24 features are extracted from the database. three feature sets are constructed using the feature fusion approach, which are then utilized to assess the classification accuracy using knn, svm, engineering, technology & applied science research vol. 12, no. 4, 2022, 9012-9017 9017 www.etasr.com kimmatkar & vijaya babu: human emotion detection with electroencephalography signals and … nns, rf, and lasso regression classification models. four feature sets were used to evaluate the performance of the knn method. for the 24 feature set, the greatest accuracy produced by knn was 33.33% for most of the k values and 36% for the feature set generated using the wrapper technique, which is extremely low due to the high dimensional database. it is calculated in a significant way for the feature set produced using the feature selection filter approach. for this small and noisy database, svm and dnn –models did not perform well. rf performed better because it is less prone to overfitting, it is typically resistant to outliers, and can deal with them on its own. after changing the hyperparameters to match the model, lasso regression works well for the 24 feature set and the feature set produced using the wrapper technique. it is quite difficult to acquire high accuracy for a self-created database of signals gathered in natural settings. v. conclusion after changing the hyperparameters for the 24 feature set, lasso regression was found to have the greatest accuracy of 78.02%. the best hyperparameters were adjusted as mentioned above, with the trial and error method. backward elimination of the wrapper approach achieved 76.64% accuracy. for all the feature sets, the rf algorithm worked admirably. when compared to other classification models, the dnn algorithm's accuracy is quite low, and the database's limited size might be the cause. also the svm model did not perform well, because the limits of target classes overlap. the experimental findings show that on small and noisy datasets, lasso regression and rf employing feature selection and feature fusion techniques perform better. institutional review board statement this research study was conducted according to the guidelines of the declaration of helsinki. this research study is not at all being conducted 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[20] d. k. suker, "deep learning cnn for the prediction of grain orientations on ebsd patterns of aa5083 alloy," engineering, technology & applied science research, vol. 12, no. 2, pp. 8393–8401, apr. 2022, https://doi.org/10.48084/etasr.4807. microsoft word etasr_v13_n3_pp10659-10663 engineering, technology & applied science research vol. 13, no. 3, 2023, 10659-10663 10659 www.etasr.com danh & cuong: surface roughness modeling of hard turning 080a67 steel surface roughness modeling of hard turning 080a67 steel bui thanh danh faculty of mechanical engineering, university of transport and communications, vietnam danhdaiduong@utc.edu.vn nguyen van cuong faculty of mechanical engineering, university of transport and communications, vietnam nguyencuong@utc.edu.vn (corresponding author) received: 17 february 2023 | revised: 15 march 2023 | accepted: 17 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5790 abstract surface roughness is an important parameter to evaluate the quality of a machining process in mechanical manufacturing. the construction of a surface roughness model of a machining process is the basis for predicting surface roughness corresponding to each certain case. this paper presents the construction of a surface roughness model in 080a67 steel turning. an experimental process was carried out with a total of 15 experiments, designed according to the box-behnken matrix. the cutting speed, feed rate, and cutting depth were changed in each experiment, and surface roughness values were measured to build a model that showed the mathematical relationship between surface roughness and the three cutting parameters. a second surface roughness model was also constructed using the box-cox transformation. the accuracy of these two models was compared through five coefficients: r 2 , r 2 (pred), r 2 (adj), percentage absolute error (pae), and percentage square error (pse). the results showed that all these coefficients of the model using the box-cox transformation were better than those of the first one. in detail, the values of r 2 , r 2 (pred), r 2 (adj), pae, and pse of the first model were 94.55%, 12.79%, 84.74%, 8.79%, and 1.42%, while for the second model were 99.09%, 85.42%, 97.44%, 2.26%, and 0.18%, respectively, showing that the accuracy of the surface roughness model was improved by using the box-cox transformation. keywords-hard turning; 080a67 steel; surface roughness; box-cox transformation i. introduction steel of the 080a67 type is manufactured using the uk standard and is equivalent to some steel types from other countries, such as 65g steel in bulgaria and poland, 66mn4, ck67 in germany, 65mn in china, 1066, 1566, and g15660 in the usa [1]. this type of steel has the advantage of high wear resistance and is used to manufacture parts that require wear resistance in the cement industry, thermoelectricity, sliding plates, etc. [2]. some studies were carried out to evaluate the characteristics of this steel type such as evaluating the degree of deformation when hot rolling [3], and evaluating friction coefficient [4]. many studies have been carried out to improve the advantages of this type of steel, such as improving wear resistance by the heat treatment method [5-8], improving compressive residual stress in magnetic processing [9], developing technical solutions to produce high-quality products from the casting process [10], investigation of solutions to reduce microcracking on the surface [11], studies on the solutions to increase the hardness of the surface [12-13], etc. this type of steel is increasingly used to manufacture parts with high-quality requirements, which usually need some finished faces to assemble with other parts. therefore, ensuring that the surfaces used for assembling have small roughness is often a requirement when machining this type of steel. however, the number of published studies on surface roughness and, in particular, on the machining process of this type of steel is quite small. the surface roughness with flat grinding was studied in [14], the surface roughness and the productivity of the machining when grinding the outer round was investigated in [15], the change of hardness of the surface layer when grinding was studied in [16-19], the cutting force when milling was evaluated in [20], and the surface hardening phenomenon when spark machining was studied in [21]. the turning method, and the hard turning method in particular, are increasingly used to machine products with high accuracy requirements [22-24]. so, this study aims to cover the lack of published studies on the hard turning of 080a67. while several different criteria can be used to evaluate a turning process, surface roughness is the most frequently used parameter [25-26]. the reason behind this is possibly that surface roughness has a direct influence on wear resistance, fatigue strength, and chemical corrosion resistance of the product surface [27]. in addition, measuring the surface roughness in an experimental process is easier than measuring other cutting parameters such as cutting force, cutting heat, etc. engineering, technology & applied science research vol. 13, no. 3, 2023, 10659-10663 10660 www.etasr.com danh & cuong: surface roughness modeling of hard turning 080a67 steel [28]. a commonly used method to study surface roughness in the turning process is the construction of a model to predict it under certain conditions. however, as the accuracy of the predicted surface roughness results relies on the accuracy of the model, it is necessary to improve it. so, this study also aims to improve the accuracy of the surface roughness model. ii. experimental process and results analysis this study used 080a67 steel in the experimental process. the steel samples had a length and diameter of 300 and 30mm, respectively. the steel workpieces were heat treated through two steps of quenching and tempering. when quenching, the steel workpieces were heated to 830°c and then cooled in an oil medium. when tempering, the steel workpieces were heated to 540°c and then cooled in an oil medium. a metrology vht-a0950d instrument was used to test the hardness of the steel workpieces. all the steel workpieces had a similar hardness, at around 52hrc. table i shows the percentages by mass of the main chemical elements in steel, which were analyzed using a gnr s3 mililab 300 emission spectrometer. table i. chemical elements of 080a67 steel element c si mn p s cr ni % 0.67 0.24 1.02 0.002 0.002 0.24 0.22 a doosan lynx 220l lathe was used for the experiments. a tin-coated kyocera tnmg160404gp was used as a cutting tool in the experimental process. this cutting piece is commonly used in the hard-turning process [29]. the cutting piece parameters, provided by the manufacturer, were: 12⁰ front angle, 6.5° back angle, and 0.4mm tip radius. straight oils were used in the experimental process, mixed with water to a concentration of 4%, and brought into the cutting zone with a flow rate of 8lt/min, and 2.6atm pressure, according to the oil manufacturer. surface roughness was measured by an sj301 gauge. to reduce the influence of random errors on the precision of the experimental process, each experiment was carried out with 3 steel samples, and the surface roughness was measured on each steel sample at least 3 times in succession. so, the surface roughness value in each experiment was the average of at least 9 measurements. the experimental matrix was designed according to the box-behnken form, which is the most commonly used type of matrix to construct the relationship between input and output parameters [30]. the values of cutting speed, feed rate, and cutting depth were altered in each experiment. these parameters can be quickly adjusted by the machine operator [31-32]. three values were chosen for each cutting parameter, corresponding to the encoding levels -1, 0, and 1. table ii shows the parameter values chosen for each level. table iii shows the experiment matrix for the fifteen experiments, built according to the box-behnken method. table ii. values of cutting parameters at levels parameter unit code symbol actual symbol value at levels –1 0 1 cutting speed m/min x1 vc 140 180 220 feed rate mm/tooth x2 fz 0.25 0.45 0.65 depth of cut mm x3 ap 0.3 0.4 0.5 the experimental process was carried out according to the sequence of the experiments, as shown in table iii. the surface roughness of each steel sample was measured at least 3 times, and the average value of the measurements was taken. the average surface roughness of the 3 steel samples is denoted as ra1, ra2, and ra3, respectively. table iii summarizes the mean of the surface roughness in each experiment. table iii. experiment matrix and results exp. code value actual value response x1 x2 x3 v (m/min) fd (mm/rev) ap (mm) ra1 (m) ra2 (m) ra3 (m) ra (m) 1 -1 -1 0 140 0.25 0.4 0.728 0.801 0.865 0.798 2 1 -1 0 220 0.25 0.4 1.055 1.026 1.210 1.097 3 -1 1 0 140 0.65 0.4 0.922 0.966 1.010 0.966 4 1 1 0 220 0.65 0.4 1.547 1.602 1.513 1.554 5 -1 0 -1 140 0.45 0.3 1.392 1.422 1.386 1.400 6 1 0 -1 220 0.45 0.3 2.224 2.432 2.331 2.329 7 -1 0 1 140 0.45 0.5 0.886 0.853 0.874 0.871 8 1 0 1 220 0.45 0.5 1.378 1.378 1.378 1.378 9 0 -1 -1 180 0.25 0.3 1.101 1.082 1.108 1.097 10 0 1 -1 180 0.65 0.3 1.623 1.499 1.387 1.503 11 0 -1 1 180 0.25 0.5 0.801 0.703 0.860 0.788 12 0 1 1 180 0.65 0.5 1.171 1.182 1.160 1.171 13 0 0 0 180 0.45 0.4 0.882 0.884 0.883 0.883 14 0 0 0 180 0.45 0.4 0.879 0.901 0.875 0.885 15 0 0 0 180 0.45 0.4 0.886 0.892 0.883 0.887 the minitab v.16 software was used to analyze the experimental data in table iii. the surface roughness model was constructed according to (1). the commonly used coefficients to evaluate the accuracy of a regression model, such as the surface roughness model, are r2, r2(pred) and r 2(adj). the closer these coefficients are to 1, the higher the accuracy of the regression model [30]. �� = 0.8850 + 0.2903 ∙ � + 0.1767 ∙ � − 0.2651 ∙ � + 0.2867 ∙ �� − 0.0680 ∙ �� + 0.3227 ∙ �� − 0.0722 ∙ � ∙ �− 0.1055 ∙ � ∙ � − 0.0057 ∙ � ∙ � (1) equation (1) had r2, r2(pred) and r2(adj) of 94.55%, 12.79%, and 84.74%, respectively. thus, although r2 has a quite large value, the other coefficients have quite small values, engineering, technology & applied science research vol. 13, no. 3, 2023, 10659-10663 10661 www.etasr.com danh & cuong: surface roughness modeling of hard turning 080a67 steel especially the coefficient r2(pred). this means that if (1) is used to predict the surface roughness, the prediction results will be much different from the experiment results [30]. therefore, the accuracy of the regression model to predict surface roughness should be increased. iii. improving the accuracy of the surface roughness model two commonly used methods to increase the accuracy of regression models are converting data according to box-cox and johnson [33, 34]. in this study, the box-cox transformation was used to improve the precision of the surface roughness model, as it was also used in several studies, such as the 65g steel surface grinding [14], scm435 steel centerless grinding [33], 3x13 steel milling [34], and en 353 steel milling [35]. the condition to perform the box-cox transformation was that the surface roughness values in the experiment were not normally distributed [30]. therefore, it is necessary to check the distribution rules of the surface roughness values when testing. figure 1 shows a distribution chart of surface roughness values. fig. 1. the distribution rule of surface roughness values. in figure 1, the red dots represent the surface roughness values and the blue lines represent the normal distribution. it can be seen that the red dots lie far away from the center line and there are red dots outside the limits of the normal distribution. this proves that the set of surface roughness values was not distributed according to the normal rule. on the other hand, the probability value p-value was 0.021, which is lower than the significance level (the significance level is usually chosen as 0.05). this also confirms that the set of surface roughness values was not distributed according to the normal rule [31], meaning that the set of surface roughness data was eligible to perform the box-cox transformation. figure 2 shows the box-cox transformation graph. it can be noted that the converted coefficient lambda () equals -1.00, which means that the relationship between the surface roughness before and after the transformation is represented by [30]: ����� . � = ��� �� = ��� (2) where ra and ra(box.) are the values of surface roughness before and after the box-cox transformation, respectively. table iv shows the surface roughness values before and after the box-cox transformation. fig. 2. box-cox transformation model of surface roughness table iv. surface roughness values before and after box-cox transformation exp. ra(m) ra(box.) (dimensionless) 1 0.798 1.253 2 1.097 0.912 3 0.966 1.035 4 1.554 0.644 5 1.400 0.714 6 2.329 0.429 7 0.871 1.148 8 1.378 0.726 9 1.097 0.912 10 1.503 0.665 11 0.788 1.269 12 1.171 0.854 13 0.883 1.133 14 0.885 1.130 15 0.887 1.127 fig. 3. distribution rule of surface roughness data after the box-cox transformation. figure 3 shows the distributions of the surface roughness values after the box-cox transformation. it can be noted that all the red dots lie inside the limits of the distribution rule. the probability value p-value was 0.348, which was a lot larger than the significance level. this also confirms that these data were distributed according to the normal rule. engineering, technology & applied science research vol. 13, no. 3, 2023, 10659-10663 10662 www.etasr.com danh & cuong: surface roughness modeling of hard turning 080a67 steel the following equation can be constructed from the surface roughness dataset after the box-cox transformation: �� ��� . � = 1.1299 − 0.1800 ∙ � − 0.1434 ∙ � + 0.1595 ∙ � − 0.1698 ∙ �� + 0.0007 ∙ �� − 0.2057 ∙ �� − 0.0125 ∙ � ∙ � − 0.0343 ∙ � ∙ � − 0.0422 ∙ � ∙ � (3) combining (2) and (3) gives the following surface roughness model: �� = ������ .� (4) where �� ��� . � is given by (3). equation (4) has r2, r2(pred) and r2(adj) coefficients of 99.09%, 85.42%, and 97.44%, respectively. these values are very close to 1, proving that (4) can be used to predict surface roughness with high accuracy. the two models were used to predict surface roughness. note that the model given by (1) is the one without data transformation, and the model given by (4) is the one after the box-cox transformation. the value of surface roughness when predicted using (1) is denoted ra (1), and the surface roughness value predicted using (4) is denoted as ra (2). table v shows the results of surface roughness when testing and predicting according to these two models. table v. surface roughness values when testing and predicting according to 2 models exp. ra (measured) ra (1) (1) ra (2) (4) 1 0.798 0.565 0.786 2 1.097 1.290 1.068 3 0.966 1.062 0.990 4 1.554 1.499 1.600 5 1.400 1.364 1.350 6 2.329 2.155 2.226 7 0.871 1.045 0.886 8 1.378 1.414 1.429 9 1.097 1.222 1.154 10 1.503 1.587 1.506 11 0.788 0.704 0.787 12 1.171 1.046 1.113 13 0.883 0.885 0.885 14 0.885 0.885 0.885 15 0.887 0.885 0.885 pae 8.79% 2.26% pse 1.42% 0.18% the pae and pse parameters were used to evaluate the accuracy of the two models, and the smaller their values, the higher the accuracy of the model. pae and pse were calculated according to [31]: !"# = �$ % ���&'�()*'+�,���-*'+./0'+� ���&'�()*'+� % ∗ 100 (5) !2# = �$ 3���45�67859� − ���:859;<=59�> � ∗ 100 (6) where n is the number of experiments (n=15). equations (5) and (6) were used to calculate pae and pse according to the data in table v, and table vi presents the results. the r2, r2(pred), and r2(adj) of the two models given by (1) and (4) are summarized in this table. table vi. parameters of the surface roughness models model r 2 r 2 (pred) r 2 (adj) pae pse without transformation (1) 94.55% 12.79% 84.74% 8.79% 1.42% using box-cox transformation (4) 99.09% 85.42% 97.44%. 2.26% 0.18% according to the data in table vi, the coefficients r2, r 2(pred), and r2(adj) of the model using the box-cox transformation (4) were higher than those of the model without data transformation (1). on the other hand, both pae and pse of the model using the box-cox transformation were smaller than those of the model without data transformation. this shows that the model with the box-cox transformation had a higher accuracy than the other model. iv. conclusion the construction of a regression model representing the relationship between input and output data is a method usually used in experimental studies in general and in the field of machine building in particular. these regression models are used to predict the output parameters that correspond to certain inputs, and the prediction accuracy relies a lot on the accuracy of the regression model. therefore, the accuracy of the regression model must be improved. this study built a regression model for surface roughness in 080a67 steel hard turning, using the box-cox transformation. accordingly, the surface roughness model when using the box-cox transformation had higher accuracy than the one without data transformation. the improved model, given by (4), provided very high accuracy in surface roughness prediction, as its pae and pse were only 2.26% and 0.18%. in the future, it is necessary to investigate a comparison of the accuracy of surface roughness prediction between the box-cox and johnson transformations. references [1] j. e. bringas, ed., handbook of comparative world steel standards, 2nd ed. w. conshohocken, pa, usa: astm, 2002. 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[35] b. bhardwaj, r. kumar, and p. k. singh, "an improved surface roughness prediction model using box-cox transformation with rsm in end milling of en 353," journal of mechanical science and technology, vol. 28, no. 12, pp. 5149–5157, dec. 2014, https://doi.org/10.1007/ s12206-014-0837-4. microsoft word 4-517-ed2.doc engineering, technology & applied science research vol. 4, no. 6, 2014, 728-733 728 www.etasr.com mitsak et al.: numerical investigation of plastic deformation in two-turn equal channel … numerical investigation of plastic deformation in two-turn equal channel angular extrusion a. mitsak b. aour f. khelil laboratory of applied biomechanics and biomaterials enp oran, algeria ali_mitsak@yahoo.fr laboratory of applied biomechanics and biomaterials enp oran, algeria. ben_aour@hotmail.com laboratory lml of lille university of lille1 france foudil.khelil@univ-lille1.fr abstract-there has been a number of investigations in recent years reporting on the structure and properties of materials deformed to super plastic deformation (spd). during spd new textures can be formed and abnormal characteristics are displayed, attracting a growing research interest. equal channel angular extrusion (ecae) is a method often used to obtain large plastic strains. however, according to experimental results, there is a large tensile stress in the sample during deformation, which may lead in some cases, to cracking in metallic alloys and large curvature in polymeric materials. in order to overcome these drawbacks, the ecae process can be conducted at high temperatures. but this contributes significantly to a decreased level of plastic deformation induced in the sample. hence, a tool with multi-pass seems to be a very appropriate solution. in this paper, a new geometry die composed of two elbows has been simulated by finite element method aiming to provide an insight into the mechanisms of deformation and to determine the optimum geometry of the tool. the numerical results show that the length and the section of the second channel play a significant role on the homogeneity of the plastic strain distribution. it has been found that good homogeneity was obtained when the second channel has the same section as that of the entrance and the exit channels and with a length equal to three times of its width. keywords — ecae; finite element modelling; equivalent plastic strain; friction. i. introduction equal channel angular extrusion (ecae) process is an effective method to improve the physical and mechanical properties of materials without alteration of the geometric shape of the extruded samples. by varying the orientation of the sample between consecutive passes, stylish microstructures can be developed in the material. initially, it was developed for metallic materials [1-5] but more recently, it has been applied to polymeric materials [6-9]. however, according to some obtained results, the main drawbacks of this process are the appearance of the cracking phenomenon in certain metallic alloys [3-5] and obtaining a relatively significant curvature for polymeric materials [7-9]. several analytical approaches have been used to explain the deformation behavior of materials in the ecae process [10-12]. however, due to the complexity of the plastic deformation induced by this process, numerical modeling becomes an indispensable tool to predict the fundamental mechanisms of the plastic yielding occurring in the extruded materials [13-15]. hence, the finite element method (fem) seems to be the most adequate technique to analyze the global and local deformation response of ecae samples, to compare the effects of various parameters, and consequently, to provide fruitful information for optimum process conditions. in order to improve the plastic strain homogeneity and circumvent the disadvantages of the traditional ecae process, an optimization of new die geometry composed of two elbows has been proposed in this present investigation. a diagrammatic representation of this geometry is shown in figure 1 and it may be considered as a two turn equal channel angular extrusion (2ecae), since the sample passes by two elbows in one pass. the various effects of the geometrical parameters of the die (the length and width of the second channel) and the processing conditions (friction) on the material behavior during 2-ecae process have been highlighted. as will be shown later, this new geometry allows us to attain higher deformation values and good homogeneity of the plastic strain distribution than that achieved by using conventional ecae dies. furthermore, the results obtained gave indications on the required forces for extrusion and the design guidelines of the new device of 2ecae to be realized. ii. geometric analysis the principle of 2-ecae process is given in figure 1. it aims to extrude the material in a die made up of two elbows with a channel angle  (equal to 90° in this case) and a corner angle  generally ranging between 0 and 90°. the equivalent plastic strain imposed on a sample as it passes through the first elbow can be estimated using a relationship which depends upon the two angles =1 and =1 as follows [2]: 1 1 1 1 11 2 cot cosec 2 2 2 23 p                       (1) engineering, technology & applied science research vol. 4, no. 6, 2014, 728-733 729 www.etasr.com mitsak et al.: numerical investigation of plastic deformation in two-turn equal channel … where 1 is the internal angle between the two intersecting channels and 1 is the angle defining the outer arc of curvature where the two channels intersect in the first elbow. the total equivalent plastic strain induced after the second pass (second elbow), if the angles are not the same as the first, can be given by: 1 2 1 1 1 1 2 2 2 2 1 2 cot cosec 2 2 2 23 1 2 cot cosec 2 2 2 23 t p p p                                                (2) in the case where 1 = 2 =  and 1 = 2 = , (2) becomes: 2 2 cot cosec 2 2 2 23 t p                       (3) figure 2 shows the variation of the total equivalent plastic strain for different combinations of corners angles 1 and 2 when the channels angles 1=2==90°. it can be seen that the high value of plastic deformation 2.31tp  is obtained when 1=2=0°. then, as the corner angles increase, the plastic deformation decreases until a minimum value of 1.81, which is obtained when 1=2=90°. consequently, to obtain high levels of plastic deformation, it is advised to use corners angles close to 0°. according to the above equations, the plastic strain is dependent only on the two angular quantities of  and  and does not take into account the length of the second channel. moreover, these equations basically assume homogeneous deformation over the whole sample, and do not provide an explanation for the non-uniform deformation induced in the extruded sample. hence, in order to investigate such a nonuniform deformation and optimize the geometrical parameters of the 2-ecae die, the finite element method (fem) seems to be the most adequate tool and was adopted in the following sections. iii. finite element modelling the isothermal two-dimensional finite element simulations under plane-strain conditions are considered. the simulations have been carried out using the finite element software msc.marc© with a mesh of 4400 four-node isoparametric elements for a sample of wtl = 1010110 mm3. in order to obtain a high level of plastic deformation, the elbows angles were taken as 1=2==90° and the two outer corners angles have been fixed to 10°. the friction factor between the die and the sample was assumed to be 0° (i.e. frictionless condition) for the first tests. then, it was changed to highlight its influence. the die and ram were considered as rigid bodies in the modeling. the displacement of 110 mm was assigned to the ram in the extrusion direction with a constant speed of 10-1 mm/s. a radii r=2 mm has been taken at the inner corners. it should be noted that this value has been selected according to a study on the effect of the inner radius described in [14]. the sample behavior was considered as being elastic perfectly plastic. in order to control the plastic strain distribution, the selected cross-section was taken at 20 mm below the second inner corner (see figure 3). iv. results and discussion a. equivalent plastic strain distribution in ecae process the homogeneity of the plastic strain distribution in the bulk material during successive passes is very important. the aim of this section is to determine the optimal conditions which allow us to improve the homogeneity of the plastic strain distribution in terms of width and length of the second channel for the two-elbows device. figure 4 shows the plastic strain distribution for six different lengths l={10, 15, 20, 30 and 50 mm} with a section of w×t=10×10 mm2 and an inner corner radii of 2 mm. it can be observed that the plastic strain is not uniform along the samples width during the first pass. however, in the second pass, the homogeneity of the plastic distribution is relatively improved except the case of l=10 mm. this can be attributed to the vacuum created at the outer corner of the second elbow. for more details, we have shown in figure 5, the distribution of the equivalent plastic strain in terms of the distance from the bottom along the selected cross-section of the sample for each width with different lengths of the second channel. it can be seen that the best homogeneity of the plastic strain distribution was obtained with a length of 30 mm and a width of 10 mm, which is the same of those of the entrance and the exit channels. moreover, one can note that the maximum heterogeneous plastic deformation is always obtained with a length of 10 mm regardless the width of the second channel. fig. 1. schematic illustration of two turn equal channel angular extrusion process. engineering, technology & applied science research vol. 4, no. 6, 2014, 728-733 730 www.etasr.com mitsak et al.: numerical investigation of plastic deformation in two-turn equal channel … 0 20 40 60 80 1.8 1.9 2.0 2.1 2.2 2.3 0 20 40 60 80 e q u iv a le n t p la st ic s tr a in corne r angle phi1 c o rn e r a n g le p h i2 1.800 1.869 1.938 2.006 2.075 2.144 2.213 2.281 2.350 fig. 2. variation of the total equivalent plastic strain for different combinations of corners angles when the elbows angles 1 = 2 =  = 90°. fig. 3. illustration of the finite element mesh of the sample and the selected cross-section for the measurement. fig. 4. equivalent plastic strain contours of the samples for different lengths b. evolution of the pressing force the magnitude and distribution of plastic strain in the sample can be seen as key parameters for the ecae process. the magnitude of the pressing force required to extrude the material defines the practical limit of the extrusion tool. the numerical results of the pressing force required for extrusion were calculated from the nodal forces in the top of the sample. this force is depicted versus time in figure 6 for different widths (w) and lengths (l) of the second channel. in general, at the beginning of the extrusion, the pressing force starts to increase quickly as soon as it contacts the first outer corner of the second channel. at this level, there will be initiation and growth of the shear band until the sample head crosses entirely the first elbow (up to the stability of the material flow). the first plateau of the curve corresponds to the steady state of the plastic flow for the first pass. it should be noted that the length of this plateau increases with the increase of the length of the second channel. the second increase in the pressing force will take place when the sample comes into contact with the second elbow. after it crosses the second plastic deformation zone, a second plateau with a slight undulation is observed. this can be attributed to the interaction between the plastic deformations induced by the both elbows of the tool. in the case of different widths with a fixed length of 30 mm (figure 6a), it can be seen that the pressed force increases rapidly when the width is small and the force required for the second pass is approximately two times the force of the first pass. in general, a slight influence of the width on the maximum required force (which is about 3000 n) is noticed. however, in the case of different lengths with a fixed width of 10 mm (figure 6b), it can be observed that the extrusion force increases quickly when the length is small and the force required for the second pass is slightly higher than twice the force of the first pass except for that of l=10 mm, in which, a value of 2400 n is recorded. in general, the maximum required force for different lengths does not exceed 3000 n. engineering, technology & applied science research vol. 4, no. 6, 2014, 728-733 731 www.etasr.com mitsak et al.: numerical investigation of plastic deformation in two-turn equal channel … (a) w=7 mm (b) w=8 mm (c) w=9 mm (d) w=10 mm (e) w=12 mm fig. 5. influence of the length of the second channel on the distribution of the plastic strain for different values of widths (a) (b) fig. 6. variation of pressing force for different (a) widths with l=30 mm and (b) lengths with d=10 mm engineering, technology & applied science research vol. 4, no. 6, 2014, 728-733 732 www.etasr.com mitsak et al.: numerical investigation of plastic deformation in two-turn equal channel … c. variation of equivalent plastic strain rate in order to reveal the spatial variation of plastic strain and the trends in the degree of in-homogeneity originated in plastic deformation zone (pdz) development, the strain rate distribution within the first and the second elbow is considered when l=30 mm for w={7, 10 and 12 mm} (figure 7). it can be seen that the best results were obtained at the second pass for w=10 mm. to confirm this result, we plotted (figure 8), the maximum difference in equivalent plastic strain rate in the case of the first pass and the second pass. the values are given for top, middle and bottom material points (1, 2 and 3) as shown in figure 7. it can be seen that the minimum difference in the equivalent plastic strain rate was obtained for a width (of the second channel) equal to 30 mm. fig. 7. variation of equivalent plastic strain rate for l=30mm and w={7, 10 and 12 mm} (a) first pass (b) second pass (c) max. difference in  . fig. 8. variation of equivalent plastic strain rate in the case of (a) first pass, (b) second pass and (c) the maximum difference in equivalent plastic strain rate. d. effect of friction in above sections, we have assumed that the friction between the sample and the tool walls is negligible (i.e. frictionless condition). in this section, the friction effects on the equivalent plastic strain distribution and the pressing force are investigated on the optimized geometry of 2-ecae tool (with w=10 mm and l=30 mm). the friction between the tool and the sample is modeled using coulomb friction law. the computations have been performed with three friction coefficients f={0.2, 0.3 and 0.5}. figure 9a shows the plastic strain distribution across the width of the sample for different friction conditions. it can be seen that the friction coefficients influence slightly the homogeneity and the magnitude of the equivalent plastic strain. this can be attributed to the perfectly plastic behavior of the considered material and to the tool geometry which improves the flow capability of the material and hence, weakens the friction effect. it should be noted however, that the extrusion force may not be independent of friction, even though the strain clearly is. figure 9b shows the friction effect on the actual values of the pressing force required for extrusion. it can be noted that the maximum force required at each friction coefficient is approximately 3000 n (for f=0), 3350 n (for f=0.2), 3620 n (for f=0.3) and 4300 n (for f=0.5). one can observe that the friction plays a significant role on the magnitude of the force required for extrusion. indeed, the difference between the forces required for extrusion with significant (f=0.5) and neglected frictions can reach about 50%. therefore, in order to reduce the friction effect and the pressing force required for extrusion, it is better to conduct the 2-ecae process with an appropriate lubricant. v. conclusion in this present study, the finite element method was used to provide fruitful information on the plastic strain distribution in the extruded material using a two turn ecae die. from a broader perspective, it can be understood that the deformation is more complicated with two turn 90° die compared to conventional ecae die, and so are the plastic strain behaviors. it was found that the length and the section of the second channel play a significant role on the homogeneity of the plastic strain distribution and the pressing force required for material engineering, technology & applied science research vol. 4, no. 6, 2014, 728-733 733 www.etasr.com mitsak et al.: numerical investigation of plastic deformation in two-turn equal channel … extrusion. we noticed that the minimal force was obtained by the minimum length of the second channel (l = 10 mm). however, the best homogeneity of plastic deformation was obtained for a die with equal sections and a length of 30 mm for the second channel. a slight sensitivity of plastic strain distribution to friction conditions between samples and die was indicated. to reduce the friction effect on the magnitude of the pressing force, it is advised to use an appropriate lubricant during the process. furthermore, it is worth noting that by using the two-turn channels the plastic strain in one pass becomes double and the productivity of the ecae process increases enormously. finally, in order to take advantage of this optimized 2-ecae process, it is essential to combine the modeling analysis of the deformation behavior of samples with experimental tests. hence, a new ecae die with the proposed geometry is to be manufactured in the near future, in order to obtain experimental data on the microstructural and mechanical aspects.   0 0.5 1 1.5 2 2.5 3 0 2 4 6 8 10 dist ance from t he bot t om (mm) e q u iv al en t p la st ic s tr ai n f = 0.0 f = 0.2 f = 0.3 f = 0.5 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 0 200 400 600 800 1000 1200 t ime (s) p re ss in g f o rc e (n ) f = 0.0 f = 0.2 f = 0.3 f = 0.5 fig. 9. effect of the friction sample/die channels on the evolution of (a) the equivalent plastic strain and (b) the pressing force references [1] v. m. segal, “materials processing by simple shear”, materials science and engineering:a, vol. 197, no. 2, pp. 157-164, 1995 [2] y. iwahashi, j. wang, z. horita, m. nemoto, t. g. langdon, “principle of 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“finite element analysis of plastic strain distribution in multi-pass ecae process of high density polyethylene”, journal of manufacturing science and engineering,vol. 131, no. 3, art. no. 031016 , 2009 (a) (b) microsoft word etasr_v12_n6_pp9546-9550 engineering, technology & applied science research vol. 12, no. 6, 2022, 9546-9550 9546 www.etasr.com hellati & boufassa: evaluation of the role of ethylene vinyl acetate on the thermo-mechanical … evaluation of the role of ethylene vinyl acetate on the thermo-mechanical properties of pet/hdpe blends abdelhak hellati faculty of science and technology mohamed bachir el ibrahimi university bordj bou arreridj, algeria abdelhak.hellati@univ-bba.dz samia boufassa faculty of science and technology mohamed bachir el ibrahimi university bordj bou arreridj, algeria samia.boufassa@univ-bba.dz received: 5 september 2022 | revised: 15 september 2022 | accepted: 17 september 2022 abstract-in this paper, blends of recycled polyethylene terephthalate (r-pet) and high-density polyethylene (hdpe) with and without a compatibilizer were prepared using a brabender haake rheocord at 270°c and 32rpm. ethylene vinyl acetate was chosen as the compatibilizer and its proportion was set to 5, 7, and 10 wt%. the thermal properties and crystallization behavior were determined by differential scanning calorimetry (dsc). micromechanical properties were also investigated using a vickers microindentation tester. the dsc analysis indicates that the melting temperature of r-pet and hdpe in all the blends, compatibilized and uncompatibilized, remains constant and almost the same as those of the pure component. on the other hand, it is shown that the degree of crystallinity of hdpe in the blends calculated by dsc depends on the composition of the polymeric mixture. however, the hardness (h) decreases with increasing r-pet content until 50/50 composition of r-pet/hdpe is reached, whereas for larger r-pet content values, h increases. the same trend was obtained with the addition of the compatibilizer. keywords-recycled polyethelene terephtalate; dsc; hardness; compatibilization i. introduction recycling plastic waste not only preserves energy and raw resources but also provides an option of plastic waste disposal [1-3]. for both economic and environmental reasons, the interest in recycling polymeric materials has significantly increased over the last few decades [4]. recycled polymers, however, are subjected throughout thermal and mechanical processes that result in structural and morphological changes, which in turn have an impact on the material qualities. blending recycled polymers with unmodified polymers could be an approach to enhance their properties. in practice, formulating polymer blends is a viable method for developing materials with relatively new combinations of specified features. an important portion of post-consumer waste is made up of high density polyethylene (hdpe) and polyethylene terephthalate (pet), which are widely utilized in the packaging of consumer and industrial items. due to the unique combination of its physical and mechanical properties, which include great thermal resistance, strong fatigue resistance, and good solvent resistance, pet has revolutionized the globe with its use [5, 6]. on the other hand, hdpe, due to its wide use in the packaging industry, contributes greatly to environmental degradation [7], in the light of the structural considerations by the absence of specific interactions and according to [8-10] affirming the noncompatibility of pet with polyolefins. due to the poor mechanical characteristics of pet/pe blends, compatibilizers must be used in order to decrease interfacial tension, which in turn increases morphological stability and interfacial adhesion. the study of the binary pet/hdpe polymeric system with the use of compatibilizing agents has been the subject of several research works. among the most commonly used compatibilizers in hdpe/pet blending systems are graft copolymers containing reactive maleic anhydride (ma), functional groups such as ma-grafted polyethylene (pe-g-ma) [11, 12], hdpe-g-ma [13], and maleic anhydride-grafted styrene-ethylene-butene copolymer (sebs-g-ma) [14]. another group of compatibilizers often used in research are the random copolymers containing gma, such as hdpe-g-gma [15], ethylene-glycidyl methacrylate copolymer (e-gma) [16], ethylene ethyl-glycidyl methacrylate (e-ea-gma) [15], and ethylene butyl acrylate-glycidyl methacrylate (eba-gma) [17]. other possibilities that are also promising have been investigated, such as compatibilizing the pet/hdpe system with an epoxy chain extender [18]. the indentation test is one of the easiest methods of determining a material's micromechanical characteristics [19, 20]. this method has been successfully used in a wide range of systems and is extremely sensitive to changes in the morphology and microstructure of polymers. in one of our previous research works [21], we investigated how combining clay and a compatibilizer sebs-mah affected the microindentation hardness (h) of pet/hdpe. the objective of the current study is to investigate the rheological, thermal, and mechanical properties of recycled corresponding author: abdelhak hellati engineering, technology & applied science research vol. 12, no. 6, 2022, 9546-9550 9547 www.etasr.com hellati & boufassa: evaluation of the role of ethylene vinyl acetate on the thermo-mechanical … pet (r-pet) and hdpe blends as a function of their composition, compatibilized with ethylene vinyl acetate (eva). ii. materials and methods the following materials were used in this investigation: recycled r-pet bottles from bangkok polyester public co., bangkok (thailand), commercial grade hdpe alcudia 6006 (repsol) with melt flow index (mfi): 0.56g/10 min. the eva used is ul00218ccn from exon chemicals with an mfi of 1.5g/10 min. before blending, the r-pet pellets were dried in vacuum at 105°c for 16h. the dried r-pet pellets were dry-mixed with the hdpe pellets in the following weight ratios: 25/75, 50/50, and 75/25, the blends were prepared in a brabender haake rheocord type m, at 270°c and 32rpm in two steps. at first, the r-pet was fed into the chamber, and once it was melted, the hdpe and the eva compatibilizer were added. from the preceding blends, films were prepared by compression molding in a 7102 zwick machine (ulm, germany), at a pressure of 150kg/cm 2 . the compression was performed at 275°c for a duration of 6min (4min for preheating and 2min for compression). a zwick universal testing machine (utm) was used to study the tensile properties of the blends as per astm d 638 standard. the crosshead speed was 50mm/min. the thermal study was performed with the help of a perkin elmer (norwalk, connecticut, usa) dsc-7 differential scanning calorimetry (dsc) instrument in an inert n2 atmosphere. the weights of the samples were 5–10mg. the studied temperature range was 50–300°c. the heating rate was 10°c/min. the crystallinity measured by dsc ( ���� ) was derived from the melting enthalpy obtained by dsc with the following expression: ���� = ∆�� ∆� � (1) where ∆�� and ∆� are the experimental melting enthalpy and the melting enthalpy for an infinitely thick crystal, respectively. for pet, the ∆� used was 140.1j/g [21] and for hdpe 293.86j/g [22]. microhardness h was determined at room temperature with a leitz (wetzlar, germany) microindentation tester with a square-based diamond indenter. the h value was derived from the residual projected area of indentation according to the following expression [23]: � = � ��� (2) where d is the length of the impression diagonal (m), p is the contact load applied (n), and k is a geometrical factor equal to 1.854. loads of 0.5 and 1n were applied. the loading cycle was 0.1min. ten indentations were performed on the surface of each sample, and the results were averaged. iii. results and discussion figure 1 shows the variation of the equilibrium torque as a function of the % r-pet in the blends. it was found that the torque of the blends without eva decreases for up to a 50% increase of the amount of r-pet. beyond this threshold, the torque values stabilize. the same trend was observed with the addition of eva to the different blends. it was observed that the r-pet/hdpe (50/50) blends show the lowest torque values for all formulations with and without eva. this can be explained by the large contact area at equivolume percentage between the two polymers, thus reducing the transformation energy of the blends. fig. 1. variation of the equilibrium torque as a function r-pet percentage. fig. 2. effect of % eva on the equilibrium torque. the change in equilibrium torque was displayed as a function of % eva in order to visualize the impact of the addition of eva on the r-pet/hdpe (50/50) blends (see figure 2). it was found that the torque increases with the addition of eva up to 5% indicating that there may have been interactions between the polymers, which increase the flow resistance. further, the torque decreases with increasing eva content, which is probably due to the increase in the free volume created by the eva. it was also noted from the results of the mfi (not shown here) that the mfi increases with the increasing percentage of the r-pet in the blends. this increase is not too significant at low concentrations of r-pet, but it is noticeable at high concentrations. it was also noted that the addition of eva affects both polymers in a significant degree, slightly decreasing the mfi of hdpe and acting as a plasticizer for r-pet, while the blend values remain very complex. however, the values of the blends of r-pet/hdpe 50/50 concentration are the lowest for all formulations with eva compared to the mfi values without eva, showing a resistance to flow, confirming the equilibrium torque results. figure 3 shows the variation of stress at break as a function of the incorporation rate of r-pet with and without the addition of eva. engineering, technology & applied science research vol. 12, no. 6, 2022, 9546-9550 9548 www.etasr.com hellati & boufassa: evaluation of the role of ethylene vinyl acetate on the thermo-mechanical … the stress at break values of r-pet are higher than that of hdpe while their blends show lower values than those of homopolymers. this can be explained by the dimixture between these two polymeric phases due to their incompatibility. it should be also noted that the stress values of the r-pet/hdpe 75/25 blends are very close to those of the greater amount of component, i.e. r-pet, while the rpet/hdpe 25/75 blend has a stress value close to that of hdpe. thus, the minor component has a dispersed spherical morphology in the major part and therefore the properties of the blends are those of the high concentration polymer as it absorbs all the stresses when subjected to a load or force. with the addition of eva, the results are better. an addition of 5% eva improves the stress at break of the blends up to 10%. this rise is caused by a decrease in interfacial tension, which in turn improves the adhesion between the two phases of the individual polymers. as a result, eva has reduced the phase border energy, increasing the phase boundary area. the greater the phase boundary area, the more effectively energy can be transferred from one phase to another, improving the mechanical characteristics. fig. 3. effect of the concentration of the eva on the stress at break of the r-pet/hdpe blends. fig. 4. effect of the concentration of the eva on the elongation at break of the r-pet/hdpe blends. the incompatibility of the r-pet blends with the hdpe of the binary blends without eva is reflected much more in the elongation at break (figure 4), where the values obtained are significantly lower than those of the homopolymers for all compositions. the calorimeters limit such resolutions and the tg of one of the components of the mixture (hdpe) is below 0°c. on the other hand, the glass transition temperature of rpet, which is around 70-80°c, was not detected in some thermograms, perhaps due to the presence of hdpe in the compositions and the melting temperature tm of the hdpe. authors in [24] were able to detect the tg of r-pet in rpet/pp blends of 75/25 composition and this temperature was almost the same as that of pure r-pet. therefore, we limited ourselves to the study of the melting temperature and the determination of the crystallinity. the thermograms in figures 5, 6 reveal that the tm values of both components were nearly constant throughout all of the compositions and were the same as those of the pure polymers. tm = 122–131°c for hdpe and 241–249°c for pet. as a result, the blending method had little effect on the cristal thikness (lc) of the components. fig. 5. dsc thermograms of neat polymers. fig. 6. dsc thermograms of the r-pet/hdpe (50/50) blends with and without eva. the thomson-gibbs equation was employed to determine the lc value of each component. consequently, the lc value calculated was 25nm and 14nm for pet and hdpe respectively. the crystallization temperatures for the r-pet component were found to have somewhat decreased values. the crystallinity decreased as the r-pet level increased for all compositions (pure blends and blends with compatibilizer). engineering, technology & applied science research vol. 12, no. 6, 2022, 9546-9550 9549 www.etasr.com hellati & boufassa: evaluation of the role of ethylene vinyl acetate on the thermo-mechanical … figure 7 shows the h of the various blends as a function of the r-pet content. the h's additivity behavior is depicted as a straight line. it is evident from the plot that neither the uncompatibilized nor compatibilized blends with eva respect the additivity law of a binary blend as a function of composition. with increasing pet content, the blends became harder and deviated from linearity. eva caused a reduction in h, which was more evident as the compatibilizer concentration increased. according to the two-phase model, the h of a semicrystalline polymer can be described by [22]: � = ������ ∅� + ��� ���� ����� + �� ���� �1 − � !�1 − ∅ (3) equation (3) considers the compositions of the blends as well as the crystalline hc and amorphous ha hardness of each individual component. the h values for the blends with eva were noticeably lower than those obtained from the additivity law in accordance with (3). it is evident that the compatibilizer's two primary effects on these blends were a decrease in their crystallinity and a concurrent decrease in their hardness. table i. pure r-pet/hdpe blends and blends with eva composition hdpe crystallinity (%) tm (°c) r-pet tm (°c) hdpe r-pet.hdpe (100/0) 0 249 129 r-pet.hdpe (75/25) 0.15 248 130 r-pet.hdpe (50/50) 0.23 249 127 r-pet.hdpe (25/75) 0.49 247 130 r-pet.hdpe (0/100) 0.53 247 129 r-pet.hdpe/eva(100/0/5) 0 248 126 r-pet.hdpe/eva (75/25/5) 0.09 249 128 r-pet.hdpe/eva (50/50/5) 0.08 248 129 r-pet.hdpe/eva (25/75/5) 0.12 246 129 r-pet.hdpe/eva (0/100/5) 0.23 249 130 r-pet.hdpe/eva(100/0/7) 0 248 129 r-pet.hdpe/eva(75/25/7) 0.09 248 127 r-pet.hdpe/eva (50/50/7) 0.03 249 128 r-pet.hdpe/eva (25/75/7) 0.09 246 130 r-pet.hdpe/eva (0/100/7) 0.10 248 129 r-pet.hdpe/eva(100/0/10) 0 246 127 r-pet.hdpe/eva(75/25/10) 0.10 249 129 r-pet.hdpe/eva (50/50/10) 0.18 248 127 r-pet.hdpe/eva (25/75/10) 0.10 247 129 r-pet.hdpe/eva (0/100/10) 0.12 249 128 fig. 7. hardness dependance on the r-pet content with and without eva. iv. conclusion it is evident from the obtained results that pet was incompatible with hdpe, but the presence of eva as a compatibilizer allowed combinations of these polymers. the compatibilization of blends with additional small quantities of eva in one processing step is an interesting proposal, particularly for recycled blends, because it does not require prior expensive synthesis and leads to better results. the rpet/hdpe 50/50 blends show the lowest torque values 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[24] r. s. porter and l.-h. wang, "compatibility and transesterification in binary polymer blends," polymer, vol. 33, no. 10, pp. 2019–2030, jan. 1992, https://doi.org/10.1016/0032-3861(92)90866-u. microsoft word etasr_v13_n1_pp10100-10107 engineering, technology & applied science research vol. 13, no. 1, 2023, 10100-10107 10100 www.etasr.com le et al.: building an application that reads secure information stored on the chip of the citizen … building an application that reads secure information stored on the chip of the citizen identity card in vietnam van-hoan le weapon institute, vietnam hoanle.aiot@gmail.com nhu-quynh luc academy of cryptography techniques, vietnam quynhln@actvn.edu.vn (corresponding author) toan thanh dao university of transport and communications, vietnam daotoan@utc.edu.vn quang-trung do academy of cryptography techniques, vietnam trungdq1980@actvn.edu.vn received: 29 november 2022 | revised: 24 december 2022 | accepted: 31 december 2022 abstract reading the information on the cic/passport is very meaningful in serving the life activities of citizens in vietnam and of foreign citizens visiting vietnam. this research is based on the operating modes, such as bac, face, and eac to read the data contained in the chip put on the citizen identity card (cic) out securely. specifically, the authors used the bac mode to perform safe data reading from the cic’s chip. bac mode uses 3des and sha1 algorithms to encrypt data to ensure security, so when the data are transmitted from the chip they are encrypted and decryption is performed by the application. in this paper, a complete application has been built for reading personal information stored securely on cic. this application is built based on the bac reading mode corresponding to cic in vietnam and meets the requirements of the icao 9303 standard, so it is able to read passports or cics of other countries that use this standard. the performance of this application when reading data stored on fields dg1, dg2, and dg13 is improved with a speed of about 1.2s 1.3s for all 3 data fields. keywords-bac; eac; pace; 3des; mrz; sha; digital signature i. introduction smart card technology was first proposed in 1977 [1]. during the '90s, there was an explosion in smart card technology in europe with the appearance of sims (in gsm devices) and the international payment systems mastercard, visa, and euro-pay [2-4]. in 1994, the emv system (euro-pay, mastercard, visa) was widely used in many countries [5, 6]. currently, smart cards are applied in many fields [7]. physically, the smart card is compact in size and embedded with an integrated circuit to control access to resources [4, 8]. communication between the smart card and the card reader is direct physical contact (contact smartcard) or through shortrange wireless connection such as radio frequency identification (contactless smartcard) [8-10]. operating systems designed for smart cards can provide personal identification, authentication, data storage, and application processing [9, 11, 12]. smart cards using chips have very high reliability and safety for practical applications because some security algorithms and biometric features are installed [13-15]. smart card technology with security is applied to digital id cards (e-passport) as legal proof for different services in many countries [13, 16-18]. in vietnam, the government promulgated the decree 577 on id cards and regulations on issuance of id cards in 1957, to engineering, technology & applied science research vol. 13, no. 1, 2023, 10100-10107 10101 www.etasr.com le et al.: building an application that reads secure information stored on the chip of the citizen … help citizens facilitate daily transactions [19]. after a while, this id card showed some disadvantages: it can be faked, many people share the same number of id cards, and the information on the id card is lost after a period of use. currently, with the trend of global digital transformation, the government of vietnam has launched a chip-based cic to store and secure user information [20], in which, if the data retrieved in the chip are exactly the same as the data recorded on the card, the user information is valid [21]. moreover, cic with chips have many other advantages such as making international, online, and digital transactions [22]. cics with chip in vietnam are manufactured based on smart card technology in compliance with icao 9303 [22, 23]. in particular, the chip used in cic has built-in cryptographic solutions to secure personal data, ensuring that information is safe and reliably authenticated. according to icao 9303, the access process to read security information stored on the cic’s chip operates in three modes: bac (basic access control), pace (password authenticated connection establishment), and eac (extended access control) [17, 22-23]. the command architecture used is the apdu (application protocol data unit) protocol [7, 21, 24]. data are stored and organized on the chip according to icao 9303 [22, 25], iso/iec 144434 [26], and iso/iec 7816-4:2013 [27] standards. in vietnam, a new chip-based cic is going to be deployed in the community in 2022. there are almost no studies related to the reading of the information contained in the cic/passport chip. almost every citizen's transactions related to finance (such as withdrawing money from an atm, buying and selling online, inter-bank financial transactions, etc.) and activities in life are related to the cic/passport. therefore, reading the information on the cic/passport will make the transaction process between citizens, government agencies, and service providers much more convenient. in this article, an application that can read security information stored on the dg1, dg2, and dg13 partitions of the cic’s chip has been built and is discussed. ii. related work a. the physical surface of the cic figure 1 shows the physical surface (front and back) design of the cic. the information recorded on cic includes full name, date of birth, expiration date, gender, hometown, portrait, and country. the back side has the information on the relevant characteristics of the citizen. the mrz information area recorded on the back of the cic is an area used to be read by a machine, facilitating inspection and reducing execution time in administrative procedures [25]. in addition, mrz also provides the ability to verify information in the viz. mrz is formatted according to icao 9303 standard to ensure machine readability in different countries. therefore, ocr-b font is used to store data in mrz [25]. the hardware design of the chip id card is organized into two main parts: power reserve and main card. in particular, the power reserve helps cic collect and reserve energy to ensure that the chip on cic works when performing transactions related to the cic. the main card part consists of the rfid chip, the cic chip, antenna, and integrated circuit. the rfid chip is in charge of receiving power and making the connection with the antenna. the data will be transmitted through the antenna and if encryption or decryption is needed, the rfid chip will make the connection and perform encryption and decryption with the cic chip. the cic chip performs the main job of executing cryptographic algorithms and communicating with the rfid chip to transmit information securely and store encrypted personal information. the cic chip is connected to the power source to ensure the energy used to store the password key and id of the card when the power is not directly supplied. fig. 1. (a) front side and (b) back side (b) of the cic. b. file organization on the operating system in the chip of the cic according to the icao standard [19, 20], the data in the chip of cic are in a hierarchical form. first, there is the root directory (master file -mf) and then the dedicated directory (dedicated file df), and finally the elementary files (ef). the root directory of the cic is divided into 2 dfs and 3 efs, in which future application is a dedicated directory for future development, ef.cardaccess is the elementary file used for pace mode access, ef.cardsecurity is the elementary file used for pace mode access. emrtd is a dedicated directory that stores the basic data files of each citizen. this is the most important folder of the cic because all user information will be located in there. the emrtd stores basic files, also known as data partitions and is described according to the international standards icao 9303 for cic/e-passport. citizens' data are stored in basic files in the emrtd application directory including ef.com, ef.sod, and dg1-16. ef.com stores unicode version information and a list of data groups available in the cic, dg1 stores individual basic details (mrz), dg2 stores citizens' facial images, dg3 stores the fingerprint, dg4 stores an iris picture, dg5 stores features of the face, dg6 is expanded to store information that will be added later, dg7 stores citizen's signature, dg8, dg9, dg10, dg11 are currently not used, dg12 stores supporting information, dg13, dg16 store citizen-related information, dg14 is used for the eac access mechanism, dg15 stores the public key, and ef.sod stores the hash value of each field. c. communication between cic and the computer the computer is connected to the card reader via a serial port, usb, or bluetooth to read the card data through either contact or contactless communication. after the cic is inserted into the slot of the card reader, the computer connected to the card reader will detect the device through the atr message sent from the cic. after receiving the card, the computer and the card establish a connection and select the protocol for data transmission (tapdu). when the data transfer protocol is engineering, technology & applied science research vol. 13, no. 1, 2023, 10100-10107 10102 www.etasr.com le et al.: building an application that reads secure information stored on the chip of the citizen … selected, the process of sending and receiving data between the computer and the card is done through apdu commands. when the computer sends the apdu command to the card, the card will receive the command and send a response back to the computer. finally, after the successful data exchange, the cic is removed from the slot. the computer will detect the discarded device through the card reader. fig. 2. reading cic data with bac, face, and eac modes. d. data reading modes the read access process of the cic chip includes three secure access modes, each of them determining the data partitions allowed to be accessed. the cic access modes are bac, pace, and eac [22, 24, 25]. the bac mode ensures that only authorized parties have access to read the data. the pace mode implements password-based access and diffiehellman key agreement. the password used for pace depends on the digital certificate of the cic, using aes or 3des algorithms to encrypt and authenticate the data [28, 29]. this mode allows reading, similar to bac mode, the user's information data including name, date of birth, card number, portrait, relative information, and other personal characteristics. eac mode is an access mode that combines advanced security features between the terminal and the cic to protect and restrict access to sensitive personal data contained on the chip. it enables mutual authentication and establishes a secure communication channel between the cic and a terminal. in contrast to ordinary personal data that can be protected by basic mechanisms, more sensitive data (such as fingerprints or iris images) must have enhanced protection to prevent unauthorized access. to access this mode, users need to establish a secure connection based on either bac or pace mode. eac access mode is implemented through two parts: chip authentication that uses the diffie-hellman key exchange algorithm to exchange new session keys and terminal authentication that uses rsa digital signature algorithm or digital signature on an elliptic curve. figure 2 describes in detail the process of reading data when combining the three modes. to retrieve the data in cic, we first need to get the mrz information contained on the cic that can be entered or scanned. then, we proceed to access with two modes, bac or pace. when either of these two modes is successfully set up, the individual can access the partitions dg1 and dg2 to get information, portraits and some information in the related data partition (if permitted). that information is then compared with the personal information contained on the cic to check whether the user information is valid. after successful data retrieval, eac advanced access mode can be selected to read data in partitions dg3 and dg4 to get information about fingerprint and iris images and compare them with other personal information. in this study, we aim to use bac mode to read information stored on the cic chip. the data read include: information of citizens themselves stored on the dg1, portrait information stored on the dg2, and citizen-related information such as parents, special identities, etc. that are stored on dg13. iii. designing and building an application to read information safely from cic with chip in vietnam a. setting up the bac mode to read data figure 3 shows the details of the four stages needed to be performed when the application connects to the cic with chip, including: first, get information from the mrz on the cic as a key seed. second, establish session key pair (kenc, kmac) from the key seed. third, authenticate and exchange new session keys with cic. finally, proceed to read the data on the chip using the new session key pair to encrypt and authenticate each other. bac mode is the access mode to the cic using 3des symmetric encryption in cbc mode to encrypt as well as generate the token authentication code. figure 3 presents details of the test execution procedure for the cic with chip to connect to the card reader with bac mode. fig. 3. software read stages with the bac mode. first, the pc will get the mrz information contained on the cic either manually or by scanning. the pc receiving the mrz will generate a key encryption code and a key message authentication code (kenc, kmac). next, the pc requests a notification from the cic via the apdu command sent to the cic. cic generates a response message m sending a response engineering, technology & applied science research vol. 13, no. 1, 2023, 10100-10107 10103 www.etasr.com le et al.: building an application that reads secure information stored on the chip of the citizen … back to the pc. the pc receives the message m from the cic and then generates a message m' and the derived key kifd. it calculates s = m || m’ || kifd, encrypts s using a kenc key, and generates message authentication code with ciphertext using the kmac key. next, the pc constructs the apdu instruction with the data e || mac sent to the cic. cic’s chip will receive decryption and authentication data with kenc and kmac keys and check if the message m sent before is correct. if it is correct, the cic will generate the derived key kic and a new key seed by xor-ing kic with the key derived from the incoming pc code (kifd). finally, the cic generates a new session key pair, i.e. kenc(new) and kmac(new), generates a new message m2 = m || m’ || kik, encrypts message m2 with the kenc key, generates the token authentication code, constructs the apdu instruction with the data e || mac, and sends a response back to the pc. at this point, the pc receives, decrypts, and authenticates the data to check if it is the message m' sent before. if it is correct, the pc will generate the key seed by xor-ing kifd and the incoming cic derived key (kic), and will generate a new session key pair kenc(new), kmac(new). when both the chip and the card reader complete the connection tests successfully, the two sides will communicate using the new session key pair to encrypt and authenticate data, with the following process: the pc sends the apdu command read data to cic, cic encrypts data and sends the apdu commands back to the pc. then, the pc receives the decoded data, validates the data, and checks the received information. this is demonstrated in the application by the following steps: first, the application will proceed to get the mrz information data as the key seed, then will calculate and set up a session key pair including kenc and kmac. the application then sends a connection to the cic and the cic authenticates and initiates a new session key exchange. when the new session key exchange is successful, the application will proceed to read the specified data partitions using the session key pair to encrypt and authenticate the data. 1) session key establishment session key establishment is the process by which a user generates a session key pair based on the mrz information provided by the cic. the mrz information serves as the key seed to generate the session key pair [25]. according to the icao 9303 standard, the process of establishing session key [22, 25] consists of four main steps:  step 1: build mrz information (organized with 24 numbers according to the following structure: document number consists of 9 digits of cic from the end, birth is 6 digits on the cic, expiry is 6 digits of the expiration date on the cic, check is 1 byte calculated by the formula check = (document number + 7 + 3 +1 + 7 + 3 +1 + 7 + 3 +1) mod 10).  step 2: generate the key (here using sha1 hash).  step 3: generate kenc encryption key (using true random source in chip).  step 4: generate key message authentication key (using sha1 and kmac). this process is detailed in the icao standard [19]. after successful session key setup, a key pair consisting of an encryption key (kenc) and a key message authentication key (kmac) will be generated for secure exchange with the cic. 2) authenticating and exchanging the new session key this process is done after the session key pair has been previously established. the application will request a message from the cic, then proceed to use the previously set session key pair to encrypt and generate an authentication code for that message, and then send it to the cic. the cic decodes and authenticates the incoming data. if successful, the card will proceed to generate a new session key pair consisting of kenc(new) and kmac(new) and then send it back to the application. the two sides of the application and the cic will be accessed through this new session key pair [25]. first, during the process of authentication and exchange, a new session key is performed, an rnd.ic message (8 bytes) is randomly requested from the cic. the application performs the following operations: generate random rnd.ifd (8 bytes), generate a random k.ifd (16 bytes) key, join s = rnd.ifd || rnd.ic || k.ifd (rnd.ic sends request to cic), encode eifd = e (kenc, s), calculate the message authentication code mifd = mac(kmac, eifd), build command apdu(eifd || mifd), and send the apdu command to the cic. then, cic receives the data sent to the apdu(eifd || mifd). eifd conducts decryption and authentication with application via mac, extracts rnd.ic from s and checks if it returns the correct value, generates k.ic key and generates kseed(new) = k.ic xor k.ifd, generates a new session key pair kenc(new), kmac(new), joins r = rnd.ic || rnd.ifd || k.ic, encrypts eic = e(kenc, r) and computes the message authentication code mic = mac(kmac, eic), constructs the pdu(eic || mic) command, and sends the apdu command back to the application. the application receives the response data from the apdu tag(eic || mic), conducts eic decryption and authentication with the cic via mac, extracts the rnd.ifd from r and checks if the tag returns the correct value, generates kseed(new) = k.ic xor k.ifd, and generates a new session key pair (kenc(new), kmac(new)). finally, the application and the cic will generate a new session key pair that is used to encrypt, decrypt, and authenticate the data when reading the data file used for secure data reading. 3) the process of reading secure data it is done after the software and the cic have authenticated and set up the session key. during the reading process, the application and the cic encrypt, decrypt, and authenticate the data based on a new session key pair to ensure that they are confidential and authenticated. card reading is done through properly constructed apdu commands sent to the chip [do'85' or do'87'] [do'97'] do'8e'. the response to the apdu command is [do'85' or do'87'] [do'99'] do'8e'. in this module, the data on each partition are different, so the structure of the apdu command sent to the card is also built differently and must follow the rules of sending access commands to that partition. after sending a command to that partition, there will be response data with status bytes. if the returned data are correct and the status bytes return "9000", then the command sent is correct. in the cics in vietnam, the data areas are: dg1 engineering, technology & applied science research vol. 13, no. 1, 2023, 10100-10107 10104 www.etasr.com le et al.: building an application that reads secure information stored on the chip of the citizen … (mrz information), dg2 (face image encoding), dg3 (fingerprint encryption), dg4…dg12 (backup), dg13 (additional personal information), dg14 (read condition of eac mode), dg15 (passive authentication), dg16 (backup). b. analysis, evaluation, and design of the application figure 4 presents the details of the system and the operation of the reading data application. the application is built with the following devices: scanner (gets mrz information from the card), card reader (communication device that transmits apdu commands from the computer to the cic and vice versa), and software (retrieve and process data in cic). the user will provide a cic chip and the scanner connected to the computer will take the mrz information from the card as input. at the same time, a card reader is connected to the computer through the built-in data reader software. after obtaining the mrz information as input to the data reader software, cic will communicate with the software through the previously connected card reader. the application then processes and retrieves data from the card. fig. 4. built-in system and program that reads the security information of the cic. fig. 5. id card security information reader program flow. figure 5 shows that the software is built into many different modules, each with different functions. the software is built based on the bac mode. the software is divided into the following modules: login module, module for setting session key, authentication and session key exchange module, personal data reading module, image data reading module, and supplementary information reading module. first, users need a password account to log in to the main module of the software. the mrz of cic is then put into the session key setup module to generate a session key pair for the next process. the session key exchange and authentication module receives the session key pair, establishes a secure connection to the cic, and exchanges a new session key pair. the personal information data read module retrieves the data from the dg1 partition. the image data reading module will get the data from the dg2 partition. the additional information reading module retrieves data from partition dg13. iv. results and discussion a. building and designing modules in cic reader software figure 6(a) describes in detail the operation flow of the login module. at first, on the login interface of the software, the user needs to enter the account/password. next, when the software's module works, if the information is valid, it will take the user to the main interface. in case of incorrect input, the software will not allow login. figure 6(b) details the operation flow of the authentication module and session key establishment. this module will process information according to the following steps:  step 1: the user enters the mrz on the cic into the software.  step 2: the entered mrz information is processed in accordance with the provisions of icao 9303 standard to get the necessary information.  step 3: after obtaining the necessary information from the mrz, the module will proceed to generate the key.  step 4: after having the key seed, the processing software generates a pair of session keys kenc (encryption) and kmac (key message authentication code). (a) (b) fig. 6. (a) login module activity flow, (b) session key exchange and authentication module activity flow. the new session key exchange and authentication module is operational:  step 1: user generates a random plaintext block. engineering, technology & applied science research vol. 13, no. 1, 2023, 10100-10107 10105 www.etasr.com le et al.: building an application that reads secure information stored on the chip of the citizen …  step 2: encrypt and generate token authentication code from plaintext block from kenc and kmac set up before.  step 3: connect the cipher-text and the generated message authentication code.  step 4: send s to the card for personal authentication.  step 5: if it is legitimate, the card will respond and receive a resend notice.  step 6: decrypt the message and authenticate with the card.  step 7: get the key seed from the card's response message.  step 8: set up a new session key for encryption and token authentication. the details of the operation flow of this module are shown in figure 7(a). (a) (b) fig. 7. (a) new session key exchange and authentication module activity flow, (b) operation flow of the data reading module (personal information). figure 7(b) shows the details of the operation flow of the personal data reading module. when this module works, the information stored on the cic read out is processed through the following steps:  step 1: send the file selection command to dg1 to read the card's personal information.  step 2: send the command to read the first 4 bytes of the dg1 file.  step 3: get a response from a valid check card and determine the length of data contained in the file.  step 4: proceed to read the entire file.  step 5: get response from the data processing card from decoding, validating, and extracting valid information. in addition, there is a module to read image data and additional information. the module that reads image data and reads additional information is basically the same as the module that reads personal data, except for the method of file selection and the processing of the received data. b. building and perfecting the functions of the cic reader software in this study, the results of the readings from the cic will be obscured, due to concerns regarding confidentiality and privacy. to build an application that reads security information on a cic, we used a number of devices and supporting tools: a duali de-620 smart card reader, a pc with visual studio 2019 installed, programming language: c/c++, openssl library. figure 8(a) shows the designed login module interface. on this interface, citizens only need to enter the correct account and password and then they can start working with the cic reader software with the main interface of figure 8(b). on this main interface, if a citizen wants to read the information stored on the cic, it is only needed to enter the mrz information string (written on the back of the cic). (a) (b) fig. 8. (a) login interface, (b) main interface. (a) (b) (c) (d) fig. 9. (a) results of reading personal information on the cccd, (b) results of reading data on dg1, (c) data reading results on dg13, (d) data reading results on dg2. figure 9 shows the results by the software when reading security information stored on the cic's chip. figure 9(a) is the citizen's output displayed on the cic reader software. figures 9(b),(c) show the detailed results of personal information read on dg1 and dg13. the read out results are saved on 2 separate corresponding txt files. figure 9(d) shows the result of a detailed portrait of an individual read on the dg2 partition that is saved on a txt file. the results obtained when reading individual data on the chip cic include: document type, issuing state, full name, cic number, nationality, date of engineering, technology & applied science research vol. 13, no. 1, 2023, 10100-10107 10106 www.etasr.com le et al.: building an application that reads secure information stored on the chip of the citizen … birth, expiration date, gender, portrait image, and other personal data. table i. reading time result of secured data on the cic chip no end-to-end authentication time (s) reading time of dg1 (s) reading time of dg2 (s) reading time of dg13 (s) sum (s) 1 0.1950 0.0260 0.9630 0.0360 1.22 2 0.1960 0.0260 0.9640 0.0380 1.224 3 0.1960 0.0260 0.9570 0.0370 1.216 4 0.1950 0.0260 0.9430 0.0380 1.202 5 0.1950 0.0250 0.9640 0.0390 1.223 average 0.1954 0.0258 0.9582 0.0376 1.217 finally, in order to evaluate the performance of the cic reader software, the time to read citizen information stored on each partition dg1, dg2, dg13 and end-to-end authentication of chip cic was determined. table i gives the results of the software's execution speed performance when reading data. it is seen that the total time to read the entire data (end-to-end authentication, dg1, dg2 and dg13) is approximately 1.217s. so, the software reading data on the cic has an average time of about 1.2 to 1.3s, which is a relatively fast read speed, which is suitable for real time applications. c. analyzing, evaluating, and testing the source code of the cic reader software the fortify static code analyzer toolkit (version 22.1.0.0166) was used to analyze and evaluate the cic reader software source code. table ii gives the detailed results. there are error issues related to buffer overflow, variable never used, integer to character, signed to unsigned, unchecked return value, but these problems are not of a serious nature and don't affect the security of the software. specifically, these issues are analyzed below.  there is a problem related to buffer overflow (buffer overflow: 1 issue), which is warned in the memcpy function (void *memcpy(void *str1, const void *str2, size_t n) of the reader, occurring when the size of the copied array is smaller than the data array size, which does not guarantee program optimization according to [3033]. the fortify static toolkit code analyzer showed how to fix the source code (check the correct copy array length and number of bytes to copy) according to [34]. table ii. results of source code of cic software testing with the fortify static code analyzer category fortify priority (audited/total) total issues critical high medium low buffer overflow 0 0 / 1 0 0 0 / 1 poor style: variable never used 0 0 0 0 / 2 0 / 2 type mismatch: integer to character 0 0 / 1 0 0 0 / 1 type mismatch: signed to unsigned 0 0 / 1 0 0 0 / 1 unchecked return value 0 0 0 0 / 1 0 / 1 weak cryptographic hash 0 0 0 0 / 5 0 / 5  there are two problems related to unused variables (variable never used: 2 issues). the error occurs because two variables, num and lretvalue have been declared but not used. the fix is to delete these two variables.  there is an issue related to integer to character conversion (integer to character: 1 issues). the error is that the function returns an unsigned char to an int type, but the return value is assigned to a char type. the fix is to resynchronize the return value with the same type.  there is an issue with the signed to unsigned conversion (signed to unsigned: 1 issues). the error occurs because the arrays ch[] (type char) and mrz_input[] (type unsigned char) are not of the same data type. the fix is to re-declare one of the two arrays with the same data type char or unsigned char. fig. 10. unused variables. fig. 11. integer to character conversion issue. fig. 12. unchecked return value issue.  there is an issue with the unchecked return value (unchecked return value: 1 issue). this error occurs when the initinstance() function returns no value. since initinstance() is an interface function of the mfc available when creating the interface, it cannot be dropped. analyzing, evaluating, and testing the problems in cic reader software with fortify static code analyzer toolkit (version 22.1.0.0166), shows that the developed and built software is guaranteed source code-safe. this is enough to confirm that the cic reader software will be secure against engineering, technology & applied science research vol. 13, no. 1, 2023, 10100-10107 10107 www.etasr.com le et al.: building an application that reads secure information stored on the chip of the citizen … some types of attacks when deployed in real-world commercial applications. v. conclusion reading citizen information stored on a cic with chip is practical for daily services, such as electronic payments, online money transfers, online public services, etc. in this paper, we used the bac mode to set up a secure channel in the process of reading citizen information stored on cic. we used cryptographic algorithms such as 3des, sha1, and mac, to ensure that during the authentication process between the chip and the terminal the communication in the process of reading citizen information from the chip on cic is secure. as a result, the software reads the information stored on dg1, dg2, and dg3 fields with safety and security. the performance of the software has a reading and data processing speed of approximately 1.2 s to 1.3 s. the cic reader software source code has been evaluated and tested with the fortify static code analyzer tool (version 22.1.0.0166) to confirm the software its robustness and safety. acknowledgment the authors thank the academy of cryptography techniques and the minister of education and training (moet) for supporting this work under grant number b2022gha-10. references [1] l. c. guillou and m. ugon, "smart card a highly reliable and portable security device," in lecture notes in computer science, new york, ny, usa: springer, 1987, pp. 464–479. 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[34] "about strsafe.h win32 apps," microsoft. https://learn.microsoft.com/ en-us/windows/win32/menurc/strsafe-ovw. microsoft word etasr_v13_n1_pp9985-9990 engineering, technology & applied science research vol. 13, no. 1, 2023, 9985-9990 9985 www.etasr.com hien et al.: stochastic higher-order finite element model for the free vibration of a continuous beam … stochastic higher-order finite element model for the free vibration of a continuous beam resting on elastic support with uncertain elastic modulus ta duy hien university of transport and communications, vietnam tdhien@utc.edu.vn nguyen dang diem campus in ho chi minh city, university of transport and communications, vietnam diemnd_ph@utc.edu.vn giap van tan hanoi architectural university, vietnam tangv@hau.edu.vn vu van hiep university of transport and communications, vietnam vvhiep@utc.edu.vn nguyen van thuan nha trang university, vietnam thuannv@ntu.edu.vn (corresponding author) received: 28 october 2022 | revised: 3 december 2022 | accepted: 4 december 2022 abstract this paper deals with a continuous beam resting on elastic support with elastic modulus derived from a random process. governing equations of the stochastic higher-order finite element method of the free vibration of the continuous beam were derived from hamilton's principle. the random process of elastic modulus was discretized by averaging random variables in each element. a solution for the stochastic eigenvalue problem for the free vibration of the continuous beam was obtained by using the perturbation technique, in conjunction with the finite element method. spectral representation was used to generate a random process and employ the monte carlo simulation. a good agreement was obtained between the results of the first-order perturbation technique and the monte carlo simulation. keywords-sfem; free vibration; continuous beam; random field i. introduction beams and frames are used in many engineering applications, such as civil engineering [1-3], bridge engineering, and aerospace engineering. the importance of dynamic problems has been the subject of many research studies [4-9]. in civil engineering, the structures resting on foundations are very important [10-15]. considering continuous beams resting on elastic foundations, elastic support is a common problem. many practical problems are idealized to continuous beams resting on elastic foundations, elastic support such as rails in the railway, and strip foundations on the soil. the nonlinear dynamic of plates on a viscoelastic winkler foundation under harmonic moving load is solved using the multiple time scales method [16]. subway dynamic problem under loads from the ground and underground transport is modeled using finite element software in [17]. the dynamic of sandwich beams with a viscoelastic core subjected to a moving engineering, technology & applied science research vol. 13, no. 1, 2023, 9985-9990 9986 www.etasr.com hien et al.: stochastic higher-order finite element model for the free vibration of a continuous beam … load is investigated using the finite element method in [18]. the natural frequencies of non-uniform axially functionally graded beams were investigated using the chebyshev collocation method in [19]. for stochastic problems, material properties, loads, and geometrical dimensions are assumed to be stochastic. stochastic dynamics problems have been the subject of many studies [20-24]. there are several types of stochastic finite element methods (sfem), e.g. the probabilistic finite element method [25, 26], the spectral sfems (ssfems) using karhunen–loève expansion series [27], the homogeneous chaos expansion method [28] for the representation of random fields, and the sfems that use weighed integration techniques [29, 30]. the effect of randomness in elastic modulus on the stochastic free vibration of non-uniform beams is investigated by using an sfem in [31]. authors in [32] dealt with the stochastic dynamics of an infinite double beam resting on a random elastic foundation subjected to a moving load. authors in [33] investigated a beam on a random foundation using the sfem. the stochastic buckling of non-uniform columns was analyzed using stochastic finite elements in [34]. in the present work, the sfem is used in the study of the free vibration of a continuous beam resting on an elastic support. the results are compared with the ones of the monte carlo simulation. ii. stochastic finite element formulation for continuous beam resting on elastic support consider a continuous beam resting on elastic support with length l as shown in figure 1. fig. 1. continuous beam resting on elastic support. the displacement fields using reddy's beam theory [35] present as formulation are:           3 0 2 0 4 , 3 , w u x z z x z x xh w x z w x                (1) the strain formulation is calculated from (1) as follows: 2 23 3 2 2 0 2 2 2 0 2 4 4 3 3 4 4 1 1 x xz w x x w h x z z z h h z z h                                 (2) the displacement fields are approximated by an interpolation functions as follows:     0 1 1 2 1 3 2 4 2 1 1 2 2 l l w x n w n n w n x n n              (3) the interpolation functions are defined as follows: 2 3 2 3 1 32 3 2 3 2 2 2 42 2 1 2 1 3 2 3 2 1 2 1 1 l l x x x x n n l l l l x x x x n x n x l l l l x x n n l l                                  (4) the displacement vector of finite element is:    1 1 1 2 2 2 t e q w w    (5) the strain energy of beam element is given as: 2 2 3 0 2 2 20 0 2 1 4 2 3 1 4 1 2 e x l e a w e y y x h x x u dx w g h x                                              (6) the potential energy of elastic support is defined as:   2 0 1 2 s su k w x    (7) one dimensional homogeneous random field of elastic modulus is assumed:    0 1 ee x e r x    (8) where  er x is one dimensional homogeneous random field with zero mean. the autocorrelation function of the random field is:   2 expr d           (9) where σ, d, are the coefficient of variation and the correlation distance for the random field of an elastic modulus, and the relative distance vector ξ is defined as j i  x x . the randomness in the elastic modulus of the beam element is illustrated in figure 2.  0 1i ie e r  (10) the random field of elastic modulus in the element is approximated by averaging random variables ri at n points in the element: 1 2 0 ... 1 e nr r re e n          (11) engineering, technology & applied science research vol. 13, no. 1, 2023, 9985-9990 9987 www.etasr.com hien et al.: stochastic higher-order finite element model for the free vibration of a continuous beam … fig. 2. beam element with randomness in elastic modulus. the stochastic stiffness matrix of the element is:           1 2 0 ... 1 e n k b d b d r r r b d b d n                     (12) the stiffness matrix of the structures consists of the stiffness matrix of the beam element and the stiffness of the elastic foundation:       supbeam port k k k  (13) the free vibration equation is:        2 0k m x  (14) the eigenvalue of the free vibration is 2  . the stiffness matrix, the eigenvector, and the eigenvalue are expanded to taylor series as:                 2 0 1 1 1 2 0 1 1 1 2 0 1 1 1 1 2 1 2 1 2 nr nr nr ei ei ej i i jei ei ej nr nr nr ei ei ej i i jei ei ej nr nr nr ei ei ej i i jei ei ej k k k k r r r r r r r r r r r r x x x x r r r r r r                                               ⋯ ⋯ ⋯ (15) and by substituting the series expressions in (6) into (5):                 2 0 1 1 1 2 0 1 1 1 2 0 1 1 1 1 2 1 2 1 0 2 nr nr nr ei ei ej i i jei ei ej nr nr nr ei ei ej i i jei ei ej nr nr nr ei ei ej i i jei ei ej k k k r r r r r r r r r m r r r x x x r r r r r r                                                             ⋯ ⋯ ⋯ (16) equation (16) is solved by comparing the terms of the random variables to obtain the solution:      0 00 0k m x    (17) and    0 0 t ei ei k x x r r     (18) the first-order approximation of the variance of the eigenvalues is:           1 2 1 1 , , , nr nr nr e ij i j ei ej var r r r e e e r r r                         ⋯ (19) the variability of response cov of the eigenvalue is defined as:     var cov e    (20) iii. numerical examples in this section, a continuous beam on 5 elastic supports, as shown in figure 1, is investigated. the geometrical and material parameters of the beam are: length l=10m, height h=0.6m, mean of young’s modulus e=30×10 5 mpa, coefficient of variation of a random field of elastic modulus σ=0.1, and mass density ρ=2400kg/m 3 . to valid the proposed approach, it is compared with monte carlo simulation. the random field of stiffness of the elastic modulus is generated using the spectral representation method [36, 37]:   1 0 2 cos( ) 2 ( ) , 0,1, 2,..., 1 n e n n n n n ff n u n r x a x a s n n n n                      (21) where u denotes the upper cut-off frequency beyond with the power spectral density function ( )ff ns  of the random field of the stiffness of the elastic modulus. the sample value of random field  er x is substituted to (11) and the stiffness matrix in (12) is deterministic. the free vibration equation (14) is repeatedly solved 10000 times to get the eigenvalue. figure 3 shows the first and second mode shapes with samples of 3 cases of stiffness of elastic support 6 7 8 10 , 10 , 10 n/msk  . it clearly shows that the first mode represents a symmetric mode shape and the second mode represents an antisymmetric mode shape. the mode shapes on figure 3 clearly show the effect of the stiffness of support on mode shapes. the effect of the correlation distance d of the random field on the variability of the eigenvalue is shown in figure 4, where the results of the proposed formulation were compared with those of the monte carlo simulation using 10,000 samples with two cases of stiffness of elastic support, i.e. 10 7 and 10 8 n/m. as seen in figure 4, the cov varies depending on the correlation distance and the coefficient of stiffness of the elastic support. in all other cases, the obtained cov has a small value e(z) e1 e2 ei en e engineering, technology & applied science research vol. 13, no. 1, 2023, 9985-9990 9988 www.etasr.com hien et al.: stochastic higher-order finite element model for the free vibration of a continuous beam … of the assumed standard deviation of the random field of elastic modulus. also, the result on figure 4 shows the good agreement between the proposed approach and monte carlo simulation. (a) (b) fig. 3. mode shapes. (a) first mode, (b) second mode. (a) (b) fig. 4. coefficient of variation of the eigenvalue. (a) first mode, (b) second mode. figure 5 illustrates the statistical probabilistic distribution of the eigenvalues of the first 2 modes obtained from monte carlo simulation corresponding with the stiffness of elastic support ks =10 7 n/m and two cases of correlation distance d=0.01 and d=0.1. on figure 5, it is shown clearly that with smaller correlation distance, the histogram is quite scattered, whereas when the correlation distance is larger, the histogram is close to the normal distribution. (a) (b) (c) (d) fig. 5. probabilistic distribution of the eigenvalue. (a) first mode with d=0.01, (b) first mode with d=0.1, (c) second mode with d=0.01, (d) second mode with d=0.1. iv. conclusions in this paper, the stochastic finite element method was employed to investigate the response variability of the eigenvalue of the free vibration of a continuous beam on elastic support. the free vibration equation used higher order beam theory to establish finite element formulas. the first-order perturbation solution exhibits a good agreement with monte carlo simulation. the response variability of eigenvalues, given in terms of the coefficient of variation, is smaller of the input standard deviation of the random process of the elastic modulus of the beam. engineering, technology & applied science research vol. 13, no. 1, 2023, 9985-9990 9989 www.etasr.com hien et al.: stochastic higher-order finite element model for the free vibration of a continuous beam … acknowledgment this research is funded by university of transport and communications (utc) under the grant number t2021-ct007tđ. references [1] p. c. nguyen, "nonlinear inelastic earthquake analysis of 2d steel frames," engineering, technology & applied science research, vol. 10, no. 6, pp. 6393–6398, dec. 2020, https://doi.org/10.48084/etasr.3855. 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[37] p.-c. nguyen, t. n. van, and h. t. duy, "stochastic free vibration analysis of beam on elastic foundation with the random field of young’s modulus using finite element method and monte carlo simulation," in 6th international conference on geotechnics, civil engineering and structures, ha long, vietnam, oct. 2021, pp. 499–506, https://doi.org/10.1007/978-981-16-7160-9_50. microsoft word etasr_v12_n4_pp9071-9077 engineering, technology & applied science research vol. 12, no. 4, 2022, 9071-9077 9071 www.etasr.com shah et al.: direct adc controlled asymmetric cascaded multilevel inverter direct adc controlled asymmetric cascaded multilevel inverter maulik j. shah department of electrical engineering, cspit, charusat charotar university of science and technology (charusat), charusat campus changa 388421, gujarat, india maulikniki@gmail.com kartik s. pandya department of electrical engineering, cspit, charusat charotar university of science and technology (charusat), charusat campus, changa 388421, gujarat, india kartikpandya.ee@charusat.ac.in priyesh chauhan electrical and computer science engineering institute of infrastructure, technology, research and management gujarat, india priyeshchauhan@iitram.ac.in received: 28 june 2022 | revised: 8 july 2022 | accepted: 8 july 2022 abstract-this paper presents an asymmetric multi-level inverter with a novel direct adc control scheme. this scheme does not use a carrier wave or a reference sinusoidal wave to generate gate pulses for power switches, but an analog to digital converter (adc) to create gate pulses. for n sources, n bit adc will generate 2 n+1 -1 levels at the output voltage of the inverter. this scheme uses the adc output for the gate pulses for power switching devices. in this topology, the inverter comprises a series of connected half-bridges to generate a more significant level. the presented topology uses binary level supply voltages. different topologies with different parameters are compared with the proposed inverter, and the operation of the proposed control scheme is verified with a simulation in matlab. the prototype of a 31-level inverter is developed in hardware, and the hardware results are discussed. keywords-analog to digital converter; cascaded inverter; reduced power switching devices; multilevel inverter i. introduction for less total harmonic distortion (thd) in the output voltage of an inverter, in medium power applications, multilevel inverters (mlis) are most preferred. mlis have become very popular due to their power topologies. they are widely used for medium voltage applications like gridconnected inverters, traction systems, and facts. the current paper presents enormous topologies and their control switching pattern [1]. mlis are classified into two categories, symmetric and asymmetric, based on their supply dc sources [5]. here, the proposed topology is asymmetric as supplied dc voltages are different in magnitude. simulated and hardware prototypes of four dc voltage sources were used. four half-bridges were connected in series in a power circuit, and the series' output was connected to one full-bridge inverter. a novel finite predictive control method was described in [2]. a three-phase inverter asymmetric fault-tolerant control scheme was illustrated in [3] to limit the fault phase's fault current. using diode rectifiers, isolated dc-dc converters were implemented to reduce the power switching devices in [4]. a home-type cascaded inverter was presented in [6]. the authors used unidirectional and bi-directional switches in the power circuit. without any additional structure like h-bridges, the given topology can generate a uniform positive and negative cycle at the output of the mli. the limitation of this topology is that it requires bidirectional switches. matlab simulation of t-type 3 level inverter is represented in [7] for the field oriented control of traction motor. pmsm motor control using multi-level inverter with active damping and current controller was described in [8]. ii. power circuit and operation based on the amplitude of the supplied dc voltage sources, output voltage levels can be adjusted. mli can be classified into two categories, depending on the dc sources: symmetric and asymmetric. in symmetric mli, all the supplied dc sources are equal in magnitude, while in asymmetric, the magnitudes of the supplied dc sources are different. in asymmetric mli, binary or trinary type dc sources are used. in the binary pattern, dc sources are, for example, vdc, 2vdc, 4vdc, etc. in trinary type, dc sources are like vdc, 3vdc, 9vdc, etc. however, in trinary type power topologies, the control scheme is somewhat complex and requires a look-up table for switching power devices. in binary type dc sources, the reference signal can be converted directly in binary form using analog to digital conversion ic or onboard an adc channel of processor or micro-controller chip. in some processors, such as the arm series, floating-point adc is available and can also give negative signals. if floating-point corresponding author: maulik j. shah engineering, technology & applied science research vol. 12, no. 4, 2022, 9071-9077 9072 www.etasr.com shah et al.: direct adc controlled asymmetric cascaded multilevel inverter adc is unavailable, then the vref signal is converted first in absolute value. for n isolated binary level dc sources: • the number of levels achieved at an output voltage of an inverter is 2 n+1 -1 • the number of power switching devices required is (2*n) + 4 • the number of gate drivers (half-bridge driver) required is n + 2 from the above, if we use four isolated dc sources, one can achieve a 31-level output voltage of an inverter with a total of 12 power switching devices and 6 half-bridge mosfet / igbt driver circuits. in the proposed adc-controlled mli, binary-type dc sources are used, e.g. 12v, 24v, 48v, and 96v. all the dc sources are connected to one half-bridge circuit of the power switching device. so, 4 half-bridge circuits are used, and 1 fullbridge circuit generates the negative and positive cycle. the output of zero-crossing logic is used as a gate pulse for the fullbridge circuit. so, the switching frequency of this full h-bridge is similar to the power frequency. gate pulses for s0 and s01 power switches are operating in inverting mode. so, in the gate pulses of these 2 switches, the dead band is generated using driver ic. similar logic is also applied for s1-s11, s2-s21, s3s31, and sh1-sh11, sh2-sh21. suppose vdc0 = vdc, then vdc1 = 2*vdc, vdc2 = 4*vdc, and vdc3 = 8*vdc. figure 1 shows the power topology for the proposed 31-level mli. table i shows the switching pattern for 31 levels. it is seen that switching is done like a binary conversation. so, for the +15 vdc output level, all dc sources are connected in series. so, this is nothing but (1111)2 in 4-bit binary, indicating the states of power switches s3, s2, s1, and s0 respectively. similarly, for +10 vdc the states are (1010)2 in binary, which means switches s3 and s1 are in on state, and s2 and s0 are in off state. fig. 1. power topology of the 31-level mli. table i. switching states of the 31-level inverter s3 s2 s1 s0 sh1 sh2 output 1 1 1 1 1 0 +15 vdc 1 1 1 0 1 0 +14 vdc … … … … … … … … … … … … … … 0 0 0 1 1 0 +1 vdc 0 0 0 0 1 0 0 vdc 0 0 0 1 0 1 -1 vdc … … … … … … … … … … … … … … 1 1 1 1 0 1 -15 vdc a. applications of the proposed inverter the proposed control scheme is straightforward to implement in a grid-tied inverter. this scheme is also applicable to a solar micro-inverter, and isolated dc sources can be implemented using a high-frequency transformer. it can also be applied for the speed control of an induction motor. especially in electric vehicle systems, this inverter can be used where isolated dc sources are available in the form of batteries. iii. direct adc-based control scheme various topologies have been invented to reduce the harmonics in the output voltage of the mli. different techniques are available to control amplitude, frequency, and maintain a nearly sinusoidal waveform at the output of an mli. the selective harmonic elimination (she) method uses optimization techniques like pso algorithm [11], pulse width modulation (pwm), hpwm (hybrid pwm), spwm (sinusoidal pwm), prspwm (prior switching pwm), svpwm (space vector pwm), etc. in the spwm technique, the sine wave is compared with high-frequency carrier waves, increasing switching losses. the arrangement of a triangular (carrier) wave in a different pattern is also needed, i.e. apod (alternate phase opposition disposition), pd (phase disposition), pod (phase opposition disposition). the direct adc-controlled technique does not require any triangular carrier wave. based on the look-up table of the first half cycle of the sine wave, it generates n-bit controlled signals. the generated signals are directly used as the gate pulses of the half-bridge of the inverter. in the direct adc method, the switching frequency is less than in all the pwm methods, so the overall efficiency of an inverter increases as switching losses decrease. the bit resolution of the adc is essential for the generation of gate pulses. in this control scheme, the bit resolution of the adc decides the number of levels of the output voltage of the mli. as with 2-bit resolution, this will make only a (2*2 2 )-1=7 level output, a 3-bit resolution will make a (2*2 3 )-1=15 level output, and a 4-bit will give (2*2 4 )-1=31 levels. as the number of resolutions increases, the required number of isolated dc sources also increases, which is the disadvantage of the proposed control scheme. in the grid-connected inverter, the proposed control method is straightforward to control an inverter's output. when the grid voltage rms value reduces, adc conversion automatically changes, and the output of the inverter also reduces. similarly, when there is a change in the supply frequency of the grid, the inverter output frequency also changes, which is the main advantage of the proposed mli. in this control method, the output of an mli always remains in synchronization with the grid voltage. in the proposed technique, the inverter is always connected to the grid at a unity power factor, and dc link utilization is also full in. in all grid-connected topologies, a pll block is required to synchronize the grid voltage with the inverter voltage. however, the proposed technique does not require a pll block. in the current paper, a 4-bit control scheme is implemented in hardware. the prototype mli is connected to engineering, technology & applied science research vol. 12, no. 4, 2022, 9071-9077 9073 www.etasr.com shah et al.: direct adc controlled asymmetric cascaded multilevel inverter the grid to check the synchronization between the voltage of the grid and the inverter output voltage. figure 2 shows the block diagram of the gate pulse generation through direct adc. fig. 2. adc control block diagram of the mli. iv. comparison with other topologies the following parameters are affected for properly evaluating different mli topologies. • reliability and total cost • efficiency • performance, control schemes, and applications • dynamic response the reliability and the cost of the inverter generally depend on the required number of power switches, the total blocking voltage capacity of that switching device, and the required dc sources (ndc). the efficiency of the inverter depends on the total number of power switching devices (ns), its blocking voltage capacity, and the switching frequency of the devices. performance, control, and dynamic response of an inverter depend on power distribution, module structure, and the number of passive components. table ii. switching states of the 31-level inverter ref. no. nl ns ndriver ndc r npc 31 60 60 1 1.935 chb 31 60 60 15 1.935 fc 31 60 60 1 1.935 14 31 16 12 6 0.516 17 31 10 10 5 0.322 18 33 28 28 8 0.903 19 17 12 12 5 0.387 20 31 12 12 4 0.387 proposed 31 12 12 4 0.3871 so the proposed topology is compared with other 31-level inverters. comparison is done considering the inverter output levels (nl), the number of switching devices used (ns), the total number of gate driver circuits (ndriver), and the required dc sources (ndc). table ii compares the various known mlis with the proposed 31-level inverter. the ratio (r) of switches to output level is also calculated. topologies with a lower ratio are better than the ones with higher. from table ii, it can be seen that the proposed inverter uses fewer switches compared to other topologies. figure 3 shows the comparison graph between the number of the required dc sources and the required number of power switching devices respectively. from all comparison graphs, it can be seen that the proposed mli is better than the other inverters. (a) (b) fig. 3. comparison graph of the proposed and other topologies: (a) no. of dc sources vs no. of levels, (b) no. of switching devices vs no. of levels. v. power loss calculation power losses in any switching device can be divided into three parts: • conduction losses (pc) • switching losses (psw) • blocking losses (pb) (normally neglected) a. conduction losses conduction losses can be found using drain-source on state resistance (rdson) and drain current (id): �� � ����� ∗ �� (1) b. switching losses switching losses occur due to the fast switching of devices. they include switching on-time (ton) and off-time (toff). switching losses on ton can be calculated from (2): ����� � � � ����������� ��� � �� ����� � � � ������� � !" # ��� �� " ����$ �� � # % ������������� (2) similarly, pswoff can be found by: ����&& � #% ��������&& (3) engineering, technology & applied science research vol. 12, no. 4, 2022, 9071-9077 9074 www.etasr.com shah et al.: direct adc controlled asymmetric cascaded multilevel inverter the total switching losses are given by: ��� � #% ���������� ' ��&&���&& (4) where fs=switching frequency (hz), vds= drain to source voltage of the mosfet, id=drain current, ton= switching ontime, and toff=switching off-time. vi. simulation results and discussion a. results the proposed direct adc control scheme is simulated in matlab/simulink with asymmetric dc sources vdc, 2vdc, 4vdc, and 8vdc. in simulations and prototype hardware, 12v, 24v, 48v, and 96v isolated dc sources were used. so, the total dc voltage is 180v. table iii shows the simulation parameters in simulink. fig. 4. matlab/simulink model. table iii. simulation parameters parameters simulation values input dc voltage sources dc0 12v dc1 24v dc2 48v dc3 96v maximum output voltage voutmax 180v output rms voltage voutrms 129v output current ioutrms 2.8a output frequency fo 50hz output voltage level at m=1 nl 31 power factor pf 0.90 the 4-bit adc control scheme is used for the control of the mli. so, for the 31-level mli, 4 half-bridge and 1 full-bridge power circuits are used. figure 4 shows the complete simulink model. subsystems 1 to 4 are used for the half-bridge, and subsystem 5 is used for the full-bridge connection. the matlab function block converts reference ac signal into digital output using 4 bit adc logic from y0 to y3. z0 gives zero crossings of the reference ac signal. figure 5 shows the output of the adc, which works as gate pulses for each half-bridge subsystem, and the zero-crossing signal as a gate pulse for the full-bridge subsystem 5. each bit has a different frequency, so each halfbridge works at a different switching frequency. figure 6 shows the output voltage and current waveforms with r=42ω and l=63.7mh at modulation index m=1. figure 7 shows the simulated output load voltage and load current waveforms with r=100ω and l=63.7mh at modulation index m=0.6. the thd of the output voltage varies between 3.16% and 6.42%, with a modulation index from m=1 to 0.5. the thd of the output current is 0.82% at modulation index 1 and 1.69% at 0.5 with a load of l=63.7mh in series with r=42ω. from figure 8, it can be seen that the thd of the output current and voltage increase as the modulation index decreases. a passive filter can be used to decrease the thd of the voltage. fig. 5. output gate pulses from matlab function block. fig. 6. output voltage and current at r=42ω and l=63.7mh at m=1.0. fig. 7. output voltage and current at r=100ω and l=63.7mh at m=0.6. fig. 8. thd (%) of the output voltage and load current with different values of m. engineering, technology & applied science research vol. 12, no. 4, 2022, 9071-9077 9075 www.etasr.com shah et al.: direct adc controlled asymmetric cascaded multilevel inverter b. efficiency of the mli in the simulations, the total switching losses of the inverter are 19w at load r=42ω and l=63.7mh. the input power to the inverter is 324w, and the output power is 305w. so, the efficiency of the inverter is 94.13%. inverter efficiency = output ac power / input dc power = (vorms*iorms*pf) / (vdc*idc). vii. hardware results an 8-bit avr microcontroller was used to generate gate pulses for the prototype hardware model of the proposed mli. it has six 10-bit on board adc channels. a reference sine wave was implemented, giving 4-bit digital output and one zerocrossing detector for the implemented power circuit. the generated 4-bit output was used as gate pulses for 4 halfbridges, and the zero-crossing output was used as a gate pulse of a full h-bridge power circuit. an ir 2104 half-bridge driver ic was used for each half-bridge mosfet. so, a total of 6 ir2104 driver ics are used for the proposed mli. ir2104 driver ic has an inbuilt dead-band facility between the upper and lower mosfets. νo additional hardware or software was required to generate the dead band between the two inverted gate pulses. irfp460n mosfets are used as power switching devices for the full h-bridge circuits, and irfb4110 mosfets are used as power switching devices for the 4 half-bridge circuits. the gate pulses from the microcontroller are isolated using 817 opt-coupler ic to protect the microcontroller. the hardware prototype was tested with a resistive and inductive type of load with different modulation indexes. the thd of the inverter's output voltage and load current was measured with a hioki power quality analyzer pq3198, and the waveforms were captured with a tektronics digital storage oscilloscope. figure 9(a) shows the output of the adc of an 8-bit avr micro-controller that is used as gate pulses (g0, g1, g2, and g3) for the half h-bridges and figure 9(b) shows the zero crossing output z as gate pulse of the full hbridge. figure 10 shows the output voltage waveform of mli and its zoomed waveform of a positive half-cycle that clearly shows 31 levels of output. the tdh of the output voltage was tested with a hioki make power analyzer which gives 2.11% thd at m=1. the output of the mli is connected with different load resistances and an inductor of 63.7mh. figures 11 to 13 show the inverter output voltage and load current waveforms, output current rms and peak value, total output power, and power factor. figure 11 shows the output waveforms and the load current thd with power at load resistance of 110ω in series with an inductor of l=63.7mh. figure 12 shows the output waveforms and current thd with power at load resistance of 78ω in series with an inductor of l=63.7mh. figure 13 shows the output waveforms and current thd with power at load resistance of 60ω in series with an inductor of l=63.7mh. figure 14 shows the prototype hardware set-up of complete mli with load circuits and isolated dc power supplies. table iv. device specifications of the hardware prototype device name device number specifications mosfet irfb4110 n-channel power mosfet vdss = 100v, rds(on) = 3.7 mω, id = 120 a mosfet irfp460n n-channel power mosfet vdss = 500v, rds(on) = 0.24 ω, id = 20 a mosfet driver ir2104 half-bridge driver ic voffset = 600 v max, io+/= 130 ma / 270 ma, vout = 10-20 v, ton/off = 680 and 150 ns, dead time = 520 ns photo-coupler ic pc817 4 pin photo-coupler vceo = 80 v, viso(rms) = 5kv microcontroller atmega328p-pu 8-bit avr microcontroller (a) (b) fig. 9. generated gate pulses using adc: (a) gate pulses of half-bridges, (b) gate pulse of the full h-bridge. (a) (b) hardware prototype results of the adc-controlled 31-level inverter: (a) output voltage, (b) zoomed view. (a) (b) (c) fig. 10. prototype hardware results for r= 110ω and l=63.7mh at modulation index m=1: (a) output voltage and current, (b) rms value and thd of the output current, (c) pf, active, and reactive power. engineering, technology & applied science research vol. 12, no. 4, 2022, 9071-9077 9076 www.etasr.com shah et al.: direct adc controlled asymmetric cascaded multilevel inverter (a) (b) (c) fig. 11. prototype hardware results for r= 78ω and l=63.7mh at modulation index m=1: (a) output voltage and current, (b) rms value and thd of the output current, (c) pf, active, and reactive power. (a) (b) (c) fig. 12. prototype hardware results for r= 60ω and l=63.7mh at modulation index m=1: (a) output voltage and current, (b) rms value and thd of the output current, (c) pf, active, and reactive power. fig. 13. prototype hardware set up in the laboratory. viii. conclusion in this paper, binary level dc sources were used to minimize the number of required dc power sources: 31 levels were achieved at the inverter output voltage using direct adc control and only 4 dc sources. the thd of the inverter output voltage was reduced to 2.11% at m=1 and the thd of the output current was also reduced to 1%. direct adc control scheme was used to control power switching devices, which is very simple compared to other control schemes such as spwm and svpwm. here, there is no need to compare the reference sine wave with any carrier (triangular) wave. an inverter's grid connection can be easily implemented using the direct adc control scheme. the rms value of the output voltage of the proposed mli will change according to the changes in the rms voltage of the grid. grid frequency and output voltage frequency are always synchronized, which is the main advantage of this control scheme. references [1] m. jagabar sathik, n. prabaharan, s. a. a. ibrahim, k. vijaykumar, and f. blaabjerg, "a new generalized switched diode multilevel inverter topology with reduced switch count and voltage on switches," international journal of circuit theory and applications, vol. 48, no. 4, pp. 619–637, 2020, https://doi.org/10.1002/cta.2732. 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[20] m. d. siddique, s. mekhilef, n. m. shah, a. sarwar, a. iqbal, and m. a. memon, "a new multilevel inverter topology with reduce switch count," ieee access, vol. 7, pp. 58584–58594, 2019, https://doi.org/ 10.1109/access.2019.2914430. microsoft word etasr_v12_n2_pp8410-8415 engineering, technology & applied science research vol. 12, no. 2, 2022, 8410-8415 8410 www.etasr.com dellosa & palconit: resource assessment of a floating solar photovoltaic (fspv) system with … resource assessment of a floating solar photovoltaic (fspv) system with artificial intelligence applications in lake mainit, philippines jeffrey t. dellosa school of engineering and architecture, ateneo de davao university, davao city, philippines and college of engineering and geosciences (cegs), caraga state university, butuan city, philippines jtdellosa@carsu.edu.ph eleonor v. palconit school of engineering and architecture, ateneo de davao university, davao city, philippines and mindanao renewable energy research and development center, davao city, philippines evpalconit@addu.edu.ph received: 22 february 2022 | revised: 27 february 2022 | accepted: 27 february 2022 abstract-the floating solar photovoltaic (fspv) system is an emerging solar pv installation, gaining traction primarily due to its distinct advantages over other forms of installations. fspv mainly solves the problem when land area is scarce and the power plant capacity is on the megawatt (mw) scale. this paper investigates the resource potential of fspv, specifically in lake mainit, caraga region, philippines. this study implemented a descriptive research design to identify the resources needed to implement an fspv system in the said lake. the lake mainit area can generate 762.96mwh per year. accounting for the needs of the community, the resources needed to put up the fspv should satisfy the 35,640whr daily energy requirement of the community. based on the analysis, the computed fspv system size is 9.90kwp. the components required to implement an artificial intelligence (ai) integrated monitoring and data processing system for fault diagnosis and detection to help mitigate impact to the fspv system with the undesirable weather conditions were also identified. keywords-floating solar photovoltaic system; renewable energy; artificial intelligence; machine learning i. introduction carbon dioxide (co2) emissions are a global environmental issue. co2 is one of the three green house gases (ghgs) that have increased in the atmosphere since pre-industrial times and is verified to be one of the leading causes of climate change [17]. many developing countries, like philippines, are highly vulnerable to climate change [8-9]. the signing of the paris agreement, in particular, paved the way for the countries' determined effort to reduce co2 and other ghgs by scaling up the use of renewable energy sources (ress) in order to mitigate the impact of climate change [10]. ress are considered clean, produce minimal waste, and are considered sustainable [11]. ress, like the solar photovoltaic (pv) systems, are regarded as a solution in mitigating co2 and other ghgs, thereby reducing global warming and slowing down the impact of climate change [12]. the global capacity for ress significantly increased the last few years, with more than 260gw capacity added in 2020 alone despite the covid-19 pandemic. at the end of 2020, a total of 714gw of capacity were deployed by various countries through the use of solar pv systems as the third-highest res installed after hydropower (1.211gw) and wind (733gw) [13]. there 5 five types of solar pv installations[14], as shown in figure 1. fig. 1. classification of solar installations. the ground-mounted system is commonly adopted by large-scale or utility-scale installations and generally performs as a power plant [15]. this type of installation is generally in the mega-watt-peak (mwp) capacity scale. at the same time, rooftop installations are commonly used by households or commercial buildings with small to medium capacity scale. households typically install one 1kwp systems and no more than 20kwp systems, depending on the energy requirements. commercial buildings often exceed 100kw or more in capacity [16]. there are also installations wherein solar pv panels are typically mounted over a canal or irrigation system. the oceans are vastly available and attractive for solar pv installations, and there offshore installation is coming in. offshore installations have a full view of the sun with no problems in shading that would affect the system's efficiency [16]. however, offshore installations are exposed to higher risks in terms of higher-level waves or even tidal waves [17]. corresponding author: jeffrey t. dellosa engineering, technology & applied science research vol. 12, no. 2, 2022, 8410-8415 8411 www.etasr.com dellosa & palconit: resource assessment of a floating solar photovoltaic (fspv) system with … a. floating solar photovoltaic (fspv) systems the floating type of installation is a newer concept gaining traction and is considered an emerging technology in renewable energy [14, 18-21]. fspv is a solar application, in which pv panels are designed and installed to float on water bodies [18]. fspv systems are commonly deployed in hydroelectric reservoirs [19, 21] and irrigation dams [22, 23], including abandoned depleted mines [24-26]. in fspv, solar panels are usually mounted upon a pontoon-based floating structure to keep its location fixed, and the floating system is anchored and moored [27]. the use of fspv protects productive lands and prevents the conversion of agricultural land to solar farms [20, 28]. unlike the ground-mounted system, the fspv currently has no commercial deployments but is primarily used in demonstrator projects deployed in various countries [29], including philippines [30]. the research and development activities of fspvs gained interest during the last decade due to benefits other from providing clean energy. fspv has several advantages over the traditional land-based solar pv systems. among these benefits are [19, 21, 39, 32, 33]: economic viability due to reduced real-estate costs, the cooling effect of water which improves the energy yield on the fspv system, the shading provided by the fspv panels on the water reduces the rate of evaporation and improves water quality by lowering algae growth, and the lesser accumulation of dust on the panel arrays as the surrounding environment of water surfaces contains less dust than land. b. artificial intelligence (ai) applications in renewable energy systems several studies have been conducted on ai in ress and specifically in solar pvs [34-36]. authors in [36] presented two of the most innovative ai algorithms for cost-effectiveness, software appropriateness, accuracy, and viability of instantaneous applications. it was established from the research that the application of ai and iot for fault detection and diagnosis (fdd), using cost-effective hardware and chips, is technically and economically viable in solar pv plants situated in far-flung areas faced with maintenance accessibility issues. ai applications and iot implementations use data loggers and monitoring systems to collect data and implement fault detection algorithms to check the pv plant performance. these methods are often used for pv systems with a few kw to hundreds of mws [37]. however, a large dataset is being used (measured currents, voltages, solar irradiance, infrared or electro-luminance images) in order to identify and diagnose faults [37]. in this paper, the authors intend to identify the resources needed to implement these data loggers to monitor and automate system operation of an fspv system. the fspv system is potentially exposed to environmental events such as typhoons, water level raises, and flooding. with the application of ai algorithms and monitoring systems, the problems are minimized. ii. brief background of the philippine lakes the philippines is home to over a hundred freshwater lakes of various sizes, from a few hundred to a thousand hectares. the lakes in the country have a total area of more than 200 thousand hectares. these lakes are known to be of particular use to the nearby communities due to their economic contributions, specifically in fishing activities [38]. table i shows the top 5 lakes in terms of area. the lakes lanao, taal, and laguna de bay, the latter in particular, are the most popular lakes due to, among others, their domestic and aquaculture uses. these lakes have the potential for fspv implementation. table i. five biggest lakes in the philippines name of the lake location area (ha) laguna de bay cavite, laguna, rizal &quezon 93,000 lanao lanao del sur 34,000 taal batangas 23,420 mainit agusan del norte, surigao del norte 17,340 naujan oriental mindoro 8,125 a. status of fspv in philippines and objectives of this study in philippines, fspvs are very much unexplored. there are very limited investigations or research and development activities related to the fspvs in the country, especially from higher education institutions (heis). there are no reports, documents or journal articles that can be found in highly regarded journals or in conference proceedings related to the fspv development in the country, when prior searches were conducted. there are no existing reports on fspv systems made known to the proponents from other heis. this paper explored the fspv potential from an academic point of view. this paper provides pioneer and preliminary information regarding the consideration of fspv placement in the local lakes. the main objective of this paper is to explore and determine the resources needed to implement an fspv system integrated with ai applications to automate its operation. the specific objectives of this study were to determine and identify the potential of fspv system implementation in lake mainit in the caraga region, philippines. this study investigated the needs of a specific community in terms of adopting the fspv system. the data collected from the community served as a baseline for consideration of the resources needed for the establishment of the fspv system. this study explored and investigated the solar pv potential in the target location with the attainment of solar irradiance and solar power output that served as input data to determine the resources required for the fspv system. the components (i.e. iot devices, microcontrollers, etc.) that will act as devices to implement the ai application aspect of the operations of the fspv were determined. iii. methodology this paper employed a descriptive research design. a desktop study was accomplished to identify the prior available information relevant to this particular investigation (figure 2). data collection for the potential resources needed consisted of field visits with officials and dialogue with the community representatives, and initial assessments of the prospective area. a literature review of the relevant studies was conducted. the use of available maps and information from relevant websites was performed to identify the potential location of the study site and the geographic characteristics of the area. this engineering, technology & applied science research vol. 12, no. 2, 2022, 8410-8415 8412 www.etasr.com dellosa & palconit: resource assessment of a floating solar photovoltaic (fspv) system with … part of the methodology was carried out to determine the latest available data on pv power potential, global horizontal radiation, and direct normal radiation. analysis was performed to determine the potential system sizing and the needed components, based on the possible resources available for the fspv system and the requirements for an ai-integrated system. fig. 2. the methodology of this study consists of a desktop study, data gathering, and analysis. iv. assessment results and discussion a. site identification and field assessment pre-assessment was conducted to determine the most viable lake for the conduct of the study based on location, potential, and viability. the lead author of this study is a professor at caraga state university, butuan city in the philippines. the most viable lake which the lead author is closest to is lake mainit in the northeast of mindanao. lake mainit is the 4th largest lake and is considered the deepest in the country [38]. it is home to several communities with their livelihoods depended on fishing activities. it is bounded by the municipalities of jabonga and kitcharao in agusan del norte and the municipalities of mainit and alegria in surigao del norte. the target location for the fspv is in the control of barangay san roque, jabonga, agusan del norte (with coordinates: 9.3754141,125.5549301). the authors surveyed the area for potential locations of the proposed implementation site. with prior cooperation with the local government unit (lgu) in jabonga, agusan del norte on other projects, the authors were referred to the fishing village with concerns about the high cost of battery charging. the authors met with the representatives of the fishers and some officials of san roque in jabonga, where the village is located along lake mainit. consultations for the proposed project were carried out to correctly identify problems with the local community and have a shared understanding and acceptability. this is a part of the design thinking methodology wherein end-users are considered when innovations and technologies are developed to ensure that the solutions provide impact to the project users. as per field inspection and consultations, 110 fishers with their family members in barangay san roque in jabonga, agusan del norte, philippines live below the poverty line and rely on their overnight fish catch at lake mainit. the fishers in this area use basic lighting systems consisting of 12v-100ah batteries and 12v led bulbs that absorb a significant chunk of their annual income. the fishers had to charge their batteries during daytime to use them on their nighttime work. according to them, this would incur further costs at php50 a day (usd1.00) to charge the batteries using the electrical power from the electricity grid, spending about 1/6 to 1/4 of their daily income depending on the previous night's harvest. this would translate to php1,500.00 (usd30.00) per month, maybe enough to buy one sack of rice for a family of five for their one-month consumption. b. solar photovoltaic power potential, global horizontal radiation, and direct normal radiation the sun is the most abundant source of energy available on earth. the sun's power output is known as solar radiation, or as emission. a common term in solar power is irradiation, and it is defined as the radiation delivered to a given surface area at any given time. solar irradiance is the measurement of the sun's radiation and is expressed in w/m 2 . the philippines is wellpositioned to maximize its potential in solar energy due to its geography. the solar radiation for the country was pegged at 161.7w/m 2 on average per day in 2013 based on the duration of the sunlight as provided by the report of the national renewable energy laboratory and the country's department of energy in 2013. recently, solargis released and updated, on october 2019, a massive collection of solar resource maps for over 140 countries to assist the solar industry in further development and implementation of solar-related projects. the countries with available maps include the philippines [39]. the data collected by solargis are much more recent, covering dates from 2007 to 2018. solargis methodology uses data inputs from geostationary satellites and meteorological models to develop the maps. based on these recent data, the year-round average global horizontal irradiance in lake mainit of jabonga, agusan del norte is at 4.4kwhr/m 2 . the solar pv power potential is at 3.6kwhr/kwp. these figures will be used in estimating the size of the fspv system and the resource potential of the lake to produce solar energy. if the entire lake mainit is covered with solar pv systems, the potential energy that can be generated from the available area will reach 762.96mwh. for practical purposes, the authors intend to identify the specific resources based on the capacity of the fspv system and primarily on the energy consumption requirements of the fishing village. c. resource analysis for the fspv system and battery storage based on the potential resources every fisher in barangay san roque uses one 100ah battery and three 9w-12v dc led bulbs to last overnight. for the 110 fishers, the total battery storage requirement is 2200ah and 330 pieces of 9 w-12 v dc led bulbs. these figures are significant in determining the minimum size of the battery storage and charging capacity and the fspv system. each day, the fspv system needs to respond to the requirement of 27w multiplied by 110 fishers as the required capacity. the batteries are assumed to be used for 12h (from sundown to sunrise). with this figure, the resources needed to put up the fspv should satisfy the 35,640whr daily energy requirement. using the solar pv power potential data at 3.6kwhr/kwp, we can solve the system size, which is 35,640whr divided by 3.6kwhr/kwp. this would give us an fspv system size of 9.90kwp. theoretically, the 12v-100ah battery can last 44.44h or around 3 days of use. the requirement to charge the battery based on the consumption of a 27w bulb in 12h (6 pmengineering, technology & applied science research vol. 12, no. 2, 2022, 8410-8415 8413 www.etasr.com dellosa & palconit: resource assessment of a floating solar photovoltaic (fspv) system with … 6 am) is 324wh per day. the total capacity needed from 324wh times the number of fishers gives us a 35,640wh energy requirement to be supplied by the fspv system each day. in battery storage, the capacity requirement is 35,640wh divided by 12v which gives 2,970ah or an equivalent of 29.7(~30) units of 100ah batteries. in order to address the community's needs, the fspv system size should be at 9.90kwp and 30 units of 100ah batteries. the 9.90kwp system can be rounded off to 10kwp and can be divided into two arrays of 5kwp. this 10kwp fspv system requires two power inverters rated at 5,000w. for solar panels, there are various sizes in the market available, from 160wp to 670wp. twenty 500wp solar panels are the expected rating for the 10kwp system. d. resource identification the fspv system with ai applications requires the essential components to implement a solar pv power plant. figure 3 shows the block diagram for the fspv system comprising of: (1) the floating solar plant, (2) the combiner box, (3) a power inverter, (4) the data acquisition and wireless transmission unit, (5) battery bank or storage, and (6) the data receiving monitoring and supervision unit. the critical components for the ai applications include the sensors that shall be applied to acquire the data coming from the floating pv plant. in figure 4 we see the block diagram concerning the sensed data to be processed and analyzed using machine learning to identify faults and diagnose electrical problems in the system. the components needed comprise current, voltage, wind speed, air temperature, relative humidity, and wave sensors. for this specific implementation of a 10kwp fspv system broken down into 2 pv arrays at 5kwp each, there will be 2 sensors for the current and voltage to monitor the arrays. fig. 3. the block diagram for the fspv system with ai application. fig. 4. block diagram for the ai applications using machine learning on the diagnosis and fault detection of the fspv system. the use of microcontrollers and wireless devices enables the system to collect data coming from the sensors and be transmitted via sms using the current telecommunication infrastructure. the data from the pv plant and battery storage shall be collected from the data receiving, monitoring, and supervision (drms) unit at a remote location, specifically in the site where the researchers are based. the ai techniques are implemented at the drms unit to monitor, detect and diagnose any faults in the fspv system and implement the actions necessary to prevent harm when the conditions at the fspv site are undesirable (i.e. strong wind conditions leading to undesired wave levels). the ai components monitor the current and voltage outputs of the two pv arrays including data such as wind speed, wave level, and temperature. various devices are available to carry out these functions. most data processing and diagnosis detection tools can be carried out by high-powered computing machinery available currently in the research laboratory or in the university's r&d center called high performing computing (hpc) center. v. summary and conclusions the motivation behind this paper was to primarily investigate and assess the resources available for energy conversion in lake mainit, caraga region, philippines. assessment was carried out to determine if it is viable to implement an fspv system based on the needs and requirements around the lake. while traditionally fspv systems are installed in dams to complement hydroelectric power generation and for power generation for the electric grid, for this particular case, a community of fishermen was explored as recipients for the fspv system output. based on the findings, the lake mainit area has a year-round average global horizontal irradiance of 4.4kwhr/m 2 and a solar pv power potential of 3.6kwh/kwp. if the entire lake mainit is covered engineering, technology & applied science research vol. 12, no. 2, 2022, 8410-8415 8414 www.etasr.com dellosa & palconit: resource assessment of a floating solar photovoltaic (fspv) system with … with solar pvs, the potential energy that can be generated will reach 762.96mwh per year. for the fishers' daily requirements, the resources needed to put up the fspv should satisfy the 35,640whr daily energy requirement. the fspv system size was computed at 9.90kwp. this is the minimum fspv system size required to provide for the community's needs. the resources needed to implement an ai-ready fspv system were also briefly highlighted. the implementation of ai using machine learning tools to automate the diagnostics and fault detection in the system mitigates or prevents misfortunes when the fspv system is deployed. the system requires various environmental sensors that cover data gathering on wind speed, wave level, temperature, humidity, voltage, and currents. these form a part of the bigger data acquisition unit installed at the system's location. the data processing and machine learning techniques will be executed at the university's r&d laboratory. based on this resource assessment and identification of the resources needed to put up the fspv system, there is an excellent motivation to pursue the implementation of the fspv system to 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[39] "solar resource maps of philippines." https://solargis.com/maps-and-gisdata/download/philippines (accessed mar. 02, 2022). microsoft word etasr_v12_n5_pp9351-9356 engineering, technology & applied science research vol. 12, no. 5, 2022, 9351-9356 9351 www.etasr.com slimani & hedjam: a hybrid metaheuristic and deep learning approach for change detection in … a hybrid metaheuristic and deep learning approach for change detection in remote sensing data yacine slimani department of computer science laboratory of intelligent systems university of ferhat abbas setif 1 setif, algeria slimaniy09@univ-setif.dz rachid hedjam department of computer science sultan qaboos university muscat, oman rachid.hedjam@squ.edu.om received: 6 august 2022 | revised: 17 august 2022 | accepted: 20 august 2022 abstract-this study aimed to adapt convolutional neural networks (cnn) to solve the problem of change detection using remote sensing imagery. specifically, the goal was to investigate the impact of each cnn layer to detect changes between two satellite images acquired on two different dates. as low-level cnn layers detect fine details (small changes) and higher-level layers detect coarse details (large changes), the idea was to assign a weight to each layer and use a genetic algorithm based on a training dataset to generalize the detection process on the test dataset. the results showed the effectiveness of the proposed approach based on two real-life datasets. keywords-change detection; remote sensing; deep learning; convolutional neural networks; genetic algorithms i. introduction the aim of binary change detection (cd) in remote sensing is to compare two images acquired at two different dates to detect meaningful differences [1]. usually, two cd approaches are used: supervised or unsupervised. supervised cd requires temporal reference data for the training phase [2, 3], while unsupervised cd is based on a direct comparison of input images without using labeled data [4-6]. in general, unsupervised binary cd techniques consist of two steps: i) compute the difference between the features of the two input images to generate a difference image or change index, and ii) generate the binary change map by segmenting (thresholding) the difference image computed in the first step into change and no-change regions. however, traditional cd methods that use handcrafted features are not effective in complex situations, because the designed features cannot accurately capture high and medium-level image representations [7]. recently, deep learning has emerged and has become a state-of-the-art approach for cd. deep learning is very effective in extracting representative features from low, middle, and higher image representation levels. the advantages of deep learning are that, it learns discriminant features and computes them automatically without relying on the involvement of an expert. several deep-learning methods for cd have been proposed. in [8], a method was proposed to compute the difference image using a backpropagation algorithm and a deep belief network. a deep belief network learns low and high-level features around a pixel neighborhood and the backpropagation algorithm builds the difference image using training samples. finally, a simple segmentation algorithm was used to compute the binary change map. a method was proposed in [9] that combined deep features, saliency detection, and convolutional neural networks (cnns) to compute the change. a patchbased siamese neural network was presented in [10], where external images, whose textures resembled the changing area, were used to generate genuine and imposter pair samples for the training process. a method that combined cnn features to create a single higher feature vector was proposed in [7], using the pixel-wise euclidean distance between the extracted feature vectors after having been transformed into matrices to compute the change map. a review of the deep learning-based cd methods can be found in [11] this study extends [12] and is related to [7]. the difference between this study and [7] lies in the combination process of the cnn layers. in [7], all cnn layers were combined into a single feature vector, but this study proposes the assignment of weights to the cnn layers before combining them. in [12], the weights were binary (i.e. 1 for considering a layer and 0 for not) and assigned manually. this study used a genetic algorithm (ga) to automatically learn the weights based on training data. the ga aims to find the best weights that lead to the best match between the cd reference (ground truth) and the change map detected by the proposed algorithm. therefore, the weight vector can be seen as a mask, where the goal is to demonstrate that the layers can be assigned different weights before being combined to detect different regions that represent the changes between the two input images. the assumption was that, to detect large changes, high-level layers are assigned higher weights, i.e. considered more. ii. the proposed approach usually, the spatial changes in remote sensing images are specific patterns with special features in terms of color, shape, and texture. therefore, their cnn characteristics are different from those of the same location in the image before the change. in other terms, an unchanged spatial area between the two corresponding author: yacine slimani engineering, technology & applied science research vol. 12, no. 5, 2022, 9351-9356 9352 www.etasr.com slimani & hedjam: a hybrid metaheuristic and deep learning approach for change detection in … inputs should have almost similar cnn features, whereas the changed areas have different. thus, it seems reasonable to compute the features of the two input images using the same cnn structures and then compute their difference to generate the difference image, where the brighter pixels represent the changed areas due to the larger difference values. to detect the changed areas, the difference image can be segmented by a thresholding method into "changed" and "unchanged" classes. in a cnn, the lower layers capture low-lever image features such as edges, color, and gradient orientation, while the midhigh level layers capture coarse patterns of the images that can represent whole objects in the images [13]. since the changes are almost a random natural process, they may affect areas with different sizes from fine to coarse. therefore, detecting changes between the two input images based on the difference between their last cnn feature is not effective. to overcome this limitation, a new change detection method was proposed, which is an improvement over [7]. the procedure obeys the following: i) extract low, mid and higher features from each image using a pre-trained cnn (e.g. vgg19 [14]), ii) resize the layers to the same size and combine them into a single feature vector for each image, iii) reshape the two feature vectors into square matrices, and finally iv) compute the euclidean distance between the two matrices to generate the difference image, which will be segmented into two classes, "changed" and "unchanged". in [12], a binary weight was assigned manually to each layer to include it or not in the combination process of the layers. in other terms, the binary vector of weights played a mask role that allowed or prevented some layers from the combination process. if the weight of a given layer was equal to one (1), it meant that this layer was included in the combination process, while if it was equal to zero (0) it was not. assigning weights to layers is application dependent. in practice, it is best to consider high-level layers when detecting large changes, while low-level layers should be taken into account when detecting minor changes. fig. 1. convolutional feature-based change detection with vgg19. in the training phase, n image tuples were used {(im1; im2; tr)}i, i=1…n, where im1 and im2 are the images before and after a change and tr is the corresponding ground truth. each image is divided into m patches of size d×d. in other terms, there is a set of s=n×m patches before the change, i.e. {pj1, j=1...s}, a set of patches after the change, i.e. {pj2, j=1...s}, and the same number of ground truth patches. each patch is fed to a vgg19 cnn to extract 5 feature maps from 5 different layers. this study used the 3 rd , 6 th , 10 th , 14 th , and 18 th layers of the vgg19. from each input patch, 5 layers (feature maps) were extracted and resized to the same size. formally, let [xj11, xj12, xj13, xj14, xj15] be the list of the feature maps extracted from pj1, and [xj21, x j22, x j23, x j24, x j25] be the list of the feature maps extracted from pj2. thus, the corresponding weighted feature maps are: ��� � ��� � ����, � � ��� , �� � ����, � � ��� , �� � ���� � �� � ��� � �� �, � � �� , �� � �� �, � � �� , �� � �� � � where w=[w1, w2 …, w5] are the continuous weights learned by a ga. the difference image for the j th patch-pair is then computed as follows (see figure 2): ��� � dist���1, ��2� � �∑ �� � ��� ! � � �� " � #� (1) fig. 2. cnn-based features vectors process. the goal is to learn the weight vector w using a ga that maximizes the fitness (f-score) between the detected change and the corresponding ground truth for all the patches used in the training phase [15]. once the optimal weights are learned, they will be used in the test phase. the overall ga for learning the weights, shown in figure 3, was: • step 1 (initialize population): the first step of ga is to randomly create and initialize the chromosomes of the initial population. nb_ind vectors $ � %$ �&�|( � 1. . *+_�-./ are generated. each $ �&� is a chromosome with five (5) real-valued genes�� �&�|0 � 1. . .5�. engineering, technology & applied science research vol. 12, no. 5, 2022, 9351-9356 9353 www.etasr.com slimani & hedjam: a hybrid metaheuristic and deep learning approach for change detection in … • step 2 (evaluation): the fitness function measures the fitness of the change map between each pair of the patch and the corresponding ground truth patches as follows: �(2-344�$ �&�� � ∑ 56789:�;<= ,>9=� ?=@a b (2) fig. 3. ga-based learning process algorithm. • step 3 (selection): the elitism selection method selects the best w (i) chromosomes from the previous population to integrate them into the next population. according to the best fitness function values fitness(w (i) ), a portion of (probselect%) from the precedent population was selected to breed a new generation. • step 4 (crossover): the crossover method creates a portion of (probcross%) from the precedent population. a onepoint crossover method was used. • step 5 (mutation): the goal of this function was to introduce diversity into the population. a portion of (probmut%) was chosen and a random value was assigned to one randomly chosen gene. • redo steps 2, 3, 4, and 5 until stability (no change in the fitness) (see algorithm 1). finally, the best w is chosen to be used in the test phase. iii. experimentation and evaluation a. dataset description two datasets were used to evaluate the proposed change detection framework, namely the sztaki airchange benchmark set [16] and the onera satellite change detection dataset [17]. the sztaki airchange benchmark set contains 13 aerial image pairs of 952×640 pixels with a resolution of 1.5m/pixel, and binary change masks (a ground truth defined by experts). the onera satellite change detection dataset consists of 24 pairs of multispectral images taken using the sentinel-2 satellites between 2015 and 2018. the locations were picked from all over the world, brazil, the united states, europe, the middle east, and asia. for each location, registered pairs of 13-band multispectral satellite images are required. the images vary in spatial resolution between 10m, 20m, and 60m. the pixel-level change ground truth is provided for the image pairs. the annotated changes focus on urban changes, such as new buildings or new roads. b. ga parameter setting in the training phase, a pre-trained vgg19 was used to extract the feature maps. the ga requires several parameters to search for the optimal layer weights: • number of generations nb_gen=200 • number of individuals nb_ind=100 • probability of selection probselect=40% • probability of crossover probcross=40% • probability of mutation probmutation=20% c. results, evaluation, and comparison to other methods the proposed method was compared with two classes of existing change detection methods, traditional and deep learning based. the traditional methods were the iteratively reweighted multivariate alteration detection method (imad) for change detection [18], slow feature analysis (sfa) algorithm for change detection [19], principal component analysis and k-means clustering (pca-kmeans) [20], and change vector analysis (cva) [21]. the deep learning-based methods were two simple cnn-based without layer weighting: the vgg19 [7], and the resnet50 [22]. table i shows the change detection results using different methods in terms of f-score, recall, precision, and accuracy, based on the sztaki dataset. based on f-score and accuracy, the proposed method gave the best results with the test images szada3, tiszadob2, and archive (accuracy was 0.90, 0.85, and 0.85 respectively). in the case of the szada4 image, the proposed method gave better results than the original vgg19 algorithm (accuracy was 0.70 versus 0.69) but had lower accuracy than imad, which can be justified by the poor quality of the ground truth. engineering, technology & applied science research vol. 12, no. 5, 2022, 9351-9356 9354 www.etasr.com slimani & hedjam: a hybrid metaheuristic and deep learning approach for change detection in … table i. change detection results of the sztaki airchange dataset images methods f-score recall precision accuracy white pixels detected szada3 imad 0.45 0.63 0.35 0.86 4261 isfa 0.35 0.38 0.33 0.89 2553 pca-kmeans 0.37 0.50 0.29 0.84 3368 cva 0.16 0.60 0.09 0.42 4062 vgg 19 0.31 0.32 0.30 0.87 2166 resnet50 0.41 0.66 0.29 0.82 4462 proposed 0.45 0.45 0.44 0.90 3078 szada4 imad 0.57 0.50 0.67 0.78 14438 isfa 0.42 0.39 0.45 0.67 11350 pca-kmeans 0.59 0.57 0.61 0.76 16548 cva 0.38 0.57 0.29 0.45 16418 vgg 19 0.27 0.20 0.45 0.69 5646 resnet50 0.50 0.45 0.57 0.73 12884 proposed 0.30 0.24 0.48 0.70 6865 tiszadob2 imad 0.39 0.48 0.32 0.70 7608 isfa 0.36 0.47 0.29 0.66 7555 pca-kmeans 0.48 0.63 0.39 0.74 10011 cva 0.32 0.67 0.21 0.45 10734 vgg 19 0.23 0.17 0.36 0.78 2664 resnet50 0.36 0.36 0.37 0.75 5769 proposed 0.44 0.35 0.60 0.85 4945 archive imad 0.40 0.45 0.36 0.76 6392 isfa 0.31 0.22 0.56 0.83 3118 pca-kmeans 0.40 0.46 0.35 0.76 6544 cva 0.31 0.71 0.20 0.45 10092 vgg 19 0.31 0.20 0.65 0.84 2863 resnet50 0.45 0.48 0.42 0.80 6776 proposed 0.32 0.21 0.70 0.85 2958 (a) (b) (c) (d) (e) fig. 4. subjective results. from left to right: (a) image (1) before change, (b) image (2) after change, (c) ground-truth, (d) cd map, (e) overlay of cd on image (2). images from sztaki, from top to bottom, szada3, szada4, tiszadob2, archive. engineering, technology & applied science research vol. 12, no. 5, 2022, 9351-9356 9355 www.etasr.com slimani & hedjam: a hybrid metaheuristic and deep learning approach for change detection in … table ii. change detection results of the onera satellite dataset images methods f-score recall precision accuracy white pixels detected beirut imad 0.46 0.58 0.39 0.90 2262 isfa 0.42 0.94 0.27 0.80 3682 pca-kmeans 0.54 0.71 0.43 0.90 2804 cva 0.17 0.82 0.09 0.35 3231 vgg 19 0.26 0.17 0.53 0.92 670 resnet50 0.43 0.55 0.36 0.89 2165 proposed 0.55 0.57 0.67 0.94 2252 chongqing imad 0.56 0.75 0.45 0.94 1897 isfa 0.52 0.77 0.39 0.93 1943 pca-kmeans 0.42 0.53 0.35 0.93 1340 cva 0.07 0.50 0.04 0.36 12682 vgg 19 0.22 0.19 0.27 0.93 492 resnet50 0.36 0.45 0.31 0.92 1125 proposed 0.41 0.43 0.44 0.94 1095 las vegas imad 0.60 0.61 0.59 0.92 3183 isfa 0.33 0.55 0.24 0.77 2858 pca-kmeans 0.54 0.49 0.60 0.91 2558 cva 0.17 0.65 0.10 0.37 3346 vgg 19 0.37 0.42 0.32 0.85 2196 resnet50 0.64 0.94 0.48 0.89 4853 proposed 0.40 0.46 0.49 0.90 2362 montpellier imad 0.67 0.65 0.69 0.92 4141 isfa 0.62 0.54 0.72 0.92 3451 pca-kmeans 0.69 0.76 0.62 0.91 4825 cva 0.26 0.75 0.16 0.47 4725 vgg 19 0.51 0.40 0.71 0.90 2554 resnet50 0.63 0.63 0.62 0.91 4014 proposed 0.44 0.35 0.60 0.85 4945 (a) (b) (c) (d) (e) fig. 5. subjective results. from left to right: (a) image (1) before change, (b) image (2) after change, (c) ground-truth, (d) cd map, € overlay of cd on image (2). images from onera. from top to bottom, beirut, chongqing, las vegas, montpellier. table ii shows the change detection results of the different methods in terms of f-score, recall, precision, sensitivity, and accuracy, based on the onera satellite dataset. the proposed method was again better than vgg19 in any case, and it was the best for beirut and chongqing test images, but weaker than imad for las vegas and montpellier. engineering, technology & applied science research vol. 12, no. 5, 2022, 9351-9356 9356 www.etasr.com slimani & hedjam: a hybrid metaheuristic and deep learning approach for change detection in … figures 4 and 5 show the results of change detection on the test image from the sztaki and the onera datasets respectively. the last column shows the overlay of the change detection map on the image after the change, where the changes are highlighted in red and the ground truth is highlighted in cyan blue. it can be noted that most of the changes that occurred were detected. unfortunately, the method detected unwanted changes, which means that it triggered more false alarms. finally, the results obtained show that the proposed method gave better results than [7] and [12], unveiling the problem with the weight of the layer. moreover, the ga learning phase made it possible to detect fine and coarse details, by finding the best weight vector. iv. conclusion this paper presented an artificial intelligence-based change detection approach for remote sensing. the challenge of finding the best weighted cnn layers to the change detection problem was solved using a genetic algorithm. the proposed approach combines a cnn (pre-trained vgg19) and genetic algorithm to build a near-optimal weight vector. this vector was combined with the feature maps to compute their difference and produce the change map. the purpose of this study was to investigate the adaptation of cnns to detect changes in remote-sensing images. two datasets were used to show that it is recommended to specify the cnn layers to be used to detect different changes. more precisely, detecting small changes requires the use of the first cnn layers, whereas large changes require the use of the last layers. therefore, a natural way to solve this problem is to use a meta-heuristic optimization method to find the best weights for the layers to be combined to generate the relevant feature maps. future work could investigate 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[22] k. l. de jong and a. sergeevna bosman, "unsupervised change detection in satellite images using convolutional neural networks," in 2019 international joint conference on neural networks (ijcnn), budapest, hungary, jul. 2019, pp. 1–8, https://doi.org/10.1109/ ijcnn.2019.8851762. microsoft word 3-664-ed.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1050-1055 1050 www.etasr.com haj aliwi et al.: a comparison between inter-asterisk exchange protocol and jingle protocol … a comparison between inter-asterisk exchange protocol and jingle protocol: session time h. s. haj aliwi school of computer sciences universiti sains malaysia hadeelsaleh12@yahoo.com n. k. a. alajmi saad al-abdullah academy for security sciences, kuwait naser.k.a.alajmi@gmail.com p. sumari school of computer sciences universiti sains malaysia putras@usm.my k. alieyan national advanced ipv6 center universiti sains malaysia kamal_alian@nav6.usm.my abstract—over the last few years, many multimedia conferencing and voice over internet protocol (voip) applications have been developed due to the use of signaling protocols in providing video, audio and text chatting services between at least two participants. this paper compares between two widely common signaling protocols: interasterisk exchange protocol (iax) and the extension of the extensible messaging and presence protocol (jingle) in terms of delay time during call setup, call teardown, and media sessions. keywords-multimedia conferencing; voip; signaling protocols; jingle; iax i. introduction with the appearance of numerous multimedia conferencing and voice over internet protocols [3, 6, 10, 12], the decision to choose the appropriate protocol to be utilized in such a service has become very difficult since each protocol has its own privileges which differ from the corresponding privileges of the other protocols. this paper defines the attributes of iax and jingle protocols because of their services compared with the other signaling protocols. therefore, the objective of this paper is mainly to make a comparative study between iax and jingle protocols in terms of quality of services (packet delay). this paper does not cover video conferencing and document conferencing services (instant messaging, file attachment and image sharing) since iax is a voip protocol, despite it can be used for any type of streaming media, but it is mainly designed for ip voice calls. choosing iax and jingle protocols to be compared is due to many reasons. iax is an interesting alternative compared to the conventional voip protocols. nowadays, iax is being deployed by service providers for their voip service offerings (e.g. h.323 and sip). iax protocol offers significant features that are not provided by other existent voip signaling protocols. furthermore, many researchers have shown that iax is slightly better than sip [4, 5, 11], h.323 [1], mgcp [8] and rsw [9, 17] in terms of quality of services. just as iax protocol has many features, jingle protocol is considered as the standard protocol for gmail chatting application with regard to audio and video conferencing services. most popular chatting applications use jingle protocol to handle the call setup, audio/video chatting, and call teardown sessions. such applications are gtalk, talkonaut, and hangouts [7]. ii. background a. iax protocol in 2004, mark spencer created the inter-asterisk exchange (iax) protocol for asterisk that performs voip signaling [22]. iax is supported by a few other softswitches, (asterisk private branch exchange) pbx systems [23], and softphones [18]. any type of media (video, audio, and document conferencing) can be managed, controlled and transmitted through the internet protocol (ip) networks based on iax protocol [25]. iax2 is considered to be the current version of iax. the iax’s first version is obsolete. iax supports the trunk connections concept for numerous calls. the bandwidth usage is reduced when this concept is being used because all the protocol overhead is shared by two iax nodes for the whole calls. over a single link, iax provides multiplexing channels [13, 14]. the three main procedures used for the audio conferencing between two iax endpoints are call setup, audio transmission, and call teardown with the steps of each procedure. endpoint a sends new packet to the endpoint b to place a call, and wait until receiving an accept packet from endpoints b, after accept reply, endpoint a sends an ack packet to endpoint b to acknowledge of receiving the accept packet by endpoint a. after that, endpoint b rings at endpoint a by sending a ringing packet, which in turn send an ack packet to endpoint b to inform about receiving the accept message. then, endpoint b sends an answer packet to endpoint a in order to start the call, and wait till sending the acknowledgment message (ack) by endpoint a. at that time, the audio conferencing is started by transferring the audio packets between the two endpoints which is carried by the iax mini and full frames. once the two endpoints complete their call, endpoint a sends hangup packets to endpoint b to end the call, finally endpoint b do reply back by sending an acknowledgment packet (ack). it can be concluded that [24]: • iax setup session time = the receiving time of the third ack message – the sending time of new message. engineering, technology & applied science research vol. 6, no. 4, 2016, 1050-1055 1051 www.etasr.com haj aliwi et al.: a comparison between inter-asterisk exchange protocol and jingle protocol … • iax media session time = the sending time of hangup message – the receiving time of the third ack message. • iax teardown session time = the receiving time of the fourth ack message – the sending time of hangup message. b. jingle protocol the extensible messaging and presence protocol (xmpp) [19] is a standard specified by the internet engineering task force (ietf) for carrying instant message service. xmpp is an open extensible markup language (xml) protocol for a realtime messaging, presence, and request/response services. first, jabber open-source community proposed and introduced xmpp. subsequently, the ietf approved and archived it in many internet specifications. originally, the scope of xmpp was only instant messaging, but as an extensible protocol, it has also come to support voip. the voip extension to xmpp is known as jingle and was developed by google [20]. there are three types of sessions used by jingle to do the negotiations between two entities. they are respectively session-initiation, session-accept, and session-terminate. considering that two entities are starting in negotiation, which are the initiator and the responder. to setup the call, the initiator sends a session initiation offer to the responder. after the responder acknowledges the receipt of the session-initiate message, it prompts the responder to choose whether he wants to proceed with the session. if he wants to proceed, he selects the appropriate interface element and his client sends a sessionaccept message to the initiator. the initiating client acknowledges receipt of the session-accept message [16]. after that, both the initiator and the responder can exchange the audio data over rtp protocol [2]. eventually, one of the clients will terminate the session. the other client acknowledges receipt of the session-terminate message and the session is ended. like the call setup, the call teardown takes place over jingle protocol [21]. it can be concluded that [15]: • jingle setup session time = the receiving time of the second ack message – the sending time of session-initiate message. • jingle media session time = the sending time of sessionterminate message – the receiving time of the second ack message. • jingle teardown session time = the receiving time of the third ack message – the sending time of sessionterminate message. iii. iax and jingle: a comparison the packet delay for both iax and jingle protocols during setup, teardown, and media sessions has been tested by using the network simulation ns2 (ns-2.35) [26]. for each session, five scenarios have been provided in order to compare the values of packet delay in iax client with the corresponding ones in jingle protocol. it can be noticed from the experiments that iax protocol has an improved performance over jingle protocol due to trunking property, so several communications can be multiplexed into the data stream. a. simulation parameters in table i, the simulation parameters with regard to nodes, peer connection, audio codec, protocols, transmission range, packet size, and simulation time are clarified. table i. simulation parameters parameter value used in scenarios nodes iax client, iax server, jingle client, jingle server peer connection one-to-one, two-to-two, three-to-three, four-to-four, five-to-five codec g.711 network protocol ip transport protocol udp, rtp signaling protocol iax & jingle transmission range 375 m propagation delay 10 milli seconds packet size 512 bytes simulation time 50 seconds b. performance with packet delay (call setup session) the experiments focused on comparing the values of the setup delay time in jingle with the corresponding values in iax. to examine the quality effects due to setup delay, both iax and jingle have been compared with a fixed packet sequence number ranging from 1 to 6 with increment of 1. five scenarios are provided starting from 1 to 5 calls. as indicated in figures 1 and 2, the iax packet delay varies between 0.00231 and 0.00314 seconds, 0.00375 and 0.00427 seconds in case of one and two calls respectively, whereas, jingle packet delay varies between 0.00254 and 0.00318 seconds in case of one call and between 0.00389 and 0.00447 seconds in case of two calls. as shown in figure 3, the packet delay value for both iax and jingle increase since one more call is added by adding two more clients to the experiment (one iax client and one jingle client). in this experiment, the packet delay value for both iax and jingle clients varies between 0.00477 and 0.00552 seconds with the note that iax has an improvement in performance over jingle. in addition, for both four-to-four and five-to-five peer connections, the maximum iax packet delay values during the setup session are 0.00635 and 0.00726 seconds respectively which are slightly less than the maximum jingle packet delay values during the same session which are 0.00648 and 0.00732 seconds respectively. in table ii, the whole setup session time is calculated for both iax and jingle within number of calls varies between 1 and 5 calls. the setup session is responsible for initiating the iax/jingle call before starting the voice chatting. table ii. iax/jingle setup session time setup session time number of calls iax jingle 1 0.01642 seconds 0.01745 seconds 2 0.02414 seconds 0.02501 seconds 3 0.03115 seconds 0.03184 seconds 4 0.03652 seconds 0.03748 seconds 5 0.04218 seconds 0.04278 seconds engineering, technology & applied science research vol. 6, no. 4, 2016, 1050-1055 1052 www.etasr.com haj aliwi et al.: a comparison between inter-asterisk exchange protocol and jingle protocol … fig. 1. iax/jingle packet delay for 1 call: setup session fig. 2. iax/jingle packet delay for 2 calls: setup session fig. 3. iax/jingle packet delay for 3 calls: setup session fig. 4. iax/jingle packet delay for 4 calls: setup session fig. 5. iax/jingle packet delay for 5 calls: setup session c. performance with packet delay (call teardown session) the comparison between the call teardown delay values in jingle and the corresponding values in iax is presented in this section. both iax and jingle are compared with a fixed packet sequence number ranging from 1 to 5 with increment of 1. based on figures 6 and 8, the minimum iax and jingle packet delay values during teardown session are in the first packet, whereas, the last packet has the maximum packet delay values for iax protocol in case of one call and for jingle protocol in case of three calls. figure 7 present iax/jingle packet delay within two active iax/jingle clients. as seen, the teardown session starts in the highest delay values for both iax and jingle, then the delay values keeps decreasing until the fourth packet sequence number where increasing later. fig. 6. iax/jingle packet delay for 1 call: teardown session fig. 7. iax/jingle packet delay for 2 calls: teardown session engineering, technology & applied science research vol. 6, no. 4, 2016, 1050-1055 1053 www.etasr.com haj aliwi et al.: a comparison between inter-asterisk exchange protocol and jingle protocol … from figure 9, it can be noticed that the delay values for both iax and jingle are much closed to each other although despite iax has lass delay values for the whole packet sequence numbers. the delay difference between iax and jingle delay values does not exceed 0.00011 seconds. on the other hand, the differences between the iax and jingle delay values in figure 10 are far apart by nearly 0.0003 seconds especially in the packet sequence numbers two to five. fig. 8. iax/jingle packet delay for 3 calls: teardown session fig. 9. iax/jingle packet delay for 4 calls: teardown session fig. 10. iax/jingle packet delay for 5 calls: teardown session table iii presents the teardown session time in case of one iax/jingle to five iax/jingle calls the teardown session has the responsibility for terminating the iax/jingle call once the two participants decided to end the voice chatting. table iii. iax/jingle teardown session time teardown session time number of calls iax jingle 1 0.01312 seconds 0.01369 seconds 2 0.01942 seconds 0.01979 seconds 3 0.02644 seconds 0.02699 seconds 4 0.03112 seconds 0.03147 seconds 5 0.03587 seconds 0.03694 seconds d. performance with packet delay (media session) during the media session, the participants exchange the speech which is transferred from the source to the distention in the form of media packets. in this section, the performance of jingle and iax in the presence of packet delay has been compared. the performance of both protocols has been tested using a fixed packet sequence number ranging from 1 to 100 with increment of 1. as shown in figures 11-15, the packet delay during the media session for both iax and jingle does not exceed 0.009 seconds. based on the media session results, during the first 100 packets the delay values vary from an increase in delays and decreasing. the media packet is exchanged with the lowest delay values of roughly 0.002 seconds in case of one call. by increasing the number of calls by one, the packet delay values increase by 0.001 to 0.002 seconds until reaching 0.0009 seconds in case of five calls. fig. 11. iax/jingle packet delay for 1 call: media session fig. 12. iax/jingle packet delay for 2 calls: media session in the experiments with more than one call, each packet delay value has been founded by calculating the average of the packet delay values for the whole call. for example, figure 13 indicates the packet delay within three calls, so to find the engineering, technology & applied science research vol. 6, no. 4, 2016, 1050-1055 1054 www.etasr.com haj aliwi et al.: a comparison between inter-asterisk exchange protocol and jingle protocol … packet delay value when the packet sequence number is 50; we have to find the summation of the delay values during call 1, call 2, and call 3 with the same packet sequence number over 3 which is the number of calls. this means that: packet 50 delay (for 3 calls) = packet 50 delay (for call 1) + packet 50 delay (for call 2) + packet 50 delay (for call 3) / 3. fig. 13. iax/jingle packet delay for 3 calls: media session fig. 14. iax/jingle packet delay for 4 calls: media session fig. 15. iax/jingle packet delay for 5 calls: media session table iv presents the media session time for the first 100 packets. the session time is founded in case of 1 to 5 calls. the media session has the responsibility for starting the voice chatting between two participants after initiating the call by the setup session and stop the call in order to terminate the call by the teardown session. table iv. iax/jingle media session time media session time number of calls iax jingle 1 0.245445 seconds 0.27061 seconds 2 0.363002 seconds 0.398217 seconds 3 0.511089 seconds 0.540154 seconds 4 0.656467 seconds 0.696029 seconds 5 0.801055 seconds 0.846396 seconds iv. conclusion this paper investigated the main differences between the interasterisk exchange protocol (iax) and the extension of the extensible messaging and presence protocol (jingle) iax and jingle by performing a comparison in terms of quality of services (packet delay) during all sessions. references [1] i. basicevic, m. popovic, d. kukolj, “comparison of sip and h.323 protocols”, 3rd international conference on digital telecommunications icdt ’08, pp. 162–167, 2008 [2] e. chow, “rtp: a transport protocol for real-time 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[4] d. geneiatakis, t. dagiuklas, g. kambourakis, c. lambrinoudakis, s. gritzalis, “survey of security vulnerabilities in session initial protocol”, ieee communications surveys & tutorials, vol. 8, no. 3, pp. 68-81, 2006 [5] j. glasmann, w. kellerer, h. muller, “service architectures in h.323 and sip: a comparison”, ieee communications surveys & tutorials, vol. 5, no. 2, pp. 32-47, 2003 [6] b. goode, “voice over internet protocol (voip)”, proceedings of the ieee, pp. 1495 –1517, 2002 [7] google developers, “google talk for developers”, 2011, available at: https://developers.google.com/talk/jep_extensions/extensions [8] t. dajiuklas, k. ioannou, a. garmpis, “a lightweight and scalable voip platform based on mgcp/h.323 interworking and qos management capabilities”, 4th wseas international conference on information security, communications and computers, tenerife, spain, pp. 548-553, 2005 [9] h. s. haj aliwi, s. a. alomari, p. sumari, “an effective method for audio translation between iax and rsw protocols”, world academy of science, engineering and technology, vol. 5, no. 11, pp. 253-256, 2011 [10] h. s. haj aliwi, p. sumari, “a comparative study of voip, mcs, instant messaging protocol and multimedia applications”, international journal of advances in computer networks and its security, vol. 4, no. 2, pp. 67-70, 2014. [11] h. s. haj aliwi, s. a. alomari, p. sumari, “an efficient audio translation approach between sip and rsw protocols”, 3rd world conference on information technology (wcit-2012), university of barcelona, spain, pp. 31-37, 2013 [12] h. s. haj aliwi, p. sumari, “a comparative study of voip protocols”, international journal of computer science and information security, vol. 11, no. 4, pp. 97-101, 2013 [13] h. s. haj aliwi, p. sumari, s. a. alomari, “an efficient interworking between heterogeneous networks protocols and multimedia computing applications”, international journal of computer science and information security, vol. 11, no. 5, pp. 81-86, 2013 [14] m. kolhar, m. abu-alhaj, o. abouabdalla, t.c. wan, a. manasrah, “comparative evaluation and analysis of iax and rsw”, international journal of computer science and information technology, vol. 6, no. 3, pp. 250–252, 2013 engineering, technology & applied science research vol. 6, no. 4, 2016, 1050-1055 1055 www.etasr.com haj aliwi et al.: a comparison between inter-asterisk exchange protocol and jingle protocol … [15] s. ludwig, j. beda, p. saint-andre, r. mcqueen, s. egan, j. hildebrand, “jingle”, xsf xep 0166, 2007, available at: http://xmpp.org/extensions/xep-0166.html [16] s. ludwig, p. saint-andre, s. egan, r. mcqueen, d. cionoiu, “jingle rtp sessions”, xep 0167, 2009, available at: http://xmpp.org/extensions/xep-0167.html [17] s. ramadass, r. k. subramanian, h. guyennet, m. trehel, “using rsw control criteria to create a distributed environment for multimedia conferencing”, proceedings on research and development in computer science and its applications, penang, malaysia, pp. 27-29, 1997 [18] e. reeves, “testing devices that handle inter-asterisk exchange, version 2 (iax2) protocol”, 2011. available at: http://blogs.ixiacom.com/ixia-blog/content-aware-testing-iax2-protocol/ [19] p. saint-andre, “extensible messaging and presence protocol (xmpp)”, rfc 3921, instant messaging and presence. internet engineering task force, 2004 [20] p. saint-andre, “interworking between the session initiation protocol (sip) and the extensible messaging and presence protocol (xmpp): media sessions”, xmpp standards foundation, 2013, available at: https://tools.ietf.org/html/draft-ietf-stox-media-07 [21] p. saint-andre, s. ibarra, e ivov, “interworking between the session initiation protocol (sip) and the extensible messaging and presence protocol (xmpp): media sessions”, xmpp standards foundation, 2015, available at: https://tools.ietf.org/html/draft-ietf-stox-media-05 [22] m. spencer, b. capouch, e. guy, f. miller, k. shumard, “iax: interasterisk exchange version 2”, 2010, available at: http://tools.ietf.org/html/ rfc5456 [23] m. spencer, “iax”, 2004, available at: http://www.voip-info.org/wiki/ view/iax [24] m. spencer, “configuring iax clients”, 2004, available at: http://www.voip-info.org/wiki/view/asterisk+config+iax.conf [25] m. spencer, f.w. miller, “iax protocol description”, 2004, available at: http://www.voipinfb.hu/content/download/iax.pdf [26] n. garg, “network simulators: a case study”, international journal of advanced research in computer science and software engineering, vol. 5, no. 1, pp. 651-655, 2015 microsoft word etasr_v13_n1_pp9968-9972 engineering, technology & applied science research vol. 13, no. 1, 2023, 9968-9972 9968 www.etasr.com bui: control design for the ward–leonard system in wind turbines control design for the ward–leonard system in wind turbines huy hai bui faculty of electronic engineering, technology university of economics technology for industries, vietnam bhhai@uneti.edu.vn (corresponding author) received: 20 october 2022 | revised: 3 november 2022 and 13 november 2022 | accepted: 15 november 2022 abstract a robust optimal controller for the ward-leonard system in a wind turbine is used to meet the performance and stability requirements when the system parameters change. however, designing according to the robust optimal method often leads to a high-order controller. this study investigated the application of order reduction algorithms to simplify the controller and help it better meet the real control problem. comparative evaluation of the order reduction controller methods showed that the second-order reduction controller according to moore's balanced truncation algorithm was the most suitable to replace the higher-order controller. the step response quality of the system was better when using a second-order reduction controller than a higher-order controller. keywords-model order reduction; ward–leonard system; wind tube system; robust optimal control i. introduction wind energy is a natural form of energy produced by the movement of air in the atmosphere. also, it is an indirect form of solar energy. wind energy is the process where wind uses its movement to generate mechanical energy. the research on the potential application of wind energy is quite diverse [1-9], but most researchers believe that the prospect of wind energy development is an inevitable future trend, as clean energy sources will gradually replace current fossil energy sources. this share is determined based on the countries' energy policies and the roadmap to reduce adverse environmental impact. wind turbines convert the kinetic energy of the air into mechanical energy. for maximum efficiency, the wind turbine blades must direct the wind with an optimum angle, must be flexible and strong to withstand disturbances and high-speed rapid oscillations, and require a suitable control system [10]. the ward-leonard dc motor speed control system is used when the speed control requirements are very wide and very sensitive. it is a suitable system for wind turbine control and antenna tracking systems [11]. the system contains a dc generator that serves as a power amplifier for the dc control signal. the generator is rotated at a constant speed from the main motor and an output voltage is generated and supplied to the dc motor, while an external dc power source powers the motor's inductor. the wind turbine control problem requires the controller to have good performance and strong stability when the parameters of the model change. a robust optimal controller is the most suitable to control the ward–leonard system in a wind turbine system. however, the design method of the robust optimal controller h∞ [12] often leads to a highorder controller. a high-order controller has many disadvantages, such as complicated programming and long computation time, resulting in slow system responses. reducing the order of a high-order robust controller while ensuring quality has a high practical significance. two basic methods are used to obtain a low-order robust optimal controller. the first method designs a high-order controller according to a stable optimal control algorithm and then applies model order reduction algorithms to obtain a lower-order stable optimal controller [13-14], while the second method uses optimization algorithms to design a low-order controller that satisfies the requirements of sustainable optimal control [15]. ii. the ward-leonard system in wind turbines and high-order robust controller the ward-leonard system contains a dc generator that serves as a power amplifier of the control signal. the dc generator is rotated at a constant speed by the main motor, and its output voltage powers the dc motor, while the field winding of the motor is supplied by a separate dc source. in [10], the ward-leonard system was used to control a wind turbine system, and its modeling gave the following results: �(�) = ��� �(� �� �� ���.�� ���) (1) the wind turbine control problem requires the controller to have good performance and strong stability when the parameters of the model change. a robust optimal controller with the following results was designed in [10]: �(�) = �.����� ������ ��� � �.���.����� ���� ��.� �� ���.��� ������ ����� �.���.����� ����� ��� (2) engineering, technology & applied science research vol. 13, no. 1, 2023, 9968-9972 9969 www.etasr.com bui: control design for the ward–leonard system in wind turbines the 6 th -order robust controller has many disadvantages when used in practice, such as slow response time and complex programming. therefore, it is necessary to reduce the order of this 6 th -order robust controller to increase the response speed of the system and better meet the requirements of robust control. fig. 1. block diagram of the control system. iii. reducing the high-order robust controller all the poles of the 6 th -order controller have negative real parts, so the 6 th -order controller is a stable model. different order reduction algorithms were used to reduce the order of the 6 th -order controller, and the different resulting controllers were compared to choose the most suitable low-order controller. this study used moore’s balanced truncation algorithm [16], lqg balancing algorithm [17], and singular perturbation approximation (spa) [18] to reduce the order of the controller. the results of the step reduction are shown in tables i-iii. table i. order reduction of the 6th-order controller according to moore’s balanced truncation algorithm [16] order rr(s) ‖� � ��‖∞ 3 2 3 2 8.968 45.54 10.7 9.531 29.82 40.12 s s s s s      0.0047 2 2 8.881 1.978 4.501 7.927 s s s    0.017 1 8.895 4.493s  1.1718 table ii. order reduction of the 6th-order controller according to lqg balancing algorithm [17] order rr(s) ‖� � ��‖∞ 3 2 3 2 8.967 46.1 10.71 9.596 30.11 40.47 s s s s s      0.0043 2 2 8.831 2.052 4.565 7.992 s s s    0.0324 1 8.945 4.552s  1.707 table iii. order reduction results of the 6thorder controller according to singular perturbation approximation [18] order rr(s) ‖� � ��‖∞ 3 2 3 2 8.967 45.79 10.62 9.561 29.95 40.2 s s s s s      0.0044 2 2 8.953 2.051 4.574 7.978 s s s    0.0335 1 8.956 4.548s  1.7029 to evaluate the reduced-order controllers, their step and bode responses were compared with the original. figures 2-7 show the results. fig. 2. the step response of the 3rd and the 6th-order controllers. the step response of the 3 rd -order controller is exactly the same as that of the 6 th -order. fig. 3. the step response of the 2nd and the 6th-order controllers. the step responses of the 3 rd and the 2 nd -order controllers are exactly the same as that of the 6 th -order. fig. 4. the step response of the 1st and the 6th-order controllers. engineering, technology & applied science research vol. 13, no. 1, 2023, 9968-9972 9970 www.etasr.com bui: control design for the ward–leonard system in wind turbines the step response of the 1 st -order controller is different from that of the 6 th -order controller. the step response of the 1 st -order controllers, according to the different order reduction algorithms, is completely coincident. fig. 5. bode response of the 3rd and 6th-order controllers fig. 6. bode response of the 2nd and 6th-order controllers. the bode response of the 3 rd and the 2 nd -order controllers completely coincides with the frequency response of the 6 th order controller. fig. 7. bode response of the 1st and 6th-order controllers. the frequency response of the 1 st -order controller, according to the algorithms, is coincident. in the frequency range ω < 29.8rad/s, the frequency response of the 1 st -order controller is different from that of the 6 th -order. in the frequency range over 29.8rad/s, the frequency response of the 1 st -order controller coincides with that of the 6th-order. the 2 nd -order controllers can all replace the 6 th -order, where the 2 nd order controller according to moore’s balanced truncation algorithm is the most suitable controller to replace the 6 th -order (due to the smallest order reduction error). the 1 st -order controllers can not substitute the 6 th -order controllers. iv. using a reduced order controller to control the ward leonard system in a wind turbine system the results of using the 2 nd -order controllers in tables i, ii, and iii and the 6 th -order controller for the ward-leonard system in a wind turbine are shown in figures 8-10 and table iv. fig. 8. simulink diagram of the control system for the ward-leonard system in a wind turbine using 6 th -order and 2 nd -order controllers. fig. 9. response of the control system for the ward-leonard system in a wind turbine using 6 th -order and 2 nd -order controllers according to moore's balanced truncation algorithm. table iv. response results of control system using 6 th and 2 nd -order reduction controllers response 6 th -order controller 2 nd -order controller moore 2 nd -order controller lqg 2 nd -order controller – spa respone time 3.61 3.633 3.62 5.75 settling time (0.5%) 11 5.25 9.08 7.7 overshoot 1.4% 0% 0.87% 0.67% engineering, technology & applied science research vol. 13, no. 1, 2023, 9968-9972 9971 www.etasr.com bui: control design for the ward–leonard system in wind turbines fig. 10. response of the control system for a ward-leonard system in a wind turbine using 6 th and 2 nd -order controllers according to lqg truncation algorithm and spa. compared to the 6 th -order controller, the ward-leonard system in the wind turbine gives better response quality (smaller settling time and overshoot) when using reduced 2 nd order controllers. using a 2 nd -order controller according to moore's balanced truncation algorithm gives the best response quality (minimum settling time and overshoot -0%). these results show that the 2 nd -order controller according to moore's balanced truncation algorithm is the most suitable controller to replace the 6 th -order controller. v. conclusions controlling the ward-leonard system in a wind turbine according to a sustainable optimization method helps the system to perform well and maintain strong stability when the parameters of the model change. the disadvantage of the controller design, according to the robust optimization method, is that the order of the controller is 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[17] e. jonckheere and l. silverman, "a new set of invariants for linear systems–application to reduced order compensator design," ieee transactions on automatic control, vol. 28, no. 10, pp. 953–964, oct. 1983, https://doi.org/10.1109/tac.1983.1103159. engineering, technology & applied science research vol. 13, no. 1, 2023, 9968-9972 9972 www.etasr.com bui: control design for the ward–leonard system in wind turbines [18] yi liu and brian o. d. anderson, "singular perturbation approximation of balanced systems," international journal of control, vol. 50, no. 4, pp. 1379–1405, oct. 1989, https://doi.org/10.1080/00207178908953437. microsoft word 5-509-ed.doc engineering, technology & applied science research vol. 4, no. 6, 2014, 734-738 734 www.etasr.com siad and gangloff: a gtn-like model for plastic porous materials a gtn-like model for plastic porous materials larbi siad ea 4691, university of reims france larbi.siad@univ-reims.fr sophie c. gangloff ea 4691, university of reims france sophie.gangloff@univ-reims.fr abstract— an extended version of the well-known gursontvergaard-needleman (gtn) isotropic hardening model is presented in this paper. the yield function of the proposed constitutive model possesses the distinctiveness to explicitly depend upon the third stress invariant. the presented constitutive model is used to analyze the necking of a round tensile bar. as long as softening initiation of specimen is not reached, the obtained numerical results highlight similarities and good agreement with those provided by the use of the gtn model. however, discrepancy shows up as soon as specimen failure starts. keywords-constitutive modelling; ductile failure; necking; porous microstructures; tensile test; numerical simulations i. introduction regarding the mechanical behavior of porous plastic materials, the first micromechanical model which introduces a strong coupling between deformation and damage is the gurson-tvergaard-needleman (gtn) model [1, 2]. the void volume fraction (vvf) f of the material at hand affects the yield function of this model and subsequently the ductile fracture behavior of this material. indeed, when f increases, the material softens and loses its capability to carry loads an extension of the gtn’s plastic potential φgt is  proposed in [3] where the authors, investigating three arrangements of spherical voids over a wide range of f, focused their study on the determination of yield surfaces for porous materials using a huge number of finite element simulations. for each of the considered three void arrangements, namely simple cubic (sc), body-centered cubic (bcc) and face-centered cubic (fcc) arrays, many thousand yield points were determined by monotonically increasing the arbitrarily-prescribed macroscopic strain. the obtained yield points were fitted by a new yield function which turned out to be similar to φgt for f ranging between a very small value to the percolation threshold fp found to be equal to 0.89. moreover, all introduced parameters may be expressed as functions of the parameters characterizing the gtn’s plastic potential φgt which, in addition, is retrieved from the plastic potential φ when some of its parameters  are set to be equal to appropriate values (refer to  section 2.). as a novelty, the yield function  φ  was found to explicitly depend upon the third stress invariant i3. in this investigation, a constitutive model, referred to the present model in this paper, is used to describe the progressive damage in ductile solids resulting in material softening and, ultimately, loss of its stress carrying capacity. numerical aspects were addressed concerning the integration of the proposed constitutive rate equations [4]. based on the backward euler integration scheme, a numerical algorithm implicit in all variables and a corresponding algorithmic operator was developed. in order to demonstrate the global accuracy and stability of the numerical solution, finite element damage simulations accounting for finite strain and using the proposed model are performed for the traditional ductile solid problems of necking of a round tensile bar [5]. ii. the proposed rate-independent plasticity model for porous materials the most popular model describing constitutive elastic-plastic equations that account for the effect of ductile damage development is that suggested by gurson and phenomenologically improved by tvergaard [1, 2]. for a material containing a volume fraction of voids the proposed approximate yield condition reads 2 2 22 gt 1 1 3 q pp (σ ; h)= +2 q csch -1-q f =0 σ 2σ             (1) where σ is the effective flow stress of the damage-free matrix material which is a function of the effective plastic strain pε , (q1, q2) are the tvergaard parameters, and h=(h1, h2) is a vector comprising the scalar state variables p 1h =ε and 2h =f . in yield condition (1), the macroscopic cauchy stress tensor is resolved as 2 3 ' p i q n with n 3 2 q       (2) with p = -1 /(3 tr σ ) representing the hydrostatic pressure, tr refers to the trace of a tensor, i is the second order identity tensor, i is the deviatoric stress tensor, and 1 / 2q = (3 /2σ ':σ ') is the von mises stress. an extension of the gtn’s plastic potential φgt with no extra parameters which fits the numerical data well and is valid for all void volume fractions and triaxial stress states has recently been proposed in [3]. for more detailed explanations of the subject, we refer the reader to this paper. engineering, technology & applied science research vol. 4, no. 6, 2014, 734-738 735 www.etasr.com siad and gangloff: a gtn-like model for plastic porous materials the porous ductile materials studied in [3] contain spherical empty voids arranged in cubic arrays, namely, simple cubic (sc), body-centered cubic (bcc) and face-centered cubic (fcc) arrays. fca was used to simulate unit cells and the macroscopic yield surfaces of the porous materials were obtained using the probing technique which goal is to obtain a yield function in an analytical expression that can be used in continuum studies. the matrix material is almost rigid, perfectly plastic and unit cells were meshed with cubes. depending on the unit cell at hand, the void volume fractions considered range from 0.02 to around 0.89 corresponding to the percolation threshold of the matrix material. let i3 and j3 be the determinant of the stress tensor σ and the third stress invariant of the deviatoric stress tensor σ΄ respectively: 3i d e tσ and 33 1 j trσ ' 3  are related by 2 3 3 3i = j + p q /3 -p . in stress space (p, q, i3), yield points were found by monotonically increasing macroscopic strain with fixed ratios until the macroscopic equivalent stress reaches a maximum. for each of the three cubic unit cells, a least-squares fit with an extension of the gtn’s yield function (1) was found only approximately with deviations becoming more pronounced as pressure or void volume fraction were increased. to account for the observed tri-lobed numerical data pattern, the gurson-tvergaard-like yield criterion proposed in [3] can be expressed as 2 22 1 1 3 23 2 1 13 3 3 pp (σ; h) 2 cosh 1 2 i 3 pp p 1 p s(f ) 2 cosh 1 0 3 2                                               (3) note that for the extended yield function φ, the q-like parameters α1 and α2 depend on f for the three considered microstructures, that is α1=α1(f) and α2=α2(f). the yield function φ is linear with respect to i3, with coefficient proportional to the hydrostatic pressure p. the parameter s also depending on f, determines the influence of the new term in the yield condition (3) which reduces to that of the gtn model (1) for s=0, α1=q1 and α2=q2. whenever the constant s is non-zero, there is an effect of the third stress invariant i3 on the plastic flow. clearly the yield function contains three functions depending upon f which are slightly different for each of the three cubic microstructures. in [3], the authors stated that their finite element data were well-fit by expressing the parameters α1 and α2 as n m 1 2 p p p p f f f f a , y z f f f f                                         (4) where n, m, a, y and z are constant parameters. note that (1) for f=0 and α1=0, the yield condition (3) is nothing else than the classical von mises one; and (2) when f=fp and α1=1, the material becomes plastic under any applied load since the matrix material is no longer connected. regarding the parameter s, if its value is too large, the tri-lobed pattern of the macroscopic yield surface almost degenerates into an equilateral triangle at some values of pressure p. in non-linear solid mechanics, the material behavior is often described by a rate-form constitutive equation. in the particular case of the proposed rate-independent plasticity model, it is assumed that the macroscopic rate of strain tensor ε is written as the sum of an elastic part eε and a plastic part pε , and the stress rate σ depends linearly on the elastic strain rate tensor eε . subsequently, the corresponding constitutive equations can be written in a rate format as: e p e p p p ε= ε + ε , σ = c : (ε-ε ) ε = λr(σ ;h ), h = λh (ε ;h )         (5) where ec is the elastic moduli tensor which can depend on the current stress state, r is the direction of the plastic flow which depends on the current stress and on a finite set of plastic internal variables h accounting for history effects and h is the direction of the rate of these plastic internal variables. as previously mentioned, h characterizing the current state of the ductile porous material includes the void volume fraction f and the effective plastic strain pε in associated plasticity, r is the gradient of the yield function, that is: ij 3 ij ' ' ' 2 ij ij ik ikj ij 3 3 r ( ; h) (p, q, j ; h) 1 3 2 q 3 p 2 q q j 9 j                             (6) then the plastic strain rate p , is given by: . . p ' 2 ij 3 1 2 i q i 3 p ' 9 j                    (7) the plastic strain rate pε is trivially decomposed into volumetric p v ε and deviatoric p q ε parts, p p p v q ε =1/3ε i+ε ,   which facilitate development of the integration algorithm. indeed, these two terms can be expressed in terms of the yield function, using (6), as: . . p v p        and . . p 2 q 3 2 q i ' 9 j           (8) it should be noted at this stage of calculation that, due to the presence of the third stress invariant in the expression of the yield function φ, and in view of (2), the deviatoric component cannot be put in the form p p q v ε =ε n  where n is the deviatoric engineering, technology & applied science research vol. 4, no. 6, 2014, 734-738 736 www.etasr.com siad and gangloff: a gtn-like model for plastic porous materials strain rate tensor normal to the yield surface φ=0 and which norm is unity. as a reminder, this form turned out to be very successful for applying the implicit integration scheme based on the aravas’s method [6]. to determine the plastic multiplier, the loading-unloading conditions should be imposed in a kuhn-tucker forma: . . 3 30, (p, q, j ; h) 0, and (p, q, j ; h) 0     (9) implying that during plastic loading φ=0, . 0  and φ 0 . this condition, the consistency condition, allows the determination of the plastic multiplier λ which specifies the magnitude of the plastic strain rate [7]. finally, the void fraction modification f* introduced in [1] was intended to simulate the rapid loss of strength accompanying void coalescence. the calculated porous plastic material response is strongly dependent on the computational procedure for stress calculation, usually called the stress integration. the presence of the third stress invariant in the yield function typically results in a high degree of non-linearity and complex numerical algorithms. for further details dealing with the description of various integration methods, the reader is referred to [7, 8] where more elaborate coverage of the closest point projection method may be found. the constitutive equations of the proposed model along with the coalescence criterion based on the effective porosity introduced in [5] are integrated using a fully implicit scheme which allows the calculation of the consistent tangent operator [7, 8, 4]. the final stress and hardening parameters are determined solving the non-linear equations iteratively so that the stress increment fulfills the consistency condition. the corresponding algorithm is programmed in appropriate user subroutines which are called by abaqus, at each element integration point, for each increment, and during each load step. iii. one numerical example: smooth bar tensile test this section illustrates the use of the present model through the analysis of damage and failure of smooth bar subject to axial tensile test. the traditional necking analysis of a round bar has been investigated. uniaxial tensile test of a smooth bar is often used to study the ductile void growth in metals for which the formation of a neck triggers the material instability. a detailed finite element analysis of the formation of the crack at the center of the neck and its subsequent growth leading to cup-cone fracture can be found, for instance, in [5]. the formation of the neck results in a triaxial state of stress at the center of the specimen. due to high hydrostatic tension, the growth of nucleated voids is accelerated and the material instability proceeds with the initiation of fracture at the center of the neck with linkage of adjacent voids. numerical simulations of the behavior of a rounded smooth bar subject to tensile test have been performed. the rounded bar has an initial length of zo 2l 8l   where the radius l  is assumed to be equal to one unit. due to symmetry about ρ=0 and z=0, only one quarter of the specimen needs to be analyzed. a slight conical imperfection is introduced near the center of the specimen such that z 0 l 0.998l     . the geometry of the studied specimen and the original used mesh are shown in figure 1. the geometry is axisymmetric, and the deformation is assumed to be axisymmetric. fig. 1. tensile test: geometry of the rounded smooth bar, original used mesh, boundary conditions, and loading. reduced integration elements (cax4r within abaqus) were used for efficient computations. a refined mesh is generated near the center of the rounded bar where softening and intense deformation are expected, whereas a relatively coarse mesh is used in the rest of the specimen where a rather uniform deformation is expected. the kinematic boundary conditions are: symmetry about ρ=0, symmetry about z=0, and all the nodes on the edge z= z l  of the specimen are given a prescribed velocity depending on time z z v v (t ) in the zdirection. the velocity z v increases rapidly from zero at the start of the analysis to its maximum 30 ms-1 in 0.0025 s and drops back linearly to zero in another 0.0025 s. it then remains at zero for the remainder of the analysis. the specimen is made of a steel alloy which workhardening characteristics are similar to those of a power law hardening material with young’s modulus e, poisson’s coefficient v, and initial yield stress σ0. using the gtn model to simulate ductile failure, a proper choice of its eight micromechanistic parameters proves to be crucial. before loading the material is assumed to be fully dense, that is f0=0.0. the damage parameters n, s and fn related to void nucleation, as well as the tvergaard constants q1 and q2 were fixed to typical values suggested in [1]. hereafter are the material parameters used in the numerical simulations: 0 0.00333   , 0.3  , p 0.1 0 (1 0.033 )     , q1=1.5, q2=1.0, 0.3  , 0.1s   , fn=0.04, fc=0.15 and ff =0.25. for the problem under consideration, it is well known that the material deforms homogeneously in the axial direction before the load becomes maximum, after which deformation becomes heterogeneous and necking starts. as a result of which the specimen softens due coalescence of voids and eventually fracture across the neck region. in this context, figure 2 displays the deformed shape of the tensile bar showing necking occurs at the mid-section of the specimen. engineering, technology & applied science research vol. 4, no. 6, 2014, 734-738 737 www.etasr.com siad and gangloff: a gtn-like model for plastic porous materials fig. 2. comparison of vvf contour plots predicted by the present models and the gtn model just before failure of the tensile specimen; . fig. 3. simulation of tensile tests on smooth round bar. predictions of overall nominal stress versus overall nominal strains based on the present models (sc, bcc and fcc microstructures) and gtn model. the global response of the specimen may be specified by the average states of strain and stress within it. the nominal elongation n z z zo l / l   and the relative diameter n z l / l       are chosen to assess the average strains of the specimen. the nominal elongation is used to assess the average strain in sections perpendicular to the tensile direction. the overall nominal stress is given by n 2 z f / l    where f is the resulting overall tensile load carried by the bar and determined from nodal forces. the evolution of n z  as functions of the nominal elongation and the relative diameter are shown in figure 3, for both the present and the gtn models. first of all, these figures clearly show that up to failure initiation points which are indicated in figure 3 using the dyadic  symbols, the agreements between predictions of considered models are quite good. in particular, maximum loads for the present model, regardless the considered microstructure, coincide with the maximum load provided by the gtn model which is reached at strains of about 11% for the nominal elongation and about 5.5% for the relative diameter. it is worth noting that the practically coincidence of the numerical predictions also holds in the softening regime ranging from maximum load and the immediate vicinity of failure points. this fact is substantiated by the deformed configuration and the void volume fraction contours depicted in figure 2 at the final edge displacements of the specimen which are very similar. as expected, the largest amount of softening localizes around the center of the mid-section of the specimen. it is implied, therefore, that failure initiation should be expected in that area. however, the onset of failure is reached at displacements of 1.12lρο for the gtn model and of 1.21lρο for the present model with bcc microstructure, (figure 2). the maximum loads along with the corresponding nominal strains predicted by both the present models and the gtn model are listed in table i. table i. maximum loads and corresponding nominal strains. n z (%) nz 0 max  n (%) n 0 max  gtn model 8.67 1.301 4.87 1.302 sc 10.27 1.302 4.87 1.303 bcc 9.72 1.303 5.02 1.30 fcc 9.45 1.30 4.86 1.301 deviations between predictions of the present models and the gtn model are observed as soon as failure of the considered specimen starts, that is when the sudden specimen capacity loss occurs (figure 3). the numerical results seem to suggest that the present model based on sc microstructure is the closer one to the gtn model. the true fracture strain is the most physical experimental indicator for quantifying the resistance to damage and fracture of a material subjected to tensile loading conditions. an average true fracture strain measure f ε using the diameter reduction is usually used to quantify the ductility [9, 10]. it is defined as f ε 2 log(l / l )    it has been well-known that the dependence of f ε on the stress triaxialit τ can be approximated engineering, technology & applied science research vol. 4, no. 6, 2014, 734-738 738 www.etasr.com siad and gangloff: a gtn-like model for plastic porous materials using an exponential function f ε exp( )   where α is a material constant. the stress triaxiality is the hydrostatic stress to equivalent stress ratio. the obtained failure strains are listed in table ιι. specimen made up of gtn material has a little lower ductility than the specimen made upof present models material, regardless the considered microstructure (bcc, fcc or sc). table ii. comparison of predicted failure strains. ductility gtn sc bcc fcc n z f( ) (%) 27.5 28.3 30.2 30.5 n f( ) (%) 36.2 37.2 42.4 42.3 iv. conclusion the main objective of this paper has been to address an extended version of the gtn model based on a pre-existing yield function for porous plastic materials proposed in [3] and its implementation within a finite element code. a fully implicit stress integration scheme is used to integrate the present model. as a numerical example, the present model is used to perform axisymmetric simulations of the ductile necking failure of a smooth round bar. similar values for the damage parameters (nucleation and coalescence) have been used for both the present model and the gtn model in order to compare their ability to predict void growth to coalescence and the corresponding failure mechanism. the obtained numerical results are summarized as follows: • the present model has shown the potential to accurately predict all the major features of ductile failure of solids (stress triaxiality dependence …). • up to the failure initiation of the specimen, the predictions based on the finite element analysis incorporating the present model are in a close agreement with those provided by the gtn model, confirming the potential of the former constitutive model to fulfill to the requirement of transferability between different loading conditions. • noticeable disagreement has been observed between predictions of both models at and beyond failure points of specimen. the necking round bar problem has shown that during the sudden specimen capacity loss, the present model based on sc microstructure is the closer one to the gtn model. references [1] v. tvergaard, “materials failure by void growth to coalescence”, in: advances in applied mechanics, vol. 27, pp. 83–151, academic press, new york, 1994 [2] a. a. benzerga, j. -b. leblond, “ductile fracture by void growth to coalescence”, in: advances in applied mechanics, vol. 44, pp. 169– 305, academic press, new york, 2010 [3] d. l. s. mcelwain, a. p. roberts, a. h. wilkins, “yield criterion of porous materials subjected to complex stress states”, acta materialia, vol. 54, no. 8, pp. 1995-2002, 2006 [4] l. siad, “ductile damage analysis based on a j3-gtn-like model”, journal of multiscale modelling, vol. 3, pp. 1-27, 2011 [5] v. tvergaard, a. needleman, “analysis of the cup-cone fracture in a round tensile bar”, acta metallurgica, vol. 32, no. 1, pp.157–169, 1984 [6] n. aravas, “on the numerical integration of a class of pressuredependent plasticity models”, international journal for numerical methods in engineering, vol. 24, no. 7, pp.1395–1416, 1987 [7] j. simo, .j.r. hughes, computational inelasticity, springer, 1998 [8] a. anandarajah, computational methods in elasticity and plasticity. solids and porous media, springer, 2010 [9] j. besson, ‘eprouvettes axisymétriques entaillées’’, in d. françois, éditeur, essais mécaniques et lois de comportement, pp. 319–351. hermès science, paris, 2001 [10] n. bonora, “identification and measurements of ductile damage parameters”, the journal of strain analysis for engineering design, vol. 34, no. 6, pp. 463–478, 1999 microsoft word etasr_v13_n2_pp10301-10305 engineering, technology & applied science research vol. 13, no. 2, 2023, 10301-10305 10301 www.etasr.com mankeed et al.: temperature evolution and heating rates of biomass undergoing ablative pyrolysis temperature evolution and heating rates of biomass undergoing ablative pyrolysis panuphong mankeed department of mechanical engineering, faculty of engineering, chiang mai university, thailand opanupong@hotmail.com nattawut khuenkaeo department of mechanical engineering, faculty of engineering, chiang mai university, thailand n.khuenkaeo@gmail.com fawad r. malik department of mechanical engineering, faculty of engineering, chiang mai university, thailand hallianmalik@gmail.com nakorn tippayawong department of mechanical engineering, faculty of engineering, chiang mai university, thailand n.tippayawong@yahoo.com (corresponding author) received: 26 december 2022 | revised: 19 january 2023 | accepted: 22 january 2023 abstract the ablative reactor may be employed to enable fast pyrolysis to produce bio-oil from relatively large-sized biomass samples. ablation mainly involves direct compressive force and conductive heat transfer between a hot surface and the biomass materials. temperature evolution and heating rates are important operating factors in the biomass thermal conversion process. in this work, experimental and analytical investigations were carried out for different vertical dimensions of the biomass samples (2-20mm) and hot plate temperatures (400-550c). it was shown that the thermal characteristics of the biomass were mainly affected by the transient conditions. it was observed that volatile release occurred during the transient heat transfer periods. it was found that at the maximum hot plate temperature of 550°c, the highest heating rate that could be achieved by ablation was more than 600c/min. keywords-ablation; agricultural residues; clean energy; heat conduction; thermal conversion i. introduction biomass is a major source of alternative energy [1, 2]. utilization of biomass is normally conducted via thermal routes such as combustion, gasification and, slow pyrolysis [3, 4]. rapid decomposition of biomass can occur at moderate to high heating rates. fast pyrolysis is a thermochemical process to convert lignocellulosic biomass materials into liquid products. in this reaction route, biomass temperature is raised to 400– 600c in non-oxidizing atmosphere at very fast heating rates (>10–200°c/s) and short reaction times (typically < 2s), releasing volatile gases that can be rapidly condensed into organic liquids or bio-oil [5]. there have been many fast pyrolysis reactors studied including fluidized bed, free-fall, auger, and ablative reactors. most reactor types require the biomass materials to be grinded into very small sizes of about 1.0mm or less whose cost represents a significant portion of the total processing cost. ablative pyrolyzer is a type of moderately fast pyrolysis reactor where raw materials are directly subjected to a hot plate. thermal erosion or melting of the biomass occurs at a contact layer as it is directly pressed against a hot solid surface. this enables high rates of conductive heat transfer, making the process fast, cheap, and highly efficient. the ablative reactor is able to utilize large pieces of wood [6]. nonetheless, ablation is surface area controlled, hence, upscaling could be a tough challenge. several ablative pyrolysis systems have been developed and studied in the past 40 years. the first pioneering work on ablative pyrolysis was conducted in [7]. it was shown that woody biomass could be thermally decomposed by ablation, producing a vaporizing layer of degrading solid. subsequent experiments on ablative heat transfer were carried out with focus on wood pyrolysis in [8, 9]. authors in [10] developed an ablative pyrolysis reactor with multiple blades engineering, technology & applied science research vol. 13, no. 2, 2023, 10301-10305 10302 www.etasr.com mankeed et al.: temperature evolution and heating rates of biomass undergoing ablative pyrolysis and reported bio-oil yield of up to 68% w/w. recently, an ablative reactor for pyrolysis of thick woodchips was developed, achieving bio-oil yield of about 60%. authors in [11, 12] employed an ablative pyrolyzer to produce bio-oils from various agricultural residues under atmospheric and vacuum conditions. it is clear that temperature characteristic, heating rate, and heat transfer between organic materials and heat sources are considered very important for pyrolysis product distribution. in ablative pyrolysis, it is known that there are steep temperature gradients occurring on the thick biomass surface. this impression could be speculative since there was no or very little data to back up the claim. so far, a modest amount of experimental results regarding the biomass heating characteristics during ablation heat transfer is available in the existing literature. therefore, in this work, ablation of thick biomass samples was carried out on a hot plate. heating rates and temperature profiles at different depths of the biomass samples were measured, evaluated and presented, along with the simplified analytical heat conduction results. information generated from this work will be useful in adopting the ablative pyrolysis technique to produce organic liquids or bio-oil from biomass. ii. materials and methods a. thermal ablation experiments the feedstock used in this study was hemp hurds (cannabis sativa l.) collected from chiang mai’s countryside, thailand. this plant is a stout and aromatic herb. its stalk is slender and hollow. it was used in this work to represent an example of agricultural residue available locally. its physical density was about 85kg/m 3 . dirt and other impurities in the feedstock were removed by washing with water, and the feedstock was then naturally dried in sunlight. the moisture content was determined to be 9-10% w/w. the dried samples were cylindrical shaped with about 2mm diameter. afterwards, they were cut into 40mm long pieces which were stored for later experiments. figure 1 illustrates the experimental setup. the thermal decomposition of hemp samples was carried out at the hot plate temperatures of 400, 450, and 550°c at 4 different depths of 2, 5, 10, and 20mm inside the biomass samples from the hot plate surface. the hot plate was heated by a cooking gas flame whose temperature was monitored and controlled via an electronic control system actuating the amount of fuel gas flow. the exterior of the reactor chamber except the bottom was fully insulated to minimize heat losses. biomass temperatures were measured using a type k thermocouple connected to a data logger at 500ms sampling rate. nitrogen was used at a flow rate of 500ml/min to purge releasing volatiles. each test case was repeated for at least 3 times. b. simplified heat conduction modeling a simple analytical study was performed for the heat transfer between the hot plate and the cylindrical shaped biomass sample. conduction is considered as the main heat transfer mode and can be expressed as: ( � � � �� (� �� ��) + � �� ��� �∅� + ��� � � ) + qg = cp� �� �� (1) where qg is heat generation inside the particle. (a) (b) (c) fig. 1. (a) schematical diagram, (b) a pictures of biomass on the hot plate, and (c) the experimental setup of the ablative reactor. we assume that heat is transferred only in one dimension (z-axis) and the system has no heat generation inside the particle. thus, the expression of conductive heat transfer is equal to the internal energy transfer within the sample body: -ka � = �� cp � � (2) therefore, the temperature evolution could be expressed by: engineering, technology & applied science research vol. 13, no. 2, 2023, 10301-10305 10303 www.etasr.com mankeed et al.: temperature evolution and heating rates of biomass undergoing ablative pyrolysis t(t) = t1 – ��� �� ������� (3) where t(t) is the biomass temperature, t1 is the hot plate temperature, k is the thermal conductivity of the biomass sample, a is the area of biomass surface in contact to the hot plate, �cp is the heat capacity of the biomass sample, v is the volume of the biomass sample, z is the depth, and t is the time. iii. results and discussion figure 2 illustrates the temperature evolution and heating rates in the biomass sample at various vertical locations from the surface contact and temperatures of the hot surface. overall, the temperature of the biomass body appeared to approach the hot surface temperature exponentially. it changed rapidly at the beginning, and after that it slowed down and stayed stable, like the result of the conduction model [13]. there were two main temperature regions: firstly, the transient or unsteady state occurred in the starting period and subsequently, the constant temperature region or steady state. the starting time of the steady state was affected by the dimension of the biomass sample. for instance, at 450 o c, and the distances between the sample and the hot plate of 2, 5, and 10mm, the steady state was reached within about 170s, while at 20mm, it took around 200s. small sized biomass was likely to reach the steady state quicker than the bigger samples. similarly, at the condition described by 450 o c, 20mm, the steady state was reached in 160s. on the contrary, at the higher temperature of 550 o c, the time to reach the steady state was not obviously affected by the biomass particle dimension. furthermore, the short depth can approach the hot plate temperature easily. for high heat transfer, smaller sized samples are desired as anticipated. however, in practice, the size of biomass may not be very small because of its processing cost [6]. a reasonable size of the biomass samples should be carefully considered for practical use. regarding the hot plate temperature, it had significant effect on conductive heat transfer. low temperature setting would take longer time to reach the steady state than high temperature setting. as shown in figure 2, for a distance of 20mm at 400 o c, it took 160s to reach the steady state while at 450 and 500 o c, it took 140 and 120s, respectively. similarly, for a fixed depth of 20mm, the time it took to reach steady state was 200s at 400 o c, but only 120s at 500 o c. the temperature and time data can be used to derive the corresponding heating rates. the factor is useful in determining if slow or fast pyrolysis occurs [14]. overall, the heating rates were found to fluctuate radically during the transient period, before reaching zero heating rate at the steady state. for instance, at 400 o c and 10mm distance, the heating rate (purple lined spots) approached zero in 180min as the temperature (green line) became constant. the smaller sized biomass samples appeared to experience higher heating rates than the bigger samples, as expected. this was due to the fact that smaller sized samples have lower heat resistance [15], hence, greater heat transfer in the initial stage than the larger sized samples. for example, the heating rates at the time of 20s and hot plate temperature of 450 o c were approximately 5.0, 4.3, and 3.6 o c/s for the biomass samples with depths of 2, 5, and 20mm, respectively. at 140s, the biomass samples with depth of 2 and 5mm had the heating rates reaching zero, while the sample with depth of 20mm exhibited a heating rate of about 2 o c/s. in addition, it was observed that the release of volatiles from the biomass decomposition occurred mainly during the transient period and it appeared to stop when the steady state was reached [16]. this observation could be useful in designing and operating the ablative pyrolysis system to obtain the fast release of volatiles. at the highest temperature setting and relatively small sized biomass samples of 2 and 5mm, the maximum heating rates obtained were about 11 o c/s or 660 o c/min at 20 and 50s, respectively. meanwhile, at the sample depth of 10mm for the same maximum hot plate temperature setting, the heating rate of nearly 10 o c/s or 600 o c/min was achieved. all the above are considered as fast pyrolysis [14]. (a) (b) (c) fig. 2. temperature profiles and heating rates at different pyrolysis temperatures and depths inside the biomass macroparticles. in this work, a simplified heat conduction analysis was also performed to predict the temperature evolution during the heat transfer between the hot plate and the biomass sample. the results are shown in figure 3. the temperature profiles show the two regions of transient and steady states. different biomass sizes spend different time to reach the steady state. the higher depths or bigger biomass samples take longer time engineering, technology & applied science research vol. 13, no. 2, 2023, 10301-10305 10304 www.etasr.com mankeed et al.: temperature evolution and heating rates of biomass undergoing ablative pyrolysis than smaller counterparts in the transient period. for instance, the biomass with 2mm depth reaches the steady state within 100s while the one with 10mm depth takes about 300s to become steady. volatiles from biomass thermal degradation are released in the transient period. for practical applications, it may imply that larger sized particles undergo longer transient period which could release more volatiles for higher bio-oil yield. nonetheless, it should be noted that even though the analytical results showed similar patterns of temperature evolution, their values are markedly different. this may be caused by the fact that the biomass properties (density, thermal conductivity, and heat capacity) used in the analytical study differ from the real values [17]. furthermore, ablative heat transfer in thick biomass samples may not be simply approximated by a one-dimensional, transient heat conduction model. a more complicated heat transfer model should be adopted in future investigation. (a) (b) (c) fig. 3. simulated temperature profiles at different pyrolysis temperatures and depths inside the biomass macroparticles. table i shows a comparison, between this work and those available in the literature, of reactor temperature and realized heating rates for various biomass types and shapes when undergoing ablative pyrolysis. it can be seen that while the reactor temperatures were in similar magnitude (365 to 800 o c), our work appeared to show higher maximum heating rates, up to 660 o c/min, compared to 174 and 20 o c/min reported in [13] and [6], respectively. this was possibly due to the fact that the biomass size used in this work was the smallest among the compared works. it is also likely that their temperature gradients were not measured directly, but estimated from temperature measurement at points some distance further from the surface than the location done in this work. table i. comparison of biomass type and shape, and thermal characteristics of ablative pyrolysis between this work and others biomass material (shape) heating rate ( o c/min) reactor temperature ( o c) dimensions (diam. × length) (mm) ref. pine wood (chip/rod) 7 – 20 500 2×2 – 35×200 [6] beechwood (rod) n/a 400 – 800 2 – 10 (dia.) [8] pine wood (cubic) n/a 400 – 600 4.75 – 6.25 [10] hard wood (sphere) 50 – 174 365 – 606 n/a [13] hemp residue (rod) 30 – 660 400 – 550 1×2 – 1×20 this work n/a: not available iv. conclusion temperature profile and heating rate are essential factors defining the biomass pyrolysis type of slow and fast pyrolysis. in this work, measurements and simplified analytical studies of biomass heating characteristics for different biomass dimensions and hot plate temperature were carried out. from the findings, it was shown that there were two temperature intervals of transient and steady states identified during the biomass thermal decomposition. the small size and high hot plate temperature enabled the biomass sample to reach the steady state within a very short time. releasing of volatiles occurred mainly during the transient period. at the highest hot plate temperature of 550 o c, the biomass underwent the maximum heating rate around 11 o c/s or 660 o c/min, in the fast pyrolysis range. this information is useful for utilizing the ablation technique for pyrolysis reactor design. acknowledgment this research project was partially supported by fundamental fund 2023, chiang mai university, and the national research council of thailand. references [1] r. espina, r. barroca, and m. l. s. abundo, "the optimal high heating value of the torrefied coconut shells," engineering, technology & applied science research, vol. 12, no. 3, pp. 8605–8610, jun. 2022, https://doi.org/10.48084/etasr.4931. 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[11] n. khuenkaeo and n. tippayawong, "production and characterization of bio-oil and biochar from ablative pyrolysis of lignocellulosic biomass residues," chemical engineering communications, vol. 207, no. 2, pp. 153–160, feb. 2020, https://doi.org/10.1080/00986445.2019.1574769. [12] n. khuenkaeo, s. phromphithak, t. onsree, s. r. naqvi, and n. tippayawong, "production and characterization of bio-oils from fast pyrolysis of tobacco processing wastes in an ablative reactor under vacuum," plos one, vol. 16, no. 7, 2021, art. no. e0254485, https://doi.org/10.1371/journal.pone.0254485. [13] c. d. r. sotelo, "heat and mass transfer limitations in the pyrolysis of wood particles," m.s. thesis, kth royal institute of technology, stockholm, sweden, 2018. [14] a. demirbas and g. arin, "an overview of biomass pyrolysis," energy sources, vol. 24, no. 5, pp. 471–482, may 2002, https://doi.org/ 10.1080/00908310252889979. 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[17] c. di blasi, "heat transfer mechanisms and multi-step kinetics in the ablative pyrolysis of cellulose," chemical engineering science, vol. 51, no. 10, pp. 2211–2220, may 1996, https://doi.org/10.1016/00092509(96)00078-4. microsoft word 4-697.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1056-1061 1056 www.etasr.com bharti et al.: controller design for dfig driven by variable speed wind turbine using static output … controller design for dfig driven by variable speed wind turbine using static output feedback technique om prakash bharti department of electrical engineering indian institute of technology banaras hindu university varanasi-221005, uttar pradesh india opiitbhu@gmail.com r. k. saket department of electrical engineering indian institute of technology banaras hindu university varanasi-221005, uttar pradesh india rksaket.eee@iitbhu.ac.in s. k. nagar department of electrical engineering indian institute of technology banaras hindu university varanasi-221005, uttar pradesh india sknagar.eee@iitbhu.ac.in abstract—this paper describes the controller design for a dfig based wind energy generation system using the static output feedback technique through the lmi toolbox. the features of the dfig, its converters and their controllers are discussed. the lower order nominal representation of dfig is obtained using numerical differentiation of the simulink model which is subsequently used for pid controller design. the obtained results are compared with existing methods for performance enhancement of the dfig and wind energy conversion systems. keywords-dfig; wind turbine; matlab simulink models; pid controller; linear matrix inequalities; sof technique abbreviations: dfig: doubly fed induction generator, pi: proportional integral, sof: static output feedback, lmi: linear matrix inequality, fact: flexible ac transmission, pfc: power factor control, vsc: voltage source converter, wec: wind energy conversion, pcc: point of common coupling i. introduction the investigation of progressively alternate energy sources, demand for electric energy is increasing very fast. among the obtainable alternate energy sources, wind energy, solar energy and fuel cells have drawn considerable attention. additional, all of these alternate energy sources are also of renewable nature. among the mentioned alternate energy sources, wind power generation systems have been the most cost competitive alternative. since the direction and speed of winds may vary from location to location as well as from time to time, the variable speed wind turbine technology offers inherent advantages over the fixed speed one [1]. the doubly fed induction generator (dfig) is used in cycle with the wind turbine to produce electric energy. the dfig through the use of the two back to back converters, rotor side and grid side converters, is able to deal with a wide variation of wind speeds by injecting a compensating variable frequency current component in the rotor circuit. this facilitates both super and sub synchronous operations of dfig. it is well known that the induction machine is widely used in industrial application due to its low cost, simplicity of construction and low maintenance cost. such type of machines can be used for electric generation where the speed of the prime mover is constant i.e. just above the synchronous speed. however, it is a fact that the wind speed varies drastically depending upon the environmental conditions and time of operation. thus, there is a large margin of speed variation. such large margins of speed variation makes wound rotor induction machines suitable for generation of wind energy [2]. in addition to its large speed variation, the wound rotor induction machine offers additional advantage of bidirectional transfer of the rotor power which depends on the rotor speed and field speed [3]. the dfig is essentially a wound rotor induction machine capable of operating in super synchronous as well as sub synchronous mode. the advantages of dfig over the fixed speed induction generators are improved power quality, reduced mechanical stress and fluctuation and advanced energy capture [4]. the operations of dfig connected to the grid are facilitated with the help of rotor side and grid side converter. it is the responsibility of the inverter connected to the rotor side to provide the necessary complementary frequency to maintain the stator frequency at a constant level, despite fluctuations in the mechanical power. the control of dfig poses a twofold problem to compensate the speed fluctuations as well as reactive power. the stability and performance of the overall setup is to be maintained in the face of model uncertainties, external noise, variation of the internal machine parameters and speed. the problem of control becomes more involved in case of unbalanced grid connected operations. it is well known that unbalanced operations lead to the flow of negative sequence currents which in turn may lead to localized heating as well as pulsations in the electric torque. in critical applications, dfigs must be disconnected from the grid when the voltage imbalance is more than 6% [5]. it was reported that even within this margin, torque pulsations can be reduced by injecting a compensation current in the dfig rotor, but with their engineering, technology & applied science research vol. 6, no. 4, 2016, 1056-1061 1057 www.etasr.com bharti et al.: controller design for dfig driven by variable speed wind turbine using static output … technique the torque pulsations could not be completely eliminated. the design of control strategy for the dfig requires its simplified models which can be integrated with flexible ac transmission system (facts) based grid models. such models can also be used for first hand analysis of the overall system. ekanayake et al. in [6] presented a comparative study of the simplified models, wherein the authors have compared the fifth and third order model of dfig followed by the study under faulted conditions. z. wang and y. sun in [7] presented the magnitude and frequency control of grid connected dfig based on synchronized model for wind power generation. in this paper the numerical differentiation based incremental model around the nominal operating point of dfig is used. the usefulness of such models can be verified from the results presented. it is worth to mention here that the typical ratings of wind turbines are between 800kw to 3 mw, whereas wind farms range from 1 mw to 200mw [8]. ii. an overview of wind turbines the wind turbine is a machine that converts kinetic energy from the wind into mechanical energy. if the mechanical energy is used to produce electrical energy, the device may be called a wind generator or wind changer. if the mechanical energy is used to drive machinery, for example to grinding grain or pumping water, the device is called a windmill or wind pump. today's wind turbines are manufactured in a range of vertical and horizontal axis types. the nominal turbines are used for applications such as battery charging or auxiliary power on seafaring boats; whereas large grid connected arrays of turbines are becoming an increasingly large source of commercial electric power. the basic principle of wind turbine is as follows, the aerodynamic power is converted into mechanical power and then electrical power. a. basic perception of dfig based wind turbine: the mechanical power which is produced by the wind turbine is proportional to the cube of the wind speed i.e. pm  v3. where pm is the mechanical power of the wind and v is the velocity of the wind speed. the maximum power which is obtained by the rotational speed of the wind turbine defers from different wind speeds. hence the operation of variable speed is necessary to maximize the energy. the variable speed turbines are fed to the grid via a power factor control (pfc) which decouples the rotational speed of the wind turbine from the grid frequency, to enable variable speed operation. there are two basic concepts that exist for variable speed turbines. the first concepts are electric generator with a converter connected with in the stator windings and the grid network which is shown in figure 1(a). for the rated power of the wind turbine the converter is to be designed. the generator is a synchronous machine which is mostly a permanent magnet. for the direct drive concepts a wind turbine with a dfig has a converter connected to the rotor windings of the wound rotor induction machine, which is shown in figure 1(b). this type of generator can be defined for a fraction (~30%) of the rated power. but the system ensures competent power conversion appropriate to variable rotor speed, which adjusts automatically in accordance with prevailing wind speeds [9]. the speed changing is possible by the directionally dependent transfer of slip power, which changes as follows. in the sub synchronous operating mode, the stator of the dfig supplies power to the grid. in the super synchronous operating mode, both stator output power and the rotor slip power are fed into the grid. a variable speed wind turbine with full size converter and doubly fed induction generator is shown in figure 1. however, the converter has to be intended for the rated power of the turbine. this problem can be taken care of by using the dfig, which has a converter connected to the rotor winding of the wound rotor induction machine (figure 1(b)). rated power has been reduced to (25% 35%) in the case of dfig. the main components of the wind turbine are given as follows. fig. 1. variable speed wind turbines (a) with full-size converter (b) with doubly-fed induction generator 1) drive train along with aerodynamics: the drive train has turbine, gear box, shafts and other mechanical components of wind turbine; a multi mass (in general two mass) model to be used for dynamic studies of wind turbines through dfig [10]. a simplified aerodynamic model is sufficient, when the speed and pitch angle changes on the aerodynamic power during the grid faults. for stability investigation, the drive train system have to be approximated by the at least a two mass spring as well as damper model while the system response to heavy disturbance [11]. there is a flexible shaft during the turbine and generator masses are associated. 2) pitch angle control system: the “pitch control” is a technique so as to mechanically adjust the blade pitch angle to change the curve of the power coefficient of the turbine [12]. pi control is used to realize the pitch angle, in servo mechanism model with time control tservo accounts for the practical response in the pitch angle control system. for the duration of the grid faults how quick the aerodynamic power can be reduced in order to stop more speeding is decided by the rate of change limit. b. modeling of wind turbine: in this section wind turbine model is discussed for optimal operations of the wind turbine at different wind speeds [13]. it must be operated at its maximum power coefficient (a) (b) engineering, technology & applied science research vol. 6, no. 4, 2016, 1056-1061 1058 www.etasr.com bharti et al.: controller design for dfig driven by variable speed wind turbine using static output … (cpoptimum=0.3-0.5) i.e. at a constant tip speed ratio, intended for operation approximately its maximum power coefficient. the aerodynamic power generated by wind turbine is given as follows. p aero =0.5  a 3),( vc p  (1) cp ( ),  =c    .)..( 643 2 1 5 cecc c i c i   (2) 1 35.0 .08.0 11 3      i , and the coefficients c 1 =0.5176, c 2 =116, c 3 =0.4, c 4 =5, c 5 =21, c 6 =0.0068 and v rt .  a=swept area of the blades (=πr2),  tip ratio speed, t rotational speed of the rotor,  = pitch angle, r= radius of the area covered through the blades. the speed of a wind turbine determines the conversion efficiency from wind energy to mechanical energy, for a given wind velocity, blades geometry, and turbine iii. an overview of the dfig operating principle the overview and operating principle of dfig discussed in this section is also mentioned in [14]. the basic diagram of dfig with converters is shown in figure 2. the ac/dc/ac converter is divided into two components: the rotor side converter (c rotor) as well as the grid side converter (c grid). crotor and cgrid are voltage sourced converters with a common dc link via a capacitor. the grid converter uses a coupling inductor l to connect to the grid. the three phase rotor winding is connected to the crotor through slip rings as well as brushes, while the three phase stator winding is directly connected to the grid. the power captured by the wind turbines is converted into electrical power by the induction generator and it is transmitted to the grid through both the stator as well as rotor windings. the control system generates the control signals to control the active, reactive power as well as currents, the injected frequency compensation to the rotor windings and lastly the dc voltage control of the common coupling link capacitor. rotor side converter operates as an inverter and stator side converter operates as rectifier. when rotor moves below the synchronous speed in generating slip power is supplied to the rotor. the mechanical power as well as the stator electric power output is given as below rmr tp  sems tp  the mechanical dynamical equations for the lossless generator are described below. )( emm r tt dt d j   at steady state, the mechanical torque balances the electromagnetic torque substitute on the machine and hence the relations are as follows. emm tt  and )( rsm ppp  it follows that: )( smr ppp  = ssemrm sptt   where srss  /)(  is defined as the slip of the generator in per unit and j is inertia constant. iv. voltage source converter controller a voltage source converter (vsc) is used in dfig to control the rotor and grid side converter as well as dc link voltage also. the general schematic diagram of a dfig and wind turbine along with vsc converters with a common dc link is shown in figure 3. the advantage of vsc based converter is that it uses very small power converter on the rotor side. the rotor side converter supplies the compensated current for frequency compensation. wide variation in the wind speed is taken care of by gear train with adjustable gear ratio. vsc control circuitry provides the necessary control signals for both rotor side as well as grid side converters. further, the control strategy maintains a constant dc voltage of the common dc link. fig. 2. basic diagram of doubly fed induction generator with converters fig. 3. the general schematic diagram of dfig control the transfer function of the overall system is obtained either via elementary modeling or using the numerical differentiation, on the basis of which the controller for the vsc is designed. component modules of the vsc based common engineering, technology & applied science research vol. 6, no. 4, 2016, 1056-1061 1059 www.etasr.com bharti et al.: controller design for dfig driven by variable speed wind turbine using static output … dc link controller is shown in figure 4. setgp and set gq shown in the diagram are the set-point values of the real and reactive power across the terminals of the wind turbine. the power factor can be made unity by letting setgq to zero. in this case all reactive power to the dfig is provided via the rotor-side converter. further, the reactive power set point value can be adjusted to maintain the voltage constant at the turbine terminals [8]. fig. 4. component modules of the vsc based common dc link controller a. simplified system model: the system chosen for the study of the supervisory control is a wind turbine connected to a step-up transformer and a local load at 1 km. the point of common coupling at the load side is connected to the utility grid via a 30 km long transmission line [15]. the grid connected wind turbine system is shown in figure 5. the supervisory control used in this paper decides the reactive power requirements from the perturbations in the power point coupling (pcc) voltage and the wind speeds. in general, for wind farms or even few wind turbines connected to local load and utility grid, it is difficult to obtain the analytical model of the overall system. fig. 5. grid connected wind turbine system b. design of supervisory controller: the pid controller for the sample system was designed considering the 10% overshoot and more than 60 degrees of phase margin. the gains of the pid supervisory controller parameters are given in table i [8]. table i: gains of the pid supervisory controller parameters ki kp kd gains 6.7122 0.4635 0.0009 this paper presents an experimental study of the dfig with help of seven pi controllers for the internal loops of the dfig and one pid controller for the supervisory control of the system under study as proposed in [15]. this model is utilized to design the sof controller for the proposed system and results are compared with the results in table i. v. static output feedback technique various techniques are available to design a pi controller. among these techniques static output feedback (sof) is the one that can be applied to the controller to make the system globally stable. figure 6 shows that the input to the pi controller is the error between the set point value and the measured value. controllers output can be written as follows.  dtykyku ip 00 (6) where, pk and ik are controller constants. equation (6) can be rewritten as follows. u [ pk ik ] [ 0y  0y ] t (7) therefore, measured output will be: y = [ 0y  0y ] t (8) and pi controller can be described as follows: gc = [ pk ik ] (9) the pi controller is in closed loop system as shown in figure 6. fig. 6. pi controller in closed loop system pi controller design based on sof method uses a pair of coupled linear matrix inequalities. sof controller that guarantees the closed loop system is impulse free and stochastically stable for the tuning of pi controller [16].by using lmi toolbox of matlab we get the gain of the sof, pi controller as given in table ii. table ii: gains of the sof pi controller parameters kp ki gains 0.0814 4.6647 vi. simulation and results a. simulation and response of the dfig system: figure 7 represents the detailed doubly fed induction generator matlab diagram and voltage (pu) at dfig terminals presented in figure 8. furthermore figure 9 shows the active power delivered. the reactive power requirement of the dfig is presented in figure 10. dc link voltage (pu) at the common link capacitor of dfig is presented in figure 11. 1 0.69/ 34.5 kv t 2 1 km ca local load 3 30 km pc tl 4 ib utility grid infinite bus 1… 4 – bus number wt – wind turbine tr – transformers ca – cable tl – transmission line pcc – point of common coupling ib-infinite bus wt  p i  plant + set point y0 error u y output engineering, technology & applied science research vol. 6, no. 4, 2016, 1056-1061 1060 www.etasr.com bharti et al.: controller design for dfig driven by variable speed wind turbine using static output … fig. 7. detailed dfig wind turbine diagram fig. 8. voltages at the dfig terminals fig. 9. active power delivered fig. 10. reactive power requirement of the dfig fig. 11. dc link voltage at the common link capacitor b. response of supervisory control with pid controller: the response of the supervisory pid designed in [8] on the system under study is as shown in figure 12. clearly the open loop system despite being stable has steady state error of 100%. further, there is an under shoot in the response of the open loop system due to the non-minimum phase nature of the system. step response of the supervisory reactive power controller (conventional pid-controller) in [8] is shown in figure 12. fig. 12. step response of the supervisory reactive power controller (conventional pid controller) c. response of supervisory control with pi controller by means of sof method using pi controller parameters designed in table ii. the step response of the system under study for the supervisory reactive power control was studied. the step response of the system is as shown in figure 13. it is clear from the comparison of the results of the pid control in [8] and the ones reported in this work, that our controller has resulted in suitably damped supervisory control without compromising the speed of response of control loop. step response of open as well as close loop reduced order system by pi controller using sof method is shown in figure 13. comparison between the step responses of figures 12 and 13 is presented in table iii. table iii: comparison of settling time and overshoot between supervisory pid controller and pi controller using sof method figure 12 13 controller supervisory pid sof based pi rise time 0.0152 0.2133 settling time 0.5291 0.5276 settling min. 0.4933 0.9111 settling max. 1.1512 0.9926 over shoot 15.1985 0 under shoot 8.1860 1.5474 peak 1.1512 0.9996 peak time 0.1419 1 fig. 13. step response of open loop and close loop reduced order system with pi controller using sof method engineering, technology & applied science research vol. 6, no. 4, 2016, 1056-1061 1061 www.etasr.com bharti et al.: controller design for dfig driven by variable speed wind turbine using static output … d. comparison between supervisory pid and pi-controller using sof method: a comparison of settling time and overshoot is given in table iii. the comparison of the performance parameters for controllers as given in table iii, are concluded as: (i) the designed pi controller is able to reduce the steady state error to zero as the existing one, (ii) the peak overshoot has been reduced to zero, the response is no more under damped and (iii) the response speed is almost the same as that of the existing controller or it is slightly better. thus the designed controller in this paper helps to eliminate the reactive power fluctuations in the dfig system. vii. conclusion although the supervisory pid controller improves the system response in comparison to the open loop system yet oscillations are not entirely removed. pi controller using the sof method not only improves the system response but in addition decreases the percentages overshoot to zero. pi controller using sof technique demonstrates that the system settles down in smaller time as in the case when supervisory pid controller employed. results presented in this paper shows that the settling time is reduced three percent approximately and that the percentage overshoot reduces to zero with pi controller using sof method in comparison to the supervisory pid controller. hence, it is accomplished that the sof control technique provides another alternative for the design of controllers in dfig. acknowledgment the authors acknowledge the partial financial support from the indian institute of technology (banaras hindu university), varanasi (u.p.) india for carrying out this work. this work is heartily devoted to sweet memories of the first author’s great grand mother patiraji devi who has passed away on november 24, 2014. appendix: simulation data dfig (pu): rs = 0.00920, rr = 0.00760, ls = 0.190, lr = 0.07920, lm = 4.59260 controller gains (pu): rotor-side converter: pi1 and pi3 controllers: kp = 0.0252, ki = 10.4832 pi2 and pi4 controllers: kp = 0.9995, ki = 20 grid-side converter: pi5 and pi6 controllers: kp = 0.7147, ki = 7.1515 dc link module: vdcref = 1, cdc = 12.7227, kp = 0.9544, ki =3.8175 transfer function of the 6th-order reduced model: 0.000324s6 − 1.75s5 − 2366s4 + 7.9e6s3 + 7.5e9s2 + 5e12s + 2.18e14 g(s) = s6 + 2340s5 + 8.67e6s4 + 4.79e9s3 + 2.7e12s2 + 1.27e14s + 9.6e14 references: [1] f. yao, r. c. bansal, z. y. dong, r. k. saket, j. s. shakya, “wind energy resources: theory, design and applications”,in handbook of renewable energy technology, section i: wind energy and their applications, pp: 03–20, world scientific publishing house, singapore, 2011 [2] a. m. atallah, a. y. abdelaziz, m. ali, r. k. saket, o. p. bharti, “reliability assessment and economic evaluation of offshore wind farm using stochastic probability”, international conference on power, circuit and information technologies, bangalore, india, 27th 28th april, 2015 [3] r. c. bansal, a. f. zobaa, r. k. saket, “some issues related to power generation using wind energy conversion system: an overview”, international journal of emerging electric power system, vol. 3,no. 2, pp: 1-19, 2005 [4] h. sun, y. ren, h. li, z. an, j. liu, h. hu, h. liu, “dfig wind power generation based on back-to-back pwm converter,” 2009 ieee international conference on mechatronics and automation, pp. 2276– 2280, changchun, china, august 9-12, 2009. [5] t. brekken, n. mohan, “control of a doubly fed induction wind generator under unbalanced grid voltage conditions”, ieee trans. energy conv., vol. 22, no. 1, pp. 129–135, 2007 [6] j. b. ekanayake l. holdsworth, n. jenkins, “comparison of 5th order and 3rd order machine models for doubly fed induction generator (dfig) wind turbines”, electric power systems research, vol. 67, pp. 207-215, 2003 [7] z. wang, y. sun, g. li, b.t.ooi, “magnitude and frequency control of grid connected doubly fed induction generator based on synchronized model for wind power generation”, iet renew. power generation, vol. 4, no. 3, pp. 232-241, 2010 [8] h. s. ko, supervisory voltage control scheme for grid-connected wind farms, ph.d. dissertation, dept. elect. and comp. eng., univ. of british columbia, vancouver, bc, canada, 2006 [9] s. engelhardt, i. erlich, c. feltes, j. kretschmann, f. shewarega, “reactive power capability of wind turbines based on doubly fed induction generators” ieee trans. energy conv., vol. 26, no. 1, pp. 364–372, 2011 [10] m. rahimi, “dynamic performance assessment of dfig-based wind turbines: a review,” renew. sustain. energy rev., vol. 37, pp. 852–866, 2014 [11] x. xi, h. geng, g. yang, “enhanced model of the doubly fed induction generator-based wind farm for small-signal stability studies of weak power system,” iet renew. power gener, vol. 8, no. 7, pp. 765–774, 2014. [12] b. bossou, m. karim, a. lagrioui, m. taoussi, “observer back stepping control of dfig-generators for wind turbines variable-speed fpgabased implementation,” renewable energy, vol. 81, pp. 903–917, 2015 [13] a. tapia, g. tapia, j. x. ostolaza, j. r. saens, “modeling and control of a wind turbine driven doubly fed induction generator”, ieee transactions on energy conversion, vol. 18, no.2, pp. 194-204, 2003 [14] b. dosijanoski, “simulation of doubly fed induction generator in a wind turbine”, xi international phd workshop owd, wisła, poland, october 17–20, 2009 [15] h. s. ko, g. g. yoon, n. h. kyung, w. p. hong, “modeling and control of dfig-based variable speed wind-turbine”, electric power system research, vol. 78, pp. 1841-1849, 2008 [16] e. k. boukas, control of singular systems with random abrupt changes, springer, 2008. microsoft word etasr_v13_n3_pp10820-10827 engineering, technology & applied science research vol. 13, no. 3, 2023, 10820-10827 10820 www.etasr.com malak et al.: effect of coarse aggregate gradation on the strength properties of bagasse ash concrete effect of coarse aggregate gradation on the strength properties of bagasse ash concrete irshad ali malak department of civil engineering, quaid-e awam university of engineering, science and technology, pakistan irshadalimalak@gmail.com (corresponding author) tulsi das narwani department of civil engineering, quaid-e-awam university of engineering, science and technology, pakistan tulsidasnarwani1@gmail.com bashir ahmed memon department of civil engineering, quaid-e-awam university of engineering, science and technology, pakistan bashir_m@gmail.com jan muhammad watoo department of civil engineering, quaid-e-awam university of engineering, science and technology, pakistan engr.janmohdwatoo@gmail.com naeem ahmed jokhio department of civil engineering, quaid-e-awam university of engineering, science and technology, pakistan naeemjokhio110@gmail.com sajid ali mallah department of civil engineering, quaid-e-awam university of engineering, science and technology, pakistan engrsajid389@gmail.com received: 22 february 2023 | revised: 14 march 2023 | accepted: 16 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5807 abstract this study investigated the coarse aggregate grades and the use of sugarcane bagasse ash as a replacement for cement to examine their effect on concrete strength. ten concrete mixes were prepared in two groups using a 1:2:4 mix ratio and a 0.48 water-to-binder ratio. sugarcane bagasse ash was used in 0 and 10% dosages by weight of cement. five grades of aggregates were used: 4.75-7, 7-10, 10-13, 13-20, and 4.7520mm. six 6"/12" concrete cylinders were prepared for each group and cured for 28 days to test their compressive and split tensile strengths. the results showed that bagasse ash caused a reduction in strength properties in both welland specific-graded concrete. it was also observed that 10-13mm aggregate concrete with and without bagasse ash had more strength than the respective well-graded. although a minimum decrease in strength was observed, a 10% dosage of sugarcane bagasse ash was optimal to save cement content in both specific and well-graded aggregate concrete. this study provides a new framework for using graded coarse aggregates and replacing cement with bagasse ash. keywords-compressive strength; tensile strength; green concrete; sugarcane bagasse; sustainability; waste management engineering, technology & applied science research vol. 13, no. 3, 2023, 10820-10827 10821 www.etasr.com malak et al.: effect of coarse aggregate gradation on the strength properties of bagasse ash concrete i. introduction concrete is the most widely used material in the industry, giving the freedom to construct the desired shapes, orientations, and sizes. however, it requires good care and control in the use of constituent materials to ensure the proper strength of the final product. the recent boom in construction gives beautiful and eye-catching infrastructures but consumes a large quantity of natural and man-made ingredients. the use of aggregates has reached an alarming situation due to the depletion of conventional natural sources. moreover, the demand for cement causes a serious environmental problem due to the emissions of harmful gases. the boom in construction has also posed a serious problem for demolition and construction waste due to the unavailability of dumping space, particularly in city centers. construction is not the only industry that produces waste at a serious level, as several other primary industrial processes also generate waste that requires proper dumping. the sugar industry is one such example, as it uses sugar cane for its primary processes and generates bagasse in large quantities. bagasse is used in the development of secondary products, but residuals remain a serious issue. the ingredients of the concrete matrix have many advantages and some disadvantages. the search for alternative materials for concrete ingredients to overcome its weaknesses and conserve natural sources or reduce the use of man-made materials is an active research area. several alternative materials have been proposed to be used in the concrete matrix, such as residual waste from primary industrial processes. bagasse ash is one of them. different materials have shown different behaviors for fresh and hardened properties with strength variation. the preparation of concrete requires good care in the use of materials to ensure the proper strength of the final product. well-graded aggregates are among them, but in many cases, coarse aggregates are not well-graded. sometimes, aggregate gradation is not performed and there is a chance that such concrete will have poor strength in its hardened state despite good care in batching, mixing, placing, and curing. the current study investigated the effect of coarse aggregate gradation on concrete strength properties using bagasse ash as a partial replacement of cement. this study not only examined the effect of gradation on strength but also used an indigenous waste material as a partial cement replacement, as it could tackle the waste management problem to some extent. ii. literature review the controlled burning of sugar bagasse produces ash that has cementitious properties and has been used in concrete as a partial replacement for cement in various studies. in [1], the use of bagasse ash in concrete was reviewed, concluding that it has good cementitious properties and can be used in concrete to alter its properties. in [2], bagasse ash was used in various dosages to develop m20 concrete, the test results of 7and 28day cured specimens showed a comparable increase in split tensile strength and workability of the 10% dosage specimens, but an additional increase in ash dosage resulted in a decrease in split tensile strength and workability. the same results were also observed in [3]. in [4], bagasse ash was used in various dosages as a replacement for cement to develop m30 concrete, and the test results of 7and 28-day cured specimens showed increased compressive, split tensile, and flexural strength for up to 20% dosage of bagasse ash, but further addition of ash resulted in decreased strength and workability of the concrete. on the other hand, in [5], bagasse ash was used to produce m20 concrete, the test specimens were cured for 7, 14, and 28 days, and the results showed that the 25% dosage was optimal for the strength properties while the 15% was optimal for workability. in [6], m20 grade concrete was made with 0-30% sugarcane bagasse ash, and the test results of cubes, cylinders, and prisms cured for 7, 14, and 28 days showed that 25% replacement of cement with ash was optimal with a negligible decrease in strength properties. in [7] and [8], sugarcane ash was used up to 15 and 25%, respectively, to produce m25 concrete, and the test results showed that 5% and 15% were the optimal dosages, respectively. in [9], bagasse ash was used in 0-25% dosages to produce m25 concrete and the test results of 7and 28-day cured samples showed that 15% was the optimal, as it reduced only 7, 1, and 6% compressive, tensile, and flexural strength, respectively. in [10], bagasse ash was used as a 20% cement replacement to develop m25 concrete, and the results showed an increase in slump with the increase in the dose of bagasse ash. maximum residual compressive strength equal to 26.45mpa in comparison to 27.7mpa, and tensile strength equal to 1.89mpa in comparison to 1.94mpa were observed at the 5% dosage, concluding that this was the optimal bagasse ash dosage for cement replacement. similarly but for m20 concrete, the 5% dosage was observed as the optimum for compressive, tensile, and flexural strength with different residual strength values [11]. in [12], the 6% dosage was found as the optimal level of cement replacement. in [13], a 2% dose was observed to be optimal in terms of strength of the bagasse ash concrete. in [14], bagasse ash was used to produce m20 and m15 concrete, where a 45% and 28% increase in slump was recorded at replacement levels of 5% and 10%, and the increase in compressive strength was recorded as equal to 11.6% and 3.5% at dosages of 5% and 10%, respectively. a similar trend was observed for the strength of m15 concrete, concluding that 5% was the optimal dosage of ash regarding the increase in compressive strength. in [15, 16], m30 and m35 concrete was produced using bagasse ash, respectively, concluding that a 15% dosage had the optimum strength parameters. bagasse ash was also used in [17-21] to examine dose optimization for the strength properties of concrete. table i summarizes the results of sugarcane bagasse ash as a cement replacement published in various studies. the strength of concrete is the key property for proper durability and serviceability during the service life of structures. well-graded aggregates in concrete matrix ensure proper strength of the final product. however, unfortunately, in many cases, the gradation of the aggregates is omitted, resulting in unevenly graded aggregates that affect the final strength of the hardened concrete. the effect of gradation on concrete strength was studied in [22]. using well-graded, uniform, and gap-graded aggregates, m20 concrete was tested for slump, compaction factor, and compressive strength. the results showed that the gradation of fine aggregates was more influential than that of coarse aggregates. the compaction engineering, technology & applied science research vol. 13, no. 3, 2023, 10820-10827 10822 www.etasr.com malak et al.: effect of coarse aggregate gradation on the strength properties of bagasse ash concrete factor test was more sensitive and gave better results for gapgraded aggregates and similar were the results of the compressive strength test. therefore, this study argued that although well-graded aggregates result in better concrete, the presence of large particles prevents homogeneity when concrete is stressed. table i. summary of literature review reference parameters of study concrete opt. dosage 1 [2], [3] workability, cs, ts m20 10% 2 [4] workability, cs, ts, fs m30 30% 3 [5], [6] workability, cs, ts, fs m20 25% 4 [7] cs, ts m25 5% 5 [8] cs m25 15% 6 [9] cs, ts, fs m25 15% 7 [10] cs, ts m25 5% [11] cs, ts, fs m20 8 [12] cs, ts, fs m20 6% 9 [13] workability, cs m30 2% 10 [14] cs m20, m15 5% 11 [15] cs, ts, fs m30 15% [16] cs, ts, voids m35 12 [17] cs, ts m20 8% 13 [18] workability, fs m25 10% 14 [19] slump, compaction factor, cs m35 10% 15 [20] cs m35 10% 16 [21] cs, fs m35 10% in [23], the effect of uniformly graded aggregates was examined in geopolymer concrete with fly ash and ggbs. a comparison of g40 and m40 showed better performance of 12.5mm size aggregates in thin precast elements than conventional concrete. in [24], the effect of different grading of the aggregates was investigated on conventional concrete by designing 8 different mixes, concluding that the compressive strength of concrete can be improved by more than 50% by altering the grade of aggregates. in [25], the effects of the type and size of aggregates were investigated on the compressive strength of concrete, examining three types, (quartzite, granite, and river gravel) and three sizes (12, 20, and 40mm) along with fly ash and superplasticizer to evaluate density, compressive strength, and tensile strength. the results showed that the 12mm quartzite aggregates had the highest strength. in [26], the effects of aggregates from different sources in pakistan were studied, using 28-day cured samples of a 1:2:4 mixture, and the results showed a very good increase in compressive strength using a combination of fine aggregates from lawrencepur and kashmore in equal proportions than aggregates from one source alone. in [27-28], the effect of gap gradation was studied on the workability and flexural strength of concrete, showing a good increase in both test parameters for mixes with aggregates less than 5mm, but gap-graded concrete required more binder contents than usual to ensure workability and strength. thus, there was an argument that although careful gap gradation may result in more strength of the final product, well-graded concrete is better for binder content and durability. in [29], a completely different phenomenon was observed regarding binder content, showing that 15% less binder can be used for the same strength with careful gap gradation of aggregates. in [30], the effect of uniformly graded 1:1.5:3 concrete was studied for its workability and strength properties, using aggregates of 9.5, 12.7, and 19.1mm. a three times higher slump value was noticed compared to well-graded aggregates with a decrease in slump values as aggregate size increased. the compressive strength was also recorded as 5%, 16%, and 21% higher than that of well-graded aggregates. moreover, cement-treated aggregates did not have any positive impact on the strength of rigid pavements. in [31-33], aggregate gradation was attempted to minimize the cost of concrete by reducing the cement content. furthermore, recycled coarse aggregates from demolished concrete have also been used in concrete to study the effect of fly ash on strength properties [34], water penetration of recycled aggregate concrete [35], compressive strength of no-fines recycled aggregate concrete [32], and flexural strength of no-fines recycled aggregate concrete [36]. the evident scatter of these results indicates that more studies are required to reach a certain level of confidence in the use of the materials. this study performed a laboratory investigation on the combined effect of different gradations of coarse aggregates and sugarcane bagasse ash as cement replacement on the strength properties of concrete. iii. materials and testing this study used ordinary portland cement under the brand name pakland, and with a value of 2.79. fine aggregates passing through the 4.75mm sieve were obtained from approved quarries, which had a specific gravity of 2.62. coarse aggregates were also obtained from the same quarries, having a size between 4.75-20mm and 2.8 specific gravity. the coarse aggregates were washed and dried before being used in the concrete mix. to achieve the proposed target, coarse aggregates were sieved and separated into groups of 4.75-7mm, 7-10mm, 10-13mm, and 13-20mm, to produce four concrete batches. additionally, one batch of concrete with coarse aggregates between 4.75-20mm (well-graded aggregates) was also prepared. therefore, five batches of concrete were prepared. filtered tap water from the city water supply, having a ph of 7.1, was used for washing the aggregates, preparing the concrete mix, and curing. the sugarcane primarily used in the preparation of sugar contained approximately 26% of bagasse, 50% moisture, and 0.62% residual ash. figure 1 shows the sugarcane bagasse obtained from a sugar mill in nawabshah. the sugarcane bagasse was dried in open air for a few days followed by controlled burning at 700°c. the residual bagasse ash contained 50% cellulose, 25% hemicellulose, and 25% lignin. table ii shows the chemical analysis of bagasse ash. it should be noticed that its silica and alumina contents provide good cementitious properties. the ash was then used as a 10% replacement of cement by weight in 5 batches with 10% bagasse ash and another 5 batches without bagasse ash to compare the test results. for all mixes, a 1:2:4 ratio and a 0.4 water-to-binder ratio were used. the batching of ingredients was performed by weight. all the ingredients were then mixed in a concrete mixer until the formation of a uniform paste, and 10 standard-size cylinders (6×12'') were prepared in each batch. the inner of the molds was oiled and the concrete was filled in three layers. a table vibrator was used to achieve the proper compaction. the molds were then left for 24 hours to let the concrete harden. figure 3 shows some selected samples. engineering, technology & applied science research vol. 13, no. 3, 2023, 10820-10827 10823 www.etasr.com malak et al.: effect of coarse aggregate gradation on the strength properties of bagasse ash concrete after 24 hours, the specimens were de-molded, allowed to dry in the air for a day, and immersed in potable water for 28-day curing, as shown in figure 4. table ii. chemical analysis of sugarcane bagasse ash # component mass percentage 1 silica (sio2) 66.89 2 alumina (al2o3) 29.18 3 ferric oxide (fe2o3) 4 calcium oxide (cao) 1.92 5 magnesium oxide (mgo) 0.83 6 sulphur tri oxide (so3) 0.56 7 loss of ignition 0.72 fig. 1. sugarcane bagasse. fig. 2. bagasse ash. fig. 3. specimens. after curing, the specimens were taken out of the water and allowed to dry in the laboratory for one day. in each batch, 5 specimens were used to evaluate their compressive strength and 5 were used to determine the split tensile strength. the specimens were tested in a compressive strength machine under gradually increasing load until failure, following the astm c39 [37]. figure 5 shows some specimens during testing. the load was then converted into compressive strength using the standard formula for the purpose σ=p/a. fig. 4. curing. fig. 5. compressive strength test. fig. 6. split tensile strength test. the specimens were laterally loaded onto a universal testing machine, following astm c496 [38], with a gradually increasing load at a rate of 0.5kn/sec to determine their tensile strength, as shown in figure 6. the crushing load was recorded and converted into split tensile strength using the standard formula f=2p/πld. table iii shows the results obtained from the compressive and tensile strength tests for all specimens. engineering, technology & applied science research vol. 13, no. 3, 2023, 10820-10827 10824 www.etasr.com malak et al.: effect of coarse aggregate gradation on the strength properties of bagasse ash concrete table iii. compressive and tensile strength concrete mix # compressive strength (mpa) split tensile strength (mpa) bagasse ash percentage (%) 0 10 0 10 m1: 1 27.15 23.99 2.66 2.45 4.75-7 2 28.41 27.95 2.82 2.24 3 29.79 19.48 2.74 2.27 m2: 1 32 29.41 2.96 2.7 10-jul 2 35.3 28.81 3.21 2.66 3 32.19 28.47 3.06 2.54 m3: 1 34.39 30.93 3.39 2.8 13-oct 2 35 31.45 3.16 2.85 3 37.67 28.93 3.11 2.7 m4: 1 31.76 27.67 3.18 2.66 13-20 2 32.97 27.95 3 2.5 3 32.61 28.07 3.12 2.51 m5: 1 33.36 31.91 2.98 2.74 4.75-20 2 33.75 27.91 3.19 2.78 3 33.51 28.51 3.19 2.73 iv. results and discussion figure 7 shows the compressive strength of concrete with 0% and 10% bagasse ash. although there is a fluctuating trend in the compressive strength of individual samples, the difference in the strength of individual samples is small. table iv and figure 8 show the average compressive strength of the samples per batch. it can be observed that the compressive strength of concrete with bagasse ash was smaller than the one without. although the ash has good cementitious properties, they are not equal to cement's, therefore cement replacement with ash affects the strength. furthermore, it can be observed that the gradation of concrete had also an impact on the final strength. the maximum strength in concrete without bagasse ash was recorded in m3 (10-13mm aggregates), as its value was even higher than the compressive strength of well-graded aggregates (+6.4%). m1 and m2 mixes had less strength than m5, due to the smaller size of aggregates which have less strength. m4 also had less strength than m5. the mix contained large-sized aggregates, and the lack of small-sized particles should have resulted in voids inside the body of concrete resulting in less strength. m3 had the highest strength among the considered mixes due to medium-sized particles being able to contribute strength and fill the voids of the concrete. the fourth column lists the deviation of the average compressive strength of concrete mixes with and without 10% bagasse ash. the lowest error was recorded in m5 with well-graded aggregates and then in m2 with 7-10mm aggregates. this shows that small-sized aggregates in the concrete matrix gave better strength results, but the effort required to separate the grades is more. the last two columns of the table list the percentage deviation of the strength concerning the well-graded aggregates without bagasse ash. figure 9 shows the percentage error of concrete with bagasse ash versus without bagasse ash and with well-graded aggregates. table iii and figure 9 show that m3 had the least reduction in compressive strength due to the reasons mentioned above. figure 10 shows the split tensile strength for individual samples with and without bagasse ash. table v shows the average split tensile strength of all specimens in each group, along with the percentage change of each group and for wellgraded aggregates without bagasse ash. the results are listed in a pattern similar to those of average compressive strength. table v and figures 10-12 show that again the m3 mix (1013mm aggregates) had the maximum split tensile strength for both concrete types. graded aggregate concrete had an increase of 3.58% compared to well-graded aggregate concrete, but when using 10% bagasse ash it had a decrease of 10.54% in tensile strength. the decrease was the lowest among all the grades used. it can be further observed that the variation in split tensile strength of m3 concrete with and without bagasse ash was approximately 9%. the same percentage was recorded for concrete with well-graded aggregates. table iv. average compressive strength average compressive strength % change mix: mm bagasse ash same group well graded agg. 0% 10% 10% 0% 10% m1: 4.75–7 28.45 23.81 -16.33 -15.18 -29.02 m2: 7-10 33.16 28.9 -12.86 -1.13 -13.84 m3: 10-13 35.69 30.44 -14.71 6.4 -9.26 m4: 13-20 32.45 27.89 -14.03 -3.26 -16.84 m5: 4.75-20 33.54 29.44 -12.22 0 -12.22 (a) (b) fig. 7. compressive strength: (a) 0% bagasse ash, (b) 10% bagasse ash. table v. average split tensile strength average split tensile strength % change mix bagasse ash same group well-graded aggregates 0% 10% 10% 0% 10% m1: 4.75-7 2.74 2.32 -15.36 -11.87 -25.41 m2: 7-10 3.07 2.63 -14.31 -1.2 -15.34 m3: 10-13 3.22 2.78 -13.63 3.58 -10.54 m4: 13-20 3.1 2.56 -17.47 -0.41 -17.8 m5: 4.75-20 3.11 2.75 -11.54 0 -11.54 engineering, technology & applied science research vol. 13, no. 3, 2023, 10820-10827 10825 www.etasr.com malak et al.: effect of coarse aggregate gradation on the strength properties of bagasse ash concrete fig. 8. average compressive strength. fig. 9. % change of compressive strength. (a) (b) fig. 10. split tensile strength: (a) 0% bagasse ash, (b) 10% bagasse ash. the above findings clearly show that the gradation of aggregates affects the strength properties of concrete. mediumsized aggregates (10-13mm) give better strength, even than well-graded aggregates, due to the binding of the bagasse ash and the fineness that fills the gaps between the aggregates, as it not only reduces the voids but also improves the strength of concrete. on the other hand, it is also evident that the effort involved in separating the aggregates in case of a normal supply of the material or grading the large blocks to the required size is large compared to the gain in strength (+6.4%). therefore, the use of well-graded aggregates is encouraged. however, if favorable, the above-mentioned grade of aggregates may be used for better strength. sugarcane bagasse ash has good cementitious properties. for the grade of aggregates mentioned above, 10% bagasse ash reduced compressive and tensile strength by 9.26% and 10.54%, respectively, which is small and may be tolerable for saving cement content. even with well-graded aggregate concrete, the percentage reduction in compressive and tensile strength was about 12%. thus, it is concluded that a 10% dosage of bagasse ash is optimal for specific or well-graded aggregate concrete. fig. 11. average split tensile strength. fig. 12. error % in split tensile strength. v. conclusion this study conducted a laboratory investigation on the effect of different grades of coarse aggregates and sugarcane bagasse ash on the strength properties of concrete, finding that both materials affect them. small-sized aggregates alone in the concrete matrix fill the voids properly but demand higher binder content due to the larger surface area, resulting in reduced strength. large-sized aggregates alone leave more voids in the concrete body, also reducing its final strength. medium-sized particles are better from both perspectives, as they reduce voids and show maximum strength properties. although bagasse ash has good cementitious properties, these are lower than cement's. the use of bagasse ash reduces both cement content and the strength properties of concrete, however, the reduction in strength is small, about 9% and 11% for compressive and tensile strength, respectively. in addition, bagasse ash in well-graded aggregate concrete showed a marginal reduction of 12% in strength. thus, a 10% dose of engineering, technology & applied science research vol. 13, no. 3, 2023, 10820-10827 10826 www.etasr.com malak et al.: effect of coarse aggregate gradation on the strength properties of bagasse ash concrete bagasse ash is proposed as optimal. the results showed that concrete with 7-13mm coarse aggregates had more strength than well-aggregated concrete, but the effort required to separate or produce this grade of aggregate is possibly higher than the strength increase (6.4%). therefore, this study proposes well-graded aggregates with sugarcane bagasse ash. references [1] m. kumar and s. s. dhriayn, "review on effect of bagasse ash on strength of concrete," international journal of engineering research & technology, vol. 7, no. 1, jan. 2018, https://doi.org/10.17577/ ijertv7is010106. 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[38] "astm c496: standard test method for splitting tensile strength of cylindrical concrete specimens," west conshohocken, pa, usa: astm c496, 2017. microsoft word 557-ed.doc engineering, technology & applied science research vol. 5, no. 2, 2015, 790-794 790 www.etasr.com dossis and dimitriou: are hls tools healthy? the c-cubed project are hls tools healthy? the c-cubed project michael dossis dept. of informatics engineering tei of western macedonia kastoria, greece mdossis@yahoo.gr georgios dimitriou dept. of electrical and computer engineering university of thessaly volos, greece dimitriu@uth.gr abstract— the increasing complexity of application specific integrated circuits (asics) and systems-on-chip (socs) that incorporate custom and standard embedded core ip blocks dictates the need for a new generation of automated and formal system eda tools and methodologies. high-level synthesis (hls) plays a critical role in the required electronic system level (esl) methodologies. however, most of the available academic and commercial high-level synthesis (hls) tools still do not play an established role in the system and hardware engineering teams. this is true for a number of practical reasons, analyzed and discussed in this work. the present article is a practical perspective of the required fully automated and formal tools, which are needed to constitute integral parts in electronic design automation (eda) flows. in addition, this article is a useful guide to the system engineer who wants to familiarize with hls tools and to select the appropriate tool for the everyday engineering practice. the advanced hls toolset that is analyzed in this paper is developed by the first author, its c-frontend by the second author, and they are both based on formal methods and fully automated techniques, thus they guarantee the correctness of the synthesized hardware implementations. this paper completes with a number of experiments that were executed using the author’s methodology and they are used to evaluate the specific hls tools. consequently, a number of conclusions are drawn as well as suggestions for the future directions of hls technology. in this way, what is practically needed by the hardware systems engineering community is outlined at the end of the paper. keywords-high-level synthesis; formal methods; eda; esl; hardware compilers; digital hardware design i. introduction nowadays, digital integrated microelectronics feature extremely complex components, control/design hierarchy and interconnection schemes. such components constitute dominant parts in embedded, high-performance and portable/consumer electronic computing systems. it is important to note that as the number of registers in a design increases linearly, the development and verification effort and engineering time increase exponentially. such complexity cannot be dealt anymore with traditional design methods such as rtl coding/synthesis/simulation, since they suffer from highly iterative design flows and prolonged product development. often, due to these problems, the products miss the market windows and engineering investment is lost. during the last couple of decades, commercial and academic organisations have invested in high-level synthesis (hls) in order to achieve automation, quality of implementations and shortened specification-to-product times [1-5, 7]. however, there are a number of practical and engineering issues related to the existing hls tools. first, they produce much lower quality of hardware implementations compared to manual techniques. second, their hardware models that are difficult to handle, and with a lot of platform assumptions and transformation heuristics that assume an ideally-matched target environments, failing to produce real-life configurations. existing and well-defined formal methodologies, such as logic programming [6], compiler generators, artificial intelligence and software compilers etc, can benefit hls tools. the most understood and explored hls tasks are high-level optimizations, scheduling, allocation and binding [1-5, 7]. high-level transformations resemble software compiler optimizations. allocation is the selection of functional units and storing resources for the data and operations objects found in high-level program code. binding is the actual mapping of the above units to real hardware elements such as flip-flops, latches and combinatorial blocks such as functional operator hardware units. scheduling is the arrangement of elementary operations to finite state machine (fsm) states or in other words real system’s clock cycles. however, the optimization of real-world, complex applications and their mapping onto custom hardware fail to produce competitive (with the manually designed) implementations due to the tools’ inability to handle arbitrary, complex, nested control flow and large data objects, as well as sophisticated interfaces through complex hierarchy and module configuration. ii. hls tools, and engineering practice high-level synthesis research commenced in the 80s, with the first academic and industrial linear processing hls tools appearing in the early 90s. usual problems that hls researchers were called to handle, were allocation, scheduling and binding, as mentioned above. the most cumbersome of these problems to deal with is the building of a reliable scheduler [3]. it is well known that when the system complexity increases linearly (e.g. in terms of number of fsm states), the complexity of the scheduler increases exponentially. for extremely complex applications, scheduling is npcomplete [3, 7]. the difficulty to handle complex code engineering, technology & applied science research vol. 5, no. 2, 2015, 790-794 791 www.etasr.com dossis and dimitriou: are hls tools healthy? the c-cubed project becomes serious, and even prohibitive especially when complex control flow hierarchy (e.g. nested while, if/then and for loops) are encountered in the source code model [4, 7]. although the need for automation is pressing, hls tools are still not widely accepted in the industrial practice because of their low quality of results, particularly for real applications with complex module/control-flow hierarchy as stated before. usually, the specification coding style has a severe impact on the type, template and quality of the delivered implementation. for real-life applications, the execution time of the synthesis transformations (front-end compilation, algorithmic transformations, optimizing scheduling, allocation and binding), increases exponentially with a linear increase of the design size [3-5]. this demanded the use of heuristics to cut down processing time, leading to suboptimal solutions. most of the available hls tools impose severe extensions or restrictions (e.g. exclusion of while loops) on the programming semantic model of the subset that they accept as specification. heuristics are applied on the hls transformations (e.g. guards, speculation, loop shifting, trailblazing) [2]. these are suitable for only linear/dataflow dominated (e.g. stream-based) applications, such as dsp, image processing and video/sound streaming. once again they cannot handle any of the excluded programming constructs, such as subprograms, records, while loops, and loop breaks. the most popular commercial hls tools include the catapult-c from calypto (previously developed by mentor graphics), and cynthesizer from forte design systems. they all accept as input a small subset of the system-c and c++ languages. these tools have very complicated for the average user interfaces, and they are the most expensive of their class since they are licensed for something less than 300k dollars per year. so, these e-cad systems are inaccessible for most of the small and medium sized asic/fpga design smes. other commercial or industrial hls tools are the symfony c compiler from synopsys, the impulse-c from impulse accelerated technologies, the cyberworkbench from nec, the c-to-silicon from cadence, and the free web-based tool cto-verilog from an israel-based group. these tools are mostly used only internally by the producing organization, and they are otherwise not well-known amongst the engineering community for reasons that were explained above. the most well-known academic or research-based hls efforts are the spark tool [2] which accepts as input a small subset of the ansi-c language (e.g. while loops are not accepted), and a conditional guard based optimization method [7]. the latter set the basis for optimizing conditional source code at the beginning of the previous decade. recent research efforts include a multi-speculative approach to synthesize complex adders during datapath synthesis, which again contributes only towards linear flow oriented designs [8], a fixed-point accuracy analysis and optimization of polynomial data-flow graphs with respect to a reference model that is found in many dsp applications [9], a technique to improve nested loop pipelining for hls, called polyhedral bubble insertion [10], an equivalence checking method of fsms with datapaths based on value propagation over model paths, for validation code motion, usually applied during the hls scheduling phase [11], a formal method for accurate high-level casting of optimal adders and subtractors [12], and an exploration approach, called spectral-aware pareto iterative refinement, that uses response surface models (rsms) and spectral analysis to predict the design quality without costly architectural synthesis procedures [13]. iii. need for formal techniques the issues discussed above dictate the need for the incorporation of intelligent and formal hls techniques on the source-to-implementation optimizing transformations. in this way, the produced hardware implementations become correctby-construction. only top behavioral level verification (e.g. with rapid compile and execute of the specs) will be needed, against spending weeks and months, on lengthy rtl or annotated gate simulations that is required with traditional methods. in our approach, constraints and designer options can be applied by the user on the automatic hls transformation, such as the number of available resources, the length of the desired schedule, the type of the micro-architecture, the generated hdl code as well as the inclusion of custom (e.g. arithmetic) logic functions throughout the hls compilation, avoiding predefined target platforms or synthesis heuristics. iv. the c-cubed eda hls framework the first author has designed and developed an intelligent hls toolset [4] that optimizes operations into control steps, achieving the maximum functional parallelism in the synthesized implementation [5]. the c-cubed compiler employs an advanced scheduler called parcs, with formal techniques such as logic programming [6] and rdf subjectpredicate-object relations [7]. thus, the delivered implementations are correct-by-construction. a detailed description of the prototype optimizing c-cubed synthesizer can be found in [4]. the c-cubed tool employs formal techniques such as predicate logic [6], rdf relations and xml schema validation to improve the synthesis results. the usability and correctness of the c-cubed hls toolset were evaluated with a large number of benchmarks, a few of which are discussed in the following sections of this paper. the c-cubed ada/c hls design and verification flow, includes the front-end and back-end hls tools, and the gnu c/ada integrated compiler, development and verification environment, as shown in figure 1. the standard programming set of the ada and ansi-c language are accepted by the ccubed synthesizer. the front-end compiler is a compilergenerator parsing and syntax processing system with all the standard software compiler optimizations. the back-end compiler is based on logic programming inference engine rules and it includes the formal parcs scheduler and optimizer. parcs attempts always to parallelize as many as possible operations in the same control step, obeying to data/control dependencies. nevertheless, the tool can be guided by external module and operator specific resource constraints. the c-cubed design and verification flows are outlined in figure 1. the designer, who should be familiar with either engineering, technology & applied science research vol. 5, no. 2, 2015, 790-794 792 www.etasr.com dossis and dimitriou: are hls tools healthy? the c-cubed project ansi-c or ada programming, uses standard programming language constructs such as routines, if/then, while/for loops, arrays and records (structures) complex control constructs and as nested as needed control flow types to build the executable specification model in any of these languages. before execution of the c-cubed compiler, the user verifies the correctness of the given algorithm by simply compiling and executing the source code model along with any benchmarkspecific code (e.g. file-i/o and conversion routines). after debugging his specification code the user passes it to the ccubed framework for hardware synthesis. c-cubed tools are fully automatic, without the slightest code modification, delivering provably-correct hardware implementations in vhdl or verilog rtl. this usually takes from seconds to a few minutes depending on the complexity of the specification model. the applications are optimized with the parcs scheduler and high-quality rtl implementations are generated. these rtl code modules are fsm-controlled datapaths of optimized operators and functional unit sets. they are fully-synthesizable to hardware with any of the available academic or commercial rtl synthesizers without the slightest intervention or modification of the synthesized rtl model fig. 1. c-cubed hls design and verification flow . the produced rtl is highly readable and including comments and object names reflecting the c or ada source code names and user identifiers. thus the designer can easily trace the code names into the delivered rtl statements and if he/she desires to execute rtl simulations for further confidence on the produced implementations, although this is not needed, due to the formality of the employed synthesis transformations by the c-cubed framework. v. experimental results arbitrary input ada or ansi-c code using any of the standard programming language constructs is rapidly and automatically synthesized into functionally-equivalent rtl vhdl/verilog hardware implementation, using the c-cubed framework. a great number of applications were synthesized with the c-cubed toolset [4], some of which are discussed here. in every case, the functionality of the produced hardware implementations matched that of the input subprograms, which was expected due to the formal nature of c-cubed [4]. after building and verifying the benchmarks in ada or c code, they were synthesized into vhdl/verilog rtl. since the c-cubed transformations utilize formal techniques there is no need to simulate the generated rtl. nevertheless for proving this argument in experimental practice we have simulated all the generated rtl tests to ensure that they are functionally equivalent to that of the source code. a rtl simulation snapshot of a computer graphics benchmark generated hdl code is shown in figure 2. this algorithm is based on the dda method to draw a straight line on a digitized screen with pixels. figure 2 demonstrates the completion of the generated hardware’s function with the synchronized done/results_read signal event, as well as all the result data storing into the external memory. fig. 2. the graphics drawing line benchmark simulation all synthesized applications were implemented on xilinx fpgas using the mentor graphics precision rtl synthesis 2013b.15_64-bit (production release) tool, and the xilinx ise place&route utilities, targeting a xilinx -family virtex-4 part 4vsx55ff1148 -speed -12 technology fpga device. table i shows the state reduction, using the parcs optimizer for six benchmarks, the line drawing algorithm, a mpeg engine, a fir filter, a diff. eq. solver a rsa crypto-algorithm and a nested loops benchmark. in some cases with complex control flow, the state reduction optimization rate reaches up to 41 per cent, or the initial fsm. the state reduction for these benchmarks is shown graphically in figure 3. all the tests were compiled with c-cubed in less than 1 minute. amongst the above applications, the mpeg engine comprises of a fsm with more than 1500 states. it has been designed in standard ansi-c code and the c frontend facility of c-cubed tools (developed by the second author of this paper) was used to convert it into ada for synthesis. such a engineering, technology & applied science research vol. 5, no. 2, 2015, 790-794 793 www.etasr.com dossis and dimitriou: are hls tools healthy? the c-cubed project complex design is practically impossible to design and verify directly in rtl. therefore the contribution of the c-cubed technology in this direction is invaluable. tables ii and iii provide resource use statistics of the fpga hardware of the mpeg video compression application. timing constraints that were used for the synthesis and implementation with a clock frequency target of 100 mhz, which was achieved with sizeable slack. the rtl synthesis with precision took less than 3 seconds real time and the c-cubed frontend optimization was completed in 45 seconds for the most complex mpeg test. the produced mpeg rtl for the initial schedule included 9145 vhdl lines, and the optimized by parcs schedule was a list of 8162 vhdl lines. figure 4 shows the xilinx resource statistics for the initial and the optimized mpeg design schedules in a graphical way. the c-cubed hls compiler can be guided by a number of options, such as local and global resource constraints, the target hdl, the massively parallel or fsm+datapath architecture, and the location of complex data objects (such as arrays) on external or embedded memories. this is the reason that table i has multiple experiment lines with “embedded” or “external” memory options. of course fruitful trade-offs can be extracted easily, with experimenting with the high performance embedded memory vs the more economic and realistic for small fpga devices external memory location of the complex data structures. in any case, the location to external memory is configured for any of the data objects of the source code, using a set of elegant memory options file, and without altering the source code as it happens to other, antagonistic hls tools. table i. state reduction optimization using parcs hardware implementation statistics module name initial fsm states parcs parallel fsm states state reduction line-drawing design 17 10 41% mpeg top routine (with external memory) 1697 1380 19% fir filter main routine 17 10 41% differential equation solver 20 13 35% rsa main routine 16 11 31% nested loops 1st routine 28 20 29% nested loops 2nd routine (with embedded memory) 36 26 28% nested loops 2nd routine (with external memory) 96 79 18% nested loops 3rd routine 15 10 33% nested loops 4th routine 18 12 33% nested loops 5th routine 17 13 24% fig. 3. state reduction rates of some benchmarks in graphical view fig. 4. xilinx implementation statistics for the intial and the optimized (parcs) fsm state schedule table ii. xilinx virtex-4 fpga implementation of the initial, unoptimized mpeg schedule initial (un-optimized) schedule xilinx utilization statistics resource used parts available parts utilization rate ios 3093 640 483.28% global buffers 1 32 3.13% luts 6193 49152 12.60% clb slices 3097 24576 12.60% dffs or latches 3836 49152 7.80% table iii. xilinx virtex-4 fpga implementation of the optimized mpeg schedule parcs (optimized) schedule xilinx utilization statistics resource used parts available parts utilization rate ios 3093 640 483.28% global buffers 1 32 3.13% luts 6088 49152 12.39% clb slices 3044 24576 12.39% dffs or latches 3836 49152 7.80% vi. prospects of hls what about the future? what should be the future directions in order to achieve industrial strength hls? more input programming languages (e.g. c++, system-c, uml, fortran, delphi-pascal, java, systemc, python, etc.) and a more globalized and integrated use of formal techniques throughout the flow of the hls toolset are needed in order to bring practical results with acceptable quality of hls results. the automatic and formal nature of future hls research is critical in order to be accepted by the engineering community. combining formal synthesis with formal verification is the only way to deal with the extrapolated complexities of nowadays integrated digital systems. moreover, hls methodologies need to be more general and adaptable to the configuration of different engineering environments, to raw programming code of high-level popular languages such as c, c++ and ada and to various targeted computing architectures and of course to all of the established industrial backend flows. furthermore, new methods need to be investigated for merging multi-cycle operation models with pipelined designs and more advanced programming constructs such as parallelism in the source code, pointers, and dynamic data structures. hls can play a critical part in the engineering practice via the re-use and acceptance as input of existing hardware and software ip. to achieve this, a wide compatibility of hls input/output with languages and formats is required, as well as engineering, technology & applied science research vol. 5, no. 2, 2015, 790-794 794 www.etasr.com dossis and dimitriou: are hls tools healthy? the c-cubed project rapid prototyping capability to the future electronics product development. furthermore, arbitrary and complex module and control flow program code in the designer’s set of system models need to be transformed with ease, speed and comparable quality with manual methods, into the required software and hardware implementations. in this way, highlycomplex applications will motivate the design engineers to use hls tools and hardware-software co-design, in their everyday practice. the most important of all: the hls transformations need to be based on formal techniques so that lengthy rtl and gate-level simulations will be avoided and rapid development cycles will be realized, with free-of-bugs, and first-time-right products. in this way, complete system hardware/software codesign flows will be realized into every day engineering practice. we believe that our c-cubed approach is an important step towards achieving the above goals. vii. conclusions and future work very often, the assumptions that many existing hls tools make (about the targeted technology attributes, the architectural template, the hdl code style, the timing and power consumption, the available operator and data resources as well as the type of communication with the external environment components such as shared memories), produce disappointing synthesis results, since there is still no established methodology for feeding target technology characteristics back into the core of the hls transformation process (although some academic attempts to model this problem have been made). in most cases these target implementation characteristics need to be fed into the synthesis flow and guide the complex synthesis transformations of the hls tool, which makes the synthesis process manual, heavily interactive, cumbersome, prone to errors and very slow. this paper contributes towards the understanding of practical issues of contemporary hls tools and underlines the future directions and achievements which should be envisaged. the most important contribution of this work is a hls esl tool, that automatically, rapidly, formally and optimally transforms input algorithmic, raw, general, arbitrary, widely accepted and re-used (from software engineering) high-level program code into optimal rtl hardware implementations. the c-cubed synthesizer is making an important step towards the requirements for the above achievements and a number of related projects are under-way to deliver better synthesis results with readable rtl code and better visibility of the design’s attributes and algorithmic features. of course, this is not the only attempt to deal with the complexities of the hls transformations and there have been a number of research projects that target a better engineering environment to alleviate the frustrations of industries about dealing with development results that are just too late to hit the market window for many electronics products. moreover, we can learn from other research efforts and also guide them with our own experience through the complexities and issues of hls research with the aim to deliver better eda tools to the design engineers and alleviate their highly-complex tasks to deliver quickly and correctly high-quality hardware and computing products. future work for the c-cubed tools include the inclusion of a number of input language formats such as ansi-c, c++, systemc and opencl, and a number of output formats like systemc and cycle-accurate c test benches for fast verification. also, a number of source code optimizations such as dynamic loop-unrolling and code motion are under development. the use of rdf and xml formalisms in the automatic validation of the internal state and structures of the c-cubed compiler is under investigation and soon will be integrated into the standard c-cubed framework. moreover, there is ongoing work on the use of parameterized components, libraries, and optimized arithmetic units as well as multi-cycle operators to help in the direction of advanced pipelined, multi-operational chained designs with high performance and optimized nested loops. references [1] b. le gal, e. casseau, s. huet, “dynamic memory access management for high-performance dsp applications using high-level synthesis”, ieee transactions on very large scale integration (vlsi) systems, vol. 16, no. 11, pp.1454-1464 , 2008 [2] s. gupta, r. k. gupta, n. d. dutt, a. nikolau, “coordinated parallelizing compiler optimizations and high-level synthesis”, acm transactions on design automation of electronic systems, vol. 9, no. 4, pp. 441–470 , 2004 [3] r. a. walker, s. chaudhuri, “introduction to the scheduling problem”, ieee design & test of computers, vol. 12, no. 2, pp. 60–69, 1995 [4] m. f. dossis, “a formal design framework to generate coprocessors with implementation options”, international journal of research and reviews in computer science, vol. 2, no. 4, pp. 929-936, 2011 [5] p. g. paulin, j. p. knight, “force-directed scheduling for the behavioral synthesis of asics”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 8, no. 6, pp. 661–679, 1989 [6] u. nilsson, j. maluszynski, logic programming and prolog, john wiley & sons ltd., 2nd edition, 1995 [7] a. a. kountouris, c. wolinski, “efficient scheduling of conditional behaviors for high-level synthesis”, acm transactions on design automation of electronic systems, vol. 7, no. 3, pp. 380–412, 2002 [8] a. a. del barrio, r. hermida, s. o. memik, j. m. mendias, m. c. molina, “multispeculative addition applied to datapath synthesis”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 31, no. 12, pp. 1817-1830, 2012 [9] o. sarbishei, k. radecka, “on the fixed-point accuracy analysis and optimization of polynomial specifications”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 32, no. 6, pp. 831-844, 2013 [10] a. morvan, s. derrien, p. quinton, “polyhedral bubble insertion: a method to improve nested loop pipelining for high-level synthesis”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 32, no. 3, pp. 339-352, 2013 [11] k. banerjee, c. karfa, d. sarkar, c. mandal, “verification of code motion techniques using value propagation”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 33, no. 8, pp. 1180-1193, 2014 [12] r. sierra, c. carreras, g. caffarena, c. a. lópez barrio, “a formal method for optimal high-level casting of heterogeneous fixed-point adders and subtractors”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 34, no. 1, pp. 52-62, 2015 [13] s. xydis, g. palermo, v. zaccaria, c. silvano, “spirit: spectral-aware pareto iterative refinement optimization for supervised high-level synthesis”, ieee transactions on computer-aided design of integrated circuits and systems, vol. 34, no. 1, pp. 155-159, 2015 microsoft word 1-626-ed.doc engineering, technology & applied science research vol. 6, no. 2, 2016, 923-926 923 www.etasr.com radhika and arumugam: variable step size maximum correntropy criteria based… variable step size maximum correntropy criteria based adaptive filtering algorithm s. radhika research scholar, faculty of electrical and electronics engineering sathyabama university, chennai, india radhikachandru79@gmail.com a. sivabalan manager, research nec mobile networks excellence centre chennai, india sivabalan.a@gmail.com abstract—maximum correntropy criterion (mcc) based adaptive filters are found to be robust against impulsive interference. this paper proposes a novel mcc based adaptive filter with variable step size in order to obtain improved performance in terms of both convergence rate and steady state error with robustness against impulsive interference. the optimal variable step size is obtained by minimizing the mean square deviation (msd) error from one iteration to the other. simulation results in the context of a highly impulsive system identification scenario show that the proposed algorithm has faster convergence and lesser steady state error than the conventional mcc based adaptive filters. keywords-maximum correntropy criteria; adaptive filter; variable step size; mean square deviation. i. introduction the minimum mean square error (mse) criterion is a widely used criterion for adaptive filters due to its simplicity and easy implementation [1]. recently, information theory criterion based adaptive filters have received much attention due to their robustness against impulsive noises, in which case mse criterion performs poorly. correntropy is one such information theory criterion which is a non linear measure of similarity between two random variables [2, 3]. the correntropy is defined as: ( , ) [ ( , )] ( , ) ( , ) (1) xy v x y e x y x y df x yk k= = ò where κ is a shift–invariant mercer kernel and ( , )xyf x y denotes the joint distribution function of (x, y). if τηε kernel is gaussian, then it is defined as: 2 2 1 ( , ) ( ) (2) 22 e e x y g e expk ss p = = æ ö÷ç ÷ç ÷ç ÷è ø where e x y  and 0 s > is the kernel width. the cost function under mcc criterion is defined as 2 2 exp (3) 2 mcc e j e s = é ùæ ö÷çê ú÷ç ÷ç ÷ê úè øë û the adaptive filter using mccj as the cost function is defined [4] as: 2 2 ( ) ( 1) ( ) exp ( ) ( ) (4) 2 e n w n w n e n x nm s + = + æ ö÷ç ÷ç ÷ç ÷è ø the steady state mse of mcc algorithm is derived in [5] using energy conservation argument. from the analysis it is evident that mcc based algorithm is an excellent candidate for impulsive interference and its performance is dependent on the step size and kernel width. also from [5] it is found that a large value of step size increases the convergence at the cost of more steady state error and vise versa. this conflicting tradeoff between convergence speed and steady state error is resolved in [6] using a combinational approach. but the major disadvantage with this approach is that the complexity is higher as two adaptive filters are used in parallel. adaptive kernel width is proposed in [7] where lesser steady state error is obtained but convergence speed is not improved especially when the kernel width is larger. the variable step size approach has long been used for better performance as it gives a more appreciable solution than the fixed step size approach [8-10]. hence, in this paper a variable step size for mcc based adaptive filter is proposed so as to have better performance in terms of both faster convergence and lesser steady state error. the criterion for variation is based on the minimization of msd as it indicates how close the filter is to optimal performance. thus the step size is increased or decreased based on the square of the instantaneous error obtained. finally the performance of the proposed algorithm is verified through simulation results for the identification of highly impulsive unknown system. ii. proposed algorithm consider an unknown system with input signal vector given by ( ) [ ( ), ( 1) , . ( 1)] t x n x n x n x n n= ¼ + where ( )x n is the input signal. let ,1 ,2 ,3 , [ , , . ]t o o o o o n w w w w w= ¼ be the optimal weights of length n. the desired response ( )d n is given by 0 ( ) ( ) ( ) t d n w x n v n  where ( )v n is a noise source with variance 2 vs which is made of both background noise ( ) b v n and impulsive noise ( ) i v n . the error signal e(n) is given as: ( ) ( ) ( ) ( ) t e n d n w n x n  engineering, technology & applied science research vol. 6, no. 2, 2016, 923-926 924 www.etasr.com radhika and arumugam: variable step size maximum correntropy criteria based… where 1 2 3 ( ) [ ( ), ( ), ( ) . ( )] t n w n w n w n w n w n= ¼ is the estimate of 0 w at the nth iteration . if the weight error vector be defined as  0 ( ) ( )w n w w n  then (4) can be written in terms of weight error vector as:   2 2 ( ) (n 1) (n) exp ( ) ( ) (5) 2 e n w w e n x nm s + = æ ö÷ç ÷ç ÷ç ÷è ø let 2 2 ( ) ( ( )) 2 e n f e n exp s = æ ö÷ç ÷ç ÷ç ÷è ø .thus (5) becomes:  (n 1) (n) f ( ( )) ( ) ( ) (6)w w e n e n x n   squaring on both sides of (6) we get:    2 2 2 [ (n 1) ] e[ (n) ] 2 re[ ( ( )f ( ( )) ( ) ( ))] (7) ( ( ) ( )f ( ( ))f ( ( )) ( ) ( )) t t t t e w w e w n e n e n x n e x n e n e n e n e n x n m m + = = + we can write (7) further as:  2 2[ (n 1) ] e[ (n) ] ( ) (8)e w w m+ = -d where  2 ( ) 2 re[ ( ( )f ( ( )) ( ) ( ))] ( ( ) ( )f ( ( ))f ( ( )) ( ) ( )) t t t t e w n e n e n x n e x n e n e n e n e n x n m m m d = thus in order to reduce the msd from one iteration to the other, ( ) should be maximized. thus differentiating ( ) respect to  and equating it to zero gives optimal value of step size as ( ) ( ) re ( )f ( ( )) ( ) ( ) ( ) (9) ( ) ( ) ( ( )) ( ( )) ( ) ( ) t o t t t e w n e n e n x n n e x n e n f e n f e n e n x n m = in order to further simplify (9) we use of the following assumptions: 1. the input ( )x n is independent and identically distributed (i.i.d) with zero mean and ( ( ) ( )) t e x n x n r . 2. the noise v(n) is i.i.d with zero mean and variance 2 v s and is independent of the input ( )x n 3. the error ( )e n is independent of ( )x n 4. the error non linearity f ( ( ))e n is independent of ( )x n assumption 1 and 2 are commonly used to analyze adaptive filters. assumption 3 is used in [11] and assumption 4 is used in [12] and they are reasonable when the actual weights converge to the optimal value. using assumptions 1 to 4 we can write (9) as: 2 2 2 ( ( ( ))) ( ( ) ) ( ) (10) ( ( ( ))) ( ) ( ( ) ) a e f e n e e n n e f e n tr r e e n m = if ( ) ( ) ( ) ( ) ( ) ( ) t a e n n x n vw n e n v n    where ( ) a e n is the a priori error ,then squaring on both sides of ( )e n and it expectation is taken we get 2 2 2 ( ) ( ) a v e e n e e n s= + thus (10) is written in terms of ( )ne as: 2 2 22 ( ( ) )(f ( ( ))) ( ) (11) (f ( ( ))) ( ) ( ( ) ) v e e ne e n n e e n tr r e e n s m = ì üï ïï ïí ý ï ïï ïî þ if we assume that the weights ( )w n are independent of the input ( )x n , then: 2 2 1 ( ) 1 (12) (f ( ( ))) ( ) ( ( )) vn e e n tr r e e n s m = ì üï ïï ïí ý ï ïï ïî þ a. practical step size from (12) it is found that variable step size may prove difficult because of the presence of expectation. therefore we replace the expectation by an instantaneous approximate value. finally using time averaging as adopted in [9], the update equation becomes: ( ) ( 1) (1 ) ( ) (13)n n nm am a b= + where 2 2 1 ( ) 1 ( ( )) ( ) ( ) vn f e n tr r e n s b = ì üï ïï ïí ý ï ïï ïî þ and a is the smoothing factor that ranges between 0 1a< < .thus we can say that whenever the instantaneous error is more or during the initial stage of the algorithm , the quantity 2 2 ( ) v e n s becomes smaller as 2 22 ( ) ( ) v a e n e ns= + and 2 2 1 ( ) v e n s ì üï ïï ïí ý ï ïï ïî þ becomes larger (nearer to but less than unity). during the same time 2 2 ( ) f ( ( )) exp 2 e n e n s = æ ö÷ç ÷ç ÷÷çè ø becomes smaller 2 2 ( ) (exp 1) 2 e n s < æ ö÷ç ÷ç ÷÷çè ø so that 1/f ( ( ))e n is more. therefore the overall step size becomes larger so as to have faster convergence. on the other hand during the steady state condition or whenever the instantaneous error becomes smaller, and 2 2 2 2 lim ( ) lim ( ) a v v n n e n e n s e s ¥ ¥ = + = + where e is the value engineering, technology & applied science research vol. 6, no. 2, 2016, 923-926 925 www.etasr.com radhika and arumugam: variable step size maximum correntropy criteria based… of steady state excess mean square error. therefore 2 2 ( ) v e n s becomes larger such that 2 2 1 ( ) v e n s < . similarly, under the same condition f ( ( )e n becomes larger than the value obtained during the initial stage with ( ( )) 1.f e n < thus 2 2 1 ( ) v e n s ì üï ïï ïí ý ï ïï ïî þ becomes very small and 1 ( ( ))f e n also becomes small. as a result, the step size becomes smaller so as to have a smaller steady state error. during the intermediate value of error, the step size is increased or decreased based on the value of the instantaneous error. thus both improvement in convergence and steady state error can be obtained simultaneously. iii. simulation results in this section, we present the simulation results to prove the performance improvement of the proposed algorithm against the fixed step size mcc based algorithm. for this purpose an unknown system with 16 coefficients is taken. it is assumed that both the filter and the system have the same number of coefficients. the input is a zero mean white gaussian noise with unity variance. the noise is made of both background noise and impulsive noise. the background noise is gaussian with variance 2 bv s .the impulsive noise is generated ( ) ( ) k n a n where ( )k n is a bernoulli process with probability of success [ ( ) 1] r p k n p= = .the performance is evaluated by normalized msd (nmsd) which is given as ( )0 2220 10 ( ) /nmsd log w n w=  .the kernel width is fixed as 2s = .the performance curves are obtained by ensemble averages over 50 independent runs. it is assumed that the variance of the noise source is known [ 9]. figure 1 examines the performance of the proposed algorithm with signal to noise ratio (snr) taken as 30 db, signal to interference ratio (sir) as -10 db and 0.001, 0.01, 0.1 r p = respectively. for comparison, fixed step size mcc algorithm with 0.05, 0.01m = and 0.001m = with the same parameters were also plotted. the plot confirms that the proposed algorithm can achieve both faster convergence and smaller steady state error than the fixed step size counter parts. also it is evident from figure 1 that the variable step size approach is robust against changing values of pr. similar conclusions can be drawn from figure 2 and figure 3 which were simulated for different values of snr, sir with pr as 0.001. the convergence behavior of our proposed algorithm can be analyzed if the time evolution of [ ( )]e nm is made. fig 4 shows the plot of [ ( )]e nm vs n. as per (13) when the instantaneous error is larger, the value of m is expected to be larger in order to obtain faster convergence .on the other hand, when the instantaneous error is smaller, then m is expected to become smaller in order to have lesser steady state error. fig. 1. performance of proposed variable step size mcc and fixed step size mcc for different values of pr.the input is white with snr=30 db, sir=-10 db. fig. 2. performance of proposed variable step size mcc and fixed step size mcc for different values of snr.the input is white with sir=-10 db and pr=0.001 fig. 3. performance of proposed variable step size mcc and fixed step size mcc for different values of sir.the input is white with snr=30 db and pr=0.001 engineering, technology & applied science research vol. 6, no. 2, 2016, 923-926 926 www.etasr.com radhika and arumugam: variable step size maximum correntropy criteria based… thus, figure 4 confirms the predicted results where [ ( )]e nm is initially larger and starts to decrease and reaches its minimum during steady state which is required for improved performance. in figure 5, the performance of the proposed algorithm is tested for colored input for the same system as above with snr=30 db, sir=-10 db and pr=0.001. the input is obtained by passing white gaussian noise through a first order system with pole at 0.8.thus, it is found from figure 5 that the proposed algorithm works well even for colored input. the tracking performance of the proposed algorithm is analyzed in figure 6 where the system is made to change abruptly after 10,000 samples with pr=0.001, snr=30db, sir=-10 db. fig. 4. time evolution of e[μ(n)] fig. 5. performance of proposed variable step size mcc and fixed step size mcc for colored input with pole at 0.8 with snr=30 db, sir=-10 db and pr=0.001. iv. conclusion step size is an important parameter which affects the performance of mcc based adaptive filters. a fixed step size gives rise to the tradeoff between convergence speed and steady state error. this paper presented a variable step size approach for mcc based adaptive filters based on largest decrease in msd. here the step size is increased or decreased based on the instantaneous error square obtained. therefore improved filter performance in terms of convergence speed and steady state error is obtained. the simulations done in the context of a system identification scenario that includes impulsive noises confirms that the proposed algorithm has better performance than the fixed step size mcc based adaptive filters. fig. 6. tracking performance of proposed variable step size mcc and fixed step size mcc for white input with snr=30 db, sir=-10 db and pr=0.001 references [1] s. haykin, adaptive filtering theory, prentice-hall, new york, ny, usa, 1996. [2] j. c. principe, information theoretic learning: renyi’s entropy and kernel perspectives, springer verlag, berlin, germany, 2010 [3] w. liu, p. p. pokharel, and j. c. principe, “correntropy: properties, and applications in non-gaussian signal processing”, ieee trans. signal process., vol. 55, no. 11, pp. 5286–5298, 2007 [4] a. singh, j. c. principe, “using correntropy as a cost function in adaptive filters”, international joint conference on neural networks, atlanta, usa, pp. 2950–2955, june 14-19, 2009 [5] b. chen, l. xing, j. liang, n. zheng, j. c. príncipe, “steady-state mean-square error analysis for adaptive filtering under the maximum correntropy criterion”, ieee signal processing letters, vol. 21, no. 7, pp. 880-884, 2014 [6] l. shi, y. lin, “convex combination of adaptive filters under the maximum correntropy criterion in impulsive interference,” ieee signal processing letters, vol. 21, no. 11, pp. 1385-1388, 2014 [7] s. zhao, b. chen, j. c. principe, “an adaptive kernel width update for correntropy” , the 2012 international joint conference on neural networks, brisbane, australia, pp. 1–5, june 10-15, 2012 [8] r. h. kwong, e. w. johnston, “a variable step size lms algorithm”, ieee transactions on signal processing, vol. 40,no. 7, pp. 1633-1642, 1992 [9] h. c. shin, a. h. sayed, w. j. song, “variable step-size nlms and affine projection algorithms”, ieee signal processing letters, vol. 11, no. 2, pp. 132-135, 2004 [10] x. d. luo, z. h. jia, q. wang, “a new variable step size lms adaptive filtering algorithm”, acta electronica sinica, vol. 34, no. 6, pp. 11231126, 2006 [11] a. h. sayed, adaptive filters, john wiley & sons, 2008 [12] w. ma, h. qua, g. gui, l. xu, j. zhaoa, b. chen, “maximum correntropy criterion based sparse adaptive filtering algorithms for robust channel estimation under non-gaussian environments”, journal of the franklin institute, vol. 352, no. 7, pp. 2708-2727, 2015 microsoft word etasr_v13_n1_pp9843-9848 engineering, technology & applied science research vol. 13, no. 1, 2023, 9843-9848 9843 www.etasr.com bouabdallah et al.: the effect of rigid inclusions on the dynamic response of highway embankment the effect of rigid inclusions on the dynamic response of highway embankment faris bouabdallah department of civil engineering, laboratory lmghu, 20 august 1955 university of skikda, algeria f.bouabdallah@univ-skikda.dz (corresponding author) kamel goudjil department of civil engineering, university of mohamed-cherif messaadia, algeria k_goudjil@yahoo.com messast salah department of civil engineering, laboratory lmghu, 20 august 1955 university of skikda, algeria msalah2007msalah@gmail.com received: 8 october 2022 | revised: 28 october 2022 | accepted: 6 november abstract soft soils are widespread in many areas of the east-west highway of algeria, covering large areas. construction projects such as highway embankments, airfields, roads, and railways in such areas experience several problems due to their low strength and permeability. this study used a fully dynamic analysis to evaluate the dynamic response of a highway embankment. the numerical analysis was carried out using the flac 2d version 8.10 software. the main objective was to evaluate the effect of rigid inclusions on the dynamic response of highway embankments by monitoring settlement, shear-strain curves, and maximum soil accelerations and displacements at different depth points. the obtained results showed that the configuration of the rigid inclusions significantly influences the dynamic response of the model. for instance, the settlement at 0.9m is 16% higher than at 0.2m from rigid inclusion. keywords-inclusions; dynamic response; flac; settlement; shear strain curve i. introduction several studies have been carried out to better understand the behavior of soft soils, due to the spread of soft soils, which cover several areas in algeria, and develop disaster prevention measures, estimate their parameters, and study the effect of some materials such as rubber concrete and lime on the behavior of composite clayey soils [1-5]. structures such as highway or railway embankments, tanks, walls, or slopes face several problems with such soft foundations. these problems relate to bearing capacity failures, intolerable total and differential settlements, large lateral pressures, and slope instabilities. several studies showed that the principal cause of several landslides, which affected the east-west highway in algeria, is the presence of clayey formations [6-7]. a variety of ground improvement techniques have been used to address the concerns on soft soil foundations, such as geosynthetic [8-11], geogrid [12-14], pile [15-16], pvd [17], soil nail [18-19], chemical injection and grouting [20], stone column [21-24], and rigid inclusions [25-27]. however, the suitable solution depends on several parameters, such as the thickness of the soft soil, the nature of the project to build, the requirements of the client, etc. rigid inclusions are a ground improvement technique that has a significant advantage over deep foundations, as they can provide the needed settlement control and retain the shallow foundation support of the structure. rigid inclusions, known by different names such as controlled modulus columns (cmc), pile-supported earth platforms, jet grouting columns, or soil column reinforcement, are vertical elements across soil layers with low bearing capacity and/or high compressibility, extending down to a more resistant layer. due to their higher stiffness compared to surrounding soil, they support a portion of the loads applied at the ground's surface. therefore, the loads taken by the soft soil can be reduced to an acceptable level of soil-bearing capacity and settlement. several studies investigated the effect of rigid inclusions to improve soft soils. some studies used the stress reduction ratio (srr) to find the optimal design [28-29]. however, they did not consider several factors that can potentially influence the srr, such as the characteristics of the subgrade soils and the influence of dynamic loadings. other approaches adopted rigid inclusions techniques to improve soft soil intended to support a railroad engineering, technology & applied science research vol. 13, no. 1, 2023, 9843-9848 9844 www.etasr.com bouabdallah et al.: the effect of rigid inclusions on the dynamic response of highway embankment embankment. the rigid inclusions reduced the ground settlements by 15-20%, depending on the subgrade plasticity index [30]. several numerical studies investigated the seismic behavior of highway embankments in improved soft soils. these studies used the linear elastic-perfectly plastic constitutive model with a mohr-coulomb failure criterion to represent the behavior of the soil and ltp [31-36]. some studies used the constitutive models ubcyst and pm4silt to take into account the nonlinear behavior of soils during seismic motions [37-40]. this paper presents a fully dynamic analysis and evaluation of the seismic response of highway embankments over rigid inclusions to improve soft soil. the ubchyst model [41] was adopted to consider the dynamic characteristics of the soil during seismic movements. the effect of ground motions of the chi-chi earthquake and two types of rigid inclusion configurations, floating and placed in hard clay, were studied. ii. numerical modeling a. the geometry of the numerical model a 3-layer soil model was considered, where 10m thick soft soil was built over a 5m thick hard soil layer. the highway was constructed on an embankment with an 11.75m width and a slope angle of approximately 18°. the toe of the embankment was at an elevation of 15m. the embankment includes a load transfer platform 0.6m thick as part of the embankment materials. to simplify the problem, the soil layers were supposed to be horizontal, as shown in figure 1. the water table was not set up in the model and drained conditions were considered. a finite difference mesh with a size of 0.25cm for each element was chosen to avoid wave distortion during seismic wave transmission through the soil [42]. the constitutive model ubchyst can be used with low and highpermeability soils, such as clayey, silty, and granular. in this hysteretic model, the shear modulus is a function of the stress ratio and varies throughout the loading cycle to give hysteretic stress-strain loops of varying amplitude and area damping throughout the earthquake excitation. a detailed description of all ubchyst model parameters was given in [41]. fig. 1. geometry of the numerical model table i. rigid inclusion parameters density (kg/m³) shear modulus g (mpa) young modulus e (mpa) 25000 12.5 30 tables i and ii present the parameters of the soil and structural elements. soil characteristics were taken from [31, 39, 43]. the calibration parameters of the constitutive ubchyst model were determined based on laboratory experiments [39, 43]. since the soft soil used in [31] was modeled as the mhor-coulomb constitutive model, a cyclic shear test was conducted to determine the calibration parameters of the ubchyst model using the modulus reduction curves from [44]. table ii. soil parameters of the ubchyst model soil parameters stiff clay soft clay ltp earth fill bulk modulus k (mpa) 76 8.33 41.66 76 shear modulus g (mpa) 38 3.8 19 38 density (kg/m³), 2000 1600 2000 2000 friction angle ф (deg) 30 25 25 35 cohesion c (kpa) 15.2 5 50 0 tensile t 0 0 0 0 dilation angle dil 0 0 0 0 stress rate factor rf 1 0.8 0.98 1 stress rate exponent n 2 2 2.5 2 first cycle factor mod1 0.75 0.75 1 0.75 large strains exponent rm 0.5 0.5 0.5 0.5 large strains factor dfac 0 0 0 0 b. rigid vertical elements numerical analysis was conducted using 12 rigid inclusions per row in the soft soil, with 10m length and 0.6m diameter. the separation between elements in both directions was equal to 1.8m. the rigid inclusion characteristics were taken from [31]. c. boundary conditions and interfaces artificial boundaries were used in the static analysis to depict the semi-infinite nature of the soil. the side boundaries were fixed in the horizontal direction while the bottom part was fixed in all directions. however, these boundary conditions were replaced in the dynamic analysis by quiet boundaries along the bottom of the model to minimize the effects of reflected waves at the bottom and free-field boundaries on the sides to avoid wave reflections[45]. to apply quiet boundary conditions along the same boundary as the dynamic input, the dynamic input must be applied as a shear stress boundary, because the effect of the quiet boundary will be nullified if the input is applied as an acceleration or velocity wave. to do this, the velocity record was converted into a shear stress boundary condition using �� � ����� �� � � �� (1) where σs is the applied shear stress, ρ is the mass density of the material at the boundary, cs is the speed of s-wave propagation through the medium at the boundary, vs is the input shear particle velocity, and the factor is generally equal to 2. figures 2 and 3 show the time history acceleration and velocity of the chi-chi earthquake. regarding soil-rigid inclusion interfaces, since the soil foundations of this study were clayey soils, the interfaces were assumed to have a zerofriction angle and the same cohesive strength as the surrounding soil [46]. the shear and normal stiffness values were determined using (2), based on the flac manual [45]. engineering, technology & applied science research vol. 13, no. 1, 2023, 9843-9848 9845 www.etasr.com bouabdallah et al.: the effect of rigid inclusions on the dynamic response of highway embankment �� � �� � 10 � ���.� � ∆��� ! (2) where k and g are the bulk and shear modulus of the adjacent soil, respectively, and ∆zmin is the smallest edge of the adjacent soil element. fig. 2. input acceleration time history of the chi-chi earthquake in 1999. fig. 3. input velocity time history of the chi-chi earthquake in 1999. iii. results and discussion the soil response in terms of settlements at the bottom of the embankment and along the depth, and shear stresses and strains were evaluated for both cases of rigid inclusions (ri), placed on hard clay and floating. all these results took into account only the influence of the dynamic loading on the soft soils improved with rigid inclusions. in the first step, an initial stress state was generated. then, the vertical reinforcements were installed, and the last static calculation step considered the activation of the earth platform and the highway embankment. the required seismic boundary conditions, free field boundaries, and quiet boundaries were added for the dynamic analysis, and the dynamic analysis was executed by applying the corresponding horizontal wave using shear stress (2) at the base of the models. a. settlements at the bottom of the embankment figure 4 shows the histories of soil settlements at the base of ltp for different points relative to the ri. it is noticeable that the settlement at 0.9m from ri is greater than at 0.2m. for example, the settlement of the point at 0.9m is 16% higher than at 0.2m from ri. the settlement decreases the closer the point is to the rigid inclusion. this can be explained by the effect of shear stiffness provided via the interaction of the rigid elements with the surrounding soil, which leads to reduce the settlement of the surrounding soil. b. settlements along the depth figure 5 shows the histories of soil settlements at different depths along the centreline axis. it is clear that the maximum settlements (6.4cm) occur at the top of the ltp layer and are reduced with depth. the maximum settlement in the middle of soft clay (3.3cm) is 23.6% greater compared to those in its base (0.78cm). fig. 4. settlement at the bottom of the embankment. fig. 5. settlements along the depth. c. shear strains and stress curves figures 6-8 show the hysteresis curve that relates shear stresses and shear strains obtained after dynamic loading in the soil. fig. 6. shear stress and strain curve at the middle of hard clay. fig. 7. shear stress and strain curve at the middle of soft clay. 0 10 20 30 40 50 60 70 80 90 -3 -2 -1 0 1 2 3 dynamic time (second) in p ut a cc el er at io n ( m /s 2 ) 0 20 40 60 80 100 -0.4 -0.2 0 0.2 0.4 0.6 dynamic time (second) in pu t ve lo ci ty m /s ) 0 20 40 60 80 100 -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 dytime (second) s et tl em en t (m ) 0.9 m from r.i 0.4 m from r.i 0.2 m from r.i 0 10 20 30 40 50 60 -0.07 -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 d y n amic t i me ( s econ d ) s e tt le m e n t ( m ) at the base of model at the top of hard clay at the middle of soft clay at 2m from the top of soft clay at the top of ltp layer -5 0 5 10 x 10 -4 -3 -2 -1 0 1 2 3 4 x 10 4 r.i placed on hard clay max shear st ress = 30.2 kpa max shaer st rain= 9.75*10-4 -5 0 5 10 15 x 10 -3 -2 -1 0 1 2 3 x 10 4 shear strain s h ea r s tr es s (k p a) r.i placed on hard clay engineering, technology & applied science research vol. 13, no. 1, 2023, 9843-9848 9846 www.etasr.com bouabdallah et al.: the effect of rigid inclusions on the dynamic response of highway embankment fig. 8. shear stress and strain curve at the middle of ltp. fig. 9. floating rigid inclusions. the values obtained were recorded in the middle of the soft clay and the ltp layer. figures 3-5 show maximum shear strain at 9.75×10-4, 13×10-3, and 8.55×10-4, respectively. the distribution of the maximum shear strain is higher in the middle of the soft clay. at the ltp layer and the middle hard clay, the maximum shear strains are very close, but the shear stresses differ. these results are due to the higher value of shear stiffness of the hard clay and the ltp layer compared to the soft clay. figure 9 shows 8m long floating rigid inclusions embedded in the soft soil. shear stresses and strains at the same points were estimated to show the efficiency of rigid inclusions. figures 10 and 11 show the hysteresis curve that relates shear stresses and strains obtained after dynamic loading in the soil for floating rigid inclusions. the obtained values were recorded at the same points for rigid inclusions placed on hard clay. the maximum shear strain value in the middle of soft clay was 15.2×10-3, having an increase of 2.2×10-3. also, the maximum value of shear strain in the ltp layer reached 9.63×10-4, having an increase of 1.08×10-4. fig. 10. shear stress and strain curve at the middle of soft clay. fig. 11. shear stress and strain curve at the middle of ltp. iv. conclusion a fully dynamic numerical modeling analysis was conducted to evaluate the seismic response of a highway embankment constructed over reinforced soft soil. two configuration types were considered to study the effect of rigid inclusions, placed on hard soil and floating. the numerical modeling results of all configurations were compared in terms of settlement, shear stress, and shear strain. settlements at the base of the embankment were evaluated in three different positions relative to the position of the rigid inclusion. the settlement was important at 0.9m from the rigid inclusions while the minimum settlement was recorded at 0.2m. this can be explained by the shear stiffness provided via the interaction of the rigid elements with the surrounding soil, which reduces the settlement of the surrounding soil.the maximum value of shear strains was recorded in the middle of the soft clay compared to the ltp layer and the middle of the hard clay for all cases. the cohesion of the ltp layer and the hard clay increases the strength of the soil and reduces shear strain. in floating rigid inclusions, the 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[46] l. hazzar, m. n. hussien, and m. karray, "influence of vertical loads on lateral response of pile foundations in sands and clays," journal of rock mechanics and geotechnical engineering, vol. 9, no. 2, pp. 291–304, apr. 2017, https://doi.org/10.1016/j.jrmge.2016.09.002. microsoft word etasr_v13_n2_pp10261-10269 engineering, technology & applied science research vol. 13, no. 2, 2023, 10261-10269 10261 www.etasr.com srivastava & kumar: critical analysis of road side friction on an urban arterial road critical analysis of road side friction on an urban arterial road kartik srivastava department of architecture and planning, national institute of technology patna, india kartiks.phd20.ar@nitp.ac.in ajay kumar department of architecture and planning, national institute of technology patna, india arajay@nitp.ac.in received: 23 december 2022 | revised: 6 january 2022 | accepted: 10 january 2023 abstract this study reviews the impact of roadside friction on urban arterial roads in the published literature and aims to identify the various side frictional parameters that impact urban arterial roads. the side frictional parameters are non-motorized vehicles, pedestrian crossing or moving along the road, street vendors, onstreet parking, animal movement, and land-use activity. the impact of all these parameters on traffic performance leads to a reduction in capacity, speed (instantaneous speed, journey speed, travel speed, time mean speed, and space mean speed), level of service, delay, travel time, and travel cost. this study considered online published studies from 1995 to 2022. the available effective width and the percentage reduction in road capacity are related. road capacity is reduced by 3.37% when the effective width is reduced by 2.95%, while road capacity is reduced by 26.08% when the effective width is reduced by 21.81%. keywords-side friction; arterial road, speed; capacity; road capacity; level of service; non-motorized vehicles i. introduction efficient transportation infrastructure is essential and critical for economic development, particularly in developing countries. economic development requires more movement of people and things. rapid urbanization and population growth in urban areas in developing countries, such as india, have resulted in increased vehicular traffic. vehicle growth is putting more pressure on the transportation infrastructure, particularly in the road transport system, and adversely affects smooth traffic flow. in india, as the road transport system handles more than 85% of passenger travel and 60% of freight flow, roads are dominantly used as a mode of transport and act as a lifeline for accessibility. urban regions are experiencing more congestion, pollution, and accidents as a result of the increase in traffic. in old indian cities, most arterial and sub-arterial roads face congestion due to the increase in vehicular population, heterogeneous traffic, and many side frictions. side friction is defined as any activity or action that occurs on the side of a road or on the road itself and interferes with the efficient flow of traffic. side friction refers to activities that cause traffic congestion on the roadway or along its sides. in [1], the effects of side friction on an urban arterial road were explained and defined as any acts related to activities occurring on the roadside or sometimes within the road that obstruct traffic movement. various side frictions include trading activities/street vendors/street trading, slow-moving cars, pedestrians crossing or walking along the road, non-motorized vehicles, turning movement, on-street parking/stopping, bus stops/bus bays, land use, animal movement, roadside accessibility, etc. side friction alters the speed and flow characteristics and reduces the capacity of roads [2], as it significantly impacts traffic movement in various ways, such as reduction in road capacity and carriageway width, impact on travel speed, instantaneous speed/spot speed, time mean speed (tms), space mean speed (sms), affecting road performance. side friction results in increased traveler discomfort, reduced speed behind stopped vehicles and abrupt volume rises on the roadway, traffic jams and time delays, loss of level of service (los), and impacts travel time and cost. the main objective of this study was to examine the side frictional parameters in urban roads as stated by different studies, this study also evaluates the various viewpoints on side friction, how they affect traffic on urban arterial roads, and shows that various side friction activities have different degrees of impact on traffic behavior characteristics. ii. research limitations this study reviewed 90 studies from 1995 to 2022. however, most studies mainly focused on four side frictional parameters: non-motorized transport/slow-moving vehicle, pedestrian crossing (on or along the road), on-street parking, and street vendors/street traders. less than 10% of the studies engineering, technology & applied science research vol. 13, no. 2, 2023, 10261-10269 10262 www.etasr.com srivastava & kumar: critical analysis of road side friction on an urban arterial road focused on other side frictional parameters, such as animal movement and land-use activity. most studies mainly dealt with how 6 sid-frictional parameters, namely, non-motorized vehicle/transport and slow-moving vehicles, pedestrian crossing or moving along the road, on-street parking, street vendors/ traders, animal movement, and land use activity impact capacity, its estimation, and the level of congestion, the level of service, delay, and congestion factors. none of the studies dealt with the impact on travel time, the impact of travel speed on cost, journey speed, travel time, flow/capacity ratio, pedestrian activity, bicycle flow, tms, and sms. as a result, studies that aim to critically examine the side friction impact on indian urban roads must incorporate multidimensional metrics. due to inherent variations that may result in inaccurate conclusions, it is critical to separate the empirical research for developed and developing countries. iii. methodology this study systematically assessed the impact of side frictional in indian urban roads through published studies in elsevier science direct, ijirset, ijsrset, ijseat, ijrte, doctoral thesis, and jstor databases from 1995 to 2022. data analysis was performed based on the aim and objectives, and the results are discussed in the result and discussion sections. iv. literature review the literature survey revealed that relatively little research has been conducted to date on the measurement of side friction and its detrimental effects on travel time, capacity, los, and other factors. table i shows some indian and international works that dealt with speed, capacity, los, travel time, etc. although it is generally acknowledged that roadside activities impact the typical traffic stream's speed, capacity, and los and increase travel time, there are only a few studies recorded that make an effort to quantify these effects. table i. identification of side friction parameters parameter study pedestrian movement [1-28] on-street parking [6, 9, 10, 12, 13, 23, 26, 28-47] nmt/nmv/smv [1, 2, 6, 10, 13, 14, 22, 36, 38, 40, 46, 48-51] v. pedestrian movements as a side frictional parameter pedestrian movements include crossing the street or walking along it. however, both negatively affect the traffic flow, as shown in table ii, and must be avoided. when pedestrians are forced to use the road alongside fast-moving cars because of no sidewalks, as is often the case on urban streets, the average speed of traffic on certain roads is slowed by 7.23km/hr [3]. vi. influence of pedestrian movements on vehicular speed in [4], a pedestrian crossing traffic model was proposed for a city street. the volumes of traffic, speeds, and numbers of people crossing in and out of traffic are the inputs to the model (1) for calculating the average speed of a certain vehicle type: �� = �� − [∑(a 'i ni vi )] − (a'k nped/vj) (1) where vi is the speed of a particular vehicle (m/s), vj is the speed of various types of vehicle, ao is the regression coefficient for the free flow speed of the jth type vehicle, a 'i and a'k are regression coefficients for the impact of density of a particular vehicle type and pedestrians on the free flow speed of the j-th type vehicle, respectively, ni is the number of vehicles (v/s), and nped/vj is the pedestrian-vehicle interaction factor (m/s). table ii. impact of pedestrian movement on speed study pedestrian crossing vol. speed reduction [1] 100 peds/h 2.5% [3] 100 peds/h 7.23 km/h [4] 100 peds/h 4.21%. [5] 100 peds/h 3.52%. [6] 100 peds/h 0.76 km/h [7] 100 peds/h 5.2% [8] 100 peds/h 5.9% [12] 100 peds/h 3.9% [15] 100 peds/h 2.9% [17] 100 peds/h 4.44% [18] 100 peds/h 4.8% [19] 100 peds/h 5.20% [20] 100 peds/h 3.33% [21] 100 peds/h 4.65% if traffic flow stays the same, this study shows that all vehicle classes, except large trucks, slow down due to an increase in pedestrian cross-volume. however, the model's iteration technique is a disadvantage because it takes a long time to predict the speed. many studies that estimated traffic speeds on urban roads treated the variable "pedestrian motion" as binary, either missing or present. only a small number of studies went further and created speed models to measure the speed reduction caused by increasing the intensity of pedestrian activity. this study used a mathematical model to estimate that when the degree of pedestrian crossing along the road is approximately 1360 peds/h, a six-lane divided urban road's capacity decreases by nearly half of what it should be according to irc recommendations [5]. furthermore, this study concluded that if the volume of pedestrian crossing volume is around 100 peds/h, it will reduce capacity by 3.52%. the rules of the irc recognize the connection between a variety of frictional roadside activities on the road and capacity. it is clear from this study that no precise methodology or guidelines have been provided to analyze or quantify each side friction effect on urban streets. in [6], a weighting factor for pedestrian mobility was suggested in addition to other side frictional elements when designing urban roadways, as shown in table iii. a. weightage factors for elements of side friction in [6], five unique categories were used to categorize the side friction index range, a weighted sum of the side friction components, as: very low, low, medium, high, and very high. free flow speed was found to be lowered by 18km/h for twolane undivided urban roads and by 16km/h for two-lane engineering, technology & applied science research vol. 13, no. 2, 2023, 10261-10269 10263 www.etasr.com srivastava & kumar: critical analysis of road side friction on an urban arterial road undivided interurban highways with significant side friction and short shoulders. on four-lane roads, it was discovered that the effect of side friction on the free flow speed was only somewhat alleviated. other studies examined the impact of pedestrian crossings on the performance of an urban road segment. table iii. side frictional parameters weights event type weight factor (wf) rate of flow of pedestrian (w + c) (p/h/200m) 0.5 parked vehicle and parking maneuvers (events/h/200m) 1.0 entry & and exit of vehicle from road-side (veh/h/200m) 0.7 smv (veh/h) 0.4 in [7], it was shown that if crossing maneuvers are carried out in an undesignated place, this has a greater impact on stream velocity. in [52], a video evaluation was carried out on two places on a split four-lane city street, where a median opening on one location allowed people to cross. this site's average speed was 7.7km/h slower than the other location, and it was also observed that friction on the sides of the road, such as parked automobiles and people waiting for buses or cars, can narrow the route and slow down the oncoming traffic. compared to automobiles, pedestrians have less impact on the speed of two-wheelers due to their better maneuverability. this study found that pedestrian crossings caused a 2km/h drop in operational speed. authors in [8] viewed "pedestrian cross movement" as a yes/no question, without investigating the slowed speed or the increased number of pedestrians crossing the road and without developing an adjustment factor or an empirical model. in [9], the usual speed on urban roads was calculated using the following mathematical model: ���� = 48.7 − 0.011 × #$%& − 0.015 × ()* (2) � = 48.7 − 0.011+, − 0.015+ where vsim is the average travel speed (km/h) from simulation runs, flow is the traffic flow per hour in both directions of travel, and ped is the number of crossing pedestrians per hour and km. in [1], a speed model was used, finding that, among all side friction factors, the pedestrian cross movement has the greatest impact on speed. in [10], the "volume of pedestrian crossing" was considered a design variable in the speed model shown in (3), and another important aspect that affects how fast incoming vehicles approach is parking and stopping on the road: � = 39.46 − 0.13+− 0.13+1 − 0.28+3 −0.013+4 − 0.15+5 (3) where v is the average speed (km/h), x2 is the volume of pedestrian cross movement (ped/h/200m), x3 is the number of stopping buses (veh/h/200m), x4 is the number of parking/stopping (veh/h/200m), x5 is the number of entry vehicles into the street (veh/h/200m), and x6 is the number of heavy vehicles (veh/h). in [11], a study was conducted to identify how pedestrian flow on/along highways impacts traffic flow speed, and to analyze aspects that affect the speed of four-lane urban roads in developing countries. this study used videography to conduct preliminary surveys in mumbai, bangalore, and thiruvananthapuram, developed a speed model from the resulting footage, and determined the categorized volume and friction factors. the study was carried out in two different phases. in the first phase, side friction was considered individually, while the second examined the combined effect of all frictions. multiple linear regression models were used to predict speed individually and in heterogeneous situations, and the analysis was completed using a speed prediction model to evaluate variations in the friction parameters. in addition, the speed prediction model was employed to examine the pedestrian side frictional influence in variations, showing that pedestrian movement is a critical element. this study generated the speed prediction model in which traffic flow speed that is exacerbated by additional pedestrian obstructions can be predicted by: � = 51.14 − 0.356789 − 0.616: −0.196-; − 0.1661; (3) where v is the average speed (km/hr), nped is the number of pedestrians per minute, nc, n2w, n3w are the number of cars, two-wheelers, and three-wheelers, respectively. b. speed prediction model for stretches with pedestrian movement in [12], a speed forecasting model was developed showing a 0.35km/h reduction in speed for each additional pedestrian on the road per minute. studies [2, 12, 52] investigated and analyzed how side friction variables affect travel time and capacity in urban environments, based on data obtained from numerous metropolitan regions, by performing macroscopic and microscopic analyses. these studies examined how every variable on side friction, such as pedestrians, bicycles, and stopped and parked vehicles, affected traffic flow, taking into account the distinct effects of each component. in [52], the relationship between various side friction parameters and the quality performance of traffic flow was investigated on different urban arterial roads, and the impact of varying side friction parameters on the speed-flow relationship was examined. this study delineated the study area roads based on the existence of extensive traffic flow situations using metrics such as the intensity of traffic flow, measured in volume/capacity ratio, traffic distribution based on direction, heterogeneous traffic scenarios, the proportion of heavy vehicles, and the extent of side friction. this study used anova and regression models to determine the relationship between speed-flow and various side frictional characteristics and showed that side friction could affect speed and capacity. in [13], walking and crossing pedestrians were mixed with static roadside friction variables, such as vegetable markets, lay-bys, gas stations, mechanic shops, vulcanizing activities, and mini-marts, finding that t-junctions and bus stops are static features that contribute to traffic congestion. static factors can be addressed by upgrading the geometric aspects of roads and this could increase the level of service (los). in [13-14, 29], engineering, technology & applied science research vol. 13, no. 2, 2023, 10261-10269 10264 www.etasr.com srivastava & kumar: critical analysis of road side friction on an urban arterial road road friction elements such as pedestrians, vehicles stopping on shoulders and highways, parking, and access to roadside premises were found on urban roads in asian countries, and side friction classes were developed for urban and interurban roads based on the weights assigned to each side friction element. c. influence of pedestrians movement on capacity the studies [15-16] are among the few that attempted to determine the effect of pedestrian cross-traffic movement on the capacity of metropolitan roads, as shown in table iv. a 30–37% decrease in capacity was observed as a result of pedestrian cross movements in [15], while a 32% decrease was discovered in [16]. in [17-18], empirical models that link the volume and capacity of pedestrian cross-traffic movement were presented, such as: < = 1550) =(>.?@a?bc.dc)ad efgg (5) where c is the capacity (veh/h), x2 is the volume of pedestrian cross movement (ped/h), and x7 is the percentage of drivers willing to give way to pedestrians. table iv. impact of pedestrian movement on capacity reference ped-crossing volume capacity reduction [4] upto 200 ped/h no impact [20] 200 ped/h negligible [4] 1550 ped/h 32% [1] 1550 ped/h 9% [6] 1550 ped/h 20% [7] 1550 ped/h 23% [8] 1550 ped/h 25% [12] 1550 ped/h 19% [15] 1550 ped/h 27% [17] 1550 ped/h 30–37% [18] 1550 ped/h 32% [19] 1550 ped/h 32% [20] 1550 ped/h 33% [21] 1550 ped/h 14% [24] 1550 ped/h 11.05-60.73% in [18], recommended techniques were employed to calculate the side friction factors. the area affected by pedestrian movement can be utilized as a quality variable to calculate equivalent pedestrian units (epu) for all activities other than walking and serves as a side friction parameter. a speed prediction model was developed to determine the relationship between traffic flow and the individuality of side friction characteristics. the chi-square test was used to validate the model at the test site and the 14% rmse test result showed that the predicted speeds were statistically significant. in [19], two urban and interurban arterial roads were surveyed. various side friction parameters were investigated for urban roads, including pedestrian movement through highways (ped/h), pedestrians crossing highways (ped/h/km), vehicle stops concerning whether the vehicle was stopped on the shoulder or the highway, vehicle parking or unparking (veh/h/km), and vehicles entering or leaving the road. additionally, several riding frictional factors were examined on interurban roads, such as the number of people walking through and crossing the road (ped/h/km). furthermore, the study considered the number of vehicles stopping and parking maneuvers (veh/h/km), the number of vehicles entering or leaving the road premises, and the course of slow moving vehicles (smvs) (veh/h). after a detailed investigation, employing various parameters and providing their influence, the study showed that the free flow speed was reduced by a factor of 0.76 on interurban roads, and the capacity was reduced by 20%. similarly, the rate on urban roads was reduced by 0.59. the study also improved the hdmq model for the prediction of speed and capacity with different side frictional characteristics. this study discussed several forms of roadside frictional parameters and their impact on urban road capacity, emphasizing the relationship between side frictional parameters, road capacity, and los. studies [20, 21] showed that the decrease in the capacity of urban streets is influenced by the activity along the roadside and varies with the degree of side friction. roadside activity, such as pedestrian movement, which is especially common in developing countries such as india, contributes to the loss of capacity on urban highways. in [13], static roadside friction factors were combined with pedestrians who were walking and crossing the street. d. influence of on-street parking on vehicular speed on-street parking has primarily two effects on the capacity of a road. it initially narrows the highway by surrounding the traffic flow and vehicles squeeze into a smaller area slowing the streams, while frequent parking and unparking maneuvers complicate the problem, adding more congestion on the already congested metropolitan highways. these two effects of onstreet parking ultimately reduce the capacity of metropolitan roads. the following subsections are devoted to presenting a range of findings on how and to what extent on-street parking affects the capacity of a road. e. reduction in the average speed due to the presence of onstreet parking on urban roads the projected speed reduction due to on-street parking was reported to vary greatly, ranging from 15 to 44% or 5.1 to 21km/h. this variation can be explained only by the existence of other elements that also significantly affect speed. several studies investigated these variables and documented the way they alter the impact of on-street parking, as shown in table v. in [28], it was found that larger roads were less likely to have side friction, in contrast to [6]. several limitations apply to [6], as the roadside environment varied depending on the type of route, traffic data were collected over a brief period and there are some concerns about the sample size, the behavior of onstreet parking was not explained, on-street parking was only taken into account as a categorical variable either as "presence" or "absence", there was no mathematical model to estimate this influence, and it was not evaluated with varied parking intensity. in [22], roadside parking occupancy was divided into three categories: (a) less than 30%, (b) 30-50%, and (c) 50100% to address the problem, but there was no statistical difference between levels b and c on free flow speed (ffs). additionally, it was discovered that level a parking had little effect on ffs. overall, the mean ffs of the streets without onstreet parking was found to be 3.7kmph higher than the mean ffs of the streets with on-street parking up to 30% parking occupancy. as in previous investigations, the parking engineering, technology & applied science research vol. 13, no. 2, 2023, 10261-10269 10265 www.etasr.com srivastava & kumar: critical analysis of road side friction on an urban arterial road parameter was once again considered a categorical variable. some recent studies investigated the variations in speed decrease throughout a wide range of parking intensity. in [23], the average speed was calculated at various volumes to capacity (v/c) levels, observing an almost steady decrease in speed with increasing parking density. this study noticed a pattern of definite speed increase at 75% parking density, but it was disregarded. in [30], the average speed and parking density were also related, finding a 13km/h decrease in average speed for every 100 vehicles per km increase in parking density. table v. impact of on-street parking on speed reference speed reduction [6] 5.1km/h [6] 32% [10] 5.5km/h [19] 36% [43] 15% [48] 22% [49] 19% [50] 27% [51] 44% in [31], a quadratic model was developed to describe the association between parking intensity and average ffs, but the study was unable to determine why ffs increased with parking intensity. in [1], the average speed v (km/h) was determined for twoand four-lane undivided urban roads as a function of flow (veh/h), carriageway width cw (m), shoulder width sw (m), and side friction fric separately. this study showed that there is a strong correlation between on-street parking and traffic congestion. urban roads account for nearly 14% of all congestion incidents, with parked or parking-related maneuvering cars being the main causes [27]. v = 79.6 − 0.008 × flow − 0.028 × fric −6.058 × cw + 11.8 × sw (6) v = 46.465 − 0.015 × flow − 0.011 × fric +1.36 × cw + 5.393 × sw (7) where v is the average speed (km/h), flow is in lvu0/h, cw is carriageway width (m), sw is the shoulder width (m), and fric is side friction. in [32, 41], simulation-based techniques were used to evaluate ffs on urban streets and show how, even at low densities, on-street parking can anticipate the change of traffic states from free to congested flow. a monte carlo simulation was run with a low traffic density to simulate a free-flow situation, finding that traffic volume significantly lowers when the proportion of parking maneuvers increases, as a 35% proportion of parking maneuvers can eventually cause a 35% reduction in capacity. parked cars could be the sole source of congestion on urban roads if they are parked irregularly or carelessly. even a very small number of vehicles might result in significant congestion if they are parked disruptively for an extended time. additionally, even when every available spot is almost full, a sizable percentage of vehicles still prefer onstreet parking, and instead of paying for off-street parking, they would rather continue looking until a spot opened up [4]. when these park-hunting vehicles are present in large numbers, they can significantly reduce both the capacity of urban roadways and stream transportation. numerous studies investigated the capacity loss caused by on-street parking, and a significant capacity reduction of up to 90% was documented as a result of on-street parking. on-street parking is typically viewed as "missing" or "present", which is a common limitation of studies, while the effect of parking with varied capacity intensities has not been studied. f. decrease in capacity brought on by on-street parking on urban roadways in [20-21], several forms of roadside frictional parameters were discussed along with their impact on urban road capacity, highlighting the relationship between side friction parameters, road capacity, and los. these studies showed that capacity reduction in urban streets depends on roadside activity and varies with side friction. loss of capacity on urban highways is caused by a variety of factors, including roadside activity such as on-street parking, pedestrian movement, the presence of street vendors, a lack of lateral clearance and lane discipline, and diverse traffic, which is particularly prevalent in developing countries like india. in [53], a microscopic simulation model was developed to investigate the impact of bus stops on mixed traffic movement, focusing on reducing traffic flow rates. the model was validated by collecting traffic data at roadside bus stops and bus bays. this study evaluated the impact of bus stops, which act as side friction on urban traffic. based on the collected data, several areas for further work were recommended, as very few studies examine mixed traffic situations [20, 53]. in [10], various side friction elements were considered, such as on-street parking, city buses stopping on the roadway, exit/entry vehicles, and vehicles about to turn. the study proposed a novel formula to update the indonesian highway capacity manual to estimate the speed and capacity of urban highways with significant side friction. in [21], three different side friction factors were used to conduct a survey and examine their impact on traffic quality performance: on-street parking, bus bay stops, and curbside bus stops. the results of this study showed an average speed drop due to side friction, a reduction in stream speed of 49-57% due to bus stops and bays, and a loss of 45-67% in speed due to onstreet parking. due to the high percentage of heavy vehicles, this study used dynamic and static pcu values. as a result of using these two different types of pcu values, a 10-53% capacity reduction was observed in bus bays and bus stops and about 28-63% due to on-street parking. authors in [1, 19, 24, 32, 52] investigated urban arterial roads, finding that parked and stopped vehicles act as frictional elements that majorly impact traffic flow, los, speed, and delay. on-street parking has been highlighted as a substantial source of side friction in urban arterial roads, and there is a relationship between the presence of on-street parking and the reduction in stream speed. according to the extensive analysis in [24-25], the impact of on-street parking as a side friction element on urban arterial roads results in a slowdown in traffic flow ranging from 15 to 44% or 5.1 to 21km/h. in [54], parking density was considered a side friction element, and after conducting a survey and analyzing the data, the results showed that parking density on engineering, technology & applied science research vol. 13, no. 2, 2023, 10261-10269 10266 www.etasr.com srivastava & kumar: critical analysis of road side friction on an urban arterial road urban arterial roads harms average traffic flow, with a decrease of around 13km/h for every 100 vehicles/km increase in parking density. in [12, 55], various types of roadside frictional activities on urban road links were examined, along with how these side frictional activities impact the speed and capacity of the urban roadway. kerbside bus stops, bus bays, and on-street parking were some of the considered side frictional elements, and their impact on travel speed and reduction in capacity on urban arterial roads was investigated. the study concluded that the duration of the dwelling time of buses has an inverse impact on capacity, and more extended bus stops on the road act as interruptions for more extended time movement of traffic, affecting travel speed. in [34, 53] various types of side frictional activities were examined, using microscopic simulation models to evaluate how bus stops impact mixed traffic movement and its relation to the reduction in travel speed. in [24, 34], parked and stopped automobiles were studied, along wiuth various other factors. these studies showed that parked and stopped vehicles are critical side frictional elements, as they harm more the regular traffic flow, speed, capacity, and los than other side frictional factors, such as pedestrian movements, etc. in [13-14, 29], t-junctions and bus stops were characterized as static features that contribute to traffic congestion. on the other hand, static factors can be addressed by upgrading the geometric aspects of roadways to increase los. roadside friction elements, such as pedestrians, vehicles stopping on shoulders and roads, parking, and access to roadside premises, were found along urban roads in asian countries. based on the weights assigned to each side friction element, side friction classes were developed for urban and interurban roads. in [35], motorcycle taxis were found to add another degree of friction when parking or loading and unloading passengers. in [13, 25, 35-37, 56], on-street parking produced a decrease in stream speed, ranging from 15 to 44% or 5.1 to 21km/h. g. non-motorized vehicles as a side frictional parameter all means of transportation that are not propelled by an engine or motor are referred to as non-motorized transportation (nmt) or non motorized vehicles (nmvs). while motorized vehicles are propelled by an engine, nmvs, including bicycles, e-rickshaws, cycle-rickshaws, hand-pulled vehicles, and animal carts, are propelled by humans or are dragged by animals. h. influence of non-motorized vehicles on vehicular speed and capacity in [26], a 6-lane multi-directional road was investigated in patna city and pune city. data were collected using videography to assess the speed variance in vehicle composition and traffic flow rate. this study presented a v-q relationship for both sites, and variables of flow parameters at the mix flow level were acquired and correlated with the irc standards. for each category, data on traffic characteristics, flow rate, peak hour factor, and spot speeds were reviewed. the results showed that the effective lane width in patna city changed from 7.0 to 10.5m, resulting in a 57% capacity reduction and a 14% capacity decline due to the occurrence of nmvs, as shown in table vi. table vi. impact on mnv on speed & capacity authors nmv (%) capacity reduction (%) speed reduction in % [2]. 15-20% 55% 33% [22] 14 % 57% [48] 10% 20% in [2], the influence of side friction on urban arterials was investigated. the authors examined numerous studies that characterized the effect of side friction in the decrease in urban arterial capacity, using nmv, passenger car unit, traffic, and shoulder activities as side friction parameters. the study concluded that the presence of side friction degrades the overall performance of traffic parameters, as an influence of nmt, up to 15-20% and reduced capacity and speed by 55% and 33%, respectively. speed was identified as a critical issue affecting road capacity and los. this study showed that mixed traffic, composed of smvs and nmvs, reduced the width of the effective road due to on-street parking, which acts as a barrier and reduces the road's qualitative performance. in [39], nmvs were also characterized as a source of side friction, and a speed model was proposed for this purpose, based on their ratio. according to the proposed model, a 10% rise in the nmv ratio would result in a 0.8mph (1.2kkm/h) reduction in average traffic flow speed. furthermore, this study suggested including nmvs in the traffic volume classification because cycle rickshaws generate greater side friction than bicycles. in [12], it was shown that when public transportation is poorly located or operates inefficiently, it forces the population to use their private vehicles, which causes an increase in heterogeneous traffic flow, slows down the speed of traffic flow, and increases travel time. the study showed that lateral clearance acts as a side friction activity on roads and affects the number of lanes in use and the average speed of vehicles. when traffic volumes are high, drivers tend to shift to the left lane more frequently, which means that the right lane is more likely to be affected by an obstruction. road capacity and los may be affected by the narrowing of the roadway as the number of obstacles along the route increases [32]. congestion and delays in traffic flow are often the result of poorly placed speed breakers, also known as "road friction" [52]. vii. discussion this study examined the impact of various side frictional characteristics on the traffic performance of urban arterial roads, conducting a literature survey. the available literature was investigated under several constraints, such as various roadside activities which act as side frictional parameters and their impact on the traffic performance of urban roads. the side frictional parameters used in the literature are street vendors/traders, pedestrian crossings or moving along the road, nmts including bicycles, on-street parking/stopping vehicles, land use, animal movement, and roadside accessibility. this study also focused on how various side friction parameters impact traffic performance, such as speed, capacity, and los. the considered studies were classified under different approaches, such as distribution by various side frictional parameters, impact on traffic performance, research methodology, and tools and techniques used for the analysis. these classifications identified various side friction parameters engineering, technology & applied science research vol. 13, no. 2, 2023, 10261-10269 10267 www.etasr.com srivastava & kumar: critical analysis of road side friction on an urban arterial road and examined their impacts. the side friction activities identified were nmv/nmt/smv, pedestrian crossing, street vendors/traders, and on-street parking. in [38, 48-51], nmt/nmv/smv dominantly affected traffic performance among all side friction parameters, reducing speed (instantaneous, spot, travel, journey, running, time and space means), capacity, and los. these studies used speed prediction models, multiple linear regression models, chi-square test, pv2 analyses, and greenshields speed-flow model to evaluate these impacts, and the degree of correlation between nmv/nmt/smv and traffic performance was identified. the nmvs were classified into various subcategories, using the proportions of nmvs, bicycles, cycle rickshaws, handcarts, and the percentage of nmvs traveling beyond 20% of the roadway width from the edge. the results showed that the correlation between n-3 and n-4 is the highest among all subcategories, while cycle rickshaws and handcarts impact traffic performance more than all nmv/nmt/smv subcategories. all side friction elements have a direct impact on the traffic performance of urban arterial roads. the nmv parameters n-1 to n-3 and n-5 had a strong positive association. increases in an individual or the aggregate nmv volume may increase their propensity to move away from the street's edge, resulting in a strong positive association between n-5 and n-1 to n-3. the nmv proportion of n-1 was chosen as the design variable because it had the strongest relationship with the output variable rc compared to the other nmv factors. as a result, n-1 nmvs significantly impact the arterial road capacity. furthermore, there is a positive relationship between nmvs and on-street parking o-1 [51]. in [10, 16, 17, 19], pedestrian crossing was the second most impacting parameter on traffic performance of urban arterial roads. in [10, 27, 41], it was shown that side friction activities impact los. based on the average delay per stop for any pedestrian crossing at the standard cfi geometries analyzed, the results showed an acceptable pedestrian los. several criteria were related to pedestrian mobility within the roadway, which impacts urban road capacity. the effects of pedestrian crossings on capacity and the correlation value of pedestrian crossing on traffic performance were discovered. in increased pedestrian volumes, people tend to deviate away from the edge of the street, resulting in a strongly positive relationship. in [32], pedestrian volume was divided into pedestrian volume along the roadway and pedestrian cross volume. on-street parking, legal or illegal, is the third most affecting parameter. this activity affects traffic congestion, which directly impacts los, reduces roadway width, and impacts traffic flow speed. the capacity of urban arterial roads decreases as parking maneuvers increase [13, 41-42]. in [11], a correlation was obtained between the available effective width and the capacity reduction percentage. the capacity decline was 3.37% at 2.95% reduction in effective width, and 26.08% at a 21.81% decrease in effective width. in [28, 43-45], onstreet parking was correlated with traffic performance. onstreet parking can be characterized by the following metrics: parking density o-1, effective parking width o-2, parking area o-3, number of parking maneuvers o-4, and number of unparking plots o-5. as all on-street parking metrics were found to have a substantial positive correlation (higher than 0.5), they aren't sufficiently independent to be used as integrated design variables. a choice of any parameter o-1 to o-5 can help in making a decision based on the correlation with rc, but o-2 is the best choice since it has the highest correlation with rc. the presence of street vendors and hawkers reduces road capacity, with delays that can exceed 30 minutes [46, 57]. viii. conclusion this study critically reviewed the literature on three different side frictional parameters: nmv/nmt/smv, pedestrian crossing, and on-street parking. the capacity of urban arterial highways decreases as the number of parking maneuvers increases. the effective width is connected with the capacity of a road. an increase in pedestrian volume walking along the road reduces road capacity. similarly, the capacity of a road is reduced as the proportion of nmvs increases. road capacity is reduced by 3.37% when the effective width of the road is reduced by 2.95%, while it is reduced by 26.08% when the effective width is reduced by 21.81%. engineers can use the proposed models to estimate the section's capacity for any level of parking maneuvers in the traffic stream. stretches with different side frictions and stretches with the combined effect of all components were tested for speed reduction. side friction had a substantial impact on vehicle speed on urban roads and might also influence the extent to which individual elements influence speed. all traffic-related studies must include side friction factors for effective urban road planning. the capacity of the base and friction sections is determined using speedvolume data acquired from field data. mathematically, there has been demonstrated that there is a link between pedestrian crossflow and capacity reduction. when the cross-flow of people is limited to 200pph, there is no influence on capacity, but when 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[57] c. kumar and r. khatawkar, "impact of road side bus stops on capacity of roadway," international journal of advanced technology in engineering and science, vol. 3, no. 7, pp. 147–157, jul. 2015. microsoft word etasr_v13_n3_pp11011-11019 engineering, technology & applied science research vol. 13, no. 3, 2023, 11011-11019 11011 www.etasr.com unni & thale: energy consumption analysis for the prediction of battery residual energy in electric … energy consumption analysis for the prediction of battery residual energy in electric vehicles keerthi unni department of electronics and telecommunication engineering, agnel charities’ fr. c. rodrigues institute of technology, india unnikeerthy@gmail.com sushil thale department of electrical engineering, agnel charities’ fr. c. rodrigues institute of technology, india sushil.thale@fcrit.ac.in (corresponding author) received: 19 march 2023 | revised: 20 april 2023 | accepted: 22 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5868 abstract the emergence of electric vehicles (evs) is a turning point in decarbonizing the road transport sector. in spite of the various apprehensions of the customers, such as range anxiety, long charging times, higher costs, and the lack of charging infrastructures, evs have managed to considerably penetrate into the market. appreciable subsidies in ev purchase and possibilities of renewable energy-based local charging equipment have encouraged more and more people to own evs. electrifying road transport also calls for scaling up of all stages of the supply chain as it involves a lot of raw materials and critical metals used for battery technology. one of the most important factors determining the range of an ev is the energy density of the battery, which has reached over 300 wh/kg, from 100-150 wh/kg a decade ago. this clearly means that the same vehicle can travel double the distance with the same mass. understanding and modeling the energy consumption in an ev is quintessential in alleviating the fear of range anxiety. this paper presents a detailed mathematical equation-based energy consumption analysis of a particular ev model for indian roads. very few researchers have worked on drive cycles suitable for india. the novelty of the current work is that the energy consumption calculation can be worked out for any ev model or vehicle type through simple mathematical equations. keywords-electric vehicle; electric vehicle charging stations (evcss); residual energy; aerodynamic drag; kinematics; tractive forces; rolling force;power electronics i. introduction electric vehicles (evs) are in the centre of attraction for researchers for quite some time. reduced dependency from fossil fuels and lower emissions and sustainability are the key advantages of evs. yet, there are still few barriers to be crossed for evs to heavily penetrate the market. these include range anxiety and the lack of charging infrastructure. undoubtedly, evs are going to be the future of transportation and mobility sector. research on new materials and battery chemistries along with other innovations form the thrust for evs to become the gamechanger in automotive sector. there are four main types of evs, namely the battery electric vehicles (bevs), hybrid electric vehicles (hevs), plugin battery electric vehicles (phevs), and fuel cell electric vehicle (fcevs). bevs, also known as all-electric vehicles (aevs) are driven using battery-powered electric drivetrain. the large battery pack which powers the vehicle can be charged by plugging into the electricity grid. the charged battery pack in turn powers one or more electric motors to run the electric car. figure 1 shows the various components and systems in a bev. the main components of a bev include the electric motor, inverter, battery pack, a control module that includes the power electronic circuitry, and the transmission gear. the power for the electric motor is derived by converting the dc voltage of the battery to ac by an inverter. for acceleration, the controller adjusts the vehicle speed by changing the frequency of the ac power from the inverter to the motor. the motor then makes the wheels move with the help of the transmission system. on deceleration, the motor works as an alternator and produces regenerative power, which charges the battery. accurate range prediction can help alleviating the range anxiety problem in evs. the range of an ev depends on the residual energy in the battery and the rate of energy consumption of the vehicle. there are various components of engineering, technology & applied science research vol. 13, no. 3, 2023, 11011-11019 11012 www.etasr.com unni & thale: energy consumption analysis for the prediction of battery residual energy in electric … energy consumption that are related to travel (velocity, topography, inclination, etc.), weather (ambient temperature, windspeed, visibility, etc.), vehicle (auxiliary usage), traffic (congested roads), and battery (state of charge-soc, capacity, etc.). the battery health and degradation form an important factor determining the energy efficiency of an ev [1-9]. fig. 1. parts of an ev. ii. energy estimation energy estimation in evs is done with two basic approaches, namely the forward approach (dynamic approach) and the backward approach (quasi-static approach) [6]. the forward approach is performed using equations of the powertrain components and the dynamic interaction between them. the backward approach assumes a reference drive cycle as input and calculates the forces acting at the wheels and proceeds the analysis backward through the powertrain. later, the model computes the motor torque and the battery energy required to power the electric motor [6]. various energy estimation models have been implemented, including longitudinal, statistical and computer-based ones. longitudinal vehicle dynamics-based model borrows its concepts from vehicle dynamics theory and calculates the required power at the wheels to overcome the tractive forces. some researchers have modelled regenerative braking as a linear function of vehicle speed to estimate the energy recovered while braking or driving downhill [7]. the instantaneous ev speed and acceleration is used to provide an accurate second-by second energy consumption estimation [7]. the impact of auxiliary devices is also considered for an improved estimation. the relationship between ev power, speed, acceleration, and road grade is explored in [8] to determine the required power at the wheels. the model can be either used for instantaneous energy consumption estimation or energy consumption prediction over a trip [8]. statistical models use real world driving data and derive empirical relationships between various factors and thus energy consumption [6]. real-world data of ev energy consumption can be useful in building energy consumption calculation models. considering vehicle dynamics equation as the foundation, multiple linear regression is used to construct three models. each model uses a different level of aggregation of the input parameters, allowing predictions using different types of available input parameters. one model uses aggregated values of the kinematic parameters of trips and allows prediction with basic input parameters such as travel distance, travel time, and temperature. the second model includes detailed acceleration data. the third model uses data of the kinematic parameters as input parameters to predict energy consumption [7]. authors in [4] used the vehicle dynamics equation to calculate the required mechanical energy and have also included added a temperature and time-dependent term to study auxiliaries and temperature-dependent efficiencies. the physical relations in the vehicle dynamics equation are used to construct three models for ev energy consumption prediction in [5]. in [6], multiple linear regression method is applied to a real-world trip and energy consumption data. the data set considers one vehicle and hence the constructed models are specific to that particular drivetrain. the influence of ambient temperature and auxiliary loads over electricity consumption is explored in [7]. an energy consumption model is proposed based on the gps observations of 68 evs in aichi prefecture, japan. the model is calibrated through ordinary least square regression and multilevel mixed effects linear regression. the results depict that the ambient temperature directly influences the output energy losses and the interactive effects associated with vehicle auxiliary loads. neglecting the interactive effects between ambient temperature and vehicle auxiliary loads will cause inaccurate readings of the energy consumption of the heater air conditioner [7]. authors in [8, 9] propose a method for soc and range estimation by considering locationdependent environmental conditions and time varying drive system losses. to validate the method, an ev was driven along a selected route and battery soc at the destination was compared with the value predicted by the algorithm. the results show excellent accuracy in the soc and range estimation. computational and statistical methods are more apt for energy estimation as they require fewer calculations than the analytical methods based on physical models. however, they are less accurate than the analytical methods. a novel methodology to estimate the driving behavior in terms of future vehicle speeds is implemented in [10]. a driving behavior model is built using a variation of artificial neural networks (anns) called nonlinear auto regressive model with exogenous inputs (narx). the context-aware narx model is trained based on previous driving behavior recordings, the recent driving reactions, and route average speed retrieved from google maps in order to perform driver-specific and selfadaptive driving behavior modeling and long-term estimation. authors in [1] used a vehicle kinetic model to evaluate the energy consumption in mini taxis in sub-saharan africa. persecond gps data gathered on minibus taxis include 62 trips across 3 routes with different driving conditions near stellenbosch, south africa. the paratransit vehicle energy consumption was estimated to range from 0.29 to 0.51kwh/km depending on the driving condition [1]. authors in [11] proposed a method to evaluate the actual driving energy consumptions of evs using real driving speed and charging energy information. using energy flow analysis in the evs, an analytic expression for estimating the energy consumption of evs is derived. the energy consumption calculation is conducted using regression analysis. equations for various energy split ups are also given. engineering, technology & applied science research vol. 13, no. 3, 2023, 11011-11019 11013 www.etasr.com unni & thale: energy consumption analysis for the prediction of battery residual energy in electric … the energy consumption models proposed in most of the literature are designed for specific vehicle types and specific road terrains. most of the researchers have worked on locations outside india and the models and drive cycles selected do not match the indian roads and climate. automobile research association of india (arai) recommends a drive cycle that suits urban transport in india. this research work follows the indian drive cycle (idc) as its input speed profile. our research work focusses on building a vehicle kinematic model wherein the residual energy in the ev battery for different vehicle types and/or for varying ambient conditions can be calculated. the modified urban idc is taken as the input speed profile in our work because its average speed and acceleration values match those on indian roads. the energy consumption in the vehicle was calculated at regular intervals for various ambient conditions and internal parameter variations. the difference between the previous energy value and the current energy consumption gives the value of the remaining energy within the battery. the residual energy in the battery gives a clear indication about the residual range of the vehicle. real time validation part with the help of actual data collected in the vehicle is not done. the distance travelled for a single drive cycle of idc (10.654kms as specified by arai) multiplied with the number of cycles before battery charge falls below the safe margin is approximately matching the manufacturer’s claim. iii. analysis of vehicle dynamics an energy consumption model can be built by using forward or backward approaches. the backward approach consists of creating a vehicle model that simulates electrical parameters based on kinematic and dynamic requirements. the forward approach utilizes statistical models based on measurements of the ev consumption from real-world data or test cycles. using real-world measurements gives more realistic values for energy consumption and relies on available data and statistical modeling [8-12]. it is mostly not associated to vehicle dynamics and drivetrain behavior. figure 2 shows the various components in an ev and their losses. fig. 2. energy consuming components in an ev. using a vehicle model provides a direct link with the vehicle dynamics and drivetrain behavior [7-9]. here, the influences of the drivetrain parameters on energy consumption are clearer. though every ev has a range value specified by the manufacturer, none of the vehicles proved them. changes that occur en-route such as wind speed, slope variations, and traffic cause mismatch in the range values due to the dynamics involved in energy consumption in real time. authors in [9, 11] used real-world measurements for energy consumption calculation, with a limited number of external parameters are included in their models. a new approach of ev modeling that incorporates battery dynamics into motor-vehicle model and accounts for the drag force is proposed in [12]. the model is called the integrated battery-electric vehicle (ibev) model. two types of batteries namely lithium-ion batteries and leadacid batteries were studied and modelled separately. the paper includes novel contributions such as ev modeling that includes the battery dynamics into the motor-vehicle model, vehicle speed and torque controller designs using lqi control, and a kalman filter based on the proposed ibev model, formulation of energy consumption performance indices for ev applications, and demonstrating the effectiveness of the proposed approach through a speed-control comparison study for different test cases. from the existing literature, it is clear that there is a need for an energy model which incorporates all the important factors governing the vehicle range with an option of varying them during the trip. including such variations can help in performing studies on real life situations that may cause the ev battery to exhaust. the current study aims to understand the energy consumption of an electric vehicle calculated from battery to wheel, thereby making it possible to predict the all electric range (aer). the energy consumed on real-time basis is evaluated by calculating the tractive requirements of the vehicle as well as additional power requirements included in the trip [10-18]. this primarily involves the auxiliary systems coming into play. table i shows the details and specifications of the ev under study. the maximum battery capacity is 40.5kwh and the motor torque is 250m. the various assumptions and ambient conditions are described below. table i. specifications of the chosen ev parts/ parameters specifications motor 250nm torque battery 40.5kwh coefficients crr = 0.02, cd = 0.29, air density = 1.225 kg/m 3 dimensions length 3993mm, width 1811mm, height 1606mm wheel base 2498mm mass 1400 kg a. indian drive cycle the drive cycle selected was corresponding to the urban drive cycle or the urban idc as suggested by arai. the complete drive cycle is subdivided into 2 parts. part 1 of the idc consists of 4 repeating cycle patterns of 195s each. part 2 is a 400s long driving pattern with higher acceleration levels. the total distance travelled is 10.647kms [19]. b. analyzed parameters 1) route slope the gradient of the route is one of the key factors that determine the total tractive power taken up by a vehicle. as the engineering, technology & applied science research vol. 13, no. 3, 2023, 11011-11019 11014 www.etasr.com unni & thale: energy consumption analysis for the prediction of battery residual energy in electric … road grade is increased, the gradient force requirement is also increased. 2) auxiliary power requirements the ac and heating systems form an important part of the auxiliary power requirement from the battery apart from navigation, power steering and brakes. 3) wind speed the effect of wind aiding /opposing the vehicle is an important energy-consuming component. 4) mass of the vehicle mass of the vehicle affects the rolling force, the gradient force, and the inertial force of the vehicle. the tractive force of a vehicle is defined as the force required to keep the vehicle in motion. the four main components of the tractive forces include aerodynamic force, rolling force, inertial force, and the gradient force. f������� f� �� � f���� � f�� ���� � f����� �� (1) where: fgradient = mveh gsinα (2) froll = crr. mveh gcosα (3) f� �� � � .ρ. a�. c�. �� v� � � v���� ! � (4) f�� ���� f"� � f"# δ. m� �. a (5) f������� �f' � f� � f( � f" . ��) *+ *+ (6) in the above equations vveh is the velocity of the vehicle, vwind is the wind-speed in km/h (positive for tailwind and negative for headwind), crr, cd represent the coefficient of rolling resistance and the drag coefficient, respectively, g is the acceleration due to gravity (m/s 2 ), α is the road inclination in degrees, af is the vehicle frontal area (m 2 ), mveh is the mass of the vehicle (kg), ρ is the air density (kg/m 3 ), a is the vehicle acceleration in (m/s 2 ), and δ is the coefficient of rotary inertia. the internal resistance of the battery is considered to be equal to 0.03725ω. an analytical study on the various factors of energy consumption is presented in the subsequent sections. iv. results and analysis an energy model suitable for a tropical country like india will require appropriate constants to be selected that can match with the weather and terrain of the place. a kinematic vehicle model should be developed in order to calculate the power consumed by the ev. in order to propose an energy consumption model, the tractive forces were calculated with the parameters of the chosen vehicle. the constants chosen are mentioned in table i. the velocity profile was selected to be the urban idc as recommended by arai [19]. each drive cycle consists of 2 sections. the first section has 3 similar speed vs time envelopes with an average speed of 19kmph and a duration of 195s while the second section has an average speed of 59.3kmph and a duration of 400s. the second section exhibits higher velocity and acceleration values than the first one. the total distance covered per cycle is 10.647km. the calculated velocity vs time values are plotted in figure 3. three drive cycles are shown in the figure. fig. 3. indian driving cycle. an analytical study on various factors affecting the energy consumption in an ev was performed in microsoft excel and the results are given below. the internal resistance of the battery is one of the key indicators that determine the runtime of the battery. the internal resistance varies with the soc of the battery. the internal resistance of lithium-ion batteries goes flat from battery empty stage to almost full charge [2, 6]. the main assumption in this paper is that the internal resistance of the battery is assumed to be a constant. a. slope of the road road gradient is defined as the rise or fall of the road level while moving along its length. in other words, it is the rate of rise or fall with respect to the horizontal distance travelled. another way of expressing grade is that it is the percentage of rise or fall. different types of gradients are defined, namely maximum gradient, ruling gradient, limiting gradient, and exceptional gradient [16]. the general method of representing grade is 1 in ‘n’ where ‘1’ is the vertical unit and ‘n’ is the horizontal distance. another common method of expressing grade is: gradient � ������ ��3���� 4���5����� ��3���� x 100 (7) indian road congress (irc) defines specific road grades for different types of road terrains (table ii [20]). the percentage value of grade is converted into degrees: grade 9 tan)� :���� �� ��� % �<< (8) table ii. road grades in india as per irc [20] terrain nature ruling gradient limiting gradient exceptional gradient plain 1 in 30 (3.3%) 1 in 20 (5%) 1 in 15 (6.7%) mountainous 1 in 20 (5%) 1 in 16.7 (6%) 1 in 14 (7%) steep 1 in 16 (6%) 1 in 14.3 (7%) 1 in 12.5 (8%) figure 4 shows the graph of the remaining energy in an ev travelling through different road gradients of 0, 3, and 7 o , respectively. engineering, technology & applied science research vol. 13, no. 3, 2023, 11011-11019 11015 www.etasr.com unni & thale: energy consumption analysis for the prediction of battery residual energy in electric … fig. 4. variation of the residual energy vs time for various gradients. it is observed that the energy consumption rate increases with increase in the road gradient. the energy plot droops down linearly with increase in road gradient. statistical analysis was conducted to determine the exact relation between road gradient and energy consumption which in turn reflects at the residual energy. table iii shows the average residual energy in the ev after running through 25 drive cycles for different road grades. supervised statistical learning is helpful for building statistical models for prediction/estimation of an output based on one or more inputs. the residual energy values were calculated and averaged for 25 drive cycles for different road gradients and plotted. table iii. residual energy vs slope slope ( o ) average residual energy after 25 drive cycles (wh) residual energy value after 25 drive cycles (wh) 0 29062.74 18441.45 4 28464.03 16361.98 5.71 24876.73 2246.85 7 18025.33 4599.49 figure 5 shows the variation of the residual energy values for the ev under various road slopes with all the other parameters, i.e. vehicle dimensions, air density (1.225kg/m 3 ), cd = 0.29, crr = 0.02, wind speed = 90mps, auxiliary load = 100w, and battery internal resistance = 0.03725ω, remaining constant. fig. 5. prediction plot of residual energy with respect to slope. the correlation study helps establishing the relationship between two or more variables. the correlation between the two variables was analyzed using the data analysis tool of microsoft excel [21]. the predicted residual energy curve is shown in the red dotted lines of figure 5 and satisfies: = �1561.7a � � 4136.9a � 26479 (9) the correlation matrix is shown in table iii. the value of the correlation coefficient is close to -1 (i.e. -0.8343) which means that the factors slope and residual energy have strong negetive correlation. table iv. correlation matrix between residual energy and slope slope energy slope 1 energy -0.8343 1 b. auxiliary load on the ev multiple factors affect energy consumption in evs including travel-related, environment-related, and vehiclerelated factors, vehicle auxiliary loads, and roadway-related and traffic-related factors [10-16]. vehicle auxiliary loads basically serve heating, ventilation, and air conditioning purposes. the auxiliary systems in evs are powered from an auxiliary battery which in turn draws power from the main battery. power steering and power brakes do not have a significant impact on the vehicle range while, the airconditioning and heating systems have a strong impact on the energy consumption, and hence range. as evs do not have an engine producing heat to warm the car, they use batterypowered heating systems. ev batteries lose range as additional power requirements come from operating the car in cold weather. depending on the outside temperature and the desired temperature in the vehicle, the range reduction can be significant. fig. 6. residual energy plot for increasing auxiliary loads. figure 6 shows the plot of remaining energy versus time for an ev connected to various amounts of auxiliary loads. the auxiliary load is increased and its influence on the energy consumption is studied. the energy calculations were done for 25 drive cycles for auxiliary loads of 100w, 300w, 600w, and 900w. it is found that the energy consumption is more for higher values of connected auxiliary loads and hence the residual energy reduces drastically as compared to lighter engineering, technology & applied science research vol. 13, no. 3, 2023, 11011-11019 11016 www.etasr.com unni & thale: energy consumption analysis for the prediction of battery residual energy in electric … loads. the correlation between the two variables was analyzed with the data analysis tool of microsoft excel and is shown in figure 7. the predicted residual energy curve is shown in red dotted lines and satisfies the fourth order polynomial equation: = �91.46af � 1260.7a g � 5391.8a � � 6742.3a � 27011 (10) fig. 7. prediction plot for residual energy with respect to auxiliary loads. the correlation matrix is shown in table iv. the value of the correlation coefficient is -0.57 which means that the factors auxiliary load and residual energy have a weak negative correlation. the r 2 value of 0.698 was observed in the statistical study of auxiliary load versus remaining energy of the ev. table v. correlation matrix between residual energy and auxiliary load aux. load energy aux. load 1 energy -0.57 1 c. influence of wind speed wind has a major impact on the range of an ev as it determines the aerodynamic drag force that needs to be overcome by the vehicle. wind can be thought of as a vector quantity as it has a particular velocity value and its direction matters. the complexity of accounting wind speed in the energy consumption calculation is that it is very dynamic in nature, since its magnitude or direction could change rapidly. wind increases the air resistance on the vehicle. the aerodynamic drag varies with the square of the vehicle velocity. about 70% of this drag is found to be accumulated from overall vehicle resistance at high speeds [22]. wind direction also holds an important place in deciding the energy consumed by an ev. winds can appear as headwinds which oppose the motion of the vehicle thus reducing its speed, or tailwinds which aid the vehicle motion. an analytical study was done on the effect of headwind and tailwind on the energy consumption of the vehicle. figure 8 shows the variation of residual energy for different wind speeds (headwind). vehicle dimensions, mass, drag, and rolling resistance coefficients were kept constant and the auxiliary load was fixed at 200w. the correlation between wind speed and residual energy was analyzed and the trendline generated in microsoft excel is shown in figure 9. polynomial trend-line of second degree was found to be the perfect fit for the generated curve. the r 2 value was found to be 0.9961 which shows a perfect fit. the polynomial equation is given by: = �9.8227a� � 66.931a � 39445 (11) the linear regression plot generated in excel is shown in figure 10. the green dots represent the actual values calculated while the blue dots represent the predicted values. the blue line connecting the blue dots shows the regression. the correlation coefficient value was found to be -0.74 indicating a negative correlation and the p value in the regression analysis was found to be 0.037 which proves that the parameter wind speed is statistically significant to the residual energy. fig. 8. residual energy plot for various wind speeds. fig. 9. prediction plot for residual energy with respect to wind speed. fig. 10. linear regression plot for residual energy vs wind speed. engineering, technology & applied science research vol. 13, no. 3, 2023, 11011-11019 11017 www.etasr.com unni & thale: energy consumption analysis for the prediction of battery residual energy in electric … d. influence of tire pressure rolling resistance force is defined as an energy loss due to tire deformation. when the tires rotate on the road surface for a loaded vehicle, the contact area is compressed and causes tire deformation. under unloaded condition, the tire is uncompressed and returns to original position. the deformation force on the tire under loading condition is greater than the deformation force for unloading condition. this is called hysteresis. low tire pressure produces more hysteresis loss than high tire pressure because the tire has larger deformation. this loss is gradually reduced when the tire pressure increases [23]. low tire pressure means low tire stiffness because the rubber molecules vibrate more than in the case of high tire pressure. the stiffness increases linearly with tire pressure [23]. figure 11 shows the variation in the residual energy with respect to change in the rolling resistance coefficient. differences in the road surface, especially uneven and rough roads, can result in change of rolling resistance coefficient. it is observed that a small change in crr can cause higher energy depletion rates. fig. 11. influence of road surface on residual energy. fig. 12. prediction plot for residual energy with respect to crr. figure 12 shows the results of correlation analysis on remaining energy and rolling resistance coefficient crr. the trendline is linear with the equation given by: = �1371.9a � 40419 (12) the r 2 value was found to be 0.7819 which shows a strong association between the parameters. the blue line in figure 12 shows the actual values of residual energy whereas the red dotted lines indicate the linear prediction trendline which approximately falls on the points. table iv shows the correlation matrix between the residual energy and the rolling resistance coefficient. table vi. correlation matrix between residual energy and crr crr energy crr 1 energy -0.903 1 e. impact of vehicle mass the mass of the vehicle impacts directly the rolling resistance force and the gradient force. although one specific vehicle is selected for the study, the variation in mass can be interpreted as the extra cargo that is added to it during the travel. the orange line in figure 13 shows the actual values of residual energy whereas the red dotted lines indicate a quadratic polynomial prediction trendline which approximately falls on the points. the correlation coefficient of mass and residual energy is -0.88 which shows a strong negative correlation. fig. 13. prediction plot for residual energy with respect to vehicle mass. modern computational tools, such as neural networks and machine learning, have been useful in studies on range detection [24-31]. the factors influencing an ev range have complex relationships and dependence over one another and hence manual calculations will not suffice. machine learning models can be very useful in analyzing them. v. conclusion range anxiety is one of the biggest hurdles in the electrification of the transport sector. accurate prediction of vehicle range and energy management methods can significantly build confidence in the minds of customers to buy evs. the existing literature contains works on the influence of various factors governing the range of an ev. a comparison of the conducted studies shows that most researchers studied the influence of these factors considering one at a time, while the others are assumed to be constants. it is very important to know that most of the publicly available datasets are made for vehicle models outside india or for higher end vehicles. data collected from ev fleets are mostly gps data taken in per minute or per second form. most studies have been conducted in countries engineering, technology & applied science research vol. 13, no. 3, 2023, 11011-11019 11018 www.etasr.com unni & thale: energy consumption analysis for the prediction of battery residual energy in electric … other than india and for specific vehicle types. the transport sector in india is significantly large and diverse. the number of vehicles on the indian roads is very large, hence demands much faster adoption of evs compared to any other country. this work considers the indian urban drive cycle as an input along with the parameters appropriate for indian weather and traffic conditions. there is a need for experimental research for energy estimation and prediction in the indian context. this research intends to build an energy consumption model for evs that run on indian roads. this paper presents an analytical study on the various factors affecting the energy consumption of evs with the help of statistical methods. the factors studied include slope, auxiliary loads, wind speed, coefficient of rolling resistance, and mass of the vehicle. the indian urban drive cycle selected for the research matches the speed profile that is possible on indian roads. first, the tractive force required to propel the ev is calculated with appropriate constants and speed values as per the idc and the energy consumed is calculated periodically. five important factors were found to be statistically significant to the energy consumption of the vehicle. the level of dependence of each of these factors to the energy consumed was studied through calculations and correlation analysis. the mathematical equations for further modelling were derived from microsoft excel. as an extension to this work, the dependency equations can be used to build an energy consumption model that can help in the prediction of the vehicle range. this research work can result in an energy estimation model that is generic in 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[31] a. amirkhani, a. haghanifar, and m. r. mosavi, "electric vehicles driving range and energy consumption investigation: a comparative study of machine learning techniques," in 5th iranian conference on signal processing and intelligent systems, shahrood, iran, dec. 2019, pp. 1–6, https://doi.org/10.1109/icspis48872.2019.9066042. authors profile keerthi unni is a research scholar pursuing phd in the department of electronics and telecommunication engineering, fr. c. rodrigues institute of technology, navi mumbai. she completed her b.s. degree from cochin university of science & technology in 2004 and post-graduated from fr. c. rodrigues institute of technology, navi mumbai, india, in power electronics and drives. her research interests include electric vehicles, power electronics and communication in microgrids. sushil thale obtained his b.s. degree in electrical engineering in 1992 and his m.e. in electrical engineering in 1996 from the university of mumbai, india. he completed ph.d. in the indian institute of technology-bombay with specialization in power electronics and power system, in 2015. he is currently working as a professor in the electrical engineering department, fr. c. rodrigues institute of technology, navi mumbai, india. microsoft word etasr_v12_n6_pp9515-9522 engineering, technology & applied science research vol. 12, no. 6, 2022, 9515-9522 9515 www.etasr.com nemdili et al.: solar-wind hybrid power generation system optimization using superconducting … solar-wind hybrid power generation system optimization using superconducting magnetic energy storage (smes) saad nemdili department of electrotechnics faculty of technology ferhat abbas university setif 1 setif, algeria snemdili@yahoo.com ian chanetsa ngaru department of electrotechnics faculty of technology ferhat abbas university setif 1 setif, algeria chanetsa11@gmail.com meriem kerfa department of electrotechnics faculty of technology ferhat abbas university setif 1 setif, algeria merymed17@gmail.com received: 3 august 2022 | revised: 22 august 2022, 5 september 2022, and 10 september 2022 | accepted: 11 september 2022 abstract-this paper proposes a renewable energy hybrid power system that is based on photovoltaic (pv) and wind power generation and is equipped with superconducting magnetic energy storage (smes). wind and solar power generation are two of the most promising renewable power generation technologies. they are suitable for hybrid systems because they are environmentally friendly. however, like most renewable energy sources, they are characterized by high variability and discontinuity. they generate a fluctuating output voltage that damages the machines that operate on a stable supply. therefore, the energy storage system smes with the function to reduce output voltage fluctuation problems is introduced. smes is found to be the most effective energy storage device as a result of its quick time response, high power density, and high energy conversion efficiency. in this paper, modeling of a hybrid system with smes is built using matlab/simulink. blocks such as the wind model, pv model, and energy storage model are built separately before combining into a complete hybrid system with smes. varying wind speed and solar irradiance values are taken as the input parameters. the obtained results from the simulation reveal that a system with smes is more reliable than a system without smes. keywords-hybrid energy storage system; renewable energy; photovoltaic (pv) system; wind; power quality; superconducting magnetic energy storage (smes) i. introduction during the last decades, the exploitation of renewable energy resources has attracted considerable attention due to the negative impact on the environment and the increased cost of fossil fuels used in conventional power plants. many renewable energy sources, like solar, wind, hydro, and tidal can be exploited. among them, solar and wind have the most rapid growth. without any hazard emission of pollutants, energy conversion is made possible through wind and pv cells. a hybrid system is more advantageous as an individual power generation system, even though it is not completely reliable. in case of a power outage or complete shutdown in one of the systems, the remaining one can still supply power. hence, in the present study, solar and wind power generations are combined to create a hybrid power system. this system, consisting of two unpredictable energy sources, will produce fluctuating output energy and thus cannot ensure the minimum level of power continuity required by the load [1-3]. combining the renewable hybrid system with batteries as a storage system, in order to increase the duration of energy autonomy, will make optimal use of the utilized renewable energy resources and this, in turn, can guarantee high supply reliability. at present, multiple energy storage technologies are being developed and such examples include flywheel energy system (fes), compressed air energy storage (caes), battery energy storage system (bess), superconducting magnetic energy storage (smes) [4], and phase-change materials (pcm). in this paper, a smes is introduced into the hybrid wind and pv power generation system. the added energy storage will store energy during the low load demand period and help stabilize the system's generated output voltage. corresponding author: saad nemdili engineering, technology & applied science research vol. 12, no. 6, 2022, 9515-9522 9516 www.etasr.com nemdili et al.: solar-wind hybrid power generation system optimization using superconducting … ii. modeling of the hybrid system a. modeling of the pv system in this project, we chose to use kc200gt pv module as a reference to develop the pv block model. the pv system was modeled and developed based on the equations from [5]. the parameters of the pv model are shown in table i. table i. pv array parameters at 250oc, 1000w/m 2 parameter value ��� 7.61 a ��� 26.3 v ��� 8.21 a ��� 200.143 w � � 32.9 v � -0.1230 v/k �� 0.0032 a/k �� 54 �� 4 the pv power system model is made up of 3 subsystem blocks (figures 1-3), which are:  photovoltaic current (ipv)  saturation current (io)  photovoltaic current output (im) fig. 1. photovoltaic current block model. fig. 2. saturation current block model. fig. 3. photovoltaic current output block model. the parameters that affect the pv power system output are solar irradiance (g) and temperature (t). both pv current and saturation current block models are connected in the pv current output block model, as illustrated in figure 3. b. modeling of wind turbine power system the wind turbine power system consists of a wind turbine model and a permanent magnet synchronous machine (pmsm) block that was already available on the simulink library of matlab. these permanent magnet machines are characterized by having large air gaps, which reduce the flux linkage even in machines with multi-magnetic poles [6-8]. the static characteristics of wind turbines can be described by the relationship between the total power in the wind and the mechanical power of wind turbines [9-11]. the wind turbine model block is connected to a pmsm and a rectifier as shown in figure 4. varying wind speed is given as the input to the wind turbine and the output mechanical torque from the turbine is directed to the pmsm that converts mechanical energy into electrical energy. the three phase ac output from the pmsm is then sent to the rectifier where it is converted into the dc output. engineering, technology & applied science research vol. 12, no. 6, 2022, 9515-9522 9517 www.etasr.com nemdili et al.: solar-wind hybrid power generation system optimization using superconducting … fig. 4. wind power system. table ii. parameters of the permanent magnet synchronous machine block parameters value nominal mechanical output power (w) 8.5e3 base power of the electrical generator (va) 8.5e3/0.9 base wind speed (m/s) 12 maximum power at base wind speed (pu of nominal mechanical power) 0.8 base rotational speed (kpu of base generator speed) 1 table iii. parameters of the wind turbine block parameter value stator phase resistance rs (ohm) 0.425 inductance ld (h) 0.000395 flux linkage established by magnets (v.s) 0.433 torque constant 5 inertia j (kg.m2) 0.1197 friction factor f (n.m.s) 0.001189 the simulation of the wind power system is shown in figure 4 and the parameters of the pmsm block and wind turbine model block are presented in tables ii and iii respectively. c. modeling of the smes system a smes device is a dc current device that stores energy in the magnetic field. the dc current flowing through a superconducting wire in a large magnet creates the magnetic field [12]. the basic operation of the smes coil can be explained by the simplified electrical model in figure 5. in this model, the smes coil is connected to the source and is loaded by three switches: s1, s2, and s3. here, the coil is a dynamic storage system. charging and discharging of the coil is maintained by a power conditioning system (pcs) which controls the switches independently by generating suitable control of a signal. the operation of the switches is described by the flowchart in figure 6. fig. 5. simplified equivalent circuit of the smes coil. fig. 6. flowchart of charging-discharging involved in the smes system. 1) first case as seen in the circuit diagram, the superconducting coil is directly connected to the input voltage, whereas the load is through the aid of power electronics switches. the supply is denoted by "s" and the demand by "d". if d< s, s1 and s2 must be closed and switch s3 is open. this combination is used to charge the coil. engineering, technology & applied science research vol. 12, no. 6, 2022, 9515-9522 9518 www.etasr.com nemdili et al.: solar-wind hybrid power generation system optimization using superconducting … fig. 7. circuit of charging smes coil. 2) second case when switches s3 and s2 are closed and switch s1 is open, the coil will be in the steady storage condition. fig. 8. circuit of the steady storage case. 3) third case in this case, switches s1 and s2 are open and switch s3 is closed and the coil will be discharging. fig. 9. circuit of the case of discharging of the smes coil. d. controller circuit an appropriate control system was required to control the charging and discharging sequence of the smes. this was accomplished by using a pi controller-based dc-dc chopper as shown in figure10. it operates by constantly comparing the reference voltage with the feedback value of the controller. the error difference between these two will be added to the voltage output from the hybrid system [13]. this total output voltage will then be compared with the expected hybrid output voltage using a comparator. if the output of the hybrid system is less than the reference value, then the dc-dc chopper sends signal zero (0) to the switch, otherwise, a signal one (1) will be sent. signal zero (0) indicates a switch open and smes discharging, whereas signal one (1) indicates that the igbt switch is closed and smes is charging. fig. 10. dc-dc chopper controller block model. iii. simulation case studies in this section, various case studies are been considered. in each case, the input solar irradiance and the wind speed were considered different. hybrid system power characteristics, i.e. input solar irradiance and input wind speed, with and without smes and smes power characteristics are plotted for each case. a. simulation results of the smes system modeling of the charge-discharge circuit for the smes is executed using matlab/simulink. the circuit (figure 14) is implemented for a purely resistive load. the parameters of the smes model are shown in table iv. table iv. smes parameters parameter value system frequency 50 hz line reactor resistance 0.0015 ω dc-link capacitance 1 f load resistance 1 ω superconducting coil 0.008h pid controller gain kp =0.5, ki = 0.00001, kd= 1 fig. 11. energy waveform during coil charging and discharging. fig. 12. power waveform during coil charging and discharging. 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 x 10 8 time (s) e n e rg y ( j ) 0 1 2 3 4 5 6 7 8 9 10 -5 -4 -3 -2 -1 0 1 2 x 10 7 time(s) p o w e r( w ) engineering, technology & applied science research vol. 12, no. 6, 2022, 9515-9522 9519 www.etasr.com nemdili et al.: solar-wind hybrid power generation system optimization using superconducting … fig. 13. current waveform during coil charging and discharging. from the results, it is evident that the smes can store very high energy, around 1000mj, whereas the power level is close to 12mw and the current increases until it reaches around 100ka. during the discharge of the coil, the power injection time is also very low (2s). b. simulation results of the hybrid system without smes the two renewable generator types are connected in series. each generator produces a voltage output of 200v, so practically the output voltage was 400v. we simulated the hybrid system for 3 cases to see the influence of the intermittency of the wind and irradiation on the charging voltage. the system supplies an electrical load (r, l) with r= 30ω and l= 2h. fig. 14. smes system block model.  case 1: irradiation and wind speed are constant, g= 1000w/m 2 , v= 12m/s. figures 15, 16 show the voltage rate and the power characteristic. fig. 15. voltage rate. fig. 16. power characteristic.  case 2: the irradiation is of step form and the wind speed remains constant. figures 17, 18 show the voltage rate and the power characteristic. 0 1 2 3 4 5 6 7 8 9 10 -2 0 2 4 6 8 10 x 10 4 time (s) c u rr e n t (a ) 0 2 4 6 8 10 0 50 100 150 200 250 300 350 400 450 time(s) v o lt a g e (v ) 0 1 2 3 4 5 6 7 8 9 10 0 1000 2000 3000 4000 5000 6000 time (s) p o w e r (w ) engineering, technology & applied science research vol. 12, no. 6, 2022, 9515-9522 9520 www.etasr.com nemdili et al.: solar-wind hybrid power generation system optimization using superconducting … fig. 17. voltage rate. fig. 18. power characteristic.  case 3: constant irradiation and step form wind speed. figures 19, 20 show the voltage rate and the power characteristic. fig. 19. voltage rate. fig. 20. power characteristic. from figures 15-20, it is clear that when the wind or irradiation or both decrease, the load voltage decreases along with power. c. simulation of the hybrid wind-pv system with smes this study seeks to stabilize the voltage in the event of loss of one or both renewable generators. so, we integrated an energy storage system using a superconducting smes coil, whose role is to intervene in the event of a voltage drop [14]. the simulation time of figure 24 is 10s. we simulated the system for the case where the loss of the two generators from which the irradiation and wind speed have a step form. figures 21-25 show the simulation results. fig. 21. charge voltage curve with smes. fig. 22. hybrid system power curve with smes. fig. 23. hybrid system charging current curve with smes. fig. 24. curve of power with and without smes. 0 1 2 3 4 5 6 7 8 9 10 0 100 200 300 400 500 time (s) v o lt a g e (v ) 0 2 4 6 8 10 0 1000 2000 3000 4000 5000 6000 time (s) p o w e r (w ) 0 1 2 3 4 5 6 7 8 9 10 0 100 200 300 400 500 time v o lt a g e ( v ) 0 1 2 3 4 5 6 7 8 9 10 0 1000 2000 3000 4000 5000 6000 time (s) p o w e r (w ) 0 2 4 6 8 10 0 100 200 300 400 500 time(s) v o lt a g e (v ) 0 1 2 3 4 5 6 7 8 9 10 0 1000 2000 3000 4000 5000 6000 time (s) p o w e r (w ) 0 2 4 6 8 10 0 5 10 15 time(s) c u rr e n t( a ) 0 1 2 3 4 5 6 7 8 9 10 0 1000 2000 3000 4000 5000 6000 time (s) p o w e r (w ) power without smes power with smes engineering, technology & applied science research vol. 12, no. 6, 2022, 9515-9522 9521 www.etasr.com nemdili et al.: solar-wind hybrid power generation system optimization using superconducting … according to figure 21, during the period from 0s to 4s the voltage reached 400v. from 4s to 7s the two generators were lost and the voltage was restored thanks to the intervention of the smes, which was able to keep it stable. therefore, we can see the great contribution of smes to the stability of the hybrid system. figure 24 represents the comparison of the power with and without smes for the case of the loss of the two generators from 4s to 7s. we noticed that the power without smes decreases when the wind and the irradiation decreased and on the other hand, with smes, the power remains stable and is fixed at a value of 5200w. fig. 25. block diagram of the hybrid wind-pv system with smes (the inside of sub-models is shown in figues 1-4, 14. d. discussion when both pv and wind generators are connected to the system, the load demand is met. if only one of the pv or the wind generators generates power, then the power demand of the system cannot be fulfilled since the two generators are connected in series to give an added output voltage. from the hybrid system power graph, it is seen that voltage drops when one generator is lost or disturbed making the system unstable. when the smes is added to the system, it provides power with very fast response time, which ensures the constant output power of the hybrid system. this is clearly shown in the graph of the hybrid system power with and without smes (figure 24). based on the simulation results, smes technology can also be used on conventional generating systems for load leveling and spinning reverse. iv. conclusions in this paper, a hybrid system that combines the wind and pv models has been developed, and the application of the energy storage system smes is presented in the developed model. the overall hybrid system with and without smes was tested with varying irradiation levels and wind speed for the pv model and the wind model to determine the function of smes inside the hybrid system. through the charging and discharging process of smes during the simulation, the output voltage fluctuations caused by the intermittent energy sources in the power generation system were reduced. it has be seen from the simulation results that smes can improve the quality of the output fluctuations, and thus increase the reliability of the hybrid power system. references [1] a. kumar, k. s. sandhu, s. p. jain, and p. sharath kumar, "modeling and control of micro-turbine based distributed generation system," international journal of circuits, systems and signal processing, vol. 2, no. 3, pp. 65–72, 2009. 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[6] p. vas, electrical machines and drives: a space-vector theory approach, 1st ed. oxford, uk; new york, ny, usa: clarendon press, 1993. [7] t. j. e. miller, brushless permanent-magnet and reluctance motor drives. oxford, uk: oxford university press, 1989. [8] k. okedu, "wind turbine driven by permanent magnet synchronous generator," the pacific journal of science and technology, vol. 12, no. 2, pp. 168–175, oct. 2011. engineering, technology & applied science research vol. 12, no. 6, 2022, 9515-9522 9522 www.etasr.com nemdili et al.: solar-wind hybrid power generation system optimization using superconducting … [9] a. manyonge, r. manyala, f. onyango, and j. shichika, "mathematical modelling of wind turbine in a wind energy conversion system: power coefficient analysis," applied mathematical sciences, vol. 6, no. 91, pp. 4527–4536, jan. 2012. [10] y. d. song, b. dhinakaran, and x. y. bao, "variable speed control of wind turbines using nonlinear and adaptive algorithms," journal of wind engineering and industrial aerodynamics, vol. 85, no. 3, pp. 293–308, apr. 2000, https://doi.org/10.1016/s0167-6105(99)00131-2. [11] a. goudarzi and f. ghayoor, "modelling of wind turbine power curves (wtpcs) based on the sum of the sine functions and improved version of particle swarm optimization (ipso)," in 2020 international saupec/robmech/prasa conference, cape town, south africa, jan. 2020, https://doi.org/10.1109/saupec/robmech/prasa48453.2020. 9041008. [12] t. ise, m. kita, and a. taguchi, "a hybrid energy storage with a smes and secondary battery," ieee transactions on applied superconductivity, vol. 15, no. 2, pp. 1915–1918, jun. 2005, https://doi.org/10.1109/tasc.2005.849333. 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[14] a. b. lajimi, s. a. gholamian, and m. shahabi, "modeling and control of a dfig-based wind turbine during a grid voltage drop," engineering, technology & applied science research, vol. 1, no. 5, pp. 121–125, oct. 2011, https://doi.org/10.48084/etasr.60. microsoft word etasr_v13_n3_pp10698-10702 engineering, technology & applied science research vol. 13, no. 3, 2023, 10698-10702 10698 www.etasr.com gowreesrinivas et al.: fpga implementation of a resource efficient vedic multiplier using spst adders fpga implementation of a resource efficient vedic multiplier using spst adders k. v. gowreesrinivas department of ece, anil neerukonda institute of technology & sciences (anits), india srinivas.ece@anits.edu.in (corresponding author) srinivas sabbavarapu department of ece, anil neerukonda institute of technology & sciences (anits), india ssrinivas.ece@anits.edu.in punniakodi samundiswary department of electronics engineering, pondicherry university, india samundiswary_pdy@yahoo.com received: 19 february 2023 | revised: 27 march 2023 | accepted: 29 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5797 abstract nowadays, the requirement for very high-speed operations in processors constantly increases. multiplication is a crucial operation in high power-consuming processes such as image and signal processing. the main characteristics of a multiplier are good accuracy, speed, reduction in area, and little power consumption. speed plays a major role in multiplication operations, and an increase in speed can be obtained by reducing the number of steps involved in the computation process. since a multiplier has the largest delay among the basic blocks in a digital system, the critical path is determined by it. furthermore, the multiplier consumes more area and dissipates more power. hence, designing multipliers that offer high speed, lower power consumption, less area, or a combination of them is of prime concern. hence, an attempt is made in this paper to achieve the above design metrics using a spurious power suppression technique (spst) adder. a resource-efficient spst-based vedic multiplier is developed and implemented using artix 7 fpga and is finally compared with the ripple carry adder-based vedic multiplier. keywords-vedic multiplier; urdhva triyakbhyam; spurious power suppression technique (spst); verilog; artix7 i. introduction the operation of multiplication plays a pivotal role in many operations and it is important to be computed fast with great efficiency in digital signal processing (dsp) and image processing, where functions like discrete fourier transform (dft) and fast fourier transform (fft) are used. the research to obtain improved multiplier versions and establish new method types for efficacious multiplier architecture is still ongoing. each multiplier is different in its own way. high performance with a less number of partial products is preferred in a multiplier. much research has been conducted regarding the ancient vedic mathematics, which bought many efficacious multipliers, dividers, squaring, and cube architectures. during the last few years, various decimal algorithms have been extended to the binary number system based on the vedic mathematics [1-4]. reducing the number of stages in a vedic multiplication process leads to a great reduction in the propagation delay. the multiplication process is based on urdhva tiryagbhyam algorithm/sutra, which belongs to the 16 sutras of vedic mathematics [5-7]. generally, most multipliers consume area, power, and work with little accuracy. therefore, the design of multipliers which offer high speed, low power consumption, less area, or combinations of all these, is of immense research interest [8-15]. ii. vedic multiplier indian mathematics has a unique technique of arithmetic computation based on 16 sutras or formulas, which is applicable in many fields. one of the fastest developing fields is dsp. so, there is a need to implement as fast as possible multiplication operation for the digital processing of signals. the vedic multiplier is mainly based on the vertical and crosswise algorithm of urdhva triyakbhyam generating all partial products and sums in a single step. the ut sutra has been conventionally utilized for the multiplication of decimal numbers in comparatively less time. we can use this to multiply two numbers. the bits on the two extremes of the number are multiplied and the result is added to the previous carry. when there are more digits in each number, all the results are added to the previous carry. the process of this scripture is discussed below with the help of an example. engineering, technology & applied science research vol. 13, no. 3, 2023, 10698-10702 10699 www.etasr.com gowreesrinivas et al.: fpga implementation of a resource efficient vedic multiplier using spst adders let us consider two decimal numbers: 234 and 159.  initially, the least significant digits of both numbers are multiplied and the result is 36.  next, we have cross-wise multiplication of the first digit of the first number with the second digit of the second number. another cross-wise multiplication of the first number’s second digit with the second number’s first digit. finally, we add those two products.  cross-wise multiplication of the first number’s least significant digit with the second number’s most significant digit and vice-versa. multiplication of the middle digits gives a total of three products which are finally added.  without considering the least significant digits of the two numbers, we perform cross-wise multiplication and addition.  vertical multiplication of most significant digits of the two numbers. for all the steps, with the exception of the first step, each compartment needs to have only one digit. if not, then the carry is forwarded to the initial digits in the previous compartment. fig. 1. the 16bit vedic multiplier. the delay of the multiplication is reduced using ut sutra and initially this was used only for decimal number multiplication, although, it can be used for binary numbers. binary multiplication can be done using this method for 2-bit, 3-bit, and 4-bit numbers, since the pps and their arithmetic sum are calculated autonomously. delay is produced due to the existence of the carry from the pps which is to be added in each next step’s partial product. figure 1 shows the process of 16-bit vedic multiplication. in the first stage, 8×8 vedic multipliers are used. the obtained products are added according to the vedic multiplication discussed above. finally, the 32-bit result is obtained. iii. spst adder an adder, either a full adder (fa) or a half adder (ha), is a combinational circuit used to calculate the sum of three or two inputs. in a parallel adder, fas are connected in series to produce an n-bit adder. in each section, the sum and carry are not computer until the input carry arises, slowing down the summation process. to avoid delay issues, the carry look ahead (cla) adder has been suggested. to improve the speed of cla, spurious power suppression technique (spst) is applied. this can reduce the dissipated power of combinational vlsi for dsp purposes. the spst consists of two parts, the most significant part and the least significant part. it disables the msp when it doesn’t modify the results saving power [1620]. the spst adder/subtractor is classified into two parts, msp and lsp. the msp of the first adder/ subtractor is modified to include:  detection unit,  data controlling unit,  sign extension unit, and  circuits for calculating cin and cout signals. in spst, the detection unit is used to detect if a transition in data bits of the result will occur in the circuits (adders or multipliers) or not. the detection logic unit works as follows:  when the detection unit disables the msp, then the output of the msp are re-compensated so that the time saved for skipping computations will cancel out the delay of the detection logic circuit.  when it enables the msp, then the msp will wait for acknowledgement of the detection unit to enable the data latches. so, the delay of the detection unit will contribute to the entire circuit’s delay.  when the detection unit stays in its decision irrespective enabling or disabling of the msp, then the delay of detection unit is insignificant. there is a data asserting control unit realized by using the registers to further remove any unwanted spurious signals of the arithmetic unit whenever the latched portion has been turned on. this asserting control obviously brings power reduction [16-20]. the 16-bit addition using the spst process is interpreted in 5 cases. the first case is the transient state, in which spurious transitions of carry signals occur in msp although the result of the msp is not altered. the second and third cases illustrate the situation of a negative operand adding to a positive operand without and with carry from lsp, respectively. the fourth and fifth cases demonstrate the condition of two negative operand additions without and with carry-in from lsp, respectively. in all the above cases, the results of the msp are predictable, so the computations in the msp aren’t required and can be neglected. removing those spurious computations will not only save the power consumed by the spst adder or subtractor but also reduce the noises which are going to affect the subsequent arithmetic circuits. engineering, technology & applied science research vol. 13, no. 3, 2023, 10698-10702 10700 www.etasr.com gowreesrinivas et al.: fpga implementation of a resource efficient vedic multiplier using spst adders iv. the proposed multiplier our main goal is to differentiate the performances of the vedic multiplier with and without using the spst adder by comparing both models. to improve the vedic multiplier's efficiency, the spst adder is introduced at intermediate stages to add the sub module outputs. finally, performance analysis is conducted with respect to area and power. to develop 16-bit vedic multiplication, four 8×8 multipliers are required. in the second stage, 16-bit spst adders are used to add intermediate partial products. fig. 2. 16-bit vedic multiplier using spst adders. both multipliers models were simulated and synthesized using xilinx vivado tool. two 16-bit vedic multipliers, one with rca and one with spst, were programmed using hdl and their performance was compared with respect to area and power. v. simulation results all the blocks were programmed and simulated using xilinx vivado tool. after verification, the proposed multiplier was implemented on nexsys 4 ddr artix 7 fpga. the synthesis and simulation results of vm using spst with respect to main modules and sub modules are shown in figures 3 to 10. fig. 3. rtl schematic of a vedic multiplier using spst blocks. fig. 4. vedic multiplier using rca simulation report. figure 2 represents the rtl diagram of the vedic multiplier which utilizes four 8-bit vedic multipliers and three spst adders to obtain the results. figure 3 gives the simulation output for two 16-bit numbers. from the synthesized results it is concluded that the vedic multiplier using rca logic requires 402 slice luts and 120 slice registers as shown in figure 5. further, it is noticed that it requires 33.77w on-chip power which includes 32.586w dynamic power as shown in figure 6. fig. 5. vedic multiplier using rca implementation report. fig. 6. power report of the 16-bit vedic multiplier using rca. table i. performance comparison vedic multiplier appearance slice luts slice registers power(w) using rca 402 120 33.54 using spst 361 0 25.49 from the synthesized results it is concluded that the vedic multiplier using spst logic (figure 7) requires 361 slice luts engineering, technology & applied science research vol. 13, no. 3, 2023, 10698-10702 10701 www.etasr.com gowreesrinivas et al.: fpga implementation of a resource efficient vedic multiplier using spst adders (figure 8) and 25.49w on-chip power which includes 24.708w dynamic power as shown in figure 9. the result comparison can be seen in table i. it can be seen that the spst-based vedic multiplier provides better performance in terms of luts and delay. fig. 7. vedic multiplier using spst simulation report. fig. 8. vedic multiplier using spst implementation report. fig. 9. vedic multiplier using spst power report. vi. hardware implementation the external hardware used for implementation consists of:  adc kit  slide switches and leds  jumper wires, 3.3v fixed voltage source (from rps)  nexys 4 ddr after simulation, the proposed vedic multiplier using the spst model was dumped into the fpga to verify the response. in this work, the proposed model was implemented on nexsys 4 ddr artix7 fpga with the help of xilinx vivado. for the implementation, the first task is to map the original input and output ports with board i/os by generating a constraint file. next, the program can be dumped to the fpga kit to verify the simulation results practically. fig. 10. implementation of the vedic multiplier with spst in artix7. vii. conclusion in this paper, a 16-bit vedic multiplier was designed using spst adders and was programmed in verilog. the proposed vedic multiplier was synthesized in the artix7 fpga family using the xilinx tool and its response in terms of area and delay was observed. this work is mainly focused on developing efficient vedic multipliers using spst adders and its performance was compared with the one of the ripple carry adder-based vedic multiplier. from the implementation results, it is observed that the performance of the vedic multiplier using spst is better by 10% in respect of area, while power dissipation is improved by 24% compared to that of vedic using the rca adder. after the validation, the spst-based vedic multiplier was succesfully implemented on nexyx 4 ddr artix fpga. references [1] m. ramalatha, k. d. dayalan, p. dharani, and s. d. priya, "high speed energy efficient alu design using vedic multiplication techniques," in 2009 international conference on advances in computational tools for engineering applications, beirut, lebanon, jul. 2009, pp. 600–603, https://doi.org/10.1109/actea.2009.5227842. 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[15] d. m. perisic, v. petrovic, and b. kovacevic, "frequency locked loop based on the time nonrecursive processing," engineering, technology & applied science research, vol. 8, no. 5, pp. 3450–3455, oct. 2018, https://doi.org/10.48084/etasr.2256. [16] k.-h. chen and y.-s. chu, "a low-power multiplier with the spurious power suppression technique," ieee transactions on very large scale integration (vlsi) systems, vol. 15, no. 7, pp. 846–850, jul. 2007, https://doi.org/10.1109/tvlsi.2007.899242. [17] h. s. k. puttam, p. s. rao, and n. v. g. prasad, "implementation of low power and high speed multiplieraccumulator using spst adder and verilog," international journal of modern engineering research, vol. 2, no. 5, pp. 3390–3397, 2012. [18] a. prashanth, r. p. waran, and s. k. and s. pawar, "low power high speed based various adder architectures using spst," indian journal of science and technology, vol. 9, no. 29, pp. 1–3, may 2016, https://doi.org/10.17485/ijst/2016/v9i29/93197. [19] v. s. narayan, s. m. pratima, v. s. saroja, and r. m. banakar, "high speed low power vlsi architecture for spst adder using modified carry look ahead adder," in proceedings of international conference on advances in computing, new delhi, india, 2012, pp. 461–466, https://doi.org/10.1007/978-81-322-0740-5_56. [20] a. purna ramesh, a. v. n. tilak, and a. m. prasad, "efficient implementation of 16-bit multiplier-accumulator using radix-2 modified booth algorithm and spst adder using verilog," international journal of vlsi design & communication systems, vol. 3, no. 3, pp. 107–118, jul. 2012. microsoft word etasr_v12_n6_pp9726-9731 engineering, technology & applied science research vol. 12, no. 6, 2022, 9726-9731 9726 www.etasr.com narang & mittal: performance assessment of traditional software development methodologies and … performance assessment of traditional software development methodologies and devops automation culture poonam narang department of computer science and applications maharshi dayanand university rohtak, haryana, india poonam.mehta20@gmail.com pooja mittal department of computer science and applications maharshi dayanand university rohtak, haryana, india mpoojamdu@gmail.com received: 10 september 2022 | revised: 25 september 2022 | accepted: 26 september 2022 abstract-successful implementations of software development methodologies significantly improve software efficiency, collaboration and security. most companies are moving away from traditional development methodologies towards devops for faster and better software delivery. devops, which is a primary need of the it industry, brings development and operation teams together to overcome communication gaps responsible for software failures. it relies on different sets of automation tools to robotize the tasks of software development from continuous integration, to testing, delivery, and deployment. the existence of several automation tools in each development phase raises the need for an integrated set of tools to reduce development time. for this purpose, we used the devops-based hybrid model integrated tool chain (itc), along with three sample java-based projects or code repositories to quantify the results. this paper evaluates and compares measurement metrics of java projects using traditional development methodologies and devops, and the results are shown in tabular and graphical format. the latest google and stack overflow trends have also been included to retrieve the best performer development methodology. this comparative and evaluative performance analysis will be beneficial to young researchers that study the metrics of software development, while also they will be introduced to the automotive environment of devops, the latest emerging buzzword in software development. keywords-automation; automation tools; devops; integrated tool chain; software development i. introduction software engineering is a branch of software design through the software development life cycle (sdlc), which consists of several development phases, from gathering requirements and thorough analysis, to design, coding, testing, deployment/delivery, and maintenance. software development has introduced various methodologies from traditional and agile to the most recent devops culture. traditional and agile development methods include models like waterfall, iterative, evolutionary, spiral, prototype, v model, scrum, xp rad, etc. the availability of multiple models necessitates their careful selection for successful and quality software delivery. as development models under traditional methodologies struggled with many defects responsible for late software delivery and budget overruns, fast and successful development was one of the major challenges for traditional development models. agile methods provided better solutions for quick releases with small sprint sizes as they introduced flexibility into their methods, but still lacked continuity in development and operations, which is where devops comes in. devops, the industry's common term for development, is based on five software development continuums, i.e. continuous integration, continuous testing, continuous delivery, continuous development, and continuous monitoring. the continuity in the environment of devops is achieved through different sets of automation tools employed at each and every phase of software development. devops works on the principles of an infinite continuous cycle that starts from continuous integration of code repositories and continues until the monitoring stage of the software development to deliver quality successfully. the current research quantitatively evaluates the performance of different software development methodologies, including devops, based on various software performance metrics. for the application of these metrics and to obtain quantitative results, three sample code repositories or javabased projects have been taken into consideration. this paper also considers our proposed [1] and implemented [2] devopsbased hybrid model of automation integrated tool chain (itc). the proposed and implemented itc model demands automation tools in each phase of software development. as there are various automation tools in each phase of software development, prior selection of automation tools will not only reduce development time but also ensure delivery within budget and quality. this study examines the proposed and verified itc [2] for devops implementation. the result of traditional methodologies and devops performance evaluation based on various software metrics validate the quality of the delivered product and also helps in recovering the best performing software development methodology. the outcome of our study will be useful for young researchers/students to understand the course of action of devops and its automation corresponding author: poonam narang engineering, technology & applied science research vol. 12, no. 6, 2022, 9726-9731 9727 www.etasr.com narang & mittal: performance assessment of traditional software development methodologies and … tools. it will also be important for software developers to choose the best execution tools from the various automation tool sets available. sdlc contains detailed edits of the various steps or processes necessary to configure the software. it covers many methodologies such as traditional and agile methodologies and now devops, while these methodologies cover various models. devops, on the other hand, includes a set of different automation tools to achieve the goal of competitiveness in the era of digital transformation and to increase the speed of adaptation or reaction to changing software requirements [3]. devops, with its principles of continuity, helps companies survive in this competitive world. the main focus of the current paper is to describe and compare devops with traditional and agile methodologies ii. traditional methodologies traditional methodologies specifically include the waterfall model, first introduced in the 1970s. the cascade model is explained stage-by-stage [4]. through these stages, including iterative approaches, the author introduced the development of large-scale systems. the step-by-step approach of traditional methodologies allows large-scale projects to be handled and developed more successfully. but on the other hand, traditional development methods are rigid and also fail to respond to aggressive or frequently changing customer requests [5]. compared to the traditional methodology, the agile development methodology provides a set of practices that allow rapid adaptation to changing customer needs. in terms of research gaps, the authors discussed the failures of traditional models very well, but did not propose any solution to overcome the major flaws of traditional development methodologies. current research included devops culture, with its validation analysis of out-performance, as a result of comparison with other development methodologies. a. agile development methods although agile methods were created to address any flaws or limitations of traditional development methodologies, they are also confirmed to be effective for large-scale distributed projects [5]. agile approaches are drivers in huge and extremely large-scale development [6]. therefore, the agile approaches encourage greater communication, continuous integration, and fast delivery of products using an incremental and iterative approach, but they also have several disadvantages, such as lack of planning, lack of documentation, lack of predictability, etc. [7.] to discover genuine constraints of agile approaches outside the existing literature review, the authors in [7] also performed an online survey. there are still research gaps in terms of solutions to the problems faced by flexible methods. basic research talks about devops development culture to overcome many of the difficulties of software development. b. devops development culture devops proposes a solution to a variety of development and delivery challenges, including the quality of the generated product. in their research on devops, authors in [8] examined the effects of devops features on software quality. increasing the speed, frequency of development and product quality is the main goal of devops. to minimize differences or fill in all kinds of communication gaps between dev and ops teams, devops promises to deliver successful projects with shorter deployment or sprint times [8]. to deliver or deploy highquality products, authors in [9] agree that development and operations teams should cooperate well [9]. although numerous studies support the use of devops, others are opposed to it and discuss the lack of quantification of performance and quality measures [10]. authors in [11] found that devops helps businesses to achieve their goals and also increases their speed in reacting to changes [11]. the literature also confirms the existence and successful implementation of various devops models in practice [12]. similarly, many papers, including [11, 16], accept the emerging paradigm as a response to the growing awareness of the existing many types of communication or collaboration and cultural gaps between dev and ops team functions. again, there are research gaps in terms of quantified quality outcomes provided by devops. c. motivation the motivation behind this research is to provide quantified results of devops quality and on-time delivery. to this end, the current research examines the proposed [1] and implemented [2] model of hybrid integrated automation tools based on devops. study is also conducted from different perspectives of model building [13, 15] to the application of cloud computing [15] or the adoption of recent approaches for development industries. based on the existing literature and our tool model, this paper performs an evaluation of different types of parameters or software metrics for quality measurement. this research has taken three sample software projects developed in jdk environment to measure devops performance and quality. lines of count (loc), number of different components/modules, development time, and risk consideration are considered as evaluation metrics. iii. devops based hybrid model of integrated tool chain for the performance evaluation of devops, we propose [1] and apply [2] a devops-based hybrid itc model as depicted in figure 8 of [1]. for the hybrid model, different tools are proposed from which only one automation tool is selected as the best performer tool based on several performance evaluators. the current research work considers the same set of automation tools [1] for the implementation of sample java projects, mentioned in table i, using devops development and deployment culture. iv. research design and data set the current research compares traditional and agile methodologies with devops development. for this purpose, three sample projects, i.e. a website for online faculty recruitment, a car search engine, and a scientific calculator tool in java have been designed through traditional methods and later on uploaded local repositories to github for implementation through devops tools. different parameters for measurement of projects were calculated. engineering, technology & applied science research vol. 12, no. 6, 2022, 9726-9731 9728 www.etasr.com narang & mittal: performance assessment of traditional software development methodologies and … fig. 1. components/modules and loc for sample java projects. figure 3, gives the total count of lines of code along with different components and other parameters to consider for metric evaluation purposes. table i shows the descriptive measures of these sample projects. table i. software metric classification of the software project name of java project size no of components/ modules project domain web site for online faculty recruitment (project1) 2430 18 web based car search application (project2) 1579 14 search application scientific calculator tool (project3) 557 8 tool the sample projects mentioned in table ii have java as the application development environment. these projects were designed in local repositories in the jdk environment and were uploaded in github, which was used as a remote repository for the smooth working of the devops environment. after the uploading of the code, the next phase is to plan and write test cases for proper execution and implementation of the code. if the test case fails, then the test case must be rewritten after code refactoring. successful test case execution is followed by code deployment and monitoring or the operations phase of the project. the complete step by step procedure in terms of process flow diagram for current research work is shown in figure 2. fig. 2. process flow diagram of the current research work. as clearly depicted in the flowchart of figure 2, writing the test cases and successful code testing is a major part of the devops process. for the implementation purpose, jenkins continuous integration tool is selected which also takes charge of continuous delivery of the product. different plugins are also installed with jenkins to ensure smooth working of the tool. code repository or maintenance is done through github. ansible with jenkins is responsible for the continuous deployment of the code. test cases were written using junit. the build work was done by maven. all these steps or procedures are fully automated and were done through the devops based hybrid model of automation tool set. v. measurement metrics of software development quality plays an important role in software acceptance. software quality is not a single factor or value, but it covers many different parameters like testability, predictability, and maintainability. so, quantification of these performance or efficiency parameters becomes more important for measuring the quality value. this research work considers three types of software metrics, i.e. project, process, and product metrics. the project metrics covered in the current work are project defect density (pdd) and release deployment frequency (rdf), to measure defect density covered in the project along with the deployment frequency of the project. similarly, process metrics cover the productivity (pp) of the whole process in the form of the throughput of the system. lastly, product metrics involve system risk identification (sri) and the reliability of the developed product. these software metrics along with their expected outcome are shown in table ii. the categorization of software metrics in table ii clearly mentions the expected results. these metrics with their calculation formulas and methods are explained below. a. project defect density (pdd) pdd refers to whether the software can be deployed. pdd actually depends directly on the presence of defects in the engineering, technology & applied science research vol. 12, no. 6, 2022, 9726-9731 9729 www.etasr.com narang & mittal: performance assessment of traditional software development methodologies and … system. as defects can occur at any stage of software development, checks at regular intervals become a necessary activity of the development. the value of pdd must be low to ensure quality delivery of the software. the pdd formula is: pdd = ∑ total number of �efects size of �oftware (in kloc) n i�1 (1) where n refers to the total number of components or modules in the system and n>0. equation (1) is used to first find the defect density of individual components or modules of the system and to get the defect density for the whole system/project by summing them up. table iii shows the pdd of the system as calculated with traditional methods of development and devops. tdm refers to traditional development methods and dc refers to devops culture. table ii. considered software metrics and their expected outcome software metric type software metric expected outcome project pdd low rdf high process sri high product pp high table iii. pdd measure of sample projects name of project size (loc) no of modules total no of defects pdd tdm dc tdm dc project1 2430 18 30 15 12.35 6.17 project2 1579 14 18 8 11.40 5.07 project3 557 8 10 4 17.95 7.18 defect density is computed by dividing the total number of defects with the size of the corresponding project as given by (1). in table iii, devops gives a low pdd value that clearly indicates more reliability and success of the underlying process. figure 3 displays a graphical comparison of these methods. fig. 3. graphical comparison of traditional and devops development for pdd measure. b. release deployment frequency (rdf) rdf reports the total number of deployments in a particular time period. in other words, rdf refers to the rate of released deployments. the higher the value of rdf, the lesser is the chance of errors/defects in the system. the calculation is rdf is done by: rdf = ∑ total number of deployments time unit (in hours) n i�1 (2) equation (2) calculates the total number of deployments or the release count in particular time units, taken in hours, for individual components and adding them all to get the rdf for the whole system/project. the deployment frequency data of the java projects with the usage of traditional principles and devops rules is shown in table iv. table iv clearly indicates the high value of deployments that leads to the acceptance of frequent changes in the system. the comparative graph of these development methodologies in figure 4 shows similar results. table iv. rdf measure of sample projects name of project size (loc) no of deployments time taken to deploy (h) rdf tdm dc tdm dc tdm dc project1 2430 18 20 1.8 1.1 10 18.18 project2 1579 15 16 1.5 0.9 10 17.78 project3 557 9 10 1 0.7 9 14.29 fig. 4. comparative graph for devops and traditional approaches. as depicted in figure 4, the devops deployment number is higher as compared to tdm. devops deployment speed is much higher for all types of development projects. automation tools and prior selection of tool chain is the major reason of devops success over the other methodologies. c. system risk identification (sri) sri refers to the assessment of risk associated with the project/system to be developed. a high value reflects the identification of more risk components and ensures safe and risk-free delivery of software. the formula for sri is: sri = ∑ wx n i�1 , n>0 (3) where n refers to the total number of components in the system, wx refers to the weightage assigned to each individual risk and the sum of all wx gives the sri number. risk coverage analysis or risk identification gives the total number of risk sets injected with risk sets executed positively and total risks not tested or broken. table vi depicts different risk set coverage calculated for traditional development approaches and devops. table v. sri estimate of sample projects project total risk tests total no of executed risks tests risks broken total risks not tested risks not executed risk coverage (%age) tdm dc tdm dc tdm dc tdm dc tdm dc project1 275 188 211 42 23 22 24 23 17 68.36 76.73 project2 150 104 116 23 12 12 13 11 9 37.81 42.18 project3 60 40 46 9 5 15 5 6 4 14.55 16.62 engineering, technology & applied science research vol. 12, no. 6, 2022, 9726-9731 9730 www.etasr.com narang & mittal: performance assessment of traditional software development methodologies and … in table vi, the number of total risk sets included, executed, broken, and even ignored or not tested at all in devops culture are compared with the similar parameters for traditional development methods. the results again indicate a better risk coverage in devops. the graphical comparative study in figure 5 confirms this statement. fig. 5. risk coverage comparative study graph. d. process productivity (pp) the productivity of any system is the total units of work done in a particular time period. it refers to the throughput of the system. process or system productivity is measured by: pp = ∑ total number of &ser �tories time 'aken to )omplete n i�1 (4) where user stories refers to the units of work done in a given time period. equation (4) finds the productivity of the process or system and computes the summation of productivity of individual components. pp is also measured as the throughput of the whole system or software. it measures the total units of work done in a particular time period. the pps for traditional methods and devops are shown in table vii. the results of table vii and of the comparative graph of figure 6 clearly indicate enhanced throughput/productivity measure for projects developed under the devops culture. table vi. pp estimation/measurement of current dataset name of java project size (loc) total no of user stories time taken (weeks) pp tdm dc tdm dc project1 2430 180 18 14 10 12.86 project2 1579 117 12 9 9.75 13 project3 557 41 4 3 10.25 13.67 fig. 6. pp comparative graph for devops and traditional approaches. figure 8 shows speedy releases or output in terms of productivity measure for devops in comparison with traditional development. each of the performance metric and graphic visualization tools proves the effectiveness of devops as a symbol of quality and speedy delivery with less defect density and high coverage of risk sets. vi. conclusion and future work fast and quality delivery is an essential indicator for assessing the power of software development methodology. this study examined the efficacy of the previously proposed and implemented devops-based hybrid model of automation tools. in this esteem, we presented three java based projects from different domains and compared the performance of devops culture with traditional methods of software development based on performance metric measurement values. the measured results showed the superior performance of devops culture. although previous studies developed many models in software development, no such model has been developed to analyze the effect of prior automation tool selection, before commencement of actual development, on delivery or deployment. our proposed, implemented and now validated, devops-based hybrid model of tool chains comes out to be more technically focused in terms of software 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[17] j. stoneham, p. thrasher, t. potts, h. mickman, and c. deardo, devops case studies: the journey to positive business outcomes. it revolution. authors profile poonam narang, is a research scholar, pursuing her phd from the department of computer science and applications, maharishi dayanand university, rohtak, haryana under the supervision of respected dr. pooja mittal. author’s qualification is m.phil. (cs), mca. she had attended many national and international conferences and has also published many research papers. pooja mittal, obtained her ph.d. from maharshi dayanand university. her areas of research and specialization include data mining, data warehousing, and computer science. she had published more than 50 research papers in renowned international and national journals and has attended more than 30 conferences. currently she is working as an assistant professor in the department of computer science & applications, maharishi dayanand university, rohtak (haryana). microsoft word 2-562-ed.doc engineering, technology & applied science research vol. 5, no. 3, 2015, 801-804 801 www.etasr.com abdul-niby et al.: a hands-free obstacle detection and avoidance system a hands-free obstacle detection and avoidance system mohammed abdul-niby mamoon alameen school of engineering the australian college of kuwait, kuwait m.nibi@ack.edu.kw school of engineering the australian college of kuwait, kuwait m.radiy@ack.edu.kw otmar irscheid mohamad baidoun hadi mourtada school of engineering the australian college of kuwait, kuwait o.irscheid@ack.edu.kw school of engineering, the australian college of kuwait, kuwait m-baidoun@hotmail.com school of engineering the australian college of kuwait, kuwait 0906440@go.ack.edu.kw abstract—in this paper, we present a low cost hands-free detection and avoidance system designed to provide mobility assistance for visually impaired people. an ultrasonic sensor is attached to the jacket of the user and detects the obstacles in front. the information obtained is transferred to the user through audio messages and also by a vibration. the range of the detection is user-defined. a text-to-speech module is employed for the voice signal. the proposed obstacle avoidance device is cost effective, easy to use and easily upgraded. keywords-intelligent navigation capabilities; electronic travel aids; ultrasonic sensor i. introduction vision is probably the most important sense for a human body, as it gets about 83% of its information through sight. statistics by the world health organization estimates that there are 285 million people in the world with visual impairment, 39 million of which are blind and 246 million are with low vision [1]. the oldest mobility aids for people with visual impairments are walking canes (sticks) and guide dogs. the most important drawbacks of these aids are the training needed, the range of motion and that the information conveyed is very little. also, that they do fairly little to counter the main problem that visually impaired people face: walking or moving in an unfamiliar area, with no prediction regarding the surrounding environment’s obstacles and obstructions. this results to both a psychological as well as a practical dependence from third-party assistance. nowadays, a great variety of improvements in hardware and software technologies may provide added help through the use of intelligent navigation capabilities. recently, there has been a wide variety of electronic travel aids (eta) designed and developed in order to make navigation easier and help visually impaired people to live their lives safely and independently. different aids have been developed, two of the most significant are listed below:  ultracane by sound foresight technology ltd: the ultracane is equipped with a dual-range, narrow beam ultrasound system that provides a 100% hazard protection envelope in front of and, uniquely, forward of the head and chest of the user. two ultrasound transducers provide range data on the closest potential hazards, such as plants, people, road signs, and over-hanging branches [2].  mowat sensor: a lightweight, hand-held device which has similar properties to a flashlight. the sensor itself detects objects by measuring the distance of a vibration of the brief pulses of hf sound it emits. the device will then inform the person how close an object may be [3]. however, these techniques focus on outdoor movement. they can obviously be used indoors but, for example, the cane can be rather disturbing indoors. on the other hand, the mowat sensor must be placed in a pocket in order to keep contact with the body so that the vibration is felt by the user. the goals set for an improved system sums up to designing a system that can help the user to navigate indoors and outdoors in such a way that:  it is hands free and easy to use  can be used by users of different ages  doesn’t interfere with the user’s daily behavior/way of living. at the same time, the design should overcome problems such as reliability, cost, availability, high cost and flexibility/upgradeability. ii. system description the system described in this paper aims to help visually impaired people secure their path and experience a safer way of living. it uses ultrasound detection and warns the user via a voice engineering, technology & applied science research vol. 5, no. 3, 2015, 801-804 802 www.etasr.com abdul-niby et al.: a hands-free obstacle detection and avoidance system signal. also, taking into consideration that some users might have a hearing problem, it vibrates once an object is detected. a. basic operation the device main stages of operation can be summarized to the four stages shown in figure 1. once an object is detected by the ultrasonic sensor, a signal is sent to the processor to inform that there is an object ahead, then the processor turns on the two outputs and thus the user hears the message and senses the vibration. a state diagram [4] is shown in figure 2 [4] whereas table i shows the truth table for the device. the sequence of the device operation is shown in figure 3. as shown, the device is initially at idle state, where it is just sensing and waiting for a signal to be detected. it moves to the next state, which is “receive”, when it detects a signal ahead. then it moves to the next state (“alert”), whose output is the activation of the two alerts present in the system, the vibrating motor, and the voice chip. fig. 1. block diagram for the general system functions. table i. the truth table for the device current state input* next state output 0 idle none idle 1 receive get signal 0 idle none receive 1 alert output is true 0 idle none alert 1 alert voice & vibration on fig. 2. the state diagram fig. 3. the sequence of the device operation the ultrasound signal, which is a sound signal above the human hearing capability is generated and transmitted by the ultrasound transceiver [5]. this transceiver transmits and receives ultrasound signals at the same time. once an ultrasonic signal propagates, it continues traveling through air until it is obstructed by an object. the signal then bounces off the obstacle and is reflected back towards the transceiver. at this stage, the transceiver detects the reflected signal; once this happens it sends a pulse to the processor’s input notifying it that an object has been detected. when the processor gets the input from the sensor, it is preprogrammed so that it turns on two outputs, which are simply two pins each connected to a distinct circuit. one pin connects to the voice playback circuit, while the other is connected to the vibrating motor. these pins can give pulses (logic outputs), and the design configuration is done such that the two alerting circuits, which are the voice message playback circuit and the vibrating motor, are activated in order to notify the user by playing a verbal message and generating a physical vibration within the box which will be mounted on the user’s waist. fig. 4. processor box b. device design the shape of the device is very simple and easy to implement or install by the user. a box containing the circuitry (figure 4), i.e. the processor, the voice message playback circuit and the vibrating motor, will be mounted on the user’s waist using a clipper. mounting the box on the waist will allow the user to feel the vibration. the transceiver (figure 5) is attached to a clipper that can be mounted on different heights of the body for flexibility of use. also, an earphone or speaker jack input is available at the back on the box that can be used to connect different kind of headsets. fig. 5. ultrasound transceiver engineering, technology & applied science research vol. 5, no. 3, 2015, 801-804 803 www.etasr.com abdul-niby et al.: a hands-free obstacle detection and avoidance system the arduino uno-r3 smd board was used in the design of the system because of its high capability of controlling inputs and outputs, due to it being based on the atmega328 atmel® board [6]; it can be programmed easily using avr® studio software provided by atmel®. the programming language used is c that the compiler translates to assembly. c. emic2 text to speech module [7] this module (shown in figure 6) is a multi-language voice synthesizer that converts a stream of digital text into natural sounding speech. it makes it simple to convert a string of text to audible voice text using the universally recognized dectalk text-to-speech synthesizer engine. a visual indication of the operating state is given with an on-board led light as shown in table ii [7]. an image of the emic2 board and a schematic diagram, are shown in figure 6. table ii. visual indication of the operating state colour state green idle state red active state orange (solid) initialization state orange (blinking) error state led off device is not receiving . fig. 6. emic2 board and its schematic diagram d. ultrasonic range finder lv-ez1 [8] lv-ez1 provides very short to long-range detection (figure 5). it can detect objects from 0-inches to 254-inches (6.45 meters) and provides sonar range information from 6inches out to 254-inches with 1-inch resolution. the interface output formats included are pulse width output, analog voltage output and serial digital output. e. vibrating motor the rob-08449 vibration motor (figure 7) is a tiny shaftless vibratory motor which is perfect for non-audible indicators. it can be used in different applications to indicate an event [9]. fig. 7. the rob-08449 vibration motor all moving parts are protected within the housing. with a 2-3.6v operating range, these units shake crazily at 3v. once anchored to a printed circuit board (pcb) or within a pocket, the unit vibrates softly but noticeably. this high quality unit comes with a 3m adhesive backing and reinforced connection wires. f. power source the system uses multi-voltage power sources, that provide each component with its corresponding power, i.e.:  the arduino board requires 7-12 volts.  the ultrasonic sensor requires 2.5-5.5 volts.  the emic 2 playback circuit requires 5volts.  the vibrating motor requires 3 volts. fig. 8. installation of the power source and the connections iii. system operation in detail the ultrasound sensor has three wires connected to it, one for the +5 volts in red color that power the sensor, a black wire connecting the gnd pin to common ground, and a white wire connecting the sensor to the input of the arduino. this white wire is connected to the pw pin of the lv-ez1 ultrasound sensor. this pin is responsible for sending a pulse with an amplitude of +5 volts to the input of the microcontroller, which is picked up by the input pin of the arduino as a logic 1. the arduino is programmed in such a way that once a logic 1 is received, the two outputs that are connected to the emic2 and the vibrating motor are also set to logic 1. this activates the emic2 and also provides power to the vibrating motor. the emic2 receives the logic 1 via the “sin” pin which is the pin responsible for receiving an input signal that will activate the verbal message. the verbal message will be played via the headset which will be connected to the jack connector. during the programming of the emic2, a suitable was input in the code, and the written text will be played as voice. meanwhile, the vibrating motor will be switched on, powered by the logic 1 given by the arduino. this process is repeated each time an obstacle is detected by the ultrasound sensor. noting that the outputs will remain switched on as long as the obstacle is present. figure 9 shows the practical connection between the different circuitry. this hands-free obstacle detection and avoidance system was set and tested to work in a range of approximately 1.5 meters. on the box, next to the onoff switch, there is a potentiometer that controls the sensor’s range. the maximum range of the sensor is 10 meters. engineering, technology & applied science research vol. 5, no. 3, 2015, 801-804 804 www.etasr.com abdul-niby et al.: a hands-free obstacle detection and avoidance system fig. 9. practical connection between the different circuitry iv. conclusion and future work the obstacle detection described in this paper provides a low cost, easy to use flexible system that can be used to aid the movement of the visually impaired. the main idea behind the system is to use an ultrasound detection system in collaboration with a voice notification system. several improvements that where added to the main idea such as the vibration notification, the adjustable range of the detector and the use of a text-tospeech module underline the flexibility of the approach. the main advantages of the system is the simplicity of the design, and thus its low-cost and upgrade possibilities, the ease of operation and hands free capability. its main weaknesses currently are that it was not designed for a rechargeable power source and that it is not weather proof. further improvement can be employed:  adding a rechargeable power source.  adding more than one ultrasound sensor that can be placed at different heights of the human body to secure and cover a wider range of angles and different directions.  adding guidance, such that the system informs the user if the object is on the left side, right side, lower level and/or higher level.  reduce the size and weight of the device by building the different circuits on a single printed circuit board and using a small sized casing made of low weight material. appendix references [1] d. pascolini, s. p. mariotti, “global estimates of visual impairment: 2010”, british journal of ophthalmology, vol. 96, no. 5, pp. 614-618, 2012 [2] http://www.ultracane.com/about_the_ultracane [3] http://psychologydictionary.org/mowat-sensor [4] http://www.techopedia.com/ definition/16446/state-diagram [5] ultrasonic transducers technical notes, olympus, 2006 (available at: www.olympus-ims.com/data/file/panametrics/ut-technotes.en.pdf) [6] http://arduino.cc/en/main/arduinoboarduno [7] emic 2 text-to-speech module (#30016), parallax inc, 2012 (available through: mouser electronics website http://www.mouser. com/ds/2/321/30016-emic2texttospeech-v1.1-27211.pdf) [8] lv-ez1maxbotixultrasonic, rangefinder, http://www.adafruit.com/ products/172 [9] sparkfun.com. 2009. vibration motor-rob-08449-sparkfun electronics (available at: https://www.sparkfun.com/ products/8449) microsoft word etasr_v13_n1_pp10067-10072 engineering, technology & applied science research vol. 13, no. 1, 2023, 10067-10072 10067 www.etasr.com rahu et al.: assessment of the flexural strength of no-fines recycled aggregate concrete prisms assessment of the flexural strength of nofines recycled aggregate concrete prisms ihsan ali rahu department of civil engineering, quaid-e awam university of engineering, science & technology, pakistan ihsanali0999@gmail.com bashir ahmed memon department of civil engineering, quaid-e-awam university of engineering, science & technology, pakistan bashir_m@hotmail.com mahboob oad department of civil engineering, quaid-e-awam university of engineering, science & technology, pakistan engrmahboob04@gmail.com (corresponding author) shakeel ahmed dahri department of civil engineering, quaid-e-awam university of engineering, science & technology, pakistan engr.shakeelahmed9@gmail.com abdul raqeeb memon department of structural engineering, faculty of engineering, conventry university, uk raqeeba2@uni.conventry.ac.uk amjad hussain bhutto department of civil engineering, quaid-e-awam university of engineering, science and technology, pakistan amjad.bhutto62@gmail.com received: 2 november 2022 | revised: 25 november 2022 | accepted: 28 november 2022 abstract this study investigated experimentally the flexural strength of no-fines recycled aggregate concrete, produced using 20-70% replacement of conventional coarse aggregates with coarse aggregates from demolished waste. six prisms in each dosage with a 1:4 mix and 0.5 water-binder ratios were prepared. a batch of prisms with conventional aggregates was also cast to compare them with the proposed concrete. an equal number of samples were cured for 7 and 28 days and tested under a gradually increasing central point load to examine failure load, central deflection, and flexural strength. the comparison of results showed an increasing trend in deflection with an increase in the dosage of recycled aggregates. the 7-day cured samples had approximately 2.6 times the deflection of conventional concrete. however, the deflection at all replacement levels remained less than that allowed by aci-318. the results showed a decreasing trend in flexural strength with an increase in the dosage of recycled aggregates. the 40% replacement sample had a less than 20% strength reduction and is recommended as the optimum level of replacement of conventional aggregates for the production of no-fines recycled aggregate concrete. keywords-flexural strength; no-fines recycled aggregate concrete; demolishing waste engineering, technology & applied science research vol. 13, no. 1, 2023, 10067-10072 10068 www.etasr.com rahu et al.: assessment of the flexural strength of no-fines recycled aggregate concrete prisms i. introduction the construction industry has used a variety of materials to build safe and reliable infrastructures and meet the needs of inhabitants and trends of society. as concrete is currently the most widely used material in the construction industry due to its versatility and durability, the rapid construction development brings a burden on its natural resources. in parallel, changes in infrastructure lead to a drastic increase in demolitions and, consequently, waste generation. in previous decades, landfills were commonly available to accommodate this waste, but nowadays the lack of space around city centers, aesthetics, and environmental policies complicates the management of such waste. furthermore, this waste cannot be dumped in or around cultivated lands, as it would cause serious impacts on the agricultural sector and the economy of the area in general. most demolishing waste is used in floors, plinth protection, or similar filling sections but still, the residual waste raises worries. a possible solution could be the reuse of concrete waste material in new concrete to produce an indigenous green product. however, there is a need to investigate better the behavior of waste materials and their effects on the fresh and hardened properties of concrete, although several studies attempted to examine the use of demolishing waste in new concrete [1]. concrete is used in a variety of forms in modern infrastructures. low-strength concrete, such as no-fines concrete, is commonly used in non-structural members, such as in partition walls in place of bricks or pavements for better drainage. however, it may also be used for other types of structures in non-structural members or low-load areas. this study investigated the use of demolition waste as coarse aggregates to produce no-fines recycled aggregate concrete and examined its flexural strength. ii. literature review the use of recycled aggregates is an globally active research field. a summary of the most recent developments was presented in [1], discussing processes, issues, and effects on the hardened product, and proposing a few recommendations for its smooth and confident use in the industry. in [2], demolition waste was used as low-grade coarse aggregates, while authors in [3] concluded that better concrete properties can be achieved if the source of the recycled aggregates is high-strength concrete. in [4], an investigation on the use of high-strength recycled concrete did not show an effect of the replacement percentage on the slump flow of the resulting concrete but about a 10% reduction in compressive, split tensile, and flexural strengths. in [5], a 5% reduction in split tensile strength was observed at equal replacement of conventional coarse with recycled aggregates. in [6], the properties of concrete from demolished waste were investigated in fresh and hardened states, along with its longterm effects. it is obvious that there is a wide scatter of results of the relevant studies. in parallel to modifications in the normal concrete matrix for better performance, several studies investigated the development of no-fines concrete. no-fines concrete was initially developed for road pavement in areas of low traffic volumes, as its main features are good drainage of surface water or recharge of the groundwater table. its initial development and progress were reviewed in [7]. several studies examined the mechanical properties of no-fines concrete for road pavement, highlighting its efficiency in lowvolume traffic areas [8-12]. the compressive strength of nofines concrete for road pavement was evaluated in [13], finding that although its strength was lower compared to conventional concrete, it was suitable for low-traffic pavements. normally, single-sized coarse aggregates are used in the development of no-fines concrete. in contrast, graded aggregates were used in [14] to develop no-fines concrete and study its compressive strength, finding that 10-20mm was the most suitable grading as it showed a compressive strength equal to 15.7mpa. different additives such as silica fume [15], limestone dust [16], fly ash [17-18], ground granulated blast furnace slag [18], etc., have also been used to improve the performance of nofines concrete. the use of additives improved the performance of the no-fines concrete but it is still not as that of the conventional concrete. therefore, additional research is required to improve its properties and performance. improvement in the performance of no-fines concrete has also been attempted using very small quantities of fines in concrete, showing improvement in strength but a reduction in its permeability characteristics, which, in some cases, is the main requirement [19]. other studies attempted to improve no-fines concrete using uncrushed aggregates [20], fly ash with admixtures [21], different mixtures and water-binder ratios [22], ggbs [23], etc. not only compressive strength is important, but also flexural strength. therefore, a variation of fly ash and plasticizer was used in [24] to study the flexural strength of nofines concrete, designing 5 different mixes, and concluding that 60% fly ash with 0.5% plasticizer and 0.17 water-binder ratio was optimum for producing equal or more flexural strength than conventional concrete. furthermore, it was noted that extreme care should be taken in dose decisions, as higher doses of plasticizer can increase slump and reduce flexural strength. in [25], 1:2 and 1:3 mixes were used to develop no-fines concrete and study its compressive, tensile, and flexural strengths, concluding that 12.5mm was the most suitable size for coarse aggregates, the 1:2 mix was better than the 1:3, and observing a 23% reduction in flexural strength in comparison to the conventional. in [26], 30% less flexural strength was observed in no-fines concrete. the development of green concrete was also attempted using plastic waste and nano-silica [27], recycled binder concrete [28], and sugarcane bagasse ash and limestone fines [29]. green concrete made with rca was also studied in [30] for strain and displacement under sustained loading of 12 months, showing only a 10.34% deviation from the control concrete. despite the scattering in the results, it is evident that many research efforts focus on improving no-fines concrete, but it is also evident that few studies focus on the use of recycled aggregates in the production of no-fines concrete. this study aimed to investigate varying percentages of recycled aggregates in the production of no-fines concrete, study its flexural strength, and provide a good insight into its use. engineering, technology & applied science research vol. 13, no. 1, 2023, 10067-10072 10069 www.etasr.com rahu et al.: assessment of the flexural strength of no-fines recycled aggregate concrete prisms iii. materials and methods demolition waste was collected from slab debris from a two-story building to prepare no-fines concrete. large pieces of concrete, as shown in figure 1, were hammered manually to produce coarse aggregates of 25mm maximum size. conventional coarse aggregates from nooriabad hills and fine aggregates from bolhari hills were obtained from the local market. conventional and demolished coarse aggregates were cleaned and washed, as shown in figure 2, and sieved to ensure their quality. figure 3 shows the gradation curve of both aggregate types, and it can be observed that the trend of both curves and the ranges on various sieves fall in the specified ranges of astm c-136 [31]. fig. 1. demolishing waste. fig. 2. aggregates. fig. 3. sieve analysis of coarse aggregates. table i shows the basic properties of both conventional and recycled aggregates. table i. properties of aggregates description ca ra water absorption 1.14 2.51 specific gravity 2.61 2.65 fineness modulus 6.2 6.43 surface texture fairly smooth rough appearance angular angular iv. results and discussion after curing, the samples were tested on a universal testing machine (utm) under a central point load following the provisions of astm c-293 [32], as shown in figure 5. the samples were carefully monitored during testing, and the crushing load and central deflection were recorded at failure. the average of the observations in each batch and curing age were calculated. flexural strength was evaluated using the standard formula: �� � ��� �� (1) where the σf is flexural strength, p is failure load, l is length, and bd is the cross-section of the prism. tables ii and iii show the average values of load, deflection, and flexural strength for 7and 28-days cured specimens, respectively. fig. 4. prism specimens. fig. 5. testing of specimens. table ii. average load, deflection, and flexural strength of 7-day cured specimens concrete load (kn) deflection (mm) flexural strength (mpa) conventional concrete 3.87 0.7 2.90 concrete with 20% rca 3.51 0.9 2.63 concrete with 30% rca 3.11 1.1 2.34 concrete with 40% rca 2.98 1.3 2.23 concrete with 50% rca 2.65 1.5 1.99 concrete with 60% rca 2.07 1.6 1.55 concrete with 70% rca 1.95 1.8 1.46 engineering, technology & applied science research vol. 13, no. 1, 2023, 10067-10072 10070 www.etasr.com rahu et al.: assessment of the flexural strength of no-fines recycled aggregate concrete prisms table iii. average load, deflection, and flexural strength of 28-day cured specimens concrete load (kn) deflection (mm) flexural strength (mpa) conventional concrete 4.42 0.6 3.31 concrete with 20% rca 4.12 0.7 3.09 concrete with 30% rca 3.81 0.9 2.85 concrete with 40% rca 3.66 1.1 2.74 concrete with 50% rca 3.15 1.2 2.36 concrete with 60% rca 2.60 1.4 1.95 concrete with 70% rca 2.36 1.5 1.77 figures 6 and 7 show a comparison of the average flexural strength for the 7and 28-days cured samples of the proposed with the conventional no-fines concrete. the average flexural strength of the no-fines conventional concrete was recorded at 2.9mpa for 7and 3.31mpa for 28-day cured samples, 71% and 62% higher than in [21]. the recycled concrete samples achieved 2.63mpa to 1.46mpa from 20% to 70% replacement of conventional coarse aggregates, which were better for up to 40% replacement than in [21]. on the other hand, for 28-day cured samples up to 50% replacement, the results were higher than in [21]. similarly to the 7-day cured samples, they showed a decreasing trend in flexural strength with increasing recycled aggregates. the maximum strength (3.31mpa) was observed at 20% replacement, while the minimum (1.77mpa) was recorded for the maximum replacement. table iv shows the percentile difference in flexural strength of no-fines recycled aggregate concrete concerning the conventional. the reduction in strength is mainly attributed to the attached mortar, the age, and the exposure of the old concrete. fig. 6. average flexural strength (7-day curing). fig. 7. average flexural strength (28-day curing). figures 8 and 9 show a comparison of the average central point deflection at failure load in all prisms to no-fines conventional concrete. an increasing pattern in deflection with increasing the replacement of coarse aggregates is recorded. the maximum deflection was 1.8mm and 1.5mm for the 7and 28-day cured specimens, respectively. table iv also lists the percentile difference in deflection for both curing ages of the proposed concrete specimens. the maximum deflection was about 2.5 times the deflection of the conventional 7-day cured no-fines concrete samples. it is also noted that all deflection values are within the allowable limits of aci-318 [33] for simply supported beams. fig. 8. average deflection (7-day curing). fig. 9. average deflection (28-day curing). table iv. percentile difference of flexural strength and deflection concrete mix 7-day curing 28-day curing deflection fs deflection fs conventional concrete ---- concrete with 20% rca 23.81 -9.22 18.92 -6.81 concrete with 30% rca 61.90 -19.45 45.95 -13.81 concrete with 40% rca 90.48 -22.99 78.38 -17.18 concrete with 50% rca 109.52 -31.42 89.19 -28.74 concrete with 60% rca 133.33 -46.58 132.43 -41.11 concrete with 70% rca 157.14 -49.61 148.65 -46.55 the observed failure mode of the beams was flexural failure, as shown in figure 10. as plain concrete prisms were used in this study, flexural failure confirmed the concrete failure mode. hence, it was concluded that recycled aggregates from demolished waste are suitable for producing no-fines concrete. however, considering the flexural strength and its loss (about 7%) compared to conventional no-fines concrete, the 20% replacement was considered as optimal. engineering, technology & applied science research vol. 13, no. 1, 2023, 10067-10072 10071 www.etasr.com rahu et al.: assessment of the flexural strength of no-fines recycled aggregate concrete prisms fig. 10. failure mode. v. conclusion based on the experimental investigation on the flexural strength of no-fines recycled aggregate concrete, the following can be concluded:  the flexural strength of no-fines recycled aggregate concrete decreases with increasing replacement level of coarse aggregates.  central point deflection increases with increasing replacement level of coarse aggregates.  the 20% replacement specimens, cured for 28 days, had maximum residual strength.  all recorded deflections for both 7and 28-day cured samples were less than the allowable deflection for simply supported beams as per aci-318.  all prisms failed in flexure mode at the center. therefore, it can be concluded that demolished waste may be used as recycled aggregates in no-fines concrete with 20% as the optimum replacement level for conventional aggregates. references [1] b. a. memon and a. h. buller, "recent development on use of demolished concrete as coarse aggregates," international journal of emerging technology and innovative engineering, vol. 2, no. 1, pp. 1– 11, 2016. 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[33] "building code requirements for structural concrete (aci 318-05) and commentary (aci 318r-05)," american concrete institute, farmington hills, mi, usa, aci 318-05, 2005. microsoft word etasr_v13_n1_pp10181-10185 engineering, technology & applied science research vol. 13, no. 1, 2023, 10181-10185 10181 www.etasr.com le: evaluation of confining pressure models for circular concrete-filled steel tube short columns … evaluation of confining pressure models for circular concrete-filled steel tube short columns under concentric loading hoang an le ho chi minh city university of transport, vietnam hoangan.le@ut.edu.vn (corresponding author) received: 5 december 2022 | revised: 2 january 2023 | accepted: 5 january 2023 abstract it is well known that the confinement effect provided by the steel tube significantly increases the strength and ductility of circular concrete filled steel tube (cfst) columns under concentric loading. the lateral pressure is an important factor to calculate the strength enhancement of cfst columns. to reliably predict the ultimate strength of circular cfst columns, many models have been developed for predicting the lateral pressure due to the confinement effect. this paper aims to evaluate some of these confining pressure models. the values of the compressive strength of confined concrete and lateral confining pressure of circular cfst short columns were calculated using these existing models and were compared with those obtained from previous test results. in addition, a comparison between the ultimate loads predicted by these models and by eurocode 4 (ec4) was carried out. based on the comparison results, some suitable models for circular cfst short columns with the use of normal-strength, high-strength, and ultra-high-strength concrete were indicated. keywords-concrete filled steel tube columns; confinement effect; strength enhancement; steel tube; confining pressure i. introduction the composite action between the steel tubes and the concrete core leads to the strength enhancement of concrete filled steel tube (cfst) columns [1, 19]. the steel tube provides confining pressure to the concrete core and shares the axial load, which puts the concrete core under a triaxial state of stress while the steel tube is stressed biaxially [1-3]. in addition, the steel tube is more stiffened by the concrete core. the inward buckling of the steel tube is prevented by the concrete core, thus leading to an increase in the stability as well as the strength of the column [4]. circular cfst columns exhibit better gain of load capacity due to the effectiveness of the confinement effect as compared with square or rectangular cfst columns [1]. therefore, the circular cfst columns are recommended to be used in practice to obtain better strength and ductility [19-21]. to calculate the ultimate strength of circular cfst columns, the lateral pressure induced by the steel tube on the concrete core should be accurately estimated. because the measurement of lateral pressure in the real test is very complicated, many researchers have proposed models to predict the lateral pressure. authors in [3] tried to find the stress-strain relationship and the ultimate strength of concrete inside cfst columns with considering the poisson’s ratios. the lateral confining pressure of the steel tube on the concrete was calculated at the point that the steel is in the plastic range and the concrete core is completely crushed. authors in [15] proposed a confining pressure model for concrete in cfst columns by taking into account the effect of geometry and material properties on the strength enhancement and post-peak behavior. authors in [3] modified the models in [4, 5] for cfst columns. authors in [6] developed a uniaxial stressstrain relationship for concrete confined by various shaped steel tubes. in [1], the efficiency of the steel tube in confining the concrete core was examined by investigating the effects of concrete strength and steel tube thickness. authors in [7] also developed a confining pressure model for concrete in circular, square, and octagonal cfst columns by employing the nonlinear finite element method in abaqus. authors in [8] suggested a model to calculate the ultimate strength of the concrete core in cfst columns depending on the hoop stress of steel tube at yield condition. authors in [9] proposed models for predict the ultimate load of circular cfst under extreme loading conditions with the use a new empirical equation for estimate the hoop stress of the steel tube. authors in [10] proposed an accurate model for confined concrete and a new design formula for determining the ultimate axial loads of cfst columns using normal strength concrete (nsc) and high strength concrete (hsc). authors in [11] presented a full elasto-plastic model and a simplified model for cfst stub columns with concrete strength ranging from 30 to 120mpa and diameter-to-wall thickness (d/t) greater than 20. all collected models have been mainly developed for nsc and engineering, technology & applied science research vol. 13, no. 1, 2023, 10181-10185 10182 www.etasr.com le: evaluation of confining pressure models for circular concrete-filled steel tube short columns … hsc filled in steel tubes. nevertheless, the application of these models for ultra-high strength concrete (uhsc) is still questionable. therefore, there is a need to investigate the suitability of these models for circular cfst short columns with various concrete strengths, i.e. nsc, hsc, and uhsc. based on the aforementioned issues, this paper aims to evaluate the existing models [1, 2, 6, 8-11] through the comparison between the predictions and the test results. the ultimate loads and lateral confining pressures of circular cfst columns under the concentric compression on the entire section from some previous experimental tests were calculated using the equations of the existing models. furthermore, the prediction of ultimate loads from eurocode 4 (ec4) was also compared with the predictions obtained from the existing models. the findings of this paper indicate suitable models for the estimation of the ultimate load and confining pressure of circular cfst short columns. ii. confining pressure models and test database the considered confining pressure models for circular cfst short columns [1, 2, 6, 8-11] were collected and are shown in table i. these models were used for the prediction of confining pressure and ultimate load of the previous tests. table i. expressions of confining pressure models for circular cfst short columns model expression explanation [6] ν�� = �.����� . �� � − �.����� . �� � + �.������ . �� + 0.4011 ν� = 0.2312 + 0.3528. ν�� − 0.1524. ���� ! + 4.843. ν�� . ���� ! − 9.169. ���� ! � ; β = ν� − ν%; f'( = β ���)�� f* ; f�� = f� + 4. f'(; n, = a�. f�� + a/. f* ν�� : empirical factor. ν%: poisson ratio of a steel tube, taken equal to 0.5. f'(: lateral pressure at the peak load. f��: confined compressive strength of concrete. n,: axial capacity of cfst column. [9] σ2 = f*. exp 6ln �� + ln9f*: − 11; . f* ; f'( = ���)�� σ2; f��� = f�� + k�. f'( f* = 0.5. �σ2 − =4. f*� − 3. σ2� ! ; >? = a�. f�� + a/. f* σ2: hoop stress of the steel. f*: yield strength of steel. [1] ν/ = 0.3, ν� = 0.2, εb = 0.002 ; ε/2' = cd.(fg)f�)6�i �.j.kg(lm�.j).k�; ε/2 = −ν/. εb + ε/2' ;σ2 = ng�)fg� . (ε/2 + ν/. ε/o); σ/o = ng�)fg� . (εb + ν/ . ε/2) ; σo/� = σ/2. �.��)�.�;k = 1.25. 1 + 0.062. qrgj��j . f�)�.��. f� f�� = f�. qrgj��j + 1 s ; >, = a� . f�� + a/ . σ/o ν/, ν� , εb : initial considered values. ε/2': restrained steel strain. ε/2: final lateral strain of steel. σ/o: steel’s longitudinal stress. σo/�: compressive confining pressure. k: reflects the effectiveness of confinement. f��: tensile strength of concrete. [11] f�� = f� + 3.4. σ',� ; qt,��� = ∅(s)�)v�i�(s)�)� ; fx/ = f�. a�(1 + s∅� ) σ',�: confining pressure around the concrete. ∅: confinement index, =�y.zy��.z� k=3 ÷ 4.3 [8] σ��\ = γ^. f�� + 4.1. σ' ; γ^ = 1.67d�)�.��� ; σ' = )���)�� σ%a σ%a = α,. σ%* with α, = −0.19 σ%c = β,� . σ%* with β,� = 0.89 n, = (a�. σ��\ + a%. σ%c) σ��\: strength of confined concrete. γ,: strength reduction factor for concrete. σ' : lateral pressure. σ%a: hoop stress of steel tube in yield condition. σ%*: tensile yield stress of steel tube. σ%c: axial yield stress of steel tube. [10] f��� = γ�. f�� + k�. f'( f'( = d 0.7(νe − ν% ) ���)�� f%* for �� ≤ 47 0.006241 − 0.0000357 �� f%* for 47 ≤ �� ≤ 150 νe = 0.2312 + 0.3528. νe� − 0.1524. f��f%* + 4.843. ν�� . f� � f%* − 9.169. i f� � f%*j � νe� = 0.88110k . �lm ! � − 2.5810n . �lm ! � + 1.95310� . �lm ! + 0.4011 γ� = 1.85d�)�.��� for (0.85 ≤ γ� ≤ 1.0) ; γ% = 1.458 �� )�.� for (0.9 ≤ γ% ≤ 1.1) n, = 9γ�f�� + 4.1. f'(:a� + γ% f%*a% f��� : strength of confined concrete. f'( : lateral pressure. γ�: strength reduction factor for concrete. γ%: strength factor for steel tube. fop : tensile yield strength of steel. νe� : empirical factor. νe : poisson ratio of a steel tube filled with concrete [3] p� = − q� �rsi�t�(rs�irsi�uv� f* ; μ� = − �� − ��(xi�) ; ξ = α � �� α = zyz� ; n, = n� + n% ; n% = rsi�t�(rs�irsi�uv� f*a% n� = (f� + 4p�)a� p�: lateral confining pressure of the steel tube on concrete. n�: sectional strength of concrete core. n%: sectional strength of steel tube. a total of 178 circular cfst columns were chosen for the calculation. these columns were tested under concentric compression on the entire section. dimensions and material properties of the selected columns are summarized in tables ii and iii. the main dimensions of the columns are described by the outer diameter (d), the thickness of steel tube (t), and the length of the columns (l). the material properties include the unconfined concrete strength (fc) and the yield strength of the steel tube (fy). the selected columns were divided into 2 groups: (1) group 1 includes cfst short columns with nsc (fc ≤ 60mpa), (2) group 2 includes cfst short columns with hsc (60mpa < fc ≤ 120mpa) and uhsc (fc > 120mpa). the test database covers a wide range of concrete strengths. engineering, technology & applied science research vol. 13, no. 1, 2023, 10181-10185 10183 www.etasr.com le: evaluation of confining pressure models for circular concrete-filled steel tube short columns … table ii. test database of circular cfst columns using nsc (group 1) tested by d (mm) t (mm) l (mm) fc (mpa) fy (mpa) [13], 18 specimens 76.4-152.6 1.68-4.09 152.3-304.9 20.9-40.9 363.3-451.6 [14], 26 specimens 101.0-318.5 3.03-10.37 305-955 23.2-52.2 371-452 [15], 42 specimens 76.5-300 1.5-4.5 276-1000 20.54-45.77 232.3-433.2 table iii. test database of circular cfst columns using hsc and uhsc (group 2) tested by d (mm) t (mm) l (mm) fc (mpa) fy (mpa) [15], 18 specimens 108-133 1.0-7.0 378-465 106-116 232-429 [16], 26 specimens 60-250 1.87-2.0 180-750 85.2-90.0 282-404 [17], 21 specimens 101.6-139.8 2.37-3.0 304.8-419.4 62.4-135.6 341-462.6 [18], 27 specimens 149-165 1.0-6.0 500 87.1-91.8 338-438 the models proposed in [1, 2, 6, 8-11] were used to predict the axial capacity and lateral confining pressure of circular cfst columns. however, the model of [6] is only applicable for fc/fy ranging from 0.04 to 0.2. the columns with hsc and uhsc have fc/fy > 0.2, thus the model of [6] was not further considered. for the assessment of the accuracy of the prediction, two statistical indicators were determined, the mean square error (mse) and the average absolute error (aae): mse = ∑ �~t��m��~���~� ! ��v � (1) aae � ∑ �~t��m��~���~� � �v � (2) where prei represents values of ultimate load from model predictions, expi represents the values of ultimate load from the experimental results, and n is the total number of test data. the confinement ratio ø is defined by: ∅ � zy.� z�.�� (3) where as is the area of steel section, while ac is the area of concrete section. iii. results and discussion the relation between the ratios fcc/fc and fl/fc, where fl is the lateral confining pressure and fcc is the confined concrete strength, is shown in figure 1. it can be seen that all the models describe a quite similar trend. this relation can be represented by a linear equation. as the ratio fl/fc increases, the ratio fcc/fc also increases considerably in the case of group 1 while the increment of fcc/fc is slighter in the case of group 2, due to the higher confinement when employing nsc for cfst columns. it could be observed that in group 1, the models of [6, 8, 9] exhibit the same predicting value of fcc/fc at a given value of fl/fc, whereas the scatter plots of the other models show a different tendency. furthermore, in group 2, the models suggested by [2, 8-11] are rather close to each other, while the model of [1] gives an unlikely trend. figure 2 illustrates the predicted value of confining pressure fl versus the confinement ratio ø. (a) (b) fig. 1. comparison of models in prediction of fcc/fc and fl/fc. (a) (b) fig. 2. comparison of models in prediction of confining pressure fl. overall, the graph indicates the variation of confining pressure fl corresponding to each model. it can be seen that when the confinement ratio increases, the confinement pressure shows an upward trend. the models of [1, 11] exhibited a very low value of confining pressure in comparison with the other models, while the models of [6, 9] presented the highest values. it is evident from the data that the confining pressure predicted from [10] was very close to [2] in the case of group 1. moreover, the model of [2] gives higher values of fl in the case fcc/fc fcc/fc fl/fc fl/fc fl (mpa) fl (mpa) engineering, technology & applied science research vol. 13, no. 1, 2023, 10181-10185 10184 www.etasr.com le: evaluation of confining pressure models for circular concrete-filled steel tube short columns … of group 2. it is apparent from the scatter plot that the confinement ratio ø has no correlation with the confining pressure. the above results can be explained by the fact that except for the model of [10], all models consider high confining pressure of steel tube in circular cfst stub columns. however, the confining pressure of steel tube decreases with increasing concrete strength. figure 3 shows the comparison of ultimate load between model predictions (npre) and ec4 [12] predictions (nec4). in order to better reflect the deviations of prediction as compared to experimental results and ec4 [12], the -10% and +10% error bounds depicted in the figure are presented in the following sub-sections. it has been demonstrated in group 1 that the predictions from [8-10] are quite close to those from ec4 [12] (around 10%), while the models from [2, 11] give less accurate values (about 20% higher and 20% lower on average, respectively). at the same time, the predictions by [1, 6] have varying values. interestingly, it could be observed in group 2 that almost all models except the one of [11] have very close values (within 10%) to the ones of [12]. the agreement of ec4 and the predicted models is generally good. it should be noted that ec4 is applicable with concrete strength up to 70mpa. therefore, the prediction by ec4 is less accurate for the circular cfst columns having concrete strength higher than 70mpa. (a) (b) fig. 3. comparison of ultimate loads between the model predictions and ec4 [12]. the comparison between the ultimate strength from the real tests (ntest) and the calculated strength from the models (npre) is illustrated in figure 4. regarding group 1, the predictions of [6, 9, 10] give a quite good correlation with the test data (around 10%), whereas the models from [2, 11] exhibit large differences between the experimental and the predicted values. in addition, all models except the ones from [6, 11] generally tend to underestimate the strength of cfst columns when the test strength increases. figure 4 clearly indicates that almost all models show a large variability in individual prediction. however, the models from [8, 10] give a better precision than the other models in estimating the ultimate strength. on the other hand, the models from [1, 9, 11] overestimate these values. the models from [8, 10] use the strength reduction factor for concrete depending on the outer diameter of the concrete core. therefore, these models give ultimate load prediction smaller than the other models. (a) (b) fig. 4. comparison of ultimate loads between the model predictions and the test results. (a) (b) fig. 5. comparison of statistical indicators aae and mse. based on the two statistical indicators, aae and mse, shown in figure 5 for the cfst stub columns employing nsc, the models from [1, 6] provide the best prediction of ultimate engineering, technology & applied science research vol. 13, no. 1, 2023, 10181-10185 10185 www.etasr.com le: evaluation of confining pressure models for circular concrete-filled steel tube short columns … strength because they have the smallest error (just under 9%), followed by the model from [10] with error around 10%. the models proposed in [8, 9, 11] show a good prediction, with error greater than 10%. conversely, the error of the model from [2] is larger, thus this model should not be used for estimating the ultimate strength of nsc filled in steel tube stub columns. regarding group 2, figure 5 shows that the models from [8, 10] give the smallest error. the errors in the prediction of ultimate strength in cfst columns using hsc and uhsc are much larger than those in cfst columns using nsc. this may partly be caused by the less effective confinement of cfst columns using higher strength concrete core, while almost all existing models consider the passive confinement in calculating the confined strength of concrete core. iv. conclusion in this paper, models for predicting the lateral confining pressure of circular cfst short columns were considered and used for the calculation of the lateral stress and ultimate load of the tested columns. the main conclusions derived from the findings of this paper are:  almost all models give more accurate predictions for circular cfst short columns using nsc than hsc and uhsc.  the prediction is less accurate with increasing concrete strength.  there are significant differences among the models in lateral stress prediction.  the models suggested in [8, 10] are suitable for predicting the ultimate strength of cfst columns with hsc and uhsc.  the models of [1, 6] give accurate prediction of the ultimate strength for cfst columns using nsc.  the ultimate load prediction obtained by the model of [11] is close to the ultimate load predicted by ec4 [12]. references [1] m. johansson, "the efficiency of passive confinement in cft columns," steel and composite structures, vol. 2, no. 5, pp. 379–396, oct. 2002, https://doi.org/10.12989/scs.2002.2.5.379. 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[21] z. h. abdulghafoor and h. a. al-baghdadi, "static and dynamic behavior of circularized reinforced concrete columns strengthened with hybrid cfrp," engineering, technology & applied science research, vol. 12, no. 5, pp. 9336–9341, oct. 2022, https://doi.org/ 10.48084/etasr.5162. microsoft word etasr_v12_n5_pp9302-9309 engineering, technology & applied science research vol. 12, no. 5, 2022, 9302-9309 9302 www.etasr.com kherfi et al.: assessment of an assumed strain-based quadrilateral membrane element assessment of an assumed strain-based quadrilateral membrane element abdelhak kherfi laboratory of development in mechanics and materials (ldmm) university of djelfa djelfa, algeria a.ak.k65@gmail.com khelifa guerraiche mechanical engineering department, faculty of technology, university of batna 2, batna, algeria nmissi laboratory, faculty of science and technology, biskra university, biskra, algeria guer.khelifa@yahoo.com kamel zouggar laboratory of mechanics of structures and solids (lmss) faculty of technology, djillali liabès university of sidi bel-abbès, sidi bel abbès, algeria zouggarkamel.zk@gmail.com received: 6 july 2022 | revised: 31 july 2022 | accepted: 4 august 2022 abstract-this paper describes the development of a simple quadrilateral strain-based element for plane stress and strain problems. this element has five nodes, four located at its corners and one at the center. each of the four corner nodes had two essential external degrees of freedom (u, v), while the center node had three degrees of freedom (u, v, ɵ); the static condensation method was used for the internal node. this element was used for both linear and dynamic analysis. its performance was assessed using a variety of membrane and axisymmetric analysis problems. the obtained results demonstrated the good performance and accuracy of the proposed element. keywords-strain approach; drilling rotation; quadrilateral element; linear analysis; dynamic analysis; axisymmetric i. introduction numerical methods, such as finite elements, finite volumes, finite differences, and discrete element methods are powerful and efficient computational tools for solving engineering problems. however, the finite element method is the most popular because of its robust mathematical basis and applicability, which is reflected in its extensive use in various applications [1-3]. in [4], the linear (constant-strain) triangle and the bilinear rectangle were formulated, based on the displacement approach in standard elements, whereas in [5] the standard bilinear quadrilateral was produced. they have been extensively used as plane-stress, plane-strain, and axisymmetric-solid models for two-dimensional structures. however, computational experience soon showed that these elements are excessively stiff for problems where linear strain gradients dominate the response. furthermore, over-rigidity grows rapidly as the rate of aspect degrades. these behaviors are referred to as mesh distortions and bending problems. much effort has been put into improving these or creating new simple elements. some studies showed that other strategies, such as hybrid stress elements [6-8], assumed strain or enhanced assumed strain elements [9-11], quasi-conforming elements [12, 13], and generalized conforming elements [1416] provide special advantages compared to classic finite elements. the development of efficient and straightforward finite elements to analyze structures is a primary motivation for scientific research in solid mechanics. a class of elements was developed using the strain-based approach. this approach produces displacement fields enriched by higher-order terms, without the necessity of introducing non-essential degrees of freedom, hence obtaining elements with more accurate results on displacements. the resulting elements from this approach are free from shear locking and parasitic shear. the state of strains for this approach is composed of rigid body motions, constant strains, and higher-order strains. this approach was used in [17] for curved structures, and it was extended for plan elasticity [11, 18-21]. a summary of this early work was presented in [22, 23], with three-dimensional elasticity problems [24-26], plate bending [9, 27-30], and shell structures [31-34]. other studies presented the treatment of non-linear problems [31, 35-36], composite materials [37], functionally graded plates [29, 38], and fracture mechanics [39]. these elements are stable and have good efficiency, and the strain approach is very practical for the development of robust finite elements which are insensitive to common problems such as mesh sensitivity and different locking problems. this paper presents a quadrilateral element based on strain formulation. the proposed element has two degrees of freedom (u, v) at each of the corner nodes. moreover, to enrich the strain field (εx, εy, and γxy) of the element, an internal node was introduced with three degrees of freedom (u, v, θ) to improve accuracy and reduce computational effort for the analysis of the plane structure, which will be subsequently eliminated by static condensation [11, 18]. after condensation, the element becomes a simple four-node quadrilateral element. each node contains the two essential translational degrees of freedom, and hence the element is free of any parasitic and shear problems and is insensitive to mesh distortion. various numerical problems (plane elasticity, axisymmetric, and dynamics) verified the high accuracy and efficiency of the proposed element compared to other existing plane elements. corresponding author: abdelhak kherfi engineering, technology & applied science research vol. 12, no. 5, 2022, 9302-9309 9303 www.etasr.com kherfi et al.: assessment of an assumed strain-based quadrilateral membrane element ii. formulation of the developed element the proposed strain based five node (sbfn) element is quadrilateral with two degrees of freedom at each of the corner nodes, corresponding to two translations (u, v), and additional in-plane translations (u, v) associated with the rotation degree of freedom �� at the internal node, as shown in figure 1. a. case of plane elasticity the strain components relations and compatibility equation for plan elasticity are respectively given as: ⎩⎪⎨ ⎪⎧εx ∂u∂xεy ∂v∂xγxy ∂u∂y � ∂v∂x (1) ∂2εx∂y2 � ∂2εy∂x2 ∂2γxy∂x⋅∂y 0 (2) where u and v are the displacements in the x and y axes respectively, εx and εy are the normal strains, and γxy is the shear strain. the rigid body modes displacement field is determined by setting the three deformations in (1) to zero, followed by integration: �u a1-a3yv a2�a3xθ a3 (3) the following equation is used for the element's drilling degree of freedom: θ 12 �∂v∂x ∂u∂y� (4) figure 1 shows the geometry of the proposed sbfn element and the corresponding nodal displacements: fig. 1. the strain based five node element. the sbfn element has eleven independent degrees of freedom, and therefore the displacement field should contain eleven independent constants. since the three constants a1, a2, and a3 represent the displacement field of the rigid body modes, as shown in (3), the remaining eight constants a4, a5,…,a11 denote the imposed strains of the elements that are expressed as: ⎩⎨ ⎧ εx=a4+a5y+a8x+ a102 �x2+y2 � εy=a6+a7x-a9y+ a10 2 �x2+y2 � γ xy =2a11+2a10�x2-y2+y-x+xy� (5) the strain functions for the present element, given above, satisfy the compatibility equation (2). these can be written in matrix form: ε! "q$ a! (6) where [q] presents the matrix relating the strain fields to the unknown constants, given by: "q$ ⎝ ⎜⎛ 0 0 0 1 y 0 0 x 0 x22 � y22 00 0 0 0 0 1 x 0 -y x22 � y22 00 0 0 0 0 0 0 0 0 2x2�2xy-2x-2y2�2y 2⎠ ⎟⎞ (7) integrating (5) and substituting (3), the final displacement functions can be obtained: ⎩⎪⎨ ⎪⎧ u a1-a3y�a4x�a5xyy22 a7� y22 a8� �x36 � xy22 2y33 �y2� a10�a11y v a2�a3xx22 a5�a6y�a7xyy22 a9� �2x33 � yx22 -x2� y36 � a10�a11x θ a3-a5x�a7y�a10� x2�y2-y-x� (8) these can be written in matrix form as: u! "t$ a! (9) where [t] is expressed as: "t$ 2"p$"r$5 (10) and: "p$ 61 0 -y x xy 0 y 2 2 x 2 2 0 x36 � xy22 2y33 �y2 y0 1 x 0 x22 y xy 0 y22 y36 � yx22 � 2x33 -x2 x7 (11) "r$ �0 0 1 0 -x 0 y 0 0 x2-x � y2-y 0� (12) the nodal displacements and the vector coefficients {a} are related as: qe ! "c$ a! (13) where: ;q e <= u1,v1,u2,v2,u3,v4,u4,v5,u5,θ5!t (14) a! a1,a2,a3,a4,a5,a6,a7,a8,a9,a10,a11!t (15) where [c] (11×11) is the matrix that relates nodal displacements to the constants (a1 to a11) as follows: "c$ ⎝ ⎜⎜⎜ ⎛"p�x1,y1�$"p�x2,y2�$"p�x3,y3�$"p�x4,y4�$"p�x5,y5�$"r�x5,y5�$⎠ ⎟⎟⎟ ⎞ (16) from (13), the following can be obtained: a! "c$-1 qe ! (17) engineering, technology & applied science research vol. 12, no. 5, 2022, 9302-9309 9304 www.etasr.com kherfi et al.: assessment of an assumed strain-based quadrilateral membrane element by substituting (17) into (6) and (9): {u}=[p][c]-1{qe }=[n]{qe } (18) and: {ε}=[q][c]-1{qe }=[b]{qe } (19) where: [n]=[p][c]-1; [b]=[q][c]-1 (20) the stress-strain relationship is given by: {σ}=[d]{ε} (21) where [d] is the elasticity matrix given in appendix a for plane stress and plane strain, respectively. the procedures to obtain the element stiffness matrix, are: the standard weak form for static can be expressed as: d  ve δ{ε}t{σ}dv= d  ve δ{u}t{fv}dv (22) by substituting (18), (19), and (21) into (22) we get: δ{qe }t�d  ve [b]t [d][b]dv�{qe }=δ{qe }t�d  ve [n]t{fv}dv� (23) where: [ke ]=�d  ve [b]t [d][b]dv� (24) [ke ]=t.[c]-t�dd [q]t⋅[d]⋅[q]dxdy�[c]-1 (25) where t is the thickness: [ke ]=t.[c]-t[k0][c]-1 (26) [k0 ]=dd [q]t ⋅[d]⋅[q]dxdy (27) using numerical integration: [k0 ]= d  1-1 d  1-1 [q]t[d][q]det|j|dξdη (28) where j presents the jacobean. the element nodal body forces vector is: {fb}= d  ve [n]t {fv}dv=[c]-t�d  ve [p]t{fv}dv� (29) after assembly over all elements, the global stiffness [k] is used in global equations for static, given as: [k]{q}=[f] (30) b. case of axisymmetric formulation the strain components in the case of axisymmetric formulation are given as: ⎩⎪ ⎨ ⎪⎧ εr= ∂u∂r εz= ∂v∂z γrz= ∂u∂z + ∂v∂r εθ= ur (31) and the element stiffness matrix in the axisymmetric case is: [ku ] = �d  vw [b]x[d][b]r. dv� (32) where r is the radial coordinate, and [d] is the axisymmetric elasticity matrix given in the appendix. it is worth noting here that the integrals calculations in the used programs use the gauss numerical integration. in the case of forced vibration, the complex response method is used [48]. iii. numerical validation several tests were selected to evaluate the accuracy of the element with different analyses such as plane strain, plane stress, axisymmetric, and dynamic. a comparative study was conducted between the proposed and the following elements: table i. elements used in the comparative study sbqm [19] 5-node quadrilateral element with in-plane rotation based on the strain approach. q4 standard four-node quadrilateral element. q8 standard eight-node quadrilateral element. q6 [20] quadrilateral element with six nodes. frq [10] 4-node quadrilateral element based on the "plane fiber rotation" concept. q4wt [21] quadrilateral element with four nodes with incompatible modes. q4ps [21] 4-node quadrilateral hybrid element. cps8 [19] classic 8-node quadrilateral element in-plane stress with exact integration (abaqus). sbrieir [40] element with strain field at four nodes with in-plane rotation. q4cst [20] the constant strain quadrilateral. qm5 [20] plane stress element and verbeke plate element boundary element formulation. sbq5 [41] strain-based quadrilateral element with five nodes. sbe [42] strain based element. cquad4 [43] msc/nastran a. linear elasticity tests 1) macneal’s beam the sensitivity of the proposed element to mesh distortion was evaluated using the macneal beam. three distinct meshes (rectangular, parallelogram, and trapezoidal) were adopted. the macneal and harder test [44] is well-known as the standard for testing the mesh distortion sensitivity. there were two loading cases under consideration: pure bending and transverse linear bending. figure 2 shows the appropriate mechanical and geometrical data, while tables ii and iii show the results obtained by the proposed versus the other elements. table ii. normalized deflection for macneal’s elongated beam subjected to end shear element force shearing at the free end p=1 mesh type rectangular (a) parallelogram (b) trapezoidal (c) sbqm [19] 0.993 0.964 0.972 q4 0.093 0.035 0.003 q8 0.951 0.919 0.854 sbe [42] 1 0.976 0.978 sbfn 0.993 0.993 0.994 reference solution [44] 0.1081 engineering, technology & applied science research vol. 12, no. 5, 2022, 9302-9309 9305 www.etasr.com kherfi et al.: assessment of an assumed strain-based quadrilateral membrane element table iii. normalized deflection for macneal’s elongated beam subjected to end pure bending element pure bending moment m=0.2 mesh type rectangular (a) parallelogram (b) trapezoidal (c) sbqm [19] 1 1 1 q4 0.093 0.031 0.022 q8 1 0.994 0.939 sbe [42] 1 0.989 0.989 sbfn 1 1 1 reference solution [44] − 0.0054 fig. 2. mcneal's cantilever beam: (a) rectangular (b) trapezoidal (c) parallelogram. low sensitivity to mesh distortion was observed for the strain-based elements sbqm, sbe, and for the standard eightnode quadrilateral element q8 for both loading cases in trapezoidal and parallelogram mesh. a neglected sensitivity in all mesh types was registered for the sbfn element, and more accuracy was observed in cases (b) and (c) compared to the other elements. however, the transverse shears locking resulting from over rigidity of the standard four-node quadrilateral element q4 affected its results. 2) beam in-plane bending the proposed element was validated in the console beam problem subjected to a uniform vertical load using [21] and [10]. the vertical displacement at the beam's free end was computed using five meshes, as shown in figure 3. timoshenko's beam theory was implemented for a reference solution: yz[\] = ^_`ab + cde^fgh (33) table iv shows the results obtained from the sbfn element for several meshes (m1, m2, m3, m4, and m5). the obtained results were compared to some other membrane element outcomes, allowing to note the following: • sbfn gave more accurate results than the q4, frq, and sbrieir elements. • similar results were noticed for q4wt, q4ps, and q8 elements for regular meshes m1, m2, and m3. • the sbfn element was more insensitive to distorted meshes than other membrane elements for m4 and m5 meshes. fig. 3. beam in-plane bending (data and meshes). table iv. vertical displacement of a beam in plane bending mesh type frq [10] q4 [21] q4wt [21] q4ps [21] q8 [21] sbrieir [19] sbqm [19] sbfn m1 2.76 0.10 3.03 3.03 3.03 2.86 3.02 3.03 m2 3.44 0.38 3.78 3.78 3.7 3.57 3.77 3.78 m3 3.56 0.75 3.92 3.92 3.84 3.71 3.91 3.91 m4 1.09 0.12 0.30 0.49 0.64 2.92 3.04 4.53 m5 1.61 0.22 1.79 1.94 1.76 3.04 3.14 4.27 reference solution [21] 4.03 3) cook's skew beam the non-prismatic beam is a popular benchmark problem for evaluating planar elements. several studies [45-57] have treated this problem. due to the lack of an analytical solution, the reference solution was obtained using the cps8 element of abaqus with a 64×64 mesh. the mechanical properties, the geometrical, and the loading data used in the treated structure are presented in figure 4. the results of the vertical deflection at point c are shown in table v. the sbfn element provided a good agreement with the reference solution, although the mesh was coarse compared to the q4, ssquad [14], cquad4 [43], sbqm [19], and cps8 [19] elements. table v. tip vertical deflection of the cook's skew beam mesh -vertical displacement at point c element 2×2 4×4 8×8 16×16 q4 11.80 18.29 22.08 23.43 ssquad [14] 25.65 24.27 24.01 23.96 cquad4 [43] 21.05 23.02 23.69 23.94 sbqm [19] 23.2173 23.4350 23.7376 23.9817 cps8 [19] 23.35 24.54 23.8793 23.8596 sbfn 23.9298 23.9282 23.9267 23.9411 reference solution [48] 23.9652 engineering, technology & applied science research vol. 12, no. 5, 2022, 9302-9309 9306 www.etasr.com kherfi et al.: assessment of an assumed strain-based quadrilateral membrane element fig. 4. cook's skew beam. b. axisymmetric elasticity test 1) simply supported circular plate uniformly loaded a simply supported circular plate under uniform load having a thickness t=1 was considered. two distinguishable meshes were used for the discretization of the plate. at first, a rectangular mesh with a distortion e=0 followed by a trapezoidal mesh with a distortion e=0.025 was applied, as shown in figure 5. the exact solution was taken from [49] as: w�r�= p⋅r04 64⋅d�1+υ� i2⋅�3υ�⋅ 21� rr0�25 -�1+υ�⋅ 21� rr0�45j (34) kwmax=w�0� wmax= p⋅r04�5+υ� 64⋅d⋅�1+υ� (35) where p and r0 are respectively the uniform load and radius of the plate, and d is the flexural rigidity expressed as: d eh312�1-2ν� (36) fig. 5. simply supported uniformly loaded circular plate. table vi. normalized vertical displacement at the center 'a' for the uniformly loaded circular plate mesh type uza element rectangular trapezoidal q4 0.696 0.694 q8 1.0079 1.0183 sbfn 0.9889 0.989 reference solution [49] −738.280 table vi shows the obtained results of displacement. it can be noted that the sbfn element gave excellent results close to the exact solution, similar to those provided by the q8 element, whereas the q4 element gave poor results. the sbfn element gave the best results for the cases where bending was dominant. 1) axisymmetric cylindrical shell a thin cylindrical shell r/e = 168 was subjected to a moment in the end [20], as shown in figure 6. this is a problem of a thin shell with axisymmetric loading where the exact solution can be found using the theory of shells in the infinite length case. a quadrilateral element through the thickness was used. the result of the theoretical solution of the shells [49] was used to compare with the numerical radial displacement for the formulated and various types of elements. the obtained results are shown in table vii and figure 7. the formulated element provided excellent results, which will be more pronounced in bending cases. fig. 6. cylindrical shell analysis. table vii. radial displacements (u) for the axisymmetric cylindrical shell radial displacements u z q4cst [19] qm5 [19] q4 [19] q6 [19] sbfn analytical solution [19] 0 39.97 98.56 46.47 100.01 100.08 100.00 3 26.04 47.87 29.17 48.98 49.01 48.88 6 14.98 13.49 15.69 14.19 14.40 14.31 9 6.56 -7.29 5.69 -6.54 -6.54 -6.57 12 0.47 -17.77 -1.31 -17.15 -17.17 -17.16 15 -3.65 -21.17 -5.82 -20.70 -20.72 -20.68 18 -6.16 -20.21 -8.35 -19.88 -19.90 -19.85 21 -7.40 -16.97 -9.39 -16.83 -16.80 -16.75 24 -7.68 -12.92 -9.33 -12.85 -12.86 -12.82 27 -7.27 -8.98 -8.55 -9.00 -9.01 -8.95 30 -6.40 -5.65 -7.32 -5.72 -5.73 -5.63 33 -5.27 -3.12 -5.87 -3.23 -3.24 -3.06 the obtained results clearly show that the q4 and q4cst elements gave very erroneous values. these elements have difficulty representing the bending phenomena. sbfn, qm5, and q6 showed very good levels of accuracy with the theoretical solution. the excellent results are remarkable for the formulated element in the case where bending is predominant. engineering, technology & applied science research vol. 12, no. 5, 2022, 9302-9309 9307 www.etasr.com kherfi et al.: assessment of an assumed strain-based quadrilateral membrane element fig. 7. radial displacements (u) for the axisymmetric cylindrical shell. c. dynamic numerical validation 1) forced vibration of a rectangular solid in-plane strain this benchmark tested the proposed element in a rectangular beam in-plane strain case to analyze forced vibrations using the complex response method. the modeled results were compared with those obtained by q8 [50] and q4, sbq5, and sbrie [41]. fig. 9. figure 8 shows the geometric components of the evaluated beam and its mechanical properties. the beam was subjected to a vertical harmonic force f=cos(ωt), where force-frequency was 0.3, time step was 1/20, the period was 2π/ω, and the ratio of depreciation was 5%. figure 9 shows the displacements for step time results. it is noticed that the proposed sbfn agreed well with the q8 element. fig. 8. geometrical and mesh presentation of the console beam subjected to forced vibration. fig. 9. displacement as a function of time for a console beam. iv. conclusion this study proposed a new quadrilateral plane element using an assumed strain approach. rigid body motions, constant strain, and application of compatibility conditions to the assumed strain field guaranteed and optimized monotonic convergence to the solution. the formulated element had five nodes with eleven degrees of freedom, whereas the fifth node of the element was located in the center having three degrees of freedom (u, v, θ). this central node was eliminated using the static condensation method. therefore, the proposed became a simple four-node element with two essential degrees of freedom (u, v) in each of the four corner nodes. the sbfn linear quadrilateral element showed acceptable performance, was insensitive to mesh distortion, and had an excellent convergence characteristic in all numerical examples. the proposed membrane element's precision was often close to that of the second-order quadrilateral plane element q8, in static and dynamic analysis for plane and axisymmetric structures. furthermore, the obtained numerical results of the proposed element were consistent and give better results when bending dominated. appendix for the case of plane stress problem, the elasticity matrix [d] is: "d$ o�pqrs� t 1 v 0v 1 00 0 pqru v (a.1) for the case of plane strain 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[50] i. m. smith, d. v. griffiths, and l. margetts, programming the finite element method. chichester, uk: john wiley & sons, 2013. microsoft word etasr_v12_n4_pp8825-8830 engineering, technology & applied science research vol. 12, no. 4, 2022, 8825-8830 8825 www.etasr.com khan et al.: an evaluation of cost optimization strategies for brt projects in pakistan an evaluation of cost optimization strategies for brt projects in pakistan farah khan afzal associates karachi, pakistan farah.iftikhark@gmail.com afzal ahmed department of urban and infrastructure ned university of engineering and technology karachi, pakistan afzalahmed@neduet.edu.pk muhammad ahmed department of urban and infrastructure ned university of engineering and technology karachi, pakistan muhammadahmed@neduet.edu.pk mirza asad ullah baig department of urban and infrastructure ned university of engineering and technology karachi, pakistan masad@neduet.edu.pk received: 29 march 2022 | revised: 13 april 2022 and 23 april 2022 | accepted: 26 april 2022 abstract-in developing countries like pakistan, economic instability, improper planning, non-optimal design, delays in construction, and unsustainability during the operations of transportation megaprojects cause an unnecessary burden on the national exchequer. recently, several bus rapid transit (brt) projects have been initiated in pakistan. the detailed evaluation of the cost and capacity of brt projects in pakistan revealed that their cost could have been optimized. this research evaluated the first brt project in karachi for potential cost optimization through proper alignment of the brt. one of the major segments of the green-line brt from surjani to nagan was evaluated, which is presently designed as an elevated section. other possible options such as curb-side, two-way side, and median alignments were explored in detail. the study showed that the cost of this section could have been reduced from the existing usd 75 million to usd 61 million by providing a twoway side aligned or curb-side aligned brt infrastructure without affecting existing capacity. this case study shows that it is necessary to critically evaluate all the possible options while planning and designing transportation megaprojects. keywords-public transport; mass transit; transportation economics; sustainable transport; brt capacity i. introduction according to the world bank, more than 50% of the world's population lives in urban areas, and it is predicted that it would increase to 68% by 2050 [1]. rapid urbanization has become one of the major global challenges, resulting in population influx and urban sprawl. urban sprawl and population growth cause an increase in travel demand and urban mobility [2, 3]. the major problems associated with the high demand for mobility are: traffic congestion, economic loss, travel time increase, fuel consumption, and air pollution [4-6]. short-term solutions to these problems include increasing the existing capacity of the road network by introducing new infrastructure facilities such as flyovers, underpasses, more lanes, and improving traffic controls. long-term solutions include changes in land-use patterns, introducing new modes into the transportation network, and increasing the share of public mass transit systems [7]. among the existing solutions, mass transport is considered one of the key solutions for the provision of high mobility and for the resolution of traffic problems by providing reliable, affordable, and sustainable means of transportation [8]. the selection of an appropriate mass transport system depends on the demands and characteristics of the city [9]. bus rapid transit (brt) is considered one of the optimal solutions due to its ability to deal with high demand at a relatively low cost compared to other mass transit solutions, such as rail transport [10]. brt was first introduced in curitiba, brazil with a 9km long corridor in 1972 [11], and is now spread at approximately 74km serving around 721,500 passengers per day [12, 13]. the transmilenio bogota brt is considered one of the most efficient systems in the world with a capacity of 49,000 passengers per hour per direction (pphpd) through 117 trunk corridors and is accessible by 107 feeder routes that serve more than 2.2 million passengers per day [12, 14-15]. the efficient brt experience in latin america has been introduced to many other countries. transport planning in megacities of many developing countries focuses on facilitating the use of private vehicles by increasing road network capacity [16]. therefore, the incorporation of transit systems causes various land-use problems. the need for extensive planning for brt systems was discussed in [15], as brts may fail due to fewer passengers and higher operating costs. pakistan is the fifth most populous country, having approximately 39.5% of the total 212 million population living in urban areas [17]. the inadequate and poor provision of public transportation in megacities of pakistan urges each corresponding author: afzal ahmed engineering, technology & applied science research vol. 12, no. 4, 2022, 8825-8830 8826 www.etasr.com khan et al.: an evaluation of cost optimization strategies for brt projects in pakistan individual to own a private vehicle to meet his travel needs, causing an increase in private vehicle ownership [18-19]. one of the main reasons for the degradation of public transport in most developing countries is the continued investment in road infrastructure while ignoring the improvement in the mass transport systems [20]. only commuters from low-income groups depend on public transport to fulfill their travel needs. therefore, there is a need to improve the existing public transport system in pakistan and other developing countries [18, 21]. in 2013, pakistan initiated the first brt project in lahore, followed by many other similar projects in other cities, including the islamabad-rawalpindi metrobus, multan metro, karachi metrobus, and peshawar metro. many brt projects started without considering their future impacts on the economic conditions of the country [17, 22-23]. in 2020, the orange-line transit project built in lahore consumed rs 1.9 billion in electricity to remain operational, which is a huge investment for a developing country [24]. it has been observed that various mass transit projects are executed without considering the cost optimization aspect. this study briefly analyzes the global brt data to evaluate the performance of brts in pakistan. furthermore, a detailed evaluation of a selected elevated segment of the first brt project constructed in karachi, pakistan, was performed. this study also examines other possible alignments of the selected segment, including median, curb-side, and two-way side alignments. the cost and capacity of each of the proposed alignments were estimated to show that the total infrastructure cost of the brt project could be significantly reduced by considering other alternatives without compromising the capacity of the corridor. ii. global data and brt in pakistan global brt data is a public platform developed by brt+coe and embarq wri brazil, in collaboration with itdp [12]. the database consists of more than 300 data points from different cities. however, data from only 50 brt corridors are considered for analysis in this study due to the unavailability of the brt cost or peak load parameters. the global brt data provide information on peak load, which is the maximum number of passengers traveling in buses per hour along the most loaded segment, and therefore can be considered as the transport capacity of the brt [12, 25]. based on this data, about 62% of the brt corridors around the world are median-aligned while only 7% have a grade-separated row. figure 1 relates the peak load served (capacity) with the infrastructure cost incurred in the construction of brt corridors around the world. the most used brt alignment is median, achieving 49,000 pphpd capacity in bogota, colombia, and constructed with usd 12.7 million per km. around usd 46 million per km was invested for the grade-separated corridor in nagoya, japan, serving a peak load of 750 pphpd. figure 1 shows the data points of the brt projects around the world, including pakistan. the 27 km route of the lahore metrobus was constructed with an infrastructural cost of usd 11.5 million per km and serves 10,000 pphpd. this brt model was based on istanbul metrobus, serving around 30,000 pphpd and constructed with usd 9 million per km. a 23 km long brt corridor was constructed to connect the twin cities of islamabad and rawalpindi (islamabad-rawalpindi metrobus), being grade-separated, and median busways constructed with an infrastructure cost of usd 20 million per km and serving only 2,100 pphpd. fig. 1. comparison of cost and capacity of corridors around the globe. the third operational brt project in pakistan was constructed in peshawar for usd 22 million per km and serves 15000 pphpd [26-27]. the green-line project in karachi costs us $13.8 million per km and has a capacity of 9708 pphpd. the detailed estimation of the green-line brt capacity and its cost are examined below. the higher capital investment for the construction of brt corridors in pakistan shows less efficient planning, which is reflected in the higher construction cost to serve comparatively fewer commuters. this is a critical concern, especially for the developing countries where the limited budget must be efficiently utilized in development and construction. most of these projects were built by acquiring loans from various funding agencies. the higher project cost increases the debt burden and reduces the resources that could have been used in human development. furthermore, a significant amount is also consumed for brt operations and providing subsidized fares to commuters [12, 22, 28]. iii. transport infrastructure in karachi karachi is a commercial and economic hub having a population of more than 20 million and generates up to 25% of pakistan's gdp [29-30]. the increase in population and the expansion of the city without sustainable means of transportation have increased traffic congestion [30]. the traffic count on four main arterials conducted in karachi shows that only 15% of commuters travel in public transport, while the remaining 85% of commuters travel using private vehicles [31]. the poor condition of the public transport systems has led commuters to use private vehicles. this causes a significant increase in traffic on the main arterials, leading to congestion, accidents, and pollution [32]. the japan international cooperation agency (jica) proposed five rapid transit lines (green, yellow, orange, blue, and red) and the rehabilitation of the karachi circular railway to improve transportation [33]. the construction of the green-line brt corridor started in february 2016 with estimated completion by december 2017. engineering, technology & applied science research vol. 12, no. 4, 2022, 8825-8830 8827 www.etasr.com khan et al.: an evaluation of cost optimization strategies for brt projects in pakistan however, due to various reasons, the brt started its operations in january 2022. iv. evaluation of green-line brt corridor a detailed survey was conducted to examine the layout and infrastructural characteristics of the existing green-line brt. this section describes the evaluation based on the route survey, capacity, and cost estimate of the existing green-line brt corridor. a. route survey and layout the green-line brt route extends from surjani to the municipal park. the green line will travel from surjani passing famous landmarks including nagan, ao clock tower, lasbela chowk, gurumandir, and numaish. the route is approximately 17.8 km, about 58% of the corridor is gradeseparated, and the remaining 42% has physically separated median aligned bus lanes. it consists of 21 stations, out of which 12 are grade-separated (2 stopping bays), and 9 at-grade (3 stopping bays). a fleet of 80 buses was obtained, each with a capacity of 160 passengers per vehicle [34]. figure 2 shows the details of the alignment of the route and the locations of the bus stations on a gis map. fig. 2. green line route map with stations (left) and intersections (right). b. capacity estimation capacity is the maximum number of passengers that can be carried past a point in a direction, during a given period along the critical section of the brt under specific operating conditions [35]. this research uses the brt planning guide for the estimation of the corridor capacity along with the saturation level for the green-line brt route [36]. equation (1) was used to calculate the capacity in pphpd, containing the main attributes that affect the capacity of brt systems including the capacity of the vehicle, load factor, frequency, and the number of stopping bays provided. the load factor of 0.9 is used considering the peak period conditions. the cycle time for a complete round trip is calculated by estimating the journey time from the origin to the destination. equation (2) was used to determine the headway in minutes between two consecutive buses. using headway, the service frequency for operations is calculated by (3). equation (4) is used to determine the saturation level of the green-line brt corridor from the estimated frequency. �� � �� ∗ �� ∗ �� ∗ � (1) � � �� �� (2) �� � �� � (3) � � ��∗�� ���� (4) table i shows the estimation of possible capacities that can be achieved in the infrastructure constructed for green-line with two and three stopping bays along with the corresponding saturation levels. the optimum saturation level is considered between 0.3 to 0.6 for brt systems. a saturation level greater than 0.6 creates a risk of congestion and may lead to crowding of buses at stations [36]. the maximum possible crushing capacity for the green-line can be 24270 pphpd with a fleet size of 200 buses, while the optimal capacity achieved for its operations with smooth flows is 14562 pphpd. table i. various possible operations for the green-line brt corridor fleet size headway (min) frequency (bph) saturation level corridor capacity (pphpd) 80 0.89 67.4 0.37 9708 100 0.71 84.3 0.47 12135 120 0.59 101.1 0.56 14562 140 0.51 118.0 0.66 16989 160 0.45 134.8 0.75 19416 180 0.40 151.7 0.84 21843 200 0.36 168.5 0.94 24270 c. existing infrastructural cost the critical elements that increase the infrastructural cost for brts are the design type of running ways and stations. the cost per unit of elements in the green-line brt corridor was obtained from the sindh infrastructural development corporation limited (sidcl), which was the authority responsible for the execution of this project. the total cost for the existing alignment was estimated based on the cost per unit in pkr million per km at 552 and 203 for elevated and atgrade busways respectively. for one elevated and at-grade station, the cost was pkr 288 and 141 million respectively. table ii. cost estimation of existing alignment section surjani to nagan nagan to golimar golimar to gurumandir type elevated atgrade elevated atgrade elevated atgrade length (km) 5.86 0.51 1.66 6.6 2.8 0.4 cost pkr million per km 3235 104 916 1340 1546 81 stations 8 2 7 4 cost pkr million (each station) 2304 282 987 1152 cost pkr million per km 930 393 868 cost usd million per km 5.85 2.47 5.46 engineering, technology & applied science research vol. 12, no. 4, 2022, 8825-8830 8828 www.etasr.com khan et al.: an evaluation of cost optimization strategies for brt projects in pakistan table ii shows the complete cost estimation for the greenline brt corridor. the segment between surjani and nagan was the most expensive segment, constructed for usd 5.85 million per km. the grade-separated segment is 5.86km long, having 10 stations along the segment. the per km cost of the nagan-golimar corridor was estimated at approximately usd 2.47 million, which is 2.3 times lesser than the unit cost of the elevated segment. the unit cost of the golimar-gurumandir segment was usd 5.46 million per km. v. optimization of green-line brt route the cost estimation and the evaluation of various brt segments shown in table ii indicate that there is a potential to reduce infrastructure costs without compromising capacity. the various options to reduce the cost of the green brt line infrastructure are explored below. a. gurumandirgolimar the existing route length of this segment is 3.2 km with 2.8 km elevated and 0.4 km as an at-grade median corridor. the cross-section of the existing alignment of the green brt line for the gurumandir-golimar segment is shown in figure 3. around 90% of the width of the segment is less than 40 m while 10% of the width is more than 40 m, showing the possible difficulty of constructing an at-grade alignment for this segment. figure 3 shows the median aligned corridor as evaluated for this segment. the segment may become more congested for general traffic if the brt is constructed in a median alignment. an at-grade busway along this corridor would significantly reduce the width of the carriageway for general traffic from 11 to 7.3m. the reduction in the right-ofway can truncate the number of lanes for general traffic, causing traffic pressure with a greater possibility of traffic congestion. fig. 3. gurumandir-golimar cross-section with existing elevated (top) and proposed median (bottom) alignment. b. golimar-nagan the existing route length for this segment is 8.26 km, with 6.6 km median aligned and 1.66 km elevated section. all the intersections in this segment are grade-separated and the remaining segment is at-grade median aligned. hence, the existing design of this section was evaluated as a cost-optimal design and no further optimization was possible without compromising capacity. c. nagan-surjani the existing nagan-surjani segment has a route length of 6.37 km, with 5.86 km elevated and 0.51 km median aligned. around 84% of the segment width is between 81-100m, 12% is less than 80m, and 4% is more than 100m, showing a clear possibility of construction for an at-grade alignment along the segment. figure 4 shows the cross-section of the existing alignment. the median alignment was considered difficult to be constructed by authorities because of the 5-8 m pylons (electric poles) on the median of the roadway. the two-way side and curb-side alignment possibilities were studied for this segment. the available right-of-way for the nagan-surjani segment is approximately 63 m. the available space provides an opportunity for its utilization as a brt corridor. therefore, it is possible to construct two-way and curb-side aligned corridors for this segment. the two-way side aligned right-ofway for brt would be a feasible option to deal with the pylons and would not reduce the width of lanes for general traffic. one major benefit of this alignment could be that it would increase accessibility for one side of commuters. the possibility of providing a curb-side alignment is also shown in figure 4. fig. 4. nagan-surjani cross-section with existing elevated alignment (top), proposed two-way side alignment (middle), and curb-side (bottom). d. existing and proposed intersections the existing infrastructure of brt has grade separation at intersections. the intersection on the brt route must be engineering, technology & applied science research vol. 12, no. 4, 2022, 8825-8830 8829 www.etasr.com khan et al.: an evaluation of cost optimization strategies for brt projects in pakistan treated so that its capacity is not affected at the intersections. the two possible ways to deal with intersections, while maintaining sufficient capacity of the corridor, could be signalized intersections with bus priority and grade separation. signalized intersections may cause delays to the general traffic as well as the brt. therefore, it is proposed that all major intersections should be grade-separated along the corridor, leaving its capacity unaffected. vi. proposed optimal alignments the surjani-nagan segment was identified as one of the most expensive segments of the green brt line. the detailed evaluation of the corridor also showed that this is the segment with the highest potential for cost optimization. table iii shows that providing an at-grade carriageway for this segment could reduce its cost by usd 14.36 million. the possible cost saving by providing a median-aligned busway in the section of gurumandir to golimar could be usd 6.69 million. however, reducing the right-of-way for general traffic could adversely affect the travel time and speed of other vehicles. table iii. alternative brt busways parameters nagan to surjani gurumandir to golimar existing curb-side/ two-way side existing median length elevated (km) 5.86 2.3 2.8 1.02 length at-grade (km) 0.51 4.01 0.4 2.17 no of elevated stations 8 1 4 1 no of at-grade stations 2 9 3 intersections elevated elevated elevated elevated accessibility low medium low low effect on general traffic carriageway reduction in row effect on capacity cost (usd million) 37.26 22.9 17.47 10.78 table iv. comparison of existing with optimal alignments existing green-line alternative 1/2 green-line alternative 3 green-line surjani-nagan elevated curbside/twoway side aligned green-line curbside/twoway side aligned green-line nagan-golimar median median median golimargurumandir elevated elevated median percent elevated 58 38 28 percent at-grade 42 62 72 cost (usd million) 75.12 61.02 54.33 the two-way side-aligned busways from surjani to nagan were the most suitable and feasible. they can significantly decrease cost without affecting capacity along with making brt stations more accessible to users. although the curbside alignment has an almost similar cost, it may not be feasible, as the transition from the curbside alignment (surjani-nagan) to the median aligned segments (nagan-golimar) may increase cost. two elevated flyovers are required to join both sides of the curb-aligned to the median, but for the two-way side alignment, it could be possible to use a one-sided elevated flyover. table iv shows the difference in cost between the existing and proposed alignments. increasing the proportion of elevated segments in the corridor causes a significant increase in cost. as the existing corridor is 58% elevated, it increased the total cost by usd 14.1 million in comparison with the proposed two-way side alignment. vii. conclusions and recommendations several brt projects have been initiated in pakistan during the past decade. the evaluation of the cost of brt projects in pakistan and its comparison with brt systems around the world reveal that those constructed in pakistan offer comparatively lower capacity and utilization. due to high construction and operational cost and unjustified delays, the economic impact of the brt projects has increased. uneven city planning and local conditions often cause delays in the construction of these megaprojects. due to the high demand for sustainable and affordable means of transport, the need for mass transit projects is also increasing in a developing country like pakistan. green-line was the first brt project started in karachi. construction of the infrastructure for the green-line brt was delayed and caused a significant increase in its initial estimated cost of pkr 25 billion. this research investigated this project in detail to evaluate the potential for cost optimization. the proposed green-line brt alignment consists of 58% of elevated sections, which have the highest cost among all possible alignments. detailed field surveys were conducted to examine the feasibility of other possible alignments, such as curb-side, median-aligned, and two-way side aligned brt infrastructure. the capacity of each of the proposed alignments was also evaluated, and it was concluded that by designing the nagan-surjani segment using a two-way side aligned option, the existing cost of this section could have been reduced from usd 75 million to usd 61 million, which is a 20% saving on the original cost without compromising the system's capacity. planners and policymakers should investigate the alternatives in detail to optimize the cost. the efficient at-grade brt with the same capacity is still an option for developing countries where the primary need is to invest resources most optimally. this solution could also benefit the government to consider various strategies to alleviate the huge investments in the construction of mega transportation projects. references [1] "68% of the world population projected to live in urban areas by 2050, says un," un desa, may 16, 2018. https://www.un.org/development/ desa/en/news/population/2018-revision-of-world-urbanizationprospects.html. 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[14] a. cain, g. darido, m. r. baltes, p. rodriguez, and j. c. barrios, "applicability of transmilenio bus rapid transit system of bogotá, colombia, to the united states," transportation research record, vol. 2034, no. 1, pp. 45–54, jan. 2007, https://doi.org/10.3141/2034-06. [15] m. h. nguyen and d. pojani, "chapter two why do some brt systems in the global south fail to perform or expand?," in advances in transport policy and planning, vol. 1, y. shiftan and m. kamargianni, eds. academic press, 2018, pp. 35–61. [16] t. satiennam, a. fukuda, and r. oshima, "a study on the introduction of bus rapid transit system in asian developing cities: a case study on bangkok metropolitan administration project," iatss research, vol. 30, no. 2, pp. 59–69, jan. 2006, https://doi.org/10.1016/s0386-1112(14) 60170-9. 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[27] "peshawar sustainable bus rapid transit corridor project," asian development bank, nov. 23, 2017. https://www.adb.org/projects/48289002/main. [28] e. j. zolnik, a. malik, and y. irvin-erickson, "who benefits from bus rapid transit? evidence from the metro bus system (mbs) in lahore," journal of transport geography, vol. 71, pp. 139–149, jul. 2018, https://doi.org/10.1016/j.jtrangeo.2018.06.019. [29] "supporting public–private partnership investments in sindh province," asian development bank, nov. 24, 2016. https://www.adb.org/projects/ 46538-002/main. [30] a. hasan, "working paper emerging urbanisation trends: the case of karachi," international growth centre, working paper c-37319-pak-1, may 2016. [31] s. m. noman, a. ahmed, and m. s. ali, "comparative analysis of public transport modes available in karachi, pakistan," sn applied sciences, vol. 2, no. 5, apr. 2020, art. no. 967, https://doi.org/10.1007/ s42452-020-2678-3. [32] responding to the transport crisis in karachi. karachi, pakistan: the urban resource centre, jul. 2015. [33] s. mustafa, "comparative analysis of kcr and brt: an exploratory study covering the mass transit needs and policies in karachi as a megacity," global journal for management and administrative sciences, vol. 1, no. 1, pp. 1–24, jun. 2020, https://doi.org/10.46568/ gjmas.v1i1.15. [34] "pakistan signs procurement deal for green line project buses," ary news, dec. 23, 2020. https://arynews.tv/procurement-deal-green-lineproject-buses. [35] m. chang et al., "characteristics of bus rapid transit for decision making," federal transit administration, fta-va-26-7222-2004.1, aug. 2004. [36] l. wright and w. hook, eds., bus rapid transit planning guide. new york, ny, usa: institute of transportation & development policy, 2007. microsoft word etasr_v12_n5_pp9217-9223 engineering, technology & applied science research vol. 12, no. 5, 2022, 9217-9223 9217 www.etasr.com maafa et al.: improvement of sliding mode control strategy founded on cascaded doubly fed … improvement of sliding mode control strategy founded on cascaded doubly fed induction generator powered by a matrix converter amar maafa department of electrical engineering akli mohand oulhadj university bouira, algeria ommafa@univ-bouira.dz hacene mellah department of electrical engineering akli mohand oulhadj university bouira, algeria h.mellah@univ-bouira.dz kaci ghedamsi laboratoire de maîtrise des energies renouvelables bejaia university, algeria kghedamsi@yahoo.fr djamel aouzellag laboratoire de maîtrise des energies renouvelables bejaia university, algeria aouzellag@hotmail.com received: 1 july 2022 | revised: 29 july 2022 | accepted: 31 july 2022 abstract-the current paper presents a sliding mode controller (smc) for indirect field-oriented cascaded doubly fed induction generator (cdfig) powered through a matrix converter (mc). the proposed smc employs a continuous control strategy to accomplish free chattering fractional-order sliding-mode control and to ensure that the control of the first dfig stator's reactive and active power is separated. an mc is used to control the current provided to the second stator of the cdfig as an alternative to standard voltage source inverters. the two mcs are controlled via space-vector pulse-width modulation (svpwm) and indirect field oriented control (ifoc). the proposed wind power generation system (wpgs) is used with the purpose to ensure maximum power point tracking (mppt) sensing under various disturbance variables such as turbulent wind. the simulation results prove the efficiency and robustness of the proposed method. keywordssliding mode control (smc); wind power generation system (wpgs); cascaded doubly fed induction generator (cdfig); matrix converter (mc) i. introduction the current interest in wind energy comes from the need to develop less expensive, clean, and sustainable wpgss [1], while reducing maintenance cost and increasing availability and production [2], hence, the need for the research regarding electromechanical converters of high reliability [2]. many wts are equipped by dfigs [3] to produce electrical energy [4-9]. furthermore, brushes and slip-rings, are fitted with woundrotor induction machines, which may pose maintenance issues. in addition, because of its similar characteristics, a cdfig is a strong candidate for dfig replacement [10-15]. in this work, a perturbation observer-based smc of cdfig associated with mc for optimal power extraction is proposed. to govern the active and reactive power injection to the electrical power grid via the wpgs, controllers with dynamical variable structure and adaptive control are applied. the purpose of this of this technology is to achieve chatter-free fractional order smc as well as decoupled active and reactive power regulation in the stator. the three-phase mc is among the recent generations of the conventional direct-power ac-ac converter. there are nine bidirectional switches in total. the mc has various advantages over traditional ac-ac converter topologies, including the ability to reverse the power flow via the mc, i.e. it can operate in all four quadrants of the voltagecurrent plane, allowing it to operate with both modes, either with a generator or with a motor. assuming hypothetical zeroloss switches, the instantaneous power input should be equalized to the power output due to the lack of energy storage devices. on the other hand, it is not required that the input and output reactive powers are in agreement. on the mc inputs and depending on the load to be supplied, it is possible to modify and preset the phase angle between the voltages and currents, which does not have to be the same as the output [16-18]. the extensive research on mc began with [19]. this method was founded on a duty-cycle matrix technics and it is introduced using time domain quantities. svm is a modulation solution, based on the representation of space vectors in complex space [20-22]. direct svm (dsvm) [23] and indirect svm (isvm) [24] are two techniques that have been developed. the isvm approach is investigated in this study. isvm is a modulation approach that divides the input current and output voltage control into two phases. to regulate the entire mc, two transfer matrices are required, and the wellknown svm approach is used for the rectifying and inverting stages respectively [14]. corresponding author: amar maafa engineering, technology & applied science research vol. 12, no. 5, 2022, 9217-9223 9218 www.etasr.com maafa et al.: improvement of sliding mode control strategy founded on cascaded doubly fed … ii. description of the wpgs the direct mc is made up of 9 bidirectional switches that allow any input phase a, b, c to be connected to any output phase a, b, c. according to figure 1, each output phase contains a set of 3 switches connected to the 3 input phases. the sinusoidal output voltage with variable frequency and/or magnitude must be calculated from the input voltages defined by a constant frequency and magnitude [14]. there are 2 major limitations on how an mc may operate: (a) no short circuits are permitted in the 3 input phases and (b) no circuits with 3 output phases may ever be opened [25]. fig. 1. matrix converter topology. a. space vector modulation (svm) the mc is represented as a two-level converter connected by an imaginary dc link in order to employ the svpwm: the first level acts as an input rectifier with the current link and the second level acts as an output voltage source inverter [17, 26]. for further information, the interested reader is directed to [2, 21-27]. fig. 2. power circuit topology of the 3×3 imc. b. svm for the rectifier stage the following transformation is used to describe the input current space vector ��� as a space vector: ��� = �� (�� + � � � �� + �� � �� �� ) (1) the neighboring switching vectors iγ and iδ are multiplied with the corresponding duty cycles dγ and dδ to create i*. �∗ = �� �� + �� �� (2) figure 3 shows the reference current vector synthesis. c. svm for the inverter stage the output voltage vector is represented as: ���� = �� (�� + �� � � �� + �� � �� �� ) (3) two consecutive switching vectors �� and � with duty cycles �� and � synthesize the reference output voltage space vector as follows: � ∗ = �! "! + � � (4) the active vectors' duty cycle is computed as: ⎩⎪⎨ ⎪⎧�! = '(') = *+ ,-.( /� − 1+ )� = '2') = *+ ,-.( 1+)�3 = '4') = 1 − (�! + � ) (5) where 1+ represents the angle between the reference voltage vector and the actual hexagon sector. the appropriate voltage transmission ratio is determined by the voltage adjustment indicator denoted as mv [28]. in this application, for all mc bidirectional switches, it is necessary to create a single modulation mechanism from the two separate space vector modulations. fig. 3. reference current vector synthesis. d. model of cdfig the cdfig consists of 2 induction generators, with p1 and p2 being their pole-pairs, connected in cascade to remove the brushes and copper rings in the conventional doubly fed induction machine (dfim) [2, 13, 29]. figure 4 shows the mechanical and electric coupling of two wound rotors. in a synchronously rotating d–q frame, the mathematical model of the electrical machine is detailed in [2]. the purpose of the choosing of a d–q reference frame where the d-axis is in agreement with the first stator flux is to have its quadrature component equal to zero [18]. fig. 4. mechanical and electric coupling of two ig equivalents to the cdfig. the second stator's active and reactive powers, voltages, and currents can be written in accordance with the rotor currents as follows: m 1 s 2 s 3 s 4 s 5 s 6 s 7 s 8 s 9 s 1 0 s 1 1 s 1 2 s dc v a b c a b c cdfig ig1 ig2 stator 1 stator 2stator 1 stator 2 αaxe βaxe i v iv iii ii vi )(1 abi )( 2 aci )( 3 bci )( 4 bai )( 5 cai )( 6 cbi αaxe βaxe c θ * i γγ id δδ id engineering, technology & applied science research vol. 12, no. 5, 2022, 9217-9223 9219 www.etasr.com maafa et al.: improvement of sliding mode control strategy founded on cascaded doubly fed … ⎩⎪ ⎨ ⎪⎧"67� = 87�-67� + (97� − :. 9<�) 6�=) 6�−,. >7 (97� − :. 9<�). -?7�"?7� = 87�-?7� + (97� − :. 9<�) 6�@) 6�+,. >7 (97� − :. 9<�). -67� + ,. abcd)a)c (6) ef7g = −:. �7 abca)c -?7�h7g = d) i).a)c j1 + �.abc a)c.ab k − :. �7 abca)c -67� (7) where , = (>7 − (lg + l�). mn )/>7 and : = 9<�/(9ng +9n� − abc a)c ). the sliding surfaces s(ids2), s(iqs2) relative to stator currents are defined as: pq(-?7�) = -?7�_nst − -?7�q(-67�) = -67�_nst − -67� (8) for the chosen variables to converge to their reference values, both surfaces must be zero: eq • (f) = 66� (-?7�_nst − -?7�) = 0q• (h) = 66� (-67�_nst − -67�) = 0 (9) the control algorithm is defined by the relations: pvxy� = vxy�_zx + vxy�_[v\y� = v\y�_zx + v\y�_[ (10) ⎩⎪⎨ ⎪⎧�?7��s? = 87�-?7� − 97g a) ��ab �d)abc f•7g]^_ −,>7g(97� − :9<�)-67� + abca)c :,�7�?7�_� = g̀(97� − :9<�) ,a.( q(-?7 )) (11) ⎩⎪⎨ ⎪⎧�?7�^@ = 87�-?7� − 97g a) ��ab �d)abc f•7g]^_−,>7g(97� − :9<�)-67� + abca)c :,�7�?7�_� = g̀(97� − :9<�) ,a.( q(-?7 )) (12) where vqs2-eq, vds2-eq are the equivalent control voltages used to maintain the variable to be controlled on the sliding surface, vqs2-n , vds2-n are switching control voltages used to check the convergence condition because the parameters of the system are imprecise. an smc block diagram applied to the cdfig is schematized in figure 6 according to (11)-(12). the goal is to capture the maximum aerodynamic power without exceeding the allowable power of the converter. furthermore, the pitch angle is raised to lose aerodynamic power when the power converter's maximum rating is reached [2]. the smc of cdfig with mppt using mc is shown in figure 8. fig. 5. the equivalent control voltage’s structure. fig. 6. sliding mode control block diagram of the cdfig. iii. simulation results and discussion the proposed wpgs was realized in matlab/simulink environment as presented in figure 7, according to the control block diagram illustrated in figure 6. we employed the dfig parameters listed in [2]. in this section, the simulation of a direct grid connection of cdfig through the first stator that is controlled through its second stator winding via ac/ac direct converter is presented. the considered system is controlled with the purpose to generate maximum energy while minimizing loads. engineering, technology & applied science research vol. 12, no. 5, 2022, 9217-9223 9220 www.etasr.com maafa et al.: improvement of sliding mode control strategy founded on cascaded doubly fed … fig. 7. the proposed wpgs model in simulink. figure 8 gives the wind speed variance applied to the wpgs. figure 9 shows the power coefficient and figure 10 gives the corresponding pitch angle. the pitch angle of the wt is controlled to ensure that it work as hard as possible with maximum power coefficient. fig. 8. wind speed profile. fig. 9. power coefficient fig. 10. pitch angle. fig. 11. first stator active and reactive powers. fig. 12. grid active and reactive powers. fig. 13. second stator active and reactive powers. the first stator's active and reactive powers are given in figure 11. we can see clearly that for the first stator, both active and reactive powers are in agreement with their references. the grid active and reactive powers are shown in figure 12 and the second stator active and reactive powers are shown in figure 13. in a hyper-synchronous operation case, it engineering, technology & applied science research vol. 12, no. 5, 2022, 9217-9223 9221 www.etasr.com maafa et al.: improvement of sliding mode control strategy founded on cascaded doubly fed … is clearly evident that a portion of the active power exceeding 1.5mw is transmitted to the grid from the second stator side of the cdfig. the first stator’s voltage and current curves are illustrated in figure 14. as we can see, the sinusoidal current and voltage are in phase opposition as illustrated in figure 15. fig. 14. first stator voltage and current. fig. 15. zoom first stator voltage and current. the voltage and current curves of the second stator are depicted in figure 16. we can conclude that according to the slip s value, the frequency of the voltage and the current change, as depicted in figures 17 and 8. furthermore, in the case of synchronous operation mode, the slip is equal to zero and the voltage and current of the second stator have continuous forms as illustrated in figure 19. fig. 16. second stator voltage and current. fig. 17. zoom second stator voltage and current (s > 0). fig. 18. zoom second stator voltage and current (s = 0). fig. 19. zoom second stator voltage and current (s < 0). many studies have dealt with dfig control issues for several applications and many approaches have been proposed [30-35]. a very interested work is proposed in [30], where the authors propose smc and an update of smc, called terminal smc to control the output voltage of cdfig. authors in [31] present a grid synchronization method founded on smc for sub–and super–synchronous mode. a promising technique called super twisting sliding mode control was applied in [3234] with the purpose of power control. all these works ignore pitch control and the cdfig is not supplied via an mc. in contrast, authors in [35] use smc with an mc but for a motor application. iv. conclusion in this paper, an smc for indirect field-oriented cdfig associated with mc was proposed. the suggested smc is intended to lower chattering phenomena levels, and this has been confirmed by the simulation results of a nonlinear controlled system. the recommended mc was simulated, and the results demonstrate that it is capable of controlling the secondary side voltage and frequency even in an operational situation with bidirectional power flow. the goal of the pitch controller is to capture the maximum aerodynamic power without exceeding the power allowable of the converter. the results of the simulation showed that the active and reactive powers closely match their reference values. a near unity input power factor has been achieved by carefully managing mc's input power factor. the lack of any energy storage element in mc preserves and prolongs the life of the proposed structure. the wind speed is applied in such a way, as to have the three operating modes of the wt, namely synchronous, hypersynchronous, and hypo-synchronous. the results obtained in this study can be found with dfig instead of cdfig, but cdfig has the advantages of reducing the maintenance cost, eliminating the contacts between copper rings and brushes, and reducing the size of the gearbox in the wpgs. engineering, technology & applied science research vol. 12, no. 5, 2022, 9217-9223 9222 www.etasr.com maafa et al.: improvement of sliding mode control strategy founded on cascaded doubly fed … references [1] h. mellah, s. arslan, h. sahraoui, k. e. hemsas, and s. kamel, "the effect of stator inter-turn short-circuit fault on dfig performance using fem," engineering, technology & applied science research, vol. 12, no. 3, pp. 8688–8693, jun. 2022, https://doi.org/10.48084/ etasr.4923. 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[35] h. wang et al., "a cascade pi-smc method for matrix converter-fed bdfim drives," ieee transactions on transportation electrification, vol. 7, no. 4, pp. 2541–2550, sep. 2021, https://doi.org/10.1109/tte. 2021.3061742. microsoft word etasr_v13_n1_pp9961-9967 engineering, technology & applied science research vol. 13, no. 1, 2023, 9961-9967 9961 www.etasr.com singh et al.: a real-time analytic face thermal recognition system integrated with email … a real-time analytic face thermal recognition system integrated with email notification ranjit singh sarban singh centre for telecommunication research & innovation (cetri), fakulti kejuruteraan elektronik dan kejuruteraan komputer (fkekk), universiti teknikal malaysia melaka (utem), malaysia ranjit.singh@utem.edu.my (corresponding author) t. joseph sahaya anand sustainable and responsive manufacturing, fakulti teknologi kejuruteraan mekanikal dan pembuatan, universiti teknikal malaysia melaka (utem), malaysia anand@utem.edu.my siti aisyah anas centre for telecommunication research & innovation (cetri), fakulti kejuruteraan elektronik dan kejuruteraan komputer (fkekk), universiti teknikal malaysia melaka (utem), malaysia aisyah@utem.edu.my biswaranjan acharya department of computer engineering-ai & bd, marwadi university, india biswaacharya@ieee.org received: 21 october 2022 | revised: 16 november 2022 | accepted: 19 november 2022 abstract covid-19 is a contagious disease caused by the severe acute respiratory syndrome coronavirus 2 (sarscov-2). the disease has spread worldwide, leading to an ongoing pandemic. the most common symptom of covid-19 is fever which can be detected using various manual screening techniques that have the risk of exposing the personnel. since the virus has globally spread, a reliable system to detect covid-19infected people, especially before entering any premises and buildings, is in high demand. the most common symptom that can be detected is fever, even though people with fever might not have covid-19. thus, a real-time analytic face thermal recognition system integrated with email notification that has the capability to scan the person’s temperature and simultaneously analyze the measured temperature with the recorded/stored information/data is presented in this paper. the proposed system is also able to send an email notification to the relevant authorities during the real-time analytical process. besides that, this information is also recorded in the system database for continuous monitoring of the respective person’s health status. the development of the proposed system is integrated with a thermal module amg8833, pi camera, and raspberry pi zero wireless. the proposed system has been tested and the captured results successfully accomplished the development objectives. keywords-covid-19; face recognition; temperature; real-time analysis; email notification i. introduction there is a high demand in face thermal recognition systems due to the covid-19 pandemic. there are many off-the-shelf face thermal recognition systems available in the market, everyone with its abilities and advantages. to enable effective monitoring which also complies with the standard operating procedure (sop), a real-time analytic face thermal recognition system integrated with email notification and having the capability to simultaneously analyze the measured person’s temperature and update recorded/stored information/data is presented in this paper. prior to the development of the proposed system, off-the-shelf systems related to detecting possible symptom of covid-19 are studied. the studied engineering, technology & applied science research vol. 13, no. 1, 2023, 9961-9967 9962 www.etasr.com singh et al.: a real-time analytic face thermal recognition system integrated with email … systems investigate the aspect of simplicity in terms of product development as well as quick and fast delivering the analyzed and processed information to the relevant authorities. although the developed system is not able to prevent the covid-19 pandemic, it can assist in controlling it more effectively and efficiently. generally, infrared and wireless thermometers are deployed as general medical tools, especially at the entries and exits of buildings. the infrared and wireless thermometers generally use body temperature sensing [1]. designing and developing systems able to assist the early detection of any fever-related illness so that it can be further examined it is covid-19 or something else is a scientific topic of major interest. in [2], fever is mentioned as the most common symptom of patients with covid-19. the off-the-shelf studied systems [35] use the pi camera to visualize the thermal data, where the temperature values are mapped into a color gradient, ranging from blue to red. the blue color is mapped to value 0 representing the lowest temperature, while red color is mapped to value 1023 representing the highest temperature. a real image of the respective person is blended with the saved image to produce the read thermal temperature value. the produced thermal temperature value is displayed in real-time and an email is sent to the person in charge at the monitoring station if any abnormality is detected. in [6], an iot smart health monitoring system that analyzes the human body temperature, pulse and spo2 has been developed and integrated into a mobile application for covid-19 detection. with the integrated system, the patient can immediately seek medical attention if a physician is not available. in [7], a smart helmet is developed to innovatively detect and monitor covid-19 using a thermal imaging system attached onto the smart helmet. the smart helmet detects high body temperature and sends the measured value into a mobile application, assisting the early detection of covid-19. thermal face recognition systems have been proven to be effective in detecting possible covid19 affected persons besides from been used to authorize the person’s authentication [5]. authors in [8] utilized the smart home concept to detect if a visiting person is infected with covid-19. infrared technology was used to detect the person’s temperature and if it was high, an integrated thermal face camera was used to scan and monitor the person’s condition at the door. authors in [9] mentioned that ct-scans and x-ray images can also be used for covid-19 early detection. the paper also explains that the use of deep learning models [10, 11] could give more precise covid-19 early detection, but systems with deep learning models is more expensive. thermal detection is a popular method to screen people during the outburst of the covid-19 pandemic. the infrared thermal scanning method is also widely used at many places as an early precaution step. such systems are often able to make buzzer sounds when a person with high temperature is detected during the scanning process. after reviewing some of the developed systems that use facial thermal measuring for early covid-19 detection, and to the best of our knowledge, features such as real-time identification/authentication and email notification are not applicable. hence, the current research project implements real-time facial identification/authentication, then analyzes the temperature reading and compares it with the preset temperature value before sending an email notification if the temperature is above the preset value. the email notification notifies the relevant authorities about the person’s condition, or records the person absence from work. phyton programming language was used to develop the proposed research project. thonny application was selected as python ide because it is free and open-source and it provides significant features such as code inspection and debugging. the standard libraries used in this project are opencv and dlib. the algorithm development begins with facial detection and face recognition. then, the amg8833 thermal camera sensor for facial temperature measuring, recording, and comparing is activated. the proposed project continuously processes the recorded/stored information/data and automatically updates the stored data into the developed system. also, the developed and deployed system tends to reduce the risk of infection of manual screening. ii. research methodology the proposed development methodology is divided into two phases. phase one focuses on the hardware development which consists of 1) the integration of the pi camera to perform the facial detection and recognition and 2) the integration of the thermal camera sensor to measure facial temperature. the integration of the pi camera is conducted to perform the face detection and recognition via existing images that have been preloaded into the raspberry pi zero wireless sd-card storage. upon the success of the face detection and recognition, the thermal camera sensor is activated to measure the human facial temperature. then, the recognized person and its measured temperature details are stored into the raspberry pi zero wireless sd-card. the second phase focuses on the embedded software development for 1) facial detection and recognition, 2) measurement of the facial temperature, and 3) configuration of the email notification. the facial detection and recognition perform real-time face recognition based on the preloaded images. upon detection of a human face, the thermal camera sensor measures the respective human facial’s temperature and stores it into the sd-card. while the recognized face and human body temperature information is recorded, the process of comparing the measured temperature with the preset temperature value is performed to detect normal and high temperature. if the measured temperature is above the preset temperature value, an email notification is delivered to the relevant authorities (security, managers, internal clinic, covid-19 screening team, etc.). a. iot face thermal recognition system integration  pi camera integration in the first phase, the pi camera performs facial detection and recognition. the integration is shown in figure 1. the pi camera is connected to the raspberry pi zero wireless via the camera serial interface (csi) connector. the integrated pi camera has the capability to capture an 8 megapixel real-time image which will be used to perform the facial detection and recognition with the images stored in the raspberry pi zero wireless sd-card storage. engineering, technology & applied science research vol. 13, no. 1, 2023, 9961-9967 9963 www.etasr.com singh et al.: a real-time analytic face thermal recognition system integrated with email …  integration of the amg8833 thermal camera sensor this section describes the amg8833 thermal camera sensor connectivity with the raspberry pi zero wireless as shown in figure 2. the general-purpose input/output (gpio) port 2 and port 3 are respectively connected to the serial information (sda) and serial clock line (scl). the power source (vcc) is connected to 3.3v at port 1 and the ground is connected to port 9. the amg8833 thermal camera sensor is activated when the facial detection and recognition is completed. fig. 1. pi camera and raspberry pi zero wireless connection. fig. 2. amg8833 thermal camera sensor connection with the raspberry pi zero wireless. b. software design and development  embedded facial detection and recognition algorithm to perform the facial detection and recognition tasks, a suitable algorithm has been implemented (figure 3). when the integrated pi camera is active, it will acquire a real-time image which will be compared with a preloaded image. upon confirming the acquired real-time image, the embedded software algorithm will perform facial recognition to confirm the person’s identity and will provide the recognized person’s name. once the name has been confirmed, it will be recorded into the attendance list. fig. 3. embedded face detection and recognition algorithm. fig. 4. embedded amg8833 thermal sensor algorithm. engineering, technology & applied science research vol. 13, no. 1, 2023, 9961-9967 9964 www.etasr.com singh et al.: a real-time analytic face thermal recognition system integrated with email …  embedded algorithm for the amg8833 thermal camera sensor and email notification the amg8833 thermal camera sensor is integrated to measure the real-time human temperature. the amg8833 sensor reads a real-time temperature value when a person’s face approaches the camera and the sensor. hence, when the face is recognized, the amg8833 thermal camera sensor is activated to measure the person’s facial temperature and match the measured temperature with the person’s name that is stored in the attendance list. if the person’s name is matched, the name and measured temperature will be displayed at the integrated liquid crystal display (lcd). otherwise, the embedded software continues to perform the person’s name search to record the measured temperature value. also, during the temperature measuring, the embedded software algorithm for the amg8833 thermal camera sensor categorizes the measured temperature into two classes, i.e. "35°c ≤ normal ≤ 37°c" or "37°c < high ≤ 40°c". if the measured temperature is normal, its value is displayed on the lcd, otherwise an email notification will be sent to the authorities to inform about the person’s condition as depicted in figures 4 and 5. fig. 5. embedded real-time email processing and notification algorithm. iii. results and discussion a. hardware system design and development figure 6 shows the arrangement of amg8833 thermal camera sensor, pi camera, and lcd for the hardware system design and development. the amg8833 and the pi camera are placed side by side to allow simultaneous facial detection and recognition and facial temperature measurement upon authentication. details such as name and temperature of the scanned face are displayed on the integrated lcd. fig. 6. placement of integrated pi camera, amg8833 thermal camera sensor, and lcd iot face thermal recognition system. fig. 7. illustration of face recognition in a rectangular box. another reason of placing the amg8833 sensor and the pi camera side by side is because this way the amg8833 thermal camera sensor picture size of 480×480 pixels is centered at the pi camera picture size of 640×480 pixels as shown in figure 7. this allows the amg8833 thermal camera sensor to effectively scan the center of the forehead for temperature measuring as can be seen in figure 7. figure 8 shows the complete integration of pi camera, amg8833 thermal camera sensor, and lcd into the raspberry pi zero wireless. fig. 8. integration of the pi camera, amg8833 thermal camera sensor, and lcd in the raspberry pi zero wireless. b. validation of the developed software this section validates the developed software algorithm which integrates the pi camera and amg8833 thermal camera sensor in raspberry pi zero wireless for face engineering, technology & applied science research vol. 13, no. 1, 2023, 9961-9967 9965 www.etasr.com singh et al.: a real-time analytic face thermal recognition system integrated with email … detection, face recognition, and face temperature reading and measurement. to perform face detection and recognition a suitable algorithm (figure 4) was implemented. the system starts with the embedded algorithm for face detection and recognition. when the integrated pi camera is activated it will acquire a real-time image, which will be compared with the stored image in the sd-card. upon confirming the acquired real-time image, the embedded software algorithm will perform face recognition to confirm the person’s identity. once the person’s face is recognized, the amg8833 thermal camera sensor will be activated to measure the person’s facial temperature which will be evaluated based on the two conditions shown in figures 4 and 5. these conditions will be matched while real-time facial temperature is measured and the information is stored into the raspberry pi zero wireless sdcard. the person attendance status is also updated upon completing the temperature measuring process. figure 9 shows the captured result from the python shell in the raspberry pi zero wireless when the program starts to operate. after the system successfully acquires the preloaded image, the person’s face detection and recognition are executed. during the execution, the person’s name is validated and the proposed system continues to measure the facial temperature by using the amg8833 sensor and stores the measured temperature value into the sd-card. figure 9 shows the name and temperature of the person after scanning, using the pi camera and the amg8833 thermal camera sensor. fig. 9. name and captured temperature– phyton shell raspberry pi zero wireless. fig. 10. person’s name and measured temperature are displayed at the integrated lcd screen. the amg8833 thermal camera sensor displays a real-time temperature value when a person’s face approaches the pi camera. hence, once the face is recognized, the amg8833 thermal camera sensor is activated to measure the person’s facial temperature and match the measured temperature with the person’s name before storing the information into the sdcard and records the person’s attendance. figure 9 also shows the phyton shell output which validates the information that has been stored into the sd-card. the output of the phyton shell is also shown on the lcd as shown in figure 10. c. conditions of the face thermal recognition system when the face detection and recognition are successfully validated, the program reads the temperature of the person. as mentioned above, fever is the most common symptom of covid-19. this stage is important to validate the system’s operation. if the system is unable to distinguish between a lowrisk and a high-risk individual, this system failure will cause possible spread of the covid-19 disease. according to the world health organization (who), normal human body temperature ranges from 35.0°c to 37.1°c as shown in figure 4 and people with this range of facial or body temperature are considered healthy and fit to work. a person with a fever is defined as someone who has a body temperature greater than 37.1°c (figure 5) [12-14]. so, the temperature scanned values are classified as normal and high for the respective temperatures as shown in table i. table i. conditions and temperatures conditions temperature (˚c) normal 35.0 – 37.0 high 37.1 – 40.0  condition 1 if the measured temperature is between 35°c and 37°c (normal), the temperature value will be displayed on the lcd when the person’s name is matched (figure 11). once the person’s name has been confirmed and the amg8833 thermal camera sensor has successfully read the normal temperature of the user, the name and the temperature will be recorded into the attendance list accordingly. similarly, the person’s data are also recorded into the system’s database to provide real-time health monitoring update of the person. this attendance record can also be sent to relevant authorities as shown in figure 11.  condition 2 if the measured temperature is between 37 o c and 40 o c, then the person is not allowed to enter the premise or building. the person's information/data are sent through an email notification to the competent authorities. also, during the temperature scanning, the status "temperature high" is displayed on the lcd and at the python shell as shown in figure 13. figure 14 shows an email notification containing information about the scanned person’s temperature. d. summary the presented results successfully validated the proposed real-time analytic face thermal recognition system integrated with email notification. the system did successfully perform the face detection and recognition tasks, measured the facial engineering, technology & applied science research vol. 13, no. 1, 2023, 9961-9967 9966 www.etasr.com singh et al.: a real-time analytic face thermal recognition system integrated with email … temperature of the scanned person, and sent an email notification when required. therefore, the proposed system's design and integration method can be implemented into premises or buildings to assist the early detection of any feverrelated illness. fig. 11. normal temperature condition. fig. 12. file csvindividual name and temperature attendance list. fig. 13. high temperature condition. fig. 14. email notification. iv. conclusion a real-time analytic face thermal recognition system integrated with email notification was developed and deployed in order to assist the early detection of any fever-related illness, especially covid-19. due to the severity of the covid-19 disease, the proposed system has integrated some features that may assist the authorities and keep the premises or buildings safe. also, the integrated hardware and software successfully validated the objectives of the real-time analytic face thermal recognition system integrated with email notification. in terms of system deployment, the system can be placed in any open space, where the respective person is needed to perform temperature scanning before entering a building or premise. acknowledgment the authors gratefully acknowledge the support of the centre of telecommunication research & innovation (cetri), fakulti kejuruteraan elektronik dan kejuruteraan komputer (fkekk), universiti teknikal malaysia melaka and the ministry of higher education, malaysia. references [1] r. saher and m. anjum, "role of technology in covid-19 pandemic," researches and applications of artificial intelligence to mitigate pandemics, vol. 2021, pp. 109–138, 2021, https://doi.org/10.1016/b9780-323-90959-4.00005-5. 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[13] k. h. rahouma and a. z. mahfouz, "design and implementation of a face recognition system based on api mobile vision and normalized features of still images," procedia computer science, vol. 194, pp. 32– 44, jan. 2021, https://doi.org/10.1016/j.procs.2021.10.057. [14] v. k. sharma, "designing of face recognition system," in 2019 international conference on intelligent computing and control systems (iccs), madurai, india, feb. 2019, pp. 459–461, https://doi.org/ 10.1109/iccs45141.2019.9065373. microsoft word 2-627-ed.doc engineering, technology & applied science research vol. 6, no. 2, 2016, 927-930 927 www.etasr.com alameen et al.: improved genetic and simulating annealing algorithms to solve the traveling… improved genetic and simulating annealing algorithms to solve the traveling salesman problem using constraint programming mamoon alameen school of engineering, the australian college of kuwait, kuwait m.radiy@ack.edu.kw mohammed abdul-niby school of engineering the australian college of kuwait, kuwait m.nibi@ack.edu.kw ayad salhieh school of engineering the australian college of kuwait, kuwait a.salhieh@ack.edu.kw ali radhi bahbahani projects kuwait city, kuwait ali.radhi@gmail.com abstract— the traveling salesman problem (tsp) is an integer programming problem that falls into the category of np-hard problems. as the problem become larger, there is no guarantee that optimal tours will be found within reasonable computation time. heuristics techniques, like genetic algorithm and simulating annealing, can solve tsp instances with different levels of accuracy. choosing which algorithm to use in order to get a best solution is still considered as a hard choice. this paper suggests domain reduction as a tool to be combined with any metaheuristic so that the obtained results will be almost the same. the hybrid approach of combining domain reduction with any metaheuristic encountered the challenge of choosing an algorithm that matches the tsp instance in order to get the best results. keywords-traveling salesman problem; genetic algorithm; simulating annealing; domain reduction i. introduction the traveling salesman problem (tsp) is a problem of “finding the shortest possible route given a list of cities and the distances between each pair of cities, such that the route visits each city exactly once and returns to the origin” [1]. the increasing numbers of vehicles and the fluctuation of oil prices as well as the need to reduce costs, ignited the search to optimize the travel of sales personnel and the daily delivery and transport plans. accordingly, the vehicle routing problem (vrp) and the tsp are important problems in the field of customer services and in the distribution network. they played a significant role in reducing the costs and time and hence improving the service. this paper considers a symmetric tsp, where a number of cities (or customers) is given as well as the distances between each pair of these cities, and the problem is to find the shortest possible routes that visits each city exactly once and return to the origin. this problem was raised, with trial for a mathematical formulation, in the early 19th century in the uk [2]. a general form of the tsp mathematically tackled for the first time by karl menger at 1930. karl menger was able to define the problem and to find out that the nearest neighbor heuristic would not provide the optimal solution. since then, the tsp is being a very popular subject and many efforts are carried out to determine the optimal solution for certain variants. in the last years, the tsp problem approach has been extended and modified to provide special solutions for other fields in life, such as for dna fragmentation or for finding the optimal insert sequence of smd components and optimal soldering points sequence. over the past decades, tsp instances had been encountered using too many types of approaches. techniques like exact methods, classical and meta-heuristics had been applied to solve tsp instances with various dimensions. it is a fact that choosing between exact and heuristics approach to solve tsp is an easy choice as it is governed by the accuracy vs time concept. choosing between classic and meta-heuristics is also an easy choice for the same reason. on the other hand, choosing the right meta-heuristics to solve the tsp could be very challenging as some of them are working excellently on one problem and fail to provide a good solution on others [3]. this paper surveys the effect of domain reduction on the final results of using genetic and simulating annealing algorithms to solve tsp. the objective is to minimize the domain of the problem in order to minimize the search iterations for the algorithms and getting close (if not similar) results. ii. mathematical formulation this paper consider the following mathematical formulation for the tsp [4]: for i = 0, ..., n, let i u be an artificial variable, and finally take ijc to be the distance from city i to city j. min     n i n jij ijij xc 0 0, (1) i u î z , 0, ...,i j n= (2) engineering, technology & applied science research vol. 6, no. 2, 2016, 927-930 928 www.etasr.com alameen et al.: improved genetic and simulating annealing algorithms to solve the traveling… 1 ,0   n jii ijx nji ,...,0,  (3) 1 ,0   n ijj ijx nji ,...,0,  (4) 1 nnxuu ijji nji 1 (5)     0 1 ijx (6) where (1) is the objective function. (2) implies that i u are integers, (3) is to get sure that each city visited at most once, (4) serves the fact that all cities must be visited, (5) is to get sure that there is only one tour for the problem and (6) implies that the value of x is 1 if the path goes from city i to city j and 0 otherwise. iii. meta-heuristics the quality of the solution obtained by any of the metaheuristic algorithms is usually much better than the ones obtained by the classical algorithms because the metaheuristic algorithms explore all the solution space deeply. however, metaheuristics take more time than the classical heuristics. the following elaborates two popular metaheuristics: a. simulating annealing (sa) [5] sa is a stochastic relaxation technique that has its origin in statistical mechanics. formerly, the process of crystallizing a solid by heating it to a high temperature and gradually cooling it down motivated the development of sa. assuming ( ) ( ) t f x f xd = , where ( )f x is the best value for the objective function found so far, and ( ) t f x is the value of the objective function at iteration t. the solution will be accepted as a new current solution if 0d £ . if 0d > , any moves with a probability of te-d increase of the objective function are accepted, where t is the temperature and its value varies from large to close to zero. the values of t are controlled by a cooling schedule that specifies the temperature values at each stage. in the literature it was proposed that a solution x is drawn randomly in ( ) t n x at t iterations. if ( ) ( ) t f x f x£ , then xt+1 is set equal to x; otherwise 1 1 t t t t x with probability p x x with probability p + = ìïïí ïïî where pt is a decreasing function of t and of ( ) ( )tf x f x. with the pre-specified values for π1, π2 and ki the sa stops when: • the value f* has not decreased by π1% for at least k1 consecutive cycles of t iterations. • the number of accepted moves has been less than π2% of t for k2 consecutive cycles of t iterations. • ki of t iterations have been executed the application of sa to solve tsp is to take an initial solution to the problem and consider it as the best solution. a parallel search for removing and adding cities from the routes follows. the adding and removing is a random process within the above mentioned boundaries, updating the best solution as the total distance is reduced. b. genetic algorithm (ga) [6] coming from a biological background for simulation of the evolution using the gens, the algorithm represents a solution as a population of chromosomes:  1111 ,, nxxx  n here is the number of vertices (or cities). to proceed, the following three steps are carried out: • two “parent” chromosomes from x 1 are selected. • these parent chromosomes are used to produce offsprings that forms the next generation. • each offspring is then mutated randomly utilizing a small probability. the above three steps will be repeated k times for each iteration t=1,…,t, where 2nk  and t is the number of generations. the next step will be applied: xt+1 from xt. this is achieved by removing the 2k worst solution in xt (the ones with the furthest distances) and replacing them with 2k new offsprings. additionally, to apply the ga to solve tsp, two points have to be considered: • initial population constructor. which means initial solution to the problem has to be provided • determine fitness, crossover and mutation operators. which means that a criterion for improving the solution (new iteration) has to be specified. the ga will be repeated for a pre-specified number of iterations. c. constraint programming (cp) [7] constraint programming techniques have been developed since early 1990s. they have two common features: • constraint propagation • distribution (labeling) connected with search. constraint propagation will lead to constraint programming (cp). it would automatically remove from the domain of variables all values that do not fulfill constraints. let us consider these examples: • let x-y=3 or x<y. these 2 given constraints would provide information about the values of the variables x and y, but it is in a poorly usable form. cp will work to simplify such information. if we have, beside xengineering, technology & applied science research vol. 6, no. 2, 2016, 927-930 929 www.etasr.com alameen et al.: improved genetic and simulating annealing algorithms to solve the traveling… y=3, another information that x+y=7, then the solution would be: x=5 and y=2. this simplification will be carried out by a special algorithm, the constraint solver, a fixed part of the cp. • if we have two variables x and y, with x∈{1..5} and y ∈{1..6}. we introduce here a constraint with x>y+1, then the constraint propagation will reduce the domains to the following values: x∈{3, 4, 5} and y∈{1, 2, 3} because values {1, 2} from x domain do not fulfill the constraint x>y+1 and the y values {4, 5, 6} also conflict with the given constraint. • in the last example, if we add another constraint x+y=6, then none of the values can be removed. usually we don’t have the joy of such simple constraints. they are often connected with each other. therefore, constraint propagation would not remove all values that are in conflict with all constraints and its performance is measured as a tradeoff between number of removed values and execution time. actually, constraint propagation does not lead to the solution (example above). this explains the need to always add a distribution connected with the search. distribution is based on incorporation of an additional constraint, often it is a constraint about equality of one variable to one value. a major task of the distribution is to find or choose a proper variable and a suitable value. as soon as this is achieved, a consistency is checked and there will be three possibilities: • a solution is found • variables domains are narrowed, but there is no unique solution, so distribution is conducted with another variable • the additional constraint is inconsistent with other constraints, so the backtrack is made and from the chosen variable domain a chosen value is removed. this is an iterative process and it is called “search”. search is responsible for stopping after finding the first solution or some number of solutions or all solutions. search forms a search tree, where each node is a state of variables. iv. computations this paper applies sa and ga to 12 benchmark problem from the tsp library [8]. the size of each problem increase by almost a factor of 2 in order to survey the effect of the reduction. tsp instances that considered in this paper are shown in table i. the distance between the cities were calculated and placed in to a symmetric distance (cost) matrix then: r*=rr 100 s (7)            otherwise 5001problem theof size750 theif ...0,20,40,60 750problem theof size250 theif ...0,15,30,45 250problem theof size theif ...0,10,20,30 s (8) r is the maximum distance in the distance matrix. all the distance values above r* should be neglected. the above domain reduction technique suggests that the arcs between far cities will not be considered. the solution starts by taking all distances, then based on the size of the problem the domain will be reduced by 10% from the maximum distance then 20% and so on until no feasible solution can be obtained (in case the size of the problem less than or equal to 250). the solution considered in this case will be the one with the least distance or cost. table ii provides the results of applying genetic algorithm and simulating annealing to solve tsp combined with domain reduction. table i. tsp instances and dimension problem number size description 1 29 bays29 2 48 gr48 3 101 eil101 4 202 gr202 5 493 d493 6 1002 pr1002 7 2103 d2103 8 3038 pcb3038 9 7397 pla7397 10 13509 usa13509 11 33810 pla33810 12 85900 pla85900 table ii. the results of the improved sa and ga problem no. sa ga optimal solution improved sa improved ga 1 2020 2020 2020 2020 2020 2 5046 5046 5046 5046 5046 3 668 670 629 629 629 4 42518 45922 40160 40992 41374 5 54229 73417 35002 37898 379524 6 285534 348604 259045 261409 261409 7 103250 127831 80450 91693 91332 8 169782 183421 137694 148972 148972 9 318864 58 418940 01 23260728 23853401 23853401 10 351098 14 357102 28 19982859 22014415 22014415 11 713231 37 751151 03 66048945 66829102 66829102 12 200219 623 265892 412 14238264 1 14792011 4 14792011 4 graphically the obtain results of table 2 can be illustrated as shown in figures 1 to 6. engineering, technology & applied science research vol. 6, no. 2, 2016, 927-930 930 www.etasr.com alameen et al.: improved genetic and simulating annealing algorithms to solve the traveling… fig. 1. tsp instances 1-4 solved by ga and sa fig. 2. tsp instances 5-8 solved by ga and sa fig. 3. tsp instances 9-12 solved by ga and sa fig. 4. tsp instances 1-4 solved by improved ga and sa fig. 5. tsp instances 5-8 solved by improved ga and sa fig. 6. tsp instances 9-12 solved by improved ga and sa v. conclusion and future work as table ii suggests, small dimension problems can be solved (optimally) sometimes no matter the algorithm applied. for medium to large sized problems the solution obtained by applying genetic algorithm is very close (if not the same) for the solution obtained by applying simulating annealing. in brief combining domain reduction with genetic algorithm and simulating annealing provides the following important advantages: • improves the solution for one or both algorithms • using either genetic or simulating annealing provides similar results once domain reduction is combined with the selected algorithm. • the domain reduction approached improved the accuracy of sa and ga and also minimized the searching process iterations for the large size instances. in order to acquire the full benefit of using domain reduction with meta-heuristics, more well-known algorithms should be considered. algorithms like tabu search and ant colony should be applied to solve tsp combined with domain reduction in the future. also, a general and more logical domain reduction approach should be taken in order to minimize the computation time. references [1] g. gutin, a. yeo, a. zverovich, “traveling salesman should not be greedy: domination analysis of greedy-type heuristics for the tsp”, discrete applied mathematics, vol. 117, no. 1–3, pp. 81–86, 2002 [2] c. h. papadimitriou, “the euclidean traveling salesman problem is npcomplete”, theoretical computer science, vol. 4, no. 3, pp. 237–244, 1977 [3] a. corberán, m. oswald, i. plana, g. reinelt, j. m. sanchis, “new results on the windy postman problem”, mathematical programming, vol. 132, no. 1-2, pp. 309-332, 2012 [4] r. martí, g. reinelt, the linear ordering problem. exact and heuristic methods in combinatorial optimization, springer, heidelberg, 2011 [5] s. kirkpatrick, c. d. gelatt jr, m. p. vecchi, “optimization by simulated annealing”, science, vol. 220, no. 4598, pp. 671–680, 1983 [6] l. m. schmitt, “theory of genetic algorithms”, theoretical computer science, vol. 259, no. 1–61, 2001 [7] f. benhamou, n. jussien, b. o' sullivan, trends in constraint programming, john wiley and sons, 2007 [8] universität heidelberg, tsplib, 2013 tsp data microsoft word etasr_v12_n4_pp8972-8977 engineering, technology & applied science research vol. 12, no. 4, 2022, 8972-8977 8972 www.etasr.com ponukumati et al.: an intelligent fault detection and classification scheme for distribution lines … an intelligent fault detection and classification scheme for distribution lines using machine learning balamurali krishna ponukumati school of electrical engineering kiit deemed to be university bhubaneswar, india and department of eee madanapalle institute of technology and science madanapalle, india pbmk20031993@gmail.com pampa sinha school of electrical engineering kiit deemed to be university bhubaneswar, india pampa.sinhafel@kiit.ac.in manoj kumar maharana school of electrical engineering kiit deemed to be university bhubaneswar, india mkmfel@kiit.ac.in a. v. pavan kumar department of eee madanapalle institute of technology and science madanapalle, india pawanrao82@gmail.com akkenaguntla karthik department of eee madanapalle institute of technology and science madanapalle, india akarthik160@gmail.com received: 28 may 2022 | revised: 8 june 2022 | accepted: 9 june 2022 abstract-the current paper focuses on the development and deployment of machine learning (ml) based algorithms for the classification and detection of different faults in the electrical distribution system. the methodology adapted using ml has higher computational accuracy than traditional computational algorithms. the parameters involved in developing ml for fault detection/classification are fundamental frequency, fault voltage, and current components at fault situations. during faults, the current and voltage waveforms consist of high-frequency transient signals. the wavelet decomposition (wd) technique is used to break down transient signals to obtain the required information. to investigate the performance of the ml-based algorithms, an ieee 33 bus system is utilized, and a fault is generated in matlab/simulink environment. the methodologies used for fault detection and classification are k nearest neighbor (knn), decision tree (dt), and support vector machine (svm). the performance of the designed algorithm is assessed by employing a confusion matrix, and the results demonstrated extraordinarily high accuracy. keywords-machine learning; wavelet decomposition; k nearest neighbor; decision tree; support vector machine i. introduction the intricacy of power system networks presents many difficulties in distributing and preserving electricity. the primary aim of the protection system is safeguarding the overall system by identifying faults and preventing malfunctions to attain adequate power supply continuity [1]. numerous domestic and commercial clients possess equipment that is susceptible to electrical interference [2]. a good protection system must ensure system stability by protecting against all types of failures at all network locations. a system built with the current technology must be trustworthy and dependable [3]. phasor measurement units (pmus) can detect a variety of typical distribution system events, including load and equipment switching transients and short circuit faults [4, 5]. convolutional neural networks (cnns) are implemented in a variety of fields, including object recognition and language recognition. cnns are getting increasingly popular, notably in power system management and control, due to their capacity and feasibility in identifying and classifying issues that arise in corresponding author: balamurali krishna ponukumati engineering, technology & applied science research vol. 12, no. 4, 2022, 8972-8977 8973 www.etasr.com ponukumati et al.: an intelligent fault detection and classification scheme for distribution lines … power systems [6-11]. the authors of [12] employed support vector regression (svr) to enhance the effectiveness of shortterm estimation techniques based on historical electricity demand information. authors in [13] suggest fault categorization in a distribution network by implementing an adaptive neuro-fuzzy inference system (anfis), and authors in [14] discuss rapid fault recognition and categorization in electrical distribution networks employing a hybrid of fuzzy logic and singular entropy theory. the application of ml is not restricted to limited fields. it is also applied to the agriculture sector in detecting plant diseases [15]. the necessity for a highly precise and resilient waveform deviation tracking system in high-voltage power systems makes research into its categorization and identification using deep learning techniques a popular subject [11, 16, 17]. in [18], a hybrid strategy of gated recurrent unit (gru) with discrete wavelet transform (dwt) involved features employed as inputs. fault recognition and categorization in microgrid employing cnns was proposed in [19] fast fourier transform (fft), dwt, s-transform (st) and statistical techniques are some examples [20-23] of ml algorithms used for fault detection and classification in distributions lines and microgrids. usually, the extraction of the feature components is specific to the system setup and might involve continued attempts, limiting generalization [24]. dwt is widely used in the feature extraction step [25]. however, the feature extraction section and functioning approaches are unique throughout respective deployments. for example, as a functional technique for defect identification, [26] employs dwt calculated singular entropy including a set of parameters. this approach works perfectly, however, the margin to greater fault impedance wasn’t addressed. in [27], dwt is employed to collect features from current signals, while particle swarm optimization (pso) is used to select the best wavelet configuration. for fault categorization and diagnosis in a microgrid, authors in [10, 25] propose ml and in [18] propose deep learning-based methods. to categorize the problem, the wavelet transform is utilized to extract data from current signals, which are then classified using svm [28] and dt [12]. techniques such as anfis, fuzzy interference systems (fis), artificial neural networks (anns), feedforward neural networks (fnns), cnns, and conventional fault identification with relay systems are some efficient ml techniques. ml focuses on extracting knowledge from a large set of information and provides conventional ways for problemsolving. it really can deal with a wide range of information and be employed in various situations. furthermore, by integrating more data for training, the accuracy of ml algorithms improves. controllers like fuzzy logic and fis are straightforward and use "if-then" relationships to handle problems with uncertainty. they are a generally strong candidate even though they require huge training data sets. incorporating anfis assists with tunable characteristics, decreases computational time, gives quick convergence and responsiveness, but the difficulty arises when large computation is expected, which is removed by adopting ml. the anns, fnns, and cnns help predict the specific fault type and are simple to apply. their use is simple, involving merely a few characteristics to be adjusted, and have many applications in real-world situations, but the training procedure is rather hard for high-dimension challenges. the gradientbased back propagation approach for non-linear discrete classification tasks provides a locally optimal solution. slow convergence is provided by anns in the back propagation method. the convergence is determined by the initial value of weight restrictions linked to the system. conventional relay systems use mechanical parts to detect a fault. these mechanical parts need periodical maintenance, otherwise their performance will be degraded and it should match the ratings of the transmission or distribution line. figure 1 depicts the flowchart of the suggested approach, where va, vb, and vc are the three-phase voltages, ia, ib, and ic are the three-phase currents, vcoff and icoff are voltage and current coefficients, and the angles between v and i are considered as inputs. these inputs are fed to the developed ml detection and classification algorithm which continuously monitors the status of inputs until a fault occurs. fig. 1. flow chart of the proposed methodology. ii. fault detection analysis wd approach is considered to detect the fault and classify it. the wd method was also utilized in [29, 30] to extract the waveform but that’s a 3-level decomposition, whereas this approach uses a 6-level wd as shown in figure 2. the fault/disturbance signal is routed via low pass filters (lpfs) and high pass filters (hpfs) until the necessary signal for analysis is achieved. the fault/disturbance signal is decomposed at 6 levels by passing via an lpf d and an hpf a. at level 1, the signal is decimated by 2 and d1 and a1 signals are obtained. d2 and a2 are obtained by passing the a1 signal through the second stage of lpf and hpf. again, a2 passes through filters until level 6 and the final obtained signals are d6 and a6. as a result, significant information is derived from the initial signal which has to be evaluated. iii. phase locked loop a phase-locked loop (pll) is a regulatory technique which produces a signal as output with a phase-matched to that of an input signal. its block diagram is illustrated in figure 3. in order to keep the inlet and outlet phases locked, the input and output frequencies must be steady. using the input voltage, vabc, vd, and vq are obtained. vd and vq are voltage values near the point of common coupling (pcc) in the dand qaxes respectively. the output is an approximation of the voltage phase. the suggested pll architecture for fault identification is depicted in figure 3. engineering, technology & applied science research vol. 12, no. 4, 2022, 8972-8977 8974 www.etasr.com ponukumati et al.: an intelligent fault detection and classification scheme for distribution lines … fig. 2. six level wavelet-decomposition. fig. 3. block diagram of the pll. in comparison to the block diagram in figure 2, the error signal e(t) relates to the waveform deviation, while the proportional-integral (pi) regulator and integrator correlate to the loop filter and voltage controlled oscillator (vco) respectively. the three-phase voltages (va, vb, and vc) that are sent into the pll are first changed to αβ quantities (vα and vβ) using clarke’s transformation. a schematic of a pq-pll block is demonstrated in figure 4. the quantities are then transferred into a reference frame. considering the proximity of the αβ quantities to the reference frame, an error signal is created. the error signal is sent into a pi regulator, which controls the error to zero. the input signals are in phase with the frame of reference once the error is zero. when the pll's output angle is in phase with the current of phase a, the error is exactly zero. when there is a transient in the system, the error signal deviates from zero. the magnitude and frequency of the deviation will vary depending on the features of the transient. fig. 4. block diagram of the pq-pll. iv. machine learning as the name implies, ml is a phrase that is used to define the field of learning algorithms. an ml model will generally have three different phases: training, validation, and real-time implementation. during the training process, the system is fed through test data with known correlations so that it can detect patterns and create predictions within the same set accurately. the validation stage is intended to assess the overall system performance utilizing similar but disjoint data, as well as previously identified responses. in terms of model training methods, ml is typically classified into four major methodologies: supervised, unsupervised, semi-supervised, and reinforced learning. models which are trained on a sample with knowing labelled outcomes are referred to as supervised learning. a list of classification algorithms that have been frequently used in the literature follows. a. support vector machine during appropriate post-fault diagnosis, a knowledge-based approach that is based on svms is offered. svms are used as an intelligence tool to detect the faulty line originating first from the substation and to determine the distance from that. svms are compared to radial-based neural networks in datasets that depict diverse transmission system challenges. b. decision tree the dt's design is simple, and we can easily follow the tree structure to describe how to make a conclusion. the vast scope of power system dts has lately been discovered to be extremely effective in applications such as online dynamic safety evaluation, stability to transients, and islanding identification. c. k nearest neighbor the knn approach is a safe, supervised ml approach utilized to tackle classification and regression issues. faults may be detected and recognized in distance protection using the knn method. engineering, technology & applied science research vol. 12, no. 4, 2022, 8972-8977 8975 www.etasr.com ponukumati et al.: an intelligent fault detection and classification scheme for distribution lines … d. bayesian learner the bayesian classifiers, also called naïve bayes are statistical classifiers that estimate the probability of class membership using supervised learning techniques. e. sequential minimal optimization (smo) training an svm necessitates the solving of a large quadratic programming optimization problem. smo divides this massive quadratic programming issue into a bunch of smaller quadratic programming problems. f. logistic regression if the dependent variable is binary, logistic regression is the best regression approach to use. like other regression studies, it is a statistical approach. the dependent variable y in logistic regression has values of 1 and 0 for the outcomes of interest. g. linear regression the relation between both the input variables (x) and output variables (y) for linear regression is generally stated as a linear equation of the form y = a + bx. as a result, the aim of linear regression would be to determine the values of coefficients a and b, where a is the interception and b is the line's slope. v. results and discussion a. the considered ml techniques to detect the fault and classify it in the distribution network, the testing data are evaluated using svm and dt algorithms. • if there are little training data (less than 1000), support vector methods are often good because they are highly regularized. • svms have better production results than anns, while they avoid the problem of over-fitting. one can use the kernel function in the svm to solve complex problems. they can effectively handle data with higher dimensions that are linear inseparable. for data preprocessing, wd is employed. matlab is used to obtain various operating and fault data. a total of 2746 input samples are considered, with 70% are used for training and 30% for testing the model’s performance. the training data are used to train a model that can predict how to respond to incoming new data. table i shows the accuracy rates of the tested algorithms. the cubic svm algorithm yielded the best accuracy rate of 87.1%. table i. performance analysis classifier accuracy fine tree 82.20% medium tree 79.40% coarse tree 55.20% linear svm 52.50% quadratic svm 78.20% cubic svm 87.10% fine gaussian svm 63.60% medium gaussian svm 67.20% coarse gaussian svm 51.80% b. case study the developed ml algorithms are tested on the ieee 33 bus system (figure 5). the suggested fault detection and classification technique was tested using the ieee 33 radial distribution scheme. a fault is developed to analyze the performance of the system. figure 6 illustrates the occurrence of an l-g fault between 0.2s and 0.4s in a three-phase voltage waveform. wd is used to assess the fault voltage signal. figure 7 depicts the lg fault voltage signal of a multiresolution wd. the db6 wavelet is used for producing a 6-step decomposition. at every frequency spectrum, the rebuilt variants of every element, along with the approximation and records of the unique signal, are represented. fig. 5. the ieee 33 bus system. fig. 6. three-phase voltage waveforms under l-g fault occurrence. c. confusion matrix the confusion matrix is the most often used method for evaluating the accuracy and correctness of a classification algorithm. it also helps identifying areas where the classifier has underperformed. it can also help understanding what the classification model is doing correctly and what sorts of errors it is producing. in figure 8, the faulty classification confusion matrix is shown. it is evident that the suggested system can classify various faults, and the prediction rate is high. figure 9 shows the true positive rate (tpr) and false negative rate (fnr) data and the tpr value is high, which says that the model can detect faults accurately. precision is a measure of how accurate a classifier is. a low accuracy might also be indicative of a massive amount of false positives. figure 10 shows the positive predictive value (ppv) engineering, technology & applied science research vol. 12, no. 4, 2022, 8972-8977 8976 www.etasr.com ponukumati et al.: an intelligent fault detection and classification scheme for distribution lines … and false discovery rate (fdr) values. it is clear that the ppv has higher value than fdr. the rows of the confusion matrix correspond to the anticipated class, while the columns are commensurate to the actual class. the diagonal cells are commensurate to suitably categorized observations. the offdiagonal cells are commensurate to observations that were wrongly categorized. fig. 7. wd analysis on lg fault. fig. 8. faulty classification confusion matrix. fig. 9. tpr and fnr values of data. fig. 10. ppv and fdr values of data. vi. conclusion the utilization of ml algorithms for fault categorization and identification on a three-distribution network was extensively investigated in this study. the created systems used instantaneous current and voltage data as inputs for fault detection and categorization. this paper described a waveformbased fault classification method for electrical distribution systems. wd was employed for bringing out the features from recorded wave data. the massive volume of wave data processing activity was treated effectively by carefully spreading the computing burden. ml modules identified and classified the faults. the fault classification and detection results demonstrate the efficacy of ml in categorizing and identifying faults in less time than other traditional relaying systems. the systems make 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[30] b. k. p, p. sinha, m. k. maharana, c. jena, a. v. pavan kumar, and k. akkenaguntla, "power system fault detection using image processing and pattern recognition," in 2nd international conference on applied electromagnetics, signal processing, & communication, bhubaneswar, india, nov. 2021, pp. 1–5, https://doi.org/10.1109/aespc52704.2021. 9708475. microsoft word etasr_v12_n3_pp8525-8531 engineering, technology & applied science research vol. 12, no. 3, 2022, 8525-8231 8525 www.etasr.com mahyoob et al.: sentiment analysis of public tweets towards the emergence of sars-cov-2 omicron … sentiment analysis of public tweets towards the emergence of sars-cov-2 omicron variant: a social media analytics framework mohammad mahyoob department of languages and translation faculty of science & arts at al-ola taibah university madinah, saudi arabia mqassem@taibahu.edu.sa jeehaan algaraady department of english taiz university yemen jihan.amu@gmail.com musaad alrahaili department of languages and translation faculty of arts & humanities taibah university madinah, saudi arabia mrahaili@taibahu.edu.sa abdulaziz alblwi department of computer science applied college taibah university madinah, saudi arabia ablwi@taibahu.edu.sa received: 22 february 2022 | revised: 16 march 2022 | accepted: 25 march 2022 abstract-while different variants of covid-19 dramatically affected the lives of millions of people across the globe, a new version of covid-19, "sars-cov-2 omicron," emerged. this paper analyzes the public attitude and sentiment towards the emergence of the sars-cov-2 omicron variant on twitter. the proposed approach relies on the text analytics of twitter data considering tweets, retweets, and hashtags' main themes, the pandemic restriction, the efficacy of covid-19 vaccines, transmissible variants, and the surge of infection. a total of 18,737 tweets were pulled via twitter application programming interface (api) from december 3, 2021, to december 26, 2021, using the sentistrength software that employs a lexicon of sentiment terms and a set of linguistic rules. the analysis was conducted to distinguish and codify subjective content and estimate the strength of positive and negative sentiment with an average of 95% confidence intervals based upon emotion strength scales of 1-5. it is found that negativity was dominated after the outbreak of omicron and scored 31.01% for weak, 16.32% for moderate, 5.36% for strong, and 0.35% for very strong sentiment strength. in contrast, positivity decreased gradually and scored 16.48% for weak, 11.19% for moderate, 0.80% for strong, 0.04% for very strong sentiment strength. identifying the public emotional status would help the concerned authorities to provide appropriate strategies and communications to relieve public worries towards pandemics. keywords-sentiment analysis; social media; sars-cov-2 omicron; twitter; text analytics; data mining i. introduction with the emergence of social media, using machine and deep learning for sentiment analysis attract many researchers because it is scalable to process and analyze big data. machine learning (ml) algorithms learn the hidden patterns of the data and can predict the class labels of unknown samples. thus, ml is widely applied in sentiment analysis to predict public sentiments [1, 2]. covid-19 emerged as an infectious disease that created a global crisis that dramatically affected the world in different sectors like education [3], health, economy, etc. amidst the crisis of coronavirus, new mutations of covid-19 emerged, such as the beta, delta, and omicron variants [4], spreading panic and fear in people. the sars-cov-2 omicron variant was first detected in south africa on november 24, 2021, and has spread to more than 57 countries [5]. the impact of the sars-cov-2 virus is still a source of concern globally. many countries announced an acceleration of booster jab rollouts, and the people fear that the variant may destabilize the efficacy of covid-19 vaccines. many countries sealed their borders to foreign visitors. measuring the public's sentiments and opinions towards the omicron version is important, not only to give us a clear picture of their sentiments, but also to explain whether the public attitude and awareness towards this variant are affected by their earlier experiences with covid-19. in addition, this evaluation would provide the policymakers with the actual public sentiments and enable them to evaluate their earlier proposed strategies, recommendations, and effectiveness messages and modify them according to the current condition. the disseminated information on the covid-19 pandemic gave birth to various mental and psychological concerns for social media users [6]. corresponding author: mohammad mahyoob engineering, technology & applied science research vol. 12, no. 3, 2022, 8525-8231 8526 www.etasr.com mahyoob et al.: sentiment analysis of public tweets towards the emergence of sars-cov-2 omicron … the impact of the omicron pandemic may affect the public in the same way and return the earlier scenario of the covid-19 pandemic. in the beginning, people in different countries were more worried than before, as the early indication is that omicron is more transmissible than other covid-19 variants, and there is a devastating consequence in its infection rate [7]. in addition, it is more capable than delta of preventing the immune defense of both the vaccinated and the previously infected people. the publics' concerns were highly raised after the world health organization (who) reports about the omicron rapid outbreak. people and health officials started sharing and expressing their opinions, emotions, clarifications, and recommendations on social media and social networking sites. the main concern of social media analytics is to collect data using various methods, processes and understand, summarize, and visualize the output [8]. social media surveillance can systematically monitor public emotions and reactions to epidemical events in real-time [9]. these expressions comprise rich and open data for researchers, especially for survey and classification studies such as sentiment analysis or opinion mining. sentiment analysis processes and identifies the data of certain domains through natural language processing. sentiment analysis using social media plays a crucial role in various fields such as social development, people's awareness, economic development [1012]. indeed, many studies applied ml, and deep learning (dl) methods and algorithms to explore and investigate the public's sentiments on social media platforms towards the outbreak of covid-19 and its emerging variants [13-15]. however, no recent studies have detected public sentiments towards the emergence of the omicron variant. only a few articles and reports such as [16, 17] investigate omicron's situation as it emerged recently. to the best of our knowledge, this study is the first to reveal and explore the public feelings and views towards the sars-cov-2 omicron variant worldwide through the sentiment analysis of social media, mainly twitter. the social media analytics sentistrength software and voyant-tools were utilized to analyze the data. this study gives us a clear picture of the public's sentiment towards this pandemic which would help the authorities provide appropriate information to relax and ease the public's panic. moreover, it helps the government address future health emergencies, including transmittable diseases, and provide better healthcare. ii. related work this study aims to explore and mine the publics' opinion and find out the percentage of the positivity and negativity toward the new covid-19 omicron variant. as the new variant emerged on november 24, 2021, a few articles and reports are investigating omicron's situation. authors in [18] commented on the omicron variant's implications for transmission, cure, and diagnosis. their recommendation is to continue in the cautions of wearing masks, social distancing, vaccination, etc. authors in [19] studied the potential prediction of the omicron variant and provided some recommendations which can be used to protect people from the omicron virus. authors in [20] studied the detection of public opinion about the effectiveness of vaccination during the omicron variant outbreak. the data were collected from youtube comments of english news channels. they classified the comments into positive, negative, and neutral using vader and textblob tools. they applied the svm algorithm to analyze the data. the results scored 63% accuracy in textblob and 70% with vader. authors in [16] studied the previous covid-19 vaccines' efficacy against the sars-cov-2 omicron variant. the study concluded that there is no or limited protection against the symptoms of the omicron variant by using some previous cures used for the other covid-19 variants [17]. many studies investigated the public sentiment since the covid-19 emergence. authors in [21] conducted a study about the outbreak of covid-19 in italy. the interest of the research was to predict the disease evolution in the country. the authors collected their data from the official channels declaring the number of infected people in different italian provinces. the model of the spatio-temporal distribution of covid-19 was used. an endemic-epidemic multivariate time-series mixed-effects generalized model has been used for counting to understand the spatio-temporal diffusion of the disease. the study results were divided into three phases. the first was related to the outbreak of covid19 over time. the second was devoted to the transmittance of the disease among the people of the same district. and the third was concerned with the spatial neighborhood and the main reasons for the contagion effect. they also found that strict control measures in some districts effectively limit contagion and disease outbreaks. a considerable amount of the literature has been published on the public’s attitudes towards the covid-19 pandemic. to the best of our knowledge, no previous study has investigated the reaction of the people to the new variant of the pandemic in social media, especially twitter, and this is the gap this study aims to fill. iii. method and data acquisition this section presents the construction of the harvested data and the proposed method. the tweets were collected by searching keywords submitted as seeds to twitter via its api, likely about covid-19 omicron variant from december 4, 2021, to december 26, 2021, using the social media analytics sentistrength software [22]. the quoted queries were "omicron", "covid-19 variant omicron", "sars-cov-2", "covid-19". the data were filtered out for cleaning and removing the duplicates, getting 18,737 posts generated by 15,388 post authors (2400 female, 3759 male, 12578 unknown) distributed across countries (56.9% none, 23.1% usa, 14.7% uk, 9.0% australia, 7.1% canada). the 'tweets' data table comprise 'id', 'date', 'tweet', 'url', 'username', 'outlinks', 'likecount', 'retweetcount', 'replycounnt', and 'quatecount'. after collecting the data, we extracted, analyzed, and visualized them using a combination of tools: sentistrength, mozdeh, and voyant-tools (free, web-based text analytics tools). we analyzed to distinguish and codify subjective content and estimate the strength of positive and negative sentiment in the data that employs a lexicon of sentiment terms and a set of linguistic rules (e.g. for idioms, negation, and booster words). figure 1 displays the model of the study. sentistrength's lexicon is a manually curated list of over 3,000 terms and term stems, each annotated with a positive or negative sentiment strength. the training data of the engineering, technology & applied science research vol. 12, no. 3, 2022, 8525-8231 8527 www.etasr.com mahyoob et al.: sentiment analysis of public tweets towards the emergence of sars-cov-2 omicron … sentistrenght library were used to compute the polarity of the word class of the harvested data. the strength range of positive sentiments varies from 1 to 5, where 1 means not positive and 5 means extremely or very strong positive. at the same time, the strength range of negative sentiment is from -1 to -5, where -1 means not negative, and -5 means extremely or strong negative. any tweet with [-1, 1] score was considered to not show any sentiment, so it was categorized as neutral sentiment. sentistrength was chosen for accuracy approaching humanlevel, and its dual system lets negative sentiments be investigated independently from positive sentiments, something that is essential for the research goal [22, 24]. the voyant-tools were employed to visualize some data. fig. 1. the model of the study. iv. results a. sentiment strength and trends figure 2 illustrates the time-series graph of the collected tweets. figure 2(a) displays the overall trends and spikes of the tweets about the omicron variant. intuitively, the general direction gives us helpful background information about topic interest and the period when the twitter users discuss it. it shows a gradual increase in the overall trend. the highest number of tweets were posted at the beginning of the second week of december 2021, mainly on 8 th , with 6087 posted tweets. this spike is followed by a steady lower level of activity and an increase in the trend in the fourth week of december. figure 2(b) represents the average post sentiment from 1 to 5, and the most down green line represents the proportion of subjective texts. the thick black line is the average negative sentiment strength, and the thick red line is the average positive sentiment strength. the thinner grey and pink lines are the same but just for the subjective texts (i.e. positive, or negative sentiment > 1). the sentiment data is bucketed into a minimum of 20 data points for smoothing. it is noted that the two sentiment polarities are close, with an apparent increase in negative sentiment during the peak. fig. 2. time series graph for the proportion of (a) tweet volume and (b) sentiment containing the word omicron. figure 3 shows the sparkline graph, representing the mentioned terms’ distribution with linear data segments. it indicates the sudden increase in the volume of the tweets. zscore is a normalized value for the terms' raw frequency compared to the other term frequencies in the same document. fig. 3. the sparkline graph of the data. fig. 4. tweets sentiment strength. engineering, technology & applied science research vol. 12, no. 3, 2022, 8525-8231 8528 www.etasr.com mahyoob et al.: sentiment analysis of public tweets towards the emergence of sars-cov-2 omicron … the sentiment strength scores of the posted tweets during the omicron spread are illustrated in figure 4. it is indicated that most public sentiments were neutral, as most of the posted tweets scored 1, which means no positive or negative sentiments were expressed because zeros were not used. positivity decreased for the weak, moderate, strong, and very strong sentiment strength scores. at the same time, negativity increased gradually and became dominant, which means people started to show significant concerns about the omicron variant. figure 5 shows the significant decrease of positive sentiments to 0.04%, which is very positive after a few days of the outbreak. in contrast, negative sentiment was dominated and scored 0.35% for very negative. fig. 5. sentiment analysis. b. tweet trends and spikes figure 6 illustrates the trends and spikes of omicron-related tweets in countries like the uk, usa, ksa, india, canada, australia, germany, and china. it is noted that the curves show an increase in the number of tweets during dec 2021, almost from 4 th to 25 th december 2021, except in ksa (kingdom of saudi arabia). this reflects the people's high interest in omicron due to their previous experience with covid-19. there are millions of expatriates who live in saudi arabia. their native language isn't arabic, and they use english on social media platforms. english is the first or second language in all other selected countries. interestingly, in china, the posts on omicron increased and covered a more comprehensive range of time during the study period. this reflects the high chinese interest in omicron due to their experience with covid-19. millions in china are using twitter and they tweet and retweet using the english language. in contrast, ksa shows less interest in the omicron variant. the bubble chart cross shows the classification of the texts for positive and negative sentiment across different countries and how positivity and negativity are associated with each other. the positive and negative sentiment scores are presented in the bubbles. as shown in figure 7, the sentiment in the listed countries is very negative with a score of 5, while there is no very positive sentiment with a score of 5 except the usa. it is found that in ksa, public sentiment was almost neutral, and no significant concerns were monitored. this may prove the positive effect of vaccination on physical and mental health [25]. due to the considerable role of the saudi government in encountering the covid-19 outbreak, the positive and neutral sentiment is highly noticed. fig. 6. distribution of omicron-related tweets across countries. c. top frequent terms and hashtags table i represents the top frequent terms, including the hashtags associated with the specified sentiment range. it illustrates the occurrence of the word "omicron" and all other related words more often in tweets containing omicron. the pmatch rate displays the proportion of omicron tweets, including the term omicron 336.4%, variant 142.9%, vaccine 75%, etc. the list of the most frequent words related to the sars-cov-2 omicron variant is ranked according to the match and order of importance. words that occur most often in the text match the search and filters compared to the remaining texts, and they are listed according to their statistical engineering, technology & applied science research vol. 12, no. 3, 2022, 8525-8231 8529 www.etasr.com mahyoob et al.: sentiment analysis of public tweets towards the emergence of sars-cov-2 omicron … significance. the chi-square value represents the association between the listed term and searches with filters. the percentage of texts that don't match the search but contain the word, the most frequent words, and their statistical significance can also be seen. fig. 7. bubble chart for sentiment analysis. table ii shows the overall sentiment average alongside 95% confidence intervals in the first phase from 3 rd to 10 th december 2021 and the second phase from 11 th to 25 th december 2021. for the positive sentiment of the first set, the average is higher, and the difference is statistically significant since the confidence intervals are (1.3963, 1.4255). the second set score is (1.3527, 1.4193), there is no overlapping between the two data sets. people tended to tweet more positively at the beginning of the omicron variant emergence. the second phase is higher for the negative sentiment, and the difference is statistically significant, since the confidence intervals are (1.8712, 1.9541). the score of the first phase is (1.8139, 1.8517) and the difference is statistically significant between the two groups. it is reasonably straightforward and statistical evident that people tend to tweet more negatively after the outbreak of the omicron variant reached at least 57 countries. table i. most frequent words and their statistical significance word nomatch matches chisq omicron 336.40% 9236 135151.6 variant 142.90% 3945 19398.1 vaccine 75.00% 2051 8350.8 new 61.20% 1682 6509.6 pfizer 52.70% 1443 5533 #omicron 51.20% 1401 5340.4 covid-19 48.10% 1322 4951.8 delta 28.10% 773 2754.3 #covid19 19.70% 540 1901.3 protection 19.60% 536 1886.4 spread 19.40% 534 1860.8 africa 16.30% 447 1559.6 sars-cov-2 17.30% 507 1491.1 health 15.80% 435 1488.8 infection 14.40% 396 1374.5 coronavirus 11.70% 325 1092.8 pandemic 11.60% 322 1073.3 symptom 9.00% 247 843.1 confirmed 9.00% 250 835.9 fear 6.10% 169 570.2 patient 5.90% 162 545.9 dangerous 3.30% 91 301 illness 3.30% 90 297.6 #coronavirus 2.70% 74 242.8 pcr 2.50% 68 222.3 contagious 2.10% 58 188.2 infectious 2.20% 62 193.3 #delta 2.20% 60 195 #sars_cov_2 0.50% 14 39 table ii. overall average of sentiment alon gside 95% confidence first phase second phase pos 1.4109 (1.3963, 1.4255) 1.3860 (1.3527, 1.4193) neg 1.8328 (1.8139, 1.8517) 1.9126 (1.8712, 1.9541) av pos av neg: -0.4219 -0.5266 figure 8 displays the fetched concordance entries and the repeated phrase forms which can be found in the text. the number of branches is shown on both sides of the keyword (omicron), and the context is retrieved as it is shown along with branches. most of the keywords (word association, contextualization, concordance, etc.) in the tweets are about covid-19 variant omicron, healthcare, vaccines, symptoms, etc. v. discussion the current content-analyzing of tweets, retweets, and hashtags on twitter study is one of the first systematic studies identifying and testing the public's attitude towards the omicron variant. the study explores the emotion of twitter users at the early stage of the variant emergence during december 2021. the results revealed that the spike of interest engineering, technology & applied science research vol. 12, no. 3, 2022, 8525-8231 8530 www.etasr.com mahyoob et al.: sentiment analysis of public tweets towards the emergence of sars-cov-2 omicron … in omicron variants worldwide was detected at the beginning of the second week of december 2021, as many cases have been detected in this period. many countries set restrictive measures to control the outbreak of omicron and minimize its subsequent effects as this variant is highly transmissible even among fully vaccinated people [26]. the results indicate that the polarized tweets concerning the new variant are inevitable as they started with negative and increased to very negative after 10 days of the omicron variant outbreak. the results also exemplify a significantly higher negative share of tweets at the end of the month compared to the beginning. that is due to people's potential worry of the surge of infection, transmissible variant, the efficacy of covid-19 vaccines, etc. that corroborates the findings of [27]. it is noted that the z-score of the term "omicron" is 3,602.925 and is the highest frequent term used by social media users in their tweets and comments, compared with other related words such as "vaccine," which scored 404.925. these scores indicate that the social media users believe that the omicron variant may expose their life and health to risk. the sentiment analysis conducted in this study clarifies the emotion of the lay audience and how the pandemic negatively influences their language and thoughts towards the new variant of covid-19. this conclusion is consistent with [28, 29]. indeed, the analysis exposes that the publics' emotions can contribute to relaxing their worries and concerns by the authorities and to an intense polarization of health care on social media. fig. 8. the concordance entries of the data. vi. conclusion and future work the purpose of the current study was to understand twitter users' views and sentiments towards the emergence of the sars-cov-2 omicron variant. the analysis conducted in this study has shown the emotion of the lay audience and how the pandemic negatively influences their language and thoughts towards the new variant of covid-19. the study reveals a worldwide increase in the overall trend and a high spike in public interest and publications about the omicron variant on twitter in the second week of december 2021. this variant is highly transmissible even among fully vaccinated individuals. many cases have been detected during this period, forcing many countries to set restrictive measures to control the outbreak and minimize its subsequent effects. it is found that the polarized tweets concerning the omicron variant are inevitable as they started with negative and increased to very negative after 10 days. the results also exemplify a significantly higher negative share of tweets at the end of the month compared to the beginning. that is due to people's potential worry of the surge of infection, transmissible variant, the efficacy of vaccines, etc. sentiment analysis can contribute to an intense polarization of engineering, technology & applied science research vol. 12, no. 3, 2022, 8525-8231 8531 www.etasr.com mahyoob et al.: sentiment analysis of public tweets towards the emergence of sars-cov-2 omicron … health care on social media. this study gives us a clear picture of the global public's sentiment towards this pandemic which would help authorities to provide timely information to relax and ease the public's concerns. moreover, it helps the governments address future health crises involving infectious diseases earlier. this study has many limitations. first, the data were collected from one social media platform (twitter) considering only english tweets. as an extension of the work, it would be interesting to investigate and assess the effect of the new variant of covid-19 on peoples' emotions and attitudes in other social network platforms and different languages. acknowledgement this study received funding from the scientific research at taibah university, ksa, under taibah university's initiative for coronavirus research, grant scheme [hum-9]. references [1] m. s. neethu and r. rajasree, "sentiment analysis in twitter using machine learning techniques," in fourth international conference on computing, communications and networking technologies, tiruchengode, india, jul. 2013, pp. 1–5, https://doi.org/10.1109/ icccnt.2013.6726818. 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[29] z. su, d. mcdonnell, j. ahmad, a. cheshmehzangi, and y.-t. xiang, "mind the ‘worry fatigue’ amid omicron scares," brain, behavior, and immunity, vol. 101, pp. 60–61, mar. 2022, https://doi.org/10.1016/ j.bbi.2021.12.023. microsoft word 1-665-ed.doc engineering, technology & applied science research vol. 6, �o. 3, 2016, 976-981 976 www.etasr.com demirdelen et al.: modeling and analysis of a multilevel parallel hybrid active power filter modeling and analysis of a multilevel parallel hybrid active power filter tugce demirdelen department of electrical and electronics engineering, cukurova university, turkey tdemirdelen@cu.edu.tr r. ilker kayaalp department of electrical and electronics engineering, cukurova university, turkey ikayalap@cu.edu.tr mehmet tumay department of electrical and electronics engineering, cukurova university, turkey mtumay@cu.edu.tr abstract—this paper introduces a new control approach for the multilevel parallel hybrid active power filter (m-phapf) which can compensate harmonics and variable reactive power demand of loads by controlling the dc link voltage adaptively in medium voltage applications. by the means of this novel control method, m-phapf obtains a better and more efficient performance in the compensation of harmonics and reactive power compared to when using conventional control methods. the performance and stability of the proposed method are verified with a simulation model realized in pscad/emtdc with different case studies. the simulation results demonstrate that harmonic compensation performance meets the requirements of the ieee-519 standard. keywordsharmonics; parallel hybrid active filter; reactive power compensation; simulation; pscad/emtdc. i. introduction in power transmission/distribution systems, the intensive use of nonlinear loads causes several power quality problems. the grid voltage and currents become non sinusoidal and harmonic distortion appears. the use of passive filters is one of the traditional solutions to reduce current harmonics. however, it provides a low filtering performance and its filtering performance depends on the changing conditions of power systems. with the remarkable development of semiconductor switching devices, active power filters (apf) have gain interest and have been put into practical use as they have the ability to overcome the disadvantages of passive filters. apf are more effective in harmonic compensation and provide superior filtering performance [1–7]. although apf are an accomplished compensation system, the cost of apf significantly increases with increasing power ratings. to overcome this contradiction, passive and active filters are used together as a single device called a hybrid active power filter (hapf). in the literature, different hapf topologies which are the combination of the series and/or parallel apf and passive filters are proposed [7–21]. the main purpose of the development of hapf topologies is to provide the compensation requirements of dominant harmonics and reactive power demand of nonlinear loads with passive filters and decrease the ratings and also costs of apf. phapf which is formed from series connection of passive filter and apf come forward in hapf topologies. the most significant advantage of the phapf topology is that the passive filter capacitor holds the major part of fundamental voltage across its terminals and apf part holds only the required voltage for harmonic compensation on the dc link with the help of series connection of passive filters and inverters. this advantage provides reduction in power ratings and switching losses of apf. the controller design of phapf is a significant and challenging task due to its impact on the performance and stability of the overall system. for this reason, different reference generation and control methods such as pq theory [12, 19, 21], fast fourier transform [19], dq theory [22–27], fuzzy controller [14, 16], proportional resonant current controller [17] etc. have been applied to phapf. the current controller, responsible for producing reference currents, is an important part of the phapf controller. according to the current control strategy, direct and indirect current controllers can be applied to phapf. a direct current controller uses only source currents to compensate harmonics and/or reactive power. an indirect current controller uses both load and filter currents to maintain harmonics and/or reactive power compensation. the indirect current control method is preferred in many of phapf studies [22–28] and direct current control method is applied and investigated in fewer studies [12, 19, 29– 32]. in indirect current control, the grid voltage and the impedance of the passive filter must be taken into account for fundamental and harmonic frequencies in order to generate a proper voltage reference for the compensation. this approach can cause complexity in control method. because of that, instead of using the grid voltage and the impedance of passive filter, a linear proportional controller is preferred for the calculation of reference voltage. however, the linear proportional controller presents moderate performance in the compensation of harmonics. in direct current control, phapf can present a faster dynamic compensation performance and the current reference is generated by comparing the reference current extracted from the load current and the filter current, so grid voltage has no direct effect on the control loop. however, the second order impedance characteristic of series connected engineering, technology & applied science research vol. 6, �o. 3, 2016, 976-981 977 www.etasr.com demirdelen et al.: modeling and analysis of a multilevel parallel hybrid active power filter passive filters causes oscillations in the step response changes of low frequency components so, complex controller methods must be preferred for the control of fundamental frequency components which are used for the dc link control and reactive power compensation. furthermore, the reactive power demand of the load is considered constant and reactive power compensation requirements are supplied by the constant reactive power capacity of the passive filter in a major number of phapf studies [12, 19, 22–32]. however, the reactive power demands of loads show variable reactive power characteristics in most industrial applications and phapf can be one of the effective solutions for harmonics compensation and variable reactive demand of industrial loads. the dynamic reactive power compensation is investigated in [29, 33]. in [21, 29, 33], the adaptive dc link voltage control is employed and the dc link voltage is changed according to the dynamic reactive power compensation requirements. in [29], adaptive dc link voltage control is achieved according to both harmonic currents and reactive power requirements of the load by using the selective harmonic extraction method. in these studies, direct current control approach is preferred for harmonics and dynamic reactive power compensation so both active and reactive parts of phapf currents must be controlled with different controllers for the dc link control in order to maintain the dc link voltage in step response changes of load. also, the dynamic reactive power compensation performance of 10 kva phapf is investigated with only a few hundred of var reactive power which is relatively low for investigating the performance of 10kva phapf. on account of the limitations in the above mentioned literature, the purpose of this paper is the following: 1. a new control approach is proposed in order to ensure ac current shaping, reactive power dynamical compensation, and dc voltage regulation. 2. this control method is applied in medium voltage levels. 3. theoretical analyses and simulation results are obtained from an actual industrial network model in pscad. 4. the simulation results are presented for a proposed system in order to demonstrate that the harmonic compensation performance meets the requirements of the ieee-519 standard. 5. to apply dynamic load changes and observe the system response. ii. parallel hybrid active power filter to explain both harmonics and reactive power compensation characteristics of the phapf, the single phase equivalent circuit is shown in figure 1(a). zs presents the source impedance and zf presents the passive filter impedance. the nonlinear load is indicated as an ideal current source (il), and the apf is shown as a voltage source. if the terminal voltage does not have a fundamental component, the voltage across the pwm inverter can be presented as k ⋅ ish at harmonic frequencies where ‘h’ shows the harmonic components and k shows the feedback gain. therefore, the source voltage can become pure 50 hz and presenting the current directions as in figure 1(b), the following equations can be obtained by applying kirchhoff’s voltage law: sh sh sh fh fh af (1)v -i z -i z -v =0 where, sh af sh (2)v =0, v =k i⋅ sh lh fh (3)i =i +i fh sh lh fh sh (4) z i = i z +z +k ⋅ zs c l (a) +vaf zf vs is il if zsh c l (b) zfh ish ilh ifh k fig. 1. (a) single phase equivalent circuit, (b) harmonic equivalent circuit equation (4) shows that the active part of the filter is connected to the system and feedback gain k acts as a damping resistor. k protects the resonance between the supply and the passive filter. theoretically, as k goes to infinity, the harmonic content of the source current goes towards zero. however due to stability problems in the control loop, the gain k should be limited to certain values [34]. hence the design procedure of phapf can be divided into two groups as the design of the passive filter and the design of the active filter part. the design of the passive filter is mainly identifying the lf, cf parameters considering the harmonic content of the load. it is clear that, the tuning frequency of the passive filter is chosen to be the most dominant harmonic component of the nonlinear load. today’s industrial loads generally use three phase diode rectifiers as ac/dc converters, instead of pwm converters, due to their low cost and efficiency. as a result, in the case of a diode rectifier, the passive filter should be adjusted to eliminate the 5th or 7th harmonic current content. the 5th harmonic current content of a diode rectifier is higher than its 7th harmonic components, so it is more reasonable to tune passive filter around 250hz. lc filter for this work is tuned at 250 hz. iii. proposed control method the proposed system is represented in figure 2. the control scheme of the m-phapf is based on the synchronous reference frame method which presents easy implementation and low computational cost. the proposed controller of the proposed system consists of four main parts. these parts are the harmonic compensation controller, the reactive power compensation controller, the dc link reference voltage calculation and controller and finally, the reference calculation and gate signal generation. engineering, technology & applied science research vol. 6, �o. 3, 2016, 976-981 978 www.etasr.com demirdelen et al.: modeling and analysis of a multilevel parallel hybrid active power filter fig. 2. the proposed system a. harmonic current controler the harmonic control of m-phapf is shown in figure 3. the first step is to isolate the harmonic components from the fundamental component of the grid currents. this is achieved through the dq transformation (6), synchronized with the pcc voltage vector, and a first order low pass filter (lpf) with a cut off frequency of 10 hz. then the dq inverse transformation (8) produces the harmonic currents in the abc referential frame. ia_harmonic_ref ic_harmonic_ref ib_harmonic_ref σ σ + + iq id d q �� pll id_lpf iq_lpf isa isc isb abc d q abc �� e a e b e c fig. 3. harmonic current control the conversion matrix is p p p 123 dq p p p 2π 2πcosθ cos(θ ) cos(θ + ) 3 3 2 2π 2πt = -sinθ -sin(θ ) -sin(θ + ) (5) 3 33 2 2 2 2 2 2                      d sa 123 q dq sb o sc i i i =t i (6) i i                         and the inverse conversion matrix is p p dq 123 p p p p 2 cosθ -sinθ 2 2 22π 2πt = cos(θ ) -sin(θ ) (7) 3 33 2 22π 2πcos(θ + ) -sin(θ + ) 3 3 2                          a_harmonic_ref d_lpf dq b_harmonic_ref 123 q_lpf c_harmonic_ref o_lpf (8) i i i =t i i i                            b. reactive power compensation control when the loading reactive power qlxf is greater than qcxfpf, in order to generate a larger icxf, the inverter should output a negative inverter fundamental active voltage (vinvxf<0) [12]. the reactive power equivalent circuit is shown in figure 4. the related equations are as follows: c l vinvxf zppff vsx isxf ilxf icxf x=a,b,c + fig. 4. reactive power equivalent sircuit invxf sx pfff cxf (9)v =v -z i invxf sx cxf ppff (10) v -v i = z ppff cf lf (11)x =x -x the reactive power provided by the passive part 2 sx cxfpf cf lf (12) v q =<0 x -x engineering, technology & applied science research vol. 6, �o. 3, 2016, 976-981 979 www.etasr.com demirdelen et al.: modeling and analysis of a multilevel parallel hybrid active power filter c. dc link voltage reference calculation and controller the reference dc link voltage is determined with (15) by using (13) and (14). moreover, a proportional-integral controller is used to control the phapf dc bus voltage shown in figure 5. �� pll calculation of reference dc link voltage calculation of reactive power qload=vdiq + vqid e a e b e c ea eb ec isa isb isc id iq eq ed v*dc abc dq σ + ∫+ ip kk vcappi_a limitter vcappi_b vcappi_c d q abc 0 v*dc vdc verror �� pll e a e b e c fig. 5. dc link voltage controller (a) calculation of adaptive dc link voltage (b) dc link pi controller for harmonic compensation only, the required dc link voltage value is: n f,h filter,h dc(harmonic) h¹1 (13)z i <v⋅∑ where h represents the order of the harmonic, ifilter,h is the filter current and zf,h is the impedance of the lc filter at the corresponding harmonic frequency. for reactive power compensation only, the required dc link voltage value is [12]: load dc(reactive) pcc passivefilter (14) q2 v =3 v 12 q * dc dc(harmonic) dc(reactive) (15)v =v +v * dc v is the dc link reference value for both harmonic and reactive power compensation. by using the error signal generated by the conventional pi controller, the dq inverse transformation (16) produces the reference dc link control signals in the abc referential frame. a limiter is also applied to avoid the overflow problem of the controller. dc link is controlled by the reactive component of the error signal. thus, only the q component is used for dq inverse transformation. cappi_a dq cappi_b 123 errror cappi_c (16) v 0 v =t v v 0                          d. multilevel inverter control, final reference compensation current and pwm control block the diode clamped inverter is the most popular and the most commonly used multilevel topology in industrial applications. three level diode clamped inverter is used for the proposed system. this topology provides three voltage levels: vdc/2, 0, -vdc/2 when the neutral point is replaced in the middle point of c1 and c2. if the neutral point is removed, the three voltage levels have become vdc, -vdc, 0. each bridge in this topology generates three different voltage levels: -to generate phase-neutral voltage which is equal to vdc/2 turn on only sn1 and sn2. -to generate phase-neutral voltage which is equal to 0, turn on only sn2 and sn3. -to generate phase-neutral voltage which is equal to -vdc/2, turn on only sn3 and sn4. the final reference current consists of three phase harmonic reference current signals, three phase reactive reference current signals and dc link control signals. the reference signal (in_harmonic_ref + in_reactive_ref + vcappi_n, n=a,b,c ) is generated using these signals together. then, the reference signals are compared with carrier signal to generate switching signals shown in figure 6. pwm gate signals switching signals s1n-4n reference vcappi_n in_harmonic_ref in_reactive_ref σ + + + carrier1 carrier2 (n=a,b,c) fig. 6. final reference compensation and pwm control method iv. simulation results in this paper, the simulation model of the system is formed by using the emtdc/pscad 4.2.0 software. the parallel hybrid power filter system and the multilevel hybrid active power filter are modelled, simulated and analysed in the pscad 4.2.0 environment. all control methods are developed in fortran language. the simulation parameters of the system are given in table i respectively. according to most articles in the literature, phapf has a reactive power compensation capability that is limited with the capacity of the used passive filter. simulation results, clearly show that the reactive power compensation capability is added (a) (b) engineering, technology & applied science research vol. 6, �o. 3, 2016, 976-981 980 www.etasr.com demirdelen et al.: modeling and analysis of a multilevel parallel hybrid active power filter to the m-phapf by using the apf part and also the dynamic dc link. in this case, the capacity of the passive filter is nearly 205 kvar. when the first load is connected, the load capacity is nearly 220 kvar. the simulation results show that the apf part of multilevel-phapf compensates nearly 15 kvar reactive power with the adjusted dc link voltage which is nearly 1 kv. when the first and the second loads are connected, the load capacity is nearly 380 kvar. the simulation results show that the apf part of multilevel-phapf compensates nearly 20 kvar reactive power with the adjusted dc link voltage which is nearly 1.5 kv. the dc link voltage is adjusted itself by changing the load capacity. the filtering performance of the system and the dc link voltage are shown in figures 7 and 8. the reactive power compensation performance is illustrated in figure 9. the total harmonic distortion (thd) is reduced from 28.4% to 3.88% when the first is connected (figure 10). the total harmonic distortion (thd) is reduced from 20% to 1.63% when the first and the second loads are connected (figure 11). table i. simulation parameters vline(v) 6300 lf(h) 0.025 fline(hz) 50 fswitching(khz) 10 ls(h) 0.001 tst(µs) 40 ll(mh) 0.6 ftuned(hz) 250 cf(µf) 16 cdc1, cdc2(µf) 1000 fig. 7. multilevel phapf operates fig. 8. dc link voltage of hapf fig. 9. source active and reactive power, load active and reactive power main : controls sourcehar 0.0464639 sourcethd 3.88092 loadhar 0.0759953 loadthd 28.4196 fig. 10. simulation results (first load connected) main : controls sourcehar 0.109564 sourcethd 1.62655 loadhar 0.051536 loadthd 19.8466 fig. 11. simulation results (first and second load connected) v. conclusions a new control approach is used, in order to ensure the ac current shaping, compensate the reactive power dynamically and regulate the dc voltage for the three phase shunt hybrid active power filter. this control scheme of the m-phapf is based on the synchronous reference frame and is simpler and easier to implement. the harmonic compensation is obtained by regulating the currents of the power systems. the reference reactive power compensation currents of the m-phapf are generated from the power systems. the dc link voltage control signals are based on the reactive power balance of system. the dynamic reactive power compensation is achieved successfully with a perceptible amount. besides, the harmonic compensation performance is satisfactory. the simulation results of the three phase three wire phapf under the dynamic reactive power compensation are illustrated to verify all discussion and analysis and also show the effectiveness of the proposed controller. hence, the proposed m-phapf system can be an effective and economic solution for both harmonic and reactive power problems caused by the large capacity of linear and nonlinear loads. acknowledgment the authors gratefully acknowledge scientific research projects unit of çukurova university, adana, turkey (project no: mmf2012yl22) for full financial support. engineering, technology & applied science research vol. 6, �o. 3, 2016, 976-981 981 www.etasr.com demirdelen et al.: modeling and analysis of a multilevel parallel hybrid active power filter references [1] x. zha, j. sun, j. gong, b. chen, “analysis and design of repetitive controller based on regeneration spectrum and sensitivity function in active power filter system”, iet power electron., vol. 7, no. 8, pp, 2133–2140, 2014 [2] m. c. shah, s. k. chauhan, p. n. tekwani,. r. r. tiwari, “analysis, design and digital implementation of a shunt active power filter with different schemes of reference current generation”, iet power electron., vol. 7, no. 3, pp. 627–639, 2014 [3] b. qin, h. zhu, s. gao, z. shu, f. gao, “five-level diode-clamped active power filter using voltage space vector-based indirect current and predictive harmonic control”, iet power electron., vol. 7, no. 3, pp. 713–723, 2014 [4] s. k. 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(corresponding author) received: 19 december 2022 | revised: 30 january 2023 | accepted: 1 february 2023 abstract the axially compressive behavior of steel tube confined concrete (stcc) columns has been experimentally investigated by many researchers throughout the world. however, it is extremely complicated to measure the stresses of steel tubes and concrete core in real tests. therefore, to investigate the fundamental behavior of stcc columns under axial compression, this paper presents a numerical study that explores the stress distribution in steel tubes and concrete core. the circular stcc columns with the use of normal strength concrete (nsc), high strength concrete (hsc), and ultra-high strength concrete (uhsc) were simulated in a finite element model (fem) in abaqus. the material model for confined concrete incorporating a wide range of concrete strength values was developed in the simulation. the obtained from fem curves of load versus strain of circular stcc columns were compared with those measured in real tests to verify the accurateness of the fem. deriving from the results of fem, the stress states and their distribution in outer steel tubes and concrete core along the column height were described. also, the longitudinal stresses on the cross-section of the concrete core were calculated corresponding with the load stage to quantify the strength enhancement of the concrete core due to the confinement effect from the steel tube. furthermore, the confining pressure provided by the outer steel tube and impacting on the concrete core was plotted. based on the findings in this paper, the effect of various concrete strengths on the stress distribution in circular stcc columns was investigated. keywords-steel tube confined concrete; nsc; hsc; uhsc; abaqus; fem i. introduction it is widely known that the confinement effect in concrete filled steel tube (cfst) columns can result in remarkable improvements in compressive strength and ductility [1-11]. therefore, cfst columns have been extensively applied in civil engineering projects. for this column type, when the steel tube and the concrete core are loaded simultaneously, the confining stress induced by the steel tube is less effective as compared to the case where only the concrete core is loaded [511]. if the ductility and strength of composite columns are considered as critical design factors, it is suggested that the load should be applied on the concrete core only in order to form steel tube confined concrete (stcc) columns [9]. many previous studies have conducted experimental tests on the axial compressive behavior of stcc columns [1-4], but they have mainly focused on the use of normal strength concrete (nsc) or high strength concrete (hsc). recently, several studies have reported the test results of circular stcc columns infilled with ultra-high strength concrete (uhsc) under axial compression [5, 10, 11, 19]. according to them, the confining stress level in stcc columns depends on concrete strength. the dilation of concrete under compression is higher with lower concrete strength, thus the interaction between the concrete core and the steel tube becomes stronger. for stcc columns, at the ultimate state, the concrete core is subjected to triaxial stress, while the steel tube is under biaxial stress. in real tests, it is complicated to measure all stresses in the concrete core and in the steel tubes. accordingly, the confining stress induced by the steel tubes and imposed on the concrete core is hardly calculated. therefore, many studies have attempted to use finite element models (fems) to simulate the mechanism in stcc columns. based on the fem results, all stresses on stcc columns can be quantified. authors in [12] presented an fem in atena-3d software to investigate the effect of concrete strength on the compressive behavior of stcc columns. authors in [9] developed an fem using abaqus software to analyze the mechanisms of stcc short columns under axial compression, however they only focused on nsc. authors in [13] introduced an analysis of circular stcc stub columns with some modifications to the drucker – prager engineering, technology & applied science research vol. 13, no. 2, 2023, 10347-10351 10348 www.etasr.com le: a numerical study addressing the stress distribution in circular steel tube confined concrete … model in abaqus, and they quantified the lateral confining pressure and the interface shear stress between the concrete core and the steel tube. authors in [15] investigated the effect of friction on axially loaded stcc short columns by utilizing an fem. equations considering the friction coefficient were developed to predict the load bearing capacity of stcc short columns. from the literature review, it is apparent that numerical studies on the mechanical performance of stcc columns remain very limited with only a handful of studies considering the stcc columns with the use of nsc or hsc. therefore additional research should be further carried out to better understand the compressive behavior of stcc columns when uhsc is infilled. furthermore, the majority of the existing studies were concerned with the comparison of load versus displacement or load versus strain curves of stcc columns between the fems and the test results and very few studies dealt with the stress distribution in the steel tubes and the concrete core of stcc columns. the interaction between the concrete core and the steel tubes through the confining stress is complex and can't be measured experimentally. to address the aforementioned research gap, this paper aims to develop an fem in abaqus software to simulate the mechanism of circular stcc stub columns with a wide range of concrete strengths, i.e. nsc, hsc, and uhsc. the constitutives of confined concrete were proposed based on some previous studies and some modifications to concrete damaged plasticity model (cdpm). the established fem was verified against the collected test results. subsequently, the confining stress and the distribution of axial load in the concrete core and the steel tube were clarified. finally, the biaxial stress state of the steel tube was quantified by plotting the longitudinal and hoop stresses along the height of the columns. ii. finite element model description a. general description the circular stcc short columns were simulated using fem in abaqus (version 6.11) [28]. due to the symmetrical nature of the circular column, only one-eighth of the column was modelled. cax4r elements with reduced integration and 4-node axisymmetric elements were used to model the steel tubes and the concrete core. based on the mesh convergence studies, the element size was chosen as t/5, where t is the thickness of the steel tube. for short columns with the ratio of l/d (length to outer diameter) smaller than 4, the initial imperfections can be ignored in fem. surface-to-surface contact was employed to model the interaction between the steel tubes and concrete core. a contact surface pair including the inner surface of the steel tubes and the outer surface of the concrete core was defined. the concrete surfaces were chosen as master surfaces, while the steel surfaces were treated as master. as suggested in [18], the friction coefficient between the steel tube and concrete was taken as 0.6. two reference points (rps) were created at the center of each upper and lower cross-section. boundary conditions (bcs) were assigned to both reference points, while the load was applied downward at the upper reference point. the "rigid body" constraints were employed to tie the reference points to both the end surfaces of the concrete core. to ensure the load was applied only on the concrete core, only the end surfaces of the concrete core were fixed against all degrees of freedom except for the displacement at the upper loaded end. figure 1 shows the fem including mesh type, boundary conditions, and loading application. fig. 1. typical fem of a circular stcc stub column. b. material models the stress – strain relationship ( ) proposed in [22] was adopted for the material model of the steel tube. this model covers a wide range of steel yield strength (fy) from 200 to 800mpa. cdpm provided in abaqus was employed to simulate the compressive behavior of confined concrete. the key parameters in cdpm include the uniaxial compressive stress – strain relationship, compressive damage variable dc ratio of the second stress invariant on the tensile meridian to that on the compressive meridian kc, ratio of initial equibiaxial compressive yield stress to initial uniaxial compressive yield stress σbo/σco, dilation angle ψ, fracture energy gf , viscosity, and eccentricity α. the values of kc, ψ, and σbo/σco were calculated by using the equations suggested by [20-22], while the remaining parameters such as α, dc, gf, and viscosity were defined as the default values in abaqus. the stress – strain relationship for nsc, hsc, and uhsc after taking into account the confinement effect was developed for circular stcc short columns, as can be seen in [22]. the   curve includes three stages: the ascending branch (oa) is expressed by the equations proposed by [23]: � ��′ � ���� �� ���� ������ ����� 0 � � � ��� (1) where: � � �� ������′ ; � � �� �� �.�� � 1; � � ��� (2) the strain εc0 at the peak stress of the unconfined concrete is calculated by [24]: ��� � ��0.067 � �#�′�� $ 29.9 � #�′ $ 1053� � 10) (3) the confined strain at the point b (cc) is determined using the equation proposed in [25]: ��� ��� � 1 $ 17.4 � +�,��′ �.�) (4) engineering, technology & applied science research vol. 13, no. 2, 2023, 10347-10351 10349 www.etasr.com le: a numerical study addressing the stress distribution in circular steel tube confined concrete … # � �.�.��/ 0�.� � 1 2 (5) where fb is the confining stress at the point b and determined by (5) suggested by [26]. the descending branch (bc) is expressed by an exponential function proposed by [27]: ��� � +�0.067 � 3#�′4 � $ 29.9 � #�′ $ 1053� 10) (6) where α and β are factors determining the shape of the descending branch. iii. finite element model verification and mechanism analysis the established fem was used to simulate 3 circular stcc short columns, taken from previous studies, under axial compression. specimens c2-30-3d-c and c1-100-3d-c reported in [16] and nb4.0-uhfb reported in [17] were considered. it is noted that, nsc (c30, fc = 32.7mpa) and hsc (c90, fc = 105.5mpa) were used for the specimens c2-30-3d-c and c1-100-3d-c, respectively, while uhsc (c150, fc = 174.2mpa) was used for nb4.0-uhfb. dimensions and material properties of the selected specimens are shown in figure 2. (a) (b) (c) fig. 2. fem verification and stress distribution on the cross section at different points. (a) test c2-30-3d-c, (b) test c1-100-3d-c, (c) test nb4.0-uhfb. point 1 point 2 point 3 0 4 8 12 16 20 0 200 400 600 800 1000 1200 1400 0 0.005 0.01 0.015 0.02 0.025 0.03 c o n fi n in g s tr e ss (m p a ) l o a d n ( k n ) strain ε (mm/mm) test c2-30-3d-c fem concrete core steel tube confining stress d = 114.3mm, t = 6mm, l = 342.9mm fc = 32.7 mpa, fy = 342.95 mpa point 1 point 2 point 3 0 4 8 12 16 20 0 300 600 900 1200 1500 1800 2100 0 0.005 0.01 0.015 0.02 0.025 0.03 c o n fi n in g s tr es s (m p a) l o a d n ( k n ) strain ε (mm/mm) test c1-100-3d-c fem concrete core steel tube confining stress d = 114.3mm, t = 3.35mm, l = 342.9mm, fc = 105.5 mpa, fy = 287.33 mpa point 1 point 2 point 3 0 4 8 12 16 20 0 1000 2000 3000 4000 5000 6000 0 0.005 0.01 0.015 0.02 0.025 0.03 c o n fi n in g s tr e ss ( m p a ) l o a d n ( k n ) strain ε (mm/mm) test nb4.0-uhfb fem concrete core steel tube confining stress d = 168.6mm, t = 3.9mm, l = 648mm fc = 174.2 mpa, fy = 363.0 mpa engineering, technology & applied science research vol. 13, no. 2, 2023, 10347-10351 10350 www.etasr.com le: a numerical study addressing the stress distribution in circular steel tube confined concrete … in order to verify the accuracy of fem, the load versus strain (n-ε) curves of the 3 specimens obtained from fem were compared with those measured by the test results. it can be seen in figure 2 that, in the ascending phase, the fem results agree well with the measured results, but in the descending phase, there is a slight difference between the predicted and the measured curves. for the descending phase of specimens c1100-3d-c and nb4.0-uhfb, the (n-ε) curves in fem exhibit similar behaviors with the real tests. there is a loss of load after the peak load, followed by a horizontal branch. overall, it can be observed that fem predicts well the complete (n-ε) curves of all tested specimens. figure 2 also illustrates the distribution of the axial load between the concrete core and the steel tube and the confining stress provided by the steel tube. for nsc filled in steel tube (c2-30-3d-c), at the ultimate state, the concrete core contributed approximately 70% to the total load. however, it is observed that the concrete core carries almost the entire load for the case of hsc and uhsc. at the ultimate state, 90% of the total load was carried by the hsc core in specimen c1100-3d-c and uhsc core in specimen nb4.0-uhfb. furthermore, the steel tube in the case of hsc and uhsc core tends to carry less axial load before the peak stress as compared to the case of nsc. accordingly, in the ascending branch of the (n-ε) curves, the confining stress in the case of nsc core is more intense and develops faster than in the case of hsc and uhsc. in the plastic stage, the confining stress steadily increases after reaching a stable value. figure 2 demonstrates the distribution of longitudinal stress in the concrete section (at the top surface of the column) corresponding to three points (1, 2, and 3) in the (n-ε) curves. for the nsc core, the confining stress reaches the maximum value of 8.2mpa, which is twice the maximum value of the confining stress in the case of hsc and uhsc core. it can be seen in figure 2 that the longitudinal stress across the concrete section is uniform along the axis of cylinder and increases gradually when the distance apart from the center of section increases. the longitudinal stress in the concrete section for the nsc core was significantly larger than that for hsc and uhsc cores. this implies that the confinement is more effective with lower concrete strength. these findings are in good agreement with the research results in [1, 8, 12-15, 22]. figure 3 shows the distribution of longitudinal stress and hoop stress in the steel tube at the ultimate state. the ratios of stress to yield strength of steel tube (σ/fy) were plotted along the height of the columns (h/h). it can be observed that the distribution of stresses in the steel tube is non-uniform. the longitudinal stress of the steel tube is zero and the hoop stress is relatively high at both ends of the columns. the longitudinal stress increases and the hoop stress decreases towards the column mid-height. also, at the mid-height of the columns, the maximum value of longitudinal stress is achieved, while the hoop stress is significantly reduced. the hoop stress was maximum at h/10, which is quite near to the end surface of the column. the maximal values of longitudinal stress and hoop stress were about 0.55fy and 0.9fy, 0.50fy, and 0.9fy, and 0.40fy and 0.9fy for nsc, hsc, and uhsc cores, respectively. the distribution of longitudinal stress in the steel tube along the column height is in line with the results reported in [9, 13, 14], however there is a difference in the distribution of hoop stress in the steel tube between this study and the results in [9, 13, 14]. the maximum value of hoop stress in this study is generally smaller than that in [9, 13, 14]. for example, authors in [9] stated that the hoop stress is highest at the column ends. it should be noted that the confining stress depends mainly on the hoop stress. based on the fem results, it can be identified that confining stress is maximum at h/10 for circular stcc columns. fig. 3. distribution of stresses in the steel tube at the ultimate state. iv. conclusions the main conclusions deriving from the fem results of the current study are:  the established fem with some modifications to cdpm in abaqus can predict well the compressive behavior of circular stcc columns with the use of nsc, hsc, and uhsc. the distribution of stress in the concrete core and steel tube, and the confining stress can be quantified by using this fem.  the confining stress or confinement effect is more effective with lower concrete strength.  the axial load carried by the concrete core becomes smaller with increasing concrete strength.  the longitudinal stress of the steel tube is zero at both ends of the 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[28] abaqus/cae users manual. usa: hibbitt, karlsson & sorensen inc, 2000. microsoft word etasr_v12_n6_pp9654-9660 engineering, technology & applied science research vol. 12, no. 6, 2022, 9654-9660 9654 www.etasr.com patil & jadhav: road segmentation in high-resolution images using deep residual networks road segmentation in high-resolution images using deep residual networks dhanashri patil department of electronics and telecommunication, d. y. patil college of engineering, akurdi, pune, india and department of electronics and telecommunication, army institute of technology, india dpdhanashripatil@gmail.com sangeeta jadhav department of information technology army institute of technology pune, india djsangeeta@rediffmail.com received: 6 august 2022 | revised: 12 september 2022 | accepted: 20 september 2022 abstract-automatic road detection from remote sensing images is a vital application for traffic management, urban planning, and disaster management. the presence of occlusions like shadows of buildings, trees, and flyovers in high-resolution images and missclassifications in databases create obstacles in the road detection task. therefore, an automatic road detection system is required to detect roads in the presence of occlusions. this paper presents a deep convolutional neural network to address the problem of road detection, consisting of an encoder-decoder architecture. the architecture contains a u-network with residual blocks. unetwork allows the transfer of low-level features to the high-level, helping the network to learn low-level details. residual blocks help maintain the network's training performance, which may deteriorate due to a deep network. the encoder and decoder structures generate a feature map and classify pixels into road and non-road classes, respectively. experimentation was performed on the massachusetts road dataset. the results showed that the proposed model gave better accuracy than current state-of-the-art methods. keywords-u-network;residual block; encoder; decoder i. introduction remote sensing (rs) is one of the most essential applications. it is related to the analysis and identification of features by measuring the physical parameters of an object at some distance with the help of electromagnetic radiation. target discrimination is possible using different characteristics of sensors such as temporal, spatial, and spectral [1]. due to the improvements in rs technology, high-resolution images with adequate spectral and temporal information are available for different applications such as disaster management, water source, land utilization, marine, glacier monitoring, urban city planning, etc. these high-resolution images are considered a primary database for automatic road extraction methods. automatic road detection from remotely sensed images is an essential task for many applications such as urban planning, geographic information systems, map updates, and automatic vehicle navigation [2]. various methods to address the problem of road detection have been presented, but it is still a challenging task due to the presence of occlusions, building shadows, and complex backgrounds in high-resolution images. these noise elements result in a false and discontinuous segmentation of roads. manual road detection is timeconsuming, complex, and involves human interpretation. artificial intelligence and deep learning have made automatic road detection more efficient and accurate than manual methods. road detection methods are of two types: road detection and centerline extraction [3]. the main objective of a road detection system is to detect road pixels from rs images, while centerline extraction locates the skeleton of a road using mathematical morphological operations. the rs characteristics of the roads depend on weather conditions and sensors. road features are classified into geometric, functional, topological, and contextual [4]. geometric features are continuous and include the length-to-width ratio of roads, where the width is always narrower than the length. functional features constitute connectivity in different areas. characteristics of road intersections and continuity in length without interruption are called topological features. contextual features include the shadows of trees, buildings, and flyovers. some road detection methods used multiple features to improve the segmentation accuracy. but it is complex to identify all the features due to occluded high-resolution images. figure 1 shows a general block diagram of road extraction from remote sensing images. several road datasets are available, including high-resolution satellite images with two classes: roads and non-roads [4]. the massachusetts road dataset [5] has 1124 vhr images with 1500×1500 resolution. as a model's performance depends on the data quality, the preprocessing step ensures that the model receives correct data in a suitable format. the filtering technique helps to remove unwanted data from the image. thresholding and binarization methods are used for grayscale conversion and normalization. the extraction of road features helps to produce different road aspects (geometric, radiometric, and contextual). in the classification technique, each pixel in an image is categorized in the road or non-road class. various supervised or unsupervised methods are used for classification. model accuracy can be evaluated using precision, recall, and iou score. the segmented map represents the output of the model containing only the road pixels of the image. corresponding author: dhanashri patil engineering, technology & applied science research vol. 12, no. 6, 2022, 9654-9660 9655 www.etasr.com patil & jadhav: road segmentation in high-resolution images using deep residual networks fig. 1. block diagram of road extraction from remote sensing images. ii. related works road detection from remote sensing images can be addressed using manual and automatic techniques. currently, it is based on a manual process that is tedious and requires human intervention, while its accuracy depends upon the interpreter's skills. automatic methods are more structured and economic. a neural network classifier approach was proposed in [6] to discriminate road and non-road pixels from ikonos images. the accuracy of segmentation was improved using texture and spectral information. this method used a backpropagation neural network and a gray level co-occurrence matrix (glcm) for the detection of road pixels. a backpropagation neural network with glcm features for semantic segmentation was proposed in [7], where its functionality was optimized by incorporating homogeneity, contrast, and entropy. many computer vision applications use deep neural networks and mark state-of-the-art performance. several studies applied deep neural networks to the semantic segmentation of roads, using different algorithms like u-net, fully convolutional networks, casnet, and deep convolutional neural networks (cnn) for the semantic segmentation of remotely sensed images. a cnn approach to detect roads from noisy labeled samples was proposed in [8]. this algorithm generated the training labels and used texture descriptors to obtain road areas, using a combination of the supervised and unsupervised methods for postand pre-training respectively. a novel cascade end-to-end cnn was presented in [3] to detect roads and their centerlines from high-resolution images. this study used two networks for the semantic segmentation of road pixels. the first network detected road pixels and generated a feature map. at the same time, the second network was cascaded with the first one to generate the centerline of the road area. this method marked the fastest computation time compared to existing networks. deep residual u-nets were proposed in [9-10], using the u-net architecture [11] with skip connections and residual blocks. the skip connection helps to propagate the information from encoder to decoder and improves the segmentation result with fewer network parameters. a linear integral convolutional algorithm was used in [12] to label road pixels using probability maps generated by cnn. post-processing was performed using the linear convolutional algorithm to join the road labels, overcoming the limitation of spectral intensity variation in high-resolution images. cnn shows improved performance in semantic segmentation. an early fusion model using a vgg-16-based cnn was proposed in [13] for the classification and detection of 16 classes, showing better training and test validity. a fully cnn for automatic road extraction was presented in [14], using resnet34 on the encoder and basic u-net on the decoder. the encoder was pre-trained on the imagenet dataset and used a data augmentation technique to increase the dataset size. in [15], semantic segmentation was proposed using an eleven-layered cnn and images of the san francisco bay area for road detection. the result was compared using average and max pooling and showed that cnn is a suitable method for remote sensing image analysis. a pre-trained cnn model was used in [16] for segmentation, proposing transfer learning using cnn. in [17], the conditional random field and landscape metrics were utilized with a deep cnn, where over-segmented roads were removed using landscape metric thresholding. unsupervised techniques such as the knowledge-based method, mean shift, graph theory, and mathematical morphology have been used to address the problem of semantic segmentation from remotely sensed images. in [18], semiautomatic road detection was presented using a mean shift. the seed points were prescribed in the images in advance by the user. then, road and non-road segments were classified using the thresholding technique and the seed points were connected to generate a road network. some studies used knowledgebased methods for road detection. the structural element can be evaluated using the energy function, which results in object detection, and the road tracker algorithm can be applied to gray-level images to find long ribbons, but this method is not suitable for occluded remote sensed images [19]. the toefinding algorithm has been used to detect road footprints, eliminating non-road segments, but had over-segmentation limitations and was also sensitive to shadows and occlusions in an image [20]. in [21], morphological operations were used for the segmentation of the image and restored the road area by filtering out noise elements. this method resulted in discontinuous segmentation, and some road gaps existed in output. in [22], the multiscale retinex algorithm was used to enhance a high-resolution image, a canny operator was used for edge detection, and the skeleton of the road was detected using morphological operations. mathematical morphology gives results for road segmentation, but accuracy depends on the size and shape of the road. there are no fixed road construction standards, as it varies from region to region. therefore, integrating mathematical morphology with other techniques can help improve the overall result. iii. methodology this paper proposes a road segmentation architecture to extract roads from remotely sensed images. the main challenge was to identify design components that regulate the performance of the road segmentation architecture. this model engineering, technology & applied science research vol. 12, no. 6, 2022, 9654-9660 9656 www.etasr.com patil & jadhav: road segmentation in high-resolution images using deep residual networks was established using u-net and residual blocks [23]. the unet architecture consists of a contraction and an expansion path, which help to propagate the feature map in all possible ways from the encoder to the decoder. therefore, the network accuracy can be improved using low-level details and highlevel semantic information. the residual block introduces identity mapping in the network, facilitates smooth training, and helps to prevent the problem of vanishing gradients. another task was to preprocess the high-resolution satellite images to produce the dataset to train and test the network. a. network architecture road detection from remote sensing images is a semantic segmentation task, and u-net is the best-suited architecture. the proposed model was inspired by the u-net architecture. figure 2 shows the detailed flow chart of the deep res-unet. the architecture consists of three parts: the encoder, the decoder, and the bridge. fig. 2. network architecture of the proposed model. an input image sized 256×256 pixels is considered at the encoder's input. four residual blocks with a 3×3 filter are implemented in the encoder part. the filter sizes of the residual blocks are respectively 16, 32, 64, and 128. an additional residual block with a filter size of 256 is connected between the encoder and the decoder, forming the bridge. the encoder helps to extract road features and generates feature maps, while the decoder classifies each pixel into a specific class. the encoder path uses the typical architecture of a convolutional network. it consists of repeated 3×3 convolutional layers followed by an exponential linear unit (elu) [24]. it also carries out a 2×2 max pooling operation with a stride of 2. the max pooling operation is required for the downsampling of the feature map and size reduction. each residual block in the encoding part is connected to the decoding part using concatenation. the residual block consists of identity mapping, which represents connections between the input and output of the residual module. the proposed architecture replaces the rectified linear unit (relu) with an exponential linear unit (elu) and adds the bn layer [25] after each convolutional layer. the elu activation function is defined as: ���� � ��, � 0��� � 1�, � � 0  the elu and bn layers have become widely used components in cnn due to their high performance during network training. the number of kernels per output layer was set to 1. the sigmoid function, shown in (2), was used for classification instead of softmax: ������� � ���� �� (2) the classification cross-entropy was minimized using the adam optimizer. cross entropy is used to represent the difference between the distribution of input data and the distribution obtained from model training. convolutional and upsampling operations were carried out in the decoder path. each decoder module first performs the up convolutional operation with a feature map provided by the concatenation path, doubling the size of the feature map and improving the resolution. the same size of the input and output images can be ensured by upsampling. then, 3×3 convolutional operation was carried out with the elu activation function. the filter size of a convolutional layer in the decoder is 128, 64, 32, and 16 respectively. the last layer is 1×1 convolutional and is used to map 128 component feature vectors to their desired classes. this layer uses a sigmoid as an activation function. table i shows the details of the network layers. table i. size of network layers unit level conv. layer filter stride output size input 256×256×3 encoding level 1 conv 1 3×3/16 2 256×256×16 conv 2 3×3/16 2 256×256×16 level 2 conv 3 3×3/32 2 128×128×32 conv 4 3×3/32 2 128×128×32 level 3 conv 5 3×3/64 2 64×64×64 conv 6 3×3/64 2 64×64×64 level 4 conv 7 3×3/128 2 32×32×128 conv 8 3×3/128 2 32×32×128 bridge level 5 conv 9 3×3/256 1 16×16×256 conv 10 3×3/256 1 16×16×256 decoder level 6 conv 11 3×3/128 2 32x32x128 conv 12 3×3/128 2 32x32x128 level 7 conv 13 3×3/64 2 64x64x64 conv 14 3×3/64 2 64x64x64 level 8 conv 15 3×3/32 2 128x128x32 conv 16 3×3/32 2 128x128x32 level 9 conv 17 3×3/16 2 256x256x16 conv 18 3×3/16 2 256x256x16 output conv 19 1×1 1 256x256x16 iv. experiment a. dataset and preprocessing the massachusetts dataset was used, where each image contains 3×1500×1500 pixels. the dataset consists of 1711 aerial images, and covers around 2600km 2 . the dataset was divided into training, validation, and testing sets. the experimental procedure used 1191 images for training, 109 images for validation, and 273 images for testing. figure 3 shows some samples of cropped satellite images with groundtruth labels. as the size of the original image is too large, it engineering, technology & applied science research vol. 12, no. 6, 2022, 9654-9660 9657 www.etasr.com patil & jadhav: road segmentation in high-resolution images using deep residual networks would be resource intensive to feed it in the first layer, and the input image was cropped into 256×256 to avoid it. all the cropped images were then processed with the data augmentation technique to increase the number of images. this was carried out using random rotation and vertical and horizontal flips. the data augmentation technique helps to prevent the model from overfitting. b. implementation details the implementation was carried out on the tensorflow platform. a deep learning framework requires lots of memory and high-performance machines. the proposed method was implemented on an nvidia gpu with 24gb of memory. the adam optimizer was used during training and the learning rate was set to 0.0001 to reduce the errors during training and improve performance. semantic segmentation is a binary classification problem. the binary cross entropy was used as a loss function: ���, ���� � � �! ∑ �� ∗ log ����� + �1 � �� × log�1 � ����� )*+, (3) where p(y) is the predicted value, y is the true label, and n is the number of samples. fig. 3. cropped satellite images with ground truth labels. c. evaluation metrics the qualitative performance of the model was assessed using the intersection over union (iou), completeness (com), correctness (cor), and f1 score. the iou expresses the correctness of generated maps and is the ratio of intersection over the predicted map and ground-truth labels to a total area of the ground-truth labels and predicted map. the iou can be calculated using the union operation. com measures the percentage of areas matched on the reference map. cor measures the percentage of the matched road area in the segmentation map, and f1 defines the overall metric by combining com and cor. iou � /0�1 23 45�0617/0�1 23 8)*2) (4) com � <=<=�>! (5) cor � <=<=�>= (6) the proposed model was trained from scratch without using any pre-trained modules. table ii shows the results of the proposed architecture and mentions the external accuracy results from [9]. this network uses skip connections and dense blocks. the results showed that the iou score on the massachusetts road dataset was 74.47%. figure 4 shows the iou and loss graphs of the proposed model. the cor metric was 96.42% and iou was 81.57%. there were two problems associated with the ground-truth labels: sometimes, an area in an image was marked as a road but it was not. some side or local roads were incorrectly labeled in the ground-truth image. the first problem increases the difficulty of extracting precise edges for the road networks. figure 5 represents the flow chart of the proposed model. table ii. results of the proposed architecture accuracy metric cor com iou f1 score proposed model 96.42% 81.03% 81.57% 88.02% external accuracy [9] 78.25% 70.41% 74.47% 74.07% engineering, technology & applied science research vol. 12, no. 6, 2022, 9654-9660 9658 www.etasr.com patil & jadhav: road segmentation in high-resolution images using deep residual networks fig. 4. iou and loss metrics of the proposed model. fig. 5. flow chart of the proposed model. d. comparison with other algorithms the proposed architecture was compared with state-of-theart models to test its validity. u-net, fcn, and segnet models were considered and trained on the massachusetts road dataset by keeping the same hyperparameters, as they are used extensively in semantic segmentation. the u-net architecture was proposed for medical image segmentation, implementing a four-layer u-net architecture using skipped connections without identity mapping [11]. a basic 7-layer fcn algorithm was implemented to assess accuracy, which was proposed for semantic segmentation in [26]. the segnet model was introduced for multiscale segmentation [27]. the proposed model was used as is, following the encoder and decoder architecture with pixel-wise labeling and using pooling indices for the maximum pooling feature map at the decoder. table iii shows the qualitative performance of the models for the road extraction task using cor, com, iou, and f1 scores. the bold and underlined values indicate the best and second-best scores per metric respectively. the proposed model had 96.42% cor and 81.57% iou values. the proposed model’s iou was about 5% higher than the u-net's, showing that the more supervised information in the proposed model helps extracting roads more precisely. the cor metric of the proposed model is nearly 8% higher than that of segnet. table iii. comparison of results model cor com iou f1 score detection time (s) proposed model 96.42% 81.03% 81.57% 88.02% 11.331s segnet [27] 88.25% 76.92% 71.03% 82.13% 14.528s unet [11]z 93.31% 79.03% 77.49% 85.54% 11.432s fcn [26] 83.13% 75.16% 68.66% 78.80% 9.144s v. results and discussion figures 6-8 show the iou and loss graphs of the segnet, unet, and fcn models, and figure 9 shows a chart of their performance. fig. 6. iou and loss of segnet. the proposed model used more skip connections in the encoder and decoder to improve the performance of u-net and propagate the feature map in all possible ways. identity mapping between the input and output of each residual block improves the network's generalization ability and enables the engineering, technology & applied science research vol. 12, no. 6, 2022, 9654-9660 9659 www.etasr.com patil & jadhav: road segmentation in high-resolution images using deep residual networks identification of deep features. the segnet model showed 71.03% iou and 82.02% f1 scores. the u-net achieved the second highest performance in iou and cor and had an 85.54% f1 score. fcn had the lowest iou and f1 scores but had the least detection time compared to the other three models. figure 10 shows sample results for road detection with original, ground-truth, predicted, and threshold images. fig. 7. iou and loss of u-net. fig. 8. iou and loss of fcn. fig. 9. chart of models performance. (a) (b) (c) (d) fig. 10. road detection results: (a) original, (b) ground-truth, (c) predicted, and (d) threshold images. vi. conclusion this paper proposes a deep convolutional resunet architecture, using cnn to extract road areas from remotely sensed images. the deep convolutional encoder-decoder architecture serves as the foundation of the network. data augmentation techniques were used to improve the performance of the network. the encoder helps to generate a feature map, and the decoder classifies each pixel into a particular class. a simulation was carried out on the massachusetts road dataset. the proposed architecture was compared with other state-of-the-art models. the results showed that the proposed network outperforms segnet, u-net, and fcn. the proposed algorithm is robust against occlusions of shadows in the image and can be used to detect roads in forests and farms. it could also be helpful in land analysis and urban planning. the proposed model can be used for the automatic generation of road maps from different datasets. at first, some pre-processing techniques, like cropping and thresholding, need to be carried out on the input data set. these images can be applied as input to the proposed model to generate a road map. in the future, different optimization techniques and activation functions along with different datasets can be used to improve segmentation results. references [1] r. r. navalgund, v. jayaraman, and p. s. roy, "remote sensing applications: an overview," current science, vol. 93, no. 12, pp. 1747– 1766, 2007. 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[23] k. he, x. zhang, s. ren, and j. sun, "deep residual learning for image recognition," 2016 ieee conference on computer vision and pattern recognition (cvpr), las vegas, nv, usa, jun. 2016, pp. 770–778, https://doi.org/10.1109/cvpr.2016.90. [24] d.-a. clevert, t. unterthiner, and s. hochreiter, "fast and accurate deep network learning by exponential linear units (elus)." arxiv, feb. 22, 2016, https://doi.org/10.48550/arxiv.1511.07289. [25] s. ioffe and c. szegedy, "batch normalization: accelerating deep network training by reducing internal covariate shift," in proceedings of the 32nd international conference on machine learning, lille, france, jun. 2015, pp. 448–456. [26] e. shelhamer, j. long, and t. darrell, "fully convolutional networks for semantic segmentation," ieee transactions on pattern analysis and machine intelligence, vol. 39, no. 4, pp. 640–651, apr. 2017, https://doi.org/10.1109/tpami.2016.2572683. [27] v. badrinarayanan, a. kendall, and r. cipolla, "segnet: a deep convolutional encoder-decoder architecture for image segmentation," ieee transactions on pattern analysis and machine intelligence, vol. 39, no. 12, pp. 2481–2495, sep. 2017, https://doi.org/10.1109/tpami. 2016.2644615. microsoft word etasr_v12_n4_pp8922-8927 engineering, technology & applied science research vol. 12, no. 4, 2022, 8922-8927 8922 www.etasr.com arun et al.: comparison of accident databases and analysis of past industrial accidents in the … comparison of accident databases and analysis of past industrial accidents in the chemical process industry p. a. arun sustainability cluster university of petroleum & energy studies dehardun, india arun.pa@ddn.upes.ac.in s. m. tauseef centre of inter-disciplinary research & innovation (cidri) and sustainability cluster university of petroleum & energy studies dehardun, india smtauseef@ddn.upes.ac.in upasana uniyal sustainability cluster university of petroleum & energy studies dehardun, india upasanauniyal1596@gmail.com received: 14 may 2022 | revised: 31 may 2022 | accepted: 6 june 2022 abstract-despite india being home to some of the worst chemical industry disasters, there is no proper accident reporting and analysis mechanism. the national informatics centre of the ministry of environment and forest (moef) presented an online accident database called cairs to assist past accident analysis (paa). this paper compares cairs with major accident databases widely used by safety professionals. the parameters considered for compassion are scope, accessibility, method of data collection, quality, and the frequency of reporting. past accident analysis showed that the total number of reported events is more or less steady and the number of major accidents is decreasing marginally in european countries, whereas in india only a few states report accidents using the cairs platform. the analysis raised serious concerns about the monitoring of reported information in the indian database. at present, the information available in this database is not reliable and any conclusion based on this information can be misleading. suggestions are offered to enhance the efficacy of the indian accident database. keywords-past accident analysis (paa); chemical process industry; accident database; cairs; emars i. introduction industrial accidents cause losses to human life, environment, and property. a critical examination of these events can bring valuable information on accident morphology, and lessons learned from past accidents can prevent similar events in the future [1, 2]. accident investigation and follow-up of the results are vital in safety management systems. learnings from past incidents can help us anticipate hazards and mitigate the associated risks by reducing the frequency and/or the consequences of the event. with the help of accident investigation, the root cause of the accident can be identified and with corrective and preventive actions, associated risks can be mitigated and make the workspace safer. to anticipate, recognize, and control accidents in the industry we need to collect and review past incident information. it is well documented that the reasons for accidents in many cases are repeated [3, 4]. if we can find out reasons or patterns which are frequently repeating, such accidents can be avoided in the future, and this is the basic objective of past accident analysis (paa). when processes are carried out at extreme temperatures and pressures, the probability of occurrence and the severity of any undesired event is higher. by properly analyzing the information obtained from past accidents, one can get to know the probable causes of failures and accidents in the chemical industry. major accidents in the process industry are caused due to loss of containment due to process failures or due to natural events such as earthquakes, lightning, and floods, which are also called natech events. unlike process equipment failure accidents, natech events can trigger accidents in the entire plant. most of the time the response against these events is delayed due to the lack of communication or the nonavailability of personnel leading to the escalation of the accidents [5, 6]. although we can’t completely safeguard against natural disasters, we can find the most vulnerable parts of the system and can add additional layers of protection for such installations. after identifying the vulnerable units/areas we can develop the system in such a way that it will have the least effect on such critical/vulnerable installations [6]. the repeated disruption in a process industry can be an indication of a major fault that can lead to an accident. if these disruptions corresponding author: p. a. arun engineering, technology & applied science research vol. 12, no. 4, 2022, 8922-8927 8923 www.etasr.com arun et al.: comparison of accident databases and analysis of past industrial accidents in the … are more frequent, they raise questions about the safety controls in the organization. authors in [7] analyzed industrial accidents from the facts database and concluded that repeated disruption can be considered a precursor to accidents, which indicates the failures in the control mechanism of the organization. by analyzing the past incident information it will become much easier to predict the common accident precursor in chemical process industries by looking at factors like the chemicals used, chemical release modes, etc. [8]. unlike other branches of science and technology, where experimental and analytical data are used, in accident analysis, performing experiments to forecast an accident is a cumbersome task. the data we get from past accidents can be used to identify the root causes, which would help prevent similar accidents in the future. so, it is important to analyze past accidents and learn from them, so that the same situation will not be repeated [9-11]. paa is possibly the most powerful and frequently utilized activity for gaining insight into the reasons accidents happen. paa gives important "intelligence of knowing the past" and techniques to forecast hazardous events or mitigate the effects of incidents [3, 12-14]. active research is being carried out in the field of accident analysis with the help of management tools and machine learning, incorporating data management tools such as business intelligence (bi) in past accident analysis, which can provide valuable insight to develop business strategy and tactics [15-18]. in the past, india has been home to several chemical industrial accidents including the world’s worst industrial disaster, the bhopal gas tragedy. to collate the accident data systematically, the national informatics centre of the ministry of environment and forest introduced a web-based accident reporting platform called chemical accident information reporting system (cairs). this paper compares the functionality of this database with other well-known accident databases and its efficacy by performing paa. ii. previous work authors in [3] analyzed 3222 major accidents in chemical process industries reported between 1926 and 1997. their study revealed that in process industries, 49% of accidents were caused by fire and explosions and 38% by toxic releases. their study concluded that although the number of accidents per year decreased during the '80s, the losses per accident have an increasing trend. the fatalities per accident for fire/explosion and toxic release incidents are 3.27 and 2.49 respectively. in the chemical industry, accidents often involve cascading effects, also known as domino effects. often devastating destructions are caused by accidents involving domino effects. predicting and forecasting a standalone accident is much easier than forecasting a domino effect by risk assessment which also requires past accident data. that is one of the reasons very little work has been carried out on managing domino accidents in process industries. paa can provide valuable information to predict and manage domino effects in process industries [9, 19]. authors in [20] conducted statistical research on 207 major industrial accidents from 1969 to 1998. they identified that 39% of major accidents involve domino effects. the risk of domino accidents was determined to be dependent on the type of substance involved and gaseous hydrocarbons pose more risk (58%) of causing domino accidents than liquid fuels (49%). authors in [9] a conducted another noteworthy study on this topic by analyzing 224 accidents involving domino effects from 1917 to 2019 and concluded that 80% of domino accidents occur in fixed installations and 20% during transportation. domino effects are frequently associated with flammable substances, and vapor cloud explosion/fire (vce/vcf) is the most common initiating cause of domino accidents. the analysis of reporting trends indicated that domino accidents are more rigorously reported in developed countries. among developing countries, india reports the highest number of domino accidents (34%). iii. chemical process industry accident databases the main motive of accident investigation is to learn from the mistakes or lapses that led to an accident and identify remedial measures to prevent recurrences [21]. if information of multiple accidents is clubbed in a single source, the analysts will be able to gather pictures on a bigger canvas. accident data clubbed under one unit consist an accident database. by analyzing this information we can identify the anatomy of accidents. inferences from such analysis are being used for making or updating legal requirements and issuing safe work guidelines for similar processes and industries. as we know, even slight negligence can lead to a major problem in chemical industries, so it becomes important to find out the reasons of such accidents. after identification of the root causes, they could be mitigated. public sharing of the accident investigation reports can help all stakeholders who deal with similar hazards. accident databases are a vast source of such information, so by reviewing them, both the industry and the regulators can plan proactive measures to prevent the recurrence of accidents. generally, the accident databases are used for the following reasons: • to gain knowledge from past incidents: to perceive what has occurred, how has it occurred, what the outcomes were, and why it occurred. by this, the designers can avoid the mistakes which have caused accidents in the past. • where adequate information is accessible, it might be feasible to create frequencies or probabilities of incidents, which can support risk assessment studies [22]. there are many databases that maintain past accident data of the process industry. some of the well-known accident databases include facts, emars, mhidas, cairs, and pupad. these databases have their advantages and limitations: some of them are not free to use, i.e they require some kind of subscription, and some of them do not have accurate data [12]. there are very few databases freely available for paa and those which are available are having issues with data accuracy. so, the need occurs to have such a free database in order to provide a single platform to search past accidents and work on the learnings from them in order to create a workplace as safe as possible. the focus of this paper is to review the existing literature on paa and by analyzing the existing databases to find out their problems and propose possible solutions. the major chemical process industry accident databases and advantages and disadvantgages are briefly discussed below. engineering, technology & applied science research vol. 12, no. 4, 2022, 8922-8927 8924 www.etasr.com arun et al.: comparison of accident databases and analysis of past industrial accidents in the … 1) major hazard incident data service (mhidas) this database was launched in 1986 by health and safety executive (uk), followed by the canvey island study, which highlighted the need for reliable data for quantitative risk assessment [22]. this database contains information on global accidents involving hazardous materials. authors in [12] identified data discrepancies in this database. mhidas provides information on the incident type, origin, causes, fatalities, injuries, and losses in the uk and abroad, but it is no longer being updated. • advantages: incidents can be analyzed based on activity, location and people affected. it is a huge inventory of past accidents, since it is one of the oldest databases. • disadvantages: a substantial fee is required to access it. it is no longer being updated. 2) emarsthe major accident reporting system the major accident reporting system, later known as emars was launched by the european commission in 1982, based on the recommendation of the seveso directive [23]. this database contains information from the major accident hazards bureau (mahb) supplied by the eu and affiliated countries and the information includes both accidents and near misses. reporting of events categorized as major accidents by seveso directive iii is mandatory for eu countries and voluntary for affiliated countries. in terms of categories of information, this is the most comprehensive accident database. the available information includes year-wise accidents, industry type, involvements of domino effects, natech events, transboundary impacts, etc. [23]. • advantages: eu member states have to report into emars compulsorily so most of the accidents do get reported here. companies' names and locations are not provided in the database. data are available in two forms i.e. short report and full report [24]. • disadvantages: as it takes almost two to three years to complete a report after proper investigation, one has to wait up to three years to access the full report. 3) failure and accidents technical information system (facts) database this is a global chemical process industry accident database launched by tno industrial and external safety. nowadays, it is maintained by the unified industrial & harbour fire department in rotterdam-rozenburg. as of date, this is the largest repository of chemical industry accidents containing information on over 27500 industrial incidents. facts database gathers information from accident reports of companies and governmental agencies [25]. advantages: abstract containing all important information is available for every accident (3 levels of reports). it contains information from professional sources (csb, aria, mars, zema, nrc, ntsb, reports by companies and publications) so data are considered to be reliable. disadvantages: only accident tables are freely accessible. a fee is required to access detailed information. 4) chemical accident information & reporting system (cairs) cairs is an indian chemical industry accident database developed by the environment & forest informatics division of the national informatics, centre govt. of india. here, accidents are reported by companies and are updated in the database by authorities specified under the mshic rule 1989 [26, 27]. the flowchart of updating the data is illustrated in figure 1. fig. 1. data updating process in cairs. • advantages: includes reports and charts that can be freely accessed. has reports from different authorities. losses outside the premises are reported (fatality, injury, and missing). • disadvantages: the root causes of most of the accidents are not mentioned, not all accidents are reported, and there are data duplicity and consistency issues. 5) known problems the reported problems while performing paa using accident databases are [12]: • improper accident reporting mechanism • record maintenance is not appropriate • hiding the actual cause of the accident • the improper strategy of investigation. hence, it is important to consider the strengths and weaknesses of the databases before performing paa. iv. past accident analysis comprehensive past accident analyses have been performed in [3, 9, 11, 28, 29]. the last well-known paa was performed in 2011 [9]. since then, significant paa research was not performed for major accidents in the chemical process industry. in this paper, ppa was performed based on the data available in emars and cairs. the selected period analysis was from 2010 to 2021. engineering, technology & applied science research vol. 12, no. 4, 2022, 8922-8927 8925 www.etasr.com arun et al.: comparison of accident databases and analysis of past industrial accidents in the … table i. database comparison database country scope accessibility data updation process no of records available information mhidas uk accidents involving hazardous materials from 1950 to 1990 subscription required no longer being updated. aea technology was used to compile data from public domain sources. 8000+ • date & location • materials involved • no of people affected • general and special causes • economic losses. emars eu major accidents and near-miss information free information provided by eu and affiliated countries under the seveso directive. 1165 comprehensive information, including: • accident, site, and installation descriptions and classification. • cause description and classification. • consequences description and classification. • emergency response and legal actions. • lessons learned. facts the netherlands global accidents accident tables are freely accessible. subscription required for detailed reports accident information from professional sources. 27500+ • an accident table contains basic information about the year, country, activity, and causes of accidents. • the coded abstracts contain detailed information about location, operations, etc. • detailed information about causes and consequences cairs india incidents reported by authorities in india free based on accident reports submitted to various governmental agencies. 100+ • accidents' date and time • company information • chemicals involved and their type. • causes • number of people killed/injured within and outside the premises 1) past accident analysis from emars database during the studied period, 495 accidents were recorded in the emars database, and detailed reports are available for 378. the event-wise yearly trends of the reported events are illustrated in figure 2. from the trends it can be inferred that the total number of reported events is more or less steady and the number of major accidents is decreasing marginally in europe. this indicates that the trends identified by [9] are still prevailing in europe. out of these 495 accidents, 73% are major, 20% are near-miss incidents, and 7% are other events (figure 3), meeting the criteria defined in the seveso directive annexure [16]. fig. 2. year-wise accident reporting trends in emars. industry-wise recorded accident analysis can indicate the vulnerability of industries. the analysis, as shown in figure 5, shows that 19% of accidents were reported in petrochemical/oil refineries followed by the general chemical manufacturing industry (10%), and the power generation, supply, and distribution (6%) industries. interestingly, there is a drastic reduction in the number of accidents reported in the general chemical industry during the analysis period compared to the previous decade (1998-2009), i.e. from 132 cases to 51, whereas the number of accidents in petrochemical/oil refineries increased from 84 to 93. emars also reports special circumstances involved with the recorded incidents such as natech or domino events, transboundary effects, and involvement of contractors. out of such 56 events, 54% of the cases involve contractors and 21% involve domino effects as illustrated in figure 4. fig. 3. types of accidents reports in emars. fig. 4. accidents involving special circumstances. engineering, technology & applied science research vol. 12, no. 4, 2022, 8922-8927 8926 www.etasr.com arun et al.: comparison of accident databases and analysis of past industrial accidents in the … fig. 5. industry-wise accidents. 2) indian chemical industry accident scenario as illustrated in figure 6, the analysis of chemical industry accidents reported to the various regulatory agencies in cairs, showed that out of 29 states, only 6 have reported accidents so far, pointing out the poor accident reporting culture in india. it was also found that there are duplicate data entries in cairs: some of the accidents are reported multiple times, e.g. the accident in accura lab pvt. ltd, telangana on 25th september 2013 is reported twice, one with the accident cause details and another without this information. similarly, if an accident was involved with multiple chemicals it is reported multiple times. fig. 6. state-wise reporting of accidents. the data collected from the cairs database were manually filtered to remove all duplicities, and 86 records were obtained, which were submitted to the chief inspector of factories. the year-wise reporting trends are depicted in figure 7. as shown, there is no particular trend in the number of accidents reported in cairs. the maximum number of accidents was reported in 2016, while the minimum in 2014, whereas there are no available data after 2018. one of the major drawbacks of cairs is that the root cause of the accident is missing in most reports. out of the 86 accidents analyzed, only 36 have their root cause mentioned, i.e. for around 58% of the accidents the root cause is not mentioned. this shows that the investigative findings of an accident are not recorded for most accidents. figure 8 depicts the accidents with regard to their type/category. it was found that 57% of the reported cases are incidents. in some cases, accidents with fatalities are considered minor accidents or incidents, while accidents with fewer casualties may be considered as major. so, there is no well-defined guideline or procedure to report an accident. this indicates a lack of monitoring of reported information in this database. at present, the information in this regard is not reliable and any conclusion based on this type of analysis can be misleading. fig. 7. year-wise accidents reported in cairs. fig. 8. accidents based on category. the conclusion of the analysis based on the available information in these two databases is that the findings of accidents are better reported in emars, as the root cause, and the event sequence of every accident is mentioned in emars, but not in cairs. emars also provides more categories of information. the indian database cairs needs urgent revisions to provide more reliable and useful data. v. conclusions and recommendations this work reviewed past accidents in the chemical process industry. a comprehensive analysis of past accidents enables us to identify the recent accident trends in the industry. accident databases aid the analysis of past accidents. global databases were compared and their advantages and disadvantages were lsited. paa of the accidents recorded in the european emars database and the indian cairs database has engineering, technology & applied science research vol. 12, no. 4, 2022, 8922-8927 8927 www.etasr.com arun et al.: comparison of accident databases and analysis of past industrial accidents in the … been performed. from the trends, it can be inferred that the total number of reported events is more or less steady and the number of major accidents is decreasing marginally in europe. the analysis of the indian chemical industry based on accidents reported in the cairs database can lead to inaccurate conclusions as accidents are not reported promptly in this database and an urgent revision to ensure data accuracy is required. some suggestions on improving the existing databases are: • accident databases available in the public domain would encourage researchers to undertake active studies in this field and would also enable risk professionals and policymakers to make 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[24] z. nivolianitou, m. konstandinidou, and c. michalis, "statistical analysis of major accidents in petrochemical industry notified to the major accident reporting system (mars)," journal of hazardous materials, vol. 137, no. 1, pp. 1–7, 2006, https://doi.org/10.1016/ j.jhazmat.2004.12.042. [25] "factsonline: chemical and industrial accident database." http://www.factsonline.nl/ (accessed may 07, 2022). [26] "welcome to cairs." http://cairs.nic.in/ (accessed feb. 15, 2022). [27] s. s. nair and a. k. gupta, "industrial sitting in multi-hazard environment: application of gis and mis," international geoinformatics research and development journal, vol. 1, no. 2, pp. 45–58, jun. 2010. [28] l. j. bellamy, t. a. w. geyer, j. a. astley, evaluation of the human contribution to pipework and in-line equipment failures frequencies. london, uk: hse, 1989. [29] r. m. darbra, a. palacios, and j. casal, "domino effect in chemical accidents: main features and accident sequences," journal of hazardous materials, vol. 183, no. 1–3, pp. 565–573, nov. 2010, https://doi.org/10.1016/j.jhazmat.2010.07.061. microsoft word etasr_v13_n2_pp10328-10337 engineering, technology & applied science research vol. 13, no. 2, 2023, 10328-10337 10328 www.etasr.com kassem et al.: techno-economic feasibility assessment for the promotion of grid-connected rooftop … techno-economic feasibility assessment for the promotion of grid-connected rooftop pv systems in botswana: a case study youssef kassem department of mechanical engineering, engineering faculty, near east university, cyprus | energy, environment, and water research center, near east university, cyprus yousseuf.kassem@neu.edu.tr (corresponding author) huseyin gokcekus department of civil engineering, civil and environmental engineering faculty, near east university, cyprus | energy, environment, and water research center, near east university, cyprus huseyin.gokcekus@neu.edu.tr fadel ali ramadan agila department of environmental education and management, ataturk faculty of education, near east university, cyprus 20215633@std.neu.edu.tr received: 7 january 2023 | revised: 24 january 2023 | accepted: 26 january 2023 abstract the main aim of the present study is to investigate the solar energy potential and evaluate the economic viability of a 5kw grid-connected rooftop photovoltaic (pv) system as an electricity generation source in three selected regions (gaborone, maun, and tshabong) in botswana for the first time. in this study, nasa power data were used for evaluating the solar potential in the selected regions. the results showed that the selected locations are suitable for the installation of various scales of pv systems due to the high global horizontal solar radiation. retscreen expert software was used to assess the techno-economic feasibility of the proposed systems. the performance of the proposed systems with various pv technologies (mono-crystalline silicon and poly-crystalline silicon) is analyzed. furthermore, economic and financial indicators such as net present value, annual life cycle savings, payback, benefit-cost ratio, and cost of energy production were calculated. the results indicate that the proposed system is very promising for all the selected locations. additionally, it was found that the pv projects with poly-si technology produced a large amount of energy and have a low electricity cost compared to mono-si technology. the results suggest that grid-connected rooftop pv systems have a significant role in covering the electricity demand and in reducing carbon dioxide emissions, especially in high population density and rural regions. this study provides some useful recommendations for decision-makers regarding the development and deployment of pv energy technology in botswana. keywords-botswana; solar energy potential; grid-connected; rooftop pv system; pv technology; retscreen software i. introduction population growth and the rising living standards led to growing demand of energy, primarily electricity, in a global scale. it is known that environmental pollution impacts human health through emissions of harmful gases caused by conventional energy generation from fossil fuels. thus, finding alternative energy sources to reduce fossil fuel consumption and environmental pollution is essential. renewable energies such as solar energy have grown due to the growing demand [1] and solar energy has been widely utilized globally to generate electricity and reduce emissions. it is an inexhaustible and environmentally friendly energy source. authors in [2] report that solar power will reduce the emission of about 69100 million tons of co2, 68-99 thousand tons of nox, and 126184 thousand tons of so2 by 2030. authors in [3] concluded that solar energy has significant potential to meet the world's electricity requirements in the future. authors in [4] mention engineering, technology & applied science research vol. 13, no. 2, 2023, 10328-10337 10329 www.etasr.com kassem et al.: techno-economic feasibility assessment for the promotion of grid-connected rooftop … that solar energy technologies have a huge potential to mitigate climate change by reducing energy-related emissions. generally, solar pv produces electrical power directly from sunlight [5-8]. authors in [5] evaluated the performance of a 6.4kw grid-connected pv system and wind system at three locations in northern cyprus. the results showed that the most economical option for electricity production in the selected locations is the pv system due to the low electricity prices and the recovery of the initial investment. authors in [7] investigated the economic and environmental feasibility of a 210kw grid-connected rooftop pv system in greece. the results showed that the successful development of small-scale residential solar energy systems in the country depends on increasing energy selling prices and/or reducing costs in the production of pv systems. authors in [8] evaluated the feasibility of a 5kw grid-connected rooftop pv system in lebanon. the results showed that the amount of output from the solar system can help reduce the shortage of energy in the region. a. energy situation in botswana botswana is located between 22.3285° s and 24.6849° e. the country is landlocked in southern africa bordering zimbabwe and south africa. presently, fossil fuels and coal are the main sources of electrical energy in the country [9]. access to electricity in botswana has reached 77% of the population in urban areas, while in rural areas it is still limited to 37% according to the world bank. the overall electrification rate at the national level is 60%. botswana relies mainly on electricity, coal, fuel wood, and oil for its energy requirements. with these sources, co2 emissions have increased over the years according to the world bank database. furthermore, more than 50% of botswana's energy requirements are imported from south africa and zambia according to united nations environment program. besides, electricity consumption has been rising over time. for example, the electricity consumption was 586.84kwh/capita in 1981 and 1815.55kwh/capita in 2014 according to the world bank database. this has exacerbated the electricity deficit over the years. according to electricity information released by the international energy agency, population and economic growth have led to an increase in electricity consumption in the country. therefore, utilizing renewable energy would reduce the consumption of conventional fuels and be a clean source of electricity generation in the country. according to the wind power density (wpd) classification [10], botswana is placed in class 1 (poor) based on the obtained values of wpd at 10m and 50m. moreover, the specific pv power output is within the range of 4.74-5.47kwh/kwp according to the world bank group (global solar atlas). moreover, botswana receives approximately 3200h of sunshine annually and has high insulation on a horizontal surface of 21mj/m 2 . the average daylight hours in botswana range from 9.9h in summer to 8.2h in winter. consequently, botswana has an abundant solar energy potential compared to wind energy. the country is a suitable region for installing pv systems due to the high value of global solar radiation and has a great chance of utilizing solar power in order to reduce the amount of imported energy from the neighboring countries [11]. additionally, installing a solar system in the country is technically reliable due to the high value of average daily radiation on the horizontal surface [12]. several studies have investigated the potential of solar energy in the country [13-19]. for instance, authors in [13] estimated the potential of concentrating solar power in botswana using the geographical information system (gis). the results indicated that the country has a huge concentrating solar power that will be able to meet the maximum energy demand. authors in [14] examined the status of solar pilot projects at different locations in botswana. they concluded that solar home systems in rural areas will significantly enhance socio-economic benefits and assist the sustainability of solar power generation in the country. authors in [15] evaluated the technical performance of solar water heaters in gaborone, botswana. authors in [16] analyzed the energy requirements of a non-electricity off-grid village in botswana. authors in [17] designed a hybrid solar-wind system for rural electrification in botswana using the homer software. the results showed that the optimal model (solar-wind-battery system) employed 100% renewable energy, resulting in zero carbon emissions. the results indicated that the minimum and maximum output power of the pv system occurred during june/july and december/january, respectively. authors in [18] utilized simulink's single diode model design to present the pv module voltage output and the annual maximum power output profile of the pv module for variable temperature and irradiance. the results demonstrated that the voltage output is generally constant throughout the year while the maximum power from the solar module closely follows the solar radiation profile. authors in [19] calculated the size of pv panels, batteries, and integrated collector-storage solar water heaters based on the demands for electricity and hot water. b. research gap and objectives to the best of our knowledge, there is not any study that investigates the economic feasibility of a grid-connected rooftop pv system in botswana. the findings of the literature review reveal a clear lack of proposed solar pv systems as a power source for households in botswana. thereby, there is no doubt that a comprehensive economic and environmental study must be conducted to obtain results that could be a roadmap for solar energy investments in the country. consequently, it can be concluded that the small-scale solar systems in the country can not only bridge the energy gap but would also reduce the environmental impact. therefore, the present paper aims to evaluate the techno-economic and environmental feasibility of small-scale rooftop grid-connected solar systems at different locations and climate conditions in botswana. to achieve this, the solar radiation data are analyzed to classify the solar resource in the selected locations. moreover, the technoeconomic feasibilities for the rooftop solar systems at three comparative locations were developed for various policy scenarios, based on variations in financial parameters using retscreen experts. engineering, technology & applied science research vol. 13, no. 2, 2023, 10328-10337 10330 www.etasr.com kassem et al.: techno-economic feasibility assessment for the promotion of grid-connected rooftop … ii. materials and methods a. study area figure 1 shows the locations of the three regions considered in this study. the solar radiation data were taken from the nasa power data over 16 years (2005-2020). fig. 1. location of the selected regions used in this work. screenshot from google earth. © terrametrice, map data © afrigis (pty) ltd. 1) gaborone gaborone (24.6282°s, 25.9231°e) is the capital and largest city of botswana with a population of over 200,000. it is located in the southern part of the country. the monthly variation of global horizontal irradiation (ghi) and average temperature (at) are illustrated in figure 2. the minimum and maximum values of ghi are recorded in june and october with values of 121.43kw/m 2 and 217.30kw/m 2 , respectively. the annual value of ghi is estimated to be 2094.52kw/m 2 . the solar resource at this location is categorized as outstanding (2035.9-2221.8kw/m 2 ) [19]. additionally, it is found that the monthly value of at is within the range of 13.24-25.20℃ with an average value of 20.69℃. 2) maun maun (19.9953°s, 23.4181°e) is located in northwest province. it is the capital of the northwest province with a population of 55,784. as can be seen in figure 2, the monthly value of ghi varies from 138.56kw/m 2 to 227.41kw/m 2 with an average value of 182.35kw/m 2 . the solar resource at this location is also classified as outstanding (annual ghi = 22188.16kw/m 2 ) [19]. the maximum mean at is recorded in october with a value of 28.03℃, while the minimum value of 16.72℃ is recorded in july. 3) tshabong tshabong (26.0208°s, 22.4113°e) is located in the kalahari desert with a population of 8,939 according to the 2011 census. the monthly value of ghi is within the range of 117.99250.38kw/m 2 with an average of 188.52kw/m 2 as shown in figure 2. the annual value of ghi at the selected location is 2262.25kw/m 2 . the solar resource at this location is categorized as superb (>2221.8kw/m 2 ). additionally, it is found that the monthly value of at is within the range of 12.93-27.89℃ with an average value of 21.58℃. b. on-grid photovoltaic system grid-connected pv systems have pv panels that supply the required power during the day and are connected to the local electrical grid to be supplied with power at night. moreover, the excess power from the pv system is fed back to the grid when the power generated is more than the load required [20]. in general, the grid-connected pv system consists of solar panels, inverters, a power-conditioning unit, and gridconnection equipment. to get more power from the pv arrays, the pv panels should have high cell efficiency and a high operating temperature. the inverter is one of the most crucial components of a grid-connected system because it converts direct current (dc) to alternating current (ac). in addition, electricity meters are utilized to read the flow of electricity to and from the grid. recently, on-grid pv systems have attracted substantial attention due to the advantages of their compatibility with the electricity grid. in this system, the output power of the pv system is connected directly to the grid and the household. the electric energy produced by the pv system can cover the energy demand of the household. when the produced energy by the pv system is high, the remaining produced energy can be fed into the grid through an electric meter. this system comprises pv panels, which absorb sunlight and produce direct current, an inverter that is used to convert the direct current to alternating current, a distribution controller, and load as shown in figure 3. generally, it is necessary to estimate the optimal sizing of grid-connected pv systems as the first step to meet the energy demands of the household. according to [21], the amount of output energy by the pv system (��� ) should be greater than the amount of electricity taken from the grid (����� ) as shown in (1). in this case, the energy demand of the household can be shared between the pv system and the electric grid. ��� > ����� (1) the generated energy from the pv system is utilized to cover the household/building instantaneous electricity load and the surplus energy is injected into the grid (i.e. if the load of the building at time t is greater than the generated pv electricity, the required energy is absorbed from the grid. in general, the effect of the ambient temperature is one of the most important factors that affect the output power of the pv system ( �� ), which can be expressed as [22]: �� = ��� �� ��� � ����� �1 + �� �� − ���� �� (2) where ��� is the pv module efficiency, �� is the inverter efficiency, ���� is the standard test conditions (stc) irradiance (1kw/m 2 ), t and ���� are the pv cell operating temperature in ℃ and the pv cell stc temperature (25℃ ), respectively, �� is the module's maximum power temperature coefficient (%/℃), and � is the derate factor to account for the losses in system performance given by [23]: � = � � �!� �!�" �#$% (3) where � � is the dc power derate factor to account for factors like module mismatch, diodes and connection losses, and dc wiring losses, �!� is the ac interconnection derate factor with a value of 0.99, �!�" is the derate factor to account for the loss engineering, technology & applied science research vol. 13, no. 2, 2023, 10328-10337 10331 www.etasr.com kassem et al.: techno-economic feasibility assessment for the promotion of grid-connected rooftop … in system performance with age, and �#$% represents the losses due to external factors like dust, shading, snow cover, or anything else that would vary the power output of the pv module to deviate from that expected under ideal conditions. fig. 2. monthly mean variation of ghi and at for all selected locations during the 2005-2020 period. moreover, (4) is used to estimate the pv cell operating temperature (t) [24]. furthermore, the solar radiation incident (g) on the tilted angle (&) can be determined by (5) [25]: � = �' + �(.* ��+,�� − 20� (4) � = �� /012�3� + 4 ∙ 0126 786 9 + : ∙ ;012�<� + 4 ∙ 2=>6 786 9?@ (5) where �' is the ambient temperature, �+,�� is the nominal operating cell temperature, �� is the direct normal irradiance, 3 is the angle between the tilted surface and the solar rays, 4 is the diffuse portion constant, : is the reflection index, and < is the zenith angle. 3 , < , and the sun azimuth angle b can be obtained from: 012�3� = �012�&� ∙ 012�<� + 2=>�&� ∙ 2=>�<� ∙ 012�b − c�� (6) 012�<� = 2=>�d� ∙ 2=>�e� + 012�d� ∙ 012�e� ∙ 012�f� (7) gh>�b� = i� �j�i� �k�∙lmi�j�nlmi�k�∙%' �o� (8) where c is the plat azimuth angle, d is the solar declination angle, e is the latitude, and f is the solar angle, defined by: f = pq(6r ��st� + �u� − 4s + 60gx� − 2� (9) where gi is the solar time depending on local standard time (lst), longitude s, time zone gx, and �u� is the equation of time that accounts for the irregularity of the earth's speed around the sun. fig. 3. components of an on-grid pv system. moreover, the maximum power ( y'$ ) of the developed on-grid solar pv system can be estimated as a function of global solar radiation �i� (kwh/m2/d), solar radiation at standard test conditions � (kw/m2), pv derating factor z�� , household daily power consumption �!� (kwh/d), and inverter yield �� [ . this relationship can be expressed as [22]: y'$ = "\� �]�^_`abc]de (10) the average daily output of the pv system coincides with the utility's peak demand period, therefore decreasing the capacity losses in the utility distribution network and improving the delay issues of the transmission and distribution (t&d) network [26-28]. moreover, this system does not require batteries hence it has lower cost than an offgrid pv system [28]. 0 5 10 15 20 25 30 0 50 100 150 200 250 ja n f e b m a r a p r m a y ju n ju l a u g s e p o c t n o v d e c a t [ ℃ ] g h i[ k w / m 2 ] gaborone 0 5 10 15 20 25 30 0 50 100 150 200 250 ja n f e b m a r a p r m a y ju n ju l a u g s e p o c t n o v d e c a t [ ℃ ] g h i [k w / m 2 ] maun 0 10 20 30 0 100 200 300 ja n f e b m a r a p r m a y ju n ju l a u g s e p o c t n o v d e c a t [ ℃ ] g h i [k w / m 2 ] tshabong ghi at engineering, technology & applied science research vol. 13, no. 2, 2023, 10328-10337 10332 www.etasr.com kassem et al.: techno-economic feasibility assessment for the promotion of grid-connected rooftop … c. retscreen expert software retscreen expert is a renewable energy management tool developed by the canadian government. it is a decision support tool that is utilized to determine the potential of energy, costs, savings, greenhouse gas (ghg) emission reduction, and economic viability [29, 30]. retscreen uses global meteorological data collected from the national aeronautics and space administration (nasa) database. retscreen is commonly employed to explore the feasibility of gridconnected wind and pv power systems. for instance, authors in [30] used retscreen to evaluate the techno-economic feasibility of a grid-connected pv system in nigeria. authors in [31] utilized retscreen to investigate the potential of pv systems for electricity generation in various locations in libya. authors in [32] evaluated the cost-benefit of 100mw solar pv in pakistan using retscreen. in the current study, the initial and operations and maintenance costs were assumed based on the previous studies related to techno-economic feasibility in african countries. capacity factor (cf), ghg reduction (aghg), and economic assessment parameters: net present value (npv), levelized cost of energy (lcoe), simple payback (sp), equity payback (ep), annual lice cycle saving (alcs), and benefit-cost ratio (b-c) are determined using the equations below. 4f = �ghi�×*kq( (11) � − �l� = ��base case ghg emission factor� − �proposed case ghg emission factor�� × end use energy delivered (12) ghg − e − rc = !���∆��� (13) � � = ∑ �d�����d+ �( (14) s4u� = ��� �� ���� ���� ����������� �� ����������� ��������  ���� �¡� �������� (15) t = �n¢�£�¤d¤_��¥¦§¦��¨©�����ªn£�g&¬��­h¤®ª (16) � = ∑ 4 + �( (17) �s4t = +��¯ _;�n ¯ �¯°_�±? (18) ² − 4 = +�����n`³����n`³�� (19) where m´% is the energy generated per year, is the installed capacity, n is the project life in years, 4 is the after-tax cash flow in year n, r is the discount rate, c is the total initial cost of the project, z� is the debt ratio, b is the total benefit of the project, µ� represents the incentives and grants, 4# #� is the annual energy savings or income, 4l'¶' is the annual capacity savings or income, 4·" is the annual renewable energy (re) production credit income, 4�¸� is the ghg reduction income, 4m&¹ is the yearly operation and maintenance costs incurred by the clean energy project, 4̀ ´#º is the annual cost of fuel, which is zero for renewable projects, and ∆�¸� is the annual ghg emission reduction. iii. results and discussion retscreen expert software was utilized to evaluate the viability of small-scale rooftop pv systems in three selected locations in botswana. a. technical viability in this study, 5kw grid-connected fixed solar tracking mode is considered for all the selected locations with the solar pv modules tilted to an angle of 25° and azimuth angle of 180°. these angles were chosen based on the highest value of solar irradiance and electricity exported to the grid for each location. in this study, the solar module cs6x-340m-fg, manufactured by canadian solar, was used (table i). the output ac power, the dc-ac conversion efficiency, and the capital cost of the inverter are the main factors when selecting a suitable inverter. growatt 5500mtl-s dual mppt 6kw solar inverter was selected (table ii). in general, the solar resource assessment is the first step of the pv system design. figure 4 depicts the monthly average daily global irradiation on a horizontal surface and the global radiation on a horizontal surface and a 25° inclined plane for all chosen sites. it is observed that june is the period with the lowest solar irradiation in botswana. the minimum tilted solar radiation was found to be 5.52kw/m 2 /d for gaborone, 5.57kw/m 2 /d for maun, and 5.40kw/m 2 /d for tsabong. the maximum value of tilted solar radiation was recorded in september (i.e. 6.69kw/m 2 /d) for gaborone, august (i.e. 6.91kw/m 2 /d) for maun, and december (i.e. 6.96kw/m 2 /d) for tsabong. table i. specifications of the selected pv module pv module technology mono-si poly-si manufacturer canadian solar canadian solar model mono-si cs6x-300m poly-si cs6x-310p nominal power [w] 300 310 open-circuit voltage [v] 45 44.9 short-circuit current [a] 8.74 9.08 voltage at point of maximum power [v] 36.5 36.4 current at point of maximum power [a] 8.22 8.52 module area [m2] 1.919 1.918 efficiency [%] 15.63 16.16 table ii. specifications of the selected inverter pv module technology value rated power [w] 6000 min ppt voltage [v] 100 max ppt voltage [v] 550 dc startup voltage [v] 100 dc shutdown voltage [v] 80 max input voltage [v] 550 max dc power [w] 6500 max ac power [w] 5000 max dc current [a] 30 warranty [ year] 10 efficiency [%] 97.9 cost [usd] 550 the performance of the pv systems in terms of pv output and cf is dependent on the orientation angles [33]. thus, the electricity exported to the grid (eeg) and the cf were engineering, technology & applied science research vol. 13, no. 2, 2023, 10328-10337 10333 www.etasr.com kassem et al.: techno-economic feasibility assessment for the promotion of grid-connected rooftop … estimated at a tilted angle of 25° and an azimuth angle of 180° for all selected locations. it should be noted that fixed-tilt mounting systems are simpler, cheaper, and require less maintenance compared to tracking systems. the mean monthly value of eeg for all the selected locations is shown in figure 5. the following are observed:  in gaborone, the eeg is within the range of 664.01793.74kwh for mono-si and 686.14-820.20kwh for polysi.  in maun, the eeg varied from 604.69 to 834.89 kwh for mono-si and from 624.84 to 862.72kwh for poly-si.  in tsabong, the eeg ranged between 665.26 and 828.70kwh for mono-si and from 677.11 and 856.33kwh for poly-si. fig. 4. monthly average daily global radiation on a horizontal surface and a 25° tilted plane.  the maximum amount of eeg is recorded in august while the minimum value is recorded in june for gaborone.  the lowest and highest values of eeg are recorded in february and august, respectively for maun.  for tsabong, the highest and lowest values of eeg occurred during june and december, respectively.  the poly-si technology delivered higher energy to the grid than the mono-si technology. the annual value of eeg and cf for each location is shown in table iv. it was found that the maximum annual eeg value of 9159.63kwh for poly-si and 8864.16kwh for mono-si occurred at tsabong. the cf values were within the range of 19.84-19.78% with an average value of 19.81%. it was noticed that the cf of poly-si technology is a slightly higher than mono-si technology. these results can be supported by [34, 35]. the authors in [34] found a cf of 15.37% for mono-si technology and 15.41% for poly-si technology, while the authors in [35] estimated that the cf value for mono-si and poly-si technology is 11.47% and 12.9%, respectively. table iii. the annual value of eeg and cf of each location location pv technology eeg [kwh] cf [%] gaborone mono-si 8854.36 19.80 poly-si 9149.50 19.82 maun mono-si 8836.07 19.78 poly-si 9130.61 19.80 tsabong mono-si 8864.16 19.82 poly-si 9159.63 19.84 b. economic sustainability the techno-economic feasibility for rooftop pv systems at the three selected locations was evaluated for different values of electricity export rate (0.03-0.21 usd/kwh with a step of 0.03 usd/kwh). the assumed input financial parameters included 7.2% inflation rate, 3.75% discount rate, 9% reinvestment rate, 25 years of project life time, 70% debt ratio, 0% debt interest rate, and 20 years of debt payments, based on previous studies. based on these input parameters, npv, alcs, sp, ep, lcoe, and the internal rate of return (irr) were estimated by retscreen. the npv was determined for each location and the calculated values of electricity export rate (eer) are listed in table v. it was found that the npv for each value of eer is positive, which indicated that the project is potentially feasible [36, 37]. there is a strong correlation between npv and eer. irr was estimated to evaluate the economic viability of the project [30, 36], as it provides the true return of interest generated by equity over the life of the project [29]. the results showed that increasing the rate of exporting electricity led to an increase in irr. in addition, it was observed that the irr of the three locations is higher than the required rate of return of the project. furthermore, alcs was calculated by using npv, discount rate, and project lifetime. it was found that alcs is within the range of 70.353099.09 usd/year. additionally, the results of economic viability using poly-si technology are higher than those for mono-si technology (table v). 0 1 2 3 4 5 6 7 8 jan feb mar apr may jun jul aug sep oct nov dec d a il y s o la r ra d ia ti o n [k w h / m 2 / d ] gaborone 0 1 2 3 4 5 6 7 jan feb mar apr may jun jul aug sep oct nov dec d a il y s o la r ra d ia ti o n [k w h / m 2 / d ] maun -1 1 3 5 7 d a il y s o la r ra d ia ti o n [k w h / m 2 / d ] tsabong horizontal tilted engineering, technology & applied science research vol. 13, no. 2, 2023, 10328-10337 10334 www.etasr.com kassem et al.: techno-economic feasibility assessment for the promotion of grid-connected rooftop … table iv. annual value of eeg and cf for each location location parameter pv technology electricity export rate [usd/kwh] 0.03 0.06 0.09 0.12 0.15 0.18 0.21 gaborone pre-tax irr-equity mono-si 5.96 17.78 28.38 39.00 49.74 60.58 71.49 pre-tax irr-assets -0.64 5.98 10.65 14.62 18.27 21.75 25.14 net present value (npv) [usd] 1171.19 8959.66 16748.13 24536.60 32325.08 40113.55 47902.02 annual life cycle savings [usd/year] 73.00 558.47 1043.94 1529.41 2014.88 2500.35 2985.81 simple payback [year] 31.68 15.84 10.56 7.92 6.34 5.28 4.53 equity payback [year] 17.94 7.09 4.13 2.88 2.20 1.78 1.49 benefit-cost (b-c) ratio 1.46 4.55 7.63 10.72 13.80 16.89 19.97 energy production cost [usd/kwh] 0.0466 0.0466 0.0466 0.0466 0.0466 0.0466 0.0466 pre-tax irr-equity poly-si 6.42 18.49 29.44 40.42 51.54 62.76 74.04 pre-tax irr-assets -0.35 6.33 11.07 15.13 18.86 22.44 25.92 net present value (npv) [usd] 1430.81 9478.89 17526.98 25575.07 33623.15 41671.24 49719.33 annual life cycle savings [usd/year] 89.18 590.84 1092.49 1594.14 2095.79 2597.44 3099.09 simple payback [year] 30.66 15.33 10.22 7.66 6.13 5.11 4.38 equity payback [year] 17.23 6.78 3.97 2.77 2.12 1.72 1.44 benefitcost (b-c) ratio 1.57 4.75 7.94 11.13 14.32 17.51 20.69 energy production cost [usd/kwh] 0.0451 0.0451 0.0451 0.0451 0.0451 0.0451 0.0451 maun pre-tax irr-equity mono-si 5.93 17.73 28.32 38.91 49.63 60.45 71.33 pre-tax irr-assets -0.66 5.96 10.62 14.59 18.24 21.71 25.09 net present value (npv) [usd] 1122.57 8844.16 16565.75 24287.34 32008.92 39730.51 47452.10 annual life cycle savings [usd/year] 70.35 554.23 1038.11 1521.99 2005.87 2489.75 2973.63 simple payback [year] 1.87 7.36 9.75 11.31 12.47 13.41 14.19 equity payback [year] 31.74 15.87 10.58 7.94 6.35 5.29 4.54 benefitcost (b-c) ratio 1.44 4.50 7.56 10.62 13.68 16.74 19.80 energy production cost [usd/kwh] 0.0468 0.0468 0.0468 0.0468 0.0468 0.0468 0.0468 pre-tax irr-equity poly-si 6.39 18.45 29.37 40.33 51.43 62.62 73.87 pre-tax irr-assets -0.37 6.30 11.04 15.09 18.82 22.39 25.87 net present value (npv) [usd] 1379.95 9358.93 17337.90 25316.88 33295.86 41274.83 49253.81 annual life cycle savings [usd/year] 86.48 586.49 1086.50 1586.51 2086.52 2586.53 3086.54 simple payback [year] 30.72 15.36 10.24 7.68 6.14 5.12 4.39 equity payback [year] 17.27 6.80 3.98 2.78 2.13 1.72 1.44 benefitcost (b-c) ratio 1.55 4.71 7.87 11.03 14.19 17.35 20.51 energy production cost [usd/kwh] 0.0453 0.0453 0.0453 0.0453 0.0453 0.0453 0.0453 tsabong pre-tax irr-equity mono-si 5.97 17.80 28.42 39.04 49.80 60.66 71.57 pre-tax irr-assets -0.63 5.99 10.66 14.64 18.29 21.78 25.17 net present value (npv) [usd] 1147.11 8893.24 16639.37 24385.50 32131.63 39877.76 47623.89 annual life cycle savings [usd/year] 71.88 557.30 1042.72 1528.14 2013.56 2498.98 2984.40 simple payback [year] 31.64 15.82 10.55 7.91 6.33 5.27 4.52 equity payback [year] 17.92 7.08 4.13 2.88 2.20 1.78 1.49 benefitcost (b-c) ratio 1.45 4.52 7.59 10.66 13.73 16.80 19.86 energy production cost [usd/kwh] 0.0467 0.0467 0.0467 0.0467 0.0467 0.0467 0.0467 pre-tax irr-equity poly-si 6.43 18.52 29.47 40.47 51.61 62.84 74.12 pre-tax irr-assets -0.34 6.34 11.08 15.14 18.88 22.46 25.95 net present value (npv) [usd] 1405.31 9409.65 17413.98 25418.32 33422.65 41426.99 49431.33 annual life cycle savings [usd/year] 88.07 589.66 1091.26 1592.86 2094.46 2596.06 3097.66 simple payback [year] 30.62 15.31 10.21 7.66 6.12 5.10 4.37 equity payback [year] 17.21 6.77 3.96 2.76 2.12 1.71 1.44 benefitcost (b-c) ratio 1.56 4.73 7.90 11.07 14.24 17.41 20.58 energy production cost [usd/kwh] 0.0451 0.0451 0.0451 0.0451 0.0451 0.0451 0.0451 the economic viability of a project is estimated by determining the payback period [30. 36]. table iv lists the payback period including ep and sp for all selected locations. it is found that the ep is within the range of 1.44-17.99 years. the developed pv project with mono-si technology in maun has the longest ep and sp of 17.99 years and 31.74 years, respectively, followed by one in gaborone. the proposed project with poly-si technology at tsabong has the shortest ep of 1.44 years and sp of 4.37. the results reveal that the increase in eer will lead to a decrease in ep and sp. besides, the results demonstrate that the sp value exceed the lifetime of the project (25 years) when the eer is equal to 0.03 usd/kwh. this indicates that installing pv projects at the selected locations is not economically viable when the eer is equal to 0.03 usd/kwh. in addition, the value of b-c, which is utilized to determine the cash flow generated viability, is higher than 1 as shown in table v. these findings indicate the feasibility of the projects [27]. moreover, the lcoe sets a minimum selling cost of electricity that may result in an npv of zero. table v shows the lcoe for each location with various pv technologies. it is observed that the lcoe is within the range of 0.0451-0.0468 usd/kwh. these values are within the range of 0.0199-3.165 usd/kwh [38]. besides, the lcoe of pv systems is less than the current electricity tariffs in botswana (0.098 usd/kwh for households and 0.117 usd/kwh for businesses). engineering, technology & applied science research vol. 13, no. 2, 2023, 10328-10337 10335 www.etasr.com kassem et al.: techno-economic feasibility assessment for the promotion of grid-connected rooftop … fig. 5. monthly average value of eeg on a 25° tilted plane. c. climate co-benefits assessment in addition to economic feasibility, an estimate of the environmental benefits in terms of reduced ghg emissions of the proposed system would be attractive. the climate cobenefits in terms of ghg emission reduction were calculated using retscreen for each location and are listed in table vi in multiple equivalent formats. the results indicate that a large amount of co2 emissions can be avoided by implementing the developed pv project in each considered location. it is noticed that the pv projects with poly-si technology have the highest amount of co2 emission reductions. it should be noted that the total amount of co2 emission reduction for each location is determined based on the electricity generated annually [39]. tsabong and maun have the highest and lowest amount of co2 emission reduction, respectively. table v. ghg emission reduction (tco2) location annual ghg emission reduction [tco2] equivalent to pv technology mono-si poly-si gaborone gross annual ghg emission reduction 15.83 16.35 care and light trucks not used 2.90 3.00 liters of gasoline not consumed 6800.39 7027.07 barrels of crude oil not consumed 36.81 38.03 people reducing energy use by 20% 15.83 16.35 acres of forest absorbing carbon 3.60 3.72 hectares of forest absorbing carbon 1.46 1.50 tons of waste recycled 5.46 5.64 maun gross annual ghg emission reduction 15.79 16.32 care and light trucks not used 2.89 2.99 liters of gasoline not consumed 6786.35 7012.56 barrels of crude oil not consumed 36.73 37.96 people reducing energy use by 20% 15.79 16.32 acres of forest absorbing carbon 3.59 3.71 hectares of forest absorbing carbon 1.45 1.50 tons of waste recycled 5.45 5.63 tsabong gross annual ghg emission reduction 15.84 16.37 care and light trucks not used 2.90 3.00 liters of gasoline not consumed 6807.92 7034.85 barrels of crude oil not consumed 36.85 38.08 people reducing energy use by 20% 15.84 16.37 acres of forest absorbing carbon 3.60 3.72 hectares of forest absorbing carbon 1.46 1.51 tons of waste recycled 5.46 5.65 iv. conclusion the solar energy potential and techno-economic feasibility of grid-connected rooftop pv systems at three selected locations in botswana were investigated in this study. for this purpose, the annual value of ghi was estimated to categorize the solar resource in the selected locations. furthermore, the feasibility of a grid-connected pv system was assessed utilizing retscreen. based on the value of ghi, the selected regions are suitable for installing large-scale or small-scale pv systems. the results demonstrated that small-scale pv projects are feasible and economical viable. besides, the price of the electricity generated by pv systems is less than that of the conventional system. it can be concluded that the developed systems provide a very good insight into the economic feasibility of such project for all the considered locations. consequently, a huge potential of solar energy exists in the country, which if used effectively can play a vital role to overcome the current energy deficit. v. limitations and future work this study has some limitations that may be addressed in the future. the impact of meteorological parameters including air temperature, and relative humidity on the performance of the pv system was neglected. the influence of these parameters can be addressed using homer [41]. the financial parameters were assumed based on previous studies. therefore, the impact of policy changes and critical variables such as the initial costs of the project, inflation rate, and discount rate on the feasibility of grid-connected rooftop pv systems should be investigated in the future. moreover, the interaction between the distribution network and the pv system must be realized in order to understand the impact of the grid-connected pv systems on the distribution network. 0 200 400 600 800 1000 ja n f e b m a r a p r m a y ju n ju l a u g s e p o c t n o v d e c e le c tr ic it y e x p o rt e d t o g ri d [k w h ] gaborone 0 200 400 600 800 1000 ja n f e b m a r a p r m a y ju n ju l a u g s e p o c t n o v d e c e le c tr ic it y e x p o rt e d t o g ri d [k w h ] maun 0 200 400 600 800 1000 ja n f e b m a r a p r m a y ju n ju l a u g s e p o c t n o v d e c e le c tr ic it y e x p o rt e d t o g ri d [k w h ] tsabong mono-si poly-si engineering, technology & applied science research vol. 13, no. 2, 2023, 10328-10337 10336 www.etasr.com kassem et al.: techno-economic feasibility assessment for the promotion of grid-connected rooftop … references [1] e. a. al-ammar, n. h. malik, and m. usman, "application of using hybrid renewable energy in saudi arabia," engineering, technology & applied science research, vol. 1, no. 4, pp. 84–89, aug. 2011, https://doi.org/10.48084/etasr.33. 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[41] a. alahmer and s. alsaqoor, "energy efficient of using chilled water system for sustainable health care facility operating by solar photovoltaic technology," energy procedia, vol. 156, pp. 65–71, jan. 2019, https://doi.org/10.1016/j.egypro.2018.11.092. microsoft word etasr_v12_n6_pp9640-9653 engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9640 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... some mineralogical characteristics of the egyptian black sand beach ilmenite part iι: rutile-ilmenite and the various titanhematite grains mohamed ismail moustafa northern border university, saudi arabia and nuclear materials authority, cairo, egypt ismail2251962@yahoo.com received: 30 august 2022 | revised: 15 september 2022 | accepted: 17 september 2022 abstract-in addition to the grains of homogeneous ilmenite, ferriilmenite, hematite-ilmenite exsolved intergrowths, and the partially altered ilmenite grains, other textures are detected in the separated ilmenite concentrate. the grains of rutile-ilmenite exsolved intergrowth represent 0.8% of the detected ilmenite grains. the ilmenite component of this intergrowth is detected to be ferriilmenite associated with geikielite, pyrophanite, and rutile, with cr2o3 content ranging between 0 and 0.5%. the exsolved rutile is ferriforrous rutile composed of rutile, hematite, geikielite, and pyrophanite, its cr2o3 content ranging between 0 and 0.4%. the detected individual titanhematite grains represent 4.4% and include 3 textures arranged, in a decreasing order of abundance, as: ilmenite-hematite, rutile-hematite, and rutileilmenite-hematite exsolution intergrowths. mgo and mno have minimum values and they do not follow fe2o3. in some homogeneous titanhematite or exsolved rutile-hematite, fe2o3 content may be replaced with sio2. in all titanhematite intergrown textures, the cr2o3 content ranges between 0 and 0.1%. only in the case of the titanhematite host with exsolved rutile, the contained mgo ranges between 1.2 and 5.3%. some ferromagnetic titanhematite grains separated with the fraction of magnetite are detected. in these grains, the cr2o3, mgo, and mno contents range between 0-0.2, 0-3, and 0-1.4% respectively. several varieties of chromite and chromspinel mineral grains are found and represent 1.1% of the detected bulk ilmenite grains. in these grains, the cr2o3, mgo, v2o3, and al2o3 contents range between 16.69-56.72%, 0.54-17.33%, 0.14-0.58%, and 1.3338.79% respectively. although they are rarely met in the ilmenite concentrate, the relatively finer grain sizes could lead to the separation of some with ilmenite fraction rather than with the ferromagnetic one. it is concluded that the problem of high cr2o3 and fe2o3 contents of the egyptian beach ilmenite concentrate is not only a mineralogical problem, but also an ore-dressing one. keywords-black sands; beach ilmenite; ferriforous rutile; titanhematite; martitization; exsolved intergrowth i. introduction the placer deposits are very important sources of many economic minerals. the egyptian black sands extend along the northern coastal stretch between abu qir to the west and rafah to the east. these deposits contain 6 economic minerals: ilmenite, magnetite, garnet, zircon, rutile, and monazite. they are present either as beach sediments or as coastal sand dunes. ilmenite alone reaches up more than 50% of the total. however, the original amount of materials transported by the river may be related to several variables such as the flow type and the sediment load [1]. most ilmenite grains are found in fine and very fine sand-sized grains. in fact, the original grain size may affect the rate of mineral alteration [2]. the grain size becomes relatively coarser on moving from rosetta to the west to rafah to the east due to drifting by alongshore currents. ilmenite also occurs in massive rock formations in the form of titaniferous ore, associated with hematite and magnetite [3]. among the titanium minerals, only ilmenite, leucoxene, and rutile have significant importance [4-7]. the ilmenite ore is the main source for the production of metallic titanium and titanium containing compounds. the mineralogy of the egyptian beach ilmenite has been studied in [8-15] among others. many authors reported the relatively lower tio2 content and relatively higher fe2o3 and cr2o3 contents and others reported the diversity of the mineralogical textures inside ilmenite grains. in the egyptian black sand, the ilmenite content varies from less than 1% in the raw beach sand up to more than 50% in the naturally highly concentrated surfacial black sands. most of the obtained egyptian beach ilmenite concentrates are characterized by a relatively lower tio2 content (44-46% of ilmenite's beach sand and 46-49% of ilmenite's sand dunes) and relatively greater cr2o3 content (0.1-0.4%). also, they have a relatively lower fe 2+ /fe 3+ ratio and relatively higher mgo and mno contents. authors in [16] explained that the general break-even grade for ilmenite is considered to be 47 to 48% tio2, a rise in the ratio from 51% to 54% tio2 will, however, double profits. the trace element concentrations of ilmenite grains show enrichment in cr and v contents indicating that these elements are probably hosted by ilmenite [8]. the cr2o3 content is negligible in the lattice of the egyptian beach ilmenite and hematite. however, up to 0.36% cr2o3 was recorded in the whole concentrate analysis that could be due to accessory crcorresponding author: mohamed ismail moustafa engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9641 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... spinel minerals. the v content in the egyptian ilmenite (av. 0.3%), which probably affects the pigment brightness, is relatively high [17]. hydrometallurgical and/or pyrometallurgical processes for converting the egyptian beach ilmenite concentrate into a marketable product are investigated in [18-19]. the separation procedures of ilmenite and other economic mineral concentrates of the egyptian beach sand and other deposits are explained in [15, 20]. to detect the reasons of the relatively higher cr2o3 and fe2o3 content in addition to the relatively lower tio2 content of most of the obtained egyptian beach ilmenite concentrates, most of the contained mineral textures within the ilmenite concentrate, associated with the other obtained magnetic fractions, will be investigated. knowing such reasons, the process of ilmenite separation, the chemical specification of the obtained ilmenite concentrate, and its corresponding marketable value can be improved. ii. materials and methods a bulk sample of about 1000tons was collected from the surfacial naturally highly concentrated beach black sand at the mediterranean coast, 7km east of the rosetta estuary. the sample represents the raw sand in a 2km stretch with variable width of a few meters to 20m. the sand was manually scraped from the mantle to a depth ranging between 10-30cm. using the difference in physical characteristics between the various economic minerals, the collected surfacial naturally highly concentrated beach raw sand was processed using the following equipment: fulland half-size wilfley shaking tables for wetgravity concentration, carpco (hp 167) high-tension roll-type electrostatic separator for electrostatic separation, reading cross–belt magnetic separator, and the carpco (mih 13-231100) industrial high intensity induced roll dry magnetic separator for magnetic separation. finally, a bulk conductor ilmenite fraction was obtained and was subjected to the refining magnetic stage using the reading cross-belt magnetic separator, after which an ilmenite concentrate assaying 99.5% ilmenite grains was obtained. four polished sections were prepared from 4 small representative samples and were studied under the reflected microscope and cameca sx-100 microprobe instrument. they were taken from the obtained final ilmenite concentrate (including 2 obtained magnetic fractions of the reading separator), a representative sample of the obtained ferromagnetic fraction, a representative sample of all the other obtained magnetic fractions of the separator, and finally a representative sample of the obtained nonmagnetic fraction of the separator. the investigation of the different ilmenite grains was carried out by a cameca sx-100 electron microprobe analyzer (empa), from the institute of mineralogy and crystal chemistry, stuttgart university, germany. the microprobe instrument is equipped with 3 wavelength dispersive spectrometers (wdss) and an energy dispersive spectrometer (eds). the whole surface of the polished sections was examined by back scattered electron (bse) images, so that ilmenite grains with 10m size or even smaller could be detected. the analytical conditions were 15kv accelerating voltage, 15na electron current, 180s counting time for each analyzed spot in the investigated grains, and 1 to 4m diameter of the focused electron beam. the following standards were used: diopside for mg and ca, albite for na, corundum for al, orthoclase for si and k, rutile for ti, rhodonite for mn, fe2o3 for fe, cr2o3 for cr, v for v, and sphalerite for zn. k lines were used for analysis. also, a stereoscopic binocular microscope, a reflected-light polarizing microscope, jones riffle splitters of various sizes, and containers of varies sizes are used. iii. calculation the calculation of fe 3+ content, the molecular formula of the contained ilmenite mineral components of the studied individual ilmenite grains, the methods of calculation of the different mineral components of the analyzed spots composed mainly of ferriilmenite and/or titanhematite with or without individual tio2 (rutile), and the calculation of different mineral components of the analyzed ferriforous rutile are as those of [21]. iv. results homogeneous ilmenite, homogeneous ferriilmenite, hematite-ilmenite exsolved intergrown grains, and the partially altered ilmenite varieties are discussed in [21], while the remaining ilmenite textures are investigated in this paper. various mineral textures are detected and analyzed. 41 analyzed spots within 7 grains of rutilo-ilmenite exsolved intergrowthed grains are investigated. several ilmenite grains were detected to enclose rutile exsolution lamellae that are frequently undulating and arranged in one direction and to somewhat similar to what is called “blitz structure” described in [22]. however, the texture is clearer under crossed nicols and with colored images. the ilmenite chemical molecular formula and the corresponding mineral component fractions are calculated. the detected individual titanhematite grains represent 4.4%. 53 analyzed spots within 8 titanhematite grains were investigated. normal hematite (pure fe2o3), showing well-defined optical properties under the reflected light is very rare. titanhemetite is sliglitly greyish white, showing a relatively lower reflectivity and is strongly anisotropic from bright slightly greyish white with pale yellowish tint to dull grey with faint bluish tint, rarely showing red internal reflections. however, titanhematite (ti-rich hematite) is slightly darker and more greyish white than the primary and secondary hematite formed by martitization of magnetite or by the alteration of ilmenite. the ilmenite-hematite exsolution intergrowth is much less common than the hematite-ilmenite exsolution intergrowth. however, it is considered the most common exsolution intergrowth in the host titanhematite grains. in the present study, the host titanhematite mineral grain encloses exsolved lamellae of ferriilmenite oriented with their long axes parallel to the (0001) plane (figure 1(1)). on the other hand, some titanhematite grains contain 2 distinct size classes of ferriilmenite exsolution lamellae, an ordinary and a coarse type of intergrowth. in both cases, relatively finer ferriilmenite exsolution bodies are observed between the coarser bodies. also, the very coarse ferriilmenite exsolution bodies may in turn contain very fine lamellae of titanhematite (figure 1(2)). the same phenomenon was engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9642 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... observed in [23]. in rare cases, twinned ferriilmenitetitanhematite individual components are observed where the exsolved ferriilmenite lamellae are arranged parallel to the (0001) plane of the host titanhematite in each component which has different oriented direction (figure 1(3)). also, some rare composite grains, consisting of differently oriented titanhematite grains are observed with exsolutions of ferriilmenite parallel to their basal planes (figure 1(4)). sometimes narrow rims or small parts of homogenous ilmenite occur on the borders of these titanhematite grains. some of these titanhematite grains can also contain fine exsolution lamellae of rutile parallel to one or more of its (224 3) directions. fig. 1. various ferriilmenite-titanhematite exsolved intergrowth samples, sometimes including rutile exsolved bodies: (1) ferriilmenite-titanhematite exsolution intergrowth with the exsolved ferriilmenite lamellae parallel to the (0001) plane of titanhematite. reflected light, ×100. (2) two different sizes of exsolved ferriilmenite in the host titanhematite. the relatively coarser exsolved ferriilmenite lamellae contain very fine exsolved lamellae of titanhematite. reflected light, ×100. (3) two twinned ferriilmenitetitanhematite exsolution intergrowths. the exsolved ferriilmenites show different oriented directions in relation to each other. reflected light, ×100. (4) granular aggregates of differently oriented titanhematite crystals, each of them containing exsolved ferriilmenite lamellae parallel to its basal plane. some of them also contain fine lamellae of exsolved rutile. reflected light, ×100. (5) titanhematite (greyish white) with rutile exsolutions (light grey) parallel to the (224 3) direction. reflected light, ×100. (6) ferriilmenitetitanhematite exsolution intergrowth associated with exsolved rutile needles. the exsolved ferriilmenite (dark grey) is parallel to the (0001) direction, while the exsolved rutile (light grey) is parallel to the (224 3) direction. reflected light, ×100. the second common exsolution intergrowth in the host titanhematite is rutile-titanhematite intergrowth. a considerable number of the detected titanhematite grains are not free of rutile exsolved lamellae. fine needles of exsolved rutile were observed in up to 6 directions parallel to the (224 3) planes of the titanhematite (figure 1(5)). the third common exsolution intergrowth in the host titanhematite is rutile-ilmenite-hematite exsolution intergrowth. in this case, some of titanhematite grains contain exsolved ferriilmenite lamellae which are podshaped or spindle-shaped and are oriented in one direction parallel to the (0001) plane of the titanhematite. the exsolved ferriilmenite lamellae are associated with the exsolved fine needles of rutile which are arranged along 1, 2 to 6 directions, parallel to the (224 3) planes of the titanhematite, and are much more elongated than the exsolved ferriilmenite (figure 1(6)). in most cases, the exsolved rutile needles cut the grain from side to side and are oblique to the direction of the ferriilmenite lamellae. the corresponding different mineral component fractions of the all the analyzed spots are calculated. finally, 49 analyzed spots within 6 grains of ferromagnetic titanhematite associated with magnetite in its ferromagnetic fraction were detected. the hematite chemical formula and the corresponding mineral component fractions were calculated. some of analyzed spots are corresponding to impurities of silica, calcite, altered silicate minerals, and pseudobrookite. the analyzed oxides of the detected spots include tio2, feo, fe2o3, cr2o3, mno, mgo, al2o3, v2o3, zno, sio2, and cao. v. discussions a. rutile-ilmenite exsolution intergrowth (0.8%) the rutile exsolutions in ilmenite are far less common than in titanhematite. these intergrowths of exsolved rutile are possibly the result of unmixing of a rutile-ilmenite solid solution, which must be very limited as the observed rutile lamellae are very few in number, extremely fine, while the intergrowth is very rare [14, 23-24]. this is in accordance with the results obtained in [25] for synthetic preparations, that not more than 6% tio2 can exist in solid solutions in ilmenite at 1050 o c. however, 6 grains were detected for this exsolution intergrowth and their chemical compositions were investigated with the microprobe. it is noticed that the content of the exsolved rutile is relatively higher than that recorded in previous studies. fig. 2. bse images of various rutilo-ilmenite exsolved intergrowth grains. engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9643 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... spots 2, 3 of grain (1) of figure 2 (table i), are ferriilmenite with considerable amounts of geikielite and minor pyrophanite and rutile in solid solutions. in these spots, the first method (m1) of calculation is used to calculate the different mineral fractions of the two spots. then, the mineral components of the two spots are: spot 2: 64.42% ilmenite, 22.9% hematite, 11.03% geikielite, 1.28% pyrophanite, and 0.16% rutile and spot 3: 66.11% ilmenite, 21.60% hematite, 10.14% geikielite, 1.28% pyrophanite, and 0.15% rutile. spot 1 of grain (1) of figure 2 (table ii) is titanhematite with considerable amounts of rutile and geikielite. it is composed of 69.48% hematite, 11.63% geikielite, 1.7% pyrophanite, and 16.9% rutile. spot 4 is mostly ilmenite. spots 5-7 of grain (2) of figure 2 (table ii) are ferriferous rutile composed mostly of rutile with considerable amounts of hematite (fe2o3), ranging between 21.91% and 33.86%, geikielite, and pyrophanite mineral components. in these spots, the third method (m3) of calculation is used to calculate the different mineral fractions. their mineral components are: spot 5: 33.86% hematite, 6.09% geikielite, 0.64% pyrophanite, and 58.59% rutile, spot 6: 27.62% hematite, 4.18% geikielite, 0.53% pyrophanite, and 67.21% rutile, and spot 7: 21.91% hematite, 2.42% geikielite, 0.43% pyrophanite, and 73.22% rutile. it is obvious that the content of tio2 (rutile) decreases as the content of geikielite and pyrophanite increases. the same relation is detected between the exsolved rutile and the mixed hematite inside it. table i. microprobe chemical analysis and molecular formulae of the analyzed spots for the rutilo-ilmenite exsolved intergrown grains of figures 2, 3 g r a in s s p o t s io 2 m g o m n o c a o z n o f e o a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l f e o f e 2 o 3 t o ta l f e 2 + f e 3 + o th e r c a ti o n s t i o g e k p y r il m h r t o ta l fig. 2 (1) 2 0.00 3.70 0.60 0.00 0.10 50.60 0.20 0.50 0.40 42.20 98.30 30.50 22.30 100.50 0.63 0.41 0.19 0.78 3 11.03 1.28 64.42 22.90 0.16 99.79 3 0.00 3.40 0.60 0.00 0.10 50.20 0.20 0.50 0.40 42.20 97.50 31.30 21.00 99.60 0.65 0.39 0.17 0.79 3 10.14 1.28 66.11 21.60 0.15 99.27 4 0.70 0.20 0.40 0.10 0.00 41.10 0.10 0.60 0.50 52.50 96.30 41.10 0.00 96.30 0.90 0.00 0.07 1.03 3 0.60 0.85 86.80 0.60 5.89 94.74 fig. 2 (2) 2 0.00 5.10 0.70 0.00 0.00 53.30 0.40 0.40 0.20 32.80 93.00 19.60 37.50 96.70 0.42 0.72 0.27 0.63 3 15.21 1.49 41.40 38.10 0.13 96.32 3 0.00 9.30 0.80 0.00 0.10 47.80 0.40 0.40 0.20 36.20 95.30 15.00 36.40 98.90 0.30 0.66 0.42 0.66 3 27.73 1.70 31.68 37.00 0.23 98.35 4 0.00 9.00 0.60 0.00 0.00 45.40 0.40 0.40 0.20 38.90 94.90 18.30 30.10 97.90 0.37 0.55 0.40 0.71 3 26.84 1.28 38.65 30.70 0.13 97.59 fig. 2 (3) 1 0.00 0.60 1.00 0.00 0.00 50.80 0.30 0.60 0.30 44.70 98.30 38.10 14.10 99.70 0.81 0.27 0.08 0.85 3 1.79 2.13 80.47 14.70 0.02 99.10 2 0.00 3.10 0.60 0.00 0.10 48.60 0.30 0.60 0.30 46.10 99.80 35.30 14.90 101.30 0.72 0.27 0.16 0.85 3 9.24 1.28 74.55 15.50 0.15 100.73 3 0.00 1.70 0.90 0.00 0.00 49.30 0.30 0.70 0.30 46.40 99.70 37.70 13.00 101.00 0.78 0.24 0.12 0.87 3 5.07 1.91 79.62 13.60 0.05 100.26 4 0.00 5.70 0.50 0.00 0.00 45.20 0.30 0.60 0.40 46.80 99.50 31.30 15.50 101.00 0.63 0.28 0.25 0.85 3 17.00 1.06 66.11 16.20 0.12 100.49 5 0.00 5.60 0.60 0.00 0.00 45.60 0.20 0.60 0.40 47.30 100.30 32.00 15.10 101.90 0.64 0.27 0.25 0.85 3 16.70 1.28 67.58 15.70 0.06 101.32 fig. 2 (4) 1 0.00 3.80 0.60 0.00 0.00 54.00 0.10 0.60 0.10 35.20 94.30 24.20 33.00 97.60 0.52 0.63 0.20 0.67 3 11.33 1.28 51.11 33.20 0.07 96.99 2 0.00 7.10 1.10 0.00 0.00 44.60 0.10 0.40 0.00 43.00 96.40 24.90 21.90 98.60 0.51 0.40 0.31 0.79 3 21.17 2.34 52.59 22.00 0.05 98.15 fig. 2 (5) 1 0.00 9.10 0.30 0.00 0.10 37.00 0.10 0.70 0.40 49.20 96.80 27.60 10.40 97.90 0.56 0.19 0.37 0.89 3 27.14 0.64 58.29 10.90 0.15 97.11 2 0.00 9.80 0.40 0.00 0.10 36.50 0.10 0.70 0.30 49.90 97.90 27.00 10.60 98.90 0.54 0.19 0.39 0.89 3 29.22 0.85 57.02 11.00 0.10 98.19 3 0.00 9.10 0.40 0.00 0.00 36.50 0.10 0.70 0.40 50.20 97.30 28.40 8.90 98.20 0.57 0.16 0.37 0.91 3 27.14 0.85 59.98 9.40 0.13 97.50 4 0.00 9.80 0.40 0.00 0.00 35.30 0.10 0.60 0.30 51.10 97.50 28.00 8.00 98.30 0.56 0.14 0.39 0.92 3 29.22 0.85 59.14 8.40 0.10 97.71 5 0.00 7.70 0.40 0.00 0.00 35.00 0.10 0.80 0.50 52.80 97.30 33.30 1.80 97.50 0.68 0.03 0.32 0.97 3 22.96 0.85 70.33 2.40 0.08 96.62 6 0.00 12.00 0.50 0.00 0.10 31.90 0.10 0.50 0.20 53.00 98.30 25.80 6.90 98.90 0.50 0.12 0.45 0.93 3 35.78 1.06 54.49 7.20 0.21 98.75 7 0.00 7.30 0.30 0.00 0.00 34.70 0.10 0.70 0.50 53.30 97.00 34.60 0.10 97.00 0.71 0.00 0.30 0.99 3 21.77 0.64 73.08 0.70 0.03 96.21 8 0.00 7.70 0.30 0.00 0.00 34.20 0.10 0.60 0.30 53.80 97.10 34.20 0.00 97.10 0.70 0.00 0.31 0.99 3 22.96 0.64 72.23 0.40 0.29 96.52 fig. 2 (6) 1 0.00 0.00 3.50 0.10 0.00 43.30 0.00 0.20 0.00 48.70 95.80 40.00 3.60 96.20 0.88 0.07 0.09 0.96 3 0.00 7.44 84.48 3.60 0.22 95.74 2 0.00 0.10 5.00 0.00 0.00 41.40 0.00 0.30 0.00 49.50 96.20 39.30 2.30 96.40 0.86 0.05 0.12 0.97 3 0.30 10.63 83.00 2.30 0.09 96.32 3 0.00 0.00 3.60 0.00 0.00 44.20 0.00 0.40 0.00 49.50 97.70 40.90 3.70 98.00 0.88 0.07 0.09 0.96 3 0.00 7.65 86.38 3.70 0.04 97.77 4 0.00 0.00 3.30 0.00 0.10 43.90 0.00 0.30 0.00 49.50 97.20 41.10 3.10 97.50 0.89 0.06 0.08 0.97 3 0.00 7.02 86.80 3.10 0.10 97.02 5 0.00 0.00 4.80 0.10 0.00 41.30 0.00 0.30 0.00 49.50 96.10 39.60 2.00 96.30 0.87 0.04 0.12 0.98 3 0.00 10.20 83.64 2.00 0.04 95.88 6 0.00 0.00 3.40 0.00 0.10 43.50 0.00 0.40 0.00 49.50 97.00 41.00 2.80 97.20 0.89 0.06 0.09 0.97 3 0.00 7.23 86.59 2.80 0.07 96.69 7 0.00 0.00 4.40 0.10 0.10 42.20 0.00 0.30 0.00 50.10 97.20 40.40 1.90 97.30 0.88 0.04 0.11 0.98 3 0.00 9.35 85.32 1.90 0.18 96.76 fig. 3 1 0.00 0.00 3.60 0.10 0.10 47.10 0.00 0.60 0.00 44.80 96.30 36.40 11.90 97.50 0.79 0.23 0.10 0.88 3 0.00 7.65 76.88 11.90 0.20 96.63 2 0.00 0.10 3.40 0.10 0.10 43.70 0.00 0.60 0.00 48.90 96.90 40.20 3.90 97.30 0.87 0.08 0.10 0.96 3 0.30 7.23 84.90 3.90 0.19 96.52 3 0.00 0.00 4.20 0.00 0.00 43.00 0.00 0.50 0.10 48.80 96.70 39.50 3.90 97.10 0.86 0.08 0.11 0.96 3 0.00 8.93 83.42 4.00 0.06 96.41 4 0.00 0.10 4.10 0.10 0.10 42.70 0.00 0.50 0.00 49.10 96.60 39.70 3.40 97.00 0.86 0.07 0.11 0.96 3 0.30 8.72 83.85 3.40 0.29 96.55 5 0.00 0.10 4.40 0.20 0.00 43.10 0.00 0.50 0.00 49.20 97.60 39.50 4.10 98.00 0.85 0.08 0.12 0.96 3 0.30 9.35 83.42 4.10 0.27 97.45 6 0.40 0.10 4.00 0.40 0.10 41.10 0.00 0.60 0.00 49.30 96.00 40.10 1.10 96.10 0.88 0.02 0.13 0.97 3 0.30 8.50 84.69 1.10 0.02 94.62 7 0.00 0.00 4.30 0.00 0.00 42.00 0.00 0.50 0.00 49.40 96.30 40.10 2.20 96.50 0.88 0.04 0.11 0.97 3 0.00 9.14 84.69 2.20 0.05 96.08 8 0.00 0.10 4.40 0.10 0.10 42.00 0.00 0.50 0.00 49.50 96.70 39.70 2.60 97.00 0.87 0.05 0.12 0.97 3 0.30 9.35 83.85 2.60 0.23 96.33 9 0.00 0.10 3.80 0.00 0.20 41.40 0.00 0.60 0.00 49.50 95.50 40.50 1.00 95.60 0.89 0.02 0.10 0.98 3 0.30 8.08 85.54 1.00 0.15 95.07 10 0.00 0.00 4.00 0.00 0.10 43.50 0.00 0.50 0.10 49.60 97.90 40.40 3.40 98.20 0.87 0.07 0.10 0.96 3 0.00 8.50 85.32 3.50 0.18 97.50 11 0.00 0.00 3.90 0.00 0.10 42.90 0.00 0.60 0.30 50.00 97.80 40.80 2.30 98.10 0.88 0.04 0.11 0.97 3 0.00 8.29 86.17 2.60 0.22 97.29 12 0.10 0.10 3.70 0.10 0.10 39.40 0.00 0.50 0.00 50.40 94.50 39.40 0.00 94.50 0.88 0.00 0.11 1.01 3 0.30 7.87 83.21 0.00 2.24 93.62 13 0.30 0.10 3.20 0.10 0.00 39.50 0.00 0.60 0.00 50.60 94.30 39.50 0.00 94.30 0.88 0.00 0.10 1.02 3 0.30 6.80 83.42 0.00 3.01 93.53 engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9644 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... table ii. calculated different mineral component fractions of each analyzed spot of of the rutilo-ilmenite exsolved intergrown grains of figures 2, 3 grain spot sio2 mgo mno cao zno feo al2o3 v2o3 cr2o3 tio2 total gek pyr h r total fig. 2 (1) 1 0.20 3.90 0.80 0.10 0.00 59.10 1.30 0.70 2.50 25.50 94.10 11.63 1.70 69.48 16.90 99.71 5 0.00 2.00 0.30 0.00 0.00 30.10 0.10 0.50 0.30 63.00 96.40 6.09 0.64 33.86 58.59 99.18 6 0.00 1.40 0.20 0.00 0.10 24.50 0.10 0.60 0.30 70.30 97.40 4.18 0.53 27.62 67.21 99.54 7 0.00 0.80 0.20 0.00 0.00 19.30 0.10 0.50 0.30 75.00 96.40 2.42 0.43 21.91 73.22 97.97 fig. 2 (2) 5 0.00 1.60 0.10 0.00 0.10 19.20 0.20 0.60 0.10 75.10 97.00 4.82 0.27 21.59 71.78 98.46 6 0.00 0.50 0.10 0.10 0.00 7.30 0.00 0.80 0.10 88.50 97.40 1.56 0.2 8.23 87.41 97.4 fig. 2 (3) 6 0.00 0.10 0.40 0.00 0.00 23.20 0.30 0.80 0.40 70.90 96.20 0.42 0.82 26.44 70.21 97.89 7 0.00 0.70 0.30 0.00 0.00 19.50 0.20 0.70 0.20 75.40 97.20 2.17 0.6 22.11 73.69 98.56 fig. 2 (4) 3 0.00 1.50 0.30 0.00 0.00 25.20 0.00 0.60 0.00 68.20 95.90 4.38 0.71 28.07 64.91 98.07 4 0.00 0.70 0.10 0.00 0.00 17.20 0.00 0.70 0.10 78.80 97.60 2.17 0.14 19.16 77.33 98.8 5 0.00 0.00 0.10 0.00 0.00 1.20 0.00 0.60 0.00 96.30 98.20 0.05 0.12 1.37 96.18 97.72 6 0.00 0.00 0.00 0.00 0.10 1.20 0.00 0.70 0.00 96.60 98.60 0.05 0.02 1.34 96.54 97.95 fig. 2 (5) 9 0.00 5.60 0.20 0.00 0.00 21.80 0.10 0.70 0.20 68.70 97.30 16.55 0.48 24.53 57.5 99.07 10 0.00 4.80 0.20 0.00 0.00 20.60 0.00 0.80 0.30 71.20 97.90 14.24 0.36 23.24 61.61 99.45 11 0.00 4.10 0.30 0.00 0.00 19.00 0.00 0.80 0.30 73.00 97.50 12.27 0.57 21.38 64.54 98.76 12 0.00 4.10 0.20 0.00 0.00 18.50 0.10 0.80 0.20 73.70 97.60 12.11 0.52 20.81 65.43 98.87 13 0.00 2.80 0.10 0.00 0.10 16.40 0.00 0.80 0.20 77.40 97.80 8.25 0.25 18.48 71.77 98.76 14 0.00 3.60 0.20 0.00 0.00 15.70 0.00 0.80 0.20 77.70 98.20 10.65 0.33 17.66 70.5 99.14 15 0.00 3.10 0.20 0.00 0.10 12.90 0.00 0.80 0.10 80.60 97.80 9.17 0.37 14.53 74.33 98.39 fig. 2 (6) 8 0.00 0.00 0.10 0.00 0.00 25.40 0.00 0.50 0.00 69.80 95.90 0.12 0.28 28.23 69.57 98.2 9 0.20 0.20 0.20 0.20 0.00 16.30 0.50 0.50 0.00 72.10 90.10 0.45 0.49 18.57 71.54 91.05 10 0.00 0.10 0.10 0.00 0.00 6.10 0.00 0.60 0.00 91.80 98.80 0.17 0.21 6.85 91.62 98.85 11 0.00 0.00 0.10 0.00 0.10 5.30 0.00 0.70 0.00 93.50 99.70 0.1 0.11 5.95 93.34 99.5 fig. 3 14 0.00 0.10 0.10 0.00 0.00 23.30 0.00 1.10 0.10 71.90 96.50 0.21 0.21 25.96 71.62 98 15 1.20 0.20 0.20 0.90 0.10 7.20 1.00 1.00 0.00 80.40 92.20 0.69 0.47 9 79.7 89.86 16 1.80 0.40 0.20 1.20 0.00 6.10 1.40 1.00 0.00 81.20 93.40 1.19 0.41 8.22 80.19 90.02 17 0.40 0.30 0.10 0.40 0.00 9.70 1.20 1.10 0.00 81.30 94.50 0.8 0.27 11.94 80.61 93.63 18 0.00 0.10 0.00 0.00 0.00 12.10 0.00 0.90 0.10 83.20 96.50 0.26 0.07 13.53 83.02 96.88 19 1.40 0.30 0.20 1.00 0.00 4.10 1.20 1.10 0.00 83.60 92.70 0.84 0.36 5.69 82.84 89.73 20 0.10 0.10 0.00 0.20 0.00 9.50 0.10 1.00 0.00 85.50 96.50 0.43 0.06 10.6 85.23 96.32 21 0.00 0.10 0.10 0.20 0.00 9.20 0.00 0.90 0.00 86.40 96.80 0.17 0.11 10.28 86.26 96.83 22 0.00 0.10 0.00 0.00 0.00 9.60 0.00 0.90 0.00 86.70 97.50 0.29 0.09 10.75 86.46 97.58 23 0.00 0.10 0.10 0.10 0.10 6.90 0.10 1.10 0.00 88.70 97.10 0.2 0.16 7.73 88.5 96.59 24 0.10 0.10 0.00 0.10 0.00 6.60 0.00 1.00 0.00 89.00 96.90 0.27 0.08 7.32 88.76 96.42 25 0.00 0.10 0.00 0.00 0.00 5.80 0.00 0.90 0.00 90.70 97.60 0.4 0.07 6.43 90.38 97.28 26 0.00 0.00 0.10 0.10 0.00 4.10 0.00 1.00 0.00 90.80 96.10 0.12 0.14 4.59 90.67 95.53 27 0.10 0.00 0.10 0.10 0.00 5.10 0.20 1.10 0.10 91.20 97.90 0.11 0.22 5.91 90.97 97.21 28 0.00 0.10 0.10 0.10 0.00 4.70 0.00 0.90 0.00 91.40 97.30 0.29 0.14 5.24 91.14 96.81 29 0.00 0.00 0.10 0.10 0.00 4.80 0.00 1.00 0.00 92.30 98.20 0.07 0.13 5.32 92.15 97.66 30 0.00 0.00 0.00 0.10 0.00 3.90 0.00 0.90 0.00 93.20 98.10 0.13 0.03 4.36 93.1 97.62 31 0.00 0.00 0.10 0.00 0.00 3.40 0.00 0.90 0.10 93.60 98.10 0.06 0.13 3.79 93.48 97.46 table iii. original microprobe chemical analysis of some spots of grains from figures 2, 3 grains spots sio2 mgo mno cao zno feo al2o3 v2o3 cr2o3 tio2 total fig. 2(2) 1 46.36 7.92 0.20 10.20 0.01 13.55 11.23 0.11 0.00 4.62 94.21 fig. 3 32 23.65 18.77 0.14 0.66 0.03 15.91 17.12 0.26 0.03 13.96 90.53 33 7.24 0.82 0.36 1.21 0.04 16.44 2.59 0.71 0.13 41.55 71.10 34 7.77 1.41 0.85 1.25 0.02 15.35 3.75 0.54 0.06 43.36 74.36 35 1.02 0.24 1.02 0.75 0.00 18.48 0.73 0.57 0.48 46.78 70.06 36 3.63 0.85 0.28 1.51 0.00 14.80 2.04 0.67 0.03 47.65 71.45 37 7.70 0.68 0.32 3.50 0.12 9.95 2.22 0.57 0.08 50.96 76.09 38 4.96 0.90 0.55 2.17 0.00 10.43 1.64 0.60 0.02 52.53 73.80 39 7.29 1.00 0.18 0.63 0.03 5.69 3.64 0.71 0.01 56.14 75.31 spot 1 of grain 2 of figure 2 (table iii) is a definite silicate mineral composed of fe, ca, mg, ti, and al-silicate. spots 2-4 (figure 2, table i), are mixtures of several mineral components. using the same method of calculation with (m1), the various mineral components of spots 24 of grain (2) are: spot 2: 41.40% ilmenite, 38.10% hematite, 15.21% geikielite, 1.49% pyrophanite, and 0.13% rutile. spot 3: 31.68% ilmenite, 37% hematite, 27.73% geikielite, 1.70% pyrophanite, and 0.23% rutile. spot 4: 38.65% ilmenite, 30.70% hematite, 26.84% geikielite, 1.28% pyrophanite, and 0.13% rutile. it is obvious that the ilmenite component in these spots is partially altered into hematite and the detected exsolved rutile bodies. it is obvious that the lightness of spot area is determined according to the amount of hematite component. as the hematite % increases, the lightness increases (spots 2 and 3), and vice versa (spot 4). engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9645 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... spots 5 and 6 of grain (2) of figure 2 (table ii) are ferriferous rutile composed mostly of rutile with considerable amounts of hematite in solid solution, ranging between 8.23 and 21.59%. using the m3 method of calculation, the mineral components for each of the two spots are: spot 5: 21.59% hematite, 4.82% geikielite, 0.27% pyrophanite, and 71.78% rutile and spot 6: 8.23% hematite, 1.56% geikielite 0.20%, pyrophanite, and 87.41% rutile. spots 1-5 of grain (3) of figure 2 (table i) are ferriilmenite with fe2o3 content ranging between 13.60 and 16.20%. both spots 6-7 of figure 2 are ferriferous rutile (table ii). spots 1 and 2 of grain (4) of figure 2 are ferriilmenite (table i), spots 3 and 4 are ferriferous rutile, and spots 5 and 6 are rutile with minor fe2o3 content (table ii). using the m1 method of calculation, the mineral components of spots 1 and 2 are: spot 1: 51.11% ilmenite, 33.20% hematite, 11.33% geikielite, 1.28% pyrophanite, and 0.07% rutile. spot 2: 52.59% ilmenite, 22%, hematite, 21.17% geikielite, 2.34% pyrophanite, and 0.05% rutile. these two spots are solid solutions of ilmenite, hematite, geikielite, pyrophanite, and traces of rutile. it is obvious that both mg and mn follow feo and not fe2o3, hence as the content of hematite decreases, as the content of geikielite and/or pyrophanite increases. geikielite and pyrophanite are mixed easier with ilmenite than with hematite. spots 3 and 4 are rutile mixed with hematite, ranging between 19.16 and 28.07%. spots 5 and 6 are mostly rutile with minor hematite, which ranges between 1.34 and 1.37%. it is obvious that the relatively larger and darker rutile exsolved intergrowths are composed mostly of rutile (more than 95% tio2), while the relatively smaller ones are mainly ferriforous rutile with considerable amounts of mixed hematite (figure 2, table ii). spots 1-6 of grain (5) of figure 2 are ferriilmenite, 7 and 8 are ilmenite (table i). all the iron of spot 8 is ferrous iron. it is obvious that most of ferriilmenite containing exsolved intergrowths of rutile contain a considerable amount of mgo as geikielite. spots 9-15 are ferriferous rutile mixed with hematite, geikielite, and pyrophanite in solid solution (table ii). using the same method of calculations of (2) and (3) grains, and converting all analyzed iron as feo to fe2o3 to be calculated as hematite, the mineral components composed for each spot are shown in table ii. spots 1-7 of grain (6) of figure 2 (table i) are ferriilmenite with fe2o3 content ranging between 1.9 and 3.7%. spots 10 and 11 are ferriferous rutile. spots 8 and 9 are ilmenite altered to rutile and hematite (table ii). spot 9 is located beside the edge of the grain. the activity of water seems to be relatively greater hence a partial leaching of hematite component occurred. the total oxide sum of this spot is 91.05%, which reflects the existence of molecular water (table ii). spots 1-13 of the grain of figure 3 (table i) are composed mainly of ilmenite and pyrophanite with minor amounts of hematite and other mineral components. spots from 1 to 11, are ferriilmenite with fe2o3 content ranging between 1 and 11.90%. spots 12 and 13 are ilmenite, in which most of the mixed fe2o3 is leached out. all the iron content is ferrous iron. some molecular water is included in these two spots. the analyzed total oxide sum of the two spots is 94.3 and 94.5% respectively (table i). fig. 3. bse image of a composite ilmenite grain. spots 1-13 are composed of ilmenite enriched with mno content. spots 14-31 are ilmenite altered to rutile and hematite, and spots 32-39 are alterations of a definite silicate mineral. spots 14-31 are ilmenite altered to rutile and hematite. they are composed mainly of rutile and hematite mineral components (table ii). spots 15, 16, and 19 are in the neighborhood of voids where the activity of molecular water is relatively higher. spots 32-39 are an alteration of a definite silicate mineral, mg fe al-silicate, attached with ilmenite altered to rutile and hematite (table iii). the hematite component is partially leached leaving the remaining rutile associated with the products of the altered silicate mineral. most of these last spots contain molecular and/or structural water. b. titanhematite (4.4%) authors in [26] explained that hematite is not so widely distributed in magmatic rocks, as it is known from the literature. authors in [27] showed that hematite is almost wholly fe2o3 and subtitanhematite is fe2o3 with 1.5 to 5% tio2 as feo.tio2 or tio2 or both while titanhematite is fe2o3 with 5-10% tio2 as feo.tio2 up to about 13% plus excess tio2 up to about 3% in solid solution. titanhematite or white ilmenite is hematite containing a maximum of 10% fetio3 in solid solution. if the fetio3-content exceeds 10%, oriented intergrowths of ilmenite and ti-hematite may be formed [28]. a number of fabrics in which the titanhematite is considered as the major component (the host mineral) have been observed. these include the following arranged in decreasing order of abundance: 1) ilmenite-ηematite εxsolution ιntergrowth the intergrowth was called ilmenohematite where micro intergrowths of ferrianilmenite or hemoilmenite are enclosed in the titanhematite host [27]. although ferriilmenite exsolution bodies are found in two different sizes in the host titanlrematite, they cannot be considered as two distinct generations. many of engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9646 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... the relatively larger ferriilmenite exsolution lamellae are observed to have coalesced, are frequently irregular, and seem to grade into smaller bodies. so, the ferriilmenite-titanhematite intergrowth may be interpreted as a result of unmixing of an original ilmenite-hematite solid solution and most of the relatively larger ferriilmenite exsolution lamellae that seem to have grown in situ by diffusion. 2) rutile-hematite exsolution intergrowth such intergrowth is called as rutilohematite where microintergrowths of rutile or exsolved rutile grains are enclosed in the titanhematite host [27]. a few exsolved rutile needles cut the host titanhematite grains from side to side, suggesting that most of them represent the unmixing of excess tio2 originally dissolved in the fe2o3 solid solution. the same intergrowth was observed in [29] in metamorphosed beach sands. 3) rutile-ilmenite-hematite exsolution intergrowth this intergrowth was called as ilmenorutilohematite where exsolved micro intergrowths of ferrianilmenite or hemoilmenite and rutile are enclosed in the host titanhematite [27]. such type of exsolved intergrowth was observed in the sands of lake oulu, finland [30]. the exsolved ferriilmenite lamellae had short, more spindle-shaped bodies parallel to the (0001) plane of titanhematite while the exsolved rutile needles were common in at least 6 directions. authors in [29] recorded the same type of intergrowth, but the exsolved rutile lamellae were found in the typical blitz texture. authors in [31] believed that the rutile lamellae are of an earlier generation than the ferriilmenite exsolution bodies. however, authors in [25] concluded that the unmixing of the ilmenite-hematite solid solution to ferriilmenite and titanhematite started before the separation of the excess tio2 as rutile. authors in [14] agreed with this conclusion, since the rutile lamellae are observed to cut the ferriilmenite exsolutions, i.e. they are, therefore, of later origin. on the other hand, authors in [32] explained the development of the rutile exsolutions as a result of the partial oxidation (under high oxidation potential) of fetio3 in a mixed crystal lying near the fe2o3-fetio3 join, on the tio2 side of the system feo-fe2o3-tio2 to hematite and rutile: 2 fetio3 + o  fe2o3 + 2 tio2 the resulting rutile is then dissolved at sufficient temperatures in the fetio3-fe2o3 solid solution (especially on the fe2o3 side). later unmixing of the rutile in solid solution takes place. we believe that the exsolved rutile lamellae are of later origin and are the result of the unmixing of the excess tio2, originally dissolved in the fetio3-fe2o3 solid solution. the frequency of these exsolved rutile lamellae is very low compared with the exsolved ferriilmenite lamellae and some of them were detected to cut the ferriilmenite exsolutions. the microprobe findings of some titanhematite grains of different fabrics are: in grain (1), all the analyzed 6 spots of figure 4 (tables iv, v) are mainly fe2o3 with only minor portions of tio2. the grain is most probably hematite. in grain (2), the analyzed 5 spots (figure 4, tables iv, v) are composed of hematite. the v2o3 content ranges between 0.18 and 0.2%. spots 1-4 of grain (3), (figure 4, tables iv, v) are hematite with minor tio2. the v2o3 content of these spots ensures that v2o3 follows fe2o3 rather than feo. also, the negligible content of mgo and mno ensures that these two oxides do not follow fe2o3. spot 5 is silica which is recorded along the edges of grain (3), (figure 4, table viii). this may reflect the ability of silica to replace fe2o3. spots 6-7 are calcite, where the remaining percentage of each spot is detected to be carbon (figure 4, table viii). fig. 4. bse images of various titanhematite exsolved intergrown grains. spots 1 and 2 of grain (4) of figure 4 (tables iv, v) are ilmenite. spot 3 is hematite altered to goethite. spots 4-13 are hematite altered to goethite where the analyzed total oxide sum decreases by about one tenth of the analyzed value of fe2o3 content which corresponds the content of structural water (oh ) necessary for converting hematite to goethite (feooh), (figure 4, tables iv, v). in these spots, v2o3 content ranges between 0.69 and 0.78%. it follows fe2o3, which ranges between 87.06 and 89.99%. tio2 content ranges between 0.81 and 1.22%. spots 1-5 of grain (5) of figure 4 (tables iv, v) are titanhematite. mgo and mno contents range between 0.06 and 0.09% and 0.16 and 0.28% respectively. tio2 content ranges between 8.29 and 9.15%, while the feo content ranges between 6.99 and 7.83%. the recorded tio2 content seems to be related to the contained ilmenite. spots 6-14 have total oxide sum ranging between 93.2 and 96.77%. tio2 content ranges between 24.05 and 45.73%, while the fe2o3 content ranges between 50.59 and 5.78%. at spot 6, the tio2 content is 24.05% while the fe2o3 content is 50.59%. on the other hand, at spot 14, the tio2 content is 45.73%, while the fe2o3 content is 5.78%. there is an obvious reverse relation between tio2 and fe2o3 inside each spot. also, it is noticed that although the spots 12, 14 are located at the same exsolved intergrowth lamella, they have widely varying contents of tio2 and fe2o3, while the analyzed total oxide sum is almost the same: 93.67 and 93.20% respectively. also, the mno and mgo contents are negligible which may indicate the absence of ferrous iron. in fact, spots 6-14 are ilmenite alteration mixtures of rutile and hematite or some of spots are pseudobrookite of the fe2tio5 engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9647 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... type, mixed with an individual tio2 phase, most probably rutile, and maybe also fe2o3. in grain (6) of figure 4 (tables iv, v), spots 1-6 are titanhematite. the feo content ranges between 1.9 and 7.86% which corresponds to the analyzed content of tio2: 2.178.82%, indicating the content of ilmenite. spots 7-13 do not give acceptable results using the ilmenite program (figure 4, table viii). spots 7-8 are made from a cafeal-silicate mineral. the area of spot 8 is darker than that of spot 7 due to the alteration of the silicate mineral and an enrichment of the content of sio2 (table viii). spot 13 is silica. in spots 9-12 of grain (6), the silica ranges between 5.57 and 90.85%, while tio2 ranges between 94.98 and 8.51%. it is obvious that the titanhematite of spot 9 is replaced by sio2, while the contained tio2 remained. spots 10-12 are most probably rutilo-hematite (spots 10, 11), or ferriforous rutile (spot 12), where fe2o3 is replaced by sio2. the analyzed total oxide sum of some spots may be greater than 100%, due to the irregularity and the voids of the measured spot surface. in grain (7) of figure 4 (tables iv, v), spots 1-3 may be the result of high temperature alteration of ilmeno-hematite fabric, producing a mixture of hematite and rutile in solid solution. spots 4-8 do not give acceptable results using the ilmenite program (table v). these spots have tio2 content ranging between 62.23 and 82.42%. by converting the analyzed feo content into fe2o3, the obtained values range between 15.22 and 34.83% and the corresponding total oxide sum of these spots ranges between 98.03 and 98.94%, respectively (table v). there is a distinct reverse relation between tio2 and fe2o3 at these spots. these spots are most probably pseudorutile or mixtures of rutile and hematite obtained by the alteration of contained ilmenite exsolved intergrowth. in grain (8), spots 1-2 (figure 4, tables iv, v) are hematite and rutile in solid solution. spots 3-6 do not give acceptable results using the ilmenite program. spots 3-5 have tio2 content ranging between 63.66 and 64.72%. by converting the analyzed feo content into fe2o3, the obtained values range between 25.94 and 33.24% (table viii). these spots are ferriforous rutile or pseudorutile obtained by the alteration of contained ilmenite exsolved intergrowth, as the last grain (7). spot 6 is a definite silicate mineral (table viii) mgfealsilicate, with some of contained structural and/or molecular water. 4) ferromagnetic titanhematite all the analyzed 6 grains (figure 5, tables vi, vii), are separated within the ferromagnetic fraction associated with magnetite and titanomagnetite grains. they are not contained within the final bulk ilmenite concentrate. in these grains, spot 5 of (4), spots 1-5 and 11 of (5), and spots 13, 14 of (6) do not give acceptable results. the other investigated spots (figure 5, tables vi, vii), of the grains are: grain (1): spots 1-6 are martitized magnetite. in spot 1, the recorded contents of sio2, mgo, cao, and al2o3 may be remnants of altered silicate mineral inclusions. grain (2): spots 1, 2 are hematite while spots 3, 4 are remnants of magnetite. grain (3): spots 1-5 (figure 5) are titanomagnetite with tio2 content ranging between 13.67 and 17.03%. spots 6-11 are titanhematite with tio2 content ranging between 22.93 and 26.5%. spots 12, 13 are most probably pseudobrookite (table viii), while spot 14 is ferriilmenite. grain (4): spots 1, 2 are pseudobrookite, while spot 5 is calcite (table viii). spots 3, 4 are titanhematite after titanomagnetite. grain (5): spots 1-5 are rutile (table vii). spots 6-8 are martitized titanomagnetite with tio2 content ranging between 8.77 and 9.55%. spots 9, 10 are martitized titanomagnetite with relatively higher content of tio2, which ranges between 17.8 and 19.54%. spot 11 is martitized titanomagnetite into titanhematite and most of fe2o3 content is leached (table viii). the recorded sio2 and al2o3 are due to the increased water activity during the alteration and leaching of titanhematite. grain (6): spots 1-9 are martitized titanomagnetite with tio2 content ranging between 13.43 and 24.37% (tables vi, vii). spots 10-12 are ilmenite (tables vi, vii), spot 13 is leached ilmenite, and spot 14 is calcite (table viii). fig. 5. bse images of various ferromagnetic titanhematite grains. they are most probably produced by the process of martitization after titanomagnetite. engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9648 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... table iv. microprobe chemical analysis and molecular formulae of the analyzed spots of the various titanhematite exsolved intergrown grains of figure 4 g r a in s p o t s io 2 m g o m n o c a o z n o f e o a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l s io 2 m g o m n o c a o z n o f e o f e 2 o 3 a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l f e r r o u s f e f e r r ic f e o th e r c a ti o n s t i o fig. 4 (1) 1 0.08 0.00 0.00 0.00 0.00 88.88 0.00 0.03 0.02 0.35 89.36 0.08 0.00 0.00 0.00 0.00 0.40 98.29 0.00 0.03 0.02 0.35 99.18 0.01 1.98 0.01 0.01 3 2 0.00 0.00 0.06 0.01 0.00 88.89 0.00 0.04 0.06 0.14 89.18 0.00 0.00 0.06 0.01 0.00 0.05 98.70 0.00 0.04 0.06 0.14 99.04 0.00 1.99 0.01 0.00 3 3 0.00 0.01 0.05 0.01 0.01 88.89 0.00 0.06 0.00 0.23 89.27 0.00 0.01 0.05 0.01 0.01 0.11 98.64 0.00 0.06 0.00 0.23 99.12 0.00 1.99 0.01 0.00 3 4 0.10 0.02 0.00 0.01 0.00 89.27 0.00 0.07 0.01 0.24 89.71 0.10 0.02 0.00 0.01 0.00 0.28 98.86 0.00 0.07 0.01 0.24 99.59 0.01 1.98 0.01 0.00 3 5 0.00 0.03 0.03 0.06 0.00 89.41 0.00 0.03 0.06 0.26 89.88 0.00 0.03 0.03 0.06 0.00 0.08 99.25 0.00 0.03 0.06 0.26 99.80 0.00 1.99 0.01 0.01 3 6 0.00 0.00 0.07 0.00 0.00 91.23 0.00 0.02 0.05 0.33 91.70 0.00 0.00 0.07 0.00 0.00 0.22 101.11 0.00 0.02 0.05 0.33 101.80 0.00 1.99 0.00 0.01 3 fig. 4 (2) 1 0.00 0.00 0.03 0.00 0.05 87.74 0.00 0.20 0.00 0.17 88.19 0.00 0.00 0.03 0.00 0.05 0.07 97.40 0.00 0.20 0.00 0.17 97.92 0.00 1.99 0.01 0.00 3 2 0.00 0.00 0.00 0.00 0.04 88.34 0.01 0.19 0.04 0.17 88.78 0.00 0.00 0.00 0.00 0.04 0.12 98.01 0.01 0.19 0.04 0.17 98.57 0.00 1.99 0.01 0.00 3 3 0.00 0.01 0.03 0.02 0.00 88.53 0.00 0.18 0.04 0.42 89.23 0.00 0.01 0.03 0.02 0.00 0.31 98.01 0.00 0.18 0.04 0.42 99.02 0.01 1.98 0.01 0.01 3 4 0.00 0.00 0.07 0.00 0.00 89.05 0.00 0.19 0.02 0.42 89.76 0.00 0.00 0.07 0.00 0.00 0.31 98.60 0.00 0.19 0.02 0.42 99.61 0.01 1.98 0.01 0.01 3 5 0.02 0.00 0.04 0.02 0.04 90.03 0.00 0.20 0.03 0.35 90.72 0.02 0.00 0.04 0.02 0.04 0.23 99.76 0.00 0.20 0.03 0.35 100.68 0.01 1.98 0.01 0.01 3 fig. 4 (3) 1 0.33 0.24 0.04 0.09 0.00 86.44 0.30 0.36 0.12 1.49 89.43 0.33 0.24 0.04 0.09 0.00 1.14 94.77 0.30 0.36 0.12 1.49 98.90 0.03 1.90 0.06 0.03 3 2 0.00 0.01 0.07 0.04 0.14 87.04 0.01 0.31 0.03 1.22 88.87 0.00 0.01 0.07 0.04 0.14 0.85 95.76 0.01 0.31 0.03 1.22 98.43 0.02 1.94 0.02 0.02 3 3 0.02 0.01 0.04 0.04 0.05 87.39 0.03 0.31 0.05 1.20 89.14 0.02 0.01 0.04 0.04 0.05 0.95 96.03 0.03 0.31 0.05 1.20 98.73 0.02 1.94 0.02 0.02 3 4 0.02 0.00 0.07 0.04 0.00 87.56 0.03 0.34 0.06 0.99 89.11 0.02 0.00 0.07 0.04 0.00 0.81 96.39 0.03 0.34 0.06 0.99 98.74 0.02 1.95 0.02 0.02 3 fig. 4 (4) 1 0.00 0.05 2.77 0.03 0.07 42.44 0.00 0.41 0.05 49.90 95.71 0.00 0.05 2.77 0.03 0.07 41.90 0.60 0.00 0.41 0.05 49.90 95.77 0.92 0.01 0.08 0.99 3 2 0.03 0.07 2.88 0.00 0.00 43.09 0.00 0.37 0.03 49.87 96.35 0.03 0.07 2.88 0.00 0.00 41.86 1.37 0.00 0.37 0.03 49.87 96.49 0.92 0.03 0.08 0.98 3 3 5.64 0.96 0.06 0.11 0.00 73.79 0.84 0.77 0.08 0.86 83.10 5.64 0.96 0.06 0.11 0.00 5.60 75.75 0.84 0.77 0.08 0.86 90.67 0.13 1.60 0.34 0.02 3 4 0.20 0.05 0.02 0.04 0.00 79.32 0.02 0.74 0.08 0.97 81.44 0.20 0.05 0.02 0.04 0.00 0.96 87.06 0.02 0.74 0.08 0.97 90.14 0.02 1.93 0.04 0.02 3 5 0.16 0.02 0.02 0.06 0.00 79.63 0.04 0.78 0.11 0.94 81.75 0.16 0.02 0.02 0.06 0.00 0.90 87.46 0.04 0.78 0.11 0.94 90.49 0.02 1.93 0.04 0.02 3 6 0.16 0.04 0.04 0.07 0.07 79.73 0.07 0.72 0.05 1.22 82.15 0.16 0.04 0.04 0.07 0.07 1.04 87.43 0.07 0.72 0.05 1.22 90.89 0.03 1.92 0.05 0.03 3 7 0.24 0.06 0.00 0.04 0.00 80.37 0.08 0.70 0.03 0.81 82.31 0.24 0.06 0.00 0.04 0.00 0.86 88.33 0.08 0.70 0.03 0.81 91.13 0.02 1.93 0.04 0.02 3 8 0.31 0.06 0.06 0.07 0.03 80.84 0.09 0.78 0.03 0.81 83.06 0.31 0.06 0.06 0.07 0.03 0.82 88.91 0.09 0.78 0.03 0.81 91.94 0.02 1.93 0.05 0.02 3 9 0.12 0.02 0.05 0.06 0.00 80.94 0.07 0.75 0.08 0.82 82.90 0.12 0.02 0.05 0.06 0.00 0.72 89.12 0.07 0.75 0.08 0.82 91.80 0.02 1.94 0.04 0.02 3 10 0.21 0.02 0.02 0.05 0.08 80.98 0.09 0.69 0.06 0.98 83.19 0.21 0.02 0.02 0.05 0.08 0.95 88.91 0.09 0.69 0.06 0.98 92.07 0.02 1.92 0.05 0.02 3 11 0.21 0.01 0.00 0.06 0.04 81.18 0.04 0.69 0.04 1.12 83.39 0.21 0.01 0.00 0.06 0.04 1.13 88.94 0.04 0.69 0.04 1.12 92.28 0.03 1.92 0.04 0.02 3 12 0.14 0.04 0.01 0.04 0.00 81.60 0.05 0.73 0.08 0.83 83.51 0.14 0.04 0.01 0.04 0.00 0.80 89.77 0.05 0.73 0.08 0.83 92.48 0.02 1.94 0.04 0.02 3 13 0.20 0.04 0.08 0.06 0.00 81.83 0.05 0.74 0.08 0.91 84.00 0.20 0.04 0.08 0.06 0.00 0.83 89.99 0.05 0.74 0.08 0.91 92.99 0.02 1.93 0.05 0.02 3 fig. 4 (5) 1 0.00 0.09 0.22 0.02 0.07 80.70 0.06 0.28 0.12 8.29 89.85 0.00 0.09 0.22 0.02 0.07 6.99 81.89 0.06 0.28 0.12 8.29 98.03 0.16 1.65 0.03 0.17 3 2 0.00 0.06 0.16 0.01 0.05 80.97 0.03 0.33 0.09 8.53 90.22 0.00 0.06 0.16 0.01 0.05 7.35 81.79 0.03 0.33 0.09 8.53 98.40 0.16 1.65 0.02 0.17 3 3 0.00 0.09 0.28 0.00 0.07 80.69 0.05 0.33 0.10 8.61 90.20 0.00 0.09 0.28 0.00 0.07 7.24 81.60 0.05 0.33 0.10 8.61 98.35 0.16 1.64 0.03 0.17 3 4 0.00 0.09 0.17 0.01 0.04 81.00 0.07 0.29 0.06 8.78 90.50 0.00 0.09 0.17 0.01 0.04 7.52 81.63 0.07 0.29 0.06 8.78 98.66 0.17 1.64 0.02 0.18 3 5 0.00 0.09 0.20 0.00 0.05 80.38 0.06 0.28 0.05 9.15 90.25 0.00 0.09 0.20 0.00 0.05 7.83 80.60 0.06 0.28 0.05 9.15 98.31 0.18 1.62 0.02 0.18 3 6 0.01 0.04 0.09 0.00 0.01 67.02 0.04 0.29 0.06 24.05 91.60 0.01 0.04 0.09 0.00 0.01 21.48 50.59 0.04 0.29 0.06 24.05 96.66 0.48 1.02 0.02 0.49 3 7 0.00 0.01 0.11 0.01 0.00 66.36 0.02 0.37 0.09 24.90 91.88 0.00 0.01 0.11 0.01 0.00 22.25 49.01 0.02 0.37 0.09 24.90 96.77 0.50 0.99 0.02 0.50 3 8 0.00 0.04 0.08 0.00 0.00 62.34 0.03 0.43 0.05 28.10 91.07 0.00 0.04 0.08 0.00 0.00 25.13 41.34 0.03 0.43 0.05 28.10 95.20 0.57 0.84 0.02 0.57 3 9 0.00 0.01 0.07 0.00 0.00 60.87 0.02 0.44 0.09 29.28 90.77 0.00 0.01 0.07 0.00 0.00 26.27 38.44 0.02 0.44 0.09 29.28 94.61 0.60 0.79 0.02 0.60 3 10 0.00 0.01 0.05 0.01 0.01 59.09 0.04 0.39 0.11 30.96 90.66 0.00 0.01 0.05 0.01 0.01 27.77 34.80 0.04 0.39 0.11 30.96 94.14 0.63 0.72 0.02 0.64 3 11 0.00 0.00 0.08 0.01 0.01 55.15 0.04 0.39 0.08 35.16 90.93 0.00 0.00 0.08 0.01 0.01 31.53 26.25 0.04 0.39 0.08 35.16 93.55 0.72 0.54 0.02 0.72 3 12 0.00 0.00 0.07 0.00 0.03 53.60 0.04 0.48 0.07 37.13 91.42 0.00 0.00 0.07 0.00 0.03 33.31 22.55 0.04 0.48 0.07 37.13 93.67 0.76 0.46 0.02 0.76 3 13 0.00 0.02 0.04 0.01 0.00 50.91 0.01 0.45 0.06 42.49 93.99 0.00 0.02 0.04 0.01 0.00 38.13 14.19 0.01 0.45 0.06 42.49 95.40 0.85 0.28 0.01 0.85 3 14 0.00 0.01 0.02 0.01 0.00 46.28 0.02 0.47 0.08 45.73 92.62 0.00 0.01 0.02 0.01 0.00 41.08 5.78 0.02 0.47 0.08 45.73 93.20 0.93 0.12 0.01 0.93 3 fig. 4 (6) 1 0.00 0.00 0.02 0.02 88.60 0.00 0.03 2.17 90.83 0.00 0.00 0.02 0.02 0.00 1.90 96.32 0.00 0.00 0.03 2.17 100.45 0.04 1.91 0.00 0.04 3 2 0.00 0.00 0.04 0.01 88.18 0.00 0.03 2.38 90.64 0.00 0.00 0.04 0.01 0.00 2.09 95.64 0.00 0.00 0.03 2.38 100.19 0.05 1.90 0.00 0.05 3 3 0.30 0.00 0.00 0.21 86.95 0.00 0.03 3.24 90.73 0.30 0.00 0.00 0.21 0.00 3.00 93.26 0.00 0.00 0.03 3.24 100.04 0.07 1.85 0.02 0.06 3 4 0.00 0.00 0.00 0.02 86.88 0.00 0.04 2.72 89.66 0.00 0.00 0.00 0.02 0.00 2.43 93.82 0.00 0.00 0.04 2.72 99.03 0.05 1.89 0.00 0.05 3 5 0.00 0.02 0.02 0.03 82.84 0.00 0.04 8.82 91.76 0.00 0.02 0.02 0.03 0.00 7.86 83.30 0.00 0.00 0.04 8.82 100.09 0.17 1.65 0.00 0.17 3 6 0.53 0.00 0.04 0.02 82.80 0.00 0.03 7.55 90.96 0.53 0.00 0.04 0.02 0.00 7.35 83.83 0.00 0.00 0.03 7.55 99.33 0.16 1.67 0.02 0.15 3 fig. 4 (7) 1 0.00 5.25 1.01 0.00 63.40 0.53 0.03 21.61 91.84 0.00 5.25 1.01 0.00 0.00 9.06 60.38 0.53 0.00 0.03 21.61 97.87 0.19 1.16 0.29 0.41 3 2 0.00 3.82 0.73 0.01 56.26 0.50 0.06 30.38 91.75 0.00 3.82 0.73 0.01 0.00 19.77 40.54 0.50 0.00 0.06 30.38 95.80 0.43 0.79 0.21 0.59 3 3 0.00 2.96 0.53 0.01 56.13 0.43 0.00 32.30 92.35 0.00 2.96 0.53 0.01 0.00 23.24 36.54 0.43 0.00 0.00 32.30 96.00 0.51 0.72 0.16 0.63 3 fig. 4 (8) 1 0.00 1.19 0.62 0.00 58.49 0.52 0.00 30.43 91.26 0.00 1.19 0.62 0.00 0.00 24.61 37.64 0.52 0.00 0.00 30.43 95.02 0.55 0.76 0.09 0.61 3 2 0.02 1.76 1.12 0.01 53.30 0.44 0.03 35.74 92.41 0.02 1.76 1.12 0.01 0.00 27.88 28.24 0.44 0.00 0.03 35.74 95.23 0.62 0.56 0.12 0.71 3 engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9649 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... table v. calculated different mineral component fractions of the spots of the various titanhematite exsolved intergrown grains of figure 4 grain spot sio2 mgo mno cao zno feo fe2o3 al2o3 v2o3 cr2o3 tio2 total method gek pyr ilm h r total fig. 4 (1) 1 0.08 0.00 0.00 0.00 0.00 0.40 98.29 0.00 0.03 0.02 0.35 99.18 m2 0.00 0.00 0.66 98.41 0.00 99.07 2 0.00 0.00 0.06 0.01 0.00 0.05 98.70 0.00 0.04 0.06 0.14 99.04 m1 0.00 0.12 0.11 98.76 0.01 99.00 3 0.00 0.01 0.05 0.01 0.01 0.11 98.64 0.00 0.06 0.00 0.23 99.12 m1 0.04 0.10 0.23 98.64 0.03 99.03 4 0.10 0.02 0.00 0.01 0.00 0.28 98.86 0.00 0.07 0.01 0.24 99.59 m2 0.07 0.00 0.36 99.04 0.00 99.47 5 0.00 0.03 0.03 0.06 0.00 0.08 99.25 0.00 0.03 0.06 0.26 99.80 m1 0.10 0.05 0.16 99.31 0.08 99.70 6 0.00 0.00 0.07 0.00 0.00 0.22 101.11 0.00 0.02 0.05 0.33 101.80 m1 0.01 0.14 0.47 101.16 0.00 101.78 fig. 4 (2) 1 0.00 0.00 0.03 0.00 0.05 0.07 97.40 0.00 0.20 0.00 0.17 97.92 m1 0.00 0.07 0.15 97.40 0.05 97.67 2 0.00 0.00 0.00 0.00 0.04 0.12 98.01 0.01 0.19 0.04 0.17 98.57 m1 0.00 0.00 0.26 98.05 0.03 98.35 3 0.00 0.01 0.03 0.02 0.00 0.31 98.01 0.00 0.18 0.04 0.42 99.02 m1 0.02 0.06 0.66 98.05 0.02 98.82 4 0.00 0.00 0.07 0.00 0.00 0.31 98.60 0.00 0.19 0.02 0.42 99.61 m1 0.00 0.15 0.65 98.62 0.00 99.42 5 0.02 0.00 0.04 0.02 0.04 0.23 99.76 0.00 0.20 0.03 0.35 100.68 m1 0.00 0.08 0.49 99.79 0.04 100.41 fig. 4 (3) 1 0.33 0.24 0.04 0.09 0.00 1.14 94.77 0.30 0.36 0.12 1.49 98.90 m2 0.73 0.09 1.82 95.57 0.00 98.22 2 0.00 0.01 0.07 0.04 0.14 0.85 95.76 0.01 0.31 0.03 1.22 98.43 m1 0.02 0.14 1.79 95.80 0.19 97.95 3 0.02 0.01 0.04 0.04 0.05 0.95 96.03 0.03 0.31 0.05 1.20 98.73 m1 0.02 0.08 2.02 96.12 0.08 98.32 4 0.02 0.00 0.07 0.04 0.00 0.81 96.39 0.03 0.34 0.06 0.99 98.74 m1 0.00 0.14 1.70 96.47 0.02 98.34 fig. 4 (4) 1 0.00 0.05 2.77 0.03 0.07 41.90 0.60 0.00 0.41 0.05 49.90 95.77 m1 0.15 5.88 88.50 0.65 0.11 95.29 2 0.03 0.07 2.88 0.00 0.00 41.86 1.37 0.00 0.37 0.03 49.87 96.49 m2 0.21 6.12 88.34 1.46 0.00 96.13 3 5.64 0.96 0.06 0.11 0.00 5.60 75.75 0.84 0.77 0.08 0.86 90.67 m2 2.86 0.12 0.00 82.95 0.00 85.93 4 0.20 0.05 0.02 0.04 0.00 0.96 87.06 0.02 0.74 0.08 0.97 90.14 m2 0.14 0.04 1.62 87.36 0.00 89.16 5 0.16 0.02 0.02 0.06 0.00 0.90 87.46 0.04 0.78 0.11 0.94 90.49 m2 0.05 0.05 1.67 87.77 0.00 89.54 6 0.16 0.04 0.04 0.07 0.07 1.04 87.43 0.07 0.72 0.05 1.22 90.89 m2 0.10 0.07 2.11 87.60 0.00 89.89 7 0.24 0.06 0.00 0.04 0.00 0.86 88.33 0.08 0.70 0.03 0.81 91.13 m2 0.16 0.00 1.33 88.72 0.00 90.21 8 0.31 0.06 0.06 0.07 0.03 0.82 88.91 0.09 0.78 0.03 0.81 91.94 m2 0.17 0.13 1.19 89.34 0.00 90.83 9 0.12 0.02 0.05 0.06 0.00 0.72 89.12 0.07 0.75 0.08 0.82 91.80 m2 0.06 0.11 1.38 89.42 0.00 90.97 10 0.21 0.02 0.02 0.05 0.08 0.95 88.91 0.09 0.69 0.06 0.98 92.07 m2 0.05 0.04 1.75 89.24 0.00 91.08 11 0.21 0.01 0.00 0.06 0.04 1.13 88.94 0.04 0.69 0.04 1.12 92.28 m2 0.02 0.00 2.09 89.21 0.00 91.33 12 0.14 0.04 0.01 0.04 0.00 0.80 89.77 0.05 0.73 0.08 0.83 92.48 m2 0.11 0.02 1.43 90.04 0.00 91.59 13 0.20 0.04 0.08 0.06 0.00 0.83 89.99 0.05 0.74 0.08 0.91 92.99 m2 0.11 0.17 1.41 90.29 0.00 91.98 fig. 4 (5) 1 0.00 0.09 0.22 0.02 0.07 6.99 81.89 0.06 0.28 0.12 8.29 98.03 m1 0.26 0.47 14.76 82.07 0.10 97.66 2 0.00 0.06 0.16 0.01 0.05 7.35 81.79 0.03 0.33 0.09 8.53 98.40 m1 0.19 0.34 15.53 81.90 0.06 98.02 3 0.00 0.09 0.28 0.00 0.07 7.24 81.60 0.05 0.33 0.10 8.61 98.35 m1 0.28 0.58 15.28 81.74 0.07 97.96 4 0.00 0.09 0.17 0.01 0.04 7.52 81.63 0.07 0.29 0.06 8.78 98.66 m1 0.26 0.37 15.89 81.75 0.05 98.32 5 0.00 0.09 0.20 0.00 0.05 7.83 80.60 0.06 0.28 0.05 9.15 98.31 m1 0.26 0.43 16.54 80.71 0.05 97.99 6 0.01 0.04 0.09 0.00 0.01 21.48 50.59 0.04 0.29 0.06 24.05 96.66 m1 0.12 0.19 45.37 50.69 0.00 96.36 7 0.00 0.01 0.11 0.01 0.00 22.25 49.01 0.02 0.37 0.09 24.90 96.77 m1 0.04 0.23 47.00 49.12 0.02 96.40 8 0.00 0.04 0.08 0.00 0.00 25.13 41.34 0.03 0.43 0.05 28.10 95.20 m1 0.10 0.18 53.07 41.42 0.00 94.78 9 0.00 0.01 0.07 0.00 0.00 26.27 38.44 0.02 0.44 0.09 29.28 94.61 m1 0.01 0.14 55.47 38.55 0.00 94.18 10 0.00 0.01 0.05 0.01 0.01 27.77 34.80 0.04 0.39 0.11 30.96 94.14 m1 0.02 0.10 58.66 34.94 0.02 93.74 11 0.00 0.00 0.08 0.01 0.01 31.53 26.25 0.04 0.39 0.08 35.16 93.55 m1 0.00 0.17 66.59 26.37 0.03 93.15 12 0.00 0.00 0.07 0.00 0.03 33.31 22.55 0.04 0.48 0.07 37.13 93.67 m1 0.00 0.14 70.34 22.66 0.03 93.18 13 0.00 0.02 0.04 0.01 0.00 38.13 14.19 0.01 0.45 0.06 42.49 95.40 m1 0.05 0.09 80.54 14.26 0.01 94.96 14 0.00 0.01 0.02 0.01 0.00 41.08 5.78 0.02 0.47 0.08 45.73 93.20 m1 0.04 0.04 86.76 5.88 0.02 92.73 fig. 4 (6) 1 0.00 0.00 0.02 0.02 1.90 96.32 0.00 0.03 2.17 100.45 m1 0.00 0.04 4.02 96.34 0.03 100.43 2 0.00 0.00 0.04 0.01 2.09 95.64 0.00 0.03 2.38 100.19 m1 0.00 0.09 4.41 95.67 0.01 100.18 3 0.30 0.00 0.00 0.21 3.00 93.26 0.00 0.03 3.24 100.04 m2 0.00 0.00 6.15 93.41 0.00 99.56 4 0.00 0.00 0.00 0.02 2.43 93.82 0.00 0.04 2.72 99.03 m1 0.00 0.00 5.13 93.86 0.02 99.02 5 0.00 0.02 0.02 0.03 7.86 83.30 0.00 0.04 8.82 100.09 m1 0.04 0.04 16.60 83.35 0.03 100.06 6 0.53 0.00 0.04 0.02 7.35 83.83 0.00 0.03 7.55 99.33 m2 0.00 0.09 14.25 84.54 0.00 98.88 fig. 4 (7) 1 0.00 5.25 1.01 0.00 9.06 60.38 0.53 0.03 21.61 97.87 m1 15.66 2.15 19.13 60.94 0.04 97.91 2 0.00 3.82 0.73 0.01 19.77 40.54 0.50 0.06 30.38 95.80 m1 11.39 1.54 41.75 41.10 0.04 95.82 3 0.00 2.96 0.53 0.01 23.24 36.54 0.43 0.00 32.30 96.00 m1 8.81 1.12 49.08 36.98 0.04 96.03 4 0.00 1.26 0.28 0.02 31.35 0.00 0.19 0.00 62.23 95.33 m3 3.76 0.58 0.00 35.03 59.43 98.80 5 0.00 0.96 0.20 0.03 23.93 0.00 0.17 0.02 70.07 95.37 m3 2.86 0.43 0.00 26.78 67.95 98.01 6 0.01 1.35 0.31 0.01 24.06 0.00 0.17 0.00 70.37 96.27 m3 4.01 0.65 0.00 26.91 67.37 98.95 7 0.00 0.90 0.23 0.01 16.52 0.00 0.09 0.05 78.69 96.49 m3 2.68 0.49 0.00 18.50 76.65 98.33 8 0.00 0.71 0.20 0.01 13.70 0.00 0.08 0.00 82.42 97.12 m3 2.11 0.43 0.00 15.30 80.80 98.64 fig. 4 (8) 1 0.00 1.19 0.62 0.00 24.61 37.64 0.52 0.00 30.43 95.02 m1 3.56 1.32 51.98 38.16 0.02 95.03 2 0.02 1.76 1.12 0.01 27.88 28.24 0.44 0.03 35.74 95.23 m1 5.25 2.38 58.89 28.71 0.00 95.23 engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9650 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... table vi. microprobe chemical analysis and molecular formulae of the spots of the ferromagnetic titanhematite exsolved intergrown grains of figure 5 g r a in s s p o t s io 2 m g o m n o c a o z n o f e o a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l s io 2 m g o m n o c a o z n o f e o f e 2 o 3 a l 2 o 3 v 2 o 3 c r 2 o 3 t io 2 t o ta l f e r r o u s f e f e r r ic f e o th e r c a ti o n s t i o fig. 5 (1) 1 6.66 0.49 0.03 0.15 0.01 78.05 2.09 0.29 0.04 0.20 88.00 6.66 0.49 0.03 0.15 0.01 7.03 78.90 2.09 0.29 0.04 0.20 95.88 0.16 1.57 0.37 0.00 3 2 0.51 0.00 0.00 0.07 0.17 86.16 0.08 0.27 0.04 0.57 87.86 0.51 0.00 0.00 0.07 0.17 0.88 94.74 0.08 0.27 0.04 0.57 97.32 0.02 1.94 0.04 0.01 3 3 0.38 0.05 0.00 0.03 0.00 88.97 0.04 0.29 0.03 0.11 89.90 0.38 0.05 0.00 0.03 0.00 0.43 98.36 0.04 0.29 0.03 0.11 99.73 0.01 1.97 0.03 0.00 3 4 0.29 0.03 0.03 0.00 0.01 89.02 0.00 0.26 0.02 0.18 89.84 0.29 0.03 0.03 0.00 0.01 0.40 98.45 0.00 0.26 0.02 0.18 99.68 0.01 1.97 0.02 0.00 3 5 0.80 0.00 0.02 0.00 0.00 89.19 0.00 0.30 0.07 0.33 90.71 0.80 0.00 0.02 0.00 0.00 1.23 97.72 0.00 0.30 0.07 0.33 100.4 7 0.03 1.94 0.04 0.01 3 6 0.12 0.01 0.05 0.02 0.00 89.67 0.00 0.29 0.07 0.24 90.48 0.12 0.01 0.05 0.02 0.00 0.26 99.34 0.00 0.29 0.07 0.24 100.4 0 0.01 1.98 0.02 0.00 3 7 0.00 0.01 0.00 0.00 0.00 94.07 0.00 0.28 0.03 0.23 94.62 0.00 0.01 0.00 0.00 0.00 0.20 104.2 9 0.00 0.28 0.03 0.23 105.0 4 0.00 1.98 0.01 0.00 3 fig. 5 (2) 1 0.06 0.00 0.11 0.00 0.00 87.62 0.01 0.06 0.09 0.89 88.83 0.06 0.00 0.11 0.00 0.00 0.76 96.50 0.01 0.06 0.09 0.89 98.47 0.02 1.96 0.01 0.02 3 2 0.06 0.01 0.23 0.00 0.00 88.24 0.00 0.05 0.03 0.22 88.84 0.06 0.01 0.23 0.00 0.00 0.02 98.01 0.00 0.05 0.03 0.22 98.63 0.00 1.99 0.01 0.00 3 3 0.00 0.00 0.19 0.00 0.12 92.38 0.00 0.12 0.01 0.35 93.16 0.00 0.00 0.19 0.00 0.12 0.01 102.6 1 0.00 0.12 0.01 0.35 103.4 1 0.00 1.98 0.01 0.01 3 4 0.00 0.02 0.19 0.00 0.09 92.78 0.00 0.06 0.00 0.27 93.41 0.00 0.02 0.19 0.00 0.09 -0.07 103.1 6 0.00 0.06 0.00 0.27 103.7 2 0.00 1.99 0.01 0.01 3 fig. 5 (3) 1 0.02 2.63 0.81 0.00 0.05 76.05 2.50 0.70 0.07 13.6 7 96.51 0.02 2.63 0.81 0.00 0.05 6.78 76.96 2.50 0.70 0.07 13.6 7 104.2 0 0.14 1.41 0.26 0.25 3 2 0.08 2.42 0.93 0.01 0.00 74.54 0.93 0.75 0.00 14.8 3 94.48 0.08 2.42 0.93 0.01 0.00 8.18 73.72 0.93 0.75 0.00 14.8 3 101.8 4 0.17 1.39 0.20 0.28 3 3 0.04 2.19 0.79 0.02 0.13 71.90 1.64 0.75 0.03 16.2 7 93.76 0.04 2.19 0.79 0.02 0.13 9.85 68.94 1.64 0.75 0.03 16.2 7 100.6 5 0.21 1.31 0.22 0.31 3 4 0.08 2.13 0.86 0.00 0.14 73.17 1.50 0.71 0.00 16.3 4 94.93 0.08 2.13 0.86 0.00 0.14 9.98 70.20 1.50 0.71 0.00 16.3 4 101.9 4 0.21 1.32 0.21 0.31 3 5 0.05 2.32 0.98 0.00 0.18 72.44 1.23 0.71 0.04 17.0 3 94.97 0.05 2.32 0.98 0.00 0.18 10.0 9 69.26 1.23 0.71 0.04 17.0 3 101.8 9 0.21 1.30 0.21 0.32 3 6 0.12 0.83 0.20 0.03 0.15 66.73 1.30 0.87 0.08 22.9 3 93.23 0.12 0.83 0.20 0.03 0.15 18.9 3 53.11 1.30 0.87 0.08 22.9 3 98.54 0.41 1.04 0.12 0.45 3 7 0.06 1.28 0.15 0.01 0.09 65.40 1.98 0.85 0.02 23.8 5 93.69 0.06 1.28 0.15 0.01 0.09 19.0 2 51.53 1.98 0.85 0.02 23.8 5 98.84 0.41 1.00 0.16 0.46 3 8 0.08 0.89 0.20 0.01 0.09 65.09 1.53 0.91 0.02 24.1 8 93.01 0.08 0.89 0.20 0.01 0.09 19.9 5 50.15 1.53 0.91 0.02 24.1 8 98.02 0.43 0.98 0.13 0.47 3 9 0.07 1.29 0.45 0.01 0.05 64.66 1.16 0.84 0.01 25.7 6 94.30 0.07 1.29 0.45 0.01 0.05 20.4 5 49.12 1.16 0.84 0.01 25.7 6 99.21 0.44 0.95 0.14 0.50 3 10 0.10 0.92 0.30 0.03 0.09 65.40 1.10 0.87 0.06 26.1 8 95.04 0.10 0.92 0.30 0.03 0.09 21.6 2 48.64 1.10 0.87 0.06 26.1 8 99.90 0.46 0.94 0.12 0.50 3 11 0.06 1.65 0.36 0.00 0.16 61.06 2.94 0.93 0.04 26.5 0 93.69 0.06 1.65 0.36 0.00 0.16 20.4 7 45.09 2.94 0.93 0.04 26.5 0 98.19 0.44 0.87 0.21 0.51 3 14 0.06 0.34 0.16 0.01 0.00 47.19 0.49 1.01 0.04 44.3 5 93.65 0.06 0.34 0.16 0.01 0.00 39.1 8 8.90 0.49 1.01 0.04 44.3 5 94.54 0.87 0.18 0.06 0.89 3 fig. 5 (4) 3 0.14 0.05 0.02 0.04 0.00 85.83 0.01 0.32 0.09 4.28 90.77 0.14 0.05 0.02 0.04 0.00 3.87 91.06 0.01 0.32 0.09 4.28 99.86 0.09 1.81 0.02 0.09 3 4 0.03 0.04 0.07 0.00 0.00 86.01 0.00 0.35 0.10 3.97 90.57 0.03 0.04 0.07 0.00 0.00 3.47 91.70 0.00 0.35 0.10 3.97 99.73 0.08 1.83 0.02 0.08 3 fig. 5 (5) 6 0.02 0.00 0.00 0.01 84.72 0.00 0.01 8.77 93.53 0.02 0.00 0.00 0.01 0.00 7.90 85.35 0.00 0.00 0.01 8.77 102.0 6 0.17 1.66 0.00 0.17 3 7 0.00 0.02 0.00 0.00 83.29 0.00 0.00 9.55 92.86 0.00 0.02 0.00 0.00 0.00 8.56 83.02 0.00 0.00 0.00 9.55 101.1 5 0.19 1.63 0.00 0.19 3 8 0.01 0.00 0.00 0.04 82.65 0.02 0.02 9.41 92.14 0.01 0.00 0.00 0.04 0.00 8.43 82.47 0.02 0.00 0.02 9.41 100.3 8 0.18 1.63 0.00 0.19 3 9 0.03 0.01 0.02 0.03 77.55 0.00 0.01 17.8 0 95.43 0.03 0.01 0.02 0.03 0.00 15.9 9 68.39 0.00 0.00 0.01 17.8 0 102.2 7 0.34 1.31 0.00 0.34 3 10 0.28 0.05 0.00 0.03 73.08 0.06 0.02 19.5 4 93.07 0.28 0.05 0.00 0.03 0.00 17.7 8 61.44 0.06 0.00 0.02 19.5 4 99.21 0.39 1.21 0.02 0.39 3 fig. 5 (6) 1 0.04 2.99 1.39 0.02 0.28 73.61 1.82 0.47 0.03 13.4 3 94.07 0.04 2.99 1.39 0.02 0.28 5.12 76.10 1.82 0.47 0.03 13.4 3 101.6 7 0.11 1.43 0.28 0.25 3 2 0.02 2.25 1.03 0.08 0.13 72.32 1.14 0.43 0.05 16.5 9 94.03 0.02 2.25 1.03 0.08 0.13 9.68 69.60 1.14 0.43 0.05 16.5 9 100.9 8 0.20 1.32 0.20 0.32 3 3 0.08 2.43 0.99 0.04 0.21 71.22 1.49 0.46 0.05 18.0 8 95.06 0.08 2.43 0.99 0.04 0.21 10.7 9 67.14 1.49 0.46 0.05 18.0 8 101.7 7 0.23 1.26 0.22 0.34 3 4 0.01 2.10 1.06 0.04 0.14 69.14 1.09 0.51 0.02 18.5 3 92.63 0.01 2.10 1.06 0.04 0.14 11.7 0 63.82 1.09 0.51 0.02 18.5 3 99.00 0.25 1.24 0.19 0.36 3 5 0.03 1.74 0.73 0.01 0.14 69.80 0.81 0.50 0.03 19.7 8 93.56 0.03 1.74 0.73 0.01 0.14 13.8 5 62.16 0.81 0.50 0.03 19.7 8 99.77 0.30 1.20 0.15 0.38 3 6 0.06 1.56 0.61 0.03 0.00 70.56 0.44 0.53 0.00 20.4 6 94.24 0.06 1.56 0.61 0.03 0.00 15.0 4 61.69 0.44 0.53 0.00 20.4 6 100.4 0 0.32 1.19 0.12 0.39 3 7 0.00 2.03 1.18 0.02 0.21 67.25 1.27 0.52 0.05 22.0 9 94.62 0.00 2.03 1.18 0.02 0.21 14.8 4 58.22 1.27 0.52 0.05 22.0 9 100.4 4 0.31 1.11 0.19 0.42 3 8 0.23 2.42 0.76 0.01 0.12 63.46 0.99 0.48 0.08 22.9 9 91.53 0.23 2.42 0.76 0.01 0.12 15.7 7 52.99 0.99 0.48 0.08 22.9 9 96.82 0.34 1.04 0.20 0.45 3 9 0.01 1.88 0.94 0.00 0.18 63.04 1.04 0.52 0.00 24.3 7 91.97 0.01 1.88 0.94 0.00 0.18 17.4 8 50.62 1.04 0.52 0.00 24.3 7 97.02 0.38 1.00 0.17 0.48 3 10 0.03 0.89 0.34 0.03 0.00 44.02 0.41 0.64 0.00 47.7 6 94.11 0.03 0.89 0.34 0.03 0.00 41.0 3 3.32 0.41 0.64 0.00 47.7 6 94.44 0.91 0.07 0.07 0.95 3 11 0.35 0.08 0.19 0.19 0.16 39.37 0.39 0.59 0.16 49.2 1 90.67 0.35 0.08 0.19 0.19 0.16 39.4 0 0.00 0.39 0.59 0.16 49.2 1 90.70 0.88 0.00 0.05 1.03 3 12 0.05 0.76 0.23 0.03 0.00 44.18 0.34 0.60 0.00 49.3 8 95.59 0.05 0.76 0.23 0.03 0.00 42.8 4 1.50 0.34 0.60 0.00 49.3 8 95.74 0.94 0.03 0.06 0.97 3 vi. conclusion the high purity egyptian beach ilmenite concentrate contains several mineral textures. the rutile-ilmenite exsolved intergrowths are far less common than in titanhematite. in this exsolved intergrowth, the ilmenite component is a ferriilmenite composed of 31.68-80.47% ilmenite, 0.4-33.2% hematite, 1.7935.78% geikielite, 0.64-2.34% pyrophanite, and 0.02-0.29% rutile. the cr2o3 contents range between 0 and 0.5%. the other component of the intergrowth is ferriferrous rutile, consisting of 57.5-87.41% rutile, 8.23-33.86% hematite, 0.42-16.55% geikielite, and 0.20-1.70% pyrophanite, while the cr2o3 content ranges between 0 and 0.4%. in these intergrowths, the content of the included hematite in the ferriilmenite component, decreases, as the geikielite (mgtio3) and/or pyrophanite (mntio3) contents increase. mgo and mno mix easier with ilmenite rather than with hematite. on the other hand, the relatively larger and darker exsolved rutile bodies are composed mainly of rutile (more than 95% tio2), while the relatively smaller ones are mainly ferriferrous rutile with considerable amounts of mixed hematite. engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9651 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... it was noticed that the ilmenite enriched with relatively higher content of mgo and individual tio2 is unstable and alters partially into rutile and hematite. increased tio2 content leads to the exsolution of rutile bodies. the difference in the geometry of the associated mixed mineral crystal structures and their corresponding contents inside the rutile-ilmenite exsolved intergrowth in addition to the prevailing physical conditions may be responsible of the different obtained textures of such intergrowth. the titanhematite intergrowth includes 3 fabrics arranged in a decreasing order of abundance as: ilmenite-hematite, rutilehematite, and rutile-ilmenite-hematite. the tio2 content attains up to 9.15%. both mgo and mno have minimum values and do not follow fe2o3. in the titanhematite host, mgo ranges between 0 and 0.2%, while mno ranges between 0 and 0.3%. only in the case of exsolved rutile within the titanhematite host, the titanhematite host contained mgo ranges between 1.2 and 5.3%, while the mno content ranges between 0.5 and 1.1%. the exsolved rutile mgo content ranges between 0.6 and 1.3%, while the mno content ranges between 0.2 and 0.7%. it was found that the contained exsolved ilmenite may be altered into pseudorutile or mixed rutile and hematite fabric. in some homogeneous titanhematite or mixed rutile-hematite, the fe2o3 content can be replaced with sio2. in all types of the titanhematite intergrowth, the cr2o3 contents range between 0 and 0.1%. table vii. calculated different mineral component fractions of the spots of the various ferromagnetic titanhematite exsolved intergrown grains of figure 5 grain spot sio2 mgo mno cao zno feo fe2o3 al2o3 v2o3 cr2o3 tio2 total method gek pyr ilm h r total fig. 5 (1) 1 6.66 0.49 0.03 0.15 0.01 7.03 78.90 2.09 0.29 0.04 0.20 95.88 m2 1.47 0.07 0.00 90.24 91.77 2 0.51 0.00 0.00 0.07 0.17 0.88 94.74 0.08 0.27 0.04 0.57 97.32 m2 0.01 0.00 1.07 95.33 96.40 3 0.38 0.05 0.00 0.03 0.00 0.43 98.36 0.04 0.29 0.03 0.11 99.73 m2 0.15 0.00 0.03 98.94 99.12 4 0.29 0.03 0.03 0.00 0.01 0.40 98.45 0.00 0.26 0.02 0.18 99.68 m2 0.10 0.07 0.15 98.91 99.22 5 0.80 0.00 0.02 0.00 0.00 1.23 97.72 0.00 0.30 0.07 0.33 100.47 m2 0.00 0.05 0.58 98.88 99.51 6 0.12 0.01 0.05 0.02 0.00 0.26 99.34 0.00 0.29 0.07 0.24 100.40 m2 0.03 0.11 0.31 99.58 100.03 7 0.00 0.01 0.00 0.00 0.00 0.20 104.29 0.00 0.28 0.03 0.23 105.04 m1 0.01 0.00 0.42 104.32 0.00 104.76 fig. 5 (2) 1 0.06 0.00 0.11 0.00 0.00 0.76 96.50 0.01 0.06 0.09 0.89 98.47 m2 0.00 0.24 1.46 96.74 98.44 2 0.06 0.01 0.23 0.00 0.00 0.02 98.01 0.00 0.05 0.03 0.22 98.63 m2 0.01 0.49 0.00 97.99 98.50 3 0.00 0.00 0.19 0.00 0.12 0.01 102.61 0.00 0.12 0.01 0.35 103.41 m1 0.00 0.41 0.03 102.62 0.11 103.17 4 0.00 0.02 0.19 0.00 0.09 -0.07 103.16 0.00 0.06 0.00 0.27 103.72 m2 0.06 0.41 0.01 103.14 103.63 fig. 5 (3) 1 0.02 2.63 0.81 0.00 0.05 6.78 76.96 2.50 0.70 0.07 13.67 104.20 m1 7.85 1.72 14.31 79.54 0.04 103.45 2 0.08 2.42 0.93 0.01 0.00 8.18 73.72 0.93 0.75 0.00 14.83 101.84 m2 7.21 1.98 17.11 74.70 101.00 3 0.04 2.19 0.79 0.02 0.13 9.85 68.94 1.64 0.75 0.03 16.27 100.65 m1 6.52 1.68 20.79 70.61 0.12 99.72 4 0.08 2.13 0.86 0.00 0.14 9.98 70.20 1.50 0.71 0.00 16.34 101.94 m1 6.36 1.83 21.09 71.70 0.06 101.03 5 0.05 2.32 0.98 0.00 0.18 10.09 69.26 1.23 0.71 0.04 17.03 101.89 m1 6.92 2.07 21.32 70.53 0.13 100.97 6 0.12 0.83 0.20 0.03 0.15 18.93 53.11 1.30 0.87 0.08 22.93 98.54 m1 2.48 0.43 39.98 54.49 0.02 97.39 7 0.06 1.28 0.15 0.01 0.09 19.02 51.53 1.98 0.85 0.02 23.85 98.84 m1 3.81 0.31 40.16 53.54 0.03 97.85 8 0.08 0.89 0.20 0.01 0.09 19.95 50.15 1.53 0.91 0.02 24.18 98.02 m1 2.67 0.43 42.14 51.70 0.01 96.95 9 0.07 1.29 0.45 0.01 0.05 20.45 49.12 1.16 0.84 0.01 25.76 99.21 m1 3.84 0.95 43.19 50.29 -0.01 98.26 10 0.10 0.92 0.30 0.03 0.09 21.62 48.64 1.10 0.87 0.06 26.18 99.90 m1 2.74 0.63 45.66 49.80 0.00 98.83 11 0.06 1.65 0.36 0.00 0.16 20.47 45.09 2.94 0.93 0.04 26.50 98.19 m1 4.92 0.75 43.23 48.07 0.09 97.07 14 0.06 0.34 0.16 0.01 0.00 39.18 8.90 0.49 1.01 0.04 44.35 94.54 m2 1.02 0.34 82.63 9.49 93.48 fig. 5 (4) 3 0.14 0.05 0.02 0.04 0.00 3.87 91.06 0.01 0.32 0.09 4.28 99.86 m2 0.13 0.05 7.91 91.29 99.38 4 0.03 0.04 0.07 0.00 0.00 3.47 91.70 0.00 0.35 0.10 3.97 99.73 m2 0.11 0.14 7.26 91.92 99.42 fig. 5 (5) 1 0.01 0.00 0.00 0.02 0.46 0.00 0.00 0.02 100.16 100.67 0.00 0.00 0.53 100.16 100.69 2 0.00 0.00 0.02 0.03 0.44 0.00 0.00 0.02 99.91 100.44 0.01 0.05 0.51 99.88 100.45 3 0.00 0.00 0.00 0.00 0.55 0.00 0.00 0.05 99.88 100.47 0.00 0.01 0.65 99.87 100.53 4 0.14 0.00 0.00 0.09 0.51 0.00 0.00 0.03 99.57 100.33 0.00 0.00 0.59 99.57 100.16 5 0.14 0.01 0.00 0.07 0.51 0.00 0.00 0.04 99.66 100.42 0.02 0.00 0.60 99.64 100.27 6 0.02 0.00 0.00 0.01 0.00 7.90 85.35 0.00 0.00 0.01 8.77 102.06 m2 0.00 0.00 16.66 85.40 102.06 7 0.00 0.02 0.00 0.00 0.00 8.56 83.02 0.00 0.00 0.00 9.55 101.15 m1 0.05 0.00 18.08 83.02 0.00 101.15 8 0.01 0.00 0.00 0.04 0.00 8.43 82.47 0.02 0.00 0.02 9.41 100.38 m1 0.00 0.00 17.79 82.50 0.05 100.34 9 0.03 0.01 0.02 0.03 0.00 15.99 68.39 0.00 0.00 0.01 17.80 102.27 m1 0.01 0.03 33.77 68.40 0.00 102.21 10 0.28 0.05 0.00 0.03 0.00 17.78 61.44 0.06 0.00 0.02 19.54 99.21 m2 0.16 0.00 36.93 61.86 98.95 fig. 5 (6) 1 0.04 2.99 1.39 0.02 0.28 5.12 76.10 1.82 0.47 0.03 13.43 101.67 m1 8.92 2.96 10.81 77.94 0.28 100.90 2 0.02 2.25 1.03 0.08 0.13 9.68 69.60 1.14 0.43 0.05 16.59 100.98 m1 6.71 2.20 20.43 70.78 0.23 100.35 3 0.08 2.43 0.99 0.04 0.21 10.79 67.14 1.49 0.46 0.05 18.08 101.77 m1 7.25 2.11 22.80 68.68 0.17 101.00 4 0.01 2.10 1.06 0.04 0.14 11.70 63.82 1.09 0.51 0.02 18.53 99.00 m1 6.26 2.24 24.71 64.93 0.19 98.33 5 0.03 1.74 0.73 0.01 0.14 13.85 62.16 0.81 0.50 0.03 19.78 99.77 m1 5.20 1.56 29.25 63.00 0.12 99.12 6 0.06 1.56 0.61 0.03 0.00 15.04 61.69 0.44 0.53 0.00 20.46 100.40 m2 4.65 1.29 31.72 62.13 99.80 7 0.00 2.03 1.18 0.02 0.21 14.84 58.22 1.27 0.52 0.05 22.09 100.44 m1 6.07 2.52 31.34 59.54 0.25 99.71 8 0.23 2.42 0.76 0.01 0.12 15.77 52.99 0.99 0.48 0.08 22.99 96.82 m2 7.21 1.61 32.98 54.26 96.06 9 0.01 1.88 0.94 0.00 0.18 17.48 50.62 1.04 0.52 0.00 24.37 97.02 m1 5.60 1.99 36.92 51.66 0.17 96.34 10 0.03 0.89 0.34 0.03 0.00 41.03 3.32 0.41 0.64 0.00 47.76 94.44 m1 2.65 0.72 86.65 3.73 0.01 93.77 11 0.35 0.08 0.19 0.19 0.16 39.40 0.00 0.39 0.59 0.16 49.21 90.16 m2 0.23 0.39 83.21 0.54 5.05 89.43 12 0.05 0.76 0.23 0.03 0.00 42.84 1.50 0.34 0.60 0.00 49.38 95.74 m1 2.28 0.49 90.47 1.84 0.00 95.07 engineering, technology & applied science research vol. 12, no. 6, 2022, 9640-9653 9652 www.etasr.com moustafa: some mineralogical characteristics of the egyptian black sand beach ilmenite... table viii. original microprobe chemical analysis of some spots of the grains from figures 4, 5 grain spot sio2 mgo mno cao zno feo fe2o3 al2o3 v2o3 cr2o3 tio2 total fig. 4 (3) 5 96.02 0.16 0.00 0.04 0.00 1.72 0.00 0.81 0.03 0.00 0.36 99.14 6 0.32 0.03 0.22 54.49 0.67 2.33 0.00 0.00 0.04 0.05 0.11 58.25 7 0.21 0.00 0.10 55.49 0.72 1.96 0.00 0.00 0.04 0.00 0.07 58.59 fig. 4 (6) 7 37.45 0.01 0.18 23.10 14.45 0.00 22.45 0.04 0.10 97.78 8 49.84 0.04 0.19 19.54 10.26 0.00 19.14 0.03 0.09 99.13 9 90.85 0.00 0.00 0.16 1.13 0.00 0.03 0.01 8.51 100.68 10 85.10 0.13 0.00 0.07 0.78 0.00 0.90 0.02 17.19 104.19 11 63.75 0.91 0.00 0.19 2.25 0.00 1.71 0.00 28.06 96.87 12 5.57 0.02 0.00 0.11 1.29 0.00 0.68 0.03 94.98 102.69 13 93.90 0.17 0.00 1.28 1.21 0.00 3.08 0.03 0.09 99.75 fig. 4 (8) 3 0.00 0.57 0.29 0.02 29.92 0.00 0.22 0.04 63.66 94.72 4 0.00 1.05 0.69 0.01 28.45 0.00 0.23 0.00 64.72 95.15 5 0.01 0.63 0.50 0.00 23.35 0.00 0.18 0.00 69.55 94.22 6 50.05 3.08 0.12 0.30 11.12 0.00 21.99 0.00 1.67 88.33 fig. 5 (3) 12 0.00 1.9 0.5 0.00 0.1 53.4 0.0 3.5 0.8 0.0 33.4 93.8 13 0.0 1.4 0.3 0 0.1 53.5 0.0 2.5 0.9 0.0 35.8 94.6 fig. 5 (4) 1 0.89 0.03 0.00 0.10 0.00 57.48 0.00 0.64 0.47 0.11 31.91 91.62 2 0.93 0.00 0.04 0.02 0.00 63.20 0.00 0.00 0.39 0.07 26.75 91.39 5 0.34 0.10 0.09 54.08 0.62 1.98 0.00 0.00 0.01 0.01 0.30 57.53 fig. 5 (5) 11 11.57 1.24 0.04 0.20 2.83 0.00 8.35 0.00 58.65 82.88 fig. 5 (6) 13 0.03 0.60 0.25 0.01 0.03 37.93 0.00 0.25 0.59 0.00 56.80 96.50 14 1.27 0.23 0.04 44.53 0.29 4.51 0.00 0.06 0.10 0.02 5.94 57.00 some ferromagnetic titanhematite varieties separated from the fraction of magnetite are detected. they are produced by the martitization of titanomagnetite. their tio2 content attains up to 24.37%. in these grains, the contents of cr2o3, mgo, and mno range between 0.0-0.2, 0.0-3, and 0.0-1.4% respectively. in fact, some of the exsolved intergrown textures included within the grains of the ilmenite concentrate contain relatively higher values of cr2o3 content, their distribution is relatively lower, and they are the only reason for the increased cr2o3 content in the obtained ilmenite concentrate. in fact, several varieties of chromite and chromspinel mineral grains are found and represent 1.1% of the detected bulk ilmenite grains. in these grains, the contents of cr2o3, mgo, v2o3, and al2o3 range between 16.69-56.72, 0.54-17.33, 0.14-0.58, and 1.3338.79% respectively. although it is rarely met with one of these high chromium grains within the ilmenite concentrate, the relatively finer grain sizes of most of them could led to the separation for some of them to ilmenite 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[32] p. ramdohr, die beziehungen von fe-ti-erzen aus magmatischen gesteinen. valtioneuvoston kirjapaino, 1956. microsoft word etasr_v12_n5_pp9282-9294 engineering, technology & applied science research vol. 12, no. 5, 2022, 9282-9294 9282 www.etasr.com guerraiche et al.: heat transfer enhancement in a receiver tube of solar collector using various … heat transfer enhancement in a receiver tube of solar collector using various materials and nanofluids djemaa guerraiche applied energy physics laboratory (lpea) department of physics faculty of matter sciences university of batna 1 batna, algeria d.guerraiche@gmail.com khelifa guerraiche mechanical engineering department faculty of technology university of batna 2 batna, algeria guer.khelifa@yahoo.com zied driss laboratory of electromechanical systems (lasem) national school of engineers of sfax (enis) university of sfax, sfax, tunisia zied.driss@enis.tn atef chibani department of chemical engineering university salah boubnider constantine 3 constantine, algeria chibaniatef@gmail.com slimane merouani department of chemical engineering university salah boubnider constantine 3 constantine, algeria s.merouani@yahoo.fr cherif bougriou mechanical engineering department faculty of technology, university of batna 2 batna, algeria c.bougriou@univ-batna2.dz received: 21 july 2022 | revised: 5 august 2022 | accepted: 8 august 2022 abstract-the solar flux distribution on the parabolic trough collector (ptc) absorber tube is extremely non-uniform, which causes non-uniform temperature distribution outside the absorber tube. therefore, it generates high thermal stress which causes creep and fatigue damage. this presents a challenge to the efficiency and reliability of parabolic trough receivers. to override this problem, we have to homogenize the heat flux distribution and enhance the heat transfer in the receiver’s absorber tube to improve the performance of the ptc. in this work, 3d thermal and thermal stress analyses of ptc receiver performance were investigated with a combination of monte carlo ray-trace (mcrt), computational fluid dynamics (cfd) analysis, and thermal stress analysis using the static structural module of ansys. at first, we studied the effect of the receiver tube material (aluminium, copper, and stainless steel) on heat transfer. the temperature gradients and the thermal stresses were compared. second, we studied the effect of the addition of nanoparticles on the working heat transfer fluid (htf), employing an al2o3-h2o based nanofluid at various volume concentrations. to improve the thermal performance of the ptc, a nanoparticle volume concentration ratio of 1%–6% is required. the results show that the temperature gradients and thermal stresses of stainless steel are significantly higher than those of aluminium and copper. from the standpoint of thermal stress, copper is recommended as the tube receiver material. using al2o3 in water as an htf increases the average output temperature by 2%, 6%, and 10% under volume concentrations of 0%, 2%, and 6% respectively. the study concluded that the thermal efficiency increases from 3% to 14% for nanoparticle volume fractions ranging from 2% to 6%. keywords-heat transfer; nanofluids; solar concentrator; receiver; non-uniform heat flux; temperature gradients i. introduction the use of renewable energies has become essential to the reduction of the consumption of fossil resources and the production of carbon dioxide (co2), which is the main gas responsible for the greenhouse effect. the technology of concentrated solar power (csp) can meet the demands for thermal and electrical energy. the benefits of using a csp technology with a ptc system are: it is best suited for a wide range of industrial applications and can contribute to thermal energy production, which can have significant economic, environmental, and social implications [1]. recently, the ptc has been developing towards a higher concentration ratio and operating temperature for the purposes of reducing the corresponding author: djemaa guerraiche engineering, technology & applied science research vol. 12, no. 5, 2022, 9282-9294 9283 www.etasr.com guerraiche et al.: heat transfer enhancement in a receiver tube of solar collector using various … investment cost and improving its thermal efficiency, especially at high temperatures. this is an important goal in order for these technologies to be energetically and financially viable [2]. however, the ptc suffers from several problems and failures, especially concentrated solar non-uniform heat flux (nuhf) distribution on the outer surface of the absorber tube. in addition, the heat flux is small near the top wall where the collimated energy is incident and is large near the bottom wall [3]. nuhf causes high local temperature and big temperature gradient in solar receivers due to the restricted thermal conductivity of the receiver tube and the thermal convection capacity inside the tube, producing an increase in thermal stress. this causes the absorber tube to deviate from the focal plane and large increase in optical losses because the selective coating degrades when the local temperature is too high, limiting the maximum working temperature. all these issues represent challenges that will have a long-term impact on the ptc's efficiency and safety [4]. authors in [5] discovered that the maximum temperature differential for safe functioning of receiver tubes is around 50k. furthermore, strong temperature gradients have many repercussions circumferentially, which may be summed by the deflection of the absorber tube. this causes the absorber tube to deviate from the concentrator's focus line, causing optical loss. when the local temperature is too high, the selective coating degrades, limiting the maximum operating temperature. as a result of the thermal breakdown of the htf, hydrogen production and penetration occur [6], resulting in increasing heat loss, material degradation, heat stress, and deformation of the absorber tube. these pose significant obstacles to the concentrated solar system's safe and efficient functioning. to solve this issue, we must homogenize the heat flow distribution by flattening the temperature distribution, lowering the peak temperature and the temperature gradient. recent studies have concentrated on improving thermal transfer and thermal distribution uniformity. a simple solution to flattening the temperature distribution is to homogenize the flow distribution. heat transfer enhancement technology can reduce thermal losses and thermal stress while increasing heat transfer rates between the absorber tube and htf at a low cost. the solutions can be roughly classified into three groups: improvements to the tube's thermal conductivity, collector optimization to homogenize solar energy, and augmentation of convective heat transfer within the absorber tube [7]. receiver tubes are subjected to a harsh operating environment. to alleviate the extreme operating conditions and ensure the receiver's durability, dependability, and integrity throughout its lifecycle, special consideration was required when selecting the receiver material. high corrosion resistance, optimal physical and mechanical properties, excellent fabricability, and a higher capacity for flux density are all critical criteria. several solutions have been adopted by enhancing the thermal conductivity of the absorber tube and employing an absorber with thermal compensator and heat transfer improvement techniques [8]. using selective materials, solution techniques aimed to improve the thermal conductivity of the absorber tube have been proposed for the ptc receiver. authors in [9] conducted a structural and thermal analysis of a ptc absorber tube to investigate the effect of material variations on temperature distribution flattening. steel, copper, aluminium, and bimetallic materials (cu-fe) have been investigated. they concluded that when using copper, the circumferential temperature non-uniformity was less bending due to less thermal load than using steel. using a bimetallic tube improves temperature distribution and reduces maximum deflection by 45–49%. authors in [2] presented an experimental investigation in which the steel tube was replaced with a copper tube. the reduced bending of the absorber tube was caused by the lower circumferential temperature variations due to copper's strong thermal conductivity. ii. homogenizing solar flux distribution a more straightforward way to flatten the temperature distribution appears to be the homogenization of the flux distribution. several researchers proposed innovative concentrators for flux homogenization. the heat flow gradient in the absorber tube must be reduced and homogenized. authors in [10] proposed improvements based on the conventional ptc and a secondary reflector was added overhead the tube. the numerical results showed that the heat flux gradient was reduced by 70.37%, and the temperature gradient from 159.39k to 24.16k. authors in [11] used a variable focus ptc, in which the focal length varied as a function of the reflector's motion relative to the receiver, significantly enhanced the flux distribution's homogeneity. authors in [12] placed a secondary reflector within the annular gap in order to reflect more sun rays onto the top of the absorber. authors in [13] investigated the heat flux distribution on the outside surface of the ptc absorber tube in order to lower the tube's temperature gradient by relocating the absorber tube away from the focal line and toward the parabola and adding a secondary reflector. the results show that installing another reflector overhead the absorber tube improves the heat flux distribution and reduces heat flux gradient by 70.37%. iii. heat transfer enhancement and optimization heat transfer improvement might result in a more uniform temperature distribution in the metal tube, reducing thermal deformation in the receiving tube. for the ptc receiver, a number of strategies for enhancing convective heat transfer have been proposed. authors in [14] used an absorber with a thermal compensator at the parabolic dish concentrated solar receiver, which contains a phase change material (pcm) to produce uniform heat distribution. thermal performance is improved by using pcms as thermal energy storage. homogeneous temperature distribution was observed on the pcm integrated receiver in the absence of solar radiation. a non-uniform temperature distribution was discovered during the charging of the pcm included within the solar receiver. authors in [15] presented a novel ptc receiver design based on a concentric absorber tube filled with pcm. the absorber was regarded as a component of transitory thermal heat storage. the results validated the suggested design and verified that combining ptc and pcm in the receiver peripheral can improve the thermal performance of the provided system. in [16], for solar cascade heat collection, a new ptc with a concentric receiver tube based on two htfs, syltherm-800 oil, was presented. the findings revealed that the absorber tube's peak temperature and circumferential temperature gradient engineering, technology & applied science research vol. 12, no. 5, 2022, 9282-9294 9284 www.etasr.com guerraiche et al.: heat transfer enhancement in a receiver tube of solar collector using various … were lower than regular ptc at the same mass flow rate. the absorber tube's maximum temperature and temperature difference lowered to 66k and 65k respectively. for the ptc receiver, several strategies for improving convective heat transfer have been proposed. this technology employs helical swirl generators, treated areas, vortex generators, displacement increase devices, extended surfaces, jagged surfaces, and nanoparticles [17]. according to these studies, the peak temperature and temperature gradient can be minimized. in [18], the impact of swirl inserts with and without nanofluids on ptcs with non-uniform heating flux was examined. the results showed that combining the swirl inserts and nanofluids improved the nusselt number by 57.4% while the maximum reduction in thermal losses was 23%. the nusselt number, on the other hand, was enhanced by 15.57% when utilizing nanofluid only. the working fluid is one of the most important components of a solar receiver since it plays an important role in heat transmission. during the last 25 years, nanotechnology has found applications in solar energy production. the use of nanofuids has transformed material science, and they have been used as potential alternative fluid solutions for increasing the efficiency and profitability of thermal systems. adding nanoparticles to the heating fluid presents the best solution to improve thermal conductivity and thermo-physical and heat transfer properties of the fluid [19]. in fact, nanofluids have a favorable effect on the performance of the ptc. the heat transfer performance obtainable with nanofluids is known to surpass the performance of heat transfer liquids available today [20]. the most used nanofluids contain nanoparticles such as al, fe2o3, al2o3, cu, tio2, and sio2 [21]. some studies on the use of nanofluids for solar energy harvesting are available in the literature. for example, authors in [22] investigated the application of nanofluids in concentrating a solar ptc. the effect of several nanofluids employed as working fluid on the performance of solar thermal collectors was studied experimentally. authors in [23] discussed the progressive application of nanofluids in solar collectors with different thermophysical properties. in addition, they evaluated the performance of different types of solar collectors. authors in [24] proposed a mathematical model for the investigation of the effect of nanofluid concentration on ptc. they found that using nanofluids in a ptc improves its thermal efficiency. authors in [25] presented an experimental study of the heat transfer and friction factor of silver nanofluids in a ptc receiver with twisted tape inserts. they confirmed that using nanofluids increases the heat transfer performance of the receiver. authors in [26] confirmed that the performance of concentrating solar thermal systems with a nanofluid as working fluid has an excellent potential for power tower applications improving efficiency by 5%–10%. authors in [27] investigated the performance of nanofluids on ptc systems and improved the efficiency by at least 5% [27]. authors in [28] presented an experimental study to evaluate the thermal efficiency of a ptc using nanoparticles of alumina (al2o3) in water with a volume fraction of 1% and 3% as htf. the results showed that with nanofluid as working fluid, the maximum efficiencies were 52.4% and 57.7%, while for water, these efficiencies were 40.8% and 46.5% for 3% and 1% volume fraction respectively. ptc thermal enhancement has recently attracted considerable attention. the enhancement of ptc performance can be achieved by modifying the material, modifying the geometry, and using nanofluids instead of conventional base fluids. even so, utilizing nanofluids on ptcs provided a positive result. these results are still facing several breaking points in the method of using a htf [29]. finding the optimal configuration of various parameters, such as receiver formation and geometry, receiver size and material, htf, and regulation of the maximum heat flow, is one of the most challenging and important research purposes for enhanced thermal systems to further improve efficiency and profitability through innovation in design and application of new fluids and new materials. this work presents a three-dimensional numerical study of the thermal and thermal stress performance of a ptc. in order to attain this goal, the suggested approach consists of two main steps. the impact of the absorber tube material on heat transmission was investigated in the first step. the performance of ptc receivers was studied using a combination of monte carlo ray-trace (mcrt), computational fluid dynamics (cfd) simulation using ansys fluent software, and thermal stress analysis using ansys' static structural module. we will solve the temperature distributions in the heat transfer analysis, and the thermal stress analysis will use the interpolated temperature distributions specified at the nodes of the cfd meshes as input data for the nodes. a comparative study of numerous materials, such as copper, aluminum, and stainless steel, is employed and compared to find which is ideal for a small-sized ptc under actual nuhf. second, the effect of the addition of nanoparticles on the working fluid, employing al2o3-h2o based nanofluid at various volume concentrations is carried out. the computational model is developed in ansys fluent environment. iv. physical model figure 1 shows the physical model considered in this work. the ptc system consists of a mirror folded into a parabolic shape with a heat collecting element at its focus. in the numerical study, the rim angle (ϕr) of the collector is 90° and the total aperture area (ap = w×l) is 1.80m 2 . the receiver of the parabolic trough solar collector consists of a metallic tube that is enclosed in a glass envelope. the absorber tube is coated with a selective coating that has a high absorptivity of the incoming solar radiation and a low emissivity of infrared radiation. the geometrical dimensions and optical properties of the ptc system are defined in table i. in this work, a threedimensional analysis of the thermal losses and thermal stress performance of a solar ptc receiver was investigated through studying the influence of the receiver tube, material type, and the nanofluid used as the working fluid. to improve the thermal performance of the ptc and homogenize the flux distribution for flattening the temperature distribution, various types of materials were used for the receiver heat transfer enhancement, namely copper, stainless steel, aluminium, and water containing nanoparticles of al2o3. 321h stainless steel was used for the absorber tube due to its low bending behavior and high strength capability [30]. the thermal properties of absorber materials are given in table ii. in these conditions, the engineering, technology & applied science research vol. 12, no. 5, 2022, 9282-9294 9285 www.etasr.com guerraiche et al.: heat transfer enhancement in a receiver tube of solar collector using various … concentration ratio and the mass flow rate are equal to 0%–6% and 0.005kg/s respectively. for our analysis, the solar collector shown in figure 2 was chosen as the geometrical model in the simulations. fig. 1. view of the parabolic trough collector and its components. table i. geometrical parameters of the ptc [15] receiver tube inner diameter of receiver tube 0.027 m outer diameter of receiver tube 0.028 m inner diameter of pyrex cover 0.048 m outer diameter of pyrex cover 0.050 m collector focal length, f 0.25 m aperture width, w 1.0 m rim angle, ϕr 90° length, l 1.80 m geometrical concentration ratio, c 13 mirrors reflectivity, ρ 0.91 slope error σslope 2 mrad specularity error σspec 2 mrad table ii. steel, alumina, and copper absorber tube physicals parameters [30] parameter 321h stainless steel alumina copper density (kg.m -3 ) 8030 3850 8978 conductivity (w.m-1.k -1 ) 17.3 36 387.6 specific heat (j.kg-1.k -1 ) 512 773 381 fig. 2. receiver parabolic trough solar collector geometry. v. numerical model and mathematical formulation a three-dimensional optic-thermal coupling model is used to analyze the heat transfer process in a ptc system employing al2o3/water nanofluid as the htf. the monte carlo ray trace (mcrt) code is used to calculate a realistic non-uniform solar radiation heat flux distribution on the outside wall of the absorber tube to expose the optical features of the proposed ptc system. the solar flux distribution created using the mcrt approach was regarded as heat flux boundary conditions in the steady state heat transfer investigation for cfd analysis. in the estimation of heat flux distributions, actual variables such as sun shape, incidence angle, optical characteristics, and numerous optical defects, were taken into consideration. the expected direct normal irradiance (dni) was 1000w/m 2 . the thermal performance of the ptc was studied utilizing a computational fluid dynamics (cfd) software tool and a nanofluid as the working fluid. the reynolds averaged navier-stokes equations were solved using the finite volume approach in the commercial computational fluid dynamics package ansys fluent 16.0. the finite volume approach was used to discretize the governing equations of continuity, nanoparticle conservation, momentum, and energy. the convective and diffusive components in momentum and energy equations were discretized using the second-order upwind approach. for pressure discretization, the presto scheme was utilized. the simple method was used to solve the velocity pressure coupling problem. nanofluid flow modeling is classified into two categories: the single-phase flow in which the base fluid and the suspended nanoparticles are assumed homogenous, taking into consideration the thermal characteristics of the nanofluid and relying on published correlations, and two-phase flow which separates the base fluid from the suspended nanoparticles. fluent supports three models: volume of fluid (vof), mixed, and eulerian. the single-phase method was utilized in this study, which is regarded as an accurate method when the nanoparticle concentration and diameter are less than 10% and 100nm respectively. [31]. vi. mesh independence verification a three-dimensional geometry was created, and a tetrahedral mesh was placed over the absorber tube's fluid domain. figure 3 depicts the absorber tube's mesh geometry. a grid independence test was performed to ensure that the mesh value is not affected by the grid. table iii shows the results of the mesh sensitivity study for the output temperature of a working fluid. fig. 3. 3d meshing of the absorber tube. table iii. grid independence study grid outlet temperature (k) 182680 328.12 256660 327.55 365760 326.51 406460 326.50 vii. heat transfer fluid properties water with al2o3, a frequently used and affordable nanoparticle, was employed as the base fluid in this study. the nanofluids' qualities are determined by the thermophysical parameters of the base fluid, the volume concentration ratio of engineering, technology & applied science research vol. 12, no. 5, 2022, 9282-9294 9286 www.etasr.com guerraiche et al.: heat transfer enhancement in a receiver tube of solar collector using various … nanoparticles, and the temperature. table iv lists the characteristics of al2o3 nanoparticles [32]. table iv. properties of the al2o3 nanoparticles density (kg.m -3 ) conductivity (w.m-1.k -1 ) specific heat (j.kg-1.k -1 ) al2o3 3850 36 773 nanofuid density, heat capacitance, dynamic viscosity, and thermal conductivity are determined from the following equations [33]. the density of the nanofluid is determined by: ( )nf f p1-f fρ = ρ + ρ (1) where ρ, f, p, nf and φ denote the density, base fluid, nanoparticle, and nanofluid and the volumetric concentration of al2o3 in the base fluid respectively. the ratio between the thermal conductivities of the nanofluid k and the base fluid kf is defined as follows: ( ) ( ) ( ) ( ) ( ) 1 1 1k k 1 1 f τ + η − − η − − τ φ = τ + η − + − τ φ (2) the ratio between the thermal conductivities of the particles kp and the base fluid is defined as: p fτ = k k (3) the aspect ratio is given by (4), where ξ is the sphericity: η = ξ/3 (4) the viscosity of the nanofluid is defined by: nf 1 2, 5 bf µ = + φ η (5) the specific heat of the nanofluid is given by: ( )nf f pcp 1 cp cp= −φ + φ (6) viii. thermal performance the thermal efficiency ηth of the ptc system is determined as follows: u th s q q η = (7) where qu is the useful gained thermal energy and qs is the available solar energy: s a b ×q = a i (8) where aa is the the aperture area of the solar collector: a a = w×l (9) the useful gained thermal energy qu is determined based on the mass flow rate of the htf, mass flow rate, and the fluid temperatures at the inlet and outlet, tin and tout [34]: ( )u out inq m cp t t= −ɺ (10) where mɺ , cp, tout, and tin are the mass flow rate, specific heat capacity, and inlet and outlet heat transfer fluid temperature. the conventional definition of the local convective heat transfer coefficient can be calculated in terms of the inner wall temperature of the absorber tube tw, surface heat flux q", and the average temperature tave of the inlet and the outlet: ( ) f w ave q h t t ′′ = − (11) ix. hydraulic performance the pressure drop in the solar absorber tube can be determined as follows [35]: av ,inl av ,out p p -p∆ = (12) the friction factor coefficient is computed as: i 2 p f u²l d ∆ = ρ      (13) several correlations and data from the literature were utilized to validate the numerical model's conclusions. to obtain the heat transfer performance in a parabolic trough receiver tube, the friction factor was calculated using the correlation of [36]: 0.1974 0.173 ref − = (14) the average nu is expressed as: f i f h d nu k ⋅ = (15) where keff is the effective thermal conductivity (wm -1 k −1 ). ( ) ( ) ( ) ( ) 0.5 2 / 3 f / 8 re 1.00 pr nu 1 12.7( f / 8 pr 1 − = + − (16) with 3 6 pr 2000 and 10 re 5 10 .≤ ≤ ≤ × the reynolds number is given by: i u d re ρ ⋅ ⋅ = µ (17) x. boundary conditions for the intake and outlet of the absorber tube, constant mass flow rate, temperature, and outflow boundary conditions were adopted. to generate more realistic findings, a non-uniform heat flow profile around the perimeter of the receiver's absorber tube was examined. soltrace calculates the solar heat flux density to derive the heat flux distribution profile under direct normal irradiation of 1000w/m 2 . the flux is centered on the lowest half, which is facing the ptc's mirror. the heat flow density is really low in the higher section. in reality, the radiation that comes into contact with the face in this section is direct radiation. engineering, technology & applied science research vol. 12, no. 5, 2022, 9282-9294 9287 www.etasr.com guerraiche et al.: heat transfer enhancement in a receiver tube of solar collector using various … xi. optical modelling (solar heat flux density) for the optical modeling of the collector, soltrace software was used to predict the effective heat flux falling on the bottom of the absorber tube and to find the effective rays concentrating on the receiver tube using the monte carlo ray tracing algorithm. the sun form is characterized by a gaussian distribution with a standard deviation of 2mrad. mirror secularity and slope flaws were both taken into account. the efficient rays focused on the outer surface of the absorber tube were discovered using the monte carlo ray tracing approach. figure 4 depicts the distribution of the solar heat flow around the outside wall of the receiving tube. the flux is concentrated on the lower part which is facing the ptc's mirror. for the upper part, the heat flux density is very low (direct solar radiation). data polynomial functions were created into a macro in fluent cfd simulation as a user defined function (udf), which is used as the boundary condition input for the heat flux wall on the absorber tube's outer surface as seen in figure 5. no-slip conditions were applied to all solid surfaces. (a) (b) fig. 4. (a) ray tracing parabolic reflector and absorber tube surface, (b) 3 dimensional view of the heat flux distribution on the absorber tube surface. xii. model validation to confirm the solution's validity, the precision of the computational modeling was calculated and a comparison with previously reported experimental and theoretical correlations for the local nusselt variation and pressure drop were performed. the model's validity is evaluated using the experimental data from [38]. the geometry and thermal boundary conditions are nearly identical to those in this simulation. (a) (b) fig. 5. (a) circumferential heat flux distribution on the absorber tube. (b) polynomial functions of heat flux profile on the outer surface of the absorber. fig. 6. comparison of the obtained nusselt number with [38]. fig. 7. comparison of nu with the result of [37]. the authors in [38] investigated the effect of incorporating al2o3 nanoparticles into pure water on the hydrodynamic and heat transfer parameters of laminar flow at re = 799.53 inside horizontal flow with uniform heat flux of 9000w/m 2 on the outer pipe wall. according to figure 6, the current study's modeling results match the experimental results of [38]. numerical results deviate from experimental data by 0 20 40 60 80 100 120 140 0 2 4 6 8 10 12 14 16 18 20 n u s e lt distance axiale (x/d) esmaeilzadeh et al.[38] present study 0 20000 40000 60000 80000 100000 120000 0 100 200 300 400 500 600 700 800 900 n u re present study gnielinski [37] engineering, technology & applied science research vol. 12, no. 5, 2022, 9282-9294 9288 www.etasr.com guerraiche et al.: heat transfer enhancement in a receiver tube of solar collector using various … approximately 3.5% for the estimation of nu when φ=1%. gnielinski correlations were used to validate the results of our numerical study for heat transfer when φ=0% [37] given by (16), as shown in figure 7, the present study results are shown to be in good agreement with the given correlations. the friction factors were compared with the results from [36], given by (14). excellent agreement was obtained, as shown in figure 8, with a deviation of less than 3%. the results indicate that the model and the calculation process are appropriate and acceptable. fig. 8. validation of present study friction factor with [36] for φ= 4%. xiii. results and discussion as a heat flux boundary condition, a udf was used to connect the acquired heat flux profile to a cfd. figure 9 depicts the heat flux distribution and temperature distribution on the outer surface of the absorber tube. for typical working condition of htf inlet mass flow rate, dni, and htf inlet temperature of 0.005m/s, 1000w/m 2 , and 300k respectively, the performance of the solar collector was tested using water as htf. (a) (b) fig. 9. (a) cfd heat flux, (b) temperature distributions on the outer surface of the absorber tube. a. effect of the absorber tube material figure 10 depicts the temperature distribution on the outside of the absorber tube for various materials. when the thermophysical properties of the absorber vary and the distribution of heat flux on the outer wall changes, the temperature distribution varies over the entire tube wall. due to its lower thermal conductivity, the steel absorber tube has a poor circumferential temperature distribution. copper has higher thermal properties than stainless steel, but it has a higher self-weight and lower mechanical strength [3]. fig. 10. distribution of the outlet temperature. (a) (b) (c) fig. 11. temperature variation from bottom wall to top wall of the absorber: (a) cooper, (b) aluminium, (c) stainless stell. figure 11 shows the temperature profiles around the diameter of the inner surface of the absorber tube at the outlet 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 0,010 0,015 0,020 0,025 0,030 0,035 0,040 f re present study mwesigye et al. [36] -0.015 -0.010 -0.005 0.000 0.005 0.010 0.015 0.020 296 304 312 320 328 336 344 352 360 368 376 384 t e m p e ra tu re ( k ) vertical line (mm) stainless steel aluminum copper engineering, technology & applied science research vol. 12, no. 5, 2022, 9282-9294 9289 www.etasr.com guerraiche et al.: heat transfer enhancement in a receiver tube of solar collector using various … section. among the three materials, the temperature of stainless steel is the maximum due to its low thermal conductivity. the temperature gradients with stainless steel are much higher than those of aluminium and copper. the radial temperature distribution is asymmetrical. this can cause higher thermal stresses and reduce the durability of the absorber tube. circumferential temperature distribution of different absorber tubes is presented in figure 12 for different absorber tube materials. (a) (b) (c) fig. 12. circumferential temperature distribution on absorber tube at outlet section (re=1400): (a) stainless steel, (b) aluminium, (c) copper. the temperature distributions changed with angle φ for the three materials. the top wall (φ=0°) temperature remains approximately constant, while for the bottom wall (φ=180°) it is maximum with a very significant gradient. this part of the absorber tube receiver concentrated solar radiation. the stainless-steel has the greatest maximum temperature. the maximum circumferential temperature of stainless steel and aluminium is approximately 10% and 6% higher than the maximum temperature obtained using copper. the temperature gradients of the stainless-steel tube receiver are much greater than those of the aluminium and copper tube receivers. it can be seen that copper has better circumferential temperature distribution than other materials. the circumferential temperature difference (∆tc) is 34k, 10k, and 6k for stainless steel, aluminium, and copper respectively. as can be seen in figure 13, the temperature increases along the length of the tube from the inlet to the outlet. due to the non-uniform circumferential heat flux distribution, temperature variation in the z direction is negligible compared to the circumferential direction temperature variation. the temperature profiles increase almost linearly and cannot create any stresses. the stress distributions are fully dependent on the wall temperature. fig. 13. axial temperature profiles at the tube inner surface (bottom wall). b. thermal stress analysis when the temperature of a continuous body varies in the presence of constraints, thermal stress can arise. in the present study, thermal stress analysis was conducted along the heat transfer fluid's current. the static structural module of ansys was used. the thermal stress of the tubes in the thermoelastic model is totally determined by the temperature profiles. the temperature data from the tubes obtained from the thermal model could be used as the boundary conditions in the thermoelastic model's nodes. in addition, the material tube was supposed to be isotropic and elastically deformed under temperature load. the stress levels and distributions are determined by the combined effects of circumferential axial and radial temperature gradients on the ptc receiver tube. figure 14 shows the axial stress profiles for the three different materials on the inner surface tube along the length direction at bottom wall. stainless steel axial compressive stress values are significantly higher than the ones of aluminium and copper. the axial stress values of all materials are close to zero at the inlet and outlet ends, and they increase rapidly to higher values that are close to the profile's peak compressive axial stress values. the temperature profiles along the axial direction at the tube inner surface illustrated in figure 13 can explain these phenomena. as can be seen from this figure, the temperature profiles at the tree tube receiver ends 0 30 60 90 120 150 180 210 240 270 300 330 360 340 342 344 346 348 350 352 354 270 90 0 180 t e m p e ra tu re ( k ) angular location on the circumference of the receiver tube (°) 0 30 60 90 120 150 180 210 240 270 300 330 360 330 335 340 345 350 355 360 365 370 270 90 0 180 t e m p e ra tu re ( k ) angular location on the circumference of the receiver tube (°) 0 30 60 90 120 150 180 210 240 270 300 330 360 343 344 345 346 347 348 349 350 270 90 0 180 t e m p e ra tu re ( k ) angular location on the circumference of the receiver tube (°) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 300 320 340 360 380 400 t e m p e ra tu re ( k ) z(m) stainless steel aluminum copper engineering, technology & applied science research vol. 12, no. 5, 2022, 9282-9294 9290 www.etasr.com guerraiche et al.: heat transfer enhancement in a receiver tube of solar collector using various … increase almost linearly along the axial direction, which cannot create any stresses and the stress distributions are fully dependent on the wall temperature. figure 15 shows the radial stress profiles on the inner surface tube along the axial direction for the different material conditions at bottom wall. the radial stresses act as tensile stress at the tube outlet and inlet ends for all the tree material, and then the radial stress values suddenly change to compressive stress. the radial stress values are approximately constant from z = 0.1 m to z = 1.7 m, which is near to zero. the highest maximum radial stress is 3.2 mpa in stainless steel. the maximum radial stress for aluminium and copper conditions is very small, at about 1.6 mpa and 0.6 mpa, respectively. fig. 14. axial stress profiles on the inner surface tube along the length direction at bottom wall. fig. 15. radial stress profiles on the inner surface tube at bottom wall. as can be seen in figure 16, the circumferential stress of the absorber tube is greatest at a circumference angle of the bottom wall because the temperature there is the highest hence the stress created in this area is the greatest. as the temperature drops, the circumferential stress decreases. the circumferential stress is lower at the top surface of the absorber tube, where the temperature is lower. on the other hand, the temperature difference between the local temperatures of the wall and the fluid influences local heat transfer from the wall, resulting in greater strain at the tube's bottom. maximum stress is found in stainless steel and the lowest stress in copper. fig. 16. circumferential stress distribution of the absorber tube. c. effect of the al2o3 concentration a numerical simulation with three different volumetric concentrations of al2o3, equal to 2%, 4%, and 6%, is used to investigate the influence of al2o3 volume fraction on the performance of the solar receiver when the mass flowrate of the htf is 5g/s. in order to investigate the solar receiver's performance, a non-uniform solar radiation heat flux distribution on the outer wall of the absorber tube is used as a boundary condition. figures 17 and 18 depict the effects of al2o3 volume fractions on the temperature distributions of the absorber wall with nanoparticle volume fractions ranging from 0% to 6%. (a) (b) (c) fig. 17. temperature distribution vs. nanoparticle concentration (re=1300): (a) φ=1%, (b) φ=2%, (c) φ=6%. -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -40 -20 0 a x ia l s tr e s s ( m p a ) z (m) stainless steel aluminum copper 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 r a d ia l s tr e s s ( m p a ) z (m) stainless steel aluminum copper 0 45 90 135 180 225 270 315 360 -1 0 1 2 3 4 5 6 7 8 9 s tr e s s (m p a ) circumferential angle (degree) copper aluminium stainless steel engineering, technology & applied science research vol. 12, no. 5, 2022, 9282-9294 9291 www.etasr.com guerraiche et al.: heat transfer enhancement in a receiver tube of solar collector using various … fig. 18. average and maximum temperature distribution of the absorber wall under different volume fractions of al2o3 (re=1300). according to these findings, the average and maximum temperatures of the absorber tube fall noticeably as the volume fraction increases. as the volume percentages of al2o3 grow from 0% to 6%, the maximum temperature drops from 408.4k to 382k. as a result, the thermal gradients in the absorber tube and the receiver's heat loss are decreased. figure 19 shows the axial variation of the local nusselt number for different volume fractions of al2o3 nanoparticles. from the results, it is clear that the addition of nanoparticles to the base fluid has a direct effect in the field of heat transfer. in these conditions, the nusselt number of the nanofluid is greater than that of pure water. it increases significantly with an increasing volume concentration of nanoparticles. so, it is confirmed that the suspension of nanoparticles in its base fluid gives a remarkable increase in heat exchange. fig. 19. variation of local nusselt number (re=1300). figure 20 illustrates the axial variation of the convection heat transfer coefficients along the axial direction of the absorber tube for re=1300 and different volume concentrations of nanoparticles. it is obvious that the convection heat transfer coefficient increases as the volume fraction of the nanoparticles increases. the main reason is that when the volume percentage of nanoparticles increases, the thermophysical properties of the fluid improve. figure 21 shows the axial temperature variation for different al2o3 nanoparticle volume fraction. it is clear that the growth in the shape of the curves is due to the increase in the volume fraction of the al2o3 nanoparticles, due to their effective thermal conductivity, which is higher than water's. this generates an increase in the exchange coefficient h and in the temperature values. at outlet (z=1.8m), the temperature reaches t=318k for φ=6% and t=310k for φ=0%. fig. 20. variation of the heat transfer coefficients (re=1300). fig. 21. axial temperature for different volume fractions of al2o3. fig. 22. heat transfer coefficient vs. nanoparticle volume fraction and reynolds number for tinl=300k. figure 22 shows the heat transfer coefficient as a function of re and nanoparticle volume fraction at inlet temperature tinl=300k. as shown in the figure, using nanofluids improves heat transfer performance when compared to the base fluid (ϕ= 0%). it can be seen that the heat transfer coefficient 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 150 180 210 240 270 300 330 360 390 h ( w /m ² k ) z(m) φ=0 φ=0.05 φ=0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 360 365 370 375 380 385 390 395 400 405 410 t e m p e ra tu re ( k ) volume fraction maximum temperature average temperature 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0 5 10 15 20 25 30 35 n u z(m) φ=0 φ=0.01 φ=0.05 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 300 303 306 309 312 315 318 321 t e m p e ra tu re (k ) z(m) φ= 0% φ= 2% φ= 4% φ= 6% 0 5000 10000 15000 20000 25000 30000 0 500 1000 1500 2000 2500 3000 3500 4000 h ( w /m ²k ) re φ= 0% φ= 1% φ=2% φ= 4% φ= 6% engineering, technology & applied science research vol. 12, no. 5, 2022, 9282-9294 9292 www.etasr.com guerraiche et al.: heat transfer enhancement in a receiver tube of solar collector using various … increases by 48%, 38%, and 33% as the volume fraction increases by 8%, 6%, and 4% respectively, especially at higher reynolds number values. as a result, the improvement in heat transfer performance must be greater than the increase in pump capacity for the usage of nanofluids to be economically viable. it is vital to understand pressure drop in order to build the best pump available. the pressure drop is also explored in this work. the pressure drop between the collector's intake and output ports was determined using the simulation data. figure 23 shows that when the volume fraction grows, the pressure drop increases dramatically, especially at higher reynolds numbers. when the particle volumetric concentration in the nanofluid increases, the density and viscosity rise, causing an increase in pressure drop. this increases flow resistance and necessitates more pumping power. this causes an increase in flow resistance and needs additional pumping force. fig. 23. pressure drop in the absorber tube vs. nanoparticle volume fraction and reynolds number. figure 24 shows the change in the velocity profile. the profile is tested at axial locations z = 0, 0.1, 0.6, 1.2, 1.80m and for volume concentrations of 1%, 2%, and 6%. the velocity of the working fluid is constant at the inlet. from this section and beyond the velocity increases, and the profile becomes less flattened. the maximum velocity is not reached at the center, and it is pushed down, due to the fact that the fluid is heated asymmetrically because the solar heat flux distribution is not uniform. there is an angle towards the end of the entering area. an increase in particle volume fraction is, therefore, advantageous in terms of energy utilization. a higher temperature rise of the nanofluid will lead to higher collector thermal efficiency. however, increased particle loading also increases fluid viscosity, which affects pressure drop. according to figure 25, the collector's efficiency decreases considerably as the volume fraction increases due to the nanofluid's increased heat conductivity. the thermal efficiency decreases continually as re increases. pressure drop increases significantly at much higher re values, therefore, the increase in pumping power outweighs by far the gain in thermal performance, leading to lower efficiency. it is concluded that for nanoparticle volume fractions ranging from 2 to 6%, thermal efficiency increases by 3 to 14%. (a) (b) (c) (d) fig. 24. velocity profiles for (a) φ=6%, (b) φ=4%, (c) φ=2%, (d) φ=0%. fig. 25. thermal efficiency vs. volume fraction and re for tinl=300k. 5000 10000 15000 20000 25000 0 25 50 75 100 125 150 p re s s u re d ro p ( p a ) re φ=6 % φ=4 % φ=2 % φ=1 % φ=0 % 0 5000 10000 15000 20000 25000 55 60 65 70 75 80 t h e rm a l e ff ic ie n c y % re φ= 0% φ= 2% φ= 4% φ= 6% engineering, technology & applied science research vol. 12, no. 5, 2022, 9282-9294 9293 www.etasr.com guerraiche et al.: heat transfer enhancement in a receiver tube of solar collector using various … xiv. conclusion in this paper, 3-dimensional numerical simulation of a ptc system under solar nuhf on the outer surface of the absorber tube were used to evaluate the influence of material selection on the thermal and the thermal stresses of tube receivers. moreover, the use of al2o3/water nanofluid as htf was proposed to improve the performances of the ptc system. this study is a preliminary overview of the key parameters which promote the optimization of the absorber tube by homogenizing heat flux distribution, reducing peak temperature and decreasing the temperature gradient to reduce thermal stresses, which are generated by the high temperature gradients. three materials (copper, stainless steel, and aluminum) and nanoparticles of al2o3 with concentration ratios ranging from 0% to 6 % were used. the results confirmed that: • receiver tube material selection is critical for ensuring reliability. the temperature gradients with stainless steel are much higher than those with aluminum and copper gradients, which can cause higher thermal stresses and reduces durability of the absorber tube. • the maximum circumferential temperature of stainless steel and aluminium is approximately 10% and 6% higher than the maximum temperature obtained using copper. the temperature gradient of the stainless-steel tube receivers is much greater than those of the aluminum and copper tube receivers. copper has a better circumferential temperature distribution than the other materials. for stainless steel, aluminium, and copper, the circumferential temperature difference (∆t) is 34k, 10k, and 6k respectively. copper is the recommended material as the receiver tube material from the point of view of thermal stress. • the temperature gradient and the maximum temperature in the absorber are greatly reduced by using al2o3/water as htf. the temperature gradient and the maximum temperature in the absorber decrease with the al2o3 particle concentration. • increase in nanoparticle volume fraction by 1%, 2%, and 6% increases the average of output temperatures by 2%, 6%, and 10% respectively. • heat transfer coefficient increases by 48%, 38% and 33% as the volume fraction increases to 8%, 6%, and 4% respectively, especially at higher reynolds numbers. the study concluded that for nanoparticle volume fractions ranging from 2% to 6%, thermal efficiency increases by 3% to-14%. in future work, the study will be focused towards the effect of other receiver tube material and the results will be used for the design and manufacturing of a more efficient parabolic trough solar receiver. references [1] n. b. khedher, "experimental evaluation of a flat plate solar collector under hail city climate," engineering, technology & applied science research, vol. 8, no. 2, pp. 2750–2754, apr. 2018, https://doi.org/ 10.48084/etasr.1957. 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(corresponding author) nguyen phung quang institute for control engineering and automation, hanoi university of science and technology, vietnam quang.nguyenphung@hust.edu.vn received: 24 february 2023 | revised: 10 march 2023 | accepted: 11 march 2023 abstract with the increasing wind power penetration, wind farms are directly influencing the power systems, so the need to improve the quality of the system is an open research topic. a doubly-fed induction generator (dfig) is often used in wind power systems. however, dfig has a complex structure and often works in harsh environments, so potential faults may occur. faults can cause the system to fall into a chaotic working state, which is a harmful phenomenon for dfig, since it makes the operating quality of the system worse, even leading to system destruction if not fixed on time. this study presents simulations of the chaotic phenomenon that occurs for a dfig under specific working conditions based on lyapunov’s exponents. the delay feedback controller is designed, and along with the selection of the appropriate controller parameters, the chaotic phenomenon is quickly eliminated, bringing the system back to stable operation. keywords-chaos; chaos control; dfig; dfc; lyapunov’s exponents i. introduction chaos can be beneficial as it may speed up chemical reactions, enhance mixing, provide a powerful mechanism for heat and mass transfer, etc. however, in many situations, chaos is an undesirable phenomenon, it can lead to increased mechanical fatigue for irregular oscillations, and nonconvection energy absorption in a turbulent regime can lead to system parameters exceeding the safe level. chaos is a phenomenon that only occurs in nonlinear systems, sensitive to initial conditions, and non-periodic but obeying certain laws. a dynamic system with chaotic motion needs to meet the following conditions [1-2]:  the system has at least three independent variables.  the equation of motion must have nonlinear terms. in addition, the phase space of the system must have a dimension of not less than 3 to ensure the existence of divergent trajectories, be confined to a finite domain of the dynamics space, and ensure uniqueness of the orbit. first of all, we need to note that in a linear dynamic system, chaos never occurs. so, when we talk about chaos, we mean nonlinear systems. however, not all nonlinear systems have chaotic motion. there are different methods of detecting chaos such as the fourier analysis method, time responses, phase portraits, bifurcation diagram of the maximum value of the state variable over time, and calculations of lyapunov exponents used to illustrate the chaotic behavior when changing the characteristic value. the main interest of this paper is focused on the lyapunov exponent because it can be calculated with relative ease and it provides confirmation of the presence of chaos in the observed data [3]. when the average lyapunov exponent is calculated as positive, it indicates chaotic behavior occurring in the system. from that, the chaotic working area of the object is drawn, and a control method is proposed to bring the system to a stable working state, engineering, technology & applied science research vol. 13, no. 2, 2023, 10588-10594 10589 www.etasr.com van et al.: chaos control of doubly-fed induction generator via delayed feedback control extinguishing the self-sustaining oscillations with high amplitude and abnormal changes. due to the harsh working environment of wind farms, the dfig parameters can change with temperature, time, load conditions, etc. dfig is prone to faults such as gearbox faults, power converter faults, stator winding faults, rotor winding faults, velocity sensor faults, etc. [4-7], from which the system may fall into a state of chaotic operation, leading to poor working quality, which can be the cause of problems and failures. among electrical failures, insulation failures in the stator windings cause the majority (30%-40%) of induction machine failures, including dfigs [8-10]. although a dfig has a complex structure, prone to failure, it is still the most used structure in wind power systems due to its outstanding advantages. therefore, there have been many research works put forth to improve the quality and performance of the system [6, 11-16]. the research on bifurcation and chaos for the dfig system is very limited [17-23] and does not cover all the potential risks. the above studies have shown that, under certain operating conditions, a dfig can be chaotic. authors in [18, 20] evaluate that phenomenon based on computer simulations but have not evaluated it on a solid theoretical basis, or do not give specific conditions on which parameter changes in the system lead to chaos [20]. authors in [21] analyzed the phenomenon of chaos and presented several risks that make the dfig system chaotic. on the basis of theoretical analysis (algorithm to test 0-1) and through simulation, authors in [23] evaluated the stability and chaos of the system. the study also gives specific conditions of the parameter set causing chaos for the dfig, however the condition of 3 simultaneous faults (stator winding fault, rotor winding fault, and rotor speed sensor fault) rarely occurs in practice. this study demonstrates that dfig faces a chaotic phenomenon when the system parameters change in case of stator winding failure, based on theoretical analysis and simulations. from there, the delay response controller will be designed to eliminate chaos, return the system to stability and avoid possible risks. ii. mathematical model of dfig, chaos control, and delay feedback control method a. mathematical model of dfig one of the main control objectives for the dfig is the independent control of active and reactive power through decoupled control of rotor currents ��� and ��� [24]. the starting point for deducing the state-space model of the dfig is the voltage equations for the stator and rotor windings [24-25]: stator voltage in stator winding system: ��� = � �� + �� �� (1) rotor voltage in rotor winding system: ��� = � �� + ������ (2) rotor and stator flux: ��� = �� � + �� � �� = �� � + �� � (3) where: ��� = �� + ��� �� = �� + ��� converting (1) and (2) to the dq coordinate system, for any internal rotation with angular speed �� we get: � �� = � � + �� �� + ���ψ��� = � � + ����� + ���ψ� (4) where �� = � + �� the generator stator is connected to the grid with constant voltage and frequency. since the stator frequency is always identical to the grid frequency, the voltage drop across the stator resistor can be neglected in comparison with the voltage drop across the mutual inductance �� and the dissipation inductance ��� stator, which can be written as follows: �� = � � + �� �� => �� ≈ �� �� or �� ≈ �ω��� (5) from (3), we obtain: � = ! (ψ� − �� � ) &� = �� � + �� ' after suppressing the stator current � and the rotor flux &� , from system (4) we get: ⎩⎪ ⎨ ⎪⎧ � ,�� = − � .� + /�. 0 1 − ��� 1+ /�� . + ��0 �23 + �!� �1 + /��!4 �2 �567�� = . 1 − . + ���0 523 + !4 �2 (6) where 523 = &� /�� , 9 = 1 − ��; /(���� ) , <� = �� / � , <� = �� / � . after decoupling both equations into real and imaginary components, we obtain the complete system of electrical equations of dfig (7). ⎩⎪ ⎪⎪ ⎪⎨ ⎪⎪ ⎪⎪ ⎧ �>�?�� = − � .� + /�. 0 ��� + �� ��� + /�� . &��3 − �&��3 0 + �!� ��� − /��!4 ��� �>�@�� = − � .� + /�. 0 ��� − �� ��� + /�� . &��3 + �&��3 0 + �!� ��� − /��!4 ����a ?7�� = . ��� − . &��3 + ��&��3 + !4 ��� �a @7�� = . ��� − . &��3 − ��&��3 + !4 ��� (7) in grid voltage, the orientated coordinates are: ��� = �� , &��3 = 0, &��3 = &�3. engineering, technology & applied science research vol. 13, no. 2, 2023, 10588-10594 10590 www.etasr.com van et al.: chaos control of doubly-fed induction generator via delayed feedback control summarizing the equation system (7) yields the following state space model for the dfig in the grid voltage orientated reference frame (8): �d�� = ed + f� �� + f� �� (8) with: state vector d. = g��� , ��� , &��3 , &��3 i , stator voltage vector ��. = g��� , ��� i, as the input vector on the stator side, and stator voltage vector ��. = g��� , ��� i as the input vector on the rotor side. the system matrix a, the rotor input matrix f� and the stator input matrix f� may be written as: (9) b. chaos control and delayed feedback control method every parameter of the system has the potential to cause bifurcation and chaos, the idea of control is to bring these two properties towards its purpose, by adjusting the system parameters, or to hit the target by methods such system parameters transformation, changes in the structure of the system, input stimulus from outside, change the controller, or a control method based on the system's strange attractor set when a chaotic phenomenon occurs, bringing the trajectory to the target orbit with the new set parameter combination compatible with the old parameter. to do so, it is necessary to know the rate at which chaos or exponential growth increases and the oscillation amplitude of the system state variable. from there, a way to approach is by using accurate measurement equipment of system state variables and thus determining the stable and unstable working parameter areas, thereby determining the appropriate control method and the way to change the structure of the system if necessary. there are many methods of chaos control applied to electric drive systems and they have certain effects. the chaotic control method based on the delay feedback controller has been studied extensively [1, 26-30]. the delayed feedback control method, described in [31], is: j(k) = lmn(k − o) − n(k)p = lq(k) where τ is the delay time. if this time coincides with the period of i th periodic orbit o = <> , i.e. n(k) = n> (k), it does not change the periodic orbits in the system. choosing the appropriate weight k of the feedback, we can achieve the stabilization of the system. the delayed feedback control method is less complex and more responsive than other control methods. it allows for noninvasive stabilization in the sense that the control force disappears when the state has reached the target. authors in [32] showed that the simple self-feedback delay controller gives better results than the sliding mode self-feedback delay controller when applied to control chaotic behavior in the ifoc of a 3-phase induction motor. today, the dfc has become one of the most popular methods in chaos control research [33]. so far the number of published works on chaos control for dfig is very limited and has not covered all the problems. to the best of our knowledge there are no works that apply dfc method to control the dfig. this study aims to fill that gap. iii. chaotic phenomena and chaos control for dfig a. chaotic behavior analysis of dfig it can be seen from (7) that dfig is a multivariable and nonlinear system (which is a necessary condition for a chaotic motion system). dfig contains many parameters and the system works in harsh environments, therefore, the parameters can vary according to temperature, time, and system operating conditions. when the parameters of the system change, the system may appear to be chaotic. to clarify this issue, this study presents the chaotic phenomenon that occurs in dfigs in cases of stator winding failure (this is the problem that accounts for the majority of electrical problems for dfigs [8-10]). from the equation of motion of the rotor [6, 17], we combine with the first two equations of (7) to obtain a system of equations representing the rotor currents (ird, irq) and the rotor speed of dfig as follows: ⎩⎪ ⎪⎪ ⎨ ⎪⎪⎪ ⎧ �>�?�� = − � .� + /�. 0 ��� + (�� − �)��� − /�� � a !4 � �!� ��� $ /��!4 �� �>�@�� � $ � .� � /�. 0 ��� $ "�� $ �%��� � /�� . a !4 � �!� ��� �r�� � s; tuv !4a w! ��� $ xw � $ tuw <! (10) from that, the structure diagram of the system is obtained as can be seen in [34], with: y � ��� ; y; � ���; ys � �; [ � $ � .� � /�. 0; [; � /��!4 &�; [s � �!�; [\ � /��!4; [] � /��!4. &� ; [^ � stuv !4a ;w! ; [_ � xw ; [` � tuw . equation (10) will be abbreviated to: ayb � [ y � "�� $ ys%y; $ [;ys �[s��� $ [\��yb; � [ y; $ "�� $ ys%y � [] � [s��� ybs � [^y $ [_ys $ [`<! "11% engineering, technology & applied science research vol. 13, no. 2, 2023, 10588-10594 10591 www.etasr.com van et al.: chaos control of doubly-fed induction generator via delayed feedback control the system's main parameters used in our simulations are listed in table i [25]. table i. main parameters of the dfig system rated power (p) 1.5mw grid voltage (u) 690v grid frequency (f) 50 hz moment of inertia (j) 2kgm2 pole pairs (np) 3 damping coefficient (d) 0.001nm/rad/s load torque (tl) 3n.m stator resistance (rs) 2.139mc stator inductance (ls) 4.05mh rotor resistance (rr) 2.139mc rotor inductance (lr) 4.09mh mutual inductance(lm) 4mh from the structural model of the system above, simulations in matlab were conducted with the following algorithm: first, simulate with the system's parameter set in normal mode, and then, simulate the case of stator winding failure, in order to be able to clarify the stable working state of the system in normal mode and the system falling into a chaotic state when the parameters of the stator windings change. in the normal operating mode, the simulation results show that the phase trajectories of ��� , ��� and � oscillated at the beginning, but soon they stabilized (figures 1 and 2). the results of calculating the lyapunov exponent also show that all 3 lyapunov exponents are negative (figure 3). thus, with a normal set of parameters, the system is stable. fig. 1. time series diagrams of ���, ���, �. fig. 2. phase trajectory diagram y , y;, ys ( ���, ��� ,�). fig. 3. variation of lyapunov's exponent over time when the system is operating under normal conditions. when stator winding failures occur, the inductance of the coil changes to other values. through the simulation on matlab with the variation of the inductance parameter of the stator winding, the results in figures 4-7 show that the orbit is attracted to the basin of attraction, but it is not stable there. the phase orbit is confined, which is possible to approach arbitrarily close to some point of the basin of attraction, but never to repeat the same at a later point in time. at the same time, the results of calculating the lyapunov exponent (figure 8 and table ii) show that the system always has 2 positive lyapunov’s exponents. thus, the dfig system is chaotic. fig. 4. phase trajectory diagram showing chaotic orbits at ls = 3.8mh. fig. 5. phase trajectory diagram showing chaotic orbits at ls = 3.3mh. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 time(s) -400 -300 -200 -100 0 100 200 300 400 ird irq w l y a p u n o v e x p o n e n ts engineering, technology & applied science research vol. 13, no. 2, 2023, 10588-10594 10592 www.etasr.com van et al.: chaos control of doubly-fed induction generator via delayed feedback control fig. 6. phase trajectory diagram showing chaotic orbits at ls = 2.7 mh. fig. 7. phase trajectory diagram showing chaotic orbits at ls = 2.2mh. fig. 8. variation of lyapunov's exponent over time when the system is chaotic. table ii. lyapunov's exponent time de df dg 0.05 3713.00 3.13 -794.31 0.15 3713.90 3.10 -862.60 0.25 3714.08 3.09 -866.10 0.35 3714.16 3.09 -848.98 0.45 3714.20 3.09 -831.52 0.55 3714.23 3.09 -852.85 0.65 3714.25 3.09 -849.68 0.75 3714.27 3.09 -859.42 0.85 3714.28 3.09 -858.06 0.95 3714.28 3.09 -854.43 1.00 3714.29 3.09 -852.66 b. chaos control for dfig as described above, the controller's structure aimed to eliminate the chaos that has occurred for dfig is: ⎩⎪⎨ ⎪⎧ yb � [ y � "�� $ ys%y; $ [;ys �[s��� $ [\�� � l my "k – o % $ y p yb; � [ y; $ "�� $ ys%y �[] � [s��� � l;my;"k – o;% $ y;p ybs � [^y $ [_ys $ [`<! (12) where k1, k2 are the experimentally tunable weights of the perturbation. we provide the following operating schedule: when the system is chaotic, at 0.1s a delay feedback controller will be added to the system. the system achieved different results during the conducted simulations with different selected values of l , l; and o , o;. the simulation results in figure 8 with k1 = 22, k2 = 25, o = 0.001, and o; = 0.01 show that the first time the phase trajectory of the system wanders in the confined space domain, then (when the controller is inserted) it is attracted to the equilibrium point and stabilizes there. similarly, with different values of k1, k2, and o , o; , the trajectory of y in the time domain also shows that the stability of the system is different corresponding to the selected parameter set (figures 9 to 14). fig. 9. phase trajectory diagram between y , y; and ys with: l =15, l;=10, o =0.001, o;=0.01. fig. 10. time plot with l =15, l;=10, o =0.005, o;=0.0001 l y a p u n o v e x p o n e n ts x 1 engineering, technology & applied science research vol. 13, no. 2, 2023, 10588-10594 10593 www.etasr.com van et al.: chaos control of doubly-fed induction generator via delayed feedback control fig. 11. time plot with l =15, l;=10, o =0.001, o;=0.0001 fig. 12. time plot with l =15, l;=10, o =0.0001, o;=0.0001. fig. 13. time plot with l =25, l;=10, o =0.005, o;=0.0001. the above simulation results show that, with the designed control law based on the delayed feedback control method, the system eliminated the chaotic phenomenon and returned to a stable state. by choosing the values of the appropriate parameters k1, k2, and o , o;, the system will achieve optimum quality. fig. 14. time plot with l =25, l;=10, o =0.001, o;=0.0001 iv. conclusion chaos is harmful to dfig. if this phenomenon is not detected and eliminated in time, the system's working quality will be poor, and the error can spread and cause great damage. this study has demonstrated the chaotic phenomenon that occurs for the dfig when the stator winding is faulty, which is confirmed by calculating the lyapunov exponent that always has two positive exponents, and simulation results show that the system has revealed the nature of chaos. this study proposes a control method to eliminate chaos for dfig. the delay feedback control method is selected and designed. before 0.1s, the curve shows strong fluctuations. at 0.1s a delay feedback controller was added to the system, the chaos was quickly eliminated, the system returns to stability, which can prevent further damage to the dfig. acknowledgment this work was supported by the institute for control engineering and automationicea for their support. and the university of transport and communication for sponsoring to implement of the university-level science and technology project, code t2022-dt-003. references [1] k. t. chau and z. wang, chaos in electric drive systems: analysis, control and application. new york, ny, usa: wiley, 2011. 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[34] p. q. nguyen, matlab & simulink for automation engineers. hanoi, vietnam: science and technics publishing house, 2004. microsoft word etasr_v13_n3_pp10703-10707 engineering, technology & applied science research vol. 13, no. 3, 2023, 10703-10707 10703 www.etasr.com albadran: the effect of pilot reuse factor on massive mimo spectral efficiency the effect of pilot reuse factor on massive mimo spectral efficiency saleh m. albadran electrical engineering department, university of hail, saudi arabia s.abadran@uoh.edu.sa (corresponding author) received: 23 december2023 | revised: 18 march 2023 and 1 april 2023 | accepted: 4 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5605 abstract due to their much increased spatial resolution and array gain, large-scale antenna arrays have the potential to significantly enhance the spectral efficiency of wireless systems. recent research in the area of massive multiple-input multiple-output (mimo) antennas shows that user channels are enhanced as the number of antennas at the base stations (bss) rises, allowing achieving high signal improvement with minimum inter-user interference. the combined effects of the pilot reuse factor and the bs number of antennas on average overall spectral efficiency in huge mimo antennas will be investigated. to examine the se of these receivers, several channel estimators will be utilized, including lmmse, zf, and mr methods. theoretically, bs could offer a substantially higher average total se if it had more antennas. keywords-massive mimo; l-mmse; spectral effecincy; base station; pilot reuse factor; zero forcing; machine to machine; channel state information i. introduction the amount of mobile data traffic worldwide in 2017 was 12.6 times greater than what it was in 2012. the entire amount of mobile traffic has grown by a factor of 10 between 2019 and 2022 [1], and this rise continues today. therefore, the cellular infrastructure of the future must be ready to serve new uses and, specifically, to satisfy the users' needs and meet the current wireless communication standards. particularly, the use of smart devices and machine-to-machine (m2m) communications systems has dramatically increased mobile data traffic over the past ten years across most applications and industries. the international telecommunication union (itu) has recently predicted that mobile traffic worldwide will grow by a factor of 660 between 2010 and 2030. every decade, mobile technologies undergo a dramatic development and the demand for wireless data is only going to increase. the more data we use, the more we need networks with faster speeds and wider coverage to keep up. each new technology generation has offered considerable performance improvements. these quick variations are reactions to the needed capacity from the significant data increase over the previous decade, mostly from video streaming. the resolution of video streaming capabilities is also rising, and phones supporting 4k video will require a higher data rate per user. users' watching duration is also rising; watching long tv shows and movies via streaming video is now common. this tendency appears to have no end in sight. massive or big-scale multiple input multiple output (mimo) technology has emerged as a viable technique for future wireless networks [2]. despite the fact that massive mimo demonstrates enormous capacity of supporting a substantial volume of data rate and wireless links, it is not that easy to implement such a system due to the high cost of hardware and higher consumption of power. researchers have been investigating energy efficient initiatives to maximize system efficiency in order to establish sustainable and clean wireless systems. massive mimo is a combination many innovations that have been combined in order to create a solution that is able to deliver incredible results. what all these technologies have in common is that they are able to significantly improve the performance of base stations (bss) by providing them with the ability to increase their capacity at cell sites. they do this primarily by improving the link between users and bss through transmitting and receiving more data from users at cell sites on both sides of the connection simultaneously. wireless networks have limited available electromagnetic spectrum while the need for higher data rates continues to increase. to reach future demands, wireless communications must be industrialized with the introduction of new and sophisticated technologies [3]. one of the recent proposed techniques is massive mimo, which has a more promising potential compared to other techniques. basically, the idea of this technology is about providing a bs with a big number of antennas to cover a much smaller number of users [4]. the time division duplex (tdd) mode of operation is used to obtain accurate channel status information (csi) [5], which is vital for maximum effectiveness and getting the advantages of this technique. since the number of training sequences is directly proportional to the number of users, any number of antennas in the bs can be achieved. large-scale mimo is a system that consists of a couple of hundreds antennas serving a large number of end users at the same time while using the same frequency [6]. this kind of engineering, technology & applied science research vol. 13, no. 3, 2023, 10703-10707 10704 www.etasr.com albadran: the effect of pilot reuse factor on massive mimo spectral efficiency technology has several advantages such as increasing spectral efficiency (se) to achieve the future needs, mainly in dense areas. also, it will provide a secure network to maintain information privacy [7]. the cost of the transmitter/receiver components will be reduced due to its lower complexity and the power efficiency should be improved while the signal processing will be much simpler. the accuracy of channel estimation is a critical factor that has the ability to affect se and for that reason it grabs the attention of researchers [8, 9]. some estimation methods are utilized in channel estimation, one of them is the minimum mean square error (mmse). this method is known for its good performing behavior that meets with any value of signal to noise ratio (snr). other methods, such as maximum ratio (mr) and zero-forcing (zf), will be investigated. to obtain maximum performance we need to have perfect channel matrix knowledge [10]. ii. literature review several studies have investigated the effect of the pilot reuse factor on the spectral efficiency of massive mimo systems. in [11], it was shown that increasing the pilot reuse factor can improve the spectral efficiency up to a certain point, after which the performance saturates. the authors also proposed a new pilot design scheme based on the use of orthogonal pilot sequences, which can further improve the performance of massive mimo systems. authors in [12] analyzed the impact of pilot reuse factor on the downlink spectral efficiency of massive mimo systems using different channel estimation techniques. the results showed that the optimal pilot reuse factor depends on system parameters such as the number of antennas, the channel coherence time, and the receiver noise level. the authors also proposed a new pilot allocation scheme based on the use of non-uniform pilot density, which can further improve the spectral efficiency of massive mimo systems. authors in [13] investigated the effect of pilot reuse factor on the uplink spectral efficiency of massive mimo systems using a realistic channel model. the results showed that increasing the pilot reuse factor can improve se up to a certain point, after which the performance saturates. the authors also proposed a new pilot allocation scheme based on the use of clustered pilot sequences, which can further improve the se of massive mimo systems. overall, the literature suggests that the choice of pilot reuse factor is an important design parameter for massive mimo systems, and that different pilot allocation schemes can be used to optimize the system performance. however, further research is needed to investigate the optimal pilot reuse factor for different system configurations and its impact on other performance metrics. in this study, we were able to identify the ideal value for the pilot reuse factors for 3 distinct channel estimators based on the number of antennas in the bs and the number of active users. our proposed system will always run at its greatest se due to these ideal pilot reuse factor values. notation: in this study, column vectors, such as x, are denoted by lower-case, bold notations. matrix symbols x, however, are upper-case, bold notations. the symbols for transpose, conjugate, and conjugate transpose x are �� , �∗ , and �� , respectively. i is the representation of the identity matrix of appropriate dimensions. ���� stands for the x operation expected value, and ���| � stands for x conditional expected value that is related to y. in the expression �~� (��, �), the covariance matrix is q and the mean is ��. iii. channel and system model the primary goal of our study is to examine the related average sum spectral efficiency for the ul channel that is susceptible to interference due to the behavior of wireless channels. the system modeling comprises of a large antenna number in the bs terminal coupled to a small number of user terminals. the system used is a subset of massive mimo, where the protocol utilized between the two sides of the link is tdd [14]. because the accuracy of estimation in tdd does not depend on n, we can use a high number of bs antennas [15]. we maintain continuous csi to identify ul data information by using reciprocity benefit of the channel. from one terminal to the other, h represents the block-fading and it has a rayleigh model as �~� (�, �), while � = ������ the bs terminal is aware of the statistical distribution. pilot for channel estimate serves as the foundation for the ul system model, and y symbolizes the signal that is received by the bs. = � + �� (1) where the received signal is denoted by d ∈ ℂ. it could be the data signal or a predetermined pilot. the average power of the signal is: � = ��|�|�� (2) channel noise is represented by n, and is composed of the following parts: � = �� !"# + �!$ (3) where �!$ is the interfering noise caused by other messages and �� !"# is the independent receiver noise with zero mean and (%&'( )) covariance. we assume that �!$ has a zero mean, ���!$�!$*� covariance, and is represented by s. +, = ���!$�!$* |,� is the definition of the conditional covariance matrix, while , represents the realization of the channel. we are supposing that r spectral norm is bounded uniformly independent of the bs's antenna number [16]. the matrix of channel covariance is produced by the exponential correlation model, which is described in greater detail in [17]. this correlation model presupposes that the value of r has the following elements (i, j): -�. = / 01 234 , 5 ≤ 7 0(1 234 )∗, 5 > 7 (4) where r represents a correlation coefficient between adjacent channels and 0 is the scaling factor. the factor of correlation value is restricted to the range from 0 to 1, and its phasor ∠1 denotes the angle of departure or arrival. this obviously is not the most suitable model for scenarios in the actual world. however, it is still a straightforward model with a manageable amount of engineering, technology & applied science research vol. 13, no. 3, 2023, 10703-10707 10705 www.etasr.com albadran: the effect of pilot reuse factor on massive mimo spectral efficiency parameters, making it possible to investigate how the correlation factor affects the estimation of the huge mimo channel [18]. the correlation factor |r| in r represents the eigenvalue spread, and ∠1 defines the associated eigenvectors. we take r to be a real number since the the mean square error is not affected by the angle of r. by comparing the signal received by bs y in (1) to the known pilot uplink signal d, where user equipment power corresponds to (�:; ), we may estimate the channel h. in this paper, different types of estimators are used, the first one is mmse. the following is a representation of the estimation of channel realization: �< = �∗�=>3?@ (5) the r matrix, the average power, the received signal covariance, and the noise, make up the y covariance matrix, which is shown as follows: => = �� *� = � �:; + a + %&'( ) (6) the following is a representation of the covariance matrix of error that is used to calculate the overall mse: b = � cd �< − �fg d �< − �fh = � − �:; �=>3?� (7) we may get the entire value of mse by finding the c value, which is the error covariance matrix shown in (8): iaj = kl(b) = � c m�< − �m� (h (8) the channel may be described as a mixture of two components based on the prior observations: � = �< + n (9) where the process of unknown error estimation is represented by n, and the value of the mmse estimate is marked by h. the mean of the values, �< and n , is 0 for both and they are uncorrelated [19]. the �< covariance matrix is generated as �o �< �< *p = � − b, and the n covariance matrix as �� nng� = b. we can disregard all the correlation matrices in the event that the conditions of the channel are favorable and the signal's interferences from nearby cells are faint. by applying that, zf combining can be generated [20]. by knowing that the combining vector's normalization has no effect on the instantaneous up link signal to noise ratio, we can generate mr combining. the primary difference is that we no longer employ exact channels and instead use estimated channels (which are unknown in practice). in contrast to the preceding systems, mr does not need any matrix inversion. since not all ues in actuality have a very low snr, it is anticipated that mr scheme will yield lower se compared to other schemes. it is assumed that there are 16 square cells in a 4×4 grid, a wrap-around topology is taken into consideration, in which every cell has numerous locations and any arbitrary bs and ue are always separated by the 9 combinations' shortest distance. the shortest path is used to derive the angular characteristics. four distinct methods of reusing pilot sequences between cells are depicted, which means that a higher pilot reuse factor denotes the need for more orthogonal pilot sequences. the distribution and reuse of the qr pilot sequences among the ues and cells can be done in a variety of ways [21]. unless otherwise indicated, we assume qr = st pilots, where f is an integer known as pilot reuse factor. that indicates that we have f times more pilots than user equipment in each cell and that a fraction of 1/f of the cells reuses the same subset of pilots. in the running example, we consider su�1,2,4,8,16�, where the same pilot group is considered to consist of the cells that employ the same pilots. every ue in a cell has a pilot allocated at random, thus the kth ue in two adjacent cells that is related to the same group of pilot utilizes the same pilot. iv. numerical illustrations in this part, we provide illustrative simulations to demonstrate how the se performs when based on various receive combining schemes and different pilot reuse factors. the use of the communication system toolbox in matlab allows us to analyze our model. to create the figures where the analysis is done, several scripts were built. the system parameters are shown in table i. v. system parameters parameter value cells number 16 number of bs antennas m= 40,70,100 number of users/cell k =10 pilot reuse factor s = 1, 2, 4, 8, 16 uplink and downlink transmit power 20 dbm for the downlink and uplink channels, the average signal to noise ratios are �[\tr(�)/`%ab( and �batr(�)/`%[\( , respectively. when using low and high snr values, we take the value of snr into account. we presume that the percentages of uplink and downlink data are identical and set at 0.45. using this assumption, we obtain equal uplink and downlink. k = 10 user equipment per cell and various numbers of bs antennas were taken into account in the simulations. each block contains fk pilots, with the remaining cr − sk samples being utilized for uplink data transfer. we utilized the channel model with gaussian local scattering. figure 1 shows the average uplink se as a function of the pilot reuse factor with 100 bs antennas. the l-mmse combination provides the highest se compared to zf and mr schemes. by increasing the pilot reuse factor form 1 to 2, both schemes l-mmse and zr are having higher se while the mr is having a lower average sum se. once the value of f is increased from 2 to 4, the se keeps increasing slightly for lmmse scheme while it is decreasing for the two other schemes, zf and mr. as the pilot reuse factor is raised from 4 to 8 and 16, all the 3 schemes deteriorate quickly. by using 70 antennas at the bs, figure 2 shows lower average sum se compared to the 100 antennas of figure 1 due to the increase interference that cannot be canceled easily. in comparison to zf and mr combining methods, the se provided by the l-mmse scheme is the greatest. the lmmse and zr systems have both greater se as a result of raising the pilot reuse factor from 1 to 2, whereas the mr has a engineering, technology & applied science research vol. 13, no. 3, 2023, 10703-10707 10706 www.etasr.com albadran: the effect of pilot reuse factor on massive mimo spectral efficiency lower average sum se. when f is increased from 2 to 4, the se for the l-mmse scheme continues to marginally grow while falling for the 2 other schemes. all the schemes quickly degrade as the pilot reuse factor is increased from 4 to 8 and 16 respectively. due to the increased interference that is difficult to be eliminated when utilizing 40 antennas at the bs, figure 3 displays the lowest average total se. raising f from 1 to 2 results in increased se for the l-mmse and zf systems, while the mr has a lower average sum se. all 3 schemes rapidly degrade as the f is increased from 2 to 4, 8, and 16 respectively. even though the l-mmse scheme provides higher se, it has much more complexity than zf and mr. fig. 1. average uplink sum spectral effeciency as a function of pilot reuse factor for 100 bs antennas. fig. 2. average uplink sum spectral effeciency as a function of pilot reuse factor for 70 bs antennas. by comparing figures 1-3 in terms of using the l-mmse scheme, it is obvious that the higher the number of antennas in the bs, the higher the se. when the number of antennas is equal to 100 (figure 1), the se exceeds 51 [bit/second/hz/cell] while the pilot reuse factor is equal to 2 or 4. if the number of antennas in the bs is equal to 70 and the f is either 2 or 4 (figure 2), the se is less than 48 [bit/second/hz/cell]. on the other hand, when the number of antennas in the bs is equal to 40 and f=2 (figure 3), the se is less than 33 [bit/second/hz/cell]. fig. 3. average uplink sum spectral effeciency as a function of pilot reuse factor for 40 bs antennas. if we compare the figures 1-3 considering the zf scheme, it is also clear that the higher the number of antennas in the bs, the higher the se. when the number of the antennas is equal to 100 in the bs (figure 1) the se is equal to 40 [bit/second/hz/cell] if the pilot reuse factor is equal to 2 or 4. when the number of antennas in the bs is equal to 70 and the pilot reuse factor is either 2 or 4 (figure 2), the se is less than 37 [bit/second/hz/cell], and when the number of antennas in the bs is equal to 40 and the pilot reuse factor is equal 2 or 4 (figure 3), the se is equal to 33 [bit/second/hz/cell]. when comparing figures 1-3 while considering the mr scheme, it is clear again that if there are more antennas in the bs, the se will be higher. when the number of antennas is equal to 100 in the bs (figure 1) the se is equal to 24 [bit/second/hz/cell] if the pilot reuse factor is equal to 2. if the number of antennas in the bs is equal to 70 and the pilot reuse factor is 2 (figure 2), the se is less than 22 [bit/second/hz/cell]. finally, when the number of antennas in the bs is equal to 40 and the pilot reuse factor is equal to 2 or 4 (figure 3), the se is less than 33 [bit/second/hz/cell]. vi. conclusion in this paper, we examined the combined impact of the pilot reuse factor and the base station number of antennas on the average total spectral efficiency in massive mimo. different channel estimators, such as lmmse, zf, and mr schemes, have been used to investigate the spectral efficiency of these receivers. according to the simulation results, a larger number of antennas in bs would provide a significantly higher average total se. on a larger number of base station antennas, raising the pilot reuse factor from 1 to 2 for both l-mmse and zr schemes would give greater spectral efficiency. in addition, it is noticeable that the 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[21] l. you, x. gao, x.-g. xia, n. ma, and y. peng, "pilot reuse for massive mimo transmission over spatially correlated rayleigh fading channels," ieee transactions on wireless communications, vol. 14, no. 6, pp. 3352–3366, jun. 2015, https://doi.org/10.1109/twc.2015. 2404839. microsoft word etasr_v13_n2_pp10377-10383 engineering, technology & applied science research vol. 13, no. 2, 2023, 10377-10383 10377 www.etasr.com malamsha & nyambo: multi-level association rule mining for the discovery of strong … multi-level association rule mining for the discovery of strong underrepresented patterns the case study of small dairy farms in tanzania glory c. malamsha nelson mandela african institution of science and technology, tanzania malamshag@nm-aist.ac.tz (corresponding author) devotha g. nyambo nelson mandela african institution of science and technology, tanzania devotha.nyambo@nm-aist.ac.tz received: 16 january 2023 | revised: 27 january 2023 | accepted: 30 january 2023 abstract increasing the milk production of small dairy producers is necessary to cover the increase in milk demand in tanzania. currently, the population of people in both tanzania and the world has increased and is predicted to increase more in the year 2050. the use of multilevel association rule mining methods to mine strong patterns among smallholder dairy farmers could help in identifying the best dairy farming practices and increase their milk production by adopting them. this study employed multi-level association rule mining to discover strong rules in three clusters, resulting in three levels of rules in each cluster. these three clusters were high, medium, and low milk producers. rules were obtained for feeding practices, milk production, and breeding and health practices. these rules represent strong patterns among smallholder dairy farmers that could help them improve their dairy farming practices and have a gradual increase in milk production, from low to medium and from medium to higher milk production. smallholder dairy producers would be provided with recommendations on their dairy farming practices, using rules based on the cluster to which they belong that could help them achieve higher milk production. keywords-association rules mining; dairy farming; smallholder dairy producers; milk yield i. introduction association rules are if-then statements that show the probability of relationships between data items or variables within large datasets [1, 2]. association rule mining is used to discover interesting patterns between item sets in large databases [3-5]. the patterns discovered from association rule mining can be represented as rules, trees, or clusters which a user can interpret into knowledge [3]. pattern matching is essential to identify relationships in datasets, and association rule extraction is among the most common techniques used in text mining [6]. association rule mining provides association rules that exceed the user-specified minimum support and the minimum confidence level threshold [7]. a minimum of 145 days is required for small dairy farmers to learn farming strategies from other farmers in order to increase milk production [8]. this is a lot of time for a farmer who also needs to perform other activities. to minimize learning time, recommendations can be derived for small farmers using association rule mining methods. association rule mining can mine data at single and multiple levels of abstraction depending on the approach used [9]. as sparse data make it difficult to identify strong rules in low or original abstract layers, there is a need to mine strong rules from multiple abstract layers. mining association rules in multiple abstract layers and formulate multilevel association rules is called multilevel association rule mining [10]. recommendation systems use collaborative, content-based, and demographic filtering methods to search and filter large volumes of data and suggest items to users [11, 12]. the syragri recommender system was created to provide recommendations to farmers on their practices. in [13], a hybrid approach was used for recommendation modeling to provide new items not rated by a user or rated by some users. as indian farmers face various problems, such as insufficient harvesting and transportation methods, the government seeks ways to help them. the collaborative recommendation system for agriculture sector (crsas) was developed using english, hindi, and marathi to provide recommendations to farmers on various available agricultural programs and increase their knowledge of available government schemes [14]. trustworthy recommendation systems are important and improve the ability of users to use them due to factors such as accuracy and good explanations [15]. engineering, technology & applied science research vol. 13, no. 2, 2023, 10377-10383 10378 www.etasr.com malamsha & nyambo: multi-level association rule mining for the discovery of strong … the tanzanian population was 34,443,603 in 2002, 44,928,923 in 2012, and was projected to increase to 59,441,988 in 2021 [16]. currently, tanzania’s population increased to 61,741,120 people in 2022 [17], while the population worldwide is expected to increase to 8.9 billion people in 2050 from 7.9 billion in 2014 [18]. as the population and the per capita income increase, the demand for protein nutrients increases [19]. ruminants, including cows, can be fed human-inedible plants such as alfalfa, pasture, and hay and produce high-quality protein products such as milk and meat [18]. these high-quality protein nutrient products would help meet the demands of an increasing population of people. therefore, milk production as a protein source needs to be increased to meet the demands of the population. small dairy farmers produce food for substantial populations of the world with small land holdings of less than 2 hectares [20]. smallholder dairy farmers use low production costs, such as low-cost feeds and low technology, to produce milk which is cost-advantageous and helps solve the problem of food insecurity by providing milk proteins [21]. the challenges that small farmers face include poverty, food insecurity, lack of knowledge, lack of technical know-how, and poor support service [20, 21]. in [22], the k-means and self-organizing map (som) models were used to group small tanzanian dairy farmers into six clusters from pearl data. farmer groups are a good tool to facilitate the development of small dairy farmers from subsistence to commercialization [22]. multilevel association rule mining through the apriori algorithm can be used to identify strong rules among various farmer groups that will ease the provision of recommendations to particular groups. grouping farmers into appropriate farm groups, based on their characteristics, could simplify the use of interventions and strategies to improve milk production [22]. recommendation systems have been currently used to develop models using big data to facilitate decision-making activities, including increasing farm yields [13]. farm groups can be analyzed in more detail and hence, recommendations can be provided on how to increase milk yield. these recommendations would guide farmers to improve from low to medium and then achieve high milk production. given these advancements, this study presents a multilevel association rule analysis as a data mining method to discover important underrepresented patterns in small dairy producer systems. tanzania's dairy farmers were used as a case study but this method can be replicated in any country with similar characteristics. ii. methodology the extraction of rules in the dataset was performed using a multilevel association rule mining method with multiple levels of abstraction [9]. the application of multilevel mining of rules is increasing, as it is necessary to acquire precise information in various fields [23]. many strong association rules are not obtained at a single level of abstraction [24]. multi-level association rule mining requires viewing rules among dairy farmers at different multiple levels of abstraction. this study adopted a pre-clustered dataset with 6 dairy production clusters [22]. the 6 clusters were evaluated based on their dairy production performance using traits such as vaccination frequency and milk production [25]. this study used 3 clusters to represent high, medium, and low dairy producers. high dairy producers were identified as cluster 1 (1180 households), medium dairy producers were identified as cluster 2 (516 households), and low dairy producers were identified as cluster 3 (295 households). in [25], cluster 1 had the best performance of 53%, while clusters 2 and 3 had 43% and 33% performance in product traits, respectively. the dataset consisted of 38 production traits that were represented with categorical data values. table i shows the production traits, data types, and range of values of this dataset. this study used the apriori algorithm used to mine the association rules. this algorithm generates sets of frequent item sets in a database in iterations using a bottom-up approach by adding one item at a time [3]. the evaluation metrics used were the support, confidence, and lift values. support and confidence are the two basic metrics in identifying association rules [2-4] while this study aimed to have a lift value greater than 1 to indicate stronger rules [7-26]. support is defined as the proportion of records that contain xy to the overall records in the database, whereas confidence is defined as the proportion of the number of transactions that contain xy to the overall records that contain x [4]. lift can be interpreted as the deviation of the support of the whole rule from the support expected under independence, given the support of both sides of the rule [7], while x and y are antecedents and subsequents of the extracted association rule, respectively. rule: x ⇒ y support �� = ������� ��� �� ��������� ������� � �!� ����"��� (1) confidence )��* = ������� ��� ������� �� (2) [4] lift ⇒ �� = ������� � ∪ �� ������� �� ������� ��� (3) [7] filtering of the rules was performed in various groups to obtain the important rules in each category with minimum support and minimum confidence for each cluster. minimum support was selected based on the frequency of items in the various groups to extract the association rules [10]. three levels of rules were obtained in each cluster. the dominating production traits were removed after levels 1 and 2 to obtain more rules with unique production traits in all clusters. minimum support and confidence were also reduced at levels 2 and level 3 of all clusters to obtain unique rules. iii. results multilevel association analysis was performed for the 3 clusters. for each cluster, level 1 included rules on feeding and yield practices, level 2 included rules on health and breeding practices, and level 3 consisted of rules on breeding and yield practices. a. cluster 1: high milk producers 1) level 1 level 1 included 81 rules from the high milk-producing cluster, with minimum support of 0.6 and minimum confidence of 0.95, and lift range between 1.003 and 1.29. strong rules engineering, technology & applied science research vol. 13, no. 2, 2023, 10377-10383 10379 www.etasr.com malamsha & nyambo: multi-level association rule mining for the discovery of strong … with lift values of 1.29, high confidence levels above 99%, and support range of 61-73% were found. the use of only stallfeeding systems in the rainy and dry seasons and bull breeding for the last calving had a high lift value of 1.29 with a support of 67%. farmers owned 1 to 3 cows, they had frequent visits from 1 to 9 extension officers per year, no land for fodder production, no employees, and no training in dairy care at a high lift value of 1.29 with support ranging from 61% to 69%. other traits included farmers preferring bull breeding, 1 to 7 years of attending school, no fodder purchases, and no household members participating in the farmer groups, so the practice of farm activities usually depends on the basic knowledge of dairy farming. table i. production features used in multilevel association rule mining s/n production features data type range of values 1 feeding system used during rainy season nominal mainly grazing, mainly stall, only ggazing, only stall feeding 2 feeding system used during the dry nominal mainly grazing, mainly stall, only ggazing, only stall feeding 3 reasons for choosing management (feeding) system nominal prevents diseases, cheap, extension officer advice, geographic conditions, insufficient land, large tracts of land, other reasons 4 months which crop residue used for feeding discrete 1-12 5 months which concentrates are used for feeding discrete 1-12 6 months which fodder/feeds were purchased discrete 1-12 7 watering frequency of the cattle discrete 1-4 8 distance to water source (kn) interval less than 1, 1-3, 3-5, 6-10 9 area under fodder production (acres) interval less than 0.5, 0.5-1, 1.1-2.5, 3.5-5, 5.5-10 10 breed rank 1 nominal ayrshire, cross, don’t know, friesian, holstein, jersey 11 breed rank 2 nominal ayrshire, cross, don’t know, friesian, guernsey, holstein, jersey, other 12 breed rank 3 nominal ayrshire, cross, don’t know, friesian, guernsey, holstein, jersey 13 traits rank 1 nominal milk quantity traits, body weight traits, calving traits, carcass traits, dairy type traits, disease traits, growth rate traits, milk feed traits, milk quality traits, reproductive traits, udder traits, other traits 14 traits rank 2 nominal milk quantity traits, body weight traits, calving traits, carcass traits, dairy type traits, disease traits, growth rate traits, milk feed traits, milk quality traits, reproductive traits, udder traits, other traits 15 traits rank 3 nominal milk quantity traits, body weight traits, calving traits, carcass traits, dairy type traits, disease traits, growth rate traits, milk feed traits, milk quality traits, reproductive traits, udder traits, other traits 16 breeding method used during last calving boolean bull or artificial insemination 17 preferred breeding method boolean bull or artificial insemination 18 distance to breeding service provider interval less than 1, 1-5, 6-15, 16-30, above 30 19 frequency of deworming cattle discrete 0-4 20 self-deworming service boolean yes or no 21 frequency of spraying cattle for pest control discrete 0-7 22 frequency of vaccinating the cows discrete 0-4 23 frequency of visit by extension officer interval none, 1-9, 10-29, 30-49, 50 and above 24 training nominal no training, one day training, one week training, two weeks training, more than one month training 25 experience in dairy farming discrete 3, 8, 13, 18, 23, 28, 35, 45, 50 26 years of schooling of smallholder farmers interval 0, 1-7, 8-11, 12-16, above 16 27 number of employees discrete 0-3 28 household member in a farmer group nominal head household, son, spouse, daughter, other 29 total land holding nominal average, below average, large 30 total number of cattle interval 1-3, 4-6, 7-10, 11-16, 17-20, above 20 31 number of livestock interval 1-20, 21-40, 41-60, 61-80, 81-100, hundreds, thousands 32 preferred buyers nominal dairy chilling plants, hotels, individual consumers, milk collection center, other institutions, private milk traders 33 distance to milk buyers interval 1-10, 11-20, above 20 34 distance to market interval less than 1, 1-5, 6-10 35 milk reserves for home consumption nominal above average, average, low 36 liters of milk sold nominal above average, average, below average 37 peak milk production of best cow nominal above average, average, below average 38 number of milking cows interval 1-3, 4-8, 9-15 2) level 2 at this level, the minimum support was adjusted to 0.22, the minimum confidence to 0.7, and the lift range was 1.02 to 1.43 for the 86 rules obtained. at lift values of 1.3, farmers dewormed their cattle 3 times a year, their distances to the market and the breeding provider were 1 to 5 kilometers, they sprayed their cattle 6 times a year, and did not self-deworm on their cattle. at lift values greater than 1.2, the cattle vaccination frequency was twice a year, the liters of milk sold by farmers were average, farmers used concentrate for 3 months, and their owned total land was average. at 1.1 lift, the number of livestock was not identified, the preferred buyers were individual consumers, the watering frequency was twice a day, and the milk production of the best cow was average. engineering, technology & applied science research vol. 13, no. 2, 2023, 10377-10383 10380 www.etasr.com malamsha & nyambo: multi-level association rule mining for the discovery of strong … 3) level 3 level 3 had 84 rules, where the minimum support was 0.164, the minimum confidence level was 0.67, and lift range was between 1.04 and 3.57. strong rules were aligned from 80% to 100% confidence level with lift values greater than 1.9 and low support from 16.4%. these rules included preferred breed rank types and milk quantity traits in trait rank 1, while farmers owned 4 to 6 cattle and had 8 years of experience in dairy farming. the preferred breed rank types were identified at a lift of 3.5, where breed rank 1 was friesian, breed rank 2 was ayrshire, and breed rank 3 was jersey. some farmers had no preferred breed types in all 3 breed ranks but had eight years of experience in dairy farming at a lift of 2.0. farmers preferred milk quality traits in trait rank 2, had average liters of milk sold, and animals were fed crop residue for 6 months with a lift value of 2.0. some farmers also had 13 years of dairy farming experience and chose the feeding system for disease prevention. b. cluster 2: medium milk producers 1) level 1 in level 1, 0.4 minimum support and 0.86 minimum confidence level were used to obtain 100 rules from medium milk producers at a lift range between 1.07 and 1.39. strong rules were located in two parts. the rules of the first part had a confidence level of 100%, 0.4-0.41 support, and 1.39 lift range. the preferred breeding method was artificial insemination at a confidence level of 100%, and farmers owned 1 to 3 milking cows. the rules of the second part had support and confidence levels between 0.4-0.42 and 0.87-0.91, respectively, with a lift range of 1.08 to 1.34. farmers used artificial insemination in the last calving and were not members of farm groups at a lift value of 1.39. at lift values more than 1.3, the preferred buyers were individual consumers, the distance from the water source was less than 1km, and the watering frequency for the cattle was once per day. farmers had average peak milk production for their best cows and the distance to the breeding service provider was 1-5km at a lift value of 1.1. at a 0.46 support, farmers received 1-9 visits from extension officers. 2) level 2 the production traits that dominated level 1 were reduced in level 2. the minimum support used was 0.2, the minimum confidence level was 0.6, and 83 rules were obtained for a lift range between 1.02 and 3.15. strong rules were determined for support between 0.22 and 0.35 and confidence levels from 0.85 to 1.0. support was low but the confidence and the lift of the rules were high. gaps in the 3 breed ranks were observed in both antecedents and consequents with a high support of 0.3 and lift of 3.0. however, at 0.25 support and lift above 3.0, the preferred breed in breed rank 1 was friesian, breed rank 2 was ayrshire, and breed rank 3 was jersey. farmers using ayrshire and friesian breeds performed deworming 3 times a year at a high lift above 2.0. farmers did not purchase fodder and had low residue milk with a high lift of 1.5. farmers with milk quantity traits in trait rank 1 performed deworming 3 times per year with a high lift above 2.0. milk quality traits preferred in traits rank 1 and friesian breed were observed with a high lift of 2.0. 3) level 3 the production traits that dominated level 2 were reduced in level 3. a minimum support of 0.125 and a minimum confidence level of 0.6 were used in the mining process, the lift range obtained was between 1.01 and 2.66, and 70 rules were obtained for medium milk producers at this level. in these rules, most farmers preferred milk quality, milk quantity, and udder traits. farmers who preferred milk quality traits in rank 2 had 1 to 20 cattle with a lift value of 2.0. in rank 1, farmers preferred milk quantity and had low residue milk for home consumption at a lift value of 2.0. farmers did not have land for feed production, did not purchase feed, preferred udder traits in rank 3, and household members had attended school for 1-7 years at a lift value of 2.0. the preferred feature in rank 1 was the dairy type with a high lift of 2.5. at 1.5 lift, farmers purchased concentrates throughout the year and had a spraying frequency 2 per year. other production traits included the use of crop residues for 4 months, farmers owned area for feeding production from 0.5 to 1 acres, and household members who had attended school for 8-11 years. c. cluster 3: low milk producers 1) level 1 at this level, the minimum support was 0.73, the minimum confidence level was 0.9, the lift range was between 1.004 and 1.14, and 76 rules were established. farmers preferred and used the bull breeding method in the last calving and had no employees at a high support of 0.77 and lift above 1.1. farmers did not have training in dairy farming at 0.75 support, did not carry out self-deworming at 0.75 support and above 1.1 lift, and did not have members in farmer groups at 0.74 support. farmers used only stall feeding in both rainy and dry seasons, owned 1 to 3 milking cows, and had frequent visits, between 1 to 9, from extension officers at 0.74 support and 1.05 lift. 2) level 2 the production traits that dominated level 1 were reduced in level 2. the minimum support was 0.34, the minimum confidence level was 0.72, the lift range was between 1.01 and 2.07, and 57 rules were obtained. strong rules with a lift value of 2.07 were located at a confidence level of 1.0 and a support range from 0.36 to 0.39. no preferred breed type was identified at 2.0 lift and 0.37 support. the total land owned by farmers was below average and the distance to the market was 1-5km with 1.1 lift and 0.35 support. the vaccination frequency was twice a year and the watering frequency was once a day at 1.1 lift and 0.35 support. there was no distance to the buyer at 1.1 lift and 0.39 support. the liters of milk sold by the farmers were average and the household members had attended school for 1 to 7 years. 3) level 3 the dominating production traits at level 2 were reduced in level 3. the used minimum support was 0.27, the minimum confidence level was 0.64, the lift range was between 1.031.85, and 51 rules were extracted. farmers chose their feeding system due to insufficient land at 1.8 lift and preferred the trait of milk quality at 1.7 lift. farmers performed spraying of cattle twice per year at 1.6 lift and deworming 3 times a year at 1.4 engineering, technology & applied science research vol. 13, no. 2, 2023, 10377-10383 10381 www.etasr.com malamsha & nyambo: multi-level association rule mining for the discovery of strong … lift. at 1.2 lift, farmers used concentrates for 3 months, had low residue milk, their distance to the breeding service provider was 1-5km, and did not purchase fodders. unique production traits included individual consumers as buyers and average milk production of the best cow. table ii shows a summary of all the rules obtained in multilevel association rule mining from small dairy farmers in tanzania. table ii. summary of rules obtained in multilevel association rule mining clusters levels number of rules minimum support minimum confidence level lift range high producers (cluster 1) level 1 81 0.6 0.95 1.003 to 1.29 level 2 86 0.22 0.7 1.02 to 1.43 level 3 84 0.164 0.67 1.04 to 3.57 medium producers (cluster 2) level 1 100 0.4 0.86 1.07 to 1.39 level 2 83 0.2 0.6 1.02 to 3.15 level 3 70 0.125 0.6 1.01 to 2.66 low producers (cluster 3) level 1 76 0.73 0.9 1.004 to 1.14 level 2 57 0.34 0.72 1.01 to 2.07 level 3 51 0.27 0.64 1.03 to 1.85 iv. discussion most milk producers in all clusters practice only stallfeeding systems in both dry and rainy seasons. feeding adequate meals to cattle with the required nutrients could help increase milk production. milk production drops during the dry season for most farmers due to inappropriate methods to cope with it [21]. apart from stall feeding, small dairy farmers provide crop residues and concentrates to their cattle. high milk producers provided crop residues to their cattle 6 months a year, medium milk producers provided crop residues for 4 months, while crop residues were not identified in small producers. the adoption of methods to produce and store crop residues is important and should be encouraged, including the treatment of crop residues for use during the dry season [21]. farmers in high and low milk-producing clusters use concentrates for 3 months per year, but the medium milkproducing cluster has farmers who use concentrates for 3 to 12 months a year. most farmers do not have or possess less than 1km 2 of land for fodder production, which is insufficient for their cattle. in addition, farmers do not purchase fodder for their cattle. the results on the feeding systems highlight a major challenge towards higher productivity, as the practices are not in agreement with the available studies [21, 27-28]. with a zero-grazing set-up, a minimum of 1 acre of napier grass per cow was emphasized to be adopted by small farmers as the primary source of fodder in kenya [27]. planting napier grass on 1 acre with good management can help small farmers to feed 2 dairy cows during a year [28]. effective feed production technologies have not been adopted due to cost, insufficient land, and high labor demands [21]. high milk producers have a higher watering frequency than the others, as they provide water at least twice a day. most farmers in highand medium-producing clusters have 3 preferred breeds: friesian, ayrshire, and jersey. low milk producers did not have preferred breed types, raising questions about their dairy orientation and breeding selections [29]. the use of improved crossbreeding types is preferred to increase milk production compared to pure exotic breeds that have low production due to the production environments that are highly resource deprived. improved breeds that are well suited for the environment of tanzania, such as friesian, ayrshire, and jersey, have been proven to be among the top 10 effective in dairy production [29]. farmers in high and low clusters preferred the use of bull breeding while farmers in the medium cluster preferred artificial insemination, which is an efficient and effective tool to increase milk production by breeding many cows with semen from good breeds in different geographic locations. studies have indicated that artificial insemination is more effective than bull breeding because, in the former case, semen is better examined for diseases, quality, and fertility [30]. these results still yield uncovered service gaps for the farmers as they still rely on poorly performing breeding methods. most high milk-producing farmers prefer milk quantity, milk quality, and udder traits. farmers in the mediumproducing cluster prefer milk quality, milk quantity, dairy type, and udder traits. farmers in the low-producing cluster prefer milk quantity and quality. in tanzania, small dairy farmers prefer mostly cows with high milk production genetics but at an affordable price [31]. farmers choose the best traits to increase milk production. this can be seen in high and medium producers who are much more aware of the good traits of their cattle than low producers. farmers in high and low milk production clusters carried out deworming of their cattle 3 times a year, but farmers in the medium cluster carried out deworming 3 to 4 times a year. farmers in the high milk-production cluster spray their cattle 6 times a year, medium producers spray their cattle twice a year, and low-milk producers do not spray their cattle. the vaccination frequency in all clusters is twice a year. most farmers in all clusters have 1 to 9 extension visits. insufficient and inadequate inputs such as feed, breed, health, and services such as lack of extension visits lead to the inability to control cattle diseases, poor livestock farming, and lack of knowledge and information [32]. most of the farmers in all clusters did not perform cattle self-deworming, had not attended training, had no employees, and were not members of farmer groups. farmers in the high cluster have more experience in dairy farming, from 8 to 13 years, than farmers in the medium and low clusters. engineering, technology & applied science research vol. 13, no. 2, 2023, 10377-10383 10382 www.etasr.com malamsha & nyambo: multi-level association rule mining for the discovery of strong … in terms of education level, farmers in high and low clusters attended school for 1 to 7 years, while farmers in the medium cluster attended school for 8 to 11 years. this highlights the gap between experienced farmers with low education levels against those who have significantly attained formal education. although there were no significant differences in formal education between high and low producers, more research is needed to determine whether formal education can promote the adoption of improved technologies, such as the use of improved breeding methods [30]. the trained farmers were shown to have higher milk production than the others in temeke [33]. knowledge of how to conduct dairy farming practices is important to achieve high milk production. farmers’ knowledge in terms of receiving frequent extension visits has shown concern in the health of their animals; high milk producers were more experienced than the others, and hence had more knowledge in breeding practices. farmers in all clusters owned 1 to 3 milking cows with their best average production quantity of milk. the best cows from most small dairy farmers with high milk production in tanzania produced 14.455.12l milk per day, the best cows from most small farmers with medium milk production small farmers produced 11.084.29l milk per day, and the best cows from low milk producers produced 9.153.25l milk per day. the cattle keepers in tanzania sell small amounts of milk to consumers and have not met the demand for milk in a country where the population, income, and urbanization continue to increase [32]. the liters of milk sold by most farmers are average in all clusters. the preferred buyers in all clusters are individual consumers at distance ranging between 1 and 5km. an increase in the quantity and quality of milk production can be achieved by an efficient milk collection system and the production of dairy products that could meet customer needs [34]. more farmers in the market will trigger more milk production since they will be confident in selling their products. milk reserves for home consumption were low for the high and low clusters whereas the medium had a mix of farmers with average milk reserves. the data mining process extracts useful information from large datasets that can uncover hidden patterns and is also called knowledge discovery or knowledge extraction [35]. association rule mining enabled the mining of association rules from a dataset that identified underrepresented patterns among small farmers. this rule-based engine gives farmers a platform to learn various farming techniques from each other in their respective farm groups while extension officers can provide timely assistance [25]. therefore, recommendations can be provided to the farmers according to their various practices. v. conclusion it is necessary to provide farmers with knowledge about the production traits that can help them achieve higher milk production. this knowledge will not only increase production, but can also contribute to market products, employ personnel, and reduce poverty and food insecurity. training small dairy farmers is also important with the available technology, such as feed technology, in a way that is easily accessible. the use of a rule-based engine to assign farmers to farm clusters enables them to connect with the extension officers and enhance the information sharing and engagement. in a rule-based engine platform, farmers can receive recommendations based on the cluster to which they belong, as they are already available. a future study should investigate the use of these rules to provide recommendations to farmers based on these production features. acknowledgement the following agencies are acknowledged: scholarship funders of the international development 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[35] a. h. blasi, m. a. abbadi, and r. al-huweimel, "machine learning approach for an automatic irrigation system in southern jordan valley," engineering, technology & applied science research, vol. 11, no. 1, pp. 6609–6613, feb. 2021, https://doi.org/10.48084/etasr.3944. microsoft word etasr_v13_n4_pp11170-11176 engineering, technology & applied science research vol. 13, no. 4, 2023, 11170-11176 11170 www.etasr.com kar et al.: dynamic soil-structure interaction of multi-story buildings using the finite element … dynamic soil-structure interaction of multistory buildings using the finite element method and minimax probability machine regression saurav shekhar kar department of civil engineering, marathwada mitramandal's institute of technology, india kar.sauravshekhar2008@gmail.com (corresponding author) anupama arunkumar athawale aissms institute of information technology, pune, india athawale.anupama@gmail.com mani bhushan department of civil engineering, government engineering college khagaria, bihar, india mani.tuntun@gmail.com lal bahadur roy department of civil engineering, national institute of technology patna, india lbroy@nitp.ac.in received: 21 march 2023 | revised: 5 april 2023 and 1 may 2023 | accepted: 10 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5870 abstract soil-structure interaction (ssi) issues are some of the most critical problems encountered in the design of structures prone to earthquake shaking. the damage caused by an earthquake mainly depends on the interaction between soil and structure. in this study, the effect of dynamic ssi on a multi-story building is examined using two methods, finite element method (fem) and minimax probability machine regression (mpmr). the mpmr was used to develop a model based on the input and output database generated from the fem model. the performance comparison of these two models shows a good correlation. the mpmr model significantly reduced the computational time and can thus be utilized as a substitute for determining the response quantities. keywords-dynamic ssi; earthquake; fem; mpmr i. introduction soil–structure interaction (ssi) becomes very crucial when massive and stiff structures are built on soft soil. structures may be subjected to dynamic loads arising due to various natural or manmade sources (e.g. blasting, machine operations, quarrying, construction activities, action of water waves, earthquakes, etc.), out of which earthquake is the most important hazard to the structure and foundation. the damage caused by an earthquake mainly depends on the dynamic response of the soil layers [1]. in many cases, the damage caused is not due to the sole structural failure or sole soil failure, but it is due to the interaction between the soil and the structure. the properties of the soil vary from one place to another or along the direction (vertical or horizontal) [2-4]. thus, in severe soil conditions, the interaction effects should be considered for the dynamic analysis of the structures built on the soil. the general structural dynamic system has mainly two characteristic differences from the ssi system which are the non-linear characteristics of the soil [5] and the unbounded nature of the soil medium [6]. the radiation damping, which is the radiation of energy towards infinity, is the most important characteristic in an unbounded soil medium and it is not experienced in a bounded soil medium. many studies have considered the effects of ssi on the dynamic behavior of the structures. authors in [7] analyzed the effect of ssi on three-dimensional building distribution resting on a layered elastic-half-space. authors in [8] proposed a simple relation to estimate the expected efficiency of the ssi engineering, technology & applied science research vol. 13, no. 4, 2023, 11170-11176 11171 www.etasr.com kar et al.: dynamic soil-structure interaction of multi-story buildings using the finite element … effects for any city. authors in [9, 10] studied the seismic response of an idealized 2d "city", constituted by 10 non equally-spaced and sized, homogenized buildings. authors in [11] introduced two analytical methods that aim to investigate the effect of the urban environment on seismic motions. in [12], the nonlinear ssi behavior was modeled through a beamon-nonlinear-winkler-foundation approach. authors in [13] studied the seismic behavior of braced and unbraced building structures affected by ssi. it was found that for the flexible buildings built on very stiff soil and rock the ssi effects may be ignored, but for structures built on comparatively soft soil, they should be necessarily considered [14–16]. during the past few decades, many analytical formulas have been developed to solve the difficult problems of ssi analysis. the effect of the non-linear nature of the soil on the dynamic response of the buildings has not been completely dealt with [17]. the use of analytical methods is very limited as the solutions are available only for systems with simple geometry. the ability of soft computing techniques like minimax probability machine regression (mpmr) has gained popularity in many research areas [18–24]. mpmr is basically a method used to arrive at a best solution for a given set of parameters. it provides an easy way to deal with a wide range of problems for which it is difficult to generate an analytical model. soft computing techniques can be applied also when an exact analytical model cannot be defined. the mpmr technique has been applied to various engineering applications and appears to perform well. in this study, the effect of dynamic ssi on a multi-story building resting on a raft foundation having different height to width (h/b) ratio, subjected to the seismic ground motion record of the ei-centro and the bhuj earthquakes, is examined. different types of soils were used and the response of the framed structure was studied. the ssi problem has been analyzed using fem and mpmr. the fem model was developed and analyzed with sap2000. response quantities like top story displacement (tsd), displacement of ground level (dgl), and relative displacement between top story and ground level (rtsd) were found out. the training and testing data sets for the mpmr were obtained from the result of the fem modeling. it is noticed that the computational time is considerably reduced for the mpmr model as compared to the fem model. ii. method of analysis the various methods used in the analysis of the ssi problem are discussed below. a. soil-structure interaction ssi analysis takes into account of all the three linked systems, i.e. the building, the foundation, and the soil neighboring and underlying the foundation. it assesses the collective response of these systems to a specified ground motion. the interaction between the earth and structures is different in different situations. the type of foundations used in the structure and the type of structures used also influence the response of the soil-structure system [25]. two types of interaction effects are observed in a ssi problem, the kinematic interaction and the inertial interaction [26]. 1) kinematic interaction the ssi effect which is related with the structural stiffness is termed as kinematic interaction. it arises due to the incapability of the foundation to conform to the dislocation of the free-field ground motion. by free-field motion we mean the motion of the soil layer which is not affected by structural vibration or by the scattering waves around the foundation. due to the kinematic interaction, the motion at the foundation deviates from free-field motion. this interaction occurs due to the presence of stiff foundation elements. when the depth of the embedded foundation is equal to the wavelength of normally propagating shear waves, then the kinematic interaction generates torsion and rocking vibration in the structure, which never happens in the case of free field motion. by considering that the foundation and structure have stiffness but are massless, the deformation occurring due to the kinematic interaction can be evaluated. the equation of motion in this case is given as [15]: �m����� u� � � + �k ∗� u� � = − �m����� u� ��t� (1) where �m���� � is the mass matrix supposing that the structure and foundation has no mass, u� � is the foundation input motion, �k∗ � is the stiffness matrix, and u� � is the acceleration at the boundary. 2) inertial interaction the ssi effect which is related with the mass of the superstructure is known as the inertial interaction. it is caused due to the mass of the superstructure which develops additional movements at the base of the foundation. due to the displacement of masses of the superstructure during a vibration, inertia forces are generated, which induce transverse shear and overturning moment to the structure. the deformation caused due to inertia interaction can be evaluated from [15]: �m� u� � + �k ∗� u � = − �m��������� � × u� � �t� + u� ��t�� (2) where �m��������� � is the mass matrix assuming that the soil has no mass. iii. minimax probability machine regression (mpmr) mpmr is based on the minimax probability machine classification by building a dichotomy classifier [23]. it maps the input vectors into a high-dimensional feature space. it reckons the mean and covariance matrix of the available data. in mpmr, the relation between input �x� and output �y� is given by: y = ∑ β� k�x�, x� + b # �$% (3) where n is the datasets number, β� and b are outputs of the mpmr, and k�x�, x� is the kernel function. one piece of data is obtained by shifting all of the training data + ∈ along the output variable axis. the other is obtained by shifting all of the regression data ∈ along the axis. in mpmr, the training data set is classified into the following two classes: u� = �y�+∈, x�%, x�), … , x�+ � (4) engineering, technology & applied science research vol. 13, no. 4, 2023, 11170-11176 11172 www.etasr.com kar et al.: dynamic soil-structure interaction of multi-story buildings using the finite element … v� = �y�−∈, x�%, x�), … , x�+ � (5) the classification boundary between u� and v� represents the regression surface. radial basis function has been used as a kernel function. matlab has been used to develop the mpmr model. for constructing the mpmr model, the design values of ∈ and σ have been evaluated by the trial and error method. the coefficient of correlation (r) values come close to or equal to 1, so the developed mpmr is considered a very good model. iv. methodology a. specification for the soil structure system the ssi problem has been analyzed using the specifications mentioned in is 456:2000. the structural details and their speciation used in the analysis are given in table i. table i. structural details used in the ssi problem b. materials seventy-five different types of soil were categorized based on young’s modulus (e), poisson’s ratio (µ), and unit weight (γ) in 5 groups, i.e. soft clay (saturated), stiff clay (saturated), sandy clay, loose sand, and dense sand. these different types of soil were used in the analysis of ssi problem having varying h/b ratio. the properties of the soils are shown in table ii. table ii. soil properties soil type e (kpa) µ γ (kn/m 3 ) soil type e (kpa) µ γ (kn/m 3 ) soil type e (kpa) µ γ (kn/m 3 ) soft clay (saturated) 2000 0.40 16.0 hard clay (saturated) 7000 0.40 18.0 dense sand 50000 0.30 19.0 2200 0.40 16.2 7200 0.40 18.1 52000 0.31 19.0 2400 0.40 16.4 7600 0.40 18.2 54000 0.32 19.0 2600 0.41 16.6 8000 0.41 18.3 56000 0.33 19.2 2800 0.41 16.8 8400 0.41 18.4 58000 0.34 19.2 2900 0.42 17.0 8800 0.42 18.5 60000 0.35 19.2 3000 0.42 17.2 9400 0.42 18.6 62000 0.36 19.4 3200 0.42 17.4 10000 0.42 18.7 65000 0.37 19.4 3300 0.43 17.6 10600 0.43 18.8 67000 0.38 19.4 3500 0.43 17.8 11000 0.43 18.9 70000 0.39 19.6 3600 0.44 18.0 12000 0.44 19.0 72000 0.40 19.6 3700 0.44 18.2 13000 0.44 19.1 74000 0.41 19.7 3800 0.45 18.4 13500 0.45 19.2 76000 0.42 19.7 3900 0.45 18.6 14000 0.45 19.3 78000 0.43 19.8 4000 0.45 18.8 15000 0.45 19.4 80000 0.45 20.0 sandy clay 27000 0.20 16.0 loose sand 10000 0.20 17.0 29000 0.20 16.3 11000 0.22 17.1 31000 0.21 16.6 12000 0.23 17.2 33000 0.21 16.9 13000 0.24 17.3 34000 0.22 17.2 14000 0.25 17.4 34500 0.22 17.5 15000 0.26 17.5 35000 0.23 17.8 16000 0.28 17.6 35500 0.23 18.0 17000 0.30 17.7 36000 0.24 18.2 18000 0.31 17.8 36500 0.24 18.3 19000 0.32 17.9 37000 0.25 18.5 20000 0.33 18.0 37500 0.26 18.7 21000 0.34 18.1 38000 0.27 19.0 22000 0.35 18.2 38500 0.28 19.2 23000 0.36 18.3 39000 0.29 19.4 24000 0.38 18.4 c. implementation the implementation of analyzing the ssi problem is conducted using two different models, which are discussed below. 1) fem model fem modelling of the ssi problem was done using the software package sap2000. the soil is considered to be a solitary stratum of 65 m depth and 270 m wide. the building members are modelled with framed elements. the interface between the soil and the structure foundation is modelled using nonlinear gap connector elements. the gap elements essentially consist of a spring combined with an opening such that no tensile force gets transmitted through the soil to the foundation. in this study, zero initial openings have been assumed for the gap elements with spring stiffness value in order of 10 4 kn/m and were distributed at every one meter over the interface surface. further, it is assumed that the sliding between the foundation and the soil is insignificant. this is demonstrated by imposing an equal horizontal displacement constraint for the interface nodes. the soil element sizes are increased as it moves away from the periphery of the soil layer. for appropriate modeling, the maximum size of the soil mesh is limited to ./10 where . is the wave length of the waves structural details specifications beam 0.35 m × 0.45 m column 0.35 m × 0.35 m storey height 3.0 m bay size 5.0 m grade of concrete m40 thickness of raft foundation 1.1 m engineering, technology & applied science research vol. 13, no. 4, 2023, 11170-11176 11173 www.etasr.com kar et al.: dynamic soil-structure interaction of multi-story buildings using the finite element … transmitted within the soil [25]. in terms of boundary conditions, a fixed boundary at the base and an absorbing boundary at the vertical edge of the soil were considered. these boundaries represent the missing soil beyond the periphery of the soil layer. transmitting boundaries are implemented using viscous dampers having damping coefficient value related to the velocity of shear waves and pressure waves travelling in the soil media. the horizontal and the vertical coefficient for the dampers are found out using the following equations: c0 = −ρv3 , c4 = �ρv�a (6) vp = √(k/ρ) , vs= √(g/ρ) (7) g = 7)�%89� , k � : 7�%;9� <�%89��%;)9� (8) where ch and cv are the horizontal and vertical damping coefficients of the viscous dampers, vp and vs are the compressive and shear wave velocities in the soil media, respectively, a is the tributary area for the node attached to the damper, and =, >, g, and ? are mass density, bulk modulus, shear modulus, and poison’s ratio of the soil material. the resulting finite element model created in sap2000, showing the transmitting boundaries is shown in figure 1. the soil medium is assumed to be isotropic and homogeneous and the damping of the structure and the soil is taken as 5% and 8%, respectively. fig. 1. the fem model in sap 2000. the fem model is subjected to time history analysis using the ground motion records of the el-centro and bhuj earthquakes. the ground motion is applied at the fixed base of the soil layer for five different types of soil and for different h/b ratios of the symmetric multi-story building. the soilstructure system used in the study has a soil layer of fixed depth and width with a concrete structure placed on the top. the foundation used is a reinforced concrete raft foundation that supports all the columns of the structure. the loads of the columns in the raft foundation are shown in table iii. table iii. design loads load type load case load value slab own weight dead 5 kn/m 2 services dead 2.5 kn/m 2 live load live 2 kn/m 2 flooring dead 1 kn/m 2 2) mpmr model the output results, such as tsd, dgl and rtsd, from the finite element analysis with sap2000 are used as the input data to the minimax probability machine regression model. along with the above obtained data, the soil properties and different height to width ratios were also used as input in the mpmr model. a total of 75 responses were obtained from sap2000 and were further divided into training and testing data sets for the mpmr model, in a 70-30 ratio. pre-processing of the response data set from finite element analysis was conducted before using it as input in mpmr. normalization was carried out to pre-process the data using the following equation: y� � @a;@bac@bde;@bac (9) where xf is any response quantity, xg�+ and xgh@ represent the minimum and maximum values, respectively, of the response quantities, and y� is the corresponding normalized value. the mpmr model of the problem as stated above is shown in figure 2. fig. 2. representation of the mpmr model. v. results and discussion a. fem the results of the fem analysis in sap2000 were obtained for different types of soil and for different height to width (h/b) ratios (i.e. h/b = 6, 5, 4, 3, 2). the response quantities tsd, dgl, and rtsd were obtained for the data of the elcentro and the bhuj earthquakes and the obtained results are shown in tables iv-viii. the obtained results of the average value of tsd, dgl, and rtsd for different soil types are presented in tables ix and x. table iv. results of the fem model for h/b = 6 soil type output el-centro earthquake bhuj earthquake tsd (cm) dgl (cm) rtsd (cm) tsd (cm) dgl (cm) rtsd (cm) soft clay (saturated) 16.71 15.88 0.83 17.87 15.32 2.55 16.75 15.94 0.81 17.72 15.36 2.36 16.83 16.01 0.82 17.63 15.42 2.21 16.64 15.81 0.83 17.30 15.20 2.10 16.73 15.90 0.83 17.27 15.27 2.00 16.53 15.68 0.85 17.02 15.03 1.99 16.63 15.78 0.85 17.06 15.12 1.94 16.73 15.88 0.85 17.06 15.20 1.86 16.49 15.63 0.86 16.77 14.92 1.85 16.59 15.72 0.87 16.79 14.99 1.80 16.31 15.43 0.88 16.46 14.66 1.80 16.40 15.52 0.88 16.52 14.74 1.78 16.07 15.17 0.90 16.15 14.37 1.78 16.16 15.26 0.90 16.20 14.44 1.76 16.25 15.34 0.91 16.25 14.52 1.73 engineering, technology & applied science research vol. 13, no. 4, 2023, 11170-11176 11174 www.etasr.com kar et al.: dynamic soil-structure interaction of multi-story buildings using the finite element … table v. results of the fem model for h/b = 5 soil type output output el-centro earthquake el-centro earthquake tsd (cm) dgl (cm) rtsd (cm) tsd (cm) dgl (cm) rtsd (cm) hard clay (saturated) 15.95 14.98 0.97 16.00 14.77 1.23 16.02 15.00 1.02 16.04 14.81 1.23 16.12 14.98 1.14 16.07 14.83 1.24 15.92 14.66 1.26 15.79 14.51 1.28 16.03 14.65 1.38 15.81 14.53 1.28 15.80 14.29 1.51 15.49 14.18 1.31 15.96 14.26 1.70 15.51 14.18 1.33 16.12 14.23 1.89 15.52 14.18 1.34 15.90 13.84 2.06 15.16 13.78 1.38 16.00 13.84 2.16 15.18 13.79 1.39 15.80 13.38 2.42 14.76 13.33 1.43 15.98 13.33 2.65 14.73 13.30 1.43 15.64 12.88 2.76 14.30 12.84 1.46 15.72 12.87 2.85 14.29 12.85 1.44 15.85 12.83 3.02 14.26 12.81 1.45 table vi. results of the fem model for h/b = 4 soil type output output el-centro earthquake el-centro earthquake tsd (cm) dgl (cm) rtsd (cm) tsd (cm) dgl (cm) rtsd (cm) sandy clay 17.25 14.41 2.84 15.17 14.86 0.31 17.15 14.54 2.61 15.25 14.94 0.31 16.99 14.56 2.43 15.22 14.96 0.26 16.87 14.69 2.18 15.29 15.04 0.25 16.86 14.73 2.13 15.32 15.10 0.22 16.99 14.91 2.08 15.48 15.26 0.22 17.05 14.95 2.10 15.53 15.33 0.20 17.10 15.05 2.05 15.62 15.43 0.19 17.09 15.02 2.07 15.60 15.43 0.17 17.07 15.07 2.00 15.63 15.46 0.17 17.05 15.03 2.02 15.59 15.45 0.14 17.02 14.98 2.04 15.54 15.43 0.11 17.05 14.98 2.07 15.55 15.46 0.09 16.99 14.91 2.08 15.48 15.42 0.06 16.93 14.83 2.10 15.39 15.36 0.03 table vii. results of the fem model for h/b = 3 soil type output output el-centro earthquake el-centro earthquake tsd (cm) dgl (cm) rtsd (cm) tsd (cm) dgl (cm) rtsd (cm) loose sand 17.15 14.52 2.63 15.66 15.16 0.50 16.95 14.35 2.60 15.42 15.00 0.42 16.79 14.28 2.51 15.31 14.90 0.41 16.62 14.20 2.42 15.18 14.80 0.38 16.43 14.11 2.32 15.05 14.68 0.37 16.24 14.02 2.22 14.91 14.59 0.32 15.94 13.76 2.18 14.59 14.35 0.24 15.62 13.47 2.15 14.23 14.07 0.16 15.38 13.33 2.05 14.05 13.91 0.14 15.14 13.17 1.97 13.85 13.74 0.11 14.88 13.00 1.88 13.64 13.56 0.08 14.62 12.81 1.81 13.41 13.37 0.04 14.33 12.61 1.72 13.18 13.15 0.03 14.04 12.39 1.65 12.94 12.92 0.02 13.50 11.87 1.63 12.42 12.36 0.06 table viii. results of the fem model for h/b = 2 soil type output output el-centro earthquake el-centro earthquake tsd (cm) dgl (cm) rtsd (cm) tsd (cm) dgl (cm) rtsd (cm) dense sand 13.02 12.33 0.69 12.42 12.19 0.23 12.76 12.10 0.66 12.15 11.96 0.19 12.48 11.87 0.61 11.87 11.72 0.15 12.30 11.72 0.58 11.69 11.56 0.13 12.00 11.47 0.53 11.40 11.30 0.10 11.70 11.20 0.50 11.09 11.02 0.07 11.48 11.01 0.47 10.88 10.82 0.06 11.12 10.68 0.44 10.52 10.48 0.04 10.78 10.37 0.41 10.18 10.16 0.02 10.48 10.09 0.39 9.89 9.87 0.02 10.11 9.75 0.36 9.52 9.51 0.01 9.77 9.43 0.34 9.19 9.17 0.02 9.38 9.05 0.33 8.79 8.76 0.03 8.99 8.68 0.31 8.42 8.38 0.04 8.23 7.92 0.31 7.63 7.59 0.04 table ix. average tsd, dgl, and rtsd values for the el-centro earthquake displacement values soil type soft clay hard clay sandy clay loose sand dense sand tsd (cm) 16.52 15.92 17.03 15.58 10.97 dgl (cm) 15.66 14.00 14.84 13.46 10.51 rtsd (cm) 0.86 1.92 2.19 2.12 0.46 table x. average tsd, dgl, and rtsd values for the bhuj earthquake displacement values soil type soft clay hard clay soft clay loose sand soft clay tsd (cm) 16.94 15.26 15.44 14.26 10.38 dgl (cm) 14.97 13.91 15.26 14.04 10.30 rtsd (cm) 1.97 1.35 0.18 0.22 0.08 b. mpmr result the results obtained from the finite element analysis were used as the input data set to the mpmr model. the obtained data were normalized before being utilized. the dataset was divided into 70 % training and 30 % testing sets. the program of mpmr was executed in matlab. the obtained results for the ei-centro earthquake are shown in figures 3-5. the obtained results from the mpmr for bhuj earthquake are shown in figures 6-8. fig. 3. tsd ρesults for ei-centro earthquake (training and testing). engineering, technology & applied science research vol. 13, no. 4, 2023, 11170-11176 11175 www.etasr.com kar et al.: dynamic soil-structure interaction of multi-story buildings using the finite element … fig. 4. dgl ρesults for ei-centro earthquake (training and testing). fig. 5. rtsd ρesults for ei-centro earthquake (training and testing). fig. 6. tsd ρesults for bhuj earthquake (training and testing). fig. 7. dgl ρesults for bhuj earthquake (training and testing). fig. 8. rtsd ρesults for bhuj earthquake (training and 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[26] e. kausel, "early history of soil–structure interaction," soil dynamics and earthquake engineering, vol. 30, no. 9, pp. 822–832, sep. 2010, https://doi.org/10.1016/j.soildyn.2009.11.001. microsoft word etasr_v13_n1_pp9872-9878 engineering, technology & applied science research vol. 13, no. 1, 2023, 9872-9878 9872 www.etasr.com al-damluji & mohammed: performance evaluation of emulsion liquid membrane on chlorpyrifos … performance evaluation of emulsion liquid membrane on chlorpyrifos pesticide removal: stability, mass transfer coefficient, and extraction efficiency studies farrah emad al-damluji department of environmental engineering, college of engineering, university of baghdad, iraq farrah.emad@coeng.uobaghdad.edu.iq (corresponding author) ahmed a. mohammed department of environmental engineering, college of engineering, university of baghdad, iraq ahmed.abedm@yahoo.com received: 8 october 2022 | revised: 2 november 2022 | accepted: 2 november 2022 abstract emulsion liquid membrane (elm) is an emerging technology that removes contaminants from water and industrial wastewater. this study investigated the stability and extraction efficiency of elm for the removal of chlorpyrifos pesticide (cp) from wastewater. the stability was studied in terms of emulsion breakage. the proposed elm included n-hexane as a diluent, span-80 as a surfactant, and hydrochloric acid (hcl) as a stripping agent. parameters such as mixing speed, aqueous feed solution ph, internal-toorganic membrane volume ratio, and external-to-emulsion volume ratio were investigated. a minimum emulsion breakage of 0.66% coupled with a maximum chlorpyrifos extraction and stripping efficiency were achieved at 96.1% and 95.7% at best-operating conditions of 250/50 external-to-emulsion volume ratio, external feed solution ph 6, 250rpm mixing speed, and 1:1 internal-to-membrane volume ratio at 10min contact time without utilizing a carrier agent. a study of extraction kinetics and estimation of mass transfer coefficient was also conducted (3.89×10 -9 m/s). the results of this work can be extended to the removal of other types of pesticides from wastewater. keywords-emulsion liquid membrane; chlorpyrifos; stability; mass transfer coefficient; extraction efficiency i. introduction emerging contaminants (ecs) such as synthetic dyes, cosmetics, pharmaceuticals (antibiotics, hormones, and others), and pesticides are considered major issues in many parts of the world [1]. the final fate of pesticides after use has different pathways: (1) soil top layer accumulation, where pesticides may be adsorbed and deposited, (2) degradation on both the plant surface and the soil, (3) plant organs translocation, and (4) dissolution-transport of contaminants from soil and plant surfaces into water runoff causing water resource contamination [2, 3]. chlorpyrifos (cp) is a broad-spectrum organophosphorus insecticide (op) and has a high value of octanol-water partition coefficient kow = 4.70 [4]. exposure to chlorpyrifos can produce nausea, diarrhea, salivation, vomiting, tremor, and convulsion symptoms [5-7]. chlorpyrifos is banned in many countries, nevertheless, monitoring still has to be carried out. the liquid membrane extraction, commonly known as emulsion liquid membrane (elm), was presented as a substitute technique for separation by a polymeric membrane as well as liquid-liquid extraction [8, 9]. the mechanism of elm depends on the diffusion of the solute (contaminant), passing through an organic liquid membrane [10]. the main advantages of elm are: (1) high diffusion rate of the contaminant through the membrane, (2) high interfacial area for solute mass transfer at the internal water-oil interface due to the small-sized droplets, (3) ability to treat an assortment of compounds and elements in an industrial setting at higher speeds along with an extraordinary level of effectiveness for various solute (contaminants) volume concentrations, and (4) simultaneous performance of both extraction and stripping at the external and the internal interfaces of a system, respectively [11, 12]. despite the promising features of elm, its instability has impeded widespread applications on a larger scale. the stability of an emulsion is defined as liquid membrane resistance to high shear stress during solute extraction. the best stability level is essential in the elm process [13], as it is produced using the appropriate surfactant to overcome the engineering, technology & applied science research vol. 13, no. 1, 2023, 9872-9878 9873 www.etasr.com al-damluji & mohammed: performance evaluation of emulsion liquid membrane on chlorpyrifos … difficulties of an elm system on a practical industrialized level [14]. this study investigated chlorpyrifos extraction from contaminated water using elms to propose a novel method for pesticide extraction. the influences of stirring speed, internal aqueous phase-organic phase volume ratio, external feed phase ph, external phase-emulsion volume ratio, and contact time were studied to determine the best conditions to achieve minimal membrane breakage in the emulsion system and reach maximum removal efficiency. ii. materials and methods a. chemicals and equipment this study used analytical reagent-grade chemicals. the cp used was purchased from the local market (om agro chemicals, india). the chemical formula of cp (c9h11cl3no3ps) can be seen in [19]. cp has a molar mass of 350.6g/mol, 1.4g/cm3 density, 1.87×10-5mmhg vapor pressure at 25°c, 41.5-42.5°c melting point, and decomposition at 160°c [15, 16]. hydrochloric acid (hcl) and sodium hydroxide (naoh) were acquired from thomas beaker in india. the organic membrane consists of a diluent and a surfactant. the nonionic surfactant was sorbitan monooleate, commonly recognized as span80, obtained from merck, darmstadt, germany (sigma aldrich); n-hexane was used as a diluent, obtained from thomas beaker, india, which was selected because of the higher rate of transport of solute than heptane and kerosene [17, 18]. all laboratory tests were carried out at a room temperature of 20±2°c, using mtops sr 30 homogenizer, heidolph rzr 2021 compact digital mixer system, quartz cells, pg instruments t80+ uv/vis spectrometer, isolab centrifuge machine, atc ph meter, and an isolab magnetic stirrer with a temperature controller. b. experimental work the membrane phase was produced by dissolving a specific amount of surfactant (span 80) in n-hexane by gently stirring via a magnetic stirrer. the emulsion was established by adding the internal phase (hcl) dropwise to the organic membrane phase (span 80 and n-hexane as a solvent) while using a homogenizer. the resulting emulsion was then added to the external phase while mixing continuously. dispersion occurs in the shape of globule formation, where each globule is made of stripping solution droplets encased in the membrane solution. samples were withdrawn from the mixture at certain time intervals of 1, 2, 4, 6, 8, 10, 15, and 20min. the sample containing both the emulsion and the external phase was filtered (pore size 0.22µ m diameter). after extraction, a separation of the emulsion from the feed solution was carried out by gravity, and a demulsification process was carried out by applying a centrifugal force to the emulsion (4000rpm for 30min) to segregate the phases, while the contaminant would be extracted as a concentrated solution. the cp concentration in the separated external phase and the filtered samples was measured periodically using an ultraviolet spectrophotometer (uv). figure 1 shows the elm process. fig. 1. flow diagram of batch process elm. iii. analysis and calculations a. extraction process of cp the cp concentration in the separated phase solution was measured by the ultraviolet spectrophotometer having 290nm uv wavelength. subsequently, the percentage of cp extraction was calculated using [20]: ��������� ������� � �� %� � ������ � 100 (1) where co and c represent the initial cp concentration and the cp concentration after a specified time interval, respectively. b. stripping the resulting emulsion was allowed to be naturally separated from the feed solution by gravity, then a demulsification process was achieved by applying centrifugal force on the emulsion. the cp concentration extracted from the internal aqueous solution was measured, and the stripping efficiency was then estimated according to [20]: ������� � �s%� � ��,� !�"���,#$! ∗ 100 (2) where cf,int and cf,ext represent the final cp concentration in the internal and external phases, respectively. c. membrane leakage/breakage stabilization is achieved by adding the surfactant, thus the extraction efficiency of any solute is mainly affected by emulsion stability [21]. the breakdown of the emulsion usually occurs after a period when the emulsion is considered unstable, causing a gradual lowering of the removal efficiency along with a significant loss of extracted species [22]. the stability of the liquid membrane is considered the most essential factor affecting the efficiency of solute removal [23]. the tracer method (h+ ion of the internal phase) was used to evaluate the stability because this tracer is easily detectable by a ph meter. breakage is the result of tracer transfer from internal-toexternal phase solutions. any alteration in the ph of the feed engineering, technology & applied science research vol. 13, no. 1, 2023, 9872-9878 9874 www.etasr.com al-damluji & mohammed: performance evaluation of emulsion liquid membrane on chlorpyrifos … phase (i.e. leaking h+ ions) results from the emulsion breaking (rupture) because of the excretion of the hcl from the internal to the external aqueous phase. the emulsion rupture or breakage (ε) signifies the internal aqueous phase volume leaked to the external feed aqueous phase ratio using [20]: &�%� � '('�° ∗ 100 (3) where vs represents the leaked volume of the stripping phase (internal phase) and *+° represents the initial volume of the internal stripping phase. vs was computed using [24]: *, � *-° ∗ ./0123�./012 ./012��24 567 (4) where *-° is the external feed phase initial volume, ph is the external feed ph having been in contact with the organic emulsion, pho is the initial external phase ph, and 89 4 +:; is the initial acid concentration (h+) of the internal phase solution. iv. results and discussion a. effect of internal to membrane phase volume ratio the volume ratio of the internal to organic membrane phase must be satisfied to achieve a better transfer rate of the solute within the organic membrane and reduce emulsion interface thickness [25]. the appropriate amount of volume ratio improves solute transport through the organic membrane. different internal-membrane phase ratios (1:3, 1:2, 1:1, 2:1, 3:1) were selected to study their influence on emulsion stability, in addition to the cp removal efficiency. figure 2 shows the profiles of emulsion breakage percentage and extraction and stripping efficiency. increasing the ratio from 1:3 to 1:1, i.e. equalizing membrane phase with internal phase volume, caused a decrease in breakage from 2.44% to 0.82% and increased the extraction and stripping efficiencies of cp to a maximum of 90.3% and 86.2%, respectively. this could be because at a lower volume ratio (1:3), an abundance of oil phase volume led to the creation of a thicker interface and more viscous emulsion that hindered internal phase diffusion into the membrane [20]. fig. 2. effect of internal-to-membrane ratio on membrane breakage percentage, extraction, and stripping efficiencies (stirring speed: 300rpm for 5min, external ph = 7, external to emulsion phase volume ratio: 10/1). additionally, at low volume ratios, the lowering in extraction efficiency due to a smaller amount of the internal phase (stripping agent) extracted the solute from the organic membrane phase. a further increase in ratio from 1:1 to 3:1, i.e. increasing the volume of the internal phase related to the organic membrane phase, caused an evident waning in stability. breakage elevated to 5.48%, while extraction and stripping efficiencies reduced to 61.1% and 62.7%, respectively. this decrease in efficiency occurred because of the insufficient membrane volume that caused a partial entrapment of the internal droplet, hence, droplets tended to leak out of the bubble towards the aqueous feed phase [26]. similar results were recorded in [27]. therefore, a 1:1 volume ratio of internal to organic membrane phase was designated and considered the best ratio to achieve the highest extraction efficiency. b. effect of external to emulsion volume ratio experiments were carried out for the following ratios: 250/10, 250/25, 250/50, 250/75, and 250/100, by altering the emulsion volume only while maintaining a fixed volume of external feed aqueous phase. figure 3 displays the extraction, stripping efficiency, and emulsion breakage percent for different treatment ratios. fig. 3. effect of external-to-emulsion phase ratio on membrane breakage percentage, extraction, and stripping efficiencies (stirring speed: 300rpm for 5min, internal to membrane ratio: 1/1, external phase ph = 7). the results show that a decrease in the treatment ratio to 250/50 improved extraction efficiency and decreased breakage from 84.3% and 2.1% to 92.1% and 0.8%, respectively. with decreasing the ratio, the swelling phenomena develop and become fast, and also an occurrence of substantial internal droplets coalescence that will eventually grow in size [20]. this could be explained that due to the volume increase of emulsion, more quantity would be available to add to the progress of cp transport. furthermore, a big volume of the emulsion favors an enormous number of globules formation in providing a vast surface area for exchange, thus an enhanced rate of solute transfer. another possible reason could be because of the increase in emulsion holdup that further increases the interfacial area for a better rate of mass transfer [28]. further decreasing the volume ratio to 250/100 causes a substantial reduction in extraction efficiency to 83.9%. this could be due to the limited interfacial area available for the solute mass transfer rate, owing to the challenges in dispersing the emulsion into the aqueous feed solution due to the emulsion's large engineering, technology & applied science research vol. 13, no. 1, 2023, 9872-9878 9875 www.etasr.com al-damluji & mohammed: performance evaluation of emulsion liquid membrane on chlorpyrifos … volume that increases its total viscosity causing an adverse effect on the interfacial area [29]. as a result, the 250/50 treatment ratio was chosen as the best ratio. c. effect of mixing time mixing time can be specified as the time required to achieve maximum extraction and is a necessary factor in the elm process [30]. mixing time, also known as contact time, is defined as the period in which the external feed phase stays in direct contact with the emulsion while continuously stirring [31, 32]. figure 4 shows the effect of mixing time on emulsion breakage and the percentages of extraction and stripping for times ranging from 2 to 20 minutes. when increasing mixing time, cp extraction and stripping efficiency keep increasing, reaching an optimal level at 10min of 93.8% and 94.7%, respectively, while the breakage percentage is reduced to a minimum of 0.73%. longer contact time would cause the internal phase solution to move toward the feed solution due to the increased emulsion breakage [33, 34]. therefore, the extracted molecules revert backward to the feed phase, decreasing extraction and stripping efficiencies. therefore, a mixing time of 10 minutes was chosen as the optimal period to extract cp. fig. 4. effect of mixing time on membrane breakage, and extraction and stripping efficiencies (stirring speed: 300rpm, external phase ph = 7, feed phase to emulsion ratio: 5/1, internal to organic membrane ratio: 1/1). d. effect of external phase ph the ph of the external phase is a significant factor for extraction purposes [35]. additionally, ph also influences membrane stability, considering that it can accelerate the emulsion demulsification process. the tests were carried out at different ph values in basic, neutral, and acidic mediums ranging from ph 3 to 8. figure 5 presents the effects of external feed ph on extraction percentage, stripping efficiency, and organic emulsion breakage. cp extraction and stripping efficiency are exceedingly influenced by the external phase ph. for a highly acidic solution of ph=3, the extraction and stripping efficiencies were 62.72% and 85%, respectively, while the emulsion breakage was found to be at its peak at 7.41%. this could be attributed to the higher h+ ion concentrations which reduce the surfactant properties [12], causing a de-stabilization process that leads to a drop in cp extraction efficiency. the higher the initial concentration of h+, the lower the extraction efficiency is [36]. when increasing ph towards a neutral medium (ph=6), increase in both extraction and stripping efficiency occurs, reaching maximum values of 95.3% and 97.2%, respectively, while the breakage percentage is reduced to 0.69% within 10min of stirring time. however, the cp extraction efficiency decreases continuously when further increasing ph, while the breakage increases gradually at 82.8% and 1.89%, respectively, for ph=8. this could be explained by the released protons as the result of an anion exchange reaction [37]. also, due to the increase in ph, a formation of other species occurs [36]. therefore, it was appropriate to maintain the ph of the external feed phase at 6. fig. 5. effect of external phase ph on membrane breakage, extraction, and stripping efficiency (stirring speed: 300rpm for 10min, feed phase to emulsion ratio: 5/1, internal to organic membrane ratio: 1/1). e. effect of stirring speed a set of experiments was conducted to study the effect of different mixing speeds (200, 250, 300, and 350rpm) on extraction efficiency, stripping efficiency, and membrane breakage, while the other parameters were: mixing time: 10 min, external phase ph=6, external phase to emulsion volume ratio: 5/1, and internal to organic membrane phase ratio: 1/1. figure 6 displays the experimental results. at lower mixing speeds (200rpm), a minimum membrane breakage value was recorded (0.81%) due to the insufficient shear that resulted from the impeller dispersing emulsion. this could be because lower stirring speeds cause the formation of large globules, increasing the membrane thickness. although low values of membrane breakage were noted, slow stirring speeds do not usually improve the extraction and stripping efficiencies (89.39% and 93.6%, respectively, for 200rpm stirring speed), since large globules of emulsion minimize the available area for mass transfer [38]. however, using high mixing speeds (over 250rpm) was not beneficial neither to emulsion stability nor to extraction efficiency (2.63% and 84.84%, respectively, for 350rpm). figure 6 proves that increasing speed above 250rpm leads to the deterioration of the organic membrane. elevated levels of membrane leakage are predicted at higher mixing speeds since the emulsion can not bear the excessive shear delivered by impellers in addition to the contactor wall [39], causing an easy rupture of the membrane wall, discharging the already extracted solute into the feed phase. as the emulsion was produced from a viscous component, the stability of the emulsion was sustained at 250rpm stirring speed engineering, technology & applied science research vol. 13, no. 1, 2023, 9872-9878 9876 www.etasr.com al-damluji & mohammed: performance evaluation of emulsion liquid membrane on chlorpyrifos … because of the rigid membrane wall. at 250rpm stirring speed, 0.66% membrane breakage, 96.1% extraction percentage, and 95.7% stripping efficiency were registered. thus, 250rpm was considered the critical speed of stirring. fig. 6. effect of stirring speed on membrane breakage, extraction and stripping efficiencies for 10min (external phase ph = 6, external to organic emulsion volume ratio: 5/1, and internal to membrane volume ratio: 1/1). f. f. evaluation of the solute (cp) extraction kinetics and estimation of mass transfer coefficient the extraction kinetics of cp using the elm method were investigated following the approach in [40, 41], using the firstorder equation: < � ���� � = >�-( . � (5) where t represents time in minutes, and kobs is the rate constant of extraction (min−1), which can be evaluated from the slope of the resulting line from the previous equation representing the kobs value. because the obtained value was positive, the extraction process follows the first-order kinetics. the obtained kobs value was 0.2173min −1. the total mass transfer coefficient for the elm system was found by [42]: . @a � .@b c . @d (6) where kt is the total mass transfer coefficient (m/s), kf is the interfacial reaction rate constant (m/s), and km represents the mass transfer coefficient of the external phase (m/s), estimated by the skelland–lee correlation [40] given by: @d √fg � 2.932 ∗ 10�k l mnomp'+o'qo'rs t� ..uk. lvws /.xyz (7) where n is mixing speed (rpm), t and d are the mixing tank and impeller diameter (m), respectively, vi, ve, and vm denote the internal, external, and membrane phase volumes, and d represents the species diffusivity (cp) in the organic membrane phase, determined using wilke–chang correlation [43] shown in (9). t� � [ v \]#$!. ^_`7. (8) where ρext. is the density (kg/m 3) and μext. is the viscosity (kg/m×s). the calculated re value was equal to 348577. a � ..k.u∗./ 0b∗�c∗∅�e.f∗w#gh. ig∗ ∅je.k (9) where m is the solvent molecular weight (n-hexane=86.18 kg/kmol), temp is the temperature in kelvin, φ is the solvent association factor (n-hexane=1), μm is the membrane viscosity (12.224×10−3kg/m×s), and φc is the molar volume of the cp evaluated using schroeder method [44]. the φc was 0.399m3/kmol, d was 6.79×10-10m2/s, and km was 2.6×10 -4m/s. kf was calculated through: < l ���s � =l . >m . � (10) kf could be calculated by comparing (10) and (5): >m � @nop q (11) where a represents the emulsion-specific interfacial area, given by [45]: l � q�m � r s vt\ (12) where ai is the interfacial area of the emulsion droplet, v is the unit volume of the emulsion, α represents the water volume fraction, and d32 represents the diameter of the emulsion droplet. finally, the calculated mass transfer coefficients were: km = 2.6×10 -4m/s, kf = 3.89×10 -9m/s, and kt = 3.89×10 -9m/s. v. conclusions this study investigated the stability and extraction efficiency of elm for removing chlorpyrifos pesticide from wastewater. a minimum emulsion breakage of 0.66% along with the highest removal percentage of 96.1% and 95.7% stripping efficiencies were achieved at the best operating experimental conditions, which were: internal-to-membrane volume ratio: 1:1, external feed solution ph: 6, stirring speed: 250rpm, external phase-to-emulsion ratio: 250:50 at 10min contact time, no requirement of an additional carrier, and the mass transfer coefficients km, kf, and kt had values of 2.6×10 4m/s, 3.89×10-9m/s, and 3.89×10-9m/s, respectively. in general, it can be concluded that elm is a productive, efficient, and suitable advanced separation method for the treatment of wastewater contaminated with pesticides. references [1] i. a. saleh, n. zouari, and m. a. al-ghouti, "removal of pesticides from water and wastewater: chemical, physical and biological treatment approaches," environmental technology & innovation, vol. 19, aug. 2020, art. no. 101026, https://doi.org/10.1016/j.eti.2020.101026. 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[45] v. karcher, f. a. perrechil, and a. c. bannwart, "interfacial energy during the emulsification of water-in-heavy crude oil emulsions," brazilian journal of chemical engineering, vol. 32, pp. 127–137, mar. 2015, https://doi.org/10.1590/0104-6632.20150321s00002696. microsoft word etasr_v13_n2_pp10601-10607 engineering, technology & applied science research vol. 13, no. 2, 2023, 10601-10607 10601 www.etasr.com harrag & harrag: fuzzy-zrp: an adaptive manet radius zone routing protocol fuzzy-zrp: an adaptive manet radius zone routing protocol nassir harrag mechatronics laboratory, ferhat abbas university, algeria nassir.harrag@gmail.com (corresponding author) abdelghani harrag mechatronics laboratory, ferhat abbas university, algeria abdelghani.harrag@gmail.com received: 25 january 2023 | revised: 24 february 2023 and 3 march 2023 | accepted: 6 march 2023 abstract a mobile ad-hoc network (manet) is a group of active mobile nodes wirelessly connected in a selfconfiguring and self-healing network without a preexisting centralized infrastructure. several studies have been conducted to improve the stability and lifetime of routes for communicating between source and destination nodes, integrating new techniques with existing protocols. this paper presents a fuzzy-based approach to improve the performance of the standard zone routing protocol (zrp) by selecting the optimal value of the zone radius. each node has a fuzzy inference system that is periodically fed with parameters, such as the remaining energy and mobility of the node, to calculate the optimal value of the zone routing radius, which makes the node autonomous and intelligent. the simulation results obtained using the ns-2 simulator showed that the proposed fuzzy radius approach outperformed the standard zrp, ovbazrp, and psozrp routing protocols in all measures considered: pdr, nrl, and e2ed. keywords-ad hoc; manet; hybrid routing protocol; zrp; fuzzy logic; radius i. introduction mobile ad-hoc networks (manets) are becoming a significant technology in telecommunication networks and have attracted considerable attention over the past decades. most manet applications are suitable in a wide range of fields that require rapid deployment, such as military battlefields, emergency searches, rescue sites, classrooms, and conferences where participants dynamically share information using their mobile devices [1-2]. a manet is a set of active mobile nodes that organize and configure themselves dynamically to form a wireless network without an administrator. each node can communicate with others directly, if within transmission range, or indirectly, by relaying by intermediate mobile nodes. manet nodes can move at any speed and in any direction independently. moreover, they can join or leave the network arbitrarily. due to the main characteristics of manets, such as high mobility, low bandwidth, and low power, developing an efficient routing protocol is a critical task [3-4]. the three main types of routing protocols in manets are proactive, reactive, and hybrid [5-6]. proactive routing saves the network topology by keeping the route to each node in a particular routing table and updating it continuously [7], which speeds up sending packets from the source to the target. on the other hand, reactive routing protocols send control messages only upon request, providing a route to send a packet from a source to a specific target [8], reducing network overload. finally, hybrid-routing protocols combine the advantages of proactive to deliver packets to nodes within the network while using reactive techniques to forward packets to nodes outside the network [9-10]. among the manet protocols that handle the above problems [11-12], zrp [13] has an advanced position. zrp is a hybrid wireless routing protocol that offers the advantage of adapting to various network conditions. typically, zrp is designed to speed up delivery and reduce processing costs by applying a proactive paradigm inside a zone and a reactive paradigm outside it. in the proactive scheme, the zrp collects neighborhood information in a local region of the network called the routing area. in contrast, reactive routing operates globally, where an on-demand routing protocol does not require neighborhood information [14-15]. to optimize the network's performance, zrp uses an essential factor, the zone radius (by default 2), which plays a critical role between the network's overload and the delay in transferring packets by dividing the network into zones. therefore, decreasing the radius value reduces proactive routing and increases the area of reactive routing, thus reducing network load and increasing delay in the message routing process, and vice versa [1]. the node's mobility significantly impacts the network's performance and depends mainly on speed and pause factors. engineering, technology & applied science research vol. 13, no. 2, 2023, 10601-10607 10602 www.etasr.com harrag & harrag: fuzzy-zrp: an adaptive manet radius zone routing protocol for example, for a high-mobility network with fast nodes and low pause time, the topology will constantly change, increasing the network's routing load and energy consumption because of the significant loss of communication between nodes due to the departure of the node. on the contrary, for a stable network with low-speed nodes and high pause times, the network topology will become more stable and the chances of communication between the nodes will increase. therefore, reducing the network's routing load reduces energy consumption. the independent zone routing protocol (izrp) depends on the local network conditions that vary considerably due to the movement of the nodes [1-5]. using this protocol, each node in the network can fine-tune its optimal area radius, making it independent and adaptable. izrp is based on a hybrid scheme that combines minimum search and adaptive traffic estimation schemes [1]. this hybrid scheme aims to create a minimal amount of extra overhead by dynamically adjusting and reconfiguring the optimal zone radius of each node in a distributed manner, which allows network nodes to adapt quickly to any changes in the network's characteristics. the minimum search scheme iteratively estimates the radius of the routing area of a node by incrementing or decrementing it by one hop. at first, the amount of routing traffic passing through the node in the current estimation interval is measured and compared to the previous interval. if it is smaller, the radius of the area is incremented/decremented in the same direction. if not, the direction of the zone radius change is reversed. this process continues until a minimum is detected. the adaptive traffic estimation scheme relies on γ(ρ), represented by the ratio of reactive to proactive traffic of the zone radius during a specific estimation interval, by comparing it with a predetermined threshold γthres. if γ(ρ) > γthres, an increment or decrement of the radius ρ will be triggered to decrease the routing of reactive/proactive traffic respectively, as shown in figure 1. (a) (b) fig. 1. (a) min searching algorithm, (b) zrp zone routing radius optimization. the enhanced zone routing protocol (ezrp) is more efficient than zrp [16], as it avoids network congestion by reducing the number of ierp packets using a fixed value for the area radius, mobility, and packet size. velocity-based adaptive zrp (vbazrp) is an enhancement of zrp in ad hoc networks [17], which allows nodes to select the radius of the area based on their respective mobility and reduces the discovery delay resulting from the incorporation of an asymmetric request and response mechanism to maintain the routing area. the speed-optimized adaptive zrp (ovbazrp) performed better than zrp in increasing network traffic loads by allowing the zone radius to be selected according to the mobility speed of the node [18]. particle swarm optimization intelligence-independent zrp (pso-izrp) dynamically determines the zone radius based on the velocity and location of the nodes by tracking the optimum in the space of solutions that satisfies the constraints of the objective function to calculate the radius at each interval [19]. another improvement of zrp was proposed in [20], by a novel technique named zone-based energy-aware hybrid multicast routing protocol (zehmrp), which selects stable routes for multicast packet delivery based on the residual energy of nodes in areas along the route to reduce control overhead and delay in packet delivery. the energy-efficient zone routing algorithm [21], improves the clustering mechanism by using the energy loss rate of the nodes in the zone and considering the nodes with the highest residual energy as cluster heads in each iteration. in zrp fuzzy-based scheduling and load balance [22], the service cycles of the border nodes are adaptively adjusted according to the state of the queue, the expected residual energy, and the distance to the border nodes. in [23], a logic-based control (flc) method was proposed to improve qos for manets. as in zrp, the mobility of the network nodes was used to establish probabilistic qos. this paper proposes a zone radius determination algorithm based on a fuzzy inference system, named fuzzy-zrp, that improves the routing performance of the standard zrp in wireless ad-hoc networks. furthermore, simulations showed that fuzzy-zrp outperformed the standard zrp. fuzzy-zrp tunes the radius value of each zone by estimating it based on the node's residual energy and speed, leading to increased network lifetime and reduced overload regardless of network conditions. this study aims to achieve the following objectives:  an adaptive algorithm where each node can rapidly adapt to network conditions.  a multi-constraint fuzzy logic controller that makes the algorithm autonomous in the sense that it can automatically estimate the optimal value of the radius zone based on the node's residual energy and speed.  different realistic scenarios with different mobility models were considered to study the performance of fuzzy zrp in terms of packet delivery rate, routing overhead, and end-toend delay. ii. materials and methods this section describes the modification of the classical zrp to improve the radius selection scheme and enhance network performance by using a fuzzy logic inference system. a. standard zrp the standard zrp is based on the division of the network in zones. each zone consists of nodes within the maximum hop distance r. the radius is defined as a circle around the node with the value r (default=2). it should be noted that the zone is defined in hops, not as physical distance [13]. zrp uses the proactive paradigm within the zone by applying the intra-zone routing protocol (iarp) [15]. in contrast, the reactive paradigm engineering, technology & applied science research vol. 13, no. 2, 2023, 10601-10607 10603 www.etasr.com harrag & harrag: fuzzy-zrp: an adaptive manet radius zone routing protocol is provided by the interarea routing protocol (ierp). a route to a destination in the local area can be established from the source routing table proactively cached by the iarp; therefore, if the source and the destination are in the same area, the packet can be delivered immediately. the hybrid zone routing protocol can adapt to a wide variety of network scenarios by proactively adjusting the range of nodes and maintaining routing zones. large routing areas are preferable when the demand for routes is high and/or the network is composed of many slow-moving nodes. in the extreme case of a fixed topology, the ideal routing area radius would be infinitely large. on the other hand, smaller routing areas are appropriate in situations where route demand is low and/or the network consists of a small number of nodes that move quickly relatively to each other. in the worst case, a onehop radius routing area is the best, and zrp defaults to a traditional reactive flooding protocol [13]. for a particular network scenario and proper configuration, zrp performs at least as well (and often better than) its purely proactive and reactive constituent protocols. in situations where network behavior varies across different regions, zrp's performance can be fine-tuned by individual adjustment of each node's routing zone [24]. b. proposed fuzzy-zrp in traditional zrp, the value used for each area radius is a constant p, manually initialized by an expert (the default is 2). it is not enough to obtain the best performance of the protocol for a given scenario either the state of the network is stable or unstable. in the proposed fuzzy-zrp, important node metrics, such as node residual energy and mobility, are considered to automatically estimate the radius zone's value. furthermore, a faster speed means that a node has to reduce its radius to guarantee the stability of the network connection, while a slower speed increases it. this is accomplished by iteratively fine-tuning the value of radius p after calculating residual energy and speed. the decision to start the process is made during a fixed period by a fuzzy logic system [25]. 1) energy and speed calculation at the initial stage, each network node starts to calculate the information needed to feed the system inference, which is represented by:  energy (en): represents the remaining energy in the battery of the node in question, valued as a percentage (%). ��������� ��� �� (1) where re(t) is the remaining energy of the node at time t, and ie is the initial energy of the node at time t0.  speed (sp): represents the speed at time t valued in m/s. 2) radius zone selection using fuzzy logic fuzzy logic is suitable for problems that require a decision [26]. a fuzzy system describes the relationship between fuzzy input and output variables using if-then-based rules [27]. as shown in figure 2, the system consists of fuzzification, defuzzification, and a fuzzy inference engine. fuzzification represents the decisive input variables in fuzzy set membership functions. in contrast, defuzzification converts the fuzzy output into decisive values using a mathematical formula. at the same time, the inference engine calculates the fuzzy output according to the rules listed in table 1. fig. 2. fuzzy system architecture. to work with a fuzzy inference system, the input and output variables must be defined as membership functions. then fuzzy rules are proposed to relate input to output memberships [28]. the membership functions should be represented by a graphical interpretation of the input and output linguistic variables. in this case, the inputs are the node's residual energy and speed, and the output is the node's radius value. equations (2) and (3) illustrate triangular and trapezoid membership functions that describe the input and output membership degrees of the input and output variables for fuzzy inference. the residual energy of the nodes is treated as a critical input value, which directly impacts the network's lifetime and communication through the transmission and reception of packets and internal computational processes [29]. the node speed input parameter also significantly affects the stability of the network, as nodes with higher speeds increase the probability of route failure and control overhead. ��� �� ⎩⎪ ⎨ ⎪⎧ 0 � � ������ ����� �� � � � �!�"# !���� � � � � $�0 � % $� (2) ��& �� ⎩⎪ ⎨ ⎪⎧ 0 � � �'���& ����& �' � � � '1 ' � � � $'!&"# !&��& $' � � � )'0 � % )' (3) the fuzzy inference engine relies on a knowledge base of rules that define the input and output membership functions. as shown in table i, the proposed system consists of nine rules calculated by multiplying the number of membership functions characterized by each input variable. these memberships are associated using a particular fuzzy operator represented by the and. for example, selecting the ninth rule, which supposes that the node's residual energy and speed are high, the node radius value should be very low. if the node's residual energy is low and the speed is high, the output of the inference is very high. defuzzification is a weighted average mathematical approach to extract a net output value from the aggregation of the fuzzy output representation. several approaches have been proposed to find crisp output, and this method used the centroid engineering, technology & applied science research vol. 13, no. 2, 2023, 10601-10607 10604 www.etasr.com harrag & harrag: fuzzy-zrp: an adaptive manet radius zone routing protocol defuzzification method that has the following mathematical expression: *+, ./�� .� 1#./�� .1# (4) where ua(x) is the weight of the output membership function defined in (2) and (3), x denotes the centroid of each output membership function, and cog (center of gravity) indicates the crisp value of the defuzzified output[26-30]. table i. fuzzy base rule set rules speed energy radius 1 low high very high 2 low medium high 3 low low medium 4 medium high high 5 medium medium medium 6 medium low low 7 high high very low 8 high medium low 9 high low medium fig. 3. membership function of the residual energy input. fig. 4. membership function of the node speed input. fig. 5. output membership function of the node radius. c. description of the proposed fuzzy logic algorithm the description of the proposed algorithm can be summarized in four basic steps: fuzzification, if-then rule evaluation, output aggregation, and defuzzification to calculate the crisp value. these steps can be described as:  step 1: the fuzzification of the crisp input parameter values represented by the residual energy and the node velocity is defined by their membership functions, as shown in figures 3-5. each input's membership degree is found by mapping the input value with the membership function.  step 2: the membership degrees found in the first step will be evaluated from the rules to determine the fuzzy output set. the and operator selects the minimum membership values from the input membership values.  step 3: the system collects all output from the previous step in union form and constructs a new aggregate fuzzy set by selecting the maximum evaluating values using the or operator.  step 4: the defuzzification process is performed using the centroid method (center of gravity) with the new aggregate function obtained in step 3 to calculate the node radius value using (4). iii. performance metrics the performance of the proposed algorithm was compared with the standard zrp, the ovbazrp, and the practical swarm-optimized zrp (psozrp) considering the packet delivery ratio (pdr), the end-to-end delay (e2ed), and the network routing load (nrl). table ii. performance of zrp and proposed algorithm parameters zrp algorithm proposed algorithm pdr avg high nrl high low e2ed high low  pdr is the fraction of the data packets successfully delivered to the destination [31]: pdr= ∑ 3�!45 6 75!58951 �: 156 8;� 8<; ∑ 3�!45 6 65; 6 �: =5 6<.7!5 � 100 (5)  nrl is the ratio of routing packets transmitted to data packets delivered [32]: nrl= ∑ 7�;6>8 51 7<. 8;? 3�!45 6 ∑ 3�!45 6 75!58951 �: =5 156 8;� 8<; (6)  e2ed is the average end-to-end delay, calculated by summing the times taken by all received packets divided by their total numbers[32]: e2ed= ∑�3�!45 6 75!58951 8>5�3�!45 6 65;1 8>5 ∑ â!45 6 75!58951 �: =5 156 8;� 8<; (7) iv. simulation environment a. simulation parameters: the simulation study considered a network area of 1000×1000m 2 and 50 wireless mobile nodes randomly distributed throughout the simulation area with a maximum speed of 50m/s. tables iii and iv show the speed scenarios and simulation parameters. engineering, technology & applied science research vol. 13, no. 2, 2023, 10601-10607 10605 www.etasr.com harrag & harrag: fuzzy-zrp: an adaptive manet radius zone routing protocol table iii. speed scenarios case 1 case 2 case 3 case 4 case 5 5m/s 10m/s 30m/s 40m/s 50m/s table iv. parameters of simulation scenario parameters value simulation time 300s simulation area 1000×1000m 2 node speed 0-50m/s propagation model two ray ground mobility model random waypoint radio frequency 2.47ghz channel bandwidth 2 mbps mac protocol ieee 802.11 type dataflow cbr number of nodes 50 assigned energy 20j transmit power 0.8w receive power 0.5w b. simulation metrics: the performance of manet routing protocols can be evaluated using many quantitative metrics. this study used packet delivery ratio (pdr), end-to-end delay (e2ed), and normalized routing load (nrl) to evaluate the performance of the proposed routing protocol simulation, as shown in (5)(7). v. results and discussion the ns-2 simulator [33] was used to simulate and compare the performance of the proposed fuzzy-zrp with zrp, ovbazrp, and psozrp, based on different speed scenarios. a. packet delivery ratio figure 6 shows the packet delivery ratio for the compared protocols with variable speeds of the nodes. it is clear that the proposed fuzzy-zrp protocol outperformed the other protocols and achieved a higher pdr. however, the pdr of all protocols decreased with increasing speed, due to the increasing number of broken links in the network which increased by the mobility rate. the proposed fuzzy-zrp algorithm achieved the highest pdr mainly due to the dynamic area radius determination adopted, which balances the iarp and ierp routing overhead. thus, channels and bandwidth are available for data traffic, improving the pdr. the psozrp dynamically determines the radius of the zone based on the speed and location of the nodes. it searches the entire space for the best optimum that satisfies the constraints of the objective function to calculate the radius at each point in time, generating additional traffic that decreases the bandwidth needed for the actual data transfer. for the ovbazrp, the determination of the radius is based only on the speed of the node and completely ignores local parameters such as the remaining energy, which is an important factor in determining the stability of the route. the zrp uses a static radius value for all nodes as a mechanism without taking into account local network parameters. this radius value setting causes an imbalance between iarp and ierp, leading to a reduction in packet transfer rates. figure 7 clearly shows the pdr gain for the proposed fuzzy-zrp compared to the others for all speed scenarios. the pdr ranged from 6.02 to 13.15% for fuzzyzrp and conventional zrp, the gain of fuzzy-zrp over ovbazrp was between 4.30 and 10.40%, the gain of fuzzyzrp with psozrp was between 1.80% and 6.20%. fig. 6. packet delivery ratio vs speed. fig. 7. packet delivery ratio gain. b. average end-to-end delay as shown in figures 8-9, fuzzy-zrp had a lower average delay than zrp, ovbazrp, and psozrp in all speed scenarios. this is because zrp uses a static zone radius regardless of the network state. however, for a stable network, the proposed fuzzy-zrp algorithm increased the area radius, forcing a larger area to be covered by the iarp protocol. therefore, the ierp protocol only controls a smaller area to reduce the latency incurred by the route discovery process. on the other hand, by increasing mobility, a smaller area radius forces the ierp to take care of a larger area to minimize the iarp overhead involved in updating and maintaining the routing table. for psozrp, the transfer time is influenced by the time taken to search for the best value of the zone radius at each timestamp. additionally, ovbazrp suffers from the inability to determine an unstable route in a short time. as shown in figure 9, the gain obtained by incorporating the proposed fuzzy-zrp in the zone radius estimation over zrp varied between 2 and 53%, over ovbazrp varied between 1.80 to 30%, and over fuzzy-zrp and psozrp varied from 0.8% to 20%. engineering, technology & applied science research vol. 13, no. 2, 2023, 10601-10607 10606 www.etasr.com harrag & harrag: fuzzy-zrp: an adaptive manet radius zone routing protocol fig. 8. end-to-end delay vs speed. fig. 9. end-to-end delay gain. fig. 10. normalized routing load vs speed. c. normalized routing load figure 10 shows the effects of node mobility on routing control packets in the two routing scenarios used in this study. as can be seen, the overhead of routing packets increases with the speed of the nodes. although fuzzy-zrp minimizes the number of control packets transmitted to the network, it maintains a different zone radius for each node depending on mobility speed and energy. the nodes in different zones have different views of the current network topology. thus, nodes can establish more stable and reliable routes by minimizing the zone radius. psozrp iteratively performs the process of finding the optimal value of the zone radius, generating additional control packets to determine information on the speed and location of each node. as shown in figure 10, the gain obtained by applying the fuzzy-zrp protocol compared to zrp varied between 21% and 46%, the difference between fuzzy-zrp and ovbazrp was 12-38%, and for fuzzy-zrp compared to psozrp was 4-8%. fig. 11. normalized routing load gain. vi. conclusion this study investigated the problem of adjusting the radius of the zrp by proposing a fuzzy-based approach that provides an auto-tuning method to automatically adjust the radius. the simulation results showed that, compared to other approaches such as psozrp, ovbazrp, and classical zrp, the proposed fuzzy-based zrp method effectively improved the overhead of control traffic without sacrificing other performance metrics, such as packet delivery ratio and average end-to-end delay, and without requiring manual configuration. compared to classical zrp, the proposed approach improved pdr by 6.02-13.15%, nrl by 21-46%, and e2ed by 2-53%. the proposed protocol achieved a significant gain compared to ovbazrp in pdr by 4.30-10.40%, nrl by 12-38%, and e2ed by 1.8-30%. finally, the proposed fuzzy-zrp outperformed psozrp with gains of 1.80-6.20% in pdr, 4-8% in nrl, and 0.8-20% in e2ed. references [1] p. samar, m. r. pearlman, 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[28] w. el-hajj, d. kountanis, a. al-fuqaha, and m. guizani, "a fuzzybased hierarchical energy efficient routing protocol for large scale mobile ad hoc networks (feer)," in 2006 ieee international conference on communications, istanbul, turkey, jun. 2006, vol. 8, pp. 3585–3590, https://doi.org/10.1109/icc.2006.255628. [29] m. youssef, m. ibrahim, m. abdelatif, l. chen, and a. v. vasilakos, "routing metrics of cognitive radio networks: a survey," ieee communications surveys & tutorials, vol. 16, no. 1, pp. 92–109, 2014, https://doi.org/10.1109/surv.2013.082713.00184. [30] g. kalpana and d. m. punithavalli, "fuzzy logic technique for gossip based reliable broadcasting in mobile ad hoc networks," journal of theoretical and applied information technology, vol. 51, no. 3, pp. 498–505, may 2005. 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[online]. available: https://www.isi.edu/nsnam/ns/. microsoft word etasr_v12_n3_pp8755-8759 engineering, technology & applied science research vol. 12, no. 3, 2022, 8755-8759 8755 www.etasr.com ribeiro do prado júnior et al.: utilizing numerical simulations to analyze the efficiency of a porous … utilizing numerical simulations to analyze the efficiency of a porous reactor wilson ribeiro do prado júnior department of basic science and environmental engineering school at lorena, university of são paulo lorena, são paulo, brasil wrpjunior@usp.br jairo aparecido martins research & development desch north america cambridge, ontario, canada jairo.martins@desch.com estaner claro romão department of basic science and environmental engineering school at lorena, university of são paulo lorena, são paulo, brasil estaner23@usp.br received: 28 march 2022 | revised: 16 april 2022 and 30 april 2022 | accepted: 7 may 2022 abstract-this paper presents a series of numerical simulations of a porous reactor, where a generic reaction between reagents is carried out, generating a product. all numerical simulations were performed by using the software comsol multiphysics, which made use of the navier-stokes and brinkman equations. these equations were utilized to govern the fluid flow in the numerical simulation. throughout the simulations, several initial parameters were altered to evaluate their impact on the reactor efficiency based on the concentration of component c. furthermore, other parameters such as the distribution of speed and geometry in the equipment were taken into consideration, and an optimal configuration for the case is demonstrated. keywords-numerical simulation; porous reactor; navier-stokes equations; brinkman equations i. introduction this works aims to study the effects of some process parameters in a reactor of porous media, to provide industrial improvements, and to maximize the obtained product for the same reactor or similar equipment. although the type of reactor studied in this work has several applications for expelling gas into the atmosphere, it is treated in a generic manner in order to reach a conclusion and extend it to any similar reactor. as an example, this type of reactor has several applications in industries, including internal combustion engines [1-3] where the post-treatment of exhausted gases can be numerically simulated [4-7]. in this paper, a generic case is assumed with a simple chemical equation to analyze this type of reactor, and the way its properties influence its performance, when the species a and b react to form the species c: ��� → � (1) since this reaction only occurs in a porous catalyst and the intention is to treat generic cases, the initial porosity is assumed as 0.3 and fixed with a low permeability established as 10 -9 , comparable with the permeability of brick or leather, which are in the range of 10 -9 to 10 -10 . this paper uses a modeled reactor with porous media as provided by comsol tm , with the adaptation shown in figure 1. fig. 1. model of the reactor of porous media showing the inlet and outlet. this paper's main idea is to numerically simulate the process of heterogeneous catalyzing between two species of reagents. it happens when the species � is injected into a reactor through a perpendicular tube while the species � gets into the tube by the tube’s main entrance (figure 1). both are partially mixed into the reactor before they pass through the porous media, where a reaction occurs and the third species � is obtained. this reaction happens with the transport of ideally inert gas in the reaction. so, it is expected with the simulations and improvements implemented to decrease the concentration of the species � being expelled out of the equipment. as described previously, this type of reactor can be utilized in combustion engines to reduce gas emissions to the atmosphere. further, several equations that govern the phenomenon are presented, also the main parameters utilized (chemical reaction, system geometry, mesh, etc.), and lastly, the obtained output is corresponding author: estaner claro romão engineering, technology & applied science research vol. 12, no. 3, 2022, 8755-8759 8756 www.etasr.com ribeiro do prado júnior et al.: utilizing numerical simulations to analyze the efficiency of a porous … shown. in addition, this work shows the way the sequence of analysis of the parameters is involved in the problem and the consequent optimization can bring benefits to the process and the economy by reducing operating costs. ii. flow in porous media a. transport of diluted species a diluted species has a very small concentration when compared with a solvent fluid. consequently, mixture properties such as density and dynamical viscosity may be considered equal to the solvent's. the equation of mass conservation used to calculate the transport of diluted species by diffusion and convection is given by [9]: ��� � � ∙� �� ∙ � � � (2) where � is the species concentration (mol/m3), � is the reaction rate of species i (mol/(m 3 ⋅s)), � is the fluid median velocity (m/s) and � is the diffusive flow vector (mol/(m2⋅s)). b. brinkman’s equations brinkman’s equations are an extension of darcy’s equation that describes the movement of a slow flow in porous media. it describes the dissipation of kinetic energy by the viscous shearing from navier-stokes equations, which describes the fast-flow movements throughout free channels. so, these equations calculate the fast movements of fluids in porous media with kinetic potential by velocity, pressure, and gravity into the flow. the flow in porous media is governed by the equation of continuity and momentum, converging to brinkman’s equation [9]: � � ������ ∙ ���� � �� (3) � �� ���� � �� ∙ � � �� � � !� ∙ " #�� $% � �� �� & ' (%� ∙ ��)*+ �κ,#% � -. ��/ �� � 0 (4) where % is the dynamic viscosity of the fluid (kg/(m⋅s)), � is the velocity vector, � is the density of the fluid (kg/m3), ! is the pressure (pa), �� is the porosity, κ is the permeability of the porous medium (m 2 ), and �� is a mass source or sink (kg/(m 3 ⋅s)). iii. modeling the phenomena the model for the phenomena of transport to diluted species utilized here is composed of the navier-stokes and brinkman equations (as mentioned above). here, an isothermal situation is adopted and the used gas transported is nitrogen. in terms of geometry, it complies with figure 2, where: h = 0.01, r = 0.01, hp = 0.003, ra = 0.0004, ha = 0.002, rai = 0.0002, d = 0.005, d = 0.003 (all in meters), that will be used in case 1. in terms of mesh building, the physical type of the element was considered, therefore, the "normal" mesh type was used, which has 166,645 domain elements, 16,556 boundary elements, and 758 edge elements. it is important to highlight that this work does not aim at a particular reaction, but rather a generic case is demonstrated. although in this simulation the kinetics of the reaction is governed by a generic equation, it is important to understand that a specific and real case requires a particular kinetics analysis. the expression that follows is the one utilized in this paper for the generic analysis: �� � �1 ∙ 2 �, 345∙6�78� ∙ �9 ∙ �: (5) where �� is the formation rate of species � (mol/(m3⋅s)), �1 is the frequency factor (m 3 /(s⋅mol)), ; is the activation energy (j/mol), �< is the universal constant of gases (j/(mol⋅k)), = >? is the isothermal temperature of reaction (k), �9 and �: are the concentrations (mol/(m 3 ⋅s)). fig. 2. geometric parameters of the reactor. iv. results and discussion even though the presented simulations came from innumerable combinations of the concentrations as inlets for each species, the velocity of each species, the adopted isothermal conditions, and the area of the region where the mixture occurs (hp), only the main results are presented in the paper. a. case 1 for this case, the following parameters are considered: � = 0.3, κ = 10 -9 m 2 , @9 = 0.025 m/s (velocity of input �), @: = 0.025 (velocity of input �), abc = abd = abe = 10-6 m2/s (diffusion coefficient of the species), �9 = 7 mol/m3 (initial concentration of species � ) and �: = 1 mol/m3 (initial concentration of species �). the concentration of species � (figure 3) is homogeneously distributed in the reactor, except in the entrance duct of species �, where the concentration is zero. we notice that in the upper part of the reactor inside and just after the porous media where the concentration of � drops approximately to 0.7 mol/m 3 . albeit this happens due to the system reaction, the lower part of the reactor remains practically the same as the initial concentration. fig. 3. case 1: distribution of the concentration of species � (mol/m3). engineering, technology & applied science research vol. 12, no. 3, 2022, 8755-8759 8757 www.etasr.com ribeiro do prado júnior et al.: utilizing numerical simulations to analyze the efficiency of a porous … fig. 4. case 1: distribution of the concentration of species � (mol/m3). the way the reaction happens is shown in figure 4. in the upper part of the reactor, almost there isn’t any formation of species � in the lower region. this matches with the result presented in figure 2, where species � has its concentration reduced in the upper region of the reactor. note that, soon after the porous media, species � starts to become homogeneous in the solution. by the dimension of the high of the duct (figure 5), it is possible to observe with more precision the concentration of the species � in the outlet of the reactor, which is between 0.78 mol/m 3 and 0.94 mol/m 3 . taking into consideration that the main objective of the process is to have the reduced concentration of the species � expelled from the reactor, it is not so efficient, since the substance entered the reactor where the initial concentration was 1 mol/m 3 and had a maximum reduction of 20%. fig. 5. case 1: concentration of species � in the reactor outlet. b. case 2 compared with case 1, a change in velocity of @9 = 0.075 m/s is adopted. the increase of the entrance velocity of species � in the reactor resulted in the consumption of species � being much more pronounced than verified in figure 6. nevertheless, since the duct entrance radius was kept the same, it resulted in a raise of the velocity and consequently a proportional increase of the flow of species � , which means that 3 times more reagent a would be required to produce a change in concentration. this condition is not satisfactory since it would end up elevating the cost of the process. fig. 6. case 2: distribution of the concentration of species � (mol/m3). c. case 3 compared with case 1, here the �9 is assumed to be 10 mol/m³. in this case, changing only the �9, resulted in a highly reduced variation of the limits presented in figures 5 and 7. this means that the superior limit of approximately 0.94 changed to 0.92 mol/m 3 , and the inferior limit from 0.78 to 0.74. both generate a very small "gain" when compared with an increase in the concentration of the species �. fig. 7. caso 3: concentration of species � in the reactor outlet. d. case 4 in this simulation a change of = >? = 400 k is adopted. fig. 8. case 4: distribution of the concentration of species � (mol/m3). an increase of the temperature (isothermal) in the system favors the reaction (figure 8), raising substantially the engineering, technology & applied science research vol. 12, no. 3, 2022, 8755-8759 8758 www.etasr.com ribeiro do prado júnior et al.: utilizing numerical simulations to analyze the efficiency of a porous … generation of a species �, which reaches close to triple its value at its maximum point, 0.59 mol/m 3 versus 0.22 mol/m 3 in the parameter of case 1. however, high heating, with an increase of 100 o c might be costly and even making unfeasible to build a reactor due to the needed material thermal properties requirements. e. case 5 in this simulation a change of hp = 4 mm is adopted. likewise case 3, this case (figure 9) does not result in an expressive benefit in the decreasing of the species � in the reactor outlet, but still ends up with an increase of 33% in the size of the porous region. fig. 9. case 5: concentration of species � in the reactor outlet. f. case 6 in this simulation, a change of d = 1 mm is adopted. an increase in the distance of entrance of species � (figure 10) towards the porous media in the reactor almost does not bring change to the process, even though it helps in the homogenously of the solution, which can be seen by the concentration of the species �. the formation happens in a more distributed shape in the porous media. fig. 10. case 6: distribution of the concentration of species � (mol/m3). g. optimization although most of the considered changes brought positive advantages, those resulted in a cost increase on the project coming from more expensive materials needed to build the reactor. this happens because the reactor had to withstand either extreme conditions or a considerable jump in the energy consumption or the reagents. a possible solution tested was to add these changes on a reduced scale, indeed, increasing the velocity of entrance of the species a by 0.05 m/s rather than tripling its value. making use of the following parameters: @9 = 0.030 m/s, �9 = 8 mol/m³, ra = 0.45 mm, rai = 0.25 mm, = >? = 350 k, hp = 3.5 mm, d = 1 mm, the results are presented in figure 11. fig. 11. optimization: concentration of species � in the reactor outlet. the results are satisfactory since a reduction of the concentration of � of approximately 50% can be obtained when compared with the inlet concentration. v. conclusions this paper made use of many numerical simulations to analyze the way the geometrical and physical-chemical properties of a reactor of porous media could influence its efficiency, analyzing them separately or in a group. it was concluded that many of the changes suggested resulted in good results or at least some impact on the reactor operation manner. however, many of them bring problems with applications like a need for more specific and expensive materials to build the reactor, something that ends up as economically unfeasible. by applying minor changes in the parameters that could result in a decrease in the residual concentration of species �, the process was optimized rather than opting for a change in only one parameter. acknowledgment the authors acknowledge the financial support by capes (process number 23038.000263/2022-19). references [1] m. weclas, "potential of porous-media combustion technology as applied to internal combustion engines," journal of thermodynamics, vol. 2010, feb. 2011, art. no. e789262, https://doi.org/10.1155/2010/ 789262. 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[5] j. p. muhirwa, s. i. mbalawata, and v. g. masanja, "markov chain monte carlo analysis of the variable-volume exothermic model for a continuously stirred tank reactor," engineering, technology & applied science research, vol. 11, no. 2, pp. 6919–6929, apr. 2021, https://doi.org/10.48084/etasr.3962. [6] h. a. maddah, "numerical analysis for the oxidation of phenol with tio2 in wastewater photocatalytic reactors," engineering, technology & applied science research, vol. 8, no. 5, pp. 3463–3469, oct. 2018, https://doi.org/10.48084/etasr.2304. [7] s. bekkouche and m. kadja, "numerical analysis of density-driven reactive flows in hele-shaw cell geometry," engineering, technology & applied science research, vol. 10, no. 2, pp. 5434–5440, apr. 2020, https://doi.org/10.48084/etasr.3349. [8] d. a. nield and a. bejan, convection in porous media. new york, ny, usa: springer, 2013. [9] subsurface flow module user’s guide v. 5.5. stockholm, sweden: comsol, 2020. microsoft word etasr_v13_n2_pp10255-10260 engineering, technology & applied science research vol. 13, no. 2, 2023, 10255-10260 10255 www.etasr.com romao et al.: numerical simulation and optimization of methane steam reforming to maximize h2 … numerical simulation and optimization of methane steam reforming to maximize h2 production: a case study estaner claro romao department of basic and environmental sciences, engineering college of lorena, university of sao paulo, brazil estaner23@usp.br (corresponding author) adriano francisco siqueira department of basic and environmental sciences, engineering college of lorena, university of sao paulo, brazil adrianoeel@usp.br jairo aparecido martins department of research & development, desch north america, canada jairophd@gmail.com received: 29 december 2022 | revised: 13 january 2023 and 16 january 2023 | accepted: 20 january 2023 abstract research in renewable energy, the preservation of the environment, and the reduction of energy generation costs are themes that go hand in hand. in this work, a case study was carried out that aims to maximize the production of hydrogen through methane steam reforming. for this, several numerical simulations, considering a laminar flow regime in a chemical reactor with a catalyst, were developed with comsol multiphysics. after an exploratory study of the data, a systematic optimization was developed using multivariate regression models formed by combinations of input parameters in an idealized reactor. the results showed that the proposed approach is capable of satisfactory optimization. keywords-numerical simulation; hydrogen production; optimization; heat transfer i. introduction although modeling solute transport in porous media is not a new research branch since there are important records of models dated in 1952 and 1953 [1, 2], research of porous media has been thriving lately, mainly because it widened to solve inherent latent problems in the environmental, industrial, and biological sectors. contamination of groundwater, diffusion of tracer particles in cellular bodies, underground oil flow in the petroleum industry, and even blow flow through capillaries are only a few relevant studies that have been bringing real and tangible contributions to the society [3, 4]. while the basic laws that govern the flow of fluids are accessible and usually make use of navier-stokes’ equations, their application is not feasible for multiple complex geometries that are present in a detailed description of the pore structure of a realistic porous medium. this level of detail is not of practical use either, and ends up desiring a description at a level of detail somewhere intermediate between darcy’s law and the pore-level flow [3]. the numerical simulation is very important for solution several engineering problems [5-8], for example, authors in [9] presented numerical models for the resolution of densitycoupled flow and transport in porous media based on mixed hybrid finite element and discontinuous finite element methods. the authors stated that the simulation presented a good agreement when tested against the standard benchmarks henry and elder test cases. authors in [10] described heat and solute transport in porous media using partial differential equations of similar form, and the study happened to interpret two push-pull tests of different durations. the authors concluded that longitudinal solute dispersivity is scale-dependent while diffusivity seems not to be. furthermore, the conductive transport of heat is much more important than the effects of velocity variations through the pore space. the contribution of the temperature in the process was studied in [11-12]. authors in [13] stated that solutes having a limited mobilization in heterogeneous porous media may end up with subsurface salinization and clear contamination in various environmental engineering, technology & applied science research vol. 13, no. 2, 2023, 10255-10260 10256 www.etasr.com romao et al.: numerical simulation and optimization of methane steam reforming to maximize h2 … settings. recent studies brought up that flow and transport driven by pressure waves in porous media under saturated conditions intensively enlarge solute displacement compared to drag-dominant (darcy) flow and transport, resulting in more thorough remediation. however, the experimental results miss the demonstration of such transport under unsaturated conditions. the authors investigated solute leaching in a flow cell, experimentally modeling solute displacement from an unsaturated, saline, fine-textured soil region to the surrounding coarse-textured soil. they concluded stating that the pressurewave pulse flux (ppf) treatment led to higher water content at and behind the front, which increased the continuity of the water phase across the fine-textured and coarse-textured soils and enhanced transport. the study is a proof of concept for pressure-wave driven flow to enhance local wetting and solute transport in unsaturated soil. when it comes to reactors, authors in [14] presented the thermochemical analysis of a packed-bed reactor via multidimensional cfd modeling using flexpde and comsol multiphysics. the temperature, concentration, and reaction rate profiles for methane production following the fischer–tropsch (f-t) synthesis were studied. to this end, stationary and dynamic differential equations for mass and heat transfer were solved via the finite element technique. as a result, all models were in good agreement with the experimental data found in the literature, especially for the 2-d and 3-d dynamic models. in terms of kinetics, the predicted reaction rate profiles from the comsol model and the 2-d dynamic model followed the temperature trend, thus reflecting the temperature dependence of the reaction. based on these findings, it was demonstrated that applying different approaches for the cfd modeling of ft processes conducts reliable results. hydrogen production was studied in [15], since mechanically and chemically stable membranes with high perm-selectivity towards hydrogen are available and are continuously further improving in terms of stability and hydrogen flux. the authors highlight recent advances in hydrogen-selective membranes (from palladium-based to silica and proton conductors) along with the advances in the different types of membrane reactors available (from packed bed to fluidized bed and from micro-reactors to bio-membrane reactors). meanwhile, the authors in [16] presented the catalytic reforming technology, which is regarded as one of the most popular hydrogen production methods. the introduction of a fluidized bed reactor provides a promising opportunity for the enhancement of catalytic reforming technology due to its good gas-solid contact and heat and mass transfer characteristics. the authors describe how, in order to improve hydrogen production, the strengthening method of reforming technology via hydrogen membrane separation has been developed in the last few years. the development and challenges of catalytic reforming technology using a membrane-assisted fluidized bed for hydrogen production are reviewed. in the current work, we present a case study to present an alternative for optimizing an idealized chemical reactor. for this, we will use numerical simulations via comsol multiphysics to solve the methane steam reforming chemical reaction given by: ��� + ��� → �� + 2�� (1) which here will be considered irreversible since the main focus is the optimization of the idealized reactor. ii. methodology a. parameters initially, we present the geometry of the case study. this is an idealized reactor with an inlet and an outlet, a region of porous medium (catalyst), and in its center there is a pipe through which a hot fluid passes, as can be seen in figure 1. fig. 1. idealized reactor (left) and inside view of the reactor (right). for the study presented here, the following characteristics will be considered:  a two-dimensional study will be carried out and symmetry will be considered in the centerline of the idealized reactor (figure 2), where � is the length before the catalyst and the measurement between the hot fluid pipe and the reactor shell [m], � is the length of the catalyst region [m], � is the length after the catalyst [m], � is the inlet velocity [m/s], and ���� is the temperature of the hot fluid [k]. fig. 2. two-dimensional domain with boundary conditions.  porosity is considered equal to 0.5 and permeability to 10 -9 m 2 .  the formula used to calculate the diffusivity between gases (���) is [17]: ��� = 1,053 × 10� ! "/$ %&$'( ) �*' + � *( +�/� (2) where t is the temperature [k], p is the pressure [atm], ,� is the molar mass of element a (���, ���, �� or ��), ,� is the molar mass of element b (air) and -�� , is defined by: -�� = .∑ v1��/ + .∑ v1��/ (3) in this work the values presented in table ι will be considered. engineering, technology & applied science research vol. 13, no. 2, 2023, 10255-10260 10257 www.etasr.com romao et al.: numerical simulation and optimization of methane steam reforming to maximize h2 … table i. diffusion molecular volumes [13] molecule σv molar mass air 16.2 28.96 �� 18.0 28.01 ��� 13.1 18.01 ��� 25.14 16.033 �� 6.12 2.016  due to the high activation energy required for the reaction proposed in (1) to occur, we will consider the inverse reaction to being negligible, and thus: 2��3 = 42���32���3 (4) 2��3 = 42���32���3 (5) where k is defined by (5) and using as reference [14], yields that: k = 7.301 × 10��7 �. "89:; <,"9×=1 (6) b. governing equations for the study of the conservation of motion, brinkman's equations (laminar flow) will be used: ∇ ∙ 2−ab + c3 − de��� + fgh|j| + klmn$ o j + p (7) q∇ ∙ j = rs (8) more details about the terms of (9) and (10) can be found in [15]. then, to carry out the study of mass transport in porous media, the following equations will be used: ∇ ∙ tu + j ∙ vwu = xu + yu (9) tu = −�z,[ ∇wu (10) \ = gh (11) more details about the terms of (9)-(11) can be found in [20]. finally, for the treatment of the temperature field, the energy conservation equation will be used as follows: -] q�hj ∙ ∇� + ∇ ∙ ^ = -] r + _� + -] rh + -] r`& (12) ^ = −-]4∇� (13) more details about the terms of (12) and (13) can be found in [21]. iii. results and discussion for the study that will be presented here, three parameters were chosen to be analyzed: the inlet concentration of ��� [mol/m 3 ] (case 1), the inlet velocity � [m/s] (case 2); and finally, the reactor length � [m] (case 3). in all cases, the following parameters will be used as fixed: inlet concentration of ��� =1mol/m3, �= 0.05m and � =0.01m. it is important to highlight that will be used the medium values of �� in the outlet of the idealized reactor in the results presented for the three cases. a. case 1: varying ��� in the first case, we were varying the inlet concentration of ��� in values between 1 and 1000mol/m3. besides, � = 0.1m and � = 0.1m/s were fixed and 5 different values for ���� were adopted: 973, 1023, 1073, 1123, and 1173k to verify the influence of hot fluid in the �� production. fig. 3. �� production with �� � (inlet) variation. in figure 3, it is possible to note that with the increasing inlet concentration of ��� , increasing of the �� production occurs, however, it is clear that the results of the 5 different values of ���� little differ. in figure 4, it is clear that near in the region of heating the major concentration of �� production occurs. fig. 4. �� concentration with ��� = 1000mol/m3 (inlet) and ���� = 1173k. b. case 2: varying � in case 1, it was clear that the major values adopted for ��� and ���� presented better results for �� production, thus, in case 2 fixed values of ��� = 1000mol/m3 and ���� = 1173k were adopted. from that, 11 different values of � were be analyzed (of 0.005 to 0.1m/s). as in case 1, � = 0.1m was considered. in case 1 (figure 3), within the values of ��� inlet, the curves show crescent. the opposite occurs in case 2 (figure 5), since for the values adopted the curve shows a maximum point in the region of � = 0.02m/s and then the curve becomes decreasing. in other words, the graph in figure 5 suggests that the region near the � = 0.02 is the possible optimum point. engineering, technology & applied science research vol. 13, no. 2, 2023, 10255-10260 10258 www.etasr.com romao et al.: numerical simulation and optimization of methane steam reforming to maximize h2 … fig. 5. �� production with � variation. fig. 6. h� concentration (case 2) with u� = 0.02m/s. figure 6 shows that the �� production into the idealized reactor and is more expressive than that presented in figure 4. c. case 3: varying � in this last case, � varied between 0.01 and 0.1m (10 points). again, some values will be fixed: ���� = 1173k and ��� = 1000mol/m3 (inlet). besides, 3 values will be considered for � (0.005, 0.01, and 0.02m/s). fig. 7. �� production with � variation. although the three variations of � were considered to present results expressibly different, the behavior is similar, that is, a behavior of the crescent curve, with a positive derivative and thus proving that the increase in � can still cause an increase in �� production. d. optimization in order to understand the way the control parameters influence the generation of hydrogen through the chemical reaction proposed in this work (1), from the highest production, �� = 0.767mol/m3 (found in the condition � = 0.10m, � =0.02m/s, ���= 1000mol/m3, and ���� = 173k among the data set analyzed in the 3 previously described cases), a new set of data was generated in the simulations, varying up and down by p% in the values of the input variables. the process was repeated, from the highest value found, generating a new data set with a sufficient number of points to test regression models with 3 independent variables and their 2 by 2 combinations, which, in this case, were 2 iterations using: p = 0.1 and (again) p = 0.1, thus forming a data set with 16 points. for this new data set, the best fit was obtained using the k-fold crossvalidation with 10 folds. the model is expressed by (14): �� = 0.5517 + 0.809 � + 1.715 � + 0.000098��� (14) the statistics about the quality of fit of the model proposed by (14) are presented in table ii. we observe that the model fits very well to the simulated data, presenting high values of adjusted r2 and cross-validation, indicating that the model presents good capacity of generalization, with anderson darling test for normal residuals p-value equal to 0.0864. table ii. summary of the quality model fit (14) s r2 r2(aj) r2(pred) 10-fold s 10-fold r2 0.0045874 94.72% 93.50% 91.84% 0.0050580 91.61% it is evident from the analysis of the p-value and the fdistribution (table iii) that the variable that most influences the generation of �� is the ��� inlet concentration while the � length is the second more important. table iii. analysis of variance for the proposed model of (15) gl sq (aj.) qm (aj.) f-value p-value regression 3 0.004910 0.001637 77.78 0.000 ef 1 0.001337 0.001337 63.52 0.000 gh 1 0.000269 0.000269 12.79 0.003 ijk 1 0.002087 0.002087 99.16 0.000 error 13 0.000274 0.000021 total 16 0.005184 the quality of the fit can be seen in figure 8. it is interesting to observe that the strategy of prospecting for new data in order to obtain a greater production of �� appears to be successful because it presents various combinations of � , �, and ��� with �� greater than 0.767mol/m3 from the initial dataset. finally, using minitab's optimizer, it is possible to envision a direction toward greater �� production. in figure 9, it is evident that a greater production of �� can be obtained by increasing � , � , and ��� . to assess whether these indications are correct, another simulation was performed in engineering, technology & applied science research vol. 13, no. 2, 2023, 10255-10260 10259 www.etasr.com romao et al.: numerical simulation and optimization of methane steam reforming to maximize h2 … that direction with � = 0.125m, � = 0.025m/s, and ��� = 1250mol/m 3 the simulation result was 0.823 and the prediction of the proposed model for these conditions was 0.818 with a prediction interval (95%) of [0.806, 0.830] showing the ability of the model to reproduce simulation data in laminar flow. fig. 8. quality of model fit to simulated �� production data. fig. 9. optimization of the proposed model to maximize �� production. iv. conclusions the production of clean energy is one of the main themes nowadays and one of the available alternatives is the production of hydrogen. although there are a considerable number of techniques and methods developed to design more efficient processes to produce hydrogen many of them using only the finite element method (fem), others checking the results of fem on experiments, the combination of numerical simulations with statistics is not observed in the literature. with that being said, the contribution of this paper is on demonstrating how this powerful combination can enhance the production of hydrogen since it allowed us to figure out precisely the significance of each variable in the system as well as the interaction among them. in this work, we present an idealized reactor with a heating pipe that would carry out the chemical reaction known as methane steam reforming and generate hydrogen gas with the greatest efficiency. through the variation of some physical and geometric parameters in the numerical simulation, we were able to present an optimization with high precision and high efficiency in the production of hydrogen by using statistics analysis. besides, the statistical approach used in this work allowed finding a better optimal point than the one obtained in the initial exploratory numerical simulation analysis. it is important to point out that the use of statistics aimed at optimizing hydrogen production for the work proposed here is considered somewhat unprecedented since we did not find any work that used this approach. in future work, an additional analysis could be carried out in maximizing the production of hydrogen with a possible reduction of co (carbon monoxide) pollutant. acknowledgment this research was funded by capes (procs. 23038.000263/2022-19). references [1] p. daniel, "the measurement of groundwater flow," in proceedings of the ankara symposium on arid zone hydrology, 1952. 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[16] x. yang, s. wang, and y. he, "review of catalytic reforming for hydrogen production in a membrane-assisted fluidized bed reactor," renewable and sustainable energy reviews, vol. 154, feb. 2022, art. no. 111832, https://doi.org/10.1016/j.rser.2021.111832. [17] m. a. cremasco, difusão mássica cremasco. blucher, 2019. [18] y. wang and c. m. kinoshita, "kinetic model of biomass gasification," solar energy, vol. 51, no. 1, pp. 19–25, jul. 1993, https://doi.org/ 10.1016/0038-092x(93)90037-o. [19] "the brinkman equations interface," comsol. https://doc.comsol.com/ 5.6/doc/com.comsol.help.cfd/cfd_ug_fluidflow_porous.10.37.html. [20] "the chemistry interface." https://doc.comsol.com/5.6/doc/com.comsol. help.chem/chem_ug_chemsptrans_re.07.31.html. [21] "the heat transfer in fluids interface," comsol. https://doc.comsol. com/6.0/doc/com.comsol.help.heat/heat_ug_interfaces.08.20.html. microsoft word etasr_v12_n5_pp9329-9335 engineering, technology & applied science research vol. 12, no. 5, 2022, 9329-9335 9329 www.etasr.com zisopol et al.: a theoretical-experimental study of the influence of fdm parameters on pla spur... a theoretical-experimental study of the influence of fdm parameters on pla spur gear stiffness dragos gabriel zisopol mechanical engineering department petroleumgas university ploiesti, romania zisopol@zisopol.ro dragos valentin iacob production department marelli ploiesti, romania dragoshicb@gmail.com alexandra-ileana portoaca mechanical engineering department petroleum – gas university ploiesti, romania alexandra.portoaca@upg-ploiesti.ro received: 6 july 2022 | revised: 24 july 2022 and 7 august 2022 | accepted: 15 august 2022 abstract-this paper studies the influence of fdm (fused depositing modeling) parameters on gear stiffness made of polylactic acid (pla). 3d printing parameters must be optimized because they influence the physical, mechanical, and quality characteristics of the additive manufactured part along with its functionality. the objective of this research is to optimize fdm parameters in order to obtain the highest stiffness. in this context, we used finite element analysis (fea) and we made experimental tests to validate its results. the experimental tests are divided into two categories, gears with the same parameters and gears with the same layer height and variable filling percentage. the average results of gear stiffness with the same parameters are 8.18% highest than the average results of gear stiffness with the same layer height and variable filling percentages. keywords–3d printing; fdm parameters; fdm parameters; stiffness; spur gears; fea i. introduction the term additive manufacturing encompasses a set of technologies and processes that use different materials to make objects by depositing material in successive layers. due to the recent improvements in additive technologies, they are used in many fields of activity. initially, they were suitable for rapid prototyping of models, now they are used for sophisticated applications such as unique parts, custom products, medical implants, etc. [1-4]. compared to formative and subtractive manufacturing, additive manufacturing technologies have many advantages: material waste is negligible, realization of very complex objects without bases and fasteners, costeffective manufacturing, simplicity in use, etc. [5, 6]. in this paper we show that fdm 3d printing with pla can be a good solution for plastic gears and we also find the optimal parameters for fdm printed gears. the novelty of this article consists in determining the influence of fdm parameters, the height of the deposited pla layer, and the percentage of filling for spur gears with straight teeth, on the rigidity gear assembly. the rigidity of pla gear assembly, 3d-printed by fdm, is theoretically determined using fea and experimentally validated using a device designed and manufactured by the authors, whereas the recording of the results was realized by a digital torque wrench [7, 9]. ii. fdm 3d printing of spur gears pla filament with a diameter of 1.75mm, verbatim brand, was the material used for fdm 3d printing of the spur gears with straight teeth. the printing methodology is shown in figure 1. fig. 1. study methodology. 2d and later 3d models of straight-tooth cylindrical gears were made in the cad solidworks program. figure 2 shows the 2d model of the drive gear module 1 with 30 straight teeths (r1) and figure 3 shows the 2d model of the drive wheel module 1 with 60 straight teeth (r2). both were designed in solidworks. using the same software, the two cad files corresponding to the 3d models obtained were saved with the stl extension. corresponding author: dragoș valentin iacob engineering, technology & applied science research vol. 12, no. 5, 2022, 9329-9335 9330 www.etasr.com zisopol et al.: a theoretical-experimental study of the influence of fdm parameters on pla spur... fig. 2. leading spur gear (r1). fig. 3. driven spur gear (r2). using the creality slicer program of the creality cr-x printer, the two files with the stl extension corresponding to the straight-tooth cylindrical gears shown in figures 2 and 3, after entering the 3d printing parameters, were transformed into a g-file code (figure 4). fig. 4. g-code commands. the parameters of 3d printing of cylindrical gears, presented in table i, are grouped in two categories, constant process parameters and variable technological parameters. the first parameters category refers to the orientation of the parts, the printing speed (vp), the extruder temperature (te), the printing bed temperature (tp), and the model used for filling. variable technological parameters refer to the height of the deposited layer (hs) and the percentage of filling, (pu) [1]. also, the number of gear pairs tested is mentioned. data in table i were used to reveal constant parameters and parameters varied to test different layer thicknesses and infill percentages. table i. 3d printing parameters constant parameters variable parameters spur gears building orientation x, y extrusion temperature (te) – 210 °c bed temperature (tp) – 60 °c speed (vp) – 80 mm/s filling model – lines 45° layer hight (hs) infill percentage (pu) r1 r2 (mm) (%) (pieces) 0.10 5 0 7 5 1 00 27 0.15 27 0.20 27 figure 5 shows the set of cylindrical gears with straight teeth r1 and r2, created with the creality slicer [3]. the gcode file was transferred to the creality cr-x printer on which 162 straight-tooth cylindrical gears were made of pla (81 r1 and 81 r2), according to the data centralized in table i. fig. 5. r1 and r2 spur gears, in creality slicer. iii. stiffness determination of the 3d printed spur gear the stiffness of the pla 3d printed spur gears was theoretically determined using fea applied in solidworks 2016 and experimentally validated using the device in figure 8 designed and manufactured by the authors. a. theorethical study for fea of stiffness gears with straight in solidworks 2016 a torque r1 equal to 0.0022kn· m was applied (minimum value at which teeth yielded). the fea results of the stiffness of the straight-tooth cylindrical gears of pla (r1 and r2) are shown in figures 5 and 6. the equivalent von mises stress obtained is 2.225mpa and the maximum linear displacement is 1.208mm. engineering, technology & applied science research vol. 12, no. 5, 2022, 9329-9335 9331 www.etasr.com zisopol et al.: a theoretical-experimental study of the influence of fdm parameters on pla spur... fig. 6. equivalent von mises stress. fig. 7. maximum linear displacement. b. experimental tests for the experimental determination of the gear stiffness of the gears, the authors designed and made the device shown in figure 8. fig. 8. gear stiffness determination device: 1 – leading gear (r1); 2 – washer; 3 – driven wheel (r2); 4– locking rod; 5 – digital torque wrench. the stiffness of the leading gear r1 (1), fixed to the device by the washer (2) and locked by the rod (4), with the driven gear r2 (3) was determined by the digital torque wrench (5) by recording the maximum torque corresponding to the gear assembly failure. a total of 162 experimental tests were performed on the device in figure 8, using cylindrical gears with straight teeth with the parameters shown in table i. c. results and discussion the results obtained from the experimental determinations performed on the device in figure 8 are shown graphically in figures 9-36. the averages of the results obtained from the experimental determinations; are presented in figure 36. fig. 9. gear stiffness r1 (hs = 0.10mm, pu = 100%) with r2 (hs = 0.10mm, pu = 100%). fig. 10. gear stiffness r1 (hs = 0.10mm, pu = 75%) with r2 (hs = 0.10mm, pu = 75%). fig. 11. gear stiffness r1 (hs = 0.10mm, pu = 50%) with r2 (hs = 0.10.mm, pu = 50%). fig. 12. gear stiffness r1 (hs = 0.15mm, pu = 100%) with r2 (hs = 0.15mm, pu = 100%). fig. 13. gear stiffness r1 (hs = 0.15mm, pu = 75%) with r2 (hs = 0.15mm, pu = 75%). 0.0240 0.0206 0.0196 0.0172 0.0202 0.0193 0.0100 0.0200 0.0300 1 2 3 4 5 6 s ti ff n e ss k n ·m test no. 0.0182 0.0191 0.0195 0.0189 0.0193 0.0189 0.0170 0.0180 0.0190 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0175 0.0220 0.0203 0.0198 0.0172 0.0206 0.0000 0.0100 0.0200 0.0300 1 2 3 4 5 6 s ti ff n e ss k n ·m test no. 0.0183 0.0182 0.0205 0.0177 0.0203 0.0186 0.0160 0.0180 0.0200 0.0220 1 2 3 4 5 6 s ti ff n e ss k n ·m test no. 0.0215 0.0217 0.0189 0.0170 0.0181 0.0173 0.0150 0.0200 0.0250 1 2 3 4 5 6 s ti ff n e ss k n ·m test no. engineering, technology & applied science research vol. 12, no. 5, 2022, 9329-9335 9332 www.etasr.com zisopol et al.: a theoretical-experimental study of the influence of fdm parameters on pla spur... fig. 14. gear stiffness r1 (hs = 0.15mm, pu = 50%) with r2 (hs = 0.15mm, pu = 50%). fig. 15. gear stiffness r1 (hs = 0.20mm, pu = 100%) with r2 (hs = 0.20mm, pu = 100%). fig. 16. gear stiffness r1 (hs = 0.20mm, pu = 75%) with r2 (hs = 0.20mm, pu = 75%). fig. 17. gear stiffness r1 (hs = 0.20mm, pu = 50%) with r2 (hs = 0.20mm, pu = 50%). fig. 18. gear stiffness r1 (hs = 0.10mm, pu = 100%) with r2 (hs = 0.10mm, pu = 75%). fig. 19. gear stiffness r1 (hs = 0.10mm, pu = 100%) with r2 (hs = 0.10mm, pu = 50%). fig. 20. gear stiffness r1 (hs = 0.10mm, gu = 75%) with r2 (hs = 0.10mm, pu = 100%). fig. 21. gear stiffness r1 (hs = 0.10mm, pu = 75%) with r2 (hs = 0.10mm, pu = 50%). fig. 22. gear stiffness r1 (hs = 0.10mm, pu = 50%) with r2 (hs = 0.10mm, pu = 100%). fig. 23. gear stiffness r1 (hs = 0.10mm, pu = 50%) with r2 (hs = 0.10mm, pu = 75%). 0.0183 0.0185 0.0169 0.0191 0.0180 0.0168 0.014 0.016 0.018 0.020 1 2 3 4 5 6 s ti ff n e ss k n ·m test no. 0.0197 0.0199 0.0213 0.0190 0.0191 0.0190 0.0160 0.0180 0.0200 0.0220 1 2 3 4 5 6 s ti ff n e ss k n ·m test no. 0.0183 0.0181 0.0161 0.0182 0.0181 0.0184 0.0140 0.0160 0.0180 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0202 0.0182 0.0183 0.0170 0.0187 0.0178 0.0140 0.0160 0.0180 0.0200 0.0220 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0170 0.0169 0.0172 0.0161 0.0186 0.0160 0.0140 0.0160 0.0180 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0174 0.0174 0.0174 0.0146 0.0154 0.0174 0.0120 0.0140 0.0160 0.0180 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0194 0.0153 0.0157 0.0145 0.0189 0.0167 0.0100 0.0150 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0135 0.0187 0.0172 0.0149 0.0177 0.0183 0.0100 0.0150 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0177 0.0187 0.0197 0.0169 0.0171 0.0183 0.0140 0.0160 0.0180 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0173 0.0193 0.0160 0.0175 0.0170 0.0153 0.0100 0.0150 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. engineering, technology & applied science research vol. 12, no. 5, 2022, 9329-9335 9333 www.etasr.com zisopol et al.: a theoretical-experimental study of the influence of fdm parameters on pla spur... fig. 24. gear stiffness r1 (hs = 0.15mm, pu = 100%) with r2 (hs = 0.15mm, pu = 75%). fig. 25. gear stiffness r1 (hs = 0.15mm, pu = 100%) with r2 (hs = 0.15mm, pu = 50%). fig. 26. gear stiffness r1 (hs = 0.15mm, pu = 75%) with r2 (hs = 0.15mm, pu = 100%). fig. 27. gear stiffness r1 (hs = 0.15mm, pu = 75%) with r2 (hs = 0.15mm, pu = 50%). fig. 28. gear stiffness r1 (hs = 0.15mm, pu = 50%) with r2 (hs = 0.15mm, pu = 100%). fig. 29. gear stiffness r1 (hs = 0.15mm, pu = 50%) with r2 (hs = 0.15mm, pu = 75%). fig. 30. gear stiffness r1 (hs = 0.20mm, pu = 100%) with r2 (hs = 0.15mm, pu = 75%). fig. 31. gear stiffness r1 (hs = 0.20mm, pu = 100%) withr2 (hs = 0.15mm, pu = 50%). fig. 32. gear stiffness r1 (hs = 0.20mm, pu = 75%) with r2 (hs = 0.15mm, pu = 100%). fig. 33. gear stiffness r1 (hs = 0.20mm, pu = 75%) with r2 (hs = 0.15mm, pu = 50%). 0.0179 0.0173 0.0177 0.0151 0.0145 0.0177 0.0100 0.0150 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0168 0.0165 0.0189 0.0146 0.0170 0.0163 0.0100 0.0150 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0171 0.0177 0.0180 0.0170 0.0176 0.0164 0.0150 0.0160 0.0170 0.0180 0.0190 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0197 0.0137 0.0195 0.0173 0.0192 0.0151 0.0100 0.0150 0.0200 0.0250 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0177 0.0168 0.0182 0.0168 0.0194 0.0158 0.0100 0.0150 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0188 0.0157 0.0132 0.0187 0.0191 0.0153 0.0100 0.0150 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0186 0.0190 0.0196 0.0181 0.0205 0.0146 0.0100 0.0150 0.0200 0.0250 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0160 0.0180 0.0187 0.0176 0.0170 0.0167 0.0140 0.0160 0.0180 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0220 0.0162 0.0212 0.0178 0.0208 0.0185 0.0100 0.0150 0.0200 0.0250 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0176 0.0176 0.0183 0.0183 0.0190 0.0176 0.0160 0.0170 0.0180 0.0190 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. engineering, technology & applied science research vol. 12, no. 5, 2022, 9329-9335 9334 www.etasr.com zisopol et al.: a theoretical-experimental study of the influence of fdm parameters on pla spur... fig. 34. gear stiffness r1 (hs = 0.20mm, pu = 50%) with r2 (hs = 0.15mm, pu = 100%). fig. 35. gear stiffness r1 (hs = 0.20mm, pu = 50%) with r2 (hs = 0.15mm, pu = 75%). fig. 36. average stiffness of the r1 and r2 gear assembly. the rigidity of the assembly of cylindrical gears was theoretically determined using fea in solidworks and experimentally validated using the device shown in figure 8. the theoretical study of the gears stiffness revealed results that are presented in figures 6 and 7, validated by the experimental results presented in figures 9-36. it was found out that the percentage difference was 9.49%. analyzing the results of the 162 experimental tests, an average value of the stiffness of the cylindrical gears with straight teeth 0.01791kn· m was obtained. for cylindrical gears, the minimum value of gear stiffness is 0.01323kn· m and was obtained for the gear with r1 (hs = 0.15mm, pu = 50%) and r2 (hs = 0.15mm, pu = 75%) and the maximum value of the gear stiffness is 0.02402kn· m and was obtained for the gear with r1 (hs = 0.10mm, pu = 100%) and r2 (hs = 0.10mm, pu = 100%). the height of the deposited layer (hs) and the percentage of filling (pu) influence the stiffness of the cylindrical gears assembly with straight teeth. increasing the height of the deposited layer from hs = 0.10mm to hs = 0.15mm increases the stiffness of the gear by 2.34% and increasing from hs = 0.10mm to hs = 0.20mm increases stiffness by 4.02%. the increase of the filling percentage from pu = 50% to pu = 75% increases gear stiffness by 0.08% and the increase from pu = 50% to pu = 100% by 4.84%. the rigidity of the gears assembly with straight teeth is influenced by the percentage of filling (pu) by 5.44% more than it is influenced by the height of the deposited layer (hs). the novelty of this work consists in obtaining results of the maximum torque that can be applied to various printed gears characterized by different layer thicknesses and infill percentages until it deforms irreversibly in order to protect the energy source used in practical applications. there is a limited number of studies conducted on the subject. in [10], 6 types of pla, from different producers, 2 types of abs and 3 types of nylon all printed with the same parameters were compared and an optimal type of pla that crushed at 0.018kn· m torque was. iv. conclusions the objective of the current study was to determine an optimal combination of gear characterization by the printing and tested parameters. furthermore, the result is similar to other studies using different pla producers [10], so the study is considered valid. the paper reveals the maximum torque supported by 3d printed pla (with certain parameters) and helps in choosing efficient variants of construction depending of the requirements of the application. the study is recommended to be applied to other types of 3d printed gears from various materials, using different additive manufacturing technologies. references [1] d. g. zisopol, i. nae, a. i. portoaca, and i. ramadan, "a theoretical and experimental research on the influence of fdm parameters on tensile strength and hardness of parts made of polylactic acid," engineering, technology & applied science research, vol. 11, no. 4, pp. 7458–7463, aug. 2021, https://doi.org/10.48084/etasr.4311. [2] d. g. zisopol, i. nae, a. i. portoaca, and i. ramadan, "a statistical approach of the flexural strength of pla and abs 3d printed parts," engineering, technology & applied science research, vol. 12, no. 2, pp. 8248–8252, apr. 2022, https://doi.org/10.48084/etasr.4739. [3] a. portoaca, i. nae, d. zisopol, and i. ramadan, "studies on the influence of fff parameters on the tensile properties of samples made of abs," iasi, romania, oct. 2021. [4] d. g. zisopol, a. i. portoaca, i. nae, and i. ramadan, "a comparative analysis of the mechanical properties of annealed pla," engineering, technology & applied science research, vol. 12, no. 4, pp. 8978–8981, aug. 2022, https://doi.org/10.48084/etasr.5123. 0.0169 0.0169 0.0185 0.0179 0.0188 0.0185 0.0150 0.0160 0.0170 0.0180 0.0190 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.0164 0.0171 0.0184 0.0178 0.0183 0.0180 0.0140 0.0160 0.0180 0.0200 1 2 3 4 5 6s ti ff n e ss k n ·m test no. 0.02014 0.01898 0.01958 0.01893 0.01907 0.01794 0.01965 0.01787 0.01835 0.01696 0.01660 0.01676 0.01671 0.01806 0.01707 0.01670 0.01669 0.01729 0.01741 0.01744 0.01679 0.01840 0.01731 0.01941 0.01805 0.01791 0.01766 0.00000 0.00500 0.01000 0.01500 0.02000 0.02500 0,1100% 0,1100% 0,175% 0,175% 0,150% 0,150% 0,15100% 0,15100% 0,1575% 0,1575% 0,1550% 0,1550% 0,20100% 0,20100% 0,2075% 0,2075% 0,2050% 0,2050% 0,1100% 0,175% 0,1100% 0,150% 0,175% 0,1100% 0,175% 0,150% 0,150% 0,1100% 0,150% 0,175% 0,15100% 0,1575% 0,15100% 0,1550% 0,1575% 0,15100% 0,1575% 0,1550% 0,1550% 0,15100% 0,1550% 0,1575% 0,2100% 0,275% 0,2100% 0,250% 0,275% 0,2100% 0,275% 0,250% 0,250% 0,2100% 0,250% 0,275% average stiffness of the gear assembley r1 and r2 (kn·m) r 1 [ h l (m m ) p i (% )] ; r 2 [ h l (m m ) p i (% )] . engineering, technology & applied science research vol. 12, no. 5, 2022, 9329-9335 9335 www.etasr.com zisopol et al.: a theoretical-experimental study of the influence of fdm parameters on pla spur... [5] h.-j. dennig, l. zumofen, and a. kirchheim, "feasibility investigation of gears manufactured by fused filament fabrication," in industrializing additive manufacturing, cham, 2021, pp. 304–320, https://doi.org/10.1007/978-3-030-54334-1_22. [6] j. c. camargo, á. r. machado, e. c. almeida, and e. f. m. s. silva, "mechanical properties of pla-graphene filament for fdm 3d printing," the international journal of advanced manufacturing technology, vol. 103, no. 5, pp. 2423–2443, aug. 2019, https://doi.org/ 10.1007/s00170-019-03532-5. [7] o. luzanin, d. movrin, and m. plancak, "effect of layer thickness, deposition angle, and infill on maximum flexural force in fdm-built specimens," journal for technology of plasticity, vol. 39, jan. 2014. [8] m. sharma, v. sharma, and p. kala, "optimization of process variables to improve the mechanical properties of fdm structures," journal of physics: conference series, vol. 1240, apr. 2019, art. no. 012061, https://doi.org/10.1088/1742-6596/1240/1/012061. [9] o. a. mohamed, s. h. masood, and j. l. bhowmik, "optimization of fused deposition modeling process parameters: a review of current research and future prospects," advances in manufacturing, vol. 3, no. 1, pp. 42–53, mar. 2015, https://doi.org/10.1007/s40436-014-0097-7. [10] "angus deveson is creating 3d printing videos," patreon. https:// www.patreon.com/makersmuse. microsoft word etasr_v13_n1_pp9955-9960 engineering, technology & applied science research vol. 13, no. 1, 2023, 9955-9960 9955 www.etasr.com chekroun & boumechra: static and seismic stability of a slope reinforced with two rows of piles static and seismic stability of a slope reinforced with two rows of piles lokmane el hakim chekroun department of civil engineering, faculty of technology, eole research laboratory, university of tlemcen, algeria lokmaneelhakim.chekroun@univ-tlemcen.dz (corresponding author) nadir boumechra department of civil engineering, faculty of technology, eole research laboratory, university of tlemcen, algeria nadir.boumechra@univ-tlemcen.dz received: 4 november 2022 | revised: 24 november 2022 | accepted: 27 november 2022 abstract the use of piles for slide stabilization is considered among the most important innovative reinforcement techniques. piles have been successfully used in many situations to stabilize slopes or as parts of a stability improvement. our case study is in the tlemcen section. the left side of the roadway collapsed following the slide of the downstream side. inclinometer readings showed signs of instability with a slip depth of about 9m near the motorway platform. the likely causes of the instability were the removal of the lower abutment of the embankment upstream of the road and the establishment of an earth deposit which overloaded the embankment and disrupted the flow of water downstream. the stabilization study is based on the installation of two rows of anti-slip piles. stability analysis study was carried out under static and dynamic loads and highlights that this solution is advantageous and effective. keywords-pile behavior; dynamic study; finite elements; slope; highway i. introduction many methods have been developed for the analysis of piles [1-4]. the limit equilibrium method was used in [3] to deal with the problem of stability of embankments containing piles. the safety factor of a slope reinforced by piles was defined as the ratio of the moment of resistance to the moment of overturning (engine) acting on the mass of the potentially unstable ground. the time of resistance consists of two components: the moment due to the resistance of the ground to the shear along the sliding surface and the moment provided by the reaction force piles. the driving moment and the moment of soil shear resistance were obtained by the simple slice method. the study of a slope includes, in addition to the recognition of the site and the choice of the mechanical characteristics of the soils, stability calculation in order to determine not only the breaking curve along which the risk of landslide is the highest, but also the corresponding value of the safety coefficient [5]. it should be noted that ground movements are very varied in nature and size. the problems of slope stability are recorded in a general way in the realization of roads, dams, and natural slopes. the landslide passes through several chronological stages of activity. there are major factors that control the type and rate of mass movement that could occur. the methods of slope stabilization by the so-called antislide piles have attracted the interest of several researchers and many studies have been conducted on slopes introducing stabilization piles. we distinguish 2 methods of calculation: limit equilibrium methods and numerical methods. the kinematic approach of treating the slope with one or more rows of piles called "passive piles" has the advantage of improving its stability [1]. we note that the major problem in the design of the slope-pile system is the determination of the appropriate and effective location of the piles. the influence of pile reinforcement on the stability of the slope was studied in [6]. a 2d numerical modeling was used to validate the proposed approach by comparing the numerical results with the field measurements. the effect of pile position as a function of soil shear parameters was also studied. the results indicate that the ideal position for this type of stabilization piles is in the average height of the slope. the slope should be between 30° and 60°. it should be noted that this study is focused on a problem that occurred at the section of pk 210+480 to 210+800 of the east-west algerian highway near the didouche mourad, constantine. the results of this study confirm that soil suction has a significant effect on slope stability. negative pressures from pore water in the slope must be taken into account. it is engineering, technology & applied science research vol. 13, no. 1, 2023, 9955-9960 9956 www.etasr.com chekroun & boumechra: static and seismic stability of a slope reinforced with two rows of piles imperative that an appropriate drainage system is in place and that it is properly maintained. authors in [7] conducted an experimental and numerical study of the stability of a slope reinforced with a concrete pile. this study showed that when the pile is located in the middle of the slope, the soil structure collapses under a pressure of about 10.9kpa, which is the highest pressure that caused the instability of the slope consisting of reinforced sand. however, when the pile is located upstream or downstream, slope failure occurs under a pressure of 7.8 or 3.12kpa, respectively. therefore, his work showed that a pile located in the middle of the slope can improve the reinforcement of the soil, providing it with optimal stability. authors in [8] investigated the stability of a slope under 3 configurations, i.e. without protection, with one row of piles, and with two rows of piles. this study focused on the analysis of the sliding mode, the distribution of bending moments, and the factor of safety of the slope. for the single-row stabilization pile reinforced slope, the optimal location of the piles is in the lower and middle part of the slope where the factor of safety takes a maximum value of 1.26. for the two-row stabilization pile reinforced slope, the appropriate location of the piles is in the lower and lower middle part of the slope. the factor of safety in this case has a maximum value of 1.38. the bending moment and thrust on the double-row piles are more reasonable than the other configurations. ii. presentation of the landslide of highway at kilometer point 52 in this article, we study the landslide that occurred on march 2, 2014 on a section of the east-west highway near the city of tlemcen (north western of algeria). the platform at pκ 52+040 to pkκ52+220 underwent major deformations, with the rear wing moving vertically, i.e. by 3 to 4m horizontally. as a result, the left side of the roadway was completely closed to traffic and the outer part was completely deformed, being subject to sliding, as shown in figure 1. fig. 1. deformation of the pavement of highway at pk52. according to the on-site observation, the landslide was rapidly developed while dense cracks were found in the body of the landslide not far from the river and there were clear deformations in the form of shearing. the vertical displacement of the slide platform was approximately 2m on an embankment section. observation of the core samples showed a highly variable lithology, with high pebble content in the boreholes taken. according to the order of destruction of the inclinometer boreholes, the borehole next to the bank of the river was damaged first and the destroyed borehole next to the platform was next, so the slip was caused by a bottom-up pull. furthermore, there is no evidence of deformation in the hole on the right side of the route. it should also be noted that the scouring of the river water on the front edge of the landslide quickly caused the landslide to appear. one day before, i.e. march 1, 2014, torrential rains that fell on the region caused water infiltration and the rise in the level of the underground water table in the body of the slope. this lubricating action accelerated the mechanism of the landslide phenomenon. figure 2 shows the evolution of displacements over time. borehole s01 boreholes03 fig. 2. the evolution of movements over time for boreholes s01 and s03. iii. geological and geotechnical profile of the site the geotechnical profile of the site was determined by reconnaissance, with 6 boreholes to a total depth of 127.4m. the determined geotechnical profile of the site shown in figure 3 shows that the area has a sloping profile. the soil layers are made up of a bedding fill of medium density, followed by a layer of brownish to yellowish silty clay, distributed mainly in the left embankment of the route. the soil is homogeneous, interspersed with a few pebbles and sand, very plastic, but not locally. overlying a layer of completely weathered sandstone distributed mainly on the bank of the river, at the foot of the left embankment and at the foot of the right embankment, a layer of completely altered marl of yellow-green color with a clay structure, interspersed with very plastic sand. the water level varies in depth from 13 to 24.5m in the various boreholes drilled, with a tendency to flow in the direction of the slope. analysis of the inclinometer reading data showed that the slip surface was at 9m, 7m, and 3m as shown in table i. engineering, technology & applied science research vol. 13, no. 1, 2023, 9955-9960 9957 www.etasr.com chekroun & boumechra: static and seismic stability of a slope reinforced with two rows of piles table i. values of the inclinometer reading [9] borehole number start date of measurement end date of measurement slip depth (m) final displacement (mm) s01 13-12-2013 29-12-2014 9 26.99 s02 18-12-2013 30-12-2013 7 s03 25-12-2103 02-03-2014 9 58.81 fig. 3. geotechnical profile of the site. the results of the displacements recorded at the foot of the slope on the right side of the platform, showed no signs of significant deformation for 3 months after the event day. iv. numerical model of the landslide the static calculations led to the assumption that the main cause of the landslide, in addition to the local geomorphological and geotechnical conditions of the site and the presence of the water table, is the head loading due to the motorway traffic. this can be neglected or at least not properly taken into account in the pre-dimensioning. figure 4 shows the distribution of horizontal displacements in the model. they are maximal at the bottom of the slope with values of 1.00m. fig. 4. horizontal displacement fields (ux =1.00m). a. static analysis the landslide section for the solution chosen for the treatment [10-12] consists of the installation of 11 piles in a single row at the edge of the landslide (in the middle of the alignment) in order to ensure the safety of the motorway users, during the emergency works, and then the realization of a row of 60 piles on the left side of the section pk52+040~pk52+220, with a beam connecting them at the head. 1) static analysis without the effect of rainfall the model area of the massif extends laterally for 30m, and to a depth of 40m. for the boundary conditions, the vertical and horizontal displacements at the model boundaries are assumed to be zero. the soil-pile system is discretized using the 3dimensional mesh options of the software into 23010 elements. each finite element has 10 nodes with 3 degrees of freedom for a total of 35295 nodes. the average element size is 2.797m [35, 7-19]. it should be noted that the bored piles are modelled by a linear elastic behavior law. the soil is modelled by an elastoplastic behavior law of the mohr-coulomb type. figure 5 shows this proposed treatment of slip which was statically modelled in plane deformation using plaxis 3d software. the piles have a diameter of 1.20m while the depth is 15m for the first row of 11 piles and 19-23m for the second row of 60 piles spaced at 3m. the nominal strength of the concrete used for the piles is 35mpa while the modulus of elasticity is e=35982mpa. the density of the concrete is 25kn/m 3 . fig. 5. numerical model after the introduction of 2 rows of piles. the analysis of the stability of the slide after the introduction of the 2 rows of anti-slip piles clearly shows that the slope is more stable than the initial configuration with an increase in the safety coefficient. therefore, the pavement is now in a safe condition. fig. 6. displacement fields ux (ux max =0.01186m, fs=1.750). figure 6 shows that the model was really stabilized after the introduction of the two rows of piles and the displacements are almost zero. the largest displacements are of the order of only 1cm at the bottom of the slope. 2) static analysis with the effect of rainfall four precipitation values were taken as follows: q = 0, 0.53, and 5.30m 3 /day. this last value corresponds to the rainfall recorded during january in tlemcen (i.e. 62mm). we note that the section of pk 52 that has undergone the slip makes a section of 2700m 2 , or 27% of the area taken in the rainfall estimate. indeed, a 1mm represents the rainfall of 10.000m 2 on an area of 100m×100m (1 hectare). figure 7 shows an example showing the introduction of rainfall in the calculation code used: 3 simulations were carried out by changing the precipitation value in order to inspect the effect of this parameter in the evolution of the stresses. the figure shows their changes according to the calculation steps, in a point b located at the bottom of the slope. engineering, technology & applied science research vol. 13, no. 1, 2023, 9955-9960 9958 www.etasr.com chekroun & boumechra: static and seismic stability of a slope reinforced with two rows of piles fig. 7. evolution of stress σxx according to the rainfall flow. figure 7 shows the rainfall which significantly influences the evolution of stresses under static loading. the recorded increase in stresses is 32%, passing from zero precipitation to 5.30m 3 /day. b. seismic analysis the seismic loading, defined by an accelerogram that was taken into account for the dynamic analysis, is that of the boumerdes earthquake of may, 21 2003, characterized by a magnitude mw of 6.8 on the richter scale. strong seismic aftershocks were recorded, in particular at the keddara site, located south-east of the capital algiers and 20km from the epicenter. the proposed landslide treatment was also the subject of dynamic modeling in plane deformation using plaxis [20]. the landslide was subjected to a combination of loads (permanent load, operational load, and seismic load from the boumerdes 2003 earthquake illustrated in figure 8). fig. 8. the applied accelerogram of the boumerdes 2003 earthquake. the peak ground acceleration (pga) reached 0.58g in the east-west component (keddara2 station) and 0.35g (keddara1 station) in the north-south component of the horizontal direction, while it was 0.22g in the vertical component [15, 21, 22]. the data for these events were obtained from the network records of the national center of seismic engineering (cgs) in algiers. although various simulations were performed, we only present the deformation of the configuration at the end of the seismic loading (t= 35s). we also note that several runs were carried out, changing the model configuration each time. 1) model with a single row of piles with length of 15m in order to analyze the influence and impact of the pile string located at the edge of the landslide (in the middle of the alignment), only one pile string was introduced [14]. it should be noted that this row was planned as an emergency solution. figure 9 shows the location of this pile string at the level of the highway platform. fig. 9. the introduced pile row (emergency treatment) (max ux= 0.8216m). 2) model with two rows of piles the analysis of the slip stability was conducted after the introduction of 2 rows of anti-slip piles subjected to dynamic loading. figure 10 shows the deformation of the model of the pile system. fig. 10. representation of the system model with two piles. the dynamic study of this model shows that it is the second row of piles, with a length of l =20.00m, that provides significant stabilization of the slide. this results in a noticeable decrease in displacement, mainly at the motorway section. note that the maximum value, which is 16.21cm, was recorded at the lower part of the model as shown in figure 10. 3) numerical model with rock at the foot of the slope although rock was not used, this modeling was initiated in order to see the rock impact on the overall behavior of the model. the new model configuration is shown in figure 11. fig. 11. numerical model after the introduction of rock at the foot of the slope. 4) effect of rainfall a parametric study was carried out, by varying the rainfall rate, the considered values were 0, 0.53, 2.4, and 5.40m 3 /day -400 -300 -200 -100 0 100 200 300 400 0 5 10 15 20 25 30 35 40 time (sec) a c c e le ra ti o n ( c m /s ²) engineering, technology & applied science research vol. 13, no. 1, 2023, 9955-9960 9959 www.etasr.com chekroun & boumechra: static and seismic stability of a slope reinforced with two rows of piles [18]. the seismic loading accelerogram taken into account for the dynamic analysis is that of the boumerdes earthquake 2003. the main objective of the study of this parameter lies in the estimation of the stresses exerted on the stabilizer piles. v. results and discussion a. under static loading figure 12 shows the evolution of the displacements under static loading from the exploitation load. his value is equal to 10kn/m². figure 13 shows clearly the very significant decrease in the stresses under the effect of the 2 rows of piles, after having reached a maximum value of 2.10 5 kn/m 2 during the landslide. fig. 12. evolution of displacements ux in a point a of the highway’s platform. fig. 13. stresses σxx in a point a of the highway platform. b. under seismic loading with the effect of rainfall the two graphic representations in figure 14 and 15 show that under dynamic loading the stresses have a very short duration. the evolution of the stresses, under the effect of the rainfall is not significant and resulted in very close curves for the case of two distinct points. table ii. simulation result summary model configurations displacement ux (cm) stress σxx (kn/m 2 ) safety factor (fs) before treatment 100.00 2.10 e+5 <1.00 1 row of piles (seismic case) 82.16 / 1.00 2 rows of piles (seismic case) 16.21 0 1.20 2 rows of piles (static case) 1.186 / 1.75 fig. 14. evolution of stresses σxx in point q at the first row of piles. fig. 15. evolution of stresses σxx at the head of the second row of piles. table iv summarizes the results found in terms of displacements, stresses, and safety coefficients for the different configurations of the numerical model. vi. conclusion in this article, the stability study of the landslide that occurred on march, 2, 2014 on a section of the east-west highway near the city of tlemcen (north-west algeria) was carried out. vertical piles were used to stabilize the highway on the right-hand side of the pκ 52 section in the boundary between the cities of tlemcen and sidi bel-abbes. it should be noted that the company carrying out the treatment work did not rely on the analysis when establishing the treatment of this slide. nevertheless, the calculations carried out in this work show that the treatment solution presents more stability compared to the initial state of the section that suffered the slide. this is justified by the maximum value of the displacement recorded, which is 16.21cm under dynamic loading and almost zero under static loading. we would like to report that it is the second row of 61 piles that brings more stability to the slip section. the first one, consisting of 11 piles, was planned as an emergency solution. on the other hand, the introduction of rock at the bottom of the slope provides optimum stability for the model, essentially by reducing both stresses and displacements. it should be noted that this solution was not foreseen in the field. we note that the dynamic analysis based on the accelerogram of a very strong seismic movement of boumerdes 2003, of the pk 52 slope shows the effectiveness of the slope stabilization technique by piles. this method is able to solve in a permanent way the phenomenon of the slides. engineering, technology & applied science research vol. 13, no. 1, 2023, 9955-9960 9960 www.etasr.com chekroun & boumechra: static and seismic stability of a slope reinforced with two rows of piles rainfall remains a crucial parameter in the treatment of sliding stability, essentially under static loading. particular attention must be paid to this parameter in order to have a correct digital model that represents the real case. this technique is mainly applicable to soils resting on coherent, sometimes soft or sensitive soil. references [1] m. ashour and h. 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[2] l. t. chen and h. g. poulos, "piles subjected to lateral soil movements," journal of geotechnical and geoenvironmental engineering, vol. 123, no. 9, pp. 802–811, sep. 1997, https://doi.org/10.1061/(asce)1090-0241(1997)123:9(802). [3] r. kourkoulis, f. gelagoti, i. anastasopoulos, and g. gazetas, "slope stabilizing piles and pile-groups: parametric study and design insights," journal of geotechnical and geoenvironmental engineering, vol. 137, no. 7, pp. 663–677, jul. 2011, https://doi.org/10.1061/(asce)gt.1943-5606.0000479. [4] r. liang and s. zeng, "numerical study of soil arching mechanism in drilled shafts for slope stabilization," soils and foundations, vol. 42, no. 2, pp. 83–92, apr. 2002, https://doi.org/10.3208/sandf.42.2_83. [5] w. gong, h. tang, h. wang, x. wang, and c. h. juang, "probabilistic analysis and design of stabilizing piles in slope considering stratigraphic uncertainty," engineering geology, vol. 259, sep. 2019, art. no. 105162, https://doi.org/10.1016/j.enggeo.2019.105162. [6] k. boulfoul, f. hammoud, and k. abbeche, "numerical study on the optimal position of a pile for stabilization purpose of a slope," geomechanics and engineering, vol. 21, no. 5, pp. 401–411, 2020, https://doi.org/10.12989/gae.2020.21.5.401. [7] m. hajiazizi, m. bavali, and a. fakhimi, "numerical and experimental study of the optimal location of concrete piles in a saturated sandy slope," international journal of civil engineering, vol. 16, no. 10, pp. 1293–1301, oct. 2018, https://doi.org/10.1007/s40999-017-0155-1. [8] h. lei, x. liu, y. song, and y. xu, "stability analysis of slope reinforced by double-row stabilizing piles with different locations," natural hazards, vol. 106, no. 1, pp. 19–42, mar. 2021, https://doi.org/10.1007/s11069-020-04446-2. [9] s. m. e.-a. bourdim, l. e.-h. chekroun, a. benanane, and a. bourdim, "treatment of a landslide by using piles system, case study of the east-west highway of algeria," in geomeast 2017: soil dynamics and soil-structure interaction for resilient infrastructure, 2018, pp. 16–24, https://doi.org/10.1007/978-3-319-63543-9_2. [10] t. ito and t. matsui, "methods to estimate lateral force acting on stabilizing piles," soils and foundations, vol. 15, no. 4, pp. 43–59, dec. 1975, https://doi.org/10.3208/sandf1972.15.4_43. [11] m. a. soomro, k. f. memon, m. a. soomro, a. memon, and m. a. keerio, "single pile settlement and load transfer mechanism due to excavation in silty clay," engineering, technology & applied science research, vol. 8, no. 1, pp. 2485–2492, feb. 2018, https://doi.org/ 10.48084/etasr.1666. [12] h. g. poulos, "design of reinforcing piles to increase slope stability," canadian geotechnical journal, vol. 32, no. 5, pp. 808–818, oct. 1995, https://doi.org/10.1139/t95-078. [13] a. bouafia, "comportement des pieux isolés chargés latéralement problèmes résolus," in calcul pratique des fondations et des soutènements, 3rd ed., algiers, algeria: editions opu, 2017, pp. 163– 181. [14] a. firoozfar, a. rostami, h. ghaderi, h. zamani, and a. rostamkhani, "assessing the effects of length, slope and distance between piles on the bearing capacity of a pile group under axial loading in granular soil," engineering, technology & applied science research, vol. 7, no. 5, pp. 1894–1899, oct. 2017, https://doi.org/10.48084/etasr.1352. [15] n. laouami, a. slimani, y. bouhadad, j.-l. chatelain, and a. nour, "evidence for fault-related directionality and localized site effects from strong motion recordings of the 2003 boumerdes (algeria) earthquake: consequences on damage distribution and the algerian seismic code," soil dynamics and earthquake engineering, vol. 26, no. 11, pp. 991– 1003, nov. 2006, https://doi.org/10.1016/j.soildyn.2006.03.006. [16] n. mangi, d. k. bangwar, h. karira, s. kalhoro, and g. r. siddiqui, "parametric study of pile response to side-by-side twin tunneling in stiff clay," engineering, technology & applied science research, vol. 10, no. 2, pp. 5361–5366, apr. 2020, https://doi.org/10.48084/etasr.3290. [17] v. maralapalle and r. a. hegde, "an experimental study on the socketed pile in soft rock," engineering, technology & applied science research, vol. 12, no. 6, pp. 9665–9669, dec. 2022, https://doi.org/10.48084/etasr.5338. [18] t. v. tran, m. t. trinh, g. lee, s. oh, and t. h. v. nguyen, "effect of extreme rainfall on cut slope stability: case study in yen bai city, viet nam," journal of the korean geo-environmental society, vol. 16, no. 4, pp. 23–32, 2015, https://doi.org/10.14481/jkges.2015.16.4.23. [19] y.-s. chung, "etude numérique de l’interaction sol-pieu-structure sous chargement sismique," ph.d. dissertation, université des sciences et technologies de lille, france, 2000. 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[22] s. m. a. bourdim, n. boumechra, and a. djedid, "calibrage du modèle numérique, cas du comportement dynamique d’un système solsoutènement (numerical model calibration, case of dynamic behavior of a soil-retaining wall system)," journal of materials and environmental science, vol. 7, no. 3, pp. 1048–1055, 2016. microsoft word etasr_v13_n1_pp9888-9892 engineering, technology & applied science research vol. 13, no. 1, 2023, 9888-9892 9888 www.etasr.com fahmi & al-zaidee: buckling and vibration estimation of girder steel portal frames using the … buckling and vibration estimation of girder steel portal frames using the bayesian updating methods fahmi h. fahmi department of civil engineering, college of engineering, university of baghdad, iraq f.fahmi1901m@coeng.uobaghdad.edu.iq (corresponding author) salah al-zaidee department of civil engineering, college of engineering, university of baghdad, iraq salah.r.al.zaidee@coeng.uobaghdad.edu.iq received: 26 october 2022 | revised: 5 november 2022 | accepted: 7 november 2022 abstract in practice, structural systems are complicated. when dealing with such systems, the use of analytical simulations is or may be impossible to apply, since the problem includes many variables with partial differential formulations. the stability and dynamic response of structures is an important aspect that must be paid particular attention to in order to ensure safety against collapse. a physical phenomenon of a reasonably straight, slender member bending laterally (usually abruptly) from its longitudinal position due to compression is referred to as buckling. two kinds of buckling can be distinguished: (1) bifurcation-type buckling and (2) deflection-amplification-type buckling. in vibration, frequencies and mode shapes must be known in order to use some methods of dynamic response analysis. to calculate frequencies and modes, an eigenvalue problem is solved in algebraic form. in structural dynamic problems, only the lowermost eigenpairs are of important interest. the highest eigenpairs are not needed and are not accurate due to discretization errors. keywords-interior supporting frame; bayesian method; sample data; prior data; posterior data; first order; mcs i. introduction the majority of engineering designs are based on deterministic variables and often do not consider the variations in the material properties and the geometry of the structure [1]. uncertainty is vital to the analysis and design of an engineering system and the effects of uncertainties must be quantified and propagated. increasing amounts of data in engineering systems are collected and stored. this information can and should be used to decrease the uncertainty in engineering models and optimize the management of these systems. a coherent and effective way for merging new with existing information is provided by the bayesian method, in which prior probabilistic information is updated with new data and observations. the bayesian framework enables the combination of uncertain and incomplete information with models from different sources and provides probabilistic information on the accuracy of the updated model [2]. the current study emphasizes the analysis of the buckling and vibration of steel portal frames, where new data have been acquired for the independent variables of the system. subsequently, the bayesian method presents an efficient way to update the prior knowledge regarding the stability and natural frequency of the frame. the first-order approximation method and monte carlo (mc) simulation have been adopted to investigate the statistical properties of the buckling and vibration. ii. the bayesian method in engineering, one often needs to use whatever information is available in formulating a sound basis for making decisions. this may include observed data (field or experimental), information derived from theoretical models, and judgments based on experience. moreover, the available information may need to be updated as new information or data are acquired [3]. the proper tool for combining and updating the available information is embodied in the bayesian approach. parameter estimation in the bayesian approach is based on the updating formula: ���� = ��������� (1) where ���� is the prior probability density function (pdf) representing the initial state of knowledge about the unknown parameters �, ���� is the likelihood function representing the engineering, technology & applied science research vol. 13, no. 1, 2023, 9888-9892 9889 www.etasr.com fahmi & al-zaidee: buckling and vibration estimation of girder steel portal frames using the … knowledge gained from a set of observations, and the constant � is a normalizing factor. the posterior pdf ���� represents the updated state of knowledge regarding the parameters �. a. prior distribution the prior distribution represents the distribution of possible parameter values from which the parameter has been drawn. the selection of the prior distribution is an important matter in bayesian modeling. since the choice of the prior distribution has a major effect on the resulting inference, this choice must be conducted with the utmost care [4]. b. posterior distribution the current information about the parameter is contained in the posterior probability distribution. it merges the information of the prior distribution and the likelihood. this results in a strong representation of the information than separate sources of information [5]. the prior and posterior densities are presented in table i and the mean and variance of the posterior parameters in table ii. table i. random variables and their prior and posterior densitiy distributions [3] basic random variables parameter prior and posterior distribution normal � � � = 1√2�� � � �− 12 � − �� ��� � normal ���� = ��� �� � �⁄ � + ̅� ���� � �⁄ + ���� �� lognormal � � �= 1√2� � � !− 12 "ln − % & �' % normal �(�%�= 1√2�� � � !− 12 "% − �� & �' table ii. mean and variance of the parameters and their posterior statistics [3] mean and variance of parameters posterior statistics )��� = �� ���� = ��� �� � �⁄ � + ̅� ����� �⁄ + ���� �� *+,��� = ��� ���� = ���� ����� �⁄ ����� �� + �� �⁄ )�%� = � ��� = .�� � �⁄ � + � � ln ̅ � �⁄ + � � *+,�%� = � � � �� = / � �� � �⁄ ��� + � �⁄ iii. statistical characteristics of the independent variables this study considers the applied loads, cross-section dimensions, modulus of elasticity, girder span, plastic section modulus, and yield strength as random variables. the sample data of the independent variables were summarized and are presented in table iii. the prior statistical characteristics of these variables have been collected from the literature and can be seen in table iv. the posterior statistical data of the input variables have been calculated from the updating process of the prior data by the bayesian method. the modulus of elasticity of steel )0 has been considered as an example of this process. updating mean, standard deviation, and coefficient of variance have been estimated based on the relations in (1)-(3). the posterior statistical characteristics of the independent variables are summarized in table v. ��� = 1 23" 4√5&678! 9:�4:�6' 1 <" 4√5&678! <�4:�6' = =̅�>:�68�:"465 &�>:�68"465 & = ��?@��ab�8��??�� <c<.ec ��ab�8�<c<.6fc � = 202gpa (1) � �� = / �>:�6�465 ��>:�68�465 � = / �ab�� <c<.ec ��ab�8�<c<.ec � = 3.24gpa (2) �mn′′ = >::�:: = p.�q�?� = 0.016 (3) table iii. sample statistical data of the variables variable stuvwxyzvu[ cov distribution type reference dead load \] 1.03 0.08 normal [6] live load \̂ 1.00 0.1 gumbel [7] moment of inertia _= 0.96 0.03 normal local survey modulus of elasticity )0 1.025 0.05 normal [8] modulus of elasticity )` 0.98 0.07 lognormal [9] member span � 1.00 0.07 lognormal [10] plastic section modulus a= 1.04 0.05 lognormal [11] yield strength of steel bc 1.10 0.07 lognormal [11] table iv. prior statistical data of the variables variable stuvwxyzvu[ cov distribution type reference dead load \] 1.03 0.08 normal [6] live load \̂ 1.00 0.1 gumbel [7] moment of inertia _= 0.96 0.05 normal [12] modulus of elasticity )0 1.00 0.02 normal [11] modulus of elasticity )` 1.00 0.03 lognormal [13] member span � 1.00 0.004 lognormal [14] plastic section modulus a= 1.00 0.04 lognormal [15] yield strength of steel bc 1.10 0.06 lognormal [12] table v. posterior statistical data of the variables variable stuvwxyzvu[ cov distribution type dead load \] 1.03 0.08 normal live load \̂ 1.00 0.1 gumbel moment of inertia _= 0.96 0.005 normal modulus of elasticity )0 1.01 0.016 normal modulus of elasticity )` 1.00 0.02 lognormal member span � 1.00 0.003 lognormal plastic section modulus a= 1.00 0.03 lognormal yield strength of steel bc 1.10 0.04 lognormal iv. parametric study a steel single-story warehouse, as shown in figure 1, with 45m total length and 15m width, consisting of 5 bays, has been considered in this parametric study. the superimposed dead engineering, technology & applied science research vol. 13, no. 1, 2023, 9888-9892 9890 www.etasr.com fahmi & al-zaidee: buckling and vibration estimation of girder steel portal frames using the … load has been determined based on the assumption of a flooring system of a concrete slab with a thickness of 100mm and a metal deck of 7.5mm, supported on ipe 300 floor beams. the first inner frame shown in figure 2 has been considered the most critical, as it includes the exterior face of the first interior support where the shear force is about 15% greater than the average value. the frame consists of ipe 600 steel girder and columns. the applied live loads on the girder have been determined based on the asce 7 specifications. the selfweight of the girder and columns have been determined depending on the cross-section dimensions and material density. fig. 1. steel single-story warehouse building. fig. 2. summary of the dead and live load on the interior supporting frame. v. derived and simulated statistical properties for the buckling and vibration of the girder two stages have been considered in the first-order approximation method and the mc simulation method. the randomness of the dependent variables, in the first stage, has been deduced based on the prior knowledge of table iv, while in the second stage, it has been deduced based on the posterior knowledge of table v. a. first-order approximation method it is possible to expand the original model into an infinite taylor series (ts) around the mean values: d�e� = d�� � + �e − � � fgf + a� �e − � �� f6gf 6 + ⋯ +ai! �e − � �i f5gf 5 (4) where the function and derivatives are evaluated at � . it is common to include only linear terms, assuming that random input variables are independent. a function d �e� of n independent random variables can be approximated by linear terms of the ts, which are as follows [16]: )�k� l d��= � (5) and *+,�k� ≃ *+,�e − � � �fgf �� = *+,� � �fgf �� (6) 1) buckling analysis the buckling \̀ n is a function of the span �, the modulus of elasticity ), and the moment of inertia _. by refereeing to (4) and (5) the mean and variance of the buckling can be estimated by: )�\̀ n � = ao6 p6qrsqtu̅vwxy� ŝ �6 (7) *+,�\̀ n � = *+,�_� �z{|yzt �� + *+,��� �z{|yz^ �� +*+,�)� �z{|yzr �� (8) based on the statistical characteristics of the independent variables illustrated in tables iv and v, the prior and posterior statistical characteristics for \̀ n have been estimated and are presented in tables vi and vii. table vi. prior statistical characteristics of the buckling of the girder random variable nominal (kn) mean (kn) standard deviation (kn) cov \̀ n 44198 42072 2172 0.051 table vii. posterior statistical characteristics of the buckling of the girder random variable nominal (kn) mean (kn) standard deviation (kn) cov \̀ n 44198 42493 750 0.017 2) vibration analysis the vibration �i is a function of the load p, span l, modulus of elasticity e, and moment of inertia i. the mean and variance of the vibration are calculated by: )��i� = 0.18 a~�� � g���y��y ⟹ 1.247� g�� � rst̅{s ŝ e (9) *+,��i� � *+,�_� �z�5zt � � � *+,��� �z�5z^ � � � *+,�)� �z�5zr � � � *+,�\� �z�5z{ � � (10) based on tables iv and v, the prior and posterior statistical characteristics for vibration are presented in tables viii and ix. engineering, technology & applied science research vol. 13, no. 1, 2023, 9888-9892 9891 www.etasr.com fahmi & al-zaidee: buckling and vibration estimation of girder steel portal frames using the … table viii. prior statistical characteristics random variable nominal (kn) mean (kn) standard deviation (kn) cov �i 3.32 7.23 0.214 0.029 table ix. posterior statistical characteristics random variable nominal (kn) mean (kn) standard deviation (kn) cov �i 3.32 7.267 0.103 0.014 b. monte carlo simulation the mc method is considered one of the most powerful and accurate simulation tools and can be applied to many practical problems allowing the direct consideration of any type of probability distribution for the random variables [17]. the mc method has been adopted to achieve the simulation processes of the buckling, and vibration for the interior supporting frame. matlab code has been used to generate pseudo-random sampling with a size of 1000 for each input variable. 1) buckling analysis the prior statistical characteristics of the buckling are presented in figure 3 and are summarized in table x. \̀ n fig. 3. histogram of the prior buckling of a typical interior girder. table x. prior statistical characteristics of the buckling of the girder random variable nominal (kn) mean (kn) standard deviation (kn) cov \̀ n 41999 2279 0.054 normal the posterior statistical characteristics of the buckling were estimated and are presented in figure 4 and table xi. table xi. posterior statistical characteristics of the buckling of the girder random variable nominal (kn) mean (kn) standard deviation (kn) cov \̀ n 42481 756 0.017 normal \̀ n fig. 4. histogram of the posterior buckling of a typical interior girder. 2) vibration analysis the prior statistical characteristics of the natural frequency are presented in figure 5 and table xii. �i fig. 5. histogram of the prior natural frequency of a typical interior girder. table xii. prior statistical characteristics of the natural frequency of the girder random variable nominal (kn) mean (kn) standard deviation (kn) cov �i 7.30 0.311 0.042 normal the estimated posterior statistical characteristics of the natural frequency are presented in figure 6 and table xiii. table xiii. posterior statistical characteristics of the natural frequency of the girder random variable nominal (kn) mean (kn) standard deviation (kn) cov �i 7.36 0.26 0.035 normal engineering, technology & applied science research vol. 13, no. 1, 2023, 9888-9892 9892 www.etasr.com fahmi & al-zaidee: buckling and vibration estimation of girder steel portal frames using the … �i fig. 6. histogram of the posterior natural frequency of a typical interior girder. vi. conclusion in this paper, buckling and vibration analysis was performed for the girder of the first inner frame for the prior and posterior statistical characteristics. through the application of the bayesian method, and from the results of the prior and posterior analysis, it was shown that the greater the knowledge gained about the independent parameters, the less randomness is in the dependent parameters, and thus the analysis and design of the system is enhanced. in the first order analysis, the covariance of the critical buckling load decreased from 0.051 to 0.017, and for the natural frequency from 0.029 to 0.014, while in monte carlo simulation, the covariance results were from 0.054 to 0.017 for the critical buckling load, and from 0.042 to 0.035 for the natural frequency. the decrement of the covariance of the dependent parameters is due to the decrement of the values of the covariance of the independent parameters because of the increased knowledge of the 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[17] m. s. m. noori and r. m. abbas, "reliability analysis of an uncertain single degree of freedom system under random excitation," engineering, technology & applied science research, vol. 12, no. 5, pp. 9252–9257, oct. 2022, https://doi.org/10.48084/etasr.5193. microsoft word etasr_v12_n4_pp9023-9027 engineering, technology & applied science research vol. 12, no. 4, 2022, 9023-9027 9023 www.etasr.com buriro & kumar: the fisher component-based feature selection method the fisher component-based feature selection method abdul baseer buriro department of electrical engineering sukkur iba university sukkur, pakistan abdul.baseer@iba-suk.edu.pk suresh kumar department of computer systems engineering sukkur iba university sukkur, pakistan suresh@iba-suk.edu.pk received: 11 june 2022 | revised: 23 june 2022 | accepted: 26 june 2022 abstract-a feature selection technique is proposed in this paper, which combines the computational ease of filters and the performance superiority of wrappers. the technique sequentially combines fisher-score-based ranking and logistic regressionbased wrapping. on synthetically generated data, the 5-fold cross-validation performances of the proposed technique were compatible with the performances achieved through least absolute shrinkage and selection operator (lasso). the binary classification performances in terms of f1 score and geometric mean (gm) were evaluated over a varying imbalance ratio of 0.1:0.9 – 0.5:0.5, a number of informative features of 1 – 30, and a fixed sample size of 5000. keywords-feature selection; regularization; dimensionality reduction; class imbalance i. introduction with the advent of low-cost electronics, the dimensions and complexity of datasets, e.g. the internet of things (iot), text classification, and medical imaging, are constantly increasing. high dimensional datasets, compared to their low dimensional counterparts, require more processing time and more space complexity, which is known as the curse of dimensionality. besides, the presence of irrelevant and/or redundant features leads to less-interpretable and over-fitted learning models. the issue becomes more severe when the number of features is more than the number of instances/samples like gene selection in microarray data, where typically the data examples are fewer than 100 and the number of raw features ranges from 6,000 to 60,000 [1]. in such a situation, a trained model may become useless as it would result in infinitely high variance [2]. furthermore, the covariance/correlation-based methods like principal component analysis (pca), fisher discriminant analysis (fda), and linear regression become ill-posed problems. a common way to address the issue is to select the informative and non-redundant features from a known feature set, which results in lower dimension datasets. the use of such datasets improves the generalized accuracy of a trained model, reduces computational time, and improves model interpretability. three categories of feature selection, i.e. filter, wrapper, and embedded methods, are widely been used. the filters measure the relevance (e.g., fisher score, mutual information, correlation [3-5]) of a feature with the target. filters are computationally fast, simple, easy to scale, and generally don’t require a learning model [6]. a filter, however, generally ignores feature dependencies and does not consider combined discriminatory power, and consequently, can result in suboptimal feature selection [7]. wrappers evaluate the usefulness of features’ subsets by training and testing a model on them, and generally use a cross-validation method. forward feature selection, backward elimination, and recursive feature elimination (rfe) are the most common used wrapper methods. the optimal feature combination that maximizes the overall performance is determined by adding and/or removing features. wrapper methods are, however, computationally expensive. greedy (best subset) selection requires 2�, whereas, both forward and backward feature selection techniques require at least ������ � models/iterations [2]. embedded (also known as shrinkage) methods intrinsically maximize the overall performance during the training/learning of a model, like a least absolute shrinkage and selection operator (lasso) or l1 regularization [4]. however, not all the models such as knearest neighbors (knn), and decision tree incorporate l1 regularization during their training. contrary to feature selection techniques, dimensionality reduction techniques project the original input data into a lower-dimensional feature space and don’t require learning/training. pca is a classical data analysis and dimensionality reduction technique, which captures the maximum variability in data. pca transforms the feature space into a new (meta) orthogonal feature space of the same dimension. its effectiveness is, however, limited to unsupervised problems. fda on the other hand is a traditional supervised dimensionality reduction technique, which respectively maximizes and minimizes the between-class distance and within-class mean distance. contrary to pca, the dimension of the fda-transformed data is one less than the number of classes (i.e. � − 1) [8, 9]. authors in [4] ranked the features per the sum of absolute values of the coefficients of the first two principal components. the ranked features were then evaluated with a wrapper. they corresponding author: abdul baseer buriro engineering, technology & applied science research vol. 12, no. 4, 2022, 9023-9027 9024 www.etasr.com buriro & kumar: the fisher component-based feature selection method compared the results with the ones from analysis of variance (anova), absolute correlation, and classifier-based ranking, and achieved higher performance. since pca is unsupervised, their method may underperform in real datasets when the classification-related information is different from the direction of the maximum variance. several feature selection techniques have been published and implemented in well-known machine learning libraries like python’s sklearn, and matlab. these techniques, however, uniquely behave with varying datasets, like different models select different features in standard wrapper feature selection techniques. for class imbalanced datasets, most of the classification models [10] and, subsequently, the wrapper and embedded feature selection techniques, perform poorly, i.e. may not accurately determine all informative features. the identification of the most suitable features with varying class imbalance ratios is therefore of much importance and requires a solid solution. in this paper, a feature selection technique is proposed, that combines the computational ease of filters and the performance superiority of wrappers. the technique sequentially combines fisher-score-based ranking and logistic regression-based wrapping. in doing so, the proposed technique requires the training of a maximum of � models. on synthetically generated data, the proposed technique gave a very compatible mean of 5-fold cross-validation f1-scores and geometric means (gm) to lasso. the binary classification performances were evaluated over a variable imbalance ratio of 0.1:0.9 – 0.5:0.5. ii. methods and experimental design a simulation study was conducted to examine the effect of informative and non-informative features on feature selection techniques. like [4], synthetic data of 30 features with varying imbalance rates and noise (i.e. non-informative features), were generated using the "make classification" library in python’s scikit-learn.datasets. each of the binary classes was a single cluster. the information features were drawn independently from the normal �0,1� distribution for each class and then combined as random linear combinations within each cluster to add covariance [11]. the non-informative features were represented by random noise. the datasets were generated with varying number of information features from 1 – 30, and with a step of 2. the imbalance rates were changed from 0.1:90 – 0.5:0.5, and the sample size was fixed to 5000 samples. the model was validated using 5-fold cross-validation. a. feature ranking feature ranking is to place the features in an order per their importance in order to identify the most important features. for this purpose, fda was used. for binary classification, fda results in one component. the features were ranked according to the absolute values of their respective coefficients in the fda component. eigenvalues and eigenvectors respectively indicate the explained variance of an fda component and the linear combination of the original features, i.e. �� = ���� + ���� + ⋯ + ���� , where �� is ��� feature and �� is corresponding weight of ��� feature. eigenvalues and eigenvectors are computed from ������ , where �� and �� are respectively the within-class and between-class scatter matrix, defined as: �� = ∑ �� ��� − � !�"� ��� − � # (1) �� = ∑ �$ − �� !$∈&' �$ − �� # (2) where �� , �� , and ( are the mean vector, the number of instances (observations) for class � , and the total number of classes respectively. b. feature selection the ranked features were further sequentially evaluated using the logistic regression-based wrapper, shown in figure 1. the top-ranked feature was first fed to the classifier and the classification performance due to class imbalance rate was recorded in terms of f1 score. then iteratively, the next consecutively ranked feature was added. at each iteration, a feature was added to the subset if its combined mean 5-fold cross-validation classification performance was higher than the previous iteration. the feature was otherwise discarded. the value of c was kept high (i.e. 1 × 10* ) to avoid inherent lasso or ridge regularization by the classifier. c. lasso lasoo, defined as ‖,‖� = ∑ .,� .��"� , is a practical strategy to perform feature selection and classification simultaneously. ‖. ‖� and > 0 are the l1-norm and regularization parameter respectively. lasso selects the features by generating a sparse weight vector (few non-zero coefficients). consequently, lasso reduces the variance and the intricacy of the model, and therefore, is an alternative feature selection technique [12]. non-zero coefficients indicate the importance of the respective features, whereas, zero coefficients indicate irrelevant and redundant features. the number of non-zero coefficients are roughly controlled via -. larger the -, sparser is the weight vector and vice versa. the optimal value of � = �1 was therefore selected from a range 10�2102 with a step of 10, using 5-fold cross-validation via grid search method. fig. 1. the proposed feature selection technique. 345� is the training feature set, where n is the number of examples/instances and p is the number of features. 645� shows n binary training labels. �� represents p coefficients/weights of the fisher component. training data ranking logistic regression add feature delete feature no yes engineering, technology & applied science research vol. 12, no. 4, 2022, 9023-9027 9025 www.etasr.com buriro & kumar: the fisher component-based feature selection method d. classification a commonly used logistic regression classifier [13] was used to validate the efficacy of the proposed feature selection technique under varying imbalance rates and number of irrelevant features. let a feature vector $ ∈ ℝ45� with n rows, and an associate class labels/target 8 ∈ 90, 1: be the training data for logistic regression classifier defined as: ��8/<� = =>?�@a�@$���=>?�@a�@$� (3) where ��8/$� is the conditional probability of a target given a feature $, and , shows the classifier’s parameters. class imbalance is generally handled by sampling the data or modifying the classifier. standard classification algorithms generally use a default threshold of 0.5 to assign class membership. any adjustments to such threshold change the class membership referred to as cost-sensitive learning. simulation studies have shown that cost-sensitive learning can increase the sensitivity and decrease the specificity and vice versa. however, the accuracy more or less remains the same. the synthetically generated datasets were skewed or classimbalanced. the cost-sensitive learning was therefore employed by assigning equal prior probabilities (0.5) to both classes to account for the class imbalance ratio in the training datasets. a generalized classification system was attained using stratified 5-fold cross-validation. e. evaluation of the feature selection techniques as the datasets were synthetically generated, we have the prior knowledge of informative and non-informative features. each row of the matrix shown in table i was used to describe the performances of the proposed and lasso feature selection methods. both feature selection techniques were evaluated using true positive rate, i.e. cde = fghi , false positive rate, i.e. �de = hghi, and true selected positive rate, i.e. cjde = fg #g. cs, is, and ts are the number of correctly, incorrectly, and total selected features respectively. if is the number of informative features used in the datasets. the performances of the proposed method and lasso at selecting features were the average of 5fold cross-validation with balanced datasets and varying number of informative features. f. evaluation of the overall classification performance for a binary-class problem, multiple confusion matrixbased performance metrics like sensitivity, specificity, and precision are commonly used. these metrics, however, by themselves are incomplete. practically, combinations of these metrics are used to summarize the entire performance. for class imbalance datasets, f1 score k���@ l mn4mopoqopr×�sn!omot4 @l×mn4mopoqopr��sn!omot4 u and geometric mean (gm) �vwx�wyzy[yz8 × w�x(y\y(yz8 have been the widely used measures of performance. the overall performances of the system under varying class imbalance ratios were therefore measured in f1 score and gm. the coefficient , shows the relative preference of sensitivity against precision [14]. in this study, both sensitivity and precision were given the same weight, and therefore, , = 1. iii. simulation results and discussion table i shows the mean 5-fold cross-validation feature selection performances of lasso and the proposed method with varying number of informative features out of a total of 30 features. with balanced datasets, and irrespective of the number of informative features, lasso compared to the proposed method had higher tpr but at the cost of higher fpr. this indicates that lasso correctly selected more features than the total number of informative features, and can therefore result in an over-complex model. besides computational requirements, such models are hard to interpret. conversely, the proposed method, compared to lasso, gave lower fpr and selected fewer features, and subsequently, can result in a simpler model. table i. mean 5-fold feature selection performances of the proposed and lasso feature selection methods if (out of 30) lasso proposed cs is ts cs is ts 10 8 17 25 5 7 12 15 11 11 22 8 6 14 20 17 9 26 12 7 19 25 24 5 29 16 3 19 figure 2 indicates the mean 5-fold performances of the proposed method and lasso with logistic regression classifier and with the balanced datasets. the number of informative features out of the total 30 features varied from 1 to 30 features with a step of 2 features. the remaining features (i.e. total features – informative features) were the irrelevant features consisting of noise. on average, both lasso and the proposed method gave similar results. irrespective of the number of informative features and the feature selection technique, both gm and f1 score exhibited similar trends, indicating a balanced dataset. the fluctuations in both the performance measures are due to the number of informative features. higher performances indicate that both feature selection techniques have correctly selected the informative features, whereas, lower performances indicate that some of the irrelevant features have also been selected, and informative features have been rejected by both methods as shown in table i. figure 3 shows the mean 5-fold cross-validation performance of the proposed method and lasso on the datasets with 20 informative and 10 irrelevant features. the class imbalance ratio varied from 0.1:0.9 to 0.5:0.5. both lasso and the proposed method gave similar results. however, the f1 score linearly increased with the decrease in the imbalance rates, and subsequently, the maximum values were achieved with the balanced datasets, whereas, the imbalance rate did not demonstrate much of its effect on the gm because it involves specificity and sensitivity, and does not tell about the number of false positives. the proposed method, compared to lasso, resulted in simpler models with comparable classification performance (see table i, figures 2-3). engineering, technology & applied science research vol. 12, no. 4, 2022, 9023-9027 9026 www.etasr.com buriro & kumar: the fisher component-based feature selection method fig. 2. effect of number of informative features on classification performances on synthetically generated class-balanced dataset. fig. 3. effect of imbalance ratio 0.1:0.9 – 0.5:0.5 on the classification performance using 20 informative and 10 irrelevant features. iv. conclusion in this paper, an alternative feature selection technique is presented that uses the simplicity of a filter and the performance superiority of a wrapper. the proposed technique requires fewer models than its counterparts, i.e. forward and backward feature selection methods. unlike regularization, the proposed method can easily be used with any classifier. furthermore, the overall classification performance of the proposed method was comparable to the one of lasso (a regularization technique), in terms of f1 score and gm. references [1] i. guyon and a. elisseeff, "an introduction to variable and feature selection," journal of machine learning research, vol. 3, pp. 1157– 1182, 2003. [2] g. james, d. witten, t. hastie, r. tibshirani, an introduction to statistical learning with applications in r, new york, ny, usa: springer. https://doi.org/10.1007/978-1-0716-1418-1. [3] s. nuanmeesri and w. sriurai, "thai water buffalo disease analysis with the application of feature selection technique and multi-layer perceptron neural network," engineering, technology & applied science research, vol. 11, no. 2, pp. 6907–6911, apr. 2021, https://doi.org/10.48084/etasr.4049. engineering, technology & applied science research vol. 12, no. 4, 2022, 9023-9027 9027 www.etasr.com buriro & kumar: the fisher component-based feature selection method [4] s. matharaarachchi, m. domaratzki, and s. muthukumarana, "assessing feature selection method performance with class imbalance data," machine learning with applications, vol. 6, dec. 2021, art. no. 100170, https://doi.org/10.1016/j.mlwa.2021.100170. 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[13] a. b. musa, "a comparison of ℓ1-regularizion, pca, kpca and ica for dimensionality reduction in logistic regression," international journal of machine learning and cybernetics, vol. 5, no. 6, pp. 861– 873, dec. 2014, https://doi.org/10.1007/s13042-013-0171-7. [14] w.-j. lin and j. j. chen, "class-imbalanced classifiers for highdimensional data," briefings in bioinformatics, vol. 14, no. 1, pp. 13–26, jan. 2013, https://doi.org/10.1093/bib/bbs006. microsoft word etasr_v12_n5_pp9120-9125 engineering, technology & applied science research vol. 12, no. 5, 2022, 9120-9125 9120 www.etasr.com rusna & kalpana: using artificial neural networks for the prediction of the compressive strength of … using artificial neural networks for the prediction of the compressive strength of geopolymer fly ash k. p. rusna department of civil engineering coimbatore institute of technology coimbatore, tamilnadu, india rusnacbe19@gmail.com v. g. kalpana department of civil engineering coimbatore institute of technology coimbatore, tamilnadu, india kalpana@cit.edu.in received: 7 july 2022 | revised: 19 july 2022 | accepted:20 july 2022 abstract-geopolymers are promising cement replacement materials as their use results in a considerable reduction of co2 emissions. geopolymer fly ash (gf) is a widely used geopolymer due to its low cost and waste management achievement. the compressive strength of gf depends on variables such as curing time, curing temperature, naoh molarity, the ratio of sodium silicate to sodium hydroxide, the ratio of fly ash to alkaline solution, etc. artificial neural networks are employed to predict the strength of gf due to their accurate prediction capability as well as saving time and cost of experimental work. the obtained root mean square error (rmse) and correction coefficient (r2) values were 4.47 and 0.972 respectively. the results illustrate the ability of the ann model to be used as an efficient tool in predicting the compressive strength and determining the optimal values of gf parameters. the maximum strength of gf was observed for 2 hours curing time at 100°c, molarity of 10, fly ash to alkaline solution ratio of 3, and sodium silicate to sodium hydroxide ratio of 1. keywords-fly ash; alkaline solution; geopolymer fly ash; artificial neural networks (anns); compressive strength i. introduction climate warming is a serious global issue. the main reasons for climate warming are human activities that result in changes in the concentration of greenhouse gases such as co2 in the atmosphere [1]. one of the main sources of greenhouse gas emissions is the construction industry. the cement used in the construction sector produces significant amounts of co2 [2]. therefore, the replacement of cement with eco-friendly alternatives such as fly ash, rice husk ash, and ggbs can significantly reduce the amount of co2 emissions [3-7]. geoplymers are a new cement replacement material with promising performance for cement with less greenhouse gas emissions [8]. geopolymer binders are produced through the reaction of aluminosilicate materials with alkaline solution. fly ash, metakaoline, and ground granulated blast furnace slag are the most commonly used aluminosilicate materials. high strength is obtained with fly ash-based geopolymers [9]. sodium hydroxide and sodium silicate or potassium hydroxide and potassium silicate mixtures are the most commonly used alkaline solutions [7]. equations (1) and (2) explain the geopolymer material forming mechanism [10, 11]. the water expelled during the chemical reaction leaves as nano-pores in the mix during curing time and imparts workability to the geopolymer mix during handling [12]. (1) (2) investigating the mechanical properties of geopolymer materials by conducting experiments is time consuming and costly. there are many factors affecting the strength properties of geopolymers which make difficult their accurate estimation [13]. mechanical modeling, analytical modeling, statistical methods, and artificial intelligence are the various methods used for the prediction of the strength properties of concrete [14]. artificial intelligence is the most extensively used method for the prediction of the compressive strength of concrete. the use of anns is the most popular and widely used method in the area of artificial intelligence due to its easiness and prediction accuracy [15]. ann modeling is a powerful machine learning technique that can solve various scientific problems [16]. in civil engineering, anns are widely used to predict the mechanical properties of concrete. the compressive strength of concrete incorporated with fly ash admixture was predicted with gene expression programming (gep), anns, and decision tree (dt) algorithm in [17]. softcomputing tools such as anns, response surface methodology (rsm), and gep have been applied to predict and analyze the compressive strength of alkali-activated strain-hardening geopolymer composites in [18]. the effect of parameters such as curing time, ca(oh)2 content, amount of superplasticizer, naoh concentration, mould type, geopolymer type, h2o/na2o molar ratio, etc. on the compressive strength of different types of geopolymers were analyzed with anns in [9]. the influence of corresponding author: k. p. rusna engineering, technology & applied science research vol. 12, no. 5, 2022, 9120-9125 9121 www.etasr.com rusna & kalpana: using artificial neural networks for the prediction of the compressive strength of … sodium silicate to sodium hydroxide ratio and fly ash to alkaline solution ratio on the compressive strength of fly ash-based geopolymers was assessed using anns in [19]. studies including the prediction of compressive strength of cement-based materials and geopolymer composites using anns are [20, 21]. in this study, anns are used to determine the compressive strength of geopolymer fly ash. parameters such as naoh molarity, na2sio3/naoh ratio, fly ash/alkaline solution ratio, curing temperature, and curing time influence the compressive strength of geopolymer fly ash. parameter optimization is conducted using anns. ii. experimental phase a. materials fly ash, sodium hydroxide (naoh), and sodium silicate (na2sio3) solutions were used. the fly ash was collected from mettur thermal power plant, tamilnadu, india and industrial grade chemicals na2sio3 and naoh pellets were collected from coimbatore, tamilnadu. the fly ash was class-f based on its chemical composition [22]. the specific gravity of fly ash was determined in accordance with is1727 [23] and the value 2.12 was obtained. the chemical composition of na2sio3 solution used is sio2=32.2%, na2o=14.01% and h2o =53.79% by mass. fig. 1. geopolymer fly ash cubes. b. sample preparation and testing sodium hydroxide solution and sodium silicate solution were mixed to prepare the alkaline solution. the alkaline solution was prepared one day before it was mixed with fly ash. fly ash and alkaline solution were mixed and geopolymer fly ash (gf) cubes of 70.6mm×70.6mm×70.6mm were cast. the gf cubes were subjected to oven curing and were demolded. the compressive strength was tested after one day by keeping the cube specimens at room temperature. figure 1 shows the geopolymer fly ash cubes ready for testing. the five considered parameters and their values are: • curing temperature: 50°c, 75°c , 100°c, 125°c, 150°c • curing time: 1hr, 2hr, 3hr • fly ash/alkaline solution ratio (fa/as): 2.5, 3, 3.5, 4 • na2sio3 /naoh ratio: 1, 1.5, 2, 2.5 • molarity of naoh: 6m, 8m, 10m, 12m iii. modeling phase anns are used in this study to predict the compressive strength of gf. a. artificial neural networks anns are a widely employed method in different fields of artificial intelligence [24]. anns are powerful machine learning methods for predicting and solving different scientific computations [16]. anns are widely used in the area of civil engineering for predicting concrete's mechanical properties. ann modeling consists of two steps: 1) network training with the available training data set and 2) the trained network is tested to compute the prediction accuracy. b. neural network model a back propagation network (bpn) was used in this study to train the ann model. the bpn training set consists of two stages, the feed forward stage and the back propagation stage. in the feed forward stage, the input node is transferred by the input layer neurons to hidden layer neurons. each hidden layer neuron calculates the weighted sum of its input, and the sum is transferred through its activation function and the activation value is given to the output layer. the output layer neurons compute the weighted sum of each neuron and the sum is transferred through its activation function, forming the network output value. the sigmoidal function is generally used as activation function. the output is given by: ( )bow f iji j +−+ = exp1 1 (3) where: wji is the connection weight from the lower layer neuron i to the upper layer neuron j, oi is the output of the neuron i, and b is the bias value. in the second stage, the output layer transfers the network error to the input layer, and the network error is minimized to an acceptable level by adjusting the weights. the utilized network consists of 5 neurons in the input layer, 5 neurons in the hidden layer, and 1 neuron in the output layer. the hidden neurons are arranged in 2 hidden layers to reduce the error percentage. table i lists the ann model parameters. the input layer consists of curing temperature, curing time, fly ash to alkaline solution ratio, sodium silicate to sodium hydroxide ratio, and naoh molarity and the output layer represents the compressive strength (cs) of gf. the data set for preparing ann model includes 63 experimental results provided in table ii. the ann prediction accuracy is validated using 66% of the data for training and the remaining data for testing. table i. ann model parameters parameter value number of inputs 5 number of hidden layers 3 number of hidden layer units 8 number of outputs 1 network architecture bpn training function sigmoidal function number of training 62 number of testing 21 engineering, technology & applied science research vol. 12, no. 5, 2022, 9120-9125 9122 www.etasr.com rusna & kalpana: using artificial neural networks for the prediction of the compressive strength of … table ii. one day cs test results for gf cubes sample no curing temperature (°c) curing time (hr) fa/as na2sio3/naoh naoh molarity cs (n/mm 2 ) 1 50 1 3 2 10 0 2 50 2 3 2 10 0 3 50 3 3 2 10 0.71 4 100 1 3 2 10 4.50 5 100 2 3 2 10 25.08 6 100 3 3 2 10 24.28 7 150 1 3 2 10 7.50 8 150 2 3 2 10 21.16 9 150 3 3 2 10 0 10 100 2 2.5 2 10 6.76 11 100 2 3 2 10 25.08 12 100 2 3.5 2 10 22.28 13 100 2 4 2 10 11.33 14 100 2 3 1 10 28.25 15 100 2 3 1.5 10 31.47 16 100 2 3 2 10 25.08 17 100 2 3 2.5 10 17.48 18 100 2 3 1 8 14.64 19 100 2 3 1.5 8 23.43 20 100 2 3 2 8 17.19 21 100 2 3 2.5 8 14.10 22 100 2 3 1 12 22.07 23 100 2 3 1.5 12 28.44 24 100 2 3 2 12 25.46 25 100 2 3 2.5 12 22.21 26 50 1 3 1.5 10 0 27 50 2 3 1.5 10 0 28 50 3 3 1.5 10 2.95 29 100 1 3 1.5 10 2.90 30 100 2 3 1.5 10 31.47 31 100 3 3 1.5 10 30.27 32 150 1 3 1.5 10 9.71 33 150 2 3 1.5 10 26.22 34 150 3 3 1.5 10 0 35 100 2 2.5 1.5 10 13.09 36 100 2 3 1.5 10 31.47 37 100 2 3.5 1.5 10 30.29 38 100 2 4 1.5 10 20.02 39 75 2 3.5 1.5 12 5 40 100 2 3.5 1.5 12 26.4 41 125 2 3.5 1.5 12 32 42 150 2 3.5 1.5 12 30.5 43 125 1 3.5 1.5 12 16.7 44 125 2 3.5 1.5 12 27.1 45 125 3 3.5 1.5 12 26.2 46 125 2 3.5 1 12 17.5 47 125 2 3.5 1.5 12 21.5 48 125 2 3.5 2 12 20.2 49 125 2 3.5 2.5 12 16.8 50 100 2 1 3 6 25.9 51 100 2 1.5 3 6 23 52 100 2 2 3 6 18.33 53 100 2 2.5 3 6 11.59 54 100 1 1 3 8 2.2 55 100 1 1.5 3 8 9.1 56 100 1 2 3 8 4.2 57 100 1 2.5 3 8 3.8 58 100 1 1 3 10 11.5 59 100 1 2.5 3 10 4 60 100 1 1 3 12 11.8 61 100 1 1.5 3 12 9.5 62 100 1 2 3 12 3.8 63 100 1 2.5 3 12 3 engineering, technology & applied science research vol. 12, no. 5, 2022, 9120-9125 9123 www.etasr.com rusna & kalpana: using artificial neural networks for the prediction of the compressive strength of … iv. results and discussion a. test results 1) one day compressive strength the cs of the gf cubes was determined by following the astmc109 [25]. the one day compressive strength of 10m gf with different curing temperatures and curing times was obtained as shown in figure 2. the gf cubes after 1 and 2hr of curing time at 50°c curing temperature were observed in wet condition and no strength was obtained. the strength was increased with rise in temperature and the maximum compressive strength of gf was observed for 100°c curing temperature. similar results were reported in [26-28]. when the curing temperature became more than 100°c, a gradual decrease in strength was noticed. the curing time also showed influence on compressive strength and the maximum strength was observed for 2hrs curing time. hence, the maximum value of 31.47n/mm 2 of strength was obtained for 100°c and 2hr curing time. fig. 2. one day compressive strength of gf with curing temperature and curing time. fig. 3. one day compressive strength of gf with fa/sa ratio. the one day compressive strength of 10m gf with different fa/as ratios is shown in figure 3. the fa/as ratio was increased by 0.5 at 100°c curing temperature and 2hrs curing time. the maximum strength of gf was observed at the ratio of 3 as 31.47n/mm 2 . the strength decreases beyond fa/as ratio of 3. the one day cs of gf with different sodium silicate to sodium hydroxide ratios and naoh molarities is shown in figure 5. the maximum strength was observed for na2sio3/naoh ratio of 1 for every molarity. an increase in cs was observed with increase in molarity due to the increase of na + ions which enhance the geopolymer reaction [29, 31]. maximum strength was observed in 10m gf cubes. similar results were reported in [26-28]. when the molarity became more than 10m, a decrease in strength was observed due to the increase in the amount of oh ions which reduce the geopolymer reaction [26]. fig. 4. the one day compressive strength of gf with curing temperature and curing time. fig. 5. comparison between the ann model predicted data and the experimental data. b. modeling results the most important step in ann model development is the ann architecture determination which suits the real problem. the ann architecture l-5-4-3-1-1 was finalized after trial and error process. the performance of the ann model was checked with the performance measures root mean square error (rmse) and correction coefficient (r 2 ) between the experimental results and the predicted results. they were computed by (4) and (5): ( ) n yx rmse ii − = 2 (4) engineering, technology & applied science research vol. 12, no. 5, 2022, 9120-9125 9124 www.etasr.com rusna & kalpana: using artificial neural networks for the prediction of the compressive strength of … ( ) ( )         − −=   2 2 2 1 i ii y yx r (5) where xi is the target value, yi is the predicted value, and n is the number of test data. table iii. experimental and predicted balues experimental cs (n/mm 2 ) ann cs (n/mm 2 ) 0.71 1.14 7.5 18.7 23.43 18.54 28.25 25.17 17.48 24.15 22.07 26.014 22.21 25.98 2.9 5.06 25.66 26.08 22.32 25.03 26.4 26.08 16.7 24.01 16.8 24.01 3 3.98 1.9 0.234 4.1 4.06 5.9 7.74 13.8 5.3 11.5 6.82 5.2 9.87 1 0 14.1 14.5 figure 5 represents the ann model predicted data and the experimental data for the one day compressive strength test. the experimental compressive strength values and the corresponding ann model predicted compressive strength values are given in table iii. the accuracy of the prediction is indicated by rmse and r 2 . the rmse and r 2 obtained values were 4.47 and 0.972 respectively, which show that the ann is effective in the prediction of the cs of gf. v. conclusions this study studies various factors affecting the compressive strength of geopolymer fly ash. the geopolymer fly ash was produced by mixing alkaline solution and fly ash. the factors considered in this study were curing temperature, curing time, fly ash to alkaline solution ratio, sodium silicate to sodium hydroxide ratio, and the molarity of sodium hydroxide. anns were employed in this study to predict the compressive strength of gf and the prediction accuracy was validated. • the selected values of curing temperature were: 50, 75, 100, 125, and 150°c. the maximum compressive strength was observed at 100°c curing temperature. • the values of curing time were as 1, 2, and 3hr. the maximum compressive strength was observed for 2hr curing time. • the fly ash to alkaline solution ratio was 2.5, 3, 3.5, and 4. the maximum compressive strength was obtained for ratio equal to 3. • the na2sio3/naoh ratio was selected as 1, 1.5, 2, and 2.5. the maximum compressive strength was obtained for the ratio of 1. • the molarity of naoh varied as 6, 8, 10, and 12. the maximum compressive strength was obtained for 10m geopolymer fly ash. • an ann was developed to predict the compressive strength of gf. the accuracy of the model was evaluated with rmse and r 2 . the obtained values were 4.47 and 0.972 respectively. these values of rmse and r 2 confirm that the utilization of ann for the prediction of the compressive strength of gf is a good choice due to its excellent correlation with the experimental results. this study suggests that anns are an effective tool in strength prediction of gf, reducing further the experimental cost and time. • the geopolymer fly ash with its optimized parameters provides sufficient strength. hence, it is applicable as a cement replacing material in concrete. references [1] a. m. fathollahi-fard, m. 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complex to be analytically calculated. in this paper, a neural network model is used to predict the correlations between the hardness of aluminum alloys in relation to certain alloying elements. a backpropagation neural network is trained using a thorough dataset. the impact of certain elements is documented and an optimum structure is proposed. keywordsaluminum alloys; hardness; neural networks i. introduction aluminum is a light metal exhibiting a high degree of corrosion resistance in normal corrosive environments [1]. aluminum is almost always alloyed, which significantly improves its mechanical properties [1, 2]. the main alloying elements are copper (cu), zinc (zn), magnesium (mg), manganese (mn), iron (fe) and silicon (si) [3]. a properly treated aluminum alloy may possess a strength level about thirty times that of pure aluminum [1, 3]. the properties of a particular aluminum product depend on the alloy chosen. the mechanical properties of aluminum alloys are defined by a number of principal microstructural features [2]. hardness is a mechanical property that measures the ability of a material to resist indentation and it is closely related to the material's strength [1]. neural networks (nns) are non-linear mapping structures inspired by the function of the human brain. they are considered powerful modeling tools especially for data with unknown underlying relationships. neural networks have been widely used in prediction problems of mechanical properties of materials [6-8]. nns consist of computational elements called neurons, operating in parallel, connected by links with variable weights which are typically adapted during the learning process [4, 5]. feed forward multilayer networks trained with the backpropagation algorithm are probably the most common kind. in this paper the relation between the hardness of aluminum alloys and the percentage of alloying elements was predicted using such nns, through several scenarios. ii. aluminum and its alloys aluminum and its alloys are rather popular in the construction, marine and aircraft industries because of its ease of fabrication, non-toxicity, strength (pound-for pound), and resistance to the corrosive atmospheres of industry and marine environments [1, 3]. aluminum and its alloys are divided in two categories, cast and wrought, and each group is further subdivided into classes according to the composition. every aluminum alloy has its own properties and characteristics which distinct it from the other aluminum alloys, and every aluminum alloy is consisted of a number of alloying elements in different percentages. each alloying element has its particular effect to the alloy’s properties such are electrical conductivity, thermal conductivity, corrosion resistance, thermal expansion, melting temperature, strength yield and hardness. a thorough dataset was employed for this research and table i shows a sample of the dataset used. table i. sample of the dataset for the aluminum alloys elements percentages (wt %) hardness cu mg mn fe si alloy number 70 4.6 0.29 0.3 0.04 0.04 1 76 4.6 0.28 0.3 0.04 0.03 2 77 4.6 0.28 0.3 0.04 0.03 3 67 4.7 0.29 0.3 0.04 0.04 4 59 0.1 0.35 0.0026 0.125 7.2 5 79 0 0.3 0 0 7 6 80.2 0.122 1.12 0.588 0.418 0.195 7 88 0.007 0.461 0 0 5.902 8 90 4.75 2 0.4 0.28 0.24 9 69.5 0 0 0 0 0 10 hardness tests are a useful tool for the evaluation of materials and the quality control of manufacturing processes in research and development work. it gives an indication of a material’s properties, such as strength, ductility and wears resistance. there is a wide range of different hardness tests. each test gives a different value for hardness. therefore, hardness is not a universal well-defined materials property, but engineering, technology & applied science research vol. 5, no. 1, 2015, 757-759 758 www.etasr.com zahran: using neural networks to predict the hardness of aluminum alloys depends on the method used for measurement. one of the most popular methods was used in this research (brinell hardness). the method relies on measuring the size of an impression left by an indenter under a known load [1, 3]. iii. neural networks and the proposed method a typical neuron has three basic parts: input weights, a soma, and an activation function [4, 5]. the input weights scale the values used as inputs to the neuron, the soma adds all the scaled values together, and the activation function produces the final output of the neuron. the backpropagation (bp) algorithm is one of the most famous training algorithms for multilayer neural networks. bp is a gradient descent technique to minimize the error e for a particular training pattern [4, 5]. several researches have been conducted on predicting some properties of materials, machining and other fields through the use of neural networks [6-12]. the initial steps followed in developing the nn used in this paper was the choice of architecture (3-layer nn), the random initialization of weighs and the definition of defining the number of neurons for the hidden layer. the alloying elements percentage in the aluminum alloys were used as input data for the nns and the hardness value was selected as the target output. before training, the dataset was randomly divided into two groups. 75% of the data were used for training and 25% for testing. at the start of the training phase, the nn was activated with several input vectors, and the output was calculated. the calculated outputs were compared to the target values to produce the error values. according to the magnitude of the error, each weight was adjusted so as to reduce the total error. then the calculation was performed once again using the adjusted weights in order to get a new set of outputs. these in turn were compared with the targets, and the weights were adjusted again. this process was repeated until an acceptable criterion was reached. for the experiments in this paper, the total error (i.e. error based on the mean squared error (mse) between the network output and target), was used as a criterion for terminating the training session. the model reached at the end of the training phase was used in the testing phase. during the testing phase, the trained neural network was tested with the data specified for this purpose, and the output was calculated. its performance was evaluated using three performance measures: the mean square error (mse), prediction error (pe) and mean absolute error (mae). iv. results and discussion the nn model is used to predict correlations between a mechanical property (hardness) of the aluminum alloys with the alloying elements. more than 72 experiments on the dataset were conducted. during the development process, three parameters were tested for suitability: the number of neurons in the hidden layer, the learning rate and the activation function. every time one parameter was kept constant and the others were changed in order to reach the best value for the parameters. the error was calculated and the weights were updated after each input/output pair was presented. in order to investigate the effect of the number of neurons on the prediction results, a trial-and-error procedure with a variable number of neurons in the hidden layer was applied. the bpnn structure of one hidden layer with a learning rate of 0.4 and a momentum rate of 0.6 was trained using various numbers of hidden neurons which varied from 3 to 15. it was seen that a network with 6 neurons in the hidden layer provided the best mapping and, therefore, an architecture of 6 hidden neurons along with one hidden layer (variable-6-1) was chosen. after that, different activation functions for hidden and output layers were tested. the activation functions tested were log-sogmoid, linear and hyperbolic tangent sigmoid. table ii shows the results when changing the activation functions and while fixing other parameters. table ii. the performance for different activation functions input parameter: activation function log sigmoid linear hyperbolic tangent sigmoid mse 0.033 0.076 0.080 mae 0.8 3 1.6 pe 2.2 3.2 2.5 the best activation function was found to be the log sigmoid for both input and output layers. the learning and regression curves of the best model are plotted in figure 1 and figure 2 respectively. furthermore, table iii shows a sample of the output of the nn model compared with the target outputs. this is achieved when the number of inputs equals 5, the number of neurons in the hidden layer equals 6, the learning rate equals 0.4 and the activation function was the “log sigmoid” for both input and output layers. table iii. sample of the target and predicted values of hardness target values of hardness predicted values of hardness 90.000 93.984 88.000 91.592 80.200 87.712 79.000 82.206 77.000 81.984 76.000 79.984 70.000 83.984 69.500 79.635 67.000 73.984 59.000 66.578 fig. 1. learning curve for the neural network best model. engineering, technology & applied science research vol. 5, no. 1, 2015, 757-759 759 www.etasr.com zahran: using neural networks to predict the hardness of aluminum alloys fig. 2. the regression curve of the nn best model. after testing several different combinations of the alloying elements in the experiments, the following were documented: • the elements that individually increase the hardness of the alloy the most are fe and cu. • the elements that individually have no significant effect on the hardness of the alloy are mg, mn and si. • the structure [cu, fe, mn and si] in alloys gave the best result regarding hardness. v. conclusions the main purpose of this paper is to investigate the relationship between hardness and the alloying elements percentages using neural networks. an optimum architecture was achieved through various tests. the nn model predicted the hardness of aluminum alloys efficiently. the impact of different individual elements on the hardness was calculated and a specific structure was found to provide the best results regarding hardness. vi. references [1] d. g. altenpohl, aluminum: technology, applications and environment: a profile of a modern metal aluminum from within, 6th edition, wiley, 2010 [2] r. s. rana, r. purohit, s. das, “reviews on the influences of alloying elements on the microstructure and mechanical properties of aluminum alloys and aluminum alloy composites”, international journal of scientific and research publications, vol. 2, no. 6, pp. 1-7, 2012 [3] l. mondolfo, aluminum alloys: structure and properties, butterworths, 1976 [4] t. m. mitchell, machine learning, mcgraw-hill, 1997 [5] d. w. patterson, artificial neural networks: theory and application, prentice hall, 1996 [6] e.alibeiki, j. rajabi, j. rajabi, “prediction of mechanical properties of to heat treatment by artificial neural networks”, journal of asian scientific research, vol. 2, no. 11, pp. 742-746, 2012 [7] s. k. das, s. kumari, “a multi-input multi-output neural network model to characterize mechanical properties of strip rolled high strength low alloy (hsla) steel”, ms’10 prague proceedings of the international conference on modelling and simulation, prague, czech republic, june 22–25, 2010 [8] x. liujie, x. jiandong , w. shizhong, z. songmin, z. yongzhen, l. rui, “use of artificial neural network in predicting mechanical properties of high-speed steel (hss)”, proceedings of the 2006 ieee international conference on mechatronics and automation, pp. 1872–1877, luoyang, henan, china, 2006 [9] f. musharavati, a. s. m. hamouda, “application of artificial neural networks for modelling correlations in age hardenable aluminum alloys”, journal of achievements in materials and manufacturing engineering, vol. 41, no. 1-2, pp. 140-146, 2010 [10] j. h. su, q. m. dong, p. liu, h. j. li, b. x. kang, “simulation of aging process of lead frame copper alloy by an artificial neural network”, transactions of nonferrous metals society of china, vol.13, no. 6, pp. 1419-1423, 2003 [11] a. kermanpur, a. ebnonnasir, a. r. k. yeganeh, j. izadi, “artificial neural network modeling of high pressure descaling operation in hot strip rolling of steels”, isij international, vol. 48, no. 7, pp. 963-970, 2008 [12] m. b. esfahani, m. r. toroghinejad, s. abbasi, “artificial neural network modeling the tensile strength of hot strip mill products”, isij international, vol. 49, no. 10, pp. 1583-1587, 2009 author profile bilal zahran received the b.sc degree in electrical & electronic eng. from the middle east technical university, turkey, in 1996, the m.sc degree in communications eng. from the university of jordan, jordan, in 1999, and the phd degree in computer information system (cis) from the arab academy for banking and financial sciences, jordan, in 2009. he is currently working as an assistant professor at the department of computer engineering, faculty of engineering technology, al-balqa applied university, jordan. his research interests include machine learning, data mining and optimization fields. microsoft word etasr_v13_n1_pp10014-10020 engineering, technology & applied science research vol. 13, no. 1, 2023, 10014-10020 10014 www.etasr.com kayahan et al.: investigation of the penetration force of disposable sterile needles through biomedical … investigation of the penetration force of disposable sterile needles through biomedical textile surfaces ersin kayahan laser technologies research and application center (latarum) and electro-optics and systems engineering, kocaeli university, turkey kayahan@kocaeli.edu.tr sayit ozbey laser technologies research and application center (latarum) and maritime faculty, marine engineering, kocaeli university, turkey sayit.ozbey@kocaeli.edu.tr ugur kosa biomedical engineering, technology faculty, kocaeli university, turkey ugrkosa@gmail.com mehmet alp ilgaz faculty of electrical engineering, university of ljubljana, slovenia mehmetalp.ilgaz@gmail.com (corresponding author) selma corovic faculty of electrical engineering, university of ljubljana, slovenia selma.corovic@fe.uni-lj.si received: 5 november 2022 | revised: 3 december 2022 | accepted: 4 december 2022 abstract disposable sterile needles are essential highly consumed medical tools. medical needles are usually manufactured according to standardized protocols, which currently do not provide the specified minimum tolerance value of the penetration force which strongly depends on needle dimensions, needle cutting edge angle, and the type of the tissue surface to be penetrated. in the present study, experimental measurements were performed according to the iso 7864 standard to investigate the needle-surface penetration effect via the experimental assessment of the influence of the needle dimensions, cutting edge angle, and three different types of biomedical textiles/artificial tissues (i.e. polyurethane (pu), polypropylene (pp), and artificial leather (al)) on the penetration force. the results indicate that the smaller the needle's cuttingedge angle, the smaller the penetration force across the target tissue surface. an exponential decaying relationship has been found between the penetration force and the needle diameter/gauge. the results also show that pp provides similar results to other materials that are already included in iso 7864, and it has a good potential to be accepted as a standardized biomedical textile. keywords-penetration force; sterile needle; biomedical textile; medical device; needle penetration i. introduction medical needle-based interventions via the insertion of disposable sterile needles into the target tissue are among the most prevalent clinical procedures [1-6]. disposable sterile needles are a prerequisite medical tool and an important component of medical devices daily used in medical settings and are produced in different diameters/gauges and lengths. medical needles are used for various purposes such as spinal applications, dental treatments, veterinary services, etc. [2-7]. engineering, technology & applied science research vol. 13, no. 1, 2023, 10014-10020 10015 www.etasr.com kayahan et al.: investigation of the penetration force of disposable sterile needles through biomedical … since a medical procedure or therapy may strongly depend on the needle-tissue interaction and the needle tissue procedure they must be manufactured according to strict requirements defined by standards (e.g. iso 7864, iso 9626). the iso 7864 standard specifies the testing procedures for stainless-steel medical needles and the necessary physical and chemical parameters related to the design and production of the needles including the procedures for injecting or withdrawing fluids from the human body via disposable sterile hypodermic needles [8]. this standard also determines the requirements for the diameter of the needles, which ranges from 0.18mm to 1.2mm. the testing procedure of sterile needles to determine the penetration force is also specified in the standard for different model materials/tissues used for testing. specifically, the following four testing materials/tissues (used as human or animal tissue models) are included in the standard describing their surface properties and thickness through which the needle penetrates: latex rubber, polyurethane (pu), silicone rubber, and polyethylene with respective thickness and their tolerance of 1±0.1mm, 0.40±0.05mm, 0.50±0.05mm and 50μm. the iso 9626 standard classifies the needle types according to the diameter values along with the diameter tolerance values for each needle. for the classification of the needle diameter the gauge (g) expression is used (i.e. the larger the gauge the thinner the needle) [9, 10]. it should be noted that despite the rigorous protocol defined in the standards, several aspects regarding the optimum needle design, needle-tissue interaction, and the adequate penetration force profile remain to be investigated. it is well known that the biggest risk factor of disposable sterile needles is the penetration procedure itself which can lead to injury when not applied optimally. although the iso 7864 standard defines protocols for the penetration testing for disposable sterile needles, there is no specified minimum limit or tolerance value for the penetration. namely, numerous scientific and clinical studies are dealing with the improvement of the medical needle designs which would penetrate the skin or other tissue surfaces easily and safely with minimum influence caused to the tissue (i.e. minimum or no pain and/or other tissue trauma) and to assure an efficient and safe medical treatment or therapy. the critical factors that influence the needle-skin/tissue interaction procedure are the needle geometrical and material properties and the insertion method by carefully taking into account the target tissue properties [11]. namely, the mechanical properties of the biological tissues vary due to their specific microstructures (i.e. homogeneity, heterogeneity, anisotropy, isotropy, etc.) and the human body itself (i.e. age, gender, bmi, stage of the disease, etc.) and thus may affect the efficacy of the needle’s penetration. for example, during the needle insertion through the skin layer, in addition to the type of the needle, deformation of the skin surface may occur due to the skin elasticity, which is an important mechanical property, affecting the efficacy of the needle penetration. authors in [12] investigated the skin penetration resistance variables such as the needle gauge, the needle insertion velocity, the preapplication pressure, and the penetration depth. their study demonstrates that adequate pre-application pressure increases the effect of the needle penetration and makes it easier to reach the desired depth. they also demonstrated that even if the diameter does not show too much effect on skin deterioration, it is directly proportional to the applied strength. moreover, the penetration depth was confirmed as an essential factor that affects skin deformation during the process of penetration [12]. authors in [13] determined the penetration force and friction force of hypodermic needles by using pu film and pigskin as models of human skin. in their experiment, 25–75% penetration was achieved successfully by a penetration force ranging from 7n to 10n. previous studies which experimentally investigated the effect of needle diameter and cutting edge angle on needle insertion showed that beveled needles are more likely to bend, while needles with larger diameter increase friction, requiring more force to be applied to the needle [14, 15]. furthermore, many recent analytical and numerical studies focused on the modeling and optimization of the needle characteristics (such as needle tip, needle diameter, and cutting edge angle) which became an important prerequisite in adequate needle design [14–16]. prior to the application of newly designed needles to human or animal tissues/body, they always must be adequately tested. in vivo experimental investigation of the needle penetration through skin is complex and often difficult to be performed. therefore, different artificial tissues/materials are often used in experimental studies and new materials are being investigated to propose reliable, useful, and cost-effective alternatives [11]. as an alternative to biological tissue, the pu substrate has been successfully used due to advantages such as being homogenous, chemically stable, and easily accessible [17]. namely, pu and polypropylene (pp) have been efficiently used for various purposes in different applications [18]. pp can also be used as a sustainable material for the production of light weight foam [19]. in addition, pp fibers can be used instead of cotton, due to their admirable chemical stability and hydrophobic nature [20]. thus, materials such as pu and pp can be used as important alternative biomaterials to efficiently simulate the tissue surface of human/animal skin in medical needle penetration studies. it should be noted that in addition to the geometrical and material properties of the needles, the needle insertion procedure and the mechanical and geometrical properties of the tissue to be penetrated must be carefully examined. therefore, the main objective of the present study is to experimentally investigate the key variables that may influence the penetration force profile of the disposable sterile needles such as needle dimensions (i.e. gauges), needle cutting edge angle, and the type of biomedical textile (i.e. human or animal tissue models) to be penetrated. first, our goal was to experimentally identify the relationship between the needle size versus penetration force value. second, we investigated different needle cuttingedge angles aiming to minimize the penetration force. finally, three different biomedical textile surfaces were examined, namely pu, pp, and artificial leather (al), to study the needle-surface penetration effect. pp and al were examined/tested for the first time in this study. they were compared to the reference material pu which has already been standardized by the iso 7864 standard. we demonstrated that the pp provides similar results to other materials that are already included in iso 7864 and therefore it has a good engineering, technology & applied science research vol. 13, no. 1, 2023, 10014-10020 10016 www.etasr.com kayahan et al.: investigation of the penetration force of disposable sterile needles through biomedical … potential to be accepted as a new standardized material for the testing procedure of sterile medical needles. ii. materials and methods experimental investigations have been conducted to examine the influence of the needle dimensions, needle cutting edge angle, and penetration surface type on the disposable needle penetration force value. all the experimental tests and measurements have been performed according to the iso 7864 standard. the experiments have been conducted using needles with 6 different diameters (i.e. 18g, 20g, 21g, 25g, 27g, and 31g). these types are among the most frequently used types of needles in medical applications. the results obtained from the experimental measurements were statistically analyzed using the commercial software package minitab. the influence of the penetration force using different needles (with different diameters) has been examined for 3 different biomedical textile surface types (i.e. pu, pp, and al). instron 5943l2393 measuring device was used to determine the force values by applying 100n load cells as depicted in figure 1. fig. 1. the experimental measurement setup: the tension testing machine to determine the needle penetration force and the geometry of typical disposable sterile needles. all analyzed parameters were tested 10 times while keeping the other variables constant. within the first part of this study, the effect of the needle diameter on the penetration force was investigated using the 6 needles with the above specified diameters on pu, pp, and al surfaces with a thickness of 0.4mm ±0.05 and cutting-edge angle of 11°±2°. to observe the needle cutting edge angle effect on the penetration force, 2 needles, 18g spinal and 18g veterinary steel were used. the cutting-edge angles were measured with the olympus 3k46661 microscope. 18g veterinary steel needles have a cutting-edge angle of 11°±2°, while 18g spinal needles have a cutting-edge angle of 17°±2°. the physical and mechanical properties of pu and pp are given in table i. the physical and mechanical properties of al, which are similar to natural leather's, are given in table ii. the needles entered into giving surfaces with a constant velocity of 100mm/min. these input values are recorded as a function of the penetration force. a force meter, such as a load cell, was used to measure the force at different stages of the process. a needle was placed in a way that allowed the friction force to be calculated at the first moment of penetration and the moment of progress. after the forward movement, the needle was removed and the overall force profile was recorded according to the protocol specified in [8]. table i. physical and mechanical properties of pu and pp [21-23] material density (g/cm 3 ) hardness tensile strength (mpa) elongation (%) pu 1.18 80 (shore a) 20 700 pp 0.95 60 (shore d) 28.18 45.13 table ii. physical and mechanical properties of al [24, 25] density (g/cm 3 ) tensile energy (gf· cm/cm 2 ) extension at max. load bending (%) shear stiffness (gf/cm· deg) geometrical roughness (μm) 0.9 1.6 25.91 13.36 8 3.12 needles are classified by gauges while they are manufactured according to iso 9626 standard [9]. the requirements of the standard are given in table iii for needles manufactured between 14g and 32g. small diameter needles (20-25 gauge) provide sufficient cytological material and often sufficient histological material. they can be used safely when multiple samples are needed and they minimize complications that can occur when reaching the target lesion. however, they are not practical, especially when reaching deep-seated lesions because they tend to deviate from the target. with larger diameter needles (14-19 gauge), it is easier to reach the lesion directly and usually a better sample with fewer entries is provided for cytology and histology, but the risk of bleeding increases with increasing needle diameter [26-29]. table iii. outer diameter requirements of needles according to the iso 9626 [9] gauge (g) minimum outer diameter (mm) maximum outer diameter (mm) 18 1.200 1.300 20 0.560 0.920 21 0.800 0.830 25 0.500 0.530 27 0.400 0.420 31 0.254 0.267 iii. results and discussion the obtained experimental results indicating the penetration force dependency on the needle diameter (the needle gauge) are shown in figure 2. the obtained results indicate that the penetration force decreases when the gauge size increases, which is in agreement with the results reported in [30]. in our study, the highest penetration force was observed when using the 18g needles with average values of 3.37n, 3.46n, and 3.14n for pu, pp, and al surfaces, respectively. the results shown in figure 2 indicate that even though the 20g needles are 28% thinner than 18g needles, the decrease in penetration force was 71% on average for the pu surface. engineering, technology & applied science research vol. 13, no. 1, 2023, 10014-10020 10017 www.etasr.com kayahan et al.: investigation of the penetration force of disposable sterile needles through biomedical … (a) (b) (c) fig. 2. the changes of the needle penetration force with the needle diameter size (gauge) for the (a) pu, (b) pp, and (c) al surfaces. the solid line shows the second order exponential decay fit function and the circles represent the experimentally measured data. by using the same comparison method, the results demonstrate that the 21g needles are 9% thinner than 20g and 25g needles are 12% thinner than 21g needles, and the decrease in penetration force was 8% and 12%, respectively for the pu surface. the diameter of 31g needles which is the smallest needle diameter in the sample group is 37% smaller than that of the 27g needles and the penetration force was decreased by 34% for the pu surface. it can be concluded that a decrease in penetration force occurs with a decrease in the needle diameter values. based on the curve fitting performed in origin lab software we demonstrated that the penetration force vs. needle diameter relationship can be described with a second-order exponential decay function for all material (i.e. pu, pp, and al) surfaces, as shown in figure 2. to determine the penetration force changes at different surfaces (i.e. different materials) which should be used for the standard material surface, al and pp were used and compared with the pu surface which is used as a reference. the obtained results are given in figure 3 and table iv. it can be seen that the al surface exhibits the best performance with the minimum penetration force in comparison with the pp and pu surfaces. the results indicate that the pp surface exhibits a significant similarity with the pu surface for the needle types of 18g, 20g, 21g, 25g, 27g, and 31g. thus, the pp surface could be a good candidate as a new standardized material surface. it should be also emphasized that pp is cheaper than pu. therefore, the pp surface could be also used as a reference surface according to the iso 7864 standard in addition to the pu surface, since it is cost-effective and more accessible. however, the pp must also satisfy other requirements to be fully accepted by iso 7864 standard. fig. 3. the variation of penetration force with al, pp, and pu surfaces. data distribution of the samples is found to be statistically significant since it passed the normality test (p-value ≤ 0.05), as shown in table v. therefore, by using an average penetration force, a significant inference can be obtained. the largest difference in penetration force between pu and pp is only 2% (0.02n) for 18g, 25g, and 31g needles. the pu and pp surfaces have almost the same results in terms of calculated penetration forces. the variation of needle cutting edge angle with the penetration force is given in figure 4. the average penetration force value was 2.15n for a cutting edge angle of 11°±2° and 3.3 n for 17°±2° for pu. the results in figure 4 demonstrate that when the needle cutting-edge angles increase, the penetration force also increases for all the examined surfaces, which is also in agreement with the results of [31]. the standard deviation (stdev) of cutting-edge angles of 11°±2° and 17°±2° is 0.1814 and 0.2387, respectively, as shown in table vi for the pu material. the results were obtained from penetration force measurements performed 10 times. the increase in the penetration force with the cuttingedge angle of 17°±2° was found to be 56%, 16%, and 12% than with 11°±2° for pu, pp, and al surfaces, respectively. this can be explained by the fact that the increase of the cuttingedge angle increases the contact area between the needle and the surface of the material, which causes a higher penetration force. engineering, technology & applied science research vol. 13, no. 1, 2023, 10014-10020 10018 www.etasr.com kayahan et al.: investigation of the penetration force of disposable sterile needles through biomedical … table iv. variation of the penetration force values with different needle gauges and surface materials gauge 18g 20g 21g 25g 27g 31g sample pu pp al pu pp al pu pp al pu pp al pu pp al pu pp al 1 3.08 3.17 2.92 0.89 1.13 0.77 0.89 1.04 0.81 0.82 0.81 0.67 0.82 0.83 0.43 0.49 0.49 0.32 2 3.51 3.83 3.99 0.93 0.94 0.88 0.99 0.92 0.78 0.75 0.77 0.56 0.84 0.92 0.49 0.48 0.51 0.46 3 2.86 3.81 2.71 0.91 1.06 0.81 0.80 0.98 0.56 0.81 0.82 0.58 0.82 0.98 0.52 0.49 0.50 0.28 4 2.89 3.31 3.93 1.18 0.91 0.72 0.78 1.03 0.61 0.76 0.77 0.87 0.70 0.76 0.56 0.48 0.51 0.30 5 4.30 3.85 3.12 0.89 1.34 0.76 1.09 1.07 0.58 0.85 0.84 0.58 0.80 0.93 0.41 0.55 0.55 0.29 6 3.71 2.96 2.27 0.93 1.12 0.91 0.99 0.91 0.65 0.76 0.85 0.64 0.83 1.02 0.47 0.45 0.56 0.37 7 3.11 3.06 3.17 1.20 1.04 0.68 1.15 1.23 0.83 0.84 0.88 0.73 0.73 0.84 0.46 0.55 0.49 0.34 8 4.28 4.13 2.88 0.80 0.98 0.79 0.80 1.02 0.71 0.80 0.85 0.61 0.63 0.93 0.51 0.48 0.52 0.29 9 3.19 3.09 3.55 0.98 1.02 0.82 0.79 0.99 0.74 0.84 0.84 0.84 0.71 0.98 0.57 0.53 0.50 0.33 10 2.79 3.38 2.82 0.93 1.14 0.74 0.81 1.05 0.59 0.75 0.81 0.83 0.79 0.89 0.48 0.59 0.52 0.40 table v. data analysis of needle penetration force values with different needle gauges and surface materials with normality test gauge (g) surface material number of tests mean 95% ci of mean stdev 95% ci of stdev min median max normality test p decision 18 pu 10 3.37 (2.97,3.77) 0.56 (0.39, 1.03) 2.79 3.15 4.30 0.111 pass 18 pp 10 3.46 (3.16, 3.75) 0.41 (0.28, 0.75) 2.96 3.35 4.13 0.190 pass 18 al 10 3.14 (2.75, 3.53) 0.55 (0.38, 0.99) 2.27 3.02 3.99 0.482 pass 20 pu 10 0.95 (0.88, 1.03) 0.11 (0.07, 0.20) 0.80 0.93 1.18 0.054 pass 20 pp 10 1.07 (0.98, 1.16) 0.12 (0.08, 0.23) 0.91 1.05 1.34 0.496 pass 20 al 10 0.79 (0.74, 0.84) 0.07 (0.05, 0.13) 0.68 0.78 0.91 0.925 pass 21 pu 10 0.91 (0.81, 1.01) 0.14 (0.09, 0.25) 0.78 0.85 1.15 0.056 pass 21 pp 10 1.02 (0.96, 1.09) 0.09 (0.06, 0.16) 0.91 1.03 1.23 0.207 pass 21 al 10 0.69 (0.61, 0.76) 0.10 (0.07, 0.18) 0.56 0.68 0.83 0.391 pass 25 pu 10 0.80 (0.77, 0.83) 0.04 (0.03, 0.07) 0.75 0.81 0.85 0.136 pass 25 pp 10 0.82 (0.80, 0.85) 0.04 (0.02, 0.06) 0.77 0.83 0.88 0.443 pass 25 al 10 0.69 (0.61, 0.78) 0.12 (0.08, 0.22) 0.56 0.66 0.87 0.142 pass 27 pu 10 0.77 (0.72, 0.82) 0.07 (0.05, 0.13) 0.63 0.80 0.84 0.141 pass 27 pp 10 0.91 (0.85, 0.96) 0.08 (0.05, 0.14) 0.76 0.93 1.02 0.702 pass 27 al 10 0.49 (0.45, 0.53) 0.05 (0.03, 0.09) 0.41 0.49 0.57 0.941 pass 31 pu 10 0.51 (0.48, 0.54) 0.04 (0.03, 0.08) 0.45 0.49 0.59 0.135 pass 31 pp 10 0.52 (0.50, 0.53) 0.03 (0.02, 0.05) 0.49 0.51 0.56 0.054 pass 31 al 10 0.34 (0.30, 0.38) 0.06 (0.04, 0.10) 0.28 0.33 0.46 0.203 pass table vi. statistical data analysis of the needle cutting-edge angle effect on the penetration force gauge (g) surface material cutting-edge angle test number mean stdev 95%ci 18 pu 11° ± 2° 10 2.15 0.181 (2.01, 2.29) 18 pu 17° ± 2° 10 3.36 0.239 (3.22, 3.50) 18 pp 11° ± 2° 10 2.48 0.091 (2.42, 2.54) 18 pp 17° ± 2° 10 2.89 0.093 (2.83, 2.95) 18 al 11° ± 2° 10 1.99 0.073 (1.93, 2.04) 18 al 17° ± 2° 10 1.23 0.086 (2.17, 2.28) iv. conclusions in this study, the effects of needle diameter, cutting edge angle, and material surface type on the penetration force were studied. based on the experimental investigation the following conclusions were derived:  the penetration force reduces with needle diameter. the penetration force versus needle diameter relationship can be described with an exponentially decreasing function (a second-order exponential decay function).  the penetration force increased when the cutting edge angle of the needle increased from 11°±2° to 17°±2° for the 18g needle type. consequently, the minimum cutting-edge angle reduces the damage to the penetrated skin.  pp surfaces exhibit similar penetration properties to the standardized pu material surfaces for the 18g-31g medical needles. therefore, the pp surfaces can be used in experiments to determine the penetration force. other advantages of the pp are its cost-effectiveness and accessibility. pp has a good potential to be accepted as a new standardized model material for the testing procedures of sterile needles. further experimental investigations should be conducted in order to characterize pu for other types of needles.  al surfaces have less penetration force than the pp and pu surfaces. however, the penetration force of al does not match the penetration values of the reference surface (pu). engineering, technology & applied science research vol. 13, no. 1, 2023, 10014-10020 10019 www.etasr.com kayahan et al.: investigation of the penetration force of disposable sterile needles through biomedical … (a) (b) (c) fig. 4. the variation of penetration force with needle cutting edge angle for (a) pu, (b) pp, and (c) al surfaces. in conclusion, the results of our study provide a promising start to specify the limit values for the penetration force which should be considered in when producing standardized needles. moreover, the limit penetration force value to be determined within the manufacturing standard should be independently calculated for each product, by considering the needle gauge size. it is also recommended to determine the limit value by taking into consideration the cutting-edge angles for needles which are manufactured at different cutting-edge angles with the same gauge size. this study provides a supplementary resource to the manufacturers' tests to evaluate the penetration force during the production stage of the needles. it should be also noted that for the first time alternative materials such as polypropylene and artificial leather were examined in this study to assess the penetration force of disposable sterile needles, and the results are reported with the standardized reference material (polyurethane) used as a reference. the obtained results indicate that polypropylene has a strong potential to be accepted as a new material for the efficient evaluation of the penetration force of sterile medical needles. acknowledgment this research was partly supported by kocaeli university laser technologies research and application center (latarum). references [1] v. d. sree, a. ardekani, p. vlachos, and a. b. tepole, "the biomechanics of autoinjector-skin interactions during dynamic needle insertion," journal of biomechanics, vol. 134, mar. 2022, art. no. 110995, https://doi.org/10.1016/j.jbiomech.2022.110995. 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[31] s. aoyagi, h. izumi, and m. fukuda, "biodegradable polymer needle with various tip angles and consideration on insertion mechanism of mosquito’s proboscis," sensors and actuators a: physical, vol. 143, no. 1, pp. 20–28, may 2008, https://doi.org/10.1016/j.sna.2007.06.007. microsoft word 3-629-ed.doc engineering, technology & applied science research vol. 6, no. 2, 2016, 931-936 931 www.etasr.com emami and javidan: an energy-efficient data transmission scheme in underwater wireless … an energy-efficient data transmission scheme in underwater wireless sensor networks yousef emami computer engineering and it department shiraz university of technology shiraz, iran yousef.emami@ieee.org reza javidan computer engineering and it department shiraz university technology shiraz, iran javidan@sutech.ac.ir abstract—energy is a precious resource in underwater wireless sensor networks (uwsns). in these networks, the number of data transmissions between sensor nodes dominates energy consumption. complex signal processing techniques also increase energy consumption. in this paper an energy-efficient data transmission scheme based on bloom filters is proposed. extensive simulation is carried out to demonstrate the effectiveness of the proposed method. simulation results indicate that the proposed scheme outperforms the primary technique in terms of energy efficiency, lifetime, load and loss rate. the results of this research suggest that exploiting bloom filters is a viable solution for reducing the number of transmissions in uwsns. keywords-energy efficiency; data transmission; bloom filter; underwater wireless sensor networks i. introduction today, underwater remote sensing systems such as sonars are used extensively for detecting and tracking of different targets using sound signals. high-resolution acoustic images obtained from these systems play an important role in underwater exploration [1]. however, these systems are costly and applying them calls for several considerations. even though other methods, such as satellite marine observation for change detection, are also applicable [2], their applications are limited. underwater wireless sensor networks (uwsns) have recently attracted significant attention due to the potential benefits for marine monitoring. they are cost effective and easy to use. it should be noted that there is a huge difference between uwsns and terrestrial wireless sensor network (twsns). from the communication point of view, twsns utilize radio signal while uwsns utilize underwater acoustic channels to transmit data usually the network model of twsns is two-dimensional while that of uwsns is threedimensional. the nodes in twsns can be replaced at any time but in uwsns this process is cumbersome due to the type of environment and costs [3]. hence, energy efficiency in uwsns is of vital importance. uwsns exploit complex signal processing techniques and support sparse deployment. hence, energy consumption is higher than terrestrial sensors. the unique challenges of uwsns are limited bandwidth, long propagation delay, high bit error rates, and limited battery power. nevertheless, uwsns enjoy myriad of applications in different area, including environmental monitoring, undersea explorations, disaster prevention, navigation, distributed tactical surveillance and mine reconnaissance [4]. many researches regarding saving energy in uwsns have been carried out [5-9]. some of them focused on clustering sensor nodes and optimizing routing protocols. less works reported on data transmission problem. the developed energyefficient transmission schemes for twsns cannot be applied in underwater environment because of the challenges of acoustic communications mentioned above. as a result, novel transmission schemes have to be implemented for uwsns. in this paper, an energy-efficient data transmission scheme based on bloom filters in uwsns is proposed. data transmission is the main source of energy consumption in uwsns. data transmission in uwsns is not cost effective. hence, to improve energy efficiency and increase network lifetime, the cardinal rule is to diminish the number of transmission. the content of this paper follows this cardinal rule. the results of this research suggest that exploiting bloom filters is a viable solution for reducing the number of transmission in uwsns. simulations on prototype data were carried out to demonstrate the effectiveness of the proposed method. simulation results showed that the proposed scheme outperforms other well-known method in term of energy efficiency, lifetime, load and loss rate. ii. related works a novel fec approach for multiple-path communication in uwsns was proposed in [6]. to reduce the consumed energy of transmission, a markov model is utilized. in addition, jettison retransmission, multiple-path communication, and hamming coding are integrated. a novel energy-efficient data transmission scheme for uwsns called egrc (energyefficiency grid routing based on 3d cubes) was proposed in [7], taking complex properties of underwater medium into consideration. in this method, the 3d network is divided into multiple parts and each part itself shapes a cluster. in essence, a new algorithm for cluster-head selection and a novel mechanism for seeking the next-hop node is proposed. a balance transmission mechanism, in which data transmission is divided in two phases was proposed in [9]. in the routing set-up engineering, technology & applied science research vol. 6, no. 2, 2016, 931-936 932 www.etasr.com emami and javidan: an energy-efficient data transmission scheme in underwater wireless … phase, an efficient routing algorithm based on the optimum transmission distance is present to optimize the energy consumption of the uwasn. after that, in data transmission phase a balance transmission algorithm is introduced. in this method one-hop or multihop data transmission of the node to the sink node can be determined based on the energy level of adjacent nodes. energy efficient transmission in uwsns using optimization problem which aims to minimize energy consumption, was investigated in [10]. the results showed that reliability and communication delay are key factors for transmission. a fair data transmission strategy in uwsns by comprising queue management, transmission control and the concept of time distance ratio, was proposed in [11]. transmission control assigns a channel in each node queue based on the maximum time distance ratio. the algorithm considers the fairness of network performance and data transmission based on network congestion. bloom filters are widely used in the realm of network security. wireless networks utilize bloom filters for authentication, anonymity and privacy-preserving firewalling, tracebacking, misbehavior detection, replay attack detection and node replication detection. wired networks used bloom filters for string matching, ip tracebacking, spam filtering and email protection, dos and ddos attacks detection and anomaly detection [12]. denh et al. [13] proposed a coordinated packet traceback protocol (captra) for wireless sensor networks. in captra each sensor dedicates a subtle memory for the bloom filter. when a packet passes through the network, each forwarding sensor records the packet in its bloom filter. later the bloom filter will be used to rebuild the attack graph. toe et al. [14] proposed a bloom filter based data dissemination protocol for wireless sensor networks. utilizing bloom filters identifies the version difference among data items and guarantee network-wide consistency. compared with above-mentioned related works, the contribution of our paper is twofold: a novel approach based on bloom filter is proposed for improving energy efficiency and lifetime in uwsns and extensive simulation experiments are conducted to evaluate the performance of the proposed method. the results indicate that this method can reduce network load and loss rate. iii. the proposed method a. bloom filter bloom filter is a simple and compact probabilistic data structure for representing a set of n elements and supporting membership queries. bloom filter utilizes an array of m bits (initially all bits set to zero). in order to add an element to the bloom filter, the element is k times hashed, the results of hashing operation produces the array’s indexes, then the corresponding bits of these indexes are set to one. in the rest of this paper such an operation is referred as bloom. to support membership query for a specific element like y, it k times is hashed, if one of the corresponding bits of the obtained array’s indexes is zero y is not member of the set. if all of the corresponding bits of the obtained array’s indexes are one, y is either in the set or is a false positive. bloom filter may result in false positive, i.e. an element considered to be in the set though it is not. the probability of a false positive is determined by: kn kn k km 1 (1-(1) ) (1-e ) (1) m » where m is array’s length, n is the number of element to be hashed and the value of k determines the number of hashing. in practice, it is better to deem k a small value since the amount of computation is reduced. for a graphical example of the process, the reader may refer to [14]. a counting bloom filter is a special version of bloom filters in which each entry in the bloom filter is a small counter instead of a single bit. upon inserting an item the relevant counters are incremented and in case of deletion the corresponding counters are decremented [15]. b. the proposed method the proposed method exploits 32 bit bloom filters to deliver maximum energy efficiency in underwater wireless sensor networks. the case study in this research is water quality monitoring. each front-end sensor node senses data for the target features (ammonia, phosphorous, nitrogen and oxygen) in the determined time intervals and bloom the sensed data for each feature in a separate bloom, according the rules of counting bloom filters. then the shaped bloom filters are sent towards the middle nodes. the middle nodes consolidate the received bloom filters from sensors and integrate them with its own sensed and bloomed data and the result are sent toward the sink using dbr routing protocol [16]. figure 1 illustrates the above procedure using a numerical example. for the sake of simplicity just one target feature is depicted. in the end, the sink extracts data from the received bloom filters so that fuzzy logic may be employed to determine the final result. in this method, many packets are converted to one packet using bloom filter; hence the amount of traffic is reduced and energy efficiency improvement is achieved. based on the extracted data in the sink, a fuzzy logic based method is used to determine the quality of the water. such a quality depends on the dissolved oxygen o2, total nitrogen n, ammonia nh3-n and total phosphorus p. one of the best features of using fuzzy logic is that it does not require complex mathematical equation and system modeling [17]. therefore, lower cost and better performance is achieved. figure 2 shows the proposed fuzzy logic inference system. using fuzzy logic, the input crisp values should be fuzzified. the fuzzified values are then processed by the inference engine. the knowledge base of the inference engine consists of a series of if-then rules. here inferencing on the rules are carried on based on the mamdani method. finally the output fuzzy values should be defuzzified to generate a crisp output. as shown in figure 2, the proposed fuzzy approach consists of four input parameters o2, n, nh3-n and p, and one output, with universal of discourse [0…19], [0…100], [0…45],[0…30] and [0…100], respectively. the proposed method uses five membership function for each input and output parameters as shown in figure 3. table i shows some of the if-then rules engineering, technology & applied science research vol. 6, no. 2, 2016, 931-936 933 www.etasr.com emami and javidan: an energy-efficient data transmission scheme in underwater wireless … used in the fuzzy approach. as an example, if o2 is high, p is low, n is low and nh3-n is high, then output is clear. in the end the defuzzification finds a crisp output value. defuzzification is done using centre-of-maxia method [18] given by: 1 1 2 2 n n 1 2 n x μ +x μ +...+x μ outpout= (2) μ +μ +...+μ where xn is the numerical value and μn is the degree of membership. fig. 1. a numerical example for bloom filter in the proposed approach inference rule basenh3-n n p o2 output fig. 2. fuzzy structure with four inputs and one output iv. performance evaluation to show the effectiveness of the proposed method, the method is compared with the well known primary method. in primary method, no blooming is occurred, each front-end node sense data in the determined times and send them toward the middle nodes, then the middle nodes receive and buffer these data, in special times the buffered data is extracted and sent for sink using dbr. it is notable that the performance of the proposed method is evaluated from two points of view. initially, the effect of sensing intervals on the proposed method is checked and finally the effect of gathering intervals is investigated. in data gathering intervals the middle nodes bloom the received packets and send them toward sink. finally in sensing interval, the front-end nodes and also the middle nodes sense the chemical features of water. low medium high 0 1 3 9 19 input 1: o2 dissolved oxyzen total nitrogen input2:n 0 1 low medium high 0.004 0.1 10 100 input3 :nh3-n ammonia 0 1 0 1 0 1 total phosporus input4:p output 0.1 10 45 low medium high high 3060.020.01 mediumlow 40 60 100 clearpollut semipollut fig. 3. membership graph for the inputs and the output table i. if-then rules antecedent consequent no o2 p n nh3-n result 1 l l l l semi p 2 l l l h semi p 3 l l h l semi p 4 l l h h p 5 l h l l semi p 6 l h l h p 7 l h h l p 8 l h h h p 9 h l l l c 10 h l l h c 11 h l h l c 12 h l h h semi p 13 h h l low c 14 h h l h semi p simulations are carried out in aqua-sim. aqua-sim is based on ns-2 and simulates the attenuation of underwater acoustic channels [19]. the utilized mac and routing protocol are broadcast mac and dbr respectively. the initial energy of sensors is 20j. two hundred nodes are scattered randomly in engineering, technology & applied science research vol. 6, no. 2, 2016, 931-936 934 www.etasr.com emami and javidan: an energy-efficient data transmission scheme in underwater wireless … a 1000 *1000 area with depth of 500 m. there is only one sink. the energy consumption parameters are set according to the uwm2000 linkquest underwater acoustic modem [20]. detailed simulation parameters are listed in table ii. table ii. simulation parameters in data processing intervals, data are processed using fuzzy logic. all obtained results in the figures have been repeated 10 times and their average have been presented. the calculated confidence interval is 95 percent. the utilized performance metrics are energy efficiency, life time, network load and loss rate. in the following a short description of each metric is presented. • energy efficiency: energy efficiency is expressed as packet delivery ratio (3) energy consumption where packet delivery ratio is the number of received packet in the sink. • life time: the time until at least 10 percent of the nodes are drained of their energy. • network load: refers to the amount of data (traffic) being carried by the network. • loss rate: the amount of lost information by the network (transmitted data not delivered to destination due to collision). in other word loss rate is equal to 1-packet delivery ratio. a. performance with sensing interval changing in this part the impact of changing the sensing intervals on the performance of the proposed method is investigated. to obtain the following results, sensing and sending intervals vary from 3 to 15 seconds, gathering interval in the middle nodes is 20 seconds and fuzzy processing interval is 50 seconds. as it can be seen in figure 4(a), the proposed method shows an improvement from energy efficiency point of view compared to the primary method. this is because the proposed method combines multiple packets into one packet using bloom filters in the middle nodes thus energy consumption is reduced and energy efficiency is improved. figure 4(b) depicts that the proposed method has longer lifetime than the primary method, since the number of transmitted packets in the middle nodes is reduced. therefore energy consumption by each sensor is diminished. lower energy consumption in sensor results in increasing the overall lifetime. the amount of generated traffic for the proposed method is clearly less than the primary method; traffic load for the proposed method is as shown in figure 4(c). figure 4(d) indicates that the loss rate for the proposed method is less than its primary counterpart. obviously decreasing the number of transferred packets reduces the number of collisions. 0/00000 0/00005 0/00010 0/00015 0/00020 0/00025 0/00030 3 6 9 12 15 sensing interval energy efficiency proposed method primary method 0 200 400 600 800 1000 1200 1400 1600 3 6 9 12 15 s e c o n d sensing interval lifetime proposed method primary method 0 2000000 4000000 6000000 8000000 10000000 12000000 3 6 9 12 15 b it sensing interval load proposed method primary method 0/0 0/1 0/2 0/3 0/4 0/5 0/6 0/7 0/8 3 6 9 12 15 p e rc e n t sensing interval loss rate proposed method primary method fig. 4. simulation results for sensing interval mac protocol broadcast mac routing protocol dbr simulation time 2000 second bandwidth 17.8 kbps contamination indicator n,nh3-n,o2,p number of repetitions for each scenario 10 number of nodes 200 investigated area 1000 m *1000 m depth(meters) 500 m sensor type linkquest2000uwm initial energy of node 20 joule sensing interval for pollution indicators 3 to 15 second data processing interval 50 second the number of front-end nodes 20 the interval for data gathering ,saving and sending in the middle nodes 25 to 45 second (a) (b) (c) (d) engineering, technology & applied science research vol. 6, no. 2, 2016, 931-936 935 www.etasr.com emami and javidan: an energy-efficient data transmission scheme in underwater wireless … 0/00000 0/00005 0/00010 0/00015 0/00020 0/00025 25 30 35 40 45 gathering interval energy efficiency proposed method primary method 0 200 400 600 800 1000 1200 1400 1600 25 30 35 40 45 s e co n d gathering interval lifetime proposed method primary method 0 1000000 2000000 3000000 4000000 5000000 6000000 7000000 8000000 9000000 25 30 35 40 45 b it gathering interval load proposed method primary method 0/0 0/1 0/2 0/3 0/4 0/5 0/6 0/7 0/8 0/9 25 30 35 40 45 p e rc e n t gathering interval loss rate proposed method primary method fig. 5. simulation results for gathering interval b. performance with gathering interval changing figure 4 investigates the impact of sensing interval on the protocol performance. figure 5 investigate the impact of buffering time in the middle nodes on the protocol performance. to obtain the results, sensing interval is set to 9 second, gathering interval in the middle nodes vary from 25 to 45 seconds and fuzzy processing interval is 50 seconds. as figure 5(a) illustrates, the proposed method outperform the primary one from energy efficiency point of view. the reason behind this is summarizing packets in the middle nodes using bloom filters. as gathering intervals in the figure step towards the end, the middle nodes have more time for buffering the received packets and blooming them, hence energy efficiency is greatly improved. reducing the number of transmissions results in increased lifetime. figure 5(b) clearly demonstrates that the proposed method has better performance in this regard. as shown in figure 5(c), it is clear that the volume of generated traffic in the proposed method is less than that of the primary method since the proposed method utilize bloom filter for data summarizing which reduces traffic load. figure 5(d) illustrates the improved performance for the proposed method in term of loss rate. the reason is that sending less number of packets will result less collision v. conclusion in this paper, a novel energy-efficient data transmission scheme using bloom filters for uwsns is proposed.. transmission and computation are the two main sources of energy consuming in uwsns but the energy required for computation is subtler than that of transmission. to save the precious energy in uwsns the best feasible option is to cut the number of transmissions with cost effective solutions. bloom filters with compact data structure can be a good selection. the proposed method utilize bloom filters to efficiently cut the number of transmissions and to prolong the overall lifetime of the network. extensive simulations on aqua-sim showed that the proposed approach can significantly outperform the primary method in terms of energy efficiency, lifetime, and load and loss rate acknowledgment yousef emami would like to express his gratitude to dr. michele nati, senior researcher at the university of surrey, for persevering with him as mentor through out the time it took him to complete this research and write the dissertation. references [1] r. javidan, m. a. masnadi-shirazi, z. azimifar, “contourlet-based acoustic seabed ground discrimination system”, third ieee international conference on information and communication technologies: from theory to applications, damascus, syria, april 711, 2008 [2] t. j. arsanjani, r. javidan, m. j. nazemosadat, j. j. arsanjani, e vaz, “spatiotemporal monitoring of bakhtegan lake's areal fluctuations and an exploration of its future status by applying a cellular automata model”, computers & geosciences, no. 78, pp. 37-43, 2015. 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[18] t. a. runkler, “selection of appropriate defuzzification methods using application specific properties”, ieee transactions on fuzzy systems, vol. 5, no. 1, pp. 72-79, 1997 [19] x. peng, “aqua-sim: an ns-2 based simulator for underwater sensor networks”, oceans 2009, mts/ieee biloxi marine technology for our future: global and local challenges, biloxi, usa, pp. 1-7, 26-29 oct. 2009 [20] linkquest inc, linkquest underwater acoustic modems uwm2000 specifications, available at: http://www.link-quest.com/html/ uwm2000.htm microsoft word 2-667-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1119-1123 1119 www.etasr.com salami et al.: a comparison among different parameters for the design of a photovoltaic/ thermal system… a comparison among different parameters for the design of a photovoltaic/thermal system using computational fluid dynamics payman salami department of biosystems engineering, faculty of agriculture, university of tabriz, iran salami@ut.ac.ir yahya ajabshirchi department of biosystems engineering, faculty of agriculture, university of tabriz, iran yajabshir@tabrizu.ac.ir shamsollah abdollahpoor department of biosystems engineering, faculty of agriculture, university of tabriz, iran shamstabriz1@yahoo.com hossein behfar department of biosystems engineering, faculty of agriculture, university of tabriz, iran behfar@tabrizu.ac.ir abstract—the purpose of this paper is to compare several fins, duct height, and velocity magnitudes to acquire a photovoltaic/thermal system designed through computational fluid dynamics. simulation of different fins (rectangular, trapezoidal, curved, and pin) with different distances among fins is performed in fluent software. the parameters such as duct height (4, 6, 8, and 10 centimeters) and velocity magnitudes (0.5, 1, 2, and 3 m/s) are also simulated. according to the results the highest cell temperature was 51°c at 0.5 m/s, while the best result was 33°c achieved with 4 cm duct height, rectangular fin and 3 m/s velocity magnitude. the findings suggest that the maximum cell temperature at the rate of 0.5 m/s is 51 °c, whereas temperature conducive to the best outputs is 33 °c. differences among the cell temperatures through the various duct and the different fin types were significant at 1% level, also velocity magnitude would be cardinal at 1% level. a logarithmic regression model has been proposed to getting the cell temperature estimated by velocity magnitude. keywords-computational fluid dynamics (cfd); energy efficiency; fin; photovoltaic/thermal (pv/t) i. introduction in a hybrid photovoltaic/thermal (pv/t) solar collector, the pv cells are combined with a solar thermal unit as a composite absorber and thus electricity and heat from the absorbed solar radiation would be generated simultaneously. most of the absorbed solar radiation by the pv modules is converted into waste heat since the cell’s conversion efficiencies are currently low [1] and this heat manifests itself as a temperature rise of the module. the high temperature has a negative effect on the electrical output of the pv module, especially in case of the dominant crystalline si based cells [2], where their conversion efficiency degrades by about 0.4–0.5% per degree rise in temperature [3-4] and a form of cooling is rather beneficial. due to the aforementioned temperature influence on the performance of pv cells, the energy that is not converted into electricity by the pv cells must be extracted to prevent excessive cell heating and the caused deteriorated performance. therefore, solar cell cooling must be an integral part of pv systems, especially in concentrated pv designs in order to minimize the effect of elevated temperatures on the pv module power output [5]. as a matter of fact, the high temperature would be affecting the electrical output of a pv module in a negative way gradually, especially with cells made from si crystalline, so it must be stated that just this very factor could reduce conversion efficiency about 0.4-0.5% per degree rise in temperature, but laying within cool status to be beneficial. performance is a crucial characteristic during the constructing of solar panels. augmenting the performance brings about thwarting amount of exorbitant and energy loss. pv cells have got the potential to be extremely efficient. it should not be forgotten that just these lucrative sets might have born a performance about 28.9%, ever in the worst case scenario [6]. as known pv cells performance of this appliance is directly related to their temperature, so electrical efficiency could be calculated as deduction of mean temperature of pv/t and nominal operating cell temperature (noct). the relationship between efficiency and temperature are shown in (1) and it is assumed that there would be a 0.45%/0c decrease in electrical efficiency [7-8]. ))(0045.01( nocttmpopel  (1) where op is the nominal efficiency of the photovoltaic cell at the nominal operating cell temperature (noct) and el is the efficiency of the photovoltaic cell at the mean absorber temperature mpt . hegazy examined four types of pvt air heating solar collectors using a numerical model [9]. the systems in the study utilized a glass cover mounted above the pv module thus forming a second air gap. this is commonly used on collectors for solar water heating to reduce convection heat losses from engineering, technology & applied science research vol. 6, no. 5, 2016, 1119-1123 1120 www.etasr.com salami et al.: a comparison among different parameters for the design of a photovoltaic/ thermal system… the top surface of the collector plate. hegazy found that getting the air circulated between the back surface of the module and the isolating layer as well as at the top of module surface and the glass cover might offer the best balance between electrical and thermal performance. some results in [10] demonstrated what were extracted by hegazy. both studies utilized a static reflector plate that conducted solar radiation from an area with same size as pvt through their collector therefore just this would offer a concentration ratio of approximately 1.3. they found that an unglazed pvt collector had a maximum thermal efficiency of 38%. glazing the system or adding the static reflector could increase the performance about 60%, if both glazing and adding the reflector to be fulfilled the efficiency would possibly reach 75%. it was also noted however, that although glazing improved the thermal efficiency it tended to increase optical losses, resulting in a decreased electrical efficiency. some studies have let cooling flat plate pv modules examined, for instance in [11-12] it was proposed that exploiting some simple low cost alterations might improve the performance of pvt air heaters. it was shown that adding fins to the rear part of the pv modules could optimize the pvt system performance. it was suggested that hegazy’s technique along with adding a flimsy metal sheet in the air passage behind the pv module would improve the thermal and electrical efficiency. one of the ways to upturn the heat transfer process is by utilizing an extending effective plane by which the contact surface with the working fluid would be increased automatically. in [13], several pv-t air collectors with additional fins at the backside of the absorber collector were developed. the fins brought about an increase in total efficiency from 49.1 to 62.8 percent. in [14], a pv-t air collector with v-groves to increase the absorber surface and thus the heat transfer process was proposed [14]. ii. materials and methods computational fluid dynamics (cfd) is a robust technique used to solving navierstokes equations numerically, based on a finite volume approach. using the fluent computational fluid dynamics (cfd) software, some series of simulations with different configurations of fins were performed. in the case of forced convection, the fluid flow was modeled for the air flowing underneath the solar panel. due to the complicated nature of fluid flow and fins, a three dimensional model was originated for each case. the design of the 3d models was conducted in autocad and model meshing was done in gambit. the motion of fluid, heat transfer (which gives temperature distribution) and turbulence are calculated. the discrete scheme for the momentum and energy equations adopted the second order upwind. the criterion of convergence for terminating the iteration is 10-3for the momentum equation and 10-6 for the energy equation. through inlet, the air pressure would be imagined as uniform and constant value. simple (semi implicit method for pressure linked equations) was adopted [15]. the standard k–ε turbulence model was used to estimating the turbulence [16]. the hydraulic diameter ( hd ), the nusselt number ( xnu ), and the reynolds number (re) for non-circular ducts are expressed, respectively below [15, 17]: p a d ch 4  (2) k dxh nu hx )(  (3)  hm du .re  (4) where ac is the cross sectional area, p is the wetted perimeter, h(x) is the local heat transfer coefficient, k is the thermal conductivity, mu is the mean velocity, and ν is the kinematic viscosity. to obtain the minimum cell temperature, different designs were simulated in fluent. different fins (rectangular, trapezoidal, curved) and pin with different distances from fins were considered (figure 1). four types of duct heights (4, 6, 8, and 10 centimeters) were assessed. four types of velocity magnitudes (0.5, 1, 2, and 3 m/s) were simulated. through the simulation process the ambient temperature and solar irradiation were assumed to be 30°c and 900 w/m2 respectively. the aim of this study is to compare different fins, duct height and velocity magnitudes. the differences among cell temperatures for the levels of the three factors were investigated by univariate analysis of variance at the 5% and 1% significance level. iii. results and discussion results show that the highest cell temperature would be 51°c at a velocity magnitude of 0.5 m/s. increased velocity magnitudes would decrease the cell temperature significantly. table i shows the cell temperature at 0.5 m/s velocity magnitude, whereas tables ii, iii and iv show the cell temperature at 1 m/s, 2 m/s and 3 m/s velocity magnitudes respectively. the best result was for 4 cm duct height, rectangular fin and 3 m/s velocity magnitude (33°c), but it’s difference with the 2 m/s velocity magnitude is not considerable (only 1°c) and thus the excess energy to cool the panel would probably prove to be not affordable. according to (1), in the absence of forced convection, the efficiency might decrease about 3.6%. as the solar irradiation was assumed to be 900 w/m2, the total waste of energy in this case is about 32.4 w/m2. obviously, based on the univariate analysis of variance (table v), the difference among cell temperatures at the different duct heights is significant at 1% level. however the cell temperature at the 4 cm duct height is lower than other duct heights. also the difference among cell temperatures at the different fin types is significant at 1% level, but what to be considerable is that, the cell temperature at the rectangular fins is lower than other fin types. like these two factors, some element playing a pivotal role in boosting cell temperature and the difference among cell temperatures at different velocity engineering, technology & applied science research vol. 6, no. 5, 2016, 1119-1123 1121 www.etasr.com salami et al.: a comparison among different parameters for the design of a photovoltaic/ thermal system… magnitudes at is significant 1% level. also the interactions of all of two way factors is significant at 1% level. as shown, the main factor which affects the cell temperature is the velocity magnitude. a regression model to estimate the cell temperature (t) by velocity magnitude (v) is shown in (5). the r square for the linear model was 0.659 and for the logarithmic model was 0.736. the velocity magnitude and cell temperature diagram for the linear and logarithmic models is shown in figure 2. 283.41)ln(352.5  vt (5) fig. 1. fin types (rectangular, trapezoidal, curved, and pin) table i. cell temperature at 0.5 m/s velocity magnitude duct height fin type 4 6 8 10 no fin 44 46 49 51 rectangular 42 44 44 47 trapezoidal 41 44 46 47 curved 41 43 45 48 pin 43 45 48 50 table ii. cell temperature at 1 m/s velocity magnitude duct height fin type 4 6 8 10 no fin 41 42 44 45 rectangular 37 38 39 41 trapezoidal 38 39 41 41 curved 38 39 40 42 pin 40 41 43 45 table iii. cell temperature at 2 m/s velocity magnitude duct height fin type 4 6 8 10 no fin 37 39 40 41 rectangular 34 36 36 38 trapezoidal 35 36 37 38 curved 35 36 37 38 pin 37 38 39 40 table iv. cell temperature at 3 m/s velocity magnitude duct height fin type 4 6 8 10 no fin 36 37 38 39 rectangular 33 34 35 36 trapezoidal 34 35 36 36 curved 34 34 36 37 pin 35 36 37 38 table v. univariate analysis of variance for cell temperature dependent variable: cell temperature source type iii sum of squares df mean square f sig. corrected model 1446.66a 43 33.64 219.21 0.00 0 intercept 126802.81 1 126802.81 826226.47 0.00 0 duct height 191.84 3 63.95 416.66 0.00 0 fin type 140.13 4 35.03 228.26 0.00 0 velocity 1083.44 3 361.15 2353.17 0.00 0 duct height * fin type 5.48 12 0.46 2.97 0.00 6 duct height * velocity 20.91 9 2.32 15.14 0.00 0 fin type * velocity 4.88 12 0.41 2.65 0.01 0 error 5.53 36 0.15 total 128255.00 80 corrected total 1452.19 79 a. r squared = .996 (adjusted r squared = .992) engineering, technology & applied science research vol. 6, no. 5, 2016, 1119-1123 1122 www.etasr.com salami et al.: a comparison among different parameters for the design of a photovoltaic/ thermal system… fig. 2. the velocity magnitude and cell temperature diagram for the linear and logarithmic models to validate the simulation results, experimental data were obtained from 2nd april 2016 to 9th april 2016 at the university of tabriz, iran. the average of ambient temperature and solar irradiation were 14.6°c and the 751 w/m2 respectively. the experimental data was obtained from 4 cm duct height, rectangular fins and also the average velocity magnitude of the fan was 1 m/s. the experimental results showed that the average cell temperature was 22°c. as the ambient temperature for the primary simulation and solar radiation were assumed 30°c and 900 w/m2 respectively, so another simulation based on the experimental condition whose temperature was 21°c was fulfilled. let’s say the simulation data could show the realistic situation (i.e. experimental data) and 1°c is the thermal difference between. in [18], an air-based pv/t solar collector which applied two low cost approaches to enhance heat transfer between the air flow and pv surface was constructed. a finned metal sheet was attained to the back wall of the air-channel to improve heat extraction from the pv modules. the experimental tests were carried out on the air-based pv/t system which used a 46 wp rated commercial pc-si pv module and has 0.4 m2 of aperture area as the absorber plate. the results showed good agreement between predicted values and measured data. it is found that the induced mass flow rate and thermal efficiency decrease with increasing ambient (inlet) temperature and increase with increasing tilt angle for a given insulation level. the results also showed that the optimum channel depth occurs between 0.05 m and 0.1 m for this system. this type of pv/t system is practical and cost effective, suitable for being integrated into buildings with both heat and electrical demands. in [19], it was mentioned that an augmented duct depth from 0.01 to 0.1 could get the thermal efficiency and outlet air temperature decreased. these characteristics may be attributed to the decreasing absorber to air heat transfer coefficients and the reduction of the radiative heat transfer coefficient for the double-glass configuration. since solar cell efficiency is strongly dependent on solar cell temperature, it also decreases with an increase in duct depth and a decrease in collector length. therefore, system efficiency which is a sum of thermal and electrical efficiencies, also decreases with an increase in duct depth and a decrease in collector length. according to the results of this study, the best duct height among 4, 6, 8, and 10 cm is 4 cm which is consistent with [18, 19]. in [20], the performance of a double pass pv/t solar air heater with and without fins was examined. it was found that the extended fin area reduced the cell temperature considerably, from 82°c to 66°c. this somehow contradicts the results of this study, as the maximum difference found in this study was only 5 °c. in [20}, it was also mentioned that the relationship between cell temperature and solar radiance is linear (i.e. increasing the cell temperature gets solar radiation increased on the collector surface). the increase in cell temperature with solar irradiance is significant at low flow rates (0.03 kg/s) compared to high flow rates (0.15 kg/s). boosting the cell temperature at low air flow rates (0.03 kg/s) reduces the thermal and electrical efficiencies of the pv/t air collector. it is shown that the velocity magnitude has a strong impact on the cell temperature. the distribution of the data are shown in figure 3. fig. 3. the distribution of the data chart iv. conclusion the objective of this study was getting a detailed comparison among various fins, ducts heights and velocity magnitudes to gain the minimum cell temperature. the results show that the highest cell temperature is 51°c at 0.5 m/s velocity magnitude, while the best result is laid at 4 cm duct height, rectangular fin and 3 m/s velocity magnitude (33°c). the difference among cell temperatures at the different duct engineering, technology & applied science research vol. 6, no. 5, 2016, 1119-1123 1123 www.etasr.com salami et al.: a comparison among different parameters for the design of a photovoltaic/ thermal system… heights and fin types are significant at 1% level, also it is significant for the different velocity magnitudes at 1% level. a logarithmic regression model was presented to estimate the cell temperature using velocity magnitude. references [1] j. k. tonui, y. tripanagnostopoulos, “performance improvement of pv/t solar collectors with natural air flow operation”, solar energy, vol. 82, pp. 1–12, 2008 [2] p. d. maycock, “pv review, world solar pv market continues explosive growth”, refocus, vol. 16, pp. 105–145, 2005 [3] b. j. brinkworth, b. m. cross, r. h. marshall, h. yang, “thermal regulation of photovoltaic cladding”, solar energy, vol. 61, pp. 169– 178, 1997 [4] s. krauter, r. g. arauja, s. schroer, r. hanitsh, m. j. salhi, c. triebel, r. lemoine, “combined photovoltaic and solar thermal systems for facade integration and building insulation”, solar energy, vol. 67, pp. 239–248, 1999 [5] s. chatterjee, g. tamizh mani, “bapv arrays: side-by-side comparison with and without fan cooling”, ieee photovoltaic specialists conference (pvsc), vol. 7, pp. 537–542, 2011 [6] m. j. y. tayebjee, l. c. hirst, n. j. ekins-daukes, t. w. schmidt, “the efficiency limit of solar cells with molecular absorbers: a master equation approach”, journal of applied physics, vol. 108, art. no. 124506, 2010 [7] l. nishioka, t. hatayama, y. uraoka, t. fuyuki, r. hagihara, m. watanabe, “field-test analysis of pvsystem output characteristics focusing on module temperature”, solar energy materials & solar cells, vol. 75, no. 3, pp. 665-671, 2003 [8] h. a. zondag, d. w. de vries, w. g. j. van helden, r. j. c. van zolengen, a. a. van steenhoven, “the thermal and electrical yield of a pv–thermal collector”, solar energy, vol. 72, pp. 113–128, 2002 [9] a. a. hegazy, “comparative study of the performances of four photovoltaic/thermal solar air collectors”, energy conversion and management, vol. 41, no. 8, pp. 861-881, 2000 [10] y. tripanagnostopoulos, t. nousia, m. souliotis, p. yianoulis, “hybrid photovoltaic/thermal solar systems”, solar energy, vol. 72, no. 3, pp. 217-234, 2002 [11] j. k. tonui, y. tripanagnostopoulos, “improved pv/t solar collectors with heat extraction by forced or natural air circulation”, renewable energy, vol. 32, no. 4, pp. 623-637, 2007 [12] j. k. tonui, y. tripanagnostopoulos, “air-cooled pv/t solar collectors with low cost performance improvements”, solar energy, vol. 81, no. 4, pp. 498-511, 2007 [13] m. alfegi, k. sopian, m. othman, b. yatim, “experimental investigation of single pass, double duct photovoltaic thermal (pv/t) air collector with cpc and fins”, american journal of applied sciences, vol. 5, pp. 866-871, 2008 [14] m. othman, k. sopian, b. yatim, w. daud, “development of advanced solar assisted drying systems”, renewable energy, vol. 31, pp. 703-709, 2006 [15] o. turgut, “numerical investigation of laminar flow and heat transfer in hexagonal ducts under isothermal and constant heat flux boundary conditions”, transactions of mechanical engineering, vol. 38, no. m1, pp. 45-56, 2013 [16] d. m. hargreaves, n. g. wright, “on the use of the k–ε model in commercial cfd software to model the neutral atmospheric boundary layer”, journal of wind engineering and industrial aerodynamics, vol. 95, pp. 355-369, 2007 [17] j. g. jiang, z. x. yuan, g. d. xia, “periodical heat transfer in parallelplate channel of improved flow-inclining inserts”, international journal of thermal sciences, vol. 48, pp. 1748–1754, 2009 [18] j. k. tonui, y. tripanagnostopoulos, “performance improvement of pv/t solar collectors with natural air flow operation”, solar energy, vol. 82, pp. 1–12, 2008 [19] h. p. garg, r. s. adhikari, “conventional hybrid photovoltaic/thermal (pv/t) air heating collectors: steady-state simulation”, renewable energy, vol. 11, no. 3, pp. 363-385, 1997 [20] r. kumar, m. a. rosen, “performance evaluation of a double pass pv/t solar air heater with and without fins”, applied thermal engineering, vol. 31, pp. 1402-1410, 2011 microsoft word etasr_v12_n5_pp9316-9328 engineering, technology & applied science research vol. 12, no. 5, 2022, 9316-9328 9316 www.etasr.com fouda et al.: thermodynamic and performance assessment of an innovative solar-assisted … thermodynamic and performance assessment of an innovative solar-assisted tri-generation system for water desalination, air-conditioning, and power generation a. fouda department of mechanical and materials engineering faculty of engineering, university of jeddah jeddah, saudi arabia aafoudah@uj.edu.sa h. f. elattar department of mechanical and materials engineering faculty of engineering, university of jeddah jeddah, saudi arabia hfalattar@uj.edu.sa saeed rubaiee department of mechanical and materials engineering department of industrial and systems engineering faculty of engineering, university of jeddah jeddah, saudi arabia salrubaiee@uj.edu.sa abdullah s. bin mahfouz department of chemical engineering faculty of engineering, university of jeddah jeddah, saudi arabia asbinmahfooz@uj.edu.sa abdullah m. alharbi department of industrial and systems engineering faculty of engineering, university of jeddah jeddah, saudi arabia amealharbi@uj.edu.sa received: 3 august 2022 | revised: 14 august 2022 | accepted: 15 august 2022 abstract-an innovative tri-generation system powered by solar energy for water desalination, air-conditioning, and electrical power production is proposed and investigated numerically in this paper. the system is designed for small and medium-sized buildings in countries that are rich in solar energy but poor in fossil fuels and water resources. the devised system includes a solar system (evacuated tube collectors and thermal energy storage unit), an organic rankine cycle (orc), a humidification and dehumidification (hdh) water desalination system, and a desiccant cooling system (dcs). a detailed parametric study of the developed system is carried out for a wide range of operating conditions and design parameters on the system’s productivity and performance parameters. it is found that: (i) the proposed tri-generation system can deliver high electrical power, fresh water, space cooling capacity, and energy utilization factor (euf) of 104.5kw, 72.37kg/h, 25.48kw, and 0.2643 respectively. in comparison to the basic system, the eufimp and asc,sav parameters were enhanced having maximum values of 69.9% and 41.14% respectively. general numerical correlations derived from the numerical data can predict the system productivity and performance parameters within reasonable error. keywords-tri-generation; organic rankine cycle; humidification-dehumidification; desiccant cooling system i. introduction due to the increasing population and pollution, the needs for fresh water productivity, electricity generation, and air conditioning have dramatically increased. the heat rejection to the environment can be overcome by double-use systems that integrate desalination and power systems, in which the lowgrade heat rejected from the power cycle is used to drive the desalination system. this significantly improves the energy efficiency of the combined plant [1-7]. on the other hand, dual solar-powered systems can play a key part in reducing co2 emissions. in addition, the integration of concentrated solar power (csp) and cogeneration systems can reduce the unit product costs of water and electricity with current developments in csp technology [8]. solar electricity and desalination systems can offer economic solutions to meet the increasing demands for both electricity and freshwater in dry arid regions such as the gulf and mena (middle east and north africa). to face the problem of rising temperatures, it is also necessary to adapt the air to achieve thermal comfort, corresponding author: a. fouda engineering, technology & applied science research vol. 12, no. 5, 2022, 9316-9328 9317 www.etasr.com fouda et al.: thermodynamic and performance assessment of an innovative solar-assisted … which can be accomplished by using a desiccant air conditioner, which is distinguished by not producing polluting gases such as chlorofluorocarbons, which are produced by traditional air conditioning systems. a hybrid system of air conditioning and desalination units was employed to lower the use of electricity in desalination and air conditioning systems. in hybrid air conditioners, renewable energy is also used to minimize the rate of power consumption. several researchers combined air conditioning and refrigeration systems with hdh water desalination systems in different configurations to obtain hybrid systems for cooling and air conditioning [9–12]. the effects of system configuration, operating conditions, and geometric parameters have been investigated. authors in [13] proposed a low-energy hdh and a/c hybrid system using an efficient design of dehumidifier (strips-finned helical coil) and packing pad material (cellulose paper in bee-hive structure). the integrated cooling or heating, fresh water generation and power systems, known as tri-generation plants, are an efficient method intended to have a lower consumption of primary energy and reduce greenhouse gas emissions. the processes and technologies for trigeneration that are currently available can provide a number of benefits [14, 15]: increasing global energy efficiency while expanding the use of renewable energy sources, lowering environmental impact in terms of carbon dioxide equivalent emissions, and reducing electrical system overloads and blackouts. tri-generation techniques are used in several areas, including buildings, industries, and manufacturing [16]. few researchers have concentrated on tri-generation system modeling. previous research has looked into multi-generation facilities for electricity, cooling or heating, and freshwater generation that are combined with renewable energy resources. authors in [17] investigated a multi-generation system that generates electrical power, freshwater, space cooling, and industrial heating using geothermal, solar, and ocean thermal energy conversion as energy inputs. authors in [18] created a tri-generation facility that includes a flat plate solar collector field, a kalina electrical power generation cycle, and a multistage desalination unit. a thermodynamic analysis of a polygeneration system comprising a solar power system (sps), a multi effect desalination (med) system, and an absorption refrigeration system (ars) was given in [19]. solar energy is used to power the plant, which is supplemented by a natural gas heater. the impacts of various design and operating parameters on the plant's energy and exergetic parameters are investigated using a parametric study. authors in [20] created a new tri-generation system for freshwater, electricity, and cooling production. a hdh unit is used as a binary cycle in this trigeneration system. according to the literature review, there are several cogeneration systems integrated with orc/hdh and dcs/hdh, and a few trigeneration systems for power, freshwater, and cooling load integrated with med/src/ars and hdh/orc/ecc, including cpvt, biogas, biomass boilers, and geothermal wells. so, tri-generation systems have not been extensively investigated up to now. for this aim, a new trigeneration set-up on the basis of an orc, a dcs, and a hdh unit is designed to generate power, cooling, and freshwater. orc power generation is only appropriate for small-scale applications and low operating temperatures [21]. low-temperature energy utilization (e.g. waste energy, solar energy), simplicity, and low operating and installation costs are advantages of hdh water desalination. a desiccant air conditioner is a type of air conditioner that does not emit polluting gases like chlorofluorocarbons. cpvt, on the other hand, is an appealing technology due to its efficiency, but its dependability and economic feasibility have yet to be proven [22]. these restrictions inspire the authors to investigate the design of a trigeneration system that can supply small-scale continuous daylight electrical power, cooling, and desalination using solar energy sources. the energy analysis of a tri-generation system comprising evacuated tube collectors, a thermal energy storage unit, an orc, a hdh, and a dcs is presented in the current study. to the best of our knowledge, no previous research has looked into such a complex system. the paper will present the following that will help in the design of the proposed system: (i) extensive energy mathematical modeling, (ii) the effect of various design and operating parameters on the proposed system’s performance, (iii) evaluation of the system and comparison with the basic system, (iv) numerical correlations for the system’s productivity and performance parameters in terms of the studied parameters. ii. system description the proposed tri-generation system, depicted in figure 1, can produce electricity, cooling, and potable water by combining orc with dcs and an hdh desalination unit. the solar system includes an evacuated tube solar collector and a thermal storage tank. for the solar field loop, a thermal oil (therminol-vp1) is used as a working fluid because it is able to remain in the liquid phase in temperatures up to 400 o c [23]. the system can be decomposed into four main loops: two closed loops (solar fluid loop and orc fluid loop) and two open loops (air loop and water loop). in the solar field loop, evacuated tubes solar collectors are used to gather the solar radiation through which the thermal oil flows, which is used to charge the storage tank during the sunlight period (state points 23 and 24). the thermal storage tank is used to supply the proposed system with constant demand during daylight. the thermal oil is used to transfer heat from/to the thermal storage tank to/from the orc (i.e. evaporator) at state points 25 and 26. in the closed orc fluid loop, heat is transferred from the secondary fluid to the orc working fluid through the evaporator where it is boiled and superheated at state point 19. then, the superheated orc fluid expands in the turbine, producing the required electrical load in a generator. lowgrade superheated organic fluid (state point 20) is rejected from the turbine and sent to the condenser (triple channel heat exchanger) where it gets condensed at state point 17 and supplies the dcs and hdh units with the required heat to keep the temperature of state points 8 and 15 the same. after that, the orc liquid is pressurized by the pump and sent to the evaporator (state point 18) for a gain and the cycle is completed. for the orc in the present study, n-octane was selected as the working fluid since it has the best performance among other organic fluids [24] due to its thermodynamic properties (e.g. tcr = 296.2 o c and pcr = 2497kpa). engineering, technology & applied science research vol. 12, no. 5, 2022, 9316-9328 9318 www.etasr.com fouda et al.: thermodynamic and performance assessment of an innovative solar-assisted … fig. 1. proposed tri-generation system layout. fig. 2. proposed tri-generation system psychrometric cycles. in the air loop, process air enters the desiccant wheel at state point 1, where it is dehumidified and heated to state point 2. the process air input to the heat exchanger is at state point 2, and it is sensibly cooled to state point 3. after that, the process air enters the direct evaporative cooler at state point 3, where it is cooled and humidified before being delivered to the airconditioned space at state point 4. at state point 5, the return air from the room inlet is directed to the direct evaporative cooler, where the air is cooled and humidified to state point 6. at this point, the return air inlet to the heat exchanger cools the process supply air, where the return air is sensible heated to state point 7. at state point 7, the return air (regeneration air) goes through the heat exchanger, which recovers a portion of the orc condenser heat, and the regeneration air is sensibly heated to the desired regeneration temperature at state point 8. after that, the regeneration air from state point 8 enters the reactivation portion of the desiccant wheel, where it is cooled and humidified to state point 9 via the desiccant wheel. the humidifier receives the hot regeneration air from the desiccant wheel on a continual basis, humidifying it at state point 10 before flowing to the dehumidifier, where it is cooled and dehumidified at state point 11. in figure 2, the psychrometric cycle depicts the passage of air through the proposed trigeneration system. in the water loop, sea water at state point 13 is pumped by a feed water pump to the dehumidifier coil in order to dehumidify the process air for producing fresh water. the seawater exits the dehumidifier at state point 14, where it is preheated during the air dehumidification process. this preheated water flows through an orc condenser and the heat recovered from the condenser is used to reheat the sea water to state point 15, and then it passes through the humidifier to humidify the air, where part of the water evaporates and is carried out of the humidifier by the incoming air, and the remaining part is drained as a brine at state point 16. iii. mathematical model and thermodynamics analysis the proposed tri-generation system is powered by solar energy for water desalination, air-conditioning, and power generation and it is integrated with a thermal energy storage unit. the system is simulated using the developed computer programs in c++ programming language and engineering equation solver (ees) software based on the energy and mass balances for all system components. the tri-generation system is divided into three subsystems: orc, hdh, and dcs in order to calculate the thermodynamic properties and subsystems and the whole system performance. in the simulating model procedure, the energy and mass conservation and first and second laws of thermodynamics are applied on each system components. the developed model is based on the following assumptions: engineering, technology & applied science research vol. 12, no. 5, 2022, 9316-9328 9319 www.etasr.com fouda et al.: thermodynamic and performance assessment of an innovative solar-assisted … • all system processes are considered in steady state conditions. • leakage (air/water) in the system components is neglected. • the temperatures of the blowdown water leaving the humidifier and the air wet-bulb temperature are equal. • the mass flow rats of process air ( ,p a m • ), return air ( ,r a m • ), and water ( w m • ) are equal. • the temperatures of the air (t8) and water (t15) leaving the condenser of orc are equal. • the temperatures of the fresh water and the air wet-bulb at the dehumidifier exit are equal. • the orc fluid’s state at the turbine inlet is superheated based on the different values of p18 and t19 • the electrical generator efficiency of the orc is 95%. • the isentropic efficiency of the turbine and the pump is 75%. • the effectiveness of all the heat exchangers is 80%. • the efficiency of direct evaporative coolers used in the dcs is 90%. in order to investigate and present the system performance, the energy utilization factor (euf), electrical power generation ( net w • ), thermal efficiency of the orc ( orc η ), fresh water productivity ( fresh m • ), gain output ratio (gor), space cooling capacity ( ), cooling q • the coefficient of performance of dcs (copdcs), space supply air temperature and humidity ratio (t4 and w4), and area of solar collectors (apsc) are considered. in the present tri-generation system, electrical power, space cooling capacity, and fresh water productivity are being produced simultaneously from the single solar energy source. a. solar radiation the technique and complete calculation for obtaining the daily average solar intensity it for jeddah are given in [25]. the it incidents on the surfaces of the air and water solar collectors (south oriented with a zero-tilt angle) are calculated for the weather conditions of jeddah city, ksa on july 21 by regression analysis and are given by: ( )2 2 3 4/ 10602.89-4332.31 614.44 -34.45 +0.66ti w m τ τ τ τ= + (1) where τ represents the hour of day measured from 7:00 to 13:00. in the current work the daily average solar intensity is taken as 2 , , 750 w/m t avg daily i = . b. organic rankine cycle • evaporator energy balance: 19 18 ( ) evap orc q m h h • • = − (2) 19 18 25 26 ( ) ( ) orc oil m h h m h h • • − = − (3) , , , evap sc ps t avg daily psc q i a η • = (4) where the average annual value of thermal efficiency of the evacuated tube solar collector is 63.2% [75]. • condenser energy balance: 20 17 ( ) cond orc q m h h • • = − (5) 15 14 , 8 7 20 17 ( ) ( ) ( ) w r a he orc m h h m h h m h h ε • • •  − + − =   −  (6) , orc r a w m mr m m • • • = + (7) • turbine power: 19 20 ( ) t orc t g w m h h η η • • = − (8) • pump power: 17 18 17 ( ) / p orc p w m v p p η • • = − (9) 18, 17 ( ) p orc a w m h h • • = − (10) • orc net power and thermal efficiency: net t p w w w • • • = − (11) net orc evap w q η • • = (12) c. desiccant cooling system the desiccant wheel is the main component of the dcs. the model developed in [27] is carried out in the present work to simulate the desiccant wheel. the related energy balance and governing equations for the components of dcs are given below. • combined potential of the desiccant wheel: ( ) [ ] 0.8624 1, 1.49 2865 4.344 / 1000 273.15 i i i f w t   = − +  +   (13) ( ) [ ] 1.49 0.07969 2, 273.15 1.127 / 1000 6360 i i i t f w  + = −     (14) • desiccant wheel's efficiency: 1,2 1,1 1 1,8 1,1 f f f f f η − = − (15) 2,2 2,1 2 2,8 2,1 f f f f f η − = − (16) the efficiencies of the desiccant wheel are considered to be at the high level and about 1f η = 0.05 and 2f η = 0.95 [28]. engineering, technology & applied science research vol. 12, no. 5, 2022, 9316-9328 9320 www.etasr.com fouda et al.: thermodynamic and performance assessment of an innovative solar-assisted … • energy and mass balances of the desiccant wheel: , 2 1 , 8 9 ( ) ( ) p a r a m h h m h h • • − = − (17) , 1 2 , 9 8 ( ) ( ) p a r a m w w m w w • • − = − (18) • heat exchanger: ( ) ( ), , 2 3 , , 7 6p a p ma r a p mam c t t m c t t− = − i i (19) ( ) ( ) , , 2 3 min 2 6 p a p ma he m c t t c t t ε − = − i (20) where min , , , ,min{ , }p a p ma r a p mac m c m c= i i . • direct evaporative coolers: 3 4 ( , ) 3 3, dec p a wb t t t t η − = − (21) 4 3 ( , ) 4, 3 dec p a ideal w w w w η − = − (22) 5 6 ( , ) 5 5, dec r a wb t t t t η − = − (23) 6 5 ( , ) 6, 5 dec r a ideal w w w w η − = − (24) • regeneration energy, space cooling capacity, and coefficient of performance: , , 8 7 ( ) in dcs r a q m h h • • = − (25) , 5 4 ( ) cooling p a q m h h • • = − (26) , cooling dcs in dcs q cop q • • = (27) d. humidification dehumidification system (hdh) the energy balance of the humidifier is given as: , 10 9 15 16 ( ) r a w brine m h h m h m h • • • − = − (28) where brine w makeupm m m • • • = − . the mass flow rate of the makeup water (sea or brackish water) supplied to the system is given as: ( ), 10 9makeup r am m w w • • = − (29) the energy balance of the dehumidifier is given as: , 10 11 14 13 12 ( ) ( ) r a w fresh m h h m h h m h • • • − = − + (30) ( ) ( ) , 14 13 min 10 13 w p w deh m c t t c t t ε − = − i (31) where 12 , 11p wh c t= and min , , ,min{ , }w p w r a p mac m c m c= i i . the condensate water mass flow rate leaving the dehumidifier is calculated as: ( ), 10 11fresh r am m w w • • = − (32) the gain output ratio for the system is given by: 15 14 , 9 1 ( ) ( ) fresh fg w r a m h gor m h h m h h • • • = − + − (33) e. system performance parameters and evaluation the euf of the proposed tri-generation and its corresponding basic system are expressed below: fresh fg cooling net ps evap m h q w euf q • • • • + + = (34) 15 14 , 8 7 ( ) ( ) fresh fg cooling net bs evap w r a m h q w euf q m h h m h h • • • • • • + + = + − + − (35) 15 14 , 8 7 , , , ( ) ( ) evap w r a sc bs t avg daily bsc q m h h m h h i a η • • • + + − + − = (36) for evaluating the system performance, the euf improvement and the saving in the area of the solar collectors can be expressed as: ps bs imp bs euf euf euf euf − = (37) , , , , sc bs sc ps sc sav sc bs a a a a − = (38) the system governing equations are solved by using c++ and ees to calculate the system performance and productivity parameters for different ranges of design and operating conditions as given in table i. table i. studied and operating parameter values parameter value turbine inlet temperature, t19 170-195°c ambient air inlet temperature, t1 25-45 o c ambient air inlet humidity, w1 12-20gv/kga sea water inlet temperature, t13 15-25 o c evaporation pressure of orc, p18 200-400kpa condensation pressure of orc, p17 5-20kpa orc fluid mass flow rate, m•orc 0.5-1.3kg/s mass flow rate ratio, mr 0.1-0.6 iv. model validation to approve the developed thermodynamic models in the present work and to determine their degree of accuracy, model validation is applied and the results of the current work are compared with those reported in the literature. the validation of the current thermodynamic models with previously published data in [27, 29, 30] for hdh, orc, and dcs subsystems is shown in figure 3. it can be seen that there is good agreement between the current study's results and those previously reported in the literature. engineering, technology & applied science research vol. 12, no. 5, 2022, 9316-9328 9321 www.etasr.com fouda et al.: thermodynamic and performance assessment of an innovative solar-assisted … fig. 3. validation of the present model with the previously published data for (a) hdh, (b) orc, (c) dcs. v. results and discussion a comprehensive parametric study was conducted to study the effects of operating parameters on the performance of the proposed tri-generation system. for this purpose, the effects of turbine inlet temperature (t19) of the orc, ambient air inlet temperature and humidity ratio (t1 and w1), evaporation pressure (p18) of the orc, condensation pressure (p17) of the orc and mass flow rate ratio (mr) on the main productivity and performance parameters (w • net, horc, m • fresh, gor, q • cooling, copdcs, t4, w4, eufps, and apsc) in addition to system assessment parameters (eufimp, asc,sav) are presented in figures 4-10. the other parameters remain constant when a certain operating parameter is changed, in order to examine its effect. the performance parameters of the tri-generation system are investigated and evaluated with n-octane as the working fluid in the orc. fig. 4. influence of t19 on the proposed system performance parameters. a. effects of turbine inlet temperature figure 4 shows the effects of turbine inlet temperature (t19) of the orc on the main productivity and performance parameters of the proposed tri-generation system. t19 is increased from the fluid’s saturated vapour temperature (170 o c) to the superheated temperature (195 o c). as shown in figure 4, increasing t19 raises w • net, m • fresh, and apsc. the increase of the orc turbine power, required input solar energy, and reject energy of the orc condenser with increasing t19, leading to the increase of orc net output power, required area of solar collectors, humidification capacity of the air in the humidifier, and space cooling capacity. also, the increase in heat input to orc, hdh, and dcs with increasing turbine engineering, technology & applied science research vol. 12, no. 5, 2022, 9316-9328 9322 www.etasr.com fouda et al.: thermodynamic and performance assessment of an innovative solar-assisted … inlet temperature, leads to the reduction of horc, gor, and eufps. it is found that the highest values of w • net, horc, m • fresh, gor, eufps, and apsc are 89.66kw, 15.03%, 57.23kg/h, 0.09634, 0.2466, and 1223m 2 respectively, while their lowest are 83.8kw, 14.5%, 53.26kg/h, 0.09246, 0.2391, and 1102m 2 . furthermore, increasing t19 from 170 o c to 195 o c increased net output power, fresh water productivity, and space cooling capacity by 7%, 7.5%, and 10.3% respectively. fig. 5. influence of t1 on the proposed system performance parameters. b. effect of air inlet temperature the effect of the air inlet temperature on the main productivity and performance parameters of the proposed trigeneration system are given in figure 5, which shows that as the air inlet temperature rises, the q • cooling, copdcs, and eufps decrease while t4 and w4 increase, due to the increased required regeneration energy in dcs with increasing air inlet temperature, while the heat rejected in the condenser of orc is fixed, leading to poor dcs performance. in addition, the highest obtained values of q • cooling, copdcs, t4, w4 and eufps are 25.64kw, 0.5146, 17.61 o c, 10.85gv/kga and 0.2516 respectively, while the lowest are 13.13kw, 0.3446, 14.02 o c, 8.354gv/kga and 0.2319, where apsc is kept constant at 1174m 2 . furthermore, the fresh water productivity, m • fresh, improved by 2.2% and the space cooling capacity, q • cooling, dropped by 48.9% with an increase of t1 from 25 o c to 45 o c. fig. 6. influence of p18 on the proposed system performance parameters. c. effect of evaporation pressure the influence of the orc evaporation pressure on the main productivity and performance parameters of the proposed trigeneration system is presented in figure 6. the increase of w • net, horc, copdcs, and eufps with the rise of the evaporation pressure can be seen. this occurs due to the decrease in heat input in the evaporator and heat reject in the condenser of orc and the increased output power of the turbine. figures 5(b)-(c) show the decrease of q • cooling and apsc with the increase of the evaporation pressure. this can be attributed to the decrease of input heat to the orc evaporator and the rejected heat from the condenser, which leads to a decrease in the humidification engineering, technology & applied science research vol. 12, no. 5, 2022, 9316-9328 9323 www.etasr.com fouda et al.: thermodynamic and performance assessment of an innovative solar-assisted … capacity of the air inside the humidifier and the fresh water yield in the dehumidifier. hence, lower fresh water production rate can be obtained. additionally, this reduces the regeneration energy of dcs and the required area of solar collectors. the highest obtained values of w • net, horc, q • cooling, copdcs, eufps, and apsc are 92.97kw, 15.8%, 20.05kw, 0.4469, 0.2524, and 1184m 2 respectively, while their lowest values are 87.34kw, 13.12%, 19.23kw, 0.4549, 0.2272, and 1164m 2 . furthermore, w • net improved by 6.4%, and m • fresh and q • cooling dropped by 3.2% and 4.2% respectively when p18 increased from 200 to 400kpa. fig. 7. influences of p17 on the proposed system performance parameters. d. effects of orc condensation pressure figure 7 shows the influence of orc condensation pressure (p17) on the proposed system performance and productivity parameters. w • net, horc, m • fresh, eufps, and apsc decrease as p17 increases. the reduction in net output power with increasing p17 is caused by the reduction in enthalpy difference across the turbine that leads to a reduction in orc thermal efficiency. decreasing the fresh water rate with rising condenser pressure is expected because of the reduced amount of heat recovered from the condenser to water and air streams before entering the humidifier, which lessens the amount of water evaporation and consequently reduces the amount of fresh water produced at the dehumidifier. the reduction in eufps is attributed to the reducing of w • net and m • fresh with increasing p17, which overcomes the reduction in the total input power of the system. the reduction in apsc with rising p17 is due to the reduction in the heat added to the evaporator at the same solar intensity input to the solar collectors. while figure 7(b) displays increasing gor with rising p17, the increase in gor is due to a decrease in both fresh water production rate and heating input power to the system that is needed to raise the temperatures of seawater and air to the humidifier inlet. the disadvantage of a decrease in fresh water production rate cannot compensate for the benefit of a decrease in system input power. it is observed that the highest w • net, m • fresh, and eufps obtained at p17 = 5kpa are 104.5kw, 56.9 kg/h, and 0.2582 respectively, while the apsc reduction is 11.98% when the condenser pressure increases from 5 to 20kpa. fig. 8. influence of mr on the proposed system performance parameters. e. effects of mass flow rate ratio figure 8 shows the influence of mass flow rate ratio (mr) on the proposed system performance and productivity parameters. figure 8(a) shows the decrease of m • fresh and gor with increasing mr. increasing mr means lowering both the air and seawater mass flow rates equally (i.e. m • a= m • w) while engineering, technology & applied science research vol. 12, no. 5, 2022, 9316-9328 9324 www.etasr.com fouda et al.: thermodynamic and performance assessment of an innovative solar-assisted … keeping m • orc constant and equal to 1kg/s, results in a lower rate of evaporation in the humidifier and a lower rate of condensation in the dehumidifier, and thus lower gor. figure 8(b) shows that q • cooling and copdcs increase with increasing mr until they reach their highest values and then they decrease with increasing mr. increasing mr has two opposing effects: i) it decreases the air mass flow rate and ii) it decreases the supply air enthalpy to the conditioned space, increasing the enthalpy difference across the conditioned space. as observed in figure 8(b), for mr=0.38, the increase in enthalpy difference across the conditioned space overcomes the reduction in air mass flow rate, which results in higher q • cooling and subsequently copdcs, and vice versa for mr>0.38. furthermore, mr=0.125 leads to negative cooling capacity, which isn’t recommended for cooling and dehumidifying applications through the conditioned space. it’s noticed from figure 8 that the maximum m • fresh and q • cooling obtained are 72.13kg/h and 19.7kw and m • fresh improved by 52.7% when mr dropped from 0.6 to 0.1. f. effects of ambient air humidity ratio figure 9 depicts the effects of ambient air humidity ratio (w1) variation with mr on the proposed system performance parameters. q • cooling, copdcs, and eufps increase with increasing mr until they reach their highest values, and then they decrease with increasing mr for any w1. also, it is found that they drop with increasing w1 for any mr. increasing w1 for the same mr increases the enthalpy of supply air, which reduces the air enthalpy difference through the conditioned space, which adversely effects the conditioned space cooling capacity as well as copdcs as seen in figures 9(a)-(b). moreover, the system operation conditions with mr less than 0.11, 0.15, 0.2, 0.25, at w1 = 14, 16, 18, and 20gv/kga respectively, are not recommended for cooling and dehumidifying applications due to the negative cooling capacity for the conditioned space. furthermore, the highest values of q • cooling that can be obtained are 26.46, 21.65, 17.93, 14.97, and 12.47kw at mr = 0.2667, 0.3222, 0.3778, 0.4889, 0.5444, and w1 = 12, 14, 16, 18, and 20gv/kga respectively. while increasing w1 causes a decrease in eufps because total system power output decreases when compared to the total system input power. increasing w1 causes a decrease in q • cooling and an increase in m • fresh but w • net doesn’t change, and the increase in m • fresh can’t compensate for the reduction in q • cooling, which results in an adverse effect on eufps as shown in figure 9(c). at mr= 0.19, 0.24, 0.2667, 0.3222, 0.3778, and w1= 12, 14, 16, 18, and 20gv/kga, the optimum eufps values are 0.2643, 0.2526, 0.2435, 0.2356, and 0.2286. additionally, w1 has no effect on the apsc due to the independence of w1 on the heating energy needed at the orc evaporator. g. system assessment and evaluation to the best of our knowledge there are no tri-generation systems for power generation, a/c, and freshwater production systems available in the literature using orc, dcs, and hdh combined integrated systems with the same operating conditions. therefore, the performance of the proposed system is compared with the performance of a basic tri-generation system in which the needed heating sources for the three subsystems are taken separately from one source (i.e. solar collector system) that gathers the whole three subsystems into one basic tri-generation system, and the used system performance parameters are eufbs and absc (see (34)-(35)). therefore, the proposed system can be evaluated and assessed at different significant influencing operating parameters (t19, p18, and p17) by using two important dimensionless performance and design parameters: energy utilization factor improvement, eufimp (36), and solar collector area saving asc,sav (37). as seen in figures 10(a)-(b), eufimp and asc,sav are enhanced with increasing t19 and p17, due to the prevailing total energy output increment and solar collector area reduction of the proposed system than the basic system with increasing t19 and p17, and the maximum values of eufimp that can be obtained are 68.4% and 69.9% at t19 = 195 o c and p17 = 20kpa. fig. 9. influence of w1 on the proposed system performance parameters at mr values. engineering, technology & applied science research vol. 12, no. 5, 2022, 9316-9328 9325 www.etasr.com fouda et al.: thermodynamic and performance assessment of an innovative solar-assisted … fig. 10. influences of studied system parameters on eufimp and asc,sav of the proposed tri-generation system. similarly, the maximum values of asc,sav that can be obtained are 40.62% and 41.14% at t19 = 195 o c and p17 = 20kpa respectively. in addition, figure 10(b) shows that increasing p18 has an adverse effect on eufimp and asc,sav due to the advantage of eufps increase and apsc reduction with rising p18 that can’t compensate for the increasing of eufbs and decreasing of absc that lead to decreasing eufimp and asc,sav with rising p18. table ii illustrates the different values for eufimp and asc,sav as system evaluation parameters for different operation and design parameters (t1, t13, m • orc, mr, w1) that have no variation effects on eufimp and asc,sav within their studied ranges. according to the table, the maximum eufimp and asc,sav obtained are 69.9% and 41.14% at t19 = 185 o c, p18 = 300kpa, and p17 = 20kpa, and the minimum values obtained are 66.7% and 40.01% at t19 = 185 o c, p18= 300kpa, and p17= 5kpa for all studied ranges of t1, m • orc, mr, and w1 . table ii. proposed system assessment and evaluation for different parameter values parameter t19 [ o c] p18 [kpa] p17 [kpa] eufimp [%] asc,sav [%] t1 (25-45 o c) t13 (15-25 o c) m • orc (0.5-1.3 kg/s) mr (0.1-0.6) w1 (12-20 gv/kga) 170 300 10 67.97 40.47 185 300 10 68.23 40.56 195 300 10 68.4 40.62 185 200 10 69.51 41.01 185 400 10 67.36 40.25 185 300 5 66.7 40.01 185 300 20 69.9 41.14 h. numerical correlations prediction the numerical results are regressed to obtain new numerical correlations for the proposed tri-generation productivity and performance parameters (w • net, m • fresh, q • cooling, t4, w4, apsc, and eufps) in terms of all studied design and operating parameters. the obtained correlations with their errors are shown in figure 11, and the presented correlations are valid in the ranges given in table i, and the values of t19,max, t1,max, t13,max, m • orc,max, w1,max, are 195 o c, 45 o c, 25 o c, 1.3kg/s, and 20 gv/kga respectively. fig. 11. numerical correlation predictions and their errors. vi. conclusion and recommendations in this article, an innovative combined orc, dcs, and hdh tri-generation solar-driven plant for electrical power, cooling, and desalinated water production was presented. the proposed system recovers the orc condenser heat to be used as a heating source and prime mover of the dcs and hdh sub engineering, technology & applied science research vol. 12, no. 5, 2022, 9316-9328 9326 www.etasr.com fouda et al.: thermodynamic and performance assessment of an innovative solar-assisted … systems. the proposed system's performance was evaluated and compared with the basic tri-generation system to find the optimum system operation conditions. the major concluding remarks of the current study are: • the proposed tri-generation system can produce electrical power and fresh water and carry out the space cooling load while keeping comfortable conditions inside the space. • the net output power increases with increasing turbine inlet temperature, orc evaporation pressure, and orc fluid flow rate, and it decreases with orc condensation pressure and does not affect ambient air inlet temperature, or mass flow rate ratio. • fresh water productivity improved with rising turbine inlet temperature and ambient air inlet temperature, while it decreased with mass flow rate ratio, orc condensation pressure, and orc evaporation pressure. • space cooling load is enhanced at higher turbine inlet temperature, orc fluid flow rate, and mass flow rate ratio and it decreases with increasing ambient air humidity ratio, orc condensation pressure, and orc evaporation pressure. • the proposed system can provide maximum electrical power, fresh water, cooling capacity, and energy utilization factor of 104.5kw, 72.37kg/h, 25.48kw, and 0.2421 respectively at t19 = 185 o c, t1 = 35 o c, w1 = 15gv/kga, t13 = 20 o c, p18 = 300kpa, p17 = 10kpa, mr = 0.4, and m • orc = 1kg/s. • with increasing t19 from 170 o c to 195 o c, net output power, fresh water productivity, and space cooling capacity improved by 7%, 7.5%, and 10.3% respectively. • m • fresh increased by 2.2% and space cooling capacity q • cooling decreased by 48.9% when t1 increased from 25 to 45 o c. • increasing p18 from 200 to 400kpa, m • fresh and q • cooling dropped by 3.2% and 4.20% respectively. • mr should be 0.21 at w1 = 15gv/kgda for cooling applications because the supply air humidity ratio (w4) should be equal to or less than the room humidity ratio (w5 = 12gv/kga). moreover, the system operation conditions with mr less than 0.11, 0.15, 0.2, 0.25, at w1 = 14, 16, 18, and 20gv/kga respectively, are not recommended for cooling and dehumidifying applications due to the negative cooling capacity for the conditioned space. • the energy utilization factor increased as the orc evaporation pressure and mass flow rate ratio increased (for mr = 0.2667 at w1 = 15gv/kga), and decreased as the orc condensation pressure, ambient air inlet temperature and humidity, turbine inlet temperature, and mass flow rate ratio decreased. • the highest energy utilization factor attained is 0.2643 at t19 = 185 o c, t1 = 35 o c, t13 = 20 o c, p17 = 10kpa, p18 = 300kpa, m • orc = 1kg/s, mr = 0.19, and w1 = 12gv/kga. • with increasing turbine inlet temperature and orc condensation pressure, system evaluation performance parameters (eufimp and asc,sav) improved, but they dropped at higher orc evaporation pressure. at t19 = 185 o c, p18 = 300kpa, and p17 = 20kpa, the maximum eufimp and asc,sav obtained are 69.9% and 41.14% respectively. • finally, general numerical correlations obtained from the numerical data can predict the system’s productivity and system performance parameters with reasonable error. experimental and transient analyses using more heat recovery approaches are recommended as future work for the proposed system. acknowledgement this work was funded by the university of jeddah, jeddah, saudi arabia, under grant no. uj-20-015-dr. the authors thank the university for the technical and financial support. nomenclature a cp f1, f2 hfg area, m 2 specific heat, kj/kg k combined potential, water latent heat of evaporation, kj/kg h it specific enthalpy, kj/kg total solar intensity, w/m 2 m • mass flow rate, kg/s q • t heat transfer rate, kw temperature, o c w w • humidity ratio, gv/kga power, kw β η ηf1, ηf2 ε τ tilt angle, o efficiency efficiency of the desiccant wheel effectiveness time, hours subscript a atm avg bs bsc cond evap air/dry air/actual atmosphere average basic system basic solar collectors condenser evaporator g hum he i= 1,2,3 imp in ma generator humidifier heat exchanger index referring to various positions of the desiccant system improvement input moist air v reg r,a p,a p ps psc sc sav water vapour regeneration return air process air pump proposed system proposed solar collectors solar collectors saving engineering, technology & applied science research vol. 12, no. 5, 2022, 9316-9328 9327 www.etasr.com fouda et al.: thermodynamic and performance assessment of an innovative solar-assisted … t w 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[30] e. galloni, g. fontana, and s. staccone, "design and experimental analysis of a mini orc (organic rankine cycle) power plant based on r245fa working fluid," energy, vol. 90, pp. 768–775, oct. 2015, https://doi.org/10.1016/j.energy.2015.07.104. microsoft word etasr_v12_n3_pp8611-8616 engineering, technology & applied science research vol. 12, no. 3, 2022, 8611-8616 8611 www.etasr.com sabah jarallah & mahjoob: supply chain management of infrastructure projects in iraq supply chain management of infrastructure projects in iraq dunya sabah jarallah civil engineering department college of engineering university of baghdad baghdad, iraq d.jarallah1101@coeng.uobaghdad.edu.iq ahmed mohammed raoof mahjoob civil engineering department college of engineering university of baghdad baghdad, iraq ahmed.mahjoob@coeng.uobaghdad.edu.iq received: 11 march 2022 | revised: 27 march 2022 | accepted: 28 march 2022 abstract-infrastructure projects take a long time, are complex, multidisciplinary, use different materials and products, and have high risk. these characteristics affect the process of supplying materials. the current paper studies the ability to improve the supply chain process and decrease its cost by identifying the factors that affect it. these factors are used as variables in the mathematical model, which is working under uncertain conditions when the consumption rate of materials is not constant. the information used in this model is obtained from building information modeling (bim) and geographical information system (gis) techniques and the genetic algorithm is utilized to determine the optimal supplier and the quantities of supplies for different materials. the case study used in this research is a concrete bridge. the obtained results show that the cost can decrease by about 28.2% by changing the supplier and the quantity of supplies. keywords-infrastructure projects; supply chain; bim; gis i. introduction supply chain is crucial for the successful completion of a construction project. construction supply chains are complex networks with various relationships of resources and product/service logistics, information, and money flows. furthermore, construction project planning and execution involve numerous participants from various organizations, necessitating intensive communication efforts to complete the project efficiently. a lack of adequate supply management in any construction project leads to cost and time overruns, claims, disputes, and low productivity, all of which can lead to project failure [1-4]. infrastructure is the backbone of the economy and a necessary input to every economic output. it is critical to a nation’s prosperity and the public’s health and welfare. infrastructure’s condition has a cascading impact on a nation’s economy, impacting business productivity, gross domestic product (gdp), employment, personal income, and international competitiveness [5]. governments invest huge amounts of capital in infrastructure projects, and programs. due to their complexity, large-scale, long duration, high investment, and longitudinal site conditions, infrastructure projects are exposed to higher risks than traditional construction projects [6, 7]. in infrastructure, poor coordination and supply chain management directly impact productivity and performance. due to the amount of information generated during the life cycle of projects and participants, they need precise regulations. new technologies are transforming the infrastructure design and construction industry. bim technology provides for the continuous sharing of a digital model that can manage the whole life cycle of a building project. recent research defines bim in many ways. bim is a product or an intelligent digital representation of a collection of structured data which defines a building project. it is a collaborative approach that improves project quality and efficiency by using open standards for information interchange. another definition of bim is that it is a facility management tool that provides a trustworthy, verifiable, transparent, and long-lasting knowledge base that can be used to run the facility throughout its life cycle. bim provides several benefits in the construction industry, such as increased productivity and efficiency, faster production and detailing, better support for automating operations, and less internal coordination errors. the use of bim effectively integrates the design and construction processes, resulting in better work quality, lower costs and faster project completion [8-12]. the i-bim (infrastructure building information modeling), [13-17] is an essential management information system for digital infrastructure processes. it is one of the most modern techniques used in the architecture, construction, and engineering (ace) sector [18, 19]. it monitors construction activities and manages construction supply chains [20, 21]. in addition to the i-bim technique, gis is considered one of the most important techniques in the supply chain. gis is a framework designed to collect, store, manage, and analyze geographic or spatial data. gis allows the representation of geospatial data for efficient collection, storage, sharing, and management. the general-purpose geodetic information system can work on the regular pcs, pdas, and on portable pcs and pdas, and even the versatile handhelds [22]. the integration of these techniques, will improve the performance of infrastructure [23-32]. corresponding author: dunya sabah jarallah engineering, technology & applied science research vol. 12, no. 3, 2022, 8611-8616 8612 www.etasr.com sabah jarallah & mahjoob: supply chain management of infrastructure projects in iraq ii. methodology this paper aims to optimize the use of bim and gis in supply chain management for infrastructure projects. a. determining the factors that affect infrastructure project supply chain management the identified factors emerged from interviews with engineers working in infrastructure projects. the questions and answers are listed in table i. table i. interviews questions and answers question answer are the engineers responsible for the purchase process? no, the contractor is responsible. is there a planning process for managing the supply chain before starting the projects? no, the suppliers are identified according to the price and distance. are there some techniques or methods used in management? no when the supply process occurs, are there connections between the design and supply process? yes, it depends on the design element to supply the materials. are there criteria for selecting suppliers except from price? price and distance. how are the import deals conducted? before the start of the project. are there any material tracking processes? yes, the quantity of materials is checked when the storage level becomes zero. what is the way of the movement of the material on the site? what factors affect the level of inventory on-site? not uniform, depends on the work performance. how do the circumstances surrounding the projects affect the supply process? they lead to delay the process and stop the projects are all quantities of materials supplied at one time? depending on the quantity of materials. if the quantity is huge, it will be divided. does the time of activity affect the supply process? yes, but it did not take in the process. from table i, the emerging factors that have important effects are: • the number of supplies describes the timing of the materials. • nature of materials: various types of materials characterize the infrastructure projects. structural, mechanical, and electrical materials are used. the traditional methods deal with different types of materials in the same way, so we will show how the nature of materials can affect the process of supply chain management while focusing on structural materials. • performance in the site of projects: the performance of projects is a factor that cannot be easily calculated and is affected by many other factors. the supply chain affects it directly because the consumption rate of materials will change depending on the performance percentage. • deficiency in tracking the projects and incomplete information: infrastructure projects are big, generating huge information. tracking this information is complicated and leads to incomplete information transfer to the other participants. • design changes and absence of coordination. • collaboration and obligation between suppliers and the entity responsible for the project. • time of activity. b. selecting proper techniques the technique most used in supply chain management is gis, but with the development in the construction industry, bim has also become popular due to its ability to model and generate information. both techniques have particular use in the supply chain (figure 1), but using these techniques individually will not return a benefit, so integration between them is required. fig. 1. bim and gis benefits in supply chain management. c. identifying control parameters on the supply chain the most critical control parameter on the supply chain process is cost. the supply chain process includes the following types of cost: • the cost of ordering, which is connected to the preparation of a supplier's order, including the cost of placing the order and other associated expenses. • the delivery cost of transporting the materials from the manufacturer to the retailer supplier to the warehouse and then to the project site or from the retailer supplier to the warehouse and then to the project site. • purchase cost and holding cost, which are the costs of keeping the materials in the warehouse, the level of inventory of materials in the site, the time of activity, the delivery capacity and performance, and the consumption rate. these main factors generate the mathematical model. d. generating the mathematical model the mathematical model improves the supply chain management of infrastructure projects by decreasing the supply cost. the model in [20] is used in the manufacturing industry, and modified in construction projects. it is subject to the following assumptions: • the total material quantity is known. • the planning horizon is long. • there is no lead time or the lead time is constant. engineering, technology & applied science research vol. 12, no. 3, 2022, 8611-8616 8613 www.etasr.com sabah jarallah & mahjoob: supply chain management of infrastructure projects in iraq • consumption rate is not constant, but varies with performance. the performance can be low, medium, or high. accordingly, the relationship between consumption rate and performance, can be also low, medium, or high. this relationship between performance and consumption will directly affect the inventory level in the site and warehouse, as shown in figure 2. (a) (b) fig. 2. material movement when the consumption rate (a) is constant and (b) varies. the mathematical model is described in (1)-(4): co � r ∗ n (1) where co is the ordering cost, r the ordering cost rate, and n is the optimal number of deliveries and orders. cd � n ∗ dd ∗ df (2) where cd represents the delivery cost, dd is the delivery distance form supplier to the site of project, and df is the delivery fee per km for each material. cm � q ∗ p (3) where cm is the material cost, q the quantity of the material, and p the unit price for the material. ch � � q/ne� dt � � ∗ ci (4) where ch is the holding cost, t the duration of activity (time), and ci is the inventory cost rate, which is proportional to the inventory level. the final mathematical model will be: minimize � � co� cd �cm � ch (5) subject to: q/n ≤ i q/n ≤ c i≥cr where c is the capacity of deliveries of each supplier, i is the level of material on site inventory, and cr is the consumption rate of the materials in site. the first condition means that the quantity of the supply divided by the number of suppliers must be less than the level of product in the site, while the second condition means that the quantity of the supply divided by the number of supplies must be less than the capacity of the supplier in order to avoid supply shortage. the third condition means that the level of the product in the site must be less than the consumption rate in order to avoid work halt. iii. case study al-mufraq bridge is a concrete key infrastructure project in diyala region. any change in plans, project halt, difference in cost, change of orders, etc. will not affect only this project, but will cause problems to the people that live in this region. information regarding this project can be seen in table ii. the project modeling in revit software can be seen in figure 3. table ii. al mufraq bridge information name al-mufraq bridge location west of diyala coordinates 33.74222, 44.61383 project start 2011 project end 22/4/2014 project cost $17032145 million description the main bridge body length is 450m long and 31m wide, with 4 lobes 150m long and 7m wide. main and right roads are approximately 2km. the number of piles is 304. obstacles the biggest problem was that the bridge roads were located within private property, so one of the road works was stopped. the works also stopped for days due to the delayed delivery of supply materials. (a) (b) (c) (d) fig. 3. (a) piles, (b) girder, (c) column, (d) the bridge. engineering, technology & applied science research vol. 12, no. 3, 2022, 8611-8616 8614 www.etasr.com sabah jarallah & mahjoob: supply chain management of infrastructure projects in iraq table iii. information about pile elements from bim-gis bim information gis information user information q (number) p ($) t (months) i (number) s (supplier) df ($/km) dd (km) r ($) ci ($) c (number) 304 2500 152 50 s1 1.2 577 30 0.3 2000 2333 s2 2.5 67 35 750 2667 s3 2.3 72 30 750 2667 s4 3.7 182 32 1000 2333 s5 3.1 215 30 2000 cr 15 piles per month (a) (b) (c) (d) fig. 4. relationship between z and n for different pile suppliers by using ga. table iv. cost of piles for various suppliers s n z ($) s1 23 794140 s2 44 727310 s3 45 828530 s4 23 844500 s5 24 742750 iv. results and discussion the piles are some of the most important elements in the bridge. the piles are responsible for a large part of the cost of the project, so they are used to test the final mathematical model. the information about the bridge is taken from bim. the information about the location of the project and the suppliers is taken from gis, as illustrated in table iii. the mathematical model was solved by using the ga in matlab. the results are illustrated in table iv and figure 4. the results show that supplier s2 has the least z value with n equal to 44 deliveries. this means that the piles should be supplied 44 times to the site to decrease the entire cost and then compare it with the real cost of piles in projects which is 1013333$. the saving in cost will be 286023$. the second material considered is the girder (table v). its information will be the input for the final mathematical model, which was solved by using the ga in matlab. the results are illustrated in table vi and figure 5. table v. information about girders from bim-gis q (m.l) 6616.222 p ($) 400 450 450 420 435 s s1 s2 s3 s4 s5 t (months) 2 i (m.l) 900 df ($/km) 1.2 2.5 2.3 3.7 3.1 dd (km) 577 67 72 182 215 r ($) 30 35 30 32 30 ci ($) 0.42 c 36000 30600 34200 36000 28800 cr 800 m.l per month engineering, technology & applied science research vol. 12, no. 3, 2022, 8611-8616 8615 www.etasr.com sabah jarallah & mahjoob: supply chain management of infrastructure projects in iraq table vi. cost of girders for various suppliers s n z ($) s1 8 2654500 s2 9 2981100 s3 9 2981000 s4 9 2787100 s5 8 2885800 the results show that the supplier s1 has the least cost with n=8, which means that the process of supply girders will be conducted 8 times during the construction in order to decrease the whole cost of supply. when it is compared with the real cost (2940000$), the savings in cost will be 285500$. (a) (b) (c) (d) (e) fig. 5. relationship between z and n for different girder suppliers by using ga. v. conclusion this study sought the ability to improve the material supply process for infrastructure projects by decreasing the supply cost through selecting the optimal supplier and the optimal number of deliveries. the factors that have effect on the process were identified and were the considered variables of the mathematical model. bim and gis were used to obtain needed information such as quantity, timeline, costs (bim), and the locations of the project and possible suppliers along with the distance between the suppliers and the projects site (gis). the mathematical model was solved with the ga. it was found that the supply process is not connected just with the cost of materials or with the distance, but there are other factors that engineering, technology & applied science research vol. 12, no. 3, 2022, 8611-8616 8616 www.etasr.com sabah jarallah & mahjoob: supply chain management of infrastructure projects in iraq should be taken into consideration, such as the time of activity, consumption rate, type of materials, design details, and correct information about the project. the traditional methods can't cover the supply process in infrastructure projects and the need to use more modern techniques, such as bim, gis, and artificial intelligent is evident. references [1] a. rezahoseini, s. noori, and s. f. ghannadpour, "integrated scheduling of suppliers and multi-project activities for green construction supply chains under uncertainty," automation in construction, vol. 122, feb. 2021, art. no. 103485, https://doi.org/10.1016/j.autcon.2020. 103485. 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[32] a. justo, m. soilan, a. sanchez-rodriguez, and b. riveiro, "scan-tobim for the infrastructure domain: generation of ifc-compliant models of road infrastructure assets and semantics using 3d point cloud data," automation in construction, vol. 127, jul. 2021, art. no. 103703, https://doi.org/10.1016/j.autcon.2021.103703. microsoft word etasr_v13_n2_pp10478-10482 engineering, technology & applied science research vol. 13, no. 2, 2023, 10478-10482 10478 www.etasr.com baali et al.: an experimental study of the influence of carburizing treatment holding time on the … an experimental study of the influence of carburizing treatment holding time on the structure and hardness of 16nc6 steel selma baali department of mechanical engineering, med boudiaf university, algeria | laboratory of materials and mechanics of structure (lmms), university of m'sila, algeria selma.baali@univ-msila.dz (corresponding author) younes benarioua department of mechanical engineering, med boudiaf university, algeria younes.benarioua@univ-msila.dz aboubaker essaddiq mazouz l2gegi laboratory, department of electrical engineering, university of tiaret, algeria aboubakeressaddiq@univ-tiaret.dz received: 13 january 2023 | revised: 17 february 2023 | accepted: 20 february 2023 abstract low carbon steel with carbon content ranging from 0.15% to 0.3% cannot be hardened through quenching and tempering processes and there is little to no martensitic transformation occurring upon quenching. to improve the surface hardness, carburizing is commonly employed. through this treatment, the surface composition of the low-carbon steel is altered by the diffusion of carbon, resulting in a hard outer casing with good wear resistance. this work investigates the effect of the carburizing treatment temperature and holding time on the crystallographic structure, hardness, and hardened surface layer dimension of commercial low-carbon steel 16nc6. the steel was carburized at 900°c for different holding times of 1, 2, and 3 hours. after the carburizing and quenching processes, the hardness values and the morphology of the crystallographic structure were measured and characterized. keywords-carburizing; quenching; low carbon steel; structure; hardness i. introduction heat treatment processes can be used to modify the surface and structural properties of low carbon steel in order to have a hard outer surface and a ductile and tough inner core, which is beneficial for engineering applications such as cams, gears, and shafts. these properties assist the resistance in wear and shock, thus extending the life of the component [1-3]. carburizing is an ancient thermo-chemical heat treatment used to harden the surface of low carbon steel by diffusing carbon into it. the steel typically must be subjected to quenching in order to achieve the desired hardness [4, 5]. carburizing is used to introduce carbon into the surface layer of steel. the process involves heating the steel in a carbon-rich environment, typically a carbon-rich gas or a bath of molten carbon-rich compounds, at a temperature above the steel's critical temperature. this allows carbon to diffuse into the surface layer of the steel, creating a hard, wear-resistant surface layer known as the case. the influence of carburizing treatment holding time on the structure and mechanical properties of low carbon steel can be significant. holding time is the time period that the steel is exposed to the carbon-rich environment during the process. a longer holding time will result in a deeper case and a higher carbon concentration in the surface layer, improving hardness, wear resistance, and other mechanical properties. however, it is important to note that holding time should not be too long, as excessive carburizing can lead to the formation of carbides and other undesirable structures. these structures can reduce the toughness and ductility of the steel and make it more brittle. as a result, it is important to carefully control holding time during the carburizing process in order to achieve optimal results. in summary, carburizing treatment can greatly improve the structure and mechanical properties of low carbon steel, but it is important to control holding time in order to achieve optimal results. the influence of holding time on the structure and hardness of low carbon steel is an important topic of research, and a deeper understanding of this relationship can engineering, technology & applied science research vol. 13, no. 2, 2023, 10478-10482 10479 www.etasr.com baali et al.: an experimental study of the influence of carburizing treatment holding time on the … lead to the development of better carburizing processes and more advanced materials [6-11]. this study aims to investigate the effects of carburizing treatment on low carbon steel and to produce cemented steel through this process. carburizing treatment involves exposing the low carbon steel 16nc6 to a carbon-rich environment for different periods, using holding time as a parameter. the study aims to examine how variations in carburizing treatment temperature and holding time affect the crystallographic structure, hardness, and dimensions of the hardened surface layer. in addition, the study seeks to provide insight into the chemical composition of the steel before and after carburizing treatment. the study aims to provide valuable information for industrial applications, such as the manufacturing of gears and other mechanical components. during the carburizing process, carbon diffuses into steel and reacts with iron to form iron carbide compounds. the study aims to examine the impact of carburizing time and temperature on the transformation rate of low carbon steel into cemented steel layers. optical microscopy was used to analyze micrographs of the samples and the thickness of the carburized areas, and micro vickers was used to measure the microhardness of cross-sectional samples of the cemented steel [11-16]. ii. materials and experimental method the low carbon steel used in this study was procured from the local market (afnor 16nc6) and underwent chemical analysis according to astm e 415-99a using spectroscopic methods. the results showed that the chemical composition of the steel, in weight percent, was: 0.17% c, 0.26% si, 0.67% mn, 0.92% cr, 1.2% ni, 0.027% mo, and 0.228% cu. the samples were machined into cylindrical shapes with 18mm diameter and 5mm length. to prepare the samples for carburizing, all specimens were mechanically polished to reduce roughness to a level of ra = 0.25μm, using sandpaper. the steel substrates then underwent pack carburizing treatment at various parameters. the samples underwent carburizing at a temperature of 900°c for time periods of 1, 2, and 3 hours. after carburizing, the specimens were immediately quenched in oil and tempered at a low temperature to further improve their behavior. after the carburizing treatment, the crosssectional samples were prepared and polished. these samples were etched in a solution consisting of 100ml water, 2ml of 40% hf, and 5ml of 30% h2o2. this type of etching is widely used to highlight the different zones of cemented steel [9-18]. a zwick roell microscope was used to examine the metallographic preparation and observe the morphological details and thickness of the cemented layers. the hardness profile of the samples was measured across the cross-sections using a zwick roellmicroindenter with a load of 500gf. iii. results and discussion a. structure figure 1 displays the optical micrographs of the microstructure of the steel before undergoing the carburizing treatment. figures 2-4 display the optical micrographs of the microstructure after undergoing carburizing at 900°c and quenching for each holding time treatment. fig. 1. microstructure of the steel before the carburizing treatment. (a) (b) fig. 2. micrograph after carburizing at 900c° and quenching for 1h. (a) surface zone,(b) inner area. figure 2 displays the micrographs of the surface zone and inner area of steel that was carburized for 1 hour at 900°c. in this case, the thickness of the cemented steel region was estimated to be 1mm and was divided into an outer zone of approximately 0.5mm and an inner diffusion layer of 0.5mm. figure 3 displays the micrographs of the steel that was carburized for 2h at 900°c. the thickness of the cemented steel region was estimated to be 1.4mm and was divided into an outer zone of approximately 0.7mm and an inner diffusion layer of 0.7mm. engineering, technology & applied science research vol. 13, no. 2, 2023, 10478-10482 10480 www.etasr.com baali et al.: an experimental study of the influence of carburizing treatment holding time on the … (a) (b) fig. 3. micrograph after carburizing at 900c° and quenching for 2h. (a) surface zone,(b) inner area. (a) (b) fig. 4. micrograph after carburizing at 900c° and quenching for 3h. (a) surface zone, (b) inner area. figure 4 shows the micrographs of the steel that was carburized for 3h at 900°c. in this case, the thickness of the cemented steel region was estimated to be 1.9mm and was divided into an outer zone of approximately 0.9mm and an inner diffusion layer of 1mm. as observed, the diffusion of carbon atoms to the surface of low steel leads to the formation of new phases with carbon atoms in the surface area. a martensitic microstructure is evident in the surface zone of the samples, and the temperature has the most significant effect on the structures and the development of the carburized layer. the thickness of the carburized zone of steel increases when the treatment holding time increases. b. chemical composition for each treatment holding time, the sample underwent chemical analysis according to astm e 415-99a using spectroscopic methods. the results, shown in table i, indicate the chemical composition of the steel in weight percent. table i. chemical composition after carburizing c % si % mn % cr % ni % mo % cu % 1h 0.63 0.25 0.65 0.91 1.188 0.031 0.222 2h 0.81 0.26 0.64 0.90 1.17 0.028 0.232 3h 1.03 0.27 0.63 0.90 1.22 0.029 0.225 c. hardness figures 5-7 show the hardness versus depth for steel carburized at 900°c for 1, 2, and 3 hours and figure 8 summarizes the results. in figure 8, it is observed that the hardness profile curve has three regions. the first region, corresponding to the outer layer, has a very high hardness due to the formation of hard martensitic compounds and new iron carbides during the carburizing treatment. the second zone, corresponding to the diffusion zone, exhibits a decrease in hardness values, which can be attributed to the reduced rate of carbon diffusion into the steel substrate. the third zone has a fixed hardness value, corresponding to the hardness of the steel substrate. fig. 5. hardness of steel carburized at 900°c for 1h. engineering, technology & applied science research vol. 13, no. 2, 2023, 10478-10482 10481 www.etasr.com baali et al.: an experimental study of the influence of carburizing treatment holding time on the … fig. 6. hardness of steel carburized at 900°c for 2h. fig. 7. hardness of steel carburized at 900°c for 3h. fig. 8. hardness of steel carburized at 900°c for 1, 2, and 3 hours. iv. conclusion based on the results and the analysis presented in this study, the following conclusions can be drawn:  the carburizing treatment of low carbon steel can effectively increase the surface hardness and produce a hardened layer, which is composed of a combination of martensite and expanded austenite.  the hardness of the carburized layer increases with increasing treatment holding time, with the thickness of the layer also increasing with time.  the crystallographic structure of the carburized layer is greatly affected by the temperature and holding time of the carburizing treatment, with a transition from ferrite and pearlite to martensite and new iron carbides observed in the outer layer.  the chemical composition of the steel is also affected by the carburizing treatment, with increase in the percentage of carbon observed after treatment.  the carburizing treatment provides a useful method for improving the wear resistance and durability of low carbon steel components, particularly in applications where high hardness and resistance to wear are critical. overall, this study provides valuable insight into the effects of carburizing treatment on low carbon steel, with important implications for industrial applications such as the production of gears and other mechanical components. it is recommended that further research should be conducted to explore the optimization of the carburizing treatment temperature and holding time in order to improve the hardness and crystallographic structure of the carburized steel. in addition, it would be interesting to investigate the impact of different quenching methods on the hardness and structure of the carburized steel. furthermore, it would be valuable to evaluate the performance of carburized steel in various applications, such as wear resistance and corrosion resistance, to fully understand the benefits of this treatment for practical use. references [1] m. ramadan, "interface structure and elements diffusion of as-cast and annealed ductile iron/stainless steel bimetal castings," engineering, technology & applied science research, vol. 8, no. 2, pp. 2709–2714, apr. 2018, https://doi.org/10.48084/etasr.1856. 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[18] s. k. alias et al., "mechanical properties of paste carburized astm a516 steel," procedia engineering, vol. 68, pp. 525–530, jan. 2013, https://doi.org/10.1016/j.proeng.2013.12.216. microsoft word etasr_v13_n2_pp10372-10376 engineering, technology & applied science research vol. 13, no. 2, 2023, 10372-10376 10372 www.etasr.com abdulla et al.: traffic accident traits and driver characteristics implication on road accidents using … traffic accident traits and driver characteristics implication on road accidents using descriptive analysis: a cross sectional study in sulaymaniyah, iraq raza abdulla college of commerce, university of sulaimani, iraq raza.abdulla@univsul.edu.iq (corresponding author) bakhtiyar qader sulaimani medicolegal institute, general directorate of health, iraq bakhtyar88@gmail.com karwan sdiq department of awareness and media, general directorate of traffic, iraq karwan.sdiq@gmai.com received: 7 january 2023 | revised: 26 january 2023 | accepted: 1 february 2023 abstract the current study focuses on disclosing the types and causes of traffic events in the sulaymaniyah governorate and their association with driver implications. the study was conducted between september 2019 and august 2020 in cooperation with the general directorate of traffic. a total of 573 traffic accident forms were directly collected at the site of crush events. the result shows that the collision type of road traffic accidents (rtas) is the most frequent type, accounting for 64.6% of the total. higher incidence of rtas was recorded in pickup, taxi, and motorcycle automobiles than in private cars. the analysis showed that the driver's faults are responsible for 81.4% of rtas followed by road issues, mechanical car faults, and environmental factors which were responsible for 15%, 2.4%, and 1.2%, respectively. the most important driver factors accountable for rtas were overspeeding, low level of education, gender, young age, and alcohol intake. driver age group 19-33 is highly associated with rtas with the peak occurring at the age of 21 years. keywords-road traffic accidents (rtas); drivers; risk factors i. introduction sulaymaniyah is one of the biggest cities in iraq and the occurrence of transportation accidents is frequent. officially, the total number of wheeled motor vehicles, excluding motorbikes, registered at the general directorate of traffic in sulaymaniyah governorate is around 600000, thus approximately 1 in 10 people own a car [1]. despite great efforts to reduce and control road traffic accidents (rtas), they are still considered a major issue, due to the increasing daily occurrences and their severity [2]. following the african region, the eastern mediterranean region was classified by the world health organization as having the highest number of fatalities due to road mishaps in the world. among eastern mediterranean counties, iraq is in the top two of the list of rta-related fatalities [3]. alertly, the ministry of health in the kurdistan regional government reported that rtas are regarded as the most common cause of citizen deaths. each year, traffic crushes cause approximately 850 deaths and 10,000 injuries [4]. furthermore, the statistical data of sulaymaniyah medicolegal institute showed that rtas are the most common type and the leading cause of civilian deaths. the causative risks of rtas can be broadly categorized as human, vehicle, and environmental factors [5, 6]. age, sex, education, medical conditions, and driving speed are key human-related factors, while environmental causes involve defective and narrow roads, poor lighting, lack of familiarity, and bad weather [1, 7-10]. authors in [7, 11] confirm that human errors comprise the major cause of rtas. driving speed is considered as a potential causative factor or rtas engineering, technology & applied science research vol. 13, no. 2, 2023, 10372-10376 10373 www.etasr.com abdulla et al.: traffic accident traits and driver characteristics implication on road accidents using … [12]. the environmental factors are the least participating risk of rtas and are responsible for only about 5% of rtas [1, 7, 9]. the aim of this study is to present an overview of rtas in sulaymaniyah governorate and analyze the role of drivers' contribution to the occurrence of rtas. ii. methodology a. study area sulaymaniyah was selected as the study area for several reasons: it is the biggest touristic city of iraq and has a very large concentration of urban population. geographically, the city is surrounded by four mountains and has a semi-arid climate with very hot dry summers and cool wet winters. the city was visited by more than 750,000 tourists in 2021 [13]. b. data collection the case study was conducted in the sulaymaniyah governorate from september, 2019 to august, 2020 including the period of covid-19 lockdown from march to july. a questionnaire was developed and administered in people involved in rtas in the governorate. the questionnaire form used included a diagram of the accident and information about the location, the date and time, weather conditions, car type and model, the sex and age of the people involved, the cause and the type of the accident, the type and license number of the drivers, the type of road, and the number of injuries and/or deaths. a copy of the accident report was stored in nearby traffic police stations. all forms were filled by trained traffic police personnel. the completed forms were transmitted to the department of forensic medicine for analysis. the questionnaire can be seen in the appendix. c. data analysis during the pre-processing stage, wrong and missing values in any section of the filled form were dealt with. records with inappropriate or incomplete values were removed from the dataset. in addition, during the analysis for the cause of accidents, uninsured cases or cases not categorized in the major causative factors were excluded. spss program (ver.23.0) was used to analyze the data. descriptive analyses were achieved calculating frequency, percentage, and cross tabulations. iii. results and discussion rtas are caused most probably by increased car ownership rate, lack of road discipline, and improper roadway features. throughout the study period, 573 rta cases were collected and analyzed. we can see from figure 1 that the most common type of rta is collision, which accounted for 64.6% of the total number of accidents and the least is road departure accounting only for 4.0%. the second most common type of rtas is rollover, while run over (pedestrian impact) and fixed object collision have almost the same rates. roughly, the findings of [4], which was conducted in the north iraq (including sulaymaniyah), are almost similar to our results except for fixed object collision that was not considered. fig. 1. the investigated types of rtas. table i. vehicles type involved in rtas variables frequency (%) number of vehicles one 225(39.5) two 348 (60.5) total 573 (100) vehicle type private 474 (51.5) taxi 121 (13.1) pickup vehicle 129 (14.0) truck 79 (8.6) motorcycle 101 (11.0) government vehicle 18 (1.9) total 921 (100) table i presents the number and the type of vehicles participating in rtas. in 474 (51.5%) of rtas, private cars, the primary type of personal transportation, were involved, which is considered as a rationally normal percentage because the number of private cars is 12 times more than the other types of automobiles on sulaymaniyah roads [14]. this is consistent with the findings in [7], which was conducted in the capital. compared to other types of vehicles, accidents resulting from pickup cars are higher, account for approximately 14.0% of the total. on the other side, taxis were involved in 13.1% of the cases. this may be interpreted from the fact that taxis tend to be more time on the road than the other car types. according to police traffic data, the ratio of motorcycles in all sorts of vehicles is roughly 2% [14]. surprisingly, the percentage of motorcycles participating in rtas is quite bigger (11.0%) and can be regarded threatening, and may be related to the divers' age, since most of motorcyclists are under 19 years old [3]. authors in [15, 16] pointed out that motorists have the primary contribution to road crashes during the recent years. the current investigation showed that 8.6% of rtas happened in trucks and that governmental vehicles participated in the least accidents (1.9%), which can be explained by the fact that they spend less time on roads and take more responsibility during driving. figure 2 shows the percentage of accidents considering causative factors. the reasons for mishaps can be divided into drivers, roads, vehicles, and weather condition faults. the investigated data of this study depicted that the human factor is responsible for 81.3% of traffic events. this finding is very close to the ones of [4, 7, 17]. engineering, technology & applied science research vol. 13, no. 2, 2023, 10372-10376 10374 www.etasr.com abdulla et al.: traffic accident traits and driver characteristics implication on road accidents using … fig. 2. causes of rtas. the second most highly ranked causal factor for rtas is vehicle faults. absence of standard support and lack of periodic vehicle maintenance are the main possible factors for car faults that prompt unexpected malfunctions [4, 18]. furthermore, it is revealed that weather and road mishaps account for 2.4% and 1.2% of rtas, respectively, indicating that adequate engineering and proper roadway structure and control of roads by traffic police play a positive role in reducing the number of rtas, although it has been reported that road status is a basic risk factor of accidents [18, 19]. additionally, minimal causative error is caused by environmental effects (1.2%) expressing that seasonal changes of sulaymaniyah weather did not have a great impact on rtas in general. the present study confirmed similar findings that the drivers have the largest contribution to the occurrence of accidents [11]. therefore, the most significant attributing risk factors related to driver errors were further investigated. table ii. contributing risk factors related to drivers variable frequency (%) gender male 880 (95.6) female 41 (4.4) education status illiterate 384 (41.7) basic school 362 (39.3) preparatory school 100 (10.8) university or higher 76 (8.2) speed allowed speed 265 (28.8) high speed 656 (71.2) alcohol drinking yes 277 (30.1) no 644 (69.9) driving license yes 749 (81.3) no 172 (18.7) driving experiences (years) 1 to 5 386 (41.9) 6 to 10 346 (37.5) 11 to 15 98 (10.6) 16 and more 90 (9.8) the results in table ii show that some contributing risk factors of rtas, such as sex, level of education, speed, driving under the effect of alcohol, driving experience, and owing driving license. the percentage of female drivers in sulaymaniyah governate in 2020 is 14.7% according to traffic police data registration. accordingly, the ratio of male to female drivers is nearly 6 to 1. however, table ii shows that the percentage of male drivers participating in the investigated accidents is 95.6% with only 4.4% being female. this high percentage is in line with the findings in [20, 21]. the level of education has an important effect on rtas as can be seen in table ii, with the illiterate, or basic educated drivers taking the lion's share with the number of accidents declining with the increasing level of education. safety education for drivers regarding safe driving and proper vehicle maintenance should start at the student age [22, 23] the speed of a car plays an imperative role in the occurrence of all types of rtas [24]. the present study noted that the speed of 656 out of 921 vehicles at the time of mishaps exceeded the upper limited speed at the site of the event. accordingly, our recorded data validated the findings of [25], where over speeding was considered as the main risk factor of rtas. further, it is scientifically proved that driving under the effect of drugs, particularly alcohol, is highly dangerous, especially for young drivers [25, 26]. in iraq, the alcohol value allowed for driving is below 60gm/dl. this study found out that 30.1% of the tested drivers were under the effect of alcohol. driving experience was categorized in four groups as shown in table ii. the highest rate of rtas (41.9%) was recorded for drivers with less than 5 years of driving experience, suggesting that the young drivers are usually at a higher risk. meanwhile, the smallest number of accidents (9.8%) happened to drivers with more than 15 years of experience. similar findings were reported in [22]. moreover, 18.7% of drivers did not have a driving license. authors in [23] reported that a high proportion of rtas occurred to unlicensed drivers. fig. 3. age distribution of drivers in rtas. in terms of age, the driver age distribution in figure 3 shows that the bulk majority of the age of drivers participating to rtas ranges between 19 and 33 years, with the peak being 21. obviously, the conclusion that younger drivers are at higher risk of mishaps is evident. young drivers have less experience, are more active, and tend more to make more car trips for educational, occupational, and social purposes. this finding is compatible with [16, 20], and with what is globally recognized [27]. meanwhile, only a small portion of rtas occurred in drivers under the age of 18, which is in accordance with what is engineering, technology & applied science research vol. 13, no. 2, 2023, 10372-10376 10375 www.etasr.com abdulla et al.: traffic accident traits and driver characteristics implication on road accidents using … internationally found [3]. this result can be attributed to the fact that the drivers within this age group are not permitted to hold a driver’s license according to iraqi rules stating that the minimum age for getting a driver’s license is 18. notably, the number of rtas obviously declines with age, mainly due to the limited number of trips that individuals in this age group make [28]. (a) (b) fig. 4. frequency plots of rtas per (a) time (24h) and (b) day. the trend timeline in figure 4(a) displays a peak of rtas in midnight. the number decreases in early morning hours to its least record and after that increases to late afternoon with a rapid drop of events during the evening. finally the number of rtas roses steeply before levelling off at midnight. two peak time occurrences of maximum accidents were recognized at 16 and 21 hours with the only causative probability being that most people going back to home after work at around 16:00 and that as sulaymaniyah is a big city with many tourists and a good night weather, making many trips on the road during night-time is accustomed. previous conducted studies analyzed that the larger proportion of rtas happened during daytime [4, 7]. the contrary present study findings may be attributed to the night activities in sulaymaniyah. on the other hand, it is clearly visible from time plot that the minimum occurrence of rtas was recorded at the evening as this is logically the resting time of daily human activity. figure 4(b) provides an overview of the total number of rtas per days of the week. we can see that the frequency of rtas in working days is nearly the same with weekend days showing a bit higher percentage. the smallest number of rtas occurred on mondays. this finding is in contradiction with [29, 30] in which most rtas occurred on thursdays, because in sulaymaniyah region wedding tradition and funny trips are not confined in a specific weekday. iv. conclusion in this paper, focus was given on the causes and attributing risk factors in various types of rtas. during the study period car collision was the most common type of accident and road departure the least. consistent with previous research, our data confirm that driver-related factors were the main cause of rtas. driver errors are the most common cause of rtas, followed by defects in vehicles, poor road infrastructure, and bad weather. in particular, the focal point was to analyze the factors related to human causes of rtas. the most rtas occurred among illiterate drivers. accidents were nineteen times more likely in males than in females. moreover, less driving experience, driving under the effect of alcohol, and overspeeding are considered as the most crucial risk factors. rtas are skewed toward involving people in younger age groups. finally, surprisingly, the majority of crush accidents were recorded during fridays and night periods. as a proposal, rtas can be greatly reduced by proper education, raising awareness, and training of safety standards. acknowledgment the authors express their gratitude to the information technology and planning unit personnel of the traffic police and the policemen who directly participated in this study. appendix road traffic accident survey questionnaire this form will be fill by an allowed employee in departmental traffic bureau form no: date: part one: accident information information about the accident time: day: date: location: type of accident a. collision b. roll over c. road departure d. run over (pedestrian) e. run over (fixed object) cause of accident a. human b. road c. vehicle d. weather number of vehicles involved in the accident: amount of speed during the accident a. allowed speed b. high speed the weather during the accident: a. normal b. rain c. snowing d. frizzing road e. foggy number of people involved: number of casualties a. injuries b. deaths c. safe reason for being safe: a. seat belt b. car seat c. motor protective equipment part two: driver information gender: male female year of birth: which one of the following is your level of education: a. illiterate b. basic school c. preparatory school d. bachelor * please write down your degree (certificate) in education, if none of the above is applicable……………………………….….….. engineering, technology & applied science research vol. 13, no. 2, 2023, 10372-10376 10376 www.etasr.com abdulla et al.: traffic accident traits and driver characteristics implication on road accidents using … marital status: a. single b. married d. other do you have a job? yes no if your answer is yes: a. public sector b. private sector car type: model year of the car: did the driver have a driving license : yes no if your answer is yes, please answer the next two questions. years of driving experience: class of the driving license: was the driver under the influence of alcohol during the time of the accident? yes no was alcohol test done on the driver? yes no is the driver registered in any insurance company yes no is the car registered in any insurance company yes no if there were other cars involved, the same information was filled and for the other drivers. refrences [1] e. leidman, m. maliniak, a.-s. s. sultan, a. hassan, s. j. hussain, and o. o. bilukha, "road traffic fatalities in selected governorates of iraq from 2010 to 2013: prospective surveillance," conflict and health, vol. 10, no. 1, feb. 2016, art. no. 2, https://doi.org/10.1186/s13031-0160070-0. 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[28] e. m. choueiri, g. m. choueiri, and b. m. choueiri, "analysis of accident patterns in lebanon," in 4th international symposium on highway geometric design, valencia, spain, jun. 2010, pp. 1–24. [29] w. meteeb, "traffic accidents in the province of diyala to the years 2009 and 2010," diyala journal of human research, no. 50, pp. 511– 536, 2011. [30] h. mohammed, a. ahmed, and h. ahmed, "statistical analysis of traffic accidents locations using geographic information system in darbandikhan townkurdistan region of iraq.," international journal of scientific & engineering research, vol. 6, no. 5, pp. 1831–1843, may 2015. microsoft word etasr_v12_n6_pp9440-9444 engineering, technology & applied science research vol. 12, no. 6, 2022, 9440-9444 9440 www.etasr.com nguyen et al.: assessment of shear strength models of reinforced concrete columns assessment of shear strength models of reinforced concrete columns van-hoa nguyen department of civil engineering vinh university vinh, vietnam vanhoakxd@vinhuni.edu.vn ngoc-minh pham department of civil engineering vinh university vinh, vietnam minhkxd@vinhuni.edu.vn trong-cuong vo department of civil engineering vinh university vinh, vietnam cuongvqc@gmail.com duy-duan nguyen department of civil engineering vinh university vinh, vietnam duyduankxd@vinhuni.edu.vn received: 7 august 2022 | revised: 21 august 2022 | accepted: 26 august 2022 abstract-shear strength is a crucial parameter in designing reinforced concrete (rc) columns considering the effects of lateral loads such as wind or earthquakes. numerous design codes and published studies have proposed equations for calculating the shear strength of rc columns. however, a discrepancy exists between the calculated models and the experimental results. the aim of this study is to evaluate the calculated models for the shear strength of rectangular rc columns based on 735 data sets, obtained from the literature. six code-based and empirical models are investigated in this paper. the four code-based models include aci 318 (2014), csa (2014), eurocode 8 (2005), and fema 273 (1997), and the two empirical models are proposed by ascheim & moehle (1992) and sezen & moehle (2004). the shear strengths of rc columns are calculated for the six models using inputs from the experimental database. finally, the results are evaluated using statistical indicators, including coefficient of determination and root-mean-squared error. the results reveal that eurocode 8 (2005) is the best model, followed by sezen & moehle (2004) and canada csa (2014) since the results of those models are close to the experimental ones and shown to be more conservative than the others. keywords-design code; empirical formula; experimental data; rectangular rc column; shear strength i. introduction reinforced concrete (rc) columns are critical structural members in buildings and bridges. failure of these members can lead to the partial or total collapse of structures. the load bearing capacity of columns depends on their geometric dimensions, materials, detailing, or applied loads [1-3]. there are three typical failure modes of rc columns under lateral loads, including flexure, shear, and flexure-shear failure modes. flexure failure occurs when the lateral stiffness is reduced due to cracking and spalling of the concrete cover, yielding of the longitudinal reinforcements, and crushing of core concrete. meanwhile, the shear failure mode is governed if diagonal cracks are predominant. flexure-shear failure forms after yielding of rebars and is combined with shear failure. it should be noted that the shear failure mode is unexpected and it is avoided in designing columns, especially structures in earthquake-prone areas. shear strength is the most important parameter in the design of rc columns, specifically when considering the effects of lateral loads such as earthquakes or wind. currently, there are numerous design codes and published studies, which proposed equations for calculating shear strength of rc columns. typical design codes are aci 318 (2014) [4], csa (2014) [5], eurocode 8 (2005) [6], and fema 273 (1997) [7]. additionally, some empirical models were developed by some authors such as ascheim & moehle (1992) [8] and sezen & moehle (2004) [9]. however, a discrepancy between calculated models and experimental results is existing. therefore, it is necessary to evaluate the different calculated models based on a large experiment database. the aim of this study is to assess the different calculated shear strength models of rectangular rc columns, in which code-based and empirical-based formulas are considered. for that, an extensive database including 735 experimental results is collected from the literature. six calculated models are investigated, consisting of the four mentioned design codes [47] and [8-9]. it should be noted that the equation proposed in [8] is also used in asce/sei-41‐06 (2007) [10]. the shear strength of rectangular rc columns is calculated for the six models using the collected database. finally, the calculated results are evaluated using statistical properties comprising of the coefficient of determination and the root-mean-squared error. ii. calculated models of shear strength of rectangular rc columns in this study, we employed 6 typical equations for calculating the shear strength of rc columns, from current corresponding author: duy-duan nguyen engineering, technology & applied science research vol. 12, no. 6, 2022, 9440-9444 9441 www.etasr.com nguyen et al.: assessment of shear strength models of reinforced concrete columns design codes and well-known previous studies, as described in table i. table i. shear strength models considered in this study model equation aci 318 [4] � = 0.166 �1 + �.� �� �� ����� + ������� � is the axial load, �� is the gross cross-section area of the column, �� is the effective shear width of column section, � is the effective depth of the column, ��� is the compressive strength of concrete, �� and �! are the area and yield strength of transversal reinforcement, and " is the spacing of stirrups. (1) csa [5] � = min &��������� + ������� cot�; 0.25�����. �� = 0.9� � is the width of column section, � is a factor accounting for the shear resistance of cracked concrete, � is the angle of inclination of diagonal compressive stresses to the longitudinal axis of the column. (2) eurocode 8 [6] � = �0 + 1(�� + �� ) �� = 0.1645670.5; 100�8 9 �1 − 0.164;< &5; =� .� �� ���� �� = �>� (� − �′)�!� �0 = @abc= min (�; 0.55�� ���) �� = �� �, (� = 0.8ℎ) �8 is the longitudinal reinforcement ratio, 5 is the distance from the maximum moment section to the point of inflection (i.e. g/�) (3) fema 273 [7] � = 0.29� �1 + �.� �� ������ + ������� � is a coefficient depending on concrete weigh (= 1.0). 1 = 1.0 for low ductility demand. 1 = 0 for moderate and high ductility demand. (4) ascheim & moehle [8] � = 0.3 �1 + �.� �� 0.8�� ���� + ������� jkl(�mn) 1 = oaµ� , µ is the displacement ductility � = 0.8q (5) sezen & moehle [9] � = 1 rm.st�uv=/� w1 + m.s �t�uvx 0.8�� + 1 ������� � = y − cover 1 = 1 for µ < 2.0; 1 = 0.7 for µ > 6.0; 0.7 � 1 = 1.15 − 0.075µ � 1.0 for 2.0 � µ � 6.0 5 is the shear span, (i.e. the distance from the loading point to the boundary). (6) iii. collected database a significant database, which covers a wide range of scenarios, was collected to evaluate the calculated shear strength models. a total of 735 experimental data sets of rectangular rc columns were extensively collected from [1136]. figure 1 depicts the configurations and reinforcement properties of the rectangular rc column. it should be noted that ` is the column height, a and q are the width and depth of the column section respectively, and �8 and �b are the longitudinal and transversal reinforcement ratios respectively. the statistical properties of the experimental results are described in table ii. the frequency histograms of input parameters and failure modes of the 735 data samples are shown in figure 2. fig. 1. configurations and properties of rectangular rc columns. table ii. summary of the database input parameters input parameter c (mm) d (mm) e (mm) f (mm) gh� (mpa) gij (mpa) gik (mpa) lj (%) lk (%) m (kn) min 225 150 100 20 20 313 215 0.20 0.01 0.0 mean 1286 284 301 101 49 448 496 2.15 0.94 1130 max 3000 610 610 457 141 745 1470 4.50 4.00 5492 ny 647 109 115 77 27 77 222 0.69 0.94 1069 op� 0.53 0.38 0.38 0.76 0.55 0.17 0.45 0.32 0.99 0.95 iv. evaluation of the calculated shear strength of the rc columns to quantitatively evaluate the shear strengths calculated from models in table i, statistical parameters are employed including coefficient of determination (qc ) and root-meansquared error (qgnr). qc value represents the percentage of data close to the regression line. the higher the qc, the more the accuracy of the calculated model and vice versa. qgnr is used for quantifying the difference (error) between the calculated and the experimental value. the smaller the qgnr, the more the accuracy of the calculated model and vice versa. the definitions of qc and qgnr are described in (7) and (8). qc = 1 − �∑ (tuavu)wxuyz∑ (tuav{)wxuyz � (7) qgnr = t& |. ∑ (}~ − �~ )c|~� (8) where }~ and �~ are the test and calculated results of the ; sample, < is number of the samples of the database, �̅ is the mean of calculated results. b h l v p �h �l engineering, technology & applied science research vol. 12, no. 6, 2022, 9440-9444 9442 www.etasr.com nguyen et al.: assessment of shear strength models of reinforced concrete columns fig. 2. distributions of input database. figure 3 shows the comparison between the shear strengths of the rc columns calculated by the six models and the test results. the dash line represents the 1:1 line, while the red line is the regression. it can be seen that the models of ec8 , sezen & moehle, and csa provide a smaller scattering than others, and results are mostly under the 1:1 line. in other words, the calculated results are smaller than those of experiments. moreover, the results based on aci 318, fema 273, and ascheim & moehle have a bigger scattering. these deviations may are caused by the ductility ratio and the diagonal compressive force in the columns. table iii summarizes the calculated statistical parameters, i.e. qc and qgnr for the investigated models. additionally, the properties of the ratio ��=8��8=t� /�t��t , are also obtained, in which minimum (min), maximum (max), mean, standard deviation (sd), and coefficient of variation (cv) are determined. the results show that ec8 [6] is the most accurate model with the highest qc value (= 0.892) and the smallest qgnr (= 163kn). moreover, [9] and [5] are also good models with qc = 0.766 and 0.68, and qgnr = 185kn and 220kn respectively. besides, the mean values of ��=8��8=t� /�t��t of those models are smaller than 1.0, thus, the results calculated by [5, 6, 9] are conservative. it can be seen that the equations of [4, 7, 8] provide lower accuracy. based on the results, we suggest the use of equations of the models of [5, 6, 9] for calculating the shear strength of rectangular rc columns. fig. 3. comparison between the six calculated models and the test results. table iii. statistical properties for the evaluation of the shear strength of rc columns model �� rmse statistical properties of �h�jh�j��� /���f� min max mean sd cv aci 318 [4] 0.608 202 0.19 20.88 1.40 1.42 1.01 csa [5] 0.680 220 0.18 9.88 0.93 0.74 0.80 ec8 [6] 0.892 163 0.07 4.84 0.64 0.37 0.57 fema 273 [7] 0.448 238 0.07 19.62 1.15 1.33 1.15 ascheim & moehle [8] 0.476 251 0.21 35.78 2.14 2.41 1.13 sezen & moehle [9] 0.766 185 0.09 8.51 1.02 0.71 0.69 v. conclusions this study presents and analyzes six codeand empiricalbased models for the shear strength calculation of rectangular rc columns. a set consisting of 735 experimental data samples of rectangular rc columns was collected. the accuracy of the models is evaluated by statistical parameters. the following conclusions are drawn from the current study:  ec8 [6] is the most accurate model for estimating the shear strength of rectangular rc columns, followed by sezen & moehle [9] and csa [6]. 0 50 100 150 200 250 n u m b e r o f sp e c im e n s column height, l (mm) 0 100 200 300 400 500 n u m b e r o f sp e c im e n s section width, b (mm) 0 100 200 300 400 500 n u m b e r o f sp e c im e n s section length, h (mm) 0 50 100 150 200 250 300 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 n u m b e r o f sp e c im e n s longitudinal reinf. ratio, �l (%) 0 100 200 300 400 500 0 1 2 3 4 5 6 7 n u m b e r o f sp e c im e n s transversal reinf. ratio, �h (%) 0 50 100 150 200 250 300 350 400 n u m b e r o f sp e c im e n s spacing of transv. reinforement, s (mm) 0 50 100 150 200 250 300 350 400 0 20 40 60 80 100 120 140 160 n u m b e r o f sp e c im e n s compr. strength of concrete, f'c (mpa) 0 50 100 150 200 250 300 350 0 200 400 600 800 1000 n u m b e r o f sp e c im e n s yield strength of long. reinf., fyl (mpa) 0 100 200 300 400 500 n u m b e r o f sp e c im e n s yield strength of transv. reinf., fyh (mpa) 0 100 200 300 400 500 n u m b e r o f sp e c im e n s axial load, p (kn) y = 0.4654x + 99.676 r² = 0.6087 0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500 v c al c u la te ( k n ) v test (kn) aci 318 (2014) y = 0.4224x + 47.586 r² = 0.6802 0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500 v c al c u la te ( k n ) v test (kn) csa (2014) y = 0.6577x 16.833 r² = 0.8922 0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500 v c al c u la te ( k n ) v test (kn) ec8 (2005) y = 0.3959x + 82.514 r² = 0.4481 0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500 v c al c u la te ( k n ) v test (kn) fema 273 (1997) y = 0.685x + 158.83 r² = 0.4759 0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500 v c al c u la te ( k n ) v test (kn) ascheim & moehle (1992) y = 0.5019x + 62.468 r² = 0.766 0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500 v c al c u la te ( k n ) v test (kn) sezen & moehle (2004) engineering, technology & applied science research vol. 12, no. 6, 2022, 9440-9444 9443 www.etasr.com nguyen et al.: assessment of shear strength models of reinforced concrete columns  the equations of aci 318 [4], fema 273 [7], and ascheim & moehle [8] have a lower accuracy.  it should be noted that this study considered rectangular rc columns. for other rc column types, such as circular or hollow sections, further investigation is required. references [1] l. hamzaoui and t. bouzid, "the proposition of an ei equation of square and l–shaped slender reinforced concrete columns under combined loading," engineering, technology & applied science research, vol. 11, no. 3, pp. 7100–7106, jun. 2021, https://doi.org/ 10.48084/etasr.4048. 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[36] k.-k. choi, g. t. truong, and j.-c. kim, "seismic performance of lightly shear reinforced rc columns," engineering structures, vol. 126, pp. 490–504, nov. 2016, https://doi.org/10.1016/j.engstruct.2016.07. 060. microsoft word etasr_v12_n6_pp9802-9806 engineering, technology & applied science research vol. 12, no. 6, 2022, 9802-9806 9802 www.etasr.com tabet: the effect of a blast load from propane gas leakage on an rc structure the effect of a blast load from propane gas leakage on an rc structure a case study in batna, algeria mohamed tabet department of civil engineering faculty of sciences and technology university of abbas laghrour khenchela, algeria mohamed.tabet@univ-khenchela.dz received: 9 october 2022 | revised: 27 october 2022 | accepted: 30 october 2022 abstract-the knowledge of the way a gas explosion affects a structure is still in its development. in this study, structural analysis software was used to construct a simplified approach to predict the impact of a dynamic blast load (dbl) from gas leakage. during the explosion process, the overpressure distribution in a room is decomposed to maximum dynamic pressure point (dppmax), where the explosion damages the most the structure. the simulation of the dbl was compared with the real consequences of gas explosion with the phenomenological data of a case study in batna, algeria. the results show that the simulation reproduced by our modeling of the dbl at structural scale is in good agreement with a real explosion. the distribution of stresses and strains over time indicates that the gas explosion inside residential buildings affected the entire surrounding of the area of the blast. keywords-dynamic blast load (dbl); maximum dynamic pressure point (dppmax); propane; gas leakage; rc structure i. introduction the global demand for natural gas is expected to increase during the next five years [1]. gas leakage and explosion incidents have often happened inside buildings. 531 gas explosions were reported in china [2] and more than 52 more were observed during 2021 with the most devastating one documented in the city of batna, algeria. many theoretical and experimental studies have been conducted on the damage caused in buildings by dynamic explosive loads [3-5]. although an explosion from gas propane leakage in a building can only be modeled in the punctual point of pressure, empirical vce (vapor cloud explosion) models are best suited for such tasks. the tnt equivalent, the tno multienergy approach, and the baker-strehlow models explain the behavior of an explosion, although they cannot be directly applied to study gas explosion events at structural size. while the structural analysis of a structure damaged by a gas explosion has been understudied, the use of fem to analyze and calibrate experimental data to fulfill the necessary requirements for the comprehension of the behavior of explosion was successful [6]. machine learning models for predicting the compressive strength are developed to determine its optimal value [7]. a machine learning model can incorporate more data for its learning process by constant feeding with more parametric simulations that can eventually enhance the compressive strength of concrete that will be considered for the design of rc structure under a dynamic blast load. our objective is to study the dynamic characteristics of gas explosions. in order to properly integrate the dynamic blast load at the structural level, we must first understand the dynamic features of gas explosions. the pressure peak is numerically simulated for various proposed models that have been experimentally calibrated. in the meantime, the modeling results are compared with the aftereffects of an actual explosion. additionally, the structural properties of explosive overpressure (stress, strain, and deformations) are examined. as a case study we will look in an unfortunate incident occurred in a residential building in batna, algeria. as shown in figures 1-2, the ceilings, floor, interior, and exterior walls were blown away. crack patterns can be seen along with extreme damages to the beams and columns on the floor level from the blast of the explosion, thus confirming the motivation toward an investigation on the effect of the blast over the integrity and stability of an rc structure. fig. 1. indoor explosion scene in the city of fesdis, batna, algeria. corresponding author: mohamed tabet engineering, technology & applied science research vol. 12, no. 6, 2022, 9802-9806 9803 www.etasr.com tabet: the effect of a blast load from propane gas leakage on an rc structure fig. 2. the damage of the frame of the rc structural elements. ii. pressure-time history and pressure models the estimation of the strength of a blast is a difficult problem which can be overcome depending on the required accuracy and the available resources. blast loads are extremely complex phenomena characterized by a sadden increase to a maximum peak value of pressure and then decaying to atmospheric pressure [3] in microseconds or even milliseconds. the ambient pressure �� is the reference or zero pressure for the positive and negative pressure values. after the explosion, the blast wave front reaches a target point in time �� and reaches the peak incident pressure ��� which is the maximum positive pressure. then it promptly decays to the atmospheric pressure ��. researchers have been in search for models that can calculate the pso along with other parameters of shock wave for free air burst and surface burst scenarios. in this paper, we will focus on the surface burst models that mimic an indoors explosion. iii. surface burst models the latest developed models that can evaluate pso are summarized in table i. =e/ps0 is the tnt equivalent weight (kg), � is the stand-off distance (m), and � is the scaled distanced defined [7] below: � = �/(e/ps0) 1/3 (1) table i. models to evaluate pso model 1 pso= 0.6784 w/r 3 +0.294 w 1/2 /r 3/2 (2) newmark and hansen model model 2 pso = 1.059 [r/w 3 ] -2.01 (3) wu and hao model model 3 pso = 1.017 [r/w 3 ] -1.91 (4) siddiqui and ahmad model model 4 pso = 2.46 [r/w 3 ] -2.67 (5) ahmad et al. model model 5 pso = 1.026 [r/w 1/3 ] -2.67 (6) iqbal and ahmad model model 6 pso= 4.34 w -2.84 (7) badshah model the results for the same initial conditions are shown in figures 3-4. the ��� values diverge, which clearly indicates the particularity of each model developed for the specification of its own calibrated experiment. the values of the tnt equivalences as functions of overpressure for propane/oxygen were found in [9] and were calculated using the fitting coefficients shown in table ii. w = j � k ln z � l (ln z)� � m(ln z)� (8) table ii. fitting coeficients j k l m propane/oxygen 0.4580 0.2150 -0.1442 0.0292 propane 1.2020 1.2464 -0.6410 0.1034 iv. blasting dynamic load an explosion generates an imposed dynamic load on any object in its field. this blasting dynamic load is characterized by a rapidly reaching maximum peak value which then decreases as the blast wave decays. the net effect of the load depends both on the nature of the blast wave and on the geometry and construction of the object [9]. the blast is predicted by: v = � � πr� (9) ps= w . v . pi (10) pi=2.5 10 -6 .s.vi 2 (11) p(t) =4 . ps.[e(-t/√2)-e(-√2t)] (12) where vi is the blasting velocity, and s the density of the explosives. v. data used table iii. propane parameters propane g/cm 3 propane kg/m 3 blasting velocity v 347 explosive density s 0.493 493 fig. 3. the peak positive incident pressure (pso). as explained above, the results for the peak positive incident pressure (pso) are very diverse due to the calibration of each model to the chemical components proprieties of the explosion. the blasting velocity and explosion density of engineering, technology & applied science research vol. 12, no. 6, 2022, 9802-9806 9804 www.etasr.com tabet: the effect of a blast load from propane gas leakage on an rc structure propane (table iii) lead us to the inevitability of more exorbitated field experiment. authors in [10] experimentally proved that sequences of explosion of the propane air mixture give symmetrical flame propagation. after ignition, the flame speed increased quickly to 2384 m/s. two milliseconds (0.002s) later the flame reaches the end and stops propagating. fig. 4. dynamic blast load history for a 75m3 chamber filled with 90% propane and the model adopted in the current study. data from [10] were used and the results were compared with the results of other models. the significance of the right set of experiments to be used to oversee the dynamic blast of propane explosion was clearly shown. figure 4 indicates the difference in the proportionality of pso over time. table iv. propane parameters used in blast load calculations sensor peak pressure (kpa) sensor peak pressure (kpa) p1 29.76 p2 14.28 p3 15.39 p4 10.98 p5 25.45 p6 12.84 p7 10.85 p8 12.33 moreover, the setting of pressure sensors shows that the maximum dynamic pressure point ddpmax, as table iv indicates, is located on the frontal central of the faces of the explosion. vi. modeling approach of dbl the structural modeling approach of the phenomena is summarized below:  designate the explosive material, in our case propane (natural) gas and its flammable characteristics.  define the dynamic blast load (dbl) history expression that we are going to use for the assessments.  assign the dbl to the corresponding ddpmax. in the case of structural walls without openings, the ddpma will be in the center of the wall, for walls with openings (windows, doors), the ddpma will be located on the center of each edge of the opening surface.  define the dbl force in a structural analysis software (ex. autodesk robot structural analysis 2022) as time history analysis as the figure 5 show. fig. 5. location of the dbl force in the structure and time history analysis. vii. results and discussion our approach follows the results of [10] and replicates the propagation wave of the dbl. we can observe that the maximal displacement measured in the damaged structure as shown in figure 2 is 38cm in a principal beam. on the contrary, our simplified approached with the adopted vce model, gave 33cm displacement along the position of the punctual point of the peak pressure of the explosion as shown in figure 6(g). figures 7-8 indicate that the distribution and arrow orientation of stress show clearly that our model mimics to a certain degree the scale of the actual damage the structure has sustained. as figure 9 shows, the crack propagation pattern is similar to that of the adopted simplified approach, since the distribution of maximum stress resembles the propagated cracks from the blast. viii. conclusions the current study showed that all the considered models are specific to a type of an explosion rather than just a generalization of behavioral phenomena, hence the pso in all the developed models shows an empirical blast load, either for free air burst or for a surface burst, something that shows a large variation. the current paper is the first milestone toward the implementation of blast load in structural design with a suitable and simplified approach, showing similar results with the case study. brick masonry is a principal component in structural construction and infill material in many parts of the world. therefore, response of clay brick masonry against blast loading will be examined in the future. engineering, technology & applied science research vol. 12, no. 6, 2022, 9802-9806 9805 www.etasr.com tabet: the effect of a blast load from propane gas leakage on an rc structure (a) (b) (c) (d) (e) (f) (g) fig. 6. nodal and column /beam displacement for each incremental time. fig. 7. distribution of stress at the maximal peak pressure. fig. 8. arrow orientation of the stress. fig. 9. distibutionof the propagted cracks from the blast. 33cm engineering, technology & applied science research vol. 12, no. 6, 2022, 9802-9806 9806 www.etasr.com tabet: the effect of a blast load from propane gas leakage on an rc structure acknowledgment the assistance of azzeddine tamene subdivision of the housing department of the wilaya of batna, algeria in providing the expertise pictures of the explosion incidents is gratefully acknowledged. references [1] m. r. martins, g. f. m. de souza, and n. h. ikeda, "consequence analysis of a liquefied natural gas floating production storage offloading (lng fpso) leakage," presented at the asme 2011 30th international conference on ocean, offshore and arctic engineering, oct. 2011, pp. 291–298, https://doi.org/10.1115/omae2011-49396. [2] k. zuo, j. tang, y. zhang, f. wang, s. cha, and m. luo, "safety management efectiveness evaluation of indoor gas facilities based on se-dea," oil & gas storage and transportation, vol. 37, no. 5, pp. 486-492+532, 2018. [3] w. m. a. khalifa and k. f. o. el-kashif, "computational model for the evaluation of reinforced concrete silos subjected to thermal load," engineering, technology & applied science research, vol. 9, no. 4, pp. 4411–4418, aug. 2019, https://doi.org/10.48084/etasr.2874. [4] a. m. remennikov and t. a. rose, "modelling blast loads on buildings in complex city geometries," computers & structures, vol. 83, no. 27, pp. 2197–2205, oct. 2005, https://doi.org/10.1016/j.compstruc.2005. 04.003. [5] p. d. smith and t. a. rose, "blast wave propagation in city streets—an overview," progress in structural engineering and materials, vol. 8, no. 1, pp. 16–28, 2006, https://doi.org/10.1002/pse.209. [6] j. u. rehman, c. n. nguyen, t. a. nguyen, t. c. vo, t. k. nguyen, and v. q. nguyen, "prediction of the stress wave amplification factor of a spherical blast source using numerical simulations," engineering, technology & applied science research, vol. 12, no. 5, pp. 9395–9399, oct. 2022, https://doi.org/10.48084/etasr.5233. [7] y. almoosi, j. mcconnell, and n. oukaili, "evaluation of the variation in dynamic load factor throughout a highly skewed steel i-girder bridge," engineering, technology & applied science research, vol. 11, no. 3, pp. 7079–7087, jun. 2021, https://doi.org/10.48084/etasr.4106. [8] a. garg et al., "machine learning models for predicting the compressive strength of concrete containing nano silica," computers and concrete, vol. 30, no. 1, pp. 33–42, 2022, https://doi.org/10.12989/cac.2022.30.1. 033. [9] d. a. crowl and j. f. louvar, chemical process safety: fundamentals with applications fourth edition, 4th ed. boston, ma, usa: pearson, 2019. [10] f. heymes, l. aprin, p. slangen, p. lauret, e. lapebie, and antoine osmont, "an experimental study on vapor cloud explosion of propaneoxygen stoichiometric mixture," chemical engineering transactions, vol. 53, pp. 61–66, sep. 2016, https://doi.org/10.3303/cet1653011. microsoft word 2-581-ed.doc engineering, technology & applied science research vol. 5, no. 5, 2015, 854-859 854 www.etasr.com prasetia: the effectiveness of high quality supplementary cementitious materials for mitigating… the effectiveness of high quality supplementary cementitious materials for mitigating asr expansion in concrete with high alkali content irfan prasetia department of civil engineering faculty of engineering, lambung mangkurat university banjarmasin, indonesia iprasetia@unlam.ac.id abstract— alkali silica reaction (asr) is influenced by external factors such as the surrounding environment of high alkalinity. countries with cold climate have a high probability to be exposed to high concentrations of nacl solution by the deicing salt. this condition will lead to serious asr problems in concrete, if the aggregates contain reactive silica. the main research work in this paper is to investigate the effect of 15% replacement ratio of high quality fine fly ash (fa15%) and 42% replacement ratio of blast furnace slag (bfs42%) on the asr mitigation in concrete with different alkali amount inside the pore solution. the experiments were conducted according to the accelerated mortar bars experiment following the jis a1146 mortar bar test method. in addition, post-analysis such as observation of asr gel formation by the uranyl acetate fluorescence method and observation of thin sections using a polarizing microscope were also conducted. the mortar bar tests show a very good mitigation effect of supplementary cementitious materials (scms). the results show that only small asr expansions, which can be categorized as “innocuous”, occurred for specimens with 1.2% na2oeq using fa15% and bfs42%. however, larger alkali amount inside the system will require more scms amount. keywords-asr expansion; alkali content; scms i. introduction alkali silica reaction (asr) is influenced by internal factors such as alkali, aggregates contain reactive silica and moisture. besides that, asr is also influenced by external factors such as the surrounding environment condition and the use of the structures. in terms of reactive aggregates, in hokuriku district, japan, there are records that show that the reactive crushed andesite stone has been used throughout the noto peninsula. the serious asr problems with a rupture of the reinforcing bar were also found on the noto expressway and the national highway route 249. moreover, in the joganji river in toyama prefecture, in the tedori river in ishikawa prefecture, and in aggregate production from the basin of the river on top of the kuzuryu river in fukui prefecture, the andesite particles contained in river sand and/or gravel show a high reactivity. in addition, the hokuriku district has a lot of local companies that make pc girder and pca product. furthermore, in the district of cold climate such as the hokuriku and the tohoku, which are heavy snow areas, the opportunity to be exposed to high concentrations of nacl solution by the deicing salt has been increasing. since 1982, asr has been noticed in some highway structures in hokuriku district by deicing salts. besides promoting the asr expansion, chloride penetrates to the concrete through the cracks caused by asr expansion will also promote corrosion of the rebar thus will lead to complex degradation in concrete structures [1-2]. the combination of these inside and outside factors result to large numbers of asr-affected pc bridge girders produced in the construction site or in the concrete factory discovered all over the nation by the recent survey of the japan concrete institute on asr mitigation [3]. for this reason, in the hokuriku district and also all over japan, long-life pc bridges is becoming one of the important issues. so far, the high durability pc girders have been produced by using high fineness blast furnace slag powder (6000 blaine value) [4]. however, the production sites of blast furnace slag powder are limited in the metropolitan and suburbs area such as tokyo, osaka, nagoya and kitakyushu. on the other hand, the hokuriku district, such as toyama, ishikawa and fukui, has coal-fired power plants in each prefecture. thus, the effective utilization of fly ash in concrete mixture has become a new regional challenge. it becomes more important to expand the use of fly ash in concrete to establish the supply system and stabilize the quality. in addition, there was a history that concrete from the manufacturer had been avoided to be used in this district. in order to solve this problem, in january 2011, the committee for promotion of effective utilization of fly ash to concrete in hokuriku district, chaired by prof. kazuyuki torii (kanazawa university), has been launched. an active work of preparing a manual of fly ash concrete and stabilizing the supply of high quality fly ash had just started [5]. in line with that, in the works of thomas, et al., interesting facts about fly ash can be found [6-8]. the test program, included both laboratory and field studies, showed that fly ash can be considered to contribute no alkalis when it is used at engineering, technology & applied science research vol. 5, no. 5, 2015, 854-859 855 www.etasr.com prasetia: the effectiveness of high quality supplementary cementitious materials for mitigating… a 25% level (or bellow) of replacement with flint sands. this replacement ratio also could control asr expansion even when the alkalis contributed by the portland cement component of the mixture are sufficient to cause asr expansion in the absence of fly ash. the main research work in this chapter is to investigate the effect of high quality fine fly ash (fa) on the asr mitigation in concrete with different alkali amount inside the pore solution. in addition, samples with additional high quality fine blast furnace slag (bfs) were also prepared to compare the asr mitigation effect between fly ash and bfs. regarding the replacement ratios, 15% replacement ratio of fa and 42% replacement ratio of bfs were selected. the replacement ratio of fa was set at 15% is due to in japan this replacement ratio is the lowest replacement ratio of fa for asr mitigation in concrete according to jisa5308. as for bfs, 42% level of bfs replacement ratio is the replacement ratio being used for blast-furnace slag mix cements type b which is the popular bfs cement in japan. in addition, japan’s researcher commonly used these replacement ratios in experimental studies [9-11]. moreover, the andesite aggregate from hokkaido, japan was used as the reactive aggregate and the accelerated mortar bars experiment will be conducted according to the jis a1146 mortar bar test method. ii. experiments a. materials ordinary portland cement (opc), from t co, ltd., (density: 3.16 g/cm3, blaine specific surface area: 3300 cm2/g) was used. in order to investigate the effectiveness of scms on asr mitigation, two types of scms were used. first is a high quality fly ash (fa) manufactured from nanao ohta coal fired power plant, i-type fly ash classified by jis a6201, (density: 2.44g/cm3, blaine specific surface area: 4780cm2/g, ig.loss: 2.0%). second is a high quality fine blast furnace slag fine powder (bfs) manufactured by s co. ltd (density: 2.91g/cm3, blaine specific surface area: 6030cm2/g, ig.loss 1.0%). the chemical compositions of fly ash and blast furnace slag powder are shown in table i. as for the reactive andesite, two kinds of hokkaido andesite, crushed andesite stone (g) and crushed andesite sand (s), were selected with particle size arranged from 0.15mm to 5.0mm. the alkali silica reactivity of these aggregates were assessed “deleterious” by chemical tests according to jis a1145 (sc: 688 mmol/l, rc: 78 mmol/l, sc/rc= 8.8) which are higher compared to hokuriku andesite which has sc: 529 mmol/l and rc: 119 mmol/l. the hokkaido andesite was also assessed as “deleterious” according to the jis a1146 mortar bar test method. the reactive components of hokkaido andesite were cristobalite, tridymite and little glass phases. table i chemical compositions of fa and bfs (%) mat. sio2 al2o3 fe2o3 cao mgo tio2 mno so3 na2o k2o fa 53.6 28.9 6.7 3.2 0.8 1.4 0.1 0.2 0.3 0.7 bfs 33.0 13.6 0.1 42.6 5.8 0.6 0.2 3.1 0.2 0.2 b. mix proportions in this study, mortar bar specimens were prepared according to jis a1146 test method. three mix proportion were prepared, which are opc, 15% replacement ratio of fa (fa15%), and 42% replacement ratio of bfs (bfs42%). water to binder ratio (w/b) was set at 50%. in each mix proportion, sodium hydroxide solution (naoh) was added for making the total alkali content equal to 1.2% and 2.4%. the dimension of mortar bar specimens is 40×40×160 mm. the mixture proportions of mortar bars specimens are listed in table ii. the name of each specimen is described as in this orders: 1. two numbers at the font are indicating the alkali amount inside the specimens. 2. the first letter afterwards is showing the aggregate which are crushed andesite stone (g) or crushed andesite sand (s). 3. the letter after that is referred to the mix proportions which are ordinary portland cement (opc), 15% of high quality fine fly ash (fa15%) or 42% of high quality blast furnace slag (bfs42%). c. test methods 1) accelerated expansion test the cement, fly ash and blast furnace slag powder are containing different forms of alkali and also have different effect on the asr [12]. thus, to investigate the effect of scms on the asr mitigation in concrete with different alkali amount, the addition of naoh solution was given to adjust the alkali content with equivalent amounts of 1.2% and 2.4% na2oeq. mortar bar specimens were cured in fog chamber with a temperature of 40oc, and more than 95% of relative humidity. length change was measured at 20oc. in jis a1146, if the expansion ratio is over 0.05% for 3 months or over 0.1% for 6 months indicates “deleterious”. 2) asr gel observation after the completion of accelerated mortar bar test, 0.1n silver nitrate solutions was sprayed on the mortar fractured surface, to observe the formation of asr gel by the uranyl acetate fluorescence method. the asr gel shows a greenishyellow coloration area on the cutting surface of the specimens. table ii mixture proportions of mortar bars specimens unit amount for 3 specimens (gr) aggregate no specimen type water naoh* cement fly ash bfs crushed andesite sand crushed andesite stone 1.2gopc 174.2 3.9 600 1350 1.2gfa15% 189.9 3.4 510 90 1350 1 1.2gbfs42% 164.7 4.2 348 252 1350 1.2sopc 174.2 3.9 600 1350 1.2sfa15% 189.9 3.4 510 90 1350 2 1.2sbfs42% 164.7 4.2 348 252 1350 2.4gopc 228.4 2.2 600 1350 2.4gfa15% 231.5 2.1 510 90 1350 3 2.4gbfs42% 226.5 2.3 348 252 1350 2.4sopc 228.4 2.2 600 1350 2.4sfa15% 231.5 2.1 510 90 1350 4 2.4sbfs42% 226.5 2.3 348 252 1350 *1n naoh for specimen with 1.2% na2oeq and 5n naoh for specimen with 2.4% na2oeq engineering, technology & applied science research vol. 5, no. 5, 2015, 854-859 856 www.etasr.com prasetia: the effectiveness of high quality supplementary cementitious materials for mitigating… 3) polarizing microscope observation after the end of the expansion test, polished thin section samples with 20 μm thickness were prepared from each mortar bar specimen. the samples were observed to determine asr gel and cracking by polarizing light microscopy. classification of asr deterioration using thin section was carried out according to the procedure shown in table iii with the reference of katayama studies [13-14]. iii. results a. expansion results 1) mortar bars using crushed andesite stone the expansion ratio results of mortar bar specimens using crushed andesite stone as the reactive aggregate can be seen in figure 1. the expansion ratio of opc samples tends to be larger in accordance with the addition of alkalis inside. starting from the early stage, the asr rate was very fast which is completed in 4 weeks. at the end of the measurement, the expansion ratio of 1.2gopc is over 0.15 and the expansion ratio of 2.4gopc is over 0.55%. thus, these results can be classified as “deleterious”. table iii petrographic classification of asr severity stages stages the progress and severity of asr i the formation of reaction rims and exudation of asr sol/gel around the reacted aggregate ii the formation of asr gel-filled cracks within reacted aggregate iii the propagation of asr gel-filled cracks (max < 25µm) from the reacted aggregate into surrounding cement paste iv the formation of asr gel-filled cracks (max 25-50µm) network and the migration of asr gel into air voids v the formation of asr gel-filled cracks (max 50µm<) network and the migration of asr gel into air voids in the contrary, specimens with fa15% and bfs42% are still enough to mitigate asr expansion with 1.2% na2oeq. however, the expansion becomes larger with the addition of alkali amount. the expansion ratio rose significantly within the span of three months and only a slight increase in expansion could be measured afterwards. in addition, it could be noted that 15% of fly ash replacement ratio and 42% of blast furnace slag replacement ratio are showing the same mitigation effect. the expansion ratio patterns are similar. at the end of the measurement, the expansion ratio was much smaller compared to opc specimens. overall, after six months, the expansion ratio of 1.2gfa15% and 1.2gbfs42% are below 0.05% which can be categorized as “innocuous”. whilst, the expansion ratio of 2.4gfa15% and 2.4gbfs42% are over 0.35% both of which can be categorized as “deleterious”. 2) mortar bars using crushed andesite sand as for expansion ratio results of mortar bar specimens using crushed andesite sand as the reactive aggregate can be seen in figure 2. the expansion ratio results and asr rates were showing the same pattern with mortar bars using crushed andesite stone. these results show that crushed andesite stone and crushed andesite sand aggregate have the same level of reactivity. this might also occur due to the same particle size. in general, asr expansion is completed in just 4 weeks for opc specimens, and around 12 weeks for specimens using fa and bfs. after six months, the expansion ratio of 1.2sopc is over 0.14% and the expansion ratio of 2.4sopc is over 0.44%, which these results can be classified as “deleterious”. in addition, the expansion ratio of 1.2sfa15% and 1.2sbfs42% are below 0.05% which can be categorized as “innocuous” and the expansion ratio of 2.4sfa15% and 2.4sbfs42% are over 0.3% both of which can be categorized as “deleterious”. (a) specimens with 1.2% na2oeq (b) specimens with 2.4% na2oeq fig. 1. expansion ratio of mortar bar specimens using crushed andesite stone aggregate engineering, technology & applied science research vol. 5, no. 5, 2015, 854-859 857 www.etasr.com prasetia: the effectiveness of high quality supplementary cementitious materials for mitigating… (a) specimens with 1.2% na2oeq (b) specimens with 2.4% na2oeq fig. 2. expansion ratio of mortar bar specimens using crushed andesite sand aggregate fig. 3. surface of opc specimens with 1.2% and 2.4% na2oeq 3) visual observation of specimen’s surface the surface of the opc specimens with 1.2% and 2.4% na2oeq after completion of accelerated mortar bar test can be seen in figure 3. in general, fine cracks begin to be visible when the expansions of the specimens reach the rate of 0.05% to 0.1%. the progress of cracking of the specimen is in accordance with the increasing rate of expansion. for opc specimens the cracks pattern observed started from the early stage. the cracks widths increased over time and begin to stop around 4 weeks afterwards. the cracks width is observed around 0.6 mm after the completion of accelerated mortar bar test. as for specimens with supplementary cementitious materials, fine cracks are observed from the second week of measurement. it was also observed that the increase of cracks width had stopped until the fourth week. however, the width of these cracks is much smaller compared with opc specimens. the largest cracks width is found around 0.2 mm. furthermore, beside cracks, leaching effects could also be observed on the surface of all specimens. leaching effect was more visible on the specimens with higher alkali content. in addition, as for opc specimens, the leaching effects could be seen on the early stage, while for the fa15% and bfs42% specimens could be observed at the latter stage. in general, this finding is in agreements with thomas results that show that alkali leaching effect occurred in the smaller laboratory specimen [15]. the leaching effect might be the reason that the expansion of all specimens stopped after 4 weeks. b. asr gel formation observation after the jis test method, uranyl acetate fluorescence method of coloring area was carried out to measure asr gel formation. asr gel observation was conducted to all specimens having large expansion (categorized as “deleterious” in jis a1146 test method). the image of asr gel observation of specimens with 2.4% na2oeq is shown in figure 4. despite the large expansion of opc specimens, only very few asr gel could be observed. it was assumed that the asr gel was extruded from the specimens. this is due to the leaching effects that occurred, as can be observed from the surface of the specimens. the asr gel could almost not be seen in 1.2sopc specimens. however, as the expansion 2.4gopc 1.2gopc 1.2sopc 2.4sopc cracks crack cracks cracks leaching leaching leaching leaching of alkalis through the crack leaching of alkalis through the crack engineering, technology & applied science research vol. 5, no. 5, 2015, 854-859 858 www.etasr.com prasetia: the effectiveness of high quality supplementary cementitious materials for mitigating… became larger, the asr gel could be easily observed, especially for specimens using crushed andesite sand aggregate. as for the fa15% specimens, the asr gel in 2.4gfa15% and 2.4sfa15% can be easily observed. especially for the 2.4sfa15% specimen, asr gel could be seen on the inner section and outer section of the sample, although only a few asr gel could be observed. thus, these results are adding more confidence on the expansion test results. however, there was no asr gel to be observed in bfs42% specimens with 2.4% na2oeq. it is assumed that the leaching of alkalis and asr gel was more pronounced in the bfs42% specimens. c. polarizing microscopic observation after the completion of accelerated mortar bar test, thin section observation of mortar bar specimens by polarizing microscope were also conducted. the results of polarizing microscopic observation of specimens with 2.4% na2oeq is shown in figure 5. the polarizing microscopic observations were conducted to the specimens that categorized as “deleterious”. in general, the observation of cracks widths, filled with asr gels, are linier with the expansion result. in the specimens with larger expansion, wider cracks can be observed. in 2.4gopc, there was observed continuous large cracks, filled with asr gel, from the aggregate (25 μm until 50 μm) to the cement paste (asr level: iv). as the expansion ratio decreased in the 2.4sopc specimen, the cracks width decreased and became less then 25 μm (asr level: iii). as for 1.2gopc and 1.2 sopc specimens, there was no progress of cracks to be observed from the aggregate to the cement paste (asr level: ii). this pattern could also be seen on specimens using supplementary cementitious materials. the largest cracks width can be observed in 2.4gfa15%, 2.4sfa15%, 2.4gbfs42% and 2.4sbfs42% specimens, which the cracks width are less than then 25 μm (asr level: iii). thus, these results confirm the expansion test results. (a) opc specimen (b) fa15% specimen (c) bfs42% specimen fig. 4. asr gel formation observations of mortar bar specimens using crushed andesite sand aggregate with 2.4% na2oeq by uranyl acetate fluorescence method (observed area: 40 mm x 40 mm) (a) opc specimen (b) fa15% specimen (c) bfs42% specimen fig. 5. polarizing microscopic observation of mortar bar specimens using crushed andesite sand aggregate with 2.4% na2oeq by uranyl acetate fluorescence method (observed area: 40 mm x 40 mm) asr gel cracks cracks asr gel cracks from aggregates to cement paste cracks inside the aggregates engineering, technology & applied science research vol. 5, no. 5, 2015, 854-859 859 www.etasr.com prasetia: the effectiveness of high quality supplementary cementitious materials for mitigating… iv. discussions the expansion ratios of all specimens using cement only (opc) exceed 0.1% after 6 months regardless of their alkali amount. this result may verify the high reactivity of the crushed andesite stone and crushed andesite sand aggregates which are produce in hokkaido. in addition, the results show that the larger alkali amount inside the system will also require larger replacement ratio of scms. in the effectiveness of fly ash and blast furnace slag on controlling asr, the amount of fly ash and blast furnace slag needed is linear with the amount of alkalis inside the concrete. however, there is a maximum number of replacement ratios of fly ash and blast furnace slag that should be considered. usually, the maximum number of replacement ratios of fly ash is until 35% and until 60% for blast furnace slag. exceeding the maximum replacement ratios will reduce the ultimate strength of concrete. beside that, differences in the asr mitigation effect will not be significant. the mitigation effect of scms, can be attributed to the alkali binding capacity of scms. by adding fly ash or blast furnace slag in concrete, it can produce more csh with a low ratio ca/si produced from the pozzolanic reaction between fly ash or blast furnace slag and portland cement. thus, there will be much more available alkalis that can bind to halt the asr process. moreover, the finer fly ash with an amorphous silica glass has higher pozzolanic reactivity. thus, the alkali binding capacity is expected to be much significant with finer fly ash. furthermore, in the future, it is expected that the effect of the addition of high quality fly ash and blast furnace slag in concrete will be more significant. especially in hokuriku district, which has three coal-fired power plants in each prefecture, fly ash certainly becomes a valuable opportunity to overcome asr problems that occurred. v. conclusions the experiment works on investigating the mitigating effect of high quality fly ash and blast furnace slag on asr expansion in accelerated mortar bar test with low and high alkali level have been conducted. the main concluding remarks obtained from the present research are summarized as follows: (1) the accelerated mortar bars test confirms the high reactivity of hokkaido’s andesite aggregate. asr expansion is completed in just 4 weeks for opc specimens. however, it was delayed, around 12 weeks, for specimens using fa and bfs. (2) the crushed andesite stone and crushed andesite sand aggregate have the same level of reactivity, which is high reactivity. this might occur due to the same particle size. (3) the application of jis a1146 made possible to determine the inhibitory effect of asr of both fa and bfs powder especially in the early stages. the addition of 15% replacement ratio of fa and 42% replacement ratio of bfs could completely inhibit the asr in specimens with 1.2% na2oeq. (4) the required amount of scms to mitigate asr depends on the alkali content inside the mortar bar specimens. the larger alkali amount inside the system will require more scms amount. (5) the alkali binding mechanism of csh, with a low ratio ca/si produced from the pozzolanic reaction between scms and portland cement, give significant contribution in binding available alkali in the pore solution. (6) in the future, it is expected that the effect of the addition of fly ash and blast furnace slag in concrete will be more significant in hokuriku district. references [1] t. habuchi, n. miyasaka, h. tsuji, k. torii, “evaluation of combined deterioration of concrete structures in marine environment due to alkalisilica reaction and seawater attack”, 4th international conference on concrete under severe conditions, vol. 2, pp. 2026-2033, 2004 [2] p. r. vassie, “a secondary of asr on bridges-corrosion of reinforcement steel”, 2nd international conference on bridge management, pp. 18-21, 1993 [3] k. torii, “the characteristic feature of fracture of steel reinforcement in asr-deteriorated concrete structures”, corrosion engineering, vol. 59, no. 4, pp. 59-65, 2010 [4] japan society of materials science, “report on the development of prestressed concrete structures using high durability powder blast furnace slag”, 1998 (in japanese). 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[13] t. katayama, m. tagami, y. sarai, s. izumi, t. hira, “alkali-aggregate reaction under the influence of deicing salts in the hokuriku district, japan”, materials characterization, vol. 53, no. 2-4, pp. 105-122, 2004 [14] t. katayama, t. oshiro, y. sarai, k. zaha, t. yamato, “late-expansive asr due to imported sand and local aggregates in okinawa island, south western japan”, 13th international conference on alkaliaggregate reaction in concrete, pp. 862-873, 2008 [15] m. d. a. thomas, b. fournier, k. folliard, j. ideker, m. shehata, “test methods for evaluating preventive measures for controlling expansion due to alkali-silica reaction in concrete”, cement and concrete research, vol. 36, no. 10, pp. 1842–1856, 2006 microsoft word etasr_v12_n4_pp8960-8966 engineering, technology & applied science research vol. 12, no. 4, 2022, 8960-8966 8960 www.etasr.com nebili et al.: decoupling control applied to the smart grid power dispatching problem decoupling control applied to the smart grid power dispatching problem salim nebili department of physics, laboratory of electrical and energetic systems, faculty of sciences of tunis, university of tunis el manar, tunis, tunisia salim.nebili@tunisietelecom.tn ibrahim benabdallah department of physics, laboratory of electrical and energetic systems, faculty of sciences of tunis, university of tunis el manar, tunis, tunisia ibrahim.benabdallah@gmail.com adnen cherif department of physics, laboratory of electrical and energetic systems, faculty of sciences of tunis, university of tunis el manar, tunis, tunisia adnen2fr@yahoo.fr received: 15 may 2022 | revised: 9 june 2022 | accepted: 13 june 2022 abstract-this paper presents controller designs of the decoupling issue dedicated to renewable decentralized generators or new generation grids known as smart grids. the control methods were based on a three-phase voltage source grid representation that integrated wind and photovoltaic generators. the utilized decoupling strategies (boksenbom and hood, zilkind and luyben, and inverted decoupling) allowed the optimization of energy transfers and costs through the routing grid distribution path. simulations were conducted in matlab/simulink. the trustworthiness of the multivariable control system design in addition to the tuning method was established using three test batches, totally decoupled and stable from input dependencies. keywords-decoupling; smart grid; demand-response; power dispatching; controller design i. introduction methods presenting only one output controlled by a single deployed variable are classified as single-input single-output (siso) systems. several processes do not imitate such a simple control shape. each unit operation needs to control no less than two variables, and consequently, there are frequently at least two control loops to deal with. systems that involve more than one control loop are known as multi-input multi-output (mimo) or multivariable systems. the electrical smart grid is essentially a massive mimo system. due to the interactions of the flow power offer and demand, it is not easy to design a robust controller for each path autonomously to lead an input x to an output y without affecting any other output. many studies have focused on several loop control structures to diminish these interactions. decoupling methods are mostly used in industrial processes but are still applicable for many electrical system parameterdecoupling purposes. a simplified, ideal, and inverted decoupling comparative study was presented in [1], which was the base for many classic studies. three decoupling methods were considered to deal with stability, robustness, and implementation aspects, while the complexity of the decoupler elements depended on the overall system size. an improvement of the two inverted decoupling methods was presented in [2] for the case of a stable linear multivariable class of processes, through no minimum-phase zeros and multiple time delays. as some multivariable processes were still unable to be decoupled due to stability issues, alternative decoupling with a unity feedback structure was suggested. the pi/pid was designed using internal model control to decouple the processes. in the case of multiplicative input uncertainty, the low bounds of the control parameters were intended to guarantee the robust stability of the system. as the disturbances influence the way of the control synthesis of a mimo system based on ideal decouplers and a pid regulator, single controller performance and robustness from the closed-loop could be prolonged to all loop systems [3]. an improved decoupling approach allowed more flexibility in the choice of transfer functions of the decoupled apparent process for general n×n processes, where the decoupler elements’ complexity appeared independent of the system's size [4]. a decoupling internal model controller design method was proposed in [5] for industrial mimo timedelay systems, based on a controlled model adjoint matrix. a decoupling compensator and an internal model controller, butterworth low-pass filter, were designed for decoupling the generalized controlled object. the last filter aimed to improve the disturbance rejection aptitude. in [6], a method of finding the forced oscillation source was proposed. the relation between the observable outputs and the mechanical power problems in a unit was decoupled by sensibly designing a luenberger observer using an aging structure task. a mimo control system with multiple time delays and a model predictive control was presented in [7], describing a method to design mimo filtered smith predictors for n×n processes through multiple time delays based on the decentralized direct decoupling structure. this allowed simple tuning of the primary controller, making simpler the problem toward multiple single loops, if realizable, and it could also be used to eliminate the interactions among process variables. the decoupling method is also applicable to electrical grid, microgrid, and smart grid annexed domains facing new intermittent and highly variable system challenges and expectations [8-17]. modeling approaches were proposed in [8] using analytical tools for control design purposes of step-up grid-connected pv systems, such as voltage source corresponding author: salim nebili engineering, technology & applied science research vol. 12, no. 4, 2022, 8960-8966 8961 www.etasr.com nebili et al.: decoupling control applied to the smart grid power dispatching problem representation of the bulk capacitor interacting with the gridconnected inverter and considering the inverter of a doublestage pv system as a norton equivalent. furthermore, both ideal and real dc/dc converter models for the pv module were presented through four mathematical models, stated in state-space representation. a decoupled inverter connected to a grid was exposed in [9], using dynamic online grid impedance measurements in a micro grid application. the controller was implemented in a synchronous reference frame and pi controllers were used, while mutual coupling was introduced between the d and q control loops. the transformation into a synchronous reference was accurately decoupled using the dynamically measured grid impedance and feedforward control. decoupling permits autonomous control of active and reactive powers following changes, and online real impedance measurement was proposed to make the decoupling more precise. in [10], a multivariable-droop synchronous current converter decoupling control strategy was proposed for the current management of weak grid/micro grid applications, offering a traditional forward design method that employs the loop determining technique. the controller mixes current regulation, management, and limitations that apply to weak and micro grids. the multivariable synchronous current converter allowed larger decoupling of dand q-axis currents in weak and/or resistive grids, anywhere these control variables are highly coupled due to the converter’s large load-angle operation. in [11], the evolution allocation for the decoupling of the electrical network was studied using pure channel component transform, addressing issues such as robustness. difficulties were efficiently overcome using singular values instead of proper decomposition. an algorithm was developed to show how the adopted transformation can be used for voltage stability analysis. in [12], a distributed generator strategy control was investigated to assist a conventional local grid by decoupling phase sequences, frequency domain unbalances, and harmonic compensation for grid-connected inverters through unbalanced loads. this strategy was considered sequential-asymmetric for unbalanced and harmonic voltage correction. moreover, a norton equivalent model in frequencydomain was used. this study showed that following a frequency-domain decoupled method, the fundamental positive, harmonic symmetrical, fundamental zero, and negative sequence components can be regulated independently. in [13], a virtual synchronous generator control method was proposed for extensive renewable energies connected to a grid. a power decoupling control method based on linear active disturbance rejection control was developed to eliminate output power deviation. using the coupling term estimates and disturbances from an extended state observer, the aforesaid matter triggered by power coupling can be lessened. furthermore, the stability of the controller was analyzed. in [14], essential limitations were defined for the islanded mode of operation of micro grids which cannot be absorbed by conventional fp methods. therefore, updates were designed for conservative approaches by including network frequency as a variable and avoiding the network soft bus. these particular aspects of the newton-raphson method modified the designs of the jacobean matrix. extended power factor equations were decoupled by reformulating the jacobean matrix based on the fact that lines are mostly resistive. furthermore, two convergence improvement methods were also incorporated. dual-buck inverters were examined in [15], reassessing volume, system weight, and power density of dual-buck singlephase grid-tied pv inverters. a new active power decoupling buffer and grid-tied photovoltaic inverter integration with single-inductor dual buck topology were proposed, using a single-loop direct input current ripple control method. several concerns arise in the case of pulse width modulation using a high-voltage current source converter based on fully controlled devices, such as high switching losses, large dc voltage fluctuations, and thin power operation range [16]. to resolve these difficulties, a current source converter-based hvdc was proposed using fundamental frequency modulation presenting the topology, an independent control strategy, and a mathematical model. a synchronized control strategy was proposed to decouple active and reactive powers with an outer and inner current controller loop to lead to lower dc voltage fluctuations, lower switching losses, and a broader power operation range. this study investigated a two-input two-output (tito) grid system, as a mimo system could be devised into several tito subsystems. the main goal was to employ decoupling methods for grid part energy aggregation, aiming to decouple demand response paths based on statue and output feedback control methods. ii. controller design and methods the control strategy of the phase grid-connected pv, wind, and storage system inverter is presented in figure 1. the elements were taken from [17-24]. fig. 1. overall grid-connected system design. the system can be described in the state representation by: ��. � �� � �� � � � �� (1) where a is the characteristic matrix, b is the order matrix, c is the output matrix, and d is the coupling matrix. a control law was defined by the output feedback as: � � � �. � (2) engineering, technology & applied science research vol. 12, no. 4, 2022, 8960-8966 8962 www.etasr.com nebili et al.: decoupling control applied to the smart grid power dispatching problem where v is the new entries vector of the dimension (m.1), k is the matrix of dimension (m.l), m is the number of outputs, l is the number of entries, y is the output vector, and e is the input vector. k is calculated by solving: |�� � �� | � 0 (3) the governing equations of the network filter defined in figure 1 are: ⎩⎪⎨ ⎪⎧������� � ���� � � � ��� �� �� � �!�! � ! � �!�"��"�� � �#�# � # � �# (4) the fundamental principles of simplification of the equations of states, such as the park model, can be used to either substitute or eliminate the effect of one or several equations, to implement and succeed in the decoupling methods by delimitating the effects of inputs on outputs. the relative park equation model from the overall grid-connected system design is given by: $�%��%�� � �� �� � � � ���&��&�� � �' �' � ' � �' (5) input and output voltages are linked by values belonging to ℝ: � � � �� �� � �' �' ' � (� �� � (' �' (6) using (5): $�%��%�� � ��� �� � � � ���&��&�� � ��' �' � ' � �' (7) substituting (6) in (7) gives: �%��%�� � ��� �� � )�� �� � �' �' * � ���&��&�� � ��' �' � )(� �� � (' �' * � �' (8) � � +,-%�% 00 ,-&�& . , � � / )�,0%*�% ,0&�%,1%�& 2�,1&3�& 4 � 51 00 17 , � � 50 00 07 (9) the transfer function matrix g(s) can be easily obtained from the state representation using: 8)9* � )9� � �*,�� � � (10) in the general case, the matrix d is null and the calculation of g(p) is simplified as: 8)9* � )9� � �*,�� (11) 8)9* � :8�� 8�!8!� 8!!; (12) the used units are l1 = l2 =16.58.10 -3 h, and r1 = r2 = 0.98ω. the transfer matrix is obtained from the a, b, and c matrices: 8)9* � + <.<=>�<<?@<.=> <.<=>�<<?@<.=>,<.<!a�<<?@�.=! <.<b!�<<?@�.=!. (13) iii. simulation results the grid inputs are two photovoltaic conversion chain outputs by two different steps: a. without decoupling after obtaining the coupled system block diagram and the transfer matrix g(p) elements, the wiring was designed in matlab/simulink to visualize the evolution of its outputs as a function of time. the simultaneous excitation of e1 and e2 inputs is shown in figure 2. ��� � c�8�� � c!8�!�! � c�8!� � c!8!! (14) � � 8c (15) with: � � d��, �! fg , c � dc�, c!fg , 8 � :8�� 8�!8!� 8!!; fig. 2. coupled system block simulink diagram. fig. 3. grid inputs. at t0=0s, a unit step is performed at each system input. then the amplitude of e1 is reduced to 0.5 at t=1500s without modifying the second input. after that, at t=2500s, the second input e2 decreases to 0.5, without modifying the first input e1. figure 4 shows the evolution of each output y1 and y2. 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.2 0.4 0.6 0.8 1 1.2 time (seconds) e 1 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.2 0.4 0.6 0.8 1 1.2 time (seconds) e 2 engineering, technology & applied science research vol. 12, no. 4, 2022, 8960-8966 8963 www.etasr.com nebili et al.: decoupling control applied to the smart grid power dispatching problem fig. 4. grid outputs without decoupling the evolution of outputs of the coupled system shows that the change in the first input could vary and affect the second output. the following subsection introduces some decoupling methods to obtain an overall system made of tito subsystems varying in parallel to figure 5. in particular, the input e1 should only affect the first output y1, and the input e2 should only affect y2. the chosen methods were boksenbom and hood [2, 10], zalkind and luyben [2], and a method based on inverted decoupling [2, 4]. fig. 5. the tito overall system. b. decoupling using boksenbom and hood method using (12), the decoupling matrix 8h∗ can be given by: 8h∗ � :8h,��∗ 8h,�!∗8h,!�∗ 8h,!!∗ ;....(16) reference signals are shown by w=[w1, w2]: 8c � � , c � 8h∗dk � �f8h∗dk � �f � � (17) � � d� � 88h∗f,�88h∗k (18) � � d� � 88h∗f,�88h∗ � lmnodp�, p!f (19) x is a diagonal matrix: 88h∗ � :8�� 8�!8!� 8!!; :8h,��∗ 8h,�!∗8h,!�∗ 8h,!!∗ ; :q� 00 q!; (20) ⎩⎪⎨ ⎪⎧q� � 8��8h,��∗ � 8�!8h,!�∗0 � 8��8h,�!∗ � 8�!8h,!!∗0 � 8!�8h,��∗ � 8!!8h,!�∗q! � 8!�8h,�!∗ � 8!!8h,!!∗ ⎭⎪⎬ ⎪⎫ (21) 8h,�!∗ � ,u� uv, ∗u�� , 8h,!�∗ � ,u �uv,��∗u (22) as the decoupled matrix functions do not influence the evaluation of the diagonal matrix decoupling, according to this method principle, the pi/pid regulators must be chosen arbitrarily. the stability condition of the system has to be respected, as follows: 8h,��∗ � 8h,!!∗ � ?@<.�? (23) the simulink transfer functions block wiring which characterizes this method are shown in figure 6. fig. 6. boksenbom and hood block simulink diagram. the same conditions were applied in this case. at t0=0s, a unit step was performed for e1 and e2. then, e1 was lowered to 0.5 at t=1500s without changing e2. next, as t=2500s, e2 declined to 0.5, without changing e1. the evolution of y1 and y2 outputs is shown in figure 7. fig. 7. boksenbom and hood grid outputs. the proposed control system is perceived as having good decoupling. due to error approximation, the decoupling system interactions are thoughtful. thus, a pi/pid must be implemented. c. decoupling using zlikind and luyben method using (11): � � 8c∗, c∗ � 8h∗c , c � 8h dk � �f (24) 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.05 0.1 0.15 0.2 0.25 time (seconds) y 1 0 500 1000150020002500300035004000 0 0.005 0.01 0.015 0.02 0.025 0.03 time (seconds) y 2 without decoupling 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.2 0.4 0.6 0.8 1 1.2 1.4 time (seconds) y 1 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.2 0.4 0.6 0.8 1 1.2 1.4 time (seconds) y 2 engineering, technology & applied science research vol. 12, no. 4, 2022, 8960-8966 8964 www.etasr.com nebili et al.: decoupling control applied to the smart grid power dispatching problem are chosen as follows: � � 88h∗c � 88h∗8h dk � �f (25) � � 88h∗ � diagdp�, p!f 8h∗8 ,�� , 8 ,� � adj)8*/ det) 8* (26) where adj(g) is the adjoint of the matrix of g, and det(g) is the determinant of the matrix g given by: det) 8* � 8��8!! � 8�!8!� (27) adj)8* � : 8!! �8�!�8!� 8�� ; (28) 8h∗ � 8 ,�� :8!!p� 8�!p!8!�p� 8��p!; ��_�)u* (29) the chosen form is a unit diagonal given by: 8h,��∗ � 8h,!!∗ � 1 (30) therefore: 8h,�!∗ � � u� u�� , 8h,!�∗ � � u �u (31) gc1 and gc2 must be pi/pid regulators chosen as follows: 8h� � 8h! � ?@<.�? (32) the simulink transfer functions block wiring of this method is shown in figure 8. figure 9 shows the evolution of the outputs y1 and y2 applying the same conditions as in the other methods. fig. 8. zlikind and luyben simulink block diagram. fig. 9. zlikind and luyben grid outputs. d. decoupling using inverted decoupling method gc11 and gc22 are placed in the forward direction which can be pi or pid controller. using (11) and (12), it is necessary that: ��! � � u� u�� , �!� � � u �u (33) the simulink transfer wiring function wedges describing this method are shown in figure 10. fig. 10. inverted decoupling block simulink diagram. fig. 11. inverted decoupling grid outputs. the inverted decoupling processes shown in figure 11 does not contain bulk sums of transfer functions. consequently, the diagonal controllers’ fine-tuning becomes more accommodating in higher multivariable processes with solid cross-couplings, even if the system elements have simple changing aspects. iv. result comparison and discussion the three methods obtained perfect decoupling, but the variation in the calculation of the terms that characterize each method and the simplicity of their use should be noted. in the boksenbom and hood method, the functions and the pi regulator were chosen in the decoupling block, but in the zalkind and luyben method they are taken equal to 1, which is simpler, and they do not appear based on a reduced decoupling block. the zalkind and luyben method requires the computation of the inverse g(p), thus the determinant of g must be non-zero, which is not necessary for the two other 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.2 0.4 0.6 0.8 1 1.2 1.4 time (seconds) y 1 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.2 0.4 0.6 0.8 1 time (seconds) y 2 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.2 0.4 0.6 0.8 1 1.2 1.4 time (seconds) y 1 0 500 1000 1500 2000 2500 3000 3500 4000 0 0.2 0.4 0.6 0.8 1 time (seconds) y 2 engineering, technology & applied science research vol. 12, no. 4, 2022, 8960-8966 8965 www.etasr.com nebili et al.: decoupling control applied to the smart grid power dispatching problem methods. the addition of a compensation block consisting of a pi controller in the direct chain for the zalkind and luyben decoupling method has the same effect as its addition in the decoupling block by the method based on the reduced decoupling block, so there is only a variation in the structure. its absence in the boksenbom and hood method makes it lose flexibility in the implementation of the non-interactive control grouping, especially regarding the stability of the system. using these criteria, the method based on a reduced decoupling block is the simplest because it requires fewer computations and has more flexibility via the pi controller. a multivariable control system design employing a finetuning filter based on an inverted decoupler, using statue or output feedback control methods, was presented. the high closed-loop system enactment was attained for predefined robustness by eliminating unnecessary control exertion and introducing adequate filtration of the controlled variables. this was verified by the results which treat an extremely intermittent pv source and chain outputs. the proposed demand response path methods improved inverted decoupling. the disturbance response was minimized within a narrow range for the intermitting nature of renewable energy processes known for their instability. v. conclusion the cogency of the proposed statue feedback multivariable control system design and tuning was confirmed using three methods. high closed-loop system performance was attained by avoiding unnecessary control exertion using the suitable controlled variables filtration. the three methods, boksenbom and hood, zilkind and luyben, and inverted decoupling, eliminated the opposing effects caused by non-minimum phase zeros and achieved dynamic decoupling. the simulation results showed that the three proposed methods could establish a decent dynamic decoupling, solid robustness, and immunity against trouble. results proved that they succeeded very effectively to limit the interactions of the inputs to the relative outputs, which opens the road to the generalization of these decoupling methods for the entire endto-end chain of different energy sources to improve and optimize energy dispatching. inverted decoupling gives more effective and precise results compared to boksenbom and hood and zilkin and luyben, given the additional regulation blocks gc11 and gc22, which leads to maintaining the input magnitudes. future work should assess more than two inputs and study a big-scale system matrix, rearranging it to a 2 by 2 matrix. references [1] e. gagnon, a. pomerleau, and a. desbiens, "simplified, ideal or inverted decoupling?," isa transactions, vol. 37, no. 4, pp. 265–276, sep. 1998, https://doi.org/10.1016/s0019-0578(98)00023-8. 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[23] m. y. allani, d. mezghani, f. tadeo, and a. mami, "fpga implementation of a robust mppt of a photovoltaic system using a fuzzy logic controller based on incremental and conductance algorithm," engineering, technology & applied science research, vol. 9, no. 4, pp. 4322–4328, aug. 2019, https://doi.org/10.48084/etasr.2771. [24] s. javadpoor and d. nazarpour, "modeling a pv-fc-hydrogen hybrid power generation system," engineering, technology & applied science research, vol. 7, no. 2, pp. 1455–1459, apr. 2017, https://doi.org/ 10.48084/etasr.760. authors profile salim nebili was born in gafsa, tunisia, in 1973. he received the engineering degree from the national engineering school of gabes (enig) in 1998 and a master's degree in 2002 from the national engineering school of tunis (enit). he is a member of the analysis and treatment of electrical and energetic signals and systems laboratory. his research interests include electrical engineering, renewable energies, and smart grids. ibrahim benabdallah was born in tunis, tunisia, in 1984. he received a master's and doctor’s degree in electronics from the faculty of sciences of tunis (fst). he is a member of the analysis and treatment of electrical and energetic signals and systems laboratory. his research interests include electrical engineering, renewable energies, and smart grids. adnen cherif received engineer, master, and phd degrees from the national engineering school (enit) of tunis, tunisia. since 1997, he is a senior professor and responsible for the analysis and treatment of electrical and energetic signals and systems (ateess) laboratory in the faculty of science of tunis, tunisia. his fields of interest concern digital signal processing, speech processing, energetic systems, renewable energies, and smart grids. microsoft word etasr_v13_n2_pp10483-10488 engineering, technology & applied science research vol. 13, no. 2, 2023, 10483-10488 10483 www.etasr.com ibrahim et al.: an experimental study of a combined oblique cylindrical weir and gate structure an experimental study of a combined oblique cylindrical weir and gate structure safa s. ibrahim chemistry department, faculty of sciences, university of zakho, iraq safa.ibrahim@uoz.edu.krd (corresponding author) rondik a. jafer water resources engineering department, faculty of engineering, university of duhok, iraq rondik.adil@uod.ac binahi m. a. said ali water resources engineering department, college of engineering, salahaddin university, iraq binahi.saidali@su.edu.krd received: 2 january 2023 | revised: 17 february 2023 | accepted: 20 february 2023 abstract in the present study, the effects of different oblique angles and diameters on the cylindrical weir and below a gate as a combined device have been studied experimentally. for this purpose, sixteen models of combined cylindrical weir-gate structures have been tested in a laboratory flume. these models had four different oblique angles α (30 0 , 45 0 , 60 0 , and 90 0 ). for each angle, the diameter of cylindrical weir-gate changed four times (4, 7.3, 9, and 11cm). the results of all models indicate that the theoretical discharge (qth) is inversely proportional to the ratio of diameter to height (d/h) and length to height (l/h). as the diameter increases and oblique angles decrease, the actual discharge (qact) increases. a general expression was established linking qth/g 1/2 h 5/2 and the discharge coefficient cd with d/h, l/h, and alfa. the discharge coefficient ranged from 0.55 to 0.99 for various oblique angles and decreased as the angle increased. a strong correlation was observed between the estimated and the calculated values. keywords-combined flow; cylindrical weir; gate; discharge coefficient; theoretical discharge i. introduction weirs and gates are the most commonly used and important structures for measuring water flow, regulating flow in irrigation channels, and redirecting it from the main channel to secondary channels [1]. weirs are structures that regulate water surface and flow control in water conveyance channels and hydraulic structures. one of their demerits is that they need to be cleaned of sediment and trash periodically. gates are used extensively for flow control and water measurement. one disadvantage of the gates is that they retain floating materials. in order to maximize their advantages, weirs and gates can be combined together in one device, so that water could pass over the weir and below the gate simultaneously. it may reduce the effect of sediments and floating materials upstream and may affect scoring downstream [2-4]. one such combination is the cylindrical weir-gate structure. regarding the form of the combined cylindrical weir-gate structures, it has some advantages including easy design, sediments and floating material flow, higher flow discharge coefficient, lower cost, and the combination of those structures in one device can minimize the disadvantages of separate use of each device. the performance of this combination has been studied extensively. authors in [5] presented the effects of hydraulic and geometrical parameters, viscosity, and surface tension in the combined flow over rectangular weirs and rectangular sharp-crested gates. they found that the trend of variation in sloping bed cases was similar to that in horizontal beds. authors in [6] studied the characteristics of free flow through a combined triangular weir and rectangular gate. they found that the values of theoretical discharge were inversely proportional to the geometrical dimensionless parameters and directly proportional to the distance between the bottom of the weir and the upper edge of the gate. authors in [7] investigated the coefficient of discharge (cd) for a combined rectangular weir with semi-circular gate. they showed that the value of cd increases when the width of the weir increases and that the average value of cd was equal to 0.695. also, it was found that the value of cd increases with increasing distance between the weir and the gate with an average value of cd equal to 0.74. authors in [8, 10] proposed new methods to improve the performance of sharp crested triangular and curved plan form weirs. in these studies, the authors varied the vertex angles and engineering, technology & applied science research vol. 13, no. 2, 2023, 10483-10488 10484 www.etasr.com ibrahim et al.: an experimental study of a combined oblique cylindrical weir and gate structure kept the weir height constant, and conducted tests to determine the discharge coefficients. based on the results of these tests, they proposed two empirical equations for estimating the discharge coefficients. authors in [11] studied the flow over a sharp crested weir and under a gate in a combined oblique structure as flow measurement structure. they found that the major parameters affecting significantly on discharge coefficient were h/a, α, l/b, d/a, while the value of c� ranged from 0.623 to 0.403. authors in [12] experimentally studied the effects of canal size on the discharge coefficients of cylindrical weir-gate by using two flumes. they found that the value of c� in large canals ranged from 0.75 to 1.05 and in small canals from 0.55 to 0.9. authors in [13] studied the effect of vertical movement of a cylindrical weir-gate on free flow hydraulics. the experimental results showed that the gate opening change was in inverse relation with the discharge coefficient change, so that the maximum and minimum discharge coefficient were visible in the cylindrical weir and cylindrical gate, respectively. furthermore, in a constant diameter and constant discharge, discharge coefficient changes had an increasing process by the decreases of the gate opening height. besides, in a constant discharge and gate opening height, the discharge coefficient decreased with an increase in the structure diameter. authors in [14] investigated the effect of weir height on the performance of sharp crested rectangular plan form weirs. they found that weirs with lower heights had higher capacity and better performance compared to those with higher heights. authors in [15] experimentally examined the behavior of sharp crested triangular plan form weirs under free flow conditions using a range of weir models that varied in vertex angle and weir height. they found that the discharge coefficient decreases with an increase in the relative head above crest and that weirs with small vertex angles have low discharge coefficients. they presented an empirical equation for predicting discharge coefficients based on the relative head above crest and vertex angle, and concluded that weirs with small vertex angles and low heights have higher efficiency and better performance. in an extensive experimental study, authors in [16] evaluated the hydraulic performance of circular crested triangular weirs under free flow conditions using multiple models with different vertex angles, weir heights, and crest diameters. they found that the discharge coefficient decreases with an increase in the relative head above crest, and that weirs with small vertex angles, low heights, and small crest diameters have better performance. they presented a simple power equation for estimating the discharge coefficient based on the ratio of water depth above crest to weir height, the ratio of head above crest-to-crest diameter, and the vertex angle. in a more recent study, authors in [17] examined the performance of semi-circular crested normal and oblique weirs with flood embankments and found that the discharge coefficient decreases when the crest radius and height increase. authors in [18] conducted an optimization study on the shape of labyrinth spillways in order to minimize construction costs and determine the discharge coefficient in terms of side wall angle and relative head above crest. noori, [19] attempted to increase the discharge capacity of oblique weirs by rounding their crests. he presented an empirical expression to determine cd in terms of h/p, h/d, and a (in radians), with a correlation coefficient of 0.90 and a standard error of 0.01. the weir with the highest discharge capacity had a = 20, p = 20cm, d = 4cm, and a d/p ratio of 0.2, and showed a percentage increase in discharge ranging from 147% to 175% compared to a sharp crested normal weir. noori's results indicate that circular crested oblique weirs generally have higher discharge capacity than other weir shapes. the main goal of the current research is to study the impact of various oblique angles and diameters on the hydraulic properties of a combined cylindrical oblique weir and gate structure. additionally, this study aims to establish relationships for the prediction of flow rate and the coefficient of discharge. ii. theoretical discharge the total theoretical discharge through a combined cylindrical weir and gate structure for free flow conditions can be obtained by adding the discharge under the gate to the discharge over the weir. q�� = q� + q (1) q�� = la�2gh + �� l� � � g h�/� (2) where q�� is the total theoretical discharge, q� is the discharge passing under the gate, q is the discharge passing over the weir, and h = h + d +a the total head above the flume bed l. the variables used in the dimensional analysis were chosen to represent the experimental conditions, see figure 1. therefore, the factors affecting the flow in a combined structure are expected to be: q��. = f��h, a, d, l, b, g, ρ, μ, σ, α! (3) where q�� is the total theoretical discharge (l3/t), a is the gate height (l), d is the diameter of the weir or vertical distance between the lower edge of the weir and the upper edge of the gate (l), l is the length of the weir (l), b is the width of the flume (l), g is the acceleration due to gravity (l/t 2 ), ρ is the mass density of the fluid (m /l 3 ), μ is the dynamic viscosity of the fluid (m/tl), σ is the surface tension (m/t 2 ), and α represents the oblique angles from the direction of flow in degrees. the general relationship among all variables is: f��q, h, a, d, l, b, g, ρ, μ, σ, α! = constant (4) using the buckingham’s pi-theorem, and selecting h, q, and ρ as repeating variables, (4) becomes: f� '(� , ) � , * � , + � , ,�./0 , 1� ./ , �2� /0 , α3 = constant (5) where μh/ρq is the reynolds number re and σh� ρq�⁄ is the weber number (we). the values of the weber number and reynolds number can be neglected at turbulent flow due to the neglected surface tension and viscosity. the values of b and a are constant during the experimental program, therefore can be dropped. inversing and taking the square root of h5g/q�, (5) can be written as: engineering, technology & applied science research vol. 13, no. 2, 2023, 10483-10488 10485 www.etasr.com ibrahim et al.: an experimental study of a combined oblique cylindrical weir and gate structure /67 ���2/0 = f8 ' ) � , * � , α3 (6) the coefficient of discharge �9: ! is determined by comparing the amount of fluid that is actually discharged in an experiment to the amount of fluid that would be discharged under ideal conditions. c� = /;<6/67 (7) where c� is the coefficient of discharge, and q(=� is the actual discharge (l 3 /t). equation (7) can be written as: c� = f5 ')� , * � , α3 (8) fig. 1. combined weir and gate structure. table i. details of the tested cylindrical weirgate models model no. oblique angle (>) diameter (cm) 1 90a 4 2 7.3 3 9 4 11 5 60a 4 6 7.3 7 9 8 11 9 45a 4 10 7.3 11 9 12 11 13 30a 4 14 7.3 15 9 16 11 iii. experimental set up the laboratory experiments were carried out in a rectangular free surface water flume, having a 2.5m long working section with a prismatic cross section 7.6cm wide and 25cm deep with toughened plastic walls as shown in figure 2. the flow rate was measured by a flow meter with a range of 0.5-2.5l/s. during the experimental program, 16 combined weir-gate models, made from pvc pipe, with 4 different oblique angles to the longitudinal axis of the channel (30 0 , 45 0 , 60 0 , and 90 0 ), were tested. for each angle, the diameter of cylindrical weir-gate changed 4 times (d = 4, 7.3, 9, and 11cm). details of the experimental program are shown in table i. each model was placed at 1cm above the flume bed, at 1.32m distance from the upstream of the flume. in each run, the flow rate was recorded and the flow head over the model crest, using a point gauge, was measured at a distance of (3-4) h upstream of the model. the zero on the gauge must correspond to the level of the model crest. a total of 173 experiments were conducted. fig. 2. a model sample during operation. iv. results and discussion a. variation of fghi with h after all models were tested and the data were collected the relationships between q(=� and total upstream head h for different oblique angle and diameter values are shown in figure 3. it is indicated that the discharge passing the cylindrical weir gate increases with the increase of the total upstream head h and decreased oblique angle. b. variation of fij with k/ℎ mno p/ℎ the variation of q�� with d/h and l/h was studied for all models with different oblique angles (α = 90°, 60°, 45°, and 30°). the results are plotted in figures 4 and 5 for d/h and l/h, respectively. from the obtained figures, one may observe that the decrease in the value of the discharge due to the increase in d/h and l/h is an inevitable result when the diameter of the pipe and the angle α (the structure length l) are constant. the increase of these two variables follows a decrease in the load over the weir (h) and thus the discharge decreases. similar curve patterns were obtained experimentally in [6, 12]. engineering, technology & applied science research vol. 13, no. 2, 2023, 10483-10488 10486 www.etasr.com ibrahim et al.: an experimental study of a combined oblique cylindrical weir and gate structure fig. 3. relation between the actual discharge and the total head h for different oblique angles and diameters. c. predication of combined discharge the relationship between the variation of q��/�gh 2 0 and the structural parameters d/h and l/h for a flow in a combination of different oblique angles was represented as a function in (6). to investigate the impact of d/h and l/h on q/�gh20, the results of experiments on flow in a combination of cylindrical weirs and gates of varying diameters and angles were used as input in a regression analysis program. this led to the development of the following empirical power expression: q6r √tj2/0 = 0.252 ' u j 3 a.v�8 ' wj3 �.v�x (9) fig. 4. relation between qth with d/h for different angles. 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0 0.05 0.1 0.15 0.2 q a c t (m 3 /s ) h (m) alfa 90 d=7.3 cm d=4 cm d=9 cm d=11 cm 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0 0.05 0.1 0.15 0.2 q a c t( m 3 /s ) h (m) alfa 60 d=4 cm d=7.3 cm d=9 cm d=11 cm 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0 0.05 0.1 0.15 0.2 q a c t( m 3 /s ) h (m) alfa 45 d=4 cm d=7.3 cm d=9 cm d=11 cm 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0 0.05 0.1 0.15 0.2 q a c t( m 3 /s ) h (m) alfa 30 d=4 cm d=7.3 cm d=9 cm d=11 cm y = 2e-05x2 0.0003x + 0.0019 r² = 0.9074 y = 4e-06x2 0.0001x + 0.0018 r² = 0.9556 y = 1e-05x2 0.0003x + 0.0026 r² = 0.9618 y = 0.0001x2 0.0012x + 0.0048 r² = 0.999 0 0.001 0.002 0.003 0 5 10 15 20 q th d/h alfa 90 d=4 d=7.3 d=9 d=11 y = 0.0004x2 0.0021x + 0.004 r² = 0.9826 y = 7e-05x2 0.0008x + 0.0036 r² = 0.9871 y = 8e-05x2 0.0009x + 0.0043 r² = 0.984 y = 0.0002x2 0.0015x + 0.0058 r² = 0.9993 0 0.001 0.002 0.003 0 1 2 3 4 5 6 7 8 q th d/h alfa 60 d=4 d=7.3 d=9 d=11 y = 0.0005x2 0.0026x + 0.005 r² = 0.9834 y = 3e-05x2 0.0005x + 0.0035 r² = 0.9861 y = 7e-05x2 0.0009x + 0.0049 r² = 0.9844 y = 3e-05x2 0.0005x + 0.0043 r² = 0.9999 0 0.001 0.002 0.003 0.004 0 2 4 6 8 10 q th d/h alfa 45 d=4 d=7.3 d=9 d=11 y = 0.0002x2 0.0018x + 0.0053 r² = 0.9615y = 0.0002x2 0.0015x + 0.0065 r² = 0.9949 y = 0.0003x2 0.0025x + 0.0089 r² = 0.9938 y = 0.0004x2 0.0033x + 0.011 r² = 0.9994 0 0.001 0.002 0.003 0.004 0.005 0.006 0 1 2 3 4 5 6 q th d/h alfa 30 d=4 d=7.3 d=9 d=11 engineering, technology & applied science research vol. 13, no. 2, 2023, 10483-10488 10487 www.etasr.com ibrahim et al.: an experimental study of a combined oblique cylindrical weir and gate structure equation (9) was obtained with a determination coefficient (r 2 ) = 0.998. a comparison between values of fij predicted by (9) and those observed experimentally show quite good agreement, as shown in figure 6. fig. 5. relation between q�� and l/h for different angles. fig. 6. the correlation between the predicted and the observed values from the experiments. d. variation of cd with the combined effects of l/h, d/h, and a the values of cd from combined flow condition were calculated based on (8) and are discussed for the case when the oblique angle of weir and gate structure increase and c� decreases. the obtained average values of cd were 0.50, 0.69, 0.72, and 0.98 for α = 30°, 45°, 60°, and 90°, respectively. the experimental results of the 16 combined weir-gate models are utilized as input data in the regression program spss in order to acquire an empirical power expression of the form: 9: = 0.0448 �z!a.[a� 'uj 3 a.a5� ' wj3 a.a\\ (10) with a correlation coefficient r = 0.88. a comparison between the values of 9: predicted by (10) and those observed experimentally are shown in figure 7. fig. 7. predicted vs experimentally observed values of cd for all test runs. v. conclusion the current work aimed to experimentally study the effect of oblique angle and diameter on the flows over oblique cylindrical weir-gates. sixteen models were designed and tested with angles varying 4 times from 30 o to 90 o and diameters from 4 to 11cm. the discharge ranged between 0.5 and 2.5lpm. the results from the study were discussed and the following conclusions can be drawn:  the main parameters that effect /67 �� �0.2 and cd were ) � , * �, and α. y = 6e-06x2 0.0002x + 0.0019 r² = 0.9074 y = 4e-06x2 0.0001x + 0.0018 r² = 0.9556 y = 2e-05x2 0.0003x + 0.0026 r² = 0.9618 y = 0.0002x2 0.0017x + 0.0048 r² = 0.999 0 0.001 0.002 0.003 0 5 10 15 20 q th l/h alfa 90 d=4 d=7.3 d=9 d=11 4y = 8e-05x2 0.0009x + 0.004 r² = 0.9826 3y = 5e-05x2 0.0007x + 0.0036 r² = 0.9871 2y = 8e-05x2 0.0009x + 0.0043 r² = 0.984 1y = 0.0002x2 0.0019x + 0.0058 r² = 0.9993 0 0.001 0.002 0.003 0 1 2 3 4 5 6 7 8 q th l/h alfa 60 d=4 d=7.3 d=9 d=11 4y = 7e-05x2 0.001x + 0.005 r² = 0.9834 3y = 2e-05x2 0.0003x + 0.0035 r² = 0.9861 2y = 5e-05x2 0.0008x + 0.0049 r² = 0.9844 1y = 3e-05x2 0.0006x + 0.0043 r² = 0.9999 0 0.001 0.002 0.003 0.004 0 2 4 6 8 10 12 14 q th l/h alfa 45 d=4 d=7.3 d=9 d=11 y = 2e-05x2 0.0005x + 0.0053 r² = 0.9615 y = 4e-05x2 0.0007x + 0.0065 r² = 0.9949 y = 9e-05x2 0.0015x + 0.0089 r² = 0.9938 y = 0.0002x2 0.0024x + 0.011 r² = 0.9994 0 0.001 0.002 0.003 0.004 0.005 0.006 0 5 10 15 20 q th l/h alfa 30 d=4 d=7.3 d=9 d=11 r² = 0.7463 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 0.2 0.4 0.6 0.8 1 1.2 1.4 c d p re d ic te d cd observed engineering, technology & applied science research vol. 13, no. 2, 2023, 10483-10488 10488 www.etasr.com ibrahim et al.: an experimental study of a combined oblique cylindrical weir and gate structure  the theoretical discharge fij decreases with increasing d/h and l/h for different angles and diameters.  the actual discharge increases as the diameter of combined weir -gate increases and the oblique angle decreases.  when the oblique angle increased, the discharge coefficient decreased, with a range of values from 0.5 to 0.98.  the values produced by the developed equation were found to closely match the observed values.  two empirical expressions, (9) and (10), in the form of power functions were obtained with correlation coefficients of 0.998 and 0.88, respectively. acknowledgment the authors acknowledge the assistance of the water resources engineers rojan m. shareef, payman m. mahmood, bishang n. mohammed, and jihan sleman, in the laboratory works. references [1] s. a. jalil, s. s. ibrahim, and r. a. jafer, “surface roughness effect on discharge coeffient of broad crested weir,” research journal of applied sciences, engineering and technology, vol. 7, no. 24, pp. 5227– 5233, 2014. 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[14] k. gupta, s. kumar, and z. ahmad, "effect of weir height on flow performance of sharp crested rectangular-planform weir," world applied sciences journal, vol. 33, no. 1, pp. 168–175, jan. 2015, https://doi.org/10.5829/idosi.wasj.2015.33.01.63. [15] b. m. a. noori and n. t. aaref, "hydraulic behavior of sharp crested triangular plan form weirs," journal of duhok university (pure engineering and science), vol. 19, no. 1, pp. 331–341, 2016. [16] b. m. a. noori and n. t. aaref, "hydraulic performance of circular crested triangular plan form weirs," arabian journal for science and engineering, vol. 42, no. 9, pp. 4023–4032, sep. 2017, https://doi.org/10.1007/s13369-017-2566-3. [17] a. bachaya, h. n. hashmi, m. a. baluch, z. ali, and a. latif, "flow characteristics over the weir with semi-circular crest in normal and oblique plane," technical journal, uet taxila, vol. 24, no. 1, pp. 1–8, mar. 2019. 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https://doi.org/10.48084/etasr.5871 abstract occasionally it is more crucial to lower the mass of a building component than to improve its rigidity, specifically in massive buildings like long-span structures where the self-weight of the floors is one of the significant challenges that engineers confront. therefore, the main objective of this work is to explore the flexural performance of lightweight concrete beams (lwcbs) reinforced with glass fiber reinforced polymer (gfrp) bars in terms of curvature, cracks and failure modes, deflection, material stress-strain relationship, and joint end rotation. the flexural performance of lwcbs reinforced with varied gfrp bars and steel reinforcement (sr) ratios is assessed and compared to that of normal concrete beams (ncbs) reinforced with sr. numerical analytical models for the tested beams were created utilizing the idiana software. both analytical and experimental test results were compared. the study revealed a high correlation between the findings of finite element models (fems) and those acquired from beam testing. the performance of lwcbs that utilized sr was equivalent to that of ncbs. the gfrp-reinforced lwcbs performed mostly as elastic deformed elements, with just little deflection post-load release. the study emphasized the significant potential for employing lwc and gfrp bars in the construction field's growth. keywords-flexural behavior; lwc beams; gfrp bars; fem of lwc beams i. introduction the analysis of prior research indicates that there are few available experimental tests for the bending response of beams made of lwcbs reinforced with gfrp bars, particularly for lwc beams with a specific gravity half that of nc. many of these researches [1-12] were concerned with the structural behavior and the mechanical characteristics affected by the type of lightweight aggregates (lwa) and the composition of the lwc blends as well as the kind and ratio of fiber reinforced polymer (frp) reinforcement. authors in [1] experimentally tested lightweight and fibered lightweight concrete (lwc and lwcf) beams in terms of bending and ductility and compared the results with that of conventional concrete beams. they stated that the lwc beams exhibited significantly better performance than that of lwcf beams. a 16% reduction was observed in the weight of lwcf beams. the ductility was improved by 0.4% and 0.5% for lwc and lwcf beams, respectively. authors in [2] conducted a series of experimental tests to explore the properties of lwc blends using expanded polystyrene beads (epbs) instead of coarse aggregates (ca). the study concluded that adding epb as a replacement of ca declined the mixes’ density to 10.9kn/m 3 , resulting in reducing the concrete compression capacity and modules of rupture. authors in [3] studied the structural performance of a lwc beam reinforced with glass-and basaltreinforced polymer (gfrp and bfrp) bars. the lwc in the study was created by replacing 50% of the normal aggregates with expanded clay lwa. according to that study, increasing the percentage of expanded clay lwa in concrete lowered its compressive strength. the ultimate load capacity and mid-span deflection for gfrp and bfrp reinforced beams were lower than those of steel-reinforced beams. authors in [4] investigated the deflection of six steel-fibered lwc beams reinforced with carbon-frp (cfrp) rods under two-point loads. the testing results demonstrated that the introduction of steel fibers at a ratio of 0.6% by volume enhanced the structural behavior of the beams in bending, resulting in a 30% reduction in maximum deflection when compared to lwc beams without steel fibers. the maximum deflection of the lwc beams reinforced with cfrp rods was less than the permitted limit specified by aci code requirements. the goal of the current experimental and numerical analysis is to explore the performance of rc-beams made of lwc, which has a specific gravity half that of normal concrete and cylinder compressive strength of 30mpa. the lwc beams were reinforced with varied ratios of gfrp and sr rods. four engineering, technology & applied science research vol. 13, no. 3, 2023, 10776-10780 10777 www.etasr.com el zareef: an experimental and numerical analysis of the flexural performance of lightweight … lwc beams were assessed in terms of bending performance, failure mode, and serviceability, in addition to two reference beams built of nc with cylinder compressive strength of 30mpa. ii. characteristics of materials utilized in beam production a. glass fiber reinforced polymer and steel rods one downside of utilizing sr in structural concrete is the likelihood of corrosion, particularly in settings with high humidity and chloride attack. one good remedy for this issue is to use gfrp bars in reinforcing structural elements instead of sr bars since they are non-corroded. the axial and lateral resistance of the gfrp rods is regulated by the kind, quantity, and configuration of the gf utilized in each rod. throughout all loading phases, the gfrp rods acted as a perfectly elastic material. the lateral resistance of gfrp rods is substantially lower than that of sr bars, but it has a higher tensile capacity. table i and figure 1 provide the design parameters of the utilized gfrp and sr rods. figure 2 displays the results of the pull-out test between the lwc utilized in the current research and various reinforcing bars. table i. characteristics of gfrp and sr rods design parameter gfrp rods str rods ultimate tension capacity (mpa) 1000 620 yield strength (design strength) (mpa) 420a 420 elastic modulus (gpa) 60×103 200×103 a. the gfrp rods have design strength and no yielding took place fig. 1. sr and gfrp bar’s stress and strain under tension load. fig. 2. relationship of bond stress between lwc and different types of bars. b. mechanical properties of the utilized lwc lwc is encouraged to be applied in the construction industry due to its favorable physical characteristics, including low heat conductivity and density. the lwc used in the present study was developed to have the half-density of nc [13]. table ii displays the design parameters of the lwc employed in the current research as well as the composition of 1m 3 expressed as a percentage of cement weight. figure 3 illustrates the splitting and flexural tensile test for the lwc employed in the study. table ii. lwc blend composition and mechanical characteristics material/mechanical properties percentage of cement weight / value cement type i 52.5 1 fine expanded clay 0/2 0.83 coarse expanded clay 2/9e 0.15 coarse expanded clay 6.5 1.06 water-cement ratio 0.63 silica fume 0.08 super plasticizer 0.01 concrete compressive strength (mpa) 34 direct tensile strength (mpa) 2.25 modulus of rupture (mpa) 2.46 elastic modulus (gpa) 12×103 fresh/dry specific weight (g/cm3) 1.43/1.25 (a) (b) fig. 3. (a) splitting and (b) flexural tensile strength tests of the used lwc. c. beam preparation and test setup four simply supported beams with a reinforcement ratio of 0.5% and 1% were manufactured using lwc, which had a specific gravity half that of nc. two other beams were built utilizing nc with the same steel reinforcement ratios of 0.5% and 1.0% for comparison. all the tested beams had a 3300mm overall length, 150mm×300mm cross-sectional dimensions, and were exposed to 2-point loads at the third span. all tested beams were subjected to displacement control technique with a loading rate of 0.01mm/s. all beams' longitudinal bars were extended to the beam's end for a total of 3300mm. lvdt gauges were affixed to the ends of the bars at the end face of the beam to measure any slippage between the longitudinal bars and the surrounding concrete at the end zone of the beam. figure 4 displays the beam dimensions and the test set up. several methods have been employed to monitor each tested beam. five different locations underneath each beam were used to detect the deflection using lvdts. four 2-gauge lvdts at the ends of the beams were used to keep record of the slippage between the longitudinal compression of tensile reinforced bars and concrete. the gauges were used to quantify the compressive and tension strains in the horizontal and vertical bars. the gauges were affixed to the beam surface 20mm in the compression area, to determine the height of the compression side at the beam's mid-span. with the help of the idiana fe software, the gauge locations were established. engineering, technology & applied science research vol. 13, no. 3, 2023, 10776-10780 10778 www.etasr.com el zareef: an experimental and numerical analysis of the flexural performance of lightweight … 150 1000 1000 1000 150 150 300 p p a's as all dimensions in mm fig. 4. dimensions and test setup for the tested beams. fig. 5. fem of the s1 tested beam. in order to design the examined beams in accordance with aci 440.1r-15 [14], and to look into model expectations for the behavior of the beams, such as the moment-curvature relationship and the transmission of stresses and strains throughout the beams, the fe model depicted in figure 5 was created using the idiana software prior to the conducted experiments. table iii displays the beams' details. table iii. features and details of the studied beams beam id s1 s2 s3 s4 s5 s6 concrete type lwc lwc lwc lwc nc nc concrete grade (mpa) 30/33 30/33 30/33 30/33 30/37 30/37 cross-section (mm) 150×300 bar type gfrp gfrp sr sr sr sr reinforcement ratio (%) 1.0 0.5 1.0 0.5 1.0 0.5 top reinforcement 2 φ 8 transverse reinforcement/m 10 φ 8 iii. finite element model validation the moment-curvature relationships produced by the developed fem were compared with those established based on the experimental data. by dividing the maximum compression strain at the topmost layer of the beam by the height of the compression zone, it is possible to compute the curvature at various bending moment values. using 6 strain gauges, each 20mm in the mid-span compression zone, it was possible to experimentally measure both the maximum compression strain and the depth of the compression zone as depicted in figure 4. the moment-curvature relationships produced by the fem and the experimentally tested beams are displayed in figure 6. two sets of beams were considered with regard to reinforcing ratio. the reinforcement ratio for sets s1, s3, and s5 was 1% and 0.5% for s2, s4, and s6. apart from b1, lwc beams reinforced with gfrp bars with 1% reinforcement ratio, there is generally no discernible variation between the numerical and the test-generated momentcurvatures. in b1, the variation in curvature between the experimental and fem curves reaches 25.2% at the breakdown. the response of lwc beams reinforced with sr rods is comparable to that of nc beams, particularly at small reinforcement ratios. nevertheless, utilizing gfrp rods boosts the lwc beams' curvature at the same load level. it should be mentioned that the moment capacity of the sr beams (lwc or nc beams) reaches a specific level and is maintained for a considerable rise in curvature prior to the collapse. the gfrpreinforced beams can, however, reveal deformation features similar to those of sr-reinforced beams before failure. the major distinction is that they have no ability to retain maximum moments with extended curvature before failure. this may be explained by the fully elastic properties of gfrp bars and the elastoplastic response of sr bars. (a) (b) fig. 6. moment-curvature relationship of the experimentally tested beams and fe models at (a) 1% and (b) 0.5% reinforcement ratio. iv. end-rotation response of the studied beams the moment end-rotation relationships for srand gfrpreinforced lwc and nc beams are shown in figure 7. the end-rotation might be computed at every load stage until the beam failure since the deflection readings at 0.5m from the support point throughout each beam's test have been recorded. the findings demonstrate that the moment-end rotation relationship for nc and lwc samples reinforced with sr bars are fairly similar. the geometry of the moment end-rotation relationship for sr-reinforced lwc and nc samples complies with the typical tendency of a moment-curvature relationship, increasing linearly till the yield of the sr bars. when the sr bars yielded, that caused a significant rise in end-rotation with a small raise in the bending moment, particularly when the reinforcement ratio was small, as in samples s4 and s6. this response indicates that the rotation-ductility of lwc and nc beams reinforced with sr bars is extremely similar. (a) (b) fig. 7. moment end-rotation relationship of the studied beams with (a) 1% and (b) 0.5% reinforcement ratio. engineering, technology & applied science research vol. 13, no. 3, 2023, 10776-10780 10779 www.etasr.com el zareef: an experimental and numerical analysis of the flexural performance of lightweight … it was noticed that the end-rotation of these samples immediately before rupture differed between 2°17' and 3°14' based on the ratios of reinforced bars. the moment end-rotation relationships for gfrp-reinforced lwc samples rise linearly until the rupture point. the greatest end-rotation for gfrpreinforced samples ranged between 2°51' and 3°31', exceeding the greatest end-rotation for sr-reinforced beams. generally, the bar's modulus of elasticity has a substantial effect on the moment end-rotation relationship. v. load-deflection relationship figure 8 depicts the load-deflection curves for the investigated beam sets (s1, s3, and s5) and (s2, s4, and s6). the lwc samples reinforced with sr bars (s3 and s4) performed similarly to the nc reference samples (s5 and s6). as predicted, the sr-reinforced lwc and nc samples turned nonlinear following the yielding of sr bars, with a dramatic rise in deflection, but a minimal rise in load capacity. nevertheless, the gf-reinforced samples functioned in a different way. the load increased with deflection, and the loaddeflection curve was nearly linear until rupture. (a) (b) fig. 8. load-deflection curves of the studied beams reinforced with (a) 1% and (b) 0.5% reinforcement ratio. prior to the sr yield, the maximum deflections of gfreinforced samples were 3 times greater than those of srreinforced samples. sr-reinforced samples with a 0.5% reinforcement ratio (s4 and s6) exhibit better ductile responses than those with a 1% reinforcement ratio (s3 and s5) at the maximum load phase. the mid-span deflection of the gfreinforced sample (s1) was 1.5-times greater than those of the sr-reinforced samples (s3 and s5) for 1% reinforcement ratio, while for samples with 0.5% reinforcement ratio, the mid-span deflection in the gf-reinforced beam (s2) was nearly equivalent to those of the sr-reinforced samples (s4 and s6). for higher reinforcement ratios, the discrepancy in mid-span deflection between gfand sr-reinforced samples is greater than at small reinforcement ratios. vi. crack number and distance the number of cracks and the distance between them, at different load stages, were recorded for all tested beams. table iv summarizes the crack behavior of the lwc and nc beams at various reinforcing ratios. the tested beams' side area was partitioned into 3 equal portions (2 outer areas and 1 central area). the number and distance between cracks were measured in each of these areas right before the beam's ultimate strength. for the reference beams made of nc and reinforced with sr bars, the number of cracks in the lower 3-quarters of the height of the central area ranged between 11 and 13, with a maximum spacing between cracks ranging from 91 to 111mm. the lower number of cracks (11:13) compared to (27:39) for gfreinforced beams (s1 and s2) may be due to the lower modulus of elasticity of gfrp bars compared to sr bars. the height of cracks up to 3-quarters of the height of the reference beams revealed a typical tension failure mode for sr-reinforced beams. when considering the gfrp reinforcement ratio, the frequency of cracks tended to raise with low reinforcement ratios. these findings may represent the impact of bar diameter and rib count on gfrp bars in enhancing bond and crack behavior, as reported in [15, 16]. the crack spacing for srreinforced beams made of nc is larger than that of beams made of lwc. this might imply that the bond and tensile strengths of nc are somewhat greater than those of lwc. another observation made during tests is that cracks in srreinforced nc and lwc beams migrated upward with steady rise in point loads. but, in gfrp-reinforced beams, cracks grew swiftly from the bottom edge up to an altitude of threequarters of the entire height, after which the cracks did not proceed further until collapse. this allows gfr rods with high strains to create the needed stresses to maintain force balance and reveals the impact of gfr rods with low modulus of elasticity. table iv. detected crack number and distance beam id ultimate load a (kn) crack spacing (mm) number of cracks failure succession left area central area right area first final stage s1 64.1 36 22 27 21 gfrp b design strength 420mpa crushing in compression zone s2 44.07 31 28 39 30 s3 61.55 61 12 21 13 yield of sr bars s4 35.81 66 10 17 13 s5 60.79 91 10 13 9 s6 36.44 111 8 11 8 a. the ultimate load value represents the value of load at each point on the beam b. gfrp bars have a perfect linear-elastic response with no yielding until rupture at 1000mpa vii. conclusions based on the outcomes of the current research, the following conclusions can be drawn:  to present the lwc and nc beams reinforced with gfrp and sr bars, fems were created and verified after the comparison with the experimental results.  in terms of maximum load capacity, moment-curvature, deflection, end-rotation, crack behavior, and failure mode, lwc and nc beams reinforced with sr bars displayed to a great extent an equivalent flexural performance.  the beams reinforced with gfrp bars had a similar load capacity, but a larger deflection than those strengthened with sr bars. this might be ascribed to the lower young's modulus of gfrp bars. engineering, technology & applied science research vol. 13, no. 3, 2023, 10776-10780 10780 www.etasr.com el zareef: an experimental and numerical analysis of the flexural performance of lightweight …  following load discharge, the remnant deformations in gfrp-reinforced beams may be ignored in comparison to those in sr-reinforced beams. this might allude to the gfrp bars' perfect linear-elastic behavior as opposed to the sr bars' elastoplastic behavior.  the progression of crack height in gfrp-reinforced beams is quicker in the early stages of loading until it reaches around three-quarters of the beam's height and then becomes significantly slower until failure.  the progression of fracture height in sr-reinforced beams behaved gradually as applied loads increased. references [1] z. h. dakhel and s. d. mohammed, "castellated beams with fiberreinforced lightweight concrete deck slab as a 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[16] m. el zareef and m. schlaich, "bond behaviour between gfr bars and infra-lightweight concrete," in tailor made concrete structures, j. c. walraven and d. stoelhorst, eds. london, uk: taylor & francis group, 2008. microsoft word etasr_v13_n3_pp10856-10860 engineering, technology & applied science research vol. 13, no. 3, 2023, 10856-10860 10856 www.etasr.com mlawa et al.: a machine learning model for detecting covid-19 misinformation in swahili language a machine learning model for detecting covid-19 misinformation in swahili language filbert mlawa school of computational and communication sciences and engineering, the nelson mandela african institution of science and technology, tanzania mlawaf@nm-aist.ac.tz (corresponding author) elizabeth mkoba school of computational and communication sciences and engineering, the nelson mandela african institution of science and technology, tanzania elizabeth.mkoba@nm-aist.ac.tz neema mduma school of computational and communication sciences and engineering, the nelson mandela african institution of science and technology, tanzania neema.mduma@nm-aist.ac.tz received: 29 december 2022 | revised: 2 february 2023 | accepted: 5 february 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5636 abstract the recorded cases of corona virus (covid-19) pandemic disease are millions and its mortality rate was maximized during the period from april 2020 to january 2022. misinformation arose regarding this threat, which spread through social media platforms, and especially twitter, often spreading confusion, social turmoil, and panic to the public. to identify such misinformation, a machine learning model is needed to detect whether the given information is true (true information) or not (misinformation). the aim of this paper is to present a machine-learning model for detecting covid-19 misinformation in the swahili language in tweets. the five machine learning algorithms that were trained for detecting swahili language misinformation related to covid-19 are logistic regression (lr), support vector machine (svm), bagging ensemble (be), multinomial naïve bayes (mnb), and random forest (rf). the study used the qualitative research method because non-numerical data, i.e. text, were used. python programming language was used for data analysis due to its powerful libraries such as pandas and numpy. four metrics were used to evaluate the model performance. the results revealed that svm achieved the highest accuracy of 83.67% followed by lr with 82.47%. mnb achieved the best precision of 92.00% and in terms of recall and f1-score, rf, and svm achieved the best results with 84.82% and 81.45%, respectively. this study will enable the public to easily identify swahili language misinformation related to covid-19 that is circulated on twitter social media platform. keywords-covid-19 pandemic; misinformation; machine learning; twitter; swahili language i. introduction social media platforms such as instagram, twitter, facebook, whatsapp, and tiktok are exceptional sources of information. they are strong tools of communication due to their accessibility, speed, and affordability [1]. these platforms are interactive communication tools and they enable smooth sharing of information, views, and thoughts. they also facilitate sharing of knowledge and experiences. they are unavoidable in our contemporary lives [2]. they gained popularity during the pandemic due to the social isolation and quarantine [3]. in spite of their advantages, social media platforms have been intentionally and unintentionally used for spreading misinformation regarding the covid-19 pandemic [4-6]. misinformation regarding covid-19 can harm people and lead them into wrong directions [4]. approximately 90% of misinformation still remain online [7]. several studies have been conducted to provide solutions for misinformation detection related to covid-19. however, no machine learning model has been developed for covid-19 misinformation detection in swahili language despite the fact that swahili is an east african language widely used in twitter and other platforms. furthermore, no swahili language datasets have been presented for detecting covid-19 misinformation. this study was conducted to address this gap. since 2019, several studies were conducted to overcome the challenge of misinformation related to covid-19. for engineering, technology & applied science research vol. 13, no. 3, 2023, 10856-10860 10857 www.etasr.com mlawa et al.: a machine learning model for detecting covid-19 misinformation in swahili language instance, the authors in [10] presented a dataset in luganda english mixed code for detecting misinformation related to pandemic from social media. several machine learning classifiers were applied including discriminative multinomial naïve bayes (dmnb), support vector machine (svm), and bagging ensemble (be). the study revealed that dmnb outperformed the other classifiers with an accuracy of 78.19% and an f1-score of 77.90%. however, the study presented the model for detecting covid-19 misinformation in lugandaenglish code-mixed. similarly, authors in [11] addressed the challenge by developing a machine learning model for detecting misinformation regarding the corona virus disease by relying on the information from un, who, and unicef. ten algorithms were employed, and decision tree (dt), logistic regression (lr), and neural networks (nns) achieved the best results. however, the developed model was limited to misinformation in english language. likewise, the authors in [9] conducted a study to address the same challenge of misinformation from twitter. a large arabic dataset was constructed. eight traditional and deep learning classifiers were applied along with features such as word embedding and word frequencies. the best accuracy results were achieved by the extreme gradient boosting (xgboost) classifier. the constructed dataset was limited to arabic content. authors in [2] conducted a similar study and three different misinformation detection models were proposed, including lstm, knn, and multichannel cnn. the proposed models were found to achieve promising results. the model was focused on detecting misinformation in english from twitter. authors in [12] presented a simple natural language processing (nlp) methodology for detecting misinformation related to the pandemic from youtube. state-of-the-art pretrained transfer learning methods such as bert base, roberta base, and xlnet base were employed. the highest accuracy achieved was 89.4%. authors in [13] proposed a simple approach that used bert embedding and shallow neural networks (snns) for detecting misinformation related to covid-19 where the bert embedding transformer was found to perform better than snns. the presented approach was limited to misinformation in english language. authors in [15] conducted a similar study using fuzzy clustering with deep learning models, focused on misinformation related to pandemic in english and chinese. authors in [14] conducted a study for detecting fake news related to covid-19 using feature extraction methods. several algorithms including random forest (rf), adaboost, knn, and dt were applied. the highest accuracy achieved was 83.50% by rf. the dataset used had approximately 1,100 records and swahili tweets were not part of it. authors in [3] presented two misinformation datasets related to covid-19 on twitter and the system known as checkvoid was developed based on machine learning and nlp technique for automatic detection of misinformation related to covid-19. this study was focused on english language. ii. research methodology the developed model follows several steps starting with collecting tweets using snscrape and ending with the evaluation of the performance of the model. figure 1 shows a conceptual framework of this study that depicts all the employed steps. jupyter notebook was used for writing the code in python. fig. 1. conceptual framework of the current study. a. data collection data were collected from twitter using snscrape. about 19,903 tweets were scraped from december 01, 2019 to january 31, 2022 based on common swahili hashtags related to the pandemic including #covid-19, #uviko19, #chanjo_korona, #barakoa_inaokoa, #ujanjakuchanja, and #homa_kaliyamapafu and #korona_tanzania. b. data cleaning and preprocessing data cleaning was conducted to remove duplicates, noise data, and data that were written in other language rather than swahili. data preprocessing was conducted to remove urls, hashtags, white spaces, punctuation marks, and other special characters such as & and %. after annotation and labelling, 682 tweets equivalent to 54.47% were found to be true information and 570 tweets equivalent to 45.53% were found to be misinformation. figure 2 and table i shows a sample snapshot and the statistics of the dataset used in this study respectively. fig. 2. sample of the dataset. table i. dataset statistics data true information misinformation total number 682 570 1,252 % 54.47 45.53 100 c. data visualization various tools and methods can be used for visualizing data. this study used the word cloud method. figures 3 and 4 show the word clouds for true information and misinformation respectively. engineering, technology & applied science research vol. 13, no. 3, 2023, 10856-10860 10858 www.etasr.com mlawa et al.: a machine learning model for detecting covid-19 misinformation in swahili language fig. 3. true information word cloud. fig. 4. misinformation word cloud. d. feature extraction term frequency-inverse document frequency (tf-idf) was used for the reduction of the dimensionality of the data by converting text features into word vector representation. it involved two aspects, i.e. tf and idf. it was computed as tf*idf, where: tf��� � � ,� ∑ � ,� (1) idf � log� � ��� � (2) where ��, � is the number of term � in the document, ∑ ��, �� is the number of all the words in the document, � is the considered document, and ��� is the total documents that have the term �. e. data splitting the dataset was split into training and testing sets. 80% of the data were used for training of the model and 20% for testing. f. model development five algorithms were trained for detecting misinformation in swahili language related to pandemic, namely lr, svm, be, rf, and mnb. 1) logistic regression lr is an algorithm for predicting discrete or categorical values. it is a supervised machine learning algorithm for solving classification problems by using the logistic function known as the sigmoid curve which is an s-shaped curve and is represented by: ���� � � � ! "# (3) it can classify data in binary or binomial, ordinal or ordered multiclass, and multinomial or multiclass classification. 2) support vector machine svm is a popular supervised machine learning algorithm used for both classification and regression problems. it aims at finding a hyperplane in an n-dimensional space for classifying data points into a number of different classes [17, 20]. equation (4) represents the general form of the hyperplane for classifying the datapoints. $� % & � 0 (4) where w is the vector normal to hyperplane (weight vector), � is the input feature, and & is the bias. 3) random forest rf is a supervised learning method based on dt. it is used for both classification and regression problems [18]. it randomly selects samples of the dataset, builds a dt for each selected sample, and makes predictions from each dt. the prediction results are combined and the final classification results are obtained by the voting method. 4) multinomial naïve bayes mnb is supervised machine learning method based on simple and probabilistic family. the classifier assumes that all features in the given class are conditionally independent. 5) bagging ensemble bagging stands for bootstrap aggregation (bootstrap aggregating). it is an ensemble learning (el) algorithm in which every predictor or model is independent of the others. it involves two key ingredients such as bootstrap and aggregation. g. model evaluation the performance of the models was evaluated by four metrics derived from the confusion matrix. these are: accuracy, precision, recall, and f1-score [10, 19]. 1) accuracy it is expressed as the ratio of the correctly classified observations to the total observations: accuracy � ./ .0 ./ 10 1/ .0 (5) 2) precision it is expressed as the ratio of the correctly classified positive observations to the total observations that were classified as positive: precision � ./ ./ 1/ (6) 3) recall it is expressed as the ratio of the correctly classified positive observations to the observations that were classified correctly: recall � ./ ./ 10 (7) 4) f1-score is the harmonic mean of the precision and recall, and is mathematically expressed as: f1 9 score � ;∗/=>?@a@bc∗d>?eff /=>?@a@bc d>?eff (8) engineering, technology & applied science research vol. 13, no. 3, 2023, 10856-10860 10859 www.etasr.com mlawa et al.: a machine learning model for detecting covid-19 misinformation in swahili language in (5)-(8), tp stands for true positive, tn for true negative, fp for false positive, and fn for false negative. iii. results and discussion a. results the results presented in figure 5 show that the svm achieved the highest accuracy of 83.67% followed by lr with accuracy of 82.47%. mnb and rf obtained the same accuracy of 80.48% while the be had the lowest accuracy of 76.01%. as for precision measure, mnb achieved the best results of 92.00%. in terms of recall and f1-score, rf and svm achieved the best results with 84.82% and 81.45%, respectively. fig. 5. evaluation. b. discussion the dataset used in this study contains only 1,252 data entries. lr and svm were found to perform much better in predicting covid-19 misinformation in swahili language. lr was then chosen as the final algorithm to be considered. iv. conclusion the threat of the covid-19 pandemic resulted to the generation of a huge amount of information related to it on social media platforms such as twitter. some of these information are true and constructive while some are misinformation and have negative consequences to the public [6]. several studies have been conducted to address the challenge of misinformation circulating on twitter and other social platforms, however, most of those studies have focused on languages other than swahili [2, 9-13]. this study was conducted to fill this gap. this study also presented a well labelled swahili language misinformation detection dataset which will be used as a starting point by practitioners and researchers for further research regarding the covid-19 pandemic. this study was limited to the twitter social media platform. future research can be extended to other social media platforms as well, such as facebook, instagram, and whatsapp. references [1] a. glazkova, "a comparison of text representation methods for predicting political views of social media users," in proceedings of the international scientific and practical conference "information technologies and intelligent decision making systems," moscow, russia, jan. 2021, art. no. 41. [2] m. n. alenezi and z. m. alqenaei, "machine learning in detecting covid-19 misinformation on twitter," future internet, vol. 13, no. 10, oct. 2021, art. no. 244, https://doi.org/10.3390/fi13100244. [3] s. dadgar and m. ghatee, "checkovid: a covid-19 misinformation detection system on twitter using network and content mining perspectives." arxiv, jul. 20, 2021, https://doi.org/10.48550/arxiv.2107. 09768. [4] b. al-ahmad, a. m. al-zoubi, r. abu khurma, and i. aljarah, "an evolutionary fake news detection method for covid-19 pandemic information," symmetry, vol. 13, no. 6, jun. 2021, art. no. 1091, https://doi.org/10.3390/sym13061091. [5] a. wani, i. joshi, s. khandve, v. wagh, and r. joshi, "evaluating deep learning approaches for covid19 fake news detection," in combating online hostile posts in regional languages during emergency situation, 2021, pp. 153–163, https://doi.org/10.1007/978-3-030-736965_15. 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[20] m. anwer, s. m. khan, m. u. farooq, and waseemullah, "attack detection in iot using machine learning," engineering, technology & applied science research, vol. 11, no. 3, pp. 7273–7278, jun. 2021, https://doi.org/10.48084/etasr.4202. microsoft word etasr_v13_n1_pp10121-10127 engineering, technology & applied science research vol. 13, no. 1, 2023, 10121-10127 10121 www.etasr.com nguyen: the improved curli method for multi-criteria decision making the improved curli method for multicriteria decision making anh-tu nguyen faculty of mechanical engineering, hanoi university of industry, vietnam tuna@haui.edu.vn (corresponding author) received: 5 december 2022 | revised: 26 december 2022 | accepted: 31 december 2022 abstract multi-criteria decision making (mcdm) investigates the best available choice in the presence of multiple conflicting criteria, whereas the collaborative unbiased rank list integration (curli) method has been proposed recently and has been applied in various fields of daily life. however, most previous works concentrated on analyzing cases in which the factor of a criterion is a specific quantity. the present paper proposes an approach developed from the original curli method, named improved curli. this improvement helps solve a problem when the factors of the criteria can be linguistic variables or a data set. the proposed method is applied to rank the alternatives for two case studies: choosing the best grinding wheel and the best service suppliers. the ranking results are compared to those obtained using other methods. furthermore, sensitivity analysis is also conducted to examine the stability and reliability of the ranking results in various scenarios. the results demonstrate the validity of the improved curli method and prove that it is applicable for making decisions in various fields. keywords-mcdm; curli method; improved curli method; data set i. introduction the concept of mcdm is increasingly being used in various fields [1, 2]. mcdm problems are mentioned as mcda or madm. the essence of mcdm is evaluating and ranking the available options in order to select the best and avoid the worst. researchers have suggested different mcdm approaches, and many of them have been applied in a variety of contexts [1, 3]. however, the original versions of the mcdm approaches are deemed inadequate for circumstances in which the criteria are expressed as a set of factors or linguistic variables [4, 5]. the main reason for this phenomenon is that the uncertainty about the object depends on a lot of factors, like experts’ opinions, time, location, the way of data collection, etc. [6]. to deal with this issue, approaches that combine the fuzzy method with mcdm have been proposed. that combination is referred to as fuzzy mcdm. many studies are progressively employing the fuzzy mcdm methods. for instance, topsis integrated with fuzzy is used in many applications such as supplier selection [7], project selection [8], healthcare software [9], supply chain management [10], manager selection [11], etc. in [12], a fuzzy vikor – mdcm is proposed to analyze and evaluate the quality of information security policies as well as the content of press agencies in gulf countries. realizing this method’s exploitation potential, numerous investigations have been launched in different tasks like warehouse location selection [13], mobile services [14], and sustainable development in islamic countries [15]. in other approaches, the fuzzy marcos method is utilized for road traffic risk analysis [16], assessment of drone-based city logistics [17], e-service quality in airline industry [18], and so on. when applying fuzzy mcdm, it is necessary to determine the weights of the criteria which play an important role to make the final decision [19-21]. in this manner, calculating the weights for the criteria is relatively complex, time-consuming, and difficult in situations requiring prompt decision-making. furthermore, the ambiguity of the decision makers (or surveyed experts) regarding the research object influences the weights determined by these methods. hence, the accuracy of the weights after the calculation is not guaranteed. as a result, no longer will the ranking of the options be certain [22-24]. in addition, most fuzzy mcdm methods still inherit some stages from the original mcdm methods, one of which is data normalization. but the data normalization processes of the mcdm methods are also not the same, leading to the ranking results of the alternatives also being highly dependent on the data normalization and sensitive to change [25-27]. generally, despite the widespread application of fuzzy mcdm approaches, they still have limitations to some extent. if a suggested mcdm method can solve two major problems, it will make significant contributions to this field. due to the mentioned limitations associated with the right determination for the criteria and the normalization of data, it is necessary to propose an mcdm approach that does not require the determination of weights for the criteria and the metric normalization. to overcome these issues, the curli method was first introduced in 2016. it is used to rank applicants for medical programs [28]. despite the fact that it has existed for engineering, technology & applied science research vol. 13, no. 1, 2023, 10121-10127 10122 www.etasr.com nguyen: the improved curli method for multi-criteria decision making six years, only a handful of research projects about this technique have been carried out. the applying curli method is proposed to inspect the quality of the x12 steel grinding process [29]. a turning test progress based on the curli approach was designed in [30]. the result reveals that the proposed method is as precise as the peg method and better than the psi method. in addition, recent works have shown that the curli method is just as accurate as the r and codas approaches to ranking robots, just as accurate as the r, saw, waspas, topsis, vikor, moora, copras, and piv approach to rating the turning process, and just as accurate as the r and mabac approaches to ranking bridge construction [31]. however, all the above mentioned studies are only considered when the criteria are clearly defined (not fuzzy set). in this paper, an approach based on the original curli method, which allows overcoming the mentioned drawbacks is proposed. the key contributions of the current paper are:  this paper proposes an improved curli method to allow solving the mcdm problems, when the factors of the criteria can be linguistic variables or a data set.  the proposed method does not need the input data to be normalized or the weights of the criteria to be evaluated.  the proposed approach is the first step towards enhancing the curli method to optimize mdcm problems as well as applying it to various fields of daily life. ii. the improved curli method the original curli method involves four steps as follows [28-31]: step 1: establish a decision-making matrix with m options and n criteria as in table i. cij is the factor of criterion j th in option i th , where i = 1 ÷ m, j = 1 ÷ n. table i. decision-score matrix alternatives criteria c1 c2 cj cn a1 c11 c12 c1j c1n a2 c21 c22 c2j c2n ai ci1 ci2 cij cin am cm1 cm2 cmj cmn step 2: create score-point matrices of level m. in criterion j, the entry corresponding to row t and column v (1  t, v  m) is determined based on the following regulations:  if the factor of criterion j in alternative at is worse than that of alternative av, the entry in the corresponding row and column will be scored as -1.  if the factor of criterion j in alternative at is better than that of alternative av, the entry in the corresponding row and column will be scored as 1.  if the factor of criterion j in alternative at is equal to that of alternative av, the entry in the corresponding row and column will be scored as 0. all the entries on the main diagonal will be blank. after this step, n square score-point matrices are established in total. step 3: create the process score-point matrix. the entries of this matrix are calculated by summing all the corresponding entries of the score-point matrix in step 2. step 4: rearrange the process score-point matrix. the arrangement will be performed by moving the rows and columns of the process score-point matrices by the following rules: the order of columns from the left to the right corresponding to the order of the rows from the top to the bottom. the number of the negative and zero entries above the main diagonal is maximal. after sorting, the solution in the first row will be the best choice. priority of selection reduces from the first to the last row. the curli approach has been used extensively to solve optimization problems in several disciplines, in which the factors of each criterion at an alternative are a specific quantity. however, in reality, a criterion may be represented by linguistic variables or a data set. this paper proposes an approach based on the original curli method for handling these issues as follows: step 1: establish a decision-making matrix as in table ii. step 2: create score-point matrices. this step is implemented similarly to the original curli. however, the score-point matrices will be determined with every factor of the criteria. the score point of each criterion is denoted as pf (1 f  k), where k is the number of factors of a criterion. table ii. decision-making matrix with multichoice of criteria in each solution alternatives criteria c1 c2 cj cn a1 (c 1 11, c 2 11,…, c k 11) (c 1 12, c 2 12,…, c k 12) (c 1 1j, c 2 1j,…, c k 1j) (c 1 1n, c 2 1n,…, c k 1n) a2 (c 1 21, c 2 21,…, c k 21) (c 1 22, c 2 22,…, c k 22) (c 1 2j, c 2 2j,…, c k 2j) (c 1 2n, c 2 2n,…, c k 2n) ai (c 1 i1, c 2 i1,…, c k i1) (c 1 i2, c 2 i2,…, c k i2) (c 1 ij, c 2 ij,…, c k ij) (c 1 in, c 2 in,…, c k in) am (c 1 m1, c 2 m1,…, c k m1) (c 1 m2, c 2 m2,…, c k m2) (c 1 mj, c 2 mj,…, c k mj) (c 1 mn, c 2 mn,…, c k mn) step 3: build the process score-point matrix. the entries of this matrix are calculated based on the sum of all points in corresponding marking point matrices. the detailed formulation is expressed as: 1 k f j j p p k   (1) step 4: rearrange the process score-point matrix. this step is the same as in the original curli method. iii. verification study and discussion a. case study 1 in this sub-section, the proposed method is applied to determine which grinding wheel to choose in an mcdm problem [32, 33]. there are 8 different types of grinding wheels (a1 ÷ a8), and each wheel is described by 7 criteria (c1 ÷ c7). each criterion has 3 alternatives. the decision is engineering, technology & applied science research vol. 13, no. 1, 2023, 10121-10127 10123 www.etasr.com nguyen: the improved curli method for multi-criteria decision making made to satisfy the conditions: (a) for c7 the smallest is the best and (b) for the other criteria, the biggest is the best. the objective of mcdm is to identify the alternative that simultaneously assures that c7 is the smallest and the remaining criteria (from c1 to c6) are maximal. this work has also been accomplished by employing the fuzzy topsis method [33] and 6 variations of the vikor method [32]. the results of rating the alternatives using these two ways will be compared to the results of ranking the alternatives using the proposed method in this study. in the first step, the decision-making matrix is composed as in table iii. in the second step, scoring for the criteria will be performed. in this case, the value of each criterion at each alternative has three levels of values. the number of alternatives that need to be ranked is 8. thus, the score for each alternative (for each criterion) is a set of numbers as shown in (2):    1 2 3p p , p , p with 1 8fj j j j j j   n (2) after the scoring process, the decision-score matrixes are illustrated from table iv to table x. in the next step, the process score-point matrix is determined based on (1) and is presented in table xi. the process score-point matrix is rearranged based on the mentioned rules in section 2. following the arranging procedure, the alternative in the first row could be seen as the best choice. the final arrangement is shown in table xii. table iii. decision-score matrix for choosing a grinding wheel [32, 33] alternatives criteria c1 c2 c3 c4 c5 c6 c7 a1 (2700, 3200, 3700) (391, 451, 511) (2925, 3475, 4025) (581, 756, 931) (12, 17, 22) (2.65, 4.15, 5.65) (12, 18, 24) a2 (2000, 2400, 2800) (590, 690, 790) (4275, 4975, 5675) (1099, 1324, 1549) (68, 98, 128) (2.2, 3, 3.8) (45, 60, 75) a3 (4400, 5000, 5600) (725, 850, 975) (6000, 6900, 7800) (1282, 1532, 1782) (9, 13, 17) (3.55, 4.5, 5.45) (714, 864, 1014) a4 (2600, 3000, 3400) (350, 400, 450) (3200, 3800, 4400) (729, 879, 1029) (21, 30, 39) (3.15, 4, 4.85) (107, 152, 197) a5 (7300, 8000, 8700) (818, 953, 1088) (5900, 6700, 7500) (4188, 4688, 5188) (950, 1200, 1450) (6.45, 8.6, 10.8) (1050, 1300, 1550) a6 (2150, 2550, 2950) (370, 440, 510) (3950, 4600, 5250) (400, 480, 560) (150, 200, 250) (2.6, 3.1, 3.6) (6.5, 10, 13.5) a7 (2400, 2800, 3200) (385, 460, 535) (1421, 1721, 2021) (425, 600, 775) (55, 90, 125) (1.95, 2.5, 3.05) (36, 50, 64) a8 (900, 1200, 1500) (115, 160, 205) (1350, 1750, 2150) (495, 620, 745) (1.4, 2.2, 3) (5.75, 8.2, 10.7) (33, 45, 57) table iv. score-point matrix for criterion c1 alternatives points p1 p2 p3 p4 p5 p6 p7 p8 a1 -1, -1, -1 1, 1, 1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a2 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 a3 -1, -1, -1 -1, -1, -1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a4 1, 1, 1 -1, -1, -1 1, 1, 1 1, 1, 1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a5 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a6 1, 1, 1 -1, -1, -1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 a7 1, 1, 1 -1, -1, -1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 -1, -1, -1 a8 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 table v. score-point matrix for criterion c2 alternatives points p1 p2 p3 p4 p5 p6 p7 p8 a1 1, 1, 1 1, 1, 1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, 1, 1 -1, -1, -1 a2 -1, -1, -1 1, 1, 1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a3 -1, -1, -1 -1, -1, -1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a4 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 a5 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a6 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 1, 1, 1 1, 1, 1 -1, -1, -1 a7 1, -1,-1 1, 1, 1 1, 1, 1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 a8 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 table vi. score-point matrix for criterion c3 alternatives points p1 p2 p3 p4 p5 p6 p7 p8 a1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 -1, -1, -1 a2 -1, -1, -1 1, 1, 1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a3 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a4 -1, -1, -1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 -1, -1, -1 a5 -1, -1, -1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a6 -1, -1, -1 1, 1, 1 1, 1, 1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 a7 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 -1, 1, 1 a8 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, -1, -1 engineering, technology & applied science research vol. 13, no. 1, 2023, 10121-10127 10124 www.etasr.com nguyen: the improved curli method for multi-criteria decision making table vii. score-point matrix for criterion c4 alternatives points p1 p2 p3 p4 p5 p6 p7 p8 a1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a2 -1, -1, -1 1, 1, 1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a3 -1, -1, -1 -1, -1, -1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a4 -1, -1, -1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a5 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a6 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 a7 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 1, 1, -1 a8 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 -1, -1, 1 table viii. score-point matrix for criterion c5 alternatives points p1 p2 p3 p4 p5 p6 p7 p8 a1 1, 1, 1 -1, -1, -1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 a2 -1, -1, -1 -1, -1, -1 -1, -1, -1 1, 1, 1 1, 1, 1 -1, -1, -1 -1, -1, -1 a3 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 a4 -1, -1, -1 1, 1, 1 -1, -1, -1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 a5 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a6 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 a7 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 1, 1, 1 1, 1, 1 -1, -1, -1 a8 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 table ix. score-point matrix for criterion c6 alternatives points p1 p2 p3 p4 p5 p6 p7 p8 a1 -1, -1, -1 1, 1, -1 1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 1, 1, 1 a2 1, 1, 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, -1 -1, -1, -1 1, 1, 1 a3 -1, -1 , 1 -1, -1, -1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 1, 1, 1 a4 -1, 1, 1 -1, -1, -1 1, 1, 1 1, 1, 1 -1, -1, -1 -1, -1, -1 1, 1, 1 a5 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a6 1, 1, 1 -1, -1, 1 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 1, 1, 1 a7 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 a8 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 table x. score-point matrix for criterion c7 alternatives points p1 p2 p3 p4 p5 p6 p7 p8 a1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 1, 1, 1 -1, -1, -1 -1, -1, -1 a2 1, 1, 1 -1, -1, -1 -1, -1, -1 -1, -1, -1 1, 1, 1 1, 1, 1 1, 1, 1 a3 1, 1, 1 1, 1, 1 1, 1, 1 -1, -1, -1 1, 1, 1 1, 1, 1 1, 1, 1 a4 1, 1, 1 1, 1, 1 -1, -1, -1 -1, -1, -1 1, 1, 1 1, 1, 1 1, 1, 1 a5 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 1, 1, 1 a6 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 -1, -1, -1 a7 1, 1, 1 -1, -1, -1 -1 -1, -1, -1 -1, -1, -1 1, 1, 1 1, 1, 1 a8 1, 1, 1 -1, -1, -1 -1 -1, -1, -1 -1, -1, -1 1, 1, 1 -1, -1, -1 table xi. score-point matrix for the evaluation process alternatives points p1 p2 p3 p4 p5 p6 p7 p8 a1 1 2.3333 -0.333 5 -1 -3.6667 -5 a2 -1 3 -3 5 0.3333 -3 -3 a3 -2.3333 -3 -3 3 -3 -3 -3 a4 0.3333 3 3 5 1 -1 -3 a5 -5 -5 -3 -5 -5 -5 -5 a6 1 -0.3333 3 -1 5 -1 -3 a7 3.6667 3 3 1 5 1 -0.3333 a8 5 3 3 3 5 3 0.3333 table xii indicates that all the entries above the principal diagonal are negative, therefore a5 is the best choice and a8 is the worst one. the rank of alternatives is as follows: a5 > a3 > a6 > a2 > a1 > a4 > a7 > a8. in table xiii, the ranking results of the present study are compared to fuzzy topsis method [33] and 6 variants of the vikor method. engineering, technology & applied science research vol. 13, no. 1, 2023, 10121-10127 10125 www.etasr.com nguyen: the improved curli method for multi-criteria decision making table xii. the process score-point matrix after rearrangement alternatives points p5 p3 p6 p2 p1 p4 p7 p8 a5 -3 -5 -5 -5 -5 -5 -5 a3 3 -3 -3 -2.3333 -3 -3 -3 a6 5 3 -0.3333 -1 -1 -1 -3 a2 5 3 0.3333 -1 -3 -3 -3 a1 5 2.3333 1 1 -0.3333 -3.6667 -5 a4 5 3 1 3 0.3333 -1 -3 a7 5 3 1 3 3.6667 1 -0.3333 a8 5 3 3 3 5 3 0.3333 table xiii. the comparison among different methods for choosing the grinding wheel alternatives methods original vikor comprehensive vikor fuzzy vikor regret vikor modified vikor interval vikor fuzzy topsis improved curli a1 6 6 6 6 6 5 6 5 a2 3 3 3 5 3 4 3 4 a3 2 2 2 2 2 2 2 2 a4 4 5 4 3 5 3 4 6 a5 1 1 1 1 1 1 1 1 a6 5 4 5 4 4 6 5 3 a7 7 7 7 7 7 8 7 7 a8 8 8 8 8 8 7 8 8 the comparison results reveal a high degree of correlation between the methodologies. all approaches offer the same optimal and secondary options. in addition, the proposed method produces 7 th and 8 th alternatives similar to the other methods. there is a variation in the arrangement of alternatives between the 3 rd and 6 th . however, the difference is small, and this does not significantly impact the overall conclusion. it is evident that analyzing the sensitivity of the method plays an important role in solving the mcdm problem [34]. in this article, we inspect the sensitivity of the proposed approach by ranking the alternatives in the case of withdrawing at least one alternative out of the group randomly. the rank of the alternatives then is compared to the ideal order. the term ideal means that there is no reverse occurring if an alternative is eliminated. in the first scenario, the worst choice a8 is withdrawn from the calculation (figure 1). fig. 1. the order of the solution after removing a8. fig. 2. the order of the solution after removing a5. fig. 3. the order of the solution after removing a4. after that, the best alternative is eliminated from the list (figure 2), and finally, the alternative in the middle of the rank is eliminated (figure 3). it is observed that in all the considered cases, the order of the alternatives is exactly the same as the ideal order. this proves that the proposed method is reliable and applicable in solving mcdm problems. b. case study 2 in the second case study, the proposed method is applied to find out the best service suppliers. each criterion is demonstrated by linguistic variables and the decision is made based on 5 criteria: product quality (c1), price (c2), delivery process (c3), service quality (c4), and past efficiency (c5). each criterion in an alternative row has 3 sub-options and the meaning of linguistic variables is illustrated in table xiv [35]. the smallest criterion c2 is the best, and for the others, the largest is the best. the fuzzy topsis method is applied to rank the alternatives [35]. the statistics of this alternate ranking approach will be compared to those of the proposed method. applying the improved curli method to estimate the alternatives in table xiv is the same as in the case study 1, and the ranking results are compared to the fuzzy topsis [35] in table xv. engineering, technology & applied science research vol. 13, no. 1, 2023, 10121-10127 10126 www.etasr.com nguyen: the improved curli method for multi-criteria decision making table xiv. decision-score matrix for choosing service supplier [35] alternatives criteria c1 c2 c3 c4 c5 a1 (m, g, g) (vg, m, g) (g, g, g) (sb, g, g) (g, sg, vg) a2 (g, g, vg) (sg, g, g) (vg, vg, vg) (m, g, g) (g, g, vg) a3 (g, g, m) (sg, vg, sg) (g, sg, sb) (g, g, g) (g, vg, sg) m – medium; g – good; vg – very good; sg – small good; sb – small bad table xv. comparison between the improved curli and the fuzzy topsis for choosing the service suppliers alternatives methods fuzzy topsis improved curli a1 2 2 a2 1 1 a3 3 3 it can be seen that the ranks of the alternatives of the two methods are precisely the same: a2 is the best and a3 is the worst alternative. this once again confirms the reliability of the proposed method. the sensitivity analysis of the alternative ranking is also performed and evaluated in detail. figures 4-6 indicate the chart of the solution ranking after eliminating a1, a2, and a3. fig. 4. the order of the solution after removing a1. fig. 5. the order of the solution after removing a2. fig. 6. the order of the solution after removing a3. the comparison shows that there is no reverse phenomenon appearing in all considered scenarios. this once again confirms the success of the proposed improved curli method in the determination of the priority order. iv. conclusion this paper proposes the improved curli approach based on the original curli method. two case studies were implemented to evaluate the methodology efficiency with different types of variables. the ranking results are compared to those of other methods to verify the reliability of the proposed method. the following conclusions are drawn:  it is notable that there was no major difference between the top and bottom positions. additionally, the sensitivity of the improved curli was examined in the case of removing some random alternatives. the results indicate that there is no reverse of rank in any of the considered case studies. this is strong evidence that supports the idea that the improved curli method is better than the old mcdm when there are problems with data and uncertainty.  it is also interesting that the proposed method can rank problems in which multiple factors influence each criterion at an alternative level without the requirement that the input data should be normalized or the criteria weights be evaluated.  the improved curli method allows solving mcdm problems when the factors of the criteria can be linguistic variables or a data set. this study is the first step towards enhancing the understanding of the curli method to optimize mdcm problems. list of acronyms mcdm multi-criteria decision-making curli collaborative unbiased rank list integration mcda multiple-criteria decision analysis madm multi-attribute decision-making topsis technique for order performance by similarity to 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[35] a. ozbek, "supplier selection with fuzzy topsis," journal of economics and sustainable development, vol. 6, no. 18, pp. 114–125, jan. 2015. microsoft word etasr_v12_n3_pp8652-8657 engineering, technology & applied science research vol. 12, no. 3, 2022, 8652-8657 8652 www.etasr.com jaballah et al.: a comparative study on hybrid vibration control of base-isolated buildings equipped … a comparative study on hybrid vibration control of base-isolated buildings equipped with atmd mohamed seghir jaballah laboratory of development in mechanics and materials civil engineering department university of ziane achour djelfa, algeria ms.jaballah@univ-djelfa.dz salaheddine harzallah built environmental research laboratory, civil engineering faculty, sciences and technology department university of houari boumediene bab ezzouar, algeria sharzallah@usthb.dz bachir nail mechanical engineering, materials, and structures laboratory faculty of science and technology tissemsilt university tissemsilt, algeria bachir.nail@cuniv-tissemsilt.dz received: 28 march 2022 | revised: 11 april 2022 | accepted: 14 april 2022 abstract-the vibration control for building structures using hybrid control (base isolators bi and active tuned mass dampers-atmds) has attracted the attention of researchers. this paper establishes a hybrid vibration control system of structure and compares structural response and active tuned mass damper performance among the structure using two different control algorithms (pid and lqr). through simulation research, from the comparative analysis of performance indexes of structural response and atmd performance, it is concluded that the lqr controller outperforms the pid controller in reducing the structural responses. keywords-pid control; lqr control; hybrid control; base isolation; atmd i. introduction one of the biggest challenges in structural engineering is the development of structural vibration control techniques [1]. with those techniques, structures can be better protected from the damaging effect of destructive environmental forces such as earthquakes, winds, and other external loads [2]. structural control has been investigated and has shown great results in reducing the vibrations in different civil structures under the effect of dynamic loads [3, 4]. the structural vibration control system can be divided by its method, or the types of devices being used, into four general types: passive control, active control, semi-active control, and hybrid control. a passive system can reduce the vibration energy without the need for external power. it uses a passive mechanism to reduce the response of the structure. this type of control utilizes two methods: seismic base isolation and supplemental damping [5]. passive control mechanisms include tuned mass (or liquid) damper (tmd/tld), viscoelastic damper, base isolation systems, etc. [5-7]. although the usage of a passive control system is very simple and affordable, it has significant disadvantages, such as being less adaptable to external environmental actions such as earthquakes and winds. the active structural control system uses actuators, sensors mounted at different locations on the structure to measure external excitations and the structural response, and a computer to calculate the appropriate force control. an external power source also is needed for actuators to apply forces to control or to modify the motion of the structure. active control devices include active tendon systems (ats), active mass dampers (amd), active brace systems, etc. [8]. hybrid structural control systems are excellent vibration control systems, because they combine the reliability of the passive system and the adaptability of the active system [9, 10]. to get the optimal control force, many methods and algorithms have been created. an analytical model for the entire system and a dynamic model of the system are needed, including all its objects such as the structure, sensor, actuators, and controller [11, 12]. in a building structure equipped with an atmd, a motor based device called actuator applies a force known as control force. one or more actuators apply these forces to a structure according to the control law and use an external energy source for their operation. these forces can be used to add or dissipate energy from the structure to be controlled. to build such a system, there are two radically different approaches: the first is to identify the seismic excitation which creates the vibrations to cancel it out by superimposing an "inverse" excitation on it. this active control strategy is called feedforward. it is mainly developed in acoustics [13, 14], but it is also very useful for the control of vibration of structures. the second is to identify the structure's response rather than the excitement that makes it corresponding author: mohamed seghir jaballah engineering, technology & applied science research vol. 12, no. 3, 2022, 8652-8657 8653 www.etasr.com jaballah et al.: a comparative study on hybrid vibration control of base-isolated buildings equipped … vibrate. it, therefore, requires the modeling of the structure to evaluate its dynamic behavior. the vibration control work that goes into this type of strategy is called feedback loop control. [15]. fig. 1. structural vibration control. base isolation systems are a well-known application of the passive control approach. these base isolators are placed between the foundations and the superstructure, these devices make it possible to decouple the movement from the ground to the superstructure, the aim of which is to reduce the forces transmitted from the ground. the isolators absorb the ground’s shaking energy and filter high-frequency accelerations so that the isolated superstructure moves essentially in a rigid mode undergoing low accelerations and almost no deformations [16]. for this reason, the base isolation system is an effective tool to ensure the seismic protection of rigid structures. to design the appropriate base isolator and to have its optimum performance many parameters should be considered, like the different characteristics of the soil and the location of the structure [17]. lrb (laminated rubber bearings) base isolators are known as one of the most used systems in isolating structures. and therefore, this type was chosen in the current study. the main purpose of this work is to compare and evaluate two different types of control algorithms (pid and lqr), that control and drive the atmd. the atmd will be placed on the top floor because it has been proven that putting the it there is a very effective strategy to reduce the structural responses. our structure will be equipped with base isolators in both cases and the performance of the two systems will be evaluated under the effect of three strong earthquakes (el centro, kobe, and northbridge). ii. pid and lqr controllers a proportional integral derivative (pid) regulator is a control organ that allows carrying out the closed-loop regulation of an industrial process. the regulator compares a value measured on the process with a setpoint. the difference between these two values (the error signal) is then used to calculate a new input value of the process tending to reduce as much as possible the difference between the measurement and the setpoint (lowest possible error signal). "pid" represents the abbreviations of the three actions it uses to make its corrections: a proportional action, an integral action, and a derivative action. adjusting this type of controller is often a matter of experience. its independence towards the model of the system is a guarantee of robustness when applied to known, linear, and little-variant systems[18]. ���� � �� ��� ��� ��� � �� ���� (1) where �� is the proportional gain, �� is the integral gain, and �� is the derivative gain. prop or tional in tegral d erivative plantr(t) + + + + output y (t)e(t) feedback fig. 2. the pid controller. linear quadratic regulator (lqr) control belongs to the family of optimal control algorithms. in optimum control, a cost function representing a performance index is chosen and then reduced to provide the optimal input. in the quadratic optimum control problem, the cost function can be designed to be quadratically dependent on the control input and the output state or response [19]: � � �� � ����� �� �� �� ��� � (2) where q is the weighting matrix (output), and r is the control vector (input). the performance index j represents the balance between the structural response and the control energy, the purpose of which is to reduce the response of the structure. the performance index shown in (3) is chosen in such a way, as to minimize the structural response and control energy over the time interval from �0 to ��. when the elements of � are large, the response of the system will be minimized to a large control force. when the elements of r are large, the control force will be small, but the structural response cannot be reduced sufficiently [20, 21]. ���� ������� (3) k (lqr gain vector) is given by: � � ������ (4) where p is the solution matrix of ricaati’s equation. fig. 3. the lqr controller. engineering, technology & applied science research vol. 12, no. 3, 2022, 8652-8657 8654 www.etasr.com jaballah et al.: a comparative study on hybrid vibration control of base-isolated buildings equipped … iii. mathematical formulation the movement equation of structure is written as: �!��� "�#��� ����� � � �$! ��� %��� (5) where m is the mass matrix, c is the damping matrix, and k is the stiffness matrix [22]. in this study, each matrix can be represented as follows: � &'(�)* )� )� … ), )�� (6) " � . . . . . . /0* 0� �0��0� 0� 0� �0� �0� ⋱ ⋱ ⋱ ⋱ ⋱ ⋱ ⋱ 0, 0�2� �0�2� �0�2� 0�2� 3 4 4 4 4 4 4 5 (7) � � . . . . . . /6* 6� �6�6 6� 6� �6� �6� ⋱ ⋱ ⋱ ⋱ ⋱ ⋱ ⋱ 6, 6�2� �6�2� �6�2� 6�2� 3 4 4 4 4 4 4 5 (8) displacement vector: 7�8� .. . / �* �� ⋮ �, ��2�3 44 4 5 , velocity vector: 7�#8� . . . / �*��# ⋮ �,# ��2�# # 3 4 4 4 5 , acceleration vector: 7�!8 � . . . / �*!��! ⋮ �,! ��2�! 3 4 4 4 5 . where �* and ��2� are the base and active mass damper displacements, 7:8 is the influence vector, in this study 7:8� ;0,0,…,1,1?�, and 7 8 denotes the applied control forces location vector [23]. the state-space representation is used to represent the equation of motion for the building structure [24-26]. @x# � b� ��c � "� d� (9) where a is the system matrix, x the state vactor, b the input matrix u the input vector, c the output matrix, y the output vector, and d the feedthrough matrix. equation (2) can be rewritten as [10]: @�#����!���e� f ;0? ;g? �; ?��;�? �; ?��;"?h@ ���� �#���e f ;0?�; ?��7:8h7����8 @ ;0? �; ?��7 8exi! ��� (10) iv. numerical simulation in this study, the performance of a hybrid control system (base isolators + atmd) is investigated. the active force is obtained by a pid and an lqr controller. a 5-story baseisolated building is considered. the top floor displacement was used as feedback in both control systems (pid and lqr). the damping and stiffness of the atmd are determined assuming a passive tmd device adjusted to the structure's first mode. the building structure parameters are shown in table i. the proportional, integral and derivative values selected for the pid controller are: kp = -20, ki = -1, kd =-300 and filter coefficient n=100. table i. building parameters floor mass (kg) stiffness (kn/m) damping (kn.s/m) base isolators 1.5 × 10 3 2.16 × 10 2 2.7 1 1.5 × 10 3 2.1 × 10 6 34 2 1.5 × 10 3 2.1 × 10 6 34 3 1.5 × 10 3 2.1 × 10 6 34 4 1.5 × 10 3 2.1 × 10 6 34 5 1.5 × 10 3 2.1 × 10 6 34 atmd 900 7.85 0.689 mn mn-1 xn xn-1 m1 x1 actuator matm d katm d catm d ba se is olators xatmd earthquake excitation fig. 4. base isolated building equipped with atmd on the top floor. engineering, technology & applied science research vol. 12, no. 3, 2022, 8652-8657 8655 www.etasr.com jaballah et al.: a comparative study on hybrid vibration control of base-isolated buildings equipped … the simulation was done in matlab/simulink. three strong historically known earthquakes were used. el centro (1940), northridge (1994), and kobe (1995) earthquakes. v. results and discussion the response results of the isolated, uncontrolled structure were compared to the same structure equipped with an atmd, using pid and lqr control algorithms. figures 5-7 show the building’s top floor displacement comparison. fig. 5. structural response under el centro seismic excitation. fig. 6. structural response under kobe seismic excitation. fig. 7. structural response under northridge seismic excitation. (a) (b) (c) fig. 8. maximum story drift for the structure under the different earthquake excitations: (a) el centro, (b) kobe, and (c) northridge. figure 5 shows the top floor displacement under el centro earthquake excitation. it can be seen that the hybrid control system using the lqr controller reduces the peak displacement by almost 60% and the pid controller by 49% in comparison with the uncontrolled structure. figure 6 shows the top floor displacement under kobe earthquake excitation. from this figure, it can be noted that the hybrid control system using the lqr controller outperforms the pid controller and reduces the engineering, technology & applied science research vol. 12, no. 3, 2022, 8652-8657 8656 www.etasr.com jaballah et al.: a comparative study on hybrid vibration control of base-isolated buildings equipped … peak displacement by almost 57%. the top floor displacement under northridge earthquake excitation is shown in figure 7. again, the hybrid control system using the lqr controller surpasses the pid controller and reduces the peak displacement by almost 62%. as these figures show, using the lqr controller to control the displacement of the top floor of the structure always gives better results than when using a pid system. it can be seen that the hybrid system designed using an lqr controller is more efficient and effective than pid control in reducing the displacement of this building in the three cases. vi. conclusion the objective of this study is to combine the application of base isolators and atmds to minimize the structural responses under the influence of seismic excitations using two different controllers, lqr and pid. according to the numerical studies for a 5-story building, and the obtained results, the following conclusions can be drawn: • the comparison between lqr and pid controllers indicates that the lqr controller is more effective in reducing the displacements and the vibration of the building and surpasses the pid controller by far. • in this study, the active control system proved to be far more efficient than the passive control systems in reducing the structural response. • more than 50% of the top floor displacement is reduced by using the hybrid control system. • using a hybrid control system to control the vibration of a structure improves its performance in resisting strong earthquake excitations and makes the structure safer and more comfortable during earthquakes. for future research, we will work in combining lqr and pid controllers in order to get the advantages of each system. references [1] a. manchalwar and s. v. bakre, "vibration control of structure by top base isolated storey as tuned mass damper," international journal of dynamics and control, vol. 8, no. 3, pp. 963–972, sep. 2020, https://doi.org/10.1007/s40435-020-00614-1. 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[26] h. bassi and y. a. mobarak, "state-space modeling and performance analysis of variable-speed wind turbine based on a model predictive control approach," engineering, technology & applied science research, vol. 7, no. 2, pp. 1436–1443, apr. 2017, https://doi.org/ 10.48084/etasr.1015. microsoft word etasr_v13_n2_pp10517-10522 engineering, technology & applied science research vol. 13, no. 2, 2023, 10517-10522 10517 www.etasr.com joseph et al.: a deep learning model for predicting stock prices in tanzania a deep learning model for predicting stock prices in tanzania samuel joseph school of computational and communication sciences and engineering, the nelson mandela african institution of science and technology, tanzania josephs@nm-aist.ac.tz (corresponding author) neema mduma school of computational and communication sciences and engineering, the nelson mandela african institution of science and technology, tanzania neema.mduma@nm-aist.ac.tz devotha nyambo school of computational and communication sciences and engineering, the nelson mandela african institution of science and technology, tanzania devotha.nyambo@nm-aist.ac.tz received: 24 january 2023 | revised: 6 february 2023 | accepted: 16 february 2023 abstract stock price prediction models help traders to reduce investment risk and choose the most profitable stocks. machine learning and deep learning techniques have been applied to develop various models. as there is a lack of literature on efforts to utilize such techniques to predict stock prices in tanzania, this study attempted to fill this gap. this study selected active stocks from the dar es salaam stock exchange and developed lstm and gru deep learning models to predict the next-day closing prices. the results showed that lstm had the highest prediction accuracy with an rmse of 4.7524 and an mae of 2.4377. this study also aimed to examine whether it is significant to account for the outstanding shares of each stock when developing a joint model for predicting the closing prices of multiple stocks. experimental results with both models revealed that prediction accuracy improved significantly when the number of outstanding shares of each stock was taken into account. the lstm model achieved an rmse of 10.4734 when the outstanding shares were not taken into account and 4.7524 when they were taken into account, showing an improvement of 54.62%. however, gru achieved an rmse of 12.4583 when outstanding shares were not taken into account and 8.7162 when they were taken into account, showing an improvement of 30.04%. the best model was implemented in a web-based prototype to make it accessible to stockbrokers and investment advisors. keywords-deep learning; stock price prediction; tanzania; dar es salaam stock exchange i. introduction a stock is a security that represents the ownership of part of a company. stock units are called shares and are traded in a stock exchange [1]. the desirable scenario with stocks is to buy when there is a good chance that a stock's price will rise and sell when there is a chance that it will decrease to gain profit from the difference between the selling and buying prices. in a nutshell, an investor aims to know when to buy and sell stocks to realize profit [2]. many studies have been conducted to predict stock prices [3], and machine learning has been proven an effective method for this [4]. ensemble techniques [5] and support vector machines [6] are some of the machine-learning techniques used in stock prediction. however, recent advances in computational power and machine learning have led to deep learning methods [7]. such methods can compute non-linear relationships among features and improve prediction accuracy [4]. deep neural networks were used to forecast stock prices showing that they can improve prediction performance. in tanzania, the only stock exchange is the dar es salaam stock exchange (dse), which was incorporated in 1996 and began trading operations in 1998 [8]. the low financial literacy of most citizens is one of the challenges that dse faces [9]. this results in low stock market uptake and infrequent activity [10]. nevertheless, machine learning and deep learning engineering, technology & applied science research vol. 13, no. 2, 2023, 10517-10522 10518 www.etasr.com joseph et al.: a deep learning model for predicting stock prices in tanzania techniques can be used to confront this challenge. such methods have been used to predict stock prices in various countries, such as morocco [11], nigeria [12], and the united kingdom [13]. this study was conducted due to the lack of similar efforts to predict stock prices in tanzania. furthermore, this study selected active stocks from dse, and instead of developing a separate model for each company, it developed one dataset and a single (joint) model to predict next-day closing prices. since each stock has a different number of outstanding shares, this study also examined whether it is significant to account for the number of outstanding shares of each stock when constructing the model. long short-term memory (lstm) and gated recurrent unit (gru) are deep learning methods designed to handle time-series data, such as stock data [14-15]. unlike traditional recurrent neural networks, lstm and gru can memorize previous information for a long time as they do not suffer from vanishing and exploding gradients [16-17], making them a good fit for stock market predictions since stock market trends tend to repeat over time [18]. numerous studies used lstm, gru, and other techniques to predict stock prices. lstm was compared with artificial neural network (ann), support vector regression (svr), and random forest (rf) models to predict the closing prices of the ishares msci united kingdom exchange-traded fund [13]. the results showed that lstm performed better than the other models, but this study used only the previous closing price as predictive input. in [19], the daily closing prices of selected listed companies on the colombo stock exchange were predicted using gru, lstm, simple recurrent neural network (srnn), and feedforward, and the previous closing, high, and low prices as predictive input. the results showed that srnn and lstm produced less errors compared to feedforward in most cases. this study used only historical stock prices as features. in [2], different machine learning methods were used to forecast the daily closing price of companies listed on the nasdaq stock exchange, concatenating data from multiple companies to form a single dataset for weekly and monthly predictions. concatenation was performed on a sector basis, where companies from one sector formed one dataset, and models were developed for each sector/dataset. linear regression, support vector machines, decision trees, ada boost, random forest, bagging, and k-nearest neighbors were used. the results showed that linear regression performed better than the other methods. however, the study did not employ a deep learning algorithm and did not consider outstanding shares. in [20], lstm and svr models were developed to predict the daily closing price of companies listed in the dow jones index. the predictive inputs were the oil and gold prices and the previous closing price. the findings showed that the lstm model outperformed the svr. however, this study used only historical prices as features. in [21], 8 sectors of the indian national stock exchange were chosen to develop the corresponding lstm models and optimum risk portfolios for each sector. the actual returns yielded by the optimum risk portfolios were calculated and compared with the predicted by lstm. the actual returns yielded by the optimum risk portfolios closely matched those predicted by lstm. however, this study used only the previous closing price as predictive input. in [22], a deep learning approach was used in a highfrequency database containing billions of transactions of us equities, finding that prediction accuracy could neither be improved by building company-specific models nor by building sector-specific models. on the other hand, including price and order flow history over many past observations improved forecast accuracy. this indicated that the patterns learned by the model are universal and not company or sectorspecific. however, this study did not consider outstanding shares. in [23], a mobile application that included a stock price prediction model was developed for east african stock markets. the model was developed using lstm and the predictive input was the previous closing price. however, the study used data from the nasdaq stock exchange, which is a us stock market, and did not state whether the resulting model was tested on actual data from east african stock markets. in [24-26], several methods were incorporated to predict future stock prices and currency exchange rates. as none of these studies attempted to study the importance of accounting for the number of outstanding shares of each stock when developing a joint model to predict the stock prices of multiple stocks, this study was conducted to address this gap. ii. methods a. data daily stock data was collected from the dse for the period from january 2018 to april 2022. the data comprised of the features: opening price, low price, high price, previous closing price, volume, outstanding bids, outstanding offers, and price change. the "price change" feature was the difference between the closing and the opening price. in addition, the study examined the outstanding shares of each company and derived the features: "volume/outstanding shares", "outstanding bids/outstanding shares", and "outstanding offers/outstanding shares". b. experimental setup 1) experiment 1 this experiment did not take into account the number of outstanding shares of each stock. therefore, the following features were employed: opening price, low price, high price, previous closing price, volume, outstanding bids, outstanding offers, and price change. 2) experiment 2 this experiment considered the number of outstanding shares of each stock/company. as a result, the features "volume/outstanding shares", "outstanding bids/outstanding shares", and "outstanding offers/outstanding shares" were used instead of volume, outstanding bids, and outstanding offers, respectively. therefore, the features used were: opening price, low price, high price, previous closing price, volume/outstanding shares, outstanding bids/outstanding shares, outstanding offers/outstanding shares, and price change. engineering, technology & applied science research vol. 13, no. 2, 2023, 10517-10522 10519 www.etasr.com joseph et al.: a deep learning model for predicting stock prices in tanzania c. selection of active companies since dse is a developing stock exchange, some companies have been inactive over time with zero or very low trading volumes [1]. this study ignored such companies to focus on companies that attract investors' attention. to identify companies with active shares, the study took the average "volume/outstanding shares" of each company over the last year. according to the study's dataset, the last year was between april 2021 and april 2022. companies whose average of "volume/outstanding shares" was greater or equal to 0.005% were selected [27]. table i shows companies whose average volume/outstanding shares was greater or equal to 0.005%. table i. companies with average of volume/outstanding shares ≥ 0.005% company volume/outstanding shares (%) crdb 0.0137 dse 0.0520 nico 0.0151 nmb 0.0099 swis 0.0310 tbl 0.0089 tcc 0.0091 tccl 0.0230 tol 0.0214 data visualizations were applied to the closing price attribute of each company in table i. tbl and tcc were eventually dropped since their closing prices were observed to be static for more than two years. according to stockbrokers, this was due to block trades that dominated their shares [28]. following the dse regulations, block trades are reflected in volume statistics but are not used to update the closing price of the stock [29]. for this reason, the "volume/outstanding shares" average of these companies appeared above the threshold but there were no corresponding price movements. this study did not use these companies to avoid distracting the model's learning. on the other hand, tpcc was appended even though its average volume/outstanding shares was 0.0034%, below the threshold of 0.005%, as its price was increasing since 2020 and therefore it was desirable for prediction. figure 1 shows the closing price history of tpcc. therefore, eight (8) companies were selected: crdb, dse, nico, nmb, swis, tccl, tpcc, and tol. fig. 1. closing price history of tpcc. d. model construction the lstm and gru deep learning methods were used to build the model. the model was developed in google colab using keras with a tensorflow backend. to ensure that all features are on a similar scale, the study utilized minmaxscaler to scale all the features in a range between 0 and 1. in total, the dataset consisted of 8668 rows of data, where 80% were used for training and the remaining 20% for testing. the adam optimizer was used together with the mean squared error as the loss function. the kerastuner bayesian optimization algorithm was used to tune the number of hidden layers, hidden units, and batch size. the regression evaluation metrics root mean square error (rmse), mean absolute error (mae), and mean absolute percentage error (mape) were used to evaluate the performance of the models. e. model deployment the extreme programming model was adopted to develop a web-based prototype to embed the model and make it accessible to stockbrokers and investment advisors. this method was chosen because it ensures rapid delivery at minimum cost while promoting stakeholder participation in the development process [30]. figure 2 shows the lifecycle of the extreme programming technique. fig. 2. extreme programming lifecycle. the planning phase is where requirements are gathered based on user stories describing various use case scenarios. figure 3 shows the use case diagram of the system. at this stage, the work was broken down into iterations (small releases) based on which functionalities needed to be delivered first. table ii shows the iterations. the design, coding, and acceptance testing phases were performed iteratively. that is, after completing the designs for the first iteration, the study continued to implement them before proceeding to design the next iteration. after completing the first iteration, acceptance testing was performed, and adjustments were made per users' reviews. thereafter, designing for the next iteration resumed, and the cycle was repeated. the design phase involved designing the user interface and logic. figure 4 shows the flow chart of the make predictions use case. the coding phase involved the actual implementation of the designs, unit testing, engineering, technology & applied science research vol. 13, no. 2, 2023, 10517-10522 10520 www.etasr.com joseph et al.: a deep learning model for predicting stock prices in tanzania and continuous integration, while acceptance testing involved users' validation of the implemented functionalities. the release phase involved the delivery of a complete system to end users, where new requirements were noted for future directions. table ii. functionalities grouped into iterations iteration functionalities first iteration  upload and manage stock data  run model to make predictions  view predictions second iteration  view market analytics third iteration  login  logout  change password  add and manage users fig. 3. use case diagram. fig. 4. flowchart of the make predictions use case. the backend was implemented using python and the django framework due to its rich collection of libraries for performing different tasks, consistent documentation, and the active developer community [31]. this framework also helped to ensure the quick development of the system while aligning with security standards. the django-plotly-dash library was used to provide interactive visualizations, and mysql was employed as the database engine. the system's frontend was built using html, css, and the bootstrap framework. furthermore, a datatable plugin was used to render interactive tables. iii. results and discussion a. model performance results tables iii and iv show the results of experiment 1 and experiment 2, respectively. table iii. experiment 1 results model rmse mae mape lstm 10.4734 6.9094 0.6359 gru 12.4583 8.8794 0.8663 table iv. experiment 2 results model rmse mae mape lstm 4.7524 2.4377 0.2147 gru 8.7162 5.8629 0.5802 the results show that accounting for the outstanding shares of each stock significantly improved the prediction accuracy. in particular, the rmse of lstm improved from 10.4734 to 4.7524 when outstanding shares were considered, which was an improvement of 54.62%. on the other hand, the rmse of gru improved from 12.4583 before accounting for outstanding shares to 8.7162 when outstanding shares were considered, which was an improvement of 30.04%. the results confirm that, for a dataset consisting of multiple stocks, taking the ratio of outstanding bids, outstanding offers, and volume of each stock to its corresponding number of outstanding shares significantly helps the model to learn from the dataset more effectively. in general, the lstm model performed better than the gru. this could be because gru keeps track of both longand short-term dependencies through only one memory cell, called the hidden state, while lstm utilizes two memory cells, one for long-term dependencies and the other for shortterm [16]. therefore, this could make lstm more efficient at learning and memorizing patterns than gru. however, these results contradict the results of [1] where gru performed better than lstm in predicting the daily closing prices of selected companies from the national stock exchange of india. one reason for this could be that the nature of the stock dataset used in this study was best captured by lstm. b. the developed prototype the prototype developed consisted of eight web page interfaces that included the login page, the data entry page, the page to manage the entered data, the page to run the model, the view predictions page, the page to view market analytics, and the change password page. on the other hand, there was a page for the administrator to add or remove users. figure 5 shows the view predictions page. engineering, technology & applied science research vol. 13, no. 2, 2023, 10517-10522 10521 www.etasr.com joseph et al.: a deep learning model for predicting stock prices in tanzania fig. 5. predictions page. iv. conclusion and future work this study developed a deep-learning model to predict the next-day closing prices of selected active companies in tanzania. two deep learning methods, namely lstm and gru, were used and the results showed that the lstm model performed better than the gru. therefore, the lstm model was deployed in a web-based prototype application for stockbrokers or investment advisors. the study laid a foundation for more research to predict stock prices in tanzania, showing how active stocks can be chosen and how the model can be developed and deployed. specifically, this study examined whether it is significant to account for the number of outstanding shares of each stock when developing a joint model to predict the stock prices of multiple stocks. the results showed that accounting for the number of outstanding shares of each stock significantly improved prediction accuracy. specifically, the rmse of lstm decreased by 54.62%, while that of gru decreased by 30.04% as a result of accounting for outstanding shares. therefore, these findings indicate that it is significant to account for the number of outstanding shares of each stock when developing a joint model to predict the stock prices of multiple stocks. these results are useful to researchers who may require to concatenate together data of several stocks to realize a sizeable dataset for stock price prediction. future studies could explore other prediction ranges, such as the next hour, week, or month. moreover, in addition to embedding a model to predict stock prices, a model can also be embedded to classify the risk tolerance level of an investor, to enable the system to provide an automated advisory tailored to his financial position. on the other hand, the use of new promising features, such as investors' sentiments, can be explored. moreover, new deep learning architectures or combinations of hybrid models can also be investigated. references [1] j. massele, c. darroux, h. jonathani, and x. fengju, "challenges faced by dar-es-salaam stock exchange market in tanzania," research journal of finance and accounting, vol. 4, no. 15, pp. 36–43, 2013. 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[31] "django introduction learn web development." https://developer. mozilla.org/en-us/docs/learn/server-side/django/introduction. microsoft word etasr_v12_n5_pp9270-9275 engineering, technology & applied science research vol. 12, no. 5, 2022, 9270-9275 9270 www.etasr.com mahmoud & ghania: a new assessment parameter to determine the efficiency of a hybrid vehicle a new assessment parameter to determine the efficiency of a hybrid vehicle khaled r. m. mahmoud university of jeddah jeddah, saudi arabia mrmahmoud@uj.edu.sa samy m. ghania university of jeddah jeddah, saudi arabia sghania@uj.edu.sa received: 25 july 2022 | revised: 4 august 2022 | accepted: 7 august 2022 abstract-this paper presents a new evaluation technique for the determination of the efficiency of a hybrid vehicle. first, the savings in fuel consumption is estimated in the ideal case considering the vehicle runs through a standard driving cycle and the engine runs at the lowest specific fuel consumption all the time. the hybridization efficiency can be defined as the ratio between the fuel savings in hybrid mode to the ideal savings according to the standard driving cycle. a case study was conducted with a medium-size passenger car according to the new european standard driving cycle. the results showed that the new proposed evaluation criterion is very effective for evaluating hybrid vehicles. keywords-fuel consumption; hybridization efficiency; standard driving cycle i. introduction the growing use of transportation based on fossil fuels has forced scientists and policymakers to take measures that would reduce the negative environmental and climate impacts, the demand for oil production, and increased fuel prices [1-3]. at present, the consumption of the transport sector represents twothirds of the global consumption of petroleum, and passenger cars and light commercial transport represent half of that consumption. therefore, the seek for alternative solutions that are highly efficient, smart, safe and clean has been among the challenges that draw the attention of researchers in both environmental and transportation fields [4-6]. hence, the development of innovative technologies of hybrid electric vehicles is a potential environmentally friendly and costeffective solution along with their applicability. logically, there is an urgent need to switch from conventional internal combustion engine (ice) vehicles to hybrid vehicles. nowadays, hybrid vehicles contribute significantly to the reduction of emissions, especially in urban areas. the use of hybrid vehicle technologies has recently accelerated not only for passenger cars but also for heavy vehicles [7-9]. many factors affect the fuel economy of passenger cars include traffic conditions, road geometry, and vehicle running modes such as idling, cruise, load, acceleration, and so on. the combination of these conditions can be summarized in two cases: city and highway driving. driving a vehicle on the highways means with semi constant engine speed and load is often associated with an economic performance featured by moderate fuel consumption with lower exhaust emissions per kilometer. city driving is usually recalling different engine modes especially idling, acceleration, and deceleration modes where low speeds and light or no loads which means low efficiency and excessive emission levels. so, the electric motor is the suitable alternative solution to reduce emissions and fuel consumption. also, the possibility of using brake regeneration energy as a further energy source helps reduce fuel consumption by up to 15% [10-12]. increase in intelligent technology used in hybrid vehicles such as the reduction of battery mass and the increased performance leads to increased number of hybrid vehicles in the auto market [13-16]. many studies indicated a significant rise in the number of hybrid vehicles due to the expected improvement in fuel consumption and reducing harmful emissions. some studies considered fuel consumption is little affected when running over vehicles for standard driving highway cycles and the effect is considerable within city roads [17-19]. the hybrid vehicle system operates the ice mostly in the high efficiency and low consumption range. in addition, the batteries of the hybrid system are charged to reach the area of minimum fuel consumption whenever possible [20-22]. however, the main source of energy in hybrid vehicle systems is the ice, and hybrid system deployment is one of the methods proven effective in achieving operating points close to the optimal operating point inherent to minimum specific fuel consumption for ice operation most of the time [23, 24]. in other words, the main goal of the hybridization of vehicles is to operate the vehicle under the most economical operating conditions or as close to the highest efficiency range as possible [25, 26]. usually, hybrid vehicles work on the basis that the efficiency of ices is relatively low and varies depending on the engine load and speed. on the other hand, the electric motor has high engine power and efficiency [27]. the operation of hybrid vehicles is an attempt to operate the vehicle engine in a high efficiency state as much as possible. the low energy demand at low vehicle speeds, especially in urban areas, requires low engine power. so, the battery motor is sufficient and efficient to power the vehicle, in what is called tailpipe zero emission mode. when the vehicle is running at a high corresponding author: khaled r. m. mahmoud engineering, technology & applied science research vol. 12, no. 5, 2022, 9270-9275 9271 www.etasr.com mahmoud & ghania: a new assessment parameter to determine the efficiency of a hybrid vehicle speed (70-120km/h), and the engine is running in a high efficiency range, then the ice can be relied upon to power the vehicle, which is known as the gasoline mode [28]. for high loads, it is possible to rely on both the ice and the electric motor. the battery charging strategy is based on the use of the difference between the torque at maximum efficiency and the actual torque of the vehicle to charge the batteries. hybrid vehicles are characterized by the fact that they use the energy resulting from regenerative braking energy recovery to charge the batteries and use it later when needed in the vehicle's motion, resulting in additional savings in fuel consumption [5, 29]. the common evaluation parameter of hybrid vehicles is the degree of hybridization, defined as the ratio between the power of the battery pack and the sum of battery reverse power and ice power [30]. in the same context, the degree of hybridization is defined as the ratio of the power developed by an electric motor in a hybrid vehicle to the total power consumed [31]. similarly, authors in [5, 32] have defined hybridization factor (hf) as the ratio of electric motor power to the sum of electric motor power and ice power. the degree of hybridization indicates the degree of improvement over the traditional situation but does not provide sufficient information on whether this improvement has reached or is close to the ideal degree. researchers have evaluated hybrid vehicles using the terms "hybridization degree" or "hybridization factor". this definition is limited to indicating the rate of reduction in fuel consumption compared to conventional vehicles. however, can the rate of the improvement increase and to what extent has this improvement reached its maximum value? the performance of any thermal or mechanical system is evaluated by calculating the efficiency, using the ratio between the actual case and the ideal condition, and for hybrid vehicles, the parameters for the ideal condition are not available until the efficiency is calculated. therefore, a new evaluation is needed to calculate the efficiency of hybridization because of the special working of that type of car. the current evaluation of the hybrid vehicles has some shortages. it adds a considerable amount of electric power to the main driving power of the internal combustion engine to save fuel consumption, but it does not provide how close this saving is to the deal saving of the fuel consumption. in this paper, hybrid vehicles are evaluated by calculating the efficiency of the vehicles when it runs over a complete standard driving cycle, as the term efficiency gives a more realistic impression of how close the system is to the ideal state. therefore, a new evaluation was needed to estimate the efficiency of hybridization. therefore, a new evaluation parameter will be introduced to evaluate the hybrid vehicles in terms of hybridization efficiency. this parameter is applied through a case study of a medium passenger car that undergoes the new european driving cycle (nedc). ii. methodology the new method for evaluating hybrid vehicles is based on the determination of hybridization efficiency. the new method can be applied according to the following steps: • calculating the total energy e required to run through the whole driving cycle: � � � ������ (1) where e is the required energy to complete the driving cycle, p(t) is the required power, and t is the total time of the driving cycle. • calculating the required fuel consumption when the vehicle runs whole driving cycle in conventional mode, βc in liters. • calculating the required fuel consumption when the vehicle runs the same driving cycle with hybrid mode, βh in liters. • minimum track fuel consumption βmin can be achieved considering the ideal case that the engine is running at minimum specific fuel consumption bsfcmin. • the minimum fuel consumption can be expressed as �� � � � ������� �� (2) where ρf is the fuel density. as shown in figure 1, it is considered that the fuel consumption with the conventional case is at 0% hybridization efficiency, while the 100% hybridization efficiency is at minimum fuel consumption. normally, the fuel consumption in the hybrid condition lies between the conventional and the ideal cases. from figure 1, the similarity of the triangles led to the following equation to calculate the hybridization efficiency. �� � ����� ������� �3� fig. 1. variation of the hybridization efficiency with fuel consumption. the engine fuel consumption map can provide the brake specific fuel consumption bsfc at any point coordinated by engine speed and brake mean effective pressure (sometimes engine torque). driving cycles are defined as a set of vehicle speed data points as a function of driving cycle time. in this study, the nedc [35] is used as the standard driving cycle. the evaluation of vehicle performance while moving along a driving cycle depends on how many liters of fuel are consumed to drive a complete cycle. brake specific fuel consumption varies according to the equivalent torque of a revolution. the vehicle specifications are shown in table i. the engine fuel map of the vehicle used in this study is shown in figure 2. βmin βh βc engineering, technology & applied science research vol. 12, no. 5, 2022, 9270-9275 9272 www.etasr.com mahmoud & ghania: a new assessment parameter to determine the efficiency of a hybrid vehicle table i. vehicle specifications displacement cm 3 1498 bore/ stroke mm 73.0/89.4 tire radius mm 320 projected area m 2 2.1 coefficient of air resistance -0.32 gear ratios 3.643, 2.08, 1.361, 1.024, 0.83, and 0.686 final drive ratio 4.105 coefficient of rotating parts � 1.05 gross vehicle mass (conventional) kg 1285 gross vehicle mass (hybrid) kg 1515 fig. 2. engine fuel consumption map. the batteries specifications used in this study are: • no of batteries: 38 • battery voltage: 8.4v • battery ampere-hours: 8.4ah figure 3 illustrates the power flow of the model. a matlab/ simulink model is built with the vehicle speed of the input driving cycle, and the model running time is the driving cycle time. the vehicle resistances are evaluated and the corresponding engine torque and power are calculated. the engine torque, the corresponding engine revolutions, and engine fuel map data are the inputs of the fuzzy controller to calculate the brake specific fuel consumption. using (6) from [34], the track’s fuel consumption can be calculated. iii. results the total energy required to complete the entire drive cycle is a key parameter for evaluating hybridization efficiency. the total energy can be calculated by integrating the engine power. the nominal power required to operate the vehicle throughout the nedc is shown in figure 4. the energy required to achieve the cycle is shown in figure 5 with and without brake energy recovery. in these figures, there are four similar urban zones between 0s and about 800s, and the vehicle travels in the highway zone after this period. the maximum power in the highway zone can be about twice that in the urban zone. in the same context, the maximum negative power of the highway zone is higher than twice the value in the urban zone. however, the total energy required by the vehicle to achieve the nedc without brake energy recovery is about 6000kj, while, the total energy required to achieve the nedc with brake energy regeneration is reduced by about 15% without brake energy regeneration. these results agree with [7, 32]. fig. 3. schematic diagram of the power flow chart of the hybrid vehicle. the track fuel consumption of the conventional vehicle running the whole nedc in ml/s is plotted in figure 6. the fuel consumption ranges from 0.12ml/s (idle case) to 3.4ml/s. in the urban region, there are four similar ranges with maximum values of about 1.5ml/s, while in the highway region, the enroute fuel consumption in ml/s is relatively higher. the total fuel consumption in conventional condition, βc in liters, can be calculated as the integration of fuel consumption with driving cycle time. in this case, it is 0.826lt. the track fuel consumption of the hybrid vehicle without regenerative braking energy recovery when running through the entire nedc is plotted in figure 7. the stae of charge (soc) is assumed to be 100% at the beginning of the driving cycle. in urban areas, the vehicle is driven by the electric motor (tailpipe zero emission mode). soc reaches about 60% at urban areas within the period of 0-840s of the driving cycle time. engineering, technology & applied science research vol. 12, no. 5, 2022, 9270-9275 9273 www.etasr.com mahmoud & ghania: a new assessment parameter to determine the efficiency of a hybrid vehicle fig. 4. engine power variations within a cycle time of nedc. fig. 5. vehicle energy variations within the nedc cycle time. fig. 6. fuel consumption of the conventional vehicle according to nedc. fig. 7. fuel consumption and soc of the hybrid vehicle without regenerative brake energy recovery running over the nedc. on the highway, the vehicle’s engine performs two tasks: it mainly drives the vehicle and the rest of the maximum engine torque is used to charge the batteries. a time period of about 70s is sufficient in this case to recharge the batteries and bring the soc back to 100%. the average fuel consumption during this period is about 4.3ml/s. finally, in the last period, the vehicle runs in gasoline mode, as this is economically feasible on the highway. the total fuel consumption on the highway when the vehicle is driven in gasoline mode and the batteries are recharged to 100% within soc is about 0.67lt, which is about 19% lower than the conventional vehicle. these results are in accordance with [33, 34]. the fuel consumption for the hybrid vehicle for the case of brake regeneration energy recovery is shown in figure 8. when the vehicle is driven in the urban area in the tailpipe zero -emission mode, the soc decreases from 100% to about 72%. when the vehicle is on the highway, in addition to charging the batteries, it also takes 55s to recharge the soc to 100%. the total fuel consumption required for highway driving, in addition to battery charging, is about 0.583lt, which is 35% less than the conventional vehicle and about 13% less than the hybrid vehicle without regenerative braking energy recovery. fig. 8. fuel consumption and soc of the hybrid vehicle with regenerative brake energy recovery according to the nedc. fig. 9. track fuel consumption of the vehicle according to the nedc. fig. 10. hybridization efficiency of the vehicle according to the nedc. it can be concluded that this comparison shows a significant improvement when using the hybrid system with and without brake energy regeneration. but have these improvements reached the maximum limits, or can the fuel savings be increased? this evaluation method does not give us an engineering, technology & applied science research vol. 12, no. 5, 2022, 9270-9275 9274 www.etasr.com mahmoud & ghania: a new assessment parameter to determine the efficiency of a hybrid vehicle indication of the fuel economy in the ideal case. equation (3) was applied to evaluate the proposed new evaluation parameter and the result is shown in figure 10. it shows the relationship between hybridization efficiency in the two usage modes and the non-use of brake energy recovery for both driving cycles. efficiency is a measurable and easily understood concept that provides a clear indication of the extent to which the hybridization efficiency reaches the ideal state. figure 11 shows the degree of hybridization of the vehicle crossing the whole nedc with and without brake regeneration energy. looking in depth at the current assessment, there are some shortcomings, which are the extent to which the optimum reduction in fuel consumption can be reached. the expression in terms of efficiency provides a clear picture of how close this is to the ideal case. fig. 11. degree of hybridization according to the nedc (current assessment). iv. conclusions in this paper, the status of hybrid vehicle evaluation was reviewed. it was found that there are some shortcomings in the current evaluation parameters, regardless of the degree of hybridization or the hybridization factor. these inadequacies, since the fuel economy savings are given as a percentage of the conventional condition, do not refer to the ideal conditions (the concept of efficiency). therefore, a new evaluation parameter can be used to evaluate the hybridization efficiency with reference to the ideal condition. hybridization efficiency can be calculated by dividing the fuel economy in hybrid mode by the maximum economy in the ideal condition when the vehicle runs the entire standard driving cycle. hybridization efficiency gives a tangible and accurate comparative formula for evaluating hybrid vehicles. in this study, two case studies are presented with a mid-size passenger car in the full nedc driving cycle with and without brake energy regeneration. the results show that the new factor, hybridization efficiency, is very effective and provides tangible and logical results. the hybridization efficiency is about 40% and 61% without and with regenerative braking energy respectively, when the vehicle goes through the whole nedc driving cycle. acknowledgement this work was funded by the university of jeddah, jeddah, saudi arabia, under grant no. 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[32] j. m. tyrus, r. m. long, m. kramskaya, y. fertman, and a. emadi, "hybrid electric sport utility vehicles," ieee transactions on vehicular technology, vol. 53, no. 5, pp. 1607–1622, sep. 2004, https://doi.org/ 10.1109/tvt.2004.832418. [33] p. lijewski, m. kozak, p. fuc, l. rymaniak, and a. ziolkowski, "exhaust emissions generated under actual operating conditions from a hybrid vehicle and an electric one fitted with a range extender," transportation research part d: transport and environment, vol. 78, jan. 2020, art. no. 102183, https://doi.org/10.1016/j.trd.2019.11.012. [34] k. ahn and h. a. rakha, "a simple hybrid electric vehicle fuel consumption model for transportation applications," in applied electromechanical devices and machines for electric mobility solutions, london, uk: intechopen, 2019. [35] a. s. khameesa and m. r. altaay, "evaluating the efficiency of finance methods in residential complex projects in iraq," engineering, technology & applied science research, vol. 12, no. 1, pp. 8080–8084, feb. 2022, https://doi.org/10.48084/etasr.4663. authors profile khaled r. m. mahmoud, is a professor in the mechanical and materials engineering department, college of engineering, university of jeddah, saudi arabia. he received his ph.d. degree from the heinz nixdorf institute, university of paderborn, paderborn, germany in 2005. he has pioneered research in vehicle dynamics and vehicle braking systems and has published more than 35 research articles. he has reviewed several research papers in isi journals, in fields such as energy conversion and management and vehicle dynamics. his current research interests lie on the dynamics of hybrid vehicle systems and internal combustion engines fueled by alternative fuels. samy m. ghania was born in egypt, in 1971. he received the b.sc., m.sc., and ph.d. degrees in electrical engineering from the faculty of engineering, benha university, cairo, egypt, in 1995, 2001, and 2005 respectively. in july 2006, he joined the university of waterloo, waterloo, on, canada, as a postdoctoral fellow. he is currently working as a professor of electrical engineering at the university of jeddah, saudi arabia. he has published several papers in international journals and conferences in electrical machines, drives, interference, and electromagnetic simulation, and effects on the human body. he has carried several projects on electrical machine control using micro-controllers, dsp, programmable logic control, and renewable energy resources. his areas of interest include modeling and simulation of electrical machines, drives for electrical vehicles, and its control systems. microsoft word 8-672-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1155-1157 1155 www.etasr.com abubakri and veladi: investigation of the behavior of steel shear walls using finite elements analysis investigation of the behavior of steel shear walls using finite elements analysis kamran abubakri department of civil engineering mahabad branch, islamic azad university mahabad, iran. kamran.abubakri13@chmail.ir hedayat veladi department of structural engineering faculty of civil engineering, university of tabriz tabriz, iran. hveladi@tabrizu.ac.ir abstract—currently, steel shear walls are considered by engineers as an economic method against lateral loads imposed by wind and earthquake in tall structures. accordingly, there is a growing need to develop accurate methods alongside approximation methods to estimate the behavior of these structural elements. the finite element technique is one of the strongest numerical methods in analysis of solid mechanics problems. finite element analysis however requires high technical knowledge of the behavioral models of materials. therefore, it is less used by designers for certain structural elements such as steel shear walls. this study examines the failure mechanism of steel shear walls using finite elements analysis and validates this modeling by comparing the results with experimental studies. keywords-steel shear wall; nonlinear analysis; post-buckling behavior; cyclic loading; lateral loading system i. introduction the most important challenge that engineers face during the design and construction of tall buildings is to design a good lateral loading system with the ability to tolerate wind and earthquake forces, particularly in high-rise buildings. one of the solutions for this problem is to use steel shear walls. several international regulations accept and allow this solution, for example the canadian regulation can/csa s16-01. according to this regulation, an equivalent brace, rather than any steel plate, is considered after distribution of the horizontal force at the height of the structure. in [1-3] the history of steel shear walls is described in detail. structurally, a steel shear wall is composed of a steel plate in the center with peripheral beams and columns. steel shear walls act like a cantilever steel plate beam in which columns are the wings of the plate beam, story beams (story bridges) are stiffeners and the steel plate is the web. empirical studies conducted so far have led to a comprehensive understanding of the behavior of this lateral loading system. these studies address the ductile connections between the plate and its frame, behavior of the infill plates, strength and stiffness of the system and others [4, 7-9]. in addition to laboratory studies, extensive studies have been conducted regarding numerical modeling of steel shear walls. in [12] the precise estimations of time periods in structures equipped with steel shear wall was discussed. moreover, there are many ongoing studies on reinforced steel shear walls. in [6] the system was reinforced by carbon fiber polymers. in [5] the effect of stiffeners and the connection between central beam and peripheral frame on mechanical behavior of the structure with steel shear wall was studied using finite element analysis. ii. bearing systems of steel shear walls steel shear wall consists of a thin steel plate, two boundary columns and horizontal beams in which the steel plates are connected by welding or bolts to the peripheral frame. it is also possible to use longitudinal and transverse stiffeners to reinforce steel plate. figure 1 shows the schematic details of a steel shear wall with stiffener. two main factors of the lateral load-resisting systems such as bracing systems, steel shear walls, moment-consuming frames, and concrete shear walls include stiffness and strength which are determined by loaddisplacement diagram. currently, there are three general methods for analysis of steel shear walls: 1) strip model, 2) frame-plate interaction or the sabouri method which is used here to control the results of finite element modeling [10, 11], 3) finite element method. fig. 1. steel shear wall with stiffeners in the strip model presented by researchers at the university of alberta, canada [2, 3, 9] shear panels are modeled as a series of diagonal strip members which are only able to tolerate tensile forces in the same direction of main tensile stresses. the strip model is only limited to steel shear walls with thin plates. moreover, this model provides no solution for steel shear walls with openings or stiffeners. to eliminate these problems, a engineering, technology & applied science research vol. 6, no. 5, 2016, 1155-1157 1156 www.etasr.com abubakri and veladi: investigation of the behavior of steel shear walls using finite elements analysis general method to analyze and design steel shear walls in different scenarios with and without stiffeners, with and without opening, with thin and thick plate was proposed in [10, 11]. this method evaluates the behavior of plate and frame separately, and considers the interaction of these two elements together. this model is called frame-plate interaction and its modeling through the use of finite element analysis can prove highly time and cost effective as well as accurate. iii. validation of finite element method in modeling steel shear wall this section validates the finite element modeling of steel shear walls by ansys software. figure 2 compares the output of the finite element modeling in ansys software and results of the experiment on one-story steel shear wall with a thin plate at the university of british columbia. the comparison between load-displacement curves shows that the computerized model is in a good agreement with the experiment. fig. 2. comparison of the finite element results (blue ansys) and the sample tested under cyclic load (black) iv. failure behavior of steel shear wall for tested samples with 0.7 mm in thickness this section presents the force-displacement curve obtained from finite element nonlinear analysis for laboratory samples of [13] which is the frame of an opening equipped with shear wall. table i lists the geometry of the samples tested in [13]. figures 3 to 5 compare the force-displacement curves obtained from finite element modeling by this study and experimental results from [13]. table i. geometry of samples with 0.7 mm in thickness for steel plate sample height of story (h in cm) width of opening (b in cm) aspect ratio (h/b) 1 120 170 0.706 2 120 120 1 3 170 120 1.42 as shown in figures 3 to 5, modeling and experimental results are reasonably close to each. in all samples, the stiffness of finite element analysis by anysy is higher than the stiffness of the experimental models. 0 2000 4000 6000 8000 10000 12000 14000 16000 0 10 20 30 40 50 displacement(mm) fo rc e( k gf ) ansys test fig. 3. force-displacement curve obtained from finite element analysis for sample 1 0 2000 4000 6000 8000 10000 12000 0 10 20 30 40 50 60 ansys test fig. 4. force-displacement curve obtained from finite element analysis for sample 2 0 2000 4000 6000 8000 10000 0 20 40 60 80 100 displacement(mm) fo rc e( k gf ) ansys test fig. 5. force-displacement curve obtained from finite element analysis for sample 3 figure 6 shows the finite element results as loaddisplacement curves for all samples. obviously, the increase in aspect ratio of the panel reduces stiffness. table ii lists the stiffness obtained for all samples. clearly, the increase in aspect ratio reduces stiffness. figure 7 shows the effect of changes in aspect ratio of the panel on the ultimate strength of the system. obviously, the increase in this ratio reduces the ultimate strength of the system. as shown in the figure, the ultimate strength is equal to 9450 kgf for the obese rectangular sample, 8600 kgf for the square sample and 7630 kgf for the thin rectangular sample. engineering, technology & applied science research vol. 6, no. 5, 2016, 1155-1157 1157 www.etasr.com abubakri and veladi: investigation of the behavior of steel shear walls using finite elements analysis 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 0 20 40 60 80 100 displacement(mm) fo rc e( k gf ) ratio=0.706 ratio=1 ratio=1.42 fig. 6. comparison of load-displacement curves for the analyzed samples table ii. lists the stiffness obtained for all samples sample aspect ratio (h/b) stiffness (kgf / mm) 1 0.706 612.7 2 1 467.8 3 1.42 279.6 fig. 7. relationship between ultimate strength of the steel shear wall and aspect ratio of the panel in this case, the ratio of the ultimate strength of obese rectangular sample to the square and thin rectangular samples is: )1( 24.1 7630 9450 09.1 8600 9450         the ratio of the ultimate strength of the square sample to the thin rectangular sample is: )2(13.1 7630 8600  obviously, ultimate strength of the obese rectangular sample is ~9% higher than the ultimate strength of the square sample and ~24% higher than that of thin rectangular sample. moreover, the ultimate strength of the square sample is ~13% higher than that of the thin rectangular sample. v. conclusion steel plates buckle when the limit load is reached. however, this does not imply systemic instability. as shown in experimental curves, there are jumps in some parts. in this load balance, the plate buckles and stiffness decreases in the loaddisplacement curve. in the buckling point, as the load increases, the system reaches a new equilibrium by geometric deformation. simultaneously, the system shifts from in-plane shear to diagonal tension. after the buckling point, stiffness increases as the load increases and diagonal tension is formed. diagonal post-buckling plate does not imply systemic instability. comparison of load-displacement curves obtained from experiments and finite element ansys shows that analytic stiffness is higher than experimental stiffness; because experimental plates are not fully flat, while finite element analysis assumes that the plate is completely flat. references [1] aisc, seismic provisions for structural steel buildings. ansi/aisc 341-10. american institute of steel construction, inc., chicago, illinois. 2010 [2] m. bruneau, c. m. uang, r. sabelli, ductile design of steel structures. 2nd ed. new york: mcgraw-hill, 2011 [3] canadian standards association (csa), design of steel structures. can/csa s16-09. willowdale, ontario, canada. 2009 [4] r. g. driver, g. l. kulak, d. j. l. kennedy, a. e. elwi, seismic behavior of steel plate shear walls, structural engineering report 215, department of civil engineering, university of alberta, edmonton, alberta, canada. 1997 [5] h. c. guo, j. p. hao, y. h. liu, “behavior of stiffened and unstiffened steel plate shear walls considering joint properties”, thin-walled structures, vol. 97, pp. 53-62, 2015 [6] f. hatami, a. ghamari, a. rahai, “investigating the properties of steel shear walls reinforced with carbon fiber polymers (cfrp)”, journal of constructional steel research, vol. 70, pp. 36–42, 2012 [7] m. rezai, seismic behavior of steel plate shear walls by shake table testing. phd thesis, university of british columbia, vancouver, bc, canada. 1999 [8] t. roberts, s. sabouri ghomi, “hysteretic characteristics of unstiffened plate shear panels”, thin-walled structures, vol. 12, no. 2, pp.145–62, 1991 [9] r. sabelli, m. bruneau, steel plate shear walls (aisc design guide) chicago, illinois: american institute of steel construction, inc. 2007 [10] s. sabouri ghomi, t. m. roberts, “nonlinear dynamic analysis of steel plate shear wallsincluding shear and bending deformations”, engineering structures, vol. 14, no. 5, pp. 309-317, 1992 [11] s. sabouri ghomi, the systems resistant against lateral loads; an introduction on steel shear walls, angizeh, tehran, 2001 [12] c. topkaya, c. o. kurban, “natural periods of steel plate shear wall systems”, journal of constructional steel research, vol. 65, no. 3, pp. 542-551, 2009 [13] h. veladi, a. armaghani, a. davaran, experimental analysis of periodic behavior of steel shear walls, university of tabriz, iran, 2006 microsoft word etasr_v12_n6_pp9732-9736 engineering, technology & applied science research vol. 12, no. 6, 2022, 9732-9736 9732 www.etasr.com alaidi et al.: increased efficiency of the artificial bee colony algorithm using the pheromone technique increased efficiency of the artificial bee colony algorithm using the pheromone technique abdul hadi alaidi programming department, computer science and information technology college, wasit university wasit, iraq alaidi@uowasit.edu.iq soong der chen college of computing and informatics universiti tenaga nasional selangor, malaysia chensoong@uniten.edu.my yeng weng leong college of computing and informatics universiti tenaga nasional selangor, malaysia ywleong@uniten.edu.my received: 1 september 2022 | revised: 15 september 2022 | accepted: 17 september 2022 abstract-artificial bee colony (abc) is a powerful metaheuristic algorithm inspired by the behavior of a honey bee swarm. abc suffers from poor exploitation and, in some cases, poor exploration. ant colony optimization (aco) is another metaheuristic algorithm that uses pheromones as a guide for an ant to find its way. this study used a pheromone technique from aco on abc to enhance its exploration and exploitation. the performance of the proposed method was verified through twenty instances from tsplib. the results were compared with the original abc method and showed that the proposed method leverages the performance of abc. keywords-artificial bee colony; pheromone; ant colony optimization i. introduction artificial bee colony (abc) is a well-known algorithm for solving continuous function optimization problems. although abc is more effective than other biologically inspired algorithms, it suffers from a slow convergence rate in large search spaces [1-3]. in addition, one of the problems of abc is the blind search strategy for food sources. in nature, honey bees interact with each other primarily through chemistry-driven behavioral communication. however, in the conventional abc algorithm, honeybees only dance to share information. therefore, it is necessary to incorporate chemistry communication in addition to behavioral to comply with the reality in nature and the basic principles of abc. the attraction pheromone and transition strategy were used in [3, 4] as a communication strategy to share information between bees and solve the blindness search. it was assumed that each bee moves to a solution and deposits the attraction pheromone that attracts other bees to the object where the pheromone strength is higher than the others. this mechanism enabled bees to search for food more effectively. other studies used pheromones to overcome the limitation of abc exploitation by making bees communicate and share their findings [3, 4]. scout bees use pheromones as a guide when looking for a new food source, and pheromones are updated at all stages. moreover, the amount of deposit pheromones is a function of fitness measures. abc integrates grenade explosion and the cauchy operator to avoid random searches and solve dynamic economic emission dispatch (deed) problems [5]. in [6, 7], methods were used for routing and improving the performance of wireless sensor networks. the memory mechanism plays a crucial role in the guide of the search process by memorizing valuable information and exploring new search spaces. in [8], the memory mechanism was used to improve abc performance, addressing the fundamental problem of abc, which is the exploration and late convergence. this study aimed to solve the problem of exploration and late convergence in abc using random memory (rm) and elite memory (em), leading to a more desirable version of abc called abcwoa. in the abcwoa algorithm, rm uses the bait search stage in the whale optimization algorithm (woa). at the same time, em is dynamically controlled based on the number of iterations and used to increase the convergence rate. furthermore, ten standard data sets from the uci machine learning repository were used for the evaluation, showing that abcwoa had an improved convergence rate and less noise. abc is used to solve many types of problems. for example, an unrelated parallel machine scheduling problem was solved with abc using a multi-sub-colony [9]. in addition, a multi-strategy evolutionary learning abc algorithm was proposed to solve the path problem of an unmanned autonomous helicopter [10]. this study aimed to increase the performance of abc using pheromone as a guide for bees and to overcome the abc exploitation and exploration problem. corresponding author: n abdul hadi alaidi engineering, technology & applied science research vol. 12, no. 6, 2022, 9732-9736 9733 www.etasr.com alaidi et al.: increased efficiency of the artificial bee colony algorithm using the pheromone technique ii. the artificial bee colony the abc is a well-studied algorithm developed to solve continuous function optimization problems [11], simulating the foraging behaviors of a swarm of bees to find food. abc is used successfully in many fields including energy management in mobile devices [12] and iot routing [13]. abc is divided into three groups: employed, onlookers, and scout bees. at first, employed bees search for food sources and share information with an onlooker. the onlooker bee tries to search for a better food source in the neighborhood using the knowledge passed from the employed bees. if the food source is abandoned to escape the limitation of food enhancement, the bees employed for that food source become scouts and randomly search for a new food source. in abc, employed and onlooker bees perform the exploitation, while scout bees control the exploration process. the employed bees use (1) to search for neighbors by moving from an old position xij to the new position vij, if and only if the new position's fitness is better than the old position's. ��� = ��� + ��� ���� − � � � (1) where xi is the old position and vi is the new position of the i th employed bee, φij is a random real number in the range [-1, 1], j is an arbitrary integer number between 1 and the problem's dimension, and k is a random number between 1 and the number of employed bees. the onlooker bee selects a food source and evaluates all employed bees depending on the probability: �� = ���∑ �������� (2) where fit is the fitness value of the solution of the employed bee: ���� = � � �� ��� � , ���� � ≥ 01 + |���� �|, ���� � < 0 (3) where f(xi) stands for the value of the objective function to be optimized. like the employed bee, the onlooker bee uses (1) to update its position and explore the selected food source. when a food source cannot be further enhanced within a pre-defined trial limit, it is abandoned and the corresponding employed bee becomes a scout and randomly searches for a new food source. the combination of exploration and exploitation search in abc is important as it enables the algorithm to search the solution space for high-quality solutions and prevents them from getting stuck in local optima. in abc, the employed bees maintain the current solution while the onlooker bees allow the best solution to be exploited. furthermore, scout bees try to remove stagnating solutions and explore new ones. initialization phase repeat employed bees phase onlooker bees phase scout bees phase memorize the best solution achieved so far until(cycle=maximum cycle number) fig. 1. the standard abc. iii. ant colony optimization another non-deterministic algorithm used to solve an optimization problem is ant colony optimization (aco). aco was inspired by ants seeking the shortest route between a source of food and their colonies [14]. aco seeks the optimal solution for the computation problem by building one solution and adding it to solution components until the wanted solution is built. aco has been successfully applied to solve the traveling salesman problem. however, as the complexity of the problem increases the accuracy of the aco algorithm decreases. in nature, ants use pheromones as indirect communication between them. in aco, pheromones are represented by numeric values modified by every solution component. these values influence the movement of ants in the next iteration in a way that edges between nodes with large values (high levels of pheromones) are more likely to be visited. furthermore, the aco model allows for the inclusion of heuristic information to guide the ants to complete a feasible solution. set parameters, initialize pheromone trails while (condition is not satisfied) do constructantsolutions daemonactions {optional} updatepheromones end while fig. 2. the aco algorithm. each ant starts from a random location and makes a trip. when being in location i at the t th iteration, ant k applies a probabilistic action before it is transmitted to the next unvisited location j. finding the probability for ant k is given by [15]: &�'( ��� = [*+,�-�]∝.[1+,]2∑ [3�44∈6�( ���]7.[8�4]9 , �� ' ∈ 6� ( (4) where η=1/dij is the value of the heuristic available in advance, a and β are two parameters that define the relative influence of the pheromone trail and the heuristic information, and 6�( is the feasible neighborhood of the ant k. parameters α and β play a main role in choosing the next location to be visited. if α = 0, there is no pheromone impact on the movement of the ants. however, if β = 0, only pheromone strengthening works. it has been suggested that all ants construct the same path consequently and a trade-off exists between the pheromone trail and the impact of the heuristic information [15]. the pheromone update procedure is performed in two steps. first, the amount of pheromone on the edge that joins two locations is decreased by a constant factor. the next step is to put a certain amount of pheromone on that particular edge. the update of the pheromone is calculated by: 3�� �� + 1� = �1 − :�. 3�� ��� + ∑ ∆3��< ���=<>� (5) where ρ is greater than 0 and equal to or less than 1. the parameter ρ is used to avoid accumulating a high level of the pheromone trail by lowering the pheromone level. similarly, it helps ant to discard bad decisions early taken and discover a new solution. moreover, ∆3�� ��� represents the quantity of pheromone that will be added, defined as: engineering, technology & applied science research vol. 12, no. 6, 2022, 9732-9736 9734 www.etasr.com alaidi et al.: increased efficiency of the artificial bee colony algorithm using the pheromone technique ∆3��< ��� = ?1 @<���a if edge ��, '� is used by the ant0 otherwise (6) where lk(t) is the length of the k th ant's trip. equation (6) shows that adding more pheromones to an edge gives a better ant trip, and edges with high pheromones are more likely to be visited in the next iteration. in as, all ants add a certain quantity of pheromone on the visited edge. this method does not provide additional support for the best solution found, although letting all ants update the pheromone trails may help the algorithm avoid an early stagnation and move to different search space. iv. using pheromones with abc to solve tsp the traveling salesman problem (tsp) was used as a test case for the proposed algorithm. tsp is an easy to describe well-known problem, but hard to solve. the purpose of tsp is to find the shortest path between groups of cities with minimum cost. a. initialization phase pheromones can integrate into abc to give memory-like behavior. the proposed algorithm initializes the parameters and then initializes the pheromones using the neighbor search algorithm to find the start path to update the pheromone using (5). finally, the food source (solutions) is generated using (4). initialize maxiteration, popsize, limit, beta & initialize pheromone trails for i = 1 to popsize/2 foodsource[i] = initializeusingpheromone() unsuccessfulcycles[i] = 0 fitness[i] = calculatefitness(foodsource[i]) end for fig. 3. initialization. b. employed bee phase the employee bee is responsible for searching in the neighborhood for new solutions and changing positions if the new position is better than the old one. figure 4 shows the employee bee phase algorithm. for i = 1 to popsize/2 newsol = neighborseach(foodsource[i], i) newcost = calculatefitness(newsol) if newcost < fitness[i] // greedy selection foodsource[i] = newsol fitness[i]=newcost unsuccessfulcycles[i] = 0 end if end for fig. 4. employed bee phase. c. onlooker bee phase onlooker bee calculates the probability pi of choosing a food source using (2). then sends onlooker bees to a food source(i) according to the associated pi and generates a new food source, as shown in figure 5. for i = 1 to popsize/2 newsol = neighborseach(foodsource[i], i) newcost = calculatefitness(newsol) if newcost < fitness[i] // greedy selection foodsource[i] = newsol fitness[i]=newcost unsuccessfulcycles[i] = 0 end if end for fig. 5. onlooker bee phase. d. updating pheromone phase after the onlooker has explored the food source, each bee will deposit the pheromone on the link using (6). then, the pheromones on all edges are reduced to prevent stagnation. figure 6 shows the step for deposit and reduction. deposit pheromone on the links reduce pheromone levels on all edges memorize the best solution achieved so far fig. 6. pheromone update e. scout bee phase in the scout bee phase, each bee that couldn't enhance anymore will abandon its food source and search for a new one. figure 7 shows the scout bee phase algorithm. for i = 1 to popsize/2 if unsuccessfulcycles [i] > limit foodsource[i] = initializeusingpheromone() newcost = calculatefitness(newsol) fitness[i]=newcost unsuccessfulcycles[i] = 0 end if end for fig. 7. scout bee phase. f. neighbor operator the neighborhood operator [16-17] is a replacement for (1) to make abc capable of solving discrete problems. random swap crossover was used to perform a neighbor search. figure 8 shows the random swap crossover operation. fig. 8. random swap crossover. engineering, technology & applied science research vol. 12, no. 6, 2022, 9732-9736 9735 www.etasr.com alaidi et al.: increased efficiency of the artificial bee colony algorithm using the pheromone technique v. results and discussion the proposed method was implemented using c# and run on a 2.80ghz intel core i7 processor with 16gb ram. the proposed algorithm was tested on 20 tsp instances from [18]. table i shows the statistical variation of the results for 20 tsps solved by the two algorithms on 30 independent runs. the results of the experiments demonstrated the superiority of the proposed method over the original abc, as the error rate and average error rate were better in all cases. figure 9 shows a comparison between the error rate of abc and the proposed method, while figure 10 shows the average rate between the two methods. the error rate was computed using: sttut tv�s = wxy� z[\]x^ _`��a[\ z[\]x_`��a[\ z[\]x × 100 (7) table i. comparative experimental results abcupt with abc problem abc proposed method error avg error error avg error att48 15.65 25.70 6.15 12.55 eil51 18.54 25.63 6.81 12.49 berlin52 15.87 26.71 6.19 12.18 st70 36.89 53.28 15.06 20.40 eil76 36.62 45.62 12.74 20.97 pr76 39.44 52.80 18.17 27.10 kroa100 74.21 95.10 20.52 31.65 krob100 65.13 89.32 23.24 35.24 kroc100 79.46 100.86 24.49 36.81 krod100 72.38 91.55 20.65 31.22 kroe100 63.70 90.23 23.79 36.58 rd100 74.34 86.08 26.99 37.33 eil101 53.58 62.87 24.64 30.86 lin105 82.29 101.68 21.41 33.98 pr107 111.54 172.57 2.40 4.94 gr120 78.68 94.62 34.72 39.89 pr124 143.39 168.81 31.57 37.88 bier127 50.72 70.09 17.25 27.23 ch130 83.01 105.02 20.41 38.49 pr136 99.81 116.42 29.14 42.61 fig. 9. comparison between abc and abcupt error rates. the results show clearly that the proposed method is better than the original abc. moreover, using pheromones in abc gives a memory-like behavior that helps exploration and exploitation but adds more complexity to abc and increases execution time. in future work, pheromones can be used lightly to improve performance without increasing execution time. moreover, using a local search algorithm to help bees in exploration could lead to better results. fig. 10. comparison of error average rate between abc and abcupt. vi. conclusions this study introduced an enhanced artificial bee colony algorithm using pheromones. the proposed method was tested on 20 tsp problems from tsplib. the results were compared with the original abc and showed that the use of pheromone improved exploration and exploitation but increased execution time. in future work, local search can be integrated to leverage results. furthermore, the use of pheromones adds memory-like behavior to the abc algorithm and, therefore, it is easy to integrate the pheromone into other algorithms. acknowledgments the authors acknowledge the financial support of the universiti tenaga nasional under uniten-iraq scholarships and uniten bold research grant (j510050002/2021150). 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[18] g. reinelt, "tsplib—a traveling salesman problem library," orsa journal on computing, vol. 3, no. 4, pp. 376–384, nov. 1991, https://doi.org/10.1287/ijoc.3.4.376. microsoft word etasr_v13_n2_pp10310-10315 engineering, technology & applied science research vol. 13, no. 2, 2023, 10310-10315 10310 www.etasr.com hien et al.: finite element analysis of a continuous sandwich beam resting on elastic support and … finite element analysis of a continuous sandwich beam resting on elastic support and subjected to two degree of freedom sprung vehicles ta duy hien university of transport and communications, vietnam tdhien@utc.edu.vn nguyen duy hung campus in ho chi minh city, university of transport and communications, vietnam hungnd_ph@utc.edu.vn nguyen trong hiep university of transport and communications, vietnam nguyentronghiep@utc.edu.vn giap van tan hanoi architectural university, vietnam tangv@hau.edu.vn nguyen van thuan nha trang university, vietnam thuannv@ntu.edu.vn (corresponding author) received: 3 november 2022 | revised: 4 december 2022 | accepted: 12 december 2022 abstract this paper has developed a finite element method (fem) to calculate the dynamic response of a continuous sandwich beam resting on elastic support subjected to moving vehicles. the equation of motion is derived using the classical beam theory and fem. the vehicle model is a two degree of freedom (2dof) system that moves with a constant velocity. the governing equation of motion is integrated by applying the wilson-θ time integration method to obtain the dynamic response in each time step. numerical examples investigate the displacement of the sandwich beam with various values of the structure and vehicle velocity. the effects of the stiffness of elastic support and the vehicle velocity on displacement are studied. keywords-fem; forced vibration; continuous beam; elastic support i. introduction structures in the construction industry can be multiform and diverse. the most commonly used structures in civil engineering are columns [1, 2], piles [3], beams [4-8], frames [9, 10], and plates [11-19]. in general, a beam is a flexural member and the normal stress has maximum values at the top and the bottom of the beam. so, sandwich beams will have optimal bearing capacity if the outer layer is a high-strength material. in practice, the fibers at the top and bottom of the beam can be made of steel and the core layer from concrete or wood. if the sandwich beam is made of a suitable material, it will have a better load capacity, reduced height, and a larger span. thus, the sandwich beam has many advantages if it is made of appropriate materials. a sandwich beam usually has two layers, i.e. the outer layer and the core layer, as shown in figure 1. structures are subjected to various dynamic loads, e.g. from wind, moving vehicles, impulsive loading, etc. structure engineering, technology & applied science research vol. 13, no. 2, 2023, 10310-10315 10311 www.etasr.com hien et al.: finite element analysis of a continuous sandwich beam resting on elastic support and … dynamics have many practical aspects, e.g. the dynamic behavior of beams [20-23] and the dynamics of plates [24, 25]. the dynamic response of an elastic plate in a viscoelastic medium, resting on a viscoelastic winkler foundation is investigated in [26]. the forced vibration of functionally graded plates resting on a viscoelastic elastic foundation was solved analytically in [27]. the effect of randomness in the elastic modulus on the eigenvalue of free vibration of nonuniform beams is studied using stochastic finite elements in [28]. the variability dynamic response of a beam subjected to a moving load with various uncertain parameters is investigated by monte carlo simulation in [29]. the dynamic response of a beam resting on a viscoelastic foundation was analyzed with a novel state-space formulation considering the interaction of the oscillator-beam-foundation system in [30]. the dynamic response of sandwich beams with a viscoelastic core subjected to moving loads was studied by fem in [31]. an analytical solution was preformed to investigate the transient response of sandwich beams in [32]. a new semi-analytical method was applied in [33] to study the dynamics of beams. the transient response of double beams with viscoelastic boundary conditions under a moving load was investigated by the analytical method in [34]. the nonlinear dynamic response of the coupled vehicle-pavement system was computed using the galerkin truncation method in [35], in which the pavement was modeled as a timoshenko beam on the six-parameter foundation. the dynamic response of bridges to moving vehicle loads was investigated using a semi-analytical approach in [36]. the arch bridge subjected to the moving loads was modeled as a continuous beam resting on interconnected springs to compute the dynamic response using the analytical method [37]. author in [38] presented an analytical and numerical method to study the dynamics of a beam–mass system. experiments and finite element simulations studied the dynamic response of metallic sandwich beams under impact loading in [39]. fig. 1. cross section of a sandwich beam. in this study, fem is used to study the forced vibration of a continuous sandwich beam resting on an elastic support. ii. finite element formulation let us consider a continuous sandwich beam resting on elastic supports, subjected to moving vehicles, with the coordinate system placed at the mid-plane of the beam as shown in figure 2. the deflection w of the beam can be written in a matrix form as [40]:                          1 1 1 2 3 4 2 2 , e w t t w x t n x n x n x n x w t t n x q t                   (1) where    e q t denotes the displacement vector of the finite element and   n x are hermite interpolation functions, defined as follows:         2 3 2 1 22 3 2 2 3 2 3 42 3 2 1 3 2 ; 1 2 3 2 ; e e e e e e e e x x x x n x n x x l l l l x x x x n x n x x l l l l                          (2) fig. 2. continuous sandwich beam resting on elastic supports and subjected to a moving vehicle. the strain energy of the beam element is: 2 2 0 2 20 2 0 2 1 2 e face a l face e core a core w e y da x u dx w e y da x                                        ����������� ����������� (3) the potential energy of the elastic support is defined as:   2 0 1 2 s su k w x    (4) where ks is the stiffness of the elastic support. the kinetic energy of the beam element is given as: 2 2 0 0 0 1 2 el e face core a a face core w w dx t t                                              ��������� ��������� (5) the governing equation of the sandwich beam is derived as: core face face engineering, technology & applied science research vol. 13, no. 2, 2023, 10310-10315 10312 www.etasr.com hien et al.: finite element analysis of a continuous sandwich beam resting on elastic support and …       tb b s wm w k k w n f            ɺɺ (6) where , , s b b k k m           are the stiffness matrix of the elastic support and the stiffness and mass matrices of the sandwich beam, respectively. the equation of motion of the moving mass m1 and the contact force fw are determined as follows:    1 0m m m mm y c y w k y w    ɺɺ ɺ ɺ (7)  1 2 2 1w mf m m g m w m y   ɺɺ ɺɺ (8) where wm is the vertical dynamic deflection of the beam at mass m2. combining (6) to (8), the governing equation is obtained:                     1 1 1 2 * 0* 0 * 0 ( ) + 0 b t m m b s t m m mx cw wm m n m c n cy ym k k k w n m m g yc x n k n k                                            ɺɺ ɺ ɺɺ ɺ ɺɺ (9) where:                 2 2 2 2 2 * * 2 ( ) * ( ) ( ) t t x t t xx x m m n n c m x t n n k m x t n n m x t n n     ɺ ɺ ɺɺ (10) iii. solving the equation of motion with the wilson- method the equation of motion of the vehicle-bridge interaction can be written in the following general form:                  m u t c u t k u t f t  ɺɺ ɺ (11) where         , , ,m c k f t are the mass, damping, and stiffness matrices, and the force vector, respectively. in order to use the wilson scheme, we introduce the effective stiffness matrix as form:      0 1k k a m a c     ɶ (12) where:   0 12 1 ; a a tt       (13) the vector of effective forces at time t+θ can be calculated as follows:                                      1 4 5 0 1 2 f t f t f t p t c a u t a u t a u t m a u t a u t a u t               ɶ ɺ ɺ ɺɺ ɺ ɺ ɺɺ (14) where 2 4 5 1 ; 1; 2 2 t a a a t                   . the values of the parameters are selected as 1 / 2, =1 / 6  , and 1.37  . the following linear system of equations computes the displacements at time after initialization of displacement, velocity, and acceleration vectors:      k̂ u t f t       ɶ (15) the vector of acceleration at the time t+θ is calculated by:                 0 2 3 u t a u t u t a u t a u t        ɺɺ ɺ ɺɺ (16) where 3 1 1 2 a    . acceleration, velocity, and displacement at time t t are calculated from:                                         6 7 8 9 1 u t t u t u t u t u t t u t a u t a u t t u t t u t t u t a u t a u t t                          ɺɺ ɺɺ ɺɺ ɺɺ ɺ ɺ ɺɺ ɺɺ ɺ ɺɺ ɺɺ (17) where:   2 26 7 8 9 1 1 ; ; ; 2 a t a t a t a t                   . iv. numerical examples a. example 1 considering the continuous sandwich beam shown in figure 3, subjected to a moving vehicle with 2dof. the rectangular sandwich beam has 3 uniform spans of 4m, the dimensions of cross-section are h=60cm, b=25cm, and the thickness of the face layer is 1cm. the parameters for the vehicle in figure 3 are: m1=1680kg and m2=840kg. the structural properties of the sandwich beam are given in table i. table i. material properties of the sandwich beam fiber material properties material young's modulus (gpa) mass density (kg/m 3 ) face layer steel 200 7800 core wood 10 700 figure 4 shows the displacement at the center of the beam for 2 cases of stiffness of elastic support. the speed of the vehicle is set to 5, 10, and 15m/s. the figure clearly shows that the displacements at the center of the beam are highly similar. so, the effect of speed of the vehicle on the displacement of the beam is small. engineering, technology & applied science research vol. 13, no. 2, 2023, 10310-10315 10313 www.etasr.com hien et al.: finite element analysis of a continuous sandwich beam resting on elastic support and … fig. 3. three-span sandwich beam subjected to a moving vehicle. (a) (b) fig. 4. displacement at the center of the beam for kgoi equal to (a) 10 7 , (b) 10 8 n/m. (a) (b) fig. 5. displacement at the contact point with the m2 mass of the vehicle for kgoi equal to (a) 10 7 , (b) 10 8 n/m. the displacement of the mass of the vehicle m2 is investigated with vehicle speed values of 5, 10, and 15m/s and stiffness of the elastic support kgoi equal to 10 7 and 10 8 n/m. when the speed is slow, the displacement is close to the static displacement. at high vehicle speed, the displacement is fluctuated around the displacement line at low speed. figure 6 illustrates the displacement at the center of the beam and at the contact point m2 of the moving vehicle with speed of 10m/s for 3 stiffening cases of elastic support. as the stiffness of the support increases, the stiffness of the structure increases, leading to a decrease in displacement. when the stiffness of the support is quite large, the displacement at the center of the beam has an almost sinusoidal shape. it is clear that the stiffness of elastic support affects the displacement of the beam. (a) (b) fig. 6. displacements for 3 stiffening cases of elastic support: (a) at the center of the beam, (b) at the contact point. fig. 7. displacements of sandwich beam resting on elastic support. b. example 2 in this example, the dynamics of a sandwich beam is investigated by replacing two rigid supports of the example 1 l k c m 1 m 2 y wm v m m w x kgoi l/3 l/3l/3 kgoi engineering, technology & applied science research vol. 13, no. 2, 2023, 10310-10315 10314 www.etasr.com hien et al.: finite element analysis of a continuous sandwich beam resting on elastic support and … with elastic supports as described in figure 7. the displacements at the center of the beam and at the contact point are shown in figure 8 for 3 stiffening cases of elastic support. figure 8 clearly shows that the displacements are greatly increased. it also shows the strong influence of the stiffness of the elastic support on the displacements. increased stiffness causes the displacement to decrease drastically. (a) (b) fig. 8. displacements for 3 stiffening cases of elastic support. (a) at the center of the beam, (b) at contact point. v. conclusions the forced vibration of continuous sandwich beams traversed by a moving vehicle has been studied in this paper. finite element method based on the classical beam theory was used to derive the governing equations of motion of the sandwich beams. the governing equations were solved with the wilson method. numerical examples were employed to investigate the effects of vehicle velocity and the stiffness of elastic support on the displacement response of the beam. the result of the numerical examples showed that changes in the stiffness of the elastic support have a significant effect on the displacement response of the beam. acknowledgment this research is funded by university of transport and communications (utc) under grant number t2021-ct007tđ. references [1] p. c. nguyen, d. d. pham, t. t. tran, and t. nghia-nguyen, "modified numerical modeling of axially loaded concrete-filled steel circulartube columns," engineering, technology & applied science research, vol. 11, no. 3, pp. 7094–7099, jun. 2021, https://doi.org/10.48084/ etasr.4157. 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[40] j. reddy, an introduction to the finite element method, 3rd ed. new york, ny, usa: mcgraw-hill education, 2005. microsoft word etasr_v12_n6_pp9590-9600 engineering, technology & applied science research vol. 12, no. 6, 2022, 9590-9600 9590 www.etasr.com theydan & mohammed: refinery wastewater treatment by a novel three-dimensional … refinery wastewater treatment by a novel threedimensional electrocoagulation system design samar k. theydan department of chemical engineering college of engineering, university of baghdad baghdad, iraq samar.kareem@coeng.uobaghdad.edu.iq wadood taher mohammed department of chemical engineering college of engineering, university of baghdad baghdad, iraq dr.wadood@coeng.uobaghdad.edu.iq received: 6 september 2022 | revised: 23 september 2022 | accepted: 24 september 2022 abstract-a novel three-dimensional electrocoagulation method was used in the current work to explore the treatment of refinery wastewater. metal-impregnated granular activated carbon (migac) was employed as a third particle electrode in the inventive design. a comprehensive investigation has been conducted to evaluate its performance. bet-specific surface area, total pore volume, x-ray fluorescence (xrf), energy-dispersive x-ray spectroscopy (eds), and scanning electron microscopy (sem) were employed for the characterization of migac particle electrodes at ph=7, 30v applied voltage, 10g of particle electrodes, 175ml/min flow rate, and a supporting electrolyte (0.063m nacl + 0.025m na2so4). the findings indicate that the effectiveness of chemical oxygen demand (cod) elimination increased quickly after 20min to 66.93, 69.88, 77.59, 74.14, 81.26, 79.87, and 87.14% for conventional electrocoagulation (cec). three-dimensional electrocoagulation with granular activated carbon (tec-rgac), tec-migac (al), tec-migac (fe), and tec-migac (al:fe) with molar ratios of (1:1), (1:2), and (2:1) respectively were utilized. while turbidity removals were 99.04, 98.87, 99.23, 94.89, 92.42, 98.85, and 99.21% for cec ,tec-rgac, tec-migac(al), tec-migac(fe), tecmigac(1:1), tec-migac(1:2), and tec-migac(2:1) respectively. the results demonstrated that the metal impregnation of gac is an interesting method for achieving effective turbidity and cod removal from refinery wastewater. in both batch and repeat recycling tests, migac with a mixture of aluminum and iron oxides removed turbidity and cod more effectively and efficiently than rgac. keywords-electrocoagulation; refinery wastewater; threedimensional electrode; metal impregnated activated carbon; cod i. introduction the aquatic environment is contaminated from sewage disposal, runoff from agricultural lands, air fallout, and waste management operations, such as the discharge of effluents from oil refining [1]. refining processes convert crude oil into petroleum and other valuable byproducts. large amounts of water are consumed throughout those activities, resulting in a proportional amount of wastewater, which consists of cooling water, process water, storm water, and sewage [2]. it was found that the amount of wastewater was about 0.4–1.6 times the amount of processed oil. in the wastewater from refineries and petrochemical plants, there are more than 20 different types of harmful chemicals, even though the contaminants in wastewater depend a lot on the way the process is set up. wastewater treatment structure, operational processes, and the kind of processed oil have significant impact on the composition of refinery wastewater [3]. suspended particles, biodegradable and refractory organics, hydrocarbons, sulfides, phenols, and nitrogen compounds are the main pollutants in these industrial wastewaters [4]. as a fundamental requirement, the quality and availability of water are very important [5, 6]. untreated effluent discharge needs to be under safety regulations [7]. so, effective and practical wastewater treatment methods for petroleum refineries are necessary. biodegradation [8, 9], ultrafiltration [10], adsorption [11], and coagulation [12] are some of these processes. the techniques used in electrochemical processes include electroflotation (ef) [13], electro-fenton oxidation (eo) [14], electrocoagulation (ec) [12], and sequential ec and eo processes [15]. they have the benefits of being simply spread and requiring the least quantity of chemicals. many studies during the recent years have focused on ec, an effective procedure for treating finely dispersed wastewater. because this technology is both sturdy and small, it has the potential to replace complicated procedures that need huge volumes and/or a variety of chemicals [16]. several parameters might be utilized to monitor the wastewater from petroleum refineries. one of them is the chemical oxygen demand (cod), which needs comparatively less time and may be used to evaluate the water quality as a whole [17]. electrochemical methods have showed substantial practicality in the treatment of many industrial wastewaters, such as refinery wastewater [18, 19], due to their unique capacity to oxidize or remove contaminants in the water near the properly maintained electrode. however, due to its low current density, the conventional electrochemical approach does not perform successfully throughout the wastewater treatment process [20].complex chemical and physical changes occur often during any ec process. positive ionic coagulants are generated as a result of sacrificial anode oxidation when a direct current or voltage is supplied. as a result of the water reduction at the cathode, hydroxyl ions (oh ) and some o2 and h2 gas bubbles can be generated [21]. to eliminate corresponding author: samar k. theydan engineering, technology & applied science research vol. 12, no. 6, 2022, 9590-9600 9591 www.etasr.com theydan & mohammed: refinery wastewater treatment by a novel three-dimensional … contaminants, ec depends on the electrochemical formation of metal ions such as aluminum and ferric iron, which act as stabilizing reagents and neutralize the electric charge. the isomeric replacement of ferric ions by aluminum ions in iron oxides breaks crystallization, resulting in a greater surface area of the total adsorbents (oxide minerals), which may increase the removal effectiveness during combined ec using aluminum and ferric electrodes [22]. traditional ec approaches for water and wastewater treatment have frequently employed single electrodes such as ferric-ferric and aluminum-aluminum, or combination electrodes such as aluminum-ferric or ferricaluminum, known as the two-dimensional electrode system [23]. combinations of aluminum-ferric or ferric-aluminum electrodes have been proved to be more successful in removing impurities than single electrode systems [24]. the use of three-dimensional electrodes in combination with carbon particles has been proposed as an alternative method that may effectively improve the working electrode's specific surface area and has been used for the removal of chloramphenicol [25], metal ions [26], and cyanides [27] from wastewater, and recently the elimination of organic pollutants, such as phenols [28], dyes [29, 30], tetracycline [31], and furfural degradation [32]. three-dimensional (3d) electrode-based electrochemical techniques have attracted a lot of attention. a particle electrode or bed electrode serves as a third electrode in 3d electrochemical methods, in addition to the two electrodes used in the traditional (two-dimensional) electrochemical systems. these particle electrodes are loaded between the anode and the cathode. in 3d electrochemical systems, granular or powdery materials are often utilized as the working electrode and as particle electrodes. when external potential is present, this particle microelectrode generates charge. depending on the kind of electrode, the degradation of organic pollutants can occur in a variety of ways. in addition to the procedure in two dimensional electrochemical systems, the fabrication of microelectrodes in 3d electrochemical systems enhances pollutant degradation [33]. additionally, active carbon, a particle electrode that is frequently used, encourages the electro-generation of hydrogen peroxide and the subsequent production of hydroxyl radicals [34]. reduced energy consumption due to a higher surface area to volume ratio, enhanced mass transfer, increased pollutant removal efficiency, generation of additional oxidants, and elimination of pollutants by sorption on particle electrodes are the major properties of 3d electrode reactors [35, 36]. the main objective of this study is to create a three dimensional electrocoagulation metal-impregnated granular activated carbon with a (tec-migac) system using metal (aluminum, iron, or both). this system was developed with the goal of using metal-impregnated carbon particles as an adsorbent and metal-support media by leveraging the collaborative action of aluminum and ferric ions. it was tested in treating wastewater from the iraq's al-daura petroleum refinery facility. migac's textural characteristics were studied using bet, xrf, eds, and sem, while cod removal, turbidity removal, total dissolved solids (tds) removal, current efficiency, and energy consumption were measured. ii. materials and methods a. materials the untreated petroleum refinery effluent sample (80l) was provided by the al-daura refinery petroleum refinery plant, baghdad, iraq. it was taken from the feeding tank and was stored in covered containers at 4 o c until use. table i lists the characteristics of this sample. because raw water's conductivity is very low, it raises the cell potential, which necessitates the addition of supportive electrolytes in order to boost conductivity. na2so4 at 3.5g/l and nacl at 2.5g/l were employed as supporting electrolytes, which resulted in a conductivity of 12.16mscm -1 , which is within the range necessary to achieve low cell potential [37]. table i. properties of the utilized effluent sample property value ph (-) 6.8 cod (ppm) 1400 conductivity (ms/cm) 2.66 turbidity (ntu) 227 tds g/l 6.64 f (ppm) 0.19 cl (ppm) 422.4 zn-(ppm) 0.08 cu (ppm) 0.025 mn (ppm) 0.33 ni (ppm) 0.5 a commercial gac was used with the physical properties shown in table ii. a mixture of anhydrous sodium sulphate (na2so4) powder from thomas baker company and sodium chloride (nacl) powder with 99.9% purity by weight were used as supporting electrolytes. anhydrous ferric chloride (fecl3) powder with 98% purity by weight, from the alpha chemike company and anhydrous aluminum chloride (alcl3) powder with 98% purity by weight, from the central drug house ltd. company, were used as metal sources for the metal impregnation process. a 1m solution of hydrochloric acid (hcl, 37%, liquid, sigma-aldrich) and sodium hydroxide (naoh, 97%, pellets, sigma-aldrich) was prepared to alter the original ph of the treated effluent. table ii. physical properties of the commercial gac parameters values test standard astm-d bet surface area (m 2 /g) 950-1200 iodine number (mg/g) 900-1150 total ash content max. 5% hardness min. 97% apparent density (kg/m 3 ) 460±40 moisture content 8% ( as packed) attrition max. 3% particle size 8×30 mesh available b. preparation of the metal-impregnated granular activated carbon (migac) after being sieved to a particle size of over 1mm in diameter, commercial gac particles with a particle size of (8×30) mesh were washed with deionized distilled water to remove impurity compounds. finally, the particles were dried engineering, technology & applied science research vol. 12, no. 6, 2022, 9590-9600 9592 www.etasr.com theydan & mohammed: refinery wastewater treatment by a novel three-dimensional … in an oven at 105°c for 24h. subsequently, the gac was impregnated with molar ratios 1:10 as al: ac, 1:10 as fe: ac, 1:1:10 as al:fe:ac, 1:2:10 as al:fe:ac, and 2:1:10 as al:fe:ac using alcl3 and fecl3 as the al and fe sources respectively. it was then mixed with 50ml deionized water at 90 o c for 4h. the resulting solution was mixed in a 500ml round–bottom flask with two necks: one neck was fitted with water–cooling reflux condenser and the other was equipped with a thermometer to measure the temperature. the reaction was carried out at atmospheric pressure. agitation and heating of the flask were done by oil bath (engine oil from al-daura refinery with flash point 220 o c) on a magnetic stirrer hot plate. heidolph™ 505-20000-00, 0-300°c, 0-1400rpm was utilized for obtaining homogeneous solution at a rotation speed of 200rpm, where the temperature of the mixture in the heated flask was kept constant by using voltage regulator (single – phase ac voltage regulator, 220v regulator adjustable 0-300v, max power 500w) to control the heat of the heater. after another wash with deionized distilled water, the migac was dried in a 105°c oven for 24h. c. experimental procedure a preliminary feasibility test was conducted to determine the suitability of the tec-migac system for cod and turbidity elimination from the refinery effluent. this performance was compared to those of other systems, including an adsorption and conventional ec (cec) system and a raw granular activated carbon with cec system (tec-rgac). all batch studies were conducted under the same experimental conditions: 1.0l working volume, duration of 120min, 10g raw activated carbon or migac, ph=7, and 30v applied voltage. the experiments were conducted by using the laboratory setup shown in figure 1. the tubular electrochemical reactor (figure 1(a)) was made from perspex glass with 30mm diameter and 140mm height. the wastewater was pumped to the cylindrical ec cell using a peristaltic pump (runze, single stage pump, made in china) with a maximum flow rate of 200ml/min. the aluminum and stainless steel disk electrodes (30mm in diameter and 5mm in thickness) were pierced with 1mm holes and were connected to a dc power source. each electrode had total effective surface area of 7.065cm 2 . the distance between the electrodes did not alter and was kept at 6cm despite the rapid electron transfer rate between the anode and the cathode that was caused by the particle electrodes [38]. the aluminum anode was positioned below the cathode, and water was circulated in the direction from the anode to cathode. in the case of 3d reactor, a packed bed of gac or migacs was placed between the anode and the cathode. during each experiment, for the purpose of delivering an adequate voltage, a digital direct current power supply of the type (uni-t, utp3315pf) that ranged from 0-30v and 0-5a was used. a multimeter was used to measure the system’s current and voltage. the effluent from the ec unit was sent to a settling tank, where the overflow was pumped back to the ec cell. to remove the electrodes’ oxide and passivation layers, they were washed in hcl solution (35%) and acetone [39]. hcl solution (0.1n) and naoh solution (0.1n) were used to adjust ph. nacl and na2so4 were used as electrolytes. nacl solution was utilized as an extra electrolyte because it has a lot of benefits, including the ability of chloride ions to considerably lessen the negative effect of other anions such hco 3 and so4 2. the carbonate ion would cause the precipitation of ca 2+ or mg 2+ ions, which create an insulating layer on the electrode surface. this insulating layer would significantly lower the electrochemical cell’s current efficiency and treatment conversion while substantially raising its ohmic resistance. as a result, it is proposed that among the current anions, 20% cl be present to enable normal ec activity in water treatment [40]. the ambient temperature for all tests was 25 ±2°c. after the experiment, the samples were filtered using filter papers with size 150mm before being analyzed. tds, ph, turbidity, and the initial and final cod concentrations were also measured. (a) (b) pump power supply voltmeter ammeter electrochemical cell liquid flowmeter reservoir fig. 1. schematic diagram of (a) the ec cell, (b) the ec system. d. methods of analysis using spectro xepos xrf (ametek co., germany), the textural qualities of raw granular and migac were evaluated. the morphology and microstructure were examined with sem. at the same surface locations as the sem, eds was also used to undertake surface element analysis concurrently (inspect, f50, rei co., netherland). physical properties, bet specific surface area, and total pore volume were determined using the sa-9600 model (horibe usa brand) using nitrogen gas as adsorbate. lovibond cod vario photometric detector (cod setup, md 200, uk) was used for cod analysis. for the cod test, a sample of 2ml of the substrate was completely thermally oxidized using a standard oxidation reagent in a cuvette tube. the combination of the substrate sample and the standard oxidation reagent was heated at 150°c for 2h to guarantee that the substrate had completely oxidized. the concentration of the cod of the organics was determined in mg/l by a cod photometer in a thermo-reactor (rd 125, lovibond, germany). turbidity was measured with a compact lovibond® infrared turbidity meter turbi check. the turbidity and cod removal engineering, technology & applied science research vol. 12, no. 6, 2022, 9590-9600 9593 www.etasr.com theydan & mohammed: refinery wastewater treatment by a novel three-dimensional … efficiency were evaluated based on (1), where ci is the initial and cf the final concentration (mg l -1 ) [41]: ��% = ����� �� × 100 (1) the quantity of electrical energy that is used up throughout the ec process in order to eliminate 1kg of cod is referred to as the energy consumption (ec). ec may be determined in terms of kwh/kg by [42]: � = �.�.�×���� ������������ (2) where codi and codf are the initial and final chemical oxygen demand (mg/l), u is the applied cell voltage (v), i is the current (a), t is the electrolysis time (h), and v is the effluent volume (l). a tds-meter (161002 purepro inc.) was used to test the tds, and a ph-meter (hanna instruments co.) was used to determine the ph. electrical conductivity was measured with a hanna hi-99301 meter. iii. results and discussion a. textural properties table iii shows the physical properties of unprocessed gac and migacs, based on nitrogen adsorption and desorption isotherms, specific surface area, and total pore volume. it is evident that following ferric-aluminum impregnation, migacs' specific surface area and total pore volume both significantly reduced to 893.7, 878, 874, 840, and 797.5m 2 /g and 0.21702, 0.20075, 0.19502, 0.19722, 0.18388, and 0.01376m 3 /g for migac(fe), migac(al), migac(1:1), migac(1:2), and migac(2:1) respectively. these decreased physical characteristic values point to a preferential distribution of metal oxides in the pore mouth. certain micropores were subsequently obstructed, along with the development of meso or macro-porous structures and the covering of binders to the active sites created by ferric or aluminum oxides [43, 44]. the evidence for this may also be seen rather obviously in the micro structural analysis. images from a scanning electron microscope of rgac (a1-4), migac(fe) (b1-4), migac(al) (c1-4), migac(1:1) (d1-4), migac(1:2) (e14), and migac(2:1) (f1-4) are presented in figure 2. while the raw gac's porous nature is easily seen in figure 2 (a1-4), it was observed that some porous structural collapse took place when the raw gac was impregnated with metal, leading to clogs, as shown in figure 2 (a1-3), (b1-3), (c1-3), (d1-3), (e1-3), and (f1-3). also, in figure 2, a4 can be seen showing the surface of raw gac before impregnation and figure 2 b4, c4, d4, e4, and f4 emphasize that the metal oxide aggregates formed on the surface of raw gac after the wet impregnation have a spherical shape. it was calculated that the average crystallite size of metal oxides was in the range of (21.2432.58), (21.32-27.38), (26.23-62.77), (55.67-76.49), (18.7526.89) nm for migac(fe), migac(al), migac(1:1), migac(1:2), and migac (2:1) respectively. from the image in figure 2 f4, it can be seen that iron and aluminum oxides were aggregated homogenously on the surface of the raw gac and the range of the size of the metal oxides was smaller than the ranges of the other gamis. table iii. raw gac and migac microstructures properties rgac migac (fe) migac (al) migac (1:1) migac (1:2) migac (2:1) bet specific surface area (m 2 /g) 1086 893.7 878.7 874 840 797.5 total pore volume (cm 3 /g) 0.21702 0.20075 0.19502 0.19722 0.18388 0.01376 table iv. eds elemental composition of raw gac and migacs element rgac migac(fe) migac(al) migac(1:1) migac(1:2) migac(2:1) weight % atomic % weight % atomic % weight % atomic % weight % atomic % weight % atomic % weight % atomic % c 88.82 92.7 83.17 88.7 85.1 89.9 78.91 87.66 80.6 88.5 73.95 83.6 o 7.28 5.7 12.13 9.7 10.7 8.5 9.5 7.9 10 8.3 13.33 11.3 fe 1.63 0.4 1.99 0.51 3.2 0.78 1.65 0.43 al 0.207 0.1 0.203 0.1 1.3 0.6 1.034 0.53 0.8 0.42 1.67 0.87 si 1.78 0.8 0.22 0.1 0.1 0.1 0.42 0.2 0.7 0.3 0.21 0.1 cl 2.66 1 2.6 0.9 8.16 3.2 4.7 1.7 9.02 3.6 ca k 1.51 0.5 mg 0.38 0.2 0.18 0.1 total 100 100 100 100 100 100 100 100 100 100 100 100 at the same surface areas where the sem was used, an element analysis of the surface was also conducted at the same time as the eds. table iv displays the weight and atomic percentages of the raw and migac elements. it can be seen that the level of al changed to 0.6%, 0.53%, 0.42%, and 0.87% for migac(al), migac(1:1), migac(1:2), and migac(2:1) respectively, and the level of fe changed to 0.4%, 0.51%, 0.78%, and 0.43% for migac(fe), migac(1:1), migac(1:2), and migac(2:1) respectively. aluminum and ferric iron were completely impregnated into raw gac, as determined by the atomic percentage following impregnation. clearly, alcl3 and fecl3 were the source of the cl after impregnation. aluminum and ferric iron were likely bonded to migac in the form of aluminum oxide and iron oxide, given the increased oxygen concentration in migac compared to the raw gac. xrf chemistry analysis was used to confirm the oxide form of the metals in both raw gac and migac. formation of oxides by metals on each other's surfaces is documented in table v, which shows that aluminum oxide and ferric oxide are the most common forms of these metals. engineering, technology & applied science research vol. 12, no. 6, 2022, 9590-9600 9594 www.etasr.com theydan & mohammed: refinery wastewater treatment by a novel three-dimensional … table v. xrf analysis was used to determine the metal oxide form in raw gac and migac components rgac (mass%) migac(fe) (mass%) migac(al) (mass%) migac(1:1) (mass%) migac(1:2) (mass%) migac(2:1) (mass%) mgo 0.4573 1.148 0.505 0.741 1.200 0.817 al2o3 0.2899 0.2153 0.9091 2.0521 1.9941 3.3345 sio2 1.039 0.8847 0.3724 0.1434 0.1846 0.1765 p2o5 0.3564 0.1924 0.2151 0.1826 0.1376 0.1732 so3 0.09675 0.09694 0.04981 0.02413 0.02272 0.03716 cl 0.05731 1.751 1.610 2.892 4.081 4.2253 k2o 2.096 0.0645 0.0645 0.0646 0.1045 0.0666 cao 2.919 1.346 1.619 1.031 1.579 1.239 tio2 0.00307 0.00317 < 0.0013 0.00344 0.00281 0.00466 v2o5 < 0.0011 < 0.00072 < 0.0013 < 0.0011 < 0.00068 < 0.00069 cr2o3 < 0.00022 < 0.00015 0.00099 0.00109 0.00050 0.00099 mno 0.00183 0.00046 0.00056 0.00203 0.00206 0.00326 fe2o3 0.03133 1.677 0.04100 1.962 3.428 1.7841 coo < 0.00039 < 0.00039 < 0.00039 < 0.00039 < 0.00039 < 0.00039 nio 0.00081 0.00064 0.00118 0.00122 0.00085 0.00086 cuo 0.00318 0.00566 0.00366 0.00618 0.00627 0.00678 zno 0.00062 0.3631 0.00126 0.00199 0.00141 0.00162 fig. 2. sem images of (a1-4) rgac, (b1-4) migac(fe), (c1-4) migac(al), (d1-4) migac(1:1), (e1-4), migac(1:2), and (f1-4), migac(2:1) at different expansion ratios. engineering, technology & applied science research vol. 12, no. 6, 2022, 9590-9600 9595 www.etasr.com theydan & mohammed: refinery wastewater treatment by a novel three-dimensional … b. influence of auxiliary electrolyte dosing the solution's conductivity is essential for increasing process effectiveness and lowering current density. the lower potential flowing in the circuit during treatment is maintained via conductivity, which also results in less electricity being used. the conductivity of the effluent caused the heterogeneous ions to transfer in the ec method. electrolytes na2so4 and nacl were employed in this treatment [41]. additionally, so4 -2 ions do not corrode as much as the chloride species. the great corrosive capability of cl ions aids in the disintegration of the coagulant. the needed voltage will be significantly lower in the presence of chloride ions than it would be in the presence of so4 -2 ions. comparing the adsorption behaviors of cl and so4 -2 ions on the al electrode, it has been discovered that cl had a lower degree of adsorption than so4 -2 [45]. chloride ions are transformed into active chlorine species when the current density is sufficiently high. these species then participate in the oxidation of ferrous ions and organic materials [46]. table vi and figure 3 show the effect of variable concentrations of electrolytes on the removal of chemical oxygen demand. ec process was performed using applied voltage of 30v, time 120min, ph 7, and 10g raw activated carbon. as shown in table vi, when the wastewater treated without any added electrolyte concentration of na2so4 or nacl, the conductivity and applied current were 2.66ms/cm and 15.1ma respectively and the cod removal was 58.8% at 20min, whereas it increased to 72.3% at 120min. the synergistic effects of raw gac adsorption in the gac-three dimensional ec system may be responsible for these results. after adding the electrolytes (2.5g nacl, 3.5g na2so4, 2.5g nacl + 3.5g na2so4, and 2.5g nacl + 7g na2so4), the conductivity and the applied current were 7, 7.44, 12.16, and 20ms/cm and 45, 56, 87, and 98ma respectively. as shown in figure 4, the cod removal rate was improved when a mixture of electrolytes (nacl + na2so4) was added to the reaction system at different concentrations. increment in removal efficiency was observed from 90.7% to 93.7% after 120min for 2.5g nacl + 3.5g na2so4. this might be attributed to the fast flow of electrolyte ions. additionally, no additional improvement in removal efficiency was observed when the supporting electrolyte concentration of na2so4 was raised to 7g/l, which may be caused by an expansion of the passivation layer. therefore, 2.5g nacl and 3.5g na2so4 were selected as the optimum electrolyte concentration and this is in agreement with the findings of the authors in [37], which used nacl with a concentration of 4g/l to obtain 13.6ms/cm conductivity for removing carbamazepine by a three-dimensional electrochemical process utilizing particle electrodes made of carbon-based adsorbent material. c. feasibility test to find out whether the tec-migac system is appropriate for removing cod and turbidity from refinery effluents, a feasibility test was carried out. an adsorption system, a cec system, and a raw gac with cec (tec-rgac) system were used and their performance was compared. because of its great adsorption capability, gac adsorption is a well-established technology used in wastewater post-treatment and water purification. the adsorption processes took place in the same cell without supplying an electric field. table vi. electrolyte dose effect on the initial conductivity and cod removal electrolyte concentration (g/l) initial conductivity (µs/cm) current (ma) cod removal (%) sec (kwh/kg cod) 20min 120min without salt 2660 15.1 58.8 72.3 0.80 2.5g nacl 7000 45 73.6 84.6 1.64 3.5g na2so4 7440 56 75.1 85.2 2.61 2.5g nacl + 3.5g na2so4 12160 87 90.7 93.7 3.68 2.5g nacl + 7g na2so4 20000 98 91.7 95.4 4.68 fig. 3. electrolyte dose effect on cod removal (30v, 120min, ph=7, and 10g raw activated carbon). (a) (b) fig. 4. (a) cod profile with time, (b) cod removal of the adsorption process on different impregnated activated carbon (1361mg/l initial cod, 10g of ac or migac dosage, and 175ml/min flow rate). in batch test i, similar experimental settings were used for each experiment in the adsorption procedure (120min, 10g of ac or migac dosage, and 175ml/min flow rate). in figures 45 and table vii, it can be seen that the raw gac system's adsorption system achieved maximum cod removal. in the adsorption system by raw gac, the cod and turbidity decreased quickly to 619mg/l and 2.48ntu respectively in the first 20min, and then slowly to 376mg/l and 2.31ntu at rgac adsorption migac(fe) adsorption migac(al) adsorption migac(1:1) adsorption migac(1:2) adsorption migac(2:1) adsorption rgac adsorption migac(fe) adsorption migac(al) adsorption migac(1:1) adsorption migac(1:2) adsorption migac(2:1) adsorption engineering, technology & applied science research vol. 12, no. 6, 2022, 9590-9600 9596 www.etasr.com theydan & mohammed: refinery wastewater treatment by a novel three-dimensional … 120min, while 72.3% cod removal and 98.9% turbidity were obtained at the 120min treatment. cod and turbidity were reduced to 638, 640, 649, 643,and 689mg/l and 13.4, 1.94, 1.89, 32.1, and 11ntu respectively in the first 20min, and then continuously to 430, 435, 444, 450, and 505mg/l and 1.165, 2.02, 8.9, 5.98, and 10ntu at 120min for migac(fe), migac(al), migac(1:1), migac(1:2), and migac(2:1), respectively corresponding to 68.41, 68.03, 67.38, 66.94, and 62.89% of cod removal at 120min. the high cod removal of raw gac compared to the migac systems may be due to the fact that metal oxides are preferentially dispersed in the pore mouth, blocking some micropores and constructing a mesoporous or macroporous structure, and overlaying binders to the activated sites created by ferric or aluminum oxides. this is in agreement with the results of [38]. a significant improving in tds removal was observed for impregnated activated carbons with highest removal by migac (2:1) as shown in table vii. (a) (b) fig. 5. (a) turbidity profile with time, (b) turbidity removal for adsorption process on the different impregnated activated carbon methods (227ntu initial turbidity, 10g of ac or migac dosage, and 175ml/min flow rate). table vii. cod and turbidity removal type of adsorbent cod removal % turbidity removal % tds removal % 20 min 120 min 20 min 120 min 20 min 120 min gac 54.5 72.3 98.9 98.9 0 2.89 migac(fe) 53.1 69.7 94.09 99.2 5.79 25.60 migac(al) 52.3 69.06 98.9 99.15 14.05 17.87 migac(1:1) * 52.9 70.24 97.6 99.16 10.14 12.07 migac(1:2) * 52.7 68.55 85.8 97.36 15.94 30.43 migac(2:1) * 49.3 66.78 95.15 97.53 50.72 52.17 in batch test ii, removing turbidity and cod from real refinery wastewater was considered and comparisons were made between the cec system with aluminum and stainless steel electrodes, tec-rgac, and tec-migac systems. table viii and figures 6 and 7 demonstrate the performance of rgac and migacs in removing turbidity and cod at an initial ph of 7 and a reaction duration of 120min, using 30v applied voltage, 10g rgac or migac, and 2.5g/l nacl + 3.5 g/l na2so4 as supporting electrolyte. in the past, stainless steel and aluminum electrodes have been widely employed in electrochemical wastewater treatment systems due to their availability and low cost. with chloride in the solution, the primary direct electrochemical reaction may occur and is heavily dependent on it. hypochlorous acid/hypochlorite ions (hocl/ocl ), which are powerful oxidants, can be generated in the solution during the direct electrochemical reaction due to the anode and cathode ionization processes, and as a result, turbidity and cod will be reduced [47-49]. in cec, as shown in figures 6 and 7, cod and turbidity decreased to 450mg/l and 2.11ntu respectively, in the first 20min, then to 200mg/l and 2.06ntu in the following 100min. after 120min of treatment, 85.3% of cod and 99.04% turbidity removals were achieved. (a) (b) fig. 6. (a) cod profile with time and (b) cod removal for performance comparison between cec system with aluminum and stainless steel electrodes, tec-rgac, and tec-migac systems (1361mg/l initial cod, 7 ph, 30v, 10g of rgac or migac dosage, 175ml/min flow rate and 2.5g/l nacl + 3.5g/l na2so4 as supporting electrolyte). as the next step, we improved and compared the removal performance of the traditional ec system by introducing tecrgac and tec-migacs particles. metal ions (aluminum and ferric iron) produced from migacs during the ec were predicted to have a greater influence on removal efficiency. the contrary of what was anticipated happened when rgac and migacs were added to the reactor and comparable efficacy was seen in both systems. after 20min response time, the turbidity and cod were promptly gone, whereas the cod removal could be attributed to the precipitation of dissolved organics. the amount of hydroxide flocs, which was associated with ec time and cell current, evaluated the effectiveness of cod removal. longer observation times and greater cell current levels indicated higher cod elimination efficiency [50]. after 120min response time, turbidity and cod removal were 99.14% and 92.65% in the tec-rgac system, and 99.36, 98.97, 99.41, 99.4, and 99.43% and 91.18, 93.46, 93.75, 93.39, and 95.74% in the tec-migac systems. these results may have been brought about by the additive effect of raw gac adsorption in the tec-rgac system, which has more rgac migac(fe) migac(al) migac(1:1) migac(1:2) migac(2:1) rgac migac(fe) migac(al) migac(1:1) migac(1:2) migac(2:1) cec tec-rgac tec-migac(al) tec-migac(fe) tec-migac(1:1) tec-migac(1:2) tec-migac(2:1) cec tec-rgac tec-migac(al) tec-migac(fe) tec-migac(1:1) tec-migac(1:2) tec-migac(2:1) engineering, technology & applied science research vol. 12, no. 6, 2022, 9590-9600 9597 www.etasr.com theydan & mohammed: refinery wastewater treatment by a novel three-dimensional … distinguishable textural properties than migac, including bet surface area, total pore volume, and micropore structure. traditional two-dimensional electrode systems have a low cod removal effectiveness (76.12% after 60min). by using a three-dimensional electrocoagulation reactor system, cod removal efficiency increased significantly to 87.06, 88.61, 85.75, 90.08, 90.44, and 92.65% after 60min. also, it was found that the migac with a 2:1 molar ratio of aluminum to ferric metal ions had the highest cod removal. results showed that migac could show substantially higher removal efficiency than the gac addition due to the impact of metal (aluminum and iron) ions created by the addition on ec. (a) (b) fig. 7. (a) turbidity profile with time and (b) turbidity removal for performance comparison between cec system with aluminum and stainless steel electrodes,tec-rgac, and tec-migac systems (227ntu initial turbidity, 7 ph, 30v, 10g of rgac or migac dosage, 175ml/min flow rate and 2.5g/l nacl + 3.5g/l na2so4, as supporting electrolyte. table viii. cod and turbidity removal of crc, tec-gac, and tec-migac systems type of particle electrode cod removal % turbidity removal % tds removal % energy consumption (kwh/kg cod) 20 min 120 min 20 min 120 min 20 min 120 min cec 66.93 85.3 99.04 99.25 46.23 50.75 12.777 tec-gac 69.88 92.65 98.87 99.14 46.23 49.84 3.697 tecmigac(fe) 74.14 91.18 99.22 99.36 45.93 53.16 3.735 tecmigac(al) 77.59 93.46 94.88 98.97 42.77 50.3 3.768 tec-migac (1:1) 81.26 93.75 92.42 99.41 48.49 52.56 3.602 tec-migac (1:2) 79.87 93.39 98.84 99.4 48.34 52.25 3.676 tec-migac (2:1) 87.14 95.74 99.20 99.43 51.35 55.57 3.920 the fundamental issue of the gac adsorption technique is that the porosity eventually gets saturated and inefficient, rendering the technique worthless [51]. as a consequence, it could be challenging to measure and evaluate gac's function as a particle electrode or adsorbent if raw gac is utilized directly as a particle electrode in a three-dimensional ec reactor system. in this respect, another test was conducted, and the reaction time for each set was lowered to 80min, since the removal efficiency increased marginally with increasing reaction time. as shown in figure 8, increasing the repetition cycle was associated with a decrease in cod removal efficiency in the tec-rgac system. however, those efficiencies were kept constant approximately in the tecmigac (2:1) system. after 10 repetitions, the apparent value of the tec-migac (2:1) system was greater than that of the tec-rgac system, with the tec-migac (2:1) system achieving 90.22% cod removal, while the tec-rgac system achieved 63.72%. metal ions (iron/aluminum) were first dissolved during the anode reaction step of the electrocoagulation process. instantaneously upon reaching a certain ph, they hydrolyzed to generate polymeric iron and aluminum oxyhydroxides (fe(oh)3 and al(oh)3) respectively, which are effective coagulating agents [52]. fig. 8. repeated test between the gac and the tec-migac system. d. comparison with previous studies authors in [20] utilized an electrochemical technique with a three-dimensional multi-phase electrode. fe particulates and air were injected into a conventional two-dimensional reactor to remediate effluents from a petroleum refinery. the initial ph and cell voltage, as well as the effect of fe particles and air have on the electrochemical process, were both subjects of the research that was carried out as a part of the process of determining the optimal experimental settings. the results of their investigation found that the effluent had a cod removal effectiveness that was good (92.8%). authors in [53] treated wastewater from a local petroleum refinery using an aluminum electrode and having two distinct cod levels in a continuous electrochemical cell. they investigated the impacts of inflow flow rate, initial ph, and current density. they demonstrated that ec may reduce cod by up to 57% when used under ideal circumstances. authors in [54] treated effluents from a heavy oil refinery using a three-dimensional electrode reactor (tder) equipped with a combination particle electrode consisting of gac and porous ceramsite particle (pcp) and an anode of the dsa type. when comparing the tder to the twodimensional electrode reactor, it was discovered that it was more effective at removing cod and that the combination particle electrode was advantageous in increasing the cod removal efficiency and decreasing energy consumption. under the best experimental conditions (gac percentage = 75%, 0 20 40 60 80 100 0 1 2 3 4 5 6 7 8 9 10 11 c o d r e m o v a l( % ) repeat cycle number tec-rgac tecgacmi(2:1) cec tec-rgac tec-migac(al) tec-migac(fe) tec-migac(1:1) tec-migac(1:2) tec-migac(2:1) cec tec-rgac tec-migac(al) tec-migac(fe) tec-rgac tec-migac(2:1) engineering, technology & applied science research vol. 12, no. 6, 2022, 9590-9600 9598 www.etasr.com theydan & mohammed: refinery wastewater treatment by a novel three-dimensional … current density = 30ma/cm 2 , not altered ph, and treatment time = 100min), the maximum removal of cod, total organic carbon, and toxicity units from the treated effluent were 45.5%, 43.3%, and 67.25% respectively. it was found that the metal impregnated granular activated carbon with a 2:1 molar ratio of aluminum to ferric metal ions had higher cod removal in comparison with that obtained from [38], which used metal impregnated activated carbon (al:fe) with a molar ratio of (1:1) as a moving particle ec electrode in a three-dimensional ec process to treat wastewater from real cotton textiles with a cod content of 685mg/l. cod removal after treatment was 81.6% after 120min of reaction time, 10g migac, and 30v applied voltage at ph=7.7. therefore, the present system exhibited excellent results in terms of cod and turbidity removal using the new design of the three dimensional electrode. iv. conclusions in this study, the treatment of refinery wastewater using a new three – dimensional electrocoagulation approach was proposed and investigated. the new cell utilizes granular activated carbon (gac) and metal-impregnated gac (migac) as third particle electrodes. the three-dimensional electrocoagulation reactor system is an interesting technology for improving refinery wastewater treatment in electrocoagulation, according to a feasibility test employing a typical two-dimensional electrode, adsorption process, and the three-dimensional electrocoagulation system ,where the cod removal efficiency for the adsorption process was 72.37, 68.41, 68.04, 67.38, 66.94, and 62.84% after 120min for raw gac (rgac), migac(fe), migac(al), migac(1:1), migac(1:2), and migac(2:1) respectively while 85.3% was in the conventional two dimensional electrode system after 120min. the cod removal efficiency was enhanced by using the three-dimensional electrocoagulation method, reaching 92.65, 93.46, 91.18, 93.75, 93.39, and 95.74% after 120min for tecrgac, tec-migac(al), tec-migac(fe), tecmigac(1:1), tec-migac(1:2), and tec-migac(2:1), respectively based on the operating conditions of: 1361 initial cod, 7 ph, 30v, 10g of ac or migac dosage for the three dimensional system, 175ml/min flow rate and 2.5g/l nacl + 3.5g/l na2so4 as supporting electrolytes. the results showed that the migac addition exhibits considerably larger removal efficiency than the rgac addition because of the influence of metal ions created by the migac on the electrocoagulation. besides, it was found that the migac with a molar ratio of aluminum to ferric metal ion (2:1) had higher cod removal in comparison with previous studies. also, in the present study, the energy consumption was reduced from 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[54] l. wei, s. guo, g. yan, c. chen, and x. jiang, "electrochemical pretreatment of heavy oil refinery wastewater using a three-dimensional electrode reactor," electrochimica acta, vol. 55, no. 28, pp. 8615–8620, dec. 2010, https://doi.org/10.1016/j.electacta.2010.08.011. microsoft word etasr_v12_n5_pp9136-9141 engineering, technology & applied science research vol. 12, no. 5, 2022, 9136-9141 9136 www.etasr.com fareh & alkama: the effect of spatial configuration on the movement distribution behavior the effect of spatial configuration on the movement distribution behavior the case study of constantine old town (algeria) fouzia fareh lacomofa laboratory department of architecture 8 may 1945 guelma university guelma, algeria fareh.fouzia@univ-guelma.dz djamel alkama lacomofa laboratory department of architecture 8 may 1945 guelma university guelma, algeria alkama.djamel@univ-guelma.dz received: 30 june 2022 | revised: 14 july 2022 | accepted: 16 july 2022 abstract-this study examines the correlation between spatial configuration and movement behavior within the traditional urban fabric of constantine city. the distribution of pedestrian movement was modeled in relation to the syntactic measures of street networks. the results showed a significant correlation between pedestrian volume with integration and choice measures at the global scale (rn), however, the local scale (r3) did not capture the variance and the presence of the movement. the measures of connectivity that are used to describe the density of street connections also revealed a weak association with the presence of people within the dense traditional layout of the research area. the results support the previous findings of space syntax theory, asserting the important role of the street network structure in assessing the configurational accessibility of a given spatial layout. however, we do not assert its exclusive role in determining the natural-movement patterns. therefore, consideration should be given to more external indicators, like the interaction with land use and socioeconomic activities. we conclude that examining the network radius-based attributes of street configuration can provide a clear understanding of spatial variations in pedestrian activity within multi-scale walkable areas, which helps planners improve the livability of the city by designing more friendly walkable streets. keywords-movement; spatial configuration; walking; pedestrian volume; space syntax i. introduction walking is a freely and accessible mode of transportation. it has become a field with a great interest in socially engaged communities. designing walkable places is gaining more attention for their positive outcomes related to sustainability, social life, health, and economy. walkability has become one of the most investigated realms, not only in architecture and urban design, but also in the fields of public health and transportation [1]. because of the growing knowledge of the walking advantages, the concept "walkable" has been newly labeled as encouraging physical activity [2]. walkability is being evaluated as an "environmental justice issue" and it can be a good indicator of the physical quality of urban areas. as a result, there is an increasing demand to understand the complexity behind the interaction between the different conditions of the built environment and the walking behavior of inhabitants [4-8]. disciplines from various scientific fields, such as urban design and planning, architecture, traffic management, and public health are taking different approaches and implementing appropriate techniques to capture how people walk in the urban environment. the association between the spatial configuration and pedestrian behavior at the street level has been investigated mostly within the conceptual and methodological framework of the space syntax approach [9-16]. this theoretical framework is based on a topological-visual analysis of the street network called the axial map, defined as the smallest set of straight axial lines covering the urban street network [12, 13, 17]. these studies have been conducted with respect to the concept of "natural movement," which means that the configuration of the street network determines extensively the distribution of movement within that network independently of other variables [17-20]. the prevalent assumption behind pedestrian volume modeling is that individuals tend to make their trips as short as possible by choosing a short trip length [21]. therefore, street centrality indices are the most widely used measures to evaluate "natural movement." it is the calculation of the shortest paths between all the network’s origin-destination pairs. based on axial or segment lines, the centrality measures are defined mainly by two main values: first, the closeness of a given axial line to all other axial lines within the network and second, the degree to which a given axial line acts as an intermediary path within the network, or the so-called betweenness. pedestrian volume models using the space syntax method through the integration level of the axial lines have revealed a squared correlation coefficient (r²) ranging from 0.55 to 0.75 in london [13] and dutch urban areas [22]. nevertheless, there is divergence regarding the dominant role of the street network centrality measures in evaluating pedestrian movement activity, different movement volume models that were applied in different cities investigated other explanatory variables like land-use layout, which is described corresponding author: fouzia fareh engineering, technology & applied science research vol. 12, no. 5, 2022, 9136-9141 9137 www.etasr.com fareh & alkama: the effect of spatial configuration on the movement distribution behavior as a non-negligible factor that has a crucial effect on pedestrian movement in urban space [23-26]. other studies combined land use and spatial variables to explore the extent the built environment influences pedestrian patterns [1, 27-29]. these studies found that spatial configuration has a significantly greater correlation than land use does to pedestrian movement, but the possibility of combining them may produce greater results in capturing pedestrian movement volume [30]. the physical dimension of the street network can also influence the amount and presence of pedestrians. many studies in this stream have emphasized an association with the sidewalk width, which tends to regulate the number of pedestrians on a given road [31, 32]. from the above, we can say that whatever the methodological framework used to evaluate pedestrian distribution, there is a consensus in the body of literature about the own social logic of space that affects human behavior, such as pedestrian movement from one place to another [33]. therefore, a clear understanding of the precise nature of the relationship between spatial configuration and movement is more than necessary for better design and planning. to address how people move in a dense urban area and by adopting appropriate measures which are sensitive to the spatial structure of street networks, we will explore in this study the movement behavior patterns related to syntactic attributes of constantine’s old town. we will attempt to clarify the extent the street network design affects pedestrian distribution movement at the scale of the town and neighborhoods. in doing so, we tend to enrich the body of literature that scrutinizes the aspects of the relationship that link movement behavior to spatial configuration as the long-term framework that influences the evolution of urban function. ii. methodology a. study area our research area is the old town of constantine city in algeria. it is the city’s earliest settlement. it was founded on a rock at an altitude of 700 meters, surrounded by a cliff at a depth of 200 meters. the urban form is a mixture of different civilizations (roman, ottoman, and colonial). each of them has left an imprint on the overall layout of the city. its street network is mainly made up of an organic grid penetrated by long rectilinear commercial roads. at the back of the town, we find the residential neighborhoods as a compact fabric with winding and straight derbs, or alleys, to allow transitioning from private to public spaces. fig. 1. the old town’s street network in the context of constantine city (© 2022 cnes/airbus, maxar technologies). like in the arab medina configuration, the old town has busy roads and quiet parts [34]. it has also traditional markets, where artisans keep their workshops half inside, half on the street. a big part of the old town is car-free, which attracts daily familiar and unfamiliar visitors. the traditional town keeps confirming constantine’s urban and historical identity due to its outstanding location and unique spatial shape. based on its specific urban network, we will attempt to investigate the walking behavior in such a complex fabric by exploring the extent this network affects the amount and the distribution of pedestrian movement. b. research method to investigate the effect of spatial layout configuration on pedestrian movement, we used the space syntax method by establishing an axial map based on the street network as demonstrated in figure 2. an axial map is a set of axial lines that refers to an abstract representation of the street network. each axial line represents the fewest and longest visible line of the street. it is equal to the smallest human-perceivable unit of space [21]. the next step was to generate a space syntax analysis by using depth map software (x) with the space syntax toolkit, see figures 2-4. depth map is a multi-platform software developed to perform multiple spatial network analyses in order to explore the complexity of social behavior in a given built environment. normally, the preliminary results of the axial analysis will show how urban space is structured and how human behavior can be predicted. according to space syntax theory, there is a strong and significant relationship between spatial layout and movement patterns, or what we call "natural movement," which means that spatial configuration orients and regulates the presence and the distribution of movement in a given open space without the intervention of any other factors [11]. based on this assumption, we will investigate the relationship between spatial pattern attributes and movement patterns in our research area. through this work, we would like to assert that our objective is not to test the already well established space syntax principles, but rather to seek a new understanding of natural movement in different urban areas with different geographically and socially built environments. fig. 2. axial map (left) and connectivity map (right). c. data collection to realize our pedestrian movement model, we have used the gate count observation technique, which consists of engineering, technology & applied science research vol. 12, no. 5, 2022, 9136-9141 9138 www.etasr.com fareh & alkama: the effect of spatial configuration on the movement distribution behavior counting the average number of pedestrians per hour on a given axis of the spatial network. the measurement locations in the research area are selected according to the degree of the people’s presence and use of street space, as shown in figure 5. the street sample represents different syntactic measures and ranges from busy to lightly used. the counting was applied to specific points in each street axis, where an imaginary crossing line was drawn virtually from these points to the other side of the street space. the number of the moving pedestrians was recorded in a prepared table to be further analyzed. the counting was carried out for 5 minutes every hour for 6 hours (9-10, 10-11, 11-12, 2-3, 3-4, 4-5) at each location on major streets, and for 10 minutes every hour on minor streets to reduce the variance of movement values between different types of roads, see figure 9. the counting was done simultaneously for all survey points on each street. the observations took place on sunny weekdays between 9 am and 5 pm. these times are chosen for two reasons: the operability of commercial activity during those time periods and because pedestrian traffic increases during rush hours, especially at the end of the workday and after school. fig. 3. integration_(r3) map (left) and integration_(rn) map (right). fig. 4. choice_(r3) map (left) and choice_(rn) map (right). the entire research data set included 20 road segments where pedestrian movement volume was sampled in different parts of the town, namely: la kasbah and souika neighborhoods, la rue de france street, etrik edjdida street, zighoud youcef street, eressif, and souk elasser subneighborhoods. the 20 sampled street segments were encoded according to the depth map output reference as the following: (26, 32, 34, 36, 38, 39, 43, 62, 80, 145, 174, 188, 227, 287, 289, 296, 308, 382, 383), see figure 7. in order to explore the relationship between pedestrian movement and space configuration, an assumption of correlation was established between the two variables by using the outcomes of gate count observation with the syntactic attributes of the research area. the association of variables was checked through the jmp package and was visualized through the geographical information system (gis). iii. results and discussion in order to examine the effect of spatial configuration on natural movement patterns, and after making an axial analysis of the urban network, pearson correlation was performed to test whether there is an association between the pedestrian volume and the syntactic properties of the urban layout as shown in table ii. the results showed significant disparities in pedestrian distribution among the different streets in the research area, figure 6 illustrates the average pedestrian volume per road section in the research areas, where we observed a higher volume of pedestrian movement in the town’s major commercial streets, such as la rue de france, etrik edjdida, and eressif streets, which are characterized by a high rate of retail and shops, compared to the other streets, such as swika, zighoud youcef, and la kasbah. figure 8 shows the distribution frequency of the average pedestrian volume per hour. this distribution can be described as heavy-tailed, in other words, most of the survey points have a low volume, while only a few survey points have a high volume of pedestrian movement. this finding is mentioned in [32, 33], which found that a minor percentage of roads have significant traffic movement, whereas their majority have low traffic volumes. since the pedestrian movement has a heavy-tailed distribution, it was normalized by using the log function (with the natural logarithm). figure 10 reveals the correlations between spatial configuration variables and pedestrian movement volume distribution. the results showed that the correlation with the street connectivity variable, which is based on the number of roads connected directly to each street, is not significant (pvalue = 0.43), so there is no association between the number of pedestrians and the degree of connectivity in the street network. however, the pedestrian volume variable was found to positively and strongly correlate with two spatial variables, which are the global integration (with r = 0.799 and p< 0.01) and the global choice (with r = 0.842 and p < 0.01). these two spatial variables tend to have the highest squared correlation coefficient. the correlation model explained this association at 63% for integration and 70% for choice. surprisingly, no correlation was found between movement distribution and spatial variables at the local scale (r3), corresponding to 400 meters, which is an appropriate distance for walking. the pvalue in this case is (p = 0.433) for integration and (p = 0.436), so correlation is not significant at this level. table i. descriptive statistics of the study variables variable n min max mean std. deviation choice_rn 20 28 1663 631.75 564.227 choice_r3 20 3 1663 481.59 564.126 integration_rn 20 11.525 18.320 14.131. 2.148 integration_r3 20 2.257 33.549 21.436 9.619 connectivity 20 3 20 9.24 5.618 pedestrian volume 20 383 3138 1215.24 918.610 engineering, technology & applied science research vol. 12, no. 5, 2022, 9136-9141 9139 www.etasr.com fareh & alkama: the effect of spatial configuration on the movement distribution behavior fig. 5. survey points in the search area. fig. 6. the average observed movement volume on 20 axes of the research area. fig. 7. the average pedestrian movement volume per street section. fig. 8. pedestrian volume frequency. fig. 9. distribution of pedestrian volume on the six-time slots on each selected street. table ii. pearson’s correlations between spatial attributes and pedestrian movement volume variable p-value significance (r) (r²) street connectivity 0.434 not significant -0.436 0.190 street integration_rn 0.000 significant 0.799** 0.639 street integration_r3 0.433 significant -0.204 0.004 steet choice_rn 0.000 highly significant 0.842** 0.709 street choice_r3 0.434 not significant -0.203 0.041 (a) (b) (c) (d) (e) fig. 10. correlation of spatial variables with the average pedestrian volume per street: (a) pedestrian volume per choice_rn, (b) pedestrian volume per choice_r3, (c) pedestrian volume per integration_rn, (d) pedestrian volume per integration_r3, (a) pedestrian volume per connectivity. from the results, we conclude that the movement rate in the research area is showing a positive and significant correlation with spatial configuration only at the global scale. however, engineering, technology & applied science research vol. 12, no. 5, 2022, 9136-9141 9140 www.etasr.com fareh & alkama: the effect of spatial configuration on the movement distribution behavior the local scale configuration cannot capture the distribution of the natural movement. the old town has the potential to attract "through-movement" through the major streets because of its central location near the active and alive colonial center. thus, configurational accessibility could be a need for a pedestrianfriendly environment. in other words, street networks with a high degree of configurational accessibility (in our case represented by radius (n) integration) may satisfy one or more people’s requirements when they are about to walk. however, walking in the old town’s local neighborhoods cannot benefit from this potential because it is seen as confusing and difficult to grasp by unfamiliar users. but in some parts of the same neighborhoods, despite the fact that the attention of users can be evaded in dense and winding roads, as in the cases of eressif and rahbat essouf, which are characterized by a high level of commercial activity and handicraft shops, we can still find a high rate of pedestrians. in other parts, however, walking activity is very low, especially in swika neighborhood, which has some local socio-cultural features. from this, we can say that part of our results goes against the natural movement theory, which stipulates the exclusive role of spatial configuration in explaining the distribution patterns of movement. iv. conclusion in this study, we have examined the correlation between spatial configuration and pedestrian traffic volume by using the configurational accessibility of the street network in the old town of constantine city. the results showed that pedestrian volume in main commercial streets with a high rate of choice and integration is more significant. however, some segment streets located inside the local residential neighborhoods carry weaker pedestrian traffic. it was also observed that by going inside the dense residential fabric, where the network has a tree-like structure and the integration has its lowest values, movement 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[36] b. jiang, "head/tail breaks: a new classification scheme for data with a heavy-tailed distribution," the professional geographer, vol. 65, no. 3, pp. 482–494, aug. 2013, https://doi.org/10.1080/00330124. 2012.700499. microsoft word etasr_v12_n4_pp9028-9033 engineering, technology & applied science research vol. 12, no. 4, 2022, 9028-9033 9028 www.etasr.com saxena & roy: the effect of geometric parameters on the strength of stone columns the effect of geometric parameters on the strength of stone columns shivangi saxena department of civil engineering national institute of technology patna, india shivangisaxenacivil0049@gmail.com lal bahadur roy department of civil engineering national institute of technology patna, india lbroy@nitp.ac.in received: 12 june 2022 | revised: 26 june 2022 | accepted: 29 june 2022 abstract-many geotechnical sites are unsuitable for construction due to their low bearing capacity. in the present study, stone column technique has been analyzed for the ground improvement of soft clayey soil. the change in bearing capacity of stone columns with variation in static parameters has been estimated using indian standard code 15284 (is code) 2003, bouassida’s method (1994), and afshar's and ghazavi's method (2014). from the analytical solution of the expression by the is code method for bearing capacity of the stone column, it is found that with the increase in diameter of the column, the bearing capacity of the stone column increases. comparison of the results from the three methods has been conducted and it was found that values obtained from is code are very close to those obtained by the other two analytical methods. also, the critical interpretation of the results shows that the is code gives safer design values for a wide range of the static parameters. the results of the is code were compared with the experimental findings to evaluate the ability of the method to design the actual load carrying capacity of the stone column. keywords-ground improvement; clay; bearing capacity; reinforced soil i. introduction the stone column is one of the most important techniques used for improving ground quality. the construction technique for stone column comes under vibro replacement. it increases the bearing capacity of the ground to remarkable extent and also reduces the post construction settlement of weak soils [1– 11]. the first use of stone columns was done in europe in 1834 [12]. stone columns act as reinforcement and vertical drains for the soft clayey soils. they increase the bearing capacity of the ground by enhancing the horizontal component of effective stress [13-14]. drainage function of stone columns is very useful in the mitigation of damages due to liquefaction. stone columns are constructed by filling cylindrical cavities in soil stratum with granular material that increases the rate of consolidation. consolidation is highly affected by the compressibility in the smear zone for smaller diameter to spacing (s/d) ratio of the stone columns [15, 16]. the techniques used for installing stone columns in indian subcontinent are explained in [17]. the authors concluded that stone columns can be installed by both displacement and nondisplacement methods. due to the reinforcement of soil by highly compacted granular material, the settlement of the soil also decreases [18, 19]. greater stiffness of stone columns compared to that of the surrounding soil causes a large portion of the vertical load to be transferred to the columns. therefore, the entire soil below the foundation behaves as a reinforced soil with higher load carrying capacity. a group of stone columns gives better stability than a single stone column of huge diameter [20, 21]. spacing and diameter of the stone columns are two critical parameters that affect their bearing capacity. several researchers have studied the deformation pattern of groups of stone columns keeping in view factors like depth and spacing [22, 23]. a lower bound solution for the estimation of the bearing capacity of a foundation resting on reinforced soil using rigorous analytical results of the yield design theory was proposed in [24]. coulomb’s lateral earth pressure theory was used to predict the stone column ultimate bearing capacity in [27]. researchers regarded an imaginary retaining wall to develop a simple analytical solution for estimating the bearing capacity. they analyzed the effect of parameters such as column diameter, friction angle of the column material, and column spacing on the ultimate bearing capacity of the stone column [24-29]. the present study deals in finding the optimum spacing of the stone columns when they are provided in group to achieve maximum bearing capacity. for different values of diameter and spacing of the columns, bearing capacity has been calculated using is 15284 part-i [30], by varying the angle of internal friction of granular column material. the estimated values of bearing capacities of the reinforced soil from is code method have been compared with the bearing capacity values obtained in [24] and [27] and finally conclusions have been drawn regarding the effect of these parameters on the ultimate bearing capacity of a stone column. ii. methodology the major materials used in the analysis of stone columns are clay (soft soil) and aggregates (stones). the range of physical parameters used in this study for the prediction of the bearing capacity of the stone columns are shown in table i. corresponding author: shivangi saxena engineering, technology & applied science research vol. 12, no. 4, 2022, 9028-9033 9029 www.etasr.com saxena & roy: the effect of geometric parameters on the strength of stone columns table i. parameters used in the analysiss parameter range reference diameter, d 0.5m –1.5m [16] spacing, s 2d – 3d [2] angle of internal friction, � 35o – 45o [20] critical length 3d – 5d [15] 2d [24] a. bearing capacity using the is code method is:15284 part i [30] is a simple analytical method for calculating the ultimate bearing capacity of a stone column which uses coulomb’s lateral earth pressure theory. 1) capacity based on the bulging of the column considering that the foundation soil is at failure when stressed horizontally due to the bulging of the stone column, the limiting (yield) axial stress in the column is given by the sum of the following: σv = σrl kpcol σv = (σro + 4cu) kpcol (1) where σv is the limiting axial stress in the column when it approaches shear failure due to bulging, σrl is the limiting radial stress, which is equal to σro + 4cu, cu is the undisturbed undrained shear strength of the clay surrounding the column, and σro is the initial effective radial stress = ko σvo, where ko is the average coefficient of lateral earth pressure for clays equal to 0.6, ko is the average initial effective vertical stress considering an average bulge depth twice as the diameter, i.e. σvo = γ (2d), γ is the effective unit weight of soil within the influence zone, and kpcol = tan 2 (45° + � � ), where �c is the angle of internal friction of the granular column material. the safe load on column alone is given by: q1 = �� � � � � (2) where ac = � d 2 is the cross-sectional area of stone column and 2 is the factor of safety. 2) surcharge effect initially, the surcharge load is carried completely by the rigid column. as the column dilates, some load is shared by the intervening soil. consolidation of soil under this load results in an increase in its strength which provides additional lateral resistance against bulging. the increase in capacity of the column due to surcharge may be computed in terms of increase in mean radial stress of the soil as follows: δσro = ����� � (1 + 2�� ) (3) where δσro is the increase in mean radial stress due to surcharge and qsafe is the safe bearing pressure of soil with a factor of safety of 2.5: qsafe = �� �� �. so, the increase in the safe load of column, q2 is given by: q2 = !"�#$ %&'# (� � (4) 3) bearing support provided by the intervening soil this component consists of the intrinsic capacity of the virgin soil to support a vertical load which may be computed as follows: the effective area of stone column including the intervening soil for triangular pattern is equal to 0.866s 2 . the area of intervening soil for each column, ag is given by: ag = 0.866s 2 �� (5) the safe load taken by the intervening soil is: q3 = qsafe ag (6) therefore, the overall safe load on each column and its tributary soil is: qsafe = q1 + q2 + q3 (7) b. bearing capacity by bouassida’s [24] method the bouassida’s formula [24] for the estimation of bearing capacity is: )�� ( = 4c + 2η [c(kp – 2) + c*�+ (8) where qcc is the lower-bound estimate for the foundation bearing capacity, c is the cohesion of the reinforcing material, η the proportion of reinforcement, kp is the coefficient of passive stress of the reinforcing material. c. bearing capacity by afshar's and ghazavi’s [27] design method to calculate the ultimate bearing capacity of stone columns, an imaginary retaining wall is assumed that extends from the edge of the columns in the vertical direction. the center to center spacing of the columns is s and the entire system is analyzed using plane strain condition by converting the stone columns into equal sized vertical strip walls. the lateral distance between the walls is estimated to be 0.866 times s. the width w of the continuous strip wall is related to spacing as: w = (� , , where as is the cross section area of the stone column (in the horizontal direction). the ultimate bearing pressure is given by: 2 cos cos 2 2 cos cos 2 2 cos 1 2 tan 2 cos 2 c c c pc pc ult c s s as as c pc s c a s c as k k q c q k k k w k ϕ ϕ ϕ ϕ ϕ γ γ η ϕ γ         = +                   + −       (9) where cc is the cohesion of the soil, φc is the angle of internal friction, kpc is the lateral passive earth pressure coefficient, kas is the lateral active earth pressure coefficient, is the surcharge pressure on passive region surface, γc is the unit weight of the column material, γs is the unit weight of the soil material, and ηa is the angle of active wedge with horizontal direction. engineering, technology & applied science research vol. 12, no. 4, 2022, 9028-9033 9030 www.etasr.com saxena & roy: the effect of geometric parameters on the strength of stone columns iii. results a. parametric study using the is code method the results of is code method [30] have been obtained for soft clays of different area ratios. the ratio of center to center spacing between the columns and the diameter of the column are taken as s/d = 1.5, s/d = 2 and s/d =3. the effect of the angle of internal friction of the stone column material (�), unit weight (γ), and soil cohesion (cu) on the bearing capacity of stone column is studied. the bearing capacity obtained by varying the above-mentioned parameters is presented in figures 1-6. to study the effect of variation of � on the bearing capacity of the stone columns, the value of bearing capacity is calculated for s/d ratio equal to 2, 3, and 1.5 for 2 sets with diameters: d = 0.5 and d = 1.5. it was observed that bearing capacity increases with decrease in s/d ratio and diameter of the stone column plays an important role in its bearing capacity. when the friction angle varied from 35° to 45°, there has been continuous increase in the value of bearing capacity. also, the percentage change in bearing capacity is 44.80% for s = 1.5 d, 34.57% for s = 2d, and approximately, 21% for s= 3d for d = 0.5m. similarly, for d = 1.5 m, when friction angle varied from 35° to 45°, the percentage change in bearing capacity is 46.42% for s = 1.5 d, 36.88% for s = 2d and 23.23% for s= 3d. figures 1 and 2 show the variation of bearing capacity (q) with the angle of internal friction (φ), at d = 0.5m and 1.5m respectively. it is observed that, bearing capacity shows direct relation with angle of internal friction. fig. 1. variation of bearing capacity with angle of internal friction φ (d=0.5m). fig. 2. variation of bearing capacity with angle of internal friction φ (d=1.5m). fig. 3. variation of bearing capacity q with diameter d. the second geometric parameter responsible for affecting the bearing capacity of the stone column is the column diameter. to study the effect of diameter (d) on the bearing capacity (q) of the stone column, the diameter was varied from 0.5 to 1.5m for 6 sets of s/d ratios = 1, 1.5, 2, 3, 4 and 5. it can be clearly seen from figure 3 that as the s/d ratio increases, the bearing capacity of the stone column decreases. when the diameter increases from 0.5 to 1.5m, the percentage change in bearing capacity is 15.26% for s = 1d, 12.01% for s = 1.5d, 9.27% for s = 2d, 5.54% for s = 3d, 3.55% for s = 4d, and 2.42% for s = 5d. it is observed that when spacing is less than two times the diameter of the column, there is higher increase in values of bearing capacity. the third parameter whose effect is studied on the bearing capacity of stone columns is the unit weight of the soil (γ). the change in bearing capacity with different values of γ is studied with two sets of diameter, d = 0.5 and 1.5m at center to center spacing, s = 1.5d, 2d, and 3d. cohesion (cu) of the soft soil and the angle of internal friction of the column material (φ) are taken as 20kn/m 2 and 38° respectively. when the values of unit weight vary from 14 to 19kn/m 3 at d = 0.5m, the percentage change in bearing capacity is 1.95% for s = 1.5d, 1.53% for s = 2d, and 0.94% for s= 3d. similarly, when the values of unit weight increase from 14 to 19kn/m 3 at d = 1.5m, the percentage change in bearing capacity is 5.27% for s = 1.5d, 4.23% for s = 2d, and 2.71% for s = 3d. therefore, the conclusion is that while designing the stone column, the unit weight of the native soil has very less significance. b. comparison between the is code and bouassida’s method the is code method basically depends upon diameter, angle of internal friction of column material, and the unit density of the native soil. the range of these parameters for the study is taken as 0.5m to 1.5m, 35 o to 45 o , 14kn/m 3 to 19kn/m 3 respectively. a comparison between the predictions made by the is code method and bouassida’s method [24] follows. the is code uses the shear strength parameter of stone column and native soil materials for the prediction of bearing capacity, whereas the important parameter in [24] is area replacement ratio. from figure 5, it can be stated that at spacing ≥ 2d, the is code method gives conservative values of engineering, technology & applied science research vol. 12, no. 4, 2022, 9028-9033 9031 www.etasr.com saxena & roy: the effect of geometric parameters on the strength of stone columns bearing capacity in comparison with bouassida’s method [24]. the difference in bearing capacity values by is code method and bouassida’s method increases as the spacing of the columns increases. it was found that the bearing capacity value by is code method is higher than the value obtained through bouassida's method for s = 1.5d (figure 5). the percentage deviation in the values of bearing capacity by using is code method and bouassida’s method was calculated for every 10% increment in design parameters. figure 4 shows that for s = 2d and s= 3d, the is code method gives lower value of bearing capacity for every 10% increase in the design parameters, i.e. d, φ, and γ. fig. 4. comparison of the bearing capacity by is code and bouassida’s method. fig. 5. comparison of bearing capacity vs φ by is code and bouassida’s method. c. comparison between is code method and afshar's and ghazavi's design method [27] the analytical solution given by afshar and ghazavi [27] was used for the same soil conditions as used in the is code method and the bearing capacity has been calculated for � = 35°, γ = 14kn/m3, and d = 0.5m. the values of bearing capacity were calculated for two sets of spacing and diameter ratio, i.e. s/d = 2 and 3. figure 6 shows the graph comparing bearing capacity obtained by the is code method [30] and the afshar – ghazavi method. it is clearly visible that for s = 2d and s = 3d, the is code method gives lower values of bearing capacity than the afshar -ghazavi method. fig. 6. comparison of bearing capacity by the is code method afshar ghazavi method. d. result comparison of the is code method and experimental findings the ultimate bearing capacity of stone columns calculated analytically is compared with the experimental results observed from model tests by [31, 19]. the bearing capacity of soft clay reinforced with a single stone column was investigated using small-scale physical model test in [31]. the test tank used in their experiment had 650mm diameter. a stone column having a diameter of 25mm and a length of 225mm was constructed at the center of the clay bed. the undrained shear strength of the clay was 20kn/m 2 and the internal friction angle (φ) of the stone column material was 38°. the ultimate load of the single load column was found to be 450n. implementing the soil parameters in is code method, the ultimate load calculated from analytical method was about 420n, which is quite close to the result obtained in [31]. a large-scale test on stone columns was conducted in [20]. the stone columns were installed in triangular pattern with s = 4m, d = 0.9 m, and length l = 6.6m. the ultimate bearing capacity of native soil was 34kn/m 2 and field load tests were carried out on stone columns using real reinforced concrete (rc) footing. considering the average cohesion of the soft soil, cu = 12kn/m 2 , maurya’s model test [20] gave an ultimate load of about 800kn. for the same soil and load conditions the is code method gave stone column ultimate bearing capacity q = 36kn/m 2 and ultimate load of about 770kn, therefore, both results are close to each other. iv. discussion after the analysis of the stone columns from the three considered analytical methods of stone column design, it has been found that the friction angle � of the stone column material increases the interlocking between particles, thus affecting the strength of columns. it was observed that bearing capacity increases with decrease in s/d ratio and the diameter of the stone column plays an important role in its bearing capacity. is code method [30] gives conservative values of bearing capacity compared to bouassida’s method [24], engineering, technology & applied science research vol. 12, no. 4, 2022, 9028-9033 9032 www.etasr.com saxena & roy: the effect of geometric parameters on the strength of stone columns whereas the afsar ghazavi method [27] gives the highest values. v. conclusions based on the above results, the following conclusions can be drawn: • the bearing capacity of a stone column mainly depends on the angle of internal friction of column material (φ), the diameter of the stone column (d), the length of the stone column (l), the spacing between the stone columns (s), the unit density of the surrounding soil (γ), and the undrained cohesion (cu) of the surrounding soft soil. • upon varying the first geometrical parameter, i.e the spacing of stone column, it was seen that stone column capacity decreases by increasing the center to center spacing to 3d. beyond this value, the decrease of the stone column capacity is negligible. if the spacing between the stone columns is less than twice the diameter, then the design of the stone column is not feasible from the construction point of view. therefore, spacing greater than 2d is suggested. • the analytical result suggests that the bearing capacity of the stone column increases with the increase in the friction angle of the stone material and the diameter of the column due to the high interlocking between the stone particles. • it was found that the variation of bearing capacity with respect to diameter is more with smaller values of s/d ratio. • the variation 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[30] is 15284 part 1(2003), design and construction for ground improvement guidelines. new delhi, india: bureau of indian standards, 2003. [31] s. narasimha rao, m. madhiyan, and y. v. s. n. prasad "influence of bearing area on the behavior of stone columns", proceedings of indian geotechnic conference, calcutta, india, 1992, pp. 235-237. microsoft word 3-524-ce.doc engineering, technology & applied science research vol. 5, no. 1, 2015, 753-756 753 www.etasr.com ofuyatan et al.: durability properties of palm oil fuel ash self compacting concrete durability properties of palm oil fuel ash self compacting concrete tokunbo ofuyatan department of building, caleb university lagos, nigeria tokunbohofuya07@gmail.com festus olutoge civil engineering department, university of ibadan, nigeria folutoge2002@yahoo.com adeoye olowofoyeku yaba college of technology, civil engineering department, nigeria adeolowoo@yahoo.com abstract—self compacting concrete (scc) is a new innovation in technology that can flow readily into place under its own self weight and fill corner areas of reinforcement structures without the need to vibrate and without segregation of its constitute. the problem of durability of concrete structures due to inadequate compaction by skilled workers has become a source of concern globally. the shortage of skilled manpower, noise and vibration of equipment on construction sites has led to the development of self compacting concrete. this paper presents an experimental study on the durability properties of self compacting concrete with partial placement of palm oil fuel ash (pofa). twelve pofa self-compacting concretes of various strength grades were designed at varying percentages of 0, 5, 10, 15, 20, 25 and 30%. the concrete with no placement of ash served as control. conplast sp432ms was used as superplasticiser in the mix. the experiments are carried out by adopting a water-powder ratio of 0.36. workability of the fresh concrete is determined by using tests such as: slump flow, t50, v-funnel and l-box tests. the durability of concrete is tested by acid resistance, sulphate attack and saturated water absorption at the age of 14, 28, 56 and 90 days. keywords-self-compacting concrete; palm oil fuel ash; pofa; water absorption; acid resistance; sulphate attack; durability i. introduction the concept of self compacting concrete was first introduced in 1988 [1]. scc offers many new solutions to the concrete industry, due to its unique rheological properties. during the past 3-4 years the utilization of scc in europe has been steadily growing each year. much research has been made on the rheological properties of scc and less on the durability of scc. zhu et al. [2] studied the transport properties as well as the durability of scc. they concluded that the chloride migration depended much on the type of solid additives used in the mix. mörtsell and rodum [3] compared scc with normal concrete and found out that for a variety of durability tests, scc only showed better frost resistance of the skin surface. makishima et al., [4] studied the frost resistance of scc. they concluded that scc has excellent resistance to freezing and thawing, but in order to achieve long-term frost resistance, entrained air is needed. persson [5] studied the frost resistance of scc. in his conclusions, he found that internal damage is much less in scc compared to normal concrete, but scaling is similar between scc and normal concrete. contrary to [4] no relationship between the air voids content and frost resistance was documented. the scope of this research is to study the durability of self compacting concrete, mainly the freeze/thaw resistance and the chloride penetration, and to a lesser extent the interaction between sea-water and concrete (in terms of sulphate attack). palm oil fuel ash is an industrial by-product, generated from the combustion of coal in the thermal power plants. the increasing scarcity of raw materials and the urgent need to protect the environment against pollution has accentuated the significance of developing new building materials based on industrial waste generated from coal fired thermal power stations creating unmanageable disposal problems. palm ash, when used as a pozzollan in concrete, improves its strength and durability characteristics. palm ash is used either as an admixture or as a partial replacement of cement. it can also be used as a partial replacement of fine aggregates, as a total replacement of fine aggregates and as supplementary addition to achieve different properties of concrete [6]. ii. experimental details materials used and mix composition a. cement the cement used for the investigation was the type 1 normal ordinary portland cement (opc) that conforms to [7] and was obtained in 50 kg bags from retailers in lagos. the sand used in this research is natural river sand, with fines less than 0.125 mm for the rheology of the scc. the sand was dried at room temperature for 24 hours to control the water content in the concrete. b. coarse aggregates since the cubes were 150x150x150 mm in size, the nominal maximum size must not exceed 20 mm size of coarse aggregate [8]. crushed aggregate was gotten from sagamu quarry with nominal size of 10 mm in accordance to [9]. engineering, technology & applied science research vol. 5, no. 1, 2015, 753-756 754 www.etasr.com ofuyatan et al.: durability properties of palm oil fuel ash self compacting concrete c. water portable water supplied which was used for concreting and curing of samples. water is needed for the hydration of cement and to provide workability during mixing and placing. d. palm oil fuel ash the replacement of cement with palm oil fuel ash (pofa) is the key element of this research. pofa was grinded to a suitable fineness which in this research is up to 45 µm before it was used in the scc mix. it was kept airtight and stored in a humid-controlled room to prevent it from being exposed to moisture. e. conplast sp432ms high performance superplastisizer complying with astm c-494 type f [10] was used to produce scc. conplast sp432ms is a recent superplastisizer for concrete and mortar. it meets the requirement for set retarding or high range water – reducing superplastisizer. the color of conplast sp432ms is brown. f. mix proportions one control and seven scc mixes with different replacements of palm ash were prepared and examined to quantify the properties of scc. table i and ii present the composition of scc mixtures and sample mix composition. the replacement was carried out at levels of 0%, 5%, 10%, 15%, 20%, 25% and 30% of cement content. after iterative trial mixes the water/powder mass ratio (w/p) was selected as 0.36. the total powder content was varied as 450 kg/m3, 500 kg/m3, 530 kg/m3 as iterative values and finally fixed at 530 kg/m3. some design guidelines have been prepared from the acceptable test methods. many different test methods have been developed in attempts to characterize the properties of scc. so far, no single method or combination of methods has achieved universal approval and most of them have their adherents. similarly, no single method has been found to characterize all the relevant workability aspects. so, each mix design should be tested by more than one test method in order to obtain different workability parameters. table i. details of samples to be used sample main composition condition a1 opc only not compacted a2 opc + pofa compacted a3 opc + pofa 5%+sp not compacted a4 opc +pofa 10%+sp not compacted a5 opc + pofa 15%+sp not compacted a6 opc +pofa 20%+sp not compacted a7 opc +pofa 25%+sp not compacted a8 opc +pofa 30%+sp not compacted table ii. details of samples mix composition sample cement (kg) sand (kg) coarse aggre. (kg) water (kg) pofa (kg) w/b conplast sp432ms (%) a1 18.97 20.54 42.78 9.76 0.36 a2 18.97 20.54 42.78 9.76 0.36 a3 21.97 20.54 42.78 9.76 3.44 0.36 2% a4 19.58 20.54 42.78 9.76 4.88 0.36 2% a5 17.01 20.54 42.78 9.76 7.32 0.36 2% a6 15.65 20.54 42.78 9.79 9.76 0.36 2% a7 13.21 20.54 42.78 9.76 12.21 0.36 2% a8 12.54 20.54 42.78 9.76 14.78 0.36 2% iii. workability test methods for determining the self-compactability properties; slump flow, t50 time, v-funnel flow time, l-box blocking ratio, ubox difference in height tests were performed. in order to reduce the effect of workability loss on the variability of test results, fresh state properties of mixes were determined within a period of 30 minutes after mixing. the order of testing was as below, respectively. 1. slump flow test and measurement of t50 cm time 2. v-funnel flow test 3. l-box test iv. durability test methods durability studies were conducted at 28, 56 and 90 days for various mixes to find out the resistance to acid attack, sulphate attack and saturated water absorption. a. acid resistance acid resistance was tested on 150 mm size cube specimens at the age of 28 days of curing. the cube specimens were weighed and immersed in water diluted with one percent by weight of sulphuric acid for 14, 28, 56 and 90 days. then, the specimens were taken out from the acid water and the surfaces of the cubes were cleaned. then, the weight and the compressive strength of the specimens were measured and the average percentage of loss of weight and compressive strength were calculated. b. sulphate attack the sulphate attack testing procedure was conducted by immersing concrete specimens of the size 100x100x100 mm over the specified initial curing in a water tank. then, they were cured in 5% sodium sulphate solution for 28, 56 and 90 days, respectively. this type of testing represents an accelerated testing procedure, which indicates the performance engineering, technology & applied science research vol. 5, no. 1, 2015, 753-756 755 www.etasr.com ofuyatan et al.: durability properties of palm oil fuel ash self compacting concrete of particular concrete mixes to sulphate attack on concrete. the degree of sulphate attack was evaluated by measuring the weight losses of the specimens at 14, 28, 56 and 90 days, respectively. c. saturated water absorption saturated water absorption test was conducted on 100mmx100mmx100mm cubes at the age of 28 and 90 days. the specimens were weighed before drying in a hot air oven at 1050 ºc. the drying process was continued, until the difference in mass between two successive measurements at a 24 hour interval closely agreed. the dried specimens were cooled at room temperature and then immersed in water. the specimens were taken out at regular intervals of time, surface dried and weighed. the difference between the saturated mass and the oven dried mass expressed as a percentage of the oven dried mass gives the saturated water absorption. v. results and discussion in this study, fresh, hardened properties and durability of self-compacting concrete were investigated by using palm ash waste materials as partial replacement for cement. 2% superplastisizer was added due to the trial mix that was initially performed. in the present study, properties of self-compacting concrete produced with oil palm ash were investigated based on fresh concrete tests, workability, strength and durability tests. a. fresh properties it was observed (table iii) that the slump test for scc collapsed, while that of a2 was okay due to its compaction. the slump flow t50 of 4, 5, 6 and 7 had good results which were within the acceptable ranges of scc mixtures. the t50 time of 2-3 secs indicate a greater flow-ability, because a lower time taken means a better flow. this indicates that the passing ability, flow-ability and resistance to segregation were within the recommended limits of 650-800 mm and 3-15 secs. table iii. result of slump flow, t50, slump test specimen slump flow test 650 800mm slump flow t50 test 2-5 (secs) slump test a1 350 30 a2 550 120 a3 400 a4 550 1 a5 670 2 a6 720 3 a7 760 3 the l-box test results from the specimen as shown in table iv indicates a high value of blocking ratio (h1/h2) which was within the standard ratio. the higher the value of blocking ratio the higher the flow-ability of the concrete to compact at its own self weight and a good passing ability without blocking through closely spaced obstacles. it was observed that with the increase in the palm ash content the weight reduction of the specimens and the compressive strength gets reduced. it was also observed that with the increase in palm ash content the weight reduction gets decreased when compared with the control mix. it is clear that palm ash added as cement replacement in concrete enhances the sulphate resistance in concrete. it was alsonoted that with the increase in palm ash content the saturated water absorption gets decreased when compared with the control mix. palm ash acts as a filter material which fills the pores and thereby reduces water absorption. detailed results are shown in tables iv to vii. table iv. l-box result specimen h1(mm) h2(mm) h2/h1(mm) a3 44 36 0.82 a4 42 34 0.81 a5 38 35 0.94 a6 39 37 0.95 a7 43 38 0.95 table v. acid resistance test result mix proportion average reduction in weight % average loss of compressive strength % 0 14 28 56 90 14 28 56 90 5 2.78 3.64 4.34 5.42 8.56 10.8 12.5 13.8 10 1.57 2.16 3.51 4.58 7.5 8.1 9.3 10.7 15 1.88 2.64 3.91 4.88 6.4 7.7 8.5 9.2 20 1.54 1.67 2.27 3.55 5.1 6.58 7.65 8,45 25 0.87 1.38 2.59 4.05 5.9 6.6 7.20 9.01 30 0.43 2.54 3.51 4.32 6.3 7.5 8.62 9.25 table vi. sulphate attack result reduction in weight % mix proportion 14 28 56 90 0 1.25 2.24 2.48 3.45 5 1.20 2.34 2.75 2.98 10 1.15 1.96 2.63 2.74 15 1.10 1.90 2.48 2.56 20 1.05 2.05 2.43 2.98 25 1.01 2.53 2.71 3.15 30 1.00 2.71 2.98 3.24 table vii. water absorption rate test result average reduction in weight % mix proportion 14 28 56 90 0 3.34 3.53 3.45 3.28 5 3.11 3.21 3.31 3.13 10 3.00 2.87 2.72 2.64 15 2.54 2.64 2.48 2.32 20 2.61 2.75 2.55 2.46 25 2.75 2,84 2.66 2.56 30 2.55 2.32 2.24 2.18 vi. conclusion. 1. high strength scc can be produced from the combination of palm oil fuel ash and conplast sp432ms superplastisizer being partially placed in cement. the optimum mix design was found to be engineering, technology & applied science research vol. 5, no. 1, 2015, 753-756 756 www.etasr.com ofuyatan et al.: durability properties of palm oil fuel ash self compacting concrete 1:2.5:2 together with 30% of pofa, water cement ratio of 0.35 and ms432 conplast superplastisizer. 2. the acid resistance test of scc with palm ash had a high value compared with concrete mixes with ash at the ages of 28, 56 and 90 days. 3. when the specimen is immersed in sodium sulphate for 14, 28, 56 and 90 days, the average reduction in weight increased and the weight is decreased when the palm ash is increased in the concrete. 4. the water absorption percentage decreased with the increase in palm ash for 30% placement of ash, the low water absorption level is a good indicator of limited open porosity that can inhibit high flow of water into the concrete. references [1] h. okamura, “self-compacting high performance concrete”, progress in structural engineering and materials, vol. 1, no. 4, pp. 378-383, 1998 [2] w. zhu, j. quinn, p. bartos, “transport properties and durability of self compacting concrete”, 2nd international symposium on selfcompacting concrete, tokyo, japan, pp. 451-458, 2001 [3] e. mörtsell, e. rodum, “mechanical and durability aspects of scc for road structures”, 2nd international symposium on self-compacting concrete, tokyo, japan, pp. 459-468, 2001 [4] o. makishima, h. tanaka, y. itoh, k. komada, f. satoh, “evaluation of mechanical properties and durability of super quality concrete”, 2nd international symposium on self-compacting concrete, tokyo, japan, pp. 475-482, 2001 [5] b. persson, “internal frost resistance and salt frost scaling of selfcompacting concrete”, cement and concrete research, vol. 33, no. 3, pp. 373-379, 2003 [6] j. john, t. m. maya, t. meenambal, “mathematical modeling for durability characteristics of fly ash concrete”, international journal of engineering science and technology, vol. 4, no. 1, pp. 353-361, 2012 [7] british standards institute, bs 12 specification for portland cement, bsi, 1996 [8] british standards institute, bs 1881 pt 108 testing concrete. method for making test cubes from fresh concrete, bsi, 1983 [9] british standards institute, bs 882 specification for aggregates from natural sources for concrete, bsi, 1992 [10] astm, c494/c494m standard specification for chemical admixtures for concrete, astm international, 2001 microsoft word etasr_v12_n5_pp9364-9371 engineering, technology & applied science research vol. 12, no. 5, 2022, 9364-9371 9364 www.etasr.com alzahrani: data mining regarding cyberbullying in the arabic language on instagram using knime … data mining regarding cyberbullying in the arabic language on instagram using knime and orange tools shumaa saeed alzahrani computer science and engineering department college of computers and information systems umm al-qura university makkah, saudi arabia shayma.s.s.alzahrani@gmail.com received: 20 july 2022 | revised: 15 august 2022 | accepted: 22 august 2022 abstract-this paper deals with data mining on verbal bullying by instagram users. it tracks people who repeatedly have abusive behavior and may cause harm to other persons or groups. in this work, a dataset holding verbal bullying in the arabic language was extracted from instagram comments, and the entries were classified as regular verbal bullying and suspicious verbal bullying. kinime and orange open source data mining tools were utilized to discover comments that involved verbal bullying on instagram and to delete previous comments while users sent their comments automatically and immediately. classification algorithms rule-based in knime and select rows in orange were used. keywords-knime tool; orange tool; instagram; data mining; instagram comments; cyberbullying; verbal bullying i. introduction social media platforms have developed rapidly during the last few years. one of them is the instagram. it is free, contains online data, and provides an easy form of communication. users can talk in private and upload, tag, like, comment on, and share posts. machine learning powers the app. instagram’s feed ranking is constantly adapting and improving based on new data [1]. the instagram algorithm predicts how much you care about a post. this way, one can find and classify bullies based on trending [1]. also, the people who use offensive of abusive words can be identified with data mining tools. a. how the instagram algorithm works six key factors influence the instagram algorithm for feed posts: interest, relationship, timeliness, frequency, following, and usage. the instagram algorithm is constantly changing. the more the instagram algorithm "likes" a post, the higher it will appear in your feed. this phenomenon is based on the "past behavior on similar content and possibly machine vision analyzing the post’s actual content." what you see in your instagram feed is a mixture of all your behaviors on instagram [1]: the people you communicate with, the stories you watch, the individuals you are tagged with, and the topics you comment and like. comments, likes, reshares, and views are the most critical engagements for feed rating, which is beneficial when you prepare content and captions [1]. b. comment of all lengths count as engagement the instagram algorithm counts comments that are less than 3 words in length. instagram comments have become essential sources of knowledge for making fast and informed decisions and understanding how people behave in the real world. national and human rights organizations are now tracking social media [2]. c. motivation bullying includes repetitive and violent physical, verbal, or emotional actions. in this paper, the target goal is verbal bulling, which includes calling names, mocking, taunting, threatening, or verbally assaulting. bullying can make you feel powerless, ashamed, depressed, or even suicidal. detecting bullying can assist authorities in taking appropriate action by copying data, deleting them from public comments, or imposing fines. using social media sites as data providers may be an effective mechanism for protecting ourselves. due to the evolving technology, bullying is no longer confined to schoolyards or street corners but can happen at home via phone calls, texts, emails, and social media. cyberbullies stalk, attack, or humiliate victims using digital technology. cyberbullying, unlike conventional bullying, does not involve face-to-face contact and is not limited to a few people at a time. it also does not necessitate physical strength or many bullies. the embarrassment can be shared by hundreds or thousands of people online with just a few clicks. cyberbullying may involve sending threatening or degrading messages via text, email, social media posts, or instant messaging, as well as breaking into an email account or stealing someone’s online identity. some cyberbullies may set up a website or a social media account to harass a victim. the approaches used to cyberbully are as diverse and creative as the technologies accessible to bullies. the effects of cyberbullying corresponding author: shumaa saeed alzahrani engineering, technology & applied science research vol. 12, no. 5, 2022, 9364-9371 9365 www.etasr.com alzahrani: data mining regarding cyberbullying in the arabic language on instagram using knime … and traditional bullying are similar. they make victims feel angry, hurt, scared, powerless, hopeless, lonely, embarrassed, and guilty. a victim's mental health is likely to deteriorate, and the victim is more likely to experience mental health issues like low self-esteem, depression, ptsd, or anxiety. because most cyberbullying on instagram is anonymous, the victims do not know who is targeting them, which can make them feel even more threatened, and it can embolden bullies, who think that because they are anonymous online, they are less likely to be exposed. while cyberbullies cannot see the victim’s reaction, they will sometimes go deeper with their harassment or mockery than they would if the victims were personally present. arabic speakers post both formal and informal comments in social media. the formal form of arabic is modern standard arabic (msa), while the informal form is the regional dialects (da), the spoken language used for everyday contact in arab countries. compared to the most common languages, such as english, dealing with arabic text poses substantial challenges. arabic has a wide range of grammatical forms, word synonyms, and meanings, dependent on factors such as word order and diacritics. there is an additional difficulty when dealing with dialect or colloquial language, commonly used in instagram comments. d. research questions the main goal of this paper is to demonstrate the ability to detect verbal cyberbullying from social media comments, with instagram being used as a case study. to identify bullies’ comments, suspicious verbal cyberbullying terms, and verbal cyberbullying words, the following are the key research questions and sub-questions i hope to answer: • rq1: how can an arabic dataset of verbal cyberbullying be built? • rq1.1: how can an arabic dataset involving verbal cyberbullying in different dialects be built? • rq1.2: how can a verbal cyberbullying dataset be appropriate for this study? • rq1.3: how can the reliability of dataset classes be ensured? • rq2: how is verbal cyberbullying distinguished from nonrelated event comments? • rq2.1: what is the most effective tool for detecting verbal cyberbullying? • rq2.2: what are the best machine learning tools that improve the performance of the approaches? e. research goals this section addresses the paper's research objectives, followed by a discussion of the targets and their justifications. the following are the main objectives of this paper: • to create an arabic instagram dataset of verbal cyberbullying comments that identifies known and suspicious verbal cyberbullying words in comments in arabic. • to determine the best method for detecting verbal cyberbullying by comparing knime and orange tools results to discover the most successful supervised learning strategy. most relevant studies have created instagram datasets for testing verbal cyberbullying detection approaches. many datasets have been built for commonly used languages such as english, but arabic has received less attention. to the best of my knowledge, no one has performed or identified verbal cyberbullying detection in arabic. as a result of the increasing demand for arabic datasets, i created a dataset specifically to assess my targeted verbal cyberbullying detection system. because unsupervised methods are typically ineffective at detecting verbal cyberbullying, researchers must monitor their approaches. most unsupervised approaches use burst detection, which compares constructed words to verbal bullying word frequencies in comments. the burst behavior of specific words may not be verbal cyberbullying. for instance, not all sentences in arabic that include animal words (حيوان) are verbal cyberbullying. table i shows examples of verbal cyberbullying-related comments and non-related verbal cyberbullying comments. table i. instagram comment examples non-related verbal cyberbullying comment "mara [a type of rodent] animal" "حيوان المارا" related verbal cyberbullying comment "an animal, may god suffice us of him" "حيوان حسبي هللا عليه" both comments in table i use the same word. this word may indicate bursts, but it is not always indicative of verbal cyberbullying. compared to unsupervised approaches, the detection domain of supervised approaches is small. ii. related work most published studies concentrate on cyberbullying identification strategies for commonly used languages like english, with arabic gaining less attention. the first subsection of this chapter is a related work overview of the most influential cyberbullying identification studies in english social media or sns. the following subsection presents studies on cyberbullying identification in arabic social media or sns. in terms of cyberbullying detection, i have divided the reviewed papers into supervised and unsupervised approaches. authors in [11] proposed a solution to dispose of verbal cyberbullying. they suggested using a new feature selection technique for the closest neighbor classifier, which involves summarizing the original training materials using a measure of sentence importance. the two measures of sentence similarity used in their method for summarizing a single document were the frequency of the terms in a sentence and the similarity of that sentence to other sentences. after the researchers ranked all sentences, they chose the best-ranking sentences for a summary (within a threshold limitation). the researchers took every document’s summary from the corpus and entered it into a new document used for summarization evaluation. in [12], the effort focused on classifying documents, a guided learning technique. text preprocessing, feature extraction, and classification are the phases that make up the document engineering, technology & applied science research vol. 12, no. 5, 2022, 9364-9371 9366 www.etasr.com alzahrani: data mining regarding cyberbullying in the arabic language on instagram using knime … categorization process. the study evaluated the performance of two classifiers (knn and naive bayes) and specific feature selection strategies with or without combining accuracy, average precision, precision, and recall. the researchers trained each experiment’s classifiers using a custom data set. the results showed that the naive bayes classifier outperformed the other classifiers in several instances. in [13], the authors employed the comparative study’s performance evaluation metrics of accuracy, precision, and f-measure. three algorithms were used for cyberbullying classification, i.e. naive bayes, svm, and c4.5. a. event detection in arabic social media in [6], the researchers built a text corpus focusing on two common arabic dialects on twitter. they proposed a 3-level hierarchical annotation schema for hate and offensive language characterization. for hate speech, their emphasis was on 4 types: religion, ethnicity, nationality, and gender, for offensive speech, they focused on posts containing nonacceptable language or general profanity. based on machine learning (svm, naive bayes, logistic regression) and deep learning (cnn, lstm, and gru), they trained numerous 2-class, 3class, and 6-class hate speech classifiers using a panoply of feature extraction techniques, including unigram, word, and character n-grams and word embeddings (random, skip-gram, cbow, and fasttext) and contextual word embedding (multilingual bert). the researchers observed that deep learning was superior to machine learning across the 3 classification tasks. in deep neural networks, the cnn+mbert model outperformed all the other learned models across the 3 prediction tasks, with 87.05% for the 2class task, 78.99% for the 3-class task, and 75.51% for the 6class task. in [7], the researchers presented a scheme to detect cyberbullying messages in arabic social media streams (twitter and youtube). the detection algorithm used a corpus of offensive words most used among arab youth. the proposed scheme involved the following steps: (i) data cleaning and preprocessing, (ii) extracting bullying keywords and attributing weights, (iii) detecting cyberbullying comments, and (iv) calculating the bullying strength and classifying the comments. this scheme only focused on labeling the comments as bullying or non-bullying and decision making. b. existing arabic datasets authors in [3] published one of the first studies on arabic abusive language identification, which included the development of an arabic dataset of abusive comments. the dataset contained 1,100 tweets gathered from controversial accounts and hashtags. three annotators classified the dataset as pornographic, offensive, or clean. the authors used a pattern-based twitter search to build a seed word list of 228 obscene arabic words for classification. then, based on their use of obscene words in the seed list, they separated twitter users into clean and obscene. they also compiled a longer list of potentially obscene terms by removing only unigram and bigram words. they assessed the utility of both lists as features for categorizing tweets as obscene or clean. experiments revealed that combining the seed word list with the extended list generated the best f1 score of 60%. authors in [4] presented a more detailed dataset for religious hate speech in dialectical arabic. the dataset comprised 6,600 tweets using religious-related keywords. the researchers used crowdsourcing to classify the tweets as hateful or not and if they were religious extremist targets. they looked at various features, including lexicon-based and n-gram features, as well as standard machine learning algorithms. they also used neural networks like gru and lstm to evaluate their theories. their experiments showed that gru had the highest prediction accuracy of 77%. authors in [5] created the levantine hate speech and abusive behavior (l-hsab) twitter dataset, which included 5,812 tweets categorized as average, hateful, or abusive. the researchers divided the learning tasks into 2-class (abusive, normal) and 3-class classification tasks (abusive, hateful, normal) for model validation. they tried various ngram ranges, such as unigrams, bigrams, and trigrams, as functions. they compared svm and naive bayes classification performance and found that naive bayes outperformed svm with an f1 score of 89.6% for 2-class classification and 74.4% for 3-class classification. iii. arabic cyberbullying dataset one of the difficulties in detecting arabic cyberbullying is the small number of arabic datasets. to detect cyberbullying, i wanted to create a dataset with comments written in msa, saudi, and other dialects. in this section, the dataset of arabic comments from instagram that i made to detect cyberbullying is presented and the research question and sub-questions rq1, rq1.1, rq1.2, and rq1.3 will be answered. a. verbal cyberbullying instagram comment collection two key measures were followed to establish a dataset to detect cyberbullying. in the first step, comments by keywords were manually collected. in the second step, the collected comments were filtered into two classes: bully or positive. the other way was by verbal keywords. the comments were manually collected from the instagram website through the author's personal account. the reason for choosing instagram was because it has a high volume of cyberbullying comments, although it is not open source. thus, i created the dataset in an excel file to use in knime and orange tools. comments were collected for a period of 11 months between january and november of 2021. by using search terms for cyberbullying, a keywords list was prepared, for example: • { ي -ي غبي -ياأغبياء-ياغبيه-ياغبي-إغبياء-أغبياء-اغبياء غبية غبيه -غبي ي أغبياء ي اغبياءغبيه }. these words mean stupid in different ways in the arabic language. • { أنت -انت حمار -يا حمارة-ياحمارة -يا حماره-ياحمارهيا حمار ياحمار النك حمار -انتي حمارة-انتي حماره –حماره ي -ي حمار إنت حمار حمار } these words mean donkey in different ways in the arabic language. cyberbullying comments were collected based on a set of keyword lists related to calling names, mocking, taunting, threatening, or verbally assaulting in singular and plural. there were approximately 1,500 comments received for cyberbullying, with about 1,000 comments filtered by 1,857 keywords. figure 1 shows a part of this dataset. most comments were collected in 6 months. they were saved in an excel spreadsheet, which is an excellent choice for storing engineering, technology & applied science research vol. 12, no. 5, 2022, 9364-9371 9367 www.etasr.com alzahrani: data mining regarding cyberbullying in the arabic language on instagram using knime … instagram data in tables. in addition, because excel is a spreadsheet that consists of field and value pairs, storing comments is easy. fig. 1. a section of table comments and verbal bullying keywords. iv. proposed approaches the goal was to examine cyberbullying comments using keywords and categorize them into two types: cyberbullying (known and suspicious) and non-cyberbullying. i used knime and orange tools to evaluate two different methods. both tools detect cyberbullying comments distinguishable from noncyberbullying comments by performing workflows using many nodes to classify data. the two tools were evaluated and compared. in this section, the rq2, rq2.1, rq2.2 question and sub-questions will be addressed. a. utilized methodologies in cyberbullying detection, classification is usually used for specific cyberbullying detection, while clustering is generally used for unspecific cyberbullying detection. two methods were assessed to detect cyberbullying on instagram. the comments were manually gathered and the dataset was created. the suggested methods aimed to identify a specific form of cyberbullying. as a result, only supervised learning methods were used. because social media features such as follower counts, mention counts, and message lengths do not apply to the cyberbullying detection task, i focused the cyberbullying detection task on the textual content of the comments. the first method used the knime tool to identify cyberbullying and non-cyberbullying comments. the second method used the orange tool. the two methods were compared to see if breaking down the issue of cyberbullying identification into two phases improved its effectiveness. regarding the negative impact of noisy and informal comment text in both proposed methods, writing the keywords in different ways, such as in chatting manners, to detect relevant comments more effectively, is recommended. b. data mining tools in this paper, cyberbullying is detected through data mining using the open-source tools knime and orange. the reason behind the existence of these tools is the existence of massive amounts of data. as a result, the traditional statistics methods are no longer useful. in the late '80s, many pieces of research appeared to solve these problems, in addition to searching for solutions that combined several disciplines, including statistics, databases, artificial intelligence, distinguishing different models, or analog computing. then, data mining and knowledge discovery emerged, which proved to be successful solutions for analyzing vast amounts of data by transforming them from accumulated and incomprehensible data into valuable information that could be exploited and used [8]. data mining is the process of analyzing data from different perspectives, drawing relationships between them, and summarizing them into useful information. 1) knime tool knime makes understanding data and developing data science workflows and reusable components accessible by being intuitive, transparent, and constantly incorporating new technologies [9]. 2) orange tool the orange tool is open-source machine learning and data visualization software. with a comprehensive and diverse toolbox, it builds data analysis workflows visually [10]. data visualizations that are parts of the orange help find hidden data patterns, provide intuition behind data analysis procedures, or support collaboration between data scientists and domain experts. scatter plots, box plots, and histograms are among the visualization widgets available, as are model-specific visualizations such as dendrograms, silhouette plots, and tree visualizations. many other visualization tools, such as network visualizations, word clouds, and geographical maps are available as add-ons. interactive visualizations allow exploratory data analysis. a user can pick interesting data subsets directly from plots, graphs, and data tables and mine them in downstream widgets. for instance, a user can perform cross-validation logistic regression on a data set and map some misclassifications to the two-dimensional projection. it is simple to transform orange into a tool that allows domain experts to explore their data, even if they have little experience with statistics or machine learning. c. cyberbullying approaches 1) knime tool a) phase 1 the workflow in figure 2 represents the data flow between different nodes, starting with excel reader, then moving on to tika language detector (to recognize used languages), column filter, filter apply row splitter, row filter, rulebased row filter, and finally excel writer. fig. 2. the workflow of extracting bullying terms by rule. the working of nodes 128, 127, and 281 has been explained above. engineering, technology & applied science research vol. 12, no. 5, 2022, 9364-9371 9368 www.etasr.com alzahrani: data mining regarding cyberbullying in the arabic language on instagram using knime … • column filter: this node allows columns to be filtered from the input table while the remaining columns are passed to the output table. within the dialog, columns can be moved between the include and exclude list. • filter apply row splitter: this node splits the input according to the filter definitions, either given in the input table itself or optional as an additional model input. filter definitions are only applied if an additional model is provided as input. if the input contains a filter defined on a column not present in the input table, the node will not fail but will display a warning message. • row filter (figure 3): this node allows for row filtering according to specific criteria. it can include or exclude certain ranges (by row number), rows with a particular row id, or rows with a specific value in a selectable column (attribute). the node does not change the domain of the data table. in other words, the upper and lower bounds or the possible values in the table spec are not adapted, even if one of the bounds or values is fully filtered out. figure 3 shows the configuration dialog of the node. fig. 3. row filter output. fig. 4. ruled-based row filter output. • rule-based row filter (figure 4): this node takes a list of user-defined rules and tries to match them to each row in the input table. the row is selected for inclusion if the first matching rule has a true outcome. otherwise (i.e. if the first matching rule yields false), it will be excluded. if no rule matches, the row will be excluded. inclusion and exclusion may be inverted (see the options in figure 4). in the dialog in figure 4, i used the simple rule $col0$ in ("bully") => true to extract just cyberbullying comments by classifying the comments as bullying (1) or positive (0). figure 5 shows a part of the cyberbullying comment results using the rule bully term, which extracted 999 comments out of 1,500. fig. 5. part of cyberbullying comments results by bully term. b) phase 2 the workflow in figure 6 represents the flow data to extract cyberbullying comments by verbal bullying keywords. fig. 6. the workflow used to extract cyberbullying by vb keywords. fig. 7. results extract cyberbullying comments by vb keywords. engineering, technology & applied science research vol. 12, no. 5, 2022, 9364-9371 9369 www.etasr.com alzahrani: data mining regarding cyberbullying in the arabic language on instagram using knime … the results in figure 7 represent 1,061 cyberbullying comments, 64 of them being positive. the knime tool is inaccurate because it does not deal perfectly with arabic (as with english). phase1 in knime has 999 right results out of 1500. in phase 2 there are 61 wrong comments. 2) orange tool a) phase 1 the workflow in figure 8 represents extracting cyberbullying comments by using the bully term through a categorical type target role in the file node description. the file classifies bully and positive comments. the results are fairly accurate. there were 999 cyberbullying comments out of 1,498, and the workflow ignored the rest. fig. 8. workflow for classifying cyberbullying and non-cyberbullying comments by the bully term. the select rows dialog in figure 9 represents the condition pattern in which the classification is a column in the original file and the type of condition. bully is one of the values in the classification column. the other value is positive for noncyberbullying comments. fig. 9. select rows dialog with condition pattern. figure 10 displays the results for extracting 999 cyberbullying comments by bully term out of 1,500 comments. b) phase 2 i changed the select rows node description in figure 8. i used the condition in select rows node that the verbal bullying must contain the cyberbullying called ( اوعى تسدى المصريين ،ايران ماتنالم فيكم عيل، استوت مثل المومياء، اسلوبها زج، اسلوبج الخايس، اعصابك التنجلطين ههههههه،اعطتها اكبر من حجمها، افلس اخالقيا من بعد ماافلس فنيا ، اقلبي وجهك ، اذا تسئل على صراويل العراقين اسئل امك عنها اكيد محتفضه فيهم .as shown in figure 11 (للذكره fig. 10. data table node results for extracting 999 cyberbullying comments by bully term. fig. 11. extracting cyberbullying comments with more than one vb keyword. fig. 12. result of extracting cyberbullying comments with more than one vb keywords. engineering, technology & applied science research vol. 12, no. 5, 2022, 9364-9371 9370 www.etasr.com alzahrani: data mining regarding cyberbullying in the arabic language on instagram using knime … the output in figure 12 represents 10 chosen rows applied by the condition in the original file of 1,500 comments classified as cyberbullying c) phase 3 i changed the select rows node description in figure 8. i used the condition in the select rows node that the comment must contain the cyberbullying term (تبقون مذلولين), as shown in figure 13. the output in figure 14 represents one row in the original file of 1,500 comments classified as cyberbullying. fig. 13. select rows with condition comment contains vb keywords. fig. 14. workflow result. phase 1 in orange tool has a right result. phase 2 extracts cyberbullying comments by just one cyberbullying term. in phase 3, only the right answer can be shown when the cyberbulling terms are less than 100. d. comparison and evaluation in this paper, orange and knime tools were used to classify instagram comments under the cyberbullying and noncyberbullying categories. two data mining methods were applied: the first used two classes, bully and positive. the second used vb keywords. each tool has its advantages and disadvantages. the advantages of the knime tool are that it can deal with an extensive dataset, different types of files, a huge variety of components, has easy code-to-write conditions that make the tool more developed, and has excellent performance. the disadvantages are the need to use a special node to define the language, accurate results within the english language but inaccurate results within the arabic language, the inability to use the remove punctuation node to get the correct result in the arabic language, and unclear descriptions for using the tool. the advantages of the orange tool are the lack of need to define the language, accurate results when the vb keywords are less than 100, easy dealing with nodes, and easy understanding of the concepts of the tool. the disadvantages are that it cannot deal with a large dataset, every single vb keyword must be chosen every time, and it cannot make a condition with comments containing more than one vb. table ii. comparison between knime and orange tool algorithm phase1 phase2 phase3 notes knime rulebased 999 of 1500 1061 of 1500 phase2 has wrong result orange select rows 999 of 1500 cyberbullying term<100 of 1500 1 of 1500 phase2 allows small data. phase3 allows one condition every time e. conclusion orange and knime tools were used in this paper to data mine cyberbullying comments and distinguish them from noncyberbullying comments on instagram. i extracted cyberbullying in two ways, one using vb keywords and the other classifying comments as bully or positive. in knime, i got inaccurate data results within the large dataset, while in orange, i got accurate data results with less than 100 vb keywords. the results in both tools in the second way were accurate. v. conclusions and future work the driving question behind this study is "how can you detect cyberbullying in social media?" in this paper, emphasis was given on detecting name calling, mocking, taunting, threatening, or verbal abuse on instagram. i addressed a complex problem in arabic social media and carried out the key research goals. to assess cyberbullying detection methods, i created a cyberbullying dataset that included written comments in msa, saudi, and other arabic dialects. i created the dataset taking cyberbullying into consideration. i evaluated two supervised learning approaches to detect cyberbullying—the knime tool and the orange tool. the keywords were the same in both approaches, as they are on social media. both methods produced positive evaluation outcomes. regarding detecting engineering, technology & applied science research vol. 12, no. 5, 2022, 9364-9371 9371 www.etasr.com alzahrani: data mining regarding cyberbullying in the arabic language on instagram using knime … cyberbullying, the orange tool outperformed the knime tool. to address the issue of cyberbullying detection tasks, i suggest using the knime tool with raw data. regarding future work on cyberbullying detection, the following two directions are suggested for further investigation: • dataset expanding. a second version of the cyberbullying keyword dataset can be published by extracting extra samples and performing labeling process (known verbal, suspicious verbal, and non-cyberbullying). • cyberbullying detection in audio files using the knime tool with the created cyberbullying keywords dataset. the utilized cyberbullying detection approach will be used in the future on the twitter platform with its open-source api. references [1] j. warren, "this is how the instagram algorithm works in 2022," later.com, jun. 21, 2022. https://later.com/blog/how-instagramalgorithm-works/. [2] f. chen and d. b. neill, "human rights event detection from heterogeneous social media graphs," big data, vol. 3, no. 1, pp. 34–40, mar. 2015, https://doi.org/10.1089/big.2014.0072. [3] h. mubarak, k. darwish, and w. magdy, "abusive language detection on arabic social media," in proceedings of the first workshop on abusive language online, vancouver, bc, canada, dec. 2017, pp. 52– 56, https://doi.org/10.18653/v1/w17-3008. [4] k. e abdelfatah, g. terejanu, and a. a alhelbawy, "unsupervised detection of violent content in arabic social media," in computer science & information technology (cs & it), mar. 2017, pp. 01–07, https://doi.org/10.5121/csit.2017.70401. [5] l. kaati, e. omer, n. prucha, and a. shrestha, "detecting multipliers of jihadism on twitter," in 2015 ieee international conference on data mining workshop (icdmw), aug. 2015, pp. 954–960, https://doi.org/10.1109/icdmw.2015.9. [6] s. alsafari, s. sadaoui, and m. mouhoub, "hate and offensive speech detection on arabic social media," online social networks and media, vol. 19, sep. 2020, art. no. 100096, https://doi.org/10.1016/j.osnem. 2020.100096. [7] d. mouheb, r. ismail, s. a. qaraghuli, z. a. aghbari, and i. kamel, "detection of offensive messages in arabic social media communications," in 2018 international conference on innovations in information technology (iit), aug. 2018, pp. 24–29, https://doi.org/ 10.1109/innovations.2018.8606030. [8] α. sayed, "data mining tool open source: analytical evaluation study," journal of taibah university arts and humanities, vol. 5, no. 10, pp. 791–865, jun. 2016, https://doi.org/10.12816/0032954. [9] "data analytics platform: open source software tools," knime. https://www.knime.com/knime-analytics-platform. [10] "orange data mining." https://orangedatamining.com/. 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[13] m. alghobiri, "a comparative analysis of classification algorithms on diverse datasets," engineering, technology & applied science research, vol. 8, no. 2, pp. 2790–2795, apr. 2018, https://doi.org/ 10.48084/etasr.1952. microsoft word etasr_v12_n6_pp9527-9531 engineering, technology & applied science research vol. 12, no. 6, 2022, 9527-9531 9527 www.etasr.com nguyen: local instability analysis for axial compressive steel columns local instability analysis for axial compressive steel columns phu-cuong nguyen advanced structural engineering laboratory department of structural engineering faculty of civil engineering ho chi minh city open university ho chi minh city, vietnam cuong.pn@ou.edu.vn received: 3 august 2022 | revised: 19 august 2022 | accepted: 20 august 2022 abstract-this study presents a nonlinear analysis method for steel columns considering local instability under axial compression. the stress-strain relationship of steel is developed while considering the effects of local instability utilizing the energy principles. the second-order effects are considered by stability functions, while the plasticity of steel is captured by a fiber finite element method. nonlinear equilibrium equations are solved by the generalized displacement control method. as a result, the proposed formulations are effective, accurate, and reliable in predicting the load-carrying capacity and local instability of steel columns. keywords-second-order effect; local instability; stability function; steel column; plasticity i. introduction steel structures are widely used in several fields (mechanical and civil engineering, aerospace, etc.). the advantages of steel are its high strength, ductility, flexibility, and fast construction, however, instability is a important weak point of steel structures that must be evaluated carefully. many experimental tests [1-7] were carried out to exam local buckling of steel columns (welded steel columns, high strength steel columns, stainless steel columns, etc.). examples of local instability of a high strength steel column can be seen in [4]. authors in [8] studied the local buckling strength of steel columns considering uniformly idealized distributed residual stress. a finite difference method was employed for predicting the plate buckling curves. boundary conditions for plates were simply supported at loading edges, and free, simply supported, and fixed at the remaining edges. the theoritical results were compared with the experimental tests of 8 square welded steel columns. author in [9] researched flange local instability of a steel beam with wide-flange shapes. authors in [10] proposed explicit expressions for the collapse and elastic post-buckling of simply supported plates considering geometric imperfection. in 1977, authors in [11] studied lateral-torsional buckling of local-buckled beams employing a finite element formulation in conjunction with the effective width concept. in this solution, both elastic stiffness and geometric stiffness matrices must be updated at each load step. authors in [12] developed a finite strip method for the post local-buckled analysis of prismatic thin walled structures under axial compression. authors in [13] investigated local instability of thin-walled steel box columns. thin-walled steel box columns were pinned at two ends and were subjected to an eccentrically applied load. in 1997, authors in [5] tested local instability of stub thin-walled circular steel tubes with or without internal restraint considering residual stress and geometric imperfection. more recently, some other studies on local instability for steel members under fire load have been published [6, 14-18]. local buckling can be easily investigated using plate, shell, or solid elements with the finite element method (fem). authors in [19] simulated and proposed the behavior analysis of short concrete-filled steel tube columns using the fem software abaqus. the effects of local buckling of steel tubes were considered by using shell elements. authors in [20] developed a finite element simulation for normal-strength cfdst members with shear connectors under bending. authors in [21-23] analyzed several types of structures using the fem without considering local instability. however, it is not efficient with regard to computational time if these 2d or 3d elements are used. using line elements, local buckling is implicitly evaluated using design equations of aisc-lrfd specification [24, 25]. authors in [26-33] studied several works on the nonlinear inelastic behavior of steel frames, but the effects of local instability were not investigated. in this study, the displacement fem using one fiber element per member [34-39] is improved to consider local instability. a numerical procedure based on the generalized displacement control method [40] is developed to solve the nonlinear equations of the structural system. the proposed formulations are shown detailly in the following sections. ii. steel behavior considering local buckling local buckling of steel profiles under axial compression is considered by the stress-strain curve as drawn in figure 2. it is assumed that the whole section will start to buckle at a critical strain c cr  greater than the yielding strain y  . the inelastic corresponding author: phu-cuong nguyen engineering, technology & applied science research vol. 12, no. 6, 2022, 9527-9531 9528 www.etasr.com nguyen: local instability analysis for axial compressive steel columns post-instability response is estimated based on a strain energy method of the component plates as formulated in (1)-(5). the relation between the effective width of the plate be and the full width b is: e b a y b b u u b u      (1) where y  is the yielding stress, y  is the yielding strain, ub and ua are the strain energy before and after the occurred inelastic local instability. they are formulated as:  1 2 1 2 b y y cr y y cr y y u                   (2)   1 2 a cr yu       (3) in which the critical strain cr  is calculated from the critical stress cr  as [41]:    2 22 12 1 / cr cr k e v b t       (4) where e and  are the elastic modulus and poisson’s ratio of material, b is the considering width of the plate, t is the thickness of the plate, and k is the buckling coefficient given in [42]. fig. 1. assumed stress-strain curve for local buckling of steel. after substituting (2) and (3) into (1), the inelastic postlocal instability behavior can be estimated by: 1 1 1 1 2 y cr y                    (5) where  is a adjusting parameter of the slope of the postinstability behavior. iii. formulas for the nonlinear column element a. second-order and shear deformation effects the stability functions proposed in [43] are employed to simulate the second-order effect by using only one element per member. from [34, 35, 38, 39], the incremental equilibrium equation of a column element, considering both shear deformation and the second-order effects is written as: 1 2 2 1 1 2 2 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ya y y ya yb y y yb za z z za zb z z zb ea p l m c c m c c m c c m c c gjt l                                                                     (6) where p , t , yam , ybm , zam , and zbm are the axial force, torsion and bending moments respectively,  ,  , ya , yb , za , and zb are the axial shortening and rotations respectively, a is the sectional area, j is the moment of inertia around the z axis, l is the element length, g is the shear modulus of steel, and 1 y c , 2 y c , 1 z c , and 2 z c are respectively the flexural stiffness coefficients considering the shear deformation, estimated as: 2 2 1 2 1 1 1 22 2 y y y sz y y y sz k k k a gl c k k a gl      (7) 2 2 1 2 2 2 1 22 2 y y y sz y y y sz k k k a gl c k k a gl       (8) 2 2 1 2 1 1 1 22 2 z z z sy z z z sy k k k a gl c k k a gl      (9) 2 2 1 2 2 2 1 22 2 z z y sy z z z sy k k k a gl c k k a gl       (10) where   1 1 / n n n k s ei l and   2 2 / n n n k s ei l . 1n s and 2 n s are the stability functions with the axis of n  ,n y z and are written as: stress strain cr y y cr engineering, technology & applied science research vol. 12, no. 6, 2022, 9527-9531 9529 www.etasr.com nguyen: local instability analysis for axial compressive steel columns                     2 1 2 sin cos 0 2 2 cos sin cosh sinh 0 2 2 cosh sinh n n n n n n n n n n n n n n n h l h l h l h l if p h l h l h l s h l h l h l h l if p h l h l h l              (11)                 2 2 2 sin 0 2 2 cos sin sin 0 2 2 cosh sinh n n n n n n n n n n n n n h l h l h l if p h l h l h l s h l h l h l if p h l h l h l              (12) which 2 n n h p ei . ea and n ei are the axial and flexural stiffnesses of the column and are calculated by: 1 1 p m j i i j i j ea w e a             (13)  2 1 1 p m y j i i i yi j i j ei w e a z i             (14)  2 1 1 p m z j i i i zi j i j ei w e a y i             (15) where p is the number of meshed sections per element, m is the number of fibres divided on the meshed sections, wj is the weight parameters for lobatto quadrature at the j th section [44], ei and ai are the elastic modulus of the material and the area of i th fiber respectively, iyi and izi are the y-axis and z-axis moments of inertia of the i th fiber around its centroid, yi and zi are the coordinates of the i th fiber to the central bending axis of the section as illustrated in figure 2. fig. 2. meshing of the steel column. b. effects of plasticity to predict the plasticity along the member, a fiber column model as plotted in figure 2 is used. figure 3 shows the residual stress pattern shape [45] used in this study. the section deformations are estimated by three strain resultants: the axial strain  and curvatures z  and y  . the force resultants are the axial force n and the flexural moments z m and y m . the sectional forces and deformations are calculated as: sectional force   t y zq n m m    (16) sectional deformation   t y zq       (17) fig. 3. assumed residual stress pattern for the steel column. iv. verification in [46], two experimental tests were carried out for isections with strengthening stiffeners at column bases. the elastic modulus is 200000mpa and the yield stress is 265mpa. the ratio of the width per the thickness (b/t) of specimens changed from 20 to 25. the initial residual stresses measured in [46] were 17% to 19% of the yield stress as listed in table i, along with the column geometries. the load ratio-axial shortening curves captured by the proposed formulation are compared with abaqus in figures 4 and 5. it can be seen that the proposed curve including local buckling nearly matches with the result of abaqus (figure 4). table ii presents a comparison of the ultimate compressive load estimated by experimetal tests, abaqus, and the proposed formulation (lb: local buckling). the ultimate load estimated by the proposed formulation is slightly higher than the results of experimental tests and abaqus. there are big differences between considering local buckling or not in the analysis procedure. the clear differences occur due to the plastic elastic regime of the steel fibers. table i. geometries of specimens tested in [46] specimen geometric characteristics b (mm) t (mm) b/t a (mm 2 ) l (mm) rc/y hi1 60 3 20 1062 900 0.18 hi2 75 3 25 1332 900 0.19 engineering, technology & applied science research vol. 12, no. 6, 2022, 9527-9531 9530 www.etasr.com nguyen: local instability analysis for axial compressive steel columns table ii. comparison of ultimate compression load specimen ptest (kn) [46] pana./ptest abaqus proposed (with lb) proposed (without lb) hi1 260 0.949 1.011 1.090 hi2 250 1.075 1.205 1.427 fig. 4. load ratio-axial shortening curve of hi1 column. fig. 5. load ratio-axial shortening curve of hi2 column. v. conclusion in this paper, the finite element analysis formulation for the second-order inelastic steel columns considering local instability was developed successfully. by using one element per member, the proposed formulation reduced computational time and computer resources. the results are in good accordance with the results of abaqus and the experimental tests. the proposed formulation can be applied in the development of practical engineering software. acknowledgment this research is funded by ho chi minh city open university under the grant number e2020.08.1. references [1] b. uy, "local and post-local buckling of concrete filled steel welded box columns," journal of constructional steel research, vol. 47, no. 1, pp. 47–72, aug. 1998, https://doi.org/10.1016/s0143-974x(98)80102-8. 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[46] b. uy, "local and postlocal buckling of fabricated steel and composite cross sections," journal of structural engineering, vol. 127, no. 6, pp. 666–677, jun. 2001, https://doi.org/10.1061/(asce)0733-9445(2001) 127:6(666). microsoft word etasr_v13_n2_pp10466-10470 engineering, technology & applied science research vol. 13, no. 2, 2023, 10466-10470 10466 www.etasr.com tran & vo nguyen: computation of limit loads for bending plates computation of limit loads for bending plates trung-dung tran faculty of civil engineering, ho chi minh city open university, vietnam dung.ttrung@ou.edu.vn phu-huan vo nguyen infrastructural technique department, faculty of civil engineering, ho chi minh city open university, vietnam huan.vnp@ou.edu.vn (corresponding author) received: 8 january 2023 | revised: 2 february2 2023 | accepted: 17 february 2023 abstract the purpose of this paper is to present a method for calculating the upper bound limit loads of plate bending using a conforming hsieh-clough-tocher (hct) element. these limit loads can be obtained from koiter’s kinematic shakedown theorem for the case of one load vertex instead of using the kinematic limit theorem. when combining this theorem with the approximated displacement field, the limit analysis turns into an optimization problem and can be effectively solved by second-order cone programming (socp). several benchmark plate problems such as square, rectangular, and l-shape plates are investigated to illustrate the effectiveness of the proposed solution. the results of the proposed method show good agreement with the results of previous studies. the maximum error is only 2.91% for the fully clamped rectangular plate problem. keywords-plate bending; limit analysis; second-order cone programming; plates; shakedown i. introduction one of the most significant issues in structure engineering is the determination of the safety load factors. limit analysis is a well-known efficient approach for resolving the issue. these limit loads can be calculated by using the loweror upperbound theorems of limit analysis. however, it is very difficult to apply these two theorems to tackle general problems when using analytical methods [1]. therefore, the current research is mainly concentrated on computational methods. authors in [2, 3] carried out experimental tests in order to understand the punching shear behavior of concrete slabs reinforced by steel collars and hybrid fibers. author in [4] studied the limit state of local instability of steel column structures under axial compression using the energy method combined with the finite element method using fiber beam-column elements. authors in [5] employed the shaft-grouted method to improve the bearing capacity of barrette piles for high-rise buildings in ho chi minh city, vietnam. authors in [6] developed a new effective finite element modeling for predicting the ultimate strength of concrete-filled steel tube columns under axial compression. authors in [7, 8] studied steel frames under static and earthquake loadings with limit load analysis methods. various discretization techniques have been developed to treat the limit problems such as finite elements [9-12], meshfree methods [1317], and isogeometric analysis [18]. limit analysis of plate bending has been extensively investigated, analytically and numerically [19, 20]. in [19], limit loads of plate bending were studied in both kirchhoff and mindlin plate models based on the upper bound theorem and the finite element method. a dual algorithm combined with dkq elements for limit and shakedown analyses of plate bending was proposed in [21]. one of the most efficient methods to conduct plate bending limit analysis was developed by canh [12, 17], where socp was utilized in conjunction with conforming the hct element or the meshless element‐ free galerkin (efg) method. based on this approach, the aim of this research is to provide a solution to determine the upper bound load factors of plate bending with the combination of the hct element and socp. however, the limit loads will be determined from koiter’s kinematic shakedown theorem for the case of one load vertex instead of using the kinematic theorem of limit analysis as in [12]. the advantage of this approach is that it can be easily extended to the shakedown problem. in addition, having calculated the stress components, it is possible to determine the failure mode of structures such as alternating plasticity for non-shakedown problems [22]. ii. limit analysis formulation of plate bending based on the shakedown approach consider a rigid-perfectly plastic plate that has a closed boundary with plane area a. let a and a denote static and kinematic boundaries respectively. neglecting the shear deformation, the kinematic relations of thin plates can be described as: engineering, technology & applied science research vol. 13, no. 2, 2023, 10466-10470 10467 www.etasr.com tran & vo nguyen: computation of limit loads for bending plates 2 x yy 2x xy       ɺ ɺ ɺ ɺ ɺ (1) where ɺ denotes the curvature rate vector, ɺ is the transversal velocity, and the operator 2 is expressed by: 2 2 2 2 2 2 2 t x yx y             let x yy 2 t x xym m m   m and p be the vector of bending moments and the transversal load, respectively. the equilibrium relation can be defined as:  2 0 t p  m (2) in this study, the von mises yield condition is adopted, and the internal dissipation power of the plate bending (or the dissipation rate) can be described as: ( )κ κ κqp t p d m=ɺ ɺ ɺ (3) where: 4 2 0 1 2 4 0 3 0 0 1          q (4) and 2 4p ym h is the plastic limit moment per unit length of a plate section in which h and y denote the plate thickness and the yield stress, respectively. next, consider a structure simultaneously submitted to nl linearly independently varying loads  ˆ 1, 2,...,kp k nl  which form a convex polyhedral load domain. according to koiter’s theorem [23], by applying mathematical programming theory, an upper bound of the shakedown load factor  can be rewritten in the form of non-linear programming as follows (the superscript p of dissipation rate function is skipped for simplicity):   1 min nl k a k d da    ɺκ   2 1 1 . 0 ˆ, 1, nl k k u nl t e k k a k s t on a x p da                     κ m ɺ ɺ ɺ ɺ κ κ (5) where m e is the fictitious elastic moment vector of the point x on the domain a. note that, when nl = 1 the problem (5) reduces that of limit analysis. then, the formulation for the upper bound limit load is determined as follows:   2 min . 0 1, p a u et a d da s t on a da                 κ κ m κ ɺ ɺ ɺ ɺ ɺ (6) compared to the kinematic theorem of limit analysis as presented in [12], the difference of (6) is that the work rate of the applied load constraint is replaced by the external work rate constraint. in general, problem (6) is complicated because it has to calculate the stress components. however, as mentioned above, it can be advantageous to develop the shakedown problem. in addition, the failure mode of alternating plasticity can be determined easily when the structure is subjected to repeated loads. iii. hct-based kinematic formulation the conforming hct element has been detailed in [12, 24]. the key idea of the hct element is to divide an original triangular element into three sub-elements as shown in figure 1. fig. 1. hct element. the number of the total degrees of freedom of the element is 12 including 3 degrees at each corner node and 3 degrees at three mid-side nodes. in terms of area coordinates  1 2 3, ,    , at each sub-triangle, we can express the displacement expansion  k w as follows:             0 , 1, 2, 3kk ke ew k    l l f q (7) where qe is the element displacement matrix ανδ the partitions    ke l and    0 k l denote the interpolation functions, respectively. f is the matrix determined from compatible conditions. then, the curvatures can be defined by: ( ) ( ) ( ) ( ) , 0, , ( ) ( ) ( ) ( ) ( ) , 0, , ( ) ( ) ( ) ( ) , 0, , ) k k k k xx e xx xx e xx k k k k k yy e yy yy e e yy e k k k k xy e xy xy e xy                                    l l f b κ l l f q b q l l f b (8) and we can obtain the plastic dissipation of the plate as: engineering, technology & applied science research vol. 13, no. 2, 2023, 10466-10470 10468 www.etasr.com tran & vo nguyen: computation of limit loads for bending plates     3 1 κ κ      qɺ ɺ ne ng t p j j j j d m (9) where ne and ng are the total number of elements and gaussian points, respectively. the upper-bound limit analysis based on the shakedown approach of plate bending is now described as:         3 1 3 1 min . 1 0 κ κ κ κ                       q b q m q ɺ ɺ ɺ ɺ ɺ ɺ ne ng t p j j j j j j ne ng e t i j j j u m s t on a (10) by formulating the objective function to a form comprising a sum of norms, the optimization problem (10) can be reexpressed as a standard socp as follows [25]:   3 1 κ     j ɺ ne ng t p j j j d m (11) where j is defined as: 2 0 0 1 1 3 0 3 0 0 1            j (12) it can be seen that j is also the cholesky factor of q. finally, by establishing supplementary variables x1, x2,…, xne3ng, problem (10) can be stated as follows:     3 1 3 1 min 1 . 0 , 1, 2,..., 3 κ κ                           m q ρ j ρ ɺ ɺ ɺ ne ng p k k k ne ng e t j j j j t k k k k m x s t on a x k ne ng (13) where ρk kx denotes quadratic cones and the k are supplementary variables. iv. numerical examples to illustrate the effectiveness of the proposed solution, in this section we investigate various benchmark problems that have numerical or analytical solutions. the following parameters are adopted for all examples: length a = 10m and plate thickness h = 0.1m. the first example considers a square plate with side length a, and restraints on all edges that are either simply supports or clamped. the plate is subjected to uniform pressure p, as shown in figure 2. due to symmetry, we only modeled the upper-right quarter of the plate as illustrated in figure 3. the results of the proposed method, normalized with mp/a 2 , are presented in table i. it can be observed that when the number of the elements increases, the collapse load factors reduce and converge. when compared with previous results, the present results are in good agreement with those obtained numerically in [18, 19, 21], in which the efg method, a c1 continuity plate element, and the the dkq element were used, respectively. in addition, table i also shows that the results of the proposed method are similar to the results obtained analytically in [20, 26]. the yield patterns in terms of plastic dissipation distribution are plotted in figure 4. it can be seen that they are very consistent with the experiment, for both simply supported and clamped plates. (a) (b) fig. 2. square slabs: geometry and loading. (a) simply supported plate, (b) clamped plate. fig. 3. square slab: finite element mesh. table i. limit load factor of the square plate (pa2/mp) method simply supported clamped ub lb ub lb proposed ne = 50 25.18 51.83 ne = 200 25.06 48.17 ne = 800 25.03 46.19 ne = 1800 25.03 45.58 [19] 25.02 45.29 [17] 25.01 45.07 [21] 25.04 25.04 45.06 45.06 [20] 26.54 24.86 49.25 42.86 [26] 27.71 23.81 52.01 ne: number of elements, lb – lower bound, ub – upper bound engineering, technology & applied science research vol. 13, no. 2, 2023, 10466-10470 10469 www.etasr.com tran & vo nguyen: computation of limit loads for bending plates (a) (b) fig. 4. square slabs: plastic dissipation distribution. (a) simply supported plate, (b) clamped plate. fig. 5. rectangular slab: geometry and loading. fig. 6. rectangular slab: finite element mesh. table ii. limit load factor of the rectangular plate (pab/mp) method simply supported clamped proposed 29.90 56.20 [19] 29.88 [17] 29.88 54.61 (a) (b) fig. 7. rectangular slabs: plastic dissipation distribution. (a) simply supported plate, (b) clamped plate. next, we consider the rectangular slab of figure 5 (dimensions ab and b/a = 2). similar to the previous example, only the upper-right quarter of the plate is modeled by 800 elements (figure 6). limit load factors are reported in table ii. when compared with the previously obtained results, the proposed method provides better solutions than in [17, 19] by 0.07% and 2.91% for the case of simply supported and clamped edges, respectively. the plastic dissipation distribution of rectangular slabs is plotted in figure 7. the last example is an l-shape plate, investigated in the case of uniform load. the geometry and uniform mesh of the l-shape plate are shown in figure 8 and the limit load factors are shown in table iii. again, the results of the proposed method show good agreement with previous studies. the maximum error is only 2.59% for the case of clamped edges. the plastic dissipation distribution using 2400 elements is plotted in figure 9. (a) (b) fig. 8. l-shape plate. (a) geometry, (b) mesh. table iii. limit load factor of the l-shape plate (pa2/mp) method simply supported clamped proposed 6.20 16.24 [10] 6.29 [15] 6.17/6.04 15.83/15.69 (a) (b) fig. 9. l-shape slabs: plastic dissipation distribution. (a) simply supported, (b) clamped. v. conclusion this paper presented a numerical solution for the computation of the limit loads of bending plates. using von mises yield criterion and the conforming hct element, the upper bound limit load can be derived from koiter’s kinematic shakedown theorem for the case of one load vertex instead of using the upper bound theorem of limit analysis. based on this approach, the work rate of the applied load constraint in the kinematic theorem of limit analysis is replaced by the external work rate constraint. the formulation based on koiter’s kinematic shakedown theorem is more complicated than the engineering, technology & applied science research vol. 13, no. 2, 2023, 10466-10470 10470 www.etasr.com tran & vo nguyen: computation of limit loads for bending plates formulations for the upper bound of the limit load, however, it can be developed to the shakedown problem and the failure mode of alternating plasticity can be determined easily. one benefit of this research is that the problems can be formulated as socp, so that they can be solved rapidly, even when many variables are involved. the accuracy and reliability of the proposed solution method were proven by numerical examples. acknowledgment this research is funded by ho chi minh city open university under grant no. e2020.01.1 references [1] w. prager and p. g. hodge jr., theory of perfectly plastic solids, 1st ed. new york, ny, usa: john wiley & sons, 1951. 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[26] j. lubliner, plasticity theory. new york, ny, usa: macmillan, 1990. microsoft word etasr_v13_n1_pp9913-9918 engineering, technology & applied science research vol. 13, no. 1, 2023, 9913-9918 9913 www.etasr.com el-ashmawy: an efficient methodology for detecting the vertical movement of structures an efficient methodology for detecting the vertical movement of structures khalid l. a. el-ashmawy department of civil engineering, college of engineering and islamic architecture umm al-qura university, makkah, saudi arabia klashmawy@uqu.edu.sa (corresponding author) received: 2 november 2022 | revised: 16 november 2022 | accepted: 21 november 2022 abstract details regarding the public safety of engineering structures can be gleaned from measurements and monitoring. the development of a methodology for monitoring and analyzing structures' vertical displacement is explained in this paper. the developed methodology aims to add a new dimension to geometric leveling, and leveling routing, by applying a least squares solution for level network adjustment and performing statistical analysis to assess the change in vertical displacement. to monitor and analyze the vertical deformation of a building in cairo, egypt, the proposed methodology was utilized. twenty monitoring points, five auxiliary points, and three local reference stations were utilized. all the measurements were taken with a geodetic invar staff and an automatic level with an attachment of a parallel plate micrometer. the observations were made for an interval of 81 months. the least squares adjustment technique was applied to obtain the adjusted levels and observations and to generate the required statistical data. the results of the subsequent epochs were compared to the results of the first epoch to determine the vertical movement of the monitoring points for each epoch. in addition, the significance of the present displacement was ascertained by comparing the values of vertical displacement to the determined 95% corresponding confidence intervals. the findings demonstrated that the building remained stable throughout the monitoring period. the case study demonstrates how effectively geometric leveling with least square adjustment can be used to monitor the vertical displacement of structures. keywords-stability and safety of engineering structures; geometric leveling; vertical displacement monitoring; least squares adjustment; accuracy analysis i. introduction the aim of measuring a structure's movement is to decide whether the structure is safe and stable. deformation can be subjected to more analysis to determine whether it is caused by seasonal factors, daily variations, or other factors and then utilize the data to estimate how the structure will move in the future [1-5]. this movement must be identified for the purposes of safety studies and the prevention of future disasters. deformation monitoring has the advantages of improving the design process of structures for use in the future and increasing safety by lowering the possibility of structural damage [6]. it is a crucial risk management tool. presently, there are many techniques for deformation monitoring. modern techniques often use geometric leveling and total stations for threedimensional (3d) control [7]. the above-mentioned techniques can be used in conjunction with a terrestrial laser scanner (tls) system [8-12] or portable digital photogrammetric stations (dpss) [13-15]. in particular, tls has evolved into a crucial tool for working with historical structures, supplying a point cloud that quickly generates a three-dimension model of a monument [8]. however, the majority of surveyors do not have access to the specialized equipment required by these remote sensing technologies. it is costly to purchase or rent this equipment, and it could cost even more to train or hire employees who can manage and model point cloud data [9, 10]. a tls system's data acquisition capacity also makes model creation challenging [10, 11]. numerous software systems can help with this, but they consume time and computing resources and require an additional instrument that must be purchased or hired. as a result, these methods are severely constrained and can only be used for architectural heritage inspection [12, 16], where resources and budgets are significantly available. in addition, these methods have other issues, including the accuracy of the measurements they produce [17] despite the cost and complexity issues. potential dimensional errors in the model can be caused by issues with close-range imaging [18], as well as variations in temperature and humidity [19], the reflectivity of various materials and colors, and the effects of incidence angle [20]. comparing to direct measurements, significant errors in measuring vertical deformations can happen based on the above-mentioned conditions, sometimes exceeding one centimeter in magnitude [21, 22]. this emphasizes the engineering, technology & applied science research vol. 13, no. 1, 2023, 9913-9918 9914 www.etasr.com el-ashmawy: an efficient methodology for detecting the vertical movement of structures significance of evaluation techniques that allow calibrating laser scanners, particularly as high-precision surveys development in architectural heritage sites. typical tests like deformation monitoring should be checked using direct measurement methods [12]. to overcome some of the issues listed above, this paper aims to:  develop a cost-effective methodology based on a mathematical model for determining the accurate levels from measurements at individual monitoring points,  adjust redundant measurements and get their precision using the least squares solution,  develop software based on the derived mathematical model and the least squares solution for determining the adjusted levels and required statistical data of deformation points, and  use the developed methodology for detecting the vertical displacement of a building as a case study at a particular time interval. ii. the proposed methodology a. development of the mathematical model leveling is the method of measuring vertical distances, either directly or indirectly, to determine elevations. there are two approaches: geometric and trigonometric leveling [23]. geometric leveling is more accurate, the required surveying instruments are more cost-effective, and the work in the field and office is easier. in geometric leveling, the difference in levels between two points can be obtained by taking the readings of the staffs, or rulers, placed on the points. a leveling instrument is used to measure the readings. the elevations of all points can be determined by knowing at least one point's elevation and the level differences between points. to apply the method of least squares in leveling adjustments, an observation equation is first written for any elevation difference [23]. figure 1 illustrates the geometrical relationship for the elevation difference observed between two stations, a and b. the equation is written as: hab hab b av h h    (1) which can be rewritten as: hab b a habv h h     (2) the observation equation (2) gives the relation between the unknown elevations of any two stations, a and b, the differential levelling observation hab  and its residual. this equation is essential in applying least squares adjustments of level nets. equation (2) is linear and can be written directly in the form [24]: .v b    (3) where δ is the vector to the current values set for the unknowns (elevations of the deformation points) in the iterative solution, b is the matrix of the partial derivatives of (2) in relation to the unknowns, v is the vector of residuals, i.e. the correction vector to the observations (height difference), and ε is the vector of discrepancies. the solution of (3) using least squares method is [23,24]: δ = ν -1 .c (4) where: . . . . t t n b w b c b w       (5) the variance of unit weight is obtained by: 2ˆ . . / ( )tv w v n u   (6) where 2ˆ is the variance of unit weight, n is the number of observations, w is the weight matrix observations, u is the number of unknowns and equals to the number of deformation points, and (n-u) present the degrees of freedom. fig. 1. geometric depiction of the proposed model. b. developing the necessary software the software for determining the adjusted level and desired statistical data for each deformation point in every loop is being developed as part of the current research. the least squares method, as explained above, is used to determine the output of the developed software, which makes use of the data in the form of level differences and distances between network points in addition to the known levels of the benchmark(s). the variance of unit weight, adjusted levels of stations and their standard deviations (optional), residuals of observations, corrected observations, and their cofactor matrix (optional), and statistical data for gross error detection (optional) are all included in the software's ascii file output. the software provides flexibility in level network adjustment as follows:  any number and distribution of network points is acceptable.  the editing of input data specifications has remained flexible for practical reasons. if the input formats are consistent, they can be accepted.  the point-numbering is another important practical feature. point-numbering is not restricted in any way by the software. the point-numbering is easy and almost natural. engineering, technology & applied science research vol. 13, no. 1, 2023, 9913-9918 9915 www.etasr.com el-ashmawy: an efficient methodology for detecting the vertical movement of structures  weighting observations is possible. from a theoretical standpoint, it is desirable to weight the observations because it greatly aids in the detection of gross errors.  determination of the necessary initial levels for unknown points in order to initiate the iterative process.  an iterative least-squares solution that can show the results of each iteration or the final iteration. the software makes use of effective methods like data structuring [25, 26], random file access, and dynamic memory allocations [27] for the purpose of automatically processing and representing the data and the results. the software was created with window-driven user interfaces in mind to make it easier to use [28]. c. classification of leveling points three categories of points are proposed in the leveling line: i) monitoring points, ii) reference or benchmark points, and iii) auxiliary points. the monitoring points are selected to be placed on the building's exterior walls and required interior walls. to ensure that each building's wall is stable, the monitoring points are strategically placed. in order to determine only relative displacements, the reference points can be situated in the controlled area and undergo displacement. absolute displacements can be obtained if the reference points are attached to solid foundation or other stationary structures outside that area. even though leveling lines only require one reference point, experience suggests placing at least 3 of them in order to recognize unstable reference points. in order to ensure that they are unaffected by the building's movements, the reference points need to be positioned at a safe distance from it. auxiliary points are positioned, for example, to connect independent sections of a levelling line. d. fixing the points regarding fixing the points, they are typically secured by utilizing drill and epoxy to seal concrete nails on a wall or floor. all monitoring points must be well connected to the structure, particularly the concrete columns otherwise the displacements might be more accurately described as displacements of the points rather than structural displacements. e. leveling instruments it is necessary to use automatic levels, also known as optical levels, that have a built-in compensator that automatically makes the line of sight horizontal. accuracy can be improved by mounting a parallel plate micrometer over the telescope objective [29]. the parallel plate micrometer permits estimated readings up to 0.01mm and direct readings up to 0.1mm on a staff of 1cm least count. digital levels may also be used. digital levels are automatic levels that have a digital image processing system built in. these levels allow for electronic recording and automatic reading of coded bars staff. the speed of leveling and the elimination of the errors brought on by human reading and recording are the main benefits of digital levels [30]. f. field work it is necessary to know the reference station levels before monitoring points can be observed. otherwise, precise leveling can be used to obtain the local levels of reference stations [29]. loops are used for the leveling of the monitoring points. each loop begins at a reference station and ends at either the same or another reference station. at various epochs of a predetermined time interval, the levels of the monitoring points are obtained. after the reference and monitoring, points have been selected and the leveling line route has been established, the necessary auxiliary points and an approximate location of the instrument in each leveling line must be marked in order to guarantee the precision required by having equal sections of leveling and by following almost the same route of line levelling. starting and stopping leveling measurements at reference stations is the only way to control the quality of the measurements. the misclosure (δ) is the difference between the determined level and the known level, and it is calculated by : misclosure (δ) =referencelevelknown – reference levelcomputed (7) following the completion of the levelling work, the misclosure is computed. the fieldwork team is able to repeat the measurements at a lower cost and, most importantly, without altering the conditions of the structure by carrying out this data pre-processing in the field. the permissible misclosure can be calculated as [6]: misclosure tolerance = 0.9 √n (mm) (8) where n is the number of set-ups. all measurements ought to be repeated when the misclosure is more than the tolerance value. in case of permissible misclosure, the points' adjusted levels can be determined applying the least squares technique as explained above. g. vertical displacement determination the developed software is utilized for computing the adjusted levels of the monitoring points for each epoch. in order to compare the results of the subsequent epochs with those of the first epoch, the results of the first epoch are used as a reference. the vertical displacement of each monitoring point can be determined as follows: dz = zfirst epoch – zcurrent epoch (9) where dz is the vertical displacement of the monitoring point and z the adjusted level of the monitoring point. h. displacement analysis comparing the level differences between the observations of the first epoch and the current epoch is the traditional method for determining the stability of reference and monitoring points, as shown in (9). in recent deformation modeling techniques, statistics are applied to each epoch of measurements to get the significance of point movements. comparing the obtained displacements to their respective 95% confidence intervals is used to obtain the significance of point displacements [31]. in case the value of the vertical movement of a point k is classified as dzk and the maximum dimension of engineering, technology & applied science research vol. 13, no. 1, 2023, 9913-9918 9916 www.etasr.com el-ashmawy: an efficient methodology for detecting the vertical movement of structures the combined 95% confidence ellipse for point k is specified as ek, two cases will arise [32]:  in the first case if |dzk| < ek, then no movement has happened in point k and the observed difference is due to measurement errors.  if |dzk| > ek then point displacement has occurred. ek can be obtained as: 1 2 2 1.96 ( ) ( ) i i ke m m    (10) where 1( )im  is the standard error in level of point k in the current epoch and ( ) i m is the standard error in level of point k in the previous epoch. iii. case study a building in cairo, egypt, was selected as a case study for monitoring the vertical displacement. the building is 110.0m long, 60.0m wide, and 20m high. there are various offices in this 3-story structure. a. choosing points the field has been identified in the initial step in order to carry out the vertical displacement monitoring of the studied building. as shown in figure 2, 3 local reference stations and 5 auxiliary points were chosen. in order to ensure that the local reference stations were unaffected by the building's displacements, these points were fixed around it at a secure distance. fig. 2. location of the case study points. twenty monitoring points were fixed on the first floor of the case study building as part of the vertical movement monitoring project to determine the structure's stability. figure 2 depicts the positions of those monitoring points on the internal and external walls. the staff could easily hold on to the monitoring points on the building walls during levelling and observation because they were about 0.3m above the ground. special nails were driven into the marked monitoring points to make them permanent. b. measurements measurements were acquired with a leica na2 automatic level, a gple3 geodetic invar staff with 1cm graduations, and an attachment for a leica (10mm) gpm3 parallel plate micrometer. before the monitoring points can be observed, it is necessary to know the levels of the reference stations b1, b2, and b3 as explained above. the level of point b1 is assumed to be 15.0m. the levels of points b2 and b3 were obtained by looping a level net from b1 to 5 auxiliary points, b2 and b3, and then closing back on b1. after determining the reference station levels, loops utilizing precise leveling were utilized to get the levels of monitoring points at 8 distinct 1-month interval epochs. observations were made in the early morning. each leveling line's misclosure did not exceed 0.4mm across all 8 observation epochs, which is an acceptable tolerance for the purposes of this work. the relatively flat topography of the study area, the experience of the observer, and the instruments used all contributed to the leveling's high accuracy. c. data processing and results the developed software was used to process the data from the level networks. the necessary data and measurements such as the levels of the reference stations and their standard deviations, height differences, and distances between stations, were inserted into the software by editing the data file. the final results, for each epoch, were obtained from the adjustment of the level network. as previously mentioned, the variance of the unit weight, the adjusted levels of the monitoring points and their standard deviations, the residuals of the observations, and the corrected observations with their cofactor matrix comprised the received results. the high precision of the adjusted observations can be seen by the fact that the first to eighth leveling epochs had maximum variances of unit weight of 1.02m 2 and standard errors of 1.01mm. the high accuracy of the adjusted levels is demonstrated by the fact that their maximum standard error was 1.06mm across all epochs. all 8 epochs' computed standardized residuals for observations or levels were less than their rejection constants of the respective standardized residual which indicates that none of the observations were rejected due to gross errors or outliers. the adjusted values of levels of monitoring points for each observation epoch and the differences in levels between the first and the subsequent epochs were respectively computed with (9) and are tabulated in table i. equation (10) was used to calculate the 95% confidence level differences between the first and respective confidence intervals of the subsequent epochs. the vertical displacement values of monitoring points and the confidence intervals that correspond to them at a 95% level of confidence are shown in table ii. at a 95% confidence level, the magnitudes of the vertical movement of the monitoring points at each epoch were obtained and compared to their identical confidence intervals to decide whether the obtained displacements were actual (significant) displacements of the structure or caused by measurement errors. according to tables i and ii, all the evaluated movement values were less than their related confidence intervals, indicating that there was no vertical movement of the building within the monitoring period. engineering, technology & applied science research vol. 13, no. 1, 2023, 9913-9918 9917 www.etasr.com el-ashmawy: an efficient methodology for detecting the vertical movement of structures table i. the adjusted levels and vertical displacement of the monitoring points point epoch (1) epoch (2) epoch (3) epoch (4) epoch (5) epoch (6) epoch (7) epoch (8) level m dz mm level m dz mm level m dz mm level m dz mm level m dz mm level m dz mm level m dz mm level m dz mm p1 15.3092 0 15.3093 -0.10 15.3095 -0.30 15.3094 -0.20 15.3093 -0.10 15.3097 -0.50 15.3097 -0.50 15.3095 -0.30 p2 15.4085 0 15.4086 -0.10 15.4082 0.30 15.4082 0.30 15.4086 -0.10 15.4083 0.20 15.4084 0.10 15.4086 -0.10 p3 15.3120 0 15.3116 0.40 15.3113 0.70 15.3114 0.60 15.3114 0.60 15.3112 0.80 15.3113 0.70 15.3114 0.60 p4 15.2960 0 15.2956 0.40 15.2957 0.30 15.2953 0.70 15.2954 0.60 15.2956 0.40 15.2954 0.60 15.2955 0.50 p5 15.8168 0 15.8166 0.20 15.8163 0.50 15.8162 0.60 15.8165 0.30 15.8163 0.50 15.8166 0.20 15.8167 0.10 p6 15.8097 0 15.8093 0.40 15.8092 0.50 15.8095 0.20 15.8096 0.10 15.8095 0.20 15.8098 -0.10 15.8096 0.10 p7 15.0963 0 15.0966 -0.30 15.0966 -0.30 15.0965 -0.20 15.0962 0.10 15.0963 0.00 15.0966 -0.30 15.0965 -0.20 p8 15.1254 0 15.1255 -0.10 15.1256 -0.20 15.1252 0.20 15.1254 0.00 15.1251 0.30 15.1253 0.10 15.1256 -0.20 p9 15.8458 0 15.8453 0.50 15.8451 0.70 15.8455 0.30 15.8457 0.10 15.8450 0.80 15.8455 0.30 15.8458 0.00 p10 15.6507 0 15.6507 0.00 15.6501 0.60 15.6505 0.20 15.6503 0.40 15.6500 0.70 15.6505 0.20 15.6502 0.50 p11 14.2996 0 14.2998 -0.20 14.2997 -0.10 14.2992 0.40 14.2995 0.10 14.2990 0.60 14.2993 0.30 14.2996 0.00 p12 14.2160 0 14.2154 0.60 14.2158 0.20 14.2157 0.30 14.2155 0.50 14.2158 0.20 14.2154 0.60 14.2158 0.20 p13 15.5106 0 15.5108 -0.20 15.5105 0.10 15.5107 -0.10 15.5103 0.30 15.5101 0.50 15.5105 0.10 15.51 0.60 p14 15.6034 0 15.6034 0.00 15.6032 0.20 15.6031 0.30 15.6036 -0.20 15.6033 0.10 15.6037 -0.30 15.6035 -0.10 p15 15.8085 0 15.8083 0.20 15.8087 -0.20 15.8086 -0.10 15.8083 0.20 15.8083 0.20 15.8085 0.00 15.8086 -0.10 p16 15.6054 0 15.6057 -0.30 15.6055 -0.10 15.6053 0.10 15.6051 0.30 15.6052 0.20 15.6055 -0.10 15.6056 -0.20 p17 15.4709 0 15.4705 0.40 15.4708 0.10 15.4703 0.60 15.4701 0.80 15.4703 0.60 15.4704 0.50 15.4705 0.40 p18 15.6615 0 15.6615 0.00 15.6616 -0.10 15.6613 0.20 15.6614 0.10 15.6612 0.30 15.6611 0.40 15.6612 0.30 p19 15.7997 0 15.7990 0.70 15.7992 0.50 15.7991 0.60 15.7995 0.20 15.7997 0.00 15.7990 0.70 15.7992 0.50 p20 15.6783 0 15.6782 0.10 15.6787 -0.40 15.6787 -0.40 15.6784 -0.10 15.6783 0.00 15.6781 0.20 15.6783 0.00 table ii. detecting the vertical displacement of the monitoring points point epoch (2) epoch (3) epoch (4) epoch (5) epoch (6) epoch (7) epoch (8) point displacement |dz| mm e mm |dz| mm e mm |dz| mm e mm |dz| mm e mm |dz| mm e mm |dz| mm e mm |dz| mm e mm p1 0.10 1.67 0.30 1.97 0.20 2.01 0.10 2.41 0.50 1.39 0.50 1.89 0.30 1.81 none p2 0.10 1.97 0.30 2.27 0.30 1.91 0.10 1.91 0.20 2.09 0.10 1.79 0.10 1.41 none p3 0.40 2.07 0.70 2.17 0.60 1.81 0.60 2.31 0.80 1.99 0.70 1.79 0.60 1.51 none p4 0.40 1.77 0.30 1.97 0.70 2.31 0.60 2.21 0.40 1.59 0.60 2.09 0.50 1.51 none p5 0.20 1.37 0.50 2.17 0.60 2.01 0.30 2.01 0.50 1.99 0.20 1.59 0.10 1.51 none p6 0.40 1.17 0.50 1.97 0.20 1.61 0.10 2.21 0.20 1.89 0.10 1.59 0.10 1.81 none p7 0.30 1.57 0.30 1.87 0.20 2.01 0.10 2.61 0.00 1.69 0.30 1.59 0.20 1.71 none p8 0.10 2.17 0.20 1.77 0.20 2.31 0.00 2.11 0.30 2.09 0.10 1.69 0.20 1.31 none p9 0.50 1.97 0.70 2.07 0.30 1.51 0.10 2.11 0.80 2.49 0.30 2.09 0.00 1.31 none p10 0.00 1.77 0.60 2.47 0.20 1.51 0.40 2.51 0.70 2.09 0.20 2.19 0.50 1.91 none p11 0.20 2.07 0.10 1.97 0.40 2.41 0.10 2.01 0.60 2.29 0.30 1.59 0.00 1.31 none p12 0.60 1.67 0.20 1.47 0.30 2.01 0.50 2.51 0.20 1.49 0.60 2.29 0.20 1.81 none p13 0.20 1.97 0.10 2.17 0.10 1.71 0.30 2.71 0.50 1.99 0.10 1.49 0.60 2.11 none p14 0.00 2.17 0.20 2.07 0.30 2.01 0.20 1.81 0.10 2.09 0.30 1.49 0.10 1.81 none p15 0.20 1.67 0.20 1.47 0.10 2.01 0.20 2.61 0.20 1.79 0.00 1.69 0.10 1.51 none p16 0.30 1.77 0.10 2.07 0.10 2.11 0.30 2.51 0.20 1.69 0.10 1.59 0.20 1.51 none p17 0.40 1.87 0.10 1.57 0.60 2.41 0.80 2.51 0.60 1.59 0.50 2.29 0.40 2.11 none p18 0.00 1.87 0.10 1.77 0.20 2.21 0.10 2.21 0.30 1.99 0.40 1.99 0.30 1.51 none p19 0.70 1.67 0.50 1.67 0.60 2.01 0.20 1.91 0.00 1.59 0.70 2.59 0.50 1.41 none p20 0.10 1.57 0.40 1.37 0.40 1.91 0.10 2.61 0.00 1.89 0.20 2.09 0.00 1.41 none iv. summary, conclusions, and recommendations the aim of measuring a structure's movement is to decide whether there is actually a movement and whether the structure is safe and stable. deformation monitoring has the advantages of improving the design process of structures for use in the future and increasing safety by lowering the possibility of structural damage. it is a crucial risk management tool. this paper explains the development of a methodology for monitoring and analyzing structures' vertical displacement. the developed methodology aims to add a new dimension to the well-known ones for geometric leveling and leveling routing. the proposed methodology is accurate and effective in determining the vertical displacement of structures. the case study demonstrates that geometric leveling is always effective for determining the vertical displacement of structures. for vertical displacement monitoring with a precision of less than 0.4mm, this approach is suggested. geometric leveling is an accurate, precise, and cost-effective method of vertical displacement monitoring but it is not considered to be cuttingedge. geometric leveling is recommended to be used extensively to monitor structures' deformation for the abovementioned reasons. the proposed method is subjected to limitations in its application areas. the proposed method can only be utilized to monitor displacements in the vertical plane, it cannot be engineering, technology & applied science research vol. 13, no. 1, 2023, 9913-9918 9918 www.etasr.com el-ashmawy: an efficient methodology for detecting the vertical movement of structures utilized to monitor displacements in the horizontal plane. the developed software and methodology are very adaptable, affordable, and of great 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[32] e. s. okiemute, m. n. ono, and o. o. fatai, "monitoring and analysis of vertical deformation of palm house benin city using digital level," international journal of advances in scientific research and engineering, vol. 9, no. 4, pp. 6–16, sep. 2022, https://doi.org/ 10.31695/ijasre.2018.32860. microsoft word etasr_v13_n2_pp10279-10284 engineering, technology & applied science research vol. 13, no. 2, 2023, 10279-10284 10279 www.etasr.com griche et al.: an economic and environmental study of a hybrid system (wind and diesel) in the … an economic and environmental study of a hybrid system (wind and diesel) in the algerian desert region using homer software issam griche department of electrical engineering, faculty of engineering, bouira university, algeria | mechatronics laboratory (lmetr), ferhat abbas university setif 1, algeria issam.grich@univ-bouira.dz (corresponding author) mohamed rezki department of electrical engineering, faculty of engineering, bouira university, algeria med_rezki@yahoo.fr kamel saoudi department of electrical engineering, faculty of engineering, bouira university, algeria saoudi_k@yahoo.fr ghania boudechiche eta laboratory, department of electronics, university of bordj bou arreridj, algeria ghania.boudechiche@yahoo.com fares zitouni transmission network management, sonelgaz, algeria zitouni.f@yahoo.fr received: 3 january 2023 | revised: 24 january 2023 | accepted: 25 january 2023 abstract this paper presents a new of economic and environmental study of a hybrid system (wind turbine and diesel generator) in algerian desert regions using homer software. the principal interests of the hybrid system are clean production at the place of consumption, the combined use of resources, energy storage, and supply security. using an experimental device outfitted with homer software, models were developed and successfully compared to reality. the obtained results confirm that the proposed system proved to be accurate enough to distinguish energy transfers and fast enough to enable optimizing the sizing and handling of the system's energy transfers. the purpose of this paper is to confirm the robustness of the homer software and to check the technical, economic, and environmental criteria of the integrated system. keywords-homer (hybrid optimization of multiple energy resources); wind turbine (wt); diesel generator (dg); hybrid system (wind-diesel); economic environemental analysis; cost of energy (coe) i. introduction algeria wants to play a role in the energy transition in africa and its energy sector development is at a critical stage. the country is noteworthy for its relative size, wealth, location, gas reserves, renewable energy potential, and greenhouse gas emissions [1-4]. knowing the disposition of the hybrid systems integrated with renewable energy their contribution on the economic and environmental sides is to compensate the diesel generators in the isolated areas. in recognition of these environmental and economic advantages, several studies have engineering, technology & applied science research vol. 13, no. 2, 2023, 10279-10284 10280 www.etasr.com griche et al.: an economic and environmental study of a hybrid system (wind and diesel) in the … been carried out in this field. among the most important of these programs is homer [5]. in [6], the analysis of a wind turbine (wt) and diesel generator (dg) hybrid system was conducted on the economic and environmental sides with homer by analyzing the cost of energy (coe) and the quantity of co2 associated with this system when it works with the dg only and when it works in its general form. the comparison of coe produced for various cases of operation was used to prove the role of the storage systems. an open topic is the efficiency of the hybrid system to supply an independent electricity network in isolated areas and to provide all the conditions and requirements of the main electricity networks (quality protection) to compensate for the use of standalone dgs. in these regions, the cost of delivering large production units, the cost of fuel, the difficulty to obtain it, and environmental risks are major setbacks [7-12]. from an economic and environmental standpoint, authors in [13] investigated the costs of electric energy when the system was only powered by dgs and the quantity of co2 associated in both cases with homer for the electrical installation with a continuous and variable load throughout the year as wind speed changed [13]. quite recently, considerable attention has been paid to the optimization of hybrid renewable energy systems for off-grid rural electrification [14]. to solve this issue, many researchers have proposed similar methods of optimization in different countries, such as chad [15] and côte d’ivoire [16]. the techno-economic assessment of a 100kw solar rooftop pv system for five hospitals in central and southern thailand was studied in [17]. it is critical to provide an energy supply that can deliver uninterrupted electric power to meet the load demand as a hybrid system (wt and dg), as has been studied using wt models in different comparative models of wind characteristics between south-western and south-eastern thailand [18]. based on the approach presented in the literature, the purpose of this paper is to establish rules and tools for optimizing energy management and the sizing of a wt and dg, coupled to the network, and equipped with an electrochemical storage device. the optimizations will be carried out based on consumption and production deposit data. the optimization criterion will be economic with a view to minimizing the total coe of the system, from its installation to its use over a long period. ii. a review of power in algerian desert the algerian desert contains several regions in the south that rely in unconnected to the national transport network dgs for the provision of electric power [1]. algerian isolated desert areas contain climate-convenient locations of renewable energy sources, particularly solar energy, and, to a lesser extent, wind energy (table i). figure 1 presents the seasonal variations in the amount of solar energy in the algerian sahara. hybrid systems integrate renewable energy sources. they are being exploited in the algerian sahara, where hybrid compact energies and renewable desert areas are isolated. figure 3 depicts some of the processes involved in the development of hybrid systems that combine renewable energies, i.e. solar and dg, wind and dg, and storage systems. table i. changes in wind speed in some algerian desert areas wind speed (m/s) region 7 adrar 6 tindouf 5 tamanrast 4 djelfa 3 ghardaia (a) (b) fig. 1. yearly produced power from the system: (a) pv and gd, (b) wt and dg. fig. 2. produced power from various system resources to feed the network in desert areas in algeria. the system uses wind energy for the most part of the year due to its better performance compared to the other renewable energy sources (figure 3). other hybrid systems involved in feeding the network in these areas include the solar (pv) and dg systems in tamanrasset, tindouf, and djelfa. several isolated areas in algeria are located in the desert. the majority of these areas rely on dgs to provide electrical power rather than utilizing hybrid systems that integrate renewable energies. despite their high climatic efficiency, these regions use solar and private pneumatic energy to a lesser extent. so, algeria's use of hybrid compact renewable energy systems is limited. through this study, the effectiveness of hybrid systems for integrating renewable energy with environmental and economic advantages will be demonstrated in order to encourage its integration in the grid, especially in the isolated desert regions of the country. hybrid system utilization and optimization are required in order to compensate the use of engineering, technology & applied science research vol. 13, no. 2, 2023, 10279-10284 10281 www.etasr.com griche et al.: an economic and environmental study of a hybrid system (wind and diesel) in the … dgs in the supply of electric power while maintaining the economic, environmental, and performance quality of these technologies [1]. (a) (b) (c) (d) fig. 3. seasonal variations of the amount of renewable energy in the algerian sahara: (a) wind speed in tindouf, (b) wind speed in adrar, (c) temperature changes in adrar, (d) solar energy in adrar. iii. economic and environmental analysis of the wind turbine and diesel generator hybrid system a. homer software overview homer (hybrid optimization of multiple energy resources) is optimization and simulation software for the study of the production of multi-source energy (pv, wind, network, storage, diesel, etc.). it is mainly intended for mininetwork simulation, whether connected or unconnected (offgrid). the main features of this tool are:  supports hourly load profiles as well as controllable loads.  it is able to simulate the behavior of many pieces of production equipment (pv, wind, hydro, biomass generator, diesel, vegetable oil) or storage equipment (electrochemical, flywheel, fuel cells).  economic optimization of production systems by comparison of different configurations and architectures.  sensitivity analysis with respect to certain input parameters (oil prices, lifetime of the modules, solar radiation, load).  the user receives the architecture and economic configuration based on homer's modeling. it is an aid to decision-making for the design of a mini-network. b. basic standards of economic analysis in homer all studies conducted to determine the economic dimensions of a specific installation focus on achieving the lowest possible cost while meeting the requirements (load). a very important factor is the coe which summarizes the standards of economic analysis on homer and is subject to the amount of energy produced and the amount of energy consumed at the time. homer determines the coe as the average cost of electrical energy produced for 1kwh and sets its value to a cost per kilowatt-hour per dollar ($/kwh). c. description of the electrical installation studied on homer figure 4 shows an electrical installation studied on homer including a type aoc 15/50 wt with a power of 65kw and 2 dgs with power of 150kw and 75kw, respectively. the ac power and the variable load equipment operate variably throughout the year at a rate of 4.9mwh/day, with the storage battery type s4ks25p having an estimated capacity of 1900ah. fig. 4. the electrical installation to be studied on homer. d. load variations the variation of the load of the installation using homer is shown in figure 5. the dmap is a diagram that shows the time distribution for the variables of each hour during the day of the year using tinted rectangles depending on the value of this variable at that time, as shown in figure 6. the dmap is a diagram that depicts the breakdown for the variable at each hour of the year. the wind speed changes for the installation study, in which the property of the power produced by the aoc 15/50 wt is used in terms of wind speed, are shown in figure 7. iv. simulation results a. produced power by the system throughout the year figure 8 depicts the contribution of the wt to the electrical energy produced by the system, as it effectively compensates for the gds most of the year, thus reducing the quantity of fuel used, which leads to a reduction in the cost of electrical energy and gas emissions, as shown in tables ii-iv. engineering, technology & applied science research vol. 13, no. 2, 2023, 10279-10284 10282 www.etasr.com griche et al.: an economic and environmental study of a hybrid system (wind and diesel) in the … fig. 5. daily load changes. (a) (b) (c) load variations: (a) annual variations, (a) load changes during october and november, (a) dmap to load variations. b. economic analysis table ii shows the cost of the power produced and the quantity of fuel used for the hybrid system in various operating scenarios as calculated by the homer program. according to table ii, the significant difference occurs when the system is integrated with the wt (wt and two dgs) and is such that the cost of electrical energy in this case is up to 0.217$/kwh with 131.527l fuel used and a total of 356,700.6kg/year gas emissions compared to their operation by dgs only. the cost of gas emissions increased in this case to 0.273$/kwh at 282.154l of fuel used per year, totaling 763.035kg. table ii. economic analysis coefficients case study coe ($/kwh) diesel (l) two dgs, wt, battery, inverter 0.201 134.635 two dgs and wt 0.217 131.527 two dgs, wt, and inverter 0.269 274.608 two dgs 0.273 282.154 october november 50 100 150 200 p o w e r (k w ) scaled data engineering, technology & applied science research vol. 13, no. 2, 2023, 10279-10284 10283 www.etasr.com griche et al.: an economic and environmental study of a hybrid system (wind and diesel) in the … c. environmental analysis table iii shows the amount of gases produced by the system over a year for various operating scenarios. the summary of the total gas emissions is given in table iv, showing the importance of the storage system in all operation cases. when the system runs by the dg and the storage system, the cost of electric energy is up to 0.269$/kwh with 274.608l fuel used and 742857kg/year gaseous emissions. (a) (b) (c) (d) (e) fig. 6. characteristics of the wind turbine: (a) property of the power for the wind turbine used, (b) wind speed according to the height of the turbine used, (c) changes in wind speed during the year, (d) average wind speed during the year, (e) dmap for wind speed changes. fig. 7. power produced by the system during the year. environmental rating analysis. table iii. economic analysis gas generated (kg / year) case study co2 co unburned hydrocarbons particulate matter so2 nitrogen oxides two dgs, wt, battery, inverter 356.011 879 97.3 66.2 715 7.841 two dgs and wt 347.336 857 95 64.6 698 7.650 two dgs, wt, and inverter 723.354 1.785 198 135 1.453 15.932 two dgs 743.003 1.834 203 138 1.492 16.365 0 5 10 15 20 25 0 10 20 30 40 50 60 70 p o w e r (k w ) pow er curve wind speed (m/s) jan feb mar apr may jun jul aug sep oct nov dec 0 5 10 15 20 w in d s p e e d ( m /s ) scaled data jan feb mar apr may jun jul aug sep oct nov dec 0 3 6 9 12 w in d s p e e d ( m /s ) wind resour ce jan feb mar apr may jun jul aug sep oct nov dec 0 6 12 18 24 h o u r o f d a y scaled data day of ye ar 0.0 3.6 7.2 10.8 14.4 18.0 m/s jan feb mar apr may jun jul aug sep oct nov dec 0 40 80 120 160 p o w e r (k w ) monthly ave rage ele ctric production wind 75kw diesel 150kw diesel engineering, technology & applied science research vol. 13, no. 2, 2023, 10279-10284 10284 www.etasr.com griche et al.: an economic and environmental study of a hybrid system (wind and diesel) in the … table iv. total gas emissions case study of the system total gaz emissions (kg/year) two dgs, wt, battery, inverter 365599.5 two dgs and wt 356700.6 two dgs, wt, and inverter 742857 two dgs 763035 v. conclusion this paper analyzes the economic and environmental impacts of hybrid distributed generation (wind turbines and diesel generators) in the algerian desert region. the dynamic models for the main system components were developed in homer software (hybrid optimization of multiple energy resources). the overall energy management strategy for coordinating the power flows among the different energy sources is presented in terms of cost of energy (coe). the simulation results show that the studied hybrid power system with renewable sources has lower operating costs. the economic and environmental reasons and the technical challenges of connecting the hybrid system units in the algerian desert region are analyzed based on cost factors. the obtained results demonstrate the significant economic and environmental benefits of the hybrid system, ensuring the continuity of electrical energy production throughout the year with the flow of load changes and wind energy at the same time, and the importance of the battery storage system. from these results, this work can be completed using dynamic models for the system components, namely the pv energy conversion system, fuel cell, electrolyzer, power electronic interfacing circuits, battery, hydrogen storage tank, gas compressor, and gas pressure regulator, to exploit the best optimal hybrid system in the algerian desert region. references [1] "algeria powers ahead with huge renewable energy plans," international energy forum. https://www.ief.org/news/algeria-powersahead-with-huge-renewable-energy-plans. 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[16] j. y. koffi, k. m. sako, b. k. koua, p. m. e. koffi, y. nguessan, and a. k. diango, "study and optimization of a hybrid power generation system to power kalakala, a remote locality in northern côte d’ivoire," international journal of renewable energy development, vol. 11, no. 1, pp. 183–192, feb. 2022, https://doi.org/10.14710/ ijred.2022.38492. [17] r. khamharnphol et al., "techno-economic assessment of a 100 kwp solar rooftop pv system for five hospitals in central southern thailand," international journal of renewable energy development, vol. 12, no. 1, pp. 77–86, jan. 2023, https://doi.org/10.14710/ ijred.2023.46864. [18] i. kamdar and j. taweekun, "a comparative study of wind characteristics between south-western and south-eastern thailand using different wind turbine models," journal of advanced research in fluid mechanics and thermal sciences, vol. 92, no. 1, pp. 149–161, feb. 2022, https://doi.org/10.37934/arfmts.92.1.149161. microsoft word etasr_v12_n4_pp8936-8941 engineering, technology & applied science research vol. 12, no. 4, 2022, 8936-8941 8936 www.etasr.com manjunatha et al.: an enhanced z-source switched mli capacitor for integrated micro-grid with … an enhanced z-source switched mli capacitor for integrated micro-grid with advanced switching pattern scheme budagavi matam manjunatha department of eee rajeev gandhi memorial college of engineering and technology nandyal, india manjunath.bmeee@gmail.com s. nagaraja rao department of eee m. s. ramaiah university of applied sciences bengaluru, india raoeee123@gmail.com a. suresh kumar department of eee rajeev gandhi memorial college of engineering and technology nandyal, india surianisetty@gmail.com v. lakshmi devi department of eee sri venkateswara college of engineering tirupati, india vldevi.eee@gmail.com p. rama mohan department of eee rajeev gandhi memorial college of engineering and technology nandyal, india rammohan.kadapa@gmail.com k. brahmanandam department of eee rajeev gandhi memorial college of engineering and technology nandyal, india brahma181@gmail.com received: 12 march 2022 | revised: 11 april 2022, 30 april 2022, and 7 june 2022 | accepted: 8 june 2022 abstract-in this paper, the enhanced z-source switched capacitor multi-level inverter (ezsc-mli) is presented, which can generate a greater number of levels and magnitude in output. the proposed mli has greater recognition due to its low harmonic profile, fewer switching components, compact size, low switch stress, isolated dc supply, high efficiency, and low cost. a high voltage boost factor is achieved by using the z-source. the switched capacitor module is used for charging all the capacitors to equal voltage magnitude based on a self-balanced scheme. the proposed topology for grid integration requires dual control loops, a primary voltage control loop, and a secondary current control loop. the performance of the proposed 7-level topology for grid integrated systems is verified with multi-carrier advanced modulation schemes and by simulations carried out in matlab/simulink. keywords-distributed energy resources; multi-carrier modulation techniques; multi-level inverter; impedance source; renewable energy sources; switched capacitor i. introduction nowadays, sustainable and renewable energy sources (ress) like wind energy and photovoltaic (pv) stacks have been highly recognized as precious substitutions of fossil fuels due to their commercial merits and reliable operation. ress integrated with power-conditioning systems play a vital role in satisfying the energy demands of a micro-grid system [1]. to improve the energy generation statistics, distributed energy resources (ders) are introduced. they have less size and easily interfacing methodology. ders improve the overall system performance by reducing total loss, transformers, and additional devices. among the ders, pv stacks are the most promising technology [2]. generally, a high-voltage gain dcdc boost converter is required to transform the low-voltage output of the pv to high voltage, which is integrated to the micro-grid by a dc-ac inverter [3]. the maximum duty ratio is restricted due to parasitic resistances and this decreases the overall system stability, causes grounding issues and high dv/dt on switches/diodes. the above mentioned problems of the two-stage module are discarded by employing an x-shaped impedance circuit, which consists of two inductors and capacitors [4]. with the modish power semi-conductor device, several well-known inverter modules have been amalgamated into grid systems. mlis are categorized as diode clamped (dc-mli) [5], flying capacitor (fc-mli) [6], and cascaded h-bridge (chb-mli) [7]. the main reasons for producing a number of levels in voltage are: to increase the rms quality, to decrease the dv/dt stress, and to eliminate large size filters. in mlis, isolated multiple dc or virtual dc-links are obtained by using transformers or capacitors with the contribution of various switching components. producing high voltage levels with a low number of isolated dc power supplies and fewer switching devices is the main challenge [8-10]. the suitable approach to limit the dc power supplies is to utilize the capacitors. yet, additional charge balance strategy is used to intercept the discharging issues [11-13]. generally, mli topologies are governed by both fundamental and high switching frequency modulation schemes [14]. the topology with symmetrical and asymmetrical voltage sources is illustrated in [15]. three phase corresponding author: budagavi matam manjunatha engineering, technology & applied science research vol. 12, no. 4, 2022, 8936-8941 8937 www.etasr.com manjunatha et al.: an enhanced z-source switched mli capacitor for integrated micro-grid with … modular topologies are presented in [16-18] with reduced complexity and losses and improved performance. balanced grid voltage was achieved using the lvrt (low voltage ride through) control approach in [19]. during a fault state, reactive power is given to ensure protection. the shunt var compensator (svc) controller was used, it was automatically engaged when a grid fault occurs. this paper proposes the novel, simple, and efficient ezscmli topology, which is validated by using advanced multicarrier pulse-width modulation schemes. dual control loop is used for controlling the voltage and current in the micro-grid system. ii. the proposed concept the configuration of the proposed pv-based ezsc-mli with grid integrated scheme is depicted in figure 1. from left to right, the scheme consists of a pv cell, impedance network, switched capacitor (sc) module, and a 7-level mli with dual loop control scheme. the pv supplies energy and feeds the impedance circuit, which transforms the low dc voltage to high dc-link voltage, maintained constant based on the active and shoot through states. the common dc-link voltage is powered by the respective capacitors in the sc module and the entire system is integrated to the micro-grid system through the 7-level inverter. the simplified mli topology is controlled using advanced modulation schemes. the working and implementation of each unit are described below. fig. 1. configuration of the proposed inverter. a. pv source a pv cell relies on the photo-electric effect to generate electrical energy. a pv cell is similar to a natural diode. when the energy of sunlight is more than the semi-conductor energy gap, current travels via the external circuit system. based on power level requirements, the pv cell is integrated in parallel and/or in series to attain high current and/or voltage. ��� = ��� − (�� exp (���������) ��� � − 1) − ��� ������ ��� � (1) where ipv is the current flowing in pv cell (a), isc is the reverse saturated diode's current (a), k is boltzmann’s constant, n is diode's ideality factor, q is the charge of the electron, t is junction's temperature, rsh and rs are the shunt and series resistances of the pv cell (ω), vpv is the pv voltage at the output terminal (v). b. z-source and self balancing module generally, vsi accomplishes the buck conversion, which restricts its usage in several areas, such as der. to amplify the pv input voltage, a two-stage boost conversion methodology is used, which requires additional switching devices, stage and control scheme. using an impedance network in x-shape will reduce the complexity. high voltage gain is achieved at output terminals by furnishing shoot through state. this state is possible when the lower and upper switches in the same leg are conducted simultaneously and it is not possible while using a multi-level inverter. the z network with single switch is proposed, since it reduces the complexity of control. the voltage across the traditional zsi is: ����, !"# = 2 × �& − ��� (2) boost factor (bf) and the peak ac voltage (�') are given by: (), !"# = * *+ -×.��. (3) �', !"# = (), !"# × ��� (4) where vl and vpv are the voltage across the z source inductor and the input. various methods are used to overcome the unbalanced voltage problems such as, feedback methods [20] or the regulated switching pattern scheme [21]. the sc balanced technique is very popular because it does not require a feedback method or continuous monitoring. the proposed switched capacitor module consists of two input capacitors cs1, cs2, three output capacitors c1, c2, c3, and six switches sc1 to sc6. the modes of operation are depicted in figure 2. in mode-i (figure 2(a)), all odd numbered switches will conduct. the capacitors cs1, cs2 charge the c1 and c2 capacitors, thus the voltage across the c1 (vcs1) is vc1 and the voltage of capacitor c2 is vcs2. in mode-ii (figure 2(b)), all even numbered switches will conduct. the capacitors cs1, cs2 charge the c2 and c3 capacitors, thus vcs1=vc2 and vcs2=vc3. the voltages across cs1, cs2, c1, c2, and c3 are: ���* = ���/ = 0 �12 / 3 (5) ��* = ��/ = ��4 = 0 �56 / 3 (6) where �#� is the output voltage of the z network. the maximum available output voltage across the inverter �',78� is: �',78� = ��* + ��/ + ��4 (7) �',78� = 0 �:; / 3 + 0 �:; / 3 + 0 �:; / 3 (8) �',78� = 0 4 /3 . �#� (9) from (8) and (9), it is clear that voltage is balanced and boosted by 1.5 times. the capacitors cs1, cs2 are powered by the zsi module. the output of the z network is given by the sc module. by considering the boost factor of 1.5, (4) and (5) can be rewritten to get the boost factor and the peak output of the enhanced z network with the self-voltage balancing network. (),=8> = *.? *+ -×.��. (10) engineering, technology & applied science research vol. 12, no. 4, 2022, 8936-8941 8938 www.etasr.com manjunatha et al.: an enhanced z-source switched mli capacitor for integrated micro-grid with … �',=8> = (),=8> × (�78 ) (11) where @�> /@ represents the duty ratio of shoot through state, the peak output voltage of ezsc-mli is 1.5 times greater than tzsi with and/or without shoot through state. the graphical representation of boost factor vs tsh/t and peak voltage vs tsh/t for tzsi and ezsi topologies are depicted in figures 3 and 4. if the shoot through ratio lies in between 0 to 0.4, the design procedure for passive devices is the same for the two zsi modules. for any given tsh/t, the peak output voltage and the boost factor of ezsc-mli are constantly 1.5 times higher than tzsi's, hence this network is named as an enhanced network [14]. if tsh/t is 0.4, the boost factor of tzsi is 5 and ezsc-mli is 7.5 and the corresponding peak output voltages are 500v and 750v (for input voltage of 100v). the proposed 7-level ezsc-mli is integrated to a micro-grid. fig. 2. operating modes of the sc circuit: (a) odd number switching, (b) even number switching. fig. 3. boost factor vs tcd/t. fig. 4. peak voltage vs @�> /@. c. controllloops in the proposed concept, dual control loops are utilized, i.e. the primary voltage control loop and the secondary current control loop. the aim of the primary loop is to regulate the output voltage of the z-source network, by changing the shoot through duty ratio as specified in (10). this maintains the mli voltage constant and greater than the grid voltage. a reference voltage signal is obtained by comparing the pv voltage and the grid voltage. the outcome is compared with the triangular carrier signal to produce the shoot through state duty ratio. the aim of the current loop is the injection of the reference current to the grid within the harmonic standards of ieee-519. grid synchronization requires the inverter output voltage, frequency and phase should match with the grid. this is furnished by single-phase phase-locked loop (pll) circuitry. the pll circuit generates the required phase sequence and fundamental frequency as a current shape (isin) which is multiplied with the reference magnitude of current (iref) established as final reference current (iref*). iref* is compared with the actual grid current (iact) and the outcome is imparted to the hysteresis current controller (hcc) for the generation of the switching states to the h-bridge module [22] in the 7-level mli. the on/off states of the respective switches in the hbridge module are highly demanded based on the reference grid current. iii. modulation scheme the working principles of the 7-level mli are level generation and polarity generation. the level generation module has three switches s1, s2, and s3, which convert the constant dc-link voltage to dc levels. the switching sequence for dc-level generation of the 7-level mli is depicted in table. i. on the other side, polarity generation has four switches, sa, sb, sc, and sd, which convert the dc-level voltage to ac voltage and are controlled by the secondary current control loop. the switching sequence for polarity generation is depicted in table ii, where n represents the onstate of the switch and f represents the off-state of the switch. table i. switching states of dc-level generation vo s1 s2 s3 vdc n f f 2vdc/3 f n f vdc/3 f f n table ii. switching states of polarity generation vo sa sb sc sd 0 f/n n/f f/n n/f positive n n f f negative f f n n the switches in the level generation scheme are controlled by advanced modulation schemes, such as the level-shifted multi-carrier modulation (lspwm) scheme, the phase-angled (papwm) scheme, and the variable switching frequency (vsfpwm) scheme. a. the multi-carrier level-shifted pwm (lspwm) scheme in the well-known control action of lspwm, all respective carriers are shifted by time. for n voltage levels, n-1 carriers are pre-requisite adjoining each other for the production of the switching pattern. the peak amplitude of triangular carrier wave-shape is differed and it is equivalent to the reference engineering, technology & applied science research vol. 12, no. 4, 2022, 8936-8941 8939 www.etasr.com manjunatha et al.: an enhanced z-source switched mli capacitor for integrated micro-grid with … sinusoidal voltage as a summation of all carrier-waves. high switching frequency is used. generally it depends on multiplication factor and fundamental frequency. the frequency value of the carrier is measured by: e� = f) × e) (12) where e� denotes carrier frequency (hz), f) denotes the multiplication factor, with an odd value more than 11, and e) denotes the fundamental frequency value (hz). the modulation index of the pulse-width modulation scheme is: f�" = �g �; (hij) (13) where �! �� denote the peak amplitudes of reference and carrier triangular wave-shapes. the production of switching states is done by relating the reference and carrier wave-shapes. when the reference wave is greater than the carrier wave, a particular switch is in the on state and/or when it is less than the carrier wave, a particular switch is in the off state. the lspwm schemes are: phase disposed (pd), phase opposed disposed (pod), alternate phase opposed disposed (apod). the pd based carrier waveform is depicted in figure 5. fig. 5. pd modulation scheme. b. multi-carrier phase-angle shifted pwm (papwm) the papwm scheme shown in figure 6 is the same with level-shifted modulation. all the carriers have equal switching frequencies and different peak amplitudes, which are vertically disposed by a certain phase-angle to vanquish the phase imbalance issues and unbalanced voltages [22]. the disposed phase-angle (∅ps) is given by, ∅lc = 4mn° pq (r+*) (14) fig. 6. papwm scheme. c. multi-carrier variable switching frequency (vsfpwm) the vsfpwm scheme is the same with the level-shifted modulation scheme. all the carriers have different peak amplitudes and unequal switching frequencies such as 5050hz, 7050hz, and 9050hz. these frequencies are selected with respect to the multiplication factor. this modulation technique has better minimization of harmonic distortions and low switch stress and increased efficiency, while it requires low-rated filter units. the vsfpwm scheme is depicted in figure 7. fig. 7. vsfpwm scheme. d. modified modulation scheme a unique modulation scheme is introduced by utilizing pa and vsfpwm schemes for getting optimal switching states. all the carriers in the proposed modulation scheme have different peak amplitudes which are vertically disposed by the respective phase-angles and have unequal switching frequencies such as 5050hz, 7050hz, and 9050hz with respect to the multiplication factor. the advanced modulation scheme is depicted in figure 8. fig. 8. advanced pd modulation scheme. iv. simulation results the performance of the zsi based 7-level sc-mli fed gridintegrated system with several modulation schemes is validated in matlab/simulink and is developed with the help of the operating parameters shown in table iii. figure 9(a) shows the complete matlab model, figure 9(b) shows the hysteresis controller, and figure 9(c) shows the controller for generating shoot through pulses. table iii. operating parameters parameter value pv source vpv =100v grid voltage & frequency vg=230v, fg =50hz impedance source l1=l2= 10mh. c1=c2= 0.01f dc-link voltage 150v switching frequency 10khz dc-link capacitor cdc= 0.01f capacitors c1=c2= c3 = 0.01f engineering, technology & applied science research vol. 12, no. 4, 2022, 8936-8941 8940 www.etasr.com manjunatha et al.: an enhanced z-source switched mli capacitor for integrated micro-grid with … (a) (b) (c) fig. 9. matlab/simulink model. (a) (b) (c) (d) (e) fig. 10. performance of the 7-level improved zsi based sc-mli using the proposed advanced modulation technique. (a) voltage across the capacitors, (b) 7-level output voltage, (c) output current, (d) output voltage and currentin phase, and (e) thd of the output voltage. a. performance evaluation of the proposed topology with advanced modulation techniques in a standalone system figure10 shows the simulation outcome of the 7-level zsi based sc-mli with advanced modulation scheme. from figure 10(e), it is observed that the harmonic content in the output voltage is high at odd multiples of the fundamental frequency. the pv input voltage 100v is transformed into 150v dc-link voltage by the sc module. the dc-link capacitor voltages are maintained constant and balanced for achieving the significant 7-level output. the thd of the output voltage is 12.54%. the performance of the proposed 7-level sc-mli is evaluated by classical and the proposed pwm schemes. it can be seen that the proposed advanced modulation scheme has better features. the thd analysis of the modulation schemes is depicted in figure 11. fig. 11. thd analysis of the considered modulation schemes. (a) (b) (c) (d) fig. 12. performance of the 7-level zsi integrated to the grid. (a) grid voltage and current, (b) in-phase grid voltage and current component, (c) grid active and reactive power, (d) thd of grid current. engineering, technology & applied science research vol. 12, no. 4, 2022, 8936-8941 8941 www.etasr.com manjunatha et al.: an enhanced z-source switched mli capacitor for integrated micro-grid with … b. grid integration scheme the proposed topology is integrated to a micro-grid with the advanced modulation technique. figure 12 represents the simulation outcome of the 7-level ezsc-mli with the advanced modulation scheme integrated to the grid with lowrated filter units. the attained grid voltage and current are puresinusoidal and maintained constant at the fundamental frequency. both the components are in-phase representing a unity power factor. the thd of the grid current is 4.16%, well within ieee-519 standards. v. conclusions in this paper, the enhanced z-source sc-mli topology with various modulation techniques is proposed. it is capable of operating with a high voltage gain factor. the proposed scmli utilizes only a single pv source and 7 active switches for the production of 7 voltage levels. effective modulation schemes are used for the generation of optimal switching states. they have better reduction of harmonic distortion over the classical schemes and attain favorable benefits. there is no need of additional balancing technique, a self-balancing technique is initiated which reduces the complex control circuitry. when using the proposed 7-level sc-mli topology, the switching components are fewer over the classical mli topologies. the proposed inverter topologies are more suitable for the der fed grid by utilizing attractive voltage and current control loops. this system can be used for integrating different renewable energy sources. references [1] m. a. hannan, s. y. tan, a. q. al-shetwi, k. p. jern, and r. a. begum, "optimized controller for renewable energy sources integration into microgrid: functions, constraints and suggestions," journal of cleaner production, vol. 256, may 2020, art. no. 120419, https://doi.org/ 10.1016/j.jclepro.2020.120419. 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[22] t. nguyen-van, r. abe, and k. tanaka, "a digital hysteresis current control for half-bridge inverters with constrained switching frequency," energies, vol. 10, no. 10, oct. 2017, art. no. 1610, https://doi.org/10.3390/en10101610. microsoft word 4-630-ed.doc engineering, technology & applied science research vol. 6, no. 2, 2016, 937-944 937 www.etasr.com al agha and el-radie: towards verbalizing sparql queries in arabic towards verbalizing sparql queries in arabic iyad al agha faculty of information technology the islamic university of gaza gaza strip, palestine ialagha@iugaza.edu.ps omar el-radie faculty of information technology the islamic university of gaza gaza strip, palestine omar.elradie@gmail.com abstract—with the wide spread of open linked data and semantic web technologies, a larger amount of data has been published on the web in the rdf and owl formats. this data can be queried using sparql, the semantic web query language. sparql cannot be understood by ordinary users and is not directly accessible to humans, and thus they will not be able to check whether the retrieved answers truly correspond to the intended information need. driven by this challenge, natural language generation from sparql data has recently attracted a considerable attention. however, most existing solutions to verbalize sparql in natural language focused on english and latin-based languages. little effort has been made on the arabic language which has different characteristics and morphology. this work aims to particularly help arab users to perceive sparql queries on the semantic web by translating sparql to arabic. it proposes an approach that gets a sparql query as an input and generates a query expressed in arabic as an output. the translation process combines both morpho-syntactic analysis and language dependencies to generate a legible and understandable arabic query. the approach was preliminary assessed with a sample query set, and results indicated that 75% of the queries were correctly translated into arabic. keywords-sparql; natural language processing; ontology; morpho-syntactic features; arabic i. introduction the semantic web is the next generation of the current web. with the dramatic growth of the linked data web in the past few years, an increased amount of rdf data has been published as linked data. intuitive ways of accessing linked data have become highly demanded as a growing number of applications rely on rdf data as well as on the w3c standard sparql for querying this data [3]. sparql is the query language for the semantic web. along with rdf and owl, it is one of three core technologies of the semantic web. sparql enables web applications and agents to query the web, similar to how the sql is used to query database tables [4]. while sparql has proven to be a powerful tool in the hands of expert users, it remains difficult to understand for ordinary users who have limited experience with the semantic web. therefore, it is necessary to bridge the gap between the query language understood by semantic data backbends, i.e. sparql, and that of the end users. existing research has approached this problem by proposing interfaces to translate sparql queries to natural languages [5]. they often take a sparql query as an input and produce a question expressed in natural language. these interfaces have benefits for both naïve and expert users: a naïve user is enabled to reliably understand the content of sparql queries. expert users can assess the correctness of the sparql queries they construct by translating them back to natural language. arabic is one of the largest members of the semitic language family and is spoken by nearly 500 million people worldwide [6]. it is one of the six official un languages. despite its cultural, religious, and political significance, arabic has received comparatively little attention in modern computational linguistics. towards supporting the arabic use on the semantic web, this work proposes a generic approach to translate sparql to arabic queries, thus enabling arab users to understand sparql and rdf data without exposing the underlying complexity. while few efforts [7, 8] presented approaches to translate sparql queries to natural language, most of these efforts focused on the english language. these approaches, however, cannot be directly used for the arabic language as it has different characteristics and morphology. in this research, we propose a generic approach to verbalize sparql queries in arabic. it exploits natural language processing and language dependencies to translate rdf triples of sparql into legible arabic sentences. it also exploits morphological analysis to realize the arabic sentences and make them easy to read and understand. ii. related works approaches to facilitate access to ontologies and owl back-ends have been the concern of many research works [912]. these works provide interfaces to enable querying rdf content by inputting natural language queries. in contrast, little research has been conducted to investigate the other way around, which is the verbalization of sparql. verbalizing sparql queries enables users to understand how the results have been retrieved and whether the right question has been asked to the queried knowledge base. in the domain of english language, some efforts aimed to generate natural language representations of portions of ontologies [13, 14]. these efforts claimed that the natural language representation of ontologies can be more informative to non-expert users than graphical representations. dong and holder [15] proposed a system that uses an ontology skeleton and handcrafted templates to generate natural language from semantic graphs. wilcock [16] presented a generic approach engineering, technology & applied science research vol. 6, no. 2, 2016, 937-944 938 www.etasr.com al agha and el-radie: towards verbalizing sparql queries in arabic for verbalizing owl and daml+oil ontologies. third et al. [17] presented a tool that generates easily-navigable english text from owl input. other works on generating textual representations of owl ontologies include [18-20]. besides the work on owl, research on generating textual descriptions of rdf triples has gained a considerable attention [5, 21, 22]. these solutions have been widely used for question answering over linked data and rdf back-ends [3, 23]. in addition, some approaches worked on the verbalization of firstorder logics [24]. some works have explored ways to translate database queries, i.e. sql queries, to natural language text [19, 25, 26]. to the best of our knowledge, only two approaches were proposed for verbalizing sparql queries in english, which are spartiqulation [8] and sparql2nl [7]. spartiqulation is based on identifying the main entity in a sparql query. the main entity is then used to subdivide the query graph into sub-graphs that are ordered and matched with pre-defined message types. spartiqulation is limited to select queries and cannot handle important sparql features such as union and group by constructs. sparql2nl aims to generate english sentences by first generating a list of dependency trees for an input query, and then it applies reduction and replacement rules to improve the legibility of the verbalization. unlike spartiqulation, sparql2nl covers a wide range of sparql features and supports better realization of the sentence structure. all the previous approaches exploited linguistic features and language patterns to generate natural language from queries. they benefited from the advancements in english nlp toolkits. however, it is difficult to generalize these approaches to the arabic language. this is due to the fact that arabic has more complex morphological, grammatical and semantic structures that make existing nlp techniques used for english inadequate for arabic. building arabic ontologies that can be used in a wide context is gaining momentum [6, 27, 28]. in addition, several ontology-based approaches have been proposed for enhancing information retrieval from the arabic content on the web [29, 30]. in line with these efforts, natural language interfaces will be demanded to enable naïve arab users to send queries and obtain results from ontologies. to address this demand, only few efforts have explored the translation of queries expressed in arabic to sparql [2, 31] to our knowledge, no work has explored the other direction, which is the verbalization of sparql queries in arabic. iii. the knowledge base before presenting the approach for translating sparql to arabic, it is necessary to give an overview of the knowledge base and the ontology used in the examples discussed in this paper. we used the diseases ontology that was used in previous research [32]. the ontology is built in owl and formally covers and classifies a range of well-known diseases in both english and arabic. the ontology models the relationships between diseases, cures, symptoms, diagnoses and the organs of human body. an excerpt of the ontology schema including ontology classes (e.g. cure, disease, symptom, organ and diagnosis) and the relationships between them, i.e. the object properties can be found in [2]. the ontology was populated with 149 ontology instances of different types. table i gives information about the ontology content and size. table i. the contents of the diseases ontology statistics on the diseases ontology number of classes 12 number of object properties 9 number of data properties 1 number of instances 149 when translating sparql to arabic, we assume that all terms of the input query should map to terms in the ontology. we also assume that the arabic translations of query terms are available either from the ontology or from a dictionary. starting with arabic words that correspond to sparql terms, our approach focuses on exploiting linguistic analysis and natural language processing to link and inflect these words, and then improve the realization of the generated sentence. in this work, the ontology was populated with the arabic translations of all ontology concepts, properties and instances, whereas a property (rdfs:label) is used to maintain the translations. these translations were retrieved from the ontology and used during the verbalization process. iv. the approach to verbalise sparql in arabic the proposed approach for translating sparql queries to arabic consists of the four consequent stages shown in figure 1. each stage has an input taken from an earlier stage, and produces an output that is fed into the following stage. these stages are: query preprocessing, converting sparql to arabic sentences, sentence realization and post-processing. each stage is explained in what follows. fig. 1. the stages of the sparql to arabic translation approach engineering, technology & applied science research vol. 6, no. 2, 2016, 937-944 939 www.etasr.com al agha and el-radie: towards verbalizing sparql queries in arabic a. sparql pre-processing the pre-processing stage aims to replace each term in the input sparql query with its corresponding translation in arabic. as mentioned earlier, we assume that the arabic translations of ontology terms are stored and can be retrieved from the ontology by referring to the property rdfs:label. a sparql query typically consists of one or more triples with one or more variables. a variable in sparql can be a subject, a predicate or an object. these variables often refer to the target words in the natural language query. when translating sparql to natural language, each variable in sparql should be replaced by an arabic word indicating its type, i.e. the ontology entity it refers to. types of variables will be used as the target words in the generated arabic question. for example, the query: “select ?x where {?x :cures :diabetes}” has one variable, i.e. ?x, which denotes the medication or the cure of diabetes. referring to the schema in [2], the variable ?x in the former query is of type :cure which translates into arabic as “عالج”. this arabic translation is then used to formulate the arabic question by appending it to the question word as the following: “ ...ما عالج ”. let ?x be a variable in sparql query, and c the set of ontology classes. to determine the type of ?x, we first search the input query for the graph patterns: “?x rdf:type c” where c c cî . if it exists, the arabic translation of the class c is retrieved from ontology by referring to the property rdfs:label. if the type cannot be explicitly determined from the query, then it can be identified by matching the query triples with the ontology content. for example, the triple <?x :cures :diabetes> matches with the ontology triple: :insulin_tips :cures :diabetes. then, the type of the variable ?x is the direct class to which the instance :insulin_tips belongs. the output of this step is a sequence of arabic words that correspond to the sparql terms. for example, if the input query is “select ?x where {?x :has_symptom :high_blood_pressure . ?x :infects :lungs}”, then the output is the following sequence (from left to right): <<مرض” عرض_له .”الرئتان<< يصيب <<مرض . ارتفاع ضغط الدم << note that this step does not consider ordering and inflecting the generated words to produce a syntactically-valid sentence. the syntactic and morphological realization of the sentence will be handled in the subsequent steps. b. decomposing the union construct part of the pre-processing step is to handle the union operator that may be part of the sparql query. the union operator is used to link multiple triples in sparql, and translates into natural language as a disjunction, i.e. "أو" . for example, the query “select ?x where {{?x :has_symptom :irritation}union{?x :has_symptom :fever}}” is translated as triples linked .”ما المراض الذي من أعراضه ارتفاع ضغط الدم أو الحمى؟“ by the union operator should be split so that they can be processed and translated separately. a complete arabic statement is then generated by joining the statements corresponding to triples by disjunctions (أو). c. arabic language dependencies the arabic words generated from the pre-processing stage should be linked together to formulate a well-structured sentence. relationships between words in a sentence are typically captured from a dependency tree constructed by a parser. in this work, we need to perform the opposite task: starting by standalone words, we need to link and inflect these words by choosing appropriate relationships that yield a valid sentence. existing efforts in the domain of english text [7] have often relied on language dependencies, such as stanford language dependencies [33], to identify relations between words. however, english dependencies cannot be directly used for the arabic language which uses different structures. therefore, we started with stanford dependencies and tried to adapt them for the arabic language. we defined a set of arabic language dependencies that resemble the structures of simple arabic sentences. these dependencies were defined by referring to similar dependencies in english and modifying them to cope with the arabic language. each dependency defines a relationship between words that occur in the text. for example, the dependency subj(يصيب ,مرض) refers to the relationship between a subject and a verb, obj(يصيب ,بنكرياس) refers to the relationship between a verb and an object. note that these dependencies do not cover all possible structures of arabic sentences. it only covers the basic structures enough to handle non-complex sparql queries. table ii. arabic dependences d. converting sparql triples to arabic sentences after defining a set of arabic language dependencies, we defined a set of rules for mapping sparql triples to arabic sentences. these rules determine what dependencies should be used based on the structure of each triple. formally, let f be an interpretation function that takes the arabic words, generated from the pre-processing stage, and generates a structured arabic sentence. the rules are as the following: dependency explanation nn a noun compound modifier: a head noun is modified by another noun. for instance: nn(السكر ,مرض ) stands for .مرض السكر subj a dependency between a subject and a verb, for example subj( أحمد , أكل ) expresses أكلأحمد . obj a verb phrase dependency between a verb and its direct object, for example obj(التفاحة,أكل) expresses to أكل التفاحة. amod an adjectival modifier of a noun phrase is any adjectival phrase that serves to modify the meaning of the noun phrase. represents the adjectival modifier dependency. for example, amod(الصماء,الغدد )stands for الغدد الصماء . neg negation modifier: the negation modifier is the relation between a negative word and the word it modifies. for example neg(ال،يحتوي)ھذا الكتاب ال يحتوي على تاريخ االندلس pron subject pronouns: defines a relation between a pronoun and a subject. for example, pron(عالج ,ھو) expresses ھو .عالج poss expresses a possessive dependency between two lexical items, for example poss(كتاب ,أحمد ) expresses كتاب أحمد. engineering, technology & applied science research vol. 6, no. 2, 2016, 937-944 940 www.etasr.com al agha and el-radie: towards verbalizing sparql queries in arabic rule 1: f (s p o) where p is a verb and s is a variable => subj (p, s) ^ obj(p, o) where s, p and o stand for the arabic words that correspond to the subject, the predicate and the object of the triple respectively. this rule means that if the predicate is a verb and the subject is a variable, then it is transformed to a natural language by using a concatenation of subj, obj dependencies from table ii. given the following sample triple: <?var :infects :organ>, the subject is unknown, and the predicate :infects refers to the verb “يصيب”. the type of the variable ?var is :disease. on applying rule1, we get: f (s p o) => f (<:disease :infects :organ>) f (s p o) => subj(:disease :infects) ^ obj(:infects :organ) f (s p o) => يب عضويص ^ مرض يصيب f (s p o) => مرض يصيب عضو (after removing redundancy). rule 2: f (s p o) where p is a noun => poss(p, o) ^ pron (s) this rule indicates that if the predicate is a noun, then the poss dependency is used to link the predicate and the subject. the generated clause is then linked with the object by using the pron dependency. for example, in the triple: <:headache :symptom_of :sinus _infection>, the predicate :symptom_of refers to the noun “عرض”. on applying rule 2, we get: f(s p o) =>f (<:headache :symptom_of :sinus_infection>) f (s p o) => poss( عرض، التھاب الجيوب األنفية ) ^ pron( ھو,الصداع ) f (s p o) => عرض التھاب الجيوب األنفية ^ھو الصداع f (s p o) => تھاب الجيوب األنفية ھو الصداععرض ال rule 3: f (s p o) where p is rdf:type => nn(s ,o) this rule indicates that if the predicate is rdf:type, the nn dependency is used to link the subject with the object. for example, given the triple <:diabetes rdf:type :disease>, rule 3 is applied as the following: f (s p o) =>f (:diabetes rdf:type :disease) => nn( :diabetes, :disease) => مرض السكر e. sentence realization the rules in the previous section define how to link the arabic words that correspond to the sparql terms. however, there are still several challenges that should be considered to support the realization of the generated verbalization. this may require inflecting, reordering or putting words in other formats. in the following we discuss these challenges: passive or active voice: the voice of generated sentences sometimes should to be changed from active to passive and vice versa. the correct voice to use depends on the variables in the sparql query, and whether these variables map to objects or subjects. the intention to change the sentence’s voice is to bring the target words, which correspond to the sparql variables, to the beginning of the sentence so that they precede other words. this will simplify the construction of the natural language query. take the following query as an example: select ?x where {:diabetes :infects ?x}. according to rule 1, the triple in the former query is translated as “ السكر is the type of the variable ”عضو“ where the word ,”يصيب عضو ?x. the word “عضو” is also the object and the target of the query. thus, the triple should be revised so that the object becomes the subject and vice versa. this means that the sentence’s voice should be changed from active to passive to become: “عضو يصاب بالسكر”. changing the sentence’s voice brings the target word, i.e. “عضو” to the beginning, thus allowing to easily construct the arabic question by adding the appropriate question word before the target word, i.e. “ ما العضو .”الذي يصاب بالسكر؟ the gender (masculine or feminine): sometimes it is necessary to reform arabic words in accordance with the intended gender. for example, the intention of the query select ?x where { :bacteria :causes ?x } is to retrieve the diseases caused by bacteria. the arabic representation of this query should look like: “ note that .” البكتيريا؟ما المرض الذي تسببه the suffix of the verb “ هتسبب ” as well as the pronoun “الذي” both refer to a masculine noun which is “المرض”. singular and plural nouns: as with the gender of nouns, singular and plural nouns should also be considered when inflecting the arabic words. note that an arabic noun may have regular or irregular plurals. the plural words may also sound feminine, i.e.”األعراض” or masculine, i.e. “مخترعون”. note also that using singular or plural formats can modify the formats of other words in the sentence such as pronouns and prefixes. for example, the plural noun “أعراض” is used with the pronoun “التي”, while the singular noun “عرض” is used with the pronoun "الذي" . to address the above linguistic challenges, the arabic sentence generated from the previous step is processed by means of linguistic analysis. for this purpose, we used the arabic toolkit service (atks) [1] which is a set of nlp components developed by microsoft and targeting the arabic language. among its various components, atks includes a full-fledged morphological analyzer that supports a variety of features such as word synthesis, part of speech tagging and generation of derivatives. we used a set of features suggested by atks morphological analyzer to improve the legibility of the arabic query. for each arabic word inputted to the analyzer, it generates a set of morpho-syntactic features. among many things, these features include the voice of the verb, i.e. “ معلوم أو the gender of nouns and the number, i.e. singular or ,”مجھول plural. we rely on these features to identify the status of arabic words and modify them if necessary. for example, a sentence can be changed from active to passive voice using the following steps: 1) the morphological analyzer is used to identify the status of the verb in the sentence, i.e. active or passive. 2) all possible derivatives of the verb are generated with the help of the morphological analyzer. 3) these derivatives are then searched for a verb that has the same grammatical tense as the original verb but has an opposite voice. 4) the voice of the sentence is finally changed by swapping the subject and the object, and replacing the verb with the derivative identified from step 3. figure 2 shows the engineering, technology & applied science research vol. 6, no. 2, 2016, 937-944 941 www.etasr.com al agha and el-radie: towards verbalizing sparql queries in arabic pseudo code of the algorithm used for changing the voice of a sentence. input: a sentence s = <s, p, o> where s denotes a subject, o denotes an object, and p denotes a predicate. output: a sentence s = <o, p , s> where the voice of s is the opposite of the voice of s . use variables: f1, f2: empty lists of morpho-syntactic features d: an empty list of derivatives v1, v2: the voice of word (active or passive) begin // analyze p using atks morphological analyzer f1:= getmorpho_syntactic_features(p) // get the voice feature from the features list v1:= getvoice(f1) // get all derivatives of p using atks morphological analyzer d := getderivatives(p) for each d in d do f2 := getmorpho_syntactic_features(d) v2 := getvoice (f2); // if the original predicate and its derivative have that same tense but different voices if (tense(v1) == tense(v2) and v1 != v2) then p := p break end if end for s := <o, p , s> end fig. 2. the algorithm of converting the sentence’s voice from active to passive and vice versa. the gender and number of arabic words can be similarly determined by morpho-syntac features. as for the output of the morphological analysis, each word is tagged as “masculine” or “feminine” words, and is tagged as “singular” or “plural” (see figure 3 for an example). if there is a need to invert the gender, or change the number, we similarly generate all possible derivatives of the word, and then choose the derivative words that fulfil the translation needs. f. aggregation and post-processing after identifying the proper voice, gender and number, the arabic query is constructed. so far, each sparql triple is translated to a single arabic sentence. the next step is to aggregate these sentences to construct the target query in natural language. the aggregation process typically involves three steps that are illustrated in the pseudo code in figure 3: 1) redundant mentions of variables are removed. if redundant variables denote nouns, they are replaced by proper pronouns to preserve the coherence of the sentence. these pronouns are chosen based on the morpho-syntactic features of the noun, i.e. the gender and the number. 2) disjunctions, i.e. “أو” or conjunctions, i.e. "و" are used to link sentences. 3) an appropriate question word is added to generate the query. the following example illustrates how the aggregation process is carried out: the query: select ?x where {?x :diagnosed_by :ct_scan . :surgery :cures ?x is translated as “ مرض يعالج بالجراحة. مرض يشخص باألشعة المقطعية ”. this output, which consists of two separate sentences, is generated after applying the dependency rules and the morphological analysis as explained in the earlier sections. the two sentences are aggregated as the following: first, redundancy is eliminated by replacing the second occurrence of “مرض” with the pronoun then, a conjunction is used to link the two sentences (a .”ھو“ disjunction to be used if union operator is used). this results in the sentence: “مرض يشخص باألشعة المقطعية وھو يعالج بالجراحة”. finally, the question word "ما" is inserted at the beginning of the sentence to formulate the final query: " ما مرض يشخص باألشعة "المقطعية وھو يعالج بالجراحة ؟ . input: a sequence of arabic sentences s that correspond to rdf triples, a connector c  {“أو”,”و”} output: an arabic query q begin for each sentence s  s for each word w  s if w is redundant then if w is a noun then replace w with a pronoun else remove w end if end if end for if q is empty then q := s else q := c ^ s end if end for q := getquestionword(q) ^ q end fig. 3. the algorithm of converting the sentence’s voice from active to passive and vice versa. v. a complete example in the following, a complete example is presented to illustrate how the proposed approach for verbalizing sparql in arabic is applied. assume that the input query is: select ?x where {?x :infects :pancreas . :insulin :cures ?x}. this query has one variable, ?x, and two triples. the query aims to retrieve diseases that infect the pancreas and are treated by insulin. the verbalization process is carried out as the following: step 1: arabic translations of query terms are extracted from the ontology: this generates the following sequence: “?x >> يعالج << األنسولين . << البنكرياس << يصيب >> ?x”. step 2: variable are replaced by their corresponding type. the query does not contain an rdf:type triple. therefore, the type of ?x can be identified by matching the query triples with the engineering, technology & applied science research vol. 6, no. 2, 2016, 937-944 942 www.etasr.com al agha and el-radie: towards verbalizing sparql queries in arabic ontology content. this can be achieved by executing the following query over the ontology: select ?type where {?x rdf:type ?type . ?x :infects :pancreas . :insulin :cures ?x} this query retrieves the type :disease which is translated as finally, the mentions of variable ?x are replaced by the .”مرض“ word "مرض" , resulting in the following sequence: .”مرض << يعالج << األنسولين . << البنكرياس << يصيب << مرض“ step 3: arabic sentences are constructed by applying the appropriate dependency rules. both triples have predicates that are verbs. then, rule 1 applies as the following: for the first triple: f (s p o) => f (<:disease :infects :pancreas>) f (s p o) => subj(:disease :infects) ^ obj(:infects :pancreas) f (s p o) => البنكرياسيصيب ^ مرض يصيب f (s p o) => البنكرياسب مرض يصي (after removing redundancy). for the second triple f (s p o) => f (<:insulin :cures :disease>) f (s p o) => subj(:insulin :cures) ^ obj(:cures :disease) f (s p o) => يعالج مرض ^ اإلنسولين يعالج f (s p o) => اإلنسولين يعالج مرض (after removing redundancy). step 4: morphological analysis is performed to determine the correct voice, gender and number. this results in the following sentences: مرض يعالج باإلنسلوين. مرض يصيب البنكرياس . note that the voice of the latter sentence is changed from active voice to passive in order to bring the word “مرض” to the beginning of the sentence. step 5: redundant words are eliminated, and a question word and proper pronouns are added, resulting in the following query: "ج باألنسولين؟ما مرض يصيب البنكرياس وھو يعال" . vi. limitations to our knowledge, this work is the first step towards verbalizing sparql queries in arabic. the main focus at this stage was to explore how the combination of morpho-syntactic features and dependency rules can be used for transforming sparql queries into legible arabic sentences. however, arabic is a rich language with a complex morphology when compared to english. hence, there are several language and semantic issues that are not currently supported. first, the processing of filter and group by constructs are not currently supported. the interpretation of these constructs is not straightforward due to the variety of formats they can have. in addition, they may entail significant modifications which can make the translation process complicated. second, the generated arabic sentence may require further realization by, for example, using appropriate pronouns, suffixes and prefixes. arabic language is a free word order language; the sentence may have different forms of word order. sometimes, it may be recommended to reorder words to improve the legibility of the sentence. however, sentence reordering has not been considered in this work. vii. preliminary evaluation a. dataset the main goal of this evaluation is to assess the ability of the proposed approach to verbalize sparql queries in arabic. while there are plenty of owl test data and questions in english [34], we are not aware of any ontology-based test data for arabic that can be used for our evaluation. therefore, we used the owl dataset which we developed and used in previous works [2, 31]. this dataset consists of the diseases ontology, of which an excerpt is shown in [2], and a set of 100 arabic questions whose answers are in the ontology. this dataset was originally designed to assess natural language interfaces that take queries expressed in arabic and generate sparql queries. as we aim to perform the opposite task, we recruited a human expert and explained the ontology content to him. we then asked the expert to choose twenty questions from the arabic question set and convert them manually to sparql. the generated twenty sparql queries were then inputted to the system, and the output verbalizations were compared with the original arabic queries. we also asked the expert to rate the similarity between each output query and the original query using a scale from 1 to 5, where 1 indicates a “weak similarity” and 5 indicates a “strong similarity”. b. results and discussion table iii shows the twenty queries inputted to the system and their representations in sparql. the verbalizations generated by the system to these queries as well as the expert’s ratings are also shown in the columns to the left. overall, fifteen of the twenty queries (75%) were rated “4” or “5”, two queries were rated “3”, while three queries were rated “1” or “2”. this result indicates that the system could verbalize most sparql queries in arabic. on comparing the generated queries with the original ones, we found they were highly similar, expect few missing pronouns and word prefixes such as “الـ” that can make the output better readable. however, the expert indicated that all queries rated “4” and “5” conveyed the same meanings as the original ones, and that they were fairly legible. looking at the queries that got lower ratings, we found that the system failed to verbalize them for different reasons: for example, query #7 was not translated correctly because our approach cannot handle filter clauses. some queries such as queries #14 and #16 did not give the intended meanings and needed better rephrasing. in fact, verbalizing these queries to capture the intended meanings may need deep reasoning that goes beyond the capabilities our approach. for example, the system is not currently able to handle queries starting with the word: “أذكر”. viii. conclusions and future work in this research, we proposed an approach to generate arabic verbalizations for sparql queries. the translation from sparql to natural language goes through several stages: first, arabic translations of terms in sparql are extracted, and variables are mapped to their corresponding types. second, we use a set of language dependencies, which we adapted from engineering, technology & applied science research vol. 6, no. 2, 2016, 937-944 943 www.etasr.com al agha and el-radie: towards verbalizing sparql queries in arabic stanford dependencies of english language, and a set of handcrafted rules to structure words into valid sentences. third, the linguistic realization of the sentence is boosted by exploiting morpho-syntactic analysis and nlp techniques. finally, aggregation and redundancy elimination is performed to improve the legibility of the sentence. there are many directions to extend this work: the limitations of the approach will be explored, especially the processing of filter clauses. we will also explore the expansion of arabic dependencies in order to support additional structures of arabic sentence, and hence, support the verbalization of more complex sparql queries. the approach will be assessed with a larger query set and different ontologies. we will also explore how the approach can be integrated into ontology-based applications to benefit users in practice. references [1] http://research.microsoft.com/en-us/projects/atks/ [2] i. al agha, “using linguistic analysis to translate arabic natural language queries to sparql”, international journal of web & semantic technology, vol. 6, no. 3, pp. 25-39, 2015 [3] s. shekarpour, a. -c. ngonga ngomo, s. auer, “question answering on interlinked data”, 22nd international conference on world wide web, pp. 1145-1156, rio de janeiro, brazil, may 13 17, 2013 table iii. evaluation results: input queries, output verbalizations and the expert’s ratings are shown original query sparql query output query rate القلب؟ تصيب التي األمراض ما 1 select ?x where {:?x rdf:type :disease . ?x :infects :heart} القلب؟ يصيب مرض ما 5 الزھري؟ بمرض اإلصابة سبب ما 2 select ?x where{ :syphilis :caused_by ?x} الزھري؟ يسبب سبب ما 3 ما األمراض التي تصيب القلب أو تسبب 3 تضخمه؟ select ?x where {:?x rdf:type :disease . {?x :infects :heart} union {?x :causes : :cardiac_hypertrophy}} أو ھو يسبب تضخمه؟ ما مرض يصيب القلب 5 ؟ما ھي االمراض المعدية 4 select ?x where {?x rdf:type :infectious_disease} 3 ما مرض معدي؟ لتھاب السحايا أو ما المرض الذي من أعراضه إ 5 ضعف اإلبصار؟ select ?x where {{?x :has_symptom :meningitis} union {?x :has_symptom :low_vision}} ما مرض له عرض إلتھاب السحايا أو ضعف اإلبصار؟ 4 ھرمون بتحليل يشخص ما المرض الذي 6 التستوستيرون؟ select ?x where {:testosterone_diagnosis :diagnoses ?x} مرض يشخص بتحليل ھرمون ما التستوستيرون؟ 5 ؟ ال تسبب ألم المعدة التي األدوية ما 7 select ?x where {?x rdf:type :cure . filter not exists {?x : causes :stomach_pain}} ؟ دواء يسبب ألم للمعدة ما 1 التدخين؟ يسببھا التي األمراض ما 8 select ?x where {?x :caused_by :smoking} يسبب بالتدخين؟ المرض ما 5 أعراضه ومن األمعاء يصيب الذي المرض ما 9 والقيء ؟ االسھال select ?x where {?x :infects :small_intestine . ?x :has_symptom :vomiting . ?x :has_symptom :diarrhea} الدقيقة و له عرض األمعاء يصيب مرض ما سھال والقيئ؟اإل 4 النفسية؟ األمراض من الالإرادي التبول ھل 10 ask{ :enuresis rdf:type :mental_disease} 4 ھل التبول الالإرادي نوع من مرض نفسي؟ عسر بنكرياس ويسبب يصيب الذي المرض ما 11 الھضم؟ select ?x where {{?x :infects:pancrias . ?x :causes :indigestion} ا مرض يصيب البنكرياس ويسبب عسر م الھضم؟ 5 اإلنفلونزا؟ وعالج أعراض ما 12 select ?x ?y where { ?x :symptom_of :influenza . ?y :cures :influenza} عالجھا؟ عرض اإلنفلونزا و ما 4 فالجيل؟ دواء يعالج ماذا 13 select ?x where {?x :cured_by :flagyl} الجيل؟بف يعالج مرض ما 5 النفسية؟ األمراض بعض أذكر 14 select ?x where {?x rdf:type :mental_disease} نفسي؟ ما مرض نوع من مرض 2 15 الجدري؟ يعالج كيف select ?x where {?x rdf:type :cure . ?x :cures :smallpox} يعالج الجدري؟ دواء ما 4 القلب؟ جراحات أنواع بعض أذكر 16 select ?x where {?x rdf:type :heart_surgery} القلب؟ جراحة ما جراحة نوع من 2 نقص البنكرياس ويسببه يصيب الذي المرض ما 17 األنسولين؟ select ?x where { ?x :infects :pancreas. ?x :caused_by :lack_of_insulin} يصيب البنكرياس ويسبب بنقص مرض ما األنسولين؟ 4 اإلجھاض؟ تسبب التي ةاألدوي ما 18 select ?x where {?x rdf:type :cure . ?x:causes :abortion} اإلجھاض؟ يسبب دواء ما 5 التوحد؟ أعراض ما 19 select ?x where {:autism :has_symptom ?x } التوحد؟ عرض ما 5 ما ھي االمراض التي تصيب الدم و من 20 أعرضھا ارتفاع ضغط الدم وتسبب عدم انتظام ضربات القلب؟ select ?x where {?x :infects :blood. ?x :causes :arrhythmias . ?x :has_symptom :high_blood_pressure} ضغط الدم وله عرض إرتفاع يصيب مرض ما الدم القلب؟ اتضرب انتظام عدم ويسبب 5 engineering, technology & applied science research vol. 6, no. 2, 2016, 937-944 944 www.etasr.com al agha and el-radie: towards verbalizing sparql queries in arabic [4] j. perez, m. arenas, c. gutierrez, “semantics and complexity of sparql”, acm transactions on database systems, vol. 34, no. 3, article no. 16, pp. 1-45, 2009 [5] h. piccinini, m, a. casanova, a. l. furtado, b. p. nunes, “verbalization of rdf triples with applications”, iswc-outrageous ideas track, 2011 [6] m. beseiso, a. r. ahmad, r. ismail, “a survey of arabic language support in semantic web”, international journal of computer applications, vol. 9, no. 1, pp. 35-40, 2010 [7] a. -c. ngonga, l. buhmann, c. unger, j. lehmann, d. gerber, “sorry, i don't speak sparql: 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dependencies manual, available at: http://nlp.stanford.edu/software/dependencies_manual.pdf [34] mooney natural language learning data, available at: https://files.ifi.uzh.ch/ddis/oldweb/ddis/research/talking-to-the-semanticweb/owl-test-data/ microsoft word 2-518-ed.doc engineering, technology & applied science research vol. 4, no. 6, 2014, 714-723 714 www.etasr.com monsia and kpomahou: simulating nonlinear oscillations of viscoelastically damped mechanical systems simulating nonlinear oscillations of viscoelastically damped mechanical systems m. d. monsia department of physics/fast university of abomey-calavi abomey-calavi, benin monsiadelphin@yahoo.fr y. j. f. kpomahou department of physics/fast university of abomey-calavi abomey-calavi, benin kpomaf@yahoo.fr abstract—the aim of this work is to propose a mathematical model in terms of an exact analytical solution that may be used in numerical simulation and prediction of oscillatory dynamics of a one-dimensional viscoelastic system experiencing large deformations response. the model is represented with the use of a mechanical oscillator consisting of an inertial body attached to a nonlinear viscoelastic spring. as a result, a second-order firstdegree painlevé equation has been obtained as a law, governing the nonlinear oscillatory dynamics of the viscoelastic system. analytical resolution of the evolution equation predicts the existence of three solutions and hence three damping modes of free vibration well known in dynamics of viscoelastically damped oscillating systems. following the specific values of damping strength, over-damped, critically-damped and under-damped solutions have been obtained. it is observed that the rate of decay is not only governed by the damping degree but, also by the magnitude of the stiffness nonlinearity controlling parameter. computational simulations demonstrated that numerical solutions match analytical results very well. it is found that the developed mathematical model includes a nonlinear extension of the classical damped linear harmonic oscillator and incorporates the lambert nonlinear oscillatory equation with well-known solutions as special case. finally, the three damped responses of the current mathematical model devoted for representing mechanical systems undergoing large deformations and viscoelastic behavior are found to be asymptotically stable. keywords-mathematical modeling; nonlinear oscillations; viscoelastic oscillator; painlevé equation; exact solution; numerical simulation i. introduction in this work the dynamics of mechanical systems undergoing large deformations and viscoelastic response is investigated. a major topic in the dynamics of viscoelastic systems is the problem of vibration. vibration phenomenon arises in all rigid or deformable systems, such as machines and engineering structures subjected to dynamic loading. so, the vibration problem is of vital importance for many fields of science and technology. vibration experiments are widely used in the characterization of dynamical mechanical properties of engineering materials. vibration is also desired for machines under working conditions. however, for most structures in mechanical, biomechanical, civil, aeronautical and automotive engineering, oscillatory events prediction and control is intensively required in order to reduce noise, and to prevent non-allowable or excessive deformations, self-excited deformations, material fatigue and failure [1]. the one-dimensional dynamics of continuous viscoelastic media idealized as a bar is described formally by the cauchy's wave equation. however, when only homogenous deformation is considered in longitudinal forced vibration experiment for a bar carrying a tip mass at the free end, under the condition that the mass of the bar may be neglected compared to that of the attached mass at the end point, the bar may be assumed to behave as a simple viscoelastic spring. so, the cauchy's equation may be reduced, based on the second newton's law, if u denotes the time history of displacement response, then in the concise form [2, 3]: 2 int2 ( ) ext d u t m f f dt = (1) where 2 2 d dt denotes the ordinary second time derivative applied to the attached mass displacement )(tu depending only on the time t, m is the mass of the attached body, fext designates an applied exciting force, and intf notes the internal axial force due to the viscoelastic stress induced in the considered mechanical system. in this context the question of viscoelastic systems vibration transforms into that of finding an appropriate constitutive equation for structural materials. viscoelastic behavior is widely mathematically analyzed through the use of rheological approach which discretizes a viscoelastic body in its elementary elastic and viscous components represented in terms of mechanical analogs. so, the rheodynamical approach models the motion of a viscoelastic system in terms of ordinary differential equations [3, 4]. according to laroze [5], internal damping can be schematized for most structural materials in practice as viscous damping. in this perspective, if it is assumed that the viscoelastic spring behaves as a kelvin-voigt medium, that is, if: int ( ) ( ) d u f k u b dt f f= + (2) engineering, technology & applied science research vol. 4, no. 6, 2014, 714-723 715 www.etasr.com monsia and kpomahou: simulating nonlinear oscillations of viscoelastically damped mechanical systems where φ(u)=u, then the basic evolution equation governing the forced viscoelastically damped linear vibrating mechanical system may be written in the form: 2 2 ( ) ( ) ( ) ext d u d u m b k u f dt dt f f f+ + = (3) or in terms of only )(tu under free vibration: 2 2 2 0 o d u du u dt dt l w+ + = (4) in which b m l = , and 2 o k m w = . the quantity ωο is defined as the angular or undamped natural frequency of the physical system, and λ is a damping factor [5, 6]. equation (4) is a classical prototype of secondorder ordinary differential equations used to describe the damped linear oscillation of a single degree of freedom oscillator. it represents the dynamics of the motion of a onedimensional viscoelastic system in terms of kelvin-voigt element with the addition of a mass in the range of linear deformation. equation (4) is the simplest differential equation that may reproduce all different types of behavior exhibited by a damped second order oscillation system in the range of linear deformation. the type of response given by (4) representing a damping linear oscillation system depends, in effect, on the strength of damping degree. in other words, the response of a damped oscillatory system is very sensitive to changes in specific value of damping. it has been observed that the oscillatory response of a real system is nonlinearly damped and geometrically nonlinear, leading to the dependence of the stiffness on the induced deformation or stress. this phenomenon is known as stiffening or softening and terminates often by failure, following the stiffness increases or decreases. such a phenomenon could not be predicted and explained by any linear model equation [611]. many systems in engineering applications are designed to behave not only viscoelastically but also nonlinearly, to say, to undergo large deformations exceeding the limiting value predicted by linear theory in loading environment [2, 6, 7, 11]. viscoelastic systems have the specific ability to experience large deformations even for moderate force levels. hence, the linear theory becomes quite unable to explain the dynamics of viscoelastic systems experiencing finite deformations [6, 7, 1215] . geometrical, damping and material nonlinearities are fundamental causes for the viscoelastic behavior of systems to be nonlinear [5]. if the stiffness or geometrical nonlinearities are relatively well captured in terms of polynomial expansion, the damping nonlinearity properties of mechanical systems are very difficult to be known [4, 7, 8]. according to [7, 8], another non-negligible source contributing to nonlinear response of a mechanical system is the inertia properties. inertia produces, to a certain extent, a force which is essentially nonlinear. nonlinear inertia forces are generally proportional to higher powers of velocity and acceleration of the mechanical system [7, 8]. the above show that an oscillatory viscoelastic system is intrinsically characterized at least by its stiffness, damping and inertia nonlinearities. therefore, a reliable representation of the nonlinear oscillatory dynamics of a viscoelastic system should have the ability to mathematically incorporate in the governing equation these basic nonlinearity principles [7]. from the above analysis, the most general second order ordinary differential equation that can model the nonlinear oscillatory dynamics of a single degree of freedom viscoelastic system under unforced conditions may take the form: 0)(),(),(  uufuuuguuuh  (5) where the dot over a symbol designates the time derivative, ),( uuh  and ( , ),g u u are function of the displacement )(tu and first time derivative ( ),u t and f(u) is function of the displacement )(tu . these functions lead to the inertia, damping and stiffness nonlinearity properties, respectively, so that for the function 0h , and hg / and 2/ ohf  , (5) gives (4) modeling a damped linear harmonic oscillator. it is interesting to note that in the majority of existing evolution models of mechanical systems, only one of these nonlinearities is often considered (see for example [16] for more details). this shows that, due to the mathematical complication arising quickly in governing equations, the enhancement, for example, of stiffness nonlinearity is often performed in models to the detriment of system damping nonlinearity and, inversely, the improvement of damping nonlinearity is made in a prejudicial fashion to that of stiffness nonlinearity [1]. moreover, very few of proposed mathematical models for studying the dynamics of viscoelastic systems with a single degree of freedom have been performed to enclose on the one hand the inertia nonlinearity, and simultaneously combined inertia, damping and stiffness nonlinearities governing the viscoelastic response as indicated by (5) on the other hand [7]. it is well known again that nonlinear problems having explicit exact solutions in terms of elementary standard functions are very limited in physical and engineering fields. so, a large part of nonlinear analysis has only been performed on the basis of qualitative theory or particular solutions derived from analytical approximate or numerical integration methods. in particular, homotopy perturbation analysis is intensively used to investigate nonlinear vibration problems in mechanical structures [17]. in mechanical system design calculations, for example, the accurate determination of dynamical characteristics from observations requires mathematical models having appropriate analytical solutions. in this context, the design of mathematical models capable of representing the nonlinear dynamics of viscoelastic systems satisfactorily in terms of analytical exact solutions, capturing also simultaneously the combined nonlinear phenomena, becomes a major necessity. in that, the bauer’s rheological-dynamical theory [7] consists of a notable progress in the field of the dynamics of continuous viscoelastic media, since it meets the essential of preceding criteria about the necessity to handle simultaneously and in combined fashion, in mathematical modeling of viscoelastic systems, the nonlinearity properties. engineering, technology & applied science research vol. 4, no. 6, 2014, 714-723 716 www.etasr.com monsia and kpomahou: simulating nonlinear oscillations of viscoelastically damped mechanical systems although the bauer's method [7] seems to be simple in formulation, it is in reality a powerful approach for solving dynamical nonlinear problems arising in viscoelastic continuum mechanics successfully. this theory [7] entails a significant mathematical modification and extension of the classical kelvin-voigt viscoelastic solid law for capturing simultaneously the combined inertia, damping and stiffness nonlinearities characterizing the dynamics of real viscoelastic systems. the bauer’s approach [7] was originally developed for modeling the dynamics of nonlinear viscoelastic response of soft biological tissues, arterial walls in particular. the basic idea underlying this theory consists in developing the total stress within a material system as the sum of three basic stresses: elastic, viscous and inertial stresses, operating in parallel. very recently, the bauer’s rheological-dynamical theory was formulated in a simple mathematical expression that may be described by a single second order evolution equation within the framework of continuum mechanics for investigating the dynamics of viscoelastic material systems [12, 13]. this formulation has successfully been applied in several papers to model creep deformation [13], creep relaxation [6] and deformation restoration process under stress relaxation conditions [14, 15] of a variety of viscoelastic solid bodies. the objective of this research work is to develop a mathematical model expressed in terms of an exact analytical solution that may be useful in numerical simulations of the oscillatory dynamics of a one-dimensional viscoelastic system exhibiting large deformations. the physical properties of the mathematical model are represented by a single degree of freedom oscillator consisting of a mass attached to a viscoelastic spring that behaves as a nonlinear kelvin-voigt continuum medium. more precisely, given a stiffness nonlinearity function, it is proposed to develop the evolution equation of the time dependent displacement response of a mechanical system experiencing viscoelastic response and large deformations by applying the bauer's theory as formulated mathematically by monsia [12, 13]. in this sense, exact analytical solutions in terms of elementary standard functions have been determined, following various types of response able to exhibit the evolution equation under unforced regime. numerical applications are carried out for illustrating the ability of the mathematical model to be used for numerical simulations. graphs of numerical and exact analytical results are compared to prove the validity of the current model. it is also shown that the developed model incorporates as special cases some oscillatory equations with well known solutions by passing to special limiting values of the model parameters. time-asymptotic system response is investigated to check the stability character of the long time behavior of the proposed model. so, in the next section, the evolution equation governing the nonlinear oscillatory dynamics of the investigated viscoelastic system will be developed. section 3 is devoted to solve the obtained second-order first-degree painlevé evolution equation in closed form exact solution following various types of damping modes of oscillation. numerical applications of the model are presented in section 4, and a discussion of the results is performed in section 5. the final section gives a brief conclusion of the work. ii. the one-dimensional nonlinear theory of viscoelastic systems a. continuum mechanical nonlinear evolution equation in this part, the monsia’s formulation [12, 13] of the bauer’s theory [7] will be briefly reviewed to make the transition from its continuum version to a constitutive expression in terms of displacement and force. the advanced procedure for modeling the dynamics of real mechanical systems, to say, viscoelastic systems, developed by bauer [7] was expressed within the framework of continuous mechanics, in other words, in terms of stresses and strains experienced by the mechanical system. the monsia’s formulation [12, 13] of the bauer’s theory [7] enables us to describe this theory, for a given stiffness nonlinearity function f , by a single second order evolution equation, with only few system parameters to be determined through fitting procedure, of the form: 2 2 ( ) ( ) ( ) ( ) (1 / ) ( ) o c tf e e f e e lf e e w f e s¢ ¢¢ ¢+ + + =   (6) where ( )ts is the scalar stress function and ( )te the scalar strain function , the prime denotes a differentiation with respect to response variable, that is, here, the strain ( )te , and 0c ¹ , is the inertia coefficient. the constants λ and o continue to have the preceding definitions of damping factor and natural frequency, respectively. for some convenience, (6) may be written, by using a differential operator b as: ( ( )) (1 / ) ( )b t c te s= (7) with: 2 2 2 2 ( / ) ( / ) ( / ) o b d dt d dt d dtf f lf w f¢ ¢¢ ¢= + + + (8) at the present time, the function  that captures the system stiffness nonlinearity is not explicitly known, but it must be specified before any further use of the theory. in the following section, an explicit expression for  will be given as function of the deformation response. b. nonlinear constitutive force-displacement equation in this section the constitutive equation in terms of force and displacement governing the dynamics of the onedimensional viscoelastic system under investigation is formulated. for a time history of displacement response )(tu and an external exciting function ),,,( uuutf  , the operator b allows the equation of motion to be represented by: ( ( )) (1 / ) ( , , , )b u t m f t u u u=   (9) or by the equation written in the developed form: ),,,()/1()()()()( 22 uuutfmuuuuuuu o    (10) where the prime denotes the differentiation with respect to displacement variable u(t). the constants m, λ and ωο are time engineering, technology & applied science research vol. 4, no. 6, 2014, 714-723 717 www.etasr.com monsia and kpomahou: simulating nonlinear oscillations of viscoelastically damped mechanical systems independent and continue to have the preceding definitions. equation (10) is a second-order first-degree painlevé equation with a forcing function [18-20] known to be subject of many studies in mathematics. according to roth [21], painlevé equations have found several applications in physics, particularly in the field of circuit oscillations. so, the perspective to model the mechanical behavior of viscoelastic systems using the second-order first-degree painlevé equation may provide a great insight on their dynamics. equation (10) gives the differential relationship between the exciting function ),,,( uuutf  and the resulting time displacement response u(t) for a given function φ(u) capturing the purely nonlinear elastic response of the system under consideration. this equation enters in the perspective of the general second order evolution equation of a mechanical system represented by (5) and consists of a general formulation requiring the specification of the nonlinear elastic spring force function φ(u) for any subsequent development. mathematically, all nonlinear function φ(u) that tends towards u, when the displacement u tends to zero, may be selected as a possible restoring force function. in other words, at small deformations, the nonlinear model under question should reduce to the associated linear law. therefore, an infinite number of functions φ may be designed. in doing so, various types of mathematical expressions for the function φ have been proposed in recent papers [6, 12-15, 22]. in general, as performed by bauer [7], the stiffness nonlinearity function φ(u) may be expanded in a power series as: ......)( 33 2 21  n nuauauauau in this perception, for mathematical reasons of simplicity, the nonlinear stiffness function φ will be expressed, in this work, basically as a power law in the form: [22] ( )φ lu u= (11) where the hardening exponent, that is the stiffness nonlinearity controlling parameter 0l ¹ . following this point of view, the equation of motion takes the form: 1 2 2 1 2( 1) ( / ) (1 / ) ( , , , ) (12)l l l lou u l u u u u l u lm f t u u ul w -+ + + =     with the mass 0m ¹ . equation (12) models then the nonlinear dynamics of the viscoelastic system with single degree of freedom for 1l ¹ under an external exciting function ),,,( uuutf  . it can be solved analytically and numerically to investigate various types of oscillatory response of the system under study. in the sequel of this work, (12) will be studied in the case of unforced regime, to say, for the external exciting function ),,,( uuutf  equal to zero. iii. exact analytical solution for the nonlinear oscillations equation this part determines for the unforced oscillatory regime, that is to say, 0),,,( uuutf  , the exact analytical solution for the equation of motion following the under-damped, critical damped, and over-damped responses of the mechanical system under question. in doing so, (12) becomes for unforced motion: 2 2 2 ( 1) ( / ) 0 o uu l u uu l ul w+ + + =   as can be seen easily, the preceding painlevé equation has 0)( tu as trivial solution. in the usual standard form, this equation becomes: [ ] 2( 1) / ( / ) 0 o u l u u u l ul w+ + + =   (13) with 0)( tu . this second order autonomous differential equation can be viewed as a nonlinearly damped equation. the damping force is a nonlinear function in both the time history of response ( )u t and the velocity ( )u t . the dependence on the variable response ( )u t introduces a nonlinear newtonian singularity at the origin as noted in central forces. the dependence on the velocity includes a combination of linear and quadratic damping terms. in this perspective (13) consists of an attractive problem to be investigated to learn more about the qualitative oscillatory dynamics of the system around the singular point origin from a viewpoint of phase plane analysis which is not the topic of the following research work. so, only a quantitative analysis of (13) will be performed concerned in this study. the graph in figure 1 illustrates the oscillatory behavior of (13) subject to arbitrary initial conditions u(t=0)=5, and 1)0( tu , from t=0 to t=20, obtained by numerical integration. the simulation is run by using matlab's routine ode45 which exploits runge-kutta methods. the parameter values are fixed at 987.0l , 01.0 , and 1o . fig. 1. a typical behavior of (13) illustrating the oscillatory nature of the mathematical model. in the following section, the ability of the developed theoretical model to mathematically exhibit various responses of the damped nonlinear oscillatory dynamics of the system under investigation is proved. to do so, (13) will be solved in closed form exact solution by using suitable initial conditions that satisfy the dynamics of the nonlinear viscoelastic system of interest. engineering, technology & applied science research vol. 4, no. 6, 2014, 714-723 718 www.etasr.com monsia and kpomahou: simulating nonlinear oscillations of viscoelastically damped mechanical systems a. reduction of the nonlinear oscillatory equation to the damped linear harmonic equation it is well known in mathematics that the range of nonlinear evolution equations that can be analytically solved in the form of elementary standard functions is very limited [23]. so, the objective to find exact solutions of nonlinear evolution equation leads often to the question about the explicit integration of this equation [23-25]. in this perspective, the painlevé analysis may be performed in order to conclude on the integration of this equation [23-25]. however, following kudryashov [25], the determination of exact solutions of nonlinear evolution equation can be investigated without having to apply successfully the painlevé test. here, the governing equation (13) under question is a typical equation of painlevé which has been, according to keckic [18, 19], integrated by quadratures . hence, the problem of integrability of (13) in terms of elementary standard functions is unnecessary to be considered again in this paper. some equations similar to (13) in terms of elementary functions have recently been solved on the basis of mathematical transformations leading to a riccati equation or a damped linear harmonic equation [12-15, 22]. in the present work, (13) will be turned in the damped linear harmonic oscillatory equation. hence, to solve (13) in the form of standard functions, a change of variable is required for the expected oscillatory solutions. performing the following suitable substitution: ly u= equation (13) transforms after a few algebraic manipulations, into: 2 0 o y y yl w+ + =  (14) equation (14) is the well known classical linear second order evolution equation previously noted as (4). therefore, the general solution of (13) becomes: [19] 1/( ) ( ) lu t y t= (15) where )(ty designates the general solution of (14) a mathematical analysis of (14) indicates that the nature of (15) solution depends on the relative magnitudes of the damping factor λ and the stiffness module, to say, the natural frequency ωο. in other words, the nature of solution depends on the roots of characteristic equation: 2 2 0 o r rl w+ + = associated with (14), that can be real or complex numbers. so, three damping modes of vibration should be distinguished. b. exact analytical solution for over-damped nonlinear response this case corresponds to a strong damping [6, 26], that is, a relative large damping where 2 o l w> . the roots 1r and 2r of the characteristic equation are real, distinct and negative. the solution of (14) becomes: 1 1 2 2 ( ) exp( ) exp( )y t a r t a r t= + where: 1 (1 ) / 2r l d= + and 2 (1 ) / 2r l d= with: 2 2 1 4 o d w l= 1a and 2a are two constants of integration defined by the initial conditions. assuming that the conditions ( ) o u t u= , and ( ) o u t v= , when 0t = satisfy the past history of the displacement, and taking into consideration (15), the time history of the displacement can be written in the explicit analytical expression: ( ) exp( / 2 ) o u t u t ll= ⋅ 1/ 2 2 2 2 2 2 2 2 42 ( ) sinh( ) 1 2 ( ) (16) 4 4 4 cosh( ) 2 l oo o o o o tlv u t l w l l w l w l w + + é é ùù ê ê úú ê ê úú ê ê úú ê ê úú ê ê úú ê ê úú ê ê úúë ë ûû c. exact analytical solution for critically-damped nonlinear response in this case 2 , o l w= the two solutions of the characteristic equation coincide and then, the solution of (14) is given by: 1 2 ( ) ( ) exp( / 2)y t b t b tl= + where 1b and 2b are real constants determined by initial conditions. proceeding in the same way for the initial conditions: ( ) o u t u= , and ( ) o u t v= , when 0t = and using (15), the solution of the equation of motion becomes [ ]1/ (17)( ) exp( / 2 ) 1 ( / / 2) l o o o u t u t l lv u tl l= + + d. exact analytical solution for under-damped nonlinear oscillations this case assumes a relative weak damping, to say, 2 o l w< . here, the roots of the characteristic equation are complex numbers. therefore, the time history of the response engineering, technology & applied science research vol. 4, no. 6, 2014, 714-723 719 www.etasr.com monsia and kpomahou: simulating nonlinear oscillations of viscoelastically damped mechanical systems of the vibrating viscoelastic system, under the same initial conditions taking into account the past history of the displacement: ( ) o u t u= , and ( ) o u t v= , when 0t = can, for: 1 2 ( ) ( cos sin ) exp( / 2)y t c t c t tw w l= + where 2 2 / 4 o w w l= , and, 1c and 2c are two constants of integration fixed by the initial conditions, take the explicit analytical form: ( ) exp( / 2 ) o u t u t ll= ⋅ 1/ 2 2 2 2 2 2 1 ( )( ) sin( / 4 ) cos( / 4 ) (18) 2/ 4 l o o o oo lv t t u l w l w l w l é ù ê ú ê ú ê úë û + + iv. numerical applications of the model the aim of this part is to develop numerical solutions in order to demonstrate the ability of the mathematical model to be used in numerical simulations. in doing so, analytical solutions are validated against numerical results. numerical integration solutions have been obtained by using the ordinary differential equation solver ode45 and ode15s available in matlab package. matlab routine ode45 uses the fourth-order runge-kutta explicit procedure. the integration function uses a variable integration step size to provide the needed accuracy as minimizing computation time. the matlab ordinary differential equation solver ode15s is based on an implicit method. it is a multistep solver that needs the solutions at numerous previous time points in order to estimate the current solution. in this perspective, (13) should be written in state-space representation, to say, represented in terms of a set of firstorder differential equations. therefore, defining the state variables: 1 ( ) ( )x t u t= , 2 ( ) ( )x t u t=  the following system of two first-order differential equations may be obtained: 21 2 2 2 2 1 2 1 ( ) ( ) ( ) ( 1) / ( / ) o x t x t x t l x x x l xl w = =   (19) in this form, numerical integration of (13) becomes more appropriate to be implemented as m-files in matlab. figures below show the results of numerical simulation of (13). numerical solution is plotted on the same graph as the analytical solution. whereas the exact analytical solution is plotted in solid line, the numerical result is graphed in circles. the mean squared error is calculated with matlab mse function to quantify the discrepancy between model predictions and numerical results. a. numerical results for overdamped nonlinear response the graph of the numerical solution for over-damped nonlinear regime is compared to that of the exact analytical solution (16) in figure 2 over the time range from 0t to 20t under the initial conditions (0) 5u = and 1)0( u . numerical results are obtained by using the matlab function ode45 for reasonable values of model parameters fixed at 1.999,l = 3 , and 9998.0o to produce the expected response. the calculated value of the mean squared error provided by matlab mse function is mse=6.5189e-010 . fig. 2. comparison between analytical (solid line) and numerical (circles) solutions for over-damped nonlinear response b. numerical results for criticallydamped nonlinear response figure 3 shows the comparison of the numerical solution with the exact analytical solution (17) of (13) subject to the initial conditions 1.0)0( u and 5.0)0(  ovu , over the time range from 0t , to 20t . reasonable model parameter values for this simulation are 5.1l , 2 , and then 1o . matlab routine ode45 has been used for the simulation. the mean squared error calculated is mse=7.3336e-010 . fig. 3. simulation results of the numerical solution compared with the exact analytical solution for critically-damped regime. engineering, technology & applied science research vol. 4, no. 6, 2014, 714-723 720 www.etasr.com monsia and kpomahou: simulating nonlinear oscillations of viscoelastically damped mechanical systems c. numerical results for underdamped nonlinear oscillations figure 4 compares the numerical solution to the exact analytical solution (18) of (13) under the initial conditions that 01.1)0( u , and 94.0)0( u , over the time interval [ ]0, 20 . here, matlab routine ode15s has been used to run the numerical simulation. reasonable system parameters that generate the expected system response are: 3/1l , 5.0 , and 7.0o . the mean squared error computed using the matlab mse function is mse=8.6863e-008 . matlab intrinsic function ode15s has been used here since ode45 becomes very inefficient. it may be suspected that, for some values of the stiffness rising parameter l , as the damping factor  becomes more small compared with the frequency o2 , (13) becomes more stiff. fig. 4. comparison of analytical and numerical solutions for underdamped oscillation v. discussions this section is devoted for analyzing model predictions and demonstrating the validity of the current mathematical model. the stability character of solutions predicted by the model is also analyzed. the model predictions are discussed on the basis of numerical results presented in the preceding section. a. analysis of model predictions vibrating material systems in real operating situation experience, as it is well mentioned previously, large deformations and viscoelastic behavior. so, their dynamics is characterized by a damped nonlinear oscillation. in this context, a reliable theory devoted for modeling the damped nonlinear oscillatory dynamics of these systems should, at least, have the ability to handle some fundamental nonlinearity problems, and predict all of three damping modes of oscillation known for a real damped oscillatory system. consequently, the following subsections investigate the aptitude of the proposed mathematical model to satisfactorily reflect these three damped oscillation responses. 1) over-damped response analysis the graphs in figure 2 illustrate the over-damped behavior of the proposed model. it can be seen, as expected, that after attaining its maximum value, the time history of the displacement u(t) declines gradually without oscillations to approach asymptotically equilibrium zero value with time. the time history of response u(t) of the system presents only, as expected again, one maximum value. analytical result, to say, solution (16) shows that the system response has a hyperbolic behavior modulated by decay exponential, similarly to the over-damped linear harmonic oscillator response, but raised to the l/1 th power. equation (16) shows that the rate of decay is not only proportional to the damping factor λ, but depends also on the stiffness nonlinearity rising parameter l . so, it may be possible to use this parameter to control the oscillatory response amplitude of the system concurrently with the damping factor λ. 2) critically-damped response analysis the curves in figure 3 show that the time dependent displacement )(tu increases during the first time period to reach a single maximum, followed by an exponential decaying to asymptotically approach equilibrium zero value with time. here again, the rate of decay depends not only on the damping coefficient λ, but also on the stiffness nonlinearity parameter l , and the same preceding remark is again valid . 3) under-damped response analysis equation (18) shows that the under-damped response predicted by the mathematical model consists of a product of sinusoidal oscillations with a decaying exponential behavior, raised to the l/1 th power. this prediction is illustrated by the curves in figure 4 showing qualitatively the dynamic behavior of under-damped mechanical systems. the curves display a decaying sinusoidal response in which the amplitude of successive peaks decreases to finally stabilize asymptotically to equilibrium zero value with time. it may be noted that following the parameter values selected the oscillations are only occurred over a brief time range. as mentioned previously, the decaying rate of the displacement is not only proportional to the damping factor λ, but depends also on the stiffness nonlinearity parameter l . this demonstrates that the damped oscillatory dynamics of the mechanical system under investigation can be again controlled from the magnitude of the stiffness rising parameter .l this again means that an assessment of the time constant 2l lt = characterizing the time displacement exponential decay may provide more info not only about the damping degree, but also on the stiffness strength of the investigated mechanical system. moreover, the formula of t shows that the stiffness nonlinearity increases or decreases as the damping factor λ respectively increases or decreases. so, the current model allows simultaneously the enhancement of stiffness nonlinearity and damping of the mechanical system under question. b. stability analysis of damped responses the above numerical simulations have shown that the system behavior relative to all of three damping modes of oscillation previously studied converges in the case where the oscillatory solution (18) is globally defined for 0t , asymptotically to equilibrium zero value at an exponential rate engineering, technology & applied science research vol. 4, no. 6, 2014, 714-723 721 www.etasr.com monsia and kpomahou: simulating nonlinear oscillations of viscoelastically damped mechanical systems of decay. exact analytical results, that is to say (16), (17) and (18), determining the system response for over-damped, critically-damped and under-damped regimes respectively, indicate moreover that the system response tends to zero when the time t . therefore, it may be concluded that the damped nonlinear dynamics response of the system under study has an asymptotic stability character. this exponential asymptotic stability is not significantly sensitive to the initial conditions. as a consequence, for the long time system behavior, a determination of initial conditions is not necessary to be known with accuracy. it is worth to note that this stability character depends not only on the damping factor  as suggested by the classical second order damped linear oscillatory equation, but also on the hardening parameter l . the positive value of l is secured by the definition of the nonlinear restoring force function luu )( that should obey in the bauer's theory [7] to the linear hooke's law when 0)( tu . next, special limits of (13) governing the nonlinear oscillatory dynamics of the one-dimensional viscoelastic system of interest will be established in order to demonstrate the ability of the developed mathematical model to capture some well known linear and nonlinear oscillatory dynamics models. c. limiting oscillatory equations the objective of this section is to develop some special limits for (13) to demonstrate that the proposed mathematical model captures the classical damped linear harmonic oscillatory equation and the lambert nonlinear oscillatory equation with well-known analytical exact solutions as special cases. one special limit of the current mathematical model may be obtained by substituting the specific value 1l of the stiffness nonlinearity parameter into (13). in doing so, (13) becomes: 2 0 o u u ul w+ + =  (20) it is easy to note that (20) is identical to the well known classical damped linear harmonic oscillator (4) previously noted, which is extensively studied in academic textbooks [26] and widely used in engineering design calculations. the damped linear harmonic oscillator (20) has a well-known exact analytical solution showing all of three damping modes of vibration following the magnitude of the damping compared to that of the natural frequency [6, 26]. another special limit of (13) is achieved by setting the damping factor 0 . as a result, (13) transforms into: 0)1( 22  u lu u lu o  (21) equation (21) is the second order lambert oscillatory equation with well-known exact analytical solution [27]. equation (21) is explored by he [27] as a strongly nonlinear oscillatory equation from lambert. following pellicer and solà-morales [28], this limiting case has a significant interest for the investigated physical problem, since the special limit 0 m b  means that the system mass m is large relative to the damping coefficient b. substituting 0 directly into (18), modeling the under-damped nonlinear oscillatory system response, it becomes possible to obtain as exact analytical solution for the lambert oscillatory equation the following explicit expression: [ ]1/ (22)( ) cos( ) (1 / )( / ) sin( ) l o o o o o o u t u t lv u tw w w= + or   loo tdtctu /1)sin()cos()(   (23) by setting louc  and o o l o vlud  1  the formula (23) is the same analytical solution found by he [27] using a variational approach. putting moreover 1l , directly into (22) or (23), the well-known sinusoidal response for the second order undamped harmonic oscillator is found. therefore, the above proves mathematically the aptitude of the developed model to capture the lambert oscillatory equation as special case. it is worth noting that, compared to solutions of the classical damped linear harmonic equation, the argument of exponential functions in the developed nonlinear solutions differs by a factor of l which represents the stiffness rising parameter. thus, the factor l appeared to be the fundamental parameter controlling the nonlinearity of the oscillatory dynamics of the system under study. from the above, it can be concluded that the proposed nonlinear oscillatory viscoelastic model captures in mathematical fashion the classical damped linear harmonic oscillator as a special case. the current mathematical model captures not only the classical second order damped linear harmonic equation as a subcase, but it has the ability to incorporate also the lambert nonlinear oscillatory equation as a special case. d. validation of the mathematical model the validity of the current mathematical model for predicting and numerically simulating the damped oscillatory response of a one-dimensional mechanical system exhibiting large deformations and viscoelastic properties is analyzed in this section. according to [26, 29, 30], exact analytical solutions found for the developed model are validated against numerical results. in this regard, exact analytical solutions determined for over-damped, critically-damped and underdamped regimes are compared in figures (2), (3) and (4) with corresponding solutions carried out by numerical integration, respectively. so, figure (2) shows that the exact analytical solution (16) matches associated numerical solution very well. this is confirmed by the low value of the mean squared error, 6.5189 010,e measuring the existing discrepancy between these two results. figure 3 leads to the conclusion that both exact analytical solution (17) and numerical result for critically-damped system response are in very good agreement as underlined by the mean squared error engineering, technology & applied science research vol. 4, no. 6, 2014, 714-723 722 www.etasr.com monsia and kpomahou: simulating nonlinear oscillations of viscoelastically damped mechanical systems 7.3336 010.mse e= a very good agreement is also observed regarding the comparison of exact analytical solution (18) with numerical result for under-damped response of the studied system, as can be noted by the value 0086863.8 e for the mean squared error. besides, (15) is the exact solution, according to keckic [18], found by painlevé. the above confirms the reliability and accuracy of determined exact analytical solution of (13) and as a consequence, the ability of the developed mathematical model to numerically simulate the results of possible experiments [26]. on the other hand, the preceding study on special limits of the proposed model demonstrates its powerfulness to be a nonlinear extension of the well known classical damped linear harmonic oscillator extensively used in engineering design calculations and to incorporate the lambert oscillatory equation as special case. in doing so, the developed model offers its mathematical ability to be applied for simulating all of three damped oscillatory responses of a one-dimensional viscoelastic system under large deformations. v. conclusions the viscoelastically damped linear harmonic equation is well known to be only applicable for a small range of deformation of mechanical systems. in these conditions, its use to characterize flexible mechanical systems in engineering applications may be the cause of catastrophe. in real working situations, mechanical systems undergo large deformations and show viscoelastic behavior. this involves the necessity to build reliable and satisfactory models for predicting, simulating and analyzing their response to an excitation. the present work was intended to develop a mathematical model that may be used in numerical simulations of the oscillatory dynamics of a onedimensional viscoelastic system experiencing finite deformations. the reliability of the proposed model is secured in the regard that it takes into consideration the nonlinearity properties of a mechanical system undergoing large deformations and viscoelastic behavior. in this perspective, a second-order first-degree painlevé equation was developed from the application of bauer's theory to model the nonlinear oscillatory dynamics of the system of interest. this equation is an extension of the damped linear harmonic oscillator equation widely employed in engineering design calculations for the nonlinear regime of behavior of real mechanical systems. the developed mathematical model captures also the lambert nonlinear oscillatory equation as a special case. it is found that the obtained painlevé evolution equation successfully models the dynamics of over-damped, critically-damped and underdamped nonlinear behaviors of a mechanical system under large deformations and viscoelastic behavior. the presented mathematical model provides the ability to control the damped oscillatory dynamics of the system under investigation concurrently from the damping coefficient or stiffness nonlinearity parameter. an estimation of the time constant characterizing the exponential decay of the time history of the displacement can, as shown by the current mathematical model, give knowledge not only on the damping strength, but also regarding the stiffness degree of the mechanical system of interest. numerical and analytical results demonstrated that the proposed damped nonlinear oscillatory equation may be satisfactorily used in numerical simulations of viscoelastic oscillators. in this sense, the bauer's theory significantly contributes to a better understanding of mathematical modeling of viscoelastic systems. this theory represents the nonlinear dynamics of viscoelastic systems in the form of painlevé equation which is subject of intensive investigation in mathematics. hence, the research work developed in this paper confirms the nature of the bauer's theory to be a powerful mathematical tool to model satisfactorily the nonlinear dynamics of mechanical systems. monsia's formulation of bauer's theory may permit also to formulate painlevé equation of the third order or in general of the nth order to describe mechanical systems by considering, instead of the linear kelvin-voigt constitutive law, the general setting of the linear viscoelastic constitutive law expressed as a single linear ordinary differential equation of the nth order relating the total strain and its time derivatives with the total stress. references [1] e. i. rivin, “use of stiffness /damping/natural frequency criteria invibration control”, iftomm world congress, besanson, june 2-6, 2007 [2] f. j. lockett, nonlinear viscoelastic solids, academic press, 1972 [3] y. m. de haan, g. m. sluimer, “standard linear solid model for dynamic and time dependent behaviour of building materials”, heron , vol. 46, no. 1, pp.49-76, 2001 [4] h. h. hilton, s. yi, “generalized viscoelastic 1-dof deterministic nonlinear oscillators”, nonlinear dynamics, vol. 36, no. 2-4, pp. 281298, 2004 [5] s. laroze, mécanique des structures. tome 3, masson, 1992 [6] m. d. monsia, “a mathematical model for predicting the relaxation of creep strains in materials”, physical review & research international, vol.2, no. 3, pp.107-124, 2012 [7] r. d. bauer, “rheological approaches of arteries”, biorheology suppl. i, vol. 1, pp.159-167, 1984 [8] g. kerschen, k. worden, a. f. vakakis, j-.c. golinval, “past, present and future of nonlinear system identification in structural dynamics”, mechanical systems and signal processing, vol. 20, no. 3, pp.505-592, 2006 [9] h. jrad, j. l. dion, f. renaud, i. tawfiq, m. haddar, “experimental characterization, modeling and parametric identification of the non linear dynamic behavior of viscoelastic components”, european journal of mechanics-a/solids, vol. 42 pp. 176-187, 2013 [10] h. jrad, j. l. dion, f. renaud, i. tawfiq, m. haddar, “a new approach for nonlinear generalized maxwell model for depicting dynamic behaviour of viscoelastic elements-parameters identification and validation”, 18th symposium of vibrations, shocks and noise, france, july 3-5, 2012 [11] m. d. monsia, “a simplified nonlinear generalized maxwell model for predicting the time dependent behavior of viscoelastic materials”, world journal of mechanics, vol.1, no. 3, pp. 158-167, 2011 [12] m. d. monsia, “modeling the nonlinear rheological behavior of materials with a hyper-exponential type function”, mechanical engineering research, vol.1, no. 1, pp. 103-109, 2011 [13] m. d. monsia, “a nonlinear mechanical model for predicting the dynamics response of materials under a constant loading”, journal of materials science research, vol.1, no. 1, pp. 90-100, 2012 [14] m. d. monsia, y. j. f. kpomahou, “predicting the dynamic behavior of materials with a nonlinear modified voigt model”, journal of materials science research, vol. 1, no. 2, pp. 166-173, 2012 [15] m. d. monsia, y. j. f. kpomahou, “a theoretical characterization of time dependent materials by using a hyperlogistic-type model'”, mechanical engineering research, vol. 2, no. 1, pp. 36-43, 2012 engineering, technology & applied science research vol. 4, no. 6, 2014, 714-723 723 www.etasr.com monsia and kpomahou: simulating nonlinear oscillations of viscoelastically damped mechanical systems [16] l. cveticanin, “oscillator with strong quadratic damping force”, publications de l'institut mathématique, nouvelle série, vol. 85, no. 99, pp. 119-130, 2009 [17] m. m. rashidi, a. shooshtari, o. anwar bég, “homotopy perturbation study of nonlinear vibration of von karman rectangular plates”, computer & structures, vol. 106-107, pp. 46-55, 2012 [18] j. d. keckić, “additions to kamke's treatise ,vi: a nonlinear second order equation”, publications de l'institut mathématique, nouvelle série, vol. 19, no. 33, pp.81-82, 1975 [19] j. d. keckić, “additions to kamke's treatise ,vii: variation of parameters for nonlinear second order differential equations”, ser. mat. fiz., vol. 544-576 , pp. 31-36, 1946, available at: http://pefmath2.etf.bg.ac.rs/files/100/549.pdf [20] p. painlevé, “mémoire sur les équations différentielles dont l'intégrale générale est uniforme”, bull. soc. math. france, vol. 28, pp. 201-261, 1900 [21] l. roth, “on the solutions of certain differential equations of the second order”, phil. mag. vol. 32, no. 211, pp.155-164, 1941 [22] m. d. monsia, “a mathematical model for predicting the nonlinear deformation response of viscoelastic materials”, international journal of applied mathematics and mechanics, vol. 8, no. 16, pp. 22-30, 2012 [23] r. conte, “partial integrability of the anharmonic oscillator”, journal of nonlinear mathematical physics , vol. 14, no. 3, pp. 462-473, 2007 [24] r. conte, m. musette, the painlevé handbook, springer, 2008 [25] n. a. kudryashov, “nonlinear differential equations with exact solutions”, arxiv:nlin/0311058v1[nlin. si] [26] d. w. jordan, p. smith, nonlinear ordinary differential equations, oxford university press, 2007 [27] j.-h. he, “some asymptotic methods for strongly nonlinear equations”, international journal of modern physics b, vol. 20, no. 10, pp.11411199, 2006 [28] m. pellicer, j. solà-morales, “analysis of a viscoelastic spring-mass model journal of mathematical analysis and applications, vol. 294, no. 2, pp. 687-698, 2004 [29] l. cveticanin, “vibrations of the nonlinear oscillator with quadratic nonlinearity”, physica a: statistical mechanics and its applications, vol. 341, pp. 123-135, 2004 [30] r. jauregni, f. silva, “numerical validation methods” in numerical analysis-theory and application , intechopen, 2011, available at: www.intechopen.com/download/pdf/19916 microsoft word etasr_v12_n3_pp8707-8711 engineering, technology & applied science research vol. 12, no. 3, 2022, 8707-8711 8707 www.etasr.com oria & palconit: performance investigation of an inflatable solar dryer with steel-can solar air … performance investigation of an inflatable solar dryer with steel-can solar air heater for drying coffee and corn charity l. oria school of engineering, ateneo de davao university davao city, philippines and college of engineering, sultan kudarat state university sultan kudarat, philippines charityoria@sksu.edu.ph eleonor v. palconit school of engineering ateneo de davao university davao city, philippines evpalconit@addu.edu.ph received: 5 april 2022 | revised: 14 april 2022 | accepted: 18 april 2022 abstract-coffee and corn are the two most important crops in the philippines. one of the most critical stages, where crop management can be improved, is drying. in coffee, a moisture level of 12% is optimum for minimizing quality degradation throughout lengthy storage periods, whereas, corn requires a moisture content of 13%. with the demand for simple and costeffective drying technologies, an inflatable solar dryer (isd) was created and adapted using a hohenheim-type solar tunnel and salvatierra-rojas’ study. a mesh wire served as a drying space and was placed inside the isd to avoid moisture condensation. a clear polyethylene (pe) film is attached to a reinforced black polyvinyl chloride (pvc) film by a zipper to produce a drying tunnel. the tunnel does not require a foundation because the pressure generated by a solar-powered fan sufficiently stabilizes it. the isd also incorporated steel cans as solar air heaters to boost the temperature of entering air into the chamber and gradually provide heated air temperature to the bottom parts of the crops. crops were scattered on the mesh wire and blended with a rake. drying in the open sun was also done in parallel for comparison purposes. after protracted drying, both crops reached the required moisture content. the trial found that the weight of both crops was affected by the drying duration. the difference in weight for coffee is 1.1kg, while for corn is 0.5kg exhibiting a significant advantage in isd. keywords-postharvest management; corn; coffee; inflatable solar dryer; solar air heater; solar-powered fan i. introduction agriculture is vital to the economies of developing countries as it is the primary source of food, currency, and employment for rural populations. on the other hand, agriculture and land-use reforms are critical for achieving food security, poverty alleviation, and overall sustainable development. according [1], farming employs 28.4% of the workforce in the philippines and contributes an average of 10.18% of the country's gdp. given this percentage, the philippines continues to import agricultural products. corn and coffee are two essential crops imported in the philippines. according to the department of agriculture (da), the philippines imports 75,000 mt to 100,000 mt of dry coffee beans from vietnam and indonesia each year at p7 billion to p10 billion [2]. at the same time, corn imports averaged 604,000 tons from 2017 to 2019. based on the data from the united state department of agriculture (usda), corn imports are predicted to remain steady from 2021 to 2022 as a result of improved local production and ample feed grain inventories [3], while the country's coffee production would increase to 214,626 mt by 2022, based on the philippine coffee roadmap [2]. by undertaking pest and disease management activities and providing seeds, fertilizers, and pesticides, many government agencies along with the private sector are working to boost the country's corn and coffee production. postharvest management, such as the provision of dryers, was, on the other hand, negligible, even though it is equally vital in the entire production of crops. according to [4], post-production losses in the country occur mainly in handling and drying, resulting in delayed, incomplete, or inefficient drying. open sun drying (osd) was introduced for agricultural product preservation and storage. this method of drying is still widely used even today. however, osd faces many inherent limitations like overexposure, which causes food damage, high losses in yield production due to insects, rodents, and birds, longer drying time, and unpredictable climate conditions [5]. in the philippines, osd is the main practice of the farmers. in fact, with the absence of drying facilities, many crops, including coffee beans and corn, are dried on highways or road pathways where vehicles may run over and ruin the products. other corn and coffee producers, on the other hand, choose to trade their crops immediately after harvesting to prevent farm losses and additional expenses. it can be noted that freshly picked coffee beans and corn when sold will have a low farm gate price as compared to dried crops. locally, newly gathered, or wet corn is priced at php.12.00 at the farm gate, whereas dry corn with an optimal moisture content of 13% is priced at php.17.00. the farm gate price for newly picked coffee beans is php.30.00, while the farm gate price for dry coffee with an optimal moisture content of 12% is php.110.00. with such corresponding author: charity l. oria engineering, technology & applied science research vol. 12, no. 3, 2022, 8707-8711 8708 www.etasr.com oria & palconit: performance investigation of an inflatable solar dryer with steel-can solar air … disadvantages and differences between the price of wet and dry crops, the need for solar dryers and their implementation has drawn the attention of researchers. many types and models of solar dryers have been studied and developed worldwide. however, in the philippines, there are limited published articles about the implementation of solar dryers. the latest solar dryer study done in the country was the isd by salvatierra-rojas in 2017, using rice as the commodity [6]. the dryer gives a promising result in drying rice in humid climates like in philippines. furthermore, the study demonstrates that the isd is an ideal dryer for small-scale farmers due to its low-cost materials and simple operation. therefore, the goal of this study is to employ such an isd to dry corn and coffee beans. the results were compared to the performance of osd in terms of drying time and final weight when reaching the desired moisture content of 13% for corn [7] and 12% for coffee beans [8]. recycled steel-can solar air heater (sah) was integrated into the isd to increase air inlet temperature and determine its contribution to the isd by closely monitoring the inlet, mid, and inside humidity and temperature. mesh wire was also placed inside the isd to prevent condensation. ii. materials and methods a. design of the inflatable solar dryer the isd was based on [6], which was constructed from the hohenheim-type solar tunnel [9] that has been developed and commercialized to dry different agricultural products in different climatic conditions. unlike the hohenheim-type dryer and the salvatierra-rojas study, which laid the grains barely in black pvc films inside the chamber, this study incorporated an elevated mesh wire inside the isd chamber to allow double pass of hot air into the lower and upper part of the dried products and to allow better circulation of the moist inside the chamber. the dryer is still collapsible, just like in [6]. the isd drying chamber comprises 150µm uv-transparent polyethylene (pe) film and is joined to a 0.52mm reinforced black pvc film by a heavy-duty zipper. a heavy-duty zipper is positioned and sewn along the margins of both plastic layers. the entire unit is placed directly on the ground. the tunnel does not require structural support and is effectively stabilized by air pressure from inflation. one 220v solar-powered fan blows air into the tunnel, which is then expelled through the opposite side's vents. the inclusion of renewable energy was based on the findings of [6], which recommended that more research should focus on incorporating photovoltaic power supply for the ventilators to enable off-grid operation [6]. the chamber's tested drying space is 2.5m long and 1.5m wide. to prevent moisture condensation inside the isd chamber, this study used a 15×15cm mesh wire supported by four pieces of 2×2ft. wood. the crops were then spread at the height of 20mm on top of the mesh wire and were mixed with a rake to minimize overheating of the top layer exposed to the sun. b. design of the solar air heater (sah) the sah was used in the study to raise the temperature of the air entering the isd. the sah was made out of 390ml steel cans. for the first layer, 49 pieces of steel cans were arranged vertically in 7 groups and for the second layer, 30 pieces of the same cans were laid in 5 groups. there was a gap between the cans for the second layer to allow air circulation inside the sah. the sah's frame was made of a 5mm plyboard and was measured to be 0.905m in length, 0.6m in width, and 0.2m in height. the sah has round perforations on one end to allow the incoming air to pass through. on the opposite end of the sah, a single rectangular hole connects to the fan and isd through a 10mm foam insulator. the sah was painted black as a coating material to increase its thermal operation [10]. the sah's top cover and glazing system were made of 5mm transparent glass to restrict the steel cans' radiant and convective heat absorbance. four heavy-duty caster wheels were installed at the bottom of the sah to make it portable and easy to transport. a two-layer design composed of insulator foam and black pvc film was stitched together, and magic tape was attached to link the sides and form a tunnel to connect the sah, fan, and isd, as shown in figure 1. table i shows the design parameters, such as the overall size of the sah, ventilator size, and the overall size of the isd. fig. 1. design of isd and integrated sah with a solar powered fan. engineering, technology & applied science research vol. 12, no. 3, 2022, 8707-8711 8709 www.etasr.com oria & palconit: performance investigation of an inflatable solar dryer with steel-can solar air … table i. design parameters of the experimental setup design parameters details solar air heater (sah) type steel can solar energy heat absorber overall size of the sah 0.905m length × 0.6m width × 0.2m height overall size of the steel can heat absorber 0.755m length × 0.6m width × 0.15m height ventilator type of ventilator solar-powered fan diameter of ventilator 16 inches ventilator 220 v ac/dc airflow rate 1.7 m/s inflatable solar dryer (isd) overall size of the isd 2.5m length x 1.5m width height of the inflated tunnel 0.75m mesh wire drying space overall size of the drying space 2.1m length x 1.1m width height from the ground 0.15m capacity (fresh) 100 kg c. drying experiment the dryer was used in the philippines' sultan kudarat province (6.5069° n, 124.4198° e). the dryer was set up in the middle of a paddy field that was completely unoccupied. the crops used in the trials were robusta coffee and yellow corn. each experiment trial was conducted a day after the crops were harvested. the initial moisture content of both crops and their initial weight were measured at the start of the drying experiment. similarly, before the crops were set aside throughout the night or during heavy rains, the weight and the moisture content were tested again to see how much had changed over the drying period within the day. the trial began at 7 a.m. and ended at 5 p.m. every day, i.e. for a daily duration of 10 hours. the coffee had a moisture content of 40.5% on a wet basis, whereas the corn had 38.9%. during each experiment trial, the solar-powered fan was permitted to run continuously within the drying duration. at 1-hour intervals, the crops were dried and scattered with a rake. each dryer had three batches of crops to dry. the osd was used as a control method, with each batch containing 16.3kg of coffee beans and 16.9kg of corn. the sample crops were spread out on a black pvc film next to the isd with a bulk height of 20mm. the crops in the osd were mixed with a rake at the same time as the isd. the crops were kept aside throughout the night or when there was severe rain but were dried the next day until the ideal moisture content for each crop was reached. d. instrumentation of drying experiments to evaluate the study's goal, four essential tools were used. a 25kg capacity digital weighing scale was used to determine the initial and final weight of the crops, whereas a digital moisture content meter (ar991 kerro smart sensor digital grain moisture meter) was used to determine the moisture content. a self-logging humidity and temperature sensor (bside mini usb humidity temperature data recording logger) was mounted on the inlet, in the middle (in the fan, where the wind is blown), and on the isd chamber to determine the temperature and relative humidity as shown in figure 2. when linked to a computer, data were logged every 10s and were automatically generated and exported. e. statistical analysis t-test experimental design was conducted using the excel statistical software, with p values less than 0.05 considered significant. fig. 2. position of humidity and temperature sensor top view iii. results and discussion a. temperature and relative humidity (sah, fan, isd) the humidity and temperature loggers were positioned in three different locations in the dryer. the first location was in the sah, where there was incoming air, the second was next to the solar-powered fan to see if the steel can sah could boost the incoming air temperature, and the third was on the top of the crops inside the isd. the dryer's ambient temperature varied from 31 to 46ºc, 31 to 51ºc, and 31 to 70ºc respectively from the sah air inlet, alongside the fan, and within the isd. figure 3 shows the air temperature and humidity profile within the dryer over 10h, using the chosen intervention phase data. in general, there was a progressive temperature rise between the engineering, technology & applied science research vol. 12, no. 3, 2022, 8707-8711 8710 www.etasr.com oria & palconit: performance investigation of an inflatable solar dryer with steel-can solar air … sah input and the fan, but the most increase was between the fan and the isd. the highest temperature of the day was between 11 a.m. and 2 p.m. however, the temperature in the three places gradually declined after sundown, eventually approaching ambient temperature. the temperature rises in the dryer continued to be minimal due to evaporative cooling provided by the crops and more significant convective losses due to a higher difference in temperature out from ambient air. (a) (b) (c) fig. 3. the dryer's temperature and humidity at (a) sah air inlet, (b) the fan in the middle, (c) isd at the top of the crops. b. moisture content and drying behavior the moisture content of the crops during isd and osd drying is shown in table ii. under isd, coffee with an initial moisture content of 40.5% reached the ideal moisture content of 12% in 3 days (27h), while in osd, coffee with the same initial moisture content dried to 12% moisture content within 5 days (47h). for the corn, the crops placed in the isd with an initial moisture content of 38.9% dried to the target of 13% within a day, while when drying under osd, the crops with the same initial moisture content dried in 2 days (14h). the target moisture content of 12% for coffee and 13% for corn may be easily obtained by continuously drying. however, when the crops were retrieved from the dryer at night, remoistening occurred, resulting in an increase in moisture content overnight. on the other hand, remoistening becomes minimal to none once the target moisture content is obtained. table ii. moisture content in isd and osd products the moisture content of the products fresh product isd osd coffee 40.5% 12.00% 12.1% corn 38.9% 12.25% 12.76% c. weight the results of coffee weight shown in table iii and figure 4 revealed a significant difference with a p-value of 0.018 under isd and osd, with a difference of 1.1kg in the final weight of coffee after reaching the desired 12% moisture content. however, corn weight results in table iv show no significant difference. the difference in the final weight of corn after reaching the 13% moisture content is 0.5kg with a p-value of 0.09. this means that the product's drying time impacts the final weight when it reaches the target moisture content. table iii. t-test of weight of coffee dryer mean sd diff. t p-value interpretation isd 7.7 0.17 0.35 3.89 0.018 sig. osd 7.35 0.1 fig. 4. coffee weight with respect to time. table iv. t-test of weight of the corn dryer mean sd diff. t p-value interpretation isd 11.40 0.1 0.23 2.21 0.09 no sig. osd 11.17 0.14 d. drying duration and condensation phenomena the drying time is determined by the time it took for the ideal moisture content to be achieved. table v and figures 4-5 show the drying duration of coffee and corn under isd and osd. the difference in drying time between coffee and corn, 20h for coffee and 6h for corn, is significant for farmers looking to save revenue on labor and other expenses. condensation in the isd's floor was eliminated due to the mesh that acts as a drying surface inside the isd. condensation engineering, technology & applied science research vol. 12, no. 3, 2022, 8707-8711 8711 www.etasr.com oria & palconit: performance investigation of an inflatable solar dryer with steel-can solar air … happens when the temperature of the crops or the dryer's surfaces falls below the drying air's moisture content. without the mesh wire, the temperature of the crops will be higher at the top than at the bottom because the top layer of the crops is subjected to solar radiation and the temperature is enhanced by heat absorption. incoming air from the sah, on the other hand, reaches the bottom portion of the crops through the mesh wire and progressively dries the crops at the bottom. another strategy to avoid condensation from forming is to increase the mixing rate after sunrise to transport the warm top layer of the crops to the bottom layer. fig. 5. corn weight with respect to time. table v. drying duration of coffee beans and corn products moisture content drying duration (hours) dried product isd osd coffee 12.0% 27 47 corn 13.0% 8 14 iv. conclusion due to the erratic rainfall, drying crops, particularly corn and coffee, is difficult in the philippines, even during the dry season. to prevent such a situation, some farmers trade their products as soon as they are harvested (wet crops). however, because the market for freshly picked corn and coffee beans has poor farm gate prices, most farmers are drying their crops on roads and walkways to increase their income, even though this results in unclean and hazardous quality. the proposed isd can help with these issues since it preserves the crops from damage, high yield losses due to pests, prolonged drying times, and uncertain weather changes. the dryer is easy to transfer, fix, and set up in a new area. since it is made out of plastic and only has a few mechanical components, its simple design is easy to maneuver and maintain. the results of the trials reveal that 3 batches of 16.3kg coffee may be dried to an ideal moisture content of 12% on the third day or an exact period of 27h of drying. however, drying the same amount of coffee in the open sun takes 5 days or 47 hours. in the case of corn, the results demonstrate that 13% moisture content can be achieved in less than a day, or 8h, whereas it must be dried for a second day, or an equivalent of 14h, in the open sun. based on the data acquired throughout the testing, the drying time will considerably impact the weight of the crops in a way. the ventilators are turned off after 5 p.m., and the crops are retrieved from the dryers since this experiment should be based on farmers' actual practice of osd. further study should concentrate on integrating solar energy storage [11, 12] on the solar air heater to continuously heat the air entering the drying chamber, even during the night or when there is no sunlight. additionally, automatic control and notification of the condition of the dryer and dried products are necessary to avoid over-drying, which results in excessive moisture loss. acknowledgement this publication, and specifically the coffee commodity, was prepared under the grant funded by wcr under the philcafe cooperative agreement/grant no. 22107cs01609 funded by usda and led by acdi/voca. the authors would also like to thank the helpful research assistants, carissa oria and the rest of the group, ms. velessa jane dulin for assessing the results, and ms. rosela sazon for proofreading the article. references [1] statista research department, share of people employed in the agriculture industry in the philippines between 2019 and 2020. statista, 2021. [2] l. c. domingo, "philippine coffee industry gets boost," the manila times, manila, philippines, mar. 23, 2018. [3] p. corpuz, philippines: grain and feed annual. usda, 2020. [4] p. udomkun et al., "review of solar dryers for agricultural products in asia and africa: an innovation landscape approach," journal of environmental management, vol. 268, aug. 2020, art. no. 110730, https://doi.org/10.1016/j.jenvman.2020.110730. [5] j. b. hussein, m. a. hassan, s. a. kareem, and k. b. filli, "design, construction and testing of a hybrid photovoltaic (pv) solar dryer," international journal of engineering research and science, vol. 3, no. 5, pp. 1–14, may 2017, https://doi.org/10.25125/engineering-journalijoer-may-2017-4. [6] a. salvatierra-rojas, m. nagle, m. gummert, t. de bruin, and j. müller, "development of an inflatable solar dryer for improved postharvest handling of paddy rice in humid climates," international journal of agricultural and biological engineering, vol. 10, no. 3, pp. 269–282, may 2017, https://doi.org/10.25165/ijabe.v10i3.2444. [7] m. angelovič, k. krištof, j. jobbágy, p. findura, and m. križan, "the effect of conditions and storage time on course of moisture and temperature of maize grains," bio web of conferences, vol. 10, 2018, art. no. 02001, https://doi.org/10.1051/bioconf/20181002001. [8] e. m. kyaw, i. w. budiastra, sutrisno, and samsudin, "estimation of moisture content in liberica coffee by using near infrared spectroscopy," iop conference series: earth and environmental science, vol. 542, no. 1, apr. 2020, art. no. 012013, https://doi.org/10.1088/1755-1315/542/ 1/012013. [9] k. lutz, w. mühlbauer, j. müller, and g. reisinger, "development of a multi-purpose solar crop dryer for arid zones," solar & wind technology, vol. 4, no. 4, pp. 417–424, jan. 1987, https://doi.org/ 10.1016/0741-983x(87)90016-6. [10] n. b. khedher, "experimental evaluation of a flat plate solar collector under hail city climate," engineering, technology & applied science research, vol. 8, no. 2, pp. 2750–2754, apr. 2018, https://doi.org/ 10.48084/etasr.1957. [11] m. a. aichouni, n. f. alshammari, n. b. khedher, and m. aichouni, "experimental evaluation of nano-enhanced phase change materials in a finned storage unit," engineering, technology & applied science research, vol. 10, no. 3, pp. 5814–5818, jun. 2020, https://doi.org/ 10.48084/etasr.3616. [12] n. b. khedher, "numerical study of the thermal behavior of a composite phase change material (pcm) room," engineering, technology & applied science research, vol. 8, no. 2, pp. 2663–2667, apr. 2018, https://doi.org/10.48084/etasr.1824. microsoft word etasr_v13_n1_pp9819-9824 engineering, technology & applied science research vol. 13, no. 1, 2023, 9819-9824 9819 www.etasr.com lemsara et al.: seismic fragility of a single pillar-column under near and far fault soil motion with … seismic fragility of a single pillar-column under near and far fault soil motion with consideration of soil-pile interaction foudhil lemsara lgc-roi, department of civil engineering, faculty of technology, university of batna 2, algeria f.lemsara@univ-batna2.dz (corresponding author) tayeb bouzid lgc-roi, department of civil engineering, faculty of technology, university of batna 2, algeria tayeb.bouzid@univ-batna2.dz djarir yahiaoui lgc-roi, department of civil engineering, faculty of technology, university of batna 2, algeria d.yahiaoui@univ-batna2.dz belgacem mamen department of civil engineering, faculty of science and technology, university of abbès laghrour khenchela, algeria belgacem.mamen@univ-khenchela.dz mohamed saadi lgc-roi, department of civil engineering, faculty of technology, university of batna 2, algeria m.saadi@univ-batna2.dz received: 10 october 2022 | revised: 30 october 2022 | accepted: 31 october 2022 abstract the soil-structure interaction is a significant challenge faced by civil engineers due to the complexity potential in terms of seismic fragility evaluation. this paper presents a seismic fragility estimation of a single pier considering seismic ground motion types. furthermore, sand type, pile diameter, pier height, and mass variation were considered to estimate their effect on the seismic fragility of the concrete pier. incremental dynamic analysis was performed using a beam on a nonlinear winkler foundation model. the analysis model condition compared nearand far-ground motion effects. dynamic analysis and fragility assessment of the single-pier structure showed that low mass center produced less vulnerability of the concrete pier in the two cases of the sand type under nearand far-ground motions. the near and far earthquake simulations at complete failure probability had a difference of less than 5% when 0.65s<t1<1s and 2.4<t1/t2, but the opposite was shown when t1<0.5s and 3<t1/t2 were present together. keywords-soil-pile-structure interaction; incremental dynamic analysis; bnwfmodel; ground motion types; seismic fragility i. introduction under seismic loading, liquefiable soil increases the seismic fragility of expansion bearing, piles, and embankment soil. the fragility of common components, such as columns, depends on the overlying liquefiable sand. the effect of soil strength for clay and sandy sites on the seismic performance of skewed bridge components and its relation with the skew angle was studied in [1, 2]. the seismic fragility of a pile was studied with different seismic demands in [3]. the nonlinear winkler foundation model is widely used to study soil-pile and soilpile-structure interactions using nonlinear dynamic analysis [4]. in [5], a comparison of soil-structure interaction and fix-base model effects on a structure's seismic fragility was presented. engineering, technology & applied science research vol. 13, no. 1, 2023, 9819-9824 9820 www.etasr.com lemsara et al.: seismic fragility of a single pillar-column under near and far fault soil motion with … a near-fault earthquake severely damages structures more than a far-fault one. this comparison was investigated in [6] through a numerical simulation of the seismic damage of arch bridges with three earthquake indicators: area intensity, energy rate, and cumulative absolute velocity. the demand/capacity ratio of an arch bridge pier is higher under nearthan far-fault earthquakes [7]. in addition to [4], pushover analysis was used to study soil-pile and soil-pile-structure interactions in [8]. in a single pile, columns fail before pile foundations [9]. soil permeability can be considered a complex property due to its influence on seismic fragility with different soil types [10]. in [11], the impact of the soil-pile interaction on the seismic fragility of wharf structures was investigated by comparing two systems: with and without soil-pile interaction. most recent studies were based on the winkler foundation model to study the seismic fragility of the soil-pile-structure interaction (s-ps). this model is a good instrument for investigating the seismic fragility of concrete bridge-soil systems using stepwise and lasso regression [12]. in [13], the mitigation of pile group spacing on scour and liquefaction effects was studied. the same results with [5] were shown in [14] considering a skewed bridge. in [15], the effect of irregular configuration and the stiffness of the substructure on the vulnerability of the bridge was shown. the soil-pile and soil-pile-structure interactions were investigated more comprehensively in [16]. the effects of the soil-structure interaction on the seismic fragility of a bridge were investigated in [17], considering the effects of wave passage. the selection of foundation type is an essential key for the construction of a superstructure and estimating its seismic fragility. the pile foundation is an improvement in superstructure performance compared to the shallow foundation [18]. the effects of soil stiffness and pile flexibility on the seismic fragility of the pile were assessed in [19] using finite element analysis. in addition to the effect of infrastructure parameters on the seismic fragility of the structure, there is the influence of the pier parameters, such as the higher-order mode of the pier bridge column that produces overestimated seismic demands of the pile foundation in terms of curvature and displacement [20]. the lateral performance of an eccentrically braced frame was investigated in [21]. the effectiveness of retrofitting a reinforced concrete structure was shown in [22]. in [23], the seismic performance of a baseisolated nuclear power plant structure was investigated taking into account near and far-fault earthquake influence. this study investigated the effects of nearand far-fault earthquakes on the seismic fragility of a single-column pile, taking into account the soil-pile spring system's p-y curve using the seismostruct software and incremental dynamic analysis. ii. near and far ground motion selections the main benchmark for selecting nearand far-fault earthquakes is the closest distance from the fault (rjb) where the near-fault has an rjb of less than 15km [24]. this study used the records of earthquakes from [25]. the ground motions were characterized by a median of pgv/pga equal to 113 for nearand 119 for far-fault. in figure 1(a, b), the thin lines define the individual spectra, and the thick line defines the mean spectrum of near (nr) and far (fr) ground motions. (a) (b) fig. 1. acceleration response spectra of (a) near-fault earthquakes, (b) farfault earthquakes. iii. numerical modeling of soil-pile interaction the seismostruct software offers different concrete materials and steel reinforcing bars. the nonlinear mander [26] and the menegetto-pinto models of steel reinforcing are shown in figures 2 and 3. the modeling of the soil-pile interaction was based on the design of the p-y curve relationship: p is the soil reaction and y is the lateral deflection. the nonlinear winkler foundation model (bnwf) [4] was employed, defined as multilinear curves. the structure was modeled using a 3d formulation, whereas the soil was modeled using a 1d formulation based on the reference p-y model as [4]: p = 0.9p�. tanh� � � �.��� y� (1) where k is the initial modulus of the subgrade reaction in soil and pu is the ultimate bearing capacity. fig. 2. stress-strain curve of concrete mander material. -0,002 0,000 0,002 0,004 -28,8 -25,6 -22,4 -19,2 -16,0 -12,8 -9,6 -6,4 -3,2 0,0 s tr e ss ( m p a ) strain [-] engineering, technology & applied science research vol. 13, no. 1, 2023, 9819-9824 9821 www.etasr.com lemsara et al.: seismic fragility of a single pillar-column under near and far fault soil motion with … fig. 3. stress-strain curve of steel menegetto-pinto model. the properties of each p-y curve derive from the parameters of homogeneous soil layers considering spring spacing of 0.5. two different pile diameter deposits, each with two sand types, loose and dense, and three different masses were considered: 1500, 3000, and 4500kn. for simplification, an abbreviation is proposed concerning different models: ls for the loose sand model, ds for the dense sand model, and d for pile diameter, where d=d1=1.5m and d=d2=2m. two different heights (h) of piers, equal to 5 and 10m, were used. the pile length (l) was fixed at 30m as in [27]. the loose and dense sand had a friction angle of 30° and 45°, respectively. figure 4 shows the soil-pile interaction model designed in seismostruct software. fig. 4. soil-pile spring interaction. the calculation of the probability exceedance of a structure at a limit state is defined in (2), which is given by [15, 28-29]: p� ����� = φ� ��������μ σ � (2) where μ and σ are the mean and the standard deviation of the logarithmic of the peak ground acceleration when the pier reaches the threshold of performance level d at each limit state, and φ is the standard normal cumulative distribution function. to estimate the probability of pier damage, the analysis procedure was (figure 5): 1. modeling of soil-pile interaction and vertical load value using seismostruct software. 2. define the drift value at each limit state of different models using nonlinear static analysis. 3. select ground motion records (nearand far-fault earthquakes). 4. generate the incremental dynamic analysis and find the median and standard deviation of the incremental dynamic analysis. 5. drawing of seismic fragility curve. fig. 5. analysis procedure. iv. results and discussion a. limit states and incremental dynamic analysis figure 6(a) shows the form of the incremental dynamic analysis example. the 20 thin lines define the individual incremental dynamic analysis and the thick red line defines its mean response. figure 6(b) shows the comparison of the mean response. the mean response of the incremental dynamic analysis increases with mass center under the two ground motion types. after realizing the incremental dynamic analysis series for each model, their mean and standard deviation were calculated. the mean and standard deviation of incremental dynamic analysis in the case of pile diameter of 1.5 and 2.0 m, and h=5m are shown in tables i and ii, respectively, and the mean value decreases with mass increase. table i. median and standard deviation values of ida with pile diameter equal to 1.5 m mass (kn) 1500 3000 4500 earthquake type near far near far near far mean (μ) loose sand 0.94 1.03 0.38 0.37 0.23 0.22 dense sand 0.90 1.00 0.40 0.38 0.25 0.23 standard deviation (σ) loose sand 0.36 0.37 0.32 0.35 0.28 0.31 dense sand 0.28 0.36 0.26 0.26 0.23 0.22 -0,006 -0,003 0,000 0,003 0,006 0,009 -614,4 -512,0 -409,6 -307,2 -204,8 -102,4 0,0 102,4 204,8 307,2 409,6 512,0 614,4 s tr e ss ( m p a ) strain [-] engineering, technology & applied science research vol. 13, no. 1, 2023, 9819-9824 9822 www.etasr.com lemsara et al.: seismic fragility of a single pillar-column under near and far fault soil motion with … table ii. median and standard deviation values of ida with pile diameter equal to 2m. mass (kn) 1500 3000 4500 earthquake type near far near far near far mean (μ) loose sand 1.73 1.70 0.82 0.76 0.50 0.47 dense sand 1.98 2.01 0.80 0.55 0.42 0.48 standard deviation (σ) loose sand 0.36 0.32 0.32 0.32 0.30 0.32 dense sand 0.24 0.32 0.23 0.49 0.17 0.24 (a) (b) fig. 6. (a) incremental dynamic analysis under nr ground motion, (b) example of mean response comparison of ida. b. fragility curves utilizing parameters from the mean and standard deviation of incremental dynamic analysis, and the standard normal cumulative distribution function (2), the fragility curves are expected and generated in the design figures for the collapse prevention state. c. effect of mass depending on the variation of pier height (h), the results of the numerical simulation are classified into two parts: figures 7 and 8 for h=5m and figures 9 and 10 for h=10m. figure 7(a) presents the seismic fragility of the concrete pier in case the pile is embedded in dense sand under a near-fault ground motion. this figure shows that when placing a different mass of 1500, 3000, and 4500kn, the pier structure needs a peak ground acceleration equal to 0.90, 0.40, and 0.25g, respectively, to exceed 50% of failure probability. these results show that the high mass needs a low peak ground acceleration (pga) to exceed 50% of failure probability under near-fault ground motion. the seismic fragility curves under far-fault ground motion show the same trend. all figures show similar trending results with a mass variation. (a) (b) fig. 7. seismic fragility of pier with dense sand condition and h=5m: (a) near (nr) ground motions, (b) far (fr) ground motions. (a) (b) fig. 8. seismic fragility of a pier with loose sand conditions and h=5m: (a) near (nr) ground motions, (b) far (fr) ground motions. d. near and far fault ground motion comparison these results show that high mass needs a low pga to exceed 50% of failure probability under near-fault ground motion. a comparison of seismic fragility curves under farfault ground motion shows the same trend. additionally, all figures show similar trending results with mass variation. figures 7 and 8 showed that the lower difference between pga of nearand far-ground motion at 50% of failure probability in the case of h=5m are: ls-d1-3000, ds-d1-3000, ls-d1-4500, ls-d1-4500, ls-d2-4500. these models keep this most negligible difference value at complete failure probability (100%). the fundamental periods of the different models are 0.81, 0.69, 0.98, 0.85, and 0.56s, and their t1/t2 ratios were 2.89, 2.46, 2.88, 2.5, and 2.94, respectively. on the other hand, some models have a slight difference at only 50% failure probability. the last figures show that in models presenting r<5%, the far-fault produced a higher failure probability than the near-fault ground motion due to its higher value of pgv/pga. these models were ls-d2-1500 and ls-d2-3000 in the case of h=5m and ds-d2-1500 in the case of h=10m. the fundamental periods of these models were engineering, technology & applied science research vol. 13, no. 1, 2023, 9819-9824 9823 www.etasr.com lemsara et al.: seismic fragility of a single pillar-column under near and far fault soil motion with … 0.41, 0.56, and 0.64s, and their t1/t2 ratios were 3.72, 3.5, and 1.82, respectively. these figures showed a higher probability of failure of the pier structure in far-fault earthquakes than in near-ground motions, as observed in [31], while a higher probability of failure was presented in [23] in near-fault earthquakes in all events. (a) (b) fig. 9. seismic fragility of pier with dense sand condition and h=10m: (a) near (nr) ground motions, (b) far (fr) ground motions. (a) (b) fig. 10. seismic fragility of pier with loose sand condition and h=10m: (a) near (nr) ground motions, (b) far (fr) ground motions. v. conclusions this study compared the seismic fragility of a single concrete pier under nearand far-fault earthquakes. the effects of mass variation, closest ground motion type, and pile diameter were considered with two sand models, loose and dense. the seismic fragility of a concrete pier exceeded 50% and 100% of failure probability when placing a higher mass value at the pier end in all cases of pile section. the difference between the peak ground acceleration of nearand far-fault earthquakes at complete failure probability was less than 5% when the analysis modal conditions (0.65s<t1<1s and 2.4<t1/t2) were verified. the pier structure was highly affected by a higher value of pgv/pga regardless of the near and far ground motions if one of two conditions was given: 1<t1<0.65s or t1/t2 < 2. the higher difference between the peak ground acceleration of near and far earthquakes at complete failure probability was concluded if the two following conditions are presented together: t1<0.5s and 3< t1/t2. references [1] b. aygün, l. dueñas-osorio, j. e. padgett, and r. desroches, "efficient longitudinal seismic fragility assessment of a multispan continuous steel bridge on liquefiable soils," journal of bridge engineering, vol. 16, no. 1, pp. 93–107, jan. 2011, https://doi.org/ 10.1061/(asce)be.1943-5592.0000131. 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[31] a. mosleh, m. s. razzaghi, j. jara, and h. varum, "seismic fragility analysis of typical pre-1990 bridges due to nearand far-field ground motions," international journal of advanced structural engineering (ijase), vol. 8, no. 1, pp. 1–9, mar. 2016, https://doi.org/10.1007/ s40091-016-0108-y. microsoft word etasr_v13_n3_pp10638-10645 engineering, technology & applied science research vol. 13, no. 3, 2023, 10638-10645 10638 www.etasr.com badawi et al.: the effect of polypropylene fibers on the fracture characteristics of lightweight… the effect of polypropylene fibers on the fracture characteristics of lightweight aggregate crumb rubber concrete composites moataz badawi civil engineering department, college of engineering and islamic architecture, umm al-qura university, saudi arabia mabadawi@uqu.edu.sa ayman g. ahmed civil engineering department, umm al-qura university, saudi arabia agahmed@uqu.edu.sa tarek a. eldamaty civil engineering department, umm al-qura university, saudi arabia tadamaty@uqu.edu.sa medhat m. helal civil engineering department, umm al-qura university, saudi arabia | department of engineering mathematics and physics, zagazig university, egypt mmhelal@uqu.edu.sa (corresponding author) received: 27 february 2023 | revised: 16 march 2023 | accepted: 18 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5821 abstract the increasing use of rubber tires and their low recycling ratio have made them a serious environmental problem. this work aims to develop and investigate enhanced lightweight aggregate crumb rubber concrete (pflwacrc) composites regarding the fracture properties of concrete. polypropylene (pp) fibers are commonly familiar with increased crack growth endurance of concrete. on the other hand, the reuse of waste rubber in concrete plays a major role in the mitigation of the effects of climate change. various concrete mixtures were designed with conventional portland cement and common lightweight coarse aggregates. the variables considered in this study are pp fibers in different percentages (0.2%, 0.4%, and 0.6% volume fraction), and crumb rubber with various substitution proportions (0%, 5%, 10%, 15%, 20%, and 25% of fine aggregates). cement with 450kg/m 3 density with 10% silica fume was used. the fracture characteristics, which involve fracture toughness (kic) and fracture energy generation (gf), of all concrete mixtures were evaluated by testing two types of samples, i.e. 54 notched concrete beams with dimensions of 10×10×52cm and 54 cylinders with diameter×height equal to 15×30cm. the results showed that the fracture toughness generation addresses the energy scattering limit of concrete mixtures. the findings showed that the existence of pp fibers increased the fracture energy and critical crack mouth opening displacement (cmodc). the pp fibers had a limited effect on the compressive strength and may even reduce it, but a remarkable enhancement of the energy absorption was observed. keywords-lightweight aggregates; silica fume; crack growth; polypropylene fibers; crumb rubber; fracture energy i. introduction fibers and waste rubber in lightweight aggregate concrete (lwac) are promising additive materials to control and improve its fracture behavior. the fracture properties of concrete altogether impact the underlying conduct of concrete constituents [1]. authors in [2] examined the fresh properties of exact low-strength rubber concrete (lsrc) and controlled low-strength rubber lightweight aggregate cement (clsrc) with unused-tire rubbers in different substitution percentages, namely 0%, 10%, 20%, 30%, and 40%. the percentage of substitution influences the unit weight and initial setting time. about 10% growth in the content of rubber fragments engineering, technology & applied science research vol. 13, no. 3, 2023, 10638-10645 10639 www.etasr.com badawi et al.: the effect of polypropylene fibers on the fracture characteristics of lightweight … diminishes the unit weight by about 70kg/m 3 . the compressive strength of clsrc and clsrlc declines even though the content of rubber substitution increments. authors in [3] examined the mechanical properties and the penetrability of rubber treated plain pervious concrete. three different sorts of rubber have been developed as a substitute for aggregates in the design of rubber-handled simple concrete combinations. in the analysis, four-detailed rubber substances by total aggregate volume were considered. the outcome showed that the utilization of rubber essentially exasperated the pervious concrete mechanical properties. generally, alternatives of common aggregates, including rubber grains, exhibit a critical increment in stiffness and ductility of concrete and a better damping limit. authors in [4] examined the appropriateness of trash tire synthetic rubber in concrete as an alternative for river sand. three water/cement ratios (0.40, 0.45, and 0.50) and 0–20% replacement of fine aggregates were used. in [5], tests were carried-out to evaluate characteristics such as compressive strength, flexural strength, abrasion resistance, microstructure, and water penetrability. it was found that a 50% replacement of aggregates with tire rubber might be used for regular fine aggregates without a significant decrease in strength. it was noticed that the replacement of mineral aggregates with tire-rubber particles showed a substantial decrease in ultimate compressive strength and modulus of elasticity. due to this reduction in ultimate compressive strength, the maximum percentage of aggregate replacement with rubber should not be more than 25% [5]. in general, the crack generation in concrete containing waste rubber is smaller than that occurring in ordinary concrete. the mode of failure in tire-rubber concrete compared to that of plain concrete exhibits higher deformation. future investigations are needed to address the energy retention of tire-rubber concrete under dynamic loads, and the toughness of tire-rubber cement under unfavorable enduring conditions. authors in [6] proposed the replacement of aggregates with 20–40% crumb rubber. it was found that concrete mixtures with such substitutions showed beneficial and superior properties. authors in [7] reported that the addition of crumb tire rubber in up to 5% volume fraction in a cement matrix does not yield a significant variation of concrete's maximum stress and elastic modulus. in terms of splitting tensile strength, portland cement concrete specimens made with 25% of rubber fibers by total aggregate volume retained 20% of their splitting tensile strength after initial failure. cement and concrete were subjected to high-level warming in [8, 9]. it was discovered that the harm due to warming from 120 to 400 o c enlarges crack energy by half. authors in [10] examined the residual fracture energy of cement paste, mortar, and concrete subjected to high temperature and found that the thermal damage due to heating from 120 to 400 o c increases the fracture energy by 50%. they reported that the post-cracking behavior of concrete specimens was unaffected by the partial substitution of fine aggregates with rubber particles having similar dimensions, whereas a good residual strength after cracking and significant energy absorption were observed for rubcrete mixes obtained by adding coarse rubber chips in place of coarse aggregates. among non-metal fibers, the impact of polypropylene (pp) compositions on the assets of lwac has been examined thoroughly. the test consequences of [11-16] demonstrated that, if pp fibers are utilized in combination with a lwac blend, they may have a moderate impact on the enhancement of the compressive strength and may even decrease it. the impact of 3 kinds of fibers on the properties of expanded clay lwac was explored. pp composition did not influence the compressive strength, while carbon composition and steel fibers had impact up to 1.0% and up to 1.5%, respectively. the pp fibers can likewise be utilized in lwac to avoid weak actions. authors in [17] used small pp fibers (l = 1.3cm and d = 0.0015cm). they announced that pp fibers marginally improve the energy ingestion while steel fibers greatly affect the energy retention of concrete under pressure. the significance of the ductility of concrete constructions exposed to seismic loading is broadly recognized and configuration codes represent this limit. these perceptions accentuate the preferred position that pp fibers add to the pliability of pumice lwac, which is viewed as weak. subsequently, more productive and more efficient arrangements might be conceived by fusing pumice insubstantial aggregates with steel rods in mixtures [18-23]. the extent of this examination is unquestionably very restricted to give some exploratory information on the impact of pp fibers and scrap rubber on fracture properties (counting gf and kic) of pp fiber lightweight aggregate crumb rubber concrete (pflwacrc). an amount 10% silica rage has been utilized to upgrade the mechanical properties of this kind of concrete. the impact of pp fibers on the properties of lwac is examined in this paper. this investigation studied the crack generation of pflwacrc. the impact of waste rubber on the crack growth of the pflwacrc with different levels of pp fibers is presented. in pflwacrc, pp fibers were utilized to improve the crack growth resistance of concrete, while the incorporation of waste rubber is eco-friendly and requires less energy. ii. experimental program a. concrete ingrendients  cement: ordinary portland concrete (type i) was used in the current study. the density of cement was kept constant as 450kg/m 3 .  fine aggregates: regular ordinary weight fine clean sand free from any contaminations was utilized. specific gravity, water absorption, and fineness modulus of the soil were 2.3, 2.9%, and 2.2, respectively, according to astm c-33.  coarse aggregates: normal lightweight aggregates (pumic), obtained from southwestern saudi arabia, were utilized. sieve analysis test for lightweight aggregates was conducted according to astm c 330. the properties of the lightweight aggregates (lwa) are given in table i.  pp fibers were added at 0.2%, 0.4 %, and 0.6%. the main properties of the fibers are shown in table ii.  the crumb rubber utilized was obtained from used and worn-out vehicle tires. the particle diameter ranged engineering, technology & applied science research vol. 13, no. 3, 2023, 10638-10645 10640 www.etasr.com badawi et al.: the effect of polypropylene fibers on the fracture characteristics of lightweight … between 14 and 20 sieve size (0.85 1.40mm), as indicated by astm-e11-09, while the specific gravity was found to be 1.20, and the melting point was 200 o c. scrap rubber with different quantities (0%, 5%, 10%, 15%, 20%, and 25%) was utilized.  admixture: super-plasticizer with a solid substance of 40% and water reduction of 25% with a density of 1,210kg/m 3 (astm c-494) was treated as intermixture to realize workable concrete mixtures (slump value of 120mm±25mm). based on slump trails and tests, super plasticizer of 1.0% by weight of cement was used.  silica fume (sf) was utilized in concrete mixes. it exhibited an explicit surface area of 19.7m 2 /gm and specific gravity of 2.27. as a partial replacement, the amount of sf used was 10% by total weight of cement.  water: potable water was used in all concrete specimens. the 0.45 water-cement ratio (w/c) was kept constant for all mixes. table i. properties of lwa property specification/value color grayish/black bulk density (kg/m³) for coarse aggregates 780 bulk specific gravity (ssd ) 1.85 oven dry specific gravity 1.66 l-a abrasion value 16.4 water absorption 9.7% porosity 8.1% n.m.s 14 mm table ii. characteristics of pp fibers property value tensile strength (mpa) 450 specific gravity 0.89 elongation at peak (%) 18 young's modulus (gpa) 5 length (mm) 60 diameter (mm) 12 table i. lwa deliberate properties lwa type deliberate properties lwa-fr0 lwa with 0% rubber at different levels of fiber content. lwa-fr5 lwa with 5% rubber at different levels of fiber content. lwa-fr10 lwa with 10% rubber at different levels of fiber content. lwa-fr15 lwa with 15% rubber at different levels of fiber content. lwa-fr20 lwa with 20% rubber at different levels of fiber content. lwa-fr25 lwa with 25% rubber at different levels of fiber content. the lightweight concrete (lwc) mixtures were divided into 6 groups based on the percentages of pp fiber replacement. each group consisted of 9 150cm×30.0cm standard cylinders in conjunction, and 9 10cm×10cm×52cm notched beams. all tests were conducted after 28 days. figure 1 shows the compressive strength vs the unit weight, and fiber percentage. fig. 1. mix proportions by weight and compressive strength. b. flexural tests three-point load setup was employed to address the rupture performance of pflwacrc as per the proposal of rilem fracture system commission (tc50-fmc) [18]. as demonstrated in figure 2(a), the notched beams had effective length of 40.0cm and a notch at 30mm (a0/h = 0.3) depth was located at the mid-span place. the test was conducted with a closed-loop electrohydraulic universal testing machine with a 1000kn capacity. control specimens comprised of 3 cylinders with zero percentage of fibers and rubber. the properties (compressive strength and unit weight) of these specimens are almost the equivalent for lwafr0. a load cell of 50kn capacity with accuracy of 1n plus a 5.0cm linear variable 0 5 10 15 20 25 30 35 40 45 50 lwa-fr0 lwa-fr5 lwa-fr10 lwa-fr15 lwa-fr20 lwa-fr25 compressive strength/(mpa) mixes (0.2% pp) mixes (0.4% pp) mixes (0.6% pp) 0 200 400 600 800 1000 w/c w opc sf lwa sand rubber mix proportions (unit weight: kg/m3) lwa-fr0 lwa-fr5 lwa-fr10 lwa-fr15 lwa-fr20 lwa-fr25 1550 1600 1650 1700 1750 1800 1850 1900 lwa-fr0 lwa-fr5 lwa-fr10 lwa-fr15 lwa-fr20 lwa-fr25 unite weight (kg/m3 ) engineering, technology & applied science research vol. 13, no. 3, 2023, 10638-10645 10641 www.etasr.com badawi et al.: the effect of polypropylene fibers on the fracture characteristics of lightweight … differential transducer (lvdt) with 0.001cm precision were utilized to determine the weight combined with refraction at the middle of length, exclusively. conversely, crack mouth opening displacement (cmod) with a 1.0cm cut on measurements and 0.0001cm precision was used. steady movement rate of 0.005cm/min was applied up to failure. the testing procedure of the 3-point twisting system (figure 2(b)) intended to minimize the influence of compressive flexible deformity at the loading points (the platform and actuator head). two lvdts were mounted on the two inverse countenances for all specimens to evaluate the rebound at the halfway of length. specimen, instrumentations, and test set-up are shown in figure 2. (a) (b) (c) fig. 2. flexural three-point load-bending test: (a) notched beam, (b) setup, (c) photo sample. c. evaluation of the fracture force the fracture force is characterized as the all-out force disseminated across a unit section of a broken ligament. it is acquired as of the work carried out (the section below the p–δ arch). the fracture force of the jagged planks comprises 4 sections [1], and is mathematically expressed as: w = w0 + w1 + w2 + w3 (1) where w0 is the work done by the external force p, which is recorded by the data acquisition system, w1 is the work performed by the ego-weight of the planks before the utilization of the outer force. it has a very small value, and can be neglected. w2 and w3 represent the extra work done for the duration of the packing cycle by the own substance of the planks. so, w2 = 0.5mg0, and w3 (the end part of the chart after 0), can't be estimated in the tests. the computational derivation of the fracture energy is: �� � � ��� � in order to compute the extra work w3 done by scaled weight, the plunging part of the deflection-load (δ–p) chart is misleadingly stretched out by curve fitting dependent upon the energy work technique [20, 21]: � � � �� � 0 � , � � 0� ��� � � � in� (2) the dependability of the matching curves addressed by the consistency factor, r 2 , and the particular fitting boundaries (for example β, �, r2) were calculated. w3 is determined by (2)-(3): �� � � � �� � �� �� � �������� ��� � (3) the physical fracture force of all concrete mixtures shows an agreement with (4), where alig is the zone of tendon, specifically alig = t (h-a0). !" � #�$# $#%$#& '()* (4) the obtained outcome of the crack force of all concrete mixtures with different percentages of waste rubber and fibers is shown in figure 3. d. evaluation of the rupture toughness the rupture force (kic) of concrete reflects its capacity to avoid break down propagation and the capacity of resisting weak rupture in particular. the rupture durability of a concrete material is basically determined by (5) as per astm e399-74. +,� ./012 34 & % 5 �64� (5) where pmax is the vertical upper limit load, h, t and s are the elevation, thickness, and length of the samples, respectively, and 5 �64� is the numerical shape element, which is computed by: 5 7648 � 2.9 7 6 48 % � 4.6 7648 & % > 21.8 7648 a % � 37.6 7648 d % > 38.7 7648 e % (6) the contribution of pp fibers in concrete is that a bridging force is developed between the fibers and the cement paste, strengthening the material. the equation of ascertaining flexural rigidity suggested by astm refers to a simple material. the impact of flexural measure region on the fracture energy of pp fiber strengthened material is incorporated by the supplanting of the efficient fracture size (ac), which is determined by ac = a0 + δac. when the checking weight (p) arrives at its peak (pmax), the crack estuary hole movement goes its critical maximum value (cmodc), and the genuine length engineering, technology & applied science research vol. 13, no. 3, 2023, 10638-10645 10642 www.etasr.com badawi et al.: the effect of polypropylene fibers on the fracture characteristics of lightweight … of pre-break is created from the first value (a0) to the critical crack length (ac). thus, as indicated by the direct asymptotic behavior of superposition, ac is determined by a lefm equation (7) [19, 23]: fg = h i �ℎ + ℎ �arctano 3p�qrstu� �h.vw/01 − 0.1135 − ℎ (7) where h0 is the width of the hardened layer employed to adjust fastening on instruments on the crack lip, (cmodc) is the significant amount of the crack lip hole movement, and e is the modulus of elasticity, calculated by: y = �3g) z3.70 + 32.60 tan h�ih 6�[4� 4$4� �\ (8) where ]^ = �qrst) �w) is an preliminary quantity defined at an capricious position, (p, cmod) on the gradient phase of pcmod curves. the estimated calculations of the fracture force (kic) of all mixtures are reviewed in figure 3. fig. 3. computed and experimental results. iii. results and discussion the densities of hardened concrete tested at 28 days are shown in figure 1. it is observed that the pp fibers bring an unimportant impact on concrete samples. however, the solid thickness is predominantly influenced by the presence of morsel elastic. the solid thickness of the reference sample was 1870kg/m 3 , the density of concrete comprised of 5%, 10%, engineering, technology & applied science research vol. 13, no. 3, 2023, 10638-10645 10643 www.etasr.com badawi et al.: the effect of polypropylene fibers on the fracture characteristics of lightweight … 15%, 20%, and 25% waste rubber was 1815, 1785, 1743, 1711, and 1681kg/m 3 , respectively. the specimens made up by 0.2%, 0.4%, and 0.6% pp fibers, almost had similar values. considering the minimal specific gravity of rubber particles, the unit weight of the mixtures with rubber was reduced as the percentage of rubber increased [4, 17]. based on the compressive strength results recorded in this study, a slight decrease in the compressive strength was observed as the pp fiber percentage increased. from figure 1, it may be stated that the expansion of pp fibers up to 0.2% of concrete volume appears to have an insignificant impact on the compressive strength of concrete. yet, adding more pp fibers, up to 0.6%, caused a reduction in compressive strength by about 10%. the impact of the substitution of fine aggregates with scrap rubber at the compressive force is shown in figure 1. it is obvious that there is degradation in compressive strength depending on the percentage of waste rubber used, around 15% for 10% of rubber used. the use of sf decreased the degradation in compressive strength [10]. the concrete samples containing rubber showed post failure pressure loads and experienced a large displacement before failure. the samples cracked and withstanded a portion of the ultimate load. the large noticed displacement and deformation are certainly related to the fact that the rubber aggregates can withstand huge distortions. it is well known that rubber materials exhibit a low elastic modulus which leads to a deferral in extending the crack and forestalling calamitous failure, which is generally experienced in plain concrete specimens. the fracture properties of pflwacrc beams with various replacement percentages of waste rubber and pp fibers were assessed by three-point loading tests. the obtained weight break cheek hole relocation (p-cmod) relationship is shown in figure 3. furthermore, the impact of pp fibers and rubber in fracture force and toughness is shown in figures 4 and 5. established on the (δ–p) and p-cmod behavior, the crack force (gf) and fracture stiffness durability (kic) of concrete for all mixtures was determined and is shown in figure 3. it should be noted that each incentive in figure 3 was the average of 3 samples in each group. obviously, the aim of inserting fibers and rubber to lwa is to enhance fracture behavior. the impacts of fibers and waste rubber on the deflection-weight (δ–p) and load crack mouth opening displacement (p-cmod) behaviors are plotted in figures 4 and 5, respectively. generally speaking, pp fibers marginally improve the energy retention and durability of the material under flexible loads. overall, pp fibers have a minimal impact on the ductility of lwc at 0.2% volume. for example, the presence of pp fibers expanded the absolute fracture energy and fracture energy of concrete as shown in figure 5. on the other side, the addition of 0.2% pp increased somewhat the total energy. figure 4 illustrates the correlation of load refraction behavior for 3 distinctive fiber sizes. figure 4 demonstrates that the beams along with greater volumes of fiber content (specifically 0.6% by volume) demonstrate a superior resistance particularly beyond large deflections. concrete mixtures containing 0.4% and 0.6% of pp fibers show more ductility than those with 0.2% pp fibers (figure 4 (b)-(c)). it appears that pp fiber volume fraction equal to 0.2% is inconsequential. in this manner, it is proposed that adding 0.4% pp fibers in mixtures improves the flexural properties of lwc. it is seen that the refraction associated to extreme weight increases with the increase of fiber size. this is recognized as the impact of fibers bridging and catching cracking. figure 4 additionally displays the liner flexible segment of the curvature prior to the propagation of micro cracks in the matrix when using pp fibers. due to lacking stiffness, it was difficult to gauge the dropping part of lwc. figure 5 depicts the cmod relations for 3 distinctive fiber volume substances. it should be noted that, at similar loads after cracking, the beam with larger volume of fibers exhibits substantially more cmod values. (a) (b) fig. 4. load-deflection curves of all mixes containing (a) 0.2% and (b) 0.4% pp. (a) (b) fig. 5. load – cmod curves of all mixes containing (a) 0.2% and (b) 0.4% pp. engineering, technology & applied science research vol. 13, no. 3, 2023, 10638-10645 10644 www.etasr.com badawi et al.: the effect of polypropylene fibers on the fracture characteristics of lightweight … a. fracture energy the values of the fracture force of the concrete mixtures are displayed in figure 3. the impacts of fibers and rubber on the rupture vitality and fracture energy of material mixtures are shown in figures 4 and 5, respectively. it is obvious that the addition of rubber effectively affects the rupture vitality of material mixtures up to 10%. this outcome demonstrates that fitting rubber waste improves the energy ingestion limit of the concrete. however, too much rubber may negatively affect the energy retention limit. accordingly, to viably improve the energy assimilation limit of concrete mixes, a fitting measure of rubber ought to be chosen. this result is in accordance with [17, 24]. on the other hand, the fracture properties can be improved with the addition of pp fibers, particularly fracture energy (figures 3-4). the fracture energy of the concrete mixtures increases by more than 3.0 by expanding the fiber content from 0.2% to 0.6%. the fibers delay the crack spread and do not go to rapid failure, which causes an expansion in the weight carrying capability of beams [25]. b. rupture durability the impact of adding rubber fibers on the durability of the mixtures is shown in figure 5. it can be noticed from figure 5 that the rupture force of the mixtures clearly changes with increasing fiber content. with the addition of rubber, the impact of fiber content on the rupture force of the material mixtures is predictable. the rupture force originally increased when up to 15% rubber substance was used and it decreased with further increment of elastic substance until 25%, with the fracture energy being the smallest at 0.2% fiber content. at 0.2% pp fiber, the fracture energy increased by about 80% and 88% when rubber was added by 10% and 15%, respectively. this increase diminished to 56% at 25% rubber substitution. a similar pattern was noticed to the 0.4% and 0.6% pp fiber concrete mixes. fig. 6. effects on fracture energy combined with elastic substance on the fiber. as shown in figures 6 and 7, the elevated addition of fibers and rubber may prompt a large increase of the rupture stiffness, maybe because the material power relies on the intensity of the substance and the aggregates are improved by the presence of fibers [18]. for concrete mixtures arranged with various replacement percentages of fiber and rubber, the distinction in the highest pressure and rupture force may be identified with the force of the interfacial connection. through vibrations, the water within the material is allowed to go to the lwa due to their extreme-water retention limit, making a moderately superior w/c incentive. accordingly, a more grounded bond may be framed between the cement paste and lwa, particularly when sf is added to the concrete blend. the above outcome showed that adding rubber improves the protection of concrete mixtures from brittle fracture. however, adding too much rubber may negatively affect that protection. it very well may be inferred that the ideal estimations of rubber to upgrade the fracture properties lie between 10% and 15%, while the pp fibers should not be under 0.4% volume fraction. fig. 7. effect of fiber and rubber on rupture stiffness. iv. conclusions in the current study, the impact of the addition of pp fibers and rubber waste in concrete mixtures on the fracture toughness and fracture energy of lwc were addressed. the progression of 3-point load on 10cm×10cm×52cm beams was examined. based on the experimental results and the derived calculations, the following conclusions were drawn:  the addition of pp fibers has irrelevant impact on the density of concrete samples. the concrete density is predominantly influenced by the use of scrap rubber. a serious dilapidation of compressive strength was observed for all concrete mixtures by expanding the rubber substance addition to more than 15%.  pp fiber addition prompts a critical expansion in the fracture toughness. for addition of the rubber substance from 5% to 10%, the fracture toughness originally increased, whereas the addition up to 25% diminished the increment of fracture toughness.  pp fibers have no recognizable impact on the hardened properties of concrete at replacement level below 0.2%. the addition of 0.4% pp fibers in concrete affects the compressive behavior. nonetheless, 0.4% pp fibers increased slightly both fracture toughness and fracture energy. the impact of pp is undeniable in the concrete mixtures. the proposed dose of pp fibers to be utilized in lightweight concrete in order to avoid brittle failure is up to 0.4%. engineering, technology & applied science research vol. 13, no. 3, 2023, 10638-10645 10645 www.etasr.com badawi et al.: the effect of polypropylene fibers on the fracture characteristics of lightweight …  suitable waste rubber level improves the concrete brittlness behavior, however, an excessive amount of rubber may negatively affect this protection. the ideal addition of rubber content to improve the crack behavior varies between 10% and 15%, while pp fiber addition up to 0.4% volume fraction was acknowledged. references [1] f. m. z. hossain, md. shahjalal, k. islam, m. tiznobaik, and m. s. alam, "mechanical properties of recycled aggregate concrete containing crumb rubber and polypropylene fiber," construction and building materials, vol. 225, pp. 983–996, nov. 2019, https://doi.org/ 10.1016/j.conbuildmat.2019.07.245. 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[23] z. h. dakhel and s. d. mohammed, "castellated beams with fiberreinforced lightweight concrete deck slab as a modified choice for composite steel-concrete beams affected by harmonic load," engineering, technology & applied science research, vol. 12, no. 4, pp. 8809–8816, aug. 2022, https://doi.org/10.48084/etasr.4987. microsoft word etasr_v13_n2_pp10578-10587 engineering, technology & applied science research vol. 13, no. 2, 2023, 10578-10587 10578 www.etasr.com kassem et al.: wind power potential assessment at different locations in lebanon: best–fit probability ... wind power potential assessment at different locations in lebanon: best–fit probability distribution model and techno-economic feasibility youssef kassem department of mechanical engineering, engineering faculty, near east university, cyprus | energy, environment, and water research center, near east university, cyprus yousseuf.kassem@neu.edu.tr (corresponding author) huseyin gokcekus department of civil engineering, civil and environmental engineering faculty, near east university, cyprus | energy, environment, and water research center, near east university, cyprus huseyin.gokcekus@neu.edu.tr ahmed mohamed salah essayah department of environmental education and management, ataturk faculty of education, near east university, cyprus 20215635@std.neu.edu.tr received: 15 january 2023 | revised: 19 february 2023 | accepted: 28 february 2023 abstract the objective of the current paper is to evaluate lebanon's wind energy generation potential as an alternative solution to the electricity supply to households and to enhance sustainable technological development. firstly, the paper aims to investigate the appropriateness of 44 distribution function models for the evaluation of wind speed characteristics and compared them with popular models at 12 locations in lebanon for the first time. the results showed that wakeby and beta distribution functions gave the best fit to the actual data for most locations. secondly, the techno-economic and environmental feasibility assessment for 10mw grid-connected wind farms was developed based on variations in financial parameters using retscreen experts software. the findings demonstrate that the proposed power plant is both technically and financially feasible. it was found that ain ed dabaa is the most viable location for the installation of a wind farm. keywords-lebanon; distribution function; wind energy potential; grid-connected; retscreen i. introduction wind energy has known increasing exploitation in power generation [1]. the use of wind as an energy source is imperative nowadays due to the lack of fossil fuel resources, particularly in developing countries like lebanon. wind energy is a clean, inexhaustible, and environmentally friendly energy source. the generation of electricity from wind energy will be an essential part of lebanon’s future development. in general, analyzing wind speed characteristics is essential to assess the potential of wind energy in a given location. probability distribution models (pdms) are utilized to describe wind speed observations [2]. thus, finding the most suitable pdm is considered the first step for evaluating the wind power potential at a specific location. two-parameter weibull and rayleigh distribution functions are the most used for modeling the wind speed at specific locations [2]. many studies focus on analyzing wind characteristics using various distribution models. authors in [3] utilized parametric models, mixture models, and one non-parametric model to evaluate the potential of wind energy in the united arab emirates. the results demonstrated that one-component parametric distributions provided the best fit to the wind speed data for all sites. authors in [4] analyzed the distribution of wind speed in northern cyprus using 2-parameter weibull (2p-w), gamma engineering, technology & applied science research vol. 13, no. 2, 2023, 10578-10587 10579 www.etasr.com kassem et al.: wind power potential assessment at different locations in lebanon: best–fit probability ... (g), lognormal (ln), logistic (l), log-logistic (ll), inverse gaussian (ig), generalized extreme value (gev), nakagami (na), normal (n), and rayleigh (r) distribution functions. the authors found that gev showed the best fit for most selected locations. authors in [5] evaluated the wind energy potential at different locations in pakistan using various distribution functions and gev was identified as the best. authors in [6] analyzed the wind speed characteristics of 5 locations in iran using 8 pdms. the authors concluded that na and 2p-w gave the best fit to the actual data. authors in [7] used 2p-w, g, and inverse gamma (ig) to study the characteristics of wind speed in peninsular, malaysia. g and 2p-w gave the best fit for the actual data. authors in [8] utilized 37 distribution functions for evaluating the wind energy potential at the güzelyurt region in northern cyprus. the authors concluded that burr (4p), wakeby, and gev provided the best fit. authors in [9] assessed the wind speed distribution at different locations in india using 9 pdms. the results showed that gev provided the best fit for the majority of the sites. authors in [10] evaluated the wind energy potential at 17 locations in sudan using 37 pdms. the authors found that the wakeby distribution function provided the best fit for the wind speed data for all locations. authors in [11] studied the accuracy of several pdms for modeling the wind speed distribution at different locations in algeria. the results showed that the gev and gamma models were the most appropriate. wais [12] studied the accuracy of 2p-w and 3-parameter weibull (3p-w) in analyzing the wind speed characteristics at 3 locations in poland. the author concluded that 3p-w gave a better fit to the wind speed data. table i. previous studies related to wind energy potential in lebanon ref. location pdms used best [13] klaiaat, cedars, daher el baydar, marjyoun, and quaraoun 2p-w [14] beirut, sidon, and tripoli 2p-w, g, ln, l, ll, ig, gev, na, n and r ll [15] klaiaat, les cedres, daher el baydar, quaraoun, and marjyoun 2p-w [16] rayak 2p-w [17] beirut, zahleh, sour, and el-abdeh r [18] beirut, sidon, and tripoli 2p-w [19] younine, birket aarous, ain ed dabaa, mqaybleh, ras ouadi ed darje, kfardebian, qaraoun, khartoum, iskandarounah and beirut 2p-w [20] abboudiye, tal keri, darine, heke el dahri, saadine, semmaqiye, talabbas and tal el bireh g, 3pg, ig, 3p-ig, ll, 3p-ll, ln, 3pln, na, 2p-w, 3p-w 3p-w and 3p-ll [21] akkar, baalbek, beirut, zahlé, baabda, nabatieh, tripoli, and sidon 2p-w [22] qlaiat, ksara, cedres, dahr el baydar, marjayoun, beirut, khaldeh, tripoli, riaq 2p-w numerous studies have evaluated the wind energy potential in lebanon using various distribution models as shown in table i. based on the findings, the most used distribution function for analyzing the wind speed distribution is 2p-w. moreover, wind energy has been widely utilized globally to generate electricity and reduce greenhouse gas emissions. authors in [4] conducted a techno-economic analysis for the generation of power utilizing a small-scale vertical axis wind turbine in 8 locations in northern cyprus. authors in [13] assessed and analyzed the electricity that 116 wind turbines in lebanon might produce. the number of studies related to the analysis of wind speed characteristics using various distribution functions is limited. furthermore, as a continuation of our study on the statistical investigation of wind characteristics in lebanon, the present paper aims to evaluate for the first time the best-fit distribution function to describe the wind speed data at 12 locations in lebanon. to fulfill this objective, 44 distribution functions were used to model the wind speed characteristics at the selected locations. the parameters of these distribution functions were estimated using the maximum likelihood method. additionally, 3 goodness-of-fit test statistics were applied to determine the best-fit pdfs. the present study was performed on power produced by a wind turbine at a maximum of 10mw that may be installed in lebanon. ii. materials and methods a. study area and data collection the wind speed characteristics of 12 locations in lebanon should be fully understood in order to evaluate the wind power potential (figure 1). table ii lists the geographical coordinate’s latitude, longitude, and elevation of the selected locations. the monthly wind speed data from 2010 to 2017 were collected from the meteorological service. b. probability distribution functions in this study, 44 probability distribution functions (pdfs) are utilized to represent the wind speed frequency distribution (table iii). the number of parameters for the selected pdfs is within the range of 1-4. the probability density functions of the selected pdfs can be found in [8-10, 23]. fig. 1. map showing the selected locations. © mapa gisrael. engineering, technology & applied science research vol. 13, no. 2, 2023, 10578-10587 10580 www.etasr.com kassem et al.: wind power potential assessment at different locations in lebanon: best–fit probability ... table ii. information on the selected locations in lebanon location latitude [°n] longitude [°e] elevation [m] younine 34.0776 36.2750 1198 birket aarous 34.2911 36.1456 2766 ain ed dabaa 34.4431 35.8992 296 mqaybleh 34.6460 36.3577 330 ras ouadi ed darje 34.2533 36.5775 1555 kfardebian 34.0017 35.8349 1670 qaraoun 33.5669 35.7193 913 khartoum 33.4079 35.3751 305 iskandarounah 33.1550 35.1685 53 beirut 33.8938 35.5018 40 khiam 33.3294 35.6148 697 hekr el dahri 34.6306 36.0237 10 c. goodness-of-fit test in this research, kolmogorov-smirnov (k-s) test is employed to select the best-fit df. the description of these tests is given below [10]. � = max���� �� � � − ��� , � − �� � �� (1) where: � � � = � × �number of observations ≤ � (2) table iii. selected df models and number of parameters (np) model no. model name np model no. model name np df#1 beta 4 df#23 log-gamma 2 df#2 burr 3 df#24 logistic 2 df#3 burr 4 df#25 log-logistic 2 df#4 cauchy 2 df#26 log-logistic 3 df#5 dagum 3 df#27 lognormal 2 df#6 dagum 4 df#28 lognormal 3 df#7 erlang 2 df#29 log-pearson 3 2 df#8 erlang 3 df#30 nakagami 2 df#9 exponential 1 df#31 normal 2 df#10 exponential 2 df#32 pareto 2 df#11 gamma 2 df#33 pareto 2 2 df#12 gamma 3 df#34 pearson 5 2 df#13 generalized extreme value 3 df#35 pearson 5 3 df#14 generalized gamma 3 df#36 pearson 6 3 df#15 generalized gamma 4 df#37 pearson 6 4 df#16 generalized logistic 3 df#38 pert 3 df#17 generalized pareto 3 df#39 rayleigh 1 df#18 gumbel max. 2 df#40 rayleigh 2 df#19 gumbel min. 2 df#41 reciprocal 2 df#20 inverse gaussian 2 df#42 wakeby 5 df#21 inverse gaussian 3 df#43 weibull 2 df#22 kumaraswamy 4 df#44 weibull 3 d. retscreen a techno-economic assessment was made for the generation of electricity using 3 wind turbines with various specifications in the selected locations using retscreen software. retscreen expert is a clean energy management tool developed by the canadian government. it is a decision support tool that is utilized to determine the potential of energy, costs, savings, greenhouse gas (ghg) emission reduction, and economic viability. the retscreen utilizes the long-term monthly average meteorological data from the national aeronautics and space administration (nasa) database as a source of meteorological information for the specific location. recently, retscreen has been commonly employed to explore the feasibility of grid-connected wind and pv power systems. capacity factor, annual power production, ghg reductions, and economic indicators are determined using retscreen [10]. iii. results and discussion a. description of wind speed data at a height of 10m the descriptive statistics of each location are listed in table iv. moreover, the monthly variation of wind speed for all the selected locations is illustrated in figure 2. it is found that the mean wind speed varied between 2.81m/s and 4.90m/s (table iv). the values for mean speed and standard deviation (sd) indicate that the wind behavior is quite consistent. the coefficients of variation (cv), which range between 6.52 and 17.25%, are relatively low. the minimum and maximum values are recorded in younine and ain ed dabaa, respectively. for the majority of the chosen locations, the skewness (s) values are negative, indicating that all distributions are left skewed. additionally, the values of kurtosis (k) vary from -1.46 to -0.19, and they are also moderately low. fig. 2. monthly average wind speed for the selected locations (20102017). engineering, technology & applied science research vol. 13, no. 2, 2023, 10578-10587 10581 www.etasr.com kassem et al.: wind power potential assessment at different locations in lebanon: best–fit probability ... table iv. descriptive wind speed dataset location mean sd cv min max s k younine 2.90 0.45 15.37 2.32 3.51 0.03 -1.46 birket aarous 3.01 0.31 10.14 2.44 3.45 -0.56 -0.26 ain ed dabaa 4.90 0.53 10.79 4.00 5.82 -0.15 -0.41 mqaybleh 2.91 0.30 10.14 2.36 3.34 -0.56 -0.26 ras ouadi ed darje 3.19 0.45 14.05 2.54 4.03 0.52 -0.19 kfardebian 3.48 0.41 11.66 3.04 4.22 0.82 -0.75 qaraoun 2.86 0.19 6.52 2.51 3.08 -0.54 -0.81 khartoum 2.81 0.18 6.52 2.47 3.03 -0.54 -0.81 iskandarounah 3.32 0.57 17.25 2.72 4.27 0.42 -1.46 beirut 3.48 0.41 11.66 3.04 4.22 0.82 -0.75 khiam 2.81 0.18 6.52 2.47 3.03 -0.54 -0.81 hekr el dahri 2.91 0.30 10.14 2.36 3.34 -0.56 -0.26 b. wind resource assessment at a height of 10m the deep assessment of wind resources using various wind speed probability functions at 12 locations in lebanon is investigated in this paper. according to [24], selecting the bestfit df is an essential step in determining the average wind turbine power production. therefore, the most suitable distribution that best fits the actual wind speed is assessed using the k-s test. figure 3 shows the statistic value of k-s for all the selected distributions. it should be noted that the best fit to the wind speed has the lowest statistic value of k-s. based on the k-s test (figure 3 and table v), wakeby distribution has the lowest value, so it is considered the best distribution function to study the average monthly wind speed characteristics for younine, birket aarous, mqaybleh, and hekr el dahri. moreover, beta is among the distributions giving better fits to investigate the distribution of wind speed at khiam, iskandarounah, khartoum, and qaraoun. gumbel min and gen. logistic provide the best fit to wind speed at ain ed dabaa and ras ouadi ed darje, respectively. additionally, to explore the distribution of the average monthly wind speed at kfardebian and beirut, 3p-log-logistic is one of the distributions offering the best fit for wind speed. fig. 3. statistic and rank for various locations based on k-s value. the essential characteristic of skewness (s), which is defined as the third central moment, measures asymmetry [11]. when the long tail is on the peak's negative (positive) side, there is a negative (positive) skew. kurtosis (k) is a measure of tailedness, defined as the fourth central moment, if the data have higher [11]. a higher (lower) k value indicates that there are more (fewer) extreme values or fatter tails (middles) on the data curve. table v compares the s and k values calculated using the best dfs distributions. these values are compared with widely used dfs (weibull, rayleigh, and gev) to show the efficacy of the selected df models. some pdf figures can be seen in figure 5. engineering, technology & applied science research vol. 13, no. 2, 2023, 10578-10587 10582 www.etasr.com kassem et al.: wind power potential assessment at different locations in lebanon: best–fit probability ... fig. 4. statistic and rank for various locations based on k-s values. c. wind power density (wpd) calculation at 10m height wpd is the expected value for the potential wind energy at a specific location. wpd for a region can be calculated by: " # = � $ %&'(�&� (3) where p is wind power density (w), & is the wind speed (m/s), a is swept area (m 2 ), ρ is the air density (kg/m 3 ) and (�&� is the pdf. additionally, the mean wpd can be determined by: ") # = � $ %&̅ ' (4) where +) is the mean wind power density and &̅ is the mean wind speed. in the literature, the air density value is 1.23kg/m 3 . using (4), the wpd was calculated and tabulated in table vi. it is found that the value of wpd is within the range of 13.26 (khiam and khartoum) 72.64 (ain ed dabaa)w/m 2 . according to the wind power density classification [5], the wind energy potential in the selected locations is classified as class 1 (poor). based on the findings, a small-scale wind turbine can use wind energy to generate electricity at the selected locations. d. summary the findings of this study are significant for the installation of wind farms and many wind energy applications in the future. no single distribution can accurately describe the wind speed distribution based on the summary of previous scientific studies. the 2p-w is a common tool used in the assessment of wind energy for a specific region. accordingly, the distribution function is chosen based on the available wind speed data and the utilized statistical methods. the main aim of this study is to evaluate the suitability of different probability functions for estimating wind speed characteristics at different locations in lebanon. in this study, various distribution functions with a various number of parameters are utilized for the first time to estimate the characteristics of wind speed. based on the findings, wakeby, beta, and gev are considered effective, since they provide the best fits for the actual wind speed data for all locations. the annual values of wpd were calculated using the best distribution functions. based on the findings, the wpd at the selected locations can be exploited using a smallscale wind turbine. engineering, technology & applied science research vol. 13, no. 2, 2023, 10578-10587 10583 www.etasr.com kassem et al.: wind power potential assessment at different locations in lebanon: best–fit probability ... table v. descriptive wind speed dataset location df parameter mean v sd s k statistic rank y o u n in e actual 2.90 0.45 0.03 -1.46 beta 1=0.38225 2=0.40879 a=2.32 b=3.512 2.90 0.20 0.45 0.06 -1.58 0.15 3 gen. extreme value k=-0.25596 =0.4583 =2.7263 2.86 0.22 0.46 0.07 -0.26 0.16 5 gen. pareto k=-0.93858 =1.501 =2.1217 2.90 0.21 0.46 0.05 -1.18 0.13 1 rayleigh =2.3107 2.90 2.29 1.51 0.63 0.25 0.40 6 wakeby =1.501 =0.93858 =0 =0 =2.1217 2.90 0.02 0.46 0.05 -1.18 0.13 2 weibull =6.5369 =3.0351 2.83 0.26 0.51 -0.42 0.12 0.16 4 b ir k et a ar o u s actual 3.01 0.31 -0.56 -0.26 dagum k=0.31321 =33.389 =3.2552 3.01 0.09 0.30 -0.83 1.52 0.12 2 gen. extreme value k=-0.56484 =0.34662 =2.9426 3.01 0.11 0.32 -0.80 0.62 0.16 4 gen. logistic k=-0.14575 =0.17083 =3.0521 0.12 3 rayleigh =2.4017 3.01 2.48 1.57 0.63 0.25 0.40 6 wakeby =3.8783 =4.3227 =0.08856 =0.20184 =2.1705 0.11 1 weibull =9.9843 =3.1091 2.96 0.13 0.36 -0.64 0.57 0.21 5 a in e d d ab a a actual 4.90 0.53 -0.15 -0.41 dagum k=0.41765 =25.218 =5.2488 4.91 0.29 0.54 -0.50 1.22 0.13 3 gen. extreme value k=-0.3961 =0.57967 =4.7359 4.90 0.30 0.55 -0.35 -0.15 0.12 2 gumbel min =0.41251 =5.1387 4.90 0.28 0.52 -1.14 2.40 0.12 1 rayleigh =3.9101 4.90 6.56 2.56 0.63 0.25 0.41 5 weibull =10.146 =5.0377 4.80 0.32 0.57 -0.64 0.59 0.18 4 m q ay b le h actual 2.91 0.30 -0.56 -0.26 dagum k=0.31334 =33.401 =3.1518 2.92 0.09 0.29 -0.83 1.52 0.12 2 gen. extreme value k=-0.56493 =0.33539 =2.8494 2.91 0.10 0.31 -0.80 0.62 0.16 4 gen. logistic k=-0.14579 =0.16529 =2.9553 0.12 3 rayleigh =2.3256 2.91 2.32 1.52 0.63 0.25 0.40 6 wakeby =3.7758 =4.3574 =0.08812 =0.19228 =2.1008 0.11 1 weibull =9.9875 =3.0105 2.86 0.12 0.34 -0.64 0.57 0.21 5 r as o u ad i e d d ar je actual 3.19 0.45 0.52 -0.19 burr k=0.73124 =14.691 =3.0386 3.19 0.22 0.47 1.19 4.69 0.09 3 gen. extreme value k=-0.07482 =0.40347 =2.9829 3.19 0.22 0.47 0.75 0.88 0.10 4 gen. logistic k=0.12273 =0.25573 =3.1353 0.09 1 log-logistic (3p) =5.5837 =1.3577 =1.7727 3.20 0.25 0.50 2.04 15.48 0.09 2 rayleigh =2.5435 3.19 2.78 1.67 0.63 0.25 0.39 6 weibull =8.2109 =3.2847 3.10 0.20 0.45 -0.55 0.36 0.14 5 k fa rd eb ia n actual 3.48 0.41 0.82 -0.75 gen. extreme value k=0.14286 =0.28756 =3.2647 3.48 0.22 0.46 -2.43 14.54 0.14 4 gen. pareto k=-0.16182 =0.58192 =2.9767 3.48 0.19 0.44 1.30 1.69 0.12 2 log-logistic (3p) =1.4625 =0.30081 =3.0211 3.79 0.12 1 rayleigh =2.7747 3.48 3.30 1.82 0.63 0.25 0.45 6 wakeby =0.58192 =0.16182 =0 =0 =2.9767 3.48 0.19 0.44 1.30 1.69 0.12 3 weibull =9.3692 =3.5804 3.40 0.19 0.43 -0.61 0.50 0.20 5 q ar ao u n actual 2.86 0.19 -0.54 -0.81 beta 1=0.7163 2=0.45516 a=2.514 b=3.077 2.86 0.03 0.19 -0.42 -1.23 0.12 1 gen. extreme value k=-0.61707 =0.21637 =2.8216 2.86 0.04 0.20 -0.94 0.98 0.13 4 gen. pareto k=-1.8226 =1.1791 =2.4405 2.86 0.04 0.19 -0.55 -0.97 0.13 2 rayleigh =2.2806 2.86 2.23 1.49 0.63 0.25 0.46 6 wakeby =1.1791 =1.8226 =0 =0 =2.4405 2.86 0.04 0.19 -0.55 -0.97 0.13 3 weibull =15.456 =2.9261 2.83 0.05 0.22 -0.80 1.03 0.16 5 k h ar to u m actual 2.81 0.18 -0.54 -0.81 beta 1=0.71911 2=0.45588 a=2.473 b=3.028 2.81 0.03 0.18 -0.43 -1.23 0.13 1 gen. extreme value k=-0.61795 =0.21306 =2.7767 2.81 0.04 0.20 -0.94 0.99 0.13 4 gen. pareto k=-1.825 =1.1626 =2.4011 2.81 0.04 0.19 -0.55 -0.97 0.13 3 rayleigh =2.2442 2.81 2.16 1.47 0.63 0.25 0.46 6 wakeby =1.8650e+5 =77661.0 =1.1613 =-1.8236 =0 0.13 2 weibull =15.442 =2.8795 2.78 0.05 0.22 -0.80 1.03 0.16 5 is k an d ar o u n ah actual 3.32 0.57 0.42 -1.46 beta 1=0.28827 2=0.45156 a=2.719 b=4.27 3.32 0.33 0.57 0.44 -1.40 0.11 1 gen. extreme value k=-0.00205 =0.48503 =3.0443 3.32 0.38 0.62 1.13 2.34 0.15 2 erlang m=33 =0.09894 3.27 0.32 0.57 0.35 0.18 0.17 3 weibull =5.9937 =3.4797 3.23 0.39 0.63 -0.37 0.03 0.20 4 rayleigh =2.6516 3.32 3.02 1.74 0.63 0.25 0.41 5 engineering, technology & applied science research vol. 13, no. 2, 2023, 10578-10587 10584 www.etasr.com kassem et al.: wind power potential assessment at different locations in lebanon: best–fit probability ... location df parameter mean v sd s k statistic rank b ei ru t actual 3.48 0.41 0.82 -0.75 gen. extreme value k=0.14286 =0.28756 =3.2647 3.48 0.22 0.46 -2.43 14.54 0.14 4 gen. pareto k=-0.16182 =0.58192 =2.9767 3.48 0.19 0.44 1.30 1.69 0.12 2 log-logistic (3p) =1.4625 =0.30081 =3.0211 3.79 0.12 1 rayleigh =2.7747 3.48 3.30 1.82 0.63 0.25 0.45 6 wakeby =0.58192 =0.16182 =0 =0 =2.9767 3.48 0.19 0.44 1.30 1.69 0.12 3 weibull =9.3692 =3.5804 3.40 0.19 0.43 -0.61 0.50 0.20 5 k h ia m actual 2.81 0.18 -0.54 -0.81 beta 1=0.71911 2=0.45588 a=2.473 b=3.028 2.81 0.03 0.18 -0.43 -1.23 0.13 1 gen. extreme value k=-0.61795 =0.21306 =2.7767 2.81 0.04 0.20 -0.94 0.99 0.13 4 gen. pareto k=-1.825 =1.1626 =2.4011 2.81 0.04 0.19 -0.55 -0.97 0.13 3 rayleigh =2.2442 2.81 2.16 1.47 0.63 0.25 0.46 6 wakeby =1.8650e+5 =77661.0 =1.1613 =-1.8236 =0 0.13 2 weibull =15.442 =2.8795 2.78 0.05 0.22 -0.80 1.03 0.16 5 h ek r e l d ah ri actual 2.91 0.30 -0.56 -0.26 dagum k=0.31334 =33.401 =3.1518 2.92 0.09 0.29 -0.83 1.52 0.12 2 gen. extreme value k=-0.56493 =0.33539 =2.8494 2.91 0.10 0.31 -0.80 0.62 0.16 4 gen. logistic k=-0.14579 =0.16529 =2.9553 0.12 3 rayleigh =2.3256 2.91 2.32 1.52 0.63 0.25 0.40 6 wakeby =3.7758 =4.3574 =0.08812 =0.19228 =2.1008 0.11 1 weibull =9.9875 =3.0105 2.86 0.12 0.34 -0.64 0.57 0.21 5 table vi. wpd (w/m2) value for each location (l) l df wpd l df wpd y o u n in e actual 14.94 q a ra o u n actual 14.36 beta 14.94 beta 14.36 gen. extreme value 14.34 gen. extreme value 14.36 gen. pareto 14.94 gen. pareto 14.36 rayleigh 14.93 rayleigh 14.36 wakeby 14.94 wakeby 14.36 weibull 13.92 weibull 13.91 b ir k et a ar o u s actual 16.77 k h ar to u m actual 13.69 dagum 16.82 beta 13.69 gen. extreme value 16.77 gen. extreme value 13.69 gen. logistic gen. pareto 13.69 rayleigh 16.77 rayleigh 13.69 wakeby wakeby weibull 15.91 weibull 13.26 a in e d d ab a a actual 72.40 is k an d ar o u n ah actual 22.57 dagum 72.64 beta 22.57 gen. extreme value 72.38 gen. extreme value 22.57 gumbel min 72.38 erlang 21.41 rayleigh 72.38 weibull 20.69 weibull 67.83 rayleigh 22.57 m q ay b le h actual 15.23 b ei ru t actual 25.87 dagum 15.27 gen. extreme value 25.87 gen. extreme value 15.23 gen. pareto 25.87 gen. logistic log-logistic (3p) 33.54 rayleigh 15.23 rayleigh 25.87 wakeby wakeby 25.87 weibull 14.45 weibull 24.10 r as o u ad i e d d a rj e actual 19.93 k h ia m actual 13.69 burr 19.93 beta 13.69 gen. extreme value 19.92 gen. extreme value 13.69 gen. logistic 0.00 gen. pareto 13.69 log-logistic (3p) 20.24 rayleigh 13.69 rayleigh 19.92 wakeby weibull 18.27 weibull 13.26 k fa rd eb ia n actual 25.87 h ek r e l d ah ri actual 15.23 gen. extreme value 25.87 dagum 15.27 gen. pareto 25.87 gen. extreme value 15.23 log-logistic (3p) 33.54 gen. logistic rayleigh 25.87 rayleigh 15.23 wakeby 25.87 wakeby weibull 24.10 weibull 14.45 e. techno-economic feasibility this section aims to encourage governments to develop wind farms to achieve sustainable energy infrastructures, particularly in developing countries like lebanon. the investigation of changing tariffs influencing the wind energy market in lebanon is discussed by proposing 9 scenarios as shown in table vii. moreover, the capital, operation, and maintenance costs associated with turbines can be assumed based on previous scientific studies [25]. in this study, the technical viability of 3 wind turbine models (wtms) is evaluated. generally, wind farm performance in terms of wind power production and capacity factor is affected by the geographic location and wind speed distribution. thus, the electricity exported to the grid (eeg) and the capacity factor (cf) were estimated for younine (it has the lowest monthly wind speed) and ain ed dabaa (it has the maximum monthly wind speed) for the selected location. the mean eeg monthly value of for all the proposed models is shown in figure 5. it is observed that the eeg is within the range of 604.383999.537mwh. the lowest value of eeg is recorded at younine using wtm#1, while the highest value is recorded at ain ed dabaa using wtm#. it is noticed that wtm#2 produced the highest eeg. moreover, for younine location, the annual value of eeg of the proposed system is 14057.47mwh for wtm#1, 17152.08 for wtm#2, and 18268.02 for wtm#3. for ain ed dabaa, the annual value of eeg of the proposed system is 32030.96, 38252.56, and 37642.62mwh for wtm#1, 2, and 3, respectively. the annual cf was calculated for all wind turbines as shown in figure 6. it is observed that the annual cf varied from 16.05% to 43.67%. the results demonstrate that among all wind turbines, the capacity factor of wtm#2 was the highest. these results can be supported by previous scientific studies. for instance, authors in [26] found that the cf values of the proposed wind farms varied from 9.79% to 51.93% and authors in [27] found that the cf values of the proposed farms were within the range of 5-42%. authors in [28] found that the proposed farm projects in pakistan have a cf ranging from 19% to 34%. the engineering, technology & applied science research vol. 13, no. 2, 2023, 10578-10587 10585 www.etasr.com kassem et al.: wind power potential assessment at different locations in lebanon: best–fit probability ... economic analysis is essential when one wants to know if the project is economically viable and sustainable. thus, the techno-economic feasibility of the proposed projects was evaluated using retscreen for different scenarios as shown in table vii. the used financial parameters include inflation rate (2.9%), discount rate (5.4%), reinvestment rate (9%), project life (25 years), debt ratio (70%), debt interest rate (8.9%), and debt payments (15 years) as input parameters, assumed based on previous studies. based on these input parameters, npv, alcs, sp, ep, lcoe, and the internal rate of return (irr) were estimated using retscreen software. table vii. the developepd three scenarios to show the impact of policy changes on the financial viability of wind power plants in lebanon input scenario a1 scenario b1 scenario c1 capacity 10mw turbine model#1 aaer-a-2000 100 project life 20 years array losses 4% airfoil losses 2% miscellaneous losses 6% availability factor 98% electricity export cost [us cents] 6.75 10.45 13.52 input scenario a1 scenario b1 scenario c1 capacity 10mw turbine model#2 dw 52 500kw 75m project life 20 years array losses 4% airfoil losses 2% miscellaneous losses 6% availability factor 98% electricity export cost [us cents] 6.75 10.45 13.52 input scenario a1 scenario b1 scenario c1 capacity 10mw turbine model#3 w2e100/2000 100m project life 20 years array losses 4% airfoil losses 2% miscellaneous losses 6% availability factor 98% electricity export cost [us cents] 6.75 10.45 13.52 the npv was determined for each location and each value of electricity export rate (eer) and is illustrated in figure 7. it is found that the value of npv for each value of eer is positive, which indicated that the project is potentially feasible [29, 30]. besides, it is noticed that there is a strong correlation between npv and eer. moreover, irr is estimated to evaluate the economic viability of the project. the irr provides the true return of interest over the life of the project. the results showed that increasing rate of exporting electricity led to an increase in the value of irr. in addition, it is observed that the value of irr of all locations is higher than the required rate of return of the project. furthermore, alcs is calculated by using npv, discount rate, and project lifetime. it is found that alcs is within the range of 67438-6790429 usd/year for all proposed projects. according to previous scientific studies, the economic viability of a project is estimated by determining the payback period, which indicates the time required to recover the initial investments, with net positive income. figure 7 shows the payback period including ep and sp for all selected locations based on various scenarios. it is found that the ep and sp are within the range of 1.1-16.1 and 2.9-15.7 years, respectively. wtm#2 has the lowest value of ep and sp compared to other models. the results reveal that the increase in eer will lead to a decrease in ep and sp. moreover, the electricity production cost (epc) is found within the range of 0.038-0.104-0.038 usd/kwh. the epc is lower compared to previous studies [25, 31] and the electricity tariff in the country [19]. fig. 5. monthly average electric production. fig. 6. annual cf. f. climate co-benefit assessment the climate co-benefits in terms of ghg emission reduction were calculated using retscreen software for each location and are listed in table viii. the results indicate that a large amount of co2 emissions can be avoided by implementing the developed wind project in each location. it is noticed that the wind farm (wf) using wtm#3 (wfwtm#3) has the highest amount of co2 emission reductions. the total amount of co2 emissions reduction for each location is determined based on the electricity generated annually [32]. engineering, technology & applied science research vol. 13, no. 2, 2023, 10578-10587 10586 www.etasr.com kassem et al.: wind power potential assessment at different locations in lebanon: best–fit probability ... fig. 7. economic performance of the developed wind project in younine and ain ed dabaa. table viii. net annual reduction of ghg emissions (tco2) location wf-wtm#1 wf-wtm#2 wf-wtm#3 younine 9244.15 11279.21 12013.05 ain ed dabaa 23142.37 27637.47 27196.79 iv. conclusion in this paper, the wind speed distribution and the potential of wind energy were assessed at 12 locations in lebanon. for wind speed 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[32] f. leon and a. ramos, "an assessment of renewable energies in a seawater desalination plant with reverse osmosis membranes," membranes, vol. 11, no. 11, nov. 2021, art. no. 883, https://doi.org/ 10.3390/membranes11110883. microsoft word etasr_v13_n1_pp9807-9811 engineering, technology & applied science research vol. 13, no. 1, 2023, 9807-9811 9807 www.etasr.com manh et al.: investigation of the influence of skewed slots and degmagnetization effects to line start … investigation of the influence of skewed slots and degmagnetization effects to line start permanent magnet assistance synchronous reluctance motors tien ho manh university of transport and communications, vietnam hotien.ktd@utc.edu.vn dinh bui minh school of electrical and electronic engineering, hanoi university of science and technology, vietnam dinh.buiminh@hust.edu.vn tu pham minh school of electrical and electronic engineering, hanoi university of science and technology, vietnam tu.phamminh@hust.edu.vne-mail address vuong dang quoc school of electrical and electronic engineering, hanoi university of science and technology, vietnam vuong.dangquoc@hust.edu.vn (corresponding author) received: 2 september 2022 | revised: 27 october 2022 | accepted: 27 october 2022 abstract a permanent magnet assistance synchronous reluctance motor can start directly with a net voltage or a power converter via a torque control method. however, this motor has usually a higher irreversible demagnetization level in comparison with interior permanent magnet motors, due to the fewer permanent magnets in rotor slots. in order to cope with this disadvantage, different arrangements of permanent magnets in the rotor of the line-start permanent magnet assistance synchronous reluctance motor are proposed in this paper. the v magnet shape taking skewed slots and demagnetization effect into account with the short circuit current are investigated by the finite element approach. the efficiency, torque, and output power of the proposed model have been also improved. finally, the rotor with 3v layered magnets is prototyped to verify the efficiency of the proposed motor. keywords-line start permanent magnet assistance-synchronous reluctance; magnet shape; skewed slots; demagnetization effect; finite element method i. introduction the line start permanent magnet assistance synchronous reluctance motors (ls-pma-synrms) have recently been presented [1]. authors in [2] proposed the design and optimization of low torque ripple and high torque by using ferrite magnets. however, the influences of skewed slots and the demagnetization effects on the ls-pma-synrms have not been mentioned so far. in this paper, different arrangements of permanent magnets in the rotor taking skewed slots and the demagnetization effects taken into account are developed to improve the efficiency of the ls-pma-synrms. normally, when the ls-pma-synrms are operated at synchronous speed, the secondary copper loss is eliminated, leading to efficiency improvement. less use of rare-earth materials, low cost, comparable constant-power speed range, maximum torque, and the efficiency of the ls-pma-synrms will be considered. in particular, this is an interesting choice for the application of electric traction because it has a special flux barrier and suitable magnet arrangement to improve the constant torque in a wide speed range. in addition, it has a lesser risk of irreversible demagnetization in the short circuit and overheat temperature [3]. engineering, technology & applied science research vol. 13, no. 1, 2023, 9807-9811 9808 www.etasr.com manh et al.: investigation of the influence of skewed slots and degmagnetization effects to line start … ii. model of ls-pma-synrms a 7.5kw ls-pma-synrm model for 6 poles is shown in figure 1. the stator has 36 slots and the 3-layer rotor has 36 round bars. the magnetic material and silicon steels are made in n38uh and 35a350. the response of magnets to the demagnetizing influence is considered in this research. depending on the type of magnets, the motor can either need to withstand irreversible demagnetization during a transient short circuit fault condition or only require that the demagnetization is avoided during the steady-state operating conditions. for the sintered ndfeb and smco magnets, an irreversible demagnetization will occur at the very high temperature of 120°c. on the other hand, the irreversible demagnetization will occur at low temperatures (i.e. below 0°c) for the sintered ferrite magnets. initially, a temperature value can be fixed to investigate the possible demagnetization. for example, it will be assumed that the magnet temperature is 160°c. hence, for a selected n38uh magnet, the knee point of the demagnetization curve at the specified temperature is indicated in figure 2 [4]. it can be seen that the flux density of the b-h curve becomes non-linear. the irreversible demagnetization in the magnet will appear if the flux density is depressed below that point. it should be noted the curve becomes non-linear at about 0.2t – at 160°c (the magnet temperature of our model). when the knee point is higher, then the magnet is more easily irreversibly demagnetized at high temperatures. fig. 1. ls-pma-synrm with 3v layer. fig. 2. magnetization curve of b-h. the magnetization curve with a higher temperature is pointed out in figure 3 [4]. the curve of irreversible demagnetization is described by [5-7]: � = �� + ���� �� − ∙ � ��������� (1) where b is the flux density, br is the remanent flux density, hc is the coercivity, e is the electrical field, and �� and �� are respectively the factors of the magnets, where the factor �� can be defined as [8, 9]: �� = �� [������� ��� .����"] �� − �� (2) the working point of the magnet is defined by the intersaction between the flux density (bm) and magnetic field strength (hm). a point on the demagnetization characteristic of the magnet and load line is also defined. the slope of the load line is called the permeance coefficient. it is determined principally by the ratio of the magnet length to the air gap (g). when the machine is under load, the whole load line shifts, usually to the left, so the working point is shifted further down the curve. once it overcomes the knee of the curve, an irreversible loss of magnetization will appear. via the computation of demagnetization, it is certain that the operating point of the magnet stays above the knee. it also needs to be ensured that the magnet is working with the worst-case parameters. in particular, temperature is critical. for highenergy magnets, when the temperature increases, both br and hc decrease. however, the knee moves to a lower value of hm, which means that less current is required to demagnetize the magnet. the maximum current that can flow and its phase angle must also be considered. normally, the current is regulated by the inverter unit, thus the maximum current is tightly controlled. but there may be fault conditions where the current reaches a value much higher than normal. fig. 3. b-h magnetization curve with higher temperature. in the worst conditions, for a three-phase short-circuit, the temperature of the magnet is 25 0 c. for that, the current can be presented as [4]: engineering, technology & applied science research vol. 13, no. 1, 2023, 9807-9811 9809 www.etasr.com manh et al.: investigation of the influence of skewed slots and degmagnetization effects to line start … $%[&�] = '(�)* (3) where eq1 is the root mean square (rms) of the electromotive force (emf) per phase and xd is the d-axis synchronous reactance. normally, this current is 2 to 5 times the maximum working current. the design parameters of lspma-synrm are given in table i. the schematic diagram of the proposed pma-synrm machine is presented in figure 4. in the proposed motor, the magnet shape is arranged with the u-shape. this arrangement is regarded as requisite for the efficient operation in the type of i-w-u shape. the total weight of the magnet segment and copper winding is presented in table ii. table i. geometry parameters of lspma-synrm parameter values unit slot number 36 slot outer stator 210 mm inner stator 132 mm tooth width 5 mm slot depth 19 mm motor length 180 mm stator lam length 180 mm magnet length 150 mm magnet size 5×2 mm air gap 0.4 mm turn per coil 20 turn fig. 4. schematice driagram. table ii. weight of lspma-synrm parameter kg stator lam (back iron) 8.26 stator lam (yooth) 5.245 stator lamination (total) 13.5 armature winding (active) 4.138 armature ewdg (front) 1.027 armature ewdg (rear) 1.027 armature winding (total) 6.193 rotor lam (back iron) 5.37 ipm magnet pole 4.833 rotor lamination (total) 10.74 magnet 0.5 total 33.98 iii. ls-pma-synrm performance in direct start and traction the proposed pma-synrm machine was designed and analyzed in traction. the electromagnetic torque is formed from two components of magnetic reluctance torques. the permanent magnet (pm) component is produced via the interaction between the air-gap magnetic field and the armature reaction magnetic field. the reluctance component is instead based on the asymmetry between the magnetic circuit of d-axis and q-axis. the electromagnetic torque can then be defined as [5-9]: +', = -..� /0.1 . 2% + 34% − 45 6. 2%. 25 7 (4) 4% = 8* 89:;* < 2% = 0 (5) 45 = 8(;( > 25 = 0 (6) where λpm is the flux linkage generated by the pm field, 2% and 25 are respectively the direct and quadrature axis currents, and 4% and 45 are the direct and quadrature axis inductances. the term λpm depends on magnet sizes. the terms (4% and 45 ) are computed following to the rotor magnet barrier and magnet pole u shape. fig. 5. comparison of dynamic starting torque and speed with different types of i-w-u. database program interface material library analytical calculations export drawings fem simulator engineering, technology & applied science research vol. 13, no. 1, 2023, 9807-9811 9810 www.etasr.com manh et al.: investigation of the influence of skewed slots and degmagnetization effects to line start … fig. 6. comparison of dynamic starting torque and time with different types of i-w-u. the dynamic starting torque and speed with different types of i-w-u are shown in figures 5 and 6. for the u-shape, the peak torque has been verified at 1500rpm. when increasing the phase current density up to 10a/mm 2 , the peak torque is 340nm. it should be noted that the ls-pma-synrm can be pre-determined by 11kw under the direct start. if this motor is operated with the power inverter, the maximum power is doubled, and the peak torque is about 800nm (figure 5). the parameter comparison of the ls-pma-synrm with different types of i-w-u is given in table iii. table iii. parameter comparison of ls-pma-synrm parameters i shape w shape u shape unit shaft torque 53.67 54.267 55.667 nm input power 9123.3 9213.4 9273.3 w output power 8644.1 8474.3 8744.1 w total losses 519.5 522.1 529.15 w system efficiency 93.24 94.3 94.68 % armature dc copper loss 340 340 340 w magnet loss 178.8 168.3 168 w stator iron loss 10.33 10.33 10.33 w phase terminal voltage 289.1 289.1 289.1 v harmonic distortion line-line terminal voltage 4.89 4.289 3.089 v harmonic distortion phase terminal voltage 13.7 12.2 11.27 % back emf line-line voltage 111 112 114 % table iv. temperature of ls-pma-synrm no component t ( 0 c) 1 t (ambient) 40 2 t (housing active) 78.717 3 t [stator lam (back iron)] 84.833 4 t (stator surface) 88.403 5 t (rotor surface) 88.65 6 t (airgap banding) 88.651 7 t (magnet) 88.197 8 t (airgap banding) 88.651 9 t (rotor lamination) 88.674 10 t (shaft center) 87.375 13 t (active winding minimum) 87.352 it can be seen that the maximum efficiency is 94%. the total loss errors between the three cases are smaller than 5%. for the errors on the harmonic distortion line, they are lower than 14%. the temperatures of the ls-pma-synrm are presented in table iv. the maximum temperature of the winding is 90.7 o c, which is much lower than isolation class h (180 0 ). the temperature of the magnet is 88.17 o c. the dynamic starting torque and speed of the u shape is shown in figure 7. the output power of the u shape is indicated in figure 8. the map distribution of the rotor temperature with the u shape is shown in figure 9. the maximum temperature is 88.7 o c. fig. 7. dynamic starting torque and speed of u shape design. fig. 8. output power and speed map of the u shape. fig. 9. rotor temperature with the u shape. iv. conclusion in this paper, the influence of skewed slots and demagnetization effects on the ls pma-synrm has been successfully investigated and analyzed. the values of dynamic starting torque and speed with different types of i-w-u have been also compared. the obtained results have shown that for the u shape, the torque and power density are noticeable improved, and the volume of magnets is the lowest. for a short starting time, the speed is considered as a constant in engineering, technology & applied science research vol. 13, no. 1, 2023, 9807-9811 9811 www.etasr.com manh et al.: investigation of the influence of skewed slots and degmagnetization effects to line start … comparison with the i and w shapes. the validation of the selected machine in the traction application and the full map of dynamic starting torque and power have been presented. in particular, the comparison of efficiency performances have been investigated with three different shapes, i.e. i, w, and u. thermal simulation is also implemented to validate overheat capacity. acknowledgement this study was funded by the university of transport and communications, hanoi, vietnam under grant number t2022dt-005. references [1] h. kim et al., "study on analysis method of asymmetric permanent magnet assistance synchronous reluctance motor considering magnetic neutral plane shift," ieee transactions on applied superconductivity, vol. 30, no. 4, pp. 1–4, jun. 2020, https://doi.org/ 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[9] y. wang, n. bianchi, and r. qu, "comparative study of non-rareearth and rare-earth pm motors for ev applications," energies, vol. 15, no. 8, jan. 2022, art. no. 2711, https://doi.org/10.3390/en15082711. microsoft word etasr_v13_n1_pp10086-10092 engineering, technology & applied science research vol. 13, no. 1, 2023, 10086-10092 10086 www.etasr.com dao-et al.: an adaptive sliding mode controller for a pam-based actuator an adaptive sliding mode controller for a pam-based actuator quy-thinh dao school of electrical and electronic engineering, hanoi university of science and technology, vietnam thinh.daoquy@hust.edu.vn vuong van dinh hanoi university of science and technology, vietnam | hanoi vocational college of high technology, vietnam vuongdv@hht.edu.vn chien tuan vu hanoi university of science and technology, vietnam chien.vt181355@sis.hust.edu.vn thuyet quang pham hanoi university of science and technology, vietnam thuyet.pq181778@sis.hust.edu.vn duc minh duong hanoi university of science and technology, vietnam duc.duongminh@hust.edu.vn (corresponding author) received: 5 december 2022 | revised: 20 december 2022 | accepted: 23 december 2022 abstract the pneumatic artificial muscle (pam) is a promising actuator for developing the human-robot interaction system. however, modeling and controlling pam-based actuators are a significant difficulty due to the inherent uncertainty and hysteresis of pam. besides, the control approach of a pam-based system also deals with unknown disturbances that always exist in any system. this study developed a sliding mode controller that employs an adaptive law to deal with issues and improve control performance. furthermore, the stability of the proposed controller is proven based on the lyapunov stability criterion. finally, through a series of tests, the effectiveness of the proposed control approach is verified. keywords-pneumatic artificial muscle; sliding mode control; adaptive law; antagonistic configuration i. introduction robotics industry has grown rapidly during the recent years, especially regarding robots that move in the same way as humans do. pam is a potential actuator mechanism that responds to this tendency, because it can stretch in the same way that human muscles can. besides its flexibility in movement, is possesses benefits such as high power-to-weight, ease of maintenance, inherent safety, and low cost [1-5]. the above characteristics have made pam a special research object, with common applications including manipulators, robotic orthosis, etc. [6-13]. however, controlling pam faces many challenges. the deviation in mathematical model estimation and the sensitivity to external disturbances are obstacles that need to be overcome if the pam control is to achieve optimal performance. many algorithms have been proposed to solve the control problem for this actuator, such as the traditional pid controller and its enhanced variations [1419]. nevertheless, the above controllers show limitations for the hysteresis and nonlinear characteristics of pam. nonlinear controllers to address the limitations of pid controllers, such as the fuzzy controller [20, 21], the neural network based controller [22], and the nonlinear adrc controller [23], have been employed in several recent studies. in addition, the sliding mode controller and its various versions are always the leading candidates for the tasks of controlling nonlinear objects [17, engineering, technology & applied science research vol. 13, no. 1, 2023, 10086-10092 10087 www.etasr.com dao-et al.: an adaptive sliding mode controller for a pam-based actuator 24-27]. nonetheless, pam is a nonlinear object, and the parameter estimation for the model of the pam-based system is approximate and if the system disturbance is very high, it definitely affects the control quality of the aforementioned methods. as a result, creating a disturbance observer will aid in overcoming pam's restrictions. in this study, a disturbance observer based on the adaptive law is developed to not only estimate the system disturbance component accurately but also to help the controller adapt to sudden external influences affecting the pam system. as a result, control performance is improved. the effectiveness of the employed control approach is verified by experiments under different conditions. in addition, the stability of the overall system is proven by lyapunov theory. ii. system description the system structure consists of two artificial muscles in antagonistic setup as shown in figure 1. two pams are supplied from an air compressor through two proportional valves (smc, itv-2030-212s-x26). one muscle bundle contracts while the other relaxes when the artificial muscle system is inflated and deflated through two proportional valves, causing the pulley to revolve about its axis of rotation. a potentiometer (wdd35d8t) measures the rotational angle produced. for software, the proposed controller is programmed on an education controller type from national instrument (myrio-1900). the controller calculates the potentiometer's feedback angle value and sends the control output to the electric control valves. labview software is used to monitor the entire procedure. fig. 1. the pam-based experiment platform. fig. 2. the working principle of pam-based antagonistic configuration. figure 2 depicts the operating principle of the pams. the two muscles are simultaneously initialized with the same amount of gas at the same pressure �� = 0.2mpa, causing them to contract to the same position �� . when the lower muscle bundle is injected with a pressurized amount of air ∆p and at the same time the upper muscle is reduced by a corresponding amount of air, the lengths of the two muscle bundles change as �� − �� and �� − � respectively. as a result, the pulley rotates at an angle of . therefore, controlling the change in air pressure inside the two muscles will result in a change in the pulley rotation angle. the internal pressure of both pams is obtained as follows: 1 0 2 0 p p p p p p       (1) the control voltage of the proportional regulator valve pam is determined using (1) as follows: 1 0 0 0 2 0 0 0 ( ) ( ) u u u k p p u u u k p p           (2) where � and �� are two voltages applied to two proportional regulator valves corresponding to the two pams, � is a constant indicating the voltage-pressure relationship on the valve, and � is the control variable that regulates the amount of pressure change ∆� because the rotation angle of the pulley is changed by altering the control output � of the two proportional valves. as a result, the control output � would be the only input variable, with the observed joint angle being the output. after introducing the disturbance, the discrete-time siso model of the system can be expressed by: 0 0 n m k i k i j k j k i j y a y b u p         (3) where �� is the control output at instant k, �� is the pulley’s angle, �� represents the system disturbances. the model parameters are �� and �� . in [17], the authors chose a secondorder discrete-time model (with m = n = 2) and the leastsquares method to determine the mathematical model for pam. the coefficients of the model are shown in table i. table i. mathematical model parameters parameter value a1 1.9567 0.0092  a2 0.9576 0.0128  b1 0.0126 0.0013 b2 0.0124 0.0049 iii. controller design the design of the adaptive sliding mode controller (asmc) is described in this section. firstly, the smc is designed based on the sliding surface theory. the system's uncertainty disturbance component is then estimated using an adaptive law-based noise observer. as a result, the control quality of the smc is improved. finally, the controller is verified for stability based on the lyapunov stability condition. figure 3 illustrates the block diagram of the overall system. the recommended smc is described in the next subsection. engineering, technology & applied science research vol. 13, no. 1, 2023, 10086-10092 10088 www.etasr.com dao-et al.: an adaptive sliding mode controller for a pam-based actuator fig. 3. block diagram of the proposed control approach. a. sliding mode controller tracking deviation is determined by: k k ke y y   (4) where �� ∗ is the reference signal. consider a sliding surface as follows: 1k k ks e e   (5) where � is the tuning parameter 0 � � � 1 . equation (5) is rewritten as: 1k k k k s y y e    (6) replacing �� from (3) and (6) can be expressed as: 1 1 0 0 n m k k i k j k j k k i j s y a y b u p e            (7) to ensure the sliding variable is driven on the sliding surface, the following reaching law is taken into consideration. 1 ( )k k k sw ks s s k sign s     (8) or: 1 ( )k k sw ks s k sign s  (9) where ��� � 0 is the control gain. by replacing � from (9) into (7), the control signal �� becomes: 1 01 1 1 1 [ ( )] n m k k i k i j k j i j k k k sw k u y a y b u b p e s k sign s                 (10) component �� in �� is a variable of the unknown system disturbance. as a result, we propose in this paper an observer that uses adaptive law to estimate that component, and thereby improving the efficiency of the smc. finally, with the estimated value �̂� of �� , the control signal �� is calculated as: 1 01 1 1 1 [ ˆ ( )] n m k k i k i j k j i j k k k sw k u y a y b u b p e s k sign s                 (11) the architecture of an adaptive law-based disturbance observer is examined in greater depth below. b. adaptive algorithm as previously stated, the unknown disturbance �� has a significant impact on the control signal �� . the proposed adaptive algorithm for estimating the �� component improves the control signal's accuracy. the following is a presentation of the adaptive law: 1 ˆ ˆ k k kp p s  (12) where " is a strictly positive constant related to the adaptation rate. it is clear that: 1 ˆ ˆ ˆ k k k kp p p s    (13) equation (13) also shows that there is no adaptation when states are on the sliding surface: ˆ 0kp  for 0ks  (14) c. stable analysis of adaptive sliding mode controller this subsection presents the stability analysis of the proposed controller using the lyapunov stability condition. it allows the asmc's parameter to be determined. consider the error value of the actual system disturbance component and the estimated component of the observer. ˆ k k kp p p ɶ (15) it is obvious that: ˆ k k kp p p    ɶ (16) when the sliding surface variable is 0, (14) indicates that there won't be any adaptation, resulting in the following calculation of ∆�#�: ˆ k k kp p s   ɶ (17) the following lyapunov function is used as the base for the stability proof of the proposed controller: 2 21 1 2 2 k k kv s p   ɶ (18) hence, we have: 2 2 2 2 1 1 1 1 1 1 1 2 2 2 2 k k k k k k k v v v s s p p           ɶ ɶ (19) consider the following expression: 2 2 2 1 1 1 1 ( ) 2 2 2 s k k k k ks s s s s       (20) on the other hand, ∆ � is represented as: 1 1 1 1 0 n k k k k i k i i m j k j k k k j s s s y a y b u p e s                    (21) substituting �� from (11) into (21) we get: engineering, technology & applied science research vol. 13, no. 1, 2023, 10086-10092 10089 www.etasr.com dao-et al.: an adaptive sliding mode controller for a pam-based actuator ( )k k sw ks p k sign s   ɶ (22) then, (20) becomes:   2 2 1 ( ) ( ) 2 1 ( ) ( ) 2 s k sw k k k k k sw k k k p k sign s s s p s k sign s s s            ɶ ɶ (23) next, we consider the following expression:  22 2 1 1 1 1 1 . 2 2 2 p k k k k k p p p p p           ɶ ɶ ɶ ɶ ɶ (24) replacing k kp s ɶ into (24), we obtain:     2 21 1 1 . 2 2 p k k k k k k p p p p s p           ɶ ɶ ɶ ɶ ɶ (25) from (19), (23), and (25) we have:     22 22 1 1 ( ) ( ) 2 2 1 1 ( ) ( ) 0 2 2 k s p k k sw k k k k k k sw k k k k v p s k sign s s s p s p k sign s s s p                       ɶ ɶ ɶ ɶ thus, the system is asymptotically stable. iv. experimental results a series of different circumstances is conducted to verify the effectiveness of the proposed asmc controller. the experiment uses two types of input signals: pure-sine and mixed-sine trajectories, as follows: ( ) 20 sin 2f t f (24) ( ) 20 sin 2 12.8 sinf t f f   (25) these types of signals change frequency, from 0.1hz to 0.8hz, during the experiments. furthermore, the system is evaluated with two scenarios, with load and no-load, for each input signal at a certain frequency. with the sample time ts of 5ms, the control algorithm will be built using the labview/myrio toolbox and then incorporated into the myrio-1900 controller. on the labview interface, the whole motion trajectory of the object will be measured and presented. the conventional smc is used as a counterpart to demonstrate the proposed controller's usefulness. table ii shows the parameters of the asmc and smc after fine-tuning. below the system is tested to track pure-sine orbitals with frequency varying between 0.1 and 0.8hz. the analytical evaluation will show the advantages of tracking the performance of asmc than of smc. a load of 5.0kg also is added to the system to evaluate the robustness of the system when there are external disturbances. in subsection b, the same test scenarios and evaluations as subsection a are repeated. however, the input signal will be mixed-sine orbitals to test the capabilities of asmc compared to smc. table ii. adsmc and dsmc parameters parameters ksw α φ asmc 0.5 0.1 0.04 smc 0.75 0.1 a. experiment with pure-sinusoidal reference signal the system is evaluated when tracking pure-sine wave signals with frequencies ranging from 0.1 to 0.8hz. the system operates with both load and no-load situations for each input signal. for example, figure 4 demonstrates the experimental results when the system tracks 0.1 and 0.5hz desired signals without a load. it can be seen that, at zero load, the tracking performance of asmc is better than smc's, especially in the steady state. particularly, the maximum deviation values of asmc and smc at 0.1hz are about 1.0 o and 3.0 o , respectively. meanwhile, the performance of two controllers at 0.5hz are 3.0 and 4.0 o , respectively. there is no significant difference between the two controllers at the transient state. (a) (b) fig. 4. experiment results for tracking a pure-sinusoidal signal without a load: (a) 0.1hz, (b) 0.5hz. with the system under loaded scenario in figure 5, we observe that both controllers are affected. however, asmc still outperforms smc in terms of tracking performance. in engineering, technology & applied science research vol. 13, no. 1, 2023, 10086-10092 10090 www.etasr.com dao-et al.: an adaptive sliding mode controller for a pam-based actuator more detail, the highest deviation values for smc and smc at 0.1 hz are 2.0 and 4.0 o , respectively. the tracking performance of both controllers is lowered at 0.5hz, with the highest errors of 4.5 and 5.0 o , respectively. table iii shows the rmse of the two controllers under the first scenarios experiment. (a) (b) fig. 5. experiment results for tracking a pure sinusoidal trajectory with a load (m = 5.0kg): (a) 0.1hz, (b) 0.5hz. b. experiment with mixed-sine reference signal finally, asmc and smc are tested with mixed-sine orbital input. figures 6 and 7 depict the tracking performance results of the two controllers when the system is tested under no-load and loaded conditions, respectively. in the case of no-load scenario, although the trajectory is more complicated, samc still performs well in terms of tracking, in contrast to smc. it is observed that the response rate of smc is slower than the change of the orbital reference signal. for example, at 0.25hz, asmc's highest deviation value is 3.0 o , while smc's is 6.0 o . at 0.4hz, the maximum error value of the two controllers is 4.0 and 7.0 o , respectively. when the system had a load, the general trend of the two controllers is still to show reduced tracking performance, but asmc still shows its ability in orbit tracking. (a) (b) fig. 6. the results of the experiments for tracking a mixed sinusoidal trajectory without a load:(a) 0.25hz, (b) 0.4hz. table iii. rmse of the two controllers with sinusoidal orbital signal frequency (hz) without load load m = 5kg asmc smc asmc smc pure-sine signal 0.1 0.7 1.8 0.8 2.5 0.5 2.8 3.5 3.3 3.9 0.8 3.9 5.0 4.1 5.2 mixed-sine signal 0.05 0.9 1.9 0.9 2.0 0.25 5.0 5.9 5.5 6.4 0.4 6.6 7.1 6.7 7.3 in both pure-sine and mixed-sine trajectories, with or without load, the asmc always shows advantages over the conventional smc. the proposed adaptive algorithm has observed the disturbance successfully. thus, the disturbance is rejected, and the tracking performance is increased significantly. in the case of sudden load change, the driving trajectory of the pam under the control of asmc almost immediately returns to the steady-state as before the load changed. moreover, in a load scenario with a pure sinusoidal input signal at low frequency (0.1hz), the rmse value of asmc is only 1.0 o , while that of traditional smc is larger (2.0 o ). with mixed-sine trajectories, the results are the same. in engineering, technology & applied science research vol. 13, no. 1, 2023, 10086-10092 10091 www.etasr.com dao-et al.: an adaptive sliding mode controller for a pam-based actuator terms of 0.4hz frequency trajectories, the asmc has a rmse value of 6.0 o , which is lower than the rmse value of the traditional smc (7.0 o ). however, the asmc still has the limitation that the transient time is larger than that of the traditional smc. this is a common disadvantage of adaptive controllers because it takes a certain amount of time to update the value of the parameter it estimates. the asmc still shows outstanding performance in the steady state in all experimental scenarios. (a) (b) fig. 7. experiment results for tracking a mixed sinusoidal trajectory with a load (m = 5.0 kg): (a) 0.25hz, (b) 0.4hz. v. conclusion this paper proposes a sliding mode controller with an adaptive disturbance observer for a pam-based actuator. the proposed adaptive sliding mode control shows accuracy quality in orbit tracking, and good adaptability to external disturbances. those qualities are all verified through different test scenarios with pure-sine and mixed-sine input signals at the frequency range from 0.05 to 0.8hz. the adaptive algorithm helps to accurately estimate the system noise, thereby improving the control quality of conventional sliding mode controllers. because of the disturbance observation process, the transient time of asmc is larger than that of the traditional smc. the asmc still shows outstanding performance in the steady state in all experimental scenarios. in following research, solutions to speed up the disturbance estimation will be studied in order to shorten the transient process for the proposed controller, thereby helping the controller to show better quality in the two aspects of transient and steady-state times for pam. acknowledgment this research is funded by the hanoi university of science and technology (hust) under project number t2022-pc-002. references [1] f. daerden and d. lefeber, "pneumatic artificial muscles: actuators for robotics and automation," european journal of mechanical and environmental engineering, vol. 47, no. 1, pp. 11–21, 2002. 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revised: 5 august 2022 | accepted: 16 august 2022 abstract-the electron impact ionization is a crucial atomic process in the collisional radiative model and the study of ionization balance. the superstatistics theory, which was originally proposed for the study of non-equilibrium complex systems, has recently been extended to studies of small systems interacting with a finite environment due to their interesting statistical behavior. this paper introduces the superstatistics formalism in the case of ionization rates with different values of the dynamical parameter q and shows how it affects the calculation of the ionization rates for li + . moreover, the distribution function for the effective boltzmann factor of superstatistics was swapped. keywords-ionization rates; boltzmann factor; superstatistics; code fac; cross-section i. introduction electron impact ionization of neutral atoms has been proven to be significant in a variety of fields, including mass spectrometry and plasma physics [1]. thomson utilized the ionization of atoms by charge impact in the early 1910s. since then, many others, have amended it [2, 3]. furthermore, electron-impact ionization has been used to measure a detailed ionization spectrum and cross-sections using various methods [4]. plasma is important in nuclear physics because many studies showed that it can take various shapes, including nonequilibrium plasma that is used to change the characteristics of the surface [5, 6]. the characteristics of non-equilibrium plasmas are known through the ionization of atoms and molecules by electron impact, which has great practical significance. experimental data, which include laboratory plasma at low and high temperatures, atmospheric physics, and mass spectrometry, are also significant as they can be compared to theoretical predictions [7, 8]. ionization occurs when an electron collides with a neutral particle with sufficient energy to produce a positive ion and a free electron [9]. superstatistics is a subfield of statistical physics or mechanics that studies nonlinear and nonequilibrium systems [10]. it is characterized by the use of a superposition of several distinct statistical models to attain the desired nonlinearity. in ordinary statistical terms, this is similar to compounding the distributions of random variables, and it can be thought of as a simple case of a doubly stochastic model [11, 12]. furthermore, superstatistics contends that in systems with temperature fluctuations, coarse-grained measurements of the energy performed over spatial and temporal scales are larger than those determined through the correlation properties of the temperature. yield statistical distributions can be considered as a superposition of canonical distributions. superstatistics [10, 1317] is a powerful modeling and/or analysis technique for complex systems with two or more distinct time scales in dynamics. the fundamental idea is to consider a superposition of several systems in local equilibrium, each with its inverse temperature, and then take an average over the fluctuating that are disseminated according to some probability density for theoretical modeling. in general, the parameter does not have to be an inverse temperature but could be any system parameter that shows large-scale fluctuations, such as energy dissipation in a turbulent flow or financial market volatility [18]. finally, all relevant expectation values for the complex system are averaged over this distribution. several applications have been previously described, including modeling the statistics of classical turbulent flow [19, 20], quantum turbulence [21], spacetime granularity [22], stock price changes [23, 24], virus infection pathways [25], and more [4, 25-27]. once incorporated into the fluctuating parameter, superstatistical systems are efficiently described by more general measures than the boltzmann–gibbs entropy. the following question can be asked: what entropy statistics appear in the case of a fluctuating control parameter? this study aimed to develop a generalization of the beck-cohen superstatistics that makes possible to appropriately consider such fluctuations. the main idea was to use superstatistics to replace the distribution function via the effective boltzmann factor and introduce the superstatistics formalism in the case of ionization rates with different values of q. ii. superstatistics long-range interactions between different ions and electrons dominate in the plasma state, causing these systems to corresponding author: samia dilmi engineering, technology & applied science research vol. 12, no. 5, 2022, 9342-9346 9343 www.etasr.com dilmi et al.: the effects of superstatistics properties on hot plasma be in highly non-equilibrium states. even when these systems achieve a steady state, they do not adhere to boltzmann-gibbs statistics [14]. the following critical question is asked: do these steady-state plasmas have a well-determined temperature? superstatistics was introduced in 2003 as an interesting suggestion for the treatment of non-equilibrium steady-state systems [10] and depends on ordinary boltzmann statistics, which are formed as a tool to study systems with complex dynamics and non-equilibrium [15]. in a nonboltzmann-gibbs distribution, where the systems are out of equilibrium and non-extensive, superstatistics displays a relative motion to explain the gain of it [27]. these statistics admit the superposition of canonical ensembles at different temperatures [28]. superstatistics is a branch of statistical mechanics that occurs in non-equilibrium and stable states with large parameter fluctuations. they were named superstatistics because they are a type of "statistics of statistics" [28]. superstatistics systems are a superposition of two (or more) different statistics: one is given by ordinary boltzmann factor, and the other by large-scale fluctuations of one (or many) intensive parameters, e.g. the inverse temperature [29]. since then, it has been used to describe a wide variety of dynamic structures with changing environmental conditions [30]. this new type relies on ordinary statistical mechanics, described by the ordinary boltzmann factor e -βe , thus an effective boltzmann factor b(e) for the full system can be defined as [31]: ���� = � ���� �� � = 〈 �� 〉 � � (1) where f(β) is the normalized probability distribution, e is the effective energy in each cell, and 1 b k t β = is approximately a constant. at the same time, the normalized probability distribution must be realized by probability density [10]: ���� = δ�� − ��� (2) where β0 is the average of β (fixed constant) and δ is the dirac delta. the probability density f(β) has to provide the following conditions: 1. it must be a normalized probability density, it may be a physically relevant density from statistics, such as gaussian, uniform, etc. [32]. 2. when there are no fluctuations in intensive quantities, the new statistics decrease to boltzmann-gibbs statistics [33, 34], and has to be normalizable [34]. there are two types of superstatistics: • type-a superstatistics, where the boltzmann factor is normalized to yield the stationary long-term probability distribution [35]: ���� = � ���� ���� �� (3) • type-b superstatistics: as the distribution in type a is not properly normalized, a better way of writing would be [36]: ���� = � � ��� ���� ���� � (4) ���� = � ���� � � � (5) where z(β) is the normalization constant of e -βe for a given β. τhis approximation represents the leading order correction to ordinary statistical mechanics for a nonhomogeneous system with small temperature fluctuations. following this approximation, it was demonstrated that the generalized boltzmann factor for any distribution is given by the following: ���� = ��� �1 + � ! � + ∑ ���# $! 〈�� − ��� $ 〉�$ �∝$'( (6) with average 〈�〉 = �� = � ����� � � � , and variance ! = 〈� 〉 − 〈�〉 . the zeroth-order approximation to b(e) corresponds, as is expected, to the "pure" boltzmann statistic: ���)�~ 〈�〉�+ . this universality indicated that the superstatistics theory is restricted by two universal parameters (β, q) with: , = 〈�-〉 〈�〉 (7) in (7), the parameter q is simply the coefficient of variation of the distribution f(β) defined by the standard deviation to mean ratio. the fluctuation of the intensive parameter β is controlled by this parameter. if there are no fluctuations, q=1 [10]. to easier deal with the boltzmann factor, it was imposed into a general form as [10]: ���� = ��� �1 + � �, − 1��� � + .�,��� (�( … � (8) where the function g(q) is determined by the used superstatistics. the following can be obtained: .�,� = 0 (uniform and 2-level) (9) = − 1 3 �, − 1� (gamma) (10) = − 1 3 �,( − 3, + 2� (log-normal) (11) = − 1 3 �, − 1��5, − 6� 3 − , (f-distribution) (12) finally, superstatistics has become a hot topic in recent years, with applications in a variety of fields of physics [37]. iii. calculation of the ionization rates from superstatistics distributions this study aims to calculate the ionization rates from superstatistics distributions. free electrons are represented by a specific energy distribution within the plasma. the ionization rates were calculated through the integration of a cross-section of a collision that depends on energy over the energy distribution functions. the ionization rates by electron impact were calculated by averaging the product of the electron's velocity and the ionization cross-section. an ionizing collision results in an electron impact process, resulting in a low-energy electron and an atomic ion if an electron receives sufficient energy (via super-elastic collisions), which is equivalent to the neutral atom's ionizing potential. the ionization rates for direct ionization are defined by [38, 39]: 4 = � 5!�6�7�6� 6 (13) engineering, technology & applied science research vol. 12, no. 5, 2022, 9342-9346 9344 www.etasr.com dilmi et al.: the effects of superstatistics properties on hot plasma where v is the velocity of the incident electron, σ(ε) is the impact ionization cross sections calculated by the fac code [40, 41], f(ε) is the electron energy distribution function, and ε is the energy of the impacting electron. the associated rate coefficients could be represented by a simple analytical formula using the appropriate approximation for the energy dependency of the cross-sections. two types of distribution functions were used in previous studies for the ionization rates: maxwellian and non-maxwellian. indeed, superstatistics provides an effective description of their tools, having demonstrated their adaptability in advanced research. as a result, the calculations were extended to the case of plasma by replacing f(ε) in (13) with the effective boltzmann factor b(e) using the superstatistics distribution function. the fac code [40] was used for the calculation of the li+ crosssections, where the relativistic distorted wave (dw) approximation method with an interpolation-factorization method [42] was used. the type of most physically pertinent averaging process for a generic system with intense parameter fluctuations is an intriguing question. the answer to this question depends on the physical problem under consideration. depending on the underlying microscopic dynamics, different non-equilibrium systems may necessitate different types of superstatistics. when using the effective boltzmann factor: 4 = � 5!������� � (14) the ionization rates become: 4 � � 5!��� ��� 81 � � �, � 1��� � � .�,���(�(9 � � � (15) where g(q) refers to the previously shown superstatistics formulas. iv. results and discussion the above definitions can be used to obtain the results of measuring the ionization rates of li + for the gamma, lognormal, and f-distributions for various values of q in figures 1, 2, and 3. li + ionization rates were calculated using (15) and the various g(q) functions, which rely on the superstatistics concept. the values of the rate coefficients in figures 1-3 increase very quickly at low temperatures. in the case of high temperatures, the ionization rate curves were very sensitive to q values, and the curves gradually moved away from each other as the q values increased. there is a convergence of the curves for the same distribution and a lot of coordination between the curves for all three functions, especially for low values of q. in general, the behavior of all superstatistics at high temperatures differs, as it is strongly dependent on the f(β) function, but the behavior at low temperatures is universal. furthermore, it should be noted that the first-order corrections to the boltzmann factor ��� for the above distribution functions can be written in a universal form. the physical meaning of this broadly defined parameter q is simply the coefficient of variation of the distribution f(β), defined by the standard deviation/mean ratio. if there are no fluctuations in β, q equals to 1. fig. 1. ionization rates of li+ obtained by the gamma distribution with different values of q. fig. 2. ionization rates of li+ obtained by the log-normal distribution with different values of q. fig. 3. ionization rates of li+ obtained by the f-distribution with different values of q. v. conclusion this study used the fac code for the calculation of the cross-sections of li + . the maxwellian distribution function of energy was replaced by an effective boltzmann factor for various distribution functions to estimate ionization rates from cross-sections. as superstatistics and maxwellian statistics have similarities when q is close to 1, the results showed a good agreement between the designed curves for various values of q. however, instead of applying deviations to a engineering, technology & applied science research vol. 12, no. 5, 2022, 9342-9346 9345 www.etasr.com dilmi et al.: the effects of superstatistics properties on hot plasma superstatistical non-equilibrium system, they were applied to an ordinary statistical mechanics equilibrium system with an inverse temperature. moreover, superstatistics theory requires the presence of temporally local equilibrium within the plasma, which appears to be a non-equilibrium thermodynamic system. thus, the introduction of superstatistics formalism in the case of ionization rates with different values of q was limited to agreement with other statistics. the connection between the maxwellian distributions and the beck-cohen superstatistics can be noted, as the relationship between the superstatistics approach and the different values of q on the calculation of lithium ionization rates li + was shown. the dynamic parameter q of (7) can be defined in superstatistics methods. it was shown that all superstatistics have universal behavior for small variances in the fluctuations. there were differences of large variance that gave information on the underlying complex dynamics [43]. in general, 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[43] n. b. serradj, a. d. k. ali, and m. e. a. ghernaout, "a contribution to the thermal field evaluation at the tool-part interface for the optimization of machining conditions," engineering, technology & applied science research, vol. 11, no. 6, pp. 7750–7756, dec. 2021, https://doi.org/10.48084/etasr.4235. microsoft word etasr_v12_n5_pp9142-9148 engineering, technology & applied science research vol. 12, no. 5, 2022, 9142-9148 9142 www.etasr.com nagao & kurachi: an experimental and analytical study on the seismic performance of piers with … an experimental and analytical study on the seismic performance of piers with different foundation bottom widths takashi nagao research center for urban safety and security kobe university kobe city, japan nagao@people.kobe-u.ac.jp yoshinao kurachi technical division oriental shiraishi corporation tokyo, japan yoshinao.kurachi@orsc.co.jp received: 17 may2022 | revised: 19 july 2022 | accepted: 21 july 2022 abstract-piers can be severely damaged by earthquakes. when an action of a massive earthquake is assumed, the seismic performance of the pier can be improved by widening the foundation width. a previous horizontal loading study indicated that extending only the foundation bottom (fb) width, rather than the complete foundation, can boost seismic resilience while suppressing the increase in building cost. however, the research dealt with only two types of fb width, i.e. normal and widened, and the data for sufficiently assessing the inclination angle of the pier with loading were not obtained. in this study, to evaluate the seismic performance of piers with different fb widths in more detail, horizontal loading tests on piers with ordinary columnar foundations and two types of piers with widened fb were conducted, and the seismic resistance of the three pier types were compared. it was shown that horizontal displacement and inclination angle of the pier can be reduced by widening the fb. furthermore, finite element analysis was carried out to reproduce the experimental results. the analysis results showed good agreement with the experimental results in terms of pier horizontal displacement and inclination angle. keywords-pier; foundation; seismic performance; finite element analysis i. introduction the pier is a major port structure that facilitates cargo shipping. since the pier is generally constructed on the soft ground in the coastal area, it can be damaged by earthquakes [1, 2]. due to the enlargement of ships, the pier is required to be deeper in water depth, which brings about an increase in seismic load. in addition, a considerable lateral spreading pressure may act during a massive earthquake, which seismic design codes [3, 4] do not adequately account for [5]. furthermore, the pier is strongly influenced by the ground deformation during earthquakes and undergoes residual displacement [6, 7], even when the structural member is not injured [8]. as a result, from the viewpoint of evaluating the serviceability of the pier, residual displacement needs to be assessed with high accuracy along with structural member safety. when the seismic resistance of the pier is insufficient against the reference earthquake, the cross-sectional width of the foundation is increased to improve the seismic resistance in design practice, but the increase of the foundation width leads to a drastic increase in the construction cost. when a broad foundation is employed, the vertical subgrade reaction operating at the foundation bottom (fb) generates rotational resistance moment opposing the inclination of the pier. however, it should be noted that the subgrade reaction modulus decreases with increasing foundation width [9, 10]. as a way to increase the seismic resistance of the pier while keeping the rise of the construction cost mild, a method of widening only the fb was suggested in a previous study [11], and the horizontal loading test showed that the seismic performance is improved by widening the fb. however, in the previous study, only two varieties of fb width were handled, namely normal and widened, and data for adequately measuring the inclination angle of the pier with loads were not collected. in addition, there is no seismic design method that evaluates the seismic performance of a fb widened pier at the moment. in the current research, in order to assess the seismic performance of piers with different fb widths in more detail, new horizontal loading tests on piers with ordinary columnar foundations and two types of pier with widened fb were performed and the seismic resistance of the models was studied. furthermore, for the development of the seismic design method of the fb widened pier, the findings of the experimental results were reproduced with two-dimensional finite element analysis (fea) and the reproducibility of the experimental results was demonstrated. ii. method horizontal loading experiments of the pier using a mega torque motor were performed. steel rigid frame models imitating piers with 150mm depth were put in the ground in a soil tank 900mm wide and 500mm deep (figure 1). these dimensions were set considering the ease of performing the experiment and to prevent the bottom slab of the soil tank from suppressing the settlement of the pier foundation with loading. the pier model was installed in the central part of the soil tank in the depth direction to avoid the effect of ground confinement by the side wall of the soil tank. a steady brace was fitted to corresponding author: takashi nagao engineering, technology & applied science research vol. 12, no. 5, 2022, 9142-9148 9143 www.etasr.com nagao & kurachi: an experimental and analytical study on the seismic performance of piers with … prevent the pier model from tilting in the soil tank depth direction with loading. figure 2 demonstrates the specifications of the model. a circular cross-section of 120mm in diameter was employed as the normal type, and pier models with the same shape of the column, fbs of 180mm in width and 120mm in depth were used as the widened 1 type, and fbs of 240mm in width and 120mm in depth were used as the widened 2 type. in the previous study [11], the scaling factor (prototype/model) was 100, whereas in this study, a reduced scaling factor of 50 was attained. the normal model weighs 20.145kg, the widened 1 model weighs 25.145kg, and the widened 2 model weighs 28.635kg. fig. 1. soil tank. (a) (b) (c) (d) fig. 2. model specifications (unit: mm): (a) plan view, (b) side view: normal, (c) side view: widened 1, and (d) side view: widened 2. the ground was prepared by air pluviation. tohoku silica sand no. 6 in dry state was used. the target relative density of the ground was 77% which corresponds to the dense ground condition. the foundation of the true pier is embedded into the bedrock to support the structure’s weight. to simulate this situation, loading tests and shake table tests have often been performed in which the fb was fixed to the soil tank [12-16]. however, in such cases, the constraint of the fb due to the bedrock is excessively expressed, leading to no settlement or inclination of the foundation due to loading. the bedrock is a very rigid ground, but it slightly deforms when a load is applied from the fb, therefore, the pier is inclined during an earthquake. in this experiment, the fb of the pier model was not fastened to the soil tank but was put at a height of 165mm from the bottom end of the soil tank. the ground’s thickness was 370mm. the loading was applied at a constant displacement speed of 1.3mm/s and the greatest displacement was 20mm, which is equivalent to 7m on a real scale by similitude [17] based on the scaling factor. the horizontal and vertical displacements of the pier and horizontal load were captured with a data logger. displacement gauges were attached to the model superstructure to measure horizontal and vertical displacements. in [11], horizontal and vertical displacements were evaluated by one displacement gauge respectively. as a result, the displacement and inclination angle of the pier could not be accurately measured. in this research, horizontal and vertical displacements were evaluated by two displacement gauges. noise in the observed data was eliminated similarly to [11] by executing fast fourier transform and inverse fast fourier transform after multiplying with a lowpass filter at 1hz. iii. experimental results the time history of the loading of each case is depicted in figure 3. in about 10 seconds after loading, the value of load decreased in each case. because the loading was done at a constant displacement speed, the pier’s displacement is progressing with decreasing load after roughly 10 seconds. this is because the main displacement mode of the pier changed from the inclination at the early stage of loading to the sliding in the latter half of loading. fig. 3. time history of load. as previously stated, this test does not fix the fb of the pier to the soil tank, therefore, sliding happens in the pier. since the fb of the actual pier is embedded into the bedrock, tilting of the pier occurs when lateral load is applied, but not sliding. following that, we will focus on the results of the first half of loading. based on the data of the four displacement gauges, the horizontal displacement at point a of the superstructure and pressure gauge 5 0 0 3 0 4 7 0 900 1 5 0 mega torque motor steady brace steady brace model (unit: mm) 205 165 plan view side view mega torque motor 0 5 10 15 20 0 0.5 1 1.5 time (s) lo a d ( k n ) engineering, technology & applied science research vol. 12, no. 5, 2022, 9142-9148 9144 www.etasr.com nagao & kurachi: an experimental and analytical study on the seismic performance of piers with … point b1 of the fb illustrated in figure 2, and the inclination angle of the pier were determined (figure 4). the tendency differs between the normal and widened types in the early stages of loading, although there is no significant variation in displacements between the two widened types. for the same load, the horizontal displacements at the fb (point b1) are almost the same, while the horizontal displacement of the superstructure (point a) is significant in the normal type and modest in the widened types. for this reason, the inclination angle of the normal type is larger than that of the widened types. figure 5 illustrates the piers' displacements when the load was 0.69kn, which was the maximum load observed for the normal type. here, the displacements are magnified by a factor of 10. both the horizontal displacement and inclination are large in the order of normal, widened 1, and widened 2 types. the horizontal displacements are 8.54, 4.84, and 4.28mm respectively and the inclination angles are 0.017, 0.008, and 0.006rad respectively. in the previous study [11], the widened type showed approximately 1/3 times the horizontal displacement compared with the normal type. in this study, the widened types have 1/2–1/3 times the horizontal displacements and 1/2 times the inclination angles compared with the normal type. fig. 4. horizontal displacement and inclination angle. (a) (b) (c) fig. 5. displacement of piers: (a) normal, (b) widened 1, (c) widened 2. as was discussed in [10], when the fb is widened, the rotational resistance moment (rrm) caused by the subgrade reaction acting at the fb surface increases and the shear deformation at the soil under the fb decreases. in addition, as was discussed in [11], in the widened type, the rotational center is closer to the center of the superstructure when compared with the normal type, therefore, rrm arm length is larger than in the normal type. those are the major reasons of the high seismic resistance of the fb widened pier when compared with the normal type. the variation in the seismic resistance of the two widened types is remarkable in the range where the horizontal displacement of the superstructure (point a) exceeds 6mm, which is equivalent to 2.1m on the real scale by the similitude [17]. the allowable displacement for quay wall during an earthquake is 1m or less in the seismic design code [6], therefore, this amount of displacement is greater than what is permitted in seismic design. as a result, widening the fb to 1.5 times the width of the foundation column would be sufficient to improve the seismic resilience of the pier. iv. finite element analysis a. analytical method two-dimensional fea was performed to reproduce the experimental results. the analysis code employed is flip [18], by which the seismic responses of port structures such as piers have been evaluated [8, 19]. the code employs a multi-spring model [20] to express the ground response under principal stress axes rotation. the nonlinearity of the ground is expressed as (1) using a hyperbolic model [21]. 00 1 1 m g gg γ τ = + (1) where g is the shear rigidity, g0 is the initial shear rigidity, γ is the shear strain, and τm is the shear strength, which is calculated by [22]: τm=σm' sin φ (2) where σm' is the effective confining pressure and φ is the shear resistance angle. the shear resistance angle of the ground is calculated using the relative density by referring to [22]. the ground shear rigidity gm at each depth is calculated by [23]: 0.5 ' ' m m ma ma g g σ σ   =     (3) where gm is the shear rigidity, gma is the reference shear rigidity, σm' is the effective confining pressure, and σma' is the reference effective confining pressure corresponding to the reference shear rigidity. the shear rigidity of the ground is calculated by (4) using young’s modulus. based on the results of a separate compression experiment, the young’s modulus was determined to be 2437kpa at the center depth of the ground. ( )2 1 m m e g ν = + (4) 0 2 4 6 8 10 0 0.5 1 point a displacement (mm) lo a d ( k n ) 0 2 4 6 0 0.5 1 point b1 displacement (mm) lo a d ( k n ) 0 0.01 0.02 0 0.5 1 inclination angle (rad) lo a d ( k n ) engineering, technology & applied science research vol. 12, no. 5, 2022, 9142-9148 9145 www.etasr.com nagao & kurachi: an experimental and analytical study on the seismic performance of piers with … where em is the young’s modulus, gm is the shear rigidity, and ν is the poisson’s ratio. the superstructure and foundations of the pier are modeled by linear beam elements, and the variation in weights of each pier is expressed by changing the density of the foundation elements. because the ground above the fb is assumed to act integrally with the pier in the widened types, the influence is accounted for in the foundation element densities. tables i and ii indicate the parameters of the ground and pier, respectively. table i. ground parameters σma' (kpa) 2.06 gma (kpa) 916.2 ρ (t/m3) 1.483 φ (°) 41.2 ν 0.33 ρ: density table ii. pier parameters superstructure foundation normal widened 1 widened 2 g (kpa) 7.69×10 7 ν 0.33 ρ (t/m3) 2.624 0.827 2.172 3.112 a (m 2 ) 0.0090 0.0113 i (m 4 ) 2.70×10 -6 1.02×10 -5 ρ : density, a: area, i: moment of inertia soil-spring elements were arranged at the boundary between the foundation and the ground except for the fb. in two-dimensional analysis, this element reproduces the effect of the soil slipping through the columnar foundations with loading, and the soil-spring force estimated using (5) is proportional to the ratio of the soil’s shear stress increment to shear strain increment (dτ/dγ). h dk d α τ β γ = (5) where kh is the soil-spring modulus and α and β are the coefficients decided following the diameter and spacing of the foundation. since the soil elements exhibit nonlinear characteristics, the spring force reflects the effect of the decrease in the soil rigidity with loading. a frictional resistance force equivalent to the initial shear rigidity of the ground acts in the axial direction of the foundation until the shear stress reaches shear strength. at the fb, nonlinear spring elements with rigidity in three directions, i.e. axial spring, perpendicular to axial spring (shear spring), and rotational spring, are arranged. the axial spring’s characteristic is defined as the relationship between the axial spring force and displacement difference. when the node of the fb is placed below the node of the ground element in contact with the fb, the displacement difference is described as negative. the subsidence of the fb is always accompanied by the same amount of subsidence of the ground due to loading; therefore, the displacement difference is not negatively generated. as a result, it was set to form a very large axial spring force when the displacement difference is in the negative range. in contrast, a positive displacement difference corresponds to the circumstance in which the fb on the loading side floats up while the pier is inclined. because there is no tensile force acting between the fb and the ground at that moment, the axial spring force is adjusted to practically zero when the displacement difference is positive. the shear spring expresses the sliding of the pier. first, maximum static friction force was assessed by assuming the friction coefficient between pier fb and the ground to be 0.5. the shear spring stiffness was set to be: (1) as much as the shear rigidity of the ground when the shear force was less than 0.5 times the maximum static friction force, (2) half of the shear rigidity of the ground when the shear force was 0.5–1.0 times the maximum static friction force, and (3) 5% of the shear rigidity of the ground when the shear force was more than the maximum static friction force. the rotational spring is bilinear, and the parameters were chosen to create the rrm in accordance with the fb width, as described in [10]. figure 6 depicts the nonlinear spring elements’ properties. figure 7 shows the fe mesh around the pier model. the soil mesh measures 15mm in height and 50mm in width. to account for the difference in ground rigidities in the vertical direction, the ground was divided into two elements: the top layer colored orange and the lower layer colored green, although the same parameters were applied to both soil elements. the side and bottom surface boundary conditions were designed to be fixed boundaries. fig. 6. characteristics of nonlinear springs. fig. 7. fe mesh. 4− 2− 0 2 4 1− 10 3 × 500− 0 500 axial spring displacement difference (mm) a x ia l fo rc e ( k n ) 1− 0 1 0.1− 0 0.1 shear spring displacement difference (mm) sh e a r fo rc e ( k n ) 0.01− 0 0.01 3− 10 3− × 2− 10 3− × 1− 10 3− × 0 1 10 3− × 2 10 3− × 3 10 3− × rotational spring rotational difference (rad) m o m e n t (k n m ) engineering, technology & applied science research vol. 12, no. 5, 2022, 9142-9148 9146 www.etasr.com nagao & kurachi: an experimental and analytical study on the seismic performance of piers with … b. analysis results figure 8 compares the analysis results with the experimental results on the horizontal displacement of the superstructure (point a), vertical displacements of the fb (points b1 and b2), and inclination angle for the normal type. when settlement occurs, the vertical displacement is defined as negative. early in the loading stage, the analytical findings of points a, b1, b2, and inclination angle showed fairly high agreement with the experimental data. however, they tended to be somewhat underestimated. in the latter half of the loading, the analysis results of the displacement and the inclination angle increased rapidly, and the deviation from the experimental results is large, because loading increased the shear stress of the soil element in contact with the fb, and the shear strain rose suddenly in the later part of loading due to the impact of the ground’s nonlinear properties. figure 9 depicts the time histories of vertical strain and shear strain of the soil element in contact with the fb (point b1). the normal strain grows steadily over time, but shear strain increases drastically when displacement and inclination in figure 7 increase rapidly. fig. 8. analysis results (normal type). fig. 9. ground strain. c. discussion the cause of the mismatch between the analysis and the experimental results in the latter half of loading is discussed in this section. in this analysis, the foundation is treated as a beam element with no breadth, such that the pier load operates as a concentrated load on the ground element in contact with the fb. as a result, the shear stress in the soil element tends to be overestimated. because the fb has a width, a distributed load is given to the ground, making the effect of ground nonlinearity unlikely to be realized. to enhance the reproducibility of the experimental results, this paper changes to an elastic element in which nonlinearity does not occur on the soil element below the fb. figure 10 depicts the analysis findings. the fb subsidence understates the experimental results slightly since soil materials at the foundation’s bottom edge do not exhibit nonlinear behavior, but reproducibility is greatly improved for horizontal displacement, vertical displacement, and pier inclination angle. fig. 10. analysis results (normal type)/ figures 11 and 12 demonstrate the analysis results of widened 1 and widened 2 types respectively using the soil element below the fb as an elastic element. because the fb is wider in the widened types, it floats with loading at point b1, but this phenomenon cannot be recreated in the analysis because the foundation is modeled by beam elements. however, the floating of point b2 at the fb on the loading side is well reproduced, and the inclination of the superstructure (point a) is also very well reproduced. as a result of referring to the modeling in this study, it can be determined that accurate analysis can be carried out for the seismic response of the pier whose foundation is embedded into stiff ground. fig. 11. analysis results (widened 1 type). 0 2 4 6 8 10 30− 20− 10− 0 10 point a: horizontal time (s) d is p la c e m e n t (m m ) 0 2 4 6 8 10 2− 1− 0 1 point b1: vertical time (s) d is p la c e m e n t (m m ) 0 2 4 6 8 10 5− 0 5 10 15 20 point b2: vertical time (s) d is p la c e m e n t (m m ) 0 2 4 6 8 10 0.01− 0 0.01 0.02 0.03 0.04 0.05 time (s) in c li n a ti o n ( ra d ) 0 2 4 6 8 10 0 5 10 3− × 0.01 0.015 0.02 time (s) st ra in 0 2 4 6 8 10 15− 10− 5− 0 point a: horizontal time (s) d is p la c e m e n t (m m ) 0 2 4 6 8 10 1− 0.5− 0 pont b1: vertical time (s) d is p la c e m e n t (m m ) 0 2 4 6 8 10 5− 0 5 10 point b2: vertical time (s) d is p la c e m e n t (m m ) 0 2 4 6 8 10 0.01− 0 0.01 0.02 0.03 0.04 0.05 time (s) in c li n a ti o n ( ra d ) 0 2 4 6 8 10 15− 10− 5− 0 point a: horizontal time (s) d is p la c e m e n t (m m ) 0 2 4 6 8 10 1− 0.5− 0 point b1: vertical time (s) d is p la c e m e n t (m m ) 0 2 4 6 8 10 5− 0 5 10 point b2: vertical time (s) d is p la c e m e n t (m m ) 0 2 4 6 8 10 0.01− 0 0.01 0.02 0.03 0.04 0.05 time (s) in c li n a ti o n ( ra d ) engineering, technology & applied science research vol. 12, no. 5, 2022, 9142-9148 9147 www.etasr.com nagao & kurachi: an experimental and analytical study on the seismic performance of piers with … fig. 12. analysis results (widened 2 type). v. conclusion in this study, in order to evaluate the seismic performance of piers with different fb widths in more detail, horizontal loading experiments for the pier with an ordinary columnar foundation and two types of the pier with widened fb were performed, and the seismic resistance difference of the three pier types was compared from the viewpoint of horizontal displacement and inclination angle. two-dimensional fea was used to replicate the experimental results, and the reproducibility of the experimental results was studied. the main conclusions obtained by this study are: • regarding the seismic performance of three pier types in which the fb width differs, there are large variations in the seismic performance between the normal type and the widened fb types, and displacement and inclination of the pier can be reduced by widening the fb. because there is no significant difference in seismic performance between the two widened types within the range of displacement allowed in seismic design, it is recommended that the fb width should be about 1.5 times the foundation width of the columnar part to improve seismic performance while keeping the increase in construction cost to a minimum. • the two-dimensional fea modeling of the ground and pier enables us to evaluate accurately the response of the pier during horizontal loading. to avoid overestimating the shear strain produced in the ground at the fb when modeling the foundation with beam elements, the ground below the fb should be modeled as an elastic body, whereas nonlinearity should be considered for the ground above it. a suitable parameter setting approach for the spring element to be deployed at the soil-foundation boundary was presented. these findings pave the way for a rational seismic design method of the pier with widened fb. acknowledgments the authors are grateful to yohei ninomiya and ryota tsutaba for their help in carrying out the experiments. references [1] s. werner, n. mccullough, w. bruin, a. augustine, g. rix, b. crowder, and j. tomblin, "seismic performance of port de port-auprince during the haiti earthquake and post-earthquake restoration of cargo throughput", earthqake spectra, vol. 27, no. s1, pp. 387–410, oct. 2011, https://doi.org/10.1193/1.3638716. 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[16] j. w. yun and j. t. han, " dynamic behavior of pile‑supported wharves by slope failure during earthquake via centrifuge tests", international journal of geo-engineering, vol. 12, no. 33, nov. 2021, https://doi.org/ 10.1186/s40703-021-00161-4. 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[19] s. iai, "seismic analysis and performance of retaining structures," in geotechnical earthquake engineering and soil dynamics iii, seattle, wa, usa, 1998, pp. 1020–1044. [20] i. towhata and k. ishihara, "modelling soil behavior under principal stress axes rotation," in international conference on numerical methods in geomechanics, 1985, pp. 523–530. [21] b. o. hardin and v. p. drnevich, "shear modulus and damping in soils: design equations and curves", curves," journal of the soil mechanics and foundations division, vol. 98, no. 7, pp. 667–692, jul. 1972, https://doi.org/10.1061/jsfeaq.0001760. [22] t. morita, s. iai, h. liu, k. ichi, and y. sato, "simplified method to determine parameter of flip," pari technical note 0869, jun. 1997. [23] i. suetomi and n. yoshida, "nonlinear behavior of surface deposit during the 1995 hyogoken-nambu earthquake," soils and foundations, vol. 38, no. special, pp. 11–22, 1998, https://doi.org/10.3208/sandf.38. special_11. microsoft word etasr_v13_n2_pp10363-10366 engineering, technology & applied science research vol. 13, no. 2, 2023, 10363-10366 10363 www.etasr.com bensaada et al.: influence of the incorporation of alluvial sand on the mechanical behavior of marl soil influence of the incorporation of alluvial sand on the mechanical behavior of marl soil abdelhalim bensaada civil engineering department, faculty of technology, university of yahia fares of medea, algeria bensaada.abdelhalim@univ-medea.dzr (corresponding author) belgacem choungache civil engineering department, faculty of technology, university of djelfa, algeria b.choungache@univ-djelfa.dz rbih zaitri civil engineering department, university of djelfa, algeria zrebih@yahoo.fr received: 25 january 2023 | revised: 5 february 2023 | accepted: 6 february 2023 abstract this study aims to evaluate the mechanical behavior of marl soil by replacing it with alluvial sand at 3, 5, and 10% by weight for a possible application in road geotechnics. after a geotechnical characterization of the materials used, the mixtures were characterized by the atterberg limits test, the soil compressibility test, and the shear strength test. the results obtained showed that replacing a part of marl soil with alluvial sand had a positive impact on its mechanical behavior, as it improved cohesion and shear strength while significantly reducing compressibility and plasticity. these results confirm the possibility of using alluvial sand as a fine soil reinforcement or stabilization material. keywords-marl soil; alluvial sand; mechanical behavior; improvement i. introduction soils are universally found in nature and used in many areas of human activity, particularly in geotechnical engineering. soils play a supporting role for various structures in civil engineering or public works and are also the basic elements of a wide range of geotechnical constructions. fine soils contain notable proportions of clays and silts that influence their intrinsic geotechnical properties. these soils deform under applied loads with amplitudes that can go from a few millimeters to a few meters. they also swell and become plastic in the presence of water, shrink with drought, and expand under the effect of freezing. soil improvement, also known as soil treatment or stabilization, is a technique that has been introduced for many years with the primary goal of making soils capable of satisfying clay soil criteria [1]. this treatment is often performed to increase strength, reduce or increase permeability, reduce compressibility, and minimize the sensitivity of fine soil to changes in water content. therefore, it is necessary to use other exterior materials to improve the geotechnical performance of the site [2]. several studies have been conducted on the phenomena related to this type of soil. the soil treatment techniques vary according to their character, such as the treatment by adding rubber fiber [3], natural or produced and product materials [4-6], and the use of waste tires, ashes and sewage sludge, which have shown good potential for soil stabilization [7]. the use of sand as a stabilizing material is a fairly recent technique and has not been widely used yet. this techique consists of replacing part of the soil with sand. studies on this subject showed that the addition of sand reduces the plasticity of the mixture (clay-sand), thus reducing its swelling potential [8-10]. this study aims to investigate the effect of the addition of coarse alluvial sand on the mechanical behavior of marl soil to use it in road construction. ii. materials and methods this study used two main materials in the composition of the test soils: alluvial sand and marl soil. the marl soil used came from gueddid in the djelfa region, algeria, where it was extracted at a depth of about 1m. after extraction, the soil was placed in plastic bags and transported to the laboratory for preparation and execution of geotechnical identification and characterization tests. this soil was extracted in its natural red color state in compact clods, therefore, it is difficult to mix it with sand to produce the test soils. for this purpose, a laboratory procedure was followed to transform it into a very engineering, technology & applied science research vol. 13, no. 2, 2023, 10363-10366 10364 www.etasr.com bensaada et al.: influence of the incorporation of alluvial sand on the mechanical behavior of marl soil fine powder, as shown in figure 1, without modifying the chemical nature of the grains. granular analysis was carried out by sieving grains superior to 80μm, according to nf p 94-056 [11]. on the other hand, a sedimentation method was carried out for grains with a diameter lower than 80μm, according to nf p 94-057 [12]. figure 2 shows the particle size distribution of marl soil. fig. 1. marl soil. fig. 2. granular distribution of alluvial sand and marl soil. the alluvial sand (figure 3) used for soil reconstitution was extracted from wade messaad in djelfa, and is commonly used to produce concrete on construction sites. the standardized test by dry voice according to nf p 18-560 [13], determines the distribution of the grains of sand according to their sizes, as seen in the granular curve shown in figure 2. table i summarizes the results of the sand equivalent test, specific gravity, and apparent density of this alluvial sand. fig. 3. alluvial sand. table i. physical characteristics of alluvial sand characteristic specific weight (g/m 3 ) apparent density (g/m 3 ) sand equivalent test (%) value 2.91 1.48 94.6 the main objective of the experimental study was to evaluate the effect of adding coarse alluvial sand at different percentages on the mechanical properties of marl soil, such as atterberg limits, soil compressibility as determined by an odometer test, and shear strength using the direct shear test. the experimental study was conducted at the nlhc in djelfa, algeria. the samples were prepared in the following way:  soil samples were dried for 24 hours.  preparation of marl and alluvial sand mixtures with mass percentages of the latter being 0%, 3%, 5%, and 10%.  humidification of the samples to a water content of 20%.  mixing of the samples.  compacting samples by static compression.  sampling using identical volumetric rings of samples of the same mass, height, and section. the atterberg limits were tested according to nf p 94-051 [14]. the test was carried out in two phases. the first was to study the liquidity limit (ll) of the water content, where a groove of standardized dimension, made in the soil and arranged in the casagrande cup, closes under the action of 25 shocks applied in a standardized way. the second phase examined the plasticity limit (pl) of the water content, where a soil cylinder of diameter 3mm, made manually, cracks when it is lifted. figure 4 shows a sample of the soil studied during the test. fig. 4. procedure of the atterberg limit test. the odometer compression test is fundamental in the soil compressibility test, according to xp p 94-090-1[15], as it is a direct application of consolidation theory. this test allows an evaluation of the amplitude of the settlements of the structures, as well as their evolutions. the study of ground deformation can be reproduced in the laboratory thanks to the terzaghi odometer. this device simulates the following configurations: a very large horizontal surface compared to its thickness, a uniform vertically applied load, and the possibility of zero horizontal displacements. the apparatus for axial loading a cylindrically shaped specimen placed in a rigid cylinder and measuring the variation δh of the height h separates the upper and lower faces of the specimen, which eventually becomes submerged, are in contact with draining disks. figure 5 presents the test procedure. the direct shear test was performed according to the nf p 94-071-1 [16] standard. this test determines the mechanical properties of the soil through the rectilinear shear of a sample 10 1 0.1 0.01 1e-3 0 10 20 30 40 50 60 70 80 90 100 p a s s in g r a te % ) sand alluvial marl soil sieve size (mm) engineering, technology & applied science research vol. 13, no. 2, 2023, 10363-10366 10365 www.etasr.com bensaada et al.: influence of the incorporation of alluvial sand on the mechanical behavior of marl soil under constant load. the shear test was used to plot the intrinsic curve of the soil under study and determine its internal friction angle ϕ and its cohesion c. figure 6 shows a mixture of the studied soils after the test. fig. 5. compressibility test on a soil sample studied during its execution. fig. 6. soil sample studied after the direct shear test. iii. results and discussion a. atterberg limit test results figure 7 shows the results of the atterberg limit test for the studied mixtures. the results show that the plasticity index decreased in all mixtures as the alluvial sand content increased, from 24.4% to 19.2% after adding 3% sand and continuing to decrease until 11.5% for 10%. this indicates a change in consistency after the addition of sand and an improvement in soil workability. several studies have also shown the same trend [5, 7]. b. compressibility test results figures 8 and 9 show the initial and final void index and compressibility curves, respectively, of the mixtures. the results show that the coefficient of compressibility decreases with an increase in alluvial sand content, and therefore the compression of the soil decreases when the sand content increases. the classification of soils according to their compressibility and void ratios was given in [17]. the compression coefficients cc of the studied soils can be determined from the curves in figures 8 and 9. table ii illustrates the classification of the studied mixtures. the results obtained show that the marl-sand soil mixtures are classified as moderately compressible soils. fig. 7. the plasticity index and the limits of liquidity and plasticity of the studied soils. fig. 8. ratio of initial and final voids of mixtures. fig. 9. compression index of mixtures. table ii. mixture classifications mixture with sand content (%) cc/ (1+ e0) soil class 0 0.159 moderately compressible 3 0.169 moderately compressible 5 0.1233 moderately compressible 10 0.063 moderately compressible 0% 3% 5% 10% 10 15 20 25 30 35 40 45 50 55 a tt e rb e rg l im it s ( % ) sand content (%) plasticity index (pi) liquid limit (ll) plastic limit (pl) 0% 3% 5% 10% 0.60 0.65 0.70 0.75 0.80 0.85 e0 ef sand content (%) in it ia l v o id r a ti o e 0 ( % ) 0.76 0.78 0.80 0.82 0.84 0.86 0.88 0.90 f in a l v io d r a ti o e f( % ) 0.29 0.277 0.213 0.122 0% 3% 5% 10% 0.00 0.05 0.10 0.15 0.20 0.25 0.30 c o m p re s s io n i n d e x (c c ) sand content (%) engineering, technology & applied science research vol. 13, no. 2, 2023, 10363-10366 10366 www.etasr.com bensaada et al.: influence of the incorporation of alluvial sand on the mechanical behavior of marl soil c. shear strength test results the shear test evaluates the mechanical characteristics of soils, i.e. the cohesion c, the angle of friction ϕ, and the shear strength τmax at the moment of failure. all tests for the different mixtures were carried out the same way as for the case of pure marl soil. figure 10 shows the friction angle and the cohesion of the studied mixtures. the results show an increase in the angle of friction and a decrease in the cohesion of soils with an increase in the alluvial sand content. the angle of friction increases from 26.58° for pure marl soil to 30.82°, 36.21°, and 40.42° for sois with alluvial sand content of 3%, 5%, and, 10%, respectively. this indicates that the incorporation of alluvial sand improves the shear strength of the marl soil. fig. 10. angle of friction and cohesion of mixtures. iv. conclusion this study evaluated the mechanical behavior of marl soil treated with alluvial sand at a content of 3, 5, and 10% by weight. the main conclusions of this experimental study are:  changes in the atterberg limits increase the liquidity limit and the plasticity limit, and, as a result, the plasticity index decreases. the decrease in the plasticity index indicates an improvement in soil workability.  the compressibility coefficient of the mixtures decreases as the alluvial sand content increases.  the angle of friction increases proportionally with the content of alluvial sand in the mixtures, whereas a rapid decrease in cohesion was observed when the alluvial sand content increased. this suggests that the addition of alluvial sand increases the shear strength of the marl soil. the advantages of improving fine soils by using local materials are technical and economic, as they improve both stability and cost, which are very important factors to consider in a project. acknowledgement the authors acknowledge the national laboratory of housing and construction (nlhc) in djelfa, algeria, for helping perform some of the presented measurements. references [1] j. l. briaud, "soil improvement," in geotechnical engineering: unsaturated and saturated soils, hoboken, nj, usa: john wiley & sons, ltd, 2013, pp. 938–961. [2] t. a. rind, h. karira, a. a. jhatial, s. sohu, and a. r. sandhu, "particle crushing effect on the geotechnical properties of soil," engineering, technology & applied science research, vol. 9, no. 3, pp. 4131–4135, jun. 2019, https://doi.org/10.48084/etasr.2730. [3] h. sellaf, h. trouzine, m. hamhami, and a. asroun, "geotechnical properties of rubber tires and sediments mixtures," engineering, technology & applied science research, vol. 4, no. 2, pp. 618–624, apr. 2014, https://doi.org/10.48084/etasr.424. [4] c. m. chan and h. y. yong, "comparing the thixotropic and lightly solidified hardening behavior of a dredged marine clay," engineering, technology & applied science research, vol. 4, no. 5, pp. 706–710, oct. 2014, https://doi.org/10.48084/etasr.494. [5] s. k. patel, "experimental investigation of glass fiber reinforced clayey soil for its possible application as pavement subgrade material," in new approaches in foundation engineering, london, uk: intechopen, 2022. [6] m. r. silveira, s. a. rocha, n. de s. correia, r. a. rodrigues, h. l. giacheti, and p. c. lodi, "effect of polypropylene fibers on the shear strength–dilation behavior of compacted lateritic soils," sustainability, vol. 13, no. 22, jan. 2021, art. no. 12603, https://doi.org/ 10.3390/su132212603. [7] m. jafari and m. esna-ashari, "effect of waste tire cord reinforcement on unconfined compressive strength of lime stabilized clayey soil under freeze-thaw condition," cold regions science and technology, vol. 82, pp. 21–29, oct. 2012, https://doi.org/10.1016/j.coldregions.2012.05.012. [8] elsawy m. b. d., "performance of sand dunes in stabilizing highly expansive soil," journal of geoengineering, vol. 16, no. 1, pp. 23–34, nov. 2021, https://doi.org/10.6310/jog.202103_16(1).3. [9] l. afriani and r. perdana, "effect of sand faction percentage in soil mixture towards soil support power for dam construction," advances in civil engineering, vol. 2022, jan. 2022, art. no. e2143842, https://doi.org/10.1155/2022/2143842. [10] y. m. al-badran, "effect of adding sand on clayey soil compressibility," key engineering materials, vol. 857, pp. 328–333, 2020, https://doi.org/10.4028/www.scientific.net/kem.857.328. [11] "analyse granulométrique: méthode par tamisage à sec après lavage," association française de normalisation, paris, france, nf p 94-056. [12] "sols : reconnaissance et essais analyse granulométrique des sols méthode par sédimentation," association française de normalisation, paris, france, nf p94-057. [13] "granulats analyse granulométrique par tamisage," association française de normalisation, paris, france, p18-560. [14] "sols : reconnaissance et essais détermination des limites d’atterberg limite de liquidité à la coupelle limite de plasticité au rouleau," association française de normalisation, paris, france, nf p94-051. [15] "sols : reconnaissance et essais essai oedométrique partie 1 : essai de compressibilité sur matériaux fins quasi saturés avec chargement par paliers," association française de normalisation, paris, france, xp p94090-1. [16] "sols : reconnaissance et essais essai de cisaillement rectiligne à la boîte partie 1 : cisaillement direct," association française de normalisation, paris, france, nf p94-071-1. [17] b. hubert, b. philipponmat, o. payant, and m. zerhouni, fondations et ouvrages en terre. paris, france: eyrolles, 2016. 0% 3% 5% 10% 26 28 30 32 34 36 38 40 42 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 a n g le o f fr ic ti o n ( °) sand content (%) angle of friction c o h e s io n ( b a r) cohesion microsoft word etasr_v13_n2_pp10419-10424 engineering, technology & applied science research vol. 13, no. 2, 2023, 10419-10424 10419 www.etasr.com le: numerical investigation of the axially compressive behavior of circular concrete encased steel … numerical investigation of the axially compressive behavior of circular concrete encased steel composite (cesc) columns hoang an le ho chi minh city university of transport, vietnam hoangan.le@ut.edu.vn (corresponding author) received: 29 december 2022 | revised: 5 february 2023 | accepted: 8 february 2023 abstract this research presents a numerical investigation of circular concrete encased steel composite (cesc) columns. to simulate the circular cesc columns under axial compression in the previous tests, a finite element model (fem) with some modifications of material models for the steel and concrete was established in abaqus software. the curves of load versus longitudinal displacement and the ultimate loads obtained from the fem were compared with those measured in previous tests. the numerical results agreed well with the test results. furthermore, the distribution of the stresses on the cross-section at different heights and the effect of initial imperfections were observed by the fem results. a highly confined concrete zone enclosed by steel web and steel flanges was observed. finally, the established fem was used in the parametric study that investigated the influence of concrete strength, steel yield strength, and spacing of the spiral hoops. keywords-composite columns; fem; ces; abaqus; concrete; steel i. introduction concrete encased steel composite (cesc) columns are being widely applied in heavy-loading structures such as in top-down construction methods, high-rise buildings, or support structures [1, 3-4, 24-28]. the utilization of circular cesc columns in construction was found to be necessary due to their ability to support higher loads than the rectangular or square cesc columns and their aesthetical appearance. a steel section is constructed inside the reinforced concrete to form a cesc column, thereby fully exploiting the advantages of steel and concrete materials [1, 24-26]. ductility and seismic resistance can be greatly enhanced by the use of a steel section, while the concrete works as a protective layer for the steel section against buckling, fire, and aggressive environments [1-2, 8, 19, 28-30]. for these reasons, several attempts have been made to test the structural behavior of cesc columns [1-5, 8, 13-14, 24, 27, 29-30]. the testing equipment for cesc columns requires very high capacity and complexity, thus restricting the range of parameters. therefore, many efforts have been undertaken to simulate the behavior of cesc columns through finite element models (fems). authors in [4] presented a fem to analyze the pin-ended axially loaded square cesc short and long columns using various concrete strengths (20-110mpa) and various steel yield strengths (275-690mpa). authors in [11] introduced a new simplified technique of fem incorporating the confinement effect of square cesc columns to construct strength interaction diagrams. authors in [7] constructed fems to compare the difference between square cesc columns and reinforced concrete columns with different concrete strengths. authors in [15] constructed a fem to study the buckling resistance of cesc columns using concrete strength up to 100mpa. authors in [9] conducted simulations to address the impact of concrete strength, steel strength, and column slenderness on the performance of square cesc columns. authors in [10] simulated a square cesc long column with 3.6m length and a steel column made of welded h-profile with the same length under axial compression and uniaxial bending to compare the difference between cesc and pure steel columns. authors in [12] constructed a fem of square cesc columns using fiber-reinforced concrete (frc) to verify the test results and the effect of tensile strength of frc. the literature review revealed that the majority of existing numerical investigations of the behavior of cesc columns were concerned with square sections, while the studies on cesc columns with circular sections are extremely limited. as compared to square or rectangular sections with the same dimensions, the use of circular sections results in some beneficial characteristics for cesc columns such as higher confining stress induced by steel profile and transverse reinforcements, higher strength and ductility, and better engineering, technology & applied science research vol. 13, no. 2, 2023, 10419-10424 10420 www.etasr.com le: numerical investigation of the axially compressive behavior of circular concrete encased steel … architectural performance [5, 7, 18, 20]. only two test results of circular cesc columns were reported in [7]. for this reason, there is a need for the study of circular cesc columns, in general, and fem studies for circular cesc columns, in particular. to fulfill this gap, this paper presents a fem to simulate the circular cesc short columns. firstly, the fem was established in abaqus software with some modifications to material models. after this, the accuracy of the fem was checked by comparing it with the test results of [7]. the distribution of stresses on the cross-section at different heights was also plotted. finally, the effect of the concrete strength, steel yield strength, and spacing of spiral hoops on the load versus displacement response of circular cesc short columns was determined by conducting a parametric study. ii. description of fem a. configuration of test specimens test specimens reported in [7] were used for the simulation. two circular cesc short columns using an i cross-shaped steel section were constructed for testing under concentric loading. table i shows the geometry and the dimensions of the columns and table ii demonstrates the properties of the materials used for the test specimens. table i. dimensions of test specimens specimens diameter (mm) height (mm) steel section hsrc-sp1 411 1233 2h206×120×12×12 hsrc-sp2 411 1233 2h206×120×12×12 specimens longitudinal reinforcement spiral hoop spacing of spiral hoop (mm) ultimate load (kn) hsrc-sp1 20d10 d10 50 11363 hsrc-sp2 20d10 d10 50 10890 table ii. material properties of test specimens specimens concrete strength fc (mpa) yield strength of steel section fy (mpa) yield strength of longitudinal reinforcement fy,r (mpa) yield strength of spiral hoop fh,h (mpa) hsrc-sp1 37 517 426 426 hsrc-sp2 37 517 426 426 b. mesh and finite elements the circular cesc columns consisted of concrete, steel section, longitudinal reinforcements, and spiral hoops. the solid element c3d8r (8-node brick element) was selected for simulating the concrete and the embedded steel profile. the truss element t3d2 (2-node) was selected to simulate the embedded longitudinal reinforcements, while the b31 beam element was adopted for modeling the spiral hoops. after the performance of different mesh sizes, a reasonable aspect ratio of solid element size of 1:3 was assumed. a coefficient of friction of 0.25 [4] was chosen in the "surface-to-surface contact" to simulate the interface of the concrete and the steel profile. it should be noted that this friction coefficient is adopted by numerous studies. master and slave surfaces were assigned to the concrete and the encased steel section, respectively. figure 1 shows the finite element mesh and type. fig. 1. finite element mesh and type c. boundary conditions and loading application two loading plates were simulated at both ends of the column and tied to the end surface of the concrete and steel section to ensure a uniform load transfer to the whole section of the column. two reference points (rp1 and rp2) were located in the middle of the upper and lower loading plates, respectively. a rigid body constraint was assigned between the reference point and the surface of the loading plate for easier loading application. all degrees of freedom of loading plates were fixed, while the axial displacement of the upper loading plate was set free to permit the axial movement. the numerical analysis in abaqus [21] was carried out using displacement control. an implicit procedure with the newton-raphson method [21] was adopted for the analysis. figure 2 demonstrates the modeling of boundary conditions, the interaction between structural steels and concrete, and the loading application. fig. 2. boundary condition and loading application. engineering, technology & applied science research vol. 13, no. 2, 2023, 10419-10424 10421 www.etasr.com le: numerical investigation of the axially compressive behavior of circular concrete encased steel … the buckling mode was determined by eigenvalue buckling analysis of the simulated columns. the eigenmode 1 as the first buckling mode was adopted to incorporate the geometric initial imperfection for nonlinear inelastic analysis of the composite column. the value of the initial imperfection for each column was selected as l/500 and l/1000, in which l is defined as the column length. d. material models the behavior of structural steels (steel section, longitudinal reinforcement, and spiral hoop) was simulated using the stressstrain model [22] as seen in figure 3. the value of poisson’s ratio was set as 0.3 for steel. in figure 3, fy represents the yield stress and εy denotes the strain at fy. the modulus e1 was taken as 0.01ey, while the modulus of elasticity ey of the first elastic stage was set as 200gpa. fig. 3. stress-strain model for structural steels. the nonlinearity of the concrete was simulated using the concrete damage plasticity model (cdpm). some parameters of cdpm employed to model the triaxial stress state of the concrete are:  angle of dilation φ=30 o .  eccentricity ε=0.1.  ratio of fbo/fc=1.16, where fbo is the biaxial compressive yield stress.  ratio of the second stress invariant on the tensile meridian for the yield function k=0.667. furthermore, the viscosity parameter µ =0.0001 was used to ensure the convergence. the ceb model [23] was adopted to estimate the curve of stress versus strain (σc-ε) of the concrete. the ceb model [23] is applicable to various concrete strengths (10-100mpa). the (σc-ε) curves can be drawn using the equations of the ceb model [23]: �� � �� ���� � � � �� � � �� � � 1 � ��� � 2� � �� �� for ε ≤ ε0 (1) �� � 0.7�����.�� � 10�� (2) �� � 22000���/10��.� (3) �� � ��1 � " ## ��$�� %� for ε > ε0 (4) & � ��� � 0.001�/�� (5) where ε0 is the longitudinal strain at fc, e0 is defined as the secant modulus at fc, and eit is the tangent modulus. the curve of stress versus plastic strain of concrete (fc = 37mpa) for the test specimens in [7] used as input in abaqus is shown in figure 4. fig. 4. stress – plastic strain relation of concrete. iii. fem validation the load versus displacement (l-d) curve and the ultimate load obtained from fem were compared with those measured in the tests conducted in [7] to evaluate the suitability of the fem. figure 5 shows the l-d curves of the fem and the test results of [7]. it can be seen that the l-d curves from the fem matched well with the test results. furthermore, the fem l-d curves of fem with and without imperfections were plotted. figure 5 shows that there is no significant change in the l-d curves with and without initial imperfections in fem. the ultimate loads measured in the tests (ntest) and fem (nfem1 and nfem2) are compared in table iii. it is evident that the ultimate loads of fem are close to those obtained from the tests in [7] with fem underestimating the ultimate loads with a difference ranging from 5% to 9%. fig. 5. comparison of the l-d curves between fem and the experimental results from [7]. engineering, technology & applied science research vol. 13, no. 2, 2023, 10419-10424 10422 www.etasr.com le: numerical investigation of the axially compressive behavior of circular concrete encased steel … table iii. comparison of the ultimate loads between fem and the experimental results specimens ntest (kn) nfem1 (kn) (with imperfection) nfem2 (kn) (without imperfections) nfem1/ ntest nfem2/ ntest hsrc-sp1 11363 10406 10393 0.92 0.91 hsrc-sp2 10890 10406 10393 0.96 0.95 based on the fem results, the stress state of the concrete of circular cesc columns in [7] is demonstrated in figure 6. it can be observed from the stress in the 3-3 direction of the concrete that the i cross-shaped steel section provides a good confinement effect to the concrete. the stress concentration of the concrete inside the steel section is maximal at both ends and decreases to the middle of the column. a highly confined concrete zone is observed as seen in figure 6. this zone is enclosed by steel web and flanges. this result is in line with the fem result reported in [8]. fig. 6. stresses in the concrete and the confined concrete zone. iv. parametric study the verified fem was adopted for the parametric study to determine the effect of fc, fy, and s on the l-d curves of circular cesc short columns. all columns for the parametric study have the same diameter of 270mm and the same height of 800mm (l/d = 2.96). a steel section of 70×140×10×12 was chosen for the i-cross shape. the grade of the steel section is s355. the diameter of longitudinal reinforcement is d13 with a s500 grade. the diameter of spiral hoops is d10 with a s500 grade. various concrete strengths (30, 100, 150mpa) and steel yield strengths (350, 550, and 650mpa) were modeled. the spacing of spiral hoops was taken as 30, 60, and 90mm. eight longitudinal reinforcements were constructed for the columns. figure 7 describes the circular cesc columns for the parametric study. fig. 7. the circular cesc columns for the parametric study. fig. 8. results of the parametric study using the verified fem. the results of the parametric study are illustrated in figure 8. as expected, higher values of fc and fy result in higher composite column strength. when increasing fc from 30 to 100mpa and from 30 to 150mpa, the loading capacity of the column was improved by about 76% and 123%, respectively. engineering, technology & applied science research vol. 13, no. 2, 2023, 10419-10424 10423 www.etasr.com le: numerical investigation of the axially compressive behavior of circular concrete encased steel … the descending stage of the l-d curves of the columns using higher values of fc was steeper than that when using lower values of fc. when increasing fy from 350 to 550mpa and from 350 to 650mpa, the strength enhancement of the cesc columns was about 13% and 19.7%, respectively. unlike the effect of fc, there was no significant improvement in the ductility of the columns with increasing yield strength fy. similar to the effect of fy, smaller spacing of spiral hoops leads to higher column strength. increasing the spacing of spiral hoops from 30 to 60mm and from 30 to 90mm decreased the column strength by about 4.7% and 7.8%, respectively. the quantitative value of strength improvement with increasing concrete strength fc was higher than that with increasing fy or decreasing s. there is no significant difference in the slope of the descending stage of the l-d curve with changes in fy and s. v. conclusions deriving from the numerical results and analysis, the following conclusions can be indicated:  the fem results agreed well with the test results in [7]. therefore the established fem is reliably adopted to analyze the compressive behavior of circular cesc stub columns.  distribution of the stresses on the cross-section at different column heights was observed in the fem results. a highly confined concrete 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[30] c. s. reshma, c. p. sudha, and p. seena, "experimental and numerical analysis of axial load capacity of encased steel–concrete composite column," in international conference on structural engineering and construction management, dec. 2021, pp. 1115–1125, https://doi.org/ 10.1007/978-3-030-80312-4_97. microsoft word etasr_v12_n6_pp9703-9708 engineering, technology & applied science research vol. 12, no. 6, 2022, 9703-9708 9703 www.etasr.com vaidya & chandrakar: exploring the enhanced performance of a static synchronous compensator … exploring the enhanced performance of a static synchronous compensator with a super-capacitor in power networks prajakta vaidya department of electrical engineering g h raisoni college of engineering nagpur, india prajakta.vaidya@raisoni.net v. k. chandrakar department of electrical engineering g h raisoni college of engineering nagpur, india vinod.chandrakar@raisoni.net received: 7 september 2022 | revised: 27 september 2022 | accepted: 29 september 2022 abstract-the use of a super-capacitor as a storage device integrated with a voltage source converter-based shuntconnected static synchronous compensator (statcom) is proposed for improving the statcom performance during sudden large disturbances in a power network. the supercapacitor was applied across the statcom capacitor during the disturbance condition. matlab simulations were carried out for the verification of a secondary function of the statcom like oscillation damping, transient stability improvement, and security of the power network with the storage device. the validation of the proposed super-capacitor was carried out in matlab. keywords-statcom; storage device; super-capacitor; transient stability; security i. introduction power demand is increasing in comparison to power production. to balance it, enlargement or modification of the power network is needed, which results in complex design and unsecure operation of the network. with this complex design, the network becomes very sensitive to various types of disturbance like faults, line switching, contingency, congestion, etc., leading to a decline in stability, security, and reliability of the power network [1-2]. power network stability plays a very imperative role in securing the network operation. the instability in power network exhibits itself in various ways, such as frequency, angle, and speed deviations, and power and voltage oscillations. power network stability status may be steady state, transient state, or dynamic. transient stability is mainly affected by major disturbances. proper power network devices are used to enhance stability and to increase security. shunt-connected voltage source converter-based reactive power compensation devices are widely adopted to overcome voltage stability issues. however, to compensate the true power in the network, super-capacitors (scs) with the additional benefit of storage are used [3-4]. in [5], a supplementary hvdc technology for statcom is considered for steady state and transient stability characteristics. in [6], a battery energy storage system was taken as a package of storing elements and vsc to provide autonomous control of the active and reactive power injection to the grid. in [7], the transient stability margin of a power network connected statcom is determined using trajectory sensitivity analysis. a sc type energy storage system is used to enhance the transient state stability analysis of a grid connected wind turbine in [8]. a unified statcom and battery energy storage system is evaluated for the enhancement of dynamic, transient stability, and transmission competence in [9]. in [10], statcom is used for transient stability enhancement. modelling of non-linear load with statcom is conducted in [11]. an ultra-capacitor is used with the statcom for power oscillation damping in [12]. in [13], a superconducting magnetic energy storage system with statcom is used for power system oscillation damping. in [14], steady state performance has been checked with statcom and an energy storage system. sub-synchronous oscillations are mitigated with a superconducting magnetic energy storage system in [15]. in [16], rotor angle and voltage stability were studied during fault conditions with fault location identification. in [17], voltage stability assessment in real time was conducted. a brief summary of different facts controller types with a focus on statcom topologies and their control strategies was done in [18]. in all the above studies, focus was towards steady state, transient state, dynamic state stability, rotor angle stability, or mitigation of sub-synchronous oscillations of the network, which are conducted by using statcom or an energy storage system. little focus has been given in the enhancement of statcom performance by connecting sc during various conditions. very few researches tested sc with shunt facts devices under transient disturbances in multimachine networks. in this paper, a storage device (sc) is connected to the statcom capacitor for improving its secondary performance under sudden large disturbances in the power network. the short duration application of the sc during disturbance conditions is tested in matlab environment. the voltage source converter based statcom is designed to provide voltage support by reactive power control and to enhance corresponding author: prajakta vaidya engineering, technology & applied science research vol. 12, no. 6, 2022, 9703-9708 9704 www.etasr.com vaidya & chandrakar: exploring the enhanced performance of a static synchronous compensator … secondary functions, e.g. reduction in power oscillation damping and improvement in transient stability and security of the multi-machine network. the sudden large disturbances are created by three phase faults of 0.3 and 0.2s duration in a multimachine network. comparative analysis of statcom with storage device and without storage devices is conducted. the results prove the improved statcom performance with the sc during the transient problem. ii. modelling of the power network a multi-machine network during transient conditions is considered. a synchronous generator, two loads, and a transformer are connected with the statcom and the supercapacitor is connected in shunt. as case studies, threephase faults are applied for transient conditions near the transformer. a. synchronous generator the synchronous generator is an electrical machine converting mechanical into electrical power. it is the chief driver of any power network. the synchronous generator plays a very important role in the monitoring of the power network at various conditions [10]. model (1.1) of ieee task force, with one equivalent damper winding on the q-axis with field circuit is represented as [11]: �� �� = �� (� -� ) (1) �� �� = � �� [-d (� − � ) + � − �� ] (2) ��� � �� = � ��� � [−�� � + !� − !� � )"� + �#� ] (3) ��� � �� = � ��� � [−�� � − $!� − !� � %"� ] (4) the electrical torque equation is given as: �� = �� � "� + �� � "� + !� � − !� � )"� "� (5) where δ is the operating rotor angle, ωb is the rated angular speed, sm and smo represent the slip, h is the generator inertia constant, d is the damping coefficient, tm and te represent the mechanical and electrical torque, e'd and e'q are the voltages for d and q axes, t'do and t'qo are the open circuit transient time constants for direct and quadrature axes, xd, x'd, xq, x'q, id, and iq are the reactances and currents of the said two axes, and efd is the output of the dynamic system. b. static synchronous compensator (statcom) the statcom and the static var compensator are members of the facts family which are shunt-connected devices. the statcom helps to control the power and enhances transient stability of power grids [1]. statcom can generate more reactive power than static var compensator during voltage lower than the normal voltage regulation range. the statcom has the ability to provide more capacitive reactive power during fault conditions. statcom regulates both inductive and capacitive modes according to the action of injection or absorption of the reactive power [12, 13]. reactive power variation is performed by the voltage source converter coupled to the coupling transformer [14, 20]. the equivalent circuit of a statcom with a sc is shown in figure 1. vdc sc v1 v2 proposed connection voltage source converter coupling transformer pcc fig. 1. equivalent circuit of statcom with an sc. mathematically, the active and reactive powers of the statcom are represented as: & = '(') * sin . (6) / = '( '(0') 123 �) * (7) figure 2 shows the control network block diagram of a statcom with an sc. it comprises of a phase locked loop which calculates the phase voltage and the three phase ac current for the direct-axis and quadrature-axis components, the measurement system for measuring the d and q components of the ac positive-sequence voltage, the currents to be controlled, the dc voltage vdc, and the ac and dc voltage regulators for controlling reactive and active power flow respectively. the current regulator controls the magnitude and the phase by the pulse width modulator converter. the sc is connected across vdc. fig. 2. block diagram of the control network of a statcom with an sc. c. super-capacitor an sc, also known as an ultra-capacitor, is an electrochemical double layer capacitor. the values of capacitance of the super-capacitor are orders of magnitude greater than the values of normal capacitors. scs can deliver vsc ac voltage measurement ac voltage regulator pll pwm modulator current regulator current measurement dc voltage measurement dc voltage regulator ~ v1 v2 i1 θ θ v i sc vdc engineering, technology & applied science research vol. 12, no. 6, 2022, 9703-9708 9705 www.etasr.com vaidya & chandrakar: exploring the enhanced performance of a static synchronous compensator … bursts of energy since charging and discharging takes place rapidly. using a single sc block, modeling can be done by connecting the sc's cell in series or parallel. beside the energy storing capacity as an advantage, when the sc is combined with statcom, the performance of the network is enhanced with active power support to the network. the equivalent circuit for a single cell in the sc block is shown in figure 3. + v r1 r2 r3 c1 cv c2 c3 rdischarge fig. 3. a single cell sc. the voltage and current across the sc block are obtained by: 456 = 7 89:;<:9 − "6=6 (8) "6 = >6 �'?@ �� (9) where v is the voltage across the block, nseries is the number of series cells, n is the branch number, in is the n th branch current, rn is the n th branch resistance, and vcn is the n th branch voltage across the capacitor. iii. test network in order to check the performance of the power network during transient condition, a 4-bus test network is considered (figure 4). the test network consists of 3 generators, 2 loads, 1 transformer, 3 lines, and 4 buses. the basic test network is modeled in matlab/simulink environment with the following parameters: the generators have 16,500mva total generation capacity, the loads have 12,500mw loading, one 1000mva transformer is used, a vsc based 100mva statcom, 500kv voltage, and a 100pf, 16v sc. g1 g3 g2 l1 l2 statcom supercapacitor 1 2 3 4 t f line 1 line 2 line 3 fig. 4. test network single line diagram. iv. simulation performance simulation performance is checked by applying 3-phase faults of 0.2 and 0.3s duration near bus 1, which implies a transient condition. various parameters like rotor speed, stator voltage, true power, imaginary power, and voltages are monitored. transient conditions or large disturbances result into very unbalanced network parameters and create tremendous oscillations in the network, upshots, or complete black-outs or total failures. it is better to prevent such types of failure by connecting some boosting or balancing elements. flexible ac transmission system elements are power devices connected to the network for enhancement. a statcom shunt facts device is connected in the network at bus 4 to support the network during disturbance conditions. figure 5 displays the rotor speed of the generator connected to bus 1. a 3-phase fault is applied for 0.2 and 0.3s. the network without statcom and sc shows more oscillations and takes more time to return to the stable condition. as compared to the earlier condition, the connected statcom stabilizes rotor speed early, with fewer oscillations. the result of connecting the sc with the statcom is more impressive because it damps rotor speed oscillations in less settling time. figure 5 indicates effective large fault duration condition and oscillation suppression by the sc-based statcom and thus, reduced settling time of the rotor speed. figure 6 depicts the generator 1 terminal voltage without statcom and sc, with statcom and sc, and with statcom only. as the fault duration increases, the system becomes more prone to instability. with statcom and sc stator, the voltage comes closer to 1pu earlier and thus the stability margin increases. during the transient period, the sc suppresses the oscillations and superior performance of the statcom is observed. (a) (b) fig. 5. rotor speed, fault time (a) 0.2s, (b) 0.3s. engineering, technology & applied science research vol. 12, no. 6, 2022, 9703-9708 9706 www.etasr.com vaidya & chandrakar: exploring the enhanced performance of a static synchronous compensator … (a) (b) fig. 6. generator 1 terminal voltage, fault time (a) 0.2s, (b) 0.3s. (a) (b) fig. 7. active power, fault time (a) 0.2s, (b) 0.3s. active power and reactive power oscillation damping is more effectively done with statcom and sc as can be seen in figures 7 and 8. larger oscillations are observed in the 0.3s fault duration. statcom with sc real power oscillations are effectively damp out and settling time reduces with a large stability margin. reactive power demand reduces and oscillations reduce as well. (a) (b) fig. 8. reactive power, fault time: (a) 0.2s, (b) 0.3s. (a) (b) fig. 9. network voltage at bus 2, fault time (a) 0.2s, (b) 0.3s. figure 9 exhibits the bus 2 voltage oscillations, which are maintained at 1pu with the sc-based statcom combination. figure 10 shows the vdc variation with an sc. the dc voltage is maintained constant. figure 11 shows the sc voltage variation during fault conditions. engineering, technology & applied science research vol. 12, no. 6, 2022, 9703-9708 9707 www.etasr.com vaidya & chandrakar: exploring the enhanced performance of a static synchronous compensator … (a) (b) fig. 10. vdc, fault time (a) 0.2s, (b) 0.3s. (a) (b) fig. 11. sc voltage, fault time (a) 0.2s, (b) 0.3s. v. conlcusion in this paper, the performance of the static synchronous compensator (statcom) is enhanced with the aid of a super-capacitor (sc). a multi-machine network was evaluated in matlab during the transient condition without statcom, with statcom and with both statcom and sc. a symmetrical 3-phase fault is applied for 0.2s as case study 1 in the network. it is observed that the oscillations are damped within 25, 12, and 105s without statcom, with statcom, and with statcom-sc respectively. with statcom-sc, the second peak reduces from 1.025 to 1.015pu. the primary function of a statcom is to maintain constant terminal voltage and bus voltage at 0.9 to 1pu, which is achieved by the proposed statcom-sc combination. similarly for the case study 2, the fault duration is 0.3s, for which the responses of statcom-sc are drastically enhanced as network oscillations are damped quickly, peak time and voltage variation are reduced, and the network quickly overcomes the issue. it is observed that as the fault duration increases, the proposed statcom-sc model works more effectively. an additional benefit to true power compensation is the energy storage which is very essential for secured power network. the energy storage with statcom-sc enhances the transient performance of the network and reduces the damage to the equipment during sudden large disturbances, which have not been tested in the published research work. scs are preferred for short duration applications of nearly 30 to 40s. in the simulations of the current study, the system was tested for 25 to 30s after the disturbance. references [1] n. g. hingorani and l. gyugyi, understanding facts: concepts and technology of flexible ac transmission systems, 1st ed. new york, ny, usa: wiley-ieee press, 1999. 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[19] a. chakraborty, s. k. musunuri, a. k. srivastava, and a. k. kondabathini, "integrating statcom and battery energy storage system for power system transient stability: a review and application," advances in power electronics, vol. 2012, dec. 2012, art. no. e676010, https://doi.org/10.1155/2012/676010. microsoft word etasr_v12_n6_pp9510-9514 engineering, technology & applied science research vol. 12, no. 6, 2022, 9510-9514 9510 www.etasr.com alaidi et al.: artificial bee colony with crossover operation for discrete problems artificial bee colony with crossover operations for discrete problems abdul hadi alaidi programming department computer science and information technology college wasit university wasit, iraq alaidi@uowasit.edu.iq soong der chen college of computing and informatics universiti tenaga nasional selangor, malaysia chensoong@uniten.edu.my yeng weng leong college of engineering universiti tenaga nasional selangor, malaysia ywleong@uniten.edu.my received: 8 august 2022 | revised: 27 august 2022 | accepted: 29 august 2022 abstract-the artificial bee colony (abc) is an algorithm designed to solve continuous problems. abc has been proven to be more effective than other biological-inspired algorithms. however, it is needed to modify its functionality in order to solve a discrete problem. in this work, a natural modification to the original abc is made to make it able to solve discrete problems. six neighborhood operators are proposed to simulate the original behavior of abc. moreover, several traveling salesman problem library (tsplib) problems were used to examine the proposed method. the results of the proposed method are promising. keywords-artificial bee colony (abc); discrete problem; tsp i. introduction a heuristic is a method for solving a problem that does not guarantee convergence to a global optimum but can offer a good enough solution. there are two types of heuristics for addressing a combinatorial optimization problem: perturbative and constructive heuristics [1]. a constructive heuristic creates a comprehensive solution from the bottom-up. a perturbative heuristic, on the other hand, changes an existing solution in order to find better solutions in the neighborhood of the present solution (i.e. operates neighborhood search operations). problem-specific heuristics are used to solve particular problems. the nearest neighborhood heuristic and the multiple fragment heuristic are examples of constructive heuristics for the traveling salesman problem (tsp), whereas perturbative heuristics include swap mutation, insert mutation, reverse mutation, order crossover, and partially mapped crossover. a problem of the abc algorithm is that it is originally designed for continuous problems so modification should be applied to make it work with other problem types. `abc integrating grenade explosion and cauchy operator to avoid random search and solving the dynamic economic emission dispatch (deed) problem was established in [2]. authors in [3, 4] used abc for routing and performance enhancement of wireless sensor networks. authors in [5] modified abc to solve constrained optimization problems. instead of the greedy selection of the original abc, the modified abc used deb’s rules for constrained problems. mabc is a modified abc for solving the stage shop scheduling problem [6]. the mabc uses tabu search in the employee phase instead of the greedy selection. moreover, the onlooker bee phase was also modified and the idea of particle swarm optimization (pso) was used instead of random search. authors in [7] analyzed the performance of a discrete abc algorithm with a neighborhood operator. the original abc uses two solutions for neighborhood search while the discrete abc uses one solution for the neighborhood search. the aim of this paper is to simulate the original neighborhood search behavior of abc. the main contribution of this work is the use of a crossover operation as a neighborhood search and the introduction of six neighborhood operators which simulate the original abc neighborhood searching behavior. ii. tηε traveling salesman problem the tsp is one of the most commonly investigated optimization problems. the statement of tsp is simple however, it remains a challenging problem. the tsp can be defined as finding the shortest path, for a given set of cities, starting from a base city, visiting all other cities once, and returning to the base city. the description of the tsp is an indirect weighted graph � =  ��,   ��, where � symbolizes the set of cities, and � symbolizes the set of links that connect the cities. each link which connects two cities is assigned a length corresponding author: abdul hadi alaidi engineering, technology & applied science research vol. 12, no. 6, 2022, 9510-9514 9511 www.etasr.com alaidi et al.: artificial bee colony with crossover operation for discrete problems value  � , where �,     ∈  � . the problem is called symmetric tsp when the distance between two cities is the same regardless of direction, i.e.  � = � . on the other hand, it is called asymmetric tsp when there is at least one link with a different distance with respect to direction, that is, the distances are direction-dependent and � ≠ � . tsp is np-hard problem. equation ( 1) can be used to find the total possible solutions [8]: ����� ��������� =   �����!� ( 1) where n is the number of nodes or cities. for example, if we have 60 cities and each city is connected to all other cities, the total possible solutions will be (60 1)! 6.9341559 79 2 e    . in the case of evaluating 1 billion possible solutions per second, it would take about 2.2×10 63 years to check all possible solutions [9]. from the above example, it is obvious how large the search space is. although good techniques are used to reduce the search space (e.g. nearest neighbor [11]), the tsp is still classified as an np-hard problem. the tsplib benchmark [10] provides a large collection of tsp cases and is represented as a standard coordinate data system. figures 1, 2 show an example of a tsp before finding the solution and the optimal solution respectively. fig. 1. a tsp problem. fig. 2. tsp solution. iii. the artificial bee colony algorithm the abc algorithm is a well-studied algorithm developed to solve continuous function optimization problems [11]. it simulates the foraging behavior a swarm of bees perform to find food. abc is successfully used in many fields like energy management of for mobile devices [12] and for routing of mobile agents in internet of things (iot) applications [13]. in abc, the bees are divided into 3 groups: employed, onlookers, and scouts. employed bees search for food sources and share information with an onlooker bee. the onlooker bee tries to search for a better food source in the neighborhood by using the knowledge passed from the employed bees. if the food source is abandoned, the employed bees responsible for that food source become scout bees and randomly search for the new food sources. in abc, employed and onlooker bees accomplish the exploitation, while scout bees control the exploration process. in abc, the employed bees use (2) to search neighbors by moving from an old position � � to the new position � � if and only if the new position's fitness is better than the fitness of the old position: � � = � � + ϕ � !� � − �#� $ (2) where � is the old position and � is the new position of �%& employed. ϕ � is a random real number in the range of [-1,1], j is an arbitrary integer number between 1 and the dimension of the problem, while k is a random number between 1 and the number of employed bees. on the other hand, the onlooker bee selects a food source and evaluates all employed bees depending on the probability calculated by: ' = ( %)∑ ( %+,-+./ (3) where fit is the fitness values of the solution (food source) of the employed bee, which is calculated by: 0�� = 1 � �2(�3) � , 0�� � ≥ 01 + |0�� �|, 0�� � < 0 (4) where 0�� � stands for the value of the objective function to be optimized. like the employed bee, the onlooker bee uses (3) to update the position and explore the selected food source. fig. 3. standard abc algorithm. when a food source cannot be further exploited within a pre-defined trial limit, it will be abandoned, and the corresponding employed bee becomes a scout bee and randomly searches for a new food source. such a combination of the exploration and exploitation search in abc is important. it allows the algorithm to search the solution space for highengineering, technology & applied science research vol. 12, no. 6, 2022, 9510-9514 9512 www.etasr.com alaidi et al.: artificial bee colony with crossover operation for discrete problems quality solutions and prevents them from getting stuck in local optima. in abc, the employed bees maintain the current solution while the onlooker bees allow the best solution to be exploited. furthermore, scout bees try to remove stagnating solutions and explore new solutions. figure 3 shows the standard abc algorithm. iv. artifical bee colony for tsp tsp is a discrete problem and abc is designed to solve continuous problems. the neighborhood operator which is a replacement for (2) is used in [7, 14] to make abc able to solve tsps. however, in the original abc, the process of updating the solution is done by choosing another solution (randomly from the employee bee and using a roulette wheel in onlooker bee) and trying to enhance a solution. in this work, six neighborhood operators are proposed to simulate the original behavior of abc. a. random swap crossover (rsc) random swap involves swapping the position of two randomly selected cities, starting from the first solution to the second solution, and rearranging the final solution to fix the position of the cities inserted. consider, for example, the following two solutions of the 7-city tsp�1,2,3,4,5,6,7� and �1,5,7,6,2,3,4�. first, select two random points as i and j. in our example i = 3 and j =5. then copy the i-th item from the second solution into the first solution (7→3). then, the repair algorithm runs to map the i-th item in the first solution to the position of the old i-th item (3 → 7) and repeats the same operation for the j-th item as shown in figure 4. fig. 4. random swap crossover b. random swap subsequence crossover (rssc) rssc operation is the same as that of rsc, with one difference, which is the subsequence to swap in a solution from solution to solution. for example, if we have two solutions like in figure 4 where i = 2 is the start position of sequence and k = 3, where k is the sequence length. first, copy the i-th item from the second solution into the first solution (5→ 2). then, the repair algorithm maps the i-th item in the first solution to the position of the old i-th item (2 → 5) and repeats the same operation k times. c. random insertion crossover (ric) in ric, a city from the first solution is randomly picked, removed from the second solution, reinserted into a random position in the second solution, and the repair algorithm is executed as explained in rsc. figure 6 shows the ric operation. fig. 5. random swap subsequence crossover. fig. 6. random insertion crossover. d. random insertion of subsequence crossover (risc) in risc, a subsequence from a solution is randomly picked and then inserted into a second solution. the repair algorithm is again executed as in rsc. figure 7 shows the risc operation. fig. 7. random insertion of subsequence crossover. e. random reversing crossover (rrc) rrc is the same as rsc, with one difference, which is the inversion of the inserted cities when copying from the first to the second solution as shown in figure 8. f. random swap subsequence reverse crossover (rssrc) it is the same as risc with the difference that the inserted sequence is inverted before insertion as shown in figure 9. engineering, technology & applied science research vol. 12, no. 6, 2022, 9510-9514 9513 www.etasr.com alaidi et al.: artificial bee colony with crossover operation for discrete problems fig. 8. random reversing crossover. fig. 9. random swap subsequence reverse crossover. v. results and discussion in this work, the proposed method was implemented using c#. the algorithm was tested in 12 tsp problems (pr76, kroa100, krob100, kroc100, krod100, kroe100, rd100, gr120, pr124, bier127, ch130, pr136) taken from the tsplib benchmark library [12]. the code was run on a 2.80 ghz intel core i7 processor with 16 gb ram. the same parameter values were used in all experiments to make sure of a fair judgment between all different methods. each method ran the same tsp benchmark 30 times. the best and the average solutions were collected for every 30 runs. the experimental results obtained by the discrete abc algorithm with crossover and abc with neighborhood operators explained in [7] are shown in table i (rsc), table ii (rssc), table iii (ric), table iv (risc), table v (rrc), and table vi (rssrc). table i. random swap crossover problem rswc rs error avg error error avg error pr76 46.99748 54.72502 73.58703 91.39779 kroa100 80.78658 96.99104 139.8036 163.6677 krob100 79.63055 88.92176 135.0029 152.0174 kroc100 74.64938 98.85922 131.963 163.369 krod100 85.98666 94.72684 136.2168 155.6664 kroe100 71.01233 92.52387 132.8938 153.7324 rd100 69.38053 85.36747 116.7762 145.2078 gr120 78.45001 94.11505 138.0726 154.8065 pr124 136.2697 168.2421 241.074 265.6827 bier127 47.11283 69.60656 105.9739 118.8277 ch130 86.30115 104.0835 161.9804 183.4746 pr136 87.92729 112.748 181.9473 197.9853 table ii. random swap subsequence crossover problem rsswc rss error avg error error avg error pr76 59.73151 71.36817 25.39687 47.79393 kroa100 86.09153 108.4756 84.81346 110.7512 krob100 77.17357 101.3199 78.25753 100.5301 kroc100 98.665 111.3994 90.92968 118.8134 krod100 85.83639 103.1306 82.44576 105.7127 kroe100 90.4749 102.0346 80.2021 106.9497 rd100 83.67889 97.02318 74.71555 98.79351 gr120 85.07635 95.13253 88.61999 113.2892 pr124 131.1164 149.0558 138.3534 185.6913 bier127 69.38587 78.58206 52.21082 70.05222 ch130 107.234 120.3644 97.10311 122.9116 pr136 102.9296 115.7102 114.7532 142.3517 table iii. random insertion crossover problem riwc ri error avg error error avg error pr76 27.94312 39.36553 10.94685 20.9037 kroa100 38.01334 61.09639 35.77671 52.17602 krob100 37.36507 55.50231 33.21892 51.09405 kroc100 52.78327 65.16459 30.12193 57.67137 krod100 47.56269 60.26111 35.18832 53.36621 kroe100 44.0638 59.97311 31.6431 52.00773 rd100 31.66877 55.39022 31.32743 58.60598 gr120 48.2858 60.77883 53.31317 72.07241 pr124 68.42453 89.73748 63.58123 101.3253 bier127 41.45855 49.50531 47.90162 69.3766 ch130 57.54501 70.97709 74.04255 116.2635 pr136 54.72967 68.41197 77.31782 104.5502 table iv. random insertion of subsequence crossover problem riswc ris error avg error error avg error pr76 49.2266 58.47 50.86031 66.37531 kroa100 76.14416 86.6875 104.2618 130.5938 krob100 69.49099 81.44588 90.89472 113.5918 kroc100 79.03031 90.92808 100.8964 130.3549 krod100 67.30065 81.70236 93.09665 119.8395 kroe100 64.37375 81.873 99.69639 124.8651 rd100 70.0885 81.38938 94.96839 115.2503 gr120 66.30654 77.97273 90.01729 121.2134 pr124 101.5297 117.2478 137.2438 200.9112 bier127 54.447 69.39636 67.83112 81.2194 ch130 79.1653 93.60993 111.9476 146.4146 pr136 74.26735 87.27759 135.192 156.8362 table v. random reversing crossover problem rrwc rr error avg error error avg error pr76 21.22307 26.50754 8.847839 13.58325 kroa100 18.54547 29.62665 8.4486 14.70384 krob100 19.15563 27.48035 4.879309 12.21972 kroc100 6.691075 17.47819 1.227822 4.689023 krod100 13.33333 18.1679 1.185185 4.019753 kroe100 15.1942 26.48397 15.15869 20.62213 rd100 25.02455 34.71413 28.01964 40.71358 gr120 19.04861 30.61965 4.089297 13.66924 pr124 16.38715 23.30662 5.198294 10.8402 bier127 32.74267 44.25733 17.94681 30.11028 ch130 26.09536 34.55156 22.58505 34.33286 pr136 21.25158 28.10493 8.609355 15.42815 the results clearly show that the proposed method is better for all considered problems and rsc, risc, rrssrc engineering, technology & applied science research vol. 12, no. 6, 2022, 9510-9514 9514 www.etasr.com alaidi et al.: artificial bee colony with crossover operation for discrete problems methods. in rssc, it got a better result in 9 cases. on the other hand, ric solves half of the problems with better results than the other methods. however, the rrc operator gives poor performance compared to the random-reverse neighborhood operator. table vi. random swap subsequence reverse crossover problem rssrwc rssr error avg error error avg error pr76 58.71911 70.09199 102.3012 114.1171 kroa100 93.22902 113.2607 182.3983 192.9061 krob100 84.36837 103.8512 168.6645 178.0544 kroc100 85.88848 111.2542 169.8588 194.1552 krod100 81.38443 105.0621 168.5404 185.8098 kroe100 90.64709 104.1044 169.0955 182.4486 rd100 84.93047 103.8972 168.8748 183.0523 gr120 85.86863 100.5695 161.8986 180.8902 pr124 131.9532 156.3919 283.1865 311.2413 bier127 67.18267 82.61759 125.0528 135.4019 ch130 107.2831 123.7621 212.455 223.1844 pr136 103.5847 120.2145 208.8197 229.9761 vi. conclusions in this work, the artificial bee colony algorithm is modified with new neighborhood operators to solve discrete problems. the proposed method was tested on 12 tsp problems from the tsplib. the results show that random swap crossover, random insertion of subsequence crossover, and random swap subsequence reverse crossover operations give a good performance. the proposed method is similar to the original artificial bee colony algorithm and gives promising results. our future work will focus on introducing new neighborhood operators and optimizing the implementation of the proposed method. furthermore, due to the encouraging result, the proposed method can be easily integrated into other optimization algorithms. acknowledgments the authors acknowledge the financial support from the universiti tenaga nasional under uniten-iraq scholarships uniten bold research grant (j510050002/2021150). references [1] q. gu, q. wang, x. li, and x. li, "a surrogate-assisted multi-objective particle swarm optimization of expensive constrained combinatorial optimization problems," knowledge-based systems, vol. 223, jul. 2021, art. no. 107049, https://doi.org/10.1016/j.knosys.2021.107049. [2] ι. marouani, a. boudjemline, t. guesmi, and h. h. abdallah, "a modified artificial bee colony for the non-smooth dynamic economic/environmental dispatch," engineering, technology & applied science research, vol. 8, no. 5, pp. 3321–3328, oct. 2018, https://doi.org/10.48084/etasr.2098. [3] s. d. chavan and a. v. kulkarni, "event based clustering localized energy efficient ant colony optimization (ebc_lee-aco) for performance enhancement of wireless sensor network," engineering, technology & applied science research, vol. 8, no. 4, pp. 3177–3183, aug. 2018, https://doi.org/10.48084/etasr.2121. [4] h. ehteshami, s. javadi, and s. m. shariatmadar, "improving the power quality in tehran metro line-two using the ant colony algorithm," engineering, technology & applied science research, vol. 7, no. 6, pp. 2256–2259, dec. 2017, https://doi.org/10.48084/etasr.1551. 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[9] j. mccaffrey, "test run ant colony optimization," msdn magazine issues, vol. 27, no. 2, feb. 2016, [online]. available: https://learn. microsoft.com/en-us/archive/msdn-magazine/2012/february/test-run-antcolony-optimization. [10] g. reinelt, "tsplib—a traveling salesman problem library," orsa journal on computing, vol. 3, no. 4, pp. 376–384, nov. 1991, https://doi.org/10.1287/ijoc.3.4.376. [11] d. karaboga and b. basturk, "a powerful and efficient algorithm for numerical function optimization: artificial bee colony (abc) algorithm," journal of global optimization, vol. 39, no. 3, pp. 459–471, oct. 2007, https://doi.org/10.1007/s10898-007-9149-x. [12] s. arunkumar, b. v. kumar, and m. pandi, "artificial bee colony optimization based energy-efficient wireless network interface selection for industrial mobile devices," computer communications, vol. 154, pp. 1–10, mar. 2020, https://doi.org/10.1016/j.comcom.2020.01.067. 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[14] s. s. choong, l.-p. wong, and c. p. lim, "an artificial bee colony algorithm with a modified choice function for the traveling salesman problem," swarm and evolutionary computation, vol. 44, pp. 622–635, feb. 2019, https://doi.org/10.1016/j.swevo.2018.08.004. microsoft word 1-513-ce.doc engineering, technology & applied science research vol. 4, no. 6, 2014, 711-713 711 www.etasr.com belahcene et al.: investigation on the rheological behavior of multigrade oil under the effect of … investigation on the rheological behavior of multigrade oil under the effect of organic and inorganic impurities brahim belahcene faculty of technology, department of mechanical engineering laepo research laboratory tlemcen, algeria belahcene.brahim@gmail.com ali mansri faculty of science, department of chemistry laepo research laboratory tlemcen, algeria a_mansri@mail.univ-tlemcen.dz abderrahim benmoussat faculty of technology, department of mechanical engineering laepo research laboratory tlemcen, algeria abbenmoussa@gmail.com abstract—the lubrication process of mechanical equipment and treatment of assembly metals structures using fluids with efficient rheological properties requires a knowledge of their behavior in the presence and in the absence of organic impurities. the intrinsic physical property of the lubricating fluids has a dependency to the mechanical and physicochemical environment. this paper is focused on the assessment of the behavior of sae20w40 multigrade oil under normal temperature and pressure, through the addition of water in vapor phase and solid paraffin. results show that there is a decrease in the dynamic and kinematic viscosity for heterogeneous oils. the rate of degradation is greater in the mixture of water with oil. the addition of paraffin in the mixture caused an increase in viscosity. however, after certain rpm points, it is noted that the data curve became similar to the first mixture. this relaxation phenomenon is caused by the turbulence created by the rotating cylinder in oil. the use of a retentate paraffin shows that the added agent has acted as a surfactant. keywordsviscosity; oil; water; relaxation; paraffin; miscibility i. introduction the mix of raw materials into oil, e.g. industrial oils, requires a continuous process of monitoring their behavior before and after their implementation in service. in the field of oil production, three main methods are applied:  compression of the material, i.e. to crush some cold or hot petroleum products, to extract the oil  distilling, i.e. heating of the material for the separation of oil from other ingredients.  chemical synthesis, i.e. to manufacture an oil through reaction with chemical reagents. each fluid is characterized by a dynamic viscosity represented by the ratio of shear stress to shear rate, which is perpendicular to the plane of shear. the latter becomes an intrinsic characteristic; if it is divided by the density ρ fluid, it gives the kinematic viscosity ʋ [1]. the viscosity index vi was first proposed in 1929 [2] and it was revised in 1945 [3]. the classification of the society of automotive engineers (sae) used particularly in the automotive industry classifies oils according to their viscosity, and defines continuous intervals of viscosity with a minimum and a maximum (sae 0w, sae 5w, sae 10w30, sae 20w40 etc). an empirical relationship showing the relationship between the viscosity (ʋ in cst) and the temperature (t in kelvin) is given in [2, 3, 8-11] and it uses two positive constants (a and b) related to the nature of the oil. in general, the presence of water molecules in lubricating oils or and its derivatives is an important issue for their physico-chemical properties. a phase of different properties relative to the fluid source, may be added (phase contamination). the separation of this new phase occurs slowly by natural settling, due to density differences. the effective viscosity of the oil-water mixture, depends on several parameters such as the volume fraction of the dispersed phase and the temperature [4]. a study of the variation of the relative viscosity of oil-water mixture as a function of the volume fraction and temperature v is performed in [5]. the thermodynamic model that shows the relationship between the relative viscosity and the volume fraction can be found in [912]. the relative viscosity has a relationship with the volume fraction and the ratio between the viscosity of the discontinuous phase and the continuous phases [10]. finally, the variation of viscosity as a function of different concentrations of the emulsions was introduced in 2001 [1113]. ii. set-up in this paper, viscosity measurements of a sae20w40 mineral oil sample are presented with the use of a brookfield dv-iii viscometer. the dependence on different temperatures in the pure state and in the presence of organic impurities and water is investigated and results are presented and discussed. the rotational viscometer used (brookfield dv-iii) is shown in figure 1. as shown, a cylindrical container contains viscous oil. this cylinder, movable on its axis of cylinder rotation, is driven by oil. engineering, technology & applied science research vol. 4, no. 6, 2014, 711-713 712 www.etasr.com belahcene et al.: investigation on the rheological behavior of multigrade oil under the effect of … before measurements are conducted, a calibration of the viscometer is performed using a non-newtonian fluid (glycerin) at room temperature, in order to find the important working parameters brookfield dv-iii. figure 2 shows the variation of the dynamic and kinematic viscosity depending on the temperature t and the number of revolution per minute (rpm). fig. 1. brookfield dv-iii fig. 2. calibration using glycerin iii. results and discussion figures 3 and 4 show the curves for the new oil and the oil with impurities. a decrease in the dynamic viscosity and the kinematic viscosity for the two heterogeneous oils is noticed. the degradation rate is important for the mixing of oil with vapor. however, for the other oil mixture (water vapor and solid paraffin), an increase in viscosity was noticed compared to the oil mixed with water vapor for 70 ≤ rpm ≤ 185. furthermore, after a certain rpm≤185, it was noted that the curve thereof is almost coincident with the oil and water into steam. this should be attributed to the turbulence relaxation phenomenon created by the rotating cylinder. fig. 3. behavior of new sae 20w40 oil (19 c° <t ≤ 25 c°) fig. 4. behavior of sae 20w/40 oil in the presence of organic impurities and water (19 c°<t≤ 25 c°) in order to define the effect of temperature on the kinematic viscosity, it is necessary to determine the constants a and b, discussed in astm d341 [6], based on the data of figure 5 [14], considering (1): log (log (ʋ + 0,7)) = a b log(t+273.15) (1) the viscosity number (vn) has been recently proposed in the characterization of the performance of lubricating oils. by applying (1) we can determine the viscosity number for different states of changes in sae 20w40. b values are inserted in (2) [7]. the nv values are shown in table i. nv= (1+ ((b*3.55)/3.55)) ) 100* (2) fig. 5. sae 20w40 variation in function of temperature table i. viscosity numbers sae20w40 sae20w40+ water sae20w40 +water +paraffin nv 424.7519 406.9362 401.6023 iv. conclusion the sae20w40 oil was mixed with water in the vapor phase and then with solid paraffin. results show that there is a decrease in the dynamic and kinematic viscosity for heterogeneous oils. their behavior was investigated in terms of viscosity in relation with temperature and rpm. the addition of paraffin in the mixture caused an increase in viscosity for smaller rpm but the results were similar for larger rpm. this engineering, technology & applied science research vol. 4, no. 6, 2014, 711-713 713 www.etasr.com belahcene et al.: investigation on the rheological behavior of multigrade oil under the effect of … relaxation phenomenon is attributed to the turbulence created by the rotational viscometer cylinder. acknowledgment the authors wish to thank the national agency for the development of university research (andru) in algeria for its support. references [1] iupac, compendium of chemical terminology, gold book, 2nd ed., 1997 [2] e.w. dean, g.h.b. davis, “viscosity variations of oils with temperature, ' chemical and. metallurgical engineering, vol. 36, no. 10, pp. 618–619, 1929 [3] e.w. hardiman, a.h. nissan, “a rational basis for the viscosity index system”, journal of the institute of petroleum, vol. 31, pp. 255–270, 1945 [4] m. a. farah, r. c. oliveira, j. n. caldasa, k. rajagopa, “viscosity of water-in-oil emulsions: variation with temperature and water volume fraction”, journal of petroleum science and engineering, vol. 48, no. 34, pp.169–184, 2005 [5] h. p. ronningsen, “correlations for predicting viscosity of w/oemulsions based on north sea crude oils”, spe international symposium on oilfield chemistry, 14-17 february, san antonio, texas, usa, 1995 [6] american society for testing and material, annual book of astm standards, vol. 05, philadelphia, usa 2001 [7] p. t. cummings, d. j. evans, “nonequilibrium molecular dynamics properties and non-newtonian fluid approaches to transport rheology”, industrial & engineering chemistry research, vol. 31, pp.1237–1252, 1992 [8] society of automotive engineers , sae handbook, vol. 124, 1968 [9] http://www.maths.usyd.edu.au/u/ug/sm/math3075/r/einstein_1905.p df [10] i. m. krieger, t. j. dougherty, “a mechanism for non-newtonian flow in suspensions of rigid spheres”, transaction of the society of rheology, vol. 3, pp. 137–152, 1911 [11] r. pal, “evaluation of theoretical viscosity models for concentrated emulsions at low capillary numbers”, chemical engineering journal,vol. 81, no. 1-3, pp. 15–21, 2001 [12] g. i. taylor, “the viscosity of a fluid containing small drops of another liquid”, proc. r. soc.,,a 138, pp. 41–48, 1932 [13] walther, the evaluation of viscosity data. erdol und teer ,v.7, pp.382– 384, 1931 [14] oil-power ltd, visccalc 2, available at http://www.oil-power.com/ microsoft word etasr_v12_n6_pp9532-9535 engineering, technology & applied science research vol. 12, no. 6, 2022, 9532-9535 9532 www.etasr.com azmat et al.: environmental noise reduction based on deep denoising autoencoder environmental noise reduction based on deep denoising autoencoder received: 4 august 2022 | revised: 31 august 2022 | accepted: 1 september 2022 abstract-speech enhancement plays an important role in automatic speech recognition (asr) even though this task remains challenging in real-world scenarios of human-level performance. to cope with this challenge, an explicit denoising framework called deep denoising autoencoder (ddae) is introduced in this paper. the parameters of ddae encoder and decoder are optimized based on the backpropagation criterion, where all denoising autoencoders are stacked up instead of recurrent connections. for better speech estimation in real and noisy environments, we include matched and mismatched noisy and clean pairs of speech data to train the ddae. the ddae has the ability to achieve optimal results even for a limited amount of training data. our experimental results show that the proposed ddae outperformed the baseline algorithms. the ddae shows superior performances based on three-evaluation metrics in noisy and clean pairs of speech data compared to three baseline algorithms. keywordsddae; limited data; noise reduction; autoencoders i. introduction speech enhancement is a key part of automatic speech recognition (asr) [1]. it has been implemented in many commercial products for decades, but in order to achieve human-level performance, it requires further improvement in real-world scenarios [2], e.g. when we talk to a person or a voice recognition system like an atm verification call, many environmental noises are added and transmitted, posing difficulties to the system. to deal with such noises, speech signal processing algorithms have been developed to improve the quality and intelligibility. neural network-based algorithms are more efficient in learning high-order statistical information automatically by using nonlinear processing units and are efficient for noise reduction [3, 4]. many algorithms are proposed to train deep neural networks efficiently for speech enhancement and noise reduction [5-7]. deep learning algorithms have been used to extract speech features and for acoustic modeling [2]. the denoising autoencoder has been used for image processing and other classification applications to extract robust features when the input is a binary masked feature for each autoencoder. for speech feature extraction, a recurrent denoising autoencoder for asr was proposed for noise reduction in [8]. there are many conventional methods for speech signal processing. for speech enhancement, the most used algorithms are log minimum mean square error (logmmse) [9], karhunen-loeve transforms (klt) [10], and robust principal component analysis (rpca) [11], which are designed with specific additive background noise based on statistical speech properties and noisy signals. however, these methods do not work in real settings when people talk in a noisy environment. consequently, it is essential to build a framework to deal with the various types of noise in real-world environments. this article introduces an explicit denoising framework called the deep denoising autoencoder (ddae), a variant of the denoising autoencoder. however, unlike previous works, where the input is noisy speech and the output is clean speech aneeka azmat institute of human-centered computing, national tsinghua university, taiwan and institute of information science, academia sinica, taiwan aneekaazmat89@iis.sinica.edu.tw imad ali department of computer science university of swat, pakistan imadali@uswat.edu.pk m. gilvy langgawan putra national taiwan university of science and technology, taiwan and institut teknologi kalimantan, indonesia gilvy.langgawan@lecturer.itk.ac.id whenty ariyanti national taiwan university of science and technology, taiwan and institute of information science, academia sinica, taiwan whenty@iis.sinica.ac.id talha nadeem comsats university islamabad, pakistan talhanadeem2397@gmail.com corresponding author: aneeka azmat engineering, technology & applied science research vol. 12, no. 6, 2022, 9532-9535 9533 www.etasr.com azmat et al.: environmental noise reduction based on deep denoising autoencoder for training, the ddae is trained on datasets of matched noisy and clean pairs of speech and mismatched noisy and clean pairs of speech for speech estimation in real and live environments. in the ddae, the parameters in the encoder and decoder (formed by multiple layers of neural networks) are optimized based on the backpropagation criterion, where all denoising autoencoders are stacked up instead of recurrent connections. the ddae has the ability to achieve optimal results even with a limited amount of training data. our experimental results of ddae were compared with the speech enhancement algorithms rpca, klt, and logmmse. based on three evaluation metrics, the ddae outperforms these three baseline algorithms in matched and mismatched noisy and clean speech. ii. the ddae framework this article uses the ddae framework presented in [12], which removes the noise quickly and efficiently. the ddae can achieve optimal results even with inadequate training data. it uses the noisy signal to produce clean speech features efficiently, even under mismatched testing conditions. unlike [13], where the denoising autoencoder was trained using clean speech only, we trained the denoising autoencoder with both noisy and clean speech data. figure 1 shows a single-layer hidden neural autoencoder, trained on clean speech with noisy and speech data as input. it consists of one nonlinear and one linear encoding and decoding stage: ℎ��� � = ��� �� + �� � � = ��ℎ���� + �� � (1) where � and �� are the weight matrices for encoding and decoding neural network connections respectively. typically, regularization takes place when � = ��� = �. also, � is the input layer’s bias vector, whereas � represents the output layer’s bias vector. similarly, �� is the noisy speech signal equivalent to the clean signal �� . the nonlinear logistic function utilized by the hidden neuron is ���� = �1 + � ���� . by optimizing the objective function in (2), the parameters are determined as follows: ���� = ∑ ||�� − � � ||��� (2) where the set of the parameters is defined as � = {�, �, �}. in addition to using � = ��� = �, we apply regularization on weights and hidden neural output. this improves the generalization and prevents overfitting, which is defined as follows: ��� = ���� + ! ||�||�� + "#�ℎ��� )) (3) where ||�||�� = ∑ $�%� . &'ℎ��� �(�% � �% is a regularization function defined on the output neurons of the hidden layers, and ! and " are its weight coefficients. thus, the parameters may be derived as follows: � ∗ ≜ arg min1 ��� (4) there are numerous unconstrained optimization algorithms to solve (4) for the estimation of �∗, �∗, �∗. in this framework, the linear search-based algorithm of quasi-newton is applied. figure 1 depicts the ddae training procedure using noisy and clean voice samples. the ddae can be constructed by stacking up several autoencoders. for the training of the ddae, a dense layer of wised pretraining and fine-tuning is employed. when another hidden layer is introduced during the pretraining phase, the output of the previous hidden layer is used as the input of the subsequent autoencoder. the transformed noisy and clean speech data are used for training in denoising. as illustrated in figure 1, the training pair for the first autoencoder is � and �, and followed by ℎ�� and ℎ�� or the subsequent autoencoder. during the fine-tuning step, the initial network parameters are fixed as those obtained from the pretraining step. these training stages may produce a better overall result than training the ddae with random initialization. fig. 1. the training process of the ddae with noisy and clean speech data. iii. experimental setting this section evaluates the proposed ddae framework and the baseline algorithms for speech enhancement tasks. a clean, continuous taiwan mandarin hearing in noise test (tmhint) data set with 100 utterances was used for training by adding 5 noise types (machine, babble, party crowd, restaurant, vacuum cleaner) and 5 signal-to-noise ratios (snr). therefore, the total training dataset for noisy speech contains 2500 utterances. the first testing scenario is a matching case in which 40 utterances are added with the same two types of noises (babble and party crowd) with 5 snr levels. thus, the total number of match case utterances are 400. more details of the dataset can be found in [14]. we have investigated the accuracy of noise reduction, speech enhancement, and intelligibility using 3 different metrics with a defined standard range set. the range for pesq is between –0.5 to 4.5. as the value of pesq increases, the quality of speech enhancement will increase. similarly, the range for short-time objective intangibility (stoi) is between 0 and 1. as the value of stoi increases, the number of words identified by the listener will increase. the speech distortion index (sdi) is the opposite of the first two metrics, ranging between 0 and 1. as the value of sdi decreases, so does the quality of speech enhancement. most conventional speech enhancement algorithms are designed to filter out noisy speech engineering, technology & applied science research vol. 12, no. 6, 2022, 9532-9535 9534 www.etasr.com azmat et al.: environmental noise reduction based on deep denoising autoencoder using the gain function estimation. this article compares 3 traditional algorithms, logmmse, klt, and rpca, with the proposed ddae. the unprocessed speech is named noisy. the experimental results were evaluated using 2 matched noise types with two snr conditions (6db, -6db) and 4 mismatched noise types with 3 snr conditions (-2, 0, 2), as shown in table i. the ddae was trained using 5 layers, each containing 2048 neurons.. table i. experimental setup of the tmhint dataset train set 2500 utterances noise type: machine, cafeteria babble, crowd party, restaurant, vacuum cleaner snr levels: -6db, -3db, 3db, 6db, 10db test set matched condition 400 utterances noise type: cafeteria babble, crowd party snr levels: -6db, 6db mismatched condition 800 utterances noise type: applause, baby cry, grocery store, pink noise snr levels: -2db, 0db, 2db iv. results in this section, we evaluate and compare the results of the baseline algorithms with ddae based on 3 evaluation criteria using different scenarios and snr levels as mentioned in table i. table ii shows the average pesq results, normalized across the different snrs. compared to the baseline algorithms, the ddae framework has a better pesq score, i.e. improved speech quality, for both matched and mismatched noise types. table ii demonstrates that the ddae framework (5 hidden layer configuration, each layer containing 2048 hidden neurons) outperformed the 3 baselines algorithms, with the exception of most pink noise, where the logmmse utperformed the ddae framework and the other algorithms under mismatched stationery noise conditions. in addition, the ddae exhibited a better pesq score of speech enhancement than logmmse, rpca, and klt by maintaining high scores for stoi. for instance, the average psesq score of the ddae is 2.55, while the pesq scores of rpca, logmmse, and klt are 2.18, 2.15, and 1.90 respectively. compared to the baseline algorithms, on average, the pesq score of the ddae is higher than rpca, logmmse, and klt by 16.97 %, 18.60%, and 34.21%, respectively. table ii. ddae comparison with the baseline algorithms based on the average pesq score noise type framework noisy klt logmmse rpca ddae matched noise (seen noise) babble 2.26 1.89 2.21 2.25 2.58 crowd party 2.26 1.85 2.15 2.24 2.61 mismatched noise (unseen noise) applause 2.13 1.76 1.89 1.99 2.95 baby cry 2.17 1.77 1.97 2.02 2.50 grocery 2.19 1.80 2.09 2.18 2.26 pink noise 2.32 2.38 2.58 2.40 2.38 avg 2.23 1.90 2.15 2.18 2.55 table iii illustrates the average stoi score for the ddae and baseline algorithms, with 6 noise types with different snrs. the table shows that the ddae has a better stoi score for all types of noise. moreover, the ddae demonstrated better average speech enhancement capabilities by maintaining high stoi scores. compared to the baseline algorithms, the average stoi score of the ddae is higher than rpca, logmmse, and klt by 16.39%, 65.11%, and 10.93% respectively. table iii. algorithm comparison based on average stoi score noise type framework noisy klt logmmse rpca ddae matched noise (seen noise) babble 0.58 0.58 0.38 0.55 0.68 crowd party 0.63 0.61 0.46 0.66 0.71 mismatched noise (unseen noise) applause 0.69 0.68 0.57 0.697 0.73 baby cry 0.71 0.71 0.54 0.71 0.73 grocery 0.45 0.58 0.29 0.45 0.60 pink noise 0.52 0.68 0.31 0.52 0.74 avg 0.59 0.64 0.43 0.61 0.71 table iv shows the average sdi results averaged over the different snrs for the 6 considered noise types. the table shows that the ddae performs better than the other algorithms for all types of noise. in addition, the ddae demonstrated better speech enhancement capabilities. compared to the baseline algorithms, the sdi score of the ddae is 22.64%, 24.07%, and 12.96%, lower than the rpca, logmmse, and the performance of ddae significantly outperformed the them. figure 2 depicts the spectrogram of a test utterance contaminated with non-stationary noise applause at snr = -2db achieved by different models. for comparison, the spectrograms of clean and noisy speech signals are also presented in figure 2(a)-(b). the spectrograms of the test utterance enhanced by logmmse, klt, and rpca algorithms are shown in figures 2(c)-(e), while figure 2(f) depicts the spectrogram of the enhanced speech signals produced by the ddae. figure 2 clearly demonstrates that the ddae framework efficiently restores clean speech under very challenging conditions (non-stationery noise, -2db snr) and effectively suppresses noise components from the noisy signal (figure 2(b)). ddae suppresses noise components more effectively and produces better speech quality than the previous approaches. table iv. algorithm comparison based on the average sdi score noise type framework noisy klt logmmse rpca ddae matched noise (seen noise) babble 0.61 0.45 0.48 0.50 0.40 crowd party 0.61 0.48 0.48 0.50 0.38 mismatched noise (unseen noise) applause 0.61 0.55 0.585 0.58 0.41 baby cry 0.61 0.56 0.59 0.56 0.38 grocery 0.61 0.52 0.55 0.53 0.50 pink noise 0.61 0.25 0.57 0.53 0.39 avg 0.61 0.47 0.54 0.53 0.41 engineering, technology & applied science research vol. 12, no. 6, 2022, 9532-9535 9535 www.etasr.com azmat et al.: environmental noise reduction based on deep denoising autoencoder (a) (b) (c) (d) (e) (f) fig. 2. spectrograms of (a) clean, (b) noisy, (c) logmmse, (d) klt, (e) rpca, and (f) ddae. a noise of -2db was added to the test utterance. v. discussion and conclusion in this study, the ddae framework for speech enhancement of environmental noise is presented. the proposed framework provides a more understandable speech to the listener. the major contributions of this study are the introduction of the ddae framework, which enhances speech intelligibility over 4 different baseline methods, and the confirmation, based on experimental data, that this proposed framework can improve speech performance. these contributions allow our proposed architecture to serve as a straightforward and efficient means of bridging the acoustic mismatch condition. the ddae framework provides better generalization and a universal approximation capability. for mismatch and nonstationery conditions, ddae has better generalization performance compared to the conventional speech enhancement techniques. the experimental results demonstrate that even with insufficient training data, our proposed framework outperformed klt, logmmse, and rpca under both matched and mismatched noise conditions at varying snr levels. this is confirmed by the evaluation results, which show that ddae outperforms the other algorithms on all levels, except for stationary noise where the logmmse approach performs better. in addition, the comparative findings demonstrate that our method provides superior enhancement performance based on 3 widely used objective metrics. it is essential to find the ideal compromise between the parameter efficiency and the speech enhancement performance of the model. however, the majority of the baseline models cannot deliver great parameter efficiency. the experimental results suggest that the proposed model is superior to other speech enhancement frameworks in terms of trade-off. 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[14] l. l. n. wong, s. d. soli, s. liu, n. han, and m.-w. huang, "development of the mandarin hearing in noise test (mhint),” ear and hearing, vol. 28, no. 2 suppl, pp. 70s-74s, apr. 2007, https://doi.org/10.1097/aud.0b013e31803154d0. microsoft word etasr_v13_n3_pp10808-10813 engineering, technology & applied science research vol. 13, no. 3, 2023, 10808-10813 10808 www.etasr.com alromema et al.: heart sound classification using the nonlinear dynamic feature approach along … heart sound classification using the nonlinear dynamic feature approach along with conventional classifiers waseem alromema applied college, computer and information science department, taibah university, saudi arabia wromema@taibahu.edu.sa (corresponding author) eman alduweib computer science department, faculty of information technology, university of petra, jordan eman.alduweib@uop.edu.jo zaid abduh engineering and it college, amran university, yemen zaabduh@gmail.com received: 22 march 2023 | revised: 5 april 2023 | accepted: 17 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5873 abstract heart sounds show chaotic and complex behavior when murmurs are present, containing nonlinear and non-gaussian information. this paper studies ways to extract features from nonlinear dynamic models. the features frequently used to describe the underlying dynamics of the heart are derived from nonlinear dynamical modeling of heart sound signals. this study incorporates nonlinear dynamic features alongside conventional classifiers in the analysis of phonocardiograms (pcgs), achieving a significant improvement in the classification performance with 0.90 sensitivity and 0.92 specificity. keywords-heart sound; phonocardiogram; cardiovascular diseases; non-linear; classification; features i. introduction world health organization (who) has reported that cardiovascular diseases (cvds) and related conditions have caused 17.7 million deaths worldwide in 2015, representing 31% of all mortality worldwide [1]. several techniques can diagnose heart disease patients. many sophisticated treatments are available but they are very expensive and cumbersome, so often they are not available to the majority of people. another cvd diagnostic method is heart sound auscultation. a stethoscope is usually used to examine patients, and if an abnormality is detected, the patient may be referred to a cardiologist. an early diagnosis of abnormal heart sounds allows physicians to take corrective measures to prevent cardiovascular disruptions and treat the underlying cause. the phonocardiogram (pcg) represents the sound heart graphically. the pcg signal enables the diagnosis of heart diseases and the evaluation of the cardiovascular system's performance [2, 3]. each pcg contains multiple cardiac cycles, each with 4 heart sound states: s1, systole, s2, and diastole. these sounds are caused by the closing of the valves at each heart period, with the mitral and tricuspid valves closing before systole, and the aortic and pulmonic valves closing before diastole. despite their importance, heart sounds are often difficult to interpret due to their low intensity and dominant frequencies near the lower limits of human hearing. therefore, auscultation requires a lot of training and experience to detect abnormalities early [3]. the pcg diagnosis can be improved by the use of computers and the development of automated diagnostic tools or computer-assisted auscultation tools for physicians. automated algorithms have been developed over the past decade to assess patients based solely on pcg measurements without synchronization between the pcg and the electrocardiogram (ecg). this approach has some difficulties due to the variations in the heart rate of the same patient. there is a possibility that a pcg will fluctuate on an individual patient. moreover, the model is limited to different types of patients. there are many approaches used in heart sounds, e.g. the unorthodox approach [2, 5], the convolutional approach [4, 610], the nonlinear feature approach [6], wavelet fractal [11], and phase space reconstruction [12-14]. other methods used in heart sounds are deep learning (dl) [15, 16], svm [11, 1719], neural networks (nns) [2, 4, 7, 19-22], and hiddenmarkov models (hmms) [23]. when murmurs are present, heart sounds exhibit chaotic and complex behavior, so they contain nonlinear and non-gaussian information. nonlinear engineering, technology & applied science research vol. 13, no. 3, 2023, 10808-10813 10809 www.etasr.com alromema et al.: heart sound classification using the nonlinear dynamic feature approach along … dynamic techniques allow projecting a signal's dynamic behavior. in this work, we study ways to extract features from nonlinear dynamic models. the features that have been suggested are based on the nonlinear dynamical modeling of the heart sound signals, which are frequently utilized to describe the underlying dynamics of the heart. ii. methodology in this study, we propose a nonlinear dynamic feature method of the heart sound signals as input for a computerassisted auscultation system, as shown in figure 1. a. preprocessing to improve the cardiac sound signal, minimizing background noise and eliminating spike noise is critical. a two-stage preprocessing system is used, with a third-order butterworth bandpass filter with corner frequencies of 15 and 800 hz in the first stage. this allows for the selection of the valuable bandwidth of the heart sound. the spectral subtraction denoising method was used in the second stage [24]. this method's adaptive noise estimation is an advantage in rebuilding the denoised signal. to obtain accurate measurements of heart sounds, the noise power of frequencies outside the range of heart sounds is measured first. a weighted version of this measured noise power is then subtracted from the power spectrum of the unprocessed heart sounds. this process ensures that the resulting measurements are precise and reliable [24]. spectral subtraction filtration with a weighting factor of 0.5 was applied in this study. b. cardiac cycle segmentation each pcg signal is divided into cardiac cycles at this stage. recognizing the systolic or diastolic states is essential for classifying abnormal states in these areas. different algorithms were used. some work was performed using a reference signal, like the ecg, which the segmentation algorithms demand to be recorded simultaneously, making simpler to hear heartbeats. in other methods, the ecg is not utilized as a reference. this work divided the pcg signal into cardiac cycles using springer's improved version of schmidt's segmentation algorithm [22]. then, the processing was carried out using each complete cardiac cycle. this method utilizes information about the estimated heart sound state lengths and employs a logistic regression hidden semi-markov model (hsmm) to estimate the most likely sequence of states without the need for ecg synchronization. in order to solve the issue of the varying time length of cardiac cycles (and thus the sizes of their digital signals) in later processing stages the size of all signals was set to be the most extended cardiac cycle observed across all pcg recordings (here, it was around 2s). the shorter cardiac cycles were zero-padded to the length. this ensures that all signals contain the same frequency resolution. c. feature extraction in this stage, features were extracted from the segmented cardiac cycles for optimum classification accuracy. when murmurs are present, heart sounds exhibit chaotic and complex behavior. projecting a signal's dynamic behavior and dealing with its nonlinearity and non-gaussianity using nonlinear dynamic techniques is feasible. so, in this work, we study the extraction of nonlinear dynamical modeling features. the proposed features are based on nonlinear dynamic modeling of cardiac sound signals, which are commonly used to describe the underlying dynamics of the heart. a multidimensional phase space or attractor representing the system dynamics and its states could be developed from the measured signals or time series [21]. thus the system's actual attractor, at which the measurements were obtained, has the same dynamical characteristics as the reconstructed phase space (rps) [24]. the calculated features for the rps of the heart sound signals are moment-invariant, distance series-based, and statisticalbased features. in the nonlinear dynamical modeling analysis of the heart sound signal, the first step is reconstructing the phase space from the heart sound measurements. the timedelay embedding method proposed in [21, 24] was used for the phase space reconstruction. time-delay embedding is a technique used to reconstruct m-dimensional vectors from a time series of observations. this is achieved by selecting � values of the time series at different � lags and repeating the process until the vectors of the phase space are obtained. therefore, the time delay embedding has two parameters: the embedding dimension � and the time lag �. let {xk∶ k = 1,2,… , n} be the observed time series, the reconstructed �-dimensional phase space �(�) can be constructed as the following matrix (1): �� (�) = ���� …�� � = �� ���� … ���(���)��� ���� … ���(���)�… … … …�� ����� … ���(���)�� (1) where � = � − (� − 1)�, � is the length of the original time series, � is the embedding dimension, and � is the delay time. we use an embedding dimension m of 18 and a time delay of 10. after the reconstruction of the phase space, different features were extracted. we calculated the following statistical features for each reconstructed phase space vector: mean value, median value, standard deviation, mean absolute deviation, 25th and 75th percentiles, signal inter quartile range feature, skewness, and kurtosis. in addition, the same 9 statistical features are extracted from a new domain called the distance series (ds) domain. it is defined by [25] as the reduction of the multidimensional phase space into a one-dimensional space. the ds is a method used to characterize complex variations in rps. it is calculated by taking the euclidian distance between every point in the phase space and the origin, resulting in a one-dimensional representation of the trajectory. the ds di can be calculated by determining the euclidian distance between each point in the phase space yi and the origin: �� = �∑ ���� . = 1.2. … … … . " ��#� (2) for i = 1, 2, 3...k. if successive values of di show smooth behavior, a slow trajectory and small region of support in the phase space are indicated by minimal changes in the values. conversely, significant changes in values suggest a moving trajectory with large steps and significant support in the phase space. this mapping allows capturing more information about engineering, technology & applied science research vol. 13, no. 3, 2023, 10808-10813 10810 www.etasr.com alromema et al.: heart sound classification using the nonlinear dynamic feature approach along … the trajectory than the traditional and more complex measures. moreover, moment invariant features are calculated for the rps of the heart sound signals. moments are quantitative measures used in statistics to describe the distribution of a random variable quantitatively. fig. 1. nonlinear dynamic feature extraction. in addition, skewness, which describes the asymmetry of the distribution, is represented by the third moment, and kurtosis, which describes the peaked ness of the probability distribution of the random variable, is described by the fourth moment. the entire set of moments from order zero to infinity describes the distribution uniquely. the term invariant denotes that the moments should remain unaffected to translation, rotation, and scaling transforms to describe the shape of the attractor optimally. the steps of calculating the invariant moments were described in [25], where the second-order moments m were calculated by: $%&…%' = ∑ … ∑ (��%& … (��%' )�#�)�#� *(()+(� … +(� (3) where ρ(() is the probability density function, ( is a column in the rps, and , is the order of the moments given by: , = ∑ ,� ��#� (4) we obtained the central moments by applying (5) to the second-order moments. from these central moments, we constructed the o matrix using (6). "the major minors for the o matrix were calculated to represent the moment invariant features of the rps, given that the number of the moment invariant features is equal to the number of the embedding dimension � of the rps". -%&….%' = ∑ … ∑ ((�� − (.�////)%&)�#� … ((�� −)�#�(.�/////)%' *(()+(� … . . +(� (5) where (�0 = )&….1)1….1 … . (�//// = )1….&)1….1 2 = 3 -�…4 … -�…�… … …… … …-�…� … -4…�3 (6) the total number of extracted features is 207. d. classification there are various classifiers available and each one comes with its own set of advantages and disadvantages. one such classifier is k-nearest neighbors (knn), which is a memorybased learning algorithm [19]. however, it is important to note that knn requires the availability of training and testing data at all times. additionally, for noisy datasets, decision tree classifiers are recommended [26]. however, boosted ensemble classifiers perform best with imbalanced data [19, 26, 30]. this study used a cross-validation approach to evaluate the performance of various conventional classifiers on a set of nonlinear dynamics features and then determine the most effective classification model, the classification methods used in this study include svms with quadratic, cubic, and gaussian kernels, knn with linear, cosine, cubic, and weighted distance metrics, and ensemble classification methods such as bagged trees, subspace knn, rusboosted tree, and boosted tree [2728]. the classifiers were tested and trained using the local holdout and cross-validation methods. the feature vector data for the cross-validation test were divided into five folds. the model was trained for each fold using all the data outside the fold, and each fold was held out for testing in turn. the performance of each model was then evaluated using the information included in the fold, and the overall results were computed as the average over all folds. the local holdout technique studies utilized 80% of the feature vector data as the training set and the remaining 20% as the testing set, both of which were randomly chosen. e. dataset description selecting the right dataset is crucial for successful model building and generalization in pattern recognition. a large, diverse and easy-to-understand dataset is necessary to effectively analyze and compare different algorithms. the physionet/computing in cardiology challenge 2016 dataset was used to test the performance of the proposed system [16]. a total of 3153 recordings are included in the dataset. only the engineering, technology & applied science research vol. 13, no. 3, 2023, 10808-10813 10811 www.etasr.com alromema et al.: heart sound classification using the nonlinear dynamic feature approach along … sure-labeled data in this collection were used to a total of 2868 recordings obtained from 6 datasets. there are 2249 normal patient records and 619 abnormal patient records, ranging from 5s to more than 120s. each track has been down-sampled to 2,000hz and is available in wav format. recordings with varying noise levels were included from several actual clinical and nonclinical settings. data from normal persons and patients, from either children or adults were collected. one to 6 recordings of the same subject may exist in the dataset. data were gathered from various body parts and locations (including aortic, pulmonic, tricuspid, and mitral areas). the fact that there are far more normal than abnormal recordings clearly shows that the data are unbalanced. eighty percent of the dataset was used for training, while 20% was used for testing. the heterogeneity of the recordings introduces differences that could make classifier training more challenging. f. performance evaluation the confusion matrix is produced with the abnormal cases as the positive class in order to evaluate the success of the classification process, and it is then used to determine the values for sensitivity, specificity, and accuracy: (567 8 9 8:((5) = ;<;< � =� (7) (,5> ? > 8:((,) = @a;� � =< (8) b>>cde>: = ;< � ;�;<�;��=<�=� (9) where tp, tn, fp, and fn are the confusion matrix entries representing true positive, true negative, false positive and false negative classifications, respectively. error rate and accuracy are insufficient for measuring classification performance for imbalanced data since they do not consider the costs of misclassification. they are hence sensitive to class skews and frequently show a considerable bias toward the dominant class [22, 29]. as a result, the official evaluation metric for the 2016 physionet/computing in cardiology challenge was an alternative evaluation score based on the average between sensitivity and specificity: (>fd5 = gh � g%� (10) iii. results and discussion a. experimental verification each pcg record was preprocessed using a butterworth band-pass filter of order 3 with corner frequencies of 15 and 800hz. each record was further enhanced using spectral subtraction denoising with 0.5 weight. there were 79492 cardiac cycles after segmenting each record into cardiac cycles. the most extended cardiac cycle observed in all pcg recordings is about 2s long. each time series was therefore zero-padded to a cardiac cycle's length of 2s if it was less. for nonlinear dynamic feature extraction, the first step is the reconstruction of the phase space from the heart sound measurements with embedding dimension m=18 and a time delay of 10. a total of 207 features were considered for each cardiac cycle. all feature vector values were normalized to the interval [0, 1] in order to optimize the classification process. the performances of several conventional classifiers, including svm and knn, and bagged trees, subspace knn, and rusboosted tree ensemble classifiers, were compared. b. results the classification results with the 5-fold cross-validation train-test approach are listed in table i. when using unbalanced data, the cross-validation train test approach is effective in reducing over-fitting and improving model evaluation. it should be noted that in our experiments only the ensemble classifiers were able to achieve relatively balanced sensitivity and specificity values. the rusboosted tree ensemble classifier had the highest score value of sensitivity and specificity of 0.90 and 0.91. on the other hand, the svm classifier with a gaussian kernel had the lowest sensitivity of 0.64. the bagged tree ensemble classifier and the knn classifier with weighted distance metric both achieved the most remarkable specificity of 0.95, while the majority of commonly used classifiers achieved lower specificity of 0.91. the classification results utilizing the local holdout train-test approach are listed in table ii. only the ensemble classifiers succeeded in achieving relatively balanced sensitivity and specificity values in our experiments. the rusboosted tree ensemble classifier scored 0.91, which was the highest, with balanced sensitivity and specificity of 0.90 and 0.92. conversely, the svm classifier with a gaussian kernel showed the lowest sensitivity, at 0.65, while the svm classifier with a gaussian kernel achieved the lowest specificity of 0.79, the bagged tree ensemble classifier and the knn classifier with weighted distance metric both achieved the highest specificity of 0.95. table i. nonlinear dynamic feature classification results using the 5-fold cross-validation train-test method" classifier classifier accuracy sensitivity specificity auc score svm quadratic 0.8470 0.6700 0.9100 0.8900 0.7900 cubic 0.8680 0.7300 0.9100 0.9100 0.8200 gaussian 0.8620 0.6400 0.9400 0.9000 0.7900 ensemble bagged trees 0.9190 0.8400 0.9500 0.9700 0.8950 rusboosted tree 0.9090 0.9000 0.9100 0.9700 0.9050 boosted tree 0.9020 0.8000 0.9300 0.9600 0.8650 knn linear 0.8700 0.7000 0.9200 0.9100 0.8100 cosine 0.8530 0.6700 0.9100 0.9100 0.7900 cubic 0.8630 0.6500 0.9300 0.9100 0.7900 weighted 0.8780 0.6600 0.9500 0.9300 0.8050 engineering, technology & applied science research vol. 13, no. 3, 2023, 10808-10813 10812 www.etasr.com alromema et al.: heart sound classification using the nonlinear dynamic feature approach along … table ii. nonlinear dynamic feature classification results classifier classifier accuracy sensitivity specificity auc score svm quadratic 0.8570 0.6700 0.9100 0. 9000 0.7900 cubic 0.7990 0.8400 0.7900 0.8800 0.8150 gaussian 0.8720 0.6500 0.9400 0.9000 0.7950 ensemble bagged trees 0.9230 0.8500 0.9500 0.9700 0.9000 rusboosted tree 0.9110 0.9000 0.9200 0.9700 0.9100 boosted tree 0.9060 0.8000 0.9400 0.9600 0.8700 knn linear 0.8830 0.7300 0.9300 0.8900 0.8300 cosine 0.8610 0.7000 0.9100 0.9100 0.8050 cubic 0.8640 0.6500 0.9300 0.9200 0.7900 weighted 0.8790 0.6600 0.9500 0.9400 0.8050 training = 80% – testing= 20% iv. discussion this research demonstrates that nonlinear dynamic features have an application to phonocardiogram analysis. heart sounds exhibit chaotic and complex behavior when murmurs are present, hence they contain nonlinear and non-gaussian information. nonlinear dynamic approaches can deal with a signal's nonlinearity and non-gaussianity and project its dynamic behavior. the features that have been proposed are based on the nonlinear dynamical modeling of the heart sound signals, which are frequently used to characterize the underlying dynamics of the heart. applying nonlinear dynamic approaches is also helpful for determining whether murmurs are present. in this paper, the rusboosted tree ensemble classifier scored the highest with a sensitivity value of 0.90 and specificity value of 0.92, resulting in an overall score of 0.91. as a result, it offered the most accurate prediction of the predictive score using both approaches, as well as relatively balanced values for sensitivity and specificity. the classifier performance evaluations in the two train-test approaches were largely comparable. the ability of the proposed system to handle various p phonocardiogram cg recordings and signal quality settings was demonstrated by the significant improvements in the classification performance obtained utilizing nonlinear dynamic features along with the conventional classifiers. observing the effect of the training data's class distribution is essential, as this is a significant factor in determining the accuracy of subsequent classification. although there seem to be many samples in the challenge database, these samples are, unfortunately, highly unbalanced, with vastly different proportions of normal and abnormal recordings. due to this, traditional classifiers frequently develop biases in favor of the majority class, increasing the misclassification rate for the minority class. as a result, two validation approaches were used to assess the performance of various classifiers on the dataset. the cross-validation train-test method is the first. it reduces the influence of over-fitting caused on by noisy records. the second approach, known as the local holdout method, simulates real-world analysis by using just 80% of the data to develop the model and the remaining 20% to assess it. noting that the dataset is significantly imbalanced, it is observed in the proposed system that only the ensemble classifiers performed very well. this confirms that ensemble classifiers are always recommended for imbalanced data in general [19, 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[30] z. abduh, e. a. nehary, m. abdel wahed, and y. m. kadah, "classification of heart sounds using fractional fourier transform based mel-frequency spectral coefficients and traditional classifiers," biomedical signal processing and control, vol. 57, mar. 2020, art. no. 101788, https://doi.org/10.1016/j.bspc.2019.101788. microsoft word etasr_v12_n5_pp9203-9207 engineering, technology & applied science research vol. 12, no. 5, 2022, 9203-9207 9203 www.etasr.com buller et al.: investigating the deflection and strain of reinforced green concrete beams made with … investigating the deflection and strain of reinforced green concrete beams made with partial replacement of rca under sustained loading abdul hafeez buller department of civil engineering faculty of engineering international islamic university malaysia, selangor, malaysia ah.buller@quest.edu.pk nadiah md. husain department of civil engineering faculty of engineering international islamic university malaysia, selangor, malaysia drnadiah@iium.edu.my mehboob oad department of civil engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan engrmahbooboad04@gmail.com bashir ahmed memon department of civil engineering quaid-e-awam university of engineering, science and technology nawabshah, pakistan bashir_m@hotmail.com irum naz sodhar department of computer science faculty of information and communication technology international islamic university malaysia selangor, malaysia iram10akber@gmail.com received: 30 june 2022 | revised: 12 july 2022 | accepted: 1 august 2022 abstract-artificial intelligence (ai) and statistical methods are used in various fields and have played a vital role in investigating the deflection and strain of reinforced green concrete beams made with partial replacement of recycled concrete aggregates under sustained loading. the methods used to assess structural contributors are time-saving and cost-effective compared to experimental evaluation. this study investigated the numerical modeling of reinforced concrete beams produced by replacing 50% of coarse natural aggregates with demolished vintage concrete under sustained loading. multivariate regression analysis was used to determine the mathematical equations for long-term deflection and stress from experimental data of 6, 9, and 12 months of loading. three software suites were used for the regression analysis, namely ncss, matlab, and microsoft excel. six beams were cast using demolished concrete as 50% of coarse aggregates to test and validate the regression equations, where three of them were examined for two months of sustained loading and the other three for three months. the regression results were in accordance with the experimental observations with a maximum error of 10.34%. therefore, the provided regression equations for deflection and pressure could be used to estimate the parameters of reinforced concrete beams. keywords-artificial intelligence (ai); green concrete; longterm loading; numerical modeling; recycled concrete aggregates; sustained loading i. introduction many structural engineering challenges remain outstanding although the sector grows its interest in technological solutions [1]. most of these problems are hard optimization problems [2], making them relatively difficult to resolve, as an increase in the dimensionality of a problem increases its complexity [3]. conventional optimization strategies cannot tackle complicated issues for numerous reasons, especially in the case of the referred curse of dimensionality. furthermore, investigating the use of gradient-primarily based strategies for engineering problems with neighborhood solutions is time-consuming, as these methods depend on the region of the initial issue [4]. all these drawbacks made researchers to extend machine learning methods consisting of metaheuristic or hybrid methods [5] to resolve engineering problems. estimation of concrete properties, particularly green concrete, before and after hardening is a key effort to ensure its quality [6]. green concrete is preferred as it is environmentally friendly and preserves the natural constituents of conventional concrete, but it requires extensive research to determine its behavior under different conditions. on the other hand, the experimental assessment of required parameters is not only time-consuming, but also requires much care, labor, and cost. moreover, any inaccuracy in an experimental setup or procedure requires repetition and modification. therefore, an alternative tool is required to avoid these problems. the best option is numerical analysis, carried out by mathematical modeling of the required parameters based on experimental data. regression analysis is the most widely used method for this purpose [7]. many concrete manufacturing methods have been proposed using domestically available substances or waste [8]. the use of demolished concrete as coarse aggregates in new concrete could reduce the environmental impact due to the transport of natural coarse aggregates and the waste dumping in landfills. in corresponding author: abdul hafeez buller engineering, technology & applied science research vol. 12, no. 5, 2022, 9203-9207 9204 www.etasr.com buller et al.: investigating the deflection and strain of reinforced green concrete beams made with … addition, it could help reduce waste control issues and the overall cost of the structure. various proportions of recyclable aggregates from demolished concrete [9, 10] or plastics [11] have been investigated in concrete mixtures, examining their compressive and tensile strength. in [12], a relationship between the cylindrical and cubic compressive strength of concrete using recycled concrete as coarse aggregate was presented, using regression analysis of the experimental observations of 400 samples. regression analysis is a process of predicting the deviation in the dependent variables for the deviation of the independent variables. this process is effectively used in civil engineering to determine mathematical equations for different properties based on experimental observations. in [13], a regression model was presented considering the variable workability of recycled aggregate concrete. in [14], regression analysis was used to model concrete delivery and placement, while in [15] the cost estimation of a project was studied using the same method. traditional strategies for modeling and optimizing complicated structures require huge amounts of computing resources. ai-based methods can provide valuable alternatives to efficiently solve issues in civil engineering [16], while many studies examined concrete's strength using numerical modeling. in [17], the age and curing period of concrete were used to predict its strength, finding correlation coefficients equal to 0.995 and 0.994 for 7 and 28 days of curing and demonstrating the validity of the model. in [18], a combination of multivariate regression analysis and neural networks was investigated to study the strength of concrete with mineral admixtures. the concrete samples, using fly ash and a blast furnace, were cast and cured from 3 to 180 days, followed by nondestructive testing. laboratory results were used as data for numerical modeling, and the neural network showed better performance. however, the combination of both methods was more suitable for non-linear relationships of the parameters. numerical modeling of the relationships between the properties of demolished concrete, recycled aggregates, and recycled concrete aggregate and the flexural behavior of amorphous concrete are some other examples of regression analysis studies [19-23]. numerical modeling of several aspects of normal and recycled aggregate concrete under short-term loading has been investigated in several studies. however, very few studies are available on the numerical modeling of concrete behavior when using green concrete produced by demolished concrete as coarse aggregates. this study presents a regression analysis of the deflection and strain of reinforced green concrete beams under sustained long-term loads (6, 9, and 12 months) [24-26]. ncss [27], matlab 2016 [28], and microsoft excel 2016 were used to perform regression analysis, and their results were compared. to validate the results, 6 rc green concrete beams were cast and tested. a comparison of the test with the predicted results showed very good agreement between the two sets. ii. method and analysis regression analysis is a statistical method to estimate a relationship between two or more variables and can be used to predict future values from available datasets. the method mainly depends on a dependent or target variable and independent or predictor variables. this process requires the declaration of dependent and independent variables, and then it fits the data for regression and gives the coefficients of a mathematical equation along with the statistical analysis of the data. this study used a dataset from experimental investigations of long-term deflection and strain under sustained load for 6, 9, and 12 months [24-26]. these studies used reinforced concrete beams cast using 50% replacement of natural coarse aggregates with demolished concrete. the beams were tested in frames with a constant central point load maintained with the help of screw jacks and load cells. the central point deflection was monitored and recorded on daily basis. the strain was measured at 11 locations along the central line (depth) of the beam, and then all these values were averaged. six beams were used for each loading duration, three made from all-natural coarse aggregates (nab) and three with an equal dosage of natural and recyclable aggregates (rab). figure 1 shows the plot of deflection in mm of all beams versus time in days and the proportion of recyclable aggregates (%). similarly, figure 2 shows the average recorded strain in all beams. both figures show the results of beams cast with allnatural and recyclable aggregates on the same axis. fig. 1. deflection in all beams. fig. 2. strain in all beams. engineering, technology & applied science research vol. 12, no. 5, 2022, 9203-9207 9205 www.etasr.com buller et al.: investigating the deflection and strain of reinforced green concrete beams made with … at first, a regression equation was produced for deflection, considering the proportion of recyclable aggregates (0 or 50) and time as independent variables. initially, the load was also considered as an independent variable, but as it was the same throughout the sustained load duration, it had no impact and was removed from the list of variables. similarly, a regression equation was investigated for strain, in this process, the strain was considered as the dependent variable while all the other parameters were kept constant. although several software suites are available for regression analysis, this study used ncss, matlab, and microsoft excel. ncss and matlab have been widely used for statistical analysis. the coefficients of the regression equation for the deflection and the strain, generated by ncss, along with standard error are given in tables i and ii. table i. coefficients and standard error for deflection using ncss independent variable regression coefficient standard error lower 95% conf. limit upper 95% conf. limit intercept 1.519958 0.0067 1.5067 1.5331 time 0.017779 0.0002 0.0173 0.0182 rca% 0.002341 0.0001 0.0021 0.0025 table ii. coefficients and standard error for strain using ncss independent variable regression coefficient standard error lower 95% conf. limit upper 95% conf. limit intercept 0.001953044 3.42×10-6 0.00195 0.00195 time 1.336448×10-5 1.20×10-7 1.31×10-7 1.35×10-5 rca% 2.200535×10-6 6.56×10-8 6.56×10-8 2.33×10-6 regression analysis on experimental observations for deflection and strain in matlab produced the coefficients of regression equations given in table iii. finally, regression analysis was conducted in microsoft excel, and the coefficients obtained for deflection and strain are shown in tables iv and v. table iii. coefficients for deflection and strain using matlab independent variable regression coefficient deflection strain intercept 1.5309459 0.0019583 time 0.0025159 1.8728203×10-6 rca% 0.0022354 2.1973138×10-6 table iv. ms excel regression results for deflection description regression coefficient standard error pvalue lower 95% upper 95% intercept 1.531000785 0.001403289 0 1.528249712 1.533751858 time 0.002515843 7.07153×10-6 0 0.00250198 0.002529707 rca % 0.002234576 2.66382×10-5 0 0.002182353 0.002286799 table v. ms excel regression results for strain description regression coefficient standard error pvalue lower 95% upper 95% intercept 0.001958191 1.23844×10-6 0 0.001955763 0.001960619 time 1.87426×10-6 6.24082×10-9 0 1.86202×10-6 1.88649×10-6 rca % 2.19487×10-6 2.3509×10-8 0 2.14878×10-6 2.24096×10-6 the regression coefficients obtained from ncss were used to write the regression equations for deflection and strain in (1) and (2), respectively: � � 1.530946 � 0.0022354 ��� � 0.0025159 � (1) � � 0.0019583 � 2.19731379 10 �� ��� � 1.8728203 10 �� � (2) where δ represents deflection, ε denotes strain, rca is used for proportions of recyclable aggregates (0 for 0%, 50 for 50%, etc), and t is time in days. similarly, the coefficients given in table iii, obtained from regression analysis in matlab, were used in (3) and (4): � � 1.5309459 � 0.0022354 ��� � 0.0025159 � (3) � � 0.0019583 � 2.1973138 10 �� ��� � 1.8728203 10 �� � (4) similarly, the regression coefficients given in tables iv and vi obtained using microsoft excel can be used for the respective regression equations for strain and deflection. these equations were used to predict the deflection and strain values. to further validate the performance of the equations, six beams were cast and cured for 28 days. the proportion of recycled aggregates in the beams was 50%. three beams were tested for 2 months of sustained load, and the other three were tested for 3 months. the load and loading mechanism was maintained the same with the test results used to develop the regression equations. figure 3 shows the loading system. fig. 3. loading system. iii. results and discussion several statistical parameters were computed and compared in regression analysis to check the authenticity of the process. the r-square value is one among them and is presented along with the standard error in table vi. the r-square values obtained from the regression analysis by ncss are equal to 0.953 and 0.9496 for deflection and strain. this shows that about 95% of deflection and 96% of strain predicted values are around the mean value. the normal probability plots of deflection and strain are shown in figures 4 and 5. both figures also verify that the vast majority of data points fall in a close band, indicating a good agreement of predicted and test values. α similar observation was made for the r-square value obtained from the matlab regression analysis. similarly to the above, microsoft excel r-square values were equal to 0.9645 and 0.9525 for deflection and strain. these values also show that about 96% of the data points are close to the mean. engineering, technology & applied science research vol. 12, no. 5, 2022, 9203-9207 9206 www.etasr.com buller et al.: investigating the deflection and strain of reinforced green concrete beams made with … additionally, the p-value for all variables computed by the software was nearly zero. both r-square and p values show the validity of the developed regression equations. table vi. summary report software ncss matlab excel dependent variable deflection strain deflection strain deflection strain r² 0.9530 0.9496 0.951 0.9642 0.9645 0.9526 adj r² 0.9527 0.9496 0.951 0.9642 0.9645 0.9526 standard error 0.0022 8.66× 10-7 0.0467 4.12× 10-5 fig. 4. normal probability plot of deflection (ncss). the three sets of regression coefficients have very minor or ignorable differences, showing the similarity of the capabilities of these suites for the purpose. the regression equations were then used to predict the deflection and stress of the concrete beams and compare them to the experimental results. table vii shows the error in the computed values. it can be observed that the maximum error in deflection computations is about 12%, whereas in stress is about 10%, proving the validity of the regression equations. the regression analysis cannot only save from the experimental procedures but additionally provides results in little time. to further verify the validity of the equations, six reinforced concrete beams were prepared and tested with the same conditions. table viii shows the variables, numerical results, and experimental observations. fig. 5. normal probability plot of strain (ncss). table vii. error % in predicted values of deflection and strain description deflection strain maximum (%) minimum (%) maximum (%) minimum (%) ncss 12.30248 -6.03898 10.107397 -4.82636 matlab 12.348812 -6.09497 10.0916 -4.84347 excel 12.30491 -6.0357 10.29922 -4.85232 it may be noted that almost the same deflection results were produced by all three equation sets. the same strain value was calculated using the regression equations of ncss and matlab, whereas a slightly higher strain value was calculated using the strain equation developed by excel. the percentage difference with the other two regression models was about 2%, which is negligible. in comparison to the findings with the average values of test results of the beams loaded for 2 months, it was observed that the regression value of deflection was about 11.8% higher than the average test results. the difference in strain for the beams was recorded as equal to 2%. the difference between regression and average test observations of deflection and strain for reinforced concrete beams loaded for 3 months was recorded equal to 1% for both parameters. therefore, it can be concluded that the regression equations predicted very well the long-term deflection and strain of the reinforced green concrete beams under sustained load, even beyond the data set. table viii. data and results for test beams # variables deflection strain t rca lab ncss matlab excel lab ncss matlab excel b1 60 40 1.58 1.7713 1.7713 1.7713 0.00211 0.002159 0.002159 0.002164 b2 60 40 1.59 0.00212 b3 60 40 1.59 0.00211 b4 90 40 1.83 1.8468 1.8468 1.8468 0.0022 0.002215 0.002215 0.002219 b5 90 40 1.85 0.0023 b6 90 40 1.85 0.0023 iv. conclusion this study used regression analysis to investigate the numerical modeling of deflection and strain under sustained long-term loads of reinforced green concrete beams, using three software suites, namely ncss, matlab, and microsoft excel. the experimental results of 6, 9, and 12 months of loading were used as input variables to develop regression equations for deflection and strain. it was observed that all software suites used developed almost similar regression engineering, technology & applied science research vol. 12, no. 5, 2022, 9203-9207 9207 www.etasr.com buller et al.: investigating the deflection and strain of reinforced green concrete beams made with … equations. the use of regression equations to predict the parameters showed good agreement between the two sets with a maximum error of 12.34%. further validation of the regression equations was performed by casting and testing six additional reinforced green concrete beams. the numerical results of these beams were observed to be 12% higher than the experimental results. therefore, the regression equations may be confidently used to predict the deflection and strain of proposed beams under long-term loading. references [1] v. plevris and g. c. tsiatas, "computational structural engineering: past achievements and future challenges," frontiers in built environment, vol. 4, apr. 2018, https://doi.org/10.3389/fbuil.2018. 00021. 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[28] mathworks, "matlab mathworks.". available: https://www. mathworks.com/products/matlab.html. microsoft word 8-675-ed.doc engineering, technology & applied science research vol. 6, no. 2, 2016, 964-971 964 www.etasr.com okasha: reliability-based design optimization of trusses with linked-discrete design variables… ` reliability-based design optimization of trusses with linked-discrete design variables using the improved firefly algorithm nader m. okasha civil engineering department university of hail hail, saudi arabia n.okasha@uoh.edu.sa abstract—in this paper, an approach for conducting a reliability-based design optimization (rbdo) of truss structures with linked-discrete design variables is proposed. the sections of the truss members are selected from the aisc standard tables and thus the design variables that represent the properties of each section are linked. latin hypercube sampling is used in the evaluation of the structural reliability. the improved firefly algorithm is used for the optimization solution process. it was found that in order to use the improved firefly algorithm for efficiently solving problems of reliability-based design optimization with linked-discrete design variables; it needs to be modified as proposed in this paper to accelerate its convergence. keywords-fierfly; rbdo; lhs; truss; linked-discrete i. introduction when design variables of an optimization problem can assume only some predetermined values, these variables are discrete. one of the approaches used to handle discrete design variables in engineering problems is to solve these problems as if the design variables are continuous and adjust the optimal design to the nearest discrete values [1]. the interest in optimization problems with discrete design variables in structural engineering applications dates back to the 1960s. early reviews about the development in this topic can be found in [2]. more recent treatments of discrete variables in structural optimization of trusses can be found in the literature [3-6]. in the case of trusses, only one section property is typically treated in the literature as a design variable for each structural member, namely the cross sectional area. in these cases, the design variables are treated as independent of each other. however, the optimization of most structural systems requires using linked-discrete design variables. practically, a structural designer selects the sections from the american institute of steel construction (aisc) standard tables [7]. if a section is selected from these tables, the section properties must all take the values pertaining to that section. accordingly, if each section property is treated as a design variable, they are naturally linked. treating these design variables as independent will surely lead to unacceptable results. in [8] the approaches that had been used to solve problems of this class of optimization to that date were reviewed. in [9] strategies to reduce the large computing time required to solve optimization problems of steel structures with standard sections were suggested. the reliability-based design optimization problem domain is complex and requires the application of robust search and optimization techniques to arrive at a near-global optimal solution [6]. in [10] an overview of various reliability-based optimization design approaches which were tested on a benchmark constituted of four examples using mathematical and finite element models, with different levels of difficulties, was given. one of the methods that have been efficiently used in solving problems of structural reliability in various engineering applications is the latin hypercube sampling [6; 11-13]. the optimization of practical structural systems involves a problem with discrete-linked design variables, and is subjected to nonlinear implicit random constraints. furthermore, the gradients cannot be explicitly expressed. therefore, gradient-based optimization algorithms are unlikely to be suitable for solving this type of problems. global search methods can overcome most of the difficulties that gradientbased algorithms cannot handle. many global search algorithms have been developed over the past few decades. some of the most promising algorithms are nature-inspired, and they are called metaheuristic algorithms. among these algorithms are genetic algorithms (ga) [14], which simulate the process of natural selection, and the firefly algorithm (fa) [15], which mimics the social behavior of fireflies based on their flashing characteristics. also, simulated annealing (sa) [16] models the physical process of heating a material and then slowly lowering the temperature to decrease defects, thus minimizing the system energy. even though sa and ga methods do not guarantee an optimum solution, they provide a reasonable solution at an acceptable computational cost [17]. in [18] a real coded genetic algorithm named mi-lxpm for solving integer and mixed integer constrained optimization problems was developed. the optimum design of trusses was investigated in the literature using ga [4,6], sa [9], and fa [3,5]. however, the reliabilitybased design optimization of trusses considering linkeddiscrete design variables using fa has not been attempted yet. engineering, technology & applied science research vol. 6, no. 2, 2016, 964-971 965 www.etasr.com okasha: reliability-based design optimization of trusses with linked-discrete design variables… ` in this paper, an approach for conducting a reliability-based design optimization of truss structures with linked-discrete design variables is proposed. the sections are selected from the aisc standard tables and thus the design variables that represent the properties of the section are linked and discrete. if a section is selected from the tables, the design variables must take the values pertaining to that section. the improved firefly algorithm (ifa) is used for the optimization. latin hypercube sampling is used to determine the structural reliability. it is found that despite the strength of the ifa in solving deterministic optimization problems, it is unstable when used in probabilistic and reliability-based optimization problems. a modification to the ifa is proposed in order to stabilize it for use in probabilistic and reliability-based optimization problems. the modification is tested on a planner truss and a space truss. the performance of the ifa is investigated with and without the proposed modification in both truss examples. then, the approach for the reliability-based design optimization with discrete-linked design variables is tested on a truss bridge and the results are compared with those of ga and sa. ii. nominal strength of truss members under tensile loads even though a ductile steel member without holes and subjected to tensile loads can resist loads larger than its yielding capacity, due to the effect of strain hardening, the reaching of strain hardening in a member results in unacceptable deformations. therefore, sections of a tension member are deemed to resist loads up to their yielding capacity. the presence of bolt holes may cause the member to fail by fracture at the net section through the holes. this fracture load may be smaller than the yielding capacity of the gross section. accordingly, the aisc [7] states that the nominal strength of a tension member, pnt, may be the smaller of the tensile yielding strength of the member, pny, and the tensile rupture strength of the member, pnr, given by (1) and (2), respectively [7]: pny = fyag pnr = fuae  in the preceding expressions, fy and fu are the specified minimum yield and ultimate tensile stresses, respectively, ag is the gross area of the cross section of the member, and ae is the effective net area that is assumed to resist the loads at the section through the holes. the effective net area is related to the net area, an, by [19]: ae = anu  where u is the shear lag reduction factor and is calculated by: 1 x u l    where x is the eccentricity of connection and l is the length where force transfer occurs as shown in figure 1a for an angle member with one row of three bolts. the net area is calculated as [19]: an = ag – ∑(dn+1/8)t  where dn is the nominal hole diameter and t is the thickness of the tension member. pn l = length of connection pn tension plane shear plane (a) (b) fig. 1: (a) a standard aisc angle section, and (b) the shear and tension planes in block shear failure of the angle section. in some cases, the strength of tension members is controlled by block shear strength, where the failure of a member may occur along a path involving tension on one plane and shear on a perpendicular plane [19] as shown in figure 1b for an angle member with one row of bolts. the aisc specifies that the block strength, pnb, is calculated as [7]: 0 6 0 6nb u nv bs u nt y gv bs u ntp . f a u f a . f a u f a     where agv is the gross area subject to shear, anv is the net area subject to shear, ant is the net area subject to tension, and ubs = 1 or 0.5 and is 1 for most tension members. iii. nominal strength of truss members under compressive loads the nominal compressive strength, pnc, can be calculated as [7]: pnc= fcrag  where fcr is the critical flexural buckling stress, which is calculated as per [7] as given in: 0 658 for 4 71 0.877 for 4 71 y e f f y y cr e y kl e . f . r f f kl e f . r f              where e is the elastic modulus, l is the length of the member, k is the effective length factor which is 1.0 for truss members, r is the minimum radius of gyration, and fe is the elastic (euler) buckling stress calculated as [7]: 2 2 π (9)e e f kl r = æ ö÷ç ÷ç ÷çè ø  engineering, technology & applied science research vol. 6, no. 2, 2016, 964-971 966 www.etasr.com okasha: reliability-based design optimization of trusses with linked-discrete design variables… ` iv. structural reliability the safety margin for truss member i, gi, also known as the performance function, is defined as the difference between the resistance of the truss member, ri, and the internal force it is subjected to, fi, and is given by: gi = ri – fi  the resistance of truss member i can be expressed by: min , , for tension members for compression members ny nr nb i nc p p p r p          the reliability associated with failure of truss member i due to the action of the internal load fi may be represented by the reliability index, fi, which is given by [20]: 2 2 ri fi fi ri fi          where ri,fi are the means of the resistance and internal force for truss member i, respectively, and ri,fi are the standard deviations of the resistance and internal force for truss member i, respectively. similarly, the reliability index, dj, associated with the exceeding of truss joint j to an allowable displacement limit, dall, is given by: ( ) ( ) all dj dj dj d abs abs       where dj and djare the mean and standard deviation of the displacement of truss joint j, respectively. standard deviation,  is related to the coefficient of variation, v, as given by: v   it is assumed in the examples of this paper that the truss members are each connected to the joint by one line of three bolts of ¾ inch diameter. the modulus of elasticity, ei, the yield stress, fyi, and the ultimate tensile stress, fui, for truss member i are all treated as normally distributed random variables with coefficient of variation 0.05 and means, 29000 ksi, 50 ksi, and 65 ksi, respectively. the cross-sectional area, ai, the eccentricity of connection, ,x and the radius of gyration, ri, for truss member i are also treated as normally distributed random variables with coefficient of variation 0.05 and means taken from the aisc tables for each angle section selected. v. improved firefly algorithm the fa is one of the newest algorithms which mimics the social behavior of fireflies based on their flashing characteristics. each firefly movement is based on absorption of the other one’s flash [21]. since its appearance, it has been through several enhancements and it has attracted many applications [15]. the light intensity, i(r), can be assumed to vary according to the inverse square law. for a medium with a fixed light absorption coefficient, the light intensity varies with the distance from the source, d, as [21]: 2 0( ) di r i e   where i0 is the intensity at the source and  is the light absorption coefficient. in a similar manner, the attractiveness of a firefly, β, varies with the distance, rij, between firefly i and firefly j and can be calculated as [15]: 2 0 re     where β0 is the attractiveness at distance r = 0, γ is the light absorption coefficient and r is the cartesian distance between firefly i and j. during the iterations of the fa, a pair-wise comparison of brightness of fireflies is conducted, where the one with lower light intensity moves toward the brighter one. the movement at iteration t of firefly i, which is attracted by a brighter firefly j, is given by [15]: ( 1) ( ) ( ) ( ) ( ) 0( ) t t t t t t i i j ix x x x          where α0 is the initial randomization parameter,  is the randomization reduction constant, and  is a vector of random numbers drawn from a gaussian distribution or uniform distribution in the range [0, 1]. in [3] an improvement to (17) was proposed. for design optimization problems with discrete design variables that can assume the index value of a standard section from a list of p standard sections xi = {1, 2, …, p}, the improved equation is formulated as [3]: ( 1) ( ) ( ) ( ) ( ) 0( ) ( 1)( 0.5) t t t t t t i i j ix int x x x p              vi. modification of the improved firefly algorithm in probabilistic and reliability analysis of practical problems, determining the exact solution is most likely unachievable. most known solution techniques suitable for practical problems are numerical and approximate at best. in some reliability analysis techniques, especially simulationbased techniques, one may repeat the solution of the same problem and obtain different results each time, albeit with a very small difference. in problems with integer design variables, (18) may lead to the same value for xt and x(t+1) in some fireflies with high brightness during advanced iterations. if the brightness of a firefly is recalculated in a new generation and the new value is slightly different from that in the previous generation, this slight difference in brightness may cause the firefly to cross a constraint. accordingly, the firefly will be penalized by assigning a large value to its objective function and thus its brightness will diminish compared to other fireflies. hence, chances are that the value of the optimum solution in one iteration may be found larger than the value of the optimum solution of the previous iteration. it should be emphasized that this issue is only encountered in problems with probabilistic constraints. in problems with deterministic constraints, if the firefly is maintained in the following iteration, its brightness of course remains unchanged even if the objective functions and constraints are re-evaluated. engineering, technology & applied science research vol. 6, no. 2, 2016, 964-971 967 www.etasr.com okasha: reliability-based design optimization of trusses with linked-discrete design variables… ` it is proposed herein to introduce a modification to the ifa to solve problems with probabilistic constraints. it is proposed that for each iteration t > 1 and within the step where the brightness is compared for the updated swarm of n fireflies, the best firefly from the previous iteration t 1 is included in the comparison and the best n fireflies are selected. the examples of this paper show that this modification improves the performance of the ifa and accelerates its convergence when used in probabilistic and rbdo problems. vii. the optimization problem formulation in the examples of this paper, the members are selected from the aisc standard tables for angle sections. these are 127 angles and are arranged in this paper in a descending order of their weights (in pound per unit foot) in order to improve the optimization process. according to this order, each section is given an id, such that the heaviest section takes id number 1 and the lightest takes id number 127. the design variables in this paper are the section id numbers for the truss members. each truss member, or group of members, is assigned an integer design variable, where its value determines the aisc angle section to be selected for it. in other words, truss member i is assigned a design variable xi that is allowed to take one of the integer values from the set {1, 2, …., 127}, which represent the id numbers of the aisc angle sections considered. in the firefly algorithm, the design variables are represented by swarms of fireflies. hence, once the position of a firefly is determined, the corresponding discrete value for each section property is determined from the aisc tables. the objective of the optimization problems in this paper is to minimize the weight of the structure. the weight of truss member i is calculated as the weight per unit foot of its aisc section with xi id number, w(xi), multiplied by the length of this member, li, in feet. the constraints of the optimization problem include the reliability index associated with failure of the truss members due to the internal forces in each of these members, fi, and the reliability index associated with the displacement of each node in each direction, di. a lower limit is assigned for fi, and di and they are given values of fl, and, dl, respectively. the optimization problem can now be formulated as follows: find: x1, x2 , …, xn  {1, 2, …., 127} to minimize: 1 ( ) n i i i w x l   subject to: for 1, 2,..., for 1, 2,..., fi fl dj dl i n j m         where n is the number of members, or group of members, in the truss and m is the number of truss nodes. in the examples of this paper, it is considered that fl = dl = 3.0. the solution of this optimization problem is an integrated process as shown in the flowchart presented in figure 2. in the framework shown in this flowchart, a loop of optimization iterations of the firefly algorithm takes place. in each iteration, the brightness of the fireflies is determined by calculating the objective function and constraints. evaluating the constraints requires reliability analysis of the truss. in order to conduct the reliability analysis, the samples of latin hypercube are generated and each sample set is used as a realization of the truss and the load the truss is subjected to. the internal forces for each truss member are determined using the direct stiffness method to analyze each truss realization. the resistance of each truss member and for each realization is determined using the section strength equations presented in this paper. the distribution parameters of the truss member resistances and the internal forces in each member are then determined from these results in order to calculate the reliability indices for the truss. calculate brightness of fireflies compare brightness of fireflies move fireflies towards brighter ones generate random initial population of fireflies define optimization parameters termination criteria fulfilled? generate lhs samples do for each lhs sample determine the resistance determine statistics of load and resistance calculate reliability index for each element and node no yes optimum solution is the firefly with highest brightness calculate strength of each truss member determine member forces and nodal displacements from structural analysis determine the load effect calculate the objective and constraints firefly optimization reliability analysis member strength analysis structural analysis fig. 2. flowchart for the rbdo framework. engineering, technology & applied science research vol. 6, no. 2, 2016, 964-971 968 www.etasr.com okasha: reliability-based design optimization of trusses with linked-discrete design variables… ` viii. examples a. ten-bar planar truss the design optimization of the truss shown in figure 3 has been investigated in different forms in the literature [3, 4, 6, 9, 22]. the load effects, p1 and p2, are each treated as a normally distributed random variable with mean and standard deviation 50 kip and 5 kips, respectively. an allowable displacement limit, dall, is considered as 2 in. the results are shown in figure 4. the details of the optimum solution are shown in table i. the modified ifa was able to find the optimum solution at iteration 51 without problems. however, without the modification, the algorithm only reached the optimum solution at iteration 89. in addition, the best solution in iteration 4 was lost when the algorithm reached the end of iteration 5 and a best solution with higher objective value was registered at the end of iteration 5. the same occurred at iteration 28. p2 p1 60 in 6 0 i n 6 0 i n 1 2 3 4 5 6 8 7 10 9 (3) (1) (5) (6) (4) (2) fig. 3. ten-bar planar truss. table i. optimum solution for the ten-bar truss. truss member aisc section designation 1 l6×4×5/16 2 l3½×3½×5/16 3 l3½×3×1/2 4 l4×3½×5/16 5 l4×3½×5/16 6 l2½×2×3/8 7 l3×2×1/2 8 l4×3×3/8 9 l2×2×1/8 10 l3½×3×5/16 in iterations, the best solution was on the boundary of the constraint related to the reliability index associated with failure of truss member 1. in order to illustrate the variability in the calculated reliability index for member 1, the reliability calculations are conducted 1000 times in an analysis isolated from the optimization problem. each time the reliability index is determined using the latin hypercube sampling with 10000 samples. accordingly, 1000 reliability indices were obtained. the histogram of the reliability index is shown in figure 5. the figure shows, as expected, that there is a small variability in the reliability index. in fact, even though there is a chance that the reliability index has a value larger than 3.0, there is a higher probability that the reliability index takes values smaller than 3.0. this explains the loss of a best solution in an iteration; as one of the reliability indices that satisfied the constraints in that iteration may have a slightly different value when re-evaluated in the next iteration and thus violated a constraint. t o ta l w ei gh t o f o p ti m u m s o lu ti on ( lb ) iteration 400 450 500 550 600 650 0 20 40 60 80 100 improved firefly algorithm modified improved firefly algorithm fig. 4. variation of the total weight of optimum solution with progress in iteration for the ten-bar truss. the presence of variability in a reliability analysis is inevitable. the small variability in the resulting reliability index shown in figure 5 is acceptable. increasing the number of samples in the simulation may provide lower variability in the obtained reliability index. however, this will impose a computational burden on the optimization process. as shown in figure 4, the suggested modification to the ifa was able to protect the algorithm from deviating from the converging solution and converge faster. the proven robustness of the ifa with the suggested modification is shown to be more efficient in handling rbdo problems with linked-discrete variables than the original ifa. reliability index of member 1 in the optimum solution of the 10-bar truss f re qu en cy o f o cc u rr en ce s mean = 2.9677 standard deviation = 0.0116 number of samples = 1000 2.90 2.95 3.00 3.05 0 2 4 6 8 10 fig. 5. histogram of the reliability index associated with failure of member 1 in the ten-bar truss. engineering, technology & applied science research vol. 6, no. 2, 2016, 964-971 969 www.etasr.com okasha: reliability-based design optimization of trusses with linked-discrete design variables… ` b. twenty-five-bar space truss figure 6 shows a twenty-five-bar space truss, which was used in different forms as a benchmark for investigating design optimization techniques in the literature [3,6,22]. the statistical parameters of the normally distributed load effects are shown in table ii. the 25 truss members are divided into 8 groups as follows: {1, 2–5, 6–9, 10–11, 12–13, 14–17, 18–21, 22–25}. 10 0 in 10 0 i n 75 in 75 in 75 in 200 in 200 in (1) (2) (4) xy z (5)(3) (6) (10) (8) (7) (9) 1 2 3 45 6 7 8 9 10 1112 13 14 15 16 17 18 19 20 21 22 23 24 25 fig. 6. twenty-five-bar space truss. table ii. load effect parameters for the 25-bar truss. node load direction mean (kip) standard deviation (kip) 1 x 2 0.2 1 y -20 -2 1 z -20 -2 2 y -20 -2 2 z -20 -2 3 x 1 0.1 6 x 1.2 0.12 the optimization of the truss is investigated using the ifa with and without modification. an allowable displacement limit, dall, is considered as 0.35 in. the results are shown in figure 7. the details of the optimum solution are shown in table iii. it is clear that the modified ifa is able to find the optimum solution without problems. without the modification, the algorithm reached the optimum solution later in the process than it did with the proposed modification. furthermore, the best solution was lost in two different iterations without the proposed modification. iteration t o ta l w ei gh t o f o pt im u m s ol ut io n ( lb ) 1300 1500 1700 1900 2100 2300 2500 0 20 40 60 80 100 improved firefly algorithm modified improved firefly algorithm fig. 7. variation of the total weight of optimum solution with progress in iteration for the twenty-five-bar truss. table iii. optimum solution for the twenty-five-bar truss. truss member group aisc section designation 1 l4×3½×5/16 2 l2½×2×3/16 3 l3½×2½×1/2 4 l3×2×1/4 5 l3½×3×3/8 6 l2½×1½×3/16 7 l2½×1½×3/16 8 l6×3½×5/16 c. sixty-five bar truss bridge the truss bridge is shown in figure 8. one design variable is used for each pair of symmetric truss members with a total of 33 design variables. the bars are numbered from left to right starting from the bottom chord then the top chord then the diagonals. the load p is treated as a normally distributed random variable with coefficient of variation 0.1 and mean of 30 kips. an allowable displacement limit, dall, is considered as 0.5 ft. the details of the optimum solutions obtained by the modified ifa are shown in table iv. also shown in the table are the results obtained by the genetic algorithm mi-lxpm, which was conducted using the global optimization toolbox of matlab [24]. also, using this toolbox, the problem was attempted to be solved by simulated annealing, and pattern search methods. however, they failed to find optimum solutions even near those shown in table iv. furthermore, the gradient-based optimization methods in the optimization toolbox of matlab [25] were tested for solving this problem. fig. 8. sixty-five-bar truss bridge. engineering, technology & applied science research vol. 6, no. 2, 2016, 964-971 970 www.etasr.com okasha: reliability-based design optimization of trusses with linked-discrete design variables… ` table iv. optimum solution for the truss-bridge. aisc section designation truss members modified ifa ga (mi-lxpm) 1-16 l6×3½×5/16 l4×4×3/4 2-15 l6×4×3/8 l4×4×1/2 3-14 l5×5×5/16 l4×3×1/2 4-13 l3½×3½×1/2 l3½×3×7/16 5-12 l6×3½×1/2 l4×3×1/2 6-11 l6×3½×3/8 l8×4×5/8 7-10 l4×3½×5/16 l4×3½×5/16 8-9 l4×3×5/16 l3½×3×1/2 17-32 l4×3×1/4 l4×3×5/16 18-31 l3×3×3/16 l3×3×3/8 19-30 l5×3½×5/16 l2×2×5/16 20-29 l3×3×5/16 l2×2×1/4 21-28 l5×5×5/16 l2×2×1/8 22-27 l2½×2×3/8 l2½×2½×3/8 23-26 l3½×3½×7/16 l3½×3×3/8 24-25 l8×6×1/2 l5×5×3/4 33-65 l2½×1½×3/16 l2×2×3/16 34-64 l2×2×3/16 l2½×1½×3/16 35-63 l2×2×1/8 l2×2×1/8 36-62 l3½×2½×1/4 l2×2×1/4 37-61 l2×2×1/8 l2½×2×1/4 38-60 l3×3×3/16 l2×2×3/16 39-59 l4×4×3/8 l2½×2×3/16 40-58 l2×2×3/8 l3×2½×5/16 41-57 l3×2×1/2 l4×4×1/4 42-56 l2×2×1/8 l3×2×5/16 43-55 l4×3×1/2 l3½×2½×1/4 44-54 l3½×2½×3/8 l2×2×5/16 45-53 l4×4×1/4 l2½×2½×3/8 46-52 l4×3×3/8 l3×2×3/8 47-51 l4×3×5/16 l5×3×7/16 48-50 l5×3½×5/16 l4×3×5/8 49 l3½×3½×3/8 l2½×2×1/4 weight (lb) 14624 14344 as expected, these methods couldn’t solve the problem either. accordingly, the only optimization methods capable of handling this problem, among those attempted by the author, were the modified ifa and the mi-lxpm. table iv shows that the total weight of the optimum solution obtained by milxpm is slightly lower than that obtained by the modified ifa. figure 9 shows the improvement in the total weight of the optimum solution with progress in iteration. it is clear from the figure that even though the mi-lxpm was capable of finding a slightly better solution than that obtained by the modified ifa, the latter method converged to its optimum solution at a fraction of the computational cost required by the former. thus, it can be concluded from this example that the modified ifa was capable of finding a reasonable solution, in a reasonable amount of computations, relative to the mi-lxpm. 14000 16000 18000 20000 22000 24000 26000 0 50 100 150 200 iteration t o ta l w ei gh t o f o pt im u m s o lu ti o n (l b ) ga (mi-lxpm) modified improved firefly algorithm fig. 9. variation of the total weight of optimum solution with progress in iteration for the sixty-five-bar truss bridge. ix. conclusions in this paper, the structural reliability of trusses was considered in the design optimization process. the sections were selected from the aisc standard tables and thus the design variables that represent the properties of the section were linked-discrete. the ifa was used for the optimization. latin hypercube sampling was used to determine the structural reliability. it was found that despite the well-known strength of the ifa in solving deterministic optimization problems, it is unstable when used in probabilistic and reliability-based optimization problems. a modification to the ifa was proposed in order to stabilize it for use in probabilistic and reliability-based design optimization problems. the proven robustness of the ifa with the proposed modification is shown to be efficient in handling the reliability-based optimum design problems with linked-discrete variables. without the proposed modification, the ifa reached the optimum solution later than it did with the modification. furthermore, it was shown by applying the presented approach to a sixty-five bar truss bridge and comparing the results with those from other methods that the modified ifa was capable of finding a reasonable solution, in a reasonable amount of computations, compared to the milxpm. it should be emphasized that the main drawback of this approach is the computational cost of conducting the reliability analysis. therefore, it is imperative that saving in computational cost during the optimization process should be a goal in a design optimization problem of this type. even though the mi-lxpm found a better solution in the truss bridge example, this solution was found in about triple the computational cost of that required by the modified ifa to obtain its optimum solution. perhaps this conclusion should encourage future attempts to create a hybrid algorithm, where the speed of convergence of the modified ifa is exploited at the beginning of the optimization process, then the mi-lxpm is used to improve the optimum solution. references [1] p. venkataraman, applied optimization with matlab programming, john wiley & sons, inc. hoboken, nj, 2009 engineering, technology & applied science research vol. 6, no. 2, 2016, 964-971 971 www.etasr.com okasha: reliability-based design optimization of trusses with linked-discrete design variables… ` [2] j. s. arora, m. w. huang, c. c. hsieh, “methods for optimization of nonlinear problems with discrete variables: a review”, structural optimization, vol. 8, no. 2/3, pp. 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river, nj, 2012 [20] a. h. ang, w. h. tang, probability concepts in engineering planning and design: decision, risk and reliability, volume ii, john wiley and sons, ny, 1984 [21] j. farkas, k. jarmai, optimum design of steel structures, springerverlag, berlin heidelberg, 2013 [22] s. rajeev, c. krishnamoorthy, “discrete optimization of structures using genetic algorithms”, journal of structural engineering, vol. 118, no. 5, pp. 1233–1250, 1992 [23] r. nakib, “deterministic and reliability-based optimization of truss bridges”, computers and structures, vol. 65, no. 5, pp. 767-775, 1997 [24] mathworks, global optimization toolbox user’s guide, 2015 [25] mathworks, optimization toolboxtm user’s guide, 2015 microsoft word etasr_v13_n2_pp10471-10477 engineering, technology & applied science research vol. 13, no. 2, 2023, 10471-10477 10471 www.etasr.com zisopol et al.: a theoretical-experimental study on the influence of fdm parameters on the … a theoretical-experimental study on the influence of fdm parameters on the dimensions of cylindrical spur gears made of pla dragos gabriel zisopol mechanical engineering department, petroleum-gas university ploiesti, romania zisopol@zisopol.ro (corresponding author) mihail minescu mechanical engineering department, petroleum-gas university ploiesti, romania mminescu@upg-ploiesti.ro dragos valentin iacob production department, marelli ploiesti romania, romania dragoshicb@gmail.com received: 29 january 2023 | revised: 12 february 2023 | accepted: 15 february 2023 abstract this paper presents the results of a theoretical-experimental study on the influence of fdm parameters (height of the deposited layer at one pass hs and percentage of filling pu) on the dimensions of cylindrical spur gears made of pla (shaft diameter d and bore diameter d). in this context, we designed the 3d model of a cylindrical gear with module m= 1 and z= 60 spur teeth, which we used for fdm 3d printing of 27 pla parts with different values of coating height deposited at a pitch hs of 0.10, 0.15, 0.20mm and different values 50, 75, and 100% of filling percentage pu. the 324 values obtained from measuring the diameters d and d of 27 cylindrical spur gears made of pla and the calculated values of statistical indicators (arithmetic mean, standard deviation, dispersion) were used to determine the dimensional accuracy of the analyzed parts. the study results show that the percentage of filling has a greater influence than the shaft diameter on the dimensional accuracy of cylindrical spur gears made of pla. keywords-3d printing; fdm parameters; experimental test; spur gears i. introduction nowadays, production processes are undergoing transformations in terms of flexibilization according to market requirements, the main objective being to reduce costs in order to strengthen market position and maintain sustainable competitive advantage [12-17]. additive manufacturing technologies are a viable solution for many industries such as automotive, aerospace, and defense due to advantages in comparison with formative and subtractive manufacturing technologies, e.g. the manufacturing costs are significantly reduced, complex geometries are achieved without special base and fixing elements, simplicity in use, material waste is negligible, use of bio materials, etc. [1, 6, 11]. fused deposition modeling is one of the most popular manufacturing technologies due to its affordability, the wide range of materials used, and the possibility of customization for printed parts. however, this technology has certain limitations such as run time and surface quality. depending on the field of use of the manufactured part, the limitations can be adjusted from the process parameters: the height of the layer deposited in one step, the filling percentage, the printing speed, etc. [9, 10]. the materials used for fdm are thermoplastics, the most popular among them being pla (polylactic acid), abs (acrylonitrile butadiene styrene), pet (polyethylene terephthalate), nylon, and pc (polycarbonate) [3]. the study of the influence of 3d printing parameters has attracted the scientific interest. authors in [1] showed a comparative study about dimensional accuracy from errors of fff printed spur engineering, technology & applied science research vol. 13, no. 2, 2023, 10471-10477 10472 www.etasr.com zisopol et al.: a theoretical-experimental study on the influence of fdm parameters on the … gears using pla and nylon and authors in [11] showed a development of a prediction system for 3d printed part deformation using sls technology. the novelty of this work consists in the theoreticalexperimental determination of the influence of fdm parameters on the dimensions of cylindrical spur gears (shaft diameter d and bore diameter d) made of pla. the greater influence between the two studied parameters hs and pu is found with statistical calculations following the measurements. ii. 3d printing of cylindrical spur gears the quality of the parts manufactured additively by thermoplastic extrusion is influenced by the material type and the 3d printer used, [9, 10]. in this context, pla filament with a diameter of 1.75mm (verbatim brand) and the creality cr-x 3d printer with a printing volume of 300×300×400mm and xy positioning accuracy of ±0.10mm were used to manufacture all cylindrical spur gears. figure 1 shows the steps taken to perform the experimental study on the influence of fdm parameters on the dimensions of cylindrical spur gears rd made of pla. fig. 1. stages of the experimental study on the influence of fdm parameters on the dimensions of cylindrical spur gears fabricated from pla. using the solidworks 2022 software, the 3d model of a cylindrical spur gear with module m=1 and z=60 was designed using the toolbox function and was converted from sld to stl format, [6, 7, 20]. the 3d model was the basis for the 2d drawing shown in figure 2 of [6]. using the stl format file, corresponding to the spur gear with spur teeth shown in figure 2, and the creality slicer of the creality cr-x 3d printer, we inserted the printing parameters shown in table i and generated the g-code file [6, 7]. the fdm 3d printing parameters of pla spur gears (rd) with module m= 1 and z= 60 spur teeth, shown in table i, fall into two categories, constant parameters and variable parameters, [5-8]. we transferred the g-code file to the creality cr-x printer and fabricated 27 cylindrical gears rd from pla with modulus m= 1 and z= 60 spur teeth. figure 3 shows the cylindrical toothed wheel rd made of pla with m= 1 and z= 60 in creality slicer, generated by using the height of the deposited layer at one pass hs=0.10mm, filling percentage pu= 50%, printing speed vp=80mm/min, and filling pattern type line oriented at 45° [8]. table i. parameters of 3d fdm printing of rd spur gears with m=1 and z=60 constant parameters variable parameters coding of the gear set material part orientation x, y temperature of the extruder, te= 210°c table temperature, tb= 60°c printing speed, vp= 80mm/s filling pattern lines 45° height of the deposited layer hs filling percentage pu rdi pla (mm) (%) (i = 1… 9) (parts) 0.10 100 rd1 3 75 rd2 3 50 rd3 3 0.15 100 rd4 3 75 rd5 3 50 rd6 3 0.20 100 rd7 3 75 rd8 3 50 rd9 3 the mass of the cylindrical gear with modulus m=1 and spur teeth z=60, shown in figure 2, is 14g (equivalent to 4.957m of pla filament) and its running time is 2 hours and 53 minutes. the g-code file of the cylindrical gear shown in figure 2 contains 108500 control lines [8]. fig. 2. rd pla cylindrical gear with m=1 and z=60 spur teeth (hs=0.10 mm, pu=50%, vp=80mm/min, 45° oriented line fill pattern) in creality slicer. iii. determination of the influence of fdm parameters on the dimensions of spur gears made of pla a. working methodology for the experimental study we used 324 values obtained by measuring with a digital caliper the diameter of the shaft (d=62±0.1mm) and the diameter of the bore (d=20.2±0.1mm) of 27 cylindrical gears made of pla, with m=1 and z=60, additively manufactured by thermoplastic extrusion (using the parameters in table i). each part was measured as shown in figure 3. the 324 values are used to determine the arithmetic mean (1), standard deviation (2), and dispersion (3), corresponding to each set of cylindrical gears rdi in pla with m=1 and z=60 [1, 18, 19]: �̅ � ������...�� (1) engineering, technology & applied science research vol. 13, no. 2, 2023, 10471-10477 10473 www.etasr.com zisopol et al.: a theoretical-experimental study on the influence of fdm parameters on the … � � �∑��� ��̅�� (2) �� � � ∑��� − �̅�� (3) a set of cylindrical gears rdi made of pla, with m=1 and z=60, contains 3 parts characterized by the same 3d printing parameters (see table i). two sets of measurements were performed for each part, resulting in 12 values 6 values for shaft diameter d and 6 values for bore diameter d, as shown in figure 3. fig. 3. measuring points of the diameters of cylindrical gears rd made of pla with modulus m=1 and spur teeth z=60. b. results the 324 values resulting from the measurement of the diameters of the 27 cylindrical gears rd made of pla, additively manufactured by thermoplastic extrusion, are graphically represented in figures 4-21. tables ii-xix show the results obtained from the calculation of statistical indicators arithmetic mean, standard deviation, and dispersion. the variation of the values of the arithmetic means �̅ of the shaft diameter d for each set of rdi gears (i= 1...9) is shown in figure 23. the variation of the values of the arithmetic means �̅ of the bore diameter d for each set of gears rdi (i= 1...9) is shown in figure 22. fig. 4. values of shaft diameter d for gear set rd1.(hs = 0.10mm, pu= 100%). table ii. values of the statistical indicators for the set of spur wheels rd1 variable parameters mean �� standard deviation � dispersion �� hs= 0.10mm, pu=100% mm mm mm 61.95 0.086 0.007 fig. 5. values of shaft diameter d for gear set rd2. (hs= 0.10mm, pu= 75%). table iii. values of statistical indicators for the set of spur gears rd2 variable parameters mean �� standard deviation � dispersion �� hs= 0.10mm, pu=75% mm mm mm 61.95 0.093 0.009 fig. 6. values of shaft diameter d for gear set rd3. (hs= 0.10mm, pu= 50%). table iv. values of statistical indicators for the set of spur gears rd3 variable parameters mean �� standard deviation � dispersion �� hs= 0.10mm, pu=50% mm mm mm 61.99 0.111 0.012 fig. 7. values of shaft diameter d for spur gear set rd4. (hs= 0.15mm, pu= 100%). table v. values of statistical indicators for the set of spur gears rd4 variable parameters mean �� standard deviation � dispersion �� hs= 0.15mm, pu=100% mm mm mm 61.98 0.070 0.005 engineering, technology & applied science research vol. 13, no. 2, 2023, 10471-10477 10474 www.etasr.com zisopol et al.: a theoretical-experimental study on the influence of fdm parameters on the … fig. 8. values of shaft diameter d for spur gear set rd5. (hs= 0.15mm, pu= 75%). table vi. values of statistical indicators for the set of spur gears rd5 variable parameters mean �� standard deviation � dispersion �� hs= 0.15mm, pu=75% mm mm mm 62 0.047 0.002 fig. 9. values of shaft diameter d for spur gear set rd6. (hs= 0.15mm, pu= 50%). table vii. values of statistical indicators for the set of spur gears rd6 variable parameters mean �� standard deviation � dispersion �� hs= 0.15mm, pu=50% mm mm mm 61.99 0.063 0.004 fig. 10. values of shaft diameter d for spur gear set rd7. (hs= 0.20mm, pu= 100%). table viii. values of statistical indicators for the set of spur gears rd7 variable parameters mean �� standard deviation � dispersion �� hs= 0.20mm, pu=100% mm mm mm 61.96 0.062 0.004 fig. 11. values of shaft diameter d for spur gear dințate rd8. (hs= 0.20mm, pu= 75%). table ix. values of statistical indicators for the set of spur gears rd8 variable parameters mean �� standard deviation � dispersion �� hs= 0.20mm, pu=75% mm mm mm 62.02 0.113 0.013 fig. 12. values of shaft diameter d for spur gear set rd9. hs= 0.20mm, pu= 50%). table x. values of statistical indicators for the set of spur gears rd9 variable parameters mean �� standard deviation � dispersion �� hs= 0.20mm, pu=50% mm mm mm 61.95 0.061 0.004 fig. 13. values of bore diameter d for spur gear set rd1. (hs= 0.10mm, pu= 100%). table xi. values of statistical indicators for the set of spur gears rd1 variable parameters mean �� standard deviation � dispersion �� hs= 0.10 mm, pu=100% mm mm mm 20.29 0.058 0.003 engineering, technology & applied science research vol. 13, no. 2, 2023, 10471-10477 10475 www.etasr.com zisopol et al.: a theoretical-experimental study on the influence of fdm parameters on the … fig. 14. values of bore diameter d for spur gear set rd2. (hs= 0.10mm, pu= 75%). table xii. values of statistical indicators for the set of spur gears rd2 variable parameters mean �� standard deviation � dispersion �� hs= 0.10mm, pu=75% mm mm mm 20.32 0.077 0.066 fig. 15. values of bore diameter d for spur gear set rd3. (hs= 0.10mm, pu= 50%). table xiii. values of statistical indicators for the set of spur gears rd3 variable parameters mean �� standard deviation � dispersion �� hs= 0.10mm, pu=50% mm mm mm 20.25 0.117 0.014 fig. 16. values of bore diameter d for spur gear set rd4. (hs= 0.15mm, pu= 100%). table xiv. values of statistical indicators for the set of spur gears rd4 variable parameters mean �� standard deviation � dispersion �� hs= 0.15mm, pu=100% mm mm mm 20.28 0.091 0.008 fig. 17. values of bore diameter d for spur gear set rd5. (hs= 0.15mm, pu= 75%). table xv. values of statistical indicators for the set of spur gears rd5 variable parameters mean �� standard deviation � dispersion �� hs= 0.15mm, pu=75% mm mm mm 20.31 0.088 0.008 fig. 18. values of bore diameter d for spur gear rd6. (hs= 0.15mm, pu= 50%). table xvi. values of statistical indicators for the set of spur gears rd6 variable parameters mean �� standard deviation � dispersion �� hs= 0.15mm, pu=50% mm mm mm 20.29 0.068 0.005 fig. 19. values of bore diameter d for spur gear set rd7. (hs= 0.20mm, pu= 100%). table xvii. values of statistical indicators for the set of spur gears rd7 variable parameters mean �� standard deviation � dispersion �� hs= 0.20mm, pu=100% mm mm mm 20.07 0.152 0.023 engineering, technology & applied science research vol. 13, no. 2, 2023, 10471-10477 10476 www.etasr.com zisopol et al.: a theoretical-experimental study on the influence of fdm parameters on the … fig. 20. values of bore diameter d for spur gear set rd8. (hs= 0.20mm, pu= 75%). table xviii. values of statistical indicators for the set of spur gears rd8 variable parameters mean �� standard deviation � dispersion �� hs= 0.20mm, pu=75% mm mm mm 20.13 0.120 0.014 fig. 21. values of bore diameter d for spur gear set rd9. (hs= 0.20mm, pu= 50%). table xix. values of statistical indicators for the set of spur gears rd9 variable parameters mean �� standard deviation � dispersion �� hs= 0.20mm, pu=50% mm mm mm 20.13 0.130 0.017 using the values of the arithmetic means �̅ of the shaft diameter d and of the bore diameter d (see tables ii-xix) for each set of gears rdi (i=1...9), the graphs in figure 22 and 23 were constructed, respectively. fig. 22. variation of the arithmetic mean values �̅ of the shaft diameter d for each set of gears rdi (i=1...9). fig. 23. variation of the arithmetic mean values �̅ of the bore diameter for each set of gears rdi (i= 1...9). c. disscusion the study was carried out using the 162 values resulting from the measurement with the digital caliper of the shaft diameter d=62±0.1mm (see figure 3) and the 162 values resulting from the measurement with the same instrument of the bore diameter d= 20.2±0.1 mm (see figure 3) of the 27 cylindrical spur gears made of pla, with modulus m= 1 and spur teeth z= 60, additively manufactured by thermoplastic extrusion (using the parameters in table i), certify the significant influence on their dimensions of the height of the layer deposited at one pass hs and the percentage of filling pu. in this context, analyzing the graphs in figures 4-23 and the result summary in tables ii-xix the following results are issued: 1) for shaft diameter d= 62±0.1mm  the best values were obtained by measuring the set of spur gears rd5 (hs= 0.15mm, pu= 75%), the calculated mean being �̅= 62mm and dispersion ��= 0.002 (see figure 9 and table vi).  the largest deviations were obtained in the measurement of the spur gear set rd2 (hs= 0.10mm, pu= 75%), the calculated mean average being �̅= 61.95mm, and dispersion ��= 0.0087 (see figure 5 and table iii);  100% of the values obtained in the measurement of the spur gear set rdi (i= 1...9) are within the tolerance of ±0.10mm, the best values being obtained for 3d printing with the height of the deposited layer at a pitch hs= 0.15mm (see figure 22). 2) for bore diameter d= 20.2±0.1mm:  the best values were obtained in the measurement of the spur gear set rd3 (hs= 0.10mm, pu= 50%), the calculated mean being �̅ = 20.25mm, and dispersion � � = 0.014 (see figure 15 and table xiii).  the largest deviations were obtained in the measurement of the spur gear set rd7 (hs= 0.20mm, pu = 100%), the calculated average being �̅ = 20.07mm, and dispersion ��= 0.023 (see figure 19 and table xvii).  only 66.6% of the values obtained in the measurement of the spur gear set rdi (i= 1...9) fall within the tolerance of ±0.10mm, very close to the upper and lower limits (see figure 23). engineering, technology & applied science research vol. 13, no. 2, 2023, 10471-10477 10477 www.etasr.com zisopol et al.: a theoretical-experimental study on the influence of fdm parameters on the … iv. conclusions the current paper presents the results of a theoreticalexperimental study on the influence of fdm parameters (height of the deposited layer at one pass hs and percentage of filling pu) on the dimensions (shaft diameter d and bore diameter d) of cylindrical spur gears made of pla. cylindrical spur gears were printed on creality cr-x 3d printer using pla filament verbatim brand. regarding the shaft diameter d, all values obtained in the measurement of fdm 3d printed spur gears are within the required tolerance of ±0.10 mm. regarding the bore diameter d, one third of the measued values were outside the tolerance limits. the difference between the extreme values of the arithmetic mean is 0.25mm. the theoretical-experimental study demonstrates that of the two fdm parameters analyzed, the pu filling percentage has a greater influence on the dimensional accuracy of spur gears made of pla. the results of the study are useful for optimizing fdm parameters for additive manufacturing of pla spur gears by thermoplastic extrusion within specified dimensional tolerances. the study can be extrapolated to other types of materials used in additive manufacturing technologies. references [1] i. buj-corral and e. e. zayas-figueras, "comparative study about dimensional accuracy and form errors of fff printed spur gears using pla and nylon," polymer testing, vol. 117, jan. 2023, art. no. 107862, https://doi.org/10.1016/j.polymertesting.2022.107862. [2] m. m. hanon, l. zsidai, and q. ma, "accuracy investigation of 3d printed pla with various process parameters and different colors," materials today: proceedings, vol. 42, pp. 3089–3096, jan. 2021, https://doi.org/10.1016/j.matpr.2020.12.1246. [3] d.g. zisopol, i. nae, a. i. portoaca, and i. ramadan, "a theoretical and experimental research on the influence of fdm parameters on tensile strength and hardness of parts made of polylactic acid", engineering, technology & applied science research, vol. 11, no. 4, pp. 7458–7463, aug. 2021, https://doi.org/10.48084/etasr.4311. [4] d. g. zisopol, i. nae, a. i. portoaca, and i. ramadan, "a statistical approach of the flexural strength of pla and abs 3d printed parts," engineering, technology & applied science research, vol. 12, no. 2, pp. 8248–8252, apr. 2022, https://doi.org/10.48084/etasr.4739. [5] d. g. zisopol, i. nae, and a. i. portoaca, "compression behavior of fff printed parts obtained by varying layer height and infill percentage," engineering, technology & applied science research, vol. 12, no. 6, pp. 9747–9751, dec. 2022, https://doi.org/10.48084/etasr.5488. [6] d. g. zisopol, d. v. iacob, and a. i. portoaca, "a theoreticalexperimental study of the influence of fdm parameters on pla spur gear stiffness," engineering, technology & applied science research, vol. 12, no. 5, pp. 9329–9335, oct. 2022, https://doi.org/10.48084/ etasr.5183. [7] "3d cad design software," solidworks. https://www. solidworks.com/home-page-2021. [8] "3d printing software of creality cloud," creality cloud. https://www.crealitycloud.com/software-firmware/software?type=8. [9] d. g. zisopol, a. i. portoaca, i. nae, and i. ramadan, "a comparative analysis of the mechanical properties of annealed pla," engineering, technology & applied science research, vol. 12, no. 4, pp. 8978–8981, aug. 2022, https://doi.org/10.48084/etasr.5123. [10] a. portoaca, i. nae, d. g. zisopol, and i. ramadan, "studies on the influence of fff parameters on the tensile properties of samples made of abs," iop conference series: materials science and engineering, vol. 1235, no. 1, nov. 2022, art. no. 012008, https://doi.org/10.1088/1757899x/1235/1/012008. [11] h. s. park, n. h. tran, v. t. hoang, and v. h. bui, "development of a prediction system for 3d printed part deformation," engineering, technology & applied science research, vol. 12, no. 6, pp. 9450–9457, dec. 2022, https://doi.org/10.48084/etasr.5257. [12] m. minescu and d. zisopol, sudarea țevilor şi fitingurilor din polietilenă de înaltă densitate (hdpe pipe & fittings welding). ploiesti, romania: upg ploieşti publishing house, 2021. [13] d. zisopol and a. dumitrescu, ecotehnologie. studii de caz. ploiesti, romania: upg ploieşti publishing house, 2021. [14] d. g. zisopol, a. dumitrescu, c. n. trifan, ecotehnologie: noţiuni teoretice, aplicaţii şi studii de caz, ploiesti, romania: upg ploieşti publishing house, 2010. [15] d. g. zisopol, m. j. săvulescu, bazele tehnologiei, ploiesti, romania: upg ploieşti publishing house, 2003. [16] d. g. zisopol, tehnologii industriale și de construcții. aplicații practice și studii de caz, ploiesti, romania: upg ploieşti publishing house, 2003. [17] m. j. săvulescu, d. g. zisopol, tehnologii industriale şi de construcţii, ploiesti, romania: upg ploieşti publishing house, 2002. [18] d. g. zisopol, ingineria valorii, ploiesti, romania: upg ploieşti publishing house, 2004. [19] t. a. cojoianu, "studiu comparativ privind influența parametrilor tehnologiei de fabricație aditivă prin extrudarea pla și abs asupra abaterilor dimensionale ale roților dințate cilindrice și rigidității angrenării acestora," m.s. thesis, petroleum-gas university, ploiesti, romania, 2022. [20] d. v. iacob, "măsurarea rigidității angrenării roților dințate fabricate din pla, folosite la antrenarea cuțitului unității de tăiere a mașinii pentru fabricarea corpurilor radiatoarelor auto", m.s. thesis, petroleum-gas university, ploiesti, romania, 2022. microsoft word etasr_v12_n5_pp9379-9387 engineering, technology & applied science research vol. 12, no. 5, 2022, 9379-9387 9379 www.etasr.com ishak et al.: a fast digital phase frequency detector with preset word frequency searching in … a fast digital phase frequency detector with preset word frequency searching in adpll for a uhf rfid reader syaza norfilsha ishak institute of microengineering & nanoelectronics (imen) universiti kebangsaan malaysia bangi, malaysia syazanorfilsha@gmail.com jahariah sampe institute of microengineering & nanoelectronics (imen) universiti kebangsaan malaysia bangi, malaysia jahariah@ukm.edu.my nazrul anuar nayan faculty of engineering and built environment universiti kebangsaan malaysia bangi, malaysia nazrul@ukm.edu.my zubaida yusoff faculty of engineering multimedia university cyberjaya, malaysia zubaida@mmu.edu.my received: 15 july 2022 | revised: 9 august 2022 | accepted: 10 august 2022 abstract-an all-digital phase-locked loop (adpll) is an architecture that is widely employed in the communication system due to the advancement of the complementary metaloxide-semiconductor (cmos) technology process. a 2.4ghz radio frequency identification (rfid) system needs a frequency synthesizer in the local oscillator architecture of the transceiver to generate a stable frequency tuning range therefore, in this paper, a digital phase-frequency detector (dpfd) is designed to achieve the phase and frequency acquisition in the adpll system. the proposed dpfd is divided into two main parts, the first is the phase detector (pd) and the second is the frequency detector (fd). the pd has managed to detect the presence of the phase difference by recognizing two different input signals. the fd, on the other hand, is capable to detect the higher frequency by identifying the output signals from the pd in digital formation. in addition, a control unit module is developed to control and adjust the preset word (pw) for the system by using a binary search scheme. comparison results show that the final value of the pw from the simulation is the same as from the manual calculation (theoretical values). the digital pfd and the pw control modules are designed and simulated by using verilog hdl code. these two designed modules will be integrated into the targeted adpll to achieve fast locking performance and ultra-low power for ultra-high frequency (uhf) rfid applications. keywords-rfid; all-digital pll; adpll; digital pfd; frequency synthesizer; local oscillator; binary search i. introduction internet-of-things (iot) is a main component of the application system of a smart city. radio frequency identification (rfid) is one of the integration applications that work with the iot that is widely employed in the biomedical and healthcare industries. with the iot, we can monitor a patient's health such and observing his severe or chronic disease [1] and tracking medical members and properties through smart application devices by using wireless sensor network (wsn) nodes [2, 3] or rfid tags that are connected to the server. rfid is a system that aims to exchange identification information or data from the tag to the rfid reader through an rf transceiver antenna [4] to carry out specific applications based on the data stored in the tag [5]. presently, rfid technology system devices have been developed to accommodate low-power devices with enhanced data transfer capabilities [6]. figure 1 depicts the typical transceiver of the 2.4ghz rfid reader and includes some basic blocks such as an rf antenna, a receiver block, a transmitter block, a switch, and a local oscillator (lo). in the transceiver, the lo plays a crucial role in the architecture by providing the tuning frequencies for the transmitter and the receiver. furthermore, in the 2.4ghz applications, a frequency synthesizer is required to produce a varying high-frequency range of the lo. pll is commonly used in the frequency synthesizer. based on the literature, the pll is built either in analogue, mixed-analogue-digital, or fully digital. in the analogue pll, the configuration typically consists of a voltage-controlled oscillator (vco), a phasefrequency detector (pfd), an analogue loop filter (lf) [7] or a charge-pump loop filter [8], and a fractional divider at the feedback loop. nevertheless, the trend of implementing the digital circuitry using the very large-scale integration (vlsi) is gradually increased due to the advancement of the cmos technology process because of its advantages over the analogue counterparts [9], such as the fast acquisition of the phase and the frequency, the smaller size, and the low power corresponding author: jahariah sampe engineering, technology & applied science research vol. 12, no. 5, 2022, 9379-9387 9380 www.etasr.com ishak et al.: a fast digital phase frequency detector with preset word frequency searching in … consumption. besides, the adpll has a better performance of a less complex design, better jitter, high stability, and good locking-in time [10]. fig. 1. rfid reader transceiver. currently, the advanced transceiver’s requirement no longer can be met by the analogue pll [11] because the analogue parts in the pll are very sensitive to a wide range of design constraints as compared to the digital parts. for instance, the operating dc bias voltage shifts, the challenge of building higher order filters (hofs), the requirement for the initial and the recurring calibration for the devices, etc. [12]. on top of that, due to its low mobility process, the analogue part is typically difficult to reuse across process technologies. nearly every analogue part needs to be modified or redesigned, and more advanced technology requirements to be implemented or imported for the sake of cost saving or performance enhancement. furthermore, the fabrication of the analogue or mixed-analogue-digital devices is typically more expensive since the capacitors required for the analogue circuits require additional processing procedures. thus, the transition of the analogue or mixed-analogue-digital pll to the adpll gradually increases. the adpll is more desirable in deep submicron process technology and it is also much preferred in the rfid application system. it is because of the advancement of digital over analogue circuits in lower voltage operation and higher tolerance to the on-chip noise, where the low supply voltage and high noise immunity are very demanding [13-15]. the process, voltage, and temperature (pvt) variations [16] form one crucial issue in the adpll design, especially in settling the time performance. however, the pre-setting and the estimating oscillator tuning word technique as introduced in [16, 17] may solve the pvt issue. moreover, the voltage variation in the dco can be reduced by the supply noise cancellation technique [18, 19]. this shows that the adpll design is robust. some research works on the fast-locking techniques have been reported. the authors in [17] improved the locking process in their proposed adpll system by improving the oscillation tuning word (otw) using the estimation and preset technique and the frequency search is utilizing one by one step. in [12, 13, 20] the frequency search is defined by a binary search scheme. both techniques are reliable to be implemented in future design but in terms of the fast-locking performance, the binary search scheme is preferred. in this paper, the digital phase and frequency detector designs are presented in the first part. in the second part, the pw for the dco operation will be investigated and discussed. ii. adpll architecture the adpll architecture is constructed with a digital phase-frequency detector (dpfd), a control unit (cu), a dco, and a divider at the loop feedback as can be seen in [21]. the dpfd is an important part of the adpll architecture which determines the difference and mismatch of the phase and frequency of two input signals, namely the frequency reference signal and the divided dco output frequency signal. the dpfd has been redesigned and restructured by many researchers [12, 22-25] to achieve fast detection and acquisition performance in adpll. the time-to-digital converter (tdc) is a famous design architecture for developing a dpfd. it has good measurement capabilities for the time difference between the edge of the two input signals [26] and it also performs well in terms of resolution [27]. reviews have been conducted in [28] about the phase-frequency detector in various adpll design topologies. in [24], the use of a bang-bang pfd in adpll is quite attractive due to the better phase locking-in time, good jitter performance, and small area as compared to the use of the full-ranged tdc. in addition, the calibrating process is needed in the adpll design [24] to minimize the quantization noise if the tdc is used in the design. in this paper, the phase detector (pd) and frequency detector (fd) as dpfd and frequency searching by using a bisection scheme are proposed to achieve fast locking detection in adpll. iii. circuit implementation a. proposed phase detector design in this part, a new design of a pfd is proposed, which combines the phase and the frequency block to accomplish fast acquisition performance, as shown in figure 2. this is an extension work from [21], but major improvements have been made. the proposed design comprises two main parts: the pd and the fd. the output of this pfd will be converted into digital form. fig. 2. the proposed dpfd design. fig. 3. logic diagram of the pd. engineering, technology & applied science research vol. 12, no. 5, 2022, 9379-9387 9381 www.etasr.com ishak et al.: a fast digital phase frequency detector with preset word frequency searching in … fig. 4. the logic diagram to overcome a dead zone in pd. the pd design in this work is adapted from [21], consisting of two d-flip-flops and a nand gate at the feedback. this configuration design is chosen due to the dead zone problem, and it is quite a famous design in phase error detection between the reference signal clock and the divided dco signal clock. based on figure 3, the pd block detects two input signals: the reference frequency clock (freq_ref) and the divided dco frequency clock (freq_div). the pd block generates the output signals that are called up_sig and dn_sig. in the initial state, both up_sig and dn_sig pulses are zero until either the positive edge of freq_ref or freq_div is received. the output of up_sig will be triggered if the pd detects the positive edge of freq_ref is leading the freq_div. on the other hand, the production of dn_sig will be triggered if the pd detects the opposite operation. the logic diagram in figure 4 is the extension circuit of the proposed pd design. this circuit is added to eliminate the dead zone pulses that produced from the logic diagram in figure 3. the purpose of the added circuit is to produce a stable output for the controller block in the next work. this circuit also generates output signals namely up_trig and dn_trig. b. modified frequency detector design the other part of the proposed pfd block is the fd. the fd in this work is an improved design based on the previous work of [21] as illustrated in figure 5. it receives the signal of up_trig and dn_trig from the previous pd block that synchronizes with the reference frequency clock and produces two exclusive outputs of "slow" and "fast" signals. the proposed fd is constructed utilizing the frequency comparison technique as described in [10], whereby a comparator is employed to compare two generated signals and produced two output signals. figure 6 depicts the proposed design’s flowchart for the frequency acquisition step. it is aimed to lock the dco target frequency to the reference frequency clock by ignoring the phase recognition. as soon as the system starts, all variables are set to zero and the counters are assigned for the reference clock, the up_trig, and the dn_trig. after that, the inputs reference clock, up_trig, and dn_trig go through a counting process. at the 14 th cycle of the reference clock, the signal of the "complete clock" will be activated, allowing the system to do comparisons between the up_trig and the dn_trig. in this comparison process, the system will be checking the output counter for both up_trig and dn_trig. if the system detects the counting of up_trig is more than dn_trig, the "fast" signal will be activated, wjile if the opposite operation is detected, the "slow" signal will be triggered. fig. 5. the proposed fd design block diagram. fig. 6. fd design flowchart. therefore, three counters (ctr1, ctr2, ctr3) are employed to count the frequency cycles of the three input signals to execute the frequency acquisition step. ctr1 is used to track the reference frequency clock, while the other two counters (ctr2 and ctr3) are used to count up_trig and dn_trig pulses. additionally, the proposed fd includes an n-bit comparator, which compares the output of the two counters from up_trig and dn_trig and as a result, generates the "fast" and "slow" signals. in further development, the dco will be operated via two of these output signals. the definition of "fast" and "slow" correspond to the accelerating and the decelerating of the operation frequency at the dco, respectively. c. control unit a cu is another approach to filter the bit control in the adpll instead of using the digital loop filter (dlf). there are many considerations in designing the dlf to achieve fast locking performance, such as by considering a proper loop gain selection for the gain controller [25], a dynamic filter bandwidth adjustment [29, 30], a voltage buffer amplifier, etc. and these make the design complex and unstable. hence, to engineering, technology & applied science research vol. 12, no. 5, 2022, 9379-9387 9382 www.etasr.com ishak et al.: a fast digital phase frequency detector with preset word frequency searching in … overcome these problems, a cu design is chosen because of the advantages of a simpler and a more stable design as compared to the dlf. a cu is a module that can change the pw of the dco adjustment operation frequency to achieve fast locking performance. there are two methods to lock the pll, first, the locking time approach in digital pll, as shown in figure 7, introduces gradual frequency changes until the target frequency is reached. this search type is a simple search scheme, but it takes a long time to lock the phase and frequency of the adpll. the second approach is by using a binary search scheme. it is a fast-searching algorithm, where the frequency changing process depends on certain rules or conditions and is quite popular and used in many research works. many binary scheme approaches have been reported, but the method in [31] is more attractive for the pw value calculation because of the successful lock-in time reduction of 80-90% in the design. the design searches the target frequency by using the bisection scheme in the pw calculation. the frequency changing process is shown in figure 8. the binary search performs faster-locking time process in adpll as compared to the linear frequency search. fig. 7. linear or sequential frequency search. fig. 8. binary frequency search. in this work, the pw calculation is adjusted using the bisection scheme which is an iteration process that determines the estimated roots from a given range of values [32]. to realize the operation of the bisection scheme, the maximum and the minimum frequency determination should be initialized. according to figure 8, it is assumed that the frequency control has 21 words, including the word 0. if the target frequency is increased, the pw would be increased by half and vice versa. the equation of the bisection scheme can be written as follows: when the target frequency increases: ���� ��� � � � � � ���� �� � (1) where � � � ���� � . when the target frequency decreases: ���� ��� � � �� � � ���� �� � (2) where � �� � ���� � . in (1)-(2), ���� ��� is the frequency control word for the next state, and ���� � is the frequency control word for the current state. the increase or the decrease in target frequency is a rule condition of the system that is produced by our digital pfd. moreover, the increase in target frequency represents the "fast" signal that is triggered in the fd, while the decrease in target frequency represents the "slow" signal that is produced by the fd. however, to program the equation as in (1) and (2) into our adpll system by using the verilog hdl code is very tricky due to the division operator. thus, the equations are reformed as follows: when the "fast" signal is triggered: ������������� � ����������� � ��� !" (3) when the "slow" signal is triggered: ������������� � ����������� # ��� !" (4) where ������������� is the frequency control word for the next state, and ����������� is the frequency control word for the current state. iv. simulation results and analysis the simulations in this paper are conducted using the verilog hdl code and they are divided in three parts: the pd simulations, the fd simulations, and the pw calculations simulations. a. pd simulations the pd simulations are conducted in two operations: a) freq_ref is faster than freq_div, and b) freq_ref is slower than freq_div. the simulation setup for a and b are set as follows: • a: reference frequency = 40mhz, assumed dco divided frequency = 35.7mhz. • b: reference frequency = 40mhz, assumed dco divided frequency = 43.48mhz. figure 9 shows the timing diagram of the pd block in this work. the circuit in figure 4 is added to the pd block to minimize the dead zone problem to produce a stable system indicated as 1 in figure 10. the new output signals of the pd are produced and named up_trig and dn_trig. after the circuit in figure 5 is added to the pd design, the dead zone signal is removed from the system indicated as 2 in figure 9. fig. 9. simulation result of the circuit in figure 4 added into the pd. figures 10 and 11 show the simulation results for the two setups. the results show that the up_trig signal goes up when the freq_ref signal is faster than the freq_div and the dn_trig signal goes up when the freq_div is faster than the freq_ref. both up_trig and dn_trig signals are presented as pulse signals. the pulse width ($%&'() ) for the up_trig and dn_trig signals represent the phase differences or phase error (∅)++�+ ) between the freq_ref and the freq_div. the relationship between the pulse width for up_trig and dn_trig is directly proportional to the phase error as shown in (5), where the smaller the pulse width of up_trig and dn_trig, the smaller the phase error between the freq_ref and the freq_div. engineering, technology & applied science research vol. 12, no. 5, 2022, 9379-9387 9383 www.etasr.com ishak et al.: a fast digital phase frequency detector with preset word frequency searching in … $%&'() ∝ ∅)++�+ (5) the second stage output for both results is presented as up_trig and dn_trig. the results clearly show that the strike pulse at the first stage output has no longer appears at the second stage output. therefore, the proposed pd in this work achieved a stable signal for the frequency detection. fig. 10. the simulation result for freq_ref is faster than freq_div. fig. 11. the simulation result for freq_div is faster than freq_ref. b. fd simulations the fd simulations are conducted in two operations. the first operation is set up for when freq_ref is faster than freq_div and the second operation is set up for when freq_div is faster than freq_ref. for this part, the fd design is integrated with the pd design by using the verilog hdl code. the rtl view of the circuit is shown in figure 12. the simulation frequencies setup is the same as in the previous part. figure 13 shows the simulation result for freq_ref faster than freq_div while the simulation result in figure 14 shows the situation when freq_ref is slower than freq_div. it should be noted that the system for this part will compare the frequency of the freq_ref and freq_div without taking into account the phase alignment but only taking into account the pulses of the output signal frequency. the output pulses will be counted and the system will compare which counter will produce the highest value. in figure 13, the system detects that the frequency of up_trig pulses is higher than dn_trig pulses through the output counter. according to the flowchart in figure 6, when the up_trig pulses produce the higher one, the system will send the "fast" signal to the dco. thus, the "fast" signal is triggered in figure 13 after the signal of counting freq_ref is completed, while in figure 14, the opposite operation is detected and the dn_trig count pulses are higher than the up_trig-count pulses. in this situation, the "slow" instruction will be sent to the dco. based on the fd simulation results, the fast detection performance is achieved because of the fd system can complete at thirteenth cycles of the freq_ref. fig. 12. the rtl view for pd and fd design architecture in verilog hdl. engineering, technology & applied science research vol. 12, no. 5, 2022, 9379-9387 9384 www.etasr.com ishak et al.: a fast digital phase frequency detector with preset word frequency searching in … fig. 13. the simulation result for fd design when up_trig pulses are higher than dn_trig pulses. fig. 14. the simulation result for fd design when dn_trig pulses are higher than up_trig pulses. table i. summary of the pw using manual calculations for the proposed system input output 1 2 3 4 5 6 7 8 9 pw1 pw2 pw3 pw4 pw5 pw6 pw7 pw8 final_pw 0 0 0 0 1 1 1 0 1 159 239 279 299 289 284 281 282 281 0 0 0 1 1 1 0 0 0 159 239 279 259 249 244 246 247 248 0 1 1 1 0 1 1 1 1 159 79 39 19 29 24 21 20 19 fig. 15. system testing for input 000 011 101. fig. 16. system testing for input 000 111 000. engineering, technology & applied science research vol. 12, no. 5, 2022, 9379-9387 9385 www.etasr.com ishak et al.: a fast digital phase frequency detector with preset word frequency searching in … fig. 17. system testing for input 011 101 111. c. simulations of the pw calculations in this work, the module of pw calculations is presented using the verilog hdl coding. the system receives the signal from the pfd block, which is a "slow" or "fast" signal. nevertheless, in the testing platform, the "slow" and "fast" signals are represented as a binary form of 0 and 1 respectively. the manual calculation of the pw for the proposed system is presented in table i. only 3 tests are shown in this section to prove that the proposed system produces the same output as the theoretical values. nine detections of input are developed in the system. when the system detects the binary 0, the pw is increased and when the binary 1 is detected, the pw is decreased. there are also 9 pw outputs presented and the 9 th detection is the last detection, which produced the final pw for the dco operation. figures 15 17 show the simulation results for the testing input of 000 011 101, 000 111 000, and 011 101 111 respectively. based on the pw shown at the bottom list for each figure, the values are matched with the manual calculation as in table i. thus, the proposed design shows that the pw searching is achieved very fast and only takes 9 cycles to calculate the desired value. based on the proposed design, the good results of the pd and the fd simulation and the pw searching are presented. in this work, the dead zone problem is considered in order to achieve the phase acquisition step and system stability. the dead zone occurs when the pfd is unable to distinguish the phase mismatch of the positive or the negative edges of the two input signals and it may lock to the incorrect phase [33]. the incorrect phase-locked may degrade the phase noise performance. thus, to achieve better phase acquisition performance, the proposed pd design architecture has successfully removed the dead zone pulses as presented in [34]. furthermore, the proposed fd design has adopted the frequency acquisition step technique to achieve locking mechanism and system accuracy. our proposed fd is able to count and compare the frequency pulses of each signal directly. our design improved the pfd block of the work of [31] where their adpll did not consider the frequency acquisition step. next, the pw frequency searching in the proposed work is to achieve the target frequency and it is based on the binary search algorithm and the changing frequency step of the proposed pw is using a bisection scheme calculation. in our pw design, the large frequency step takes place in the early pw calculation, and it saves a lot of time to reach the target frequency which takes only 9 steps for 320 frequency control codes. our frequency searching is simpler as compared to using the oscillator tuning word (otw) algorithm in [16, 35]. v. conclusion a digital pfd for the rfid-adpll architecture is proposed and designed in this paper with the verilog hdl system. the design of the pfd is divided into two main parts, which are the phase-detection and frequency-detection to achieve the phase acquisition and the frequency acquisition respectively. the proposed pd module consists of two components of d-flip-flop and a nand gate at the reset feedback. the outputs of the up_trig and dn_trig signals are well-produced by eliminating the dead zone signal and presented a stable output for the fd module. in addition, the fd module is designed by comparing the counting value of the up_trig and the dn_trig signals. as a result, the "fast" and "slow" signals are produced at the thirteenth cycle of freq_ref and represent the increase and decrease of the operation of the future dco respectively. moreover, to search the target frequency for the dco, a binary search scheme is used to calculate the pw for controlling the dco operation in the future. the manual calculation of the pw has also been tabulated for the theoretical comparison. the comparison shows that the pw calculation in simulations is matched with the theoretical values and finished the calculation at the nineth cycle detection of freq_ref. based on the results of the dpfd and the pw searching, fast detection performance is achieved in this work. in future research work, the control code output generated from the proposed digital pfd and the pw searching will be connected to the dco block acknowledgment this work is funded by the malaysian ministry of education under the grant frgs/1/2018/tk04/ukm/02/1. references [1] g. maniam, j. sampe, r. jaafar, and m. ibrahim, "smart monitoring system for chronic kidney disease patients based on fuzzy logic and iot," international journal of advanced computer science and engineering, technology & 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[35] g. yu, y. wang, h. yang, and h. wang, "a fast-locking all-digital phase-locked loop with a novel counter-based mode switching controller," in ieee region 10 conference, singapore, singapore, jan. 2009, pp. 1–5, https://doi.org/10.1109/tencon.2009.5396168. microsoft word 5-530-ce.doc engineering, technology & applied science research vol. 5, no. 1, 2015, 760-763 760 www.etasr.com iliev et al.: a novel 2d z-shaped lectromagnetic bandgap structure a novel 2d z-shaped electromagnetic bandgap structure ilia iliev dept. of radiocommunications and videotechnologies technical university of sofia sofia, bulgaria igiliev@tu-sofia.bg marin nedelchev dept. of radiocommunications and videotechnologies technical university of sofia sofia, bulgaria mnedelchev@tu-sofia.bg evgeni markov dept. of radiocommunications and videotechnologies technical university of sofia sofia, bulgaria emarkov@tu-sofia.bg abstract—this paper researches a novel 2d z-shaped electromagnetic band-gap (ebg) structure, its dispersion diagram and application field. based on a transmission line model, the dispersion equation is derived and theoretically investigated. in order to validate theoretical results, a full wave analysis is performed and the electromagnetic properties of the structure are revealed. the theoretical results show good agreement with the full wave simulation results. the frequency response of the structure is compared to the well know structures of jerusalem cross and patch ebg. the results show the applicability of the proposed 2d z-shaped ebg in microstrip patch antennas, microstrip filters and high speed switching circuits, where the suppression of parasitic surface wave is required. keywordselectronic band-gap (ebg) structures; microstrip patch antennas; microwave filters; high speed switching circuits. i. introduction the concept of ebg structures originates from solid state physics and optics, where photonic crystals with forbidden band gaps were proposed in [1-3]. in the following years, photonic crystals have gained the interest of the scientific community, and a number of researches have been made upon them [4-6]. the terminology photonic band gap (pbg) structures were used in these years. in recent years, structures, similar to the pbg, were studied in microwave frequencies [7]. the band gap attribute was first researched and documented in the early 1990’s [8]. since then, many researches and applications for this novel technology have been applied to microwave devices, reducing the switching noise in high speed switching circuits, reducing the surface wave in planar microstrip antennas, giving forbidden frequency bands in microwave filters, and used in other types of microwave devices, like power amplifiers, dividers, mixers etc. [1-14]. the ebg structures can be divided into three major categories – volumetric 3d structures, 2d planar structures, and 1d transmission line structures. the 1d transmission line structures have been analyzed as a periodic array of drilled holes in the dielectric substrate under the transmission line [13] or as a composite right-left handed transmission line [14]. another classification of the ebg also consist of mushroomtype [1] or uni-planar type [15]. the main difference is the via to the ground metalized plane, that can lead to significant change in the structure’s behavior. the design of ebg structures can be performed by two different methods: the transmission line method and the fullwave analysis method. the transmission line method approximates the structure with transmission lines and their physical parameters. the dispersion equation of the structure can be derived according to the circuit theory using the transmission line matrix representation. the transmission line method is preferred when an approximate solution to given structures is necessary. it is of lower computational complexity and it is faster than the other methods used. the transmission line method however, suffers from approximation errors. the full-wave method of analysis is the other method, used in the analysis and simulation of ebg structures. it solves the maxwell equations with periodic boundary conditions to a unit cell. it gives more accurate results compared to the transmission line method. different computational methods for full wave analysis are implemented in the software products. the most used of them are the finite difference time domain (fdtd) and frequency domain (fdfd) methods, the method of moments (mom) and the finite element method (fem). depending on the topology of the periodic structure and its application, different techniques may be used in different design scenarios. a more detailed survey of the different types of full-wave computational electromagnetic analysis methods can be found in [17]. in this paper, a novel z-shaped ebg periodic structure is proposed. a theoretical model based on transmission line theory is presented and a closed form dispersion equation for the structure is derived. the properties of the structure are investigated using the k-β diagrams. in order to validate the theoretical results, a finite difference time domain (fdtd) based full wave simulation is performed. the theoretical and simulation results show good agreement in the cut-off frequencies of the bandgaps of the structure. the frequency response of the proposed structure is compared to jerusalem cross and patch ebg and it shows similar characteristics and applicability in microwave devices. engineering, technology & applied science research vol. 5, no. 1, 2015, 760-763 761 www.etasr.com iliev et al.: a novel 2d z-shaped lectromagnetic bandgap structure ii. transmission line model and dispersion diagram the transmission line method, applied for the novel zshaped ebg structure consists of two 90 degree rotated, zshaped segments, interconnected and via grounded in the center. it is represented by a section of main transmission line and open end arms in both ends. the arms of one unit cell form a coupled lines with the adjacent unit cells in x and y direction. the z-shaped 2x2 unit cells and the important points of the structure are shown in figure 1. from point a to point b is the length of the main transmission line of the z-shaped structure la. the line from point b to point c forms the coupling with the adjacent cell with length lc. the space period is denoted with d. fig. 1. 2x2 periodic unit cells z-shaped ebg structure. in order to derive the structure dispersion diagram is necessary to evaluate the complete abcd matrix of one unit cells in x or y direction. a unit cell is shown in figure 2, which is presented with the equivalent transmission line matrices in each direction. fig. 2. unit cell of a periodic structure, presented with the equivalent transmission matrices the structure is modeled with its equivalent circuit, shown in figure 3. opposite open ended coupled lines can be represented by their t-equivalent circuit. the dashed line shows the line of symmetry of the unit cell. the coupled lines can be divided into two identical l sections. fig. 3. transmission line model of the z-shaped ebg. the abcd matrix of the l section is [19]:  1 (1)1 1 2 2 a a cl c c z a b z c d z z = + é ù ê úé ù ê úê ú ê úê úë û ê úë û where  )sin( 1 2 )cot( 2 0000 c oe c oe a l zz jl zz jz        0 0 1 (2) 2 sin( ) e o c c z z z j lb =  z0e and z0o are the even and odd impedances of the coupled lines, β is the propagation constant. the second part is the main transmission line, from point a to b. the abcd matrix of a transmission line is [19]:               )cos()sin( 1 )sin()cos( aa tl atla tl ll jz ljzl dc ba    where ztl is the characteristic impedance of the microstrip line. the complete abcd matrix is a product of both matrices in x or y direction:  cl tl a b a b a b c d c d c d                     za za 2zc 2zc l l ztl z 0 e, z 0o lc a b c ztl, la ztl, la ztl, la line of symmetry a b c d       b lc la a c d a 5 b5 c 5 d5 i y i x yi e -jkyd ix e -jkxd engineering, technology & applied science research vol. 5, no. 1, 2015, 760-763 762 www.etasr.com iliev et al.: a novel 2d z-shaped lectromagnetic bandgap structure sin( ) cos( ) sin( ) cos( ) cos( ) sin( ) sin( ) 1 1 cos( ) 2 2 2 2 (3) a a a tl a a a tl a a a tl a a a c c tl c c z l l jz l z l jz l z l jz l z l z z jz z z b b b b b b b b é ù ê ú+ + ê ú ê ú= ê úæ ö æ ö÷ ÷ê úç ç÷ ÷+ + + +ç ç÷ ÷ê úç ç÷ ÷ç çè ø è øê úë û according to the structure line of symmetry shown on figure 2 , it can be written:  1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 5 51 (4) a a a a a b b b b b c c c c c d d d d b d b j l                     the dispersion equation can be obtained, if the determinant of the matrix is set to zero. for the z-shaped structure, applying the equations in [14, 18], the dispersion equation is derived as: (5) 1 cos( ) cos( ) 2 4 x y k d k d ad bd j lw + = + +  where kx and ky are the wave numbers for x and y direction, and l is the inductivity of the via hole. iii. analysis and results for the z-shaped 2d ebg structure a z-shaped structure has been analyzed in order to verify the derived dispersion equation based on the transmission line method. the normalized parameters of the structure are given in table i for f=1.14ghz. table i. normalized parameters (1.14 ghz) parameters cl  al  a  d  0 ,ez    0 ,oz    values 0.185 0.3 0.56 0.118 59.45 37.54 the diameter of grounding via is 0.75 mm. the solution of the dispersion equation is graphically represented in the brillouin diagram, which shows the propagation of the electromagnetic wave in the x, y and diagonal direction. the dispersion diagram of the analyzed structure is shown in figure 4. the z-shaped structure has a bandpass behavior, because of the opposite open ended coupled lines [19]. thus the structure suppresses the low frequencies from dc to its first resonance. as the unit cell is a resonating structure, the passband and stopband alternatively changes. the main drawback of the transmission line model is that it loses accuracy at higher frequencies, where higher modes appear. in order to verify the applicability of the transmission line model, a full wave fdtd simulation of infinite periodic structure consists of z-shaped unit cells is performed in ansoft hfss. 0 1 2 3 0 1 2 3 4 5 6 7 wavenumber f re q u e n cy , g h z dispersion diagram x m  stopband 2 stopband 1 passband 2 p as sb an d 1 γ x m fig. 4. dispersion diagram for z-shaped structure. iv. full wave analysis of z-shaped 2d ebg structure performing fdtd full wave simulations to the infinite 2d z-shaped structure, the scattering parameters of the structure are analyzed. the dielectric substrate used in the simulations is fr-4, h=1.5mm, εr=4.4, tgδ=0.02. figure 4 shows the reflection coefficient s11 and the transmission coefficient s21. in the structure, the center resonance frequencies for both stopbands are located at 1.8 ghz and at 5.78 ghz, with s21 dropping to -39db at the first band and to -43db at the second stopband. the frequency response of the periodic structure is shown in figure 5. 0 1 2 3 4 5 6 7 8 9 -50 -40 -30 -20 -10 0 frequency, ghz s 1 1 , s 2 2 , d b s21 s11 fig. 5. scattering parameters of the structure. as expected the transmission line equivalent model of zshaped structure suffers from accuracy at higher frequencies, because of the higher modes. in order to define the applicability of the proposed z-shaped structure, it is simulative compared to other known periodic structures [14] that exhibits bandpass characteristics. figure 6 shows a comparison between full wave fdtd simulations of z-shaped structure, jerusalem cross and a patch ebg [14]. the z-shaped structure has the same response behavior as the jerusalem cross but at lower frequencies, because its topology. the patch ebg has another response behavior with wider stopband compared engineering, technology & applied science research vol. 5, no. 1, 2015, 760-763 763 www.etasr.com iliev et al.: a novel 2d z-shaped lectromagnetic bandgap structure to the other two structures. this is due to the different coupling mechanism between the unit cells. 0 1 2 3 4 5 6 7 8 9 -50 -40 -30 -20 -10 0 frequency, ghz s 1 1 , s 2 2 , d b z shaped jerusalem cross patch fig. 6. comparison of different ebg structures. v. conclusion in this paper, a novel 2d z-shaped ebg structure topology, dispersion equation and research is proposed. the structure exhibits two suppression bands and two passbands. a theoretical model, based on transmission line theory is proposed that allows analysis and synthesis of z-shaped structures for different design requirements. the results from the theoretical and full wave fdtd simulations show good agreement at low frequencies. the comparison of the simulation results with two known structures show the applicability of z-shaped structures in microstrip patch antennas, microstrip filters and high speed switching circuits where the suppression of parasitic surface wave is required. references [1] d. sievenpiper, l. zhang, r. f. j. broas, n. g. alexopolous, e. yablonovitch, “high-impedance electromagnetic surfaces with a forbidden frequency band,” ieee transactions on microwave theory and techniques, vol. 47, no. 11, pp. 2059-2074, 1999. [2] e. yablonovitch, “inhibited spontaneous emission in solid-state physics and electronics”, physical review letters, vol. 58, pp. 2059–2063, 1987 [3] s. john, “strong localization of photons in certain disordered dielectric super lattices”, physical review letters, vol. 58, pp. 2486–2489, 1987 [4] j. d. joannopoulos, r. d. meade, j. n. winn, photonic crystals, princeton university press, 1995 [5] c. m. bowden, j. p. dowling, h. o. everitt, “development and applications of materials exhibiting photonic band gaps”, journal of the optical society of america b, vol. 10, pp. 280-282, 1993 [6] g. kurizki, j. w. haus, “special issue on photonic band structures”, journal of modern optics, vol. 41, pp. 171–172, 1994 [7] ieee transactions on microwave theory tech., special issue on electromagnetic crystal structures, designs, synthesis, and applications, vol. 47, no. 11, 1999 [8] k. m. ho, c. t. chan, c. m. soukoulis, “existence of a photonic gap in periodic dielectric structures”, physical review letters, vol. 65, pp. 3152–5, 1990 [9] c. c. chang, y. qian, t. itoh, “analysis and applications of uniplanar compact photonic band gap structures”, progress in electromagnetics research, vol. 41, pp. 211–235, 2003 [10] c. k. wu, h. s. wu, c. k. c. tzuang, “electric–magnetic–electric slowwave microstrip line and bandpass filter of compressed size”, ieee transactions on microwave theory and techniques, vol. 50, no. 8, pp. 1996-2004, 1999. [11] j. s. lim, c. s. kim, j. s. park, d. ahn, s. nam, “design of 10 db 90° branch line coupler using microstrip line with defected ground structure”, electronics letters, vol. 36, no. 21, pp. 1784-1785, 2000 [12] i. chang, b. lee, “design of defected ground structures for harmonic control of active microstrip antenna”, ieee antennas and propagation society international symposium, vol. 2, pp. 852-855, 2002 [13] v. radisic, y. qian, r. coccioli, t. itoh, “novel 2-d photonic bandgap structure for microstrip lines”, ieee microwave and guided wave letters, vol. 8, no. 2, pp. 69–71, 1998 [14] c. caloz, t. itoh, “electromagnetic metamaterials: transmission line theory and microwave applications”, wiley, 2005 [15] f. r. yang, k. p. ma, y. qian, t. itoh, “a uniplanar compact photonicbandgap (uc-pbg) structure and its applications for microwave circuit”, ieee transactions on microwave theory and techniques, vol. 47, no. 8, pp. 1509–1514, 1999 [16] e. p. irzinski, “the input admittance of a tem excited annular slot antenna”, ieee transactions on antennas and propagation, vol. 23, no. 6, pp. 829-834, 1975 [17] r. mittra, c. h. chan, t. cwik, “techniques for analyzing frequency selective surfaces-a review,” proceedings of the ieee, vol. 76, no. 12, pp. 1593–1615, 1988 [18] a. grbic, g. v. eleftheriades, “periodic analysis of a 2-d negative refractive index transmission line structure”, ieee transactions on antennas and propagation, vol. 51, no. 10, pp. 2604 – 2611, 2003 [19] g. matthaei, e. m. t. jones, l. young, microwave filters, impedancematching networks, and coupling structures, artech publishing, 1980 microsoft word 1-496-ed.doc engineering, technology & applied science research vol. 4, no. 5, 2014, 690-695 690 www.etasr.com jordanova et al.: constellation and mapping optimization of apsk modulations used in dvb-s2 constellation and mapping optimization of apsk modulations used in dvb-s2 l. jordanova l. laskov d. dobrev department of telecommunications, department of telecommunications, department of telecommunications, technical university of sofia, bulgaria technical university of sofia, bulgaria technical university of sofia, bulgaria jordanova@tu-sofia.bg laskov@mail.com dobrev@tu-sofia.bg abstract—this article represents the algorithms of apsk constellation and mapping optimization. the dependencies of the symbol error probability ps on the parameters of the 16apsk and 32apsk constellations are examined and several options that satisfy the requirements to the minimum value of ps are selected. mapping optimization is carried out for the selected apsk constellations. ber characteristics of the satellite dvb-s2 channels are represented when using optimized and standard 16apsk and 32apsk constellations and a comparative analysis of the results achieved is made. keywords-satellite dvb channel; m-ary apsk constellation and mapping; concateneted bch-ldpc codes; dvb-s2 channel noise immunity; qef reception i. introduction in the contemporary digital video broadcasting (dvb) systems it is necessary to provide quasi-error-free (qef) reception while the values of the carrier to noise ratio (cnr) parameter are relatively low and the encoding and decoding equipment is not very complex [1]. the term “quasi-errorfree” means that the bit error rate (ber) at the input of the mpeg demultiplexer is less than 10−10 to 10−11. the requirement of contemporary communication systems to provide a higher rate of transmitted data requires the application of modulation methods with a greater spectral efficiency. when an m-ary modulation technique of higher order is used then both the spectral efficiency and the bit rate are increased but, in turn, the channel noise immunity is decreased. in satellite systems, apart from noise and interference, the channel nonlinearity also causes a problem. the nonlinearity exists because the working mode of the power amplifier board is set near the saturation point in order to reach the maximum level for the transmitted signal. the nonlinear signal distortions, similarly to the noise and interference in the radio channel, are the reasons for the increase of error probability. an essential requirement to the satellite dvb systems is ensuring high power efficiency without excessively penalizing the spectrum efficiency. this is achieved by using noise resistant types of modulation and effective channel codes. as known, the apsk modulation provides great resistance to nonlinear distortion in a radio channel [2, 3], which is the reason why this modulation is used in the second-generation satellite dvb systems. the 16apsk and 32apsk have been proposed in the dvb-s2 standard [4] and their performances have been widely investigated over the awgn channel, by considering typical satellite scenarios, also in the presence of high power amplifiers (hpas). in order to enhance the noise immunity of a dvb-s2 channel, a concatenated error protection of bose-chaudhuri-hocquenghem (bch) outer code and low density parity check (ldpc) inner code was chosen [4, 5]. the aim of this paper is to study the influence of the 16apsk and 32apsk constellation parameters and mapping on the noise immunity of satellite dvb channels. ii. algorithm for apsk constellation and mapping optimization the apsk constellation consists of a n number of concentric circles, where the k-th circle contains nk signal points. each of the circles in the constellation is characterized by a primary phase shift φk and radius rk . in the general case, the apsk constellation can be described as follows: 1 1 1 1 2 2 2 2 2 .exp 0,1,..., 1 2 .exp 0,1,..., 1 (1) ... ... 2 .exp 0,1,..., 1n n n n r j n n n n r j n n n n r j n n n n                                                     for convenience, instead of the radiuses, their ratios relative to the radius of the innermost circle – γk=r(k +1) /r1 may be used. the apsk modulation is usually denoted as n1-n2-…apsk. figure 1 and figure 2 show 16apsk and 32apsk standard constellations that are used in the dvb-s2 systems. the parameters of these constellations are as follows: n=2, n1=4, engineering, technology & applied science research vol. 4, no. 5, 2014, 690-695 691 www.etasr.com jordanova et al.: constellation and mapping optimization of apsk modulations used in dvb-s2 n2=12, φ1=45 o, φ2=15 o and γ1=r2 /r1=2.6 (for 16apsk) and n=3, n1=4, n2=12, n3=16, φ1=45 o, φ2=15 o, φ3=0 o, γ1=r2 /r1=2.54 and γ2=r3 /r1=4.33 (for 32apsk). these constellations are determined to be optimal at an ldpc code rate of 8/9 and bch code rate of 0.983. fig. 1. standard 4+12 apsk constellation fig. 2. 32apsk constellation there are several known algorithms for the optimization of apsk constellations [6, 7]. the aim of the optimization, presented in this paper, is to provide minimum symbol error probability. after processing the basic expressions, given in [8], the following dependence for the determination of the symbol error probability ps was obtained: 01 1, 1 1, 1 1 1 ( ) erfc 2 2 (2) s i j i j m m m m i j j i i j j i d p p s s m m n                   in this expression, p(si → sj) denotes the probability that instead of the i-th symbol the j-th one is accepted, m is the modulation order, n0 is the noise power density and dij is the euclidean distance between the i-th and j-th points of the constellation. the value of the error complementary function is obtained by [9]:  21erfc( ) exp (3)x x x     in order to determine the euclidean distance between two points which define the i-th and j-th positions of the apsk signal vector, we can use the cosines theorem, i.e. 2 2 ( ) ( ) ( ) ( ) 2. . . cos (4) i j p i q j p i q j i j d r r r r    , where rp(i) and rq(j) are the radiuses of the circles where the two points are located and θij is the angle between the signal vectors studied. the value of θij is derived by [7]:   1 12 (5)i j p q p q i j n n                , where φp and φq denote the relative phase shifting of the signal points located on the p-th and q-th circles, np and nq is the number of these points. the relation between the radiuses of the circles in the apsk constellation and the energy per symbol es can be described by the following dependence: 2 2 2 2 2 2 1 1 2 2 1 1 2 1 1 ... ( ... ) (6)n n n ns n r n r n r n n n e m m r          where γi=r(i+1) /r1. the mathematical model described allows the optimization of the following parameters of apsk constellations: the number of phase states nk of the signal vector with amplitude rk , the ratios between the amplitudes of the signal vector γ(k-1)=rk /r1 and the relative phase shifting of the symbol points φk , where k=1, 2, … n. for the optimization of the apsk constellation parameters, we need to find the minimum value of the functional dependence which is presented by (1). in order to evaluate the efficiency of the power used, the papr parameter (peak to average power ratio) is used. it is the ratio between the maximum and the average signal power s(t) for a period t and is obtained using the expression [10]: 2 2 [ 0 , ] 22 ( ) 10 max | ( ) | 1 | ( ) | (7),t t n t m p i i s t m r papr rs t dt t      where rn denotes the radius of the outermost circle, and rp(i) denotes the radius of the circle on which the i-th signal point is located. in order to ensure the minimum bit error probability pb, it is required to select an appropriate combination of log2m bits (mapping) for each signal point of the apsk constellation. the following dependence can be used when mapping optimization is carried out: 2 2 0 1 1, 1 1, 1 ( ) ... log 1 ... erfc 2 log 2 ,(8) i j b i j i j i j m m i j j i m m i j j i h p p s s m m h d m m n                     where hij is the hamming distance between the i-th and j-th signal points. engineering, technology & applied science research vol. 4, no. 5, 2014, 690-695 692 www.etasr.com jordanova et al.: constellation and mapping optimization of apsk modulations used in dvb-s2 iii. parameters of the optimized 16apsk constellations in order to determine the optimal parameters of the 16apsk constellation, different combinations of parameters n1, n2 and φ1 were used and for each of them, the minimum of the functional dependence of the symbol error probability ps on parameters φ2 and γ1 was established. the analysis of the results achieved shows that the initial phase shift φ2 of the signal points of the outer circle does not impact considerably the ps . therefore, in this study it is assumed that φ2=0 o. figure 3 shows the dependences of the symbol error probability on the ratio between the outer and inner circles of the 16apsk constellation γ1 for four combinations of parameters n1, n2 and φ1, for which the best results have been achieved. these dependences have been obtained at an energy per symbol to noise power density ratio of es /n0=12 db. when determining the value of es /n0 parameter, the real carrier to noise ratio (cnr) at the input of the satellite receiver has been considered (usually varies from 9 to 12 db). the values of the parameters of the four studied constellations at which a minimum symbol error probability is achieved are given in table i. the table also shows the calculated values of the papr parameter for the evaluation of the power efficiency of these constellations. obviously, the highest radio channel noise immunity can be ensured at using the fourth 16apsk constellation (cn4), but in that case the power efficiency of the system is the lowest. the best power efficiency is achieved at the first of the compared constellations (cn1), but it would provide the lowest radio channel noise immunity. so when choosing an apsk constellation, a compromise between the noise immunity and the power efficiency is to be made. the mapping optimization carried out demonstrates that there is more than one possible combination of m=log2(m) bits corresponding to the signal points, which provide a minimum of the functional dependence. the optimization is based on two constraints that define the permissible number of differing bits for two adjacent signal points ζ. the first one relates to the signal points of one and the same circle, and for them ζ=1. only one breach of this rule is allowed, and then ζ=2. the second constraint requires that the value of the parameter ζ for the adjacent signal points from different circles is not higher than 2. for each of the 16apsk constellations presented in table i, one of the possible m=4 bits combinations at which a minimum value of bit error probability pb is achieved is shown in table ii. table i. parameters of the optimal 16apsk constellation. constellation number (cn) γ1 n1, n2 φ1 ps min papr cn1 2.99 3, 13 60 0.1524 1.197 cn2 2.61 4, 12 45 0.1291 1.266 cn3 2.37 5, 11 36 0.1175 1.335 cn4 2.20 6, 10 30 0.1166 1.403 table ii. optimal symbol mapping symbol point № cn1 cn2 cn3 cn4 1 0000 1100 0000 0000 2 1000 1110 1000 1000 3 1100 1111 1100 1100 4 0100 1101 1110 1110 5 0110 0100 1010 0110 6 0010 0000 0010 0100 7 0011 1000 0011 0011 8 0001 1010 0001 0010 9 1001 0010 1001 1010 10 1011 0110 1101 1011 11 1010 0111 0101 1001 12 1110 0011 0100 1101 13 1111 1011 0110 1111 14 1101 1001 0111 0111 15 0101 0001 1111 0101 16 0111 0101 1011 0001 fig. 3. dependence of ps on γ1 at es/n0=12 db and φ2=0 о iv. parameters of the optimized 32apsk constellations at determining the optimum parameters of the 32apsk constellation, different combinations of parameters n1, n2, n3, φ1, φ2 and φ3 have been used, and for each of them the values of γ1 and γ2 for which the symbol error probability ps was minimal were determined. figure 4 shows the dependence of ps on γ1 and γ2 of the 4+12+16 apsk constellation, for which the most favorable results are achieved. the parameters of this constellation, denoted by cn1, as well as the calculated values of ps and papr are given in table iii. similar studies have been carried out for other combinations of the 32apsk constellation parameters and after an analysis of the results achieved another four options have been selected and marked as cn2, cn3, cn4 and cn5. figure 5 and 6 show the dependences of the symbol error probability ps on parameters γ1 and γ2 of the 4+8+20 apsk (cn2) and 5+11+16 apsk (cn3) constellations. it is assumed that es /n0=15 db for these dependences. as seen from table iii, the 5+11+16 apsk constellation would provide the minimum symbol error probability, and the 4+8+20 apsk the most efficient use of the transmitter’s power. engineering, technology & applied science research vol. 4, no. 5, 2014, 690-695 693 www.etasr.com jordanova et al.: constellation and mapping optimization of apsk modulations used in dvb-s2 the mapping optimization carried out shows that a minimum of the functional dependence can be achieved for various bit combinations in the 32 symbol points of the studied apsk constellations. the combinations, for which the lowest values of the pb parameter are obtained, are given in table iv. v. noise immunity of the dvb-s2 channel in order to assess the noise immunity of the dvb-s2 channel, the dependence of bit error probability pb, respectively ber at the output of the channel decoder, on the energy per symbol to noise power density ratio eb /n0 has been used. the expressions for determining the pb are given in [11], and the values of eb /n0 parameter are calculated by: ldpc bch 0 0 10.lg( ) 10.lg( ) 10.lg( ) (9)s b e e m r r n n     , where m=log2(m) denotes the number of bites in one symbol, and rldpc and rbch are the rates of the channel codes used. figure 7 shows the dependences of ber on the eb /n0 of dvb-s2 channels at using the four studied constellations and the standard 16apsk one. these dependences have been obtained at channel code rates rldpc=8/9 and rbch=0.983. the values of the parameter eb /n0, for which the bit error rate is 10−11, are given in table v. as it is evident in table v, the best radio channel noise immunity can be provided when the fourth apsk constellation is used. in comparison with the apsk constellation which is standard for dvb-s2, the achieved benefit is 0.1 db. the assessment of the noise immunity of dvb-s2 channels at using the studied constellations and the standard 32apsk one can be derived from figure 8. in this case also, it is assumed that the channel code rates are rldpc=8/9 and rbch=0.983. the values of the parameter eb /n0, for which the bit error rate is 10−11, are given in table vi. obviously, the best radio channel noise immunity can be provided when the first 32apsk constellation is used. in comparison with the 32apsk constellation which is standard for dvb-s2, the achieved benefit is 0.085 db. vi. conclusion the analytic and graphic dependences presented in this paper make it possible for the parameters and mapping of 16apsk and 32apsk constellations to be determined. these dependences can be used in any other communication system in which such types of modulations are applied. the researches on the noise immunity of dvb-s2 channels, for the formation of which the studied 16apsk and 32apsk constellations have been used, show that there are several options for achieving similar results to those set out in the standard. acknowledgment the research described in this paper is supported by the bulgarian national science fund under the contract no ddvu 02/74/2010. fig. 4. dependence of ps on γ1 and γ2 of 4+12+16 apsk constellation at es/n0=15 db fig. 5. dependence of ps on γ1 and γ2 of 4+8+20 apsk constellation fig. 6. dependence of ps on γ1 and γ2 of 5+11+16 apsk constellation engineering, technology & applied science research vol. 4, no. 5, 2014, 690-695 694 www.etasr.com jordanova et al.: constellation and mapping optimization of apsk modulations used in dvb-s2 table iii. parameters of the optimal 32apsk constellation. constellation number (cn) cn1 cn2 cn3 cn4 cn5 n1, n2, n3 4, 12, 16 4, 8, 20 5, 11, 16 5, 10, 17 6, 10, 16 γ1 2.54 2.32 2.3 2.26 2.13 γ2 4.23 4.07 3.75 3.73 3.41 φ1 45 45 36 36 30 φ2 0 22.5 16.36 18 0 φ3 11.25 0 11.25 0 0 ps 0.1365 0.1644 0.1331 0.1368 0.1348 papr 1.557 1.401 1.561 1.522 1.567 table iv. optimal symbol mapping symbol point № cn1 cn2 cn3 cn4 cn5 1 00000 00000 00000 00000 00000 2 10000 10000 10000 10000 10000 3 11000 11000 11000 11000 11000 4 01000 01000 11100 11100 11100 5 00001 00001 10100 01100 01100 6 00101 00101 00100 01001 01000 7 00100 00100 00110 00001 01001 8 10100 10100 00010 10001 00001 9 10101 11100 10010 11001 10001 10 10001 11101 11010 11011 11001 11 11001 11001 01010 11010 11011 12 11101 01001 01000 11110 11010 13 11100 00011 01100 01110 11110 14 01100 10011 01110 01010 01110 15 01101 10001 11110 01000 01010 16 01001 10101 10110 01101 01011 17 00011 10111 00101 01111 01111 18 00111 00111 00111 00111 01101 19 00110 00110 00011 00101 00101 20 10110 00010 00001 10101 10101 21 10111 10010 10001 11101 11101 22 10011 10110 10011 11111 11111 23 10010 11110 11011 10111 10111 24 11010 01110 01011 10011 10011 25 11011 01100 01001 10010 10010 26 11111 01101 11001 10110 10110 27 11110 01111 11101 10100 10100 28 01110 11111 01101 00100 00100 29 01111 11011 01111 00110 00110 30 01011 11010 11111 00010 00010 31 01010 01010 10111 00011 00011 32 00010 01011 10101 01011 00111 fig. 7. ber characteristics of 16apsk channels table v. values of eb /n0 that provided ber=10 -11 (16apsk) cn1 cn2 cn3 cn4 dvb-s2 8.443 db 7.809 db 7.741 db 7.721 db 7.821 db fig. 8. ber characteristics of 32apsk channels table vi. values of eb/n0 that provided ber=10 -11 (32apsk) cn1 cn2 cn3 cn4 cn5 dvb-s2 9.275 db 9.727 db 9.326 db 9.393 db 9.319 db 9.36 db references [1] etsi en 300 421 v1.1.2, digital video broadcasting (dvb): framing structure, channel coding and modulation for 11/12 ghz satellite services, european telecommunications standards institute, 1997 [2] a. morello, v. mignone, “dvb-s2: the second generation standard for satellite broad-band services”, proceedings of the ieee, vol. 94, no. 1, pp. 210-226, 2006 [3] r. muller, u. wachsmann, j. huber, “multilevel coding for peak power limited complex gaussian channels”, ieee international symposium on information theory, ulm, germany, 1997 [4] etsi en 302 307 v121, digital video broadcasting (dvb): second generation framing structure, channel coding, and modulation systems for broadcasting, interactive services, news gathering and other broadband satellite applications, european telecommunications standards institute, 2009 [5] etsi tr 102 376, user guidelines for the second generation system for broadcasting, interactive services, news gathering and other broadband satellite applications (dvb-s2), european telecommunications standards institute, 2005 [6] r. de gaudenzi, a. guillen i fabregas, a. martinez, “turbo-coded apsk modulations design for satellite broadband communications”, international journal of satellite communications and networking, , vol. 24, pp. 261-281, 2006 [7] k. liolis, r. gaudenzi, n. alagha, a. martinez, a. fаbregas, “amplitude phase shift keying constellation design and its applications to satellite digital video broadcasting”, in: digital video, isbn 978-9537619-70-1, intech, 2010 [8] o. afelumo, a. awoseyila, b. evans, “simplified evaluation of apsk error performance”, electronics 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vol. 5, no. 9, pp. 2396-2407, 2006 [13] s. jonson, iterative error correction: turbo, low-density parity-check and repeat-accumulate codes, cambridge university press, 2010 [14] m. luby, m. mitzenmachery, m. shokrollahiz, d. spielmanx, “analysis of low density codes and improved designs using irregular graphs”, proceedings of the 30th acm symposium on theory of computing, pp. 249-258, new york, 1998 [15] w. fisher, digital video and audio broadcasting technology, springer, 2008 [16] c. thomas, m. weidner, s. durrani, “digital amplitude-phase keying with m-ary alphabets”, ieee transactions on communications, vol. 22, no. 2, pp. 168-180, 1974 [17] c. berrou, codes and turbo codes. springer, 2010 [18] m. eroz, f. sun, l. lee, “dvb-s2 low density parity check codes with near shannon limit performance”, international journal of satellite communications and networking, vol. 22, no. 3, pp. 269-279, 2004 [19] l. ippolito, satellite communications system engineering, john wiley & sons ltd., 2008 [20] newtec el470, ip satellite modem, www.newtec.eu. [21] k. liolis, n. alagha, “on 64-apsk constellation design optimization”, proceedings of 10th international workshop on signal processing for space communications, rhodes, greece, 2008. [22] w. sung, s. kang, p. kim, d. chang, “performance analysis of apsk modulation for dvb-s2 transmission over nonlinear channels”, international journal of satellite communications and networking, vol. 27, pp. 295-311, 2009 microsoft word 5-631-ed-f.doc engineering, technology & applied science research vol. 6, no. 2, 2016, 945-951 945 www.etasr.com kara and cengiz savaş: design and simulation of a decentralized railway traffic control system design and simulation of a decentralized railway traffic control system tolgay kara eee dept, university of gaziantep gaziantep, turkey kara@gantep.edu.tr m. cengiz savaş turkish state railways corporation (tcdd) gaziantep, turkey cengizsavas@hotmail.com abstract—with the increasing use of railway transportation, various methods have been developed for the control and management of train traffic. train traffic control systems that are currently in use are overwhelmingly centralized systems. in this study, the development of the general structure of railway traffic control techniques is examined, centralized and decentralized control systems are investigated, and an alternative train traffic control system, the decentralized train traffic management system (dtms), is suggested. simulation results on the possible application of the proposed method to a railway line in south-east turkey are employed to evaluate the performance of the developed system. keywords-train traffic control; railway traffic; decentralized control; decentralized train traffic management system i. introduction management and control of railway traffic has been an appealing field of research in recent years. reliable and fast train traffic control systems are needed to cope with the increasing traffic density and high speed trains of today. in the last few decades, the common approach to train traffic control has been the use of automatic train control (atc) systems along with radio communication. in europe, the commonly used atc system is the european train control system (etcs) and global system for mobile communications for railways (gsm-r) is the basis of the radio communication functions of level 1 with radio infill, level 2 and level 3. combination of etcs and gsm-r constitutes the european railway traffic management system (ertms) [1, 2]. the majority of railway traffic management (rtm) systems currently in use today are centralized systems where train traffic is monitored and controlled by a supervisor. train traffic control is managed by a single center in many countries, whereas in turkey different regions are controlled by separate control centers, which are unable to follow or control the operations of other regions. in turkey, train traffic operations are managed by the use of traffic signals. train positions are sensed and notified to the control center via rail track circuits wired to the control centers where available. ordinary railway signal systems mainly consist of logic relay circuits, which need specific electric wiring. atc systems receive data from trackside components by local wireless units [3]. in conventional train traffic management, it is necessary to develop a time distance diagram in order to determine and solve the problems of a railway system. in high-density lines this diagram cannot be recovered quickly since information of the train traffic in stations is insufficient or not available. the centralized train traffic control (ctc) system that uses telephone lines in turkey is called tmi, where the train management by dispatchers and staff in the station is congested and effective working time of the staff for the maintenance work is reduced by telephone, as shown in figure 1. tmi system used in many regions of turkey remains weak and unreliable in many aspects [4]. an alternative to tmi tested in sections of railway network is the global system for mobile communication (gsm) based version, shown in figure 2. the railway network in the region of interest of this study is covered thoroughly by the gsm network supplied by a local operator and tmi-gsm system is practiced for the narlinusaybin line. fig. 1. configuration of tmi system fig. 2. configuration of tmi-gsm system engineering, technology & applied science research vol. 6, no. 2, 2016, 945-951 946 www.etasr.com kara and cengiz savaş: design and simulation of a decentralized railway traffic control system in the current study, a decentralized, flexible, low cost and reliable train traffic control system is investigated. using simulations of a real railway line in turkey, results illustrate the performance of the proposed system in usual and unusual scenarios. ii. a glance to train traffic control in early years of railway transportation, railway companies used simple mechanical operation signals. the roadside employees transmitted the information during railway traffic and passed commands to the train drivers by means of flags or signs, manually. then they would report the current situation of the train and line back to the control center. the control center handled all train traffic with this information [1]. today, the methods of train traffic control and management vary from similar to these early practices to cutting edge high technology applications. despite the fast progress and emerging methods in train traffic control, decentralized systems are still rare. a. a review the ordinary signaling system mainly consists of logic circuits using relays, which need electric wiring. the programmed route control (prc) system is an automatic computer controlled system developed for the sakaisuji line in 1971 and sanyo shinkansen in 1972 instead of ctc, which is a system of manual control by dispatcher [5]. a different system was developed for driver errors in 1980's, when mechanical automatic train stop (ats) was used, and then electrical ats was introduced along with line side equipment to prevent hazardous human errors. one advanced control method for train operation management developed in the 1980’s was the predictive fuzzy system by the hithachi company in japan. yasunobu and miyamoto suggested a fuzzy control system, which combined ats with the automatic train operation (ato) system [6]. the first mention of a management system that is not centrally controlled was in [7]. a distributed approach to railway traffic control, which overcame the upper bounds imposed on the size of areas under control by the requirement for real-time processing when centralized methodologies are applied was described [7]. in a large scale critical real time control system, in [8] a real time control system constructed step by step over 8 years without halting train operations was reported. to enable testing during system operation, an autonomous decentralized online expansion technique was proposed, then the effectiveness of the technique was demonstrated in a real system [8]. the "distributed positive train control system” presented the idea of decentralized train traffic control in [9]. this system also aimed to control train movement in a distributed manner [9]. an autonomous decentralized traffic management system, different from the conventional ctc was described in [5]. the problems of traffic management systems (tms) were described and solutions were presented [5]. high degrees of safety and reliability in this system needed high assurance technologies in high density operational regions. this required the use of latest technologies of communication for reliability and safety [10]. computer and internet technologies gradually had their impact on railway systems too. a novel railway control system that operated in a distributed fashion was proposed in [11]. in these years, the thales company developed net-trac 6617 ctc 1000. every train moving along a line controlled by this system could be monitored and displayed on supervision pictures and time distance diagrams [12]. in turkey, the most significant breakthrough in train traffic control in the last few decades took place in 2009 with the introduction of the national railway signaling project (udsp) by the turkish state railways corporation (tcdd) in cooperation with the scientific and technological research council of turkey-informatics and information security research center (tübi̇tak-bi̇lgem) and i̇stanbul technical university. at a cost of 4.6 million pounds, the system was developed by turkish engineers and for system testing purposes, mithatpaşa-adapazari station was commissioned, the purpose of which is to facilitate the border crossing between eu countries [13]. currently in turkey, all railway traffic control systems have a centralized nature commanded by a dispatcher at the control center. internet technologies and optics are used in the interlocking areas or in between control centers and local stations, one example of which is the autonomous decentralized transport operation control system (atos), but railway traffic control system as a whole is ctc in nature [3]. the decentralized approach to control systems for railway traffic management is becoming popular with its lower costs and practicality [14]. b. conventional train traffic control in rtm, electrical systems have replaced mechanical ones almost entirely today. two common features of these systems are the central position of control or supervisory system and transmission of railway information by track circuits. modern train control systems provide time-saving, traffic safety and efficient train management using atc. atc includes three subsystems; automatic train protection (atp), ato, and ats [1]. for the purpose of train control, the creation of a specific standard and the widespread use of it are required, so in european countries, ertms has been employed [2]. in recent years, ertms has been widely used in most european countries, and various signaling and control systems have been employed in other countries including turkey to comply and communicate with ertms. new standards are being planned and established for the adaptation to ertms and its communication structure. in ertms, atc systems are standardized in the context of etcs, which has evolved in recent years in three levels: etcs level 1, level 2, and level 3. in level 2 and level 3, gsm-r communication system is integrated into ertms along with etcs. the first two levels are depicted in figure 3. etcs level 3, a radio-based system where track occupancy detection and marker board of roadside are not necessary, is still in testing phase [15]. c. future of train traffic control one important problem of train traffic control is the need to ensure compliance and standard for the different train control systems. a solution to this problem is suggested to be ertms/etcs [16-18]. in near future, railway lines will be engineering, technology & applied science research vol. 6, no. 2, 2016, 945-951 947 www.etasr.com kara and cengiz savaş: design and simulation of a decentralized railway traffic control system used in a similar fashion to motorways. different railway companies will be able to use the lines paying transit fees. they will have their own locomotives and track-mounted equipment and operate each train independently from other trains, which implies companies may need to have their own control system and track equipment. as a result of this necessity, on-board systems must be available and compatible with each other [14]. current technology and future plans of public and private railway companies concentrate on a central train traffic control system that uses the best communication technologies, and permits integration of local central control systems into the network without any problem. however, this central approach will require extra effort to integrate systems. the new system proposed in this study will eliminate the necessity of this effort being a decentralized and modular system without any central control [19]. fig. 3. ertms/etcs level 1 (a) and level 2 (b). iii. a new approach: dtms in this study, a decentralized train traffic control methodology that we call dtms is presented. dtms is developed as an alternative to the previously described conventional train traffic control systems and components needed for the implementation of dtms are commercially available and [20, 21]. in dtms, every driver is able to monitor their own route via the driver machine interface (dmi) system. station personnel and dispatchers can monitor the whole region and drivers can communicate with stations, supervisors, and each other, eliminating the risk of blind spots in railway operations. in extraordinary circumstances, drivers and station personnel are notified immediately. the supervisors are able to control the system in cases of emergency and disable drivers with atc/atp/ats if necessary. dtms eliminates the need for field elements. dmi displays information about the situation along the road with the proper signal and gives according instructions. the most appropriate way to interact with the dispatcher and station personnel is maintained by the dtms. if the operator of the system feels the necessity, switch positions can be submitted to the driver and changed by gsm-data. the human factor for the control system is minimized in the proposed approach and investment costs are lowered by decreasing the number of personnel. a. components and communication system the main component of dtms is a computer that has access to the internet, whose function is similar to the european vital computer (evc) in ertms. the proposed system is designed to run in microsoft operating systems for the time being, but it can be modified for compatibility with linux based systems. the computer must be resistant to external disturbances such as vibration, heat, dust and shock in accordance with european standards. a 3g modem is required to connect to the internet via any operator. the gsm operator is assumed to cover the entire region and a gps device is used to obtain time, speed, and position information of the train. location data can also be received via the 3g modem for confirming the gps. a schematic diagram of signal flow and control in the region as it is currently operated is given in figure 4 and the diagram of the proposed dtms is schematically presented in figure 5. there is no need for roadside signals since all signals can be monitored from inside the locomotive. this signaling approach is a solution to the problem that roadside signals are difficult to follow at high speeds and the driver may not have sufficient time to react to a roadside signal in the conventional system. it also eliminates hazards that may arise due to roadside equipment failure or broken cables. in dtms, communication is provided by a 3g modem. if 3g connection is interrupted, the gsm/gprs support may be used. the driver manually inputs commands in accordance with supplied data and instructions by the dtms, which are displayed on the dmi screen and read out loud simultaneously by the system. fig. 4. train traffic control diagram of tmi-gsm engineering, technology & applied science research vol. 6, no. 2, 2016, 945-951 948 www.etasr.com kara and cengiz savaş: design and simulation of a decentralized railway traffic control system fig. 5. train traffic control diagram of dtms iv. software for dtms the dtms software has been created using the delphi programming language, and special attention has been paid that it complies with the rules and regulations of railway transport in turkey. the functions of all users are unified in a single package. upon arrival of the train to the station, dtms program controls the train traffic automatically. a diagram of the algorithm in terms of data flow and decision processes is given in figure 6. the driver must follow all directives on screen while dtms processes the condition of the railway, the status of the train and other data such as speed, arrival time, departure time and destination station, and displays a green or red signal on dmi to handle the train traffic. when there is no emergency situation on the line, no train approaching from opposite direction, or a contradicting order from the supervisor, it is concluded that the route is available and the train motion can be started with a green signal. the software and log-in screen are common for each dtms user. if the dtms user is a train driver, they should input the driver number and password to access the dtms interface. if the dtms user is a supervisor, then what they need to do is input the supervisor number and password, and click on the button for the supervisor screen. the log-in screen of the dtms software is shown in figure 7. examples of driver’s and supervisor’s view of dtms are given in figures 8 and 9, respectively. v. simulation of dtms a. assumptions and application area for the simulation of proposed dtms, the program has been executed in accordance with a number of assumptions and a priori knowledge about the region of application. in train traffic management, straight roads are always easier to handle and curves are generally undesirable. the speed on a straight road is higher than the speed of diverse road because of switches of the railway. if the train is for passenger transport, preferred road of train is always the road where the passenger platform exists. fig. 6. data flow and decision diagram of dtms fig. 7. log-in screen for dtms switch positions are observed by means of switch lights, and the train must stop in front of the railway switch in tmi and tmi-gsm systems. similarly, the train will stop in front of the switch, and then move according to the switch position in dtms. all roads of the station and the main lines are identified in terms of length in kilometers. this length information engineering, technology & applied science research vol. 6, no. 2, 2016, 945-951 949 www.etasr.com kara and cengiz savaş: design and simulation of a decentralized railway traffic control system combined with gps and gprs position data is processed in a database so that location can be accurately determined and reported to the system. fig. 8. driver’s view of dtms fig. 9. supervisor’s view of dtms commonly four roads in every station exist, two being in the east direction and two in the west direction. dtms permits a maximum of three trains in every station in one direction and keeps one line as a spare for a possible train in opposite direction. all trains are numbered and it is assumed that, if the train number is known, then the direction of motion, type of train, region, and maximum speed are available. in the region of application, which is the railway line between narli and gazi̇antep stations as given in figure 10, tmi-gsm is currently in use. tmi and tmi-gsm are basically two versions of the same system that differ in the used communication technology. in this area, there exists no signaling system or ats, atc, atp system, its vehicles and field equipment. this region is the test area of tmi-gsm, which has been in use for five years. dial up telephones are equipped with fixed-to cellular terminal (ftc) and trains have mobile receivers. the entire region is covered by the gsm operator. during the application of gsm-supported communication and traffic control for more than five years, the system has proven itself as a flawless control system. tmi has been improved in quality of voice communication, which has made it easier for trains in motion and at stations to contact with the tmi-gsm center, as shown in figure 2. b. simulation results train traffic control in the region of application has been simulated in three scenarios for normal operation and an unusual case. the first two simulation tests are for the assessment of the proposed system as it controls the operation of the train traffic when no risk appears. the third scenario is simulated for testing a case where the trains move unexpectedly and some unusual traffic situations occur. in scenario i, train a (ta) travels from narli to şehi̇tari̇f, train b (tb) travels from akçagöze to narli, and train c (tc) travels from şehi̇tari̇f to narli. all trains depart simultaneously. the schematic diagram of the scenario is given in figure 11. time distance diagram for the current case of tmi and the proposed dtms as simulated in accordance with the actual distances and train speeds is given in figure 12. two control methods result in the same travel times and dispatching schedules for this case. evidently, dtms follows accurately the planned train traffic, but does not improve the travel times. scenario ii considers a more complicated traffic schedule. here, ta and tb are supposed to travel from narli to şehi̇tari̇f, while tc and train d (td) will move in the opposite direction from akçagöze and şehi̇tari̇f to narli, respectively. diagram of the scheduled train traffic for scenario ii is presented in figure 13. simulation results reveal that both tmi and dtms give the same time distance diagram that is presented in figure 14. in this scenario, train traffic is controlled accurately as in tmi automatically by dtms, and travel times are the same. fig. 10. region of application for dtms simulations: narlı-gaziantep railway line engineering, technology & applied science research vol. 6, no. 2, 2016, 945-951 950 www.etasr.com kara and cengiz savaş: design and simulation of a decentralized railway traffic control system in scenario iii, as ta approaches şehi̇tari̇f, the driver is informed that all roads at the station are occupied by four trains at halt. in this scenario, tmi and dtms yield different time distance diagrams. tmi, which manages this traffic situation using dispatchers’ commands, keeps ta waiting at the nearest station to şehi̇tari̇f until a road at the station is evacuated. however, dtms takes into account the departure time of tb and estimated travel time of ta, and reaches the conclusion of a vacant road at destination. consequently, dtms permits a continuous trip from narli to şehi̇tari̇f. travel times of trains and total time saved by dtms are given in table i. fig. 11. scheduled train traffic in scenario i fig. 12. time distance diagram for scenario i with tmi and dtms fig. 13. scheduled train traffic in scenario ii fig. 14. time distance diagram for scenario ii with tmi and dtms fig. 15. scheduled train traffic in scenario iii fig. 16. time distance diagram for scenario iii with tmi in table i, travel time is the total duration of time from departure to arrival, and dwell time is the total extra time spent at the stations when the train is at halt, which excludes loading engineering, technology & applied science research vol. 6, no. 2, 2016, 945-951 951 www.etasr.com kara and cengiz savaş: design and simulation of a decentralized railway traffic control system and unloading times. total time saved by dtms in comparison with conventional tmi is at the last column. this saved time is generally a result of zero dwell time in dtms, but train speeds between stations are also adjusted by dtms for flawless operation, which results in saved time being less than or equal to the dwell time for each train. fig. 17. time distance diagram for scenario iii with dtms table i. travel and dwell times for tmi and dtms, and time saved for scenario iii (all times in minutes) train travel time for tmi travel time for dtms dwell time for tmi dwell time for dtms time saved by dtms ta 250 205 80 0 45 tb 130 125 15 0 5 tc 160 150 10 0 10 td 145 140 5 0 5 te 105 90 10 0 15 vi. conclusion train traffic control applications and related technologies are prominently appealing to researchers in recent years. despite the progress in utilized technologies, the systems for train traffic control remain to be essentially and dominantly centralized (centralized traffic control or ctc systems). nevertheless, decentralized train traffic control may be promising as the future of automatic train control (atc). this study proposes a decentralized traffic management system (dtms), which has been designed, coded and simulated for a number of real cases. simulations are executed for three scenarios, first two of which reveal the capacity of dtms to attain the same traffic control goals of tmi automatically. this proves the power of dtms to manage a train traffic situation without the need for supervisor and extra personnel for dispatching the trains. the third scenario investigates the assessment of dtms in an unexpected traffic situation. the results prove that dtms not only gives good atc operation, but may also save significant amount of travel time, as all trains in this scenario completed the expedition without any problem in less time than tmi. dtms is currently under inspection by turkish patent institute (tpe) for domestic patenting. future work is the implementation of dtms to suitable lines of turkish railway network. vi. references [1] r. palacin, r. mauck, mapping control systems, improving european railways retrack an eu-project, eu 6th framework programme project report, 2011 [2] s. dhahbi, a. abbas-turki, s. hayat, a. el moudni, “study of the highspeed trains positioning system: european signaling system ertms/etcs”, 4th international conference on logistics, pp. 468-473, hammamet, 2011 [3] y. çetin, demiryollarında atc ve ato sistemler, m.s. thesis, dept. elec. electronics eng., i̇nönü univ., malatya, turkey, 2008 [4] turkish ministry of education, raylı sistemler teknolojisi: tmi̇ sistemi, educational report, ankara, 2011 [5] f. kitahara, k. kera, k. bekki, “autonomous decentralized traffic management system”, proc. of ieee assurance conference, pp. 87-91, chengdu, 2000 [6] s. yasunobu, s. miyamoto, “automatic train operation system by predictive fuzzy control”, in industrial applications of fuzzy control, m. sugeno (ed.), pp. 1-18, 1985 [7] g. vernazza, r. zunino, “a distributed intelligence methodology for railway traffic control”, ieee transactions on vehicular technology, vol. 39, no. , pp. 263-270, 1990 [8] f. kitahara, t. iwamoto, k. kikuchi, k. fujiwara, “widely-distributed train-traffic computer control system and its step-by-step construction”, 2nd international symposium on autonomous decentralized systems, (isads 95), pp. 93-102, phoenix az, 1995 [9] j. b. hungate, distributed positive train control system, us patent, 1999 [10] m. matsumoto, s. kitamura, m. sato, “high assurance technologies for autonomous decentralized train control system”, 6th ieee international symposium on high assurance systems engineering hase’01, pp. 220-227, boco raton fl, 2001 [11] y. fukuta, g. kogure, t. kunufuji, h. suguhara, r. ishima, m. matsumoto, “novel railway signal control system based on the internet technology and its distributed control architecture”, 8th international symposium on autonomous decentralized systems (isads'07), pp. 77-82, sedona az, 2007 [12] thales group, nettrac 6617 ctc 1000 centralized traffic control system, public report, thales security services and solutions division, 2007 [13] republic of turkey ministry of transport maritime affairs and communication, demiryolu, public report, 2013 [14] t. kara, m. c. savaş, “a distributed control system for railway traffic management”, international federation of automatic control (ifac), turkish national meeting on automatic control, tok'12, pp. 349-354, niğde university, 2012 [15] l. aliadiere, r. heinisch, “global perspectives for ertms etcs and gsm-r”, etf – editions techniques ferroviaires, railway technical publications, 2007 [16] c. r. page, ertms for australia, westinghouse signals australia, institution of railway signal engineers australian section inc, 2001 [17] alstom transport, an advanced communication based train control system for toronto, public report, 2010 [18] transport canada, railway signal and traffic control systems standards, public report, 2013 [19] a. s. tanenbaum, m. van steen, distributed systems principles and paradigms, prentice hall, us edition, 2002 [20] l. bakule, “decentralized control: an overview”, annual reviews in control, vol. 32, pp. 87-98, 2008 [21] b. g. liptak, h. eren, process software and digital network, instrument engineers' handbook, fourth edition, crc press, usa, 2012 microsoft word etasr_v12_n3_pp8640-8645 engineering, technology & applied science research vol. 12, no. 3, 2022, 8640-8645 8640 www.etasr.com guediri et al.: modeling and comparison of fuzzy-pi and genetic control algorithms for active and … modeling and comparison of fuzzy-pi and genetic control algorithms for active and reactive power flow between the stator (dfig) and the grid abdelhafid guediri university of el oued, vtrs laboratory, faculty of technology, el oued, algeria abdelhafid-guediri@univ-eloued.dz abdelkarim guediri university of el oued, vtrs laboratory, faculty of technology, el oued, algeria karim_elect@yahoo.fr slimane touil university of el oued, vtrs laboratory, faculty of technology, el oued, algeria slimanetouil@yahoo.fr received: 11 march 2022 | revised: 27 march 2022 and 31 march 2022 | accepted: 4 april 2022 abstract-this paper performs a comparison between fuzzy-pi regulators and genetic algorithm (ga) for controlling an active and reactive doubly-fed induction generator (dfig) for providing power to the electrical grid. theoretical analysis, modeling, and simulation studies are provided. control strategies were developed for both active and reactive forces in order to optimize energy production. the performance of the two control strategies was examined and compared using benchmarks for durability and reference traceability. this paper studied a system consisting of a wind turbine operating at variable wind speed and a two-feed asynchronous machine (dfig) connected to the grid by the stator and fed by a transducer at the side of the rotor. the conductors were separately controlled for active and reactive power flow between the stator (dfig) and the grid, which was achieved in this article using conventional pi and fuzzy logic controllers. the considered controllers generated reference voltages for the rotor to ensure that the active and reactive power reached the required reference values. this was done in order to ensure effective tracking of the optimum operating point and the maximum output of electrical power. system modeling and simulation were examined in matlab/simulink. dynamic analysis of the system was performed under variable wind speed. keywords-genetic algorithm (ga); fuzzy logic controller (fc); doubly fed induction generator (dfig); variable speed wind turbine; conventional pi controller; maximum power point tracking (mppt) i. introduction globally, wind power has become the fastest growing renewable energy source. wind turbine speed control is generally used to improve energy production. dfig-based wind power transmission systems offer various advantages, including reducing stress on mechanical structures and acoustic noise with the ability to control active and reactive energy. another feature of the dfig system is that the connected ac/dc/ac pwm transformers between the grid and the rotating circuit of the induction generator are designed for only a portion of the generator power [1]. wind power generation implementation was introduced on the basis of dfig, a fuzzy pi gain scheduling developed for dfig vector control units used in variable speed wind turbines [2]. upon theoretical analysis of the wind turbine and dfig processing, due to mathematical models of the system, a dfig separation control was developed based on a fuzzy-pi controller in [3]. wind power generation by dfig can be connected directly to the grid via the stator, which is driven by a direct ac/dc inverter. the relative complexities (in size or structure) of the research space and the function to be improved lead to the use of radically different precision methods [4]. while the stochastic methods are the more efficient and effective, they use processes based on stochastic exploration of the space of possible solutions [5]. among the latter, we find genetic algorithms (gas) that represent a rich and interesting family of stochastic optimization algorithms. they are inspired by concepts of evolution and natural selection and the probabilistic research based on the mechanism of natural selection and genetics. gas are highly effective and robust in a general set of problems. gas maintain a set of encoded solutions and this group is geared towards the optimal solution [6]. in order to find an ideal solution to a problem in a complex space, it is necessary to find a compromise between two goals: to explore better solutions and to aggressively exploit the search space. analytical studies have shown that gas manage this trade-off optimally [7]. ii. dfig model with stator flux orientation the orientation of the voltage and the stator flux is shown in figure 1. the dfig electrical state can be modeled using the park transform, as follows [8]: corresponding author: abdelhafid guediri engineering, technology & applied science research vol. 12, no. 3, 2022, 8640-8645 8641 www.etasr.com guediri et al.: modeling and comparison of fuzzy-pi and genetic control algorithms for active and … �� � �� v�� � r�i�� � �� ��� v�� � r�i�� � ω�φ�� v�� � r�i�� � ������ � �ω� � ω�φ�� v�� � r�i�� � ������ � �ω� � ω�φ�� (1) �� � φ�� � l�i�� � mi�� � φ� φ�� � l�i�� � mi�� � 0 φ�� � l�i�� � mi�� φ�� � l�i�� � mi�� (2) fig. 1. direction of stator voltage and flux. to obtain separate control over the stator reactive and active forces, the dfig model is required to express all quantities. this is in accordance with the concept of stator flow direction and assumes that the stator resistance is small compared to the stator reactance of a dfig of medium and high power volume, where the stator flux can be computed as [9]: � v�� � �� ��� � 0 v�� � ω�φ�� � v� (3) φ� � � ! (4) from the system of equations (2), we obtain: " i�� � � # � $ # i�� i�� � � $ # i�� (5) the stator reactive forces for dfig are: % p� � v��i��q� � v��i�� (6) ( p� � �v� $ # i�� q� � � � # � � $ # i�� (7) the electromagnetic torque is expressed as: c*+ � �p $# φ� i�� (8) the relationship of rotor voltage is given as: "v�� � r�i�� � gω��l� � $² # �i�� v�� � r�i�� � gω��l� � $² # �i�� � gω� $� # (9) iii. indirect closed loop fuzzy control in this method, decoupling is performed at the level of the outputs of the rotor current regulators with system feedback. this allows the regulation of powers. one thus distinguishes a control by a loop in a cascade of the power and the rotor current for each axis, since this makes possible to separately control the currents ird and irq and the powers qs and ps in a closed loop [10]. according to the reference torque delivered by the maximum power point tracking (mppt) control, the rotor side converter guarantees a decoupled active and reactive stator power control, ps and qs (mppt). by holding the dc bus at a steady voltage level and imposing the reactive power ql at zero, the grid side converter controls the power flow exchange with the grid through the rotor [11]. the simplified diagram of this control assembly is illustrated in figure 2. fig. 2. indirect closed loop fuzzy control diagram. iv. fuzzy inference rules the rules of inference can be described in several ways, either linguistically, symbolically or by inference matrix. in the latter case, a so-called inference matrix brings together all the inference rules in the form of a table. in the case of a two dimensional array, the array entries represent fuzzy sets of the input variables [12]. table i. rule table of the fuzzy controller ∆u e ng nm np ez pp pm pg ∆e ng ng ng ng nm np np ez nm ng nm nm nm np ez pp np ng nm np np ez pp pm ez ng nm np ez pp pm pg pp nm np ez pp pp pm pg pm np ez pp pm pm pm pg pg ez pp pp pm pg pg pg the linguistic variables are noted as follows: ng for large negative, np for small negative, ez for approximately zero, pp for small positive, pg for large positive, nm for mean negative, and pm for mean positive. e is the error, ∆e is the engineering, technology & applied science research vol. 12, no. 3, 2022, 8640-8645 8642 www.etasr.com guediri et al.: modeling and comparison of fuzzy-pi and genetic control algorithms for active and … error variation, and ∆u the controller output. the table gives forty-nine rules. for example: r1 : if e = ng and ∆e = ng then ∆u = ng. v. description and development of the fuzzy controller our goal is to control the rotor currents of a dual-power dfig. the developed controller uses the scheme proposed by [13]. this diagram is represented by figure 3. the output of the regulator is given by: v��1 � v��1 �k � 1� � du�k� (10) fig. 3. block diagram of the fuzzy controller. the considered uses of the fuzzy controller include [14]: • the triangular and trapezoidal membership functions. this choice is done due to the simplicity of implementation. • a universe of standardized discourses. • the universe of discourses is divided into seven fuzzy sets (fine tuning) for the input and output variables. a very fine subdivision of this universe on more than seven fuzzy sets does not generally bring any improvement in the dynamic behavior of the system to be regulated. • mamdani's [13] implication for inference. • the center of gravity method for defuzzification. for every gene that mutates, we take numbers 6 and r. the first can take the values +1 for an effective alternate and -1 for a negative trade. the second is a randomly generated range within the variety (0 1). it determines the value of the trade. under those conditions, the c78 gene, which replaces the mutated gene, is calculated from one of the following relationships [15]: ��� ��c78 � c7 � �c+9: � c7�;1 � r=>?@a@bcde if τ � �1 c78 � c7 � �c7 � c+7i�;1 � r=>?@a@bcde if τ � �1 (11) where cmax and cmin denote, respectively, the lower and higher limits of the price of the parameter ci, and gf≤gt represents the era for which the amplitude of the mutation cancels out. the procedure for optimizing the parameters of the regulators can be summarized by the following steps [16]: • randomly generate an initial population. • evaluate this population. • apply genetic operators (selection, crossing, mutation). • evaluate the new population created by the genetic operators. in the following, we will apply this procedure to the two regulators, classical pi and fuzzy pi. hybridization method: simplex. the complete control diagram is shown in figure 5. fig. 4. principle of optimization by genetic gradient or simplex algorithm. fig. 5. global block diagram of the command of the ga based on dfig. vi. comparison of the classic ga and fuzzy-pi regulator fuzzy logic or fuzzy set theory has attracted the attention of a large number of researchers. fuzzy logic control is regarded higher than the ga because it does not require precise mathematical models of the system [17]. its strength and simplicity are the primary reasons for its use. in this work, we will develop a blur controller. the feasibility and performance of this controller have been verified in simulations of the control element that controls the exchange of active and reactive powers generated by an asynchronous machine with a dual power supply connected to a medium voltage network by acting on rotor signals via a bidirectional converter. the obtained numerical simulation results prove the growing interest in such control of electrical systems [18]. tuning by fuzzy logic may override tuning by pi with respect to the quality of the dynamic response of the system. indeed, the latter further reduces the response time by producing a limited overshoot accompanied by weak oscillations around the setpoint. in steady state, the precision is not as good as that of a pi regulator, where the integral action eliminates the static error; this then suggests the combination of the two types of regulators: engineering, technology & applied science research vol. 12, no. 3, 2022, 8640-8645 8643 www.etasr.com guediri et al.: modeling and comparison of fuzzy-pi and genetic control algorithms for active and … • a fuzzy regulator for the transient regime and • a pi regulator for the steady state. the major drawback of fuzzy regulators is the matching of gains, ensuring system stability. in addition, the order is calculated only from two values: the error and its variation [19]. vii. simulation results the results of the wind energy system simulation (turbine + dfig) are controlled by fuzzy logic and ga. this paper displays the results of the different curves obtained by controlling the energetic and reactive forces generated at the stator level of the dfig. this allows separating the expressions of the active and reactive powers of the generator or bears those of the flow and torque. the system first starts up without load. then, an active reference force is applied: active power: • between t = 0s and t =0.2s (pref = 0 var). • between t = 0.2s and t = 0.6s negative scale (pref = -5000w). • between t = 0.6s and t = 1s (pref = 0w). reactive power: • between t = 0s and t =0.2s (qref = 0 var). • between t = 0.2s and t = 0.6s negative scale (qref = -5000 var). • between t = 0.6s and t = 1s (qref = 0 var). the simulation results will allow the analysis of the behavior of dfig magnitudes for the stator flow direction with reactive force control and rotational speed adjustment in order to maximize the active energy provided by the stator windings. for this, matlab-simulink was used. figures 6 and 7 show the simulation results of the active and reactive stator forces. according to these figures, the measured stator forces follow their active references. it is noted that this difference affects the direct rotor current, ird, and does not affect the rotor current irq, which explains why there is a separation between the active power and the ird current. fig. 6. stator active power (w). fig. 7. stator reactive power (var). fig. 8. the direct current of the rotor (a). fig. 9. the quadrature current of the rotor (a). fig. 10. the direct current of the stator (a). figures 8 and 9 show the simulation results of rotating currents along the d and q axes. figures 10 and 11 show the simulation results of the stator currents along the d and q axes. 0 0.2 0.4 0.6 0.8 1 -1 -0.5 0 0.5 1 x 10 4 time (s) ps-fuzzy ps-ref ps-ga ps-pi 0 0.2 0.4 0.6 0.8 1 -1 -0.5 0 0.5 1 x 10 4 time (s) qs-ga qs-ref qs-pi qs-fuzzy 0 0.2 0.4 0.6 0.8 1 -20 0 20 40 60 80 100 time (s) ird-fuzzy ird-pi ird-ga 0 0.2 0.4 0.6 0.8 1 -50 0 50 100 150 200 time (s) irq-ga irq-pi irq-fuzzy 0 0.2 0.4 0.6 0.8 1 -40 -20 0 20 40 time (s) isd-ga isd-pi isd-fuzzy engineering, technology & applied science research vol. 12, no. 3, 2022, 8640-8645 8644 www.etasr.com guediri et al.: modeling and comparison of fuzzy-pi and genetic control algorithms for active and … fig. 11. the quadrature current of the stator (a). viii. discussion and comparison with other works the novelty of this work is the application of ga to dfig and its comparison with the traditional pi regulator and fuzzy logic, where in previously published works the comparison between the traditional and fuzzy regulators was made only in addition to the improvement in the obtained results. good results were obtained compared to previously published works . • the base table of the mysterious console was a 7×7 table, while in previously published works it was applied to a 5×5 table. • the number of iterations increased in order to obtain more precise and better results in terms of error compared to previously published works. for a smaller number of iterations, the results were less precise. figure 12 shows the improvement of the objective function applied to these results. fig. 12. optimization of the objective function. ix. matlab simulation code kp_p=kp_pmin+(kp_pmax-kp_pmin)*kp_pde/gmax; kp_i=kp_imin+(kp_imax-kp_imin)*kp_ide/gmax; ki_p=ki_pmin+(ki_pmax-ki_pmin)*ki_pde/gmax; ki_i=ki_imin+(ki_imax-ki_imin)*ki_ide/gmax; %%%%%%%%%%%%%%%%%%%%%%% selection and crossing %%%%%%%%%%%%%%%%%%%%%%% [fun,index]= fate (fan); for i1=1:nc/2 paron(i1,:)=pop(index(i1),:); end lu=randsrc(1,1,[1:nb-1]); child (1:nc/4,:)=[paron(1:nc/4,1:lu) paron(nc/4+1:nc/2,lu+1:nb)]; child (nc/4+1:nc/2,:)=[paron(nc/4+1:nc/2,1:lu) paron(1:nc/4,lu+1:nb)]; pop=[paron ; child]; %%%%%%%%%%%%%%%%%%%%%%%% mutation %%%%%%%%%%%%%%%%%%%%%%% mu=rand(nc,nb); for i=1:nc for j=1:nb if mu(i,j)<=pm if pop(i,j)==1 pop(i,j)=0; else pop(i,j)=1; end end end end i9=i9+1; fanf(i9)=val; end figure stud (funf,'-o') title(' function optimization objective ') xlabel ('itération') ylabel('function') grid x. control law this law is a function of the error and its variation (u = f (e, ∆e)). it is given by: ujk> � uj � g∆m.∆ujk> (12) where g∆m is the gain associated with the order ujk> and ∆ujk> is the variation of the order. error e and the variation of the error ∆e are normalized as follows: % op � q p. r o∆p � q∆ p.∆ r (13) where g * and g∆ * are the scaling (normalization) factors. we vary these factors until we can have a transient phenomenon of suitable adjustment. indeed, it is the latter, which will determine the performance of the command. xi. conclusion in this paper, a fuzzy logic controller and an active and interacting ga connected to a stator network (dfig) are considered. the fuzzy controller's effectiveness test against ga and conventional pi control under different operating conditions showed the optimum and effective performance of fuzzy controller in terms of changing rotor resistance, insensitivity to torque disturbance, low response time, accuracy, and overtaking speed, as well as faster dynamics with little error in steady state under all dynamic operating 0 0.2 0.4 0.6 0.8 1 -150 -100 -50 0 50 time (s) isq-fuzzy isq-pi isq-ga engineering, technology & applied science research vol. 12, no. 3, 2022, 8640-8645 8645 www.etasr.com guediri et al.: modeling and comparison of fuzzy-pi and genetic control algorithms for active and … conditions. the simulation results showed good control behavior directed towards better performance of the fuzzy controller. its superiority is particularly evident compared to the performance of the traditional control system and the ga. however, we can observe the appearance of a small error in the response of the system controlled by this type of control. the reason for this error is that the adaptation law is not fast enough to detect sudden changes in wind speed. this drawback can be limited by short sampling time. however, this choice can increase calculation time. in practice, good continuity of control allows saves energy (increases energy efficiency), increases component service life, and system performance, with more efficiency and stability. appendix parameters of 1.5 mw dfig symbol parameter value pn rated power 1.5mw vs stator voltage 300v fs stator frequency 50hz rs stator resistance 0.012ω ls stator leakage inductance 0.0205h rr rotor resistance 0.021ω lr rotor leakage inductance 0.0204h m mutual inductance 0.0169h p pairs of poles number 2 j rotor inertia 1000kg.m 2 parameters of the turbine symbol parameters value r blade radius 35.25m n number of blades 3 g gearbox ratio 90 j moment of inertia 1000kg.m 2 fv viscous friction coefficient 0.0024n.m.s -1 v nominal wind speed 16m/s vd cut-in wind speed 4m/s vm cut-out wind speed 25m/s references [1] a. k. guediri and d. ben attous, "modeling and fuzzy control of a wind energy system based on double-fed asynchronous machine for supply of power to the electrical network," international journal of system assurance engineering and management, vol. 8, no. 1, pp. 353–360, jan. 2017, https://doi.org/10.1007/s13198-015-0367-1. 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[19] i. sefa, n. altin, s. ozdemir, and o. kaplan, "fuzzy pi controlled inverter for grid interactive renewable energy systems," iet renewable power generation, vol. 9, no. 7, pp. 729–738, 2015, https://doi.org/ 10.1049/iet-rpg.2014.0404. microsoft word etasr_v13_n1_pp9812-9818 engineering, technology & applied science research vol. 13, no. 1, 2023, 9812-9818 9812 www.etasr.com babu et al.: efficiency analysis and design considerations of a hysteretic current controlled parallel … efficiency analysis and design considerations of a hysteretic current controlled parallel hybrid envelope tracking power supply ambily babu ece department-vtu, amc engineering college, india ambily_babu@outlook.com (corresponding author) b. g. shivaleelavathi ece departmentvtu, jss academy of technical education, india shivaleelavathi1963@gmail.com veeramma yatnalli ece departmentvtu, jss academy of technical education, india veeramma71@gmail.com received: 15 october 2022 | revised: 1 november 2022 | accepted: 2 november 2022 abstract this paper presents the realization of an envelope tracking power supply (etps), for a sinusoidal envelope input signal. a parallel hybrid topology is chosen for the implementation. in this topology, a voltage-controlled class-ab linear amplifier stage and a current-controlled switching converter stage operate in parallel. a hysteretic current control scheme is employed to control the operation of the switching converter. block-level implementation of the etps is done using simulink 2017b, continuous mode simulation. simulations are performed using a sinewave input envelope signal = 1.94+ 1.2 sin(ω∙t). the input frequency varied from 1mhz to 60mhz. as the input frequency is increased, the etps moves from the linear to the non-linear region of operation. during the transition, the slew rates of the load current and the switching current match at a particular input frequency of 2mhz while the efficiency peaks. the maximum obtained efficiency while tracking the sinewave input signal is 82.3%. the way the efficiency can be optimized by focusing on the matching of the slew rates of load and switching currents is explained. also, an insight into the study of various circuit parameters and the trade-offs that the designer needs to consider while designing an etps, is provided. keywords-envelope tracking; rf power amplifiers; supply modulators; etps; etpa; mobile communication; design considerations i. introduction to cater to the ever-increasing demands of customers, rf power amplifiers in mobile communications need to deal with signals that have a very high peak to average power ratio (papr). operating such an rf power amplifier with a fixed supply is no longer a viable option, as it reduces the overall efficiency as well as battery lifetime between charges. envelope tracking is an assuring supply modulation technique [1-4] that helps improving the efficiency of such an rf power amplifier. envelope tracking power supply (etps) is a vital block of an envelope tracking power amplifier (etpa), since the overall efficiency of the etpa [5] depends on the efficiency of the etps as given by: �����= ����� * ����� (1) the primary goal of an etps designer is to develop an efficient power supply, operating at higher bandwidths. various etps topologies exist [6-9], aiming to provide high efficiency while maintaining signal fidelity. a hysteretic current controlled parallel hybrid etps, as shown in figure 1, is employed in this paper, as it operates efficiently at high frequencies. in this topology, a switching converter will track most of the low frequency signals, at high efficiency. the remaining high frequency signals will be tracked by the linear amplifier at a lower efficiency. the linear amplifier stage also needs to compensate for the ripples created by the switching converter, which is controlled by a hysteretic current control mechanism. the hysteretic current control mechanism offers a fast response engineering, technology & applied science research vol. 13, no. 1, 2023, 9812-9818 9813 www.etasr.com babu et al.: efficiency analysis and design considerations of a hysteretic current controlled parallel … since it employs a window comparator and hence is ideal for high bandwidth mobile applications [10-11]. fig. 1. hysteretic current controlled etps [12]. ii. block level implementation of hysteretic current controlled parallel hybrid etps a block level implementation [13] of hysteretic current controlled parallel hybrid etps is depicted in figure 2. a sinusoidal signal denoted by (2) is provided as the input envelope signal: �� �= �_�� + �_�� sin(� ) (2) where �� � is the instantaneous input signal, �_�� the dc component of the input signal, �_�� sin�� � the ac component of the input signal, and �= 2π.� /� , where � /� is the input signal frequency. a class ab amplifier with an operational trans conductance amplifier input stage is used as the linear stage, as shown in figure 3. a single stage buck converter is used as the switching stage, as shown in figure 4. fig. 2. block level implementation. fig. 3. linear stage. fig. 4. switching stage. linear stage current, ��� is sensed by the resistor ������ and the direction of this current controls the operation of the hysteretic controller. the value of ������ is kept very small in order to sense the current accurately. a relay block in simulink is used to function as a hysteretic controller. hysteresis h is chosen to be equal to ±7mv. initially, the linear stage starts [14-18], providing current and when the voltage drop across the ������ exceeds +7mv, the hysteretic controller will turn on the switching converter. the switching stage starts providing the majority of the load current, as given by (3). the linear stage needs to source only the difference current during this time. � !��=��" # ��� (3) as the current provided by the switching stage increases and when the ��" exceeds the � !��, the current through ������ starts flowing in the opposite direction. when the voltage drop across ������ falls below -7mv the hysteretic controller turns the switching converter off. the linear stage now needs to sink current. iii. regions of operation of hysteretic current controlled parallel hybrid etps fig. 5. regions of operation. the working of the hysteretic current controlled [19-24] parallel hybrid etps can be explained in 3 regions, as shown engineering, technology & applied science research vol. 13, no. 1, 2023, 9812-9818 9814 www.etasr.com babu et al.: efficiency analysis and design considerations of a hysteretic current controlled parallel … in figure 5. the circuit parameters considered for performing simulations in the 3 operating regions are mentioned in table i. table i. parameters considered for simulation parameter value input envelope signal � =1.94+1.2 sin(2. π.� /� .t) rsense 1ω rload 47ω l 11µh h ± 7mv vdd 5.5v a. linear region of operation in this region of operation, the slew rate of switching current is greater than the slew rate of load current as represented by (4). sr i%& > sr i'()* (4) simulations were conducted at 1mhz input frequency and the obtained results are shown in figure 6. it can be observed that the slew rate of the switching current is greater than that of the load current. as a result, the switching frequency �� of the switching stage increases and the calculated average switching frequency of the buck converter is 6.6mhz. the linear stage current is within the hysteresis values of ±7ma. fig. 6. ���, ��", � !�� at 1mhz � � . the load current is the sum of linear stage current and the switching stage current, as is clearly visible from figure 6. when the inductor current ��+ is rising, the current provided by the linear amplifier decreases and vice-versa. hence, the three currents obey (5): ��" � � # ��� (t) = � !�� (t) (5) ��" � �+ ,-.�/�0,1�/� �23.23 = 45�/� �6178 (6) now, the switching current is: ��" � � 9 ��"_�! �� � � +��"-.:;< 2-=.76 � � 9 ��"_�! �� � � + ,-. �/� �6178 (7) substituting the (7) in (6), we get: ! (t) �(t) = ������ . ��"_�! �� (t) ��"_�! �� (t) = ,>�/�0,-. �/� ?@ab@a (8) this ripple current needs to be absorbed by the linear stage and, hence, the ripple voltage due to the switching current is given by: ��"_�! �� (t) . ������ = ! (t) �(t) (9) the corresponding ripple voltage, ! (t) � (t) obtained during the simulation is given in figure 7. it can be observed that the ripple voltage falls within the hysteresis value of ±7mv. fig. 7. ripple voltage at 1mhz � � . b. matching slew rate point the slew rate of the switching current is equal to the slew rate of the load current in this operating region, as given by (10): sr i%& = sr i'()* (10) the simulation results at 2mhz input frequency are given in figure 8. fig. 8. ���, ��", � !�� at 2mhz � �. the average switching frequency of the converter is calculated to be 2mhz, which is equal to the input frequency. the linear stage current is slightly higher than the hysteresis values. the switching frequency is observed to be minimum at this point. the obtained corresponding ripple voltage is given in figure 9. it can be observed that error is slightly greater than the hysteresis value of ±7mv. c. non-linear region of operation in this operating region, the slew rate of the switching current is lower than the slew rate of the load current as represented by (11): engineering, technology & applied science research vol. 13, no. 1, 2023, 9812-9818 9815 www.etasr.com babu et al.: efficiency analysis and design considerations of a hysteretic current controlled parallel … sr c�+ < sr c !�� (11) simulations were conducted at 20mhz input frequency and the resulting current waveforms are given in figure 10. as can be observed, the switching stage is able to provide only the dc components of the load current. the linear stage needs to provide the ac components of the load current. the average switching frequency of the converter is calculated to be 20mhz. fig. 9. ripple voltage at 2mhz � �. fig. 10. ���, ��", � !�� at 20mhz � �. the error ripple voltage obtained during the simulation is given in figure 11. it can be observed that the error has significantly increased. fig. 11. ripple voltage at 20mhz � �. iv. efficiency and loss analysis of etps the efficiency of an etps is given by (12): ����� = �1;<�7d� �1;<�7d�e��612232e�f612232 (12) where g!h/��i� is the average output power of the etps, jk !���� represents the losses occurring in the linear amplifier stage, and lm !���� the losses occuring in the switching converter stage. a. linear stage losses class ab linear stage comprises of nmos and pmos devices, referring to figure 3 and the occurring total losses are the sum of the losses in nmos and pmos devices, as stated in (13): jk !���� = nopl !���� + gopl !���� (13) where: nopl !���� = (��"� !�� ) !h/ gopl !���� 9 (� !�� ��" ) ( �� !h/ ) b. switching stage losses switching stage losses comprise of conduction losses in the diode and mosfet, switching losses in the mosfet, and driver losses: sk !����= mqrstu cqr !���� + lvc uℎcrx !���� + yzc[\z !���� (14) where: mqrstu cqr !����= pn_scqs\ !����+ pn_opl !���� (15) pn_scqs\ !���� 9 �1 ^ y�. ��"_�� . !�_� !�� where d = !h/_�� / �� . pn_opl !���� = d. ��"_�� _ . �!� (16) where �!� is the on resistance of the mosfet. lvc uℎcrx !���� = ��" . !`` .( !� + !`` ) ��+_�i� /2 where ton = fa ,a b8c-d3c�de→g� and !`` = fa,a b8c-d3c�ge→d� . yzc[\z !���� = hi i� ��+_�i� (17) linear region of operation: ��+_�i� = �23.23 � ,88 _.j d (1-d. ,2_ck2 l ,2_8m l ) non-linear region of operation: ��+_�i� = � /� . v. etps simulation measurements for varying input frequency �= 1.94+ 1.2 sin(2. π.� /� t) is the input signal considered for simulation. the input frequency � /� is varied over a wide range from 1mhz to 60mhz. correspondingly, the average switching frequency of the switching converter, ��+ is noted down. linear amplifier and switching converter losses are also obtained (table ii). the efficiency is calculated by (12). it can be observed that the efficiency peaks at an input frequency of 2mhz. at this frequency, sr c�+ = sr c !�� and ��+ is minimum. as a result, switching losses are minimum, as highlighted in table ii and the efficiency peaks, as shown in engineering, technology & applied science research vol. 13, no. 1, 2023, 9812-9818 9816 www.etasr.com babu et al.: efficiency analysis and design considerations of a hysteretic current controlled parallel … figure 12. for � /� lower than 2mhz, sr c�+ > sr c !�� and hence the increased switching losses result in lowering the efficiency. for � /� higher than 2mhz, sr c�+ < sr c !�� . in this condition, the switching converter will be able to provide only the dc components of the load current. as a result, the linear amplifier needs to provide the ac components, which results in increased linear stage losses and consequently, a drop in efficiency. hence, the efficiency of a hysteretic current controlled parallel hybrid etps drops as the input signal frequency increases. table ii. efficiency analysis for varying input frequency nop (mhz) nqr (mhz) stuv (w) wxytqqzq (w) {|ytqqzq (w) } 1 6.6 0.094 0.00077 0.02151 80.8% 2 2 0.093 0.00217 0.0179 82.3% 5 5 0.094 0.03706 0.02333 60.9% 10 10 0.093 0.03915 0.02825 58.2% 20 20 0.093 0.03920 0.03821 54.6% 40 40 0.092 0.03906 0.05799 48.8% 60 60 0.093 0.03981 0.07759 44.2% fig. 12. input frequency versus switching frequency and efficiency. vi. design considerations various parameters like ������ , � !�� , l, h, �� need to be analyzed and considered while designing an etps. the main goal of an etps designer is to accurately reproduce the input envelope signal at maximum circuit efficiency. ������ is chosen to be very much smaller then � !�� to reduce the losses occurring in the current sense resistor. inductor l, hysteresis h, and supply voltage �� ~ ′ are parameters determined by the designer. the simulations conducted in section v are taken as the base to study the variations in efficiency with respect to parameter variations. the input signal considered is: �= 1.94+ 1.2 sin(2. π.� /� t) a. inductor, l variations the inductor value selected for simulation in section v was 11µh. the average slew rate of the switching current is given by (18): l� �+_�i� = _ � (1 ,-._8m ,88 ) �_�� (18) reducing the inductor value to 5µ h increases the slew rate of the switching current. sr c�" exceeds sr c !�� and hence lk !���� increases as shown in table iii. this brings down the efficiency. increasing the inductor value to 30µh reduces the slew rate of the switching current. sr c�" goes below sr c !�� as shown in figure 13. as a result, the switching stage will be able to provide only the dc components of the load current and the linear stage will be forced to provide the ac components. this increases the losses occurring in the linear stage and consequently lowers the efficiency. table iii. efficiency analysis for varying inductor values nop = 2 mhz l (µh) nqr (mhz) wxytqqzq (w) {|ytqqzq (w) }}}} 5 6.69 0.0007802 0.02147 80.1% 12 2 0.002172 0.01798296 82.3% 30 6.7 0.03757 0.02386 60.05% fig. 13. changes in slew rate as l changes. b. hysteresis variations the hysteresis value selected for the simulation was ±7mv. when it reduces to ±2mv, the switching frequency increases tremendously and hence the switching losses increase as shown in table iv. as a result, the efficiency drops. when the hysteresis value increases to ±20mv, the switching frequency of the converter reduces drastically and the switching converter now fails to provide the entire load current. as mentioned above, this results in increased losses occurring in linear stage. efficiency again drops. table iv. efficiency analysis for varying hysteresis values h (mv) wxytqqzq (w) {|ytqqzq (w) }}}} 2 0.006895 0.02237 76.3% 7 0.002207 0.01798 82.3% 20 0.03045 0.02001 65.1% c. �� variations the selected �� for simulations in section v is 5.5v. the average slew rate of the switching current is given by (16). simulations are performed at 1mhz input frequency and the corresponding slew rates can be observed in figure 14. the corresponding average switching frequency obtained from simulations is 8mhz. as the �� drops to 4.5v, the l� �+_�i� drops as shown in figure 15. the corresponding average switching frequency obtained from simulations is reduced to 6mhz. engineering, technology & applied science research vol. 13, no. 1, 2023, 9812-9818 9817 www.etasr.com babu et al.: efficiency analysis and design considerations of a hysteretic current controlled parallel … fig. 14. l� �+ and l� !�� at �� =5.5v. fig. 15. l� �+ and l� !�� at �� =4.5v. fig. 16. l� �+ and l� !�� at �� =6.5v. as the �� increases to 6.5v, the l� �+_�i� increases as shown in figure 16. the obtained corresponding average switching frequency has increased to 9mhz. hence, by varying the supply voltage �� of the switching converter, the slew rates of the switching current can be varied to match with the slew rates of the load current and thereby to obtain maximum efficiency. vii. conclusion the current paper presents a novel idea to the hysteretic current controlled parallel hybrid etps designers, that they should focus on matching the slew rates of switching and load currents for all frequencies of operation, in order to obtain maximum efficiency at all operating frequencies. in this paper, the hysteretic current controlled parallel hybrid etps is implemented in simulink and simulations were performed using a sinusoidal envelope input signal. efficiency analysis is performed by varying the input frequency from 1mhz to 60mhz. it was observed that the efficiency peaks for an input frequency of 2mhz, when the slew rates of the load current and the switching current matches. ripple voltage was found to be increasing from 5.5mv to 28mv as the region of operation moved from linear to non-linear. various circuit parameters that the designer needs to consider while designing an etps and its trade-offs are also discussed in length. the simulated etps could work for a peak efficiency of 82.3% for a switching frequency of 2mhz, while tracking the sinusoidal envelope input signal at 2mhz input frequency. one major advantage of the current work is that it is using a single level switching converter whereas most of the existing 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[24] a. shabbir, h. r. khan, s. a. ali, and s. rizvi, "design and performance analysis of multi-tier heterogeneous network through coverage, throughput and energy efficiency," engineering, technology & applied science research, vol. 7, no. 6, pp. 2345–2350, dec. 2017, https://doi.org/10.48084/etasr.1256. microsoft word etasr_v13_n1_pp10108-10115 engineering, technology & applied science research vol. 13, no. 1, 2023, 10108-10115 10108 www.etasr.com miyashita & nagao: a simplified deformation estimation method for anchor piles of sheet pile quay … a simplified deformation estimation method for anchor piles of sheet pile quay walls under kinematic forces during earthquakes kenichiro miyashita pacific consultants co, ltd, japan kenichirou.miyashita@os.pacific.co.jp (corresponding author) takashi nagao kobe university, japan nagao@people.kobe-u.ac.jp received: 6 november 2022 | revised: 26 december 2022 | accepted: 29 december 2022 abstract in the seismic design of quay walls, it is necessary to evaluate the deformation of the walls during earthquakes as well as the safety of structural members. however, conventional seismic design methods for sheet pile quay walls cannot accurately determine the degree of deformation. one reason for this is that conventional methods do not consider kinematic forces acting on an anchor pile due to the deformation of the ground. this study proposes a simplified estimation method for anchor pile deformation under the influence of kinematic forces. the results of two-dimensional finite element analysis reveal that anchor pile deformation involves rotational and translational components caused by the kinematic forces, which the conventional methods do not consider. the deformation of the anchor pile caused by kinematic forces was 30%–40% of the total deformation at the pile head. it was clarified that unlike horizontally stratified ground, shear stress is generated in the ground before an earthquake resulting in the kinematic force acting on the anchor pile during the earthquake. furthermore, a simplified method for estimating the deformation of the anchor pile under kinematic forces that uses one-dimensional seismic response analysis considering the predicted shear stress based on a theoretical equation is proposed. it was demonstrated that the proposed method accurately reproduces the anchor pile deformation. keywords-sheet pile quay wall; seismic design; finite element analysis; anchor pile; kinematic force i. introduction in the seismic design of structures, the seismic safety of structural members is the main focus of the assessment [1, 2]. quay walls are a major part of port facilities, and are constructed on soft ground in coastal areas. in the event of an earthquake, seaward deformation of the quay walls can occur, which may interfere with the use of berths, even if the structural members are safe [3–6]. therefore, in seismic design of quay walls, it is necessary to evaluate the degree of deformation of the quay wall with high accuracy. a sheet pile quay wall is a structure that is often constructed in quite soft ground. in areas where significant ground motions can occur, an anchor pile is often driven into the ground at a position away from the sheet pile to resist seismic forces. conventional seismic design of anchor piles generally only considers tie rod tension and subgrade reaction as loads acting on the anchor piles [1]. although this conventional method has been effective for designing safe cross-sections of piles to resist seismic forces, it predicts the deformation degree with low accuracy [7, 8]. various studies have shown that two-dimensional (2d) finite element analysis (fea) can accurately reproduce the seismic deformation of quay walls [9–18]. however, 2d fea is not a standard technique in design practice, due to its large computational burden. one reason for the low deformation calculation accuracy by the conventional method is because it does not consider the force generated by the deformation of the ground (kinematic force). both inertial and kinematic forces act against a sheet pile quay wall during earthquakes [19–21]. however, the conventional method only considers inertial forces, such as hydrostatic and seismic earth pressure. although several studies have been conducted on applying kinematic force to seismic design of piles [22–24], they focused on piles driven into horizontally stratified ground. to date, no studies have been conducted on piles under kinematic forces installed in uneven ground, such as that behind a sheet pile wall. this study proposes a simplified estimation method for the deformation of the anchor pile during earthquakes by kinematic forces. first, deformation of the anchor pile of a sheet pile quay wall was evaluated using 2d fea. the bending engineering, technology & applied science research vol. 13, no. 1, 2023, 10108-10115 10109 www.etasr.com miyashita & nagao: a simplified deformation estimation method for anchor piles of sheet pile quay … deformation of the anchor pile was calculated based on its curvature. by subtracting the bending deformation from the deformation of the anchor pile, its deformation due to kinematic forces was obtained. because the ground in front of the anchor pile is not horizontally stratified, but irregular, shear stress is generated in this area before an earthquake and residual deformation occurs in the quay wall during the earthquake. we clarified that this is responsible for the kinematic force acting on the anchor pile during an earthquake. this paper proposes a simplified estimation method for the deformation of an anchor pile by kinematic forces. the method applies one-dimensional (1d) seismic response analysis considering an initial shear stress distribution in the ground predicted by a theoretical equation. ii. conventional seismic design method for anchor piles the conventional method [1] assumes that an active failure region is generated behind the sheet pile and a passive failure region in front of the anchor pile. these regions are independent and do not affect each other (figure 1). here, each region is determined based on the seismic earth pressure by mononobe-okabe theory [25]. the anchor pile is located at the point where the active failure line is generated behind the sheet pile at the seabed level, which intersects the passive failure line generated in front of the anchor pile at ���/3 below the tie rod mounting height, where ��� is the depth at which the bending moment of the anchor pile first becomes zero below the tie rod mounting height according to the winkler foundation model. by installing the pile at this position, the conventional method assumes that the pile is embedded in horizontally stratified ground. figure 2 shows the application method of the winkler foundation model to the anchor pile. by applying the tie rod tension as a concentrated load and the subgrade reaction as a distributed load, the deformation magnitude and the crosssectional force of the pile are calculated by solving the differential equation (1). since the elongation of the tie rod is negligible, the deformation of the anchor pile is assumed to be equal to that of the quay wall. �� � �� � � = − � (1) where �� is the flexural rigidity of the pile, � is the depth, � is the lateral displacement of the pile at depth �, � is the subgrade reaction, and is the pile width. fig. 1. profile of the studied sheet pile quay wall. note: values in parentheses are the ones for water depth of 5.5m, el: elevation. fig. 2. forces applied to the pile. the nonlinear load–displacement relationship of a pile is often modeled considering the nonlinear characteristics of the soil [26−28]. a nonlinear relationship between � and � is considered based on experimental test results as follows [1]: � = �� ��.� (2) � = �� ���.� (3) where �� and �� are the subgrade reaction modulus (srm) values for s-type and c-type ground, respectively. the ground is classified as s-type when the n-values obtained from the standard penetration test increase with increasing depth and as c-type when the n-value is independent of the depth. the current study used (2), assuming c-type of ground. the srm is often considered to be dependent on the foundation width [29, 30], however, in the design of anchor piles, this dependence is ignored [1]. iii. methods two sheet pile quay wall profiles designed according to [1] were used. as shown in figure 1, the water depths were −5.5 and −11.0m, and the seismic coefficients were 0.10 and 0.15, respectively. the elevation of the ground surface was 4.0m. these values were set considering typical values used in design practice. tables i and ii list the ground conditions and dimensions of the structural members. the natural period of the ground was set to 0.8s for both ground conditions based on the values typically observed in the field. this study applied the fea code flip [31], which is widely used for evaluating the seismic response of port facilities. accurate reproduction of the seismic responses of various quay walls and grounds has been demonstrated using this code [32–34]. the code includes the multi-spring model for the ground [35] which considers the ground response under principal stress axis rotation. the nonlinear characteristics of the soil were modeled using the hyperbolic model [36] and (4) and (5). the hyperbolic model shows a substantial damping coefficient compared with the experimental result in the large shear strain range. thus, the code modifies the hysteresis curve to reduce the area of the hysteresis loop compared to that given by the masing rule [37] to prevent the damping coefficient from exceeding the maximum value, as shown in table i [38]. the shear modulus of the soil was assumed to be dependent on the effective confining stress, as shown in (6). � = �� (��� ����) (4) engineering, technology & applied science research vol. 13, no. 1, 2023, 10108-10115 10110 www.etasr.com miyashita & nagao: a simplified deformation estimation method for anchor piles of sheet pile quay … ! = "#$ %&' ( � (5) ) = )�* ( "+ $ "+$, )� (6) where ) is the shear modulus (kn/m2), � is the shear stress (kn/m 2 ), is the shear strain, ! is the reference shear strain, .′� is the effective confining stress (kn/m2), 01 is a parameter indicating the dependency on the confining pressure and 01 = 0.5 in based on [39]. the standard method for setting the parameters of the soil properties in [40] was followed in the present analysis. the effects of liquefaction were neglected. table i. ground condition soil 2 (t/m 3 ) 345 (kn/m 2 ) 6′45 (kn/m 2 ) 7 (°) backfill sand 2.0 58300 89.8 38 soil 1 2.0 72200 198.5 39 soil 2 2.0 125000 279.2 39 backfill stone 2.0 101250 98 40 wall friction angle (°) in front of the wall: 8 = 15 behind the wall: 8 = 0 common physical properties ℎ�*: = 0.24, ;< = 2200000 kn/m2 = = 0.33 > is the saturated unit weight, )�* is the reference shear modulus, .′�* is the reference average effective confining stress, ? is the shear resistance angle, ℎ�*: is the maximum damping coefficient, ;< is the bulk modulus of pore water, = is the poisson’s ratio. table ii. dimensions of the structural members water depth (m) sheet pile tie rod depth of embedment (m) moment of inertia of area (m 4 /m) area (m 2 /m) length (m) −5.5 −11.8 0.000104 0.00063 13.5 −11.0 −20.1 0.000791 0.00128 18.9 water depth (m) anchor pile pile length (m) are moment of inertia (m 4 /m) −5.5 14.2 0.000304 −11.0 12.5 0.000516 elastic modulus of all structural members is 200kn/mm 2 sheet pile, anchor pile, and tie rod were modeled as linear beam elements. a thin steel-pipe pile was used as the anchor pile. viscos boundaries were applied to both bottom and side boundaries. a bi-linear joint element was applied to the boundary between the wall (i.e. sheet pile and capping beam of the anchor pile) and the soil to consider wall friction. the friction between the tie rod and the soil was neglected. as the current study used 2d analysis, special care was required in setting the boundary conditions between the anchor pile and the surrounding soil. the 3d effect at the boundary between the soil and the pile was considered using a soil spring element [41]. the soil spring force �@a calculated using (7) is proportional to the ratio of the increments of shear stress to shear strain of the soil (b� b ⁄ ), where the coefficients da and ea were selected according to the diameter and installation interval of the pile: �@a = fg �h ig�� (7) figure 3 shows the fe mesh around the quay wall that was used in the calculations of water depth −5.5m as an example. the fe model had a horizontal length of 310m. the mesh height was set to transmit seismic waves up to 15hz. two ground motions were used in the calculations: the hachinohe wave and the iwakuni wave. these ground motions were calculated using seismic hazard analysis considering the source, path, and site amplification characteristics at the hachinohe port and iwakuni port, japan, with a return period of 75 years [42]. the site amplification characteristics considered here are the ones due to shallow and deep subsurfaces [43–45]. figure 4 shows the time history waveforms for the two ground motions. the maximum acceleration values were 1.0 and 1.5m/s 2 for the hachinohe wave and the iwakuni wave, respectively. the predominant frequency ranges are different between the hachinohe and iwakuni waves. the hachinohe wave is dominated by low frequencies in the range of 0.4–1.5hz, whereas the iwakuni wave is dominated by high frequencies around 4.0hz. fig. 3. fe mesh. fig. 4. ground motion. iv. results and discussion a. effect of the kinematic force on the deformation of anchor piles figure 5 presents the residual displacement of the anchor pile calculated using fea and the conventional method. the displacement of the anchor pile using the conventional method assumed the abovementioned nonlinear relationship between the pile displacement and subgrade reaction. the tie rod tensile force was set to the residual tensile force of the tie rod calculated by fea, as shown in table iii. -1.5 -1 -0.5 0 0.5 1 0 10 20 30 40 50 60 a c c e le ra ti o n (m /s 2 ) time (s) hachinohe wave -1.5 -1 -0.5 0 0.5 1 1.5 2 0 10 20 30 40 50 60 a c c e le ra ti o n ( m /s 2 ) time (s) iwakuni wave engineering, technology & applied science research vol. 13, no. 1, 2023, 10108-10115 10111 www.etasr.com miyashita & nagao: a simplified deformation estimation method for anchor piles of sheet pile quay … (a) (b) fig. 5. displacement of an anchor pile. water depth (a) -5.5m, (b) -11.0m. table iii. residual tensile force of a tie rod water depth (m) hachinohe wave (kn) iwakuni wave (kn) −5.5 216 185 −11.0 349 300 it is seen that the hachinohe wave left larger displacements than the iwakuni wave. the explanation is that the hachinohe wave is dominated by the low frequency range, which has a large influence on ground deformation, while the iwakuni wave is dominated by the high frequency range, which has a little influence on the ground deformation. the bending deformation was calculated using fea by double integration of the residual curvature of the anchor pile when both the translation and rotation angles were zero at the pile tip. translation and rotation were obtained by subtracting the bending deformation from the residual displacement. translation and rotation at the pile head were 30%–40% of the residual displacement, which cannot be neglected. the translational and rotational displacements are due to the kinematic force. no study has shown explicitly that the displacement of anchor pile includes three components, i.e. translation, rotation, and bending deformation, however, it can be confirmed by model experimental results [13] and analytical results [8] that the displacement of anchor pile includes components other than bending deformation. in contrast, the conventional method assumes that the anchor pile is restrained by the ground at its base and cannot deform, so its deformation is only the bending deformation. the kinematic force is not considered in the conventional method, which contributes to its low estimation accuracy for the deformation degree of the anchor piles. several studies estimated the amount of the anchor pile displacement assuming the occurrence of a slip line in the ground passing through the lower end of the anchor pile [15, 46]. however, it has been pointed out that the technique underestimates the displacement amount of the anchor pile [15]. to accurately calculate the displacement amount of the anchor pile, it is required to evaluate the kinematic force appropriately. when the degrees of bending deformation calculated by fea and the conventional method are compared, the depth at which the bending deformation begins to increase greatly differs. therefore, in the case of a hachinohe wave applied to a quay wall with a water depth of −11m, the deformation at the pile head obtained by the conventional method is much smaller than that calculated by fea. this difference is attributed to the differences in the resistive properties of the ground in front of the anchor pile assumed by the two methods. b. origins of the kinematic force sheet pile quay walls have a heterogeneous geometry, resulting in shear stresses being generated over a wide area of the nearby ground. figure 6 shows a contour map of the initial shear stress. the initial shear stress above the seabed level is small in the active area behind the sheet pile and large in other areas between the sheet pile and the anchor pile. the initial shear stress below the seabed level is generated over a wide area around the sheet pile quay wall. for this reason, the shear stress of the ground fluctuates around the initial shear stress value, rather than zero, at the time of the earthquake. this leads to the generation of considerable shear strain during an earthquake due to the nonlinearity of the soil, which can result in significant residual ground deformation. to examine the influence of the initial shear stress on the residual deformation of the soil, 1d nonlinear seismic response analysis of the ground was performed by applying the initial shear stress extracted from the 2d fea, where the initial shear stress refers to that at the positions shown in the red column in figure 6. this is because the 1d analysis should use the initial shear stress free from the effects of the displacement of the anchor pile, and the large initial shear stress that causes soil deformation. as a reference, 1d analysis without the initial shear stress was also performed. figure 7 compares the residual displacements of 1d analysis and 2d fea results. in the case of the 2d fea results, the translational and rotational displacements shown in figure 5 are illustrated. as expected, -14 -12 -10 -8 -6 -4 -2 0 2 4 -0.45 -0.35 -0.25 -0.15 -0.05 0.05 e le v a ti o n (m ) displacement (m) hachinohe wave -14 -12 -10 -8 -6 -4 -2 0 2 4 -0.45 -0.35 -0.25 -0.15 -0.05 0.05 e le v a ti o n (m ) displacement (m) iwakuni wave (a) water depth －5.5 m -12 -10 -8 -6 -4 -2 0 2 4 -0.45 -0.35 -0.25 -0.15 -0.05 0.05 e le v a ti o n (m ) displacement (m) hachinohe wave -12 -10 -8 -6 -4 -2 0 2 4 -0.45 -0.35 -0.25 -0.15 -0.05 0.05 e le v a ti o n (m ) displacement (m) iwakuni wave residual displacement bending deformation translation and rotation conventional method engineering, technology & applied science research vol. 13, no. 1, 2023, 10108-10115 10112 www.etasr.com miyashita & nagao: a simplified deformation estimation method for anchor piles of sheet pile quay … 1d analysis without the initial shear stress resulted in almost no residual displacement, while 1d analysis with the initial shear stress resulted in a larger seaward residual displacement. hence, the initial stress was found to act as implicit lateral force acting on the ground. the displacements determined by 1d analysis with the initial shear stress agreed well with those calculated by the 2d fea. (a) (b) fig. 6. contour map of the initial stress, water depth:(a) -5.5m, (b) -11m. (a) (b) fig. 7. comparison of displacements. water depth:(a) -5.5m, (b) -11m. c. a simplified estimation method of anchor pile deformation under kinematic force a simplified method for estimating the deformation of anchor piles under kinematic force is proposed in this paper, which does not require reference to the results of 2d fea. since a wharf constitutes irregular ground, the effective weight at the same depth is different in the ground at the front and the back of the sheet pile wall. thus, shear stress is generated in the ground. an equation for calculating the ground shear stress when a distributed load is applied, based on boussinesq's equation [47], is presented here. the simplified estimation method calculates the shear stress in the ground using the effective weight of the ground as a distributed load based on (8)-(10) and figure 8. �: (y) = k �l mn � cos 2d�(s)bs − k �l mn tu � cos 2dm bs (8) d�(z) = − tant� z[ t\ (9) dm(z) = tant� z] tut\ (10) where � is the unit weight of the ground (kn/m3), s is the depth (m), d� and dm are the angles between the vertical line and the line connecting the estimation position and the edge of the distributed load (°), ^ is the wall height (m), _` is the distance between the sheet pile wall and the anchor pile (m), and _z is the distance from the sheet pile wall to the intersection of the passive failure line generated at the bottom of the sheet pile meets the seabed (m). the passive failure angle is 17° based on the coulomb passive earth pressure. fig. 8. schematic diagram of the simplified estimation method for shear stress. the first and second terms on the right side of (8) are the shear stress due to the effective weight of the ground behind and in front of the sheet pile wall, respectively. the range of the distributed load behind the sheet pile wall was determined from the wall to the anchor pile as the range where large shear stresses are generated (based on 2d fea results). the range of the distributed load in front of the sheet pile wall is defined by the width of the passive failure region generated at the bottom of the sheet pile wall. this is assumed to be the region that mainly affects the shear stress. since the simplified estimation method does not consider active failure regions behind the wall, the shear stress is maximum at the wall position, which was thus used to calculate the shear stress in the proposed estimation method. translation and rotation by 2d fea displacement by 1d analysis with initial stress displacement by 1d analysis without initial stress engineering, technology & applied science research vol. 13, no. 1, 2023, 10108-10115 10113 www.etasr.com miyashita & nagao: a simplified deformation estimation method for anchor piles of sheet pile quay … (a) (b) fig. 9. comparison of the shear stress. water depth:(a) -5.5m, (b) -11m. (a) (b) fig. 10. comparison of the displacements under various conditions. water depth:(a) -5.5m, (b) -11m. left: hachinohe wave, right: iwakuni wave. figure 9 compares the shear stress estimated by the simplified method and that shown in figure 6. although the method somewhat overestimates the shear stress near the seabed, it generally reproduced the shear stress distribution obtained by the 2d fea from the ground surface to the seabed. at depths below the seabed, the shear stress determined by 2d fea decreased from the seabed to a position slightly deeper than the sheet pile bottom and increased at deeper depths, whereas the shear stress determined by the simplified estimation method decreased monotonically below the seabed. however, it is assumed that the shear stress below the seabed has no significant effect on the degree of deformation of the anchor pile. the deformation obtained using the 1d simplified estimation method and the translational and rotational deformation of the anchor pile obtained by 2d fea are compared in figure 10. although the deformation obtained by the simplified estimation method is a little larger than that obtained by the 2d fea at the pile head, the results are in accordance in general. therefore, the simplified estimation method is considered an effective method for estimating the degree of deformation of the anchor piles under kinematic forces. v. conclusions this study investigated the effect of kinematic forces on the deformation of the anchor pile of a sheet pile quay wall. the main conclusions drawn from the current study are:  the deformation of the anchor pile due to the kinematic forces is 30%–40% of the total deformation at the pile head, which is a non-negligible amount. therefore, the low accuracy of the deformation obtained by the conventional method is attributed to the fact that it only considers inertial and not kinematic forces.  shear stress is generated in the ground between the sheet pile and the anchor pile before an earthquake due to the irregular shape of the quay wall. this initial shear stress results in large shear deformation of the ground during an earthquake, resulting in kinematic forces acting on the anchor pile.  a simplified method was proposed for estimating the shear stresses generated in the ground around the sheet pile quay wall and the deformation of the anchor pile under kinematic forces, without reference to the 2d fea results. it was demonstrated that the simplified estimation method effectively reproduces the 2d fea results, but with a much lower computational effort. therefore, this strategy is useful for evaluating the deformation of anchor piles under kinematic force. references [1] technical standards and commentaries for port and harbour facilities in japan. tokyo, japan: the overseas coastal area development institute of japan, 2009. 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[47] j. h. michell, "on the direct determination of stress in an elastic solid, with application to the theory of plates," proceedings of the london mathematical society, vol. s1-31, no. 1, pp. 100–124, 1899, https://doi.org/10.1112/plms/s1-31.1.100. microsoft word etasr_v13_n2_pp10489-10495 engineering, technology & applied science research vol. 13, no. 2, 2023, 10489-10495 10489 www.etasr.com nguyen: expanding the data normalization strategy to the macont method for multi-criteria … expanding the data normalization strategy to the macont method for multi-criteria decision making anh-tu nguyen faculty of mechanical engineering, hanoi university of industry, vietnam tuna@haui.edu.vn (corresponding author) received: 8 january 2023 | revised: 16 february 2023 | accepted: 20 february 2023 abstract the mixed aggregation by comprehensive normalization technique (macont) is a well-known multicriteria decision-making (mcdm) method with significant benefits compared to traditional approaches. the key difference that distinguishes this method from most others is the use of data normalization techniques and aggregation approaches. macont uses three different data normalization techniques simultaneously along with two aggregation approaches throughout its evaluation process. this reduces the derivation of evaluation values and enhances the reliability of the final decision results, making the process more precise and convergent. however, the original macont emphasizes the integration of multiple normalization techniques of the same type of criteria that might perform badly in some circumstances. this paper proposes combination strategies of six normalization techniques to be coupled with the macont to help the normalized data synthetically reflect the original information and solve different types of data, criteria, and alternatives. the proposed approach was applied in four case studies. in all studies, the ranking results were compared with the other mcdm methods, producing the same best alternatives and overcoming the cases when the original macont did not work properly. keywords-mcdm; macont method; data normalization i. introduction multi-criteria decision-making (mcdm) is a common action in various fields to select the best option among available alternatives [1-4]. data normalization is one of the most important tasks in the mcdm process. however, since the process of data normalization in each mcdm method differs, the final ranking of alternatives based on different mcdm methods also varies [5]. in addition, using the same mcdm method but combining different data normalization algorithms could produce different outcomes [6]. mixed aggregation by comprehensive normalization technique (macont) is a recent mcdm method that differs from most others, especially in data normalization. in contrast to the majority of other mcdm methods, the macont utilizes three data normalization procedures simultaneously: linear sum-based normalization (n1), linear ratio-based normalization (n2), and linear max-min normalization (n3). with this distinction, the macont can reduce mistakes in comparison to other mcdm systems that employ a single data normalization method [7, 8]. this strategy has been successfully applied to the selection of supply chain management [7] and retirement service providers [8]. however, the n1 and n2 normalization procedures cannot be utilized if there is a criterion that is as minimal as feasible and whose value at some variant is zero. if the highest value of a particular as large as the feasible criterion is zero, n2 will likewise not be applied. therefore, the macont approach cannot be used by just employing n1, n2, and n3. to overcome these issues, this paper proposes combination strategies from six normalization methods for coupling with the macont. the proposed approaches were examined and compared in 4 case studies, with different types of data, criteria, and alternatives. ii. literature review data normalization plays an important role in mcdm. this process is conducted using mathematical formulas to transform the factors that have different units into dimensionless [9]. the 6 normalization methods (n1 to n6) that have been widely used for mcdm problems are [10]:  linear sum-based normalization (n1). for criteria where the biggest value is the best: ���� = ���∑ ��� ��� (1) for criteria where the smallest value is the best: ���� = � ��∑ � �� ��� (2) engineering, technology & applied science research vol. 13, no. 2, 2023, 10489-10495 10490 www.etasr.com nguyen: expanding the data normalization strategy to the macont method for multi-criteria …  linear ratio-based normalization (n2). for criteria where the biggest value is the best: ���� = ������ ��� (3) for criteria where the smallest value is the best: ���� = ��� ������ (4)  linear max-min normalization (n3). for criteria where the biggest value is the best: ���� = ������� ������ ������� ��� (5) for criteria where the smallest value is the best: ���� = ������� ������ ������� ��� (6)  linear max normalization (n4) for criteria where the biggest value is the best: ���� = ������ ��� (7) for criteria where the smallest value is the best: ���� = 1 − ������ ��� (8)  half-linear vector normalization (n5). for criteria where the biggest value is the best: ���� = ����∑ ���� ��� (9) for criteria where the smallest value is the best. ���� = 1 − ����∑ ���� ��� (10)  linear max-min sum-based normalization (n6). for criteria where the biggest value is the best: ���� = 1 − �� �������∑ !�� �������" ��� (11) for criteria where the smallest value is the best: ���� = 1 − ������#���∑ !��� ���#���" ��� (12) in these methods, yij is the value of criterion j in the alternative i, i=1÷m, j=1÷n, and ���$ is the normalization method number k. previous studies combined more than one normalization methods in coupling with different mcdms to solve certain decision-making problems. methods n1 to n5 were used in combination with combinative distance-based assessment (codas) to rank robots, air quality in an office, and lathe processing, while the results showed that n1, n2, n3, and n5 were suitable for use with the codas method [11]. the proximity indexed value (piv) method was used with n1, n3, n4, and n5 in [12], and the results showed that the piv method provided reliable decisions only when combined with n3 [12]. in a study on ranking the financial state of companies, the results showed that all methods were not suitable using the range of value (rov) method [13]. among n1, n3, n4, and n5, only n4 was proven to be suitable for coupling with the analytic hierarchy process (ahp) method to rank smart car parking [14]. in food processing decisions, n1, n2, n3, and n5 were used with weighted aggregates sum product assessment (waspas) and technique for order preference by similarity to ideal solution (topsis) methods [15]. n1, n3, and n5 were applicable in coupling with the weighted sum product (wisp) method when studying the rank of random numeric sets [16]. in a study to investigate the landing methods of unmanned autonomous vehicles, of the considered n1, n2, n3, and n5, only n2 was compatible with topsis [17]. when combining the n2, n3, and n5 with the "vlsekriterijumska optimizacijai kompromisno resenje" (vikor) method to rank a wifi network, the results showed that only n3 was applicable [18]. however, when ranking products based on the responses of the clients, only n5 among n1, n2, n3, and n5 was suitable for coupling with the vikor method [19]. in a study to combine n1, n3, n4, and n5 with waspas to classify different types of robots, n3 was determined as the most suitable [20]. using a data normalization method in a certain mcdm process is a complex problem, as normalization methods only solve the problem in certain cases. therefore, investigating the suitability of combination normalization methods with certain mcdm methods is important and must be carried out before applying it to rank alternatives. the macont has been recently developed as an mdcm method with numerous advantages. however, this technique uses simultaneously three normalization methods, and therefore it is necessary to study the suitability of the normalization methods for macont. iii. macont method this section presents the macont method for ranking alternatives as follows [7]:  establish a decision-making matrix with m alternatives and n criteria. supposing yij is the value of criterion j in the alternative m, where i=1÷m and j=1÷n.  normalize data using n1, n2, and n3.  calculate normalized balance values using: ��� = %. ���� + (. ���� + (1 − % − (). ���� (13) where λ ≥ 0 and μ ≤ 1. normally, % = ( = 1/3.  determine -�(��), -�(��) as: -�(��) = . /��∑ (/� )� ��� + (1 − .) 0� �∑ (01)� ��� (14) -�(��) = 2. 345 67� !��� − �8�� "9 + (1 − 2). min 67� !��� − �8�� "9 (15) where and . ≥ 0 and 2 ≤ 1 . normally choose . = @ =0.5. the factors pi and qi in (14) and (15) are calculated using: engineering, technology & applied science research vol. 13, no. 2, 2023, 10489-10495 10491 www.etasr.com nguyen: expanding the data normalization strategy to the macont method for multi-criteria … b� = ∑ 7� . !��� − �8�� "#�c� , i = 1÷m (16) d� = ef��g !#���#8�� "h�ei��g !#���#8��"h�, i = 1÷m (17) where =1÷n are the criteria that satisfy ��� < �8�� , and η=1÷n are the criteria that satisfy ��� ≥ �8��.  calculate the score of the alternative using: -(�� ) = �� k-�(��) + l�(m�)�∑ 6l�(m�)9� ��� n (18)  rank the alternatives using the rule that the higher score, the better the alternative. iv. combining strategies of normalization methods in the original macont, the n1, n2, and n3 data normalization methods were used simultaneously. nonetheless, these methods cannot be used if the value of yij becomes zero. this paper proposes normalization combination strategies for coupling with the macont to solve the alternative ranking problems. each combination strategy t involves three independent techniques selected from n1 to n6. table i shows the detailed combinations, where the combination t1 belongs to the original macont version. table i. strategies for combining normalization techniques combination strategy noramlization techniques n1 n2 n3 n4 n5 n6 t1 (original macont)    t2    t3    t4    t5    t6    t7    t8    t9    t10    t11    v. case studies and discussion in the case studies, the criteria were divided into two categories: category b defines the criteria related to benefit and positive effectivity with high optimal value, while category c defines the criteria related to cost and negative aspects with low optimal value. a. case study 1 table ii shows the information on 8 logistics providers [7]. three groups of criteria were applied to evaluate the general quality of these providers. a series of evaluation criteria were established from three dimensions of sustainability as follows:  the basis group: quality (c1), lead time (c2), cost (c3), delivery and services (c4), relationship (c5), and innovativeness (c6).  the expanding group: pollution controls (c7), resource consumption (c8), remanufacture and reuse (c9), green technology capability (c10), and environmental management system (c11).  the human care group: health and safety (c12), employment stability (c13), customer satisfaction (c14), reputation (c15), respect for the policy (c16), and contractual stakeholders' influence (c17). only c2, c3, and c8 belong to category c where the optimal value is small, while the rest belong to category b. the weights of these criteria were calculated as 0.048, 0.067, 0.085, 0.026, 0.017, 0.034, 0.098, 0.087, 0.065, 0.113, 0.046, 0.079, 0.047, 0.025, 0.072, 0.080, and 0.011, respectively [7]. the objective of mcdms was to identify a logistics provider that simultaneously ensured that c2, c3, and c8 were the smallest variables while the remaining criteria were considered the highest (category b). this procedure was completed using the t1 normalization strategy [7]. in addition, this case study also employed ten more combination strategies (t2-t11). steps to rank the options according to macont were applied, and table iii and figure 1 present their ranking results. the order of the alternatives with different strategies was extremely similar. in particular, all 11 combination strategies implied that option a8 was the best and option a7 was the second best. in other words, they can be applied to find the optimal solution in this case. b. case study 2 this study evaluated the quality of several robot models. a series of evaluation criteria were established, including loads (c1), maximum speed (c2), time response (c3), memory storage (c4), and working distance for the operator (c5). in these five criteria, only c3 belongs to category c, and the rest belong to b. the weights of these criteria from c1 to c5 were calculated as 0.036, 0.326, 0.192, 0.326, and 0.120, respectively. table ii. detailed figures of case study 1 [7] alt. c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12 c13 c14 c15 c16 c17 a1 22 22 850 34 3.5 13 17 11039 46 6 7 27 3.8 78 5 57 3.4 a2 34 38 1450 67 7.9 6 4 14326 37 3 2 63 5.9 89 6 66 6.8 a3 27 30 1068 29 5 21 11 12765 41 5 4 64 7.3 80 4 74 4.3 a4 19 41 729 37 4.3 26 9 10343 16 7 5 82 4.1 67 3 85 3.7 a5 15 76 697 45 2.8 8 13 6390 32 4 3 45 6.3 56 4 90 3.2 a6 32 25 1371 74 6.7 5 8 15789 24 2 4 38 5.2 92 7 69 7.5 a7 28 68 1190 63 5.4 23 14 13270 62 8 2 50 6.4 82 5 73 4.6 a8 17 64 798 42 3.1 19 16 8356 58 6 3 57 4.7 34 8 92 3.9 engineering, technology & applied science research vol. 13, no. 2, 2023, 10489-10495 10492 www.etasr.com nguyen: expanding the data normalization strategy to the macont method for multi-criteria … table iii. rank alternatives according to different data normalization strategies alt. t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 a1 4 3 3 3 3 3 3 4 4 4 3 a2 8 8 8 8 8 8 8 7 7 7 8 a3 6 6 6 6 6 6 6 5 5 5 5 a4 3 4 4 4 4 4 4 3 3 3 4 a5 5 5 5 5 5 5 5 6 6 6 6 a6 7 7 7 7 7 7 7 8 8 8 7 a7 2 2 2 2 2 2 2 2 2 2 2 a8 1 1 1 1 1 1 1 1 1 1 1 fig. 1. the graphical of the alternative ranking. table iv presents the figures for seven robot models [21, 22]. the best alternative was the one where c3 was the smallest and the other four criteria had the highest values. in this instance, the codas [21], ranking of the attributes and alternatives (r), and collaborative unbiased rank list integration (curli) [22] methods were also used to determine the best one. table v and figure 2 illustrate the alternate rankings when the macont was combined with 11 data normalization combination methods, along with other mdcms. the ranking alternatives using the macont with all forms of data normalization combination strategies were identical and correspond to the results obtained by employing r and curli. in addition, a2 was determined to be the optimal selection in every circumstance, even when using the codas method. when paired with the macont method, all these data normalization methods were found to be adequate. table iv. figures of case study 2 [21, 22] alt. c1 c2 c3 c4 c5 a1 60 0.4 2540 500 990 a2 6.35 0.15 1016 3000 1041 a3 6.8 0.1 1727.2 1500 1676 a4 10 0.2 1000 2000 965 a5 2.5 0.1 560 500 915 a6 4.5 0.08 1016 350 508 a7 3 0.1 1778 1000 920 fig. 2. graphical representation of the alternative ranking. table v. rank alternatives according to different data normalization combination strategies alt. macont codas r curli t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 a1 3 3 3 3 3 3 3 3 3 3 3 3 2 2 a2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 a3 4 4 4 4 4 4 4 4 4 4 4 2 4 4 a4 2 2 2 2 2 2 2 2 2 2 2 5 3 3 a5 5 5 5 5 5 5 5 5 5 5 5 7 5 5 a6 7 7 7 7 7 7 7 7 7 7 7 6 7 7 a7 6 6 6 6 6 6 6 6 6 6 6 4 6 6 c. case study 3 this study was based on data collected from multiple grinding procedures, where the performance was measured and assessed based on three criteria: the arithmetic average of the absolute values of the profile heights (c1), the average value of the absolute values of the heights of the five highest-profile peaks and the depths of the five deepest alleys (c2), and the material removal capacity (c3) (table vi). c1 and c2 belong to category c, in contrast to c3 which belongs to category b [23]. the weighted sum model (wsm), the weighted product model (wpm), and topsis were also used for the mcdm with the weights of c1, c2, and c3 being 0.1932, 0.1998, and 0.6070, respectively [23]. table vii and figure 3 show the rankings using the macont with 11 combination strategies and the wsm, wpm, and topsis methods. table vii and figure 3 show that the results of ranking alternatives using the macont with different strategies are similar. in addition, a10 was determined to be the optimal choice in every 0 1 2 3 4 5 6 7 8 9 t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 a1 a2 a3 a4 a5 a6 a7 a8 r a n k 0 1 2 3 4 5 6 7 8 a1 a2 a3 a4 a5 a6 a7 r a n k engineering, technology & applied science research vol. 13, no. 2, 2023, 10489-10495 10493 www.etasr.com nguyen: expanding the data normalization strategy to the macont method for multi-criteria … circumstance, even when using the codas method. in other words, when paired with the macont, all 1 data normalization methods were found to be adequate in this scenario, and equivalent to wsm, wpm, and topsis. hence, each data normalization combination strategy can be used to precisely identify the optimal solution in this case study. fig. 3. graphical representation of the alternative ranking in general, there are substantial differences between the 3 case studies listed above, including distinct fields, number of possibilities, and number of criteria. however, it is remarkable that the optimal solution was always determined when the macont was applied with various strategies. the best choice chosen by the macont was similar to the best alternative determined by other decision-making methods. moreover, the macont method was compatible with each strategy, pointing out its applicability and convenience. table vi. the figures of case study 3 [23] alt. c1 c2 c3 a1 2.6 12.6 0.75 a2 3.1 14.2 3 a3 3.7 15.3 6.75 a4 1.8 6.4 3 a5 2.3 9.8 9 a6 2.8 12.8 4.5 a7 0.9 4.1 6.75 a8 1.6 7.6 4.5 a9 2.1 9.7 13.5 d. case study 4 assuming that there is a ranking problem for 5 alternatives (a1-a5), each alternative involving 4 criteria (c1-c4). table viii presents the calculated values of the criteria. c1 and c2 belong to category b, whereas c3 and c4 belong to c. without losing generalization, the weights of the 4 criteria were chosen equal to 0.25. as shown in table viii, the value of c1 in alternative a2 was zero, which was the highest value among the 5 alternatives. therefore, neither (3), (7), and (8) nor n2 nor n4 can be used. the normalization combinations t1, t2, t3, t4, t5, t6, t7, t8, t9, and t11 do not function properly due to their dependence on n2 and n4. this phenomenon shows that in some divergent cases, the macont method cannot be used to rank the alternatives when only using t1. table vii. rank alternatives according to different data normalization combination strategies alt. macont wsm wpm topsis t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 a1 9 9 9 9 9 9 9 9 9 9 9 9 9 9 a2 8 8 8 8 8 8 8 8 8 8 8 5 6 8 a3 4 4 4 4 4 4 4 4 4 4 4 2 2 4 a4 6 6 7 6 6 6 6 6 6 6 7 8 8 7 a5 3 3 2 3 2 2 2 2 3 2 2 3 3 2 a6 7 7 6 7 7 7 7 7 7 7 6 4 4 6 a7 2 2 3 2 3 3 3 3 2 3 3 6 5 3 a9 5 5 5 5 5 5 5 5 5 5 5 7 7 5 a10 1 1 1 1 1 1 1 1 1 1 1 1 1 1 table viii. the criteria values alt. c1 c2 c3 c4 a1 -4 2.2 5 32 a2 0 1.8 1 19 a3 -3 2.4 4 41 a4 -3 2.5 0 35 a5 -1 1.6 -6 21 since c3 at a4 is zero, (2) and (4) along with n1 and n2 cannot be used, the combinations t1 through t7 fail. in other words, the macont cannot be used to rank alternatives if the t1 normalization combination is used alone. according to the two scenarios analyzed above, only t10 can be coupled with macont to rank this problem. to verify the macont coupling strategy with t10, the ranking result was compared with the results of the topsis and piv methods. these methods were chosen because they do not use (2), (3), (4), (7), and (8). furthermore, topsis is considered the most popular mcdm [24, 25], and piv was proven to have a lower reverse phenomenon rate [26, 27]. both topsis and piv methods are only used (1) for normalizing data. detailed procedures for these methods can be found in [24-27]. table ix shows the ranking results for this problem. the comparison shows that the ranking result using the macont algorithm with the normalization combination t10 was the same as the topsis and the piv. this demonstrates the effectiveness of the proposed combination of macont and t10 to classify problems when the other methods cannot be used. table ix. ranking results comparison among different methods alt. macont + t10 topsis piv a1 5 5 5 a2 2 2 2 a3 4 4 4 a4 3 3 3 a5 1 1 1 0 1 2 3 4 5 6 7 8 9 10 a1 a2 a3 a4 a5 a6 a7 a9 a10 engineering, technology & applied science research vol. 13, no. 2, 2023, 10489-10495 10494 www.etasr.com nguyen: expanding the data normalization strategy to the macont method for multi-criteria … vi. conclusion this paper proposed 10 combination strategies of normalization techniques for integration with macont. four case studies were conducted independently, in which the type of data, the number of criteria, and the alternatives varied to assess the efficiency and the response capacity of the proposed methods. the conclusions are drawn as follows:  when combining all 11 data normalization strategies with the macont method, the optimal solution was always the same as the optimal solutions when using the other mcdm methods.  when yij = 0, the normalization strategy t1 cannot be adapted to determine the final result. to overcome this issue, a new normalization strategy (t10) was presented, which can be applied to rank alternatives.  this study combined and investigated only 6 data normalizing methods that result in 11 distinct data normalization combination strategies. future research should 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[22] hanoi university of industry, faculty of mechanical engineering and d. d. trung, "comparison r and curli methods for multi-criteria decision making," advanced engineering letters, vol. 1, no. 2, pp. 46–56, jul. 2022, https://doi.org/10.46793/adeletters.2022.1.2.3. [23] c. m. rao, k. j. rao, and k. l. rao, "multi-objective optimization of mrr and rz using topsis," international journal of engineering sciences & research technology, vol. 5, no. 9, pp. 376–384, jun. 2016, https://doi.org/10.5281/zenodo.154209. [24] d. d. trung, "a combination method for multi-criteria decision making problem in turning process," manufacturing review, vol. 8, art. no. 26, 2021, https://doi.org/10.1051/mfreview/2021024. [25] d. d. trung, "application of topsis and piv methods for multicriteria decision making in hard turning process," journal of machine engineering, vol. vol. 21, no. 4, pp. 57-71, 2021, https://doi.org/ 10.36897/jme/142599. [26] d. d. trung, "the combination of taguchi – entropy – waspas – piv methods for multi-criteria decision making when external cylindrical grinding of 65g steel," journal of machine engineering, vol. vol. 21, no. 4, pp. 90-105, 2021, https://doi.org/10.36897/jme/144260. engineering, technology & applied science research vol. 13, no. 2, 2023, 10489-10495 10495 www.etasr.com nguyen: expanding the data normalization strategy to the macont method for multi-criteria … [27] d. d. trung, h. x. thinh, and l. d. ha, "comparison of the rafsi and piv method in multi-criteria decision making: application to turning processes," international journal of metrology and quality engineering, vol. 13, 2022, https://doi.org/10.1051/ijmqe/2022014. microsoft word etasr_v13_n2_pp10505-10510 engineering, technology & applied science research vol. 13, no. 2, 2023, 10505-10510 10505 www.etasr.com stan & zisopol: modeling and optimization of piston pumps for drilling modeling and optimization of piston pumps for drilling marius stan mechanical engineering department, petroleum-gas university of ploiesti, romania mstan@upg-ploiesti.ro dragos gabriel zisopol mechanical engineering department, petroleum-gas university of ploiesti, romania zisopol@zisopol.ro (corresponding author) received: 25 january 2023 | revised: 20 february 2023 | accepted: 28 february 2023 abstract this study highlights the operational and practical advantages of using triplex mud pump systems in favor of duplex systems to optimize drilling capabilities under specific operational conditions. additionally, the material selection of the piston subassembly was analyzed and simulated under operational parameters in solidworks to determine the advantages of using hnbr over nbr elastomer materials. keywords-pumps; piston; elastomer; finite element method; analysis i. introduction mud pumps ensure the flow required for the drilling rig process within the circulation system, as shown in figure 1. mud pumps are powerful machines that pull the drilling fluid from the tank, inject it through the drill rods to and from the foot of the well, and bring the fluid loaded with detritus resulting from the drilling process to the surface [1]. in optimal operating conditions, mud pumps consume more than 60% of the power used in the rotary drilling process. two, to four mud pumps are normally used in drilling rigs, mainly in turn, while others are kept as spare parts in the event of a failure at the main working pump. sometimes the pumps are tied together to lift large amounts of mud to the surface [1-4]. modifications to the construction type of pump are required by the drilling process, such as types 3.1, 2.2, and 6.1. pumps 3.1 and 6.1 are high-flow and medium-pressure, and 2.2 are high-pressure pumps with a smaller and more uniform flow. mud pumps must be able to achieve a pressure of 1400 bar, within the individual power limit of 1830kw. ii. technical and theoretical bases of mud pump calculation mud pumps generate hydraulic energy to achieve efficient and optimized drilling [1]. research conducted in rock dislocation laboratories to develop a new drilling technology led to the practical conclusions shown in table i. a. piston size calculation the piston metal disc is calculated as a circular plate embedded in the cylindrical hub of diameter dp=80mm, under pressure pr=8.6347mpa, and a contour load given by the friction force between the piston and the cylinder, fr=108n. the maximum unit efforts are calculated for circular with interior diameter constraint [1]: ����� = �� � ℎ � ��⋅��� ℎ � (1) �� = −0.405 , � = −0.121 , �� � = −0.71 , and � � = −0.213. where ����� is the maximum radial tension, �� is the stiffness constant of the plate in the radial direction, �� is the load force, ℎ� is the thickness of the plate, � is the stiffness constant of the plate in the axial direction, �� is pressure, and �� is the radius. the area of maximum stress is the upper area of the hub. the unitary efforts are: � = − � !!"� (2) �� = − ! �"� (3) �# = −86.347 (4) where � , ��, and �# are the main tensions, and thickness h is calculated according to the energy theory of rupture: �&'"() = *� � + ��� + �#� − ,� �� + ���# + �#� ≤ �� (5) where σechiv is the equivalent stress in the stress resistance theory. the piston is made of e355 steel, which is a highstrength and low-alloy steel, good for manufacturing. it is allowed �� = 120n/mm2. equation (2) admitted h=20mm to calculate the sizing of the lantern lid. the cover of the lantern is required by a uniformly distributed pressure corresponding to engineering, technology & applied science research vol. 13, no. 2, 2023, 10505-10510 10506 www.etasr.com stan & zisopol: modeling and optimization of piston pumps for drilling the test pressure. the lid can be assimilated with a doublerecessed circular plate pb=19.4mpa and r=100mm. table i. working parameters of pumps column [in] /0 1 23 " /1 1 53 " 6 7 53 " 0 7 53 " q [dm 3 /s] 104 69.60 34.20 16.50 p [mpa] 8.6347 12.8860 7.56512 12.91255 fig. 1. circulation system diagram: 1: battle, 2: suction pipe, 3: mud pump, 4: pushing pipe, 5: shock absorber, 6: charger, 7: hydraulic hose, 8: hydraulic head, 9: drilling rig, 10: screed holes, 11: annular space, 12: gutter system, 13: cleaning device. fig. 2. piston calculation scheme. fig. 3. lantern cover calculation scheme. 8 = − �9 ⋅ �2 : :� ; 1 � ⋅ : :� ⋅ ,�<-= = − 8 > : :� ; 1 � ⋅ : :� ⋅ ,�<-= = − �9 ⋅ � 2 ⋅ > (6) where t is the cut force, pb is the pressure on the gross surface of the piston, r is the radius, d is the rod diameter, and d is the cylindrical bending stiffness of the plate [1]: ?@ = −a ⋅ > ⋅ :< :� ⇒ ?@ = −a ⋅ > ⋅ �9 16 ⋅ > ⋅ ,c � − 3 ⋅ � � ?� = −> ⋅ :< :� ⇒ ?@ = −> ⋅ �9 16 ⋅ > ⋅ ,c � − 3 ⋅ �� (7) where ?@ , ?� is the bending moment in the tangential or radial direction of the circular plate. table ii shows the results for r=r. table ii. results for � = c efforts in plate mθ mr values[kn] -8.08 -24.25 unitar tensions in plate σθ σr values relations calculus for thickness h [kpa] 14.550/h2 4.848/h2 the resistance condition is given by: �� ⋅ �@ > 0 ; |�� | ≤ �� ; |�@ | ≤ �� (8) the lantern cover is made of e355, aisi/sae/astm 1024, with σα=180n/mm 2 and h=35mm. double-acting mud pumps have two-sided active pistons, and single-acting pistons use either plunger-type pistons or single-sided active pistons. α single-sided active piston has only one construction seal that is structurally similar to that of a two-sided active piston and removable seals. this lining is met on the back with a thick cloth insert that stops discharge. the piston rod connects the piston and the crosshead. at both ends of the piston, the rod ends with a conical and a cylindrical threaded part that connects to the piston body and the cross-head or with the extending rod [5-6]. the rod and the piston have parts such as the connecting thread, the conical head of the rod, and the interchangeable piston hole, as regulated by the api 7k norms. b. determination of the efforts in the piston rod figure 4 shows the forces acting on the piston rod. fig. 4. piston rod loading scheme. engineering, technology & applied science research vol. 13, no. 2, 2023, 10505-10510 10507 www.etasr.com stan & zisopol: modeling and optimization of piston pumps for drilling � = �� + �� (9) where ft is the total force acting on the piston rod for the single-acting triplex pump, fp is the force due to pressure on the active face of the piston, and ff is the friction force that appears between the jacket and the piston. �� = f ∙ h � i ∙ � (10) where � is the pressure acting on the piston face. �� = µ ∙ k ∙ > ∙ l1 (11) where μ is the coefficient of friction, μ = 0.02 …0.1, n is the normal reaction of the cylinder-piston interaction, d is the piston diameter, and l1 is the length of the sealing element. c. calculation of piston thickness the thickness of the piston metal disc is calculated by considering the disc as a circular plate embedded in the cylindrical hub of diameter :n subjected to pressure. figure 5 shows the piston loading diagram. this problem can be solved by considering the symmetrically charged flat plates, as in figure 6. fig. 5. piston rod loading pattern. fig. 6. charging scheme corresponding to symmetrically charged plates. fig. 7. piston-cylinder concentricity for mud pumps: 1: the insertion end of the piston, 2: piston lining; a nominal diameter tolerance. iii. modeling and simulation a. the 7k api recommendations for design basics according to the api 7k standard, mud pumps are piston pumps that have certain construction bases. the most important considered for this study are:  the main load-bearing components perform the pump discharge pressure, except for consumables and shut-off components such as gaskets, pistons, piston rods, seals, valves and seats, caps, clamps, bushings, and fasteners.  pressure-evaluated components must be subjected to a test pressure 3.5 times higher than the operational working pressure. hydraulic testing is performed according to api chapter 8.7.  the design of the suction components of the mud pump of the hydrostatic circuit must take into account that the suction pressure during the test will have a value twice higher than the one required by the applicant.  for double-acting pumps, the fluid outlets from the mud pump cylinders and from the piston body.  mud pump pistons must match the standard concentricity of the piston rod. the outer diameters of the piston must be suitable for the use of gaskets or cylinders with increases or changes in diameter. the standardized dimensions of the main components of mud pumps are presented in the appendices of the api 7k standard. for example, annex c provides recommendations for the mud pump piston, terminology, and maintenance, while the provisions regarding the outlet area of the drilling fluid in annex c.3 are very important. the recommendations for mud pump piston standardize the terminology for the main parts of the mud pump, except for a relatively small number of related parts. this provides a common language for the industry, which is especially important for communication. b. 3d modeling of the piston mud pump piston modeling is performed using 3d graphic modeling and a finite element calculation program. this piston was made of low alloy medium carbon steel 34crmo4 in sr en 10083-3 and made of an nbr elastomer with an elastic modulus of 3.99mpa [7-9]. according to [10], the material yield strength is σc=450mpa. the pump piston was machined in steps and its diameter varied in different sections [8]. the piston assembly had 190.5mm outer diameter and 100mm thickness. the function 'sketch' was used to model the metal part of the piston and choose the drawing plan, as seen in figure 9. after that, a circle was drawn on the front plane, which would be extruded to obtain a cylindrical body to represent one of the steps of the drive piston. the 2d sketch of the lower diameter was made, after which the extrusion was to create the 3d shape of the metal part of the piston, as seen in figure 10. then, the piston elastomer was made using the same steps. instead of the 'extrude' function, the 'cut extrude' was used to get the desired shape for the metal piston, as seen in figure 11. finally, an assembly was made that consisted of the metal part of the piston and the elastomer. engineering, technology & applied science research vol. 13, no. 2, 2023, 10505-10510 10508 www.etasr.com stan & zisopol: modeling and optimization of piston pumps for drilling fig. 8. drawing plane of the piston. fig. 9. metalic part of the piston. fig. 10. piston elastomer. fig. 11. complete assembly of the piston. c. finite element analysis of 3pn-1000 pump piston strain study to rated operating pressure a simulation was performed to complete the study. the piston components were: the metal piston had a material of 34crmo4 and the elastomer was nitrile butadiene rubber (nbr) [8, 12]. a full 3d model was chosen for the finite element analysis [13]. a fixed face was established, that defined the metal part of the piston as fixed. this action can be done from the study toolbar by right-clicking on "fixture", then choosing the "fixed geometry" module [14]. fig. 12. defining the fixed face of the piston. fig. 13. pressure applied to piston elastomer (rear). fig. 14. pressure applied to the piston elastomer (outside). the next step was to define the nominal pressure to which the piston would be subjected, namely the pressure between the elastomer and the top cover of the piston jacket. the nominal pressure was set to 156mpa. the same procedure was applied to the upper part of the elastomer for the pressure between the piston sleeve and the elastomer. then a simulation was performed to examine how the piston deforms under the assigned loads. as can be seen in figures 15-18, the deformation of the piston was free, that is, the piston deformed in an open space but not inside the cylinder. due to this deformation, there is a possibility of fluid leakage between the piston sleeve and the piston. table iii presents the principal properties of the nbr material for the first simulation [2, 5, 9]. the dimensions for the finite element analysis were d=133/5mm, d=80mm, and h=40mm, which impact the results obtained from the analysis. the area that suffers the most engineering, technology & applied science research vol. 13, no. 2, 2023, 10505-10510 10509 www.etasr.com stan & zisopol: modeling and optimization of piston pumps for drilling deformation is marked in red. the images show the initial position of the piston elastomer and how it deformed. table iii. material of the nbr elastomer [11] property value units elastic modulus 3990000 n/m 2 poisson ratio 0.49 n/a shear modulus 2900000 n/m 2 mass density 1000 kg/m 3 tensile strength 13787100 n/m 2 compressive strength n/m 2 yield strength 9237370 n/m 2 thermal expansion coefficient 0.00067 /k thermal conductivity 0.14 w/(m•k) fig. 15. deformation of the nbr piston at ½ from the nominal pressure. fig. 16. deformation of the piston with nbr at nominal pressure. table iv. material of the hnbr elastomer property value units elastic modulus 3430000 n/m 2 poisson ratio 0.49 n/a shear modulus 2900000 n/m 2 mass density 1200 kg/m 3 tensile strength 20787100 n/m 2 compressive strength n/m 2 yield strength 9237370 n/m 2 thermal expansion coefficient 0.00067 /k thermal conductivity 0.14 w/(m•k) in terms of stress, a "strain" graph can be used to determine the most requested point of the piston when operating at a pressure of 15.6mpa. table v shows the deformation details of the piston with the nbr and hnbr materials. fig. 17. equivalent strains of hnbr elastomer. fig. 18. deformation of the piston with hnbr. table v. results obtained from the processing of fea diagrams no . type parameter fea pressure in pump (mpa) nbr (mm) hnbr (mm) 1 equivalent strain (estrn) 35 2.84 1.94 15.6 2.499 1.447 2 resultant displacement (ures) 15.6 6.708 9.016 7.8 3.354 4.508 iv. conclusions this study investigated new types of rubber-to-gasket piston connections, namely nbr and hnbr. the mechanical performance of both was systematically studied using theoretical and finite element analysis methods. compared to the traditional criteria, the following conclusions were obtained:  simulations of nbr and hnbr piston elastomer materials [9] showed that in a mud pump with large diameter pistons operating at low pressures, the nbr can be used as it deforms sufficiently so that fluid losses are not high and the friction between the jacket and the piston is optimal.  in the case of mud pumps with small diameter pistons and high pressures, the hnbr elastomer can be used because it engineering, technology & applied science research vol. 13, no. 2, 2023, 10505-10510 10510 www.etasr.com stan & zisopol: modeling and optimization of piston pumps for drilling deforms much more easily than the nbr, the liquid losses will be lower, but instead, there would be more friction between the piston and the cylinder, but in no case excessive.  the operating season of the mud pump can be taken into account. for example, in winter, the hnbr can deform much more easily at low temperatures compared to nbr, while in summer both can be used. the stresses on the hnbr elastomer are distributed differently than those on the nbr. in the case of the hnbr elastomer, there are no longer stresses on the contact surface between the elastomer and the metal piston.  the solidworks software can perform finite element analysis studies of both parts and assemblies to validate rig performance. this capacity enables the custom rig manufacturer to improve the strength and performance of its equipment while decreasing weight, material usage, and associated costs in the process.  the material and weight of the rigs should be reduced because they are frequently assembled on the back of a truck. using professional software, linear static stress analyses can run not only on critical components but also on each sub-assembly of the piston pump. this capability allows for reducing the weight of the rigs by a small percentage while maintaining strength and performance. references [1] m. stan, metode avansate de proiectare a utilajului petrolier. ploiesti, romania: editura universităţii petrol-gaze din ploiesti, 2010. [2] d. g. zisopol, m. minescu, m. badicioiu, and m. m. caltaru, "theoretical and experimental investigations on 20 inches threaded casing connections failure under field conditions," engineering, technology & applied science research, vol. 11, no. 4, pp. 7464–7468, aug. 2021, https://doi.org/10.48084/etasr.4318. [3] m. elashmawy, "3d-cfd simulation of confined cross-flow injection process using single piston pump," engineering, technology & applied science research, vol. 7, no. 6, pp. 2308–2312, dec. 2017, https://doi.org/10.48084/etasr.1561. [4] d. g. zisopol, "experimental research concerning drill pipe geometry optimization," lucrarile sesiunii de comunicari stiintifice, vol. 4, pp. 169–178, jan. 1997. [5] d. g. zisopol, "experimental research related to the behaviour of the materials afferent to the liners and the pistons for production pumps under wear conditions," 2004, [online]. available: https://essuir.sumdu. edu.ua/handle/123456789/10739. [6] m. m. caltaru, r. g. ripeanu, m. badicioiu, and d. g. zisopol, "experimental researches to establish the optimum hardbanding technology and materials of the heavy weight drill pipe," matec web of conferences, vol. 318, 2020, art. no. 01017, https://doi.org/ 10.1051/matecconf/202031801017. [7] d. g. zisopol and a. dumitrescu, ecotehnologie. studii de caz. ploiesti, romania: editura universității petrol-gaze din ploiesti, 2020. [8] d. g. zisopol and a. dumitrescu, materiale si tehnologii primare. aplicații practice și studii de caz. ploiesti, romania: editura universitatii din ploiesti, 2005. [9] m. minescu and d. zisopol, sudarea țevilor şi fitingurilor din polietilenă de înaltă densitate. ploiesti, romania: editura universității petrol-gaze din ploiesti, 2021. [10] d. g. zisopol, m. minescu, and d. v. iacob, "a theoreticalexperimental study on the influence of fdm parameters on the dimensions of cylindrical spur gears made of pla," engineering, technology & applied science research, vol. 13, no. 2, pp. 10471– 10477, apr. 2023, https://doi.org/10.48084/etasr.5733. [11] "solidworks 3d cad design software." dassault systemes, [online]. available: https://www.solidworks.com/. [12] m. m. caltaru, m. badicioiu, a. dinita, d. g. zisopol, r. g. ripeanu, and m. minescu, "influence of chemical corrosive environment with h2s on drill strings, experimental researches," revista de chimie, vol. 71, no. 4, pp. 29–37, may 2020, https://doi.org/10.37358/rc.20.4.8040. [13] i. lambrescu and d. g. zisopol, "complex analysis of collapse strength for tubulars used in the oil and gas industry," geoenergy science and engineering, vol. 221, feb. 2023, art. no. 111275, https://doi.org/ 10.1016/j.petrol.2022.111275. [14] d. g. zisopol, d. v. iacob, and a. i. portoaca, "a theoreticalexperimental study of the influence of fdm parameters on pla spur gear stiffness," engineering, technology & applied science research, vol. 12, no. 5, pp. 9329–9335, oct. 2022, https://doi.org/10.48084/ etasr.5183. microsoft word etasr_v12_n5_pp9357-9363 engineering, technology & applied science research vol. 12, no. 5, 2022, 9357-9363 9357 www.etasr.com el-ashmawy: simulated photogrammetric data for testing the performance of photogrammetric … simulated photogrammetric data for testing the performance of photogrammetric instruments and systems khalid l. a. el-ashmawy department of civil engineering college of engineering and islamic architecture university of umm al-qura makkah, saudi arabia khalid85_2002@yahoo.com received: 26 july 2022 | revised: 12 august 2022 | accepted: 18 august 2022 abstract-the generation of mathematical photograms (photos) as data is universally accepted as the basis for photogrammetric studies. new development in the field of computer technology has had a major influence on photogrammetry. this paper aims to describe the development of a computer system called simuphotos designed to produce simulated data in different forms for testing photogrammetric methodologies, software, and instruments. simuphotos is capable of generating photogrammetric blocks with different specifications. it generates the simulated data for the whole block, strips, or selected photos. the simulated free error data include the camera interior orientation parameters, ground coordinates of points, and for each photograph, camera exterior orientation parameters, and the photo coordinates of imaged points. to increase the capabilities of the developed system, it has a special error generator to get normally distributed error(s) with arbitrary mean(s) and standard deviation(s). the obtained errors are then, if required, applied to the error-free photo and ground coordinates of points. the developed system interfaces cad technology to generate simulated photogrammetric data in dxf and raster formats which are suitable for testing the photogrammetric instruments and softcopy systems. simuphotos has been used for testing the analytical photogrammetric system photomap. the results showed that photomap is free of system error and is functional. also, the results showed that simuphotos can effectively provide a convenient, economical, and accurate testing tool for photogrammetric systems. the developed system is quite versatile and affordable. keywords-simulated photogrammetric data; numerical data; graphical data; simuphoto; testing photogrammetric systems; softcopy photogrammetry i. introduction photogrammetry has experienced significant changes caused by advances in optics, electronics, imaging techniques and computer technology. it is applied in the form of mechanical systems such as stereo plotters, combinations of mechanical and computerized systems such as analytical plotters, and fully computerized systems like softcopy systems. testing the results of the developed software or the performance (calibration) of the instrument’s mechanism requires error free and well-defined input and output data in a compatible form. generally, data enter the available photogrammetric system in the form of paper-based photographs, diapositives, or numbers or pixels. the data of actual photographs are characteristically incomplete because the object coordinates of all image points are unknown. furthermore, the actual data are full of errors that disturb the results of computations and analysis, and it is difficult to estimate how the data, the geometry of the problem, the software, and the instrument’s mechanism might affect the results. the main sources of actual data errors are the variation of the irregular photo errors from one photo to the next, the correlation of the irregular errors and the difficulty of determining their degree, incomplete elimination of systematic errors, investigation of undetected errors, poor image quality and control data, poor image identification, and inadequate redundancy of control data [1]. the specifications of data required for photogrammetric research studies include high quality stereo photographs from cameras of precisely known interior orientation, considerably more than the minimum required ground control data, so that a large number of check points may be selected for the study of error vectors. ground control data must be of considerably higher precision than the errors expected and ground control points must be suitably located, precisely described, and unmistakably identified on the photographs [2]. actual photographs taken with the best photogrammetric cameras on the best quality film may not meet the above specifications. further, available methods of ground survey cannot produce control data of the highest desired precision (1/10 micron in photo coordinates and equivalent in ground control for studying the effects of computational rounding off, and photogrammetric errors). on the other hand, entering the actual photo in pixel form causes a series of problems to image matching [3-6]. these problems corresponding author: khalid l. a. el-ashmawy engineering, technology & applied science research vol. 12, no. 5, 2022, 9357-9363 9358 www.etasr.com el-ashmawy: simulated photogrammetric data for testing the performance of photogrammetric … include foreshortened effects such as changing the value of the sampled gray level due to the elements smaller then pixel size, lab processing noise, e.g. scratches or spots on the photographic material due to uneven processing or aging chemicals, digital camera radiometric calibration differences like integration time, gray level range definition and exposure setting, digital camera noise during image digitization and textural problems such as existence of distinguishable structures, repetitive texture, hanging surfaces, ambiguous levels, and thin objects. fortunately, the problems of non-availability of error free photogrammetric data and using actual photographs for testing the photogrammetric systems and instruments can be alleviated by a combination of the simulated data generation through software and merging them with the capabilities of the computer aided drafting (cad) technology for preparation of the data in a compatible form for the photogrammetric instruments and systems. this paper deals with: • the development, description and evaluation of a system called simuphotos for automatic generation of simulated photogrammetric data in numerical and graphical forms. simuphotos is an acronym that specifies the generation of simulated photographs for testing the available photogrammetric instruments, methodologies, and systems. • the use of the capabilities of simuphotos for testing the results of a photogrammetric system called photomap [2]. ii. concept of generating the simulated photogrammetric data a block of simulated photographs for aerial platforms is planned to be obtained in much the same way as in actual photography. the present work is limited to near vertical photography. a set of mathematical photogrammetric data should consist of the following values for strips or photogrammetric blocks: • interior orientation of camera selected for photography. • ground coordinates of each exposure station. • angular orientation of each photograph. • ground coordinates of some ground points. • photo coordinates of all ground points available within the format of each photograph. to provide a means for performing computational operations, for generating the mathematical photogrammetric data, the following steps are taken: • adopting standard specifications for longitudinal and lateral overlaps, camera angular orientations (ω, φ, κ), camera displacements ( , y z b b ), etc. • assignment of the ground coordinates ( , , o o o x y z ) to each camera station in the block. • assignment of height values and planimetric positions to the ground points. • computation of photo coordinates of image points on each photograph using the collinearity condition [7]. iii. specifications for generating the simulated data the specifications for generating the simulated photogrammetric data include built-in and floating specifications. built-in specifications outline the general layout of the ground, the location of points whose values are fixed during the computational session, and the proposed photography. floating specifications refer to camera specifications and the terrain type. their values can be changed by the researcher, depending on the study aims and the available data. a. built-in specifications the following specifications were taken into account during the development of the software. they outline the general layout of the simulated block: • unit block: the maximum size of the block has been adopted to be 5 strips of 21 photographs each, to a total of 105 photographs. this block size represents the average size that is generally used in photogrammetric practice. a strip of 21 photographs may be considered as of medium length. the ground area covered by a block is variable depending on the camera and format used. • scale: the hypothetical ground system is chosen such that photos of near-vertical specification are produced at an approximate scale of 1:1. this decision conforms to the international society of photogrammetry's relevant resolution on the desirability of reporting all photogrammetric errors at the negative scale [8]. fig. 1. points transferred per photograph (single photograph numbering system). engineering, technology & applied science research vol. 12, no. 5, 2022, 9357-9363 9359 www.etasr.com el-ashmawy: simulated photogrammetric data for testing the performance of photogrammetric … fig. 2. points transferred per photograph (block numbering system). • precision of image coordinates: the photo coordinates of the image points are computed mathematically to a precision of ±0.1 micron. a precision of about ±0.1 micron may be considered high enough to reduce into insignificance the effect of image errors on photogrammetric data processing [8]. • numbering code for strip and photos: for identifying each photograph, an alpha-numerical code system is used. strips and photographs are identified by serial numbers 1 to 5 and 1 to 21 respectively. • number of points transformed per photo: on each photograph, as shown in figure 1, 30 points are selected for transformation from ground system into the photo coordinate system and 6 points (31-36) for transformation from the photo coordinate system to the ground system. of the 30 points, 9 (points 1-9) are primary, 18 (points 10-27) auxiliary, 2 (points 28 and 29) are transferred principal points from preceding and following photographs, and one is the nadir point (point 30). points 31-36 are the image (fiducial) points and their ground coordinates help in defining the extent of the photograph's ground coverage. for photogrammetric studies, primary points may be used as orientation points, while auxiliary points may be used as auxiliary orientation and scale transfer points [2]. • numbering codes for points: points are identified by 2 numbering systems, single photograph and block numbering. in single photograph numbering system, as shown in figure 1, the points are directly identified by serial numbers (1 to 36). this numbering system is suitable for all single photograph studies, for example, studying the effects of dimensional distortions [9]. in the block numbering system, the alpha-numerical code system is used for identifying each point of the block points. each of the three longitudinal sections of a strip has (n+2) and 2(n+2) primary and auxiliary points respectively, n being the number of photographs per strip. for a block with m laterally overlapping strips, there are (n+2) (2m+1) and 2(n+2) (2m+1) primary and auxiliary block points respectively. thus, the block has 23*11=253 and 2*23*11=506 primary and auxiliary points, and each strip 69 and 138 primary and auxiliary points, which are common with the adjoining strip. to differentiate the primary points from the auxiliary points, cp and ap numbering codes are added to their numbers respectively as shown in figure 2. • the block numbering system is suitable for block studies such as determination of strip deformations, studying the effects of systematic and random errors on the results of block adjustment, comparison of the results of the different procedures of block adjustment, e.g. sequential and bundle, and helping in the development of new methodologies for block adjustment and investigation of the effect of changing one or all block specifications on the results. • ground coordinates of block points: the planned x and y coordinates of the perspective center of the first photo of the first strip in the block are taken as the coordinates of block origin ( , o og g x y ). • applied mathematical model: as mentioned above, perfect perspective projection (collinearity condition [7]) from ground to photograph and from photograph to ground, and absence of all error sources have been assumed for generating the mathematical photogrammetric data. b. floating specifications floating specifications can be changed, depending on the study and the available data and are entered to the software operating system by editing the data file. • camera focal length and format: these values depend on the camera used. • x and y ground coordinates of block origin: x and y ground coordinates of block points and camera stations are referred to the coordinates of block origin , . o og g x y • height variation: height variation of ground points is taken as a percentage of the flying height. this factor defines the terrain type. • longitudinal and lateral overlaps: these are entered as percentages of the width of the photograph (longitudinal%, lateral%), and are necessary for strips and block formations, and photogrammetric studies. • flight specifications: these include the values of , , , y z b b ω ϕ and κ for each of 105 photographs of the block. engineering, technology & applied science research vol. 12, no. 5, 2022, 9357-9363 9360 www.etasr.com el-ashmawy: simulated photogrammetric data for testing the performance of photogrammetric … iv. the simuphotos system software suites designed to support cad have become popular. the most well-known software package in this regard is autocad, from autodesk, inc. [10]. of equal importance has been the development of software designed to utilize efficient user interfaces, e.g. window-driven and menus [11]. these advances in technology have enabled the development of the simuphotos system. the applied methodologies in simuphotos development provide automatic generation of the simulated data in numerical and graphical forms. the numerical form enables the testing of analytical processing methodologies and systems. the graphical form in drawing exchange format (dxf) and numerical forms are used for testing photogrammetric instruments, e.g. stereoplotters and analytical plotters. furthermore, the graphical form is suitable for testing the digital systems by scanning the plotted photos using ccd cameras or scanners. also, the graphical form in dxf format can be directly converted to pixel or raster format using the capabilities of software such as coreldraw [12] and autocad [10]. one of the most important aspects of automatic generation of graphical simulated data is the prevention of manual graphical presentation, e.g. using hand or software drawing of the numerical simulated data which is time consuming and may have additional mistakes. the structure of generating the simulated data process is shown in figure 3. four main modules (generating simulated photos mathp module, generating autocad files dxfgen module, control interface, and autocad software) can be seen. fig. 3. simuphotos system architecture and its intermediate communication to the hardcopy devices. central to the system is the mathp module that reads the floating block specifications from the input data file (3 data files are available to the system) and uses these specifications along with built-in block specifications for generating the free error simulated photos. the module has a special error generator to get normally distributed error(s) with arbitrary mean(s) and standard deviation(s). the obtained errors are then, if it is required, applied to the error free photo and the ground coordinates of points of the generated blocks. mathp module stores the generated data in ascii format for further processing. mathp module is a window-driven program consisting of two master windows. the main master window consists of 5 menus, depending upon the user's choice. these menus are basically for generating the simulated data for the whole block, selected strips and selected photos, helping the user and exiting to the system main window. the second master window consists of 2 menus for choosing the numbering system, single photo or block numbering system. also, the user interface helps the user to move across the generated data and send the required data to the available hardcopy interfaces. the dxfgen module reads the generated data and prepares the suitable autocad drawing files in dxf format. a menu pad is provided, allowing the user to work without knowledge of autocad command sequences. each key on this pad invokes a different mapping function. map scale, legends, title blocks, border, and coordinate gridding can be entered. the dxfgen module is supported by default values for automatic map generation without user choices. the main functions of using autocad are (1) enabling the user to add his modification(s) to the resulting map, (2) sending the generated maps to the hardcopy interfaces, and (3) engineering, technology & applied science research vol. 12, no. 5, 2022, 9357-9363 9361 www.etasr.com el-ashmawy: simulated photogrammetric data for testing the performance of photogrammetric … converting the dxf file into a raster format file, such as bmp, jpg, png, and tiff, with the required resolution. the simuphotos system generates the necessary data for both analytical and digital processing systems. basically, these data are classified as numerical and graphical simulated data. • numerical simulated data: they include photos per each strip, ground coordinates of the origin point, camera format, height variation, and camera interior orientation parameters and photo-oriented elements (which include photo and strip numbers, camera exterior orientation parameters, point numbers with respect to the chosen numbering system, and photo and ground coordinates of points). • graphical simulated data: they consist of the generated maps for location of the camera stations, location of points and for each photo, showing the image locations and their numbers as indicated in figures 1 and 2. v. testing photomap the photomap system [2] is an analytical data processing and presentation photogrammetric system. photomap is under continuous development and new capabilities are developed and added to widen its applications. photomap contains 7 modules namely bundle [2], self-calibration [9], dlt [13], coplanarity [9], distance-control [14], no-control [15], intersection [2] and generate [2]. simuphotos was used for generating the necessary data for testing all computational stages of the developed modules of photomap. the bundle, self-calibration, dlt, coplanarity, distancecontrol modules were developed to generate control points, compute the parameters of camera exterior orientation, and store the output in the system data bank. the intersection module utilizes the computed/known parameters of camera exterior orientation for computing the object coordinates of desired number of points for specific application. these are stored in the system data bank. the generate module reads the stored data in the system data bank and generates the desired graphical output in digital format compatible with the available cad and dtm (digital terrain model) packages for plotting and statistical error analysis. the most important function of generate module is its ability to generate the maps in dxf file format which is suitable for many commercially available gis (geographic information system) packages. testing a photogrammetric system is a complex task. it includes the availability of appropriate data for testing, decisions regarding the number and type of tests to be accomplished, photogrammetric tasks for each test to be achieved, and many other considerations. after completing the development stages, photomap was subjected to a series of tests. these tests provided an opportunity to verify that the developed system satisfies the required general performance, specifically the flexibility and feasibility of photogrammetric data processing. testing the system error and functionality of bundle and intersection modules could be offered right here. system errors consist of (a) error due to the rounding off of values throughout intermediate computations which may be minimized by using double precision computations as far as possible and (b) errors because of truncation of higher order terms while forming the linearized observation equations from the nonlinear condition equations. for instance, in bundle adjustment the errors in triangulation process may be generated because of the use of simplified linearized correction equations derived from the non-linear collinearity condition equations by truncating a few terms [2, 7]. a. planning for testing photomap the simulated photogrammetric block utilizing the depicted specifications in table i was used for testing the system error of photomap. table i. specifications for the used simulated photogrammetric block specification value a. photograph scale 1:1 b. camera format 230.0*230.0 mm c. camera focal length 150.00 mm d. longitudinal and lateral overlaps 65% and 30% respectively e. total number of points available per model 18 f. terrain configuration hilly type with height variation of 25% of flying height. b. testing the results of bundle module bundle module carries the photogrammetric operations using the following methodologies [2]: • exterior orientation determination, • bundle block adjustment. each of these methodologies has been independently tested for the system error as described below. 1) testing the system error for camera exterior orientation determination the available 18 points in the model were considered control points and this control distribution pattern was used to test the results of camera exterior orientation determination. error free photo and ground coordinates of the 18 control points and their a priori standard deviations were processed simultaneously in the bundle module. the known quantities were photo and ground coordinates of the control points and camera interior orientation parameters. the unknowns to be estimated were the 6 exterior orientation parameters of each photograph. the residual errors between the actual and the computed values of camera exterior orientation parameters were found out, along with standard errors [16] as tabulated in table ii. table ii. photomap system error for camera exterior orientation determination standard errors camera ground coordinates (μm) orientation angle (rad) x σ y σ z σ ϕ σ ω σ κ σ 0.001 0.001 0.001 0.000 0.000 0.000 * values at 1:1 photograph scale engineering, technology & applied science research vol. 12, no. 5, 2022, 9357-9363 9362 www.etasr.com el-ashmawy: simulated photogrammetric data for testing the performance of photogrammetric … these standard errors are small and negligible, and it can be concluded that bundle module is free from system error for camera exterior orientation determination. 2) testing the system error for bundle block adjustment for testing the results of bundle block adjustment, suitable location and number of control points were chosen [2]. the block size was 5 strips, each with 21 photographs. in this case, the block contained 253 and 506 control and check points respectively. error free photo coordinates of control and check points, ground coordinates of the control points and their standard deviations were processed simultaneously with the bundle module. the output was the adjusted camera exterior orientation parameters and the ground coordinates of the check points. table iii lists the standard errors for camera exterior orientation parameters and ground coordinates of the check points. table iii. photomap system error for bundle block adjustment a. camera exterior orientation parameters standard error camera ground coordinates (μm) orientation angle (rad) x σ y σ z σ ϕ σ ω σ κ σ 0.002 0.002 0.003 0.000 0.000 0.000 b. ground coordinates of check points standard error (μm)* x σ y σ z σ 0.001 0.001 0.002 * values at 1:1 photograph scale these results lead to following conclusions: • the bundle block adjustment has system error for the z coordinate larger than for planimetric (x, y) coordinates which was expected [9, 14, 15] and • the maximum system error is 0.002μm for the ground coordinates of check points, which is negligible. from the above, it is obvious that the bundle module is free from system error and that it is functional. c. testing the system error of the intersection module the ground coordinates of the 18 points of each model for which image coordinates were known, were computed with the intersection module. the error free values of camera exterior orientation parameters for each photograph as generated by simuphotos were used. the residual errors between the actual and the computed ground coordinates of these intersected points were obtained for computing the shown standard errors in table iv. table iv. photomap error for testing space intersection methodology standard error of ground coordinates of check points (μm)* x σ y σ z σ 0.002 0.002 0.004 * values at 1:1 photograph scale the results indicate negligible standard errors and hence the intersection module of photomap is also free from system error in performing space intersection operation and is functional. vi. conclusions this paper discusses a new application of cad technology for automatic preparation of the necessary data for calibrating photogrammetric instruments. using the colored facilities of the hardcopy devices, inkjet or laser printer or plotter, the gray level of graphical simulated data can be changed. simuphotos provides a real time solution for testing the photogrammetric systems and eliminates the need of manufactured plates which are costly and not always available, and preventing manual graphical presentation such as using hand or software drawing of the numerical simulated data which is time consuming and may pose additional mistakes. the numerical and graphical simulated data are useful for academic studies such as error behavior investigations, determination of the suitable number of control points and their location, testing the results of the suggested methodologies of data processing, etc. the photomap testing results clearly showed that simuphotos system can effectively provide a convenient, economic, and accurate testing tool for photogrammetric systems. moreover, the results showed that photomap is free of system errors and is functional. simuphotos provides a window-driven system that is both portable and suitable for use by non-technical users after a short training period. the developed system is quite versatile and provides an affordable tool to the researchers in universities and academic canters. references [1] f. j. doyle, "fictitious data generator for analytical aerotriangulation," photogrammetria, vol. 21, no. 5, pp. 179–194, oct. 1966, https://doi.org/ 10.1016/0031-8663(66)90011-1. [2] k. l. a. el-ashmawy, "a cost-effective photogrammetric system for engineering applications," ph.d. dissertation, university of roorkee, roorkee, india, 1998. [3] s. rani, y. chabrra, and k. malik, "an improved denoising algorithm for removing noise in color images," engineering, technology & applied science research, vol. 12, no. 3, pp. 8738–8744, jun. 2022, https://doi.org/10.48084/etasr.4952. [4] s. banerjee, a. bandyopadhyay, a. mukherjee, a. das, and r. bag, "random valued impulse noise removal using region based detection approach," engineering, technology & applied science research, vol. 7, no. 6, pp. 2288–2292, dec. 2017, https://doi.org/ 10.48084/etasr.1609. [5] r. vadhi, v. s. kilari, and s. s. kumar, "an image fusion technique based on hadamard transform and hvs," engineering, technology & applied science research, vol. 6, no. 4, pp. 1075–1079, aug. 2016, https://doi.org/10.48084/etasr.707. 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[10] i. autodesk, autocad reference manual. sausalito, ca, usa: autodesk, inc., 1986. [11] k. gregory, using visual c++ 6, special edition. indianapolis, in, usa: que pub, 1998. [12] coreldraw® 2020 user guide. corel corporation, 2020. [13] k. l. a. el-ashmawy, "using direct linear transformation (dlt) method for aerial photogrammetry applications," geodesy and cartography, vol. 44, no. 3, pp. 71–79, oct. 2018, https://doi.org/ 10.3846/gac.2018.1629. [14] k. l. a. el-ashmawy, "block adjustment using control distances constraint," international journal of innovation scientific research and review, vol. 3, no. 3, pp. 948–953, mar. 2021. [15] k. l. a. el-ashmawy, "photogrammetric block adjustment without control points," geodesy and cartography, vol. 44, no. 1, pp. 6–13, apr. 2018, https://doi.org/10.3846/gac.2018.880. [16] c. d. ghilani, adjustment computations: spatial data analysis, 6th ed. wiley, 2017. microsoft word etasr_v13_n3_pp11026-11031 engineering, technology & applied science research vol. 13, no. 3, 2023, 11026-11031 11026 www.etasr.com alblwi et al.: a deterministic finite-state morphological analyzer for urdu nominal system a deterministic finite-state morphological analyzer for urdu nominal system abdulaziz alblwi department of computer science, applied college, taibah university, saudi arabia ablwi@taibahu.edu.sa mohammad mahyoob department of languages and translation, faculty of science and arts, taibah university, saudi arabia mqassem@taibahu.edu.sa (corresponding author) jeehaan algaraady centre of languages, taiz university, yemen jihan.amu@gmail.com khateeb syed mustafa department of linguistics, aligarh muslim university, india khateebsyedmustafa@gmail.com received: 28 february 2023 | revised: 29 april 2023 | accepted: 2 may 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5823 abstract the morphological analyzer is a computational process that combines lemmas with other linguistic features to produce new lexical word forms. this paper investigates the processing of a nominal system in the urdu language. it focuses on the inflections of noun forms and studies number, gender, person, and case representations, using a finite state machine (fsm) to analyze and create all the possible forms of the standardized registers. the application of the analysis using this tool provides and displays all the possible structures and their declensions. this study adds all the necessary features and values to the lexical concatenating nouns according to their patterns. the accuracy score of the output is 92.7, where the actual output depends on the detailed design of the fsm and the specific morphological processes provided to the finite state tools. keywords-computational morphology; urdu language; morphological analyzer; finite-state automata; inflection; derivation i. introduction hindustani is the lingua franca of india and pakistan, which was developed into two standardized registers: hindi and urdu. the main difference between these two registers is the use of different scripts [1]. for example, hindi uses the devanagari script, while urdu uses an extended form of the perso-arabic script. urdu, kaithi and devanagari scripts are indigenous to india. the urdu script is primarily used to write the urdu language, while the kaithi script is used for various languages, including bhojpuri, maithili, and magahi. on the other hand, the devanagari script is used for several languages, including hindi, marathi, nepali, and sanskrit. it is important to note that these scripts have evolved and have been influenced by various other scripts, such as arabic, persian, and sanskrit. these scripts' continued use and preservation are crucial in maintaining india's diverse linguistic and cultural identity. in urdu grammar, nouns are classified into two genders: masculine and feminine. this classification is based on the natural gender of the object being referred to. the number of nouns in urdu can be singular or plural. the plural form of a noun in urdu is formed by adding a suffix to the singular form. this system of gender and number classification is an essential aspect of the urdu language and is used extensively in its literature and everyday communication [2]. a. urdu morphology it is suggested that hindi and urdu share 82% of their daily vocabulary [1, 3], but this number drops if we move to a more specific domain to 69% for tourist phrases. "hindi" is a very loose term covering widely varying dialects. it has been used to develop multilingual grammars that can be used for translation. authors in [3] demonstrated that hindi and urdu share a grammar, but the lexicons diverge hugely beyond basic and general registers. telugu/kannada uses a sanskrit-based lexicon essentially identical to that of hindi. morphology engineering, technology & applied science research vol. 13, no. 3, 2023, 11026-11031 11027 www.etasr.com alblwi et al.: a deterministic finite-state morphological analyzer for urdu nominal system studies how words are formed out of smaller units called morphemes [4]. the various morphological processes employed in urdu are: (i). affixation, (ii) zero-modification, (iii) reduplication, (iv) internal-change, and (v) suppletion. morphology is about the structure of words and is mainly concerned with the formation of words in human languages [5]. urdu has many examples in which certain words are formed by repetitions of the same form. bloomfield referred to inflection as the outer layer of the morphology of word forms and derivation as the inner layer. this inflectional affixation is not used to produce new words in urdu, they are used only to indicate aspects of the grammatical function of a word. the urdu post-positions: /par/, /se/, and /ne/ may be grouped in locative case markers. in three cases, urdu nouns are inflected for two numbers, i.e. singular and plural, direct, oblique, and vocative. urdu verbs have persons, numbers, gender, tense, mood, and aspect categories. the urdu verb form agrees in gender and number with the subject. b. inflection the affixations that precede or follow a language's root depend on the language typology [6]. the inflections of the language itself decide the concatenative and non-concatenative morphology. many languages combine between regularity and irregularity of their word formation. the decision to address the morphology of a language as concatenative or nonconcatenative depends on the grammarians. it is not valid for a language to be called non-concatenative language if some irregular word-formation processes are detected. what criteria have been followed to cluster language inflections or derivational? like other languages, urdu has regular and irregular word formations [7]. the distinction of gender and case in nouns in urdu is inflected for two classes: the first is the number, singular or plural, and the second is based on declension, marked and unmarked types. table i shows inflection paradigms in nouns. table ii shows noun inflections with examples [8]. the distinction is overtly noticed in number, gender, and case. table i. inflection paradigms in nouns singular plural direct oblique direct oblique vocative masculine 1st -ã -e -õ -o 2 nd +õ +o feminine 1 st -ī, -i, -i, -yã -iyā̃ -iyõ -iyo 2 nd +ẽ +õ +o table ii. noun inflection examples singular plural direct oblique direct oblique vocative masculine 1 st larkã kuā̃ larke kuẽ larkõ kuõ larko 2 nd seb vãlid cãkū ãdmĩ sebõ vãlidõ cãkuõ ãdmiyõ 4 pitão ãdmiyo ii. urdu computational morphology urdu computational morphology studies the way urdu forms and structures words [9]. this field is concerned with analyzing and understanding the rules and patterns that govern the formation of words in urdu and using this knowledge to develop computational tools to process and analyze urdu text. one of the main challenges in urdu computational morphology is dealing with the complex inflectional and derivational morphological processes present in the language [10-12]. for example, urdu verbs have a rich system of inflectional forms, which can change depending on factors such as tense, aspect, and person. urdu nouns can also be inflected to indicate case and number and can be formed through various derivational processes. to address these challenges, researchers in the field of urdu computational morphology have developed several different tools and techniques. one popular approach is to use rule-based methods, where a set of rules are defined for each morphological process, and these rules are then applied to words to analyze and generate new forms. another approach is the utilization of statistical methods, where patterns in large text corpora are used to train computational models that can automatically identify and analyze morphological forms. in recent years, there has been a growing interest in using deep learning approaches for performing different natural language processing (nlp) tasks, e.g. text classification (tc), question answering (qa), name entity recognition (ner), sentiment analysis (sa), etc. [13-15]. in the same way, deep learning techniques have been used for urdu computational morphology. these techniques are effective in learning complex patterns in the language and have been used to develop many state-of-the-art tools for morphological analysis and generation in urdu [16]. urdu is a morphologically rich language with a complex system of inflections and derivations [17-19]. the main inflectional categories in urdu include gender, number, case, and tense, while the main derivational processes include affixation, compounding, and conversion. in computational morphology, the task of analyzing and generating the inflected and derived forms of words is known as morphological analysis and generation [20]. some computational approaches have been proposed for urdu morphological analysis and generation, including rule-based, finite-state, and machine learning-based methods. rule-based methods rely on manually crafted rules to analyze and generate inflected and derived forms, while finite-state methods use finite-state transducers to model the morphological processes of a language [21, 22]. on the other hand, machine learning-based methods use datadriven techniques such as neural networks to learn the morphological patterns of a language. one of the significant challenges in the computational morphology for urdu is the large number of inflected and derived forms that a word can have. the rich inflectional system of urdu, combined with relatively free word order, makes it challenging to analyze and generate inflected and derived forms fully automatedly. however, recent advances in machine learning techniques have shown promise in addressing this challenge. the research on urdu computational morphology is ongoing, focusing on developing more accurate and efficient morphological analysis and generation methods. this includes the use of neural networks, lstm, and attention-based architectures for morphological analysis and generation, which perform well in urdu. engineering, technology & applied science research vol. 13, no. 3, 2023, 11026-11031 11028 www.etasr.com alblwi et al.: a deterministic finite-state morphological analyzer for urdu nominal system iii. research questions the research questions for this study focus on the lexical processing of urdu nouns inflection.  question one: does the urdu language have a concatenative inflective morphology system?  question two: can finite-state machines process urdu nouns systematically? iv. related work urdu and hindi are quite similar on a spoken level, but hindi is written in devanagari script, which is entirely different from the urdu script. regarding linguistics, morphology refers to the formation of words by focusing on their internal structure. morphology is divided into two classes: inflectional morphology and derivational morphology. nlp is the primary interface between humans and computers. it is considered a branch of artificial intelligence (ai). authors in [23] studied rule-based stemmer in urdu and presented a rule-based stemmer for urdu. they stated that stemming is a process in which affixes are separated from their root word. their work was restricted to the urdu language, which meant that the root word was not extracted from other languages like english, persian, and arabic. this stemming algorithm separated prefixes, suffixes, and infixes. it matched the word with the affixes and pulled out the word. the system and evaluation exhibited 86.5% accuracy. authors in [24] developed an approach for building a finite-state morphological analyzer for urdu and hindi that is compatible with the xfst tools already used in both scripts. that was a part of the pargram project, and they developed a grammar for south asian urdu. very few resources exist for this language, and no broad-coverage finitestate morphological analyzer existed before this study. the approach allowed for an underlyingly similar treatment of urdu and hindi via a cascade of finite-state transducers that transliterate the very different scripts into a standard ascii transcription system. the paper has addressed several issues in building a finite-state morphological analyzer for urdu. the authors further explored the reduplication in urdu, again based on solutions proposed concerning xfst. the discussion in their study mainly revolves around where and how information should be encoded concerning the morphology-syntax interface that has been defined between finite-state morphological analyzers and lexical-functional grammar. an improved statistical morph analyzer for hindi, urdu, telugu and tamil, was conducted in [25]. the authors proposed a statistical morph analyzer for indian languages. the gender, number, person, and case accuracy was 86.81% for telugu and 78.97% for tamil. they studied two families of indian languages, indic and dravidian, because most indian languages fall into these two groups. morphological analysis for indian languages was conducted using the rule-based approach. experiments were conducted for the four indian languages [ils] mentioned above. the results were compared to morfette (m) [26] and sma [27] .the authors reported that for all four ils, sma++ outperforms the other smas. for hindi and urdu the l+g+n+p+c accuracy was 85.87%. for telugu, the accuracy was 86.81%, and for tamil, it was 78.97%. authors in [28] reported a rule-based implementation of a morphological analyzer for hindi. the study focused on designing a morphological analyzer for hindi, a language rich in morphemes, which can be used for machine translation, which works on a rule-based approach and maintains a database for exceptions. the authors propose that the system's accuracy is very high as all the possible exceptions are covered. the word sense disambiguation can be integrated with this analyzer so that the words having multiple senses can be analyzed accurately. authors in [29] studied the influence of morphology on word recognition in hindi and urdu. hindi showed priming for morphologically and form-related primes, but the morphology study was not advantageous. urdu showed faster latencies for targets preceded by morphologically related primes relative to those preceded by form-related primes. the evidence shows that the phonological, orthographic, and semantic/syntactic characteristics influence the visual recognition of the words presented in isolation. targets were urdu words of one syllable paired with two-syllable primes of three types. v. finite state machine (fsm) an fsm is a mathematical model representing a language's morphological processes [30]. in the case of urdu, an fsm could be used to model the language's inflectional and derivational processes and generate inflected and derived forms of words. fsms are used to identify the regularity forms in a language by using a regular expression to perform the process of inflection morphology. the computational and linguistic components are represented together to produce the correct grammar forms using fsms. the machines are used in nlp to construct lexical analyzers and to compile derivational and inflectional rules of language morphology using finite state tools, and a lexical analyzer was developed for the urdu nominal system. a regular expression and the inflectional rules of the natural language can represent the set of strings s. the processing and the output can be represented and recognized by the fsa as shown in figure 1. fig. 1. finite-state automaton. formally, a finite-state is represented by m =(s, ∑, s0, δ, f) where: s a finite set of states, s= {s0, s1, s2, s3}, σ is a finite set of input symbols called the alphabet (root. reg, infl. reg, num., gen), δ is a transition function (δ: s × σ → s), s0 is the start state (s0 ∈ s), and f is a set of finite states called accepting or final states. in figure, it is f ⊆ s3). vi. lexicon lexicon generates entries for computational morphological analysis in the framework of finite-state morphology and uses engineering, technology & applied science research vol. 13, no. 3, 2023, 11026-11031 11029 www.etasr.com alblwi et al.: a deterministic finite-state morphological analyzer for urdu nominal system the concepts of the xerox/helsinki finite-state transducer lexc tools. dictionaries often list many inflection classes and different types of lexc entries [4]. a lexicon entry needs a general method that is prepared to accept almost any surface word. the resulting entries are combined with affixes and composed-intersected with the rule fsts. the string pairs represented by the fst are produced in a human-readable form. the system is extensively redesigned and built using xerox finite-state technology. figure 2 shows a lexicon sample for creating the rules and the necessary morphological information for urdu noun forms. the symbols used in the lexicon are based on the root and the inflectional information and are added based on rules which process all the entries and produce the output. fig. 2. lexicon sample. vii. results after performing the morphological parsing and building the dictionary using the finite-state algorithm, given the roots and linguistic information, a determination algorithm is used to get the p-subsequential transducer. the determinization algorithm performs the composition in which the transitions are labeled with the input and output linguistic features. they must be added to the root as the input. the output is the various word forms along with linguistic features. figure 3 represents the process of morphological parsing for the noun forms of urdu. the processing starts from zero state to state one, where the base form is linked with all the possible forms, such as plural, number, gender, and case. for example, in the roots /lark/, and /ādm/, the transitions are labeled with the category and inflection features, such as noun, masculine/feminine, and singular/plural suffixes. another example is processing the root with the oblique/vocative forms and all other possible forms. the components seen in figure 3 are:  thirteen states  the first state is s0 and the final state is s12.  21 transitions (arcs)  σ: {(roots: lark, adam), (suffixes: ā, õ, ī, iyā̃, iyo, e, iyõ)}  used symbols: +pl/p refers to the plural form, +sg/s stands for singular, +ms/m stands for masculine, +f stands for feminine, +d stands for direct, +o stands for oblique, and +v stands for vocative. fig. 3. data representation sample using finite-state automata. viii. transition function matrix table iii shows the transition process of the fsm and the linguistic layers of morphological forms of the proposed model. table iii. transition table from to output 0 s1, s8 lemmas s1, s8 s2, s3, s4, s5, s6, s7, s9, s10, s11 various inflections s1, s2, s3, s4, s5, s6, s7, s9, s10, s11 s12 all the possible linguistic features fig. 4. data processing with linguistic information. figure 4 represents the transition processing of the deterministic algorithm using the developed lexicon. for engineering, technology & applied science research vol. 13, no. 3, 2023, 11026-11031 11030 www.etasr.com alblwi et al.: a deterministic finite-state morphological analyzer for urdu nominal system instance, this sample has 10 roots and 12 inflection forms. the transition performs using 70 states, 85 arcs, and 20 paths. all the possible forms are generated with other linguistic information related to nouns in urdu. figure 5 shows a sample of one possible output wordlist of an fsm for the urdu language and the readable output with all the needed features of the urdu nominal systems. the first generated form is the singular and the plural nouns. then the number, gender, and person singular and plural nouns are generated. the output data extracted from the developed lexicon are evaluated with the correct forms of the different types of nouns in urdu: the proposed computational algorithm and linguistic analysis were assessed with the high accuracy of 92.7%. table iv displays the obtained results. fig. 5. singular and plural output wordlist sample. table iv. statistical analysis data and results data (roots) correct output generated forms accuracy 2000 95.4% 30.000 92.7% 1000 96.6% 15.000 90.4% the above statistical analysis shows that urdu has a concatenative morphological system. the deterministic finitestate morphological analyzer tool is designed to analyze the morphology of urdu nouns. it operates based on a fsm, which allows it to accurately identify and classify the various morphemes that make up a given word. this tool is highly effective in identifying the root of a word, as well as its various inflections and derivations. its deterministic nature ensures consistent and reliable results, making it an essential tool for researchers working with language data. ix. discussion in this work, an attempt was made to develop a morphological analyzer for the low-source language urdu. the first research question focused on the concatenative nature of urdu noun forms. the study utilized an fsm to generate a morphological analysis of urdu nouns. figure 3 displays the regularity in most of the nominal forms of urdu, which is consistent with previous research on the topic [9, 18, 24]. the study's findings reveal that urdu has a concatenative system in the context of the noun forms, consistent with [18] in which it was reported that urdu has a concatenative inflective morphology system. however, there are some exceptions when it comes to causative verbs, which can exhibit stem-internal changes in some instances. the data highlight the significance of comprehending the linguistic characteristics of all potential inputs that can be utilized by the tool. this understanding can ultimately result in improved output quality. the finite-state tool was utilized to process noun inflection in urdu. figure 2 shows the lexicon development and rule generation to enable the fsm to produce all possible noun forms, each with its corresponding linguistic description. this approach effectively addressed the research question two. this study analyzed the rules and patterns that govern the formation of words in urdu. the goal was to develop computational tools to process and analyze urdu inflections. by understanding the intricacies of urdu word formation, the accuracy and efficiency of language processing tools can be improved. the output displays various inflected forms of urdu nouns, such as singular and plural forms, cases, and different grammatical genders. the specific morphological processes provided by the finite state tools and the detailed design of the fsm determine the actual output. the accuracy score of the analysis is above 90%. the fsm ensures accuracy and completeness in analyzing and creating these forms. this approach achieves a comprehensive understanding of noun forms, allowing for precise communication in written language. x. conclusion this paper focused on the urdu computational morphology using finite states to generate a morphological analysis for urdu nouns. this study is concerned with analyzing and understanding the rules and patterns governing the formation of urdu words. the objective is to use this knowledge to develop computational tools to process and analyze urdu nouns. the output showcases urdu nouns' inflected and derived forms, including singular and plural forms, various cases, and grammatical genders. the specific morphological processes used by the finite state tools, along with the detailed design of the finite state machine, determine the precise output. overall, this paper contributes to computational morphology by comprehensively understanding finite-state technology's use in analyzing urdu nouns' morphology. this study is limited to engineering, technology & applied science research vol. 13, no. 3, 2023, 11026-11031 11031 www.etasr.com alblwi et al.: a deterministic finite-state morphological analyzer for urdu nominal system urdu noun forms analysis, and future studies will focus on other lexical categories of urdu. references [1] m. g. a. malik, c. boitet, and p. bhattacharyya, "hindi urdu machine transliteration using finite-state transducers," in 22nd international conference on computational linguistics, stroudsburg,pa, usa, aug. 2008, pp. 537–544. 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[30] m. hulden, "finite-state technology," in the oxford handbook of computational linguistics, r. mitkov, ed. oxford, england: oxford university press, 2022, pp. 230–254. microsoft word etasr_v12_n6_pp9737-9741 engineering, technology & applied science research vol. 12, no. 6, 2022, 9737-9741 9737 www.etasr.com yerri veeresh et al.: modeling and analysis of time response parameters of a pmsm-based electric … modeling and analysis of time response parameters of a pmsm-based electric vehicle with pi and pid controllers m. yerri veeresh department of eee, jawaharlal nehru technological university anantapur, anantapuramu, india and santhiram engineering college, nandyal, india saiveerushamu8@gmail.com v. naga bhaskar reddy department of eee rajeev gandhi memorial college of engineering and technology, nandyal, india chaitu.bhaskar@gmail.com r. kiranmayi department of ee jawaharlal nehru technological university anantapur anantapuramu, india kiranmayi0109@gmail.com received: 9 september 2022 | revised: 26 september 2022 and 4 october 2022 | accepted: 9 october 2022 abstract-this paper presents the mathematical modeling of a vector-controlled permanent magnet synchronous motor (pmsm) drive with either a proportional integral (pi) controller or a proportional integral derivative (pid) controller as a propulsion system for an electric vehicle (ev). most commercial drives use a standard pi controller as a speed regulator. the vector control system model consists of the pmsm, a pwm inverter, the speed controller, and vehicle dynamics for speed control. the performance analysis of the drive is evaluated under transient conditions for settling time, rise time, steady state error of speed, and the vehicle’s acceleration at the wheel axle for specifically designated values validated by matlab/simulink. keywords-permanent magnet synchronous motor (pmsm); electric vehicle dynamics; proportional integral (pi) controller; proportional integral derivative (pid) controller i. introduction in recent years, several situations related to the environment have led to reduced carbon emissions from vehicles. electric vehicles (evs) can be alternatives to traditional si or ci engine automotives [1-2]. pmsms have been used in various industrial applications like cnc machines, industrial robotics, air-conditioners, washing machines, wind power generation systems, evs, etc. the pmsms are more suitable in evs due to their high efficiency, high power/torque density, smaller size, high torque/weight ratio, and maintenance-free operation [3]. better dynamic responsiveness and fewer torque ripples are provided by a vector-controlled pmsm drive, which needs a constant switching frequency. the outer loop speed control significantly impacts system performance [4]. the pi controller performs well under steady-state conditions. a lot of approaches have been proposed for the tuning of the pi controller. the ziegler-nichols method is the most popular, which dispenses with the need for a system design and control parameters [5]. the pi and pid controllers are simple and effective, consequently, they are often used for the control of the pmsm systems [6]. controlling of a battery ev (bev) is not a simple task as the ev is essentially timevariant. the ev’s primary limiting factor is the short running distance (range) per battery charge. another limiting factor is its acceleration time to reach the maximum speed limit [7]. the ev dynamics must be suitably selected to achieve better performance. ii. vehicle dynamics the performance of vehicle modeling is initially obtained by the tractive effort equation. the force that drives the vehicle forward and is transmitted to the ground through the drive wheels is known as the tractive effort. this force has to overcome the rolling resistance force, aerodynamic drag force, and the elements of the vehicle’s weight (including payload) acting down to the slope. it also accomplishes the force required to accelerate the vehicle for the linear and angular motion of drive wheels [7-8]. the tractive force and the corresponding force equations depend upon the vehicle dynamics, shape, size, and structure parameters, such as rolling resistance coefficient, air density, drag coefficient, gear ratio and gear efficiency, wheel radius, etc., are illustrated in figure 1 of [9]. the respective equations for rolling resistance force ��� , aerodynamic drag force ��� , hill climbing force ��� , acceleration force f� , and angular acceleration force � � are respectively given by: ��� = µ�� ∗ � ∗ � (1) corresponding author: m. yerri veeresh engineering, technology & applied science research vol. 12, no. 6, 2022, 9737-9741 9738 www.etasr.com yerri veeresh et al.: modeling and analysis of time response parameters of a pmsm-based electric … ��� = �� ∗ � ∗ � ∗ �� ∗ �� (2) ��� = � ∗ � ∗ sin � (3) ��� = � ∗ � (4) � � = � �� !�� (5) the total tractive force necessary to drive the vehicle is the sum of all forces: �"# = ��� + ��� + ��� + ��� + � � (6) the tractive torque corresponding to the tractive force with wheel radius r, is given by: %& = �"# ∗ ' (7) the speed and torque at the axle of the wheel are given by: (�)�# = *+� (8) %�)�# = ,-� %# (9) the vehicle equations are used to understand the vehicle dynamics for different force inputs [10]. the mathematical model of the speed-toque equation of the vehicle at the axle of the wheels is given by: (�)�# = . �/0��12�3245 6%�)�# − %& 8 d: (10) the specifications of the vehicle chassis chosen for the simulation are given in table i. table i. vehicle chassis specifications parameter quantity net mass, m 1200kg area of frontal surface, a 2.2m2 gear ratio, g 2 rolling coefficient, µ�� 0.01 gear efficiency, -� 0.9 wheel radius, r 0.2m drag coefficient, cd 0.26 slope angle, � 0o iii. mathematical model of the permanent magnet synchronous motor a three-phase salient-pole sinusoidal wave shape back emf pmsm with 87.75nm, 560vdc, and 3000rpm preset model parameters was designed mathematically. the model specifications are given in table ii. the mathematical model of the pmsm is given in (11)-(22). the rotor reference frame is chosen because the rotor magnet's position will be determined independent of the stator phase voltages, instantaneous induced phase emfs, stator phase currents, and torque of the machine [11]. for synchronous motors, the rotating speed of the rotor and the space vector of the rotor flux are both equal to the rotating rate of the reference frame (� = (� = ( [12-13]. in the rotor reference frame, the stator q and d axes voltage equations in terms of flux linkages are: v<= = >? @?a + bcdeb" + (� f�a (11) g�a = >� @�a + �che�" − (� f?a (12) the stator flux linkages are given by: f?a = i? @?a (13) f�a = i� @�a + i0 @j (14) table ii. pmsm specifications parameter value stator phase resistance, rs (rd = rq = rs) 0.05ω d-axis inductance, ld 0.0007552h q-axis inductance, lq 0.0008348h flux linkage, f�j 0.192 wb-turn inertia, j 0.011kgm 2 viscous damping, b 0.001417nms pole pairs, p 4 static friction, tf 0nm the stator voltage equations in terms of electrical parameters are obtained by substituting the flux linkages in the stator voltage equations as: k g?ag�a l = m >? + �nd�" (� i�−(� i? >� + �nh�" o k @?a@�a l + k(� i0 @j0 l (15) the electromagnetic torque is given by: %# = q� r� sf�a @?a − f?a@�a t (16) the torque equation in terms of inductances and currents upon the substitution of flux linkages is given by [14]: %# = qru vf�j @?a + si� − i? t@?a@�a w (17) where f�j is the rotor flux linkage that links the stator and is given by: f�j = i0@j (18) the angular speed (# and the instantaneous angle of the rotor x� of the machine are given by: (# = r� y �4a1z[ 6%# − %0 8 (19) x� = . (#\:] ^:"_ + x� \0] (20) the stator q and d axes currents for a balanced three-phase operation are given by: k@?a@�a l = �q m cos x� cos bθd − �eq f cos bx� + �eq fsin x� sin bθd − �eq f sin bx� + �eq f o g @�@h@� i (21) the abc-to-dq transformation equations for stator voltages are given by: y�?a��a [ = �q mcos x� cos bx� − �eq f cos bx� + �eq fsin xd sin bx� − �eq f sin bx� + �eq f o g v vkvl i (22) engineering, technology & applied science research vol. 12, no. 6, 2022, 9737-9741 9739 www.etasr.com yerri veeresh et al.: modeling and analysis of time response parameters of a pmsm-based electric … iv. proposed system model with pi and pid controller for applications in control theory, the proportional (p), the pi, and the pid controllers are the most commonly used controllers. as illustrated in figure 1, the pi controller will affect the performance of the system by increasing the system's order by one and by reducing steady state error, disturbance signal rejection, and relative stability. the system's sensitivity with respect to parameters also decreases [15]. the transfer function of the pi controller is given by: ,� \m] = no + pqr (23) the pi controller reduces rise time and minimizes the steady-state error [16]. peak overshoot, settling time, order, and type of the system will be increased [15]. it functions as a low pass filter. the output equations of the pi and pid controllers are given by: s\:] = not\:] + nu . t\:] ^: (24) s\:] = not\:] + nu . t\:] ^: + n� ��" t\:] (25) a command speed ω * is compared with the motor's speed ωr and provides the change or error in speed δω, which is given to the pi or pid controller to obtain the command torque component of stator current iq * . a limiter is used ahead of the controller to avoid decreased stability. fig. 1. pi controller block diagram. the complete model block diagram of the pi controller of the pmsm-based bev is illustrated in figure 2. the command speed has been compared with the actual speed of the pmsm. an error speed signal is given to the pi controller to tune the signal with kp and ki values and provide the torque-producing current reference component iq * , which is essential to control the error speed by calculating the three-phase reference currents ia * , ib * , ic * . a li-ion battery with 100c capacity was used as the supply, which is converted into a three-phase supply voltage using a pwm inverter. the li-ion battery is operated with a current-controlled device with the feedback current provided by the pmsm. a sinusoidal pwm approach with the reference currents ia * , ib * , ic * corresponding to command speed and the actual currents ia, ib, ic produced by the pmsm are collectively compared with a triangular reference signal to produce the gate pulses. such desired gate pulses drive the three phase two-level inverter and will produce the three phase voltages for the pmsm. the characteristic equations of the pmsm building blocks are operated with inverter voltages and produce the instantaneous current, position, speed ωw, and torque tw of the motor. the pmsm will drive the vehicle's wheels through the transmission and differentials by considering the vehicle's dynamic losses. fig. 2. model analysis diagram of the speed control of the ev with pmsm drive using a pi controller. fig. 3. simulink model of dq to abc reference signals. fig. 4. simulink model of the pwm inverter. fig. 5. simulink model of pmsm. engineering, technology & applied science research vol. 12, no. 6, 2022, 9737-9741 9740 www.etasr.com yerri veeresh et al.: modeling and analysis of time response parameters of a pmsm-based electric … finally, the vehicle is operated smoothly with the required speed and torque. the performance results are discussed below. in matlab simulink version r2017a, the proposed work was simulated with the ode 23tb solver in continuous time mode. the design sub models like dq to abc reference, pwm inverter, pmsm model, and vehicle dynamic models are shown in figures 3-7. fig. 6. simulink model of pmsm internal characteristics. fig. 7. simulink model of vehicle dynamics (motor to wheels). v. simulation results simulations have been carried out with the pi and pid speed controllers for a 3-phase, 550vdc, 1500rpm, 97.96nm pmsm at a load torque of 80nm and operating speed of 1500rpm or 157.079rad/sec. it can be observed that the rise time (90% of the command speed) is attained in 50.1ms with the pi controller, which is a better response than that of the pid controller. the motor speed stabilizes at a reference speed (with 2% tolerance) of 157.079rad/s in 70.1ms with the pid controller, which is slightly better performance than the one of the pi controller and with the steady state error of 0.0075rad/s or 0.0716rpm in both pi and pid controllers, as shown in figure 8. the vehicle's acceleration (the speed at the wheels or the axle) was measured, and the time taken to reach the speed of 100km/h is 48.1ms with the pi controller, which is superior to the performance of the pid controller, as shown in figures 11-12. in the steady state, for a command torque of 80nm, the torque developed by the pmsm is 80nm. table iii. performance results of the proposed system model motor side speed axle side speed controller type and its gain values applied load (nm) rise time required to reach 90% of final value (ms) settling time needed to get steady-state value with 2% tolerance (ms) steady state error time to reach 100km/hr (ms) pi (kp=0.35 ki=16) 80 50.1 71.0 0.0075rad/s or 0.0716rpm 48.1 pid (kp=0.35 ki=16 kd=0.01) 80 54.8 70.1 0.0075rad/s or 0.0716rpm 53.0 fig. 8. simulated speed responses with pi and pid controllers. fig. 9. simulated torque responses with the pi controller. fig. 10. simulated torque responses with the pid controller. the torque available at the wheel axle is 72.5nm, with net tractive resistance loss of 7.5nm due to rolling resistance, aerodynamic, and hill-climbing torque losses in both pi and pid controllers. the initial transient is higher in the pid controller than in the pi controller, as seen in figures 9-10. the pulsating ripple torques are noticed due to the residual flux variation. the data of the mathematical model of the performance of the pmsm-based electric vehicle with pi and pid controller through matlab simulations are given in table iii. engineering, technology & applied science research vol. 12, no. 6, 2022, 9737-9741 9741 www.etasr.com yerri veeresh et al.: modeling and analysis of time response parameters of a pmsm-based electric … fig. 11. simulated vehicle acceleration pointing at the top speed of 100km/hr with the pi controller. fig. 12. simulated vehicle acceleration pointing at top the speed of 100km/hr with the pid controller. vi. conclusion in this paper, the mathematical model of a vector controlled pmsm drive with pi and pid controllers as a propulsion system for an electric vehicle is developed, and its simulation results are presented. the results demonstrate that the pi controller achieves more robust tracking response of the command speed with less steady-state error than the pid controller. good execution time and time are noted in the performance analysis. the vehicle acceleration at the wheel axle reached the desired value within a minimal time. the overall output responses of the model show that the vehicle can run smoothly with good static and dynamic performance characteristics with the pi controller. references [1] c. c. chan and k. t. chau, "an overview of power electronics in electric vehicles," ieee transactions on industrial electronics, vol. 44, no. 1, pp. 3–13, oct. 1997, https://doi.org/10.1109/41.557493. [2] global electric vehicle outlook 2022. france: international energy agency, 2022. [3] s. morimoto, "trend of permanent magnet synchronous machines," ieej transactions on electrical and electronic engineering, vol. 2, no. 2, pp. 101–108, 2007, https://doi.org/10.1002/tee.20116. [4] r. n. hajare and a. g. thosar, "modeling and simulation of permanent magnet synchronous motor using matlab," vol. 7, no. 3, pp. 413– 423, 2014. [5] v. v. patel, "ziegler-nichols tuning method," resonance, vol. 25, no. 10, pp. 1385–1397, oct. 2020, https://doi.org/10.1007/s12045-020-1058z. [6] e.-c. shin, t.-s. park, w.-h. oh, and j.-y. yoo, "a design method of pi controller for an induction motor with parameter variation," in iecon’03. 29th annual conference of the ieee industrial electronics society, roanoke, va, usa, aug. 2003, vol. 1, pp. 408–413, https://doi.org/10.1109/iecon.2003.1280015. [7] "electric and hybrid vehicles, design fundamentals [book review]," ieee circuits and devices magazine, vol. 21, no. 5, pp. 26–27, sep. 2005, https://doi.org/10.1109/mcd.2005.1517392. [8] j. larminie and j. lowry, electric vehicle technology explained, 2nd ed. wiley, 2012. [9] m. y. veeresh, v. n. b. reddy, and r. kiranmayi, "range estimation of battery electric vehicle by mathematical modelling of battery’s depth-of-discharge," international journal of engineering and advanced technology, vol. 8, no. 6, pp. 3987–3992, aug. 2019, https://www.doi.org/10.35940/ijeat.f8800.088619. [10] m. yildirim, m. c. catalbas, a. gulten, and h. kurum, "computation of the speed of four in-wheel motors of an electric vehicle using a radial basis neural network," engineering, technology & applied science research, vol. 6, no. 6, pp. 1288–1293, dec. 2016, https://doi.org/10.48084/etasr.889. [11] p. t. giang, v. t. ha, and v. h. phuong, "drive control of a permanent magnet synchronous motor fed by a multi-level inverter for electric vehicle application," engineering, technology & applied science research, vol. 12, no. 3, pp. 8658–8666, jun. 2022, https://doi.org/ 10.48084/etasr.4935. [12] p. pillay and r. krishnan, "modeling of permanent magnet motor drives," ieee transactions on industrial electronics, vol. 35, no. 4, pp. 537–541, aug. 1988, https://doi.org/10.1109/41.9176. [13] c. bowen, z. jihua, and r. zhang, "modeling and simulation of permanent magnet synchronous motor drives," in icems’2001. proceedings of the fifth international conference on electrical machines and systems, shenyang, china, dec. 2001, vol. 2, pp. 905– 908, https://doi.org/10.1109/icems.2001.971825. [14] a. mansouri and t. hafedh, "torque ripple minimization and performance investigation of an in-wheel permanent magnet motor," engineering, technology & applied science research, vol. 6, no. 3, pp. 987–992, jun. 2016, https://doi.org/10.48084/etasr.644. [15] j. c. basilio and s. r. matos, "design of pi and pid controllers with transient performance specification," ieee transactions on education, vol. 45, no. 4, pp. 364–370, aug. 2002, https://doi.org/10.1109/ te.2002.804399. [16] s. mikkili and a. k. panda, "shaf for mitigation of current harmonics with p-q and id-iq control strategies using both pi and fuzzy controllers," in international conference on sustainable energy and intelligent systems (seiscon 2011), chennai, india, jul. 2011, pp. 358– 362, https://doi.org/10.1049/cp.2011.0389. authors profile m. yerri veeresh was born in kurnool, india. he received the b.tech (electrical and electronics engineering) degree, m.tech (power electronics and electric drives) from jawaharlal nehru technological university anantapur, india in 2009 and 2013 respectively. presently, he is pursing his ph.d. in the department of electrical engineering, jntu anantapur and is also working as an assistant professor in the santhiram engineering college, nandyal. his fields of interest include electric vehicles, power electronics and drives, and energy sources. v. naga bhaskar reddy was born in kurnool, india. he received the b.tech (electrical and electronic engineering) degree from the bangalore university, bangalore in 2000, m.tech (power electronics and drives) from the bharath institute of higher education research (biher), chennai, india in 2005. he attained his doctoral degree from the jawaharlal nehru technological university, kakinada in 2012. he is currently a professor and the head of the department of electrical and electronic engineering, r.g.m college of engineering and technology, nandyal. his areas of interest are power electronics, microcontrollers, and power electronic converters. r. kiranmayi received the b.tech (electrical and electronic engineering) degree, m.tech., and doctoral degree from jawaharlal nehru technological university anantapur, india in 1993, 1995, and 2013 respectively. she is presently working as a professor the head of the department of electrical engineering at jntua, anantapuramu. she has published more than 40 research papers in international and national conferences and journals. her areas of interest include electrical power systems and photo voltaic systems. microsoft word etasr_v13_n1_pp9991-9996 engineering, technology & applied science research vol. 13, no. 1, 2023, 9991-9996 9991 www.etasr.com arya: development of a graphical user interface for reflection loss calculation in perovskite-rgo … development of a graphical user interface for reflection loss calculation in perovskite-rgo based microwave absorbing composites aayushi arya department of electrical engineering, indian institute of technology hyderabad, india aayushi.arya@outlook.com (corresponding author) received: 7 november 2022 | revised: 24 november 2022 | accepted: 9 december 2022 abstract in this paper, a novel method is investigated wherein the theoretical and mathematical analysis of the perovskite-reduced graphene oxide (rgo) based composite microwave absorber is used to form a machine learning model using linear regression to predict the reflection loss and the effective dielectric permittivity of a selected perovskite compound in an rgo-based composite. at first, the theoretical derivation is carried out to find a mathematical relationship between the reflection loss and the dielectric permittivity of the composite and the cationic radii of the perovskite structure, which is then used to form the base for the machine learning model to directly calculate the microwave absorption characteristics from the atomic parameters of the given composite structure. linear regression is used for the machine learning algorithm which is verified with an r 2 of 0.869 with the atomic radii as the input parameters. the model is further used to develop a graphical user interface (gui) to make the prediction more appealing and user-friendly. the current paper provides a new approach to the integration of theoretical knowledge with advanced computing tools to form innovative predictive tools for current microwave-absorbing materials. keywords-atomic radius; microwave absorbers; machine learning; perovskite; reflection loss; reduced graphene oxide i. introduction microwave absorbing composites have become an important field of research due to their growing applications. this field has seen a variety of research articles dedicated to the experimental studies of the absorbing properties of microwave absorbers [1-3]. there are many theoretical works also, modeling the permittivity and permeability of microwave absorbers [4-7], but they do not analyze their atomic fundamentals. in this work, an effort was conducted to form a machine learning model based on a theoretical framework for a microwave absorber that directly relates the refection loss to the atomic radii of the elements in the observed compound. further, a graphical user interface (gui) was developed for predicting the reflection loss of perovskite-reduced graphene oxide (rgo)-based microwave absorbing composites from their ionic radii using the machine learning model. the base equation and the electromagnetic parameters for the model are theoretically evaluated for the given absorber composite. the considered parameters include the combined dielectric permittivity of the filler and matrix material also referred to as the effective dielectric permittivity, the effective magnetic permeability, the radius of the filler particles considered as spherical inclusions, and the effective radius of anion and cation in the perovskite unit cell. in this work, a pervoskite-reduced graphene-based microwave absorbing composite is considered. a combination of perovskite filler and rgo-based matrix was chosen as the microwave absorbing composite. pervoskites are chosen as filler materials due to their good electrical and magnetic properties along with physical and chemical stability [8]. similarly, rgo has gained popularity in microwave absorbing composites replacing the conventional polymer-based matrix materials [9], due to its high conductivity and excellent physical and chemical properties. having the advantage of increased point defects and attached functional groups, rgo facilitates the occurrence of interfacial polarization and enhanced polarization sites thereby increasing the overall absorption rate. for an effective microwave absorption in a composite, there has to be good impedance matching for maximum wave absorption followed by high dissipation of the absorbed energy. the given model can be used to form new and efficient perovskite-based microwave absorbing compounds. perovskite-based absorbers are cost effective, nontoxic, and environmentally friendly. hence, they can be widely used as microwave absorbers in applications with large human contact like schools, hospitals, etc. they can be applied as microwave absorbing paints, coats, or integrated with absorber foams. engineering, technology & applied science research vol. 13, no. 1, 2023, 9991-9996 9992 www.etasr.com arya: development of a graphical user interface for reflection loss calculation in perovskite-rgo … ii. polarization and magnetism polarizability is the tendency of an atom to allow charge separation when exposed to an electromagnetic wave. there are different polarization kinds that can occur inside a composite system including electronic, ionic, interfacial, and dipole relaxation-based polarizations [10-12]. as depicted in figure 1(a), for a perovskite and graphene-based composite absorber, all the above phenomena happen at different points resulting in strong em wave absorption. dipole polarization occurs across the graphene layers due to the relaxation of dipoles formed between the graphene layers that are loosened with the penetration of perovskite particles between them. similarly, in abo3-type perovskite structures, ionic polarization occurs at the oxide ions formed by the presence of positively charged a-site cation deficiency. interfacial polarization is induced by the interaction of the a-site cation with the matrix material that is graphene. this is caused by the interaction across a heterogeneous boundary creating a charge separation on both sides of the boundary. electronic polarization is attributed to the flow of oxide ions in the 2d and 3d layers across the perovskite particles. the 2d oxide ion conduction occurs across the b-o-b plane, however the introduction of the graphene matrix between the perovskite structure has enabled 3d movement of the oxide ion. graphene forms interfacial polarization with the a-site cation hence weakens its restricting force over the movement of oxide ions from one-unit cell to another. this phenomenon results in the formation of electronic polarization as well. (a) (b) fig. 1. (a) polarization mechanism, (b) energy band diagram showing the occurrence of magnetism in perovskite-rgo composite microwave absorber. the occurrence of magnetism in a perovskite compound occurs via double charge mechanism and involves the influence of rgo which forms a boundary material across the perovskite. the spin coupling in the perovskite filler particles is supported by the rgo layer. as shown in figure 1(b), cation a is not disturbed by the bond formation and provides a higher single energy level. on the other hand, cation b when combined with oxide ion and forming a b-o-b bond, splits its energy level into higher ( �� ) and lower ( ��� ) [13] energy orbitals. in a well ordered perovskite structure, the d-orbital of the b cation overlaps with the p-orbital of the oxide ion in a covalent manner with equal charge distribution. however, due to the presence of an additional energy level of rgo, the octahedron perovskite structure shifts from its center of symmetry. the perovskite oxide can show either ferromagnetic or magnetic properties when the electron charge distribution in the b-o-b bond is such that, one of the b cations is empty while the other is half filled following goodenoughkamamori’s rule on superexchange interactions [14-15], thus increasing the overall magnetic permeability of the compound [23-24]. iii. theoretical framework the effective relative permittivity can be calculated from the maxwell garnett equation [16]: ���� = � � � � � � ��� ��� �� �� �� � � �� �� (1) the dielectric permittivity for the matrix material (rgo) is taken as constant, � = 118. the maximum value of the dielectric constant is taken to compensate for the high temperature effects on account of the dissipation of the absorbed microwaves [17]. the volume fraction of the filler particles is taken as the critical percolation threshold for the filler particles in an infinite cubic lattice. its value is 0.1454 in all three dimensions [18]. similarly, the effective relative magnetic permeability (���� ) can be calculated from [19]: ���� = �� �1 + ��� �� �� ���� � �� (2) where ��� is the atomic radius of the filler inclusions. in this case it is taken as the pseudo cubic lattice constant of the perovskite structure [25]. to determine the pseuodocubic lattice constant ��� of the perovskite filler particles, the effective anion radius, accounting for the effect of oxygen vacancies must be calculated which in turn should be determined from an estimated size of the spherical filler particles from the given dielectric permittivity [20]. the atomic size of the filler particles which are assumed to be spherical can be calculated by the claussius mosotti equation: " = � ��� ��� � # (3) the value of " is taken as 2.36×1028 from [13] on the theoretical predictions of electric and magnetic parameters of microwave absorbers. rearranging (6), it can be rewritten as: �# = " $ � ��� + � � ��% (4) in (7), the first term accounts for the effect due to the electronic polarizability, while the second term represents the effect due to the dipole polarizability. since the dipole engineering, technology & applied science research vol. 13, no. 1, 2023, 9991-9996 9993 www.etasr.com arya: development of a graphical user interface for reflection loss calculation in perovskite-rgo … polarization is the dominant at microwave frequencies, the first term can be dropped giving the modified equation for the atomic radii of the spherical filler inclusion as: � = &" $ � ���% ' (5) this approximated value is used to calculate the effective oxygen anion radius in the perovskite unit cell: () ��� = *� − (, (6) the overall pseudo cubic lattice constant of the perovskite structure can be calculated as: ��� = -�./�0(*1 (7) where ./ = .2 .3 .4 is the product of the valence electron of cations a and b and o anion respectively. similarly (*1 is the average of the atomic radii of the a, b, and o atoms. k and s are constants with values 2.45 and 0.09 for cubic pervoskites. equation (7)is used to find the effective magnetic permeability from (2). effective permittivity and permeability are further used to calculate the input impedance of the absorber as follows: 567 = &89:: 9:: 8; ; (8) where �< and �< are the permeability and permittivity of free space respectively. after finding all the above parameters, the final reflection loss (rl) is calculated by: => = 20log �d�e�d;d�e�d; (9) where 5< is the characteristic impedance of the input medium taken as free space. iv. machine learning model-linear regression the multiple linear regression model is used to relate the rl which is the most important absorption characteristic of an absorber to the fundamental value of an atom that is its atomic radius. a plot between the cationic radii and the rl is presented in figure 2 suggesting an almost linear relationship between the output and the input parameters. the straight lines connecting the different data points and the shaded area indicate the change in rl with the change in individual atomic radius. the flowchart in figure 3 shows the flow of the given work and how the different parameters are ultimately fed to the machine learning algorithm. in order to first apply the multiple linear regression model, the validation of the significance of the input features is conducted by applying the ordinary least square (ols) method. there are two results in the ols model summary that are of interest, the coefficient of determination (=�) and the p-value. =� measures the amount of variation in the output feature captured by the corresponding variations in the input parameters while the p-value provides a conditional probability of a null output hypothesis. (a) (b) fig. 2. linear relationship between the rl and the cationic radii. fig. 3. step flow and parameter merging of the machine learning algorithm. if the p-value is less than 0.05, the input features do not fulfil the null hypothesis. in the ols model summary for the current model, both the above two requirements are met, thus both of our input features have significant effect on the output and can be successfully used in a linear regression relation with the output. after validating the parameters, multiple linear regression is applied. the linear regression forms a linear equation between the input and the output parameters and provides the intercept with the coefficient of the individual input parameters. from the given equation, rl can be predicted for the given dataset, and can be compared with the actual result. table i describes the dataset [20] for the various abo3 type perovskite materials with their respective permittivity values. this dataset was used for the calculations and the formation of the empirical results. engineering, technology & applied science research vol. 13, no. 1, 2023, 9991-9996 9994 www.etasr.com arya: development of a graphical user interface for reflection loss calculation in perovskite-rgo … table i. input and calculated electromagnetic parameters of pervoskite structures material fg hi hj hik lmnn i op iqr smnn tgu vw vwqhmx catio3 160 10.99 9.94 2.31 1170 1.437 48 8.022 3893.957 687.12 -14.07 -11.33 cazro3 27 10.99 16.79 2.71 957.3 2.628 48 9.4 5346.693 890.31 -9.93 -11.97 srzro3 30 18.57 16.79 3.32 964.1 2.534 48 11.524 8035.893 1087.63 -7.84 -9.13 bazro3 35 28.07 16.79 3.92 975 2.403 48 13.607 11203.44 1277.02 -6.55 -6.28 lagao3 27 22.86 6.26 3.42 957.3 2.628 54 11.984 8690.231 1135.05 -7.47 -7.53 srtio3 300 18.57 9.94 2.86 1292 1.164 48 9.941 5979.781 810.4 -11.19 -8.49 ndalo3 22.5 14.68 4.08 2.57 947 2.8 54 8.998 4899.176 856.86 -10.42 -11.59 laalo3 23 22.86 4.08 3.47 948.2 2.779 54 12.159 8945.896 1157.14 -7.31 -7.38 pralo3 23 16.67 4.08 2.78 948.2 2.779 54 9.746 5747.551 927.5 -9.45 -10.42 eralo3 16 7.51 4.08 1.89 931.6 3.157 54 6.62 2651.9 635.6 -15.9 -14.91 dyalo3 18 8.56 4.08 1.96 936.4 3.028 54 6.876 2860.948 658.49 -15.02 -14.4 gdalo3 18 9.94 4.08 2.11 936.4 3.028 54 7.416 3327.942 710.19 -13.39 -13.72 smalo3 20 11.85 4.08 2.29 941.2 2.918 54 8.034 3905.686 767.42 -12.03 -12.78 yalo3 16 17.64 4.08 3.40 931.6 3.157 54 11.942 8629.466 1146.57 -7.38 -8.21 fig. 4. 3-d model visualization of the given machine learning model. fig. 5. the developed gui. all the values provided in table i are used to calculate the various electromagnetic parameters derived in the previous theoretical framework which are also tabulated in table i along with the theoretical and predictive values of the rl. 3d graphical visualization of the variation in the rl with respect to cation a and b radii is presented in figure 4. the inclusion of the two cationic radii as input variables provides a rectangular model area, which covers all the data points provided for model training. the data plots are well contained within the model scope. from the given machine learning model, a gui is developed, as shown in figure 5, for the calculation of the rl of the perovskite compound and its effective permittivity based on the atomic radii provided by the user. the gui takes the cations' a and b radii as input and suggests a suitable microwave absorbing perovskite compound. it also shows the output rl and the effective permittivity based on the machine learning predictive model. the gui is tested by taking two sets of input atomic radii and the output results are matched with the results of table i. the results are in good accordance showing the high accuracy of the developed gui. table ii. modeling parameters of the proposed linear regression model intercept coefficients -17.605 [-2.944 -0.73] engineering, technology & applied science research vol. 13, no. 1, 2023, 9991-9996 9995 www.etasr.com arya: development of a graphical user interface for reflection loss calculation in perovskite-rgo … v. conclusion in the present work, a new and innovative method has been suggested of utilizing a theoretical framework to develop a machine learning gui for estimating the reflection loss in microwave absorbers. this work includes the diverse mechanisms and phenomena working behind the application of microwave absorption in a single equation using machine learning tools. this helps not only the simplification of the accurate calculation of reflection loss without going into huge depths of the physical processes of polarization, magnetism, and dissipation across the absorber, but also opens a new window to develop advanced software and algorithms devoted to the formation of new and complex kinds of microwave absorbers. using this approach, the microwave absorber can become a part of more general engineering. it is time we take advantage of the true potential of microwave absorbers because such materials can be used for the benefit of society, as in hospitals, schools, libraries, etc. reducing the harmful effects of the em wave radiation exposure in the ambient surroundings. vi. data availability statement the data that support the findings of this study can be accessed at [22]. nomenclature parameter notation effective relative permittivity ���� effective relative permeability ���� filler permittivity �6 radii of the spherical filler particle � effective radius of oxygen anion () ��� pseudo cubic lattice constant ��� volume fraction of filler inclusion y6 product of valence electron of cation a, b, and o ./ = .2.3 .4 average atomic radius of the a, b, and o atoms (*1 input impedance of the absorber 567 reflection loss (db) rl references [1] m. green and x. chen, "recent progress of nanomaterials for microwave absorption," journal of materiomics, vol. 5, no. 4, pp. 503– 541, dec. 2019, https://doi.org/10.1016/j.jmat.2019.07.003. 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[21] h. ohsato, "microwave dielectrics with perovskite-type structure," in perovskite materials synthesis, characterisation, properties, and applications, l. pan and g. zhu, eds. intechopen, 2016, https://doi.org/ 10.5772/61718. [22] a. arya, "microwaveabsorbergui." accessed: dec. 13, 2022. [online]. available: https://github.com/aayushiarya25/microwaveabsorbergui. [23] a. e. irmak, "structural and electrical properties of ca2+ doped lafeo3: the effect of a-site cation size mismatch," engineering, technology & applied science research, vol. 10, no. 2, pp. 5538–5546, apr. 2020, https://doi.org/10.48084/etasr.3443. [24] s. c. a. bikkina and p. v. y. jayasree, "development of a wire mesh composite material for aerospace applications," engineering, technology & applied science research, vol. 12, no. 5, pp. 9310–9315, oct. 2022, https://doi.org/10.48084/etasr.5201. engineering, technology & applied science research vol. 13, no. 1, 2023, 9991-9996 9996 www.etasr.com arya: development of a graphical user interface for reflection loss calculation in perovskite-rgo … [25] s. boumous, s. belkhiat, and f. kharchouche, "mgo effect on the dielectric properties of batio3," engineering, technology & applied science research, vol. 9, no. 3, pp. 4092–4099, jun. 2019, https://doi.org/10.48084/etasr.2705. authors profile aayushi arya is currently pursuing her phd from the ee department, indian institute of technology, hyderabad, india. with keen interest in fundamental and physical concepts, i have done research works in deriving the theoretical and mathematical framework of microwave absorbers followed by the integration of the derived concepts in advanced modeling tools such as machine learning. microsoft word etasr_v12_n5_pp9229-9232 engineering, technology & applied science research vol. 12, no. 5, 2022, 9229-9232 9229 www.etasr.com abdullah & hatem: assessing critical criteria for historical archeological buildings in iraq assessing critical criteria for historical archeological buildings in iraq oday hammoody abdullah department of civil engineering university of baghdad baghdad, iraq 10984@uotechnology.edu.iq wadhah amer hatem baquba technical institute middle technical university baghdad, iraq wadhah1970wadhah@gmail.com received: 18 june 2022 | revised: 13 july 2022 | accepted: 14 july 2022 abstract-this research was conducted to identify and evaluate the relative importance of the criteria in an archaeological building. open and closed questionnaires were used and interviews with experts and specialists from many ministries and governorates were conducted to identify the most important criteria. the aim determines what factors influence historic archaeological building success, and which criteria should be used to determine the best response. the data were analyzed with the spss v25 program using the relative importance index (rii) method to determine the relative importance of the considered 15 variables. rii allows the identification of the most important criteria based on responses from participants, and it is a useful tool for prioritizing indicators rated on likert-type scales. the data were analyzed using a formula from a previous study's relative index analysis method. providing information or a database of historic old buildings ranked first with rii = 92%, and providing information on the changes taking place in old buildings ranked second with rii = 88%. keywords-construction projects; historic archaeological buildings; relative importance index i. introduction architectural and art historians, historical geographers, and local historians are among those who study the environment of historical archaeological buildings [1]. archaeological discoveries of buried structures are frequently dismissed in favor of artifacts recovered from buried deposits associated with them [2]. the original architectural and structural system of approximately 25% of structures changes by restoration [3]. as a result, in some historical archaeology overviews, the study of buildings is virtually invisible. instead, surveys of vernacular architecture studies are being conducted [4]. others, aware of the importance of more integrated archaeology of buildings, find such perspectives strangely limited, whether in interpretations of neolithic europe or descriptions of mediaeval britain [5]. archaeologists around the world have used a variety of methods to focus their research and cultural resource management efforts on building remains that have survived above or below ground as wall foundations, floor surfaces, or post holes over the past 40 years, despite the general lack of attention paid to the study of buildings in the mainstream historical archaeology literature. some of this material is reviewed in [6]. we argue that built structures are an important part of the material remains of the past 500 years and that their study should be integrated with the study of sites, artifacts, and landscapes. to quantify the relative importance indices of an exhaustive list of the criteria of historical archaeological building in malaysia, the relative importance index (rii) technique was used in [7]. the paper is divided into five sections based on the importance of historical, archaeological building factors. in this study, the rii technique was used to rank historical and archaeological building criteria [8]. the survey's findings revealed that ignorance of planning and building regulations, insufficient housing schemes, unrealistic zoning, and the location of land are important factors that influence unauthorized building sitting [9]. data from previous related studies were analyzed using a formula for the relative index analysis method for historical/ archaeological buildings. the results revealed that site maintenance ranked first (rii = 0.836), warranty clauses in contract specifications to incorporate construction quality ranked second (rii = 0.830), and construction personnel training ranked third (rii = 0.826) [10]. the rii of the main criteria in descending order in [11] is: experience & past performance (ep), financial stability (fs), personnel capabilities (pc), equipment capabilities (ec), managerial capabilities (mc), health & safety (hs), past relationships (rr), and geographic location of contractor (gl) [11]. ii. identifying important criteria for historical archeological buildings because different criteria apply to different areas, different authors considered different criteria for historical buildings. previous research has identified a number of critical standards for historical and archaeological constructions (see table i). iii. research objectives the research objectives are: • to determine the factors that should be examined and taken into account when recommending a historical or archaeological structure. • criteria ranking according to their rii values. corresponding author: oday hammoody abdullah engineering, technology & applied science research vol. 12, no. 5, 2022, 9229-9232 9230 www.etasr.com abdullah & hatem: assessing critical criteria for historical archeological buildings in iraq table i. identified criteria from previous studies no. criterion symbol ref. 1 providing information or a database of historical old buildings c01 [10] there are differences and intersections between architectural, construction, electrical and other disciplines c02 existence of complete plans as a reality for the old buildings c03 2 having a regular maintenance system c04 [11] providing a schedule to determine the times of processing materials for maintenance c05 3 existence of a facility management system c06 [12] availability of specialized staff using bim technology c07 there is coordination between the members of the team that design the architectural, construction, electrical, and other specializations c08 4 presence of information on the changes taking place in old buildings, including additions and removals through time c09 [13] existence of a facility management system c10 availability of specialized staff using bim technology in the department c11 5 provides 3d models of old buildings c12 [14] there is documentation of information on ancient buildings c13 damage and lost items are controlled on site c14 there is continuous work to improve the quality of the design c15 iv. research methodology the following points describe briefly the methodology of the current research: • obtaining the necessary information and data during theoretical and field research on the study topic and using the research map to locate the historical/archaeological structure criteria. • using an open questionnaire to collect data from a group of experts to identify the criteria. • determining the criteria and selecting the study sample by using a closed questionnaire to collect data from the open questionnaire. • ranking the criteria with the rii method from higher to lower importance on the given scale, i.e. 1-very low, 2-low, 3-medium, 4-high, and 5-very high. v. pilot study for the closed questionnaire form a pilot study can be used to validate and evaluate closed questionnaires. risk is vital to contractors, clients, and consultants within the construction industry; however, the problems of risk assessment are complex and poorly understood in practice [15]. a questionnaire run that includes testing of question formulation is known as a pilot study, in which the effectiveness of various data collection methods is assessed by identifying and testing the most challenging inquiries [16]. in this phase, the questions are checked for clarity and any issues that may arise are discovered. an assessment group with at least 15 years of experience was used for this pilot study's closed questionnaire distribution. evaluation and assessment of the validity of the closed questionnaire form was carried out by experts, who confirmed the validity and suitability of the sections of the closed questionnaire form. all suggestions and comments were collected and rated, and all suggestions and proposed changes were discussed [17]. vi. closed questionnaire form distribution closed questionnaires were handed out to a selected group of participants. fifty survey forms were collected out of 60 sent forms and some samples were excluded due to lack of data and information. in the end, 45 closed questionnaire forms were considered and analyzed. vii. quantitative analysis data quantitative data were gathered and analyzed using a statistical program (ibm/spss v25). the factors were calculated for ranking using the rii technique. rii was used to rank the importance of each recommendation provided by the respondents [18]. the rii of the criteria is calculated by [19]: rii = � ∑��∗ � (1) where rii ranges from 0 to 1, w is the weight given to the factors by the responders, ranging from 1 to 5 (1 is less important and 5 is highly important), a is the total number of responses for that factor or option, and z is the highest weight (in this case, 5). viii. reliability and validity tests validity and reliability consider the most important method conditions for research tool design. therefore, validity and reliability of the closed questionnaire forms must be provided before any statistical analyses data. the value of reliability can be founded by finding the value of (cronbach's alpha, α) [20]. 1) reliability of closed questionnaire the term "reliability" refers to the measurement of true results and the stability and equality checks. reliability is a necessary, but not sufficient factor in determining the viability of a tool for measuring historical building criteria. 2) validity of closed questionnaire more than any single statistical tool, it is necessary to establish a relationship between the assessment and the behavior it is meant to measure in order to determine its validity. it is critical that the test be valid to use and interpret the results correctly. validity is equal to the square root of the coefficient of reliability [21]: v = √�� (6) where v is the validity and � the reliability. ix. statistical analysis the top test criteria were determined using the spss v25 statistical program. the results are provided in the form of tables to make them more understandable and straightforward. following the distribution and collection of completed engineering, technology & applied science research vol. 12, no. 5, 2022, 9229-9232 9231 www.etasr.com abdullah & hatem: assessing critical criteria for historical archeological buildings in iraq questionnaire forms, the next step was to determine a specific method for statistical and measurement purposes to complete the calculations and data analysis. 1) reliability most the social science research situations use the cronbach’s alpha. if it is more than 0.7, then the consistency index shows high reliability and it would be acceptable [18]. table ii shows the closed questionnaire's reliability for each criterion. table ii. cronbach's alpha for the closed questionnaire no. criterion cronbach's alpha {����} 1 c01 0.920 c02 0.810 c03 0.780 2 c04 0.800 c05 0.70 3 c06 0.77 c07 0.87 c08 0.88 4 c09 0.90 c10 0.65 c11 0.95 5 c12 0.88 c13 0.75 c14 0.77 c15 0.70 2) validity table iii shows the validity of each criterion for the historical archaeological building in the closed questionnaire. table iii. validity no. criterion ���� validity coefficient 1 c01 0.920 0.959 c02 0.810 0.900 c03 0.780 0.883 2 c04 0.800 0.894 c05 0.700 0.836 3 c06 0.770 0.877 c07 0.870 0.932 c08 0.880 0.938 4 c09 0.900 0.948 c10 0.680 0.824 c11 0.950 0.974 5 c12 0.880 0.938 c13 0.750 0.866 c14 0.770 0.877 c15 0.700 0.836 x. analysis of the closed questionnaire forms the first stage of a closed questionnaire is a description of the sample members' general experience. the second stage is an assessment of the criteria. respondents were asked to mark (spot) the criteria of historical archaeological buildings that they thought were important in a closed questionnaire and riis were calculated. the analysis and discussion of the results will be according to the parts mentioned, so each axis will be analyzed and discussed separately. a. part οne: (personal information) part one includes the personal information in closed questionnaire forms. 1) scientific qualifications table iv shows the frequency distribution of respondents according to their scientific qualification. table iv. scientific qualifications scientific qualification frequency percentage bsc 23 51.00% msc 12 27.00% phd 10 22.22% total 45 100.00% 2) engineering specialization table v shows the engineering specialization of the respondents. table v. engineering specialization engineering specialization frequency percentage civil 24 53.33% electricity 6 13.33% architectural 5 11.11% mechanical 4 8.89% environment 3 6.67% chemical 3 6.67% total 45 100.00% 3) actual experience table vi shows the experience of the respondents. table vi. experience actual experience frequency percentage (15-20) 15 33.33% (21-25) 5 11.11% (26-30) 11 24.45% more than 30 14 31.11% total 45 100.00% 4) labor sector the respondents' distribution according to the labor sector is shown in table vii. table vii. labor sector labor sector frequency percentage public 35 77.78% private 10 22.22% total 45 100.00% b. part two: evaluation of the criteria part two includes the evaluation of the criteria for historical archaeological buildings from the respondents. each question will be analyzed by rii to find the criteria ranking. table viii shows the analysis and ranking of the criteria from higher to lower importance. engineering, technology & applied science research vol. 12, no. 5, 2022, 9229-9232 9232 www.etasr.com abdullah & hatem: assessing critical criteria for historical archeological buildings in iraq table viii. criteria analysis and ranging by rii for historical archaeological buildings criterion very high high medium low very low ranking c01 30 12 3 0 0 92% c09 26 15 3 1 0 88% c15 21 16 8 0 0 86% c10 21 14 8 2 0 84% c02 12 28 4 1 0 82% c03 8 30 7 0 0 80% c11 7 29 9 0 0 79% c08 15 15 10 5 0 78% c12 8 23 13 1 0 76% c06 8 21 15 1 0 75% c04 10 19 10 6 0 74% c07 7 17 20 1 0 73% c05 13 13 11 5 3 72% xi. conclusion the development of a set of evaluation criteria for historical and archaeological structures is described in this paper. based on a thorough literature review, fieldwork, and discussion with selected experts from many governorates, a total of 15 criteria were identified in this study. rii calculation and analysis was used to rank the criteria from the most to the least important. the researchers were able to compare the relative importance of the criteria as perceived by respondents using these rankings. the first criterion is the provision of information or a database of old historical buildings which received the 92% of the vote, indicating that this criterion is very important. most of the criteria are construction activities, indicating that respondents agreed that historical and archaeological building criteria should be implemented. ministries and local governments can use the findings of this study to develop historical and archaeological structures, as well as using it as a pilot study to get feedback from a group of experts. experts were contacted to assess the questionnaire's validity and to confirm the suitability of the items for the research goals in order to identify any flaws in the questionnaire. acknowledgement this project is supported by the ministry of planning, iraq, and the university of baghdad. references [1] e. ziglio, gazing into the oracle: the delphi method and 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[22] m. a. akhund, h. u. imad, n. a. memon, f. siddiqui, a. r. khoso, and a. a. panhwar, "contributing factors of time overrun in public sector construction projects," engineering, technology & applied science research, vol. 8, no. 5, pp. 3369–3372, oct. 2018, https://doi.org/ 10.48084/etasr.2276. microsoft word 7-678-ed.doc engineering, technology & applied science research vol. 6, no. 5, 2016, 1149-1154 1149 www.etasr.com sheikhhasani et al.: investigation of the effect of friction stir spot welding of bh galvanized steel plates… investigation of the effect of friction stir spot welding of bh galvanized steel plates on process parameters and weld mechanical properties hamed sheikhhasani department of materials engineering karaj branch, islamic azad university karaj, iran hamedsheikhhasani@yahoo.com hamed sabet department of materials engineering karaj branch, islamic azad university karaj, iran h-sabet@kiau.ac.ir mehrdad abasi department of materials engineering karaj branch, islamic azad university karaj, iran mabbasi@kiau.ac.ir abstract—this study evaluates the effect of friction stir spot welding (fssw) pin shape on overlapping galvanized bh plates. fssw is done at 4, 6 and 9 seconds dwell time at two rotational speeds (1500 and 1800 rpm) by tools with 10 and 14 mm shoulder diameter. microstructural properties (om and sem), vickers micro hardness and tension are tested on the welded spots. by increasing shoulder diameter from 10 to 14 mm to joint two plates, microstructural grain size decreases by 23% in sz and 15% in tmaz. maximum fracture increases as shoulder diameter increases to 32%. keywords-friction stir spot welding; galvanized steel bh; pin shape i. introduction steel is the main material for structures of light and heavy vehicles. the emphasis on corrosion protection and safety has led to the increased utilization of galvanized steel in vehicles. however, galvanized steel welding causes some technical problems for producers and end consumers due to the certain differences between galvanized steel and similar uncoated steel. compared to low carbon steel, different electrical or physical properties lead to completely different weld ability and connection [1]. due to its advantages, friction stir welding (fsw) is used in different industries. a particular fsw process developed in the automotive industry is friction stir spot welding (fssw), which provides high quality joints. fssw galvanized steel is considered as a challenging alternative. however, little is known on the effect of fssw parameters on steel joints. according to some claims, fssw results in 90% savings in energy and 40% savings in equipment. moreover, investment and operating costs of fssw are relatively lower compared to resistance spot welding (rsw). hence, fssw is considered as an alternative for rsw [2-6]. four main fssw parameters include rotation speed (in rpm), tool shape, plunge depth and dwell time (interaction time). in fssw, a cylindrical rotating tool with a protruding pin plunges at a specific rate into the overlapping plates to a predetermined depth. it is then retracted rapidly either immediately or after the dwell period. the frictional heat generated softens the metal; the rotating pin causes material flow in both lateral and axial directions. the forging pressure exerted by the shoulder forms an annular, solid-state bond around the pin. the retracted pin leaves a characteristic exit hole. figure 1 depicts a scheme of fssw [7-13]. this study evaluates the effect of fssw tool shape on overlapping galvanized bh plates. fig. 1. schema of fssw steps (a) plunging; (b) stirring; (c) retracting. ii. experiment galvanized steel bh plates (0.7 mm in thickness) are used for the experiments. tables i and ii list the mechanical properties and composition of base material. fssw is performed by a cnc milling machine, made in usa. tungsten carbide tools with a convex scrolled shoulder and a protruding pin is used for fssw as shown in figure 2. in absence of a quality standard for fssw, a rsw standard (aws-d17.2) is used as a reference [14]. tensile shear is tested on butt-welded plates (175×25 mm) with an overlapping joint (25×25 mm), as shown in figure 3. fssw parameters include z-axis force, tool rpm, depth of penetration and dwell time. the milling machine was used is able to control the position where the required z-axis force is automatically applied by the machine. the welding parameters adopted include 8 mm/min feed rate (fr) at zaxis, 1500 and 1800 rpm rotation, 0.9 mm depth of penetration ( include 0.7 (a) (b) (c) engineering, technology & applied science research vol. 6, no. 5, 2016, 1149-1154 1150 www.etasr.com sheikhhasani et al.: investigation of the effect of friction stir spot welding of bh galvanized steel plates… mm depth of pin and 0.2 mm depth of shoulder ) and 4-9 s dwell time (dt). the diameter considered for each joint is an average of three specimens. tension of different fssw specimens is tested by a 1-ton static tension test machine (5 mm/min crosshead speed). the load values reported are an average of three welded specimens with similar parameters. the cross-section of welded specimens is mechanically sanded, polished and etched by 5% nital. a microscope is used to observe the microstructure. traverse micro hardness is tested on the polished and etched specimens under 30 gf load. table i. chemical composition (wt%) of the used bh plate c 0.006 si 0.006 s 0.012 p 0.016 mn 0.328 ni 0.017 cr 0.013 v 0.001 cu 0.006 al 0.035 zn 0.011 table ii. mechanical properties of the base metal bh material uts (mpa) ys (mpa) elongation (%) hardness (v) back hardanable (bh) 300 189 41 107 fig. 2. tungsten carbide tools used in this study with different shoulder diameters; a) 10 mm; b) 14mm. iii. results and discussion a. microstructure of the welded joint figure 4 shows a schematic cross section of a fssw joint. three zones are clear: і) stirred zone (sz); іі) thermo mechanically affected zone (tmaz); ііі) base metal (bs). the approximate position of these zones is shown in the macro graphic transverse section of a fssw specimen. fssw material experiences severe plastic deformation and high temperature caused by friction. tool shape influences material flow. figure 5 shows a soft coarse-grained ferritic bh microstructure. sz microstructure consists of fine-grained ferrite (figures 6a and 7a). in sz under the shoulder, the penetrating and rotating pin and shoulder exert a mechanical work and produce heat. in general, the heat is produced by the rotating pin when the shoulder contacts the plate. however, the plates are thin and the heat is largely produced by the shoulder contacting the plate. therefore, dynamic recrystallization will occur during simultaneous exertion of work and heat. as shown in figures 6a and 7a, the upper sz which is close to the pin is quickly cooled by retracting the pins from the plate; therefore, the recrystallized grains will not grow. this will provide a very fine microstructure. by traversing from sz to tmaz, the grain size will progressively be enlarged (figures 6b and 7b). tmaz is further away from the pin; therefore, the effect and the work of the rotating pin are lower than sz. thus, tmaz is influenced by heat, rather than mechanical work. static recrystallization will occur in tmaz. thermal conductivity of steel is lower than that of aluminum; therefore, cooling rate is lower and grains will spend more time at high temperature. as a result, the recrystallized grains will grow. the increase in shoulder diameter leads to a reduction in sz grain size; this reduction will increase as the rotation speed and dwell time increase. moreover, the increase in shoulder diameter increases tmaz grain size. in general, tmaz grains including polygonal ferrite and pearlite are finer than base material. table iii and figure 8 show the changes in grain size for bm, sz and tmaz. in addition, figure 9 compares different specimens; obviously, the shift from tool 1 to the tool 2 (10 mm shoulder diameter to 14 mm shoulder diameter) leads to 23% reduction in sz grain size and 15% reduction in tmaz grain size, on average.another important factor in determining the good joints is the bond width. figure 10 is a close-up view of bh joint. clearly, upper and lower work pieces are metallurgically bonded around the penetrating pin. the bond width is a critical factor determining the strength of the joint, which is relatively good in this study. fig. 3. tensile shear test in accordance with aws-d17.2 fig. 4. macro graphic fssw joint for galvanized bh plate (a) (b) engineering, technology & applied science research vol. 6, no. 5, 2016, 1149-1154 1151 www.etasr.com sheikhhasani et al.: investigation of the effect of friction stir spot welding of bh galvanized steel plates… fig. 5. microstructural bh fig. 6. microstructural fssw (a) sz, (b) tmaz (1800 rpm, pin 2) fig. 7. microstructural fssw (a) sz, (b) tmaz (1800 rpm , pin 1) table iii. sz and tmaz grain sizes tmaz grain size (mm) sz grain size (mm) diameter (mm) rotation speed (rpm) dwell time (s) specimen 13.00 6.80 10 1800 4 1 11.42 6.10 10 1800 6 2 10.00 5.70 10 1800 9 3 13.62 8.00 10 1500 4 4 12.10 7.20 10 1500 6 5 10.00 6.25 10 1500 9 6 11.42 5.80 14 1800 4 7 9.50 5.15 14 1800 6 8 8.50 4.30 14 1800 9 9 11.89 6.20 14 1500 4 10 10.00 6.00 14 1500 6 11 9.89 4.90 14 1500 9 12 (a) (b) (a) (b) engineering, technology & applied science research vol. 6, no. 5, 2016, 1149-1154 1152 www.etasr.com sheikhhasani et al.: investigation of the effect of friction stir spot welding of bh galvanized steel plates… fig. 8. variations in sz and tmaz grain size fig. 9. changes in grain size by the changes in tools for the compared joints fig. 10. intersection of the joint. galvanized steel bh, 9 s dwell time, pin 2 b. mechanical properties of joints: tension-shear and micro hardness table iv reports the results of tension test for joints. note that, one of the goals of tension-shear test is to determine the mechanically reasonable or unreasonable properties of the joints. tension of a welded specimen is reasonable when the fracture locally occurs around the nugget in the base metal, or the upper plate, entirely or partially, remains as a nugget at least on the lower plate. as shown in table iv, the increase in shoulder diameter leads to an increase in friction, heat and fracture which increases by higher rotation speed and dwell time (figures 11 and 12). the increase in shoulder diameter leads to an increase in friction, thereby more input heat; this increases sz volume and eventually causes fracture. table iv. results of tension-shear test on spot welded joints group fracture position diameter (mm) rotation speed (rpm) dwell time (s) tension (n) specimen 1 fracture in joint 10 1800 4 2486 1 1 fracture in joint 10 1800 6 2838 2 3 fracture in base metal 10 1800 9 3067 3 1 fracture in joint 10 1500 4 1600 4 1 fracture in joint 10 1500 6 2770 5 3 fracture in base metal 10 1500 9 3023 6 2 fracture around the nugget 14 1800 4 3419 7 2 fracture around the nugget 14 1800 6 3838 8 3 fracture in base metal 14 1800 9 5026 9 2 fracture around the nugget 14 1500 4 3210 10 2 fracture around the nugget 14 1500 6 3750 11 3 fracture in base metal 14 1500 9 4020 12 fig. 11. welding strength versus rotation speed at the dwell times for pin 2 fig. 12. comparison of tension-shear curves versus dwell time for different pins engineering, technology & applied science research vol. 6, no. 5, 2016, 1149-1154 1153 www.etasr.com sheikhhasani et al.: investigation of the effect of friction stir spot welding of bh galvanized steel plates… figure 13 shows the fracture levels and cross section of the lap shear specimens joined at two different shoulder diameters. there is a marked change in the fracture position as the shoulder diameter increases. fractures also show the exact shear strength of the specimens. based on their fracture behavior, joints can be divided into three groups: 1) through the fracture, the upper plate partially remains under the lower plate (figure 13a), 2) cracks occur and expand around the nugget and concave shoulder (figure 13b), 3) cracks occur and expand farther away from the nugget and in base metal (figure 13c). in the first group, nugget is small, sz is limited and cannot penetrate enough into the lower plate. thus, the bond is weak. in the second group, the nugget is small, sz is limited and cracks start to propagate and expand in sz around the nugget and the upper plate which becomes thinner by the penetrating shoulder. in the third group for which the tool with larger shoulder diameter is used, nugget is larger, suggesting that sz penetrates enough into the lower plate; in this case, fracture occurs mostly in base metal. accordingly, strength is lower in the first group than the second group and in both groups than the third group where fracture occurs in the base metal. as shown in figure 14, the shift from tool 1 to tool 2 (changing the shoulder diameter from 10 mm to 14 mm) increases the fracture by 32%, on average. fig. 13. types of fractures in the tension-shear test fig. 14. the increase in fracture (%) by changing the tool for compared specimens figures 15 and 16 show the variations in micro hardness by changing tool, dwell time and rotation speed. the highly hard zone corresponds to sz. sz and tmaz micro hardness increases as the shoulder diameter increases to 14 mm. the average hardness of the base metal is about 107 hv. the maximum sz hardness is seen in the joints welded by tool 2 in 9s dwell time, 1800 rpm. in general, sz and tmaz micro hardness will increase as the shoulder diameter, rotation speed and dwell time increase. therefore, higher sz and tmaz hardness results from larger grain boundaries compared to bm. fig. 15. variations in hardness versus distance from nugget (shoulder diameter 10 mm) fig. 16. variations in hardness versus distance from nugget (shoulder diameter 14 mm) in general, there is a direct relationship between reduced grain size and increased strength and hardness; in fine-grained structures, fracture is higher and thus the joint is stronger. iv. conclusion the main results found in this paper can be summarized as: 1. tool shoulder diameter directly influences the strength and microstructure of fssw galvanized steel joints. 2. the increased shoulder diameter from 10 to 14 mm reduces the grain size in sz and tmaz microstructure by 23% and 15%, on average. moreover, the increased shoulder pin diameter increases fracture) by 32%. 3. based on tool shoulder diameter, rotation speed and dwell time, fracture of the specimens can be divided to three groups. 4. the highest fracture (5026n) is related to the joint welded by the tool with 14 mm shoulder diameter, 1800 rpm rotation speed and 9 s dwell time. 5. by increasing shoulder diameter, rotation speed and dwell time of the tool, mechanical work and consequently heat will increase and the grain sizes will be dramatically reduced. thus, hardness will increase in the welded zone. however, moving away from the joint will reduce hardness, which results from the increased grain sizes. (a) (b) (c) engineering, technology & applied science research vol. 6, no. 5, 2016, 1149-1154 1154 www.etasr.com sheikhhasani et al.: investigation of the effect of friction stir spot welding of bh galvanized steel plates… references [1] s. w. baek, d. h. choi, c. y. lee, b. w. ahn, y. m. yeon, k. song, s. b. jung, “microstructure and mechanical properties of friction stir spot welded galvanized steel”, the japan institute of metals, pp.1044-1050, 2010 [2] j. m. piccini, h. g. svoboda , “effect of pin length on friction stir spot welding (fssw) of dissimilar aluminum-steel joint”, procedia materials science, vol. 9, pp. 504-513, 2015 [3] a. gerlich, p. su, t. h. north, “tool penetration during friction stir spot welding of al and mg alloyes”, journal of materials science,vol. 40, pp. 6473-6481, 2005 [4] m. awang, “simulation of friction stir spot welding (fssw) process: study of friction phenomena”, phd thesis, college of engineering and mineral resources, west virginia university, 2007. [5] j. zhang, y. shen, b. li, h. xu, x. yao, b. kuang, j. gao , “numerical simulation and experimental investigation on friction stir welding of 6061-t6 aluminum alloy”, materials & design, vol. 60, pp. 94-101, 2014 [6] v. x. tran, j. pan, t. pan, “effects of processing time on strengths and fracture modes of dissimilar spot friction welds between aluminum 5754-o and 7075-t6 sheets”, journal of materials processing technology, vol. 209, pp. 3724-3739, 2008 [7] y. tozaki, y. uematsu, k. tokaji, “effect of tool geometry on microstructure and static strength in friction stir spot welded aluminium alloys”, international journal of machine tools & manufacture, vol. 47, pp. 2230-2236, 2007 [8] m. awang, v. h. mucino, z. feng, s. a. david, “thermo-mechanical modeling of friction stir spot welding (fssw) process use of an explicit adaptive meshing scheme”, science and engineering, vol. 01, pp. 1251-1256, 2006 [9] s. venukumar, s. yalagi, s. muthukumaran, “comparison of microstructure and mechanical properties of conventional and refilled friction stir spot welds in aa 6061-t6 using filler plate”, transactions of nonferrous metals society of china, vol. 23, no. 10, pp. 2833-2842, 2013 [10] h. badarinarayan, y. shi, x. li, k. okamoto,”effect of tool geometry on hook formation and static strength of friction stir spot welded aluminum 5754-o sheets”, international journal of machine tools & manufacture, vol. 49, pp. 814-823, 2009 [11] a. gerlich, p. su, m. yamamoto, t. h. north, “effect of welding parameters on the strain rate and microstructure of friction stir spot welded 2024 aluminum alloy”, journal of material science, vol. 42, pp. 5589-5601, 2007 [12] c. gao, r. gao, y. ma , “microstructure and mechanical properties of friction spot welding aluminium–lithium 2a97 alloy”, materials & design, vol. 83, no. 15, pp.719-727, 2015 [13] j. m. piccini, h. g. svoboda, “effect of the tool penetration depth in friction stir spot welding (fssw) of dissimilar aluminum alloys”, procedia materials science, vol. 8, pp. 868-877, 2015 [14] g. buffa, l. fratini, m. piacentini, “on the influence of tool path in friction stir spot welding of aluminum alloys”, journal of materials processing technology, vol. 208, pp. 309-317, 2008 microsoft word etasr_v13_n3_pp10781-10784 engineering, technology & applied science research vol. 13, no. 3, 2023, 10781-10784 10781 www.etasr.com zisopol et al.: comparison of the charpy resilience of two 3d printed materials: a study on the … comparison of the charpy resilience of two 3d printed materials: a study on the impact resistance of plastic parts dragos gabriel zisopol mechanical engineering department, petroleum gas university ploiesti, romania zisopol@zisopol.ro nae ion mechanical engineering department, petroleum gas university ploiesti, romania inae@upg-ploiesti.ro alexandra ileana portoaca mechanical engineering department, petroleum gas university ploiesti, romania alexandra.portoaca@upg-ploiesti.ro (corresponding author) received: 23 march 2023 | accepted: 20 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5876 abstract charpy impact testing is a widely used method for the evaluation of the toughness of materials, including 3d-printed plastic parts. this study performed charpy test on 3d-printed samples made of pla and abs. factors such as layer thickness and infill percentage varied (0.10, 0.15, and 0.20mm layer height and 50, 75, and 100% infill percentage) to investigate how they affect the mechanical properties of 3d printed parts, including their toughness. keywords-3d printing; fdm; charpy test; resilience i. introduction charpy impact testing is a widely used method for evaluating the toughness of materials, including 3d-printed plastic parts. the charpy test involves striking a notched sample with a pendulum and measuring the energy absorbed by it as it fractures. there is a growing interest in the use of 3d printing technologies for producing plastic parts, but concerns remain about their impact resistance and durability, leading to extensive studies on the charpy resilience of 3d-printed plastic parts [1-3]. some studies have shown that the charpy resilience of 3dprinted plastic parts can vary significantly depending on the printing process, material properties, and design parameters, as factors such as layer thickness, infill density, and printing orientation can affect the mechanical properties of the 3dprinted parts, including their toughness [4-7]. despite these challenges, there have been promising developments in the use of 3d printing technology for producing high-strength plastic parts with good impact resistance [3]. various approaches have been explored, such as optimizing printing parameters and incorporating fillers into the printing material to improve the charpy resilience of 3d-printed plastic parts [4, 8]. overall, the charpy resilience of 3d printed plastic parts remains an important area of research for improving the performance and durability of 3d printed products, particularly in applications where impact resistance is critical [9-12]. the charpy resilience of 3d-printed plastic parts could play a crucial role in many applications, such as aerospace [3], automotive industry [7], medical industry [8], and sporting goods industry. this study investigated how different printing parameters affect the mechanical properties of 3d-printed parts by varying layer height and infill percentage. the layer height is the thickness of each material layer deposited by the 3d printer. a smaller layer height can result in a smoother surface finish but may also decrease the strength of the part due to the lower interlayer bonding strength. the infill percentage refers to the amount of material used to fill the interior of the part. a higher infill percentage generally results in a stronger part, but may also increase weight and printing time [14-17]. the printing process can be optimized to produce parts with the desired balance of strength, weight, and surface finish by varying both these parameters [18]. this approach can lead to the development of new 3d printing materials and printing processes that can produce parts with improved mechanical properties, and ultimately expand the range of applications for 3d-printed parts [19-22]. in industrial equipment, 3d-printed plastic parts with good charpy resilience could be used in the engineering, technology & applied science research vol. 13, no. 3, 2023, 10781-10784 10782 www.etasr.com zisopol et al.: comparison of the charpy resilience of two 3d printed materials: a study on the … production of heavy machinery which can be subjected to high loads and impact forces [23-27]. in general, any application where the 3d-printed plastic part is expected to be subjected to impact loads, shock, or vibration, could benefit from improved charpy resilience [27-28]. ii. materials, methods, and procedures a. parameters setup table i shows the technical specifications provided by the filament producers (raise for pla and verbatim for abs). this study fabricated samples with 3 infill percentages: 50, 75, and 100%. resilience tests were performed on both materials (pla and abs) to assess their mechanical characteristics, as shown in table ii. the height of the layer was also varied, taking values of 0.1, 0.15, and 0.20mm, as listed in table ii. table i. 3d-printed sample characteristics parameters material specifications pla abs nozzle diameter 0.40mm 0.40mm build orientation flat flat top solid layers 4 layers 4 layers bottom solid layers 4 layers 4 layers outline/perimeters shell 3 outlines 3 outlines internal fill pattern lines lines external fill pattern rectilinear rectilinear internal infill angle offsets 45°-135° 45°-135° extruder temperature 210°c 240°c heated bed temperature 60°c 110°c default printing speed 70mm/s 45mm/s cooling fans on on filament diameter 1.75mm 1.75mm filament density 1.24g/cm3 1.04g/cm3 b. sample preparation a raise e2 3d printer was used to fabricate the samples with a volume capacity of 330×240×240mm. the samples were designed with the solid edge software and were converted into stl format. the slicing parameters, including internal structure pattern, infill percentage, and layer thickness, were fine-tuned with the idea maker [29]. the samples were x-y oriented and printed with a bed platform for better adhesion to the printing table, as shown in figure 1. the tests were performed on an instron charpy resilience tester (figure 3), according [30]. this test can be used to explore how particular types of 3d-printed samples behave under specified impact conditions and to gauge the brittleness or toughness of samples within the constraints of the standard test environment (20°c and 45% humidity). figure 2 shows the dimensions of the samples. a type a notch was included in the sample design with a radius rn= (0.25±0.05)mm. c. charpy test a series of tests were conducted to assess the mechanical performance and impact resistance. table ii shows the sample sets number for each printing parameter. the impact properties test was performed at the liea laboratory, in isim timișoara, on an instron pendulum charpy tester. table ii. printing parameters constant parameters building orientation x, y extrusion temperature: te bed temperature: tp speed: vp variable parameters spur gears layer hight (hs) infill percentage (pu) abs pla (mm) (%) no. samples 0.10 50 75 100 15 15 0.15 15 15 0.20 15 15 (a) (b) (c) fig. 1. printed samples for 3 different layer thicknesses: 0.10, 0.15, and 0.20mm. fig. 2. sample dimensions. fig. 3. instron testing machine. iii. results and discussion charpy impact tests were conducted to examine the energy absorption and damage type of the various configurations. this test utilizes a dynamic three-point bending experiment on a notched specimen using a charpy device. the experimental arrangement involves the specimen, anvils that provide free support for it, and a pendulum attached to a rotating arm that is pinned to the machine frame. the pendulum is elevated to a predetermined height and then released to fall along a circular path, striking the specimen at its midpoint. this impact transfers kinetic energy to the specimen and causes the engineering, technology & applied science research vol. 13, no. 3, 2023, 10781-10784 10783 www.etasr.com zisopol et al.: comparison of the charpy resilience of two 3d printed materials: a study on the … pendulum to rise to a measurable height [31]. tables iii and iv show the values and averages of maximum energy absorbed for each combination of layer height and infill percentage of the pla and abs materials studied. the total fracture energy was determined by [31]: �� = ���ℎ� − ℎ � ± 0.2 (j) (1) where et is the total energy, m is the mass, g is the gravitational acceleration, h₀ is the original height, and hf is the final height. table iii. average values of pla impact energy sample no. pla energy (j) 0.10 100% 0.0781374 0.10 75% 0.0884992 0.10 50% 0.071886 0.15 100% 0.0809428 0.15 75% 0.0749916 0.15 50% 0.0780908 0.20 100% 0.0821652 0.20 75% 0.0799704 0.20 50% 0.0764726 table iv. average values of abs impact energy sample no. abs energy (j) 0.10 100% 0.3244052 0.10 75% 0.2304624 0.10 50% 0.287763 0.15 100% 0.2698752 0.15 75% 0.247020 0.15 50% 0.2491146 0.20 100% 0.313584 0.20 75% 0.2775298 0.20 50% 0.2841294 fig. 4. range of maximum energy absorbed for pla samples. the maximum impact energy was significantly different when using pla or abs. as shown in table iii, the average values of layer thickness and infill percentage for pla samples were very similar. in particular, layer thickness did not influence the dispersion of the average values. as expected, some notable values were noticed for the 100% infill specimens. in addition, the abs material exhibited a much higher toughness. this printed material is more likely to withstand high levels of impact without fractures, as its results were 75.91% higher in 0.1mm layer thickness and 100% infill, as shown in figure 6. lower differences in maximum energy can be noticed for the combinations: hs=0.10mm, pu=50%:68.81%; hs=0.10mm, pu=75%:69.28%; hs =0.15mm, pu=75%:69.64%; hs=0.15mm, pu=50%:68.65%. as noted in [32-34], the average values of the mechanical characteristics were different for abs and pla. figure 7 shows that although the tensile strength is higher for pla, abs behaves better in terms of absorbed impact energy. the impact energy of a material depends on its composition, microstructure, geometry, temperature, loading rate, and testing method. these factors also affect the deformation and failure behavior of the material under impact loading. fig. 5. range of maximum energy absorbed for abs samples. fig. 6. comparison of maximum energy absorbed for pla and abs. fig. 7. variation of impact energy. iv. conclusions this study investigated the impact resistance testing of the two most common materials used in 3d printing with fdm technology to compare them to help users choose the right material for different practical applications. the pla material is more brittle in the charpy test because it absorbs a small amount of energy during testing, while abs has a ductile behavior because it absorbs a large amount of energy. it is important to note that the maximum charpy energy for a printed part can be influenced by a variety of factors, including the printing parameters, such as the variation of layer height and infill percentage, part design, and post-processing techniques. pla has a fragile comportment at the charpy test because it absorbs a small amount of energy during testing, while abs behaves as ductile because it absorbs a large engineering, technology & applied science research vol. 13, no. 3, 2023, 10781-10784 10784 www.etasr.com zisopol et al.: comparison of the charpy resilience of two 3d printed materials: a study on the … amount of energy. therefore, it's a good idea to test and validate the toughness and impact resistance of 3d-printed parts under actual use conditions. references [1] d. r. hetrick, s. h. r. sanei, o. ashour, and c. e. bakis, "charpy impact energy absorption of 3d printed continuous kevlar reinforced composites," journal of composite materials, vol. 55, no. 12, pp. 1705– 1713, may 2021, https://doi.org/10.1177/0021998320985596. 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[34] b. belarbi, m. e. a. ghernaout, and t. benabdallah, "implementation of a new geometrical qualification (dq) method for an open access fused filament fabrication 3d printer," engineering, technology & applied science research, vol. 9, no. 3, pp. 4182–4187, jun. 2019, https://doi.org/10.48084/etasr.2689. microsoft word etasr_v13_n2_pp10285-10291 engineering, technology & applied science research vol. 13, no. 2, 2023, 10285-10291 10285 www.etasr.com mangnejo et al.: a three-dimensional parametric study of the effects of a fault rupture on a … a three-dimensional parametric study of the effects of a fault rupture on a multi-story building dildar ali mangnejo department of civil engineering, mehran university, pakistan dildarali@muetkhp.edu.pk (corresponding author) israr ahmed channa department of civil engineering, quaid-e-awam university of engineering, science & technology, pakistan israrchanna8@gmail.com muhammad auchar zardari department of civil engineering, quaid-e-awam university of engineering, science & technology, pakistan muhammad.auchar@quest.edu.pk received: 4 january 2023 | revised: 21 january 2023 | accepted: 23 january 2023 abstract earthquake events have shown that besides the earthquake forces, the interaction between the fault rupture and structures could cause a lot of damage. field observations have revealed the need to design structures for fault-induced loading in regions with active faults. in this study, three-dimensional numerical simulation was carried out to evaluate the performance of a 20-story frame building subjected to the propagation of normal fault rupture. a parametric study was conducted with the propagation of the fault slip (h) with outcrop to the right (s/b=-1.0), at the mid (s/b=0.5), and left (s/b=2.0) of the raft. an advanced hypoplastic sand model (which can capture small-strain stiffness and stress-state dependent dilatancy of sand) was adopted. the concrete damaged plasticity (cdp) model was used to capture the cracking behavior in the concrete beams, columns, and piles. the computed results revealed that the performance of the building due to the propagation of the normal fault rupture depends on the position of the outcrop of the rupture with respect to the building. among the three simulated cases, the maximum differential settlement occurred when s/b= 0.5. in each case, the lateral movement of the building caused inter-story drift which may induce distress in the structural components of the building. the beams and the columns of the first story were fully damaged in tension when s/b was equal to -1.0 or 0.5. keywords-high-rise building; normal fault rupture; differential settlement; damage i. introduction high-rise buildings are often planned in areas with intensive active faults [1]. faults are lengthy areas where the layers of the ground are fractured and produce a zone. these fractures are often slant and are not vertical. thus, it has become important to investigate the effects of fault rupture causing damage to the infrastructure [2]. with surface rupture there are many unknowns, so a probabilistic analysis is currently the best approach for the development of a range of expected displacements. however, the actual displacement that occurs with surface rupture can vary drastically from the expected values. to understand the failure mechanism of these foundation systems, including strip and caisson foundations, experimental and theoretical studies have been conducted [3-8]. the position of the foundation relative to the bedrock fault and the magnitude of the bedrock fault movement were found to be crucial influencing factors. in addition, the presence of foundation systems modifies the path of fault ruptures, as the latter propagates from the bedrock to the ground surface. pile foundations, as deep foundations, behave differently from shallow ones when subjected to faulting-induced deformation [3, 9]. in some specific cases [10], ground movement after an earthquake reportedly caused cracks and deformation of pile foundations. the mechanism behind this type of failure is significant for the performance of structures. researchers have engineering, technology & applied science research vol. 13, no. 2, 2023, 10285-10291 10286 www.etasr.com mangnejo et al.: a three-dimensional parametric study of the effects of a fault rupture on a … recently developed theoretical methods to evaluate the behavior of piles subjected to soil movement induced by normal faults [5]. although the main characteristics of fault-rupture propagation can be well described by advanced constitutive models, physical modeling is necessary to derive deeper insight into the interaction mechanisms and to offer experimental data for model validation. in addition, very limited field data are available to verify the theoretical methods because it is practically impossible to simulate a bedrock fault movement in the field. among those numerical studies, however, responses of framed building to excavation were reported in some. however, most of the previous studies have focused on the fault effects on shallow foundations. therefore, there is a gap of systematic research on the response of a high-rise building subjected to live load and resting on piled raft to the propagation of a normal fault rupture outcrop at different distances from the building. to obtain a satisfactory numerical model of twin excavation effects on high-rise buildings, the analysis needs to take into account the small strain nonlinearity of the soil. in view of the aforementioned issues, this study aims to systematically investigate the effects of a normal fault rupture on an existing 20-story high rise building in sand. to achieve these objectives, three-dimensional finite element analysis was conducted. ii. characteristics of a soil-pilestructure system a. general with the prime objective of investigating the effects of propagation of normal fault rupture on a high-rise building, three-dimensional finite element analysis was adopted in this study. a normal rupture with dip angle of 60 0 was imposed at the proximity of a 20-story high-rise building which is resting on a 4×4 piled raft foundation in sand (with relative density, dr=70%). figure 1(a) illustrates the general setup of the 20story building founded on the piled raft. (a) (b) fig. 1. (a) schematic illustration of a normal fault rupture interaction with a high-rise building, (b) piles arrangement in the raft. a 60m high, 15m wide 20-story concrete building with 3 spans in each direction was selected in study. the building was founded on a square raft, 15m wide and 1.5m thick, supported by a group of piles in a 4×4 configuration with center-to-center distance of 3.75m (see figure 1(b)). the diameter (dp) and the length (lp) of each pile were 1m and 20m, respectively. a normal rupture (having length of fault slip h=60cm) with dip angle of 60 0 with the horizontal was imposed at the proximity of the building. the prime objective of this study is to assess the impact of normal fault rupture on the 20-story building under dead and live loads. a live load of 5kpa was adopted in this study. with this adopted piled raft system, the numerical prediction showed that settlement of the building due to dead and live load was 8mm (0.8% dp) which is within the limit of the allowable foundation settlement of 50mm [11]. the parametric study was conducted with propagation of the fault slip (h) with an outcrop to the right (s/b=−1.0), at the mid (s/b=0.5), and the left (s/b=2.0) of the piled raft (where s is the distance between the left edge of the raft and the emergence of the fault at ground surface and b is the width of the raft). b. features of the building figure 2(a) shows the sections (with reinforcement details) of a typical beam and column of the high-rise building. the sections were designed by a routine design procedure using sap2000 based on aci. all the sections of the beams and columns are rectangular in shape having sizes of 230mm by 600mm and 230mm by 460mm, respectively. each beam is reinforced with tension and compression steel bars. tension and compression reinforcement consist of three 12mm diameter bars and three 12mm diameter bars, respectively. the bars have 60mm center to center spacing. these main bars are confined by 10mm diameter stirrups with center to center spacing of 125mm. each column is reinforced with six 12 mm diameter main bars. these main bars are confined by the lateral ties having diameter 10mm at center to center spacing of 150mm. (a) (b) fig. 2. (a) schematic illustration of a normal fault rupture interaction with a high-rise building, (b) pile arrangement in the raft. c. features of the foundation the building was founded on a 15m size and 1.5m thickness square raft supported by a group of piles in a 4×4 configuration with center to center distance of 3.75m (figure 1(b)). the diameter (dp) and length (lp) of each pile were 0.8m and 20m, respectively. figure 2(b) shows the section of a engineering, technology & applied science research vol. 13, no. 2, 2023, 10285-10291 10287 www.etasr.com mangnejo et al.: a three-dimensional parametric study of the effects of a fault rupture on a … typical pile with reinforcement. the pile is reinforced with six 20mm diameter longitudinal bars which are equally spaced around the pile. these bars are connected with spirals of 10mm diameter with center to center spacing of 200mm. d. characteristics of the numerical model figure 3 shows the finite element mesh developed in abaqus software. the size of the mesh numerical run was taken as 120m×60m×30m. the different structural components of the building frame (i.e. beams and columns) and the slabs and raft were modelled by eight-node hexahedral brick elements (c3d8) and four-node shell elements (s4), respectively. the concrete damaged plasticity constitutive model is based on the fracture energy theory and the plasticdamage model of [11] is adopted to simulate the nonlinear behavior of the building frame. elastic perfectly-plastic constitutive model is used to model the mechanical behavior of steel reinforcements. the detailed steel reinforcement and concrete material properties are listed in table i. eight-node hexahedral brick (c3d8) elements were used to model the soil and the piles, while two-node truss elements were adopted to model the steel reinforcements of beams, columns and piles. the size of the elements was chosen as 1.5mm. table i. mechanical properties of the frame of the building material constitutive model input parameter value concrete damage plasticity model mass density (kg/m 3 ) 2400 elastic modulus (kpa) 3.15×10 7 poisson's ratio (v) 0.2 dilation angle ( o ) 30 eccentricity 0.1 stress ratio 0.666 ultimate strength ratio 1.16 tensile yield stress (kpa) 1.32×10 3 compressive yield stress (kpa) 6.17×10 3 steel reinforcement elastic-perfectlyplastic mass density (kg/m 3 ) 7850 elastic modulus (kpa) 2000 poisson's ratio (v) 0.3 yield stress (kpa) 4×10 5 fig. 3. 3d finite element mesh (showing the building and the foundation). since the stress-strain relationship of soils is highly nonlinear even at very small strain and the stiffness of the soil depends on the recent stress or strain history of the soil [12], an advanced hypoplastic model was used in this study to simulate the behavior of sand. the basic hypoplastic soil model requires 8 material parameters to describe the non-linear behavior of the sand (′c, hs, n, ed0, ec0, ei0, α and β). parameter ′c is soil frictional angle at the critical state. parameters hs and n are used to describe the shape of limiting void ratio lines. parameters ed0, ec0, and ei0 are reference void ratios of isotropic normal compression line, critical state line, and minimum void ratio line, respectively. the effects of soil relative density on peak frictional angle and shear stiffness are characterised by α and β. to consider the small strain stiffness and stress path-dependent soil behavior, the concept of intergranular strain is incorporated into the basic model [13], which includes additional five parameters (mr, mt, r, βr and χ). by using the concept of intergranular strain, the modified hypoplastic sand model has the ability to capture effects of shear strain and stress path on soil stiffness. these five parameters were obtained by fitting the stiffness degradation curves of toyoura sand obtained from the stress-path triaxial tests carried out in [11]. the model parameters were taken from [14]. the authors calibrated and validated all the parameters of the hypoplastic sand model against their centrifuge test results (which was performed to simulate excavation in sand). these parameters are summarized in table ii. table ii. hypoplastic model parameters of sand description parameter effective angle of shearing resistance at critical state: ’c 31 o hardness of granulates, hs 2.6gpa exponent n 0.27 minimum void ratio at zero pressure, ed0 0.61 maximum void ratio at zero pressure, ec0 1.10 critical void ratio at zero pressure, ei0 0.98 exponent α 0.14 exponent β 6 parameter controlling initial shear modulus upon 180 strain path reversal, mr 11 parameter controlling initial shear modulus upon 90 strain path reversal, mt 6 size of elastic range, r 2×10 -5 parameter controlling degradation rate of stiffness with strain βr 0.1 parameter controlling degradation rate of stiffness with strain χ 1.0 the lateral coefficient of earth pressure (k0) is estimated by the empirical equation �1 � sin φ, proposed in [15], where φ' is the internal friction of soil at the critical state. since the internal friction angle of toyoura sand at the critical state is 31°, thus, the k0 value is estimated as 0.5. e. soil structure interactions and boundary conditions when modeling the excavation-pile-soil problem, one of the most important aspects of modeling soil structure interaction (ssi) is to establish the interaction between the pile and the surrounding soil, because relative pile soil movement and separation between the raft and the soil can occur during the propagation of the normal fault rupture. to incorporate the interactions between pile-soil and raft-soil, surface-to-surface contact technique provided in abaqus software package was engineering, technology & applied science research vol. 13, no. 2, 2023, 10285-10291 10288 www.etasr.com mangnejo et al.: a three-dimensional parametric study of the effects of a fault rupture on a … used. the interface was modeled by the coulomb friction law, in which the interface friction coefficient (μ) and limiting displacement (γlim) are required as input parameters. a limiting shear displacement of 5mm was assumed to achieve full mobilization of the interface friction equal to μ×p', where p' is the normal effective stress between two contact surfaces, and a typical value 0.35 of μ for a bored pile was used in all analyses [14]. roller and pin supports were applied to the vertical sides and the base of the mesh, respectively. therefore, the movements normal to the vertical boundaries and in all directions of the base were restrained. f. fault simulation since the primary goal of this study is the interactive mechanism between the fault rupture and the foundation, the bedrock was simulated as a rigid boundary. to model fault rupturing in the bedrock, the bottom boundary which corresponded to the surface of the bedrock was split into two parts, as shown in figure. 3. the left part represented the hanging wall (i.e. the moving block), and the other part simulated the footwall. as figure 3 shows, during the fault rupturing the boundaries of the hanging wall (i.e. the moving block) moved downwards parallel to the dip angle (i.e. α = 60°). note that in order to satisfy the equilibrium, the bottom and left boundaries of the hanging block were subjected to displacement to simulate fault rupturing. g. numerical simulation procedure numerical simulations of three cases were carried out in the following steps:  step 1: initial geostatic stresses were generated in the mesh by applying gravity load. the considered coefficient of lateral earth pressure was 0.5.  step 2: the piles were constructed and the raft was placed on the top of the pile group and soil deposit.  step 3: the 20-story building was constructed on top of the pile raft. a live load of 5kpa was applied on the floor slab of each story. displacements were applied to the base and side boundaries of the hanging wall to simulate a fault rupture in the rock layer beneath, with a dip of 60° (as shown in figure 3). iii. interpretation of computed results a. evolution of differential settlement of the piled raft with propagation of the fault rupture figure 4 shows the differential settlement (between point a and point b, see the inset) with propagation of the fault slip (h) which has an outcrop to the right (s/b=−1.0), mid (s/b=0.5), and left (s/b=2.0) of the raft. the positive and negative values of the differential settlement represent the tilting of the building towards the hanging wall and the footing wall, respectively. it can be seen from the figure that the induced differential settlement increased as the fault rupture propagated in all cases. however, no further increment in the differential settlement was induced as the fault rupture increased beyond 0.15m when s/b=−1.0, because the location of the outcrop of the fault rupture at the ground surface in that case is 15m away from the left pile (discussed in section a), hence the piled raft is within the (stationary) footwall and further increase of the fault rupture height did not increase the height of the fault slope. on the other hand, the differential settlement kept increasing when s/b=0.5. this can be attributed to the outcrop of the fault rupture which crossed the middle of the piled raft and, as a result, the intensive shear zone due to the fault rupture passed through the middle of the raft (as discussed above). therefore, the movement of the hanging (moving) wall tended to pull down the piles located to the left of the piled raft middle whereas the piles right to the piled raft middle were fixed within the (stationary) footwall. this results in the maximum differential settlement when s/b=0.5. consequently, substantial counter clockwise rotation of the piled raft (hence building) was induced. the resulting differential settlement caused the distress not only in the rcc frame of the building but also in the pile head accompanied by the extensive yielding in reinforcement of the frame (also discussed above). in addition, significant shear force and bending moment were developed in the piles. in contrast to the two previous discussed cases (s/b=−1.0, 0.5), negative differential settlement was induced as the fault rupture propagated beyond 0.15m for s/b= 2.0, because the rupture crossed the toe of the right piles and outcrop away from the piled raft and the location of the outcrop of the fault rupture at the ground surface in this case is 15m away from the right pile, hence the piled raft is within the hanging (moving) wall. consequently, the piles located at the right side of the piled raft were subjected to intensive shear strain. this led the piled raft to rotate clockwise (induced negative differential settlement). among the three simulated cases, the maximum differential settlement occurred for s/b=0.5. the final computed differential settlement values were 14, 48, and −9mm for s/b=−1.0, 0.5, and 2.0, respectively. fig. 4. induced piled raft settlement during the propagation of the fault rupture. b. induced lateral displacement of the high-rise building figure 5 illustrates the lateral movement of each floor of the building after the occurrence of the fault rupture for s/b=−1.0, 0.5, and 2.0. the general trend of the lateral deflection profile engineering, technology & applied science research vol. 13, no. 2, 2023, 10285-10291 10289 www.etasr.com mangnejo et al.: a three-dimensional parametric study of the effects of a fault rupture on a … is consistent with differential settlement. it can be seen that the lateral movement of each floor is larger than that of its bottom floor when s/b=−1.0, 0.5. the maximum lateral deflection occurred at the top of the building (the roof level of the 20 th story), because the location of the outcrop of the fault rupture at the ground surface for s/b=−1.0 is 15m away from the left pile, hence the piled raft is within the (stationary) footwall and further increase of the fault rupture height did not increase the height of the fault slope. therefore, the movement of the hanging (moving) wall tended to pull down the piles located to the left of the piled raft middle whereas the piles right to the piled raft middle were fixed within the (stationary) footwall, resulting in lateral movement of the building. consequently, substantial counter clockwise rotation of the piled raft (hence building) was induced. the resulting lateral movement caused the distress not only in the rcc frame of the building but also in the pile head accompanied by the extensive yielding in the reinforcement of the frame. in contrast to the two cases discussed above (s/b=−1.0, 0.5), the lateral movement of each floor is smaller than that of its bottom floor when s/b=2.0. moreover, the largest lateral movement was induced, due to the rupture that crossed the toe of the right piles and the outcrop away from the piled raft. the location of the outcrop of the fault rupture at the ground surface for s/b= 2.0 is 15m away from the right pile hence the piled raft is within the hanging (moving) wall. consequently, the piles located at the right side of the piled raft were subjected to intensive shear strains zone. this led the piled raft to rotate clockwise (induced lateral movement). among the three simulated cases, the maximum lateral movement values in the 20 th floor of the building for s/b=−1.0, 0.5, and 2.0 were computed as 100, 270, and 260mm, respectively. in each case, the lateral movement of the building due to the occurrence of the fault rupture caused inter-story drift which may induce distress in the structural components of the building. the interstory drift of the building can be defined as the ratio of difference of deflections of two storys to story height. fig. 5. induced lateral displacement. c. evolution of damage (damage indices) in the frame of the building during the occurrence of fault ruptures the induced differential settlement and the lateral deflection of the building due to twin excavation can generate substantial plastic strains which can cause cracks in the building. as discussed above, the nonlinear (elasto-plastic) concrete behavior is simulated with a concrete damage plasticity model. in that model, compressive and tensile damage indices (damagec and damaget, respectively) range between 0 (no damage) and 1 (full damage). it was observed from the software output that both types of damage occurred only in the beams and the columns of the first story of the building. therefore, the key locations were selected in the beams and the columns (see inset in figure 6) to investigate the evolution of the damage during the occurrence of the fault rupture. figure 6 shows the tensile damage index in the selected locations during the occurrence of fault rupture for s/b=−1.0, 0.5, and 2.0. fig. 6. tensile damage in beams and columns. in figure 6, it can be observed that the beams and the columns at the selected locations were fully damaged in tension when s/b=−1.0, 0.5. however, the damage evolved earlier when s/b=−1.0 than when s/b=0.5. the resulting tensile damage occurred due to the substantial induced differential settlement (see figure 4) and the lateral movement of the frame (see figure 5). the induced differential settlement induced additional bending moment at the first story of the building. because the frame of the building was rigidly connected to the raft, the additional bending moment resulted in tensile damages at the bottom of the column and both the left and right ends of the beam of the first story of the building. in contrast, the magnitude of tensile damage in the frame when s/b=2.0 was smaller than that for s/b=−1.0 and 0.5, due to the smaller differential settlement induced to the fault rupture and the rupture crossed the toe of the right piles and outcrop away from the piled raft. the location of the outcrop of the fault rupture at the ground surface for s/b=2.0 is 15m away from the right pile, hence the piled raft is within the hanging (moving) wall. consequently, the piles located at the right side of the piled raft were subjected to intensive shear strains. this led the piled raft to rotate clockwise (induced negative differential settlement). engineering, technology & applied science research vol. 13, no. 2, 2023, 10285-10291 10290 www.etasr.com mangnejo et al.: a three-dimensional parametric study of the effects of a fault rupture on a … the magnitudes of maximum tensile damage at each location were computed as 1.when s/b=−1.0 and 0.5, impying that the building failed in both these cases. in addition to tensile cracks developed in the frame of the building, crushing of the concrete at the base of the columns of the first story of the building occurs. the crushing of the concrete is expressed in terms of compressive index (damagec). figure 7 shows the compressive damage index in at the base of the column (connection point between the raft and the column) during the occurrence of the fault rupture when s/b=−1.0, 0.5, and 2.0. similar to tensile damage index, the compressive indices are larger when s/b=−1.0, 0.5 than when s/b=2.0. however, the development of crushing of the concrete initiated the fault rupture increased beyond 0.3m in every case. the concrete crushing resulted due to the additional bending moment due to the differential settlement of the building. the resulting additional bending moment due to the fault rupture induced stress in the concrete at the base of the column. the magnitudes of the compressive damage (0.4) are much less than that of the magnitude of full damage (1.0), implying that the failure of the frame occurred due to tensile cracks at the base of the frame. fig. 7. compressive damage in columns. iv. conclusions based on sand density and the high-rise building geometry, the following conclusions can be drawn:  the performance of the building due to the propagation of the normal fault rupture depends on the position of the outcrop of the rupture with respect to the building.  among the three simulated cases, the maximum differential settlement occurred when s/b=0.5. this can be attributed to the outcrop of the fault rupture which crossed the middle of the piled raft and as a result the intensive shear zone due to the fault rupture passed through the middle of the raft. therefore, the movement of the hanging (moving) wall tended to pull down the piles located to the left of the piled raft middle whereas the piles at the right of the piled raft middle were fixed within the (stationary) footwall.  in contrast to s/b=−1.0, 0.5, negative differential settlement was induced as the fault rupture propagated beyond 0.15m when s/b=2.0 because the rupture crossing the toe of the right piles and the location of the outcrop of the fault rupture at the ground surface for s/b=2.0 was 15m away from the right pile, hence the piled raft was within the hanging (moving) wall.  the lateral movement of each floor is larger than that of its bottom floor when s/b=−1.0 and 0.5. the maximum lateral deflection occurred at the top of the building (the roof level of the 20 th store). in every case, the lateral movement of the building caused inter-story drift which may induce stress in the structural components of the building.  the beams and the columns of the first story were fully damaged in tension when s/b=−1.0, 0.5. in contrast the magnitude of tensile damage in the frame when s/b=2.0 was smaller.  in addition to tensile cracks developing in the frame of the building, concrete crushing occurred at the base of the columns of the first story of the building. references [1] m. loli, m. f. bransby, i. anastasopoulos, and g. gazetas, "interaction of caisson foundations with a seismically rupturing normal fault: centrifuge testing versus numerical simulation," géotechnique, vol. 62, no. 1, pp. 29–43, jan. 2012, https://doi.org/10.1680/geot.9.p.153. [2] m. f. bransby, m. c. r. davies, and a. el. nahas, "centrifuge modelling of normal fault–foundation interaction," bulletin of earthquake engineering, vol. 6, no. 4, pp. 585–605, nov. 2008, https://doi.org/10.1007/s10518-008-9079-0. [3] j. shi et al., "effects of construction sequence of double basement excavations on an existing floating pile," tunnelling and underground space technology, vol. 119, jan. 2022, art. no. 104230, https://doi.org/10.1016/j.tust.2021.104230. [4] j. wang, g. ma, h. zhuang, y. dou, and j. fu, "influence of diaphragm wall on seismic responses of large unequal-span subway station in liquefiable soils," tunnelling and underground space technology, vol. 91, sep. 2019, art. no. 102988, https://doi.org/10.1016/j.tust.2019. 05.018. [5] m. a. soomro, k. f. memon, m. a. soomro, a. memon, and m. a. keerio, "single pile settlement and load transfer mechanism due to excavation in silty clay," engineering, technology & applied science research, vol. 8, no. 1, pp. 2485–2492, feb. 2018, https://doi.org/ 10.48084/etasr.1666. [6] m. f. bransby, m. c. r. davies, a. el nahas, and s. nagaoka, "centrifuge modelling of reverse fault–foundation interaction," bulletin of earthquake engineering, vol. 6, no. 4, pp. 607–628, nov. 2008, https://doi.org/10.1007/s10518-008-9080-7. [7] n. mangi, d. a. mangnejo, h. karira, m. kumar, a. a. jhatial, and f. r. lakhair, "crack pattern investigation in the structural members of a framed two-floor building due to excavation-induced ground movement," engineering, technology & applied science research, vol. 9, no. 4, pp. 4463–4468, aug. 2019, https://doi.org/10.48084/etasr.2923. [8] a. behshad and m. r. shekari, "seismic performance evaluation of concrete gravity dams with penetrated cracks considering fluid– structure interaction," engineering, technology & applied science research, vol. 8, no. 1, pp. 2546–2554, feb. 2018, https://doi.org/ 10.48084/etasr.1729. [9] c. w. w. ng, m. shakeel, j. wei, and s. lin, "performance of existing piled raft and pile group due to adjacent multipropped excavation: 3d centrifuge and numerical modeling," journal of geotechnical and geoenvironmental engineering, vol. 147, no. 4, apr. 2021, art. no. 04021012, https://doi.org/10.1061/(asce)gt.1943-5606.0002501. [10] e. faccioli, i. anastasopoulos, g. gazetas, a. callerio, and r. paolucci, "fault rupture–foundation interaction: selected case histories," bulletin of earthquake engineering, vol. 6, no. 4, pp. 557–583, nov. 2008, https://doi.org/10.1007/s10518-008-9089-y. [11] a. w. skempton and d. h. macdonald, "the allowable settlements of buildings.," proceedings of the institution of civil engineers, vol. 5, no. 6, pp. 727–768, nov. 1956, https://doi.org/10.1680/ipeds.1956.12202. [12] i. anastasopoulos, g. gazetas, v. drosos, t. georgarakos, and r. kourkoulis, "design of bridges against large tectonic deformation," earthquake engineering and engineering vibration, vol. 7, no. 4, pp. 345–368, dec. 2008, https://doi.org/10.1007/s11803-008-1001-x. engineering, technology & applied science research vol. 13, no. 2, 2023, 10285-10291 10291 www.etasr.com mangnejo et al.: a three-dimensional parametric study of the effects of a fault rupture on a … [13] a. niemunis and i. herle, "hypoplastic model for cohesionless soils with elastic strain range," mechanics of cohesive-frictional materials, vol. 2, no. 4, pp. 279–299, 1997, https://doi.org/10.1002/(sici)10991484(199710)2:4<279::aid-cfm29>3.0.co;2-8. [14] j. jaky, "the coefficient of earth pressure at rest," journal of the society of hungarian architects and engineers, pp. 355–358, 1944. [15] j. lubliner, j. oliver, s. oller, and e. oñate, "a plastic-damage model for concrete," international journal of solids and structures, vol. 25, no. 3, pp. 299–326, jan. 1989, https://doi.org/10.1016/0020-7683(89)900504. microsoft word etasr_v13_n3_pp10714-10720 engineering, technology & applied science research vol. 13, no. 3, 2023, 10714-10720 10714 www.etasr.com mwita et al.: the effect of hyperparameter optimization on the estimation of performance metrics in … the effect of hyperparameter optimization on the estimation of performance metrics in network traffic prediction using the gradient boosting machine model machoke mwita school of computational and communication science and engineering, department of information technology development and management (itdm), the nelson mandela african institution of science and technology, tanzania machokem@nm-aist.ac.tz (corresponding author) jimmy mbelwa university of dar es salaam, tanzania jimmymbelwa@gmail.com johnson agbinya school of information technology and engineering, melbourne institute of technology, australia jagbinya@mit.edu.au anael elikana sam school of computational and communication science and engineering (cocse), department of communication science and engineering (cose), the nelson mandela african institution of science and technology, tanzania anael.sam@nm-aist.ac.tz received: 7 december 2022 | revised: 10 february 2023 | accepted: 18 february 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5548 abstract information and communication technology (ict) has changed the way we communicate and access information, resulting in the high generation of heterogeneous data. the amount of network traffic generated constantly increases in velocity, veracity, and volume as we enter the era of big data. network traffic classification and intrusion detection are very important for the early detection and identification of unnecessary network traffic. the machine learning (ml) approach has recently entered the center stage in network traffic accurate classification. however, in most cases, it does not apply model hyperparameter optimization. in this study, gradient boosting machine prediction was used with different hyperparameter optimization configurations, such as interaction depth, tree number, learning rate, and sampling. data were collected through an experimental setup by using the sophos firewall and cisco router data loggers. data analysis was conducted with r software version 4.2.0 with rstudio integrated development environment. the dataset was split into two partitions, where 70% was used for training the model and 30% for testing. at a learning rate of 0.1, interaction depth of 14, and tree number of 2500, the model estimated the highest performance metrics with an accuracy of 0.93 and r of 0.87 compared to 0.90 and 0.85 before model optimization. the same configuration attained the minimum classification error of 0.07 than 0.10 before model optimization. after model tweaking, a method was developed for achieving improved accuracy, r square, mean decrease in gini coefficients for more than 8 features, lower classification error, root mean square error, logarithmic loss, and mean square error in the model. keywords-network traffic; machine learning; big data; data loggers; feature selection; gradient boosting machine prediction engineering, technology & applied science research vol. 13, no. 3, 2023, 10714-10720 10715 www.etasr.com mwita et al.: the effect of hyperparameter optimization on the estimation of performance metrics in … i. introduction to provide secure and successful communications in any organization at the local, national, and global levels, network management of both incoming and outgoing traffic is critical. the internet, wide area networks (wans), local area networks (lans), e-commerce, and other online services are widely used in businesses for communication and transaction purposes. network connectivity is essential for the efficient operation of firms or the supply of daily services to their clientele [1]. network management tasks, including classification and monitoring of network traffic are crucial for quality of service (qos) control, anomaly detection, and other activities related to network troubleshooting [2]. voice, data, and multimedia services currently can be merged into one application/software thanks to the advancements in the telecommunications and application/software industries. several protocols have been developed to support file transfer within the network such as user datagram protocol (udp) and transmission control protocol (tcp) through the internet. during the early stage of the internet, static ports (ssh, http, ftp, smtp, etc.) were used by network security experts for the classification and mapping of network traffic [3]. the internet has changed the development of an application because they can work without using the assigned port numbers e.g. in peer-to-peer (p2p), gaming, and other online applications [4]. due to the diversification of software applications that require a different level of bandwidth usage, it is very crucial to be able to identify applications that consume more resources in the network, breach network security, and generate unnecessary traffic. prediction of network traffic in advance can assist organizations in improving their service provision, both internally and externally by changing the network design or improving areas with weaknesses [5]. this can be done by implementing new network architectures or by deploying equipment with higher capacity. the advancement of gadgets used in information and communication technology (ict), particularly smartphones, poses a new challenge to information access and sharing. currently, most services, such as social media networks and banking are accessed via smartphones [6]. accessing the services through smartphones generates traffic which may breach the security of the organization and lower qos provision. with the growth of network complexity, network specialists and engineers employ a variety of strategies and alternatives to identify and optimize network traffic. machine learning (ml) is one of them. ml is a branch of artificial intelligence (ai) that enables computers to learn from previous data and improve through experience [7]. there are 4 categories of ml algorithms, namely supervised, unsupervised, semi-supervised, and reinforcement. the ml approach has been applied in several fields such as finance, healthcare, ict (i.e. data anomaly detection, information security, etc.), image recognition, fraud detection, and others, while some companies like facebook, google, apple, netflix, and amazon use ml in their daily business operations. in ict data security, ml can be used to classify network traffic from different sources such as internet of things (iot) devices, wireless sensors, lan, and wan and identify threats or malicious activities. different ml methods or techniques have been applied in the classification of network traffic to supplement existing network management tools, for instance, the k-nearest neighbors algorithm (k-nn), support vector machine (svm), and clustering. although ml has advanced to the forefront of effectively identifying network traffic, it rarely employs model hyperparameter optimization procedures in this process. network traffic classification and optimization are very crucial to attain the maximum usage of the communication network infrastructure. this will assist an organization to avoid investing a lot of money without getting value for money or a return on investment. understanding network traffic flow is very important for both ict experts and the organization for planning human and financial resource alignment. in [8], the xgboost algorithm was used in the classification of network packet trace capture data. four performance metrics, namely accuracy, precision, f1 score, and recall were used and the predicted mean accuracy per class was about 99.5%. a deep packet inspection (dpi) study using a convolution neural network (cnn) to classify encrypted packets by using a deep learning approach was conducted in [4]. authors in [1] showed that a port-based approach can be used to classify flow-based traffic with some limitations, especially in applications that can be accessed using p2p software such as utorrent, limewire, winny, edonkey, winmx, and transmission. using adaptive network traffic can be estimated by using probability distributions such as pareto, log-normal distribution, exponential distribution, poisson, etc. [9]. however, due to the non-stationary nature or properties of the network traffic, only a non-stochastic mathematical model was applied [10], and a part of the stochastic model known as gbm was used and compared to the adaptive approach. there are 3 common methods used in classifying network traffic, namely payload-based, flow-based and port-based. portbased assumes the network traffic uses common port numbers through either udp or tcp. network traffic packets in the port-based [11] are inspected by using the source and destination ports of the internet protocol (ip) of the package (http(80), smtp(25), ftp(20, 21), etc.). another technique that is used to identify malicious activities is the use of dpi, however, it can work only in the encrypted packets and when the packets are not encrypted this approach doesn’t work [8]. authors in [12] showed that the accuracy of the model can be improved by using distance and similarities from the clusters. ml can be used to address some of the drawbacks of dpi and port-based package inspection techniques [13]. classification of network traffic is done in different ways but the most common one is by estimating performance metrics such as accuracy, area under the curve, sensitivity, kappa values, etc. [14]. standard metrics like root mean square error (rmse) and mean square error (mse) of deep learning classification techniques knn and svm have low performance [15]. in [16], gbm was used for attack detection in traffic flows. a linear regression model was used and the deep learning techniques achieved higher performance compared to the linear regression model. engineering, technology & applied science research vol. 13, no. 3, 2023, 10714-10720 10716 www.etasr.com mwita et al.: the effect of hyperparameter optimization on the estimation of performance metrics in … in this paper, we used gbm which is an ensemble supervised learning technique to classify packet flows, because, after a thorough literature review and to the best of our knowledge, there are no studies related to gbm hyperparameter tuning in network traffic prediction. the model was optimized by using different hyperparameter configurations, such as interaction depth, number of trees, learning rate, sampling, etc. to estimate the prediction performance metrics accuracy, rmse, mse, logarithmic loss (log loss), and r 2 . the performance metrics were compared with the default gbm performance metrics. ii. materials and methods network traffic data were collected through an experiment set by using cisco netflow (flow viewer) and sophos firewall. cisco 4000 series and sophos xgs 3100 1u model were used for the experiment setup (figure 1). data for both incoming and outgoing network traffic were recorded in log files. the data were downloaded and stored on a computer in csv and txt formats. a detailed process from data collection up to model evaluations is shown in figure 1. fig. 1. data collection up to model comparison flows. a detailed description of the gbm input and the classification and optimization steps can be seen in figure 1. the main steps are: 1. dataset captured in the experiment. 2. convert categorical features (labels column) to numerical values (benign, malicious, and outliers). 3. normalize the dataset by imputing median to all features except the label feature which is categorical with multi labels. 4. partition the dataset into training and test subsets. 5. build the gbm classifier model by using the training dataset. 6. validate gbm by using the test dataset with 5-fold classification based on 3 features (benign, malicious, and outliers). 7. performance evaluation. 8. model hyperparameter tuning (optimization). 9. output: accuracy, rmse, mse, log loss, and ��. a. data pre-processing network traffic data that were collected were converted into csv files with 18 columns with 3 feature classes (benign, malicious, and outliers). the preproces package in r software [16] and rstudio integrated development environment (ide) [17] were used to normalize and scale the data. before data scaling, duplicate data were deleted. after duplication removal and normalization, the data were converted into an h2o package [17] format, so that they can be run in a distributed and low memory management h2o package on top of the r software [18, 19]. the dataset was partitioned into two subsets, 70% model training and 30% for testing. open-source h20 software which is embedded in r software was used to build both models. h2o uses in-memory cluster computing and distributed systems and supports both supervised and unsupervised ml algorithms [20]. in-memory usage can compress the dataset by using columns to increase the classification speed and time in cluster computing [21]. h20 builds all the models in a sequence where all the data are fully distributed in the memory. b. model development gbm framework was developed in [22] as an additive model which uses a stage wise decision tree. gbm is a technique used in developing very powerful predictive models in ml [23]. gbm is an ensemble learning model which can work for regression and classification [24]. ensemble learning merges weak learners into strong learners to improve their performance [25] by using the recursive tree partitioning approach. gbm is a forward learning ensemble technique that uses decision trees. before model tuning, the model was developed and feature importance (variable importance) was estimated. the importance variable provides the contribution of each variable to model development and its output. the values extracted from the model identify and describe all features that are relevant to the model. gbm aims to optimize a generalized ensemble model [26] as indicated in figure 1 and in the detailed process in algorithm 1. gbm always minimizes the loss function so that it can be optimized during model generations. the model was developed by using the h2o gbm framework. h20 gbm framework [21] is a package in r software version 2.4.0 [17] and rstudio version 2022.02.2 [27] was used as an ide. this study used r packages extreme gradient boosting (xgboost), gbm and classification and regression training (caret) to implement gbm models [28] by using different parameter configurations (table i). algorithm 1: pseudocode based on [29]. input d =����, � , ���, � , … … . . , ���, � �, �� , ��� � begin initialize: ���� = ������� ∑ �� �, � �!� for m = 1:m "�# = − �� �,���� � ���� train weak learner %# �� on training data engineering, technology & applied science research vol. 13, no. 3, 2023, 10714-10720 10717 www.etasr.com mwita et al.: the effect of hyperparameter optimization on the estimation of performance metrics in … calculate w: �# = &"'#� � ∑ �� �, �# (� + � �!� ��� + �%#��� update: �#�� = �# (� + �#%# �� end for end table i. parameter configuration of the proposed approach parameter values algorithm gbm feature class categorical interaction depth 1 to17 learning rate 0.01, 0.1, 0.2, 0.3, 0.4 sample rate 0.4, 0.8, 1.0 column sample 0.4, 0.6, 1.0 number of folds 5 bagging fraction 0.8, 1.0 number of trees 100, 1000, 2500, 5000 c. tuning process hyperparameter tuning by using the grid search method was applied in model development, and a combination of different techniques was used for all values of the hyperparameters provided figure 2. the evaluation of the model was based on the best performance metrics estimated by using different parameters and architectures. different values of number of trees were used to evaluate the model by changing the number of trees (ntrees) as described in figure 2. the ntrees = {100, 1000, 2500, and 5000} were used with the learning rate values of {0.01, 0.1, 0.3, 0.4}. the interaction depth was set and varied from 1 up to 17 to optimize the model and attain maximum accuracy. interaction depth (maximum depth) which provides maximum accuracy was selected with its learning rate for model training. the sampling rate values were {0.4, 0.8, and 1.0} during model optimization (table i). fig. 2. graph of model turning parameters. d. performance evaluation the model was turned using two types of parameter tuning: boosted categories and tree specific parameters [30]. boosted tuning includes ntree, learning rate, and sampling rate, while tree specifics are interaction depth, minimum samples, and feature to split. five-fold cross-validation technique was used to evaluate the predictive performance of the model. to evaluate the turning parameters in table i, the following model performance evaluation metrics were used. 1) accuracy in multiclass classification, the set of labels predicted for a sample must exactly match the corresponding set of labels in the feature classes. in ml, model accuracy is a common performance metric which considers the features that are correctly classified by the model. accuracy = �*+,*�*+,.+,*-,.………… (1) where tp, fp, tn, and fn represent true positive, false positive, true negative, and false negative, respectively. 2) logarithmic loss log loss is a performance metric used when the input feature is continuous or categorical. in this study we used categorical features, namely benign, malicious, and outliers. log loss shows how the probability of the predicted values is close to the actual values. when the predicted probability diverges from the true values, the log loss values get higher. log loss can be expressed mathematically as: log loss = 4 5 ∑ ∑ �67�89 .: ln�<9 ,: � � 5 :!4 5 9 !4 (2) where n is the total number of rows (observations) of our corresponding data frame, w is the per-row user-defined weight (default is 1), c is the total number of classes (c=2 for binary classification), p is the predicted value (uncalibrated probability) assigned to a given row (observation), and y is the actual target value. 3) root mean squared error (rmse) rmse is the error between the predicted values and the observed values [31] as indicated below: rmse = 4 5 ∑ �87 − 8ai 59 ! 4 � … (3) where n is the total number of rows of the corresponding data frame, y is the actual target value, and 8̂ is the predicted target value. 4) r squared (��) r 2 is defined as the variance proportional to the dependent variable which is predicted from the independent variable. it is defined by: �� = ccdef ccghg = ∑ �ij(ik � l j ∑ �im(ik l m (4) where 8: represents the predicted labels, 89 the true labels, nnopq is the regression sum of squares, and nnrsr the total sum of squares. iii. results several configurations were used during model optimization. the highest accuracy and r 2 values were attained for ntree =2500, interaction depth = 14, and learning rate = 0.1 as indicated in figures 3 and 4. at the same parameter configuration, minimum classification error, rmse, log loss, and mse were also achieved, as indicated in figure 4. the contribution of an individual attribute in the model was ranked by using relative importance values as shown in figure 6. engineering, technology & applied science research vol. 13, no. 3, 2023, 10714-10720 10718 www.etasr.com mwita et al.: the effect of hyperparameter optimization on the estimation of performance metrics in … a. before model tuning before model tuning, the model was developed and executed with the 5-fold cross-validation technique. the performance metrics were estimated as shown in figure 3. the accuracy values ranged from 0.897 to 0.902. accuracy was maximum at the second fold (0.899). �� at the second fold was maximum (0.856) and minimum at the first fold (0.851). the overall estimate for �� was about 0.853. there is an inverse relationship between mse and �� as indicated in figure 2. as the estimated values of mse increased, there was a decrease in the estimated values of ��. the values of accuracy increased until when it reached 0.90 and it stabilized at 0.899 as shown in figure 3. the interaction depth of 14 was the one that attributed the model to attain maximum accuracy (figure 3). the values of �� were at increasing trends until they reached 0.86, then started to stabilize and remained constant while the value of rmse was increasing. fig. 3. graphic representation of the performance metrics before model tuning. b. after model tuning the second phase of the model was to tune the model by using the parameters indicated in table i and figure 1. the values of accuracy increased from 0.899-0.90 to 0.920-0.95 in the 5-fold cross-validation as indicated in figure 4. after model tuning, the values of log loss decreased to about 0.21 from 0.23 before tuning, as shown in figure 4. the estimates of mse decreased from 0.08 to 0.07 after model tuning, �� increased up to the maximum value of about 0.88 after model tuning from about 0.85 before model tuning. the estimated metrics for rmse and classification error decreased after model tuning (figure 2). fig. 4. performance metrics estimation at 5 – fold cross-validation. c. result comparison before and after model tuning the overall accuracy before model tuning was about 0.90, however, after model tuning, it was improved up to 0.930 (figure 5). the value of r 2 after model tuning was higher compared to the one before which varied from 0.85 to 0.87. the values of mse decreased from 0.08 to 0.07 after hyperparameter tuning. classification error estimated values decreased as well from about 0.10 before model tuning to 0.08 after model tuning and rmse values also decreased from 0.28 to about 0.25 (figure 5). overall, there is an improvement in all performance metrics after model tuning. fig. 5. graph showing the overall performance metrics before and after tuning. d. comparison with other studies the results of this study were compared with other studies as indicated in table ii. the accuracy generated in our study is higher than those reported in [12, 30, 33], while the results of 0.93 [34, 35] and 0.94 [36, 37] are equivalent or above this study's results. the estimated values of �� of this study lie between the minimum �� as per [33] and below [38]. rmse was also supported by other studies [16, 30, 39, 40]. mse from previous studies varied from 0.053 [32] up to 0.4612 [39] while the result of this paper is 0.074 which is supported by other studies as well. the findings of this study are supported by other studies as detailed in table ii. table ii. comparison with other studies performance metrics reference accuracy mse rmse t� [39] 0.4612 0.2127 [38] 13830 0.887 [16] 0.41 0.480 0.836 [12] 0.902 0.280 0.340 [32] 0.907 0.053 0.229 0.780 [33] 0.746 0.259 0.509 0.769 current study 0.930 0.074 0.272 0.872 e. variable of importance features of importance were compared in all phases of the model. before tuning the model, the overall entropy contributed more than 50% to the model, while after tuning it only provided about 30%. before model tuning, most of the feature's contributions were below 5% except for bytes out and total entropy. the time between the traffic inters into the network and when it ends is about 1%, showing that the contribution of these two features to the model is very minimal even after model tuning. after the model tuning process, there was an improvement in the contribution of individual features to the model. the following features improved up to more than 10% their contribution to the model: number of packets in, duration, bytes out, total entropy, and average inter packet engineering, technology & applied science research vol. 13, no. 3, 2023, 10714-10720 10719 www.etasr.com mwita et al.: the effect of hyperparameter optimization on the estimation of performance metrics in … time. the contribution of time start and time end was about 1% to 2%. therefore, their contribution to the model is not very important (figure 6). fig. 6. graph showing the importance variation before and after tuning. iv. conclusion, recommendations, and future work the results from this study show that by using hyperparameter optimization (tuning), the accuracy of the model improved from 0.90 to 0.93. classification errors were reduced from 0.10 to about 0.07 after model tuning. the estimated values of �� were 0.85 before tuning and 0.87 after tuning. based on these findings, the use of hyperparameter tuning is proposed because it improves several performance metrics. the proposed approach increased the accuracy, r 2 , and mean of network traffic classification variables and lowered classification error. furthermore, different machine learning approaches can be used to improve the performance of the model like artificial neural networks, deep learning, and others. the current study can be extended and used in different conditions in order to extract more variables of importance based on different parameters and experiments. more research is needed in the area of the comparison of the hardware-based approach and machine learning. this study contributes scientific knowledge related to network traffic management and can be used by any organization or internet service provider to manage network traffic. funding the current study was funded by the european union’s horizon 2020 research and innovation grant number [641918] through the africanbioservices project in tanzania under tanzanian wildlife research institute (tawiri). the authors extend their appreciation to the reviewers for their valuable remarks, tanzania 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region are the main cause of breast cancer development. it is important to detect breast cancer as early as possible as this might increase survival rate. the existing research methodologies have the problems of increased computation complexity and low detection accuracy. to overcome such problems, this paper proposes an efficient breast cancer detection and classification system based on mammogram images. initially, the mammogram images are preprocessed so unwanted regions and noise are removed and the contrast of the images is enhanced using homo morphic adaptive histogram equalization (hmahe). then, the breast boundaries are identified with the use of the canny edge detector. after that, the pectoral muscles present in the images are detected and removed using the global pixel intensity-based thresholding (gpit) method. then, the tumors are identified and segmented by the centroid-based region growing segmentation (crgs) algorithm. next, the tumors are segmented and clustered and feature extraction is carried out from the clustered tumors. after that, the necessary features are selected by using the chaotic function-based black widow optimization algorithm (cbwoa). the selected features are utilized by the convolutional squared deviation neural network classifier (csdnn) which classifies the tumors into six different categories. the proposed model effectively detects and classifies breast tumors and its efficiency is experimentally proved by comparison with the existing techniques. keywords-classification; feature selection; chaotic functionbased black widow optimization algorithm (cbwoa); convolutional squared deviation neural network (csdnn) classifier i. introduction cancer is one of the most challenging and fatal diseases worldwide. it is responsible for the loss of millions of lives every year [1]. the instances of growth of breast cancer (bc) amongst women in the age group of 30-40 years have increased significantly over the last few decades in india [2]. bc is one of the most frequent cancers in developed and developing countries [3]. bc starts when malignant lumps begin to grow from the breast cells [4]. globally, bc is the second most common type of cancer and a major cause of human morbidity and mortality, disproportionately affecting women [5, 6]. however, according to [7], more than 30% of cancer cases will survive in the long term if they accept accurate early detection [7]. therefore, early detection of bc is crucial for patients' health and treatment. early detection relies on testing and examining the pre-presentation of any symptoms [8]. any suspected breast lump or growth should be immediately checked by the appropriate medical professional, in addition to regular screening tests [9]. mammography bc diagnostic methods include x-rays, ct scans, ultrasound imaging, etc. it is complicated for doctors to diagnose cancer based on mammogram images due to the complexity of premature bc, combined with the low brightness of mammogram images [10]. thus, enhancing the detection efficiency via the cad system of deep learning techniques is essential. ii. literature review authors in [11] developed an effective computer-aided diagnosis system for breast cancer. feature weighting was employed because it boosted the classification performance more than feature subset selection. the results showed that the proposed wrapper method had a better ability to attain higher accuracy as compared to the existing techniques. the method had low specificity in breast cancer diagnosis. authors in [12] explored an improved computer-aided diagnosis (cad) model for the classification of breast masses into the normal or abnormal and benign or malignant categories. it utilized lifting wavelet transform (lwt) to extract the features from the region of interest in mammogram images. finally, classification was performed using a combination of an extreme learning machine and moth flame optimization (mfo-elm) technique. the recommended cad model obtained better performance and also, achieved minimum computational time as compared to other existing models. authors in [13] proposed multi-scale generalized radial basis function (msrbf) neural networks for image feature extraction, medical image analysis, and classification for breast cancer detection. initially, the image data were rendered into a multiple-input-single-output (miso) system. the forward regression orthogonal least squares (frols) algorithm was used to solve the system as a model structure detection problem and found the output layer weights. the experimental results showed that the method reached classification accuracy above corresponding author: nishant behar engineering, technology & applied science research vol. 12, no. 6, 2022, 9496-9502 9497 www.etasr.com behar & shrivastava: a novel model for breast cancer detection and classification 93% in the two mammography databases and 86.7% in breakhis. however, the dct method needs large processing power. interested researchers in healthcare can also find interesting research on the automatic detection of breast cancer and biomedical images [14-27]. iii. methodology a. the proposed model bc which grows in the breast cells is a malignant tumor, which has the potential of spreading to other body parts. bc infects 2.1 million women every year and is the most common sort of cancer, according to the world health organization (who). furthermore, amongst women, the highest number of cancer-associated deaths is associated with bc. in general, the causes for bc are not defined and an exact justification for the occurrence of bc in certain women over others has not been provided yet. nevertheless, to specify the incidence of bc, there are some common facts about bc symptoms. most of these symptoms do not appear in the early development stages. therefore, the process of detecting cancer in its early stage is quite challenging. in order to identify the bc development in the earlier stages itself, a non-invasive methodology termed digital mammography is utilized. dbt along with breast masses or tumors can be seen at increased radiological densities, i.e. they are seen as white, on mammograms. thus, owing to overlay with dbt, the identification of malignant breast masses becomes a complicated task. thus, false positives, false negatives, and over-diagnosis are issues which affect mammography. radiologists are aided with the usage of artificial intelligence (ai) via enhanced bcd utilizing mammography. in this paper, ground on the mammogram images, an effectual bcd system has been proposed by utilizing a csdnn classifier. analyzing the mammogram images by utilizing csdnn and mining detection methodologies and classifying the tumor is the main aim of this work. figure 1 presents the block diagram of the proposed model. fig. 1. the general structure of the proposed model for breast cancer classification. b. preprocessing preprocessing is an important step for removing undesirable noise and irrelevant details and for improving the quality and information content of the original image. the proposed work begins with preprocessing which consists of two steps, i.e. removing unwanted regions and contrast enhancement and noise removal. adaptive histogram equalization (ahe) is an image processing technique that is used to enhance the contrast of images. ahe divides the image into distinct blocks and computes histogram equalization for each section. thus, ahe computes many histograms, each corresponding to a distinct section of the image. it enhances the local contrast and definitions of edges in all distinct regions of the image. hence, in order to improve the performance of the ahe algorithm, in this work, the homo morphic (hm) filtering is incorporated with the existing ahe algorithm. initially, the input images are filtered by the hm filter. hm filtering is commonly used for correcting the non-uniform illumination in images. moreover, it simultaneously normalizes the brightness across an image and increases contrast. c. breast boundary detection after preprocessing, the pre-processed images are applied to canny edge detector, which is a widely used edge detection algorithm to locate sharp intensity changes and find object boundaries in an image. the proposed work utilizes the canny edge detector for detecting breast boundaries. it contains 5 steps called noise reduction, gradient calculations, non-maximum suppression, double threshold, and edge tracking. d. pectoral detection and removal the output images from the canny edge detector with the detected breast boundaries ( )ced mr are applied to the global pixel intensity-based thresholding (gpit) method for removing the pectoral muscles. if the pectoral muscles are present in the images, they may complicate the feature extraction process and result in false classification. to overcome this problem, the pectoral muscles are identified and removed with the gpit method. the normal thresholding method has the drawback that the selected threshold should correspond to a valley of the histogram. this method does not work well with variable illumination. so, to overcome this drawback, the threshold value is calculated from the pixel intensity of an image. here, the mean intensity value of all the pixels in the image is used as a global threshold. it can be computed as: (1) where n is the total number of pixels, _ ( ) ( , ) pec rem mr i i j denotes the intensity of the pixel, and δth denotes the threshold value computed based on the mean value of the pixel intensity value. e. tumor identification after the pectoral muscles were removed, the images are inputted to the centroid-based region growing segmentation (crgs) algorithm for tumor segmentation in the breast. in general, a tumor occurs when cells divide and grow excessively in the body. region growing is a simple and efficient approach to segment the objects from an image. the process of region growing is to map the individual pixel to a set of pixels representing distinct image )(mprer    nji rth jii n mced),( ),( 1 )(  )(_ mrempeecr engineering, technology & applied science research vol. 12, no. 6, 2022, 9496-9502 9498 www.etasr.com behar & shrivastava: a novel model for breast cancer detection and classification regions and to grow them until they cover the entire image. the existing region growing algorithm has a limitation, that is, to choose the appropriate seed points and region growing criteria. the random selection of these two factors directly affects the quality of image segmentation. to overcome this limitation, in this paper, the initial seed point is calculated by using the centroid of the maximum area covered by the image. this improvisation drastically increases the segmentation accuracy and overcomes the over and under segmentation issues. f. tumor clustering after segmentation, the images with the segmented regions are clustered by divisive similarity clustering (dsc). divisive clustering is a top-down clustering approach, which separates the number of objects successively into finer groupings. the dsc algorithm mostly uses euclidean distance to calculate the distance between the data points. although it is a common distance measure, euclidean distance is not scale invariant which means that the computed distances might be varied and inaccurate. moreover, the euclidean distance is not suitable for a large amount of data so that the cosine similarity function is calculated, which provides a better similarity result than the euclidean distance and achieves better clustering accuracy. g. feature extraction after clustering, the important features are extracted from the clustered benign lben and malignant lmal regions. feature extraction helps reducing the amount of redundant data from the data set. in the end, data reduction increases the speed of the learning process. in the proposed work, the important features such as grey-level co-occurrence matrix (glcm), shape features, local tetra pattern (ltrp), color intensity, and gabor features are extracted.  the glcm method is a way of extracting second-order statistical texture features. the extracted texture features are autocorrelation, contrast, correlation, cluster shade, dissimilarity, energy, entropy, homogeneity, maximum probability, and difference variance.  shape features correspond to the physical structure or the geometric shapes of the objects present in the image.  ltrp demonstrates the spatial structure of the local texture using the direction of the center pixel. it is the first-order derivative of the center pixel along the 0o and 90o directions.  gabor features extract local pieces of information which are then combined to recognize an object. from the response of the gabor filter, the gabor features are constructed at several orientations and frequencies.  color intensity represents the image from a different perspective. it represents the frequency distribution of color bins in an image. it counts similar pixels and stores them. these features extracted from images are then used for image recognition. the extracted features are denoted as: (2) where nℏ denotes the number of the extracted features. h. feature selection after feature extraction, the important features are selected using the chaotic function-based black widow optimization algorithm (cbwoa). the bwo algorithm is a meta-heuristic algorithm that delivers fast convergence and avoids local optima. bwo is a good method to solve several types of optimization problems as it keeps the balance between the exploration phase and the exploitation phase. its fundamental steps and flowchart are given in figures 2-3. in the proposed model, the optimal features, which enhance the classification accuracy, are selected by utilizing the optimization algorithm. fig. 2. pseudo-code of the proposed cbwoa. fig. 3. flowchart of the proposed cbwoa. i. csdnn classification the selected optimal features are inputted to the convolutional csdnn classifier. a cnn is a multilayer neural )(msegr },.........,,{ 321 nn ℏℏℏℏℏ  )(optnℏ engineering, technology & applied science research vol. 12, no. 6, 2022, 9496-9502 9499 www.etasr.com behar & shrivastava: a novel model for breast cancer detection and classification network that contains many hidden layers that perform two important functions, convolution and pooling. generally, neural networks suffer from the weight initialization problem. in the traditional neural network, the weight value is randomly initialized which causes the classifier to produce a false classification. so, in the proposed classifier, the weight value is initialized based on the mean and variance of its input. the architecture of the proposed csdnn is shown in figure 4. fig. 4. architecture of the proposed csdnn. 1) convolution layer the convolution layer performs the convolution operation between the input features and the weight values (kernels) which is then applied to the non-linear activation layer to return the rectified feature map. the weight updating of csdnn is done by the mean and variance of the input values. it can be expressed as: (3) (4) where ( )n opt  ℏ , ( )n opt  ℏ are the mean and variance of the input features, and n is the total number of features. the progress of feature maps in the convolution layer is expressed in (5): (5) where denotes the obtained feature map, ω is the nonlinear activation function, denotes the weight values generated based on the mean and variance of the input, and denotes the bias value for each feature map. 2) pooling layer this layer reduces the size of the input feature map obtained after the convolution. for dimensionality reduction, the max-pooling function is used which detects the most dominating features for faster classification. thus, the pooled feature map of the pooling layer is expressed as: (6) where denotes the pooled feature map and denotes the max-pooling function. 3) fully connected layer after a number of convolution and pooling operations, the pooled output is flattened and is applied to the fully connected layer. the fully connected layer feeds the input to the softmax layer, which uses the softmax function to convert the input scores into a sum of output probabilities. iv. experimental results in order to examine the proposed system (figure 2), numerous experiments were conducted to evaluate the performance of the proposed model and are presented in this section. the proposed breast cancer detection system is developed in the working platform of matlab. the dataset description is described in the next section. all chosen samples were first stored into major classes as benign, malignant, and normal classes and subsequently into sub classes. a. dataset description the performance of the proposed methodology is evaluated by using publicly available data. sample images have been collected from [28]. the dimension of the input image is 1024×1024 pixels in ‘pgm’ format. the input mammogram images consist of dense tissue variations, breast density percentage, and breast density variations. these features are helpful to detect breast cancer. thus, the dataset has 3 main classes: normal, benign (dcis), malignant and their subclasses. b. pre-processing performance analysis in this section, the proposed hmahe’s performance is analogized with the prevailing histogram equalization (he), contrast limited adaptive histogram equalization (clahe), along with contrast stretching (cs) techniques regarding minimum squared error (mse), structure similarity index measure (ssim), peak signal to noise ratio (psnr), and variance ratio values. the ratio of the maximum possible power of an image to the power of corrupting noise, which affects the quality of its representation, is named psnr. the psnr performance of the proposed and other known methods is analyzed in figure 5. good image quality along with fewer errors introduced to the image is attained by achieving a high psnr value. accordingly, the psnr value for the proposed methodology is 61.89734. the psnr values for clahe, he, and cs frameworks are 58.86085, 58.00242, and 58.37713 respectively, which are lower than that of the proposed technique, proving that the proposed system shows better performance. c. segmentation performance analysis by analogizing specificity, accuracy, f-measure, and sensitivity with the outputs of prevailing active contour (ac), watershed (ws), and region growing (rg) methodologies, the accuracy of the proposed crgs segmentation model is determined.    n n optn noptn 1 )( 1 )( ℏ ℏ     n n optn optnoptn n 1 )( )( 1 )()( ℏℏ ℏ  )( ),()( )( )()(   optnoptn wtoptn nfea conv l ℏℏ ℏ  )(nfea conv l ),( )()( optnoptn wt ℏℏ    )()( nfea convmp nfea pool ll  )( nfea pool l )( mp engineering, technology & applied science research vol. 12, no. 6, 2022, 9496-9502 9500 www.etasr.com behar & shrivastava: a novel model for breast cancer detection and classification fig. 5. performance estimation based on psnr. fig. 6. performance analysis based on sensitivity, specificity, accuracy, and f-measure. to estimate the performance of segmentation frameworks utilized to extract objects of interest from images, metrics like specificity, accuracy, f-measure, and sensitivity are important. the proposed and previous segmentation mechanisms’ performance in terms of accuracy, f-measure, sensitivity, and specificity is depicted in figure 6. the sensitivity and specificity values achieved by the proposed technique are 0.794568 and 0.998382. the previous systems have sensitivity and specificity of 0.525349 and 0.113123 for ac, 0.377702 and 0.988604 for rg, and 0.395193 and 0.947311 for ws. the accuracy and f-measure of the proposed system are 0.991286 and 0.846746, which are higher than the existing frameworks'. therefore, it is concluded that the proposed model segments the objects from the images more effectively. d. clustering performance analysis clustering methods that have high accuracy and time efficiency are more efficient for discovering the required number of clusters. in this sub-section, the performance of the proposed dsc clustering method is evaluated based on the clustering accuracy. for performance evaluation, the proposed method is weighted against the existing hierarchical clustering (hc), fuzzy c-means (fcm), and k-means clustering techniques. table i shows the accuracy of the proposed and existing clustering techniques. the clustering accuracy achieved by the proposed method is 0.961111, whereas the existing methods gave lower accuracy of 0.694444 (hc), 0.544444 (fcm), and 0.627778 (k-means), indicating that the proposed method has better performance. the graphical representation of the above discussion is shown in figure 7. table i. comparative analysis based on clustering accuracy methods clustering accuracy proposed dsc 0.961111 hc 0.694444 fcm 0.544444 kmeans 0.627778 fig. 7. performance analysis of the proposed and existing methods based on clustering accuracy. e. feature selection performance analysis the performance of the proposed cbwoa optimization method used for selecting the optimal features was evaluated by comparing the fitness level attained for the number of iterations, and computation time with the existing methods of genetic algorithm (ga) and particle swarm optimization (pso). fig. 8. fitness vs. iterations. the convergence graph of fitness value vs. iteration number is shown in figure 8. compared to the existing methods, the fitness value achieved by the proposed method is higher for a varying number of iterations. the proposed method has a 0.957153 fitness value at a minimum of 5 iterations and a 0.988095 fitness value at a maximum of 50 iterations. in the same way, the existing methods have fitness values lower than the proposed method. it is concluded that the proposed method has higher optimal prediction nature than pso and ga. f. classification performance analysis table ii shows the performance of the proposed and existing classifiers with reference to some quality metrics such as sensitivity, specificity, accuracy, and f-measure. sensitivity delivers the ability to label positive breast cancer cases as positive, whereas specificity indicates the ability to identify engineering, technology & applied science research vol. 12, no. 6, 2022, 9496-9502 9501 www.etasr.com behar & shrivastava: a novel model for breast cancer detection and classification negative breast cancer cases as negative. in order to get an accurate prediction, these values should be high. f-measure is a measure of the model's accuracy, which is calculated by using the precision and recall value. table ii. performance analysis of proposed and existing classifiers metrics csdnn cnn nn anfis svm sensitivity 0.958333 0.325 0.566667 0.808333 0.575 specificity 0.993056 0.8875 0.927778 0.968056 0.929167 accuracy 0.988095 0.807143 0.87619 0.945238 0.878571 f-measure 0.958333 0.325 0.566667 0.808333 0.575 fig. 9. roc curve. the roc graph for estimating the performance of the proposed and existing classifiers is shown in figure 9. an overview of true positives and false negatives is provided by the roc graphs. the better performance is indicated by the classifiers that give curves closer to the top-left corner. the test is less accurate when the curve comes closer to the 45-degree diagonal of the roc space. accordingly, we can see that the proposed model is more accurate than the prevailing techniques. v. discussion the proposed method efficiently removes the unwanted regions from breast mammogram images, and outperforms existing works with their inefficient preprocessing functions. the proposed method uses an effective feature selection phase. the main contribution of the feature selection phase is to reduce the complications of the classifier. thus, the classifier can classify the features with least resource consumption. most of the existing methodologies have inadequate feature extraction and selection phase [29], drastically reducing their precision level. furthermore, in the proposed work, a modified classifier is used, in which the optimal weight values are selected by the mean and variance of its input. in most of the existing works, the classifier deals with random weight values [30]. when compared to existing methodologies, the proposed work exhibits better accuracy rates. moreover, the proposed work classifies the multiple types of breast cancer with less time and cost. vi. conclusion and future work the main goal of the proposed model is to detect breast tumors and classify them according to the type of the detected tumor. in this framework, mammogram images are analyzed and tumors are identified by crgs methods. if the tumor is found in a mammogram image, then the type of tumor is identified with the csdnn method. the performance of the proposed crgs and csdnn methods were compared with some traditional methods with respect to 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[30] n. kumar, n. narayan das, d. gupta, k. gupta, and j. bindra, "efficient automated disease diagnosis using machine learning models," journal of healthcare engineering, vol. 2021, pp. 1–13, may 2021, https://doi.org/10.1155/2021/9983652. microsoft word etasr_v12_n6_pp9445-9449 engineering, technology & applied science research vol. 12, no. 6, 2022, 9445-9449 9445 www.etasr.com pudipeddi & jayasree: investigation of the effect of normal incidence of rf wave on human head … investigation of the effect of normal incidence of rf wave on human head tissues employing cu and ni grid pet films sai spandana pudipeddi department of eece school of technology gitam deemed to be university visakhapatnam, india psspandana26@gmail.com pappu v. y. jayasree department of eece school of technology gitam deemed to be university visakhapatnam, india jpappu@gitam.edu received: 11 august 2022 | revised: 27 august 2022 | accepted: 29 august 2022 abstract-the rising number of frequency bands and the demand for wireless communication devices has become a growing concern regarding health and safety. the human head is a vulnerable body part when exposed to mobile phones. to ensure a high level of protection of the head from undesirable electromagnetic field (emf) emissions, a shield is incorporated in this paper between the head and the mobile smartphone. the shielding material used to protect the head from the rf emissions is copper (cu) grid transparent polyethylene terephthalate (pet) film and copper (cu) grid transparent pet film with nickel (ni) coating forming a laminated mesh. the rf emission metric from the smartphone is determined to evaluate the specific absorption rate (sar) numerically with a variation in frequencies ranging from 850mhz to 5.47ghz at normal wave incidence by the transmission line method. the variation in frequency is observed in two head models, one of an adult and one of a child. compared with the no shield condition, a significant sar reduction is observed when pet-cu or pet-cuni conductive coating transparent shielded mesh is embodied on the front part of the mobile phone between the phone and the head. in the child 7-layered head model at 5.47ghz, a significant reduction in sar is observed from 10.5w/kg to 0.00001w/kg using the cu grid pet film and to 0.0000032w/kg using cu and ni grid pet film. keywords-rf radiation emissions; specific absorption rate (sar); shielding effectiveness; copper grid pet film; conductive coating i. introduction many researchers have recently proposed altogether new designs of 5g antennas for cellular or wireless application to mitigate the effect of rf absorption emitted from mobile handsets [1-3]. the wireless communication devices emit most of the electromagnetic fields (emfs) from unwanted electromagnetic interference [4]. a proper electromagnetic compatibility (emc) technique is the need of the hour to mitigate such undesirable emissions from the devices, such as mobile smartphones [5]. though many regulatory bodies specify the specific absorption rate (sar) permissible limits, as and when the devices migrate to 5g frequency bands and higher and the radiation emission from the devices surges [6]. the emfs and radiation spectrum consist of an extensive range of frequencies covering non-ionizing and ionizing radiation [4]. the non-ionizing radiation results in thermal and non-thermal effects on human bodies. the thermal effects are caused due to heating of the body due to a temperature rise in the tissues. the national radiological protection board (nrpb) discussed the possibility of reducing the body sar limit over 10g of tissue from averaged 10w/kg to 5w/kg, because the data indicated that the temperature rise in the eye and brain may exceed 1c [7]. there is a fear of biological hazards occurring with the rise of temperature in the biological tissues of the brain of humans. in order to protect the human head from the non-ionizing radiation of mobile smartphones, a shield can be incorporated between the human head and the mobile phone on the front side. the property of shielding effectiveness (se) for a single or a laminated shield can be determined as a metric to measure the performance of any shielding material used. many shielding materials have been used in the past to shield em waves, such as polymer-based composites that include polymer matrixes and structured polymer composites, foams and aerogels, textile-based shielding materials, graphene, cntbased or nanocomposites-based materials, etc. due to various disadvantages and fitting the material for a particular scientific application, the researchers are now shifting their focus to transparent shielding material [4-5]. most materials and their blends have been used in shielding the em wave in various applications such as aerospace, electrical and electronic equipment, medical electronics, and wireless networks and devices. a very limited literature is available for the sar measurement and distributions studies and implementation using shielding for mobile phone applications. even with the implementation of sar distribution, mobile phone emissions have been reduced using the usual electromagnetic software simulations [8-9]. most of corresponding author: sai spandana pudipeddi engineering, technology & applied science research vol. 12, no. 6, 2022, 9445-9449 9446 www.etasr.com pudipeddi & jayasree: investigation of the effect of normal incidence of rf wave on human head … the relative published studies have considered a modification in the mobile antenna design for their theoretical or experimental validation of sar reduction. authors in [10] fabricated a transparent conductive electrode made of metal mesh film composed of nickel mesh embedded on pet substrate achieving optical transparency of 84%. the ni mesh was embedded with polymer poly (3,4 ethylenedioxythiophene): poly (styrenesulfonate) (pedot: pss) for supercapacitor application [10]. galvanic deposition of cu-ag and ni-ag on ag seed mesh was obtained in x-band and k-band respectively. the se increased from 23.2 to 43.7db with 82.2% transparency, while 47.6db se was achieved for cu-ag mesh and ni-ag mesh respectively for electronic devices [11]. a cu mesh with pet sheet as substrate was fabricated with visible transmittance of 85% in [12]. the shielding efficiency was tested in the range 12-18ghz and was 41db. indium tin oxide (ito) layer was doped on pet substrate with 83.5% transparency for flexible electronics in [13]. the cu/ni/pedot: pss transparent conducting film (tcf) was fabricated with a transmittance of 86% for joule heating purposes in [14]. a transparent shielded mesh film is employed as a shield in the current study, considering the disadvantages of several shielding materials. the primary properties of transparent materials are light weight, non-corrosiveness, flexibility, and durability for applications in electronics. an alternative to transparent conducting oxides (tco) is transparent conductive coatings exhibiting the non-variant nature of electrical properties under flexing. optical transparency is a crucial feature of transparent materials, which is inversely proportional to se. se of more than 60db can be achieved with transparent shielded mesh film [15]. the novelty of the proposed work is the theoretical mitigation of the sar absorbed in two head models of different ages from mobile smartphones operating at various bands from (850 to 5470mhz). moreover, the sar is minimized with the aid of se of the laminated shielded mesh film by transmission line method at the worst-case normal incidence of em rf wave. the shielding material is transparent pet film with conductive cu and ni coatings forming a laminated mesh film. ii. materials and methods a. transparent conductive metal mesh pet film the transparent material used for the mathematical analysis is pet film with copper and nickel mesh conductive coatings. the structure constitutes a laminated shielded mesh. it is essential to derive shield and conductive mesh impedance and propagation constant in terms of conductivity, permeability, and permittivity [16]. equations (1) and (2) give the pet film's shield impedance. � = �1 + ���� ��� (1) = ������ + ���� (2) �� = � ���������� � � !"# (3) $� = %& �− (# )*+ �,-+ �" #�. (4) /� = �01 ��� + �$� � (5) where rm and xm are the resistance and reactance respectively of the cu and ni conductive coating.  is the skin depth, g and 2a are mesh spacing and line-width, and lm is the mesh thickness which is 100 and 50nm for cu and ni coating respectively [17]. the impedance zm of conductive mesh coatings is, thus, given by (5). b. head models with tissues the head height of the adult and child head models is 25 and 23.5cm with diameters of 16.01 and 14.06cm respectively [18-20]. multi-layered head models are considered in the current research. head models with 4 and 7 layers of tissues are taken for analysis. skin, fat, bone, and brain are the layers considered in the 4-layered model, whereas skin, fat, bone, dura, csf, gray matter, and white matter are the tissue layers considered in the 7-layered model [21]. their representation is shown in figures 1 and 2. the analysis using the transmission line method considers the spherical models to be planar (4 and 7 layers) as in figures 3 and 4. the tissue thickness of the head is given in tables i and ii. fig. 1. four-layered adult or child head model (table i). table i. tissue thickness of 4 layers in adult and child head models [19-20] model tissue layer thickness (mm) adult skin 1 fat 2 bone 7 brain 70.05 child skin 1 fat 0.5 bone 6.5 brain 62.3 c. se derivation the reflection and transmission coefficients are derived from tissue medium's thickness, impedances, and propagation constants [22]. the conductivity and relative permittivity of each tissue medium is obtained from [23]. engineering, technology & applied science research vol. 12, no. 6, 2022, 9445-9449 9447 www.etasr.com pudipeddi & jayasree: investigation of the effect of normal incidence of rf wave on human head … fig. 2. seven-layered adult or child head model (table ii). table ii. tissue thickness of 7 layers in adult and child head models [21] model tissue layer thickness (mm) adult skin 1 fat 2 bone 7 dura 1.5 csf 2 gray matter 3.7 white matter 62.85 child skin 1 fat 0.5 bone 6.5 dura 0.5 csf 1.5 gray matter 3.6 white matter 56.7 also, the total transmission coefficient for the radiated em wave is derived for the head model alone and then with the copper and nickel grid pet film (pet film with cu mesh, and pet film with cu, ni mesh) from (6), (7), and (8). 2 = 3 ∏ 5�1 − 6789:�!;<=>?<=> �@: �;<=>?<=>ab"c e"ff�b8gh8ij (6) 2 = 3 ∏ 5�1 − 6789:�!;<=>?<=> �@: �;<=>?<=>ab"c e"ff�b8gklmnop (7) 2 = 3 ∏ 5�1 − 6789: �!;<=>?<=> �@:�;<=>?<=>ab"c e"ff�b8gklmnopnqi (8) where p represents the transmission coefficient, which is the product of the intrinsic impedances across the media and q represents the reflection coefficient, calculating the impedances across two consecutive interfaces. d. sar computation from the se of head models equation (6) represents the total transmission coefficient t of the radiated electromagnetic wave, considering the power entered into the skin through the layers of fat, bone, dura, csf, and gray matter and propagated into the white matter. equation (7) represents t of the radiated electromagnetic wave, considering the power entering into the cu grid pet film through the intermediate tissue layers and gray matter respectively. the total radiated power into the white matter goes through the layers of cu and ni grid pet laminated shielded mesh film, skin, fat, bone, dura, csf, and gray matter. the se (db) is evaluated from t as in (9) [24]. the ei is computed from the incident wave power density delegated by the icnirp standard for mobile phone frequencies [25]. et is obtained from the se of the head without and with the laminated shielded mesh from (10). rs = −20 *vw�&|2| (9) rs = 20 *vw�& �lylz# (10) the sar is computed from the se of the human head models (adult and child). by the icnirp guidelines, the power densities of the incident wave at frequencies of 5.47, 4.5, 3.6, and 2.3ghz, are 40w/m 2 , 36.556w/m 2 at 1.8ghz and 19.175w/m 2 at 0.85 ghz [25]. the sar absorbed (w/kg) by i (brain/white matter) in a (4/7-layered head model) of an adult and child is given by: sar = �^lz_`^ (11) the allowable sar limit proposed by icnirp is 2w/kg for absorption by local body parts such as head/limbs. fig. 3. four-layered planar head model with the adult/child tissue thickness. fig. 4. seven-layered planar head model with the adult head tissue thickness [23]. reproduced, courtesy of the electromagnetics academy. iii. results and discussion the se plots of 4and 7-layered head models of adult and child for frequencies ranging from 850 to 5470mhz without shield, with transparent conductive metal (cu and ni), and with mesh pet film for normal incidence of em wave is shown in figures 5 and 6 and figures 7 and 8 respectively. the wave's frequency in any medium is directly proportional to the medium's se. the se against the frequency of the head model in the child is less than that of the adult head model in figures 5-8. the se of a child's 7-layered head model from figure 8 is only around 20db without the laminated shield and around 100db with the copper grip pet film with ni coating. coincidence in graphs of the se with frequency variation is noticed in the figures because the thickness difference between cu and ni metal mesh coatings is only 50nm. the sar emission absorbed by the brain in the 4layered adult and child head models is tabulated in tables iii engineering, technology & applied science research vol. 12, no. 6, 2022, 9445-9449 9448 www.etasr.com pudipeddi & jayasree: investigation of the effect of normal incidence of rf wave on human head … and iv. at 5.47ghz frequency, the cu grid pet film with ni coating has absorbed a sar of 5.91e-7w/kg in the adult 4layered model and the child head model absorbed a comparatively higher sar of 0.00002w/kg. regarding the 7layered model, the sar absorbed by the white matter in the adult head model is 5.27e-09w/kg, which is less compared to that of the child's head model, which is 3.16e-06w/kg at 5.47ghz. fig. 5. se with frequency variation of an adult 4-layered head model for no shield condition, with transparent cu pet mesh film, and transparent cu and ni pet mesh film for normal incidence of em wave. fig. 6. se with frequency variation of a child 4-layered head model for no shield condition, with transparent cu pet mesh film, and transparent cu and ni pet mesh film for normal incidence of em wave. fig. 7. se with frequency variation of an adult 7-layered head model for no shield condition, with transparent cu pet mesh film, and transparent cu and ni pet mesh film for normal incidence of em wave. fig. 8. se with frequency variation of a child 7-layered head model for no shield condition, with transparent cu pet mesh film, and transparent cu and ni pet mesh film for normal incidence of em wave. table iii. brain sar of the adult 4-layered model frequency ghz sar (w/kg) without shield with cu grid pet film with cu grid pet film with ni coating 0.85 31.8 9.47e-05 5.74e-05 1.8 49.11 6.08e-05 3.71e-05 2.3 42.14 4.19e-05 2.56e-05 3.6 14.77 1.03e-05 6.34e-06 4.5 5.82 3.37e-06 2.07e-06 5.47 2.05 9.58e-07 5.91e-07 table iv. brain sar of the child 4-layered model frequency ghz sar (w/kg) without shield with cu grid pet film with cu grid pet film with ni coating 0.85 43.34 1.6e-4 7e-5 1.8 90.55 1e-4 6.16e-5 2.3 103.12 9.29e-5 5.68e-5 3.6 100.52 6.62e-5 4.07e-5 4.5 87.57 5e-5 3.07e-5 5.47 66.83 3.25e-5 2e-5 table v. white matter sar of the adult 7-layered model frequency ghz sar (w/kg) without shield with cu grid pet film with cu grid pet film with ni coating 0.85 9.84 5.84e-05 1.77e-05 1.8 9.32 2.29e-05 7.04e-06 2.3 6.1 1.20e-05 3.70e-06 3.6 0.33 4.49e-07 1.40e-07 4.5 0.15 1.63e-07 5.14e-08 5.47 0.02 1.67e-08 5.27e-09 table vi. white matter sar of the child 7-layered model frequency ghz sar (w/kg) without shield with cu grid pet film with cu grid pet film with ni coating 0.85 24.51 1.3e-4 3.97e-05 1.8 43.77 9.67e-05 2.97e-05 2.3 44.73 7.96e-05 2.46e-05 3.6 20.86 2.70e-05 8.43e-06 4.5 20.08 2.24e-05 7.03e-06 5.47 10.55 1.00e-05 3.16e-06 engineering, technology & applied science research vol. 12, no. 6, 2022, 9445-9449 9449 www.etasr.com pudipeddi & jayasree: investigation of the effect of normal incidence of rf wave on human head … iv. conclusion a theoretical investigation for the determination of the specific absorption rate (sar) of age-dependent multilayered head models exposed to rf emissions from mobile phone operating frequencies of 850mhz-5.47 ghz for normal incidence of em wave is assessed in this paper. absorption is found with the relevance of shielding effectiveness of the human head in the absence of any shield and in the presence of cu grid pet film (transparent conductive metal mesh pet film/transparent cu pet laminated mesh) and cu grid pet film with ni coating. the result analysis at 5.47ghz showed that the child head model had absorbed a higher radiation level of 66.83w/kg in the 4-layered model and 10.55w/kg in the 7layered model. the same model with the transparent pet and cu laminated shielded mesh had absorbed a sar of 0.0000325w/kg (4-layered model) and 0.00001w/kg (7layered model). with the pet/cu/ni laminated mesh, 0.00002w/kg was absorbed by brain tissue by the 4-layered model, and white matter absorbed 0.00000316w/kg in the 7layered head model of a child. thus, a higher amount of sar is reduced in adult head models compared to child head models using the transparent cu grid pet film with ni coating. without a shield, the child model had absorbed maximum radiation of around 67w/kg and the pet laminated mesh film absorbed a comparatively negligible amount of sar in every case. references [1] d. t. t. my, h. n. b. phuong, t. t. huong, and b. t. m. tu, "design of a four-element array antenna for 5g cellular wireless networks," engineering, technology & applied science research, vol. 10, no. 5, pp. 6259–6263, oct. 2020, https://doi.org/10.48084/etasr.3771. 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[23] s. s. pudipeddi and p. v. y. jayasree, "numerical computation of sar in human head with transparent shields using transmission line method," progress in electromagnetics research m, vol. 105, pp. 31– 44, 2021, https://doi.org/10.2528/pierm21080405. [24] international commission on non-ionizing radiation protection (icnirp), "guidelines for limiting exposure to electromagnetic fields (100 khz to 300 ghz)," health physics, vol. 118, no. 5, pp. 483–524, may 2020, https://doi.org/10.1097/hp.0000000000001210. microsoft word etasr_v13_n2_pp10432-10438 engineering, technology & applied science research vol. 13, no. 2, 2023, 10432-10438 10432 www.etasr.com abdulkader: controller design based on fractional calculus for auv yaw control controller design based on fractional calculus for auv yaw control rasheed abdulkader department of electrical engineering, imam mohammad ibn saud islamic university (imsiu), saudi arabia rmabdulkader@imamu.edu.sa (corresponding author) received: 16 january 2023 | revised: 8 february 2023 and 12 february 2023 | accepted: 15 february 2023 abstract this research presents a fractional order integral controller strategy, which improves the steering angle for autonomous underwater vehicles (auvs). the auv mathematical modeling is presented. a fractional order proportional integral (fopi) control scheme is implemented to ensure the yaw angle stability of the auv steering under system uncertainty. the fopi controller is validated with matlab/simulink and is compared to the conventional integer order pi (iopi) controller to track the yaw angle of the structure. the simulation results show that the proposed fopi controller outperforms the iopi controller and improves the auv system steering and the overall transient response while ensuring the system's stability with and without external disturbances such as underwater current and different loading conditions. keywords-autonomous underwater vehicle (auv); nelder mean simplex (nms); fractional calculus; fopi i. introduction water covers more than 70% of earth's surface and the oceans holds nearly 96.5% of all the earth’s water. the scientific area of exploration of new resources in the ocean is in rapid increase. however, investigating under sea water levels can have some limitations with manned or human operated systems, while the use of automatous underwater vehicles (auv) can provide huge benefits in terms of reducing the risk of human lives, exploring deep sea levels, underwater surveillance, and cost saving [1]. auvs are unmanned robots that have the capability to move under the water surface typically on a pre-defined mission, with satellite networks used for communication. in the modeling and design stage, an important aspect is the mission requirements and objectives. additional details on the process of designing underwater vehicles can be found in [2]. underwater vehicles can be categorized into two major types, remotely operated vehicles (rovs) or manned vehicles, which need a human to function and send control instructions in order to operate. the other type is the auv or unnamed vehicles, which can completely function independently. currently, auv’s are rapidly used in a wide range of applications, which include environmental monitoring, underwater surveillance, scientific research, antisubmarine warfare, oceanographic discovery, subsea structure inspection, oil and gas natural research exploration, etc. [1]. the dynamics of underwater vehicles are well-known to contain significantly nonlinear dynamics and are dependent on a variant number of the system parameters. these nonlinearities can generate system uncertainties, time-varying dynamic model and severe effect by external disturbances such as unpredicted under water current, waves and environmental disturbances [1]. controlling the auv system is a challenging problem, and high control accuracy is needed to keep the system safe and stable when threatened by unpredicted factors. in order to handle auvs' uncertainty and disturbance and to enhance their tracking performance, numerous control methods have been applied to ensure the stability of auv systems, including the lqr control [3], neural networks [4], fuzzy control [5], pi/pid control [6], and sliding mode control (smc) [7]. research findings on non-integer controllers indicate better quality control than integer order (io) controllers. some studies showing the advantages of implementing this control technique to stabilize the steering system of auv’s are [8-12]. in this paper, a control method is proposed that is essentially found in fractional calculus theory, a non-integer or fractional order control. at present, fractional order controller based on nelder-mead simlex (nms) algorithm has not been utilized for controlling and stabilizing the yaw angle of auv’s. the main contribution of this research is the development of a fractional order proportional integral (fopi) controller scheme applied to enhance the steering stability and yaw angle for auv dynamics with disturbances being present. the performance of the auv structure and transient response is improved by designing the coefficients of the fopi controller using the nms method. the proposed controller is examined and its effectiveness to maintain the system stable with uncertain conditions such as underwater currents and load variation is shown. engineering, technology & applied science research vol. 13, no. 2, 2023, 10432-10438 10433 www.etasr.com abdulkader: controller design based on fractional calculus for auv yaw control ii. auv modeling a. auv dynamics (coordinate system) to derive a mathematical model and the equations representing the auv structure, analysis of the system dynamics and kinematics is demonstrated, as three subsystems are considered. figure 1 shows the two coordinate systems describing the movement of the auv in 6 degrees of freedom (dof). the o-xyz axis is the motion coordinates and is static to the underwater vehicle, which is denoted as the body-fixed refence system. the movement of the body-rigid system is demonstrated to the earth (e) fixed system (�, �, ψ� [13,14]. thus, a non-integer order pi with feedback control scheme would be implemented to the auv structure to achieve robust yaw angle stability with/without disturbances. table i indicates the used auv parameter values. fig. 1. auv 6-dof coordinate system. b. auv kinematics the physical demonstration of the auv structure and the equation of motion follow fixed body dynamics. consequently, it is valuable to utilize the physical system components by diminishing the number of coefficients needed to control the system. thus, it is the main incentive for the development of the vertical description of the equations of motion, which are successful for computer processing [13]. the 6-dof auv equation of movement follows fixed body dynamics. �� � �� �� � , �� � � � � � is the position vector and �� � � � � � is the orientation vector of the body and earth fixed reference system. the linear and angular velocities are specified as �� � � � � � , �� � � � � � where � � �� �� � . the two essential equations to model the auv dynamical system are obtained from newton's laws of motion. these equations can be defined as [13]: �� � ���� � (1) ��� � ����� � ����� � ��� � ! (2) where ���� is the transformation matrix, ! is the control input matrix, � , "��� , ���� , and ��� symbolize mass, coriolis forces, damping matrix, and the gravitational matrix respectively. by including in the auv system non-linear equations of motion, the kinematics equation can be expressed as [13]: �� � �#� "���� � ����� � ��� � !$ (3) table i. auv parameters parameter name value unit � auv mass 50 kg %& cross flow drag -131 kg/m %' cross flow drag -0.632 kg.m/rad� +$ cross flow drag -94 kg.m� /rad +& cross flow drag -3.2 kg ./� additional mass -0.9 kg %$� additional mass 1.93 kg.m /rad %&� additional mass -36 kg +$� additional mass -4.9 kg.m� /rad 01 moment of inertia 3.45 kg.m� /rad �2 auv speed 10 m/s c. auv model decoupling due to the auv system extreme nonlinear dynamics and coupling, a reduced system model is considered and linearized for the controller design, to ensure the stability and control of the auv steering system. the vehicle model can be reduced and decoupled to study the yaw angle steering behavior. by considering the following three states, the sway v, yaw velocity r, and the yaw rate �. the steering movement can be acquired from the rudders and fins. also, by disregarding the gravity forces, system damping and assuming an equilibrium point, the auv system model can be decoupled as follows: 3 4 %&� �� � �./� 4 3��5 � � %& � � %$ �, (4) 01 4 +$� �� � �%&� #./� �� � � %$� �2� �+&� � +$ � � !$ (5) where �� � � . the linear auv system can be expressed in state-space as: �� � 6� � 7� , � � "� � �� (6) where: 6 � ⎣⎢ ⎢⎡ ;<=#;<� �>?� #=�/@a;b=#;<� 0d<ef#db� ;b� /@adbeg#db� 00 1 0⎦⎥ ⎥⎤, (7) 7 � ��� � l 0�ef #db�0 m, � � !$ . (8) from the state-space model in (7)-(8), the transfer function of the yaw angle control can be computed as follows: �n� � 2.��pq ra2.�2strua�2.sv rwa�x.xy r (9) where a fractional controller is developed and applied to the auv system dynamics in a feedback formation as shown in figure 3. engineering, technology & applied science research vol. 13, no. 2, 2023, 10432-10438 10434 www.etasr.com abdulkader: controller design based on fractional calculus for auv yaw control iii. fractional order pi control the controller technique implemented in this study is based on fractional calculus, a non-integer or fractional order pi control. for auv dynamics structure, it is crucial for the control scheme to track the required vehicle position and yaw angle in a precise manner to help the system obtain steering stability. by introducing fractional integral and differential operators, the perception of only io operators can be stretched over a wider range, which results in better accuracy in system modeling or control. one critical advantage of a fractional system is the memory and hereditary annotation, which can be described with fractional order calculus theory. however, for classical io plants the memory aspect and hereditary annotation are of a major concern [11]. fractional calculus theory is a general notion to fractional order of differentiator and integrator simple operator �z[\ defined in (10) [10]: �z[\ � ⎩⎨ ⎧`[ `a[b ℜ�d� e 0,1 ℜ�d� � 0,f �`a�#[ ℜ�d� g 0.z\ (10) where h and a are bounds of the process and i indicates the fractional component. i is assumed real, but it can be an imaginary component [10]. fractional operators can be applied directly to systems or can be approximated as io operators applied into the system. further, a control system can be controlled by either an io or non-integer order controller, hence the system plant can also possibly be derived as a fractional or classical io system. four distinct combinations can occur to implement a fractional order control: fractional order controller with a fractional order plant, fractional order plant with an io controller, io plant with a fractional order controller, and io plant with an io controller [14]. in this paper a linear fractional order controller scheme is developed and the controller would be implemented to an io plant (auv system). describing the control options by implementing a noninteger order controller in a graphic representation, figure 2 indicates that all io pid controllers are special cases of the non-integer order pid controller. it can be observed in figure 2 that the io pid controller only transforms at four rigid points, whereas any point on the graphical plane can be used with a fractional order pid controller, i.e. the control order can interchange continuously and smoothly throughout the entire shaded region, which makes the fractional order pid design more flexible more effective with system uncertainties than iopid [17]. thus, in this study, the value examined for the fractional order integral operator j, lies in region [0-1] shown in figure 2, since the system requires a lower order integral value to improve the transient response and maintain stability. the differential equation of the fractional order k0 l control is provided by: u�t� � kp e�t� � rstu e�t� (11) by applying the laplace transformation to (11) and with the assumption of zero initial conditions, the transfer function can be obtained as [16]: v �n� � wx � yzr{ (12) fig. 2. graphical representation of the range values of the fopid controller. a block diagram representation of the fopi controller for a closed loop structure is shown in figure 3, where the plant is the auv system dynamics and g} �s� is the non-integer controller expressed as: v �n� � wx � yzr{ . (13) and j is the non-integer operator. the added tunable component j with the fopi control in comparison to the iopi control generates more flexibility in controlling the structure and at the same time enhances the control quality implementation and helps minimizing the steady-state error and improves the transient response of the auv system. proper tunning of the fopi controller is required to meet the system specifications. with a fopi controller, reaching closed-loop zero steady-state error and diminishing the amplification of high-frequency disturbances can be achieved for the auv system. moreover, when using the iopi control there would be a lagging phase of 90° for the system, while with the fopi scheme, it delivers a reduced constant lagging phase to the system due to the fractional element j which improves the transient response of the system dynamics as compared to the iopi control. fig. 3. fopi structure applied for the auv. iv. the nelder-mead simplex method the simplex algorithm developed by nelder and mead in 1965 has been widely used to solve parameter estimation and optimization problems. the nelder-mead simplex (nms) has been applied by the united states army corps engineers for engineering, technology & applied science research vol. 13, no. 2, 2023, 10432-10438 10435 www.etasr.com abdulkader: controller design based on fractional calculus for auv yaw control hydrologic engineering center-hydrologic modeling system (hec-hms) software as a search technique for optimizing the hydrologic parameters [18]. in this research, the value of the fractional operator j is tunned using the nms method. the nms method can solve unconstrained optimization problems of the form 3��� ����, � � ℝ' . there are four basic operational steps of the nms algorithm: reflection, expansion, contraction, and shrinking as demonstrated in figure 4 [10, 18]. the five stages for implementing the nms algorithm are [18]: 1. order. order � � 1 vertices in order to meet: ����� � ���� � ⋯ � ���'a�� 2. reflect. calculate the reflection point �$ : �$ � �̅ � ���̅ 4 �'a�� (14) where: �̅ � �' ∑ ��'��� , (15) is the centroid of the � best points. then, �$ � ���$ � . if �� � �$ � �' , set the point �$ and terminate the iteration. 3. expand. if �$ g ��, evaluate the expansion point �� by: �� � �̅ � ���$ 4 �̅� (16) then compute �� � ���� � . if �� g �$ then set �'a� � �� and terminate the iteration. otherwise, set �'a� � �$ and terminate the iteration. 4. contract. if �$ � �', compute a contraction between �̅ and the best of �'a� and �$ :  outer contraction. if �' � �$ g �'a�, compute: �v � �̅ � ���$ 4 �̅� (17) then determine �v � ���v � . if �v � �$ , set �'a� � �v , and terminae the process, else proceed to the next stage performing a shrinkage.  inner contraction. if �$ � �'a� , execute the inner contraction by computing: �vv � �̅ 4 ���̅ 4 �'a�� (18) then compute �vv � ���vv �. if �vv g �'a�, set �'a� � �vv , and terminate the iteration. else proceed to the next stage performing a shrinkage. 5. shrink. calculate � new points by: �� � �� � ���� 4 ���, (19) where � � 2, … , � � 1. then compute � at those vertices. the scalar coefficients � , χ , � , and � denote the coefficients, expansion, contraction, and shrink reflection, respectively. these cofficients should obey: � e 0, χ e 1, 0 g � g 1, and 0 g � g 1. fig. 4. nms flowchart. v. results and discussion the fractional order pi controller has been applied for auv dynamics using matlab/similink and the fomcon toolbox. figure 5 shows the simulink model for the auv system yaw angle response for the pi/fopi controller, as a step disturbance is added to emulate an underwater current disturbance applied to the auv system. the fopi control is developed with the vehicle travelling at a speed of 10m/s, and maintains the yaw angle and steering stability for the auv structure. the fopi controller was designed using nms with the minimum integral square error, as the bound of fractional integral inspected between the closed interval [0, 1]. further, by applying the nms technique the local minimization can be reached by eliminating the smallest needed vertex in a given function. the integral term j of the fractional controller is optimized to be 0.1 with �x = 200 and �� = 79. hence, the developed fractional controller is compared to the classical integer-order pi (iopi) controller. a. simulation results with the fopi controller for different auv travelling speeds figure 6 shows the simualtion results of the auv operating at different speeds with the fopi controller. it is demostarted that the vehicle reaches the desired steering angle of 40 o in 3s with a 50% increase and decrease in the auv speed. as the speed is increased, the overshoot slightly increases, while the system still maintains its regulation to reach the desired yaw angle response. b. simulation of the yaw angle of the auv with pi/fopi controllers figure 7 displays the response of yaw angle with the fopi and iopi controllers being applied for a desired yaw angle of 40 o . the response indicates improved performance of the fopi over the iopi controller, with a faster time response, settling time, lower overshoot, and increased damping. table ii shows the perfomrance comparison of the transient response of the controllers. we can see that the fractional controller has better performance in any feature. engineering, technology & applied science research vol. 13, no. 2, 2023, 10432-10438 10436 www.etasr.com abdulkader: controller design based on fractional calculus for auv yaw control fig. 5. simulink model of the yaw angle for auv using pi/fopi. fig. 6. yaw angle for different auv speeds with fopi controller. fig. 7. yaw angle of the auv with fopi/iopi controller. table ii. transient response response info controller iopi fopi settling time 4.75 1.48 rise time 0.46 0.39 overshoot 16.1 6.8 undershoot 0 0 peak 46.17 42.95 c. simulation of the yaw angle of the auv under the presence of disturbancet figure 8 presents the yaw angle reposne with an external disturbance, such as ocean curernt waves, being applied on the auv system. it is seen that the fopi controller outperforms the iopi in terms of time response, overshoot, and settling time to reach the desired yaw angle with the presence of external disturance. table iii shows the respone comparizon between the controllers. it can be seen that the fractional controller improved the transisent response in all aspects. fig. 8. yaw angle with external disturbance applied to the auv. engineering, technology & applied science research vol. 13, no. 2, 2023, 10432-10438 10437 www.etasr.com abdulkader: controller design based on fractional calculus for auv yaw control table iii. transient response with system disturbance response info controller iopi fopi settling time 4.55 1.51 rise time 0.47 0.38 overshoot 9.3 17.1 undershoot 0 0 peak 43.66 46.97 d. simulation of the yaw angle with load variation on the auv system figure 10 demonstrates the response of the uav with the load being increased and deceased by 50% along with the presence of disturbances. the fopi controller shows its robustness in handling uncertain environmental disturbances with different loading conditions, in stabilizing the system, and in achieving the desired yaw angle with improved time response, stetting time, and minimized overshoot in comparison with the classical iopi controller. fig. 9. fopi/iopi control of the yaw angle for auv with varying loads. vi. conclusion in this paper, a non-integer (fractional) order controller is implemented on the auv dynamical system. it is demonstrated that the proposed fopi control, which adds an additional tuning parameter, improves the system transient response, stability, and the yaw angle control of the auv structure. the underwater vehicle yaw angle control is a very challenging problem and with the fopi controller the system can preserve improved regulation and faster time response under system uncertainties and disturbances such as, underwater current waves and load variations. the fopi controller was compared to the classical integer order controller, and the simulation results confirm that the fractional controller outperforms the iopi controller and provides improved time response and reduced system overshoot and settling time to achieve the desired yaw angle. regarding future work, the applied fractional order controller can be applied to an auv system modeled as a fractional order system, which can provide more precision and accuracy to the system model dynamics and thus, improve the system overall performance. references [1] m. t. vu et al., "robust position control of an over-actuated underwater vehicle under model uncertainties and ocean current effects using dynamic sliding mode surface and optimal allocation control," sensors, vol. 21, no. 3, jan. 2021, art. no. 747, https://doi.org/10.3390/s21030747. [2] v. upadhyay et al., "design and motion control of autonomous underwater vehicle, amogh," in 2015 ieee underwater technology (ut), chennai, india, oct. 2015, https://doi.org/10.1109/ut.2015. 7108287. [3] l. priyadarshini, s. kundu, m. k. maharana, and b. p. ganthia, "controller design for the pitch control of an autonomous underwater vehicle," engineering, technology & applied science research, vol. 12, no. 4, pp. 8967–8971, aug. 2022, https://doi.org/10.48084/ etasr.5050. [4] r. hernández-alvarado, l. g. garcía-valdovinos, t. salgado-jiménez, a. gómez-espinosa, and f. fonseca-navarro, "neural network-based self-tuning pid control for underwater vehicles," sensors, vol. 16, no. 9, sep. 2016, art. no. 1429, https://doi.org/10.3390/s16091429. [5] x. xiang, c. yu, l. lapierre, j. zhang, and q. zhang, "survey on fuzzy-logic-based guidance and control of marine surface vehicles and underwater vehicles," international journal of fuzzy systems, vol. 20, no. 2, pp. 572–586, feb. 2018, https://doi.org/10.1007/s40815-0170401-3. [6] f. kong, y. guo, and w. lyu, "dynamics modeling and motion control of an new unmanned underwater vehicle," ieee access, vol. 8, pp. 30119–30126, 2020, https://doi.org/10.1109/access.2020.2972336. [7] n. wang, s. lv, w. zhang, z. liu, and m. j. er, "finite-time observer based accurate tracking control of a marine vehicle with complex unknowns," ocean engineering, vol. 145, pp. 406–415, nov. 2017, https://doi.org/10.1016/j.oceaneng.2017.09.062. [8] b. bourouba and s. ladaci, "a novel non-integer indirect adaptive control for non-integer order systems with non-prior knowledge," engineering, technology & applied science research, vol. 10, no. 1, pp. 5186–5190, feb. 2020, https://doi.org/10.48084/etasr.3236. 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[12] r. abdulkader and r. mccann, "fractional controller for improved lateral stability control using afs," in 2020 6th international conference on control, automation and robotics (iccar), singapore, apr. 2020, pp. 242–246, https://doi.org/10.1109/iccar49639.2020. 9108059. [13] t. fossen, hanbook of marine craft and motion control. west suusex, uk: wiley and sons, ltd, 2011, https://doi.org/10.1002/ 9781119994138. [14] r. abdulkader, "non-integer controller for autonomous underwater vehicle steering control," in 2021 ieee international conference on robotics, automation, artificial-intelligence and internet-of-things (raaicon), dhaka, bangladesh, sep. 2021, pp. 102–105, https://doi.org/10.1109/raaicon54709.2021.9929838. [15] i. pan and s. das, intelligent fractional order systems and control: an introduction. berlin heidelberg, germany: springer, 2013, https://doi.org/10.1007/978-3-642-31549-7. [16] r. abdulkader and r. mccann, "fractional order state feedback control for improved lateral stability for tractor-trailers in platooning," international. journal of heavy vehicle systems, vol. 28, no.5, pp. 698725 2020, https://doi.org/10.1504/ijhvs.2021.10037405. engineering, technology & applied science research vol. 13, no. 2, 2023, 10432-10438 10438 www.etasr.com abdulkader: controller design based on fractional calculus for auv yaw control [17] c. i. pop, c. ionescu, r. de keyser, and e. h. dulf, "robustness evaluation of fractional order control for varying time delay processes," signal, image and video processing, vol. 6, no. 3, pp. 453–461, sep. 2012, https://doi.org/10.1007/s11760-012-0322-4. [18] r. barati, "parameter estimation of nonlinear muskingum models using nelder-mead simplex algorithm," journal of hydrologic engineering, vol. 16, no. 11, pp. 946–954, nov. 2011, https://doi.org/10.1061/(asce)he.1943-5584.0000379. microsoft word 3-563-ed.doc engineering, technology & applied science research vol. 5, no. 3, 2015, 805-810 805 www.etasr.com khaskhoussy et al.: effect of treated wastewater irrigation on heavy metals distribution in a tunisian soil effect of treated wastewater irrigation on heavy metals distribution in a tunisian soil khawla khaskhoussy besma kahlaoui besma messoudi nefzi institute of rural engineering, waters and forest and inat ariana, tunisia khawla.khaskhoussy@yahoo.fr inrgref ariana, tunisia besma.kahlaoui@gmail.com inrgref ariana, tunisia messoudi.b@gmail.com omar jozdan abdullah dakheel mohamed hachicha acsad damascus, syria omar62@hotmail.com icba, oman a.dakheel@biosaline.org.ae inrgref ariana, tunisia hachicha.mohamed@iresa.agrinet.tn abstract—treated wastewater (tww) may contain toxic chemical constituents that pose negative environmental and health impacts. in this study, soil samples under treated wastewater irrigation were studied. for this purpose, six plots were made in an irrigated area in north of tunisia and treated with two water qualities: fresh water (fw) and treated wastewater (tww). five soil depths were used: 0-30, 30-60, 6090, 90-120 and 120-150 cm. the tww irrigation increased significantly (p≤0.05) the soils’ ec, na, k, ca, mg, cl, sar, cu, cd and ni and had no significant (p ≤0.05) effect on the soils’ ph, zn, co and pb contents. ec, na, cl, sar, zn and co increased significantly with soil depth. the results for k, ca, mg, cd, pb and ni exhibited similar repartition in different layers of soil. it was also shown that the amount of different elements in soil irrigated with fresh water (fw) were less compared with the control soil. keywordstww; fw; soil; salinity; heavy metals; tunisia i. introduction in many arid and semi-arid regions, natural fresh water (fw) resources are limited, whereas the demand is constantly increasing due to industrial and population growth. the greater challenge to meet water demands and manage its limited natural resources has led to the use of alternative irrigation sources [1]. one of these alternatives is to use nonconventional water resources, such as treated waste water (tww). the reuse of tww for purposes such as agricultural irrigation has become, for many countries, an important element in water resources planning [2]. tww can be used to help in reducing natural water consumption, in restoring and preserving degraded land and in aiding the growth of vegetation [3-7]. the reuse of tww for irrigation is considered an environmentally sound wastewater disposal practice compared to its direct disposal to the surface or ground water bodies. in addition, tww provides convenient disposal of waste products [8] and constitutes a significant source of plant nutrients and organic matter needed for maintaining the fertility and productivity levels of the soil [9, 10]. however, besides these beneficial effects, tww is often associated with environmental and health risks. the main health risks are associated with the contamination of crops or ground waters by tww due to its chemical composition being somewhat different from most natural waters used in irrigation [11]. this water may contain high levels of salts, toxic ions, heavy metals, and organic residues. accumulation of these pollutants in soil can be harmful in fields irrigated for longs periods of time and poses a threat to agricultural production and the environment [12]. several studies have reported some changes in the physicochemical characteristics of soil due to tww application [13, 14] such as the increase of soil salinity, electrical conductivity (ec), organic matter, exchangeable na, k, ca, mg, plant available phosphorus and microelements [1417] and the decrease of soil ph [16]. in general, heavy metals combine with other anions or anionic compounds to form stable substances and tend to accumulate in the topsoil (0–35 cm). furthermore, their uptake by plants increases with decreasing ph, due to the dissolution of metal–carbonate complexes that releases free metal ions into the solution [18]. however, when the capacity of soils to retain toxic metals is reduced due to continuous loading of pollutants or changes in ph, metal ions that have a relatively high mobility can migrate in depth and contaminate groundwater by percolation into the ground [19]. the purpose of the present work is to study and compare the effects of fw and tww irrigation on a tunisian clay loam soil properties and its macroand micro-nutrients, and heavy metal content, in order to establish the basis for safe tww agricultural reuse. engineering, technology & applied science research vol. 5, no. 3, 2015, 805-810 806 www.etasr.com khaskhoussy et al.: effect of treated wastewater irrigation on heavy metals distribution in a tunisian soil ii. materials and methods a. experimental design the experiment was located in cebela borj-touil field located 20 km north of tunisian the low valley of medjerda. climate of the region is semi-arid with an annual rainfall close to 470 mm and an average yearly evapotranspiration of 1400 mm. the soil is clay-loam. the experiment included two sources of irrigation water: (a) tww and fw (b). the experiment was carried out in strip plot design with three replications and a total of 2x3 = 6 plots of 3mx3= 9 m2 size. the experimental plots were irrigated by wastewater from chotrana treatment plant located in north of tunis city. the tww and fw were applied during the summer period. in each plot, soil samples were collected from five successive depths 0-30, 30-60, 60-90, 90-120 and 120-150 cm. control soil samples were collected in the beginning of the experiment. water samples were collected periodically during the experimental period and the chemical characteristics are summarized in table i. table i. chemical properties of fw and tww parameter irrigated water innorpi (nt-1989)* fw ph 8.5b 6.5-8.5 6.5-8.5 ec (dsm-1) 1.42a 7 7 so4(mgl-1) 9.47a na+ (mgl-1) 6.45a ca++ (mgl-1) 6.28a mg++ (mgl-1) 4.91a cl(mgl-1 9.39a 2000 2000 k+ (mgl-1 0.14a cd (mgl-1) 0.045a 0.05 0.05 co (mgl-1) 0.033a 0.1 0.1 cu (mgl-1) 0.019a 0.2 0.2 ni(mgl-1) 0.06a 0.2 0.2 pb (mgl-1) 0.16a 5 5 zn (mgl-1) 0.010a 2 2 *tunisian standard b. soil sampling and analysis collected soil samples were transported to the laboratory, oven, dried at 105° c and sieved for chemical analysis. the ph and the electric conductivity (ec) were respectively measured with ph-meter and conductivity-meter in a soil–water suspension. the sodium absorption ratio (sar) [20] was calculated by the following formulae: 2+ 2+ [na] sar= [ca ]+[mg ] concentrations of ca and mg were measured using the edta titration method. na and k contents were measured using flame photometer [20]. soil samples were digested for heavy metal (cu, zn cr, cd, ni and pb). the procedure based on acid digestion induced by microwave energy was optimized in order to measure the total heavy metals contents in soils. each soil sample (1 g) was placed in a teflon vessel (100 ml) with hf (10 ml) and hclo4 (5 ml) and then digested in a microwave. after that, 70 ml of perchloric acid was added to the mixture. after digestion, the samples were filtered and transferred into 100 ml volumetric flasks and brought to volume of 100 ml by added of distilled water. the filtrate was analyzed by atomic absorption for the determination of the following: mn, cu, fe, pb, co and ni (iso 14869-1, 2001). c. statistical analysis the statistical analyses were performed for each parameter in each soil layer and for different treatment. the data were subjected to one-way analysis of variance (anova) using statistica software, version 5 (statsoft france, 1997). mean comparison was carried out using lsd test at the significant level of 0.05. iii. results a. soil ph as showed in table ii, ph of soil has not been significant altered in the treated soils. the ph is low in the depth of soil of 90-120 cm. a low value of ph was noted in all treated soils. b. soil electrical conductivity (ec) according to table ii, the soil ec was significantly increased in two depths (30–60 and 60–90 cm). this increase was, respectively, from 2.72 to 4.49 and 7.9 to 8.21 dsm-1. the data obtained after fw application indicated that ec was decreased, respectively, from 6.13 to 4.38 and from 7.91 to 5.78 dsm−1 in 90-120 and 120-150 cm soil depth. table ii. effects of tww on ph and ec of soil c. major elements contents the results for na, k, ca, mg and cl are summarized in table iii. the tww treatment led to an increase in na content in the soil particularly at the depth of the 0-30 cm. in comparison to the control treatment, the na content was increased from 19.5 to 32.75 meq.l-1. for k content, the tww treatment applied increased significantly the k content in a soil depth of 0-30 cm compared to the control and fw treatment of soil. the k amount in th control soil was 0,34 meq.l-1 and was increased significantly to 4.47 meq.l-1 with the irrigation with tww. the ca content in soil irrigated with tww was significantly higher in the soil depth of 0-30 cm compared to the control treatment. the application of tww led to an soil layers (cm) parameter treatment 0-30 30-60 60-90 90-120 120150 control 8 bcd 8 bcd 8,21 cd 7,71 ab 8.17 c fw 8 bcd 8 bcd 8,2 cd 7,7 ab 8.2 cd ph tww 7.9bcd 8bcd 8.17 cd 7.58 ab 8.2 cd control 2,73 a 2,72 a 3,53 ab 6,13 c 7,91 d fw 2,73 a 2,72 a 3,51 ab 4,38 b 5,78 c ec tww 3,25 a 4,49 b 5,94 c 6,13 c 7,97 d engineering, technology & applied science research vol. 5, no. 3, 2015, 805-810 807 www.etasr.com khaskhoussy et al.: effect of treated wastewater irrigation on heavy metals distribution in a tunisian soil increase of mg content especially in the soil depths of 0-30 and 90-120 cm. as showed in the table iii, the cl content was greater in soil depths of 0-30 and 90-120cm with the tww application. d. soil sodicity (sar) as shown in table iii, the sar values were not significantly affected by the different waters qualities. however, in all treatments, the sar level increased significantly with the increasing of soil depth. . table iii. oil chemical characteristics soil layers (cm) paramet er treatment 0-30 30-60 60-90 90-120 120-150 control 19,5 a 27 ab 45,79 de 54,05 efg 61,15 g fw 17,17a 19,4 a 41,3 cd 53,3 defg 51 defg na tww 32,7bc 29 ab 48,2 def 54,56 fg 61,44 g control 0,34 a 0,09 a 0,17 a 0,11 a 0,17 a fw 0,11 a 0,07 a 0,1 a 0,11 a 0,13 a k tww 4,47 b 0,79 a 1,75 a 1,28 a 1,16 a control 6,7abc 6,1ab 8,7abcd 14 e 11,4 cde fw 5,44 a 5,03 a 8,1 abcd 8,23 abcd 8,56 abcd ca tww 11 bcde 6,7 abc 10abcde 14,14 e 12,93 de control 3,22a 5 abc 6,64 cde 8,38cde 8,8 de fw 5 abc 3,7ab 6,5 abcd 8,26 cde 7,6 cde mg tww 7,6cde 5,2abc 6,73 bcd 10,29 e 9,29 de control 15,68a 22 ab 30,22 bc 54,75 ef 54,14 ef fw 14,77a 14,9 a 34,6 abc 45,47def 45,24 def cl tww 30,3bc 24 ab 41,7cde 74,77 f 58,01f control 8,3 a 10,8 a 17,35 b 17,41 b 18,85 b fw 7,87 a 9,33 a 15,58 b 16,40 b 18,01 b sar tww 10,77a 11,9 a 16,45 b 18,57 b 19,0 b e. heavy metal concentrations in soils 1) zinc (zn) according to figure 1a, the zn content in the soil samples irrigated with tww was higher in the soil depth of 90-120 cm and didn’t show a significant change in others soil depths compared to the control soil. 2) cobalt (co) as shown in figure 1b, the tww treatment had a significant effect on co content with the soil depth in comparison to the control treatment. the maximum co content was 30.63 mg.kg-1 and was found in the soil depth of 90-120 cm. 3) cupper (cu) the tww application increased significantly the cu content with the soil depth in comparison with the control treatment. the highest increase was detected in the soil depth of 30-60 and 90-120cm. this increase was from 8.56 and 8.1 mg.kg-1 to 16 and 16.66 mg.kg-1 respectively (figure 1c). 4) cadmium (cd) the results in figure 1d showed a high accumulation of cd contents in the case of tww treatment in all soil depths compared to cd content in the control soil and soil treated with the fw. 5) plomb (pb) results shown in figure 1e indicate that tww application increased significantly the pb concentration (126 mg.kg-1) in the soil depth of 0-30 of tww irrigated soil as compared to control soil. while pb concentration decreased due to irrigation with fw in all soil layers. 6) nickel (ni) as presented in figure 1f, tww application to the soil led to significant increase of ni content in all soil depths compared to the control soil and the soil treated with fw. indeed, the highest levels of ni, with an average of 105.33 mg kg-1, were foundthe first soil depth (0-30 cm). fig. 1. concentration of heavy metals (mg/kg) in the soil layers at the beginning of experiment and after irrigation with tww and fw. iv. discussion soil ph is well known for his important role in the mobility of metals as in their bioavailability for plants [21, 22]. indeed, metal availability is relatively low when ph is around 6.5 to 7, as for lower ph would favor availability, mobility and redistribution of the metals. in the present study, result showed that the ph is around 7.5 and 8.2 and this statement limited the mobility of metal. although irrigation with tww led to a slight decrease of soil ph with depth, the soil was alkaline. some investigations showed that irrigation with wastewater engineering, technology & applied science research vol. 5, no. 3, 2015, 805-810 808 www.etasr.com khaskhoussy et al.: effect of treated wastewater irrigation on heavy metals distribution in a tunisian soil decreased the soil’s ph. this decrease was due to the decomposition of organic matter and production of organic acids. others authors [23, 24 25] found that irrigation with tww raised the soil ph, respectively, by 1.3 and 0.2 u of ph. other researchers [10, 11] explained this increase by the long term impact of irrigation with sewage and wastewater effluents on soil properties. results indicated that the electrical conductivity of soil irrigated with tww increased significantly compared. similar results were reported in [10, 12-13]. this increase has been attributed to the higher concentration of cations such as na and k in wastewater [10]. this increase concerned soil depths of 30–60 and 60-90 cm. however, fw irrigation led to significant decrease of ec. in a similar way, al-nakshabandi et al. [14] explained this decrease by the leaching and displacement of salt after irrigation. the results for na showed high concentrations in the upper soil layer of tww irrigated soil. this is in line [6]. however, a significant decrease of na level was recorded in the first layer of fw irrigated soil. this decrease is probably due to the leaching of soluble na into deeper soil layers [15]. the k concentration in tww irrigated soil increased significantly compared to the control and fw irrigated soils. these results were in accordance with [13] but not in agreement with [16] that reported a decrease of k soil levels with tww irrigation and explained this by root uptake and the leaching of k+ into deeper soil. the concentrations of ca in the first soil layer (0-30) of tww irrigated soil samples were significantly higher than those in fw irrigated soil. similarly, heidarpour et al. [6] reported that irrigation with wastewater generated a greater ca concentration than groundwater. they explained this statement by the difference in plant yield using two different irrigation waters and consequently the effect of plant uptake on the soil solution. fw led to a significant decrease on the average of ca in most of soil layers. this reduction in soil ca could be due to leaching, plant uptake and reaction of ca with carbonate and sulfate, which were present in the water [6]. as for mg, tww increased significantly the mg concentration in the first layer of soils compared to control soil in agreement with [6]. however, a significant decrease (of mg level occurred in the case of the fw irrigation. this reduction has been reported as a possible in [1]. for cl content, tww caused significant increase of this element in soil. similar results have been reported in [13, 17]. in general, the cl increased with increasing soil layers for both irrigated and control soils. similarly, it has been reported that chloride is usually not adsorbed or held back by soils but it moves easily with soil water [16]. both tww and fw irrigation had no significant effect on sar. the results showed an increase of sar with depth. this significant increase could be explained by the leaching of na+ into deeper soil. this increase below soil layers disagrees with the findings of [18] which noted that sar diminished with increasing depth. the high level of sar (>13) indicated that tww irrigation increased the soil sodicity. result showed that cu concentration was significantly higher in the tww irrigated soil than in the control soil. our results corroborate with these obtained in [16]. on the other hand, it has also been reported in [2] that the application of wastewater had no significant effect on the amount of cu compared with the beginning stage and with the groundwater treatment. in fact, saber in [26] showed that a seven-year application of wastewater had no significant effect on the concentration of cu in the soil. also, adriano [27] stated that cu is stabilized in soil by clay minerals, organic matters and fe, al and mn oxides. the vertical distribution changed over time with alternation of increase and decrease trend. this tendency agrees with [28] where it is reported that cu has certain mobility from upper horizons to lower horizons. the co level increased significantly in tww irrigated soil. these results were in accordance with [2] where it is reported that tww irrigation had a significant increase on the amount of co compared with the beginning of the growing season and with the groundwater treatment. in [29] it was reported that application of wastewater for irrigation for a period of 47 years caused a significant increase of the total and available co in soil. in general, the accumulation of co increases with increased soil depth and these results were in accordance with those in [2]. as for zn, application of tww had no significant effect on the accumulation of zn. these results are in agreement with findings obtained previously [2]. however, a significant increase of zn concentration was shown in 90-120 cm depth. these results contradict the findings in [30] where a significant accumulation of zn in the upper (25-30 cm) soil with wastewater irrigation was reported. this increase might be attributed to the leaching and displacement of zn by irrigation into upper soil layers. we can, also, deduce that zn concentration in fw irrigated soil decreased compared with the control soil. application of tww increased significantly the cd content. similar results were observed in [31] where it is reported that the concentration of cd in soil irrigated under wastewater was increased. on the other hand, in [10, 20, 32] it was shown that irrigation with wastewater does not effect the concentration of cadmium. overall, the cd levels in various soil depths were similar and no tendency was noted. these results were in concordance with those obtained in [33]. result for pb showed that, with the exception of the surface layer, tww irrigation had no significant effect on the soil. similar results were reported in [2, 10]. moreover, no significant effect was noted regarding depth. however, many authors have shown a significant decrease of pb through the soil layers [33, 34]. the pb content was reduced in fw irrigated soil. these results might be explained by the lixiviation of the element in soil due to precipitation events after irrigation season [35, 36]. in the case of nickel, soil irrigated with tww exhibited significant decrease of this metal in comparison with the control soil. these results were in disagreement with [19]. ni level was higher in all depths of tww irrigated soils compared to both other cases (control and fw treatment). this is in line with finding reported in [37]. according to our study, no differences were found for soil depth expected the slight engineering, technology & applied science research vol. 5, no. 3, 2015, 805-810 809 www.etasr.com khaskhoussy et al.: effect of treated wastewater irrigation on heavy metals distribution in a tunisian soil increase of ni in the tww soil in the depth of 90-120 cm. in similar way, mclaren et al. [28] found that about 57% of ni applications were lixiviated from upper soil horizons to lower soil horizons. based on our study, the concentration of heavy metals (zn, co, cu, cd, pb and ni) was higher in most of depths of tww irrigated soil compared to those of fw irrigated soil. it has been reported that high concentration of heavy metals in wastewater leads to an increase of their content in soil [31, 3739]. heavy metals are priority toxic pollutants that severely limit the beneficial use of water [40]. soil may adsorb and retain important amount of heavy metals from wastewater. in this study, the comparison of zn, cu, pb and ni with a standard level of heavy metals in soil showed that cd and ni of control soil and soils irrigated with the both tww and fw were higher than their maximum permissible limit (3 and 50 ppm) in soil by usepa ([41]). it can be predicted that cd and ni have been, probably added to the water and soil from other sources. the results for zn, cu, pb were far less than the usepa maximum permissible limits (50, 200 and 300 ppm). the contamination of soil by some heavy metals as cd and ni presents a worrying situation that should be monitored to prevent further environmental and health risks. v. conclusion this study contributes to the evaluation of tww effects on clay-loam soil properties, in order to test the possibility of tww safe reuse. indeed, after one cycle of irrigation, we found some variations in the soil properties as a result of tww application. we have detected an increase in ec, na, k, ca, mg, cl, sar, cu, cd and ni content in soil irrigated with tww in comparison with soil irrigated with fw. however, no remarkable changes in soil ph, zn, co and pb was shown. we saw a significant increase in ec, na, cl, sar, zn, co and ni level with depth. but, no significant change in ph, k, cu, cd, pb and ni was shown, for different depths. the results of this study show that tww reuse in irrigation must be conditioned by some management measures such as soil texture, plant selection and the choice of irrigation methods. acknowledgment this study was carried out under the inrgref/acsadicba project for the safe reuse of tww in arab agriculture and piseau ii project for tww and sludge use in agriculture. references [1] a. m. hassanli, m. javan, y. saadat, “reuse of municipal effluent with drip irrigation and evaluation the effect on soil properties in a semi-arid area”, environ. monit. assess., vol. 144, pp. 151-158, 2009 [2] j. abedi-koupai, b. mostafazadeh-fard, m. afyuni, m. r. bagheri, “effect of treated wastewater on soil chemical and physical properties in an arid region”, plant soil environ., vol. 52, pp. 335-344, 2006 [3] usepa, environmental protection agency, offices of water and wastewater and compliance, (ed.) guidelines for water reuse, u.s. epa, washington, w. a. state water strategy, 1992 [4] a. gregory,“strategic direction of water recycling in sydney”, the first symposium water recycling, australia, adelaide, pp.35-41, 2000 [5] p. madejon, t. maranon, j. m. murillo, “biomonitoring of trace elements in the leaves and fruits of wild olive and holm oak trees”, sci. total environ., vol. 355, pp. 187-203, 2006 [6] m. heidarpour, b, mostafazadeh-fard, j. abedikoupai, r. malekian, “the effects of treated wastewater on soil chemical properties using subsurface and surface irrigation methods”, agric. water man., vol. 90, no. 1-2, pp. 87-94, 2007 [7] k. aggeli, i. k. kalavrouziotis, s. bezergianni, “a proposal of a treated wastewater reuse design system in urban areas”, fresenius environmental bulletin, no 18, no. 7b, pp. 1295-1301, 2009 [8] y. lui, h.l. xu, k. y. show, j. h. tay, ”anaerobic granulation technology for wastewater treatment”, world journal of microbiology &. biotechnology., vol. 18, pp. 99-113, 2002. [9] b. jimenez-cisneros, “wastewater reuse to increase soil productivity”, water science and technology, vol. 32, no. 12, pp. 173-180, 1995 [10] m. j. rusan, s. hinnawi, l. rousan, “long term effect of wastewater irrigation of forage crops on soil and plant quality parameters”, desalination, vol. 215, no. 1-3, pp. 143-152, 2007 [11] r. k. rattan, s. p. datta, p. k. chhonkar, k. suribabuand, a. k. singh, “long-term impact of irrigation with sewage effluents on heavy metal content in soils, crops and groundwatera case study”, agric. ecosyst. environ., vol. 109, no. 3-4, pp. 310-322, 2005 [12] m. jahantigh, “impact of recycled wastewater irrigation on soil chemical properties in an arid region”, pak j biol sci, vol.11, no. 18, pp. 2264-2268, 2008 [13] a. mojiri, “effects of municipal wastewater on physical and chemical properties of saline soil”, j. biol. environ. sci., vol. 5, no. 14, pp 7176, 2011 [14] g. a. al-nakshabandi, m. m. saqqar, m. r. shatanawi, m. fayyadand, h. alhorani, “some environmental problems associated with the use of treated wastewater for irrigation in jordan”, agricultural water management, vol. 34, no. 1, pp. 81-94, 1997 [15] f. m. kiziloglu, m. turan, u. sahina, y. kuslu, a. dursun, “effects of untreated and treated wastewater irrigation on some chemical properties of cauliflower (brassica olerecea l. var. botrytis) and red cabbage (brassica olerecea l. var. rubra) grown on calcareous soil in turkey”, agricultural water management, vol. 95, no. 6, pp. 716-724, 2008 [16] g. l. tarchouna, p. merdy, m. raynaud, h. r. pfeifer, y. lucas, “effects of long-term irrigation with treated wastewater, part i: evolution of soil physico-chemical properties”, applied geochemistry, vol. 25, no. 11, pp. 1703-1710, 2010 [17] p. najafi, s. nasr, “comparison effects of wastewater on soil chemical properties in three irrigation methods”, research on crops, vol. 10, no. 2, pp. 277-280, 2009 [18] g. murtaza, a. ghafoor, m. qadir, m.k. rashid, “accumulation and bioavailability of cd, co and mn in soils and vegetables irrigated with city effluent”, pak. j. agri. sci., vol. 40, no. 1-2, pp. 18-24, 2003 [19] s. vaseghi, m. afyuni, h. shariatmadari, m. mobli, “effect of sewage sludge on some nutrients concentration and soil chemical properties”, journal of isfahan water and wastewater, vol. 53, pp. 15-19, 2005 [20] m. j. mohammad, n. mazahreh, “changes in soil fertility parameters in response to irrigation of forage crops with secondary treated wastewater”, communications in soil science and plant analysis, vol. 34, no. 9-10, pp. 1281-1294, 2003 [21] r. p. gambrell, “trace and toxic metals in wetlands-a review”, journal of environmental quality, vol. 23, no. 5, pp. 883-891, 1994 [22] d. w. sparling, t. p. lowe, “metal concentrations in aquatic macrophytes as influenced by soil and acidification”, water, air and soil pollution., vol. 108, no. 1-2, pp. 203-221, 1998 [23] r. n. cromer, d. tompkins, n. j. barr, p. hopkins, “irrigation of monterey pine with wastewater: effect on soil chemistry and groundwater composition”, journal of environmental quality, vol. 13 no. 4, pp. 539-542, 1984 engineering, technology & applied science research vol. 5, no. 3, 2015, 805-810 810 www.etasr.com khaskhoussy et al.: effect of treated wastewater irrigation on heavy metals distribution in a tunisian soil [24] h. stewart, p. hopmans, d. flinn, t. hillman, “nutrient accumulation in trees and soil following irrigation with municipal effluent in australia”, environ. pollut., vol. 63, pp. 155-177, 1990 [25] c. f. manchino, i. l. pepper, “irrigation of turfgrass with secondary sewage effluent: soil quality”, agron. j., vol. 8, pp. 650-654, 1992 [26] m. s. m. saber, “prolong effect of land disposal of human waste on soil conditions”, water science & technology, vol. 18, no. 7-8, pp. 371374, 1996 [27] d. c. adriano, trace elements in terrestrial environments, springerverlag, new york, 2001 [28] r. g. mclaren, l. m. clucas, m. d. taylor, “leaching of macronutrients and metals from undisturbed soils treated with metalspiked sewage sludge”, soil research, vol. 43, pp. 159-170, 2005 [29] m. b. pescod, a. arar (eds), “treatment and use of sewage effluent for irrigation”, proceedings of the fao regional seminar on the treatment and use of sewage effluent for irrigation held in nicosia, cyprus, 7–9 october, 1985 [30] s. lawes, “analysis of heavy metal-contaminated soil and anaerobically digested sewage sludge”, b.sc. thesis, department of agric. chem. and soil sci., university of sydney, 1993. [31] m. s. brar, m. p. s. khurana, b. d. kansal, “effect of irrigation by untreated sewage effluents on the micro and potentially toxic elements in soils and plants”, 17th world congress soil sci., bangkok, thailand, pp. 198-1—198-10, 2002 [32] a. mojiri, a. jalalian, h. radnezhad, “effects of urban wastewater treatments on chemical properties of saline and alkaline soil”, journal of applied sciences research, vol. 7, pp. 222-228, 2011 [33] v. m. maldonado , h.o. arias, r. quintana, r. a. saucedo, m. gutierrez, j. ortega, g. nevarez, “heavy metal content in soils under different wastewater irrigation patterns in chihuahua, mexico”, int. j. environ. res. public health, vol. 5 pp. 441-449, 2008 [34] b. a. adelekan, a. o. alawode, “contributions of refuse dumps to heavy metal concentrations in soil”, j. appl. biosci., vol. 40, pp 27272737, 2011 [35] d. p. stevens, m. j. mclaughlin, t. heinrich, “determining toxicity of lead and zinc runoff in soils: salinity effects on metal partitioning and on phytotoxicity”, environ. toxicol. chem., vol. 22, pp. 2017-3024, 2003 [36] m. bongers, b. rusch, c. a. van gestel, “the effect of counterion and percolation on the toxicity of lead for the springtail folsomia candida in soil”, environ. toxicol. chem., vol. 23, no. 1, pp 195-199, 2004 [37] f. mapanda, e. n. mangwayana, j. nyamangara, k. e. giller, “the effect of longterm irrigation using waste water on heavy metal contents of soils under vegetables in harare zimbabwe”, agriculture, ecosystems & environment, vol. 107, no. 2-3, pp. 151-165, 2005 [38] l. huerta, r. contreras-valadez, s. palacios-mayorga, j. miranda, g. calva-vasquea, “total elemental composition of soils contaminated with waste water irrigation by combining iba techniques”, nuclear instruments and methods in physics research section b, vol. 189, pp. 158-162, 2002 [39] z. nan, j. li, j. zhan, g. cheng, “cadmium and zinc interaction and their transfer in soil-crop system under actual field conditions”, sci. total environ., vol. 1, pp. 187-195, 2002 [40] r. petrus, j.k. warchol, “heavy metal removal by clinoptilolite: an equilibrium study in multi-component systems", water research, vol. 39, no. 5, pp. 819-830, 2005 [41] c. masona, l. mapfaire, s. mapurazi, r. makanda, “assessment of heavy metal accumulation in wastewater irrigated soil and uptake by maize plants (zea mays l) at firle farm in harare”, journal of sustainable development, vol. 4, no. 6, pp. 132-137, 2011 microsoft word 3-490-ed.doc engineering, technology & applied science research vol. 4, no. 5, 2014, 702-705 702 www.etasr.com erturk and maharjan: developing activities for teaching cloud computing and virtualization developing activities for teaching cloud computing and virtualization emre erturk senior lecturer, school of computing eastern institute of technology napier, new zealand eerturk@eit.ac.nz bhuwan maharjan postgraduate student, school of computing eastern institute of technology napier, new zealand bhuwankomail@gmail.com abstract— cloud computing and virtualization are new but indispensable components of computer engineering and information systems curricula for universities and higher education institutions. learning about these topics is important for students preparing to work in the it industry. in many companies, information technology operates under tight financial constraints. virtualization, (for example storage, desktop, and server virtualization), reduces overall it costs through the consolidation of systems. it also results in reduced loads and energy savings in terms of the power and cooling infrastructure. therefore it is important to investigate the practical aspects of this topic both for industry practice and for teaching purposes. this paper demonstrates some activities undertaken recently by students at the eastern institute of technology new zealand and concludes with general recommendations for it educators, software developers, and other it professionals. keywords-information technology; computer engineering; cloud computing; virtualization i. introduction the recent ‘cloud computing’ paradigm incorporates some key aspects such as ‘pay per use’, high degree of availability, flexibility, scalability, and pervasiveness [1]. cloud based resources also play an important role in online and mobile learning [2]. cloud computing delivers a broad range of standardized and customizable applications and services via the internet. infrastructure as a service (iaas) is one of the basic models of service, and highly relevant to this paper. in iaas, clients can outsource storage, hardware, servers and networking components from the provider. aside from simplifying and outsourcing certain aspects of information technology (it) operations and projects, cloud computing also inspires software developers to address the critical next-gen programming challenges of multi-cores, parallel programming and virtualization [1]. conducting software testing within virtualized environments is becoming a more common practice. cost saving is another attractive feature of developing software using resources and tools that are hosted on the cloud [3]. traditional and in-house it operations and projects required organizations to make upfront investments for infrastructure. this drawback can be by passed through present-day global and cloud based software development. this paper’s content is aimed at teaching cloud computing and virtualization by describing the experience from a course taught at the eastern institute of technology new zealand along with a brief theoretical background. such a course should be considered as a broad course for students with a variety of interests and thus it should not formally require them to do any programming or coding scripts. the figures shown in this paper also provide a basic blueprint to the activities practiced during the course. ii. understanding and implementing virtualization a virtual machine is a representation of a real machine using software that provides an environment in which it can run. through virtualization, server utilization is dramatically improved. virtualization provides an opportunity for hardware resource sharing and multiple operating systems whereby generic hardware drivers are cloned and assigned to each virtual machine. a hypervisor is a software layer that logically partitions the physical hardware and guest operating systems. the latest trend of virtualization is the bare-metal approach where the hypervisor directly runs on the hardware without needing a host operating system [4, 5]. vmware and xen are the most common virtualization products used by datacenters. these hypervisors offer a high level of security through a variety of features such as guest isolation, small code base, operating system separation, and privilege access. furthermore, an important feature of the xen hypervisor is its neutrality toward various operating systems and that it allows various operating systems (e.g. linux, solaris, bsd, etc.) to be the domain0, which is used for configuring and controlling the virtualization activities [6]. microsoft azure (known as windows azure prior to being renamed) is a cloud computing platform and infrastructure for building, deploying and managing applications and services using microsoft managed datacenters [7]. virtual machines can be created using microsoft azure cloud infrastructure services. subscribing to azure is easy, robust, and suitable for a variety of users including students. figure 1 shows a logical pictorial design of a small datacenter where only few server racks are installed. it is divided into three layers. the top layer is a consumer network engineering, technology & applied science research vol. 4, no. 5, 2014, 702-705 703 www.etasr.com erturk and maharjan: developing activities for teaching cloud computing and virtualization where all of the virtual pcs are connected to a local area network (lan). below this layer, there is a vmware vsphere distribution switch (vds). the vds abstracts the physical network and provides access-level switching in the vsphere hypervisor. this is useful for network virtualization because it enables logical networks that are independent of physical constructs [8]. finally, figure 1 illustrates the creation of a virtual local area network (vlan), where the physical network is logically divided into two different vlans (bhuwan-vlan-1 and bhuwan-vlan-2). these vlans work above the routing and switching layer (i.e. layer 3). layer 2 devices are mainly smart switches that are used to interconnect the datacenter’s layer 3 components with the core layer (i.e. layer 1) switches. fig. 1. designing a small data center. iii. learning activities using microsft azure figure 2 shows a windows server 2012 machine with eight processor cores and 14 gb of ram. the domain name server (dns) address for this virtual machine was set as bhuwan.cloudapp.net. the next task (shown in figure 3) is to name and configure this virtual server. the virtual machine in this example is called sqlserver. then powershell (for managing operating system and administrative tasks) and remote desktop services for the virtual machine are configured as shown in figure 4. this happens prior to provisioning and running the new virtual server. there is also an option to choose and add security extensions to further enhance and protect the virtual machine. students (or trainees) can also create a virtual network to connect many virtual machines and databases. in this network example, four different sub-networks are created as shown in figure 5. each subnet may have a fixed number of usable internet protocol (ip) addresses. for example, in the bhuvsubnet-4, the classless inter-domain routing (cidr) value is set to /29. this provides just eight ip addresses to be managed by this new host. the last column in figure 5 shows the actual ip addresses that are available. after the creation of virtual resources, it is important for students to work on setting up user permissions and access. this is called an active directory (ad). here the existing dns name i.e. bhuvmhzoutlook.onmicrosoft.com can be used for the ad domain name. new users can be added and be assigned with different roles. figure 6 shows how a new user profile created and given a user administrator role. figure 7 shows how a remote connection can be made to the virtual machine called bhuwanji. after logging onto the bare-metal virtual machine, the information observed are shown in figure 8. finally, figure 9 shows an example of how students can use the power shell integrated scripting environment (ise) to interact with the server using a command line interface. fig. 2. creating a new virtual machine. fig. 3. configuring a virtual machine. fig. 4. configuring a virtual machine continued. engineering, technology & applied science research vol. 4, no. 5, 2014, 702-705 704 www.etasr.com erturk and maharjan: developing activities for teaching cloud computing and virtualization fig. 5. creating a virtual network. fig. 6. creating new users. fig. 7. making a remote desktop connection. fig. 8. virtual system information. fig. 9. virtual system administration. iv. conclusion the practical work that is involved in producing the types of results shown in this paper requires initial familiarization, trouble-shooting, and self-guided technical learning for students and providing solid background beforehand should be considered necessary. one tutor should be sufficient for a number of ten students. learning also involves students understanding the bigger picture, and teachers need to appeal to students’ overall business perspectives and values. it needs to be emphasized that cloud computing and virtualization offer additional benefits in terms of freeing up physical resources, migrating resources and services elsewhere, and enhancing disaster recovery. these tools and ideas also have positive implications for the environment, which many students tend to appreciate. each company is a unique case; if virtualization is considered and implemented appropriately for a given scenario, energy consumption for power and cooling can be better controlled. this paper also recommends software developers to consider using online resources and virtual environments for building and testing. this is more relevant in the current market with ever increasing numbers of web based applications, mobile applications, and software-as-a-service (saas) provisions. in conclusion, cloud computing has moved from being an initial hype to providing greater productivity to companies. overall, the cloud continues to offer new opportunities to a diverse group of it professionals. references [1] p. yara, r. ramachandran, g. balasubramanian, k. muthuswamy, d. chandrasekar, “global software development with cloud platforms”, software engineering approaches for offshore and outsourced development, lecture notes in business information processing, vol. 35, pp. 81-95, 2009 [2] e. erturk, “an intelligent and object-oriented blueprint for a mobile learning institute information system”, international journal for infonomics, vol. 6, no. 3-4, 2013 [3] n. oza, j. münch, j. garbajosa, a. yague, e. ortega, “identifying potential risks and benefits of using cloud in distributed software development”, product-focused software process improvement, lecture notes in computer science, vol. 7983, pp. 229-239, 2013 [4] d. bouley, “impact of virtualization on data center physical infrastructure”, the green grid library & tools, white paper #27, pp. 1-10, 2010 engineering, technology & applied science research vol. 4, no. 5, 2014, 702-705 705 www.etasr.com erturk and maharjan: developing activities for teaching cloud computing and virtualization [5] microsoft corporation, “datacenter virtualization”, http://download.microsoft.com/download/a/7/a/a7ad1735-40d7-45089462-bcb79577b17b/virtualization_whitepaper_v2_1.pdf [6] s. spector, “why xen?: xen compared to other hypervisors”, http://www-archive.xenproject.org/files/marketing/whyxen.pdf [7] m. tulloch, introducing windows azure for it professionals, microsoft press, 2013 [8] vmware, “vmware network virtualization design guide”, http://www.vmware.com/files/pdf/techpaper/virtual-network-designguide.pdf authors profile emre erturk received his ph.d. from the university of oklahoma in 2007. he has later taught as an assistant professor with the university of maryland (usa) in the areas of business, economics, and it. currently, he is a senior it lecturer at the eastern institute of technology, new zealand. bhuwan maharjan is a postgraduate student at the eastern insittute of technology in new zealand. he is also an avid it professional and software developer. he has previously worked at the college of information technology & engineering in kathmandu, nepal. microsoft word etasr_v12_n6_pp9565-9569 engineering, technology & applied science research vol. 12, no. 6, 2022, 9565-9569 9565 www.etasr.com badla: seismic assessment of steel frames subjected to multi-hazards seismic assessment of steel frames subjected to multi-hazards oualid badla civil engineering department faculty of technology university of khenchela khenchela, algeria badla.oualid@univ-khenchela.dz received: 3 september 2022 | revised: 13 september 2022 | accepted: 21 september 2022 abstract-this paper investigates the effects induced by thunderstorm downbursts to steel building structures that have been previously damaged during strong directivity ground motion events. to achieve this objective, one four-story steel moment-resisting frame that was tested at the e-defense laboratory, japan was analyzed in the nonlinear range using opensees. the seismic response was numerically simulated, obtaining a satisfactory agreement with the experimental evidence, revealing that the effects of such wind events and vertical ground motions were significant. these effects should be addressed during the design of low and medium buildings subjected to initial damage and subsequent thunderstorm downbursts and the ductility demands on structures subjected to multi-hazards can be quantified. the wind loads are applied as an externally applied dynamic load and the revised ductility demands are determined directly. the obtained results are compared to what is expected by experimental tests. keywords-steel building; thunderstorm downbursts; ductility demands; wind; earthquake; non-linear analysis i. introduction the devastating effects of severe thunderstorms observed over the last decade have inspired researchers to study this complex phenomenon [1, 2]. actual evidence shows that buildings damaged by earlier hazards are prone to secondary effects from consecutive multi-hazards, such as thunderstorm downbursts [3, 4]. this can increase damage after a disaster, eventually leading to the collapse of structures left unprotected after the primary hazards. a thunderstorm downburst differs from synoptic winds as it produces a small-scale follow-up divergence within a 5km radius, accompanied by intense microbursts. this configuration can cause damage corresponding to a synoptic wind sequence of 70m/s within a time interval of 5 to 20min [5, 6]. due to the nose shape profile with different heights above the ground, the wind speed reaches its peak between 30 and 100m above the ground [7]. this phenomenon poses risks related to the collapse mechanism of low to high buildings [8, 9] there are still important knowledge gaps ranging from the design aspects to the evolution of contingency plans and strategies to increase resilience. the current guidelines have such limitations because they ignore the co-occurrence of natural events such as earthquakes and winds [10-12]. a design framework that takes into account seismic loading and strong synoptic wind has recently been proposed [13]. other studies focused on dealing with multihazards are [14, 15], although no studies have been conducted to determine the ductility requirements of damaged structures under additional effects of thunderstorm downbursts. this paper investigates the seismic response and the effects of the downburst outflow wind at mean speeds ranging between 33m/s and 75m/s on the ductility of damaged buildings. the proposed methodology combines the principles of nonlinear static adaptive pushover analysis [16], which aims to reproduce the damage caused by the primary hazard event, and the sequential dynamic analysis [17-23], aiming to estimate the damage caused by the secondary sequential thunderstorm event. ii. considered steel frame a. tested bare frame the tested steel frame is described in [24-26] and only a brief explanation is given here. the test specimen consists of a 2-span 4-story moment-resistant steel frame shown in figure 1. the two span-lengths in the main direction are 5m, while in the transversal direction the span-length is 6m. the heights of the ground floor and of the upper floors are 3.875m and 3.5m respectively. the ground floor columns are rigidly connected to 1.5m high load-bearing concrete blocks. the blocks, in turn, are clamped into the shaking table. the beam-column connections are inherently rigid and, following the practice developed after the 1995 hyogoken-nanbu earthquake, were detailed to force the formation of plastic hinges from the joints. b. description of the e-defense experiments the experiments consisted of shaking the sample frame with 3 scaled 3-d versions of the ground motion recorded in takatori during the kobe earthquake. the inputs were scaled at 40%, 60%, and 100%. the 40% input aimed to create only elastic deformations in the frame, the 60% input created inelastic deformations and nearly collapsed the frame, and the 100% input caused the frame to collapse. corresponding author: oualid badla engineering, technology & applied science research vol. 12, no. 6, 2022, 9565-9569 9566 www.etasr.com badla: seismic assessment of steel frames subjected to multi-hazards fig. 1. tested steel frame iii. earthquake ground motions the earthquake records used in this investigation are the horizontal and vertical components of the newhall records from the 1994 northridge earthquake, available from the pacific earthquake engineering research (peer) center [27] (figure 2). the record represents a range of severe ground motions and exhibits a near-fault effect. it has been indicated [28] that the structural response depends primarily on the peak acceleration impulse in the ground motions and that the continued motion of lower amplitude has little effect on the maximal responses. the peak ground accelerations for the horizontal and vertical components are 0.578g and 0.537g respectively. iv. wind database record the present study created a wind recording database based on the simulation method reported in [29, 30] and on the algorithm proposed in [31]. the database was previously used to study the inelastic analysis of multi-degree of freedom systems damaged by earthquakes posteriorly subjected to wind load [19]. the cross-spectral density of the turbulent fluctuation is taken into account in the simulation of the wind field. therefore, the wind actions on the building frame borders have been integrated into the concentrated load acting on the supporting members of the structures. the there-second peak velocity time series at the height of maximum velocity, i.e. z����= 10m, 50m, and 75m above the ground, are illustrated in figure 3. the maximum velocities, ����, are 59, 70, and 78m/s for z���� =10, 50, and 75m. this defines three different velocities along the height of the structure and thus affects the lateral load distribution and the energy absorption capacity of the structure. fig. 2. earthquake records. the static forces induced by wind were calculated using (1). �� � � �� � � � ���� � (1) where the reference height (zr) was taken as 10m, ρ represents the air density, �� is a drag coefficient, and a is the area exposed to the wind. eurocode 1 gives values for α between 0.12 and 0.3, whilst a value of α = 0.22 was used to represent the wind profile in suburban areas. v. results and discussion a nonlinear static pushover analysis is initially presented to induce the ductility demand of the primary hazard events and identify the correlation between the base shear forces and the lateral roof displacement up to a target plastic deformation. the pushover analysis is used in order to bring the structure at a engineering, technology & applied science research vol. 12, no. 6, 2022, 9565-9569 9567 www.etasr.com badla: seismic assessment of steel frames subjected to multi-hazards pre-defined ductility demand level, including the descendant branch of the load-deformation curve, permitting direct control of the initially imposed damage. the transient non-stationary wind loads are subsequently applied as externally applied dynamic loads and the revised displacement ductility requirement is determined directly. then, the ductility demands for different ductility levels can be calculated using (2): � � ������ (2) where �max is the target roof displacement, and �������� is the corresponding yielding. the �max is 0.04516, 0.05793, 0.1004, and 0.1828 for ld (limited damage), sd (significant damage), nc (near collapse), and cs (collapse start) damage states respectively, corresponding to roof displacement ductility. the yielding drift �������� is 0.04516. the base shear force-roof displacement relationship of the considered steel frame is shown in figure 4. fig. 3. time history of the horizontal velocity at the height of the maximum velocity. fig. 4. pushover capacity curves of considered steel frame. nonlinear analysis was carried out for different cases of the considered steel frame subjected to: (a) horizontal and vertical motions, (b) transient wind loads alone, and (c) to a combination of wind and both vertical and horizontal motions using the finite element program opensees [33]. figures 5 and 6 show the comparison of the experimental results, the pavan post-test results, and the numerical results of displacements and shear forces at each floor. it is observed that once the actual input ground motion was considered in the analysis, the numerical predictions agreed relatively well with the experimental results. fig. 5. maximum relative displacement at every floor level. fig. 6. maximum story shear. initially, the transient wind loads (i.e. !"#$% = 10m, !"#$% = 50m, and !"#$% = 75m) are applied on the steel frame alone and the results are shown in figures 7 and 8. the deformations of the steel frame are within the elastic range under thunderstorm downburst for !"#$% = 10m, since the ductility is less than 1, i.e. 0.61997 (table i). higher ductility can be observed under thunderstorm downburst, !"#$% = 50m and 75m, as shown in figure 7. the structural deformations entered to the plastic range and the maximum ductility demands are 1.26209 and 1.74921 respectively. the base shear forces-roof displacement relationship for the sequential multi-hazards analysis is shown in figures 9 and 10. the 3 simulated thunderstorm downburst scenarios are applied to the damaged steel frame which has previously attained a target ductility demand level (i.e. dl, sd, nc, and cs). the maximum ductility demands of the sequential analysis are summarized in table i. this table demonstrates, in general, that the ductility demands of the sequential wind event tend to increase as the initial target ductility level increases. 0 20 40 60 80 100 120 140 160 180 0 10 20 30 40 50 60 70 80 zumax=10 m zumax=50 m zumax=75 m time (s) u ( m /s ) 0.00 0.05 0.10 0.15 0.20 0.25 0 200 400 600 800 1000 1200 1400 1600 b a s e s h e a r (k n ) displacement (m) analysis idealized dl sd nc cstart 0 50 100 150 200 250 300 1 2 3 4 5 l e v e l maximum relative displacement [mm] experiment analysis (h+v) pavan (post-test) 0 400 800 1200 1600 2000 1 2 3 4 l e v e l maximum story shear [kn] experiment h+v pavan engineering, technology & applied science research vol. 12, no. 6, 2022, 9565-9569 9568 www.etasr.com badla: seismic assessment of steel frames subjected to multi-hazards fig. 7. maximum relative displacement under downburst at every level. fig. 8. maximum story shear under downburst. fig. 9. maximum relative displacement under multi-hazards at every level. under the sequential analysis of downburst outflow wind, the structure responded inelastically and higher plastic deformations than during the initial static pushover analysis were observed. the maximum ductility was found to be 5.73476, 6.02261, and 6.17760 respectively. the ductility demands increased significantly to 3.18725%, 8.36653%, and 11.15538% when the downburst reached the peak-velocity time series at the height of maximum velocity, i.e. !"#$% = 10m, 50m and 75m above the ground than the ductility level of the primary event (simultaneous horizontal and vertical excitations). under these ductility demand levels, a collapse mechanism was formed. the proposed approach can successfully identify the capacity limits and predict the failure mechanism of structures under sequential hazard events and can be implemented to appraise the increased ductility demands within a multi-hazard assessment framework. fig. 10. maximum story shear under multi-hazards. table i. ductility demand for various downburst scenarios zumax (m) 10 50 75 wind alone 0.61997 1.26209 1.74921 limited damage (dl) 5.73476 6.02261 6.17760 significant damage (sd) 4.47039 4.69477 4.81559 near collapse (nc) 2.57860 2.70803 2.77772 collapse start (cs) 1.41685 1.48796 1.52626 vi. conclusions the seismic behavior of steel frame structures under sequential hazard loads in the nonlinear range is investigated in the current paper. the main conclusions from the analysis can be summarized as follows:  the input energy from the sequential downburst outflow wind event can push the structure into plasticity, exceeding the single hazard ductility demand. the damage level experienced by the structure during the secondary hazard event increases with the ductility demands of the primary event.  under the sequential analysis of downburst outflow wind, the ductility demand increases significantly by 3.18725%, 8.36653%, and 11.15538% from the ductility level of the primary event when the downburst reaches the peak velocity time series at the height of maximum velocity of 10, 50, and 75m above the ground (simultaneous horizontal and vertical excitations).  the proposed approach can successfully identify the capacity limits and predict the failure mechanism of structures under sequential hazard events and can be implemented to appraise the increased ductility demands within a multi-hazard assessment framework. 0 20 40 60 80 1 2 3 4 5 l e v e l maximum relative displacement under downbrust [mm] zumax= 10 m zumax= 50 m zumax= 75 m 0 100 200 300 400 500 600 1 2 3 4 l e v e l maximum story shear under downbrust [kn] zumax= 10 m zumax= 50 m zumax= 75 m 0 50 100 150 200 250 300 1 2 3 4 5 h+v h+v+ w(33 m/s) h+v+ w(50 m/s) h+v+ w(78 m/s) l e v e l maximum relative displacement [mm] 0 400 800 1200 1600 2000 1 2 3 4 h+v h+v+w(33 m/s) h+v+w(50 m/s) h+v+w(78 m/s) l e v e l maximum story shear [kn] engineering, technology & applied science research vol. 12, no. 6, 2022, 9565-9569 9569 www.etasr.com badla: seismic assessment of steel frames subjected to multi-hazards references [1] h. e. brooks, "severe thunderstorms and climate change," atmospheric research, vol. 123, pp. 129–138, apr. 2013, https://doi.org/ 10.1016/j.atmosres.2012.04.002. 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[33] "open system for earthquake engineering simulation home page." https://opensees.berkeley.edu. microsoft word etasr_v12_n5_pp9208-9216 engineering, technology & applied science research vol. 12, no. 5, 2022, 9208-9216 9208 www.etasr.com le: multi-criteria decision making in the milling process using the paris method multi-criteria decision making in the milling process using the paris method hong ky le vinh long university of technology education vinh long, vietnam kylh@vlute.edu.vn received: 8 july 2022 | revised: 25 july 2022 | accepted: 25 july 2022 abstract-the multi-criteria decision-making (mcdm) process of milling sncm439 steel is presented in this study. in this experimental study, 3 cutting tool parameters, namely the number of pieces, cutting piece material, and tip radius were considered and 3 cutting mode parameters, i.e. cutting speed, feed rate, and depth of cut changed in each experiment. sr and mrr are selected as the output parameters of the milling process. the paris method was used for mcdm, in which, the weights of sr and mrr were determined by 3 methods, namely aw, ew, and mw. twenty-seven sets of ranking results for 27 alternatives (experiments) are presented. the gini index was used to evaluate the stability of ranking alternatives. the results have determined the value of 6 input parameters to ensure the minimum sr and the maximum mrr simultaneously. keywords-mcdm; paris; average weight; entropy weight; merec weight; gini index; milling i. introduction milling the plane with a face milling cutter is a machining method that gives the highest productivity of all cutting machining methods, because it has many teeth simultaneously involved in cutting and a tool with a large diameter can be chosen [1-3]. therefore, this method is increasingly used in machine manufacturing. thanks to the development of machine tools as well as cutting tool manufacturing technology, the accuracy of this method is increasingly improved. this method is even used instead of grinding when it is necessary to machine surfaces that require high precision. in addition, the residual stress on the surface layer of the part during milling is usually compressive residual stress, whereas the residual stress on the surface layer during grinding is usually tensile residual stress. this is also the advantage of milling over the grinding method. among many criteria to evaluate the machining process, such as mrr, surface hardness, cutting force, cutting heat, etc., sr and mrr are the two most used parameters in published documents. this can be easily understood because mrr is an important parameter to evaluate cutting productivity, while sr is a parameter that has a great influence on the workability as well as the life of the product. on the other hand, determining the value of sr and mrr is also quite simple, specifically an sr measuring device is quite more popular than a force measuring device or a heat measuring device, and mrr can be calculated from simple math formulas. as with most machining processes, it is desirable to have minimum sr and maximum mrr when milling the plane with a face mill. however, these requirements cannot be achieved simultaneously with each specific machining condition. some examples to support this statement follow. in [4], when performing 27 tests of milling scm440 steel, the one with the smallest sr was also the one with the smallest mrr. when performing 9 tests for milling 060a4 steel, the one with the smallest sr is had a very small mrr [5]. among 27 skd11 steel milling experiments, the one with the smallest sr almost had the smallest mrr [6], etc. thus, in cases like these it is necessary to define an experiment where sr is considered smallest and mrr is considered maximum, i.e. an mcdm [4-6] problem. there are various mathematical methods that support mcdm such as: saw, waspas, topsis, vikor, moora, copras, piv, psi, edas, marcos, codas, waspas, wpas, etc. these methods have been widely applied to mcdm in many different fields. the common feature of these methods is that each method gives only one set of ranking results for the alternatives. the paris method was first proposed in 2020 by ardil [7]. paris is also an mcdm method, but, unlike the above techniques, it performs threefold data normalization in 3 different ways. in addition, for each data normalization method, the ranking of the alternatives is performed in 3 stages. thus, when applying this method, 9 different ratings will be conducted for the alternatives. in the next section of this paper, this method will be presented in detail. this method has been applied to make multi-criteria decisions in some specific cases such as: when deciding in choosing 1 of 6 aircraft types, each aircraft is evaluated through 7 criteria. the paris method was applied to accomplish this in [7]. in this study, two methods, i.e. aw and ew were used to determine the weights for 7 criteria. the topsis method was also used and compared with the paris method. when using the paris method with two different weighting methods (aw and ew) it gave 18 ranking options. when using the topsis method with two different weighting methods two ranking options were proposed. an interesting result was obtained that all 20 ranking options identified the best aircraft according to the 7 given criteria. besides, ardil also used the paris method [8] to decide which one of the 3 types of military aircraft to choose. in this case, each aircraft is evaluated on 7 criteria. aw and ew were again corresponding author: hong ky le engineering, technology & applied science research vol. 12, no. 5, 2022, 9208-9216 9209 www.etasr.com le: multi-criteria decision making in the milling process using the paris method used to determine the weights of the criteria and topsis was also used and compared with the paris method. the calculated results showed that all 20 ranking options (including 18 options of paris and 2 options of topsis) identified the same best aircraft. in [9], the paris method was also used to select 1 out of 5 software candidates, considering 8 criteria. in total, there were 31 sub-criteria out of which 8 were applied. in addition, 3 different sets of weights that are random numbers (rn) have been assigned to the criteria. the calculated results showed 27 rating options. in particular, the different best alternatives depended on the random weights assigned to the criteria. the above results show that the use of paris method is quite effective. however, the paris method has only been used in the mentioned studies. up to now, and to the best of our knowledge, there have been no studies using this method in mcdm for the milling process and mechanical processing in general. aw, ew, and rn methods were used to determine the weights for the criteria in the above studies when applying the paris method. this is understandable because aw is the simplest method to determine the weights for criteria where the weights of the criteria are equal, and ew is a method with high accuracy that has been widely used. its use is recommended in mcdm [10]. the rn method was used because out of the 31 criteria for software evaluation, there are both qualitative and quantitative criteria. however, for quantitative criteria it is not necessary to use this method. the mw weighting method was first proposed in 2021 [11]. it has been used in several studies to determine weights in mcdm [12, 13]. however, this method has not been used to determine weights for the criteria of any milling process. therefore, the use of the mw method for determining the weights for the criteria of the milling process along with the two methods already used (aw and ew) ensures the novelty of the current study. the use of 3 methods of determining weights in a study is the basis for assessing the stability in determining the best solution. sncm439 steel (according to jis standard japan) is a high-alloy steel and products like gears, wood cutters, dies, etc. are usually made from it. this steel is equivalent to some steels according to other standards such as, aisi 4340, en 36crnimo4, bs en24, jis sncm439, din 150cr14, gost 9crsi (or 9xc or 9hs or 9khs). there have been a few studies regarding the milling of this steel (or equivalent steels). in [14], the authors investigated the influence of the parameters of the mql-type cooling lubrication on sr when hard milling of 9crsi steel. in [15], the response surface method (rsm) and an artificial neural network (ann) model were combined to predict the value of tool wear and cutting force for the dry milling of en24 steel. in [16], the shear force and friction force were investigated when milling en24 steel with different cooling lubrication conditions. in [17], the optimal values of cutting speed, feed rate, and depth of cut were determined to ensure minimum sr when milling en24 steel. the influence of cutting speed, feed rate, and depth of cut on sr on cutting temperature when hard milling aisi-4340 steel were investigated in [18]. in [19], it was determined that the value of cutting speed, feed rate, and depth of cut improve the surface hardness when milling aisi-4340 steel. research on milling steel sncm439 (or equivalent steels) has been conducted in a number of studies as described above. however, to date, there has not been any research done in mcdm when machining this steel. this is the reason that this steel was chosen as the research object in this paper. like the sr parameter, the mrr is a very common parameter used to evaluate the milling process. this parameter reflects the processing capacity. considering both sr and mrr in a study makes both economic and technical implications. that is why this study has selected both sr and mrr as the criteria to evaluate the milling process. besides, the three cutting parameters (cutting speed, feed rate, and depth of cut) that have been investigated in many studies, the parameters of the cutting tool (number of inserts, cutting tool material, and nose radius) are also parameters that have a great influence on the surface roughness during milling [20-22]. however, until now, no study has been found that considers all 6 of these parameters during the milling process. therefore, the consideration of all these 6 parameters is also a novelty of this work. this study will conduct sncm439 steel milling experiments. in each experiment, 6 parameters will be changed including cutting speed, feed rate, depth of cut, number of inserts, insert material, and nose radius. sr and mrr were selected as the two output criteria. paris method is used for mcdm with 3 weighting methods including aw, ew, and mw. ii. the paris method the paris method is performed according to the following steps [7]. step 1: building of the decision matrix. � = � ��� ��� ��� �� ��� ��� ��� �� � � � � � � � ��� ��� ��� �� � (1) in which: m is the number of options, i = 1, 2, …, m and n is the number of criteria, j= 1, 2, …, n. if xij is negative then do the calculation x’ij = xij = min(xij), then x’ij is used to calculate the next steps. step 2: normalizing the decision matrix. normalizing way 1 (vector normalization): � = � ��∑ � ��� �� if j is the criterion, the bigger the better (2) � = 1 − � ��∑ � ��� �� if j is the criterion, the smaller the better (3) normalizing way 2 (linear normalization): � = � ������ if j is the criterion, the bigger the better (4) engineering, technology & applied science research vol. 12, no. 5, 2022, 9208-9216 9210 www.etasr.com le: multi-criteria decision making in the milling process using the paris method � = ��� � � if j is the criterion, the smaller the better (5) normalizing way 3 (max min linear normalization): � = � � − ��� ����� − ��� if j is the criterion, the bigger the better (6) � = ����� − � ������ − ��� if j is the criterion, the smaller the better (7) step 3: calculating of the weighted normalized value: � � = �� ∙ � (8) step 4: summarizing the weighted normalized values as: � � = ∑ �� ∙ � ��� (9) where i = 1, 2,… m; j = 1, 2,..., n. step 5: rank the alternatives. the solution with the largest value of � � is the best solution. step 6: identify the elements of the reference ideal solution: ��∗ = ���∗, … , ��∗� = �� !� � � �" ∈ $%, � &' � ��" ∈ (%� (10) where b represents a criterion as large as possible, c represents a criterion as small as possible. step 7: calculate the distance from the reference ideal solution: � ∗ = ∑ ���∗ − � � % ��� (11) step 8: rank the alternatives according to the principle that the one with the smallest value of πi is the best one. step 9: calculate the distance from the alternatives to the ideal solution: ) = ��� � − � �,��� %� + �� ∗ − � ∗,� %� (12) step 10: rank the alternatives according to the principle that the one with the smallest ri value is the best one. iii. methods of determining weights a. the average weight method aw is determined according to the following formula [23]: +� = � (13) where n is the number of criteria. b. the entropy weighted method ew is determined according to the following steps [10]. step 1: determine the normalized values for the indicators: ,ij = �ij�-. �ij/0123 (14) where xij is the value of criterion j corresponding to option i and m is the number of alternatives. step 2: calculate the value of the entropy measure for each indicator with: ( ) ( ) j ij ij1 ij ij1 1 ln(p ) 1 ln 1 m i m m i i me p p p = = =  = − ⋅ −  − ⋅ −    (15) step 3: calculate the weight for each indicator: +� = �4�56∑ ��4�56%0623 (16) c. the merec weight method mw is determined according to the following steps [11]: step 1: is similar to step 1 of the paris method. step 2: calculate the normalized values according to: ℎ � = � �16�16 if j is the criterion, the bigger the better. (17) ℎ � = �16����16 if j is the criterion, the smaller the better (18) step 3: calculate the overall efficiency of the alternatives according to: 8 = 9' :1 + ;� ∑ <='�ℎ � %< � >? (19) step 4: calculate the performance of the alternatives according to: 8 �@ = 9' :1 + ;� ∑ <='�ℎ � %< a,ab� >? (20) step 5: calculate the absolute value of the deviations according to: c� = ∑ <8 �@ − 8 <� (21) step 6: calculate the weight for the criteria according to: +� = d6∑ de0e (22) iv. milling experiment a. experimental design experiments were carried out on a 3-axis machining center. the values of the 6 input parameters are presented in table i [1, 24]. as the number of inserts varies in each experiment, 3 different types of inserts have been used. in addition, each type of tool head has several insert positions of 2, 3, and 4. all 3 types of cutters have a diameter of 40mm. the basic geometrical parameters of the selected insert types are the same. specifically, the main cutting angle is 90 0 , the main cutting-edge length is 10mm, and the blade width is 6.8mm [24]. the taguchi method was used for the experimental design due to its advantages [25, 26]. in this experiment, an experimental matrix of 27 experiments was designed (table ii). engineering, technology & applied science research vol. 12, no. 5, 2022, 9208-9216 9211 www.etasr.com le: multi-criteria decision making in the milling process using the paris method table i. input parameters parameter symbol unit value at level 1 2 3 number of insert n 2 3 4 insert material m tin ticn tialn nose radius r mm 0.3 0.5 0.8 cutting speed vc m/min 120 150 180 feed rate vf mm/min 300 400 500 depth of cut ap mm 0.2 0.35 0.5 table ii. experimental matrix and results trial n m r (mm) vc (m/min) vf (mm/min) ap (mm) mrr (mm 3 /min) sr (µµµµm) 1 2 tin 0.3 120 300 0.2 2400 2.287 2 2 tin 0.3 120 400 0.35 5600 3.152 3 2 tin 0.3 120 500 0.5 10000 4.017 4 2 ticn 0.5 150 300 0.2 2400 1.377 5 2 ticn 0.5 150 400 0.35 5600 2.242 6 2 ticn 0.5 150 500 0.5 10000 3.107 7 2 tialn 0.8 180 300 0.2 2400 0.490 8 2 tialn 0.8 180 400 0.35 5600 1.240 9 2 tialn 0.8 180 500 0.5 10000 2.105 10 3 tin 0.5 180 300 0.35 4200 0.245 11 3 tin 0.5 180 400 0.5 8000 0.793 12 3 tin 0.5 180 500 0.2 4000 1.163 13 3 ticn 0.8 120 300 0.35 4200 1.104 14 3 ticn 0.8 120 400 0.5 8000 1.969 15 3 ticn 0.8 120 500 0.2 4000 2.339 16 3 tialn 0.3 150 300 0.35 4200 0.838 17 3 tialn 0.3 150 400 0.5 8000 1.703 18 3 tialn 0.3 150 500 0.2 4000 2.073 19 4 tin 0.8 150 300 0.5 6000 0.345 20 4 tin 0.8 150 400 0.2 3200 0.456 21 4 tin 0.8 150 500 0.35 7000 0.890 22 4 ticn 0.3 180 300 0.5 6000 0.611 23 4 ticn 0.3 180 400 0.2 3200 0.241 24 4 ticn 0.3 180 500 0.35 7000 0.624 25 4 tialn 0.5 120 300 0.5 6000 0.657 26 4 tialn 0.5 120 400 0.2 3200 1.027 27 4 tialn 0.5 120 500 0.35 7000 1.892 b. results and discussion the sr for each experiment can be seen presented in table ii. these values are the mean values of at least 3 consecutive measurements. in addition, the mrr at each experiment is also been summarized in table ii. the values are calculated by (23), where vf, ap and bw are the feed rate, the depth of cut, and the wide cut respectively. f)) = gh ∙ !i ∙ jk (23) the extent and influence of the parameters on sr are shown in figure 1. from this graph, it is shown that: • the number of inserts, cutting speed, and feed rate have a great influence on sr. the nose radius and depth of cut also affect the sr, but to a lesser extent than the 3 mentioned above parameters. the insert material has no significant effect on sr. • when the number of insert increases, the sr decreases. this can be explained by the fact that as the number of inserts increases, each area of the machined surface is cut more than once. that means that after a insert cuts off a layer of the material, the metal layer on the surface of the part will be elastically deformed. this metal is then removed by other cuttings, which causes the sr to decrease. • as the cutting speed increases, the cutting tool rotates at a faster speed. then a point on the surface of the workpiece will be repeatedly cut by the cutting edges, even the undulations caused by plastic deformation will be eliminated, which leads to a reduced sr. the case is similar with the increasing of the number of inserts discussed above. • as the feed rate increases, the time the cutting tool is in contact between an area of the part surface and the cutting edge decreases, causing plastic layers of metal on the surface to not be removed, leading to an increase in sr. increasing the nose radius will cause the sr to decrease. it can be understood that the height of the surface undulation is inversely proportional to the nose radius, as discussed in [27]. furthermore, the large sr at large feed rates and small nose radius are also consistent with the sr calculation formula used in some studies [27]: )� = 1000 ∙ 0.0321 ∙ gh�/ fig. 1. main effects plot for surface roughness. from figure 1, if the sr has a small value, choose a large cutting speed, a small feed rate, and a small depth of cut. however, according to (23), when the feed rate and cutting depth are small, the mrr will also be small, which is undesirable. therefore, choosing the value of the cutting parameters to ensure that the sr is small and the mrr is large, it is necessary to make the right decisions. this right decision can be made with a mcdm method. in this problem, the paris method will be used. v. multi-criteria decision making a. determining the weights of the criteria equation (1) is used to build the decision matrix. the last two columns in table ii are the decision matrix. equation (13) was applied to determine the weights of the criteria according to the aw method. in addition, (14)-(16) are used to determine the weights for the criteria according to the ew method. equations (17)-(22) determine the weights of the criteria of the mw method. the results are shown in table iii. engineering, technology & applied science research vol. 12, no. 5, 2022, 9208-9216 9212 www.etasr.com le: multi-criteria decision making in the milling process using the paris method table iii. criteria weights method ra mrr aw 0.5 0.5 ew 0.6859 0.3141 mw 0.3663 0.6337 b. applying the paris method equations (2) and (3) are used to normalize the matrix in way 1. equations (4) and (5) are applied to normalize the matrix in way 2. equations (6) and (7) are used to normalize the matrix in way 3. the results are presented in table v. table iv. value of z*j normalization sr mrr way 1 0.255 0.200 way 2 0.030 0.500 way 3 0.000 0.500 to rank the alternatives for weight calculation according to the aw method we apply (8) to calculate the weighted normalized value (zij) and (9) to calculate the weighted normalized sum (π ω i). the results are presented in table vi. the results of ranking the alternatives according to the value of π ω i are also presented in this table. equation (10) was applied to determine the factors of the ideal solution (z * j) and the results are presented in table iv. equation (11) is used to determine the distance from the reference ideal solution (πi). the results are presented in table vii. the results of ranking the alternatives according to the value of π * i are also presented in this table. the distance from the alternatives to the ideal solution (ri) is calculated by (12). the results are presented in table viii. the results of ranking options according to the value of ri are also shown in this table. table v. normalized matrices trial. way 1 way 2 way 3 sr mrr sr mrr sr mrr 1 0.721 0.096 0.105 0.240 0.458 0.000 2 0.616 0.224 0.076 0.560 0.229 0.421 3 0.511 0.400 0.060 1.000 0.000 1.000 4 0.832 0.096 0.175 0.240 0.699 0.000 5 0.727 0.224 0.107 0.560 0.470 0.421 6 0.622 0.400 0.078 1.000 0.241 1.000 7 0.940 0.096 0.492 0.240 0.934 0.000 8 0.849 0.224 0.194 0.560 0.735 0.421 9 0.744 0.400 0.114 1.000 0.506 1.000 10 0.970 0.168 0.984 0.420 0.999 0.237 11 0.903 0.320 0.304 0.800 0.854 0.737 12 0.858 0.160 0.207 0.400 0.756 0.211 13 0.866 0.168 0.218 0.420 0.771 0.237 14 0.760 0.320 0.122 0.800 0.542 0.737 15 0.715 0.160 0.103 0.400 0.444 0.211 16 0.898 0.168 0.288 0.420 0.842 0.237 17 0.793 0.320 0.142 0.800 0.613 0.737 18 0.747 0.160 0.116 0.400 0.515 0.211 19 0.958 0.240 0.699 0.600 0.972 0.474 20 0.944 0.128 0.529 0.320 0.943 0.105 21 0.892 0.280 0.271 0.700 0.828 0.605 22 0.926 0.240 0.394 0.600 0.902 0.474 23 0.971 0.128 1.000 0.320 1.000 0.105 24 0.924 0.280 0.386 0.700 0.899 0.605 25 0.920 0.240 0.367 0.600 0.890 0.474 26 0.875 0.128 0.235 0.320 0.792 0.105 27 0.770 0.280 0.127 0.700 0.563 0.605 table vi. some parameters in paris ranked by the value of πωi trial way 1 way 2 way 3 zij ππππ ωωωω i rank zij ππππ ωωωω i rank zij ππππ ωωωω i rank sr mrr sr mrr sr mrr 1 0.361 0.048 0.409 27 0.053 0.120 0.173 27 0.229 0.000 0.229 27 2 0.308 0.112 0.420 26 0.038 0.280 0.318 21 0.115 0.211 0.325 26 3 0.255 0.200 0.455 23 0.030 0.500 0.530 8 0.000 0.500 0.500 18 4 0.416 0.048 0.464 22 0.088 0.120 0.208 26 0.350 0.000 0.350 24 5 0.363 0.112 0.476 21 0.054 0.280 0.334 19 0.235 0.211 0.446 22 6 0.311 0.200 0.511 18 0.039 0.500 0.539 7 0.120 0.500 0.620 10 7 0.470 0.048 0.518 16 0.246 0.120 0.366 17 0.467 0.000 0.467 20 8 0.424 0.112 0.537 12 0.097 0.280 0.377 16 0.368 0.211 0.578 13 9 0.372 0.200 0.572 7 0.057 0.500 0.557 4 0.253 0.500 0.753 2 10 0.485 0.084 0.569 8 0.492 0.210 0.702 1 0.499 0.118 0.618 11 11 0.452 0.160 0.612 1 0.152 0.400 0.552 5 0.427 0.368 0.795 1 12 0.429 0.080 0.509 19 0.104 0.200 0.304 22 0.378 0.105 0.483 19 13 0.433 0.084 0.517 17 0.109 0.210 0.319 20 0.386 0.118 0.504 17 14 0.380 0.160 0.540 11 0.061 0.400 0.461 13 0.271 0.368 0.640 9 15 0.358 0.080 0.438 25 0.052 0.200 0.252 25 0.222 0.105 0.327 25 16 0.449 0.084 0.533 14 0.144 0.210 0.354 18 0.421 0.118 0.539 15 17 0.396 0.160 0.556 9 0.071 0.400 0.471 12 0.306 0.368 0.675 8 18 0.374 0.080 0.454 24 0.058 0.200 0.258 24 0.257 0.105 0.363 23 19 0.479 0.120 0.599 3 0.349 0.300 0.649 3 0.486 0.237 0.723 4 20 0.472 0.064 0.536 13 0.264 0.160 0.424 14 0.472 0.053 0.524 16 21 0.446 0.140 0.586 4 0.135 0.350 0.485 10 0.414 0.303 0.717 5 22 0.463 0.120 0.583 5 0.197 0.300 0.497 9 0.451 0.237 0.688 6 23 0.485 0.064 0.549 10 0.500 0.160 0.660 2 0.500 0.053 0.553 14 24 0.462 0.140 0.602 2 0.193 0.350 0.543 6 0.449 0.303 0.752 3 25 0.460 0.120 0.580 6 0.183 0.300 0.483 11 0.445 0.237 0.682 7 26 0.437 0.064 0.501 20 0.117 0.160 0.277 23 0.396 0.053 0.449 21 27 0.385 0.140 0.525 15 0.064 0.350 0.414 15 0.281 0.303 0.584 12 engineering, technology & applied science research vol. 12, no. 5, 2022, 9208-9216 9213 www.etasr.com le: multi-criteria decision making in the milling process using the paris method table vii. π*i values and ratings trial way 1 way 2 way 3 ππππ * i rank ππππ * i rank ππππ * i rank 1 0.047 27 0.357 27 0.271 27 2 0.035 26 0.212 21 0.175 26 3 0.000 23 0.000 8 0.000 18 4 -0.009 22 0.322 26 0.150 24 5 -0.020 21 0.196 19 0.054 22 6 -0.055 18 -0.009 7 -0.120 11 7 -0.063 16 0.164 17 0.033 20 8 -0.081 12 0.153 16 -0.078 13 9 -0.116 7 -0.027 4 -0.253 2 10 -0.114 8 -0.172 1 -0.118 6 11 -0.156 1 -0.022 5 -0.295 1 12 -0.054 19 0.226 22 0.017 19 13 -0.061 17 0.211 20 -0.004 17 14 -0.085 11 0.069 13 -0.140 10 15 0.018 25 0.278 25 0.173 25 16 -0.078 14 0.176 18 -0.039 15 17 -0.101 9 0.059 12 -0.175 9 18 0.002 24 0.272 24 0.137 23 19 -0.144 3 -0.119 3 -0.223 4 20 -0.081 13 0.106 14 -0.024 16 21 -0.130 4 0.045 10 -0.217 5 22 -0.127 5 0.033 9 -0.188 7 23 -0.094 10 -0.130 2 -0.053 14 24 -0.147 2 -0.013 6 -0.252 3 25 -0.125 6 0.047 11 -0.182 8 26 -0.046 20 0.253 23 0.051 21 27 -0.069 15 0.116 15 -0.084 12 table viii. ri values and ratings trial way 1 way 2 way 3 ri rank ri rank ri rank 1 0.287 27 0.748 27 0.976 27 2 0.271 26 0.543 21 0.750 18 3 0.221 23 0.243 8 0.418 3 4 0.209 22 0.699 26 0.912 26 5 0.193 21 0.521 19 0.681 14 6 0.143 18 0.231 7 0.343 2 7 0.132 16 0.475 17 0.860 25 8 0.106 12 0.459 16 0.624 13 9 0.056 7 0.204 4 0.298 1 10 0.060 8 0.000 1 0.700 15 11 0.000 1 0.212 5 0.427 4 12 0.145 19 0.563 22 0.757 19 13 0.134 17 0.541 20 0.737 17 14 0.101 11 0.340 13 0.454 6 15 0.246 25 0.637 25 0.834 24 16 0.111 14 0.492 18 0.724 16 17 0.078 9 0.327 12 0.444 5 18 0.223 24 0.627 24 0.814 22 19 0.018 3 0.074 3 0.563 10 20 0.107 13 0.393 14 0.791 21 21 0.037 4 0.306 10 0.499 8 22 0.041 5 0.289 9 0.569 11 23 0.088 10 0.059 2 0.781 20 24 0.014 2 0.224 6 0.495 7 25 0.045 6 0.309 11 0.570 12 26 0.156 20 0.600 23 0.820 23 27 0.123 15 0.408 15 0.536 9 table ix. ranking when the weights are determined with the ew method trial ranking by value of ππππ ωωωω i ranking by value of ππππ * i ranking by value of ri way 1 way 2 way 3 way 1 way 2 way 3 way 1 way 2 way 3 1 25 27 26 25 27 25 25 27 27 2 26 23 27 26 23 27 26 23 24 3 27 13 25 27 13 26 27 13 13 4 20 26 20 20 2 20 20 26 26 5 21 22 22 21 22 22 21 22 17 6 23 12 21 23 12 21 23 12 3 7 10 9 13 10 9 13 10 9 22 8 12 17 14 12 17 14 12 17 12 9 17 11 10 17 11 10 17 11 1 10 4 1 5 2 1 5 2 1 14 11 3 6 1 4 6 1 4 6 2 12 16 20 17 15 20 17 15 20 18 13 13 19 15 13 19 15 13 19 16 14 18 15 16 18 15 16 18 15 5 15 24 25 24 24 25 24 24 25 25 16 11 16 11 11 16 11 11 16 15 17 14 14 12 16 14 12 16 14 4 18 22 24 23 22 24 23 22 24 23 19 1 3 2 1 3 2 1 3 8 20 9 5 9 9 5 9 9 5 20 21 8 10 7 8 10 7 8 10 7 22 5 7 4 6 7 4 6 7 9 23 7 2 8 5 2 8 5 2 19 24 2 4 3 3 4 3 3 4 6 25 6 8 6 7 8 6 7 8 10 26 15 21 18 14 21 19 14 21 21 27 19 18 19 19 18 18 19 18 11 engineering, technology & applied science research vol. 12, no. 5, 2022, 9208-9216 9214 www.etasr.com le: multi-criteria decision making in the milling process using the paris method table x. ranking when the weights are determined with the mw method trial ranking by value of ππππ ωωωω i ranking by value of ππππ * i ranking by value of ri way 1 way 2 way 3 way 1 way 2 way 3 way 1 way 2 way 3 1 27 27 27 27 27 27 27 27 27 2 24 18 22 24 18 22 24 18 15 3 14 3 9 14 3 10 14 3 3 4 25 26 26 25 26 26 25 26 26 5 20 17 16 20 17 17 20 17 14 6 10 2 3 9 2 3 10 2 2 7 21 21 23 21 21 23 21 21 25 8 13 15 13 13 15 14 13 15 13 9 2 1 1 2 1 1 2 1 1 10 11 5 14 11 5 15 11 5 16 11 1 6 2 1 6 2 1 6 4 12 19 22 20 19 22 8 19 22 19 13 18 20 18 18 20 19 18 20 18 14 9 10 7 10 10 7 9 10 6 15 26 24 25 26 25 25 26 24 23 16 16 19 15 16 19 16 16 19 17 17 6 9 5 6 9 5 6 9 5 18 23 23 24 23 23 24 23 23 21 19 5 4 8 5 4 9 5 4 10 20 17 16 19 17 16 20 17 16 22 21 4 11 6 4 11 6 4 11 8 22 7 12 10 7 12 11 7 12 11 23 15 8 17 15 8 18 15 8 20 24 3 7 4 3 7 4 3 7 7 25 8 13 11 8 13 12 8 13 12 26 22 25 21 22 24 21 22 25 24 27 12 14 12 12 14 13 12 14 9 the ranking results in tables v-x show 27 different ranking options. from these results it is shown that: • 22/27 times experiment #1 was determined to be the worst. in this experiment, mrr = 2400mm 3 /min was one of the 3 smallest values in table ii (equal to the mrr in experiments #4 and #7). in addition, ra = 2.287µm is very large compared to the surface texture in other experiments (only smaller than the surface texture in 4 experiments: #2, #3, #5, and #15). that allows the claim that the experiment #1 is the worst to be entirely reasonable. • 8/27 times determined experiment #9, 6/27 times determined experiment #10, 10/27 times determined experiment #11, and 3/27 times determined experiment #19 as the best. thus, determining which experiment is the best would not be achieved if the work stopped here. to determine the best experiment, in addition to the ranking results, it is also necessary to add the stability of the ratings. in this study, the gini index value will be used to determine the stability in ranking the alternatives [29]. the gini index value is determined by [29, 30]: qr)s = tr�4�s;u/4vwxy ru∙z/sv> ∑ ∑ |)\ − )] |u]�\-�u4�\�� (24) where m is the number of options, z is the number of mcdm methods used, rh and rl are the ranking values of the alternatives of the decision method h and l, and d(r) ∈[0,1]. when d(r) = 0, the rank of an alternative is the same when ranking by different methods. in contrast, when d(r) = 1, the ranking of the alternatives is most different when using different ranking methods. when comparing two alternatives, the one with the smaller gini index value is the better one. equation (24) has been applied to calculate the gini index value for the data in tables v-x. the results are presented in table xi. table xi. gini index value of the alternatives experiment gini index experiment gini index 1 0.002536 15 0.003381 2 0.018808 16 0.015427 3 0.048605 17 0.017751 4 0.018174 18 0.004861 5 0.012468 19 0.013314 6 0.040152 20 0.019231 7 0.01754 21 0.019019 8 0.014159 22 0.015216 9 0.019442 23 0.040997 10 0.032967 24 0.012046 11 0.016272 25 0.015216 12 0.018597 26 0.016061 13 0.014582 27 0.011834 14 0.017117 the results in table xi show that: • in experiment #1, the minimum gini index value is 0.002536. this proves that experiment #1 has the highest stability when ranking in different times. up to 22/27 options confirmed this experiment as the worst (ranked 27th), 4/27 options indicate that this experiment is the second worst (ranked 26), and 1/27 indicates that this experiment is the third worst (ranked 25). on the other hand, 27th or 26th or 25th ranking is very close. that proves that experiment #1 has the highest stability when ranking according to different options. engineering, technology & applied science research vol. 12, no. 5, 2022, 9208-9216 9215 www.etasr.com le: multi-criteria decision making in the milling process using the paris method • in experiment #3, the largest gini index value was 0.048605, proving that this experiment has the lowest rank stability when ranking according to the alternatives. according to the data in tables vi, viii-xi, experiment #3 came 5 times at the 3rd place, 3 times at the 8th, 1 time at the 9th, 1 time 10th, 4 times came at the 13th, 3 times at the 14th place, 2 at the 18th, 3 at the 23rd place, and 1 at the 25 th , 26th time, and 27th place. so, the stability in the ranking of experiment #3 is very weak. this experiment ranked in a variety of categories, with both good (3) and bad (27) ranks. • among the 4 experiments #9, #10, #10 and #19, experiment #19 has the smallest gini index value. that proves that experiment #19 has a higher stability rating than the other 3 experiments. thus experiment #19 is the best of these 4 experiments and it is also the best of the 27 experiments performed. the best values of the input parameters to ensure minimum sr and maximum mrr at the same time are: 4 as the number of inserts, tin as the insert material, 0.8mm nose radius, 150m/min cutting speed, 30mm/min feed rate, and 0.5 mm depth of cut. • the use of different weighting methods leads to different ranking orders. responding to different data normalization ways will result in different ranking orders for the alternatives. however, the simultaneous use of multiple weighting and multiple data normalization methods to give different ranking results, and then the use of the gini index to choose the best solution will form the basis for determining which option is the best. vi. conclusions in this study, 27 sncm439 steel milling experiments were performed. at each experiment, 6 parameters were considered: number of inserts, cutting material, nose radius, cutting speed, feed rate, and depth of cut. sr and mrr were determined in each experiment. the paris method was used to rank the alternatives, and the stability in ranking was evaluated by the gini index. some drawn conclusions are: • the number of inserts, cutting speed, and feed rate have a great influence on surface roughness. increasing the number of inserts or cutting speed reduces the surface roughness, while increasing the feed rate increases it. the nose radius and depth of cut also affect the surface roughness. surface roughness is reduced if the tip radius is increased, or the depth of cut is decreased. on the other hand, the insert material does not significantly affect surface roughness. • the use of 3 data normalization methods is what distinguishes the paris method from other methods. for each data normalization method, the paris method also gives 3 ranking results for the alternatives. this is also its difference from the other mcdm methods. • the combination of the paris method and 3 different weighting methods (aw, ew, and mw) resulted in 27 different ranking options. the combination of the paris method and the gini index to determine the best solution has higher reliability instead of using just one method that only gives a ranking solution for the alternatives. • to ensure minimum sr and maximum mrr simultaneously, it is recommended to use the tin insert with parameter values of the number of inserts, tool radius, cutting speed, feed rate, and depth of cut respectively as 4 pieces, 0.8mm, 150m/min, 30mm/min, and 0.5mm. nomenclature paris preference analysis for reference ideal solution saw simple additive weighting waspas weighted aggregates sum product assessment topsis technique for order of preference by similarity to ideal solution vikor vlsekriterijumska optimizacija i kompromisno resenje in serbian moora multiobjective optimization on the basis of ratio analysis copras complex proportional assessment piv proximity indexed value psi preference selection index edas evaluation based on distance from average solution marcos measurement alternatives and ranking according to compromise solution codas combinative distance based assessment waspas weighted aggregated sum product assessment wpas weighted product assessment mcdm multi-criteria decision-making merec method based on the removal effects of criteria aw average weight ew entropy weight mw merec weight references [1] d. d. trung, "application of edas, marcos, topsis, moora and piv methods for multi-criteria decision making in milling process," strojnicky casopis journal of mechanical engineering, vol. 71, no. 2, pp. 69–84, nov. 2021, https://doi.org/10.2478/scjme-2021-0019. 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houda adamou-mitiche laboratoire de recherche modélisation, simulation et optimisation des systèmes complexes réels university ziane achour djelfa, algeria amelmitiche@yahoo.fr received: 10 april 2022 | revised: 21 april 2022 | accepted: 26 april 2022 abstract-this paper introduces a new algorithm for reducing large dimensional second-order dynamic systems through the second order arnold reduction (soar) procedure, with a stopping criterion to select an acceptable good order for the reduced model based on a new coefficient called the numericalrank performance coefficient (nrpc), for efficient early termination and automatic optimal order selection of the reduced model. the key idea of this method is to calculate the nrpc coefficient for each iteration of the soar algorithm and measure the dynamic evolution information of the original system, which is added to each vector of the krylov subspace generated by the soar algorithm. when the dynamical tolerance condition is verified, the iterative procedure of the algorithm stops. three benchmark models were used as numerical examples to check the effectiveness and simplicity of the proposed algorithm. keywords-model order reduction; second-order systems; second-order krylov sub-spaces; second-order arnoldi procedure (soar); structure preserving; stability; projection; state space i. introduction the large-scale second-order model is considered a wellknown representation for the modeling of the dynamic behavior of multivariable complex systems in various fields of science and engineering, such as electrical, mechanical, structural, electromagnetic, and micro-electromechanical systems (mems). some of these systems encounter computational problems in simulation due to the huge model order to treat this problem. therefore, a reliable approximate model with reduced order is intended, which could replace the original in simulation or control and preserve the second-order structure of the original system and the same key properties, such as stability [1, 2]. this study examined the following large-scale system given in the second-order form: ∑� ∶ ���� � + �� � + �� � = �� �� � = ��� � (1) where m ∊ ℝn×n is an invertible matrix, q(0)=q0 and q̇(0)=q̇0 are initial conditions, m, d, and k ∊ ℝn×n are respectively the mass, damping, and stiffness matrices as known for mechanical models, q(t) ∊ ℝn is the state variables vector, and b, l ∊ ℝn represent the input and the output measurement matrices, respectively [1]. a model order reduction (mor) of the second-order system σn using the second-order arnoldi (soar) algorithm was investigated. the soar approach has attracted many researchers in recent years and has been used to solve the following problems: a quadratic eigen-value [3, 4], the mor of second-order dynamical systems [1, 6], and in the analysis of structural acoustics [5, 6]. from a mathematical point of view, the soar design is based on a projection-based mor technique that uses a second-order krylov subspace and the soar procedure to generate the projection matrix as follows: in the first step a recurrence formula is defined for the two matrices coefficient a and b and one or two initial vectors, and then, in the second step, an orthonormal basis of projection subspaces from the famous second-order krylov subspace defined in the recurrence formula is generated. the soar method is used in mor, which constructs another reduced second-order state-space system σn with reduced order, where the input-output behavior dynamics are completely recovered, corresponding author: abdesselam tamri engineering, technology & applied science research vol. 12, no. 3, 2022, 8712-8717 8713 www.etasr.com tamri et al.: a second order arnoldi method with stopping criterion and reduced order selection for … i.e., preserving the basic characteristics of the full order system [1, 2]. this study proposes an automated method to generate the best reduced-order model for a large second-order system using the soar procedure, by defining a new criterion to auto-stop the iteration process in the soar procedure and auto-select an acceptable reduced order of the projection matrix. the efficiency and robustness of the proposed algorithm were validated by various well-chosen numerical examples of second-order models. ii. model order reduction and problem formulation a. problem formulation the analysis of the second-order system σn leads to building a very large complex model. thus, mathematical tools are needed to reduce the computational complexity and accelerate the modeling task by constructing a reduced-order system σn. the proposed tools preserve the characteristic properties of the original system, such as the second-order form and stability [2,10]. the reduced second-order system σn is defined by: ∑� ∶ ����� �+ ��� �+ ��� � = ��� ��� � = ���� � (2) where z(t) represents the state vector with dimension n ≪ n, and the matrices mn, dn, and kn ∊ ℝn×n are the mass, damping, and stiffness matrices respectively, as known in structural dynamics. the vectors bn and ln ∊ ℝn are the input distribution and output measurement respectively. applying the laplace transform, the transfer function of the original second-order model is given as: ℎ �� = �� ��� + � +�� ! � (3) the power series of the laplace transformation q(s)=l(q(t)) can be expressed as: " �� = #$ + #!� + … = ∑ #& � &'&($ (4) with rl being the l th order system moments. the above secondorder system σν can be rewritten in first-order form by taking the following state vector ) � = *�� �� �+: ,./� 00 12*�� ��� �+− /− −�1 0 2*�� �� �+ = /�02 � � � � = 40 ��5*�� �� �+ (5) equation (5) can be expressed in matrix form as: 6)� �− 7) � = 8� �, � � = :�) � (6) where: 6 = /� 00 12, 7 = /− −�1 0 2, 8 = /�02 , :� = 40 ��5 are respectively the input and the output of the first-order system representation. the transfer function h(s) can be rewritten as: ℎ �� = :� 6� −7� ! 8 (7) and the power series of the transfer function h(s) as: ℎ �� = ;$ +;!� + … = ∑ ;& �&'&($ (8) the design of mor krylov subspace techniques is based on moment matching methods. its principle is to replicate the moments of the original system σn on the moments of the reduced system σn [11-13]. b. soar algorithm for second-order systems this section describes the definition of a second-order krylov subspace using the soar algorithm. the second-order krylov subspace is defined as: 7� <,=,>� = ?@��abcde$, e!,…,e� !f (9) where: � e$ = >, e! = <e$eg = <eg ! + =eg � , h = 2,3,…. (10) where a, z ∊ ℝn×n are square matrices called constant matrices and w ∊ ℝn×1 is a column vector called the starting vector. the sequence r0, r1, ..., rn-1 is known as krylov second-order basic blocks [1]. the gn(a, z; w) subspace defined in (9) is called an n th second-order krylov subspace [2, 10, 11]. there is a connection between the subspace gn(a, z; w) and the standard krylov subspace kn(a, w) defined in (11), while gn(a, z; w) can be considered as a generalization of kn(a, w). �� <,>� = �abc >,<>,<�>,…,<� !>� (11) in the case of the matrix z = 0, the second-order krylov subspace gn(a, z; w) is equal to the general krylov subspace kn(a, w). the application of the vector sequence {rj} of the second-order krylov sub-space to obtain an orthonormal basis {r0, r1, ..., rn-1} is called soar (second order arnoldi) algorithm [2]. the following lemma 1 can be used in the proof of theorem 1 [10]: • lemma 1: let tn ∈ ℝn×n be an upper hessenberg matrix. the k entry m�no!is zero for k = j+2, ..., n and j = 0, 1, ..., n1. in particular, o��m�no! = 0 for j=0, 1, ..., n-2 [1]. • theorem 1: let qn be the orthonormal matrix defined by the sequence vectors qn={q1, q2,…, qn}, where the vectors qi with i =1, ..., n are generated by the soar procedure after the execution of n iterations. then the analysis of the relationship between the j th system’s moment rj and the output of the soar procedure can be expressed as [1]: / enen !2 = pnq = *"�r� +m�no!, s@e t = 0,1,…,v −1 (12) in particular: en = "�m�no! , and, en ! = r�m�no!, for j = 0, 1, ..., n-1 [10]. engineering, technology & applied science research vol. 12, no. 3, 2022, 8712-8717 8714 www.etasr.com tamri et al.: a second order arnoldi method with stopping criterion and reduced order selection for … theorem 2 provides a sufficient condition for the n first output vectors moment of the reduced and the original systems to match. • theorem 2: let qn be the projection matrix generated by the soar algorithm to reduce the order of the second-order model. if eg ∈ colspan "� � for j = 0, ..., n then en = "�ên [1]. this theorem helps to verify that the condition of the output moment matching can be maintained. • theorem 3: the first unmatched moment is obtained after the execution of the n th iteration of the soar procedure, and the error ∆;�`! between the two moments ∆;�`! of the original and ;a�`! of the reduced system can be given by an analytical expression [1]: ∆;�`! = ;�`! −;a�`! = 6�b∏ n`!,n�n(! d��`! (13) c. soar procedure with deflation and memory saving in the soar algorithm, the pn set vector is closely related to qn, and the bi-product vector pn is utilized. to avoid explicit references and updates of p vectors, a new version of soar, shown in figure 1, was presented in [10] to reduce the memory requirements by almost half [15]. since p1 = 0: "� = r�`!me� = r�`! : ,2: c � 1�me� 2: c � 1, 1: c� (14) fig. 1. soar with deflation and saving memory algorithm – algorithm 1. iii. proposed stopping criterion for soar finding a suitable order q for the reduced model that leads to a better approximation is an important component of order reduction. the question is when to pause an iterative order reduction [16]. the two traditional techniques to stop an iterative mor approach based on the krylov subspace are: a. finding the zero vector although it has an automatic implementation, the conventional approach consisting of finding the zero vector (tj+1 = 0 in the soar procedure) to interrupt the process is extremely ineffective. the major drawback of this method is that it adds a lot of redundancy to the transformation matrix and duplicates the same information about the dynamic behavior of the original model once and again. b. time response comparison and manual termination in this method, a reduced-order model is generated in each iteration of the soar procedure, a time response comparison is made for both models, the reduced and the original one, and the process is terminated if the errors are acceptable. some fundamental definitions of matrix factorization should be presented before the implementation and application of the new criterion for stopping and selecting the reduced order in the soar procedure. • definition 1: let a ∊ cn×m, and suppose rank(a) = r, and n ≤ m. then, there exist matrices u ∊ cn×n, v ∊ cm×m, and σ ∊ ℝn×n such that: < = g h i∗ (15) u and v are unitary, and ∑ � *∑k 00 0+. where ∑k is a diagonal matrix with ∑k=diag{σ1…σr} and σ1 ≥ σi ≥ ...≥ σr > 0. positive numbers σi for i = 1,…,r are determined uniquely by a and called singular values of a. εquation (15) is called the singular value decomposition (svd) of matrix a. columns u and v are called the left and right singular vectors respectively. the index r of the smallest singular value is called the theoretical rank of matrix a. • definition 2: let σr be the calculated singular values of the matrix a ∊ cn×m, and let δ be a positive real number, δ > 0. the numerical δ-rank is defined as the number of singular values greater than δ. the numerical δ-rank is written as k, if: σ1 ≥ σ2 ≥ ….σk ≥ δ ≥ σk+1 ≥ … ≥ σr , r = min(n, m) (16) for each iteration of the soar algorithm, the contribution of the second-order krylov vectors, taking into consideration the knowledge about the model dynamics stored in them, decreases monotonously. it is therefore expected that each generated vector ri will be less effective to the numerical rank of the transformation matrix qn. the suggested stopping criteria rely on the estimation of a signal of progress in the numerical rank of the generated transformation matrix with each iteration in the soar procedure, exactly before adding the new normalized vector. to measure this signal, an indicator is assigned for each vector generated by the iterative process before being fed to the normalization routine (line 12 in algorithm 1). this indicator is called nrpc and has a value range of [0,1]. the greater value of the nrpc for the nominee vector harmonizes an important contribution of that vector to the improvement of the numerical rank and the dynamic progression of the original system and must hence be included in qn. the nrpc for the candidate vector ri is given as the inverse of the sum of singular values of the current transformation matrix ql, obtained by appending the new non-normalized vector r to the transformation matrix qn of the previous iteration. v#r6 = !∑ lmnmop (17) engineering, technology & applied science research vol. 12, no. 3, 2022, 8712-8717 8715 www.etasr.com tamri et al.: a second order arnoldi method with stopping criterion and reduced order selection for … therefore, it is possible to approximate the stopping criteria as: • in each iteration calculate the nrpc indicator using (17). • the iteration can be halted as soon as nrpc < ε, where ε > 0 some specified value. algorithm 2 demonstrates how to integrate this stopping criterion into algorithm 1 of soar. fig. 2. soar with stopping criterion algorithm – algorithm 2. iv. numerical applications numerical applications were conducted to demonstrate the efficiency and accuracy of the soar method with the proposed stopping criterion and the robustness of the terminating mechanism for the krylov-based reduction method. three practical engineering examples were studied: (i) a shaft on bearing supports with a damper originating from a finite element (fe) [7], (ii) the butterfly gyroscope problem [8], and (iii) the fe model of the 3d cantilever timoshenko beam [20]. table i displays the size of these and their corresponding reduced models and some parameter settings used in the simulation, such as the expansion point s0 and the frequency range. the output of the relative errors between the original and the reduced systems and the related frequency responses [7, 8] were considered for comparison. table i. model examples with parameter settings model full size reduced sizes parameters s0 frequency range fe model of a shaft on bearing supports 400 10,20,40 150×2π [0,3000] hz butterfly gyroscope 17361 10,19,39 1.05x10 5 [10 3 ,10 6 ]hz fe model of 3d cantilever timoshenko beam 600 10,19,39 0 [0,1200] hz figure 3 shows the pattern of the stopping criterion and the nrpc coefficient, which is the inverse of the sum of the singular values of the current transformation matrix ql, obtained by appending the new non-normalized vector r to the transformation matrix qn of the previous iteration. after the 20 th iteration, nrpc decreases slowly and it can be assumed that a good reduced-order model can be selected at around 20 and above. in other terms, an acceptable good approximation model can be obtained for nrpc values in [0, 0.5]. a fixed tolerance value ε in [0, 0.5] was defined to implement a condition to select a good reduced order and stop the soar procedure. fig. 3. pattern of variation of nrpc vs number of iterations. fig. 4. example 1 frequency responses of the exact and reduced transfer functions h(s) and hn(s). fig. 5. example 1 the relative errors ||h(s)−hn(s)||/||h(s)||. fig. 6. example 1 poles distribution for three reduced models. fig. 7. example 2 frequency responses of the exact and reduced transfer functions h(s) and hn(s). engineering, technology & applied science research vol. 12, no. 3, 2022, 8712-8717 8716 www.etasr.com tamri et al.: a second order arnoldi method with stopping criterion and reduced order selection for … fig. 8. example 2 the relative errors ||h(s)−hn(s)||/||h(s)||. fig. 9. example 2 poles distribution for three reduced models. fig. 10. example 3 frequency responses of the exact and reduced transfer functions h(s) and hn(s). fig. 11. example 3 the relative errors ||h(s)−hn(s)||/||h(s)||. fig. 12. example 3 poles distribution for three reduced models. v. conclusion this paper introduced a new mor approach with an efficient stopping criterion to find the suitable order of a reduced model, by using a modified soar algorithm as a krylov mor approach with auto-selection of the reduced order. based on the obtained results, the proposed algorithm showed high efficiency and accuracy in terms of relative error against the original systems, while the key properties of the second-order form in the reduced model were still preserved. furthermore, its superiority was proven compared to conventional soar in terms of robustness, where a suitable and optimal reduced-order was chosen systematically. the proposed approach worked very well for the three examples used in numerical tests (fe 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[21] s. s. desouky, a. z. el-dein, r. a. a. el-aal, and n. a. a. el-rahman, "a new contribution in reducing electric field distribution within/around medium voltage underground cable terminations," engineering, technology & applied science research, vol. 7, no. 5, pp. 1962–1966, oct. 2017, https://doi.org/10.48084/etasr.1357. microsoft word etasr_v12_n4_pp9034-9037 engineering, technology & applied science research vol. 12, no. 4, 2022, 9034-9037 9034 www.etasr.com raja & gopikrishnan: drought analysis using the standardized precipitation evapotranspiration index … drought analysis using the standardized precipitation evapotranspiration index (spei) at different time scales in an arid region azmat raja civil engineering department national institute of technology patna patna, india azmatr.phd18.ce@nitp.ac.in t. gopikrishnan civil engineering department national institute of technology patna patna, india gktphd@gmail.com received: 16 june 2022 | revised: 30 june 2022 | accepted: 1 july 2022 abstract-drought causes insufficient soil moisture and crop water balance damage. one of the most commonly used indicators in drought monitoring is the standardized precipitation evapotranspiration index (spei). in this study, the performance of the spei at 1-, 3-, 6-, 9-, and 12-month timescales was compared and analyzed from temporal and spatial variations at 12 meteorological stations in the barmer arid region from 1979 to 2013. to determine the significance of drought characteristic trends, the modified mann-kendall (m-k) test is used. the results revealed that as the timescale increased, the temporal variations in the spei became more consistent. the m-k test revealed that the spei showed decreasing trends at 1 and 3 months, but increasing trends at 6, 9, and 12 months. the findings of this study are instructive and practical for drought assessment, risk management, and decision-making. keywords-drought; spei; mann-kendall; arid region; meteorology i. introduction drought has had devastating effects on the ecology in a global scale during the recent decades. severe drought, particularly in arid and semiarid areas, poses a long-term danger to human livelihoods. climate change, on the other hand, will become more common in the twenty-first century [12]. the severity of drought is determined by its duration, frequency, intensity, and the geographical distribution of rainfall, as well as the water requirements of humans, animals, crops, and the vegetative cover of the region. drought features are difficult to define and analyze because of their complexity and intensity [3-5]. drought is divided into four categories based on its impact: meteorological drought, agricultural drought, hydrological drought, and socioeconomic drought [68]. drought can reduce crop production and threaten the socioeconomic sustainability of communities [9]. furthermore, dry weather during a drought can cause forest fires, which are another major environmental issue [10]. since india is an agrarian society and agriculture engages 68% of the population, analysis and forecasting of agricultural drought are more important than for other types of drought. the arid region of western india is threatened by severe droughts due to water scarcity, irregular rainfall, and severe climatic conditions [11]. drought cannot be avoided, but it can be mitigated with forethought and planning. as a result, many studies have been conducted to provide an objective and quantitative assessment of drought severity. drought indices are widely used to measure drought impacts [12]. they are proxies based on climate data that are assumed to adequately describe the degree of drought hazard. over 150 drought indices have been developed and are widely used in drought assessment, monitoring, and forecasting [13]. the standardized precipitation index (spi) developed in [14] is a precipitationbased drought index that, unlike other indices, requires precipitation as an input. it is widely used due to its data minimalism. the spei [13], is a modified form of spi that involves monthly climatic water balance (difference between precipitation and potential evapotranspiration) as input parameters. the objective of this paper is to show the spatial and temporal variation of meteorological drought using spei at different time scales over the barmer district from 1979 to 2013. the modified m-k test is used to determine the significance of drought characteristic trends. ii. materials and methods a. the study area the study area is the barmer district in western rajasthan, india. this district covers an area of 28,387km 2 . the district of barmer is the third largest in rajasthan and the fifth largest in india, and is known for its vegetation. it lies between 24°58' and 26°32'n and 70°05' and 72°52'e. the district is located in the western part of the state and is part of the thar desert. because of the arid thar desert and the sandy soil, temperature varies greatly throughout the year. during summer the temperature rises to 46-51°c, whereas, during winter, it drops to 0°c. the barmer district is primarily a desert, with an annual rainfall of 277mm. the district experiences frequent drought. because of rapid urbanization and poor management, the corresponding author: azmat raja engineering, technology & applied science research vol. 12, no. 4, 2022, 9034-9037 9035 www.etasr.com raja & gopikrishnan: drought analysis using the standardized precipitation evapotranspiration index … district is also dealing with recent flood problems. with agriculture and cattle rearing being the only means of livelihood of the residents, persistent drought forces them to migrate to other parts of the state. b. data collection daily and monthly weather data for the barmer district were downloaded from global weather data [15] for 12 weather stations in western rajasthan from 1979 to 2013. c. standardized recipitation evapotranspiration index spei [13], is derived from spi and calculates the monthly climatic water balance using precipitation and potential evapotranspiration (pet) as input parameters. � = � − ��� (1) where d is a simple aggregation of water shortages or excesses over time, p is precipitation in mm, and pet is the potential evapotranspiration in mm. pet is calculated using the penmanmonteith (pm) equation [16]. table i. spei drought category classification drought class spei no-drought greater than -0.5 mild -0.5 to -0.99 moderate -1 to -1.49 severe -1.50 to -1.99 extreme less than -2 on various time scales, the d values can be summarized: ��� = ∑ ���� − ����� �, � ≥ ��� ��� (2) where k is the monthly time scale and n is the number of calculations. the difference in water balance is normalized as a loglogistic probability distribution to estimate the value of spei. the probability density function is expressed by: � �� = �� ����� ��� �1 + ����� �� ! �" (3) where α, β, and γ are scale, shape, and origin parameters respectively. as a result, the probability distribution function can be written as: # �� = �1 + � ������ ! � (4) spei can be calculated using the standardized values of f(x) given in [17]: spei = ( − )*+),-+).-. +/,-+/.-.+/0-0 (5) where ( = √−23�� for p ≤ 0.5. p is the probability of exceeding a determined d value, p =1-f(x). if p > 0.5, then p is replaced by 1 p and the sign of the resultant spei is reversed. the constants are 4� = 2.515517, 4 = 0.802853, 4" = 0.010328, 5 = 1.432788, 5" = 0.189269, and 56 = 0.001308. spei can be classified mainly in 5 classes [14], as shown in table i. d. the modified mann–kendall test to auto-correlate data, the modified m-k trend test is used [17-19], which is recommended by the world meteorological organization for analysing meteorological and hydrological variables. under the no trend null hypothesis, the original m-k statistic value z has a standard normal distribution with a mean of 0 and a variance of 1. after introducing a correcting factor � 7 in z, the modified m-k statistic 8∗ can be estimated by the following equations: 8∗ = :;�,< (6) � 7 = =1 + "�, ∑ � − 1� >> �?@ >> > 1�,� bb� 1 + 2 c,d,e,��,c,.+ �,� � c,.�, c,� �. �?@ >> = 1 (7) where @bb is a sample’s self-correlation coefficient, and jj is lag. significant change is observed, if |z| or |z*| ≥ 1.96 and β (confidence) value 0.05. the significant change is increasing in magnitude, if z or 8∗ are positive, else the magnitude is decreasing if z or 8∗ is negative. the spei drought indices at various time scales are used to assess drought in arid regions. the main advantage of using spei over the commonly used spi in determining drought is that spei takes into account both precipitation and pet. as a result, in comparison to the spi, the spei captures the primary impact of rising temperatures on water demand. the m-k statistical test is used to determine whether a set of data values is increasing or decreasing over time, and whether the trend in either direction is statistically significant. iii. results and discussion figure 1 shows the temporal variation in monthly precipitation from 1979 to 2013. the monthly variation shows that the wet period lasts from july to september, and the dry period from november to january. in barmer, the monthly precipitation ranges from 0 to 330mm. the variation of monthly pet is shown in figure 2. pet value varies from 80 to 270mm. fig. 1. temporal variation of precipitation from 1979 to 2013. a. temporal variation of spei the monthly spei is calculated at 5 time scales (1, 3, 6, 9, and 12 months) from 1979 to 2013 (figure 3). there are engineering, technology & applied science research vol. 12, no. 4, 2022, 9034-9037 9036 www.etasr.com raja & gopikrishnan: drought analysis using the standardized precipitation evapotranspiration index … significant differences in the sensitivity of spei values at different time scales, with the smaller time scale indicating more obvious wet and dry changes. spei and spi can produce better results with a time lag of more than one month and a minimum of 30 years of data. the intensity of the drought increased as the timescale increased. it has also been observed that a continuous mild drought leads to a severe drought. at 1 and 3 months, the spei value generally indicates meteorological drought, while at 6 and 9 months, it indicates agricultural drought. droughts of severe intensity occurred in 1986, 1987, 2002, 2004, 2006, and 2009. fig. 2. temporal variation of pet from 1979 to 2013. (a) (b) (c) (d) (e) fig. 3. spei at (a) 1-, (b) 3-, (c) 6-, (d) 9-, (e) 12-month time scale. b. trends of drought characteristics the trends of spei at various time lags, obtained using the modified m-k method, and the sen's slopes for the years 1979– 2013 are shown in table ii. spei showed decreasing trends at 1 and 3 months, but increasing trends at 6, 9, and 12 month time scales. only the spei at 12 months found significant trends, while the spei at other time scales showed insignificant trends. spei has a low sen's slope (-0.01) at 1 month, indicating a clear downward trend, and zero at the other time scales. table ii. m-k test for spei parameters z trends and significance sen's slope spei1 -1.46 insignificant decrease -0.01 spei3 -1.1 insignificant decrease 0 spei6 0.47 insignificant increase 0 spei9 1.59 insignificant increase 0 spei12 2.29 significant increase 0 c. spatial variations in spei for the spatial interpolation of drought characteristics, the inverse distance weighted (idw) interpolation method has been used. a severe drought was observed in 2002, followed by a period of good precipitation in 2003. as a result, we analyse the spatial distribution of drought in 2002 and 2003. the spatial distribution of the spei at 6-month time scale in barmer for the drought (2002) and wet (2003) year is shown in figure 4 during the wet months of the year (july to september). throughout the region, high drought intensity was observed during the drought year and reflected in very poor vegetative conditions. during the wet year, wetness is observed in the starting of the monsoon and as monsoon passes, the degree of wetness decreases rapidly due to the high temperature variation and thar desert. as long as the spei values are high during the wet year of 2003, they improve plant conditions. fig. 4. spatial distribution of drought indices for the drought year 2002 and the wet year 2003. d. comparison of spei drought with the observed drought the spei drought classification on a 12-month time scale is compared to the observed drought data from 1979 to 2005. the observed data are taken from the central arid zone research institute, jodhpur. the predicted by spei and observed number of drought years is shown in figure 5. the drought year 1991 predicted by spei as moderate drought while observed showed it was severe drought year. the spei drought index is one of most recently developed drought indices. drought in the arid district of western rajasthan is assessed using the spei drought indices at various time scales. because the district has experienced frequent engineering, technology & applied science research vol. 12, no. 4, 2022, 9034-9037 9037 www.etasr.com raja & gopikrishnan: drought analysis using the standardized precipitation evapotranspiration index … droughts due to climate change, it has become necessary to assess the droughts over time in order to reduce their impact. crop yield loss occurs during drought years. drought assessment helps in reducing the impact of agricultural droughts by effectively managing available water resources. drought knowledge, both spatial and temporal, reduces risks, so the idw interpolation method was used to show its spatial variation, which indicated that whenever there is a drought, the western region of barmer is adversely affected. fig. 5. comparison of predicted and observed drought. iv. conclusion in this paper, spei was used at different time scales to calculate the drought in rajasthan's arid barmer district, from 1979 to 2013. the index fluctuated the most on the shortest timescale. the fluctuations in the spei tended to be gradual over the longest timescale. as a result, the spei-reflected drought may be consistent over long timescales. throughout the region, the spatial distribution showed a high level of drought intensity during the drought year. spei showed decreasing trends at 1 and 3 months, but increasing trends at 6, 9, and 12 month time scales. from 1979 to 2005, the annual spei showed 17 drought years out of the 19 totally observed drought years. spei can be used to estimate drought in arid regions at different time scales. references [1] a. a. mahessar et al., "flash flood climatology in the lower region of southern sindh," engineering, technology & applied science research, vol. 9, no. 4, pp. 4474–4479, aug. 2019, https://doi.org/10.48084/ etasr.2726. 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[19] h. b. mann, "nonparametric tests against trend," econometrica, vol. 13, no. 3, pp. 245–259, 1945, https://doi.org/10.2307/1907187. microsoft word etasr_v12_n5_pp9126-9135 engineering, technology & applied science research vol. 12, no. 5, 2022, 9126-9135 9126 www.etasr.com bulum et al.: application of a seat-based booking control mechanism in rail transport with customer … application of a seat-based booking control mechanism in rail transport with customer diversion ahmet z. bulum department of industrial engineering karabuk university karabük, turkey ahmetbulum@karabuk.edu.tr muharrem dugenci department of industrial engineering karabuk university karabük, turkey mdugenci@karabuk.edu.tr mumtaz ipek department of industrial engineering sakarya university sakarya, turkey ipek@sakarya.edu.tr received: 1 july 2022 | accepted: 10 july 2022 abstract-the ticket booking control mechanism is a part of the revenue management (rm), commonly used in the airline industry. this study aims to optimize seat allocation in the railway industry and compare the performance of three booking control techniques by considering customer behavior. the preferences of customers who cannot find their desired ticket are considered as a customer diversion matrix, which also includes waiting and no-purchase probability. α ticket booking system (tbs) with buckets, which assigns seats to buckets, was adapted and implemented on the turkish railway for the first time. a genetic algorithm that is specifically written to apply the tbs, including customer diversion, is used in simulations to obtain approximate solutions. it is seen that tbs gave successful results with a revenue increase of around 5.8%. we can also suggest, considering customer behavior, that the revenue can be raised by sales in periods. keywords-revenue management; railway transportation; customer behavior; genetic algorithm; seat inventory control i. introduction revenue management (rm) can improve the profitability of firms in the service industry. rm has been used for pricing, forecasting, seat inventory control, and overbooking in airlines [1]. as a part of rm, seat inventory control or seat allocation deals with the decision to allocate a finite seat capacity optimal to demands [2]. authors in [5] compared a deterministic linear and a probabilistic nonlinear programming model for the network problem with non-nested seat allocation. authors in [6] suggested a multi-train seat inventory control model to control the seat inventory capacity among different trains. authors in [7] proposed a stochastic dynamic model with some properties related to the profit-to-go functions. authors in [8] used three seat inventory control methods and modelled them under a single-fare class. with the spread of high-speed railway (hsr), rm's applicability in the railway industry has also increased [5, 10]. in the railway industry, rm is utilized as a management technique that aims to maximize the total revenue by finding an optimal strategy controlling the availability and/or the price of train tickets without any changes in the resources (e.g. adding trains or carriages) [11]. articles regarding capacity allocation and prices in railway transport are mostly originated from countries where hsr is widely used [6, 8, 12–22]. while train tickets were sold formerly in railway stations or by authorized agents, online ticket reservation has become preferable nowadays. according to the classification in [23], there are different types of ticket booking mechanisms, such as virtual nesting (vn) and partitioned booking limit control (pblc). vn, widely used in the airline industry, uses single-source nested controls to allocate each resource in the network. in practice, both the indexing process of vn and the control logic of mapping products to virtual classes is complex [23]. pblc is a booking mechanism that allocates a fixed amount of capacity on each resource for every product offered, i.e. the seats are assigned to the tickets at the beginning of the booking horizon. studies in which pblc is used mainly aimed to find the optimal allocation of seats [5, 24, 25]. however, because of the fixed use of seats in pblc, it is considered inefficient when the demand is stochastic and is seldom used in practice [23]. customer behavior has been acknowledged as an important element for increasing revenue and has been included in modeling rm problems in some previous studies [26, 27]. authors in [11] proposed a seat-based control mechanism and considered customers' purchase preferences as customer corresponding author: ahmet z. bulum engineering, technology & applied science research vol. 12, no. 5, 2022, 9126-9135 9127 www.etasr.com bulum et al.: application of a seat-based booking control mechanism in rail transport with customer … behavior while optimizing seat allocation in china railway. authors in [28, 29] proved that customer behavior is an essential factor affecting the ticket sale profit: the railway companies can collect more information with online reservation systems, such as the ticket booking time and purchase preferences of customers. this research concentrates on evaluating the seat allocation performance of booking control mechanisms under diverse customer conditions. unlike the previous studies, the diverted customer has more than two options: buying another ticket, waiting for an available seat, or leaving without buying. the customer diversion is utilized as a percentage matrix in this study. the ticket reservation process is utilized by the simulation method and a genetic algorithm (ga) is designed to cope with the complexity of the process. the methods were evaluated and compared through an experimental case and a real-world case using data from the turkish railway. one contribution of this study is the application of customer diversion as customer behavior while optimizing seat allocation in the railway industry. another contribution is the application of a ticket booking mechanism with buckets to the turkish railway for the first time. ii. ticket booking modeling with buckets figure 1 shows an example of a railway line with three stops. in rm, resources are the seats in a train, and resources 1 and 2 (res1, res2) consist of three seats. products 1, 2 and 3 (pr1, pr2, pr3) use the same seats but different resources. if a customer books a ticket for pr3, for example seat 1 (s1) will be occupied in res1 and res2. then res1 and res2 have only two empty seats for booking, s2 and s3. but if the customer books a ticket for pr1, then s1 will be removed only from res1. fig. 1. a representative railway line with three stops. a product is referred to the used resources, i.e. occupied seats in a train, between an origin-destination (o-d) pair. in the reservation process, customers send requests for products. after an accepted request, the seats related to that product will be assigned and occupied. then different ticketing policies are involved: in pblc a ticket will be printed immediately, but a ticket is generated before printing in the proposed ticket booking system with buckets (tbs). modeling of the ticket booking process starts by allocating products and resources to the buckets. a bucket is a combination of tickets, and it contains a seat set and an offered product set. the bucket describes which products can be sold from the available resources [11]. the ticket pool is designed to collect the tickets generated for reusing. some resources can remain unused after selling a ticket from a bucket. the remaining seats are assigned to appropriate products, which are collected in the ticket pool to sell additional tickets. here, the exception is the ticket for travel from the first station to the last station. fig. 2. the working mechanism of tbs. fig. 3. the working mechanism of tbs. figures 2 and 3 show the different working mechanisms of pblc and the proposed tbs. as seen in figure 2, in pblc all seats are assigned to some partitions and all tickets are generated and await their owner. however, in tbs, most seats are assigned to the buckets, and the remaining seats are sold by creating tickets according to the arriving passengers (figure 3). the general assumptions of seat allocation problems are that the demand for cheap tickets is higher than for the expensive ones, and price-sensitive customers and long-distance travelers arrive earlier than the time-sensitive customers and shortdistance travelers. the rules and assumptions made for tbs modeling are [11]: (1) the number of buckets is fixed during the ticket booking period, (2) a seat can be put in only a single bucket, (3) a product can relate to at most one bucket, (4) at the beginning of the reservation period, all the seats must be assigned to a bucket, (5) the ticket pool should be set to be empty before the ticket booking process starts, (6) the ticket pool has priority over the buckets for selling tickets, (7) demand for each product is assumed to be stochastic and representable by a probability distribution (mostly normal), (8) the number of seats is assumed to be fixed during the ticket booking period, and (9) no overbooking is considered. tickets with lower prices to occupy the seats instead of more expensive ones are undesirable because airline or railway companies always prefer to sell seats at a higher price. therefore, the allocation of products and seats in the buckets is the most critical factor affecting the profit. iii. formulation and simulation steps two parameters must be set at the beginning of the booking horizon to start the ticket booking process: the number of seats reserved for each bucket ��� and the product set for each bucket, which can be represented by the bucket-product engineering, technology & applied science research vol. 12, no. 5, 2022, 9126-9135 9128 www.etasr.com bulum et al.: application of a seat-based booking control mechanism in rail transport with customer … relationship ���. the value of ��� is assumed to be equal to 1 if product k is in bucket b, and 0 otherwise. all necessary notations are given in table i. table i. notations c total capacity of the train nbuc total number of buckets nprod total number of products b bucket number (b=1, 2, ..., nbuc) k product number (k=1, 2, ..., nprod) cb seat capacity for bucket b δ bucket-product relation vector (δ ∈ {0,1}) pr product vector buc bucket vector rev total revenue or sale income t a small time interval of the ticket booking time horizon t rt revenue of a time interval t decij diversion matrix for products divk number of the diverted customers of product k rcb remaining capacity of bucket b p price vector for products/tickets u product/ticket availability vector (u ∈ {0,1}) dmnd demand vector for products/tickets m mean demand vector for products/tickets s standard deviation vector of demand for products/tickets restk number of customers who did not buy a ticket for product k yet rs random number representing customer requests a ticket for prod rs sale income/revenue vector from sales of each product tk ticket pool that contains the unoccupied seats or tickets qtkk quantity of seats in ticket pool for product k sold vector indicating the number of tickets sold from each product the objective of the seat allocation problem is to find an optimal combination of parameters (��, �) that maximizes total revenue � (��, �) . it can be written as a mathematical formulation as follows: max��,� � (��, �) (1) ∑ ��� = ������ (2) ∑ ��� ≤ 1������ ∀" (3) where ��� ∈ #$, ��� = %0,1', " = 1, … , )*+�. the first constraint in (2) is for the capacity to ensure that each seat is placed in only one bucket. the second constraint (3) states that a product can be found in at most one bucket. the ticket booking process begins when customers arrive to purchase tickets. in an appropriate sampling time, the customer arrival sequence can be approximated as a bernoulli process. the ticket booking horizon is divided into t time intervals in the simulation process. if we assume that at most one customer can book a ticket in each time interval t, all the customers will arrive in the total ticket booking period -. thus, . = 1,2, … , and are equal to the total number of customers. if �0 denotes the revenue from ticket sale in time interval ., then the total revenue � (��, �) is expected to be the sum of each revenue in all time intervals. � (��, �) can be written as: � (��, �) = 123%∑ �0 |���,5 = ��6075 , 8.9�,5 = 0' (4) at the beginning of the booking process, the initial number of seats is determined and fixed, and the ticket pool is empty ( 8.9�,5 = 0 and ���,5 = �� with " = 1, … , )*+� and 9 = 1, … , ):�;< ). �� represents the seat capacity of each bucket, ���,0 denotes the number of remaining seats in bucket b in time interval t and 8.9�,0 denotes the remaining number of product k in the ticket pool in time interval t. revenue in time interval t can be represented as: , , , if product is sold in period 0, if no product is sold in t or 0 k k t t k t p u k t r rest ⋅ =  = (5) revenue �0 depends on the ticket price (p) and the available product (u). the price of product k ( 3� ) is fixed during the ticket booking process, and b�,0 denotes the availability of product k for booking in time interval t. the value of b�,0 is 1 if the product k is available for booking in time interval t, and 0 otherwise (8). � c.�,0 represents the remaining demand, that has not been processed yet, from product k in time interval t and its value can be determined as: � c.�,0 = d� c.�,0 − 1 , if product 9 ls sold in time period .� c.�,0 + 1 , if rl �,0 ≥ 1 � c.�,0 , otherwise (6) rl �,0 denotes the number of diverted customers who could not find tickets for product k in time interval t. rl �,0 may increase by the customer diversion matrix r �vw (will be discussed below) depending on the availability of product k in time interval t or decrease by 1 if the diverted customers find the ticket they want. thus, the value of rl �,0 can be calculated by: , pr , , , | 1,...., , if 0 and no product is sold in time period 1, if product is sold in time period k t kj od k t k t k t div dec j n u div t div k t + = =  =   − (7) the availability of a product for booking depends on whether it is offered by any bucket (∑ ���,0 . ���,0 > 0) or if it is in the ticket pool (8.9�,0 > 0). b�,0 = y 1 , lz ∑ ���,0 . ���,0 > 0 or 8.9�,0 > 00 , otherwise (8) the remaining seat capacities ( ��� ) and the remaining products in the ticket pool (8.9� ) in time interval t+1 depend on the sold product in time interval t. ���,0$[ and 8.9�,0$[ are determined as: ���,0$[ = d���,0 − 1 , if product k sold in time period tand 8.9�,0 = 0 and ���,0 = 1���,0 , otherwise (9) 8.9�,0$[ = ⎩⎪⎨ ⎪⎧ 8.9�,0 − 1 , if product 9 is sold in timeperiod . and 8.9�,0 > 0 8.9�,0 + `�,0 |∀9 , if product 2 is sold in time period . and 8.9a,0 = 08.9�,0 , otherwise (10) `�,0 ∈ %0,1' (for 9 = 1, … , ):�;< ) shows whether there are any available products left for booking when product x is sold. after product x is sold, more than one products can be engineering, technology & applied science research vol. 12, no. 5, 2022, 9126-9135 9129 www.etasr.com bulum et al.: application of a seat-based booking control mechanism in rail transport with customer … transferred to the ticket pool. in each time interval t, the maximum number of products to be transferred to the ticket pool is one less than the total number of products. there are some restrictions in rail transport that are different from those in airlines. there can be as many passengers as the train capacity simultaneously during the whole trip, including the passengers who keep sitting, get on and off the train. these restrictions make the problem very difficult, especially as the number of stops and trains increases. so, revenues cannot be evaluated by simply calculating the difference between demand and capacity. calculating the objective function by the booking process model can be difficult due to the curse of dimensionality. in addition, the fact that the number of products to be sold can be huge and it is challenging to express the parameter `�,0 analytically makes it very hard to find an absolute solution to the problem. therefore, a ga was applied to solve the problem approximately, its steps will be described below. a. customer diversion matrix (cdm) the author in [30] considered the buy-up possibility of customers, i.e. diversion. he defined diversion as the willingness of customers to purchase tickets in a different price class than they initially requested. other studies with diversion are [31-33]. there are very few studies with customer diversion, and they are all related to the airline industry [3437]. this study uses a cdm based on the customers' decisions. table ii shows an example of a cdm, which contains the diversion percentage of customers who decide to make a buyup, wait, or buy nothing. cdm has as many rows as the number of products but has two more columns than the number of products. one of these two extra columns is for customers who prefer to wait and the other for customers who do not want to buy anything. it is not easy to create the r �vw matrix. whereas it was challenging to create an exact profile in the past, as most sales were made at the box offices in stations, nowadays, a lot of data about the booking process can be obtained thanks to online sales. r �vw is the percentage of customers who want to buy a ticket from product j because they could not buy a ticket from product i. for instance, r �bc = 0.4 means that 40% of the customers who could not find any ticket from product 2 decide to buy a ticket from product 3. the total percentage of customers who decide to wait, buy-up, or buy nothing should always be 100%. in other words, the summation of each row in the diversion matrix never exceeds 100%. it is important to note here that in pblc and first-come first-served (fcfs), no waiting list is used, as all tickets are generated before the reservation period begins. table ii. example matrix for dechi 1 2 3 4 5 6 7(w) 8(nb) 1 0 0 0 0 0 0 0 1 2 0.4 0 0 0 0 0 0 0.6 3 0 0.2 0 0 0 0 0.3 0.5 4 0.1 0.2* 0 0 0 0.2* 0 0.7 5 0 0.2 0 0.2 0 0 0.3 0.3 6 0 0 0 0.3 0 0 0.4 0.3 * customers who cannot find product (ticket) 4 can maketheir trip by purchasing ticket 2 and ticket 6 together b. genetic algorithm (ga) the ga is an optimization method and one of the adaptive heuristic search algorithms. at first, the solution parameters are encoded in chromosomes. each chromosome consists of a certain number of gene blocks representing the buckets, and is a solution candidate. the sum of the generated chromosomes constitutes the starting population. if we have a railway line with n stations and seat capacity c on a train, there will be n-1 resources and ):�;< = )() − 1)/2 products. if the example from section ii is considered, table iii illustrates the way the products and buckets are encoded. there are 3 products and 2 buckets. pr1 uses res1 and res2 and it is placed alone in bucket 1 (buc1). zero stands for the absence of any candidates. table iii. encoded buckets and products for a three-stop line example n=3 stations encoded products encoded buckets from..to.. pr1 1->3 pr1=[1 2] buc1=[pr1 0] pr2 1->2 pr2=[1 0] buc2=[pr2 pr3] pr3 2->3 pr3=[0 2] buckets have a predetermined number of cells, symbolized as l*+�. the number of seats, i.e. capacities of related buckets ��, allocated for each bucket is placed in the last cell of a gene, so that the size of a gene should be l*+� + 1. as seen in table iv, a chromosome is encoded as an integer array with the genes arranged in a row. therefore, the chromosome size depends on both the number of buckets used ()*+�) and the size of a gene. table iv. encoded genes and chromosomes for a threestop line example parameters: lbuc=2, nbuc=2, c=100 encoded buckets buc1=[pr1 0] buc1=[pr1 0] buc1=[0 pr1] buc2=[pr2 pr3] buc2=[pr2 pr3] buc2=[pr2 0] encoded genes gene1=[buc1 50] gene1=[buc1 60] gene1=[buc1 60] gene2=[buc2 50] gene2=[buc2 40] gene2=[buc2 40] encoded chromosomes cr1= [gene1 gene2] cr2= [gene1 gene2] cr3= [gene1 gene2] fitness: the performance of a chromosome is evaluated by fitness, which can be calculated using the objective function. genetic operators expand the solution space by producing generations with better characteristics. three basic genetic operators are selection, crossover, and mutation. selection: the selection process copies the existing chromosome to the next generation without making any changes in its genetic structure. we used the roulette method for selection in this research. crossover: crossover is the formation of new individuals by randomly combining the structures of two individuals, namely chromosomes. we use the point-to-point uniform crossover rule, in which a coin is flipped for each gene to decide whether or not it will be included in the offspring. since the chromosomes consist of the bucket and the number of seats allocated to it, the crossover was also performed in two steps according to the crossover rate. mutation: a mutation is performed by replacing one or more of the genes of an existing individual with entirely new engineering, technology & applied science research vol. 12, no. 5, 2022, 9126-9135 9130 www.etasr.com bulum et al.: application of a seat-based booking control mechanism in rail transport with customer … genes. we adopt the uniform mutation rule. the mutation also takes place in two steps. first step: the products in the genes of the randomly selected chromosome are replaced according to the mutation rate with new products that were never selected. buckets with empty cells are filled and the filled ones can be empty. second step: the number of seats in the randomly selected gene of the randomly selected chromosome is increased by 5 or decreased by 5. while performing this, it is essential to check that the number of seats does not fall below zero and does not exceed the capacity. c. simulations in this research, ticket booking is treated as a timedependent process. only one customer arrives in a time interval t, which is a small part of the time horizon. so, the time horizon is divided into t time periods. the arrival of customers is simulated according to poison distribution. a random demand vector is generated with the average demand and standard deviation of demand provided. the customer behavior is simulated by using the cdm. the sales from any product depend on the sales from all other products. therefore, in our model, the demand for a product consists of partially the customers who initially request that product and partially the customers diverting from other products. several algorithms have been written in matlab to simulate the booking process with the procedure shown in table v. various random demands are generated as over, under, and close or equal to the average demand to analyze the different scenarios. in the beginning, the buckets used in the simulation have random initial values that come from the ga. after many simulation rounds, buckets with higher revenue can be achieved in ga via feedback of the simulation results. the values of the ga parameters, i.e. population size, mutation rate and crossover rate, were decided using the experimental design technique proposed by taguchi [38]. ticket requests are primarily responded to by sales from tk, i.e. ticket pool. if there is no appropriate ticket in tk, all the buckets are scanned for the product. it is not enough to find the product in a bucket, it is also necessary to have an empty seat for that bucket. after the sale from buckets, some seats can remain unoccupied. so these are added to tk for reuse next time. if there is no available seat for a product, customers who request a ticket for that product can either choose another product, wait for a seat for that ticket, or leave without purchasing (see figure 4). the simulation algorithm runs until there is no demand and all ticket requests, positive or negative, are met. evaluation and comparison of the techniques are made over a fictional railway line and a real-life example with different demand scenarios. we aim through simulations to observe how tbs differs from the other two ticket booking mechanisms and the effects of customer behavior on the booking process. apart from different random demand scenarios and random arrival sequences, special demand situations were also examined. we specifically set low, high, and equal-to-mean demand scenarios with appropriate random demands. low and high demand represent the demand that is lower and higher than the capacity respectively. equal-to-mean demand is equal or random but too close to the average historical demand. each simulation has been run 100 times with various scenarios. the exhibited results are the average values obtained at the end of the simulation trials. table v. simulation steps start 1. set initial parameters: c, buc, dmnd, decij, tk 2. if there is no request for pr(rs) → go to end 3. else 4. if tk contains available resource(s) for pr(rs) → sale from tk, go to line 2 5. else 6. if buc contains available resource(s) for pr(rs) 7. sale from buc 8. if there is remaining resource(s)/seat(s) → add the remaining resource(s)/seat(s) to tk, go to line 2 9. else 10. if customer wants to buy nothing (with decij) → add pr(rs) to no-buy list, go to line 2 11. else if customer wants to wait (only in tbs !!!) → add pr(rs) to wait list, go to line 2 12. else if the customer wants to buy another ticket → distribute demand to re-buy list by decij, go to line 2 13. else 14. add wait list and rebuy list to dmnd, go to line 2 end fig. 4. flowchart of the booking process steps with customer diversion. iv. computational experiments a. fictive railway line example in this test example, there is a 5-stop railway line with a single train, whose seat capacity is 100. for the stations from a to e, the ticket price in us$ and the demand information of the products is given in table vi. table vi. ticket fares and demand information products 1 2 3 4 5 6 7 8 9 10 a-e a-d a-c a-b b-e b-d b-c c-e c-d d-e price ($) 80 50 30 20 70 40 20 60 30 40 mean demand 75 50 13 5 38 25 5 37 12 63 st. dev. of demand 11.3 6.7 3.1 2.9 4.2 1.7 2.6 4.7 2.8 7.1 engineering, technology & applied science research vol. 12, no. 5, 2022, 9126-9135 9131 www.etasr.com bulum et al.: application of a seat-based booking control mechanism in rail transport with customer … the diversion matrix of this example is generated from random values. as described above, the values in columns 11 and 12 of the 10×12-matrix are the waiting and non-purchase rates respectively. the results for different demand scenarios (under, over, and equal to the mean of the fictional demand) can be seen in figures 5 and 6. the figures show the expected revenue and the number of rejected requests for each scenario. in the figures, tbs_axb stands for tbs with a buckets, each b cells long. the algorithm suggests 3 buckets with a length of 4 cells in this example, but we put some alternative bucket solutions in the figures. as seen in figure 5, in all demand levels, tbs gives a better performance than pblc and fcfs. at every demand level, even if the arrival sequence of customers changes, the performance ranking by revenue is tbs > fcfs > pblc. the way the integration of the customer's behavior into the booking process affects the income can be seen in figure 5. while the effects of customer behavior are minimal on tbs, it appears to have the most significant impact on pblc. especially at low demand level, sales revenue is significantly increased in pblc compared to the case without customer behavior. figure 6 shows that considering customer behavior has not only resulted in improvement in revenue. the number of rejected customers decreased at all demand levels and for all techniques. the amount and rate of change vary according to the customers' demand and arrival sequence. (a) (b) (c) fig. 5. comparison of expected income with/without customer diversion: (a) low demand, (b) mean-equal demand, and (c) high demand. b. real-life railway example as a real-life example, the railway line between ankara and istanbul in turkey was examined. the data were obtained from the statistical and annual reports published on the turkish national railway company website. the incompatible and irrelevant data were extracted or neglected. the company has 7 trains, each with 419 seats, daily departing from ankara to istanbul. there are 9 stations on the line, the first station is in ankara and the last station is in halkali in istanbul. there are 36 products (see table vii) and 8 resources in this example. price and product numbers (in square brackets) of each o-d pair are listed in table vii. average demand and standard deviations of demand (shown in parentheses) of each product can be seen in table viii. (a) (b) (c) fig. 6. comparison graphs showing the number of rejected customers with/without customer diversion: (a) low demand, (b) mean-equal demand, and (c) high demand. table vii. ticket price information and product numbers (in square brackets) for the real-life example price (tl) p o la tl i e sk is e h ir b o z u y u k b il e c ik a r if iy e iz m it is ta n b u l (s .c e sm e ) is ta n b u l (h a lk a li ) ankara 19.5 [8] 37.5 [7] 49.5 [6] 61.5 [5] 73.5 [4] 79.5 [3] 85.5 [2] 96 [1] polatli 28 [15] 43.5 [14] 55.5 [13] 61.5 [12] 67.5 [11] 79.5 [10] 90 [9] eskisehir 19.5 [21] 31.5 [20] 52.5 [19] 52.5 [18] 55.5 [17] 64 [16] bozuyuk 19.5 [26] 37.5 [25] 52.5 [24] 55.5 [23] 64 [22] bilecik 31.5 [30] 49.5 [29] 55.5 [28] 64 [27] arifiye 19.5 [33] 31.5 [32] 38.5 [31] izmit 19.5 [35] 26.5 [34] istanbul (s.cesme) 24 [36] engineering, technology & applied science research vol. 12, no. 5, 2022, 9126-9135 9132 www.etasr.com bulum et al.: application of a seat-based booking control mechanism in rail transport with customer … table viii. mean demand and standard deviation of the demand (in parathesis) for given o-d pairs demand (std.dev.) p o la tl i e sk is e h ir b o z u y u k b il e c ik a r if iy e iz m it is ta n b u l (s .c e sm e ) is ta n b u l (h a lk a li ) ankara 8 (4.1) 121 (6.5) 4 (1.7) 6 (2.4) 7 (7.4) 15 (5.0) 219 (9.1) 32 (4.9) polatli 4 (4.0) 1 (1.4) 1 (2.8) 1 (1.7) 2 (2.2) 7 (6,6) 1 (7.0) eskisehir 1 (1.1) 2 (1.7) 7 (3.2) 17 (5.4) 112 (8.4) 13 (3.2) bozuyuk 1 (2.8) 1 (1.3) 1 (1.6) 3 (6.5) 3 (1.7) bilecik 2 (2.9) 2 (2.6) 6 (4.5) 4 (3.6) arifiye 1 (2.4) 6 (5.7) 4 (5.2) izmit 23 (7.4) 20 (10.9) istanbul (s.cesme) 1 (3.8) the diversion matrix, for this example was created based on the opinions of expert. as mentioned above, the diversion data can be obtained online using new technologies and can be replaced easily in tbs. the matrix has a size of 36×38 and contains zero values for some products. column 37 represents the rate of customers who desire to wait. similarly, column 38 is the rate of customers who prefer to leave without purchasing. the simulation results are summarized in the tables according to the demand levels and whether customer behavior is considered. the obtained results are shown in table ix and figure 7 comparatively. table ix. calculated expected revenues (in tl), sold tickets and rejected customers according to demand scenarios revenue (tl) demand diversion tbs_7x7 pblc fcfs low no 36976 36976 36976 yes 36976 36976 36976 mean-equal no 39079 38084 37787 yes 39154 38159 37811 high no 42567 40793 38663 yes 42634 41020 38742 sold tickets (pcs) demand diversion tbs_7x7 pblc fcfs low no 589 589 589 yes 589 589 589 mean-equal no 624 618 617 yes 629 621 618 high no 709 659 642 yes 719 664 644 rejected customers (persons) demand diversion tbs_7x7 pblc fcfs low no 0 0 0 yes 0 0 0 mean-equal no 35 41 42 yes 30 38 41 high no 95 145 162 yes 85 140 160 the algorithm for tbs suggests 7 buckets with a length of 7 cells after trials of many bucket combinations. in low demand, the expected revenues of all booking techniques are the same or very close to each other. one reason for this may be that all customers can get the tickets they want due to the low demand and sufficient capacity. in high and mean-equal demand scenarios, the differences between the booking mechanisms are evident (figure 7(b)-(c)). tbs shows clearly better performance than pblc and fcfs. if we take the customer behavior into account in simulations, the changes in revenue can be seen in figure 8. again, there are no differences in revenue with or without customer diversion in low-demand scenarios and the reason explained above also applies here. in other demand levels, customer behavior shows its effect. its most significant impact is on tbs, then on pblc, and fcfs. in the simulation, experiments were carried out by diversifying customer arrivals. it has been observed that the effect of the changes in the customers' arrival is shallow, and there is no change in the performance order even though there are minor changes in the revenues. figures 8 and 9 show that incorporating customer behavior into the system increased the expected revenues and decreased the number of rejected customers. in particular, the decrease in the number of rejected customers is quite evident, except for the low demand level (figure 9(a)). (a) (b) (c) fig. 7. expected income with/without customer diversion according to the demand scenarios for the real-life example: (a) low demand, (b) mean-equal demand, and (c) high demand. c. impact of customer behavior simulations were performed with different valued matrices of r �vw to evaluate the customer behavior impact. the tests were carried out in two stages. first, simulations were run with different demand levels while keeping cdm constant. changes were made in cdm in the second stage while keeping the demand constant. engineering, technology & applied science research vol. 12, no. 5, 2022, 9126-9135 9133 www.etasr.com bulum et al.: application of a seat-based booking control mechanism in rail transport with customer … (a) (b) (c) fig. 8. comparison of expected revenues with/without customer diversion according to the demand scenarios for the real-life example: (a) low demand, (b) mean-equal demand, and (c) high demand. (a) (b) (c) fig. 9. changes in the number of rejected customers with/without considering customer diversion according to the demand scenarios: (a) low demand, (b) mean-equal demand, and (c) high demand. as can be seen in figure 10, in low demand, the revenue and the number of tickets sold are not affected by the customer behavior. as the demand increases, the change in income becomes more pronounced and is most significant in tbs. the impact of customer behavior on revenue and ticket sales was primarily monitored in aboveand near-average demands. in the tests conducted with high demand, it has been observed that the effect of customer behavior decreases gradually due to the exhaustion of capacity if the demand is too high. in the second phase, changes were made in r �vw by keeping the demand high above average and keeping it constant. it is important to note that the waiting behavior in the pblc and fcfs methods does not affect revenue and ticket sales, because in these methods, after the capacity of a product is reached, the same product does not open for sale again. in tbs, the re-opening possibility is always present according to the order of the customer's arrival. except for the waiting or no-buy columns, the changes are limited to cells with zero value. it would be easier to reduce the no-buy percentage by encouraging those who leave without buying anything to buy any product. the changes made in columns 1-36 (columns 37 and 38 are adjusted accordingly) had a more significant impact on revenue and ticket sales in pblc and fcfs than in tbs. fig. 10. changes in the expected revenue with considering customer diversion according to the demand scenarios: (a) low demand, (b) mean-equal demand, and (c) high demand. the effect of changes made in the waiting and no-buy columns on revenue and sales can be analyzed by assigning a value of zero to the other columns. so, in figures 11 and 12, w0/nb0 refers the results without cdm. in the expression w01/nb09, w01 represents that all cells in the waiting column get the value 0.1 and nb09 means that all cells in the no-buy column have the value 0.9. similarly, numbers in other expressions (w0x/nb0y) represent ratios for columns 37 and 38. it should be noted that since the ratios in the cells represent a probability, their sum should not exceed 1, so the sum of each row cannot exceed 1. it has been observed that changes in the waiting column significantly impact the revenue and sales with tbs. this impact increases positively as the waiting rate increases (see figures 11-12). in the tests with pblc and fcfs, the slight changes in revenue and sales seen in the figures can be interpreted as a result of the change in the nobuy percentage. the modification of cdm has a remarkable impact on revenue and ticket sales in tbs (up to 3.49% and 2.12% respectively) when the waiting rate (column 37) is changed. this will be instrumental for the development of a different sales strategy or policy to be based on the examination of the effects of customer behavior. engineering, technology & applied science research vol. 12, no. 5, 2022, 9126-9135 9134 www.etasr.com bulum et al.: application of a seat-based booking control mechanism in rail transport with customer … fig. 11. changes in expected revenue with various values of the decij matrix (in percentage). fig. 12. changes in the number of sold tickets with various values of the decij matrix (in percentage). v. conclusion the turkish railway company sells 593 tickets and has an income of 36.866 tl on average in a day per train (2019). with the proposed algorithm (tbs), approximately 630 tickets can be sold in the case of average demand. an income raise of around 2100 tl per train can be expected with revenue up to 39000 tl, which is a good result compared to the current level. tbs gave the best results among the three examined methods. an annual revenue increase of 5.3m tl can be expected if our proposed model is implemented. unlike previous research in which only the customers' choice of a train before departure has been taken into account, this study regards customers' preferences when they cannot find the ticket they want. this research concentrates on evaluating the performance of tbs under customer diversion conditions, which is utilized in our research as a percentage matrix. according to the experts' opinion, customers have 3 possibilities: buying another product, waiting for a seat of the same product or not purchase anything when the desired ticket is unavailable. adding customer behavior to the simulation process helps us find a better revenue-generating bucket. this study is the first application of an alternative booking system for turkish railways and implements a booking system with buckets in turkish railways. this paper also contributes in terms of considering customer behavior in a booking system with buckets. to the best of our knowledge, customer diversion has never been applied before in the railway industry. the proposed tbs performs better than the pblc and the fcfs. when the demand is high, all methods have yielded their best results, i.e. the highest revenue. at low demand, the success of all techniques is very close to each other. the positive aspects of the tbs are the more profitable use of the empty seats with the ticket pool and the effective distribution of the capacity to the products through the buckets. on the negative side, finding the optimum buckets takes time and processing power. if we ignore the misleading results due to the missing data, we can say that the gain will improve with tbs with the available data, even in its pure form. if capacity cannot be increased, it may be wise to encourage customers to wait. thus, empty seats can be sold to customers who prefer to wait for a second sale-period. considering the effects of customer behavior, we can argue that selling tickets in two or more periods will increase revenue. in addition to the increase in revenue, the decrease in the number of rejected customers is obviously important in terms of customer satisfaction. the seat allocation and ticketing processes of high-speed trains are similar to those on airplanes. for this reason, it would be appropriate for railway transportation companies to use technological advances in software to capture customer behavior more precisely. in the railway sector, hybrid algorithms can be tried with artificial intelligence on seat allocation and booking optimization. acknowledgement this paper is a part of the phd thesis of ahmet z. bulum in the graduate education institute, karabuk university, karabuk 2021 [advisor: assoc. prof. dr. muharrem dugenci, coadvisor: dr. mumtaz ipek]. disclosure statement no potential conflict of interest was reported by the authors. references [1] j. i. mcgill and g. j. van ryzin, "revenue management: research overview and prospects," transportation science, vol. 33, no. 2, pp. 233–256, may 1999, 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[38] r. k. roy, design of experiments using the taguchi approach: 16 steps to product and process improvement. new york, ny, usa: wiley, 2001. microsoft word etasr_v12_n6_pp9601-9606 engineering, technology & applied science research vol. 12, no. 6, 2022, 9601-9606 9601 www.etasr.com alsnaie et al.: study and design of a multi-range programmable sensor for temperature measurements study and design of a multi-range programmable sensor for temperature measurements khalid alsnaie electrical engineering department college of engineering imam mohammad ibn saud islamic university riyadh, saudi arabia kalsnaie@imamu.edu.sa sidi m. ahmed ghaly electrical engineering department college of engineering imam mohammad ibn saud islamic university riyadh, saudi arabia smghaly@imamu.edu.sa md. asad ali electrical engineering department college of engineering imam mohammad ibn saud islamic university riyadh, saudi arabia asadali@imamu.edu.sa received: 6 september 2022 | revised: 15 september 2022 | accepted: 17 september 2022 abstract—in this paper, a wide-range high-precision sensor has been designed in order to accurately measure the temperature in a medium with arbitrary temperature variation and the implementation of a wide-spectrum temperature measurement system with a self-selected multi-sensor has been realized. this multi-sensor core is made up of different sensors combined to measure different temperature ranges. this concept can be used for high-precision temperature measurement in electrical capacitance tomography applications. the proposed technique is well suited for temperatures in boilers, industries, and everywhere high temperature measurement sensitivity is needed by using different combined temperature sensors of high precision. keywords-thermocouple; simulation; thermistor; rtd; temperature; linearization; labview i. introduction temperature sensors are among the most widely used sensors in the electronics industry, with applications ranging from safety calibrations to heating, ventilation, and air conditioning (hvac) in various industries. despite their widespread use, temperature sensors and their implementation can present challenges for designers to achieve the best performance at the lowest possible cost. there are many ways to detect temperature. the most common methods use temperature sensors like thermistors, resistance temperature sensors, thermocouples, or silicon thermometers. however, choosing the right sensor is only part of the solution because that sensor must be connected to a signal chain that maintains the integrity of the signal, while providing precise compensation for the unique characteristics of the specific sensing technology to ensure an accurate digital temperature representation [1-4]. this article presents a usb-powered circuit solution to perform this task with a multi range system. this solution uses three sensors which are a negative temperature coefficient (ntc) thermistor, a resistance temperature detector (rtd), and a thermocouple to accurately monitor temperature [5-6]. ii. identification of sensors and their range rtds can be constructed in different forms and have good performance in terms of stability, accuracy, and repeatability. the rtd requires a power source to operate and uses an electrical resistance for measurement of temperature. the operation of the rtd sensor is based on the resistancetemperature relationship of the material used in its construction. the amount of change observed in the resistance value of the material due to a temperature rise per degree is measured and the sensor is calibrated accordingly [7-8]. the resistive element is fragile and always requires insulation, so insulator wires are attached to the element. for temperatures below 250°c, insulators such as silicon rubber and pvc are used for this purpose. a metal alloy chemically inert at this temperature is used as a protective sheath to house the measurement point and the leads. a. rtd wiring configurations rtds come with two-lead, three-lead, or four-lead wires per element. a two-wire rtd is the least expensive, but the lead wire resistance unavoidably affects the measurement results. two-wire rtds are mostly used with short lead wires or where high accuracy is not required. the advantage of the three-wire rtd is that it removes the lead wire resistance from the measurement by adding a third lead wire. four-wire rtd are used where superior accuracy is critical [5]. the callendarvan dusen equation is commonly used to approximate the rtd curve [9]. equation (1) is used for – 200 < °c < 0 and (2) for 0 < °c < 850. 2 3 0[1 ( 100)]tr r at bt ct t     (1) 2 0 [1 ]tr r at bt   (2) where rt is the resistance of the wire at temperature t°c, r0 is the resistance of the wire at temperature 0°c, a, b, and c are constants used to scale the rtd, with a = 3.9083×10 -3 °c‾ 1 , b = -5.775×10 -7 °c‾ 2 , and c = -4.183×10 -12 °c‾ 3 . corresponding author: khalid alsnaie engineering, technology & applied science research vol. 12, no. 6, 2022, 9601-9606 9602 www.etasr.com alsnaie et al.: study and design of a multi-range programmable sensor for temperature measurements the temperature coefficient α = 0.00385c‾ 1 for a platinum wire rtd is given by: 100 0 0( / / c) ( ) / 100 c) o a r r r       (3) b. wheatstone bridge measurement circuit wheatstone bridge circuits are used in sensor circuits. the bridges can be symmetric or asymmetric, balanced or unbalanced. wheatstone bridge circuits can be used to accurately measure unknown impedance. the wheatstone bridge has a single impedance-variable element that is inherently nonlinear, away from the balance point. bridge circuits are commonly used to detect the temperature of a boiler or a process situated away from the actual circuit. usually a sensor element, typically an rtd situated in the hot/cold environment provides the information about resistance change to calculate temperature [10]. resistance-variable wheatstone bridge circuits perform most of the front-end tasks in a design that uses inexpensive and accurate discrete parts. by incorporating an rtd element, the bridge's inherent resistance variations are kept within the accepted linearity and tolerance limits, depending on the manufacturer of the rtd [10]. fig. 1. wheatstone bridge circuit. c. linearization of the output bridge the feedback compensation scheme is used to linearize the output of the bridge. the proposed scheme is shown in figure 2, which is used with an rtd. the output of the bridge vop is amplified by an instrumentation amplifier of gain a to obtain the final output vout. a part of the output is added to a reference voltage vr, employing a unity gain adder and the output of the adder provides the bridge excitation vb. fig. 2. feedback compensation scheme with rtd rt. ��� = �+ � � � � � ���� �� � � (4) ��� = ����� + ���� � (5) where rf = rin, rf is the feedback resistor, rin is the input resistor of the opamp, vout is the the output voltage of the bridge, vref is the reference voltage, and vop the summing voltage of the opamp d. thermistors a thermistor is a temperature sensing element made of sintered semiconductor material that is characterized by large variations in resistance proportional to small changes in temperature. thermistors generally have negative temperature coefficients (ntc thermistors), which means that the resistance of the thermistor decreases as the temperature increases [5]. thermistors are made from a combination of metals and metal oxide materials. once combined, the materials are formed and fired into the desired shape. the thermistors can then be used as disc-shaped thermistors or can be formed and assembled with lead wires and coatings to form bead-shaped thermistors. e. characteristics of an ntc thermistor a thermistor is a temperature-sensitive resistor available in two forms: the positive temperature coefficient (ptc) thermistor and the ntc thermistor. the polycrystalline ceramic ptc thermistor has a high ptc and is generally used in switching applications. the ntc ceramic semiconductor thermistor has a high resistive ntc, which causes its resistance to decrease as the temperature increases. this feature makes it a suitable device for precision temperature measurement. an ntc thermistor has 3 modes of operation: resistance versus temperature, voltage versus current, and current versus time. the mode that exploits the characteristics of resistance versus temperature provides the most accurate results. the circuits of the resistance versus temperature mode configure the thermistor in a "zero power" condition. the zero-power condition assumes that the current or voltage excitation of the device does not cause the thermistor to self-heat. the resistor formula of the thermistor is: 0 0 1 1 exp[ ( )]thr r t t   (6) where rth is the resistance at temperature t°c, r0 the resistance at temperature 25°c, � is the temperature constant, t is the temperature of thermistor, and t0 the temperature at 25°c. equation (6) shows the high degree of nonlinearity of the 4.7kω thermistor. the rate at which the resistance of an ntc thermistor decreases with temperature is the constant β. correction of the non-linear response of the thermistor can be done using a simpler and less expensive hardware technique which, when applied, keeps the linearization problem of the thermistor under control for a range of temperatures of ±25°c. a simple approach to first-level linearization of the thermistor output is to place the thermistor in parallel with a standard (1%, metal-film) resistor and a voltage source. the value of the parallel resistance determines the median of the linear region of the thermistor circuit. the resistance value of the thermistor engineering, technology & applied science research vol. 12, no. 6, 2022, 9601-9606 9603 www.etasr.com alsnaie et al.: study and design of a multi-range programmable sensor for temperature measurements (rt) and the steinhart-hart equation determine the temperature of the thermistor (figure 3). the steinhart-hart equation has proven to be the best mathematical expression for determining the temperature of an ntc thermistor. the equation of the output voltage with linear thermistor is: 2 2 1 1 2 ( ( t out in t r r v v r r r r r r      (7) fig. 3. thermistor circuit with thermistor rt. f. thermocouple the operating principle of thermocouples is essentially based on the seebeck effect. when a temperature difference occurs along a wire, charge transfer occurs. the amount of charge transfer depends on the electrical characteristics of the chosen material. when two wires of different materials are soldered on one side and a temperature difference occurs, a voltage is formed at both free ends. this voltage depends on the temperature difference along the two junctions. to measure the temperature at the junction point, the temperature at the free end must be known. when the free end temperature is unknown, the end must be extended with a compensation cable to a known temperature zone (compensation point) [11]. the compensation point temperature must be known and constant. g. thermocouple linearization techniques a novel circuit for linearization of thermocouple signals using analog – to – digital (adc) converter is proposed. the present method utilizes the ratio metric property of adcs and the converter performs analog to digital conversion as well as linearization. the resulting circuit also has provision for scaling the linearized digital output to obtain a desired fullscale value. the digital count output l of dual-slope integration type a/d converter with differential input is given by: � = �( � ! � " ) (8) where v + in and v in are the analog input voltages, vref an analog reference voltage, and c is the digital count output when [(v + in) – (v in) ] if v + in the voltage signal e(x) from a transducer circuit (x being measured), following an approach proposed by ayman a. ali –a linear relation between l(x) and x can be achieved by suitably modifying (8) such that: �(%) = �(&�')(())/(�&�'(())/(� (9) where the analog reference voltage is: �+,-(%) = (��'(())&�' for positive k �+,-(%) = .`� + 0.(%) for negative k (10) where k is a linearizing coefficient, whose optimum value is to be determined. the linearizing coefficient in terms of circuit resistances is k=r2/r1, where x is the temperature t under measurement and e(x) is e(t) the thermo-e.m.f. from the thermocouple after appropriate reference junction compensation. as an alternate approach, the linearizing arrangement is designed so that the scaling and linearizing mechanisms are independent of each other. then the digital output count is given by: �(%) = �1(&�')(())/(�&�'( ())/(� (11) where a is the scaling constant. if er is adjusted to e(xf), the full-scale digital output is l(xf) = ac. then: �(%) = 2()�)(&�')(())/(�&�'( ())/(� (12) the block diagram representation of the relevant circuit is given in figure 2 of [12]. the proposed circuit's linearity of multi range sensors has been simulated with the virtual process having a temperature variation from 0°c to 100°c and the corresponding flowchart is shown in figure 4. fig. 4. flowchart of the multi-range sensor system. a simulation of the proposed circuit characteristic was conducted in labview [10]. for the linear ntc thermistor, the given parameters were vin = 3.3v, r1= 100ω and b = 3000. the simulated thermocouple had a linear relation between temperature and output voltage, in a temperature range from 0°c to 60°c. for the third sensor, an rtd was used to measure the resistance change and output voltage with temperature with the following parameters: vin = 5v, r1 = r2 = r3 = 100ω, rin = rf = 1000ω, gain = 3.9 and vref = 5v. engineering, technology & applied science research vol. 12, no. 6, 2022, 9601-9606 9604 www.etasr.com alsnaie et al.: study and design of a multi-range programmable sensor for temperature measurements h. multi range temperature sensor simulation block diagram the multi-range sensor system works through a varied range and employs multiple temperature sensors. each sensor has a specific range to measure and to obtain value on the digital display and the corresponding sensor calculation. a simulation of the proposed characteristic was conducted with three linearized sensors (rtd, thermocouple, and thermistor). the diagram that integrates the graphic code of multi range sensor is shown in figure 5. fig. 5. multi range temperature sensor simulation block diagram. iii. simulation results the ntc thermistor sensor was simulated for temperatures from 0°c to 60°c with the circuit shown in figure 3. a good linear relation of the output voltage of the thermistor with temperature was acquired, as shown in figure 6. the thermocouple sensor was simulated at the same range, with the circuit shown in [12]. a good linear relation of the output voltage with the temperature was acquired, as shown in figure 7. for the rtd sensor, linearity was observed in the widest range (from 0°c to 850°c). after applying the feedback compensation method, it has been clearly improved as shown in figure 8. the blue line graph is of the rtd sensor without linearity for the circuit diagram shown in figure 1, and the orange line shows the obtained linearity of the rtd sensor for the circuit diagram shown in figure 2. fig. 6. thermistor voltage output vs input temperature. fig. 7. thermocouple voltage output vs input temperature. fig. 8. rtd voltage output vs input temperature the proposed simulated system consists of three sensors (rtd, thermistor, and thermocouple). the ranges allocated to the rtd sensor, the thermistor, and the thermocouple were from 51°c to 60°c, from 41°c to 50°c, and from 31°c to 40°c respectively. the circuit and parameters for each sensor are the ones mentioned before, but with different ranges. this is an overall temperature measurement system which means that a temperature can be sensed by any sensor in the system as shown in figure 9. the diagram that integrates the graphic code of multi range sensors is shown in figure 10. when the temperature of the system is within the specified sensor range, the sensor starts to measure and shows that with a white led for the measuring sensor and red leds for the sensors which are not measuring (figure 9). fig. 9. representation of measuring sensors with leds. the multi range system provides a linear temperature with auto-selected response over a approximate temperature range from 0°c to +50°c for the thermistor, from 50°c to +70°c for the rtd, and from 70°c to +100°c for the thermocouple. engineering, technology & applied science research vol. 12, no. 6, 2022, 9601-9606 9605 www.etasr.com alsnaie et al.: study and design of a multi-range programmable sensor for temperature measurements fig. 10. simulation of the multi-range temperature system. fig. 11. the auto-selected temperature response of the proposed multirange temperature measurement system. a sufficient number of measurements were carried out by changing temperature ranges assigned to each sensor and the results were preserved. thus, using the proposed method, the devised instrument can measure temperatures from a range of 50°c to around 1000°c. iv. experimental part in this part, we present the experimental results obtained with the developed multi range sensor (figure 12). three temperature ranges were selected for all sensors and the measurements were carried out with the proposed circuits as shown in figures 2-3 and figure 2 of [12] for the respective sensors, with the same parameters used in the simulations for each one. as seen in figure 12, the obtained range of the corresponding output voltage for thermistor is from 1.41v to 1.65v, which corresponds to 41°c to 50°c. in this range, the thermistor is active (on). for the thermocouple, the obtained range of the output voltage is from 1.41v to 1.65v, which corresponds to 41°c to 50°c. in this range, the thermocouple is active (on). finally, for the rtd, the obtained range of the output voltage is from 1.41v to 1.65v, which corresponds to 41°c to 50°c. in this range, the rtd is active (on). fig. 12. photo of the implemented and experimented upon multi-range temperature system. v. conclusion as a part of our study of a wide-spectrum temperature measurement system with self-selected multi-sensor, we presented the design and testing of a high-precision wide-range sensor comprising of three different sensors (thermocouple, thermistor, rtd). a range was assigned to each sensor and simulations were performed in labview. the results from the carried out experiments were in good agreement with the simulation. this concept can be used for different applications such as mri and ect. engineering, technology & applied science research vol. 12, no. 6, 2022, 9601-9606 9606 www.etasr.com alsnaie et al.: study and design of a multi-range programmable 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[12] a. a. aly and a. s. a. el-lail, "international journal of information technology and computer science(ijitcs)," international journal of information technology and computer science, vol. 5, no. 3, pp. 56–60. microsoft word etasr_v13_n2_pp10367-10371 engineering, technology & applied science research vol. 13, no. 2, 2023, 10367-10371 10367 www.etasr.com vu: prediction of the adhesion strength of coating in plasma spray deposition prediction of the adhesion strength of coating in plasma spray deposition duong vu school of engineering technology, duy tan university, vietnam duongvuaustralia@gmail.com (corresponding author) received: 8 january 2023 | revised: 21 january 2023 and 28 january 2023 | accepted: 4 february 2023 abstract the goal of this work is to validate the existing plasma spray mathematical models, using a calculation method and the comparison with experimental data, in order to determine their validity. a preliminary evaluation of the adhesion based on the velocity and temperature of the particles is useful to be calculated by using the mathematical model. given the thermal-physical properties and chemical composition of a febased amorphous x-5 powder, a modified model was suggested. for comparison, a series of experiments using plasma spraying of the x-5 powder were conducted. the significance of the current study consists of the model validation by using the data of the plasma spraying of the fe-based amorphous material as a potential substitution for saving production costs by using ordinary air as the plasma generation gas. the findings show the discrepancy between the models and the experimental results. the prediction of adhesion using the mathematical models does not cover essential parameters such as the enthalpy of the particle stream. it is necessary to improve the mathematical models, including the modified one, based on the experiment results, with different pairs of particles and substrate materials. the proposed formula is applicable during the preliminary design of the spray process and the development of a new torch construction. keywords-adhesion; coating; particle velocity; particle temperature; validity; prediction i. introduction plasma spray deposition is an additive manufacturing technology whose application range extends beyond the traditional thermal spraying approach, including the plasma spraying approach, which relies heavily on melting. the plasma energy encourages the nitriding process to modify the structure and mechanical properties of the surface, but the temperature and chemical process prevail [1]. many engineers and researchers have worked to produce thermal spray technology without melting, and the velocity of the particles is the primary driver in creating the deposition. cold spraying (cs) is the term for this procedure. particles stick to and deposit onto a substrate in cs without melting, allowing functional coatings to be deposited. in recent years, technologies that use particle kinetic energy in addition to thermal energy, such as high-velocity oxy-fuel (hvof) flame spraying and thermal spraying, have been developed. the most common example of these new approaches is the cs method. the natural oxide film on the surface is damaged by repeated particle impacts during the activation phase, known as incubation, and an increase in chemical activity due to the creation of the nascent surface is critical to adhesion. due to the quick impact of the solid particles, it was inferred that the contribution of atomic diffusion to adhesion is low. plastic deformation occurs when the substrate material and particles undergo explosive bonding upon particle contact, undulating in a wavy pattern, and layers are created by mixing in tiny interfacial areas [2]. during this collision, however, severe plastic deformation caused by particle impact might dramatically affect the bonding process, causing shear instability. the natural oxide films on the particle and substrate are removed, and the surface is activated, resulting in the formation of a strong sticky area. the particle and substrate constituent parts are in intimate contact, as shown in tem images, in the absence of inclusions such as the oxide at the adhering interface. as a result, surface activation is a critical element in particle adhesion mechanisms, and the cs technique's massive plastic deformation following impact significantly adds to this surface activation. figure 1 depicts a method in which plastic deformation is triggered by the kinetic energy released by the collision of cs material particles. a material jet in the outer peripheral direction caused by thermal shear instability breaks and eliminates the particles and oxide coating on the substrate surface. a new chemically active surface is revealed, and the new surfaces are strongly connected to each another. in recent publications, some mathematical models describing the plastic deformation have been introduced, including the thermal spraying when the heating particles deposit on the substrate. however, the main disadvantage of these models is the lack of technological parameters, which limits their application in the prediction of adhesion strength in coatings as a significant criterion for deposition evaluation. in engineering, technology & applied science research vol. 13, no. 2, 2023, 10367-10371 10368 www.etasr.com vu: prediction of the adhesion strength of coating in plasma spray deposition this context, a new modified mathematical model dealing with the sufficient prediction of adhesion strength must be introduced and validated. in the event of a disagreement, the empirical formula should be considered the most important recommendation. in this paper, the digital method for the calculation of the predicted adhesion by the digital own program progx100 is described and the amorphous powder x-5 is proposed for the plasma spraying, while in the experimental part the relationships between enthalpy and air flow rate and between adhesion, power of plasma, and velocity of particles were specified, while some significant recommendations and the direction of future studies are presented. ii. methodology significant plastic deformation was found at the interface edge due to the presence or absence of the remaining oxide film, and fracture and strong bonding were observed due to the ease with which the oxide film was removed. on the other hand, the quantity of plastic deformation in the area of the particle center was tiny hence the oxide film persisted even after the impact, generating a very weak bond. according to [3], in addition to substrate hardness, particle velocity and spray angle can influence deformation behavior and the ultimate state of the oxide film. the equation in [1] justifying the role of the critical velocity (vcr) as the condition governing the feasibility of bonding was impacted by a rise in the local temperature beyond the melting point. 667 14 0.08 0.1 0.4cr p m u piv t t          (1) where ρp is the density of the particle, tm is the melting point of the particle, σu is the tensile strength of the particle, and tpi is the initial temperature of the particle. due to adiabatic deformation, when particles hit at high speeds, the particle temperature quickly rises to the melting point. during the collision, much of the kinetic energy of the particle will be transformed into heat, encouraging plastic deformation. softening is expected to produce particles that constitute the material jets. the johnson-cook (jc) model [4] is widely used in manufacturing to simulate high-speed deformation and can be used for high-velocity particle spraying [5, 6]: � = � a + b × �� � � × 1 + × �� × �� ��� � � × �1 − � � � ������ � ���� � � (2) where σ is the flow stress, a, b, c, m, and n are the material constants, �� � is the plastic strain, ��� and ��! are the actual strain and the reference strain rates, respectively, and t, tm, and tref are the actual, melting, and reference temperatures, respectively. the restriction of models (1) and (2) is the practical reference because, in the thermal spray, the activation energy and temperature of the contacting surface at the time of the impact must prevail. in this regard, the kudinov v.v. model should be examined since it simplifies the computation of adhesion in terms of its prediction for designing the thermal process [7]: " #(%) "% = '() − ((*)+×v×exp − ,-. × �/ �×exp 0 . � (3) where ea is the activation energy in this case, v is the frequency of the atoms own oscillation, tk is the contact's absolute temperature, n0 is the number of atoms on the surface of the substrate or particle that make up the mutual physical contact, n(t) denotes the number of atoms energized during the activation time t, s denotes the activation entropy in the chemical reaction zone, and k is the boltzmann constant. since the predominant metal has a bcc or fcc crystal structure, (3) will be transferred to the new type: " #(%) "% = '() − ((*)+×v×exp − ,-. × �/ � (4) the rate of the chemical interaction on the phase boundary is defined by the relative adhesion of the particle with the substrate: 1 (%)1�-2 = #(%)#3 (5) where � (*) is the adhesion resulting for duration t, ��45 is the maximum adhesion obtaining for the entire cycle of the spraying. the influence of the particle velocity on the adhesion can be calculated according to [8]: σ = v 2 ×ρ, where v is the particle velocity and ρ is the density of the particle material. by the integration, (4) will be changed as follows: 1 (%)1�-2 = 1 – exp 6− 7 ×%89: ;-/ ×</= (6) in (6), it is accepted that [7]: ea ≈ k×tk×(lnt0 + 30), t0 = > ?@ab@× c4d (7) for most of the materials, e = 1013×c-1; h = 0.1×d, where d is the diameter of the particle and ea ≈ 1.35 – 1.65 ev. equation (7) describes the change in adhesion depending on the activated temperature during the collision of the particle with the substrate. on the other side, the quantity tk can be calculated with respect to the known equation [7]: tk(t) = t0 + tk 0 ; tk 0 = ( �� f ��)×g�g�h i(a) (8) where h is the height of the solidified particle in the collision on the substrate, t0 is the time during which the particle is solidified and the constant contact temperature tk is activated, t0 is the initial temperature of the substrate, and a1 is the coefficient of the thermal conductivity of the particle. α = f(j�, kl) and α varies in 0 1 depending on j� and kl. j� = kdkl × m4l4d; kl= n ×��c.pp ×q (9) where j� is the criterion of the thermal activity of the particle in relation to the substrate, kl is the criterion defining the latent heat of fusion of particle material, λ1 and λ2 are the coefficients of the thermal conductivity of the particle and the substrate, respectively, a1 and a2 are the coefficients of the thermal diffusivity of the particle and substrate, l is the latent heat of the fusion, c is the heat capacity of the particle, tm is the engineering, technology & applied science research vol. 13, no. 2, 2023, 10367-10371 10369 www.etasr.com vu: prediction of the adhesion strength of coating in plasma spray deposition melting point of the particle material, f(α) is the integral of the probability, and α = f(j�, kl), the root of the function. j� + f(α) = kl r�sla (10) α can be defined by using the φ-α diagram [7], where α is the abscissa of the intersection between the two curves [7]:  = j� + f() = ( j�; ) (11) t = kl × e-s2a = t (kl; α) (12) the temperature during the solidification of the particle is defined by [7], with t1 being the temperature of the particle: tk = �d  g� g�h i(a) (13) given the properties of the particle and the substrate materials, the prediction of the change in adhesion in thermal spraying can be calculated using (6)-(9). the second method is to use (10) and (11) to find the root of the contacting temperature given j� and kl. since the adhesion depends not only on the heating effect, but also on the plastic deformation during the collision of the melting particle on the substrate, it is useful to consider a modified model for the prediction of changes in the adhesion: 1 (%)1�-2 = 1 – exp v− 7 ×%89:w ×( xfy ×z;)[ ×s ×</ \ (14) where ξ is the strain in which the atomic bond in unstable,    is the coefficient of the local overload, σ and σ are the local and average tensile strengths. in case of the collision of the melting particle on the substrate: χ = 1; q = ]^/α, where ]^ and α are the coefficients of thermal extension on the surface and in the volume of the stiff body. the theoretical value of the predicted adhesion is calculated using (13) and (14) by the digital program progx100, given the thermal-physical properties of the materials as follows: the substrate is mild carbon steel, and the particle material is febased amorphous powder x-5 [9]. the chemical composition of powder x-5 is given in table i. table i. chemical composition of x-5 (%,wt) c cr b mo ni mn si nb v w fe 0.73 5.0 0.25 4.20 1.25 0.84 0.54 1.20 remain iii. experimental part the general scheme of the plasma spraying system can be seen in [10]. g1 is the source of power, g2 is the plasma torch, r1 and r2 are the rotameters, v1 and v2 are the valves, n1, n2, n3, n4, and n5 are the nipples, t1 is the thermometer, and t2 is the throttle. the power source is a direct current source with a steep volt-ampere slope, an idle voltage of 300v, and a voltage adjustment limit of 50 to 600v. the plasma arc is conducted according to a two-step scheme. water serves as the coolant, with inlet and outlet via valve v1 and rotameter r1. the thermometer t1 is used to measure the temperature and provide the data needed to calculate the enthalpy of the plasma jet. the accuracy degree of this rotameter is 2.5%. the water flow pressure at the inlet is 0.4-0.6mpa. the primary gas and secondary gas are fed through the v2 valve. the flow rate of gas is determined by the rotameter r2. the throttle t2 is used to smooth the current pulsation. the plasma spraying of powder x-5 experiment was carried out under the following conditions: atmospheric plasma spraying was utilized (sg-100 tafa-praxair, usa). the primary gas was air, and the carrier gas was nitrogen. the chemical composition of fe-based powder was analyzed by energy dispersive spectroscopy with the sm-6510lv. the experimental data are shown in table ii. to measure the velocity of spraying particles, the special highspeed camera shimadzu hpv-1 was used [11]. it is useful to mention that the velocity of the particle stream was measured instead of that of separate particles. the measurement was conducted based on the principles of photogrammetry [12]. the average mass temperature of a plasma jet is evaluated indirectly by enthalpy. because deposition is a continuous process of buildup from the particle stream, it is preferable to compare the average mass temperature to the temperature of the individual particle. the plasma stream containing the particles is a non-equilibrium system with temperature fluctuations over spatial and temporal scales [13]. the enthalpy is defined as the effective power of the plasma jet divided by the consumption of the primary gas [14]. the adhesion strength of the coatings on the steel substrate was determined by the universal compression testing machine (model ht-2101a300, taiwan) according to the astm c633 standard. experiments were conducted with a measurement error of about 2.5%. the empirical equation was derived using the least squares method. on one side, the theoretical calculation using the mathematical models derived with the assumption of separate particles during the collision on the substrate. but on the other side, the experiment was conducted in real conditions when the plasma stream included numerous particles with their own velocity and temperature. the significant value of the validation underlies this work, helping reduce the existing gap between the mathematical models and the experiments. the context stimulates the new modified model as it approaches the real condition and applicable empirical equations for the prediction of the adhesion of the coating. a. case study 1: plasma spray of amorphous powder x-5 the influence of the plasma power and the flow rate of the air on the enthalpy will be investigated in this case. the interval of variation for the flow rate of the air is 0.5g/s in the range of 0.5–3.0g/s. particle size ranges between 40 and 100μm. the spray distance is 120mm. increased power of the plasma stream is expected when the flow rate of the air increases, resulting in the elevated enthalpy of plasma stream with particles (figure 1) [9]. in figure 1, x, ●, and ■ denote current of 120, 180, and 220a, respectively. b. case study 2: investigation on adhesion the material used was again x-5 powder, with particle size ranging in 40–100μm, with 9mm nozzle diameter. the current varied as: 120, 150, 180, 220, and 240a. the flow rate varied engineering, technology & applied science research vol. 13, no. 2, 2023, 10367-10371 10370 www.etasr.com vu: prediction of the adhesion strength of coating in plasma spray deposition between 0.46 and 3.17g/s. the results of the measurement of adhesion bond and velocity are shown in figure 2. c. case study 3: relation between particle velocity and air flow rate this series of experiments occurs when the gas flow rate and the power of the plasma stream (via the current) are changing simultaneously. the data from the measurement of the particle velocity will be used for the evaluation of the adhesion of the coating. the experiment parameters were: x-5 material, size of particles: 40–100μm, nozzle diameter: 9mm (figure 3). fig. 1. relation between enthalpy, plasma power, and air flow rate. fig. 2. relation between adhesion, plasma power, and particle velocity. fig. 3. relation between particle velocity, plasma power, and air flow rate. iv. results and discussion the theoretical result calculation according to (13) and (14) gave the values shown in table ii, given: q = 5, ξ =0. 2, χ = 1, α = 0.33×10 -4 °k -1 , t0 = 300°k (without the preheating) for x-5 powder. table ii. calculation of relative adhesion no tk, ° k vparticle, m/s d, μm σ (t) / σ max, % 1 960 5 70 100 2 960 10 70 100 3 960 15 70 100 4 960 20 70 100 5 960 25 70 100 6 960 30 70 100 7 960 35 70 100 8 960 40 70 100 9 960 45 70 100 10 960 50 70 100 11 960 75 70 100 12 960 100 70 100 13 960 125 70 100 14 960 150 70 100 15 960 175 70 100 16 960 200 70 100 from table ii, the relative adhesion is monovalent (100%) when the particle velocity is changing, which is inconsistent over the course of the experiment in case study 2. when the particle's velocity is low, its kinetic energy is also low, resulting in low plastic deformation and a significantly lower level of dislocation in the structure. this effect probably caused the reduction of the adhesion between the coating and the substrate. this could be taken into account by the coefficient in (14). in case study 1 (see figure 1), the increase in the flow rate had a positive influence on the particle velocity and its temperature (indirectly via the enthalpy of particle flow). however, there is a shroud surrounding this increase, in which the enthalpy of the particle decreases due to the particle's short in-flight time. to create a high density and a good adhesive bond in the coating, one should increase both the velocity and the enthalpy of the particle. however, it is difficult to assess their partial contribution theoretically. as the velocity is increasing, there is a small difference in adhesion bonds for small velocities (less than 40m/s), but in the intensive case, the adhesion bond is approaching the value of 80mpa, which exceeds the maximum limit reported in recent publications [15]. when changing adhesion bonds, the maximum number of them (the pick) tends to shift toward higher velocity as plasma power increases. this means that the adhesion bond depends on both velocity and enthalpy (plasma power). except for very low air flow rates, the tendency of the wear resistance to change with the flow rate of the air almost coincides with the change in the adhesion bond. this can be understood, due to the fact that the low velocity impacts not only the good coherence bond, but also the poor adhesion bond. based on the experimental results in figures 1-3, an empirical formula demonstrating the relationship between adhesion bond, velocity, enthalpy, and current was proposed in [16]: 3 5 6 71 2 4 8 1 δ δ x x x xx x v h i x v h i x   i i i i i i (15) 0 20 40 60 80 100 120 140 160 180 200 0 20 40 60 80 100 a d h e s io n   m p a velocity v, m/s i = 120 a i = 150 a i = 180 a i = 220 a i = 240 a 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 50 100 150 200 p a rt ic le v e lo c it y v  m /s gas flow rate g, g/s i = 120 a i = 150 a i = 180 a i = 200 a i = 220 a coating material: x-5 particle size: 40-100 m nozzle diameter: 9 mm engineering, technology & applied science research vol. 13, no. 2, 2023, 10367-10371 10371 www.etasr.com vu: prediction of the adhesion strength of coating in plasma spray deposition where: x1 = -1.454, x2 = 0.926, x3= -0.398, x4 = 0.003, x5 = 0.836, x6 = 1.182, x7 = 0.9, and x8 = 3598. v denotes the velocity [m/s], δh [j/g] the enthalpy, and i the adhesion bond [mpa]. v. conclusions in this work, the analysis of some mathematical models related to the plastic deformation applicable in the case of plasma spray deposition revealed their limitations for the prediction of the adhesion strength of the coating due to the lack of specific technological parameters such as the power of plasma, the velocity, and the enthalpy of the plasma stream, including particles. the newly modified model takes into account some specific physical and mechanical properties of the material and approaches more the real conditions of the collision of the heating particle onto the substrate. however, the discrepancy with the experiment results requires a significant improvement. meanwhile, the plasma sprayring of fe-based amorphous powder using ordinary air as a plasma generation gas once again proved the importance of the velocity and enthalpy of the particle stream for the strengthening of the adhesion since they positively encourage the plastic deformation according to the johnson-cook model. it is useful to note that as plasma power increases, the maximum values of adhesion shift to higher powers that can reach 80mpa when the power of plasma is approaching 80kw. to the best of the author's knowledge, the empirical formula (15) showing the relative correlation between qualitative parameters of the coating and spray process parameters, including the current, flow rate, plasma power, enthalpy of the torch, and velocity of the particles, had not been published before. this formula can be applied to the preliminary design of not only the plasma gun construction but also the technological process of the deposition. it is useful to continue the research in the future to cover the gap between the mathematical models and the empirical equations in the applicable prediction of the adhesion of the plasma-sprayed coatings. it is necessary to include the technological parameters of the spraying process into the model instead of the typical physical and mechanical properties of the given materials. references [1] h. k. le, "a study on the influence of plasma nitriding technology parameters on the working surface deformation of hypoid gears," engineering, technology & applied science research, vol. 12, no. 6, pp. 9760–9765, dec. 2022, https://doi.org/10.48084/etasr.5365. [2] y. ichikawa and k. shinoda, "current status and challenges for unified understanding of bonding mechanism in solid particle deposition process," materials transactions, vol. 62, no. 6, pp. 691–702, 2021, https://doi.org/10.2320/matertrans.t-m2021813. [3] s. yin, x. wang, w. li, h. liao, and h. jie, "deformation behavior of the oxide film on the surface of cold sprayed powder particle," applied surface science, vol. 259, pp. 294–300, oct. 2012, https://doi.org/ 10.1016/j.apsusc.2012.07.036. [4] g. r. johnson and w. h. cook, "a constitutive model and data for metals subjected to large strains, high strain rates, and high temperatures," in proceedings 7th international symposium on ballistics, 1983, pp. 541–547. [5] m. murugesan and d. w. jung, "johnson cook material and failure model parameters estimation of aisi-1045 medium carbon steel for metal forming applications," materials, vol. 12, no. 4, jan. 2019, art. no. 609, https://doi.org/10.3390/ma12040609. [6] m. j. azizpour, s. norouzi, and d. sajedipour, "an axisymmetrical finite element model for prediction of the bonding behavior in hvof thermal spraying coatings," journal of applied sciences, vol. 12, no. 5, pp. 492–497, 2012, https://doi.org/10.3923/jas.2012.492.497. [7] v. v. kudinov and g. v. bobrov, spray coating. theory, technology and equipment. moscow, russia, 1992. [8] v. i. frolov, v. x. klubnhikin, g. k. petrov, and b. a. iiushin, teknika i tehnologiya termicshexkovo napylieniya. saint peterburg, russia, 2008. [9] d. vu and q. l. thu, "the correlation between main parameters in the air-plasma spraying of fe-based amorphous coatings," in proceedings of the international conference on advanced mechanical engineering, automation, and sustainable development 2021 (amas2021), 2022, pp. 499–506, https://doi.org/10.1007/978-3-030-99666-6_72. [10] d. vu, "designed modification of torch for air-plasma spraying," in proceedings of the international conference on advanced mechanical engineering, automation, and sustainable development 2021 (amas2021), 2022, pp. 453–461, https://doi.org/10.1007/978-3-03099666-6_66. [11] n. a. buchmann, c. cierpka, c. j. kähler, and j. soria, "ultra-highspeed 3d astigmatic particle tracking velocimetry: application to particle-laden supersonic impinging jets," experiments in fluids, vol. 55, no. 11, nov. 2014, art. no. 1842, https://doi.org/10.1007/s00348-0141842-1. [12] k. l. a. el-ashmawy, "simulated photogrammetric data for testing the performance of photogrammetric instruments and systems," engineering, technology & applied science research, vol. 12, no. 5, pp. 9357–9363, oct. 2022, https://doi.org/10.48084/etasr.5224. [13] s. dilmi, f. khalfaoui, and a. boumali, "the effects of superstatistics properties on hot plasma," engineering, technology & applied science research, vol. 12, no. 5, pp. 9342–9346, oct. 2022, https://doi.org/10.48084/etasr.5223. [14] n. zhang et al., "measurement of specific enthalpy under very low pressure plasma spray condition," journal of thermal spray technology, vol. 21, no. 3, pp. 489–495, jun. 2012, https://doi.org/ 10.1007/s11666-012-9738-1. [15] v. matikainen, h. koivuluoto, a. milanti, and p. vuoristo, "advanced coatings by novel high-kinetic thermal spray processes," tiede & tekniika, vol. 2015, no. 1, pp. 46–50, jan. 2015. [16] d. vu, "study of atmospheric plasma spraying of fe-based materials for obtaining wear-resistant coatings," the international journal of modern engineering, vol. 22, no. 1, pp. 50–56, 2021. microsoft word etasr_v13_n1_pp10060-10066 engineering, technology & applied science research vol. 13, no. 1, 2023, 10060-10066 10060 www.etasr.com roy & sahu: technoeconomical analysis of a hybrid energy system for an academic building technoeconomic analysis of a hybrid energy system for an academic building suchismita roy school of electrical engineering, kiit deemed to be university, india roysuchismita@yahoo.co.in (corresponding author) pradeep kumar sahu school of electrical engineering, kiit deemed to be university, india pksahu.nitrkl@gmail.com received: 14 october 2022 | revised: 28 november 2022 | accepted: 30 november 2022 abstract this work is mainly based on the optimal design of a standalone hybrid renewable energy system (hres) consisting of pv/diesel/battery systems, implemented in an academic building. different hybrid system configurations such as pv-diesel generator-battery, diesel generator-battery, and pv-diesel generator are compared based on net present cost (npc) and cost of energy (coe) to find out the best economically viable and environmentally friendly solution. li-ion and lead-acid batteries were taken into consideration, and the optimization was done in homer pro software. the pv-dg-li-ion battery configuration emits approximately 2825387kg/year co2 whereas the conventional dg system emits 4565074kg/year. it is concluded that the pv-dg-li-ion battery configuration provides the cleanest and most environment-friendly and techno-economically feasible solution. keywords-hybrid system; homer; npc; coe; technoeconomical analysis i. introduction nowadays, clean renewable energy sources (ress) play an important role in fulfilling the increasing energy demands and environmental pollution issues, since most are not only abundant in nature, but also environment friendly. the pv system is considered as the most suitable among ress due to several advantages like low cost, environment-friendly nature, and higher efficiency. but due to its intermittency nature, it is often used as sole distributed generation in residential buildings, offices, and academic buildings commonly integrated with storage systems to enhance the stability of the system and power quality issues [1-2]. energy storage techniques such as li-ion and lead-acid batteries were commonly providing services from small to large power applications [3]. li-ion batteries have several advantages over the lead-acid batteries, such as fast charging operation, higher density in power and energy, and lower maintenance cost [3]. different studies on battery energy storage systems reveal that the plays a major key role in energy generation power system when incorporated with ress. two key parameters, npc and coe, are used for evaluating the performance of the battery storage system. the npc of a li-ion battery is relatively better than its counterpart lead-acid battery. moreover, the life cycle of the li-ion battery is more than five years longer than the lead-acid battery when it is interfaced with a solar pv system. the environmental effect along with the maintenance of li-ion battery is also less [3]. though the li-ion battery wins over the lead-acid battery, but still for stationary applications, lead-acid batteries provide better efficiency. the energy storage system not only counter effects the unpredictability and variation in the output power produced by ress but also increases the reliability and efficiency of the system [4-6]. a pv system can also be integrated with wind energy and a diesel generator (dg), in an installment also known as a hybrid energy system (hes) for efficient energy generation and enhanced reliability. if only the dg is operated for the generation of energy, then the overall maintenance and fuel cost will be much higher. hes has also several other disadvantages, such as a higher level of noise and emission of greenhouse gases. when the sources of the hes are integrated with the battery storage system, then the operational cost is drastically reduced. moreover, the daily and seasonal variation demand affects the operational cost. during summer and winter seasons the fuel costs for weekends are higher compared to weekdays. due to lower solar radiation, the use of conventional energy sources increases during winter. so, the variation of daily and seasonal energy demands changes is an important aspect as these affect the operational cost [7-8]. the reliability and compatibility of the pv solar system increases when it is integrated with other energy sources like dgs, wind farms, and battery. such a system is called a hes. presently, the hes powered by ress is the most cost-effective and reliable. engineering, technology & applied science research vol. 13, no. 1, 2023, 10060-10066 10061 www.etasr.com roy & sahu: technoeconomical analysis of a hybrid energy system for an academic building past works have mainly concentrated on the optimal sizing and the economic aspect of the designed hybrid system configuration either with solar pvwind system, solar pv wind-diesel generator system coupled with battery storage system [9-13]. only a few published papers are available that consider the wind resource not adequately available in a particular location. anyhow, the techno economic analysis and the optimal sizing of the hybrid system consisting of pv panels, dg, and a battery system consisting of li-ion and lead acid battery is not available in previous works. since the wind energy resource is not abundantly available for the location under study, it is not considered for the present work. in this paper, the technical and economic analysis of solar/ dg/battery storage hes implemented in an academic building is proposed. the proposed hybrid system consists of pvs, a dg, and a battery storage system consisting of li-ion and/or lead-acid batteries. the techno-economic analysis of the hybrid system is carried out in homer (hybrid optimization model for electric renewable) software based on npc and coe and the results are compared regarding cost-effectiveness and efficiency. the optimal sizing of the system is estimated based on total energy deficit (ted), npc, and coe to meet the load demand of the system. the dg and battery bank are designed to compensate for the load demand during night time when the solar energy is not available. according to the developed methodology, the configurations suggested should ensure 0% ted. the optimal system is decided based on the minimum npc and coe. the optimal hybrid system is designed and compared with other energy sources by using the solar radiation data and ambient temperature obtained from homer for the particular location under study [14-15]. the proposed configuration consists of a solar pv system, a dg along with a battery storage system, a converter, and an inverter system. the converter coverts the ac voltage produced by the dg to dc voltage and the inverter converts the dc voltage produced by the hybrid system into ac to meet the household load requirements. ii. source and load assesment to develop an efficient hybrid system in a particular location, source and load assessment are essential for its techno economical analysis. a. site location the site under consideration is the academic institution kiit deemed to be university, located in the city of bhubaneswar, odisha, india. it consists of 5 academic blocks a, b, c, d, and e (figure 1). block a consists of 10 classrooms, 1 conference hall, 12 laboratories, and 5 washrooms. block b contains the dean's office and 5 administrative offices. block c consists of 12 classrooms, 5 laboratories, and 5 washrooms. block d consists of 6 classrooms, 12 faculty cabins, and 6 washrooms. block e consists of 20 classrooms, 4 laboratories, and 6 washrooms. b. source assessment the institute is located at 20.3555°n, 85.8161°e and solar radiation is plentifully available. during the summer season, the electrical load is quite high, so there is a necessity for grid independent hybrid ress. for this location, solar power is abundantly available. figure 2 shows the monthly variation of solar irradiance and figure 3 shows the monthly temperature variation. fig. 1. building blocks. fig. 2. monthly solar irradiance. fig. 3. monthly temperature variation. c. load assessment maximum load occurs during the daytime hours, from 8 am to 8 pm when the academic activities are carried out. during night time, the load is minimal. during spring months the load is at its peak. during vacations the load is less. the total load demand of the institute is 10427.5kwh/day and the peak load is 1038.1kw. the proposed system is designed to satisfy all the demands economically. the system is designed to mitigate the peak load demand during summer and provide a reliable solution for all the existing energy problems. the hourly load demand and the monthly average solar global horizontal irradiance are plotted with variation of clearness index. with seasonal changes the temperature also varies, so the variation of daily temperature over one year is also plotted. table i provides detailed load calculation of the institution under consideration. the hourly load profile is plotted in figure 4 and the monthly load profile is plotted in figure 5. the total load is maximum at 2pm, obtained from the daily load curve and the monthly peak is during may, i.e. during summer time. iii. resource assessment in this paper, pvs, dg, and batteries were considered as the resources for homer optimization. the location of the institute under study receives plenty radiation all over the year, so it is suitable for harnessing solar energy. engineering, technology & applied science research vol. 13, no. 1, 2023, 10060-10066 10062 www.etasr.com roy & sahu: technoeconomical analysis of a hybrid energy system for an academic building table i. load assesment campus 3, block a load (kw) h/day kwh/day light load 12.072 8 96.576 fan load 6.08 12 72.96 ac and laboratory load 320.234 5 3202.34 total 338.386 3371.876 campus3, block b load (kw) light load 2.357 8 18.856 fan load 2.4 10 24 ac and laboratory load 40.16 5 481.92 total 44.917 524.776 campus 3, block c load (kw) light load 9.395 8 75.16 fan load 4.56 12 54.72 ac and laboratory load 281.145 5 2811.45 total 295.1 2941.33 campus 3, block d load (kw) light load 7.087 8 56.696 fan load 5.12 12 61.44 ac and laboratory load 120.639 5 1206.39 total 132.846 1324.52 campus 3, block e load (kw) light load 26.517 8 212.136 fan load 24.56 12 294.72 ac and laboratory load 175.816 5 1758.16 total 226.893 2265.01 fig. 4. daily load curve. fig. 5. monthly load curve. during summer the temperature can go as high as 45 o c. solar radiation is available for approximately 10-12 hours with longer sunny days during summer whereas during winter the radiation is available for almost 8-10hours with shorter sunny days. during the rainy season, it is hardly available for almost two months. the solar radiation data for this particular location are obtained from the site of nasa using the solar energy database from homer software. the annual average solar radiation is 4.81kwh/m�/day with an average clearness index of 0.519. figure 2 shows the monthly variation in daily radiation which indicates the ample solar radiation available. the energy generated by the pv panels can be expressed as: ��� = � × ɳ × � × � (1) where ��� is the total energy output of the pv panel, ɳ is solar panel efficiency, a is the total panel area (m 2 ), h the average solar irradiance on a tilted panel annually (kwh/m 2 /day), and pr the performance ratio of the panel iv. system description and components the hres can be designed consisting of a pv module, a dg, a power converter, and a battery bank consisting of leadacid or lithium-ion batteries. in this configuration, the pv panels and the battery bank are connected to the dc bus system while the dg is connected to the ac bus system. the electrical load is connected to the ac bus system. the solar pv system generates the power to compensate for the electrical load demands and the excess generated power will charge the battery bank which can be used along with the dg during adverse weather conditions or during night time. the size of all the components used here is chosen such that there is no undue load on the system. the system configuration is given in figure 6. if the energy generated by the hybrid system is more than what is required by the load, the excess energy is stored in the battery. if the energy generated is less than the load demand, then the battery bank will be used. in that scenario, the dg will operate and meet the deficit energy if the state of charge of the battery drops to the minimum value. fig. 6. system configuration. a. pv module in india, there is ample scope for using solar energy which is a major res. the generated power is dc in nature from which the maximum power can be extracted by using the mppt technique. by changing the tilt angle of the solar panel the maximum solar radiation can be received according to the changing position of the sun. the pv power generated can be given by [16]: ��� = ��� ��� �� �� (2) engineering, technology & applied science research vol. 13, no. 1, 2023, 10060-10066 10063 www.etasr.com roy & sahu: technoeconomical analysis of a hybrid energy system for an academic building where ��� is the pv power (w), ��� is the derating factor of pv which includes the effect of dust accumulation and temperature rise, ��� is the rated capacity of the pv panel, �� is the incident solar radiation under operating conditions, and �� is the incident solar radiation under standard operating condition (w/m�).the details of the pv module are given in table ii. table ii. details of τηε pv module variotrack vt -65 value rated capacity 1000kw panel type flat plate operating temperature 45 o c efficiency 17.3% capital cost 602$/kw replacement cost 602$/kw o&m cost 100$/kw b. diesel generator the dg gives the best possible combination for hess incorporating solar res with batteries. in the case of grid integrated systems, dgs provide an efficient backup during power shutdown periods. the capital cost of the dg is minimal but the operation and management cost is quite significant due to the fuel cost. the dg is incorporated into the system to evaluate its environmental impact. the details of the dg are given in table iii [17]. table iii. details of the diesel generator cat 1750 value capital cost 500$/kw replacement cost 450$/kw o&m cost 0.03$/hour lifetime 15000h efficiency 45% c. battery bank the energy produced by the solar pv system depends upon the intermittent solar irradiance. during night time or in bad weather conditions, it is not available. the main constraint of using ress is that they are fluctuating in nature. so, in order to reduce the dependency on res availability, battery energy sources are used in this study. in this work, both lithium-ion and lead-acid batteries were taken into consideration. the details of the battery bank systems are given in tables iv-v. lead-acid batteries are used for residential applications for storing the energy produced by the solar pv system and to provide energy during adverse weather conditions and night time. these batteries have good reliability, low cost, and reduced discharge capacity. despite all their advantages, they have reduced lifetime due to continuous loading and discharges. the lead-acid battery of the surrette s-260 model with a nominal voltage of 12v and string size 2 is considered in this work. the initial state of charge of the battery is 100% and the minimum state of charge is 30%. the throughput of the battery is 1704kwh and its lifetime is 10 years. its capital cost is 205$ and the operation and management cost is 50$/year [6]. table iv. details of lead-acid battery surrette s-260 value nominal voltage 12v nominal capacity 3.12kwh maximum capacity 260ah round the trip efficiency 80% capital cost 205$ replacement cost 205$ o&m cost 50$ lifetime 10years table v. details of lithium-ion battery generic 1kwh li-ion battery value nominal voltage 6v nominal capacity 1kwh maximum capacity 167ah round the trip efficiency 90% capital cost 132$ replacement cost 100$ o&m cost 10$ lifetime 10years lithium-ion batteries can be used as alternatives because they have high efficiency and reliability and prolonged lifetime. their only drawback is that they are quite expensive compared to the lead-acid batteries. the generic 1kwh li-ion battery with a nominal voltage of 6v and string size 4 is considered in this paper. the initial and minimum state of charge is of 100% and 30%, the throughput is 3000kwh, and its lifetime is 10 years. its capital cost is 132$ and the operation and management cost is 10$ [6]. the battery rating should be designed such that it can meet the load demand of the hes. the wh capacity of the battery system is given by (3): ��� = �� × �� × ɳ��� × ɳ��� × � � (3) where c"# represents the wh capacity of the load, �$ is the daily average load in kwh/day, ad is the autonomy of the battery, ɳ%&' and ɳ()* are the efficiency of the battery and the inverter, respectively, and dod is the battery depth of discharge. d. power converter the system consists of both ac and dc systems, so the power converters act as bridges that transfer power between these two systems. the solar pv produces dc power and the dg and the load are connected to the ac. so, power converters act as an interface between these two. the rating of the converter under consideration is 1725kw. the efficiency is 95% and the lifetime of the converter is 10 years. its capital cost is 32189$ and its operation and maintenance cost is 8000$/year [18]. v. homer optimization homer software is used to optimize the hes based on certain input parameters to provide the best possible combination in terms of techno-economical feasibility. the optimization aims to minimize the npc and coe as objective functions. it also computes the size of the pv array, the number of batteries, and the size of the dg and the converter [19-20]. engineering, technology & applied science research vol. 13, no. 1, 2023, 10060-10066 10064 www.etasr.com roy & sahu: technoeconomical analysis of a hybrid energy system for an academic building the npc of the system includes all the installation, operational, and management costs minus the revenue generated over the period. the npc is calculated by: +�� = ,�-.,011203 ,45(7,�) (4) where ��9�,���:�; is the annual total cost of the system ($/year), i is the real interest rate annually (%), t is the time period of the project work (years), and � �(<, =) is the capital recovery factor. fig. 7. hybrid system configuration in homer. coe represents the cost of the production of electricity by the hes under consideration on an annual basis. it is calculated by: �>� = ,�-.,011203 ?@ (5) where ��9�,���:�; is the annual total cost of the system and �a is the annual energy supplied. the payback period (pbp) of the optimal system can also be calculated to ensure that the time period required for the recovery of capital or investment cost should be less: pbp= �9��; ,�b7��; c9d� ,e?×f��:�; ?�ghij ,9�d:kb�79� (6) the proposed hes model developed in homer software is shown in figure 7. the optimization is done based on the input data given in tables ii-v. the project lifetime is 25 years with an expected inflation rate of 2% and a nominal discount rate of 8%. vi. result analysis and discussion the simulation is carried out with the following configurations:  pv-dg-battery (li-ion and lead-acid)  dg-battery  pv-dg  dg the optimization is done on the above-mentioned configurations and the npc and coe of these architectures are determined accordingly in homer. the first configuration is considered for two types of batteries, li-ion and lead-acid. the result analysis shows the list of hybrid energy configurations based on the lowest npc and coe. table vi gives the optimal size of different possible hybrid energy configurations. table vi. optimal size of different configurations system configuration pv (kw) dg (kw) no. of li-ion battery strings no. of leadacid battery strings converter (kw) pv-dg-li-ion batteryconverter 584 1400 274 670 dgli-ion batteryconverter 1400 279 690 pv-dg-leadacid batteryconverter 2921 1400 304 604 dg-lead-acid batteryconverter 1400 306 592 dg 1400 pv-dgconverter 869 1400 172 the total npc, the levelized coe, and the operating cost of all configurations are given in table vii. table vii. cost analysis of all configurations system configuration npc($) coe($) operating cost ($) pv-dg-li-ion battery-converter 21.5m$ 0.437$ 1.65m$ dgli-ion battery-converter 21.58m$ 0.438$ 1.65m$ pv-dg-lead-acid battery-converter 22.91m$ 0.465$ 1.76m$ dg-lead-acid battery-converter 22.98m$ 0.467$ 1.76m$ dg 33.6m$ 0.684$ 2.603m$ pv-dg-converter 33.6m$ 0.684$ 2.603m$ from the above configurations, the pv-dg-li-ion batteryconverter system gives the most cost-effective solution. from table vii, it can be observed that the above mentioned system has an npc of 21.5m$, coe of 0.437$, and overall operating cost of 1.65m$. out of the 6 system configurations, the system containing only dg has the highest fuel cost. among the pvdg-li-ion battery-converter and the pv-dg-lead-acid batteryconverter, the first one gives a better economical solution. although the initial cost of a li-ion battery is more, the life cycle cost is less compared to the lead-acid battery. so, the overall npc, coe, and operating cost of the configuration containing a li-ion battery is less compared to the total cost of a system with a lead-acid battery. the optimal system consists of a pv cell of 584kw capacity, a 1400kw dg, a 670kw converter, and 274 strings of li-ion batteries. the highest amount of electricity is produced in april and may as the solar radiation is the highest during these two months. until around 18:00hr, the pv and the dg of the hes meet the load demand of the system and the surplus energy is used to charge the engineering, technology & applied science research vol. 13, no. 1, 2023, 10060-10066 10065 www.etasr.com roy & sahu: technoeconomical analysis of a hybrid energy system for an academic building battery system. but after that, the solar radiation decreases and it eventually becomes zero by 19:00hrs. during that time the dg alone can't meet the load demand so the battery will be utilized. the load demand decreases after 20:00hrs. therefore, excess power is generated by the dg and the surplus energy is used to charge the battery. figure 8 depicts the cost analysis of all 6 possible configurations in terms of npc, coe, and operating cost. the pbps of all possible configurations are estimated by assuming a project life period of 25 years with inflation rate and nominal discount rate of 2% and 8%, respectively. the pbp of the proposed optimal system consisting of pv-dg-li-ion battery is calculated as 5.6 years which is sufficient to recover all the cost invested in the system. fig. 8. cost chart of various configurations of the hybrid system. vii. environmental effect ress produce clean and sustainable energy. table viii shows the emission of pollutant gases like carbon dioxide (co2), carbon monoxide (co), unburned hydrocarbons, sulphur dioxide (so2), and nitrogen oxide (no) from the different configurations obtained from homer software. compared to the conventional dg system which emits 4565 tons of co2, the optimal hybrid energy system emits 2825 tons which are quite less. this co2 emission reduction is due to the penetration of the res in the system. the other pollutants are also reduced significantly. figure 9 shows the graph of the emission of harmful pollutants by the 6 possible configurations under consideration and it can be observed that the pv-dg-liion battery-converter system emits less pollutants than the other systems. fig. 9. pollutant emissions. table viii. pollutant emissions emissions (kg/year) system configurations pv-dg-li-ion battery-converter dg-li-ion battery-converter pv-dg-lead-acid battery-converter dg-lead-acid battery-converter dg pv-dg-converter co2 2825387 2836377 2887232 2898694 4565074 4561485 co 1187 1191 1213 1217 1917 1916 unburned hydro carbons 385 386 393 395 622 621 particulate matter 160 161 164 165 259 259 so2 7010 7037 7163 7192 11326 11317 no 25389 25488 25945 26048 41022 40990 viii. conclusion in this paper, the techno-economic analysis of a hybrid energy system in homer software for an educational institute is briefly discussed. the annual average solar radiation of the site under consideration is 4.81kwh/m� /day with an average clearness index of 0.519. this is the potential location for the installation of pv/dg/battery system which gives the best economically viable solution by optimizing through homer software. the optimal system consists of a pv cell of 584kw capacity, a diesel generator of 1400kw capacity, a 670kw converter, and 274 strings of li-ion batteries with a nominal voltage of 6v and nominal capacity of 167ah. the conventional diesel generator system is not an economically viable solution due to its high fuel cost. it has also a hazardous effect on the environment due to its high level of emissions. in the present system, the hybrid energy system model is combined with the conventional dg system and the resulting system model gives the best possible result in terms of economy. the system not only reduces the number of operating hours of the diesel generator and hence the fuel cost, but also reduces the emission of harmful gases. it is found that pv-dgli-ion battery system emits approximately 2825387kg co2 per year, when the conventional diesel generator system emits 4565074kg/year. the 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[20] b. u. kansara and b. r. parekh, "modelling and simulation of distributed generation system using homer software," in 2011 international conference on recent advancements in electrical, electronics and control engineering, sivakasi, india, sep. 2011, pp. 328–332, https://doi.org/10.1109/iconraeece.2011.6129804. microsoft word etasr_v13_n3_pp10946-10950 engineering, technology & applied science research vol. 13, no. 3, 2023, 10946-10950 10946 www.etasr.com bargos & romao: predicting the equilibrium product formation in oxy-fuel combustion of octane … predicting the equilibrium product formation in oxy-fuel combustion of octane (c8h18) using numerical modeling fabiano fernandes bargos department of basic and environmental sciences, lorena school of engineering, university of sao paulo, brazil fabianobargos@usp.br estaner claro romao department of basic and environmental sciences, lorena school of engineering, university of sao paulo, brazil estaner23@usp.br (corresponding author) received: 24 march 2023 | revised: 12 april 2023 | accepted: 14 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5881 abstract preserving the environment is a major challenge for modern society, and reducing the greenhouse effect caused by combustion processes is a primary concern. it is known that nitrogen compounds (nox) negatively impact air quality and public health. internal combustion engines, responsible for nearly half of the atmosphere's pollutants, have prompted public policymakers to phase out gasoline and diesel-powered vehicles in the near future. carbon capture and storage technologies, including oxy-fuel combustion, are being developed to address these environmental challenges. to predict exhaust pollutants such as no and co, assuming that the exhaust gases resulting from fuel and air combustion are in chemical equilibrium is a useful approximation. in the current case study, a numerical investigation on the impact of modifying the oxygen content of the reaction mixture from 21% to 100% on the equilibrium composition of c8h18 airenriched combustion was conducted. specifically, the equilibrium-constant approach routines were tailored for 10 species reported in the literature to the conditions of oxy-fuel combustion. additionally, a comprehensive analysis was performed by varying the temperature and equivalence ratio alongside the oxygen level. the results emphasize the intricate interplay between various factors in oxy-combustion and provide valuable insight into the equilibrium product formation in oxy-fuel combustion. notably, the nonuniform reduction of n2 as a function of o2 is highlighted, with an overall reduction rate of 0.93 observed across the range of o2 percentages from 21% to 99%. keywordsair pollution; carbon capture and storage; nitrogen compounds; air-enriched combustion i. introduction the reduction of greenhouse gas emissions, particularly carbon dioxide (co2) from combustion processes, is a crucial challenge in addressing environmental concerns [1-2]. according to [3], it is anticipated that by approximately 2050, co2 emissions will raise by approximately 70% in comparison to the levels observed in the mid-2010s. although co2 is a major contributor to global warming, nitrogen compounds are also a significant environmental concern due to their negative impact on air quality and public health. no (nitric oxide) is a toxic gas that is formed at high temperatures during combustion processes, particularly in internal combustion engines. no can cause respiratory problems, particularly in those with pre-existing respiratory conditions [5, 6]. internal combustion engines, which power most motor vehicles, are responsible for generating nearly half of the atmosphere's nox, co (carbon monoxide), and hydrocarbon pollutants [7]. according to studies carried out in 2011, vehicles powered by internal combustion engines are responsible for 90% of the air pollution in sao paulo, brazil [8]. meanwhile, internal combustion engines have contributed during the last 20 years between 4 and 40% of world pollution [9]. thus, in view of the environmental challenges posed by the use of diesel and gasoline-powered vehicles, public policies are being formulated to phase out the sale and circulation of such vehicles in the near future. france and the united kingdom announced the end of the sales of cars powered by these engines by 2040. this example is followed engineering, technology & applied science research vol. 13, no. 3, 2023, 10946-10950 10947 www.etasr.com bargos & romao: predicting the equilibrium product formation in oxy-fuel combustion of octane … by other european countries, such as germany, and in emerging countries, such as china and india [10]. numerous research centers and industries are currently directing their attention towards the development of carbon capture and storage (ccs) technologies. some of these technologies include pre-combustion capture, post-combustion capture, and oxy-fuel combustion [3, 11]. oxy-fuel combustion is the process of combusting hydrocarbon fuel in a nearly pure oxygen environment, as opposed to air. due to the absence of nitrogen in the intake charge, nox emissions will be eliminated. as a result, co2 and water vapors are the only combustion products [12]. to assume that the exhaust gases resulting from fuel and air combustion are in chemical equilibrium is a useful approximation. this equilibrium scheme serves as the foundation for predicting the quantities of exhaust pollutants, such as no and co, in a kinetically controlled manner [13]. the process of combustion in which a fuel is entirely consumed in the presence of stoichiometric air is referred to as theoretical (or stoichiometric) combustion. this theoretical scenario represents an optimal state in which the ideal balance between oxygen and fuel generates the most heat possible, and maximum combustion efficiency is achieved. there are no unburned combustibles and no excess air [14]. in this case, for ch type fuel, n2, co2, and h2o are the only reaction products. despite the presence of ample oxygen to completely oxidize all fuel, this approach may not yield precise results due to the dissociation of combustion products that occur at high temperatures [10, 15]. the product composition resulting from fuel-air combustion depends on stoichiometry. for example, if the reactants are fuel-rich, there is not enough oxygen to react completely with the fuel, resulting in the formation of additional products such as co and h2, and if the mixture is fuel-lean, there is not enough fuel to consume the oxygen, so there will be unburned oxygen in the product mixture [16]. the equilibrium composition of octane (c8h18)-air mixtures for different temperatures at � = 0.8, 1.0, and 1.2 is presented in [16], with the assumption that the air is composed of 21% oxygen and 79% nitrogen by volume, which means a molar ratio of 1:3.76 between o2 and n2. at low temperatures, for the rich case, the major product species present are n2, h2o, co2, co and h2 whereas for the lean case n2, h2o, co2, and o2. but at higher temperatures (greater than 2200k), these major species dissociate and react to form additional species in significant amounts [9, 10, 15]. to propose a numerical model that accurately predicts the equilibrium products present in a combustion chamber, a chemical equilibrium scheme that accounts for a specific number of species must be utilized [9, 10]. thus, in this case study, we consider the equilibrium combustion model with 10 species, applied for equivalence ratio ∅ < 3 , as suggested in [16]. the equilibrium compositions are determined by adapting the equilibriumconstant approach routines of [13], as presented in [16], to the specific conditions of oxy-fuel combustion. the aim of the present study is to numerically investigate the effect of altering the oxygen content in the reaction mixture from 21% to 100% on the equilibrium composition of c8h18 combustion. ii. methodology we modify the chemical reaction from the 10 species model [16] to allow changes in the oxygen and nitrogen percentage to simulate oxy-fuel combustion. let us consider the following reaction: ϵ∅c�h o�n� + xo� + �1 − x�n� → y� co� + y�h�o + y�n� + y�o� + y� co + y�h� + y�h + y� o + y�oh + y� no (1) where x �0.21 < x < 1.0� is the oxygen percentage. the atomic balance yield is described by four equations: c: ϵ∅α = �y� + y��m (2) h: ϵ∅β = �2y� + 2y� + y� + y��m (3) o: ϵ∅γ + 2x = �2y� + y� + 2y� + y� + y� + y� + y� �m (4) n: ϵ∅δ + 2�1 − x� = �2y� + y� �m (5) where m is the total number of moles. the sum of mole fractions results in: ∑ y+ − 1 = 0� +,� (6) this equation introduces the six equilibrium constants that will give 11 equations for the 10 unknown mole fractions (y+) and the number of moles (m). the reactions are: � � h� ⇌ h k� = /012 3⁄ /5 2 3⁄ (7) � � o� ⇌ o k� = /612 3⁄ /7 2 3⁄ (8) � � h� + � � o� ⇌ oh k� = /8 /7 2 3⁄ /5 2 3⁄ (9) � � o� + � � n� ⇌ no k� = /29 /7 2 3⁄ /: 2 3⁄ (10) � � o� + h� ⇌ h�o k� = /3 /7 2 3⁄ /512 3⁄ (11) � � o� + co ⇌ co� k� = /2 /;/7 2 3⁄ 12 3⁄ (12) the equilibrium constants k+�t� are fitted as: logk@ = aln c d � e + f d + c + dt + et � (13) where t is the temperature, 600 < t < 4000k [13]. the equilibrium constant expressions can be rearranged to express the mole fractions of the 10 species, all in terms of y�, y� , y� and y� , i.e., molar fractions of n2, o2, co and h2, respectively. y� = c�y� � �⁄ , c� = l2 12 3⁄ (14) y� = c�y� � �⁄ , c� = l3 12 3⁄ (15) y� = c�y� � �⁄ y� � �⁄ , c� = k� (16) y� = c�y� � �⁄ y� � �⁄ , c� = k� (17) y� = c�y� � �⁄ y�, c� = k�p� �⁄ (18) engineering, technology & applied science research vol. 13, no. 3, 2023, 10946-10950 10948 www.etasr.com bargos & romao: predicting the equilibrium product formation in oxy-fuel combustion of octane … y� = c�y� � �⁄ y�, c� = k�p� �⁄ (19) by establishing connections between the derived equations and eliminating shared terms, 4 equations can be derived, each with 4 unknownsy�, y�, y� and y�, i.e.: n�o�, o�, o�, o� � = 0 (20) equation (20) constitutes a nonlinear equation system that necessitates an iterative solution via a numerical approach. in this study, we employed the newton-raphson method, and initialized the iterative process with mole fractions derived from a low-temperature combustion model featuring 6 species. we developed a matlab code based on the computational routines of [13], as presented in [16], adapted to the specific conditions of oxy-fuel combustion. a more comprehensive account of the methodology can be found in [16, 17]. iii. results and discussions we compared the equilibrium composition of octane (c8h18)-air mixtures for 21% o2 and 79% n2 to the reaction products when using the parameters in table i. table i. parameters used in numerical simulations fuel % oxygen temperature fuel-air equivalence ratio pressure octane (c8h18) 21, 50, 65, 80, 95 and 99 1500k 3150k 0.8, 1.0, and 1.2 50 bar figures 1-3 illustrate the composition shifts with temperature and equivalence ratio for the combustion of c8h18 considering the parameters presented in table i. in figure 1, c8h18-air mixture (21% oxygen and 79% nitrogen by volume) is assumed and the results are very similar to those found in [13, p. 87]. at low temperatures, for the stoichiometric (∅ = 1) case, the major products species present are n2, h2o, and co2 (table ii). for lean (∅ = 0.8) and rich (∅ = 1.2) cases, although n2, h2o and co2 are still the main product species, other species arise. for the lean case, a significant amount of o2 is present, whereas for the rich case there are co and h2. when the temperature of the reaction rises, the predominant species dissociate and react resulting in relevant additional species. notice that in this case there is an exponential rise in product species such as co, no, oh, o2, o, h2, and h. for lean conditions, the o2 fraction remains relatively unaffected by the changes in temperature. for rich conditions, the h2 fraction initially decreases, but subsequently rises with increasing temperature. the product species co and h2 generally increase with equivalence ratio, while the o2, no, oh, and o mole fractions decrease. it is important to notice that, at high temperatures, a considerable amount of no is produced, which is significant even in relatively low concentration because it is an air pollutant. figures 2-3 clearly show that n2 mole fraction decreases for all equivalence ratios and temperatures while h2o and co2 rise as the oxygen percentage increases. in general, the whole of the analysis done for the case with 21% o2 still stands because the curves have analogous behavior. at lower temperatures, significant amounts of oxygen can still be observed in the lean case, while the rich case shows high levels of co and h2. as the temperature increases, the levels of other species continue to rise exponentially. table ii. percentage of the sum n2+h2o+co2 for ∅ = 1.0 % oxygen temperature 21 50 65 80 95 99 2000 k 99.52 99.23 99.12 99.04 98.97 98.96 3150 k 83.54 69.74 64.12 59.23 55.02 54.07 table ii provides insight into the impact of varying the oxygen input on the sum of products n2, h2o, and co2 at different temperatures for the stoichiometric case (∅ = 1.0). it is noteworthy that for a temperature of 2000k, the sum of products is relatively insensitive to changes in oxygen input. however, at a higher temperature of 3150k, although n2 still tends to zero, there is a significant decrease in the sum of products with increasing oxygen input. notice that for 99% of oxygen at 2000k the percentage of h2o and co2 are 52.19% and 46.04% (table iii) and at 3150k they are 35.49% and 18.10% (table iv), respectively. thus, there is a reduction on co2 and h2o formation with increasing oxygen amount and temperature, which is also observed in air combustion (figure 1). overall, the results presented in tables ii-iv underscore the complex interplay of various factors in oxy-combustion, and emphasize the importance of a holistic approach to achieving the desired outcomes in combustion systems. fig. 1. equilibrium composition of c8h18-air mixtures for different temperatures at ∅ = 0.8, 1.0 and 1.2 for 0.21o2 + 0.79n2. figure 4 shows the ratio between the molar fraction of product species for 80% o2 (figure 3) and 21% o2 (figure 1) combustion. the figure provides a visual representation of the changes for all 10 product species when the oxygen percentage is increased. in this representation, all product species with ratios smaller than 1 decrease with an increase in oxygen engineering, technology & applied science research vol. 13, no. 3, 2023, 10946-10950 10949 www.etasr.com bargos & romao: predicting the equilibrium product formation in oxy-fuel combustion of octane … concentration. conversely, those product species with ratios greater than one exhibit an increase with an increase in oxygen concentration. fig. 2. equilibrium composition of c8h18 combustion for 0.5o2 for different temperatures at ∅ = 0.8, 1.0, and 1.2. fig. 3. equilibrium composition of c8h18 combustion for 0.8o2 for different temperatures at ∅ = 0.8, 1.0, and 1.2. it should be noticed that the molar fraction of n2 for 80% o2 combustion has decreased to around 20% compared to the 21% o2 combustion. in addition, it is observed that n2 reduction is almost insensitive to temperature. in the case of no, it is observed that it also reduces but for the lean (∅ = 0.8) case, 85% of its content remains. nevertheless, when ∅ = 1.2, the concentration of no remains approximately 45% at low temperatures, but it progressively increases at higher temperatures, reaching nearly 60% at 3000k. the amount of co2, h2o, and o2 at low temperature and ∅ =0.8 increased nearly 3.3 times. the amount of co2 tends to rise with the temperature for all values of equivalence ratio. co generally increases with the equivalence ratio and with temperature for ∅ = 0.8 and ∅ = 1.0 but tends to decrease for high temperatures and ∅ = 1.2. tables iii and iv show the percentages of all products from some variations of the parameters shown in table i. it is worth noting that for t = 2000k (table iii), the variation of all products is very low between 95-99% oxygen, except for n2 and no. tables v and vi show the reduction rates of n2 in intervals of input o2. the reduction of n2 as a function of o2 is not constant. from 21%-50% of o2, for every 1% increase in o2, there is a reduction of 1.07% of n2, while between 95%99% of o2, for every 1% increase, the reduction of n2 is 0.74%. overall, from 21% to 99% of o2, the rate of reduction of n2 is 0.93. fig. 4. ratio (0.8o2 / 0.21o2) of the product species for different temperatures at ∅ = 0.8, 1.0, and 1.2. table iii. variation of the % of each product versus % of oxygen input for t=2000k and ∅ = 1 % oxygen 21 50 65 80 95 99 n2 73.31 42.24 28.26 15.46 3.70 0.73 h2o 13.96 30.30 37.67 44.41 50.62 52.19 co2 12.25 26.68 33.20 39.16 44.65 46.04 co 2.25e-01 3.66e-01 4.19e-01 4.63e-01 4.99e-01 5.06e-01 o2 1.03e-01 1.83e-01 2.16e-01 2.47e-01 2.76e-01 2.85e-01 h2 5.66e-02 9.19e-02 1.05e-01 1.16e-01 1.25e-01 1.27e-01 no 5.48e-02 5.56e-02 4.94e-02 3.90e-02 2.02e-02 9.10e-03 engineering, technology & applied science research vol. 13, no. 3, 2023, 10946-10950 10950 www.etasr.com bargos & romao: predicting the equilibrium product formation in oxy-fuel combustion of octane … oh 4.26e-02 7.25e-02 8.43e-02 9.45e-02 1.04e-01 1.06e-01 h 1.70e-03 2.20e-03 2.40e-03 2.50e-03 2.60e-03 2.60e-03 o 1.00e-03 1.30e-03 1.40e-03 1.50e-03 1.60e-03 1.60e-03 table iv. variation of the % of each product versus % of oxygen input for t=3150k and ∅ = 1 % oxygen 21 50 65 80 95 99 n2 67.39 36.56 23.79 12.61 2.80 0.48 h2o 9.08 20.62 25.70 30.27 34.43 35.49 co2 7.07 12.56 14.63 16.35 17.79 18.10 co 4.56 11.47 14.70 17.69 20.50 21.26 o2 2.73 4.89 5.72 6.44 7.09 7.27 h2 2.56 5.12 6.19 7.17 8.14 8.46 no 1.90 1.98 1.76 1.38 0.69 0.29 oh 1.88 3.02 3.42 3.74 4.00 4.04 h 1.51 1.91 2.03 2.13 2.20 2.21 o 1.32 1.87 2.06 2.21 2.36 2.40 table v. decay rate analysis, t=2000k, ∅ = 1 % oxygen (interval) 21-50 50-65 65-80 80-95 95-99 21-99 decay rate -1,07 -0.93 -0.85 -0.78 -0.74 -0.93 table vi. decay rate analysis, t=3150k, ∅ = 1 % oxygen (interval) 21-50 50-65 65-80 80-95 95-99 21-99 decay rate -1,06 -0.85 -0.745 -0.65 -0.58 -0.858 iv. conclusions the study of the oxy-combustion of c8h18 presented in this paper provides valuable insights into the equilibrium products that can be formed during the combustion of this fuel using a 10-species model. significantly, we emphasize that the reduction of n2 is not uniform and varies with the amount of present o2. the reduction rate of n2 was observed to be 0.93 overall, covering the range of o2 percentages between 21% to 99%. the methodology and approach used in this study can also be applied to analyze the products of other types of hydrocarbon fuels (cαhβoγnδ), which is important for predicting the quantities of exhaust pollutants such as no and co in a kinetically controlled fashion. furthermore, the assumption that the burned gases produced by the combustion of fuel and air are in chemical equilibrium is a good approximation for steady-state operating conditions in internal combustion engines. this simplifies the modeling of the combustion process and enables the use of thermodynamic cycle models to estimate engine performance. although significant progress has been made in the study of oxy-combustion during the recent years, it remains a rapidly evolving field with several challenges and open questions that require further investigation. these challenges include issues such as flame instability and the cost of operating an oxycombustion system. in conclusion, while oxy-combustion offers many potential benefits, there are still significant technical and economic challenges that need to be addressed. further research and development efforts are needed to overcome these challenges and fully realize the potential of oxy-combustion for clean and efficient energy production. acknowledgment this research was funded by capes (procs. 23038.000263/2022-19) and cnpq (procs. 426823/2018-4). references [1] v. h. m. nguyen, l. d. l. nguyen, c. v. vo, and b. t. t. phan, "green scenarios for power generation in vietnam by 2030," engineering, technology & applied science research, vol. 9, no. 2, pp. 4019–4026, apr. 2019, https://doi.org/10.48084/etasr.2658. 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[16] c. r. ferguson and a. t. kirkpatrick, internal combustion engines: applied thermosciences, 3rd ed. chichester, west sussex, uk: wiley, 2015. [17] h. k. kayadelen and y. ust, "prediction of equilibrium products and thermodynamic properties in h2o injected combustion for cαhβoγnδ type fuels," fuel, vol. 113, pp. 389–401, nov. 2013, https://doi.org/ 10.1016/j.fuel.2013.05.095. microsoft word etasr_v13_n2_pp10439-10446 engineering, technology & applied science research vol. 13, no. 2, 2023, 10439-10446 10439 www.etasr.com sundaralingam & ramanathan: a deep learning-based approach to segregate solid waste generated … a deep learning-based approach to segregate solid waste generated in residential areas sathiyapoobalan sundaralingam department of electrical engineering, annamalai university, india sathiyapoobalan@gmail.com (corresponding author) neela ramanathan department of electrical engineering, annamalai university, india neelaaueee@gmail.com received: 26 january 2023 | revised: 9 february 2023 | accepted: 11 february 2023 abstract residential waste is a substantial contributor to solid waste generation, which is approximately around 36.5 million tons annually in india. the waste created in households is not separated at the source. all waste is accumulated in a single waste bin and stashed in a nearby public waste bin, resulting in a massive amount of waste being dumped in landfills and also infused with other types of waste, causing environmental pollution. the core objective of this research is to develop a household waste segregator using the tensorflow object detection model and arduino microcontroller. the ssd mobilenet v2 model has been trained with a household dataset consisting of paper, plastic, metal, organic waste, glass, and one more additional empty class to detect whether waste is placed for detection or not. this proposed system can predict the waste class and segregate it into their specific dustbin with mean average precision (map) and recall of 86.5% and 88.3%, respectively. waste segregation and recycling can reduce landfills, lower carbon footprints, increase recycling, recover value from garbage, and lower greenhouse gases emitted from waste. segregation at the source will reduce the cost of the segregation process carried by the municipal solid waste management. keywords-deep learning; waste management; computer vision; embedded system; arduino i. introduction according to the indian central pollution control board's (cpcb) annual report, the country generates 160038.9 tpd (tons per day) of solid waste, of which 152749.5 tpd is collected with a collection efficiency of 95.4%, 79956.3 tpd is processed at 50%, and 29427.2 tpd is landfilled at 18.4%, , and 31.7% (50655.4 tpd), remains unaccounted for [1]. authors in [2] published a spatio-temporal approach to reduce the waste dumped into landfills. waste segregation is the biggest issue encountered in solid waste management, which is the process of accumulating, transferring, processing, and discarding solid waste in a municipality under the purview of a municipal authority. the waste could be collected door to door or by placing public trash bins. the collected waste would be transported to the municipal storage area where they will be processed and the unprocessed waste would be dumped into landfill sites (there are 3184 such dumpsites in india). so far, the waste is segregated manually at the storage location. even though the government takes necessary actions to segregate waste at the source, only a few states can achieve it. in the long run, it is hard for people to maintain separate bins for each waste, so commonly all waste are dropped into a single bin and are handed to the municipal waste collection units. as an outcome, more amount of waste gets dumped into landfills. authors in [3] proposed a reversal approach to handle the municipal solid waste generated in south africa. authors in [4] proposed a real-time deep learning system to sort waste disposed of in public places. authors in [5] developed a robot that can classify waste as organic and non-organic using computer vision [5]. over the past decade, the implementation of deep learning in real-time applications has increased drastically. researchers have been using artificial intelligence techniques to unravel day-to-day problems. deep learning is the subsidiary of machine learning. machines can perform tasks such as prediction, classification, pattern recognition, and clustering [6, 7] when trained. deep learning offers cutting-edge approaches to fully comprehending human behavior [8]. tensorflow is a free and open-source ai and machine learning software library that is used many scenarios but emphasizes especially on deep neural network training and inference [9]. nowadays, machines can extract significant information from digital images, videos, and other visual inputs utilizing an area of artificial intelligence termed as computer vision, and they can act based on that information. the model developed in this work will be trained using a learning method named transfer learning. in this engineering, technology & applied science research vol. 13, no. 2, 2023, 10439-10446 10440 www.etasr.com sundaralingam & ramanathan: a deep learning-based approach to segregate solid waste generated … method the intelligence of one model is transferred to a new model [10], assuming that the model can be thus trained faster and achieve better results quicker than other training methods. authors in [11] developed a model using a convolution neural network (cnn) to classify different types of plastics in waste. to improve the classification accuracy, authors in [12] developed the wastenet model using deep learning with high accuracy. authors in [13] compared the support vector machine (svm) with cnn based on waste classification performance. the pre-trained resnet-34 model [14] was used to classify the waste data collected from the waste bin and the system does not have any segregation unit. authors in [15] developed a model with transfer learning to classify public waste images. the smart waste separator in [16] has been used to classify waste based on shape. the model was developed using hu’s invariant moments and k-nearest neighbor algorithms. authors in [17] developed the model recyclenet to perform classification, especially for recyclable waste with a test accuracy of 81% [17]. authors in [18] developed a deep learning model that can detect and classify waste into seven categories. in [19], images of solid waste were classified using the gabor wavelet transformation (gwt), which combines an image with gabor wavelet kernels of various scales and orientations. authors in [20] implemented a waste segregation model with internet of things (iot) and deep learning. machine learning and iot were used in [21, 22] to isolate the biodegradable and non-biodegradable waste and also to detect the presence of harmful gases in the bin. to segregate waste, the model should be trained on the dataset collected from the area in which the segregator needed to be placed. the current work is mainly focused on segregating household waste. ii. modeling of the waste segregation system in this work, an automatic household waste segregator is proposed. this system can classify household waste into five categories, i.e. paper, plastic, organic, glass, and metal. the dimensions of the segregation system are displayed in figure 1(a). the system has two units: one fixed and one movable as illustrated in figure 1(b). the movable unit of the segregation system has three major parts: (i) platform, (ii) metal track, and (iii) dustbin. the platform of the waste segregation system can move bi-directionally in a metal track and the dustbins are placed below the track. the position of each dustbin is marked in the aluminum using black color and arduino can identify the position of the dustbin using an infrared sensor. waste needs to be placed on the movable platform and the camera placed over the platform would capture the frame and forward it to the custom-trained object detection. the model has been trained in google colab using the tensorflow object detection application programming interface. the object detection model would identify the category of waste and transmit the data to the arduino through serial communication. arduino will use infrared sensors and motors to control and modify the position of the platform based on the information collected. the mobility of the platform is controlled by 2 dc motors connected to wheels and 2 more supporting wheels. when the position of the platform matches the position of the dustbin, the waste will be dropped into the dustbin using the slider which is also controlled by the arduino. (a) (b) (c) fig. 1. waste segregation system: (a) dimensions, (b) block diagram, (c) graphical representation. iii. object detection model tensorflow pre-trained object detection model was used in the automatic household waste segregator. the household waste image dataset was collected using a webcam, with a pixel size of 640×480 and the dataset was trained and tested with 3 pre-trained object detection models. based on the average precision, average recall, and f1 score, ssd mobilenet v2 fpn lite 640×640 was preferred for this work. figure 2 represents the performance evaluation of the models for the household waste image dataset. mobilenet v2 has higher precision, recall, and f1 score than resnet 50 and efficientdet d0. engineering, technology & applied science research vol. 13, no. 2, 2023, 10439-10446 10441 www.etasr.com sundaralingam & ramanathan: a deep learning-based approach to segregate solid waste generated … fig. 2. evaluation of the pre-trained models. a. ssd mobilenetv2 the mobilenetv2 has been designed to be implemented in low-powered devices with moderate performance on classification, as shown in figure. 2. mobilenet is small in size and consumes low computing power. while compared to the architecture of the mobilenet v1 model, the main difference is the inclusion of 1×1 expansion and 1×1 projection layers. table i represents the transformation of data fed into the bottleneck residual block. where m×n represents the size of the input block, k is the size of the input and the output channel, and s is the value that represents the stride. fig. 3. mobilenet v2 block. table i. bottleneck residual architecture input operator output m×n×k 1×1 pointwise conv2d, relu6 m×n×(t k) m×n×(t k) 3×3, depthwise s=s, relu6 (m/s)×(n/s)×(t k) (m/s)×(n/s)×(t k) 1×1 pointwise conv2d (m/s)×(n/s)×k the bottleneck residual block has three layers, the 1×1 expansion layer expands the input value based on the expansion factor which has a default value of t = 6. consider stride=1 in figure 3. the input fed to the expansion layer is 1×160×160×24. the input channel 24 is multiplied with the expansion factor and the output of the layer is 1×160×160×144. the output forwarded to the 3×3 depthwiseconv2d layer applies filters to the input 1×160×160×144, which is forwarded to the 1×1 projection layer. in this layer, the input will be reduced to 1×160×160×24 due to the bottleneck feature. in figure 3, stride=1 is the bottleneck residual block and stride=2 is the formation used to reduce the features of input data [23]. mobilenet base network is used to extract the features from the input image, and the features extracted from the image are forwarded to the ssd network as presented in figure.4. fig. 4. ssd mobilenet architecture. b. data collection and labelling. the household waste image dataset was collected using a webcam and the pixel size was determined to be 640×480. the dataset consists of 6 classes, i.e. organic, paper, metal, glass, and plastic waste. one additional class (empty) was included for determining whether the waste holding platform is free. in [24-26], ultrasonic sensor and pir sensor are used to detect the condition of the platform or waste holding area, to detect whether the waste is placed or not for prediction. this method will eliminate the usage of the ultrasonic sensor in detecting the presence of waste. altogether 1188 images were collected for training the object detection model. in figure 5(a), the number of images per class was presented and the images were labelled using labelimg software as shown in figure 5(b). once the image was annotated labelimg will generate an annotation file with an xml extension. for training the object detection model, google colab platform was preferred. google provides 16gb of workstation gpu free of cost. training the model using gpu will reduce the training period and correspondingly supports achieving the loss convergence faster. however, authors in [27] suggested an algorithm that can generate better results even in non-gpu machines [27]. the model was trained for 5000 steps with a batch size of 4. the number of training steps was limited to avoid overfitting. a momentum optimizer with a cosine decay learning rate of 0.08 is used in the training process. the model was trained with a batch size of 4, which helps the model to be well generalized and also consumes less gpu. it consumes more time for computation but this offers better results in the case of a low dataset scenario. training stops when the total loss of the model drops to 0.2. the frozen inference graph was generated after the training and was downloaded from google colab. engineering, technology & applied science research vol. 13, no. 2, 2023, 10439-10446 10442 www.etasr.com sundaralingam & ramanathan: a deep learning-based approach to segregate solid waste generated … (a) (b) fig. 5. (a) dataset distribution, (b) labelimg interface. iv. automatic household waste segregator prototype a. the prototype most of the parts of the prototype are made up of plastic, except the track which is made up of aluminum. the platform is placed over the track and dustbins were placed below. there is a ridge in the track that holds the wheel of the platform in position. this ridge is responsible for the linear mobility of the platform. the position of the components is shown in figure 6. the object detection python script was running on the laptop, the webcam captures real-time video from the waste platform. if the waste is not placed in the platform, the object detection model will send class empty to the controller through serial communication using the pyserial library. the communication takes place with a baud rate of 115200 bps. when a sample waste is placed on the platform, the object detection model sends the prediction results to the controller. from the perspective of the controller side, the controller waits for the incoming serial data. most of the time the controller receives empty. during that period, the controller stays still. if the controller receives other class names like metal, plastic, paper, glass, and organic as input, the controller will initiate the function to activate the motors in the platform. the infrared sensor in the platform form will locate the position of the respective dustbin with the black mark placed in the tracks. once the position is reached, the motor of the slider gets activated and the waste will be dropped in the dustbin. after this, the platform moves back to the starting position. figure 6 illustrates the process of segregation. in figure 6(a), the platform is in the initial position holding paper waste, whereas in figure 6(b) the platform moves to the paper waste dustbin. (a) (b) (c) (d) fig. 6. (a) initial platform position, (b) platform dropping waste, (c) front view, and (d) top view of the household waste segregation system. b. the algorithm step 1: initiate a webcam interfaced with a laptop, and capture video. step 2: predict the video input, and send the predictions to the arduino controller. step 3: controller reads the serial data. engineering, technology & applied science research vol. 13, no. 2, 2023, 10439-10446 10443 www.etasr.com sundaralingam & ramanathan: a deep learning-based approach to segregate solid waste generated …  if serial data = empty then do nothing.  if serial data = organic then put motors forward until dustbin id = ir sensor variable=1, slider open, drop waste and close, motor reverse until dustbin id = ir sensor variable=1.  if serial data = metal then put motors forward until dustbin id = ir sensor variable=2, slider open, drop waste and close, motor reverse until dustbin id = ir sensor variable=2.  if serial data = glass then put motors forward until dustbin id = ir sensor variable=3, slider open, drop waste and close, motor reverse dustbin id = ir sensor variable=3.  if serial data = plastic then put motor in reverse until dustbin id = ir sensor variable=1, slider opens, drop waste and close, put motors forward until dustbin id = ir sensor variable=1.  if serial data = paper then put motor in reverse until dustbin id = ir sensor variable=2, slider open, drop waste and close, motors forward until dustbin id = ir sensor variable=2. step 4: the controller reads the serial data. in the track, from the initial position of the platform, there will be 3 markings on the right side and 2 markings on the left side as shown in figure 6(a)-(b). figure 6(c) shows the front view and figure 6(d) the top view of the waste segregation system. (a) (b) (c) (d) (e) (f) (g) fig. 7. (a) loss of the model, (b) glass, (c) organic, (d) plastic, (e) empty, (f) metal, (g) paper. v. results and discussion a. object detection model the model has been trained on the household waste image dataset in google colab for 5000 steps. the frozen inference graph generated from the training process was subsequently imported and utilized within python scripts for object detection. these scripts were executed via jupiter notebook on a local machine. the total loss is the sum of classification loss, localization loss and regularization loss. the classification and localization loss are 0.05 and 0.01, demonstrating the model's competence in object classification and localization. the losses at 5000 steps are displayed in figure 7(a) and table ii. the model performance was evaluated using 120 waste images and engineering, technology & applied science research vol. 13, no. 2, 2023, 10439-10446 10444 www.etasr.com sundaralingam & ramanathan: a deep learning-based approach to segregate solid waste generated … was found to have a mean average precision of 86.5% at an intersection over union (iou) threshold of 0.50:0.95, with an average recall of 88% in the same iou range, as presented in table iii. the model's precision and recall can be improved by increasing the sample size of the dataset or modifying the hyperparameters to increase the model's learning rate and detection efficiency. figure 7(b)-(g) displays the real-time detection results, with lower confidence scores for the empty class compared to other classes. this discrepancy is attributed to the comparatively small dataset of 121 images used for empty class training compared to other classes. although the confidence score can predict the class more accurately, a confidence threshold of 0.6 was defined for this model, meaning that the bounding boxes are drawn only when the detection confidence score exceeds 60%. table ii. total loss for 5000 steps metrics intersection over union range (iou) value mean average precision 0.50:0.95 0.865 average recall 0.50:0.95 0.883 table iii. mean average precision and average recall step classification loss localization loss regularization loss total loss 5000 0.053084 0.018455 0.130954 0.202493 b. segregation of waste when the arduino microcontroller receives the data from the object detection model, it activates the motor and moves to the corresponding dustbin. the shown above algorithm, programmed in the controller, locates the position of each dustbin based on the black marking placed in the metal track over each dustbin shown in figure 6(a)-(b), based on the position of the black marking from the center point dustbin id was assigned. the infrared sensor is used to track the corresponding dustbin by detecting the black marks placed, once the platform reaches the destination, the slider will open and waste will drop into the dustbin. then the slider will close as shown figure 8(a)-(b). after the waste is segregated into the dustbin, the platform moves back to the initial position and the process is repeated as illustrated in figure 8(c). in all conditions, dustbin id will be the same for reaching the dustbin as and the starting point. vi. comparison with other waste management systems in the existing waste management systems, the work stops after training and evaluation of the deep learning model. only a few works have developed the hardware for waste segregation. in all segregation systems, the hardware starts the segregation process only after the waste is placed in the waste holding area. the waste placed, can be detected by an ultrasonic sensor and a passive infrared sensor (pir) [24-26]. a comparison between the proposed and existing systems is shown in table iv. in the proposed system, the sensor used to detect the presence of waste was eliminated. instead, images of the empty waste holding platform were collected and included in training, as shown in figure 7(e). the object detection model itself can detect the presence of waste and also predict its category. (a) (b) (c) fig. 8. (a) controller receives serial data, (b) platform reaches to initial position, (c) comparing dustbin id with black mark count value to initiate waste drop sequence. vii. conclusion this article outlines a household waste segregation system utilizing the tensorflow-based object detection model, ssd mobilenet v2 640×640. the model is pre-trained and finetuned on a custom household waste dataset to enable real-time waste segregation. the dataset is comprised of 6 classes, including five major waste categories, namely paper, plastic, organic, glass, and metal. the sixth class, "empty", was added to detect the presence of waste without the need for an ultrasonic sensor. within each class, multiple waste items are included, regardless of their features. for instance, the plastic waste category includes images of various products with engineering, technology & applied science research vol. 13, no. 2, 2023, 10439-10446 10445 www.etasr.com sundaralingam & ramanathan: a deep learning-based approach to segregate solid waste generated … differing shapes, sizes, and colors, such as dairy product covers, chocolate wrappers, toothpaste tubes, soft drink bottles, hair conditioner containers, water bottles, and grocery product wrappers. this heterogeneity in waste generated by households is a result of varying geographical locations and lifestyles, and thus requires a large and diverse dataset and training in a tpu environment. tpus demonstrate improved results and faster convergence compared to gpus, even with larger batch sizes. to optimize the practical implementation of this system, it is necessary to minimize the prototype size. although the waste segregation process is automated, the disposal process still requires manual intervention, with the segregated waste being handed over to the municipal waste collection unit. in the future, mobility can be added to the dustbin through a path guidance system, and a network connecting household bins to municipal waste collection units can be developed to further automate and improve the reliability of the system. table iv. comparision of the proposed system with existng waste management systems author contributions the corresponding author contributed in data collection, model training, hardware design, and drafted the manuscript. the second author supervised the process and proofread the manuscript for publication. references [1] annual report 2020-21 on implementation of solid waste management rules, 2016. delhi, india: central pollution control board, 2022. 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[29] n. m. yusof, a. z. jidin, and m. i. rahim, "smart garbage monitoring system for waste management," matec web of conferences, vol. 97, 2017, art. no. 01098, https://doi.org/10.1051/matecconf/20179701098. microsoft word 4-565-ed.doc engineering, technology & applied science research vol. 5, no. 3, 2015, 811-817 811 www.etasr.com adebimpe et al.: preventive maintenance interval prediction: a spare parts inventory cost… preventive maintenance interval prediction: a spare parts inventory cost and lost earning based model o. a. adebimpe dept of industrial and production engineering, university of ibadan, ibadan, nigeria sebolic@yahoo.com v. o. oladokun dept of industrial and production engineering, university of ibadan, ibadan, nigeria victordokun@yahoo.com o. e. charles-owaba dept of industrial and production engineering, university of ibadan, ibadan, nigeria oecharlesowaba@yahoo.com abstract— in this paper, some preventive maintenance parameters in manufacturing firms were identified and used to develop cost based functions in terms of machine preventive maintenance. the proposed cost based model considers system’s reliability, cost of keeping spare parts inventory and lost earnings in deriving optimal maintenance interval. a case of a manufacturing firm in nigeria was observed and the data was used to evaluate the model. keywords-preventive maintenance; maintenance cost; spare parts inventory. i. introduction the term maintenance can be defined as all actions appropriate for retaining an item/part/equipment in, or restoring it to a satisfactory condition [1]. more specifically, maintenance includes the repair of broken equipment, the preservation of equipment conditions and the prevention of their failure, which ultimately reduces production losses and downtime and also reduces environmental and associated safety hazards. with the increasing pressure of high competition and stringent environmental and safety regulations, maintenance has shifted from being perceived as a “necessary evil” to being recognized as an effective tool for increased profitability. maintenance has become an integrated part of the production process rather than a supporting or peripheral activity. developing effective and optimum maintenance strategies and models has thus become a subject of research both in academic and in industry. preventive maintenance tends to inspect, adjust, replace, lubricates etc the machine components to avoid any likely failure. this involves the usage of consumables and spare parts. some of the components that need replacement have to be replaced, the ones that need adjustment have to be adjusted properly etc in accordance with manufacturers’ specification. in [2], a preventive maintenance system is indicated to consist of routine actions taken in a planned manner to prevent breakdowns and to ensure smooth operational accuracy. industries carry out preventive maintenance (pm) on machinery and equipment to prevent or slow down deterioration. it is important to note that pm is justified only when it is cost effective, reduces the occurrences of failure and extends the useful life of the equipment. the spare parts involved in this activity need to be planned for and well managed to avoid shortages and also unnecessary tying down of capital. the question of how, when and what spare parts to be ordered becomes a challenge to be dealt with by the maintenance team. failure to make proper planning on the spare parts inventory has led to disrupted or poor maintenance operations resulting in economic loss for many organizations. maintenance activities are increasingly becoming complex in view of the rapidly expanding product diversification and the challenge for improved efficiency of manufacturing systems. hence, existing models have considered a lot of ways to predict the optimal preventive maintenance interval, but many have excluded some of the pertinent costs associated with maintenance activities. in order to reflect reality there is the need to capture cost components associated with the spare parts inventory and lost earnings during the preventive maintenance intervals. this study is aimed at determining the optimal preventive maintenance interval that minimizes the cost of spare parts inventory and sum of lost earnings during preventive maintenance activities as a result of loss of production. numerous researchers have demonstrated great efforts towards the study of the preventive maintenance models. an (s, s) pm policy in which the pm work-orders are performed as soon as inventory reaches a certain threshold value, s was described in [3]. pm and safety stock strategies were formulated assuming that the pm tasks are scheduled every m units of time and derived m by minimizing expected cost per unit time. a control policy where the system undergoes repair once it breaks down was described in [4]. the production resumes immediately after repair, continuing until the inventory level reaches a threshold value. a multi-criteria preventive maintenance optimization model to find the optimal preventive maintenance intervals of components in a production system was developed in [5]. an economic manufacturing quantity (emq) model was proposed in [6] and an improvement to a stochastic pm model to find an optimal engineering, technology & applied science research vol. 5, no. 3, 2015, 811-817 812 www.etasr.com adebimpe et al.: preventive maintenance interval prediction: a spare parts inventory cost… policy, where manufacturing quantity and safety stock are derived minimizing the cost per unit time was described in [7]. the basic cost-based approach to maintenance planning that was developed by jardine in 1973 was studied in [8] and was later extended in [9]. machine reliability and preventive maintenance planning were considered for a cellular manufacturing system for an improved performance. a simulation model to find the best preventive maintenance strategy in semiconductor manufacturing plants was described in [10]. an analytical model for the joint determination of an optimal age-dependent buffer inventory and pm policy in a production environment that is subject to random machine breakdowns was formulated in [11]. the optimal preventive maintenance schedules by considering two modes of failure (maintainable and non-maintainable) and the number of pm tasks dependent on different failure rates of the system was investigated in [12]. a development of a combined opportunity cost and reliability model, taking into consideration a factor that was not considered in [8], was described in [13]. a computer-aided preventive maintenance program was developed in [14] in order to improve system availability and maintenance resources. the pm labor force requirement was, the availability of the equipment, reliability and total maintenance cost were modeled. genetic algorithms were employed to find optimum solution for different maintenance planning and scheduling with multi-objective optimization research on multi parallel machine in [15] made. the reliability and time were the two main constraints and due to that, a lower bound for reliability was introduced. an optimal preventive maintenance model for steam turbines where weibull distribution was applied to study the problems of a thermal power station was presented in [2] and it was shown that the total cost of replacement was decreasing as the cycle length was increasing. the model didn’t consider how the components to be replaced are being ordered or the cost which is attached to it. the preventive maintenance strategy and minimal repair were incorporated into the production process in the traditional integrated inventory model in [16] but didn’t take into consideration the inventory of the spare parts needed for the preventive maintenance activities itself rather, they tried to address the problem involved with the supply chain and production. it should be noted that past works on models of preventive maintenance are yet to incorporate the cost of the spare parts inventory cost and the lost earnings during preventive maintenance. consequently, this work develops a model to incorporate these using weibull distribution. ii. model development in this section, the procedure for identifying preventive maintenance cost related parameters for a manufacturing firm is presented. also, outlined are the preventive maintenance cost function development process and the definition and solution procedure to the preventive maintenance optimization problem. to identify preventive maintenance cost parameters, relevant literature was reviewed, some manufacturing firms in nigeria were visited, relevant personnel interviewed, maintenance process observed and relevant records examined. a. model notations this model uses the cost based approach to minimize total maintenance cost that assures the desired level of machine reliability. the following notations of the model are defined: 1. tpm is the preventive maintenance interval. 2. tc is the total maintenance cost for a planning horizon... 3. oc is the fixed cost of carrying out a planned preventive maintenance (preparation cost). 4. pmc is the estimated average preventive maintenance cost per maintenance to return machine to the “as-goodas-new” condition. 5. fc is the breakdown maintenance cost during the interval tpm 6. )(tpmh is the average number of machine failures during the interval tpm 7. md is the estimated average duration for a breakdown maintenance. 8. td is the estimated duration of time used for a preventive maintenance activities. 9. lp is the estimated profit loss per hour by the company due to downtime. 10. occ is the cost of placing an order for the materials that are used in carrying out preventive maintenance activities. 11. hcc is the holding cost of the materials used for preventive maintenance activity in a year. 12. r is the demand of the preventive maintenance material per year. 13. α and β are respectively the scale parameter and the shape parameter of the weibull distribution for the machine in question. 14. t is the total operating time of the machine in a planning horizon. b. model assumptions a. the failure of the machine is characterized by weibull distribution (increasing rate of failure with age). b. there is a fixed cost for carrying out preventive maintenance and it is deterministic c. the cost of executing one breakdown repair is constant and deterministic. d. the preventive maintenance spare parts are ordered in bulk and received in bulk e. there is minimum acceptable reliability of the machine. engineering, technology & applied science research vol. 5, no. 3, 2015, 811-817 813 www.etasr.com adebimpe et al.: preventive maintenance interval prediction: a spare parts inventory cost… f. the ordering cost and holding cost for the bulk preventive maintenance materials are deterministic. g. the replenishment size of the preventive maintenance material is constant and replenishments are made whenever the inventory reaches the prescribed zero level. h. demand is deterministic at a constant rate of r . i. the duration for preventive maintenance is deterministic. j. the depreciation of the equipment is negligible since we assumed that the machine is as good as new each time they are maintained. k. the labors used for the maintenance are the employees of the company so they are always available. c. the cost function development expanding on the cost function of [8], the cost component of this model can be summarized as follows: developing the total maintenance cost function for a planning horizon, where total maintenance cost is defined as the summation of all the costs involved in the maintenance made up of the following components. total maintenance cost={preparation cost of preventive maintenance+cost of executing preventive maintenance+cost of executing breakdown maintenance+lost earnings during breakdown maintenance+lost earnings during preventive maintenance}+cost of preventive maintenance materials inventory management we now describe and develop mathematical expression for each cost component. 1. preparation cost for the preventive maintenance activities oc : this is a fixed cost per preventive maintenance encompassing all cost for mobilizing resources, equipment into site, and cost of all preparatory paper works. 2. cost of executing preventive maintenance pmc : this includes costs of tools materials and labour (include portion of employees’ salary for the involvement in preventive maintenance) 3. cost of executing breakdown maintenance bmc : this includes cost of materials, labour, tools used, for breakdown maintenance within an interval tpm expressed as  )( tpmcc fbm  where, fc is the cost of breakdown maintenance per machine failure and )(tpmh the average number of machine failures during a preventive maintenance interval. note:  )()( tpmtpmh   )(tpmcc fbm  4. lost earnings during breakdown maintenance bmle : this accounts for earning opportunities forfeited during downtime due to sudden failure:  )( tpmpdle lmbm    5. lost earnings during preventive maintenance pmle : this accounts for earning opportunities forfeited during downtime associated with preventive maintenance activities: ltpm pdle  6. cost of spare parts inventory to support preventive maintenance tc : the inventory cost has two components, the holding cost and the ordering cost based on the economic order quantity inventory model. that is, holding cost 2qchc and ordering costs qrcoc . if )(itc is the total cost of inventory per unit time then. qrcqcitc ochc  2)( (1) since rqt  which is the schedule period of ordering then, trq  (2) from (1) and (2) tcrtcitc ochc  2)( (3) since (3) is the unit cost per unit time, therefore the total unit cost over the planning horizon t. then: tctrttctctitc ochc  2.)( note: t is actually equivalent to tdtpm  for a preventive maintenance cycle hence: )(2)(.)( tocthc dtpmctrdtpmtctctitc  (4) therefore: )()( itclelecccttc bmpmpmbmo  i.e tocthclt lmfpmo dtpmctrdtpmtcpd tpmpdtpmcccttc   2)(} )()({)(   (5) therefore, a cost minimization problem can be defined based on the above cost function to determine the optimal values of the preventive maintenance decision variables as follows. engineering, technology & applied science research vol. 5, no. 3, 2015, 811-817 814 www.etasr.com adebimpe et al.: preventive maintenance interval prediction: a spare parts inventory cost… min ( ) { ( ) ( ) ( ) 2 } (6) o pm f t t t m l t l hc t t t oc t t t t tc t c c c tpm d tpm d tpm d tpm t t d p tpm d p tc tpm d r d tpm d tpm t c d tpm b b a a = + + + + + + + + + + + + subject to    1)(1{ tpmrintpm  (7) upperboundtpmr )( (8) where tpmd t t  (9) the model when solved computes the optimum cost and pm interval combination using the objective function (i.e., the total cost tc (t)), the reliability of the machine and the determined values of α and β. the procedure can be repeated for various values of reliability. a series of preventive maintenance intervals and total cost combinations corresponding to different reliability probabilities will be generated to provide a basis for choosing the appropriate maintenance interval that will best suit the needs of the organization depending on the reliability level desired for the concerned machine. d. solution procedure step 1. specify the values of the parameters oc , pmc , fc , td , lp , hcc , r , coc , upperbound ,  and  step 2: compute the optimum tpm using the reliability function of the model developed in (7) step 3: substitute the tpm in the cost objective equation to compute the total cost tc in the model at a minimum reliability and the preventive interval tpm computed. step 4: repeat this for a range of reliability and check for the minimum cost. iii. application, results and discussion the manufacturing firm under study is a cash crop processing company in south-west of nigeria. this company is one of the famous beverages company in nigeria whose products are widely consumed on daily basis across the country and in the neighbouring countries as well. because of the high demand and competitive market in which the firm is involved, there is need for a fact based determination of a realistic planned preventive maintenance interval to avoid downtime experienced as a result of frequent failures, particularly of the critical machine under consideration. the reliability of this machine is of importance as its failure could cause a serious production problem. we shall now apply the firm’s internal data to the developed model to test its validity and realism, and in the process establish an optimal preventive maintenance interval for the critical machine under study. we begin by establishing values of the weibull distribution parameters α and β and other parameters as specified in the solution procedure. the data used are shown in table i. table i. manufacturing firm data used item no. parameters values 1 mtbf (hours) 187 2 β 1.21 3 α 199.61 4 co (naira) 1400 5 cpm (naira) 2560 6 cf (naira) 15190 7 (naira) 4500 8 dm (hours) 2.5 9 t (hours) 8760 (1year) 10 td (hours) 8 (9.13x10-4year) 11 occ (naira) per order 1650 12 hcc (naira)per quantity 250 13 r 700 iv. discussion of results the results of the model are as shown in table ii and figures 1 and 2. this work first considered the inclusion of the spare parts inventory cost which is shown in table ii. the results in table ii show that there is a minimum point at the total maintenance cost (tc) at which the preventive maintenance could take place. this minimum point for the total maintenance cost at 100 percent inventory cost consideration (i.e i=1) is 1,349,105 naira at tpm 173.58 for a planning horizon shown in figure 1 for different percentage of inventory cost. table ii shows that at the 40 percent and 50 percent consideration of inventory cost the tpm are the same though with different total maintenance costs. also, for 70 percent and 80 percent inventory. this implies that there could be a uniform preventive maintenance interval tpm for the machines in a production line even when they have different cost implication, so far the minimum total maintenance cost is considered. considering the lost earning due to preventive maintenance, the results are shown in table iii and described in figure 2. as shown, there is an inverse relationship between the preventive maintenance interval tpm and the total maintenance cost (tc). considering the lost earnings due to preventive maintenance, the total maintenance cost (tc) decreases continually with an increase in the preventive maintenance interval tpm and consequently reducing the reliability of the machine without giving a concise answer of when the maintenance could be done should the cost be given a priority. this suggests that the preventive maintenance interval should not be attached to the money that could be probably lost during the period of maintenance as this could lead to more catastrophic failures if the lost is prioritized. engineering, technology & applied science research vol. 5, no. 3, 2015, 811-817 815 www.etasr.com adebimpe et al.: preventive maintenance interval prediction: a spare parts inventory cost… fig. 1. graph showing the relationship between the total maintenance cost and preventive maintenance interval of a manufacturing firm with spare parts inventory cost consideration at different percentage (i.e. i = 0.1 to 1) fig. 2. graph showing the relationship between the total maintenance cost and preventive maintenance interval of a manufacturing firm with lost earning at 100 percent spare parts inventory cost consideration (i.e. i= 1) engineering, technology & applied science research vol. 5, no. 3, 2015, 811-817 816 www.etasr.com adebimpe et al.: preventive maintenance interval prediction: a spare parts inventory cost… table ii. results of tpm and total cost of maintenance of a manufacturing firm. min r pm interval tpm total cost of maintenance (naira) at i=0.1 i=0.2 i=0.3 i=0.4 i=0.5 i=0.6 i=0.7 i=0.8 i=0.9 0.75 78.66 1297552  1316005  1334459  1352913  1371367  1389821  1408275  1426729  1445182  0.73 84.84 1286017  1303139  1320260  1337382  1354503  1371625  1388746  1405868  1422989  0.71 90.6 1277878  1293923  1309967  1326011  1342055  1358099  1374143  1390187  1406232  0.69 96.11 1271966  1287101  1302236 1317371 1332506 1347641 1362776  1377911 1393046 0.67 101.5 1267620  1281962  1296304 1310646 1324987 1339329 1353671  1368013 1382355 0.65 107.75 1264032  1277554  1291076 1304598 1318120 1331642 1345164  1358686 1372208 0.63 113.81 1261768  1274582  1287396 1300210 1313024 1325837 1338651  1351465 1364279 0.61 119.61 1260519  1272723  1284927 1297130 1309334 1321538 1333742  1345945 1358149 0.59 *125.18 1260021  1271692  1283364 1295036 1306707 1318379 1330051  1341722 1353394 0.57 *131.58 1260155  1271271  1282388  1293504  1304620  1315737  1326853  1337970  1349086  0.55 *138.69 1261036  1271597  1282157  1292717  1303278  1313838  1324398  1334959  1345519  0.53 *145.46 1262463  1272545  1282627  1292709  1302791  1312874  1322956  1333038  1343120  0.51 *151.91 1264262  1273929  1283595  1293262  1302929  1312595  1322262  1331928  1341595  0.49 *158.94 1266627  1275880  1285133  1294385  1303638  1312891  1322144  1331396  1340649  0.47 *166.45 1269537  1278387  1287237  1296087  1304937  1313787  1322637  1331487  1340337  0.45 *173.58 1272601  1281102  1289602  1298102  1306603  1315103  1323603  1332104  1340604  0.43 181.83 1276444  1284574  1292705  1300836  1308967  1317098  1325229  1333359  1341490  0.41 189.63 1280314  1288126  1295937 1303749 1311561 1319372 1327184  1334996 1342807 0.39 193.7 1282410  1290065  1297721 1305376 1313032 1320687 1328343  1335999 1343654 0.37 206.66 1289359  1296559  1303760 1310961 1318161 1325362 1332562  1339763 1346963 0.35 215.78 1294445  1301359  1308273 1315187 1322101 1329015 1335929  1342843 1349757 table iii. results tpm and total cost of maintenance of a manufacturing firm with inventory consideration and lost earning. min r pm interval tpm total cost (naira) min r pm interval tpm total cost (naira) min r pm interval tpm total cost (naira) i=1.0 0.75 78.66 5220784 0.61 119.61 4006922  0.47 *166.45 3243810  0.73 84.84 5157225  0.59 *125.18 3884318 0.45 *173.58 3165904 0.71 90.6 4903070  0.57 *131.58 3756919 0.43 181.83 3083988 0.69 96.11 4689421  0.55 *138.69 3629927 0.41 189.63 3013647 0.67 101.5 4503691  0.53 *145.46 3521220 0.39 193.7 2979394 0.65 107.75 4312505  0.51 *151.91 3427228 0.37 206.66 2880148 0.63 113.81 4148027  0.49 *158.94 3334047 0.35 215.78 2818160 v. summary and conclusion the maintenance records of an existing manufacturing firm reveals that a structured way of determining the preventive maintenance interval will help manufacturing companies to appropriate maximum benefits from application of preventive maintenance policy. the identification of parameters helped improve the existing model and will enhance the practitioners’ idea in capturing the comprehensive costs that are involved in the preventive maintenance activities of the firm. the developed model is suitable for predicting an optimal preventive maintenance interval in a profit oriented manufacturing or service organization, where emphasis is laid on carrying out the preventive maintenance activities at a minimum cost. the model is able to predict an optimum interval for preventive maintenance at a minimum cost for the company and can be used as a decision support system. also it can help determining the actual maintenance cost for each machine and thus evaluate the excesses of the company’s maintenance team. references [1] b. s. dhillon, engineering maintenance: a modern approach , crc press. boca raton fl, 2002 [2] m. g. sobamowo, s. o. ismail, s. j. ojolo, a. a. adebayo, “optimal preventive maintenance models for steam turbines: a case study of egbin thermal station, lagos, nigeria”, international journal of mechanical computational and manufacturing research, vol. i, no. 1, pp 6-11, 2012 [3] m. m. srinivasan, h. s. lee, “production-inventory systems with preventive maintenance”, iie transactions, vol. 28, no. 11, pp. 879– 890, 1996. [4] r. d. meller, d. s. kim, “the impact of preventive maintenance on system cost and buffer size”, european journal of operational research vol. 95, no. 3, pp. 577-591, 1996 [5] c. chareonsuk, n. nagarur, m. t. tabucanon, a multicriteria approach to the selection of preventive maintenance intervals, international journal of production economics, vol. 49, no. 1, pp. 55-64, 1997 [6] k. l. cheung, w. h. hausman, “joint determination of preventive maintenance and safety stocks in an unreliable production environment”, naval research logistics vol. 44, no. 3, pp. 257–272, 1997 engineering, technology & applied science research vol. 5, no. 3, 2015, 811-817 817 www.etasr.com adebimpe et al.: preventive maintenance interval prediction: a spare parts inventory cost… [7] t. dohi, h. okamura, s. osaki, “optimal control of preventive maintenance schedule and safety stocks in an unreliable manufacturing environment”, international journal of production economics vol. 74, no. 1-3, pp. 147–155, 2001 [8] k. das, r. s. lashkari, s. sengupta, “machine reliability and preventive maintenance planning for cellular manufacturing systems”, european journal of operations research vol. 183, no. 1, pp. 162-180, 2007 [9] m. s. talukder, g. m. knapp, “equipment assignment to multiple overhaul blocks in series system”, journal of quality in maintenance engineering, vol. 8, no. 4, pp.319-330, 2002 [10] a. crespo márquez, the maintenance management framework: models and methods for complex systems maintenance, springer series in reliability engineering. springer-verlag. berlin, 2007 [11] j. p. kenne, a. gharbi, m. bei, “age-dependent production planning and maintenance strategies in unreliable manufacturing systems with lost sale”, european journal of operational research, vol. 178, no. 2, pp. 408-420, 2007 [12] i. t. castro, “a model of imperfect preventive maintenance with dependent failure modes”, european journal of operational research vol. 196, no. 1, pp. 217–224, 2009 [13] g. v. ojeih, development of a combined opportunity cost and reliability model for preventive maintenance interval determination, msc project, unpublished, 2012 [14] s. afefy, “maintenance planning based on computer-aided preventive maintenance policy”, international multi conference of engineers and computer scientists (imecs), hong kong, march 14-16, 2012 [15] s. n. mirabedini, h. mina, s. h. iranmanesh, “multi-objective optimization research on multi parallel machine with different preventive maintenance planning and scheduling with genetic algorithm”, international journal of academic research in business and social sciences, vol. 2, no. 12, 2012 [16] f. y. ming, m. s. chien, c. l. ming, h. l. hsu, c. t. wei, “integrated inventory model with decreasing probability of imperfect maintenance in a supply chain”, international multi conference of engineers and computer scientists (imecs), hong kong, march 13-15, 2013 microsoft word etasr_v13_n2_pp10523-10528 engineering, technology & applied science research vol. 13, no. 2, 2023, 10523-10528 10523 www.etasr.com berrag et al.: an experimental study of the dielectric parameters of pvc nano-composites under … an experimental study of the dielectric parameters of pvc nano-composites under corona conditions amine berrag dac hr laboratory, department of electrical engineering, ferhat abbas setif i university, algeria berrag_amine@yahoo.fr (corresponding author) lakhdar madani dac hr laboratory, department of electrical engineering, ferhat abbas setif i university, algeria madani_lakhdar10@yahoo.fr saad belkhiat dac hr laboratory, department of electrical engineering, ferhat abbas setif i university, algeria belsa_set@yahoo.fr received: 13 january 2023 | revised: 28 february 2023 | accepted: 4 march 2023 abstract poly-vinyl chloride (pvc) is a commonly used material used in cable insulation sheaths, but its dielectric properties can be negatively impacted by electric aging. this study investigates the use of nano-fillers, specifically alumina (al2o3), titanium dioxide (tio2), calcium carbonate (caco3), and barium titanate (batio3), in order to improve the dielectric properties of pvc. films of pvc were doped with nano-fillers and were then exposed to an alternating voltage of 15kv for various time periods (1, 2, and 3 hours). the dielectric properties of pvc were measured using an impedance analyzer, and the results indicated that the use of these nano-fillers had a positive effect on the dielectric characteristics of pvc. keywords-pvc; polymer composite; dielectric parameters; corona discharge i. introduction polymeric electrical insulation is subjected to electric fields and thermal stresses in distribution power lines, making it crucial to develop new insulation coordination procedures to improve electric insulation parts in substations. in recent years, nanotechnology has been increasingly utilized in the synthesis of polymer-nano-composites, which have shown improved mechanical, electrical, and chemical properties [1-4]. dielectric spectroscopies in time and frequency domains are useful tools for evaluating and diagnosing electrical insulation and understanding the dynamics of complex solid polymer systems [5-7]. metal oxide nanoparticles in polymers have been studied as alternative materials for electrical applications [8-11]. studies have demonstrated that the incorporation of nanoparticles in similar systems can have both positive and negative effects on breakdown strength [12-14]. furthermore, it has been established that the production of artificial reinforcement fillers can lead to either an increase or decrease in the dielectric strength of polymeric composite insulation, which is utilized in high voltage outdoor applications [15]. polyvinyl chloride (pvc) is a commonly used polymer in industrial and communication applications. it is preferred due to its ease of production and processing, good adhesion with reinforcing elements, and resistance to corrosive environments. in addition, pvc has ductile electrical performance and excellent dielectric strength, low dielectric permittivity, low loss factor, and favorable thermo-mechanical behavior. pvc has been utilized as electrical insulators in distribution for a long time due to these properties [16]. a study of pvc's compression behavior was conducted in which its dielectric reaction was evaluated within the frequency range of 20hz-1ghz [17]. various research efforts have focused on developing high-performance materials with exceptional dielectric properties [18-23]. modern polymer nano-composites have gained significant attention for their expanded applicability. there has been a growing interest in utilizing nanotechnology to improve the dielectric properties of materials. in this regard, research has been conducted to investigate the impact of different nanoparticles, such as clay, fumed silica, zinc oxide, and titanium dioxide, on the electric and dielectric loss performance of pvc in experimental settings. as the field of polymer nano-composites continues to engineering, technology & applied science research vol. 13, no. 2, 2023, 10523-10528 10524 www.etasr.com berrag et al.: an experimental study of the dielectric parameters of pvc nano-composites under … advance, this study examines how the type and concentration of nanoparticles at various voltages and frequencies (10hz10khz) affect the electric and dielectric characteristics of pvc [24-32]. corona discharge is a significant factor that can have a notable impact on the properties of polymeric insulating materials like pvc. several studies have investigated the effect of corona discharge on the surface properties of rtv and htv silicone rubber filled with micro-sized alumina trihydrate (ath) fillers, utilizing various corona generation techniques [34, 35]. authors in [36, 37] reported improved corona resistance performance of silicone rubber composites. the focus of the current paper is to examine the impact of different types of nano-fillers and their loading on the dielectric characteristics of pvc composites when subjected to ac corona discharge. ii. experimental setup table i provides information on the composition of the samples analyzed in this study. the main component of the samples was pvc resin of the 4000m type, which is commonly used in the algerian industry. an antioxidant (barium-zinc) was added to ensure thermal stability, and dicumyl peroxide was used as a linking agent, along with lubricant and plasticizer dop (di-octyle phatalate) from zhengzhou p&b chemical co., ltd (99.5%). according to [38], two types of samples were prepared: standard pvc and 4 ceramic-doped pvc samples with 10% of batio3, al2o3, tio2, and caco3, respectively. the formulation was mixed in a two-roll mixer at a temperature of 160°c for 10 minutes. the resulting mixture was then formed into sheets of predetermined thickness, which were subsequently cut into 10cm×10cm squares with a thickness of 0.3mm. some of the composite samples were subjected to electric discharge at 15kv for 1, 2, and 3 hours, as shown in figure 1. table i. samples used 1 2 3 4 5 pure pvc pvc + 10% batio3 pvc + 10% al2o3 pvc + 10% tio2 pvc + 10% caco3 fig. 1. samples before and after electric aging. the electrical aging of the specimens was performed in the high voltage test chamber of the hv laboratory at the mouloud mammeri university of tizi-ouzou. the experimental setup for electrical aging is shown in figure 2(a), and the test protocol involved the following steps [39]:  the test protocol for electrical aging involved placing the specimen between 2 flat-tip electrodes, with the upper electrode connected to the high voltage and the lower electrode connected to the ground. the electrodes were carried by a bakelite support designed to be perfectly opposite and perpendicular to the plane, and to facilitate adjustment of the inter-electrode distance and ensure good contact with the sample. an alternating voltage of 15kv was applied to the specimen for 1, 2 and 3 hours.  to avoid the phenomenon of contentment, a green plastic plate or other material with a surface area greater than that of the sample was placed between the contact electrode (lower) and the test specimen, as shown in figure 2(b).  after placing the specimen between the electrodes and the plastic plate, the chamber door was closed, and the main circuit breaker for the faraday chamber was powered on.  next, the manual circuit breaker of the control console was powered on.  after powering on the circuit breaker of the control console, the green button was pressed to power the system. the voltage was varied and monitored on a voltmeter until it reached the desired voltage of 15kv, which was obtained by using the autotransformer located in the control panel. this process was repeated for 1, 2, and 3 hours of electrical aging. (a) (b) fig. 2. experimental setup for electrical aging impedance analyzers are commonly used to measure the electrical properties of materials, such as capacitance and resistance, as a function of frequency. in this case, the rlc 817 meter was used to measure the dielectric response of the samples up to 10mhz. the samples were placed between two plane electrodes made of copper, and an alternating electric field of 1v/m was applied. from these measurements, tgδ (dissipation factor), ɛr (relative permittivity), and loss index were calculated. the measurement error was to be ±0.05%. fig. 3. samples in electric aging. engineering, technology & applied science research vol. 13, no. 2, 2023, 10523-10528 10525 www.etasr.com berrag et al.: an experimental study of the dielectric parameters of pvc nano-composites under … iii. results and discussion in this research, the dielectric parameters tgδ, ɛr, and loss index were measured at frequencies ranging from 10hz to 10khz for all the manufactured samples, including the standard pvc. a. relative permittivity figure 4 shows that for all types of pvc samples, the relative permittivity initially increases with frequency up to a certain point, and then decreases with further increase in frequency. additionally, the magnitude of the relative permittivity peaks varies with aging time and type of nanoparticle filler. it is worth noting that the observed behavior in the low frequency range (12hz 500hz) may be related to the presence of electrode polarization effects, which can lead to inaccurate measurements of the material's dielectric properties in this frequency range. (a) (b) (c) (d) (e) fig. 4. variation of the relative permittivity as a function of frequency and aging time. (a) pure pvc, (b) pvc+10% al2o3, (c) pvc+10% tio2, (d) pvc+10% caco3, (f) pvc+10% batio3. b. dissipation factor the values of tgδ come directly from the rlc meter. figure 5 represents the variation of the dissipation factor as a function of frequency and aging time. (a) (b) (c) (d) (e) fig. 5. variation of the dissipation factor tgδ as a function of frequency and aging time. (a) pure pvc, (b) pvc+10% al2o3, (c) pvc+10% tio2, (d) pvc+10% caco3, (f) pvc+10% batio3. the analysis of the results of the evolution of the dissipation factor allowed us to note that it decreases with the increase in frequency (500hz-10khz) and increases with the increase in the duration of application of the stress (electric corona discharge). c. dielectric losses the variations of dielectric losses as a function of frequency and aging time for the 5 considered types of pvc are shown in figure 6. we notice that all the curves show almost the same pace, with a peak at low frequencies (between 5080hz) and then stabilize for the other frequencies. losses increase with increasing corona discharge time but with a slight difference (especially for high frequencies > 1khz). figure 7 shows a comparison between the results of relative permittivity, dissipation factor and dielectric losses of all nanocomposites after electric aging for 3 hours. it is observed that the curves have the same pace (increase in the low frequencies and consequently decrease until they stabilize in high frequencies). it seems that batio3 is the most effective dopant among the 5 tested, with the smallest values for dielectric losses. al2o3 comes second, followed by caco3. this information can be useful for selecting the most appropriate dopant for improving the electrical properties of pvc. 0,1 1 10 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0 9,5 10,0 10,5 11,0 11,5 12,0 r e la ti v e p e rm it ti v it y frequency (khz) pure pvc (0h) pure pvc (1h) pure pvc (2h) pure pvc (3h) 0,1 1 10 10 r e la ti v e p e rm it ti v it y frequency (khz) pvc+10% al 2 o 3 (0h) pvc+10% al 2 o 3 (1h) pvc+10% al 2 o 3 (2h) pvc+10% al 2 o 3 (3h) 0,1 1 10 0 5 10 15 20 25 30 35 40 r e la ti v e p e rm it ti v it y frequency (khz) pvc+10% tio 2 (0h) pvc+10% tio 2 (1h) pvc+10% tio 2 (2h) pvc+10% tio 2 (3h) 0,1 1 10 3 4 5 6 7 8 9 10 11 r e la ti v e p e rm it ti v it y frequency (khz) pvc+10% caco 3 (0h) pvc+10% caco 3 (1h) pvc+10% caco 3 (2h) pvc+10% caco 3 (3h) 0,1 1 10 1 2 3 4 5 6 7 8 r e la ti v e p e rm it ti v it y frequency (khz) pvc+10% batio 3 (0h) pvc+10% batio 3 (1h) pvc+10% batio 3 (2h) pvc+10% batio 3 (3h) 0,1 1 10 0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35 0,40 0,45 0,50 0,55 0,60 0,65 l o s s i n d e x frequency (khz) pure pvc (0h) pure pvc (1h) pure pvc (2h) pure pvc (3h) 0,1 1 10 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 l o s s i n d e x frequency (khz) pvc+10% al 2 o 3 (0h) pvc+10% al 2 o 3 (1h) pvc+10% al 2 o 3 (2h) pvc+10% al 2 o 3 (3h) 0,1 1 10 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 l o s s i n d e x frequency (khz) pvc+10% tio 2 (0h) pvc+10% tio 2 (1h) pvc+10% tio 2 (2h) pvc+10% tio 2 (3h) 0,1 1 10 0,0 0,2 0,4 0,6 0,8 1,0 l o s s i n d e x frequency (khz) pvc+10% caco 3 (0h) pvc+10% caco 3 (1h) pvc+10% caco 3 (2h) pvc+10% caco 3 (3h) 0,1 1 10 -0,1 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 l o s s i n d e x frequency (khz) pvc+10% batio 3 (0h) pvc+10% batio 3 (1h) pvc+10% batio 3 (2h) pvc+10% batio 3 (3h) engineering, technology & applied science research vol. 13, no. 2, 2023, 10523-10528 10526 www.etasr.com berrag et al.: an experimental study of the dielectric parameters of pvc nano-composites under … (a) (b) (c) (d) (e) fig. 6. variation of dielectric losses as a function of frequency and aging time. (a) pure pvc, (b) pvc+10% al2o3, (c) pvc+10% tio2, (d) pvc+10% caco3, (f) pvc+10% batio3. (a) (b) (c) fig. 7. comparisons between nanocomposites after electric aging for 3 hours of: (a) relative permittivity, (b) dissipation factor, (c) dielectric losses. iv. discussion in general, the existing literature indicates that the dielectric constants and loss tangents of insulators are influenced by various physical, chemical, and structural changes that occur during their use [8, 19-22]. in order to enhance the performance of insulators, new polymeric composites have been developed that incorporate ceramic powders. to assess the impact of different nano-fillers such as batio3, caco3, al2o3, and tio2, as well as the aging under corona discharge conditions, the dielectric properties of pvc were analyzed. incorporating nano fillers into the pvc matrix allows for the modification of the composite's dielectric parameters. these values are dependent on the type of filler, the integration rate, and the dielectric parameters of the fillers themselves [1, 21, 35]. specifically, in our study, the dielectric constant (ɛr) increased and the loss tangent (tgδ) decreased as the nano-filler content increased, as shown in figures 4 and 5. as demonstrated in figure 4, for a frequency of 100hz, the values of ɛr for batio3, tio2, caco3, and al2o3 decrease by approximately 57%, 50%, 35%, and 37%, respectively, compared to the value of ɛr for pure pvc prior to aging. these findings are in agreement with the findings of [13, 25, 33], and can be validated through (1) [1]: ����� ����� ����� � � = 1 − p��� (1) where εb, ε1, and εc represent the relative permittivity’s of pei, batio3 nano-particles, and the nano-composite, respectively, ppar is the volume fraction of the particles, and μ is a parameter that depends on subtleties of the microstructure such as particle clustering and surface roughness. the doped samples exhibit greater resistance than pure pvc to the aging process. specifically, at a frequency of 100hz, the values of ɛr for batio3, tio2, caco3, and al2o3 increase by 45%, 14%, 18%, and 16%, respectively. the observed reduction in space charge in the pvc matrix, as evidenced by the capturing behavior of ceramics, supports the findings of [16, 40]. the primary current carriers were attributed to free ions generated from ingredients used in the polymerization reaction of pvc, such as the stabilizer, as well as ingredients in the plastifier itself. additionally, the similarity in the shape of the curves of all the sample types of pvc/doped pvc can be attributed to interfacial polarization and rearrangement of the molecular structure. this relaxation is reflected in the peaks observed in the ɛr curves, which are consistent with those reported in [5, 29-31, 41]. the dielectric parameters of the composites are affected by aging, as demonstrated by the decrease in ɛr values and the increase in tgδ values over time for all composites. however, the incorporation of the load helps to slow down the electrical aging effect and alter the dielectric parameter values. composite aging is characterized by a broadening of the peak in the low-frequency region, as shown in figures 4 and 5. this result is consistent with previous research on batio3 doped pvc [28], where a peak in the dielectric constant curve was observed around 50hz, and a second peak was detected at 500hz. the same relaxation phenomena were also observed in our previous work [1, 28] and in [29]. specifically, the first and 0,1 1 10 0,00e+000 5,00e-009 1,00e-008 1,50e-008 2,00e-008 2,50e-008 3,00e-008 3,50e-008 4,00e-008 l o s s f a c to r frequency (khz) pure pvc (0h) pure pvc (1h) pure pvc (2h) pure pvc (3h) 0,1 1 10 0,00e+000 1,00e-008 2,00e-008 3,00e-008 4,00e-008 5,00e-008 6,00e-008 7,00e-008 8,00e-008 l o s s f a c to r frequency (khz) pvc+10% al 2 o 3 (0h) pvc+10% al 2 o 3 (1h) pvc+10% al 2 o 3 (2h) pvc+10% al 2 o 3 (3h) 0,1 1 10 0,00e+000 5,00e-008 1,00e-007 1,50e-007 2,00e-007 2,50e-007 3,00e-007 l o s s f a c to r frequency (khz) pvc+10% tio 2 (0h) pvc+10% tio 2 (1h) pvc+10% tio 2 (2h) pvc+10% tio 2 (3h) 0,1 1 10 0,00e+000 1,00e-008 2,00e-008 3,00e-008 4,00e-008 5,00e-008 6,00e-008 l o s s f a c to r frequency (khz) pvc+10% caco 3 (0h) pvc+10% caco 3 (1h) pvc+10% caco 3 (2h) pvc+10% caco 3 (3h) 0,1 1 10 0,00e+000 1,00e-008 2,00e-008 3,00e-008 4,00e-008 5,00e-008 6,00e-008 l o s s f a c to r frequency (khz) pvc+10% batio 3 (0h) pvc+10% batio 3 (1h) pvc+10% batio 3 (2h) pvc+10% batio 3 (3h) 0,1 1 10 0 5 10 15 20 25 30 35 40 r e la ti v e p e rm it ti v it y frequency (khz) pure pvc (3h) pvc+10% al 2 o 3 (3h) pvc+10% tio 2 (3h) pvc+10% caco 3 (3h) pvc+10% batio 3 (3h) 0,1 1 10 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 l o s s i n d e x frequency (khz) pure pvc (3h) pvc+10% al 2 o 3 (3h) pvc+10% tio 2 (3h) pvc+10% caco 3 (3h) pvc+10% batio 3 (3h) 0,1 1 10 0,00e+000 5,00e-008 1,00e-007 1,50e-007 2,00e-007 2,50e-007 3,00e-007 l o s s f a c to r frequency (khz) pure pvc (3h) pvc+10% al 2 o 3 (3h) pvc+10% tio 2 (3h) pvc+10% caco 3 (3h) pvc+10% batio 3 (3h) engineering, technology & applied science research vol. 13, no. 2, 2023, 10523-10528 10527 www.etasr.com berrag et al.: an experimental study of the dielectric parameters of pvc nano-composites under … second relaxation phenomena occurred at low frequencies around 50 and 500hz, respectively, as shown in figures 4 and 5. based on the analysis of figure 7 and a comparison of the various doped pvc samples, it is observed that an increase in nano filler content resulted in an increase in ɛr values and a decrease in tgδ values. among the different nano fillers studied, batio3 exhibited better resistance to aging. this can be attributed to the reduction of space charge, which is a result of the capturing behavior of ceramics in the pvc matrix [25, 43]. the main carriers present in the samples were attributed to free ions from the ingredients used in the polymerization reaction of pvc, such as the stabilizer, as well as ingredients in the plasticizer itself. in addition, the breakdown strength of the samples, as shown in figure 7, was found to be dependent on the ceramic content, with values decreasing as the ceramic content increased up to a certain practical limit, as reported in [27-28]. the formation of void defects and the resulting electromechanical stress led to the formation of cracks, which played a crucial role in the injection of electrons from the electrodes, providing them with enough energy to increase the probability of macromolecule ionization and the initiation of electron avalanche. this process accelerated the development of conducting channels and ultimately led to breakdown, as reported in [29-31]. this phenomenon can be explained by the reduction of space charge due to the capturing behavior of ceramics in the pvc matrix [26, 42-44]. v. conclusion it is important to note that the choice of nanoparticles and their concentration should be carefully considered to avoid any negative impact on other properties of the insulation material, such as 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[44] s. h. soomro et al., "synthesis and characterization of poly(styrene)block-poly(acrylic acid) and organoclay based hybrid composite materials," engineering, technology & applied science research, vol. 8, no. 5, pp. 3411–3415, oct. 2018, https://doi.org/10.48084/etasr.2273. microsoft word etasr_v12_n5_pp9295-9301 engineering, technology & applied science research vol. 12, no. 5, 2022, 9295-9301 9295 www.etasr.com almasoudi & albayati: statistical analysis of component deviation from job mix formula in hot mix … statistical analysis of component deviation from job mix formula in hot mix asphalt saba s. almasoudi department of civil engineering college of engineering university of baghdad s.khudair1901m@coeng.uobaghdad.edu.iq amjad hamad khalil albayati department of civil engineering college of engineering university of baghdad a.khalil@uobaghdad.edu.iq received: 26 july 2022 | accepted: 3 august 2022 abstract-the main objective of this research is to find out the effect of deviation in the aggregate gradients of asphalt mixtures from the job mix formula (jmf) on the general mixture performance. three road layers were worked on (wearing layer, binder layer, and base layer) and statistical analysis was performed for the data of completed projects in baghdad city and the sieve that carried the largest number of deviations for each layer was identified. no.8 sieve (2.36mm), no.50 sieve (0.3mm), and 3/8'' sieve (9.5mm) had the largest number of deviations in the wearing layer, the binder layer, and the base layer respectively. after that, a mixture called mix 1, was made. this mixture was selected from a number of completed mixtures, and it represents the worst mixture. mix 1 was compared with two other mixtures, mix 2 and mix 3, mix 2 representing the middle of jmf for the gradients of aggregates, and mix 3 is the same as mix 1 except for the sieve that contains the largest number of deviations, so the gradient of aggregates for it is the middle of jmf. fifteen marshall specimens were made for each mixture and for each layer in order to know the differences in marshall properties between the mixtures. also, 6 specimens were made for each mixture (the total is 18 specimens for each layer) to check the indirect tensile strength, for the purpose of knowing mixtures susceptibility to moisture. finally, 1 specimen was made for each mixture for repeated load test for the purpose of knowing the performance of the mixtures with respect to permanent deformation. the tests showed that the performance of mix 2 and mix 3 was improved in comparison with mix 1. the deviation of the aggregate gradients in specific sieves may be higher than the limits of the jmf or it may be less, and in both cases, the implementation of a mixture like mix 1 for the streets is bad for the performance of the road and failures occur due to the wrong implementation of the jmf. on the other hand, there are much better mixtures in all respects such as mix 2 and mix 3, and if they are implemented on the streets, they will certainly have much better. keywords-hot mix asphalt; jmf; deviation; aggregate gradations i. introduction road construction industry faces the challenge of designing and constructing high-performance asphalt materials to meet the ever-growing demand of increasing traffic volumes and axle loadings. quality control over the production of hot asphalt compounds is a significant issue. when the asphalt components are manufactured to have high performance under weather and road conditions, this increases asphalt pavement life and consequently reduces additional maintenance and rehabilitation costs. one of the most important issues that affect pavement design is the occurrence of defects. the reasons for these defects may be the quality of the used materials, laboratory equipment, unqualified staff, the lack and delay of necessary maintenance after the implementation of the pavement, wrong construction, or a flaw or wrong execution of the jmf resulting in aggregate gradients that do not conform to jmf contain deviations. generally, the deviations in aggregate gradations are not accidental, but are caused by external factors [1]. the method to verify that the produced mix complies with the project specifications is the jmf or dense gradation mix submittal. a successful mix design should meet the suggested proportion of aggregates and asphalt binder. this suggested mixture also includes the type of asphalt binder, the aggregate gradation, and the permissible specification bands for inherent material and production variability. the mix designer is free to select a specific jmf gradation, and the manufacturer is expected to produce the mix according to this jmf gradation closely [2]. the iraqi standard specifications for roads and bridges, scrb r/9 2003, allowed some tolerances in jmf with regard to the following properties: coarse aggregate gradients, fine aggregate gradients, filler content, asphalt concrete content, and mixing temperature (table i) [3]. the characteristics of the asphalt mixture's components have a significant and obvious impact on the performance of the pavement, especially the aggregates that make up a significant portion of the asphalt mixture. aggregates are the largest and most important volumetric component of the asphalt mixture and its performance and are the basis of the homogeneous and solid texture of the asphalt mixture. in addition to serving as the base for the design of asphalt mixtures, aggregates play a significant role in determining the quality of the road, the loads applied on it, and the nature of road layers. the type and viscosity of the asphalt used are impacted by the gradient of the aggregates and internal friction. the fundamental concept of choosing the aggregate quality and corresponding author: sabs s. almasoudi engineering, technology & applied science research vol. 12, no. 5, 2022, 9295-9301 9296 www.etasr.com almasoudi & albayati: statistical analysis of component deviation from job mix formula in hot mix … size is to get the highest consistency and homogeneity of the asphalt mixture, creating the perfect layer to receive and distribute the load of wheels and vehicles on the sub base without failures [4-6]. table i. allowed tolerances from jmf [3] sieve size tolerance aggregate materials passing through sieve 4.75mm (no.4) or larger ±6% aggregate materials passing through sieve 2.36mm (no.8) to sieve 0.3mm (no.50) ±4% filler passing through sieve 0.075mm (no.200) ±1.5% asphalt ±0.3% mixing temperature ±15 o c aggregate gradation, which is measured by sieve analysis, is the distribution of aggregate particle size. while aggregates of varying size made the mixture have fewer voids, the aggregates that have no variety in sizes make the compacted mass to have more voids due to the uniformity of the particles. aggregate gradation significantly affects hot mix asphalt (hma) properties. the component content in the hma mixture has been shown to have an impact on the mixture's structure and properties, which in turn affects the dependability and durability of the pavement [7]. it is concluded that the deviations related to the gradient of the asphalt mixture aggregates are considered to be effective and common deviations, which requires taking appropriate procedures to avoid these failures, including doing the correct jmf in a manner appropriate to the use of the intended layer in addition to the use of materials that successfully pass laboratory testing and ensure the correct implementation of the required thickness and compaction, thus, improving the quality and performance of the implemented road in a way that meets its purpose [8]. in order to find some performance requirements, designers are interested in aggregate gradation. for good permanent deformation resistance, superpave defines the "restricted zone" within the gradation of aggregates and recommends that the limited area should not be violated. depending on the nominal maximum particle size, the restricted zone is between the mid-size particles (4.75 or 2.36mm), and the 0.3mm at the maximum dense line [9-11]. aggregate gradation determines how well an asphalt pavement performs. any changes in aggregate gradation cause changes in many factors, such as directions and contact points, which in turn affect the performance of asphalt pavements [12]. authors in [13] showed the use of 4 different aggregate gradations and the wheel tracking test showed that they were superior to fine aggregates regarding permanent deformation. authors in [14] showed that aggregate gradation was a significant factor of the perfect mixture. with three grades and various percentages, they produced a hot and a warm mix of asphalt from a single source. the test results showed that the aggregate gradations had a variety of effects on the introduced mixtures' rutting resistance, particularly their sensitivity to moisture. authors in [15] examined the way aggregate gradation affects the different characteristics of asphalt concrete mixtures. the effects of different aggregate types and gradations on the mixing properties have been investigated for blends with fine, medium, and coarse aggregate gradations. the mixtures' asphalt content remained constant at the job mix design content. they looked at the properties of marshall stability, marshall flow, unit weight, air voids, and mineral aggregates. analysis of the different aggregate types made clear that the fine-coarse and coarse-fine variations had the greatest impact on the mix. authors in [16] estimated the effect of asphalt and aggregate gradation type on hma found in asphalt concrete mixtures. additionally, the effect of the aggregate characteristics on the marshall mix properties was investigated. finally, an estimation of the relationship between rutting potential and hma mixing was made. the study showed that characteristic mineral aggregates had a significant influence on the construction of local highways, giving the possibility to develop resistance to various externally applied loads and environmental conditions. furthermore, it illustrated how aggregate properties have a long-term impact on the way hotmix asphalt is deformed. many studies have been conducted to identify the effect of aggregate gradation on moisture susceptibility and permanent deformation of hma. rutting has recently taken over as the main mode of flexible pavement failure as a result of increased truck tire pressure and the lack of maintenance [17]. rutting is mainly brought on by the accumulation of permanent deformations in the pavement or its layers. heavy axle loads and high tire pressure contribute significantly to rutting in the flexible pavement surface layer. high tire pressure increases stress and reduces the area of contact between the tire and the pavement, which aggravates deformation in flexible pavements. additionally, the pavements' top layer is significantly impacted by environmental conditions [18]. the asphalt mixtures used in road construction must be resistant to cracking and permanent deformations. they are composed of voids, aggregates, and binder. to obtain relevant properties that affect the way the asphalt behaves, appropriate materials must first be chosen in advance, and their proportions in the asphalt mixture must be determined. it's essential to know how asphalt mixtures are built in, in addition to how they are produced [6]. it is widely accepted that coarser gradation results in an hma mixture that is more rut resistant. however, some studies have discovered that mixtures with finer gradations have lower rut potential [19]. authors in [20] observed that, a significant contributing factor to the asphalt binder film's loss of adhesion may be the fine aggregates. they also noted that the presence of crushed sand may reduce moisture damage and that maximum aggregate size and mixture gradation have a significant impact on rutting resistance. ii. data used and most common deviations for the purpose of knowing the sieve that carries the largest number of deviations in the aggregate gradients (the most frequent) and for the three considered layers (wearing, binder, and base layer) a data set was acquired from road projects implemented in baghdad governorate. the data were randomly selected. data were taken from 140 wearing layer specimens, 33 binder layer specimens, and 30 base layer specimens. the percentage of passing through each sieve can be easily plotted for each sieve and the conclusion is that the largest number of deviations in the aggregate gradients from jmf of wearing layer were sieve no.8 (2.36mm) for the wearing layer, no.50 engineering, technology & applied science research vol. 12, no. 5, 2022, 9295-9301 9297 www.etasr.com almasoudi & albayati: statistical analysis of component deviation from job mix formula in hot mix … (0.3mm) for the binder layer, and sieve 3/8" (9.5mm) for the base layer. iii. selection of aggregate gradations the sieve that has the largest number of deviations in aggregate gradations was determined for each considered layer. figures 1-3 show the aggregate gradients for the worst implemented chosen mixture, and the amount of its deviation from iraqi specification for roads and bridges (scrb) and jmf. this mixture was called mix 1. the performance of this mixture (mix 1) was compared with mixtures without or less errors and deviations, in order to determine how bad these mixtures are being implemented. another mixture, called mix 2, was made. its aggregate gradients represent the midpoint of the jmf for mix 1. a third mixture, called mix 3, was prepared with the same gradations of aggregates as mix1, except for the sieve containing the largest number of deviations (the sieve that deviates from the jmf). so we have: • mix 1: as it is. • mix 2: mean of jmf. • mix 3: as it is, mid for deviated sieve. the above were implemented on all layers (wearing, binder and base). figures 1-3 show the gradations of aggregates for each mixture and for each layer. fig. 1. wearing layer aggregate gradients. fig. 2. binder layer aggregate gradients. fig. 3. base layer aggregate gradients. iv. material characterization a. aggregates crushed quartz was used as aggregates in this research. in the city of baghdad, this aggregate type is frequently used in asphalt mixtures. routine tests were performed on the aggregates to assess their physical characteristics. table ii provides a summary of the results along with the specification limits established by the scrb. the test results indicate that the selected aggregates meet the scrb specifications. table ii. physical properties of aggregates property coarse aggregates fine aggregates scrb bulk specific gravity (astmc127 and c128) 2.646 2.63 …… apparent specific gravity (astmc127 and c128) 2.656 2.667 …… percent water absorption (astm c127 and c128) 0.14 0.523 …... percent wear (los-angeles abrasion) (astm c131) 19.69 30 max fractured pieces (%) 98 90 min sand equivalent(astm d 2419) 55 45 min superpave (sp-2) soundness loss by sodium sulfate solution,%(c-88) 3.4 12 max table iii. physical properties of ac 40/50 tests unit 40/50 ac specification scrb specification penetration at 25 o c, 100gm, 5sec (astm-d5) 0.1mm 45 40-50 softening point r&b (astmd36) o c 48 ….. specific gravity at 25 o c (astmd70) ...... 1.04 ….. flash point (astm-d92) o c 290 min. 232 ductility (astm-d113) cm 132 min. 100 residue from thin film oven test (astm-d1754) retained penetration ,% of original (astm-d5) 0.1mm 59 min. 55 ductility at 25 o c, 5cm/min, (astm-d113) cm 90 min. 25 engineering, technology & applied science research vol. 12, no. 5, 2022, 9295-9301 9298 www.etasr.com almasoudi & albayati: statistical analysis of component deviation from job mix formula in hot mix … b. asphalt cement the penetration grade (40/50) of asphalt cement, which is frequently used in paving construction projects in iraq, was considered in this study. for the purpose of determining the fundamental physical characteristics of asphalt cement, a number of astm tests were carried out. the asphalt cement used in this study complies with the necessary (scrb/r9 2003 revision) specification, as shown in table iii. c. filler the filler is a non-plastic material passing through sieve no.200 (0.075mm). the filler used in this work is limestone dust. its physical properties are presented in table iv. table iv. physical properties of mineral filler. property test result specific gravity 2.78 passing sieve no.200 (0.075mm) 85 v. specimen preparation and testing procedure to evaluate the performance of the three mixtures, three types of tests were performed, the marshall test (astm d6926-2010a) in order to obtain the optimum asphalt content, density, stability, flow, and other properties, indirect tensile strength test (astmd-4867-96) in order to evaluate the moisture sensitivity of the mixes, and finally the repeated load test for permanent deformation evaluation. a. marshall test in marshall design there are two kinds of test: stability-flow tests and density voids tests. the marshall method (astm d6927) is used to determine the optimum asphalt content of the hma pavement. for the purpose of calculating the optimum asphalt content, 5 different percentage values 4, 4.3, 4.6, 4.9 and 5.2%, were used for asphalt cement (binder course), while 3.4, 3.7, 4, 4.3, and 4.6% were used for base course, and 4.3, 4.6, 4.9, 5.2, and 5.5% were used for the wearing course. three specimens were prepared for each ratio. therefore, 15 specimens were prepared for each mix, i.e. 45 specimens for each layer (to a total of 135 specimens for the three layers). the aggregate gradations for all mixtures (mix 1, mix 2, mix 3) and for all layers were as explained above and the marshall specimens were made after the calculation of the optimum asphalt content for each mixture. the marshall test steps have been performed. b. indirect tensile strength test to assess the moisture sensitivity of mixes, indirect tensile tests (itss), according to astmd-4867-96 were performed for each mix: two subsets, 3 specimens each were compacted with blow range between 30 to 50 for wearing course, binder course, and base course. so, 6 specimens were prepared for each mixture and for each layer, to a total of 54 specimens. the first subset was tested in a dry condition (soaked in water for 2hr at 25 o c). the second subset was tested in wet condition, i.e. it was inundated for 24hr at 60 o c followed by 25 o c for 2hr in water bath. the marshall device applies a compressive load to a cylindrical specimen through two diametrically opposed rigid strips consisting of 10×10mm (0.39×0.39in) rectangular steel bars of 102mm (4in) diameter specimens to induce tensile stress along the diametric vertical axis of the test specimen. a series of splitting tensile strength tests were conducted at a constant strain rate of 2in/min vertically until vertical cracks appeared and the sample failed. the peak compressive load was recorded and used to calculate the tensile strength of the specimen using (1): st = 2 pu/ πtd (1) where st is the tensile strength (psi), pu is the max. load (lb), t is specimen's height immediately before tensile test (in), and d is specimen's diameter (in.). the tensile strength ratio (tsr, %) was calculated by: tsr = (stm/std) ×100 (2) where stm is the average tensile strength of the moisture conditioned subset (psi) and std is the average tensile strength of the dry subset (psi). c. repeated load test a total of 9 cylindrical specimens (1 specimen for each mix for the 3 layers) were fabricated to investigate the effect of deviation in the gradation of aggregates on permanent deformation of asphalt concrete mixture at 40 o c. the cylindrical specimens produced for this study had initial dimensions of 101.6mm (4in) diameter × 152.4mm (6in) height. the tests were performed at single stress level of 20psi (138kpa). repeated compressive loading for 10,000 repetitions was conducted with a loading cycle of 60 cycles per minute in duration and consisting of a 0.1s load period followed by a 0.9s rest period (the 0.1s load duration was selected in order to simulate the loading of truck moving at the highway with a speed of 50km/hr). this test was applied to determine the permanent deformation characteristics of paving materials. permanent axial deformation was recorded throughout the test using linear variable differential transducer (lvdt) to measure the deformation in the upper face of the sample via a data acquisition system. a pneumatic repeated load system (prls) apparatus manufactured under the auspices of university of baghdad's civil engineering department was used to calculate the permanent strain values [21]. the values of the permanent strain were obtained at 1, 2, 10, 100, 500, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, and 10000 load repetitions. the permanent strain (ɛp) was calculated by: ɛp = ��×�� � � (3) where ɛp is the axial permanent microstrain, pd is the axial permanent deformation, andh is the specimen's height. authors in [22, 23] suggested a log-log relationship between ɛp and n, as in (4): ɛp = an b (4) where n is the number of load repetitions, and a and b are positive regression constants. as depicted in figure 4, the parameter a is the intercept with the permanent strain axis, and b is the slope of the linear portion of the logarithmic relationship. engineering, technology & applied science research vol. 12, no. 5, 2022, 9295-9301 9299 www.etasr.com almasoudi & albayati: statistical analysis of component deviation from job mix formula in hot mix … fig. 4. log-log relationship between permanent microstrain and number of load repetitions. vi. results and discussion as mentioned above, mix 1 is the mixture that has already been implemented in some of the streets of the city of baghdad. this mixture shows some deviations in the gradients of the aggregates from the mixing equation and for the 3 layers of the road. these deviations surely did not occur intentionally, but due to defects in the jmf specified for each project, implementation errors, or errors of weighing and determining the exact amount of aggregate required for each sieve and for each mixture. some of these deviations were beyond the upper limits of the mixing equation and even exceeded the amount of tolerance specified according to the scrb. on the other hand, some of the deviations were less than the minimum limit of the mixing equation. both cases can cause defects in the mixture. the occurrence of defects in the aggregate gradients prescribed for a particular road, means an increase or decrease of fine or coarse materials in the mixture, leading to problems in the mixture and weakened performance of the road, making it prone to failures. this was made clear from the test results. to clarify the difference between the performance of the 3 mixtures, the results of each test and for each layer, will be discussed. for the wearing course, the deviated sieve is sieve no. 8 (2.36mm). for mix 1, the passing percentage of aggregates for this sieve is 24%, which is outside the lower limit of jmf (it is even outside the tolerance limit ±4) and is also less than the lower limit of iraqi standard specifications, which is 28%. for binder course, in mix 1, the value of the aggregates that passed through the sieve no. 50 is 8%, which is less than the lower limit of the jmf and its tolerance limit, but within the limits of the iraqi specification, as the percentage of passing through sieve no. 50 of binder course according to it must be within 5-19%. for base course, in mix 1, the transit ratio of aggregates to a 3/8" sieve was 72%, which is outside the upper limits of the mixing equation, and the tolerance limits of the mixing equation, but it is within the limits of scrb, as the value of aggregates for this sieve and the base layer according to the scrb is from 48 to 74%. mix 2 is the best (ideal) mixture. figures 5-11 show how the properties of mix 2 and mix 3 were significantly improved in comparison to mix 1. the values of stability, flow, and density of the asphalt mixture improved. also, an increase in the itr value was observed, which means more moisture resistance. a decrease in the values of slope and intercept was also noticed for mix 2 and mix 3 compared to mix 1 for all the considered layers of the road (wearing, binder and base). the higher the value of the intercept, the larger is the strain and hence the larger the potential for permanent deformation [24], while slope b represents the rate of change in the permanent strain as a function number of loading cycles (n) in the log-log scale. high-slope values of a mix indicate an increase in the material deformation rate, hence less resistance against rutting. a mix with a low slope value is preferable as it prevents the occurrence of the rutting distress mechanism [25]. fig. 5. tests results of asphalt concrete percentage for each layer. fig. 6. tests results of marshall stability for each layer. fig. 7. tests results of marshall flow for each layer. engineering, technology & applied science research vol. 12, no. 5, 2022, 9295-9301 9300 www.etasr.com almasoudi & albayati: statistical analysis of component deviation from job mix formula in hot mix … fig. 8. tests results of marshall desity for each layer. fig. 9. tests results of indirect tsr for each layer. fig. 10. intercept value from log-log relationship between microstrain and load repetition for each layer. fig. 11. slope value from log-log relationship between microstrain and load repetition for each layer. vii. conclusion in this research, three types of mixtures and three pavement layers were studied. the first mixture is already implemented in some of the road projects in the city of baghdad, and it shows deviations in the aggregate gradients from the mixing equations, suffering from weak performance and noticeable failures in some roads. knowing the importance of adjusting the aggregate gradients in the asphalt mixture according to the specifications, noticeable performance improvement was noticed when mix 2 and mix 3 were produced (correcting deviant aggregate gradients according to the mixing equations). even if it is difficult to implement mix 2 (which represents the gradients of aggregates at the mean values of the mixing equation), it is possible to implement mix 3, which is closer to the reality of implementation, and all its properties are better than mix 1, guaranteeing an improvement in road performance, fewer failures, and greater durability. references [1] y. h. huang, pavement analysis and design. hoboken, nj, usa: prentice hall, 1993. 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[25] w. a. gul, "effect of recycled cement concrete content on rutting behavior of asphalt concrete," m.s. thesis, middle east technical university, ankara, turkey, 2008. microsoft word 2-546-ed.doc engineering, technology & applied science research vol. 5, no. 4, 2015, 825-831 825 www.etasr.com charles-owaba et al.: development of the contiguous-cells transportation problem development of the contiguous-cells transportation problem oliver charles-owaba victor oladokun oladunni okunade department of industrial and production engineering, university of ibadan nigeria oeowaba@yahoo.com department of industrial and production engineering, university of ibadan, nigeria victordokun@yahoo.com department of industrial and production engineering, university of ibadan, nigeria dunymola@yahoo.com abstract—the issue of scheduling a long string of multi-period activities which have to be completed without interruption has always been an industrial challenge. the existing production/maintenance scheduling algorithms can only handle situations where activities can be split into two or more sets of activities carried out in non-contiguous sets of work periods. this study proposes a contiguous-periods production/maintenance scheduling approach using the transportation model. relevant variables and parameters of contiguous-cells scheduling problem were taken from the literature. a scheduling optimization problem was defined and solved using a contiguous-cells transportation algorithm (ccta) which was applied in order to determine the optimal maintenance schedule of a fleet of ships at a dockyard in south-western nigeria. fifteen different problems were solved. it is concluded that the contiguous-cells transportation approach to production/ maintenance scheduling is feasible. the model will be a useful decision support tool for scheduling maintenance operations. keywordscontiguous-cells transportation model; production maintenance scheduling; linear optimization; i. introduction one of the oldest problems of human societies is the allocation of limited resources. this problem is multifaceted in nature because it can still be divided into several sub problems. distribution of goods and commodities from one point to another has been a major issue encountered in day–today activities. its cost implication as well as satisfying the needs of clients and customers is of prime importance. the above problem is described by the term transportation problem or tp. however, this term in general also includes other important applications such as scheduling, production planning, inventory control, employment scheduling, production mix problem etc. the transportation problem has been the focal point of many researchers because of its wide application and usefulness to solving real life problems. the extensions of transportation problem are given in [1]. some manufacturing processes have to be carried out without interruption to get the intended end product at the required composition e.g. casting processes, forging processes and most steel making processes. steel making process requires some processes which have to take place systematically in a definite order. the heating, soaking, and cooling processes must not be interrupted in order to achieve the required composition and quality for the product. pre-emption may not be feasible or allowed in the maintenance of certain types of equipment because of the size of the equipment, the limited maintenance facility, the set up cost and time associated with loading and unloading equipment in and out of maintenance facility. in ship maintenance, the moment a ship is loaded into the dockyard, it has to stay there for the required period to carry out maintenance activities until completion. to permit pre-emption in the maintenance of ship, the ship have to be unloaded from the dockyard, load another ship of higher priority and then bring in the former to complete its maintenance activities later. there are situations, however, where non-preemptive execution is preferable that is in situations where the cost required in the operating system to handle the preemption may be regarded as too large or if the system needs to support critical sections where preemption is not allowed. this calls for a model that can handle non-preemptive scheduling problem using transportation model. contiguous-cells transportation model is proposed to solve non-preemptive scheduling problem using the transportation problem. it differs from the traditional transportation model used in scheduling in that it has a uniform period and once the process or operation starts at the beginning of a period, it must be completed at the end of a period without interruption. the beginning of a period to the end of a period which represents the period used to carry out the process or operation is depicted with cells that are connected together without a break within a common boundary called contiguous-cells. also, the demand constraint is distributed across the blocked cells i.e. contiguouscells. ii. literature review scheduling is a decision-making process that is used on regular basis in many manufacturing and service industries and this form of decision-making process plays an important role in procurement and production, in transportation and distribution and in information processing and communication. scheduling rely on mathematical techniques and heuristics methods for allocation of limited resources which must be done in such a engineering, technology & applied science research vol. 5, no. 4, 2015, 825-831 826 www.etasr.com charles-owaba et al.: development of the contiguous-cells transportation problem way to optimize the objectives and achieve the goals of the organization [2]. pre-emption is the act of temporarily interrupting a task being carried out in order to run a higher priority task with the intention of resuming the task later. non-preemptive scheduling when compared with preemptive scheduling has received considerable less attention in the research community [14]. however, non-preemptive scheduling is widely used in industry practice, and it may be preferable to preemptive scheduling for a number of reasons [8, 18, 30]. non-preemptive scheduling algorithms are easier to implement and have lower runtime overhead than preemptive scheduling algorithms; the overhead of preemptive scheduling algorithms is more difficult to characterize and predict than that of non-preemptive scheduling algorithms due to inter-task interference caused by caching and pipelining. work with nonpreemptive scheduling algorithms has typically been confined to consideration of models where processes are invoked only once, there is a precedence order between the processes, and each process requires only a single unit of computation time and must be completed before a deadline [10, 12]. several approaches have been used to solve production and maintenance scheduling problems [11, 13, 16-17, 19-22, 27, 31]. researchers have developed algorithms applicable in models with variables and structure similar to the standard transportation problem that is extensions of transportation model [3, 5-6, 15, 23-26, 28-29]. bowman [7] was the first to suggest solving the production scheduling problem by a transportation method framework. and he further stated that many transportation problems could be extended to include a multi-time period. however, several extensions of the tp [3, 6-7, 9, 25-26, 28-29] have the structure of the traditional transportation problem which only solves problems where preemption is allowed. charles-owaba [9] mentioned the contiguity concept in scheduling of operation and maintenance periods of machines on gantt charts (the gantt charting problem) which was formulated, defined and solved as a transportation model. though, the contiguity concept was mentioned in gantt charting problem but it was formulated, defined and solved as that which is pre-emptive. the stringency attached to some real life situation as earlier illustrated may not allow pre-emption. this brings about the development of a contiguous-cells transportation model. therefore, the contiguous-cells transportation model (cctm) formulation is the main subject of this study. iii. model formulation a. notations the following are the notations used in the model: i: index indicating source identity j: index indicating destinations identity which is time period for contiguous-cells tm m: total number of supply sources t: total number of demand destinations (i.e. number of periods in time horizon for cctm) number of periods required to process demand source i it : the number of periods source i stays in the system ih : period at which activities was completed on source i is : period at which activities commence on source i mi: period that precedes the commencement of activity on source i :ik the period source i is ready for processing :ii the number of periods source i waited before being processed or attended to :ijc unit cost of processing source i at period j ijy : a contiguous variable and it is defined as:                otherwise taskthe forassignedcellscontiguoustheamong celllasttheisjcellifbjfrom commencingcellscontiguousnumbersb y th i i ij ,0 ,1 , b. mathematical model formulation the model is developed as an lp transportation model for problems that do not allow pre-emption such that cost is minimized under the following assumptions: 1. the total numbers of periods (t) are fixed and contiguous. 2. the problem parameters are known. 3. a ready source has its activities commenced only when resources are available. otherwise, it waits. 4. a source is either on queue or in for processing at any moment. 5. when a source is ready, activities commenced at the beginning of a period while completion is at the end of a period. 6. ready times are known. 7. the unit cost of source i is given for the contiguous period required. 8. the span of a period may be in seconds, minutes, hours, days, weeks, months, e.t.c.. 9. there is no pre-emption; that is a running task is executed till completion; it must not be interrupted. :ib engineering, technology & applied science research vol. 5, no. 4, 2015, 825-831 827 www.etasr.com charles-owaba et al.: development of the contiguous-cells transportation problem c. development of cost objective function, constraint and problem definition the unit cost of source i at period j without contiguouscells consideration, is given as cij. the total cost for item i in t periods is given by the expression: ( ) 1 , t ij ij ij j c t y c y = = å  1 for all m items, the total cost is given as ( ) 1 1 , , m t ij ij ij i j c t m y c y = = = åå  2 the cumulative cost over the contiguous period is given as ije and it is defined as follows:              hjif hjifc e h kj ij ij , ,  3 the symbol “–” in (3) implies “not applicable”, that is the cell does not form a contiguous-cells. the definition of cumulative cost over the contiguous period in (3) is described as follows and shown in table i. the horizontal movements on table i indicate destination which is the period for contiguouscell tp while the vertical movement across the table shows the source identity with the supply for each source i (where i = 1, 2, 3,…,z) and demand for each destination j (where j=1,2,3,…, x). ije implies the cumulative cost over the contiguous period which is the summation of cost from the start of operation at the beginning of period to the completion of operation at the end of period. table i. structure of contiguous-cells transportation tableau matrix for cost function destination j source i 1 2 3 4 . . x supply 1 e12 e13 e14 . . e1x m 2 e24 . . e2x 3 e33 e34 . . e3x . . z ezx demand n here are the mathematical expressions of some values of ije given in table i: 2 12 1 1 , j j e c = = å 4 24 2 1 , j j e c = = å 3 33 3 1 , j j e c = = å 1 x zx zj j e c = = å the “-” in some cells show that the cell cannot form a contiguous-cell yet. for example, for source 1, 2 cells form the contiguous-cells, thereby making the first cell not applicable. also, for source 2, 4 cells form the contiguous-cells, thereby making cell 1, 2, and 3, for that row not applicable. the actual cost of processing source i in the contiguous period is given as oij i j i h i mo e e=  4 where m is the period that precedes the start of activity on source i and m is given as (h-bi) ( )iij ih i h b o e e -=  5 the average cost of source i in period j taking into consideration all the bi contiguous-cells is given as ijo and it is defined as follows: i j i j i o o b =  6 the total cost for item i in t periods for contiguous-cells transportation model is given by the expression: ( ) 1 , t ijij ij j c t y o y = = å  7 the total cost for all m items for contiguous-cells transportation model is given as: ( ) 1 1 , , (8) m t ijij ij i j minimise c t m y o y = = = å å   the demand constraint is expressed mathematically as: 1 m ij j i i y a b= £å  9 the supply constraint which also caters for the non preemption constraint is given as: 1 (10) t ij i j y b = =å   equation (10) implies that the constraint must be satisfied at once which depicts the contiguous cells for nonpre-emption. engineering, technology & applied science research vol. 5, no. 4, 2015, 825-831 828 www.etasr.com charles-owaba et al.: development of the contiguous-cells transportation problem the contiguous-cells transportation problem model is given as:     m i t j ijij yocminimize 1 1 subject to j m i i ij a b y  1 and i t j ij by  1 where bi, aj ,m, and t are as defined earlier. d. contiguous-cells transportation algorithm (ccta) the approach to solve the cctp is adapted from revised distribution method of finding optimal solution of tp [4]. this solution approach will make use of allocation by minimum supply. the procedure is as follows: step 1: start with the minimum value in the supply column; if tie occurs select the supply with the least cost. step 2: allocate all the supply in that row and also meet the demand constraint that can be met alongside. it should be noted that all the supply constraint is first met at once for it to be contiguous. step 3: if all the supply in the row and demand in the column are satisfied, repeat the procedure from step 1. but, in case there is no demand to accommodate the supply for the least cost on supply row, select the next minimum cost that can accommodate the demand constraint for the supply on that row. it should be noted that the minimum cost to be considered is non-zero least cost. e. solution procedure for the contiguous-cells transportation model step 1: determine the value of problem parameters:  iijjii ntmcakb ,,.,,, step 2: set up the transportation tableau by computing eij which defines the cumulative cost over the contiguous period to find the optimal yij and this cumulative cost is defined as follows: ( )3 , , i je i f s o u r c e i i s r e a d y i n p e r i o d j o t h e r w i s e ìïïï= í ïïïî ¥ step 3: solve the cost minimizing transportation problem with the above defined cost using the algorithm given above to determine the optimal value of yij for the contiguous period. step 4: compute ijo the average cost of source i in period j from the optimal value of yij and then the total cost of source i in t period for contiguous-cells and the total cost of m sources for contiguous-cells transportation model as given by expressions (6), (7) and (8) respectively iv. model application the model developed was applied to schedule the maintenance of a fleet of ships for a shipping company in south-western nigeria. the company has a successful operation record of transporting goods outside nigeria and importing other goods into nigeria from distant and near countries. the company engages majorly in crude oil transportation to refineries outside nigeria. it also imports petroleum products from these refineries in to the country. this shipping company is faced with the challenge of lacking an effective methodology for maintenance and operation scheduling for optimum profitability. due to the operation of the shipping company, an effective maintenance system is required to avoid breakdown which may lead to loss of profit, good will, and towing charges. the ship maintenance activities include sand blasting, welding of damaged ship parts and bodies, pump servicing, generator servicing, fixing strainers, raider repair, engine repair, ship reconstruction, propeller fabrication, rudder fabrication, electrical system maintenance. the company’s total maintenance cost is influenced by the period it takes to carry out the maintenance task, the labor cost which increases with time, the amount of consumables item, spares and other materials used. the contiguous-cells transportation model is defined as maintenance scheduling problem for a fleet of ships. the problem parameters are: • the number of visits per machine (ni) within the t periods, • the duration per maintenance visits (bi), • number of ships (m) • the maintenance capacity in period j (aj) • the arrival period of ship i (ki) • the number of periods in planning horizon (t) • the direct maintenance cost of ship (aij) the operations period in a planning horizon is given as the difference in the total number of periods on planning horizon and the actual maintenance period and this given as: i i p t b=  11 1 t i i tp p = = å )12( in case where the machine waited before being serviced, the actual operations period is given as the difference in the total number of periods on planning horizon and in time spent in maintenance system which is expressed mathematically as: i i o t t= ( )1i io t j k= + 1 (13) i i o t j k= + 1 (14) t i i to o = = å engineering, technology & applied science research vol. 5, no. 4, 2015, 825-831 829 www.etasr.com charles-owaba et al.: development of the contiguous-cells transportation problem idle period is the difference in the period spent in the maintenance system and the period for maintenance activities on ship i and it is given as: iii bti   15 iii opi   16 1 (17) t i i ti i = = å v. results table iii illustrates the ships-periods final transportation tableau matrix with yij indicated for the contiguous-cells transportation model. the total maintenance cost of ships; operation and idle period in months for the ships were computed and the results are shown in table ii. table ii. total maintenance cost (tmc) of ships, total operation period (top) and total idle period (tip) problem tmc (million naira) top (month) tip (month) 1 74.45 168 0 2 87.33 164 0 3 81.85 164 0 4 91.24 160 0 5 83.01 163 0 6 53.24 167 0 7 86.31 165 0 8 93.19 161 0 9 90.76 162 0 10 93.36 160 0 11 91.86 159 1 12 82.39 157 11 13 59.00 168 0 14 109.78 168 0 15 118.98 163 5 table iii. ships-periods final transportation tableau matrix ship i 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 5.06 1 ∞ 4 6.82 8.11 9.77 11.5 13.2 14.5 16.9 18.3 19.0 19.8 21.8 23.8 25.7 27.8 29.1 6.34 2 ∞ ∞ ∞ ∞ ∞ ∞ 4 7.66 10.0 11.4 12.2 14.1 15.4 17.4 19.3 21.4 22.7 7.66 3 ∞ ∞ ∞ ∞ ∞ ∞ 5 10.0 11.4 12.2 14.1 15.4 17.4 19.3 21.4 22.7 4 ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ 34.9 5 ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ 2 36.9 38.8 40.9 42.2 3.73 6 ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ 2 5.06 5.8 7.7 9.06 11.0 12.9 15.0 16.3 6.3 7 ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ 2 11.7 15.5 18 25.1 31.1 39.5 48.2 58.1 64.5 6.62 8 ∞ ∞ ∞ ∞ 2 7.9 9.56 11.3 12.9 14.3 16.7 18.1 19.3 20.0 21.9 23.2 25.2 27.1 29.2 9(d) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 aj 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 table iii. (continued) ships-periods final transportation tableau matrix ship i 21 22 23 24 bi 1 30.4 32.1 32.9 43.6 4 2 23.9 25.6 26.5 28.2 4 3 23.9 25.6 26.5 28.3 5 3.83 4 3 6.2 3 5 43.5 45.2 46.5 48.9 2 6 18.3 19.9 20.9 28.3 2 7 71.2 80.0 85.1 94.6 2 8 30.5 32.1 33.1 34.7 2 9(d) 0 0 0 0 aj 3 3 3 3 vi. discussion of results from the result it is seen that the algorithm gives the set of maintenance cost {74.45, 87.33, 81.85, 91.24, 83.01, 53.24, 86.31, 93.19, 90.76, 93.36, 91.86, 82.39, 59.00, 109.78 ,118.98} million naira with idle periods of {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 11, 0, 0, 5}in months for the fleet of ship. elimination of idle time in the maintenance activities minimizes the period the ships spent in the maintenance system thereby increasing the operation period of the ships. the company’ return on investment will also increase with increased operation period and the availability of the ships. productivity is also increased when idle time is eliminated. it can be seen from the results that the little or no idle time in the maintenance of ships shows that the cost is reduced. also, the little or no idle period will also increase the operation periods of the ship thereby increasing the return on investment. the algorithm uses the revised distribution method of finding optimal solution of tp. the revised distribution method is based on allocating units to the cells in the transportation matrix starting with minimum demand or supply to the cell with minimum cost in the transportation matrix and then try to find an optimum solution to the given transportation problem. this gives an optimal solution as the existing modified distribution method with less iterations. engineering, technology & applied science research vol. 5, no. 4, 2015, 825-831 830 www.etasr.com charles-owaba et al.: development of the contiguous-cells transportation problem fig. 1. chart showing the total maintenance cost, total operation period and total idle period for problem parameters considered. vii. conclusion this study proposes contiguous-cells transportation model (cctm) which is an extension of traditional transportation problem which aims at solving nonpreemption scheduling problems. the study develops a mathematical model to define and solve cctm with the criterion of minimizing the total cost. the approach defines the unit cost of activity per period with no pre-emption allowed for any set of activities to determine the set of contiguous cells for each set of activities. the tableau for the traditional transportation problem is first formed and then transformed into a non-pre-emptive tableau by combining sets of appropriate cells into one contiguous-cell. it turned out that the optimal solution procedure for the traditional also solves the contiguous-cell problem. the variables and parameters of the problem were identified and defined. contiguous-cells transportation model was formulated, defined and applied to solve maintenance scheduling of a fleet of ships. several scenarios for changes in the arrival period and maintenance activity duration were considered. the results show that the contiguous-cells transportation model formulation is feasible as demonstrated in its application to solve maintenance scheduling problem and this contiguity concept can be applied to real life situations. references [1] t. alam, r. rastogi, “transportation problem: extensions and methods – an overview”, vsrd international journal of business & management research, vol. 1, no. 2, pp. 121-126, 2011 [2] m. pinedo, planning and scheduling in manufacturing and services, springer science & business media. llc, new york, 2005 [3] v. adlakha, k. kowalski, b. lev, “a branching method for the fixed charged transportation problem”, omega, vol. 38, no. 5, pp. 393397, 2010 [4] s. aramuthakannan, p. kandasamy, “revised distribution method of finding optimal solution for transportation problems”, iosr journal of mathematics, vol. 4, no. 5, pp. 39-42, 2013 [5] k. 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embedded systems: a pilot study”, 20th euromicro conference on real-time systems (ecrts 2008), prague, czech republic, pp. 83-91, 2008 [31] h. tamaki, m. ochi, m. araki, “application of genetics-based machine learning to production scheduling”, 1996 japan-usa symposium on flexible automation, pp. 1221-1224, 1996 microsoft word etasr_v12_n5_pp9233-9238 engineering, technology & applied science research vol. 12, no. 5, 2022, 9233-9238 9233 www.etasr.com kumar & maurya: a study of isotherms and kinetics of mangifera indica bark adsorbent used for … a study of isotherms and kinetics of mangifera indica bark adsorbent used for fluoride removal form drinking water abhishek kumar department of civil engineering national institute of technology patna patna, india abhishek.ce18@nitp.ac.in nityanand singh maurya department of civil engineering national institute of technology patna patna, india nsmaurya@nitp.ac.in received: 14 july 2022 | revised: 26 july 2022 | accepted: 2 august 2022 abstract-in this paper, we have investigated the bark of mango (mangifera indica) as an adsorbent for fluoride removal. chemical treatment and aluminum hydroxide coating increased the adsorption capacity of the adsorbent from 0 to 15mg/g. aluminum hydroxide-coated adsorbent (al-mibac) was subjected to a batch study by considering different operational parameters such as adsorbent dose, reaction time, and ph. the kinetics of the adsorbent strongly followed second-order behavior, indicating the chemo-sorption adsorption process. the r2 value for langmuir isotherm is 0.999 and it was found to be fitted well with the experimental data. it is hence assumed that the adsorption of fluoride is homogeneous and monolayer. the maximum fluoride adsorption amount of al-mibac was 56.81mg/g, which was superior to those of other adsorbents derived from bark. al-mibac was highly effective in reducing the fluoride concentration from 20mg/l to less or equal to 1.5mg/l which is safe for drinking purposes. keywords-adsorption; al-mibac; activated carbon; fluoride removal; isotherm; kinetics; mangifera indica i. introduction fluoride is a well-known pollutant present in drinking water. as per who, the allowable limit of fluoride concentration in drinking water is 1.5mg/l, whereas bis, recommended 1mg/l [1]. fluoride is beneficial for the bones and teeth if present in acceptable limits, otherwise it may cause dental and skeletal fluorosis, brittle bones, thyroid disorder, alzheimer’s syndrome, arthritis, brain damage, infertility, cancer, osteoporosis, and damage dna structure [2, 3]. natural process such as weathering and leaching of fluoride rich minerals, and anthropogenic processes like industrial discharging, biomass burning, mining, and extensive use of fertilizers are major sources of fluoride contamination in groundwater [4]. authors in [5] reported the appearance of excessive fluoride concentration in drinking water in more than 25 countries. approximately 200 million people around the world are facing serious problems of very high fluoride exposure through drinking water [5]. therefore, there is a high priority to deal with this problem, to ensure safe drinking water [6]. for this purpose, several methods such as precipitation, electro-coagulation, ion-exchange, membrane technology, and adsorption have been used to remove such pollutants [7]. each of them has some benefits and drawbacks [8]. precipitation/coagulation and electrocoagulation produce huge amounts of sludge. in ion-exchange process, the high operational cost is a major drawback. membrane process has high initial and maintenance cost coupled with wasting huge amounts of water. frequent fouling or scaling results in reduced useful life of membrane filters [7]. among all the removal methods, adsorption is eco-friendly, with low cost, is less tedious in operation, and possesses high removal capacity [9]. several studies have been conducted on various types of adsorbents, such as biological materials (bio-adsorbents), metal hydroxides and oxides, geomaterials, industrial by-products, etc. the best outcome and greatest adsorption capability among the adsorbents mentioned above are demonstrated by carbonaceous materials, particularly those loaded with oxides and hydroxides of metals. activated carbon derived from indian mulberry (morinda tinctoria), gular bark (ficus racemosa), babool bark (acacia nilotica bark), and mangifera indica bark have been previously used in the removal of fluoride from drinking water [10-12, 14]. to enhance the performance, activated carbon has also been treated with metal hydroxides and oxides, such as al-impregnated eucalyptus bark ash, aluminum hydroxide coated morinda tinctoria bark, etc. [11, 13]. in the present study, a novel adsorbent is proposed and prepared using aluminum hydroxide coated activated carbon of mango (mangifera indica) bark for the effective removal of fluoride from drinking water. the parameters considered were ph, adsorbent dose, and reaction time. three widely used kinetics and isotherm models were employed to the experimental data. this paper will investigate the mechanism of adsorption followed between adsorbent's surface and fluoride ions. the developed adsorbent exhibits an adsorption capacity of 56.81mg/g which is significantly higher in comparison to many other materials as presented in table i. corresponding author: nityanand singh maurya engineering, technology & applied science research vol. 12, no. 5, 2022, 9233-9238 9234 www.etasr.com kumar & maurya: a study of isotherms and kinetics of mangifera indica bark adsorbent used for … table i. adsorption capacity of different plant barks adsorbent reaction time dose (g/l) adsorption capacity (mg/g) ref. ac acacia nilotica bark 8 h 5 1.891 [10] ac morinda tinctoria 60 min 0.1 26.028 [11] alimpregnated eucalyptus bark ash 30 min 0.1 3.922 [13] ac ficusracemosa plant 60 min 4 1.549 [12] ac mangifera bark 90 min 2 1.862 [14] al (oh)3 coated mango bark 24 h 0.3 56.81 present work ii. materials and methods a. plant description there is a variety of plant barks indicated in the literature and tested against the adsorption of fluoride present in surface or ground water. in the present study, mangifera indica (mango) bark (mib) was used to prepare the adsorbent. mangifera indica, an evergreen tree of anacardiaceae family is commonly found in tropical regions like india. it grows to a hight of 10-45 m, dome shaped with dense foliage, typically heavy branched from a stout trunk. different parts of mangifera indica have different pharmacological and therapeutic properties: the juice of unripe mango fruit is used in heat strokes, the seeds are used in asthma and astringent treatment, fumes of burning leaves are used for hiccups, and the bark is used in the treatment of menorrhagia, anaemia, scabies, cutaneous infections, syphilis, diabetes, diarrhoea, etc. [15, 16]. b. bark collection the bark was carefully removed from the stem, without disturbing its inner parts, from the top (25 cm below the lowest branch) to the bottom (25 cm above the highest root). the cut width was not larger than 20 cm, thus the environmental impact of mango stem bark collection was minimal. c. chemicals analytical grade chemicals were used in the present study. sodium fluoride (naf), aluminum sulphate (al2(so4)3.16h2o), sodium hydroxide (naoh), and hydrochloric acid (hcl) were obtained from the local market. test solutions were prepared using distilled water. d. preparation of the activated carbon after collection, the mib was cut into small pieces and dried in hot air oven at 65℃ to remove moisture. the dried bark was powdered using a kitchen grinder. to obtain the desired particle size bark powder, the grinded bark was sieved using a 425 µ m mesh size. for removal of dust and color, it was shocked in diluted nitric acid solution for 24 hours with occasional mixing and was washed several times with distilled water until the wash water ph approached neutral value. the washed mbi powder was dried in hot air oven. to obtain activated carbon from the mbi, it was placed in muffle furnace under anoxic condition at 450℃ for 1 hour with uniform increase in temperature of 2℃/min. e. coating of aluminium hydroxide on activated carbon firstly 600 ml, 0.6m aluminum sulphate solution were poured into the beaker, followed by the slow addition of 100 gm ready mibac to the beaker as shown in [17]. proper mixing was done to ensure complete mixing of mibac into the aluminum sulphate solution. afterwards, 3m of sodium hydroxide were slowly added into the mixture. sodium hydroxide reacts with aluminum sulphate and precipitates of aluminium hydroxide were formed. the precipitates were deposited on the mibac surface. the ph of the reaction mixture controls the addition of sodium hydroxide, which stopped once the ph reached the target range of 5-7. the resultant mixture contains aluminum hydroxide coated mibac and sodium salt. this slurry was filtered with vacuum pressure filter. the filtered materials were dried at 110 ℃ to complete the coating of aluminum hydroxide. to eliminate the sodium sulphate salt before conducting further tests, the al-coated mibac was thoroughly rinsed with distilled water. washing continued until the output water contained less than 1 mg/l of sulphate ions. the washed mibac was dried at 65 ℃ for 12 hours and was stored in an air tight bottle for adsorption experiments [17]. iii. experimental procedure a. fluoride stock and test solution preparation an amount of 2.21g sodium fluoride were dissolved in 1 l distilled water, to make a stock solution of 100 mg/l concentration stored in 1 l reagent bottle. to prepare the test solution the fluoride stock solution was diluted 5 times to achieve 20 mg/l concentration. b. adsorption experiment batch adsorption equilibrium isothermal study was conducted by adding an appropriate dose of adsorbent in 200 ml reagent bottles containing 100 ml fluoride solution of 20 mg/l concentration. the bottles were loaded on an orbital shaker at 100 revolution per minutes at 25 ± 2 ℃. by ensuring adequate reaction time, the resultant mixture was separated using 0.45 µ m whatman’s filter paper and the filtrate was collected for residual fluoride. kinetics experiment was performed in a cylindrical vessel of 2 l capacity. a speedcontrolled mixer was used to mix the solution at the desired mixing speed. the experiment was conducted at adsorbent dose of 0.3 g/l, initial concentration 20 mg/l, and initial ph 6.5. the cylindrical vessel was partially submerged in water bath to maintain a constant temperature of 30 ± 2 ℃. to study the effect of the initial ph on the removal percentage, the ph was adjusted from 2.35 to 10.25 using 0.1m naoh and 0.1m hcl solutions. to determine the effect of adsorbent dose on fluoride removal and adsorption capacity, 100 ml of fluoride solution having 20 mg/l concentration reacted with different adsorbent doses of 100, 300, 600, 900, and 1200 mg/l. the experiments were performed in triplicates. the fluoride adsorption capacity was calculated as: q� = (�����)×� � (1) where ci and ce are the initial and equilibrium concentrations of test solution, q� is the equilibrium adsorption capacity engineering, technology & applied science research vol. 12, no. 5, 2022, 9233-9238 9235 www.etasr.com kumar & maurya: a study of isotherms and kinetics of mangifera indica bark adsorbent used for … (mg/g), w is the mass of the absorbent (mg), and v the volume of test solution (ml) [18]. the percentage removal was calculated from (2): % removal = ����� �� × 100 (2) iv. results and discussion a. batch adsorption studies 1) effect of ph on the removal of fluoride in order to investigate the effect of initial ph on fluoride removal from drinking water, the initial ph of the fluoride solution varied ph from 2.35 to 8.49 using 0.1m naoh and 0.1m hcl solutions. the initial concentration of fluoride and the adsorbent dose were kept similar at all ph values. figure 1 indicates that fluoride removal efficiency is a function of ph and maximum fluoride removal took place at ph=5.35. authors in [19] observed maximum removal efficiency at ph=7 during the adsorption of fluoride on aluminum hydroxide-coated activated carbon of morinda tinctoria. authors in [8] also reported maximum adsorption at ph=6 for a composite adsorbent prepared activated carbon of egg cell and rice straw. at lower ph values, removal efficiency decreases due to the formation of weak hydrofluoric acid and complexations of fluoride ions with aluminium [19]. after ph=5.35, continuous decrease in fluoride removal was observed. the main reason behind this decrease is the repulsive force between the hydroxide and fluoride ions available on the adsorbent surface and aqueous solution. it was also reduced due to the competition of hydroxide and fluoride ions to bind on the surface of al-mibac [20]. fig. 1. effect of ph. 2) effect of the adsorbent dose on fluoride removal to investigate the impact of adsorbent dose on fluoride removal from polluted drinking water, varying adsorbent doses of 0.3 g/l to 1.2 g/l, at ph 6.5, and temperature 25 ± 2 ℃ were mixed with 20 mg/l initial fluoride concentration. from figure 2, it is observed that removal efficiency increases drastically from 21 to 86.5%, when the dose of the adsorbent increased from 0.1g/l to 0.9 g/l. further increase of the dose up to 1.2 g/l results to gradual increase to 90%. the rise in removal efficiency with increasing adsorbent dose is caused by the increase of the presence of active sites. however, with increase in adsorbent dose, the amount of fluoride absorbed per unit weight of the adsorbent decreased. this decrease may be caused by the increase of adsorbent-adsorbent contact instead of fluoride contact with adsorbent surface. as a result, adsorbent-adsorbent contact causes the adsorbent particles to aggregate [21]. because of this overlap, there are fewer active sites on the adsorbent particles' surface, which inhibits the surface area from growing as a result of increased adsorbent dosages. authors in [22] reported similar results during the adsorption of fluoride on potent nanocrystalline hydroxyapatite surface. fig. 2. dose effect. b. batch adsorption equilibrium isotherm fluoride removal capacity was investigated by varying the dose of adsorbent from 0.3 g/l to 1.2 g/l at 20 mg/l initial fluoride concentration, initial ph 6.5, contact time 24 hours, and 25 ± 2 ℃ temperature. three commonly used isotherm models namely langmuir, freundlich and temkin isotherm models were employed to fit the experimental data. the related parameters are presented in table ii. table ii. obtained isotherm parameters isotherm parameters value langmuir kl 0.182 qm 56.81 r 2 0.9991 freundlich kf 11.3516 n 2.0157 r 2 0.9812 temkin at 1.5478 b 13.249 r 2 0.9975 1) langmuir isotherm model (lim) lim considers a specific number of active adsorption sites present on the surface of the adsorbent. only one adsorbate molecule can be absorbed by each active site. the adsorption process may be considered completed if all the active sites are occupied by the adsorbate. this adsorption is monolayer in nature with constant adsorption energy [23]. the linear from of lim is expressed as: �� �� = � ���� + �� �� (3) where q! is the maximum adsorption capacity, c� is the equilibrium concentration, k# is the langmuir constant, q! and k# are calculated by plotting the graph between �� �� vs c� (figure 3). the values of q! and k1 obtained from lim are 56.81 and 0.182 respectively. the regression coefficient r 2 is 0.9991 indicating a very good fit. authors in [8, 11] reported that aluminium impregnated composite adsorbent follows the langmuir isotherm. engineering, technology & applied science research vol. 12, no. 5, 2022, 9233-9238 9236 www.etasr.com kumar & maurya: a study of isotherms and kinetics of mangifera indica bark adsorbent used for … fig. 3. langmuir isotherm. 2) freundlich isotherm model (fim) fim is an empirical model applicable for multilayer adsorption process. it considers heterogeneous absorbent surface with varying affinity for adsorption. the experimental data were employed in fim to obtained the value of freundlich constants (n) and (kf) [23]. this model is expressed as: lnq� = lnk% + � & lnc� (4) the graph between lnq� and lnc� is shown in figure 4. the values of freundlich constant and exponent were determined by slope and intercept respectively. fig. 4. freundlich isotherm. 3) temkin isotherm model (tim) tim was proposed in 1940. this model describes that the heat of adsorption between adsorbate and adsorbent molecule decreases linearly due to the interactions between adsorbed molecules on the surface [24]. tim model is expressed as: q� = '( )* lna( + '( ) (5) q� = blna( +blnc� (6) where b = '( )* , b( is the temkin isotherm constant, a( is the binding constant at equilibrium (l/g), b is a constant corresponding to the heat of sorption (j/mol), r is the universal gas constant (j/mol k), and t the temperature in kelvin. fig. 5. temkin isotherm. the r 2 value of tim is 0.997 and fitted well with the experimental data. to evaluate the b and a(, a graph q� vs lnc� is plotted figure 5. the obtained values of b and a( from slope and intercept are 13.294 j/mol and 1.5478 l/g. among the models applied to the experimental data in the present study, langmuir was the better fitted model with r 2 = 0.9991 regression. thus, lim describes better the adsorption isotherm behavior as compared to tim (r 2 = 0.9975) and fim (r 2 = 0.9812). c. kinetics study adsorption kinetics provides relations between reaction time and adsorption capacity (figure 6). the effect of reaction time on fluoride adsorption was observed by changing reaction time from 5 min to 37 hours, with initial fluoride concentration of 20 mg/l, at ph=6.5 and temperature 30 ± 2℃. kinetics also provides information about the mechanism of adsorption, the surface, and the nature of the adsorbent. the linear from of the three kinetics models, namely pseudo first order (pfo), pseudo second order (pso), and intra-particle diffusion (ipd) model were employed on the experimental data. 1) pseudo first order pfo is based on the assumption that the change in solute uptake rate over time is directly proportional to the difference in saturation concentration and quantity of the solid uptake with time. the linear from of pfo is: ln�q� . q/ � lnq� . k�t (7) where q� and q/ are the adsorption capacity at equilibrium and at time t (mg/g), k� is the rate constant, and t is the reaction time. the plot ln�q� . q/ vs t, gives slope = -0.0015 and intercept = 2.3169 with a regression coefficient r² = 0.5675, indicating that pfo does not fit the observed data. fig. 6. adsorption capacity. 2) pseudo second order it is based on the assumption that the rate-limiting step is chemical sorption or chemisorption and predicts the behavior over the whole range of adsorption. in this condition, the adsorption rate is dependent on the adsorption capacity, not on the concentration of the adsorbent. the main difference of pso over pfo is that, in pso equilibrium, the adsorption capacity is obtained from the model and does not need to be calculated theoretically form adsorption experiments [25]. the linear from of pso is: / �1 � � �2�� 2 / �� (8) where k3 is a seconded order rate constant (mg/g min). engineering, technology & applied science research vol. 12, no. 5, 2022, 9233-9238 9237 www.etasr.com kumar & maurya: a study of isotherms and kinetics of mangifera indica bark adsorbent used for … the linear fit as per (8) is given in figure 7, and indicates excellent fit with a very high regression coefficient r² = 0.9996. the adsorption capacity obtained from pso kinetics is 45.24 mg/g and k3 = 1.063× 10 -3 . the lower value of k3 indicates that the rate of fluoride sorption is fast. 3) intra-particle diffusion the mass transfer diffusion model [26] is described by: q/ � k4t 5.7 c (9) where k4 is the intra-particle diffusion rate constant and c is a constant related to boundary layer thickness if ipd controls the adsorption process, the q/ vs t 5.7 plot will be a straight line indicating ipf is a rate determining step. however, if nonlinearity is observed, it would indicate that several processes control the mechanism involved in rate limiting steps. from the plot in figure 8 between q/ and t 5.7, it is observed that three steps control the adsorption process. each step among the three is the rate limiting step at specific time intervals. the rate of adsorption calculated from the slope of linear portion, if the slope is increased at a sharp rate, the adsorption is faster. as a result, the beginning of the straight line with a step slop passing close to the origin indicates that the rate of initial diffusion through micropores and mesopores is high. the second straight portion of plots indicates fluoride diffusion through micropores and the last straight segments represents the modest adsorption on the adsorbent [8]. it is reported that pseudo second order are best fitted during adsorbent kinetics of fluoride on aluminum hydroxide coated activated carbon prepared from bark of morinda tinctoria [11]. authors in [8] also reported that during the adsorption, second order kinetics nicely fit the kinetics of fluoride on aluminum impregnated composite adsorbent. fig. 7. pseudo second order. fig. 8. intra-particle diffusion model. v. conclusion mangifera indica, commonly known as mango, is a significant herb in the ayurvedic and traditional medicine. in this study, we used mangifera indica bark for fluoride removal from drinking water. its fluoride adsorption efficiency was improved by chemical treatment. aluminum hydroxide coated mangifera bark adsorbent was developed for fluoride removal. aluminum coating on the activated carbon of mibac not only increased the affinity towards fluoride, but also increased the adsorbent surface, thus improving its adsorption capacity. a batch study on al-mibac was conducted by considering different operational parameters like dose, reaction time, and initial ph at constant temperature of 25 ± 2 ℃. the best fitted kinetics of al-mibac was the second order kinetics with r 2 = 0.9996. all analyzed models fitted good, but the langmuir model exhibited the best fit with the experimental data with r 2 = 0.9991, which indicates monolayer and homogeneous adsorption. temkin and freundlich isotherms also assumed to contribute partially in the adsorption. references [1] s. ayoob and a. k. gupta, "fluoride in drinking water: a review on the status and stress effects," critical reviews in environmental science and technology, vol. 36, no. 6, pp. 433–487, dec. 2006, https://doi.org/10.1080/10643380600678112. 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[26] j. c. morris and w. j. weber, "removal of biologically-resistant pollutants from waste waters by adsorption," in advances in water pollution research, london, uk, sep. 1962, pp. 231–266, https://doi.org/10.1016/b978-1-4832-8391-3.50032-4. microsoft word etasr_v13_n2_pp10389-10394 engineering, technology & applied science research vol. 13, no. 2, 2023, 10389-10394 10389 www.etasr.com nguyen: anti-vibration control of turntable ladders by a steel rope-hydraulic control system anti-vibration control of turntable ladders by a steel rope-hydraulic control system van tinh nguyen faculty of mechanical engineering, hanoi university of civil engineering, vietnam tinhnv@huce.edu.vn (corresponding author) received: 31 december 2022 | revised: 1 february 2023 | accepted: 9 february 2023 abstract anti-vibration control of turntable ladders is effective by controlling the steel ropes inserted in the hollow handrails. previous studies that considered idealized conditions, such as ignoring friction, piston mass, and hydraulic oil compressibility, can not be strongly generalized. this study addresses these problems by describing in detail the equipment serving the anti-vibration solution, building a mathematical model for the steel rope hydraulic control system considering the above factors, and controlling the rapid extinguishing of vibrations on a model simulated in matlab-simulink. furthermore, the simulation of the relationship between the control signal and oil flow through the proportional distribution valve produced a signal flow curve that was asymptotic to the actual. the results showed a difference compared to previous studies. although the solution was only implemented on the lowest ladder section with the most unfavorable conditions, the time for vibration on the top ladder reached amplitudes of 3 and 5mm in 3 and 5s for empty and full baskets, respectively. keywords-aerial extension ladder; anti-vibration control; dynamic equation; steel rope hydraulic control; turntable ladder i. introduction the study on vibration reduction, fast vibration quenching, and anti-swing for load transport equipment has high scientific and practical significance. various control methods have been proposed to bring the load to the desired position quickly and accurately [1-4]. this activity makes more sense for turntable ladders because they transport rescued people and should help them feel safe in a rescue basket. authors in [5-7] presented effective control methods to eliminate vibrations on turntable ladders. in [8-11], a new solution was presented to eliminate vibrations and overcome large static displacements on ladders, putting steel ropes inside the hollow of the handrails. these steel ropes were tensioned and controlled by small hydraulic cylinders mounted on the handrail tops, using the available hydraulic power of the truck. this method showed that the tension of the steel ropes had a positive effect on the antivibration on the top ladder [8] and the control of the steel ropes rapidly reduced the vibrations on the ladder [9]. in [10], stress reduction on key ladder elements and significant reduction of static displacements were demonstrated by evaluating the ladder structure with additional steel ropes according to the standards [12-13]. the hydraulic circuit design and cylinder control according to the control principle [9] were presented in [11]. however, the control system model in [11] was not very accurate and comprehensive, as it did not consider the elasticity of hydraulic oil, ignored friction forces and the mass of the piston rod, and used approximate mathematical models for the flow-signal curve. this study investigated the detailed structure of the anti-vibration device, the dynamic model of the steel rope hydraulic control system, the establishment of a mathematical model of the system with an accurate flow-signal curve, and the practice of controls for rapid suppression of vibrations on turntable ladders. ii. steel rope-hydraulic control system figure 1 shows the structure of the devices attached to the hollow handrails of a ladder, omitting the ladder structure. the hydraulic cylinder is integrated with the position sensor mounted on the lower end of the handrail. fig. 1. added components into a hollow handrail. a threaded joint connects the piston rod to one end of the steel rope. the steel rope with a high damping coefficient is threaded in the handrail and supported by supports. the engineering, technology & applied science research vol. 13, no. 2, 2023, 10389-10394 10390 www.etasr.com nguyen: anti-vibration control of turntable ladders by a steel rope-hydraulic control system supports are lightweight plastic evenly spaced to eliminate the rope sag. the other end of the rope is fixed by a threaded joint to the other end of the ladder. additional devices were implemented in the lowest ladder section for anti-vibration to match the size of the 30m set including the three ladder sections described in [14]. the control on the third ladder is the most effective [9]. the most effective vibration control is when placing the actuator closest to the fixed end of a cantilever beam [15]. figure 2 shows the mechanical model of the ladder structure, the steel rope, and the force generated by the cylinder. the control system commands the actuator to generate a force to reduce vibration. this force moves with a variable velocity rule that follows or nearly follows a predefined rule. based on the data in [8-11], all parameters in this model were entirely determined. fig. 2. multi-body dynamics model of ladder set and steel rope in hollow handrails. figure 3 shows the model of the steel rope hydraulic control system. during the operation of the proportional directional valve, when the p-a ports are connected, the highpressure hydraulic oil pushes the piston to the left to pull the steel rope. in contrast, when the a-t ports are connected, the oil in the cylinder chamber flows to the tank through the pressure sequence valve due to the tension of the rope pulling the piston. in this model, kc3 and cc3 are the stiffness and damping coefficients of the ropes in the third ladder section, ap, pp are the area and the pressure of the oil chamber, and xp and xr are the displacements of the piston and the remaining fixed end of the steel rope, respectively. fig. 3. mechanical model of steel rope-hydraulic control system. iii. equation of movement according to [9], during the vibration control performance, the acceleration vector of the addition motion is determined as: �� = −�(�) �(�)�� − �(�) (�)� +�(�) (� + ��� �contr�) (1) where �� , �� , and � are the acceleration, velocity, and displacement vectors of the addition motion of the rigid bodies, m(t), c(t), and k(t) are the mass matrix, the damping matrix, and the stiffness matrix, d is the load matrix including ti (bending moment) and di (damping load) caused by the steel rope in the i-th ladder section, f is the load matrix excluding the load components caused by the steel rope, and ��� =��(�)/�� with f(t) being the total generalized load matrix. �contr = �����1 1 1 1 �!" ��"# (2) where kt3 and kt3 are the controlling factors corresponding to t3 and d3 in the third ladder section, respectively. the motion equation of the piston is given by: $%&% − �'"()'*" − +'"()�'*" − �, = -%.�% (3) where ()'*", ()�'*" represent the length change range and the length change speed of the steel rope, ff is the friction force, mp is the piston mass, and .�%is the piston acceleration. the exact determination of the friction force is very complicated and it is necessary to conduct experiments on each specific object. to simplify the simulation, it was determined as follows [16]: �, = ⎩⎨ ⎧ �2 + +% ⋅ 4$%&%4       for .� % > 9:;�2 + +% ⋅ 4$%&%4< =�>=�?   for − .�: ≤ .�% ≤ 9:−�2 − +% ⋅ 4$%&%4        for .� % < −9: (4) engineering, technology & applied science research vol. 13, no. 2, 2023, 10389-10394 10391 www.etasr.com nguyen: anti-vibration control of turntable ladders by a steel rope-hydraulic control system where v0 is the velocity whose value is a very small positive around zero, fs=10 5 ap, and cp=2%. the change range of the steel rope length during work is given by: ()'*" = .% + .%: − .b (5) and the length change speed of the steel rope is given by: ()�'*" = .�% − .�b (6) with xr being the longitudinal displacement of the upper end of the handrail. the dynamic equation for the oil compressibility inside the cylinder chamber can be written as [17]: $�% = cdef ;g= − h�' < (7) where $�% denotes the change rate of the chamber pressure, ij is the oil bulk modulus, vc denotes the oil volume, and qx denotes the rate of flow entering the chamber. h' = hj' + &% ;.% + .:< (8) h�' = &% .�% (9) where x0 is the oil length in the cylinder chamber when it is set to create the initial tension load, xp is the displacement of the piston, and voc is the oil volume in the pipe. replacing (8) and (9) in (7) gives: $�% = cd;edfkl>=?<kl> => ;g= − &% .�%< (10) the flow rate depends on the pressure drop which is the pressure difference between the inlet and outlet ports and the corresponding nominal flow. this is detailed in: g= = gmjn∗ ⋅ p q%rq%sdt (11) where δpnom is the pressure drop when the flow rate is nominal, and the command signal is maximum, δpnom=5×10 5 pa, δpx is the pressure drop when working, and gmjn∗ is the flow rate depending on the command signal. gmjn∗ is determined as: gmjn∗ /gmjn = u(v) (12) where u=u/umax, u is the control voltage, umax is the maximum control voltage, and qnom is the nominal flow at umax. equation (10) is rewritten in the case of the piston pulling the steel rope: $�% = cdw,(x)⋅ysdt⋅p >dℎz>>[>sdt l>=�>\;edfkl>=?<kl>=> (13) and in the case of the steel rope pulling the piston: $�% = cdw,(x)⋅ysdt⋅p >>z>d][>sdt l>=�>\;edfkl> =?<kl>=> (14) with poh and pou being the pressure at p and t ports, respectively. iv. anti-vibration control based on the parameters and the original characteristic curve of the proportional directional valve presented in [18], to simplify the numerical simulation process in its half corresponding to the positive signal, (12) can be approximated as: ysdt∗ysdt = ⎩⎪ ⎨ ⎪⎧ 0     for 0 ≤ v < :"`axb :: − c"x :: + " ::    for    : ≤ v ≤ `d ::"ax ": − a":          for `d :: < v ≤ 1 (15) figure 4 shows the original flow curve and the approximate curve generated by (15). they almost coincide. fig. 4. flow characteristic according to command signal percentage. the steel rope hydraulic control system model was established in matlab-simulink, as shown in figure 5. the main parts of this model are:  ladder structure model: a subsystem created from the ladder dynamic model in matlab-simulink, as presented in [9].  signal generator: the velocity sensor at the top of the third ladder section provides a signal to the control signal generator, which is the original signal that is smoothed and amplified before reaching the valve. as the original signal is taken from the ladder structure model, the phase delay of the control signal must be considered. here, the tensioner model starts 30ms after the ladder model. a delay time of 4ms was selected. when the amplitude of the vibration at the top ladder is small enough, the signal generator will stop working. this amplitude value can be preset.  function blocks of the hydraulic devices: they determine the dynamic parameters of the piston and the oil pressure in the chamber through (3) and (13)-(15).  damping load block: it receives the piston and rope end velocity signals and creates the damping force (+'"()�'*").  rope tension block: it has the function of generating rope tension (�'"()'*") based on the longitudinal deformation of the steel rope. table i shows the modeling parameters. the largest vertical vibration at the top ladder may occur when the ladder is horizontal and fully extended. therefore, this study implements anti-vibration control in this ladder state. engineering, technology & applied science research vol. 13, no. 2, 2023, 10389-10394 10392 www.etasr.com nguyen: anti-vibration control of turntable ladders by a steel rope-hydraulic control system fig. 5. steel rope-hydraulic control system model in matlab-simulink. table i. model parameters of control system ef (pa) gh (m) gih (m) ji (kg) ki (m2) 1.8×10 9 0.02 0.01 1.1 10 -3 lfm (m3) ifn (pa) ifo (pa) mmp (ns/m) qmp (n/m) 2.1×10 -4 21×10 6 5×10 6 1650 1.29×10 6 figures 6-12 show the parameters obtained during the control process, including control signal, oil flow, oil pressure, friction force, piston speed and displacement, and damping force in the empty basket case. figure 13 shows the displacement graphs on the top ladder for both basket cases. despite the control signal's late start and phase delay, the vibration control through the steel rope hydraulic control system was highly effective. compared to [9] and [11], these results overcome the expected effect after control. in the empty basket case, the vibration amplitude after only 3s of control reaches 3mm for the top ladder instead of 67mm. the control systems in the other studies need more than 8s to achieve this amplitude. in case of a full basket, the vibration amplitude of the top ladder after 5s of control reaches 5mm compared to the others that need more than 14s to achieve such amplitude. fig. 6. control signal percentage. in addition to the steel rope having the effect of damping, the hydraulic equipment also suppresses the vibration when operating. the pressure and flow rate values for the cylinders presented in figures 7-8 are suitable for the hydraulic system of a turntable ladder. the speed and displacement of the piston shown in figures 10-11 are also consistent with the kinematic parameters of a piston used to control a precise motion system. fig. 7. oil flow through a proportional directional valve. fig. 8. oil pressure in the cylinder chamber. engineering, technology & applied science research vol. 13, no. 2, 2023, 10389-10394 10393 www.etasr.com nguyen: anti-vibration control of turntable ladders by a steel rope-hydraulic control system fig. 9. friction force between piston and cylinder. fig. 10. piston velocity. fig. 11. piston displacement. fig. 12. damping force. v. conclusion the paper presented a new approach to anti-vibration methods for turntable ladders. it also shows the feasibility of carrying out the novel control solution presented in [9] with available devices in the market. a steel rope hydraulic system dynamic model, including tension and damping load of steel the ropes, friction force between the piston and the cylinder, oil compressibility, piston mass, and the proportional directional valve characteristics, was established and simulated. this model was combined with the ladder set's multi-body dynamics model to control the vibration's rapid quenching at the top ladder with a unique signal generator. friction, oil compressibility, and the inertia force of the piston significantly influence the damping of the ladder's vibrations. this model extinguished vibrations by controlling the steel rope hydraulic system more efficiently, controlling only the steel ropes. the vibration reduction rate was approximately three times faster than in other studies. fig. 13. displacement of the top ladder. references [1] j. neupert, e. arnold, k. schneider, and o. sawodny, "tracking and anti-sway control for boom cranes," control engineering practice, vol. 18, no. 1, pp. 31–44, jan. 2010, https://doi.org/10.1016/j.conengprac. 2009.08.003. 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[5] n. zimmert, a. kharitonov, and o. sawodny, "a new control strategy for trajectory tracking of fire–rescue turntable ladders," ifac proceedings volumes, vol. 41, no. 2, pp. 869–874, jan. 2008, https://doi.org/10.3182/20080706-5-kr-1001.00149. [6] n. zimmert, a. pertsch, and o. sawodny, "2-dof control of a firerescue turntable ladder," ieee transactions on control systems technology, vol. 20, no. 2, pp. 438–452, mar. 2012, https://doi.org/ 10.1109/tcst.2011.2116021. [7] a. pertsch and o. sawodny, "modelling and control of coupled bending and torsional vibrations of an articulated aerial ladder," mechatronics, vol. 33, pp. 34–48, feb. 2016, https://doi.org/10.1016/j.mechatronics. 2015.11.009. [8] v. t. nguyen, t. schmidt, and t. leonhardt, "effect of pre-tensioned loads to vibration at the ladder tip in raising and lowering processes on a turntable ladder," journal of mechanical science and technology, vol. 33, no. 5, pp. 2003–2010, may 2019, https://doi.org/10.1007/s12206019-0402-2. 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[11] v. t. nguyen, "a solution to increase the flexural stiffness and quickly extinguish vibrations on a ladder of turntable ladders," tạp chí khoa học công nghệ xây dựng (khcnxd) đhxdhn, vol. 16, no. 3v, pp. 138– 149, jul. 2022, https://doi.org/10.31814/stce.huce(nuce)2022-16(3v)-11. [12] "rules for the design of hoisting appliances," federeation europeenne de la manutention, fem 1.001, oct. 1998. [13] "high rise aerial appliances for fire and rescue service use turntable ladders with combined movements safety and performance requirements and test methods," european committee for standardization, european standard en 14043:2014, 2014. [14] m. j. burman, s. e. goodson, and j. d. aiken, "telescopic aerial ladders; components; and methods," us20090101436a1, apr. 23, 2009. [15] k. g. aktas and i. esen, "state-space modeling and active vibration control of smart flexible cantilever beam with the use of finite element method," engineering, technology & applied science research, vol. 10, no. 6, pp. 6549–6556, dec. 2020, https://doi.org/ 10.48084/etasr.3949. [16] m. k. bak and m. r. hansen, "analysis of offshore knuckle boom crane part one: modeling and parameter identification," mic journal, vol. 34, no. 4, pp. 157–174, jan. 2013, https://doi.org/10.4173/ mic.2013.4.1. [17] m. g. rabie, fluid power engineering, 1st ed. new york, ny, usa: mcgraw hill, 2009. [18] "hydraulic valves industrial standard," parker hannifin corporation, 2015. microsoft word etasr_v13_n2_pp10357-10362 engineering, technology & applied science research vol. 13, no. 2, 2023, 10357-10362 10357 www.etasr.com ha: torque control of an in-wheel axial flux permanent magnet synchronous motor using a fuzzy … torque control of an in-wheel axial flux permanent magnet synchronous motor using a fuzzy logic controller for electric vehicles vo thanh ha faculty of electrical and electronics engineering, university of transport and communications, vietnam vothanhha.ktd@utc.edu.vn (corresponding author) received: 17 january 2023 | revised: 31 january 2023 | accepted: 3 february 2023 abstract this paper presents the control design of an in-wheel axial-flux permanent magnet synchronous motor with one stator and one rotor, using a fuzzy logic controller for electric vehicles. in this controller, the surgeon ambiguous inference file is built by two input vectors, the stator current error and the derivative of the stator error. these input variables include five membership functions: negative big (nb), negative small (ns), equal zero (ze), positive small (ps), and positive big (pb). the fuzzy logic controller was implemented using a 5×5 matrix to meet the required output stator voltage of the controller. the fuzzy logic torque controller was compared with the pi controller in stator current response, torque, and speed. the proposed controller was evaluated using simulation results from matlab/simulink. keywords-afpmsm; fuzzy logic; pi; foc; electrical vehicles (evs) i. introduction electric cars are a revolutionary trend in today transportation. electric cars have advantages compared to cars with internal combustion engines as they eliminate complicated gearboxes and emissions and are environmentally friendly [12]. the powertrain structure of electric vehicles (evs) tends to use an in-wheel distributed electric drive system consisting of multiple motors, which ensures traction at the front or rear of a car on two or four wheels, using a front, rear, or four-wheel drive system [3-4]. this electric powertrain improves driving performance by differentiating between wheels, makes full use of vehicle energy, improves transmission efficiency, increases range, eases braking, has good heat dissipation, and is more convenient for installation and maintenance [5-6]. the axial flux permanent magnet synchronous motor (afpmsm) is widely used in in-wheel motor drive systems because it has short shaft length characteristics, is lightweight, has good vibration resistance, and has a long service life, thus improving reliability and safety [7]. although afpmsm motors enhance the performance of evs, each vehicle should have installed multiple motors, resulting in a complex control system [8]. inwheel motors increase the cost of a vehicle and have high requirements for control procedures, such as power balancing, electronic differential, and energy recovery. in addition, electric car in-wheel motors require small size, light weight, small torque, high efficiency, large overload capacity, and wide speed range [9]. therefore, scientists have been interested in studying the control of traction and torque of in-wheel afpmsms and their response to wheels. torque and speed controllers are controlled based on direct torque control (dtc) and field-oriented control (foc). these controllers are designed using linear and nonlinear control methods such as pi, lqr, dead beat, sliding mode, flatness, fuzzy [10-14], or hybrid controllers such as fuzzy-neural, fuzzy-sliding, and pifuzzy [14-17]. however, the torque response has a slight pulsation, and the actual speed response quickly and accurately tracks the required speed [17-20]. therefore, the study of intelligent control solutions to improve an integrated in-wheel afpmsm torque in an ev should be combined with the required components and physical properties, such as brake and accelerator pedals, road inclination, and wind resistance. consequently, these parameters are necessary to improve the performance and torque of evs. this study presents the control design of an in-wheel afpmsm, one stator, and one rotor, using a fuzzy logic controller (flc) for ev systems. in this controller, the surgeon ambiguous inference file is built by two input vectors, the stator current error and the derivative of the stator error. these input variables include five membership functions, negative big (nb), negative small (ns), equal zero (ze), positive small (ps), and positive big (pb). the flc was implemented with a 5×5 matrix so that the output stator voltage of the controller is met. the fuzzy logic torque controller was compared with the pi controller in stator current response, torque, and speed. engineering, technology & applied science research vol. 13, no. 2, 2023, 10357-10362 10358 www.etasr.com ha: torque control of an in-wheel axial flux permanent magnet synchronous motor using a fuzzy … ii. model and control of the electric car power system a. mathematical model of an afpmsm it is possible to utilize the standard pmsm model for an afpmsm. stator parameters, such as the inductor calculation, change between the two models. furthermore, the back-emf produced by an excitation coil and a permanent magnet is the same. therefore, the radial pmsm of a afpmsm and the model are mathematically related. the stator voltage equation in the d-q frame of reference is given by: �� = �� + ��� �� + �� (1) �� = ���� + ��� �� − �� (2) the stator voltage equation is as follows: ̱�� = ��. �̱�� + ��̱���� (3) where rs is the stator resistance and �̱�� is the stator flux. then, converting (3) from the phase winding system of the stator to the coordinate system, quasi-rotor flux gives: ̱�� = ��. �̱�� + ��̱���� + � ��̱�� (4) the relationship between stator and rotor flux is described by: �̱�� = ���̱�� + �̱�� (5) where �̱�� is the polar flux vector. since the d-axis of the coordinate system coincides with the axis of the polar flux, the perpendicular component (q-axis) of �̱��will be zero. thus, the flux vector has only real components. ��̱��� = �� (6) the equation of flux components is given by: ���� = ������ + ����� = ������ (7) where isd, isq are the d and q coordinate stator currents, and lsd, lsq are the d and q coordinate inductance. substituting (5) and (6) into (4) and passing through the d-q coordinate system gives the system of equations of the pmsm motor: � �� = ��� ������ + ����� − ������ �� = ��� ��� �� + ����� + ������ + �� (8) the torque of the motor is described by: !" = #$ %�&����� + '��� − ���(������) (9) the motor torque is comprised of two components: the primary component ����� and the reactive component. to create a control system, the stator current vector must be adjusted so that the vertical current vector is parallel to the polar flux. therefore, there is a torque-generating current component, not a magnetizing current component, and motor torque is given by: !" = #$ %������ (10) b. mathematical model of the electric vehicle the gearbox model shows the angular speed and torque relationships according to the gear ratio *+ ,≺ 1, as shown in: � !"*+ ,= !0ℎ 0ℎ = "*+ , (11) where !" is the motor torque, !0ℎ is the torque acting on the wheel, !� = !0ℎ is the load torque, and j is the inertia torque of the motor. applying newton's second law in the rotation of the motor gives: ! " − !01 = 2 �34�� (12) the drive wheel model can be expressed as: � 501 = 01�01!01 = !6 = 7��01 (13) the vehicle will act on the road surface with a force f while the wheel is resting on it with a force n and is being propelled by a torque twh. in contrast, the road surface will act against the vehicle with a point of the same value in the opposite direction of ft. in this scenario, the reasonable force that propels the car at speed is the frictional force ft given by: 7� = 89.:.; (14) where μ is the grip coefficient. the following equation results from applying newton's second law to the parts of the outside force operating on the vehicle's body: 89 �9<=�� = 7� − 7, -> − 7->?? − 89.:.@�a(c) (15) air resistance is given by: 7, -> = ef�gh$ (5 9 + 5i�j�)$ (16) in some cases, the wind speed can be set to �i�j� = 0. the rolling resistance exists in the case of an underinflated tire and can be given by: 7->?? = l-7mn (17) 7mn = 89:op@(c) (18) where 7mn is the vertical surface reaction and lis the rolling resistance coefficient. iii. flc torque controller design the flc controls the system by calculating the necessary voltages usd and usq so that the difference between the currents isd and isq is as tiny as possible. the exactly planned isd and isq stator currents are used to regulate the motor's torque control current. this paper outlines the modern controller design for the isd and the control strategy for an in-wheel afpmsm, one stator, and one rotor, utilizing an flc. this controller uses the stator current error and the derivative of the stator error as the two input vectors to build the ambiguous inference file. engineering, technology & applied science research vol. 13, no. 2, 2023, 10357-10362 10359 www.etasr.com ha: torque control of an in-wheel axial flux permanent magnet synchronous motor using a fuzzy … (a) (b) (c) fig. 1. (a), (b) inputs, (c) output, and fuzzy rules of the flc controller. the input variables include five membership functions: positive big (pb), positive small (ps), equal zero (ze), negative big (nb), and negative small (ns). table i and figure 1 show the flc constructed using a 5×5 matrix. the flc consists of 25 rules, which are implemented as follows:  if (input 1 is nb) and (input 2 is nb), then (output is nb)  if (input 1 is nb) and (input 2 is ns), then (output is nb)  if (input 1 is nb) and (input 2 is ze), then (output is nb)  if (input 1 is pb) and (input 2 is pb), then (output is pb) table i. matrix of flc controller input 1 (e) / input 2 (δe) nb ns ze ps pb nb nb nb nb ns ze ns nb nb ns ze ps ze ns ns ze ps pb ps ze ze ps pb pb pb ze ps pb pb pb iv. simulation results a. building trajectories of accelerator, brake, and operating modes of electric vehicles the trajectories of accelerators and brakes of electric cars are built according to a function f(x1, x2, …xn). figure 2 shows the trajectories of the accelerator and brakes. the f function can be obtained experimentally and the output is calculated by looking up or interpolating the defined table using the block parameters according to a method, such as linear (linear gradient), lagrange (linear lagrange), closest point, block spline, and akima spline interpolation. the fcos function can range in size from 1 to 30. the first and second inputs define the row and column dimension breakpoints, respectively. figure 3 shows the determination of the accelerator and brake trajectories. fig. 2. the trajectories of the accelerator and brakes. fig. 3. the parameters trajectories of accelerator and brakes. b. simulation results and evaluation figure 4 shows the control structure of the traction drive system for electric cars using the in-wheel afpmsm, and table ii displays the simulation parameters. engineering, technology & applied science research vol. 13, no. 2, 2023, 10357-10362 10360 www.etasr.com ha: torque control of an in-wheel axial flux permanent magnet synchronous motor using a fuzzy … the proposed controller was simulated in matlab to evaluate its effectiveness for the traction transmission system in electric cars using an in-wheel afpmsm, with the following simulation scenario:  assume the speed of the wind is 0.  the car moves on a flat road, but at t = 3.5s to 4.3s, the car goes downhill.  at time t = 0s, the car starts to accelerate and the accelerator value increases from 0 to 1 after 0.45s. torque reaches a maximum of 205nm and remains there for 2s.  at t = 2s, the vehicle starts to decelerate, and the brake reaches a value from 0 to 1 at t = 3.5s. the torque gradually decreases to -205nm and returns to 0 at t = 4.66s. c dq cq dq uvw cq afpmsm cq cq sdu sq u s u  s u  si  si  sdi sqi  tv tu tw s  torrque controller s  * s di voltage source inveter * sq i sd i sqi inputs incline brake accelerato *t wind vehicle controller  dcu sdi sqi fig. 4. the control structure for electric cars using an in-wheel afpmsm motor, based on a foc method. table ii. parameters for afpmsm motor parameters value symbol value power pđm 35kw rated speed nđm 1800rpm rated voltage uđm 275v number of pole pairs zp 8 magnetic flux density r 0.0437 maximum torque pmax 205nm armature resistance rs 0.0101ω shaft inductance d ld 2.4368e-4h shaft inductance q lq 2.9758e-4h fig. 5. the matlab/simulink control structure for electric cars using an in-wheel afpmsm. table iii shows the parameters of the simulated pi controller. figures 6 and 7 show the stator current responses of the flc and the pi controller. these figures show that the stator current response in the steady-state method is fast (0.4s) and accurate in the steady-state mode (the actual signal follows the set call). however, the proposed flc gives better results than the pi controller in over-regulating (no over-throttling), while the pi controller with an over-regulating current at an over-regulating time is 10%. table iv presents the evaluation criteria for the stator current responses of the pi and the flc controllers. table iii. parameters for the pi controller controller ki kp current controller id 7.103004e+2 0.8779 current controller iq 1.0615e+3 1.0744 table iv. results of evaluation responsibility controller pi flc stator current isd accelerated setting time (s) 0.4 0.4 over-adjustment 10% 0% stator current isq set-up time (s) 0.4 0.4 over-adjustment 10% 0% torque controller engineering, technology & applied science research vol. 13, no. 2, 2023, 10357-10362 10361 www.etasr.com ha: torque control of an in-wheel axial flux permanent magnet synchronous motor using a fuzzy … (a) (b) fig. 6. stator current responses (a) isd and (b) isq for the pi controller. (a) (b) fig. 7. stator current responses (a) isd and (b) isq for the flc controller. figures 8 and 9 show the comparison of the torque and speed responses of the flc and the pi controller. these figures show that the torque of the two controllers has the same form as the isq current. the flc has less pulse rate (3%) for the torque response than the pi controller (8%). table v shows the torque and speed response criteria of the pi and the flc controllers. table v. results of evaluation responsibility controller pi flc torque responses shape same as isq current response same as isq current response torque ripple 8% 3% speed responses accelerated setting time 2.2 (s) 2.2 (s) over-adjustment 0% 0% fig. 8. torque responses of the pi controller. fig. 9. torque responses of the fcl controller. figure 10 shows the speed responses of an electric car transmission system using the pi controller and the flc. the actual speed response of an electric car in both cases is in line engineering, technology & applied science research vol. 13, no. 2, 2023, 10357-10362 10362 www.etasr.com ha: torque control of an in-wheel axial flux permanent magnet synchronous motor using a fuzzy … with the set requirements, and the speed response does not have too much speed adjustment at starting, accelerating, and decelerating. fig. 10. speed responses of the pi controller and the flc. v. conclusion this paper presented an in-wheel afpmsm motor torque controller design for a traction drive system using a fuzzy logic control method. the proposed controller was compared with the pi controller and its efficiency was demonstrated through matlab simulations. the proposed controller provides better torque and speed response results than the pi controller in terms of steady-state time, over-adjustment, and torque pulsation. however, this controller has a complicated design, so it is necessary to study more simple but intelligent control solutions in the future. acknowledgment this study was funded by the university of transport and communications (utc) under grant number t2023-dt001td. references [1] x. zhang, d. göhlich, and j. li, "energy-efficient toque allocation design of traction and regenerative braking for distributed drive electric vehicles," ieee transactions on vehicular technology, vol. 67, no. 1, pp. 285–295, jan. 2018, https://doi.org/10.1109/tvt.2017. 2731525. 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[20] q. d. nguyen and s. ueno, "analysis and control of nonsalient permanent magnet axial gap self-bearing motor," ieee transactions on industrial electronics, vol. 58, no. 7, pp. 2644–2652, jul. 2011, https://doi.org/10.1109/tie.2010.2076309. microsoft word etasr_v12_n6_pp9752-9759 engineering, technology & applied science research vol. 12, no. 6, 2022, 9752-9759 9752 www.etasr.com al-baghdadi et al.: one-dimension finite element modeling of grouted ground anchor one-dimension finite element modeling of grouted ground anchor nadher h. al-baghdadi department of civil engineering faculty of engineering university of kufa najaf, iraq nadhir.albaghdadi@uokufa.edu.iq balqees a. ahmed department of civil engineering college of engineering university of baghdad baghdad, iraq balqees.a@coeng.uobaghdad.edu.iq ala n. al-jorany department of civil engineering college of engineering university of baghdad baghdad, iraq alaljorany@gmail.com received: 11 september 2022 | revised: 5 october 2022 and 9 october 2022 | accepted: 10 october 2022 abstract-in the present research work, a one-dimension finite element model has been developed to simulate both compression and tension types of grouted ground anchors. the steel tendongrout interface has been modeled by using the local bond-slip model, while the soil-grout interface has been modeled with a series of perfectly elastic plastic springs. the verification of the proposed one-dimension finite element model has been made by comparison of the model results with a three-dimension finite element model developed by commercial finite element software plaxis, and with the results of field tests of tension-type grouted ground anchor. a parametric study has been made to study the load-transfer mechanism for both types of anchors, compression, and tension. the compression-type anchor exhibits less displacement than the tension one under the same applied load. the developed strain in the grouted body of the compression-type anchor is much smaller than the tension-type one, regardless of the type of strain. keywords-ground anchor; finite element; sandy soil; compression anchor; grout i. introduction one dimensional finite element modeling has been widely used to model pile foundations with all types of loadings, i.e. axial, lateral, and torsional [1-3]. a pile foundation is modeled by dividing it into a certain number of elements, the type of which depends on the geometry of the problem, loading type, and boundary conditions. two noded bar elements, with one degree of freedom per node, can be used effectively in axial loading conditions in both compression and tension. the soil resistance is modeled by using linear or nonlinear springs connected to every node. the grouted ground anchor could be modeled by the same method of pile foundation modeling, with adjustments due to differences between the two geotechnical elements. many researchers have used one-dimension finite elements to model the grouted ground anchor. authors in [4, 5] presented a one-dimensional finite element model of the compression grouted ground anchor pull-out test. two noded bar elements with one degree of freedom in the axial direction at each node have been used to simulate the grouted body. since the anchor is a compression type, i.e. the grouted body is always subjected to compression stress, a linear elastic model is used to model the grout. according to the loading mechanism of the compression anchor, the point of load application is located at the bottom node of the grouted body, so the strand has not been involved in the finite element model. the surrounding soil has been simulated by a nonlinear spring model governed by a (t-z) hyperbolic relation. authors in [6] used a one-dimension finite element to simulate an instrumented field test of grouted ground anchor. spring elements have been used to model separately the strands and the grout. along the free length of the anchor, there are no connections between the adjacent nodes of the strand and the grout, while these nodes have been connected along the bonded length of the anchor, to model the bond between the strand and the grout, by using the damage model proposed in [7, 8]. according to it, the interface stiffness decreases as the relative displacement between adjacent nodes of strand and grout increases. the surrounding soil has been modeled by linear elastic springs connected to the nodes of the grout elements. this model was used because the strength of the surrounding soil in the field test has not reached its peak strength. steel strand behavior has been modeled as linear elastic. the grout under compression has been modeled as linear elastic, while it has been considered to have zero stiffness under tension. corresponding author: nadher h. al-baghdadi engineering, technology & applied science research vol. 12, no. 6, 2022, 9752-9759 9753 www.etasr.com al-baghdadi et al.: one-dimension finite element modeling of grouted ground anchor ii. finite element modeling a finite element model has been developed to simulate the tension-type and the compression-type ground anchors in this work. two noded rod elements have been used to model the grouted body along the free and bonded lengths. each node has one degree of freedom in the axial direction. the tendon has been modeled along the bonded length only, by using the same element that has been used to simulate the bonded length of the grouted body. the stiffness of the bar element for both grout and tendon is calculated by using (1) and (2): ��� ����� = �� ������ � × � 1 −1 −1 1 � (1) ��� � ����� = �� ������� � × � 1 −1 −1 1 � (2) where l is the length of the element, e is the modulus of elasticity, and a is the cross-section area respectively, for both grouted body and tendon according to the subscript. p bonded length, grout + tendon unbonded length, only grout grout-soil interface a. tension type ground anchor p unbonded length, only grout grout-soil interface b. compression type ground anchor fig. 1. one-dimensional finite element modelling of ground anchor, a: tension type and b: compression type. the stiffness of the bonded length is the summation of the stiffnesses of the grout and the tendon, as shown in (3). the tendon along the free length is not considered, as the load application point is located at the top end of the bonded length, for tension anchor type, as shown in figure 1. for compression-type anchors, the load application point is located at the toe of the anchor, and the total length of the anchor is considered a free length. the stiffness of the element along the free length is only the grout stiffness, as shown in (4). the load is applied at the top node of bonded length the in the case of the tension anchor, while the load is applied at the tip nod of the anchor model. figure 1 shows a schematic diagram of the onedimensional finite element model for tension and compression types of ground anchors. ��� � ����� = ������� + ��� ����� (3) ��� �"��� = ������� (4) a. soil-grout interface modeling the interface between soil and grouted body is modeled using a nonlinear spring connected to all the grouted body nodes to represent the soil's reaction forces. elastic perfectly plastic (t-z) relation for sandy soils, suggested by the american petroleum institute [9], is used to represent the nonlinearity of soil springs. an elastic-perfectly plastic model has been used to simulate the pile shaft resistance, [2, 9-12]. it has been also used to model the grout-soil interface in grouted ground anchors [6, 13-15]. as shown in figure 2, the y axis represents a percent of the mobilized shear stress along with the anchorsoil interface τ to maximum shear stress (τmax), which is calculated by [16]: #$%& = '́) × � × *+, (5) where '́) is the vertical effective stress, k is the coefficient of lateral earth pressure, and φ is the angle of internal friction of the soil. φ was used instead of the interface angle between the grout and the soil δ, because δ is equal to φ in a good construction method and cast in place concrete to provide a rough grout interface, [17, 18]. the value of k is estimated based on field tests. it ranges from 1 to 2 for coarse silt and fine sand to dense sand and gravel, with grouting pressure less than 10 bar [19]. the stiffnesses of soil springs are added to the global stiffness matrix, as shown in (6): ������ %� = ������ %� + ���./�0�� (6) fig. 2. (t-z) load transfer relation for sand, (after api, 2005). b. grout modeling due to the similarity of the grout material with the concrete material, the stress-strain relation of the concrete under uniaxial compression, suggested by european standards [20] has been used to model the grouted body under compression. figure 3 shows the used constitutive model of grout under uniaxial compression. equations (7)-(13) describe the adopted model. '1 = 21$ 3 45657 89�46:�5; (7) < = 8.>?×�@a|c@d|"@a (8) e = c@c@d (9) 21$ �mpa� = 214 + 8 (10) engineering, technology & applied science research vol. 12, no. 6, 2022, 9752-9759 9754 www.etasr.com al-baghdadi et al.: one-dimension finite element modeling of grouted ground anchor j1�8�%� = 0.35, for 214 s 50mpa (11) j18(%) = 0.07 × 21$ >.u8 s 0.28% (12) w1$ = 22 �"@a8> � >.u (13) where fck is the cylinder compression strength at 28 days, in mpa, fcm is the mean of cylinder compressive strength, and all the other parameters are shown in figure 3. fig. 3. constitutive model of grout under compression, (after bs en 1992-1-1:2004). a linear elastic constitutive relation has been used to model the grout material under tension stresses before reaching the initial crack. the cracking strain of the grout under tension is about (1×10 -4 ) [21, 22]. the grout stiffness is ignored after reaching the cracking strain. c. strand-grout interface model the grout-tendon interface is modeled by the local bond stress-slip model for a smooth bar [23], under tension stresses, along the bonded length of the anchor. the adopted model is shown in figure 4 for smooth bars. equations (14)-(16) describe the adopted strand-grout interface model. fig. 4. local bond stress-slip model for smooth bar, after ceb fip, 1990. # = #$%& (x x8⁄ )z , for 0 s x s x8 (14) # = #$%& , for x [ x8 (15) #$%& = #" = 0.3\214 (16) where τ is the shear stress between grout and bar, τmax is the maximum shear stress between the grout and the bar, which is equal to τf, which is the residual shear stress after slippage occurs, s is the relative displacement between the grout and the bar, s1 is the relative displacement at τmax (s1=0.1mm), fck is the cube strength of the grout, and α=0.5. the finite element formulation of the strand-grout interface model is made by modifying the applied load vector, according to the relative displacement, and the shear stress between the strand and the grout is calculated according to (14)-(16). the main applied load is reduced by ( ∑ 0̂0_�0_8 ), where n is the number of elements that the slip of the occurred strand-grout interface, and f is the strand-grout interface force which is calculated from: 0̂ = #0 × ` (17) ` = a. × b���$�� (18) a. = c × �de×f×g�$e: � (19) where # is the shear stress between the strand and the grout, i refers to the number of elements that the slip has occurred, a is the total outside area of all strands surrounding the grout, ps is the outer perimeter of the strand wires, as shown in figure 5, lelement is element length, m is the number of strands used in the grouted ground anchor, ds is the diameter of the strand outer single wire, (which is typically equal to 5mm), and nums is the number of outer wires in the single strand as illustrated in figure 5. each interface force calculated from (17) is applied to the specified element at the end of each node, and one-half force is applied to each node. the location of the main applied force is changed according to the last element in which the slippage does not occur, i.e. magnitude, number, and location of the applied load are changed according to the bond-slip model between the strand and the surrounding grout, as shown in figure 6. the interlock between grout and strand group due to using centralizers and spacers ([24]) is neglected. d ps (strand perimeter) ds fig. 5. section in the strand and outer perimeter of outer wires. in the case of a compression anchor, there is no connection between the grout and tendon under compression stress (unbonded length of the anchor). d. nonlinearity procedure the nonlinear behavior of interface spring has been achieved by using the direct iteration method as shown in figure 7. in this method, the stiffness will be modified in each iteration as described in the algorithm below [25]. engineering, technology & applied science research vol. 12, no. 6, 2022, 9752-9759 9755 www.etasr.com al-baghdadi et al.: one-dimension finite element modeling of grouted ground anchor p bonded length, grout + tendon unbonded length, only grout no slip occurred in strand-grout interface p-ʃfi, i=1 to 3 1/2f1 slip occurred in strand-grout interface for 3 elements slip occurred in strand-grout interface for n elements 1/2fi 1/2fi applied interface force due to slip occurrence per element p-ʃfi, i=1 to n 1/2fn ½(f1+f2) ½(f2+f3) e 1 e 2 ½(f(n-1)+fn) 1/2f1 ½(f1+f2) ½(f2+f3) 1/2f3 e 3 e n-1 e n e 1 e 2 e 3 element i fig. 6. change of loads locations and magnitude according to the slip model for tension anchor. fig. 7. direct iteration method. the following steps illustrate the iteration procedure used to calculate the stiffness of the soil interface, see figure 8:  calculation of the initial stiffness of soil spring using [26]: �._0�0 0%� = :fij k l (20) where l is the length of the element, ğ is the average shear modulus at the node depth, m = n, 32o$ pq ;, rm is the max. radius at which soil deformation is very small and it could be neglected, and p is the anchor grouted body diameter.  adding the calculated above initial stiffness of soil spring, to the global stiffness matrix, as presented in (6). [k]s(initial) [k]g=[k]g(initial)+[k]s [δ]i=[k]g -1 {f} i=1 [δ]i+1-[δ]i ≥ error or i≤ max no. of iteration τi=f{δi}, from t-z relation no no yes pi=τi*a(side area) ksi=pi/δi end yes start fig. 8. flow chart of the iteration loop of soil spring calculation.  solving the finite element equation to obtain the nodal displacement (21): rst0 = ������ %�68 × r2t (21)  using the nodal displacement obtained in the third step to obtain the shear stress of anchor skin at the node depth from the (t-z) curve. nodal force is calculated by multiplying the shear stress with the side surface area of the grouted body between the centers of adjacent elements {a}, as presented in (22): r2t0 = r#t0 × r`t (22)  calculating a new spring stiffness: u�./�0�� v0 = r2t0 rst0w (23)  adding the calculated spring stiffness to the global stiffness matrix as in (6).  repeat steps 3 to 6 to find the nodal displacement {δ}i+1.  comparing the difference between two successive calculated displacements with the convergence criterion, as in (24): |rst098 � rst0 | s xooyo (24) engineering, technology & applied science research vol. 12, no. 6, 2022, 9752-9759 9756 www.etasr.com al-baghdadi et al.: one-dimension finite element modeling of grouted ground anchor as long as the convergence criterion doesn’t match, steps 3 to 6 shall be repeated until reaching the maximum number of trials, which have been chosen to be 10 3 . e. boundary conditions all nodes of the model have one degree of freedom in the vertical direction, which is the direction of the force application and no movements are allowed in the other directions. in the case of an existing structure at the head of the anchor, like the retaining structure or foundation, node no. 1 will be restricted in the vertical direction. f. failure criteria the failure criteria of the grouted ground anchor are considered below. they take place first in each element, according to the models explained previously:  debonding between grout and soil.  debonding between grout and tendon.  crushing of the grouted body under both tension and compression stresses.  tendon failure, by reaching the yield strength of the strand. g. development of algorithms and verifications fortran 90 programming language has been used to code the finite element algorithm, both the pre-processing and equation solver parts, to model the one-dimensional simulation of the ground anchor. finite element fortran 90 subroutines [27] have been used to build the present finite element algorithm, as described in table i. open-source code blocks (release 20.03) ide platform has been used to compile and run the fortran finite element code. table i. fortran 90 subroutines used [27] subroutine purpose formnf forms nodal freedom array num_to_g forms element connectivity vector fkdiag forms the bandwidth vector according to the skyline storage system rod_km forms the stiffness matrix of the rod element fsparv solve the finite element equation system using cholesky’s factorization method sparin spabac 1) 3-d plaxis model verification the finite element code has been verified with another finite element solution of grouted ground anchor to verify both the pre-processing and the equation solver. the verification is achieved by using a 3-d finite element model of the ground anchor by plaxis software [28]. this model is presented in plaxis verification manual for verifications purposes. the properties of the ground anchor model are listed below, as stated in plaxis verification manual. the fixed length is 4m and the free length is 5m, which means that the total length of the anchor is 9m. the strand property is ea=4.095×10 5 kn. the pullout force is estimated to be 752kn [29]. the maximum skin friction along the bonded length is obtained by dividing the pullout force by the bonded length (188kn/m). the skin friction is assumed to be uniform along the bonded length. despite this unrealistic assumption, it has been adopted in the developed model for verification purposes. the diameter of the grouted body is 0.125m, with a modulus of elasticity equal to (e=2.0×10 7 kn/m 2 ). the elements used are: 180 bar elements, with equal length of 0.05m. the load-displacement curves of the grouted body proximal end, presented in figure 9, show very good agreement between the two models. this agreement gives validation for the developed finite element algorithm to be used in the modeling of the grouted ground anchors. fig. 9. load-displacement curves for the proximal end of the verification model of the ground anchor. 2) field tests modeling of the tension anchors the proposed finite element model has been used to simulate pullout tests of three tension-type ground anchors constructed vertically in an-najaf city in iraq [30, 31]. the performance test is adopted for all the tested anchors according to the post tension institute [30]. anchors were trial anchors, they were tested to evaluate their pullout capacity for design purposes. all the tested anchors have a borehole diameter of 150mm and a strand steel area of 560mm 2 . strain gauges were instrumented along the grouted body of anchor no. (1), therefore, the developed strains were measured, and internal forces were calculated from these measurements. all the tested anchors did not reached failure load which makes the prediction of failure load inaccurate. instead of that, the safe working load has been determined. the soil profile and corrected spt number with depth, for the test site, are shown in figure 10. the first three trial anchors were installed at the natural ground level, while the other five anchors were installed at 8m below the natural ground. low grouting pressure was used for grouting all the tested anchors (10kpa=0.1bar) [32]. the properties of tested anchors with the number of elements used for each anchor model are listed in table ii. the modulus of elasticity for the strand is (es=200×10 3 mpa), while the modulus of elasticity of the grout is calculated according to (25) [33], which is equal to eg=22.044×10 3 mpa. w� = 4700 × {21| (25) engineering, technology & applied science research vol. 12, no. 6, 2022, 9752-9759 9757 www.etasr.com al-baghdadi et al.: one-dimension finite element modeling of grouted ground anchor table ii. properties of tested ground anchors anchor no. bonded length (m) unbonded length (m) unbonded length from the pullout point * (m) total embedded length (m) no. of elements used in the fe models 1 7 3.6 5.2 10.6 212 2 7 5.9 7.2 12.9 258 3 7.5 6 7.3 13.5 270 figures (11)-(13) show the total displacement of the anchor head vs the applied load for the measured model and the finite element. the displacement consists of the following components:  elastic elongation of the tendon free length.  elastic displacement of anchor grouted body.  plastic displacement of anchor grouted body. 0 2 4 6 8 10 12 14 16 18 20 d e p th ( m ) fill material brown, red, white medium to very dense fine to coarse sand+ gypsum+ pebbles w.t. pale brown very dense clayey silty sand (cemented sand) brown, red, white medium to very dense fine to coarse sand+ gypsum+ pebbles red silty clay (ch) brown, yellow very dense clayey sand+ pebbles green, white hard clay (ch) green, brown very dense silty sand+ cemented sand red, brown hard silty clay+ iron oxide brown silty sand soil profile bh1 bh2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 0 20 40 60 80 100 120 140 d p e th ( m ) spt (n60) bh1 bh2 fig. 10. soil profile and corrected spt (n60) values for the test site. fig. 11. load-displacement curves for field test and finite element model anchor (1). comparison with only residual displacement is not possible in the present case, because the measured displacement represents only the plastic component of the anchor head displacement while the calculated one, through the finite element, represents both plastic and elastic components of the anchor head displacement. through figures 11-13, a very good agreement could be noticed between the measured and calculated displacement, taking into account that the elastic elongation of the tendon free length represents around (80%) of the total displacement. fig. 12. load-displacement curves for field test and finite element model anchor (2). fig. 13. load-displacement curves for field test and finite element model anchor (3). fig. 14. strain along the grout of the anchor body. figure 14 presents the measured strain along the grout under four loading steps vs the calculated (via finite element modeling) strains. the comparison between the measured and engineering, technology & applied science research vol. 12, no. 6, 2022, 9752-9759 9758 www.etasr.com al-baghdadi et al.: one-dimension finite element modeling of grouted ground anchor the calculated strains shows good agreement in the bonded length part with underestimation of the peak point. there is an overestimation of the strain towards the anchor end. on the other hand, the calculated strain is less than the measured strain in the free length part. iii. parametric study according to the previous verifications, the suggested 1-d finite element model is considered reasonably valid for producing parametric studies to investigate some properties of grouted ground anchors. a. compression anchor a comparative study has been made between compressiontype and tension-type anchors, by using the exact data of surrounding soil and anchor properties of trial anchor (1). the applied load in the case of compression anchor is at the lowest node of the anchor’s mesh, while it is at the proximal end of the bonded length in the case of tension anchor, as stated in figure 1. figure 15 shows the load-displacement curves for both tension and compression anchors. it is noticed that the displacement of the compression-type anchor is less than the half of the displacement of the tension-type one, because the compression stiffness of the grout member is much higher than the tension stiffness. the calculated displacement represents the elastic and plastic components of the anchor head regardless of the elastic elongation of the strand. both anchors are reached to fully pull out at the same load (400kn), due to the adopted failure modes and grout-soil shear stress distribution as stated in (5). fig. 15. load-displacement curves for compression and tension anchor types. the calculated strains, for both compression and tension anchors, are presented in figure 16. obviously, in the tension anchor, the developed strains along the bonded length are tension strains, while its compression strains are along the unbonded length. the maximum value of strain is located at the loading point, at the beginning of the bonded length with shifting towards the anchor toe when the applied load has increased according to the adopted model of debonding between the strand and the grout, see (14)-(16). in the case of a compression anchor, all the developed strains along the anchor body are compression strains. the maximum value of strains is located at the anchor toe, i.e. the loading point, and it decreases until it vanishes at the anchor tip. the tension cracking strain of the grout, which is equal to 1×10 -4 , has been reached and exceeded since the 1 st loading (100kn) in the case of the tension anchor, while the developed strains did not reach the maximum compression strain of grout (0.003) [34] for the maximum applied load. a comparison of the mobilized skin friction between tension and compression types is shown in figure (18). it could be noticed obviously that the compression anchor has a larger maximum mobilized skin friction value than the tension anchor. the distribution of skin friction along the anchor body is not similar for the two types of anchor under consideration, the location of maximum skin friction value is at the anchor toe in the case of compression anchor, while the location of the maximum point is shifted from the proximal end of the bonded length toward the anchor toe with increasing of loading in the case of the tension-type anchor. the total mobilized skin friction force of both types of anchors is approximately equal. the shifting process of skin friction peak point reflects the debonding process between the strand and the grout in bonded length. fig. 16. strain in the grouted body for compression (dotted line) and tension (continuous line) anchors. fig. 17. skin friction along anchor length, for compression-type (broken line), and tension-type (continuous line). iv. conclusions a one-dimensional finite element model was developed and used to simulate both tension and compression types of grouted ground anchors. the tendon (steel) grout interface was modeled using the local bond-slip model, while the surrounding soil was modeled using a series of perfectly plastic springs. verification of the adopted finite element model was made by comparing the results with a three-dimensional finite element model of grouted ground anchor, developed in engineering, technology & applied science research vol. 12, no. 6, 2022, 9752-9759 9759 www.etasr.com al-baghdadi et al.: one-dimension finite element modeling of grouted ground anchor plaxis, and with the result of field tests of grouted ground anchors. the developed one-dimensional finite element model was used to make a comparison between compression and tension types of grouted ground anchors. from the verification and both comparisons, the following conclusions can be made:  load-displacement curves show very good agreement between the developed model and the finite element threedimensional model, showing very good agreement with the filed test result. the comparison between the calculated and measured strains in the field test results shows some differences along the unbonded length part, but with good agreement in the bonded length part.  the displacement of anchor head is smaller in the case of compression anchor, which makes it bear high design load.  the developed strain in the grouted body of the compression anchor is much smaller than the tension-type, which means less cracking in the grouted body providing 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[28] plaxis manual of verification and validation, bently systems inc., 2018. [29] u. smoltczyk, geotechnical engineering handbook, procedures. berlin, germany: john wiley & sons, 2003. [30] n. h. al-baghddi and b. a. ahmed, "field tests of grouted ground anchors in sandy soil of najaf, iraq," open engineering journal, accepted for publishing on 19 july 2022. [31] e. m. kara, m. meghachou, and n. aboubekr, "contribution of particles size ranges to sand friction," engineering, technology & applied science research, vol. 3, no. 4, pp. 497–501, aug. 2013, https://doi.org/ 10.48084/etasr.361. [32] pti dc35(2014), recommendations for prestressed rock and soil anchors. post tensioning institute, 2014. [33] p. xanthakos, ground anchors and anchored structures. new york, ny, usa: john wiley & sons, 1991. [34] aci 318-(2019),building code requirements for structural concrete and commentary. farmington hills, mi, usa: aci concrete, 2019. microsoft word etasr_v13_n3_pp10670-10674 engineering, technology & applied science research vol. 13, no. 3, 2023, 10670-10674 10670 www.etasr.com nguyen et al.: analysis of electromagnetic parameters of hybrid externally excited synchronous … analysis of electromagnetic parameters of hybrid externally excited synchronous motors for electric vehicle applications duc-quang nguyen faculty of electrical engineering, electric power university, vietnam quangndhtd@epu.edu.vn linh dinh hai faculty of electromechanical engineering, vietnam national university of forestry, vietnam hailinhdinh1512@gmail.com dinh bui minh school of electrical and electronic engineering, hanoi university of science and technology, vietnam dinh.buiminh@hust.edu.vn vuong dang quoc school of electrical and electronic engineering, hanoi university of science and technology, vietnam vuong.dangquoc@hust.edu.vn (corresponding author) received: 28 february 2023 | revised: 19 march 2023 | accepted: 22 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5824 abstract this paper presents two different approaches to improve the electromagnetic torque and output power of the hybrid externally excited synchronous motor (eesm) applied to electric vehicles (evs). an analytical approach is first considered to define the main parameters of the proposed machine. based on the obtained results from the analytical model, the hybrid eesm is designed with different rotor shapes and step-skewing magnet segments to reduce the total losses and improve torque ripple. then, finite element analysis (fea) is applied to compute and simulate electromagnetic parameters, such as the magnetic flux density, mean torque, and output power. the development of these two approaches is validated on an actual eesm machine and the agreement with the theory is shown. keywords-hybrid electrically excited synchronous motor (eesm); electromagnetic torque; output power; analytical method; finite element method (fem) i. introduction hybrid eesms are widely used in industry and electric vehicles due to their good overload capability, high torque density, and efficiency. however, these electromagnetic parameters depend on the magnet rotor structure [1, 2]. different approaches in eesm have been considered. authors in [1] presented the skewing method to minimize the cogging torque and torque ripple. this way, the design is able to maintain the maximum available torque, which can improve the performance of the machine. in [2], a dual-rotor design of permanent-magnet (pm) machine was proposed to reduce the cogging torque. both analytical and experimental results were presented to prove the effectiveness of the proposed design. in [3], an analytic model was proposed for hybrid eesm to improve and analyze the torque density and magnetic flux density at the air gap. in [4], finite element analysis (fea) was extended to evaluate the electromagnetic performance of a proposed machine. the obtained results offer several advantages, including a simple and robust structure, high torque density, and low cogging torque. the results are compared with experimental tests and good agreement between simulation and measurement was reported. in [5], the finite element method (fem) was employed for pm syncrhonous motors (pmsms) to find the optimal pm structure. additionally, sub-group optimization and parallel computation were used to reduce the computational load, making the approach more efficient. in [6, 7], the performance of 3 different ipm rotor designs used by major car manufacturers was studied. the results of this study have practical engineering, technology & applied science research vol. 13, no. 3, 2023, 10670-10674 10671 www.etasr.com nguyen et al.: analysis of electromagnetic parameters of hybrid externally excited synchronous … implications for the development of high-performance traction systems, specifically those used in hybrid electric vehicles. although the eesms have been studied extensively, the minimization of losses (copper and iron) is more complex than that of other 3-phase motors, because the excitation current of the eesm will cause a saturated case in a high speed up to 20000 rpm. this is the reason why the study of the minimization of the losses of eesm drives is still a challenge for researchers and designers. in this paper, an analytical approach is first considered to define the main parameters of the proposed machine. based on the obtained results from the analytical model, a hybrid eesm is designed with different rotor shapes and step skewing magnet segments to reduce the total losses and improve torque ripple. then, fem is applied to compute and simulate electromagnetic parameters such as the magnetic flux density, mean torque, and output power. the development of this approach will be validated on an actual eesm of continuous rated power of 80kw (with peak power of 150kw and maximum speed of 20000 rpm) to show the agreement with the theory. ii. modeling of eesm design the topology structure of the eesm design is shown in figure 1. the topology is built to combine the analytical calculations in matlab with the fem into one program. the process is divided into 3 main parts: analytical calculation, export drawing, and magnetic simulation. the analytical calculation is first computed in matlab and the obtained results, a detailed rotor and stator laminations, will be exported to cad files. finally, they will be coupled to the simulation environment of fem via the program interface developed by matlab gui. fig. 1. topology structure of eesm design. the topology structure shows the basic sizes (such as rotor and stator diameters, the lengths of rotor, airgap, and stator, and rotor and stator slots) of the proposed machine which need to be defined for the calculation process, i.e. performance specifications, limits of material properties, and temperature rise. however, there are some cases of machine designs already existing in the database. so, the properties of material components should be changed in order to minimize the total losses with technical constraints of the everage torque and output power. the geometry parameters of the stator and rotor are calculated by the process shown in figure 2. fig. 2. the calculation algorithm. if the rotor diameter d is assumed to be equal to the rotor length l of the eesm, the electromagnetic torque (nm) can be defined as [16-18]: � = � � . ��. . ��� (��) (1) where ls is the length of core (m) and the trv is the volume density (nm/m 3 ), which can be expressed as [17, 18]: ��� = � √� ����. � (��/��) (2) � = ��.���� � � (�/�) (3) based on the general expression in (1) and in order to compute the electromagnetic torque and the output power at a synchronous speed, the phasor diagram presenting a salientpole eesm machine with the reactance components xd and xq is shown in figure 3, where xd and xq are the dand qaxis reactances, and id and iq are the dand qcurrent components. the terms iqxq and idxd are the voltage drops aligned along the dand q-axes. the diagram is herein only presented for phase a. it is divided into two parts: the electrical voltage and current quantities are on the left side of the phasor diagram, and the magnetic flux linkages are on the right side. generally, the magnetic flux linkages are usually neglected [12], however it can be considered as a physical reality that rotates in space. engineering, technology & applied science research vol. 13, no. 3, 2023, 10670-10674 10672 www.etasr.com nguyen et al.: analysis of electromagnetic parameters of hybrid externally excited synchronous … fig. 3. phasor diagram of the eesm. the physical orientation of a flux can be represented using a space vector, which is a mathematical construct that describes the magnitude and the direction of a physical quantity in 3dimensional space. in the context of electromagnetism, space vectors are often used to represent the orientation of magnetic fields. the electromagnetic torque is computed as [8-11]: � = �� ["#$ + #$ #& '( $ − & *, (4) where id and iq can be expressed as: id =-i sin  and iq= -i cos, (5a-b) where e is the electromagnetic force (emf) and the products ldid and lqiq are the dand q-axis flux-linkages. the wound poles of a traditional pm machine are generally replaced by pms. the daxis is the direction of the magnetic flux produced by the rotor, while the qaxis shows the quadrature direction perpendicular to the daxis. this means that the pms are located inside the rotor and have different inductive properties along the dand qaxes. this can result in differences in the permeability along these axes, which can affect the motor performance. in contrast, in an exterior-ipm motor, the pms are located on the surface of the rotor. the pm-assisted reluctance motors are a motor type that uses both pms and salient poles to generate torque. iii. theorical background the minimization of the total losses of an eesm is a significant challenge for designers because it requires determination of all system parameters. additionally, implementing control strategies for an eesm is complex, and it can take a long time to find the minimum loss point due to the additional degree of freedom provided by the excitation current. to address these challenges, a new optimization approach called copper-losses minimization control (clmc) has been proposed for the eesm. the goal of this approach is to control the motor so that copper losses are minimal at every operating point. it is important to note that copper losses constitute a significant portion (about 60%) of the total losses of the eesm drive, especially when the motor operates in the optimal control range. by minimizing copper losses in the motor, the efficiency of the eesm drive can be considerably improved. thus, copper losses occur in the stator and excitation windings of the eesm and can be modeled through the stator and excitation resistances as follows [12-15]: ,-. = � � � (/$� + /&�* + �01 /01� (6) where � and �01 are respectively the stator and excitation resistances. these parameters can be expressed via the change of temperature as [14, 15]: � (��) = � (�2 )(1 + 45 (�� − �2 )* (7) �01 (�0 * = �01 (�2 )(1 + 45 (�� − �2 )* (8) where 4r is the material temperature coefficient at the reference temperature �0. its value is usually given at 20oc, e.g. for copper conductor 4r = 0.004041 (1/k). if the constraints of the stator voltage and current are neglected, the expression of loss minimization becomes [12, 13]: �/67 89,8:,8; < ,-. (/$ , /& , /01 * =. > �? (/$ , /& , /01 * = �?,@?0 (9) it should be noted that the degree of freedom in the excitation current control for the eesm can make the problem of optimal control more challenging compared to loss minimization problems of other 3-phase machines, because the excitation current is not directly tied to the load. one challenge in the optimal control of eesms is determining the optimal excitation current for a given load condition. this is because the excitation current affects both the electromagnetic torque and the iron and copper losses in the machine. thus, an optimal control strategy needs to consider both torque and loss components to achieve the desired performance. another challenge is the non-linear nature of the eesm. the machine response to changes in excitation current and load conditions may not be linear, and this can make it difficult to develop an accurate model for control purposes. furthermore, the eesm may exhibit hysteresis effects due to the saturation in the magnetic core, which can further complicate the control problem. to overcome these challenges, advanced control techniques such as model predictive control, adaptive control, and neural network-based control may be used. these techniques can help optimize the excitation current for a given load condition, while also compensating for the non-linearities and hysteresis effects of the eesm. iv. analysis of electromagnetic performance based on the theory presented above, in this section, a practical eesm of 80kw rated power (with peak power of 150kw and maximum speed of 20000 rpm), applied to an electric car, byd atto 3 model [16], is considered. the main parameters of the proposed machine are given in table i. the cross section of stator and rotor laminations of the eesm (model byd atto 3) of 150kw-16000 rpm is presented in figure 4. the distribution of magnetic flux density along the air gap of the hybrid and normal eesm motors is presented in figure 5. the obtained results show that the value of the magnetic flux density in the hybrid eesm motor is higher than that in the normal eesm motor, due to the flux-concentration engineering, technology & applied science research vol. 13, no. 3, 2023, 10670-10674 10673 www.etasr.com nguyen et al.: analysis of electromagnetic parameters of hybrid externally excited synchronous … effect of the pm in the hybrid eesm. in the hybrid eesm, the pm is placed on the rotor surface, which causes the magnetic flux to be concentrated in the area around the pm, resulting in a higher magnetic flux density in the air gap compared to the normal eesm, which does not have a pm on the rotor. the higher magnetic flux density in the air gap of the hybrid eesm motor can lead to several benefits. it can increase the electromagnetic torque produced by the motor, resulting in higher performance. figure 6 shows the torque and speed curves of the hybrid and normal eesm motors. with the imposed current of 10a, there is a difference in the average torque between the hybrid and normal eesm motors. the average torque of the normal eesm has a lower value than that of the eesm when the speed is lower than 7000 rpm. table i. main parameters of the considered car parameter value unit byd atto 3 2020 peak power 150 kw hairpin winding stator assy weight 23.6 kg stator lamination weight 17.98 kg copper weight 5.388 kg stator assembly 6.36 kg copper 27.40 kg stator iron 8.30 kg cooling system (liquid cooling) voltage 394 volt slot number 48 pole number 8 shaft diameter 60 mm rotor outer diameter 138 mm stator inner diameter 139.4 mm airgap length 0.7 mm stator stack length 140 mm rotor stack length 141.6 mm average stack 140.8 mm fig. 4. cross section of stator and rotor laminations of eesm (byd atto 3 model) of 150kw-16000 rpm. fig. 5. magentic flux density distribution along the air gap of hybrid and normal eesm motors. fig. 6. comparison of average torque distribution of the two models (hybrid and normal eesm). in addition to the evarate torque, the output power of the hybrid and normal eesm motor under the full range of speed is presented in figure 7. the obtained results show that the output power of the hybrid eesm is improved in the higherspeed region, due to the presence of the pm on the rotor surface, which provides additional magnetic flux and improves the motor performance. the higher magnetic flux density in the air gap of the hybrid eesm results in a higher electromagnetic torque, as well as better output power at higher speeds. the detailed comparison of the parameters of hybrid and normal eesm is presented in table ii. table ii. parameter comparison of normal and hybrid eesm motors parameters hybrid eesm normal eesm unit maximum torque possible (dq) 233.32 212.51 nm average torque (virtual work) 234.9 211.79 nm average torque (loop torque) 233.41 210.45 nm torque ripple (msvw) 28.235 7.6187 nm torque ripple (msvw) [%] 12.028 3.5959 % cogging torque ripple (vw) 2.5773 0 nm electromagnetic power 98327 88748 w input power 1.02e+05 92767 w output power 97681 88173 w system efficiency 95.445 95.047 % armature dc copper loss 1938 1938 w field dc copper loss 2077 2082 w damper cage loss 10 10 w stator iron loss 541.7 540.8 w rotor iron loss 27.09 27.4 w wedge loss 7 7 w windage loss 7.035 7.035 w friction loss 8 8 w shaft loss 4.82e-08 5.06e-08 w total losses 4591 4595 w fig. 7. power distribution of the two models (hybrid and normal eesm). 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0 50 100 150 200 250 300 350 400 m a g n e ti c f lu x d e n si ty b ( t ) angle hybrid eesm normal eesm 0 50 100 150 200 250 0 2000 4000 6000 8000 10000 t o rq u e ( n .m ) speed (rpm) hybrid eesm normal eesm 0 20 40 60 80 100 120 140 0 2000 4000 6000 8000 10000 12000 14000 p o w e r (k w ) speed (rpm) hybrid eesm normal eesm engineering, technology & applied science research vol. 13, no. 3, 2023, 10670-10674 10674 www.etasr.com nguyen et al.: analysis of electromagnetic parameters of hybrid externally excited synchronous … v. conclusion the current paper has analyzed and compared the magnetic flux density, average torque, and output power of two types of electric motors (hybrid and normal eesm) used in electric vehicle applications. once of the significant contributions of the current study is that it highlights the improvement in the magnetic flux density, average torque, and output power of the hybrid eesm motor compared to the normal eesm motor over a wide range of speeds. the improved performance of the hybrid eesm motor is likely caused by its unique design and construction, which combines features of both the pmsm and eesm. references [1] w. zhao, t. a. lipo, and b.-i. kwon, "torque pulsation minimization in spoke-type interior permanent magnet motors with skewing and sinusoidal permanent magnet configurations," ieee transactions on magnetics, vol. 51, no. 11, pp. 1–4, aug. 2015, https://doi.org/10.1109/ tmag.2015.2442977. [2] e. yıldırız, m. güleç, and m. aydın, "an innovative dual-rotor axialgap flux-switching permanent-magnet machine topology with hybrid excitation," ieee transactions on magnetics, vol. 54, no. 11, pp. 1–5, aug. 2018, https://doi.org/10.1109/tmag.2018.2848878. [3] y. liu, z. zhang, and x. zhang, "design and optimization of hybrid excitation synchronous machines with magnetic shunting rotor for electric vehicle traction applications," ieee transactions on industry applications, vol. 53, no. 6, pp. 5252–5261, aug. 2017, https://doi.org/ 10.1109/tia.2017.2720671. [4] w. li, t. w. ching, and k. t. chau, "design and analysis of a new parallel-hybrid-excited linear vernier machine for oceanic wave power generation," applied energy, vol. 208, pp. 878–888, dec. 2017, https://doi.org/10.1016/j.apenergy.2017.09.061. 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[12] w. l. soong and n. ertugrul, "field-weakening performance of interior permanent-magnet motors," ieee transactions on industry applications, vol. 38, no. 5, pp. 1251–1258, sep. 2002, https://doi.org/ 10.1109/tia.2002.803013. [13] p. guglielmi, b. boazzo, e. armando, g. pellegrino, and a. vagati, "permanent-magnet minimization in pm-assisted synchronous reluctance motors for wide speed range," ieee transactions on industry applications, vol. 49, no. 1, pp. 31–41, jan. 2013, https://doi.org/10.1109/tia.2012.2229372. [14] x. liu, h. chen, j. zhao, and a. belahcen, "research on the performances and parameters of interior pmsm used for electric vehicles," ieee transactions on industrial electronics, vol. 63, no. 6, pp. 3533–3545, jun. 2016, https://doi.org/10.1109/tie.2016.2524415. [15] j. wang, x. yuan, and k. atallah, "design optimization of a surfacemounted permanent-magnet motor with concentrated windings for electric vehicle applications," ieee transactions on vehicular technology, vol. 62, no. 3, pp. 1053–1064, mar. 2013, https://doi.org/ 10.1109/tvt.2012.2227867. [16] "byd yuan plus," chinamobil. https://www.chinamobil.ru/eng/byd/ yuan-plus/. [17] d. b. minh, l. d. hai, t. l. anh, and v. d. quoc, "electromagnetic torque analysis of srm 12/8 by rotor/stator pole angle," engineering, technology & applied science research, vol. 11, no. 3, pp. 7187–7190, jun. 2021, https://doi.org/10.48084/etasr.4168. [18] d. b. minh, l. d. hai, t. l. anh, and v. d. quoc, "electromagnetic torque analysis of srm 12/8 by rotor/stator pole angle," engineering, technology & applied science research, vol. 11, no. 3, pp. 7187–7190, jun. 2021, https://doi.org/10.48084/etasr.4168. microsoft word 2-679-ed.doc engineering, technology & applied science research vol. 6, �o. 3, 2016, 982-986 982 www.etasr.com teymoori and ahangarkolaei: a tunable capacitor based on mems technology for rf applications a tunable capacitor based on mems technology for rf applications mir majid teymoori department of electrical engineering firoozkooh branch, islamic azad university firoozkooh, iran mteymoor@yahoo.com jaber merrikhi ahangarkolaei department of electrical engineering firoozkooh branch, islamic azad university firoozkooh, iran jmerrikhi@yahoo.com abstract—a tunable capacitor based on mems technology is presented in this paper. the proposed structure consists of two fixed-fixed parallel movable plates with 4 supports. movability of two plates makes it possible to actuate the plates with a small voltage. when the actuation is applied, two plates move together and their distance is decreased, hence the capacitance is increased and tuning is achieved. the structure is simulated through the finite element method using comsol and a*soft hfss software. simulation results show that the actuation voltage required to access the 59% tuning, is 7 v. the effective area of the designed tunable capacitor is 200 x 200 µm2 with a thickness of 2 µm. the quality factor is 91 at 11 ghz which is sufficient for various rf communication applications such as filters, transceivers and so on. the low stress induced on the plates and low actuation voltage, are the main advantages of the design. keywords-mems; tunable capacitor; fixed-fixed beam; quality factor; finite element method i. introduction the growing demands for the wireless communication systems enforce researchers to design and implement new components required for this purpose. the variable capacitors and variable inductors as main components of a wireless system play a main role and can be employed in frequency based circuits. diverse applications of he tunable capacitors such as filters, voltage controlled oscillators, super-heterodyne transceivers and so on make them an attractive subject. as technology advances, the quality of tunable capacitors (tuning range, quality factor and broad frequency) increase [1-5]. mems (micro electro mechanical systems) have a very significant impact on the development of tunable devices e.g. varactors. the capability of employing electrostatic actuation and air dielectric makes possible to implement high quality factor and low power consumption through the mems technology [6]. there are many methods to design and develop mems variable capacitors. the parallel plate capacitors have been used very well in communication transceivers due to their simple tuning mechanism, low area consumption, high quality factor achievement and mems fabrication possibility. a number of mems tunable capacitors have been designed, fabricated and widely studied [7, 8]. generally, there are three methods to change the capacitance of the parallel plate capacitors: the gap tuning method [9-12], the area tuning method [13, 14] and the dielectric displacement method [15]. different actuations are employed in the parallel plate variable capacitors such as electrostatic [16], piezoelectric [17] and thermal actuator [18]. the integrated fabrication compatibility and low power consumption of the electrostatic actuation almost enforce the researchers to employ it. low actuation voltage and high tuning range are the thermal actuation advantages, however high power consumption is its drawback. in this paper we present a new low actuation voltage and four-support beam for tunable mems capacitors which are studied using fem software e.g. comsol and ansoft hfss. the paper includes two main sections. first section explains the design and analytical considerations, and the second section covers the computer simulation results. ii. design and analytical considerations a. proposed structure based on the gap tuning method of the parallel plate capacitors, we introduce a new design for the tunable capacitor. as depicted in figure 1a and figure 1b, the proposed structure consists of a bottom plate which is located on the etched silicon and can be moved. the upper plate is attached to four supports and is on top of the bottom plate. the idea of the two plates moving is before introduced in [19] in 2002 for mems switches and in [20] for fixed-free cantilever beam tunable capacitors. other researches have also proposed two moveable plate tunable capacitors [21-24]. however, the novelty of the proposed tunable capacitor design is the simultaneous movability of the two plates with an idea to reduce the spring constant of the structure. we employ the fixed-fixed cantilever-section beam which has the smaller spring constant with respect to the fixed-fixed beam counterpart. in our proposed structure, the plate is attached to four supports and hence the stiffness of the plate is reduced considerably. engineering, technology & applied science research vol. 6, �o. 3, 2016, 982-986 983 www.etasr.com teymoori and ahangarkolaei: a tunable capacitor based on mems technology for rf applications fig. 1. schematic of the proposed tunable capacitor: a) isometric view and b) front view b. tuning mechanism when the voltage is applied between the bottom and upper plate, the two plates start to move together toward each other and the gap between them (d) is decreased and regarding to (1) the capacitance change is achieved. d a c r εε0 = (1) assuming the gap between two plates d, the structure is designed so that each plate displaces only d/6 and total displacement is d/3. the one-third displacement has three main advantages: the first it prevents the pull-in effect of the electrostatic actuation and makes it possible to have good control on the capacitance change. the second benefit is the structure's stress and strain reduction, which increases the lifetime of the designed capacitor. third advantage is the linearity behavior of the capacitance change in the one-third of gap between two plates. d d/6 d/6 d d/6 d/6 fig. 2. tuning mechanism of the designed tunable capacitor c. analytical considerations 1) structure stiffness the designed plates for the tunable plate can move simultaneously. referring to figure 3a, the relationship between the electrostatic force induced by the voltage applied between the two plates and the plate displacement is expressed as: 101 xxkf −= (2) 232 xxkf −= (3) where k1 and k2 are the spring constant of the up and bottom plates, respectively. for figure 3b, we would have: 40 xxkf −= (4) where, k is spring constant of the upper plate individually and f is the same as the figure 3a. considering figure 3: )32()( 1040 xxxxxx −+−=− (5) combining (3), (4) and (5): 21 k f k f k f += (6) if two plates have the same configurations and the same boundary conditions, then k1 = k2 and hence k = k1/2, that is the spring constant of the total structure is the half of the one plate moving structure and therefore the electrostatic voltage will be small. regarding this phenomena, to achieve the low actuation voltage we choose two movable plates for our design. fig. 3. comparison of two plates: a) two plates moving b) only one plate moving according to euler-bernoulli equation, the governing equation for bending of the isotropic beams of constant cross section is as [25]: )( )( 4 4 xq dx xwd ei = (7) where e is the young's modulus, i is the moment of inertia, w(x) is the deflection point and q(x) is the applied transverse load. for a fixed-fixed plate, assuming no residual stress, the spring constant can be approximately calculated as [26]: 3 )(16 l t ewk = (8) where w, t and l is the width, thickness and length of the plate, respectively. equation (8) is true for two sides completely fixed plate. in our designed plate, we reduce the (a) (b) engineering, technology & applied science research vol. 6, �o. 3, 2016, 982-986 984 www.etasr.com teymoori and ahangarkolaei: a tunable capacitor based on mems technology for rf applications boundary condition employing four supports, hence the stiffness and the applied voltage is diminished considerably. 2) pull-in voltage when the voltage is applied between two parallel plates, the plates start to deflect downward, decreasing the gap g and increasing the electrostatic pressure on the plates. the governing equation is: 2 '' ' 0 2 (9)( ) 2( ) e d r av mg bg k g g f t g ε ε + + − = = + where m is the mass, b is damping coefficient and k is the stiffness of the plate, g0 is the gap between two plates, a is the plate's effective area, td is the thickness of the dielectric, ε is the air permittivity, fe is the electrostatic force and v is the applied voltage. neglecting the mass and damping force, (9) has a critical point at 0 (2 3) d g g t= ⋅ + . replacing this value in (9), we have [27]: a kd vp 0 3 27 8 ε = (10) this voltage (vp) is known as the pull-in voltage and is a critical voltage for two plates contacting. equation 10 shows that when the distance between the two plates is decreased, the actuation voltage can be reduced. iii. simulation to evaluate the actuation voltage and frequency response of the designed tunable capacitor, the structure is simulated employing the finite element method with comsol and ansoft hfss software. the comsol software is used to find the required voltage for one-third displacement of two plates and the hfss software gives us the frequency characteristics of variable capacitor such as quality factor and tuning ratio. a. pull-in voltage simulations two structures are considered in the comsol software simulation: one structure is a two clamped membrane with size of 200 x 200 x 2 µm 3 (figure 4a) and the other is our designed structure (figure 4b). the main aim of this simulation is to compare the two structures with varying stiffness (different spring constants k). to simplify, in all simulations it is assumed that the residual stress on the membrane is zero. it is evident that residual stress will increase the actuation voltage. the mechanical properties of the beam material (gold) are stated in table i for this simulation. based on the simulation results, the pull-in voltage for the structure shown in figure 4a is approximately 64v. the displacement and stress distribution of this simulation is shown in figures 5 and 6, respectively. as shown in figure 6, the maximum stress on this structure is 23.6 mpa which is much smaller than the critical stress of gold (205 mpa). 200 µm 200 µm 15 µm 100 µm 200 µm 200 µm 15 µm 100 µm fig. 4. schematic of the simulated beams: a) our designed beam b) two clamped beam fig. 5. two clamped beam displacement fig. 6. total stress distribution on the two clamped beam for the proposed structure shown in figure 4b, the same simulation is accomplished and the displacement and total stress distribution on the beam is depicted in figures 7 and 8, respectively. it should be mentioned that the deformation in both figures was exaggerated for visualization purposes, so the bottom plate extends in the area of the upper plate and vice versa. (a) (b) engineering, technology & applied science research vol. 6, �o. 3, 2016, 982-986 985 www.etasr.com teymoori and ahangarkolaei: a tunable capacitor based on mems technology for rf applications based on figure 8, the stress on the designed structure is 7.1 mpa which is almost 3 times smaller than the figure 4a structure and very smaller than the gold material critical stress, hence the lifetime of the proposed structure can be very good. as shown in figure 7, the actuation voltage (for one-third displacement) in this structure is approximately 7 v which is the main advantage of the 4-support beam structure. fig. 7. four-support beam displacement fig. 8. stress distribution on the proposed four-support beam b. frequency simulation to evaluate the frequency behavior of the designed capacitor, we employ the ansoft hfss software which is very suitable for the rf applications. table 2 shows the electrical properties of the designed beam material. the main aim of this simulation is to find the capacitance ratio (tuning range) and the quality factor. the hfss simulation results are shown in the figures 9 and 10. as depicted in the figure 9, the capacitance is changed from 312ff to 497ff in the frequency of 11ghz; hence we would have 59% tuning range. in this frequency, the quality factor is 90, which is very suitable for rf communication applications. fig. 9. the capacitance of the proposed varactor a) before and b) after actuation fig. 10. the quality factor of the proposed varactor a) before and b) after actuation (a) (b) (a) (b) engineering, technology & applied science research vol. 6, �o. 3, 2016, 982-986 986 www.etasr.com teymoori and ahangarkolaei: a tunable capacitor based on mems technology for rf applications table i. mechanical properties of beam material (gold) value parameter 76.52 gpa yong's modulus 0.41 poisson ratio 19300 kg/m 3 density 205mpa yield stress 200 x 200 µm 2 area 2 µm thickness 2 µm gap 100 µm support length 15 µm support width table ii. electrical properties of the used material relative permittivity conductivity material 11.9 0.003 s/m silicon substrate 7 0.001 s/m silicon nitride 1 41e6 s/m gold 1.0006 0 air conclusion a low voltage tunable capacitor based on micromachining technology is designed and simulated. the tuning mechanism is based on the gap tuning of a new structure. two plates move-ability design decreases the stiffness of the total structure and hence the applied voltage is considerably decreased. the structure is simulated with fem comsol and ansoft hfss software. the results show 7 v applied voltage for deflection of the 0.35 µm of plates individually and a 59% tuning range with quality factor of 90 at 11 ghz which is compatible with the rf applications. acknowledgment the authors would like to thank the department of electrical engineering, firoozkooh branch, islamic azad university, firoozkooh, iran for the financial support. references [1] h. l. krauss, c. w. bostian, f. h. raab, solid state radio engineering, new york, ny, usa: john wiley & sons, 1980. 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timoshenko, mechanics of materials, pws publishing company, 2003 [26] s. afrang, g. rezazadeh, “design and simulation of simple and varying section cantilever and fixed-fixed end types mems switches”, ieee international conference on semiconductor electronics, kualalampur, pp. 593-596, malaysia, 2004 [27] m. m. teymoori, design and simulation of a novel electrostatic micromachined pump for medical applications, msc, urmia university, iran, 2003 microsoft word etasr_v12_n4_pp9056-9062 engineering, technology & applied science research vol. 12, no. 4, 2022, 9056-9062 9056 www.etasr.com bellum et al.: the performance of spectral clustering algorithms on water distribution … the performance of spectral clustering algorithms on water distribution networks: further evidence farid belloum laboratory of civil and hydraulic engineering civil and hydraulic engineering department university of guelma guelma, algeria belloum.farid@univ-guelma.dz larbi houichi department of hydraulic engineering faculty of technology university of batna 2 batna, algeria l.houichi@univ-batna2.dz mazouz kherouf laboratory of civil and hydraulic engineering civil and hydraulic engineering department university of guelma guelma, algeria kherouf_maz@yahoo.fr received: 2 june 2022 | revised: 15 june 2022 | accepted: 17 june 2022 abstract-the aim of the current paper is to revisit the performance of spectral clustering algorithms for water distribution networks. in the literature, there have been attempts to introduce improved algorithms based on graph theory. we focus on a class of these algorithms that applies the concepts of the spectral clustering approach. we assess the performance of spectral clustering algorithms on a wider range of water network types (i.e. large, medium, and small sized networks) using a wider range of clustering methods (both partitioning and hierarchical) and performance indicators. our findings suggest that partitioning methods, such as k-means are not consistently efficient in all types of networks. nonetheless, the partitioning around medoids (pam) algorithm shows a relatively good performance according to modularity, while the internal indices of k-means and hierarchical clustering algorithms are more efficient. stability indices show that pam and clara algorithms are more efficient. keywords-sectorization; clustering methods; spectral clustering algorithms i. introduction water distribution networks (wdns) are large and complex networks designed and built to serve the water supply needs of an urban area. proper and efficient control and management of wdns is one of the key aspects in the operational practices of water supply networks and a major challenge [1, 2]. this is particularly true for large urban areas and cities, where the network becomes larger and more complex. in order to manage and monitor unusual demands caused generally by leaks the common practice involves using district metered areas (dmas) [3, 4], which allow water network systems to monitor water inflows and outflows to reduce water and revenue losses. thus, an optimal and efficient approach to optimally partition the water network into dmas is of crucial importance. although wdn is an efficient approach for the partitioning of the dmas [5], achieving optimal partitioning remains challenging, due to the existence of many parameters that need to be accounted for, such as hundreds of valves, tanks, pipelines, and pumps [6-8]. although many methods have been proposed, the literature does not offer a conclusive result on the best performing approach to cluster dmas. for example, authors in [9] developed an algorithm based on graph theory, which divides the water distribution system into clusters according to the direction of the flow in the pipes. this algorithm is general enough to be applied for various purposes including the enhancement of water security by assigning sensors to clusters, and/ or the efficient isolation of a containment intrusion. authors in [10] propose the use of pressure sensitivity matrix analysis combined with clustering techniques to optimally characterize and determine a sensor configuration that maximizes the degree of locatability subject to the budget constraint of sensor configuration. furthermore, they show that their proposed method is successfully implemented to identify the optimal set of pressure sensors that need to be installed in a dma in the barcelona wdn. authors in [36] propose a multistage approach that involves the simultaneous application of sectorization of a large wdn – into dmas – and optimization of rehabilitation of the network with new components such as pipes, valves and tanks. finally, authors in [34] conduct a comparative analysis of three commonly used corresponding author: name of corresponding author engineering, technology & applied science research vol. 12, no. 4, 2022, 9056-9062 9057 www.etasr.com bellum et al.: the performance of spectral clustering algorithms on water distribution … methods to create dmas, fast greedy, random walk, and metis. the performance of these methods is evaluated on two cases of a large and complex wdn exnet with unweighted and weighted edges. they conclude that fast greedy has an overall better performance and was found to be more effective in weighted graph partitioning. in this context, water network partitioning has become one of the most popular methods and strategies adopted to improve the optimal wdn control and management, within which spectral graph theory is central tool for developing clustering algorithms. in particular, authors in [11] propose a holistic analysis framework to support water utilities for an efficient supply management. the proposed approach is based on graph spectral methods that employ the properties of eigenvalues and eigenvectors of matrices associated with graphs. the approach aims to reduce the challenges urban water supply may face in an increasingly complex city-based environment, which is characterized by various heterogeneous and interconnected infrastructures often affect the process of supplying households with safe water. the approach is tested on two wdns, c-town and an operational network. as a result, they show that their proposed approach is useful and optimal to efficiently manage wdns. despite the attractive features of this holistic approach, the extent to which this approach is robust is not known. for example, the authors in [11] offer limited evidence that spectral based algorithms are useful and lack robustness checks. thus, the main aim of this paper is to extend the analysis offered by [11] by testing the sensitivity and robustness of the graph spectral methods in two ways. first, we test these methods on three different types of wdns: a complex and large network (exnet), a medium-sized network (c-town), and a smallsized operational network (oued el ma). these networks represent different types of water networks in terms of structure and size. second, we assess the performance of the spectral based algorithms using the pam, clara, and diana clustering methods. we apply these algorithms on the three types of networks described above. then, the performance of each algorithm is assessed based on three criteria, namely modularity, internal indices, and stability indices. our findings suggest that the performance of algorithms differs depending on the performance criterion and the type of network. in this context, according to modularity, the pam algorithm is found to perform better. k-means and hierarchical clustering are found to be the most efficient according to the internal indices, while pam, hierarchical clustering, and clara have better stability index. thus, one cannot generalize the approach of [11] as a generic method applicable to all types of networks. ii. materials and methods a. spectral clustering a water network can be represented as a graph whose edges and nodes represent network pipes and pipe junctions, respectively [12, 13]. this graphical structure makes the spectral clustering approach suitable for solving water network problems. the spectral clustering approach has many attractive features. it is simple to implement and can be solved efficiently by standard linear algebra software [14-17]. in addition, it outperforms standard clustering techniques such as k-means [14]. this method is implemented in three steps, namely: (i) computing a similarity graph, (ii) projecting data onto a lowdimensional space, and (iii) identifying clusters. figure 1 illustrates the workflow of the spectral clustering algorithm highlighting further the computations involved throughout all the steps. this includes associating both adjacency and laplacian matrices to graphs. next, their eigenvalues are computed, which are then related to the structural properties of graphs [18, 19]. fig. 1. spectral clustering algorithm. finally, spectral k-means clustering algorithm is applied to extract the final clusters from the eigenvectors’ matrix when all clusters are assumed to have equal size and homoscedastic. in most of the cases this assumption is not satisfied. clusters will differ in their size, density, and variance [20]. violating this assumption does not necessarily rule out the use of k-means algorithm. it simply implies one needs to correct the algorithm for the times this assumption is violated. in addition, and given the recent advances in computer processing power, using other alternative algorithms that relax the assumption of clusters’ size and variance constancy is necessary to achieve robust results. thus, in this paper, we conduct a comparative exercise using different clustering algorithms. this includes the following: clustering large applications (clara), partitioning around medoids (pam), agglomerative, divisive analysis (diana), and k-means. this setting will allow us to extract the best partitioning scheme according to internal quality and stability indices available in the literature. b. clustering methods there are two broader classes of clustering methods: (i) partitioning and (ii) hierarchical clustering methods. while partitioning methods divide the data into mutually exclusive partitions (i.e. clusters), hierarchical methods classify the data into multi-levels or a hierarchy of clusters. in general, these methods have key differences. partitioning clustering methods are faster. they require, however, stronger assumptions such as engineering, technology & applied science research vol. 12, no. 4, 2022, 9056-9062 9058 www.etasr.com bellum et al.: the performance of spectral clustering algorithms on water distribution … initial parameters and number of clusters. in contrast, hierarchical clustering methods require only a similarity measure and not initial parameters such as the number of clusters. figure 2 illustrates the different methods used under each clustering class. in this paper, we discuss two types in each clustering method. this includes the k-means and kmedoids under partitioning methods and agglomerative and divisive under hierarchical. fig. 2. most popular clustering methods. 1) partitioning clustering k-means algorithm is one of the oldest and most commonly used clustering algorithms. it attempts to partition the dataset into k predefined clusters where each observation belongs to the cluster with the nearest mean. authors in [21] used k-means on large-scale networks to determine clusters in order to minimize the sum of squared distance error between nodes for developing dmas configuration. pam is a variant of k-means in which instead of using the mean point as the center of a cluster. it uses an actual point in the cluster to represent it. authors in [22, 23] combined pam partitioning method with spectral clustering to introduce a greedy heuristic that reassigns the nodes belonging to minor connected components to major connected components of an electric power network. clara is an extension to k-medoids (pam). it is used to deal with data containing a large number of objects. authors in [24] highlighted the advantages of using spectral clustering over clara and showed that spectral clustering has better performance to analytically localize leaks in a wdn. in addition, authors in [25] compared pso algorithm to partitional clustering performed by other algorithms that work with various attribute types (such as pam and clara). the findings obtained by these algorithms were consistently similar. authors in [25], however, show that pso is more efficient. 2) hierarchical clustering agglomerative algorithms are based on graph theory concepts. they iteratively merge the nodes to build a bottomup hierarchy. authors in [26] presented an algorithm that uses a computationally efficient spectral and hierarchical clustering algorithm to reveal the internal connectivity structure of a network representing a power grid, subject to any choice of electrical parameter associated to the transmission. hierarchical spectral clustering has revealed a static internal structure of the network. diana is a technique that constructs the hierarchy in the inverse order [27]. first, all the data points are considered as a single cluster. then, using iterations, the dataset is divided into clusters until reaching the optimal n clusters in the last iteration. 3) quality measures of graph clustering for robustness purposes, we apply various measures of quality. this includes the following: modularity (m): this measure is the most common quality measure for graph clustering [28]. it captures the trade-off between the number of edges bridging clusters and a measure accounting for the number and the similarity among each other [29]. modularity can be defined as: ),( 2m2m 1 ji ij ji ij cc kk am δ       −= (1) where aij is the value of the adjacency matrix between vertices i and j, ki is the sum of the weights of the edges adjacent to i, m is the number of edges in the graph, and δ is the kronecker delta which takes value of 1 if its arguments are equal and 0 otherwise. authors in [29] presented the classical modularity index and tailored and modified it for wdns in order to optimize the framework based on the maximization of the wdn-oriented modularity-based index versus the minimization of the cost of newly installed devices to obtain network segments. 4) internal measures connectivity: it uses vertex distances to measure cohesion and separation of clusters. it is formally defined as [30, 31]:  = = n i l j nni ji x 1 1 , )( (2) where l is a parameter that determines the number of neighbors that contribute to the connectivity measure, nni(j) as the j is the nearest neighbor of observation i, xi;nni(j) is 0 if i and nni(j) are in the same cluster and 1 otherwise. the connectivity value should be minimized. dunn (d): dunn's index [32] shows the distance between objects in a cluster and its intercluster separation. it uses the minimum pairwise distance that each cluster has to reach to be compact. to calculate the dunn index, we adopt [31]: � = �����,� ∈�,����� ( ��� �∈��,�∈�� ����(�,�)) ��� ��∈� �����(��) (3) where diam (cm) is the maximum distance between observations in cluster cm. the dunn index has a value between zero and 1 and should be maximized. silhouette (s): the silhouette value measures the degree of confidence in the clustering assignment of a particular engineering, technology & applied science research vol. 12, no. 4, 2022, 9056-9062 9059 www.etasr.com bellum et al.: the performance of spectral clustering algorithms on water distribution … observation, with well-clustered observations having values near 1 and poorly clustered observations having values near 0 [31]. for observation i, s is formally defined as: ),max( )( ii ii ab ab is − = (4) where ai is the average distance between i and all the other observations in the same cluster, and bi is the average distance between i and the observation in the nearest neighboring cluster. 5) stability measures clustering is considered stable if the corresponding partitioning remains unchanged with its minimum change [33]. as a sub-category of internal indices, there are many stability measures that help validate cluster solutions available: average proportion of no overlap (apn), average distance (ad), average distance between means (adm), and figure of merit (fom) [31]. iii. water distribution networks for robustness purposes, we assess the performance of spectral clustering algorithms on three different types of water networks. this is in contrast to [11] as it presents conclusions limited to medium sized networks. in this context, we consider 3 types of water networks, chosen according to their type (looped or mixed) as well as their size based on the number of nodes and edges (i.e. small, medium, and large). fig. 3. wdns: (a) exnet, (b) c-town, (c) oued el ma. the first network is exnet (figure 3(a)),which is largesized and complex. it serves a population of approximately 400,000 inhabitants. the network system consists of 2416 pipes and 1891 nodes. elevated reservoirs provide the energy to the entire system [34]. the second network is the mediumsized and operational oued el ma wdn, as illustrated in figure 3(c), which is located in an algerian medium-sized city with a population of 14000. the water network consists of 621 nodes and 630 edges. c-town network– as depicted in figure 3(b) – is a small-sized wdn. c-town is a benchmark water network model employed in the field of water distribution system analysis with 444 pipes and 396 nodes [35]. iv. critical discussion authors in [11] focused on the sectorization of the c-town network for 5 sectors using the k-means algorithm. in this section, we assess the performance of the algorithm proposed in [11] and compare it to alternative algorithms including pam, clara, hierarchical clustering, and diana using the same experimental settings. in other words, we use the same conditions including c-town network with 5 sectors. figure 4 illustrates the sectorization using the k-means and our proposed alternative clustering methods. in general, our replication is successful and consistent with the original work [11]. fig. 4. clusters of c-town. fig. 5. c-town network sectorized: (a) k-means (a), (b) pam, (c) clara, (d) hierarchical, (e) diana. engineering, technology & applied science research vol. 12, no. 4, 2022, 9056-9062 9060 www.etasr.com bellum et al.: the performance of spectral clustering algorithms on water distribution … figure 5 reports the internal, stability, and modularity indices for the 5 algorithms on a c-town wdn with 5 sectors. according to the findings, k-means clustering algorithm is reported to be stable by only 1 criterion (ad). it performs, however, better based on modularity and internal criteria including connectivity and dunn. our findings suggest, that hierarchical clustering performs relatively well in terms of stability and internal criteria. however, our evidence show that the k-means performs better only in a very special setting, i.e. for small-sized wdns with a small number of sectors. for larger number of sectors and medium to large-sized networks k-means performs poorly compared to pam and hierarchical clustering in general. v. results and discussion in this section, we report and discuss the findings of our simulations. in this context, spectral partitioning was carried out for the three considered wdns using the techniques discussed above. for each wdn, we report the identified clusters using the k-means, pam, clara, general hierarchical clustering, and diana. furthermore, for each network, the performances of clustering methods are evaluated on different number of clusters. our experimental setting allows 6 different partitions of clusters as follows: • large water network allowing 10, 20, 25, 30, 40, and 50 partitions. • medium sized network allowing for 4, 6, 8, 10, and 12 partitions. • small-sized network: allowing for 3, 4, 5, 6, 8, and 10 partitions. a. large and complex network (exnet) figure 6 illustrates the performance of clustering algorithms across 6 different partition combinations. fig. 6. exnet wdn spectral clustering. the number of clusters across these partitions ranges between 10 and 50. there are 8 performance criteria reported for each of the 5 clustering algorithms. according to these criteria, pam has been found to perform consistently well across all 6 combinations of partitions. in particular, pam is dominant as the number of clusters increases to 40 and 50. hierarchical is found to perform relatively well, especially when the number of clusters is lower than 40. furthermore, the performance of hierarchical clustering methods is as good as that of pam when the number of clusters is 10, 25 and 30. based on the overall performance, pam seems to meet all the criteria when the number of clusters is 50. in other words, pam is found to be better in terms of internal, stability, and modularity performance. b. oued el ma water distribution network figure 7 reports the performance of the algorithms for a medium-sized wdn. according to the findings, the hierarchical clustering algorithms perform better when the number of clusters is smaller (3 to 6). in contrast, the overall performance of partitioning methods is better when the number of clusters increases as shown in the cases of 8, 10, and 12 clusters. fig. 7. oued el ma wdn spectral clustering. c. c-town water distribution network figure 8 reports the performance of clustering algorithms across the 6 different partition combinations for a small-sized wdn. similar to the medium-sized network, the findings suggest that portioning-based clustering algorithms perform better than the hierarchical based methods when the number of clusters increases. for example, when the number of clusters is 10, pam performs better than any other algorithm in terms stability and modularity performance criteria. hierarchical based methods, however, perform, better when the number of clusters is 3 and 5 in terms of stability and internal performance. fig. 8. c-town wdn spectral clustering. engineering, technology & applied science research vol. 12, no. 4, 2022, 9056-9062 9061 www.etasr.com bellum et al.: the performance of spectral clustering algorithms on water distribution … vi. conclusions improving the management of wdns can be achieved by dividing the network into sectors (dmas). among the most used methods for network partitioning is spectral partitioning, which consists of generating a spectral space from the eigenvectors of the laplacian matrix associated with the network. the final phase of this partitioning is often done by the k-means algorithm, which is not always adequate. it is, therefore, useful to consider the performance of other existing algorithms in order to highlight the most efficient in terms of clustering quality indices such as modularity, internal indices (connectivity, silhouette, and dunn) as well as stability indices such as apn, ad, adm, and fom. a simulation exercise was conducted to assess and evaluate the performance of 5 clustering algorithms on 3 types of wdns. the studied networks were chosen according to their type and size. our findings show that k-means is not consistently effective either in terms of type of network or number of sectors. our critical study of [11], shows further that k-means performs well only under special conditions including small-sized networks with a very limited number of sectors. thus, one cannot confirm the validity of using k-means as a tool to sectorize dmas in larger and medium-sized networks. acknowledgements this research paper would not have been possible without the exceptional support of dr. issam malki from the university of westminster, department of economics and quantitative methods (eqm). references [1] k. b. adedeji, y. hamam, b. t. abe, and a. m. abu-mahfouz, "pressure management strategies for water loss reduction in 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[36] d. gilbert, e. abraham, i. montalvo, and o. piller, “iterative multistage method for a large water network sectorization into dmas under multiple design objectives,” journal of water resources planning and management, vol. 143, no. 11, nov. 2017, art. no. 04017067, https://doi.org/10.1061/(asce)wr.1943-5452.0000835. microsoft word 554-ed.doc engineering, technology & applied science research vol. 5, no. 3, 2015, 795-800 795 www.etasr.com issawi et al.: efficient adaptive load balancing algorithm for cloud computing under bursty workload an efficient adaptive load balancing algorithm for cloud computing under bursty workloads sally f. issawi faculty of information technology islamic university of gaza (iug) gaza, palestine sally.issawi@gmail.com alaa al halees faculty of information technology islamic university of gaza (iug) gaza, palestine alhalees@iugaza.edu.ps mohammed radi faculty of applied science al-aqsa university gaza, palestine moh_radi@alaqsau.edu.ps abstract—cloud computing is a recent, emerging technology in the it industry. it is an evolution of previous models such as grid computing. it enables a wide range of users to access a large sharing pool of resources over the internet. in such complex system, there is a tremendous need for an efficient load balancing scheme in order to satisfy peak user demands and provide high quality of services. one of the challenging problems that degrade the performance of a load balancing process is bursty workloads. although there are a lot of researches proposing different load balancing algorithms, most of them neglect the problem of bursty workloads. motivated by this problem, this paper proposes a new burstness-aware load balancing algorithm which can adapt to the variation in the request rate by adopting two load balancing algorithms: rr in burst and random in non-burst state. fuzzy logic is used in order to assign the received request to a balanced vm. the algorithm has been evaluated and compared with other algorithms using cloud analyst simulator. results show that the proposed algorithm improves the average response time and average processing time in comparison with other algorithms. keywords-cloud computing; cloud analyst; burstness; fuzzifier; load balancing algorithm i. introduction nowadays most developments in the it industry come to meet the demands for utilizing more resources in lower costs. this technological trend has enabled the evolution of a new computing model called cloud computing, in which resources and services are available on the internet and can be leased and released on demand [1]. cloud computing can improve business performance by minimizing the overhead of buying, managing and controlling it resources. the financial model applied in cloud computing is “pay-per-use” so the consumer only pay for his needs. the scale up in demands make load balancing a major concern in cloud computing. this is defined as a method to distribute the workload across one or more servers, network interfaces, hard drives, or other computing resources. load balancing is used to make sure that none of the existing resources are idle while others are being utilized [2]. one of the most challenging problems that dramatically degrade the performance of a load balancing process is the burstiness in workloads. bursty traffic refers to an uneven pattern of data transmission: sometimes very high data transmission rate while other times low [3]. several load balancing algorithms had been proposed which focus on key elements such as processing time, response time and processing costs. however these algorithms neglect the case of bursty workloads. according to that, in this research we proposed an efficient adaptive load balancing algorithm for cloud computing under bursty workloads. the proposed algorithm adapt to the variation in the received request rate by adopting two different load balancing algorithms according to the workload state. it detects the start of the burst by calculating the average received requests and use round robin (rr) in the burst case, otherwise the random algorithm is used. those two load balancing algorithm select a suitable vm based on the knowledge provided by a fuzzifier. the algorithm has been evaluated and compared with other algorithms using the cloud analyst simulator. results show that the proposed algorithm improves the average response time and average processing time compared to other algorithms. ii. cloud computing the core idea behind cloud computing is not a new one. it was actually pronounced way back in 1960 [4]. cloud computing is a type of parallel and distributed system. it consists of a collection of interconnected and virtualized computers that are dynamically provisioned and presented as one or more unified computing resources. the services delivered to the consumer are based on service-level agreements (sla), established through negotiation between the service provider and consumers [5]. the objective of cloud computing is to provide secure, qualitative, scalable, quick, more responsive, on demand, cost-efficient and automatically provisioned services such as computation services, storage services, networking etc. although those services are geographically distributed all over the world, they are provided in a location independent way [4]. cloud computing can help improve business performance while making a contribution to control the cost of delivering it resources to any organization. it minimizes the overhead of buying, managing and controlling it resources. the financial model applied in cloud computing is “pay-per-use” so the consumer only pay for his needs. research on cloud computing is still at an early stage. several new challenges keep emerging from industry engineering, technology & applied science research vol. 5, no. 3, 2015, 795-800 796 www.etasr.com issawi et al.: efficient adaptive load balancing algorithm for cloud computing under bursty workload applications, and many issues need to be properly addressed. some of the challenging research issues in cloud computing are: security and privacy, performance, resource management and scheduling. resource management is a very important issue in cloud computing, as large numbers of users share the same resources. so in order to meet quality of service (qos) standards and insure best resource utilization, proper resource management mechanisms should be used in deferent levels such as management of memory, disk space, cpu’s, cores, threads, vm images, i/o devices etc. resource provisioning can be defined as allocation and management of resources to provide desired level of services. job scheduling is an essential process in resource provisioning where the order of the job execution is established in order to optimize performance parameters such as response time, processing time, waiting time etc. [4]. one of the most important issues in job scheduling is load balancing which is the interest of this work. iii. load balancing the scale up in demands make load balancing a major concern in cloud computing. it is defined as a method to distribute workload across one or more servers, network interfaces, hard drives, or other computing resources. load balancing is used to make sure that none of the existing resources are idle while others are being utilized [2]. basically there are 2 types of load balancing algorithm depending on their implementation method: 1) static algorithms in this type, the load is divided equivalently between nodes. this algorithm depend on prior knowledge of the system, it does not consider the current state of the node and will degrade the performance of the system. this type of algorithms is referred to as round robin algorithms [2, 6]. 2) dynamic algorithms dynamic algorithms make decisions based on current state of the system. no prior knowledge is needed [2]. so workloads can be distributed efficiently over nodes. dynamic load balancing can be done in two ways: [7]  distributed dynamic load balancing: in the distributed one, all nodes in the system execute the dynamic load balancing algorithm and the task of load balancing is shared among them. its advantage is that if one or more nodes in the system fail, the system performance will be affected to some extent, but it will not cause the total load balancing process to halt.  non-distributed dynamic load balancing: in the non-distributed one, the load balancing algorithm is executed by a single node of the system and the task of load balancing is dependent only on that node. a failure in this one node will cause the total load balancing process to halt. static (round robin) algorithms are based on a simple rule in dividing the loads among nodes but this leads to more loads conceived on servers and thus imbalanced traffic discovered as a result. however; dynamic algorithm predicated on a query that can be made frequently on servers, but sometimes prevailed traffic will prevent these queries to be answered, and correspondingly more added overhead can be distinguished on the network [6]. iv. bursty workload one of the most challenging problems that dramatically degrade the performance of load balancing process is burstiness in workloads. bursty traffic refers to an uneven pattern of data transmission: sometime very high and other times very low [3]. burstiness occurs in workloads in which bursts of requests aggregate together during short periods of time and create periods of peak system utilization. figure 1 shows three different levels: strong, week, and no burstiness. this problem is often observed in large systems including web based applications [8], grid services [9], multitier architectures [10], and large storage systems [11]. it can dramatically degrade system performance, make the system unavailable and lead to a total failure. burstiness considered as one of the most complex problem nowadays in cloud computing, as the number of users that uses cloud services increases day by day, so load balancer must consider the performance of each instance under both bursty and non-bursty workloads for efficient resource utilization. fig. 1. different levels of burstness v. related works several approaches had been proposed to handle the load balancing issues in cloud computing systems. all these works aimed to improve the process of distributing the workload among cloud nodes and try to achieve optimal resource utilization, minimum data processing time, minimum average response time, and overload avoidance. however most of these engineering, technology & applied science research vol. 5, no. 3, 2015, 795-800 797 www.etasr.com issawi et al.: efficient adaptive load balancing algorithm for cloud computing under bursty workload approaches neglected the effect of burstiness on the load balancing process. sethi, et al in [12] designed a new load balancing technique using fuzzy logic based on a round robin (rr) algorithm to obtain measurable improvements in resource utilization and availability of cloud-computing environment. the proposed technique uses a fuzzifier to perform the fuzzification process that converts two types of inputs which are the processor speed and the assigned load of the virtual machine (vm), and one output which is the balanced load to create an inference system. the fuzzy based round robin (frr) load balancer compared to the conventional round robin (rr) load balancer minimizes the data center processing time and overall response time. the problem with round robin algorithms in general however, is that they are not able to handle bursty workloads. even with the proposed enhancement on rr by using fuzzy logic, burstiness is not considered. in [13], a fuzzy logic load balance algorithm focused on a public cloud was proposed. the main idea of the algorithms was to partition the cloud to several cloud partitions with each partition having its own load balancer, and a main controller to manage all these partition. results showed enhancements in resource utilization and availability in the cloud computing environment. the drawback of this approach is the difficulty of testing the technique in a real environment to make sure that it has achieved good results. in [14], a smart burstiness-aware algorithm (ara) to balance bursty workloads across all computing sites, and thus to improve overall system performance, was proposed. the presented algorithm predicts the beginning and the end of workload bursts and automatically on-the-fly shift between two schemes: “greedy” (i.e., always select the best site) which has better response time under the case of no burstiness and “random” (i.e., randomly select one) which has better response time under burstiness. both simulation and real experimental results show that this algorithm improves the performance of the cloud system under both bursty and non-bursty workloads. although this algorithm gives good results, it does not consider an important factor in load balancing, which is the current utilization of available resources. in [7], a dynamic load balancing model that considers utilizing resources under burstiness cases was proposed. the suggested architecture consists of four parts: cloud controller server, node controller server, agents, and virtual machines. all requests first go to the cloud controller server and then they are transferred to the load balancer. finally a virtual instance is selected by the load balancer based on the information supplied by the monitoring agent about cpu usage, memory and storage space usage. the researchers claimed that this algorithm should ensure the optimum utilization of cloud resources, faster response time, and cut the economic cost for an organization. however they did not do any experiments or evaluations for their work. in [15], load balancing under bursty environment for cloud computing was also investigated. a dynamic load balancing algorithm which maintains the state of all virtual machine (vm) resources was proposed. the algorithm. based on cpu, memory and storage space utilization, selects the less utilized vm resource to handle the request. a monitoring agent was used to continuously monitor cpu usage, memory and storage space usage, and the current and the expected load for each virtual machine. based on this information a pheromone (or probability) was assigned for every vm. when a request arrives to the datacenter, the load balancer transfers the request to the vm which has the least pheromone. authors mentioned that their algorithm improved the performance but they did not provide any comparisons with other load balancing algorithms and they did not share any experiments results. in [16], an approach to overcome the un-utilized resource provisioning and the power consumption problems under bursty and fractal behavior workload was proposed. it consists of two phases for resource utilization provisioning, called “predictive and reactive provisioning”. firstly the forecasting module predicts the work load for the next control horizon, and then the controller estimates the number of necessary resources, such as processing cores, for the predictable part of the incoming load. in order to avoid the consequences of forecasting errors, the system allocates extra resources that can be used to serve unpredictable loads. this allocation is made based on the history of the system operation. the proposed approach improves the resource utilization and the power consumption. on the other hand, if some prediction error happens beyond the estimation of the extra resources, it would be subject to delay in getting the resource till the system allocates available resources. vi. adaptive load balancing algorithm the request rates received by the datacenter are not constant all the time. sometimes large number of requests aggregated in a small period of time creating a burst. this affect the performance of the load balancing algorithm as it increase the processing time and the repose time of the datacenter. the performance of several load balancing algorithms differs according to the users’ requests rate. for example some algorithms work efficiently under low workload while their performance is degraded under high workload and vice versa. to overcome burst problem and benefit from different load balancing algorithms advantages we propose a new load balancing algorithm called adaptive algorithm. adaptive algorithm is a load balancing algorithm used by the datacenter to distribute the received tasks efficiently over the virtual machine under bursty workload by swapping between two policies depending on the requests rates. it consists of three main components as follows: 1burst detector. 2load balancing algorithms. 3fuzzifier.  when the datacenter receives a request, the burst detector determines the workload state (normal or burst). depending on the burst detector decision, the datacenter will select the appropriate load balancing policy for that state. after that, the selected load balancing algorithm will assign the received task to a suitable vm depending on the information supplied by the fuzzifier. when the vm complete its assigned task, it informs engineering, technology & applied science research vol. 5, no. 3, 2015, 795-800 798 www.etasr.com issawi et al.: efficient adaptive load balancing algorithm for cloud computing under bursty workload the data center. the main steps of the adaptive algorithm are shown in figure 2. a. burst detector the burst detector is responsible for detecting the variation in the workload, and determining whether the state of the workload is burst or not, using a specific threshold. when a request arrives, the burst detector checks the rate of the requests in the last 15 minutes and if it exceeds the threshold it indicates that the status is burst. depending on experiments, we found that 15 minutes is a suitable time interval. depending on the detector decision, the datacenter will select the proper load balancing policy. fig. 2. adaptive load balancing algorithm flow chart b. load balancing algorithm the proposed approach uses two load balancing algorithms, one efficient in normal cases and another efficient in burst cases. according to experiments done on three load balancing algorithms (rr, esce and random), random policy performs the best in low workload and round robin performs best in high workload. 1) random policy: when the burst detector decides that the workload state is normal, the random policy will be applied. the fuzzifier supply the random policy with a candidate list of balanced vms in the data center, then the policy will select one of these vms randomly and assign the received task to it. 2) round robin policy: round robin will be used when workload state is burst. the same as random, the fuzzifier will provide a candidate list of the most balanced vms for round robin policy. then round robin will use this list to allocate vms in a cycle manner. c. fuzzifier the main function of the fuzzifier is to enhance the decision of the load balancing algorithm by providing a list of the most balanced vms in the data center and deliver it to the load balancer to allocate one vm from this list. the fuzzifier is consisted of a fuzzy inference system (fis) to simulate the way of human decision making by using fuzzy control rules and linguistic parameters. in our wok, the fis uses two inputs which are processor speed and the load in vm, and balanced load as the output. twelve if-then rules are employed as shown in figure 3. for the fis, an open source java library called jfuzzylogic [17] was used. this library offers a fully functional and complete implementation of a fuzzy inference system, providing a programming interface and eclipse plugin to easily write and test code for fuzzy control applications [18, 19]. vii. experments and results in order to test and evaluate the performance of our new proposed algorithm, the cloudanalyst simulator was employed. cloudanalyst is a tool developed at the university of melbourne. it is a graphical simulation tool based on cloudsim for modeling and analyzing the behavior of a cloud computing environment, which supports visual modeling and simulation of large-scale applications that are deployed on cloud infrastructures [20-22]. experiments had been done to test the efficiency of the proposed scheme. two metrics were measured in order to evaluate the performance: response time and processing time. the results were compared with three of the most popular load balancing algorithms: rr, esce, and random. a. configurations in order to build the simulation environment, two main components had to be configured: user base (ub) and data center (dc). for the three experiments the following configurations was used. 1) user base the number of ubs used is 6. all ubs are in the same region with dc to ignore the transmission delay. number of requests per user per hour for every ub is 12 and the data size per request is 100 byte. table i illustrates the user bases characteristics. 2) data center one data center was used in the experiments. the data center had 5 physical hosts with different processor speeds. data center configurations are shown in detail in table ii and table iii. the simulation time was set to one day. experiments had been done with three different instruction lengths (250, 500 and 1000 bytes). engineering, technology & applied science research vol. 5, no. 3, 2015, 795-800 799 www.etasr.com issawi et al.: efficient adaptive load balancing algorithm for cloud computing under bursty workload table i. user base configrations name peak hours start (gmt) peak hours end (gmt) avg. peak users avg. offpeak users ub1 1 2 100000 10000 ub2 4 5 200000 20000 ub3 6 7 700000 70000 ub4 9 10 400000 40000 ub5 13 14 500000 50000 ub6 20 21 800000 80000 table ii. data center main configrations data center #vms image size memory bw dc1 50 10000 1024 1000 table iii. data center hosts configrations id memo ry (mb) storage (mb) availabl e bw num. of proces sors proce ssor speed vm policy 0 204800 100000000 1000000 4 2000 time_sh ared 1 204800 100000000 1000000 5 5000 time_sh ared 2 204800 100000000 1000000 2 9000 time_sh ared 3 204800 100000000 1000000 2 1000 time_sh ared 4 204800 100000000 1000000 2 15000 time_sh ared b. results the data center hourly loading during the simulation time is shown in figure 3. the experiment results showed that the adaptive algorithm recorded the best response and processing time compared to rr, esce, and random algorithms. as shown in figures 4-6, when the instruction length is 250 bytes, the adaptive algorithm has better response time than rr (which is better than esce and random) with a difference of 2 ms. this difference is remarkably increased when the instruction size is increased to 500 bytes and 1000 bytes (7ms). fig. 3. data center hourly loading. the processing time results show a similar trend with the response time results. as presented in figures 4-6, the adaptive algorithm has the best processing time compared to the others. the improvement in processing time became clearer when the instruction length was increased inst. length 250 bytes 280 300 320 340 360 380 400 1 2 3 4 algorithms  (1=rr, 2=esce, 3=random, 4=adaptive) t im e  ( m s) response time processing time fig. 4. experment results when inst. length is 250 bytess inst. length 500 bytes 600 620 640 660 680 700 720 1 2 3 4 algorithms  (1=rr, 2=esce, 3=random, 4=adaptive) t im e  ( m s) response time processing time fig. 5. experment results when inst. length is 500 bytes inst. length 1000 bytes  1260 1280 1300 1320 1340 1360 1380 1400 1 2 3 4 algorithms  (1=rr, 2=esce, 3=random, 4=adaptive) t im e  ( m s) response time processing time fig. 6. experiment results when inst. length is 1000 bytes viii. conclusion cloud computing nowadays has become a quite popular model by offering a variety of resources shared over the engineering, technology & applied science research vol. 5, no. 3, 2015, 795-800 800 www.etasr.com issawi et al.: efficient adaptive load balancing algorithm for cloud computing under bursty workload internet. in such a complex system, the need for an efficient load balancing scheme is essential in order to satisfy peak user demands and provide high quality of services. one of the challenging problems that degrade the performance of load balancing process is bursty workloads. in this paper, we proposed a load balancing algorithm called adaptive algorithm. the proposed algorithm is based mainly on swapping between two different algorithms (rr and random) according to the workload status. selecting vm to handle the received request is based on knowledge about cpu speed and the current load of the vm provided by a fuzzifier. experiments were conducted using the cloudanalyst simulator. results showed that the adaptive algorithm decreased the response and the processing time and thus improved the performance of the cloud system. references [1] q. zhang, l. cheng, r. boutaba, "cloud computing: state-of-the-art and research challenges", journal of internet services and applications, vol. 1, no. 1, pp. 7-18, 2010 [2] r. mishra, a. jaiswal, "ant colony optimization: a solution of load balancing in cloud," international journal of web & semantic technology, vol. 3, no. 2, pp. 33-50, 2012 [3] j. dong, network dictionary, javvin technologies inc, 2007 [4] m. sajid, z. raza, "cloud computing: issues & challenges," international conference on cloud, big data and trust 2013, rgpv, india, november 13-15, 2013 [5] j. uma, v. ramasamy, p. vivekanandan, "load balancing algorithms in cloud computing environment a methodical comparison", international journal of engineering research and technology, vol. 3, no. 2, pp. 272-275, 2014 [6] z. chaczko, v. mahadevan, s. aslanzadeh, c. mcdermid, "availability and load balancing in cloud computing", 2011 international conference on computer and software modeling, 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jena, "efficient load balancing in cloud computing using fuzzy logic", iosr journal of engineering, vol. 2, no. 7, pp. 65-71, 2012 [13] u. singhal, s. jain, "a new fuzzy logic and gso based load balancing mechanism for public cloud," international journal of grid distribution computing, vol. 7, no. 5, pp. 97-110, 2014 [14] j. tai, j. zhang, j. li, w. meleis, n. mi, "ara: adaptive resource allocation for cloud computing environments under bursty workloads", 2011 ieee international performance computing and communications conference, pp. 1-8, usa, november 17-19, 2011 [15] n. d. naik, a. r. patel, "load balancing under bursty environment for cloud computing", international journal of engineering research and technology, vol. 2, no. 6, pp. 17-26, 2013 [16] m. ghorbani, y. wang, y. xue, m. pedram, p. bogdan, "prediction and control of bursty cloud workloads: a fractal framework", 2014 international conference on hardware/software codesign and system synthesis, pp. 1-9. new delhi, october 12-17, 2014 [17] jfuzzylogic, http://jfuzzylogic.sourceforge.net/html/index.html [18] p. cingolani, j. alcalá-fdez, "jfuzzylogic: a java library to design fuzzy logic controllers according to the standard for fuzzy control programming", international journal of computational intelligence systems, vol. 6, suppl. 1, pp. 61–75, 2013 [19] p. cingolani, j. alcalá-fdez, "jfuzzylogic: a robust and flexible fuzzylogic inference system language implementation", 2012 ieee international conference on fuzzy systems (fuzz-ieee), australia, june 10-15, 2012 [20] s. r. pakize, s. m. khademi, a. gandomi, "comparison of cloudsim, cloudanalyst and cloudreports simulator in cloud computing", international journal of computer science and network solutions, vol. 2, no. 5, pp. 19-27, 2014 [21] b. wickremasinghe, r. n. calheiros, r. buyya, "cloudanalyst: a cloudsim-based visual modeller for analysing cloud computing environments and applications", 2010 24th ieee international conference on advanced information networking and applications (aina), pp. 446-452, australia, april 20-23, 2010 [22] b. wickremasinghe, "cloudanalyst: a cloudsim-based tool for modelling and analysis of large scale cloud computing environments", 433-659 distributed computing project, csse dept., university of melbourne, australia, 2009 microsoft word etasr_v12_n3_pp8628-8633 engineering, technology & applied science research vol. 12, no. 3, 2022, 8628-8633 8628 www.etasr.com doan & nguyen: fusion machine learning strategies for multi-modal sensor-based hand gesture … fusion machine learning strategies for multi-modal sensor-based hand gesture recognition huong-giang doan control and automation faculty electric power university hanoi, vietnam giangdt@epu.edu.vn ngoc-trung nguyen control and automation faculty electric power university hanoi, vietnam trungnn@epu.edu.vn received: 14 march 2022 | revised: 26 march 2022 | accepted:1 april 2022 abstract-hand gesture recognition has attracted the attention of many scientists, because of its high applicability in fields such as sign language expression and human machine interaction. many approaches have been deployed to detect and recognize hand gestures, like wearable devices, image information, and/or a combination of sensors and computer vision. however, the method of using wearable sensors brings much higher accuracy and is less affected by occlusion, lighting conditions, and complex background. existing solutions separately utilize sensor information and/or only use sensor information processing and decision-making algorithms over conventional threshold comparison algorithms and do not analyze data or utilize machine learning algorithms. in this paper, a multi-modal solution is proposed that combines information for measuring the curvature of the fingers and sensors for measuring angular velocity and acceleration. the provided information from the sensors is normalized and analyzed and various fusion strategies are used. then, the most suitable algorithm for these sensorbased multiple modalities is proposed. the proposed system also analyzes the differences between gestures and actions that are almost similar but in fact, they are just normal moving gestures. keywords-hand glove; acceleration sensor; hand gesture recognition; flex sensor; human-machine interaction i. introduction hand gestures are one of the most natural ways of interaction between people (e.g. sign language [1-6, 24]) or human computer interaction–hci [7-9]. conveying messages in sign language through hand gestures has attracted the attention of many researchers and technology developers. as a consequence, many hand gesture recognition approaches have been proposed, such as using the change of radar waves when the user changes the state of the hand [10-11, 25], utilizing image information [12-14], or sensors physically attached to the hand [15-17]. the radar-based method [10] is easy and convenient for end-users because of independent equipment but it is dramatically affected by environmental noises and the number of antennas [27]. there are many moving objects in the normal environment that can also cause changes in feedback waves such as movement of other people, or other body parts. for the image-based approach [12], hand gesture recognition systems often face many challenges such as high time cost for hand detection and hand recognition, effects of illumination, occlusion, complex background conditions, etc. the hand mounted sensor-based method [15], although limited due to device dependence that has much higher accuracy compared to other methods and especially it face to many criteria when the actual control system requires high accuracy. thus, this solution is preferred in many special cases. hand-mounted sensors were applied to measure the change in the hand shapes and hand movements that were quite efficient because of their accuracy and real-time response. many solutions have been proposed, such as the electronic gloves [17-18]. these gloves have integrated flex sensors, mounted on the fingers, to collect the hand’s curvature changing. however, this solution only measures the change in the flexure of the fingers, but it cannot obtain the movement of the hand. in [19-20], the authors proposed a method to attach the sensors on the hand for receiving velocity and angular acceleration. this method achieves the alternation of hand movement, but it is not possible to obtain the changes of hand shapes. in [21-23], the authors combined both curvature and velocity sensors, but the classification of hand gesture categories was performed by the conventional comparison structures with simple instruction sets of microcontrollers (e.g. arv, 8051 with compare and check condition instructions), without evaluation or survey changing of parameters of sensors or machine learning algorithms. quantitative evaluations were not implemented to compare the defined activities with normal human activities. in this paper, a new solution is proposed, one that combines both hand shape and hand movement sensors with various fusion strategies of features. the obtained results have success rates of up to 99.87% for the stable hand gesture dataset and 97.59% when both mobile and immobile hand gesture datasets are considered. these results are higher than the 97.4% and 86.3% for seen and unseen users of 12 gestures in [28] that fed the data of finger’s curvatures to a convolution neural network. there are no published hand gesture datasets based on mounted sensors and the published ones do not provide both hand’s curvatures and position at the same time. so, in this research, we collected two new hand gesture databases, one with stationary hand and one with moving hand. corresponding author: huong-giang doan engineering, technology & applied science research vol. 12, no. 3, 2022, 8628-8633 8629 www.etasr.com doan & nguyen: fusion machine learning strategies for multi-modal sensor-based hand gesture … fig. 1. proposed framework for hand gesture recognition. the data flows will be fed into classifiers with various fusion strategies of machine learning techniques to find the most optimal and suitable classification solution. ii. proposed method our proposed framework for hand gesture recognition is illustrated in figure 1. in this research, multiple modalities of hand �� ∈ �1,��,� 3 corresponding to � ∈ ��, ,��� are captured by two streams: • finger’s curvature: five flex sensors are used to present the curvature variation of fingers. • hand’s motion tracking and angle: sensor mpu6050 is integrated by 3-axis mems of gyroscope and 3-axis mems of accelerometer. all features are processed and synchronized by an mcu (microcontroller unit) and are transferred to a pc. finally, various classification strategies were used, either single or multi-modalities. the cascade steps in our proposed framework will be presented in detail at the following sections. a. hardware design for multiple features of the hand glove the detailed hardware design of the electronic glove is illustrated in figure 2. five flex sensors are permanently mounted along the fingers of the glove to collect the curvature based on the change of the corresponding resistance value. the resistors' data are preprocessed to convert into voltage value before conversion from analog to digital with a 10-bit adc (analog to digital converter) resolution, corresponding to a range of values from 0 to 1023. the values of flex sensors from the thumb to the little finger are denoted by �� to �� ����, ��,��, ��,���/��1,2,3,4,5� corresponding to the curvature data of the five fingers. at the same time, the values of the 3-axis mems gyroscope and 3-axis mems accelerometer of the mpu6050 sensor were collected. the resolution of adcs is 16 bits with a range from 0 to 65535, denoted by ���,��,���/���,�,�� and ( �, �, �)/g��,�,��. after the mcu collects the two data streams (flex sensors and mpu sensor) at the same time, all data are packaged and sent to the pc via the usb port according to the uart standard. fig. 2. harware design of the hand glove. in addition, each time, the information of the hand gesture is transferred by a feature vector which is composed by eleven elements in total: a ��, �,�� , g ��,�, �� , and f(1,2,3,4,5), respectively. this feature is presented in detail in (1) and will be utilized in various strategies in detail in the next section: �� ! ����,��� , …,��#�,�$ 11) ����,�,��; ��,�,��;��1,2,3,4,5�� (1) &��,��,��, �, �, �,��,��,��,��,��' b. hand gesture dataset in this paper, twelve hand postures are used, as illustrated in figure 3. each hand gesture is captured when the end-user is immobile or in movement. in practice, the system will recognize the hand gestures at any time and any place, i.e. hand morphologies during normal human activities that could have similar characteristics to the previously defined dataset. in addition, the feature of hand shape is only based on the curvature of the fingers that are collected by the five flex sensors. it is apparent that the accelerometer sensors and velocity sensors provide useful information about the movement and the direction of the hand’s movement. engineering, technology & applied science research vol. 12, no. 3, 2022, 8628-8633 8630 www.etasr.com doan & nguyen: fusion machine learning strategies for multi-modal sensor-based hand gesture … fig. 3. the twelve hand postures of our dataset. figure 4 illustrates hand tracking with three accelerator parameters a��,�,�� and three velocity features g��,�,�� of four hand gestures in two cases: (1) the end-user raises the hand in front of his/her body and performs a gesture (blue, white, violet and grey colors in figure 4) and (2) the end-user implements the same hand shape but hand and body are moving (green, yellow, red and orange colors in figure 4). it is clear that feature a(x,y,z) or feature g(x,y,z) of the same hand gesture represent the hand’s movement. it could effectively separate between immobile hand mobility hands while they do not have meaning for stable gestures. (a) (b) fig. 4. (a) a(x,y,z) and g(x,y,z) elements of the same hand gesture. in practice, the users are usually immobile when they want to control the device and often put their hands in front of their body. meanwhile, the end-user’s hand shapes exist at both stable and moving situations. therefore, we collected 12 gestures as shown in figure 3 when the hand is in front of the user's face, when the hand is immobile and during normal movement. each category will be separately labeled by ()*� (gesture of class k, hand is frontal of body and stable) and ()*� (gesture of class k, hand is at any position and movement). we divided the data into two datasets named handglove1 and handglove2. handglove1 is composed by � ()*���+ ∈ �1, ,�, , 12� and handglove2 by � ()*�; ()*���+ ∈ �1, ,�, , 12�. this means that handglove2 dataset has a duplicated number of categories up to k = 24 classes. each gesture was collected three times and each time consists of about 200 samples. a total of 15 adults �-)(./ �0 ∈ �1, 1�, 1 15�� , including 7 females and 8 males were invited to collect our dataset at different days and at various times of the day. these databases were normalized and classifiers were used. c. data processing as described above, the data collected from the flex sensors are denoted by f(1,2,3,4,5) and have a value range of 0 to 1023. the data from the mpu6050 sensors include a��, �, �� and g��, �, �� have a range of values from 0 to 65535. a sensor component has a different value range and 11 components must be processed to obtain the same range. each characteristic component �� ! 2 of the 12 gestures � ()*�� and/or � ()*�; ()*���+ ∈ �1, ,�, , 12� of 15 collectors �-)(./�0 ∈ �1, 1�, 1 15�� is normalized. firstly, the maximum value �� !_45�2 and the smallest value �� !_4262 can be determined: �� !_45�2 $7� 8�� !2 9: 7�� ; ()*; -)(./<= �+ ∈ �1, ,��; �0 ∈ �1, 1�� (2) �� !_4262 $>? 8�� !2 9: 7�� ; ()*; -)(./<= �+ ∈ �1, ,��; �0 ∈ �1, 1�� (3) each component ��_6@a2 will be recalculated as (4): �� !_6@a2 bcdef gbcde_hfi f bcde_hjk f gbcde_hfi f (4) as a result, the feature vector could be presented by: �� ! ��� !_6@a� ,�� !_6@a� ,… ,�� !_6@a�� � . figure 6 illustrates the t-sne (distributed stochastic neighbor embedding) for all the 12 gestures. figure 6(a) uses [ �� !_6@al ;…,�� !_6@a�� � elements, figure 6(b) utilizes [ �� !_6@a� ;… ,�� !_6@a�� � , and figure 6(c) utilizes [�� !_6@a� ;…, �� !_6@a�� �. this figure shows that, if only using the curvature feature from the flex sensors, the data distribution of the gestures is not segregated than using combinations of the motion features. the composition of 6 motion features enables gesture types to be separated into more distinct spatial domains. this result is only qualitative but not quantitative. these normalized features will be put into classifiers with single patterns and combined features as described in section iii.d. d. hand gesture classification multi-modal data stream is presented above with f, a, and g which are combined using different fusion techniques. in this research, three fusion techniques are investigated: late fusion, early fusion, and multiple kernel learning (mkl) [2]. in the following, we will briefly survey these methods that are utilized in the classification block of figure 1. 1) early fusion for early fusion, all normalized feature vectors of the 3 modalities are concatenated into a final feature vector as presented in (5): �m &��_6@a � , ��_6@a � ,… ,��_6@a# ' (5) then, the feature vector �m is used as an input of a final multiple svm classifier to predict the hand gesture label. 2) late fusion for late fusion, each modality is used with multiple svm classifiers nop# q with � ∈ �1, ���� 3� . the outputs of the classification step are the score vectors rq �)�q,)�q ,… ,)sq �. next, the maximum operator for these score vectors rq is applied to obtain the final score vector as presented in (6): r �)�,)�,…, )s� otuovuow � [ !ttu!tvu!tw � , !vtu!vvu!ww � , …, !xt u!xvu!xw � � (6) then, the final decision is obtained as illustrated in (7): y()z[.( �7\(� 7.y]7�*∈��,s��)*� (7) engineering, technology & applied science research vol. 12, no. 3, 2022, 8628-8633 8631 www.etasr.com doan & nguyen: fusion machine learning strategies for multi-modal sensor-based hand gesture … 3) multiple kernel learning mkl is an algorithm that combines a set of base kernels that could represent different similarity measures of different sources of data. as a result, each feature vector from the �^_ �� ∈ �1,��� modality utilizes a kernel function to compute the corresponding kernel matrix as shown in (8): ,(.?(�s` )>]>�7.>z��;�� !a ,�� !� <,��� !a ,�� !b �, ;�� !b ,�� !� <� (8) where b ∈ �1,c�,�c 3�. then, kernel matrices ,(.?(�s` are used to combine for ,(.?(� factor as presented in (9): ,(.?(� :[?ef;g,(.?(�,b h`i�p |f< (9) where :[?e denotes the function form. the combination coefficient k sees that the values are bound to the predefined rules or are optimized by the learning process of mkl [1, 2]. in this research, easymkl [1] with a binary margin maximization mkl algorithm is chosen which uses the convex summation function. the coefficients µ are restricted to be non-negative and sum to 1. a final kernel machine classifier will decide the label based on the combined kernel matrix ,(.?(� by a svm classifier. iii. exprimential results in this paper, two datasets (handglove1 and handglove2) were utilized. the "leave-one-subject-out cross-validation" protocol is followed [3]. this means that, we took samples from one subject for testing and samples from the remaining subjects for training. then we compute the average accuracy of every experiment. a. single modality for hand gesture recognition in this section, we used handglove1 dataset in separating the following data types: five components are the finger curvature sensors f(1,2,3,4,5), 3 components measure the angle of the hand a(x,y,z), and 3 components show the angular velocity g(x,y,z). each type is firstly normalized. it is then put into the svm classifier. the classification results on each modality are presented in table i. table i shows that the finger’s curvatures of the hand gesture dataset (figure 3) obtained the highest recognition result (92.15%) while a(x,y,z) cue has the lowest at only 36.48%. although the result of the g(x,y,z) modality is higher than the cue modality, but it still is ineffective for the defined dataset with 42.76%. this result shows that each data type gives low results, not suitable to control in practice. table i. single modality for hand gesture recognition accuracy (%) with svm classifier modality accuracy (%) a(x,y,z) 36.48 g(x,y,z) 42.76 f(1,2,3,4,5) 92.15 b. hand gesture recognition on various fusion strategies in this part, we will investigate different strategies (early fusion, late fusion, and mkl) on the three streams. evaluations are conducted on handglove1 dataset. the results are shown in figure 5. fig. 5. hand gesture recognition on various fusion strategies. fig. 6. t-sne of 12 gestrures with various modalities. figure 5 shows that: • kml obtains the highest accuracy at 94.58%, 90.18%, 97.31%, and 99.87% with combination of a and f, a and g, g and g, and a+g+f respectively. the late fusion method reached the lowest accuracies on all data combinations (around 75% and the smallest at 46.17% for a+g modality). we can see that early fusion is quite simple while its results are lower than kml's. the late fusion method requires many classifiers but its accuracy is far smaller than kml's. therefore, the kml solution will be utilized in the rest of the testing. • combinations of the 3 modalities are the highest on all classifiers and account for 97.69%, 86.02% and 99.87% for early fusion, late fusion, and kml respectively. these results can be explained through figure 6 that shows the distribution of data using the t-sne method [26]. when g is used, the hand gesture classes distribute in the overlap domains. when f and a are combined as shown in figure engineering, technology & applied science research vol. 12, no. 3, 2022, 8628-8633 8632 www.etasr.com doan & nguyen: fusion machine learning strategies for multi-modal sensor-based hand gesture … 6(b) or f and g as illustrated in figure 6(c) the distribution of the categories has improved but the separation is not clear enough. in figure 6(d), a, g, and f are utilized and the data distribution domains of the 12 hand gestures are completely separated. • association of the three modalities accounts for slightly higher results in handglove1 dataset because the gestures in this dataset have negligible displacement. the hand rotations are almost the same and the hand is raised in front of the body. however, the system is trained by handglove1 dataset, and then this trained model is deployed in real application. as a result, the online system has many mistakes. to see the effectiveness of a and g modalities, we will be evaluated in the below section iv.c. c. distinction between command action and normal gestures in this section, the kml fusion strategy will be used for testing on the handglove2 dataset. all gestures belonging to the group ()* � are labeled with labels from 13 to 24. the recognition accuracy is considered only with gestures with labels from 1 to 12. these gestures are defined and expected to be correctly recognized by the system. the user raises his/her hand in front of the face and the state of the hand is stationary. only the hand shape changes according to the specified gesture means. in this test, a combination of different modalities will be used, such as: a and f, g and f, and a, g, and f. the evaluation results are shown in figure 7. fig. 7. efficient of modalities combination for hand gesture recognition accuracy (%) in a real environment. in handglove1 dataset, the recognition results of the ways of combining data have not a big gap from 92.15% to 99.87%. hand gestures are distinguished with other hand postures. in addition, end-user’s hand and body are immobile so that the curvature of the fingers could provide enough cues of hand shapes in this dataset, so, the recognition results are quite good. however, in handglove2 database, the recognition accuracy is low when the 5 flex sensors are utilized. this is because of for the same changing shapes, i.e. the same five f elements, one of them moves like normal hand movement (different a and g elements). gestures 1 to 12 have the same hand shape with corresponding gestures 13 to 24 (figure 8). therefore, using only the curvatures of the fingers does not give enough information to distinguish between a control operation and a normal operation as shown in figure 8. for example, gesture 1 (red color) and gesture 13 (slow brown color) in figure 8 have the same hand shape but hand gesture 1 is immobile while gesture 13 is in movement. distributions of these gestures overlap in figure 8(a), but are reparative in figure 8(b). thus, there is a big gap between single modal (56.72% with f) and multi-modal (97.59% with a, g, and f) in the second row of figure 7. in handglove2 dataset, combining f and a or f and g showed a significant improvement in accuracy, increasing up to 33% and 36% respectively (figure 7). especially, the coherency of the 3 components (a, g, and f) obtained the highest recognition accuracy, which was increased up to 97.59% in this dataset. the proposed framework could apparently distinguish between the 12 hand gestures in both immobile and mobile states. the efficiency of the system dramatically increased and practical applications can now be deployed. fig. 8. t-sne of 24 gestrures with various modalities. iv. conclusion and discussion this paper presents a comparative analysis of recent fusion strategies for static hand gesture recognition on three modalities of an electronics hand glove. among the evaluated fusion strategies (late fusion, early fusion, and kml), kml performed better, achieving the highest recognition accuracy. the evaluation results on two datasets show great interest in combining multi-modalities (5 curvature fingers from flex sensors, 3-axis gyroscope and 3-axis accelerometer from mpu6050 sensor) to increase accuracy. in most cases, multimodal kml models can achieve an accuracy rate above 97%. this performance is remarkable and promises a feasible solution for deploying gesture-based applications in practice. finally, it was found that there is a notable gap in recognition accuracy between the same hand shapes but different normal hand movements. the last remark opens up new research directions that require further investigation on data combination with image information, using deep convolutional neural networks, and online learning. once these bottlenecks are resolved, the development of a gesture-based interface in practical applications is straightforward. acknowledgement this research was funded by the electric power university (epu) under the grant project titled 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hanoi, vietnam bvhung.tkm@utc.edu.vn received: 12 august 2022 | revised: 26 august 2022 | accepted: 2 september 2022 abstract-the additive manufacturing (am) process is applied in industrial applications. however, quality issues of the printed parts, including part distortion and cracks caused by high temperature and fast cooling, result in high residual stress. the theoretical calculation equation shows elastic behavior which is the linear behavior between strain and stress. however, in practice with the additive manufacturing process, strain and stress have nonlinear behavior. so, the prediction of the deformation of a printed part is inaccurate. the contribution of this research is the creation of an inherent strain (is)-based part deformation prediction method during the selective laser melting (slm) process. to have the deformation in the design stage, we developed software for calculating the is value and predicting the deformation. the difference between the calculated results and the experimental results is still there, so, we proposed an algorithm and developed an optimization module for the system to minimize this difference. in the final optimal printing process, the parameters are derived in order for the real printing process to have the required quality of the slm printed part. keywords-selective laser melting; predicting deformation; inherent strain; heat treatment effect zone i. introduction layer by layer manufacturing or additive manufacturing has been used in many application fields such as aerospace, automotive, biomedical, and energy production and distribution. the printed parts are made from plastic or metal powder materials [1-4]. however, the quality issues of the printed parts, including part distortion, as well as the cracks caused by high temperature and fast cooling, result in high residual stress. this is a challenge that limits the industry acceptance of am. to overcome this challenge, a numerical modeling method for predicting the part distortion at the design stage plays an important role, which enables design engineers to remove failures before carrying out printing as well as to determine the optimal printing process parameters to minimize part deformation. currently, with the rapid growth of this technology, many am processes have been applied in industrial applications. selective laser melting (slm) is one of these am processes. slm is an am process that directly produces parts from metal powder. slm is a complex thermalphysical-chemical process of the interaction between a laser source and metallic powders [1, 5]. the slm mechanism is shown in figure 1. the slm system includes the laser source, the optical system, and the deposition system. the optical system has the optical mirrors which enable the laser source to be directed onto the powder bed surface. the thin powder layer is distributed by the deposition system and melted by the laser source through the optical system. the deposition system that is the scraper or roller system enables the distribution of the powder onto the printed area. the printed layer thickness is determined by the distance of moving down of the build platform. then, another powder layer is added on the top of the printed previous layer. this step is repeated until the entire 3d model is completed. for printing the metal parts, there are currently many different am processes using different combinations of stock material form, material delivery, and heat source. slm is the most attractive method for layer by layer building of metal parts due to advantages such as the lack of post-processing. however, as the same with other am processes, the distortion and cracks of the printed parts still occur due to the residual stress caused by the rapid heating and cooling process [6]. in the slm process, high temperature is required for the melting of the metallic powders. due to high temperature and fast cooling, residual stress will be generated in the printed part. the large residual stress results in part distortion which is a negative effect of the product performance. part distortion caused by the tensile residual stress not only reduces the part corresponding author: vu-hung bui, ngoc-hien tran engineering, technology & applied science research vol. 12, no. 6, 2022, 9450-9457 9451 www.etasr.com park et al.: development of a prediction system for 3d printed part deformation geometrical accuracy, but also affects the functional performance of the printed parts. to acquire good printed part quality, key factors such as powder properties, printing process parameters, and slm machine characteristics must be considered. fig. 1. mechanism of the selective laser melting process. currently, the method for keeping the quality of the printed part is trial-and-error testing. this method depends on the user’s experience and requires larger manufacturing costs, while producing waste and scrap [7]. therefore, it is necessary for predicting the part’s quality at the design stage which enables to remove failures before carrying out the real printing. many researchers have used the inherent strain method for predicting part deformation in welding processes. however, some proposals for modifying the conventional is method have been applied to apply this method to am processes such as the slm process, [8, 9]. authors in [9] proposed the extraction of the is value from micro-scale thermo-mechanical analysis. this is value was applied to the part-scale model to have the part deformation. however, it is challenging to predict the residual deformation in the part-scale model [10]. to overcome this challenge, a multi-scale modeling approach is proposed in [11, 12]. currently, some commercial tools based on the is method enable the prediction of deformation. however, the algorithms to calculate the is value and how to apply this value to the part-scale model are not publicly available [13]. this paper presents a new method for predicting the deformation of the 3d printed part using the iss. for carrying out this research, a method for calculating the is value is proposed. these is values are used for calculating the deformation. both simulation and experiments were implemented for comparing the is values and deformations. ii. model for determining the is value a. theoretical model the term of is was firstly introduced in 1975 for analyzing the welding process. it is a general name for the expression of non-elastic strains which include the thermal strain �������� , phase transfer strain � �� � , plastic strain � �� ��� , and creep strain ����� [7]. during the slm process with the heating and cooling cycles, the total strain is the sum of the elastic strain ���� ��� and is � ∗, as shown below: ������ = ���� ��� + � ∗ (1) the inherent strain is calculated as: �∗ = �������� + � �� ��� + � �� � + ����� (2) strain and stress are unknown variables. we can determine the value of one of these variables by experiments. the remaining variable is determined by the equation showing the relationship between strain and stress. the commercial tools enable engineers to estimate the is value. however, the algorithms for calculating the is value are not published. during the printing process, the material begins at the melting temperature via the heating stage and is changed to a lower temperature via the cooling stage at a high rate. the material of the printed part will receive a compressive force due to the thermal change. thus, the three-dimensional iss are compressive strains, and the equations can be defined as [14]: ��∗ = − ���� ; ��∗ = − �� �� ; ��∗ = − �� �� (3) in which fx, fy, and fz are the zone areas where wx, wy, and wz respectively are distributed. the total volume wx of ��∗, the total volume wy of ��∗ , and the total volume wz of ��∗ in unit length are calculated as follows: wx = ξ ∙ qv ; wy = wz = k ∙ qv (4) in which qv is the linear energy density (j/mm) [15]: �� = ���� "#$%&�' (5) ξ and k (mm/j) are longitudinal and transverse inherent strain coefficients, respectively. figure 2 shows the components of the inherent strain εx, εy , and εz with these parameters. fig. 2. inherent strain components. the inherent strains in the x, y, and z directions for the first layer are calculated as follows: ��(�)� = − * ∙ ,-�� ; ��(�)� = − . ∙ ,�� ; ��(�)� = − . ∙ ,�� (6) figure 3 shows the calculation of the is for n layers. after printing the first layer, the is value is ��(� . if we add the second layer via the slm process mechanism, the first layer is re-melted with the new heat treatment effect zone, so the remaining is value for the first layer is: engineering, technology & applied science research vol. 12, no. 6, 2022, 9450-9457 9452 www.etasr.com park et al.: development of a prediction system for 3d printed part deformation �/0 = ��(� − 1� ��(� (7) when the second layer is added, its is value is: �2 = �/0 + ��(� = 2��(� − 1� ��(� (8) if a third layer is added, the remaining is value in the second layer is: �20 = �2 − 1� ��(� = 2��(� − 21� ��(� (9) and the is value in the third layer is calculated as: �4 = �20 + ��(� = 3��(� − 21� ��(� (10) repeating this slm process for n layers, we can calculate the is value for the n th layer as follows: �( = �()/0 + ��(� = 6��(� − (()/)1� ��(� (11) for whole part, in x, y, and z directions, we have the is value as follows: ⎩⎪ ⎨ ⎪⎧�� (( �����) = 6��(�)� − (()/)1 � ��(�)� �� (( �����) = 6��(�)� − (()/)1� ��(�)� �� (( �����) = 6��(�)� − (()/)1� ��(�)= (12) fig. 3. method for calculating inherent strain for whole part. b. simulation and experiments 1) simulation results the mathematical model of the heat transfer, which we used to determine the temperature distribution during the slm process, is [16]: >? @a@� + >?u ∇d = ∇(e∇d) + fg (13) where t is the temperature, ρ, с, and k are density, thermal capacity, and thermal conductivity factor respectively, u is the printing speed. qg is the power distribution given by the moving goldak’s double-ellipsoid heat source model as shown in figure 4 [17], this heat source model from the welding process, however, it is also suitable for research on the slm process. qg is the total of the absorbed laser in front and rear of the goldak heat source model [18]. we used this heat transfer model and printing process parameters (as shown in table i) for simulation using comsol tm . we also run tests with the same material (316l steel), however, with differences in the printing process parameters (300w laser power, 1300mm/s laser velocity, and 0.045mm layer thickness). in this case, the inherent strain in z direction is -0.153 [19]. fig. 4. goldak heat source in the finite element model of the am process. the temperature distribution during the slm process is shown in figure 5. the heat treatment effect zone (htez) surfaces are shown in figures 6-8. the htez surface in the zx plane as shown in figure 6 is calculated as follows: h� = (i + j) ∙ k − j ∙ l (14) with d = 0.112mm, c = 0.0522mm, e = 0.5255mm, and x = 2.429mm, we have fx = 0.3035mm 2 . the htez surface in the xy plane as shown in figure 7 is calculated as follows: h� = 2(i + j) ∙ (m + n) − 2m ∙ j − o ∙ 6 (15) with a = 0.089mm, b = 0.137 mm, e = 0.5255 mm, f = 0.258, n = 3.166, and x = 2.429 mm, we have fy = 0.425 mm 2 . the htez surface in the zy plane as shown in figure 8 is calculated as: h� = 2[(m + n) ∙ k − m ∙ l] (16) with a = 0.089mm, b = 0.137mm, d =0.112mm, and c = 0.0522mm, we have fz = 0.0413 mm 2 . fig. 5. goldak heat source in the finite element model of the am process. engineering, technology & applied science research vol. 12, no. 6, 2022, 9450-9457 9453 www.etasr.com park et al.: development of a prediction system for 3d printed part deformation table i. printing process parameters [18] name description value x0 path center x-coordinate 0mm y0 path center y-coordinate 0mm qheat source laser power 250w p length of the y-semi-axis of ellipsoid (mm) 0.173mm c length of the z-semi-axis of ellipsoid (mm) 0.230mm af length of the x -semi-axis of front ellipsoids (mm) 0.173mm ar length of the x -semi-axis of rear ellipsoids (mm) 0.347mm u laser velocity 1100mm/s c thermal capacity 500×10 -3 j/(g.k) λ thermal conductivity factor 19.4×10 -3 w/(mm.k) ta ambient temperature 293k h layer thickness 0.05mm ha hatch distance 0.07mm fig. 6. htez surface in in the zx plane. fig. 7. htez surface in in the xy plane. fig. 8. htez surface in in the zy plane. the inherent strains in the x, y, and z directions for the first layer are calculated by applying (6) with ξ =1.57×10 -3 mm 3 /j, k =0.58×10 -3 mm 3 /j [14], and qv = 0.2273j/mm for 316l stainless steel, fx = 0.3035mm 2 , fy = 0.425mm 2 , and fz= 0.0413mm 2 , we have: ��(�)� = −0.00118, ��(�)� = −0.00031 and ��(�)� = −0.003. in comparison with the reported is value for the first layer in the welding process, which also considers the influence of the temperature distribution to the is value, the calculated is value is acceptable. in the z direction, where the highest temperature is 1500 0 c (or 1773 0 k) the inherent strain value is 0.0017 [20]. thus, the is value for the whole part after 60 printed layers (with layer thickness of 0.05mm and printed part height of 3mm) is calculated as follows: assuming that the depth (d) that affects the inherent strain distribution equals to (1/3) of the layer thickness (h), we have the following is values using (12): �� (r���� ���) = −0.04742, �� (r���� ���) = −0.0125, �� (r���� ���) =−0.1286. 2) experimental results experiments on printing a cantilever beam were carried out on an slm machine at the laboratory of production engineering, ulsan university, republic of korea (figure 9). the geometrical model of the cantilever beam and the printing direction (0, 45°, and 90°) are shown in figure 10. specimens were printed on the metalsys 250. fig. 9. experiments on the slm machine. the highest deformation of the cantilever beam at the position in the z direction with 0° printing direction after cutting the part from the base plate by the electrical discharge machining (edm) machine is 1.45mm as shown in figure 9 and table ii. the is is calculated as follows: � = − � )�s�s = − /4.uv)/2.v /2.v = −0.116 (17) where lo is the part length before cutting by edm and lt is the part length after cutting by edm. considering the z direction, with the part height before and after cutting being 12.5mm and 13.95mm, we have εz = −0.116, and the deformation in the z direction is 1.45mm. the is value in the z direction predicted by simulation is −0.1286. the difference between simulation and experiment is considered acceptable. table ii. geometry measurement after cutting geometry measurement distortion (mm) 1 2 3 4 5 average scan pattern (0 o ) 13.93 13.94 13.96 14.02 13.90 13.95 scan pattern (90 o ) 13.24 13.19 13.21 13.19 13.12 13.19 scan pattern (45 o ) 13.50 13.48 13.50 13.51 13.43 13.484 with the proposed method, the is value in the z direction is εz = −0.1286. from this is value, with a total part height of h = 12.5mm, the deformation (δ) of the printed part in the z direction is 1.608mm, which is calculated by: δ = |εz(whole part)|∙h (18) engineering, technology & applied science research vol. 12, no. 6, 2022, 9450-9457 9454 www.etasr.com park et al.: development of a prediction system for 3d printed part deformation fig. 10. specimens printed by slm. iii. architecture of functionality modules a. module for calculating the htez surfaces to develop the proposed system, we drive out the architecture of functionality modules. figure 11 shows the architecture of the module for calculating htez surfaces. with the input parameters such as 3d model of part, layer thickness (h), hatch distance (ha), scanning speed (u), and laser power (q), the databases of the system are updated which are printing parameter database and part dimension database. in the printing parameter database u, q and the heat source (goldak model) with parameters such as c, b, af, ar, are used for calculating the absorbed laser. other databases are also built which are the material properties (thermal capacity, thermal expansion, and thermal conductivity factor), and the coefficient for printing (lattice parameter, laser interaction time). the thermal capacity (c) in material properties database and the absorbed laser are used for calculating the temperature distribution through the heat transfer equation. from the temperature distribution and the material properties and coefficient for printing databases, we have the htez parameters (x, e, c, d, a, b, f, n). then, we calculate the htez surfaces (fx, fy, fz). fig. 11. architecture of the module for calculating htez surfaces. b. module for calculating the is for one layer figure 12 shows the architecture of the module for calculating the is value for one layer. with the input parameters including the printing process parameters, and the htez surfaces, the system allows to calculate the melting energy, the laser power, and the linear energy density. then, the linear energy density (qv) and the layer thickness are used for calculating the longitudinal, transverse is coefficients (ξ, k). from the qv, ξ, and k, we calculate the is value for one layer using (6). fig. 12. architecture of the module for calculating is for one layer. c. module for calculating the is for the whole part figure 13 shows the architecture of the module for calculating the is value for whole part. with the input parameters including the is value for one layer, part dimension, and printing parameters, the layer number and the htez depth are calculated. then, these data are used for calculating the is value for the whole part using (12). fig. 13. architecture of the module for calculating the is for the whole part. engineering, technology & applied science research vol. 12, no. 6, 2022, 9450-9457 9455 www.etasr.com park et al.: development of a prediction system for 3d printed part deformation d. module for optimizing the difference between the simulations and the experiments figure 14 shows the architecture of the module for optimizing the difference between the simulations and the experiments. from the simulation and experimental results, the system enables to calculate the new is value in case the difference between them in the printed part deformation is more than 0.01. fig. 14. architecture of the module for optimizing the difference between the simulation and experiment. iv. implementation of the system fig. 15. architecture of the system for calculating inherent strain. to acquire the deformation in the design stage, we developed software for calculating the is and for predicting the printed part deformation. the developed system includes 4 modules: a module for calculating the htez surfaces, a module for calculating the is for one layer, a module for calculating the is of whole part, and a module for optimizing the difference between the simulations and the experiments. for programming the proposed system, we used c++ language in visual studio 2019 environment. the system architecture is shown in figure 15 which describes the information flow among the modules. figure 16 shows the interface module which shows the integration of modules for one complete system. with the input data including printing process parameters (such as volumetric energy density, layer thickness, hatch distance, scanning speed, and efficiency) and the htez surfaces, the developed system allows to calculate the is value for one layer as shown in figure 17. the volumetric energy density value is 40j/mm 3 [21]. from the calculated is values for one layer and part information (such as length, width, and part height), the developed system enables to calculate the is value of the whole part in x, y, z directions as shown in figure 18. fig. 16. screenshot of the system interface with four modules. v. conclusion the contribution of this research is the creation of an inherent strain-based part deformation prediction method during the selective laser melting (slm) process. to determine the inherent strain (is) value, a micro-scale model for analyzing the temperature distribution was created. the is value for one layer is calculated from the temperature gradient. for calculating the is value for the whole part, the htez is used. then, the is value is used to determine the part deformation. the proposed methodology has been developed and evaluated using 316l stainless steel cantilever beams, and both simulated and experimental results were obtained. to acquire the deformation in the design stage, we developed the is-based deformation prediction software. the functionality of the developed system was tested successfully. future research can be conducted with the consideration of other factors affecting the printed part quality in order to minimize part deformation. in addition, other printing processes also should be added to the developed system. engineering, technology & applied science research vol. 12, no. 6, 2022, 9450-9457 9456 www.etasr.com park et al.: development of a prediction system for 3d printed part deformation fig. 17. screenshot of the module for calculating inherent strain for one layer. fig. 18. screenshot of the module for calculating is of whole part. engineering, technology & applied science research vol. 12, no. 6, 2022, 9450-9457 9457 www.etasr.com park et al.: development of a prediction system for 3d printed part deformation acknowledgment this research is funded by the university of transport and communications (utc) under grant number t2022-ck-12, supported by the university of ulsan. references [1] t. sunar and m. cetin, "an experimental study on boron carbide reinforced open cell aluminum foams produced via infiltration technique," engineering, technology & applied science research, vol. 8, no. 6, pp. 3640–3645, dec. 2018, https://doi.org/10.48084/etasr.2419. 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[21] a. leicht, m. fischer, u. klement, l. nyborg, and e. hryha, "increasing the productivity of laser powder bed fusion for stainless steel 316l through increased layer thickness," journal of materials engineering and performance, vol. 30, no. 1, pp. 575–584, jan. 2021, https://doi.org/10.1007/s11665-020-05334-3. microsoft word 7-682-ed.doc engineering, technology & applied science research vol. 6, no. 3, 2016, 1010-1012 1010 www.etasr.com saidaiah et al.: a new olympic ring shaped antenna for uwb applications a new olympic ring shaped antenna for uwb applications b. saidaiah department of ece malineni lakshmaiah women's engineering college, india saidaiahbandi@gmail.com a. sudhakar department of ece rvr & jc college of engineering india alapati_sudhakar@yahoo.com k. padma raju department of ece jawaharlal nehru technological university kakinada, india padmaraju_k@yahoo.com abstract— in this paper, we propose a new olympic ring shaped antenna for uwb applications. the proposed antenna is designed to operate from 3.1 to 10.6 ghz. it consists of a five circular ring shapes form an olympic ring shape with a partial ground plane. a detail of proposed antenna simulation is done using cst software and measured results are presented and discussed. keywords-ultra wideband antenna; olympic ring; cst; i. introduction since the acceptance of the ultra wide band (uwb) impulse radio technology in the usa, there has been a considerable research effort put into uwb radio technology worldwide [1]. uwb antennas are specially designed to transmit and/or receive very short time durations of electromagnetic energy [2]. therefore in the progress of uwb technology the transmitting and receiving antenna design has become a challenging topic. uwb technology is based on the use of very narrow pulses, in the order of nanoseconds, which covers a very wide bandwidth (3.1 to 10.6 ghz) in the frequency domain. in this paper, we propose a new ultra wideband antenna for uwb applications. the proposed antenna consists of five rings that form an olympic ring shape with a partial ground plane. investigations based on experiments and simulations are conducted. the simulation is performed using the commercially available simulation software cst microwave studio. the proposed antenna is successfully implemented and the simulated results show reasonable agreement with the measured results. in this design, a 3.1 to 10.6 ghz frequency range for s11 < -10 db is obtained, radiation patterns and vswr are also examined. ii. antenna design figure 1 shows the configuration of the proposed antenna, which consists of five rings that form an olympic ring shape with a partial ground plane. the antenna, which has compact dimensions of 32 x 40.57 mm2, is printed in front of substrate fr4 of thickness 1.6 mm and relative permittivity 4.3. the width dimension of each circular ring is 1 mm and the dimension of ground plane is chosen to be 32 x 18.8 mm2. the excitation is a 50 ohm micro strip line printed on the partial grounded substrate. note that the design dimensions of the proposed antenna are obtained using cst microwave studio. by selecting these parameters, the proposed antenna can be tuned to operate in the 3.1 – 10.6 ghz frequency range. fig. 1. cst model amd picture of the proposed antenna. iii. results and discssion the cst software is used to simulate the proposed model. the anritsu vector network analyzer (37397c) is used to measure the return loss s11 and vswr. the simulated and measured return loss result of the proposed antenna is shown in figure 2 . the simulated bandwidth of s11 < 10db varies from 3.1 ghz to 10.6 ghz and the measured one from 3.1 ghz to 10.6 ghz. the simulated and measured vswr results of the proposed antenna are shown in figure 3. the simulated bandwidth of vswr ≤ 2 ranges from 3.1 ghz to 10.6 ghz and the measured one from 3.1 ghz to 10.6 ghz. both of them cover the uwb range of 3.1 to 10.6 ghz for short wireless communications. figure 4 shows the simulated far field radiation patterns at different frequencies. figure 5 shows the simulated e-field distribution at different frequencies. iv. conclusion a new ultra wideband (uwb) antenna has been proposed for uwb applications. the simulated results conducted by the cst microwave simulator show reasonable agreement with the measured results. the entire frequency band almost obtained for s11 < 10 db and vswr ≤ 2 is obtained from 3.1 – 10.6 ghz. engineering, technology & applied science research vol. 6, no. 3, 2016, 1010-1012 1011 www.etasr.com saidaiah et al.: a new olympic ring shaped antenna for uwb applications fig. 2. frequency vs. return loss. fig. 3. vswr curve. fig. 4. the simulated far field radiation patterns at different frequencies. top row from left to right: 3.1ghz, 4 ghz, 5 ghz. middle row from left to right: 6 ghz, 7 ghz, 8 ghz. bottom row from left to right: 9 ghz, 10 ghz, 10.6 ghz. engineering, technology & applied science research vol. 6, no. 3, 2016, 1010-1012 1012 www.etasr.com saidaiah et al.: a new olympic ring shaped antenna for uwb applications fig. 5. simulated e-field distribution at 3.1 ghz (up), 6 ghz (middle) and 9 ghz (bottom) acknowledgment the authors would like to thank the university grants commission, govt. of india, new delhi and the management of rvr & jc college of engineering for their financial support for this work. references [1] w. mazhar, m. a. tara, f. a. tahir, s. ullah, f. a. bhatti, “compact microstrip patch antenna for ultra-wideband applications”, piers proceedings, stockholm, sweden, aug.12-15, 2013 [2] r. khalilpor, j. nourinia, c. ghobadi, “an optimized monopole microstrip patch antenna with gradual steps for ultra wide band applications”, piers proceedings, xi’an, china, march 22-26, 2010 [3] i. m. rafiqul, a. a. h. m. zahirul, m. f. a. j. khan, s. alkaraki, “design of microstrip patch antenna using slotted partial ground and addition of stairs and stubs for uwb application”, journal of selected areas in telecommunications, vol. 3, no. 5, pp. 1-8, 2012 [4] j. liang, c. c. chiau, x. chen, c. g. parini, “study of a printed circular disc monopole antenna for uwb systems”, ieee transactions on antennas and propagation, vol. 53, no. 11, pp. 3500-3504, 2005 [5] c. c. lin, y. c. kan, l. c. kuo, h. r. chuang, “a planar triangular monopole antenna for uwb communication”, ieee microwave and wireless components letters, vol. 15, no. 10, pp. 624 – 626, 2005 [6] s. h. choi, j. k. park, s. k. kim, j. y. park, “a new ultra-wideband antenna for uwb applications”, microwave and optical technology letters, vol. 40, no. 5, pp. 399-401, 2004 [7] r. pillalamarri, g. s. b. rao, s. s. kumar, “compact printed semi circular disc micro strip line fed monopole antennas for uwb applications”, journal of physical sciences, vol. 13, pp. 217-222, 2009 [8] m. n. srifi, s. k. podilchak, m. essaaidi, y. m. m. antar, “compact disc monopole antennas for current and future uwb applications”, ieee transactions on antennas and propagation, vol. 53, no. 11, pp. 4470-4480, 2005 [9] n. hecimovic, z. marincice, “the improvements of the antenna parameters in ultra wideband communications”, available at http://www.ericsson.com/hr/etk/dogadjanja/mipro_2008/1207.pdf [10] f. yan, j. xu, “design of planar monopole antenna with annulus shape for ultra wideband applications”, piers proceedings, xi’an, china, march 22-26, 2010 [11] g. kumar, k. p. ray, broadband microstrip antennas, norwood: artech house, 2003 microsoft word 1-634-ed.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1035-1044 1035 www.etasr.com xefteris et al.: behavioral biometrics in assisted living: a methodology for emotion recognition behavioral biometrics in assisted living: a methodology for emotion recognition stefanos xefteris distributed knowledge and media systems laboratory, dept. of electrical and computer engineering, national technical university of athens athens, greece xefteris@gmail.com nikos doulamis photogrammetry and computer vision lab, dept. of rural and survey engineering, national technical university of athens ndoulam@cs.ntua.gr vassiliki andronikou distributed knowledge and media systems laboratory, dept. of electrical and computer engineering, national technical university of athens athens, greece vandro@mail.ntua.gr theodora varvarigou distributed knowledge and media systems laboratory, dept. of electrical and computer engineering, national technical university of athens athens, greece dora@telecom.ntua.gr george cambourakis division of communication, electronic and information engineering, department of electrical and computer engineering, national technical university of athens athens, greece gcamb@cs.ntua.gr abstract—behavioral biometrics aim at providing algorithms for the automatic recognition of individual behavioral traits, stemming from a person’s actions, attitude, expressions and conduct. in the field of ambient assisted living, behavioral biometrics find an important niche. individuals suffering from the early stages of neurodegenerative diseases (mci, alzheimer’s, dementia) need supervision in their daily activities. in this context, an unobtrusive system to monitor subjects and alert formal and informal carers providing information on both physical and emotional status is of great importance and positively affects multiple stakeholders. the primary aim of this paper is to describe a methodology for recognizing the emotional status of a subject using facial expressions and to identify its uses, in conjunction with pre-existing risk-assessment methodologies, for its integration into the context of a smart monitoring system for subjects suffering from neurodegenerative diseases. paul ekman’s research provided the background on the universality of facial expressions as indicators of underlying emotions. the methodology then makes use of computational geometry, image processing and graph theory algorithms for the detection of regions of interest and then a neural network is used for the final classification. findings are coupled with previous published work for risk assessment and alert generation in the context of an ambient assisted living environment based on service oriented architecture principles, aimed at remote web-based estimation of the cognitive and physical status of mci and dementia patients. keywords: ambient assisted living; dementia; emotion; image processing; telemedicine i. introduction people older than 64 represent an average of 18.5% of the total european population and growing notably is the age group over 84, as reported by eurostat in 2015[1]. such remarkable steady increase of older population in europe requires innovative approaches, to make possible and maintain the independence, autonomy and quality of life of our elderly. the impact of an increasing aging population also affects greatly formal and informal care providers. an aging population is also associated with an increase in the number of people suffering from mild cognitive impairment (mci), such as the range of dementia [24]. these conditions are very challenging from the outset, ranging from the problem of reaching and obtaining a diagnosis, to the tailoring of appropriate care and support for the individual and their caregivers both family and professional [5-6]. there is therefore the need for an innovative approach, to explore different ways of working with increased collaboration across disciplines: healthcare experts and technologists and greater working partnerships between older people and their formal and informal caregivers [7-9]. progress in information and communications technology (ict) in the past years has led in exciting advances with direct effect in aspects of everyday life activities. especially concerning modern healthcare, ict has permeated deeply the current paradigm providing new frameworks for telecare, with comprehensive multi-stakeholder benefits, for the individual subject and direct carers, local healthcare infrastructures and healthcare system as a whole [10-12]. ict provides frameworks that enable internet based, decentralized, costeffective and efficient services to patients. ambient assisted living (aal) systems are being constantly on the cutting edge of ongoing research, aiming at improving home-base patients’ quality of life, provide them with means to cope with their diseases, delay institutionalization and alleviate burden of family members [12-14]. the need for a paradigm shift from remedial to preventive measures in the field of assisted living is engineering, technology & applied science research vol. 6, no. 4, 2016, 1035-1044 1036 www.etasr.com xefteris et al.: behavioral biometrics in assisted living: a methodology for emotion recognition apparent and currently in its early stages. in this context, modern aal systems comprise significant tools, providing better information processing, extraction of patterns, analysis and comparison of data for adverse event prediction and also patient profiling capabilities to improve subject’s lives delaying hospitalization/institutionalization as much as possible. a systematic flow of information to and from the subject along with identification of adverse events and assessment reports leads to a more effective care system, socially and financially beneficial to the subjects. remote monitoring of patients under a risk prediction framework is crucial for shifting the current paradigm from remedial to preventive action [7, 15-19]. patient profiling as well as activity recognition in the context of aal systems, opens new routes and possibilities, aiming at actively and measurably aiding subjects to cope with their activities of daily life (adls) and their physical and psychological status. supplemental to the regimented physiological measurements, profiling the subject’s mood changes, emotional reactions to stimuli, attitudes and conduct can be of great aid to attending doctors and family members. information can be acquired and processed in order to not only detect abnormalities but identify behavioral trends in order to prevent both physical and physiological adverse events [17, 2021]. the next step in patient profiling is behavioral and activity monitoring as parts of decision support implementations in aal context [22]. within this context, biometrics, as a source rich in profiling information related to the physiological and behavioral characteristics of a person, form the basis for a very promising technology that can further boost and enhance patient profiling. the strength of biometric traits lies in four fundamental characteristics [23] :  sufficient inter-person variability for distinctiveness  short-term temporal invariability  collectability/measurability and  universality in this paper, we discuss a methodology for emotion recognition targeting applications in the framework of an ambient assisted living system following service oriented architecture (soa) principles, making use of extracted biometric facial features of the subjects. in the case of emotion recognition, the methodology makes use of the latter two characteristics of biometric traits, i.e the ease of collection and measurability and universality with the added benefit of the non-invasive nature of collection method. in our methodology, biometric information is not used to directly characterise the subject (explicit biometric profiling) but provide the background for extraction of regions of interest on a subjects’ facial structure and the abstract generalisation of emotion as a geometric shape on a surface. ii. biometric profiling in aal systems ict applications are gaining more acceptance as solutions that can act complementary to the caregiver’s work by actively providing information and continuously monitoring and assisting subjects with reduced cognitive (or even physical capacity). this is also augmented by the ease of installation in home environments of a multitude of sensors – from simple “binary” sensors, to temperature and lighting sensors [24-25] and from movement trackers on floors [26] to more complex sensors that provide audio and video recordings [27]. we use biometric profiling information as a part of the whole patient profile and assist in the detection and prediction of physical and psychological adverse events. in this context researchers usually make use of biometric technologies such as voice analysis, gesture and gait classification and emotion recognition. emotion recognition is the task of processing a specific stream of data in order to classify the underlying emotional state. it is easier to use basic (or archetypal) emotions such as joy, sadness, anger, fear, disgust and contempt [28]. in general, emotion recognition systems are built on three distinct levels: acquisition, feature extraction and interpretation [29]. in our case, sensor technologies used in biometric data capturing are cameras which provide the advantage of being non-intrusive and cheap. facial expressions as the basis of emotion recognition contain all the necessary information and are easily captured and analysed. the design and implementation of monitoring systems to enable the self-management of neurodegenerative disease patients at home, impose many issues. the focus of this approach lies on prevention and prediction of adverse events through the early identification of risk factors. thus, our methodology aims to be integrated into a risk assessment and detection component that processes patient data and if necessary, creates alerts for the clinicians. such a component, can be based on an existing set of “rules” and implemented to process both physical and psychological data as well as answers to cognitive and behavioral evaluation tests, to produce its warnings[30]. the main functionalities of such a component would include:  generate warnings for the attending physicians for situations where the patient’s physiological and/or psychological measurements indicate an alarming condition for the patient’s health.  compile automatic reports for the attending physicians on a scheduled regular basis  generate warnings for the subject’s caregivers in case of emergencies  present evidence for the produced warnings generation of warnings is based on an easily reconfigurable rule-based schema , that attending clinicians can individualize according to each subject’s personal needs, as seen in figure 1. iii. facial expressions and emotion faces are essentially very effective systems for the transmission of multiple signals and multiple messages [31]. they transmit voluntary and involuntary messages regarding emotions, mood, character, age, sex, race etc. when humans respond to a stimulus, internal or external and feel something, engineering, technology & applied science research vol. 6, no. 4, 2016, 1035-1044 1037 www.etasr.com xefteris et al.: behavioral biometrics in assisted living: a methodology for emotion recognition their face responds accordingly. muscles contract, wrinkles appear or disappear, mouths change shape, eyes open wide or close etc. emotions as expressed by our faces are not static structures, but dynamic and short-lived. in this paper we concern ourselves with “emblematic” messages. the term “emblematic” is used to describe messages that have a clearly defined content, formed by specific and easily recognizable facial expressions [32]. before venturing forth, we have to answer to 3 specific questions: a) which emotions can be expressed by the human face? b) is the initial recognition accurate? and c) can we use emotion as a behavioral biometric trait? a. which emotions can be expressed? before proceeding to the technical aspect of automatic emotion recognition from the image of a human face we must set concrete foundations, based on psychology and anthropology centred on how emotion is pictured on the human face. research on the expression of emotion begins even from the time –and personof charles darwin [33]. since then there has been a plethora of research and hundreds of experiments whose results have been described in the works of dr. paul ekman [32, 34-35]. according to this research, the human face can express (in a meaningful way for observers) six basic and archetypal emotions [31]: joy, sadness, surprise, anger, disgust and fear. there are obviously more emotions in the expression range of the human face (such as shame and enthusiasm) but these have not shown to have the same constant qualities as the 6 archetypal ones [32, 36-37]. fig. 1. rule based risk assessment scheme b. can we recognize emotions accurately? researchers here faced the following issue: it is not enough to just simply discern human emotion inside an expression. it is essential to discover if the interpretation by the observers is accurate or not. in ekman’s experiments researchers who knew a priori the emotion expressed by the subject, categorized the answers of observers chosen from different cultural backgrounds, as right or wrong. the subjects ranged from healthy people who were shown a horror film/comedies etc to psychiatric hospital patients subjected to stress or relaxation experiences. the accuracy of the answers can be seen in table i. table i. results of ekman’s experiment on the recognition of emotion expression by multicultural observers observer’s country of origin u.s.a brazil chile argentina japan total observers 99 40 119 168 29 emotion percentage of correct answers (%) fear 85 67 68 54 66 disgust 92 97 92 92 90 joy 97 95 95 98 100 anger 67 90 94 90 90 c. can emotion be used as a biometric trait? in order to categorise emotion as a soft biometric trait – because it is obvious that emotion is a dynamic feature that cannot be used for identification or verification as other biometric traitsit has to fulfil the fundamental requirements of biometric characteristics, as they were earlier described. it is obvious that it is easily collectible, but it also needs to fulfil the universality requirement. everybody expresses emotions through facial expressions but are emotional expressions themselves universal among people of all ages and cultural backgrounds? we have to establish here that the expressions of the six archetypal emotions are the same on people, irrelevant of cultural background, race, education, sex and age. research has proven exactly that: the expression of emotions of the human face is the same for the six basic emotions, regardless of cultural background, age, sex and educational status. the only influence on recorded results was found when cultural background interfered on when it was appropriate to show or hide one’s emotions. the same expressions indicated the same emotions whether the observers came from the u.s, chile or brazil [31, 38]. in order to remove any possible objection, researchers travelled to the highlands of new guinea to measure reactions and expressions of people totally unaffected by the western civilization and found the exact same results: the expression of emotion on the human face is universal across all cultures [31, 35, 38-41]. thus, it can be used as a biometric trait. iv. methodology in this research the authors used, after signing the relevant user agreement that gave them the right to reproduce parts of the dataset with the relevant copyright notice, the cohn-kanade extended dataset of facial expressions [42, 43], which engineering, technology & applied science research vol. 6, no. 4, 2016, 1035-1044 1038 www.etasr.com xefteris et al.: behavioral biometrics in assisted living: a methodology for emotion recognition incorporates 593 sequences from 123 different people. each sequence consists of pictures taken as the subject faces the camera, begin from neutral expression and end in a final expression depicting one of the six basic emotions along with meta-information concerning the emotion depicted and an encoding according to ekman’s facs system. in this research only the final categorization was used, for verification of classification results. the methodology followed, based on the fact of complete emotion expression universality aimed at providing an algorithm that needs no individual training of specific users (although training can be used in a future implementation to further improve acquired results). also the proposed methodology aims at being easily incorporated into a soa based telemedicine system, based on reconfigurable rules [30], or as part of a multi-algorithmic pool in a biometrics system as the one proposed in [44]. the methodology follows the classic steps of biometric traits recognition: collection, extraction of features, comparison and classification as shown in figure 2. fig. 2. the proposed methodology a. identification of regions of interest the first concern in the preprocessing stage, was to crop out parts of the face that are completely irrelevant with emotion and could function as noise, such as the ears and hair, as well as totally irrelevant elements of the image itself (like timestamps). for this reason, we employed the well-known viola-jones face detection algorithm [45]. the viola-jones algorithm is a very fast an efficient solution on face detection, scale and location invariant, based on haar-like features and the adaboost training algorithm coupled with cascading classifiers. moreover, it also performs extremely well in realtime applications so in a future implementation for real-time emotion recognition, it would not add delay to the methodology. the second concern is to identify which areas on the face are of interest in our case and try to separate them from the others. these regions are in order of significance: mouth, eyes, forehead and nose area. observing facial expressions, how they form on the human face and where the human eye focuses to perceive them, it is clear to see that where emotion appears, we have creases in the skin or facial features that define changes in luminosity. the “background” of the face can be considered as a canvas on which harsh lines appear when we express emotion. that same “background” is not needed in the processing phase and so we employ an edge detection algorithm to remove useless parts of the phase and at the same time significantly lessen the amount of data the algorithm uses. while the employment of edge detection may seem as a vulnerability of the algorithm, due to its intolerance in high luminosity environments, we keep in mind that the target application concerns the detection inside home environments where the average luminosity is kept at regular levels. at this stage, we must segment the regions of interest in specific sub-clusters. for this purpose we first perform voronoi tessellation [46-47] and its dual, delaunay triangulation [47-48] on the edge detection generated matrix of points. with this transform, the separate points in 2d space that the edge detection provided, become an undirected graph, which both preserves the geometric properties of the structure and provides an easy input for the application of clustering algorithms. moreover, having our input in the form of a graph, makes it easily processable by a multitude of algorithmic approaches. to define the voronoi tessellation of a set of points on a metric space, we let x be the space and d the metric. also, let k be a set of pointers and kkkp )( a tuple of non-empty subsets in space x. the voronoi tessellation vi of (pi) is the set of points in x whose distance from (pk) is less or equal from their distances of every other pj, with j a different set of pointers. formally: if aaaxdaxd  |),,inf{),( then }),(),(|{)( ijxdxdxxv ppp jii  the voronoi tessellation diagram vor(p) corresponding to the edge detection points in two-dimensional euclidean space is the representation of a tuple . in our case, where the space is euclidean and on it the regular distance metric l2, we have a set of non-overlapping points and each voronoi tessellation is a convex polygon. with this step we have created a polygon model of the human face with low area polygons in areas of expression. at this point in our methodology the goal is to transform this set of polygons to an undirected graph representation. to facilitate this we employ the dual method of voronoi tessellation, the delaunay triangulation. we define the delaunay triangulation of a voronoi diagram of points p as follows : let p= {p1,p2,….,pn} a set of points on a space ε m and vor(p) the voronoi diagram of p, with vi as each tesselation. the delaunay triangulation del(p) of p is: the complex del(p) includes the k-simplex {p1,p2,…pk+1) if  121 ... kvvv ø with mk 0 . the complex del(p) is the delaunay triangulation of the convex hull of p. in essence, the delaunay triangulation creates an edge between two points in voronoi tessellation p, if these engineering, technology & applied science research vol. 6, no. 4, 2016, 1035-1044 1039 www.etasr.com xefteris et al.: behavioral biometrics in assisted living: a methodology for emotion recognition two points have a common edge among their polygons. with the delaunay triangulation we have now available an undirected graph representation of the expression of the human face, on which we can apply a graph clustering algorithm. in order to facilitate input for the neural network classification, we must first separate these clusters one by one and lessen the total number of the points that define them. as we have sets of vertexes, connected via edges in 2d space, and the basic criterion of definition of a cluster is how close these edges are, the simplest way of defining separate point clusters is the use of a density based scanning algorithm such as dbscan [49]. this algorithm, dbscan, was selected instead of other clustering algorithms due to the inherent properties of the clusters:  there is not a priori knowledge of the number of appearing clusters so k-means clustering cannot be applied.  clusters are not organized in regular shapes and in some cases, one cluster can encompass another. given the geometric nature of facial expressions, we should be aware of the single link effect (two clusters linked by a thin line of points) and negate it so there are no overlapping.  we need an algorithm that is resilient to noise and outlier points. dbscan fulfils these requirements [50] with good results. dbscan parses an input of a set of d points in the two dimensional euclidean space and works on the assumption that each cluster around a point fulfils the requirement that there is a specific minimum number of points inside a given radius around that point. in this case, the normal euclidean distance was used as a metric. the algorithm discerns between core and border points, removes outliers and noise and performs well regardless of the sequence of visiting points. fourier shape descriptors [51, 52] on the selected clusters are then used to reduce the number of vertexes needed for the definition of a specific shape, normalizing it. this makes it easier for pattern recognition and classification since it reduces the total number of input points needed and thus provides a specific number of input points every time. b. classification having defined the regions of interest and extracted the geometric features of the facial expression, we then need to classify the data to identify facial expressions. it is apparent from the previous sections that the geometric shapes of the regions of interest provide irregular shapes and thus a nonlinear classification scheme should be adopted to improve classification accuracy. in this case we make use of a back propagating neural network for irregular shape classification [53]. the neural network classifies shapes according to their convex hulls. since forehead and nose wrinkles are widely irregular shapes and cannot be described by a convex hull, we indicate their presence with 1 for yes’s and 0 for no’s. shape of the eyes and the mouth are described by the respective significant fourier descriptors. we have 7 different classes (happiness, sadness, fear, anger, disgust, surprise and neutral) therefore in the output layer we need 4 nodes. to demonstrate the effectiveness of the methodology, an experiment with practical examples was performed. the cohnkanade+ database contains 593 sequences from 123 different people. this subject pool was divided according to emotions depicted among different faces and part of it was used for training, part for verification. the number of available samples is shown in table ii. table ii: number of samples for each emotion, manually checked from peak frames emotion available samples happiness 69 sadness 28 fear 25 anger 45 disgust 59 surprise 83 neutral 123 c. problem formulation let us assume in the following that some features have been extracted from a human face analysis and included in a feature vector say if , where index i corresponds to the ith human individual. let us also assume that p humans’ emotions are recognized by the proposed eri computing architecture and thus each vector if is classified to one of the p available classes ωj, j=1,2,…,p, i.e., emotions. as it can be shown in several publications, six emotions are basic; the happiness, sadness, fear, anger, surprise, and disgust [31]. it is not in doubt that these basic emotions are key points of reference and can be described as ‘archetypal emotions’, which reflects the fact that they are undeniably the obvious examples of an emotion state. new studies attempt to define a set of terms covering a wider range of emotions without becoming unmanageable. let us denote in the following as )( ify , a p-dimensional vector, the elements of which )(i ek p contains the degrees of coherence of vector if to one of the kth emotional state among the p available, ti e i e i ei p ppp ][)( )()()( 21 fy (1) let us assume in the following, for simplicity purposes and clarification reasons, a two-class classification problem, where the two classes 1 , 2 refer, for example, to two emotional states, such as happiness and sadness. extension to multiple emotional states can be performed in a similar way. in this case the model output is scalar, say )( iy f instead of a vector (output values close to one (1) correspond to the first emotional state, while values close to zero to the second emotional state.). then, using concepts derived from functional analysis, it can be proved that any continuous non-linear function can be expressed as a parametric relation of known functional components )(l within any degree of accuracy. then, the model output can be written as engineering, technology & applied science research vol. 6, no. 4, 2016, 1035-1044 1040 www.etasr.com xefteris et al.: behavioral biometrics in assisted living: a methodology for emotion recognition            l l p k kilklli fwvy 1 1 ,, )()(f (2) where kif , refers to the kth element of feature vector if , the lv and lkw , to the model parameters (coefficients), and q the size of the feature vector if . variable l corresponds to the approximation order of the model. in particular, the larger the number of l is the higher the approximation accuracy becomes at the expense of the model complexity. the most familiar class of functional components )(l is the sigmoid functions, which are equal to tl e x   1 1 )( (3) the model parameters lv and lkw , are estimated using a set of representative samples and then by applying a training algorithm. let us denote as     nn dds ,,,, 11 ff l this set, where n is the total number of samples and id the desired output vector for the ith human individual. the values of id is equal to 1 for the first emotional state and 0 for the second emotional state. let us also denote as w a vector, which contains all parameters lv and lkw , of (2), so t kli wv ][ w . d. adaptable emotionally rich architecture although the general expression of archetypal emotions is the same, we nevertheless have to take into account what would be considered as noise: more specifically, since we are targeting an elderly user-base, the most important noise inducing factor would be the appearance of wrinkles. moreover, we should take into account also micro-changes in the expressions, owed to individual quirks. thus, direct application of the model of (2), in which the model parameters are considered constant, would not work well, since the model cannot be adapted to the slight changes in the way that humans use to express their emotions. to overcome this difficulty, we equip the proposed architecture with an adaptable mechanism, as seen in σφάλμα! το αρχείο προέλευσης της αναφοράς δεν βρέθηκε.figure 3, which can update the system response with respect to the current way that the individual use to express their emotions. fig. 3. weight adaptation mechanism in this way, a new set of parameters, say aw , should be created for each emotional state, which are capable of updating the response of the eri architecture to the current actual way that the users express their emotions. to perform the adaptation, a new set of representative samples, say     mmc dds  ,,,, 11 ff should be created, which has a similar form to the set s . then, the new parameters aw are estimated by minimizing the following error criterion,    n i i n i iia edye 11 2 2 1 ))(( 2 1 minarg fw w w for all data in s (4) and )( ii dy a fw csmi in data allfor ,,...,1  (5) in (4, 5) we added the dependence of the model output )( iy fw on the model parameters w. equations (4,5) indicate that the new model parameters are estimated so that the current data, as expressed by the set cs , are satisfied as much as possible, while simultaneously a minimal degradation of the previous obtained knowledge is derived e. optimal estimation of the model parameters in this section, we describe a novel, fast and reliable algorithm for estimating the new model parameters aw . initially, we assume that a small perturbation of the model parameters before the adaptation is enough to achieve good classification performance. then, www a (6) where w is a small incremental vector. this assumption leads to an analytical and tractable solution for estimating aw , since it permits linearization of functional components )(l of (2, 5) using a first order taylor series expansion. it can be shown [54] that linearization of (5) with respect to the weight increments w is equivalent to a set of linear equations wac  (7) where vector c and matrix a are appropriately expressed in terms of the previous model parameters w . in particular,    tmtm yyyy aa )()()()( 11 ffffc wwww  (8) indicates the difference between model outputs after and before the adaptation for all input vectors in cs . engineering, technology & applied science research vol. 6, no. 4, 2016, 1035-1044 1041 www.etasr.com xefteris et al.: behavioral biometrics in assisted living: a methodology for emotion recognition the size of vector c is smaller than the number of unknown weights w , since in general a small number m, of current data are available. thus, many solutions exist for (7), since the number of unknowns is much greater than the respective number of equations. uniqueness, however, is imposed by an additional requirement, which takes into consideration the previous network knowledge. among all possible solutions that satisfy (7), the one which causes a minimal degradation of the previous model knowledge is selected as the most appropriate. this is expressed by equation (4). it can be shown [54] that (4) takes the form of wkkw  tte )( 2 1 (9) where the elements of matrix k are expressed in terms of the previous network weights w and the data in the set s . thus, the problem results in the minimization of (9) subject to constraints of (7). minimize wkkw  tte )( 2 1 (10) subject to wac  (11) the error function defined by (10) is convex since it is of squared type, while the constraints of (11) are linear equalities. thus, the solution should lie on the hyper-surface defined by (11) and simultaneously minimize the error function given in (10). the gradient projection method is used in this paper to solve this problem. the gradient projection method starts from a feasible point and moves in a direction, which decreases e and simultaneously satisfies the constraints; a point is called feasible, if it satisfies all constraints. the weights are adapted as follows: )()()()1( nnnn hww  (12) where n is the iteration index and )(n is a scalar that determines the rate of convergence. using the methodology of σφάλμα! το αρχείο προέλευσης της αναφοράς δεν βρέθηκε. we can estimate vector )(nh as wqph  en)( (13) with a)a(aaip 1 tt and kpkq t (14) using e computed from (13). the computational complexity required to independently update each network weight is proportional to the number of network weights. f. computational complexity the computational complexity of the adaptation algorithm, in contradiction to the generally long training periods of the initial model parameters, is very small. in particular, the adaptation process is separated in two phases; the initialization phase where matrix q, which projects the negative gradient of function e onto the surface defined by the constraints of (11), is estimated, and the iteration phase where the weight increments w are updated. the iteration phase involves a simple multiplication of matrix q, of size ww nn  , by vector w , of size 1wn , where wn denotes the number of model parameters. for a typical value of wn equal to 500, the product )(nwq  in (13) requires few msec to be executed (~10 ms on a core i7 pc). the number of iterations n that the gradient projection method requires to derive the optimal solution is in general small (8-12 iterations are usually sufficient to obtain a weight increment close to the optimal one). thus, the computational cost of the iteration phase is about half a sec. in the initialization phase, matrix q is estimated as a product of matrix p and matrices kk t . the main computational load of p is the estimation of the inverse matrix 1)(  taa . however, the size of taa  is equal to the number of constraints, which is usually very small since it refers to the number of representative data of the current environment. consequently, the computational complexity for matrix 1)(  taa is significantly low (in the order of few msec). finally, computation of kkp  t requires about few seconds for a typical network size of 500 weights. thus, the total cost of retraining is small (of order of few seconds), allowing the efficient use of the proposed scheme to real-life interactive multimedia systems. after the classification, results of the process can be stored in xml format as seen in figure 4σφάλμα! το αρχείο προέλευσης της αναφοράς δεν βρέθηκε.. for the evaluation of the classification we used ten-fold cross validation. available data are divided into ten non-overlapping sets of roughly equal size, and nine of them are used for training, one for validation. the classification accuracy of the bpn ranges from ~47% to 98,4%. lowest success rates where noted in the expressions of anger and fear, where facial expressions are of similar geometric attributes, while sadness, happiness and surprises were met with the highest success rates. fig. 4. detection report v. conclusion the implementation of the proposed methodology was specifically designed to be flexible and scalable so as to fit into telemedicine based aal systems. providing a ready xsd engineering, technology & applied science research vol. 6, no. 4, 2016, 1035-1044 1042 www.etasr.com xefteris et al.: behavioral biometrics in assisted living: a methodology for emotion recognition schema, the results of the methodology can be easily integrated into a reconfigurable rule based risk assessment module, as part of a telemedicine system [30]. the results from this methodology are promising and useful, especially in the aforementioned context, and can be used to evaluate –and even predictthe overall health status of subjects suffering from neurodegenerative diseases. depressive symptoms are widely present in people with the onset of mci and can even further aid at the deterioration of their mental and cognitive status [5558]. it is thus crucial for the attending clinician to be able to monitor not only the physical but also the psychological status of subjects. the proposed algorithm, although having some shortcomings, such as lack of real-time properties and strong illumination sensitivity, is a first step towards the full emotional status estimation and prediction of adverse events in the framework of an internet-based aal system for people with mci or other neurodegenerative disease. these disadvantages though, are not deemed deteriorating for the overall efficacy of the methodology: the methodology is able to grab image frames from a web-camera at regular intervals (several times a minute), which can be adjusted as deemed necessary and provide the relevant results to a rule-based implementation of risk detection [30]. moreover, since this methodology is aimed at home based aal systems, it is considered a given that subjects are lit by a home’s natural lighting which in everyday life activities are not usually extreme so they don’t induce significant errors in the process. finally, the proposed methodology is ready to be incorporated into a metadata-aware biometric architecture as the one proposed in [44] specifically targeted in ambient assisted living systems. future improved implementations of the methodology aim to encompass real time capabilities, especially based on constrained local models [59-60] and deep learning networks for better hierarchical multimodal classification of the subject’s emotional status [61-63]. acknowledgment the authors would like to acknowledge the aladdin project, funded under the first call of aal joint programme, aal-2008-1, as well as the people of the distributed knowledge and media systems lab of the electrical and computer engineering school of the national technical university of athens. finally, this work would not have been possible without the work of cohn-kanade and their database of facial expressions, the images of which provided the basis for our research. references [1] eurostat, “population structure and ageing,” 2015, available at: http://ec.europa.eu/eurostat/statistics-explained/index.php/population_ structure_and_ageing [2] a. l. busse, g. gil, j. m. santarém, w. j. filho, “physical activity and cognition in the elderly: a review”, dement. neuropsychol., vol. 3, no. 3, pp. 204–208, 2009 [3] a. di carlo, m. baldereschi, l. amaducci, s. maggi, f. grigoletto, g. scarlato, d. inzitari, “cognitive impairment without dementia in older people: prevalence, vascular risk factors, 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vipulrajput16986@gmail.com received: 11 july 2022 | revised: 27 july 2022 | accepted: 1 august 2022 abstract-an artificial neural network (ann) is one of the most powerful tools to predict the behavior of a system with unforeseen data. the feedforward neural network is the simplest, yet most efficient topology that is widely used in computer industries. training of feedforward anns is an integral part of an ann-based system. typically an ann system has inherent non-linearity with multiple parameters like weights and biases that must be optimized simultaneously. to solve such a complex optimization problem, this paper proposes the levy enhanced cross entropy (le-ce) method. it is a population-based metaheuristic method. in each iteration, this method produces a "distribution" of prospective solutions and updates it by updating the parameters of the distribution to obtain the optimal solutions, unlike traditional meta-heuristic methods. as a result, it reduces the chances of getting trapped into local minima, which is the typical drawback of any ai method. to further improve the global exploration capability of the ce method, it is subjected to the levy flight which consists of a large step length during intermediate iterations. the performance of the le-ce method is compared with state-of-the-art optimization methods. the result shows the superiority of le-ce. the statistical anova test confirms that the proposed le-ce is statistically superior to other algorithms. keywords-artificial neural networks; cross entropy method; feedforward neural networks; levy step; training i. introduction the artificial neural network (ann) [1] is the one of the most popular artificial intelligence methods. it is inspired from the communication and computation abilities of the human brain and it mimics the learning techniques of human brain to find out relationships between the input and the output (target) variables of a test system. the human brain consists of millions of neurons which are interconnected in a complex network which takes input signal to perform voice recognition, image classifications, etc. at remarkable speed and accuracy. similarly, an ann may consist of many neurons which are subjected to input signals through the connection links. every connection link has an associated weight, which is multiplied with the signal. weights are the control variables which are used to solve the optimization problem. weights and biases are updated in every iteration to finally obtain their optimal values which will minimize the mean square error (mse) function. this procedure is known as the training (learning) of an ann. a. related work feedforward neural networks (fnns) with two layers are a widely used ann topology [2]. it has been proved that twolayer fnns can approximate any nonlinear or linear function with a good accuracy [3]. training is an integral part of fnns. various optimization methods have been suggested in the literature to train fnn. back propagation (bp) is a popular gradient-based classical optimization method to train fnns. but it is susceptible to slow convergence [4] and may get trapped into local minima [5]. newton’s method [6] is another classical method which has quadratic convergence that largely depends upon the choice of initial starting point (guess). a wrong initial guess will lead to a local optima of the problem under consideration. the last two decades, population-based meta-heuristic methods that solve the fnn training problem effectively have emerged. authors in [7] proposed the use of anns to detect the vibration of the rotor shaft of a gas turbine. authors in [8] suggested the use of genetic algorithm (ga) to precisely recognize sign gesture using feature extraction, but mutation strategy makes ga very time consuming and it is preferred for binary solution sets. also, it is vulnerable to premature convergence. authors in [9] proposed a new approach to address the optimal design of a fnn using selfadaptive penalty functions. authors in [10] proposed a particle swarm optimization (pso)-based neuro-fuzzy model to corresponding author: kartik pandya engineering, technology & applied science research vol. 12, no. 5, 2022, 9196-9202 9197 www.etasr.com pandya et al.: levy enhanced cross entropy-based optimized training of feedforward neural networks enhance dynamic voltage stability of a wind connected grid. authors in [11] proposed a pso-powered back-propagation neural network load-shedding strategy in the post-fault condition in a microgrid. another ai method is gravitational search algorithm (gsa) [12], which has been inspired from the law of gravity and mass interactions. even though it is a simple method, the unbalance between the application of gravitational law and mass interactions may create premature convergence. differential evolutionary (de) method [13] is another powerful method which uses mutation, crossover, and selection operators on various vectors to get optimal solutions, but the selection of crossover rate greatly affects its convergence. pso [14] is one of the most popular metaheuristic methods, as it is easily implementable and it has less parameters to be tuned. b. aims and objectives the related work (literature survey) reveals that many classical optimization methods suffer from premature convergence, whereas artificial intelligence methods are population-based with generated randomly initial solutions, and as a result, in each simulation run it gives different optimal solutions. so, the aim and objective of this research is to suggest a proper solution methodology which trains an ann more effectively and with better accuracy. this paper proposes the levy enhanced cross entropy (le-ce) optimization method, which is an extension of the cross entropy (ce) method. the contributions of this paper are summarized below. c. research outline • the le-ce method is proposed for the optimization of the weights and biases of the ann with the aim to minimize the mse function. • the incorporation of levy flight increases the global exploration capability of the ce method, which improves the quality of the solution. • the le-ce method has fewer parameters to be tuned, so it is a fast method. • the practical iris classification system is used to check the effectiveness of the le-ce method. • the performance of the le-ce method is compared with the wcci 2018 award winning evdepso [15] and gecco 2019 award winning hl_ps_vnso [16] computational intelligence methods. • the le-ce method outperformed the compared methods in terms of optimal solutions. • anova statistical test and tukey’s hsd test also proved that the proposed method is statistically different from the other compared methods. ii. levy enhanced cross entropy method for training fnns and encoding strategy ce method was proposed by rubinstein [17]. it is a population-based meta-heuristic optimization method similar to the differential evolutionary method. however, unlike traditional meta-heuristic methods which directly update prospective solutions (particles) to obtain sub-optimal solutions, this method produces a distribution of prospective solutions and updates it by updating the parameters like mean and standard deviation of each dimension to obtain sub-optimal solutions. as a result, it decreases the probability of getting stuck into local minima. it has a very few parameters to be tuned and it can be easily executed. the basics of le-ce method are explained below. the population of particles is randomly generated and they obey the probability distribution function (pdf) f (.;φ), where φ is the vector of parameters which are to be optimized. generally, f(.;φ) is the gaussian distribution parameterized by its mean m and variance σ 2 , i.e. ( )2,m σφ = . secondly, a threshold value (χ) of the fitness function is selected and only those particles whose fitness values are less than the set threshold value, i.e. f(x)<χ are considered in the subsequent iterations. such particles are known as elite particles μe. then, the new parameterized distribution function ( ).; nf φ with elite particles is updated in such a way that it coincides the target distribution function ( ).;f φ ∗ by minimizing the kullbackleibler (kl) divergence. this procedure finishes one iteration. in the subsequent iterations, a family of distribution functions ( )( ) ( )1 *.; ... .;f fφ φ are produced in accordance with χ(1)....χ(*) to reach the sub-optimal distribution function f(.;φ * ). the following section shows the step-by-step implementation of le-ce. 1) step 1: initialization of mean and standard deviation for each dimension assume iteration iter=0, total no. of iterations 500 max iter = , no. of particles n, dimension (control variables) of the problem d, elite particles μe (20% of n), smoothing parameters s α and s β , ( )iter d e m ∈r is the mean value of the search distribution for each dimension at iteration iter, ( )iterσ +∈r is the standard deviation at iteration iter. min x and max x are the minimum and maximum limits of the d th dimension particle. mean and standard deviation of population are initialized as: ( )(0) 0.5 *e min maxm x + x= (1) ( ) ( ) 0 0.25 * max min x xσ = (2) 2) step 2: generate the population of particles the generation of the population of particles from the sampling distribution ( ) ( )( )2normal ,iter iterem σ occurs as: � � (������) = �� (����) + (����)randn()  for � = 1, . . . . . ,� (3) where n is the population size, ( 1)iter d i x + ∈r is the i th particle obtained at iteration ( )1iter + , ( )iter dem ∈r is the mean value of the search distribution for each dimension at iteration iter, ( )gσ +∈r is step-size (standard deviation) at iteration iter, engineering, technology & applied science research vol. 12, no. 5, 2022, 9196-9202 9198 www.etasr.com pandya et al.: levy enhanced cross entropy-based optimized training of feedforward neural networks randn() is a normally distributed random variable with parameters normal(0,1). 3) step 3: fitness function evaluations the fitness values of the whole population are determined as follows: the fnn consists of i n input nodes, i h hidden nodes, and t o output nodes. in each iteration of learning, the output of each hidden nodes is calculated using (4): ( ) 1 1 / 1 e x p * , 1, 2 ..... in k jk j k j i f y w x k h θ =     = + − −          =  (4) where 1 in k jk j k j y w x θ = = − , jkw is the connection weight from the j th node from the input layer to the k th node in the hidden layer, θk is the bias of the k th hidden node, and xj is the j th input. the final output is calculated following the output of hidden nodes as given by (5): ( ) , 1 * 1, 2,...., ih t lk k l t j o w f y l oθ = = − = (5) where lk w is the connection weight between the kth hidden node to the l th output node and θl is the bias of the l th output node. eventually, the mean square error (el) is calculated from: ( ) 1 ih l l l tj j j e o d = = − (6) 1 t l l e e t= =  (7) where t represents the training samples and l j d is the desired output of the j th input when the l th training sample is considered. so, the fitness function of the j th training sample can be defined as follows: fitness(xj) = e(xj) (8) 4) step 4: ranking of fitness functions sort (rank) all fitness function values in ascending order as given in (9): ( ) ( )1 2 ... ( )f x f x f n< < < (9) where ( ) j f x is the fitness of the th j particle and 1 x is a global best ( )bestg particle having the best (minimum) fitness among all particles. consider the top best 20%-30% of the particles as elite particles. 5) step 5: updating mean and standard deviation of the elite particles the mean ( )( )1itertm µ + of the selected elite particles is found by: ( ) ( )1 1 : 1 1 eiter iter t j n je m x µ µ µ + + = =  (10) where ( )1 : iter j n x + is the th j best particle among the whole population at iter+1iteration. the index j:n denotes the index of the th j rank particle. standard deviation ( )( )1itert µσ + (step-length) of elite particles is found by (11): ( ) ( ) ( )( ) 2 1 1 1 : 1 1 1 e iter iter iter t j n e je x m µ µ σ µ + + + = = − −  (11) 6) step 6: apply smoothing of mean and standard deviation of the whole population as elite particles are in the vicinity of optimal solutions, more smoothing (weightage) is applied to their mean value as compared to mean of whole population as per (12): ( ) ( ) ( ) ( ) 1 1 1 1 iter iter iter e t e m m m µ α α + + + = + − (12) where 0.9, 0.1α β= = are the smoothing parameters. similarly, the standard deviation of the elite particles should be updated to a very small extent as they lie near the optimal solutions. so, less smoothing is applied to them as compared to the standard deviation of all particles which requires more exploration of the search space and thus more smoothing as given in (13): ( ) ( ) ( ) ( ) 1 1 1 1 iter iter iter t tuµ σ βσ β σ + + + = + − (13) 7) step 7: apply levy flight for global exploration levy flight [18-19] is a random walk whose length is derived from the levy distribution as described in (14), where u and v are obtained from the normal distribution. many species (e.g. swordfish and silky sharks) use levy flights to search for food. the function of levy step is to efficiently explore the search space by taking a large step size during the intermediate iterations to obtain the global optimum solution. 1 / l evy-step u v β = (14) where: u = rand(0,1)*sigma (15) v = rand(0,1) (16) 1 / ( 3 ) (1 ) * sin( * ) s igm a [(1 ) / 2 ] * * 2 β β β β β β −  γ + π =   γ +  (17) where (=3/2) is a levy coefficient and: β engineering, technology & applied science research vol. 12, no. 5, 2022, 9196-9202 9199 www.etasr.com pandya et al.: levy enhanced cross entropy-based optimized training of feedforward neural networks ( ) ( )1 1iter iter e e m m levy step + + = + − (18) 8) step 8: increment of iteration count set : 1iter iter= + and go to step 2 until the maximum number of iterations is reached. the detail flowchart of the le-ce method to train fnns is shown in figure 1. fig. 1. flowchart of the le-ce method for training fnns. iii. ann encoding strategy figure 2 shows the typical structure of an ann. it consists of 2 input nodes, 3 hidden nodes, and 1 output node. for the training of ann, the most popular matrix encoding method is used in this paper as follows: (:, ) , , 1, 1 2 2 t particle i w b w b  =    (20) 13 23 361 , , , 1 14 24 1 2 2 46 2 4 15 25 3 56 w w w t w w w b w w b w w w θ θ θ θ                = = = =                 (21) where w1 is the weight matrix of the hidden layer, b1 is the bias matrix of the hidden layer, w2 is the weight matrix of the output layer, w2 t is the transpose of the w2 matrix, and b2 is the bias matrix of the hidden layer. fig. 2. ann typical structure. iv. simulation results and discussion the performance of the proposed le-ce algorithm is not tested on a small system because, as per the no-free lunch theorem [20], the average performance of all the optimization methods remains the same for small test systems which consist of a small number of control variables. so, in order to check the effectiveness of the proposed le-ce algorithm, it is tested on the practical iris classification [21] problem and its output results, convergence, and statistical results are compared with wcci 2018 international award winning evdepso [15] and gecco 2019 international award winning hl_ps_vnso [16] computational intelligence methods. both these methods had secured 2 nd ranks in the aforementioned conference competitions. evdepso (enhanced velocity differential evolution particle swarm optimization), is a meta-heuristic iterative method which has been inspired from the behavior of bird flocking and fish schooling. mathematically, each bird represents the prospective solution of the optimization problem and its position is adjusted depending upon the position of the best bird and their past best positions in every iteration to obtain optimal solutions. the process is continued until no significant improvement in the optimal solutions is observed. the detail theory of evdepso is available in [15]. hl_ps_vnso (hybrid levy particle swarm variable neighbourhood search optimization) algorithm is a hybridization of pso and variable neighborhood search algorithm. its key elements are perception, cooperation, and the levy step. it consists of a perception term for the local exploitation of search space in which a particle follows its personal best position, a cooperation term in which the particle follows the global best particle with mutated weights, and the levy step to globally explore the search space. its detail theory is given in [16]. a. practical iris classification problem the iris classification problem was used in [21]. the iris dataset contains 4 features (length and width of sepals and petals) of 3 species of iris (iris setosa, iris virginica, and iris versicolor) as shown in [22, 23]. the data contains 150 samples. these measures were used initially to create a linear model to classify the species in machine learning. different hidden nodes such as h=4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 were set to test the performance of the algorithms. the simulation results have been performed on matlab 2017a engineering, technology & applied science research vol. 12, no. 5, 2022, 9196-9202 9200 www.etasr.com pandya et al.: levy enhanced cross entropy-based optimized training of feedforward neural networks environment, intel core i5 with 16 gb ram. all tested methods find the optimal combinations of the weights and biases which results into minimum error of the fnn. a total of 20 trials were executed as the le-ce is a meta-heuristic method and as a result in every simulation run it yields different optimal solutions. finally, the mean recognition rate was obtained from the results of the 20 trials. table i shows that the proposed le-ce outperforms the other methods in recognizing the output correctly with different hidden nodes in all cases, due to fact that le-ce method’s mean and standard deviation updating using smoothing parameters yield better solutions as the elite particles are in the vicinity of the optimal solution (as per (12) and (13)). also, ce is powered by levy flight, which has the ability to take larger step size during optimization. as a result, the search space is being explored more efficiently. so, le-ce yields better solutions as compared to original ce method and other tested algorithms. table i. mean recognition rate with different hidden nodes hidden nodes (h) le-ce (%) ce (%) evdepso (%) hl_ps_vnso (%) 4 99.92 98.32 90.12 89.14 5 100 97.25 91.18 87.17 6 99.45 95.36 92.78 89.35 7 100 96.65 90.07 90.14 8 99.32 93.45 91.95 87.88 9 100 92.32 90.45 83.41 10 99.12 93.85 88.35 87.12 11 99.85 92.65 91.98 83.45 12 100 96.36 89.45 76.3 13 99.85 94.36 90.42 86.32 14 100 93.95 88.01 83.25 15 99.36 94.15 91.05 87.05 it is cleared from table ii that the proposed le-ce outperforms the other methods in all 12 cases for average mse, std. dev mse, and best mse. hidden nodes are increased from 4 to 15 in each case. as a result, the complexity of the ann increases as more mathematical equations have to be solved by the algorithm. also, the convergence characteristics of le-ce for different hidden nodes are better than the compared algorithms' as shown in figures 3-5, because, unlike other meta-heuristic methods, the le-ce method is a tuning free algorithm and its adaptive mean and standard deviation updating strategy makes it quite suitable to obtain optimal solutions. traditional ce has not a levy flight step, so its performance remains inferior to le-ce. evdepso's and hlpsvnso’s performance is worse that le-ce's because both these methods have a large number of parameters to be tuned which affects convergence, whereas le-ce has a very small number of parameters to be tuned and it searches solutions by updating the mean and standard deviation of elite particles. as a result, it can achieve better solutions as compared to the other tested algorithms. figures 3-5 clearly show that the le-ce has better convergence characteristics as compared to the other methods for the set termination criteria. the other methods have many step length updating operators, which increase the computational burden on the algorithm. table ii. average, standard deviation, and best mse in 20 independent runs with different hidden nodes hidden nodes (h) algorithm average mse std dev mse best mse 4 le-ce 1.9021e—02 1.1905e—03 1.3538e—02 ce 2.1926e—02 2.0907e—03 1.4538e—02 evdepso 2.7048e—02 2.0825e—02 7.0291e—03 hl_ps_vn so 4.1936e—02 1.0413e—02 4.0013e—02 5 le-ce 1.8127e—02 1.6252e—03 1.3085e—02 ce 1.9457e—02 1.7267e—03 1.6525e—02 evdepso 2.4756e—02 1.7638e—02 1.3629e—02 hl_ps_vn so 4.4355e—02 1.1071e—02 4.0770e—02 6 le-ce 1.3593e—02 2.2182e—03 1.2013e—02 ce 1.6932e—02 2.0082e—03 1.5113e—02 evdepso 1.8453e—02 7.2653e—03 1.6253e—02 hl_ps_vn so 1.0441e—01 1.0374e—01 4.4510e—02 7 le-ce 1.3682e—02 1.2446e—03 1.2128e—02 ce 2.6122e—02 1.0746e—03 2.4358e—02 evdepso 1.7691e—02 4.0023e—03 1.4523e—02 hl_ps_vn so 5.5226e—02 6.6222e—03 5.0238e—02 8 le-ce 1.7042e—02 3.2045e—03 1.2511e—02 ce 1.8142e—02 6.2545e—03 1.3011e—02 evdepso 2.1454e—02 6.0198e—03 2.0378e—02 hl_ps_vn so 4.7541e—02 7.2863e—03 3.8607e—02 9 le-ce 1.3294e—02 3.2993e—03 1.0070e—02 ce 1.6302e—02 6.5093e—03 1.0670e—02 evdepso 5.0615e—02 1.2549e—02 5.0301e—02 hl_ps_vn so 3.8314e—02 1.3757e—02 3.0293e—02 10 le-ce 1.2521e—02 1.0021e—03 1.1021e—02 ce 1.8221e—02 1.1821e—03 1.4321e—02 evdepso 3.9265e—02 1.3342e—02 3.0427e—02 hl_ps_vn so 4.4245e—02 1.3204e—02 4.3230e—02 11 le-ce 1.2646e—02 1.8009e—03 1.0840e—02 ce 1.5246e—02 2.1709e—03 1.0880e—02 evdepso 1.4203e—02 1.2120e—02 1.0393e—03 hl_ps_vn so 4.1536e—02 6.7323e—03 3.7538e—02 12 le-ce 1.2006e—02 2.2091e—03 1.0049e—02 ce 1.6806e—02 2.9391e—03 1.3849e—02 evdepso 1.7889e—02 6.9515e—03 1.3409e—02 hl_ps_vn so 1.2098e—01 1.3702e—01 1.0316e—02 13 le-ce 1.1753e—02 1.3090e—03 1.0021e—02 ce 2.3453e—02 1.8740e—03 2.2422e—02 evdepso 1.8013e—02 5.0128e—03 1.5113e—02 hl_ps_vn so 3.1724e—01 1.3744e—01 3.0250e—02 14 le-ce 1.1270e—02 1.0086e—03 1.0592e—02 ce 2.6250e—02 1.0186e—03 2.3592e—02 evdepso 1.5241e—02 1.0171e—03 1.1297e—02 hl_ps_vn so 4.3257e—02 1.0214e—02 4.1200e—02 15 le-ce 1.2189e—02 1.3530e—03 1.1509e—02 ce 3.3589e—02 2.7530e—03 3.1725e—02 evdepso 2.145e—02 2.5846e—03 2.1153e—02 hl_ps_vn so 5.3539e—02 6.2441e—02 5.2546e—02 engineering, technology & applied science research vol. 12, no. 5, 2022, 9196-9202 9201 www.etasr.com pandya et al.: levy enhanced cross entropy-based optimized training of feedforward neural networks fig. 3. convergence curve with 5 hidden nodes. fig. 4. convergence curve with 11 hidden nodes. fig. 5. convergence curve with 15 hidden nodes. v. statistical analysis a. one-way anova statistical test the anova statistical test [24] is used to verify whether the mse of all algorithms evaluated for each simulation run shows any significant difference. in this test, the degree of significance is set to 0.05 to check the statistical difference between the tested algorithms. during the comparison, if it is found that the p-value is less than 0.05, then it inferred that all tested algorithms are substantially different from one another. from table iii, it is seen that the f-ratio value is 6.75541. the p-value is 0.000758. so, the result is significant at p<0.05. this implies that at least one of the means of the groups is significantly different from the others. however, it is not known which group(s) contribute to this difference, hence tukey’s honestly significant difference (hsd) test was carried out. b. tukey's hones honestly significant difference test to further check the statistical difference between two algorithms, the pairwise comparison test entitled tukey's hsd test [25] was carried out. in this test, the first step is to find the critical value (qcrit) from the studentized range distribution table [26] based on the a=4 treatments (algorithms) and df=44 degrees of freedom. the critical value obtained from the studentized range distribution table is 3.777. then, the qi,j is calculated as per (22) for all the pairwise comparisons with the proposed algorithm. the result values are given in table iv. , ( ) i j i j runs y y q ms n − = (22) where i, j = 1,..a, i ≠ j. is the difference between the optimal fitness values of the compared pair of algorithms. table iii. results of the one-way anova statistical test variation sum of square due to source (ss) df mean sum of square due to source (ms) f ratio value p-value f crit between algorithms 0.03278 3 0.0109 6.7554 0.00075 2.816 within algorithms 0.07117 44 0.0016 total 0.10395 47 table iv. tukey hsd test results pairwise comparisons q (statistic) le-ce and ce 0.61 le-ce and evdepso 0.85 le-ce and hl_ps_vnso 5.64 table iv reveals that for all pairwise treatments, the proposed algorithm is substantially statistically different from the other algorithms. the algorithm has been developed in matlab environment and the source codes can be provided to the enthusiastic learner by the main author upon request. vi. conlcusion the levy enhanced cross entropy method to train feedforward neural network has been proposed in this paper. the le-ce method has less parameters to be tuned and its adaptive updating for mean and standard deviation of the solutions make it quite powerful in terms of local exploitation and global exploration of the solution space. to further improve its global search exploration, the ce method is powered by the levy flight. the simulation on the practical iris test system reveals that the proposed le-ce method outperforms the contemporary optimization methods in terms of solution quality, iterations, average mse, standard deviation mse, and best mse. the proposed method is confirmed to be statistically different from the other compared optimization methods. the proposed method can be used in highly complex nonlinear ann systems. in the future, the same algorithm will be applied to train more realistic training sets of neural networks with hundreds of variables and constraints. engineering, technology & applied science research vol. 12, no. 5, 2022, 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[26] h. l. harter, "critical values for duncan’s new multiple range test," biometrics, vol. 16, no. 4, pp. 671–685, 1960, https://doi.org/10.2307/ 2527770. microsoft word etasr_v12_n5_pp9400-9403 engineering, technology & applied science research vol. 12, no. 5, 2022, 9400-9403 9400 www.etasr.com bhangwar et al.: analysis of particulate matter emissions and performance of the compression … analysis of particulate matter emissions and performance of the compression ignition engine using biodiesel blended fuel sajjad bhangwar mechanical engineering department, quaid-e-awam university of engineering science and technology, nawabshah pakistan sajjadbhangwar@quest.edu.pk sher muhammad ghoto mechanical engineering department, quaid-e-awam university of engineering science and technology, nawabshah pakistan ghotosher@yahoo.com aijaz abbasi mechanical engineering department, quaid-e-awam university of engineering science and technology, nawabshah pakistan aijaz-abbasi@quest.edu.pk muhammad kashif abbasi mechanical engineering department, quaid-e-awam university of engineering science and technology, nawabshah pakistan muhammadkashif@quest.edu.pk arif ali rind mechanical engineering department, quaid-e-awam university of engineering science and technology, nawabshah pakistan engineerarif344@yahoo.com muhammad ramzan luhur mechanical engineering department, quaid-e-awam university of engineering science and technology, nawabshah pakistan luhur@quest.edu.pk zohaib khan faculty of mechanical and manufacturing engineering, universiti tun hussein onn malaysia, malaysia and department of mechanical engineering, quest, pakistan aghazohaib03@gmail.com umair ahmed rajput department of mechanical engineering, quaid-e-awam university of engineering, science and technology, nawabshah, pakistan engr.umair@quest.edu.pk sanaullah mastoi department of mathematics, quaid-eawam university of engineering science and technology, campus larkana, sindh, pakistan sanaullah.mastoi@quest.edu.pk received: 19 july 2022 | revised: 16 august 2022 | accepted: 24 august 2022 abstract-as the world becomes more urbanized, the market for petroleum products increases. the supply of crude oil-based products such as diesel, gasoline, and natural gas is limited. furthermore, natural resources are finite and their reservoirs are located in certain parts of the globe. countries with low to no fossil fuel resources are experiencing a scarcity of petroleum products, necessitating the exploration of alternative energy resources. in this research, tests regarding the exhaust particulate emission, sound pressure level, and performance have been carried out using samples from diesel and biodiesel (waste cooking oil) blended fuel. two fuel samples have been used, b25 (biodiesel 25% and 75% diesel) and 100% diesel as a baseline in a ci engine at constant rpm of 1350 and variable loads of 0.0 to 1.6 at an interval of 0.2kg-m. the results show that particulate emissions are reduced by about 7.29% when using biodiesel blended fuel, whereas brake-specific fuel consumption of biodiesel blended fuel has decreased as brake power increased, and brake thermal efficiency increased as brake power increased. the sound pressure level was measured from different locations of the engine (back, front, left) and for varying load. the results show that b25 produces less noise than d100 in each case. keywords-biodiesel (waste cooking oil); pollution; diesel engine; particulate emissions; noise i. introduction greenhouse gas (ghg) emissions contribute to global warming and harm the environment [1, 2]. a higher quantity of pollutant emissions come as a result of fossil fuels [3]. the compression ignition (ci) engine was developed soon after the spark ignition (si) engine and has become quite popular. to reduce environmental pollutant emissions, bio-ethanol has been used in the ci engine, fulfilling the demand of diesel fuel, increasing job opportunities, and conserving natural energy resources [4]. biodiesel blend nbd25 is a mixture of neem oil methyl ester (25% vol.) and mineral diesel (75% vol.) and can be used as fuel. nickel oxide nanoparticles were dosed in nbd25 blend at four levels in [5]. jbd100 biodiesel produces a lower level of carbon monoxide (co), hydrocarbons (hc), and smoke emissions with notable increase in nox and carbon dioxide (co2) emissions [6]. methane gas can be produced from wastewater, animal waste, and city garbage landfills. this gas can be produced by the gasification process of wood. corresponding author: sajjad bhangwar engineering, technology & applied science research vol. 12, no. 5, 2022, 9400-9403 9401 www.etasr.com bhangwar et al.: analysis of particulate matter emissions and performance of the compression … biofuels [7] are generally considered environment-friendly because they emit fewer ghg emissions than conventional fuels. fatty acid methyl ester (fame) is also referred to as pure biodiesel (b100). the lower concentration of biodiesel is known as "biodiesel blend", with b25 representing a mix of 25% of biodiesel in diesel fuel [8, 9]. biodiesel is the most emerging and green fuel due to its similar properties to the ordinary diesel fuel. it is capable to blend in any proportion with diesel fuel [10, 11]. it is also defined by the time it takes to pass out the liquid from some specified size orifice so it is known as thick oil [12]. the physicochemical properties of gasoline, can affect engine the efficiency and emission characteristics. biodiesel does not have the same property values with diesel fuel, so researchers blend biodiesels in various proportional ratios to diesel fuel [13, 14]. the use of biodiesel increases agricultural value and income, allowing for greater freedom of energy use and reduces the need for imported petroleum goods [15, 16]. examples of greenhouse gasses are methane (ch4), carbon dioxide (co2), and nitrous oxide (n2o). these gases are responsible for global warming [17]. due to the increased smoke associated with high fuel-air ratios, the brake specific fuel consumption of the ci engine increases at high loads, the mechanical efficiency decreases at lower loads, and the brake specific fuel consumption (bsfc) increases [18, 19] due to its higher oxygen contents, higher cetane number and proper spray timing. the emission of co2 (2.3%), co (22%), nox (0.97%), and smoke (6.54%) decreased comparatively at 50% load in [20]. a few properties of biodiesel fuel significantly affect brake power, e.g. kinematic viscosity, calorific value, and lubricity [21]. an increase in the temperature of the combustion chamber improves thermal efficiency with a limited quantity of methanol and ethanol. it has been observed that vegetable oil blends give lower thermal efficiency than diesel fuel [21, 22]. meanwhile, smoke opacity, brake specific particulate emissions, and particle geometric mean diameter drop as the quantity of soluble organic components increases, and biodiesel blends showed more variance [23]. ii. research methodology in this study, two fuel samples have been tested in a ci engine and parameters like engine performance, exhaust gas emissions, and noise emissions were analyzed. initially, fuel properties have been tested on astm standards. engine performance, exhaust gases, and sound pressure level tests have been analyzed on variable loading conditions and constant speed. the used engine specifications are shown in table i. a. engine exhaust particulate matter emission the results of pm (particulate matter) emissions from a diesel engine have been taken while running diesel fuel and biodiesel (waste cooking oil) blended fuel. the engine emissions depend on speed, load, fuel properties and injection timings. the load on the engine can be controlled by using a dynamometer coupled with the engine shaft directly. the instrumentations installed in the test bed were manually controlled. in this work, 3 particle sizes (pm 1.0, pm 2.5, and pm 7.0) were considered. table i. used engine specifications stroke 80mm output (12hr rating) 4.4kw/2600r/min displacement 0.353l compression ratio 21-23 mean effective pressure 576kpa piston mean speed 6.93m/s specific fuel consumption 278.8g/kwh specific oil consumption 4.08g/kwh cooling water 1360g/kwh injection pressure 14.2+0.5mpa valves clearance inlet valve 0.15-0.25mm maximum engine power 7.7kw maximum engine torque 80nm b. engine performance analysis during the experiments, two fuel tanks were connected to the diesel engine test bed. fuel was delivered to the engine through a single pipeline. both fuel tanks were linked by a common line, and flow could be regulated by two separate valves. based on fuel selection, one tank was filled with diesel fuel (d100) and the other with biodiesel blended fuel. engine torque, brake strength, brake thermal efficiency, and brake specific fuel consumption were measured in the engine output. variable loads were applied to calculate separate rpm on each load. c. engine noise emissions the noise level (sound pressure level) of the ci engine was calculated when using diesel and biodiesel blended fuels at different loading conditions and constant speed. iii. results and discussion a. particulate matter emissions a ci engine is known as being high fuel-efficient and robust, but unfortunately, it is responsible for high pm emissions. biodiesel (waste cooking oil) on the other hand, generates less pm emissions. however, there are different reasons of pm production from a diesel engine. incomplete combustion of diesel fuel due to temperature variation of fuel is one of these reasons. it is observed that, overall, diesel fuel is mainly responsible for pm generation in pm 1.0, which is a higher particulate matter on idling condition of diesel fuel d100. biodiesel blend b25 produces less pm emissions as compared to diesel fuel. fig. 1. comparative results of exhaust pm1.0 emissions. engineering, technology & applied science research vol. 12, no. 5, 2022, 9400-9403 9402 www.etasr.com bhangwar et al.: analysis of particulate matter emissions and performance of the compression … fig. 2. comparative results of exhaust pm 2.5 emissions. fig. 3. comparative results of exhaust pm 7.0 emissions. b. brake thermal efficiency the thermal efficiency of the brake was studied next. as the calorific value of the biodiesel decreased, the fuel consumption increased for the same power output as shown in figure 4. fig. 4. comparative results of brake thermal efficiency. fig. 5. comparative results of brake specific fuel consumption. in comparison to b25, the thermal brake performance of d100 has been increasing with increased load of the engine from 0.2kw to 1.6kw as shown in figure 5. bsfc varies depending on engine load, rpm, and biodiesel blending ratio. it was discovered that brake b25 has higher bsfc than d100 because b25 has high oxygen content, which results in a lower heating value. the lower density and lower heating values of the fuels need higher mass of fuel for the same energy output from the engine. it was observed that density and calorific value have a high impact on the degree of un saturation. c. sound pressure level at a constant 1350 rpm, the sound pressure level results were calculated with variable brake loads such as 0.27212, 0.54424, 0.81636, 1.08848, 1.3606, 1.63272, 1.90484, and 2.17696 as shown in figure 6. in comparison to the back and left sides of the engine, the front side has a higher sound pressure level. the results show that when using d100 in the engine, the sound pressure level is higher than when using the biodiesel blend b25. as a result of the higher oxygen content in gasoline, the cetane number is a key parameter to understand when it comes to ignition delay. during compression ignition, the cetane number plays an important role, as the higher cetane number gives a shorter ignitions delay. b25 has a lower sound pressure because there is more oxygen available. (a) (b) (c) fig. 6. comparative results of sound pressure level at (a) the front side of the engine, (b) the left side of the engine, the back side of the engine. engineering, technology & applied science research vol. 12, no. 5, 2022, 9400-9403 9403 www.etasr.com bhangwar et al.: analysis of particulate matter emissions and performance of the compression … iv. conclusion in this research, two fuel samples have been used, b25 (biodiesel 25% and diesel 75%) and d100 (100% diesel), which was the baseline in the ci engine, at constant 1350 rpm with variable loads from 0.0 to 1.6 at an interval of 0.2kg∙m. exhaust particulate emissions, sound pressure level, and performance tests have been carried out. the results of the current study are: • d100 has lower brake specific fuel consumption than the b25 and higher bte. • the results show that the use of biodiesel (waste cooking oil) causes a decrease in sound pressure level. • the use of b25 reduces exhaust particulate emissions of the compression ignition engine by 7.29%. regarding future work, nanoparticles (aluminum oxide and silica oxide) can be added in biodiesel blends to analyze further their performance in the compression ignition engine. acknowledgment the authors are grateful to the mechanical engineering department, quaid-e-awam university of engineering science and technology nawabshah, pakistan, for their assistance in this research work. references [1] g. paul, a. datta, and b. k. mandal, "an experimental and numerical investigation of the performance, combustion and emission characteristics of a diesel engine fueled with jatropha biodiesel," energy procedia, vol. 54, pp. 455–467, jan. 2014, https://doi.org/ 10.1016/j.egypro.2014.07.288. 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abdelhamid.rabhi@u-picardie.fr fatma ben salem cem laboratory, national engineering school of sfax, tunisia fatma.bensalem@isgis.usf.tn received: 26 september 2022 | revised: 1 november 2022 | accepted: 2 november 2022 abstract predictable and unpredictable variations are two major causes of renewable energy-related intermittency. such a drawback could be overcome by applying new energy management strategies, particularly storage systems. this paper investigates the feasibility of introducing a photovoltaic management string, enabling the maintenance of continuous energy supply storage capacity. accordingly, the pv system is liable to perform at maximum efficiency following the implementation of an mppt-controlled dc/dc boost converter of the perturb and observe (p&o) type. most of the energy-management approaches target goals lie mainly in optimizing the energy resources’ operational and storage capacities. the current matlab/simulink-based simulation study achieved results that turned out to testify well to the advanced design’s high performance and efficiency in maintaining the load’s energy autonomy while increasing the battery’s life span. keywords-pv-battery; storage system; energy management strategy; p&o; matlab/simulink i. introduction given the increased global demand in energy supply, renewable energy development continues to undergo rapidly frequent changes. in effect, the depletion of fossil fuel reserves has enticed research and development programs to offset the deficit by turning to alternative sources of energy [1-2]. petroleum-based resources, such as natural gas, coal, and oil, have for long been the unique available energy sources. still, their uneven and random distribution across territories, along with their limited reserves and supply have spurred international conflict and fierce competitions. also noteworthy, is the fact that the fossil-based conventional sources are usually available for only a few decades, while nuclear power generating plants often produce dangerous pollutants, including radioactive waste. to meet the world’s growing energy demands, it is therefore necessary to find adequate solutions and diversify the sources of energy. the current research is focused on retrieving and developing new environmentally friendly, renewable, and inexhaustible power sources. still, energy extraction techniques require further research and development strategies to improve efficiency and reliability. the renewable energy sources fall into three categories: engineering, technology & applied science research vol. 13, no. 1, 2023, 9849-9854 9850 www.etasr.com njeh et al.: energy management of an autonomous photovoltaic system under climatic variations  mechanical energy (wind, waterfall, and wave hydrodynamics).  electrical energy (photovoltaic (pv) and thermoelectric conversion).  heat energy (geothermal and solar thermal). it is worth noting that most of these power sources rely predominantly on the sun as a major source. indeed, as a viable source of renewable energy, the sun has been the focus of intensive global research for several decades [3]. it is worth mentioning, in this respect, that the pv panels’ drawn energy is not only powerful, but also convertible into electricity thanks to an array of pv installations: isolated "stand-alone" installations, grid connected installations, and hybrid facilities [4]. regarding the present paper, the modeling and simulation of an autonomous renewable-energy electrical system are treated with respect to the following main axes:  the theoretical study is focused on the detailed analysis of the boost converter.  highlights of an advanced stand-alone pv system with maximum power point tracking (mppt) control and the relevant energy management strategy are outlined.  analysis and comparison with various storage technologies allow us to identify the load necessary power requirements, the climatic conditions, and the most convenient storage modes fit for an autonomously sustained pv. the energy management strategy is used to optimize the system’s regulatory and supervisory tasks while controlling the charge and discharge status to extend the battery’s life. actually, such a process is deemed critical in an environment where electrical energy consumption is constantly increasing, due to the remarkable growth of industrial development, communication, and transport. in this context, we put forward special battery-stand-equipped indirect storage systems. similarly, a backup power supply seems essential in case of energy shortage in the batteries’ stores [5]. regarding the present work, our choice is set on applying lithium-ion batteries, given the significant advantages they offer (see table i). more particularly, they display noticeable energy density, very fast charging process, and a diversity of life cycles. the proposed pv system involves a pv generator, lithium-ion battery, and resistive load. to this end, a special energy management strategy is enrolled to ensure the system’s perpetual continuity and improve the battery’s life cycle. table i. battery technologies and performance technology lead-acid (pb-ac) lithium-ion (li-ion) nickel cadmium (ni-cd) energy density (wh/kg) 25–45 80-150 20-60 power density (w/kg) 80–150 500-2000 100-800 discharge time (h) 0.3-3 0.3-5 0.3-3 return (%) a few days a few months less than 1 month efficiency (%) 60-98 90-100 60-80 cycle life 300-1500 >1500 300-1500 cost ($/kwh) 100-300 500-1200 200-800 the advanced pv system exhibits not only a high power output, but also an abrupt response to climate as well as load variations. accordingly, a relevant energy management strategy is considered, whereby the system’s continuous functioning and battery’s life cycle could be maintained. the strategy is so simple to implement that it requires a low processing amount, and enhances the system’s overall storage efficiency and lifetime while allowing to avoid total load disconnect. ii. sizing and modeling of photovoltaic chain components the general diagram of the pv convention chain under examination is depicted in figure 1. fig. 1. block diagram of the pv conversion chain. a. pv system modeling for an effective pv design to be achieved, accurate measurements and a reliable mathematical approach are necessary. more particularly, the design control rests on the knowledge of the subsystems’ various technical characteristics. basically, the design background requires fulfilling the following steps [6]:  selecting the pv modules: the voltage to be delivered, the appropriate technology, and the peak power.  determining the storage capacity and battery type.  pinpointing the power converters’ fit sizes. b. photovoltaic single model the single-diode pv cell corresponding circuit displays two resistors: a shunt resistor rsh connected in parallel, designating the leakage current in the pn junction, and a series resistor rs connected in series, which stands for the connections’ various resistances [7]. on substituting the two currents id (diode current) and ish with their relevant expressions, the following equation is drawn: exp 1pv s pv pv s pvpv ph s t sh v r i v r i i i i v r                (1) where /tv k t q  , k is the boltzmann's constant, t the cell temperature, and q the electron's charge. c. boost converter model a step-up boost converter is frequently used to transform a low-input voltage into a high output value [8]. it incorporates a engineering, technology & applied science research vol. 13, no. 1, 2023, 9849-9854 9851 www.etasr.com njeh et al.: energy management of an autonomous photovoltaic system under climatic variations continuous input voltage u, an inductor l, a diode d, and two capacitors ce and c. d. p&o mppt control strategy thanks to its simplicity, exclusively requiring current and voltage measurements of the pv array, the perturb and observe (p&o) method is considered an effective strategy frequently applied in the mppt research area. the idea of this approach lies in regularly changing the voltage of the pv array, by comparing the previously delivered power to that actually delivered, following a particular disturbance. due to this technique, identifying the power peak turns out to be a feasible procedure, regardless of temperature or irradiation fluctuations. figure 2, depicts the p&o approach corresponding algorithm [9-10]. the associated duty cycle d(t) is highlighted by the following expression: ( ) ( 1) * d d t d t q δ= − + (2) where q is either equal to 0 or ±1, depending on the pv power and voltage variation, and δd denotes the disturbance value. fig. 2. flowchart of the p&o mppt technique. e. energy computation requirement of a standalone pv system the first step to follow when sizing a pv installation consists in estimating the energy consumption amount and determining the load-specific profile [11]. hence, the consumed energy corresponding expression turns out to be: dc dc je p t  (3) where edc denotes the energy consumed on a daily basis, tj stands for the daily usage time, and pdc designates the dailyconsumed power. f. sizing a photovoltaic generator the total number of modules necessary for maintaining the load provision constitutes an initial step in sizing a solar generator [12]. the pv generator’s peak power is determined by: 1000 tot c cg e p g f    (4) where etot denotes the total energy consumed on a daily basis, g refers to the irradiation, and fcg designates the global factor correction. the total number ntot of pv modules is computed as: tot tot m m cg e n g s f     (5) where sm denotes the module area and ƞm the module efficiency. depending on the load and module peak power, ntot is determined by: 0 c c m s tot cm p p g s n p      (6) where pcm designates the pv module’s peak power. the number of modules in series is: max bat ms v n v  (7) where nms represents the number of pv modules connected in series and vbat and vmax are the battery voltage and the maximum power voltage, respectively. the number of parallel modules is determined by: tot mp ms n n n  (8) the size of the photovoltaic surface is computed as: mp ms msurface n m s   (9) the peak pv power is calculated as: (1 ) ch pv e p g pertes    (10) the storage system capacity is sized by: s j batt batt batt db e n c u p     (11) where pdb denotes the battery discharge depth and nj the number of autonomy days. iii. energy management algorithm an adequate operation of the autonomous pv system entails optimal management of the energy flows exchanged among the system’s various components. at this level, it is necessary to introduce our special management system architecture [13-16]. we anticipate that the batteries are fully charged at the start of the pv installation to monitor the entire engineering, technology & applied science research vol. 13, no. 1, 2023, 9849-9854 9852 www.etasr.com njeh et al.: energy management of an autonomous photovoltaic system under climatic variations system [13]. the energy management strategy is mainly concerned with monitoring the charge state and protecting the battery (minimum charge state edcmin = 30% and maximum charge state edcmax = 95 %) as depicted in figure 3. it should be also noted that the pv/battery system involves 4 operating modes, as illustrated in figure 4, where pava is the difference between the power of the pv generator and the load. fig. 3. ulm diagram of the energy management algorithm. fig. 4. operating mode management flowchart. in case of excessive pv energy:  mode 1: the batteries are charged. the pv generator is adequately ready to meet the demand.  mode 2: the pv generator is fit to satisfy the load. the produced energy excess is to be stored in the batteries. in case of lack of pv energy:  mode 3: only the batteries are to supply the charge.  mode 4: the batteries are completely discharged with no pv production. the management algorithm helps supervise the energy exchanges between the installation elements, depending on the two scenarios highlighted in figure 4:  supply of receivers and storage by pv panels if pv energy is sufficient  supply of receivers exclusively by the storage system if the pv energy is insufficiency. iv. global system simulation figure 5 shows the system corresponding diagram for a 5kwp pv field, 220v (50ah) storage lithium-ion battery, and a boost converter, modeled and simulated in matlab/ simulink. fig. 5. the global system’s diagram in matlab/simulink. a. simulation results considering one-day profiles figure 6 depicts a day-long sunshine and temperature actual representations, as applied for the subsequent simulation results. to analyze the system’s operation during the interval [5h, 18.5h], a simulation of the global system was performed over a sunny day. as proof of the management algorithm’s effective robustness, figure 7 outlines two different curves:  the first curve depicts the maximum power drawn by the ppv photovoltaic panels.  the second curve highlights the load power profile ps. the open state (level 0) or closed state (level 1) operating moments, relevant to the three power switches (k1, k2, and k3), are illustrated in figure 8. based on figure 8:  suppose that the pv panels’ generated power is greater than that of the load, which is the case for the intervals [(6h7h24), (7h36-9h), (9h54-10h54), (11h54-16h36), and (17h18h30)]. in this case, an excess production mode will be adopted at these intervals considering modes 1 and 2. as shown in figure 8, the power switches k1 and k2 are off, and k3 is on during mode 1 operation, and k1, k2, and k3 are closed during operation in mode 2.  suppose that the consumption amount is lower than the production rate (i.e. when the panel's generated power proves to be lower than the load required power), as it is the case for the intervals [(7h25-7h35), (9h-9h53), (10h551153), (16h37-17h), modes 3 and 4 will then be applied, as engineering, technology & applied science research vol. 13, no. 1, 2023, 9849-9854 9853 www.etasr.com njeh et al.: energy management of an autonomous photovoltaic system under climatic variations the consumption rate turns out to exceed the production rate. the curve depicted in figure 8 shows that in mode 3 the switch k1 is off and the switch k2 is on, while in mode 4, all the switches k1, k2, and k3 are on.  once the system's power consumption and production rates are equal to zero, the system will be disconnected from its load, as is the case during the period span [18:30-6:30]. fig. 6. sunshine and daytime temperature. fig. 7. pv system generated power and load power profile. fig. 8. operation of the three switches. the curve appearing on figure 9 depicts the load as well as the batteries respective voltage vbat, which is almost equal to the standard reference value of 240v. regarding the illustrated curve in figure 10, it highlights well the variations in the battery's charge levels over time. note that the battery's soc (state of charge) appears to vary depending on the power demand divergence from the charge and the pv generator’s power supply. fig. 9. load and battery voltage. fig. 10. battery charge status. under the advanced strategy, the continuous bus-provided voltage can be maintained at the desired voltage level of 240v. accordingly, the dc bus voltage is subject to significant voltage fluctuations on applying this method. v. conclusion the novelty of the current study lies in the investigation of the capacity of an autonomous pv-battery conversion system to maintain the load with continuous energy supply under distinct climatic variations. in this respect, a matlab/simulink study context enabled the execution of a simple energy-management technique with various switching modes. the suggested energy management strategy has been able to provide the load with a continuous energy supply, maintained even in the conditions of solar unavailability. in addition, it helps in extending the battery's lifespan, by dealing with the frequent charging and discharging processes. the simulation study results, achieved by the proposed energymanagement strategy under distinct operating modes, verified the scheme’s remarkable performance and effectiveness not only in maintaining the pv-battery system’s continuity, but also in increasing the battery’s lifecycle and durability. references [1] c. r. kumar. j and m. a. majid, "renewable energy for sustainable development in india: current status, future prospects, challenges, employment, and investment opportunities," energy, sustainability and engineering, technology & applied science research vol. 13, no. 1, 2023, 9849-9854 9854 www.etasr.com njeh et al.: energy management of an autonomous photovoltaic system under climatic variations society, vol. 10, no. 1, jan. 2020, art. no. 2, https://doi.org/10.1186/ s13705-019-0232-1. [2] j. a. gow and c. d. manning, "development of a model for photovoltaic arrays suitable for use in simulation studies of solar energy conversion systems," in 1996 sixth international conference on power electronics and variable speed drives (conf. publ. no. 429), nottingham, uk, sep. 1996, pp. 69–74, https://doi.org/10.1049/ cp:19960890. [3] f. r. arroyo m. and l. j. miguel, "the role of renewable energies for the sustainable energy governance and environmental policies for the mitigation of climate change in ecuador," energies, vol. 13, no. 15, jan. 2020, art. no. 3883, https://doi.org/10.3390/en13153883. [4] d. gielen, f. boshell, d. saygin, m. d. bazilian, n. wagner, and r. gorini, "the role of renewable energy in the global energy transformation," energy strategy reviews, vol. 24, pp. 38–50, apr. 2019, https://doi.org/10.1016/j.esr.2019.01.006. 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[13] d. keiner, m. ram, l. d. s. n. s. barbosa, d. bogdanov, and c. breyer, "cost optimal self-consumption of pv prosumers with stationary batteries, heat pumps, thermal energy storage and electric vehicles across the world up to 2050," solar energy, vol. 185, pp. 406–423, jun. 2019, https://doi.org/10.1016/j.solener.2019.04.081. [14] m. b. ammar, m. a. zdiri, and r. b. ammar, "fuzzy logic energy management between stand-alone pv systems," international journal of renewable energy research (ijrer), vol. 11, no. 3, pp. 1238–1249, sep. 2021. [15] m. b. roberts, a. bruce, and i. macgill, "impact of shared battery energy storage systems on photovoltaic self-consumption and electricity bills in apartment buildings," applied energy, vol. 245, pp. 78–95, jul. 2019, https://doi.org/10.1016/j.apenergy.2019.04.001. [16] j. goop, e. nyholm, m. odenberger, and f. johnsson, "impact of electricity market feedback on investments in solar photovoltaic and battery systems in swedish single-family dwellings," renewable energy, vol. 163, pp. 1078–1091, jan. 2021, https://doi.org/10.1016/j.renene. 2020.06.153. microsoft word etasr_v12_n6_pp9426-9430 engineering, technology & applied science research vol. 12, no. 6, 2022, 9426-9430 9426 www.etasr.com mohammed & al-hadithi: the effect of adding expanded polystyrene beads (eps) on polymer… the effect of adding expanded polystyrene beads (eps) on polymer-modified mortar zainab essam mohamed department of civil engineering university of baghdad baghdad, iraq zainab.mohammed2001m@coeng.iobaghdad.edu.iq abdulkader ismail al-hadithi department of civil engineering university of anbar ramadi, iraq abdulakder.alhadithi@uoanbar.edu.iq received: 26 july 2022 | revised: 10 august 2022 | accepted: 11 august 2022 abstract-this study assessed the efficiency of expanded polystyrene (eps) waste as a 10, 20, 30, 40, 50, and 60% substitute for fine aggregate in the manufacturing of lightweight cement composites. a 4% low-cost latex paint emulsion was added to the cement mortar to reinforce it as an alternative to the more expensive polymer admixtures. this improved the bonding between the cement matrix and the eps particles because sbr films were produced in the cement matrix. the flexural strength of regular eps concrete may also be significantly increased by sbr treatment. eight alternative mix designs were created and evaluated for compressive and flexural strength, thermal conductivity, water absorption, and dry density. the polymermodified mortar was created using a 0.4 water/cement ratio of local cement, polymer, and polystyrene. the results showed that compared to the standard combination at 28 days of aging, the compressive strength increased up to 29.26mpa, flexural strength increased to 6.83mpa, dry density increased up to 1930kg/m³, and absorption decreased by 4.95. thermal conductivity decreased by 0.8291w/m.k. keywords-polymer modified mortar (pmm); polymer; polystyrene; compressive strength i. introduction chemically or steam-processed polystyrene foam components are heated at high temperatures to produce expanded polystyrene (eps), a lightweight artificial aggregate (lwa). round, closed-cell polystyrene particles have a density between 20 and 35kg/m³ and are composed of 98% air [1, 2]. sandwich panels, floor decks, and curtain walls with increased thermal and acoustic insulation often use these lightweight nonstructural components. [2]. environmentally friendly and inexpensive sound materials are becoming more popular. eps is often used in packaging with minimum absorption and low cost because of its low density, hydrophobic characteristics, and excellent thermal insulation. globally, an estimated amount of 14 million metric tons of polystyrene are manufactured each year and a large portion of the produced waste is placed in landfills [3, 4]. styrene butadiene rubber (sbr) latexes may reduce bleeding and segregation in the cementitious matrix [5]. the network and the filler are two distinct parts of a polymeric composite. the dispersed stage and fortification are other names for this stage. the disseminated media is responsible for further structural progress. the goal is to better connect the matrix to the filling [6] polymer-modified mortar (pmm). with the right mix of cement and latex, pmm is an ideal product for use in the construction industry. concrete and mortar characteristics may be altered by polymers. this material has higher tensile strength, improved chemical resistance, long-term use, and less environmental impact [7]. latex improves the adhesive or bonding strength of materials such as pastes, mortars, concretes, tiles, bricks, steel, wood, and stone compared to the industry's unaltered counterparts [8]. instead of cement, sbr is used in civil engineering to improve the hardened properties of concrete [9]. adding sbr to strong concrete alters its physical properties. sbr is the most often used cement mortar modifier. the resulting cement hydrate and polymer layer have excellent adhesion properties. this results in less deformation and a more excellent crushing and flexural strength than conventional concrete [10]. sbr latex is widely used in a variety of modified solutions to enhance impermeability and frost resistance. sbr latex has often been used to repair reinforced concrete structures. several studies found that adding sbr latex to cement mortar increased bonding and flexural and tensile strength. this study attempts to improve the bonding between eps particles and cement paste by including sbr latex in eps concrete mixtures, improving compressive strength, flexural strength, thermal conductivity, and water absorption. ii. material characterization a. cement this study used opc cement i 42.5n. tables i and ii show its chemical and physical characteristics, which are in accordance with iraq's specification no. 5/2019 [11]. b. fine aggregates the used fine aggregates met the criteria in [12], had excellent gradation, were free of dangerous chemicals that might affect the examination's findings, went through the 0.6mm sieve, and passed the sieving test. corresponding author: zainab essam mohammed engineering, technology & applied science research vol. 12, no. 6, 2022, 9426-9430 9427 www.etasr.com mohammed & al-hadithi: the effect of adding expanded polystyrene beads (eps) on polymer… c. water according to [13], the utilized water was pure and devoid of contaminants. d. polymer the sbr polymer was utilized without any treatment to make the polymer cement mortar (pcm) mixes. table iii lists the sbr polymer's physical characteristics. e. expanded polystyrene beads this study used spherical eps beads with a maximum nominal size of 5mm instead of fine aggregates in certain instances. table iv shows the physical characteristics of the eps beads and the particle size gradient discovered during the eps sieve analysis. figure 1 shows the prepared eps beads in a spherical shape. table i. cement's chemical components oxide composition result limits of [12] cao 62 sio2 20.1 al2o3 4.24 fe2o3 4.16 so3 2.15 ≤ 2.8% if c3a>3.5 ≤ 2.5% if c3a<3.5 mgo 3.65 ≤ 5% loss on ignition 3.42 ≤ 4% insoluble residue 0.71 ≤ 1.5% cement compounds [24] c3s 59.02 c2s 29.65 c3a 4.21 c4af 12.65 table ii. physical properties of cement physical properties test result limits of [12] specific surface area, blaine method, (m²/kg). 295 ≥ 250 m 2 /kg setting time -initial setting (min) -final setting (min) 1:38 3:45 ≥ 45 min ≤ 600 min compressive strength of mortar (mpa) 2-days 28-days 20.4 27.5 ≥ 10 n/m 2 ≥ 42.5 n/m 2 soundness % (autoclave) 0.35 ≤ 0.8 table iii. physical properties of sbr polymer specifications given by the company appearance milky white specific gravity 1.02 ± 0.2 @ 250 o c chloride content nil (en 934-2) ph value 7 10.5 table iv. chemical and physical properties of eps sieve size passing% astm c 330 4.75mm 6.5 5–40 2.36mm 1.5 0–20 physical properties so3% – specific gravity – absorption 0 maximum particle size 5 fig. 1. expanded polystyrene beads. iii. experimental work a. mixing an electric mechanical mixer with a capacity of 0.1m 3 was used. cement and fine aggregates were first added to the mixer and stirred for 1min. following the proper dilution with water, the sbr polymer dispersion was added and mixed for around 3min at low speed. finally, the other eps particles were blended with the initial materials for an additional two minutes. due to their low density, compared to other ingredients in the combination, this was done to guarantee that the polystyrene granules would not volatilize. the remaining water was added to the components that had already been mixed slowly and steadily for another 3 to 5min to get a homogeneous mixture free of segregation. table v displays the percentages of the materials utilized in this production. table v. details of mixture proportions mix c:s w/c% polymer:cement% eps% flow (mm) e1 1:3 0.58 0% 0% 85 e2 1:3 0.4 4% 0% 100 e3 1:3 0.4 4% 10% 145 e4 1:3 0.4 4% 20% 147 e5 1:3 0.4 4% 30% 150 e6 1:3 0.4 4% 40% 155 e7 1:3 0.4 4% 50% 165 e8 1:3 0.4 4% 60% 190 b. casting, compaction, and curing metal sheets were placed on top of the molds to prevent the samples from evaporating while remaining in the molds for 24h. this is the most effective way to cure polymer-containing concrete [14]. after being soaked in water for 72h, the samples were removed from the molds and left to dry until evaluation. the total number of samples prepared in this study was 168. iv. results and discussion a. flow test figures 2 and 3 illustrate how an increase in replacement% helped boost the flow for eps samples [15], validating that the hydrophobic properties of eps aggregates were the higher value of the cause of the flow test. the natural aggregates exhibited angular shapes, while eps particles were spherical. therefore, more eps causes more lubrication between the particles, which reduces friction and increases the flow test [16]. engineering, technology & applied science research vol. 12, no. 6, 2022, 9426-9430 9428 www.etasr.com mohammed & al-hadithi: the effect of adding expanded polystyrene beads (eps) on polymer… fig. 2. flow and effect relationship of eps and sbr addition. fig. 3. flow test. b. compressive strength this test was conducted using cubic specimens 50×50×50mm in size [17]. the test ages were 3, 7, and 28 days, and 3 cubes were examined for each age. the sbr concrete without eps had the maximum compressive strength (up to 42.6mpa), surpassing the benchmark mix. in terms of combinations, the percentages of eps by weight of fine aggregates were 10, 20, 30, 40, 50, and 60%. adding more polystyrene, the inadequate film formation caused a considerable reduction in the compressive strength of the polymer eps concretes. the greatest compressive strength value was found for the 10% polystyrene replacement ratio (up to 29.26mpa), as shown in figures 4 and 5. compressive strength dropped as the percentage of polystyrene increased [18]. fig. 4. relationship of compressive strength and eps. fig. 5. testing cubic concrete sample. c. flexural strength flexural strength determines how materials react to simple beam loads [19]. this test employed dimensional prismatic specimens (40×40×160mm) with various curing ages (7, 14, and 28 days). three prisms were examined for each age. figures 6 and 7 show the results. figure 6 shows that the sample with a 10% substitution with eps had flexural strength values that were greater than the standard, and even greater than the values of the sbr 4% mixing container. as the eps ratio decreased, the flexural strength increased. an increase in flexural strength was accompanied by a rise in density because polymeric coatings increased the flexural strength of cured concrete [20]. fig. 6. relationship between flexural strength and eps. fig. 7. testing a prismatic concrete sample. d. thermal conductivity cylinders measuring 100×200mm were produced to measure thermal conductivity [21]. the test was carried out at 28 days of age on 3 samples for each age. thermal conductivity and density were shown to be closely related. figures 8 and 9 show that thermal conductivity decreased when density declined. porosity increased with eps levels, which resulted in a reduction in heat conductivity. adding sbr to the combinations had a considerable negative impact on thermal conductivity. the findings demonstrate that the density and volume of eps impacted the thermal conductivity of the concrete. the partial replacement of fine aggregate with eps was responsible for the change brought about in the lower density and greater air spaces of eps beads, which resulted in the reduction of thermal conductivity outcomes of mixtures [22]. e. water absorption the beads were hydrophobic because they were made of polystyrene sulfonate eps. figure 10 shows that the results of the absorption test worsened as eps content increased. with increased eps particles, mortars become more porous internally, making it easier for water to enter the mortar [23]. engineering, technology & applied science research vol. 12, no. 6, 2022, 9426-9430 9429 www.etasr.com mohammed & al-hadithi: the effect of adding expanded polystyrene beads (eps) on polymer… fig. 8. relationship between thermal conductivity and density. fig. 9. testing a cylinder concrete sample. fig. 10. relationship between absorption (%) and eps. v. conclusion the evaluation of thermal conductivity, flexural strength, and compressive strength of polymer-modified mortar and expanded polystyrene beads led to the following conclusions:  at 28 days, the reference mixture's compressive strength at 10% replacement increased by 5.46%. systematic reductions were made when the use of eps use increased.  at 28 days, the 10% replacement attained the greatest flexural strength of 6.83mpa.  sbr enhanced overall porosity, decreased density, and created artificial micropores. because of this, the partial substitution of aggregate with eps may be blamed for the lower thermal conductivity. the material's insulating quality also increased due to the samples' decreased thermal conductivity.  eps demonstrated a successful use as a substitute material in the construction of nonstructural elements. it also provided a solution to the disposal of expanded polystyrene waste. concrete's density and compressive strength decreased as the proportion of eps substitute increased. the 10% eps was best suited for non-structural uses, such as wall building and ornamental moldings. however, since it tends to break quickly under strain, 30, 40, 50, and 60% replacement should not be utilized for non-structural reasons. therefore, it is advised to include polystyrene in concrete mixtures when low-density (lightweight) concrete is desired and resistance is unnecessary.  at 28 days, the 10% eps replacement combination's water absorption was 4.95% lower than the reference mixture. references [1] k. n. lakshmikandhan, b. s. harshavardhan, j. prabakar, and s. saibabu, "investigation on wall panel sandwiched with lightweight concrete," iop conference series: materials science and engineering, vol. 225, dec. 2017, art. no. 012275, https://doi.org/10.1088/1757899x/225/1/012275. 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[24] a. m. neville and j. j. brooks, concrete technology, 6th ed. uk: longman scientific and technical, 1995. microsoft word etasr_v13_n3_pp10738-10743 engineering, technology & applied science research vol. 13, no. 3, 2023, 10738-10743 10738 www.etasr.com nawel et al.: a force-based method for the numerical simulation of a reinforced concrete shear wall … a force-based method for the numerical simulation of a reinforced concrete shear wall building benlaala nawel lgc-roi, department of civil engineering, faculty of technology, university of batna 2, algeria bna.wel@hotmail.com (corresponding author) abdkrim kadid lgc-roi, department of civil engineering, faculty of technology, university of batna 2, algeria a.kadid@univ-batna2.dz djarir yahiaoui lgc-roi, department of civil engineering, faculty of technology, university of batna 2, algeria d.yahiaoui@univ-batna2.dz received: 9 january 2023 | accepted: 30 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5675 abstract reinforced concrete (rc) shear walls are structural elements that resist lateral loads. this research aims to present the numerical modeling of rc shear walls in order to evaluate the seismic performance of structures. various types of numerical models of rc frame elements are implemented in nonlinear analysis packages. these numerical models are based on different theories and assumptions, something that poses a significant difficulty to practicing engineering and limits confidence in the analysis of the numerical results. in this study, inelastic force-based elements and distributed plasticity methods are used for the modeling of the inelastic behavior of these elements (infrmfb). the efficiency of the inelastic forcebased element and distributed plasticity method is evaluated through the comparison with the experimental results of a shear wall structure subjected to seismic loadings. the accuracy of the numerical model is assessed in terms of top displacement, inter-story drift, base shear force, and the absolute maximum values of the overturning moment. keywords-shear wall; infrmfb element; force-based; nonlinear numerical model; rc frame elements; distributed plasticity i. introduction shear walls are used as the primary lateral load-resistant system of reinforced concrete (rc) structures. earthquake engineering is focused on simulating the nonlinear response of shear wall structures to seismic excitations, through experimental studies [1, 2] and numerical modeling [3-5]. new performance-based seismic design guidelines [6] require that structures should be analyzed using nonlinear static pushover analysis or nonlinear dynamic analysis to control global and local demands. the use of nonlinear frame analysis necessitates the availability of robust and computationally efficient models for performing computations in a reasonable amount of time [7, 22]. in the numerical modeling approach, ground motion loading analysis of rc shear wall buildings is generally conducted with beam-column elements, which should be capable of fully taking into consideration the inelastic behavior of the actual member [8, 23]. distributed plastic hinges in beam–column elements used to model the nonlinear behavior of rc structural elements are thus required in order to simulate the seismic response and to evaluate the performance of structural systems [9]. several studies have investigated the performance of different nonlinear modeling strategies for the numerical simulation of the response of a rc shear wall subjected to seismic loads. authors in [10] studied the numerical strategy 3s-r adopted in the laboratory for the simulation of the nonlinear behavior of the specimen. multi-fiber timoshenko beam elements were used for the finite element mesh of the rc walls. constitutive mechanical damage models were used for rc. the proposed modeling strategy accurately describes the overall behavior of the structure. the comparison with the experimental results helped identifying the shortcomings of the original numerical model and suggested remedial measures to improve its performance. authors in [11] studied the nonlinear dynamic behavior and response of rc walls. they used a engineering, technology & applied science research vol. 13, no. 3, 2023, 10738-10743 10739 www.etasr.com nawel et al.: a force-based method for the numerical simulation of a reinforced concrete shear wall … continuous damage model, and simplified numerical strategies were proposed. they chose two dimensional (2d) euler beam theory for the modeling of walls whose behavior was controlled effectively by bending. for 3d problems, a multifiber timoshenko beam element with higher-order interpolation functions was developed. as for walls with a small slenderness ratio, they used the equivalent rc model. comparisons with the experimental results of rc walls tested on a shaking table or reaction wall showed the advantages and limitations of the approach. authors in [12] developed a constitutive model for rc under cyclic or dynamic loading based on existing experimental results. the proposed model featured hysteretic characteristics of concrete in tension, compression, shear along the crack direction, and the bond between concrete and the reinforcing bars. they also developed a non-orthogonal multi-directional smeared crack model for the realistic representation of concrete cracking under stress reversals. the applicability and efficiency of the proposed models were demonstrated through simulation with various types of rc specimens subjected to cyclic loads or seismic excitation on a shaking table. authors in [13] studied the nonlinear response of rc moment-resisting frames considering the bond-slip effect between concrete and bars along the lengths of the beam, column, and common elements. they used the fiber model theory to simulate the behavior of rc in the nonlinear domain. the ideal bond hypothesis between concrete and bars has been removed. they showed that the proposed method can accurately model the nonlinear behavior of rc frames by comparing the experimental and numerical models of two specimens under cyclic loading. in this study, the structural response is assessed by nonlinear dynamic (time history) analysis to estimate the seismic response using the force-based inelastic frame elements (infrmfb) method. emphasis is made on the applicability of the representative numerical model of the rc shear wall. its efficiency is evaluated by comparison with the experimental results for a 7-story rc structural wall [14] that can be readily performed with existing software packages. ii. numerical tool and modeling strategies the numerical analysis developed and described in this paper and the nonlinear modeling strategies were conducted using the seismostruct v7 (seismosoft and 2021) [15]. the program includes models for the representation of the behavior of spatial frames under static and dynamic loading, considering both material and geometric nonlinearities. seven types of analysis can be performed: dynamic and static time history analysis, conventional and adaptive pushover, incremental dynamic analysis, modal analysis, and static analysis (possibly nonlinear) under quasi-permanent loading. all the features are based on force or displacement formulations. while the evaluated numerical models are based on different assumptions, the input parameters for these elements are primarily physical properties, such as section geometry and the uniaxial behavior of materials. hence, as long as the limitation of the element can be clearly defined, engineers can use the elements with confidence and without much effort to calibrate model parameters. therefore, in this study, the numerical simulation of nees-ucsd rc shear wall structure was investigated using the nonlinear modeling strategy of forcebased inelastic frame element (infrmfb). the experimental results obtained from previous shaking table tests of these shear wall structures are compared with the results of the numerical nonlinear seismic analysis. the experimental study uses the needs-ucsd design [16, 17, 24, 25]. the response of an rc structure consisting of shear walls is simulated under the seismic loading recorded during the 1994 northridge earthquake. iii. element formulation – the flexibility (force) method in this study, the force fields are described by the flexibility method and the nonlinear analysis of the rc shear wall structures is conducted using the infrmfb method. rc structures that consist of shear walls are simulated by a 7-story system available from the european laboratory for structural assessment (elsa) [14]. the numerical analysis results are compared with the experimental results in terms of absolute values of base overturning moment, base shear force, and tip displacement. a time history plot of the top displacement response of the shear wall structure is also used for comparison. this can easily be done with existing software packages. the structural response is evaluated by nonlinear dynamic (time history) analysis to estimate the seismic response: d(x) =b(x) q (1) where b(x) contains the force interpolation functions, which relates the generalized nodal forces q to the internal forces d(x). replacing δd from the incremental form of (1) in the inverse from the constitutive relation δd = kδd, namely δd(x) = k��δd(x) yields the incremental deformation field [18]: δd(x) = f(x) δd(x) = f(x) b(x) δq (2) where f(x) = k -1 (x) is the section flexibility matrix. the principle of virtual forces leads of the compatibility condition are described by (3): q= b�(x)d(x)dx � (3) and its linearization: fδq = r (4) in the form of a displacement-force relation, where q = element end displacement and f = �� �� = b�(x)f(x)b(x)dx � � (5) is the element flexibility matrix, while δq and r are the vectors of force increments and residual displacement, respectively. note that a meaningful expression for the flexibility matrix f can only be derived for the beam element without rigid-body modes [19]. engineering, technology & applied science research vol. 13, no. 3, 2023, 10738-10743 10738 www.etasr.com nawel et al.: a force-based method for the numerical simulation of a reinforced concrete shear wall … fig. 1. discretisation of the cross‐section and section fiber. iv. inelastic force-based frame element this force-based 3d beam-column element type can model spatial frame members with geometric and material nonlinearities. cross-section-related stress-strain states of beam-column elements are obtained by integrating the nonlinear uniaxial material responses of individual fibers whose cross-sections are divided by the depth of the crosssection. the infrmfb element is the most accurate of the four seismostruct frame element types, due to the fact that the inelastic behavior can be captured over the entire structural element length, even when using one element per structure. therefore, it provides very accurate analysis results and allows users to output element chord rotations for seismic code validation (e.g. eurocode 8, ntc-08, kanepe, fema-356, atc-40, etc.). one must define the number of section fibers used in the equilibrium calculations performed on each integrated section of the element. the ideal number of profile fibers sufficient to adequately reproduce the stress-strain distribution across the cross-section of the element depends on the element's geometry and material properties and on the element's degree of inelasticity. as a rough rule of thumb, the user can assume that sections made of a single material are typically well represented by 100 fibers. in more complex sections, subjected to high inelasticity, typically 200 or more fibers should be used. a sensitivity study on a case-by-case basis can undoubtedly determine the optimum number of cut fibers [20]. v. structure, materials, and loads in the present study, a full-scale 7-story structure with two main perpendicular walls: the web wall and the flange wall linked with slabs (figure 2), was modeled. a pre-cast column is needed to limit torsional behavior and gravity columns to support the slabs are also present. the rc frame was tested on the nees (earthquake engineering simulation network) large high‐performance outdoor shake table at the university of california at san diego (ucsd)’s englekirk structural engineering under dynamic conditions [12] by applying 4 subsequent uniaxial ground motions. the structure has been designed with the displacement-based capacity approach for a site in los angeles. hence, the lateral design forces are smaller than those currently specified in u.s. building codes for regions of high seismic risk. a. structural geometry a 7-story rc earthquake-resistant wall designed by the nees was considered in this study. it was seismically loaded on a shaking table at the ucsd [16]. this structure comprises two types of shear walls located on the central axis and the pier columns on the corners of the structure. one of the shear walls is called the web wall, while the other is the flange wall. the walls are built perpendicular to each other. the slab is connected to the flange wall, and slotted connections join the two shear walls. the basement and floor heights are 0.76m and 2.74m, respectively. the total height of the structure is 19.96m. the structure is fastened to the ground, and its mass is 226 tons. the cross-sections of the flange wall and the web wall are different. the width of the flange wall is 4.88m and the thicknesses of the flange wall are 203mm and 152mm for the last floor and the other floors, respectively. the width of the web wall is 3.65m and its thickness is 203mm for the first and the last floor, while it is 152mm is for the other floors. the columns and shear walls supported 3.65×8.13m slabs on each floor. post-tensioned precast piers are joined to the web wall and slabs via bracing. the full-scale rc shear wall structure details are shown in figure 3. the geometry of the structure is summarized in table i. the mass values of the structure are summarized in table ii. two different views of the finite element (fe) model are presented in figure 3. (a) (b) (c) fig. 2. the 7-story rc shear wall building tested at the nees. engineering, technology & applied science research vol. 13, no. 3, 2023, 10738-10743 10739 www.etasr.com nawel et al.: a force-based method for the numerical simulation of a reinforced concrete shear wall … table i. geometry of walls and gravity columns story web wall (m 2 ) flange wall (m 2 ) gravity volumns 7 3.658×0.203 4.877×0.152 d= 0.102 m, t = 0.033 m 6 3.658×0.152 4.877×0.152 d= 0.102 m, t = 0.028 m 5 3.658×0.152 4.877×0.152 d= 0.102 m, t = 0.028 m 4 3.658×0.152 4.877×0.152 d= 0.102 m, t = 0.028 m 3 3.658×0.152 4.877×0.152 d= 0.102 m, t = 0.028 m 2 3.658×0.152 4.877×0.152 d= 0.102 m, t = 0.028 m 1 3.658×0.203 4.877×0.152 d= 0.102 m, t = 0.028 m (a) (b) fig. 3. fe model view. fig. 4. acceleration time history. fig. 5. response spectrum of the accelerograms—5% damping. b. input accelerations and spectrum the 1994 northridge earthquake acceleration record, obtained from the sylmar olive view medical centre, was used as the seismic input parallel to the web wall and was successfully applied to the shaking table with amplifying acceleration magnitude. the acceleration record of the earthquake is shown in figure 4, with a peak ground acceleration of 0.85g. during the test, global and local measurements were made (displacements, accelerations, moments, etc.). the apparent mode was measured after the examination to follow the stiffness evolution. detailed information on the experimental program and results are described in [20]. the response spectrum of these motions corresponding to 5% viscous damping is shown in figure 5. table ii. mass of different components components mass (tons) foundation 21.432 slabs 101.604 web wall 24.947 flange wall 33.263 pt column 30.158 gravity columns 4.717 braces 0.181 c. material properties authors in [21] proposed a unified stress–strain approach for confined concrete applicable to both circular and rectangular-shaped transverse reinforcement. its characteristic parameters are: ƒc = 16300kpa, ƒt= 1900kpa, εc = 0.002m/m, and ec = 18975mpa. the menegotto-pinto steel model is employed for defining the steel with the following properties: es = 2.00e+ 008 kpa, fy = 343000 kpa, µ = 0.0024. the materials considered at the design phase were: low-strength concrete of class c16/20 (cen, 1991) and smooth reinforcement steel class fe b22 k (italian standards). the latter refers to smooth bars with a yield stress of 235mpa and ultimate strength of 365mpa. vi. results and discussion a. displacement to evaluate the level of accuracy obtained with the modeling strategy, the first step is to assess the global response of the structure under seismic action. the roof timedisplacement trends for the studied frame are presented in figure 6. fig. 6. lateral displacements at the top versus time. engineering, technology & applied science research vol. 13, no. 3, 2023, 10738-10743 10740 www.etasr.com nawel et al.: a force-based method for the numerical simulation of a reinforced concrete shear wall … they are obtained by using inelastic force-based elements with distributed plasticity. the results indicate a good agreement with the experimental results when the time is less than 12s. for a time greater than 12s, the results diverge from the experimental ones. the lateral displacements from numerical analysis for each story are close to those of the experimental ones, see figure 7. fig. 7. maximum lateral displacement. b. inter story drift the lateral deformability of structural systems is measured through the horizontal drift. in buildings, story drift δ is the absolute displacement of any floor relative to the base. in contrast, inter-story drift δ defines the relative lateral displacement between two consecutive floors. the inter–story drift is generally expressed as the ratio δ/h of the displacement to the story height h. the drift of the roof δ normalized by the total height h of the building (roof drift, δ/h) is also used to quantify the lateral stiffness of structural systems. figure 8 shows the vertical distribution of the maximum story drift of the main frame. the analytical model can predict the results of the 7 floors. however, at the base, the results are not close to the experimental values. for example, the difference in interstory drift is about 0.67% in the first story, in the second story the difference is about 0.28%, and above this floor, the difference is negligible. fig. 8. maximum interstory drift ratio in the structure. c. base overturning moment the base moment was determined by summing the moments at the base of the web and flange walls and the couple generated by the gravity columns that had about 10–24% contribution to the base overturning moment. figure 9 compares the experimental and analytical values for a base moment using inelastic force-based elements with distributed plasticity. the results indicate that the peak values of the numerical and experimental results varied by about 25%. fig. 9. comparison of experimental and analytical base moment values. d. story shear forces figure 10 compares the experimental and analytical values for base shear using inelastic force-based elements and distributed plasticity. again, the numerical model underestimates the maximum measured base shear force value during the input of the motion by about 12%. fig. 10. comparison of the experimental and analytical values of the shear force at the wall base. vii. conclusions in this study, the numerical simulation of reinforced concrete shear wall structure is undertaken in order to evaluate the efficiency of the numerical model inelastic force-based element with distributed plasticity. the numerical analysis results for the strongest input motion are compared with the experimental shaking table test results and the accuracy of the numerical model is assessed, considering the time-history engineering, technology & applied science research vol. 13, no. 3, 2023, 10738-10743 10741 www.etasr.com nawel et al.: a force-based method for the numerical simulation of a reinforced concrete shear wall … graphs of top displacement, inter-story drift, base shear force, and the absolute maximum values of the overturning moment. the main outcomes for the considered method are:  the numerical simulation predicts a satisfactory maximum displacement, especially in the y direction, where the loading is more severe. there is a slight shifting in the time history curves, the same remarks apply to the inter-story drift curve, the base shear force, and the absolute maximum values of the overturning moment.  the model was able to reproduce the response of the structure with good approximation. this confirms that the level of discretization and the type of numerical elements adopted in the model are sufficient to describe the nonlinear behavior of the reinforced concrete shear wall structures subjected to severe ground motion. references [1] s.-t. huang et al., "experimental study 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[22] h. i. polat, "analysis of a frame-shear wall concrete structure by using base isolation and evaluation of structure-soil interaction," engineering, technology & applied science research, vol. 7, no. 6, pp. 2282–2287, dec. 2017, https://doi.org/10.48084/etasr.1611. [23] f. abdelhamid, d. yahiaoui, m. saadi, and n. lahbari, "lateral reliability assessment of eccentrically braced frames including horizontal and vertical links under seismic loading," engineering, technology & applied science research, vol. 12, no. 2, pp. 8278–8283, apr. 2022, https://doi.org/10.48084/etasr.4749. [24] m. saadi and d. yahiaoui, "the effectiveness of retrofitting rc frames with a combination of different techniques," engineering, technology & applied science research, vol. 12, no. 3, pp. 8723–8727, jun. 2022, https://doi.org/10.48084/etasr.4979. [25] a. zendaoui, a. kadid, and d. yahiaoui, "comparison of different numerical models of rc elements for predicting the seismic performance of structures," international journal of concrete structures and materials, vol. 10, no. 4, pp. 461–478, dec. 2016, https://doi.org/10.1007/s40069-016-0170-7. microsoft word etasr_v12_n4_pp8901-8909 engineering, technology & applied science research vol. 12, no. 4, 2022, 8901-8909 8901 www.etasr.com ubare & sonawane: performance assessment of the bldc motor in ev drives using nonlinear model … performance assessment of the bldc motor in ev drives using nonlinear model predictive control pramod ubare department of instrumentation and control college of engineering pune maharashtra, india upr18.instru@coep.ac.in d. n. sonawane department of instrumentation and control college of engineering pune maharashtra, india dns.instru@coep.ac.in received: 11 april 2022 | revised: 28 april 2022 | accepted: 8 may 2022 abstract-in this paper, the nonlinear model predictive control (nmpc) technique is proposed for the control of brushless direct current (bldc) motors to address the problem of overexcitation, specifically in electric vehicle (ev) applications. this over-excitation increases the overall energy consumption of the machine and eventually reduces the vehicle’s driving range. the developed nmpc incorporates a nonlinear model of the bldc motor with ev load and obtains the optimal current through the optimal voltage applied to the machine to regulate the motor torque. the proposed nmpc is compared with three conventional control techniques, the field-oriented control (foc), the direct torque control (dtc), and the hybrid (the combination of dtc and foc) control. it is observed from the simulation results that the proposed nmpc controller is more energy efficient while maintaining performance. this paper also discusses the selection of the motor based on the specified vehicle requirements. this has been done by matching the vehicle speedtorque characteristic curve with the motor’s one. keywords-bldc motor; model predictive control; nonlinear systems; optimization; electric vehicle i. introduction electric vehicles (evs) are a zero-emission solution for vehicular technology. they are the attractive alternative to the traditional internal combustion (ic) engines [1]. the, technology advancement in ev and energy management solutions are the top priority areas of the relative research. traction motor, the main component of the power-train, consumes the most power from the batteries [1]. several types of electric motors are used for the traction in evs, such as induction motors (ims), permanent magnet motors (pmms), switched reluctance motors (srms), etc. in this work, a brushless direct current (bldc) motor, which is a type of pmm [2, 3], is considered. the driving range can be improved by the optimal usage of the available energy for the traction system. the application of control system engineering to control the bldc motor has gained significant attention by ensuring the efficient and reliable operation of the motor [2-4]. conventional control techniques have been utilized in the speed/torque control of bldc motor for various applications. its combination with fuzzy logic improves performance [5, 6]. the foc is a vector control technique proposed mainly for the control of ac synchronous and ims [7]. however, features like ripple reduction and better efficiency have been used in the bldc motor control [8-10]. due to these advantages, authors in [11, 12] tried the foc principle to find the optimal current excitation component as an extension over the main controller. another widely accepted control technique for the ac motors is the dtc [13, 14]. it has been primarily proposed for ims and has been then utilized in bldc motor control [15, 16]. in the dtc technique, the control actions (stator voltages and currents) are obtained from a switching table implemented with a look-up-table (lut). foc and dtc have their own advantages and disadvantages. recently, authors in [4] demonstrated the advantages of hybrid control (a combination of dtc and foc) for the bldc motor control in aerial drones. the experimental results show that the hybrid controller reduces the speed ripple in the steady state region compared to dtc and decreases the response time compared to foc. generalized predictive control (gpc) for a bldc motor is presented in [17]. in gpc, the objective function needs to be computed for all possible switching states, which increases the controller's computational complexity [12, 18]. in this paper, the use of nmpc technique for the torque control with the bldc prediction model is proposed. the objective function comprises of: (1) torque reference tracking, (2) current d-component minimization, which avoids the overactuation of the motor, and (3) input regulation to minimize the required voltage in order to achieve the desired torque, while it also works as an integrator to reduce steady-state errors. applicability of the nmpc in the bldc motor control has been less addressed in the literature, but it has been successfully applied to permanent magnet synchronous motors (pmsms) [11], where motor current excitation is always sinusoidal. in this paper, we improved the bldc motor control performance using nmpc in various directions. the result was compared with 3 control techniques considering various key performance indices. all the control methods were validated through their speed-torque characteristics against the ideal characteristic of the ev, which is generated through the vehicle's effective weight, required acceleration, maximum grading, and speed range. all techniques were realized in corresponding author: pramod ubare engineering, technology & applied science research vol. 12, no. 4, 2022, 8901-8909 8902 www.etasr.com ubare & sonawane: performance assessment of the bldc motor in ev drives using nonlinear model … matlab, and the proposed nmpc was realized in the casadi [19] platform with a matlab interface. ii. modeling of system dynamics this section presents the nonlinear mathematical model of the bldc motor and the ev coupled with the bldc motor model. a. bldc motor model the electrically modeled 3-phase bldc motor is shown in figure 1. for simplicity reasons, self and mutual inductance were considered constant. the mathematical model for the bldc motor is expressed as: a a a a di v ri l e dt = + + (1) where a v is the phase voltage (v), a i is the phase current (a), �� , �� , and �� are the back-emf phase in (v), r is the resistance per phase (ω), l is the inductance per phase (h). similar equations can be produce by replacing the suffix a with b and c to get the electrical equations of the other phases. this motor is supplied with 3 phase voltages which are in 120 0 phase shift from each other. the mechanical dynamics for the motor are: m e f m l d t k j t dt ω ω= + + (2) where te is the generated electrical torque to handle motor load (nm), tl is the mechanical load on the motor (nm), j is rotor's inertia (kgm 2 ), f k is the frictional constant (nm/rad), and �� is the rotor speed (rad/sec). the bemf in the stator is a function of rotor position (electrical angle � ) and it is trapezoidal in nature: 2 1, 0 3 1 2 2 1 ( ), 3 3 ( ) 5 1, 3 6 5 5 1 ( ), 2 3 3 e e e e e e e f θ θ θ θ θ θ θ π ≤ ≤  π π − − ≤ ≤ π  ∏ =  π − π ≤ ≤   π π  − + − ≤ ≤ π  ∏ (3) the phase-wise bemf and the electric torque generated are given by: ( ) 2 e m e k e fω θ= (4a) 2 2 ( ) ( ) ( ) 2 3 3 t e e a e b e c k t f i f i f iθ θ θ π π  = + − + +    (4b) b. d-q modeling of the motor the control aspect abc frame of reference is not suitable, as in the abc frame of reference, the motor voltage and current are oscillatory, even under constant speed and load. this makes it unsuitable to use in control law formulation. in the d-q frame of reference, the voltage and currents are constant for constant speed and torque. therefore, using clerk and park transformation, the abc frame of reference will be converted into the d-q frame of reference. in the d-q domain the equations become: d d d r q d di v ri l li e dt ω= + + + (5a) q q q r d q di v ri l li e dt ω= + + + (5b) where d e , q e are the bemf functions of the electrical angle theta generated from the (4a). c. vehicle model all the effective forces are taken into account. figure 1 represents the schematic of these forces [20], which are: the aerodynamic drag ( � ), the acceleration resistance ( � ), the rolling resistance ( � ), and the uphill resistance ( ). the tractive force ( � ) required to drive the car is cumulative of all the above-mentioned forces [20]. it is represented as: t r w g a f f f f f= + + + (6) substituting the respective equations for all forces we have: 21 cos( ) sin( ) 2 s t rr f d s dv f mg mg a c v m dt µ θ θ ρ λ= + + + (7) where λ is the rotational inertia constant and �� is the vehicle velocity (m/sec). the details of the other variables are given in table ii. the total tractive force � is nothing but the mechanical load on the motor in the form of linear force (n). the load torque applied to the bldc motor is: w l t r t f g = (8) where �� is vehicle's wheel radius (m) and g is the gear ratio. fig. 1. schematic of the vehicle showing the tractive forces acting on it. the ev and bldc motors are coupled, this modifies the torque equation (2), which becomes [21]: 2 ( ( ) ) ( ) w m w e f m r w g r d r t k j m f f f g dt g ω ω= + + + + + (9) d. motor sizing and driving cycle the vehicle requirements specified in table i were considered to obtain the motor torque requirement. the vehicle parameters given in table ii are taken from [20]. engineering, technology & applied science research vol. 12, no. 4, 2022, 8901-8909 8903 www.etasr.com ubare & sonawane: performance assessment of the bldc motor in ev drives using nonlinear model … table i. three wheeler ev operating parameters parameter value unit maximum speed 50 km/h maximum acceleration 2 m/s 2 maximum grading 10 % using the vehicle model from section ii, we can get the different characteristic curves of the vehicle, by substituting the values for acceleration, speed, grading (road angle), etc. the speed-torque characteristic specified vehicle is generated and presented in figure 3. t1 is the minimum torque required to maintain the respective speed, t2 is the minimum torque required to get an acceleration of 2m/s 2 for the respective speed, t3 is the minimum torque required to maintain the respective speed under 10% grading, and p1, p2, p3, p4 are constant power profiles of 1, 2, 3, and 4kw respectively. out of these lines, the 3kw line fulfills the requirement with maximum speed of 60kmph and can maintain constant speed of 26kmph on maximum grading of 10%. therefore, the 3kw motor is appropriate for the three-wheeler ev. its specifications are given in table ii [21]. table ii. ev specifications [21] parameter notation value unit mass m 600 kg gravitational constant g 9.81 m/s 2 air density ρ 1.225 kg/m 3 drag coefficient cd 0.5 area af 2.09 m 2 rolling resistance coefficient μrr 0.0015 gear ratio g 5 wheel radius rw 0.19 m road angle θ 1 rad taking reference from figure 2, the torque and speed values are noted in table iii. this derives the gear ratio of 10 to match the vehicle and motor's torque and speed. fig. 2. vehicle torque-speed characteristic curves. (a) vehicle characteristics with constant power profiles and constant acceleration lines, (b) minimum torque required for the desired speed with the 3kw powered vehicle. table iii. gear ratio design based on vehicle requirements and motor specifications object torque (nm) speed (r/s) vehicle (maximum required) 378 81 motor (rated) 80 367 gear ratio 1:5 figure 3(b) shows the minimum requirements of speed and torque to match the vehicle requirements. the speed-torque curve of the controller should be above the shown curve in figure 3(b). iii. control techniques this section presents the design and implementation of 4 control techniques (dtc, foc, hybrid, and nmpc) under consideration for the assessment of bldc motor with ev as the load. a. field oriented control the fundamental idea behind the foc technique is making torque and flux components distinct and then control them independently. the block diagram of foc for the bldc motor control is shown in figure 3. fig. 3. block diagram of the bldc motor control in foc technique. even though this method efficiently controls the machine, it is a parameter-dependent method, for example, the stator or rotor resistances are affected by temperature. therefore, the foc is not robust to parameter variations. b. direct torque control dtc allows direct controls of the electromagnetic torque and stator flux through a suitable combination of control signals applied to inverter switches. as it directly controls the inverter switches, it is a simpler, but non-linear control structure with reduces computational complexity. fig. 4. block diagram of the bldc motor control using dtc. engineering, technology & applied science research vol. 12, no. 4, 2022, 8901-8909 8904 www.etasr.com ubare & sonawane: performance assessment of the bldc motor in ev drives using nonlinear model … the schematic of dtc is shown in figure 4. dtc has two control loops, (i) the external speed control and (ii) the internal torque and flux hysteresis loop. two independent hysteresis controllers produce torque error and stator flux error, and based on those hysteresis controllers’ output and stator flux angle, optimum switching logic selects one of the six voltage vectors and two zero voltage vectors from switching table. c. hybrid controller the principle of the hybrid controller is based on the switching between the two mentioned above techniques. dtc is used in the transient region and foc in the steady-state region. the transient and steady-state regions are identified by calculating the error (e) between the current speed and the reference value of the speed (e = �� �). the control action of the hybrid controller is obtained as follows: , if , otherwise dtc e u foc ε≤ =   (12) where ε is the threshold valued of speed error to switch between transient and steady-state regions. here, we consider ε=0.1. fig. 5. block diagram of bldc motor control using the hybrid technique. the schematic of the hybrid controller is shown in figure 5. the controller selection block selects the foc and dtc with e value, and finally, the control signal, u is applied to the inverter. d. non-linear model predictive controller it is an optimal control method, where the control actions are obtained by solving a constraint finite-time optimal control (cftoc) (see chapter 1 in [22]). figure 6 shows the idea of using centralized nmpc for the speed control of the bldc motor. the nmpc algorithm is comprised of the nonlinear prediction model, integrator, userdefined constraints, and cost function, and a non-linear programming (nlp) solver to solve the constructed optimization control problem (ocp). we used a zero-order hold sampling for discretization and the runge kutta 4th order method for the approximation of the nonlinear function. the nmpc as a direct solution of the cftoc problem for the reference track is represented as follows: 2 , , 2 2 1 , (|| || min || || || || ) r n m k m k q u k k r d k p u i ω ω = − + ∆ +  (13a) subject to: ( , ), 1,....... sk t k k x f x u k n + = = (13b) , ( , ), 1,....... m k k k g x u k nω = = (13c) 1 , 1,.........., k k k u u u k n − ∆ = − = (13d) 48 48, 1,.........., k u k n− ≤ ≤ = (13e) 1 ( ), 1,.........., s u u t t k n − = − = (13f) 0 ( ), 1,..........,x x t k n= = (13g) where, x ϵ �� , ��,�ϵ � �� , and u ϵ ��� are the vectors of state, output, and input respectively. � � � is the reference trajectory of speed reference and �� is the output or the measured speed. the function f in (13b) describes the nonlinear dynamics of the combined bldc motor as given by (9), g in (13d) is the speed measurement function. fig. 6. block diagram of the bldc motor control using nmpc. iv. results and discussion in this section, the controllers are tested for step-change response and edc profile. moreover, we present the numerical analysis of control techniques based on several key performance indices (kpis) and energy consumption. the current and voltage of phase c are shown as representatives, as all phases are having the same trend with a phase shift of 120°. a. speed torque characterisitc speed torque characteristic gives information about the maximum possible torque delivered by a controller at each speed value. as per (4b), it is the product of bemf and current, hence different current control techniques produce different torques and different speed-torque characteristics. it must be noted that the torque and speed plotted in the characteristic plot of figure 7 are measured at the shaft of the motor. along with controller’s characteristics, figure 7 also contains three reference profiles, which are designed as per the requirements from table i, named as constant acceleration engineering, technology & applied science research vol. 12, no. 4, 2022, 8901-8909 8905 www.etasr.com ubare & sonawane: performance assessment of the bldc motor in ev drives using nonlinear model … (t1), constant energy (p4), and zero acceleration (t3) torque profiles. the t1 torque profile is nothing but the torque required to maintain an acceleration of 2m/s 2 at each speed value, the p4 torque profile indicates the torque at each speed value for constant energy of 3kw, and t3 torque profile indicates the torque required to cruise the vehicle at a constant speed. fig. 7. controller's speed-torque characteristics against minimum speedtorque characteristics required for the considered ev. in the case of the hybrid controller, the maximum torque delivered for the respective speed is decided by dtc. therefore, the torque-speed characteristic curve of dtc and hybrid is the same. if we observe figure 7 closely, all controllers except foc are above reference lines t2 and p4. therefore, dtc, hybrid, and nmpc guarantee the fulfillment of performance specifications. due to this, foc delivers less torque than the required and makes it sluggish. even though foc does not provide sufficient acceleration, it can maintain the current speed because its generated torque is greater than t3. this is the reason why the hybrid controller switches to foc in steady-state. to get more insight into the above discussion, we will further analyze the step and edc speed profile responses. b. step response all controllers are tested considering the reference step input of 15kmph and speed, torque, current, and voltage of each one were monitored. 1) field oriented control figure 8 shows the performance of the foc in tracking the desired speed. figure 8(a) depicts the speed response, figure 8(b) the generated torque, figure 8(c) the sinusoidal current excitation required to achieve the desired speed, and figure 8(d) shows the input voltage applied by the foc controller. the foc achieves reference speed after 9.7s. this sluggish response is acquired because the generated torque is smaller than the required value. 2) direct torque control figure 9 shows the performance of dtc for step response. the dtc technique tracks the reference speed sooner than foc at the cost of higher current and torque ripples. due to the higher current, dtc consumes more energy. fig. 8. foc control with step change in reference input for bldc motor control with ev load: (a) speed, (b) torque, (c) current, and (d) voltage. fig. 9. dtc control with step change in reference input for bldc motor control with ev load: (a) speed, (b) torque, (c) current, and (d) voltage. 3) hybrid control figure 10 shows the step response of the hybrid control technique. the hybrid controller exhibits the combined effect of foc and dtc with fast reference tracking like dtc (figure 10(a)), reduced torque ripples (figure 1(b)) due to the foc, and reduced current and energy consumption due to the foc (figure 10(c)). figure 10(a) also shows the controller selection mode, with zero as dtc during transients’ region and 5 for foc in steady state region. engineering, technology & applied science research vol. 12, no. 4, 2022, 8901-8909 8906 www.etasr.com ubare & sonawane: performance assessment of the bldc motor in ev drives using nonlinear model … fig. 10. hybrid control with step change in reference input for bldc motor control with ev load: (a) speed, (b) torque, (c) current, and (d) voltage. fig. 11. nmpc control with step change in reference input for bldc motor control with ev load: (a) speed, (b) torque, (c) current, and (d) voltage. 4) nonlinear mpc figure 11 shows the step response of the nmpc technique. it can be seen that the nmpc achieves the desired speed much faster than other controllers (figure 11(a)). but this faster response comes at the cost of more torque ripples and higher current and energy consumption during transients (figure 11(b)-(d)). in steady-state, torque ripples, current, and voltage consumption are comparatively less. one more interesting observation is that as the motors speed approaches the setpoint, the ripples are reducing. table iv. kpis of the control techniques for step kpis in reference output kpi foc dtc hybrid nmpc transient time 11.25 1.41 1.41 1.25 rmse (%) 100 2.02 12.34 0.10 me (%) 100 1.55 12.31 0.08 iae (%) 100 2.01 12.34 0.10 ise (%) 100 0.04 1.52 0.0001 isce (%) 99.82 99.54 100 99.0 5) result comparison table vi gives the summary of all the kpis for the controllers and their performance regarding step response. from table vi, it can be seen that the nmpc technique outperforms the other techniques, because the other techniques (dtc, foc, and hybrid) are based on a fixed or finite combination of current excitation, whereas nmpc does optimal modulation in the current excitation. this optimal modulation in the current reflects on the total harmonic distortion (thd) of the in-phase current. in the trapezoidal control (dtc), the thd is around 8%, in foc it is 3% and for nmpc, as the optimal excitation varies, the thd varies between 4% and 7%. these ripples are required by considering the non-sinusoidal bemf of the motor. in case of a sudden change in the set-point, the controller has to drive the motor with maximum torque, so nmpc tries to deliver maximum current without much caring about torque ripples, but as the motor approaches the set-point, the current approaches the minimum value with minimum ripples in current and torque. c. ramp response the hybrid controller selects either foc or dtc based on the error threshold, but during the ramp type speed reference, if the controller selects the dtc, then the response cannot be energy efficient and if foc is selected, then the controller cannot track the reference speed. in this view, a hybrid controller either toggles the two sub-controllers or selects only dtc without much caring about energy efficiency. this problem occurs only in the case of the hybrid controller. therefore, in this section, this problem is addressed and the outcome is compared with nmpc. 1) hybrid to get efficient operation if the controller follows the toggling case, the results will be as shown in figure 12. due to the continuous switching between dtc and foc there are ripples in speed and eventually this is reflected on voltage and current. this frequent switching can be avoided by using a hysteresis controller for dtc/foc selection, but this controller will be either overexcited (dtc) or sluggish (foc). 2) nmpc figure 13 depicts the nmpc response for ramp type speed reference. the nmpc shows better tracking with minimum error. this is due to the modulation in current excitation as per engineering, technology & applied science research vol. 12, no. 4, 2022, 8901-8909 8907 www.etasr.com ubare & sonawane: performance assessment of the bldc motor in ev drives using nonlinear model … the operating conditions. this modulation in current excitation helps making a smooth transition from transient region to steady-state region, with the desired performance. fig. 12. enhanced view of motor speed tracking in ramp type reference. fig. 13. ramp response of the nmpc for speed control of a bldc driven ev. d. european driving cycle the hybrid controller combines the advantages of dtc and foc. therefore, in this section, we test the performance of hybrid control and nmpc techniques in real-life scenarios, which can be tested through the edc. both the controllers are tested for speed tracking as per torque given through edc. figure 14 depicts the response of both techniques. figure 14(a) shows the speed and figure 14(b) shows the desired and achieved torque. it can be seen that both controllers perform well regarding the tracking of the desired speed. however, the hybrid controller shows higher torque ripples and overexcitation of the motor with high oscillation in the current due to the higher voltage input during the dtc selection. as a consequence, the hybrid controller consumes more energy. similar inference is generated by the different kpi’s in table v. table v. kpis of the control techniques for edc kpi foc dtc hybrid nmpc rmse (%) 100 4.38 0.29 0.02 me (%) 100 3.46 0.29 0.026 iae (%) 100 5.43 0.74 0.022 ise (%) 100 0.192 0.025 0.0001 isce (%) 99.001 100 99.019 99.008 energy (%) 53 100 50 47 according to table v, foc does not perform well. it shows higher rmse and generates less torque. foc can't compete, even in minimum energy consumption. also, it is worth noting that the hybrid controller shows better rmse and iae, but consumes more energy. overall, the proposed nmpc controller works smoothly and outperforms the other techniques. in summary, the drawbacks of the dtc and foc techniques are removed by the hybrid controller by selecting dtc and foc as per requirements based on the speed error value. however, due to the sudden switching between dtc and foc, a smooth transition is not possible for variable reference. this smooth transition requires an optimum modulation of excitation current waveform, which can produce the best solution to avoid over-excitation and torque ripples, and this has been achieved with the nmpc controller. fig. 14. hybrid and nmpc controllers response over the european driving cycle profile: (a) speed and (b) torque. fig. 15. current response of hybrid and nmpc controllers over the edc profile: (a) phase a, (b) phase b, and (c) phase c. engineering, technology & applied science research vol. 12, no. 4, 2022, 8901-8909 8908 www.etasr.com ubare & sonawane: performance assessment of the bldc motor in ev drives using nonlinear model … v. implementation aspects in real life, we need to implement motor control techniques on portable and resource-limited hardware like microcontrollers and/or fpga. below, we will discuss the implementation aspects of the nmpc technique. • prediction model: the success of nmpc depends on the accuracy of the system model. therefore, it is important to have an accurate model of the motor to capture nonlinear dynamic behavior. • embedded implementation: in recent years, there have been several works on the embedded implementation of nmpc solvers, which allow deploying the whole algorithm on embedded devices [22, 24]. • controller complexity: due to the optimization, nmpc is a complex controller, and its complexity increases with the problem size (number of states, inputs, constraints, and prediction horizon). several approaches have been presented to design low-complexity nmpc [22, 24]. • state and disturbance estimation: as an nmpc is a statefeedback control technique, it is important to obtain accurate values of the states. furthermore, estimation methods can be used to estimate model parameters. vi. conclusion in this paper, we showed the applicability of a nonlinear mpc to control the bldc motor for a three-wheeler ev. the proposed nmpc technique improves the closed-loop control performance, reduces energy consumption and steady-state errors. the nmpc is designed with a nonlinear model of the bldc motor with an electric three-wheeler load to obtain the optimal voltage for the regulation of motor torque. another significant contribution of this paper is the performance assessment of the four considered control techniques. the proposed nmpc 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[24] v. patne, d. ingole, and d. sonawane, "fpga implementation framework for low latency nonlinear model predictive control," ifac-papersonline, vol. 53, no. 2, pp. 7020–7025, jan. 2020, https://doi.org/10.1016/j.ifacol.2020.12.443. microsoft word etasr_v13_n3_pp10754-10758 engineering, technology & applied science research vol. 13, no. 3, 2023, 10754-10758 10754 www.etasr.com zenati et al.: wastewater assessment and biochemical oxygen demand value prediction from mining … wastewater assessment and biochemical oxygen demand value prediction from mining operations: a case study fella zenati environmental laboratory, mining institute, echahid chikh larbi tebessi university, algeria fella.zenati@univ-tebessa.dz adel djellali environmental laboratory, mining institute, echahid chikh larbi tebessi university, algeria adel.djellali@univ-tebessa.dz (corresponding author) debojit sarker department of civil engineering, texas state university, usa dsarker@txstate.edu received: 27 january 2023 | revised: 1 april 2023 | accepted: 4 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5721 abstract wastewater is a byproduct of industrial or household waste processes, and its contamination level must be determined before treatment. discharges of liquid effluents generated by mining operations, one of the most prevalent forms of industrial waste water, pose a risk to human health and the environment. this study evaluates the physicochemical quality of industrial liquid effluent discharges from the boukhadra mine (algeria). samples were collected from the washing water to identify the level of contamination of these liquid discharges and to measure physicochemical parameters such as temperature (t), hydrogen potential (ph), electrical conductivity (ec), suspended solids (ss), chemical oxygen demand (cod), biological oxygen demand for 5 days (bod5), oils and greases (o&g), iron (fe +2 ) and kjeldahl nitrogen (ntk). it was found that the concentration values of those effluents exceeded the maximum contamination limits specified by international industrial waste standards. a simple and reliable prediction model was developed to estimate dbo5, based on mes, cod, and o&g, by using classical regression analysis and fitting design of experiments (doe) methodology. when comparing the analytical results, it was found that the quadratic model provided a better estimation, with a high correlation coefficient (r 2 ) of 0.9976. the parameters determined in this study will enable engineers to quickly estimate the degree of wastewater contamination and choose adequate treatment strategies. keywords-characterization; wastewater; bod5; design of experiments (doe); environment; anova i. introduction water pollution has become a global problem that requires a sustained effort to mitigate it, as the increasing demand for agricultural and industrial products is responsible for it [1]. the increase in solid and liquid waste is directly related to the economic development of many countries, and in fact, the latter leads to detrimental impacts on the environment, the mismanagement of industrial sites, in particular, has consequences on public health and environmental problems [2]. industry discharge wastewater containing organic matter, salts, hydrocarbons, heavy metals, biocides, micropollutants, and various chemicals, often causes permanent environmental damage [3]. the impact of these industrial effluents on the environment is a reality, and they significantly contribute to the degradation of the quality of surface and ground water, therefore, for public health reasons, these materials must be treated before being released directly into streams or lakes [4]. numerous studies have been conducted on the characterization, evaluation, and treatment of hazardous substances in textilerelated effluents [5], sludge [6], sewage sludge [7], paper waste [8], petroleum wastewater [9] and aerobic oil and greasedegrading bacteria in wastewater [10]. additionally, studies on wastewater produced by mining operations have been conducted in cases of coal mines [11], gold mines [12], marble mines [13], and iron mines [14]. those researchers have attempted to remove inorganic pollutants, recycle trash, segregate materials, and indirectly evaluate hazardous substances present in wastewater to treat them better. among the industrial activities, the algerian mining sector, which has experienced exponential economic growth, has raised many engineering, technology & applied science research vol. 13, no. 3, 2023, 10754-10758 10755 www.etasr.com zenati et al.: wastewater assessment and biochemical oxygen demand value prediction from mining … environmental issues relating to its activity [15-17]. therefore, adopting feasible environmental assessment methods is desirable. as a case study, the boukhadra iron mine in tebessa province in algeria, is one of the largest operational iron mines in the country. the annual production of iron ore is 5 million tons, with approximately 50 thousand m 3 of wastewater generated each month by washing machinery production equipment. the mine represents a critical contamination point, as all fluid discharges are discharged into the washing plant and contain significant contaminants, and the mine does not include wastewater treatment plants (wwtps). the installation is old, as the washing pit was constructed before 1926, and since the opening of the mine, it has not been connected to the sewage network even though it is present, but in a neglected state (soak pit). these liquid ejections are directly discharged into nature and cause considerable damage. the environmental impact of these industrial effluents causes severe threats to public health. the effluents must be studied and treated before discharging. recent investigations have focused on the development of numerical models using machine learning techniques for estimating the biological oxygen demand for 5 days (bod5) of wastewater [18, 19], but those models are complicated and difficult to use. however, none of the previous studies have used the design of experiments (doe) technique to produce an adequate model for predicting the parameters of wastewater. the advantage of doe technique is that it allows the variation of different factors simultaneously to screen the reaction space for optimum values. in this study, the physicochemical quality of industrial liquid effluents was evaluated to detect the level of contamination. classical regression analysis (cra) and (dao) techniques with linear, 2fi, and quadratic models were employed to quickly estimate bod5 and to reveal its experiential relationship with liquid effluent discharge parameters. the experiential relationship of bod5 with wastewater parameters was identified and the performance of the resulting model was assessed. ii. general setting and available data the study area is located in the eastern part of tebessa city, algeria (figure 1). the iron mine is located between longitudes 8°01'30" to 8°03'18" and latitudes 35°45'54" to 35°44'42", covering an approximate area of 3.7km 2 . the mine was discovered in 1903 and produces iron ore since 1926, with exploitable reserves exceeding 50 million tons. the boukhadra iron deposit consists mainly of hematite and is one of the largest in the algerian-tunisia border region. [20]. there is a washing station which is used to wash equipment and drain oil from construction machinery. the waste wastewater from this wash station exceeds 10 thousand m 3 daily. the liquid discharge contains significant polluting substances, and the mine does not include wwtps. also, it is not connected to the sewage, and the liquid ejections are directly discharged to the nature causing considerable environmental damage. the environmental impact of these industrial effluents causes serious threats to the quality of surface water, groundwater, and public health, while the boukhadra town is located at the vicinity of the mine. fig. 1. location of the study area. © google earth, gebco landsat, copernicus ibcao. iii. materials and methods to evaluate the physicochemical quality of liquid discharges, samples were collected from the washing pit located in boukhadra mine. temperature (t), ph, electrical conductivity (ec), suspended solids (ss), chemical oxygen demand (cod), bod5, oils and greases (o&g), iron (fe +2 ), and kjeldahl nitrogen (ntk) were measured to determine the level of contamination. twenty five samples were collected from 2016 to 2021, 1 every 3 months. the samples were taken from the equipment and production machinery washing station (final discharge) with a stainless steel bucket of 1.5l, attached to large polyethylene terephthalate (pet) bottles. bottles were filled after 2 to 3 rinses with the same sample. to ensure the traceability of the sample, a tag was associated with each sample (date, location, and gps coordinates), and the samples were hermetically sealed and conserved [21]. the samples were transported to the laboratory in an icebox at 4°c and were stored for 48h before being analyzed. the statistical analysis results of the physical and chemical parameters of the industrial wastewater discharge from boukhadra mine are shown in table i, where, the mean value (xmean), standard deviation (), variance ( 2 ), maximum value (xmax), and minimum value (xmin) are presented. the statistical variation intervals are performed for each parameter, checking for measurement errors and values outside logical bounds. table i. basic statistics of boukhadra mines wastewater xmean   2 xmax xmin t (°c) 19.852 3.980 15.842 26 9.1 ph 8.051 0.359 0.129 8.67 7.31 ce (µs/cm) 2580.92 2172.42 4719414 7830 840 cod (mg/l ) 134.36 18.609 346.323 163 95 ss (mg/l ) 106.52 18.888 356.76 136 67 ntk (mg/l ) 0.884 0.550 0.303 2.1 0.4 fe +2 (mg/l ) 1.812 0.502 0.252 2.6 0.4 o&g (mg/l ) 98.88 21.044 442.86 133 60 bod5 (mg/l ) 45.64 18.843 355.073 74 5 cod/bod5 (mg/l) 3.930 3.40 11.599 19 2.202 engineering, technology & applied science research vol. 13, no. 3, 2023, 10754-10758 10756 www.etasr.com zenati et al.: wastewater assessment and biochemical oxygen demand value prediction from mining … iv. results and discussion a. wastewater assessment most of the measured values do not meet the international discharge of industrial wastewater standards. temperature is an essential factor in biological activity. referring to the standard limits, it can be noted that the measured temperatures were below 30°c (figure 2(a)), which is considered the standard for algerian industrial waste [22]. the ph is also one of the most significant parameters affecting the biological activity of the microorganisms in the water, whose majority grows in the range of 4.5-8 [23]. the average ph values of the wastewater ranged between 7.31 and 8.67, slightly exceeding the standard value (figure 2(b)). high cod [24] values were found, as indicated in figure 2(c). most values were above the standard limit of 120mg/l [25] for industrial waste. they ranged from 95 to 163mg/l, indicating the presence of biodegradable load [26]. these values would be related to the presence of large amounts of machine oil and ss due to the washing of mine equipment. the calculated results of ss show that it exceeds the threshold of acceptable values (20mg/l), with the highest value found in the wash station (136mg/l) due to the presence of heavy oils of large molecular mass (figure 2(d)). ntk and fe +2 comply with the standards (figure 2(e)-(f)), while the average concentration of o&g (98.88mg/l) is very high and exceeds the limit value of 20mg/l (figure 2(g)). this high quantity could lead to severe environmental pollution. the bod5 values (mg/l) at 20°c in the dark were between 5 and 74mg/l, with the most values exceeding the allowable standard industrial waste limit of 35mg/l. those values could be explained by the fact that the wastewater is highly loaded with oils, which create inhibited microbial activity similar to that found in anaerobic conditions. the cod/bod5 ratio gives a first estimate of the biodegradability of the organic matter of an effluent. an increase in this ratio indicates a rise in nonbiodegradable organic materials [27]. the test results showed that the cod/bod ratio ranged from 2.20 to 19, with an average value of 3.93. (a) (b) (c) (d) (e) (f) (g) (i) fig. 2. evaluation of physicochemical parameters of effluent discharges. engineering, technology & applied science research vol. 13, no. 3, 2023, 10754-10758 10757 www.etasr.com zenati et al.: wastewater assessment and biochemical oxygen demand value prediction from mining … b. anova study the developed model was performed using doe, designexpert version 10. the input data were the values of cod, ss, and o&g. the statistical analysis included the analysis of variance (anova), which is used to obtain suitable models and suitability studies. the anova table of the effluent discharges, with linear, 2fi, and quadratic models, was employed to ensure the most appropriate model. the comparison between the influence of the main factors and their interactions can be carried out using the f-value of each factor. the presented results for the quadratic model confirm that the cod and ss and og are significant at ≤5% (probability level), but this is not true for linear and 2fi models. table ii shows that the f-values of cod, ss, and og are 3779.12, 3327.85, and 1656.90, respectively. therefore, it is clear that in the proposed model, the influence of cod is more considerable than the weight fraction. therefore, it can be said that the quadratic model is the most expressive and the changes in bod5 can be accurately estimated using the proposed model. the proposed quadratic model for estimating bod5 related to cod, ss, and o&g is defined as: bod5 = −47.41946 − 1.20218 × cod + 1.29202 × ss+0.917706 × og − 0.023951 × cod × ss − 0.027619 × cod × og + 0.025533 × cod² + 0.001488 × ss² + 0.002399 × og² (1) the model incorporates all the necessary main factors and their interactions. table ii. anova results for wastewater with the quadratic model source sum of squares mean square (ms) f-value p-value model 8521.74 946.86 8.654e+05 < 0.0001 a-cod 4.14 4.14 3779.12 < 0.0001 b-ss 3.64 3.64 3327.85 < 0.0001 c-og 1.81 1.81 1656.90 < 0.0001 ab 1.81 1.81 1654.43 < 0.0001 ac 11.43 11.43 10450.61 < 0.0001 bc 3.93 3.93 3591.32 < 0.0001 a² 5.36 5.36 4901.37 < 0.0001 b² 0.6547 0.6547 598.38 < 0.0001 c² 0.1202 0.1202 109.82 < 0.0001 residual 0.0164 0.0011 total 8521.76 it can be seen from figure 3 that the residual sum of squares (rss) for the quadratic model is very small (0.0164). it was also observed, that the coefficient of variation (cv) had a small value (0.0725), indicating that the proposed model provides the best reliable measurement. cv is less than 5% is deemed acceptable [28]. therefore, it is clear that in the proposed model, the influence of the cod is more considerable than the weight fraction. c. adequacy of the proposed model one practical and efficient way to test the adequacy of the proposed model is the normal distribution of errors. examining the normal probability of the studentized residuals can confirm the normal distribution of errors [29]. one interesting feature of a proper model is the agreement between the experimental and the predicted values. figure 4 shows the correlation between the actual values obtained during the experiments and the predicted values of the proposed bod5 model. the graph shows that there is a good agreement between the actual and the predicted values. therefore, the proposed model can predict the dbo5 activity in effluents under the experimental conditions. fig. 3. verification results for the responses on bod5. fig. 4. comparison between the predicted and the actual values of dbo5. v. conclusions in this research work, physicochemical characterization of industrial liquid effluent discharges, collected from the washing water from the boukhadra mine (algeria) was conducted. the samples were evaluated, to identify their level of contamination. the analysis showed that the values of cod, ss, bod5, and o&g are very high. their presence indicates strong and unbalanced biological pollution, which could be dangerous to the environment. to control and quick estimate the main effluent parameter, classical regression analysis without measuring bod5 value was conducted by the doe methodology to fit the appropriate model. after simulation, and by the combination of ss, cod, and o&g parameters, the quadratic model was adopted. to control errors and engineering, technology & applied science research vol. 13, no. 3, 2023, 10754-10758 10758 www.etasr.com zenati et al.: wastewater assessment and biochemical oxygen demand value prediction from mining … resemblances according to the experimental values, the ms, rss, and p-values were used to compare the performance of the model with the actual results. the quadratic model provided a high correlation coefficient (r 2 ) of 0.9976. based on the anova results, is clear that the effect of cod is more than that of the weight fraction and the interaction between the other parameters. also, the statistical parameters of the proposed model revealed that this model could predict the dbo5 activity of the samples strictly, 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adnan.novalic@ibu.edu.ba received: 16 june 2022 | revised: 6 july 2022 | accepted: 13 july 2022 abstract-female engineers go through different stages during their professional careers due to natural life processes and factors. in developing countries, it is not rare for managers to avoid hiring female engineers, due to these factors and the conservative belief that construction is a male-dominated industry. in bosnia and herzegovina (b&h) there are a few studies that refer to the motivation in the construction industry, but none that refer to the position of women in the construction industry and their motivation based on the selected demographic factors. this study aims to fill this research gap, utilizing quantitative research methods. the sample included female engineers of different profiles, working in the construction industry, who were required to fulfill the multidimensional work motivation scale (mwms). the five considered demographic factors are age, family status, number of children, education level, and professional experience. the results of this research showed that family status does not affect any motivation dimension, whereas professional experience affects all motivation dimensions except the identified regulations. external–material regulations consist the most influential motivation dimension for female engineers in the construction industry in b&h, whereas amotivation, and introjected regulations were the least. it is recommended for managers and human resources to use the findings of this research in order to keep the female construction engineers motivated and satisfied in their workplace or to know what motivation dimensions to use during the hiring process. keywords-motivation; female engineers; construction industry; bosnia and herzegovina i. introduction motivation is an important factor, but yet it is a vague concept in work [1]. various profiles of engineers require diverse motivation systems, but there is not a standard motivation model that could be used for all engineers. the reason for that is that the profiles of engineers change over time, due to the nature of human life. in bosnia and herzegovina (b&h) only a few studies refer to the motivation in the construction industry [2]. to the best of our knowledge, there is no study that refers to the motivation of women in the construction industry, based on specific demographic factors. that is why this study will fill that research gap and aims to find out what motivates female construction engineers in b&h. a relevant study that was conducted in nigeria resulted that financial reward is mostly used to motivate supervisors, whereas contractors prefer nonfinancial incentives. an important result is that in nigeria construction industry, motivation of workers is not related to their needs [3]. the motivational factor that has the largest influence on female engineers is good work discipline, whereas the leading factor for motivation of male engineers is company name and stability [4]. authors in [5] discovered 5 key motivational factors: achievement, proper recognition and awards, interesting work, involvement in decision making, and adequate training and development. during the last 50 years, the productivity in construction has remained low and when compared to other industries it can be said that the construction industry has fallen behind [6]. the top five most frequent problems that women in construction encounter are [7]: • slow advancement in career that leads to disappointment with the industry and construction culture. • difficulties with work–family balance. • attitude barriers that were the result of the male workers’ domination in the construction industry. • "job hopping" to overcome barriers caused by slow progress and inflexible work structure. • the culture because it consists of disputes, aggression and large percentage of men. corresponding author: ahmed el sayed engineering, technology & applied science research vol. 12, no. 5, 2022, 9372-9378 9373 www.etasr.com hodzic et al.: motivation of female engineers in the construction industry in bosnia and herzegovina still, the main reason why women are withdrawing from the construction industry and why women are not looking at it as viable career is culture. the potential solution for this, offered by some papers, is that the substantial change in the culture of the construction industry and its first impression will be needed in order to bring and keep large number of women at all levels [7]. a. female engineers in the construction industry when the construction industry exhibited the greatest degree of vertical segregation by sex, women were less than 1% of the employed in construction trades in uk [8]. construction’s negative public image is that it is dirty and dangerous which results in a decrease of women’s participation [9]. it is interesting to mention that previously conducted studies on women’s construction careers did not reflect the nature of women’s careers and why women encounter barriers more often and advance more slowly than their male coworkers [10]. a lawsuit was filed against the usa department of labor for its failure to fulfill its duties that prohibit discrimination in employment decisions on the basis of race, religion, gender, or national origin for federal construction contractors and subcontractors who do over $10,000 in government business in one year. this action resulted in the establishment of regulations that were issued to integrate women into the construction industry by requiring specific steps [11]. three out of five women that were interviewed in [12] stated that they had experienced harassment on the construction site, such as whistling, cat calls, a constant feeling to prove oneself, and so on. career frustration and increased intentions to leave the industry are some of the factors that have been connected to the lower number of entries of female engineers in the construction industry [13]. it is important for construction managers to understand that what motivates male engineers, does not have to apply for female engineers. women have different perceptions and priorities than male engineers, which results in different ways of motivation [14]. promotion of stem (science, technology, engineering, and mathematics) careers is more common these days than it was in the past. but there are not so many opportunities to bring in and explain construction management to new generations. so again, girls are deprived because chances are quite low for them to have some practical experience with construction or buildings design in comparison to the boys [15]. the main focus on how to transform the construction industry is through building relationships between the industry itself and universities [16, 17]. in the education process, ways to motivate workers should also be included because having qualified manpower is very important for the achievement of quality [18]. effective construction project management is crucial in order to have good performance [19]. employers could support female engineers in construction management by making the environment more respectful for them. it is concluded that it is imperative for the management to support women, create respectful environment with zero tolerance for harassment and try to provide them quality training opportunities in order for them to grow and develop their professional career [12]. b. maslow’s theory motivation gives a goal that a person seeks to achieve. every person has that need and if that need is withheld it will have a mobilizing effect, and if satisfied, a new goal of satisfying a new need on the hierarchy will be set [20]. two main conclusions that can be derived from maslow's need hierarchy are [21]: • satisfaction of one need does not serve as motivator. • when needs on the lower part of the hierarchy become satisfied, then the next needs on the hierarchy determine the person’s behavior. authors in [22] used motivation factors from maslow’s theory in the construction industry. it can be said that motivation is a main reason for the increased productivity of workers. it consists of powers and mechanisms that serve to direct a person’s behavior in a desired way. this means that all the activities in the purpose of convincing and encouraging workers are the reasons they do their tasks willingly. c. the effect of demographic factors on motivation the relationship between motivation factors and gender in the case of engineers in the construction industry was tested in [14]. the results of that research showed no difference in the factors that motivate and demotivate them. it was also concluded that different things attract males and females to the workplace. the findings of [23] state that the age has very low level of influence on motivation, while education level has a large impact on achieving organizational goals. the professional qualification does have an influence on motivation, even when in relation with professional experience. additionally, the overall motivation is not statistically impacted by the relationship between the age of the workers and the years they spent in a company. it is important to add that safety is the only motivational factor that depends on the age of the respondents because employees with different professional experiences do not have similar attitudes towards safety [23]. factors such as the working hours, recognition received for a job well done, and colleague relationships play a major role in motivating engineers [24]. d. literature review summary the summarized findings of the literature review are: • the motivational factor that has the most influence on female engineers is the good discipline at work. • it is imperative for the management to support women in construction industry by: 1. creating respectful environment with zero tolerance for harassment (solving the "being ignored at meetings" issue). 2. providing quality training opportunities for continued professional development. • professional qualification has an influence on motivation, but none when in relation with professional experience. • safety is the only motivational factor that depends on the age of employees. engineering, technology & applied science research vol. 12, no. 5, 2022, 9372-9378 9374 www.etasr.com hodzic et al.: motivation of female engineers in the construction industry in bosnia and herzegovina ii. research methodology the target population for this study consists of female engineers in bosnia and herzegovina that work or are educated in construction related fields. they have to have at least a bachelor’s degree in construction related fields such as architecture, civil, mechanical, or electrical engineering. no other minimal requirements were taken into consideration. sampling included all kinds of construction companies, architecture studios, schools, universities, and all other job positions where female construction engineers work. snowballing technique was used. no names will be mentioned for confidentiality reasons. data collection started on 18th of december, 2021. the questionnaire consisted of the multidimensional work motivation scale (mwms) with a total of 19 items and 5 demographic factors. the questionnaire was made by using google forms, and all questions were marked as required fields to be answered. questions were answered in a likert scale of 5 points, ranging from 1 for strongly disagree to 5 for strongly agree [25]. the online questionnaire was made in english and bosnian. on the 13th of march, 2022 there were 200 respondents who filled out the questionnaire. the data collection process lasted for 2 months and 26 days. due to the established effect of demographics on the motivation in the literature findings and because women go through different phases in life, from being only a worker to being a worker, wife, and a mother by going through physical and mental changes, the following demographic factors were chosen in order to find solutions to the research problem: age, family status, number of children, educational level, and professional experience. the hypotheses assumed in this study, are: • hypothesis 1 (h1): professional experience, as a demographic factor of female construction engineers in b&h, has a larger effect on intrinsic regulations than on other motivation dimensions. • hypothesis 2 (h2): education level, as a demographic factor of female construction engineers in b&h, has a larger effect on external regulations social than on other motivation dimensions. • hypothesis 3 (h3): family status, as a demographic factor of female construction engineers in b&h, has a larger effect on external regulations material than on other motivation dimensions. • hypothesis 4 (h4): family status in relation with the number of children has a larger effect on identified regulations than on other motivation dimensions. • hypothesis 5 (h5): education level in relation with professional experience has a larger effect on external regulations social than on other motivation dimensions. the research questions of this paper are: 1. the demographic factor amotivation, as a motivation dimension for female engineers in construction industry in b&h, could be used? 2. the demographic factor external regulations social, as motivation dimension for female engineers in construction industry in b&h, could be used? 3. the demographic factor external regulations – material, as motivation dimension for female engineers in construction industry in b&h, could be used? 4. the demographic factor introjected regulations, as motivation dimension for female engineers in construction industry in b&h, could be used? 5. the demographic factor intrinsic regulations, as motivation dimension for female engineers in construction industry in b&h, could be used? 6. which demographic factor is the most common and which is the least common effect on motivation dimensions of mwms scale for female construction engineers in b&h? 7. what motivation dimension is most widely used for motivating female construction engineers in b&h and what the least? in this paper, the motivational dimensions are the dependent variables and the demographic factors the independent variables, meaning that the motivational dimensions used in this research depend on the demographic factors. there are 19 items that are sorted in 6 different dimensions in the mwms [26]: 1. amotivation 2. external material regulations 3. external social regulations 4. introjected regulations 5. identified regulations 6. intrinsic motivation the mwms dimensions and their questions are given below [26]. a. amotivation mwms1: i don't put any effort on the current job, because i really feel that i'm wasting my time at work. mwms2: i do put a little effort on the current job, because i don’t think this work is worth putting efforts into. mwms3: i don't put any effort on the current job, because i don’t know why i’m doing this job, it is a pointless job. b. external regulations social mwms4: i put an effort in the current job to get others’ approval (e.g. supervisor, colleagues, family, clients). mwms5: i put an effort in the current job because others will respect me more. mwms6: i put an effort in the current job to avoid being criticized by others. engineering, technology & applied science research vol. 12, no. 5, 2022, 9372-9378 9375 www.etasr.com hodzic et al.: motivation of female engineers in the construction industry in bosnia and herzegovina c. external regulations material mwms7: i put an effort in the current job because others will reward me financially only if i put enough effort in it (e.g. employer, supervisor). mwms8: i put an effort in the current job because others offer me greater job security if i put enough effort in it. mwms9: i put an effort in the current job because i risk losing my job if i don’t put enough effort in it. d. introjected regulations mwms10: i put an effort in the current job because i have to prove to myself that i can. mwms11: i put an effort in the current job because it makes me feel proud of myself. mwms12: i put an effort in the current job because otherwise i will feel ashamed. mwms13: i put an effort in the current job because otherwise i will feel bad about myself. e. identified regulations mwms14: i put an effort in the current job because i personally consider it important to put efforts in this job. mwms15: i put an effort in the current job because putting efforts in this job aligns with my personal values. mwms16: i put an effort in the current job because putting efforts in this job has personal significance to me. f. intrinsic motivation mwms17: i put an effort in the current job because i have fun while doing it. mwms18: i put an effort in the current job because what i do in my work is exciting. mwms19: i put an effort in the current job because the work i do is interesting iii. results and discussion tests for analyzing the hypotheses will be chosen based on the types of included variables. regression test will be used for the hypotheses where an independent continuous variable affects a dependent continuous variable. when an independent categorical variable affects a multiple dependent continuous variables, the one-way manova (multivariate analysis of variance) will be applied, whereas mancova (multivariate analysis of covariance) will be applied when categorical and continuous variables affect multiple dependent continuous variables. the dependent variables are amotivation, external regulations – social, external regulations – material, introjected regulations, identified regulations, and intrinsic regulations. a total of 200 female engineers filled out the questionnaire. those engineers are architects, civil engineers, electrical engineers and mechanical engineers. the demographic questions were year of birth, family status, number of children, educational level, and professional experience. the range of respondents’ years of birth is 1959-1999. this shows that there is a 40-year difference between the youngest and the oldest female engineer in the construction industry that participated in this research. a. reliability for testing and measuring reliability, cronbach’s alpha coefficient was used. ibm spss statistics software showed the results of the reliability test and the results of exploratory factor analysis (efa). cronbach’s alpha for all dimensions ranges from 0.759-0.922. reliability is good if cronbach’s alpha values are higher than 0.7 [27]. a conclusion can be made that the alpha coefficients are reliable as they are all higher than 0.7 (table i). the minimum accepted loading of efa is 0.4 [28]. the analysis was carried out for all items of 6 the dimensions of mwms. the efa results showed that all correlations (loadings) for the given items regarding all variables in the mwms scale are above the minimum value of 0.4. this shows that the validity of the questionnaire for all variables is satisfactory. table i. calues of cronbach's alpha coefficient and internal consistency [27] cronbach's alpha internal consistency α ≥ 0.90 excellent 0.90 ≥ α ≥ 0.80 good 0.80 ≥ α ≥ 0.70 acceptable 0.70 ≥ α ≥ 0.60 questionable 0.60 ≥ α ≥ 0.50 poor 0.50 < α unacceptable b. testing the hypotheses in statistics, it can be stated that the population mean lies within a 95% confidence interval. this means that as an approximate population number, the mean of the sample size can be used [29]. the following significant terms are used in reporting [29]: • p < 0.05 (significant at 5%) "the difference was significant" • p < 0.01 (significant at 1%) "the difference was highly significant". 1) testing hypothesis 1 professional experience, as a demographic factor of female engineers in b&h construction industry, has a larger effect on intrinsic regulations than on other motivation dimensions. in the case of hypothesis 1, the independent discrete variable is professional experience, whereas motivation dimensions are dependent continuous variables, linear regression was used for testing. the confidence interval is 95%. the significance level or p-value is higher than 0.05 for all factors, except for identified regulation, which is 0.126 which means that professional experience has no significant effect on identified regulations [29]. this leads to the conclusion that the identified regulations should not be used as a motivation dimension regarding the professional experience of female engineers in the construction industry. the value of r-square will tell the strength of correlation. engineering, technology & applied science research vol. 12, no. 5, 2022, 9372-9378 9376 www.etasr.com hodzic et al.: motivation of female engineers in the construction industry in bosnia and herzegovina table ii. correlation of determination [30] r-squared value strength of association r 2 =0 no correlation 0 < r 2 < 0.25 very weak correlation 0.25 ≤ r 2 < 0.50 weak correlation 0.50 ≤ r 2 < 0.75 moderate correlation 0.75 ≤ r 2 < 0.90 strong correlation 0.90 ≤ r 2 < 1 very strong correlation r 2 =1 perfect correlation table iii. hypothesis 1 r square & association strength dependent variables independent variable: professional experience r square adjusted r square strength of association amotivation 0.015 0.010 very weak external regulations-social 0.044 0.040 weak external regulations-material 0.051 0.046 weak introjected regulations 0.020 0.015 very weak intrinsic regulation 0.059 0.054 moderate when comparing the adjusted r square of the dependent variables, it can be said that intrinsic regulations is the most associated with the other motivation dimensions. it has a moderate correlation with the age of female engineers. based on the results in this section, it can be concluded that hypothesis 1 is accepted. 2) testing hypothesis 2 education level, as a demographic factor of female engineers in b&h construction industry, has a larger effect on external regulations social than on other motivation dimensions. education level is, as a family status, a categorical independent variable. the hypothesis of the effect of the independent categorical variable on dependent continuous variable will be tested and one-way manova was used. the results showed that education level, as a demographic factor of female engineers in the construction industry in b&h, affects both external regulations, but does not affect any other motivation dimension. since both external regulations are affected by the education level, then the amount of effect that education level has on them should be measured. table iv. partial eta squared effect size [29] partial eta squared effect size 0.01 small effect 0.06 moderate effect 0.14 large effect table v. partial eta squared – hypothesis 2 dependent variables association strength external regulations-social 0.091 external regulations-material 0.054 the effect of education level on external regulation – material is small, very close to being moderate. on the other side, external regulations – social is moderately affected by the education level, since partial eta squared is larger than 0.06 [29]. from the results and the information presented in this section, it can be stated that hypothesis 2 is accepted. 3) testing hypothesis 3 family status, as a demographic factor of female engineers in b&h construction industry, has a larger effect on external regulations material than on other motivation dimensions. after the conducted manova, the significance level is one of the most important parts of the results. those results are shown in table vi. based on them, it can be seen that family status does not affect any motivation dimension if confidence interval is 95% [29]. then, hypothesis 3 is rejected. table vi. one-way manova results hypothesis 3 dependent variables significance value number of children amotivation 0.110 external regulations-social 0.184 external regulations-material 0.272 introjected regulations 0.850 identified regulations 0.071 intrinsic regulations 0.072 4) testing hypothesis 4 family status in relation with the number of children has a larger effect on identified regulations than on other motivation dimensions. mancova will be used for this hypothesis because independent variables are categorical and continuous and affect multiple dependent continuous variables. table vii shows the mancova results. when the number of children and family status are in relation, they do not have an effect on any motivation dimension [29]. with that result, hypothesis 4 is rejected. table vii. one-way mancova results hypothesis 4 dependent variables significance value family status number of children amotivation 0.333 0.592 external regulations-social 0.488 0.491 external regulations-material 0.393 0.093 introjected regulations 0.817 0.613 identified regulations 0.624 0.076 intrinsic regulations 0.580 0.119 5) testing hypothesis 5 education level in relation with professional experience has a larger effect on external regulations social than on other motivation dimensions. table viii. one-way mancova results hypothesis 5 dependent variables significance value education level professional experience amotivation 0.646 0.295 external regulations-social 0.004 0.318 external regulations-material 0.147 0.076 introjected regulations 0.661 0.215 identified regulations 0.331 0.577 intrinsic regulations 0.840 0.007 the results show that education level in relation with professional experience does not affect external regulations – material as it did on its own. it affects only external regulations – social. professional experience in relation with education engineering, technology & applied science research vol. 12, no. 5, 2022, 9372-9378 9377 www.etasr.com hodzic et al.: motivation of female engineers in the construction industry in bosnia and herzegovina level affects only intrinsic regulations, whereas on its own it affects all regulations except the identified regulations. as mentioned, education level in relation with professional experience affects only external regulations – social [29]. this leads to the conclusion that hypothesis 5 is accepted. 6) research questions amotivation could only be used for female engineers with regard to their professional experience. the findings state that external regulations – social, as motivation dimension, is the most useful for motivating with regard to the education level of female engineers in the construction industry in b&h. external regulations – material is affected by all demographic factors except family status. this means that this motivation dimension could be used for any of these demographic factors. based on the results, introjected regulations could only be used for motivating when it comes to professional experience. for all demographic factors except family status and education level, intrinsic motivation regulations could be used. family status does not affect any motivation dimension, whereas professional experience affects all motivation dimensions except the identified regulations. external – material regulations is the most influential motivation dimension for female engineers in the construction industry in b&h, whereas identified regulations, amotivation, and introjected regulations are used the least. 7) summary this section will show the comparison between the findings of the current research and the literature findings. table ix. results comparison with literature findings research results literature findings external – material regulations have the most impact on motivation dimension for female engineers in construction industry in b&h the motivational factor that has the most influence on female engineers is good discipline at work both external regulations are affected by education level, but when in relation with professional experience it affects only external regulations social professional qualification has an influence on motivation, but none when in relation with professional experience table x shows the status of hypothesis testing and the explanations in case a hypothesis was rejected. table x. hypotheses result summary hypothesis status association h1 accepted moderate association (adjusted r square) h2 accepted moderate association (partial eta squared) h3 rejected family status does not affect any motivation dimension h4 rejected family status and number of children in relation do not affect any motivation dimension h5 accepted decreased association with external regulations – social (from moderate when on its own to weak when in relation). iv. conclusion when education level is used as a demographic factor of female construction engineers in b&h, both external regulations could be used for motivation. intrinsic regulations is the most associated with professional experience than other motivation dimensions, since it has moderate association. family status does not affect any motivation dimension, whereas professional experience affects all motivation dimensions except the identified regulations. external – material regulations is the most influential motivation dimension for female engineers in the construction industry in b&h, whereas identified regulations, amotivation, and introjected regulations are used the least. to the best of our knowledge, there are no studies that refer to the motivation of women in the construction industry in b&h, based on the selected demographic factors. the current study fills that research gap. the results of this research could be used in construction companies in order to motivate their female engineers. regarding the demographic factors used, the motivation dimension for each employee should be found. it would be a duty of management or human resources to update these applications as female engineers go through different stages in their professional careers due to natural life processes and factors and their motivation regulation might 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[30] "interpreting the correlation year 12 mathematical applications." https://sites.google.com/site/year12mathematicalapplications/statisticsand-working-with-data/linear-correlation/interpreting-the-correlation (accessed aug. 26, 2022). microsoft word etasr_v13_n3_pp10785-10790 engineering, technology & applied science research vol. 13, no. 3, 2023, 10785-10790 10785 www.etasr.com mathew & gunasundari: a cluster-based undersampling technique for multiclass skewed datasets a cluster-based undersampling technique for multiclass skewed datasets rose mary mathew department of computer science, karpagam academy of higher education, india rosem.mathew@gmail.com (corresponding author) ranganathan gunasundari department of computer applications, karpagam academy of higher education, india gunasoundar04@gmail.com received: 12 march 2023 | revised: 29 march 2023 and 4 april 2023 | accepted: 8 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5844 abstract imbalanced data classification is a demanding issue in data mining and machine learning. models that learn with imbalanced input generate feeble performance in the minority class. resampling methods can handle this issue and balance the skewed dataset. cluster-based undersampling (cus) and near-miss (nm) techniques are widely used in imbalanced learning. however, these methods suffer from some serious flaws. cus averts the impact of the distance factor on instances over the majority class. near-miss method discards the inter-class data within the majority of class elements. to overcome these flaws, this study has come up with an undersampling technique called adaptive k-means clustering undersampling (akcus). the proposed technique blends the distance factor and clustering over the majority class. the performance of the proposed method was analyzed with the aid of an experimental study. three multiminority datasets with different imbalance ratios were selected and the models were created using knearest neighbor (knn), decision tree (dt), and random forest (rf) classifiers. the experimental results show that akcus can attain better efficacy than the benchmark methods over multiminority datasets with high imbalance ratios. keywords-k-means clustering; multiclass; resampling; skewed; undersampling i. introduction most of the real-world available data, e.g. for medical diagnosis, credit card transactions, fault detection, and activity recognition, are imbalanced. the term imbalance is a reflection of the difference in frequency of data distribution over the various classes in the dataset. the frequency of data present in one class is often higher than the frequency of the other classes. in terms of probability, the prior probabilities of various classes are different. for a binary class imbalanced problem, there is one minority class and one majority class. training a model with this imbalanced data induces a bias towards the majority class. for a multi-class environment, imbalance has a bit different presentation. data imbalance can occur in one of two ways: one majority class with numerous minority classes (multiminority case) and one minority class with numerous majority classes (multimajority case) [1]. three things should be noted while working with imbalanced data. (a) there is a great difference in the frequency of the elements present in majority and minority classes. (b) minority class data have a small probability of occurrence, so it is challenging to obtain new minority instances from the real world. (c) the classification result is much more influenced by the majority class instances, so the classification model is biased towards the majority data [2]. however, the interesting fact is that while the overall accuracy of the model is high, the minority classification is near to zero. this is corrected with the aid of resampling techniques. resampling techniques make the skewed dataset balanced. resampling can be done in the form of oversampling, undersampling, or in hybrid mode. oversampling techniques add new synthetic data to the minority classes for making the dataset balanced. undersampling techniques eliminate data from the majority classes. hybrid techniques are combinations of both to make the dataset balanced [3]. oversampling technique expands the real data with synthetic samples and these synthetic data may overlap with the actual instances of other classes. random oversampling, synthetic minority oversampling technique (smote), and adaptive synthetic (adasyn) are the most popular oversampling techniques. undersampling techniques eliminate data from the majority class and this elimination will sometimes be reflected in the form of prominent data loss [4]. for balancing the skewed data, an appropriate resampling technique can be chosen from the available techniques. the major contribution of this study is the proposal of an undersampling technique for multiminority dataset engineering, technology & applied science research vol. 13, no. 3, 2023, 10785-10790 10786 www.etasr.com mathew & gunasundari: a cluster-based undersampling technique for multiclass skewed datasets classification. the proposed work is implemented with adaptive k-means clustering algorithm [5]. the proposed technique is named adaptive k-means clustering undersampling (akcus). another important factor to be considered is the imbalance ratio of the datasets which is used for model training. another contribution of this work is the reduction of the ratio of skewness among various classes. the effectiveness of the proposed algorithm over 3 multiminority datasets with imbalance ratios of different levels is described. ii. related works several undersampling techniques are proposed in the literature. most of them recognize the less informative occurrences, on account of the redundancy involved. tomek links are pairs of instances which belong to different classes and are mutually nearest neighbors. these tomek links from the dataset were eliminated in [6]. edited nearest-neighbor (enn) rule, removes those data points which belong to different classes from a majority set with k nearest neighbors [7]. condensed nearest neighbor (cnn) is another undersampling technique which chooses a subset from the training set such that each data in the training set and its nearest neighbors in the subset belong to the same class. this technique is slower as it requires multiple passes over the training dataset [8]. near-miss (nm) method performs data undersampling in the majority class [9]. this is done by identifying their distance to every other data in the same class. authors in [10] proposed the underbagging technique, in which in every iteration the dataset is undersampled randomly. sorting of undersampled data depending on the corresponding weighted euclidean distance from the minority data was proposed in [11]. authors in [12] proposed a method which uses a collection of hardness measures for classification and they found that instance hardness is mainly caused by the overlapping of classes. authors in [13] proposed a clusterbased approach of undersampling to balance the dataset and the classification was done with the aid of back propagation neural networks [13]. authors in [14] proposed a hybrid algorithm which combines methods like eus, adaboost, cost sensitive modification, and adaptive boundary decision strategy. eusboost [15] incorporates random undersampling (rus) with boosting algorithm and outperforms the existing proposals with the use of evolutionary undersampling approach. easyensemble [16] is an ensemble of ensembles which trains a classifier for every new bag, and each bag is trained by adaboost. for multiclass skewed distributions, no specific methods are proposed. in this study, a resampling mechanism for multiminority datasets is proposed and its effectiveness is measured. iii. proposed work undersampling is the process of removing excess data from a skewed dataset in order to make it balanced. majority class data are considered for clustering and in this work, adaptive kmeans clustering is done over the majority class. the different clusters are identified, and data elimination was conducted over these clusters. the proposed method can be applied in real world multiminority datasets. in cluster center-based undersampling, the primary stage is to split the skewed binary class dataset into training data and testing data. the training data are arranged based on the majority and minority sets. undersampling is applied in order to eliminate the excess number of elements present in the majority set. in this method, the majority data are portioned into different bags and on each bag rus is performed. each undersampled bag is clubbed with the minority class for training the model. k clusters are formed, this k being the same with the number of elements present in the minority set (k=n). these k clusters are produced over m samples of the majority set. the entire majority set is replaced by cluster centers. the mean of data present in a cluster is treated as the cluster center. the nearest k neighbors of the cluster center are removed in order to obtain a balance among the majority class and the minority class [17]. the proposed adaptive k-means clustering undersampling (akcus) technique uses the adaptive kmeans algorithm. this algorithm calculates the cluster center effectively. the center points for multiclass data clusters can be identified by the algorithm. the majority class data are considered for clustering. this algorithm selects k elements from the set of the majority class. these selected elements are treated as seed. the properties defined by each element define the properties of the corresponding cluster. euclidean distance is used to compute the distance [15]. the distance between each element and a cluster, the distance between two elements, and the distance between two clusters are computed. for two elements, p1 and p2, with n dimensions, the distance can be calculated as:       2 2 2 11 21 12 22 1n 2n p p p pd . p p      (1) where p1= (p11, p12, p13, …. p1n) and p2= (p21, p22, p23, …. p2n). in this algorithm, the distance between the clusters is identified and the value is stored in an array in the form of a triangular matrix. the shortest distance between the clusters dmin is recognized and the nearest clusters are also recognized. cluster formation, corresponding centroid calculations, and farthest data elimination are mentioned in the algorithm: algorithm of the proposed akcus: step 1: get the multiclass imbalanced dataset and identify the majority and minority classes. step 2: compute the mean frequency of the minority class records and let it be stored in a variable called freq. step 3: identify the excess data of the majority class from the freq data and let it be stored in a variable called excess. step 4: take one majority class data for under-sampling. step 5: apply adaptive k-means clustering algorithm to find the cluster points of the majority class. 1. convert the data format from array to vector. 2. select k elements from the majority class and assign these elements as seed of the cluster. engineering, technology & applied science research vol. 13, no. 3, 2023, 10785-10790 10787 www.etasr.com mathew & gunasundari: a cluster-based undersampling technique for multiclass skewed datasets 3. compute the distance between each element and seed using the euclidean distance formula. 4. compute the threshold value of the shortest distance between clusters dmin. 5. compare every distance with this threshold value and then update the cluster centroid. a. for any element pi, which does not belong to any cluster, the distance of pi from each cluster is computed. if the distance is 0 for a cluster, pi is assigned to that cluster, and the algorithm proceeds to the next non-clustered element. b. element pi is assigned to the closest cluster when the distance between pi and the cluster is less than distance dmin. c. if the value of dmin is below the distance of the element from the nearest cluster, the two closest clusters c1 and c2 are selected and are merged in c1. cluster c2 is eradicated by eliminating all the instances belonging to it and its image is removed. after that, the new instance is added to this empty cluster for creating a new cluster. 6. the above steps are repeated based on the threshold value, and the centroid values are updated. step 5: find the distance between each element and the corresponding centroid of the cluster. step 6: the elements with the largest distance are discarded from the dataset. step 7: apply step 6 for excess/k number of times in each cluster. step 8: apply step 4 to step 7 for the other majority class data. step 9: finally concatenate the minority class subset and reduced majority class subsets. iv. experimental study the proposed resampling technique in conjunction with various machine learning algorithms was used in this study. the input dataset was extracted from the keel data repository. multiminority datasets with different imbalance ratios were chosen. the implementation was done in matlab. figure 1 shows the different stages of the experiment. the different stages are:  selecting three multiminority datasets with different imbalance ratios from the keel repository. these datasets are of 3-class classification.  data pre-processing was done over the selected datasets for removing noisy data.  the data were split in 75:25 training-testing ratio.  classifiers like k-nearest neighbors (k-nn), decision tree (dt), and random forest (rf) were applied, and the corresponding model performance was evaluated.  resampling techniques like akcus, rus, enn, and nm were applied to the training data.  the resampled data with different techniques were used to create models with k-nn, dt, and rf and the model performance was evaluated.  the performances of various models before and after applying various resampling techniques are analyzed. fig. 1. various stages in the study. a. data used a list of experiments was conducted to study the effectiveness of the proposed akcus algorithm. the empirical review was conducted on multiclass skewed datasets available in the keel data repository [18, 19]. three multiminority datasets, namely new-thyroid, thyroid, and wine were chosen. the information related to these datasets is given in table i. the original data distribution plots of the datasets are shown in figure 2. b. resampling methods used in the data pre-processing stage, records were validated, and imbalanced datasets were transformed into balanced with the aid of resampling techniques. the proposed akcus was applied over the datasets and the classification results were compared with those of the existing undersampling techniques rus, enn, and nm. engineering, technology & applied science research vol. 13, no. 3, 2023, 10785-10790 10788 www.etasr.com mathew & gunasundari: a cluster-based undersampling technique for multiclass skewed datasets c. selected classifiers k-nn, dt, and rf were chosen for creating models in this experiment. d. performance evaluation the performance of different models that were built with the several resampling techniques and classifiers were assessed with the aid of the confusion matrix [20]. confusion matrix denotes true positive (tp), true negative (tn), false positive (fp), and false negative (fn) values. using the confusion matrix, different metrics like accuracy, error, precision, f1score, and g-mean of various models can be calculated. table i. dataset information dataset name no of instances imbalance ratio attributes class label no. of records new-thyroid 215 5 6 normal 150 hyper 35 hypo 30 thyroid 720 40.16 22 1 17 2 33 3 666 wine 178 1.48 14 1 59 2 71 3 48 v. results and discussion the learning capability of different models can be identified with the help of performance metrics. in this study, all the datasets employ a data split of 75:25 ratio of model training and testing. the data distribution before and after applying the resampling methods is represented in table ii. both rus and nm bring similar numbers of elements after resampling. the selected datasets have multiple minority classes and a single majority class. in this experiment, the resampling occurs over the majority class. table ii. data distribution before and after resampling dataset skewed data distribution after undersampling rus/nm enn akcus c1 c2 c3 c1 c2 c3 c1 c2 c3 c1 c2 c3 newthyroid 147 35 37 20 20 20 113 20 18 25 25 25 thyroid 17 37 666 11 11 11 11 3 458 12 12 12 wine 57 71 38 29 29 29 40 38 29 30 30 30 to evaluate the effectiveness of akcus, a comparison was made between the performance metrics of different datasets. the results of a selected dataset with different balancing techniques as well as with different classifiers were considered. initially, consider the new-thyroid dataset and its performance metrics (table iii). it is evident that the model with rf classifier and akcus resampling technique over the newthyroid dataset achieved better performance than the other models. k-nn classifier works its best with the rus sampled dataset. classifiers dt and rf give promising results with akcus balanced datasets. figure 3 represents the comparative chart of performance over various techniques applied over the new-thyroid dataset. fig. 2. data distribution of the datasets. fig. 3. result comparison of various techniques over the new-thyroid dataset. table iii. performance metrics of new-thyroid dataset resampling technique classifier accuracy error precision f-score g-mean imbalanced set k-nn 0.875 0.125 0.9477 0.8079 0.8051 dt 0.9063 0.0938 0.9275 0.8725 0.8737 rf 0.9531 0.0469 0.9783 0.9379 0.9289 rus k-nn 0.9454 0.0546 0.9687 0.9425 0.9387 dt 0.8545 0.1455 0.8439 0.8549 0.8597 rf 0.9531 0.0469 0.9783 0.9361 0.9305 nm k-nn 0.8363 0.1637 0.8438 0.8369 0.8539 dt 0.8181 0.1819 0.8303 0.8207 0.8414 rf 0.8545 0.1455 0.8558 0.8567 0.8763 enn k-nn 0.9090 0.091 0.9509 0.9031 0.9109 dt 0.8727 0.1273 0.893 0.8733 0.8763 rf 0.9272 0.0728 0.9595 0.9213 0.9266 akcus k-nn 0.875 0.125 0.9477 0.8079 0.8051 dt 0.9688 0.0313 0.9589 0.9589 0.8051 rf 0.9818 0.0182 0.9888 0.9828 0.9832 the thyroid dataset (table iv) is another multiminority dataset. the model with dt classifier along with akcus resampling achieves better performance than the other models. knn classifier performs its best with imbalanced data and akcus balanced dataset. dt and rf classifiers achieve their engineering, technology & applied science research vol. 13, no. 3, 2023, 10785-10790 10789 www.etasr.com mathew & gunasundari: a cluster-based undersampling technique for multiclass skewed datasets best with akcus balanced dataset. figure 4 shows the comparative chart of the performance over various techniques applied over the thyroid dataset. fig. 4. result comparison of the thyroid dataset. table iv. performance metrics of thyroid dataset resampling technique classifier accuracy error precision f-score g-mean imbalanced set k-nn 0.9954 0.0046 0.9983 0.9735 0.9673 dt 0.9861 0.0139 0.949 0.9204 0.9295 rf 0.9815 0.0185 0.8804 0.848 0.9004 rus k-nn 0.3944 0.6059 0.3623 0.2603 0.384 dt 0.9611 0.0389 0.7679 0.9 0.8567 rf 0.95 0.05 0.7476 0.8348 0.8567 nm k-nn 0.1111 0.8889 0.3473 0.1443 0.4008 dt 0.9611 0.0389 0.7976 0.8726 0.8867 rf 0.8555 0.1445 0.6623 0.7052 0.7694 enn k-nn 0.9111 0.0889 0.4198 0.3927 0.4019 dt 0.9277 0.0723 0.8455 0.569 0.6712 rf 0.9333 0.0667 0.8957 0.5882 0.6922 akcus k-nn 0.9954 0.0046 0.9983 0.9735 0.9673 dt 0.9907 0.0093 0.9507 0.937 0.9673 rf 0.9861 0.0139 0.949 0.9204 0.9295 the last multiminority dataset taken into consideration is the wine dataset. table v shows the metrics for the wine dataset with different resampling methods and classifiers. τhe models with akcus did not perform better than the other models. knn classifier performs its best with rus sampled data. dt classifier achieved its best with nm and enn. rf achieved its best with the imbalanced dataset, because the difference in the ratio of data among different classes is very low in wine, so the proposed algorithm is not able to achieve better performance and this dataset can be considered as a special case. figure 5 shows the comparative chart of the performance of various techniques over the wine dataset. the performance of the imbalanced dataset with different resampling techniques and classifiers are specified above. from the metric tables it was clear that akcus technique produces better results for all the datasets except the wine dataset. the ratio of data imbalance was also considered while performing resampling. for the wine dataset, the imbalance ratio is very low, so the balancing techniques were not much reflected. the imbalance ratio also acts as a factor while resampling measures are applied. undersampling techniques sweep out some data that are available in the dataset and this will sometimes reflect badly on the data distribution. the proposed method sweeps out samples which are not very relevant for the learning process. fig. 5. result comparison of the wine dataset. the thyroid dataset, with a high imbalance ratio of 40.16, shows promising results with the proposed resampling technique. the new-thyroid dataset with imbalance ratio of 5 shows better results with our proposed resampling technique. however, in the wine dataset, with imbalance ratio of 1.48, the proposed method did not show much success. table v. performance metrics of wine dataset resampling technique classifier accuracy error precision f-score g-mean imbalanced set k-nn 0.7042 0.2958 0.6951 0.687 0.7733 dt 0.8592 0.1408 0.8478 0.8314 0.8756 rf 0.97 0.03 0.96 0.947 0.95 rus k-nn 0.9761 0.0239 0.9666 0.9717 0.9728 dt 0.9047 0.0953 0.9166 0.9166 0.9166 rf 0.95 0.05 0.939 0.947 0.9494 nearmiss k-nn 0.97 0.03 0.966 0.97 0.9724 dt 0.9285 0.0715 0.9473 0.9196 0.9265 rf 0.95 0.05 0.939 0.947 0.9494 enn k-nn 0.97 0.03 0.966 0.97 0.9724 dt 0.9285 0.0715 0.9166 0.9178 0.9269 rf 0.95 0.05 0.939 0.947 0.9494 akcus k-nn 0.7183 0.2817 0.7313 0.7054 0.7928 dt 0.8451 0.1549 0.8397 0.8205 0.7928 rf 0.9577 0.0423 0.95 0.9534 0.9722 vi. conclusion machine learning models for classification created with imbalanced data have a bias towards the majority class, affecting the classification process. in this study, a new undersampling technique named adaptive k-means clustering undersampling (akcus) is proposed for multiclass skewed data classification. akcus performs well with multiminority cases of imbalanced data. as undersampling removes elements from the actual dataset, sometimes this removal will affect the loss of prominent data. the proposed akcus algorithm is concerned about the prominent elements in multiple classes and its removes data which are not very relevant to the classification process. in this work, the imbalance ratio was engineering, technology & applied science research vol. 13, no. 3, 2023, 10785-10790 10790 www.etasr.com mathew & gunasundari: a cluster-based undersampling technique for multiclass skewed datasets considered as an important factor. the proposed algorithm works well with multiminority datasets that have high imbalance ratio. if the imbalance ratio is low, the result is not much affected by the resampling procedure. so, the proposed algorithm produces promising results for datasets with high imbalance ratio. this work can be extended to tackle the bias over big data models. 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[20] m. o. ojo and a. zahid, "improving deep learning classifiers performance via preprocessing and class imbalance approaches in a plant disease detection pipeline," agronomy, vol. 13, no. 3, mar. 2023, art. no. 887, https://doi.org/10.3390/agronomy13030887. authors profile rose mary mathew is a research scholar in the karpagam academy of higher education, coimbatore. currently she is working as an assistant professor (special grade) in the department of computer applications, federal institute of science and technology, angamaly. she has more than ten years of teaching experience. she obtained her master of computer applications degree from mahatma gandhi university, kottayam in 2009 and mba from bharathiyar university, coimbatore in 2018. her areas of specialization is machine learning, deep learning, and artificial intelligence. she has participated and presented several papers in national and international seminars and conferences. ranganathan gunasundari is presently working as a professor in the department of computer applications, karpagam academy of higher education, coimbatore. she has more than fifteen years of teaching experience. she has participated and presented several papers in national and international conferences. her research interests include data mining, cryptography and network security. microsoft word etasr_v12_n6_pp9720-9725 engineering, technology & applied science research vol. 12, no. 6, 2022, 9720-9725 9720 www.etasr.com terki hassaine et al.: push-over analysis of optimized steel frames push-over analysis of optimized steel frames mohammed i. e. terki hassaine laboratory of materials and construction processes department of civil engineering university abdelhamid ibn badis mostaganem, algeria issam.terkihassaine@univ-mosta.dz sidi m. e. a. bourdim laboratory of materials and construction processes department of civil engineering university abdelhamid ibn badis mostaganem, algeria sidimohammed.bourdim@univ-mosta.dz humberto varum laboratory of earthquakes and structural engineering department of civil engineering university of porto porto, portugal hvarum@fe.up.pt abdelkader benanane laboratory of materials and construction processes department of civil engineering university abdelhamid ibn badis mostaganem, algeria abdelkaderbenanaen@yahoo.fr abdelkader nour laboratory of materials and construction processes department of civil engineering university abdelhamid ibn badis mostaganem, algeria nour.abdelkader@univ-mosta.dz received: 12 september 2022 | revised: 28 september 2022 | accepted: 1 october 2022 abstract-the traditional optimization methods are effective when dealing with small-scale problems. however, for large-scale problems, these methods fail to obtain optimal solutions, and after a long operation, several solutions are obtained. new methods, known as metaheuristics, have provided new implementations to be used in many applications. they have enabled the resolution of many complex industrial and technical problems. they have the merits of avoiding local optima and finding optimal solutions, due to their ease of understanding, flexibility, adaptation simplicity, and ability to get out of local optima traps. this article aims to model a 2d metal frame gantry with two spans and two levels already optimized by robot millennium software in order to show the effect of structural optimization in the pre-design phase and of obtaining its nonlinear behavior by the pushover method. three optimal dimensional configurations of this gantry were taken into account and the best was chosen, one which satisfied an adequate behavior in the non-linear domain while respecting the cm66 and eurocode3 regulations. keywords-optimization; vulnerability; push-over method; nonlinear behavior i. introduction there is an increasing tendency to analyze structures using probabilistic information on loads, geometry, material properties, and boundary conditions. design notes were prepared manually and as new and complex requirements and demands arose, much more urgent actions were taken to meet these requirements. progress has been made in the construction technology sector, especially in the search for productivity gains, which has led to two main thrusts [1]:  industrialization, therefore prefabrication of building elements, with the verification of the validity of an object previously designed and checking its operation afterwards.  the creation of the computer, i.e. an efficient and fast tool to automate the calculation and the verification of construction elements. optimization algorithms are written to minimize a function (to maximize a function, it will be simple to minimize its opposite). optimization is a method that uses mathematics and computer science, seeking to model, analyze, and solve analytically or numerically the problems of determining which solution(s) satisfy a quantitative objective while respecting possible restraints. the quality of the results and predictions depends on the relevance of the model and the efficiency of the used algorithm. traditional and heuristic optimization algorithms have been widely used to find the global optimum in a problem or cost function. the reason may be their reliable approaches to solve difficult optimization problems. many metaheuristic algorithms have been proposed during the recent years, such as the ant lion optimizer [2], the artificial algae algorithm [3], the binary bat algorithm [4], the black hole algorithm [5], the binary cat swarm optimization [6], the firefly algorithm [7], the fish swarm algorithm [8], and the grey wolf optimizer [9]. some examples of the first generations of these algorithms are the genetic algorithm [10], genetic programming [11], evolutionary programming [5], tabu search [12], and simulated annealing [13]. these are metaheuristic algorithms that are also classified into three sections [14, 15], which are: evolutionary algorithms, physicsbased algorithms, and intelligent algorithms. the traditional approach to the optimization of steel structures is essentially based on minimizing the weight of the structure while taking into account the reliability and/or vulnerability which is calculated using mathematical and numerical methods such as the finite element method (fem) to obtain a detailed structural response. corresponding author: sidi m. e. a. bourdim engineering, technology & applied science research vol. 12, no. 6, 2022, 9720-9725 9721 www.etasr.com terki hassaine et al.: push-over analysis of optimized steel frames the aim of this work is to show the effect of structural optimization in the pre-design phase, using robot millennium software, on the final response of the non-linear behavior of a steel portal frame through a comparative study of three different configurations. we will model a two-span, twolevel portal frame in a simple steel frame and then proceed to determine its shear forces and bending moments using the sap2000 software while respecting the cm66 and eurocode 3 codes. finally, we try to determine the vulnerability of this gantry frame by the non-linear static pushover method. ii. materials and methods a. optimization problems and criteria optimization problems can be classified as single-objective or multi-objective, depending on the number of objective functions [16-17]. in civil engineering, building optimization studies often use up to 2 objective functions [18], with the exception of 3-objective functional optimization in different techniques where the objective function [19] can be linear or non-linear, convex or non-convex, unimodal or multimodal, differentiable or not, continuous or discontinuous, expensive or unaffordable in terms of computing. this results in heuristic and meta-heuristic optimization methods, simulation-based optimization, and surrogate-based optimization [20-21]. most real-world optimization problems are described with several, often conflicting, objectives or criteria that need to be optimized simultaneously [22]. for the steel frame building design optimization problem, the variables are the components of the structure, since the variation of their characteristics directly influences the global production cost criterion chosen as the optimization objective in this research [23]. a steel frame is the result of the assembly of different components. this assembly must be designed to ensure that the resulting structure is suitable for the intended use. the early design phase, prior to any detailed calculation, concretely implies a process of analysis and verifications that can be adopted at the "maximum" according to the class of the cross-sections (eurocode3). a comparative study will be carried out on a twodimensional steel portal frame using the profiles available on the algerian market, namely ipe, ipn, hea, and heb in order to have optimal dimensioning in the plastic domain. b. optimization module in robot millennium in order to facilitate the work, the use of robot millennium is proposed, which has a vast set of tools simplifying the study of structures. in robot millennium, the notion of objects and the creation of the model of the structure are carried out with typical construction objects: beams, columns, bracing, floors, and walls. during the study stage, the elements of the structure take on specific attributes of their own (including regulatory attributes), thus, at the model definition stage, all the regulatory parameters of the structure are defined, which allows the regulatory analysis to be carried out immediately after the static calculations. the same applies to the nodes. the notion of nodes has lost its traditional meaning since they are automatically defined during the creation of the various objects. the available optimization criteria are: weight, maximum and minimum section height, minimum flange thickness, and minimum web thickness. the option calculations for the entire profile family is available. the entire accessible profile database will be scanned to find the optimal profile. the sizing module is used to find the optimal profile in terms of stress. for example, we see that robot recommends an ipe 240 that is identical to our initial choice (a first estimate). however, the verification of the ipe 240 in deflection shows that the profile is insufficient. indeed, the deflection is the dimensioning element in certain structures, so it would be logical to make dimensioning in deflection. unfortunately, automatic dimensioning in deflection is impossible. to justify this observation, we must explain how sizing works. iii. case study the main objective of this project was to design a building structure in cm66. however, the achievement of this objective was done in several steps. first, it was necessary to:  determine the load applied to the structure.  determine the different types of possible structures.  carry out the design and finally choose the most advantageous design in relation to the client's needs. a. description of the structure the project is located in oran city, that is located in an average seismic activity zone (zone ii-a) according to the algerian earthquake code rpa99, in zone b for snow density, and zone i for wind force according to the rnv2013. depending on the plan view, the dimensions of the structure are shown in table i. table i. dimensions of the structure total length total width height from the ground level height of the ground floor height of the floors total height of the building 30.64m 13.4m 2.80m 3.80m 3.80m 57m the light roof is made of tn 40 industrialized ribbed sheet metal, transoms, purlins, and bracing. the purlins and trusses are made of ipe profiles. the columns are made of hea profiles, the distance between two purlins is 1.3m, and the external masonry walls have 6m of high. the cladding is made of the same type of sheet metal as the tn 40 roof. the cladding rails are fixed to posts or possibly to posts. the loads to the building are transmitted to the ground through the insulated reinforced concrete footings. the value of the permissible soil stress is 2.5 bars. the characteristics of reinforced concrete in the foundations are: strength of the concrete fc28 = 25 mpa, elasticity modulus of concrete ec = 32164mpa, safety factor of concrete c = 1.5, safety factor of steel s = 1.15, and yield steel stress fe = 400mpa. the steel elements are made with steel grade s235, fy = 2350dan/cm². the modulus of elasticity of the steel is e = 2100000dan/cm². the connections are made by means of ordinary and high strength welds and bolts. a calculation with robot software: engineering, technology & applied science research vol. 12, no. 6, 2022, 9720-9725 9722 www.etasr.com terki hassaine et al.: push-over analysis of optimized steel frames  defines a structure made up of portal frames (columns + truss) in accordance with the project data. the wind actions are calculate  creates the load combinations  analyzes the structure and dimensions of the different elements of the structure (purlins, cladding rails, truss elements, columns, and posts).  calculates the connections (truss elements, truss-post, and post foot). subsequently, the gantry was analyzed using etabs software to apply the pushover method and see the vulnerability of the gantry. the type of structure is a planar portal frame with a total mass of 594.79kg. figure 1 shows the studding gantry in cm with the optimized metallic profiles. however, three configurations were selected after the first step of the present study, which is the optimization of the structure with different profile sections available in the algerian market, especially hea, heb, ipe, and ipn profiles. fig. 1. the metal frame of the case study. b. deformation of the gantry each variant was subjected to nonlinear analysis according to the pushover method. figure 2 shows the deformation form and the plastic hinges of the gantry with the optimized metallic profiles for all three configurations. fig. 2. shape deformation with plastic hinges. iv. results and discussion in this section, we present and compare the results. we illustrate and compare the results of two frames of the same number of stories according to the period, base shear, maximum displacement, and stiffness. a. first variant (columns : heb180, beams: hea240) table ii represents the distribution of plastic hinges in the metallic gantry according to the first configuration. from table ii, we can see that 80% of the plastic hinges are in the first segment (a-io), 20% in the second segment (io-ls), 0% in the 3rd segment (ls-cp), and 0% in the last segment, which corresponds to failure or collapse. figure 3 shows the evolution of the capacity curve and the performance parameters of the studied structure according to the first configuration. the capacity curve (figure 3(a)) is defined by the elastic state corresponding to an elastic shear force of vy = 58.37kn for an elastic displacement of dy = 30.5mm and initial stiffness k0 = 1913.91knm which represents the product of the elastic shear force and the elastic displacement. the ultimate limit state corresponding to the shear force is vu = 92.70kn. from figure 3(b) and table ii, it can be said that the performance point, which represents the intersection of the response spectrum curve with the capacity curve, is at the point that connects the shear force of 342.30kn with the displacement of 18.7mm. (a) (b) fig. 3. response of the nonlinear analysis of the first variant. (a) capacity curve, (b) performance parameters. engineering, technology & applied science research vol. 12, no. 6, 2022, 9720-9725 9723 www.etasr.com terki hassaine et al.: push-over analysis of optimized steel frames table ii. base shear, max displacement, and stiffness of the first variant of the two-storey frame step monitored displacement (mm) base force (kn) a-b b-c c-d d-e >e a-io io-ls ls-cp >cp total 0 0.1 0 20 0 0 0 0 20 0 0 0 20 1 30.5 58.37 20 0 0 0 0 20 0 0 0 20 2 60.9 116.74 20 0 0 0 0 20 0 0 0 20 3 91.3 175.12 20 0 0 0 0 20 0 0 0 20 4 121.7 233.49 20 0 0 0 0 20 0 0 0 20 5 152.1 291.87 19 1 0 0 0 20 0 0 0 20 6 172.9 324.75 18 2 0 0 0 19 1 0 0 20 7 189 344.92 17 3 0 0 0 19 1 0 0 20 8 240.7 380.51 16 4 0 0 0 17 3 0 0 20 9 298.1 409.22 15 5 0 0 0 16 4 0 0 20 10 304.1 411.71 15 5 0 0 0 16 4 0 0 20 table iii. base shear, max displacement, and stiffness of the second variant of the two-storey frame step monitored displacement (mm) base force (kn) a-b b-c c-d d-e >e a-io io-ls ls-cp >cp total 0 0.3 0 20 0 0 0 0 20 0 0 0 20 1 30.7 32.50 20 0 0 0 0 20 0 0 0 20 2 61.1 65.00 20 0 0 0 0 20 0 0 0 20 3 64.6 68.71 19 1 0 0 0 20 0 0 0 20 4 113.6 107.05 17 3 0 0 0 20 0 0 0 20 5 144 128.05 17 3 0 0 0 20 0 0 0 20 6 183.5 151.65 16 4 0 0 0 20 0 0 0 20 7 213.9 168.96 16 4 0 0 0 18 2 0 0 20 8 244.3 186.27 16 4 0 0 0 18 2 0 0 20 9 274.7 203.58 16 4 0 0 0 17 3 0 0 20 10 304.3 219.88 15 5 0 0 0 16 4 0 0 20 table iv. base shear, max displacement, and stiffness of the third variant of the two-storey frame step monitored displacement (mm) base force (kn) a-b b-c c-d d-e >e a-io io-ls ls-cp >cp total 0 0.4 0 16 4 0 0 0 20 0 0 0 20 1 30.8 13.74 16 4 0 0 0 20 0 0 0 20 2 51.9 23.31 15 5 0 0 0 20 0 0 0 20 3 82.3 33.85 15 5 0 0 0 20 0 0 0 20 4 112.7 44.39 15 5 0 0 0 20 0 0 0 20 5 143.1 54.93 15 5 0 0 0 20 0 0 0 20 6 182.6 66.94 14 6 0 0 0 19 1 0 0 20 7 213 75.80 14 6 0 0 0 17 3 0 0 20 8 254 86.37 13 7 0 0 0 17 3 0 0 20 9 284.4 93.85 13 7 0 0 0 16 4 0 0 20 10 304.4 98.76 12 8 0 0 0 16 4 0 0 20 b. second variant (columns : heb180, beams: ipe 200) table iii represents the distribution of the plastic hinges in the metallic gantry. we can see that 80% of the plastic hinges are in the first segment (a-io), 20% in the second segment (io-ls), 0% in the 3rd segment (ls-cp), and 0% in the last segment, which corresponds to failure or collapse. figure 4 shows the evolution of the capacity curve and the performance parameters of the studied structure according to the second configuration. the capacity curve (figure 4(a)) is defined by the elastic state corresponding to an elastic shear force of vy = 32.50kn for an elastic displacement of dy = 30.7mm and initial stiffness k0 = 1058.63knm which represents the product of the elastic shear force and the elastic displacement. the ultimate limit state corresponding to the shear force is vu = 219.88kn. from table iii and figure 4(b), it can be said that the performance point, which represents the intersection of the response spectrum curve with the capacity curve, is at the point that connects the shear force of 0.00kn with the displacement of 0.0m. so, the performance point is not found. c. third variant (columns : heb140, beams: ipe180) table iv represents the distribution of plastic hinges in the metallic gantry. from table iv, we can see that 80% of the plastic hinges are in the first segment (a-io), 20% in the second segment (io-ls), 0% in the 3rd segment (ls-cp), and 0% in the last segment, which corresponds to failure or collapse. figure 5 shows the evolution of the capacity curve and the performance parameters of the studied structure according to the third configuration. engineering, technology & applied science research vol. 12, no. 6, 2022, 9720-9725 9724 www.etasr.com terki hassaine et al.: push-over analysis of optimized steel frames (a) (b) fig. 4. response of the nonlinear analysis of the second variant. (a) capacity curve, (b) performance parameters. the capacity curve (figure 5(a)) is defined by the elastic state corresponding to the elastic shear force of vy = 13.74kn for an elastic displacement of dy = 30.8mm and initial stiffness k0 = 446.10knm which represents the product of the elastic shear force and the elastic displacement. the ultimate limit state corresponding to the shear force is vu = 98.77kn. from table iv and figure 5(b), it can be said that the performance point, which represents the intersection of the response spectrum curve with the capacity curve, is at the point that connects the shear force of 0.00 kn for the displacement of 0.0m. so, the performance point is not found. d. comparison between the results of the treated variants after analyzing each model separately, the results obtained are compared according to the capacity curve and the following criteria: elastic shear force, displacement, initial stiffness, and ultimate shear force as detailed in table v. regarding to the elastic shear force, it can be easily noticed that variant 1 presents the highest value compared to the other two, mainly due to the geometrical characteristics of the profiles used in this variant. in the same context, variant 1, gives the lowest elastic displacement. it also presents the highest initial stiffness and ultimate shear force. it can be said that the columns have good resistance to the applied loads and the under dimensioning of these elements can lead to low resistance. (a) (b) fig. 5. response of the nonlinear analysis of the third variant. (a) capacity curve, (b) performance parameters. table v. comparison between the treated variants variant 1 2 3 elastic shear force vy (kn) 58.37 32.50 13.74 elastic displacement dy (m) 0.0305 0.0307 0.0308 initial stiffness k0 (kn/m) 1913.91 1058.63 446.10 ultimate shear force vu (kn) 92.70 219.88 98.77 on the other hand, it can be said that variant 1 has the highest weight among the considered variants. this has a considerable influence on the cost of the structure. however, among the three different optimized configurations, the first variant with (heb180 for columns and hea240 for beams) shows the best-optimized configuration in robot compared to the other two optimized configurations. v. conclusions the analysis showed that the selected models and the interpretation of the results, allow us to conclude that the choice of the profiles is appropriate, either for the columns and/or for the crossbeams, which ensure an adequate resistance, and add in the weight of the structure. the latter is one of the major criteria among the main optimization parameters. it should be noted that many questions are still open in the field of behavior of steel frames, in particular questions related to the dependence of the response on the non-linear domain. engineering, technology & applied science research vol. 12, no. 6, 2022, 9720-9725 9725 www.etasr.com terki hassaine et al.: push-over analysis of optimized steel frames finding optimal solutions to engineering problems is always a difficult task. due to the many conditions and limitations, structural engineers usually have to proceed and repeat through trial and error, in search of better design solutions in terms of improved structural performance and cost reduction. in this paper, nonlinear analysis of a 2d steel frame was conducted and the results were compared for three different optimized configurations. the results obtained showed that in order to properly design a metallic gantry frame that meets the regulatory requirements with a light structure and minimum cost, it is necessary to introduce several parameters in the form of an algorithm that allows us to arrive at the most appropriate profiles in a simple way. for this reason, we can say that the use of genetic algorithms in this case is adequate. they are beneficial for tackling problems that are considered difficult or that require a lot of computation time with a classical algorithmic approach. it is also easy to show that when using genetic algorithms, one can improve the solution speed and make it possible to solve something in adequate time that used to be very time consuming, given the complexity of the data of physical problems. future work will focus on three-dimensional models to properly analyze this type of steel structure. acknowledgment the authors would like to thank professor cherif zine-elabiddine, university of tlemcen, for his help. references [1] m. i. e. terki hassaine, s. m. bourdim, a. benanane, and y. zelmat, "optimization of metallic structures by applying genetic algorithm," in proceedings of the international conference on automation innovation in construction (ciac-2019), leiria, portugal, 2019, pp. 341–348, https://doi.org/10.1007/978-3-030-35533-3_41. 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[23] h. a. m. yazdi and n. h. r. sulong, "optimization of off-centre bracing system using genetic algorithm," journal of constructional steel research, vol. 67, no. 10, pp. 1435–1441, oct. 2011, https://doi.org/10.1016/j.jcsr.2011.03.017. microsoft word etasr_v13_n2_pp10529-10534 engineering, technology & applied science research vol. 13, no. 2, 2023, 10529-10534 10529 www.etasr.com gupta & agarwal: recognition of suspicious human activity in video surveillance: a review recognition of suspicious human activity in video surveillance: a review neha gupta computer science & engineering department, iftm university, india | computer science & engineering department, moradabad institute of technology, india discoverneha@gmail.com (corresponding author) bharat bhushan agarwal computer science & engineering department, school of computer science and applications, iftm university, india bharat_agarwal@iftmuniversity.ac.in received: 11 february 2023 | revised: 21 february 2023 | accepted: 25 february 2023 abstract over the past few years, there has been a noticeable growth in the use of video surveillance systems, frequently functioning as integrated systems that remotely monitor key locations. in order to prevent terrorism, theft, accidents, illegal parking, vandalism, fighting, chain snatching, and crime, human activities can be observed through visual surveillance in sensitive and public places like buses, trains, airports, banks, shopping centers, schools, and colleges. in this paper, a review of the state-of-the-art is provided, showing the overall development of identifying suspicious behavior from surveillance recordings over the past few years. we give a quick overview of the issues and difficulties associated with recognizing suspicious human activity. the purpose of this publication is to give this field's scholars a literature evaluation of several suspicious activity recognition systems along with their general structure. keywords-suspicious activity; video surveillance; human activity; deep learning i. introduction suspicious human behavior (sha) recognition through video surveillance is a well-known topic of research in the fields of image processing and computer vision and involves classifying human activity as normal and abnormal. unusual or suspicious behaviors, which are rarely displayed by persons in public settings, can be classed as abnormal. today, more and more people are using video surveillance to keep an eye on human activity and stop any questionable behavior. during the recent years, human activity recognition has been realized by a wide variety of applications in military, intelligence, masstransit agencies, and research and academia as a measure to counter crime and terrorism, public health monitoring, detection of public violent protests and attacks, etc. [1-3]. due to the technological improvement, the means of surveillance are easily available, yet the means of continuously and effectively processing, analyzing, and detecting are not. intelligent systems that can detect and classify suspicious human activities have been established as a crucial means to carry the necessary counter-action mechanisms, for controlling the situation, and/or for post situation/scenario analysis [4]. in general, sha recognition involves identification of human activities that can be classified as normal and abnormal. the first classification refers to the common human activities at public places. normal activities are the typical human behaviors that occur in public spaces, such as hand-waving, applauding, jogging, boxing, and walking. the latter category includes behaviors like leaving bags behind, dodging crowds, robbing, fighting and attacking, vandalism, crossing borders, etc. [5]. the focus is to employ efficient techniques/systems to identify the abnormalities in human activities which can be used to predict/decide the appropriate course of action. the abnormalities can be of several kinds and be mixed with normal activities. for example, in the first category, while running, a person might drop a bag with explosives, while a walking person might point a weapon towards another person, and so on. on the other hand, in the second category the abnormalities can be classified incorrectly, e.g. a running crowd in a marathon does not need to be identified as a negative behavior. there is a wide range of activities to be identified in sha recognition [5], as shown in figure 1. explosives left in unattended objects by terrorists in crowded places or secluded places have a complex range of tasks to be looked into before making appropriate decisions. illegal parking on roads causing traffic jam or accidents needs quick decisions in real life applications. activities involving violence such as street engineering, technology & applied science research vol. 13, no. 2, 2023, 10529-10534 10530 www.etasr.com gupta & agarwal: recognition of suspicious human activity in video surveillance: a review fighting, vandalisms, etc. also require quick action to ensure minimum damage of life and property. manual monitoring and intervention fail to deal with such situations. thus, fully automatic, effective intelligent surveillance systems that are efficient enough to handle real-time scenarios are important to develop and install. this survey provides a comprehensive detail regarding the different aspects of developing such systems, discusses existing works, and finally puts forward the prospects. fig. 1. activity recognition. ii. solution approaches and discussion the following approaches are used by the existing solutions for sha recognition:  object tracking and detection by background subtraction: this is the most common initial phase rule followed by the existing solutions for sha recognition. in this phase, items are tracked and identified using changes in the order of the frames, and then the foreground objects are retrieved. tracking-based or non-tracking-based methods are used to identify objects in video frames [6].  feature extraction: certain features of objects such as motion and shape are extracted using various algorithms to identify objects [7].  object classification: in this step, a method is used to distinguish between the various things in the video, such as people, guns, cars, etc. various methods, including svm, bayesian, haar-classifier, knn, face recognition, and skin color detection are used.  suspicious activity detection: the final stage after classifying the items in the video stream is a comparison with several threshold values categorically to check for aberrant behavior. the specifications as to what can a suspicious event be are discussed below.  loitering individuals: we have loitering when a person is present at a particular location for a longer period than required. the related mathematical formulations can be quantified depending on the applications type [8].  unattended/missing objects: the suspicious objects have to be detected in the video frames. however, identification of abandoned/unattended object is very difficult in video frames in crowded environment. to tackle the problem different techniques have been proposed, such as frame differencing, optical flow, and background subtraction [9, 10].  intruder detection: intruder detection approaches utilize multiple cameras for sha analysis in cases such as bank robberies, chain snatching, etc. another proposed technique is based on ontology, and is also used in airports and banks to recognize sha. the optical flow technique is employed to detect the snatch theft from crowd movement pedestrian video footage.  abnormal activity/behavior: it includes fall detection, accident detection, crowd detection, fire detection, etc. fall detection is predominantly used in the health monitoring system. herein, static cameras are used for patient care in hospitals and unattended elderly people at home in modern times [11]. iii. literature review in this section we discuss the relevant works regarding sha recognition. author in [12] considered the current camera surveillance systems that simultaneously capture dynamic images from areas using multiple web cameras. these images are matched against the enormous amount of dynamic images, which makes the process very tedious for the observer. meanwhile, if some of the images are missed by the observer, the system will fail. authors in [13] proposed a dcnn model called diatradharnet designed for sha classification. the following concepts serve as the framework for the scheme: depthwise separable convolutions, channel weighting (chw) based on importance, multiple filter sizes in the depthwise section, and application of various size kernels to the same input tensor. authors in [14] proposed an object detection algorithm for video surveillance and real-time security camera systems. to do this, a modified version of the kanade-locusthomasi extraction algorithm was presented for object tracking. the proposed scheme detects and analyzes a small number of features instead of a large number of objects. the problem of noise creation is dealt with a kalman filter. authors in [15] proposed a real-time sha recognition scheme based on a convolutional neural network (cnn) and 2d pose estimation technique which is beneficial in a wide range of surveillance areas. the skeletal images of humans are extracted from the input frames of the video through 2d pose estimations. then, these are then fed to a pre-trained cnn to categorize them into different human activities like fall or not fall, trespassing or no trespassing, etc. finally, based on the classification, appropriate action can be taken, such as sending messages on mobile phones, triggering alarms, etc. authors in [16] proposed an sha recognition technique known as yolov3, which handles the complex problem of human detection. for this, the video is first converted into a few frames then, each frame is analyzed to recognize and detect any suspicious activity. engineering, technology & applied science research vol. 13, no. 2, 2023, 10529-10534 10531 www.etasr.com gupta & agarwal: recognition of suspicious human activity in video surveillance: a review in [17], the authors handle the complexity of associating the skeleton inputs for recognition of both abnormal human activity and daily activity by reducing the number of features of the datasets through an rnn-based approach. moreover, an lstm model was used to classify suspicious activities in medical applications. in [18], a hierarchical approach was used to detect different shas such as fainting, loitering, unauthorized entry, etc. at first, all shas are defined using a semantic approach. then, background subtraction is employed to detect the object. then, a correlation technique is used to track the objects. authors in [19] based their method on two features: shape moments and histogram of normalized distances (hnd) from the center of gravity and contour points of the object shape. for categorizing human activities, naive bayes classifier and multi-class support vector machine were utilized. authors in [20] focused on detecting gun-based crimes and abandoned luggage based on a deep neural network model capable of detecting handguns in images. in [21], the authors provided an sha detection and tracking recognition system based on artificial neural networks. the silhouette pattern of the human blob created through segmenting the cameracaptured video is used in this technique. in [22], the authors combined the bi-lstm network with skeleton activity forecasting (saf) to create a deep learning-based sha recognition system. the pose estimation in this case uses the human skeletal joints, which are viewed as points. on a streaming video from an ip networked camera, the skeleton tracking and places of interest are approximated. in [23], a deep learning based approach is used for sha recognition wherein, at first, the features are calculated from video frames. then, a feature classifier is used to predict whether the activity is suspicious. in [24], at first the videos were broken down into frames. then these frames were analyzed using background subtraction to detect humans. then, after using a cnn to extract features from the frames, a discriminative deep belief network (ddbn) was used. the ddbn is also given some labeled movies of various shas, and its associated features are also retrieved. the two sets of features are then compared to determine if there are normal or suspicious behaviors. in [25], a 63 layer-deep cnn model called l4-branchedactionnet is proposed. the framework is first trained using an object detection dataset called cifar-100 with the help of the softmax function. after that, the dataset for sha recognition is then input to the trained model to obtain a set of features. these are then improved utilizing an ant colony system and coded features with an entropy-based structure. to produce the final results, a variety of svm and knn-based classifiers are fed with the optimized features. authors in [26] proposed an algorithm for tracking a moving object by the video samples captured during movement. this method consists of multiple subparts including video sample creation, an experimental setup for capturing the data, and applying the object tracking algorithm using mean shift algorithms. this system can be used for calculating vehicle speed, number of vehicles passed, etc. and it has been tested over multiple frame rates. the results were not compared with the existing work. suspicious activity detection will be a major breakthrough in the video surveillance for behavior identification, action recognition, activity classification, etc. authors in [27] proved the usability of automated surveillance systems. surveillance plays an important role in maintaining law and order and in detection of possible threat. usually, this process happens manually and requires a significant amount of manpower, which can be reduced if we automate the process. authors in [28] explored the situation awareness (saw) which is used for many crucial applications. the main challenge in saw is faced during the instant changes while identifying objects. it also becomes challenging, whenever it focuses on huge video frames. the developed system is question-answer based, and chooses content as per interest. the interest-based traits can be more intricate in some situations than the facial features. authors in [25] developed a cnn model having 63 deep layers. the given name of the model is l4-branchedactionnet. the alexnet has been modified using four blanched sub-structures. it is first turned into a network that has already been trained using the cifar-100 object detection dataset and the softmax algorithm and the crucial details are spotted. to optimize feature subsets, these features are used. entropy is employed to code these traits initially, and an ant colony optimization method is then applied. different variants of svm and knn were used for classification. cubic svm provides the highest efficiency of 0.99. several machine learning approaches as described in [29-37] can be utilized in a similar way. authors in [38] proposed a classroom activity detection approach using video surveillance. this method's drawback is that it is difficult to differentiate between students and teacher in the class and to develop a generalized model for all scenarios. also, data from real surveillance can be noisy and of low-quality. the proposed work was tested on real environment using siamese neural network for classification from classroom recordings. authors in [39] also worked to improve the classroom learning outcome. a brief comparative summary of the relevant works is shown in table i. similar work has been done in [40-42]. iv. motivation and challenges the motivation of adopting smart and intelligent video surveillance systems is mainly to identify human activities which are suspicious in nature. in various highly sensitive places these systems will aid in the prevention of thefts, terrorist acts, hooliganism, fighting, and attacks, and fire. the following areas are shielded against shady behavior via intelligent video surveillance [7]:  universities and other academic institutions utilize video surveillance to keep an eye on student activity to protect property from theft and vandalism. additionally, they assist in preventing student fighting and inappropriate behavior. when exams are being given, video surveillance may be also utilized.  video surveillance helps to prevent theft, vandalism, fighting, disease identification, growing crowds, and explosive attacks to protect the population and public infrastructures including borders, laboratories, jails, military bases, temples, etc.  the use of video surveillance to identify sha is expanding in the retail sector, both for internal security in places like engineering, technology & applied science research vol. 13, no. 2, 2023, 10529-10534 10532 www.etasr.com gupta & agarwal: recognition of suspicious human activity in video surveillance: a review warehouses and stores as well as for external security in places like parking lots. even tiny businesses are using cameras to keep an eye on people and record video proof in case of theft or an incident.  in every nation, the safety of travelers, runways, and aircrafts is paramount in airports, which are highly sensitive security zones. such security-sensitive places are protected with high levels of protection thanks to a real-time system that detects sha in video monitoring.  in the banking industry, video monitoring is crucial for ensuring security. the use of weapons during armed robberies and assaults is prevented by the presence of cameras. automated banking devices are frequently targeted by criminals. one way a security camera can help in the identification of fraud is by installing a device to read the magnetic information on bank cards.  recognizing suspicious behavior from video surveillance can assist in finding frauds, heists, and other crimes. intelligent video surveillance is an intriguing technique to assist security officers because monitoring a casino necessitates seeing human movement in a congested setting.  in hospitals, video surveillance is also used to keep an eye on patients. at home, it can be used to keep an eye on elderlies or children. table i. sha literature review summary ref object detection method noise removal method remarks [12] background subtraction smoothing filter finds the detection point of sha and evalueates the corresponding degree of risk [13] lighweight deep cnn spatial filter efficient classification with high accuracy [14] klt and kalman filter efficient real time tracking [15] 2d pose estimation and cnn effective response system [16] yolov3 quick processing, accurate detection [17] multilayer lstm network less training data, better cross-view and cross-subject evaluation [18] background subtraction a thresholding technique less complexity, high accuracy [19] naïve bayes classifier effective and accurate detection and prediction [20] deep neural network gun-crime andabandoned laggage detection [21] ann high accuracy and robustness [22] bi-lstm network adaptive thresholding skeleton tracking [23] cnn and rnn apriori detection, simple, yet powerful [24] cnn and ddbn high accuracy [25] entropy-coded ant colony system high accuracy [26] mean shift algorithm efficient object tracking. box and image sequence segmentation [27] faster region-based cnn inception v2 framework sha detection in public places [28] i-vise and deep neural networks smoothing filter emphasis is given on ensuring that the photos analyzed have significant content and good quality [29] siamese neural framework textual windows across segment superior prediction perfomance for online and offline classrooms [30] deep fully connected convonutional and recurrent neural network precice estimates of the total amount of time spent in classes or activities to develop an intelligent video surveillance system that can automatically detect sha, there are several issues and challenges to overcome [7]:  moving object recognition is challenging to accurately process due to dynamic fluctuation in natural environments, such as slow illumination changes brought on by day-tonight shifts and quick illumination differences brought on by weather changes.  the look of an object is altered by its shadow, making it difficult to track and identify the specific object in a video. characteristics like shape, movement, and background, are more delicate for a shadow.  occasionally, noises made by swaying tree branches make it difficult to identify an object in a video.  finding the object in a busy location is a difficult process. it is quite challenging to discover abandoned objects, theft, or violence in such a circumstance.  full or partial object occlusions occur occasionally, the objects in video are entirely or partially obscured, making identification difficult.  it might be quite difficult to identify foreground items in low-resolution films. identification of object boundaries becomes extremely challenging.  the creation of a real-time, intelligent monitoring system is the more difficult task. when extracting and tracking the foreground objects from films with complicated backgrounds, processing time increases.  since background subtraction in abandoned object detection only recognizes moving things as the foreground, static object detection is a difficult task. v. measures to detect sha in general, the measures used to detect sha follow a hierarchical structure as shown in figure 2. at first the video is split into a sequence of frames. then, background subtraction is used to detect changes in the sequences of the frame and then extraction of foreground objects. following this, the different types of objects are attempted to be extracted by the system. then, the different obstructions in the form of noise, shadow etc. are removed from the frame containing the object. finally, the recognizable object is obtained from the surveillance engineering, technology & applied science research vol. 13, no. 2, 2023, 10529-10534 10533 www.etasr.com gupta & agarwal: recognition of suspicious human activity in video surveillance: a review footage. figure 3 represents the specific steps regarding the general steps in entity (object) detection in sha recognition. the first step is the identification of the different kinds of steps. to stop terrorist bomb attacks, suspicious activity detection also includes the detection of abandoned objects. background approaches in video surveillance treat stationary items as the background and moving things as the foreground. therefore, a newly arrived object is absorbed into the backdrop when it becomes static. fig. 2. general steps in entity detection. fig. 3. specifications regarding the general steps in entity (object) detection in sha recognition. finding foreground objects that are free from noise, illumination, or shadow is incredibly challenging in computer vision. noise makes it difficult to identify an object, illumination produces false detection, and shadow alters the object's appearance, making object tracking particularly challenging. the right features must be chosen in order for video surveillance to automatically detect anomalous activity. finding the most valuable information in the captured video is the main goal of feature extraction. after determining whether there are foreground-moving or still objects in a frame, the object categorization stage is used to determine whether the behavior is normal or abnormal. a static human is distinguished from a static abandoned object, a fight is distinguished from a boxing match, a face is distinguished from an object that has skin color, fire is distinguished from a flashlight, the sun, or any other artificial light source, and so on. vi. conclusion and future work the current paper reviews various intelligent and automatic sha recognition surveillance techniques. the reviewed papers cover a wide range of applications associated with real-time implementation. the applications range from health-care systems to perimeter monitoring in war fields. the techniques and dataset used are the most common ones pertaining to the sha domain. note that recognition of human behavior is a complex process, and monitoring and analyzing human activities is difficult. despite the complex nature of the problem, it is also required in day-to-day life in order to improve safety in modern society. on the other hand, recognition of suspicious activity of non-living things is relatively less complex but requires a great deal of expertise to deduce correct results. we discussed the related works and mentioned their shortcomings. the weaknesses can be significantly improved and pave the way for a wide range of open research. refereneces [1] j. 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[42] n. kumar, a. hashmi, m. gupta, and a. kundu, "automatic diagnosis of covid-19 related pneumonia from cxr and ct-scan images," engineering, technology & applied science research, vol. 12, no. 1, pp. 7993–7997, feb. 2022, https://doi.org/10.48084/etasr.4613. microsoft word etasr_v13_n3_pp10630-10637 engineering, technology & applied science research vol. 13, no. 3, 2023, 10630-10637 10630 www.etasr.com tebbal & hamida: effects of crossover operators on genetic algorithms for the extraction of solar … effects of crossover operators on genetic algorithms for the extraction of solar cell parameters from noisy data ibtissam tebbal department of electronics, laboratory of optoelectronics and components, university of ferhat abbas setif 1, algeria ibtiss08@yahoo.fr (corresponding author) abdelhak ferhat hamida department of electronics, laboratory of optoelectronics and components, university of ferhat abbas setif 1, algeria a_ferhat_h@yahoo.fr received: 28 january 2023 | revised: 12 march 2023 | accepted: 16 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5417 abstract this study analyzed the accuracy of solar cell modeling parameters extracted from noisy data using genetic algorithms (gas). three crossover operators (xos) were examined, namely the uniform (uxo), arithmetic (axo), and blend (bxo) operators. the data used were an experimental benchmark cell and a simulated curve where noise levels (p) from 0 to 10% were added. for each xo, the analysis was carried out by running gas 100 times and varying p and population size (npop). simulation results showed that uxo and axo suffered from premature convergence and failed to provide parameters with good precision even with very high npop, although they provided good fitting. in all analyzed cases, bxo outperformed uxo and axo and the results showed that it can compete with the most efficient methods. for the benchmark curve, bxo reproduced the best rmse found in the literature (0.7730062 ma) while providing the exact values of the parameters and a very low rmse (1e-13) for the clean curve (p=0). for noisy curves, the errors of the extracted parameters were smaller than 10% for p lower than or equal to 6%. for higher values of p, the errors were smaller than 30%. keywords-solar cells; parameter extraction; genetic algorithms; crossover operators i. introduction the current-voltage (i-v) characteristic of a solar cell (sc) is often predicted by the single diode model (sdm) [1]:     / 1s thv r nvph i s p s ii i i e g v r        (1) where vth = kt/q is the thermal voltage, t is the temperature, k is the boltzmann constant, and q is the elementary charge. the photocurrent iph, the reverse saturation current is, the ideality factor n, the series resistance rs, and the parallel conductance gp are sdm parameters that are commonly supposed constants independent of temperature and voltage. the non-linear nature of this equation makes the extraction of sdm parameters from i-v characteristics a very hard task. since the '60s, many methods have been proposed [1-12]. despite their huge number, none is wholly satisfactory and there is a need and a challenge to propose new methods. the proposed methods are either analytical or numerical [12-13]. the analytical methods, mainly published before 2000, often operate in specified regions of i-v curves and require prior knowledge of some defined points, such as the short-circuit current isc, the opencircuit voltage voc, the current im, and the voltage vm at the maximum power point [13]. the numerical methods are based on deterministic or metaheuristic optimization algorithms (moas) that process over the whole curve and do not require any specified points. deterministic algorithms are based on initial conditions, require curve derivatives, and do not guarantee a global solution. these drawbacks were overcome by moas [14], where evolutionary algorithms (eas) constitute an important subclass. hence, they are increasingly used in sc parameter estimation [1, 4]. despite the huge number of proposed methods, only a few deal with the effects of noise levels on the extracted parameters [9-13, 15, 16]. this is an important issue, since noise is always present in the measured data and may vary with environmental conditions. only [12] and [13], by proposing a least squares-based method and four metaheuristic-based methods, namely, the self-adaptive differential evolution algorithm (sade), the performance guided jaya algorithm (pgjaya), the self-adaptive teaching-learning-based optimization algorithm (satlbo), and the biogeo-graph-based heterogeneous cuckoo search engineering, technology & applied science research vol. 13, no. 3, 2023, 10630-10637 10631 www.etasr.com tebbal & hamida: effects of crossover operators on genetic algorithms for the extraction of solar … algorithm (bhcs), respectively, evaluated in-depth the effect of noise on the extracted parameters. these studies investigated the effect of noise levels from 0 to 10% on each method and parameter. in addition, in [13], the performance of the methods was analyzed by varying the population size. this study investigated the effects of noise on the extracted parameters of scs using gas, compared 3 distinct crossover operators (xos), and showed that the performance depends on the chosen xo. experimental and synthetic noisy and noisefree curves were used. the study of the effects of xo on gas applied to the extraction of sdm from noisy curves has not been considered before. ii. problem formulation the sc parameter estimation problem is formulated as finding a vector p=(iph, is, n, rs, gp) such that n synthetic data (is,i-vi), generated with the sdm (1), fit the experimental ones (ie,i-vi). the problem is solved by minimizing an objective function (of) that calculates the error between the experimental and synthetic data. this study used the root mean square estimation (rmse) defined by (2) as of, which is the most used in fitting problems [1-12]: rmse = ��� ∑ ��,� − ��,�� ����� (2) iii. genetic algorithm tuning since their introduction in [17], gas have been increasingly studied, developed, and used in solving complex problems in science and engineering [18-19], machine learning [20], economics and finance [21], vlsi design [22], embedded system design [23], and others [24-25]. gas are metaheuristic methods that mimic darwin’s natural selection principles and genetics, that is, survival of the fittest [14, 26], and use selection, mutation, and crossover genetic-like operators. when using gas, decisions have to be made on the stopping condition, the alphabet used, the population size, the genetic operators, and the corresponding probabilities to use. the program was set to stop when either it reached 20000 generations or all solutions in the population were in a prescribed standard deviation of 10 –12 . real coding (rcga) was used to provide good resolution, where each chromosome was a p vector with the sdm parameters. the selection and mutation operators were set to the 'roulette wheel' and 'gaussian', respectively, and the probabilities were fixed to pcross=0.9 and pmut=0.01 for the crossover and the mutation operators, respectively. the population size was taken as a variable in the range of [20, 20000]. since gas are considered to get their power from the xo [27-28], three widely used xos were compared: the uniform, the arithmetic, and the blend operators [29-31]. a. uniform operator the uniform crossover operator (uxo) is inherited from binary coding and was historically the first one to be used [26]. when two chromosomes are crossed, each gene of the offspring randomly comes from the first or the second parent. when used with rcga, uxo does not create new values of genes other than those initially created. only mutation can do this. b. arithmetic operator given two parents x and y with genes xi and yi, respectively, and αi in [0, 1], the arithmetic crossover operator (axo) creates two offsprings z and w whose genes zi and wi are: �� = ���� + �1 − ����� �� = ���� + �1 − ����� (3) where αi are either uniform random numbers or constants in uniform and non-uniform axo, respectively. axo reduces the range of gene values in the population. c. blend operator given di=abs(xi-yi) and a fixed α, usually 0.5, the blend crossover operator (bxo) creates an offspring u whose genes are uniform random numbers in the interval ui given by [32]: �� = �� !���, ��� − �"�, �#����, ��� + �"�$ (4) bxo enlarges the range of gene values in the population. iv. computational procedure the gas were coded in c++ using the galib library [33], and applied to the experimental and the synthetic versions of the most used benchmark i-v curve [34]: a 57mm diameter crystalline silicon sc from rtc france, operating at 33°c and 1000w/m 2 . the synthetic version was simulated with (1) in the voltage range of [0-0.6v] using the parameters of [13], shown in table i, along with the restricted search intervals. since the exact values are known, the convergence can be easily analyzed. to study the effect of noise on the extracted parameters, an artificial noise was added to the synthetic curve [9, 12-13, 15, 35]: �%&��' = ��'% × �1 + ) × rand� (5) where inoisy is the noisy current, isyn is the synthetic noise-free current, rand is a random number between -1 and +1, and p is the noise level from 0 to 10%, to be added. for each xo considered, gas were run by varying p and npop. to obtain a statistical evaluation, 100 ga runs were executed for each pair (p, npop), and the best solution and related parameters (rmse, p) were saved for each run. the parameter values corresponding to the best rmse on the 100 runs were then selected as the solution. two other important quantities, the absolute (δ) and the relative error (δβ) between the exact and the best values, respectively, were also computed. table i. exact values and search intervals of the parameters applied to ga iph (a) is (µa) n rs (ω) gp (ω -1 ) exact 0.7608 0.3223 1.4808 0.0367 0.0173 low 0.0000 0.1000 1.0000 0.0001 0.0001 high 1.0000 1.0000 2.0000 1.0000 1.0000 engineering, technology & applied science research vol. 13, no. 3, 2023, 10630-10637 10632 www.etasr.com tebbal & hamida: effects of crossover operators on genetic algorithms for the extraction of solar … v. results and discussion this section presents the results of applying gas to the parameter extraction of the noise-free and noisy curves and the benchmark cell considering the three xos. a. synthetic curve 1) noise-free curve figure 1 shows the rmse obtained for the 3 considered xos as a function of npop. according to [13], a good rmse for this sc should be smaller than 9.86022×10 -4 . as such, the fittings obtained by using bxo with all npop and uxo and axo with npop of at least 150 and 100, respectively, are good. for uxo and axo, the rmse achieved was not less than 2×10 -5 and 2×10 -4 , respectively, while for bxo it steeply decreased to smaller values by several orders of magnitude: 5×10 -4 , 2×10 -5 , 2×10 -8 , 1×10 -13 , and 2×10 -16 for npop=20, 50, 100, 150, and 20000, respectively. running gas using bxo with npop=50 gives an equivalent performance to using uxo with npop=20000. for greater npop, bxo outperformed uxo and axo. however, bxo converges very slowly, in more than 2000 iterations. on the other hand, uxo and axo perform between 45 and 200 iterations until convergence is reached. the fast convergence to a non-optimal value and the slow decrease of the rmse indicate that these xos favor premature convergence. uxo does not create new genes other than those initially generated, and axo does not explore the space outside the parents. the iterations quickly reach a state where there is no population diversity. several techniques have been proposed to avoid premature convergence, but their study is beyond the scope of this work. fig. 1. rmse of the noise-free curve as a function of population size (npop) for the three crossover operators. a) the uxo operator figure 2 shows the relative error δb of the extracted parameters as a function of npop and the slow increase of precision (decrease of the error) as npop increases. iph is the parameter extracted with the highest precision, followed, in not less than one order of magnitude away, by n, rs, gp, and is. with npop greater than 150, the errors were always smaller than 20%, and for 20000 they were smaller than 0.4%. this corresponds to the region where the rmse was less than 1×10 -3 %. this increase is ascribed to the increase in the resolution of the initial population. better performance can be achieved by increasing npop at the expense of huge memory space and execution time. despite these results, a smaller rmse was expected since the exact parameter values were known and the noise-free data. it was expected to get all the significant digits (sds) of the parameters given in table i to generate the curve using (1). such performance can be easily obtained with the newton-raphson method. given the values and precision of each parameter, it can be easily shown that the errors must be smaller than 6.5×10 -3 %, 1.5×10 -2 %, 3.3×10 -3 %, 0.14%, and 0.29% for iph, is, n, rs, and gp, respectively, to extract all sds of each parameter. so, each error must be smaller than 3.3×10 -3 % to extract all sds from the 5 parameters. this can be verified in table ii which shows the rmse, the extracted parameters, and the errors obtained with npop=100, 1000, and 20000. a comparison of tables i and ii shows that for npop=20000, the extracted parameters were close to the exact values. however, there is a lack of precision since, although all sds of iph and rs were found, there was a loss of two sds for is and n and one for gp. for more practical cases, i.e. npop =100 and 1000, all sds were lost for is and 2 were lost for iph, rs, and gp. for n, 4 and 3 sds were lost for npop values of 100 and 1000. despite this lack of precision, a good fit was obtained and all rmses for npop greater than 150 were better than the value of 9.86022×10 -4 found in [13]. table ii. results for noise-free curve using uxo npop 100 1000 20000 param value δb(%) value δb(%) value δb(%) iph(a) 0.76156 9.99e-2 0.76102 2.87e-2 0.76082 2.75e-3 is(µa) 0.56704 75.94 0.26864 16.65 0.32390 0.4978 n 1.54066 4.043 1.46262 1.228 1.48131 3.47e-2 rs(ω) 0.03419 7.011 0.03736 1.614 0.03673 8.29e-2 gp(ω -1 ) 0.01839 6.190 0.01609 10.25 0.01738 0.3698 rmse 1.193e-3 3.287e-4 2.154e-5 fig. 2. errors of the extracted model parameters of the synthetic noise-free solar cell as a function of the population size for the uxo operator. b) the axo operator figure 3 shows δb as a function of npop. iph was extracted with the highest precision, followed by n, rs, gp, and is at several orders of magnitude away. the precision increased very slowly with increasing npop and the errors were smaller than 50% only for npop greater than 500. figure 1 shows that the rmse was less than 1×10 -3 for npop greater than 100. the effect of premature convergence was stronger and the precision of the extracted parameters was lower than in uxo. table iii shows the rmse, the extracted parameters, and the errors obtained with npop=100, 1000, and 20000, where there was a lack of precision, although all rmses were good. although 3 sds were found for iph, all sds of is were lost, and only 1 was found for the other parameters. engineering, technology & applied science research vol. 13, no. 3, 2023, 10630-10637 10633 www.etasr.com tebbal & hamida: effects of crossover operators on genetic algorithms for the extraction of solar … fig. 3. errors of the extracted model parameters of the synthetic noise-free solar cell as a function of the population size for the axo operator. table iii. results for noise-free curve using axo npop 100 1000 20000 param value δb(%) value δb(%) value δb(%) iph(a) 0.76085 6.75e-3 0.76065 1.97e-2 0.76072 9.90e-3 is(µa) 0.54841 70.15 0.44515 38.12 0.42017 30.37 n 1.53643 3.7570 1.51404 2.2446 1.5081 1.845 rs(ω) 0.03460 5.908 0.03531 3.959 0.03568 2.969 gp(ω -1 ) 0.01433 17.27 0.01501 13.30 0.01553 10.33 rmse 8.780e-4 5.766e-4 4.047e-5 c) the bxo operator figure 4 shows that the δb of the extracted parameters using bxo was less than 1% for all considered npop. iph was the parameter extracted with the highest precision, as its corresponding error was always lower than 1×10 -3 %, and for npop greater than 400 it was 0% (it was set 1×10 -15 % in figure 4 for the sake of logarithmic scale). this parameter was followed, not less than one order of magnitude away, by n, rs, gp, and is. the increase of precision was very fast as npop increased from 20 to 400. the error of is decreased from 1% to 1×10 -11 %. when npop increased from 400 to 20000, the precision slowly increased and the error of is decreased from 1×10 -11 to 1×10 -13 %. the errors obtained, less than 1%, show that for npop as low as 20, at least one sd was found for each parameter. for npop=100, the absolute errors were 1.31×10 -6 %, 1.88×10 -3 %, 5.92×10 -4 %, 2.39×10 -5 %, and 3.62×10 -5 % for iph, is, n, rs, and gp, respectively. this is only a loss of two sds in is and one in n. for npop greater than or equal to 150, all sds of the parameters were exact in each ga execution. table iv. results for noise-free curve using bxo npop 150 1000 20000 error δ δb(%) δ δb(%) δ δb(%) iph(a) 9.4e-15 1.2e-12 0.0000 0.0000 0.000 0.000 is(µa) 1.1e-11 3.55e-9 6.7e-11 2.1e-12 5.6e-12 1.7e-13 n 3.6e-12 2.4e-10 2.1e-11 1.4e-13 1.7e-12 1.2e-14 rs(ω) 1.5e-13 4.1e-10 8.7e-13 2.4e-13 7.0e-14 1.9e-14 gp(ω -1 ) 2.3e-13 1.38e-9 1.6e-12 9.3e-13 1.7e-13 1.0e-13 rmse 1.418e-10 2.686e-15 2.695e-16 table iv shows the rmse, δ, and δb of the extracted parameters for npop=150, 1000, and 20000. the maximum δ (1.14e-11), was seven positions away from the last sd of is. hence, increasing npop to over 150 did not improve the precision. figure 1 shows that running gas using bxo with npop=50 gave equivalent rmses as using uxo with npop=20000. figures 2-4 for these npop show that bxo had better precision, and outperformed uxo and axo with npop=150. fig. 4. errors of the extracted model parameters of the synthetic noise-free solar cell as a function of the population size for the bxo operator. d) comments the precision of the sc parameters extracted by gas from noise-free data was greatly affected by the xo used. as reported in [36], obtaining a good fit, a synonym for good rmse, does not prove the validity of the model parameters. parameter extraction can have many purposes. if the goal is a good fitting regardless of the parameter precision, gas can be run several times either by using bxo with a very low npop, such as 20, or by using uxo or axo with a low npop, such as 150, and pick the best solution. if the goal is good precision (δb<10%), gas can be run several times using uxo with a high npop, such as 2000, and pick the best solution. if the goal is a high parameter precision (δb<1%), gas can be run using uxo several times with a very high npop, such as 20000, and pick the best solution. for all purposes, gas can be run only once using bxo with a relatively low npop, such as 150, and get very good fitting and parameter precision. axo gives parameters with very low precision for all npop, and can only be used for good fitting. 2) noisy curve a noise level p varying from 0.1 to 10% was added to the synthetic curve using (5). the parameters of the noisy curves were extracted by gas using uxo, axo, and bxo. for all cases, the solutions were picked as the best over 100 runs of gas. a) the uxo and axo operators figures 5 and 6 show the errors of the parameters extracted by the gas with npop=20000 using uxo and axo, respectively, as a function of noise levels. the errors were independent of noise levels for all npop values. for the two xos, iph was the parameter extracted with the highest precision for all noise levels, with errors less than 1.2% and 0.5% for uxo and axo, respectively. although the errors were acceptable for rs and n, with 14% and 7% for uxo and axo, respectively, they reached very high values for gp and is. the is and gp values were 120% and 210% for uxo and 45% and engineering, technology & applied science research vol. 13, no. 3, 2023, 10630-10637 10634 www.etasr.com tebbal & hamida: effects of crossover operators on genetic algorithms for the extraction of solar … 80% for axo, respectively. therefore, axo performed better than uxo. b) the bxo operator figure 7 shows the results obtained with ga using bxo with npop=250 as a function of p, where the errors increased with p. all errors were lower than 10%, except for is which reached 30% for p more than 6%. the errors of iph, n, rs, and gp were always less than 0.1%, 2%, 2%, and 10%, respectively. for practical cases with p less than 5%, all errors were less than 10%. thus, bxo outperformed axo and uxo for noisy curves. fig. 5. errors of the model parameters of the noisy synthetic solar cell as a function of the noise level for the uxo operator and npop=20000. fig. 6. errors of the model parameters of the noisy synthetic solar cell as a function of the noise level for the axo operator and npop=20000. fig. 7. errors of the model parameters of the noisy synthetic solar cell as a function of the noise level for the bxo operator and npop=250. c) curve fitting figures 8-10 show the noisy curves corresponding to p=1, 2, 5, and 10%, along with the corresponding fitting curves by uxo, axo, and bxo. comparing the curves with the synthetic curve (p=0%) shows the good fit obtained by axo and bxo. in the region isc-im, uxo gave a less good fit, which is acceptable only when considering that the curves are noisy. fig. 8. noisy synthetic data and corresponding fitted curves with parameters extracted by using uxo with npop=20000. fig. 9. noisy synthetic data and corresponding fitted curves with parameters extracted by using axo with npop=20000. fig. 10. noisy synthetic data and corresponding fitted curves with parameters extracted by using bxo with npop=250. d) comments for the noise-free curve, the quality of fit and the precision of parameters extracted by gas were highly affected by the used xo. while axo and bxo give good fitting, only bxo gives good parameter precision. for uxo, neither the fitting nor the parameter precision is good. b. experimental data the gas were applied to the parameter extraction of the most used sc in the literature [34]. table v shows the optimal obtained results along with those of some recently published studies, namely grouping-based global harmony search engineering, technology & applied science research vol. 13, no. 3, 2023, 10630-10637 10635 www.etasr.com tebbal & hamida: effects of crossover operators on genetic algorithms for the extraction of solar … (gghs) and innovative global harmony search (ighs) [37], self-adaptive differential evolution (sade), performance guided jaya (pgjaya), and self-adaptive teachinglearning-based optimization (satlbo) [13], and differential evolution with dynamic control factors (dedcf) [38]. figure 11 shows the obtained fitting. the results of uxo and axo were obtained with npop=20000 and were very close to those of bxo. however, they were obtained only once in all gas runs, and there is no guarantee that they will be reproduced in other runs. axo gave better results than those of [13] and [37], but worse than bxo, due to the strong effect of premature convergence. table v. parameters extracted by different methods work iph(a) is(µa) n rs (ω) gp (ω -1 ) rmse (×10 -4 a) this work bxo 0.7608 0.3107 1.4773 0.0365 0.0189 7.73006 uxo 0.7606 0.3059 1.4757 0.0367 0.0181 7.87296 axo 0.7606 0.4455 1.5143 0.0349 0.0157 9.65930 previous works gghs [37] 0.7609 0.3262 1.4822 0.0363 0.0188 9.9097 fébba [13] (a) 0.7068 0.3230 1.4812 0.0364 0.0537 9.8602 decdf [38] 0.7608 0.3107 1.4767 0.0365 0.0189 7.73006 ighs [37] 0.7608 0.3435 1.4874 0.0361 0.0188 9.9306 a: de, pgjaya, and satlbo [13] fig. 11. experimental data and fitted curves for the rtc solar cell. bxo gave the same rmse, iph, is, rs, and gp as decdf which had the smallest rmse (7.730062×10 -4 ) for this sc [38]. there is only a small difference of 0.04% in the value of n, 1.4773 for bxo against 1.4767 for decdf. the concordance seems perfect. it can also be noticed that the results shown in table v for bxo were reproduced in each ga run for all npop greater than or equal to 150 (1100 executions). differences were observed only beyond the 7 th sd. hence, bxo outperforms uxo and axo and competes with the most efficient methods. vi. conclusion this study analyzed the accuracy of the 5 sdm parameters of scs using gas by considering the effect of 3 xos, namely the uxo, the axo, and the bxo. three datasets were used, an experimental benchmark cell and simulated curves with noise levels (p) of 0-10%. the analysis was performed by varying npop from 20 to 20000. for each triplet (xo, p, npop), 100 ga runs were conducted and the solution was picked as the result of the best run. the simulation results showed that the performance of gas varied significantly with the employed xo. when using uxo or axo with very high npop (as high as 20000), gas only produced good accuracy in the two following cases:  with uxo for the noise-free curve  with axo for the benchmark cell, obtaining an rmse of 7.87296×10 -4 . as this result was obtained only once in more than 1400 runs, there is no guarantee that it can be reproduced. for all other cases, the parameter accuracy is very low, explicitly:  with uxo, for noisy data and the benchmark cell  with uxo, for the noise-free curve with low and moderate npop  with axo, for noise-free and noisy data  with axo, for the benchmark cell with low and moderate npop. this performance is a consequence of premature convergence, a well-known problem of eas. as such, gas with uxo or axo are not appropriate for sc parameter extraction. on the other hand, gas give very high accuracy when using bxo with a npop as small as 150, for all analyzed cases:  for the noise-free curve, the parameter errors were smaller than 10 -13 %  for noisy data, the parameter errors were smaller than 10% for practical cases, i.e. for noise up to 5%, and smaller than 30% for p up to 10%  for the benchmark data, gas gave the same rmse as dedcf [38], which has provided the smallest rmse for this sc equal to 7.730062×10 -4 . it is important to note that the above results were reproduced in each of the 100 ga runs for each npop and had the same quality as the 5 methods considered in [13]. these results demonstrate that for sc parameter extraction, gas with bxo should be classified at the top of the most efficient eas. previous studies carried out on clean data, concluded that gas give bad precision or/and are not appropriate for scs parameter extraction [1-4, 6, 39, 40]. this study used clean and noisy data, showing that if such conclusions are correct for uxo or axo, they are not correct for bxo. therefore, this study recommends the use of ga with bxo for sc parameter extraction. this result has to be confirmed with other ofs, other experimental data, and other xos. future works on eas must study the effects of varying the genetic operators on the extracted parameters. acknowledgment the authors acknowledge the support of the directorategeneral for scientific research and technological development (dgrsdt), algeria. the software of this study engineering, technology & applied science research vol. 13, no. 3, 2023, 10630-10637 10636 www.etasr.com tebbal & hamida: effects of crossover operators on genetic algorithms for the extraction of solar … used the galib genetic algorithm package, written by matthew wall at the massachusetts institute of technology. references [1] v. j. chin, z. salam, and k. ishaque, "cell modelling and model 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[40] n. barth, r. jovanovic, s. ahzi, and m. a. khaleel, "pv panel single and double diode models: optimization of the parameters and temperature dependence," solar energy materials and solar cells, vol. 148, pp. 87–98, apr. 2016, https://doi.org/10.1016/j.solmat.2015.09.003. microsoft word etasr_v13_n2_pp10232-10238 engineering, technology & applied science research vol. 13, no. 2, 2023, 10232-10238 10232 www.etasr.com najim: electrical behavior of lanthanum aluminate (lao) and gadolinium doped ceria (gdg) … electrical behavior of lanthanum aluminate (lao) and gadolinium doped ceria (gdg) composite electrolyte for electrochemical devices mohd najim department of electrical and electronic engineering, college of engineering, university of jeddah, saudi arabia mngalib@uj.edu.sa (corresponding author) received: 9 november 2022 | revised: 12 january 2023 | accepted: 15 january 2023 abstract the lao-gdc solid composite electrolyte has been proposed for use in solid oxide fuel cells (sofc). the material conductivity of solid carbonate-ceria (scc) composite electrolytes is 0.04scm -1 between 400 and 700°c. for this purpose, mixtures of laalo3 (lao) and gadolinium doped ceria ce0.8gd0.2o2 (gdc) were created in weight ratios of 3:1, 2:2, and 1:3. the composite electrolyte material was studied separately to improve conductivity. the phase structure and microstructure were studied using an x-ray diffractometer (xrd) and scanning electron microscopy (sem), and the electrical behavior was investigated using impedance spectroscopy (is). the sem and energy dispersive x-ray spectroscopy (edx) demonstrated a compact structure with an acceptable atomic percentage of constituent elements and a uniform grain distribution. experimental investigation showed that this composite electrolyte had a high density of laalo3 (lao)-ce0.8gd0.2o2 (gdc) composites and an approximate 97% density of its theoretical. the electrical behavior of lao-gdc composites had the highest value of 0.1scm -1 at 700°c, which is more extreme than the individual conductivities of lao and gdc, according to electrochemical impedance spectroscopy (eis) techniques. among the three composite ratios of the system, only the weight ratio of 3:1 had better conductivity. the laalo3 (lao)-ce0.8gd0.2o2 (gdc) composite material has a higher activation energy of 1.5ev. keywords-x-ray diffractometer (xrd); lanthanum aluminate (lao); solid electrolyte; electrical conductivity; solid oxide fuel cells (sofcs) i. introduction solid oxide fuel cells (sofcs) have attracted a lot of attention due to their environmental friendliness, low cost, and lack of possible safety risks [1, 2]. fuel cell electrolytes are the primary focus of research, since they are the base component of sofcs. zro2, ceo2, bi2o3, lagao3, and rare earth zirconates are the most widely used solid oxide electrolytes for sofcs, with y2o3 stabilized zro2 being the most prominent [2-6]. to achieve high electrical conductivity, ysz requires a high operating temperature of nearly 1000°c. the high operating temperature does not alone pose a significant challenge in terms of electrode selection, however, the cost of materials will rise as a result [4, 7]. the ionic conductivity of ysz is lower at low temperatures than that of ceria-based electrolytes such as gadolinium-doped ceria (gdc) [8-11]. the conductivity order of both sdc and gdc is around 10 -2 scm -1 at 750°c, which is comparatively higher than that of stabilized zirconia [12-13]. the closest ionic radius of gd 3+ and ce 4+ may cause the highest electrical conductivity of gdc [14-15]. in terms of price, processing, and quality, ceria-based electrolytes have been evaluated as a low-temperature alternative. in sofcs, laalo3 may be a good alternative perovskite candidate for the oxide ions conductor (electrolyte) [16-18]. however, in an oxidizing environment, pure laalo3 has lower ionic conductivity and more flexible conduction behavior [19]. the ionic conductivity of electrolytes can be best used through composition change by choosing a suitable aliovalent dopant and its optimum concentration [20]. doping may be uniform or nonuniform depending on whether to form a solid mixture or a composite [21]. this study focused on a composite material as an electrolyte. in general, composite electrolytes are made up of two phases: one that contains regular oxygen ionic conductors and another that contains inorganic salts or oxides. as a result, lao-gdg is an effective novel electrolyte with a relatively high ionic conductivity at low temperatures [2, 22]. due to engineering, technology & applied science research vol. 13, no. 2, 2023, 10232-10238 10233 www.etasr.com najim: electrical behavior of lanthanum aluminate (lao) and gadolinium doped ceria (gdg) … their high oxygen ion conductivities, doped ceria and lanthanum gallate are investigated as potential ion conductor materials for lt-sofcs [23-24]. a combination of lanthanum aluminate (lao) and gdc was recently proposed as a lowcost electrolyte for sofcs with significantly improved conductivity. in intermediate/low-temperature sofcs, composite electrolyte materials have been extensively studied for their excellent consistency, electrical conductivity, and thermophysical properties [25-28]. as lao has a perovskite structure and gdc has a cubic fluorite structure, their combination, perovskite-fluorite, is a great oxide-ion conductor. the gdc-based composite electrolyte material can be prepared using a variety of synthesis methods. in [4], a mechanical mixing process was proposed to create a gdsmzr2o7-(li0·52na0.48)2co3 composite oxide ion conductor with a conductivity of 0.54scm -1 at 600°c, which was substantially higher than that of pure gdsmzr2o7 [27]. most studies recorded low sintering temperatures for composites after mixing with an automated ball mill [4]. the sintering temperatures of composite electrolytes have been reported to be lower than those of ancient oxygen-ion ceramics, such as gdc and rare earth zirconates [27-35]. according to [32], a composite electrolyte based on samarium-doped ceria (sdc)– yttria stabilized zirconia (ysz) exhibits improved electrical conductivity. by molten salt infiltration, a dual composite sdc-lnc was prepared with oxideand carbonate-ion conductors with a conductivity of 0.46scm −1 at 600°c. coating ysz with a new composite electrolyte of yttria doped ceria (ydc) and gdc for lt-sofc was proposed in [33]. only one cell evaluation revealed that ysz with doped ceria composite electrolyte, fitted by the sol-gel dip-drawing process, had better cell output than ysz electrolyte without ceria substrate separation. however, the interdiffusion of constituents at the boundaries can be a disadvantage of ysz and doped ceria composites, resulting in a decrease in conductivity [21, 34]. it has been discovered that an sdc-lsgm composite electrolyte with a weight ratio of 9:1 has a high oxide ion conductivity [19, 36]. this study investigated the lao-gdc composite system in terms of phase formation, elemental analysis, and electrical properties. the composites were made using the solid-state reaction process, however, lao and gdc were prepared and structurally analyzed separately. ii. methodology a solid-state reaction method was adopted to prepare this lao-gdc-based composite material whereas the lao was prepared by the auto-combustion method [37]. the following were used to prepare pure lao, gdc, and the composite material lao-gdc: la(no3)3.6h2o (alfa aesar, 99%), al(no3)3.6h2o (alfa aesar, 98%), ceo2 (99.9%, sigma aldrich, usa), and gd2o3 (99.9%, alfa aesar, usa). weighted lao-gdc composites with lao:gdc ratios of 3:1, 2:2, and 1:3 were produced. stoichiometric amounts of lao and gdc powder substances were mixed by a planetary ball mill using zirconia balls with a diameter of 3mm with ethyl alcohol for 24 hours. after the completion of ball milling, the composite powder was crushed manually in an agate mortar for 4 hours. the residual powder was then calcined at 700℃ for 8 hours and then uniaxially pressed into pellets under a pressure of 7 tons (0.711kg/cm 2 ). the prepared uncured pellets were sintered at a temperature of 1400℃ for 12h with a heating-cooling rate of 5℃/min. sintered pellet xrd patterns were observed using a rigaku miniflex ii desktop x-ray diffractometer under cu-ka radiation (30kv, 20ma) in the 20-80 range. the microstructure of sintered samples was captured using a quanta 200 fesem scanning electron microscope (sem). the existence of critical elements was investigated using energy-dispersive x-ray spectroscopy (edx). the sintered pellets were refined with emery paper to create a clean and smooth surface layer, and then silver (ag) paste was pasted on both sides of the pellet and fired for half an hour at 700°c. the electrical behavior of these pellets was studied using a wayne kerr 6500 p impedance analyzer in the range of 400-700°c at a step of 25°c in the frequency range of 20hz to 1mhz. based on archimedes' theory, the experimental densities of prepared sintered pellets were calculated using a density measurement instrument (sartorius, bsa2245cw). fig. 1. solid-state reaction synthesis techniques iii. results and discussion this study investigated lao-gdc with weight ratios of 3:1, 2:2, and 1:3, called l3g1, l2g2, and l1g3, respectively. a. structural and morphological properties figure 2(a) shows the xrd patterns of all the lao-gdc structures investigated, and the composites l3g1, l2g2, and l1g3. lao and gdc phases are represented by the symbols ♦ and *, respectively, and the phases of all explored system components are also indicated. the expanded view shown in figure 2(b) of the more intense peak between 20-35c clearly shows the minor right shifting of the peaks as the gdc doping concentration increased. the intensity of the peak corresponding to a 121 plane decreases with increasing gdc concentration, showing decreasing crystallite size in the sem micrograph. the xrd phase patterns of lao and gdc are also listed as references, with single-phase rhombohedral perovskite structure and cubic fluorite structure, respectively, having space groups r-3c and fm3m that suit well with the jcpds files no. 82-0478 and 81-0792. the system shows single-phase formation as a result of high-temperature sintered pellets. this study achieved an optimized conductivity of 0.46×10 -1 scm -1 for the l1g3 system; therefore, the physical behavior of this composite is discussed. engineering, technology & applied science research vol. 13, no. 2, 2023, 10232-10238 10234 www.etasr.com najim: electrical behavior of lanthanum aluminate (lao) and gadolinium doped ceria (gdg) … fig. 2. (a) xrd pattern of lao, gdc, and their composites l3g1, l2g2, and l1g3, (b) expanded view of the more intense peak between 20-35c (crystal structure). fig. 3. sem microstructure of composites (a) l3g1, (b) l2g2, and (c) l1g3. elemental mapping of composites: (d) l3g1, (e) l2g2, and (f) l1g3. the xrd pattern of sintered composite pellets consists of perovskite rhombohedral structure (r-3c) lao as a major phase along with minor gdc cubic fluorite structure (space group, fm3m). peaks were indexed using the above-mentioned space group [16, 38]. using the archimedes principle, the densities of sintered composite pellets were measured at 6.4, 6.6, and 6.7g/cm 2 for l3g1, l2g2, and l1g3, respectively, which is 97% of the theoretically calculated va;ues. the sem micrographs of the sintered pellets' rupture surface were logged for all systems. figure 3 illustrates the sem micrograph of the fractured samples of all three composites. the sem image clearly shows hexagonal and cubic grains having dense and well-connected structures. the sem micrographs clearly show the white color cubic structure of the gdc and are in good agreement with xrd patterns. the captured sem microstructure shows a very dense and compact shape for l1g3 than the others, which is congruent with observed experimental density values. furthermore, sem micrographs depict comparatively small grain sizes when increasing the gdc ratio. the average particle size of all three compositions was calculated using the linear intercept process, yielding values in the range of 1.27-1.98nm. the average grain size value for l1g3 was found to be lower than those of the other compositions. using scherer's formula, the average crystallite size was calculated to be in the 40-50nm range [16]. the structure with a smaller particle size or a large grain boundary has more oxygen vacancies resulting in higher conductivity [13, 19, 38]. the energy-dispersive spectroscopy (eds) study, shown in figure 4, shows all the atomic constituents and their atomic percentage. the percentage of the atomic value of o, ce, and gd is higher in l1g3. the elemental mapping (figure (3 (d-f)) for all composite systems showed the presence of all elements in their appropriate ratio which is also confirmed by the edx study in figure 4. fig. 4. eds of the composites l3g1, l2g2, and l1g3. b. electrical properties the electrical behavior of composites was studied using complex plane impedance analysis in the frequency range of 20hz to 1mhz. two constraints were used to estimate the electrical conductivity: conductance (g) and dielectric constant (d). the real (z) and the imaginary (z) part of impedance were used in the complex plane impedance analysis [16] and can be calculated with the help of the formula given in (1) and plotted on the x and y axes, respectively. �� � �� ����� and ��� � �� � (1) figure 5 shows the representative nyquist graph of the l1g3 composite in different temperature ranges of 475-700c. complete conductivity is the sum of all individual conductivities attributable to the grain, grain boundary, and electrode-specimen interface in high-, intermediate-, and lowfrequency regions, respectively [34, 39-40]. a wide semicircular arc near the origin was observed at low temperatures (400°c), indicating a high-frequency field, due to grain influence. engineering, technology & applied science research vol. 13, no. 2, 2023, 10232-10238 10235 www.etasr.com najim: electrical behavior of lanthanum aluminate (lao) and gadolinium doped ceria (gdg) … fig. 5. nyquist plots of l3g1 composite in the temperature range of 475700c. increasing temperature, this large semicircular curve due to grain contribution (near the origin) becomes small at intermediate temperatures and disappears at high temperatures. this movement of the semicircular arc to the right-hand side is due to the relaxation frequency of polarization processes [34, 39-41]. therefore, with increasing temperature, the semicircular arc related to grain contribution disappears, as shown in figures 5 and 6 (the latter being plotted in log scale). the semicircular arc due to electrode polarization starts to appear at a high temperature and is visible at ~700℃. at high temperatures (700℃), at first the straight line due to the grain contribution appears, and then the single semicircle, as shown in figure 6(b), at the in-between frequency indicates that conduction is primarily through grain boundaries [39-42]. since the ratio of grain boundary resistance (rgb) to grain resistance (rg) is not important, grains play a significant role in total conductivity at low temperatures, i.e. rgb<rg. however, on increasing temperatures, this ratio increases slowly and becomes large at high temperatures (~700c), i.e. rgb>rg. finally, at 700°c and above, the grain resistance (rg) vanishes, and the overall conductivity of the sample is calculated by the grain boundary resistance (rgb). as a result, at high temperatures, the conductivity due to grain boundary influences conductivity due to the grain (~700c). the grain resistance (rg) and grain boundaries resistances (rgb) can be calculated by calculating the intercepts of respective arcs on the real axis (z). temperature dependence activation energy for the composite l1g3 is exposed by the arrhenius plot with log (σt) on the y-axis vs 1000/t on the x-axis, as shown in figure 5. a linear relationship (straight line) was observed in the complete temperature range (400-700c). the activation energy (ea) of the composite l1g3 is determined by the slope of this straight line, as shown in figure 5. the formation energy and migration barrier may be triggering the activation energy for conduction. the conductivity of a material is related to the defect and is measured as σ=neμ, where n, e, and μ are the concentration, the charge of the defect, and the mobility, respectively. the concentration n, on the other hand, consists of both thermally activated and athermal defects [41], i.e., n=na+nt, where nt is the concentration of defects that are thermally stimulated in the measurements at predetermined temperatures and na is the athermal concentration involving defects, e.g. prior in the material before the conductivity measurements but at lower temperatures. this study measured samples at intermediate temperatures from 400 to 700c and therefore the thermally activated defects play an important role, i.e. nt>na. furthermore, since ea=ef+em [41], the measured value of the activation energies (ea) was found to be approximately 1.5ev, which is in good agreement with the values of lao and gdc in [20, 43], and indicates that the activation energy of ionic conduction is comparable to the activation energy of vacancy mobility [19]. the mobility of oxygen ions is a temperaturedependent property that decreases as the temperature increases [44-45]. equation (2) can be used to express the temperaturedependent ionic conductivity: � � � exp � ��� ��� (2) where σ0 is a fixed exponent factor and reverse temperature dependent. the measured activation energy values reveal that the movement of oxide ions is caused by ionic transport [20, 44, 46]. the activation energy of an electrolyte device (oxide ion conductor) is estimated to range between 0.9 and 1.8ev [20, 47, 49-50]. therefore, the investigated composite system is ionic in nature, and its conductivity is mainly determined by thermally activated oxygen ions [49-51]. the ionic conductivity of all investigated compositions, at 700c, was found to be of the order of 10 -1 scm -1 and l1g3 showed the highest conductivity magnitude. the ionic conductivity was found to be related to the development of oxygen vacancies at high temperatures. the conductivity of the investigated laogdc composite systems increases as the gdc ratio increases due to the formation of oxygen ion vacancies, which are primarily formed by gd 3+ ions. consequently, dopant concentration, grain boundaries, and grain size play an important role in determining conductivity and its variation. fig. 6. (a) representative fitted nyquist plot of l1g3 at 700°c, (b) arrhenius representation of conductivity of l1g3 at different temperatures (insight). engineering, technology & applied science research vol. 13, no. 2, 2023, 10232-10238 10236 www.etasr.com najim: electrical behavior of lanthanum aluminate (lao) and gadolinium doped ceria (gdg) … the influence of gd 3+ ions on the lanthanum site plays a role when the conductivity is rising and then falls off activation energy accordingly. the activation energy of pure laalo3 was reported as 0.90±0.01ev [52], while the activation energy of gdc was reported as 0.55-1.04ev [11, 14] and for the laogdc composites was found to be 1.51ev. the value of the observed activation energy for this composite shows enhanced ionic conductivity which rises with a rise in the gdc ratio. furthermore, the improvement in conductivity is consistent with the compact microstructure of the composites. the conductivity of the l1g3 composition was found to be the highest among the three compositions investigated and provides a better option for cost-effective solid electrolyte applications in electrochemical devices. iv. discussion at moderate temperatures, the conductivities of gdc are approximately 10 -2 scm -1 , which is inflated when compared to stabilized zirconia. the maximum electrical conductivity of gdc may be a result of the fact that gd 3+ and ce 4+ have close ionic radii. ceria-based electrolytes have been examined as a low-temperature alternative in terms of cost, processing, and quality. laalo3 might be a good substitute perovskite option for the oxide ion conductor in sofcs. improved electrical conductivity can be found in a composite electrolyte made of samarium-doped ceria (sdc) and yttria stabilized zirconia (ysz). in this paper, a dual composite sdc-lnc constructed with oxideand carbonate-ion conductors with a conductivity of 0.46scm -1 at 600°c was infiltrated with molten salt. cell evaluation showed that the sol-gel dip-drawing procedure fitted ysz with a doped ceria composite electrolyte had better cell output than the ysz electrolyte without ceria substrate separation. however, ysz and doped ceria composites may suffer from the inter-diffusion of components at the borders, which would reduce conductivity. an sdc-lsgm composite electrolyte with a weight ratio of 9:1 has previously been found to have a high oxide ion conductivity. v. conclusion this study successfully synthesized lao-gdc composites employing a quick, simple, and efficient solid-state reaction method, with typical crystallite sizes of 41-50nm. lao and gdc, respectively, made the hexagonal and cubic fluorite structures visible. when these two were joined, lao-gdc composites showed the same phase. the density of the highdensity composite systems sintered at 1400°c was 97% of the theoretical. the l1g3 samples had a microstructure that is more dense and fine than the other samples. as the amount of gd 3+ doping was increased, gdc's conductivity rose. the l1g3 composition obtained its maximum conductivity of 0.4×10 -1 scm -1 with an activation energy of 1.51ev. the laogdc composite is predominantly an l1g3 system, as seen by this peculiar electrical behavior. acknowledgment this work was funded by the deanship of scientific research (dsr), university of jeddah, saudi arabia, under grant no. uj-20-006-dr. therefore, the author acknowledges the university for the technical and financial support. the author is also grateful to the indian institute of technology in kanpur, for providing the experimental facilities. references [1] s. a. saadabadi, a. thallam thattai, l. fan, r. e. f. lindeboom, h. spanjers, and p. v. aravind, "solid oxide fuel cells fuelled with biogas: potential and constraints," renewable energy, vol. 134, pp. 194– 214, apr. 2019, https://doi.org/10.1016/j.renene.2018.11.028. 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17 july 2022 | accepted: 21 july 2022 abstract-columns are the structural members of buildings that ensure structural stability. a fire can severely affect the columns' structural performance by degrading the properties of their constituent materials, thereby reducing the strength capacity, stiffness, and stability. in seismic zones, the knowledge of the post-fire behavior of these elements is a fundamental requirement for a realistic seismic performance assessment. this study utilized numerical analysis using the parametric fire model of eurocode-1 to estimate the post-fire axial and lateral performance of reinforced concrete columns. in the first step, the axial loadbearing capacity was evaluated from a parametric study for cantilever columns. in the second step, the lateral load capacity, force-displacement behavior, stiffness, ductility, energy dissipation capacity, and residual displacements were estimated to determine the impact of fire damage on the behavior of columns under lateral loads. the results showed that both the lateral load capacity and the ductility of the reinforced concrete columns decreased significantly due to fire exposure. this also indicated that fire damage decreases the vertical load-bearing capacity, and the reduction in lateral capacity was attributed to the loss of concrete's compressive strength. the column characteristics that significantly influence the residual response behavior were identified as section size, column height, axial load ratio, and concrete's compressive strength. keywords-natural fire; columns; post-fire behavior; fire damage; residual strength; lateral load capacity i. introduction fires and earthquakes are among the most severe conditions buildings may face. in the case of fire, the structural and nonstructural elements may undergo different changes depending on the intensity and exposure duration. the fire safety of reinforced concrete (rc) structures highly depends on their fire resistance, which relies on the thermal conductivity and the resistance of load-bearing elements such as walls, columns, and beams. fire damage leads to a decrease in the strength and deformation properties of structures. a post-fire earthquake (pfe) is an eventual disaster, but its damage to rc members is complicated and usually affected by uncertain factors. the reinforced concrete structure can remain standing after a fire, or after an earthquake. the full or partial collapse of concrete buildings during a fire is rare, however, earthquakes following a fire can cause significant damage depending on the residual properties of the structural elements. in post-fire performance assessment, it should be decided whether to repair and strengthen or demolish and rebuild the entire structure, taking into account the earthquake loads during its remaining service life. the behavior of a structure after a fire is related to its residual bearing capacity, so it is necessary to determine, quantify, and compare it with the safety levels. the study of the impact of earthquakes on structures damaged by real fires is a fundamental issue in assessing concrete's structural behavior in severe load combinations. although the sequential application of these extreme loads may be too severe in most cases, this strategy may be appropriate for the design of important structures, where cost and technology are no barrier. however, current regulations do not consider fire and earthquake hazards [1]. several studies investigated the influence of fire on the mechanical strength of rc members and structures [2-4]. postfire material tests showed that concrete's mechanical properties degrade after fire exposure and do not fully recover after cooling [5-7]. different models were proposed in [8, 9] on the post-fire full stress-strain response of fire-damaged concrete and the residual stress-strain relationship after exposure to high corresponding author: mohamed baghdadi engineering, technology & applied science research vol. 12, no. 5, 2022, 9113-9119 9114 www.etasr.com baghdadi et al.: a parametric study of fire-damaged reinforced concrete columns under lateral loads temperatures. numerical investigations in [10, 11] evaluated the impact of fire duration and intensity on the residual loadbearing capacity and delayed failure of reinforced concrete columns. experimental research and test results on the post-fire behavior of rc columns were presented in [12, 13]. a new modified finite element model was developed in [14] to predict the behavior and strength of concrete-filled steel tubular subjected to axial compression, considering the influence of some determinant parameters. a numerical study examined the fire behavior of thermally insulated strengthened rc beams subjected to fire exposure in [15]. the effect of fire on the flexural behavior of rc beams was studied in [16, 17]. an experimental study on the seismic behavior of highperformance concrete frames after a fire was presented in [18], showing that fire exposure can transform the failure mode of a frame subjected to reverse-cyclic loads from strong-columnweak-beam to strong-beam-weak-column with poor cyclic performance. another study was conducted in [19] on the seismic performance of reinforced concrete beam-column joints after a fire and their practical strengthening. the performance of rc frame structures in post-earthquake fire loading and their failure times were analyzed in [20, 21]. in [22, 23], the seismic performance of rc short columns with light transverse reinforcement and rc beam-column joints under varying axial forces was investigated. several studies on fire resistance and post-fire seismic behavior of concrete shear walls were carried out experimentally and numerically [24-27]. a limited number of studies attempted to estimate the postfire lateral capacity performance of concrete columns. although the behavior of reinforced concrete columns at elevated temperatures has been extensively investigated under service loads after cooling, studies on post-fire seismic behavior of rc structural elements are extremely rare. the results of [28, 29] evaluated the post-fire seismic performance of reinforced precast concrete columns damaged by fire to determine the impact of fire damage on force-displacement behavior, moment-curvature relationship, and residual displacements. an experimental study investigated the seismic performance of shear critical post-heated rc columns that had been repaired [30]. in [31], the results of a study on the seismic resistance of strengthened concrete members after fire exposure were presented. furthermore, a numerical investigation of the response simulation of rc columns under lateral loads was conducted in [32]. in [33], the residual strength and lateral/seismic load capacity of rc columns after fire exposure were evaluated using numerical analysis. this paper presents a numerical analysis that investigates the behavior of rc columns damaged by fire under vertical load and evaluate the lateral bearing capacity under horizontal loads, including a parametric study to identify the influential column characteristics. this study employed the structural analysis software safir [34], which is capable of 3d simulation of building structures in fire. the parametric natural fire curves of eurocode-1 were selected to perform the simulations. ii. evaluation of vertical residual load-bearing capacity of columns each column was first subjected to constant loading, and then a section of the column was exposed to natural fire to assess its residual characteristics. loading was applied in successive simulations in a decreasing and monotonous manner, and the time of the collapse was calculated for each loading level. the corresponding loading level represents the load-bearing capacity of the column to resist natural fire, including the heating and cooling phases. a. time-temperature curves used the fire curves were taken from the parametric fire model of annex (a) of en 1991-1-2(2002) [35] that represents the action of a natural fire, including the cooling phase. figure 1 shows the various used fire curves, differing by the duration of the heating phase of 15, 30, 60, 90, and 120 minutes. fig. 1. time-temperature curves. b. parametric studies the following parameters were considered to evaluate the total residual capacity: • the section size of the column: 20×20cm, 30cm×30cm, 40×40cm, 60×60cm, and 80×80cm. • the duration of the heating phase of the fire (tpeak): 15, 30, 60, 90, and 120 minutes to assess the influence of the maximum temperature on the residual characteristics. • the height of the column: 3, 4, and 5m. • the columns were cantilever, fixed in rotation at the bottom and free at the top. c. results and discussions 1) influence of the effective height of the column table i shows the results for columns, considering their height, before and after fire exposure. a 30×30cm section was chosen to perform the simulations. for the same height, the influence of the maximum temperature during fire was considerable: a loss of 70% of vertical capacity (nr) was found for the fire of tpeak=60min for 3m columns. considering the variation in column height for the same fire, the residual vertical capacity (nr) of the 3m column was found to be greater than the 5m column's (about 90%). engineering, technology & applied science research vol. 12, no. 5, 2022, 9113-9119 9115 www.etasr.com baghdadi et al.: a parametric study of fire-damaged reinforced concrete columns under lateral loads table i. vertical load bearing capacity before (n20°c) and after fire exposure (nr) for columns height (m) before fire n20°c(kn) nr (kn) after exposure fire of tpeak=15min fire of tpeak=30min fire of tpeak=60min fire of tpeak=90min fire of tpeak=120min 3 1978 798 669 589.5 559.5 540 4 1446 589.5 498 441 420 406.5 5 972 396 339 304.5 292.5 283.5 2) influence of section size table ii presents the results of different-sized sections having the same height (4m). for the 40×40cm section, a loss of 75% was found for a 60min fire and a loss of 85% was found for the section of 80×80cm. the maximum temperature during fire exposure and cooling time was among the most important parameters responsible for the degree of concrete damage. the greater the section size, the higher the temperature gradient during the cooling phase and therefore, the higher damage induced in the concrete. with natural cooling, the interior temperature gradient within the concrete can be higher than during the heating phase. table ii. vertical load bearing capacity before (n20°c) and after fire exposure (nr) of sections section before fire n20°c (kn) nr (kn) after exposure fire of tpeak=15min fire of tpeak=30min fire of tpeak=60min fire of tpeak=90min fire of tpeak=120min sec20×20cm 295.5 123 108 99 96 93 sec30×30cm 1446 589.5 498 441 420 406.5 sec40×40cm 1725 652.5 537 466.5 439.5 421.5 sec60×60cm 8988 2847 2185.5 1776 1621.5 1521 sec80×80cm 16410 4689 3433.50 2658 2365.50 2175 iii. lateral load capacity evaluation of firedamaged rc columns the horizontal load capacity was also evaluated to examine the column's behavior under combined vertical and horizontal loads, which is a real situation that a column must survive in frame structures. the lateral load was assumed to be a seismic load. this process utilized a numerical safir model in a cold situation to investigate the lateral load response of the columns. the axial load was 25% and 50% of the residual vertical capacity nr and was held constant throughout the analysis. the lateral load was applied horizontally at the top of the columns in displacement-controlled mode and incremented from zero up to the column failure, as shown in figure 2. it was possible to estimate the maximum horizontal load hu that the column can support. the horizontal load hu represents the shear force that an earthquake can induce in a column. fig. 2. evolution of hu and nr. a. horizontal load-bearing capacity (hu) with vertical load the column was subjected to both axial load and lateral deformation. the axial load used was the vertical load capacity of the column after fire exposure. two loading rates were used: 25 and 50% of the residual bearing capacity. 1) effect of effective height for each fire and different heights, 44% and 42% loss of lateral capacity were found when applying 25% and 50% axial load of nr respectively, as shown in figure 3. (a) (b) fig. 3. hu as a function of various heights for (a) 0.25 of nr, (b) 0.5 of nr. engineering, technology & applied science research vol. 12, no. 5, 2022, 9113-9119 9116 www.etasr.com baghdadi et al.: a parametric study of fire-damaged reinforced concrete columns under lateral loads however, as can be observed in figure 3, the reductions in the lateral load capacities for the same height were less than the reductions in the compressive strength, which minimized the impact of the compressive strength on the column behavior. 2) influence of the size of the sections figure 4 shows the evolution of hu considering the effect of the section and the properties of the residual material after fire exposure. as the duration of fire increases, the residual properties of the material decrease, and a loss of 10% to 35% was evaluated for all columns considering the same height (4m). this degradation was due to the additional loss of the concrete’s compressive resistance caused by the continuity of the evolution of temperatures in the massive sections. for the same fire, the horizontal load-bearing capacity of the column can increase by 97% depending on the section's dimensions. (a) (b) fig. 4. hu as a function of section size: (a) 0.25 of nr (b) 0.5 of nr. b. evolution of the maximum lateral displacement 1) influence of the height of the column figure 5 shows the maximum lateral displacements at the top of the column for heights of 3, 4, and 5m using the same section of 30×30cm. considering the residual resistance of the materials after the fire, the maximum lateral displacement was calculated for each fire. the results showed that the displacement value increased about 36% at the top of the 5m column compared to the reference column of 3m. the largest lateral displacement was 16cm for the 5m column exposed to fire with a heating phase (tpeak) of 15 minutes. fire exposure has a greater effect on the residual compressive strength of concrete, and the structural response is governed by the geometrical properties of the column, such as inertia and height. fig. 5. evolution of maximal lateral displacement. 2) influence of the sections of columns figure 6 shows the influence of the section’s size on the maximum lateral displacement. for the 20×20cm sections, the displacement increased gradually and its maximum was about 13cm. this growth was due to fire damage to the mechanical residual property of the materials, and the strength of the columns decreased following the degradation of the strength. for the 80×80cm sections, the displacement of 5cm has a small variation, showing that a column's behavior depends on its geometrical properties. fig. 6. influence of section size on the maximum lateral displacement of a 4m column height. c. lateral loads and displacement response analysis horizontal displacements were calculated using the incremental method, evaluating the displacement for each time step. figure 7 shows the load-lateral displacement which traces the development of lateral displacement on the top of columns under the incremental loading. 1) energy dissipation the area enclosed by the curve and the horizontal axis in figure 8 is defined as the energy dissipated by the columns, representing the ability to consume seismic energy through plastic deformations. figure 7 shows that these curves are approximately straight lines before cracking. within each curve, the decrease in secant stiffness caused by fire loading is somewhat insignificant, leading to small energy dissipation. however, they bend towards the displacement axis towards the end of loading. in other words, the top lateral displacements develop at accelerating rates before the failure of the column. engineering, technology & applied science research vol. 12, no. 5, 2022, 9113-9119 9117 www.etasr.com baghdadi et al.: a parametric study of fire-damaged reinforced concrete columns under lateral loads the curves indicate that the stiffness of an unheated column is higher than that of a heated one. this is because elevated temperatures cause more damage to the stiffness of the column subjected to greater temperature exposure (120min fire). figure 8 also shows that the stiffness of the column exposed fires of 60, 90, and 120 minutes is very similar. this can be attributed to the damage caused by the high-temperature effect on the residual resistance of concrete. among the curves presented, the stiffness of the column that has not been exposed to elevated temperature is the highest. the loading curves indicate that an elevated temperature has a significant effect under these conditions. energy dissipation can be divided into two phases: pre-cracking and post-cracking. the energy dissipation capacity in the pre-cracking phase is very small. fig. 7. load-displacement curves of 3m columns. fig. 8. energy dissipated by the column. 2) ductility degradation the displacement ductility factor μδ, which is the ratio of the ultimate displacement δu to the yield displacement δy, was calculated for each column to compare the performance in terms of sustained ductility. under a particular drift level, table iii shows that the ductility of the unheated column is about 60% of the fire-damaged column. the differences in ductility mainly reflect the effect of fire on mechanical properties. furthermore, the differences in ductility mainly reflect that elevated temperature exposure reduces the capacity of the column. it can be concluded that the exposing temperature has a remarkable effect on the load-bearing capacity of the columns. the ductility of the columns was not found to be affected by fire exposure up to 30min. table iii. ductility parameters of the columns before fire (at 20°c) after fire of tpeak=15min after fire of tpeak=30min after fire of tpeak=60min after fire of tpeak=90min after fire of tpeak=120min lateral yield displacement δy(cm) 3.387 4.544 5.506 5.36 5.01 5.1 lateral ultimate displacement δu(cm) 5.405 6.368 5.506 5.36 5.01 5.1 ductility factor: μδ=δu/δy 1.6 1.40 1 1 1 1 iv. conclusions the following remarks can be extracted from this study: • the results showed that the lateral load capacity and ductility decreased substantially as a result of fire exposure. • post-fire lateral load capacities were not considerably affected by the increase in fire duration up to 60min. after 60min of fire exposure, a little reduction in the lateral load capacity of the column was observed, which minimized the impact of the concrete compressive strength loss on the post-fire lateral capacity of the columns. • the reduction in lateral load capacity appeared to be caused by the residual properties of the concrete after fire exposure. for low axial loads (25% of nr), the effects of vertical compressive load on the behavior of the columns were considerable. • the energy dissipation of the columns was not significantly affected by fires with duration up to 30min. for a column subjected to a 90min fire, the reduction was about 25% compared to an unheated one, which was attributed to the loss of compressive strength. the stiffness of the column after a 30min fire was not affected. the slope of energy dissipation curves was confusing after a 30min fire. • ductility reduction was significantly affected compared to an unheated column after a 15min fire. this reduction was attributed to the post-fire loss in the mechanical properties of concrete. this can be explained by the greater loss in concrete’s compressive strength and thereby the lower lateral load-bearing capacity of the columns. • the application of the available eurocode model for concrete after fire exposure resulted in a good estimation of the residual capacity of fire-damaged columns compared to the available existing results. nomenclature nr = vertical load-bearing capacity of a column. hu = horizontal load-bearing capacity of a column. engineering, technology & applied science research vol. 12, no. 5, 2022, 9113-9119 9118 www.etasr.com baghdadi et al.: a parametric study of fire-damaged reinforced concrete columns under lateral loads tpeak = time corresponding to the end of the heating phase duration of the heating 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[35] eurocode 1: actions on structures: part 1.2 general actions : actions on structures exposed to fire. london, uk: bsi, 2002. microsoft word etasr_v12_n6_pp9477-9482 engineering, technology & applied science research vol. 12, no. 6, 2022, 9477-9482 9477 www.etasr.com lavanya et al.: a deep learning technique for detecting high impedance faults in medium voltage … a deep learning technique for detecting high impedance faults in medium voltage distribution networks s. lavanya department of electrical and electronics engineering sri chandrasekharendra saraswathi viswa mahavidyalaya kanchipuram, tamilnadu, india lavanya@kanchiuniv.ac.in s. prabakaran department of electrical and electronics engineering sri chandrasekharendra saraswathi viswa mahavidyalaya kanchipuram, tamilnadu, india prabakaran@kanchiuniv.ac.in n. ashok kumar department of electrical and electronics engineering sri chandrasekharendra saraswathi viswa mahavidyalaya kanchipuram, tamilnadu, india ashokeee@kanchiuniv.ac.in received: 29 august 2022 | revised: 8 september 2022 | accepted: 9 september 2022 abstract-utility companies always struggle with the high impedance fault (hif) in the electrical distribution systems. in this article, the current signal is seen in situations involving 10,400 different samples, with and without hif, like linear, nonlinear load, and capacitance switching. a better method that processes signals very fast and with low sample rates, requiring less memory and computational labor, is demonstrated by mathematical morphology (mm). for hif identification, deep convolution neural networks (dcnns) are being developed. this paper presents a novel method for signal processing with low sample rates, high signal processing speed, and low computational and memory requirements. the suggested sixlayer dcnn is compared with other models, such as the fourlayer and eight-layer dcnn models and the results are discussed. keywords-high impedance fault; mathematical morpologhy; deep convolution neural networks i. introduction for a power system to operate securely and dependably, an adequate protective mechanism that can recognize, classify, and locate the system's defects is essential. even though standard protection relays are able to quickly recognize lowimpedance network faults [1-3], but they can't notice hifs' small fault current, something that represents a significant safety threat. in addition, the power network experiences cascading failures as a result of the hifs spreading into a functioning area of the grid system. therefore, hif detection is very important in a distribution system. feature extraction and classifier development are the first two steps in the detection of hif. numerous signal processing techniques (spts) have been presented to extract features for the purpose of training and testing classifiers during the pattern recognition stage using time-frequency transforms to obtain the proper patterns. this technique separates the different disturbances. the fast fourier transform (fft) includes information on signal loss and the time loss while analyzing the data for feature extraction [4, 5]. the short time fourier transform (stft) has been often used for fault analysis. it is, however, inadequate for evaluating nonstationary transient signals that have both temporal and frequency components due to its constant window length. time-frequency analysis performs well across all detection criteria and is particularly sensitive to non-stationary signals. however, the length of the computations raises questions about the technology's suitability for protection applications. the signal can be processed using the wavelet transform (wt) approach by examining its lowand high-frequency components. using the wavelet decomposition coefficient of a voltage waveform, a wt-based approach may identify hifs. wavelet packet transform is applied to features extracted from voltage and current signal data in order to identify and distinguish hifs. the level 5 and level 7 approximation coefficients as well as the standard deviation of detail of the db4 mother wavelet are employed for such detection process. wt offers greater signal processing resolution. however, the implementation of this approach in protective applications is limited by its high computational complexity, high data rate, and storage space requirements [6]. recently, mathematical morphology (mm) was used in hif detection, although the technique needs to be improved. the majority of detection techniques observe the input signal for processing while selecting a high sample rate. high sampling rates increase the amount of the needed computational space. the current study shows an improved technique that processes signals extremely quickly and with corresponding author: s. lavanya engineering, technology & applied science research vol. 12, no. 6, 2022, 9477-9482 9478 www.etasr.com lavanya et al.: a deep learning technique for detecting high impedance faults in medium voltage … low sampling rates, which requires less memory and computational work. to gather the hif and non-hif current signal data, a precise matlab/simulink model of a genuine power distribution network was used. mm is a timedomain, nonlinear signal transformation technique. processing time is reduced because of the usage of simpler calculations [7, 8]. additionally, mm filters are appropriate for real-time power system activities like transmission line protection. the most important task in the signal processing technique is the extraction of critical features, which is made possible by the interaction between the signal and the structured element (se). se shape plays a key role in signal processing. the mm filter is used in this study to pre-process the current signal. while preserving fault current characteristics, this filter lowers the signal's noise level. deep learning (dl) is very good at automatically extracting features from speech and image analysis. dl can capture both temporal and spatial data from the input without the need for signal manipulation [9-11]. by removing manually created feature extraction, the use of dl in fault and non-fault detection not only increases accuracy, but also streamlines the process. convolution neural networks (cnns) were used to solve the high impedance fault problem, and performance against noise, training time, parameter count, and overall performance have all been discussed. for the purpose of detection and classification, a deep convolution neural network (dcnn) receives a 2d image that has been converted from the fault and non-fault signal. the 1d signal data and the 2d signal image are completely different things [12-14]. previous literature has not taken into account multiple power quality disturbances. the proposed method is using dcnn for the problem of multiple fault and non-fault detection and signal classification. the mm filter is used in this study to pre-process fault and non-fault current signals while maintaining fault current characteristics [15-18]. this filter reduces the signal noise level. then, using a cnn, the output signal of the mathematical morphology with and without faults is detected. the following is a list of the current study's contributions.  by analyzing the fault and non-fault mm output signal, the dcnn layer minimizes the manual extraction of features and permits automatic feature extraction.  due to the high computational complexity of the cnn, a batch normalization (bn) layer is implemented to speed up the training procedure and minimize the number of parameters. ii. τhe mathematical morphopology the structure of signals is altered via a non-linear signal processing method termed mm. this method was created in its natural shape in 1975. integral geometry and set theory are the foundations of mm. mm operates entirely in the time domain and does not compute the frequency content of a signal, as opposed to fourier or wavelet transforms, which separate the signals' frequency information. recently, mm has been applied to power distribution systems, particularly for fault identification [19, 20]. as a result, an effort has been made to leverage mm in pre-processing the signals in order to lessen the workload on the computer, the amount of memory needed, and the overall detection latency. the se is the foundation of the mm processing applications. for the execution of any mmbased operation, the choice of se is a crucial step. the type and frequency content of the fault signal affect the choice of se. erosion and dilation are two essential mm changes [21, 22]. these two transformations can be creatively coupled to create other transformations that can be applied in the right situations. it has been stated that various mm-based tools are used for power system applications [23]. these instruments are produced using a variety of replications and mixes of dilation and erosion employing various structuring components [24]. a. the choice of a structuring element the se is a necessary component of mm-based signal processing. it is an operator used in signal processing that separates a signal into sub-signals of various important properties. depending on the types of applications, it could have different geometrical structures [25]. the onedimensional signals obtained from power systems are examined using linear ses. signal transformations depend significantly on the ses' length and height (magnitude). b. structuring element length the window size for any mm function is determined by the length of a se, which also determines the delayed in output. with respect to the mm operation, the output delay is equal to (m-1) δt, where t is the sampling interval, and m is the length of the se. it should be observed that the output delay constantly grows as the se lengthens. therefore, linear se with a length of 3 has been regarded as the best for fault detection applications in order to decrease time in mm transformations. c. structuring element height in power systems, various current and voltage densities are employed. therefore, the samples of current or voltage signals must be standardized using the peak magnitude of their rating value before mm modifications in order to have a more general option of the se. in normal conditions, the normalization limits the signal magnitude to roughly 1 despite the various system voltage and current levels. as a result, a se will always be at its best for any voltage or current levels. the magnitude (or height) of each se element can be any small arbitrary value once the waveform has been adjusted [26]. iii. the filters of mathematical morphorlogy assume that x(n) is a signal that needs to be translated and specified in the domain dx = {a0, a1...an} and y(m) is a se defined in the domain dy = {b0, b1….bm}. the dilation (+) of the signal x(n) by y(m) is given by: dilation(n) = (x(n)+y(m))=max{x(n-m)+y(m)} (1) where 0 ≤ (n-m) ≤ n, m ≥ 0, n > m, and n, m are integers. the erosion (-) of signal x(n) by y(m) is given in (2): erosion (n) = (x(n)–y(m))=min{x(n+m)–y(m)} (2) where 0 ≤ (n+m) ≤ n, m ≥ 0. engineering, technology & applied science research vol. 12, no. 6, 2022, 9477-9482 9479 www.etasr.com lavanya et al.: a deep learning technique for detecting high impedance faults in medium voltage … as indicated above, the opening (α) and closing (+) functions are defined based on (1), (2) in (3) and (4) respectively. opening (n) = (x(n)@y(m))=[(x(n)+y(n))–y(m)] (3) closing (n) = (x(n)*y(m))=[(x(n)-y(m))+y(m)] (4) different mathematical morphological filters (mmfs) are developed from these mm functions and employed in real-time signal processing applications. closing – opening(0) and opening – closing(α) are defined by: co(n) = (x(n) * y(m)) @ y(m) (5) oc(n) = (x(n) @ y(m)) * y(m) (6) the mean closure – opening filter (mcof) is designed as the arithmetic mean of close and open: mcof(n) = [opening(n) + closing(n)]/2 (7) the mean closing – opening and opening – closing filter (mcoocf) is the mathematical mean of co and oc: mcoocf(n) = [co(n) + oc(n)]/2 (8) iv. system description authors in [5, 6] analyzed hif with non-hif scenarios using the 33kv feeder model shown in figure 1. this model has a distribution transformer connecting its 11kv bus to its 33kv bus. the feeders in a subsystem model have seven numbers. the sixth feeder serves as a candidate feeder. both hif and non-impedance fault conditions were applied to this model to analyze the capacitance switching and non-linear loads for non-high impedance fault circumstances. fig. 1. system fescription. a. fault and non-fault signal data in this work, both kinds of distribution signals—fault and non-fault signal data—are taken into account. the non-fault signal data represent normal switching, load switching, and capacitance switching, while the fault signal data represents the hif [27]. the data set, which is obtained from various simulation cases taken into account and is shown in table i, is used in the proposed fault and non-fault signal detection method [28]. table i. various simulation hif and non-hif cases event simulation conditions total cases hif resistance of the hif model varied from 100 to12k. the hif model's dc voltage varied from 1kv to 11kv. angle of origin of the fault at 0°, 30°, 45°, 60°, 90°. phase angles of the source voltage are 0°, 30°, 45°, and 60°. 1500 (60×5×5) switching loads load level changes at 10 cases. angle changes in a cycle of 0°, 30°, 45°, and 60°. phase angles of the source voltage are 0°, 30°, 45°, and 60°. 250 (10×5×5) switching of nonlinear loads nll load level changes at 24 cases. angle changes in a cycle of 0°, 30°, 45°, and 60°. phase angles of the source voltage are 0°, 30°, 45°, and 60°. 600 (24×5×5) switching of capacitance switching a 1mvar on and off depending on the load. angle changes in a cycle of 0°, 30°, 45°, and 60°. phase angles of the source voltage are 0°, 30°, 45°, and 60°. 250 (5×2×5×5) a total of 1500 hif cases and 1100 non-hif cases, such as linear load switching, non-linear load (nll) switching, and capacitor switching, were considered (table i). the generated signal has 2600 sampling points and a fundamental frequency of 50hz (10 cycles, 0.2s). data have been produced in each fault (1500) and non-fault (1100) case using different parameters. thus, a total of 2600 sample points of fault and non-fault signal data examples have been produced. however, when the signal is actually acquired from the actual system through sensors, additional distortion is always imposed on the signal. signal-to-noise ratios (snrs) of 20db to 40db are added to the fault and non-fault signal data set in order to bring the total number of data samples up to 10,400. the specifications of the data set used in this analysis are listed in table ii. table ii. the data set counting samples quantity of noise training set 2600*4 = 10,400 20 db 40 db validation set 10,400*0.01 =104 20 db 40 db test set 10,400*0.01 =104 20 db 40 db b. the convolution layer the main layer in cnn is the convolution layer (cl), in which low-level features are transformed into high-level features. in order to create features, a kernel is used with the convolution operator on the input. the following is the cl's output: y � f�wr ∗ xi � br engineering, technology & applied science research vol. 12, no. 6, 2022, 9477-9482 9480 www.etasr.com lavanya et al.: a deep learning technique for detecting high impedance faults in medium voltage … where y is the result of cl. the weight and bias of the r th layer are w r and b r respectively, and the activation function is f(x). it understands how a neuron becomes active and produces. the tanh function is not chosen in dl, but rather the rectified linear unit activation functions. frelu = max(0, y) c. pooling layer usually, the cl is followed by a pooling layer. its primary use is in down sampling. the pooling layer is used to decrease the dimension of the input and retrieve crucial information after the cl. it can lessen the effects of data volatility. max pooling is used in this work because it performs better than average pooling for both fault and non-fault waveforms. the mathematical formula for max pooling is: f(y) = maxi (yi) d. bn layer the bn method is used for to speed up neural networks. it is used to normalize the input by altering and scaling the activations. unlike the previous layers, it allows each network to learn independently. additionally, compared to dropout, it efficiently reduces over fitting. the following formula can be used to normalize the input data batch xi: y� � γ ∗ �������� �� � � β where �� � represents the batch variance and �� represents the batch mean. � and provide the learned scale and shift parameters respectively, guaranteeing that the input data have the same distribution. e. completely joined layer the learning parameter d is included in this layer, which is also known as a "dense layer." the output of the dense layer is calculated using the formula below: y � f�x ∗ d" � b" f. softmax layer the probability distribution of each output class with "n" outputs is computed by the softmax layer. thus, the softmax layer predicts the class to which the input data belong. the probability distribution is calculated using the following equation: p� � $ �� ∑$�& , j � 0,1,2, … … … . . n where the input is xi. the sum of all probabilities will equal to 1 if the output of p is between 0 and 1. in this work, fault and non-fault classification is done using the softmax layer [29]. v. the proposed method-dcnn algorithm figure 2 shows the proposed dcnn model's structure, which consists of two completely connected dense layers at the end of three convolution layers with pooling layers layered on top. fig. 2. the proposed dcnn architecture. vi. simulation results a. assessment metrics the proposed method was evaluated with the following criteria:  the confusion chart is employed to evaluate a model's capability for classification.  accuracy is calculated as (true positive + true negative)/ total test instances.  the product of the true positive and true negative determines precision.  recall equals the product of true positives and false negatives.  the f1 score is determined as: (precision + recall) 2 × precision b. results and discussion as stated above, 10,400 samples have initially been created. one percent is utilized for validation, 1% for testing, and 98% of the total data set were used for training. in dl, the training process is often carried out using a small batch. in order to appropriately calculate the training time for various scenarios, the mini-batch size for all 3 dcnn cases is set at 64. a total of 100 epochs of validation loss were tracked. in order to avoid over fitting, the training method would be completed before the scheduled epochs, since the validation loss does not decrease continuously for 20 epochs. the final model is determined by whatever model performed best in the validation set. the suggested dcnn's entire architecture was coded in python using a tesla k80gpu in this study. engineering, technology & applied science research vol. 12, no. 6, 2022, 9477-9482 9481 www.etasr.com lavanya et al.: a deep learning technique for detecting high impedance faults in medium voltage … all models' accuracy and loss values during training are calculated using the dcnn with 4, 6, and 8 layers. table iii shows the 3 final models' variables, training period, number of epochs that have passed, accuracy level, and validation losses. table iii. dcnn training model performance model type epoch's duration (s) optimum validation losses maximum validation precision epochs dcnn with 4 layers 32 0.0038 0.98 49 dcnn with 6 layers 46 0.0022 0.999 32 dcnn with 8 layers 72 0.003 0.996 36 less training parameters and classification accuracy of 99.9% are produced by the 6-layer dcnn model. the confusion matrices for each of these dcnn models, hif (600 samples) and non-hif (440 samples), which were trained on a total of 1040 samples, are shown in tables iv-vi. the dcnn with 6 layers correctly identified 600 hif samples, with 0 samples being misclassified, yielding a 99.99% accuracy rate. a total of 592 hif samples were accurately diagnosed by the 4-layer model, whereas 8 samples were incorrectly classified, giving it a classification accuracy of 98%. also, 598 hif instances were accurately diagnosed by the 8-layer dcnn model, whereas 2 samples were incorrectly classified, yielding a classification accuracy of 99.6%. table iv. dcnn6's confusion matrix actual event predicted hifs nhifs hifs 600 0 nhifs 1 439 table v. dcnn8's confusion matrix actual event predicted hifs nhifs hifs 598 2 nhifs 2 438 table vi. dcnn4's confusion matrix actual event predicted hifs nhifs hifs 592 8 nhifs 12 428 table vii displays the precision, recall, and f1 score performance of the 6-layer dcnn model. while the 4-layer and 8 layer dcnn models generated 98.66% and 99.6% precision respectively, the suggested 6-layer model delivers 100% precision. similar to this, the f1 score for a dcnn with 6 layers is 99.9%, compared to 98.33% and 99.66% of the 4 and 8-layer models respectively. as a result, the proposed 6layer dcnn model outperformed the competition in terms of the evaluation parameters. also, the 6-layer dcnn method outperforms the other models when compared to noisy environments. this approach reduces the detection delay to 23.66ms, making real-time applications possible. table vii. parameters of evaluation of the three models actual event dcnn 4 precision recall f1 score hifs 0.98666667 0.9801325 0.9833887 actual event dcnn 6 precision recall f1 score hifs 1 0.99833611 0.99917 actual event dcnn 8 precision recall f1 score hifs 0.99666667 0.99666667 0.99667 c. comparing the computation lengths to get greater performance, the dcnns may be run on gpu. the gpu processor has more overall units than the cpu processor. as a result, dcnn computations run relatively quickly on a gpu. due to its simultaneous gpu calculation, dcnn has a significantly shorter computation time. table viii compares the computation times on the gpu and cpu for the dcnn models using 2600 and 10400 samples. table viii. processor effect on training duration processor time interval (s) 2600 examples are included 10400 examples are included tesla k80 gpu 6 24 intel i7 processor, cpu 18 72 vi. conclusion in order to classify hifs and non-hifs, this study suggests the use of a 6-layer dcnn model. the study demonstrates a new method that processes signals very quickly, with low sampling rates and reduced computational and memory load. the suggested dcnn with 6 layers is compared with other models, namely the 4and 8-layer dcnn models. the findings show that the proposed 6-layer dcnn model has a greater accuracy while requiring less training than the other models. the 6-layer dcnn model outperforms the other models in noisy environments, it has fewer parameters, and is 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[29] d. khalil ibrahim, e. s. t. eldin, e. m. aboul-zahab, and s. m. saleh, "real time evaluation of dwt-based high impedance fault detection in ehv transmission," electric power systems research, vol. 80, no. 8, pp. 907–914, aug. 2010, https://doi.org/10.1016/j.epsr.2009.12.019. microsoft word etasr_v13_n2_pp10270-10278 engineering, technology & applied science research vol. 13, no. 2, 2023, 10270-10278 10270 www.etasr.com kout et al.: a hybrid optimization solution for uav network routing a hybrid optimization solution for uav network routing akram kout ferhat abbas setif 1 university, algeria | misc lab, abdelhamid mehri constantine 2 university, algeria akram-kout@univ-setif.dz (corresponding author) bilal bouaita ferhat abbas setif 1 university, algeria bilal.bouaita@univ-setif.dz abdesselem beghriche ferhat abbas setif 1 university, algeria abdesselem_beghriche@univ-setif.dz said labed misc lab, abdelhamid mehri constantine 2 university, algeria said.labed@univ-constantine2.dz salim chikhi misc lab, abdelhamid mehri constantine 2 university, algeria salim.chikhi@univ-constantine2.dz el-bay bourennane imvia laboratory, university of burgundy, france ebourenn@u-bourgogne.fr received: 5 january 2023 | revised: 21 january 2023 | accepted: 23 january 2023 abstract an unmanned aerial vehicle (uav) network specifies a novel type of mobile ad hoc network (manet) in which drones serve as nodes and facilitate the retransmission of messages to their final destinations. aside from its military application, it has recently begun to seep into the civilian sector. similar to manet and vehicular ad hoc networks, flying ad hoc networks (fanet) are a subset of ad hoc networks. an fanet is different because it is founded on uavs. due to the characteristics of this sort of network, which is defined by a highly changing topology in a 3d environment, we must employ an adjusted configuration method to ensure good routing performance. therefore, to deal with this problem, a technique that responds to any change in topology by always finding the best route is required. in this work, we propose a new protocol based on the hybrid optimization of the 2-opt heuristic and honey badger algorithm (hba), called hb-aodv. in order to locate its prey, a badger must move slowly and continuously while using scent markers and mouse-digging skills to catch it. in other words, the most efficient routes in terms of the number of hops are identified. several simulations were conducted via the 3d version of network simulator (ns-2) on different deployment strategies. in comparison to aodv, dsdv, and anthocnet, the obtained results demonstrated the proposed scheme’s good performance in terms of quality of service metrics. keywords-ad hoc networks; uav network ; honey badger algorithm; heuristic ; optimization ; 3d environment engineering, technology & applied science research vol. 13, no. 2, 2023, 10270-10278 10271 www.etasr.com kout et al.: a hybrid optimization solution for uav network routing i. introduction at present, wireless technologies offer interesting prospects in the telecommunications area. ad hoc networks include a set of mobile entities that move arbitrarily, interconnected with each other by wireless technology and organize themselves without a previously defined infrastructure. this type of network has limited bandwidth, energy constraints, limited security, unpredictable topology, and heterogeneous nodes. there are many different ways that ad hoc networks can be put to use. we reference the most well-known example of their application, which is in the realm of military operations, in addition to other tactical applications, such as rescue and research missions. to retransmit messages to their final destinations, uavs construct a novel type of manet with drones as nodes [1]. recent studies have been conducted on the development of collaborative multi-drone systems, where many drones work together to complete a mission with improved performance [2-6]. many industries, including agriculture, arts (television, cinema, tourism development), cartography (public works, georeferencing), environment (natural disasters, flora detection, counting and detection of fauna), health(transportation of emergency materials and medicines), and fire safety, have found use for fanets. in networks like manets, vehicle ad hoc networks (vanets), or fanets, each node serves as a terminal or a router. an ad hoc protocol creation must take into account issues such as mobility, unexpected changes in topology, route maintenance, and energy management during packet routing. routing is a critical problem in ad hoc networks since it ensures that any two nodes in the network are connected at any time, determines valid routes from a source to every precise destination, maintains these routes, and adapts them to topology changes. proactive, reactive, and hybrid routing methods can be categorized based on how the routes are created and maintained throughout data routing (figure 1). fig. 1. routing protocol classification. networks using proactive routing techniques ensure that all feasible destinations can be reached at any given time. even if a route is never utilized, it is preserved. the paths’ update messages interchange continuously, ensuring a permanent update of the routing tables. dsdv [7] and olsr [8] are two examples of proactive routing protocols. in order to provide routing services in wireless networks, reactive protocols, or ondemand routing protocols, have been introduced. protocols of this category construct and maintain routes when needed. routing information can only be obtained by conducting route discovery procedures when the network needs a route. aodv [9] and dsr [10] are two examples. hybrid protocols, e.g. zrp [11], try to combine the advantages of the two prior techniques in order to reap the benefits of both. observing nature has led researchers to adapt the principles observed in natural phenomena to develop effective algorithms for solving certain difficult problems. a new era is opening with nature-inspired (bio-inspired) algorithms, which are metaheuristics imitating nature to solve optimization problems. bio-inspired approaches for solving problems have immense potential for research, specifically in the area of routing for all types of ad hoc networks. ad hoc network routing issues can be resolved using bio-inspired algorithms. in the current article:  fanet routing protocols are discussed, including traditional proactive, reactive, and hybrid routing methods as well as bio-inspired methods based on various metaheuristics.  hb-aodv, a routing algorithm for uavs networks, is described in detail.  the proposed protocol has been thoroughly analyzed in the field of a fanet. the findings in ns-2.35, in its 3d version, simulations and deployment strategies, all with random waypoint mobility and free-space propagation model, are presented along with the analysis’s main conclusions. ii. related works for their study on traffic monitoring in fanets, the authors in [12] relied on oslr routing. from the simulation findings, it is deduced that the oslr routing protocol is not optimal for low-density, highly dynamic fanets due to its excessive overhead. however, oslr allows quick connection and minimal delay. to ensure efficient and secure data transmission in uav networks, the lta-olsr protocol (linkquality and traffic-load aware) was developed in [13]. the received signal strength indication (rssi) of packets is analyzed to determine the quality of the link between a node and its neighbors. with channel contention at the mac layer and the number of packets held in the buffer in mind, the authors devised a traffic load method to ensure light-load routing. authors in [14] analyzed fanet connectivity using aodv routing. the simulation findings demonstrate that the aodv protocol delivers excellent network connectivity with a high packet delivery ratio while being responsive to a variety of network conditions. a hybrid of on-demand routing and the reynolds method for keeping routes and connections up and running for data transmission was presented in [15] as braodv in order to keep communication between uavs stable despite frequent topology changes. the aodv protocol was used because it enables the uav nodes to obtain routes on demand, making it ideal for real-time message transmission between uavs. in terms of packet delivery ratio, end-to-end delay, and packet loss, br-aodv outperforms aodv. link state routing is contrasted with a reactive routing strategy proposed in [16]. for the precision agriculture scenario, in which unexpected climate changes pose a serious engineering, technology & applied science research vol. 13, no. 2, 2023, 10270-10278 10272 www.etasr.com kout et al.: a hybrid optimization solution for uav network routing threat to crops and cultivation quality, the reactive flooding routing (rfr) was proposed. uavs are equipped with a specialized sensor that sends data to farmers in real time. uav deployment was addressed in [17] to set up a wireless network for usage in situations such as disaster relief, search and rescue, and user connectivity in hostile or remote locations. to account for both ground-to-air and air-to-air propagation, the authors suggested a mathematical approach. both the traditional cplex branch-and-cut algorithm and the hybrid metaheuristic biased randomized-iterated local search (br-ils) were employed to optimize the mixed integer linear programming formulation. the latter was suggested as a means to simultaneously attain optimal or near-optimal answers at a lower computing cost. the experimental results demonstrated that br-ils significantly outperformed cplex solver for both small and large-sized instances in terms of performance metrics chosen on cases for which cplex could find an optimal solution. due to the need to maximize the minimal data transmission throughput, the authors in [18] proposed a dual sampling bandwidth efficient transmission technique in relation to the uav flight trajectory. they devised a recursive algorithm that alternatively optimizes bandwidth scheduling and uav trajectory to get the best solution. additionally, the algorithm enabling the dual-sampling (ds) technique has been iterated with power balance in mind at every step. while the ds approach consumed the second-least energy over extended time periods, it had the highest max-min average data rate. authors in [25] employed the genetic algorithm (ga) to provide the best data operation routes and extend the life of wireless sensor networks by reducing energy consumption. the ga's performance was compared with that of teen algorithm. in [26], the authors presented a self-organization-based clustering technique for cluster formation and management that was inspired by a behavioral study of glowworm swarm optimization (gso). the choice of the cluster head and the creation of the cluster both depend on the uavs' connection with the ground control station as well as the value of their luciferin and the amount of energy they have left over. the technique for managing the cluster uses gso's behavioral research by continually revising the luciferin value in accordance with the location of the uavs. in addition, they provided a system for route selection for effective communication that depended on the neighbor range, residual energy, and location of the uav. the harmony search method was modified in [27] to identify the best solution to the cell placement problem. the experimental results demonstrate that this algorithm is effective for resolving the investigated problem and is characterized by good performance, solution quality, and optimality likelihood. in the same context, the research presented in [28] presents a red deer optimization algorithm inspired by clustering-based routing protocol (rdoaicrp) for reducing the problems of instability and mobility that arise during the process of distributing trustworthy data in fanets. the proposed algorithm included the advantages of the red deer optimization algorithm for the selection of cluster heads and the generation of energy-aware clusters. in order to ensure effective communication, this system made use of a function for route recognition that was determined by the distance between the uavs, the number of nearby neighbors, and the weighted residual energy. the feasibility of the proposed rdoaicrp was investigated using the benchmarked clustering-based routing protocols in terms of the cluster lifespan, the likelihood of successful packet delivery, the amount of energy used, and the amount of the time required for cluster building. the cluster based routing protocol (cbrp), a single path manet protocol, was improved in [29] to employ multiple paths. to lessen network traffic congestion and delay, the traffic will be split up across several paths. for both the multipath and single path cbrp routing protocols in manets, an analytical model was utilized to calculate the end-to-end delay and queue length. the analytical findings demonstrated the efficiency of the suggested plan. the authors in [30] proposed a bio-inspired clustering technique for fanets called bicsf. this approach employs a hybrid process that combines gso with krill herding (kh). the gso method is used for the generation of energy-aware clusters and the selection of cluster heads in the system. in addition, an effective cluster management algorithm was presented that makes use of the behavioral research of kh. this algorithm makes use of genetic operators such as mutation and crossover in order to locate the uav. the effectiveness of bicsf is measured in terms of the amount of time it takes to build a cluster, the amount of energy it uses, the amount of time it lasts, and the probability that a delivery will be successful using clustering algorithms based on grey wolf optimization (gwo) and ant colony optimization. (aco). authors in [31] proposed an aware cluster-based route planning scheme, which is an application of honey badger based clustering with african vulture optimization based routing (hbac-avor) protocol for wsn and validated with comparative simulations in which it performed very well. the discussed routing protocols are summarized in table i. table i. related work ref. algorithm year advantages disadvantages [12] olsr on fanet 2018 quick connection, minimal delay excessive overhead [13] lta-olsr 2018 light-load introduces delays [14] aodv on fanet 2018 excellent network connectivity, with a high packet delivery ratio introduces delays [15] br-aodv 2018 high packet delivery ratio, low end-to-end delay and packet loss excessive overhead [16] rfr 2019 high packet delivery ratio introduces delays [18] ds technique 2020 highest average data rate consumes more energy [26] gso on fanet 2019 good cluster construction time introduces routing delays [27] has 2018 good performance and optimality likelihood excessive overhead [28] rdoaicrp 2022 good packet delivery, delay, and energy used excessive overhead [31] hbac-avor 2023 hbac-avor outperformed existing techniques with maximum lifetime introduces more overhead engineering, technology & applied science research vol. 13, no. 2, 2023, 10270-10278 10273 www.etasr.com kout et al.: a hybrid optimization solution for uav network routing iii. the honey badger algorithm (hba) in the semi-deserts and tropical forests of africa, southwest asia, and the indian subcontinent, a mammal with black and white fluffy fur called honey badger is found [19]. they are recognized for their brave temperament, a body length of 60 to 77cm, and a weight of 7 to 13kg. this adventurous forager eats 60 various kinds of species, including snakes, even though honey is its favorite food. it is an intelligent creature that can use tools. only when mating with another badger does it venture out in the open. so far, 12 distinct badger species have been identified. because cubs are born all year round, badgers have no specific breeding season. even larger predators could not attack them given the courageous nature of the badgers. these animals can also easily climb trees. the badger uses a mouse’s sense of smell to track down its prey. digging begins the process of locating the prey’s approximate position, and the animal eventually captures the prey. when searching for food, it can dig up to 50 holes in a 40-kilometer radius in a single day. the badger likes honey, although it is not very skilled at finding hives to investigate. it uses honey guides (birds) to find their hives and extract the honey. due to this, a partnership is formed between these two animals, in which they work together to get honey from the hives by using badgers’ long claws to open them. the mathematical formulation of hba [19] follows. 1. updating the density factor. randomization is controlled by density factor (α), which ensures a smooth transition from exploration to exploitation. equation (1) is used to update the decreasing factor, which decreases with time to reduce randomization. � = � ∗ �(� / �� ) (1) the t-value corresponds to time-varying randomization to ensure smooth transition from exploration to exploitation which is represented by the current iteration of the algorithm. this value is the principal parameter to calculate the decreasing factor α. ���� = max iterations possible, while c is a constant bigger or equal to 1 (default = 2). 2. updating agent positions. the digging phase and the honey phase are the two phases of the hba position updating process (xnew).  digging phase: a badger engages in activity resembling the cardioid form when digging. equation (2) simulates the cardioid motion: ���� = ����� + � ∗ � ∗ � ∗ ����� + � ∗ r� ∗ � ∗ ! ∗ | cos(2π()) ∗ *1 − cos(2π(-). | (2) the best position thus far discovered for the prey is at position xprey. β is the honey badger’s capacity to gather food (bigger or equal to 1, default = 6), di is the distance between the honey badger and the prey, r3, r4, and r5 are different random numbers between 0 and 1. f works similar to the flag that changes the direction of the search. it is determined by: 61 if 0.5 1 otherwise r f     (3) where r6 is a random number between 0 and 1. the prey’s odor intensity i, the distance between the badger and the prey di, and the time-varying foraging influence factor α, all have a significant impact on a badger’s behavior during the digging phase. a badger may also experience any disturbance f while foraging, which helps it locate its prey even more accurately.  honey phase: to recreate the scenario where a badger follows a honey guide bird to the hive, do: ���� = ����� + � ∗ (/ ∗ � ∗ (4) where r7 is a random number between 0 and 1. ���� denotes the badger’s new location and ����� denotes the prey’s location. equations (3) and (1) are used to calculate f and α, respectively. according to (4), a badger explores close to the location where xprey has so far been discovered based on di. at this point, the time-varying search behavior (α) has an impact on the search. a badger might also discover a disturbance f. the hba flowchart, including population initialization, population evaluation and parameter update is given in figure 2. fig. 2. hba steps. iv. the proposed hb-aodv approach the purpose behind using the hba is that this technique seeks to create a balance amongst the exploration and exploitation stages by traveling the searching space rapidly and avoiding local optimal solutions. in addition, the hba is engineering, technology & applied science research vol. 13, no. 2, 2023, 10270-10278 10274 www.etasr.com kout et al.: a hybrid optimization solution for uav network routing proven effective in resolving empirical problems with difficult searching spaces. a. mapping between communication in hba and fanet an analogy between hba (implemented in hb-aodv) and manets is shown in table ii, where the process mapping between them is carried out. b. detailed approach our approach begins with the implementation of the hbaodv protocol step by step and is followed by the creation of simulation scenarios, in order to test how the proposed routing protocol performs. we consider the aodv reactive protocol, the basis of our work is to improve its performance with the hba metaheuristic. finding the shortest path from the source node to the destination node is the objective of the hb. the proposed algorithm can be summarized in two phases: table ii. mapping between hba and manets hba ad hoc network honey badger node initial position source badger food destination possible path between honey badger and his food possible path shortest path between honey badger and his food shortest path between source and destination 1) 2-opt heuristic application for the construction of the initial population source-to-destination topology explorations are carried out to identify a population of possible initial solutions as the starting point of the second step. the 2-opt heuristic [20], a powerful local search technique, is then performed. it is typically used to enhance a solution in hybrid techniques. the 2-opt method starts with a predetermined solution and then searches in its neighborhood to optimize the current configuration. the topology is detected following a request triggered by the source node in the event that it requires a route that is unavailable by sending rreq (route request) reaching the destination d. this occurs when d is not known from before or if the current route to d has expired or is no longer functional. following a set of requests acquired at the destination level, the population is constructed and processed by the hba. we modified the format of the rreq to keep track of the nodes through which it passed [21], by adding a record_path field (see figure 3), which is a vector of intermediate nodes, its identifier is added in the record_path vector each time an intermediate node receives an rreq to gradually build a solution. fig. 3. the modificaion of the rreq packet. the record_path field is an array containing the identifiers of the nodes starting with the source node (the first box) passing through the intermediate nodes which have received rreqs associated with the source. it ends with the destination node (the last box) d, where the whole vector represents an initial solution. in order to generate a population of solutions, the destination saves the rreq packet header in record_path with the rreqs from the same source and destination. its solution is sufficient to represent the network in the format of a graph to apply the graph theory. a graph g = (v, e) can be used to depict an uav network of communicating stations, where the vertex set v represents the stations and the edge set e the communication links [22]. we use this information to define the links between the nodes of the graph to build an adjacency matrix (see figure 4), following the construction of a population, where each element is a set of links between nodes, being 1 if there is a link and 0 otherwise [26]. fig. 4. an example of a graph and its adjacency matrix. the last thing to do in this step is the application of the 2opt heuristic. the latter checks each solution (route) in the initial population to see if exchanging two edges results in a shorter path during the improvement process. the algorithm keeps running until no further improvement is possible. the algorithm’s flowchart is shown in figure 5. the result is the initial population to be exploited in the second step. fig. 5. 2-opt heuristic improvement. 2) finding the best solution by applying hba the hba metaheuristic is used on the population that was generated in the first step. a method for finding the most efficient path between two nodes is implemented. the number of hops between the source and the destination is the metric to be optimized. the value of the objective function is found in the hop_count field at the level of the rreq request, and this value is suitable for the new solution calculated by (2) and (4). we have adapted these equations for our problem whilst always preserving the philosophy of the method. new solutions engineering, technology & applied science research vol. 13, no. 2, 2023, 10270-10278 10275 www.etasr.com kout et al.: a hybrid optimization solution for uav network routing are generated by using equations, with only intermediate nodes changing while the source and destination nodes kept unchanged. the process of our contribution is described in the algorithm shown in figure 6. the result obtained by the equations is real and often invalid when compared with the adjacency matrix. in addition, our protocol provides results of positive integer type to approximate the solutions of integer value, followed by a repair process (repair algorithm) to guarantee, with high probability that valid solutions are obtained. the result is not always valid. τo repair invalid solutions, we have used a repair algorithm based on the adjacency matrix [21]. the steps of the repair algorithm are:  the first step is to see if two consecutive nodes are connected, and if they are, they are kept. if not, move on to the next step.  the second step is to see if the first node is connected to any of the following nodes. in this case, we only remove intermediary nodes. otherwise, we’ll move on to the next step.  the final step is to look for a node that connects to the second node in the neighborhood of the first, and then establish a connection between the two. an explanatory example is given in figure 8. fig. 6. the hb-aodv algorithm. fig. 7. an example of hba application. v. implementation and experimental results a. implementation details 1) simulation platform using discrete event simulation, ns-2.35 is a freely available network simulator [23]. using c++ and otcl (object tool command language), ns-2.35 can be used on windows or unix systems. the development and implementation of low-level operations are done using c++, while code script simulation is conducted with otcl (figure 8). for the purpose of obtaining the third dimension z for uav movement, we added the 3d environment to ns-2.35 [24]. fig. 8. general structure of ns-2. 2) simulation parameters table iii lists the various simulation parameters. table iii. physical characteristics of mobile nodes parameter value simulator version ns-2.35 routing protocols aodv, dsdv, anthocnet, hb-aodv topology 1500 * 1500 * 200 channel type channel/wirelesschannel mobility model random waypoint (rwp) radio propagation model propagation/freespace packet length 512 antenna type omni directional simulation time 300 number of nodes 15, 20, 25, 35 transport agent udp speed (min/max) 5 15 m/sec 3) radio propagation model since there is only one direct channel between the transmitter and the receiver in the ideal scenario, we used the free-space propagation model to simulate this situation (fanet case). the communication range is shown in this form as a circle surrounding the transmitter. the receiver receives all the packets that are inside this circle. in any other case, it gets nothing. 4) mobility model we used the rwp model wherein the mobility of the nodes is typically random, and all the nodes are distributed uniformly within the simulation space. the destination and speed of each mobile node that aims to move are random and limited to a well-determined interval. after moving, the mobile nodes are stopped for a determined time. then, they move again in the same way as before, until the end of the simulation. engineering, technology & applied science research vol. 13, no. 2, 2023, 10270-10278 10276 www.etasr.com kout et al.: a hybrid optimization solution for uav network routing 5) performance metrics we opted to compare with other routing to verify the effectiveness of the proposed protocol hb-aodv. we mainly considered the following parameters as determining the routing performance:  packet delivery ratio (pdr) is calculated by dividing the number of packets received at the destination by the number of packets sent from the source. the maximum network throughput is limited by the packet loss rate, which is specified by pdr. high pdr is an indication of a more reliable network. pdr is calculated by: pdr (%) = ∑ 56789:9;<9= > ? ∑ 567@9>a > ? ∗ 100 (5)  a data packet’s average end-to-end delay (e2ed) is the time it takes to move from source to destination. this metric is determined by subtracting the time it took for the source to transmit the first packet from the time it took it to reach its destination. during the latency of route discovery, the interface queues, the mac layer retransmission delays, propagation time, and transfer are all included in this calculation. this step is critical in determining the amount of time it will take to discover a new route. low values of e2ed denote the best possible performance for the network. e2edis calculated by: e2ed (de) = ∑ (56789:9fa;g> h;�9 � ∑ 567@9>a h;�9 > ? ) > ? 56789:9fa;g> h;�9 (6)  throughput (thr) is the rate of successfully received packets. thr is calculated by: thr (klme) = nopqrost uvwxoyz [\]^os _owo`yqab cq]o (7) vi. results and discussion a. pdr figure 9 shows how the pdr varies amongst the several routing protocols that were examined with a change in speed. pdr is higher in aodv and hb-aodv than dsdv and anthocnet. as the number and the speed of nodes increase, hb-aodv continues to deliver satisfactory results that reach 96.73%, due to the use of the reactive approach, removes load from the network. on the contrary, in the proactive or hybrid approach, the update of the routing tables is periodic even if no request for connections (useless calculations are performed to reach destinations not requested) is made. the results of hbaodv are better than those of aodv in terms of pdr in almost all scenarios. the chosen bio-inspired technique (hba), dropped fewer packets than the other algorithms. b. e2ed figure 10 shows that hb-aodv and aodv provide good performance in terms of the average e2ed with a change in speed. the reactive approach (with high mobility) finds a way to the destination more quickly. hb-aodv is better than aodv in some cases, due to the enhancement of the initial population using the 2-opt heuristic, and the use of a bioinspired technique that is a fast and gives the optimum route between two nodes in reasonable time. fig. 9. pdr vs. uavs density and speed. fig. 10. e2ed vs. uavs density and speed. engineering, technology & applied science research vol. 13, no. 2, 2023, 10270-10278 10277 www.etasr.com kout et al.: a hybrid optimization solution for uav network routing c. throughput figure 11 shows how the number of nodes affects the throughput with a change in speed of the investigated routing protocols. the aodv and hb-aodv outperform dsdv and anthocnet in terms of throughput given the behavior of protocols of a reactive and/or bio-inspired nature (combined in the case of hb-aodv), which provides more stable links (large number of received packets) in a short time. fig. 11. thr vs. uavs density and speed. by observing the results, we can conclude that when compared to the other routing protocols, hb-aodv provided an excellent compromise between the 3 performance criteria used. we finish by stating that the proposed solution is appropriate for the addressed problem. hba is a modern metaheuristic that mimics the foraging behavior of badgers. it shows some efficiency in terms of diversification and intensification whilst exploring the most promising areas using badger scents and by digging or tracking a honey guide bird. the efficiency, which is the goal of our study, was demonstrated by integrating this approach to deal with the routing problem at the uav networks. we used the 3d version of ns-2 simulator to implement hb-aodv and evaluate its performance so that it could be compared with the existing protocols. our protocol was compared with the previously mentioned protocols in terms of quality of service (qos) metrics. we found that the proposed protocol performs efficiently with good results. its performance is impressive and could still be improved in the future. in addition, it provides packet transmission speed close to aodv's, which is more effective than anthocnet and dsdv. the monitoring of the results indicates that the hb-aodv is an evolutionary protocol because it presents excellent findings with each extension of the network. vii. conclusion the effectiveness of the reactive approach including the bio-inspired aspect for solving the routing problem in uavs network has been demonstrated in this paper, especially the hb technique, which when implemented in aodv protocol performed better than other routing protocols of various categories (aodv, dsdv, and anthocnet), due to the rapid reaction (route discovery) and the strength of metaheuristics, 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[31] k. arutchelvan, r. s. priya, and c. bhuvaneswari, "honey badger algorithm based clustering with routing protocol for wireless sensor networks," intelligent automation & soft computing, vol. 35, no. 3, pp. 3199–3212, 2023. microsoft word etasr_v13_n3_pp10731-10737 engineering, technology & applied science research vol. 13, no. 3, 2023, 10731-10737 10731 www.etasr.com kammouna: enhancing the properties of sulfate-resisting cement enhancing the properties of sulfate-resisting cement zainab kammouna al-nahrain university, iraq zainab.m.ismaiel@nahrainuniv.edu.iq (corresponding author) received: 1 march 2023 | revised: 20 march 2023 | accepted: 22 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5827 abstract sulfate-resisting cement is used in construction works when a sulfate attack is probable. this type of cement withstands sulfates due to its low c3a content. on the other hand, the decrease in the quantity of c3a leads to a reduction in the rate of early strength development. to overcome this problem, a hardening accelerator was added to the cement mix. to estimate the effect of the accelerator on some properties of hardened cement, compressive and flexural strength, and drying shrinkage tests were carried out. four series of cement mortar mixes were made. the hardening accelerator was not added to the control series, while it was added to the others with three different percentages (of cement mass) of 0.5, 1, and 1.5%. the results revealed that the hardening accelerator enhances the compressive strength of all mortar ages while it slightly promotes flexural strength only at early ages. it was also observed that the hardening accelerator strongly inhibits the drying shrinkage strain. keywords-sulfate-resisting cement; hardening accelerator; flexural strength; compressive strength; draying shrinkage i. introduction when a cement matrix is in contact with soil contaminated with sulfate, harmful reactions occur in the presence of water. these reactions, which are called the sulfate attack, finally lead to the deterioration of the construction member. in hardened cement paste, tricalcium aluminate hydrate (the result of reacting c3a with water) reacts with sulfate to produce calcium sulfoaluminate (ettringite 3cao.al2o3.3caso4.32h2o), which is formed within the framework of the hydrated cement paste and has a larger volume than the reacted solid material. at early ages, the ettringite is helpful as it fills the capillary pores and thus makes the cement matrix denser [1]. however, if this reaction continues, even when the cement takes its strength, it leads to damages of the cement matrix due to the stresses generated by the expanded ettringite [1-3]. to overcome this problem and enhance the resistance of mortar or concrete of a structural member to the sulfate attack, sulfateresisting (sr)-cement is employed. this type of cement resists the sulfate due to its low c3a content [4]. on the other hand, c3a is one of the cement phases that contribute to the early strength of cement paste due to its fast hydration reaction. since sr-cement has low content of c3a, it has a low early strength. there are cases that require high early strength of cement matrix, e.g. when the need arise to remove formworks in a short time for reuse in casting another member, whereas the concrete should acquire adequate strength before removing the formwork [5-7]. in addition, speeding up the early strength development is one of the most important requirements for repair works [8]. it gets worse when the construction work is carried out in cold weather, as cold slows down the reaction of the cement compounds. generally, in construction works, different types of accelerators [9] are used to reach the required strength quickly enough. the accelerators act as the reaction catalyst for one or more cement phases, specifically c3s, c3a, and c4af [10-15]. according to bs en 934-2 [16], the accelerators are subdivided into two main categories, setting accelerators which are used to reduce setting time and hardening accelerators for increasing the early strength of cement paste. in the implementation of various construction works and researches, different types of accelerators have been used with ordinary portland cement (opc) [17-19]. the studies conducted on the effect of accelerators on the performance of sr-cement are rare, with [20] being one of the few. the current study aims to increase the early strength of this type of cement by adding a hardening accelerator. hence, compressive and flexural strength tests were investigated. in addition, drying shrinkage tests were performed to check the cracking tendency as it affects the durability and the sustainability which is the focus of many studies nowadays [22-24]. ii. experimental program a. mortar mix properties and proportions the sr-cement used in this research is classified under the type cem i-sr 3 [24]. its fineness is 4875cm 2 /g, while its initial and final setting times are 2:45h and 4:45h, respectively. the oxide and the compound compositions of this cement are shown in table i. engineering, technology & applied science research vol. 13, no. 3, 2023, 10731-10737 10732 www.etasr.com kammouna: enhancing the properties of sulfate-resisting cement table i. compositions of sr-cement oxide compositions (%) compound compositions (%) cao 60.71 c3s 48.48 sio2 20.02 c2s 21.06 al2o3 4.23 c3a 2.30 fe2o3 5.27 c4af 16.02 mgo 1.81 so3 2.38 loi 3.69 the sr-cement has lower strength than opc at early ages. to enhance the strength of sr-cement at early ages, a chloridefree hardening accelerator type sikarapid-1 (table ii) was added to the cement mix. its performance meets the requirements of [16]. table ii. technical data of the hardening accelerator property quantities and values ph 8.3 chloride ion nil conventional dry material content 35% density 1.17kg/l at +23°c viscosity 10mpa.s at +23°c the water/cement ratio is designed to be 0.45 as per aci 225r recommendation [25], which states that this ratio should be between 0.45 and 0.50 where there is a potential for sulfate attack. to evaluate the effect of the hardening accelerator, 4 series of sr-cement mortar mixes were prepared. the hardening accelerator was not added to the mix of the control series (s0.0). for the other series, i.e. s0.5, s1.0 and s1.5, the accelerator was added with percentages (of cement mass) equal to 0.5, 1, and 1.5%, respectively. it is worth mentioning that these percentages were chosen to be within the range mentioned in the data sheet of sikarapid-1. the water/cement ratio varied from one series to another to achieve the same consistency as the control series. primarily, this study was conducted to improve the performance of sr-cement at early ages by using a hardening accelerator. to avoid the effect of other factors and to achieve reliable results, standard sand conforming to bs en 196-1 [26] was used to the mortar of all the series. this sand is natural, siliceous, and consists of rounded particles whose size distribution is presented in table iii. the cement: sand ratio was set at 1:3 for all the mixes. table iii. particle size distribution of the standard sand square mesh size (mm) 2 1.6 1 0.5 0.16 0.08 cumulative sieve residue (%) 0 7 33 67 87 100 when an admixture is to be added, it is recommended that the prepared mix should have the same aggregate:cement ratio with the control mix, while the water percentage should be changed to maintain the same consistency [27]. therefore, the water/cement ratio of the control mix (0.45) was manipulated by relying on the flow table test, which was performed according to bs en 1015-3 [28]. firstly, the test was carried out for the control series where the mean of 4 measured diameters of mortar was 128mm. subsequently, for the other series, water was adjusted to achieve the same diameter of control mix (figure 1). fig. 1. flow table test. the constituents of mortar of all the mixes are shown in table iv. the method proposed by [27] was adopted in mixing the materials of the 4 series. table iv. properties and quantities of mortar compositions mortar compositions and properties quantity (kg/m 3 ) cement: cem i-sr 3 586 standard sand 0.8/2 1758 series symbol * s0.0 s0.5 s1.0 s1.5 water 263.70 261.75 256.54 251.33 hardening accelerator 0.0 2.93 5.86 8.79 * for each symbol, the letter (s) refers to the word (series) while the number next to it indicates the percentage of the added hardening accelerator (%). b. specimen preparation and curing conditions the hardening accelerator is defined as an admixture that increases the rate of early strength development [16]. therefore, flexural and compressive strength tests were performed to evaluate the accelerator effects. to perform the flexural and the compressive strength tests, according to [26], 3 specimens with dimensions of 40×40×160mm were prepared from each batch of mortar. the fresh mortar was cast into the prismatic molds in 2 layers and each layer was compacted by using the jolting apparatus (60 jolts per layer), (figure 2). fig. 2. a prisms-mold with 3 holes (of 40×40×160mm) installed on the jolting apparatus, before cooling the mortar and at the end of compacting (2 layers each 60 jolts). (a) top view, (b) side view. to assess the durability of the hardened cement mortar in terms of restricted members and to verify the possibility of cracking that may occur, the drying shrinkage test was carried out. the test was conducted according to astm c 596 [29]. four prisms were prepared from each batch of mortar. the (a) (b) engineering, technology & applied science research vol. 13, no. 3, 2023, 10731-10737 10733 www.etasr.com kammouna: enhancing the properties of sulfate-resisting cement molds that are used for this test have internal dimensions of 25×25×285mm, where 2 stainless steel studs (gauge studs) are inserted at their ends to be embedded into the casted mortar. the distance between the inner ends of the gauge studs which is called gauge length, is 250mm [30] (figure 3). the mortar was placed in two layers and each layer was compacted with a tamper [31]. fig. 3. shrinkage mold of 25×25×285mm with steel studs inserted at the ends. for all the mentioned tests, after casting the mortars, each mold was covered with a plate of glass to prevent water evaporation. then, the molds were placed in a moist air cabinet where the temperature was 23°c and the relative humidity (rh) was 95%. after 24h, the specimens of the flexural strength test were taken out of the molds and then placed in a water tank until the age of testing. it should be noted that bs en 196-1 [26] recommends performing the compressive test on the halves of the prisms broken by the flexural test. for shrinkage molds, astm c 596 [29] states that when the strength of the mortar is inadequate to allow proper removal from the molds at 24h, the moist curing in the molds is continued for another 24h. since sulfate-resisting cement has low strength at an early age, the specimens were kept in molds (in a humid air cabinet) for up to 48h. after they were removed from the molds, the specimens were stored in water for another 24h [29]. at the age of 72h, the specimens were transferred to be stored under laboratory conditions at 23°c and 52% rh, until the end of the test. c. experimental procedure of flexural strength test this test is used to evaluate indirectly the tensile strength. the flexural strength test was performed using the 3-point loading method (figure 4) according to [26]. the load was applied at a rate of 50n/s until the fracture of the hardened mortar prism. as stated in [26], the two halves of a broken prism were covered with a damp cloth and were kept for the compression strength test. to evaluate the effect of the hardening accelerator on the flexural strength at early ages and to ensure that it does not have detrimental effects at late ages, the test was carried out at different ages of sr-cement mortar (1, 3, 7, 14, and 28 days). for each of the 4 series, 5 mixes were prepared (1 per age) where 3 prisms were cast from each, i.e. 15 prisms were cast for each series with a total of 60 prisms being used in flexural strength tests. the flexural strength rf was calculated according to: �� = �.�× ×� � (1) where ff is the maximum applied load to the middle of a prism, b is the square section side of a prism, and l is the distance between the supports. fig. 4. mechanical strength test: (a) flexural strength test, (b) compressive strength test executed on the halves of a broken prism from the flexural test. d. experimental procedure of the compressive strength test the compressive strength test was conducted according to [26]. depending on this standard, the test was carried out on the two halves of a prism broken in the flexural test. thus, as the flexural test, the compressive test was done at the mortar ages of 1, 3, 7, 14, and 28 days, for each of the 4 series. τwo auxiliary plates of 40×40mm were placed over and under a prism half during the loading time to make the applying load be projected on a length of 40mm (and an area of 40×40mm). the prism half was laterally centered to the platens and longitudinally in such a way that the end face of the prism overhanged the auxiliary plates. the load was applied with a rate of 2500n/s (figure 4). for each series, since the flexural strength test was performed on 3 prisms per age, the compressive strength test was performed on 6 prism halves at each of the 5 testing ages (1, 3, 7, 14, and 28 days). therefore, for the 4 series, the compressive strength test was carried out on 120 prism halves. e. experimental procedure of drying shrinkage test drying shrinkage is a term used to describe the contraction in the length of a test specimen. the contraction is caused by any factor except externally applied forces under stated conditions of temperature and rh [29]. the drying shrinkage test was performed on 4 prisms (of 25×25×285mm) for each of the 4 series (s0.0, s0.5, s1.0, and s1.5) [29]. thus, in total, 16 prisms were prepared for the test. the accuracy of the dial gauge used in this test was 0.001mm. it was reset to zero by a reference bar each time just before taking the reading of a test specimen (figure 5). according to [29], at the age of 3 days (2 days in the moist air cabinet, plus 1 day in water), the specimens were removed from the water, swept with a wet cloth, and then the initial reading was taken and recorded. subsequently, the specimens were placed in the air under laboratory conditions (temperature of 23°c and 55% rh) until the end of the test. readings for each prism were taken after 4, 11, 18, and 25 days of air storage, according to [29]. for greater accuracy and certitude, additional readings were taken at 7, 14, 21, and 28 days (of air storage). at each testing time, the drying shrinkage (of a series) was computed as the average strain of the 4 test prisms. the drying shrinkage strain at any time of air storage is computed as: �� = (�����) �� (2) where ɛx is the shrinkage strain of a specimen at time x, �� is the reading of the specimen (stored under air conditions) at time x, li is the initial reading of a specimen, and lo is the nominal stud stud gage length = 250mm prism length = 285mm (a) (b) engineering, technology & applied science research vol. 13, no. 3, 2023, 10731-10737 10734 www.etasr.com kammouna: enhancing the properties of sulfate-resisting cement gauge length, i.e. the distance between studs (250mm, see figure 3). fig. 5. length change measuring instrument. (a) adjusting the dial gauge to zero before taking a reading, (b) taking the reading of a specimen. iii. results and discussion a. flexural strength results the experimental results of the flexural strength tests are shown in figure 6. each curve represents a series where each point represents the average strength of 3 prisms tested at a given age. it could be seen that there is not a big difference between the flexural strength from one series to another. however, the series containing accelerator (s0.5, s1.0, and s1.5) have slightly higher flexural strengths at the very early ages (1 and 3 days). inversely, at late ages, the strengths of the control series become the highest. this result corresponds to the results (performed on cement type i) of [32-34]. these studies agree that the hardening accelerator increases the flexural strength of the cement matrix at early ages while at the late age of 28 days, the flexural strength becomes lower than (or about identical to that) of the control mix. it seems that, at late ages, the mix containing more accelerator becomes more brittle, thus exhibiting lower flexural strength. in [14, 35, 36], it was found that the chloride-free hardening accelerator primarily speeds up the hydration of the tricalcium aluminate where ettringite forms. hence, for the present study (where a chloride-free hardening accelerator is used), at early ages, the ettringite fills out the capillary pores and thus increases the strength of the cement matrix. therefore, the mix that includes the hardening accelerator will have less pores and higher strength. with time and in the presence of water, the hydration reactions of the other cement phases proceed to form the main cement product of calcium silicate hydrate (c-s-h). this product begins to fill the capillary pores that have not been filled by ettringite. c-s-h is the densest component of the hydrated cement paste [1]. in contrast, ettringite is an expansive compound, and its formation increases the porosity of the cement matrix as a whole [1, 38]. porous materials are generally considered as brittle materials and have low tensile and flexural strength [38, 39]. accordingly, at late ages, the mix that does not contain or contains a smaller amount of the accelerator will be denser, less brittle, and will have higher flexural strength than the other mixes. the relative flexural strength (strength of a hardened mortar containing the accelerator to the reference one at a given age) was calculated and is presented in figure 7 to clarify this result in another way. it is clear that s0.5 has the highest relative flexural strength, i.e. the strength of the mix with the lowest percentage of the accelerator (0.5%) is higher than the other two mixes with accelerator for all the cement mortar ages. fig. 6. flexural strength development with age for the four series. fig. 7. relative flexural strengths of the series with accelerator vs. mortar age. b. compressive strength results the results of the compressive strength tests are shown in figure 8. each point in a separate series represents the average compressive strength of 6 halves (of the 3 broken prisms at the flexural test). it could be seen that the control series has lower compressive strength than the other series for all mortar ages. this result indicates that the hardening accelerator has a beneficial effect on the development of compressive strength at early as well as at late ages (until 28 days) of the mortar. this result agrees with the findings in [32, 33], where the hardening accelerator increases the compressive strength at early ages and maintains it higher than the mix without accelerator even at the late age of at 28 days. the results of [34] also confirm that the hardening accelerator increases the compressive strength of the cement matrix at the early ages, while at the late age of 28 days, the strength of the mix with the accelerator becomes the lowest. the hardening accelerator increases the reaction rate of the cement components, especially c3a (to form ettringite), and leads to the early completion of this cementation phase. since ettringite is an expansive material, it fills the capillary (b) (a) dial gage of accuracy 0.001mm shrinkage specimen reference bar engineering, technology & applied science research vol. 13, no. 3, 2023, 10731-10737 10735 www.etasr.com kammouna: enhancing the properties of sulfate-resisting cement pores, increasing the strength of the cement matrix at early ages [1]. due to the low amount of c3a in the sr-cement, and with the presence of the accelerator, this compound appears to be consumed early. therefore, it is not expected to continue producing ettringite which has a detrimental effect on the cement matrix when it is formed at a later age, i.e. when the cement has become sufficiently hard. thus, the mix with accelerator has higher compressive strength than the control one, even at late ages. to evaluate the best percentage of the accelerator, the relative strength was computed, i.e. the compressive strength of a series to that of the control series (figure 9). from this figure, it is clear that the different percentages of the accelerator (0.5, 1, and 1.5%) have about the same effect on the strength of a given age of mortar, even though it seems that s1.0 has the best performance since its relative strengths are higher than those of s0.5 and s1.5 for almost all the mortar ages. that means 1% is the best percentage of the accelerator to be added in order to enhance compressive strength. fig. 8. compressive strength development with age of the four series. fig. 9. relative compressive strengths of the series with accelerator vs. mortar age. c. drying shrinkage results the readings (4 prisms per series) were taken during the air storage period of 4, 7, 11, 14, 18, 21, 25, and 28 days. the average shrinkage strain of the 4 prisms was computed at each test time (figure 10). as shown in figure 10, for about all the test times, the drying shrinkage strain of the control series is higher than those of the other series. also, as the percentage of the hardening accelerator is increased, the shrinkage strain decreases. that could be related to the fact that the drying shrinkage decreases with increasing strength of the cement paste [40]. since the strength of sr-cement mortar has been enhanced due to the hardening accelerator (figure 8), the specimens that include the accelerator exhibit lower shrinkage than the control ones. however, in [41], it was found that the drying shrinkage strain increases with increasing percentage of accelerator. to clarify the extent of the effect of the accelerator, the relative shrinkage strain (the strain of a mortar with the accelerator to the reference one at a specific age) was calculated (figure 11). at the end of the shrinkage test (after 28 days of air storage), the strains of s0.5, s1.0, and s1.5, respectively, became 0.7, 0.62, and 0.55 of that of the control series. fig. 10. drying shrinkage strain vs. time of air storage. fig. 11. relative drying shrinkage of mixes with accelerator vs. time of air storage. iv. conclusions since the sulfate-resisting cement has a slow rate of early strength development, this study aimed to increase the strength at early ages by adding a hardening accelerator. to evaluate the effects of the accelerator, four series of cement mortar mixes were implemented (using standard sand). the accelerator was not added to the mix of the control series, while for the other three mixes, it was added with different percentages of 0.5, 1, and 1.5%. flexural and compressive strength tests were carried out at different mortar ages (from 1 day to 28 days). drying shrinkage test was also performed to check the cracking potential. from the obtained results, the following points could be drawn:  for the flexural strength, the results were approximately close. however, at the early ages of cement mortar, the strengths of the series with the hardening accelerator are somewhat higher than that of the control. inversely, at late ages, the flexural strength of the control series becomes the engineering, technology & applied science research vol. 13, no. 3, 2023, 10731-10737 10736 www.etasr.com kammouna: enhancing the properties of sulfate-resisting cement highest. comparing the series containing the accelerator, it was observed that the mix with 0.5% accelerator has the best performance since its relative strength is higher than those of the other series for all mortar ages.  the compressive strength of the control series is lower than those of the series with the hardening accelerator for all mortar ages. although the relative compressive strength decreases with age, it has never been less than one, i.e. the compressive strength of the series with the accelerator never becomes less than that of the control. this indicates that the hardening accelerator enhances the compressive strength at the early age 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[41] y. tomita et al., "evaluation of mechanical and shrinkage behavior of lowered temperatures cementitious mortars mixed with nitrite– nitrate based accelerator," materials, vol. 13, no. 17, jan. 2020, art. no. 3686, https://doi.org/10.3390/ma13173686. microsoft word etasr_v13_n3_pp10797-10807 engineering, technology & applied science research vol. 13, no. 3, 2023, 10797-10807 10797 www.etasr.com aghaei et al.: hydrogeochemical assessment of groundwater quality and suitability for drinking and … hydrogeochemical assessment of groundwater quality and suitability for drinking and agricultural use. the case study of fars province, iran yasamin aghaei faculty of civil engineering, iran university of science and technology, iran yasamin_aghaei@civileng.iust.ac.ir mohammad nazari-sharabian department of mathematics, engineering, and computer science, west virginia state university, usa m.nazari@wvstateu.edu (corresponging author) hossein afzalimehr faculty of civil engineering, iran university of science and technology, iran hafzali@iust.ac.ir moses karakouzian dpt. of civil and environmental engineering and construction, university of nevada, las vegas, usa mkar@unlv.nevada.edu received: 25 march 2023 | revised: 18 april 2023 | accepted: 20 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5884 abstract this study aims to evaluate the hydrogeochemistry of aquifers in fars province, iran, from 2007 to 2017 and assess the groundwater’s suitability for drinking and agricultural uses. a total of 35,000 samples were collected from wells and qanats across the province. piper, gibbs, and durov diagrams were used to assess the hydrochemical facies and processes. cross plots of different ions were investigated to assess ion exchange and determine the effects of anthropogenic activities, as well as the weathering and dissolution of different rocks and minerals in the aquifers. groundwater quality and suitability for agricultural and drinking purposes were also assessed using physicochemical parameters including ph, electrical conductivity (ec), total dissolved solids (tds), total hardness (th), and calcium, magnesium, sodium, potassium, bicarbonate, sulfate, and chloride concentrations. suitability for domestic purposes was assessed by comparing these values with the who standards. sodium and alkalinity hazards, including sodium adsorption ratio (sar), sodium percentage (na%), permeability index (pi), magnesium hazard (mh), and residual sodium carbonate (rsc) were used to assess irrigation suitability, along with plotting wilcox and ussl diagrams. keywords-groundwater chemistry; geographic information system (gis); hydrochemical facies; suitability analysis i. introduction groundwater resources, especially in arid and semi-arid regions, are important for the social and economic development. iran, a developing country with a high population growth rate and relatively dry climate, suffers from severe decline in groundwater levels and is considered a hotspot for groundwater depletion. easy groundwater access and inadequate supervision have exposed these valuable resources to over-exploitation in different parts of iran. excessive groundwater extraction has had a significant impact on both groundwater level and quality. there are many environmental challenges as well, including saline intrusion and severe quality effects from both environmental and anthropogenic factors. since it is important to rely on an efficient and healthy water resource to meet iran’s drinking, agricultural, and industrial needs, water quality assessment, especially for groundwater, (between 55 and 80% of water demand in iran is supplied from groundwater resources) has become significant. water quality engineering, technology & applied science research vol. 13, no. 3, 2023, 10797-10807 10798 www.etasr.com aghaei et al.: hydrogeochemical assessment of groundwater quality and suitability for drinking and … refers to the natural, physical, and chemical characteristics of water and any type of change that occurs for any reason [1-10]. groundwater quality, which is usually controlled by physiochemical parameters, represents a response to all the processes and reactions that occur due to natural changes and anthropogenic activities [11]. many factors including soil type, regional geology and topography, land use, the recharge source, climate change, atmospheric inputs, and interactions between surface and groundwater can affect groundwater chemistry [12-14]. investigating the major ions to determine chemical indices and their spatial distribution can provide a clear picture of hydrochemical processes in aquifers. to this end, molar ion ratios can clarify the origins of solutes and characterize the occurring processes. groundwater quality assessment in iran is mostly limited to specific areas and periods, presenting significant gaps in knowledge, since there is a limited number of sampling wells and it is difficult to examine these sources over a long period. thus, there is a need for a more thorough investigation of the issue. considering the importance of investigating groundwater quality in iran, the main objectives of this research were (1) to assess the groundwater’s major ion chemistry and identify the hydrogeochemical processes affecting it and (2) to characterize the groundwater’s suitability for agricultural and drinking purposes using relevant methods, diagrams, indices and standards based on a rich and reliable dataset. ii. material and methods a. study area fars province covers approximately 122,400km 2 (6.7% of the country). it is located in the southwest of iran. the average annual minimum and maximum temperatures vary between -7 and 2°c, and 25 and 40°c in this province. the average annual rainfall has been 320mm since about 2000, representing about 40×10 9 m 3 [15]. the province's four climate zones are cold, temperate, hot, and very hot. agriculture is important in fars, with the main products being cereal (wheat and barley), citrus fruits, dates, sugar beet, and cotton. some 71% of the province’s agricultural area is allocated to irrigation farming and 29% to dry farming. annual water consumption is approximately 10.5×10 9 m 3 , of which 8×10 9 m 3 is supplied from groundwater. about 95% of the water used goes to the agricultural sector. fars is a diverse province with varied geological characteristics. different geological features in fars, including the zagros mountains, are part of the alpinehimalayan orogenic belt and are composed of sedimentary and metamorphic rocks, fars ophiolite complex that contains a variety of igneous, metamorphic, and sedimentary rocks, including pillow lava, sheeted dikes, gabbros, serpentinites, and cherts as well as miocene-pliocene sedimentary rocks, quaternary volcanic rocks, and active faults. b. data analysis the physiochemical parameters of 72 different districts in fars, each with more than 1000 sampling locations, were investigated. some 35,000 samples were collected from wells and qanats from 2007 to 2017. the sampling frequency depends on several factors including the type of well and the purpose of the sampling and the regulations and guidelines set by the local and national authorities. in iran, the ministry of energy is responsible for managing and regulating the use of groundwater resources. the recommended frequency of sampling wells for drinking water is once per month. however, some regions in fars province were required to be sampled more frequently up to 4 times per month. (a) (b) fig. 1. (a) fars province, (b) schematic view of well (sampling point) distribution in fars. in order to manage the sampling point data and determine the groundwater hydrochemistry and its suitability for different purposes, the data were clustered with variables such as cations, anions, ph, electrical conductivity (ec), total dissolved solids (tds), and total hardness (th). the suitability of groundwater resources for drinking use was assessed by comparison of the water samples' physiochemical characteristics and state variables with the limits recommended by the world health organization (who) [16], salinity laboratory and wilcox diagrams [17, 18], and the interpretation of several indices, including the sodium absorption ratio (sar) [19], sodium percentage (na%) [18], magnesium hazard (mh), residual calcium carbonate (rsc), and permeability index (pi) for all zones [20]. piper, durov, and gibbs diagrams were used to determine the dominant water types and hydrochemical processes in fars sub-basins [21-23]. all groundwater samples used were taken and analyzed under the supervision of the iran water resources management company [24]. groundwater quality data were measured in trusted water and wastewater laboratories licensed by iran’s department of environment, using the standard methods suggested by the american public health association [25]. groundwater quality data included major cations (i.e., ca�� , mg�� , na� and na� ), major anions (i.e., hco� � , so� �� , cl� ), ph, ec, tds, and th. analytical accuracy was calculated from (1): b = ����� ����� × 100 (1) where c and a are the sums of the cationic and anionic concentrations determined, respectively, in meq/l, and b is the ionic balance error (%) [26]. the ionic balance error did not exceed 8% in any sample analysis. kriging interpolation, in arc-gis, was used to investigate groundwater quality spatially for drinking and irrigation. the statistical results of the analyzed samples are shown in table i. engineering, technology & applied science research vol. 13, no. 3, 2023, 10797-10807 10799 www.etasr.com aghaei et al.: hydrogeochemical assessment of groundwater quality and suitability for drinking and … table i. descriptive statistics of ec, ph, tds, and major ions, determined in the groundwater samples. parameter unit minimum median mean maximum variance std. deviation ca�� mg/l 40.07 100.2 159.21 551.25 12,974.67 113.9064 mg�� mg/l 6.99 60.76 85.64 413.98 4,569.25 68.07734 na� mg/l 5.98 69.00 227.99 1,293.865 101,534.60 318.645 k� mg/l 0.78 3.13 5.55 34.79 30.93 5.561512 hco� � mg/l 170.82 244.04 252.89 366.06 1,434.63 37.87644 so� �� mg/l 73.88 222.86 342.16 1,597.24 100,883.30 317.6213 cl� mg/l 8.88 124.25 491.65 5,145 506,802.70 711.9007 tds mg/l 245.27 1,229.99 1,917.94 8,734.18 2,573,619.00 1,604.25 ec µs/cm 429 1,887 2,984.8 14,218 6,290,427 2,508.072 ph 6.77 7.54 7.54 8.33 0.009,052 0.095,144 th mg/l 170.669 715.94 928.18 3075 436,500.00 656.01 fig. 2. piper diagram. fig. 3. durov diagram. engineering, technology & applied science research vol. 13, no. 3, 2023, 10797-10807 10800 www.etasr.com aghaei et al.: hydrogeochemical assessment of groundwater quality and suitability for drinking and … iii. results and discussion a. ionic types and hydrogeochemical facies piper and durov diagrams were used in this study to determine hydrochemical facies. in the piper diagram, ca�� and mg�� (alkaline earth metals) and na� (alkali metal) are the most common cations, while hco� � (a weak acid) and so� �� and cl� (strong acids) are the most abundant anions. to determine the groundwater’s hydrogeochemical facies, the analytical results were plotted on a piper ternary diagram [20], using aqqa software [27] (figure 2). the two basal triangles in the piper diagram show that ca 2+ is the dominant cation in 42 of the 72 districts, and hco� � , followed by cl� , are the dominant anions. the calcium-bicarbonate type indicates that alkaline earth metals and weak acidic anions exceed alkali metals and strong acidic anions, respectively. such water has temporary hardness. the dominance of these ionic species is evidence of anthropogenic activity. while calcium bicarbonate is the dominant water type, mixed types, and calcium chloride waters are also present. the plots show that most water samples fell in the alkaline earth metal field (ca�� , mg�� ), which dominates the alkali metals (na�, k�), while the weak acid (hco� � ) dominates the strong acids (cl� , so� �� ). fresh recharge waters rich in ca�� are characteristic of most zones in fars. the durov diagram [21, 22] in figure 3 was plotted to determine the dominant hydrochemical processes and the type of ion exchange. it is clear from the durov diagram that most of the water lies along the dissolution or mixing line, i.e. ion exchange and reverse ion exchange are both feasible. the increasing trend of both tds concentration and ph can also be seen in the graph. b. hydrochemical process identification scatter plots of ion concentrations enable interrelationships between the ions and the chemical reactions occurring in the aquifers to be recognized. major ion concentrations were plotted as a function of calculated tds values to identify the effective ions in groundwater mineralization. as shown in figure 4, k� , cl� and mg�� are correlated strongly with tds with correlation coefficients of 0.96, 0.9, and 0.88, respectively. these ions contribute the most to the groundwater mineralization and salinization in the study area. a plot of ca�� + mg�� versus na + (figure 5) is used to identify the ion exchange process. the data points fall above the 1:1 line, indicating reverse ion exchange, which normally takes place in the presence of clays. the plot of ca�� versus so� �� provides evidence of predominating cation exchange [28]. plotting na�/cl� versus ec (figure 6(a)) is used to determine the effect of evaporation on groundwater chemistry. the graph should have a horizontal line to indicate the effect of evaporation and evapotranspiration [29]. the graph’s trendline is inclined, showing that evaporation cannot be the main groundwater hydrochemical process in the area. tds changes can arise from land use and/or pollution. in rural areas, nitrate, sulfate, sodium, and chloride ions originate from agricultural fertilizers, animal wastes, and wastewater [30]. the high correlation coefficient, 0.843 (figure 6(b)), between tds and (no� �� + cl� / hco� � ) shows the effects of human activity on water chemistry [31, 32]. (a) (b) (c) (d) (e) (f) (g) fig. 4. plots of major ion concentrations versus tds. (a) ca��, (b) mg��, (c) na�, (d) cl�, (e) k�, (f) so� ��, and (g) hco� � and co� ��. (a) (b) fig. 5. plots of (a) ca�� and mg�� versus na� and (b) ca�� versus so� ��. c. ion exchange generally, groundwater is rich in sodium where there is the precipitation of calcite and/or cation exchange. in contrast, ca�� – cl� type water commonly arises from reverse ion exchange. both cation exchange and reverse ion exchange are engineering, technology & applied science research vol. 13, no. 3, 2023, 10797-10807 10801 www.etasr.com aghaei et al.: hydrogeochemical assessment of groundwater quality and suitability for drinking and … encouraged by aquifer materials leading to na or ca release into groundwater and ca or na adsorption, respectively [3335]. as the piper diagram indicates the possibility of ion exchange reactions, schoeller chloralkali indices were employed to understand them. chloroalkaline indices 1 and 2 (cai 1 and cai 2) were calculated for the study region groundwater using (2) and (3) [36, 37]. (a) (b) fig. 6. (a) na�/cl� versus ec and (b) tds versus no� �� and cl�/hco� �. cai 1 = cl� − �na� + k��/cl� (2) cai 2 = cl� − �na� + k��/�so� �� + hco� � + co� �� + no� ��� (3) if the index values are negative materials are exchanged with mg�� and ca�� in the water, whereas the reverse process will give a positive value (cl� > na� + k�). the host rocks are the primary sources of dissolved solids in the water. the chloralkali indices for 21% of the study area were negative, indicating an exchange between na� and k� in the water and cl�and mg�� in the soil. in 79% of the areas, however, reverse ion exchange occurred. the gibbs diagram (figure 7) is widely used to establish the relationship between solutes in water and aquifer lithology. the diagram shows three fields: precipitation, evaporation, and rock-water interaction-dominated areas [23]. gibbs plots of log tds against na� /( na� + ca�� ) and cl� /(cl� + hco� � ) were used to identify groundwater interactions that reflect that rockwater interaction and evaporation occur in this groundwater system. the dense clustering of points in the evaporation domain can be a sign of anthropogenic activity [37]. fig. 7. gibbs diagram. it should be mentioned that several sources of contamination and anthropogenic activities affect the groundwater quality in fars province. agricultural activities, which are the main source of income in the province, and the extensive use of fertilizers, pesticides, and herbicides, can lead to groundwater contamination. the excess use of nitrogen and phosphorus fertilizers can lead to nitrate and phosphate contamination. industrial activities including oil and gas extraction, mining, and manufacturing can generate hazardous waste that may contaminate groundwater. the discharge of industrial wastewater into surface waters can also lead to groundwater contamination. besides, the rapid urbanization and population growth in fars province has led to increased wastewater generation and disposal. d. groundwater quality evaluation 1) drinking suitability there are several groundwater quality assessment studies that regard fluoride concentration in regions facing groundwater contamination problems using the water quality index (wqi) and other physiochemical parameters [38-40]. cations, anions, ph, ec, tds, and th are used to determine the groundwater’s suitability for drinking in this study. the concentration minima, maxima, means, and standard deviations of contributing parameters are shown in table i. the values were compared with who’s guideline recommendations. figure 8 shows the spatial distribution of all parameters. table ii. chemical parameter concentrations compared with who recommendations water quality parameters who max allowable limit (1993) percentage of samples exceeding the standard concentration in the study area undesirable effect produced beyond the maximum allowable limit ca�� (mg/l) 200 (mg/l) 31.95 (40.07-551.98) essential for human bone growth, high concentration cause hardness and inefficiency mg 2+ (mg/l) 150 18 (6.99-413.16) essential for human bone growth, but high concentrations cause water hardness na� (mg/l) 200 (mg/l) 31.95 (5.98-1293.865) high blood pressure or posing a risk for people suffering from kidney or heart diseases k� (mg/l) 12 (mg/l) 13.89 (0.78-34.79) high blood pressure, blood lipids due to k� deficiency hco� � (mg/l) 300 (mg/l) 9.72 (170.82-366.06) unknown so� �� (mg/l) 400 (mg/l) 31.95 (73.88-1197.24) dehydration, gastrointestinal irritation-laxative effect cl − (mg/l) 600 26 (8.88-5145) salty taste tds (mg/l) 1500 39 (245.89-8761.21) taste-gastrointestinal irritation ph 6.5-8.5 0 (6.98-8.33) taste effects on mucus membrane and adverse effects on the water supply system th as caco3 (mg/l) 500 50 (170-3075) encrustation in water supply and adverse effects on domestic uses engineering, technology & applied science research vol. 13, no. 3, 2023, 10797-10807 10802 www.etasr.com aghaei et al.: hydrogeochemical assessment of groundwater quality and suitability for drinking and … (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) fig. 8. spatial distribution of major ions and hydrochemical parameters related to drinking suitability: (a) cl�, (b) k�, (c) ca��, (d) hco� �, (e) mg��, (f) so� ��, (g) na�, (h) tds, (i) th, (j) ph, (k) ec. city names: 0: abadeh, 1: eqlid, 2: khorrambid, 3: bavanat, 4: mamasani, 5: marvdasht, 6: sepidan, 7: arsanjan, 8: shiraz, 9: neyriz, 10: kazerun, 11: estahban, 12: fasa, 13: firuzabad, 14: farashband, 15: jahrom, 16: darab, 17: zarrindasht, 18: qirkazin, 19:larestan, 20:mohr, 21:lamerd. the average values of individual groundwater parameter concentrations were all within who’s recommended limits, whereas some individual samples reported higher concentrations (see table ii). to investigate groundwater suitability for any purpose, it must be classified depending on its hydrochemical properties based on its tds content [41, 42]. according to table iii, 63.91% of the samples were brackish water, and 36.09% were fresh water. in the classification based on [43], 15.27% of the samples were desirable and 20.82% were considered permissible for drinking purposes based on tds (table iv). table iii. nature of groundwater based on tds values tds nature of water percentage up to 1000 freshwater 36.09 1000-10000 brackish water 63.91 10000-100000 saline water 0 >100000 brine water 0 the groundwater classification based on th shows that 13% of the water is hard, and the rest is very hard. the who recommended maximum for th for drinking is 500mgcaco3/l, and 66% of the study area exceeds that limit. the ph value suitable for drinking water is specified as 6.5-8.5. the ph engineering, technology & applied science research vol. 13, no. 3, 2023, 10797-10807 10803 www.etasr.com aghaei et al.: hydrogeochemical assessment of groundwater quality and suitability for drinking and … value of most groundwater samples in the study area was between 6.98 to 8.33, with an average of 7.33 indicating an overall alkaline nature. table iv. classification of groundwater based on tds tds water type percentage up to 500 desirable for drinking 15.27 500-1000 permissible for drinking 20.82 <3000 useful for irrigation 70.83 >3000 unfit for drinking or irrigation 29.17 table v. classification of groundwater based on th [44] total hardness as caco3 (mg/l) water class < 75 soft 75 – 150 moderately hard 150 – 300 hard > 300 very hard ec is a measure of water's capacity to convey an electric current. the recommended ec limit for drinking water is 1500µs/cm [16]. the ec of the groundwater varies from 429 to 14184µ s/cm with an average value of 2984µ s/cm (table ι). higher ecs indicate higher salt concentrations. the ec can be classified as type i if the enrichments of salts are low (ec < 1,500µmhos/cm), type ii if the enrichment of salts is medium (ec 1,500 and 3,000µ mhos/cm), and type iii if the enrichments of salts are high (ec > 3,000µmhos/cm). according to the above classification, 56% of the total groundwater samples fell under type i and 26% under type ii. the remaining 18% of zones fell into the high salinity class and thus have wide applicability with respect to agricultural use. however, for drinking use, a high value of ec denotes a proportionately high value of calcium, magnesium, sodium, and potassium. calcium and magnesium are the most abundant elements in the planet's surface, and groundwater ca�� concentrations vary from 40.1 551.9 (table ii). the desirable limit of calcium concentration for drinking water is 75mg/l [16] and 32% of the zones fell beyond the permissible limit. higher ca�� content can cause hardness and is undesirable for domestic uses as it causes encrustation and scaling. magnesium content varies between 6.99 and 413.98mg/l (table ii). the maximum permissible limit of mg concentration for drinking water is 150mg/l [16]. the concentration of na + varies between 5.98 and 1,293.865mg/l. its maximum permissible limit is 200mg/l and 32% of the samples exceeded it (table ii). groundwater with high sodium content is not suitable for agricultural use as it tends to deteriorate the soil. potassium concentrations are low compared to ca�� , mg�� , and na� , with those in drinking water seldom reaching 20mg/l. the sample k� concentration varied between 0.78 and 25.4mg/l. the maximum permissible limit of k� in drinking water is 12mg/l, and it was found that 86% of the samples had concentrations below it (table ii). the value of hco�� was between 170.03-366.06mg/l, and only 10% of the samples exceeded the who limit. sulfate is one of the major anions occurring in natural waters. the upper limit for sulfate concentration in drinking water is 400mg/l [16]. the sulfate concentration in the study area ranged between 73.88 and 1,196.24mg/l with an average concentration of 342.16mg/l, indicating that 68% of the samples were within the allowable limit. the chloride in groundwater may come from diverse sources [45]. in the study area, the concentration of chloride was between 8.88 and 5,145mg/l. the excess chloride in the water is usually taken as an index of pollution and considered a tracer for groundwater contamination [46]. chloride determination may indicate water intrusion of different compositions, or trace and measure the rates and volumes of water mass movements. 2) irrigation suitability it is important to develop successful projects supplying irrigation water in addition to controlling salts and alkalis in the soil. in this regard, salinity indices such as na%, sar, rsc, pi, and mh were examined. salinity and alkalinity hazards are important parameters for determining the suitability of groundwater for agricultural use and influence crop yields. united states salinity laboratory (ussl) classification and the wilcox diagram were also used for better assessment. a) salinity and alkalinity hazards ec is a good measure of salinity hazard to crops, as it reflects the tds in groundwater and is the most important parameter in determining water suitability for irrigation. tds refers to any minerals, salts, metals, cations, or anions dissolved in the water. excess salinity reduces the osmotic activity of plants and thus interferes with water and nutrient absorption from the soil [47]. different types of water based on ec values are presented in table vi and ec and tds spatial distribution in figure 8. according to the wilcox diagram, only 47% of the samples were below the permissible limit of ec. according to the aqqa software results, 33%, 40%, and 26% of samples were reported in the range of very high, high, and medium salinity hazards, respectively. based on tds classification, the groundwater in around 80% of the study area was classified as permissible for agricultural use at tds < 3000. sar is an important parameter in determining the suitability of groundwater for irrigation because it is a measure of alkali/sodium hazard to crops as excess sodium in water can cause undesirable effects [48]. sar is calculated by: sar = !" #$%&"" '(&"& (4) where sodium, calcium, and magnesium are measured in meq/l. the sar value can be an indicator of the extent to which sodium is absorbed by soils. sodium concentration can reduce soil permeability, deteriorate soil structure, and influence crop yield [49]. the waters were classified for irrigation based on the ranges of the sar values [19]. based on the sar values, 94% of the samples were excellent and 6% were good for irrigation (table vi). in addition, for better insight, the ussl plot presented in figure 9 indicates that 7% of the groundwater samples fell in the c1s1 (low salinity-low sodium), and 18% of the samples fell in the c2s1 category. about 20% of the groundwater samples fell in the c3s1, indicating high salinity or high sodium type. only 9% fell in the very high salinity to low sodium category (c4s1), and the rest of the samples had very high salinity and are not shown in the diagram. engineering, technology & applied science research vol. 13, no. 3, 2023, 10797-10807 10804 www.etasr.com aghaei et al.: hydrogeochemical assessment of groundwater quality and suitability for drinking and … fig. 9. ussl diagram used to classify irrigation water suitability. in addition to the sodium adsorption ratio, na% can be a risk indicator for soil in agriculture. high sodium in the soil can be detrimental to soil structure, aeration, and infiltration [26, 49]. the sodium in irrigation waters is usually denoted as a percent of sodium. in all natural waters, na% is a common parameter for the evaluation of their suitability for irrigational purposes [50]. na% values are obtained by: na% = !"�)** �!&"� +,&"� !"� -" (5) all ionic concentrations are expressed in meq/l. fig. 10. wilcox diagram. table vi. classification of groundwater based on th, ec, sar, na%, rsc, mh, and pi classification category range sample % th [44] soft less than 75 0 moderately hard 75-150 0 hard 150-300 20 very hard more than 300 80 ec [18] excellent less than 250 0 good 250-750 13.88 permissible 750-2250 47.88 doubtful 2250-5000 17.12 unsuitable more than 5000 21.12 sar [19] excellent less than 10 94.38 good 10-18 5.62 doubtful 18-26 0 unsuitable more than 26 0 na% [18] excellent 0-20 38.02 good 20-40 0 permissible 40-60 36.62 doubtful 60-80 19.71 unsuitable more than 80 4.22 rsc [53] good less than 1.25 98.6 medium 1.25-2.5 1.41 bad more than 2.5 0 mh [52] good less than 50 81.69 poor more than 50 18.3 pi [51] class 1 more than 75 0 class 2 75-25 97.2 class 3 less than 25 2.8 as shown in table vi, 38%, 36%, 19.71%, and 4.22% of the samples are considered excellent, good, permissible, and doubtful, respectively, based on na%. na% is plotted against ec in a wilcox diagram [18]. as shown in figure 10, 16% of the groundwater samples were excellent to good, 41% good to permissible, 10% doubtful to unsuitable, and the rest of the samples were considered unsuitable for irrigation due to the aforementioned reasons. b) permeability index a water suitability classification for irrigation was developed in [51] based on the pi, as soil permeability is impacted by the long-term use of water containing sodium, calcium, magnesium, and bicarbonate. the pi is calculated by: pi � 100 � !"� /0�123 !"��!&"�+,&" (6) all ion concentrations are expressed in meq/l. the pi in the study area was between 1.93 and 28.14 with an average value of about 15.48 (table vi). a classification based on pi was proposed by who for assessing the suitability of groundwater for irrigation purposes. according to the pi values, 97.2% of the samples fell into class 2, and only 2.8% belonged to class 3 which is considered unsuitable for irrigation. c) magnesium hazard in most waters, calcium and magnesium maintain a state of equilibrium. there is evidence that mg�� can be detrimental to soil texture in water with a high sodium content in particular. mh index was developed in 1972 [52]. high mh harms crop yields as the soil becomes more alkaline. engineering, technology & applied science research vol. 13, no. 3, 2023, 10797-10807 10805 www.etasr.com aghaei et al.: hydrogeochemical assessment of groundwater quality and suitability for drinking and … magnesium ratio � +,&"(�!&"�+,&") � 100 (7) in the study area, the mh ranged between 14.28% and 59.45%. the 81.69% of the collected samples showed an mh ratio below 50% (suitable for irrigation), while 18.4% were unsuitable and can cause adverse effects on agricultural yields (figure 11). (a) (b) (c) (d) (e) fig. 11. spatial distribution of (a) na%, (b) pi, (c) sar, (d) rsc, (e) mh. d) residual sodium carbonate the rsc index of water samples in the study site was estimated by [19]: rsc � (co��� + hco��) − (ca�� + mg��) (8) all ion concentrations are expressed in meq/l. irrigation water based on rsc is classified as good, medium, and bad [33, 53]. for irrigation purposes based on rsc values, 98.6% of the groundwater samples were found good for irrigation, and the remainder belonged in the medium category. iv. conclusions groundwater is a major water source for domestic and agricultural uses. groundwater quality and its suitability for drinking and agricultural use, as well as hydrogeochemical processes, in fars province, iran, were assessed in this paper. in this regard, 35,000 groundwater samples were collected from 2007 to 2017 and analyzed for ph, electrical conductivity, major ion concentrations, total dissolved solids, and total hardness. interpretation of the hydrochemical analyses revealed that in most zones, the groundwater was hard to very hard, fresh to brackish, and alkaline in nature. based on the piper diagram, ca�� was the dominant cation in 42 out of the 72 districts, and bicarbonate followed by chloride, were the dominant anions in the province. effects of anthropogenic activities were evident in this region due to the dominance of the aforementioned ions. the dominant type in the province was calcium bicarbonate, followed by mixed types and calcium chloride. according to the durov diagram, the hydrochemical reactions in this area were mixed reactions with different origins, mixing and reverse cation exchange reactions, and water infiltration with calcium bicarbonate types. k� , cl�, and mg�� were strongly correlated with tds, which shows that these ions contribute the most to the mineralization and salinization of the study area’s groundwater. the plot of calcium versus sulfate can be evidence of cation exchange predominance. the high correlation coefficient between tds and (( no��� + cl� )/ hco�� ) also shows the effect of human activities on water chemistry-agricultural fertilizers. based on the chloralkali index, 21% of the areas had a negative value, indicating the exchange between sodium and potassium in water, chlorine, and magnesium in the soil. the plot of ca�� + mg�� versus na� was used to identify the ion exchange process indicating the occurrence of ion reverse exchange in about 90% of the study area. the same was observed in 79% of the districts according to the chloralkali index. the gibbs diagram demonstrated the rock dominance domain towards the evaporation dominance domain, which reflects that rock-water interaction and evaporation occurring in the groundwater system. assessment of water samples according to who standards indicated that, except a few places, the concentrations of major ions in groundwater were within the permissible limits for drinking. the suitability of groundwater for irrigation use was assessed by sar, rsc, na%, mh, and pi. the results ranged from good to permissible and indicated that most of the samples were suitable for this purpose. based on ec, due to high to very high salinity hazards, the groundwater in nearly 40% of the study area was beyond the maximum allowable limit for irrigation, even though it had a low alkalinity hazard. therefore, the groundwater in a few places can be used for plants that have a good salt tolerance, but it also restricts its suitability for irrigation, especially in soils with restricted drainage. the spatial distribution of different parameters either related to drinking or irrigation purposes was presented to grant engineering, technology & applied science research vol. 13, no. 3, 2023, 10797-10807 10806 www.etasr.com aghaei et al.: hydrogeochemical assessment of groundwater quality and suitability for drinking and … a better insight into the general condition of groundwater quality in fars. the results of this study demonstrate the basic requirements for fars's groundwater quality adaptation process, considering the water requirements for different allocation purposes. based on the groundwater hydrogeochemical characteristics, policymakers and stakeholders in fars province should consider monitoring and controlling anthropogenic activities and implementing proper waste management practices that are essential for the protection of groundwater resources. regular and systematic monitoring of groundwater quality is essential for understanding the hydrogeochemical characteristics of the aquifers and identifying potential sources of contamination. policymakers and stakeholders should develop and implement groundwater monitoring programs that use appropriate sampling and analytical methods to assess groundwater quality parameters and track changes over time. promoting sustainable groundwater use is of great importance because groundwater resources in fars are under stress due to the increasing 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[53] l. a. richards, "diagnosis and improvement of saline and alkali soils," soil science, vol. 78, no. 2, aug. 1954, art. no. 154. microsoft word etasr_v13_n4_pp11064-11069 engineering, technology & applied science research vol. 13, no. 4, 2023, 11064-11069 11064 www.etasr.com basarudin et al.: evaluation of climate change effects on rain rate distribution in malaysia using … evaluation of climate change effects on rain rate distribution in malaysia using hydroestimator for 5g and microwave links hafiz basarudin lee kong chian faculty of engineering and science, universiti tunku abdul rahman, malaysia hafizba@utar.edu.my noor hidayah mohd yunus universiti kuala lumpur, malaysia | british malaysian institute, malaysia noorhidayahm@unikl.edu.my (corresponding author) aizat faiz ramli universiti kuala lumpur, malaysia | british malaysian institute, malaysia aizatfaiz@unikl.edu.my zuhanis mansor universiti kuala lumpur, malaysia | british malaysian institute, malaysia zuhanis@unikl.edu.my aduwati sali wipnet research centre of excellence, malaysia | deparment of computer and communication systems engineering, faculty of engineering, universiti putra malaysia, malaysia aduwati@upm.edu.my gan hong seng department of data science, universiti malaysia kelantan, malaysia hongseng.g@umk.edu.my mohd azlan abu department of electronic systems engineering, malaysian-japan international institute of technology, universiti teknologi malaysia, malaysia mohdazlan.abu@utm.my received: 8 december 2022 | revised: 27 december 2022 | accepted: 31 december 2022 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5552 abstract wireless transmissions at more than 10ghz can experience signal fading caused by the presence of hydrometeor particles in the atmosphere. among these hydrometeors, rain is the largest contributor to the fading mechanism. rain fade can be predicted or calculated using rain rate measurements. with climate change affecting the world due to the rise of carbon dioxide in the air, it is expected to affect the distribution of rainfall, which ultimately affects rain fade. this paper investigates the effects of climate change on rain rate distribution in malaysia. ten years of hydro-estimator data containing rainfall rates in peninsular malaysia and the sabah and sarawak region from 2011 to 2020 were collected and analyzed. using the linear regression method, a small increment of rain rate distribution at 0.01% annual probability was detected for all regions, indicating a climate change effect on the rain rate distribution. for peninsular malaysia, the rate was 0.2356mm/hr per year while for the sabah and sarawak region, it was 0.4046mm/hr per year. an increase in the rain rate would increase the rain fade, causing signal losses and engineering, technology & applied science research vol. 13, no. 4, 2023, 11064-11069 11065 www.etasr.com basarudin et al.: evaluation of climate change effects on rain rate distribution in malaysia using … distortions in high-frequency wireless communication signals. the evaluation of climate change effects on the rain rate and rain fade distributions can help in developing a long-term prediction of the signal performance in 5g systems and high-frequency radio link frequencies due to hydrometeors. keywords-hydrometeor; itu-r model; millimeter-wave band; rain fade; 5g concerns; wireless transmission i. introduction the use of wireless communication technology has become essential in daily life. with the technology getting more advanced, more data are transmitted and received in various forms of complex multimedia, including images, videos, and advanced mobile applications that demand more bandwidth and faster data transmission [1-4]. thus, mobile communication is in dire need of improvements to meet the growing demands. the development of the 5g radio communication system includes wireless backhaul services that use higher frequencies, such as millimeter waves (mmwave), to meet the need for more flexible wireless data services [5-7]. ideally, the mmwave band, which is a frequency range from 30 to 300 ghz, is considered the most optimal region to achieve high channel bandwidth, while at the same time degrading the interference, allowing high-speed data communication, and improving propagation characteristics, making it more homogeneous [8]. however, the implementation of 5g faces great challenges, as higher frequency signals experience significant signal losses due to scattering and absorption by hydrometeor particles such as rain, clouds, fog, and sleet in the atmosphere. the largest and most dynamic contributor to these losses is rain fade, as it can cause interruption or complete loss of signal when the rain becomes too intense [9-10]. rain events are highly dynamic in terms of space and time since they can shift to different places at high speed and last from a few minutes to hours. typical heavy rain events can move up to 8 m/s and can be extremely challenging to measure [11]. in satellite communications, such as the ka-band satellite channel, system performance is severely degraded due to atmospheric fading effects, especially rain attenuation [9-14]. moreover, in tropical regions that suffer severe weather conditions, heavy rainfall, and higher rain intensity, the effect on radio links becomes significantly high for frequencies above 7 ghz [13-15]. this poses greater challenges to optimizing the 5g functionality in a tropical country like malaysia. furthermore, with global climate change, the rain trend is expected to change over the years [16], considerably affecting the rain fade of 5g links. rain attenuation or rain fade can be estimated from the rainfall rate in mm/hr. rain gauges, radars, and weather satellites provide rainfall rate estimation in mm/hr and can be converted to rain attenuation or fade in db using the standard itu-r 838 model [11-12, 17]. the plot of annual rain attenuation or rain fade distributions for statistical analysis typically requires a 1-minute integration time of annual rain rate distribution, according to the itu p.837 and 530 recommendations. unfortunately, the methodological approach to predict rain attenuation in any terrestrial radio link does not perform well in tropical climates because it is based on data collected from temperate regions [18]. moreover, the existing theoretical itu rain model lacks climate change features [15]. climate change affects rain intensity and frequency. this evidence was further verified in [19], which stated that climate change causes an increase in the frequency and intensity of extreme rainfall. in [20], human-caused climate change was found to intensify the heaviest downpours and increase flooding events, as the increase in water vapors due to global warming creates more moisture. extreme weather events have become more frequent and intense due to climate change, for example, tropical cyclone activity with increased intensity, more hot days and hot nights, heat waves, and more heavy precipitation [21]. therefore, it is important to consider the effect of climate change on the rain distribution to effectively analyze rain fade. this study considered 10 years, from 2011 to 2020, of hydro-estimator data by the national oceanic and atmospheric administration/national environmental satellite data and information service (noaa/nesdis) [22] to investigate the effect of climate change on rain rate distribution in peninsular malaysia and sabah and sarawak regions. table i compares different meteorological measurement methods. table i. comparison of meteorological measurement methods parameter meteorological measurement methods rain gauge rain radar weather satellites hydroestimator spatial coverage hundreds of m to a few km hundreds of km continents or globally globally temporal sampling time 1 min to 1 h 5 to 15 min 30 min to 1 h 1 h meteorological measurements are typically used for hydrological purposes, such as flood risk prediction and agriculture planning. most of these measurement sources are adequate for such endeavors but, according to itu, for rain fade prediction on microwave or millimeter wave radio links, accurate rain rate measurements preferably with 1 min sampling or integration time are needed. most of these measurements provide rainfall data in mm/hr with different integration or sampling times. however, these can be converted to 1 min integration or sampling time using a regression equation provided by itu to convert various integration times to 1 min integration time to predict rain rate and consequently, rain fade [17]. rain gauges provide the most accurate rain rate measurement and are often used by other measurement sources as "ground truth" for validation and calibration purposes. in addition, the cost per rain gauge is significantly cheaper compared to other sources. however, the maximum spatial coverage for a rain gauge is typically around hundreds of meters, and the cover of an entire country would require an extremely large amount of rain gauges. weather radars or rain radars lie between rain gauges and weather satellites. rain radars provide significantly better spatial coverage compared to rain gauges. typically, only several rain radars are needed to cover a small country. rain radars rely on measuring reflected electromagnetic waves from rain events at the s or c band to measure rain rate. the engineering, technology & applied science research vol. 13, no. 4, 2023, 11064-11069 11066 www.etasr.com basarudin et al.: evaluation of climate change effects on rain rate distribution in malaysia using … sampling times for rain radars are longer than rain gauges, ranging from 5 to 15 min between scans, which slightly reduces their accuracy [9]. weather satellites provide the best spatial coverage since they can measure rain rates globally, but with a longer sampling time of 30 min to 1 h and with a maximum of 37 mm/hr rain rate measurement in the case of eumetsat weather satellites. additionally, weather satellites are less accurate as they observe rain events from above and calculate rain rates by measuring the temperature of the cloud tops using infrared devices [22]. the hydro-estimator provides a global map of rain rate using global measurement sources, including rain gauges, rain radars, and weather satellites, blending them with numerical weather prediction models using specific techniques to increase accuracy [22-23]. the sampling time of the hydro-estimator is 1 h for global coverage, but this can be solved by using a regression technique provided by itu to convert 1 h to 1 min integration time for rain rates, and consequently, rain fade. this platform can be a great asset to provide rain rate measurements, especially in areas without rain gauges and rain radars [24]. furthermore, this platform is freely available, quick, and easy to access compared to other sources. this study used hydroestimator data to obtain rain rate measurements and investigate the effect of climate change on rain fade of 5g millimeter wave backhaul links or other wireless communications that use frequencies above 10 ghz. ii. theoretical hydro-estimator algorithm the hydro-estimator is a meteorological platform that contains rainfall rate information and is currently operated by noaa/nesdis in the united states. it combines and consolidates rain rate data from rain gauges, rain radars, and weather satellites to provide rain rate data on a global scale. the data have 1 h sampling time but can be converted to 1 min integration using the regression model in itu-r 839: ��(�) = �[� (�)] � (1) where rτ(p) is the rain rate with 1 h sampling rate at probability p% and r1(p) is the new 1 min sampling time rate at the same probability. coefficients a and b carry fixed values of 0.564 and 1.288, respectively. it is worth noting that the raw data in the hydro-estimator need a direct conversion to be interpreted as rain rate in mm/hr. the rain rate can be calculated from the raw data using the following equation provided by noaa [22]. � = (�� �� − 2) ∗ 0.3048 (2) where r is the rain rate in mm/hr and value is the raw data. iii. computer program: validation and verification the process of extracting, calculating, analyzing, and plotting rain rate data from the hydro-estimator was performed in matlab. hydro-estimator rain rate data between 2011 and 2020 were compared to the itu-r 837 rain rate distribution model, which is regarded as reliable or acceptable by most radio engineers. the yearly rainfall rate distributions between 2011 and 2020 were compared between hydro-estimator and itu-r 837 along with the 10-year average rain rate distribution for verification purposes. the annual rain rate distribution was calculated using the probability exceedance method, which is the percentage probability of how much rain rate is equal to or exceeded at that probability level. the calculation method for exceedance probability is: �(%) = ��(���)��� ��(���) (100%) (3) where p(%) is the exceedance probability, cf(max) is the maximum cumulative frequency of the rain rate and cf is the range of all cumulative frequencies of the yearly rain rate. the next step was to plot the rain rate with a 0.01% exceedance probability yearly from 2011 to 2020 to observe the effects of climate change on the rain rate distribution. the exceedance probability of 0.01% was selected as it is a telecommunication standard by the global community to measure signal quality. a yearly 0.01% exceedance probability represents approximately 20 min of total time in a year. iv. performance evaluation table ii shows a comparison of similar studies in estimating rain rate distribution using the methods in table i. table ii. comparison of related works study methods spatial area coverage integration time spatial shapes of rain events climate change analysis maximum range of rain rate [1] hydroestimator globally 1 h yes no ~100 mm/hr [25] rain gauge ~2.8 km2 1 min no no ~250 mm/hr [26] rain radar and rain gauge ~ 3 to ~28 km2 5-6 min yes (rain radar) no ~250 mm/hr [27] weather satellites, rain radar, and rain gauge ~3 km2 (rain gauge), ~100 km2 (rain radar) 1 h (for all) yes (rain radar and weather satellite) no ~120 mm/hr this study hydroestimator globally 1 h yes yes ~100 mm/hr this study used hydro-estimator data to integrate a climate change analysis on rain rate distribution. in [15], it was stated that over the past 30 years, there is growing proof suggesting that the incidence of rain rates at intensities associated with an outage on terrestrial links has exhibited increasing trends, but there is no evidence of increased outage rates or fades of microwave links. this study provided evidence that trends in the size of rain events lead to changes in the relationship between point rain rates and rain fade. however, these trends have been shown to vary significantly across the uk. malaysia, however, has a different climate from the uk. therefore, this can result in different conclusions on how climate change has affected the rain rate and rain fade. a. simulation environment all extraction, conversion, and plotting processes were performed in matlab. rain rate data in 2011-2020 of peninsular malaysia and the sabah and sarawak region were engineering, technology & applied science research vol. 13, no. 4, 2023, 11064-11069 11067 www.etasr.com basarudin et al.: evaluation of climate change effects on rain rate distribution in malaysia using … downloaded from the hydro-estimator in raw format, then were extracted, and converted to mm/hr using (2). subsequently, the data were analyzed for their exceedance probability distribution using (3). the obtained results were analyzed yearly and 10-year averaged and compared to the itu-r 837 rain rate distribution model for verification. each year was plotted with a 0.01% exceedance probability, and a regression model was used to observe the trend. b. simulation parameters figure 1 shows the results for 2011 with 1 h and 1 min integration. this step was performed for each year from 2011 to 2020. the rain rate distributions of peninsular malaysia and the sabah and sarawak region with 1 h integration time were significantly lower when compared to the itu model. however, rain rate distribution results from the same regions and with 1 min integration, after conversion using (1), appears to be plausible when compared with the itu-r model, particularly for the sabah and sarawak region. this is significant since the itu-r 837 model was developed based on numerous rain rate measurements with a 1-minute integration time. further analysis of the rain rate distributions in figure 1 shows a wide difference between the hydro-estimator and itu-r models, beyond 0.01% exceedance probability. however, this study focused on achieving plausible results down to 0.01% exceedance probability only, since this is a common quality standard practiced by telecommunication industries, and translates to 99.99% signal availability throughout the year [28-29]. fig. 1. rain rate distributions for 2011 compared with the itu-r model. c. ten year rain rate distribution figures 2 and 3 show the rain rate data at 0.01% exceedance probability for each year between 2011 and 2020 for the peninsular malaysia and sabah sarawak regions, respectively. by performing linear regression analysis, the figures show increasing trends of rain rate distribution throughout these years. for peninsular malaysia, the rate was 0.2356 mm/hr per year while the sabah and sarawak region had 0.4046 mm/hr per year. this shows that climate change affects the distribution of rain rates in tropical regions such as malaysia. fig. 2. rain distribution trend from 2011-2020 for peninsular malaysia. fig. 3. rain distribution in 2011-2020 for the sabah and sarawak region. d. average rain rate distribution the rain rate distribution was further compared with the itu-r 837 model. figures 4 and 5 show the results for each year for peninsular malaysia and the sabah sarawak region, respectively. figure 6 shows the 10-year average of the rain rate distribution result and its comparison with the itu-r 837 model. figure 6 shows that the hydro-estimator rain rate distribution had a slight agreement with the itu-r 837 model for both the peninsular malaysia and the sabah and sarawak region. the peninsular malaysia result seems to underestimate the itu-r model, especially at a lower exceedance probability, while the two models seem to be in more agreement for the sabah and sarawak region. the differences between the hydro-estimator and the itu-r results can be attributed to variations in rain rate distribution from year to year, as shown in figures 4 and 5. it can be deduced that hydro-estimator provides reliable rain rate distributions and can be further used for rain fade simulation on microwave and millimeter wave links. engineering, technology & applied science research vol. 13, no. 4, 2023, 11064-11069 11068 www.etasr.com basarudin et al.: evaluation of climate change effects on rain rate distribution in malaysia using … fig. 4. rain rate distribution from 2011 to 2020 for peninsular malaysia. fig. 5. rain rate distribution from 2011 to 2020 for the sabah and sarawak region. fig. 6. comparison of the average ten-year rain rates of the proposed with the itu-r model. v. conclusions this study used hydro-estimator data from 2011 to 2020 to plot the trend of rain rate distribution over malaysia. the simulated rain rates from the hydro-estimator were compared with the itu-r 837 model for verification. the results showed a reasonable agreement between the data and the model. the results showed an increasing trend in rain rate distribution for the peninsular and sabah and sarawak regions in malaysia, and indicate that climate change had an impact on rain rate distribution over the years. the change in rain rate distribution over the 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[29] a. guidotti, c. sacchi, and a. vanelli-coralli, "feeder link precoding for future broadcasting services," ieee transactions on aerospace and electronic systems, vol. 58, no. 4, pp. 3126–3146, dec. 2022, https://doi.org/10.1109/taes.2022.3144243. microsoft word 3-568-ed.doc engineering, technology & applied science research vol. 5, no. 4, 2015, 832-840 832 www.etasr.com perneel et al.: business hypervisors for real-time applications business hypervisors for real-time applications luc perneel h. fayyad-kazan long peng fei guan martin timmerman department of electronics and informatics, vrije universiteit brussel, belgium luc.perneel @vub.ac.be department of electronics and informatics, vrije universiteit brussel, belgium hafayyad@vub.ac.be department of electronics and informatics, vrije universiteit brussel and dedicated-systems experts, belgium longpeng@vub.ac.be department of electronics and informatics, vrije universiteit brussel, belgium feiguan@vub.ac.be department of electronics and informatics, vrije universiteit brussel, belgium and dedicatedsystems experts, belgium martin.timmerman @vub.ac.be abstract— system virtualization is one of the hottest trends in information technology today. it is not just another nice to use technology but has become fundamental across the business world. it is successfully used with many business application classes where cloud computing is the most visual one. recently, it started to be used for soft real-time (rt) applications such as ip telephony, media servers, audio and video streaming servers, automotive and communication systems in general. running these applications on a traditional system (hardware + operating system) guarantee their quality of service (qos); virtualizing them means inserting a new layer between the hardware and the (virtual) operating system (os), and thus adding extra overhead. although these applications’ areas do not always demand hard time guarantees, they require the underlying virtualization layer supports low latency and provide adequate computational resources for completion within a reasonable or predictable timeframe. these aspects are intimately intertwined with the logic of the hypervisor scheduler. in this paper, a series of tests are conducted on three hypervisors (vmware esxi, hyper-v server and xen) to provide a benchmark of the latencies added to the applications running on top of them. these tests are conducted for different scenarios (use cases) to take into consideration all the parameters and configurations of the hypervisors’ schedulers. finally, this benchmark can be used as a reference for choosing the best hypervisor-application combination. keywords: esxi; hyper-v; virtualization; xen; real-time i. introduction system virtualization is a technology that allows the physical machine resources to be shared among different virtual machines (vms) via the use of a software layer called hypervisor or virtual machine monitor (vmm). the hypervisor can be either type-1 which runs directly on the system hardware and thus is often referred to as bare-metal hypervisor, or type-2 which runs as an application on top of a conventional operating system (os) and is referred to as hosted hypervisor [1, 2]. due to the low cost availability of multi-core chips used in a symmetrical multiprocessor way, virtualization in the server and desktop world has already matured with both software and hardware solutions available for several years [3]. currently, there are numerous virtualization products ranging from opensource hypervisors such as xen, kvm, and openvz to commercial ones as vmware vsphere esxi, virtualbox, okl4, parallels workstation and microsoft hyper-v [3]. theoretically speaking, as a bare-metal hypervisor has direct access to the hardware resources rather than going through a hosting operating system, it is more efficient, delivers greater scalability, robustness and performance [4]. therefore, bare-metal hypervisors are our focus in this paper. virtualization is successfully used with many business application classes where cloud computing is the most visual one. however, the growing set of applications also includes soft-real time applications such as media-based ones. it is obvious that the hypervisor layer between the hardware and the os running in a vm incurs extra overhead compared to a nonvirtualized system. this overhead can vary from one hypervisor type to another. moreover, there is no quantitative benchmark of these overheads (added latencies), which in turn makes it difficult for users to choose the hypervisor that fits their requirements. currently, there are just some technical publications [5, 6], initiated by the hypervisor vendors themselves, comparing mainly the hypervisors’ supported features. more recently, a number of unbiased scientific papers originated by researchers focused on the i/o performance, network throughput and cpu utilization, using public benchmark tools which are not really adapted for the comparison job [7, 8]. as a consequence, most publications are not at all quantifying their statements; others give only a limited scientific proof. our contribution started from this point. we want to go beyond theoretical statements and quantify the performance differences (in matters of latencies) between virtualization solutions by focusing on their architectures and internal components such as scheduling policies. to achieve this, different types of tests (explained further on) are executed on the top three market hypervisors: microsoft (ms) hyper-v server 2012r2, xen 4.2.1 and vmware vsphere esxi 5.1u1. all these versions were the latest shipping releases at the time of doing this study. the tests are conducted for different use cases to take into consideration all the parameters and configurations of the hypervisors’ schedulers. engineering, technology & applied science research vol. 5, no. 4, 2015, 832-840 833 www.etasr.com perneel et al.: business hypervisors for real-time applications ii. hypervisors architectures a. microsoft hyper-v server 2012 r2 microsoft hyper-v is a bare-metal micro-kernerlized hypervisor that enables platform virtualization on x86-64 systems [9]. it exists in two variants: as a stand-alone product called hyper-v server [10] and as an installable feature in windows server os. in both versions, the hypervisor is exactly the same and must have at least one parent, or root vm, running windows os 64-bit edition [11]. the difference between the two products are the features and components found in the parent (privileged) vm guest os. once hyper-v is installed, vms atop it are created. all the vms except the parent vm are called child vms (unprivileged). hyper-v supports a number of different types of guest oss running in the child vms. they can be either hyperv aware (enlightened/para-virtualized) windows oss, hyperv aware non-windows oss and non hyper-v aware oss [12]. the hypervisor needs to deal with cpu scheduling. the cpu scheduler shares the same role as conventional operating systems. this role is to assign execution contexts to processors in a way that meets system objectives such as responsiveness, throughput, and utilization. on conventional operating systems, the execution context corresponds to a process or a thread; on hypervisor, it corresponds to a vm. when a vm is created atop hyper-v, several configurations have to be set to define its behaviour when accessing hardware resources. the basic ones are shown in figure 1 below followed by their explanations. fig. 1. hyper-v vm configuration for resources access virtual machine reserve: this setting specifies the percentage of the physical machine’s overall cpu resources reserved for this particular vm. this value can range from 1100% and is relative to the number of processors assigned to the virtual machine (a vm can have more than one virtual processor). for instance, if a physical machine has four cores and you set the vm reserve value to 100 %, then the equivalent of an entire processor core will be reserved for a vm. if the vm sits idle at 10% most of the time, the other 90% of the processing time is still unavailable to any other vms. note that using the “reserve” setting limits the amount of virtual processors that can be shared on a physical machine, and therefore limits the number of concurrent virtual machines you can power on. for example, if you have 20 vms where each one is configured to have one single virtual processor whose “reserve” value is 100%, and the physical machine has four cores, then you can only power on only four virtual machines. if you try to start a 5th vm, you would get an error message stating that you cannot initialize the virtual machine. note that you will get this error even if all four running virtual machines are completely idle and are not using any cpu resource (reason mentioned before). a final interesting note about the virtual machine reserve is that by default it is set to “0%” – which means the reserve is disabled. furthermore – if you have a configuration like the one where all cpus are reserved, you can still start extra virtual machines as long as their cpu reserve is set to 0% [13]. virtual machine limit: this setting is the opposite of “virtual machine reserve” setting. it allows you to specify the maximum amount of processing power that a virtual machine can consume and is relative to the number of processors assigned to a vm. relative weight: it specifies how hyper-v allocates resources to a vm when more than one vms are running and compete for resources. this value ranges from 0-10000 and the vm with high value receives more cpu time. by default, all vms are assigned the same weight value (100). there is no official document explaining the scheduling algorithms of hyper-v. fortunately, ben armstrong, virtualization program manager at microsoft, posted a four part article about cpu scheduling in hyper-v [13]. from these articles, the scheduling algorithm of hyper-v can be summarized as follow: if there is only one vm which has one virtual cpu (vcpu), and the hosting machine has many physical cores, then this vcpu shares the processing resources of all the physical cores. it runs on all the cores in round-robin way. the parent vm is the only vm that stays parked on the first core (core 0) [14]. thus, hyper-v uses a weighted round-robin scheduling algorithm. the time a vcpu spends on one physical core before being scheduled to another is not specifically mentioned in any of the public resources. this is something we measured in the testing phase. b. xen xen is an open source hypervisor developed by barham et al. [30] at the university of cambridge in 2003. it is released under the gnu general public license (gpl), which means that it is open source, free for use and can be modified. it is a bare-metal micro-kernelized hypervisor. its architectural design is the same as hyper-v. the parent vm is termed as domain0 (dom0 for short) and runs para-virtualized (xen-enabled) linux os. this vm helps in creating/configuring guest vms and has the native device drivers to assist them in performing engineering, technology & applied science research vol. 5, no. 4, 2015, 832-840 834 www.etasr.com perneel et al.: business hypervisors for real-time applications real i/o operations [15]. all the other vms atop xen are guest vms and referred as domus. domu pv guests are modified oss such as linux, solaris, freebsd, and other unix operating systems. domu fv guests run standard windows or any other unchanged operating system. xen’s default scheduler is called credit [16]. this scheduler acts as a referee between the running vms. in some ways it’s a lot like the linux scheduler. the xen team designed it to fairly share the physical cpus among guest vms (minimize wasted cpu time). this makes it a "work-conserving" (wc) scheduler, in that it tries to ensure that the cpu will always be working, whenever there is work for it to do. as a consequence, if there is more real cpu available than the vms are demanding, all vms get all the cpu they want. when there is contention -that is, when the vms in aggregate want more cpu than actually exists -then the scheduler arbitrates fairly between the vms that want cpu [31]. credit scheduler algorithm: xen is a non-preemptive scheduler based on the wrr (weighted round-robin) scheduling algorithm [17]. it assigns each vm a weight and, optionally, a cap. weight decides the amount of cpu time it can get and cap fixes the maximum amount of cpu a vm will be able to consume even if the host system has idle cpu cycles. if the cap is 0, then the vm can receive any extra cpu (work conserving-mode). a non-zero cap (expressed as a percentage) limits the amount of cpu a vm receives (nonwc-mode). for example, a cap value of 100 means using only 1 physical cpu, 50 is half a cpu, 400 is 4 cpus, etc... [18] figure 2 is an example of a vm (domain-0) which has a weight of 256 and cap 0. fig. 2. xen vm properties in the xen credit scheduler, every physical core has one run queue (runq), which holds all the runnable vcpus (vcpu with a task to run) [16]. the scheduler transforms the weight into a credit allocation for each vcpu, using a separate accounting thread. vcpus consume credit as they run, and are divided into two categories in the runq: under, and over. a vcpu is put into the under category if it has remaining credit, and over if it runs out of credit. when inserting a vcpu into the queue, it is put after all other vcpus of equal priority to itself [18]. the scheduler picks vcpus in the order of under and then over. within each category, it is important to note that vcpus are scheduled in a round robin fashion. every 10ms, the scheduler ticks, and then subtracts credits the vcpu owns. when a vcpu consumes all its allocated credits (the value of the credit is negative), the state of its priority changes into over, and then the vcpu cannot be scheduled. every 30ms, the value of credit each vcpu owns is to be accounted again, and all vcpus will get new value of credit [16]. an example would be a vcpus waiting in two queues: one for vcpus with credits and other for those that are over their allocation. once the first queue is exhausted, the cpu will pull from the second. an idle vcpu for each physical core is also created at boot time. it is always runnable and placed at the end of the runq. when the idle vcpu is scheduled, the physical core becomes idle. another important setting of the credit scheduler is called “ratelimit”. it is a value in microseconds. it refers to the minimum amount of time a vm is allowed to run without being preempted. the default value is 1000μs (1ms). so if a vm starts running, and a second vm with higher priority wakes up, if the first vm has run for less than 1ms, it is allowed to continue to run until its 1ms is consumed; only after that will the higher-priority vm be allowed to run. c. vmware esxi vmware esxi (elastic sky x) is a bare-metal monolithic hypervisor developed by vmware inc. it is an operating system-independent hypervisor based on the vmkernel os, interfacing with agents and approved third-party modules that run atop it [19]. vmkernel is a posix-like (unix style) operating system developed by vmware and provides certain functionality similar to that found in other operating systems, such as process creation and control, signals, file system, and process threads [19]. it is designed specifically to support running multiple virtual machines and provides such core functionality as resource scheduling, i/o stacks, and device drivers [19]. vmware esxi is the core component of the vmware vsphere software suite which in turn has many software components such as vmware vcenter server, vmware vsphere client and vsphere web client and many others [20]. all the virtual machines are installed on the physical machine running esxi hypervisor. to install, manage and access those virtual machines, another part of vsphere suite called vsphere client or vcenter is installed on another physical machine [20]. in earlier versions of vmware vsphere, the hypervisor was available in two forms: vmware esx and vmware esxi [32]. the esxi server is an advanced, smaller-footprint version of the vmware esx. virtualization administrators can configure vmware esxi through its console or the vmware vsphere client and check vmware's hardware compatibility list for approved, supported hardware on which to install esxi [21]. due to its architecture, vmware esxi uses fullvirtualization with hardware-assisted approach. the major goals of the vmware cpu scheduler are fairness, throughput, and responsiveness (how promptly a vcpu is scheduled after it becomes ready). esxi implements a proportional share–based scheduling algorithm, which allocates cpu resources to vcpus based on their resource specifications. users can specify the cpu allocation (resource specification) for a vm using three settings: shares, reservations, and limits (figure 3) [22]. the aim of these three settings is exactly the same as hyper-v but using different names. limit: places a limit on the cpu consumption for a vm. it is specified in mhz (hyper-v also uses the same word). reservation: this is a guaranteed amount of resources reserved for a particular vm. when a vm is powered on, the engineering, technology & applied science research vol. 5, no. 4, 2015, 832-840 835 www.etasr.com perneel et al.: business hypervisors for real-time applications reserved amount of resources are given to that vm and are "eliminated" from the pool of open resources that other vms can use [23]. a vm can (should) not power on if the host it resides on does not have enough resources to meet the reservations of that vm. its value is expressed also in mhz. (same naming as hyper-v) fig. 3. vm scheduling settings in esxi hypervisor shares: they are simply used to prioritize resources for use by vms when there is active resource contention. if you give a vm 1000 shares of cpu and another 500, when resource contention arises, the vm with 1000 shares will be granted access to twice as much cpu as the vm with 500 shares. same idea as relative weight in hyper-v [23]. scheduler algorithm: in esxi, a virtual machine consists of one or more vcpus on which guest instructions are executed. for example, a 4-vcpu virtual machine has 4 vcpus. there are other vcpus associated with the virtual machine that execute management tasks like handling the mouse and keyboard, snapshots, and legacy i/o devices. therefore, it is theoretically possible that a 1-vcpu virtual machine can consume more than 100% of a processor, although this is unlikely because those management vcpus are mostly inactive [22]. so if you create a vm on top of esxi and you assign for it one vcpu, then this vm has in fact many vcpus, one for executing the guest os instructions, and other “hidden” vcpus added automatically by the esxi scheduler for management purposes. the number of the “hidden” vcpus is not specified by any documentation. there are also vmkernel management vcpus performing management tasks on behalf of the esxi host. for example, there are a number of vcpus handling the communication with a management server. a few vcpus execute periodic tasks for the resource management algorithm. however, the cpu demand of the vmkernel management vcpus is not significant and most of the cpu resources are available for virtual machines [22]. esxi cpu scheduler is invoked when the time quantum given to a currently running vcpu expires. since it is common that a vcpu changes its state to wait before the current quantum expires, the size of a time quantum (50 milliseconds by default) does not affect performance much [22]. time quantum expiration or the state change from run to wait invokes the cpu scheduler, which then searches for the next ready vcpu to be scheduled. the ready vcpu can be found from a local ready queue or from a remote queue. if none is found, an idle vcpu is scheduled. when a vcpu wakes up and changes its state from wait to ready, likely from an interrupt or a signal, the cpu scheduler is invoked to determine where the newly ready vcpu can be scheduled. it may be put into the ready queue waiting to be scheduled in the next iteration, migrated to a different physical cpu with less contention, or the currently running vcpu may be preempted. the decision depends on many factors like fairness and execution efficiency [22]. iii. experimental configurations as mentioned earlier, the three enterprise hypervisors evaluated are: microsoft (ms) hyper-v server 2012r2, xen 4.2.1 (opensuse 12.3 is running in dom-0 vm) and vmware vsphere esxi 5.1u1. all these versions were the latest shipping releases at the time of doing this study which started in may 2012. a. evaluation hardware platform: these hypervisors need to run on a physical platform. this platform should meet the hardware requirements for all the chosen hypervisors. looking at the vendors technical documents [24, 25, 26], the following hardware features are needed: a 64-bits x86 processor that includes the following: • at least two cores. • hardware-assisted virtualization. this is available in processors that include a virtualization option— specifically processors with intel virtualization technology (intel vt) or amd virtualization (amd-v) technology. • hardware-enforced data execution prevention (dep) must be available and enabled. • a time stamp counter (tsc) running at a constant rate, which is the tool used for measuring the time intervals. • a minimum of 2 gb of physical ram to meet these requirements, the most cheap and convenient solution was decided to be the following hardware: intel® desktop board dh77kc, intel® xeon® processor e3-1220v2 with four cores each running at a frequency of 3.1 ghz without hyper-threading support. the cache memory size is as follows: each core has 32 kb of l1 data cache, 32 kb of l1 instruction cache and 256 kb of l2 cache. l3 cache is 8mb accessible to all cores. 16 gb of physical ram is used. engineering, technology & applied science research vol. 5, no. 4, 2015, 832-840 836 www.etasr.com perneel et al.: business hypervisors for real-time applications b. vm guest os: evaluating the hypervisors is achieved by executing a test suite in a vm running atop each one. this vm is called undertest vm (utvm). as mentioned earlier, microsoft hyper-v and xen support both full-virtualization (fv) and paravirtualization (pv) vms, while esxi supports only fv. for consistency of our evaluation, a guest os that can be configurable for usage as fv and pv vms is needed. being open source and matching the requirements, linux is chosen. more specifically, a real-time version of linux called linux preempt-rt is used. the motive for choosing a real-time kernel is to minimize the latencies that could occur in the guest os, which in turn produces more accurate measurements. therefore, linux preemprt-rt version 3.6.11-rt25 is the utvm guest os. iv. testing setup although the test metrics explained below are mostly used to examine the real-time performance and behaviour of realtime oss on bare-machines [27, 28], they are useful to be used in other os test cases. nowadays, as virtualization together with real-time support is used in an increasing amount of use cases, these tests are a good fit for this paper evaluation. a. measuring process in order to perform our quantitative tests, a tool is needed to measure the time intervals. the cheapest solution is to use an on-processor chip timer running on the constant frequency of the processor clock giving as a value the number of cycles occurred on the processor. its value is set to zero every time the processor is reset. this timer is called time stamp counter (tsc). it is a 64-bits register present on all x86 processors and has an excellent high-resolution. in order to access the tsc, the programmer has to call the read time-stamp counter (rdtsc) instruction from assembly language. b. testing metrics below is an explanation of the evaluation tests. note that the tests are initially done on a non-virtualized machine (further called bare-machine) as a reference, using the same os as the utvm. 1) clock tick processing duration like any time-sharing system, linux os allows the simultaneous execution of multiple threads by switching from one thread to another in a very short time frame. the linux scheduler supports multiple scheduling classes, each using different scheduling algorithms. for instance, there are the two real-time (strict priority) scheduling classes sched_fifo and sched_rr, a normal scheduling class (sched_other) using dynamic and thus non strict priorities, and finally the sched_batch class for background threads. to be able to use timeouts, sleeps, round robin scheduling, time slicing and etc…, some notion of time is needed. on the hardware, there is always a clock responsible for this called the clock timer system. it is programmed by linux preempt-rt to generate an interrupt each tick. depending on the kernel configuration used at build time the tick frequency can be selected. we used the 1000 hz configuration, so that the interrupts occurs each millisecond. this tick period is considered the scheduling quantum. the aim of this test is to measure the time needed by the os to handle this clock interrupt. its results are extremely important as the clock tick interrupt being on a high level interrupt on the used hardware platform will bias all other performed measurements. this test helps also in detecting “hidden” latencies that are not introduced by the clock tick. in such cases, the “hidden” latency will be different and its event time will not be aligned with the rtos clock tick frequency. the test method can be described as follows: a real-time thread with the highest priority is created. this thread does a finite loop of the following tasks: get the time using rdtsc instruction, start a “busy loop” that does some calculations, get time again using the same instruction. having the time before and after the “busy loop” provides the time needed to finish its job. in case we run this test on the bare-machine, this “busy loop” will only be delayed by the interrupt handlers. as we remove all other interrupt sources, only the clock tick timer interrupt can delay the “busy loop”. when the “busy loop” is interrupted, its execution time increases. when executing this test in a guest os (vm) running on top of a hypervisor, it can be interrupted or scheduled away by the hypervisor as well, which will result in extra delays. figure 4 presents the results of this test on the bare-machine, followed by an explanation. the x-axis indicates the time when a measurement sample is taken with reference to the start of the test. the y-axis indicates the duration of the measured event; in this case the total duration of the “busy loop”. fig. 4. clock tick processing duration of the bare-machine the bottom values (68.1 μs) present the “busy loop” execution durations if no clock tick happens. in case of a clock tick interruption, its execution is delayed until the clock interrupt is handled, which is 76.5 μs (top values). the difference between the two values is the delay spent handling the clock tick interrupt (executing the handler), which is 8.4 μs. this test detects all the delays that may occur in a system together with its behaviour for a short period. to have a longtime view of the system behaviour, we execute the same test but for a long period. we call the long-duration test as clock tick processing duration = 76.5 – 68.1 =8.5 µs engineering, technology & applied science research vol. 5, no. 4, 2015, 832-840 837 www.etasr.com perneel et al.: business hypervisors for real-time applications “statistical clock tick processing duration”. the importance of the figure obtained by “clock tick processing duration” test is to show the exact tracing values and the moments of their occurrence while the figures of “statistical clock tick processing duration” test (explained below) show their distribution over time and the predictability of the system latencies. 2) statistical clock tick processing duration this test is exactly the same as the previous one except that it is done for a longer period. it is executed 5 times, each time for one hour. the motivation for this (5 times) is to take into consideration all the circumstances that may happen in and around the system, like the room temperature, running the test immediately after the machine start-up, run it after one day of keeping the machine on, etc. after 5 tests, the variance was negligible showing the stability of the system. the test with the greatest worst case value was then taken for further processing. figure 5 below presents the statistical distribution of the samples obtained during the 1 hour test on the bare-machine. before looking at the figure results, we first provide an explanation of how we obtain the statistical samples. the measured delay values are counted in binary based bins. this can be done without much overhead as an assembler instruction exists to find the highest bit set in the measured delay. the highest bit set is used as first level bin selection, while the next couple of lower bits are used for the second level bin selection. this makes it possible to statistically collect a huge amount of samples without significant overhead caused by the measurement system itself. fig. 5. statistical clock tick processing duration for a bare-machine note that the bin distribution using this method is presented in logarithmic way. sixty million samples are captured during the 1-hour test. the x-axis represents the delay values in the binary bins, while the y-axis is a logarithmic presentation of the number of obtained samples and their corresponding percentage. for the benchmark provided further on, only the “statistical test” results are used. after explaining the tests and executing them on the baremachine, now it is time to run them on the selected hypervisors using several scenarios (use cases). v. scenarios seven scenarios are used in the evaluation of each selected hypervisor. below is a detailed description of each scenario. it should be reminded that hyper-v and xen supports fv and pv vms. therefore, in all the scenarios, the evaluation tests are executed in both vms types, whereas only in fv vm for vmware esxi hypervisor. 1) scenario 1: one-to-all (no-affinity) the aim of this scenario is to measure the extra overhead added to the vm performance, compared to the bare-machine, due to the insertion of the virtualization layer. also, we aim to discover the following scheduling behaviour: does the hypervisor keep the utvm running permanently on the same cpu or switches it over all the available cores? in this scenario, the utvm (always with one vcpu) is the only running vm. in case of ms hyper-v, the utvm “virtual machine reserve” parameter is set to 100 % (means one physical cpu is dedicated to it). the aim of this parameter is to ensure that no other services (or vms) share the same processor with utvm which may influence its performance. a similar parameter (reserve) is set for the utvm atop vmware esxi. there is no such parameter for vms on xen. note that in ms hyper-v and xen, there is also a parent partition (dom-0) running but in idle state. the parent partition in hyper-v runs by default on cpu0 [29]. in xen, we manually configured it to run permanently on cpu0. the scenario setup is illustrated in figure 6a. 2) scenario 2: one-to-one (affinity) the aim of this scenario is similar to the previous one except that the utvm vcpu is explicitly assigned to run permanently on one physical cpu using the affinity (pinning) configuration options of esxi and xen. hyper-v does not support affinity, and therefore three cpus are disabled from the bios. the aim of this scenario is to show the performance (latencies) difference (if any) between affinity and no-affinity cases. the scenario setup (considering hyper-v as example) is shown in figure 6b. 3) scenario 3: contention with one cpu-load vm this scenario simulates the real life situation where the number of vms running atop hypervisor can be higher than the available physical cores, which causes resource contention. its setup has two vms: utvm and cpu-load vm which are both configured to run on the same physical cpu (figure 6c). the cpu-load vm is running a cpu-stress program which is an infinite loop of mathematical calculations. the aim of this scenario is to explore the scheduling mechanism of the hypervisor between competing vms. 4) scenario 4: contention with one memory-load vm two vms sharing the same cpu means also sharing the caches. the aim of this scenario is to detect the effect of cpu caches on the utvm performance. its setup is exactly the same as scenario 3 except that a memory-load vm is used instead of a cpu-load vm (figure 6d). this memory-load vm is running an infinite loop of memcpy() function which copies 9 mb (a value that is larger than the total cache size) from one object to another. with this memory load, the caches are always flushed. engineering, technology & applied science research vol. 5, no. 4, 2015, 832-840 838 www.etasr.com perneel et al.: business hypervisors for real-time applications fig. 6. (a) scenario 1: one-to-all (b) scenario 2: one-to-one (affinity) in hyper-v (c) scenario 3: contention with 1 cpu-load vm atop hyper-v (d) scenario 4: contention with one memory-load vm atop hyper-v 5) scenario 5: all-to-all with 3 cpu-load vms in this scenario (figure 7), we run concurrently four vms: the utvm and three cpu-load vms. theoretically, with such setup, each vm should run on a different physical cpu. the aim of this scenario is to confirm whether this expected behavior occurs. in case it is true, then the results of this scenario should be close to the ones of scenario 1. the answer for this is provided in the benchmark table. fig. 7. scenario 5: all-to-all with three cpu-load vms 6) scenario 6: all-to-all with three memory-load vms this scenario setup (8) is exactly the same as scenario 5 except using memory-load vms instead of cpu-load vms. the aim of this scenario is to clarify whether the type of workload in the vms has any effect on the performance of the utvm (figure 8). 7) scenario 7: two-to-all with one memory-load vm this scenario (figure 9) has two running vms: the utvm and a memory-load vm. the aim of this scenario and executing it as the last one is justified in the analysis of the benchmark. fig. 8. scenario 6: all-to-all with three memory-load vms fig. 9. scenario 7: two-to-all with one memory-load vms the tests were executed on the hypervisors using the described scenarios. the results are provided in a benchmark table in the next section together with a detailed analysis. vi. the benchmark this section provides the benchmark table and analysis of the results. table i shows the tested hypervisors together with the type of used utvm (fully-virtualized or para-virtualized) and the experimental scenarios. microsoft uses the name emulated for full-virtualization, and enlightened for paravirtualization, which are shown in the hyper-v fields. a. analysis of each hypervisor through the scenarios hyper-v: • our analysis for the scheduling behaviour of hyper-v especially in scenario 1 showed that its policy is to run a vm on one specific cpu for one second before switching it to the other. this value if obtained by running the short clock test many times. thus, this value is not obtained from the benchmark table. • scenario 2 has a similar setup as scenario 1 except that the vm is explicitly fixed to run permanently on the same cpu. with this configuration, the overheads in scenario 2 are almost double the ones of scenario 1. therefore, fixing a vm to run all the time on a specific physical cpu is a non-desirable mechanism in hyper-v. • the scheduling quantum (the time a vm is allowed to run before being preempted) in case of contention (scenario 3) is nearly doubled (10 ms) for emulated vm compared to enlightened (5 ms). these values are obtained by comparing the values of scenario 2 (the vm is fixed to run on same cpu) and scenario 3. (a) (b) (c) (d) engineering, technology & applied science research vol. 5, no. 4, 2015, 832-840 839 www.etasr.com perneel et al.: business hypervisors for real-time applications table i. benchmark table for results on all the tested hypervisors maximum overhead by statistical clock tick duration test bare machine value = 10 μs hyper-v server 2012r2 xen 4.2.1 vmware esxi 5.1 hypervisor scenario emulated vm enlightened vm fully-vitualized vm para-virtualized vm fully-vitualized vm 1: one-to-all 4.25 ms 1.62 ms 35 μs 23 μs 59.61 ms 2: one-to-one 7.19 ms 4.08 ms 35 μs 23 μs 185.7 ms 3: contention with one cpuload 18.56 ms 9.16 ms 30.16 ms customized = 7.44 ms 30.13 ms customized = 6.74 ms 281.71 ms 4: contention with one memory-load 21.03 ms 11.8 ms 30.18 ms customized = 8.53 ms 30.15 ms customized = 7.4 ms 286.5 ms 5: all-to-all with three cpu-load 5.21 ms 2.55 ms 35 μs 23 μs 51.4 ms 6: all-to-all with three memoryload 15.18 ms 4.53 ms 102 μs 62 μs 70.79 ms 7: two-to-all with one memory-load 5.3 ms 2.12 ms 49 μs 32 μs 60.14 ms • the overheads in scenario 4 are increased by 3 ms due to the effect of the memory load vm on the shared cpu caches. therefore, the cpu caches have an effect on the system performance (degradation of 3 ms). • scenario 5 proved its theory by having very close values compared to scenario 1. • the results of scenario 6 are around three times greater than the ones of scenario 5 even though the same number of vms is running. therefore, this scenario’s results confirm our hypothesis about the effect of vm workload type on others performance. the reason for this performance degradation is due to “system memory bus” bottleneck in a symmetric multiprocessor system (smp). i.e. : comparing the workload of both scenarios (5 and 6), scenario 5 is not causing high overheads because the cpu stress program in the cpu-load vms is quite small and fits in the core cache together with its data. therefore, the three cpu-loading vms are not intensively loading the system memory bus which in turn will not highly affect the utvm. in scenario 6, the three memory-load vms are intensively using the system memory bus. the utvm is also running and requires the usage of system bus from time to time. therefore, the system bus is shared most of the time between four vms (utvm and three memoryload vms), which causes extra contention. thus, the more cores in the system that are accessing the system bus simultaneously, the more contention will occur and thus the overhead increases. to explicitly show this effect, scenario 7 was created where only one memory-load vm is sharing the resources with the utvm. scenario 7 values clearly show the big performance enhancement if less memory-load vms are running simultaneously and competing for the system bus. xen: • the values or scenarios 1 and 2 are exactly the same, which means that xen uses same scheduling policy in both cases (affinity and non-affinity). these values are very close to the bare-machine ones. • for scenarios 3 and 4, there are 2 values in each field. as already mentioned before, xen uses the credit scheduler where each vcpu of a vm is scheduled to run for a quantum of 30 ms in a round-robin fashion. but, as xen is an open source hypervisor, this quantum can be changed depending on the usage arena, with a minimum value of 1 ms. therefore, in these two scenarios, we conducted the tests on xen using the default and minimum scheduler quantum values (30 ms and 1 ms). • the analysis of the other scenarios is exactly the same as explained for hyper-v. the analysis of vmware esxi results is also the same as hyper-v. the high values in vms atop vmware esxi are due to it scheduling policy, which was explained earlier in this paper (section 2, c). b. general conclusion about each hypervisor as presented in this paper, ms hyper-v is tested first. the evaluation results indicated the following findings: • a pv vm atop hyper-v performs on average twice better than fv vm. despite that, pv vm performance is slower than the bare-machine to a big extent. • the performance of any vm atop hyper-v is unpredictable with unbounded worst-case latencies (the evaluation test was done 5 times, each with different value). xen is tested next, indicating the following findings: • pv vm atop xen is on average 1.5 times better than fv vm. • pv vm performance is very close to the bare-machine. engineering, technology & applied science research vol. 5, no. 4, 2015, 832-840 840 www.etasr.com perneel et al.: business hypervisors for real-time applications • vm performance atop xen is always predictable and with bounded worst case latencies. vmware esxi is tested lastly ending up with the following findings: • vm performance is not comparable to the bare-machine due to the huge difference. even though, vm performance is predictable with bounded worst case latencies vii. conclusion the work done in this paper aims to measure the latencies that happen in a virtualized system, especially when used for hosting real-time applications. to achieve this, a test suite was executed on the top three market hypervisors, vmware esxi, microsoft hyper-v and xen. these tests are conducted in different scenarios to take into consideration all the parameters and configurations of the hypervisors’ schedulers, which are the main sources for influencing the latencies. a benchmark is provided where the results show that the xen vms incur the lowest latencies, and its application latencies are comparable to the bare-machine (non-virtualized system) ones. vms atop vmware incur the highest latencies and is ranked as the last, while microsoft hyper-v is the second. this ranking does not intend to eliminate any hypervisor from being qualified for soft real-time applications usage, but gives a clear idea on whether a certain hypervisor can be used for a specific real-time application. moreover, these values can help users choose the best hypervisor that meets their application requirements. also, this benchmark provides the scenarios where the best performance of a real-time application can be obtained. finally, the work shows that latencies in a system are not only software related, but also hardware-related especially in share-memory symmetric multiprocessor systems (smps). references [1] f. bazargan, c. y. yeun, m. j. zemerly, “state-of-the-art of virtualization, its security threats and deployment models”, international journal for information security research,vol. 2, no. 3-4, pp. 335-343, 2012 [2] a. desai, r. oza, p. sharma, b. patel, “hypervisor: a survey on concepts and taxonomy”, international journal of innovative technology and exploring engineering, vol. 2, no. 3, pp. 222-225, 2013 [3] a. j. younge, r. henschel, j. brown, g. von laszewski, j. qiu, g. fox, "analysis of virtualization technologies for high performance computing environments", ieee international conference on cloud computing (cloud), washington, usa, pp. 9-16, july 4-9, 2011 [4] vmware, "understanding full virtualization, paravirtulization, and hardware assist", http://www.vmware.com/files/pdf/vmware_ paravirtualization.pdf [5] e. yuen, “how would explain the core differences in hyper-v from vmware’s offerings?”, http://itknowledgeexchange.techtarget.com/ itanswers/how-would-explain-the-core-differences-in-hyper-v-fromvmwares-offerings/ [6] a. syrewicze, “vmware vs. hyper-v: architectural differences”, http://syrewiczeit.com/vmware-vs-hyper-v-architectural-differences/ [7] j. hwang, s. zeng, f. wu, t. wood, “a component-based performance comparison of four hypervisors", 13th ifip/ieee international symposium on integrated network management (im) technical session, ghent, belgium, pp. 269 – 276, may 27-31, 2013 [8] j. li, q. wang, d. jayasinghe, j. park, t. zhu, c. pu, "performance overhead among three hypervisors: an experimental study using hadoop benchmarks", ieee international congress on big data, santa clara, usa, pp. 9-16, june 27-july 2, 2013 [9] microsoft, "hyper-v architecture", http://msdn.microsoft.com/enus/ library/cc768520%28v=bts.10%29.aspx [10] microsoft, "windows server 2012 r2”, http://www.microsoft.com/enus/server-cloud/products/windows-server-2012r2/#fbid=nqbnx04c5st [11] microsoft technet blogs, "hyper-v: microkernelized or monolithic", http://blogs.technet.com/b/chenley/archive/2011/02/23/hyper-vmicrokernelized-or-monolithic.aspx. [12] virtuatopia, "an overview of the hyper-v architecture”, http://www.virtuatopia.com/index.php/an_overview_of_the_hyperv_architecture. [13] b. armstrong, "hyper-v cpu scheduling–part 1 ben armstrong site home msdn blogs”, http://blogs.msdn.com/b/virtual_pc_guy/ archive/2011/02/14/hyper-v-cpu-scheduling-part-1.aspx. [14] microsoft technet articles, "hyper-v concepts vcpu (virtual processor)", http://social.technet.microsoft.com/wiki/contents/articles/ 1234.hyper-v-concepts-vcpu-virtual-processor.aspx?wa=wsignin1.0. [15] xen project software overview, http://wiki.xen.org/wiki/ xen_project_software_overview [16] linux foundation, "credit scheduler”, http://wiki.xen.org/ wiki/credit_scheduler [17] s. yoo, k. h. kwak, j. h. jo, c. yoo, "toward under-millisecond i/o latency in xen-arm", second asia-pacific workshop on systems, apsys 2011, shanghai, china, july 11-12, 2011 [18] x. xu, p. sha, j. wan, j. yucheng, "performance evaluation of the cpu scheduler in xen", international symposium on information science and engineering, pp. 68-72, shanghai, china, december 20-22, 2008 [19] vmware, "the architecture of vmware esxi”, http://www.vmware.com/files/pdf/esxi_architecture.pdf [20] mustbegeek, "difference between vsphere, esxi and vcenter”, http://www.mustbegeek.com/difference-between-vsphere-esxi-andvcenter/ [21] c. janssen, "what is vmware esxi server? definition from techopedia”, http://www.techopedia.com/definition/25979/vmwareesxi-server [22] vmware, "the cpu scheduler in vmware vsphere 5.1", performance study-technical report [23] vmware, "vsphere resource management”, http://pubs.vmware.com/ vsphere51/topic/com.vmware.icbase/pdf/vsphere-esxi-vcenter-server51-resource-management-guide.pdf. [24] microsoft, "hyper-v overview”, http://technet.microsoft.com/enus/library/hh831531.aspx [25] linux foundation, "xen project beginners guide”, http://wiki.xenproject.org/wiki/xen_project_beginners_guide. [26] vmware, "minimum system requirements for installing esx/esxi", http://kb.vmware.com/selfservice/microsites/search.do?language=en_us &cmd=displaykc&externalid=1003661 [27] l. perneel, h. fayyad-kazan, m. timmerman, “android and real-time applications: take care!”, journal of emerging trends in computing and information sciences, vol. 4, no. iccsii, pp. 38-47, 2013 [28] h. fayyad-kazan, l. perneel, m. timmerman, “linux preempt-rt vs. commercial rtoss: how big is the performance gap?”, gstf journal of computing, vol. 3, no. 1, 2013 [29] m. t. wiki, “hyper-v concepts vcpu (virtual processor)”, http://social.technet.microsoft.com/wiki/contents/articles/1234.hyper-vconcepts-vcpu-virtualprocessor.aspx?wa=wsignin1.0 [30] p. braham, b. dragovic, k. fraser, s. hand, t. harris, a. ho, r. neugebauer, i. pratt, a. warfield, "xen and the art of virtualization", sosp '03 proceedings of the nineteenth acm symposium on operating systems principles, pp. 164-177, 2003 [31] c. takemura, l. crawford, in the book of xen, a practical guide for the system administrator, san francisco, william pollock, 2010. [32] windowsadmins, "introduction of vsphere 5 and its components", 2011, http://winadmins.wordpress.com/page/29/ microsoft word etasr_v13_n2_pp10239-10242 engineering, technology & applied science research vol. 13, no. 2, 2023, 10239-10242 10239 www.etasr.com cheriet et al.: development of a geotechnical database using the geographic information system … development of a geotechnical database using the geographic information system approach the case of djelfa, algeria fayssal cheriet civil engineering department, ziane achour university of djelfa, algeria | faculty of civil engineering, leego, usthb, algeria cheriet.fayssal@yahoo.fr (corresponding author) abderahman zerguine civil engineering department, ziane achour university of djelfa, algeria | faculty of electronics and informatics ltir, usthb, algeria addresszerguineaer@yahoo.fr anfal rehab cheriet civil engineering department, geomaterials laboratory, hassiba benbouali university, algeria cherietrihab@gmail.com received: 10 january 2023 | revised: 20 january 2023 | accepted: 22 january 2023 abstract the present work aimed primarily to carry out a synthesis of the nature of the soil in the town of djelfa and to develop a database of existing geological and geotechnical data that are available in order to put them at the disposal of all potential users, whether scientific or operational. the carried out work consisted in collecting and organizing the existing geological and geotechnical data on a geographical information system. the criteria were first identified (allowable stresses, allowable depths, etc.) and then maps with the different important factors were developed. subsequently, these maps were superimposed to arrive, after a succession of generalizations of the geotechnical map, at an official final map with geotechnical terms. the interpretation of the obtained results allows for identifying the contributions and placing limits to the results and then trying to apply this method to other sites presenting similar problems and context. it should be noted that the maps produced are intended to enlighten decision-makers and planners when dealing with areas that are expected to be urbanized. they can also be helpful when conducting a preliminary study before the geotechnical study. keywords-geotechnical mapping; gis; multi-criteria analysis (mca); djelfa i. introduction in geotechnics, the physical and mechanical characteristics of the site are acquired from in situ tests and laboratory tests. the existing historical information can be found in the form of hard, electronic and paper copy, site investigation reports. the traditional data collecting procedure can be a laborious job [1, 2]. over the past four decades, geotechnical information has been integrated into a computerized database management system called geographic information system (gis), which is a process of mapping and integrating computer founded information [3]. it is an excellent means of geographic access to spatial data acquired from different sources because of its ability to manage large amounts of data. it is a tool for capturing, displaying and, analyzing geographically referenced data [2-6]. gis played a very important role in geotechnical engineering including preliminary site investigations, better understanding of the scope of possible solutions, the integration of any type of information, interpolation for obtaining data at inaccessible locations and less time may be spent on data analysis and acquisition than on data integration [2, 7]. in the geotechnical engineering field, the traditional procedures for making a soil site investigation require consulting previous conducted geotechnical reports in order to obtain better information of the soil properties. these reports are usually found as the format of electronic and saved paper documents in the archive rooms. however, the data processing can be highly complex and time-consuming due to the reports' condition and abundance. engineering, technology & applied science research vol. 13, no. 2, 2023, 10239-10242 10240 www.etasr.com cheriet et al.: development of a geotechnical database using the geographic information system … in order to facilitate the performance of geotechnical engineers as well as to save time and effort, geotechnical data from several years have been collected for building a database and converting them into maps. the resulted maps can be used by geotechnical engineers to obtain a better idea of the site's geotechnical data (the main lithological units, the permissible depths, the allowable bearing capacity, and the aggressiveness rates). the objective behind developing a database for the town of djelfa is to present and reference all the geotechnical data in gis. for this, all the data collected were classified in thematic tables in order to be manageable in gis. thematic analyses were visualized in the form of maps. ii. stydy area from a geographical point of view, the wilaya (province) of djelfa is located in the very heart of the high steppe plains (high plateaus), at an altitude of 1200m. the town of djelfa is considered a crossroads of transit between the north and the south and between the east and the west within algeria. this strategic position can itself be a major asset that allows this city to assume the role of a regional hub and capital of the central highlands of algeria. it must be recognized that this role has been entrusted to it for quite a long time by the regional scheme of the highlands in the central region of the country [8]. the town of djelfa is bounded by [9]:  the municipality of ain maabed (daira of hassi bahbah) in the north and north-west.  the municipality of dar chioukh in the north-east.  the municipality of moudjbara (daira de ain el bel) in the east.  the municipality of zaâfrane (daira de hassi bahbah) in the west.  the municipality of zaccar (daira de ain el bel) in the south.  the municipality of ain el ibel in the south-west. the town of djelfa covers an area of 542.17km 2 . it is characterized by a semi-arid and humid continental climate. the winters are cold and harsh and the summers are hot and dry. the temperature amplitude is relatively high. it is widely acknowledged that, from a geotechnical perspective, both dry and wet climatic periods can trigger shrinkage-swelling phenomena of certain clayey geological formations, which subsequently cause soil settlement [8]. furthermore, the rainfall in the area under study is marked, from one year to another, by great irregularity. the study area is characterized by sudden precipitations and stormy rains, which accentuates the phenomenon of soil erosion. these precipitations often cause flooding. iii. the gis-based spatialization approach application to the study area the approach adopted in this work for the preparation of the geotechnical maps is principally based on gis. this method allows the development of several maps with the geotechnical characteristics of the town of djelfa. these maps were developed based on the weighted sum model (wsm). it is worth specifying that the exploitation of data gis in the form of a computerized geotechnical map, makes it possible to carry out a fine and detailed spatial analysis of the underground geological formations. furthermore, one should know that the database can be organized and structured using gis. each element of the database (lithology, categories of sites, etc.) comes from the digitization of its source map which is placed in an information layer. then, each layer is georeferenced in the map projection system (universal transverse mercator utm, zone 31) [10, 11]. a. data sources the data from the geotechnical surveys used in this study were provided by the soil reports established by the national laboratory for housing and construction of the unit of the wilaya of djelfa. these data, which are archived in paper format (soil study, 2010 2017) have been analyzed and organized in a database (access, 2007) in order to obtain recent surveys and the various geotechnical characteristics such as the allowable stresses, aggressiveness rate, site categories, and the allowable depths. the data used were collected from 47 projects and 115 surveys distributed through different under consideration land use plans (lups) of the city (figure 1) [12]. in addition, in order to carry out the geotechnical characterization, statistical treatment was used to determine the average values of the physical and mechanical parameters of different formations. the extreme values were recorded and made available. afterwards, all these values were analyzed, interpreted, and discussed. fig. 1. geotechnical drilling locations. b. layer maps it should be emphasized that, in the present article, we tried to develop new working methodologies that are founded on engineering, technology & applied science research vol. 13, no. 2, 2023, 10239-10242 10241 www.etasr.com cheriet et al.: development of a geotechnical database using the geographic information system … structural analyses and epistemologies (access, mapinfo, map basic) in such a way that the system (application) that was established can be employed to facilitate the transition between the maps used by the mapinfo software and the databases which were already stored in access. the layer of soil types (lithology), the layer of allowable stresses, the layer of allowable depths, the layer of site categories, and the layer of aggressiveness rates are shown in figures 2, 3, 4, 5, and 6, respectively. fig. 2. the main lithological units of the study area. fig. 3. the allowable bearing capacity map of the study area. fig. 4. the permissible depths map of study area. fig. 5. the site category map of the study area. it is worth specifying that the original geotechnical data are considered as entirely satisfactory in this study. however, the number of geotechnical reports could be increased to obtain more information and to achieve a better geotechnical characterization of the study area. for the preparation of the data layers, the continuous surfaces were formed by linear interpolation from the first points (drillings or mechanical boring) and the lines that join these different points. engineering, technology & applied science research vol. 13, no. 2, 2023, 10239-10242 10242 www.etasr.com cheriet et al.: development of a geotechnical database using the geographic information system … fig. 6. the aggressiveness rate map of the study area. iv. conclusion the approach adopted in this work for the preparation of the spatial distribution map for the purpose of evaluating the lithology, soil bearing capacity, embedment depth, site category, and soil aggressiveness, is based on the geographic information system (gis). the utilized data were taken from previously established geotechnical reports. these data were then incorporated in the gis program (mapinfo) in order to draw the initial maps. this study made possible to highlight the advantages of using the above mentioned techniques, namely the low cost, the ease of use of data, and their rapid updating process. it is worth emphasizing that the study area was divided into four different zones, depending on the effectiveness of the foundations: 1) zones with low soil bearing capacity, 2) zones with medium soil bearing capacity, 3) zones with high soil bearing capacity, and 4) zones with very high soil bearing capacity. moreover, the lithological map shows that there is a certain lithological diversity, in addition to an alternation of limestone facies with clays. in addition, the aggressiveness map allows asserting that the upper part of the study area is strongly aggressive. the methodology used in the selected study area can be applied to other regions, and other procedures can be adopted for the selection of sites. this approach can also be used to establish the necessary standards in an appropriate manner. references [1] a. h. aldefae, j. mohammed, and h. d. saleem, "digital maps of mechanical geotechnical parameters using gis," cogent engineering, vol. 7, no. 1, jan. 2020, art. no. 1779563, https://doi.org/10.1080/ 23311916.2020.1779563. [2] a. singh, s. noor, r. chitra, m. gupta, and n. k. vel, "gis applications in geotechnical engineering some case studies," international journal of latest trends in engineering and technology, vol. 5, no. 2, pp. 36–42, 2015. [3] f. t. benaissa and b. khalfallah, "industrial activity land suitability assessment using delphi and ahp to control land consumption¨: the case study of bordj bouarreridj, algeria," engineering, technology & applied science research, vol. 11, no. 5, pp. 7738–7744, oct. 2021, https://doi.org/10.48084/etasr.4362. [4] a. hallil and a. redjem, "assessment of urban vulnerability to flooding using multi-criteria analysis: the case study of el bayadh city, algeria," engineering, technology & applied science research, vol. 12, no. 2, pp. 8467–8472, apr. 2022, https://doi.org/10.48084/ etasr.4828. [5] w. n. s. wan-mohamad and a. n. abdul-ghani, "the use of geographic information system (gis) for geotechnical data processing and presentation," procedia engineering, vol. 20, pp. 397–406, jan. 2011, https://doi.org/10.1016/j.proeng.2011.11.182. [6] r. luna et al., "introduction of gis into civil engineering curricula," presented at the 2008 annual conference & exposition, pittsburgh, pa, usa, jun. 2008, pp. 13.808.1-13.808.12, https://doi.org/10.18260/1-2-4433. [7] k. loumi and a. redjem, "integration of gis and hierarchical multicriteria analysis for mapping flood vulnerability: the case study of m’sila, algeria," engineering, technology & applied science research, vol. 11, no. 4, pp. 7381–7385, aug. 2021, https://doi.org/ 10.48084/etasr.4266. [8] e. arour, "carte de situation géographique de la wilaya de djelfa," découpage administratif de l’algérie & monographie. http://decoupageadministratifalgerie.blogspot.com/2014/10/cartegeograp hiquedjelfa.html. [9] n. kherfane, "les outils de gestion de l’espace et la réalité du développement urbain non maitrisé ‘approche géomatique’ (cas de la ville de djelfa).," m.s. thesis, université de batna 2, batna, algeria, 2014. [10] a. guettouche and f. kaoua, "using a gis to assessment the loadcarrying capacity of soil case of berhoum area, hodna basin, (eastern algeria)," journal of geographic information system, vol. 5, no. 5, pp. 492–497, oct. 2013, https://doi.org/10.4236/jgis.2013.55046. [11] a. guettouche, "cartographie géotechnique par approche sig basée sur l’analyse multicritères," ph.d. dissertation, university of science and technology houari boumediene, algiers, algeria, 2015. [12] a. r. cheriet, "elaboration d’une base de données géotechniques par sig application à la commune de djelfa," m.s. thesis, ziane achour university, djelfa, algeria, 2018. microsoft word 2-635.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1045-1049 1045 www.etasr.com rajamohan et al.: kinetic modeling and effect of process parameters on selenium removal … kinetic modeling and effect of process parameters on selenium removal using strong acid resin n. rajamohan department of chemical engineering, sohar university, sultanate of oman rnatarajan@soharuni.edu.om. r. rajesh kannan department of chemical engineering, annamalai university, india kannan_vrr007@yahoo.com m. rajasimman department of chemical engineering, annamalai university, india simms@rediffmail.com abstract—heavy metal pollution due to the contamination of selenium above the tolerable limit in the natural environment is a challenging issue that environmental scientists face. this study is aimed at identifying ion exchange technology as a feasible solution to remove selenium ions using 001x7 resin. parametric experiments were conducted to identify the optimal ph, sorbent dose and speed of agitation. selenium removal efficiency of 85% was attained at ph 5.0 with 100 mg/l selenium concentration. the increase in resin dose was found to increase removal efficiency. however, metal uptake decreased. the experiments on the effect of concentration proved the negative effect of higher concentrations of selenium on removal efficiency. the ion exchange process was proved to be optimal at an agitation speed of 200 rpm and a temperature of 35 °c. pseudo second order model was found to fit the kinetic data very well compared to the pseudo-first order model and the pseudo second order rate constant was estimated as 8.725x10-5 g mg-1 min-1 with a solution containing 100 mg/l selenium. keywords-metal removal; kinetics; selenium; acid resin i. introduction selenium is one of the metals which is present naturally in earth’s crust with black shale, phosphate rocks and coal as major sources[1]. selenium is distributed in many oxidation states and forms like selenite (se3 2-, se(iv)),selenide (se2-) and selenite (seo4 2, se vi)), in different phases depending on the aquatic, terrestrial and atmospheric geological resources with se(iv) and se(vi) commonly found in aqueous media [2]. se(iv) is reported to be more toxic than se(vi).the threshold permissible limit of selenium is 10 µg/l according to world health organization (who) regulations while usepa allows a maximum level of 50 µg/l [3]. depending on the type of release sources, the selenium levels and forms vary. the choice of the appropriate method of treatment is dependent on the speciation of selenium and the presence of competing ions. various physico-chemical methods like evaporation, chemical precipitation, coagulation and membrane processes are applied for the removal of metals [4]. but, the physical and chemical processes suffer from demerits like high operating costs, excessive usage of chemicals and production of secondary pollutants [5-6]. biosorption has been proposed as an alternative method for the removal of metals with special attention to naturally available biomass as a sorbent material [7]. biosorptive removal of selenium using dried biomass of saccharomyces cerevisiae has been reported [8]. studies on removal of se(iv) and se(vi) using fe-based and al-based coagulants were reported to achieve high removal percentages [2]. but the feasibility of biological methods was not investigated for high concentrations of selenium [6]. among these various methods, ion exchange offers a suitable choice for application. ion exchange method utilizes the ion exchange resins which are high molecular weight polysaccharides in insoluble form and the resins possess the ability to exchange their mobile ions for ions of similar charges from the surrounding environment [9]. removal of nickel and zinc using amberlite ir-120 resin has been reported and the kinetic data were presented [10]. two macro porous resins, d-201 and d301, have been utilized to remove mono butyl phthalate and physical adsorption was identified as the mechanism [11]. in this research study, the main objective was to investigate the feasibility of utilizing a strong acid cation exchange resin, 001x7, for the removal of selenium from aqueous solutions. the effect of process parameters, namely initial ph, selenium concentration, resin dose, shaking speed and operating temperature was studied. kinetic modeling was performed using pseudo-first order and pseudo-second order models. ii. experimental a. resin and chemicals preparation in this experimental study, a strong acid cationic resin 001x7 containing sulphonic acid (so3h) as the functional group, was chosen. this resin consists of so3h groups on styrene based polymer and the acidity of this resin is similar to hcl and h2so4. this cation exchange resin has moisture content in the range of 45–55% and was used for water softening applications. the particle size of the supplied resin was in the range of 0.42-1.2 mm in diameter. the resin was washed with deionized water repeatedly for several times and dried at 50 °c in a vacuum oven for 12 h. selenium stock solution containing se(iv) ions was prepared by diluting 1000 mg/l of na2seo3 standard solution (aldrich, germany) with deionized water. ph adjustments were performed using analytical reagent (ar) grade hcl, naoh and buffer solutions (merck, germany). ftir characterization of the resin have been reported in [12]. engineering, technology & applied science research vol. 6, no. 4, 2016, 1045-1049 1046 www.etasr.com rajamohan et al.: kinetic modeling and effect of process parameters on selenium removal … b. parametric experiments the parametric experiments were conducted under shaking conditions with ph studies as the primary step. batch ion exchange studies were conducted using a sample of 100 ml of the metal solution and agitated in an orbital shaker at different experimental conditions based on the experimental design for an equilibrium time of 150 min which was fixed after preliminary experiments. the effect of ph was studied in the range of 2.09.0 at fixed operating conditions. the adjustment of ph of the samples was done by adding either 0.1n hcl or naoh as the buffering agent. different resin quantities ranging from 0.25 to 2.0 g/l were tested at optimal ph and an initial metal concentration of 100 mg/l. the effect of different initial selenium concentrations on the percentage metal removal was studied in the range of 0-200 mg l-1 at a predetermined optimal ph and resin quantity. the effect of agitation was studied in the range of 0-300 rpm while the temperature effect was investigated at 30, 35 and 40 °c respectively. at fixed time intervals, a sample of solution was withdrawn and filtered. the filtered sample was analysed for residual metal concentrations using inductively coupled plasma – optical emission spectrometer (thermo fischer scientific, japan). in order to determine the mechanism of removal, kinetic studies were conducted. the experimental data were fitted to pseudo-second order and intra particle diffusion models and linearity of fit is verified. the metal uptake was calculated by using the following equation: o eq=(s -s )v/r (1) where q is the amount of metal adsorbed by the resin at any time, t (mg g-1); so and se are the initial and final selenium concentrations (mg l-1), respectively; v is the volume of sample solution (l) and r is the resin quantity (g). the percentage selenium removal is defined by: o e o (s -s ) %selenium removal= ×100 (2) s c. kinetic models the pseudo-first order kinetic model is represented as: e e 1ln(q -q)=lnq -k t (3) where qe is the amount of metal adsorbed by the resin at equilibrium(mg/g) and k1 is the first order rate constant (g mg -1 min-1). the slope and intercept of the linear plot ln(qe-q) vs time will give the values of the model constants. the pseudo-second order model [13] can be represented as: 2 e t 1 t = + (4) q h q where, qe, the amount of dye adsorbed at equilibrium (mg g 1), h2=k2qe 2 , the initial exchange rate (mg g-1 min-1) and the pseudo-second-order constant k2 (g mg -1 min-1) can be determined experimentally from the slope and intercept of plot t/q versus t. iii. results and discussion a. effect of ph ion exchange studies were strongly influenced by ph conditions as the speciation of ions are restricted by ph variations. moreover, ph changes were reported to induce precipitation of compounds. the fraction of free ions is dependent on the ph conditions [10]. in this set of experiments, the initial ph of the solution was varied in the range of 2.0–9.0 and the selenium removal percentages were estimated. figure 1 presents the influence of ph on the selenium removal efficiency studied at fixed initial metal concentration of 100 mg/l. the maximum removal of selenium was determined as 91% obtained at a ph of 5.0. in the acidic ph range of 2.0-4.0, the removal efficiencies attained were low which could be due to the competition posed by hydrogen ions with selenium ions for exchange with the resin. the reduction in removal efficiency when the ph was greater than 5.0 was related to precipitation phenomenon. nickel removal using the 001x7 resin reported a similar influence of ph [12]. zinc, copper and lead removal using dowex 50w resin reported similar observation. most of the studies reported poor metal removal when ph<4.0 [14]. in addition, high acidity was reported to be unfavorable for efficient metal removal [15]. b. effect of resin dosage resin dosage, which is defined as the quantity of resin added per unit volume of sorbate solution, is an important process variable. the effect of 001x7 resin dosage was studied in the range of 0.25–2.0 g/l while the initial metal concentration was fixed at 100 mg/l and ph at optimal value of 5.0 and presented in figure 2. the metal removal efficiency depends on the availability of free sites for exchange and thus increased with increase in resin dose. the efficiency increase was considerably high in the resin dose range of 0.25 to 1.0 g/l and the increase was not proportionate at the higher dosages of 1.5 and 2.0 g/l. the optimal resin dosage was identified as 1.0 g/l and used further in all other parametric experiments. excessive presence of actives sites could be the reason. the metal uptake exhibited a contrary behaviour with increase in resin dosage leading to decrease in selenium uptake. the split in the flux and aggregation of sites were reported to be responsible for the decrease in metal uptakes with increase in sorbent dose [7]. c. effect of initial selenium concentration the selenium concentrations reported in various industrial effluents were found to be in the range of 0 -74 mg/l [6]. with reference to this range, the effect of concentration study was conducted in the selenium concentration of 50-200 mg/l. the experimental conditions were fixed at ph=5.0 and resin dose=1.0 g/l with an equilibrium time of 150 min. figure 4 presents the effect of the initial metal concentration on the removal efficiency of selenium. the equilibrium removal efficiencies attained at lower selenium concentrations of 50 and 100 mg/l were found to be 95% and 85% respectively. with an increase in initial selenium concentration, the removal efficiency is decreased. limitations on the availability of ion exchange sites for different concentration and free surface with engineering, technology & applied science research vol. 6, no. 4, 2016, 1045-1049 1047 www.etasr.com rajamohan et al.: kinetic modeling and effect of process parameters on selenium removal … the cation exchange resin could be the reasons for this effect [12]. the equilibrium efficiencies were attained at 150 min for all the concentrations except 50 mg/l. various studies on the removal of metals by ion exchange and adsorption report a similar relationship between concentration of metal and efficiency [7, 12, 16]. d. effect of agitation speed ion exchange is a surface exchange process where an efficient contact between the ions to be exchanged is very vital. the agitation speed, found to be responsible for effective contact, was varied in the range of 0-400 rpm and its effect on selenium uptake are presented in figure 4. the initial concentration of selenium and ph were maintained at 100 mg/l and 5.0, respectively. the metal uptake increased from 5.4 to 74.0 mg/g when the speed increased from 0-300 rpm. the change in uptake was appreciable in the range of 0–200 rpm whereas no significant increase was observed at 300 rpm. the stirring velocity in the rpm range of 0-200 rpm was much more beneficial and resulted in better uptakes. at a very high speed of 400 rpm, a decrease in uptake was observed which could be contributed by the excessive shear force. similar effects of high agitation speeds on metal uptakes have been reported in studies on mercury removal [7]. the controlling mechanism in an ion exchange process could be either chemical rate or intraparticle diffusion or both. since no appreciable increase in uptake was observed at high speeds, the optimal agitation speed was chosen as 200 rpm. reduced or no influence on metal uptake at speeds greater than 150 rpm confirms the presence of more than one rate controlling mechanisms. copper(ii) ions removal using purolite c 100: mb resin reported identical observations [17]. e. influence of temperature separation processes are temperature dependent as diffusion and solubility are influenced by temperature effects. the studies on effect on temperature on the selenium removal was conducted at 30, 35 and 40 °c respectively at uptake at constant experimental conditions of initial metal concentration 100 mg/l, ph 5.0 and speed of agitation 200 rpm. from figure 5, it can be observed that the metal uptake capacities increased with an increase in temperature which proves the endothermic nature of the ion exchange process. surface energy of the resin was reported to be influenced by the surrounding temperature. similar effects on ion exchange studies using dowex resin [14] and 001 x7 resin have been reported [12]. f. kinetic studies kinetic experiments are performed to identify the chemical or physical nature of the removal mechanism. the following ionic stoichiometry represents the ion exchange process mechanism [18] as given in: 4+ + s 4si +4r-na r si+4na (5) figures 6 and 7 depict the linearized forms of equations of the pseudo-first order and pseudo-second order models. the linearity of the data was verified using correlation coefficients and the pseudo-first order model was found to fit the results with values of r2>0.950.the kinetic model constants, namely the rate constants (k1, k2) and uptakes (qe), were determined form the slopes and intercepts of the kinetic plots. the values of the kinetic constants for the two models selected are presented in table i at different initial metal concentrations. the variation in the pseudo second order model (the best fit model) rate constant with respect to the metal concentration are presented in figure 8 and an inverse proportionality was found to exist between the rate constant and initial metal concentration. gulipalli et al [19] reported the suitability of pseudo-second order model for the removal of selenium by adsorption using rice husk ash. similar observations on rate constant variations have been reported [12]. table i. kinetic model constants kinetic model initial selenium concentration(mg/l) 50 100 150 200 pseudo first order qe (mg/g) 2.28 2.26 1.689 1.849 k1x10 3(g mg-1 min-1) 11.9 14 13.6 12.5 r2 0.821 0.806 0.797 0.892 pseudo second order qe (mg/g) 108.7 113.6 122.0 129.9 k2x10 5 (g mg-1 min-1) 9.36 8.725 8.25 7.72 r2 0.984 0.952 0.983 0.962 fig. 1. effect of ph on selenium removal using resin 001x7 (t =150 min, c0 = 100 mg/l). fig. 2. effect of resin dosage on % selenium removal and uptake (t =150 min, c0 = 100 mg/l). engineering, technology & applied science research vol. 6, no. 4, 2016, 1045-1049 1048 www.etasr.com rajamohan et al.: kinetic modeling and effect of process parameters on selenium removal … fig. 3. effect of initial selenium concentration on % metal removal using resin 001x7(t=150 min, ph =5.0) fig. 4. effect of speed of agitation on metal uptake (t =150 min, c0 = 100 mg/l) fig. 5. effect of temperature on metal uptake using resin 001x7 (t =150 min, c0 = 100 mg/l) fig. 6. pseudo-first-order kinetic model plot for the removal of selenium fig. 7. pseudo-second-order kinetic model plot for the removal of selenium fig. 8. effect of selenium concentration on the pseudo second order rate constant iv. conclusions the strong acid cation resin 001x7 was utilized for the removal of selenium ions from its aqueous solution. the optimal operating conditions were determined as: ph 5.0, resin dosage 1.0 g/l, agitation speed 200 rpm and temperature 35°c. highly acidic conditions were found to decrease the metal removal efficiency. the selenium uptake was estimated as 70 mg/g at an optimal ph of 5.0 and initial selenium concentration of 100 mg/l. the selenium uptake decreased with increase in resin dosage and the ion exchange process was found to be endothermic as higher temperatures led to better removal. the correlation coefficients for the pseudo second order model was higher (>0.95) and the model constants were estimated at different selenium concentrations. thus, the feasibility of utilizing 001x7 for selenium removal was validated and the kinetic mechanism was investigated. references [1] p. m. chapman, w. j. adams, m. l. brooks, c. g. delos, s. n. luoma, w. a. maher, h. m. ohlendorf, t. s. presser, d. p. shaw (eds) ecological assessment of selenium in aquatic environment, setac press, pensacola, fl, 2010 [2] c. hu, q. chen, g. chen, j. qu, “removal of se(iv) and se(vi) from drinking water by coagulation, separation and purification technology”, vol. 142, pp. 65-70, 2015 [3] m. r. awual, m. m. hasan, m. a. khaleque, “efficient selenium(iv) detection and removal from water by tailor-made novel conjugate adsorbent”, sensors and actuators b, vol. 209, pp.194-202, 2015 engineering, technology & applied science research vol. 6, no. 4, 2016, 1045-1049 1049 www.etasr.com rajamohan et al.: kinetic modeling and effect of process parameters on selenium removal … [4] f. fu, q. wang, “a review of removal of heavy metal ions from wastewaters”, journal of environmental management, vol. 92, no. 3, pp. 407-418, 2011 [5] m. a. barakat, “new trends in removing heavy metals from industrial wastewater”, arabian journal of chemistry, vol. 4, no. 4, pp. 361-377, 2011 [6] s. soda, m. kahiwa, t. kagami, m. kuroda, m. yamashita, m. ike, “laboratory scale bioreactors for soluble selenium removal from selenium refinery waste water using anaerobic sludge”, desalination, vol. 279, pp. 433-438, 2011 [7] n. rajamohan, m. dilipkumar, m. rajasimman, “parametric and kinetic studies on biosorption of mercury using modified phoenix dactylifera biomass”, journal of the taiwan institute of chemical engineers, vol. 45, pp. 2622–2627, 2014 [8] h. khakpour, h. younesi, m. m. hosseini, “two stage biosorption of selenium from aqueous solution using dried biomass of the baker’s yeast saccharomyces cerevisiae”, journal of environmental chemical engineering, vol. 2, no. 1, pp. 532-542, 2014 [9] t. e. kose, n. ozturk, “boron removal from aqueous solutions by ionexchange resin: column sorption–elution studies”, journal of hazardous materials, vol. 152, no. 2, pp. 744-749, 2008 [10] p. e. franco, m. t. veit, c. e. borba, g. d. c. gonclaves, m. r. f. kle, r. bergamasco, e. a. dasilva, y. r. suzaki, “nickel(ii) and zinc(ii) removal using amberlite ir-120: ion exchange equilibrium and kinetics”, chemical engineering journal, vol. 221, pp. 426-435, 2013 [11] z. xu, y. zhao, j. shi, j. lu, l. cheng, m. chen, “adsorption of mono butyl phthalate from aqueous phase onto two macro porous anion exchange resin”, journal of chemistry, vol. 2014, article id 689734, 2014 [12] n. rajamohan, “parametric experiments and kinetic studies on the removal of nickel using strong acid cation exchange resin 001x7”, desalination and water treatment, vol. 56, no. 9, pp. 2477-2484, 2015 [13] y. s. ho, g. mckay, “pseudo-second order model for sorption processes”, process biochemistry, vol. 34, no. 5, pp. 451-465,1999 [14] e. pehlivan, t. altun, “the study of various parameters affecting the ion exchange of cu2+, zn2+, ni2+, cd2+ and pb2+ from aqueous solution on dowex 50 w synthetic resin”, journal of hazardous materials b, vol. 134, no. 1-3, pp. 149-156, 2006 [15] b. pan, h. qiu, b. pan, g. nie, l. xiao, l. lu, w. zhang, q. zhang, s. zheng, “highly efficient removal of heavy metals by polymer supported nano sized hydrated fe(iii) oxides: behaviour and xps study”, water research, vol. 44, no. 3, pp. 815-824, 2010 [16] g. moussavi, b. barikbin, “biosorption of chromium(vi) from industrial waste water onto pistachio hull waste biomass”, chemical engineering journal, vol. 162, pp. 893-900, 2010 [17] o. hamdaoui, “removal of copper(ii) from aqueous phase by purolite c100-mb cation exchange resin in fixed bed columns: modeling”, journal of hazard materials, vol. 161, no. 2-3, pp. 737-746, 2009 [18] b. alyuz, s. veli , “kinetics and equilibrium studies for the removal of nickel and zinc from aqueous solutions by ion exchange resins”, journal of hazardous materials , vol. 167, no. 1-3, pp. 482-488, 2009 [19] c. s. gulipalli, b. prasad, k. l. wasewar, “batch study, equilibrium and kinetics of adsorption of selenium using rice husk ash (rha)”, journal of engineering, science and technology, vol. 6,no. 5,pp. 586-605, 2011 microsoft word 11-685.doc engineering, technology & applied science research vol. 6, no. 4, 2016, 1093-1098 1093 www.etasr.com zafar and ejaz: sctp-aware link layer retransmission mechanism for smart-grid communication … sctp-aware link layer retransmission mechanism for smart-grid communication network saima zafar department of electrical engineering national university of computer & emerging sciences lahore, pakistan saima.zafar@nu.edu.pk umar ejaz department of electrical engineering national university of computer & emerging sciences lahore, pakistan umar.ejaz.89@gmail.com abstract—the smart grid delivers electricity from suppliers to consumers and uses bidirectional communication to exchange real-time information between supply system and smart meters at the user end. with a combined communication infrastructure, smart grid manages the operation of all associated components to provide reliable and supportable electricity supply. the neighborhood area network (nan) of smart grid supports bidirectional data transfer between smart meters (installed at customer premises) and control center of the utility company through an aggregator. this communication suffers low throughput and excessive delays due to the head of line (hol) blocking when the transmission control protocol (tcp) is implemented for reliability. in this paper we propose sctpaware link layer retransmission mechanism (sctp-llr) which augments the stream control transmission protocol (sctp) with link layer retransmissions at the aggregator. sctp-llr uses the multi-streaming feature offered by sctp and implements link layer retransmissions at the aggregator to mitigate the effect of hol blocking. we carried out simulations using network simulator and compared the performance of sctp-llr against tcp and sctp. our results show that sctp-llr outperforms both tcp and sctp in terms of throughput and packet delays and is a promising protocol to be implemented in smart grid nan for reliable and efficient communication. keywordshead of line blocking; link layer retransmission; neighborhood area network; smart grid network; stream control transmission protocol i. introduction smart grid communication is the key concept of integrated information technology in modern power control system. the smart grid comprises of power delivery from generation system to electrical sub-stations, distribution system substations to the consumers and digital communication network for consumer’s data collection from smart meters. in smart grid communications, transport layer plays an important role for data transfer between end users and the grid system. conventionally in internet, the transport layer provides two types of services to the application layer namely connectionless service and connection-oriented service. the connectionless transport protocol user datagram protocol (udp) provides high data rates but does not provide guaranteed data delivery. the connection-oriented service is provided by transmission control protocol (tcp) which provides reliability in addition to congestion control and flow control. although tcp is suitable for the typical wired internet, it does not meet the requirements of smart grid nan communication. some of the requirements for the transport protocol in smart grid nan communication are security, ease of availability, reliability, scalability and real time response. an important challenge which limits the performance of transport protocols in nan of smart grid communication network is head of line (hol) blocking which occurs due to the large number of consumers connected to the grid. in order to cope with the hol blocking in nan of smart grid communication network, we suggest augmenting the stream control transmission protocol (sctp) with link layer retransmissions (sctp-llr). sctp is a reliable transport protocol with multi-streaming features which open multiple streams between end systems or peers. in our proposed sctpllr mechanism, we use the multi-streaming feature at the end systems (smart meters and control center) and implement link layer retransmissions at the aggregator which connects wirelessly with the smart meters. through simulations in network simulator (ns-allinone-2.35), we analyze sctp-llr mechanism in terms of throughput and delay for nan in smart grid and compare it against tcp and sctp. we find that sctp-llr outperforms both tcp and sctp. ii. related work in [2] the tcp-aware link layer retransmission method for cellular networks called snoop was proposed and evaluated. in this scheme, the link-layer protocol takes advantage of the knowledge of the higher layer transport protocol. the snoop protocol introduces a module at the base station where the snoop agent monitors every packet which passes through the tcp connection in both directions, that is wired and wireless. it maintains a cache for the unacknowledged packets which are sent by the receiver across the link. a packet loss is detected by the arrival of a small number of duplicate acks from the receiver or by a local timeout. the main advantages of this approach are: 1) duplicate acknowledgments for tcp segments are suppressed and 2) local packet retransmission is carried out to avoid unnecessary fast retransmissions and congestion. the engineering, technology & applied science research vol. 6, no. 4, 2016, 1093-1098 1094 www.etasr.com zafar and ejaz: sctp-aware link layer retransmission mechanism for smart-grid communication … snoop approach suffers from not being able to completely shield the sender from wireless losses. our protocol closely matches the snoop operation, however we select the access point of ieee 802.11ah for link layer retransmissions and implement multiple streams of sctp at the higher layer. in [3] several schemes for enhancing tcp performance over different networks were evaluated. the schemes were organized into three wide categories: link-layer protocols that arrange local reliability, end-to-end tcp where loss retrieval is executed by the sender and split-connection protocols where the end-to-end link is divided into two portions at the base station. wireless channels were categorized by the propagation phenomenon, along with fading, the reason of irregular high bit error rates causes packet loss in the wireless link. the throughput suffers due to packet loss through wireless link in the end-to-end connection. their results support the idea of retransmissions in wireless domain for better results. in [4] the performance of session initiation protocol (sip) over tcp was measured. sip located in application layer, is a session initiation and signaling protocol used to create, maintain and close a connection between two end points. the analysis showed that sip suffers from hol blocking due to out of order delivery of tcp packets. it is concluded that sctp gives encouraging results for sip instead of other transport protocols like udp or tcp. in [5], sctp performance for the iptv applications was investigated and found suitable. in [6], the iptv technology invented to provide tv streaming for the end clients over internet protocol was described. iptv offers several features in order to provide high degree of reliability of network resources to meet client’s satisfaction. the authors proved that sctp is a reliable transport protocol which has a mechanism to improve the performance of iptv applications and give better results than udp and tcp. in [7] the benefits of sctp over tcp and udp were explained and it was stated that in tcp, the sender can send only one stream of bytes to the receiver whereas sctp maintains multiple streams between sender and receiver within single association. this feature is known as sctp multistreaming. sctp has a multi-streaming feature within an association to send data on multiple streams, these streams inside the association contains a unique number to send inorder data delivery. tcp includes a three way handshake mechanism to prevent the risk of denial of service (dos) attacks. whereas, sctp establish a four way handshake mechanism to avoid dos problem by using a cookie called init-ack chunk [8]. we enforce our choice of ieee 802.11ah at the link layer by observing that this standard achieves higher throughput [9]. ieee 802.11ah is a new global wlan standard which uses sub-1 ghz frequency band. this standard performs better than the other low-rate wireless standards in terms for internet of things (iot) for the real time machine-to-machine (m2m) communication in smart grid. iii. smart grid communication network the smart grid communication network provides bidirectional intelligent services, different from the conventional data communication services. from the architectural perspective, the smart grid communication network comprises of three layers:  communication layer: performs bi-directional interface functions between utilities, consumers, operators and grid components.  physical and control layer: deals with the core functions such as power generation, transmission and distribution.  application layer: concerned with providing services to several applications to facilitate consumer or control systems. the communication layer of the smart grid was designed to exchange data between smart meters and collection points. smart grid communication requires high level of integration for multiple combinations among applications [10]. a wellengineered model is required to provide guarantee of data delivery among all smart grids. however, many smart grid communication architectures exchange information among smart grid tiers and also provide information to connect these tiers with the integrated smart grid networking architecture. the smart grid communication layer consists of the following parts as defined in [11]:  customer premises connect their devices with in the home network as an end user. in this manner, home area network (han), building area network (ban), or industrial area network (ian) exists to connect groups of devices with smart grids.  advanced metering infrastructure (ami) works separately with neighborhood area network (nan)/ field area network (fan).  control center observes smart meters for data storage and data analysis through wlan network of ami enterprise. nan plays the role in information collection from multiple hans and delivery of data to the utility company. the key communication parameters in smart gridw are network range, data rate and prospective technology. power line communication is common for both han and nan [12, 13]. some of the important dynamic requirements for smart grid network design are listed below:  ip network  scalability for future deployment plans  real-time capability  robustness and reliability  broad coverage  security  cost effectiveness iv. sctp-aware link layer retransmission mechanism a. sctp overview stream control transmission protocol (sctp) is a connection oriented transport protocol running over ip which is a connectionless network layer protocol. internet engineering task force (ietf) developed this protocol for transporting public switched telephone network (pstn) engineering, technology & applied science research vol. 6, no. 4, 2016, 1093-1098 1095 www.etasr.com zafar and ejaz: sctp-aware link layer retransmission mechanism for smart-grid communication … signaling messages on top of ip networks. further, it holds promise to support a variety of applications. sctp is an end to end connection for exchanging information between two end points and uses multi-streaming feature for transmission of data. each sctp supports multiple independent streams which are unidirectional. transmission sequence number (tsn) distinguishes between multiple streams in each sctp. each stream contains a sequence number known as stream identifier (si). these two parameters are needed to provide uniqueness of each data chunk. stream sequence number (ssn) discriminates data fragments into a stream. stream identifier is the most important number to differentiate one stream from other streams. when using multiple streams in multiple associations, the order of delivery is not considered. however, all streams within an association should be insequence. the hol blocking can only affect messages inside a single stream, and other streams while other streams remain unaffected [1]. any delay or retransmission in a stream does not affect other streams. a scenario of in-order data delivery in multiple streams of an sctp is further described in [1]. each stream is allocated a buffer at the transport layer of receiver. stream identifiers are unique in order to direct fragments with the same stream sequence number to the proper stream. stream sequence numbers are used to ensure in-order data delivery within a stream. in case fragment with ssn-22 is lost and does not reach the receiver while fragment with ssn-23 reaches the receiver, ssm-23 is buffered till ssn-22 is retransmitted and received thus delivering in –order data to the upper layer. b. ieee 802.11ah ieee 802.11ah standard provides higher throughput for internet of things (iot) and machine to machine (m2m) applications. the goal of this standard is to develop a global wireless lan (wlan) standard that can perform functions in sub-1 ghz frequency in ism band to send burst-data between low energy devices. it can cover up to one kilometer of area. the operating technology contains one or more bands as follows: 917-923.5smz (korea), 950.8-957.6smz (japan), 863-868.6smz (europe), 902-928smz (usa) and 314316smz, 430-432smz, 433.0-434.8smz (china) [14]. this standard increases the coverage area for the iot and improves the efficiency for the m2m communicating devices. it is possible to achieve low costs by using simplified hardwarestructure for the iot device components. overall these characteristics make this standard suitable for use in smart grid communication networks. some of the notable features of ieee 802.11ah standard are:  compatible with the 802.11 wlan legacies.  coverage range up to 1000m much higher than bluetooth and zigbee.  supports data rate of 100 kbps and more. c. design of sctp-llr our proposed protocol sctp-llr is designed for smart grid communication networks, for end to end bi-directional communication between smart meters and control center through data-concentrator or aggregator. figure 1 shows the network model for sctp-llr. sctp is implemented at the smart meters and control center at the transport layer while link layer retransmissions are carried out by the aggregator through a link layer module. sctp-llr design includes details of operation both at the transport layer and the link layer though the main emphasis is on the link layer module implemented at the aggregator. each packet is temporarily cached at the data-concentrator (aggregator) which performs local retransmissions across the link in case of packet loss. typically, the cache size is proportional to the propagation window size. sctp has the same congestion control mechanism as tcp with some small changes. one of the differences between the two is that in sctp the initial window size is equal to 2 times the link mtu, the congestion window increases based on the acknowledgment of bytes and sctp does not have the fast recovery mechanism. since we are implementing sctp as the transport layer protocol, we support multi-homing and multistreaming features of sctp as discussed in earlier sections. during sctp handshaking process, the link layer module at the aggregator saves sender and receiver information. also instead of caching packets, actually chunks are cached at the aggregator. 1) data transfer from control center to smart meters after sctp handshaking between the control center and smart meters, data from control center is sent to smart meters through the aggregator. when the aggregator receives a new data chunk from the control center, it caches it and then forwards it to the smart meter. when it receives acknowledgment from the smart meter, it removes the chunk from its cache. however, in case of a loss, the aggregator retransmits the lost chunk through an alternate path and does not allow the duplicate acknowledgment to reach the control center. this way data is recovered from the aggregator instead of recovering it from the control center. the aggregator keeps track of all data and acknowledgements which pass through it. when a new chunk arrives from the control center to the aggregator, it is cached and forwarded to the smart meter. a timestamp is added for estimation of round trip time. when an out-of-sequence chunk is received from the control center is discarded. when a new acknowledgment is received, the aggregator clears its cache and updates the round trip time for the wireless link. this acknowledgment is forwarded to the control center. if the aggregator receives acknowledgment which is less than the last acknowledgment (that situation rarely happens), it discards that acknowledgment and continue packet processing. when a duplicate acknowledgment is received, if it is for a packet which is not in the aggregator cache, it is forced to be retransmitted by the control center through congestion control. if it is an ordinary duplicate acknowledgment, the aggregator retransmits the lost packet, is repeated duplicate acknowledgment is received, it is discarded. engineering, technology & applied science research vol. 6, no. 4, 2016, 1093-1098 1096 www.etasr.com zafar and ejaz: sctp-aware link layer retransmission mechanism for smart-grid communication … 2) data transfer from smart meter to control center the smart meter monitors negative acknowledgment (nacks) from the aggregator for selective retransmission of lost packets. a modification is required at the smart meter to enable selective acknowledgment (sack) processing. no change is required at the control center. the llr module has the ability to generate sacks at the aggregator and process them at the smart meter retransmit lost chunks v. results a. simulation scenario we simulate the smart grid network model of figure 1 with smart meters connected to aggregator wirelessly and control center connected through wired connection. ieee 802.11ah standard is implemented for wireless connections and llr mechanism is implemented through the addition of a module at the aggregator which caches packets and retransmits in case of packet loss. we increase the number of smart meters connected to the nan and observe throughput and delay when tcp, tcp-llr, sctp and sctp-llr are implemented. the transport protocols work at the control center and the smart meters while llr mechanism is implemented at the link layer in aggregator. we implement ftp at the application layer for file transfer. the focus of our data transfer is from smart meters to control center through aggregator such that as the number of smart meters increase, the chances of hol blocking also increases, affecting the throughput and delay. b. simulation parameters table i lists the simulation parameters which are almost constant throughout simulations. the simulations were performed by increasing the number of smart meters and throughput and delay were observed in case of tcp, tcp-llr, sctp and sctp-llr. table i. simulation parameters parameter value simulation time 25 seconds buffer size equal to window size application layer protocol ftp network layer protocol dsdv mac protocol ieee802.11ah (wireless links) queue type droptail queue size 50 bit rate 250 kbps antenna model omnidirectional packet size 160 bytes c. simulation results 1) average packet delay average packet delay is the average time taken by a packet to reach from sender to receiver. it is given by equation 1 where davg is the average packet delay, dagg is the aggregate delay of all the received packets and k is the total number of packets received. fig. 1. network model for sctp-llr mechanism davg=(dagg/k) (1) equation 2 gives expression for dagg where dj is the delay of the jth packet. )2( 1    n j jagg dd figure 2 shows average packet delay comparison of tcp, tcp-llr, sctp and sctp-llr for 25% and 50% network error rate respectively when transmission rate is low (500 kbps). figure 3 shows same comparison but when transmission rate is high (2 mbps). in both cases, the number of smart meters is increased progressively to observe the impact of increasing number of users getting connected with the nan of engineering, technology & applied science research vol. 6, no. 4, 2016, 1093-1098 1097 www.etasr.com zafar and ejaz: sctp-aware link layer retransmission mechanism for smart-grid communication … smart grid. our results show that average packet delays in tcp and tcp-llr is high and increases as number of smart meters increase while it is low in sctp and sctp-llr and does not get affected much as number of smart meters increase. the most promising performance is given by sctp-llr which outperforms all other transport layer protocols. fig. 2. average packet delay comparison of tcp, tcp-llr, sctp and sctp-llr for 25% and 50% error rates when transmission rate is 550 kbps fig. 3. average packet delay comparison of tcp, tcp-llr, sctp and sctp-llr for 25% and 50% error rates when transmission rate is 2 mbps 2) average throughput throughput is defined as the fraction of time used by the network to successfully deliver one packet payload. throughput provides the ratio of channel capacity used for successful transmission and it is one of the most important and useful network metrics. throughput is calculated using: )3(1 agg n i i d p t      where throughput is represented by t, δ is the packet size, pi is the ith packet and dagg is the aggregate packet delay. some of the parameter values defined in table i have been used in these simulations. throughput is compared when tcp, tcp-llr, sctp and sctp-llr are implemented in the network model of figure 1 and number of smart meters is increased. we first carry out simulations with 25% error rate and the results are shown in figure 4. we observe that the best results are shown when sctp-llr is implemented. in this case, throughput is high from the start and either increases or keeps constant while in all other protocols, throughput either remains low or suffers as time follows. also in sctp-llr, throughput is not affected much by the increasing number of smart meters. figure 5 shows throughput comparison when error rate is set to 50%. the same results are observed and we conclude that sctp-llr outperforms other protocols in terms of throughput. fig. 4. throughput comparison of tcp, tcp-llr, sctp and sctp-llr for 25% error rate as number of smart meters increases engineering, technology & applied science research vol. 6, no. 4, 2016, 1093-1098 1098 www.etasr.com zafar and ejaz: sctp-aware link layer retransmission mechanism for smart-grid communication … fig. 5. throughput comparison of tcp, tcp-llr, sctp and sctp-llr for 25% error rate as number of smart meters increases vi. conclusion in this paper, sctp aware link layer retransmission (sctp-llr) mechanism is presented to deal with wireless link losses in nan of smart grid communication network. the basic idea is to implement a link layer module at the aggregator which connects wirelessly with smart meters and wired with the back end control center. this link layer module enables retransmissions of chunks from smart meters thus suppressing end to end retransmissions between control center and smart meters. we tested this mechanism through simulations in network simulator which show that sctpllr mechanism shields the sender from duplicate acknowledgments arising from wireless losses resulting in throughput improvement and delay reduction. the results demonstrate that the sctp-llr mechanism outperforms other transport protocols like tcp, tcp-llr and sctp in terms of throughput and packet delay. references [1] network working group (r. stewart ed), rfc 4960 stream control transmission protocol, 2007, available at: https://tools.ietf.org/pdf/ rfc4960.pdf [2] h. balakrishnan, s. seshan, r. h. katz, “improving reliable transport and handoff performance in cellular wireless networks”, acm wireless networks, vol. 1, no. 4, pp. 469 – 481, 1995 [3] h. balakrishnan, v. padmanabhan, s. seshan, r. h. katz, “a comparison of mechanisms for improving tcp performance over wireless links”, ieee/acm transactions on networking, vol. 5, no. 6, pp. 756 – 769, 1997 [4] m. happenhofer, p. reichl, “measurement-based analysis of head-ofline blocking for sip over tcp”, ieee international symposium on modeling, analysis & simulation of computer and telecommunication systems (mascots 2010), pp. 244 – 253, 2010 [5] s. t. kim, s. j. koh, y. j. kim, “performance of sctp for iptv applications”, 9th international conference on advanced communication technology, pp. 2176 – 2180, 2007 [6] s. zeadally, h. moustafa, f. siddiqui, “internet protocol television (iptv): architecture, trends, and challenges”, systems journal, vol. 5, no. 4, pp. 518 -527, 2011 [7] r. stewart, p. d. amer, “why is sctp needed given tcp and udp are widely available?”, internet society, member briefing 17, september 10, 2007 available at: https://www.isoc.org/briefings/017/ [8] p. natarajan, f. baker, p. d. amer, j. t. leighton, “sctp : why, what, and how”, internet computing, vol. 13, no. 15, pp. 81 – 85, 2009 [9] b. olyaei, j. pirskanen, o. raeesi, a. hazmi, m. valkama, “performance comparison between slotted ieee 802.15.4 and ieee 802.1 lah in iot based applications”, 9th ieee international conference on wireless and mobile computing, networking and communications (wimob 2013), lyon, pp. 332-337, october, 2013 [10] j. g. cupp, m. e. beehler, “implementing smart grid communications”, tech briefs, vol. 4, 2008 [11] b. gohn, “smart grid communications architecture”, navigant research, 2011 [12] z. fan, p. kulkarni, s. gormus, c. efthymiou, g. kalogriddis, m. sooriyabandara, z. zhu, s. lambotharan, w. chin, “smart grid communications: overview of research challenges, solutions, and standardization activities”, communications surveys & tutorials, vol. 15, no. 1, pp. 21-38, 2012 [13] gridcom™, a secure distribution area network architecture. tropos gridcom, 2012 [14] s. aust, r.v. prasad, i. g. m. m. niemegeers, “ieee 802.11ah: advantages in standards and further challenges for sub 1 ghz wi-fi”, 2012 ieee international conference on communications (icc), ottawa, pp. 6885 – 6889, june 10-15, 2012 microsoft word etasr_v12_n6_pp9742-9746 engineering, technology & applied science research vol. 12, no. 6, 2022, 9742-9746 9742 www.etasr.com nguyen et al.: survey and design of individual housing projects: situation and solutions for ha tinh … survey and design of individual housing projects: situation and solutions for ha tinh province, vietnam sy-minh nguyen faculty of engineering and technology ha tinh university ha tinh, vietnam minh.nguyensy@htu.edu.vn van-binh tran faculty of engineering and technology ha tinh university ha tinh, vietnam binh.tranvan@htu.edu.vn duy-duan nguyen department of civil engineering, vinh university vinh, vietnam duyduankxd@vinhuni.edu.vn received: 10 july 2022 | revised: 21 september 2022 and 3 october 2022 | accepted: 14 october 2022 abstract-survey and design processes are considered essential stages and directly affect the quality and cost of construction works. this study aimed to investigate the existing limitations in the survey and design stages of individual housing projects in ha tinh province, vietnam, and to propose specific solutions to improve them. these solutions can contribute to eliminating unexpected problems or errors during the construction process of individual housing projects in vietnam. keywords-survey; design; individual housing; ha tinh province i. introduction the quality management of the construction of individual houses has not attracted serious attention in vietnam, as the regulations focus on key works and public investment projects [1-8]. for individual houses, although the state has issued regulations, the responsibility for the survey, design, supervision, and construction is on the investor [1, 4, 7]. as investors often hire a consultant or even skip the survey and design stage to save costs, without meeting the requirements, this leads to many problems and affects the safety of people and surrounding structures. several studies investigated existing problems in construction management in various regions around the world and proposed methods or strategies to improve the management process [9-12]. very few studies conducted in vietnam investigated the effects of the limitations of the survey and design stages on individual housing projects. the theoretical basis of the survey and design of public investment projects was presented in [13]. experience and lessons on housing management from some countries were investigated in [14], proposing an application for tien giang province in vietnam. several studies related to housing theory, research, and policies have been conducted around the world [15, 16]. a survey on user satisfaction with the mass housing projects was presented in [17], led by a district municipality in konya-karatay, turkey. in [18], an overview of the effects of housing conditions on human health was presented. a systematic study on the limitations of the survey and design process of individual housing projects in vietnam has not yet been carried out. ha tinh is a province located in the central region of vietnam. with a population of more than 1.3 million people, the demand for housing construction is increasing, especially when the economy is growing. the construction of individual houses is very crucial to satisfy the needs of each individual and household. therefore, it is necessary to study the current situation of the survey and design stages of individual housing projects in ha tinh to propose solutions to improve them. ii. challenges of survey and design in ha tinh in recent years, the construction of individual houses in ha tinh has seen many changes, as the growing economy has increased the number of households that want to build individual houses. individual housing projects appear more and more, not only in urban areas, but also in many rural areas throughout the province. several investors pay attention to the survey and design stages before construction to create a project that meets the requirements of function, aesthetics, stability, and reasonable cost. the increasing importance of the design and survey stages in ha tinh province has increased the number of individual housing projects that hire survey and design units. these works satisfy the needs of people's lives corresponding author: duy-duan nguyen engineering, technology & applied science research vol. 12, no. 6, 2022, 9742-9746 9743 www.etasr.com nguyen et al.: survey and design of individual housing projects: situation and solutions for ha tinh … and beautify urban spaces. however, the construction of individual housing projects still has many problems, especially in the survey and design stages. a. data and limitations a survey was conducted on 100 individual housing projects in the districts of ha tinh province, through data from the construction department of ha tinh province [19], to explore limitations in the survey and design stages. the survey results showed that the survey, design, and construction stages of individual housing projects in ha tinh province still have some shortcomings and limitations, as follows: 1) geological and topographic survey figure 1 shows the proportion of individual housing projects with and without geological and topographic surveys. a small percentage (approximately 12%) carried out such a survey before design. most individual housing projects did not perform survey work before design and construction. failing to conduct geological surveys or improper technical surveys can lead to no or inaccurate data and can reduce the quality of the projects, increase their cost, and cause unpredictable technical problems. in addition, many works used cadastral maps, which do not ensure precise elevation and do not comply with the regulations on the transmission and protection of landmarks. also, not using the coordinate system can lead to location deviations. fig. 1. survey results: individual housing projects that carried out geological and topographic surveys. 2) design stage many problems arise during the design process, such as over-estimated structural capacity, no or incorrect structural calculations, and improper application of regulations and standards. figure 2 shows that most individual housing projects have typical problems. the number of projects having an authorized design registration following standards accounts for only 15%. meanwhile, another 15% of projects are wasteful by design. the number of projects designed with unsafe and unsatisfactory structural requirements represents 25%, while 45% of the projects did not hire a design unit. this is a major problem that needs to be seriously considered and resolved. 3) cost estimation figure 3 shows the status of individual housing projects in ha tinh, according to cost estimation before construction. most individual housing design documents do not include a cost estimation or include a useless document. only 10% of the projects had a proper cost estimation. without an estimation of project cost, financial risks can occur. 4) incidents figure 4 shows the results of the incident survey of individual housing projects in ha tinh. as can be observed, only 25% of projects meet structural safety and serviceability requirements. most projects are unstable structures or affect the surrounding projects. more specifically, the number of projects with cracked walls, floor cracks, and uneven settlement accounts for 45%. fig. 2. survey results: individual housing projects having design issues. fig. 3. survey results on individual housing projects relating to cost estimation. b. reasons the shortcomings and limitations in the survey and design stages of individual housing projects are mainly due to the following reasons: 1) state management agency most ha tinh localities do not have an official state management agency in charge of survey and design works. currently, in the whole province, only ha tinh city, ky anh town, and hong linh town have a specialized agency named urban management department (umd). individual housing is managed in part-time form. the local wards and communes have only 2 cadastral officers to manage both land and basic engineering, technology & applied science research vol. 12, no. 6, 2022, 9742-9746 9744 www.etasr.com nguyen et al.: survey and design of individual housing projects: situation and solutions for ha tinh … construction fields. the inspection, appraisal, and permits for the construction of individual houses also face many difficulties. according to the regulations for individual housing projects, the authorities are only interested in works with a floor area greater than 250m 2 and buildings with more than 3 floors or a height of more than 12m [1, 4, 7]. as a result, the construction process is not inspected and supervised, seriously affecting the planning and causing unsafety for people and properties. moreover, there are many separate housing projects managed by state agencies, but violations are not handled promptly, causing difficulties and economic damage to investors in handling the consequences. in addition, the mechanisms and policies to manage the quality of construction are currently unclear, and there are no additional plans to attract human resources [2, 5, 6]. fig. 4. incident survey results of individual housing projects in ha tinh. 2) investors as investors in individual housing projects often lack experience and professional knowledge, there are shortcomings and limitations in the survey and design stages due to the following reasons:  investors often do not hire a survey and design quality management unit.  there is no plan to choose a survey or design contractor or choosing a contractor that is unreputable, inexperienced, or has low capacity.  investors do not understand or have little understanding of construction. usually, they do not employ a professional to supervise or check the process, and there are many cases where the consulting unit and the construction contractor collide. as a result, the cost increases and the quality of the project can decrease.  investors who build individual houses often do not make contracts when hiring a survey and design unit or, if any, the contract is made by the latter. thus, the terms in the contract, if it exists, are often not beneficial to the investor.  many investors skip the survey and design stage to save costs, as it is an expensive procedure.  survey and design companies are not always sufficient. this can lead to over-designed (i.e. high redundancy in design) or under-designed conditions (i.e. unsafety). figure 5 shows the survey results regarding the reasons investors do not hire survey companies. the number of projects that do not hire a surveying agency because they do not trust them is 17%, while 20.5% do not hire a survey agency for fear of delaying the schedule, and 22.73% do not hire a survey unit because of cost. moreover, the number of projects that do not hire a survey because the investor lacks understanding and follows the opinions of others accounts for approximately 40%. fig. 5. results on reasons why investors do not hire a survey unit. 3) geological and topographic survey unit figure 7 summarizes the capacity of the survey units. it was found that only 25% of the projects hire qualified survey companies, while the remaining 75% do not meet the requirements of the survey process, as they lack the equipment or geological engineers. these are the main reasons for the unsatisfactory geological survey results. fig. 6. results on the capacity of survey units. 4) design unit the number of small design offices is increasing in ha tinh. small design offices are located where few people can notice, even in their own homes. their main form of business is engineering, technology & applied science research vol. 12, no. 6, 2022, 9742-9746 9745 www.etasr.com nguyen et al.: survey and design of individual housing projects: situation and solutions for ha tinh … through social networks; thus, it is difficult for the authorities to check. figure 7 shows that only 115 design companies (51.11%) have full capacity and are registered as a business. design units that do not register as businesses but are created by qualified individuals account for 28.45%, while the proportion of design units without business registration made up of non-professional individuals accounts for 20.45%. figure 8 shows the results of the reasons investors do not hire design companies. the main reason is the lack of understanding of the importance of the design process (40%) followed by design costs (27%), trust in the design company (22%), and concerns about effects on design time (11%). fig. 7. individual housing design offices in ha tinh. fig. 8. reasons why investors do not hire a design unit. iii. proposed solutions to improve survey and design quality based on these results, this study attempted to propose solutions to improve the quality of the survey and design stages of individual housing projects in ha tinh, as follows: a. for state authorities  improve organizational structure: at the district level, it is necessary to add an urban management unit with the same function as a city or town. communes must have a full-time official to supplement the role of individual housing management for the cadastral staff.  strengthen inspection and supervision: district, town, or commune urban management divisions are required to regularly inspect individual housing works before granting construction permits, and even during construction.  the urban management department should strengthen the inspection of the capacity of design units and contractors to improve the quality of the survey stage. for example, they can check staff, machinery and equipment, office address, and contractor capacity in documents and reality. the above solutions could reduce problems and errors in the survey, design, and construction stages of individual houses. moreover, it is necessary to strengthen the inspection and appraisal of individual housing projects according to regulations. this task must be performed seriously and promptly to assess the safety of the survey and design stages and to inspect the surrounding works or the safety conditions during construction.  train and foster urban management staff: in addition to the above solutions, it is necessary to organize professional training for civil servants and public employees.  improve mechanisms and policies: it is important to improve the role and responsibilities of the urban management department. in addition, it is necessary to have a reasonable remuneration mechanism and policy for personnel in the construction of individual houses. b. for investors the survey results show that many investors do not hire a survey and design unit before construction due to lack of knowledge or funding. therefore, many projects do not meet the requirements in terms of usability, structural safety, or architectural beauty, or have high costs. it is recommended that before construction, the investor needs to take care of the survey and design stage. the following solutions are proposed to improve the quality of the survey and design stages:  the investor needs to hire a qualified unit for survey and design. the quality of construction works significantly depends on the survey and design stage. therefore, the investor needs to hire professional staff, not only to supervise the investment implementation stage but also the investment preparation stage.  before choosing a design survey contractor, the investor should check its capacity in practice, staff, equipment, and experience based on previous contracts. simultaneously, multiple pieces of information can be investigated to evaluate the contractor’s capacity.  the investor should regularly inspect consulting activities or hire a second individual or unit. this is essential as the owner hires a supervision consultant to check the contractors, but there is no one to check the latter. the investor or the employed person must have a thorough understanding of professional expertise, responsibilities, and the order and content of contractors' tasks. engineering, technology & applied science research vol. 12, no. 6, 2022, 9742-9746 9746 www.etasr.com nguyen et al.: survey and design of individual housing projects: situation and solutions for ha tinh …  the administrative method is to communicate the investor's requirements through form requests or reports. the quality of a project is described by economic contracts. the quality requirements should be detailed in the contract or the contract addendum. this is a mandatory legal requirement. c. for survey and design contractors the quality of the survey and design stages depends not only on the role of the investor and the supervision of state management agencies but also on the capacity of the contractor. to improve the contractor's capacity, it is necessary to improve the apparatus and quality management system and develop human resources.  improve apparatus: it is necessary to consolidate the titles according to the regulations on capacity conditions. additionally, they should have the necessary apparatus from the office to the field. moreover, employees must be reinspected and supervised by inspecting staff.  build quality assurance and management system: another solution is to develop a quality assurance and management process, incorporating the company's goals, roadmap, and content with the quality management model. the company should have a quality policy consistent with a roadmap. at the same time, it is necessary to focus on a quality assurance plan for each project with specific measures and generate daily, weekly, and monthly reports.  build, train, and retrain staff: in addition to the organizational structure, it is required to enhance the team's qualifications. the contractor must have a plan for annual professional training of technicians and surveyors, especially for new employees. iv. conclusion this study evaluated the limited situations in the survey and design stages of individual houses in ha tinh province, vietnam, and proposed some solutions to improve the quality of such construction projects. these results can contribute to better management and reduced potential risks in the survey, design, and construction stages of individual houses in this region. furthermore, the results of this study are helpful references for investors, businesses, employees, and state management agencies to ensure and enhance quality management during the construction of individual houses in 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[19] v. t. pham, "situations on individual housing projects in ha tinh province," department of construction, ha tinh, vietnam, 2020. microsoft word etasr_v12_n5_pp9224-9228 engineering, technology & applied science research vol. 12, no. 5, 2022, 9224-9228 9224 www.etasr.com boulaouad et al.: analysis of a frictionless electro viscoelastic contact problem with signorini … analysis of a frictionless electro viscoelastic contact problem with signorini conditions abla boulaouad department of mathematics ferhat abbas university setif 1 setif, algeria a_boulaouad@yahoo.fr abbes ourahmoun institute of optics and precision mechanics ferhat abbas university setif 1 setif, algeria abbes.ourahmoun@univ-setif.dz touffik serrar department of mathematics ferhat abbas university setif 1 setif, algeria toufik.serrar@univ-setif.dz received: 10 july 2022 | revised: 27 july 2022 | accepted: 31 july 2022 abstract-this study considered a mathematical model to describe the process of a quasi-static contact between a piezoelectric body and an electrically conductive foundation. the behavior of the material was modeled with a nonlinear electro-viscoelastic constitutive law, the contact was frictionless, and the result was described with the signorini condition. a variational formulation was derived for the problem, proving the existence and uniqueness of a weak solution of the model. the proof was based on arguments for nonlinear equations with maximal monotone operators. keywords-elecro-viscoelastic materials; frictionless contact; signorini conditions; maximal monotone operators; weak solution i. introduction considerable progress has been achieved recently in modeling, mathematical analysis, and numerical simulations of various contact processes and, as a result, a general mathematical theory of contact mechanics is currently emerging. mathematical structures underlie general contact problems with different constitutive laws for materials, varied geometries, and different contact conditions, [1, 2]. the piezoelectric effect is characterized by the coupling between the mechanical and electrical properties of materials. the appearance of electric charges on some crystals submitted to the action of body forces and surface tractions was observed and their dependence on the deformation process was examined. conversely, it was proved experimentally that the action of an electric field on the crystals may generate strain and stress. a deformable material having such behavior is called a piezoelectric material. piezoelectric materials are used extensively as switches in many engineering systems such as radio electronics, electro acoustics, and measuring equipment. some general models for electro-elastic materials can be found in [3, 4]. a static frictional contact problem for electro-elastic materials was considered in [5, 6]. ii. notations and preliminaries this study considered a body made of a piezoelectric material that occupies the domain with a smooth boundary ��=� and a unit normal �. a body force of �0 density acts on the body and has volume-free electric charges of �0 density, constrained mechanically and electrically on the boundary. to describe these conditions, a partition of � was considered into three open disjoint parts �1 , �2, and �3. α partition of �1 ∪ �2 was in two open parts � and �� . it was assumed that �� ��� >0 and �� ��� > 0. the spatial and time variables were denoted as � ∈ � ∪ � and � ∈ [0, �] respectively. the body was clamped on �1 and the displacement field vanished there. surface tractions of density �� act on �2 . it was also assumed that the electrical potential vanishes on � and a surface-free electrical charge of density �2 is prescribed on ��. the notation � � was used for the space of second-order symmetric tensors on ℝ� , while · and ∥·∥ represent the inner product and the euclidean norm on � � and ℝ� respectively, where: ". $ = "& $& , ‖$‖ = ($. $) * +, ∀", $ ∈ ℝ� -. . = -&/ .&/ , ‖-‖ = (-. -) * +, ∀-, . ∈ � � (1) where i, j=1,…,d. the summation over repeated indices is used and the index which follows a comma indicates a partial derivative. let � ⊂ ℝ� be a bounded domain, x = (xi) a point in � ∪ �, while � = �& denotes the outward unit normal at γ. also, the inner products on the hilbert spaces 1�(�)� and 1�(�)� are given by: corresponding author: abbes ourahmoun engineering, technology & applied science research vol. 12, no. 5, 2022, 9224-9228 9225 www.etasr.com boulaouad et al.: analysis of a frictionless electro viscoelastic contact problem with signorini … (", $)2+(3)4 = 5 ". $6� 3 ; (", $)2+(8)4 = 5 ". $6 8 (2) the associated norms will be denoted by ‖. ‖2+(3)4 and ‖. ‖2+(8)4 respectively. the closed subspace of 9�(�)� is defined by: : = ;$ ∈ 9�(�)� ∶ $ = 0 => �� ? (3) @ = a. = b.&/ c / .&/ ∈ 1�(�)� : .&/ = ./& f (4) which are hilbert spaces with the following scalar products: (", $)g = 5 h("). h($)6�,3 (-, .)i = 5 -. .6� 8 (5) the associated norms are ‖. ‖g and ‖. ‖i , respectively. the deformation tensor h ∶ 9�(�)� → @ is given by: h($) = kh&/ ($)l , h&/ ($) = �� b$&/ + $&/ c; ∀$ ∈ 9�(�)� (6) therefore (:, |. |g ) is a real hilbert space. moreover, by sobolev's trace theorem, a constant op exists which depends only on ω, ��, and �q such that: ‖$‖2+(8r)4 ≤ op‖$‖g , ∀$ ∈ : (7) given a hilbert space t, for a function u ∶ t → ]−∞, +∞]: x=�(u) = ;" ∈ t ∶ u(") ≠ ∞?, �u" = ;� ∈ t ∶ u($) − u(") ≥ (�, $ − "), ∀", $ ∈ t ?. so, the following existence and uniqueness result can be concluded: lemma: let t be a real hilbert space and let u ∶ t → [−∞, +∞] be a convex proper lower semicontinuous function. then for every � ∈ 1�(0, �, t) and "p ∈ x=�(u) , a unique function " ∈ [�,�(0, �, t) exists which satisfies: "\ (�) + �u"(�) ∋ �(�) , . �. � ∈ (0, �), "(0) = "p. (8) more details can be found in [7]. iii. problem statement this section describes the process model and clarifies the assumptions about the data. the process starts from the physical framework, and the law of behavior and the conditions of contact should be specified. it was supposed that the body was electro-viscoelastic, rested on a rigid foundation by the part �q of its border, this contact was affected without friction, and the tangential movements were completely free. additionally, as the quasistatic case was studied, the body ω had a behavior law of the form of (9), see [8-10]. under these considerations, the studied mechanical problem can be formulated as follows: problem 1. find the displacement field " ∶ � × ℝ_ → ℝ� , the stress field ∶ � × ℝ_ → � � , the electric potential ` ∶ � × [0, �] → ℝ , and the electrical displacements field x ∶ � × [0, �] → ℝ� , such that: = ah(") + ℱh(") − h ∗d(`) e> � × (0, �) (9) x = ℰ(") + gd(`) e> � × (0, �) (10) xe$+ �p = 0 e> � × (0, �) (11) 6e$ x = �p e> � × (0, �) (12) " = 0 => �� × (0, �) (13) -h = �� => �� × (0, �) (14) i "h ≤ 0, -h ≤ 0"h -h = 0, -j = 0 => �q × (0, �) (15) ` = 0 => �� × (0, �) (16) x. � = �� => �k × (0, �) (17) " = "p e> � (18) equations (9) and (10) represent the constitutive electroviscoelastic law, (11) and (12) represent the equilibrium equations, (13) and (14) are the boundary conditions in displacement and traction respectively. the boundary condition (15) represents the conditions of contact without signorini friction, (16) and (17) are the electrical boundary conditions, and (18) represents the initial condition. it should be noted that = b-&/ c is the stress tensor, h(") denotes the linearized strain tensor, a and ℰ = (�&/l ) represent the third-order piezoelectric tensor, ℰ ∗ is its transpose, g = b�&/ c denote the electric permittivity tensor, and x = (x₁, . . . , x� ) is the electric displacement vector. the tensors ℰ and ℰ ∗ satisfy: ℰ-. $ = -. ℰ ∗$; ∀b-&/ c ∈ � � , $ ∈ ℝ� and xe$ and 6e$ denote the divergence operator for tensor and vector-valued function. for the electric displacement field, two hilbert spaces were used. n = 1�(�)� ; n� = ;x ∈ n: 6e$x ∈ 1�(�)? endowed with the inner products: (x, d)n = o x& 3 d& 6� (x, d)n* = (x, d)n + (6e$x, 6e$d)2²(3) the electric potential field was defined by: [ = ;q ∈ 9�(�): q = 0 => �� ? since �� ��� > 0 the friedrichs-poincaré inequality holds, thus: ‖rq‖n ≥ st ‖q‖u¹(3); ∀q ∈ [. the assumptions on the problem data were listed for the study of problem w . then, the viscosity a , the operator of elasticity ℱ , the piezoelectric tensor ℰ , and the electric permittivity tensor g satisfy the following properties: ⎩⎪ ⎨ ⎪⎧ ( ). a = b &/l| c ∶ � × � � → � �(�). &/l| = |&/l ∈ 1�(�)(s). �ℎ�~� ��e�� �� > 0 �"sℎ �ℎ � &/l� .&/l� ≥ �� ‖.‖�; ∀. ∈ � � , . �. � ∈ � (19) engineering, technology & applied science research vol. 12, no. 5, 2022, 9224-9228 9226 www.etasr.com boulaouad et al.: analysis of a frictionless electro viscoelastic contact problem with signorini … ⎩⎪ ⎪⎨ ⎪⎪ ⎧ ( ). ℱ ∶ � × � � → � � .(�). �ℎ�~� ��e�� 1ℱ > 0 �"sℎ �ℎ � ‖ℱ(�, h�) − ℱ(�, h�)‖ ≤ 1ℱ ‖h� − h�‖,∀h�, h� ∈ � � , . �. � ∈ �.(s). �ℎ� � ��e>� � → ℱ(�, h) e� �� �"~ ��� => �, ∀h ∈ � � ,(6). �ℎ� � ��e>� � → ℱ(�, 0) ∈ ℋ. (20) �( ). ℰ = b�&/l c ∶ � × � � → ℝ��&/l = �&l/ ∈ 1�(�) (21) ⎩⎪ ⎨ ⎪⎧(�). ( ). g = bg&/ c ∶ � × ℝ� → ℝ� . g&/ = g/& ∈ 1�(�).�ℎ�~� ��e�� �� > 0 �"sℎ �ℎ �g&/ d& d/ ≥ �� ‖d‖�∀d ∈ ℝ� , �. �. � ∈ � (22) the densities of body forces and surface tractions have regularity: �p ∈ [�,�(0, �; 1�(�)� ), �� ∈ [�,�(0, �; 1�(��)� ) (23) and surface free charge densities satisfy: �p ∈ [�,�b0, �; 1�(�)c, �� ∈∈ [�,�b0, �; 1�(�� )c (24) ��(�) = 0 => �q ; ∀� ∈ �0, �� (25) condition (19) allows providing the space : with the scalar product and the associated norm defined by: (", $)g = bah("), ah($)cℋ ; ‖"‖g = �(", ")g (26) this norm on : is equivalent to that of 9¹(�)� . convex � which will be the space of admissible displacements, i.e. compatible with the connections (boundary conditions and unilateral conditions): � = {$ ∈ :; $� ≤ 0 => �q} (27) finally, the following assumption was made: "₀ ∈ � (28) for the rest, the following functional space was considered: [ = {q ∈ 9¹(�) | q = 0 => �� } the operator � was said to be maximal monotone if it is monotone and if for all � and � in space t: < � − ��, � − � >≥ 0 �=~ �� � ∈ 6=�(�) ⇒ � ∈ �� now all the necessary ingredients are available to provide a weak formulation of problem w and present the main result of the existence and uniqueness of the weak solution. iv. variational formulation this section starts by giving a variational formulation in terms of displacement and electric potential. once this weak formulation is established, a result of the existence and uniqueness of the weak solution emerges: let � ∶ �0, �� → : �� � ∶ �0, �� → [ be the functional (�(�), $)g = 5 �p(�). $6� + 5 ��(�). $6 8+3 (29) (�(�), q)� = 5 �p(�). q6� − 5 ��(�). q6 8+3 (30) for all $ ∈ :, q ∈ [, � ∈ �0, ��. the conditions (23) and (24) imply: � ∈ [�,�(0, �; :) , � ∈ [�,�(0, �; [) (31) using green's formula and assuming that (", -, u, x) are regular functions satisfying (11) and (17): "(�) ∈ �, ( -(�), h($) − h("(�)))u ≥ (�(�), "(�) − $)g (32) (x(�), ∇q)2+(3)4 + (�(�), q)� = 0 (33) for all $ ∈ �, q ∈ [ and � ∈ �0, ��. now, putting (9) in (32), (10) in (33), and keeping in mind that d(u) = −ru as well as the initial condition (18), the variational formulation of the mechanical problem w can be obtained in terms of displacement and electric potential following: problem 2: find the displacement field ": �0, �� → : and electric potential u ∶ �0, �� → [ such that: ⎩⎪⎪ ⎨ ⎪⎪⎧ "(�) ∈ �, kahb"\ (�)c, h($) − hb"(�)clℋ +kℱhb"(�)c, h($) − hb"(�)clℋ +kd∗∇ϕ(�), h($) − hb"(�)clℋ ≥ b�(�), $ − "(�)cg∀$ ∈ �, �. �. � ∈ �0, ��, (34) �(g∇ϕ(�), ∇q)2+(3)4 − bℰhb"(�)c − ∇qc2+(3)4 =(�(�), q)� ; ∀q ∈ [, ∀� ∈ �0, ��, (35) "(0) = "p (36) the well-posedness of the above wg problem is examined in the next section. v. existence result this section states and proves the existence and the uniqueness of the result. theorem 1: assume that (19), (25), and (28) are verified. then the variational problem wg has a unique solution (", u), having the regularity: " ∈ [�,�(0, �; :) , u ∈ [�,�(0, �; [) (37) a quadruplet (", -, u, x) satisfying the (9) and (10) is called a weak solution to the mechanical problem w. it can be concluded from theorem 1 that problem w admits a unique solution. regarding the regularity of the weak solution, it follows to refer to the regularity of the element (", u) ∈[�,�(0, �; :) × [�,�(0, �; [), to the constitutive laws (9) and (10), and also to the hypotheses (19) and (22). then: ∈ 1�(0, �; 9), x ∈ 1�(0, �; 1²(�)� ) now, taking $ = "(�) ± �, where � ∈ op�(ω)� in (32) and q ∈ op�(ω) in (33), and using the notations (29) and (30) we get: engineering, technology & applied science research vol. 12, no. 5, 2022, 9224-9228 9227 www.etasr.com boulaouad et al.: analysis of a frictionless electro viscoelastic contact problem with signorini … xe$-(�) + �₀(�) = 0 , 6e$x(�) = �₀(�) for all � ∈ �0, ��. from (23) and (18), it follows that xe$∈1�(0, �; 1�(�)� ) and 6e$x ∈ 1�(0, �; 1�(�)), and therefore: ∈ 1�(0, �; ℋ�), x ∈ 1�(0, �; [) (38) so, it is concluded that the solution (", -, u, x) of problem w will have regularity (37) and (38). proof: the abstract result will be used to obtain the existence and the uniqueness of the solution. for that, let's suppose in the continuation that the hypotheses (19), (25), and (28) are verified. using the riesz representation theorem, the operators ℬ: [ → [ and o: : → [ are defined as follows: (ℬ`, q)� = (gru, rq)2+(�)4 (39) (o$, `)� = (ℰh($), r`)2²(3)4 (40) for all `, q ∈ [, $ ∈ :. from (22), it is deduced that ß is a linear, symmetric, and positive operator. consequently, ß is a revertible and continuous operator on [. now, using (26) and (21), it follows that o is a linear and continuous operator on :. let o ∗: [ → : be the adjoint of o. so: (o ∗`, $)g = (d∗ru, h($))u ; ∀$ ∈ :, ` ∈ [ (41) let � ∈ �0, ��. by putting (39) and (40) in (35) we have: (`(�), q)� = (o"(�), q)� + (�(�), q)� , ∀q ∈ [ consequently, `(�) = o"(�) + �(�) on the other hand, �: [ → [ is invertible. the previous equation then becomes: u(�) = ℬ⁻¹o"(�) + ℬ⁻¹�(�) (42) using (42) in (34) and the definitions of operators ß, o, o ∗ given by (39-41) we get: "(�) ∈ �, kahb"\ (�)c, h($) − hb"(�)clℋ +kℱhb"(�)c, h($) − hb"(�)clℋ +bo ∗ℬ⁻¹o"(�), $ − "(�)cg ≥ b�(�) − ℬ⁻¹�(�), $ − "(�)cg∀$ ∈ :, �. �. � ∈ �0, �� (43) let the operator 1: : → : be defined by: 1($) = o ∗ℬ��o($); ∀$ ∈ : (44) and keeping in mind the properties of the operators ß, o, and o ∗, it is deduced that 1 is a linear operator, continuous on :. ‖1"₁ − 1"₂‖g ≤ ‖1‖‖"₁ − "₂‖g ; ∀"₁, "₂ ∈ : (45) �: : → : denotes the operator based on the representation of riesz given by: (�", $)g = (ℱh("), h($))ℋ + (1", $)g : ∀", $ ∈ : (46) now, taking into account (19), (20), (26), and (46) we have: ‖�"� − �"�‖g ≤ k 2ℱ�a + ‖1‖l ‖"� − "�‖g , ∀"₁, "₂ ∈ : (47) this relation proves that the � is a lipshitz operator. now, let the function �: �0, �� → : given by: �(�) = �(�) − o ∗ℬ���(�); ∀� ∈ �0, �� (48) using (39) and the fact that o ∗ℬ�� is linear and continuous, it comes by observing (48) that: � ∈ [�,�(0, �; :) (49) on the other hand, the operator: � + k 2ℱ�a + ‖1‖l �: : → : (50) is a lipshitz operator on :. now, the indicator function ql : : → �−∞, +∞� of the set � is introduced as well as its sub-differential �ql . being the set � non-empty, closed, and convex, the sub-differential �ql is a strongly monotone operator on the space :. the domain of this sub-differential is thus: x(�ql ) = �. it can be said that the sum: �ql + � +   1ℱ�a + ‖1‖¡ �: � ⊂ : → 2g is a strongly monotone operator. being the hypotheses (49) and (28) satisfied, (8) can be applied with: t = : ; � = �ql + �: x(�) = � ⊂ : → 2g and: ¢ = 1ℱ�a + ‖1‖ this result deduces that there is a unique element " ∈[�,�(0, �; :) which verifies: "\ (�) + �q£ ("(�)) + �"(�) ∋ �(�) �. �. � ∈ (0, �) (51) and: "(0) = "₀ (52) in addition, for all � ∈ : there is the equivalence: � ∈ �q£ (") ⇔ " ∈ � , (�, $ − ")g ; ∀$ ∈ � the differential inclusion (51) is equivalent to the variational inequality: "(�) ∈ �, ("\ (�), $ − "(�))g + (�"(�), $ − "(�))g≥ (�(�), $ − "(�))g ∀$ ∈ �, �. �. � ∈ (0, �). (53) from (53), (46), and (26) comes that " satisfies the inequality: "(�) ∈ �, (ah("\ (�)), h($) − h("(�)))ℋ+bℱ"(�), $ − "(�)cg + (1"(�), $ − "(�))g≥ b�(�), $ − "(�)cg ; ∀$ ∈ �, �. �. � ∈ (0, �). (54) from (53), (46), (44), and (48), it is concluded that " satisfies (43). let ` be the function given by (42). using (43), (52), and (42), it follows that (", `) is the solution to the variational problem w: . regarding the regularity of the function `, it follows to refer to the regularity of the element engineering, technology & applied science research vol. 12, no. 5, 2022, 9224-9228 9228 www.etasr.com boulaouad et al.: analysis of a frictionless electro viscoelastic contact problem with signorini … " ∈ [�,�(0, �; :) and to the hypotheses (42) and (31). then it is obtained that function ` has the regularity ` ∈ [�,�(0, �; [). a solution (", `) of regularity " ∈ [�,�(0, �; :), ` ∈[�,�(0, �; [) was just shown. the uniqueness part of the function ` is deduced from the uniqueness of the function " ∈ [�,�(0, �; :) solution of (51) and (53) given by lemma 1, thus taking into account (42). vi. conclusion this paper investigated a mathematical model to describe the quasistatic contact between a piezoelectric body and a deformable foundation. the contact was frictionless and described with signorini conditions. the proof of the existence and the uniqueness of the weak solution was presented using a classical result of elliptic variational inequalities and a maximal monotone operator. references [1] y. letoufa, h. benseridi, s. boulaaras, and m. dilmi, "on the asymptotic behavior of solutions of anisotropic viscoelastic body," boundary value problems, vol. 2021, no. 1, nov. 2021, art. no. 89, https://doi.org/10.1186/s13661-021-01567-w. 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[10] t. n. le, h. m. v. nguyen, t. a. nguyen, t. t. phung, and b. d. phan, "optimization of load ranking and load shedding in a power system using the improved ahp algorithm," engineering, technology & applied science research, vol. 12, no. 3, pp. 8512–8519, jun. 2022, https://doi.org/10.48084/etasr.4862. authors profile abla boulaouad, m.c. of mathematics scale functional analysis option, faculty of technology, university ferhat abbas setif 1, algeria, and member of the mathematics laboratory lama. abbes ourahmoun, institute of optics and precision mechanics, university ferhat abbas setif 1, setif, algeria touffik serrar, department of mathematics, university ferhat abbas setif 1, setif, algeria. microsoft word etasr_v13_n2_pp10496-10500 engineering, technology & applied science research vol. 13, no. 2, 2023, 10496-10500 10496 www.etasr.com bouaita et al.: a new approach for optimizing the extraction of association rules a new approach for optimizing the extraction of association rules bilal bouaita ferhat abbas setif 1 university, algeria bilal.bouaita@univ-setif.dz (corresponding author) abdesselem beghriche ferhat abbas setif 1 university, algeria abdesselem_beghriche@univ-setif.dz akram kout misc laboratory, ferhat abbas setif 1 university, algeria akram-kout@univ-setif.dz abdelouahab moussaoui ferhat abbas setif 1 university, algeria abdelouahab.moussaoui@univ-setif.dz received: 28 january 2023 | revised: 19 february 2023 | accepted: 23 february 2023 abstract association rule methods are among the most used approaches for knowledge discovery in databases (kdd), as they allow discovering and extracting hidden meaningful relationships between attributes or items in large datasets in the form of rules. algorithms to extract these rules require considerable time and large memory spaces. this paper presents an algorithm that decomposes this complex problem into subproblems and processes items by category according to their support. very frequent items and fairly frequent items are studied together. to evaluate the performance of the proposed algorithm, it was compared with eclat and lcmfreq on two actual transactional databases. the experimental results showed that the proposed algorithm was faster in execution time and demonstrated its efficiency in memory consumption. keywords-kdd; data mining; association rules; frequent itemset i. introduction association rule methods [1, 2] are widely used in data mining [3, 4] which is the heart of knowledge discovery in databases (kdd) [5, 6]. this approach was introduced to analyze the shopping cart or transaction data [2]. as each database transaction contains all items purchased by a customer, an association rule method identifies attributes or items that are often purchased together and discovers some meaningful dependencies and relationships between items sold for making predictions or decisions [7]. these relations are in the form of a rule: if x, then y (x→y (75%)), where x is the condition of the rule and y is its conclusion. in addition, 75% support of the rule indicates that 75% of the customers who buy item x also buy item y at the same time. these rules provide a decision support tool [8] in many areas, including the commercial sector. the association rule extraction is an essential two-step process that discovers frequent item set lists and generates association rules from these. the first step is the most costly in terms of execution time and memory space [9]. in databases that contain thousands of items, the larger the number of items, the larger the number of generated itemsets. this condition produces an explosion in the number of association rules. in a database that contains n items, 2 n -1 itemsets can be generated [10], producing a very large number of rules. each item or itemset is characterized by its support (supp) [7]. the apriori algorithm [11] minimizes calculations and the number of itemsets based on the support value. it only maintains frequent itemsets, where supp is above a predefined threshold by the user (minimal support, minsupp). minsupp belongs to the interval [0,1], varies in decreasing order from 1 to 0, and depends on the database characteristics. the complexity of extracting frequent itemsets is sensitive to engineering, technology & applied science research vol. 13, no. 2, 2023, 10496-10500 10497 www.etasr.com bouaita et al.: a new approach for optimizing the extraction of association rules minsupp, as it increases rapidly when it decreases, given that more items exist. therefore, the number of generated itemsets increases, which implies more complexity in terms of computation time and memory space. several methods were developed to extract frequent itemsets and restrict search memory space and computation time. these methods can be grouped into two categories: the candidate generation approach and the pattern growth approach [12]. the candidate generation approach generates a list of candidate itemsets of size k to find the list of sets of frequent kitemsets. then these itemsets are generated to build a list of new candidate itemsets of size k+1. this procedure is repeated until the set, k+1-frequent itemsets, is empty. this method allows a decrease in the amount of search memory space required based on the antimonotone property. if an itemset is not frequent, then all its super-itemsets are also not frequent. the apriori algorithm [11] is the most well-known algorithm of this family. nevertheless, other algorithms that belong to the same category are dhp [13], dic [14], eclat [15], and bitmap [16]. the main drawback of these algorithms is the scanning of the transactional database several times. the pattern growth approach suggests removing the need to generate candidates to extract frequently occurring itemsets. this approach uses certain data structures, in particular trees, to accurately describe the transactional database. one of the most well-known algorithms in this family is the fp (frequent pattern)-growth [17], which uses a specialized data structure called fp-tree. the h-mine [18], afopt [19], mfis [20], and lcmfreq [21] are other methods that apply this approach. recently proposed ideas employ prefix trees as a data structure to find frequent itemsets [22-26]. these approaches have the benefit of not performing candidate generation and avoiding multiple database scans. on the contrary, the data structures used in these algorithms result in significant memory consumption, and the development of these algorithms is more complex than in the candidate solution approach. this study proposes a new algorithm based on apriori because it is the foundation of other algorithms and is regarded as a reference. the proposed algorithm reduces the amount of memory space and time required for the discovery of frequent itemsets. ii. basic notions let i = {i0 ,i1,...,in} be a set of n items, t = {t1,...,tm} a database of m transactions, where each transaction ti has a unique identifier and is a subset of items ti ⊆ i.  definition 1: an itemset x is any item subset of i. for example {i1 i5 i8} is an itemset composed of three items.  definition 2: a k-itemset is a set of itemsets, where each itemset is composed of k items. for example, the itemset {i1 i5 i8} is considered an element of the 3-itemset.  definition 3: the support supp(x) of an itemset x is the frequency of appearance of this itemset in the transactions of a database t or the ratio between the number of transactions t containing x (x ⊆ t) and the total number of transactions in the database t. ����(�) = | �∈ /� ⊆ �| | | (1) where || is the cardinal operator in the sets theory.  definition 4: an itemset x is frequent in a database t if its support is greater than or equal to a given threshold: supp(x) ≥ minsupp.  definition 5: an association rule is an implication expression among itemsets of the form x→y, where x⊂i, y⊂i, and x∩y=∅. iii. the proposed algorithm a. example in a transaction database that contains n frequent items, the apriori algorithm can generate a large number of itemsets kitemset (a subset of items of size k), which is equal to all possible combinations �� � . for example, for n=100 items, 3921225 itemsets of size 4 can be generated. the proposed algorithm can reduce the number of generated k-itemsets by studying the items by category according to their support. to better understand the proposed algorithm, its principle of operation is illustrated through the following example: table i shows the transaction base t, which contains 10 transactions and 14 items (a, b, c, d, e, f, g, h, m, n, p, x, y, z), where each transaction contains one or more items. table i. example of transaction database transaction id items 1 a, b, f, n, x 2 a, n 3 b, c, d, f, g, h, m 4 b, c, g, h, m, n 5 a, b, f, z 6 a, f, g, y 7 a, b, c, f, g, n 8 a, c, d, e, h, y, n, p 9 a, f, n 10 a, d, e, g, h, y, p the support of each item is: supp(a) = 0.8, supp(f) = supp(n) = 0.6, supp(b) = supp(g)= 0.5, supp(c) = supp(h)= 0.4, supp(d) = supp(y)= 0.3, supp(e) = supp(m) = supp(p) = 0.2, supp(x) = supp(z)= 0.1. the following parameters are used: maxsupp1 is the greatest support, minsupp1 is the first minimum support, minsupp is the minimum support, and a parameter α ∈ ]0, 1[. in this example, maxsupp1= 0.8, a = 0.72, minsupp1 = 0.35, and minsupp= 0.2. then, instead of processing all items that are greater than minsupp at the same time as the majority of the algorithms do, the items are considered by the group of intervals [maxsuppi, minsuppi], and the intersection between two successive intervals must be non-empty. the following equations are used to find the maxsuppi and minsuppi: �������� = � ∗ ���������� (2) �������� = � ∗ ���������� (3) table ii shows the items obtained in each interval. table iii shows the complexity of (�� � ) to generate the 2and 3-itemsets by the proposed and the apriori algorithms: engineering, technology & applied science research vol. 13, no. 2, 2023, 10496-10500 10498 www.etasr.com bouaita et al.: a new approach for optimizing the extraction of association rules table ii. example of the new algorithm step (i) maxsuppi minsuppi items of each interval number of items 1 0.8 0.35 a, f, n, b, g, c, h 7 2 0.576 0.252 b, g, c, h, d, y 6 3 0.414 0.181 c, h, d, y, e, m, p 7 stop minsupp = 0.181 < 0.2 table iii. computational complexity algorithm k=2 k=3 proposed � !+�" !+� != 21+10+21=42 � #+�" #+� !#= 35+20+35=90 apriori ��! ! =66 ��! # =220 the apriori algorithm builds up to 220 3-itemsets, whereas the proposed algorithm builds 90. thus, the proposed algorithm reduced the number of generated itemsets, implying a reduction in the number of product association rules and, therefore, reducing calculation time. b. constraints the parameters α and minsupp1 must be selected in a way to have acceptable and non-disjoint intervals to maintain the association between the items of the different intervals.  disjoint intervals: for example, α = 0.6, maxsupp1= 0.7, and minsupp1=0.6 gives the first interval [0.7, 0.6]. maxsupp2= α × maxsupp1 = 0.6 × 0.7 = 0.42 and minsupp2 = α × minsupp1 = 0.6 × 0.6 =0.36 gives the second interval [0.42, 0.36]. therefore, the items that support the interval ]0.6, 0.42[ are ignored and the association between the items of the two intervals [0.7, 0.6] and [0.42, 0.36] is lost.  acceptable intervals: avoid intervals that are sufficiently close to each other to ignore the same items (repetitive intervals). for maxsupp1=0.7, minsupp1=0.6, and α=0.98, the next interval is [0.686, 0.588]. therefore, the same items of the interval [0.7, 0.6] can be studied. the selection of α and minsupp1 must be studied. c. the proposed algorithm the principles of the proposed algorithm are: 1. the following parameters are set in advance: maxsupp1, minsupp1, minsupp (minsupp1>minsupp), α ∈ ]0, 1[. 2. the apriori algorithm is applied to the items with support in [maxsupp1, minsupp1] to find the generated k-itemsets. 3. step 2 is repeated for the intervals [maxsuppi, minsuppi] until minsupp > minsuppi, using (2) and (3). the final global set of k-itemsets obtained is the union of the sets of k-itemsets obtained in each interval. the pseudocode representation for this algorithm is: algorithm frequent_itemsets input: t, α, minsupp1, maxsupp1, minsupp //knowing that minsupp<minsupp1<maxsupp1, 0<α<1) output: list of frequent itemsets (lfi) 1. repeat 2. l1i = list of items ∈ [maxsuppi, minsuppi] 3. apply the apriori algorithm on l1i to find the lfii list that represents the set of frequent kitemsets in the interval [maxsuppi, minsuppi] 4. i++ 5. maxsuppi= α×maxsuppi-1 6. minsuppi= α×minsuppi-1 7. until (minsupp>minsuppi) 8. lfi= uilfii iv. experimental results and evaluation a. dataset description to measure the performance of the proposed against the apriori algorithm, their computational complexity was compared on two real benchmark databases of different sizes (i.e. different numbers of items and transactions) [27]. table iv shows the characteristics of these databases. table iv. characteristics of experimental data dataset name number of items number of transactions chess 75 3196 mushroom 119 8124 b. experiments and validation different values of α, minsupp1, and minsupp were examined for each database to find the lower computational complexity. table v presents the obtained experimental results. table v. database test results dataset minimum support (minsupp) apriori algorithm proposed algorithm number of frequent items settings α, minsupp1 intervals number of items in the interval [maxsuppi, minsuppi] chess 0.6020 34 α = 0.9 minsupp1 =0.85 [0.9997, 0.85] [0.8998, 0.765] [0.8098, 0.6885] [0.7288, 0.6020] 16 9 8 10 mushroom 0.0666 66 α = 0.55 minsupp1= 0.4 [0.9654, 0.4] [0.5310, 0.22] [0.2921, 0.121] [0.1607, 0.0666] 21 28 25 20 engineering, technology & applied science research vol. 13, no. 2, 2023, 10496-10500 10499 www.etasr.com bouaita et al.: a new approach for optimizing the extraction of association rules the computational complexity according to the k items appearing in the itemsets for the two algorithms was studied. table vi shows the results of applying the two algorithms on the two datasets, pointing out the performance of the proposed algorithm in the reduction of the number of generated itemsets, indicating time-saving. for example, the number of 3-itemsets generated from the mushroom database was 45760 itemsets for apriori and 8046 itemsets for the proposed algorithm. further experiments were carried out to compare execution time and memory space required by the proposed algorithm, eclat, and lcmfreq. the total runtime was determined in seconds (s) and the memory space in megabytes (mb) at the end of each algorithm for the two databases. tables vii and viii show the obtained results. table vi. computational complexity comparison for k=2 and k=3 dataset computational complexity ($% &) k=2 k=3 apriori proposed apriori proposed chess 561 229 5984 820 mushroom 2145 1078 45760 8046 table vii. total runtime comparison dataset proposed eclat lcmfreq chess 15.054 17.565 52.245 mushroom 26.192 40.419 81.292 table viii. used memory space comparison dataset proposed eclat lcmfreq chess 312.33 743.16 631.90 mushroom 531.14 814.19 749.27 figures 1 and 2 show the execution time and the memory space used by the three algorithms applied to the two transaction databases. figure 1 shows that the time obtained by the proposed algorithm is less than the other two algorithms with times of ~15s and ~26s for the chess and mushroom databases, respectively. figure 2 shows that the proposed algorithm is more efficient in terms of memory space used during execution, as it consumed only ~312mb and ~531mb for the chess and mushroom databases, respectively. fig. 1. total runtime of each algorithm. fig. 2. memory consumption of each algorithm. v. conclusion this paper presented a new, based on apriori, algorithm that allows the optimization of the extraction of association rules from databases. this optimization was based on the classification of items by categories according to their support. experiments were carried out using the two transactional databases chess and mushroom [27] to compare the performance of the proposed algorithm with the eclat and lcmfreq algorithms, showing that the proposed algorithm was faster in both cases and consumed less memory space. for example, the proposed algorithm can save more than half of the memory on the chess database compared to the eclat and lcmfreq algorithms. in future extensions of this study on improving the process of extracting frequent itemsets, the best value of the parameter α and the optimal number of intervals for reducing computational complexity in terms of execution time and memory consumption should be determined automatically. furthermore, data structures, such as trees, could be investigated for the data representation of each interval of the 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[27] "chess and mushroom datasets," frequent itemset mining dataset repository. http://fimi.uantwerpen.be/data/. microsoft word etasr_v12_n6_pp9551-9559 engineering, technology & applied science research vol. 12, no. 6, 2022, 9551-9559 9551 www.etasr.com kassem et al.: wind power generation scenarios in lebanon wind power generation scenarios in lebanon youssef kassem department of mechanical engineering engineering faculty near east university nicosia, cyprus yousseuf.kassem@neu.edu.tr huseyin camur department of mechanical engineering engineering faculty near east university nicosia, cyprus huseyin.camur@neu.edu.tr hüseyin gokcekus department of civil engineering civil and environmental engineering faculty near east university nicosia, cyprus huseyin.gokcekus@neu.edu.tr abdalla hamada abdelnaby abdelnaby department of mechanical engineering engineering faculty near east university nicosia, cyprus 20213582@std.neu.edu.tr received: 13 august 2022 | revised: 10 september 2022 and 16 september 2022 | accepted: 18 september 2022 abstract-renewable energy in terms of solar and wind energy can be an essential part of lebanon's strategies to add new capacity, increase energy security, address environmental concerns, and resolve the electricity crisis. in this regard, there is an urgent need to develop road maps in order to reduce the effect of global warming and enhance sustainable technological development for generating clean power in the country. therefore, the present paper evaluates lebanon's wind energy generation potential as an alternative solution to supply electricity to households in various locations distributed over lebanon. in the present study, the measured data are used to evaluate the wind energy potential in lebanon and to find suitable locations to install wind farms in the country. accordingly, the results demonstrated that ain ed dabaa is the most suitable location for the installation of a wind farm. moreover, the study aims to develop a wind energy cost analysis techno-economic model for eight conventional wind turbines and a barber wind turbine, which was found to be very competitive. consequently, this study showed that the implementation of a wind turbine could provide clean, economical, and continuous production of electricity in countries that suffer from daily blackouts. keywords-lebanon; wind potential; conventional wind turbines; barber wind turbine; techno-economic model i. introduction energy demand growth, global warming, climate change, and increasing consumption of fossil fuels has led to the transition from conventional fuels to renewable energy resources [1-3]. moreover, the use of fossil fuels in the generation of electricity contributes significantly to greenhouse gas (ghg) emissions, which further contributes to climate change [4, 5]. according to [6], utilizing renewable energy as an alternative energy source will help reduce environmental problems, essentially ghg emissions and air pollution. the use of renewable energy, including wind and solar energy, is rapidly increasing because it is economically viable and has limited environmental impact [7]. during the recent years, many studies have evaluated wind and solar energy potential as clean power sources for electricity generation in various countries. for instance, authors in [8] analyzed the performance of a 5kw rooftop photovoltaic (pv) system in northern india. the results indicated that the annual average capacity utilization factor was 16.39%. authors in [9] evaluated the wind potential in taza and dakhla cities, morocco using the weibull distribution function. the results demonstrated that the value of wind power density is 435.96w/m 2 and 122.91w/m 2 in dakhla and taza respectively. authors in [10] estimated the potential of rooftop pv electricity in lethbridge, canada using lidar data and arcgis. the results showed that the developed system has a huge potential to offset the energy demand of the city. authors in [11] assessed the performance of the aventa av-7 wind turbine for electricity generation in medina. it was found that the annual generation of energy from the selected turbine is 8648kwh. a. electricity situation in lebanon lebanon is located on the eastern edge of the mediterranean sea, between 33.8547°n latitude and 35.8623°e longitude. at present, fossil fuels (97%) and hydropower (3%) are the main sources of electrical energy in lebanon. generally, the production capacity of electricity reaches 3600mw, while the actual production capacity currently does not exceed 2000mw. currently, lebanon has 7 thermal power plants, 6 hydroelectric plants, and 2 power ships operating to generate electricity. the electricity consumption has increased due to the growth of the population and the continuing demand for new large and small appliances as shown in figure 1 [12]. besides, only 70% of total generated power covered the energy needs in the country as shown in figure 2. corresponding author: youssef kassem. engineering, technology & applied science research vol. 12, no. 6, 2022, 9551-9559 9552 www.etasr.com kassem et al.: wind power generation scenarios in lebanon fig. 1. electrical power demand distribution [12]. fig. 2. electrical power demand distribution [13]. the electricity crisis is one of the most important issues affecting the daily lives of citizens, shop owners, and small businesses in lebanon for years. the electricity crisis in lebanon is not new and the electricity sector has suffered from decades of mismanagement, weak policies, and the absence of proper planning. the country has been suffering from a severe shortage of energy due to the dilapidation of old power stations that were accompanied by sabotage operations during the past years. as a result, duration of power cuts for citizens increased to more than 20 hours a day. for this reason, citizens rely on domestic power generators or small home generators, both of them adding great financial burdens. according to [14, 15], private generators are utilized in all the country to meet the energy demand, and they are considered the third main source of production of electricity. b. the renewable energy situation in lebanon according to [14, 16], the power sector in the country contributes about 58% of total co2 emissions, of which 25% come from private generators. consequently, utilizing renewable energy would reduce the consumption of fossil fuels and could be a clean source for electricity generation in the country. authors in [17] concluded that wind power systems could be alternative sources to fulfill the electrical power required and reduce the co2 emissions. moreover, according to [17], standalone wind turbines are privately utilized for the generation of electricity for homes and small private companies. approximately 2.06% of wind power is currently used for electric power generation in lebanon [18]. authors in [19] found that wind energy could be utilized in the country for electricity generation during the night. authors in [20] concluded that the utilization of small-scale wind systems could be used for the generation of electricity from wind energy in beirut, sidon, and tripoli. authors in [21] concluded that wind turbine systems could be installed to complement the main grid with electric power during the peak hours. numerous researchers have investigated the potential of renewable energy, particularly wind energy in different locations in lebanon [16, 19-25]. for instance, authors in [25] investigated the wind potential in 9 locations in lebanon. the author concluded that a small-scale wind system could be more profitably used for these areas. authors in [23] studied the characteristics of wind energy in five locations in lebanon. their results showed that the wind energy system can be an alternative solution and more cost-effective than conventional power sources. authors in [24] assessed the wind energy potential in 8 locations in the northern lebanon. the results showed that wind power system can be utilized to reduce the energy shortage in the country. according to [16, 19-25], it can be concluded that:  the utilization of wind power systems in lebanon is limited.  renewable energy systems can solve the electricity crisis and reduce co2 emissions.  only a few studies investigated the wind turbine performance for generating electricity in lebanon. according to the literature review, no studies evaluated the potential and variability assessment of wind energy over lebanon considering various climate conditions. c. the importance of the current study globally, wind energy and its associated technologies are essential to support electricity consumption and supply power in order to mitigate the electricity crisis. besides, as an ongoing study on the assessment of renewable energy systems, primarily wind and solar energy in different locations, the present study aims to investigate the wind potential in various locations distributed over lebanon. to achieve this, measured data for the period 2010-2017 were collected from meteorological agencies. consequently, the weibull distribution function was used to evaluate the characteristics of wind speed in the selected locations. the distribution parameters were estimated using the maximum likelihood method. the power density was calculated and was used to evaluate the potential of wind energy in each location. additionally, the power-law exponent method was utilized to estimate the wind speed at various hub heights. based on the literature, wind power is low and unsustainable in many regions in lebanon. consequently, this study aims to evaluate the techno-economic performance of the ferris wheel-based barber wind turbine, which is a new wind turbine technology, at low wind speed locations. furthermore, the performance of the selected wind turbine is compared with conventional wind turbines under the same economic conditions. 0 10 20 30 40 50 a g ri c u lt u re a n d f is h e ry t e rt ia ry in d u s tr ia l r e si d e n ti a l e le c tr ic p o w e r d e m a n d d is tr ib u ti o n [ % ] -500 500 1500 2500 3500 2011 2012 2013 2014 2015 d e m a n d [ m w ] peak power demand peak power generation difficiency engineering, technology & applied science research vol. 12, no. 6, 2022, 9551-9559 9553 www.etasr.com kassem et al.: wind power generation scenarios in lebanon ii. materials and methods the proposed methodology aims to assess the wind energy potential in 12 locations in lebanon in order to identify suitable locations for future wind power systems. then, the economic viability of wind systems is evaluated. figure 3 illustrates the proposed methodology used in this study. a. study area and dataset this examination was undertaken to identify the best location for installing wind power systems among the chosen locations in lebanon. table i summarizes the geographic information of the selected locations. table i. the selected locations location latitude [°n] longitude [°e] elevation [m] younine 34.0776 36.2750 1198 birket aarous 34.2911 36.1456 2766 ain ed dabaa 34.4431 35.8992 296 mqaybleh 34.6460 36.3577 330 ras ouadi ed darje 34.2533 36.5775 1555 kfardebian 34.0017 35.8349 1670 qaraoun 33.5669 35.7193 913 khartoum 33.4079 35.3751 305 iskandarounah 33.1550 35.1685 53 beirut 33.8938 35.5018 40 khiam 33.3294 35.6148 697 hekr el dahri 34.6306 36.0237 10 b. wind speed distribution the correct determination of the probability distribution of wind speed is a prominent factor in evaluating the wind energy potential in a region. thus, knowing the wind speed distribution at a specific location is necessary for determining its potential. a 2-parameter weibull distribution is commonly utilized to study the characteristics of wind speed. the weibull probability density function (pdf)���� and the cumulative distribution function ���� expressions are [26]: ���� = �� �� �� ��� �− �� � � (1) ���� = 1 − ��� �− �� � � (2) where � is the mean wind speed (m/s), � is the shape parameter, and c is the scale parameter of the weibull distribution. to determine the distribution parameter, the maximum likelihood (ml) method is used to determine k and c [27]: � = �∑ ��� ����� ��� ∑ ����� − ∑ �������� � �� (3) � = � � ∑ ���� �⁄ (4) following the weibull distribution, (5) and (6) are utilized to estimate the average wind speed and the standard deviation of the wind speed respectively. � = �γ �1 + � (5) # = $�% &γ �1 + %� − γ% �1 + � ' (6) c. wind power density to assess the potential of wind energy, (7) is utilized to determine the wind power density (wpd) at a specific location: �() * = % +�,γ �1 + ,� (7) the average value of wpd can be estimated by [21]: () = % +�, (8) () = % +�,���� (9) (.) = % +�̅ , (10) where p is wind power density (w), 0. is the mean wind power density (w), a is the swept area (m 2 ), ρ is the air density (kg/m 3 ), ���� is the pdf, and � 1 is the mean wind speed (m/s). d. wind speed data extrapolation at different hub heights generally, wind speed measurements are carried out at a height of 10m above the ground. to obtain energy from wind turbines, it is necessary to estimate wind speeds at various hub heights using (11) [28]: ���2 = � 33�2 2.5672.2889��:�2��72.2889��;�2 �2⁄ � (11) where � is the wind speed at the wind turbine hub height z, � < is the wind speed at the original height = <. e. energy output of a wind turbine the produced energy by the wind turbine >?@a can be estimated by [28]: >?@a = ∑ pcde f��g (12) where f is time and 0?@a is determined by: 0?@a = ⎩⎪⎨ ⎪⎧ 0 when � < � �(r �s���s�� ��r� + � (r�r���s�� � � � when � � ≤ � ≤ �u 0u when �u ≤ � ≤ � ? 0 when � > � ? (13) where 0u is the rated power of the wind turbine, � � the turbine’s cut-in speed, � ? turbine’s cut-off speed, and �u is its rated wind speed. the average power generation of the turbine can be expressed as [29]: 0?@a = 0u wxyz[��:s�s �\�xyz[��:rs �\�:rs ���:s�s � − ��� ]− ��s^ � _` (14) the capacity factor (cf) is estimated [29, 30]: a� = b^cdefg<(r (15) engineering, technology & applied science research vol. 12, no. 6, 2022, 9551-9559 9554 www.etasr.com kassem et al.: wind power generation scenarios in lebanon fig. 3. flowchart of the proposed methodology. in this study, various wind turbines assumed the load profile for all months of the year. nine wind turbines (table ii) with various characteristics including the capital cost of acquisition (cc) and o&m cost (omc) are selected as shown in tables ii-iii. generally, conventional wind turbines (cwts) are designed to generate electricity at high wind speeds. the cut-in speed and rated wind speed for these turbines are within the range of 3-5m/s and 12-15m/s respectively [30, 31]. cwts are heavy and expensive to buy, install, and maintain. therefore, the performance of the ferris wheel wind turbine (fwwt) is compared with the selected cwts due to its advantages, such as its light design, lower weight to power ratios, etc. [32]. table ii. selected wind turbines model no. wind turbine model manufacture model#1 enercon e5 enercon gmbh model#2 enercon e44 enercon gmbh model#3 ewt dw61 emergya wind technologies b.v. model#4 ge sle 1.5 winergy/eickhoff/bosch. model#5 an bonus 1 mw/54 siemens wind power a/s model#6 dewind-62-91.5 m dewind model#7 neg-micon neg micon a/s model#8 vestas-v66 vestas wind systems a/s model#9 barber wind turbine barberwind turbines table iii. characteristics and specifications model no. hh [m] hi [kw] jkl [m/s] ji [m/s] jkm [m/s] cc [usd] omc [usd/y] model#1 76 800 3 13 25 1750000 51250 model#2 55 900 3 16.5 34 2337500 51250 model#3 69 900 2.5 10 25 1918770 57158 model#4 85 1500 3 14 25 3375000 57158 model#5 50 1000 3 15 25 863530 25043 model#6 91.5 1000 2.5 11.5 23 1124758 32618 model#7 70 1000 4 14 20 1162460 33711 model#8 67 1650 4 16 25 1768000 51272 model#9 70 800 3 9.6 20 1400000 42000 f. economic viability of a wind system the wind energy farm’s viability is dependent on its ability to generate energy at low operating cost. in this paper, the levelized cost of electricity (lcoe) is utilized to calculate the electricity generated cost (egc) of the wind turbine [32]: nao> = p ���q�����q���7�efg<r���&�st)�5uv ' w [1 + u^x��x &1 − � yx y� �'\ (16) engineering, technology & applied science research vol. 12, no. 6, 2022, 9551-9559 9555 www.etasr.com kassem et al.: wind power generation scenarios in lebanon where +=1.23kg/m3 is air's density, z is the swept area (m2), az is the betz limit power coefficient (theoretical value az =0.59), � is the escalation rate of operation and maintenance, { is the interest rate, | is the useful lifetime of the turbine in years, and a? is the operation and maintenance costs during the first year. additionally, (17) is used to determine the simple payback period (spp) [32]: spp = ~efg<r���&�st)�5uv'(� (17) where � is the installed capital cost of the wind turbine plus the costs of civil works and 0x is the price of electricity ($/kwh). iii. results and discussion a. characteristics of the wind speed at 10m height the statistical description of monthly wind speed includes mean value, standard deviation (sd), coefficient of variation (cv), minimum (min.), maximum (max.), kurtosis (k), and skewness (s) as summarized in table iv for all selected locations. according to the findings, it is noticed that the maximum mean monthly wind speed of 4.90m/s is recorded in ain ed dabaa, while the minimum of 2.81 is recorded in khiam and khartoum. the monthly wind speeds for ain ed dabaa and khartoum are illustrated in figure 4. it is observed that the maximum value of monthly wind speed of 5.82m/s is recorded in january. the highest value of 3.03m/s for khartoum is recorded in june as shown in figure 4. it can be seen that the cv values are moderately low, ranging from 6.52% to 17.25%. additionally, all s values for most of the selected locations are negative, indicating that all distributions are left skewed. fig. 4. mean monthly wind speed at a height of 10m. table iv. statistical estimators of monthly wind speed variable younine birket aarous ain ed dabaa mqaybleh ras ouadi ed darje khiam mean 2.90 3.01 4.90 2.91 3.19 2.81 sd 0.45 0.31 0.53 0.30 0.45 0.18 cv 15.37 10.14 10.79 10.14 14.05 6.52 min. 2.32 2.44 4.00 2.36 2.54 2.47 max. 3.51 3.45 5.82 3.34 4.03 3.03 s 0.03 -0.56 -0.15 -0.56 0.52 -0.54 k -1.46 -0.26 -0.41 -0.26 -0.19 -0.81 variable kfardebian qaraoun khartoum iskandarounah beirut hekr el dahri mean 3.48 2.86 2.81 3.32 3.48 2.91 sd 0.41 0.19 0.18 0.57 0.41 0.30 cv 11.66 6.52 6.52 17.25 11.66 10.14 min. 3.04 2.51 2.47 2.72 3.04 2.36 max. 4.22 3.08 3.03 4.27 4.22 3.34 s 0.82 -0.54 -0.54 0.42 0.82 -0.56 k -0.75 -0.81 -0.81 -1.46 -0.75 -0.26 b. determination of weibull parameters the weibull distribution parameters for the selected locations using monthly wind speed data were determined using the ml approach. the calculated shape k and scale c parameters of all selected locations at 10m height are shown in figure 5. the value of k ranged from 5.99 to 15.45 with an average value of 10.49. the annual value of c range was 2.885.04m/s with an average value of 3.32m/s. moreover, the average wind speed and its sd were calculated using from (5) and (6) and are shown in figure 5. it is observed that the mean wind speed and sd are within the range of 2.78-4.8m/s and 0.22-0.63m/s respectively. moreover, the pdf indicates the frequency of different levels of speed. it can be utilized to estimate which level of wind speed is prevalent in the location. the wind speed where the distribution curve peaks are the most frequently observed wind speed for the location. figure 6 illustrates the pdf of all selected locations. c. wind power density to evaluate the wind potential in the selected locations, the annual wpd is computed from (7). the value of wpd for each location is tabulated in figure 7. it is found that the value of wpd ranged from 13.18w/m 2 to 67.44w/m 2 with an average value of 21.03w/m 2 . based on these values, the wind energy generation potential of these locations is classified as class 1 (poor) as shown in table v. therefore, small-scale wind turbines are suitable to be used in the selected regions for exploiting the available wind energy potential. furthermore, it can be concluded that high-capacity wind turbines (mws) with a height of 90m and above can be suitable for gathering the wind energy potential in the selected locations. this is investigated using the power-law method, i.e., the collected data at 10m height is synthesized to the 90m height at which most of the 1mw or above capacity wind turbine height is. engineering, technology & applied science research vol. 12, no. 6, 2022, 9551-9559 9556 www.etasr.com kassem et al.: wind power generation scenarios in lebanon fig. 5. weibull parameters for all selected locations at a height of 10m. fig. 6. the probability density function for all selected locations. table i. wind power classification at 10m height power class h1[w/m2] 1 (poor) ≤100 2 (marginal) ≤150 3 (moderate) ≤200 4 (good) ≤250 5 (excellent) ≤300 6 (excellent) ≤400 7 (excellent) ≤1000 fig. 7. the annual value of wind power density for all selected locations. d. techno-economic model as mentioned above, 9 wind turbines with various characteristics were selected and the wind speed at various hub heights was calculated using (11). for instance, figure 8 illustrates the monthly variation of wind speed at various hub heights for 3 selected locations. it can be seen that the value of wind speed increases with the increasing hub height of the wind turbine. fig. 8. monthly average wind speed for 3 selected locations at various hub heights. engineering, technology & applied science research vol. 12, no. 6, 2022, 9551-9559 9557 www.etasr.com kassem et al.: wind power generation scenarios in lebanon fig. 9. the estimated results in terms of aep, cf, egc, and spp. to investigate the performance of wind energy, 9 wind turbines with various rated powers were considered. the aim is to select the turbine that best matches the wind regime at the selected locations. the electricity cost per kwh in lebanon, the annual interest rate, the capital cost of acquisition, operation, and maintenance costs of wind turbines, and the life of the wind turbines are required for economic viability. these data were obtained from previous studies, trading economics, and global petrol prices. the annual energy produced (aep) and cf for the selected turbines were determined by (12) and (15) respectively. egc and spp were determined by (16) and (17). figure 9 illustrates the estimated results in terms of aep, cf, egc, and spp for all selected locations. it is found that the ape values ranged from 339.55mwh to 5017.35mwh with an average value of 1241.875mwh. the maximum and minimum values of ape are recorded in ain ed dabaa and khartoum for a hub height of 91.5m (model#6) and 55m (model#2) respectively. the highest and lowest cf values are 59.23% (ain ed dabaa) and 2.79% (khiam) respectively with an average value of 14.28%. furthermore, the egc values are within the range of 0.033-0.761usd/kwh with an average value of 0.287usd/kwh. furthermore, the shortest payback period of 1.54 years is observed at ain ed dabaa for a hub height of 91.5m (model#6). other researchers who analyzed the performance of a wind farm system in terms of cf, spp, and egc support these observations [30, 33-39]. for instance, authors in [35] found cf values within the range of 31.1-49% and 37.3-56.6% for 50m and 75m hub-height turbines. authors in [30] found that the bwt 61m–800kw wind turbine has a payback period of 1.9-27.3 years and its egc values were within the range of 0.04-0.43usd/kwh. in [36], it was found that the payback period for different wind farms with a capacity of 100mw ranged from 6.34 to 19.9 years. authors in [33] found that the values of cf and egc produced by various wind turbines were within the range of 32-38% and 0.255-0.306 usd/kwh respectively. authors in [37] found that the cf values varied from 6.8% to 47.6% using various wind turbines with various characteristics. according to the finding of [34], the cf values of different wind turbines are estimated to be within the range of 22.9-50.6%. it should be noted that when the value of spp exceeds the assumed lifetime of the wind turbine, it means that installing the wind turbines in locations is not economically viable for energy production for the selected wind turbine model. moreover, according to [30, 31, 38], the spp value for small and medium-scale wind turbines is within the range of 512 years. therefore, more than 50% of the selected cities fall within the range of spp. based on these results, it can be concluded that:  the results demonstrate the competitiveness of bwts for operation compared to cwts, especially at locations with low wind conditions.  although model#6 has a lower egc in all selected locations, model#9 has a robust design and a wider range of applications for all classes of wind resources. thus, model#9 would have a lower cost in the long run.  fwwt technology is a strong candidate to increase the availability of economic, green, and sustainable energy in lebanon. the egc values obtained from the current study are compared with the current electricity prices in lebanon in engineering, technology & applied science research vol. 12, no. 6, 2022, 9551-9559 9558 www.etasr.com kassem et al.: wind power generation scenarios in lebanon figure 10. it is clear that the price of the electricity generated by wind turbine systems is less than the one from conventional systems. it can be concluded that the developed systems ensure the economic feasibility of the project for all locations. wind energy will be able to solve the problem of a chronic lack of electricity and reduce the electricity bills in lebanon. fig. 10. monthly average wind speed for some selected locations and various hub heights. iv. conclusions lebanon is experiencing a serious water and electricity crisis. the growing challenges faced by the population and energy sectors are outpacing the government's efforts to provide high-quality, affordable, and accessible electricity. in this context, utilizing wind energy is considered an alternative solution to supply electricity to households, reduce the effect of global warming, and enhance sustainable technological development. therefore, there is an urgent need to develop road maps for the exploitation of renewable energy sources. in this regard, the techno-economic model for the assessment of wind energy in selected locations in lebanon is presented in this research. in 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[40] t. r. ayodele, a. a. jimoh, j. l. munda, and j. t. agee, "viability and economic analysis of wind energy resource for power generation in johannesburg, south africa," international journal of sustainable energy, vol. 33, no. 2, pp. 284–303, mar. 2014, https://doi.org/ 10.1080/14786451.2012.762777. microsoft word etasr_v12_n5_pp9258-9264 engineering, technology & applied science research vol. 12, no. 5, 2022, 9258-9264 9258 www.etasr.com yahiou et al.: effects of inrush current on the hysteresis loop and load influences on the transient … effects of inrush current on the hysteresis loop and load influences on the transient current of a singlephase transformer abdelghani yahiou automatic laboratory of sétif (las) department of electrical engineering university of bouira bouira, algeria abdelghani.yahiou@univ-bouira.dz abdelhafid bayadi automatic laboratory of sétif (las) department of electrical engineering university of sétif-1 sétif, algeria a_bayadi@univ-setif.dz hacene mellah automatic laboratory of sétif (las) department of electrical engineering university of bouira bouira, algeria h.mellah@univ-bouira.dz mokhtar abid department of automatic and electrical engineering university of blida-1 blida, algeria oussama.electrotechnique@gmail.com received: 15 july 2022 | revised: 4 august 2022 | accepted: 7 august 2022 abstract-when putting any unloaded transformer into service, a high-value current that can be very dangerous, called the inrush current, appears. the latter may cause problems and consequences in the electrical system. the challenges of visualizing the effects of transient regimes on the iron core's characteristics and the influence of the type of load on inrush current characteristics are covered in this study. the main purpose of this paper is to treat the influence of this transient phenomenon on the hysteresis loop of a single-phase transformer, in terms of its size, area, or position, and therefore, the influence of the load on the transient regime. a general study of the electromagnetic characteristics of the transformer iron core will be presented. then, using the atp-emtp program, the purpose of the realized simulations is to visualize the relationship between the hysteresis loop and the magnetizing inrush current in the transient state. the results show the decrease of the hysteresis loop area and their shift with respect to the origin of the axes following the increase in the transient inrush current peak. as the second part of this article, there is a study of the influence of the load on the transient regime, i.e. inrush current. this is accomplished by adding a load with different configurations and various connections. the purpose is to find the effect of the load on the reduction of the transient inrush current phenomenon. keywords-transformer; inrush current; transient regime; hysteresis loop; load influence; atp-emtp i. introduction inrush current is caused by the saturation of a power transformer due to variations in the magnetization voltage [1, 2]. when an unloaded transformer is energized, a transient phenomenon called inrush current may appear in the excited circuit side. therefore, necessary research must be carried out in order to anticipate a suitable protecting system for the transformer. there are many works in the literature that fall into this framework, such as [3-5], where many numerical and analytical tools have been developed. furthermore, the majority of studies on the field of transformer transient study are in the context of finding effective and inexpensive techniques to reduce this inrush current. among these methods, there is the technique proposed in [6], in which four different methods to reduce the inrush current were compared. the required result is the ability to use the circuit breakers with an independent pole, as well as the ability to deem the residual flux in the iron core of the transformer. the measurement and simulation studies performed in [7, 8] consist pioneering work, simulation, and measurements, in the area of inrush current reduction in threeand singlephase transformers. taking into account the residual flux values, the authors propose three schemes in this technique, by closing the circuit breakers in a synchronous, quick, and delayed manner. authors in [9] utilized the technique of making a modification in the transformer bobbin. this is intended to decrease the inrush current peaks by increasing the transient inductance value. taking into account the phase shift between the three phases of the transformer during its energization, the authors in [10-13] introduce a resistance between the ground and the transformer neutral. authors in [14], while taking into account the switching moment, used the reversed flux technique to investigate the reduction of the inrush current using an existed photovoltaic generator. the idea proposed in [15], is in the corresponding author: abdelghani yahiou engineering, technology & applied science research vol. 12, no. 5, 2022, 9258-9264 9259 www.etasr.com yahiou et al.: effects of inrush current on the hysteresis loop and load influences on the transient … same context with what was accomplished in [10-13], where the residual flux is taken into account, and a controlled circuit breaker is used to isolate the neutral of the three-phase transformer with respecting of the three phases sequential. authors in [16] present several methods to protect and reduce the various interactions of transformer relays as well as the introduction and removal of the load in a random or studied manner by the circuit breakers. authors in [17] depended on formal methods to solve differential equations based on the equivalent circuit represented using the state space equation. authors in [18] raised the resistance value of the transformer winding, using the transformer tap changer to reduce the effect of the inrush current power system as well as mitigating its peak value. the main contribution in [19] is the application of a technique using a real-time measurement setup to eliminate the sympathetic inrush current. the latter results from the interaction of two transformers, one is energized and the second is already supplied. moreover, there is a comparison of the results (measurement and simulation) to prove the efficacy of the proposed technique found in [20] to mitigate also this sympathetic inrush current. authors in [21] presented an important technique in the field of inrush current mitigation, especially by using renewable energies, where the reverse flux is applied. authors in [22] presented a review of some factors which affect the resistance during breakdown of transformer oil. authors in [23] exposed a generator differential protection relay system, its disadvantages and its advantages. in [24], a real power transformer was used in the experiments, and a uhf-pd detection system was built. the supply of the transformer primary, under its nominal voltage, is accompanied by a transient regime during which the intensity of the inrush current can take values much higher than those of the nominal intensity, depending on the instant of appreciation of the voltage and the induction remanence of the magnetic circuit. hence the need to predetermine through the study of the transient regime the approximate value of this inrush current which may be greater than or equal to several times the current of the transformer [25]. holcomb in [5] is considered among the first who raised the idea of the inrush current calculation, but without going far. the author studied only a method to compute the peak inrush current for the first and any succeeding cycle, without considering its effect on hysteresis loop. in [25], the authors used a developed model to estimate the inrush current and hysteresis loop. however, they did not make a comparison between the relationships of the position of the hysteresis loop wave according to the corresponding inrush current. the same weakness was observed in [26, 27], where the authors estimated the saturation curve from the inrush current waveform. this major drawback of these previous works has been studied and dealt with in the present work, where the comparison has been made between different effects of transformer energization on the nature of the iron core. authors in [28] exploited a real model of a transformer to study different phenomena such as the application of the nonlinear load. however, limited their study to the load effects on the steady-state regime. the first part of this paper is devoted to the study of the transient inrush current effect on the hysteresis loop of a transformer. therefore, a quick rundown is presented on how to identify the equivalent circuit parameters for the used transformer and the iron core magnetizing characteristic (air core-inductance). then, a simulation using atp-emtp program is performed using the nonlinear type 98 inductance and the nonlinear type 92 resistance, as well as the system that measures the hysteresis cycle (flux-current). finally, the presented simulation results show the variation of the area of the hysteresis cycle and the shift of this loop according to the increase and decrease of the inrush current peak. a comparison is made with respect to the hysteresis cycle in the steady state. the next part is devoted to the study of the load insertion effect on the transient inrush current of a transformer. simulation is done using the same model and the same transformer characteristics, only a load with different values of impedance and different connections is added in the secondary side. the simulation results show the variation of the inrush current waveforms with the application of deferent types of loads. ii. materials and methods this section is devoted to a presentation of the real transformer used in the simulation, the identification of the parameters of its equivalent circuit, and the representation of the model with nonlinear parameters. the single-phase transformer (figure 1) used in the simulations of this paper is manufactured by the company delorenzo, italy and is available at the laboratory of the power system, university of sétif 1. all the experimental tests of this paper were carried out in this laboratory. table i shows some parameter values of the used transformer. the parameters of the transformer equivalent circuit obtained by applying the classical equations are presented in table ii. the study of any transformer transient regime such as ferro-resonance and inrush current requires careful modeling of the iron core nonlinearities and precision in the equivalent circuit parameters of the transformer determination. fig. 1. the used transformer. table i. test transformer nameplate data. power (va) frequency (hz) phase voltage ratio (kv) turn (tr) current ratio (a) class (isolated) 2000 050 01 0.22/0.025 0330/0037 9.10/080 e table ii. transformer parameters parameter value shunt resistance r� 2847.05ω shunt reactance x� 609.72ω equivalent resistance ré� 3.48ω equivalent reactance xé� 2.69ω engineering, technology & applied science research vol. 12, no. 5, 2022, 9258-9264 9260 www.etasr.com yahiou et al.: effects of inrush current on the hysteresis loop and load influences on the transient … a. nonlinearities of the iron core the representation of the transformer model with linear resistors and inductances does not reflect the actual behavior of the electrical transformer. so, the effects of hysteresis and saturation must be introduced using non-linear branch elements. figure 2 shows the saturation curve λ = f�i � which represents the air core inductance. the nonlinear resistance characteristic v = f�i � is depicted in figure 3. both figures use the data of [1]. fig. 2. air core inductance characteristic λ = f�i � [1]. fig. 3. nonlinear resistance characteristic λ = f�i � [1]. the curves of figures 2 and 3 are computed by the method based on the improved technique presented in [20, 29], and they have been inserted in the transformer models (saturable) found in atp-emtp program to simulate the effect of the inrush current phenomenon on the hysteresis loop. b. residual flux residual flux plays a basic role in the occurrence of inrush current in an unloaded transformer. it represents a continuous flux value that persists in the magnetic circuit, which can generate an inrush current after switching off if the transformer is not completely demagnetized [30, 31]. the instantaneous equation for flux in the iron core is: λ�� � �t� = λ� + � u��� �t�dt � ������ λ�� � = −λ� ! cos�ω ∗ t� +λ� ! cos�ω ∗ t� �'� � + λ� �1� c. simulation of the influence of the inrush current on the hysteresis loop in this section, the simulation and the results will be presented in detail. figure 4 shows the simulation diagram using the atp-emtp program to visualize the influence of the transient inrush current on the hysteresis loop. fig. 4. simulation diagram. iii. results a. steady state in the steady state, a voltage source is placed in the primary of the test transformer while the secondary is unloaded. the obtained simulated magnetizing current curve is shown in figure 5 and the corresponding hysteresis loop curve is shown in figure 6. fig. 5. unloaded steady state current waveform. fig. 6. unloaded steady state hysteresis loop. it should be noted that the current waveform in the no-load state is distorted non-sinusoidal due to the harmonics caused by the non-linearity of the transformer core. figure 6 represents the variation of the flux as a function of current in the unloaded test. it should be noted that the hysteresis loop is symmetrical with respect to the origin of the reference. the surface occupied by this loop is approximately bounded from -1.2 to 1.2a and beyond this interval we enter the saturation phase. this area represents the losses in the iron core. 0 10 20 30 40 50 60 0 0.5 1 1.5 2 reactive magnetizing current (a) l in k a g e f lu x ( v .s ) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0 100 200 300 400 500 600 resitive magnetizing current (a) p e a k v o lt a g e ( v ) 0 0,01 0,02 0,03 0,04 0,05 -1.5 -1 -0.5 0 0.5 1 1.5 time (s) c u rr e n t (a ) -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 -1.2 -1 -0,8 -0,6 -0,4 -0,2 0 0,2 0,4 0,6 0,8 1 1.2 current (a) f lu x ( v .s ) engineering, technology & applied science research vol. 12, no. 5, 2022, 9258-9264 9261 www.etasr.com yahiou et al.: effects of inrush current on the hysteresis loop and load influences on the transient … b. transient regime (inrush current) in these applications, the simulation time is fixed to 2s, and a controlled circuit breaker is exploited to vary the closing time and see the first peak of the inrush current and its attenuation up to the magnetizing current until reached the steady state. the hysteresis loop corresponding to each closing time of the circuit breaker will be drawn. 1) closing time tf = 0.5808s when the circuit breaker closes at tf = 0.5808s, the first peak of inrush current is reached at 2.25a, and continue to decrease until the steady state current, as shown in figure 7. the hysteresis loop is distorted and asymmetrical with respect to the origin. the saturation phase in the positive part follows the inrush current peak of 2.25a corresponding to a flux value of 1.26v.s. while the current of the negative part does not exceed the value of -0.2a and the flux the value of -0.3v.s. figure 8 shows the complete hysteresis loop. fig. 7. transient inrush current for closing time)* = 0.5808 /. (a) (b) fig. 8. hysteresis loop at tf=0.5808s for (a) several periods, (b) one period. 2) closing time tf = 0.5828s when the circuit breaker closes at tf = 0.5828s, the first peak of inrush current is reached at 18.72a and continues to decrease until the steady state current, as shown in figure 9. the inrush current peak is very large in this application compared to the peak in the first application. this leads the hysteresis loop to withdraw completely to the positive part according to the direction of the inrush current. for the positive part, it follows the inrush current peak of 18.72a corresponding to a flux value of 1.52v.s, while that of the negative part does not exceed the values of -0.03a and -0.38v.s. figure 10 shows the complete hysteresis loop. fig. 9. transient inrush current for closing time tf = 0.5828s. (a) (b) fig. 10. hysteresis loop at tf=0.5828s for (a) several periods, (b) one period. 3) closing time tf = 0.5848s when the circuit breaker closes at tf = 0.5848s the first peak of inrush current reached 26.50a and continued to decrease until the steady state current, as shown in figure 11. when compared to the peak in the previous application, the inrush current peak is considerably large. according to the direction 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 -1 -0.5 0 0.5 1 1.5 2 2.5 time(s) c u rr e n t (a ) zoom -1 -0.5 0 0.5 1 1.5 2 2.5 -1 -0.5 0 0.5 1 1.5 current (a) f lu x ( v .s ) zoom -0.5 0 0.5 1 1.5 2 2.5 -1 -0.5 0 0.5 1 1.5 current (a) f lu x ( v .s ) 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 -5 0 5 10 15 20 time(s) c u rr e n t( a ) 0.592 0.596 18.64 18.68 18.72 zoom -5 0 5 10 15 20 -1 -0.5 0 0.5 1 1.5 2 current (a) f lu x ( v .s ) zoom -5 0 5 10 15 20 -1.5 -1 -0.5 0 0.5 1 1.5 current (a) f lu x ( v .s ) zoom -0,4 0 0.6 -0,2 0 0,6 engineering, technology & applied science research vol. 12, no. 5, 2022, 9258-9264 9262 www.etasr.com yahiou et al.: effects of inrush current on the hysteresis loop and load influences on the transient … of the inrush current, this causes the hysteresis loop to entirely retreat to the positive part. the inrush current peak of 26.50a, corresponding to a flux value of 1.57v.s, is followed by the positive portion. the negative component, on the other hand, does not surpass the current value of -0.03a and flux value of -0.18v.s. the whole hysteresis loop is shown in figure 12. fig. 11. transient inrush current for closing time tf = 0.5848s. (a) (b) fig. 12. hysteresis loop at tf=0.5848s for (a) several periods, (b) one period. iv. load effects on the inrush current the goal is to apply different loads with different values in the secondary side of the transformer to observe the influence of this variation on the transient inrush current phenomenon. the simulation is carried out using the model of figure 4, and the same transformer characteristics, but with adding load. a. resistive load in the first application, and after the unloaded operating of the transformer as seen in the first part of this article, a pure resistance load is added in the secondary side. figure 13 shows a comparison between transient current waveforms with different proportions of resistive load (100%, 50%, and 120% of the nominal resistive load). fig. 13. primary current waveforms for the resistive load. b. r-l load in the second application, a resistance-inductance (r-l) load is added in the secondary side. figure 14 shows a comparison between transient current waveforms with different proportions of r-l load. fig. 14. primary current waveforms for the r-l load. c. r-l-c load in the last application, a resistance-inductance-capacitance (r-l-c) load is added in the secondary side. figure 15 shows a comparison between transient current waveforms with different proportions of r-l-c load (100%, 50%, and 120% of the nominal r-l-c load). the values of figures 13-15 are summarized in table iii. fig. 15. primary current waveforms for the r-l-c load. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 -5 0 5 10 15 20 25 30 time(s) c u rr e n t( a ) 0.59 0.594 0.598 26.44 26.46 26.48 -5 0 5 10 15 20 25 30 -1 -0.5 0 0.5 1 1.5 2 current (a) f lu x ( v .s ) zoom -5 0 5 10 15 20 25 30 -1.5 -1 -0.5 0 0.5 1 1.5 current (a) f lu x ( v .s ) -0.4 0 0.4 0 0.2 0.4 0.6 0.8 zoom 0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 -20 -15 -10 -5 0 5 10 15 20 25 time (s) c u rr e n t (a ) nominal load 50% nominal load 120% nominal load 0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 -20 -15 -10 -5 0 5 10 15 20 25 time (s) c u rr e n t (a ) nominal load 50% nominal load 120% nominal load 0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 -20 -15 -10 -5 0 5 10 15 20 25 30 time (s) c u rr e n t (a ) nominal load 50% nominal load 120% nominal load engineering, technology & applied science research vol. 12, no. 5, 2022, 9258-9264 9263 www.etasr.com yahiou et al.: effects of inrush current on the hysteresis loop and load influences on the transient … table iii. current values for diferent load values resistive load r-l load r-l-c load inrush current first peak (a). 16.48 19.9 18.4 nominal load steady state current (a) 12.73 12.04 13.8 inrush current first peak (a) 21.45 23.13 22.57 50% of nominal load steady state current (a) 7.037 6.82 7.9 inrush current first peak (a) 15.14 18.70 17.5 120% of nominal load steady state current (a) 14.74. 14.74 15.79 v. discussion from the obtained results in the first part, it can be concluded that the transient inrush current of the transformer has a direct influence on the hysteresis loop waveform. this impact results in the reduction of the area of this loop according to the increase of the inrush current peak, therefore it can explain the reduced iron core losses with the inrush current appearance. moreover, there is a withdrawal of the hysteresis loop according to the direction of the transient inrush current, which means that the hysteresis loop shifts towards the value and direction of the peak inrush current. o n the other hand, figures 13-15 represent the transient currents waveforms when different types of loads at 50% and 120% of the nominal values are inserted. the figures show that the energization of transformer lightly loaded causes transient inrush current almost similar to that of energizing an unloaded transformer. moreover, the energization of a highly loaded transformer causes transient inrush current much less to that acquired after energizing an unloaded transformer . the above applications, by adding load in its various forms and values, prove that a decrease in the load leads to an increase in the transient inrush current. on the other hand, the current in the steady state (after removing the transient regime) is proportional to the value of the load. in the unloaded test, when the current waveform takes its permanent regime, it was not sinusoidal. however, adding load leads to the return of the sinusoidal waveform after crossing the transient regime. these simulations prove that the transformer loading decreases the amplitude of the transient inrush current. so, it can be concluded that the inrush current exists only at energization of an unloaded or lightly. vi. conclusion this work is concerned with the visualization of the effect of transient regimes on the characteristics of the iron core, as well as the influence of the load on the inrush current characteristics. in the present paper, a summary of the parameter identification method of the transformer equivalent circuit has been presented and a magnetizing characteristic representing the transformer iron core has been illustrated. parameter identification was achieved using classical tests such as open circuit and short-circuit. a simulation using atpemtp was performed using the type 98 nonlinear inductance and the type 92 nonlinear resistance, and a system that measures the hysteresis cycle (flux-current). finally, the simulation results were presented and show the variation of the area of the hysteresis cycle and the shift of this loop according to the increase and decrease of the inrush current peak. the comparison was conducted with respect to the hysteresis cycle in steady state. energizing an unloaded transformer causes transients at large amplitudes, with the effect of the non-linear behavior of the magnetic circuit on the current waveform occurring in this mode of operation. increasing the load value decreases the transient regime. therefore, the application of the load 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[31] t. liu, "manoeuvre controlee des transformateurs de puissance avec flux remanent.," ph.d. dissertation, supelec, paris, france, 2011. microsoft word etasr_v12_n5_pp9087-9091 engineering, technology & applied science research vol. 12, no. 5, 2022, 9087-9091 9087 www.etasr.com pham et al.: application of the grey system theory in construction management application of the grey system theory in construction management a case study of construction paint supplier evaluation and selection criteria cuong phu pham faculty of transport and economics, campus in ho chi minh city, university of transport and communications, vietnam cuongpp_ph@utc.edu.vn phong thanh nguyen department of project management ho chi minh city open university ho chi minh city, vietnam phong.nt@ou.edu.vn phuong thanh phan department of project management ho chi minh city open university ho chi minh city, vietnam phuong.pthanh@ou.edu.vn received: 18 june 2022 | revised: 6 july 2022 | accepted: 20 july 2022 abstract-material management is an important task in building construction. they account for a substantial proportion of investment capital and construction volume. however, as material prices are often affected by the market, choosing the right construction supplier is not an easy decision for contractors, especially for those materials required during the finishing phase of the construction. as one of these finishing materials is paint, identifying core criteria for evaluating and selecting the best construction paint supplier is a crucial economic choice for construction contractors. assessing the importance of these criteria is a complex multi-criteria decision-making problem. to reflect the risks and uncertainties in this problem, the current paper presents a grey system theory approach to prioritize important criteria for selecting paint material suppliers in construction projects. keywords-construction management; project management; evaluation and selection criteria; material management; paint supplier; grey theory i. introduction material management is an essential task in the construction management of any civil engineering project because construction materials account for a high proportion of the total construction cost [1, 2]. in this regard, evaluating and selecting an efficient supplier of construction materials is a very important economic decision and helps the contractor manage materials effectively [3]. one definition of an efficient supplier is a company that specializes in distributing highquality products in the proper quantity, at the proper time, for a fair price [4]. in a construction project, one commonly required and evaluated material is construction paint. determining the critical criteria in selecting the construction paint supplier is essential to choosing the material supplier. however, traditional assessment methods (e.g. scoring methods) are often based on the subjective opinions of construction experts, which often do not consider uncertainty in their expert judgments or opinions. this results in a final decision that is often irrational and sometimes inconsistent with reality. to improve this issue, this paper proposes a new quantitative model for prioritizing paint supplier evaluation and selection criteria based on the grey system theory. ii. research background construction paint in civil engineering projects is available in liquid, paste, or powder form. the effect of construction paint is to create a solid film that adheres firmly to the building surface for building structure protection and esthetics. choosing an efficient construction paint supplier is crucial for construction managers. in addition to helping the construction project attain the highest quality, it also helps reduce project cost and shorten the project implementation time. this study identifies the eight most important factors to consider when selecting the construction paint supplier in civil engineering projects based on a literature review of research papers and indepth interviews with experts [5-21]. these criteria are: (f1) the reputation of the paint supplier, (f2) the quality management system certification of the paint supplier, (f3) the quality of construction paint materials, (f4) the number of paint categories and products, (f5) delivery time, (f6) terms and conditions of payment, (f7) price of the paint product, and (f8) the warranty period. iii. research methodology one approach in studying uncertainty is the grey theory, introduced by deng in [22-24]. it excels at analyzing mathematical systems with uncertain knowledge. when corresponding author: phong thanh nguyen engineering, technology & applied science research vol. 12, no. 5, 2022, 9087-9091 9088 www.etasr.com pham et al.: application of the grey system theory in construction management working with discrete data and insufficient knowledge, grey system theory can be utilized to handle uncertainty or indeterminate problems. a grey system is defined as a system that includes grey variables and a grey number to provide ambiguous information [25]. figure 1 illustrates the grey system theory. fig. 1. grey system theory. the degree of information and connections between black and white systems are also explained by grey systems, in which grey numbers represent numbers with unknown precise values. information that is partial, incomplete, or missing can take many different forms. this study uses grey numbers to reflect subjective judgments and reduce evaluation variance among construction experts. table i [26] compares black, grey, and white systems. table i. comparison of black, grey, and white systems parameter black system grey system white system information unknown incomplete completely known appearance dark blurred clear processes new changing old properties chaotic multivariate order methods negation change for better confirmation attitude letting go tolerant rigorous outcomes no solution multi-solutions unique solution table ii. linguistic scales with grey numbers level of importance linguistics scale grey numbers 1 ei = equivalent importance [1, 2] 3 mi = medium importance [2, 4] 5 si= strong importance [4, 6] 7 vsi = very strong importance [6, 8] 9 emi = extreme importance [8, 10] let x denote a closed and bounded set of real numbers. a grey number, denoted as ⊗x, is a number with an unknown exact value but within a known range. these grey numbers represent uncertain and ambiguous data. in this study, we propose a combination of grey system theory and the analytical hierarchy process (ahp) decision-making method to reduce subjective judgments in prioritizing weights of important criteria in evaluating and selecting paint suppliers for a construction project. in the grey ahp approach, grey numbers are used instead of crisp sets and crisp numbers. the grey ahp method uses pairwise comparisons with linguistic scales and gray scales. the main computational steps to use grey ahp in this study are [27-47]: step 1. define the research problem using traditional ahp. in this step, we identify the research problem, create the hierarchical structure, and construct the pairwise comparison matrix using construction experts’ evaluations with linguistic scales containing grey numbers in table ii. the grey comparison matrix using the geometrical mean formulation is constructed as follows: 11 12 1 21 22 2 1 2 n n m m mn x x x x x x d x x x ⊗ ⊗ ⊗    ⊗ ⊗ ⊗  =     ⊗ ⊗ ⊗  ⋯ ⋯ ⋮ ⋮ ⋮ ⋮ ⋯ (1) where ij x⊗ is the pairwise comparison concerning the i th criterion over the j th criterion. step 2. calculate the normalized grey comparison matrix. the normalization for the grey numbers is given in (2)-(4). * * ** * * 11 11 12 12 1 1 * * ** * * 21 21 22 22 2 2* * * ** * * 1 1 2 2 , , , , , , , , , n n n n m m m m mn mn x x x x x x x x x x x x d x x x x x x                            =                   ⋯ ⋯ ⋮ ⋮ ⋮ ⋮ ⋯ (2) * 1 11 1 2 1 2 ij ij ij m mm m ij ijij ij i ii i x x x x xx x = == = = =   ++       (3) * 1 11 1 2 1 2 ij ij ij m mm m ij ijij ij i ii i x x x x xx x = == = = =   ++       (4) step 3. calculate the grey weight of each criterion by determining the averages of the rows using (5): ** * 1 1 , n n ij ij ij j j i x x x w n n = =  ⊗   ⊗ = =   (5) where n = {1, 2, . . . , n} is the criterion set. step 4. calculate the whitenization of the grey weights. the whited value of an interval grey weight is a crisp number with a potential value between the interval grey weight’s upper and lower bounds, as follows: (1 ) i i i m w wλ λ= − + (6) where λ is the whitening coefficient and [0,1]λ ∈ . step 5. calculate the consistency ratio (cr): to determine whether the decision-comparison preparers were consistent, this step involves examining the cr of the pairwise comparison matrix. the calculation of the cr from construction experts is [48-52]: max 1 1 nci cr ri n ri λ − = = × − (7) where ci is the consistency index, ri is the random index, and max λ is the largest eigenvalue. engineering, technology & applied science research vol. 12, no. 5, 2022, 9087-9091 9089 www.etasr.com pham et al.: application of the grey system theory in construction management iv. results and discussion for calculation simplicity, table iii presents the integrated grey comparison matrix, developed based on the synthesis of construction expert opinions using the geometrical mean formulation for grey numbers given in table ii. next, we calculated the normalized grey comparison matrix using (2)(4), as shown in table iv. after obtaining the normalized grey comparison matrix, we calculate the grey weight of each criterion for evaluating and selecting the construction paint supplier by determining the row averages using (5). the whitenization of the grey weights, obtained by applying (6), is shown in table v. we choose the value of λ to be 0.5 [52, 53]. finally, we applied (7). the cr of this pairwise comparison matrix is cr = 2.02% < 10%, so the evaluation result is reliable because the pairwise comparison matrix is consistent. the top 5 most important criteria for evaluating and selecting the paint supplier in construction projects were determined to be f7, f1, f3, f2, and f6. currently, the price of fuel (f7), especially gasoline, is quite high due to scarcity resulting from the conflict between russia and ukraine. this causes the paint prices on the market to increase. therefore, construction contractors are more interested in the price than other criteria. related to the second most important criterion, the reputation and branding of a paint supplier (f1): some large suppliers spend much money promoting their brands and products on all kinds of media, gaining notoriety in the business world, industry associations, and business partners. in contrast, some suppliers do not choose aggressive advertising methods but rely on their positive reputation to help them promote their branding. terms and conditions of payment (f6) are usually provided in the purchase contract. contracts are documents that detail agreements between transaction objects created to achieve the needs of all parties. there are many forms of payment, including one-time payments or partial payments. the ability of the supplier to permit customers to owe money with attractive conditions will make the method of partial payment very popular because the contractor’s cash flow is rarely consistent. in addition, to assist customers, the payment process needs to include whether the currency of the transaction is local (vnd) or foreign (usd). the variety of options and convenience in financial transactions by the supplier will provide the contractor with more payment options. because each contractor has its own form of currency storage and its own trading methods, some businesses pay in cash. others pay through bank transfers, and foreign-owned companies use usd in their projects. v. conclusion applying a grey ahp, a new quantitative method, by integrating grey system theory with the ahp, we prioritize the critical criteria in the evaluation and selection process of building paint suppliers in construction projects. this new method has an advantage over traditional methods because it supports group decision-making. in addition, it also accounts for uncertainty in the judgments of construction professionals and data incompleteness. the 5 most important criteria for evaluating and selecting the paint supplier in construction projects are (f7) the price of the paint product, (f1) the reputation of the paint supplier, (f3) the quality of construction paint materials, (f2) the quality management system certification of the paint supplier, and (f6) the terms and conditions of payment. table iii. integrated grey comparison matrix [1.0000, 1.0000] [1.5874, 3.1748] [1.2599, 2.5198] [4.5789, 6.6039] [3.1748, 5.2415] [2.5198 4.5789] [0.6300, 1.2599] [5.2415, 7.2685] [0.3150, 0.6300] [1.0000, 1.0000] [0.7937, 1.5874] [2.0000, 3.6342] [1.2599, 2.5198] [1.2599, 2.5198] [0.1733, 0.2752] [5.2415, 7.2685] [0.3969, 0.7937] [0.6300, 1.2599] [1.0000, 1.0000] [3.1748, 5.2415] [2.0000, 3.6342] [1.5874, 3.1748] [0.3969, 0.7937] [3.6342, 5.7690] [0.1514, 0.2184] [0.2752, 0.5000] [0.1908, 0.3150] [1.0000, 1.0000] [0.7937, 1.5874] [0.3467, 0.6300] [0.1376, 0.1908] [0.7937, 1.5874] [0.1908, 0.3150] [0.3969, 0.7937] [0.2752, 0.5000] [0.6300, 1.2599] [1.0000, 1.0000] [0.6300, 1.2599] [0.1733, 0.2752] [0.7937, 1.5874] [0.2184, 0.3969] [0.3969, 0.7937] [0.3150, 0.6300] [1.5874, 2.8845] [0.7937, 1.5874] [1.0000, 1.0000] [0.1733, 0.2752] [2.0000, 3.6342] [0.7937, 1.5874] [3.6342, 5.7690] [1.2599, 2.5198] [5.2415, 7.2685] [,3.6342 5.7690] [3.6342, 5.7690] [1.0000, 1.0000] [6.6039, 8.6177] [0.1376, 0.1908] [0.1376, 0.1908] [0.1733, 0.2752] [0.6300, 1.2599] [0.6300, 1.2599] [0.2752, 0.5000] [0.1160, 0.1514] [1.0000, 1.0000] table iv. integrated grey comparison matrix [0.2399, 0.2399] [0.1474, 0.2948] [0.1724, 0.3448] [0.1908, 0.2752] [0.1769, 0.2921] [0.1642, 0.2984] [0.1794, 0.3589] [0.1690, 0.2343] [0.0756, 0.1511] [0.0929, 0.0929] [0.1086, 0.2172] [0.0833, 0.1514] [0.0702, 0.1404] [0.0821, 0.1642] [0.0494, 0.0784] [0.1690, 0.2343] [0.0952, 0.1904] [0.0585, 0.1170] [0.1368, 0.1368] [0.1323, 0.2184] [0.1115, 0.2025] [0.1035, 0.2069] [0.1130, 0.2261] [0.1172, 0.1860] [0.0363, 0.0524] [0.0255, 0.0464] [0.0261, 0.0431] [0.0417, 0.0417] [0.0442, 0.0885] [0.0226, 0.0411] [0.0392, 0.0543] [0.0256, 0.0512] [0.0458, 0.0756] [0.0368, 0.0737] [0.0377, 0.0684] [0.0260, 0.0530] [0.0557, 0.0557] [0.0411, 0.0821] [0.0494, 0.0784] [0.0256, 0.0512] [0.0524, 0.0952] [0.0368, 0.0737] [0.0431, 0.0862] [0.0660, 0.1200] [0.0440, 0.0880] [0.0652, 0.0652] [0.0494, 0.0784] [0.0645, 0.1172] [0.1904, 0.3809] [0.3374, 0.5357] [0.1724, 0.3448] [0.2184, 0.3029] [0.2025, 0.3215] [0.2369, 0.3760] [0.2848, 0.2848] [0.2129, 0.2778] [0.0330, 0.0458] [0.0128, 0.0177] [0.0237, 0.0377] [0.0263, 0.0525] [0.0351, 0.0702] 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accepted: 17 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5852 abstract artificial intelligence (ai) is widely used in dermatology to analyze trichoscopy imaging and assess alopecia areata (aa) and scalp hair problems. from this viewpoint, the attention-based balanced multitasking ensembling deep (ab-mtedeep) network was developed, which combined the faster residual convolutional neural network (frcnn) and long short-term memory (lstm) network with cross residual learning to classify scalp images into different aa classes. this article presents a new data augmentation model called aa-generative adversarial network (aa-gan) to produce a huge number of images from a set of input images. the structure of aa-gan and its loss functions are comparable to those of standard gan, which encompasses a generator and a discriminator network. to generate high-quality aa structure-based images, the generator was trained to extract the 2d orientation and confidence maps along with the bust depth map from real hair and scalp images. the discriminator was also used to separate real from generated images, which were provided as feedback to the generator to create synthetic images that are extremely close to the real input images. the created images were used to train the abmtedeep model for aa classification. finally, the experimental results exhibited that the aa-gan-abmtedeep achieved 96.94% accuracy. keywords-artificial intelligence; alopecia areata; deep learning; data augmentation; gan i. introduction hair loss or scalp problems are usually caused by stressful situations [1]. nowadays, many individuals have scalp illnesses like psoriasis, baldness, etc., as a result of several issues, including bad daily routines, unequal weight growth, extreme weariness, and dangerous environments [2-3]. the function of iron and nutritional supplements in the diagnosis of baldness was examined in [4]. the most common kind of hair loss, known as alopecia areata (aa), affects up to 70% of men and 40% of women [5]. problems with scalp hair can be influenced by internal factors such as endocrine, hereditary, illness, and others. many cases of psoriasis, cellulitis, and associated signs and symptoms were reported in france [6]. according to many studies, psoriasis affects about 18% of children in the us and australia. as a result, both adults and children might experience scalp problems. therefore, it is important to know how to properly manage the scalp and prevent diseases linked to baldness. recently, specialized therapies have emerged to address severe scalp disorders [7]. the state of a patient's scalp is assessed manually in the most frequently used analytical processes for treating baldness. however, these manual diagnostic examinations can provide a wide range of findings and raise questions about the diagnosis and health of the scalp since they depend on the skills of the physiotherapist [8]. a substantial amount of effort and money have been invested in continuously developing physiotherapy skill sets [9]. another significant problem is the variations in how scalp hair microscope pictures should be interpreted, even among licensed and experienced physiotherapists. such discrepancies in medical interventions might be attributed to ignorance [10]. scalpeye [11] is a deep learning-based scalp identification system developed to overcome these issues. a minority of people experience a patch of hair loss, while other people report more severe or uncommon issues [12]. in recent years, numerous scalp and dermoscopic images have been employed in recognizing and diagnosing aa. trichoscopy and biopsies are frequently necessary to identify and diagnose aa as the reason for hair loss [13]. one of the main problems with these diagnostics is the number of tests required for a reliable engineering, technology & applied science research vol. 13, no. 3, 2023, 10895-10900 10896 www.etasr.com saraswathi & pushpa: the ab-mtedeep classifier with agan for the identification and … diagnosis. additional research on aa diagnosis and detection using ai methods, such as support vector machine (svm), artificial neural networks (anns), convolutional neural networks (cnns), and others, is highly encouraged [14]. according to this perspective, a correct diagnosis requires the simultaneous recognition of aa and scalp condition. to achieve this, an ensemble parameter optimized lstm-based pre-learned dl (epolstm-pdl) model, which combined lstm and pre-trained cnns such as alexnet, resnet, and inceptionnet was proposed in [15]. the pre-trained cnns were used to capture the deep features from the hair and scalp images, which were learned by the lstm network. the lstm’s hyperparameters were chosen by the battle royale optimization (bro) algorithm. but, if the network depth is increased, degradation problem occurrs causing overfitting. therefore, the attention-based balanced multi-tasking ensembling deep (ab-mtedeep) model was developed, which adopted cross-residual learning in the lstm with frcnn to improve efficiency [16]. however, the robustness and generalization ability of the deep learning models largely depends on the amount of data available in the training phase. according to this, it is essential to have an adequate number of images for efficient training. this paper proposes a new data augmentation model called aa-gan to generate a large number of images from given input images. the design and loss functions of this aa-gan are analogous to tose of the standard gan, which comprises both a generator and a discriminator. for real hair and scalp images, the generator was trained to reconstruct high-quality aa structure-based images according to the extraction of the 2d orientation and confidence maps, along with a bust depth map. moreover, the discriminator was used to distinguish real and generated images which were given as feedback to the generator to generate synthetic images very closer to the real input images. furthermore, the created images were used to train the ab-mtedeep model, which was used to classify the test images into different aa classes. thus, the aa-gan can increase the number of training images for more effective classification of aa conditions. ii. related works in [17], a novel data augmentation method was proposed, called random image cropping and patching (ricap), which randomly cropped and patched an input image to generate a new training image for cnn. also, the class labels of the actual images were mixed to gain the benefit of soft labels, however, it needed to choose the appropriate hyperparameters for effective performance. in [18], the presented stylegan was used to generate high-quality nodule images fed to the transfer-resnet50 to classify tumors, but it needed further enhancement in the diversity of the created images. in [19], an enhanced framework of gans (ef-gans) was designed for vgg16, integrating geometric transformation schemes and gans for image augmentation. in [20], the self-attention progressive growing of gans (spggans) was proposed to create more fine-grained nodule scans by fusing details from all feature positions, and the two-timescale update rule (ttur) was applied to enhance the model's robustness. in [21], the zero shot augmentation learning (zsal) framework was presented for health signal processing. initially, the contour of a lesion was recognized by a skilled physician, and a background image without a lesion was chosen. in [22], a novel inception-augmentation gan (iagan) was proposed to create new x-ray scans that could help detect pneumonia and covid-19. in [23], a generic adversarial data augmentation model called advchain was proposed to enhance the diversity and efficiency of learning data for medical image segmentation. in [24], a new model called xtremeaugment was developed for labeling and augmenting images, using hardware dataset augmentation (had) and object-based augmentation (oba). the had was used to enable users to acquire more data, whereas the oba was used to increase the training data variability and maintain the distribution of the augmented images being similar to the actual data. but, this approach needed annotated images for efficient training and was not effective with very limited images. iii. proposed methodology figure 1 presents an overall schematic of the proposed aagan. fig. 1. schematic representation of the proposed study. a. image collection this system used the following 2 openly accessible datasets for analysis:  figaro1k dataset, which is a public dataset enclosing 1050 hair photos, evenly allocated into distinct types like straight, wavy, and curly [25].  dermnet dataset, which is a public dataset accessible on dermnet [26], enclosing 23 types of dermatological illnesses with aa. overall, 108 photos were obtained for 3 distinct aa types: mild, moderate, and severe. figure 2 shows a few examples of scalp hair photos in multiple labels from the given databases. engineering, technology & applied science research vol. 13, no. 3, 2023, 10895-10900 10897 www.etasr.com saraswathi & pushpa: the ab-mtedeep classifier with agan for the identification and … normal (0) mild aa (1) moderate aa (2) severe aa (3) fig. 2. scalp hair photo examples of the dermnet and figaro1k databases. b. data preparation for aa-gan a fused model space was initially defined to create the training dataset. at first, a bounding box was defined as the boundary of the model space, where the ground-truth 3d hair orientation volume was generated and 2d hair orientation and confidence maps were extracted. bounding box: the model space was constrained by a bounding box defined by the bust model and each hair model of the dataset, excluding a few extremely long hairs. after that, a 3d volume with a resolution of 128×128×128 was split in the bounding box. 2d capture: to obtain 2d information maps x under the defined model space, the center of the image plane matched with the center of the bounding box. the 2d image was obtained by orthogonal projection with a scale of 1024/h. so, the dimension of the obtained image was 1024×1024. after that, the dataset was doubled by flipping all models, and constrained hairstyles such as braids and bounds were eliminated. in the considered dataset, 1050 hairstyles were available, which differ from straight to curly and short to long. the hair around the center of the bounding box was rotated arbitrarily. the rotation ranged from -15° to 15° for the x-axis, -30° to 30° for the y-axis, and -20° to 20° for the z-axis. as each dataset model was prepared by polygon strips, they were transformed to a dense 3d orientation volume viewed as the ground truth y and grew strands later. afterward, the hair strands were rendered to the 2d image at the camera view pose. additionally, the bust model was considered a condition for aa-gan because hair grows on the scalp and circulates the body. the bust depth map was determined by ray tracing, pixel by pixel, to obtain the distance from the bust to the camera, and the distance was split by d to vary the value within [0,1]. finally, the network input x was created using the 2d orientation map, confidence map, and bust depth map. every 2d map was valued within [0,1] and the 3d and 2d orientation vectors were encoded in color space. for all dataset models, n pairs of x and y were determined as training data. c. design and training of alopecia areata – generative adversarial network with the 2d maps and the bust depth map captured from the input image, aa-gan aimed to create a 3d orientation volume encoding both occupancy and orientation data to guide the aa scalp hair image augmentation. the input of the network was a 2d tensor x with a dimension of 1024×1024, consisting of 4 feature channels, which were acquired in the unified model space: hair orientation map (the 2d direction vector xy encoded as the color of rg), confidence map (the confidence value as the color of gray), and bust depth map (the depth value as the color of gray). the output was a 3d tensor y of dimension 128×128×96, where the hair orientation vectors were encoded in rgb. 1) loss functions the gan is trained by the game-theory approach between the generator and discriminator. the aim was to train the generator g(x) that maps the input 2d tensor to a required output 3d tensor �� : �� = ����. meanwhile, the discriminator maximizes the wasserstein-1 distance between the generator distribution of g(x) and the target distribution of y with a conditional latent projection p(x). the objective of the discriminator is to reduce the loss as: = � � ��� , ������ − �� ��, ������ + �� ���∇�� ��� , ������� − 1� � (1) where the third term is the gradient penalty for random samples �� , that �� ← "� + �1 − "��, and " is a random number in [0,1]. the coefficient � was set to 10, ��∙� is the cnn to map 2d tensor � into a 3d latent space to be combined with � or �� , and the parameters in ��∙� are trained along with those of . similarly, the loss function for a generator is described by: = −� � ��� , ������ (2) this function does not perform well to fine-tune the generator, because the distribution variance between the actual and the counterfeit cannot be simply calculated by the plus or minus signs. according to the fact that only selected layers of pre-learned networks are used as feature representations to transfer texture style from a source to the target image, the losses of style and content were adopted, where the features were defined in the domains of selected discriminator layers. so, the objective of fine-tuning the generator was to reduce the loss: $∗ = & '()*+)* + , -*./+ = & ∑ '()*+)*// + , ∑ -*./+// (3) where α and β are the weighting factors. the content loss was taken as the square-error loss between feature representations: '()*+)*/ = 2� ∑ �345 / ��, ����� − 345/ ��� , ������ � 45 (4) engineering, technology & applied science research vol. 13, no. 3, 2023, 10895-10900 10898 www.etasr.com saraswathi & pushpa: the ab-mtedeep classifier with agan for the identification and … where l is a selected layer, i is the i th feature map, k is the index in the feature tensor, and f describes the discriminator features. the style loss is defined by the mean-squared distance between the gram matrices, where all elements were computed by the inner product between the vectorized feature maps i and j: 647/ = ∑ 345/ 375/5 . the objective was: -*./+/ = 289:;<:; ∑ �647 / ��, ����� − 647/ ��� , ������ � 47 (5) where nl was the number of feature maps and ml was the size of feature tensors. 2) design table i shows the generator and discriminator structures. the following notations were used to define the structure of the proposed aa-gan: the input and output data fo the processing units are in(resolution, feature channels) and out(resolution, feature channels), c(input channels, output channels, stride) is the convolutional layer with a relu activation, = is the dimensional expansion layer, and ζ is the fully connected node. also, + was used as the element-wise addition in the residual blocks created by c, and i was the input tensor of the current layer. for each 2d convolutional layer c2, the filter size was 5 and 3 for each 3d convolutional layer c3. the processing units for x-, y-, and z-info contain similar strategies. table i. generator and discriminator structure generator >?�1024 × 1024,4� ⇐ � e��4,16,2� + ge� �4,8,2�, e��8,16,1�i e��16,64,2� + ge� �16,32,2�, e��32,64,1�i e��64,256,1� + ge��64,128,2�, e��128,256,1�i l + ge��256,256,1�, e��256,256,1�i mno�128 × 128,256� x-, y-, z-blocks >?�128 × 128,256� l + ge��256,256,1�, e��256,256,1�i l + ge��256,256,1�, e��256,256,1�i e��256,128,1� e��128,96,1� = mno�128 × 128 × 96,1� concatenation of the qrs from x-, y-, z-blocks >?�128 × 128 × 96,3� l + get�3,3,1�, et�3,3,1�i l + get�3,3,1�, et�3,3,1�i mno�128 × 128 × 96,3� ⇒ �� d is c r im in a to r v�∙� block >?�1024 × 1024,4� ⇐ � e��4,32,2� e��32,64,2� e��128,96,1� = mno�128 × 128 × 96,1� concatenation of wx/w with v�z� >?�128 × 128 × 96,4� et�4,32,2� et�32,64,2� et�64,128,2� et�126,256,2� et�256,512,2� [ generator: the initial block with input x, consisting of 4 residual network elements-wisely adding activation from the previous layer to successive layers to obtain a residual correction from highto low-level data, downsamples feature maps to a latent code from 1024×1024 to 128×128, along with the number of features increasing from 4 to 256. after that, x-, y-, and z-blocks independently encode the latent code to features with 96 channels and the resolution along the z-axis in the resulting volume. as well, = transforms the series of 2d features into a single channel of 3d features. then, the output from x-, y-, and z-blocks are concatenated and given to the following 3d residual convolutional networks. discriminator: considering the correspondence between the 2d input � and the 3d desired output �� /�, the latter was concatenated with ���� , a feature map encoding � to a 3d latent space with a similar resolution as �� /�. subsequently, the concatenated 3d feature tensor was convoluted by several filters until the layer of ζ to finally differentiate the actual and τηε counterfeit. 3) learning policy the two-timescale update rule was applied to optimize the discriminator only once rather than many times, increasing time efficiency. the adam optimizer was applied with ,2 = 0 , and ,� = 0.9 for training. the training rate for the discriminator was set at 0.0003, and 0.0001 for the generator. this proposed aa-gan was designed to create a 128×128×96 3d volume encoded in both the occupancy and orientation fields, utilizing 2d maps as input with a size of 1024×1024. the batch size for learning was set to 5. for the generator objective, the style and content weighting factors were set as: & = 1] − 2 and , &^ = 5] + 2. the selected layers for content loss were 0, 3, 6, and l=0,1,2,3,4 for style loss. if l=0, p(x) was eliminated from '()*+)*_ and -*./+_ . thus, by training the aa-gan, more training images were generated and used to train the abmtedeep classifier model. the trained classifier was applied to classify the test images into the mild, moderate, and severe aa classes. iv. experimental results the effectiveness of the aa-gan-ab-mtedeep model was assessed and compared with the ones of existing models by implementing them in matlab 2017b using the figaro1k and dermnet databases. of the images collected, 70% was used for training and the remaining 30% was used for testing. the considered existing models were the ab-mtedeep [16], ricap-cnn [17], ef-gan-vgg16 [19], and iagan [22], which were applied to the figaro1k and dermnet databases for the aa classification, using the same proportions for the training and testing of the models. figure 3 shows the generator and discriminator loss curves in the aa-gan model, while figure 4 depicts the training progress of the aa-gan-abmtedeep model for aa classification. table ii presents the confusion matrix for the aa-gan-ab-mtedeep model for testing, and table iii presents the performance results of the models for aa classification. figure 5 illustrates the accuracy values of various data augmentations with classification models on the dermnet and figaro1k databases. the accuracy of the aa-gan-abengineering, technology & applied science research vol. 13, no. 3, 2023, 10895-10900 10899 www.etasr.com saraswathi & pushpa: the ab-mtedeep classifier with agan for the identification and … mtedeep was 17.6% higher than ricap-cnn's, 14% higher than the ef-gan-vgg16's, 8.6% higher than the iagan's, and 1.9% higher than that of the ab-mtedeep model. this is due to the augmentation of the number of training images to create an effective classification model. fig. 3. loss curve for generator and discriminator during training. fig. 4. training progress of the aa-gan-ab-mtedeep model for aa classification (training accuracy curve and loss curve). table ii. confusion matrix of the aa-gan-abmtedeep testing actual classified classes 0 1 2 3 0 29 0 1 0 1 0 7 0 0 2 1 0 9 0 3 0 0 0 9 table iii. performance analysis for the aa classification models on figaro1k and dermnet metrics ricap -cnn ef-ganvgg16 iagan abmtedeep aa-ganabmtedeep precision (%) 81.48 84.05 88.19 94.06 95.8 recall (%) 82.22 84.68 88.46 95.3 96.8 f-measure (%) 81.85 84.365 88.325 94.68 96.3 accuracy (%) 82.31 84.86 89.22 95.11 96.94 fig. 5. accuracy of aa-gan-ab-mtedeep and existing models. v. conclusion this study presented the aa-gan model designed to generate a large number of training images for aa classification. in this model, the structure and loss functions were similar to those of the standard gan, which involves the generator and the discriminator network. the generator network was trained to create high-quality images based on the aa structure by retrieving the 2d orientation and confidence maps, along with the bust depth map from the original hair and scalp images. the discriminator was trained to distinguish original from synthetic images, which was given as feedback to the generator for minimizing its error. furthermore, the generated synthetic images were used to train the abmtedeep model for aa classification. the test results showed that the aa-gan-ab-mtedeep had a 96.94% accuracy, which was higher than the ones of the other variants of gan with the ab-mtedeep model to classify aa and scalp conditions. in the future, hybrid deep learning models with hyperparameter optimizers can be developed to improve aa classification performance. references [1] k. york, n. meah, b. bhoyrul, and r. sinclair, "a review of the treatment of male pattern hair loss," expert opinion on pharmacotherapy, vol. 21, no. 5, pp. 603–612, mar. 2020, https://doi.org/10.1080/14656566.2020.1721463. 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[26] "dermnet skin disease atlas," dermnet | dermatology resource. https://dermnet.com. microsoft word etasr_v12_n4_pp8982-8989 engineering, technology & applied science research vol. 12, no. 4, 2022, 8982-8989 8982 www.etasr.com mahmoud: overview of green roof technology as a prospective energy preservation technique in … overview of green roof technology as a prospective energy preservation technique in arid regions abubakar sadiq mahmoud safety technology program dammam community college king fahd university of petroleum & minerals dhahran, saudi arabia mahmouds@kfupm.edu.sa received: 15 march 2022 | revised: 12 june 2022 | accepted: 20 june 2022 abstract-concerns about climate change and rising energy demands have grown as a result of fast population rise and global industrialization. the construction industry has a huge impact on the energy and environmental sectors, accounting for about 40% of global energy consumption and a large portion of overall territorial emissions. there is a need for a shift in mindset when it comes to energy usage, as well as enhanced energy efficiency approaches and radical energy efficiency initiatives. as an energy-saving solution, the green roof, also known as the living roof has suitability and environmental benefits on many levels, while also strengthening aesthetic features and provoking structural innovation. moreover, drought-prone areas, e.g. saudi arabia, have significant household energy demands. the saudi building sector consumes more than 76% of the country's total electric power generation. as a result, the purpose of this study is to provide a general overview of living roof technology and its potential in saudi arabia as an energy-saving strategy. an overview of the building envelope, the impact of cladding design considerations on power usage, the benefits of a living roof, costbenefit analysis, green policies, and examples from other countries are included in the paper. other environmental benefits, besides the energy-saving potential of living roofs, were shown to boost the quantitative benefits of the living roof idea. a more detailed study is needed, among other things, to evaluate the energy-saving potential of living roofs based on the weather of various locations. keywords-sustainability; energy performance; living roof; energy saving potential; building insulation i. introduction the world's growing economy has inevitably resulted in increased energy demands for corporate, industrial, residential, and transportation purposes [1], while concerns regarding the environmental impact of increased energy demands have surfaced. some climate-related issues, such as zero-energy buildings, global warming, and greenhouse gas emissions, are gaining increasing attention [2-3] according to [4], energy consumption went up drastically from 4,674 mton in 1971 to 8,918 mton in 2011, with non-renewable fuels including oil, natural gas, and coal accounting for the majority of this increase [5]. according to statistics, the middle east consumes the most energy, with 33 of 4,674 million tons of oil equivalent (0.7%) in 1971 and 224 million tons of oil equivalent (4.8%) in 2011. fossil fuels are the region's principal energy source. in 2015, almost 200 countries signed a climate deal in paris under the auspices of the united nations framework convention on climate change (unfccc) in a serious effort to phase out the use of fossil fuels. as a result, it is vital that the rapidly developing gcc countries invest what they have in order to develop energy sources that will be sufficient in the long-term. when it comes to overall development and economic size, the kingdom of saudi arabia is the largest country in the middle east, and its housing sector has seen an increase in energy demand from 2000 to 2014, that is estimated to be over 100%. according to [6], buildings that are used for residential purposes consume almost half of the total energy output. as a result, the construction industry has a significant demand for energy. to satisfy this rising need for energy, better ways must be developed to lower the amount of energy consumed by buildings, which can be accomplished by utilizing living roofs to improve energy efficiency [7]. apart from the positive effects on the environment and its long-term viability, the usage of living roofs improves the architectural and aesthetic appeal of buildings. this approach of energy saving has been recognized internationally [8, 9]. the living roof offers the advantage of maintaining a balanced environment and temperature stability [10]. however, despite its benefits in terms of energy saving, it is not as extensively used in the high-energy-demanding middle east as one might expect. this could be due to the lack of scholarship and high upkeep costs [11]. the living roof has received commercial interest because it offers answers to some of the most pressing issues regarding energy and the environment. furthermore, an architectural model of a structure in the middle east has not been developed with a clear plan on how to apply a living roof [5]. it is clear that the middle east has not received adequate empirical research on this topic. as a result, a full study through research is required in order to investigate the possibilities of the living roof technology in relation to the hot saudi weather in order to have a strong grasp of the living roof as a response to the topic of energy consumption. corresponding author: abubakar sadiq mahmoud engineering, technology & applied science research vol. 12, no. 4, 2022, 8982-8989 8983 www.etasr.com mahmoud: overview of green roof technology as a prospective energy preservation technique in … ii. methodology to achieve the purpose of this paper, extended literature review was conducted that looked into the use of living roof technology around the world and the long-term viability of its use in the desert climate of saudi arabia. the study would be of tremendous importance to the arid regions because it attempts to examine solutions to reduce high energy usage and its hazardous environmental consequences on structures. an assessment is provided that contains a broad description of the building envelope system and the effects of envelope design considerations on the structure's energy consumption. the advantages of a living roof, the estimated costs, and the green regulations from sampled countries are provided. finally, the article draws some conclusions and offers some recommendations regarding the arid regions. iii. the building envelope a. overview buildings consume roughly one third of global energy and nearly 40% of all assets used [13, 14]. the bad and good ecological effects of the technology on buildings have been discussed. authors in [11] indicated that the yearly direct and indirect ecological effects of the industry of building comprise 42% energy use, 40% emissions to the atmosphere, 30% unprocessed use of materials, and 25% water consumption. in addition, the energy supplied is less than the demanded energy due to population growth and globalization. therefore, efforts are ongoing to conserve and maximize energy [15]. the reduction of the overall energy use in the course of buildings' life span through good use of the building envelope is one of the efforts employed [16]. a building envelope shields a building's interior environment from the outside hostile environment. thermal comfort (temperature and humidity control), visual comfort (natural light regulation), and acoustic comfort (noise control to acceptable levels) are a few of the building envelope's tasks [3]. the building envelope's responses to heating, cooling, ventilation, and regular lighting requirements are critical in evaluating the envelope's efficiency in reducing energy usage. in this context, building envelope materials with high evapotranspiration and thermal emissivity are good passive cooling energy demand reduction solutions. the overall thermal gain to a building is governed by the uvalue, which is controlled by the materials used and the design of various elements of the building envelope, and can range from 40 to 45% of the total heat load [17]. the primary goal is to reduce transmission of heat loads in order to save considerable amounts of energy. authors in [16] looked into the impact of construction materials, thermal insulation, and envelope layer layout as solutions for lowering building energy usage. the heat resistance of a roof can be increased by 0.4m 2 k/w for every 10cm increase in thickness when the substrate layer is made of clay [18]. in [19], the effects of different thicknesses of building insulation on thermal performance in hot, dry areas, were evaluated. when thermal shielding is installed on the exterior of the building envelope, the study found that significant energy savings can be achieved. in their investigations of level roof surfaces in the harsh weather of the kingdom of saudi arabia, authors in [6] advised the use of lighter surface colors for roofs. authors in [20] assessed up to 6 distinct types of roof structures, in riyadh, saudi arabia. to improve heat efficiency, the insulating layer should be placed closer to the inside surface of the roof structure, according to this study. b. variables in envelope design and their effect on energy consumption 1) insulation the most significant aspect in decreasing building energy use and ensuring acceptable indoor environmental quality is heat insulation [18]. due to its thermal qualities, the exterior of the building envelope is vulnerable to the outside environment, posing a significant danger of heat gain or loss [21]. thermal insulation reduces the need for heating and cooling and the risk of fire [22]. with walls and roofs forming practically a unitary portion of the building's envelope, the probability of absorbing or losing heat increases, thus, the envelope should have some heat insulation [5]. thermal insulation prevents heat from moving through channels of conduction, convection, and/or radiation. climate, environmental impact, indoor air quality (iaq), thermal conductivity of the components, economic implications, specific heat capacity, fire resistance, sound impacts, density, and other factors are all taken into account when selecting the appropriate insulating materials [23]. 2) thermal mass thermal mass is essential for reducing building energy costs, which can be accomplished by making hvac systems smaller. thermal mass also reduces peak load shift conditions and total heat yield or loss, resulting in a smaller hvac system and lower overall building energy expenditures [2]. the absorption and subsequent release of heat as needed is characterized by the thermal mass (also known as thermal lag). this is because the materials need time to absorb, store, and then release heat [24]. thermal mass is best placed on the first floor for easy heat release and absorption since it absorbs and then releases heat effortlessly [25]. 3) lighting climate consideration in eco-friendly design has numerous advantages. regarding lighting, orientation is important. the requirement for electric lighting can be considerably reduced by using proper building architecture and orientation while also boosting occupant satisfaction, which can be achieved by varying the direction of apertures [26]. the planned space use, the lighting equipment required, the occupants' living style, and window placement in relation to the sun's path, are all important considerations in lighting design. energy-saving bulbs, smart technologies, dimmer switches, automation techniques, motion detectors, and compact fluorescent lights (cfls) can all help minimize lighting energy use [27]. 4) orientation orientation is an important consideration in building design, because it ensures the optimum use of solar energy depending on a site's geographical axes and the earth's axis. when the envelope's thermal performance needs to be improved, the conductive heat flow must be restricted. to do so, the building's form factor, also known as the building shape engineering, technology & applied science research vol. 12, no. 4, 2022, 8982-8989 8984 www.etasr.com mahmoud: overview of green roof technology as a prospective energy preservation technique in … [28], is taken into account. because of the forms' intricacy, they may produce leaks by exposing a portion of the structure to the outside environment. as a result, compatibility must be established in order to reduce surface area and thus reduce the risk of heat absorption or loss. corners should be avoided as much as possible by maintaining tight compactness [25]. the window-to-wall area ratio should be examined in order to create a window that is suited for a specific orientation. the floor-to-envelope area ratio should also be investigated in order to increase floor area relative to the envelope area. to fit the windows, the best elevation must be chosen. when compared to heights in the east and west, a rising window-to-wall area ratio can favor the southern elevation [6]. outside, shading mechanisms should also be built to minimize solar gain during the summer and ensuring it during the winter when the sun is low [6]. to reduce solar energy acquisition in the summer, minimum window-to-wall area ratio could be situated on the eastern and western elevations. because it is not exposed to direct sunlight, the north elevation is important for daylighting [29]. 5) occupants’ contribution depending on the type and intensity of occupant activities, vapor discharge has a significant impact on the energy usage of a residential building [30]. occupant actions, according to a study conducted in the netherlands, can result in a 4.2% increase in power use, whereas individual residents' behaviors may have a significant impact on overall energy usage [2]. iv. the living roof a. overview according to [31, 32], living roofs are becoming more popular globally. the living roof is a construction made of composite materials [18]. soil is transported onto a roof coated with a waterproofing layer [23]. the inner source (root) obstacles are above them, accompanied by a runoff cover (with adaptable profile element) that directs excess release to roof drains and provides water storage for planting during dry periods. a living roof can also be built by hoisting previously established plants with mechanical means. the growing medium has the benefit of being easily removed in the event of leaching or maintenance work due to its off-site prefabrication [33]. living roofs have specific sections designed to keep the roof drainage system in good working order. roots and natural materials must be kept out of the drainage pathway to ensure that it functions properly [34]. living roof frameworks also improve the total insulating value of the roof system because they are used in conjunction with the basic material used in traditional roof systems. living roofs have many advantages, including cost saving, energy conservation, and aesthetic appeal [11]. the substratum layer of the living roof plays a big role in this [35]. the plant layer, for example, has some aesthetic value and might also be used as a green product source [36]. physical qualities of plants have an impact on their contribution to the environment [37]. a study of the ability of 5 plant species (sedum pachyphyllum, sedum clavatum, sedum spurium, disphyma crassifolium, and carpobrotus modestus) to withstand multiple dry period treatments (wet and non-wet) discovered that a living roof layer of diverse plant species was more effective in terms of its capacity to withstand multiple dry period treatments (wet and non-wet) [38]. b. advantages of the living roof technology 1) energy saving potential living roofs are designed to reduce the amount of direct and dispersed radiation striking the roof, saving large amounts of energy [23, 39]. incorporating living roof technology into buildings resulted in a total energy decrease of 17%, according to a research conducted in jordan [1]. similarly, based on the soil density and thermal pressure, a study comparing the energy saving potential of living roofs with typical roof systems in egypt's desert climate indicated that yearly power savings of 15-32% can be reached [40]. energy savings of 48% for retrofitted/insulated roofs (u-value of 1.99w/m 2 .k) and 7% for moderated insulation (u-value of 0.8w/m 2 .k) were discovered in an analysis conducted in athens using trnsys software [41]. in schools and buildings with living roofs in mediterranean climates, significant energy savings between 6 and 49% have been seen [42, 43]. 2) influence of living roofs on indoor environmental quality the energy savings from a living roof contribute directly to lower interior temperature maintenance cost [44]. according to a study in germany that compared living roof technology to a common roofing structure, living roofs improve the internal climate of buildings [45]. it was found that living roofs reduce the temperature of the roof top and improve the inside environment of building structures. 3) environmental benefits of the living roof authors in [25] revealed that storm water management is one of the environmental advantages of living roofs. rainwater runoff from vegetated roofs could be reduced by up to 40%. according to a study conducted in singapore [5], living roof technology was able to lower the maximum flow by 65%, while saving overall runoff by 11.6% during peak strength rainfall (1mm/min). the study also found that living roofs can reduce surface heat by 7.3 degrees, extending the life of roof membranes. when factory and car emissions travel through the plant foliage/leaf index, air pollution is minimized, particularly for extensive living roof systems (trees and shrubs) [37]. living roof technology may be used to enrich urban areas, giving a home for birds and insects while also maintaining indigenous species. living roofs also have the benefit of reducing the heat island effect. on the temperature differential between position roofing and traditional roof surfaces, a medium of 20°c was recorded in [34]. vegetated envelopes are more favorable in hot and sunny locations, according to [17], because the temperature of urban heat can be reduced. 4) cost-effectiveness analysis without a cost-benefit analysis, the benefits of the proposed sustainable measures cannot be assured. a plan that has a higher cost than its benefit cannot be considered feasible. the cost-benefit analysis is a method for weighing the benefits of various solutions while accounting for the total cost of implementation. it is the basis for making decisions that benefit the economy [12]. the net present value (npv) is a common method for determining a system's current benefit after it has engineering, technology & applied science research vol. 12, no. 4, 2022, 8982-8989 8985 www.etasr.com mahmoud: overview of green roof technology as a prospective energy preservation technique in … been constructed and utilized for a period of time [46]. if the npv of an investment is greater than zero, it could be realized. when making a comparison of various options, choose the one that has the largest npv. the following equation is used to calculate the npv [47, 48]: 0 1 (1 ) n t t t f npv c p = = − + +  (1) where t refers to the time period, which is commonly calculated annually, ft is the net cash flow for year t, calculated using the formula ft = bt ct. the advantages or benefits accumulated for the year t are represented by bt. the cost outflows for year t are represented by ct. c0 denotes the initial investment (including all funds spent on items as well as installations). the cost of capital is denoted by the letter p. the number n denotes the number of years for which a financial evaluation needs to be done. 5) cost of green roof installation the value of a living roof system is determined by several elements, including the growing medium, material layer, seepage structure, barrier or palings use, and the quantity of plants. according to [49], the low-cost, largest living roof costs $10 per square foot (0.09m 2 ), whereas in-depth living roofs cost $25 per square foot [50, 51]. in germany, living roof prices range from $8 to $15 per m 2 . because of the manufacturers' business interests and experience, the cost in the united states may be higher [52]. local sources in saudi arabia estimate the cost to be $9 per square foot. as a result, it is possible to estimate that the prices will range from $8 to $25 per square foot. 6) maintenance cost the maintenance cost makes up a major amount of the total cost of such a system. the type of vegetation utilized determines the cost of maintaining living roofs, which is higher in the first year of operation as the living roofs mature. these prices might range from $0.75 to $1.50 per square foot [48]. local costs are expected to be roughly $0.23 per square foot in saudi arabia. 7) cost due to increased property value property and company owners gain from regular landscaping since their properties' market values rise, although no direct link has been shown between the presence of green rooftops and the property value. anyhow, if a structure is located near a forest spread, its market value could be improved by 7.1% [53]. the purchase of trees/greenery could improve the overall value of properties by 15% to 25% [53]. 8) cost due to longevity benefit green rooftops have an average lifespan of 40 to 55 years [12], while regular rooftops have an average lifespan of just approximately 20 years [25]. the cost of re-roofing a conventional roof is projected to be up to $160 per m 2 [5]. furthermore, the ability of diverse plants to convert oxygen to carbon dioxide varies. previous studies have found that 1 hectare of living roofs may remove up to 72kg to 85kg of pollutants [55]. the cost of reducing carbon emissions can be as high as $20 per ton [54]. 9) reduced cost as a result of better air quality reducing the effects of urban heat islands green rooftops are viewed as both an air pollution remover and a source of innovation [55]. the quality of the air is defined by measuring dust, particles, and nitrates (no2), with a cost of $3375/ton gained owing to nox gas losses in the atmosphere [56]. in addition, natural habitat creation and protection are critical in reducing the negative effects of urban environments [57]. green rooftops use plants and soil to replace traditional rooftops, attracting insects such as butterflies, birds, bugs, and honey bees [58]. in the summer, the combination of dull surfaces and the lack of vegetation cause increase in urban air temperature [59]. because of the use of hvac systems, an increase in temperature causes an increase in energy demand [59]. authors in [60] discovered that for every 1°c increase in temperature, power demand increases by 2% to 4% in 6 u.s. metropolitan areas. heat island effect increases power consumption by up to 1gw 1.5gw annually in the los angeles basin [44]. 10) global policies on living roofs (case studies) several cities give incentives in the form of grants to property owners who want to establish green spaces on their roofs, in order to encourage both commercial and residential owners to undertake arrangements for more green spaces on their roofs. singapore, for example, has developed a thorough program to promote rooftop greening in order to fulfill a target of 50 hectares of new skyrise greenery area by 2030. the creation of a roof floor incentive program, the allocation of city gardens, and technical consultation are all part of this [61]. the program also includes a monetary recompense for sustainable landscaping of current building structures in regions with a higher need for green spaces, and remuneration for new construction project designation of living roofs [49]. portland, located in the northwest of the usa, favors living roof strategies due to the benefits of sustainably managing rainfall [11]. germany discovered that light modifications of green rooftops can assist energy conservation. green roofing is now used in many german cities. this strategy is backed up by accepted design standards and legal backing. as of 2005, germany had planted 13.5 million m 2 of roof spaces [54, 62]. munich, the bavarian regional capital (germany), is implementing a variety of living roof-related initiatives [63]. such approaches include land use management rules, start-up grants for voluntary living roof construction, and a reduction in storm water levies [64]. living roofs are particularly wellknown in munich. thanks to a 14-year-old legislation requiring all appropriate roofs of any flat with a surface area greater than 100m 2 to be landscaped. japan began with a light-hearted stimulus program that included free consultancy services. following that, a subsidy program was implemented, resulting in the installation of 7000m 2 of living roofs. worries about the environment's impact on buildings led the authorities to enact a regulation requiring construction works greater than 10,000 square feet or government buildings bigger than 25,000 square feet to landscape the 20% of the roof surface, or risk annual fines [24]. from these instances, it is clear that many cities are engineering, technology & applied science research vol. 12, no. 4, 2022, 8982-8989 8986 www.etasr.com mahmoud: overview of green roof technology as a prospective energy preservation technique in … employing a variety of hybrid strategies to promote living roofs, even though there are differences in nature and equipment, as well as institutional inequities. the ultimate purpose of city living roof initiatives is to maximize any positive impact by utilizing human and financial resources as efficiently as possible. 11) building energy modeling programs (bemps) computer simulation is a highly valuable and cost-effective technique for estimating and analyzing energy usage and overall building efficiency [65]. since 1960, hundreds of building energy modeling programs (bemps) have been developed and implemented all over the world [66]. wellknown bemps include esp-r, tas, trnsys, beopt, ecotect, ies virtual environment, equest, and design builder [67, 68]. aed is becoming increasingly reliant on technologies that can answer particular queries during the design phase. furthermore, aed can predict a building's thermal behavior before it is constructed [65]. it can model energy costs in new and old buildings in their existing state, determining the best way to use energy. a non-technical profession would benefit from an essay detailing how to use software interface. it should include enough depth to conduct research [69]. to take advantage of the benefits of other programs via data-sharing file formats, inter-software operability is also required [70]. it is vital for credibility to demonstrate conformance with criteria used in similar building performance studies. it is vital to utilize an appropriate instrument in performance analysis to ensure the functioning and capabilities of software [14]. there are a variety of software options available, each with its own set of features. the researcher's user choice condition suggests its capabilities to be toned down [68]. 12) software package comparison many simulation programs have been developed over the few previous decades. this is evident from the us department of energy's homepage dedicated to generating energy simulation software tools, which lists over 240 such programs. the tools on the site range from research-grade software to commercial versions. many studies and comparative assessments were conducted to analyze the elements and capabilities of some of the instruments in this group. authors in [71] proposed evidence-based validation, comparative study, and analytical verification as methods for ensuring the accuracy of construction energy devices. following a series of testing and validations, energy plus was found to work with the doe2.ie, esp-r, and blast simulation tools. authors in [66] used energy plus to construct and test a vrv air conditioning system that is empirically connected to a new simulation unit. the monitored simulation data revealed a total energy cooling and utilization range of 25.19 to 28.3%. by comparing the building energy performance simulation program to other readily available building energy programs, a complete assessment of the program's capabilities may be established [72]. the comparison is based on general modeling descriptions, zone loads, building envelopes, hvac systems, economic analysis, emissions, electrical systems, and electrical equipment. some of the most commonly used comparison programs include bsim, blast, dest, ener-win, energy – 10, energyplus, equest, ida ice, esp-r, ies ve>, trace, trnsys, tas, sunrel, heed, powerdomus, and hap. authors in [72] investigated 6 building performance simulation tools in order to provide early design support to architects. a set of criteria was used to evaluate the simplicity of use of numerous tools. furthermore, none of the tools were deemed appropriate for use by architects. according to them, designbuilder stood out because it provides a graphical user interface for energyplus, a well-known energy modeling program. authors in [67] used an online poll to assess the usability of 10 distinct architectural tools. heed, equest, ies /ve, greenbuilding studio, ecotect, design builder, energy – 10, doe 2. ie, sketch up plug-ins, and energyplus each had 249 valid results when these tools were considered. the program was evaluated on its usability, information management (uim), and connection with the intelligent design knowledge base (iikb). the study found that iikb had a stronger preference for tool interfaces than uim. v. conclusions a description of living roof technology as a means of energy preservation is provided in this paper. the goal of the literature review is to emphasize the theoretical foundations for the subject as well as the potential benefits and economic implications of green roofing solutions. the literature review demonstrated that one of the most important benefits is determining the level of sustainability required by the construction industry in hot and arid climates. furthermore, when alternative software was examined, it was found that designbuilder and energy plus have greater capability for analyzing various energy conservation measures, including the green roofing model. the proper paradigm for living roof implementation is in the design of buildings with decked roofs, as is the case in saudi arabia. hot weather and energy cost may pose challenges for the implementation of sustainable techniques such as living roofs, but a gradual and steady shift is underway. according to saudi vision 2030, a recently created strategic policy framework, attempts are being made to eliminate more than 200 billion saudi riyals in energy subsidies by 2030. however, the advancement of living roof technology depends on a number of factors, one of which is the importance of living roof policies. results and case studies from various cities around the world show that a lot of work was put into advocating ideas for adapting and modifying green roofing to meet local conditions. aside from the energy saving potential of living roofs, there are other, environmental advantages in their utilization, such as heat island abatement, habitat creation, increased property value, improved air quality, increased roof membrane longevity, and reduced carbon emissions. vi. recommendations the following suggestions are provided to guide future research: • comprehensive investigation into the energy-saving possibilities based on meteorological data from diverse places will go a long way toward proving the claim of the prospective advantages this technology could 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[72] l. weytjens, s. attia, g. verbeeck, and a. de herde, "the ‘architectfriendliness’ of six building performance simulation tools: a comparative study," international journal of sustainable building technology and urban development, vol. 2, no. 3, pp. 237–244, sep. 2011, https://doi.org/10.5390/susb.2011.2.3.237. microsoft word etasr_v13_n1_pp10021-10026 engineering, technology & applied science research vol. 13, no. 1, 2023, 10021-10026 10021 www.etasr.com adware & chandrakar: power quality enhancement in a wind farm connected grid with a fuzzy … power quality enhancement in a wind farm connected grid with a fuzzy-based statcom ramchandra adware department of electrical engineering, g h raisoni college of engineering, india ramchandra.adware@raisoni.net (corresponding author) vinod chandrakar department of electrical engineering, g h raisoni college of engineering, india vinod.chandrakar@raisoni.net received: 9 november 2022 | revised: 30 november 2022 | accepted: 2 december 2022 abstract integrating wind farms with electricity transmission networks presents several problems, and power quality plays a vital role among these. this study proposed a novel fuzzy logic controller to reduce the effect of power quality issues in such applications and investigated two different facts (flexible ac transmission system) devices, the static var compensator (svc) and the static synchronous compensator (statcom). the fuzzy logic controller was designed as a voltage controller to improve power quality. detailed analysis was carried out to investigate the successful mitigation of voltage sag/swell, active and reactive power improvement, and voltage flickers control by two controllers in a multi-terminal load (mtl) system consisting of wind generators. the results were verified in matlab simulations, and a comparison was performed between the proposed shunt controllers. furthermore, the design of a fuzzy interference system based on vref (reference voltage) and the voltage measured at statcom location signals was investigated and compared with the svc in terms of voltage sag, voltage swell, voltage flickers, and total harmonic distortions (thd). the proposed fuzzy system was compared with a pi-based statcom and svc. the power quality issues were exacerbated when using multiterminal load (mtl) in the transmission network. keywords-voltage sag/swell; voltage distortion; thd; svc; statcom; flc i. introduction wind power's contribution to power generation is rapidly increasing these days. however, the inherent problem of wind power generation is its low quality due to the intermittent power generation that influences the connected grid. power quality problems, such as harmonic distortions, voltage instability due to voltage sag, voltage swell, and reliability, are concerns that must be addressed [1-2]. wind energy generation systems (wegs) with double-fed ig are used in power generation due to their low cost and variable speed constant frequency operation [3]. however, since wind power is typically located far from consumers, it is necessary to provide shunt compensation at points of common coupling (pcc) [4], while multi terminal load (mtl) connected to the wind farm at pcc produces power quality issues such as frequency variations and voltage sags/swells [5]. voltage flickers are abrupt frequency changes for short durations due to load switching and integration of compensatory devices [6]. as a result, voltage stability suffers from reactive power demand in pcc [7]. if the voltage sag persists for longer durations, it may lead to voltage collapse and longer-lasting voltage swells or flickers can introduce harmonics into the system [8]. the current produced due to sags/swells or flickers affects the switchgears and the protection system of the pcc. therefore, various compensators with filters have been adopted to mitigate these power quality problems [9-12]. many power quality conditioners have been implemented to address power quality issues in distribution networks, such as upqc, dvr, and dstatcom [4, 9, 13, 14]. among the different facts controllers, svc and statcom play an important role in reactive power compensation [12, 16]. in [8], two types of facts controllers, svc and statcom, were considered to mitigate power quality issues. however, when selecting a facts device, the performance of different types of shunt compensators should be examined based on fast response, reactive power compensator range, switching losses, resonance problems, energy source requirements, and dc link capacitor value [13]. various control techniques have been proposed for the operating performance of various shunt compensators, such as nonlinear control, lyapunov function-based control [17], instantaneous p-q theory [18], negative and zero sequence engineering, technology & applied science research vol. 13, no. 1, 2023, 10021-10026 10022 www.etasr.com adware & chandrakar: power quality enhancement in a wind farm connected grid with a fuzzy … control [6, 19-20], instantaneous d-q theory [13], backpropagation control [4], and the instantaneous id-iq method [7, 16]. hybrid structures were introduced in [7, 21] to improve statcom operation with lower current rating apfs and ppfs. a hybrid structure fails during capacitive load and gives better performance only during inductive loading [13]. to improve the compensation range with lower current characteristics of the apf, one more hybrid device with svc in parallel with an active power filter in the phase distribution system was evaluated. the apf was used primarily to eliminate harmonics and compensate for reactive power on the load bus left by svc [8]. however, it does not work on highvoltage transmission lines because the cost of apf is higher with multilevel structures. some studies investigated the use of pi controllers [12]. furthermore, controllers such as pi and pid require an intensive mathematical model of the system, making them more sensitive to changes in the system parameters [20]. as a result, they failed to meet the requirements of robust system performance. many studies investigated the reactive power compensation for the stability of a power system, however, very few tested power quality issues. shunt facts devices such as svc and statcom are popular for voltage regulation and voltage stability improvements. pi-based svc and statcom are mainly used in industry. the pi gains kp and ki are fixed and unchanged under changing system operating conditions, therefore statcom and svc performance suffers. fuzzybased svc and statcom are more suitable to replace pi. very few studies addressed fuzzy-based facts shunt facts devices for power quality issues. ii. proposed test system the test system consists of two generator systems of 500kv, 3000mva, and 500kv, 2500mva, connected with buses b1, b2, and b3, as shown in figure 1. the multiterminal load system of 6000mw load with a wind generator of 9mw was connected to bus b3. power quality issues were considered while the wind farm was connected to pcc or at load bus b3. power quality analysis was performed while b3 was connected to the mtl load with the wind generator. the proposed model was simulated in matlab/simulink to investigate the performance of the shunt compensator with svc, statcom, and statcom with flc3. fig. 1. proposed system model. a. proposed system with svc as shown in figure 2, svc dynamically generates static reactive power to adjust the characteristics of a transmission line by altering the reactive impedance in its network. svc is mostly used to maintain reactive power using different static power electronics controllers, such as a thyristor controlled reactor (tcr) and a thyristor switched capacitor (tsc). the transmission line requires reactive power, which is supplied and absorbed by the svc. the svc keeps the system voltage constant at its endpoints. when the system voltage is low, it produces capacitive reactive power. when the system voltage is high, inductive reactive power can be produced by simply changing the impedance using a thyristor switching circuit. due to their ability to quickly compensate for power loss with minimal maintenance, shunt compensators are increasingly widely used in power systems. fig. 2. test system with svc. b. proposed system with statcom as illustrated in figure 3, the converter output is changed to achieve reactive power transfer between the ac transmission network and the converter. if the output voltage exceeds the system bus voltage, the converter supplies capacitive reactive power and the converter's reactive current will go to the utility. the converter absorbs inductive reactive power from the utility when the output voltage is lower than the system voltage. as a result, there is no reactive current between the utility and statcom, as it serves as a floating element in the system when the utility and the converter output voltages are equal. fig. 3. test system with statcom. c. implementation of the proposed flc the hybrid fuzzy controller was designed using the fis gui editor tools in the fuzzy logic toolbox. the suggested fuzzy controller was modeled on mamdani's controller, which employs an "if-then" logic as part of its inference engine. each controller input is taken into account as a fuzzy variable using engineering, technology & applied science research vol. 13, no. 1, 2023, 10021-10026 10023 www.etasr.com adware & chandrakar: power quality enhancement in a wind farm connected grid with a fuzzy … membership functions. a triangular membership function is used for input and output variables. figure 4 shows the function of the fuzzy controller, which consists of three functional blocks: fuzzification, rule inference, and defuzzification. error e and the change in error de are the input variables in the proposed system, and the flc output is a reactive current. fig. 4. fuzzy logic flow diagram. d. hybrid flc for statcom figure 5 shows the flc scheme and the hybrid controller being the hybridization of a pi controller with a fuzzy logic controller. to obtain precise output from the proposed controller, the initial error signal generated by computing vref and measured values from the pi controller is then tuned, and an iqref value is obtained to compensate for the reactive current. the error signal is once again sent to the flc in the proposed hybrid controller, along with the error and change in error as a second variable to obtain the accurate estimation of iqref. table i shows a list of the proposed flc governing rules. the error and the change in error are provided for the fuzzy sets. to eliminate inaccuracy and improve the dynamic response of the controller, conditions for 9 sets of rules were applied. fig. 5. proposed f uzzy h ybrid c ontroller. table i. fuzzy rules de/e n z p n n n z z n z p p z p p iii. power quality case studies this section investigates the performance of the proposed hybrid fuzzy controller in a system with svc, statcom, and statcom with flc, under various power quality issues, when connected with an mtl and a 9mw wind farm. a. voltage sag analysis voltage sag is a frequent and severe issue caused by system faults, rapid increases in load, or the start of powerful motors. figure 6 shows a line-to-line ground fault that occurred between 0.2 and 0.3s with an 80ω fault resistance and a 0.001ω ground resistance close to bus 1. the voltage sag was developed in the given system and computed with svc and statcom. fig. 6. proposed system with voltage sag. at pcc, a statcom and an svc are placed independently. four parameters were used to investigate the dynamic behavior of the system. the first step was to investigate the effect of voltage sag on transient voltage stability by measuring the vrms voltage at the pcc with and without a compensator. similarly, active, reactive power, and harmonics were measured during fault, pre-fault, and post-fault phases. when the reactive power absorbed by the load bus increases, the voltage decreases, requiring facts controllers to compensate for the reactive power consumed in the system. a short-circuit line-to-line fault was simulated at generator bus b1 to investigate the effects of voltage sag. figure 7 shows the system's condition during a short circuit without a compensator. the vrms voltage drops to 0.64pu after a defect, is maintained at 0.77pu with the svc and pi controller, becomes 0.84pu with the statcom pi controller, and increases to 0.85pu with the suggested fuzzy controller. similarly, statcom with the fuzzy controller effectively maintains active power during faults compared to other compensators. reactive power during faults demands approximately 35var power without a compensator, whereas with svc it delivers 312var reactive power, -470 var with statcom and pi controller, and with fuzzy-based statcom it delivers approximately 485var reactive power. figures 7-9 show how statcom executes superior compensation to restore the system voltage to normal. in this instance, voltage recovery cannot be achieved with the installed capacity of the svc. fig. 7. vrms during voltage sag. engineering, technology & applied science research vol. 13, no. 1, 2023, 10021-10026 10024 www.etasr.com adware & chandrakar: power quality enhancement in a wind farm connected grid with a fuzzy … fig. 8. active power during voltage sag. fig. 9. reactive power during voltage sag. table ii. performance parameters (voltage sag) performance parameter without comp. svc statcom (pi) statcom (pi+fuzzy) vrms (pu) i 0.71 0.88 0.945 0.955 ii 0.64 0.775 0.84 0.85 iii 0.72 0.88 0.945 0.955 active power (w) i 825 1040 1100 1116 ii 538 637 670 675 iii 825 1040 1100 1116 reactive power (var) i 325 -170 -300 -310 ii 35 -312 -470 -485 iii 325 170 -300 -310 % thd 485.89 417.52 329.02 320.28 (i-prefault, ii-during fault, iii-post fault) b. analysis of voltage swell the mtl load system consisted of a parallel load with 500mw active power, 100var inductive reactive power, and 100var capacitive reactive power to produce voltage swell. figure 10 shows the three-phase circuit breaker to produce the voltage swell condition. table iii shows the proposed system including flc-based statcom, statcom, and svc with pi controller. figures 11-13 show the analysis of the test system with and without compensation. the impact of various compensators was examined taking into account a momentary voltage swell lasting 0.2-0.3s. fig. 10. proposed system with voltage swell. table iii shows that when there is a sudden loss of load at load bus b3, the electrical mode's stability drops and becomes unstable in the absence of statcom. furthermore, the rms voltage under fault conditions without a compensator is 0.708pu and improves with svc to 0.785, whereas it is 0.945 with statcom and reaches 0.95 with the suggested statcom with fuzzy, as it gradually increases towards the rated value. the active and reactive power during the same period without a compensator is 826w and 325var, but with svc and statcom, the compensator delivers approximately 1039w and -171var, and 1106w and -297var, respectively. using fuzzy-based statcom produced around -230var of reactive power and 1050w of active power. similar results for the thd percentage demonstrated improved results compared to the results with and without compensation. fig. 11. vrms during voltage swell. fig. 12. active power during voltage swell. fig. 13. reactive power during voltage swell. table iii. voltage swell performance parameters performance parameter without comp. svc statcom (pi) statcom (pi+fuzzy) vrms (pu) i 0.643 0.785 0.865 0.87 ii 0.708 0.882 0.945 0.95 iii 0.644 0.784 0.864 0.87 active power (w) i 767 944 1040 1050 ii 826 1039 1106 1116 iii 766 944 1040 1050 reactive power (var) i 400 -77 -219 -231 ii 325 -171 -297 -310 iii 400 -78 -220 -230 % thd 485.72 449.14 407.95 401.96 (i-prefault, ii-during fault, iii-post fault) c. analysis of capacitor bank switching at load bus load voltage distortion and voltage flickers are the most frequent problems in a power system. capacitor banks were engineering, technology & applied science research vol. 13, no. 1, 2023, 10021-10026 10025 www.etasr.com adware & chandrakar: power quality enhancement in a wind farm connected grid with a fuzzy … connected to b3 through a switch to imitate voltage distortion or flickers, as shown in figure 14. capacitor banks were used as shunt compensators with the load bus to compensate for reactive var power on the load bus. load voltage distortion occurs at the load bus whenever capacitor banks are switched on or off. the simulations in this section ran in transient mode, with the capacitor switched at load bus b3. when a capacitor is turned on during steady-state operation or when load compensation is required, sudden voltage flickers or voltage distortion are introduced at the bus, which is analyzed at pcc with and without a compensator, as well as with the proposed fuzzy-based statcom. fig. 14. proposed system with capacitor switching. table iv shows the performance of various compensators under different transient conditions for all transmission line performance parameters. figures 15-17 show that the vrms voltage at the pcc increased up to 0.975, closer to the rated value, using the proposed fuzzy-based hybrid statcom. similarly, simulations of other performance metrics, such as active and reactive power, demonstrated that the proposed fuzzy-based statcom was capable of producing better active and reactive power than the pi-based svc and statcom. the results reveal that the proposed controller improved thd by 10 to 15%. fig. 15. vrms with c apacitor switching. fig. 16. active power with c apacitor switching. fig. 17. reactive power with c apacitor switching. table iv. performance parameters (cap. switching) performance parameter without comp. svc statcom (pi) statcom pi+fuzzy vrms (pu) i 0.645 0.884 0.945 0.955 ii 0.71 0.903 0.964 0.975 iii 0.644 0.883 0.944 0.954 active power (w) i 767 1040 1106 1116 ii 846 1104 1166 1176 iii 766 1139 1107 1117 reactive power (var) i 400 -170 -300 -310 ii 325 -270 -400 -415 iii 401 -171 -301 -310 % thd 485.86 420.56 326.86 310.16 (i-prefault, ii-during fault, iii-post fault) iv. discussion this study investigated a novel hybrid fuzzy controller for ac voltage control of statcom. many studies used either pi controllers or replaced pi with fuzzy controllers. this study used both pi and fuzzy controllers, introducing a novel hybrid fuzzy controller. other studies showed that the proposed hybrid controller can be easily implemented with simple fuzzy rules and improve system voltage stability and power flow. similarly, other studies presented techniques based on a smib system with an ideal nonlinear load. this study used two dynamic sources connected on either side with a multiterminal load considering the connected wind farm. different power quality issues were presented, showing that the proposed hybrid controller improves rms voltages in every power quality issue near the rated values. furthermore, there is a 10% to 15% improvement in active and reactive power. on other hand, results in tables ii, iii, and iv showed 10% to 20 % improvements in thd. v. conclusion this study investigated the modeling of a system with and without a compensator in several transient situations, revealing power quality concerns in matlab simulink. simulation results showed that statcom and svc with a pi controller both efficiently alleviated voltage sag/swell, but their efficacy varied. the results obtained by simulating the system with a fuzzy-based hybrid controller with statcom were superior. in comparison to svc, statcom with pi, and the system without a compensator, the vrms during voltage sag, swell, and capacitor bank switching in the suggested statcom was substantially more stable. moreover, the suggested statcom enhanced the system voltage at the point of common coupling. statcom quickly restores the system 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[21] p. jagtap and v. chandrakar, "comparative study of upfc controllers to improve transient and dynamic stabilty of power system," in 2021 ieee 4th international conference on computing, power and communication technologies (gucon), kuala lumpur, malaysia, sep. 2021, pp. 1–7, https://doi.org/10.1109/gucon50781.2021.9573804. microsoft word etasr_v12_n5_pp9239-9246 engineering, technology & applied science research vol. 12, no. 5, 2022, 9239-9246 9239 www.etasr.com scussiato et al.: a numerical model for heat and moisture transfer in porous media of building … a numerical model for heat and moisture transfer in porous media of building envelopes talita scussiato civil engineering department aeronautics institute of technology sao jose dos campos, brazil talita.scussiato@gmail.com jaqueline ramis civil engineering department aeronautics institute of technology sao jose dos campos, brazil jacramis23@gmail.com william hideki ito civil engineering department aeronautics institute of technology sao jose dos campos, brazil ito.william@yahoo.com paulo ivo braga de queiroz civil engineering department aeronautics institute of technology sao jose dos campos, brazil pi@ita.br received: 1 january 2022 | revised: 2 february 2022 | accepted: 3 march 2022 abstract-this study presents a one-dimensional quantitative analysis of unsaturated flow in natural stones using a numerical model (finite difference method) and a mass balance for the heat flow. for that, we considered heat and moisture transfer between the external environment and a porous media (sandstone and limestone) with homogeneous characteristics. for unsaturated water flow, richards’ equation and the formulation proposed by gardner for volumetric water content and hydraulic conductivity were considered. the results of the numerical analysis showed that the evaporation of porewater throughout summer days (january 3 rd and 4 th ) considerably reduced the temperature of the roof by about 8°c. the accumulated conductive heat flow and the volumetric water content also had a reduction due to the evaporation process. this fact indicates that evaporation can be useful in providing thermal comfort and, consequently, in improving the energetic efficiency of buildings with natural stones as envelope. keywords-richards’ equation; heat transfer; thermal comfort; porous media i. introduction natural stones are used as major components of building envelopes of several historical constructions. the porosity of these natural stones can be greater than those found in other cladding materials, which might influence the decrease of water content absorbed by the capillarity due to evaporation. some studies have suggested that the moisture transfer between cladding materials and the external environment plays a major role in the thermal comfort inside these buildings [1]. the use of evaporative processes in roofs to enhance thermal comfort in buildings is not an innovation per se, and numerical and experimental modeling of these solutions is frequent in research nowadays. a review of the evaporative method to improve thermal comfort due to the reduction of heat flux through the roof was discussed in [2], whereas authors in [3] presented a review of evaporative cooling systems for buildings. numerical studies became more frequent in the literature due to the improvement of personal computer processing capacity in recent years. authors in [4] presented a model based on the finite differences method to evaluate the external surface temperature of a roof using the accumulated internal surface heat flux and the evaporation rate. authors in [5] carried out a two-dimensional numerical model of evaporation on a plate of the heat exchanger. they showed that ambient temperature, relative humidity, and wind speed have a significant impact on the evaporation and on the reduction of plate temperature. authors in [6] showed the efficiency of phase change materials (pcm) in the thermal comfort of buildings. similar results were achieved by other researchers, e.g. in [7-12] among others. moisture exchange with the external environment has a great importance to the thermal comfort inside buildings, mainly because the water absorbed by the pores of the rock (or other cladding materials like concrete) migrates to the surface and evaporates. as a result, the absorption of the latent heat cools it [4, 8]. since the reduction of co2 emissions has become a priority to many countries due to the concern of climate change, many studies have focused on improving thermal comfort in building environment with minimal energy consumption. meantime, there are only a few researches that take in account the influence of the moisture in thermal flow. following this trend and improving the works already done in this field, the present paper suggests a novel method to evaluate the evaporative process applied to thermal exchanges in a building’s roof. to do so, we present a numerical study where we solved the richard’s equation by finite difference method in a one-dimensional model. we compared two types of material envelop in two different days, one humid and other corresponding author: talita scussiato engineering, technology & applied science research vol. 12, no. 5, 2022, 9239-9246 9240 www.etasr.com scussiato et al.: a numerical model for heat and moisture transfer in porous media of building … dry, and analyzed the influence of external weather conditions in the variation of internal temperature. ii. theoretical framework modeling heat and moisture transfer in porous materials is considered a complex task mainly because several phenomena must be evaluated, such as: • energy balance • solar and nocturnal atmospheric radiation • gray body radiation emission by the roof • heat conduction in roof slab • convective heat transfer between roof and atmosphere • heat transfer in evaporative processes • water flow in unsaturated porous media. the following sections briefly describe each of these processes and their equations adopted in this work. a. energy βalance in steady-state conditions, the energy flow balance is written as the sum of the heat flows involved in the thermal exchanges, as indicated in figure 1 and expressed in (1) �"� � �" � �"� � �"� � �" (1) where �"� is the solar radiation flow, �" is the conductive heat flow, �"� is the convective heat flow, �"� is the gray body radiation flow, and �" is the evaporative heat flow. fig. 1. heat flow on the roof of a building. solar radiation is by far the most important heat source in buildings. for this reason, there are several models available to calculate this parameter [14], which have been used [15] to study the sol-air temperature in a natural stone (marble). following the work of [13], the authors evaluated the induced stress by daily variation of temperature in external façades using a model developed by [16], which is the model that supported the development of the simplified model by [14] for clear-sky radiation. according to several solar radiation models, a building envelope (wall or roof) absorbs 3 different types of radiation from its surroundings, as shown in (2): �"� � �� � � ∙ cos �� � � � � � (2) where �� is the shortwave radiation absorbance, � is the direct solar radiation attenuated by the atmosphere, �� is the zenith angle, � is the diffuse sky radiation, and � is the solar radiation reflected by surrounding buildings. night sky radiation can be considered by (3) [17]: �"�,���� � �1 � �� �� ∙ 8.78 # 10%&'() *.+*�,-.../&0* (3) where �� is an index that depends on the cloud cover, () is the air temperature, and ,is the relative humidity. radiation energy is transmitted via electromagnetic waves, and it can be represented by gray body radiation. it is defined by the modified stefan law presented in (4) [18]: �"� � 12(34 (4) where 2 is the radiation emissivity, 1 is the stefan-boltzmann constant (5.67×10 -8 w/m 2 k 4 ), and (3 is the surface temperature of the outer (outdoor) portion of the roof. fourier law describes heat conduction in a continuum medium, and it can be represented by (5) and (6): �" � � 5�6 �(7�� � (3 � (5) where (89: is the indoor temperature, ,3 is the thermal resistance of the roof, and ; is the roof slab thickness. the hypothesis of steady-state flow assumed in the present work seems reasonable, since a great part of the transient condition (over 90%) is dissipated in less than two hours. convective heat transfer between roofs and the external environment can be calculated by two distinct formulations: artificially or naturally induced convection. both models assess the convective heat transfer by (6): �"� � ℎ� �() � (3 � (6) where ℎ� is the convective heat transfer coefficient. heat transfer by forced convection was estimated through a dimensionless model in [10, 20], where ℎ� is estimated by (7) for nusselt number (nu): => � ℎ� ?@a bc � 0.036 ∙ fg..4'�,h ..+ � 9200� klml6 n ..�* (7) where o p is the equivalent length, qr is the air thermal conductivity, fg is the prandtl number, ,h is the reynolds number, s) is the absolute air viscosity in the atmosphere, and s3 is the absolute air viscosity at the roof temperature. the viscosity correction klml6 n ..�* can be neglected for gases. the equivalent length refers to the longest building length in the wind direction for a finite length building, expressed by: o p � tuv w x y89 z , ? [\y z] (8) where ^ is the building plan width, o is the building plan length, and θ is the wind direction. the free convection coefficient is estimated by the model presented in [20, 21]: engineering, technology & applied science research vol. 12, no. 5, 2022, 9239-9246 9241 www.etasr.com scussiato et al.: a numerical model for heat and moisture transfer in porous media of building … => � _��g ∙ fg�� (9) `ℎ = _��g ∙ `_�� (10) where �g is the grashof number, sh is the sherwood number, and _ and v are constants (see table i). grashof number (�g) is defined by (11) [17]: �g = abo p ' �c6%cm�de �11� where b is the gravitational acceleration (9.81m/s2) and a is the coefficient of the thermal expansion of the air, which is the inverse of the temperature for an ideal gas. the estimates of the evaporative flux and the heat transfer due to this process are calculated using an iterative process, given that one depends on the other. according to the model presented in [22], the evaporation flow is estimated in a very similar way to the convective flow process, which involves forced or free convection. the evaporative flow is calculated by: f g = − hij∙�k∙�l6%lm�?@a m (12) where f g is the evaporative mass flux, ng is the molecular diffusivity of water vapor in the air, and o3 , o∞ are the mass concentration of water vapor at the surface and in the free atmosphere respectively. in this study, the forced convection uses the dimensionless sherwood number �`ℎ� for mass transfer, as presented in (13): `ℎ = 0.036`_..4'�,h ..+ − 9200� (13) where `_ is the schmidt number. mass concentration of water vapor (absolute humidity or o) can be expressed as in: o = p6∙qkcrs�c (14) where t3 is the molar mass of water, >gr7� is the partial pressure of water vapor, and , is the universal gas constant. table i. constants _ and v for free convection on a horizontal plate at uniform temperature by [20, 21] surface orientation uv. wv x y regime hot surface up 10 5 to 2×10 7 0.54 1/4 laminar cold surface down 2×10 7 to 3×10 10 0.14 1/3 turbulent hot surface down or cold surface up 3×10 5 to 3×10 10 0.27 1/4 laminar the partial pressure of water vapor �>gr7� � is calculated with the relative humidity �,-� given by: ,= qkcrsqkzcrs (15) where >g.r7� is the saturation pressure of water vapor. in the present study, this variable is given by tetens equation, as shown in [23, 24]: >g.r7� = 0.61078 exp k &/.�/∙cc~�'/.'n (16) where ( is the temperature (°c). according to [22], the difference of air density above the roof must be considered for simultaneous heat and water vapor transfer analysis. hence, the concept of virtual temperature is introduced to conveniently express the difference in density between dry and moist air at temperature (. this relationship is represented by: (g = c�&%�&%�6��kcrs�� c � ≈ ( k1 + �1 − 23 � qkcrsq�c n (17) where 23 is the ratio of molecular weights of water vapor and air, taken as 0.622, and >�r is the absolute pressure of the airvapor mixture. hence, (3 − (∞, in (11) should be replaced by: (g3 − (g) ≈ �(3 − ()� + ..'+�c6qk6crs%cmqkmcrs�qc���� (18) where >g3r7� and >g∞r7� are the partial vapor pressure near the roof and in the atmosphere respectively. heat loss/gain due to evaporation/condensation is expressed by: �" = ℎgr� ∙ f g (19) where ℎgr� is the enthalpy of water evaporation. b. water flow in unsaturated porous media a great number of numerical models considering the unsaturated flow in porous media rely on richards’ equation, which can be represented in a mixed form by [25]: �z6�� = ��� w���� ���~���� ] (20) where �3 is the volumetric water content, t is the time, � is the hydraulic conductivity and ψ is the water matric suction, that is, the difference between air pressure and pore water pressure. the unsaturated formulation was proposed by gardner [35] where the volumetric water content of a porous medium can be estimated as: �3 � �� � ��� � �� �h �� (21) where �� is the residual water content, �� is the saturated water content, � is the air entry suction parameter, and � is the matric suction. in the formulation proposed by [35], water hydraulic conductivity (k) is represented by: � � q� h �� (22) where q� is the saturated hydraulic conductivity. iii. materials and methods the input data used in this work are representative of a typical summer day in brazil. the analysis was conducted using porous rock materials (sandstones and limestones), which are used in several historical buildings. a c++ code was implemented to solve the differential equations. engineering, technology & applied science research vol. 12, no. 5, 2022, 9239-9246 9242 www.etasr.com scussiato et al.: a numerical model for heat and moisture transfer in porous media of building … c. assumptions assumed prior to the analysis the following assumptions were considered to simplify the modeling: • the flow is one-dimensional • the heat flow is in steady-state condition • the water flow is in a transient regime • the airflow is negligible • the indoor temperature ((7�� ) is constant at 23°c • the porous media are considered homogeneous • the thermal conductivity of the porous media is constant concerning the volumetric water content and temperature. d. weather data in the present study, meteorological data of ouro preto – minas gerais, brazil (latitude: 20°23'8'', longitude: 43°30'13'', altitude: 1.200m above sea level) are considered. the location was chosen because many of the preserved historical buildings in brazil are located in this area. meteorological data, including wind velocity ��� and direction ���, relative humidity �,-�, and air temperature �( ∞ � were obtained from a weather station at the federal university of ouro preto. the proposed methodology was applied in the interval between january 3 rd , 2013 and january 4 th , 2013, to evaluate the evaporative-cooling roof effect. the input data used in this paper are presented in figure 2. on january 3 rd , the air temperature varied from 27°c to 17°c, mean wind velocity was about 3.8m/s from 10:00 to 19:00, relative humidity varied from 34% to 100%, and the maximum solar radiation of 870w/m 2 occurred at 11:13. similar behavior was verified for january 4 th , in which the air temperature varied from 25°c to 17°c and the mean wind velocity was about 4m/s, relative humidity varied from 55% to 100%, and the solar radiation was almost coincident with the preceding day. according to these data, we can conclude that january 4 th was wetter, colder, and less windy than january 3 rd . e. heat flow and evaporation considering an internal environment with constant temperature (7�� =23oc, a quasi-newton-raphson scheme was used to find temperature (3 , as shown in (23): (3,7~& = ��6cr��~p"�~jcm~'��c6� %jkc��@k��6~j~4��c6� (23) f. porous roof slab sandstone and limestone slabs are the unsaturated porous media considered in this study. both materials were assumed to be homogeneous and without cracks. they were chosen because they are abundant in southeast brazil, where ouro preto is located. in order to characterize two hypothetical constructions with these materials, some of their properties were taken from the literature (table ii). both models have a thickness of 0.1m, a building plan width b of 8m, and a building plan length l of 10m. figure 3 shows the water retention curves of sandstone and limestone used, obtained by the use of van genuchten parameters [33] described in [32]. (a) (b) (c) (d) fig. 2. environmental conditions for january 3rd and 4th, 2013: (a) air temperature, (b) relative humidity, (c) wind velocity and direction, (d) solar radiation � � ∙ cos ��� where �� is the zenith angle. fig. 3. water retention curve for limestone and sandstone fitted with the van genuchten (vg) model. engineering, technology & applied science research vol. 12, no. 5, 2022, 9239-9246 9243 www.etasr.com scussiato et al.: a numerical model for heat and moisture transfer in porous media of building … table ii. properties of sandstone and limestone used in this study parameter sandstone limestone unit ref. thermal conductivity (q�) 1.83 2.5 w/m.k [26, 27] radiation emissivity (2) 0.935 0.87 [28, 29] saturated hydraulic conductivity (q�) 8x10-5 5x10-7 m/s [30, 31]* saturated water content (��) 0.036 0.061 [32] residual water content (��) 0 0 [32] air-entry parameter (�) 0.084 0.005 m-1 [32] porosity (v�) 3.4 1.75 % [32] bulk density (��) 2.35 2.3 g/cm3 [32] *mean value g. unsaturated flow the calculation of unsaturated flow was based on the work developed by mannich [34]: �3 = �� + ��� − �� �h ��, � = q� h �� mannich uses a finite volume in spatial discretization and a crank-nicholson scheme in time. in this scheme, the equations system is solved simultaneously and the richards' equation (20) can be rewritten as (24): ���� ���� = �p�� (24) where � and ���� can be defined as: � = ���� ���� + ���� , ���� = �z�� (25) the equation for internal nodes, representing the capillary potential calculated at the end of the time interval, can be expressed as: f7 �7�~& = �7 �7%&�~& + �7 �7~&� ~& + 7̂ (26) where �7� is the matric suction in grid node u at time �. the coefficients of (26) are expressed as: �7 = br �e ¡¢� £�e , �7 = br¢�e ¡¢� £�e , f7 = ¤r ¡¢�e £� + �7 + �7 (27) 7̂ = ¤r¡¢ �e�r¡∆� + &∆� ¦q7~�e� h�r¢� ¡ %�r¡£� + 1m − q7%�e� h�r ¡%�r �¡£� + 1m + q7~�e�~& + q7%�e�~&§ (28) half indexes like in q7%�e�~& denote that the hydraulic conductivity is calculated with the average suction between �7%&�~& and �7�~& . hence, �7�~�e is the derivative � = �z6�� calculated with the average suction � = �r¡¢�~�r¡� . the bottom of the slab was taken as a moist environment, where �. = ^. = 0, �. = 0, �. = 0, and f. = 0. for the top of the slab, evaporative mass flux �f g ) was imposed, which means that the coefficients of (26) become �� = 1, �� = 0, f� = 1, and �̂ = ¨p ¡%b� �e ¡ b� �e ¡ © ∆ª. the coefficient � � is represented by: � � = f g (29) for the finite element difference grid, the time interval �∆«) considered was of 15 minutes over the course of a day, and the space interval (∆ª) was 0.01m for a total thickness o=0.1m for sandstone roof slab. the main goal of the proposed methodology is the consideration of the evaporative processes through the coefficients of water flow in the heat flux. iv. results and discussion a. roof temperature figures 4 and 5 show, respectively, the results of the temperatures calculated for january 3 rd and 4 th in sandstone and limestone hypothetical roofs. the external air temperatures are also plotted. two different conditions were considered: with and without evaporation. from 12:00 am to 6:00 am, the external air temperature was about 20°c, but the theoretical temperature on the external surface of the roof was about 13°c for sandstone and 15°c for limestone. these almost constant temperatures are explained by the absence of direct solar irradiation. however, from 6:00 am to 4:00 pm, the temperature of the roof rises until it reaches a peak, and then it falls. during a great part of this interval, the temperature calculated for the external surface of the roof is higher than the external air temperature for both conditions (with and without considering evaporation). temperature differences occur due to the solar radiation effect, which starts to increase at 6:00 am and reaches its peak around 12:00 pm (coinciding with maximum roof temperature). after that, the solar radiation continuously decreases until it becomes negligible. from 4:00 pm on, the roof temperature is lower than the temperature of the air for both hypotheses (with and without evaporation). fig. 4. temperature of the roof and air on a sunny day (january 3rd). engineering, technology & applied science research vol. 12, no. 5, 2022, 9239-9246 9244 www.etasr.com scussiato et al.: a numerical model for heat and moisture transfer in porous media of building … these results show that the theoretical temperature is almost the same for both materials if the evaporation effect is considered. without this effect, the difference in temperature reaches 2°c. this can be explained by solar radiation, which was the major phenomenon involved in the calculation. the value of shortwave radiation absorbance (�) used was the same for both materials. the reduction of temperature due to evaporation on january 3 rd and 4 th (figures 4 and 5), was about 8°c-7°c for sandstone and 6°c-5°c for limestone. in figure 4, the outliers observed at 11:30 am and at 01:15 pm can be explained by the changes in wind direction. fig. 5. temperature in the roof and air on a mild and humid summer day (january 4 th ). b. heat τransfer figure 6 presents the conductive heat flow calculated for the examples described above. one can notice that the accumulated conductive heat flow is positive until 9:00 am. afterward, a reduction in accumulated heat flow from 9:00 am to 15:00 pm on january 4 th is noticeable. then, it asymptotically stabilizes near -0.4 and -0.2 for conditions neglecting and considering the evaporation effect respectively. this phenomenon occurred due to the absence of wind during this period. without wind, the roof’s temperature does not change, and the system does not exchange heat.΅ fig. 6. accumulated conductive heat flow in sandstone and limestone roofs on two different summer days (january 3 rd and 4 th ). on january 3 rd , the decrease in accumulated heat flux occurred until 03:00 pm. it reached a minimum, and then increased until 06:00 pm, and stabilized in –0.25 for both materials. this happened in a condition without evaporation, and 0 for limestone and 0.05 for sandstone when the evaporation process was taken into consideration. this occurred because the system only reaches stability when wind velocity is zero. the cumulative conductive heat flow is lower for processes that consider the evaporative effect than for those which do not, mainly because the roof loses a lesser amount of energy to the environment due to the lower gradient of temperature between the surfaces. similarly, if evaporation is not considered, the heat flow is higher because the temperature of the external surface of the roof is also higher. therefore, it is possible to conclude that the evaporation process causes the reduction of temperature, that is, it consumes heat. c. water flow figure 7 shows the cumulated evaporative rate through roof thickness throughout the day. we can see that the maximum evaporation rate is close to 4.5l/m 2 for sandstone on a summer day in ouro preto (january 3 rd ). the minimum evaporative rate of 2.5l/m 2 was verified for limestone on january 4 th . one can notice that the cumulated evaporative rate was smaller on january 4 th than on january 3 rd in both materials. the difference occurred due to the difference in the temperature verified in these two days, which was 2°c lower on january 3 rd . the relative humidity was 20% higher and there was less wind throughout the day. it can be pointed out that, for january 4 th , the accumulated evaporative rate was smaller than on january 3 rd for both materials, because on the 4 th the temperature was 2°c lower, the relative humidity 20% higher, and there was less wind during that day. fig. 7. the accumulated evaporative rate in sandstone and limestone roofs on january 3 rd and 4 th . fig. 8. volumetric water content (θw) on january 3 rd in sandstone roof. figures 8 and 9 show the volumetric water content for sandstone and limestone roofs on january 3 rd and 4 th respectively. it is noticeable that the volumetric water content engineering, technology & applied science research vol. 12, no. 5, 2022, 9239-9246 9245 www.etasr.com scussiato et al.: a numerical model for heat and moisture transfer in porous media of building … did not reduce significantly due to the evaporation on sandstone (about 2%). on the other hand, for the limestone roof model, the reduction was of about 15% on january 3 rd around 12:00 pm. fig. 9. volumetric water content (θw) on january 4th in limestone roof. d. discussion the current study uses weather data and properties of facade materials to calculate roof temperature. its main purpose is to model how evaporative roofs improve thermal comfort in buildings. following the world trend of nzeb (net zero energy buildings) [35], this study shows that the internal environment temperature may be reduced by the evaporative process. the choice of appropriate envelope material can reduce the use of air-conditioning. the main contribution presented here is the method of accounting for the evaporative process in the boundary condition of water flow in a finite volume scheme for unsaturated materials. similar works [1, 34] do not consider the coupled effects of water flow and evaporation associated to heat flow. v. conclusion this study presented a numerical calculation, in onedimensional finite difference method, for unsaturated flow using richards’ equation and gardner’s formulation for volumetric water content and saturated hydraulic conductivity. for the heat flow, the balance of 5 heat fluxes (solar radiation, conductive, convective, gray body radiation, and evaporative) were considered. the heat and moisture transfer model was carried out for 2 different natural stones (sandstone and limestone) in a hypothetical building located at a historical city in brazil (ouro preto-mg) and under two conditions: with and without evaporation. this study showed that, for both materials, the evaporation process of the porewater throughout the day considerably reduces the temperature of the roof. around 12:00 pm, the roof temperature dropped approximately by 8.5°c on january 3 and 7.5°c on january 4 due to the evaporation of the water contained within the pores of the sandstone roof. the temperature was 2°c higher on sandstone roofs when compared to limestone roofs. on january 3, during an entire summer day, we observed a maximum accumulated evaporation rate of about 4.5l/m 2 of sandstone roof area. moreover, the maximum reduction of water content for the limestone roof was about 15%, around 12:00 pm. the numerical analysis results show that the evaporation of porewater throughout summer days considerably reduces the temperature of the roof and the accumulated conductive heat flow. the results indicate that evaporative processes can be useful in order to provide hygrothermal comfort with energetic efficiency for buildings having sandstone or limestone as 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[35] w. r. gardner, "some steady-state solutions of the unsaturated moisture flow equation with application to evaporation from a water table," soil science, vol. 85, pp. 228–232, apr. 1958, https://doi.org/ 10.1097/00010694-195804000-00006. microsoft word etasr_v12_n6_pp9560-9564 engineering, technology & applied science research vol. 12, no. 6, 2022, 9560-9564 9560 www.etasr.com ijaz et al.: assessment of protective clothing used by chemical industry workers in pakistan assessment of protective clothing used by chemical industry workers in pakistan chemical resistance of protective clothing mehreen ijaz department of home economics lahore college for women university lahore, pakistan mehreenijaz@hotmail.com namood-e-sahar department of home economics lahore college for women university lahore, pakistan n.sahar6282@gmail.com zohra tariq department of home economics lahore college for women university lahore, pakistan zohra.tariq@lcwu.edu.pk rafia fatima department of home economics lahore college for women university lahore, pakistan rafia.fatima@lcwu.edu.pk zahra rasheed department of home economics lahore college for women university lahore, pakistan zahrarasheed29@gmail.com madeeha tariq department of home economics lahore college for women university lahore, pakistan madeeha.tariq@lcwu.edu.pk hibba munir dar department of home economics lahore college for women university lahore, pakistan dar_hiba@yahoo.com received: 27 august 2022 | revised: 18 september 2022 | accepted: 20 september 2022 abstract-protective clothing serves as a barrier against many hazards faced by workers in the industry. this study aimed to investigate the performance of locally manufactured clothing used by workers in the chemical industries in pakistan. the construction parameters were determined using international test procedures for all samples. then, these were assessed for their chemical resistance behavior after various laundering intervals, following the iso 6530:2005 test method. after the investigation, it was observed that the collected samples failed to meet the minimum criteria for penetration and repellency through their structure. the samples were unable to repel a minimum of 95% liquid chemical and penetrated it more than 5%, even at zero wash. these conditions worsened with each washing interval. clothing materials should always be checked for their performance before use. keywords-chemical resistance; penetration; repellency; protective clothing; laundering; chemical industry; pakistan i. introduction clothing is considered the second skin for the wearer and protects him against physical, chemical, and environmental hazards. while many advancements have been achieved in the manufacture of protective clothing, there is a lack of a comprehensive and detailed evaluation system in terms of experimentation and regulation [1]. standard procedures and regulations are very necessary to implement in industries for the welfare of personnel [2]. chemical protective clothing materials are supposed to be the last defense line for workers dealing with toxic chemicals. efforts must be made to make the best clothing to provide safety to its wearer. chemicals vary in their nature from acute to chronic. the industrial working conditions require the wearing of protective clothing to protect the operating staff [3]. the clothing materials should be assessed for their performance before use. chemical resistance can be evaluated by certain factors such as permeation time, breakthrough time, repellency, retention, penetration index, etc. [4]. protective clothing is generally classified into various levels according to the protection rate it provides and is made of natural and synthetic fibers or a blend of both [5, 6]. protective coveralls are generally worn by industry workers [7]. a regulatory body assesses the best protective ensemble for workers based on the toxicity and flammability of the chemicals used in various processes [8]. accidents caused by chemical exposure in workplaces are horrendous. workers are often exposed to toxic chemicals without safety measures while working in the industrial sector in pakistan, resulting in many fatal accidents. many workers, more than one-third of the respondents in [9], reported high risks associated with chemical exposure. it has been observed that although many toxic substances pose serious risks to their lives, workers expose themselves without wearing an adequate type of protective clothing. occupational assessment related to the health and safety of workers in pakistan has yet to receive great importance. therefore, it is very important to determine corresponding author: mehreen ijaz engineering, technology & applied science research vol. 12, no. 6, 2022, 9560-9564 9561 www.etasr.com ijaz et al.: assessment of protective clothing used by chemical industry workers in pakistan measures and evaluate the performance of the provided protective equipment. the increase in the rate of deaths and injuries of factory employees is caused by the absence of a safety framework or the adoption of poorly administered safety measures [10]. the wages and salaries of most workers in pakistan are very low. workers usually do not bother about their health conditions and try hard to do more work regardless of checking the adequate protective measures. a survey carried out by the government of pakistan showed that approximately 4.1 workers are seriously injured in industrial settings every year [11]. one of the main reasons for injuries is the lack of awareness about the use of protective equipment [12], while 60.9% of the workforce is not familiar with personal protective equipment (ppe) [13]. it should be the responsibility of the employer to provide safety equipment to the workers. an assessment of the risks associated with chemical industries must be made to avoid accidents and injuries. workers must have a proper protective ensemble to protect themselves from fire and chemical hazards during the handling and storage of hazardous chemicals [14]. as most chemical industries in pakistan use locally manufactured protective clothing materials for their staff, there is a dire need to evaluate their performance before use. protective clothing loses its quality with time due to the abrasion caused during work, rubbing during washing, and lack of proper care and cleaning procedures. this study aims to determine the clothing materials used by local chemical industries for their workers, in terms of protection against certain liquid chemicals after various washing intervals. ii. materials and methods chemical industries with head offices located in the punjab province were approached and locally manufactured protective clothing used by their workers was collected (figure 1). a total of five categories were identified according to their fiber content. fig. 1. flowchart of the research methodology. the identification of textile fibers is of great importance. there are multiple methods to identify the generic group of fibers, such as burning, microscopic, and chemical tests [15]. the construction specifications of the collected samples were determined through qualitative and quantitative fiber analysis, as shown in table i. table i. construction parameters of collected clothing materials sample code fiber content yarn count: warp×weft (thread count) fabric mass (gsm) linear density (warp × weft) ab-1 cotton 40% polyester 60% 113×95 (208) 150 17.21×15.43 ab-2 cotton 70% polyester 30% 95×75 (170) 138 16.34×16.34 ab-3 cotton 95% rayon 5% 105×68 (173) 162 17.29×18.91 ab-4 cotton 98% polyester 2% 99×76 (175) 125 18.32×15.63 ab-5 cotton 50% polyester 50% 110×85 (195) 121 15.34×18.45 qualitative analysis was performed using the aatcc test method [16] to find the generic group of fibers. the samples were dipped in distilled hot water to remove impurities and were then treated with a 0.5% solution of sodium hydroxide to separate the vegetable matter. after that, the samples were washed out and dried. the dyed samples were stripped with 0.5% sodium hydrosulfite at 50°c for half an hour. afterward, a visual examination was performed of physical parameters such as color, yarn length, fineness, number of neps, thickness, and uniformity. fibers were identified at pre-burning, during burning, and post-burning stages through a burning test. microscopic evaluation was also performed with longitudinal and cross-sectional views of the samples. a quantitative analysis was followed using the chemical test adopting the instructions given in the aatcc test procedure [17]. the samples from each group were taken and treated with the relative reagent to measure the solubility ratio given in the standard. the yarn count in both the warp and weft directions was determined using the standard test procedure [18]. the number of yarns in the test area of one inch was counted with the help of a magnifying counting glass. the thread count was calculated by adding the number of warp and weft yarns. the fabric mass was determined by following the standard procedure of [19]. the samples were measured in a weighing balance and the mass per unit area of m 2 was recorded with an accuracy level of ±0.1%. the linear density in both directions was also identified [20]. the length and mass of the yarns were determined with the respective scales and calculations were carried out to measure the linear density. the performance behavior of protective clothing must be evaluated after various washing intervals. standard laundering procedures must be followed to verify the efficiency and adequacy of textile materials up to a specific number of intervals [21]. after identifying the construction specifications of the samples, they were laundered through the american association of textile chemists and colorists (aatcc) monograph [22] in a front load washing machine under the agitation speed of 45±10rpm. the temperature was set to 54°c engineering, technology & applied science research vol. 12, no. 6, 2022, 9560-9564 9562 www.etasr.com ijaz et al.: assessment of protective clothing used by chemical industry workers in pakistan for 11±1 minutes. an approximate 0.1g/liter standard detergent was added in each wash cycle. the samples were spun at 1300rpm for about12 minutes. the tumble drying was made at 68°c for one and a half hours. a total of 15 laundering cycles were applied to the samples from each category. after every 5 cycles, they were labeled and processed for further testing. all test samples were kept at a temperature of 21°c and 65% relative humidity for one day [23]. the samples were assessed for their resistance against 4 liquid chemicals, i.e. sulphuric acid, sodium hydroxide, xylene, and butanol, according to the procedure defined by iso 6530:2005 [24], through their ratios of penetration and repellency. this method helps determining the rate of penetration and repellency against these liquid chemicals [25]. the samples from each group were cut into 14×9 inch pieces and were taken as an upper layer. an absorbent sheet with a plastic back of the same dimensions was also acquired and weighed separately. their distance was approximately 1 inch and they were placed on a collector layer. this test assemblage was tilted at 45°. ten milliliters of each chemical were poured off through a nozzle from the test fabric and were collected in a beaker placed beneath it. after a minute, both layers were separated and weighed again. the chemical retained by the collector layer was considered for the penetration rate. the chemical in the beaker was recorded as the repellency rate. at least one of the chemicals should repel 95% and penetrate less than 5% of the samples. the rate of penetration was measured as: � = �×��� � (1) where a is the chemical retained by the absorbent sheet and b is the chemical retained by the test specimen. the rate of repellency was calculated as: � = × ��� � (2) where c is the chemical collected in a beaker and b is the chemical retained by the test specimen. iii. results and discussion the tested clothing materials did not pass the minimum performance criteria for protecting against liquid chemicals. the samples did not repel 95% of any chemical, even at the initial washing cycles. moreover, more than 5% of each chemical penetrated them even at zero washes. the condition worsened with each washing interval. one of the main reasons was the increase in the porosity of the fibers due to the laundering cycles, as they opened their structure and allowed the chemical to pass through more easily. the difference between samples was due to the variation in fiber content. it is always necessary to study the chemical resistance of protective clothing worn by workers for protection. laundering thins the fibers due to the constant rubbing in the washing machine and weakens them, letting the liquid pass through them [26]. the kind of polymer plays an important role in determining the chemical behavior of fabrics [27]. it was found that specimen ab-1 performed well, followed by ab-5 and ab-2, due to the presence of polyester fibers which helped repel the chemicals. it was also found that the fabrics were made in a single layer with low mass rates, which also caused them to allow the penetration of more chemicals and repel less [28]. the increase in mass and the number of layers increases the time it takes for any chemical to penetrate the structure [29, 30]. the lamination and coating applied on the surface of fabrics also makes them strong and durable against the penetration of liquids. it was observed that the tested samples were laminated with weak finishing treatments that leaked the chemicals in the very initial washing cycles. this treatment was removed at the last interval and all liquid chemicals permeated through the fabric structure, as seen in table ii. table ii. rate of penetration and repellency of tested specimens laundering cycle sample code sulphuric acid sodium hydroxide xylene butanol p r p r p r p r 0 ab-1 21.7 78.7 29.6 70.8 34.8 65.7 23.8 75.4 0 ab-2 38.5 61.5 48.6 49.8 64.2 34.8 49.8 45.8 0 ab-3 51.2 45.7 68.6 32.4 79.6 22.7 57.6 39.6 0 ab-4 50.9 41.1 66.2 32.9 78.5 20.7 73.9 25.1 0 ab-5 29.7 69.6 44.8 54.9 48.2 49.2 59.1 41.4 5 ab-1 39.7 61.5 49.7 51.4 49.3 48.1 48.9 49.7 5 ab-2 42.3 56.8 55.7 41.9 49.7 49.3 48.6 47.3 5 ab-3 50.8 38.3 73.6 27.9 72.3 24.2 78.5 19.6 5 ab-4 62.6 35.4 75.8 24.8 86.6 13.2 68.3 29.6 5 ab-5 48.6 51.7 55.8 43.6 59.8 41.8 58.2 41.8 10 ab-1 41.2 61.9 49.8 49.7 63.5 33.6 41.2 58.6 10 ab-2 59.8 41.8 67.8 32.1 78.1 21.5 42.8 37.5 10 ab-3 71.2 28.4 82.5 14.9 88.5 17.3 81.1 18.5 10 ab-4 68.9 29.2 80.5 19.5 88.5 11.2 83.5 15.8 10 ab-5 68.6 31.4 65.9 31.7 83.1 15.6 82.2 18.5 15 ab-1 79.7 22.5 69.2 29.5 76.3 22.4 82.9 17.4 15 ab-2 77.8 20.9 81.4 17.2 90.9 7.5 88.9 11.4 15 ab-3 80.4 18.7 88.5 11.6 92.5 7.3 88.6 10.2 15 ab-4 88.7 10.5 90.7 9.5 94.2 5.4 91.4 8.4 15 ab-5 76.7 22.7 85.6 13.5 89.3 9.9 89.1 10.8 note: p=penetration %age, r=repellency %age engineering, technology & applied science research vol. 12, no. 6, 2022, 9560-9564 9563 www.etasr.com ijaz et al.: assessment of protective clothing used by chemical industry workers in pakistan the penetration and repellency of the tested specimens were directly proportional to the laundering cycles. analysis of variance (anova) was applied to measure the difference between specimens after washing intervals of 0, 5, 10, and 15 cycles. the p-values, 0.00 and 0.001, show that specimens deteriorate in their performance with each washing interval for penetration and repellency respectively, as seen in table iii. table iii. statistic analysis at various washing intervals chemical resistance washing interval mean square f p-value penetration linear 17965.23 46.76 0.00 repellency linear 15674.52 38.91 0.01 iv. conclusion this study concluded that the locally manufactured protective clothing does not provide complete protection against liquid hazards. the variation in the results was due to the variation in the construction parameters of the collected samples. the performance of the materials worsened with the increasing number of washing cycles. this study can help textile manufacturers to make amendments to their construction parameters and techniques in order to provide better protection against chemical hazards. every industry has its performance requirements. v. future work and limitations this study was limited to the chemical industries, while follow-up studies should evaluate the performance of clothing used by the textile sector and medical or agricultural personnel. follow-up studies should also investigate other items of protective clothing, such as gloves and masks, as this study was limited only to protective coveralls. moreover, future studies should examine the risks of fire hazards. furthermore, future studies should also investigate the perceptions and experiences of employees and employers 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[30] international labour organization, "encyclopaedia of occupational health and safety," 2012. https://www.ilo.org/safework/info/ publications/wcms_113329/lang--en/index.htm. microsoft word etasr_v13_n1_pp9926-9931 engineering, technology & applied science research vol. 13, no. 1, 2023, 9926-9931 9926 www.etasr.com thuy et al.: an analytical solution for the dynamics of a functionally graded plate resting on … an analytical solution for the dynamics of a functionally graded plate resting on viscoelastic foundation dang thu thuy university of transport and communications, vietnam dtthuy@utc.edu.vn nguyen ngoc lam university of transport and communications, vietnam nngoclamkc@utc.edu.vn (corresponding author) dao ngoc tien hanoi architectural university, vietnam tiendn@hau.edu.vn hoang van thanh vietnam maritime university, vietnam hoangvanthanh@vimaru.edu.vn received: 16 october 2022 | revised: 5 november 2022 | accepted: 12 november 2022 abstract this paper deals with the dynamic response of functionally graded material (fgm) plates resting on a viscoelastic foundation under dynamic loads. the governing equations are derived by using hamilton’s principle using the classical plate theory and the higher-order shear deformation plate theory. using statespace methods to find the closed-form solution of the dynamic response of functionally graded rectangular plates resting on a viscoelastic foundation. numerical examples are given for displacement and stresses in the plates with various structural parameters and the effects of these parameters are discussed. the result of the numerical example shows a marked decrease in displacement and stresses as the coefficient of viscous damping is increased. keywords-dynamic; fgm plate; viscoelastic; viscoelastic foundation; analytical method i. introduction structural engineering problems such as in beams, frames, plates, and shells can be solved by experimental methods [1-3], analytical methods [4, 5], and numerical methods such as finite elements [6-11]. the dynamic problem of beams or plates on foundations has been investigated by many researchers [12-17]. when using analytical and semi-analytical methods, we depend on the boundary condition to choose the approximation function of the displacement fields. usually, the navier approach [18] and the ritz method [19] are used for simple rectangular plates, and the ritz method [20] and fourier-bessel series [21] for circular plates. the dynamic stability of the orthotropic plates subjected to an arbitrary dynamic load was studied with the galerkin method in [22]. the dynamic response of plates [23] on an elastic foundation is subjected to moving loads using the strip method. an asymptotic theory was used in [24] to study the dynamic response of anisotropic inhomogeneous and laminated plates. the galerkin method was used to deal with the analysis of the nonlinear dynamic response of a laminated composite plate subjected to blast loading in [25]. the wave propagation of the rectangular fgm plates [26] with clamped supports under impulse load using the dispersion relation and integral transforms. the dynamic behavior of fiber-reinforced plastic sandwich plates with pvc foam core was analytically studied in [27]. the dynamic stiffness matrix was constructed in [28] for an infinite or semifinite timoshenko beam on the viscoelastic foundation to the harmonic moving load. the stochastic finite element method was utilized for the calculation of the variability of the eigenvalue coefficient of the function of the graded beam. engineering, technology & applied science research vol. 13, no. 1, 2023, 9926-9931 9927 www.etasr.com thuy et al.: an analytical solution for the dynamics of a functionally graded plate resting on … in this paper, the governing equation of the functionally graded plates resting on viscoelastic foundation is solved by hamilton’s principle. the sinusoidal function and the navier approach are used to find the dynamic solution of functionally graded simply supported rectangular plates subjected to step loading. ii. governing equation of the fgm plate we consider an fgm plate resting on a viscoelastic foundation. the geometry of the plate and the coordinate system is shown in figure 1. fig. 1. the geometry of the fg plate. the viscoelastic foundation is modeled as a winkler model with stiffness coefficient k and damping coefficient c. the displacement fields at an arbitrary point (x,y,z) in the plate are shown below. using the classical plate theory we have:             , , , , , , , , , , , , , , , , , w u x y z t u x y z t z x w v x y z t v x y z t z y w x y z t w x y t          (1) using higher-order shear deformation plate theory proposed by shimpi [30] we have:               2 2 1 5 , , , , , , 4 3 1 5 , , , , , , 4 3 , , , , , , , b s b s b s w wz u x y z t u x y z t z z z x h x w wz v x y z t v x y z t z z z y h y w x y z t w x y t w x y t                               (2) the mechanical properties of fgm, such as young’s modulus e and mass density ρ are assumed as:         1 2 1 2 n c m m n c m m z e z e e e h z z h                       (3) where the subscripts m and c represent the metallic and ceramic constituents, respectively, and n is the power index of the volume fraction. the linear constitutive relations of plate can be written as: 11 12 12 22 44 55 66 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 x x y y yz yz xz xz xy xy q q q q q q q                                                    (4) where:     11 22 11 122 2 44 23 55 13 66 12 , , 1 1 , , e z ve z q q q q v v q g q g q g         using hamilton’s principle we obtain the equations of motion of a plate as follows:  using the classical plate theory (cpt): 0 1 0 1 2 22 2 2 2 0 1 2 2 xyx xy y xy yx nn w i u i x y x n n w i v i x y y m mm kw cw f x yx y u v i w i i w x y                                        ɺɺ ɺɺ ɺɺ ɺɺ ɺ ɺɺ ɺɺ ɺɺ ɺɺ (5)  using the higher-order shear deformation plate theory (hsdt):       0 1 1 0 1 1 2 22 2 2 0 1 2 22 2 2 2 2 2 2 2 xyx b s xy y b s b bb xy yx b s b s b s ss xy yx b s nn w w i u i j x y x x n n w w i v i j x y y y m mm k w w x x y y u v c w w q i w w i x y m mm i w j w x x y                                                           ɺɺ ɺɺ ɺɺ ɺɺ ɺɺ ɺɺ ɺɺ ɺɺ ɺ ɺ ɺɺ ɺɺ ɺɺ ɺɺ       2 2 2 0 1 2 2 s yzxz b s b s b s b s y qq k w w c w w q x y u v i w w j j w k w x y                           ɺ ɺ ɺɺ ɺɺ ɺɺ ɺɺ ɺɺ ɺɺ (6) where:   / 2 22/ 2 2 1 4 62 4 2 2 2 2 2 1 5 , 4 3 1 5 25 16 6 9 h i i i i i h i z z dz j i i h k i i i h h x y                 the force and moment resultants of the plate are defined by: engineering, technology & applied science research vol. 13, no. 1, 2023, 9926-9931 9928 www.etasr.com thuy et al.: an analytical solution for the dynamics of a functionally graded plate resting on …   / 2 / 2 / 2 / 2 / 2 / 2 / 2 / 2 ˆ ˆ x x h y y h xy xy b x x h b b y y h b xy xy s x x h s s y y h s xy xy hx xz h y yz n n n dz n m m m z dz m m m m f dz m q g q                                                                                                        dz  (7) iii. analytical solution for τηε dynamic response of τηε fgm plate the sinusoidal function based on the navier approach is chosen to satisfy all boundary conditions, as follows:                     1 1 1 1 1 1 1 1 , , cos sin , , sin cos , , sin sin , , sin sin mn n m mn n m b bmn n m s smn n m u x y t u t x y v x y t v t x y w x y t w t x y w x y t w t x y                                     (8) where , m n a b      . substituting (8) into (5) and (6) the forced vibration of the functionally graded plate can be written as follows:  using the cpt: 11 12 13 12 22 23 13 23 33 33 11 13 22 23 13 23 33 0 0 0 0 0 0 ˆ0 0 0 0 0 0 mn mn mn mn mn mn mn mn mn mn s s s u u s s s v v s s s w c w m m u m m v m m m w f                                                          ɺ ɺ ɺ ɺɺ ɺɺ ɺɺ (9)  using the hsdt: 11 12 13 14 12 22 23 24 13 23 33 34 33 14 24 34 44 44 11 13 14 22 23 24 13 23 33 34 14 24 43 44 0 0 0 0 0 0 0 0 ˆ0 0 0 ˆ0 0 0 0 0 mn mn mn mn bmn bmn smn smn s s s s u u s s s s v v s s s s w c w s s s s w c w m m m m m m m m m m m m m m                                            ɺ ɺ ɺ ɺ 0 0 mn mn mnbmn mnsmn u v fw fw                                  ɺɺ ɺɺ ɺɺ ɺɺ (10) where: 0 0 4 sin sin b a mnf q x ydxdy ab     (11) we consider uniformly distribution loads as follows:  0q q f t ⌢ (12) the function of time  f t ⌢ of dynamic loadings is considered as step loading:   1 1 1 0 0 t t f t t t      ⌢ (13) in this work, we use the state-space method to solve (9) and (10), which must be rewritten in order to find a solution, as follows:  ɺz az b (14) where:    1 2 3 40 0 0 0 t mn mn bmn smn mn mn bmn smn t u v w w u v w w b b b b   ɺ ɺ ɺ ɺz b the solution of (14) is obtained as:          0 0 0 t t t t t t e t e d       a a z z b (15) where t0 is the initial time,  0tz is the initial response, and  0t te a is the exponential matrix. this exponential matrix can be formulated in terms of the matrix of eigenvectors and eigenvalues associated with matrix a. iv. numerical examples we consider a simply supported rectangular fgm plate with side-to-thickness ratio a/h=10, rectangular dimensions of a=0.3m, b=0.5m, and power index p=3. the elastic moduli and mass density are chosen to be the same as in [31]: ρm = 2707kg/m 3 , em = 70gpa, ec = 380gpa, ρc = 3800kg/m 3 , with poisson’s ratio being 0.3. the uniform load is written as  20 kn100 mq  and the duration of load application time is t1 = 0.002s. we note the normalized stiffness coefficient and the normalized damping coefficient of the foundation as follows: 4 2 , m m ka ca k c d d   (16) where   3 2 12 1 m m e h d v   is the flexural rigidity of a full-metal plate. the first two mode shapes are shown in figure 2. engineering, technology & applied science research vol. 13, no. 1, 2023, 9926-9931 9929 www.etasr.com thuy et al.: an analytical solution for the dynamics of a functionally graded plate resting on … (a) (b) fig. 2. (a) first and (b) second mode shapes of the simply supported rectangular fgm plate. we consider two cases of viscoelastic foundation to investigate the effect of the damping coefficient of the viscoelastic foundation: case 1: 5, 0.05 case 2: 5, 0.1 k c k c      (a) (b) fig. 3. the deflection response at the central plate. cases (a) 1, (b) 2. (a) (b) fig. 4. the normal stress σx at the top of the central plate (z=h/2). cases (a) 1, (b) 2. (a) (b) fig. 5. the normal stress σy at the top of the central plate (z=h/2). cases (a) 1, (b) 2. figure 2 illustrates the transverse deflection due to step loading as functions of time. figures 3–4 show the transient response of stress at the center of the plate for the two considered cases. the amplitude of dynamic responses decreases due to the influence of viscous damping. the displacements computed by hsdt are clearly larger than those using the cpt because the plate modeled by cpt is relatively stiffer. however, the deviation of stresses σx, σy between cpt and higher order plate theories is small. so, the effect of shear deformation is more significant in predicting displacement than engineering, technology & applied science research vol. 13, no. 1, 2023, 9926-9931 9930 www.etasr.com thuy et al.: an analytical solution for the dynamics of a functionally graded plate resting on … predicting stresses. in the forced vibration regime, it can be seen in figures 2–4 that the deflection and stresses predicted for functionally grade plates with c=0.05 are moderately larger than for the plate with c=0.1. it is observed that when the damping coefficient increases, the deflection and stresses become smaller, as expected. v. conclusions this research computed the vibration of the functionally graded plate resting on the viscoelastic foundation by the analytical method, using both classical plate theory and higherorder shear deformation plate theory. the analytical solution for the dynamic functionally graded plate was solved to be a double sine series based on the navier approach. dynamic responses are considered for both forced and free vibrations. the results show that the damping coefficient of the foundation has a significant influence on the dynamic response of the functionally graded plate. the damping factor of the foundation dissipates energy, reducing the ambient vibrations in forced and free vibrations. this work is significant to structural engineering, and the results can be used in practical design structures. acknowledgment this research is funded by university of transport and communications (utc) under grant number t2022-ct-023. references [1] z. h. dakhel and s. d. mohammed, "castellated beams with fiberreinforced lightweight concrete deck slab as a modified choice for composite steel-concrete beams affected by harmonic load," engineering, technology & applied science research, vol. 12, no. 4, pp. 8809–8816, aug. 2022, https://doi.org/10.48084/etasr.4987. 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[31] a. hasani baferani, a. r. saidi, and h. ehteshami, "accurate solution for free vibration analysis of functionally graded thick rectangular plates resting on elastic foundation," composite structures, vol. 93, no. 7, pp. 1842–1853, jun. 2011, https://doi.org/10.1016/j.compstruct.2011.01. 020. microsoft word etasr_v13_n3_pp10675-10679 engineering, technology & applied science research vol. 13, no. 3, 2023, 10675-10679 10675 www.etasr.com jeevakala & ramasangu: classification of cognitive states using task-specific connectivity features classification of cognitive states using taskspecific connectivity features siva ramakrishna jeevakala m. s. ramaiah university of applied sciences, india jsrkrishna3@gmail.com (corresponding author) hariharan ramasangu relecura inc., india rharihar@ieee.org received: 6 march 2023 | revised: 24 march 2023 | accepted: 29 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5836 abstract human brain activity maps are produced by functional mri (fmri) research that describes the average level of engagement during a specific task of various brain regions. functional connectivity describes the interrelationship, integrated performance, and organization of these different brain regions. this study investigates functional connectivity to quantify the interactions between different brain regions engaged concurrently in a specific task. the key focus of this study was to introduce and demonstrate task-specific functional connectivity among brain regions using fmri data and decode cognitive states by proposing a novel classifier using connectivity features. two connectivity models were considered: a graph-based taskspecific functional connectivity and a granger causality-transfer entropy framework. connectivity strengths obtained among brain regions were used for cognitive state classification. the parameters of the nodal and global graph analysis from the graph-based connectivity framework were considered, and the transfer entropy values of the causal connectivity model were considered as features for the cognitive state classification. the proposed model achieved an average accuracy of 95% on the starplus fmri dataset and showed an improvement of 5% compared to the existing tensor-svd classification algorithm. keywords-functional mri; functional connectivity; nodal analysis; graph analysis; causal connectivity; cognitive state classification i. introduction functional connection in neuroscience is the covariation between spatially dispersed brain regions or brain signals. typically, brain signals are captured using a functional neuroimaging technique, such as electroencephalography (eeg), functional near infrared spectroscopy (fnirs), functional mri (fmri), magnetoencephalography (meg), and electrocorticography (ecog). in general, functional connectivity (fc) experiments are conducted under resting state conditions (without any task demands or external stimulation). however, understanding how external stimuli modulate fc has attracted the research interest. during the recent decades, fmri has been highly successful in establishing functional relations between brain regions. functional mri is the most popular method for learning and delineating human brain regions that change their activation level while performing a specific task. the brain imaging modality can reveal information about neural systems that are functionally coupled together for specific stimuli or tasks. functional neuroimaging can provide deep insight into the neurobiological underpinnings of disabilities. the concept of finding cognitive functions, as referred to by the connectivity networks of brain regions, is crucial in interpreting neuroscientific data [1]. the fc patterns computed over some time comprise enough details to identify the task the individuals are working on [2]. however, whether task-specific or resting-state available connectivity interactions are two manifestations that arise from the same underlying neural phenomenon is still under debate. human cognition generally involves dynamic and complex interactions between dispersed cortex and subcortical areas [3]. the brain at rest is usually represented in a small number of networks compared to the number of functions it performs. revealing the putative correspondence between specific fc features and different aspects of task performance is very important. the studies on distributed patterns of fc are used to classify or decode cognitive states [4]. task-based connectivity studies produce different fc patterns for different cognitive tasks. researchers have been measuring functional relationships among brain areas using neurophysiological data acquired from neural components. functional and effective connectivity are the two aspects of functional interactivity [5]. when the actions of two brain components are correlated, they are said to be linked. the impact of one neuronal entity on another is referred to as an effective connection that establishes a causal relationship between the brain areas. fc analysis is a modelengineering, technology & applied science research vol. 13, no. 3, 2023, 10675-10679 10676 www.etasr.com jeevakala & ramasangu: classification of cognitive states using task-specific connectivity features free approach; on the contrary, effective connectivity is a model-based approach [6]. fc is a simple phenomenon observed from correlations and represented in terms of covariance. the key aspects of the covariance are the patterns of correlated activity delimited by pairwise covariances. modeling human brain networks is an essential step in determining connectivity patterns. in this work, the human brain is shown as a network through graph-based approaches. the model provides a graphical representation in the form of nodes and edges. the causal connectivity among the brain areas is analyzed using a pipeline framework formed by granger causality and entropy. machine learning classifiers have been used for the detection and classification of objects in several scientific applications [7-9]. resting-state neuroimaging studies soon identified a list of canonical fc patterns that are consistently discovered when at rest and fc patterns and task-evoked activation patterns [10]. the correlations between functional time series are used to assess patterns of brain functional connectivity. traditional correlation techniques can capture fc and provide a relationship between two regions of interest (rois) while ignoring the interaction between other rois. for instance, the second-ordered relations could give a significant understanding of neurological processes associated with brain regions [11]. as a hypergraph's edges may connect any number of rois rather than just two, it has been used to specify the high-order interactions between many rois (or vertices) [12]. instead of simply setting each hyperedge's weight to 1, the hypergraph is used to learn adaptively more flexible hyperedge weights, assuming that all rois at each time point are seen as a smooth signal on the hypergraph. a typical fc network for different subjects is represented by a graph-based hypergraph derived from the fmri time series. the obtained connectivity is further used to classify alzheimer’s disease [13]. inter-individual variations in resting fc patterns have been linked to various phenotypic qualities, as well as clinical problems (e.g., mental and neurological illnesses), and can be used to predict behavioral performance and identity [14]. beyond what mechanistic insight they may (or may not) provide on interregional brain interactions and their relation to cognition, fc estimates can be useful, according to the results of [15]. the graph-based method provides more information on topological reconfiguration in response to external stimuli or task modification [16-17]. the framework explains how brain functions and structure are related. both functional and structural networks have been shown to organize intrinsically when information is transferred and related hub regions are formatted [18-19]. most fc methods used with bold fmri data are constrained in their ability to provide details on the specific topology of the underlying causal graph, but still, they restrict the range of network topologies that may be considered [20]. even though resting state fc research has contributed to a deeper grasp of how the brain works in various subjects, it has been limited by the application of approaches that cannot resolve critical motivating difficulties concerning task-specific fc in the context of cognitive task categorization and effective connectivity among the brain areas. this study used graphbased fc analysis and entropy-based causal connection for connectivity analysis, and the connectivity parameters obtained were used as features to decode cognitive states. ii. proposed task-specific connectivity analysis for cognitive state classification the study of fc of the human brain has piqued the interest of the scientific community. defining and comprehending how various brain regions interact requires identifying functional connectivity networks using fmri data. fc aims to find statistical connections between two or more rois. the utility of connectivity analysis is also applied to the classification of fmri data. the connection characteristics are used to create a classifier to categorize cognitive states. figure 1 shows the proposed task-specific connectivity analysis framework. fig. 1. proposed connectivity analysis framework for decoding the cognitive states. the proposed model is a 5 step approach for cognitive state classification. in step 1, brain regions or rois are selected from the fmri dataset. since fmri data comprise a significant number of rois, it is often essential to select appropriate rois from the pool. step 2 involves the extraction of the voxel time course. as fmri data are usually represented in rois, each roi comprises a voxel time course. since the proposed model operates with time series, the required voxel time course is extracted from each roi to perform connectivity analysis. step 3 involves the connectivity analysis over the extracted time series. this step performs the functional and causal connectivity analyses to find the connectivity relation among the rois. connectivity analysis includes the graph-based connectivity analysis and the granger causality transfer entropy (te) framework. the details of the graph-based and causal connectivity analyses are elaborated below. a. graph-based connectivity analysis the behavior of networks is described in terms of nodes and their connections in a graph theory study on fmri data. in the human brain network, brain areas are nodes and engineering, technology & applied science research vol. 13, no. 3, 2023, 10675-10679 10677 www.etasr.com jeevakala & ramasangu: classification of cognitive states using task-specific connectivity features connections are edges. histological, functional, or anatomical parcellation schemes can be used to designate the sections of the brain graph nodes. interactions among the regions are used to define the edges. after pooling the pairwise connections between nodes in the network, the characteristics of a brain graph are assessed to estimate connections at local and global levels. relationships that are both temporal and functional with other regions are characterized by these qualities. this study investigates the functional connection strengths among the brain areas for task-specific fmri data. the interconnectedness between rois (nodes) would be quantified once the cohorts for each participant and the brain atlas are built. using brain network analysis, the connection between the rois (nodes) is assessed and the statistical correlation between them is measured using graph analysis. this study utilized pearson's correlation for both individual and group analyses. a weighted undirected graph was used to create a functional connectivity graph and several global and nodal parameters were computed for the study. b. task-specific connectivity analysis using grangercausality and transfer entropy framework. causal connectivity is the comprehension of the causal connection between different brain areas. to conduct task-and disease-specific research, it is assumed that fmri-based causal connectivity approaches would shed light on these connection differences. the results of a causal connection study show a causal or significant reliance between rois. effective connection explores the causal chain between different brain areas. the co-activation of brain regions is the basis for fc. understanding the causal connection between various brain areas is referred to as causal connectivity. effective connection analysis is provided by the granger causality (gc) [21] technique using a data-driven methodology. each roi is regarded as a variable for the gc analysis when assessing causal connection. a time series t1 impacts t2 if the information from t1's history may be used to anticipate the values of t2's future observations. when this criterion is met, information flows from t1 to t2. a time series-based brain connectivity estimate was carried out to investigate the functional interconnections between the rois. in this connection investigation, the primary goal was to estimate the granger causality-based task-specific causal interactions between the rois. te calculates the causal strength in a given situation. the suggested human brain cognitive connectivity analysis was applied to starplus fmri data and the granger causality technique was used to assess the influential connections among brain areas. in step 4, the feature vectors were formed from the nodal and global parameters of functional connectivity analysis, and te values were obtained for the granger causality. the obtained features were treated as attributes for cognitive state classification. in step 5, a classifier was developed using features extracted in the previous step. three classifiers, namely gaussian naïve bayes, support vector machine, and knn classifiers, were built for cognitive state classification. the proposed classification model based on the connectivity features was verified on standard starplus fmri data. iii. starplus fmri data the suggested approach was confirmed based on the starplus fmri data [22], which provide easily accessible fmri data for the categorization and study of the human brain's cognitive states. the captured brain volumes are divided into a set of trials in the two-phase experimental design. for each trial, subjects are required to determine if a statement or symbol was followed by a different sentence or symbol and negotiate properly. the first phase involved displaying one of two sentences to the subject: "the star is above the plus" or "the star is below the plus." after 4 seconds, this will disappear from the screen and an empty screen will appear. an image stimulus will be shown for 4 seconds following 4 seconds of the screen being blank. the individual is required to touch the button after 4 seconds of visual stimulation to indicate whether or not the statement accurately describes the image. brain images are captured during the experiment every 0.5 seconds. throughout the experiment, each participant has a 15-second rest or fixation interval. the experiment is repeated in the second phase, but this time, the picture and phrase stimuli are exchanged. the subjects in the dataset have approximately 5000 voxels marked as 25 rois. as reported in the literature, 7 out of 25 rois, calc, ldlpfc, lips, lipl, loper, lt, and ltria, are used for the classification and analysis of the cognitive behavior of the brain. iv. results and discussion functional brain networks show how the brain's architecture and behavior are related. functional networks built using fmri data tailored to a certain activity aid in gaining insight into how multitasking affects brain structure. in [23], the graph-based connectivity model was used to determine the connectivity strengths among the cognitive tasks. the graphbased connectivity model has not been used to build the classifier for cognitive state classification. in [24], the causal connectivity model was used for cognitive state classification, where the model considered 11 rois from a similar starplus dataset. this study combined both connectivity model parameters as features for the classification of cognitive states. there are several disciplines in which graph theory and gc analysis are useful. nevertheless, graph theory and gc are new when applied to cognitive fmri data. for cognitive data, nodal and global parameters are used to evaluate the interconnectedness between rois, and te is used to assess the causal potency of those connections. the starplus fmri dataset voxels are grouped into 25 rois. of these, the 7 most important rois were chosen for further study. the roi level analysis reveals two distinct functional networks for image and sentence tasks, as shown in figure 2. the connectivity graphs are defined from nodal measurements for each task. figure 3 shows the correlation matrix for each task (visual and verbal) for the starplus fmri data. engineering, technology & applied science research vol. 13, no. 3, 2023, 10675-10679 10678 www.etasr.com jeevakala & ramasangu: classification of cognitive states using task-specific connectivity features (a) (b) fig. 2. (a) obtained fc network for a sentence task, (b) obtained connectivity network for a visual task. (a) (b) fig. 3. (a) acquired binary weighted matrix for the visual task, (b) acquired a binary weighted matrix for the verbal task. the causal connectivity analysis was conducted using the gc approach, and the corresponding causal strengths were obtained from transfer entropy (te). although it is used to analyze neuroimage data, the gc-te framework is unique in the context of task-specific connectivity analysis. consequently, 6 subjects from the starplus fmri data were subjected to the gc test. an analysis utilizing a vector autoregressive model (varm) can characterize gc. the model’s order was set to 2, meaning the roi time course will be modeled using the previous two values of the time series data. this study used a classifier based on graph analysis and causal connection characteristics to identify the cognitive states in the starplus fmri data. voxels selected using a maximum margin criterion based on clustering define the roi time series. feature vectors are formed by the concatenation of graph analysis, such as nodal and global parameters, and te values from causal connectivity analysis. table i shows the classification accuracy for the svm, gnb, and knn classifiers. the classification was carried out in a leave-oneout fashion. table ii shows the classification accuracy results for the training-test scheme, where 80% of the data was utilized for training and 20% for testing. the proposed classification framework achieved an average accuracy of 95% for the 6 subjects in the starplus fmri data. these results were compared with those reported in [25] using the tensor singular value decomposition (t-svd) framework for the classification of cognitive states. the t-svd framework achieved a classification accuracy of 90%. table i. leave one out classification accuracy (%) for starplus fmri data across the classifiers s. n. subject svm (%) knn (%) gnb (%) 1 05710 78 95 84 2 05680 78 96 78 3 05675 82 98 95 4 04847 64 94 80 5 04799 74 92 70 6 04847 76 94 75 average 75.3 94.8 80.3 table ii. training-test scheme classification accuracy (%) for starplus fmri data across the classifiers s. n. subject svm (%) knn (%) gnb (%) 1 05710 60 98 75 2 05680 75 96 78 3 05675 82 95 94 4 04847 60 93 78 5 04799 75 94 72 6 04847 64 94 76 average 69.3 95 78.8 v. conclusion the classification of cognitive states is achieved using connectivity features. the functional connectivity models considered in this work included the graph analysis framework and the granger causal connectivity analysis framework. the analysis was conducted using functional mri data having a pair of cognitive states. the roi connectivity analysis provides insight into the roi connectivity strengths. this work was identified by a graph analysis method. data from rois’ voxel time series were fed into the system, a brain atlas was developed, and both global and nodal factors were considered while calculating connection strengths. in the case of causal connectivity analysis, the granger causality transfer entropy paradigm was applied to assess the strength of causal connections between rois. connectivity analysis was carried out using the starplus fmri data. the connection of each roi was evaluated and granger causal connectivity was used to perform causal or influential connectivity. nodal and global graph analysis parameters of the graph-based connectivity framework were considered, and the transfer entropy values of the causal connectivity model were considered as features for cognitive state classification. the proposed classification model achieved an average classification accuracy of 95%. the results obtained were compared with the existing tensor svdbased classification which achieved a 90% classification accuracy. this study used graph-based and causal connectivity analysis parameters for the classification of cognitive states. the proposed framework produced a new classifier with connectivity features as input in the context of decoding brain states. references [1] j. chen et al., "shared and unique brain network features predict cognitive, personality, and mental health scores in the abcd study," engineering, technology & applied science research vol. 13, no. 3, 2023, 10675-10679 10679 www.etasr.com jeevakala & ramasangu: classification of cognitive states using task-specific connectivity features nature communications, vol. 13, no. 1, apr. 2022, art. no. 2217, https://doi.org/10.1038/s41467-022-29766-8. 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[25] k. keegan, t. vishwanath, and y. xu, "a tensor svd-based classification algorithm applied to fmri data." arxiv, oct. 31, 2021, https://doi.org/10.48550/arxiv.2111.00587. microsoft word etasr_v13_n1_pp10051-10059 engineering, technology & applied science research vol. 13, no. 1, 2023, 10051-10059 10051 www.etasr.com ali et al.: danger sign detection and recognition using convolutional neural networks substation danger sign detection and recognition using convolutional neural networks wajid ali school of automation and electrical engineering, lanzhou jiaotong university, china wajidaliustb@gmail.com guo wang school of automation and electrical engineering, lanzhou jiaotong university, china wangguo@lzjtu.edu.cn (corresponding author) kalim ullah university of science and technology bannu, pakistan engr_kalim125@yahoo.com muhammad salman school of automation and electrical engineering, lanzhou jiaotong university, china salmankhan5780@gmail.com sajad ali school of automation and electrical engineering, lanzhou jiaotong university, china sajad8371@gmail.com received: 14 november 2022 | revised: 7 december 2022 | accepted: 15 december 2022 abstract this paper focuses on the training of a deep neural network regarding danger sign detection and recognition in a substation. it involved applying the concepts of neural networks and computer vision to achieve results similar to traffic sign and number plate detection systems. the input data were captured in three distinct formats, i.e. grayscale, rgb, and ycbcr, which have been used as a base for comparison in this paper. the efficiency of the neural network was tested on a unique data set involving danger signs present in industrial and processing facilities. the data set was unique, consisting of four distinct symbols. the trained data were selected so that they would not facilitate overfitting and also would not be under fitted. the accuracy of the model varied with the input type and was tested with two distinct classifiers, cnn and svm, and the results were compared. the model was designed to be fast and accurate, and it can be implemented on mobile devices. keywords-cnn; neural networks; danger sign detection i. introduction signs play an important role in everyday life and come in a huge variety of color schemes [1], symbols, and words, originating from different regions, countries, and working environments. the main objective of this study was to recognize four different and distinct types of signs used in the industrial process worldwide. automatic danger sign detection can help prevent accidents that could endanger employees and civilians. the presence of an application on a smartphone that can recognize and warn about the meaning and danger associated with a sign can save lives. it is an ideal device for new and less experienced workers. nowadays, almost every person has a mobile phone, and about 80% of these are smartphones, able to integrate with the internet and run complex applications [2-4]. a neural network-based application can easily run on this type of phone. the target audience of this research is huge. it can benefit seasonal engineering, technology & applied science research vol. 13, no. 1, 2023, 10051-10059 10052 www.etasr.com ali et al.: danger sign detection and recognition using convolutional neural networks workers, new industrial recruits, engineers, etc. the study focuses on using neural networks (nns) to distinguish several danger signals. the application will be entirely web-based, having a mobile application to integrate with the user and even a web page for a direct online interface. the world has become heavily reliant on it, and the covid19 pandemic has shown that the potential of mobile applications and software is at its peak. a danger sign detection technique can be used in any application. the impacting factors are the sample size and training parameters, which have been tuned to give promising results and can be generalized to other symbols with slight modification and testing. the application shows it can accurately identify and classify data and warm people by recommending the prescribed precautions. this information is easy and can be quickly accessed on a phone. the database used in this study was compiled from scratch, as no dataset of this kind existed. this involved extracting images from online repositories and personal sight visits. image modification techniques were also used to add diversity and unpredictability to the dataset. the data set can be consistently updated and improved by adding more images. the more the images in the data set, the more accurate the training and testing will be. although this paper is focused on the danger signs found explicitly in the substation, the same techniques could be used with other data sets to recognize danger signs in different environments. the concept involves computer vision and nn integration. the main objective is to replicate an accurate and similar response to that of traffic sign detection and number plate identification. they both use similar tools and techniques. while extensive literature exists in the field of traffic sign detection, studies related to the identification of signs in other environments are limited at best and non-existent to the best of our knowledge. this study aims to fill this scientific gap. ii. basic about cnns a typical convolutional neural network (cnn) contains pooling, activation, normalization function, convolutional and multinomial logical regression (mlr) layers. usually, the last layer of the network is the mlr. this layer has a subpart known as the softmax function, which determines the final classification of data. the structure of the cnn model is chosen according to the difficulty and the problem that needs to be solved. the cnn model is designed with specific layers and neurons in mind. we can aim for higher accuracy for our results, but this will require more training time, a larger data set, and a more complex network structure [5]. iii. related work the ongoing progress in the field of nns includes improvements in the processing power required, reduction of the complexity of the algorithm, and advancements in computer vision. the closest mainstream topic related to computer vision, cnn, and image identification, is traffic sign or number plate detection. many papers have been published regarding traffic sign detection with various techniques and methods [1, 6-8]. most of these studies have existing data sets. these sets are classified into groups and are ready to be fed into the nn algorithm. in the current study, we had to make and classify the data and set and test the identifying markers and check their accuracy for our algorithm from scratch. iv. convolutional neural networks nns are often used to train and identify objects. these can be images, trends, anything that can be quantized in the form of data. though cnns are a powerful tool, they require high computational power and resources to function properly [9]. as microelectronics gets smaller, is makes nano electronics more prevalent and viable in the electronic landscape. accurate nn models require several layers, increasing the algorithm's complexity, the computational power required, and the energy needed to execute and process it. fortunately, the semiconductor industry has made this possible, providing handheld devices with the power of a modest computer. researchers have tried bringing deep learning models implemented in cnns to mobile devices. these belong to one of the three following categories:  network pruning [10]  network quantization [11]  training small networks directly. finding the ideal number of layers and neurons required for the accurate and efficient working of the network is necessary. overfitting, excess complexity, and several hidden layers can make the model accurate regarding the corresponding training data but sensitive to change, lacking robustness. the effects of overfitting and its correlation with robustness, validation, and training data were studied in [12]. there have been improvements in different techniques and methodologies to advance the techniques used in nns, such as [13, 14]. cnns have strong discrimination powers in terms of classifying objects. they can also accurately localize a portion of an image or data cluster using tools such as regression. in our efforts to deploy a model of cnn compatible with image extraction, we took inspiration from literature such as [14-16]. the main methodology applied in recent literature for detection networks are:  direct detection [14, 15]  regional detection [13, 17] a. direct detection the direct detection and prediction algorithms are based on the position or class of the target object. this information is provided with either regression or classification, depending on the problem and type of learning involved [18]. this can be extracted from the convolutional layer of the algorithm, making runtime faster in comparison. b. regional detection in regional detection, several regions are generated for the data in question, then data classes, and then the prediction operation is performed on object position and class for every region. in this method, regression and classification are conducted twice in different stages. this makes the regional detection method longer and more processing intensive, but more accurate in the computation of direct detection. engineering, technology & applied science research vol. 13, no. 1, 2023, 10051-10059 10053 www.etasr.com ali et al.: danger sign detection and recognition using convolutional neural networks for our purpose of danger sign identification and recognition, the regional detection method is preferred, as accurate identification of hazardous symbols can help prevent accidents and provide precautionary safety information for workers. there is no processing and time restraint, thus, the delay is an acceptable trade-off for higher accuracy. v. boundary detection techniques many cnn object identifiers use boundary boxes and class labels to identify and extract the exact image for learning [19, 20]. this can be useful in predicting the exact boundary boxes for the classified images. a danger sign varies depending on the type of hazard. some are triangular, while others are square or circular. these distinct and different bound conditions for the sign make image extraction significantly more accurate. we can identify an image using its boundary estimation, segmentation of the image itself, or sign and symbol category classification. the pixel segmentation mask would require high processing power and would be slower in identifying the letters and words shown on the symbol. however, this is possible and has many potential applications, such as universal danger sign detection software [20]. this could be compatible with all languages and work environments. such ideas have been forgone, as failure to identify a single letter in the sign can cause false or inconclusive results. thus the main techniques used were boundary detection and symbol recognition. vi. deep neural networks deep neural networks (dnns) have become an indispensable tool in image classification used in many applications, such as facial recognition, voice analysis, word or text analysis, etc. using dnn models helps in achieving high accuracy because of their ability to train and recognize complex input data [21]. the definition of a dnn is defined as a network with a level which is represented by the presence of three or more hidden layers. vii. convolutional neural networks support vector machine support vector machine (svm) is a supervised model in machine learning [22] that needs to be given labelled input data and a classification algorithm is used to train itself for each given label. its main advantage lies in its speed and higher accuracy with a lower input sample count. this can make this algorithm ideal for a task requiring robust classification [2325]. the svm technique is used mostly as a classifier in data evaluation. the ability of svm in data analysis can help find the ideal margin between two distinct classifications. svm is used to determine a hyperplane for each set of distinct outcomes from a given input. if the hyper plain is situated ideally between the trained data sets, it can provide a degree of robustness to the system. svm is used in traffic signal recognition and training. the basic cnn is used for convolution and training, while the support vector classifer (svc) is used for classification. the hybrid combination of scv and cnn is combined to give accurate results for a small number of training sets [26]. viii. methodology the training of the system involved five basic steps: 1. making a data set appropriate for integration. 2. deciding the most appropriate and accurate type of nn to choose. 3. training strategy used and data optimization in order to acquire the best results. 4. model selection involves the layers and neurons in the algorithm, basically determining the complexity of the algorithm and its robustness. 5. the model in question used for the training of our model has 3 convolutional layers followed up by a pooling layer each. the end results of the layers are fed into a flattened layer to convert a 3-dimensional image into 1-dimensional weights. these weights are used in the deep layer to find the weight coefficients to recognize and categorize the image into one of 4 different categories. the first step was taking in the respective input format. the images captured for processing could be used in one of three ways:  grayscale [27]  rgb [28]  ycbcr [29] ix. image analysis a. rgb the rgb data set is the default spectrum used as input for most image recognition applications. though it is thoroughly used, our results indicated that a modification of rgb, known as ycbcr, gives better results. the luminance information, known as y, is scattered in all the dimensions of rgb. this information can be used to get better image parameters for training data. below is a simple conversion from rgb to ycbcr [31]. y = 0.299r+0.587g+0.114b (1) cb = 0.564(b−y) (2) cr = 0.713(r−y) (3) b. ycbcr the respective training error was the least in ycbcr results for the limited training data set. the ycbcr is inherently superior to grayscale and rbg, as in grayscale many colors and contact information are lost and therefore are not taken into account while training. any colored image can be converted into a grayscale by multiplying the colored coefficients (usually rgb) with constants. this converts 3-dimensional data into a 1-dimensional data set. grayscale results were faster to train but had a training error twice that of the ycbcr data set [30]. the model was trained with the same image data but with different feature extraction. engineering, technology & applied science research vol. 13, no. 1, 2023, 10051-10059 10054 www.etasr.com ali et al.: danger sign detection and recognition using convolutional neural networks c. grayscale the following converts an rgb image to grayscale: grayscale = 0.299r + 0.587g + 0.114b (4) the grayscale image is less complex as the data can only vary in one parameter. this can help make the data set more robust and less prone to overfitting, though much of the image information is lost when converting an image into grayscale data. the decrease in complexity did not adversely affect the results. quite the contrary, the grayscale results proved better than the rgb. x. training information the training process involved using four distinct image types for categorization. these were:  electric hazard  flammable risk  radiation danger  toxic materials fig. 1. image categories. we chose similar image shapes as already much work has been done on boundary identification markers. instead of focusing on the shiny shape, we trained the cnn to identify the color pattern and the symbols present [32]. each image was similar to the others to an extent, e.g. similar sign shape and base color contrast (yellow and black). thus, the main objective was convolving the image and using the dnn nodes to recognize the district shapes. xi. image standardization we used bounding box regression to standardize the extracted image from the input. it can be taken from an angle and still correctly extract the image [14]. the regression vector can compress or expand the image to the ideal size for data input. we used shape classification for images with different shapes. most images are of similar shape, including circular, triangular, rectangular, square, hexagonal, and octagonal. for the ease of data usage, we normalized the coordinates of both the x and y-axis. we can use this to find the exact extraction of all shapes except circular images and in our data set, there were no circular image boundaries, so that was not a major concern. circular images are detected with small sheer errors, though the cnn-trained system was still able to recognize the symbols and give accurate results. fig. 2. image fitting using regression vector. xii. model overview the model was trained on the gathered images that made a completely new and authentic data set. the network parameters were tuned during training and validation. relu, softmax deep cnn in a combination with svm were used. figure 3 shows some randomly selected images from the data set. fig. 3. samples of the training set. the data used for training consisted of 425 images, and the testing set included twice that number. the convolutional layers were used to segment the image into 64 blocks, each for a different color, for both rgb and ycbcr sets. the network architecture is shown in figure 4. we used 3 convolutional layers for quick response. more can be incorporated to increase the accuracy of the results. the training images were transformed into ycbcr-colored data. feature map size = n-f+1 (5) fig. 4. network architecture. engineering, technology & applied science research vol. 13, no. 1, 2023, 10051-10059 10055 www.etasr.com ali et al.: danger sign detection and recognition using convolutional neural networks xiii. detailed working of the model in our training, we passed 3 convolutional layers followed by max pooling. the input image was sized at 64×64 pixels. after passing through the convolution and relu layer, our resulting image was a 62×62-pixel image and our kernel was 3×3. we extracted 16 feature maps in these two stages. we have monitored and identified 448 parameters in this step. then, max-pooling by a 2×2 pool size and 2 unit stride took place, and the processed image reduced in size to 31×31 pixels. this input image was fed to the second convolution layer, resulting in a 29×29-pixel image, granting 32 feature maps and 4046 parameters. the next max pooling layer resulted in a 14×14-pixel image. pool size, kernel, and stride were kept constant for all convolution and pooling layers. by the last convolution layer, we had 64 feature maps of a 6×6-pixel image. after, a flatten operator was used to convert all the data into a linear array which passed as weights to the neurons. our model has a total of 388 neurons, 256 in the 1 st layer, 128 in the 2 nd layer, and 4 in the last layer for the respective outputs. figures 5-6 show the features of the modeled system. fig. 5. cnn model data. fig. 6. flow diagram. xiv. svm the system was tested using both svm and cnn, and both linear and non-linear svm types were tested. linear svm uses a dot product between two features, and its product is the linear product combination of the input features. ����� , ��� = ����� + ����� (6) in non-linear svm, this rule is not valid. instead, it uses kernel. this reduces the dimensionality of the input into various classifiers, replacing the dot product of linear svm. this svm can be used to learn shapes in higher dimensional data when using the kernel. xv. neural network an nn with more than one layer is non-linear, and there are 3 main activation functions used in such cases, which are: logistic function z = σy (7) hyperbolic tangent z = tanh y (8) softmax ∅�y = ��� ∑ ������� (9) xvi. comparison for our study, we used the softmax function. a basic understanding of nns is necessary for the classification of data and while comparing svm and nn. in contrast, svm was a multipurpose non-linear nn designed for classifying the problem. thus we based our classification approach on the nn. another reason for choosing svm was the lack of a large data set. svm is simpler than the complex nn and has given better results on smaller data sets. thus our cnn model used the relu classifier and our svm model used the softmax activation function to clearly identify the effect on filter training and its effect. xvii. cnn in our cnn, we have used relu (rectified linear unit) as activation function and the dropout layer. the nn is assumed to have:  linear independence in the input features.  low dimensionality in the input space. by implementing various convolution layers and pooling, we lowered the dimensionality of the image. this helps us resolve the problem of dimensionality by reducing the data size and making learning easier. the purpose of an activation function is to provide non-linearity, but we don't want any negative activation function because that would not assume that the data are independent. we used relu as our activation function because it is positive and very easy and simple to model [33]. it is easy to calculate and involve the only comparison between the input and 0. ����: ��� = !���0, � (10) this is the last part of feature extraction before it is fed into the hidden layer for training and finding the neuron coefficient weights. the weights are necessary for classification as they engineering, technology & applied science research vol. 13, no. 1, 2023, 10051-10059 10056 www.etasr.com ali et al.: danger sign detection and recognition using convolutional neural networks assign the neuron their values which recognize features and result in the identification and classification of an image. for a probabilistic result, we used the softmax activation function [34]. this will give us as output one of the four considered classes each time. fig. 7. relu function. fig. 8. softmax function. #$�%!���&' = �() �*+ ∑ �() �*+ + (11) for loss calculation, we used categorical cross-entropy loss [35]. this gives us the error caused due to training the data set. ce = . ∑ t/ log�f�s / 5 / (12) ce = . ∑ t/ log�f�s / = .t/ log6f�s7 8 . 59:; /:7 �1 . t7 =$> �1 . f�s7 (13) xviii. experimental results figure 9 shows the training accuracy and loss of the respective data. the model was run for 100 epochs, approaching a maximum accuracy of 91%. the loss is approaching a value close to 8%, signified by the value of 0.3. the grayscale and the ycbcr sets used the cnn classifier, but the rgb data set were modified to use the svm classifier. the results showed that the rgb classifier did not increase by any significant value after 100 epochs, maybe due to the data limitation. still, the validation accuracy was very dynamic and fluctuated consistently. in contrast, both grayscale and ycbcr dataset verification accuracy increased and showed a much smoother increase with a few disturbances and small dynamic behaviors, providing concrete proof that the cnn classifier is better and more accurate than svm for smaller data sets. the results show that the model's training and validation accuracy are consistently increasing with a slight offset. this is the ideal result required. it is trained on the modal parameters while still having a significant variation to be considered robust. thus we conclude that the ycbcr model is well-trained and has a high validation accuracy to be considered robust and accurate. the loss graph shows the training and validation losses. it is based on (12) and (13). the cross-entropy loss is used to distinguish two distinct probability distributions. we can see this as proof of the model's ability to recognize and identify the images. the validation loss function traces a similar path in a logarithmic pattern. this is all consistent with accurate and reliable results. fig. 9. training results and loss comparison (ycbcr 100 epochs). up: loss, down: accuracy. similarly, we trained the model with rgb and grayscale images. the results are apparent in figure 10. it is clear that the rgb data are under-fitted. in the literature, it has been observed that using svm as a classifier with a small or limited data pool will result in a less accurate and under-fitted plot. the exact pattern is being observed here. regarding the grayscale results, they are accurate, robust, and ideal. the data are accurately trained and validated, and the loss function is within range. the reason for comparing grayscale and rgb images was to test how the classifier's variation would affect the training and validation results. the rgb dataset used an svm classifier, while the grayscale dataset used a nn classifier, specifically a cnn classifier. the grayscale data were simpler and less detailed but had better results. as mentioned above, a small dataset could be the reason for low accuracy while using svm, but the cnn classifier gave ideal results, both with the grayscale data set and ycbcr data. so in our study, the cnn classifier was found to be superior. figure 11 shows how increasing training time and duration affected the training accuracy. the ycbcr model validation engineering, technology & applied science research vol. 13, no. 1, 2023, 10051-10059 10057 www.etasr.com ali et al.: danger sign detection and recognition using convolutional neural networks data closely followed the training results with a slight set. we increased to training duration to observe the highest accuracy provided by this dataset. we kept all the other parameters, such as the learning rate and the dataset, constant. the training accuracy peak values were achieved at 200 epochs, after which its increase in accuracy was minuscule, while it even started to decrease at 400 epochs. the observed results are consistent with the literature and show that our model's ideal training time is 200 epochs for our specified learning rate. over-training can result in a loss of accuracy, and this concept is demonstrated here. we also identified a peak accuracy of 99.6% (a) (b) fig. 10. (a) rgb image training, (b) grayscale image training (100 epochs). up: loss, down: accuracy. the effect and duration varied for the number of epochs the network was trained. the result for training and validation accuracy achieved at 500 epochs for the image dataset are shown in table i. only the training duration was varied, and readings at 10, 100, and 500 were plotted. the table values were gathered using the same above-mentioned plots extended to 500 epochs, but a smoothing filter was used in order to make the results more consistent and trends easier to identify. fig. 11. ycbcr image training for 500 epochs. up: loss, down: accuracy table i. results of variation of image input type and training time (s) epochs training accuracy validation accuracy type of input image 19.13 10 70.7% 66.3% grayscale 19.79 10 73% 68% rgb 20.10 10 86.0% 71.1% ycbcr 174.11 100 85.3% 80.1% grayscale 175 .91 100 89.4% 79.9% rgb 178.35 100 91.4% 86.7% ycbcr 952.58 500 93.5% 83.7% grayscale 972.32 500 94.4% 80.3% rgb 982.11 500 97.1% 92.5% ycbcr table i compares the grayscale and ycbcr accuracies. the training model is identical. the only difference is that the image set input was extracted in ycbcr format, which is a 3dimensional input in matrix form, while grayscale is a 1dimensional matrix input. this is also evident in the fact that the grayscale program runs in a shorter duration. also, the ycbcr data show the highest accuracy, followed by the grayscale, and rgb models. xix. conclusion in this paper, we observed the effects on cnn with some slight modifications on a totally new dataset. we used a dataset with 4 different types of images. we varied several factors and compared their effects on the data training and validation accuracy. the image inputs varied and grayscale, rgb, and ycbcr images were utilized. the most accurate results came from the ycbcr model, as it was able to incorporate the effects engineering, technology & applied science research vol. 13, no. 1, 2023, 10051-10059 10058 www.etasr.com ali et al.: danger sign detection and recognition using convolutional neural networks of grayscale and normal colors in the mathematical model. the difference was not significant but noticeable nevertheless. thus the ycbcr image input proved to be a better input type for data extraction. cnn and svc were used for image classification. the results were recorded, and it was observed that cnn provided better validation accuracy. the most possible reasons for this could be the smaller data set or the lower training duration and the average learning rate. we observed the accuracy variation due to under and over-training from 5 to 500 epochs and their results. the best results are between 100 and 200 epochs regarding time and accuracy. we varied the classification method, the kernel used, and the number of convolution layers. other factors affecting the accuracy are the optimizer and the loss function calculation, but we did not observed any effect of these factors. we also confirmed the superior behavior of the cnn classifier for this dataset in comparison to the svm. for future recommendations we should use a model with more layers and a bigger dataset, in order to have a more robust model with better classification ability. the limitations of this study include the effects of optimizer calculation of the loss function for various values in order to find the optimal position. these steps were not monitored and can be considered as a project for future work and possible improvements. this study was helpful in identifying that the best method to classify input image is cnn, at least for smaller datasets, and finally, it shows that cnn provides better classification results than svm. references [1] h. s. lee and k. kim, "simultaneous traffic sign detection and boundary estimation using convolutional neural network," ieee transactions on intelligent transportation systems, vol. 19, no. 5, pp. 1652–1663, feb. 2018, https://doi.org/10.1109/tits.2018.2801560. 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[35] z. zhang and m. r. sabuncu, "generalized cross entropy loss for training deep neural networks with noisy labels," may 2018. available: https://ui.adsabs.harvard.edu/abs/2018arxiv180507836z. microsoft word 9-642-ed.doc engineering, technology & applied science research vol. 6, no. 2, 2016, 972-975 972 www.etasr.com narayanamurthy and samsuri: perspectives of a farmer digital expert assistant system perspectives perspectives of a farmer digital expert assistant system vigneswaran narayanamurthy faculty of electrical and electronics engineering, universiti malaysia pahang pekan 26600, malaysia. pel13006@stdmail.ump.edu.my fahmi samsuri faculty of electrical and electronics engineering, universiti malaysia pahang pekan 26600, malaysia. fahmi@ump.edu.my abstract—global positioning system (gps) based farmer digital expert assistant systems (fdeas) are capable of analyzing the agricultural field and environmental factors associated with the field. the agricultural yield to be harvested, depends on the liquidity content of the soil, the mineral content of the soil, the geographical position of the field, the microbial content of the soil and the temperature of the environment. other parameters include irrigation, spraying of chemicals, animals or intruders getting into the field, etc. such a system monitors all these parameters and provides the appropriate values and suggestions to the farmers. several factors are monitored using different set of sensors. the location, specified by the gps, can be compared to existing databases of soil maps and thus provide the nature and type of crop to be cultivated with all specifications to obtain maximum yield at that location. cameras may be employed to continuously monitor the field and initiate alerts. all sensor outputs and systems can be integrated with a gsm modem which sends alert messages as sms or recorded audio alerts when required. such a system would ensure real time monitoring and should provide expert assistance for attaining maximum efficiency. it would act as a holistic system for analyzing, monitoring, alerting and assisting farmers at different stages of farming. keywords-global positioning system; agriculture; sensors; agricultural system; gsm; farming expert system i. introduction agriculture needs to be assisted by technology in order to enhance its efficiency. in fact, a country is tagged as developed only when the field of agriculture grows in parallel or in pace with the other fields such as infrastructure, technology, equipments, etc. the implementation of advanced and efficient techniques by engineers to improve the yield quality and quantity has become a necessary criterion [1]. several works have been published regarding technology implementation in agriculture aiming to improve productivity and sustainability. several expert systems have been developed for agriculture applications, but still none is able to provide a holistic solution [2-16]. laser level technology has been tested on farm-level information from moga district of punjab and it has shown that it can help save irrigation water and energy by 24 per cent and obtain 4.25 per cent higher yields [17]. theories about biotechnology institutions and their evolution in sectoral innovation systems with concept and model application from complex system theory have been studied in [18]. studies also have measured inequality and lagging states by applying the convergence principle by taking both per capita income and per capita agricultural income as the sources of convergence. indian agricultural sector is not performing in pace with the national economy and need for strategies to improve the performance of this sector has been felt [19]. emerging trends and innovations in agricultural field demand the private sector to be involved to enhance productivity but also the public sector for guidance [20]. varieties of sensors and techniques can be applied to perform diverse measures in wide research areas. use of spectral reflectance techniques for aiding decisions relating to crop establishment, weed control, crop protection and crop nutrition has been studied. uses, limitations, areas requiring further work and future potential as a commercial tool for precision agriculture have also been mentioned. spectral reflectance techniques have been concluded to not be that suitable for measuring soil properties as other technologies are found to be better suited for this application. it is also stated that spectral reflectance techniques are capable of detecting weeds against a soil background and are capable of providing useful information about crop canopy that can be used as a component in determining the fungicide, growth regulator and nitrogen inputs to a cereal crop [21]. different sensing methodologies to provide accurate information on crop, soil, climate, and environmental conditions are strongly recommended for modern agricultural management. it should be noted that is has been stated that almost every sensing technique may find an application in agriculture and food industry [22]. stresses identification and removal by suitable mechanical working have been studied. engineering, technology & applied science research vol. 6, no. 2, 2016, 972-975 973 www.etasr.com narayanamurthy and samsuri: perspectives of a farmer digital expert assistant system body part discomfort score and overall discomfort rating experienced by the subjects have been estimated. oxygen consumption rate and heart rate have been used for physiological cost estimation [23]. central composite rotatable design based experiments have been conducted to determine the optimum processing conditions of expansion ratios of extruded snacks made from millet and legume using response surface methodology. the evaluated variables included die head temperatures, barrel temperatures, screw speed, blend ratio and moisture content [24]. digitized city maps along with a gps sensor on a mobile computer can be used to provide location and directions to drivers [25]. gps can also be used to identify the grazing areas [26]. techniques have also been developed for land use planning [6]. a knowledge based system may be designed to simulate problem-solving behavior of an expert in a narrow domain or discipline in which expert systems unite individual expertise in all disciplines, e.g., plant pathology, entomology, horticulture and agricultural meteorology. since the evolution of artificial intelligence various expert systems have been employed on agriculture [9]. mainly six types of farming systems analysis and intervention have been evolved over the last 40 years, namely: (1) economic decision analysis based on production functions, (2) dynamic simulation of production processes, (3) economic decision analysis linked to biophysical simulation, (4) decision support systems, (5) expert systems, and (6) simulation-aided discussions about management in an action research paradigm. a recent advance was made in increasing model comprehensiveness in simulating farm production systems via reference to agricultural production systems simulator (apsim) [10]. environmental concerns have led to the emergence of the integrated management of pest and pesticides (impp). although the environmental and economic benefits of impp are beyond doubt, its use has been somewhat limited due to the required amount of knowledge on climate, topography, soil type of the farm, agronomic practices, crop phenology, biology and damage potential of the pests and options available for suppressing their population below the economic injury levels. since this knowledge is within expert’s level, in order to make it available to farmers, an expert system namely cpest for managing pest and diseases of coffee in a developing country has been developed [11]. an evaluation research study was conducted for the effectiveness of expert systems in india. it concluded that there was an enhancement in decision making of the extension personnel after using the expert system on maize [12]. expert systems were found to be feasible to use as a decision support tool for transfer of agricultural technologies to the farming community [12]. a decade review on expert system methodologies concluded that expert systems methodologies mainly evolve using the following eleven categories: rule-based systems, knowledge-based systems, neural networks, fuzzy ess, objectoriented methodology, case-based reasoning, system architecture, intelligent agent systems, database methodology, modeling, and ontology together with their applications for different research and problem domains [3]. suggestions were made that different social science methodologies, such as psychology, cognitive science, and human behavior could implement expert systems as another kind of methodology. the ability to continually change and obtain new understanding is the driving power of such systems [3]. expert systems were also used in land-use planning in general and site selection in particular. assessment of the usefulness of each system for the urban planner has been investigated in [6]. as an initiation step to the implementation of advanced technology in agriculture, a farmer digital expert assistant system (fdeas) is described in this paper. the goal of the system is to help farmers in cultivation using advanced engineering techniques at low cost and thereby reduce the gap between farmers and latest technological advancement. most of the existing studies were on the implementation of technologies to improve individual processes like the efficiency of seeds, pesticides and insecticides application, etc. in this case the approach it to incorporate electronic, instrumentation and information technology to develop an integrated digital assistant to address a system of processes. the system developed is designed to bridge the adoption gap between the farmer and technology by bypassing the complexities involved in handling the device and exposing only the simple procedures. ii. process design and instrumentation the fdeas carries out a sequenced range of actions starting before the process of sowing the seed and reaching the final stage of harvesting. it would constantly monitor the field and provide alerts, suggestions, solutions and inferences to the farmer in audio, visual and sms (short message service) form. the fdeas comprises of several input modules and sensors to consider all the environmental factors that contribute to the quality and quantity of the yield. its basic architecture is depicted in figure 1. an fdeas would basically comprise of global positioning system (gps) receivers, temperature sensors, liquidity sensors, chemical sensors, gas sensors, cameras, lcd displays, speakers, gsm infrastructure and battery power boxes. the heart of the fdeas module would be a microcontroller based system which would acquire, analyze and evaluate various sensor information and store data for future use. the system components would be customized by the farmer as per the budget and the nature of the field. gps provides reliable positioning, navigation, and timing services to civilian users on a continuous worldwide basis freely available to all [27]. the gps system in this module would acquire the location of the field. the location identified would be compared to the database of soil and watershed atlas developed by agricultural engineering department of the indian government [28]. results should provide soil chemical properties, erosion factors, available water supply, soil qualities, list of crops that can be grown and the estimated amount of yield that can be obtained at that particular season and location. this data is not known to many of the practicing farmers in villages and they infer these details by using a trial and error method by cultivating different varieties of crops and checking their yields. thus, consuming a huge amount of time, labor and money to reach a simple decision. once the crop is chosen, the fdeas would provide complete specifications of engineering, technology & applied science research vol. 6, no. 2, 2016, 972-975 974 www.etasr.com narayanamurthy and samsuri: perspectives of a farmer digital expert assistant system temperature, liquid content of soil, microbial activity and amount of fertilizers, insecticides and pesticides to be added for the perfect growth of crops. in addition, the latitude and longitudinal information of fdeas module would be linked to the weather station database [30, 31] to evaluate the current temperature and forecast it for the specified region. the developed system would simplify this task and provides results instantaneously. a. sensor components the following sensors should be implemented: temperature sensor, liquidity sensor, absorption technique based chemical sensors, gas sensor and a camera. the atmospheric ambient air temperature can be implemented using a commercially available sensor (e.g. linear temperature sensor lm35). the output from the temperature sensor would be interfaced with the microcontroller for further conversion of sensor voltage to temperature readings. the sensor would constantly monitor atmospheric temperature and alert the farmer stating whether the temperature is favorable or not so that he could perform certain remedy measures. regarding the liquidity sensor and supply voltage an example would be: 3.3v or 5v, operating current: less than 20ma, output voltage :0-2.3 v [2.3v is completely immersed in water voltage value], 5v power supply. an analog output sensor should be chosen. these sensors will be placed under the ground to determine the liquid/moisture content present in the soil through electrical conductivity (which is directly related to the moisture content). the analog output voltage readout would be further processed by the microcontroller. if the soil water content threshold is not reached, the microcontroller would release a mechanical valve to irrigate the field. the valve would be shut automatically once sufficient water content is attained. chemical sensors would be used to monitor the concentration of fertilizer, pesticide and insecticide applied. these chemical sensors can be customized based on field requirements. nutrients usually present in soil are ammonium nitrate, available phosphorus, potassium, organic matter, total nitrogen, nitrogen and other nine trace elements like calcium, magnesium, sulfur, iron, manganese, boron, zinc, copper, chlorine and silicon. fertilizer nutrients are elemental fertilizer nitrogen, phosphorus and potassium; complex (mixed) in hefei and urea ammonium nitrogen, nitrate nitrogen, phosphorus, potassium, biuret; organic fertilizer available nitrogen, available phosphorus, k, total nitrogen, total phosphorus, total potassium, organic matter, various humic acid, and other trace elements like calcium, magnesium, sulfur, iron, manganese, boron, zinc, copper, chlorine, silicon. the system should be designed in such a way that when safety threshold limit exceeds, the farmer would be alerted to stop chemical spraying. the thresholds can be varied based on the nature of the crops. microbes play a major role in healthy growth of crops and to perform efficient cultivation the amount of microbes present should be monitored constantly. to achieve this task n2o and other types (depending on the microbes) of gas sensors can be employed which would monitor the concentration of gas liberated by the microbes, which is directly proportional to the amount of microbes. thus, it will be able to detect ch4, h2s, co2. the nitrous oxide sensor employed may be a typical infrared sensor which measures concentrations ranging from 01000 ppm. working current for these sensors is less than 1ma. cameras should be employed to provide security to the system and to the crop from theft and intruders. simple image subtraction techniques may be employed to detect movement. these methods can also be extended to detect animal grazing and presence of life threatening animals. as another alternative, a set of motion sensors widely distributed throughout the field may be used. the latter would be a better option to employ if vast fields are to be monitored, as the field of vision would be a limitation to the camera. b. output modes output modules would consist of three modes of communication to farmers which are lcd, speaker and sms using gsm. all sensor alerts mentioned above will be displayed in the lcd present in the fdeas module. in order to keep the farmer continuously updated even during his absence, two more output modules (speaker and sms) should be implemented. fig. 1. fdeas architecture. iii. discussion and future prospective fdeas should be evaluated in field trials to decide its efficiency and stand-alone capability. sensors calibration is to be checked and corrected in regular intervals. initial cost should be expected to be high, as it involves monitoring of several parameters, but in the end affordable for the service rendered by the system. since the system is of standalone type, the optional accessories of sensors can be omitted depending upon the budget. government support in manufacturing would help in further reducing the cost. in future ivrs can also be used for further improvement. solar energy can be used to charge the batteries. security against theft and robustness against tough climatic conditions should also be considered. references [1] j. v. stafford, “implementing precision agriculture in the 21st century”, journal of agricultural engineering research, vol. 76, pp. 267-275, 2000 engineering, technology & applied science research vol. 6, no. 2, 2016, 972-975 975 www.etasr.com narayanamurthy and samsuri: perspectives of a farmer digital expert assistant system [2] a. rafea, “expert system applications: agriculture," central laboratory for agricultural expert systems, po box, vol. 100, 1998. [3] s.-h. liao, “expert system methodologies and applications—a decade review from 1995 to 2004”, expert systems with applications, vol. 28, pp. 93-103, 2005 [4] j. mckinion, h. lemmon, “expert systems for agriculture”, computers and electronics in agriculture, vol. 1, pp. 31-40, 1985 [5] r. e. plant, “expert systems in agriculture and resource management”, technological forecasting and social change, vol. 43, pp. 241-257, 1993 [6] f. witlox, “expert systems in land-use planning: an overview”, expert systems with applications, vol. 29, pp. 437-445, 2005 [7] r. doluschitz, w. schmisseur, “expert systems: applications to agriculture and farm management”, computers and electronics in agriculture, vol. 2, pp. 173-182, 1988 [8] p. jones, “agricultural applications of expert systems concepts”, agricultural systems, vol. 31, pp. 3-18, 1989 [9] g. prasad, a. v. babu, “a study on expert systems in agriculture”, extension of technologies: from labs to farms, p. 297, 2008 [10] b. a. keating and r. mccown, "advances in farming systems analysis and intervention," agricultural systems, vol. 70, pp. 555-579, 2001. [11] g. mansingh, h. reichgelt, k. m. o. bryson, “cpest: an expert system for the management of pests and diseases in the jamaican coffee industry”, expert systems with applications, vol. 32, pp. 184-192, 2007 [12] s. sivakami, c. karthikeyan, “evaluating the effectiveness of expert system for performing agricultural extension services in india”, expert systems with applications, vol. 36, pp. 9634-9636, 2009 [13] t. trivedi, d. ahuja, “integrated pest management: approaches and implementation”, the indian journal of agricultural sciences, vol. 81, 2011 [14] h. ravisankar, u. sreedhar, k. sivaraju, “expert system for insect pests of agricultural crops”, the indian journal of agricultural sciences, vol. 84, 2014 [15] v. kumar, a. kumar, c. chattopadhyay, “design and implementation of web-based aphid (lipaphis erysimi) forecast system for oilseed brassicas”, the indian journal of agricultural sciences, vol. 82, 2012 [16] b. gangwar, k. prasad, “cropping system management for mitigation of second-generation problems in agriculture”, indian journal of agricultural science, vol. 75, pp. 65-78, 2005 [17] b. kaur, s. singh, b. garg, j. singh, j. singh, “enhancing water productivity through on-farm resource conservation technology in punjab agriculture”, agricultural economics research review, vol. 25, pp. 79-85, 2012 [18] j. niosi, “complexity and path dependence in biotechnology innovation systems”, industrial and corporate change, vol. 20, pp. 1795-1826, 2011 [19] t. k. das, l. mishra, “including agriculture in sustaining economic growth of india”, iup journal of applied economics, vol. 9, p. 69, 2010 [20] a. gulati, “emerging trends in indian agriculture: what can we learn from these”, agricultural economics research review, vol. 22, pp. 171-184, 2009 [21] i. scotford, p. miller, “applications of spectral reflectance techniques in northern european cereal production: a review”, biosystems engineering, vol. 90, pp. 235-250, 2005 [22] s. li, a. simonian, b. a. chin, “sensors for agriculture and the food industry”, the electrochemical society interface, vol. 19, p. 41, 2010 [23] m. s. khidiya, a. bhardwaj, “an ergonomic approach to design hand tool for agricultural production”, work (reading, mass.), vol. 41, pp. 1335-1341, 2011 [24] s. k. chakraborty, d. s. singh, b. kumbhar, s. chakraborty, “process optimization with respect to the expansion ratios of millet‐and legume (pigeon pea) ‐ based extruded snacks”, journal of food process engineering, vol. 34, pp. 777-791, 2011 [25] g. dommety, r. jain, “potential networking applications of global positioning systems (gps)”, arxiv preprint cs/9809079, 1998 [26] s. rutter, n. beresford, g. roberts, “use of gps to identify the grazing areas of hill sheep”, computers and electronics in agriculture, vol. 17, pp. 177-188, 1997 [27] j. agarwal, “innovations & developments in financing and investment in agriculture and rural development (with special reference to india and hungary) ”, finance india, 2007 [28] a. e. department. (1998, 17-11-2015). district soil & watershed atlas website. available: http://www.aedatlas.tn.nic.in/ [29] usdanrcs. web soil survey. available: http://websoilsurvey.nrcs.usda.gov/app/homepage.htm [30] k. s. k. k. apurva sanghi, and james w. mckinsey, jr., india agriculture and climate data set, available: http://ipl.econ.duke.edu/dthomas/dev_data/datafiles/india_agric_climate. htm [31] k. k. kumar, j. parikh, “indian agriculture and climate sensitivity”, global environmental change, vol. 11, pp. 147-154, 2001 microsoft word etasr_v13_n1_pp10116-10120 engineering, technology & applied science research vol. 13, no. 1, 2023, 10116-10120 10116 www.etasr.com gurkan aydin & ozgen: bio-based jet fuel production by transesterification of nettle seeds bio-based jet fuel production by transesterification of nettle seeds sinem gurkan aydin department of faculty of applied sciences, aircraft maintenance and repair, istanbul gelisim university, turkey sgurkan@gelisim.edu.tr (corresponding author) arzu ozgen department of medical services and techniques, istanbul gelisim university, turkey aozgen@gelisim.edu.tr received: 12 december 2022 | revised: 23 december 2022 | accepted: 5 january 2023 abstract the use of petroleum-based fuels in air transport and the increase in oil prices over the years have increased fuel costs. due to this increase, fuel manufacturers and airline companies have started to search for alternative fuels. since aviation has an important place in the transportation sector, biomass has the greatest potential in the search for renewable energy sources. biological substances of plant and animal origin and containing carbon compounds are energy sources, and the fuels produced from them are called biofuels. biofuels are an important source of sustainable energy, which greatly reduces the greenhouse gas effect, improves weather conditions, reduces dependence on oil produced from fossil fuels, and is important for new markets. the nettle seed oil used in the current study was purchased from the local market and was obtained using the cold-pressing method at low temperatures. after the completion of the transesterification process, a two-phase mixture consisting of biofuel-glycerin was obtained, and the upper phase containing fatty acids was taken and transferred to a clean tube. after the final washing processes, bio jet fuel was obtained by adding chemicals at certain rates. the analysis of the obtained fuel was conducted at the tubitak marmara research centre. when the report was evaluated and compared with international standards, consistent results were obtained. it can be predicted that sustainable fuels can replace fossil fuels in the future. keywords-sustainable energy; bio-based jet fuel; transesterification;nettle seeds i. introduction sustainable and renewable fuel production ways have an important place in terms of environmental, social, and economic aspects. jet fuels constitute an important part of the relevant economy with a growing rapidly share [1]. when we look at the transportation sector in particular, it needs 2627.02 million tons of oil equivalent, which represents 27.9% of the total energy produced in the world [2]. in order to change the aircraft design and reduce fuel consumption, several attempts have been made to reduce co2 emissions, but these measures have yielded lower results than co2 emissions from the increase in flights [3, 4]. as a result, airline operators have sought different ways to solve this problem. biofuels are a likely solution due to their renewable nature and low co2 emissions [4-6]. in addition, these fuels bring a new approach to the sector, increase safety, and reduce harmful emission particles [7-11]. sustainable biofuels are important alternative fuels that require a large amount of raw material resources. these fuels can be obtained by means such as ficher troph synthesis [12-14] and alcohol synthesis [15-17], which have become known ways of sustainable fuel production using intermediates such as alcohol and synthesis gas. the goal of minimizing the co2 emissions in the carrying sector has become a major driver for the advance of renewable fuels [18]. according to the estimations of the international energy agency, it is predicted that by 2050, sustainable biofuels will supply 27% of all energy in the field of transportation. for this reason, sustainable fuels have been the focus of attention [19, 20]. traditional fossil-based jet fuels consist of approximately 20% paraffins, 40% isoparaffins, 20% naphthenes, and 20% aromatics [19]. this composition gives physical properties such as a freezing point of -47 o c and 43.28mj/kg energy [20]. renewable bio jet energy sources consist of hydrocarbons in the boiling range of traditional fossil-based energy sources, showing that they have a structure close to the traditional fossil-based jet fuel. in the absence of aromatic compounds, harmful particles emitted from renewable bio jet fuels are lower than those emitted by fossil fuels [22]. engineering, technology & applied science research vol. 13, no. 1, 2023, 10116-10120 10117 www.etasr.com gurkan aydin & ozgen: bio-based jet fuel production by transesterification of nettle seeds the most accepted jet fuel standard is astm d1655-17 [23]. the limits of this standard allow biodiesel blending up to 50ppm, however, their use in air transport is still limited despite their advantages. several hydrotreating routes have been proposed to manufacture renewable aviation fuel [24-30]. in addition, there have been new developments in the methods of obtaining rich aromatic and cycloparaffin hydrocarbons during the production of renewable jet fuels [31-33]. after that, the fuel standard astm d1655 can be limited as the high aromatic and/or cycloparaffin content in the fuel meets the density requirements, low heating value, and especially smoke point limits. to date, 5 different fuels that can be mixed with fossil-based jet fuel and used in gas turbine engines have been approved by the american society for testing materials (astm). astm d7566-19 describes the detailed requirements and compositions [34]. the genus urtica, a member of the urticaceae family, is in the main group of angiosperms (flowering plants) [35, 36]. the main varieties of the genus urtica, known for their painful hairs on their leaves and stems, are urtica dioica l., urtica urens l., urtica pilulifera l., urtica cannabina l., urtica membranacea poiret, and urtica kiovensis rogoff [38]. urtica spp. is more commonly known as nettle. it grows all over the world, especially in regions with temperate climates. it prefers open or partially shaded habitats with plenty of moisture and is often found in forests, rivers or streams, and along roadsides. it is common in europe and north america, north africa, and parts of the asia [35]. nettle seeds are rich in oil, and nettle seed oil contains monounsaturated fatty acids, which is one of the reasons why that plant is preferred in biodiesel studies. the fatty acid content of nettle seed is palmitic acid, stearic acid, oleic acid, linoleic acid [37, 39]. ii. materials and methods pure oil obtained from the nettle plant seeds was obtained. methanol, ethanol, naoh, fuel system anti-icing, kerosene, isooctane, nettle seed oil, and purified water were used. a single-stage basic reaction method, which is generally preferred for refined and crude vegetable oils, was used for transesterification. the flow chart of the procedure is given in figure 3. 200ml methanol and 10g naoh were used in appropriate proportions for every 1000ml of nettle seed oil. they were mixed with 200ml methanol in 10g naoh for 30 minutes in a magnetic stirrer heater (figure 1). the sodium methoxide (ch3ona) obtained as a result of this process was kept in an oven at 60°c in order to maintain its temperature. then, the nettle seed oil was heated to 70°c using a magnetic heater and ch3ona was added to it, and the mixture was stirred at 60-70°c for 4 hours. the mixture was left at room temperature for 120 hours for the transesterification process to be completed. at the end of this process, a twophase mixture consisting of biofuel-glycerin was obtained, and the upper phase containing fatty acids was carefully removed with the help of a pipettor and transferred to a clean tube (figure 2). the fatty acid-glycerin boundary part was centrifuged at 1000 rpm for 5 minutes and the fatty acid part was recovered. fig. 1. formation of ch3ona by a single-stage basic reaction method. fig. 2. bi-phase product resulting from the transesterification process. fig. 3. flowchart of the procedure. in order to remove soap, glycerin and mono-di-tri glycerides that may be present in the biofuel, washing process was carried out 10 times by spraying on the biofuel using pure water (1:1) heated up to 100°c. after the last washing, the washing water was separated from the biofuel and settled to the bottom. the biofuel in the upper phase was carefully removed and dried in an oven at 110-120°c, and the remaining pure water and alcohol were completely removed. at the last stage, 3.5lt 70% bio-based bio jet fuel were obtained by mixing 25% kerosene, 4% octane increaser, and 1% antifreeze chemicals and was sent to tubitak marmara research centre in order to determine its properties (figure 4). engineering, technology & applied science research vol. 13, no. 1, 2023, 10116-10120 10118 www.etasr.com gurkan aydin & ozgen: bio-based jet fuel production by transesterification of nettle seeds fig. 4. bio-based jet fuel obtained by transesterification of nettle seed iii. results and discussion generally, triglycerides, lignocelluloses, and syngas are used to produce renewable aviation fuels. biofuels can be obtained from plants, animal fats, and biomass. especially biofuels produced from plant and organic waste reduce co2 emissions, in addition to reducing the dependence on fossil fuels. there are also bacteria, yeast, and algae that have the capacity to produce fuel molecules and are used in the production of biofuels. the assortment can be enhanced by modifying the existing methods or by engineering applications and synthetic means. in such applications, genetic optimization is necessary, although the selection of organisms takes up a lot of space to increase efficiency. hefa technology is a production method of sustainable fuels. it is conducted by hydroprocessing vegetable oils and animal fats. approximately 1.2 tons of vegetable oil is required to produce 1 ton of hefa fuel. one of the main advantages of this technology is to integrate this process into an oil refinery (with an additional step) and eliminate the need to develop a dedicated production facility. the hefa production process is proven and approved for mixing ratios of up to 50%. in addition, current investments in infrastructure show that the process has an economically viable scope in the near future. in our study, a 70% biologicalbased mixture was tried and successful results were obtained. pure vegetable oil cannot be used as fuel in aircraft gas turbines. for this reason, its combustion characteristics should be approximated to diesel. four techniques can be used for fuel regulation, aiming to reduce viscosity and eliminate atomization problems. these techniques are heating, dilution/mixing, microemulsion ,and transesterification. the jet fuel sample produced with nettle seed oil was analyzed in the laboratory in accordance with the international standards. the characteristics of the fuel produced in our study and its comparison with the standards are given in table i. as a result, it has been concluded that the characteristics of the fuel are compatible with the characteristics determined by international authorities. the distillation profile is made in accordance with the astm d 86 standard test. by evaporation and recondensation of 100ml sample, the temperatures at which 5, 10, 20, and 30 volume fractions were collected and determined, and a temperature-volume curve, i.e. a distillation profile, was obtained. a highly volatile fuel makes the engine easier to start, but increases problems such as vapor plugging, icing, and fuelscalding. in order to minimize these problems, it is necessary to balance the volatility characteristics of avgas. the distillation graph of the produced jet fuel is given in figure 5. fig. 5. distillation graph of the bio-based jet fuel obtained with transesterification of nettle seeds. fuel instability is a process of multi-step oxidation reactions that occur between some of the compounds it contains. the initial reaction products are hydroperoxides and peroxides. these products are dissolved in the fuel, but they affect the elastomeric materials of the fuel system and shorten its useful life. in addition, soluble gum and insoluble particles are formed with the ongoing reactions. these substances clog fuel filters and cause residue to build up on fuel system walls, making it difficult for fuel to flow. the existing gum and potential gum values in our product are in the range of values that are quite suitable for use. the bio jet fuels studied before include 50% sustainability, while the product in our study has 70% sustainability [38]. we have previously discussed the fuel additives used with a detailed unit analysis [39]. factors that act as drivers for switching from one fuel to another to improve energy efficiency have been identified in the literature, including various performance parameters that support environmental protection [40]. biofuel has been previously produced using cheap waste cooking oil collected from pakistan's nawabshah local market [41]. the fuel produced in our study will provide a very good approach in the aviation industry. iv. conclusion air transport is a feature of our modern, globalized world that connects people, commerce, and most importantly, businesses across continents. the benefits and importance of air travel are undisputed, but there are also important aspects to consider. traditionally, environmental problems involving aviation have focused on noise and air pollution and the recent issue of global climate change has focused the attention on the co2 emission volumes of airplanes. when greenhouse gases produced from fuels burned in flights are emitted into the atmosphere, they have a significant negative impact on the environment. aviation is likely to need around 450-500 million tons of sustainable aviation fuel per year by 2050. jet fuels produced using renewable bio-based are important for the aviation industry and reduce its dependency on fossil fuels. it an important breakthrough, as it will contribute to the targets of reducing emissions against global problems. engineering, technology & applied science research vol. 13, no. 1, 2023, 10116-10120 10119 www.etasr.com gurkan aydin & ozgen: bio-based jet fuel production by transesterification of nettle seeds table i. analysis results of bio-based jet fuel obtained by transesterification of nettle seeds parameter jet a jet b analysis result analysis method density (15 o c) 775-840 751-802 803.5 kg/m 3 astmd 4052 distillation astmd 86 initial boiling point 151.5 152.7 102.5 o c %10 205 129.5 o c %50 200 190 186.9 o c %90 246.7 245 320.9 o c ultimate boiling point 300 341.0 o c distillation residue 1.5 1.5 0.8%v/v distillation loss 1.5 1.5 0.2%v/v flash point 38 16.5 o c astmd 3228 color (saybond) -15 astmd 6045 electrical conductivity 500-600 504 ps/m astmd 2624 copperstrip corrosion 2h100 o c 1b 1b astmd 130 mercaptan sulfur 0.003 -0.0004%m/m astmd 3227 acid number 0.1 <0.1 mgkoh/g astmd 664 current gum 2000 2000 2254mg/100ml astmd 381 potential gum -3454 mg/100ml astmd873 sulfur 0.064%m/m astmd 4294 kinematic viscosity 8 3.948 mm 2 /s astmd 445 doctor test negatif ts 2884 freezing point -40. -47 -50 -31 o c astmd 2386 smoke point 25 25 26 mm astmd 1322 heat of combustion 42.8 42.8 43.3mj/kg astmd 3338 fia aromatic 15-25 25 17.7%v/v astmd 1319 fia olefin %0.2%35 0.9%v/v fia saturated 81.4%v/v thermal stability control temperature 260 o c min 450 450 450ml astmd 3241 pressure difference 252mmhg heating pipe sediment class 1 1 <3 water reaction 3 3 4 ml astmd 1094 aniline point 54 astmd 611-a octane number ron 0-100 0-100 50.1 astmd 2699 octane number mon 0-100 0-100 48.0 astmd 2700 the current project deals with aspects such as global warming, sustainability, and reduction of carbon emissions. unlike the previously produced planetary fuels, the proposed fuel is not separated due to its high efficiency and 70% biological nature. in conclusion, the biojet fuel under study is produced using a sustainable resource, nettle seed oil, and is an excellent candidate product, with the highest biological rate. acknowledgment the authors wish to thank the istanbul gelisim university scientific research projects application center for funding this work. project number: dup-100920-sga, year 2021. the authors 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january 2023 | revised: 6 february 2023 | accepted: 20 february 2023 abstract a low-cost small 500w wind generator was used as a basis for the prototype development. the research was primarily focused on the determination of the type of aerofoil for improved rotor blades and pitch angle, and for adapting the number of blades in order to optimize the power output from the prototype, for low wind-speed inland conditions in soweto. naca-4412 type aerofoil was chosen as a departure point for the blade design, and a variation of the maximum pitch angle of 6°, 10°, and 12° at an optimum angle of attack of 5°, 7°, and 9° were implemented respectively for designs 1, 2 and 3. with the soweto area having an average wind speed of 2.3m/s (8.28km/h), 3-, 5-, and 7-blade sets were subsequently developed, implemented, and tested. prototype 1 produced a maximum output power of 8.2w at 4.2km/h wind speed. prototype 2 yielded a maximum output power of 12.5w at 4.2km/h, and prototype 3, generated a very useful power output of 39.5w during testing. the maximum power output was achieved at an average wind speed of 1.17m/s (4.2km/h). moreover, the developed prototype designs were also tested for selfregulation in case of high-speed gust conditions. prototype 3, with a 12° maximum pitch angle during operation in high gust conditions, had its blades control high speed. a drawback pressure occurred on the back side of the blades and tangent drag was developed normally to the blade rotation direction, consequently limiting the maximum speed of the rotor and acting as a self-regulation mechanism with regard to maximum achievable speed. the other two designs suffered from over-speeding tendencies in high gust speed conditions, also causing noise and turbulence. keywords-swt design prototypes; self regulation; experimental results i. introduction population and technology use growth result in increased energy consumption and increased emissions of greenhouse gases (ghgs). the use of fossil fuels in the generation of electricity contributes significantly to ghg emissions, which contribute to climate change [1, 2]. utilizing renewable energy as an alternative energy source will reduce environmental problems, essentially ghg emissions and air pollution [3]. wind energy has seen a dramatic increase in development during the last 20 years [4]. this development occurred especially in the implementation of small-scale wind farms at households and business premises in urban areas, and in huger large-scale wind turbines in far off rural areas, where high wind speeds prevail. large scale wind turbine systems are complex and expensive technology and energy has to be transported over large distances, while small scale wind turbines in urban areas can be implemented in an autonomous and low-cost basis. a preliminary review on recent designs and developments on horizontal axis wind turbines (hawts) will be discussed below. small wind turbines are characterized as having an output power of less than 50kw and operating at low wind speeds and low reynolds numbers, which is common in the industry. the engineering, technology & applied science research vol. 13, no. 2, 2023, 10553-10558 10554 www.etasr.com sithole et al.: implementation and evaluation of a low speed and self-regulating small wind turbine … rotor blades are considered as the most critical component, as their aerodynamic efficiency has a direct effect on the turbine system's overall performance [5]. the blade design is influenced by various parameters, the most important of which is the aerofoil, which dictates the cross-sectional geometry of the blade. numerous aerofoils have been designed expressly for small wind power generation [6-8]. numerous methods and techniques have been developed over the last few years to increase the efficiency (performance) of wind turbines. these methods and techniques were supported by the empirical analysis and optimization of the wind turbine blade design characteristics. blade element momentum (bem) theory is a critical method for simulating and optimizing the performance of wind turbine blades [9]. a small wind turbine blade was designed and optimized to maximize blade number and tip speed ratio for solidity in [10]. in [11], a variety of bem parameters for the design and optimization of small (less than 1kw) wind turbine blades at rated wind speed of 8.4m/s, was simulated in qblade, and plots of cp and power versus tip speed ratio were shown. the sg6043 airfoil was selected because it had the maximum lift coefficient of 1.63. qblade was used to simulate a 1.2m blade length. authors in [12] investigated the performance of the rotor blade (horizontal axis) of a small wind turbine. the wind turbine was considered to operate ideally at low wind speeds and low reynolds number (5×10 5 ). the rotor had a 2m diameter and 3 blades. the blade model was built utilizing 3 aerofoils (du86-084, e387, and sd2030) with a tip speed ratio of 7. e387 outperformed the other two simulated aerofoils. it is necessary to ensure that the turbine's protection is not compromised by turbulence and vibration effects. thus, a critical feature of a wind turbine is power control, which prevents the wind turbine from being damaged at extremely high wind speeds [13]. in this article, the results of the undertaken work on the low cost mechanically self-regulating hawts, that were optimally designed and eventually implemented and tested in a residential area in soweto, johannesburg, south africa, is presented. these test prototypes can be implemented at large volumes in middle-income households and can make a significant contribution to the generation of clean energy in south africa. ii. methods the methodologies applied in this project considered different perspectives and routes. the plan of action was eventually taken after a thorough literature review. basic design choices would be made based on known considerations [13, 14]. a. bem theory considerations [12] in this analysis, the theoretically inter-relationships between pitch angle, blade solidity, maximum power coefficient, and tip speed ratio were studied. the study was conducted using the following theoretical considerations: a fixed experimental design route was chosen and implemented and predictive data were derived. one twisted blade design, fixed chords and varying number of blades (3, 5, and 7) mounted on a rotor diameter of 0.95m, were considered. the derived conclusion was that the optimum power coefficient is mainly dependent on pitch angle and tip speed ratio for the dimensions chosen in our design. b. chosen design procedure the basic design choices considering low wind speed operating conditions were [15]:  not too large rotor diameter since noise, turbulence, and vibration, would be the primary functions of blade radius size.  high pitch angle of the blades near the hub region of the blade. this approach would maximize the torque on the rotor axis at low wind speeds, while it would not cause an excessive apparent wind on the outer edges of the rotor. the optimum power coefficient is mainly dependent on the pitch angle and tip speed ratio.  since many physical and dynamic parameters, such as apparent wind speeds, apparent wind directions, and stall speeds are quite difficult to derive theoretically, it was decided to primary focus on designing and investigating the effect of (i) the number of blades and (ii) the pitch angle of the blade and the variation of these along the blade radius as a primary variation parameter. increasing the radius and number of blades on the rotor, would increase the total wind capture area of the blades and the total power transfer.  after reviewing the published specifications of commercially available wind turbines on the market, it was decided to implement a known and proven design within the naca 44 family, and then vary the blade radius and the attack angle along the radius of the blade, and adapt these to the specific conditions in soweto.  using the bem theory and blade specifications of the naca 44 family, it was derived that the electrical power output goal of about 380, 420, and 430w could be a reasonable output choice for a 3-, 5-, and 7-bladed, 1m radius systems, respectively. these power levels seemed to be enough to generate and store a few kwh per day and power basic essential appliances in a medium scale house for a day or two. c. flow chart of the proposed research the flowchart of the undertaken research can be seen in figure 1. iii. experiments and results the soweto small wind turbine (swt) set contained a three-phase 500w synchronous generator which was used as a basis for optimizing the power output of the designed blades (3, 5, 7). the performance testing steps of the rotor-blade prototypes required the assembly of the following equipment associated with the wind turbine:  charge controller  two 12v batteries connected in series  an off-grid inverter engineering, technology & applied science research vol. 13, no. 2, 2023, 10553-10558 10555 www.etasr.com sithole et al.: implementation and evaluation of a low speed and self-regulating small wind turbine …  output load  unit-b anemometer and power wattmeter these components were coupled to the designed prototypes that were implemented. figure 2 shows a block setup test diagram for the soweto project. fig. 1. the flowchart of the followed methodolody. the prototypes were tested under conditions of full load (discharged batteries) and the experimental data were collected. all the tests were done at output voltage of approximately 19.0v, corresponding with a charger state of approximately 70% of the storage batteries. the same reference voltage of 19.0v was used at the start of each test. appliances (lcd tv, sound equipment, dstv decoder, and camera) were connected to the storage batteries, output controller, and off-grid inverter, especially during non-charging periods. load conditions varied with power usage during the day and the passive resistive load was added. the tests were always initiated in early afternoon when wind speeds were picking up in soweto. these provided the most practical conditions for testing and were nearest to true operational conditions. the 3-blade wind turbine system (prototype 1) was implemented, as shown in figure 3 and the experimental data shown in table i were collected. fig. 2. block setup test diagram for the soweto project. fig. 3. 3-bladed system design view with maximum blade pitch angle of 6°. fig. 4. 5-bladed system design view with maximum blade pitch angle of 10°. purchase a low cost imported product with good efficiency generator a 500 w wind generator with a rated recommended wind operational speed of 10.5m/s was imported from china. the generator would be used to implement the 3 different designs of blades to be tested in soweto. implementation of specific blade design (design 1) and evaluation of its performance incorporate with 3 blades and test the purchased wind generator. investigate the maximum rotation speed, turbulence, and noise characteristics of the turbine. implementation of specific design 2 and evaluation of its performance evaluate the performance of design 1. perform some basic theoretical and simulation analyses. implement a 5 blade-rotor system with a moderate pitch angle along the blade radius. also adapt the radius and chord length along the blades in order to obtain maximum power. investigate the maximum rotation speed of the turbine, turbulence and noise characteristics. implementation of design 3 and evaluation of its performance evaluate the performance of design 2. perform some basic theoretical and simulation analyses. implement a 7 blade-rotor system with a higher maximum pitch angle along the blade radius. also adapt the radius and chord length along the blades in order to obtain maximum power. try to limit the maximum rotation speed of the turbine and to protect the turbine against possible high wind speed gust conditions by introducing speed regulation mechanisms. investigate the maximum rotation speed of the turbine, turbulence, and noise characteristics. evaluate the performance of each design in terms of energy yield, self-regulation and cost efficiency an arduino uno r3 microprocessor, circuit boards and software, dpa-3051 software and power wattmeter, and a wind speed anemometer would be used to monitor the power output performance of the prototypes as a function of wind speed and prevailing weather conditions in soweto. moreover, evaluation of cost efficiency and self-regulation for the 3 different designs will be performed. engineering, technology & applied science research vol. 13, no. 2, 2023, 10553-10558 10556 www.etasr.com sithole et al.: implementation and evaluation of a low speed and self-regulating small wind turbine … table i. experimental data for prototype 1 wind speed (km/h) measured current (a) turbine speed (rpm) measured voltage (v) real power (w) calculated power (w) 1.2 0.069 61 19.3 1.33 0.049 1.4 0.072 72 19.4 1.4 0.051 0.9 0.015 35 19.0 0.285 0.009 2.8 0.15 85 19.2 2.88 0.12 1.9 0.1 75 19.0 1.9 0.065 0.8 0.016 34 18.9 0.302 0.008 3.1 0.2 142 19.3 3.86 0.19 2.9 0.16 86 19.3 3.088 0.13 1.5 0.073 73 19.5 1.42 0.052 3.2 0.21 141 19.3 4.05 0.2 1.5 0.073 73 19.4 1.41 0.053 2.0 0.11 76 19.1 2.10 0.075 0.9 0.017 35 19 0.323 0.009 1.6 0.074 74 19.6 1.45 0.053 4.2 0.41 165 19.8 8.2 6.42 2.1 0.12 77 19.2 2.31 0.085 1.6 0.074 74 19.4 1.44 0.053 1.4 0.072 72 19.4 1.4 0.051 0.9 0.015 35 19.0 0.285 0.009 0.8 0.016 34 18.9 0.302 0.008 1.2 0.069 61 19.3 1.33 0.049 1.6 0.074 74 19.6 1.45 0.053 1.7 0.075 75 19.5 1.46 0.054 1.9 0.1 75 19.0 1.9 0.067 1.5 0.073 73 19.5 1.42 0.053 figure 4 illustrates the 5-blade wind turbine system (prototype 2) implementation. table ii provides the experimental data collected for prototype 2. figure 5 illustrates the implementation of prototype 3 (7-blade wind turbine system) and table ii shows the collected experimental data. fig. 5. 7-bladed system design view with maximum blade pitch angle of 12°. a. power performance comparison during the design of the wind turbine blade for prototype 3, it was predicted that the rated output should be 40w at rated soweto wind speed of 2.3m/s (8.28km/h) [15]. as can be seen in figure 6, during the comparison of the three prototypes, 40w was achieved at an average wind speed of 1.17m/s (4.2km/h). table ii. experimental data for prototype 2 wind speed (km/h) measured current (a) turbine speed (rpm) measured voltage (v) real power (w) calculated power (w) 1.2 0.085 55 19.7 1.67 0.221 1.4 0.095 99 19.5 0.175 0.212 0.9 0.019 66 19.2 0.36 0.009 2.8 0.19 45 19.5 3.70 0.102 1.9 0.098 135 19.7 1.93 0.27 0.8 0.058 125 19.9 1.15 0.068 3.1 0.24 85 19.8 4.75 0.75 2.9 0.15 98 19 2.85 0.36 1.5 0.096 89 19.1 1.83 0.145 3.2 0.23 141 19.4 4.46 0.68 1.5 0.096 89 19.1 1.83 0.155 2.0 0.099 136 19.8 1.96 0.27 0.9 0.019 25 19 0.361 0.015 1.6 0.1 90 19.7 1.97 0.156 4.2 0.64 179 19.6 12.5 9.25 2.1 0.12 114 19.2 2.30 0.28 1.6 0.1 85 19.3 1.93 0.156 1.4 0.095 35 19.5 1.85 0.154 0.9 0.057 65 19.7 1.123 0.067 0.8 0.056 45 19.4 1.08 0.066 1.2 0.069 141 19.7 1.35 0.221 1.6 0.1 129 19.4 1.94 0.156 1.7 0.187 102 19 3.55 0.157 1.9 0.196 35 19.9 3.9 0.27 1.5 0.152 45 19.5 2.96 0.155 table iii. experimental data for prototype 3 wind speed (km/h) measured current (a) turbine speed (rpm) measured voltage (v) real power (w) calculated power (w) 1.2 0.14 141 19.7 2.75 1.25 1.4 0.12 99 19.5 2.34 1.58 0.9 0.1 121 19.2 1.92 0.089 2.8 0.15 123 19.5 2.93 1.36 1.9 0.13 101 19.7 2.56 1.58 0.8 0.09 112 19.9 1.79 1.989 3.1 0.43 85 19.8 8.55 1.997 2.9 0.33 99 19 6.9 1.37 1.5 0.28 102 19.1 5.5 1.57 3.2 0.39 141 19.4 7.58 1.898 1.5 0.27 126 19.4 5.3 1.58 2.0 0.36 123 19.2 6.9 1.59 0.9 0.16 99 19 3.2 0.088 1.6 0.31 75 19.7 6.1 1.55 4.2 0.98 225 19.6 39.5 28.5 2.1 0.37 110 19.2 7.2 1.61 1.6 0.28 99 19.9 5.6 1.59 1.4 0.26 141 19.5 5.2 1.58 0.9 0.16 121 19.7 3.2 0.089 0.8 0.16 113 19.4 3.1 0.090 1.2 0.21 121 19.7 4.2 1.25 1.6 0.31 99 19.4 6.1 1.55 figures 7-9 illustrate the delivered output power observed at different pitch angles as implemented in the prototype designs. prototypes 1, 2 and 3 were respectively implemented with a maximum pitch angle of 6°, 10°, and 12° near the rotor of the turbine and were tested for wind speed values of 0, 0.4, 0.8, 1.2, 1.6, 2, 2.4, 2.8, 3.2, 3.6, 4, and 4.2km/h. it can be seen in figure 9, that prototype 3, which was designed for a 12° pitch angle, generated a maximum power output of 39.5w engineering, technology & applied science research vol. 13, no. 2, 2023, 10553-10558 10557 www.etasr.com sithole et al.: implementation and evaluation of a low speed and self-regulating small wind turbine … when compared with prototype 2 (figure 8), which was designed for pitch angle of 10°, whereas maximum power output of 12.5w was observed. for prototype 1 (figure 6), which was designed for pitch angle of 6°, the maximum power output was only 8.2w. fig. 6. wind speed vs. real power. fig. 7. prototype 1, delivered power vs variation of maximum pitch angle. fig. 8. prototype 2, delivered power vs variation of maximum pitch angle. fig. 9. prototype 3, delivered power vs variation of maximum pitch angle. the results shown here are of course also dependent on the number of the blades. nevertheless, a deduction can be made that the high pitch angle setting in prototype 3 had a substantial impact on the higher power delivery observed in figure 9. a. prototype energy delivered versus time of day/month figure 10 shows the delivered energy versus time for a 24hour period. it can be seen that prototype 3’s performance significantly outclassed those of prototypes 2 and 1 during the day as there was a consistent generation of energy. figure 11, shows the energy production of prototypes 1, 2 and 3 per month during operation at soweto. it can be seen that prototype 3 outclassed prototype 1 and 2 in terms of energy generated per month. prototype 3 achieved 39.5w output for a wind speed of 1.17m/s and was predicated to generate a maximum 40 kwh per month. fig. 10. delivered power vs time per day. fig. 11. predicted total energy delivered per month in soweto. iv. discussion the results showed that a prototype 3 with a 7-blade design and with a maximum pitch angle of 12° produced maximum output power of 39.5w during testing, achieved at about 1.17m/s (4.2km/h) wind speed. the prototype 2, with a 5blade design and blade pitch angle of 10°, produced maximum output power of 12.5w at 4.2km/h wind speed, and prototype 1 with a 3-blade design and a pitch angle of 6°, produced a maximum power output of 8.2w at 4.2km/h wind speed. the results, furthermore, confirm that increasing the pitch angle from the standard 6° used for naca 4412 specifications to 10° and 12° near the hub and tapering/twisting to lower angles of engineering, technology & applied science research vol. 13, no. 2, 2023, 10553-10558 10558 www.etasr.com sithole et al.: implementation and evaluation of a low speed and self-regulating small wind turbine … the tip of the blade, and optimizing the attack angle to about 5, 7, and 9° along the section of the blade radius for 1, 2, and 3 designs, respectively, definitely increased the power delivery and the total energy capture of the rotor. these settings were derived from the available specifications and the published literature. the 7-blade prototype with naca-4412 blade design is an original implementation in soweto, johannesburg environment. derivation of the results and predictions for other areas in south africa (specifically, soweto and port-elizabeth) [16], contributed to new knowledge created within the field of the study. v. conclusions the current study is primarily focused on determining and adapting low-cost technologies applicable to south african conditions. this included the choice of the type of aerofoil, the number of blades, and optimizing the pitch angle along the blade radius in order to maximize the power output for low wind speed conditions in soweto. the main conclusions derived from the current study are:  in soweto area, having an average wind speed of 2.3m/s (8.28km/h), 3-, 5-, and 7-blade sets were developed and tested. the obtained results definitely indicate that for very low wind speed conditions, the implementation of more blades on single rotor/hub increased the captured power and energy significantly.  moreover, the developed prototype designs were also tested for self-regulation in case of high speed gust conditions. the results showed that the blades of prototype 3, with 12° maximum pitch angle during operation in high gust conditions, would control high speed, then cause a drawback pressure on the back side of the blades and tangent drag developed normally to the blade rotation direction, consequently limiting the maximum speed of the rotor and acting as a self-regulation mechanism of the maximum achievable speed. the other two designs suffered from over-speeding tendencies in high gust speed conditions, also causing noise and turbulence.  finally, it can be deduced that the power derived from the 7-blade system would be close to the expected optimum power that would be delivered for the designed 1m blade rotor system. any implementation of a higher pitch angle along the blades would, according to the theoretical considerations, probably lead towards an excessive angle of attack. references [1] b. memon, m. h. baloch, a. h. memon, s. h. qazi, r. haider, and d. ishak, "assessment of wind power potential based on raleigh distribution model: an experimental investigation for coastal zone," engineering, technology & applied science research, vol. 9, no. 1, pp. 3721–3725, feb. 2019, https://doi.org/10.48084/etasr.2381. [2] y. kassem, h. gökçekuş, and h. s. a. lagili, "a techno-economic viability analysis of the two-axis tracking grid-connected photovoltaic power system for 25 selected coastal mediterranean cities," engineering, technology & applied science research, vol. 11, no. 4, pp. 7508–7514, aug. 2021, https://doi.org/10.48084/etasr.4251. [3] f. elmahmoudi, o. e. k. abra, a. raihani, o. serrar, and l. bahatti, "elaboration of a wind energy potential map in morocco using gis and analytic hierarchy process," engineering, technology & applied science research, vol. 10, no. 4, pp. 6068–6075, aug. 2020, https://doi.org/10.48084/etasr.3692. [4] n. j. stannard and j. r. bumby, "energy yield and cost analysis of small scale wind turbines," in proceedings of the 41st international universities power engineering conference, newcastle upon tyne, uk, sep. 2006, vol. 1, pp. 108–112, https://doi.org/10.1109/upec.2006. 367725. 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[9] o. o. ajayi, o. okeowo, a. s. aasa, a. o. aboyade, and a. willoughby, "novel airfoil design for small horizontal axis wind turbine: a preliminary result," in third southern african solar energy conference, kruger national park, south africa, may 2015, pp. 181– 186. [10] p. gigue`re and m. s. selig, "new airfoils for small horizontal axis wind turbines," journal of solar energy engineering, vol. 120, no. 2, pp. 108–114, may 1998, https://doi.org/10.1115/1.2888052. [11] f. mahmuddin, "rotor blade performance analysis with blade element momentum theory," energy procedia, vol. 105, pp. 1123–1129, may 2017, https://doi.org/10.1016/j.egypro.2017.03.477. [12] m. k. chaudhary and a. roy, "design & optimization of a small wind turbine blade for operation at low wind speed," world journal of engineering, vol. 12, no. 1, pp. 83–94, jan. 2015, https://doi.org/10.1260/1708-5284.12.1.83. [13] s. n. bhadra, d. kastha, and s. banerjee, wind electrical systems. oxford university press, 2013. [14] a. azam, a. ahmed, h. wang, y. wang, and z. zhang, "knowledge structure and research progress in wind power generation (wpg) from 2005 to 2020 using citespace based scientometric analysis," journal of cleaner production, vol. 295, may 2021, art. no. 126496, https://doi.org/10.1016/j.jclepro.2021.126496. [15] t. s. sithole, v. r. veeredhi, and t. sithebe, "small wind turbine blade optimization using blade elementary method theory (bemt)," international journal of innovative science and research technology, vol. 7, no. 12, dec. 2022, https://doi.org/10.5281/zenodo.7444983. [16] t. s. sithole, v. r. veeredhi, and t. sithebe, "techno economic feasibility studies of small wind turbines for soweto, johannesburg, south africa," international journal of conceptions on electrical and electronics engineering, vol. 4, no. 2, sep. 2022. microsoft word etasr_v12_n6_pp9779-9786 engineering, technology & applied science research vol. 12, no. 6, 2022, 9779-9786 9779 www.etasr.com alquraish: modeling and simulation of manufacturing processes and systems: overview of tools … modeling and simulation of manufacturing processes and systems: overview of tools, challenges, and future opportunities mohammed alquraish department of mechanical engineering college of engineering university of bisha bisha, saudi arabia malqraish@ub.edu.sa received: 26 september 2022 | revised: 13 october 2022 | accepted: 21 october 2022 abstract-manufacturing is an important part of the modern economy. it is characterized by complexity in terms of systems, approaches, and interactions with intrinsic and extrinsic factors. numerous efforts have been developed to use modeling and simulation tools to improve manufacturing efficiency and productivity and to achieve maximum quality, especially with the different mutations in the factories of today. this paper reviews the conventional and modern tools used in manufacturing system design and production improvement. challenges that need to be addressed by the simulation community are discussed in depth. finally, the evolution, advances, current practices, and future opportunities are discussed in the context of the contemporary manufacturing industry. keywords-production processes; systems; tools; simulation; modeling; mutation; industry 4.0; indystry 5.0 i. introduction the majority of factories today face many challenges when trying to define how to acquire and maintain their position in the competitive business environment. a major challenge is to ensure that production, supply, and customer processes are correctly implemented and stabilized. these processes transform the input material and increase its value [1-3]. the main goal of the factories and enterprises today and in the future is to increase the value of the product effectively and to produce the smallest possible amounts of waste [4-6]. therefore, production processes have attracted a strong interest in the modern factory design [7-9]. consisting of various devices which have a set of tasks, trigged by specifics commands, a manufacturing system is traditionally evaluated and analyzed by simulation [10-11], which is a powerful and widely recognized technique [12]. while most previous works were focused in the simulations and modeling of manufacturing systems as a tool of analysis and development, the orientation of our research into new manufacturing approaches is directed towards the area of modern manufacturing systems, using reconfigurable manufacturing systems, adaptive logistics, and the concept of industry 4.0. new simulation systems which must be adapted to this new requirement are therefore discussed. the article deals with the description of the simulation tools and modeling of conventional and modern manufacturing concepts that are potentially highly applicable for use in future factories and the core descriptions of these tools in the process control for the industry 4.0 and the emerging industry 5.0. therefore, after considering factory mutations, the paper investigates the evaluation, advances, current practices and future trends of simulation methods and approaches. digital twins, suitable performance, lean in manufacturing system, iot-enabled forms, and virtual reality (vr) in process design, planning, and verification are examined. ii. mutation of factories during the last decade, an increase on the demand of individualized products and natural resources has been noticed [13]. besides, the huge evolution in technology and the smart concepts stimulate the user demand [14-17]. as a consequence, strong mutations in the society behavior, lifestyle, and consumption are noticed and are considered as new indicators of globalization [18-21]. the manufacturing systems represent a significant growing share to the global trade and become more and more challenging [22-24]. authors in [25] are among the first who introduced the virtual manufacturing concept by integrating different factory models, whereas authors in [26] proposed virtual facilities for different ways in a smart manufacturing system, including simulation, virtual organization, and emulation facility. actually, the most important point in the factory mutation is the appearing of the factory of things (fot) [27]. fot is based on technology characterized by the embedment of physical devices and many electronic compounds, with a wireless internet connection, known as the internet of things (iot) [2830]. it is fueling the industry 4.0 and space, health, and nanotechnology factories [30-32]. new challenges are raised by the industry 4.0 which drives smart factories by: i) data corresponding author: mohammed alquraish engineering, technology & applied science research vol. 12, no. 6, 2022, 9779-9786 9780 www.etasr.com alquraish: modeling and simulation of manufacturing processes and systems: overview of tools … volumes and connectivity, ii) business intelligence capabilities, iii) human machine interaction, iv) emergence of modern transferring digital instructions to the physical world [33-37]. as a consequence, iot is considered to be a key technology, required to support the propagation of successful smart manufacturing as the extension of the iot concept to manufacturing systems [38-41]. besides, as information is the most required input for a smart factory, advanced technologies like wireless sensor networks and cyber physical systems are needed to provide the parameters used in the analysis platform for seamless, automated simulation, optimization of shapes and geometry, and management of data and outputs [42-44]. these elements create a smart environment, and make communication between machine process compounds with central processing or various other possibilities [45]. this new concept is resumed as [26]: evolution of a system of data in terms of time, process, and manipulation: i) calculation of the time between a stop and the next start event in a manufacturing operation, ii) calculation of the number of produced parts between two steps as a second service [46]. iii. digital twins to create production process models, a digital twin of a physical process is needed, one that will enable process monitoring, real-time decision making, and control [47]. a digital twin represents a virtual model of a physical object which can simulate the object's behavior [48]. in that way it is possible to simulate production steps and to predict the impact on the product [49]. these simulations are highly utilized in industry 4.0 to simulate products, robots, and humans in order to reduce failures and optimize resource consumption [50]. numerical models are used for different manufacturing domains, beside the expansion of available data sources. they are particularly used for proving simulations of various parameters difficult to measure [51]. therefore, hybrid digital twins are used to model the usual behavior of the underlying manufacturing process or system [52]. this hybrid concept offers new services like detecting data-driven anomalies on simulations for new protective data, virtual prototyping, or a virtual instance of a physical system (twin) [53]. the objective is to lead high precision models showing not only physical parameters, but also a representation of their behavior, for monitoring, simulation, optimization, and developing of new products [54]. iv. manufacturing processes and systems: modeling and simulation for suitable performance a manufacturing process is a system characterized by a continuous evolution, interaction, and mutation, as it is a complex dynamic system, composed of several elements: management approaches, production facilities, control and monitoring equipment, and machining tools and operators [55]. with the variation in user demand, the search for better performance, environmental constraints, stability of production systems, and increased competition, the manufacturing processes are becoming more and more complex [56]. decomposition of a production system into subsystems of various depths is a necessity for the suitable analysis and effective study at the different levels of its specification [57]. optimization of production and manufacturing processes is established through data processing tools [58]. this approach allows dissecting and deriving, the relations between elements of technology, transport, storing, and layout subsystems. however, it is not an evident or easy engineering task [59]. therefore, models and simulations are used to achieve effective and efficient production, by improving existing processes, or innovating a required system, to reduce time cost, improve productivity, achieve competitively, and ensure quality [60]. it can be accomplished through a simulation of varied schemes of production on relation to different intrinsic and extrinsic factors (for example, parallel, sequential, or mixed schemes of production, different types of plant layout (process layout, product layout, combination layout, fixed position layout), design of manufacturing value chain, etc.) [61-69]. it is planned as consequent data usage, transformation, integration, and aggregation driving real innovation [70]. v. simulation-based multi-objective optimization and lean manufacturing a. conventional tools to develop and improve manufacturing processes and different related systems, we use different simulation models. a good formulation of a model which describes the function, evolution, and interaction with different related elements is based on data analysis and study [70]. different techniques for process improvement are exploited. linear programming, discrete-event simulation (des), system dynamic (sd), markov chain analysis, and monte carlo simulation are considered the most popular conventional simulation tools [7174]. various modeling formalisms have been established to describe the manufacturing processes and systems for varied fields and engineering applications (e.g. model of a machine, cell, line, site, etc.) [75, 76]. 1) discrete event simulation parameters the manufacturing systems are described with much formalism. the discreet event system (devs) specification is the most popular tool for modeling deterministic systems [7779]. the elements are interchangeable in many cases and are related by graphs, diagrams, and petri-net formalism [80-82]. as it is a rigorous and able tool to describe discrete event models in hierarchical and modular manner, devs is considered an efficient way to describe production processes mathematically when they are divided into different stages within a sequence of production steps [83, 84]. complex and stochastic flows in production lines and logistics systems are also described by this simulation tool [85-87] with relatively minor investment. as indicated in [88], devs can provide several scenarios despite the need of a large amount of modeling time in order to analyze system performance and to converge to an optimum solution. however, as the simulation is not an optimization tool by itself, in some cases, the improved scenario cannot give an optimized solution [89, 90]. unavoidable parameters in this stimulation tool are illustrated in table i. 2) simulation based optimization simulations of processes, machines, lines, or entire factories are built for a variety of reasons including virtual engineering, technology & applied science research vol. 12, no. 6, 2022, 9779-9786 9781 www.etasr.com alquraish: modeling and simulation of manufacturing processes and systems: overview of tools … experimentation, prediction, and optimization [91]. in order to be confident in any result of such a model, it must be validated against the real system [92]. the opposite also happens, when we wish to know whether the machines are operating as expected. this is done by comparing the data gathered from the simulation to the data gathered from the smart factory [93]. it is possible to perform this validation using summary statistical information, but it can hide the dependencies present in the underlying data [94]. stimulation based optimization (sbo) combined with incline devices has a tremendous potential for the framework and handle advancement in fabricating. while sbo can be utilized to analyze complex energetic frameworks with high inconstancy and an expansive sum of conceivable arrangements, incline devices can make up a base for persistent change in individual processes [95]. be that as it may, there is frequently a need of information in order to begin working with incline devices and reenactment approaches, particularly in production lines with a long history and tradition [22]. table i. parameters of different simulation models failures amounts of different kinds distribution of durations distribution of intervals cycle times of processes of assemblies of manual task (distribution) steps times (distribution) dependencies between articles batches container sizes delivery quantity frequencies b. modern tools vr, 3d discrete event simulation (des), data analytics, and real-life data from the products, processes, and production systems are considered the most popular modern tools for simulation and optimization [96-98]. 1) virtual reality (vr) integration of training in an immersive vr environment, with simulation, modeling, and data analytics, is planned to make harmonization and dissemination of knowledge more accessible [99, 100]. demonstrating the 3d vr recreation based on genuine production line and item information envelops the as-is show of the fabricating plant, counting the consistent connections. in this stage, the substances within the vr can be considered computerized models of their physical partners [101]. the virtual tests of a computerized exhibition are based on the standards of simulation-type modeling [102]. tests are utilized to survey the robustness and the ability of the physical equipment to comply with the prerequisites of the terms of reference (tor) described within the virtual machine by the specialized computer program (sw) components [103]. 2) data analytics and real-life data from products, processes, and production systems a virtual representation of fabrication frameworks utilizing the information from genuine industrial facilities can offer arrangements for item advancement and bolster item presentation forms, from design-to-manufacturing to simulation-based information analytics. it can allow shrewd generation frameworks [104-108]. appropriately, the virtual plant is a coordinated, high-fidelity recreation demonstration of a fabricating plant, which offers a progressed choice bolster capability and can back the assessment and reconfiguration of unused or existing fabricating frameworks [109, 110]. therefore, real-time information integration between vrenabled vf recreations is considered to be superior with higher exactness, precision, and unwavering quality [111-113]. 3) 3d discrete event simulation (des) using flexsim simulation tool flexsim simulation tool was utilized to create a vr recreation in [114]. it is a 3d des computer program which contains common and health-care-focused items [115-116]. its user-friendly drag and drop interface and comprehensive visual capabilities were considered important for quick experimentation. flexsim’s inserted vr capability permits clients to show, run, and control the recreations and collect the factual information in 3d graphical vr environment [117119]. this capability brought significant preferences in diminishing the time for approval after each reconfiguration/redesign of the vr. the interesting sentence structure of the instrument makes it challenging to create customized models [25]. 4) simulation for learning factories: the example of fischertechnik manufacturing plant models manufacturing businesses are transitioning towards more independent and smart generation lines within the industry 4.0. learning production lines as small-scale physical models of shop floors is done in order to conduct inquiries about the shrewd fabricating zone without depending on costly genuine generation lines or totally mimicked information. learning factories are used for conducting investigations within the setting of commerce administration and iot [120]. the physical fischertechnik manufacturing plant model mimics complex generation lines. three case studies of combined bpm and iot were considered in [121-125], i.e. the execution of a bpm deliberation stack on behalf of a learning manufacturing plant, the experience-based adjustment and optimization of fabricating forms, and the stream processing-based conformance checking of iot-enabled forms. by utilizing physical manufacturing plant models as test beds for assessment, investigation is more realistic–but more challenging–than utilizing artificial information in this kind of profoundly energetic cpps. physical plant models empower the approval and exhibition of inquiries about artifacts in an ensured environment [125]. at the same time, this close-toreality recreation of a genuine generation line encourages the exchange of created concepts into hone. c. model-based system engineering (mbse) mbse could be a key enabler for building complex frameworks as can be seen by the expanded number of related distributions [125-127]. for effectively building industry 4.0 frameworks, the mbse community plays a pivotal part by empowering the previously mentioned plan standards. modelbased framework designs have appeared to encourage the improvement of such frameworks, but their application to engineering, technology & applied science research vol. 12, no. 6, 2022, 9779-9786 9782 www.etasr.com alquraish: modeling and simulation of manufacturing processes and systems: overview of tools … industry 4.0 has not been efficiently explored [128]. to comprehend the commitment of mbse to industry 4.0, precise mapping has been conducted in [30, 129-130], which uncovered that computerized representation of robotized frameworks, i.e. their interfacing and information models, as well as their integration and (re)configuration are the prime industry 4.0 concerns tended to by mbse. most published papers contribute strategies and ideas to illuminate specific challenges of industry 4.0. vi. future opportunities and challenges investigation on the evolution and recent developments of industrial simulation technology and describing the gaps and future trends in this field are important in order to explore future opportunities for more effective manufacturing processes and system implementations. in the complex item digital twin arrangement, the items display and reenact procedures that create and expand tremendous sums of (generally organized) information. the arrangement of models along the complete lifecycle of a complex item (e.g. as outlined, as fabricated, as kept up) requires advanced modeling-simulation techniques. looking at the mechanization within the machine fabricating field and mechanical autonomy, the larger challenge is signified by the working program, particularly planning program frameworks. another distinctive challenge is the actual execution. in this way, projection and enhancement of the computerization and mechanical autonomy program frameworks ended up critical and with issues. in this manner, the information analytics capability was not most centered on advancement. the da capability of the recreation device was utilized to produce standard diagnostics for the shop-floor operations [131]. nowadays, the concept of the shrewd plant is rising with the joining of the virtual and physical universes. as indicated above, the shrewd manufacturing plant could be a fabricating environment that can handle turbulences amid utilizing decentralized data and communication structures for ideal administration of generation forms. within the case of a conventional plant, it is not fundamental to consider turbulences since the planning and execution tasks are consecutively performed. in other words, a conventional production line does not begin execution before the ultimate affirmation of the generation planning. a shrewd manufacturing plant, in any case, permits the concurrent advance of the planning and execution errands, since it has the means to handle turbulences in real-time generation [132]. this issue lead us to talk about the next generation of simulation systems, especially the need of more humancentered technology approaches, nascent in industry 4.0, and now central to the emerging industry 5.0, which is a valuedriven concept based on three principle cores: humancentricity, sustainability, and resilience [133-135]. simulation tools and modeling must adapt to the requirements of the new concepts of industry 5.0: changes do not happen overnight in the systems that will use these new trends. the challenges are to find suitable modeling and simulation tools to introduce the concepts of the new paradigm in each essential segment of the manufacturing and to draw a connection matrix between key enablers for industry 4.0 and 5.0, particularly people, companies, and technology [136, 137]. vii. conclusion this paper at first highlighted the conventional and modern simulation and modeling tools used in manufacturing system design and production improvement. challenges needed to be addressed by the simulation community were discussed in depth. finally, evolution, advances, current practices and future opportunities were discussed in the context of the contemporary manufacturing industry, particularly the 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2022 | revised: 26 september 2022 | accepted: 27 september 2022 abstract—understanding climatic behavior, particularly that of semi-arid regions, is essential in order to optimize water resources management and provide protection from climatic risks. water resources have great socio-economic and environmental importance. this paper focuses on the statistical analysis of the rainfall regime of northwest algeria and estimates its spatial distribution and temporal variation. to this end, time series and principal component analysis were performed on rainfall series recorded from 1913 to 2009, representing the annual precipitation from thirty meteorological stations to discover patterns and trends in the studied region. furthermore, the applied spectral analysis of the time series reveals the existence of a period of approximately 97 years at all stations. arcgis along with statistical and analytical tools like spss and xlstat were utilized in this study of the climatic behavior in northwest algeria. keywords-rainfall series; statistics analysis; cartography; spectral analysis; climate variability i. introduction learning about climatic behavior in a region improves hydraulic constructions and plays a critical part in the management of water resources in various term lengths [1]. researchers are trying to answer questions such as if there is there a climate change in the study region and how can the existence of any change be confirmed. in response to these complex questions, a verification of climate change parameters is required, such as the temporal homogeneity of hydrometeorological time series, in particular stating the presence of trends in the case of annual rainfall series. numerous studies analyze the variability of precipitation in the mediterranean basin and african regions. linear trends from 1901–2005 show high spatial variability [2]. in comparison to other regions, positive annual precipitation trends were detected in north and south america, the eurasian continent, and australia. on the other hand, several observations were made concerning a significant decrease in annual totals in western africa, sahel, the western coast of south america, and the mediterranean basin [2]. in the zone of sahel, there are several indicators of decreasing trend in rainfall series from 1970 to 1990 [3-7]. consequently, it was observed that alteration in climatic parameters can result in modification of the hydrological cycle which affects the quantity and quality of rainfall and water resources [8]. the drought affected other countries around the gulf of guinea in the late '60s [9-11] and altered the rainfall regime of sahel from 1990 to 2007, increasing it by 10% in comparison with the rainfall regime of the 1970–1989, but it was still lower than the 1950–1989 average (a 20-year wet period (1950-1969) and 20-year dry period (1970-1989)). while the rainfall deficit continued in western sahel, central sahel gradually recorded more wet years beginning from the late 1990s, but the recovery was considerably limited (1990-2007). as a conclusion, there are numerous differences between western and central sahel regarding the inter-annual variability pattern and the seasonal cycle. in mediterranean regions, several researchers have observed a decrease in annual precipitation. yearly and seasonal precipitation series from 32 stations from 1833 to 1996 were examined in [12]. declining trends in several yearly series were noticed, which were remarkable, considering the statistics, only in southern italy. on a seasonal basis, a declining trend was significant only during spring in southern italy and autumn in northern italy. in southern italy (calabria), statistical analysis of annual and seasonal precipitation on 109 series with over 50 years of processed data was performed in [13]. the rainfall data segment was first calculated following a pre-whitening technique to lower the autocorrelation of the rainfall series. the study showed a decreasing trend for annual and winter fall rainfall and an increasing trend for summer rainfall. in addition, raised percentages of rainfall series show breaks during the 19601970 period. nonetheless, the analysis on parts of the mediterranean area shows that the surging progression is a non-considerable reduction in precipitation or a lack of linear trend during the last century or a shorter period [14-16]. corresponding author: sarra bouraoui engineering, technology & applied science research vol. 12, no. 6, 2022, 9632-9639 9633 www.etasr.com bouraoui & medjerab: a spatiotemporal approach in detecting and analyzing hydro-climatic change … a study of the changes in data series of climate variables at annual and monthly scales in the western part of the french mediterranean area showed that annual precipitation was too low [17]. moreover, the study stated that monthly rainfalls were decreasing in june and increasing in november throughout the area. the changes in precipitation of the balearic islands (spain) were studied in [18], considering the daily time series from the 1951-2006 period, confirming a negative trend of annual precipitation. an abrupt decrease in a year's rainfall of 65mm has been identified in the time series around 1980. in the current study, spatiotemporal analysis of precipitation with a set of statistical methods is used to recognize trends and identify break dates and spatial patterns of precipitation variability of the southern mediterranean region. for this purpose, a series representing the total annual precipitation of approximately 30 stations in western algeria, with the recorded data spreading over a period of 97 years (1913-2009) were examined. the data were analyzed with the use of the spearman test for the detection of trends, the mann-kendall and pettitt tests for the detection and localization of these trends, spectral analysis to study the nature of the variations, and principal component analysis (pca) to identify regions of consistent precipitation variability [8]. ii. study area and precipitation data the considered region extends between the meridians -2° west and 1° east, and between the north 36°33’ and 33°91’. it includes the catchments of cheliff (01), oraneese coast (04), mactan (11), and tafna (16) (the numbers in parentheses indicate catchment codes). the area is bordered in the north by the mediterranean sea, in the west by the algerian-moroccan borders, in the south by high plains, and in the east by the mountainous massif of ouarsenis. in algeria, the climate of the northwest is affected by diverse factors, such as the atmospheric circulation and topography. from december to february, the winds are directed west-northwest. these winds must cross the narrow arm of the sea that distinguishes the study area from spain, to access northwestern algeria. before leaving spain, the winds discharge part of their moisture on the high peaks of the sierra nevada. the air masses do not have enough time to accumulate sufficient water vapor and reach northwestern algeria relatively dry. during their journey over the mediterranean sea, the water-laden easterly winds favor the appearance of heavy precipitation, but this occurs rarely during the winter. heterogeneity characterizes the area. west tellian atlas has a fragmented relief. the high west plains are arid steppes. in morocco, the middle atlas rif ridge protects northwestern algeria. it exposes a complex topography with a split mountainous character, which increases the areas of shelter while the exposure to sea influences and disturbs flows. figure 2 shows the location and geographical features of the region. the aforementioned factors contribute to the lowering of the precipitation and consequently to the surface and subsurface water resources. the atmospheric circulation forms the climate of northwest algeria and is composed of cells with latitudinal extensions. among these cells, we can mention the following:  the azores high, a zone with permanent high pressure that grows in the middle of the atlantic, in the region of the azores islands. its propagation to the maghreb area deflects the meteorological troubles towards europe.  the saharan anticyclone is much more stable than the previous anticyclone from the general circulation point of view. irregularity is the most important index of precipitation: spatial and temporal irregularity from one region to another, eminently an inter-annual irregularity. sometimes, heavy rainfalls cause catastrophic floods. most of the region has precipitation totals between 200 and 800mm. the southwestern zone is the driest, with the lowest annual rate of 100mm. another significant aspect is the low number of rainy days (between 14% and 21%). the rainfall data were provided by the national agency of hydraulic resources (anrh). the original database comprises daily precipitation records from 30 stations distributed throughout the area, covering various periods with more than 97 years of observations. analysis of precipitation variability requires long data sets in excellent condition. in addition, analyzing the spatial distribution of a general term in all stations should be chosen carefully. for this reason, we had to balance the length of the periods and the number of included stations. the number of missing data records influences precipitation analysis, so only series with < 10% missing values were maintained. fig. 1. elevation map of western algeria with principal mountains (2020). the quality controls on the selected data sets had two main steps, the first of which was to discover possible errors and suspect precipitation records. in the second step, the data sets were subject to a homogeneity test. data homogenization helps conceive observations conditionally, so the temporal variations of the adjusted data are only brought in by the climatic processes. the most frequent causes of the lack of homogeneity of the climatic data are the changes in the location of the stations, alterations in screen designs, or environmental changes around the station. the cumulative residuals had to be tested to detect such anomalies in the series. the test allows for a qualitative evaluation at a given significance level of the engineering, technology & applied science research vol. 12, no. 6, 2022, 9632-9639 9634 www.etasr.com bouraoui & medjerab: a spatiotemporal approach in detecting and analyzing hydro-climatic change … homogeneity of the precipitation series concerning the confirmed homogeneous series by comparing the packed residuals of linear regression with an elliptical confidence interval (bois ellipse). only series that did not show heterogeneities were selected. finally, 30 annual precipitation time series passed the above described quality control, which were also acceptably distributed throughout the study area, covering the 1913–2009 time period, and missing less than 10% values (figure 2). the missing values were interpolated by linear regression based on a series from adjacent stations. linear regression equations were established separately with complete series of 1 or 4 adjacent stations as independent variables and incomplete series as the dependent variable. the relative error in evaluating the interpolation was obtained by averaging 5 relative errors calculated from 5 observed and predicted values near the missing data. the linear regression equation with the lowest relative error rate was the chosen equation for predicting the missing data. the maximum relative error did not exceed 15%. iii. methodology several parametric and nonparametric tests were used for trend detection. parametric trend tests are more cumbersome than nonparametric tests, which require independent and properly distributed data. in contrast, nonparametric tests require only independent data and may allow for outliers. to detect trends in the precipitation time series, we decided to use nonparametric tests that overcome the obstacles of other methods. mann–kendall test [19, 20] and spearman’s test are widely used to detect trends in time series. their efficiency and power have been proven significant in similar applications [21]. additionally, when implemented in a sequential version, the mann-kendall test positions itself notably well in synchronization with the trend appearance. to reinforce the results of both tests, we performed another nonparametric test, the pettitt test, which can detect the breakpoint of serial average at any level of significance. it designates a highly precise magnitude of the detected trend. spectral analysis helps determine the periodicities in the precipitation time series [22]. afterward, principal component analysis is applied to deduce a spatiotemporal regionalization of the precipitation variability. fig. 2. station positions in the study area. iv. spearman’s test spearman’s test is a rank-based nonparametric statistical test that can be used to detect monotonic trends in a time series [23, 24]. the spearman test was used to analyze hydrometeorological trends in [25-27]. for a given sample of data (xi, i = 1, 2…, n), the null hypothesis h0 states that all xi are independent and identically distributed. the alternative hypothesis is that xi increases or decreases with i, i.e. there is a trend. the test’s statistics are given as [24]: �� � 1 � � �� �� ∑ ��� � � � ��� (1) where yi is the rank of the i-th observation xi in a sample of size n. the diffusion of this statistic is asymptotically correct under the null hypothesis with the mean and variance of (2) and (3): ���� � 0 (2) var��� � � �� (3) the exceedance probability a1 is computed using the normal cumulative distribution function with zero mean and variance var��� : �� � ��|�| � |���� | (4) ���� � ��√ � 1 (5) then, the null hypothesis is adopted or not at a significance level of 0 depending on whether �� > �% or �� < �% . significant values of |rs| show a decreasing or increasing trend. v. mann–kendall test the mann–kendall test is also a rank-based nonparametric test which associates a number ni to each xi where xi is the number of elements, such that i>j , and &� � &' . mann-kendall statistic is: ( � ∑ �� ��� (6) under the null hypothesis, the statistic is, for a large sample, normally distributed with mean and variance assigned by: ��( � � �� ) (7) ��( � � �� ) (8) its reduced form is: *�( � +�,�+ -./0�+ (9) the null hypothesis is unacceptable for high values of the reduced statistic. positive values of u(t) indicate increasing trends, while negative values show decreasing trends. when testing either increasing or decreasing monotonic trends at a significance level, the null hypothesis was rejected for an absolute value of u(t) greater than u1-a/2, and u1-a/2 is the critical value obtained from the standard normal cumulative distribution tables. in this research, a significance level of 0.05 engineering, technology & applied science research vol. 12, no. 6, 2022, 9632-9639 9635 www.etasr.com bouraoui & medjerab: a spatiotemporal approach in detecting and analyzing hydro-climatic change … was applied. the sequential version of the test (in a forward and a backward sense) enables us to identify the star to trend within the data series. note that u(t) is the forward sequence. τhe backward sequence u'(t) is studied with the same function but with the opposite data series. in the absence of any trend, the graphical representation of the curves u(t) and u'(t) overlap many times. when the null hypothesis is rejected (i.e. when any of the points in u(t) exceeds the confidence interval ±1.96), an increasing or decreasing trend is indicated. the test statistic applied in this study allows finding the approximate moment of the appearance of the trend by locating the intersection of the curves u(t) and u'(t). a point of intersection with the confidence interval shows a point of change. the parts of the curves ahead of the confidence lines show the time domain of a sudden change. detailed descriptions of this nonparametric test can be found in [24]. vi. pettitt test the pettitt test is a nonparametric test derived from the mann–whitney test [28]. the absence of a break constitutes the null hypothesis. pettitt defines the variable ut, n as: *+, � ∑ ∑ 234�5 '��6� + ��� (10) 7 � 8� � 8' (11) where sgn(z) = 1 if z > 0, 0 if z = 0 and -1 if z < 0. he suggested testing the null hypothesis by using the statistic kn defined by the maximum value of ut,n for t=1,…,n-1. from the rank theory, pettitt demonstrates that if k indicates a value of the kn series, under the null hypothesis, the exceedance probability of the k value is given by: ��9: �; � ; < 2 exp��6 ; � � a b � ⁄ (12) for a type i error a, if the exceedance probability estimated is less than a, the null hypothesis is rejected. the time series demonstrate a trend at time t where the kn appears. vii. principal component analysis pca is a classical factorial procedure. it changes several (possibly) correlated variables (here, the annual precipitation stations) into a (smaller) number of synthetic uncorrelated variables called principal components (pcs). every time series (factor score) is linked to a component. pca ensures the detection of coherent and recurring modes in the total domain. rotation methods allow us to improve the interpretability of the results through a linear transformation of the pc. compared to the non-rotated solution, orthogonal rotations (preserving the correlation between the pcs) are less affected by the domain form, and the instability of the subdomain (the fact that the pca is performed only on a part of the field leads to different results from those of the pca of the entire field) and the sampling errors between the pcs. varimax is the most commonly used rotation [29]. its goal is to maximize the variance of the factorial weights between each component for a given variable, increasing the segregation between the various pcs. viii. spectral analysis the spectral density takes the frequency content of a stochastic process and allows the identification of periodicities. the spectral density function resembles the passage from a temporal mode to a frequency mode by a fourier modification of the autocorrelation function. the interpretation of the spectral density function, s(f), through the recognition of the different peaks indicating periodic phenomena, leads to the characterization of the system: 2�d � 2e1 b 2 ∑ f�g ��g cos�2kdg lm�� n (13) f�g � ��6opq r s t � (14) where j=1 to m, f is the frequency and d(k) ensures that the estimated values s(f) are not biased (tukey filter). r(k) is the autocorrelation function expressed by: ��g � u�v u �% (15) w�g � � x ∑ �&+ � 8y x�v +�� �&+6v � 8y (16) where k is the time lag (k = 1… m), n is the length of the time series, x is a single event, x is the mean of the events and m is the cutting point. the cutting point is usually determined based on the interval of the analysis and the given circumstances. ix. results and discussion a. temporal analysis spearman and mann–kendall tests were applied to the data series of annual rainfalls of the 30 selected stations and a significantly decreasing trend was detected at a significance level of 5% for 29 stations (figure 3). only the ghriba station, in the eastern zone of the studied domain, presents a significantly increasing trend at a 5% level. in the region, this station is behind an isolated station. fig. 3. trends in annual total precipitation during 1914–2004 detected by the mann–kendall method. the curves overlap (e.g. figure 4(a) for mostaganem 1 station) and the statistical values do not surpass the limits of the critical significance levels, except for the series of youb that present significant statistic variations, indicating the presence of dry periods. the intersection point between both curves (forward and backward) within the confidence interval demonstrates the change point that compares to the break date. engineering, technology & applied science research vol. 12, no. 6, 2022, 9632-9639 9636 www.etasr.com bouraoui & medjerab: a spatiotemporal approach in detecting and analyzing hydro-climatic change … the graph in figure 4(b) shows the forward and backward results of the test for the youb station. the intersection of the two curves marks a change that occurred in 1955. the evident results obtained previously and the location of the break years in different levels of significance is provided by analyzing the whole series with the pettit test. evidently, the results show that an abrupt change (decrease in rainfall) within the time series is observed mainly from the end of the 1940s until the beginning of the 1950s. for 6 stations, the beginning of the trend was detected between 1953 and 1980, 26 stations led to a very significant decreasing trend between 1975 and 1996, and the others appeared to be stationary and confirmed the previous results. hence, the presence of a rainfall deficit is evident in the eastern zone from the beginning of the 1930s and accentuated during the 1950s and 1970s by its extension to the whole region. (a) (b ) fig. 4. mann–kendall progressive test applied to stations: (a) mostaganem 1, (b) youb. trends can be detected using pettitt’s and mann–kendall’s tests. however, these tests cannot find more than one break date. this represents the drawback of these tests when investigating rainfall time series, which could have multiple increasing and decreasing trends and/or breaks, specifically for long series. when the number of stations used is not very large, a limit is triggered by the difficulty of interpreting the results on a regional scale. these results suggest that further investigation is needed. we tried to perform spectral density analysis to seek possible periodicities and supplementary pca was carried out, and regionalization of rainfall variability was performed. b. spatiotemporal rainfall variability pca was applied with the stations as variables and the 97 annual precipitation values. the analysis without and with rotation underlines that the first 4 components account for most of the total variance (57.8%), as shown in table i. table i. explained variances by the four first pcs before and after rotation (f: factors) pc (without rotation) rpc (rotated) f1 f2 f3 f4 f1 f2 f3 f4 variance % 45.988 6.575 5.250 4.830 29.292 14.156 5.049 14.147 cumulative variance % 45.988 52.563 57.813 62.643 29.292 43.448 48.496 62.643 the first component accounts for a large part of the variance (45.988%). it describes the inter-annual variability of the precipitation for the whole region (opposing humid and dry years). all stations are correlated positively with this component, considering varying coefficients between 0.85 and 0.2. the greatest coefficients are noted in the deepest region (figure 5). the objective of the test here is to identify regions with the same variation mode. this geographical consistency can be justified by the large homogeneity of the weather regimes (winter rains and summer drought), but it denotes that a long stretch of years presents large deficits or excesses over the whole region. the observation complies with the result that is found by the nonparametric statistical test of trend detection, as shown above. fig. 5. spatial distribution of the first pc (pc1) fields in the area of study (pca without rotation). fig. 6. temporal factorial scores of pc1without rotation. the straight line represents the chronicle trend. the time series of the amplitudes of the first component (figure 6) highlights wet years (1927, 1933, and 1950) and the succession of dry years that most stations of the region recorded. a decreasing trend with a significant determination engineering, technology & applied science research vol. 12, no. 6, 2022, 9632-9639 9637 www.etasr.com bouraoui & medjerab: a spatiotemporal approach in detecting and analyzing hydro-climatic change … coefficient of 0.2287 is clear starting from the end of 1975 to 2007 (with an absolute minimum in 1981). the following components (figure 7) account for smaller proportions of the variance. the second component accounts for only 6.575% of the variance (table i). it shows opposite amplitudes between parts of the eastern region correlated positively (heavy rainfall) and the west and southwest (areas affected by the foehn phenomenon. the distance from the sea influences the rainfall flows and, therefore these areas have low rainfall). the third component shows 5.25% of the variance. it represents the southwest and southern parts to the north and center of the study area. the first component accounts for the largest amount of total variance, however, some stations are correlated with this component. we performed a rotation of the factorial axes according to the varimax method. varimax orthogonal rotation is the option used to avoid some of the domain shape dependences [29] and to obtain a stable and physically meaningful pattern. the principle is to determine the components that correlate best with the variables [16, 30]. (a) (b) fig. 7. spatial distribution of (a) pc2 and (b) pc3 fields in the study area (pca without rotation). we retained the first 4 components accounting for 62.643% of the variance. the percentage of variance demonstrated by the eigenvalues is different from the pca without rotation, with less variance demonstrated by the first component and more variance detailed by the other models. the first component shows the western and central parts of the region (coastal plains). the stations most related to this component are those with elevations between 5 and 215m. the eastern region is known for its low relief and low precipitation (annual rainfall <500mm) with a weakly explained variability (variation coefficients <0.30), see figure 8(a). the second component characterizes the eastern part of the study area (dahra mountains). this region is well-watered, expressing the simultaneous influence of topography and atmospheric circulation on rainfall (figure 8(b)). the third component characterizes the variability of the western part of the study region (figure 8(c)). the fourth component represents the tellian plateau and the high plains in the east, characterized by weak rainfall with a low estimate of 450mm and a very sporadic character due to the shelter effect that reduces the influence of the rainy systems covering the west and northwest (figure 8(d)). (a) (b) (c) (d) fig. 8. spatial distribution of (a) pc1, (b) pc2, (c) pc3, (d) pc4 fields in the study area (pca with varimax rotation). the time series associated with the first component (figure 9(a)) reflect an evolution mode identical to the one described by the pca component without rotation, with some differences like excesses, less accentuated from 1918 to 1953 in contrast with the other three pcs. engineering, technology & applied science research vol. 12, no. 6, 2022, 9632-9639 9638 www.etasr.com bouraoui & medjerab: a spatiotemporal approach in detecting and analyzing hydro-climatic change … c. spectral analysis it should be noted that the semi-arid character of northern algeria, particularly the western zone, is partly defined by the changes in the general atmospheric circulation. several studies connect precipitation compression to the north atlantic oscillation (nao), which impacts the mediterranean climate [31-36]. the phenomenon is studied quantitatively by the nao index, which describes a normalized pressure difference between the measurements made in the azores and iceland. the index differs from year to year, but also shows a tendency to stagnate in one phase during long intervals [37]. recently, its sign changed, mainly because of two concurrent trends observed during winter over the last three decades, leading towards a positive phase. these winters are related to higher than usual pressure in the subtropics and lower pressure in the arctic. thus, winters are dry and warm in southern europe, wet and warm in northern europe, and dry and cold in greenland. on the other hand, during the negative periods of the nao, winters are usually cold in northern europe, wet and humid in southern europe, and milder in greenland. climate anomalies combined with the nao have effects on rainfall in north africa, as demonstrated in [38-42]. the periodicity demonstrated for this part of the study area can also be tuned to the 25 years of the positive observed phase of the nao (as it was a depiction of the correlation analysis). (a) (b) fig. 9. temporal evolution of the annual nao index and the factorial scores pc1. thus, a study taking into account the observation period of 2005–2011 could reveal that the negative phase of nao led to increased precipitation. from the middle of 1970's to 2000, the nao annual index enters a positive phase, and the regional precipitation regime, represented by the first component, presents a decreasing trend. furthermore, a negative association (pearson’s r = 0, pearson’s r = 0.209) was found between the first component and nao during 1975–2000. the association will be clear on a seasonal scale, as the nao phenomenon affects winter precipitation. x. conclusion the use of principal component analysis (pca) allowed us to identify 4 significant geographical regions with coherent precipitation variability showing the influence of two regimes in the investigated area: a central zone from the north toward the south of algeria that is affected by the rainfall deficit and two lateral zones registering no deficits. the reliefs of the analyzed area are essential to the high mountain plateau type, and the noticed phenomena are less dependent on the intrinsic characteristics of the domain. however, this would require a considerable change of the meteorological variations over a wider area, determining the transit corridors of the rainy currents. it precedes the unique effect of the approach of moroccan atlas mountain range. the central region of the domain becomes the most targeted for climate change. nonparametric statistical tests of the annual precipitation series show a weak trend at most of the studied stations in algeria. the result is in line with the results received in several trend analysis studies. one of the suggested recommendations to describe wet and dry sequences precisely is the analysis of precipitation time scales over the years, which enable the study of possible changes in rainy and dry times. references [1] a. a. mahessar et al., "rainfall analysis for hyderabad and nawabshah, sindh, pakistan," engineering, technology & applied science research, vol. 10, no. 6, pp. 6597–6602, dec. 2020, https://doi.org/10.48084/etasr.3923. 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[42] a. n. laghari, w. rauch, and m. a. soomro, "a hydrological response analysis considering climatic variability: case study of hunza catchment," engineering, technology & applied science research, vol. 8, no. 3, pp. 2981–2984, jun. 2018, https://doi.org/10.48084/etasr.2056. microsoft word etasrtemplate.doc engineering, technology & applied science research vol. 5, no. 4, 2015, 818-824 818 www.etasr.com gong et al.: optimum shape design of metal-enclosed 550 kv disconnectors based on response… optimum shape design of metal-enclosed 550 kv disconnectors based on response surface method and finite element analysis ruilei gong school of electrical engineering, xi’an jiaotong university, shaanxi, xi’an, 710049, china shuhong wang school of electrical engineering, xi’an jiaotong university, shaanxi, xi’an, 710049, china xianjue luo school of electrical engineering, xi’an jiaotong university, shaanxi, xi’an, 710049, china michael g. danikas department of electrical and computer engineering, democritus university of thrace, 67100 xanthi, greece abstract— in this paper, the optimum shape design of 550 kv disconnectors in gas insulated switchgears (gis) are firstly presented employing the finite element method (fem) for electric field analysis coupled with an optimal design method. for effective analysis, the fem is conducted in transient quasistatic electric field, using a finite element fortran code. the structure parameters of disconnectors that provide the required electric field strength are obtained by the response surface method (rsm) and the optimal values are presented by the variation in maximal electric field strength. the rsm and optimal design methods are also conducted by fortran codes. the optimal result reveals that a uniform electric field distribution is achieved in 550 kv disconnectors. additionally, the optimal result of disconnectors is verified by the proposed disconnector undertaken power frequency withstanding voltage of 740 kv for 1 minute, lightening impulse of 1675 kv, and operating impulse of 1300 kv, respectively. keywords—disconnectors; response surface method (rsm); optimization; structure design; finite element method (fem) i. introduction disconnectors in gas insulated switchgears (gis) are a switching device without an arc extinguishing device. an opened state should be obvious (visible) and a breakdown is not allowed under any circumstances, in order to ensure the safety of the maintenance personnel. furthermore, disconnectors in the closed state must reliably carry normal and/or short circuit currents. because of the special role of disconnectors, there is the need to consider its two working states: the opened state, to meet the insulation design, and the closing state, to meet the through flow capacity design and insulation design. therefore, the insulation of disconnectors design is essential. the insulation performance of disconnectors mainly depends on the electric field distribution in the breaking. the electric field distribution in the breaking state is directly related with the structure shape of shielding. therefore, the optimization of disconnectors mainly concerns the optimization of the shielding structure. because of the structural complexity of disconnectors, it is difficult to determine the field distribution in the inside, and therefore a finite element method (fem) is employed [1-2]. 3d modeling is more realistic but due to the axial symmetry, a simplified twodimensional calculation can be considered not to affect the analysis results. herein, a commercial software is used and it is compared with a simplified two-dimensional calculation and three dimensional calculation and analysis. the result reveals that the simplified model meets the accuracy required. in addition, the model of disconnectors employs a twodimensional model of transient quasistatic electric field considering the conductivity and permittivity of materials in order to obtain more accurate results. at present, several optimization methods, e.g. genetic algorithms and the simulated annealing method, have been used in combination with fem, but they usually suffer from low efficiency. the response surface method (rsm) has been successfully combined with fem as an efficient way to realize the optimization of structure parameters of different electric devices [3-5]. rsm uses discrete points obtained according to some experimental design rules and constructs the optimal approximate function to attain optimal results. rsm combined with fem can effectively reduce the calculation and workload, and also obtain high accuracy results. in this paper, this is the first time that rsm and fem are successfully applied to the optimization of a high-voltage disconnector in gis. additionally, in order to realize optimization analysis for automatic calculation, rsm, fem and subsequent optimization algorithm programs are written using the fortran language. ii. transient quasistatic electric model analysis of the internal electric field of disconnectors, due to the lightning impulse voltage, is a function of time as well as of the conductivity of the insulating medium. therefore, this paper adopts the quasi-static electric field model for transient analysis. a transient electric analysis determines the effects of time-dependent current or voltage excitation in electric devices. for this reason, the time-varying electric and magnetic fields engineering, technology & applied science research vol. 5, no. 4, 2015, 818-824 819 www.etasr.com gong et al.: optimum shape design of metal-enclosed 550 kv disconnectors based on response… are uncoupled, and the electromagnetic field can be treated as quasistatic [2, 6-8]. in a quasistatic electric model, the circulation of the electric field is essentially zero for any path; this allows the electric field e  to be represented by a scalar potential function  as: e    (1) the potential function  is continuous in the domain, i.e. there are no charge double layers. from the ampere-maxwell equation follows that: ( ) 0 d j t         (2) where j  is the conduction current density and d  is the electric displacement. we assume that at 0t  there are no ‘free charges’ in the system. the electric displacement in the linear isotropic materials is simply related to the electric field: d e   (3) in the nonconducting regions, from (1), (2) and (3) follows that the laplace equation for the potential holds: 0( ) 0j      (4) where 0  is the permittivity of free space and j is the relative permittivity of the insulating material. in the materials considering the conductivity, the current density and the electric field are related by: ( )j e e   (5) where  e is a field dependant conductivity. in the regions considering conductivity, from (1), (2), (3) and (5) it follows that the dynamics of the electric potential is described by a diffusion-like equation: 0[ ( ) ] [ ( )]je t              (6) in order to analyze the field distribution of the conductive materials, (6) can be discretized by applying the backward euler method: 2 2 0 ( ) ( ) [ ( ( )) ( )] j t t t e t t t                (7) where t is the time and t is a suitable small time interval. equation (7) can be rewritten as: 2 0 0 ( ) [ ( ( ( )) ) ( )] j j t t e t t t t                   (8) summarizing, (4) and (8) can be written as: [ ( ) ] 0c f     (9) where 0 0 ( ) ( ( )) j j c e t t in insulating materials in conductive materials            0 0 ( ) ( ( )) j j c e t t in insulating materials in conductive materials            2 0 0 ( )j f t t t in insulating materials in conductive materials           the electric field distribution in disconnectors is symmetric. by adopting a cylindrical reference system with the z-axis coincident with the axis of the conductor of disconnector, the variational problem of (9) is shown as: 0 0 ( ) 2 ( ( ( ) ) )es s l f c e de rdrdz f rdrdz                 (10) the corresponding finite element equation is: ( ) ( )k p   (11) where  k  is the n n nonlinear matrix,  is the n column vector of the nodal potentials, and  p  is the sum of the n column vector produced by dealing with dirichlet boundary conditions and produced by equivalent charge density. equation (11) can be iteratively solved by means of the newton-raphson method. starting from a guess n of the solution, an improved approximation 1n  is obtained by solving the series linearized problem. this iterative algorithm is repeated until the condition 1n n n        (12) is verified.  is a prescribed small value, and the corresponding value 1n  is assumed as the solution of the system at time instant t . the solution at time instant t t  could be finished through solving (11). and last, in all time domains the solution can be attained. this numerical model represents an improvement of the quasistatic electric field approach presented in [9] for two main engineering, technology & applied science research vol. 5, no. 4, 2015, 818-824 820 www.etasr.com gong et al.: optimum shape design of metal-enclosed 550 kv disconnectors based on response… reasons. the first one concerns that the model can finish the transient electric field analysis. and the second is that the model considers the conductivity of the material, thus providing more accurate results.. iii. response surface method the response surface method (rsm) is a powerful tool to build up a macro model for an approximation of the desired system response. the main advantage in this macro model would be the significant reduction of the needed number of simulations to characterize the electric insulation performance of disconnectors, and thus make the electric field optimization of disconnectors feasible and efficient. the macro model generally comprises a simple, mathematical expression that describes the desired objective or response, obtained from either measurements or simulations, as a function of the specified design parameters, which are the input variables to the simulations. the expression is usually one, two or higher degrees of the design parameters. the technique engaged in model fitting is originally stemmed from the design of experiments techniques. the computational cost needed for deriving the expression is orders of magnitude much less than that needed for simulations. once this expression is obtained, it can be used to replace the simulations, and furthermore, it makes feasible for the search of the optimal combinatorial set of design parameters that minimize the desired goal. a. basic principles constructing the response surface model requires an iterative process. in this study, numerical simulation that adopts the fe analysis is applied to carry out the maximum of electric field strength associated with selected design points, which are needed to fit all the coefficients in the regression model. first define  0,1, ,j j k   the coefficients of the regression model and  the error. by further assuming that there are n numerical experiments  n k , the variance of the error  is equal to 2 and each i  is a random variable, the relation between the dependent response t and the independent variables  1 2ˆ , , , kx x x x x  can be denoted as: x̂ t   . (13) by further performing the minimization of the least square error norm of the random error vector, the regression model can be derived as: ˆy xb (14) where y is the estimated response and b the estimated solution of the regression coefficients to this minimization problem, denoted as: 1ˆ ˆ ˆ( )t tb x x x t (15) where y is the estimated response and b the estimated solution of the regression coefficients to this minimization problem, denoted as:   1ˆ ˆ ˆt tb x x x t (16) note that the mathematical expression can be linear or nonlinear. the choice of the degree of the assumed polynomial model would be dependent of the number of simulations to be performed and the desired accuracy. in fact, it would not be practical in real applications to have a polynomial degree greater than 2 because of the significant increasing of the number of simulations. for one degree of polynomial expression, it is presented as 0 1 k j j j y x       (17) where y is the response,  1, 2, ,jx j k  the independent variables,  0,1, ,j j k   the coefficients of the regression model, which are to be determined using regression analysis techniques, and  the random error. as the numerical simulators are deterministic, the error would only emanate from the fitting inaccuracy. furthermore, when the linear regression model is incapable of accurately describing the response as function of the specified design variables, the nonlinear regression model can be then attempted. a quadratic regression model with k independent variables is denoted as 0 1 1 1 k k k j j ij i j j i j y x x x             (18) the experimental design plan used in this work is the central composite design (ccd) proposed by box and wilson [10]. it is essentially an orthogonal one such that it would allow a better estimation of the coefficients of the regression model. it consists of all the two-level factorial points, the central point and the axial points or star points. in total, there are 2k factorial points, 2k axial points and a central point in a ccd model, where k is the number of independent design variables. basically, the model is formed by two parts: 1) two-level factorial points with an added central point; 2) the symmetrical star points aligned in the axes of the factors and the central point. note that the first part can provide the estimation of the first order and two-factor interaction polynomial terms while the second part can allow the fit of the quadratic terms. once the important design parameters are determined, a complete ccd plan for design parameters can be then defined. the experimental design plan used for a 2-independent-variable system is specifically listed in table i where 1x and 2x are the independent variables,  1, 2, , i y i n  the desired response, engineering, technology & applied science research vol. 5, no. 4, 2015, 818-824 821 www.etasr.com gong et al.: optimum shape design of metal-enclosed 550 kv disconnectors based on response… and “+1” is the upper limit, “  1” the lower limit, and “0” the central point of the independent variables. b. statistical tests it would be generally required to check the validity of the mathematical expression constructed from the regression analysis, and also the importance of the included factors. one of the possibilities is to examine the relative and absolute errors between the exact analysis and the responses based on the mathematical expression. other can be sought through statistical tests. in this context, two simple statistical hypothesis-testing procedures, including f-test and r2 test, are used to get a basic indication of the validity of the constructed model. the f-test that basically adopts the analysis of variance examines the significance of the regression model while the r2 test provides an informal indication of how well the estimated regression model describes the relationship between the independent and dependent variables. in other words, the r2 gives the fraction of variation accounted for by the regression model fit to the observed data. moreover, the verification of the regression model is also tested by a new selected design point that is not included in the fit. in f statistics, the statistical index f0 is defined as  0 1 ssr sse f k n k            (19) where n is the total selected design points in the experimental design plan, k denotes the number of independent design variables in the model, ssr expresses the sum of squares due to regression, and sse is the sum of squares due to residual. accordingly, the total sum of squares sst can be expressed as: 2 1 n i it y sst ssr sse t t n           (20) where iy is the i -th actual response. if 0 , , 1k n kf f   , where  is the specified significance level in the f distribution, the null hypothesis, 0h is shown in the following two-sided hypotheses: 0 1 2: 0kh       and 1 : 0 { 1, 2, , }jh for some j in j k    (21) is rejected, implying that at least one independent design variable is significant to estimated response. in the 2r test, the coefficient of multiple determinations 2r is defined as: 2 1 ssr sse r sst sst    (22) note that 20 1r  . if  1, 2, , 0j k  , then 2 0r  . furthermore, if all responses derived from the exact numerical simulations are fully equivalent to the estimated responses, then 2 1r  , suggesting that the fit of the least square line to the data points is perfect. table i. experimental design plan of two-independentvariable system 1x 2x result 1 +1 +1 1y 2 +1  1 2y 3  1 +1 3y 4  1  1 4y 5 +1.414 0 5y 6  1.414 0 6y 7 0 +1.414 7y 8 0  1.414 8y 9 0 0 9y iv. the model of disconnectors the structural model of disconnectors in gis is shown in figure 1, where the horizontal break is of disconnectors, and the vertical break is of the earthing switch. the analysis model in disconnectors can be simplified to a two-dimensional one without affecting the calculation results. the disconnector model for the simplified two-dimensional analysis is shown in figure 2, and the key parts of disconnectors are marked. the relative permittivity and conductivity of each part are given in table ii, in order to finish finite element calculation under the lightning impulse voltage. lightning impulse voltage waveform applied on the conductor is shown using the following function [11]. 1 2( ) 1675 ( ) t t t te t e e      (23) where 1 68t s , 2 0.4t s 。 v. the electric field analysis in disconnectors in figure 2, several parameters, which may have an effect on the electric field distribution, have been described. the original parameters of disconnectors are listed in table iii. according to relative standards, lightning impulse withstand voltage with 1675 kv peak value should be applied on one side of the break in the disconnectors, the opposite peak value of power frequency withstand voltage 450 kv applied on the other side. the disconnector model with original parameters was solved using a fortran. the potential distributions and electric field distributions are depicted in figure 3. engineering, technology & applied science research vol. 5, no. 4, 2015, 818-824 822 www.etasr.com gong et al.: optimum shape design of metal-enclosed 550 kv disconnectors based on response… table ii. the relative permittivity and conductivity of each part conductor and shield metal part insulation sf6 j   3.3 1   s m 3.5×10 7 3.5×107 1×10-13 0 fig. 1. structural model of disconnectors fig. 2. simplified model of disconnectors (1,4-the conductor and the shield, 2-the metal part, 3-the insulation, 5-sf6) table iii. the design parameters of disconnectors (mm) parameters l h t 1r 2r initial value 180 111 20 25 95 fig. 3. the potential distribution and field distribution in the model of disconnectors as shown in figure 3, the maximal electric field strength is 29.591 kv/mm with the reference value being 24 kv/mm in [12] (when the gauge pressure value of sf6 is 0.4 mpa, the reference value can be computed). the results indicate that the design of disconnectors should be modified because the maximum electric field strength value has exceeded the allowable value. in figure 2 and table iii the several main design parameters are shown. next, the present study focuses on the change of electric field by altering the design parameters. the relative results are listed in table iv to vi. a) altering parameter t , which is the distance between the contact and insulation (table iv). the results show that parameter t has almost no effect on the maximal electric field strength in disconnectors. table iv. the relation between parameter t and the max electric field strength parameter t (mm) maxe （kv/mm） 20 29.59 10 29.56 5 29.56 b) altering parameter l , which is the distance between the contacts (table v). the results demonstrate that parameter l has almost no effect on the maximal electric field strength in disconnectors. table v. the relation between parameter l and the max electric field strength parameter l (mm) maxe (kv/mm) 180 29.59 190 29.33 200 29.20 c) structural parameters h , 1r and 2r of the shield are rather significant to the electric field distributions, so these three parameters are considered together. in table vi the electric field distributions in disconnectors can be more uniform owing to the change of these three parameters. table vi. relation between parameters h , 1r and 2r and the maximal electric field strength maxe no. h （mm） 1r （mm） 2r （mm） maxe （kv/mm） 1 121 60 95 24.67 2 121 60 150 24.72 3 111 25 95 29.59 based on the aforementioned analysis, it is concluded that parameters t and l have almost no effect on the field distributions, but parameters h , 1r and 2r are vital, namely, the structural parameters of the shield have more effect on the engineering, technology & applied science research vol. 5, no. 4, 2015, 818-824 823 www.etasr.com gong et al.: optimum shape design of metal-enclosed 550 kv disconnectors based on response… field distributions. so, parameters h , 1r and 2r should be selected as design variables. vi. optimum shape desgin of disconnectors the shape design optimization mathematical equations of disconnector model can be described as follows. 1 2 3 maxmin ( , , )f x x x e (24) where maxe is the maximal electric field strength value, 1x , 2x and 3x represents the parameters h , 1r , and 2r in figure 2, respectively. the regions of the design variables are listed as follows according to the relative working experience. 1 2 110 150 20 60 60 120 h r r         (25) the values of design variables and the code of central composite design are listed in table vii and viii respectively. the  value is 1.216. table vii. the initial values of design variables design variable code  -1 0 +1 +  h (mm) 1x 117.8 120 130 140 142.2 1r (mm) 2x 27.8 30 40 50 52.2 2r (mm) 3x 77.8 80 90 100 102.2 table viii. the codes of central composite design comprising three design variables design points code points no. h /mm 1r (mm) 2r (mm) 1x 2x 3x 1 120 30 80 -1 -1 -1 2 120 30 100 -1 -1 +1 3 120 50 80 -1 +1 -1 4 120 50 100 -1 +1 +1 5 140 30 80 +1 -1 -1 6 140 30 100 +1 -1 +1 7 140 50 80 +1 +1 -1 8 140 50 100 +1 +1 +1 9 130 40 90 0 0 0 10 117.8 40 90  0 0 11 142.2 40 90 +  0 0 12 130 27.8 90 0  0 13 130 52.2 90 0 +  0 14 130 40 77.8 0 0  15 130 40 102.2 0 0 +  the results can be obtained by calculating the design values using the fem in turn. based on the second order model, the response surface model can be obtained as follows: 1 2 3 1 2 3 1 2 2 2 2 1 3 2 3 1 2 3 ( , , ) 26.81 1.78 0.62 0.55 0.05 0.13 0.13 0.21 0.3 0.25 f x x x x x x x x x x x x x x x           (26) equation (26) can be solved using sequential quadratic programming, and the optimal results are shown in table ix the electric potential distributions and electric field distributions in the disconnector with optimum structural parameters have been depicted in figure 4 using fem. table ix. the contrast between the initial and optimal results parameters h /mm 1r /mm 2r /mm maxe (kv·mm -1) optimal value 138.16 33.96 86.76 22.90 initial value 111 25 95 29.59 fig. 4. the potential and electric field distributions in the disconnector with optimum structural parameters as shown in figure 4 and table ⅸ the maximum electric field strength is 22.9kv/mm, lower than the allowable electric field strength 24.0kv/mm. so the optimal results meet the design requirements, increase the withstanding voltage, and improve the reliability of disconnectors. vii. conclusion in this paper, rsm coupled with fem are successfully applied, for the first time, for the optimization of 550kv disconnector in gis. the electric field distributions in 550kv disconnectors have been analyzed and calculated based on fem in transient quasistatic electric field, through a fortran code. then the optimum shape design in 550kv disconnectors was completed based on the rsm coupled with fem. the optimal results indicate that the electric field distributions in the optimized disconnector model are more uniform than those of the initial model. so, setting the optimal structural parameters in electric devices is feasible and highly efficient using rsm coupled with fem. the proposed disconnector model with optimum structure parameters has undertaken all withstanding voltage tests. the work discussed in this paper can be employed to improve the insulation performance and operational reliability of 550kv disconnectors in gas insulated switchgears. references [1] g. zhang, finite element method, beijing, mechanical industry press, 1991 engineering, technology & applied science research vol. 5, no. 4, 2015, 818-824 824 www.etasr.com gong et al.: optimum shape design of metal-enclosed 550 kv disconnectors based on response… [2] j. sheng, numerical analysis of electromagnetic field. xi’an, xi’an jiaotong university press, 1991 [3] y. j. kim, j. d. lee, b. j. lee, h. k. shin, s. c. hahn, “design optimization of permanent magnetic actuator for vacuum circuit breaker by response surface method”, international conference on electrical machines and systems (icems), pp. 1-4, saporo, japan, october 21-24, 2012 [4] k. w. jeon, t. k. chung, s. c. hahn, “nema class a slot shape optimization of induction motor for electric vehicle using response surface method”, international conference on electrical machines and systems (icems), pp. 1-4, beijing, china, august 20-23, 2011 [5] b. h. lee, k. s. kim, j. p. hong, j. h. lee, “optimum shape design of single-sided linear induction motors using response surface methodology and finite-element method”, international conference on electrical machines and systems (icems), pp. 1-5, beijing, china, august 20-23, 2011 [6] l. egiziano, v. tucci, c. petrarca, m. vitelli, “a galerkin model to study the field distribution in electrical components employing nonlinear stress grading materials”, ieee transactions on dielectrics and electrical insulation, vol. 6, no. 6, pp. 765-773, 1999 [7] j. kuang, j. d. lavers, s. boggs, “program for transient nonlinear finite element analysis with applications to coupled field programs”, 10th international symposium on high voltage engineering, montreal quebec, canada, pp. 25-29, 1997 [8] x. ma, electromagnetic theory and applications, xi’an, xi’an jiaotong university press, 2000 [9] g. lupo, g. miano, v. tucci, m. vitelli. “field distribution in cable terminations from a quasi-static approximation of the maxwell equations”, ieee transactions on dielectrics and electrical insulation, vol. 3, no. 3, pp. 399-409, 1996 [10] z. zhang, b. xiaofeng, “comparison about the three central composite designs with simulation. advanced computer control”, international conference on advanced copmuter control (icacc), singapore, pp. 163-167, january 22-24, 2009 [11] c. petrarca, l. egiziano, v. tucci, m. vitelli “impulse performances of cable terminations employing stress grading accessories”, 1999 annual report conference on electrical insulation and dielectric phenomena, austin, usa, vol. 1, pp. 146-149, october 17-20, 1999 [12] b. li, sf6 high voltage apparatus, beijing, mechanical industry press, 2008 microsoft word etasr_v12_n5_pp9192-9195 engineering, technology & applied science research vol. 12, no. 5, 2022, 9192-9195 9192 www.etasr.com nguyen et al.: the feasibility of applying waste concrete as coarse aggregates in new concrete the feasibility of applying waste concrete as coarse aggregates in new concrete tien hông nguyen faculty of construction vinh university vinh city, vietnam tienhongkxd@vinhuni.edu.vn thi thanh tung nguyen faculty of construction vinh university vinh city, vietnam ntttung@gmail.com thi thu hien nguyen faculty of construction vinh university vinh city, vietnam thuhien.tvna@gmail.com van tien phan faculty of construction vinh university vinh city, vietnam vantienkxd@vinhuni.edu.vn received: 17 july 2022 | revised: 26 july 2022 | accepted: 27 july 2022 abstract-this paper presents a study on the possibility of replacing natural coarse aggregates with recycled aggregates in concrete in terms of strength, namely compressive strength and flexural strength. the concrete was designed to have a 25mpa compressive strength and an 8cm slump. the replacement rates of natural aggregates with recycled coarse aggregates were 0%, 10%, 15%, and 20%. the test samples were compressed to determine their strength value after 28 days of curing. the research results give a more complete assessment of the efficiency of the use of recycled raw aggregates instead of natural aggregates in concrete. the results indicate that using recycled aggregates is feasible due to the small decrease in concrete strength. the experiment shows that up to 20% replacement, the recorded reduction in the strength of concrete is lower than 15%. however, it is indispensable that the strength of concrete should be enhanced when recycled aggregates are used. according to previous works, fiber reinforcement may be an effective solution. therefore, to further develop research using recycled aggregates, it is necessary to consider using different fibers to strengthen the concrete. the fiber content can be used in the range of 0-1% of the weight of concrete. keywords-compressive strength; flexural strength; waste concrete; demolishing work i. introduction recycling of waste construction materials from demolishing works in order to reduce the environmental impact has been investigated by numerous researchers [1-5]. the use sustainable construction materials coming from demolishing works, like recycled concrete, could help produce sustainable materials with advantages such as good quality and low cost while reducing the environmental impact. besides, the growth in population in big cities leads to continuously rising in the demand of construction materials, which leads to a negative impact on the environment. aggregates in concrete are prepared by crushing rocks into different sizes, then sieving and classifying particle sizes according to standards, and mixing to ensure a standard grading curve. this process poses many serious health and environmental hazards, and disrupts ecosystems, necessitating the search for alternative sources of aggregates. on the other hand, the volume of waste concrete generated from the dismantled works is very large and the produced materials are considered waste. as a hard material like stone, waste concrete can be used as aggregates for new concrete. the possibility of replacing natural coarse aggregates with recycled aggregates in concrete has been evaluated by many authors on many aspects. authors in [2] found that recycled coarse aggregates and natural aggregates can be mixed in a proportionate ratio to be used in pavement and building construction. various strength tests, including compressive and tensile strength tests of cylinder with 0, 25, 50, 75, and 100% recycled coarse aggregate replacement were performed. authors in [1] investigated the use of recycled concrete in improving the quality and enhancing the mechanical and microstructure properties of concrete [1]. the designed concrete strength is 35mpa with a fixed water to cement ratio of 0.48. various characteristics of concrete, including density, workability, temperature, compressive strength, split tensile strength, flexural strength, and microstructural analysis, were investigated. in [6], the authors fully replaced natural coarse aggregates with recycled coarse aggregates and they investigated the bulk density and the compressive strength of concrete for various curing durations. the results show that bulk density and compressive strength of concrete with recycled coarse aggregates were lower than those of concrete using natural coarse aggregates. authors in [7] carried out various experiments to determine the properties of concrete made with crushed concrete as coarse aggregates. it was found that the recycled coarse aggregates have lower specific gravity corresponding author: van tien phan engineering, technology & applied science research vol. 12, no. 5, 2022, 9192-9195 9193 www.etasr.com nguyen et al.: the feasibility of applying waste concrete as coarse aggregates in new concrete and higher absorption capacity than the original crushed granite aggregates. the use of recycled coarse aggregates leads to reduced compressive strength up to 25%, reduced modulus of elasticity up to 30%, improved damping capacity up to 30%, and higher amounts of drying shrinkage and creep. to summarize, it is possible to produce concrete with recycled aggregate as coarse aggregates. the quality of the original concrete from which the recycled aggregates are produced seems to have little influence upon the properties of the produced concrete [7]. however, the study and evaluation of the feasibility of using recycled aggregates in concrete needs to be further studied in terms of strength, including compressive strength, split tensile strength, and bending strength. ii. experimental setup before casting, slump measurement was performed to determine the slump of concrete in fresh state. concrete with slump values that are too low or too high can be identified and corrected prior use. compression test was carried out on cubical specimens. in the present research, cube specimens with size 15×15×15cm were used. compression experiments were conducted by loading the cube specimens between two plates, and then applying force by moving the crossheads together. during the test, the specimens were compressed and the applied load was recorded. the yield strength and compressive strength of concrete were then measured. flexural strength is a measure of the tensile strength of concrete. unreinforced concrete beams sized 10×10×40cm were used. the peak force when the beam specimen begins to appear failure in bending was measured. after curing at room temperature for 28 days, the concrete samples were tested for compressive strength and flexural strength. the experimental setup is shown in figures 1 and 2. fig. 1. four-point bending test. fig. 2. compressive test. in this study, all concrete sample constituents were acquired from local sources, namely vietnamese standard portland cement, river sand used as fine aggregates, local naturalcrushed rock used as coarse aggregates with diameters ranging from 5 to 20 mm (table i). four cements sets with 0%, 10%, 15%, and 20% of recycled coarse aggregates were cast. each set consisted of 5 specimens. the specimens were cast in composite molds and compacted through an external vibration machine. the specimens were demolded at least 24h later. table i. mix components of concrete (per 1m3) content of recycled aggregates cement (kg) sand (kg) natural aggregates (kg) recycled aggregates (kg) water (kg) 0% 292.5 648.3 1216.3 0 195 10% 292.5 648.3 1094.7 121.6 195 15% 292.5 648.3 1033.9 182.4 195 20% 292.5 648.3 973 243.3 195 iii. results and discussion the failure loading values, recorded in the compression test are presented in table ii. these values will be used to calculate the compressive strength of concrete for various percentages of recycled aggregates. the compressive strength values of concrete, calculated according to the vietnamese standard 3118:1993, are shown in table ii. table ii. failure loads in compression test percentage of recycled aggregates specimen failure load (kn) compressive strength (mpa) 0% 1 505.2 22.45 2 512.7 22.78 3 501.3 22.28 4 499.9 22.22 5 510.4 22.68 10% 1 497.2 22.1 2 479.2 21.3 3 490.5 21.8 4 489.1 21.74 5 482.4 21.44 15% 1 455.2 20.23 2 465.8 20.7 3 472.4 21.0 4 477.7 21.23 5 485.1 21.56 20% 1 460.3 20.46 2 427.4 19.0 3 435.5 19.36 4 418.7 18.61 5 422.9 18.79 the compressive strength of concrete using different contents of recycled aggregates is plotted in figure 3. it can be easily seen that using recycle aggregates leads to a decrease of the compressive strength of concrete, although the result arrangement varies in several specimens corresponding to the usage of recycle aggregates. however, the compressive strength of concrete generally decreases with the increasing use of recycled aggregates. this result is in agreement with the results of [3, 5-7]. the drop in percentage of the average compressive strength of concrete using various contents of recycled aggregates was calculated. the result is plotted in figure 4. we can see that the drop rate of compressive strength of concrete is almost linearly declining with the increase of the using rate of recycled engineering, technology & applied science research vol. 12, no. 5, 2022, 9192-9195 9194 www.etasr.com nguyen et al.: the feasibility of applying waste concrete as coarse aggregates in new concrete aggregates, with less than 15% reduction in strength when 20% recycled aggregates are used. from this, the use of recycled coarse aggregates can be considered feasible. fig. 3. compressive strength of concrete samples using recycled aggregates. fig. 4. the drop rate in the compressive strength of concrete using recycled aggregates. the destructive forces, recorded in the 4-point flexural test, are presented in table iii. the flexural strength, defined as the maximum stress in a material just before it yields in a bending test, was calculated according to the vietnamese standard 3119:1993. table iii. destructive forces and flexural strength of concrete percentage of recycled aggregates specimen load (kn) flexural strength (mpa) 0% 1 1003.61 3.16 2 1013.7 3.19 3 1138.1 3.59 4 1026.25 3.23 5 1009.8 3.18 10% 1 987.34 3.11 2 968.25 3.05 3 972.21 3.06 4 979.08 3.08 5 991.06 3.12 15% 1 932.5 2.94 2 955.01 3.01 3 960.23 3.02 4 934.1 2.94 5 963.17 3.03 20% 1 872.6 2.75 2 889.13 2.8 3 905.74 2.85 4 919.2 2.89 5 879.04 2.77 the flexural strength of concrete using different content values of recycled aggregates is plotted in figure 5. it indicates that using recycle aggregates leads to a slight decrease of flexural strength. the drop in the percentage of the average flexural strength using various content values of recycled aggregates was calculated and the result is plotted in figure 6. it indicates that the drop rate of compressive strength of concrete is almost linearly declining with the increase of the using rate of recycled aggregates, with less than 15% reduction in flexural strength when 20% recycled aggregates are used. so, the use of recycled coarse aggregate can be considered feasible in terms of flexural strength. fig. 5. flexural strength of concrete samples using recycled aggregates. fig. 6. the drop rate in the flexural strength of concrete using recycled aggregates. thus, in order to be able to use recycled aggregates in concrete, it is necessary to find solutions to enhance its compressive and flexural strength. fiber reinforcement may be considered for the enhancement of the strength of concrete [810]. the quantity of fibers has been selected as 0.5% and 1.0% of the weight of concrete [8]. it has been concluded that increased quantity of fibers, improves the flexural strength of concrete beams [8]. therefore, to further develop the research in the use of recycled aggregates, it is necessary to consider using different fibers to strengthen the cement. the fiber content can be used in the range of 0-1% of the weight of concrete. iv. conclusion in this paper, the compressive strength and flexural strength of concrete with recycled aggregates have been investigated. the recycled aggregates came from demolition works, and were used at different contents, namely 0%, 10%, 15%, and 20%. the results indicate that using recycled aggregates is feasible because of the low decrease of concrete strength. the experiment shows that for up to 20% of recycled engineering, technology & applied science research vol. 12, no. 5, 2022, 9192-9195 9195 www.etasr.com nguyen et al.: the feasibility of applying waste concrete as coarse aggregates in new concrete concrete used, the recorded reduction in the strength of concrete is lower than 15%. however, it is indispensable that the strength of concrete should be enhanced when recycled aggregates are used. according to previous studies, fiber reinforcement may be an effective solution. therefore, to further develop the research on the use of recycled aggregates, it is necessary to consider the use of different fibers to strengthen concrete. the fiber content can be used in the range of 0-1% of the weight of concrete. references [1] m. t. el-hawary, c. koenke, a. el-nemr, and n. f. hanna, "using recycled concrete as a replacement for coarse aggregate in the production of green concrete," in sustainable issues in infrastructure engineering, cham, switzerland, 2021, pp. 127–151, https://doi.org/ 10.1007/978-3-030-62586-3_9. [2] b. panda, n. t. imran, and k. samal, "a study on replacement of coarse aggregate with recycled concrete aggregate (rca) in road construction," in recent developments in sustainable infrastructure, singapore, 2021, pp. 1097–1106, https://doi.org/10.1007/978-981-154577-1_91. [3] d. d. nguyen and v. t. phan, "compressive strength studies on recycled binder concrete," engineering, technology & applied science research, vol. 11, no. 4, pp. 7332–7335, aug. 2021, https://doi.org/10.48084/etasr.4230. [4] v. t. phan and t. h. nguyen, "the influence of fly ash on the compressive strength of recycled concrete utilizing coarse aggregates from demolition works," engineering, technology & applied science research, vol. 11, no. 3, pp. 7107–7110, jun. 2021, https://doi.org/10.48084/etasr.4145. [5] x. h. vu, t. c. vo, and v. t. phan, "study of the compressive strength of concrete with partial replacement of recycled coarse aggregates," engineering, technology & applied science research, vol. 11, no. 3, pp. 7191–7194, jun. 2021, https://doi.org/10.48084/etasr.4162. [6] h. opara, u. eziefula, and c. ugwuegbu, "experimental study of concrete using recycled coarse aggregate," international journal of materials and structural integrity, vol. 10, no. 4, pp. 123–132, dec. 2016. [7] r. sri ravindrarajah and c. t. tam, "properties of concrete made with crushed concrete as coarse aggregate," magazine of concrete research, vol. 37, no. 130, pp. 29–38, mar. 1985, https://doi.org/10.1680/macr. 1985.37.130.29. [8] a. namdar, i. b. zakaria, a. b. hazeli, s. j. azimi, a. s. b. a. razak, and g. s. gopalakrishna, "an experimental study on flexural strength enhancement of concrete by means of small steel fibers," frattura ed integrità strutturale, vol. 7, no. 26, pp. 22–30, sep. 2013, https://doi.org/ 10.3221/igf-esis.26.03. [9] s. t. kang, b. y. lee, j.-k. kim, and y. y. kim, "the effect of fibre distribution characteristics on the flexural strength of steel fibrereinforced ultra high strength concrete," construction and building materials, vol. 25, no. 5, pp. 2450–2457, may 2011, https://doi.org/ 10.1016/j.conbuildmat.2010.11.057. [10] h. binti hashim et al., "improving the mechanical properties of polycaprolactone using functionalized nanofibrillated bacterial cellulose with high dispersibility and long fiber length as a reinforcement material," composites part a: applied science and manufacturing, vol. 158, jul. 2022, art. no. 106978, https://doi.org/10.1016/j.compositesa. 2022.106978. microsoft word etasr_v12_n5_pp9252-9257 engineering, technology & applied science research vol. 12, no. 5, 2022, 9252-9257 9252 www.etasr.com noori & abbas: reliability analysis of an uncertain single degree of freedom system under random … reliability analysis of an uncertain single degree of freedom system under random excitation mohammed s. m. noori department of civil engineering college of engineering university of baghdad baghdad, iraq m.noori1901m@coeng.uobaghdad.edu.iq rafaa m. abbas department of civil engineering college of engineering university of baghdad baghdad, iraq dr.rafaa@coeng.uobaghdad.edu.iq received: 10 july 2022 | revised: 4 august 2022 | accepted: 7 august 2022 abstract—in practical engineering problems, uncertainty exists not only in external excitations but also in structural parameters. this study investigates the influence of structural geometry, elastic modulus, mass density, and section dimension uncertainty on the stochastic earthquake response of portal frames subjected to random ground motions. the north-south component of the el centro earthquake in 1940 in california is selected as the ground excitation. using the power spectral density function, the two-dimensional finite element model of the portal frame’s base motion is modified to account for random ground motions. a probabilistic study of the portal frame structure using stochastic finite elements utilizing monte carlo simulation is presented using the finite element program abaqus. the dynamic reliability and probability of failure of stochastic and deterministic structures based on the first-passage failure were examined and evaluated. the results revealed that the probability of failure increases due to the randomness of stiffness and mass of the structure. the influence of uncertain parameters on reliability analysis depends on the extent of variance in structural parameters. keywords-reliability; monte carlo simulation; uncertain system; random excitation; stochastic; finite element analysis i. introduction in practical engineering problems, the external excitations, such as wind loading and seismic waves, and the parameters of a structure exhibit uncertainty. structural parameter uncertainty may strongly influence structural response and reliability [1]. earthquakes are the most disastrous natural phenomena. therefore, the seismic response of many types of structures and buildings has been widely investigated. however, most modeling attempts of seismic random response analysis of structures belong to deterministic models in which all structural parameters were regarded as deterministic parameters. from another aspect, most engineering structures can be classified as random due to the variability in their geometric or material properties. therefore, the problem of stochastic structures subject to stochastic seismic excitation is of great importance [2]. considering that ground motion induced by an earthquake represents a type of random excitation, the theory and methods of random vibration should be applied to analyze the seismic response of structures. the random excitation is usually specified regarding its power spectral density (psd) [3]. the random vibration theoretical framework has been well established. the dynamic analysis of systems with deterministic structural parameters to random excitations is available. however, the dynamic analysis of systems with stochastic structural parameters under random excitations has not been developed to the same extent [4]. a natural frequency represents one of the most influencing parameters on system response. uncertainty in the natural frequency can arise from uncertainties in the stiffness or inertia properties of the structure. in this case, probabilistic-based analysis methods should be utilized. thus, the considered statistical parameters associated with the distribution of random variables should be determined. in general, the stochastic finite element-based method is a probabilistic analysis method and is well suited to deal with random parameter problems [5]. given the random nature of loading, material specifications, and implementation issues, probabilistic-based analysiss should be utilized. thus, considering the statistical parameters associated with the distribution of random variables should be determined. the reliability-based analysis is a new approach to structural analysis and design that takes uncertainty into account [6]. a survey of previous studies indicated that structural reliability methods have been mainly developed for rationally evaluating the safety of deterministic structures with excitation. however, the studies on nondeterministic structures to investigate statistical uncertainty characteristics are limited. the current study emphasizes on reliability analysis of a stochastic structure with uncertain parameters and excitation to assess the reliability and safety of this system. to achieve the goal of this study, a single degree of freedom system subject to seismic base excitation is examined using a probabilistic finite element abaqus code using monte carlo simulation (mcs) and python script to generate pseudo-random values for the considered random parameters. ii. random excitation the stochastic earthquake analysis in this study is based on the stationary assumption, in which the statistical parameters' corresponding author: mohammed s. m. noori engineering, technology & applied science research vol. 12, no. 5, 2022, 9252-9257 9253 www.etasr.com noori & abbas: reliability analysis of an uncertain single degree of freedom system under random … mean and variance do not vary with time. a stationary model makes them less sophisticated, simplifies computations, and gives satisfactory results [7]. as a single record is insufficient for producing general conclusions, an ergodicity assumption is applied. moreover, only one earthquake record from the local area can be utilized. the psd function of acceleration seismic motion is assumed to be in the form of a filtered gaussian white noise ground motion. the model was suggested in [8, 9] and was later modified in [10]. this model can be expressed as: ���� ���� = �� �� ��� ��� �� [���� ��� ��]�� �� ��� ��� �� �� ��� �� [���� ��� ��]�� ����� ��� �� �� (1) where �� , �� , �� , and �� represent the damping ratio and natural frequency of the soil and high pass filter respectively, and �� is the intensity of the white noise of ground motion. to estimate the filter parameters, the method of the spectral moment [11] is the key statistical parameter of the psd function [12]. the i th spectral moment �� is defined as: �� = � �� ������ � (2) the variance of the excitation is the zero spectral moment: �� = !�" = � ������ � (3) the central frequency, �# , and the shape factor, $ , of the random process can be directly evaluated from the first few spectral moments: �# = %�" ��⁄ , (4) $ = '1 − ��� " �"��⁄ � (5) as the central frequency and shape factor are functions of the spectral moments (�� , �� , and �" ), they are expressed in terms of the filter parameters, i.e. ��, ��, and ��. hence, they can be computed by matching the variance of acceleration, the central frequency, and the shape factor of the actual and theoretical psd. iii. stationary random vibration analysis the equation of motion for a single degree of freedom (sdof) structure subjected to random ground acceleration is: *+� �,� + .�+�,�/ + 0+�,� = −*+�� �,� (6) where +�� , m, .� , and k are the ground acceleration process, structural mass, viscous damping, and elastic stiffness respectively. the psd of the displacement response may be represented as in (7) if the ground motion acceleration (+�� ) is considered a stationary gaussian random process [10]. �11��� = 2��� 2���∗���� ��� (7) where ���� ��� is the psd function of the ( +�� ), 2��� is the frequency response function as in (8), and (*) stands for complex conjugate: 2��� = ��4�����" � �4�4 � (8) where �5 and �5 are the jth order inherence frequency and mode damping of structure respectively. the mean square and the root mean square of the relative displacement can be expressed as in (9) and (10) respectively [10]: !6" = � �11��� � (9) !6 = '� �11��� � (10) iv. monte carlo simulation although being a highly time-consuming computational method, the mcs method is considered one of the most powerful and accurate simulation tools to estimate numerically the reliability and failure probability of uncertain structures [18]. this method is used to calculate the response uncertainty and the numerical estimate of failure probability. it uses random sampling from random variable distributions. the "crude" or "direct" mcs, which is a pseudo-random sampling, is the basic version [13]. in mcs, the failure probability is described as: 7̂� = 9�9 (11) where n is the total number of samples and :� is the number of samples in the failure domain. mcs is a most general approach for the stochastic finite element method (sfem) [14]. the deterministic fem and the mcs technique are merged in this methodology. sfem can express randomness in one or more of the main components of the classic fem, such as geometry, material properties, and external forces [15]. v. dynamic reliability the reliability of a system is closely related to the concept of level crossing. this case is particularly true for first-passage failure, in which the system is considered to fail only when a particular stress process or displacement +�,� reaches a critical level b in the time interval [0, t]. when the structural response of a deterministic structural parameter is a stationary gaussian process, the crossing time of the response ;�,� and limit b submit to the poisson process. the dynamic probability of failure of a sdof structure can then be obtained from [16]: 7� �,� ≈ 1 − =;7 >−?�@ =;7 a− �" b c def "gh (12) i�,� ≈ =;7 >−?�@ =;7 a− �" b c def "gh (13) where t is the duration of the stationary process, !6 is a root mean square of the response, and ?� is zero mean cross rate expressed as follows: ?� = �"j ' k� kl (14) where �� and �" are zero and the second spectral moment respectively, defined as follows: �m = � �m �n ������o� for m = 0,1,2 (14) engineering, technology & applied science research vol. 12, no. 5, 2022, 9252-9257 9254 www.etasr.com noori & abbas: reliability analysis of an uncertain single degree of freedom system under random … when the structural parameters and the excitation are random, the system reliability may be evaluated by calculating the probability of an equivalent extreme-value event. hence, the seismic excitation and structural response are assumed to have a zero mean. 1w and !6 are the extreme value and standard division of structural response 1�,� respectively. the dimensionless parameters are explained below [16]. x = yzde (15) assuming a poisson process for the number of horizontal crossings, taking parameter uncertainty into account, the estimated mean of the extreme value is: [�x� = �%2 ln ?�@ + �._``"%" ab cld� (16) and the variance of x is: ! "�x� = j�e de� �" ab cd� (17) the extreme value of the stochastic process 1�,� is expressed as: 1w = [�x� × !6 (18) the limit state function of the inter-story drift system is expressed as: ��∆� = i�∆� − h�∆� (19) where i�∆� is the structure drift limit equal to 0.01, 0.015, and 0.02 from story height, and h�∆� represents the extreme value of the structural drift because of the loading, including the uncertainties of the structural parameters. limit state function g(∆) ≤ 0 is the failure state, and g(∆) > 0 is a safe state. table i shows the target reliability of the steel structure system. table i target reliability indices [17] component type loading condition d+(l or s) d+l+w d+l+e members 3.0 2.5 1.75 connections 4.5 4.5 4.5 vi. numerical example a numerical example is presented and analyzed to demonstrate the reliability analysis for a case study of a simple frame structure, as shown in figure 1. the stochastic response due to the uncertainty in structure physical properties and seismic excitation force is taken into account. a. proposed structural system uncertainty and reliability analysis have been executed for an interior frame of the shear building system, as shown in figure 1. the floor system consists of a concrete slab 200mm thick supported by 3 steel girders with a w12×190 crosssection and the girders are supported by steel columns with a w10×33 cross-section, as shown in figure 2. in addition to the own weight, uniformly distributed pressures of 2 and 1kpa were adopted for the superimposed and live loads respectively. fig. 1. one-story two-bay frame. fig. 2. interior frame. b. random ground motion in this study, the north-south component of the 1940 el centro earthquake was chosen as the ground motion. using the spectral moment method, the acceleration spectral density function parameters of filtered white noise ground motion have been estimated, as shown in figure 3. the calculated values of natural frequency and the damping ratio for the first and second filters were ��= 18.5rad/s, � � = 0.43, and �� =1.5rad/s, and �� = 0.6 respectively. the intensity factor of the earthquake was �� = 0.00282m2/s3. fig. 3. actual and theoretical psd of the el-centro earthquake. c. stochastic earthquake analysis with deterministic structural parameters the dynamic characteristics of the deterministic portal frame structures have been analyzed with abaqus finite element software [18]. the two-dimension portal frame has been modeled with wire part b21, as shown in figure 4. the inertia mass has been selected based on the effective weight of the concrete slab, superimposed, and a quarter of the live load according to asce7-16. the girder and columns were engineering, technology & applied science research vol. 12, no. 5, 2022, 9252-9257 9255 www.etasr.com noori & abbas: reliability analysis of an uncertain single degree of freedom system under random … discretized using a mesh size of 100mm. a rigid body constraint has been adopted for the girder. in addition, the density of the column has been reduced to achieve the assumption of a shear frame of the rigid girder supported by weightless columns with fixed supports. the structure’s natural frequency was obtained by modal analysis, and two values were extracted, as shown in figure 5 and table ii. fig. 4. 3d portal frame view. fig. 5. first two mode shapes. table ii natural frequency and mass participation factor mode frequency (hz) frequency (rad∕sec) mass precipitation factor direction 1 1.98 12.46 99% along x-direction 2 22.10 138.85 99% along y-direction random vibration analysis was conducted with a base motion of the portal frame in the x-direction. the frequency range of interest and the response have been set. hence, the psd of the relative displacement was obtained as shown in figure 6. one peak detected in the vibration responses refers to the resonance occurrence at the first natural frequency of the investigated system. fig. 6. response psd of relative displacement. by integrating the response psd, the mean square and root mean square (rms), of relative displacement were 7.48×10 −5 m 2 and 8.65×10 −3 m respectively. the displacement resistance limit of the structure has been taken from asce 7– 16 structural design codes, where the allowable story drift is related to the risk categories and the structural system. thus, this research intends to investigate the different allowable limits, i.e. 1.0%, 1.5%, and 2%, of story height. the probability of failure of the system has been estimated for 3 response intervals of 10, 15, and 20s, as shown in figure 7. based on this estimate, the reliability index was obtained and is presented in table ii. the results showed that the probability of failure slightly increased when the response time increased. therefore, the reliability index of the system was not significantly affected. from another aspect, comparing the reliability index with the target reliability shown in table i reveals that the structure meets the specified safety level. table iii failure probability and reliability index for a deterministic system threshold 10s 15s 20s lm n lm n lm n 0.01h 1.11×10 -3 3.06 1.66×10 -3 2.94 2.21×10 -3 2.85 0.015h 5.32×10 -9 5.72 7.98×10 -9 5.65 1.06×10 -8 5.60 0.02h ≈ 0 − ≈ 0 − ≈ 0 − fig. 7. first-passage failure for the three-time response interval. d. stochastic earthquake analysis with nondeterministic structural parameters to illustrate the effect of the randomness of structural parameters, including stiffness k and mass m on the natural frequency and random seismic response, mcs was performed to update the random variables of interest for each finite element analysis (fea) trial. python programming was used to develop the deterministic fe model, and then, the random input variables of interest were updated based on the idea of parameter updating functionality. in this study, the crosssection dimensions, modulus of elasticity, column length, and the applied load were considered as random variables. table iv shows the statistical characteristics of these parameters. probabilistic modal analyses of random structural parameters of the interior portal frame were estimated using sfem with python script coding. matlab function was used to generate 5000 pseudo-random samples of cross-section dimensions, modulus of elasticity, column length, and engineering, technology & applied science research vol. 12, no. 5, 2022, 9252-9257 9256 www.etasr.com noori & abbas: reliability analysis of an uncertain single degree of freedom system under random … structural effective mass. figure 8 depicts the natural frequency result obtained from the sample data. mean value, standard deviation, and coefficient of variance were 12.34rad/sec, 1.3576, and 0.109 respectively. notably, the mean value for the natural frequency is very close to that shown in table ii for the deterministic analysis, indicating the validity of the dynamic analysis with random properties and excitation. due to the randomness in the natural frequency, the system response was affected. figure 9 shows the rms of relative displacement. mean, standard deviation, and cov were 0.0105m, 0.0016, and 0.1483 respectively. the results for the coefficient of variance indicate the effectiveness of randomness in the stochastic structure properties and excitation on the response properties. table iv statistical characteristics of variables random variables mean/ nominal cov distribution type ref. cross section dimension depth of the web 1.0009 0.004 normal [20] width of the flange 1.0139 0.009 normal thickness of the flange 0.9927 0.044 normal thickness of the web 1.054 0.037 normal modulus of elasticity 0.993 0.034 normal [21] column length 1 0.07 lognormal [22] load weight of a girder 1.03 0.1 normal [23] weight of a slab 1.05 0.1 normal superimposed load 1.03 0.1 normal live load 1 0.1 gumbel [24] fig. 8. histogram of the first natural frequency. fig. 9. histogram of the rms of the relative displacement. figures 8 and 9 show the failure probability estimates for the threshold level of 1%, and table iv presents the summary. notably, the monte carlo estimate for 1.5% and 2% levels is not shown in the figure because the sample size is not large enough to provide sufficiently accurate estimates for the probability of failure corresponding to this threshold level. the results revealed that randomness in the system’s stiffness and mass influences the system’s reliability. moreover, generally, the probability of failure increased due to the randomness in the stiffness and mass of the structure. this conclusion is confirmed by comparing the results presented in tables iii and v for deterministic and stochastic systems. the probability density function (pdf) in figure 10 shows that the distribution ranges of the equivalent extreme value have a trend of moving toward the right-hand side with increasing response time intervals. this case accords to the trends of increasing the probability of failure. the cumulative density function in figure 11 shows the boundary between the safe and failure domains, which is described by the limit of 0.04m on the xaxis. table v failure probability and reliability index for a stochastic system threshold 10s 15s 20s lm n lm n lm n 0.01h 2.8×10 -3 2.77 9.4×10 -3 2.34 21.4×10 -3 2.02 fig. 10. probability density function for the extreme value of drift. fig. 11. cumulative density function for the extreme value of drift. engineering, technology & applied science research vol. 12, no. 5, 2022, 9252-9257 9257 www.etasr.com noori & abbas: reliability analysis of an uncertain single degree of freedom system under random … vii. conclusions in this study, a reliability analysis of portal frames excited by random ground motion with deterministic and stochastic structural parameters was performed. the following conclusions can be drawn: • the probability of failure and the reliability index of the deterministic structure were affected slightly by the excitation time interval. the probability of failure increased and the reliability index decreased with increasing time interval. • the reliability index of the deterministic structure was greater than the target reliability index for members subject to seismic base motion. • the results for the mean values of the dynamic response for the sdof system with random properties and excitation correlate well with the deterministic analysis results. • randomness in the system’s stiffness and mass influences the system’s reliability and probability of failure. generally, the probability of failure increased due to the randomness in stiffness and mass of the structure. references [1] j. li and s. liao, "response analysis of stochastic parameter structures under non-stationary random excitation," computational mechanics, vol. 27, no. 1, pp. 61–68, jan. 2001, https://doi.org/10.1007/ s004660000214. 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[24] s. g. buonopane and b. w. schafer, "reliability of steel frames designed with advanced analysis," journal of structural engineering, vol. 132, no. 2, pp. 267–276, feb. 2006, https://doi.org/10.1061/ (asce)0733-9445(2006)132:2(267). microsoft word etasr_v12_n6_pp9584-9589 engineering, technology & applied science research vol. 12, no. 6, 2022, 9584-9589 9584 www.etasr.com fahmi & al-zaidee: strength and deflection reliability estimation of girder steel portal frames using … strength and deflection reliability estimation of girder steel portal frames using the bayesian updating method fahmi h. fahmi department of civil engineering college of engineering university of baghdad baghdad, iraq f.fahmi1901m@coeng.uobaghdad.edu.iq salah al-zaidee department of civil engineering college of engineering university of baghdad baghdad, iraq salah.r.al.zaidee@coeng.uobaghdad.edu.iq received: 14 august 2022 | revised: 30 august 2022 | accepted: 22 september 2022 abstract-uncertainty is ubiquitous in any engineering system at any stage of product development and throughout a product's life cycle. as information and sensor technology develops, more and more data about engineering systems are gathered. a strong technique for calibrating models using new information and observations is bayesian updating. the applied loads, yield strength, plastic section modulus, span, cross-section dimensions, and modulus of elasticity from the international literature have been updated through the local literature and a data survey for the interior girder portal frames to investigate the reliability index and the probability of failure of the system. first order reliability method (form) and monte carlo (mc) simulations have been used to estimate the reliability and probability of failure of strength and serviceability limit state function. the results reveal that for shear force, the reliability index increased significantly from 9.03 to 16.01. at the same time, the reliability index of the bending moment and deflection increased from 4.34 to 5.30 and from 6.90 to 7.66 respectively. keywords-interior supporting frame; bayesian method; sample data; prior data; posterior data; form; mc; reliability i. introduction most structure engineering designs are based on deterministic variables and often do not consider the variations in the material properties and the geometry of the structure [1]. for the purpose of determining the structural system's reliability, the effects of uncertainties must be quantified and propagated. uncertainty and reliability are vital to the analysis and design of an engineering system. the reliability of the system can be stated in reference to some performance criteria. the need for reliability analysis stems from the fact that there is a presence of uncertainty in the definition, understanding, modeling, and behavior prediction of the models that describe the system [2]. increasing amounts of data on engineering systems are collected and stored. this information can and should be used to reduce the uncertainty in engineering models and optimize the management of these systems. a coherent and effective framework for merging new information with existing models is provided by bayesian analysis, in which prior probabilistic models are updated with data and observations. the bayesian framework enables the combination of uncertain and incomplete information with models from different sources and provides probabilistic information on the accuracy of the updated model [3]. the current study emphasizes on the reliability analysis of the strength and deflection of steel portal frames as new data are acquired for the independent variables of the system. the bayesian method presents an efficient way to update the prior knowledge regarding the stiffness and strength of the frame. finally, the form and mc simulations have been adopted to investigate the reliability of the deflection and strength. ii. the bayesian method in engineering, one often needs to use whatever information is available in formulating a sound basis for making decisions. this may include observed (field or experimental) data, information derived from theoretical models, and expert judgments based on experience. moreover, the available information may need to be updated as new information or data are acquired [4]. the proper tool for combining and updating the available information is embodied in the bayesian approach. parameter estimation in the bayesian approach is based on the updating formula: ���� = ��������� (1) where ���� is the prior probability density function (pdf) representing the initial state of knowledge about the unknown parameter �, ����, is the likelihood function representing the knowledge gained from a set of observations, and the constant � is a normalizing factor. the posterior pdf, ����, represents the updated state of knowledge regarding the parameters �. a. prior distribution the prior distribution represents the distribution of possible parameter values from which the parameter has been drawn. the selection of the prior distribution is an important matter in bayesian modeling. since the choice of the prior corresponding author: fahmi h. fahmi engineering, technology & applied science research vol. 12, no. 6, 2022, 9584-9589 9585 www.etasr.com fahmi & al-zaidee: strength and deflection reliability estimation of girder steel portal frames using … distribution has a major effect on the resulting inference, this choice must be conducted with the utmost care [5]. b. posterior distribution the posterior probability distribution contains all the current information about the parameter. it merges the information in both prior distribution and likelihood. this typically results in the posterior representing stronger information than separate sources of information [6]. the prior and posterior densities are presented in table i, the mean and variance of the posterior parameters are presented in table ii. table i. random variables and their prior and posterior densitiy distributions [4] basic random variables parameter prior and posterior distribution normal � � � = 1√2�� � � �− 12 � − �� ��� � normal ���� = ��� ��� �⁄ � + ̅� ���� � �⁄ + ���� �� lognormal � � �= 1√2� � � !− 12 "ln − % & �' % normal �(�%�= 1√2�� � � !− 12 "% − �� & �' table ii. mean and variance of the parameters and their posterior statistics [4] mean and variance of parameters posterior statistics )��� = �� ���� = ��� �� � �⁄ � + ̅� ���� � �⁄ + ���� �� *+,��� = ��� ���� = ���� ���� � �⁄ ����� �� + � � �⁄ )�%� = � ��� = .�� � �⁄ � + � � ln ̅ � �⁄ + � � *+,�%� = � � � �� = / � �� � �⁄ �� � + � �⁄ iii. reliability analysis the reliability analysis of an engineering structure requires the limit state function to evaluate its performance [7]. the concept of a limit state is used to help define failure in the context of structural reliability analysis. it is a boundary between desired and undesired performance of a structure. the limit state function can be defined as [8]: 0�1, 3� = 1 − 3 (2) where r represents the resistance and q represents the load effect. the state of the structure can be described using various parameters 56, 5�, ⋯ , 58 , load and resistance parameters. the limit 0�5� = 0 separates the failure domain �0�5� < 0� and the safety domain �0�5� > 0� [9]. iv. reliability analysis methods due to the randomness of nature events, the complexity of the applied loads and initial imperfections, many times it is impossible to describe the response of structural systems. as a result, various analytical and numerical approaches have been developed. taylor series (ts)-based approaches, such as the form, and simulation-based methods, such as the mc simulation [4]. a. first-order reliability method (form) it is possible to expand the original model into infinite ts around the mean values: 0�5� = 0�� � + �5 − � � <=< + 6� �5 − � �� <>=< > + ⋯ +68! �5 − � �8 <@=< @ (3) where the function and derivatives are evaluated at � . it is common to include only linear terms, assuming that random input variables are independent. a function 0 �5� of n independent random variables can be approximated by linear terms of the ts, which are [10]: )�a� ≈ 0��c � (4) *+,�a� ≃ *+,�5 − � � �<=< �� = *+,� � �<=< �� (5) the limit state function is 0� � = 1 − 3, where 1, and 3 both being random variables uncorrelated and assumed to be normally distributed. the reliability index e is evaluated as a function of mean and standard deviation of resistance 1 and load 3 as given by [9]: e = �f g�hijf> kjh> (6) the probability of failure is given by: lm = φ�−e� (7) where φ is the cumulative probability distribution function of the standard normal variate. b. monte carlo (mc) method the mc method is considered one of the most powerful and accurate simulation tools to estimate the reliability and failure probability of uncertain structures numerically. it can be applied to many practical problems allowing the direct consideration of any type of probability distribution for the random variables. using mc simulations, an estimate of the probability of structural failure is obtained by [11]: lm = opo (8) where qm is the number of samples in the failure domain and q is the total number of samples. v. statistical characteristics of independent variables this study considers the applied loads, yield strength, plastic section modulus, girder span, cross-section dimensions, and modulus of elasticity as random variables. the sample data of the independent variables are summarized in table iii. the prior statistical characteristics of these variables collected from the literature are presented in table iv. the posterior statistical data of the input variables have been calculated from the updating process of the prior data by the bayesian method. the yield strength of steel rs , has been considered as an example to engineering, technology & applied science research vol. 12, no. 6, 2022, 9584-9589 9586 www.etasr.com fahmi & al-zaidee: strength and deflection reliability estimation of girder steel portal frames using … explain that process. updating mean, standard deviation, and coefficient of variance have been estimated based on the relations in (9)-(11). the posterior statistical characteristics of the independent variables are summarized in table v. ��� = t uv " w√@&> xk! yz�wz�>' t [" w√@&>xk! [�wz�>' = c̅�jz�>k�z"w>@ &�jz�>k�w>@ � = ��\] ���\]^_._a�>k��\]�"�>bc^d.db�>[ &��\]^_._a�>k��>bc^d.db�>[ � = 275mpa (9) � �� = / �jz�>�w>@ ��jz�>k�w>@ � = / ��\]^_._a� >��>bc^d.db�>[ ���\]^_._a�>k��>bc^d.db�>[ � = 12.5mpa (10) �ef′′ = jzz�zz = 6�.]�\] = 0.04 (11) table iii. sample statistical data of the variables uncertainty in variables hijklmnokjp cov distribution type reference dead load, lq 1.03 0.08 normal [12] live load, lr 1.00 0.1 gumbel [13] moment of inertia, sc 0.96 0.03 normal local survey modulus of elasticity, )t 1.025 0.05 normal [14] modulus of elasticity, )u 0.98 0.07 lognormal [15] member span, � 1.00 0.07 lognormal [16] plastic section modulus, vc 1.04 0.05 lognormal [17] yield strength of steel, rs 1.10 0.07 lognormal [17] table iv. prior statistical data of the variables uncertainty in variables hijklmnokjp cov distribution type references dead load, lq 1.03 0.08 normal [12] live load, lr 1.00 0.1 gumbel [13] moment of inertia, sc 0.96 0.05 normal [18] modulus of elasticity, )t 1.00 0.02 normal [17] modulus of elasticity, )u 1.00 0.03 lognormal [19] member span, � 1.00 0.004 lognormal [20] plastic section modulus, vc 1.00 0.04 lognormal [2] yield strength of steel, rs 1.10 0.06 lognormal [18] table v. posterior statistical data of the variables uncertainty in variables hijklmnokjp cov distribution type dead load, lq 1.03 0.08 normal live load, lr 1.00 0.1 gumbel moment of inertia, sc 0.96 0.005 normal steel modulus of elasticity, )t 1.01 0.016 normal concrete modulus of elasticity, )u 1.00 0.02 lognormal member span, � 1.00 0.003 lognormal plastic section modulus, vc 1.00 0.03 lognormal yield strength of steel, rs 1.10 0.04 lognormal vi. parametric study a steel single-story warehouse, as shown in figure 1, with a total length of 45m and width of 15m, and consisting of 5 bays has been considered in this parametric study. the superimposed dead load has been determined based on the assumption of a flooring system of a concrete slab with a thickness of 100mm and a metal deck of 7.5mm, supported on floor beams of (ipe 300). the first inner frame shown in figure 2 has been considered the most critical one as it includes the exterior face of the first interior support where the shear force is about 15% greater than the average value. the frame consists of ipe 600 steel girder and columns. the applied live loads on the girder have been determined based on the asce 7 specifications. the self-weight of the girder and columns have been determined depending on the cross-section dimensions and material density. fig. 1. steel single-story warehouse building. fig. 2. summary of the dead and live load on the interior supporting frame. vii. derived and simulated statistical properties for the strength and deflection of the girder two stages have been considered in the form and the mc simulation method. in the first stage, the randomness of the dependent variables has been deduced based on the prior knowledge of table iv. in the second stage, they have been inferred based on the posterior knowledge of table v. a. first-order approximation method 1) flexure analysis the bending moment w is a function of the load l and the span �. with refereeing to (4) and (5), the mean and variance of the bending moment can be estimated by: )�w� = �x ^ 0.904 ^ l{�{ (12) engineering, technology & applied science research vol. 12, no. 6, 2022, 9584-9589 9587 www.etasr.com fahmi & al-zaidee: strength and deflection reliability estimation of girder steel portal frames using … *+,�w� = *+,��� �|}|r � � + *+,�l� �|}|~ � � (13) where �x is a deterministic dimensionless factor, equal to 0.56, that correlates the aforementioned bending moment to the bending moment of the corresponding simple span. the constant 0.904 is the mid-span bending moment due to the reactions from different floor beams. the nominal flexural strength w8 is a function of the yield strength rs and the plastic section modulus vc . refereeing to(4) and (5), the mean and variance of w8 can be estimated from: )�w8� = r{s v̅c (14) *+,�w8� = *+,�rs � "|}@|�� & � + *+,�vc � �|}@|�u � � (15) based on the statistical characteristics of the independent variables illustrated in tables iv and v, the prior and posterior statistical characteristics for bending moment m and nominal flexural strength mn have been estimated and are presented in tables vi and vii. table vi. prior statistical characteristics of the girder's strength random variables nominal (kn.m) mean (kn.m) standard deviation (kn.m) cov m 577.11 585.08 53.08 0.0907 mn 878 965.8 69.64 0.072 table vii. posterior statistical characteristics of the girder's strength random variables nominal (kn.m) mean (kn.m) standard deviation (kn.m) cov m 577.11 585.08 53.06 0.0906 mn 878 965.8 48.29 0.05 2) shear analysis the shear force v, is a function of the load p. the mean and variance of the shear force are calculated by: )�*� = ��3.5l{ (16) *+,�*� = *+,�l� �|�|~� � (17) where �� is a deterministic dimensionless factor to correlate the aforementioned shear force to the shear force of the corresponding simple span and is equal to 1.0. the constant 3.5 is the shear at the support due to the reactions from different floor beams. the nominal shear force vn is a function of the yield strength rs and the area of the web �� . the mean and variance of the nominal shear force are calculated by: )�*8 � = 0.6r{s �̅� (18) *+,�*8 � = *+,�rs � "|�@|�� & � + *+,��� � � |�@|��� � (19) table viii. prior statistical characteristics of shear force random variables nominal (kn) mean (kn) standard deviation (kn) cov * 266 296.67 24.14 0.081 *8 1011 1112 86.909 0.078 based on the statistical characteristics of the independent variables illustrated in tables iv and v, the prior and posterior statistical characteristics for * and *8 , have been estimated and are presented in tables viii and ix. table ix. posterior statistical characteristics of shear force random variables nominal (kn) mean (kn) standard deviation (kn) cov * 266 296.67 24.14 0.081 *8 1011 1112 44.856 0.040 3) deflection the deflection ∆ is a function of the load p, span l, modulus of elasticity e, and moment of inertia i. the mean and variance of the deflection are calculated by: )�δ� = �� a6�6000 ~{r{� �{�̅ (20) *+,�δ� = *+,�s� �|�|� � � + *+,��� �|�|r� � + *+,�)� �|�|�� � + *+,�l� �|�|~� � (21) where �� is a deterministic dimensionless factor that correlates the aforementioned deflection to the deflection of the corresponding simple span, equal to 0.32. the constant 613/6000 is the deflection at the mid-span due to the reactions from different floor beams. based on tables iv and v, the prior and posterior statistical characteristics for deflection are presented in tables x and xi. table x. prior statistical characteristics of deflection random variables nominal (mm) mean (mm) standard deviation (mm) cov ∆ 45 48.08 5.05 0.105 table xi. posterior statistical characteristics of deflection random variables nominal (mm) mean (mm) standard deviation (mm) cov ∆ 45 48.57 4.49 0.092 (a) (b) fig. 3. histogram for prior (a) w and (b) w8 sample of the typical interior girder. b. monte carlo simulation the mc method has been adopted to simulate the processes of the flexural strength, shear, and deflection for the interior supporting frame. a matlab code has been used to engineering, technology & applied science research vol. 12, no. 6, 2022, 9584-9589 9588 www.etasr.com fahmi & al-zaidee: strength and deflection reliability estimation of girder steel portal frames using … generate pseudo-random sampling with a size of 1000 for each input variable. 1) flexure analysis the prior statistical characteristics of the bending moment w and nominal bending moment w8 are presented in figure 3 and table xii. the estimated posterior statistical characteristics are presented in figure 3 and table xiii. table xii. prior statistical characteristics of m and mn of the girder random variables mean (kn.m) standard deviation (kn.m) cov distribution types w 583.53 38.4 0.065 normal w8 968.48 69.5 0.071 lognormal (a) (b) fig. 4. histogram for posterior prior (a) w and (b) w8 sample of the typical interior girder. table xiii. posterior statistical characteristics of m and mn of the girder random variables mean (kn.m) standard deviation (kn.m) cov distribution types w 583.52 38.29 0.06 normal w8 964.81 49.12 0.05 lognormal 2) shear analysis the prior statistical characteristics of the shear force * and nominal shear force *8 were estimated and are presented in figure 5 and table xiv. the posterior statistical characteristics of v and vn were estimated and are presented in figure 6 and table xv. (a) (b) fig. 5. histogram for prior (a) v and vn of the typical interior girder. table xiv. prior statistical characteristics of v and vn random variables mean (kn) standard deviation (kn) cov distribution types * 269.84 17.40 0.064 normal *8 1111.5 86.300 0.077 normal (a) (b) fig. 6. histogram for posterior (a) v and vn of the typical interior girder. table xv. posterior statistical characteristics of v and vn. random variables mean (kn) standard deviation (kn) cov distribution types v 269.35 17.62 0.065 normal vn 1112.8 43.70 0.039 normal 3) deflection the estimated prior and posterior statistical characteristics of deflection are presented in figure 7 and table xvi. (a) (b) fig. 7. histogram for (a) prior and (b) posterior deflection sample of the girder. table xvi. prior and posterior statistical characteristics of girder deflection random variables mean (mm) standard deviation (mm) cov distribution types ∆����� 48.38 4.14 0.085 normal ∆��t������ 47.51 3.33 0.070 normal viii. reliability analysis for strength and deflection of the girder the form has been adopted to estimate the reliability associated with girder's flexural strength, shear, and deflection. in the form, it has been assumed that all independent variables have a normal distribution. the mean and standard deviation of girder's flexural strength, shear, and have been used to evaluate the reliability index e and the probability of failure lm due to the randomness in the load effects and resistance characteristics. regarding flexure analysis, the mean and standard deviation of the bending moment ()} , �} ) and the nominal flexural strength ()8 , �8 ) have been estimated in tables vi and vii. the prior and posterior e and lm are summarized in table xvii. engineering, technology & applied science research vol. 12, no. 6, 2022, 9584-9589 9589 www.etasr.com fahmi & al-zaidee: strength and deflection reliability estimation of girder steel portal frames using … table xvii. prior and posterior e and pf for the flexure strength of the girder strength due to �� � �lq + lr ������ 7.12414×10-6 4.34 �lq + lr ���t������ 5.79013×10-8 5.30 for shear analysis, the mean and standard deviation of the shear force ( )� , �� ) and the shear strength ( )8 , �8 ) were estimated and can be seen in tables viii and ix. the results for the prior and posterior e and lm are summarized in table xviii. table xviii. prior e and pf for the shear of the girder strength due to �� � �lq + lr ������ 8.58359×10-20 9.03 �lq + lr ���t������ 5.44049×10-58 16.01 the estimated mean and standard deviation of deflection ()∆, �∆) and nominal deflection ()∆@ , �∆@ ) shown in tables x and xi comply to the limitations of ibc 2009. the results for the prior e and lm are summarized in table xix. table xix. prior and posterior e and pf for the girder deflection deflection due to �� � �lq + lr ������ 2.60013×10-12 6.90 �lq + lr ���t������ 9.29665×10-15 7.66 ix. conclusion this paper has performed a prior and posterior statistical characteristics reliability analysis of the girder of the first inner frame. through the application of the bayesian method and the results of the prior and posterior analysis, it was shown that the greater the knowledge gained about the independent parameters, the less is the randomness in the dependent parameters, and thus enhances the reliability of the system. the results revealed that the reliability index for shear force significantly increased from 9.03 to 16.01, when the statistical parameters of the system were updated, while the reliability index of the bending moment and deflection increased from 4.34 to 5.30 and 6.90 to 7.66 respectively. references [1] d. v. ngo, k. v. pham, d. d. le, k. h. le, and k. v. huynh, "assessing power system stability following load changes and considering uncertainty," engineering, technology & applied science research, vol. 8, no. 2, pp. 2758–2763, apr. 2018, https://doi.org/ 10.48084/etasr.1892. 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[17] k. atua, i. assakkaf, and b. m. ayyub, "statistical characteristics of strength and load random variables of ship structures," in probabilistic mechanics and structural reliability, proceeding of the seventh specialty conference, worcester, ma, usa, 1996. [18] h. zhang, h. liu, b. r. ellingwood, and k. j. r. rasmussen, "system reliabilities of planar gravity steel frames designed by the inelastic method in aisc 360-10," journal of structural engineering, vol. 144, no. 3, mar. 2018, art. no. 04018011, https://doi.org/10.1061/(asce) st.1943-541x.0001991. [19] aci committee 318, building code requirements for structural concrete: (aci 318-19); and commentary (aci 318r-19). farmington hills, mi, usa: american concrete institute, 2019. [20] indian standard, tolerances for fabrication of steel structures. new delhi, india: bureau of indian standards, 1974. microsoft word etasr_v12_n4_pp8978-8981 engineering, technology & applied science research vol. 12, no. 4, 2022, 8978-8981 8978 www.etasr.com zisopolo et al.: a comparative analysis of the mechanical properties of annealed pla a comparative analysis of the mechanical properties of annealed pla dragoș gabriel zisopol mechanical engineering petroleum – gas university ploiesti, romania zisopol@zisopol.ro ion nae mechanical engineering petroleum – gas university ploiesti, romania inae@upg-ploiesti.ro alexandra-ileana portoacă mechanical engineering petroleum – gas university ploiesti, romania alexandra.portoaca@upg-ploiesti.ro ibrahim naim ramadan mechanical engineering petroleum – gas university ploiesti, romania ing_ramadan@yahoo.com received: 7 june 2022 | revised: 16 june 2022 | accepted: 18 june 2022 abstract-in order to obtain better performance, 3d printed parts can be the subject of post-processing operations like sanding, gap filling, polishing, annealing, epoxy coating, and metal plating. this paper takes into consideration the most commonly used material filament for fff technology pla and studies the mechanical characteristics through tensile and 3-point bending tests. the obtained results reveal significantly higher values of the mechanical properties after applying a 3-hour heat treatment at 75°c, for the following combinations of parameters: layer thickness of 0.10, 0.15, and 0.20mm and infill percentage of 50%, 75%, and 100%. keywords-3d printing; annealing; tensile test; 3 point bending test; flexural strength i. introduction the need to achieve time and cost reduction of part fabrication allowed 3d printing technology to attract scientific interest. although fff is a commonly used method for obtaining parts, it has several disadvantages, like low cohesion between the fused layers, low tensile properties, and low resistance to humidity. in order to improve the mechanical characteristics and increase the percentage of crystallinity in the parts obtained by fff annealing, a post-process heat treatment can be applied [1-3]. after a 3d printed filament is heated to be extruded through a nozzle, it is often relatively rapidly cooled. uneven cooling may cause the shrinkage of the layers, which results as the effect of inadequate heat propagation in the structure of the printed part, especially in in the extremities. therefore this process causes the tensile and compressive stresses to accumulate in the structure of the polymer. annealing consists in gradually heating in the oven of the samples or parts, at a temperature between the glass transition and the melting temperatures. this treatment consists of heating and cooling slowly in order to increase the bounding crystalline structures in the polymer and redistribute the stresses inside the printed part which will give higher crystallinity, mechanical resistance, and rigidity. recrystallized pla products also present a huge advantage compared to amorphous products: much higher heat deflection temperature (hdt). while amorphous pla products have an hdt of 50°c, semi-crystalline pla products have an hdt of 130°c. although pla can be recrystallized after processing into a product, the products shrink and significant warpage occurs during recrystallization due to the increasing crystallinity. distortion-free semi-crystallized pla products can only be made during the process using nucleating agents [3-5]. the aim of this paper is to compare the influence of signaling factors, such as layer thickness and percentage of filling of pla printed parts on the tensile and bending properties with annealed pla printed parts in terms of various printing parameters. ii. materials, methods and procedures a. set-up process parameters although 3d printing offers a wide range of applications, it still has certain limitations that may be improved through annealing. because 3d printed materials have an amorphous molecular structure and no precise melting point, they gradually soften until they completely melt. this feature can be used as an advantage because in the event of annealing, the molecules in the material rearrange themselves, which can result in improved mechanical characteristics, i.e. making an object stronger. the specifications collected from filament producers of the pla material used in this study are shown in table i. in this experimental study, three infill percentages were used: 50%, 75%, and 100%, and in order to asset the corresponding author: ibrahim naim ramadan engineering, technology & applied science research vol. 12, no. 4, 2022, 8978-8981 8979 www.etasr.com zisopolo et al.: a comparative analysis of the mechanical properties of annealed pla mechanical characteristics, tensile and flexural tests were conducted on the annealed and unannealed samples and the results were compared. for the annealing heat treatment, the samples were kept for a period of 3h at a temperature of 60 0 c, with a very slow cooling. all samples were cooled together in an oven. table i. 3d printed sample parameters parameters material specifications pla nozzle diameter 0.40mm build orientation flat top solid layers 4 layers bottom solid layers 4 layers outline/perimeters shell 3 outlines internal fill pattern lines external fill pattern rectilinear internal infill angle offsets 180◦ extruder temperature 210◦c heated bed temperature 60◦c default printing speed 70mm/s filament diameter 1.75mm filament density 1.24g/cm 3 b. sample preparation the samples were printed with a raise e2 3d printer with a volume capacity of 330×240×240mm. the design of the samples, later converted in stl format, was made in autodesk inventor and idea maker software was used to adjust process parameters such as internal structure pattern, infill percentage, and layer thickness. the printing speed was set to 80mm/s in x-y deposition direction at a deposition temperature of 200°c. fig. 1. tensile and flexural sample testing on the lloyd lrx plus testing machine. the process parameters considered as variables were the thickness of the deposited layer (0.1, 0.15, and 0.20mm) and the infill percentage (50%, 75%, and 100%). a lloyd lrx plus testing machine (figure 1) was used for both tensile and flexural tests. c. tensile tests in order to evaluate the mechanical behavior, in the first phase, tensile tests were performed [6]. sets of 5 specimens were printed for each of the characteristics considered in the study, with standard dimensions of 165mm length, 5mm thickness, and 13mm width. d. flexural tests this method is used to study the bending behavior and to determine the flexural strength. the test speed was set at 1mm/min and the distance between the supports was determined to be 64mm (l=16h, where h is the height of the sample [7]). all tests were performed at 20°c and the samples were acclimatized for 24h. the geometrical features of the samples were made with standard dimensions of 10mm width, 4mm thickness, and 80mm length. iii. results and discussion a. tensile tests due to the vast volume of content resulting from the testing of a large number of samples, instead of presenting the tables with the values of all 5 determinations, it was opted to do it only for layer thickness of 0.1 and only for the ultimate tensile strength. for 0.15 and 0.20 layer thicknesses, only the values of the averages of the determinations of linear specific deformation and young's modulus are given. the average of the 5 determinations made for each sample, is also presented in graphical form for the better understanding of the differences between the samples with heat and without heat treatment. table ii. ultimate tensile strength test values of unannealed pla for 0.1 layer thickness infill % ultimate tensile strength, mpa sample 1 2 3 4 5 average 50% 24.64 24.90 24.77 24.69 24.18 24.64 75% 25.90 25.92 26.54 27.04 26.36 26.35 100% 31.92 33.82 32.25 33.74 35.82 33.51 table iii. ultimate tensile strength test values of annealed pla for 0.1 layer thickness infill % ultimate tensile strength, mpa sample 1 2 3 4 5 average 50% 32.06 30.42 30.61 30.23 31.76 31.02 75% 35.44 34.99 34.90 37.10 37.10 35.90 100% 42.60 43.49 41.09 43.80 48.72 43.94 as can be seen in tables ii and iii, the ultimate tensile strength values of all tested samples are higher, which reveals that annealing modifies the mechanical characteristics of the parts obtained by 3d printing in a positive way. they have been increased by enriching the material's crystallinity, which carried out higher values of ultimate tensile strength, as can be graphically seen in figures 2-4. for each value of layer thickness studied, an ascending trend can be observed with increasing infill percentage. table iv. ultimate tensile strength test values of unannealed pla for 0.1 layer thickness mechanical characteristics infill percentage 50% 75% 100% wa a wa a wa a ultimate tensile strength, mpa 24.64 31.00 26.35 35.90 33.51 43.91 linear specific deformation, % 6.47 5.52 5.73 5.01 5.64 4.85 young’s modulus, mpa 2312 2120 2423 2146 2523 2224 engineering, technology & applied science research vol. 12, no. 4, 2022, 8978-8981 8980 www.etasr.com zisopolo et al.: a comparative analysis of the mechanical properties of annealed pla as can be seen in tables iv and v, a comparison was made between the average values of samples without annealing (wa) and of the annealed (a). an increasing trend of about 30% for the values of ultimate tensile strength can be observed, regardless of the infill percentage of the samples. the linear specific deformation and young’s modulus both have a decreasing tendency. table v. ultimate tensile strength test values of annealed pla for 0.15 layer thickness mechanical properties infill percentage 50% 75% 100% wa a wa a wa a ultimate tensile strength, mpa 25.94 30.04 28.04 34.77 40.07 48.05 linear specific deformation, % 3.54 3.01 4.19 3.90 4.72 4.08 young’s modulus, mpa 2124 1931 2266 2130 2607 2528 table vi. ultimate tensile strength test values of annealed pla for 0.2 layer thickness mechanical properties infill percentage 50% 75% 100% wa a wa a wa a ultimate tensile strength, mpa 23.80 27.49 26.96 31.95 35.58 41.63 linear specific deformation, % 3.76 3.45 3.71 3.52 3.59 3.31 young’s modulus, mpa 1813 1586 2132 2076 2248 2187 fig. 2. ultimate tensile strength variation of 0.1 layer thickness for varying infill procentage. fig. 3. ultimate tensile strength variation of 0.15 layer thickness for varying infill procentage. fig. 4. ultimate tensile strength variation of 0.2 layer thickness for varying infill procentage. the average of the determinations made for the values from tables iv-vi, is being presented in graphical form in order to highlight the differences between the a and the wa samples. b. flexural tests as with the tensile tests, 5 test samples were performed for each of the 3 infill percentages of 50%, 75%, and 100%. as can be seen in the comparative graphical representations of figures 5-7, the values of maximum flexural strength are clearly higher in the case of annealed samples. as in the tensile tests, there is a tendency for values to increase by about 15% for 0.1 and 0.15mm layer thickness [8]. the values obtained for 0.2mm layer thickness are lower, although here too there is an upward trend. fig. 5. maximum flexural strength comparison between pla and annealed pla for 0.1mm layer thickness. fig. 6. maximum flexural strength comparison between pla and annealed pla for 0.15mm layer thickness. engineering, technology & applied science research vol. 12, no. 4, 2022, 8978-8981 8981 www.etasr.com zisopolo et al.: a comparative analysis of the mechanical properties of annealed pla fig. 7. maximum flexural strength comparison between pla and annealed pla for 0.2mm layer thickness. iv. conclusions the objective of this paper was to highlight the variation of mechanical characteristics of annealed pla 3d printed materials, with different parameters of the technological process. when comparing the average values of samples with and without annealing, an increased trend of about 30% for the values of ultimate tensile strength can be observed, regardless of the infill percentage of the samples. both linear specific deformation and young’s modulus have a decreasing tendency. similar results have been obtained in other studies, for example a 30.25% increase in the ultimate strength compared to the asprinted samples was found in [9-11]. an annealing of 1h duration resulted in 24% increase in ultimate strength in [12]. maximum flexural strength values are clearly higher in the case of annealed samples. there is a tendency for values to increase by about 15%, very similar to the 11%–17% obtained in [13]. several signal factors such as deposition style and orientation and also raster gap and width can influence the values of the mechanical characteristics of the 3d printed samples without annealing. also, soaking time and cooling rate can lead to different values for the heat treated parts. so, having taken into account all these aspects, the differences between the values in this article and the values from other studies [8, 10, 11, 14] can be explained. future work will focus on the way the main factors of the annealing process influence the main mechanical properties of 3d printed parts. references [1] j. butt and r. bhaskar, "investigating the effects of annealing on the mechanical properties of fff-printed thermoplastics," journal of manufacturing and materials processing, vol. 4, no. 2, jun. 2020, art. no. 38, https://doi.org/10.3390/jmmp4020038. [2] c. yang, x. tian, d. li, y. cao, f. zhao, and c. shi, "influence of thermal processing conditions in 3d printing on the crystallinity and mechanical properties of peek material," journal of materials processing technology, vol. 248, pp. 1–7, oct. 2017, https://doi.org/ 10.1016/j.jmatprotec.2017.04.027. [3] t. tabi, i. e. sajo, f. szabo, a. s. luyt, and j. g. kovacs, "crystalline structure of annealed polylactic acid and its relation to processing," express polymer letters, vol. 4, no. 10, pp. 659–668, 2010, https://doi.org/10.3144/expresspolymlett.2010.80. [4] s. k. lee, y. r. kim, s. h. kim, and j. h. kim, "investigation of the internal stress relaxation in fdm 3d printing : annealing conditions," the korean society of manufacturing process engineers, vol. 17, no. 4, pp. 130–136, aug. 2018, https://doi.org/10.14775/ksmpe.2018.17.4.130. [5] y. liao et al., "effect of porosity and crystallinity on 3d printed pla properties," polymers, vol. 11, no. 9, sep. 2019, art. no. 1487, https://doi.org/10.3390/polym11091487. [6] d20.10 astm subcomitee, "astm volume 08.01: plastics (i): c1147– d3159," in standard test method for tensile properties of plastics by use of microtensile specimens, astm, 2018, https://doi.org/10.1520/ d1708-18. [7] iso/tc 61/sc 2 technical committee, iso 178:2019 plastics — determination of flexural properties. iso, 2019. [8] d. g. zisopol, i. nae, a. i. portoaca, and i. ramadan, "a statistical approach of the flexural strength of pla and abs 3d printed parts," engineering, technology & applied science research, vol. 12, no. 2, pp. 8248–8252, apr. 2022, https://doi.org/10.48084/etasr.4739. [9] v. slavković, n. grujović, a. disic, and a. radovanović, "influence of annealing and printing directions on mechanical properties of pla shape memory polymer produced by fused deposition modeling," in conference: international congress of serbian society of mechanics, tara mountain, serbia, jun. 2017. [10] d. g. zisopol, i. nae, a. i. portoaca, and i. ramadan, "a theoretical and experimental research on the influence of fdm parameters on tensile strength and hardness of parts made of polylactic acid," engineering, technology & applied science research, vol. 11, no. 4, pp. 7458–7463, aug. 2021, https://doi.org/10.48084/etasr.4311. [11] a. portoaca, i. nae, d. zisopol, and i. ramadan, "studies on the influence of fff parameters on the tensile properties of samples made of abs," in innovative manufacturing engineering & energy international conference, iasi, romania, oct. 2021. [12] a. szust and g. adamski, "using thermal annealing and salt remelting to increase tensile properties of 3d fdm prints," engineering failure analysis, vol. 132, feb. 2022, art. no. 105932, https://doi.org/ 10.1016/j.engfailanal.2021.105932. [13] r. a. wach, p. wolszczak, and a. adamus-wlodarczyk, "enhancement of mechanical properties of fdm-pla parts via thermal annealing," macromolecular materials and engineering, vol. 303, no. 9, 2018, αρτ. νο. 1800169, https://doi.org/10.1002/mame.201800169. [14] h. yilmaz and m. k. turan, "fahamecv1:a low cost automated metaphase detection system," engineering, technology & applied science research, vol. 7, no. 6, pp. 2160–2166, dec. 2017, https://doi.org/10.48084/etasr.1464. microsoft word etasr_v13_n2_pp10292-10300 engineering, technology & applied science research vol. 13, no. 2, 2023, 10292-10300 10292 www.etasr.com alqurashi: arabic sentiment analysis for twitter data: a systematic literature review arabic sentiment analysis for twitter data: a systematic literature review tahani alqurashi college of computer and information systems, information system department, umm al-qura university, saudi arabia tmqurashi@uqu.edu.sa (corresponding author) received: 5 january 2023 | revised: 22 january 2023 and 24 january 2023 | accepted: 26 january 2023 abstract social media platforms have a huge impact on our daily lives. they have succeeded in attracting many people to spend time communicating and expressing themselves. twitter is a social media platform that could be considered as a source of public opinion about products, services, and events. sentiment analysis is the art of studying public feelings about certain topics, which may be positive, negative, or neutral. this paper provides a systematic review of arabic tweet sentiment analysis on papers published from 2012 to 2021 in digital libraries including ieee explorer, science direct, springer link, and google scholar. the main aim of this systematic review is to investigate the trends in the topics reported and to highlight potential new research lines. to achieve that, three main stages were implemented: planning, conducting, and reporting the review. our findings suggest the need for an open-source large arabic tweet dataset that can be used by researchers. also, it was found that researchers have used various classification techniques, which led to different results. keywords-arabic sentiment analysis; systematic review; social media; twitter i. introduction social media are considered a major source of news, marketing, and advertisements. these platforms have huge numbers of users, which are increasing daily. the number of global monthly active users of twitter recently averaged to 330 million people [1]. users express their feelings and opinions using short messages called tweets and they can refer tweets to other users, called followers. therefore, the content of these platforms may be evaluated to extract insights from these data. sentiment analysis (sa), also known as opinion mining, is one of the natural language processing fields. sa focuses on analyzing text to extract people’s opinions and emotions and identify these as positive, negative, or neutral [2]. many researchers have directed their attention to this area and while most research has focused on english, chinese, and other indoeuropean languages, few studies have addressed sa in morphologically rich languages, such as arabic. the number of arabic texts existing on the internet has seen a significant increase. according to internet world statistics, arabic is the fourth most commonly used language on the internet, after english, chinese, and spanish, reaching 5.2% of all internet users [3]. due to the exponential growth in arabic internet users and arabic online content, arabic sa (asa) has gained the attention of many researchers over the last decade [4]. in this paper, we systematically review the literature in the field of arabic tweet sa. ii. overview of the systematic review method in this review, the systematic literature review methodology proposed in [5] was followed. it consists of 3 main stages: planning, conducting, and reporting the review. the main aim of this review is to perform a comprehensive review of asa for twitter data and cover the methodologies and approaches of data processing, sa techniques and approaches that have been used in the literature, and the challenges asa faces. figure 1 illustrates the steps of the systematic literature review methodology, which are explained in more detail in the following sections. a. research questions in the planning phase, the research questions are specified. in this study, the research contributions are highlighted through answering the following research questions (rqs):  rq1: what are the different machine learning techniques that have been applied/proposed for asa?  rq2: what data pre-processing techniques have been used for arabic tweets in asa research? b. search strategy after determining the research questions, the search terms and data resources are specified. first, to identify the search terms, the research questions were analyzed and the following search strings were developed: "arabic", "arabic text", engineering, technology & applied science research vol. 13, no. 2, 2023, 10292-10300 10293 www.etasr.com alqurashi: arabic sentiment analysis for twitter data: a systematic literature review "sentiment analysis", "twitter", and "tweets". moreover, the boolean operators "or" and "and" were used to search for all possible combinations of these terms. we covered only asa studies using twitter data as the application. fig. 1. the steps of the systematic literature review methodology. secondly, a search was carried out on the following six academic databases: ieee explore, acm, springer, sciencedirect/elsevier, google scholar, and wiley. these were chosen as they are the top databases in the computer science field. the titles, abstracts, and keywords of all indexed papers were searched using the search terms we developed, and the search was conducted on studies from 2012 up to 2021. table i. search results database relevant search results ieee explore 38 acm 4 sciencedirect/elsevier 9 springer link 5 google scholar 16 wiley 1 total 73 c. inclusion and exclusion criteria in this stage, inclusion and exclusion criteria were delineated to thoroughly assess the relevance of the potential primary studies. these were:  include papers written in english only.  include papers published in journals, conference papers, and book chapters.  include papers published from 2012 to 2021.  include papers that focus on arabic text analysis on the twitter platform. exclude papers that focus on all other platforms.  exclude duplicate papers.  exclude secondary studies (i.e. literature reviews).  exclude papers that are not peer-reviewed, such as technical reports and theses. d. data extraction after collecting the data from the above-mentioned databases and extracting the relevant papers based on our inclusion and exclusion criteria, 73 papers were selected for analysis. table i shows the search results. the papers were classified based on the type and the year of publication. from 2012 to 2021, a gradual increase in the numbers of conference papers and published journal articles was noted, as shown in figure 2. the number of publications peaked in 2019, with 19 identified publications in total. the average number of publications is around 9 studies per year over the past 10 years. the most common form of publication was conference papers (42), followed by journal articles (30), and 1 book chapter, as shown in figure 3. fig. 2. number of publications per year. fig. 3. type of publications. iii. primary studies and discussion sa is a set of processes that are applied widely in computer science studies to analyze and examine semantics, words, and tweet syntax to determine the emotions in the text [6]. the main purpose of sa using twitter data is to classify tweets into three polarities (positive, negative, or natural) based on the statements or words contained in that tweet [7]. in this section, the main finding of this systematic review regarding asa using the twitter platform are presented and discussed. a. arabic tweet sentiment analysis approaches we found that asa approaches can be classified into three main categories: corpus-based, lexicon-based, and hybridbased. table ii summarizes the reviewed papers based on their 0 2 4 6 8 10 12 14 16 18 20 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 n u m b e r o f p u b li c a ti o n s years 58% 41% 1% journal conference book chapter engineering, technology & applied science research vol. 13, no. 2, 2023, 10292-10300 10294 www.etasr.com alqurashi: arabic sentiment analysis for twitter data: a systematic literature review categories, the following subsections discuss each of these separately. 1) the corpus-based approach in this approach, the main aim was to collect and use the available twitter dataset to build machine learning models in order to determine the sentiments of each tweet. our findings indicate that the most commonly used methods are the supervised learning approach, and in particular naive bayes (nb), support vector machine (svm), decision tree (dt), knearest neighbor (knn), ensemble classifiers (bagging and voting), and deep learning [2, 8-11]. moreover, a few studies used an unsupervised learning approach [12, 13]. in the supervised learning approach, authors in [8] used svm, multinomial nb and rule-based classification algorithms to classify sentiments based on their collected dataset of 134,194 arabic tweets, which had been labelled automatically using emojis. they concluded that svm outperformed the other algorithms used, reaching an accuracy of 75.7%. authors in [9] investigated the state-of-art english sa techniques and used them for solving the problem of asa through a machine translation (mt)-based approach. they first collected arabic tweets (a total of 937 tweets), translated them into english, and then applied stanford sentiment classifiers to classify each tweet, either as positive or negative sentiment. by comparing this method with lexicon-based techniques, they found that their mt sentiment approach outperformed the other approaches. authors in [2] utilized machine learning algorithms and neural networks to perform sa on health services. they collected twitter data using trending hashtags about health services, and their results show that the accuracy of the svm approach outperformed the other algorithms, including cnn and dnn. authors in [10] collected arabic tweets related to political events in 2018. they analyzed their dataset using machine learning and data mining algorithms such as nb, svm, dt, knn, and ensemble classifiers. they observed that ensemble, and in particular the voting classifier, outperformed the other techniques. authors in [14] examined tweets on women’s issues in saudi arabia. they collected their dataset from popular twitter hashtags, and classified them as positive, negative, and neutral. the nb algorithm was used to automate classification. authors in [15] built a predictive model and applied it to data gathered from the gulf region to predict whether a user’s tweet indicated a depressed or nondepressed user. they applied the common machine learning algorithms, rf, nb, adaboost1 and linear svm, and concluded that linear svm outperformed the other classifiers reaching an accuracy of 87.5%. authors in [16] aimed to investigate sentiments from tweets that were collected from popular hashtags about women’s problems in saudi arabia. the data was pre-processed and classified, and their results indicated that the nb algorithm achieved greater accuracy than the other classifiers available in weka. in a deep learning approach, authors in [17] proposed a multi-channel embedding convolutional neural network (mce-cnn) for arabic sentiment classification and thoroughly assessed it using balanced and imbalanced datasets. the mce-cnn was trained on different sentiment features, including word and character n-grams. their proposed model achieved high accuracy. authors in [18] proposed a sentiment and emotion system for regression and classification tasks using the cnn and lstm algorithms. they implemented different feature extraction techniques, a word embedding model (aravec), a document embedding model (doc2vec), and a set of semantic features such as deepemoji and unsupervised sentiment nerous. their proposed system outperformed the svm unigrams baseline model’s performance applied to the semeval2018 dataset [19]. authors in [20] developed a new architecture based on cnns and rnns for handwritten arabic word understanding and classification. the most powerful technique for analyzing arabic tweets and social media stata is the cnn technique. the use of a sub-word-level rnn module and a character-level cnn module helps in gaining a better understanding of handwritten text. this technique is efficient, especially with a short text written in an uncontrolled language format. an approach to tweet-based word correction that uses arabic text classification to find abusive accounts on twitter was proposed in [21]. the classification of arabic tweets without stemming was investigated and compared to classification using stemming. this approach proved better than other popular approaches to arabic word correction on twitter. authors in [22] proposed the classification of arabic tweets as positive or negative using an improved algorithm. the approach consists of two phases. in the first phase the dataset was prepared by normalization, while the second phase involved classifying tweets using a dmnb approach. the experimental results showed that this improved approach reached an accuracy level up to 87.5%. in an unsupervised learning approach, authors in [12] used sentiment classification of people’s opinions during the covid 19 pandemic using k-means and mini-batch k-means algorithms on arabic and english datasets. they observed that k-means classification takes longer than mini-batch k-means classification. authors in [13] aimed to assess the integration of the similarity functions with pre-processing methods for clustering tweets. k-means clustering algorithms were used to cluster arabic tweets into two clusters: positive and negative. the results showed that the stemming (pre-processing method) with the kullback-leibler divergence function is more effective than other competitive pre-processing techniques. other studies compared different approaches. authors in [23] compared the corpus-based and lexicon-based approaches. for the first approach, they collected 2000 arabic tweets and used svm, nb, knn, and dt algorithms. for the lexicon approach they manually built a lexicon of 3479 words. they concluded that the svm approach outperformed the others. authors in [24] applied three types of classification methods (supervised, unsupervised, and hybrid learning) on tweets collected randomly from three different domains (sports, politics, and social). the results indicate that hybrid learning is better than the supervised or the unsupervised approaches in terms of classification accuracy. 2) the lexicon-based approach this approach, considered to be unsupervised learning, aims to build a sentiment lexicon of terms and then compute the sentiment of a certain text based on the sentiment values of the terms composing it. our findings indicate that there are two engineering, technology & applied science research vol. 13, no. 2, 2023, 10292-10300 10295 www.etasr.com alqurashi: arabic sentiment analysis for twitter data: a systematic literature review different lexicon-based approaches used in asa: the double polarity (dp) [25] and the simple polarity (pl) [26] approaches. the latter is based on counting both the positive and negative words in each sentence, while the dp approach is based on the frequencies of positive and negative words in the sentence. in [26], a pl lexicon was built manually, consisting of 3982 adjectives from two arabic datasets that were classified as positive, negative, and neutral. the authors applied pl to classify individual tweets on the basis of including positive, negative or neutral adjectives. they called their system samar and they concluded that using pl improves the accuracy of asa. authors in [27] proposed a weighted lexicon-based algorithm (wlba) for the saudi dialect. in their approach, the weight of each word was calculated based on the corpus, not upon the lexicon. moreover, they compared their proposed algorithm with the dp and pl algorithms, and concluded that wlba outperformed the dp approach, but not the pl approach. the lexicon-based approach depends on the creation of a lexicon. we found that there are two different methods of lexicon creation: manual and automatic. the manual method is the most popular and it provides more accurate results, but is domain-independent [27-29]. table ii. reviewed papers classified based on the approach used approach paper dataset size algorithms features language corpus based [8] 134194 tweets svm, mnb and rule-based tf-idf msa, dialects [10] 14419 tweets svm, nb, nt, knn, ensemble (bagging, voting) tf-idf unspecified [14] 9096 svm, nb bow, bi-gram, and tri-gram dialects [15] 6122 tweets from 89 users rf, svm, nb, adaboost and liner svm unigrams, negative features msa, gulf dialect [17] astd dataset, 10000 tweets mce-cnn word and character n-grams msa, dialects [20] astd stacked model with cnn and gated recurrent unit character level model msa [37] nb, svm, multinomial logistic regression, knn dialect [64] astd (3,315 tweets) svm, recursive neural tensor network character n-gram model [3,5], word n-grams [1,4], count of negated words and positive and negative words based on lexicons from [65-67] egyptian dialect [68] 2591 tweets svm, nb, knn msa and dialects [2] 2026 tweets svm, nb, lr, cnn, dnn tf-idf, word frequency, word2vec msa [70] svm msa, dialects [71] 17748 tweets svm tf-idf msa, dialects [72] semeval, arasenti, astd deep learning, svm word embedding (arevec), set of related lexicon features msa, dialects [73] 2.3m tweets on news semi-supervised technique msa, dialects [9] 937 tweets machine translation approach, stanford sentiment classifier msa lexicon based [69] 22550 svm, nb binary model jordanian dialects [26] 3015 tweets, 2798 tweets polarity lexicon of size 3982 msa, dialects [28] 2000 tweets on politics and arts manual lexicon of size 4815 words msa, jordanian dialects [9] 937 tweets machine translation approach, stanford sentiment classifier msa [52] svm msa, dialects [73] 5400 tweets and emoji data msa, saudi dialect [74] 6000 tweets rule-based algorithm semantic and lexicons features msa, tunisian dialect hybridbased [75] merging of two available lexicons (mpqa and arabsenti) with manually collected lexica svm, libsvm stems, twitter language independent, semantic features egyptian dialects [53] 4800 tweets semantic orientation, svm, nb unigram, bi-gram, tri-gram egyptian dialect [30] lexicon of 5376 words rf, svm, max-ent, bagging, boosting, ann, dt, nb pos and lexicon features msa, dialect [31] 1500 tweets and lexicon of 452 words bagging and boosting msa, dialect [18] semeval2018 regression and classification tasks, cnn, lstm word embedding (aravec), document embedding (doc2vec) and a set of semantic features msa, egyptian and gulf dialects engineering, technology & applied science research vol. 13, no. 2, 2023, 10292-10300 10296 www.etasr.com alqurashi: arabic sentiment analysis for twitter data: a systematic literature review 3) the hybrid-based approach authors in [30, 31] worked on sa for arabic tweets using a hybrid approach. in [30], a combination of the lexicon and corpus techniques for asa was proposed. the authors used a lexicon to replace words in sentences with their sentiment labels to enable classifier algorithms to consider rare and important words in the corpus. they concluded that this hybrid approach outperformed the corpus-based approach, reaching an accuracy of 96.3%. the hybrid approach in [31] comprised machine learning algorithms, the bagging and boosting approaches. the authors started by building a unified dataset of text and audio which was later converted to text, to analyze sentiments. however, some of the audio analysis was not accurate, which had a negative effect on this prediction approach because some audios contained laughing and yelling. authors in [32] proposed an incremental learning system for sentiment classification. their system was able to update a lexicon with any upcoming changes. in fact, this system integrated the machine learning and lexicon approaches to improve the accuracy of the proposed system, and it has been tested with different datasets. b. tools used to collect arabic tweets as we only focus on the twitter platform, we found various techniques have been used to collect arabic tweets. most studies used twitter’s official application programming interface (api) to collect arabic tweets [2, 33-39]. other studies used trending hashtags to extract data manually [8, 40]. authors in [16] used keyhole and netlytic tools to collect their data from twitter. authors in [41] developed a python script connecting with twitter’s official api to collect their data. authors in [42] developed a twitter data grabber tool, a small desktop application using c# to connect to the twitter api to collect their data. authors in [10, 15] used a java library called twitter4j, which can be connected to the twitter api to collect twitter data. authors in [43] used a tool called archivist4 to collect tweets using hashtags. in fact, archivist4 can be used to archive and analyze visual tweets using hashtags, usernames, boolean, and complex search terms. c. data pre-processing data pre-processing is a technique used to prepare data for sentiment classification [78, 79]. the preparation involves cleaning, formatting and sorting the tweets that have been collected from twitter to be saved in a dataset ready for analysis [45]. data pre-processing for arabic tweets includes several steps to clean the data, such as tokenization, stop-word removal, text cleaning, part of speech (pos) tagging, normalization, and stemming. table iii shows the most commonly used methods for data pre-processing found in the papers we reviewed. we note that normalization, text cleaning and tokenization were the most frequently used techniques in these papers. these techniques are described below. table iii. data pre-processing methods used in the reviewed papers reference tokenization stop word removal text cleaning pos tagging normalization stemming [23] ∅ � � ∅ � � [10] � � ∅ ∅ ∅ � [51-53] ∅ � � ∅ � � [15] � � � ∅ ∅ � [44, 46] � � � ∅ � � [54] � ∅ ∅ ∅ � ∅ [55] � ∅ � ∅ � ∅ [56] � ∅ ∅ � � ∅ [42] � � ∅ ∅ � � [45] � ∅ � ∅ � � [57] � � � ∅ ∅ � [8] ∅ � � ∅ � ∅ [58] � � ∅ ∅ � ∅ [47, 59] � ∅ � � � ∅ [30] ∅ ∅ � ∅ � ∅ [60] ∅ � ∅ ∅ ∅ � [66] ∅ ∅ � ∅ � � [61] � ∅ � ∅ � ∅ [62] ∅ � � ∅ � � [32] � ∅ � ∅ � ∅ [63] ∅ ∅ ∅ ∅ � � [33] ∅ � � � � ∅  tokenization is the process of the segmentation of a stream of text to segments consisting of words or phrases. each segment is called a token and each token has a meaning and can be used for the later stages of sa [46].  stop-word removal involves removing words that have no meaning for polarity classification [42], such as ( من, على).  text clearing: arabic tweets may have inconsistent text and can be noisy or incomplete. therefore, data cleaning tends to remove noise, complete missing values, or correct inconsistent state data [33]. this also including removing arabic articles [8], such as (ال، بال، كال).  pos tagging involves mapping words to their tags, such as verbs, nouns and adjectives. there are different types of machine tools for pos tagging [47]. engineering, technology & applied science research vol. 13, no. 2, 2023, 10292-10300 10297 www.etasr.com alqurashi: arabic sentiment analysis for twitter data: a systematic literature review  normalization: most reviewed papers applied normalization to arabic tweets, which includes removing repetitive letters or normalizing similar letters to the same letter [42], such as the letters ( آأ ) which is normalized to (ا).  stemming is the process of transforming a word to its base forms, while the meaning of the words is preserved. for example, in arabic the word (يكتبون, يكاتبون) is replaced with as the arabic language has a complicated .(كتب) morphological structure, stemming is considered a very difficult task. our findings indicate that there are two popular steaming methods used in asa: light10 stemming [48] and khoja’s stemmer [49]. iv. challenges in arabic sentiment analysis the arabic language is one of the most widely spoken languages in the world. it is the most frequently spoken and written language in the arab world, especially in the middle east and north african regions [77]. the arabic language has 26 letters and is written from right to left. it uses diacritical marks that denote correct pronunciation of a word. in addition, diacritical marks are used to distinguish words that have the same letters but different meanings. moreover, the arabic language has three forms: classical arabic, which is seen in religious and very formal texts, modern standard arabic (msa), which is associated with modern news media [77], and dialect or informal arabic, which is the arabic spoken with different local accents across the middle east and north african countries, and has no particular standards [6]. according to [50], saudi twitter covers 90% of dialects, compared to msa. as a result, it is very challenging for researchers to construct models of arabic text classifiers to use for sa. in terms of translation, when translating arabic to english, good results may be obtained with msa, but arabic dialects are difficult to translate because their meaning is purely context-related [27]. v. conclusion and future work the twitter platform is considered a rich source for sentiment analysis. people use social media platforms to express their opinions of products, services, or political events. in this paper, we have provided a systematic review of arabic tweet sentiment analysis. we have reviewed the main techniques that can be used to prepare the data for sentiment analysis. moreover, we 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[80] i. a. kandhro, s. z. jumani, f. ali, z. u. shaikh, m. a. arain, and a. a. shaikh, "performance analysis of hyperparameters on a sentiment analysis model," engineering, technology & applied science research, vol. 10, no. 4, pp. 6016–6020, aug. 2020, https://doi.org/10.48084/ etasr.3549. microsoft word etasr_v13_n2_pp10395-10400 engineering, technology & applied science research vol. 13, no. 2, 2023, 10395-10400 10395 www.etasr.com albaker: reliability-based optimal integrated microgrid scheduling in distribution systems reliability-based optimal integrated microgrid scheduling in distribution systems abdullah albaker department of electrical engineering, college of engineering, university of ha’il, saudi arabia af.albaker@uoh.edu.sa (corresponding author) received: 28 january 2023 | revised: 8 february 2023 | accepted: 11 february 2023 abstract this paper proposes a reliability-based optimal scheduling model of integrated microgrids. the proposed model is capable of delivering optimal scheduling of each individual microgrid and aggregated system. in addition, it is compatible with both grid-connected and islanded operation modes. the developed problem formulation of the proposed model takes into account the reliability indices saidi, saifi, and caidi to evaluate the reliability of the integrated system. numerical simulations on a modified ieee-33 bus test system, involving four integrated microgrids, were performed to investigate the advantages and the robustness of the developed model. furthermore, the impact of merging battery energy storage systems (besss) on the optimization outcome is examined, which demonstrates its significant effectiveness in improving the power systems' reliability. keywords-distributed energy resource; grid-connected operation; integrated microgrids; islanded operation; optimal scheduling; reliability indices i. introduction continuously optimizing and developing distribution systems' reliability is significant in the power systems optimization segment. power outages may cause serious and massive difficulties for the end-users, such as the disruption of industrial, commercial, educational, and health systems [1-4]. the reliability of the distribution systems can be assessed and evaluated by reliability indices, including but not limited to, system average interruption duration index (saidi) to measure the aggregated duration of an interruption, customer average interruption duration index (caidi) to measure the average time of restoration, and system average interruption frequency index (saifi) to measure the average number of times customers experience outages during the study period [56]. consequently, several studies have been conducted toward improving and assessing distribution systems' reliability. authors in [7] investigated the impact of the integration of a large-scale solar photovoltaic (pv) system with wind turbines on the system reliability. an ieee-40 bus test system was utilized in the proposed study, and the zone branch methodology was performed to evaluate the system reliability. authors in [8] investigated the potential capability of the vehicle-to-grid with the grid-connected battery swapping station in improving the reliability of distribution networks by proposing a comprehensive methodological framework based on quantitative and latin hypercube sampling (lhs) methods. authors in [9] proposed an electric vehicle (ev) charging station placement strategy based on a voltage stability, reliability, and power loss (vrp) index for distribution networks considering the impact of the resulting fast ev charging station loads. in [10], a new approach based on a general probability formulation was developed to capture the availability of generation and transmission capacities and the randomness related to the load level. in addition, it was developed to calculate various quality measures and reliability indices. authors in [11] solved the reconfiguration problem of distribution systems to improve the reliability indices and minimize the total active power losses based on a proposed mixed integer second-order conic programming (misocp) model. microgrids, as an intelligent technique to integrate distributed energy resources (ders), can significantly improve the range-specific reliability of the system within the microgrid’s served area [12-15]. ders could include renewable units, dispatchable distributed generators (dgs), and battery energy storage systems (besss) [16-18]. microgrids support the islanding operation capability [19-21]. nevertheless, in some conditions, microgrids can provide ancillary services to other parts of the distribution network by supplying their excess generation back to the utility grid. the impact of the microgrids on the distribution networks' reliability is discussed in [22-24]. in [22], the impact of the microgrid control strategies during the islanded operation mode on distribution network reliability was investigated based on a probabilistic methodology and the use of the sequential monte carlo simulation. authors in [23] developed a probabilistic approach for the optimal operation of active distribution networks based on the multi-microgrid framework considering technical indices of the system such as the system reliability and efficiency, and solved the problem by the non-dominated engineering, technology & applied science research vol. 13, no. 2, 2023, 10395-10400 10396 www.etasr.com albaker: reliability-based optimal integrated microgrid scheduling in distribution systems genetic algorithm-ii. authors in [24] proposed an improved binary genetic algorithm approach to determine the optimal control and scheduling of ders in hybrid microgrids to reduce the negative impact of outages on customers and improve system reliability. nonetheless, the integrated operation of the microgrids opens the horizon to further advantages. enabling the local power exchange among the integrated system can significantly impact the microgrids’ total operation costs by permitting their excess generation to be sold during the islanded operation. in addition, it will positively impact the distribution networks’ reliability by supplying power to other parts with power deficiency. in this paper, the impact of the integrated microgrids on the power distribution networks’ reliability is investigated based on the developed model. the contributions of the developed model are summarized as follows: (i) it significantly minimizes, individualand integrated-base, microgrids’ total operation cost, (ii) it distinctly improves the overall reliability of the distribution network, (iii) it explicitly supports the optimal operation of bess in the integrated system, and (iv) it efficiently enables optimization during the islanded operation. ii. model outline the proposed reliability-based optimal integrated microgrid scheduling model ensures minimizing each individual microgrid’s operation cost and the aggregated total operation cost of the integrated system. in addition, it significantly expands the reliability of the distribution network including the integrated microgrids. in the grid-connected mode, each microgrid in the system optimally schedules the local dispatchable dgs and bess, and exchanges the power conventionally with the utility grid, i.e. imports power when needed and exports its excess generation, to increase its economic benefits from this process. on the other side, in the islanded mode, i.e. when the upstream grid faces interruptions or disturbances, all microgrids would be switched into the islanded operation mode. however, during the islanded mode, the integrated microgrids would exchange the power locally to support each other and to supply the other parts of the distribution network that are electrically connected to the microgrids. it is worth mentioning that the microgrids are typically connected to the other parts of the distribution network by the points of common coupling (pcc), as depicted in figure 1. the primary aim of this process is to minimize the amount of the load curtailments in the distribution network, i.e. to maximize the entire distribution system reliability, which will be evaluated by calculating the formulated reliability indices. nevertheless, the impact of exchanging the power locally calls attention to the total operation cost, which is predicted to be further minimized due to the export of further excess generation. one-hour time periods are considered over a 24-hour scheduling horizon when solving the given problem. in addition, 25 different operation scenarios were applied to investigate the robustness of the proposed model. shorter time periods could be deployed for more accurate results in order to follow fast changes in the proposed model without loss of generality. fig. 1. ieee-33 bus distribution test system involving four integrated microgrids. iii. problem formulation the objective of the reliability-based optimal integrated microgrid scheduling problem is to minimize the microgrids’ total operation cost and to improve the integrated system reliability, as in (1): min ∑ � � ∑ � � ∑ �∑ � � ��� ����� ����� � ��� ��� � � ∑ �,��� � ���� ���� � � ��� ���� � ��� �� � (1) the first term in the objective function refers to the microgrids’ dispatchable dgs, which includes the generation cost and the commitment status throughout the specified horizon. the second term refers to the cost of the power exchange with the utility, which could be a revenue once the power flow direction is from the microgrids to the utility, i.e. as it would be considered a negative cost. the third term represents the local power exchange among the integrated microgrids, i.e. it will be a cost for the buyer microgrid and a revenue for the seller microgrid. the fourth term represents the load curtailments, where it is multiplied by the value of lost load (voll). the last term is included as an auxiliary value of the reliability indices in the proposed model. these cost expressions are calculated based on investigated operation scenarios that define the operation mode, i.e. gridconnected or islanded. the operation modes are recognized in the objective and in the developed constraints by the scenario index s, where s = 0 refers to the grid-connected mode and other values of s refer to the islanded operation mode over the selected horizon. the proposed objective is subjected to a set of linearized power flow constraints [25], and the following operation constraints: the power balance constraint, dispatchable dgs constraints, bess constraints, and reliability indices constraints. ∑ ���� � � � ∑ ���� � ! � ��� � � ��� � � ���� " #�� ∀%, ∀&, ∀' (2) (��,max +� , ��� � , ��,max+� ∀%, ∀&, ∀' (3) engineering, technology & applied science research vol. 13, no. 2, 2023, 10395-10400 10397 www.etasr.com albaker: reliability-based optimal integrated microgrid scheduling in distribution systems (��,max�1 ( +� � , ��� � , ��,max�1 ( +� � ∀%, ∀&, ∀' (4) constraint (2) represents the integrated system power balance equation to guarantee that the total power generated and imported matches the local demand. however, it is worth mentioning that the non-dispatchable generations, such as pvs and wind turbines, have predicted values based on the units' characteristics and the historical data, hence, they are handled as constant negative loads in the problem formulation. in addition, it is noted that the load curtailment variable is included to the power balance constraint to achieve a feasible solution during the islanded operation. the power exchange of the integrated system with the utility grid is subjected to a maximum power exchange limitation, as in constraint (3), and is further imposed to zero (using a binary islanding indicator) once the system operates in the islanded mode. the local power exchange among the integrated microgrids is subjected to the line flow limits of (4). nevertheless, the binary islanding indicator is added to the constraint to impose the local power exchange to zero during the grid-connected mode due to the fact that each microgrid in the system prefers to export or import power with the utility when it would be more economically beneficial. for example, when the local hourly bid price is higher than the hourly market price, the microgrids with power deficiency would prefer to import power from the utility. on the other side, when the local hourly price is lower than the hourly market price, the microgrids with excess generation would prefer to export power to the utility. �� min���� , ���� , �� max���� ∀%, ∀. ∈ g, ∀&, ∀' (5) ���� ( �����12� , +3�� ∀%, ∀. ∈ g, ∀&, ∀' (6) �����12� ( ���� , #3�� ∀%, ∀. ∈ g, ∀&, ∀' (7) 4�� on , +4�� ����� ( �����12�� ∀%, ∀. ∈ g, ∀&, ' " 0 (8) 4�� off ≥ #4�� ������12� ( ����� ∀%, ∀. ∈ g, ∀&, ' " 0 (9) dispatchable dgs' optimal operation is subjected to the following constraints. the capacity limit of each dispatchable dg is subjected to minimum and maximum limitations, as in (5), and is further subjected to the commitment status using the binary variable. generated power by dispatchable dgs is also subjected to the ramp up and down rate limits, as in constraints (6) and (7). in addition, they are subjected to the minimum up and down time limits once they are switched on/off, as in constraints (8) and (9). dispatchable dgs could be also restricted by fuel and emission constraints, which are however neglected in this paper. ���� , ���� 9:;,max<��� ( ���� :;,min=��� ∀%, ∀. ∈ s, ∀&, ∀' (10) ���� ≥ ���� 9:;,min<��� ( ���� :;,max =��� ∀%, ∀. ∈ s, ∀&, ∀' (11) ?��� " ?����12� ( ���� <��� @ a�b ( ���� =��� @ ∀%, ∀. ∈ s, ∀&, ∀' (12) ?�� min , ?��� , ?�� max ∀%, ∀. ∈ s, ∀&, ∀' (13) 4�� :; , c?�� d<��� ( <�� ��12� e ∀%, ∀. ∈ s, ∀&, ' " 0 (14) 4�� 9:; ≥ c#�� d=��� ( =����12� e ∀%, ∀. ∈ s, ∀&, ' " 0 (15) <��� � =��� , 1 ∀%, ∀. ∈ s, ∀&, ' " 0 (16) bess is subjected to maximum and minimum charging and discharging limits, as in constraints (10) and (11). the stored energy in the bess is computed based on the charging and discharging processes over the specified horizon, considering the bess efficiency, as in constraint (12). the bess is further restricted by the minimum and maximum capacity limits, as in constraint (13). in addition, besss are restricted by minimum charging and discharging time limits, as in constraints (14) and (15). moreover, they are regulated by adding the binary variables u and v to ensure that they operate only in one mode (i.e. either charging or discharging), at each time-period, as in constraint (16). 0 , f.� , ���� g�⁄ ∀%, ∀&, ∀' (17) 0 , i.� , 60�1 ( +� � ∀%, ∀&, ∀' (18) saidi " ∑�i.�f.�� �� f4�⁄ ∀%, ∀&, ∀' (19) saifi " ∑ f.� �� f4�⁄ ∀%, ∀&, ∀' (20) caidi " ∑�i.�f.� � �� ∑ f.�⁄ ∀%, ∀&, ∀' (21) reliability indices are formulated in (17)-(21). the number of interrupted customers who have suffered from power outages for each sustained interruption event is computed by (17). the restoration time for each interruption event, once the outage occurs, is formulated by (18). the reliability indices saidi, saifi, and caidi are computed by (19), (20), and (21), respectively. the auxiliary binary variable  is added to provide value and significance of minimizing the reliability indices in the objective. iv. numerical simulations a modified ieee-33 bus test system was utilized to investigate the proposed reliability-based optimal integrated microgrid scheduling problem. the investigated test system involves four integrated microgrids, named mg 1 to 4, as demonstrated in figure 1. in addition, the test system involves 33 buses, 32 distribution lines, and 11 fixed loads [26]. the total number of served customers, in the proposed study is assumed to be 50,000. furthermore, based on the declared average annual electricity consumption per customer by the u.s. energy information administration for residential sector, i.e. 10,715kwh [27], the parameter w for the hourly average power consumption per customer is assumed to be 1.223kw. the microgrids’ hourly fixed load and the forecasted hourly market price for the 24-hour period can be found in [26]. in addition, it is assumed that the price of the power exchange among the integrated microgrids λ is higher than the forecasted market price by 10% in ($/kwh). engineering, technology & applied science research vol. 13, no. 2, 2023, 10395-10400 10398 www.etasr.com albaker: reliability-based optimal integrated microgrid scheduling in distribution systems the aggregated hourly forecasted fixed load for buses beyond the area covered by the microgrids is shown in table i. the characteristics of the microgrids’ dispatchable units are illustrated in table ii, which includes the cost coefficient ($/kwh) of all dispatchable dgs, the ramping rates (kw/h), the up/down time limits (h), and the minimum and maximum capacity limits of the dgs (kw). the impact of installing besss is considered, and the bess characteristics are shown in table iii. the bess efficiency  is assumed to be 90% [16]. it is worth mentioning that the proposed problem is solved for one complete operational day over a 24-hour horizon considering 25 islanded operation scenarios (i.e. one scenario presents the grid-connected operation, while the other scenarios present a power outage for every hour). moreover, a relatively small voll of $10/kwh is assumed [28], to specify the value of the undesired load curtailment. the proposed problem is programmed and solved in cplex 11.0 [29]. the following case studies are investigated: case 0: optimal individual scheduling without bess: in this case, the microgrids are optimally scheduled independently, i.e. there is no power exchange at all among the microgrids in the system, based on the islanded operation scenarios horizon and without installing besss. the optimal scheduling results of the microgrids ensure minimum operation cost and maximum reliability "locally", i.e. within the microgrids’ served area. however, the other parts of the distribution network would not gain any advantages from this process. the microgrids' total operation costs are computed as $176.72, $191.25, $543.96, and $641.86 for mg 1, mg 2, mg 3, and mg 4, respectively (table iv). three islanded operation scenarios are arbitrarily nominated to investigate the reliability of the entire distribution network, i.e. islanded hours 9, 16, and 17, by calculating the reliability indices. table v illustrates and summarizes the results of the reliability indices calculations in this case. the reliability indices saidi, saifi, and caidi are calculated as 3.78min, 0.03776, and 100.23min, respectively. case 1: optimal integrated microgrid scheduling without besss: in this case, the local power exchange among the integrated microgrids is activated by utilizing the distribution network’s lines. this case study investigates the impact of exploiting the unused capacity of the microgrids on the distribution system. enabling local power exchange could significantly impact the microgrids’ total operation costs and the overall reliability of the system. comparing the microgrids’ total operation costs in this case study with the obtained results in the base case, the microgrids’ total operation costs are computed as $71.56 (–59.51%), $133.76 (–30.06%), $499.04 (–8.26%), and $587.36 (–8.49%) for mg 1, mg 2, mg 3, and mg 4, respectively, as shown in table iv. furthermore, this pointedly influences the reliability of the distribution network by supplying the fixed load on buses beyond the microgrids' covered area in case of outages. the reliability indices saidi, saifi, and caidi in this case are calculated as 3.02 (–20.11%), 0.02992min (–20.76%), and 99.95min (–0.28%), respectively, as illustrated in table v. table i. fixed load on buses beyond the microgrids covered area fixed load over 24h time (h) 1 2 3 4 5 6 7 8 load (kw) 744 741 738 738 738 738 781 763 time (h) 9 10 11 12 13 14 15 16 load (kw) 761 763 773 773 775 773 773 773 time (h) 17 18 19 20 21 22 23 24 load (kw) 775 758 744 741 741 741 738 733 table ii. characteristics of microgrids’ dispatchable units dg mg 1 mg 2 mg 3 mg 4 price ($/kwh) dg 1 0.065 0.072 0.085 0.089 dg 2 0.039 0.064 0.065 0.069 dg 3 0.017 0.019 0.025 0.029 minimum – maximum capacity (kw) dg 1 20 – 100 14 – 70 20 – 100 30 – 150 dg 2 20 – 100 16 – 80 40 – 200 50 – 250 dg 3 40 – 200 30 – 150 80 – 400 60 – 300 minimum up/down time (h) dg 1 3 4 5 3 dg 2 3 4 4 3 dg 3 1 2 2 1 – ramp up/down rate (kw/h) dg 1 50 35 50 75 dg 2 50 40 100 125 dg 3 100 75 200 150 table iii. microgrids’ bess characteristics microgrid bess characteristics storage capacity (kwh) min.max. ch/dch power (kw) min. ch/dch time (h) mg 1 bess 100 4 – 20 5 mg 2 bess 50 2 – 10 4 mg 3 bess 60 8 – 20 4 mg 4 bess 120 16 – 40 5 table iv. summary of total operation cost microgrid total operation cost case 0 case 1 case 2 mg 1 $176.72 $71.56 (–59.51%) $41.39 (–76.58%) mg 2 $191.25 $133.76 (–30.06%) $118.75 (–37.91%) mg 3 $543.96 $499.04 (–8.26%) $489.77 (–9.96%) mg 4 $641.86 $587.36 (–8.49%) $561.45 (–12.53%) table v. summary of reliability indices calculations index reliability indices case 0 case 1 case 2 saidi (min) 3.78 3.02 2.66 saifi 0.03776 0.02992 0.02641 caidi (min) 100.23 99.95 99.31 case 2: optimal integrated scheduling considering the impact of besss: in this case, the impact of installing the besss on the optimization outcome is investigated. the microgrids’ total operation cost is computed as $41.39 (–76.58%), $118.75 (–37.91%), $489.77 (–9.96%), and $561.45 (–12.53%) for mg 1, mg 2, mg 3, and mg 4, respectively, as shown in table iv. the achieved results show further minimization in the microgrids’ total operation costs due to the exploitation of besss in storing energy during lower hourly market prices and exporting it back to the utility grid engineering, technology & applied science research vol. 13, no. 2, 2023, 10395-10400 10399 www.etasr.com albaker: reliability-based optimal integrated microgrid scheduling in distribution systems during higher price periods. the optimal scheduling of the power exchange between the microgrids and the upstream grid is illustrated in figure 2, while figure 3 demonstrates the bess optimal scheduling results. moreover, the examined distribution network’s reliability is obviously improved. the reliability indices saidi, saifi, and caidi are calculated as 2.66min (–29.63%), 0.02641 (–30.06%), and 99.31min (–0.92%), respectively, as illustrated in table v. accordingly, the integration of besss in power systems significantly expands the anticipated outcome and enhances the optimization results. fig. 2. optimal power exchange with the utility grid in case 2. fig. 3. optimal bess scheduling in case 2. v. discussion microgrids can promote the anticipated minimization of the total operation cost and maximize the local points of reliability. however, further benefits can be achieved once the microgrids are integrated with each other. this paper investigates the potential impact of the integrated system on the microgrids and on the entire distribution system by the proposed optimization model. in addition, it examines the optimal operation of besss and investigates their impact on the optimization results. moreover, the probability of the islanded operation of the integrated system is efficiently inspected in the proposed optimization model using the developed islanded operation scenarios. the proposed model is mathematically formulated as a mixed-integer linear programming (milp) problem and is solved using cplex. the key features of the proposed optimization model can be outlined as follows:  it significantly minimizes the total operation cost of each microgrid and of the whole integrated system.  it explicitly enhances and improves the integrated system's reliability.  it supports the optimal operation of besss.  it considers optimal islanded operation. nonetheless, the proposed model is generic, and larger test systems and additional reliability indices can be carried out without loss of generality. vi. conclusion an efficient reliability-based optimal scheduling model of integrated microgrids was developed in this paper. the proposed model was capable of optimally minimizing the microgrids’ total operation costs and significantly boosting the overall reliability of the integrated system including the microgrids and the other parts of the power distribution grid. in addition, it was capable of identifying the optimal scheduling of the integrated system during the islanded operation. numerical simulations on a modified ieee-33 bus test system were performed to investigate the merits and the effectiveness of the proposed model in improving the system's power distribution reliability. the reliability indices saidi, saifi, and caidi were calculated by the formulated problem in all the considered case studies. furthermore, the impact of installing battery energy storage systems (besss) was also studied and examined, and their significant weight, in minimizing the microgrids’ total operation costs and enhancing the overall reliability of the power distribution system, was emphasized. nomenclature indices: ch superscript for bess charging mode. dch superscript for bess discharging mode. i index for ders. m,n index for microgrids. s index for scenarios. t index for time. sets: dg set of dispatchable units. m set of microgrids. k set of islanded operation scenarios. s set of energy storage systems. t set of time periods. parameters: dr ramp down rate. dt minimum down time. f(.) generation cost of dispatchable units. mc minimum bess charging time. md minimum bess discharging time. nt total number of customers served for the area. ri restoration time for each interruption event. u islanding state (0 when islanded, 1 otherwise). ur ramp up rate. ut minimum up time. w average power consumption per customer.  forecasted market price.  price of local power exchange.  auxiliary value of reliability indices.  battery energy storage efficiency.  value of lost load. variables: c stored energy in battery energy storage systems. engineering, technology & applied science research vol. 13, no. 2, 2023, 10395-10400 10400 www.etasr.com albaker: reliability-based optimal integrated microgrid scheduling in distribution systems d forecasted load demand. i commitment state of dispatchable units. ls load curtailment during islanded operation. ni number of interrupted customers for each sustained interruption event. p der generated power. pg local power exchange among the microgrids. pm power exchange with utility grid. tch number of bess successive charging hours. tdch number of bess successive discharging hours. ton number of successive on hours. toff number of successive off hours.  auxiliary binary variable for reliability indices (1 during outage, 0 otherwise).  time period. u bess discharging state. v bess charging state. references [1] s. peyghami, p. palensky, and f. 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[29] "cplex," gams. https://www.gams.com/latest/docs/s_cplex.html. author profile abdullah albaker received his m.s. and ph.d. degrees in electrical engineering, specializing in electric power engineering, from the university of denver, denver, co, usa, in 2014 and 2018, respectively. he is currently an assistant professor of electrical engineering at the university of ha’il, ha’il, saudi arabia. his research interests include microgrid planning and operation, renewable energy and distributed generation, power system economics and reliability, smart electricity grids optimization, and machine learning. microsoft word etasr_v13_n3_pp10849-10855 engineering, technology & applied science research vol. 13, no. 3, 2023, 10849-10855 10849 www.etasr.com kausar et al.: sentiment classification based on machine learning approaches in amazon product … sentiment classification based on machine learning approaches in amazon product reviews mohammad abu kausar department of information systems, university of nizwa, oman kausar@unizwa.edu.om (corresponding author) sallam osman fageeri department of information systems, university of nizwa, oman sallam@unizwa.edu.om arockiasamy soosaimanickam department of information systems, university of nizwa, oman arockiasamy@unizwa.edu.om received: 15 march 2023 | revised: 14 april 2023 | accepted: 23 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5854 abstract online retailers and merchants increasingly request feedback from their clients on the products they purchase. this has led to a significant increase in the number of product reviews posted online, as more people are making purchases online. the opinions expressed in these customer reviews have a significant impact on other customers' purchase decisions, as they are influenced by other customers' recommendations or complaints. this study used amazon, a well-known and widely used e-commerce platform, to examine sentiment categorization using several machine learning techniques while analyzing an amazon reviews dataset. at first, the reviews were transformed into vector representations using the bag-of-words approach. word cloud was used to illustrate the text data in terms of the frequency they appear in the review. subsequently, the machine learning methods decision trees and logistic regression were used. the two models used in this study achieved high levels of accuracy in analyzing the dataset. specifically, the decision tree model outperformed the logistic regression one, achieving an impressive accuracy of 99% compared to the 94% of the latter. keywords-sentiment analysis; amazon customer reviews; dataset; feature extraction; text classification; machine learning i. introduction over the past decades online marketplaces have grown in popularity, leading to the trend of asking customers for feedback on purchased products to improve the overall customer experience. every day, millions of reviews about different goods, services, and locations are created online. as a result, the internet has become the key resource for knowledge and opinions regarding products and services. however, the vast amount of product reviews and the multiple perspectives to consider may further complicate the decision-making process, leading to confusion and uncertainty, as it is difficult for customers to choose wisely when there are several viewpoints on the same product and different ratings. therefore, e-commerce businesses should evaluate this content to get feedback on their products and help customers decide. sentiment analysis and classification is a field of computer science that attempts to answer this problem by sifting through given natural language texts to extract attitudes and views, using numerous approaches, such as biometrics, computational linguistics, natural language processing, and text analysis. due to their accuracy and effectiveness, machine learning (ml) approaches have lately grown in favor of the semantic and review analysis fields. this study considered amazon as one of the most popular e-commerce vendors. potential customers may read hundreds of reviews posted by previous customers regarding the products they're interested in [1-2]. these reviews provide valuable information on a product, helping shoppers understand most of its features. customers benefit from this, but it also helps retailers or producers to get a greater knowledge of customers' needs. this study used supervised algorithms to address the problem of sentiment classification for online reviews and engineering, technology & applied science research vol. 13, no. 3, 2023, 10849-10855 10850 www.etasr.com kausar et al.: sentiment classification based on machine learning approaches in amazon product … determine the overall significance of customer evaluations and characterize them as positive or negative. the data used were reviews of amazon titan men watches, collected from amazon.in. the study employed supervised algorithms to address the issue of sentiment classification for online reviews. the goal was to determine the overall importance of customer evaluations by categorizing them as either positive or negative. ii. related works many studies used data collected from numerous sources, such as twitter [3-4], product reviews, consumer feedback, etc. customer engagement programs help businesses to strengthen their emotional relationships with clients from all over the world. customer involvement is also influenced by product reviews [5]. the study of product reviews allows a company to learn how customers feel about its products. according to [6], online consumer reviews have an important influence in molding customers' online shopping decisions. the term "review" refers to the process of determining whether a product or service is suitable for a certain purpose. every day, a massive quantity of fresh information is added to the web [7], hence a method was proposed based on simultaneous web crawling using mobile agents. sentiment analysis is used by businesses to increase their competitiveness in the market, as it enables them to comprehend the opinions and experiences of their clients on their products and services [8]. sentiment analysis is also used to capture market sentiments to design a better forecasting model for the stock market [9]. modern organizations use sentiment analysis to improve their word-of-mouth marketing approach. competitive companies use text-mining tools to better understand client experiences and extract valuable information from social networking platforms, newspapers, and other sources. in [10], k-nearest neighbors (k-nn), decision trees (dt), and artificial neural network (ann) models were used to identify client behavior in the banking industry. as a result, a mix of sentiment analysis, text mining, and other methods is critical in ensuring that businesses understand and capitalize on online consumer evaluations. sentiment extraction is an excellent method of understanding customer assumptions online [11], as the data collected from internet platforms and product review sites allow businesses to improve their marketing methods. product reviews also influence client purchase decisions. competitive organizations, such as amazon, use such information to make decisions [12], and leading merchants in the united states rely on internet product reviews to improve their marketing efforts and company procedures [13]. for example, if a given product receives a large number of unfavorable reviews for its cost or quality, the company examines the problem and tries to address it as soon as possible. according to [6], most of the product evaluations on the internet are less polar and more positively balanced. also, the distribution of product reviews for similar items differs by platform [14]. the diversity of reviews is driven by several factors, including the rating system, the business strategy of the online platform, and the review frequency [6]. in [15], a web crawling model based on java aglets was presented. furthermore, it is important to mention that firms use sentiment analysis to improve company operations and client retention, as analyzing product evaluations allows a company to understand client experiences [16]. a client can leave a review to indicate whether he is happy or unhappy with a particular product or service. however, the majority of product reviews do not represent the level of client happiness. in [16], a study was conducted based on reviews on the internet to classify consumer happiness, according to auditory and language characteristics, into four classes: extremely positive, positive, neutral, or highly unfavorable. the findings of this study on the impact of review length on online sentiments were consistent with [17]. customers prefer to rely on comprehensive and insightful product reviews before making a final purchase [18]. as a result, companies must discover the true degree of customer satisfaction with their products and services in order to make an informed decision based on online product reviews. authors in [19] evaluated the way internet reviews influence amazon book sales. according to this study, customers view online reviews as a reliable source of information and prefer more accessible and detailed reviews. according to this study, internet reviews have a major impact on user experiences and product costs. these findings were in agreement with those of [20] on online reviews and feelings. the study also looked at the valence of internet reviews. in [19], the influence of online reviews on purchases was found to be contradictory. some studies concluded that the valance of online reviews has a major influence on sales, while others found that it has no impact. the impact is also affected by variables such as product categories and qualitative text qualities. in [21], an analysis was conducted on 142.8 million amazon user reviews, focusing on determining the usefulness and unhelpfulness of each review by examining the summary headline, the product remark, and helpfulness information, filtering out blank and non-english product evaluations to improve the accuracy of the results, and choosing only those with the most votes. the study concluded that an investigation of online product evaluations on amazon plays an important part in today's e-commerce. helpful reviews provide thorough information on specific products or services based on client feedback [22]. customers rely on reviews with the most votes to make a purchase decision. the results are congruent with the findings of [23] on how customer reviews impact internet purchases. positive product reviews enable clients to build greater trust in the things they want to buy online. sentiment analysis has gaps due to issues with the accuracy and reliability of the utilized methods, as well as the lack of standardization in sentiment interpretation and classification. more research is needed to optimize customer engagement programs and improve the understanding of customer sentiments. this study aims to address the potential gaps in the sentiment analysis based on machine learning approaches in amazon product reviews using decision trees and regression models. specifically, this study investigated the effectiveness of different customer engagement strategies in influencing customer sentiments and explored the impact of these strategies on sentiment classification accuracy. engineering, technology & applied science research vol. 13, no. 3, 2023, 10849-10855 10851 www.etasr.com kausar et al.: sentiment classification based on machine learning approaches in amazon product … iii. methodology sentiment analysis is considered a study of people's sentiments, feelings, and views as conveyed via writing, and is useful in understanding other peoples' points of view on any subject. opinions can be positive, negative, or neutral. the suggested method was based on an ml prediction model, to analyze both positive and negative reviews by binary classification. figure 1 shows the steps of this method, beginning with data collection and ending with the evaluation of each classification model. fig. 1. overall sentiment analysis approach for amazon reviews. a. programming environment python is one of the most used programming languages in data science and ml, as it offers a large library collection for solving various ml problems. python was chosen due to its extensive libraries and ease of use. scikit-learn is a python package that provides supervised ml algorithms [24], including many classification algorithms, such as svm and naive bayes, and feature extraction techniques. b. the dataset figure 2 presents an example of an amazon review to better grasp the dataset's structure and format. an amazon user review consists of the following four key components that assist in comprehending and analyzing the reviews:  summary: the title of the review.  review text: the review's actual content.  rating: the product's user rating on a scale of 1 to 5.  helpfulness: the percentage of persons who considered the review beneficial. fig. 2. actual amazon customer review sample. data collection was the initial stage of the study. raw data were obtained from the website amazon.in and converted to comma separated values (csv) format. the data set contained 4960 titan men watches reviews. c. data cleaning this is a critical stage in examining any type of data and has a significant influence on the success of ml models. there are numerous types of pre-processing procedures and the appropriate ways must be selected. this study employed four distinct data preparation steps in the reviews: 1. remove emojis. 2. remove html tags. 3. lowercase all letters. 4. filter numbers and special characters. 1) emoji removal although people use emojis to express their feelings, they were removed since they did not affect the identification of the polarity of the review. 2) html tag removal the html tags of the retrieved reviews were removed because they did not affect the determination of the polarity of the review. 3) converting all letters to lowercase in different reviews, there is a good chance that identical words will appear in different situations and the system will recognize them as distinct words. converting all letters to lowercase was used to avoid such problems. 4) filtering numbers and special characters all the unnecessary elements in determining the review's polarity were eliminated to make the data tidy and clean. the special letters and digits were eliminated. d. feature extraction ml algorithms interpret data in specified formats. the text data were turned into numerical feature vectors, a process known as vectorization. bag of words is one such approach that involves tokenization, normalization, and counting. this study used countvectorizer to represent words in terms of bag of words. countvectorizer requires specifying an n-gram range, which is a tuple consisting of the lowest and maximum length of the sequence of words to be regarded as features. engineering, technology & applied science research vol. 13, no. 3, 2023, 10849-10855 10852 www.etasr.com kausar et al.: sentiment classification based on machine learning approaches in amazon product … e. word cloud of reviews the word cloud is a method of displaying text data where each word's size corresponds to its frequency or importance. a word cloud can be used to highlight significant textual information, and they are widely used in social network data analysis. this study used word clouds to represent the most often-used terms in reviews. iv. exploratory data analysis exploratory data analysis (eda) is a method of displaying and evaluating data concealed in rows and columns, using several charts to provide maximum insight into the dataset. this study investigated the positive, negative, and neutral review categories of amazon reviews based on the sentiment score. figure 3 shows the amazon product review categories. this study scrapped 4960 reviews of a specific product and stored them, after cleaning, in a csv file. fig. 3. distribution of reviews' categories. the text data were presented graphically using python's word cloud package. figures 4-6 show the most common words used in reviews, as positive reviews, and as negative reviews, respectively. fig. 4. most common words used in the reviews. fig. 5. most common words used in positive reviews fig. 6. most common words in negative reviews. a. unigrams unigrams determine the frequency of single words in the reviews. figures 7-8 show the unigrams of the top 20 positive and negative reviews, respectively. b. bigrams unigrams do not offer a clear understanding of a consumer's intended message. bigrams can capture the meaning behind consecutive pairs of words in the reviews. combining two adjacent words into a single unit can offer valuable insight into the context and meaning of a text. bigrams show the frequency of two-word combinations in a text review. for instance, in the sentence "i love this product", the bigram "love this" would be generated, while "i hate this product" would produce the bigram "hate this". analyzing the most prevalent bigrams in a collection of reviews can help to understand what consumers are attempting to convey regarding their encounter with a product or service. engineering, technology & applied science research vol. 13, no. 3, 2023, 10849-10855 10853 www.etasr.com kausar et al.: sentiment classification based on machine learning approaches in amazon product … fig. 7. top 20 positive review unigram. fig. 8. top 20 negative review unigram. fig. 9. top 40 positive and negative review bigrams. engineering, technology & applied science research vol. 13, no. 3, 2023, 10849-10855 10854 www.etasr.com kausar et al.: sentiment classification based on machine learning approaches in amazon product … figure 9 shows the top 40 positive and negative review bigrams. the bar plot shows that the most common bigrams in positive reviews were "value for money", "lovely watch", "good product", etc. these bigrams suggest that customers were satisfied with the quality and value of the product they purchased. in contrast, the most commonly used bigrams in negative reviews were "media could", "could not", "titan watch", etc., implying that consumers experienced problems with the product, such as difficulty with media playback or loading times. overall, bigrams are a useful tool in natural language processing and sentiment analysis, providing valuable insight into the opinions and experiences of consumers. by identifying and analyzing the most common bigrams in a set of reviews, a better understanding of the strengths and weaknesses of a product or service can be gained. this information can then be used to make more informed decisions. v. results and analysis this study used python and jupyter, in conjunction with supporting libraries, to perform data purification, visualization, pre-processing, and ml modeling. supervised ml was used to create sentiment classification models, by building training and testing sets. a collection of features was then taken from the training and testing data and supplied into a classifier model, such as logistic regression (lr) and decision tree (dt). the complete review dataset was separated into two parts: 75% of the data was used to train the models, while 25% was used to assess their performance. the performance of the models was validated using accuracy and confusion matrix. a. accuracy (a) accuracy (a) is defined as the proportion of correctly predicted occurrences to the total number of occurrences by: a � tp � tn tp � tn � fp � fn where tp stands for true positive, tn for true negative, fp for false positive, and fn for false negative. table i shows the accuracy results of the models used in this study. table i. accuracy of models model accuracy logistic regression 94% decision tree 99% the results show that both logistic regression and decision tree were effective. however, the two models had different levels of accuracy, as dt achieved 99% outperforming lr, which achieved 94%, as shown in table i and figure 10. this could be attributed to dt's ability to handle complex decision-making processes that may not be captured by lr. the difference in accuracy between the two models is significant, and it may impact the model selection decision depending on the importance of the classification task. for example, in a high-stakes classification task, such as in medical diagnosis, the higher accuracy of dts could be crucial to make accurate and reliable predictions. fig. 10. accuracy comparison for the methods used. b. confusion matrix it is worth noting that the accuracy values reported are not the only performance metrics to consider when evaluating the models. other metrics such as precision, recall, and f1-score can provide a more nuanced view of the models' performance and should be considered alongside accuracy. they can be used to assess the performance of the categorization methods. these parameters are important for measuring the efficacy of supervised ml algorithms since they are based on the confusion matrix [25]. a confusion matrix is widely used to visualize an algorithm's performance. classification terms tp, tn, fn, and fp are used to compare class labels in this matrix, as shown in table ii and figure 11. based on the data of the confusion matrix, precision, recall, f-measure, and accuracy can be used to evaluate the performance of the classifier. table ii. confusion matrix p v predicted-negative predicted-positive a v actual negative tn fp actual positive fn tp fig. 11. the confusion matrix of the lr model. engineering, technology & applied science research vol. 13, no. 3, 2023, 10849-10855 10855 www.etasr.com kausar et al.: sentiment classification based on machine learning approaches in amazon product … vi. conclusion sentiment analysis is a necessary and popular technique for collecting information from text data on e-commerce websites. e-commerce platforms produce enormous volumes of text data every day in the form of suggestions, reviews, tweets, and comments. additionally, emoticons, ratings, and reviews all suggest people's opinions. a customer can learn more about a product and make an informed choice by extrapolating information from reviews. this study used multiclass and binary classification for amazon reviews of a product using supervised machine learning methods such as logistic regression and decision tree. logistic regression produced an excellent outcome with 94% accuracy and decision tree produced outstanding results with 99% accuracy. e-commerce websites should consider various feature extraction methods and machine learning techniques, examine additional product categories, analyze unstructured data, and incorporate sentiment 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[2] j. mcauley, "amazon product data," recommender systems and personalization datasets. https://cseweb.ucsd.edu/~jmcauley/datasets. html#amazon_reviews. [3] m. a. kausar, a. soosaimanicka, and m. nasar, "public sentiment analysis on twitter data during covid-19 outbreak," international journal of advanced computer science and applications, vol. 12, no. 2, 2021, https://doi.org/10.14569/ijacsa.2021.0120252. [4] m. mahyoob, j. algaraady, m. alrahiali, and a. alblwi, "sentiment analysis of public tweets towards the emergence of sars-cov-2 omicron variant: a social media analytics framework," engineering, technology & applied science research, vol. 12, no. 3, pp. 8525–8531, jun. 2022, https://doi.org/10.48084/etasr.4865. [5] n. nandal, r. tanwar, and j. pruthi, "machine learning based aspect level sentiment analysis for amazon products," spatial information research, vol. 28, no. 5, pp. 601–607, oct. 2020, https://doi.org/ 10.1007/s41324-020-00320-2. [6] v. schoenmueller, o. netzer, and f. stahl, "the polarity of online reviews: prevalence, drivers and implications," journal of marketing research, vol. 57, no. 5, pp. 853–877, oct. 2020, https://doi.org/ 10.1177/0022243720941832. [7] md. a. kausar, v. s. dhaka, and s. k. singh, "an effective parallel web crawler based on mobile agent and incremental crawling," journal of industrial and intelligent information, vol. 1, no. 2, pp. 86– 90, jun. 2013, https://doi.org/10.12720/jiii.1.2.86-90. [8] i. karamitsos, s. albarhami, and c. apostolopoulos, "tweet sentiment analysis (tsa) for cloud providers using classification algorithms and latent semantic analysis," journal of data analysis and information processing, vol. 7, no. 4, nov. 2019, art. no. 69212, https://doi.org/10.4236/jdaip.2019.74016. [9] u. p. gurav and s. kotrappa, "sentiment aware stock price forecasting using an sa-rnn-lbl learning model," engineering, technology & applied science research, vol. 10, no. 5, pp. 6356–6361, oct. 2020, https://doi.org/10.48084/etasr.3805. [10] a. rahman and m. n. a. khan, "a classification based model to assess customer behavior in banking sector," engineering, technology & applied science research, vol. 8, no. 3, pp. 2949–2953, jun. 2018, https://doi.org/10.48084/etasr.1917. [11] v. k. jain, s. kumar, and p. mahanti, "sentiment recognition in customer reviews using deep learning," international journal of enterprise information systems (ijeis), vol. 14, no. 2, pp. 77–86, apr. 2018, https://doi.org/10.4018/ijeis.2018040105. [12] j. lim, m. park, s. anitsal, m. m. anitsal, and i. anitsal, "retail customer sentiment analysis: customers’ reviews of top ten u.s. retailers’ performance," global journal of managment and marketing, vol. 3, no. 1, pp. 124–150, 2019. [13] r. s. jagdale, v. s. shirsat, and s. n. deshmukh, "sentiment analysis on product reviews using machine learning techniques," in cognitive informatics and soft computing, singapore, 2019, pp. 639–647, https://doi.org/10.1007/978-981-13-0617-4_61. [14] v. vyas and v. uma, "approaches to sentiment analysis on product reviews," in sentiment analysis and knowledge discovery in contemporary business, igi global, 2019, pp. 15–30. [15] md. a. kausar, v. s. dhaka, and s. k. singh, "web crawler based on mobile agent and java aglets," international journal of information technology and computer science, vol. 5, no. 10, pp. 85–91, sep. 2013, https://doi.org/10.5815/ijitcs.2013.10.09. [16] s. govindaraj and k. gopalakrishnan, "intensified sentiment analysis of customer product reviews using acoustic and textual features," etri journal, vol. 38, no. 3, pp. 494–501, 2016, https://doi.org/10.4218/etrij.16.0115.0684. 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[20] a. y. l. chong, b. li, e. w. t. ngai, e. ch’ng, and f. lee, "predicting online product sales via online reviews, sentiments, and promotion strategies: a big data architecture and neural network approach," international journal of operations & production management, vol. 36, no. 4, pp. 358–383, jan. 2016, https://doi.org/10.1108/ijopm-03-20150151. [21] j. du, j. rong, s. michalska, h. wang, and y. zhang, "feature selection for helpfulness prediction of online product reviews: an empirical study," plos one, vol. 14, no. 12, 2019, art. no. e0226902, https://doi.org/10.1371/journal.pone.0226902. [22] meenakshi, a. banerjee, n. intwala, and v. sawant, "sentiment analysis of amazon mobile reviews," in ict systems and sustainability, singapore, 2020, pp. 43–52, https://doi.org/10.1007/978981-15-0936-0_4. [23] k. q. anh, y. nagai, and l. m. nguyen, "extracting customer reviews from online shopping and its perspective on product design," vietnam journal of computer science, vol. 06, no. 01, pp. 43–56, feb. 2019, https://doi.org/10.1142/s2196888819500088. [24] f. pedregosa et al., "scikit-learn: machine learning in python," the journal of machine learning research, vol. 12, pp. 2825–2830, 2011. [25] a. tripathy, a. agrawal, and s. k. rath, "classification of sentiment reviews using n-gram machine learning approach," expert systems with applications, vol. 57, pp. 117–126, sep. 2016, https://doi.org/10.1016/ j.eswa.2016.03.028. microsoft word 6-643-ed.doc engineering, technology & applied science research vol. 6, no. 2, 2016, 952-955 952 www.etasr.com touileb et al.: effect of viscosity on the gta welds bead penetration in relation with surface… effect of viscosity on the gta welds bead penetration in relation with surface tension elements kamal touileb department of mechanical engineering prince sattam bin abdulaziz university al-kharj, saudi arabia touilebk@yahoo.com rachid djoudjou department of mechanical engineering prince sattam bin abdulaziz university al-kharj, saudi arabia djoudjour@yahoo.com abousoufiane ouis department of mechanical engineering prince sattam bin abdulaziz university al-kharj, saudi arabia absoufiane@hotmail.com abstract—the aim of this paper is to study the effect of the viscous dissipation on the surface tension and its role on the shape of weld pool. experiments were conducted on four different casts of ferritic stainless steel with different content in the sulfur and titanium. the results show in particular that the presence of titanium solid compounds affects the role of sulfur as surfactant element. titanium in the presence of carbon and oxygen, titanium forms solid compounds which affect the marangoni convection due to the sulfur element in the weld pool. the viscous dissipation due to these compounds alters the flow rate of the molten metal. we expect that the viscosity of metal liquid was altered by these solid compounds. the viscous dissipation due to these compounds contributes to heat the molten metal leading to larger weld bead. keywords-gta welding; marangoni; viscosity; ferritic stainless steel; solid compounds; hardness i. introduction gas tungsten arc welding (tig welding or gtaw) is the process of welding used extensively for the last several decades as one of the most commonly used joining techniques for various metallic structures including ships, airplanes, automobiles, bridges, pressure vessels, etc [1-9]. tig is a process in which the joining of metals is produced by heating therewith an arc between a tungsten (non-consumable) electrode and the workpiece. a shielding gas is also used. the weld bead is very sensitive to chemical composition of the base metal [1, 3-4, 6-7]. cast-to-cast variations in base material compositions lead to different weld shape [2, 6]. the theory based on marangoni convection attests that the active surface elements such as oxygen or sulfur in the molten pool change the fluid flow patterns by altering the surface tension gradient [5]. the surface tension temperature gradients of pure metal are invariably negative, the flow of the molten weld pool motion is directed from the center towards the edge; consequently the weld bead is wide and the deep is shallow [5, 7-9]. the presence of surface active elements such as sulfur or oxygen has a noticeable effect on the surface tension in the sense that the surface tension increases with temperature. moreover, the surface tension temperature gradient becomes positive, leading to a narrower and deeper weld shape. in the this paper, the effect of solid compounds on the weld shape is been investigated; the presence of solid compound alters the flow of molten metal in sense that it affects the role of the marangoni convection. the increase of viscosity increases the viscous stresses between layers of molten metal in weld pool. the micro-hardness value of the welded zone has been measured at the cross section to understand the changes in mechanical properties of the welded zone. scanning electron microscope (sem) analysis has been carried out on the top of weld zone to detect the main element present in the solid compounds. this study reveals that titanium, carbon and oxygen were the main elements in the solid film. ii. experimental procedure experiments were carried out on four different casts of ferritic stainless steel plates of 1.75 mm thick using gas tungsten arc welding (gtaw) with automatic welding speed equipment. welding parameters used in the present work are given in table i. chemical compositions of the four different casts are given in table ii. metallurgical characteristics of the welds were determined by metallographic analyses and microhardness measurements. all specimens were prepared by mechanical grinding and polishing, followed by etching in a solution of 2% nitric acid hno3. hardness profiles were plotted in the weld bead in two orthogonal directions, one being parallel to the plane of the plate and the other perpendicular to that plane and inside the fusion zone as shown in figure 1. table i. welding parameters parameters value welding current 100 a travel speed 50 cm/min gas flow rate 10 l/min shielding gas argon arc length 1 mm nozzle piece distance 1 mm engineering, technology & applied science research vol. 6, no. 2, 2016, 952-955 953 www.etasr.com touileb et al.: effect of viscosity on the gta welds bead penetration in relation with surface… table ii. chemical composition of the stainless steel samples samples elements elements a b c d c % 0.019 0.011 0.010 0.001 si % 0.32 0.29 0.37 0.30 s % 0.002 0.006 0.002 0 p % 0.017 0.019 0.024 0.018 mn % 0.43 0.46 0.43 0.424 cr % 17.40 17.72 17.76 17.60 ni % 0.15 0.28 0.22 0.130 mo % 0.022 0.024 0.23 0.010 ti % 0.618 0.567 0.469 0.110 n % 0.01 0.012 0.015 0.008 cu % 0.01 0.024 0.028 0.033 al % 0.025 0.014 0.026 0.022 sn % 0.012 <0.005 0.009 0 pb % 0.001 0.0005 0.001 0 the measures in the horizontal direction were performed at a distance of 0.075 mm of the surface and the 25 points have been measured with a range of 0.5 to 1mm between two successive points. in the vertical direction 7 measuring points have been performed with a range of 0.05 to 0.1mm between two successive points. all measures were performed under an indentation load of 200 g. a sem was used to determine the major elements in solid film. the measures were carried out at different points on the surface of weld bead as shown in figure 2. fig. 1. different points of micro-hardness measure in two orthogonal directions. fig. 2. points of measures on the top of weld bead. iii. results and discussion a. weld shape morphology the weld morphology is characterized by the penetration depth d and bead width w. table iii shows the geometric parameters of the ferrite stainless steel welds produced with different specimens. the welds exhibit a significant variation in weld depth and bead width. welds of specimen b, c and d created partial penetrated beads (figure 3a), while the weld with specimen a created a full penetrated weld bead (figure 3b). (a): partial penetrated weld bead (b) : full penetrated weld bead. fig. 3. weld bead morphology. table iii. geometric parameters of different casts a b c d wf (mm) 3.22 2.96 3.10 3.19 d (mm) full penetration 1.36 1.26 0.86 wb (mm) 1.77 although the weld beads of the four casts were obtained under the same conditions, different penetration depths were observed. the possible explanation of these results is associated with the presence of some elements in the weld pool. cast a presents the widest weld bead, the largest size of the weld shape geometry and is the richest cast on titanium. the formation of solid compounds increases the viscosity of the weld pool which leads to the increase of viscosity stresses between layers. consequently there is more heat and the weld is fully penetrated. cast d which is poor on titanium and without trace of sulfur presents the lowest penetration depth. cast d reacts as the pure metal with negative thermal gradient of surface tension. without presence of surface tension element the molten weld pool flows from the center point toward the edge and the shape is wider. this cast is poor on ti so the formation of solid compound is negligible and the effect of viscous stresses on marangoni convection is negligible too. cast c behaves like pure metal generating outward flow in the weld pool but the high level presence of titanium (0.469%) alters the marangoni convection. cast b which is the most rich on sulfur (0.006%) shows a deep penetration (comparatively to casts c and d). the presence of sulfur generates the inward molten flow. however, the high quantity of titanium leads to the formation of solid compounds which alter the marangoni convection, consequently the penetration is partial. b. effect of welding conditions on the formation of solid compound on surface of weld bead the tests were carried out on the cast a which is the richest one in titanium. the welding parameters (current intensity i and travel speed v) have been chosen accurately in order to avoid total penetration. identification of solid compounds nature has been carried out by varying the welding speed. in order to identify the nature of solid compounds, welding speed has been increased to permit the apparition of solid film on the weld bead surface. by moving with high speeds, the front arc welding is slightly deformed as shown in figure 4. therefore engineering, technology & applied science research vol. 6, no. 2, 2016, 952-955 954 www.etasr.com touileb et al.: effect of viscosity on the gta welds bead penetration in relation with surface… oxygen is drawn into the weld pool. the oxygen reacts with the elements present in the weld pool and forms solid compounds. fig. 4. deformation of the front arc welding by increasing welding speed. in table iv, y means appearance of solid compound and n means that solid compound is not visible at the surface. as shown in table iv, the solid compound appears with a welding current intensity of 100 a at a travel speed of 80 cm/min. using a current intensity of 150 a the solids compounds appears at 70 cm/min. high energy input due to high welding current intensity induces a fast formation of the solid film. table iv. parameters which permit the appearance of film on top of weld bead. travel speed welding current v=40 cm/min v=50 cm/min v=60 cm/min v=70 cm/min v=80 cm/min 100 n n n n y 130 n n n y y c. hardness measurement micro-hardness profiles obtained across parallel and vertical beads are respectively shown in figure 5 and figure 6. from these profiles it is observed that as the indentor traverses near the solid film, micro-hardness increases from 140 to 210 hv. these results confirm that this layer of solid compound contributes to the increase of hardness. the possible reason could be associated to the composition of this film which is probably rich on t, tio, tio2 and ti. d. sem analysis the measures were taken at points (1, 2, 3, and 4) as shown in figure 7. results presented in table v show that the bright layer (points 1and 3) is rich on titanium comparatively to points (2 and 4) far from layer appearing on the surface. this analysis confirms the above prediction and the layer is rich of titanium solid compound. fig. 5. vertical hardness measure from the bottom to the top of weld bead. fig. 6. longitudinally hardness measure at the top weld bead. fig. 7. points of measure on the top of weld bead. table v. sem analysis results on the surface of welding line.       elements region fe% cr% ti% mn% 1 80.67 17.70 1.03 0.6 2 80.56 17.91 0.84 0.67 3 80.51 17.86 1.03 0.59 4 80.37 17.91 0.92 079 iv. conclusion the basic conclusions are given below: • cast with no sulfur and low titanium content behaves like pure metal in the sense that the formation of solid compounds is negligible and the flow is principally generated by the marangoni convection. the flow circulation is oriented from the center to the edge of the weld pool leading to a wider and less deep weld bead. • cast with high level content of titanium and poor level of sulfur gives a full penetrated weld bead with large back width. in this case the formation of solid compound increases the viscosity of molten weld pool. as a result the friction between layers increases and generates more heat. engineering, technology & applied science research vol. 6, no. 2, 2016, 952-955 955 www.etasr.com touileb et al.: effect of viscosity on the gta welds bead penetration in relation with surface… • cast with high level of both titanium and sulfur gives a weld pool size in between of the above cases. the presence of solid compounds alters the effect of the inward convection flow due to the presence of sulfur. • the hardness has a higher value (about 210 hv) near the layer film solid and decreases to 140 hv far from this layer. • sem analysis reveals that the solid film is rich on titanium, oxygen and carbon. • the compounds are characterized by a very high dissociation temperature which exceeds the temperature in the weld pool. thus, they remain in the weld pool during the welding operation forming solid films. references [1] c. r. heiple, j. r. roper, “mechanism for minor element effect on gta fusion zone geometry", welding research, vol. 61, no. 4, pp. 97-102, 1982 [2] c. r. heiple, j. r. roper, “interaction between impurities and welding variables in determining gta weld shape", welding journal, vol. 65, no. 6, pp. 150-155, 1986 [3] s. marya, a. shahab, k. touileb, “effect of minor chemistry elements on pulsed gas tungsten arc weld profiles”, welding, joining, coating and surface modification in advanced materials (proc. pre-assem. symp. of 47th iiw ann. assem.), dalian, china, pp. 91-97, 1994 [4] s. marya, k. touileb, j. binard, “effect of minor chemistry variations on the laser melts profiles of two stainless steels", international conference on welding and melding by electron and laser beams, france, pp. 267-274, june 14-18, 1993 [5] k. touileb, j. m. a. dandachi, “modeling of arc welding in relation with surface tension, viscosity and lorentz electromagnetic forces", 2nd saudi technical conference and vocational training, pp. 26-30, kingdom of saudi arabia, 2002 [6] a. traidia, f. roger, j. schroeder, e. guyot, t. marlaud, “on the effects of gravity and sulfur content on the weld shape in horizontal narrow gap gtaw of stainless steels”, journal of materials processing technology, no. 7,no. 213, pp. 1128-1138, 2013 [7] o. savytsky, m. savytsky, d. bajić, y. shkrabalyur, “influence of the impurities on the depth of penetration with carbon steel welding”, metalurgija, vol. 53, no. 2, pp. 167-170, 2014 [8] k. s. prasad, c. s. rao, d. n. rao, “an investigation on weld quality characteristics of pulsed current micro, plasma arc welded austenitic stainless steels”, international journal of engineering, science and technology, vol. 4, no. 2, pp. 159-168, 2012 [9] d. li, s. lu, w. dong, d. li, y. li, “study of the law between the weld pool shape variations with the welding parameters under two tig processes”, journal of materials processing technology, vol. 212, no. 1, pp. 128– 136, 2012 microsoft word etasr_v13_n2_pp10608-10621 engineering, technology & applied science research vol. 13, no. 2, 2023, 10608-10621 10608 www.etasr.com kassem et al.: economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in … economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in northern cyprus: a case study youssef kassem department of mechanical engineering, engineering faculty, near east university, cyprus | energy, environment, and water research center, near east university, cyprus yousseuf.kassem@neu.edu.tr (corresponding author) huseyin gοkcekus department of civil engineering, civil and environmental engineering faculty, near east university, cyprus | energy, environment, and water research center, near east university, cyprus huseyin.gokcekus@neu.edu.tr osama abduljalil mohammad hamad biotechnology research center, libyan authority for scientific research, libya osamaabdli387@gmail.com faed mahmod buojaylah fayid department of botany, qubbah branch, university of derna, libya faed.mahmoud.fayid@gmail.com received: 1 february 2023 | revised: 22 february 2023 | accepted: 28 february 2023 abstract in this paper, an in-depth analysis of small-scale pv in northern cyprus is conducted for the first time at 37 locations in northern cyprus. no previous study has investigated the viability of off-grid pv systems with various sun-tracking systems in northern cyprus. in order to achieve this, nasa power data were used for the evaluation of the solar resource in the selected locations. the results showed that the selected locations are suitable for the installation of various scales of pv systems due to the high global horizontal solar radiation. the mathematical modeling method was utilized for the design and analysis of pv systems with various sun-tracking systems and for the assessment of their economic viability and feasibility. energy production, capacity factor, payback period, and cost of energy production were calculated. the results indicate that the proposed systems are very promising for all the selected locations. the pv projects with a 2-axis sun-tracking system produce a large amount of energy and have a low electricity cost. it was found that the electrical energy cost of the developed systems was within the range of 0.4851-0.6641tl/kwh. the payback periods varied from 4.57 years to 8.49 years, depending on the type of solar pv panel and suntracking system. this study provides some useful recommendations for decision-makers regarding the development and deployment of pv energy technology in the country in order to achieve sustainable development goals. keywords-northern cyprus; solar energy potential; off-grid; small-scale pv system; sun-tracking system; mathematical modeling method i. introduction population growth and the rising of people’s living standards have led to the growing global demand for energy, primarily electrical, from fossil fuels. it is known that environmental pollution impacts human health through the emissions of harmful gases caused by conventional energy generation from fossil fuels. thus, finding alternative energy sources to reduce fossil fuel consumption and environmental pollution is essential [1]. solar energy has been widely utilized globally to generate electricity and reduce harmful gas emissions. it is clean energy from an inexhaustible and engineering, technology & applied science research vol. 13, no. 2, 2023, 10608-10621 10609 www.etasr.com kassem et al.: economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in … environmentally friendly energy source. generally, solar photovoltaic (pv) panels produce electrical power directly from the sunlight. authors in [2] found that solar power will reduce gas emissions by about 69-100 million tons of co2, 6899 thousand tons of nox, and 126-184 thousand tons of so2 by 2030. authors in [3] reported that solar energy has a significant potential to meet the global electricity requirements in the future. authors in [4] found that solar energy technologies have a huge potential to mitigate climate change by reducing energyrelated emissions. the solar power system is most commonly used today due to improvements in the harvesting of solar energy [5], greater awareness about this energy [6], and low electricity cost compared to feed-in tariffs [7]. generally, pv power systems are classified into two types (on-grid and offgrid pv systems). they, especially small-scale pv systems, are an effective solution to generate electricity for urban and rural regions [8, 9]. globally, the share of pv generation capacity could be increased from 2% in 2017 with nearly 400gw installed to 10% in 2040 due to falling pv costs [10]. in northern cyprus, fossil fuels are the main source of electrical energy. the electrical energy is produced by steam power plants (teknecik steam unit no. 1 and teknecik steam unit no. 2), diesel electricity generating plants (kalecik diesel and teknecik diesel), and serhatköy pv plant [11]. according to cyprus turkish electricity authority (kib-tek), 44.17%, 26.53%, 11.67%, and 11.95% of electricity is generated by kalecik diesel, teknecik diesel, teknecik steam unit no. 1, and teknecik steam unit no. 2, respectively, whereas the rest of the energy is produced by serhatköy pv plant (0.1%) in 2021. the total electricity production increased from 1444.01gwh in 2015 to 1551.06gwh in 2019 with an average annual increase percentage of 7.41%. furthermore, the average annual increase is approximately 3.4% in terms of electricity consumption per capita. besides, the total installed capacity for these plants is 482.3mw according to kib-tek and northern cyprus renewable energy board (yek-kurulu). recently, northern cyprus has experienced outages with duration of more than one to two hours [12] due to the fast growth of population and constructions. according to t-vine [13], northern cyprus has suffered multiple blackouts due to outages at the power plants inability to produce sufficient electricity to cope with the excessive demands during the intense summer heat. in addition, approximately 30% of total energy consumption and 20% of electricity consumption are spent on residential and commercial buildings, respectively, according to kib-tek. table i lists the costs of electricity in northern cyprus according to kib-tek. kib-tek utilizes the net metering system for allowing end users to generate and export energy surplus to the utility grid. four new solar pv plants have been constructed and utilized at various locations in northern cyprus [14]. northern cyprus's climate is moderate and suitable for investing in solar energy, as there are 300 sunny days throughout the year. this increases the efficiency of relying on solar energy as an energy source. global horizontal irradiation (ghi) and direct normal irradiation (dni) values are within the range of 4.805.44kwh/m 2 /day and 4.89-6.15kwh/m 2 /day, respectively according to the solar atlas map. numerous studies have investigated the solar energy potential in various locations in northern cyprus as shown in table ii. based on the results of the previous studies, the following can be concluded: (1) solar energy is expected to contribute to electricity generation in northern cyprus in the future, (2) pv systems can be a good solution for reducing the fossil fuel consumption and co2 emissions in the island, (3) the use of solar power systems could help the island to become more independent from fossil fuels, and (4) pv systems have the ability to reduce the household electricity bills in northern cyprus. table i. energy costs in northern cyprus before march 2022 energy consumption based on time period cost 0.7:00-17:00 0.98 tl/kwh 17:00-22:00 1.29 tl/kwh 22:00-07:00 0.65 tl/kwh 22:00-00:00 (weekend) 0.98 tl/kwh presently energy consumption based on kw energy consumption cost 0-250 kw 0.98 tl/kwh 250-500kw 1.70 tl/kwh 501-750 kw 2 tl/kwh 751-1000kw 2.25 tl/kwh greater than 1000kw 3.3tl/kwh therefore, this paper represents a first effort to use a strategic perspective to explore how viable solar energy systems are in northern cyprus. the present study aims to investigate the techno-economic and environmental sustainability of rooftop pv systems and large-scale pv in various locations in northern cyprus. to achieve this, the solar radiation data are analyzed to classify the solar resource in the selected locations. moreover, the techno-economic viability of an off-grid pv system with different sun-tracking systems including fixed tilt and 2-axis systems is evaluated using the mathematical modeling approach. ii. materials and methods the proposed methodology aims to assess the solar energy potential in 37 locations in northern cyprus to identify suitable locations for future installations of solar pv systems. the economic viability of these pv systems is evaluated. figure 1 illustrates the methodology used in this study. a. study area this study aims to identify the best locations for installing solar pv power systems in northern cyprus. figure 2 shows the selected locations. table iii provides the names and geographical coordinates of the selected locations. due to the lack of actual weather data, satellite database helps in estimating the potential of wind and solar energy. it has led to the development of satellite-generated or interpolated synthetic meteorological data, which are available in grids with various spatiotemporal resolutions [39]. the gridded database nasa/power provides global coverage of complete weather data with a horizontal resolution of 1° of latitude and longitude [40] thus being a potential source for the study of the potentiality of renewable (wind and solar) energies [41, 42]. engineering, technology & applied science research vol. 13, no. 2, 2023, 10608-10621 10610 www.etasr.com kassem et al.: economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in … table ii. summary of previous studies focusing on solar energy potential in northern cyprus reference year description/aim remarks and key findings [15] 2011 investigation of the feasibility of a 1m grid-connected pv plant in 3 locations (lefkoşa, güzelyurt, dipkarpaz) in northern cyprus. the feasibility of the developed system increased when the 2-axis pv system was utilized. [16] 2012 assessment of the performance of parabolic trough (pt) and fresnel pv systems in northern cyprus. fresnel systems have higher absorption o solar radiation, lower co2 emissions, and operating cost compared to pt systems. [17] 2014 installation of 30mw hypothetical solar chimney power plant under northern cyprus conditions. the annual electricity production of the proposed system was found to be 94.5gwh, which can provide for the annual electricity needs of over 22,128 residences without any co2, nox, and sox emissions. [18, 19] 2015 build 1.275gw pv plant in serhatköy site. the plant will improve the electricity sector and will be able to reduce emissions to an acceptable level. [20] 2016 design and techno-economic analysis of a standalone pv system to meet the electricity of a house in the rural fringe of famagusta. the electricity generation cost was found to be 0.43tl/kwh and the developed system is a viable technology for the electrification of a house in cyprus. [21] 2016 techno-economic and environmental feasibility of 40mw pv power plant and 40mw pt power plant in nicosia and famagusta. power plants in nicosia have higher profitability than in famagusta and the utilizing solar power plant will reduce large amounts of co2 emissions. [22] 2017 development of a hybrid system to generate electricity for a household in nicosia the pv-wind hybrid system needs less capital cost, which is considered a more attractive option to set up in the selected location. [11] 2018 development of a 12mw grid-connected wind farms and fixed-tilt pv power plants in lefkoşa and girne. the selected locations were found suitable to build a pv system for energy production and reduce the fuel consumption [23] 2018 proposing a 1mw grid-connected pv power plant with various sun-tracking systems in lefke town. the electricity cost was found within the range of 0.109-0.150 $/kwh and annual ghg emission reduction varied from 1321 to 1829 tco2. [24] 2018 investigation of the utilization of solar energy in famagusta. famagusta has a huge solar energy potential, but the city is not able to generate the required amount of solar energy due to its inappropriate urban design. [25] 2018 finding the best location for installing a pv power plant based on the highest profitability of the project. among 19 locations, güzelyurt was the best to install a pv power plant due to the net present value, payback period and internal rate of return, and levelized cost of electricity. [26] 2018 proposal of a 4.85 kw grid-connected pv rooftop systems in nicosia, morphou, and dipkarpaz all selected locations have a high solar energy potential. [27] 2019 development of a 6.4kw grid-connected pv wind system for a household in lefkoşa, girne, and gazimağusa the pv systems are a more economical option for generating electricity in the selected locations compared to wind systems due to the low electricity production cost [28] 2019 proposition of a 45kw rooftop-building grid-connected pv power system in lefke town. the electricity cost of the proposed system was found to be 0.056$/kwh, which is lower than the energy cost of traditional energy (0.15$/kwh) [29] 2019 using of pv as a shading device for solving the heating problems in the residential sector in famagusta. utilizing the pv as a shading device can provide up to 50% of the electricity demand of the single-family building and raises the comfort level of the building by about 20%. [30] 2019 evaluation of the performance of a 110kw grid-connected pv system with different pv technologies based on performance ratio, cf, and energy cost. cdte pv system has a higher performance ratio compared to other pv technologies and the proposed system can help reduce green gas emissions and supply electricity to the near east university. [31] 2019 evaluation of the performance of a 110kw grid-connected pv system in 25 locations. the annual average performance ratio was within the range of 75-80%. [32] 2019 techno-economic feasibility evaluation of a solar-powered seawater desalination plant in güzelyurt. solar desalination could be a profitable investment with governmental incentives and can be considered a sustainable option for solving water scarcity and reducing greenhouse gas emissions. [33] 2019 technical, environmental, and economic aspects for developing pv/wind hybrid system in the middle east technical university northern cyprus campus the proposed system will reduce the annual fuel consumption of the island by 9920 barrels which will also reduce the annual co2 emissions by 3622 tons. [34] 2020 development of a 30kw grid-connected pv system for near east university grand library with various types of pv systems used in building pv technologies. the performance of a freestanding mounting position system with thin film (cdte) was found better than building-integrated pv. [35] 2020 techno-economic feasibility of 100mw grid-connected pv system in lefkoşa. the proposed system would reduce fuel consumption, electricity tariffs, and greenhouse gas emissions. [36] 2020 development of a 6kw pv-wind hybrid system to meet a single household electricity demands in güzelyurt. the proposed system provided alternative incentives to the consumers and it is economically feasible. [37] 2021 investigation of the techno-economic feasibility of smallscale pv systems with different sun-tracking systems for producing household electricity and desalination systems in the güzelyurt region. the small-scale grid-connected pv systems will reduce the electricity bill. [14] 2021 design of a pv system for covering the power demands in near east university hospital the pv system will help solve the electricity crisis and reduce the fossil fuel consumption. [38] 2021 evaluation of the techno-economic feasibility of a pvbattery system for a house in güzelyurt. the electricity generation cost is less than the grid tariff rate. engineering, technology & applied science research vol. 13, no. 2, 2023, 10608-10621 10611 www.etasr.com kassem et al.: economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in … table iii. summary of previous studies focusing on solar energy potential in northern cyprus location no. name elevation [m] latitude [°n] longitude [°e] optimum orientation angles fixed-tilt vertical inclined slope angle [°] azimuth angle [°] slope angle [°] slope angle [°] 1 akdeniz 89 35.300 32.965 31.0 2.0 52.0 34.0 2 camlibel 277 35.316 33.071 31.0 3.0 52.0 33.0 3 lapta 168 35.336 33.163 29.0 -5.0 51.0 31.0 4 girne 10 35.342 33.331 31.0 -1.0 52.0 33.0 5 beylerbeyi 225 35.297 33.354 28.0 -22.0 46.0 29.0 6 bogaz 300 35.288 33.285 31.0 0.0 52.0 34.0 7 tatlisu 168 35.225 33.451 32.0 -3.0 52.0 34.0 8 kantara 480 35.401 33.914 31.0 -4.0 51.0 33.0 9 esentepe 183 35.333 33.579 31.0 0.0 52.0 33.0 10 guzelyurt 52 35.189 32.982 31.0 0.0 52.0 34.0 11 gaziveren 19 35.173 32.922 31.0 0.0 52.0 34.0 12 lefke 129 35.097 32.841 30.0 -8.0 52.0 32.0 13 yesilirmak 20 35.166 32.737 30.0 -2.0 52.0 33.0 14 ercan 119 35.159 33.502 32.0 -4.0 52.0 34.0 15 serdarli 111 35.252 33.610 32.0 -5.0 52.0 34.0 16 degirmenlik 168 35.253 33.472 31.0 -1.0 51.0 33.0 17 gecitkale 45 35.233 33.729 32.0 -2.0 52.0 34.0 18 gonendere 75 35.270 33.657 32.0 -3.0 52.0 34.0 19 vadili 54 35.139 33.652 32.0 -2.0 52.0 34.0 20 beyarmudu 87 35.047 33.696 31.0 0.0 52.0 34.0 21 cayirova 67 35.349 34.031 31.0 2.0 52.0 34.0 22 iskele 39 35.286 33.884 31.0 0.0 52.0 34.0 23 mehmetcik 99 35.422 34.078 31.0 2.0 52.0 34.0 24 gazimagusa 10 35.136 33.936 31.0 2.0 52.0 34.0 25 salamis 6 35.181 33.897 31.0 1.0 52.0 34.0 26 alevkaya 623 35.286 33.535 31.0 2.0 51.0 33.0 27 zumrutkoy 129 35.174 33.049 31.0 0.0 52.0 34.0 28 alaykoy 166 35.185 33.257 32.0 -2.0 53.0 34.0 29 lefkosa 134 35.196 33.352 32.0 -3.0 52.0 34.0 30 ziyamet 82 35.454 34.125 30.0 3.0 51.0 33.0 31 dipkarpaz 136 35.599 34.379 31.0 5.0 51.0 33.0 32 yenierenkoy 123 35.536 34.189 31.0 5.0 52.0 33.0 33 dortyol 54 35.179 33.759 32.0 -1.0 52.0 34.0 34 kalecik 7 35.334 33.981 29.0 49.0 55.0 36.0 35 sınırüstü 28 35.276 33.856 34.0 49.0 55.0 36.0 36 sadrazamköy 68 35.383 32.949 32.0 51.0 54.0 35.0 37 selvilitepe 879 35.321 33.158 27.0 49.0 54.0 35.0 fig. 1. flowchart of the proposed methodology. engineering, technology & applied science research vol. 13, no. 2, 2023, 10608-10621 10612 www.etasr.com kassem et al.: economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in … fig. 2. the selected locations. b. classification of solar potential the potential of solar energy is divided into two classifications, namely geographical potential and technical potential [43]. in general, the annual amounts of total solar radiation at a specific location, factoring in existing geographical, social, environmental, and cultural constraints, are the factors that define the geographical potential. at the same time, the technical potential of a specific location is defined as the amount of geographical potential that can be translated into electricity using a pv [43]. according to [44], the solar energy potential was classified based on the annual value of ghi and dni. in general, global solar radiation is considered applicable for the evaluation of the energy generation for the flat pv system. table iv shows the classification of solar energy. table iv. classification of solar energy class annual ghi [kwh/m 2 ] annual dni [kwh/m 2 ] 1 (poor) <1191.8 <936.9 2 (marginal) 1191.8-1419.7 936.9-1255.7 3 (fair) 1419.7-1641.8 1255.7-1546.8 4 (good) 1641.8-1843.8 1546.8-1840.9 5 (excellent) 1843.8-2035.9 1840.9-2149.9 6 (outstanding) 2035.9-2221.8 2149.9-2533.7 7 (superb) >2221.8 >2533.7 table v. definition of the frequency distribution type according to the range of the skewness and kurtosis values distribution type number distribution curve skewness range kurtosis range i normal -0.4 < s < 0.4 -0.8<k< 0.8 ii almost normal with positive tail s≥0.4 -0.8<k< 0.8 iii narrow peak with positive tail s≥0.4 k≤-0.8 k≥0.8 iv almost normal with a negative tail s≤-0.4 -0.8<k< 0.8 v narrow peak with negative tail s≤-0.4 k≥0.8 vi bimodal, symmetrical with a flat peak -0.4 < s < 0.4 k≤-0.8 c. statistical analysis different distribution functions have been utilized to study the characteristics of solar radiation. for example, authors in [11] utilized normal, logistic, nakagami, and rician distribution models to analyze the characteristics of global solar radiation in urban regions in northern cyprus. authors in [45] determined the best probability distribution (gamma, generalized extreme value, weibull, extreme value, logistic, normal, and lognormal) for analyzing the global solar radiation of ibadan, nigeria. authors in [46, 47] defined the frequency distribution type as a function of the range of the skewness and kurtosis values of solar radiation at two locations in cyprus. in this study, the best frequency distribution type for modeling the monthly solar radiation is selected based on the range value of skewness and kurtosis as shown in table v. d. off-grid photovoltaic system the off-grid solar pv system is a common configuration. this system requires a battery for storing the remaining produced energy. therefore, evaluating the daily electrical load and daily solar energy are important parameters for performing the optimal modeling of the pv array. the peak power of pv (��� ) is the first parameter that should be estimated. according to [48], pv power array (������) depends upon solar radiation and it can be expressed as: ������ = ���� ��� × ���� × �������� (1) where ���� ��� is the nominal power of the panel under standard test conditions (stc), ���� is the derating factor of the solar pv panel due to shade, dirt, temperature, and so on, �� ��� is the hourly/daily/monthly global solar radiation at the surface of the solar pv panel in kwh/m 2 and �� is the standard incident radiation (1 kw/m 2 ). additionally, ������ depends on absorption capacity, panel area, and cell temperature [49]: ������ = �������� × ���� ��� × ��� × �1 − �� � ! − !,#�! $% (2) where ��� is the percentage of the power reduction factor of the pv panels, ! ,#�! is cell the temperature under stc, �� is the pv temperature coefficient, and ! is the cell temperature under operating conditions: ! = ������&'' × �()* − 20� + ./ (3) where noct is the normal operation cell temperature and ./ is the ambient temperature. furthermore, the ������ can be expressed as [50]: p����� = �� ��� × 1�2 3 4� × 4�56 × �4��� × �576� � ×(81 − �� − 1� × 9�� : (4) where 1�2 3 4� is the net surface area of pv modules, 4�56 is the fraction of the surface area with active solar cells, �4��� is the module conversion efficiency, which can be determined from the manufacturers' specifications, �576� � is the inverter conversion efficiency, ( is the quantity of the pv modules, � is the time expressed in years (� ≥ 1), and 9�� is the degradation rate of the pv system. the power output of the pv array can be estimated by [17]: engineering, technology & applied science research vol. 13, no. 2, 2023, 10608-10621 10613 www.etasr.com kassem et al.: economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in … ������ = 1�2 3 4� × ��� × �576� � × ���� × 8<� + =� + >�: (5) where � �3 is the referenced efficiency of the pv panels, < �3 is the temperature coefficient of the pv panel, �?@!� is the incident solar radiation for the noct test, is the ambient temperature, �3 is the reference temperature of the pv panels, ?@!� is the nominal operating cell temperature at test conditions, ,?@!� is the ambient noct, <� , =� , and >� are the hourly beam, reflected and diffuse component of the solar radiation on a tilted surface, and ��� is the efficiency of the solar panels provided by: ��� = � �3 a1 − < �3 b − �3 + � ?@!� − ,?@!� $ �c�defcgh (6) ������ is considered the first parameter that needs to be estimated. it can be expressed as [51]: ������ = i jkf����lmnompqrmst �5 ��� (7) where ��� is the pv modules efficiency, �576 is the inverter efficiency; 4 is the temperature coefficient, and �u is the battery efficiency. moreover, designing a battery system is required due to the limitation of daily hours of sunshine and the stochastic nature of solar energy and to support electricity generation sustainability and energy storage [52]. consequently, the number of autonomy dat (( v ), the battery efficiency (�u ), the inverter efficiency (�576 ), the depth of discharge (>v�v ), and the size of the electrical load (wx! ) should be considered for designing the battery system. equation (18) is used to determine the battery storage capacity (bsc) in wh [51]: <y* = jkf?z[\[][mpqrms (8) furthermore, the number of autonomy hours (( ^) can be determined by [53]: ( ^ = _smpqr`�am[`lb\[][jkf (9) where �v�4^ is the battery storage system discharging efficiency (%), >v�v is the battery storage system depth of discharge, cu is the voltage of the battery block, and du is the battery storage system's nominal capacity in kwh provided by: du = ?zbjkfmpqrm[`lb\[][ (10) additionally, a charge controller (cc) has been designed to support the battery of the off-grid system. the cc should be designed with at least 25% more of the ������ current to permit cold temperatures [20]. the cc is equipped with a maximum power point tracker (mppt) that is required to charge and protect the batteries avoiding both the risk of overcharging and reaching excessive discharge level [20]. the main function of cc is to support electrical load power consumption and promote the battery's lifespan [54]. as mentioned above, an inverter is a component of the system. the capacity of the inverter should be higher than p����� by 20% in order to be able to handle the maximum power of electric loads [55]. e. off-grid photovoltaic system in the literature, several methods and software simulations have been utilized for the evaluation of the life cycle cost of standalone and hybrid pv systems [17, 20, 51, 55-59]. for instance, authors in [17] developed an economic model to evaluate the cost-benefit of an off-grid pv system in rural gusau, nigeria. author in [20] used mathematical modeling to assess the techno-economic feasibility of an off-grid pv system to electrify a house in the rural fringe of famagusta, cyprus. authors in [51] examined the feasibility of an off-grid pv system to drive the electricity consumption of a residential building in jos, nigeria using mathematical modeling. authors in [58] used homer software to evaluate the feasibility of wind–pv–diesel hybrid power systems for a village in saudi arabia. authors in [57] investigated the economic viability of a hybrid system that can be used to supply electricity to a rural community in sri lanka using homer. authors in [58] evaluated the performance of residential solar pv systems with utility backup in nagpur, india using mathematical modeling and software simulation. authors in [55] utilized mathematical modeling to evaluate the feasibility of an off-grid pv system for the electrification of a single residential household in faisalabad, pakistan. authors in [59] investigated the technoeconomic feasibility of a stand-alone solar pv system for an isolated locality in bangladesh using spreadsheet modeling. the mathematical equations that are used in the current study to evaluate the life cycle analysis, which covers all the pv system life stages including the initial capital cost or acquisition cost and the operation and maintenance costs, are expressed below. cost of a pv array (*�� ) in us$: *�� = ������ × unit price of pv module (11) initial cost of batteries (icb) in us$: �*< = bsc × unit price of battery (12) present worth of the battery for various battery lifespans ((): �*< = *< × i yz5yzvt ? (13) where { is the inflation rate, 9 is the discount rate, and *< is the cost of the battery in us$. cost of an inverter system (*576 ) in us$: *576 = ������ × unit price of inverter (14) cost of a charge controller (*!! ) in us$: *!! = size of charge controller × unit cost of charge controller (15) cost of a pv installation (*��� ) is us$: engineering, technology & applied science research vol. 13, no. 2, 2023, 10608-10621 10614 www.etasr.com kassem et al.: economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in … *��� = 10% × initial cost of pv (16) maintenance cost (*. ): *. = 2% × initial cost of pv (17) furthermore, the present worth (pw) of the *. is estimated by considering the depreciation rate, the inflation rate, and the pv system life span. ��*. = i��7�^�� t × i yz5yzvt × �y�i ��p��[t d y�i ��p��[t � (18) where 9 is the depreciation rate percentage. levelized cost (�**) in us$: �** = *�� + cb + *576 + *!! + *. + *��� (19) annualized life cycle cost (1�**): 1�** = �** � y�i ��p��[ty�i ��p��[t?� (20) unit electricity cost (�j! ) in us$/kwh: �j! = x�!!���×jkf (21) annual savings (as) in us$: 1y = annual energy generation × feedin tariff rate for solar power purchase (22) payback period (pp): �� = ������� ����������x# (23) f. solar panel and inverter a large number of pv modules with different specifications are available on the market. mono-crystalline pv modules have the highest efficiency compared to poly-crystalline cells and amorphous silicon modules [54]. furthermore, cell type, system cost, warranty, size, and power are important factors to select the best pv panel [60]. therefore, a selection criterion is needed to select a specified pv module to be used in a specific project. a survey of the characteristics of most of the available pv modules from different manufacturers and technologies is done (table vi). based on the previous studies, several panel selection (ps) criteria are used to select the suitable pv module: �y =  ¡ �¢£¤�� ¥�¦�¥��§×¨¢£¤�� �©©�¥���¥§ �¢£¤�� ¦ª�¥� שª��� �ª�� ¢© �¢£¤�� (24) �y =  ¡ �¢£¤�� ¥�¦�¥��§ «ª��� �ª�� ¢© �¢£¤�� (25) �y =  ¡ �¢£¤�� ¥�¦�¥��§ �¢£¤�� ¦ª�¥� שª��� �ª�� ¢© �¢£¤�� (26) �y = ¬¢�� ¢© y­®  ¡ �§���� ¯��ª°§ ¦ª¢£¤¥��¢� ¢© y ­®  ¡ �§���� (27) based on the calculations (figure 3), uz158mhc340-60, ae410hm6-72, and ns-290p6 solar modules offer a better ratio compared to other models. it should be noted that these models have been selected based on the selection criteria among the pv modules surveyed. table vi. characteristics of most available pv modules module no manufacturer module type maximum power [w] efficiency module area [m2] module price [$] 1 jinko jkm330m-60-v 330 19.78 1.668 115 2 solar fabrik 340 20.14 1.687 237 3 panasonic 325 19.4 1.674 257 4 ankara solar as-m60-310w 310 19 1.63 77 5 axitec ac-430mh/144v 430 19.33 2.174 120.4 6 suntech stp325-24/ vfw 335 17.2 1.944 81 7 sunlink 435 20 2.1073 105 8 ae solar ae410hm6-72 410 20.69 1.674 115 9 tide solar 450 20.4 2.208 90 10 regitec solar rmh60/380s1 380 20.9 1.853 110 11 austa energy au410-27v-mhb 410 20.97 1.955 99 12 horay solar hs166-380-120m 380 20.5 1.823 84 13 münchen energieprodukte gmbh 440 19.9 2.209 110 14 fortunes solar fds-m6m-60-355bk 355 19.26 1.868 82 15 sunket skt375m6-20/hc 375 20.1 1.868 90 16 smart solar system hcm60x9-345w 345 20.4 1.689 72.75 17 mysolar ms400pm5-66sa 400 21.3 1.876 83.51 18 ae solar ae m6-60 320w 320 19.27 1.661 62.42 19 uzinsemi uz158mhc340-60 340 20.1 1.695 57 20 betop (eu) tech gmbh sr-325-340-120m 340 20 1.6873 64.89 21 exiom solution ex340m-120 340 20.1 1.692 70.98 22 energypal asp345p6-72 345 17.8 1.94 64.02 23 betop (eu) tech gmbh ns-290p6 290 17.8 1.626 47.24 24 ankara solar as-p60-290w 290 17.83 1.63 30 25 ankara solar as-p72-345w 345 17.78 1.94 35 26 ankara solar as-b60 -320w 320 21 1.61 47 27 canadian solar mono-si cs6x-300m 300 15.63 1.919 249 28 canadian solar poly-si cs6x-310p 310 16.16 1.918 248 engineering, technology & applied science research vol. 13, no. 2, 2023, 10608-10621 10615 www.etasr.com kassem et al.: economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in … fig. 3. ps criteria and efficiency of the surveyed pv modules. furthermore, output ac power, dc-ac conversion efficiency, and capital cost of the inverter are the main factors to select a suitable inverter. as mentioned above, this study aims to design a small-scale on-grid and off-grid pv system, thus, a hybrid inverter, the combination of an on-grid and offgrid solar inverter, is selected in this study. iii. results and discussion mathematical modeling methods and retscreen expert software were utilized to evaluate the viability of small-scale rooftop and large-scale pv systems in different locations in northern cyprus. a. solar irradiation characteristics analysis in this section, the ghi data were analyzed. ghi is an essential parameter to analyze the solar resource at the project location to evaluate power generation for flat-panel pvs [51, 61]. the statistical description of ghi for the period of 20052020 is listed in table vii. the description includes the mean, standard deviation (sd), coefficient of variation (cv), minimum (min.), maximum (max.), kurtosis (k), and skewness (s). it can be seen that the mean monthly value of ghi is within the range of 142.0-162.3kwh/m 2 . the maximum and minimum values of mean ghi are recorded in ercan and beylerbeyi, respectively. the cv values are moderately low, ranging from 36.6% to 47.53%. additionally, all s values are negative, indicating that all distributions are left skewed. the k values varied from -1.7 to -1.68. moreover, type vi, which is bimodal, and symmetrical with a flat peak, characterizes the mean monthly ghi. figure 4 illustrates the annual value of ghi for all selected locations. it is seen that the annual ghi values varied from 1704.07 (beylerbeyi) to 1948.00 (ercan) kwh/m 2 , respectively. furthermore, the solar resources at project locations are categorized as good, excellent, outstanding, and superb as shown in table viii. based on the value of ghi, it is observed that the solar resource of all selected locations expect beylerbeyi is categorized as class 5 (excellent). it is concluded that the selected locations are suitable for the installation of largeor small-scale pv systems due to the values of ghi and dni. accordingly, all selected areas are suitable for the installation of pv/flat panels and csp systems. fig. 4. annual value of ghi for all selected locations. fig. 5. sun's path over a year for some selected locations. engineering, technology & applied science research vol. 13, no. 2, 2023, 10608-10621 10616 www.etasr.com kassem et al.: economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in … table vii. statistical estimators of the monthly ghi in kwh/m2 for the 2005-2020 period location mean sd cv min. max. s k distribution type akdeniz 159.5 61.1 38.3 75.4 238.2 -0.11 -1.68 bimodal, symmetrical with a flat peak camlibel 159.9 61.1 38.23 75.8 238.7 -0.11 -1.68 bimodal, symmetrical with a flat peak lapta 155.4 65.7 42.29 63.6 238.2 -0.15 -1.69 bimodal, symmetrical with a flat peak girne 160 61 38.1 76.1 238.5 -0.11 -1.68 bimodal, symmetrical with a flat peak beylerbeyi 142 67.5 47.53 51.5 227.8 -0.09 -1.7 bimodal, symmetrical with a flat peak bogaz 159.9 60.5 37.84 76.4 237 -0.12 -1.69 bimodal, symmetrical with a flat peak tatlisu 162 60.5 37.33 78.2 239.2 -0.12 -1.68 bimodal, symmetrical with a flat peak kantara 156.5 57.2 36.55 76.1 227.7 -0.16 -1.69 bimodal, symmetrical with a flat peak esentepe 160.5 60.8 37.87 76.2 238.6 -0.11 -1.68 bimodal, symmetrical with a flat peak guzelyurt 160.8 60.8 37.79 77.3 239.2 -0.11 -1.68 bimodal, symmetrical with a flat peak gaziveren 160.8 60.8 37.81 77.3 239.4 -0.1 -1.68 bimodal, symmetrical with a flat peak lefke 160.4 60.3 37.61 77.3 237.2 -0.12 -1.69 bimodal, symmetrical with a flat peak yesilirmak 159.7 60.1 37.66 76.8 236 -0.12 -1.69 bimodal, symmetrical with a flat peak ercan 162.3 60.2 37.11 78.4 238.8 -0.13 -1.68 bimodal, symmetrical with a flat peak serdarli 160 60.6 37.86 76.2 237.3 -0.12 -1.69 bimodal, symmetrical with a flat peak degirmenlik 159.7 60.7 37.99 75.8 237 -0.12 -1.69 bimodal, symmetrical with a flat peak gecitkale 162.2 60.3 37.17 78.1 238.7 -0.13 -1.68 bimodal, symmetrical with a flat peak gonendere 160.4 60.7 37.86 76.2 238.3 -0.11 -1.68 bimodal, symmetrical with a flat peak vadili 162.3 60.2 37.13 78.2 238.7 -0.13 -1.68 bimodal, symmetrical with a flat peak beyarmudu 162.2 60.2 37.13 78.2 238.6 -0.13 -1.68 bimodal, symmetrical with a flat peak cayirova 159.2 60.2 37.81 75.6 235.7 -0.12 -1.68 bimodal, symmetrical with a flat peak iskele 160.3 60.6 37.78 76.2 237.8 -0.12 -1.68 bimodal, symmetrical with a flat peak mehmetcik 159.2 60.2 37.82 75.6 235.7 -0.12 -1.68 bimodal, symmetrical with a flat peak gazimagusa 161.8 60 37.1 77.8 237.5 -0.13 -1.68 bimodal, symmetrical with a flat peak salamis 161.8 60 37.1 77.8 237.5 -0.13 -1.68 bimodal, symmetrical with a flat peak alevkaya 160.5 60.8 37.88 76.3 238.6 -0.11 -1.68 bimodal, symmetrical with a flat peak zumrutkoy 161.2 60.7 37.66 77.7 239.3 -0.11 -1.68 bimodal, symmetrical with a flat peak alaykoy 160.5 60.8 37.88 76.3 238.6 -0.11 -1.68 bimodal, symmetrical with a flat peak lefkosa 162.1 60.4 37.28 78.6 239.3 -0.12 -1.68 bimodal, symmetrical with a flat peak ziyamet 159 60.2 37.85 75.5 235.2 -0.12 -1.69 bimodal, symmetrical with a flat peak dipkarpaz 158 60 38 74.2 232.9 -0.13 -1.69 bimodal, symmetrical with a flat peak yenierenkoy 157.8 60.4 38.29 74 234.6 -0.12 -1.68 bimodal, symmetrical with a flat peak dortyol 161.9 60 37.09 77.9 237.5 -0.13 -1.68 bimodal, symmetrical with a flat peak kalecik 160.3 60.6 37.8 76.1 237.7 -0.12 -1.68 bimodal, symmetrical with a flat peak sınırüstü 160.3 60.6 37.78 76.2 237.8 -0.12 -1.68 bimodal, symmetrical with a flat peak sadrazamköy 159.5 61.1 38.33 75.4 238.3 -0.11 -1.68 bimodal, symmetrical with a flat peak selvilitepe 155.5 59 37.96 74.9 230.4 -0.11 -1.74 bimodal, symmetrical with a flat peak table viii. solar energy classification for all locations based on the annual ghi in kwh/m2. location ghi class location ghi class akdeniz 1914.023 5 beyarmudu 1946.873 5 camlibel 1918.425 5 cayirova 1910.374 5 lapta 1865.277 5 iskele 1923.826 5 girne 1920.575 5 mehmetcik 1910.203 5 beylerbeyi 1704.069 4 gazimagusa 1941.646 5 bogaz 1919.021 5 salamis 1941.734 5 tatlisu 1944.539 5 alevkaya 1925.431 5 kantara 1877.795 5 zumrutkoy 1933.877 5 esentepe 1925.804 5 alaykoy 1925.431 5 guzelyurt 1929.479 5 lefkosa 1945.419 5 gaziveren 1929.953 5 ziyamet 1908.114 5 lefke 1925.094 5 dipkarpaz 1896.059 5 yesilirmak 1916.061 5 yenierenkoy 1893.448 5 ercan 1948.001 5 dortyol 1942.426 5 serdarli 1920.338 5 kalecik 1923.242 5 degirmenlik 1916.306 5 sınırüstü 1923.958 5 gecitkale 1946.526 5 sadrazamköy 1913.993 5 gonendere 1924.809 5 selvilitepe 1866.323 5 vadili 1947.005 5 the sun's direction for one year is illustrated in figure 5 for some selected locations. the gray fills represent the terrain horizon, while the unit horizon (represented by blue fill) may have a shading effect on solar radiation. the black dots represent true solar time, while the blue markers indicate the local hourly time. a gray line is used in the illustration to depict three paths of the sun in three curves. the sun's lowest gray path is at the winter solstice, the mean curvature at the equinox, and the upper curvature at the summer solstice. the curves of the sun show that in winter, the sun has a low horizon and in summer, the sun has a high horizon. b. electric energy production and capacity factor of 6.5kw off-grid pv systems in this study, the pv system is designed according to the minimum value of ghi to satisfy the occupants' electricity demands for the whole year for the selected household. based on the previous section, the maximum pv power is estimated to be 14.783kwh based on the minimum value of ghi on the horizontal surface for beylerbeyi. according to the renewable energy board (yek-kurulu), the customers can install 5kw single-phase grid-connected and up to 8kw three-phase gridconnected pv systems. consequently, the capacity of the developed system is assumed to be 6.5kw. accordingly, the economic viability of off-grid pv systems with various sunengineering, technology & applied science research vol. 13, no. 2, 2023, 10608-10621 10617 www.etasr.com kassem et al.: economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in … tracking systems is discussed in this section. based on the selection criteria, uz158mhc340-60, ae410hm6-72, and ns-290p6 with 340w, 410w, and 290w peak capacity are selected in this study. in the following sections, the results obtained from the mathematical model are summarized. the performance of the pv systems in terms of pv output and capacity factor (cf) is dependent on the orientation angles [14]. thus, the electric energy production (eep) and cf were estimated for the different sun-tracking systems. it should be noted that eep and cf for the fixed-tilted, vertical axis and inclined system are determined at the optimum orientations angles. the mean annual values of eep for all selected locations are shown in figure 6. it is found that the maximum and minimum values of eep are recorded in sadrazamköy and beylerbeyi, respectively. it should be noted that the monthly (mpvp) and annual (apvp) pv energy production can be determined by (28) and (29), respectively. as an example, the annual pv electrical energy production for beylerbeyi and sadrazamköy is shown in figure 7. ±�c� = ��� × 1�� × ±²³�ℎµ¶ �·� (28) 1�c� = ∑ ��� × 1�� × ±²³�ℎµ¶ �·�y¹5ºy (29) fig. 6. annual eep value of all selected locations. among the pv models, the results indicate that the highest monthly/annual eep is achieved when ns-290p6 is used, as shown in figure 7. besides, the solar tracking system can increase the annual energy production up to 20% and 40% using single-axis and 2-axis systems, respectively according to [62, 63]. it can be noticed that the amount of output power increases when the sun-tracking system is used. these results are supported by the findings in [54, 64]. as mentioned above, cf is an important parameter to evaluate the performance of pv systems. figure 8 illustrates the annual value of cf for all selected locations. it is found that the cf values range from 22.43 to 39.77%. the highest average annual value of cf was recorded in sadrazamköy while the lowest value was obtained in beylerbeyi for a 2-axis pv system and a fixed-tilted pv system, respectively. other researchers who analyzed the performance of off-grid pv systems in terms of cf can support these observations. authors in [65] found that the annual value of cf for the solar off-grid system is 24.6%. authors in [66] found that the cf values of off-grid pv/hydrogen fuel cells are within the range of 16.4– 31.2%. moreover, authors in [67] found that the value of cf lies in the range of 16.2-30.3%. based on these findings, it can be concluded that the value gained during the current study for each location is consistent with the accepted values. thus, it is technically sustainable to install off-grid pv systems at all the selected locations in northern cyprus. fig. 7. monthly pv energy production using uz158mhc340-60 for beylerbeyi and sadrazamköy with various sun-tracking systems. c. economic viability of 6.5kw off-grid pv systems the performance of the proposed systems is evaluated by estimating the economic factors of each system. in this study, the value of 4 is assumed to be 80% due to a 15–20% loss in efficiency as a result of increasing cell temperature to around 60℃ [20]. moreover, the efficiency of the selected battery is 85% and the efficiency of the pv panels is listed in table vi. fig. 8. annual cf value of all selected locations. additionally, the required bsc is determined based on the assumption value of the ( v as 2 days and maximum >v�v as engineering, technology & applied science research vol. 13, no. 2, 2023, 10608-10621 10618 www.etasr.com kassem et al.: economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in … 80%. moreover, trojan sagm batteries were utilized in this study (nominal voltage = 12v, round trip efficiency = 85%, throughput = 2285.1kwh, capital cost = 538 usd, replacement cost = 500usd, and operating and maintenance cost = 8 usd/year). fig. 9. unit electricity cost for all the proposed pv systems (the prices are estimated based on the us dollar exchange rate during the wrtiting of the paper). generally, assessing the economic viability of the proposed system is important. based on the mathematical modeling method, the costs of pv modules, inverter, battery, charge controller, installation, and operation and maintenance were calculated. further, the lcc, alcc, pp, and �j! are mathematically estimated for various pv technologies and suntracking systems. it should be noted that the initial investment, battery replacement, and operation and maintenance of the system are determined using current market prices. additionally, the financial parameters inflation rate and discount rate are 8% and 6%, respectively. the total life cycle cost (lcc) of the proposed pv systems including the initial investment cost, the present value of battery replacement cost, and the present value of operation and maintenance cost was estimated. it was found that lcc values are within the range of 286903.39-656408.00 usd. moreover, figure 9 illustrates the value of pp and �j! for all selected locations. it was found that the �j! values varied from 0.4851tl/kwh to 0.6641tl/kwh. the lowest �j! value of 0.4851tl was obtained from the proposed system with a 2-axis system. these values are compared with the current electricity prices in northern cyprus (see table i) and [20]. authors in [20] estimated �j! to 0.43tl/kwh. therefore, it is clear that the price of the electricity generating by pv systems is less than that of a conventional system. it can be concluded that the developed systems provide a significant insight into the economic feasibility of the project for all locations. moreover, the pp for the off-grid pv systems with various sun-tracking systems and pv technologies is determined. it should be noted that the feed-in tariff rate varied from one country to another. for example, the value of the feed-in tariff during the first year after the system installation in iran is 0.247$/kw for a pv system with a capacity smaller than 20kw [68]. according to [69, 70], the feed-in tariff for pv systems in turkey is 13.3 $ cents/kwh, for an application period of 10 years. in this study, the feed-in tariff rate for solar power purchase is assumed to be 0.133 usd/kwh. it is observed that pp values varied from 4.57 to 8.49 years, depending on the type of the panel and the sun-tracking system, as shown in figure 10. fig. 10. payback period of all the proposed pv systems. engineering, technology & applied science research vol. 13, no. 2, 2023, 10608-10621 10619 www.etasr.com kassem et al.: economic viability of a 6.5kw off-grid solar pv with various sun-tracking systems in … iv. conclusions the current study is one of the first attempts to assess the techno-economic validity of using an off-grid pv system with various sun-tracking modes in northern cyprus. to fulfill this objective, nasa power data were used to categorize the solar resource in the selected locations. additionally, the mathematical modeling method was used to estimate the energy production, capacity factor, payback period, and the cost of energy production of the proposed systems. the main results of the current study are:  ercan is the most suitable location for the installation of various sizes of pv systems.  the conducted analysis showed that the development of the proposed 6.5kw off-gird pv power system is very promising in all the selected locations.  an economic comparison between different tracking modes revealed that the use of a 2-axis tracking system is the most economical option for all locations.  the electricity price of the developed systems was found within the range of 0.4851-0.6641tl/kwh for off-grid pv systems. these values were compared with the current electricity prices in northern cyprus and previous scientific studies regarding northern cyprus (0.43tl/kwh [20], 0.286-0.826tl/kwh [27], 1.376tl/kwh [35], 1.6172.217tl/kwh [23], and 1.711-1.788tl/kwh [38]). the results demonstrated that the technical and economic viability of the proposed systems for power production can serve as a model for the successful development of real applications of the systems. further, the model can encourage the stakeholders in the renewable sector to provide support mechanisms for the adoption of pv systems in residential buildings. references [1] e. a. al-ammar, n. h. malik, 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engineering research, civil engineering department, ziane achour university of djelfa, algeria guettalasalim@yahoo.fr hicham charrak laboratory of risam, civil engineering department, abou bekr belkaid university of tlemcen, algeria c.hicham1988@gmail.com tounsia boudina civil engineering department, university of bejaia, algeria boudina_tounsia@yahoo.fr received: 20 january 2023 | revised: 29 january 2023 | accepted: 31 january 2023 abstract earth dams remain the most used means of water mobilization in algeria, due to their lower cost compared to concrete gravity dams and their capacity to resist better to seismic excitations. a study of the hydraulic structure was carried out in this paper, according to simple rules and empirical approaches. during the last decade, several high earth dams have suffered significant failures of the upstream or downstream slopes at the end of construction, after the initial impoundment, and under seismic loads. to prevent this occurrence or to minimize the damage in these hydraulic structures, a reexamination of the earth dams' behavior using more elaborate calculation methods is necessary. the purpose of the current study is to numerically model the behavior and analyze the stability of earth dams in terms of displacements at the end of construction, after the initial impoundment, during an earthquake, and compare these displacements with those measured in situ. a case study was conducted for the taksebt tizi ouzou dam by using the plaxis 2d calculation code and the finite element method. the comparison of the obtained results shows a close concordance with the monitoring results of the dam carried out by various specialized organizations. keywords-earth dam; failure; stability; slope; earthquake; finite element modeling; plaxis engineering, technology & applied science research vol. 13, no. 2, 2023, 10384-10388 10385 www.etasr.com allout et al.: a comparative study of the dam stability at various stages using numerical modeling … i. introduction homogeneous or zoned earth dams are important constructions commonly used in algeria [1, 2]. these structures are subjected to displacements during construction, at the initial impoundment, and throughout the years of exploitation. their safety requires monitoring of their behavior in order to prevent hazards susceptible to happen. the in-situ monitoring from geotechnical and geodetic measuring devices is doubtless the most used and most reliable means nowadays [3, 4]. however, this technique is not sufficient and cannot escape some difficulties of interpretation of some local aspects inside the dam body, which can neither be measured nor interpreted from in-situ measurements [5, 6]. one of the possibilities to improve the knowledge on the behavior of earth dams is to generate information from an analysis of the phenomena that intervene inside the dam and its different boundaries [7]. in this concept, numerical modeling and simulation form an essential tool, which allows the prediction of the response and the behavior of the dam with respect to various loading cases [8, 9]. the finite element method is widely used in the modeling and simulation of complex physical phenomena. it is very well suitable for the modeling of earth dams by considering loading conditions, complex boundaries, irregular geometries, and material characteristics. it enables simulation of their behavior using various behavior laws, resulting in a more realistic imaging [10, 11]. based on these considerations, it can be concluded that the measurements provided by geotechnical and geodesic methods and the results obtained by fem can only be complementary [12]. the prediction of the dynamic response of an earth dam to seismic loads is an important issue in the safety assessment of these structures in seismic zones. the failure of a dam or a dike, when it occurs, usually has heavy consequences, either in terms of cost or in terms of human lives [8, 9, 13]. numerical modeling is one of the most complex applications in the study of zoned earth dams. this study involves different numerical models, associated to each load case and submersion level. it requires the recognition of the various geotechnical characteristics, the variation of which is depending on the considered zone state (dry or submerged) and on the behavioral models to be retained. the purpose of this paper is to present a methodology for modeling a zoned earth dam to simulate its behavior in terms of displacement for stability verification using fem through plaxis software and compare these displacements with those measured in situ [14]. the taksebt zoned earth dam is considered as the case study. the calculation of the displacements of the dam is carried out in three steps: after the completion of its construction, during its initial impoundment, and during an earthquake. ii. materials and methods the taksebt dam is located on the oued aissi, main stream of the oued sebaou [15], 10km southeast of the tizi-ouzou city and at 100km from the algeria capital. this dam is an embankment made of silty-gravelly alluvium with a core of degraded clay, its crest level is 171.5m, and its height from the valley bed is 76m. the regular annual volume of sand is 180×10 6 m 3 with a total capacity of 175×10 6 m 3 and a watershed of 448km 2 . the dam is mainly made of several materials placed in layers 0.3m thick and its foundation is mostly composed of weathered shale. the physical and mechanical characteristics of the materials used are presented in table i. sealing is provided by a centered clay core 53m in width at the base and 8.6m in width at the top [15]. the analysis of the static behavior of the dam is carried out by the finite element method with plaxis using triangular elements with two degrees of freedom per node, i.e. the displacements ux along x and uy along y. the transversal profile of the considered dam has an asymmetrical trapezoidal shape and it will be modeled by a 2d plane geometric model. the reference model is realized by triangular elements with 15 nodes, in a total of 926 elements and 7589 nodes. we adjusted the fineness of the mesh (global coarseness), as shown in figure 2. the mohr-coulomb model was used on all layers of the dam to calculate displacements and safety factors at the end of construction and during reservoir filling [10, 16]. table i. materials of taksebt dam and its foundation material type saturated unit weight (kn/m 3 ) cohesion (kn/m 2 ) friction angle (°) modulus of elasticity (kn/m 2 ) permeability (m/s) clay core 19.7 10 15 15000 10 -8 u/s d/s rockfill 23.1 2 30 90000 10 -5 filter 21.2 2 32 120000 10 -5 drain 21.8 2 28 30000 10 -3 riprap 22.5 2 40 190000 10 -3 upstream cofferdam 22.3 5 35 190000 10 -2 alluvium 21.5 2 38 30000 10 -5 weathered shale 21.8 20 28 300000 10 -8 the settlements at the end of the construction of the hydraulic structure may vary significantly from one structure to another [11]. they depend, among other factors, on the compressibility of the materials used, the height of the structure and the level of compaction. the settlements related to the filling may reach up to 1 to 2% of the height of hydraulic structure for central core dams. these settlements are typically more favored when the height of the hydraulic structure is high and the rockfill has low compressive strength. in general, for earth dams with a central core, there is an acceleration of the settlement of the structure crest due to the pressure exerted by the water [13]. to study the seismic response of the dam, the system was applied to the accelerations of the boumerdes earthquake on may 21st 2003, as shown in figure 2 recorded at station no. 2 of the keddara dam (the east west e.w. component), the velocity of the recorded peak is estimated at engineering, technology & applied science research vol. 13, no. 2, 2023, 10384-10388 10386 www.etasr.com allout et al.: a comparative study of the dam stability at various stages using numerical modeling … 0.10m/sec, the acceleration at peak is 0.338g. the viscous damping ratio was equal to � �5%. the values of rayleigh coefficients were �� �0.19 and �� � 0.012 and the values of the integration parameters are taken as � � 0.5 and � � 0.25 with ∆� � 0.005 time step [17]. fig. 1. finite element mesh of the taksebt dam with its materials. fig. 2. recording of the e.w. component of the boumerdes earthquake (may 21st, 2003. acceleration). iii. results and discussion a. displacements at the end of the construction of the dam figures 3 and 4 show the vertical and horizontal displacements at the end of the dam construction. the maximum obtained displacements show the cumulative displacement during the construction phases. the maximum horizontal displacement is equal to 0.43m and the maximum vertical displacement is equal to 0.58m which means a settlement that represents 0.76% of the dam height. the maximum settlement calculated is 0.68m at the bottom upstream side of the dam, representing 0.89% of the dam height. it is inferior to 2% of the dam height, which is in accordance with the expected behavior of a rockfill dam with a clay core during the filling operation. fig. 3. vertical deformations at the end of the construction. fig. 4. horizontal deformations at the end of the construction. b. settlements after the intial impoundment figures 5 and 6 show the vertical and horizontal displacements of the dam body for the normal reservoir level of 165m. fig. 5. vertical deformations for the normal reservoir level of 165m. mat erials legend clay core u/s d/s rockfill filt er drain riprap upst ream cofferdam alluvium weat hered shale engineering, technology & applied science research vol. 13, no. 2, 2023, 10384-10388 10387 www.etasr.com allout et al.: a comparative study of the dam stability at various stages using numerical modeling … fig. 6. horizonal deformations for the normal reservoir level of 165m. c. settlements at the end of the earthquake the obtained results of the vertical and horizontal displacements are shown in figures 7 and 8. the maximum horizontal displacement is approximately 0.42m and is located in the downstream side near the crest. the maximum vertical settlement is approximately 0.07m and is located in the upstream side near the crest. the crest of the dam is displaced toward downstream by 0.37m [9]. fig. 7. vertical displacements at the end of the earthquake. fig. 8. horizontal displacements at the end of the earthquake. fig. 9. comparison between the calculated and measured displacements at the crest of the dam during the earthquake. fig. 10. the displacement on the earth dam's crest. fig. 11. comparison between calculated and measured displacements at the crest of the dam during its initial impoundment. figures 9 and 11 show the comparison between the calculated and the measured displacements at the crest of the dam during the boumerdes earthquake in may 21 st , 2003 and between the calculated and measured displacements at the crest of the dam during its initial impoundment, respectively. figure 10 shows a real picture of the displacement on the dam's crest. concerning the vertical displacements at the level of the crest after the initial impoundment, figures 9 and 11 show that on the upstream side, the calculated displacements are inferior engineering, technology & applied science research vol. 13, no. 2, 2023, 10384-10388 10388 www.etasr.com allout et al.: a comparative study of the dam stability at various stages using numerical modeling … to the measured ones. this can be explained by the deformation due to the creep of the rockfill, which is not considered by the calculation model. on the contrary, on the downstream side, a slight swelling of the wet clay that is not loaded can be seen. iv. conclusion the analysis of the dam in the three stages of its life (at the end of the construction, after the initial impoundment, and under seismic loading) gave the following results: the maximum displacements obtained show the cumulative displacement during the construction phases. the maximum horizontal displacement is equal to 0.43m and the maximum vertical displacement is equal to 0.58m which means a settlement that represents 0.76% of the dam height. on the first filling of the reservoir, it was concluded that the displacements are maximum on the upstream side of the dam. the settlement calculated at the crest of the dam is less than 2% of the height, which is in accordance with the expected behavior of a rockfill dam with clay core. the maximum settlement calculated at the crest is approximately equal to the settlement measured in situ but slightly less. this can be explained by the deformation due to the creep of the rockfill which is not considered by the calculation model. for the seismic computations, this work gives encouraging results: very good seismic stability of earth dams is found, and the displacements observed do not affect the stability of the 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[17] r. w. jibson, "methods for assessing the stability of slopes during earthquakes—a retrospective," engineering geology, vol. 122, no. 1, pp. 43–50, sep. 2011, https://doi.org/10.1016/j.enggeo.2010.09.017. microsoft word etasr_v13_n2_pp10352-10356 engineering, technology & applied science research vol. 13, no. 2, 2023, 10352-10356 10352 www.etasr.com vo nguyen et al.: effect factors on unconfined compressive strength of soil-cement columns: the … effect factors on unconfined compressive strength of soil-cement columns: the case study of ba ria, vung tau, vietnam phu huan vo nguyen infrastructural technique department, faculty of civil engineering, ho chi minh city open university, vietnam huan.vnp@ou.edu.vn trung-dung tran faculty of civil engineering, ho chi minh city open university, ho chi minh city, vietnam dung.ttrung@ou.edu.vn (corresponding author) phu-cuong nguyen structural engineering department, advanced structural engineering laboratory, faculty of civil engineering, ho chi minh city open university, vietnam cuong.pn@ou.edu.vn, henycuong@gmail.com received: 11 january 2023 | revised: 30 january 2023 | accepted: 3 february 2023 abstract this paper presents the effect of the curing environment on the unconfined compressive strength of soilcement samples and in finding the optimum output mix ratio and estimating the effect of silica fume in the admixture. this work is based on the data from the cai mep-thi vai inter-port road project and results from laboratory experiments. the results show that the specimens with the highest strength were cured in soil, lowered in city water with nacl 2.5% and then nacl 5%. the optimum silica fume admixture ratio equals to 1% (in comparison with the weight of cement content). keywords-soil cement; soil improvement; unconfined compressive strength; mixture ratio; silica fume; soft soil i. introduction the deep soil mixing method or soil-cement column method is an advanced technology in which the cement is blended with in-situ soft soil. materials in dry and slurry form could be used in the soil-cement method. the hollows are made by using a rotated mixing machine which combines several types of cutting tools. the cementitious materials are also injected during the execution process. currently, there are many researched and developed deep mixing terminologies [1, 2]. the three main developing phases include: chemical mixing (lime cement or soil cement), mixed-in-place columns, and soil mixing. in these terminologies, the deep soil mixing (dsm) has certain advantages such as: rapid stabilization, accelerated construction in site, higher soil strength at lower cost. authors in [3-5] showed that dsm is suitable for application in some problematic soils, especially expansive soils. typical dsm has been applied in reclaimed and soft native soils in the transportation sector in japan [6]. the dsm technique is an advanced technology of improvement. some projects in vietnam have used this method, e.g.: the ba ngoi harbor project (khanh hoa province), can tho airport, bac lieu airport, etc. more and more projects use this technology for soft soil treatment. ii. investigation of the reaction in soil cement columns portland cement (pc) is created in a controlled chemical process with the combination of aluminum, calcium, iron, silicon, and other compounds. in order to construct blended portland cement (bpc), an amount of gypsum, and several minerals are mixed with pc or clinker in the hydraulic adhesive process [3, 4]. hydration reaction and hydrated cement (to form primary cementitious product): when using cement to stabilize the ground, minerals on the cement surface react with the hydrated engineering, technology & applied science research vol. 13, no. 2, 2023, 10352-10356 10353 www.etasr.com vo nguyen et al.: effect factors on unconfined compressive strength of soil-cement columns: the … cement from the pore water of the soil quickly to form three compounds: calcium hydroxide, hydrate calcium silicate, and hydrated calcium aluminate. the first cementitious products are the primary cementitious product. water and cement react as described below: 6h + 2c3s = 3ca(oh)2 + c-s-h (hydrated gel) (1) 4h + 2c2s = ca(oh)2 + c-s-h (2) 27h + 2c3a = c2ah8 + c4ah19 (3) 3csh2 + 26h + c3a= c6as3h32 (ettringite) (4) 4h + c6as3h32 + 3 c3a = 3c4ash12 (monosulfate) (5) the structure and strength in the soil matrix are determined by the hydration process which makes agglomeration, and cation exchange, and stabilizes the soil clay and flocculation. iii. effect factors on unconfined axial compression of soil cement samples many soil types such as sandy sand, soft clays, clayey silts, clays, and sands are in turn used to test with the soil-cement column method [7-10]. in these studies, some major soil factors that have the main influence on the compression development of soil-cement columns are il (index liquid), wn, fc, and ph. authors in [11, 12] showed that some soils have il > 15% and ph < 5, and the unconfined axial compression strength becomes too low, even though they had high other stabilizer properties. the main reason is the reduction of the ion ca 2+ for the pozzolanic reactions process. authors in [8] also showed that with more organic content, the unconfined compress strength decreases. the interference of organic contents in compression gain are not entirely understood, however authors in [13, 14] pointed out that the mechanisms of organic properties are:  the structural composition and cementing compound can be changed by organic matter via the hydrated process and other extraneous matter.  the organic matter can hold more than 10 times its dry weight in water, therefore the hydration may be faced with a water limit. the axial compression could be augmented by some parameters of soil such as soil minerals, sand consistency of fine, plastic index, etc. [5, 8, 9]. soil cement column quantity depends on the type of clay or sand and the characteristics of each soil, which is especially important given the low ph values (from 5.4 to 5.8) in mekong delta, vietnam [15]. some of the conditions at the site during the treatment process such as the mixing duration, the rate of installation, the shape of the mixing, etc. affect directly the unconfined compressive strength of soil-cement columns [1, 10, 15-16]. however, not much research has been conducted on the effect of these characteristics of soft soil, as it is difficult to reflect these characteristics in lab conditions. iv. laboratory assessment of the case study results the road in port terminal cai mep-thi vai along the thi vai river helps to develop and connect the traffic infrastructure and the industrial areas. soft soil improvement in the area utilizes soil-cement columns. the road cross-section is illustrated in figure 1. fig. 1. embankment supported by deep mixing in a component project. a. the effect of cement content on the unconfined compressive strength (ucs) in general, ucs varies from 900.4 to 1320.4kpa at 28 days, and from 1256.2 to 1732.5kpa at 60 days. the optimum cement content is 240kg/m 3 (1175 – 1300kpa). it is lower than that in [17] (300kg/m 3 ). fig. 2. the effect of cement content on (ucs) at 28 days. fig. 3. variation of ucs with water/cement ratio at 28 days. engineering, technology & applied science research vol. 13, no. 2, 2023, 10352-10356 10354 www.etasr.com vo nguyen et al.: effect factors on unconfined compressive strength of soil-cement columns: the … b. variation of ucs with water/cement ratio the optimum water/cement ratio is 0.8. increased water/cement ratio means increased water content. water content is needed to be enough for the hydrate reaction to occur. if the added water content is superfluous, it will make holes full of water in the product, decreasing its strength (figure 3). c. variation of ucs with silica fume/cement ratio the highest ucs occurs when silica fume/cement equals to 1%. if silica fume/cement ratio is more than 1%, the ucs will decrease (figure 4). fig. 4. variation of ucs with silica fume/cement ratio at 7 days. in summary, the ucs with silica fume/cement=1%, at 7, 14, 28, and 60 days ranges between 129 and 125%, 112 and 124%, 125 and 138%, and 113 and 135%, respectively. the strength of the soil-cement column increases the stability in the soil environment more than in other environments. pozzolanic reaction occurs between ca(oh)2 and silica fume to increase the strength of the specimen when silica fume is added. when the silica fume addition is more than 1% and if the mixed process is not widespread, it will surround the cement gain, preventing the hydrate reaction. d. variation of ucs with curing time the longer the curing time the higher the strength of soil cement samples is. the strength develops fastest from 0 to 7 days (equal to around 40% to the strength at 60 days) and then increases in a slower pace (see figure 5). fig. 5. variation of ucs with curing time for various soils. in comparison with its values at 7 days, ucs is around 163 – 192% at 28 days. these values are bigger than the ones obtained in [5] (140 150%). authors in [11] reported strength ratio at 7 to 28 days about (12.0 210%). the test result depends on the type of cement, the type of soil treatment, the water/cement ratio, etc. ucs varies from 121 to 131% at 60 days. v. analysis and variation of core sampling at site a. effect of cement content the optimum cement content equals to 240kg/m 3 . this value is the same with the laboratory research result. fig. 6. variation of usc with cement content. b. variation of ucs with water/cement ratio maximum strength of soil cement column is reached when the water/cement ratio is 0.7 and lowers a bit when water/cement ratio is 0.8. ucs decreases remarkably when the water/cement ratio is 0.9. fig. 7. variation of ucs with water/cement ratio at 14 and 28 days. c. relation between stress and strain the variation of ucs with strain can be seen in figure 8. vi. variation result comparison between laboratory and field the strength of laboratory mixed specimens and mixed field samples was compared in order to determine the correlation between them (figure 9). engineering, technology & applied science research vol. 13, no. 2, 2023, 10352-10356 10355 www.etasr.com vo nguyen et al.: effect factors on unconfined compressive strength of soil-cement columns: the … fig. 8. usc vs strain at 28 days. (a) (b) (c) fig. 9. laboratory and field ucs result comparison: (a) 220kg/m3 cement content, 0.7 water/cement ratio, (b) 240kg/m 3 cement content, 0.7 water/cement ratio, and (c) 260kg/m 3 cement content, 0.7 water/cement ratio. in the same mixture steps, the results in the laboratory are often more worked-out than in the field. vii. conclusion the main conclusions derived from the research results of this study are: 1) optimum mixture ratio the optimum cement content in laboratory and field mixed specimens is equal to 240kg/m 3 . the optimum water/cement ratio is 0.8 in laboratory mixed specimens and 0.7 in the field mixes. 2) effect of the curing environment the curing environment affects negligibly the compression values of soil cement columns. the highest strength of specimens is cured in soil environment, whereas it is lower in city water with nacl 2.5% and 5%. 3) the effect of silica fume the optimum silica fume admixture equals to 1% of the weight of cement content for 60 days of curing in the laboratory. more research regarding long term curing is needed in order to evaluate the effect of silica fume. the pozzolanic reaction between ca(oh)2 and clay material is crucial, especially in the research area, where the type of clay is montmorillonite which is the most active clay. 4) variation between the strength of cement column in the site and in the laboratory the strength of soil-cement columns depends heavily on contraction. in the current study, the strength of specimens mixed by the contractor a varied from 100 to 115% of the values of laboratory-mixed specimens. the values of the specimens mixed by the contractor b may varied from 42 to 67%. references [1] d. t. bergado and g. a. lorenzo, "economical mixing method for cement deep mixing," in geo-frontiers congress 2005, austin tx, usa, may 2012, https://doi.org/10.1061/40783(162)12. [2] a. j. puppala, r. s. madhyannapu, s. nazarian, and l. r. hoyos, "deep soil mixing technology for mitigation of pavement roughness," the university of texas at arlington, arlington, tx, usa, technical report 0-5179–1, oct. 2007. [3] g. a. lorenzo, d. t. bergado, and s. soralump, "new and economical mixing method of cement-admixed clay for dmm application," geotechnical testing journal, vol. 29, no. 1, pp. 54–63, nov. 2005, https://doi.org/10.1520/gtj12129. [4] g. a. lorenzo and d. t. bergado, "fundamental characteristics of cement-admixed clay in deep mixing," journal of materials in civil engineering, vol. 18, no. 2, pp. 161–174, apr. 2006, https://doi.org/10.1061/(asce)0899-1561(2006)18:2(161). [5] t.-o. ho, d. c. w. tsang, w.-b. chen, and j.-h. yin, "evaluating the environmental impact of contaminated sediment column stabilized by deep cement mixing," chemosphere, vol. 261, p. 127755, dec. 2020, https://doi.org/10.1016/j.chemosphere.2020.127755. [6] w. frikha, h. zargayouna, s. boussetta, and m. bouassida, "experimental study of tunis soft soil improved by deep mixing column," geotechnical and geological engineering, vol. 35, no. 3, pp. 931–947, jun. 2017, https://doi.org/10.1007/s10706-016-0151-2. engineering, technology & applied science research vol. 13, no. 2, 2023, 10352-10356 10356 www.etasr.com vo nguyen et al.: effect factors on unconfined compressive strength of soil-cement columns: the … [7] h. ahnberg, c, ljungkrantz, and l. holmqvist, "deep stabilization of different types of soft soils," in proceedings 11th ecsmfe, copenhagen, denmark, 1995, vol. 7, pp. 167-172. [8] b. b. k. huat, s. maail, and t. a. mohammad, "effect of chemical admixtures on the engineering properties of tropical peat soils," american journal of applied sciences, vol. 2, no. 7, pp. 1113–1120, jul. 2005, https://doi.org/10.3844/ajassp.2005.1113.1120. [9] a. mosadegh, f. szymkiewicz, and h. nikraz, "an experimental investigation of the impact of specimen preparation and curing conditions on cement-treated material strength (deep mixing method)," australian journal of civil engineering, vol. 15, no. 1, pp. 49–60, jan. 2017, https://doi.org/10.1080/14488353.2017.1372685. [10] m. syarif and m. w. tjaronge, "a comparison of organic cement made from recycled waste material and portland cement," engineering, technology & applied science research, vol. 11, no. 4, pp. 7442–7445, aug. 2021, https://doi.org/10.48084/etasr.4323. [11] r. babasaki, s. saito, and y. suzuki, ", r., s. saito, and y. suzuki. ‘temperature characteristics of cement improved soil and temperature analysis of ground improved using deep cement mixing method.’jssmfe. 1984.," in symposium on strength and deformation of composite ground., 1984, pp. 33–40. [12] a. saand, m. a. keerio, and d. k. bangwar, "effect of soorh metakaolin on concrete compressive strength and durability," engineering, technology & applied science research, vol. 7, no. 6, pp. 2210–2214, dec. 2017, https://doi.org/10.48084/etasr.1494. [13] m. janz and s.-e. johansson, "the function of different binding agents in deep stabilization," swedish deep stabilization research center, linkoping, sweden, report 9, 2002. [14] j. f. hou and m. y. li, "test on cement deep mixing soil strength," applied mechanics and materials, vol. 401–403, pp. 738–742, 2013, https://doi.org/10.4028/www.scientific.net/amm.401-403.738. [15] s. horpibulsuk, n. miura, and t. s. nagaraj, "assessment of strength development in cement-admixed high water content clays with abrams’ law as a basis," géotechnique, vol. 53, no. 4, pp. 439–444, may 2003, https://doi.org/10.1680/geot.2003.53.4.439. [16] p. h. v. nguyen and p. c. nguyen, "effects of shaft grouting on the bearing behavior of barrette piles: a case study in ho chi minh city," engineering, technology & applied science research, vol. 11, no. 5, pp. 7653–7657, oct. 2021, https://doi.org/10.48084/etasr.4389. [17] s. horpibulsuk, n. miura, h. koga, and t. s. nagaraj, "analysis of strength development in deep mixing: a field study," proceedings of the institution of civil engineers ground improvement, vol. 8, no. 2, pp. 59–68, jan. 2004, https://doi.org/10.1680/grim.2004.8.2.59. microsoft word etasr_v12_n6_pp9676-9679 engineering, technology & applied science research vol. 12, no. 6, 2022, 9676-9679 9676 www.etasr.com nguyen & nguyen: one-dimensional site response analysis and liquefaction evaluation of can tho … one-dimensional site response analysis and liquefaction evaluation of can tho city, vietnam trong-kien nguyen department of civil engineering vinh university vinh, vietnam nguyentrongkien82@gmail.com van-quang nguyen department of civil engineering vinh university vinh, vietnam nguyenvanquang240484@gmail.com received: 16 september 2022 | revised: 25 september 2022 and 29 september 2022 | accepted: 1 october 2022 abstract-can tho is the biggest city in the mekong river delta, one of the five national central cities in vietnam. however, it has not been studied regarding seismic hazard estimation. for this purpose, one-dimensional nonlinear site response analysis of this city was performed in this paper. the measured in-situ profiles and corresponding geotechnical site investigation and laboratory test data were utilized to develop the site model for site-specific ground response analysis. a suite of earthquake records compatible with the vietnam rock design spectrum (tcvn 9386:2012) was used as input ground motions at the bedrock. the results show that peak ground acceleration (pga) increases from the bedrock to the surface. maximum pga is 0.083g for o mon district (p1) and 0.073g for cai rang district (p2). the maximum shear strain is reported to be 0.35% for p1 and 0.45% for p2. the recommended amplification factors are 1.7 for p1 and 1.9 for p2. even though can tho city is composed of soft layers, liquefaction is unlikely to occur. keywords-response spectra; one-dimensional nonlinear site response analysis; peak ground acceleration; shear strain; liquefaction assessment i. introduction seismic hazard assessment plays an important role in the sustainable development of urban infrastructure. site response analysis and evaluating soil liquefaction potential is commonly used for that purpose. a total of 1645 earthquakes recorded in vietnam with magnitude (ml) of 3.0 or higher were considered in [1, 2]. in the 20th century, up to 90% of earthquakes occurred in northern vietnam because that area lies on indochina and south china faults [3]. the studies on seismic effects in southern vietnam are almost non-existent. in recent years, several earthquakes have been recorded in south vietnam, such as the earthquake that occurred on the coast of vung tau province in 2005, with ml = 4.5, shaking the whole ho chi minh city, the earthquake at the coast of binh thuan province in 2020, with ml = 4.7. these earthquakes are related to the thuan hai – minh hai fault, which has a closet distance of about 45km from can tho city. there is a need for studies that assess the effects of earthquakes on the southern region of vietnam, especially in large cities with dense population. regarding the central of can tho city, and to the best of our knowledge, no studies have been conducted on onedimensional site response analysis and evaluation of ground behavior under earthquake effects. can tho is one of the 5 biggest cities in vietnam, with nearly 1.3 million residents (2019). can tho is also the capital of the southwest region and the economic center of the cuu long river delta. the stratigraphy is mainly clay and sandy clay with large thickness, interspersed with fine sand layers with a thin thickness and deep. the groundwater level is shallow and changes seasonally due to the interlaced system of canals. this study aims to perform site response analysis and then propose design spectra for the ground in the area of can tho city. two site classes, c and d, and 15 earthquakes, were adopted in this research. also, the liquefaction assessment of this city is evaluated. fig. 1. central of can tho city and investigated sites. ii. investigated soil profiles figure 1 shows the two investigated soil profiles of can tho city considered in this study. these profiles represent site class c (o mon district, named p1) and d (cai rang district, named p2) according to the vietnam code [4]. the typical soil stratigraphy includes fill, clay or sandy clay/clayey sand, and gravel. the groundwater level is 0.6m and 2.2m depth for the soil profiles of p1 and p2. details of the soil properties and shear wave velocity is presented in tables i-ii and figure 2. corresponding author: van-quang nguyen engineering, technology & applied science research vol. 12, no. 6, 2022, 9676-9679 9677 www.etasr.com nguyen & nguyen: one-dimensional site response analysis and liquefaction evaluation of can tho … table i. soil properties of p1 no material type thickness (m) depth (m) density (kg/m 3 ) shear wave velocity (m/s) 1 fill 1.3 1.3 1500 100 2 sandy clay 5.1 6.4 1570 100 3 clay 6.2 12.6 1940 214 4 clay 4.8 17.4 1940 219 5 clayey sand 5.3 22.7 2000 259 6 clay 3 25.7 2000 263 table ii. soil properties of p2 no material type thickness (m) depth (m) density (kg/m 3 ) shear wave velocity (m/s) 1 fill 1.2 1.2 1500 100 2 sandy clay 1.4 2.6 1680 100 3 clay 6.8 9.4 1650 100 4 clay 6.5 15.9 1790 141 5 sandy clay 7.8 23.7 1720 209 6 clay 5.7 29.4 1950 214 fig. 2. shear wave velocity profiles. iii. input ground motions the critical unknown in site response analysis is earthquake ground excitation. due to the lack of available earthquake records in can tho city, ground motions recorded in other regions, but with similar characteristics to those likely to occur in vietnam are selected. the recorded ground motions were selected from the nga-west2 database (https://ngawest2. berkeley.edu/). the ground motions with the following features were selected:  range of moment magnitudes �� 5.5-7.0.  rupture distance ����: 0.92-85.17km.  time-averaged shear-wave velocity to a depth of 30m (�� ): 760-1500m/s. a total of 15 motions with peak ground acceleration (pga) ranging from 0.04g to 0.25g were selected from 12 earthquake events, as shown in table iii. the ground motions were scaled to the representative shaking intensity levels of each analyzed district, in which pga levels at p1, and p2 were scaled to 0.0546g, and 0.0515g respectively. also, the mean response spectrum of selected ground motions was matched closely to the spectrum of site class a of the vietnam design code (moc, 2012), as shown in figure 3. these motions were also used in [1, 2]. fig. 3. input motions and design response spectra (a) p1, (b) p2. table iii. selected earthquake events [1, 2] event year station �� mechanism ��� (km) ���� (m/s) san fernando 1971 pasadena old seismo lab 6.61 reverse 21.5 969.07 whittier narrows-01 1987 pasadena cit kresge lab 5.99 reverse 18.12 969.07 loma prieta 1989 piedmont jr high school grounds 6.93 reverse oblique 73 895.36 loma prieta 1989 point bonita 6.93 reverse oblique 83.45 1315.92 loma prieta 1989 sf pacific heights 6.93 reverse oblique 75.96 1249.86 loma prieta 1989 so. san francisco_ sierra pt. 6.93 reverse oblique 63.15 1020.62 northridge01 1994 la wonderland ave 6.99 reverse 20.29 1222.52 northridge01 1994 vasquez rocks park 6.99 reverse 23.64 996.43 chi-chi_ taiwan-05 1999 ttn042 6.20 reverse 85.17 845.34 umbria03_ italy 1984 gubbio 5.60 normal 15.72 922 kobe_ japan 1995 kobe university 6.90 strike slip 0.92 1043 chi-chi_ taiwan-05 1999 hwa002 6.20 reverse 45.03 789.18 iv. one-dimensional analysis one-dimensional (1d) nonlinear analysis was performed using deepsoil v7.0 [5-9]. the most widely used pressuredependent hyperbolic, the modified kodner–zelasko (mkz) model [10], implemented in deepsoil, was used. darendeli model [11] was employed to generate the dynamic properties of soil layers. the variables required to generate the nonlinear curves for each layer are the coefficient of lateral earth pressure (ko), plasticity index (pi), number and frequency of cycles (n), loading frequency (f), and the over consolidation ratio (ocr). due to the unavailability of site-specific index properties, pi and ocr were taken as 0 and 1 respectively. n and f were set to 10 and 1 as recommended in [11], whereas ko was specified as 0.5. figure 4 presents a flowchart of the site response and liquefaction evaluation procedure implemented in this study. the flowchart illustrates that a suite of nonlinear site response analyses are used to determine the site-specific spectral shapes, pga, and maximum shear strain profiles of the p1 and p2 areas. moreover, the proposed response spectra resulting from this study provide insights into the discrepancies between the design and site-specific spectra. the cyclic stress engineering, technology & applied science research vol. 12, no. 6, 2022, 9676-9679 9678 www.etasr.com nguyen & nguyen: one-dimensional site response analysis and liquefaction evaluation of can tho … ratio (csr) was also obtained from 1d site response analysis and was used for the liquefaction evaluation purpose. fig. 4. response spectra comparison of the surface, input motion, and bedrock design. v. results and discussion figure 5(a) shows the pga along with the depth of p1 and p2 soil profiles. pga increases from the bedrock to the surface except at the 2.5 – 7.5m depth. the decrease at that depth can be attributed to a significant thickness of the soft soil. surface pgas are 0.083g at p1 and 0.073g at p2. shear strain profiles are shown in figure 5(b). the shear strain of p1 and p2 reached 0.35% and 0.45% respectively. the maximum value of shear strain occurs at the approximate position of the boundary between the soil layers with a significant shear wave velocity difference. fig. 5. pga and shear strain profiles. figure 6 presents the surface response spectra for p1 and p2. the average response spectrum of the input earthquakes and the design spectrum according to the vietnamese code (bedrock) are also shown. the maximum values of spectra acceleration of p1 and p2 are at periods of 0.4s and 0.3s respectively. figure 7 depicts the proposed surface response spectra against the calculated and design ones. the proposed surface response spectra were computed based on [12]: � = ���������� (1) where � is the soil factor and !"#$ and %&'( are the spectral acceleration index of soil and rock respectively: !"#$ "� �")* = + �,(.)0.2 . 2 (2) � was 1.7 and 1.9 for p1 (site class c) and p2 (site class d). in the vietnam design code [4], these values are 1.15 and 1.35 for site class c and site class d. fig. 6. response spectra comparison of the surface, input motion, and bedrock design. fig. 7. response spectra comparison of the calculated surface, proposed surface, and bedrock design. in this study, the empirical correlation proposed in [13] is used to assess the liquefaction potential of the soil, which relates �� to ccr as follows: crr = 5, 67�89:; < 0 + > ? ;89:∗ a7� 89: − ; 89:∗ cd msf (3) where , = 0.022, > = 2.8, hi = correction factor for high value of ��; caused by cementation, msf is the magnitude scaling factor, and ��; = �� corrected for the effect of overburden pressure. they are determined as follows: msf = 6jkl.2 < a0.2m (4) ��1 = �� 6o,pq′ < 0.25 (5) where �v is the moment magnitude, ow is the atmospheric pressure, �xy is the effective overburden stress (kpa), and ��;∗ is the critical value of ��; that separates the contractive and dilative behavior of soil. the recommended ��;∗ value is dependent on the fines content (fc) as follows:  ��;∗ = 215m/s for sand and gravels with fc ≤ 5%.  ��; ∗ = 215 0.5(fc 5)m/s for sand and gravel with 5% < fc < 35%.  ��; ∗ = 200m/s for sand and gravels with fc ≥ 35% engineering, technology & applied science research vol. 12, no. 6, 2022, 9676-9679 9679 www.etasr.com nguyen & nguyen: one-dimensional site response analysis and liquefaction evaluation of can tho … for a conservative estimate, fc ≤ 5% and ��; ∗ = 215m/s are used. ��; based on the measured �� profiles are shown in figure 8. liquefaction potential assessment for can tho city area was performed utilizing the maximum csr calculated from the nonlinear site response analyses presented in section iv and the csr presented in this section. because not the entire soil profile is susceptible to liquefaction, liquefaction potential was assessed only for the fill, sandy clay layer with ��; ∗ < 215m/s. the averaged results from the input motions are shown in figure 9. the liquefaction assessment shows that eventhough the soil profiles at can tho city are composed of soft layers, liquefaction is unlikely to occur due to the low seismic hazard of the region. it should also be noted that the assessment is based on the significantly conservative estimate that even layers with clay content are susceptible to liquefaction. fig. 8. overburden stress-corrected shear wave velocity ��1 profiles. fig. 9. overburden stress-corrected shear wave velocity ��1 profiles. vi. conclusions this study evaluates the behavior of the ground under earthquake loading at the center of can tho city, vietnam. a total of 15 recorded input motions and two investigated soil profiles were considered and one-dimensional nonlinear ground analysis and liquefaction potential assessment were performed. the following conclusions were drawn:  pga increases from the bedrock to the surface. the maximum values of pga are 0.083g for p1 (site class c) and 0.073g for p2 (site class d).  the maximum shear strain occurs at the boundary between two soil layers with a large difference in shear wave velocities. the maximum values of the shear strain are 0.35% for p1 and 0.45% for p2.  design response spectra are proposed in this study area. the recommended soil factor is 1.7 for p1 and 1.9 for p2.  the liquefaction potential is assessed using the empirical liquefaction triggering chart based on the in-situ measured �� . the results demonstrated that there is no liquefaction susceptibility in can tho city. references [1] v.-q. nguyen, m. aaqib, d.-d. nguyen, n.-v. luat, and d. park, “a site-specific response analysis: a case study in hanoi, vietnam,” applied sciences, vol. 10, no. 11, jan. 2020, art. no. 3972, https://doi.org/10.3390/app10113972. [2] n.-l. tran, m. aaqib, b.-p. nguyen, d.-d. nguyen, v.-l. tran, and v.q. nguyen, “evaluation of seismic site amplification using 1d site response analyses at ba dinh square area, vietnam,” advances in civil engineering, vol. 2021, aug. 2021, art. no. e3919281, https://doi.org/10.1155/2021/3919281. [3] t. v. hung, “study on earthquake ground motion prediction and its application to structural response of bridge in vietnam,” ph.d. dissertation, waseda university, tokyo, japan, 2012. [4] tcvn 9386:2012 design of structures for earthquake resistances. hanoi, vietnam: moc, 2012. [5] y. m. a. hashash, deepsoil user manual. champaign, il, usa: university of illinois at urbana-champaign, 2016. [6] a. behshad and m. r. shekari, “seismic performance evaluation of concrete gravity dams with penetrated cracks considering fluid– structure interaction,” engineering, technology & applied science research, vol. 8, no. 1, pp. 2546–2554, feb. 2018, https://doi.org/ 10.48084/etasr.1729. [7] t. nagao, “maximum credible earthquake ground motions with focus on site amplification due to deep subsurface,” engineering, technology & applied science research, vol. 11, no. 2, pp. 6873–6881, apr. 2021, https://doi.org/10.48084/etasr.3991. [8] a. razmyar and a. eslami, “geotechnical characterization of soils in the eastern and western areas of tehran,” engineering, technology & applied science research, vol. 7, no. 4, pp. 1802–1810, aug. 2017, https://doi.org/10.48084/etasr.1200. [9] s. sadiq, q. van nguyen, h. jung, and d. park, “effect of flexibility ratio on seismic response of cut-and-cover box tunnel,” advances in civil engineering, vol. 2019, jul. 2019, art. no. e4905329, https://doi.org/10.1155/2019/4905329. [10] n. matasović and m. vucetic, “cyclic characterization of liquefiable sands,” journal of geotechnical engineering, vol. 119, no. 11, pp. 1805–1822, nov. 1993, https://doi.org/10.1061/(asce)07339410(1993)119:11(1805). [11] m. b. darendeli, "development of a new family of normalized modulus reduction and material damping curves," ph.d. dissertation ph.d. dissertation, university of texas at austin, austin, tx, usa, 2001. [12] j. rey, e. faccioli, and j. j. bommer, “derivation of design soil coefficients (s) and response spectral shapes for eurocode 8 using the european strong-motion database,” journal of seismology, vol. 6, no. 4, pp. 547–555, oct. 2002, https://doi.org/10.1023/a:1021169715992. [13] r. d. andrus and k. h. stokoe ii, “liquefaction resistance of soils from shear-wave velocity,” journal of geotechnical and geoenvironmental engineering, vol. 126, no. 11, pp. 1015–1025, nov. 2000, https://doi.org/10.1061/(asce)1090-0241(2000)126:11(1015). microsoft word etasr_v13_n3_pp10652-10658 engineering, technology & applied science research vol. 13, no. 2, 2023, 10652-10658 10652 www.etasr.com dhouib et al.: analyzing the effects of mbpss on the transit stability and high-level integration of … analyzing the effects of mbpss on the transit stability and high-level integration of wind farms during fault conditions bilel dhouib cem laboratory, engineering school of sfax, tunisia bilel.dhouib@enis.tn (corresponding author) mohamed ali zdiri cem laboratory, engineering school of sfax, tunisia mohamed-ali.zdiri@enis.tn zuhair alaas department of electrical engineering, faculty of engineering, jazan university, saudi arabia zalaas@jazanu.edu.sa hsan hadj abdallah cem laboratory, engineering school of sfax, tunisia hsan.hajabdallah@enis.tn received: 7 march 2023 | revised: 19 march 2023 | accepted: 22 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5838 abstract as the demand for renewable energy continues to increase, wind power has emerged as a prominent source of clean energy. however, incorporating wind energy into the power generation system at a high level can significantly impact the dynamic performance of the power system, resulting in increased uncertainties during operation. this study investigated the effectiveness of the multi-band power system stabilizer (mbpss), a new power system stabilizer, in suppressing dynamic oscillations in a multi-machine power system connected to a wind farm. this research focused on analyzing the transient stability of a nine-bus network, commonly known as the western system coordinating council (wscc), integrated with a doubly fed induction generator (dfig) using matlab/simulink. the study evaluated the dynamic performance of the proposed system under fault conditions, including line-to-line-to-line-to-ground (lllg) faults. simulation results showed that mbpss effectively dampened oscillations and improved the stability of the power system, even in the presence of severe faults and high-level integration of wind farms. keywords-wind farm; dfig; mbpss; lllg fault; multimachine power system; transit stability i. introduction wind is a highly promising source of renewable energy, thanks to its environmental-friendly characteristics and widespread availability [1]. however, the current rate of integration of wind energy into the electricity grid remains relatively low. the large-scale integration of wind power sources presents potential technical challenges due to their intermittent nature, which must be carefully examined and addressed as part of the development of a sustainable energy system for the future [2-4]. the 9-bus system has been extensively used in power system analyses. in [5], a probabilistic load flow analysis was presented for the 9-bus wscc system, using a stochastic approach to validate the effectiveness of probabilistic analysis techniques to gain a more comprehensive understanding of power systems compared to deterministic analysis. the transient stability analysis of the ieee-9 bus system under multiple contingencies was investigated in [6]. this study compared and employed both the euler and runga methods to examine changes in the frequency and rotor angle of the system under various fault conditions. the simulation results showed that the runga method had a faster response. in [7], transient stability analysis was conducted on the ieee 9-bus system, taking into account the integration of dfigand scig-based wind turbines. the simulation results showed that the dfigbased wind turbine had a lower peak value of relative power angle than the scig-based one, but the results for settling time engineering, technology & applied science research vol. 13, no. 2, 2023, 10652-10658 10653 www.etasr.com dhouib et al.: analyzing the effects of mbpss on the transit stability and high-level integration of … were reversed. in [8], the transient stability assessment of an ieee 9-bus system integrated with a wind farm was investigated to evaluate its stability with dfig integration. two techniques are used to improve oscillation damping and ensure system stability: power system stabilizers (psss) and facts systems have effects extensively documented [911]. however, while pss is effective in damping local modes, it may not sufficiently address inter-zonal modes. hence, various design approaches have been proposed to enhance pss efficiency in damping diverse oscillation modes, such as the optimization of performance criteria to achieve optimal control [12], the use of neural networks in smart stabilizers [13], robust control [14], and fuzzy logic [15]. in summary, these controllers have been proven effective in addressing stability issues. this motivates the proposal of a novel power system stabilizer that integrates wind power generation for multimachine systems. the implementation of mbpss can significantly improve the primary frequency response of a power system. this is exemplified by the use of mbpss at hydro-quebec (hq) for several years [16]. several studies, such as [17-19], highlighted the favorable effects of certain techniques on power systems. these techniques were shown to improve frequency response, global and electromechanical mode damping, and voltage stability. the improvements in the hq transmission system can be attributed, at least in part, to its unique characteristics. hq is isolated from the rest of the eastern interconnection and is characterized by a long radial structure, with power flow patterns established predominantly in the north-to-south direction. this study investigated the integration of a wind farm that utilized dfig as variable speed generators directly connected to the grid into a 9-bus network at a high level. the primary objective was to analyze the impact of wind farm integration on the transient stability of the power system, focusing on evaluating the effects of the mbpss stabilizer. the evaluation of the system's transient state was based on analyzing the power angles, angular speeds, and frequencies of the synchronous generators. additionally, fault scenarios, such as the lllg fault, were considered to assess the system's dynamic performance. the main contributions of the current paper are:  this study explored the effectiveness of an mbpss that featured a three-frequency band structure (i.e. low-, intermediate-, and high-frequencies) for analyzing the system's transient stability.  high-level integration of the wind farm was taken into account to improve the robustness of the mbpss.  the suggested system was exposed to high-level perturbation scenarios, including the lllg fault, and the robustness of the controller was demonstrated to facilitate swift system recovery from these faults. ii. wind farm model a. wind speed model accurate modeling of wind turbines is highly dependent on the wind speed model. while wind is often viewed as a random phenomenon, its variability can be modeled using various approaches [20]. one way to represent the wind speed is to decompose it into a sum of harmonics, as demonstrated by [21]: �� ��� = 10 + 0.55�sin�0.0393��− 0.875 sin�0.1178��+ 0.75 sin�0.1963��− 0.625 sin�0.3927��+ 0.5 sin�1.178��+ 0.25 sin�1.9634��+ 0.125 sin�3.9269��� (1) b. wind turbine model a wind turbine aims to utilize wind energy and convert it into torque that rotates the rotor blades. the amount of wind energy converted into mechanical energy by the rotor is determined by three factors: density of the air, swept area of the rotor, and wind speed. air density and wind speed are unique to each location and are considered climatic parameters [22]. the mathematical expression for the mechanical power output of a wind turbine is given by [23]: �� = �� ��, �� !" �#$ (2) the mechanical power harvested by the wind turbine and transferred to the rotor is represented by pm (w). the turbine power coefficient is denoted by cp, while p (kg/m 3 ) represents the density of the air, a (m 2 ) indicates the area swept by the rotor, vω (m/s) represents the wind speed, � stands for the speed ratio, and β (°) is the blade angle of inclination. each wind turbine has its distinct power coefficient characteristics. as an example, the power coefficient for a 1.5mw wind turbine can be estimated through measurements and be approximated using [24]: �� ��, �� = 0.5176 %&&'() − 0.4� − 5* + ,"& ()⁄ + 0.0068 � (3) the value of the λi parameter is determined by: &() = &(/0.012 − 0.0$324/& (4) c. dfig model the utilization of dynamic modeling for the dfig in the rotating d-q reference frame yields the following equations [2325]: ⎩⎪⎪ ⎨ ⎪⎪⎧ 9:; = <; =:; − >;?@; + :abc:d 9@; = <; =@; + >;?:; + :aec:d 9:f = <f =:f − �>; − >f �?@f + :abg:d9@f = <f =@f + �>; − >f �?:f + :aeg:d (5) where: ⎩⎨ ⎧?:; = h; =:; + h� =:f?@; = h; =@; + h� =@f ?:f = hf =:f + h� =:;?@f = hf =@f + h� =@; engineering, technology & applied science research vol. 13, no. 2, 2023, 10652-10658 10654 www.etasr.com dhouib et al.: analyzing the effects of mbpss on the transit stability and high-level integration of … the variables uds, uqs, udr, and uqr denote the d-q axis stator and rotor voltages, while ids, iqs, idr, and iqr represent the stator and rotor currents on the same axis. additionally, ψds, ψqs, ψdr, and ψqr indicate the stator and rotor flux components on the d-q axis. the stator and rotor resistances per phase are denoted by rs and rr. the stator and rotor inductances are represented by ls and lr, respectively, and lm denotes the magnetizing inductance. iii. system model a. synchronous generator model the equations governing the two-axis models of the i-th synchronous machine in a multiple-machine network are [26]: ⎩⎪ ⎪⎪ ⎪⎪ ⎪⎨ ⎪⎪ ⎪⎪ ⎪⎪ ⎧ i:0j kl@j = −k@j − m n: − n: j −obpqqobpq rbqqrbq �n: − n:j �s =: + kt: i:0jj kl@jj = −k@jj + k@j − m n: j − n:jj +obpqqobpq rbqqrbq �n: − n:j �s =: + kt: i@0j kl:j = −k:j − un@ − n@j − oepqqoepq reqqreq vn@ − n@j wx =@ i@0jj kl:jj = −k:jj + k:j − yn@ − n@j + oep qq oepq reqqreqvn@ − n@j w z =@ [l = \] �> − 1� ^>l = v�� − �_ − `�> − 1�w (6) the equation includes multiple terms. k:,@j and k:,@jj indicate the machine's transient and subtransient voltages along the d-q axis per unit (pu), kt: represents the machine's excitation voltage (pu), =:,@ signifies the current on the d-q axis (pu), n:,@ , n:,@j , and n:,@jj , represent the synchronous, transient, and subtransient reactances along the d-q axis (pu), i:0,@0j and i:0,@0jj express the machine's transient and subtransient time constants along the d-q axis (s), δ denotes the machine's rotor angle (rad), \] represents the machine's synchronous base speed (rad/s), ω signifies the machine's rotor speed (pu), m refers to the machine's inertia coefficient (pu.s 2 /rad), d stands for the machine's damping coefficient (pu.s/rad), �� indicates the mechanical power applied to the machine shaft (pu), and �_ denotes the electrical power generated by the machine (pu). b. mbpss model the hydro-québec-developed mb-pss [27-28] differs from traditional stabilizers that usually use a series of stacked filters (high-pass and phase-lead-lag). instead, the mb-pss consists of three separate stages that work autonomously at low, medium, and high frequencies, making it more robust in different circumstances. the process of selecting the optimum values for multi-band power system stabilizer (mbpss) parameters involves a combination of theoretical analysis, simulation studies, and field testing. by utilizing the genetic algorithm as an optimization technique, the optimal mbpss parameters can be ascertained [29]. based on the simulation studies, the mbpss parameters are tuned to optimize the controller's performance. the tuning process involves adjusting the gain and time constants of the controller's different bands to achieve the desired damping ratio and bandwidth. the simplified structure comprises three gains kl, ki, and kh, which are categorized as low, intermediate, and high, and three frequencies fl, fi, and fh that correspond to low, intermediate, and high frequencies measured in hz. iv. results and simulation a. 9-bus network a 9-bus test system was employed for all simulations, as shown in figure 1. the system consists of three voltage levels, namely 16.5, 18, and 13.8kv, and includes three generators with a 567.5mva total power output, six transmission lines, and three load nodes with 315mw combined consumption. the generator parameters are specified in the appendix. fig. 1. nine bus network. fig. 2. nine-bus network with a wind farm. b. modified nine-bus network multiple strategies can improve the effectiveness of the electrical grid across various stages of the power supply chain, including power generation, transmission, and distribution [30engineering, technology & applied science research vol. 13, no. 2, 2023, 10652-10658 10655 www.etasr.com dhouib et al.: analyzing the effects of mbpss on the transit stability and high-level integration of … 32]. various tests were conducted to determine the optimal wind turbine integration rate and the results showed that bus 7 was the best location for the wind farm. as a result, this location was selected to install a farm consisting of 74 turbines, each generating 1.5mw, for a total capacity of 111mw. the turbine parameters are shown in the appendix. figure 2 shows an updated illustration of the grid structure. c. applying a fault in the proposed system at time t=1s, there was a fault with a duration of 0.1s on the transmission line between nodes 5 and 7. the fault was located in the middle of the line and was classified as an lllg fault. the modified 9-node wscc network simulation model was implemented using matlab/simulink. a random wind profile was used to simulate realistic wind conditions, with wind speeds fluctuating between 8 and 14m/s for 10s. figure 3 shows this time-varying profile which was the basis of the case study. fig. 3. wind speed profile. as mentioned above, the presence of a defect combined with a high level of wind energy integration (35%) results in changes to the power angle and angular speed differences of generators 2 and 3, as well as the frequency at each synchronous generator. to visualize these changes, the figures below show the evolution of these parameters for two scenarios: (1) without mbpss, and (2) with mbpss. the simulation results show that the implementation of mb-pss in a high wind power integration scenario results in reduced overshoot and faster convergence to the stable equilibrium point, compared to the system without mbpss. table i shows a comparison of the damping duration periods for the two scenarios. table i. duration of damping command duration of damping without mbpss >10s with mbpss 3s these data highlight the effectiveness of mbpss in significantly reducing the damping period of the system. figures 4 and 5 depict the power angle differences of generators 2 and 3. the power angles δ21 and δ31 undergo an increase to approximately 58.22° and 33.07°, respectively, followed by subsequent declines to 38.34° and 31.07° for generators 2 and 3. it can be noted that the inclusion of mbpss results in a reduction of power angle, compared to the system without it, indicates system stability without any oscillations. the effectiveness of mbpss in damping oscillations across all frequency ranges is demonstrated in figures 6 and 7. specifically, when subjected to an lllg fault and a 35% wind turbine integration, the system with mbpss outperforms the one without it. this can be attributed to its multi-stage structure and the presence of three distinct bands, which enable it to efficiently mitigate low-, intermediate-, and high-frequency oscillations. fig. 4. power angle variation δ21. fig. 5. power angle variation δ31. fig. 6. angular speed variation ω21. figures 8-10 illustrate a significant increase in generator frequencies leading to system instability before the implementation of the mbpss power regulator. implementing mb-pss, the generator frequencies were stabilized and consistently maintained the nominal frequency of 50hz. following a severe disturbance (lllg fault), the simulation results for a 35 % wind turbine integration scenario with the mbpss regulator indicate a faster response time and shorter stabilization period, compared to the same scenario without it. engineering, technology & applied science research vol. 13, no. 2, 2023, 10652-10658 10656 www.etasr.com dhouib et al.: analyzing the effects of mbpss on the transit stability and high-level integration of … fig. 7. angular speed variation ω31. fig. 8. frequency profile generator 1. fig. 9. frequency profile generator 2. fig. 10. frequency profile generator 3. v. conclusion this study extensively investigated the modeling and simulation of a high-level wind farm system connected to an electrical network. dynamic simulations were conducted on a 9-bus multi-machine network that included a wind farm to evaluate the effectiveness and robustness of the mbpss stabilizer. a wind farm with a capacity of 111mw was installed at bus 7. using matlab/simulink, this study analyzed the impact of mbpss on the transient stability of the power system under failure scenarios, including lllg faults, and high-level integration of the wind farm. the simulation results indicate a direct correlation between wind farm capacity and power system transient stability. integrating wind generation at higher levels led to an increase in transient instability. moreover, the mbpss was highly effective in enhancing power system stability during high-level integration of wind energy and severe faults and provided adequate damping to all oscillation modes as it consisted of multiple stages with three distinct frequency bands, enabling it to effectively dampen low-, intermediate-, and high-frequency oscillations. appendix table ii displays the generator parameters in 'per unit' based on the nominal mva and kv values. tables iii-v outline the parameters for the wind turbine linked with a dfig. tables vi and vii present the mbpss data for the simplified settings mode and the detailed settings mode, respectively. table ii. generator parameters generator no: #1 #2 #3 rated mva 247.5 192 128 ab 0.1460 0.8958 1.3125 abj 0.0608 0.1198 0.1813 abjj 0.0483 0.0891 0.1072 cbdj 8.96 6 5.89 cbdjj 0.04 0.033 0.033 ae 0.0969 0.8645 1.2587 aej 0.0969 0.1198 0.1813 aejj 0.0483 0.0891 0.1072 cedj 0.31 0.535 0.6 cedjj 0.060 0.08 0.07 fg 0.0006 0.0013 0.0032 ah 0.0336 0.0521 0.0742 i(sec) 23.64 6.4 3.01 table iii. dfig data parameters value jklm(va) 1.5e6/0.9 nklm(v) 575 o(hz) 50 fp(pu) 0.00706 qrp(pu) 0.171 fsj (pu) 0.005 qrsj (pu) 0.156 qm(pu) 2.9 i(s) 5.04 t 3 table iv. turbine data parameters value uméw_klm (mw) 1.5 yt 500 z (deg) 50 engineering, technology & applied science research vol. 13, no. 2, 2023, 10652-10658 10657 www.etasr.com dhouib et al.: analyzing the effects of mbpss on the transit stability and high-level integration of … table v. converters data parameters value umg{ (pu) 0.5 [ q f ] (pu) [0.15 0.0015] [rq �|}� t~_rq ����� ] [0 90] nbw(v) 1200 � (f) 10000e-6 table vi. mbpss data for simplified settings mode parameters value low frequency band: [oq (hz) yq] [0.2 20] intermediate frequency band: [or (hz) yr] [0.9 25] high frequency band: [oi (hz) yi] [12 145] signal limits [nqmg{ nrmg{ nimg{ njmg{] [0.75 0.15 0.15 0.15] table vii. mbpss data for detailed settings mode parameters value low frequency gains: [yq� yq� yq] [66 66 9.4] low frequency time constants: [cq� cq� cq� cq� cq� cq� cq� cq� cq� cq�d cq�� cq�� yq�� yq��] [1.667 2 0 0 0 0 2 2.4 0 0 0 0 1 1] intermediate frequency gains: [yr� yr� yr] [66 66 47.6] low frequency time constants: [cr� cr� cr� cr� cr� cr� cr� cr� cr� cr�d cr�� cr�� yr�� yr��] [1 1 0.25 0.3 0 0 1 1 0.3 0.36 0 0 0 0] intermediate frequency gains: [yi� yi� yi] [66 66 233] low frequency time constants: [ci� ci� ci� ci� ci� ci� ci� ci� ci� cr�d ci�� ci�� yi�� yi��] [0.01 0.012 0 0 0 0 0.012 0.0144 0 0 0 0 1 1] references [1] y. wang et al., "where is the most feasible, economical, and green wind energy? evidence from high-resolution potential mapping in china," journal of cleaner production, vol. 376, nov. 2022, art. no. 134287, https://doi.org/10.1016/j.jclepro.2022.134287. 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[32] m. a. zdiri, b. dhouib, z. alaas, f. b. salem, and h. h. abdallah, "load flow analysis and the impact of a solar pv generator in a radial distribution network," engineering, technology & applied science research, vol. 13, no. 1, pp. 10078–10085, feb. 2023, https://doi.org/ 10.48084/etasr.5496. microsoft word etasr_v12_n6_pp9471-9476 engineering, technology & applied science research vol. 12, no. 6, 2022, 9471-9476 9471 www.etasr.com thakur & roy: soil liquefaction potential in different seismic zones of bihar, india soil liquefaction potential in different seismic zones of bihar, india ishwar chandra thakur civil engineering department national institute of technology patna patna, india ishwart.phd20.ce@nitp.ac.in l. b. roy civil engineering department national institute of technology patna patna, india lbroy@nitp.ac.in received: 28 august 2022 | revised: 8 september 2022 | accepted: 9 september 2022 abstract-liquefaction potential analysis for the liquefiable as well as non-liquefiable soils of bihar state has been performed in this paper based on the actual field data from three seismic zones, i.e. zone iii, zone iv, and zone v. the analysis has been performed following the simplified procedure given in [1] and later modified in [2]. the results show that districts under seismic zone iii are comparatively more resistant to liquefaction in most cases, districts of zone iv are relatively more prone to liquefaction up to a few depths, and districts of zone v are most liquefiable. liquefaction resistance is primarily depending upon the fine content of soil and spt n-values. keywords-standard penetration test; cyclic stress ratio; cyclic resistance ratio; soil liquefaction i. introduction liquefaction is the phenomenon in which the strength and stiffness of the soil are reduced by earthquake shaking and/or another dynamic loading. when an earthquake of suitable intensity shakes a deposit of loose saturated coarse-grained cohesionless soils, then the grain structures are triggered towards a more compact packing. however, it is not possible to drain off the pore water because it does not have sufficient time to do so during an earthquake. the pore water pressure then shoots outward because the applied stresses are taken up by the incompressible water and the effective stresses approach zero: � � = � − � (1) where � � is the effective stress, � is the total stress, and � is pore water pressure. in the case of cohesionless soil (� = 0), shear strength (�) reduces to zero when effective stress approaches zero. � = � + σ� tan � � (2) where � � is the effective internal resistance of the soil. liquefaction is one of the most disastrous seismic hazards. india has experienced the world’s greatest earthquakes in the last few decades which lead to soil liquefaction and consequential damages. authors in [1] presented a simplified procedure for the evaluation of the liquefaction potential of soil using the assemblage of available field data of liquefied or non-liquefied soil during earthquakes. the author in [3] studied the field data from different countries for the evaluation of the liquefaction potential of soil in earthquake magnitude mw = 7.5 and the result was then extended to earthquakes of other magnitudes and for silty soil. authors in [4] presented a critical review of sandy soil deposits. it was found that the sand that has more than 10% fine content has a much higher resistance to liquefaction than clean sand having the same spt n value. for clean sands with spt n1 values greater than 25, silty sands containing more than 10% fines with spt n values greater than 20, or sandy silts with more than 20% clay will not undergo any extensive damage. sands containing gravel particles have lower resistance than the clean sands without gravel for the same spt n-values. authors in [5] presented the influence of spt procedures in the evaluation of liquefaction resistance. they also proposed the curve of liquefaction resistance for sands with the variations of spt n-values and fines content. authors in [6] proposed a simple correction factor to counteract the effect of overburden pressure on the results of the standard penetration test (spt) performed in sands. authors in [7] studied the possible frequency of earthquakes in india and found that india has relatively higher frequencies of great earthquakes and lower frequencies of moderate earthquakes. authors in [8] studied the liquefaction potential as per the case history of the bihar-nepal earthquake on 21 august 1988. based on three prevailing approaches, they found the differences with regard to relative density and depth of liquefaction potential and suggested further research. authors in [9] studied the mechanism of liquefaction and soil failure during the 1994 northridge earthquake with detailed subsurface investigations. they found that the variation of the ground water table (gwt) in combination with the heterogeneous nature of alluvial fan sediments is responsible for complex patterns of ground deformation. authors in [10] found that clay particles are mainly responsible for the liquefaction characteristics of the soil. authors in [2] convened a workshop sponsored by the national center for earthquake engineering research (nceer) with 20 experts to review developments in the field of liquefaction in the past. they have given many updates and augmentations to the simplified procedure proposed in [1]. authors in [11] studied the corresponding author: ishwar chandra thakur engineering, technology & applied science research vol. 12, no. 6, 2022, 9471-9476 9472 www.etasr.com thakur & roy: soil liquefaction potential in different seismic zones of bihar, india likelihood of the initiation of soil liquefaction by spt-based probabilistic and deterministic correlations. authors in [12] closely studied the possible factor of the bhuj 2001 earthquake and found that deep fluid inflow plays a crucial role in the intensity of disasters. authors in [13] studied the liquefaction potential index (lpi) of mumbai city. they evaluated the factors of safety to predict the liquefaction potential along the depths of soil with a 2% probability of exceedance in 50 years using an spt-based simplified procedure. authors in [14] described the influence of earthquake ground motion on the liquefaction resistance of the soil. authors in [15] investigated the paleoliquefaction from four sites in north bihar and one site in eastern uttar pradesh. based on the available data, they found the recurrence interval of 124 ± 63 years for great earthquakes like the 1934 earthquake in bihar. they also concluded that the plains of bihar are most vulnerable to the seismic activity originating from the himalayas as well as the terai plains of nepal. authors in [16] studied the quality of groundwater in bihar. authors in [17] studied the postearthquake effect in kathmandu valley after gorkha, nepal earthquake on 25 april 2015. they found seven locations of sand blows based on geotechnical investigation records. authors in [18] reinterpreted the dynamic behavior of sandy soils subjected to recent historical earthquakes in japan and demonstrated that the aged soils have higher resistance towards liquefaction than that suggested by their current design code. authors in [19] studied four districts of bihar, i.e. samastipur, darbhanga, west-champaran, and araria based on reliability techniques for the prediction of seismic liquefaction. authors in [20-26] described stability methods for the soil types in bihar. authors in [27] evaluated the effect of plasticity on the liquefaction potential of fine-grained soil in the seismically active regions of bihar based on multi-linear regression (mlr) analysis and reliability analysis, i.e. first order second moment (fosm), and established a co-relation between the factor of safety against liquefaction, reliability index, and liquefaction probability. according to the literature survey, bihar is one of the most vulnerable states concerning seismic activities. tremendous work has been conducted in the field of liquefaction, but little in the region. this study has been done to overcome this shortcoming and to have more accurate predictions of liquefaction in the seismic zones of bihar, i.e. zone iii, zone iv, and zone v and their relative vulnerability towards liquefaction. here, a general correlation between liquefaction potential, depth, fines content, and spt-n value has been established to be used as a handy tool. the method adopted here for the analysis is the method recommended by indian standard which is originally based on the simplified empirical method of [1] and later on modified by different researchers in this field. ii. methodology the prime concern is to know whether the soil is susceptible to liquefaction or not, so that suitable measures can be adopted in advance if required. for this purpose, the factor of safety (fos) against liquefaction is estimated according to the method described in annex f of indian standard code [28] is 1893 (part 1): 2016, which is based on the simplified procedure proposed in [1] and later modified in [2]. the proneness of soil towards liquefaction is assured by estimating the fos at different depths below natural ground level (ngl). the fos is estimated by dividing the cyclic resistance ratio (crr) required to induce liquefaction in the soil by the cyclic stress ratio (csr) produced by an earthquake. fos = ������ (3) a. evaluation of csr authors in [1] formulated the following expression for the calculation of (csr): csr = 0.65 ������ � !"# !"#$ %& (4) where '(�) = peak ground acceleration (pga) at the ground surface, * = gravity acceleration, �,= total vertical stress at the point of interest, �,-� = effective vertical stress at the same point, and %& = %eduction factor. the value of the reduction factor was initially given in [1] which was later approximated in [29]: %& = ..///0/.1..23 4.56/./1/7836/.//.9723:.5 ..///0/.1.9934.56/./798;30/.//<8/73 :.56/.//.8./3= (5) is 1893 (part 1):2016 recommends using the ratio ('(�) /*) equal to seismic zone factor if the value of pga is not available. table i. seismic zone factor seismic zone factor ii iii iv v z 0.10 0.16 0.24 0.36 b. evaluation of crr crr = abb9.7(cde)f! fg (6) where abb9.7 = ccr for earthquake magnitude mw = 7.5, msf, f! , and fg are the correction factors for earthquake magnitude other than 7.5 (commonly known as magnitude scaling factor), overburden stress, and static shear stress respectively. authors in [2] re-evaluated the 1982’s data set to get the revised msf given by: msf = 108.81 ∕ ck8⋅7< (7) the high overburden correction factor is required for a depth greater than 15m is [30]: f! = (�,-� ∕ m� )n0. (8) where m� is the atmospheric pressure measured in the same unit as effective overburden pressure ( �,-� ) and the value of o depends on relative density (pq ): o= r 0.8~0.7 for pq = 40% to 60% 0.7~0.6 for pq = 60% to 80% (9) as per the report correction for static shear stress [28], fg, is required only for sloping ground which may be assumed to be in routine practice. engineering, technology & applied science research vol. 12, no. 6, 2022, 9471-9476 9473 www.etasr.com thakur & roy: soil liquefaction potential in different seismic zones of bihar, india the spt n-value measured in the field is corrected for the 60% hammer efficiency and standardized equipment using the expression: [</ = [a</ (10) where a</ = a\] ∗ a\_ ∗ a`` ∗ aab ∗ acd and a\] , a\_ , a`` , aab , and acd are the correction factors for the height of fall, hammer weight, sampler setup, rod length, and borehole diameter respectively. the n60 value computed is normalized to approximately 100kpa effective overburden pressure as suggested in [6]: ([.)</ = ae [</ (11) where: ae = (m� /�,-� )/.7 ≤ 1.7 (12) authors in [22] developed an equation for counteracting the effect of fines content to get an equivalent clean sand value ([.)</fg: ([.)</fg = h + i([.)</ (13) where: 2 190 1.5 [1.76 ] 0 1 for 5% 0.99 for 5% 35% 1000 0.5 1.2 for 35% fc a fc fc a e fc a fc                (14) an expression for cyclic resistance ratio for a 7.5 magnitude earthquake was formulated in [31] based on a clean sand base curve plot originally proposed in [5]: abb9.7 = .210(e:)j4kl + (e:)j4kl .27 + 7/ m./×(e:)j4kl617o= − .8// (15) this expression is valid for ([.)</ < 30. for ([.)</ ≥ 30, soils are too dense and non-liquefiable. iii. data analysis analysis has been done based on the big input data set which includes the depth of strata, its dry density, moisture content, fineness content, and spt n-values. the rotary method of boring was adopted with a borehole diameter of 150mm throughout the project. for the analysis of the whole project the magnitude of the earthquake, mw, was taken as 7.5. three major district data from seismic zone iii, five from seismic zone iv, and three from seismic zone v are summarized here in tables ii-iv for representation. the other districts from that zones show almost similar results. the soil of nawada and buxar districts has initially lower resistance to liquefaction which is almost near to the fos-1 line but at 3m depth there is a sudden increase in the fos of buxar due to the increase in spt n-value. bhojpur has comparatively higher resistance against liquefaction in seismic zone iii. fig. 1. variation of the factor of safety with depth in seismic zone iii table ii. liquefaction analysis of zone iii (pga: 0.16, msf: 1, ka: 1) district depth (m) ϒ (kn/m 3 ) fc n-value σv (kpa) σ´v (kpa) rd csr c60 n60 cn (n1)60 (n1)60cs kσ crr7.5 crr fos buxar gwt: 1.10m 1.50 19.62 95.20 10 29.43 25.51 0.990 0.12 0.65 6.50 1.70 11.04 13.75 1.00 0.15 0.15 1.24 3.00 19.91 97.20 22 59.74 41.10 0.979 0.15 0.69 15.25 1.56 23.78 29.04 1.00 0.41 0.41 2.78 4.50 19.72 97.20 14 88.73 55.38 0.969 0.16 0.74 10.31 1.34 13.85 17.12 1.00 0.18 0.18 1.13 6.00 19.82 94.10 18 118.90 70.83 0.958 0.17 0.82 14.81 1.19 17.60 21.62 1.00 0.24 0.24 1.42 7.50 19.82 94.20 20 148.62 85.84 0.943 0.17 0.82 16.46 1.08 17.76 21.82 1.00 0.24 0.24 1.41 9.00 19.91 96.40 21 179.23 101.73 0.923 0.17 0.82 17.28 0.99 17.13 21.06 1.00 0.23 0.23 1.35 10.50 19.91 96.60 23 209.10 116.89 0.894 0.17 0.87 19.92 0.92 18.43 22.61 1.00 0.25 0.25 1.51 nawada gwt: 3.50m 1.50 18.64 3.20 9 27.96 27.96 0.990 0.10 0.65 5.85 1.70 9.94 9.94 1.00 0.11 0.11 1.09 3.00 18.64 4.30 11 55.92 55.92 0.979 0.10 0.69 7.62 1.34 10.19 10.19 1.00 0.11 0.11 1.13 4.50 18.34 5.00 22 82.55 72.74 0.969 0.11 0.74 16.20 1.17 18.99 18.99 1.00 0.20 0.20 1.78 6.00 18.25 6.80 26 109.48 84.95 0.958 0.13 0.82 21.40 1.08 23.21 23.49 1.00 0.26 0.26 2.06 7.50 18.25 2.70 25 136.85 97.61 0.943 0.14 0.82 20.57 1.01 20.82 20.82 1.00 0.23 0.23 1.64 9.00 18.25 3.00 26 164.22 110.26 0.923 0.14 0.82 21.40 0.95 20.38 20.38 1.00 0.22 0.22 1.54 10.50 18.25 6.30 28 191.59 122.92 0.894 0.14 0.87 24.26 0.90 21.88 22.05 1.00 0.24 0.24 1.67 12.00 18.15 7.00 31 217.78 134.40 0.857 0.14 0.87 26.85 0.86 23.16 23.48 1.00 0.26 0.26 1.83 13.50 18.05 3.10 35 243.68 145.58 0.811 0.14 0.87 30.32 0.83 25.13 25.13 1.00 0.29 0.29 2.09 15.00 18.05 3.50 39 270.76 157.94 0.761 0.14 0.87 33.78 0.80 26.88 26.88 0.87 0.34 0.29 2.15 bhojpur gwt: 6.90m 1.50 19.72 74.30 11 29.58 29.58 0.990 0.10 0.65 7.15 1.70 12.15 15.08 1.00 0.16 0.16 1.56 3.00 19.72 84.60 12 59.15 59.15 0.979 0.10 0.69 8.32 1.30 10.81 13.47 1.00 0.15 0.15 1.42 4.50 19.72 85.50 14 88.73 88.73 0.969 0.10 0.74 10.31 1.06 10.94 13.63 1.00 0.15 0.15 1.45 6.00 19.82 79.30 17 118.90 118.90 0.958 0.10 0.82 13.99 0.92 12.83 15.90 1.00 0.17 0.17 1.70 7.50 19.82 80.30 19 148.62 142.74 0.943 0.10 0.82 15.64 0.84 13.09 16.20 1.00 0.17 0.17 1.69 9.00 19.91 77.40 23 179.23 158.63 0.923 0.11 0.82 18.93 0.79 15.03 18.53 1.00 0.20 0.20 1.82 10.50 19.91 78.40 25 209.10 173.78 0.894 0.11 0.87 21.66 0.76 16.43 20.21 1.00 0.22 0.22 1.95 engineering, technology & applied science research vol. 12, no. 6, 2022, 9471-9476 9474 www.etasr.com thakur & roy: soil liquefaction potential in different seismic zones of bihar, india table iii. liquefaction analysis of zone iv (pga: 0.246, msf: 1, ka: 1) district depth (m) ϒ (kn/m 3 ) fc nvalue σv (kpa) σ´v (kpa) rd csr c60 n60 cn (n1)60 (n1)60cs kσ crr7.5 crr fos nalanda gwt: 3.85m 1.50 18.25 92.95 5 27.37 27.37 0.990 0.15 0.65 3.25 1.70 5.52 7.13 1.00 0.09 0.09 0.57 3.00 18.25 93.75 6 54.74 54.74 0.979 0.15 0.69 4.16 1.35 5.62 7.24 1.00 0.09 0.09 0.59 4.50 18.34 90.95 11 82.55 76.17 0.969 0.16 0.74 8.10 1.15 9.28 11.64 1.00 0.13 0.13 0.78 6.00 18.34 88.92 14 110.07 88.98 0.958 0.18 0.82 11.52 1.06 12.21 15.16 1.00 0.16 0.16 0.87 7.50 18.44 91.32 17 138.32 102.51 0.943 0.20 0.82 13.99 0.99 13.82 17.08 1.00 0.18 0.18 0.91 9.00 18.44 90.44 21 165.99 115.46 0.923 0.21 0.82 17.28 0.93 16.08 19.80 1.00 0.21 0.21 1.03 10.50 18.44 92.59 24 193.65 128.41 0.894 0.21 0.87 20.79 0.88 18.35 22.52 1.00 0.25 0.25 1.19 12.00 18.44 90.09 29 221.31 141.36 0.857 0.21 0.87 25.12 0.84 21.13 25.85 1.00 0.31 0.31 1.48 13.50 18.74 91.20 30 252.95 158.28 0.811 0.20 0.87 25.99 0.79 20.66 25.29 1.00 0.30 0.30 1.47 15.00 18.74 89.77 31 281.06 171.68 0.761 0.19 0.87 26.85 0.76 20.50 25.09 0.85 0.29 0.25 1.29 patna gwt: 4.50m 1.50 19.33 90.90 7 28.99 28.99 0.990 0.15 0.65 4.55 1.70 7.73 9.78 1.00 0.11 0.11 0.72 3.00 19.52 90.90 9 58.57 58.57 0.979 0.15 0.69 6.24 1.31 8.15 10.28 1.00 0.12 0.12 0.76 4.50 19.62 90.90 12 88.29 88.29 0.969 0.15 0.74 8.84 1.06 9.40 11.78 1.00 0.13 0.13 0.85 6.00 19.72 91.70 16 118.31 103.59 0.958 0.17 0.82 13.17 0.98 12.94 16.02 1.00 0.17 0.17 1.00 7.50 19.72 91.70 20 147.89 118.46 0.943 0.18 0.82 16.46 0.92 15.12 18.65 1.00 0.20 0.20 1.08 9.00 19.91 91.70 23 179.23 135.08 0.923 0.19 0.82 18.93 0.86 16.29 20.04 1.00 0.22 0.22 1.13 10.50 19.91 92.90 24 209.10 150.24 0.894 0.19 0.87 20.79 0.82 16.96 20.85 1.00 0.23 0.23 1.17 12.00 20.01 92.90 28 240.15 166.57 0.857 0.19 0.87 24.26 0.77 18.79 23.05 1.00 0.26 0.26 1.34 13.50 20.01 92.90 30 270.17 181.88 0.811 0.19 0.87 25.99 0.74 19.27 23.62 1.00 0.27 0.27 1.42 15.00 20.11 90.90 33 301.66 198.65 0.761 0.18 0.87 28.59 0.71 20.28 24.84 0.81 0.29 0.23 1.30 saran gwt: 2.00m 1.50 19.23 92.70 6 28.84 28.84 0.990 0.15 0.65 3.90 1.70 6.63 8.45 1.00 0.10 0.10 0.65 3.00 19.52 92.70 9 58.57 48.76 0.979 0.18 0.69 6.24 1.43 8.93 11.22 1.00 0.12 0.12 0.68 4.50 19.62 92.70 10 88.29 63.77 0.969 0.21 0.74 7.36 1.25 9.22 11.57 1.00 0.13 0.13 0.61 6.00 19.23 91.90 12 115.37 76.13 0.958 0.23 0.82 9.88 1.15 11.32 14.08 1.00 0.15 0.15 0.67 7.50 19.23 91.90 15 144.21 90.25 0.943 0.24 0.82 12.34 1.05 12.99 16.09 1.00 0.17 0.17 0.73 9.00 19.33 91.90 18 173.93 105.26 0.923 0.24 0.82 14.81 0.97 14.44 17.83 1.00 0.19 0.19 0.80 10.50 19.33 93.00 23 202.92 119.53 0.894 0.24 0.87 19.92 0.91 18.22 22.37 1.00 0.25 0.25 1.04 12.00 19.62 93.00 26 235.44 137.34 0.857 0.23 0.87 22.52 0.85 19.22 23.56 1.00 0.27 0.27 1.16 13.50 19.62 93.00 28 264.87 152.06 0.811 0.22 0.87 24.26 0.81 19.67 24.10 1.00 0.28 0.28 1.25 15.00 19.72 91.70 30 295.77 168.24 0.761 0.21 0.87 25.99 0.77 20.04 24.54 0.86 0.28 0.24 1.16 west champaran gwt: 5.10m 1.50 19.13 94.90 28 28.69 28.69 0.990 0.15 0.65 18.19 1.70 30.93 37.61 1.00 0.00 0.00 0.00 3.00 19.03 96.50 7 57.09 57.09 0.979 0.15 0.69 4.85 1.32 6.42 8.20 1.00 0.10 0.10 0.64 4.50 19.03 96.60 6 85.64 85.64 0.969 0.15 0.74 4.42 1.08 4.77 6.23 1.00 0.08 0.08 0.54 6.00 19.03 95.10 12 114.19 105.36 0.958 0.16 0.82 9.88 0.97 9.62 12.04 1.00 0.13 0.13 0.81 7.50 19.23 95.30 23 144.21 120.66 0.943 0.18 0.82 18.93 0.91 17.23 21.18 1.00 0.23 0.23 1.31 9.00 19.23 95.30 25 173.05 134.79 0.923 0.18 0.82 20.57 0.86 17.72 21.76 1.00 0.24 0.24 1.29 10.50 19.33 95.40 28 202.92 149.95 0.894 0.19 0.87 24.26 0.82 19.81 24.27 1.00 0.28 0.28 1.47 begusarai gwt: 4.00m 1.50 19.52 84.30 9 29.28 29.28 0.990 0.15 0.65 5.85 1.70 9.94 12.43 1.00 0.14 0.14 0.87 3.00 19.52 84.30 11 58.57 58.57 0.979 0.15 0.69 7.62 1.31 9.96 12.45 1.00 0.14 0.14 0.89 4.50 19.91 84.30 19 89.61 84.71 0.969 0.16 0.74 13.99 1.09 15.20 18.74 1.00 0.20 0.20 1.25 6.00 19.91 84.30 23 119.49 99.87 0.958 0.18 0.82 18.93 1.00 18.94 23.23 1.00 0.26 0.26 1.46 7.50 19.91 87.20 25 149.36 115.02 0.943 0.19 0.82 20.57 0.93 19.18 23.52 1.00 0.27 0.27 1.39 9.00 19.91 87.20 26 179.23 130.18 0.923 0.20 0.82 21.40 0.88 18.75 23.00 1.00 0.26 0.26 1.30 10.50 20.01 79.40 28 210.13 146.37 0.894 0.20 0.87 24.26 0.83 20.05 24.56 1.00 0.28 0.28 1.41 12.00 20.01 79.40 30 240.15 161.67 0.857 0.20 0.87 25.99 0.79 20.44 25.03 1.00 0.29 0.29 1.47 13.50 20.11 82.40 32 271.49 178.30 0.811 0.19 0.87 27.72 0.75 20.76 25.41 1.00 0.30 0.30 1.56 15.00 20.11 82.40 38 301.66 193.75 0.761 0.18 0.87 32.92 0.72 23.65 28.88 0.82 0.40 0.33 1.80 fig. 2. variation of the factor of safety with depth in seismic zone iv. fig. 3. variation of the factor of safety with depth in seismic zone v. engineering, technology & applied science research vol. 12, no. 6, 2022, 9471-9476 9475 www.etasr.com thakur & roy: soil liquefaction potential in different seismic zones of bihar, india table iv. liquefaction analysis of zone iv (pga: 0.36, msf: 1, ka: 1) district depth (m) ϒ (kn/m 3 ) fc n-value σv (kpa) σ´v (kpa) rd csr c60 n60 cn (n1)60 (n1)60cs kσ crr7.5 crr fos madhubani gwt: 0.85m 1.50 17.96 23.20 3 26.95 20.57 0.990 0.30 0.65 1.95 1.70 3.31 7.73 1.00 0.09 0.09 0.31 3.00 17.95 17.20 6 53.85 32.76 0.979 0.38 0.69 4.16 1.70 7.07 10.56 1.00 0.12 0.12 0.31 4.50 18.04 93.68 9 81.20 45.40 0.969 0.41 0.74 6.63 1.48 9.84 12.30 1.00 0.13 0.13 0.33 6.00 18.07 21.08 10 108.39 57.87 0.958 0.42 0.82 8.23 1.31 10.82 15.55 1.00 0.17 0.17 0.39 7.50 18.05 13.30 12 135.35 70.11 0.943 0.43 0.82 9.88 1.19 11.79 14.23 1.00 0.15 0.15 0.36 9.00 18.06 7.35 28 162.55 82.59 0.923 0.43 0.82 23.04 1.10 25.35 25.78 1.00 0.31 0.31 0.72 10.50 18.29 6.73 32 192.07 97.40 0.894 0.41 0.87 27.72 1.01 28.09 28.38 1.00 0.38 0.38 0.93 12.00 18.35 37.70 12 220.26 110.88 0.857 0.40 0.87 10.40 0.95 9.87 12.35 1.00 0.13 0.13 0.34 13.50 18.43 41.34 15 248.77 124.68 0.811 0.38 0.87 12.99 0.90 11.64 14.46 1.00 0.15 0.15 0.41 15.00 18.45 4.25 28 276.73 137.92 0.761 0.36 0.87 24.26 0.85 20.65 20.65 0.91 0.22 0.20 0.57 darbhanga gwt: 2.30m 1.50 18.04 94.80 5 27.07 27.07 0.990 0.23 0.65 3.25 1.70 5.52 7.13 1.00 0.09 0.09 0.38 3.00 18.57 93.10 7 55.70 48.83 0.979 0.26 0.69 4.85 1.43 6.94 8.83 1.00 0.10 0.10 0.39 4.50 18.26 86.46 9 82.18 60.60 0.969 0.31 0.74 6.63 1.28 8.51 10.72 1.00 0.12 0.12 0.39 6.00 18.22 16.75 15 109.31 73.02 0.958 0.34 0.82 12.34 1.17 14.45 18.24 1.00 0.19 0.19 0.58 7.50 18.68 15.50 10 140.08 89.07 0.943 0.35 0.82 8.23 1.06 8.72 11.80 1.00 0.13 0.13 0.37 9.00 18.61 16.70 11 167.47 101.75 0.923 0.36 0.82 9.05 0.99 8.97 12.44 1.00 0.14 0.14 0.38 10.00 18.25 16.75 13 182.51 106.97 0.905 0.36 0.87 11.26 0.97 10.89 14.48 1.00 0.15 0.15 0.43 supaul gwt: 1.00m 3.00 19.33 71.00 8 57.98 38.36 0.979 0.35 0.69 5.54 1.61 8.95 11.24 1.00 0.12 0.12 0.36 4.50 19.33 7.00 13 86.97 52.63 0.969 0.37 0.74 9.57 1.38 13.19 13.43 1.00 0.14 0.14 0.39 7.50 19.33 9.00 17 144.94 81.18 0.943 0.39 0.82 13.99 1.11 15.53 16.35 1.00 0.17 0.17 0.44 9.00 19.33 8.00 18 173.93 95.45 0.923 0.39 0.82 14.81 1.02 15.16 15.65 1.00 0.17 0.17 0.42 10.50 19.33 8.00 19 202.92 109.72 0.894 0.39 0.87 16.46 0.95 15.71 16.21 1.00 0.17 0.17 0.45 12.00 19.33 8.00 22 231.91 124.00 0.857 0.37 0.87 19.06 0.90 17.11 17.63 1.00 0.19 0.19 0.50 13.50 19.33 5.00 25 260.90 138.27 0.811 0.36 0.87 21.66 0.85 18.42 18.42 1.00 0.20 0.20 0.55 15.00 19.33 6.00 28 289.89 152.55 0.761 0.34 0.87 24.26 0.81 19.64 19.76 0.88 0.21 0.19 0.55 18.00 19.33 7.00 35 347.86 181.09 0.667 0.30 0.87 30.32 0.74 22.53 22.84 0.84 0.25 0.21 0.71 21.00 19.33 8.00 44 405.84 209.64 0.598 0.27 0.87 38.12 0.69 26.32 26.96 0.80 0.34 0.27 1.00 in seismic zone iv, begusarai has the highest resistance towards liquefaction as the district is liquefiable only up to 3.5m depth below ngl. saran is liquefiable up to 10.5m depth below ngl which shows that this district is the most susceptible to liquefaction in seismic zone iv. all the districts of zone v have a factor of safety almost below the fos-0.5 line which means that they are most susceptible to liquefaction. madhubani has a sudden increase in factor of safety at 9m to 10.5m depth below ngl due to a slight decrease in fines content and drastically increase in spt n-value. iv. discussion from the above data set, it is found that among the districts of seismic zone iii, buxar and bhojpur have higher fines content than nawada, whereas the spt n-value of nawada is comparatively high. begusarai districts have comparatively lower fines content than the districts of seismic zone iv. darbhanga district has a sudden decrease in fines content from 4.5m to 6m depth, whereas madhubani shows two local peaks at 4.5m and 13.5m. authors in [4] found that more than 10% of fines content values of soils are less liquefiable, but in the present study, it has been found that the fines content and spt nvalues are both critical factors for the liquefaction potential of the soil. liquefaction may occur at higher or lower fines content values if the spt-values are lower and higher respectively. v. conclusion based on the analysis results and the graphs of the fos versus fines content and spt n-value, the following conclusions have been made relative to the different seismic zones of bihar: in seismic zone iii, the soil shows comparatively more resistance to liquefaction in most cases. the fos value is more than 1 in all cases. bhojpur shows comparatively more resistance to liquefaction, whereas nawada shows the lowest resistance in the mentioned zone. the soil of seismic zone iv is relatively more prone to liquefaction. the soil of begusarai district is liquefiable up to 3.5m depth below ngl. saran district is 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[31] a. f. rauch, private communication, 1998. microsoft word etasr_v13_n1_pp9837-9842 engineering, technology & applied science research vol. 13, no. 1, 2023, 9837-9842 9837 www.etasr.com pathala & jayasree: design of a shielded room against emp signal as per mil-std 461 design of a shielded room against emp signal as per mil-std 461 venkata sai charishma pathala department of eece, gandhi institute of technology and management, deemed to be university, india cpathala@gitam.in (corresponding author) pappu v. y. jayasree department of eece, gandhi institute of technology and management, deemed to be university, india jpappu@gitam.in received: 30 september 2022 | revised: 3 november 2022 | accepted: 5 november 2022 abstract electromagnetic shielding is the best technique to protect equipment from the electromagnetic pulse (emp) signal. this paper explains how effectively the equipment will be protected within a shielded room against emp signals. the shielded room is designed with different points of entry used to provide electrical connections to the equipment under test (eut) in a honeycomb structure for ventilation to protect the equipment from the emp signal. the shielded room with four points of entry and honeycomb structures is designed, analyzed theoretically, and simulated in the cst studio. the points of entry (poe) and the honeycomb structure are designed based on mil-std-461 e/f/g (by following this standard the maximum frequency of emp signal is 100mhz). it is observed that by increasing the size of the poe the shielding effectiveness value decreases by 20db for perfect electrical conductor (pec) material of 2mm thickness. it is concluded that the equipment will be more protected when it is placed nearer to the front wall or in the middle of the shielded room. the performance of the shielded room will not be affected with honeycomb structures which will provide 220db shielding effectiveness (se). keywords-electromagnetic pulse (emp); point of entry (poe); honeycomb structure; mil-std-461 e/f/g; shielding effectiveness (se); perfect electrical conductor (pec) i. introduction in the present electromagnetic environment, the protection of equipment related to medical or military applications is of utmost priority. equipment shielding is achieved by designing a shielded room. usually, the shielded room will be designed by placing gaskets during the design of the door of the room, a honeycomb structure for ventilation, and apertures for the routing of cables. the main motto of this shielded room is to protect the electronic equipment from the interference of the dangerous signal strength of emps. the most effective method to safeguard the equipment from electromagnetic interference (emi) is shielding and filtering [1-4]. the performance of a shield is defined by its se value which is obtained from taking the difference between the received power with shield material and without it [5]. the shielding technique is used in many fields like aerospace engineering or medical and military equipment. in aerospace applications, different combinations of shielding materials are used to provide shielding to the aircraft [6]. even the human brain can be protected from mobile radiation by placing shields coated with different types of shielding materials [7]. the simulated data for electromagnetic calculations can be acquired by various numerical methods [8], but the computations usually require long time. so, the analytic method has a better performance than the numerical methods. the analytical methods are classified in two types, i.e. based on aperture coupling between the aperture [9, 10] and based on the transmission line theory. the design of metallic shielded rooms is used to reduce the leakage signals from external electromagnetic fields. according to the ieee standard 299, the se is used for the calculation of the effectiveness of metallic shielded enclosures [11]. the materials used in the design of shielded rooms are considered based on their conductivity and the frequency of operation. in this paper, the material used in the design was a perfect electrical conductor, in theoretical calculations the conductivity value of the materials is not considered while calculating the se of the shielded room. the calculations of se can be done with many methods. one of these is to add three parameters (reflection loss (r), absorption loss (a), multiple reflections (m)) to obtain the se value. sedb = rdb +adb + mdb (1) engineering, technology & applied science research vol. 13, no. 1, 2023, 9837-9842 9838 www.etasr.com pathala & jayasree: design of a shielded room against emp signal as per mil-std 461 another method for the calculation of electrical se (ese) is achieved by considering the difference between the field signal in the presence and the absence of the shield as in (2). ea and ep are the electric field intensities without and with an enclosure, respectively. ese = 20 log �� ��[db] (2) the se value depends on the size and the number of points of entry (poe). the poe is defined by the frequency of the input signal. the maximum frequency of the emp signal is 100mhz, so that the poe are designed with a cut of frequency greater than the frequency of the input signal. leakage of signal occurs when the wavelength of the signal is shorter than the size of the poe. ii. design of the shielded room the shielded room was designed to protect equipment against emp signals. the emp signal has a high amplitude and short duration. the characteristics of an emp signal is a double exponential voltage pulse with amplitude of 55kv, rise/fall time 2.3ns, pulse width 22.73ns as per mil-std 461 e/f/g [12] (figure 1). the emp signal is given as an input to the shielded room, the equipment in the shielded room is protected by providing all power connections to the equipment. the design of poe for a shielded room must consider the frequency component of the emp signal. the frequency of the emp signal is calculated by taking the inverse of its period. the maximum frequency of the emp signal is 100mhz, considered from the military standard mil-std 461 e/f/g and the poe are designed such that they should not allow the entry of the emp signal. fig. 1. emp signal waveform. fig. 2. a shielded room with different poe. the shielded room with different poe for routing the power cables and honeycomb structure to provide ventilation to the equipment is shown in figure 2. the shielded room was designed with 4 poe with different cutoff frequencies to protect. the poe is considered as the waveguide. the maximum frequency of the emp signal is 100mhz so that the waveguides are designed with a cutoff frequency greater than that, so that the equipment is protected from the emp signal. the frequency of the poe is shown in table i. honeycomb structures were considered for vendilation. two honeycomb structures with cutoff frequency of 40ghz were placed in parallel at the top of the room. the design dimensions of the shielded room with honeycomb structure are also given in table i. table i. shielded room dimensions parameters length width height rf shielded room d = 2m a = 2m b = 2m honeycomb panel r = 0.45m poe l (m) w (m) cutoff frequency (fc) p1 0.1 0.05 1.5ghz p2 0.075 0.0375 2 ghz p3 0.06 0.03 2.5 ghz p4 0.05 0.025 3 ghz iii. mathmatical analysis a. single point of entry the effectiveness of the metallic shielded room can be determined mathematically by considering a single poe by using the transmission line model (tlm) method [13]. the equivalent circuit of the shielded room with poe is represented here. fig. 3. circuit model of the shielded room with poe. from the equivalent circuit model, thevenin’s theorem is applied to calculate the value of se. the q point represents the position of the equipment. the length of the poe is l. the applied input voltage is denoted by v0, the input impedance of the equivalent circuit is z0, a single poe is considered in the circuit model, and its impedance is zpoe. the se value is calculated at distance x from the aperture. �� � �� � � �� � � (3) ��� � �� � � � �tan � ��� � � (4) � � � � � �� � � (5) k v engineering, technology & applied science research vol. 13, no. 1, 2023, 9837-9842 9839 www.etasr.com pathala & jayasree: design of a shielded room against emp signal as per mil-std 461 the dominant mode of propagation in the rectangular waveguide is the te10 mode and its characteristic impedance is: � � �����( )" (6) where # � $�� and the propagation constant %� is: %� � %� ∗ �1 − (#)�) (7) where %� � �*$� . zg and pg are imaginary frequencies below the cutoff frequency. then v1, z1, which are the short circuit terminals of the wave guide to q are transformed by attributing an equivalent voltage v2, source impedance z2, and load impedance z3: �� � �+,-./�012�345+506.78/�012 (8) � � +�39:;8/�012��345+506:;8/�012 (9) < � � � tan(= − >) (10) the voltage at point q is: �? � �� <( �� <) (11) the se is: se = -20 log10|2vq /v0| (12) b. multiple points of entry a shielded room with multiple poe of different sizes was designed to protect the equipment from the emp signal. the maximum frequency of the emp signal should be considered while designing the poe, so that no external signal is allowed inside the room. the multiple poe of the side wall of the shielded room can be seen in figure 4. fig. 4. hardening of emp signal with multiple poe. a shielded room with length and breadth a and b, respectively, with an array of entries with dimensions of l, w is considered. the distance between the poe is defined as dh and dv. @� and y0 are the free-space wavelength and the intrinsic admittance. each poe is considered as a rectangular hole denoted as d, where h, s are its length and width. d = 0.636(h + s) (13) the se calculation for multiple poe when an emp signal is applied to shielded room follows. the admittance of the equivalent circuit is given by [19]: a� �b a� � −c <de df $� *dg + � �ii *$�d" j∑ ∑ 4 ∈m n" df" + ∈o p" de" 6 c��(>)qnr�qpr� s (14) the argument of the bessel function is: > � t*d(p" /de" �n" /df" )/�)+/"v(p" /de" � n" /df")/�)+/" (15) zpoes = 1/ypoes represents the poe array connecting the free space [14]. figure 4 shows multiple poe placed on the shielded room wall. the effective wall impedance zpoes 1 is the inverse of zpoes. using an impedance ratio concept, zpoes becomes: zah 1 = zah�w∗x�∗y � (16) where the length l and width w of multiple poe are: z � d[� + \(] − 1) ∗ =ℎ) + d[ � (17) w� d_� + \(` − 1) ∗ =a) + d_ � (18) where m and n represent the number of apertures in length and width of the array, respectively. �� � /��∗ �[ +2 ( �� �[+ ) (19) � � ( �∗ �[ + ) ( �� �[+) (20) the se is: se = -20 log10|2vq /v0| (21) c. honeycomb structure the attenuation constant for the wave guide is given below [15]. the attenuation constant is used for the calculation of the se value of the wave guide: b � c(d ∈)+"e f − 1 (22) where fc is the cutoff frequency of the waveguide. the attenuation constant of the waveguide in db can be calculated by placing the cutoff frequency value in (22). the se value for a single hexagon cell (honeycomb structure) is calculated by using (23): seij � 17.5 d� e1 − � �n oppqr� � (23) in [16], an infinite array of parallel-plate waveguides is analyzed by the wiener-hopf method. the resulting equation is shown below. the first part gives the se of the unit cell of a hexagon waveguide, while the second term is the se of an infinite array of parallel-plate waveguides [24]. seij � 17.5 d� e1 − � �n oppqr� � − 20 log�� �x0 * cos { (24) where k is the wave number, g is a transverse dimension of the waveguide, and φ is the angle of an incident wave. engineering, technology & applied science research vol. 13, no. 1, 2023, 9837-9842 9840 www.etasr.com pathala & jayasree: design of a shielded room against emp signal as per mil-std 461 the se equation for a hexagon structure has been modified by adding a third term to (24), so the performance of the hexagon structure at lower frequency is increased. the normalized frequency during the design of the honeycomb structure should be greater than 5 times the radius of the cell of the honeycomb structure. se value does not depend on the number of hexagon cells in the honeycomb structure, but on the size and the length of a single cell. |}d~ = 17.5 d� e1 − � �n oppqr� � −20 log�� �x0 * cos { − 20 log�� ��0 (25) iv. simulations a. shielded room with a single point of entry a shielded room with a size of 2m×2m×2m with a single poe of size 0.075m×0.0375m is shown in figure 5. the probe was placed at the center of the shielded room. the position of the probe varied inside the room to find the fields inside the room with an emp signal transmitted continuously to the shielded room. the material used in the design of the shielded room is perfect electrical conductor (pec). the thickness of the shielded material is 2mm. se value varies with the size of the poe. a poe of size 10cm×5cm is considered and the se value is 255db. if the size of the aperture is decreased, the se value is increased as shown in table ii. the size of the poe depends on the frequency of the emp signal. figure 6 shows the se value for 4 apertures. table ii. se values for different points of entry poe a (m) b (m) se (db) p1 0.1 0.05 290 p2 0.075 0.0375 310 p3 0.06 0.03 320 p4 0.05 0.025 330 fig. 5. shielded room with a single poe. b. shielded room with multiple points of entry the shielded room with different entries was designed in cst simulation tool as shown in figure 6. the se value for an individual poe is shown in figure 7. let us consider shielded rooms with 4 poe with different dimensions. the dimensions of an entry depend on its cutoff frequency. the cutoff frequency should be greater than the frequency of the emp signal. in this condition the se value meets the military standards mil-std-188-125-1 and 2. figure 8 shows the total se value of 4 different dimensions. the se value decreases with the frequency of operation, which is below the resonant frequency. the resonant frequency of the shielded room was calculated by considering the room dimensions along with mode of propagation. the electric field probe is considered at the center of the shielded room, so that maximum se value is obtained at that point. the se value for 4 different poe is 250db. fig. 6. shielded room with 4 poe with different sizes. fig. 7. se value for different poe sizes when an emp signal is given as input. fig. 8. effect of se when an emp is applied to multiple poe. engineering, technology & applied science research vol. 13, no. 1, 2023, 9837-9842 9841 www.etasr.com pathala & jayasree: design of a shielded room against emp signal as per mil-std 461 c. shielded room with honeycomb structures the shielded room was designed with honeycomb structures used for ventilation, placed at the top of the room. the honeycomb structures were designed such that no external signal would enter the shielded room. figure 9 shows the honeycomb structure. the honeycomb structures placed on the shielded room are shown in figure 10. the se value is calculated when the emp signal is applied to the room. (a) (b) fig. 9. cell dimension details of the honeycomb structure, (b) total honeycomb structure. fig. 10. shielded room with 2 honeycomb structures. d. shielded room with points of entry and honeycomb structure the shielded room was designed with 4 poe and 2 honeycomb structures, as shown in figure 11. the emp signal is incident on the shielded room with a voltage of 55kv. the se value is calculated by placing the field probe at the center of the room. the total shielded room se value is given in figure 12. fig. 11. shielded room with 4 poe and 2 honeycomb structures. fig. 12. the electric field value for a totally shielded room with 4 poe and 2 honeycomb structures. total se is calculated by taking the difference between the electric field with and without shield. e. effect of varying field probe the emp signal is incident directly to the shielded room, which has dimensions of 2m×2m×2m with a single poe. the emp signal is parallel to the shielded enclosure. in this case the polarization type is fixed, so the field probe inside the enclosure is varied so that the se value varies with changes in the position of the probe. the field probe gives the position of the equipment so that maximum se is noted. the shielded room with a single poe is shown in figure 4. the change in the value of se with the position of the field probe is shown in figure 8. consider a point q at a different distances x1, x2, x3 from the front panel of the shielded room. the se value increases when the position of the probe is near the wall of the shielded room as clearly observed in figure 13. fig. 13. varying position of the field probe in the shielded room when the emp is applied. engineering, technology & applied science research vol. 13, no. 1, 2023, 9837-9842 9842 www.etasr.com pathala & jayasree: design of a shielded room against emp signal as per mil-std 461 by observing the graph of figure 13, we note that the se value increases when the position of the probe is to the shielded room front wall and at the center of the room, and decreases when the probe is near to the back wall of the shielded room. v. conclusion theoretical calculations and simulation analysis were conducted in this paper for a shielded room against emp signals. the transmission line method was used in the theoretical calculations of the shielded room with 4 different poe dimensions. the smallest poe with 0.05m length and 0.025m width has better se value of 330db than a poe with greater size, with 0.1m length and 0.05m width, where the se value decreases to 250db. simulation analysis is done with 3dem cst modeling tool to verify the combined effect of multiple poe and honeycomb structures. the total se value for a shielded room with 4 poe and 2 honeycomb structures is 140db. the novelty of this paper is that it was conducted as per mil-std-188-125-1/2 to protect the equipment from external emp signals. this design of shielded room is useful for rf engineers that need to estimate the interference levels in sensitive equipment due to emp signals. references [1] j. chen and j. wang, "a three-dimensional semi-implicit fdtd scheme for calculation of shielding effectiveness of enclosure with thin slots," ieee transactions on electromagnetic compatibility, vol. 49, no. 2, pp. 354–360, feb. 2007, https://doi.org/10.1109/temc. 2007.893329. 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[15] h.-r. im, i.-k. jung, j.-g. yook, and h.-r. song, "analysis of emp penetration into an enclosure with electromagnetic shielding material," in 2018 usnc-ursi radio science meeting (joint with ap-s symposium), boston, ma, usa, jul. 2018, pp. 31–32, https://doi.org/ 10.1109/usnc-ursi.2018.8602763. [16] w. a. bereuter and d. c. chang, "shielding effectiveness of metallic honeycombs," ieee transactions on electromagnetic compatibility, vol. emc-24, no. 1, pp. 58–61, oct. 1982, https://doi.org/10.1109/ temc.1982.304013. microsoft word etasr_v13_n1_pp10093-10099 engineering, technology & applied science research vol. 13, no. 1, 2023, 10093-10099 10093 www.etasr.com godbole & george: a novel algorithm for optimal harmonic load flow including harmonic … a novel algorithm for optimal harmonic load flow including harmonic compensation prachi godbole department of electrical engineering, fr. c. r. institute of technology, university of mumbai, india prachipgodbole@gmail.com (corresponding author) sincy george st. francis institute of technology, university of mumbai, india principal@sfit.ac.in received: 10 november 2022 | revised: 18 december 2022 | accepted: 21 december 2022 abstract load flow analysis is widely used for finding voltage at various parts of a large, interconnected power system. the exponential increase in the use of power electronic devices and the noticeable percentage of integration of renewable energy sources in modern power systems result in the occurrence of nonsinusoidal voltages at various parts of the power system. by reformation of the newton-raphson load flow method, a few harmonic load flow algorithms have been developed for modern transmission systems. however, for larger transmission systems, complexity and heavy computational burden are often encountered in the load flow solution process due to the increased size of the jacobean matrix that further increases with multiple non-linear load buses and compensation requirements. this leads to convergence problems and increased execution time. in this paper, an optimal harmonic load flow algorithm is proposed, that employs a modified pso technique to select control variables and the harmonic load flow method to find solutions for load flow analysis with a reduced size of the jacobean matrix. the formulated method uses a simple technique to take into account nonlinear loads and results in faster convergence. the novelty of the algorithm is that an optimal load flow solution with the desired amount of reactive and harmonic compensation currents is obtained. the algorithm can help in getting load flow solutions in future power systems with distorted voltage and currents with compensation. the performance of the proposed algorithm is tested on a modified ieee 30-bus system with multiple non-linear load buses and is validated with the simulink model of the system. keywords-compensation; harmonic load flow; optimization; particle swarm optimization (pso); power system; transmission losses i. introduction load flow analysis plays an important role in power system operation, control, and planning. in modern power systems, the proliferation of power electronic-based nonlinear loads for industrial and commercial use results in the occurrence of nonsinusoidal bus voltages at various parts of the power system. as per [1], the indian transmission system voltage and current were found to be rich in 5 th and 7 th harmonics due to large industrial loads such as rolling mills driven by variable speed drives and arc furnaces. also, due to the integration of renewable energy sources in power grids [2], there is a noticeable decrease in voltage quality in modern transmission systems. the standard regulations and recommendations for harmonic studies [3] provide harmonic distortion limits for system voltage. as distributed generation and non-linear loads are increasing day by day, it is needed to find the desired reactive and harmonic compensation under non-sinusoidal voltage conditions while conducting load flow analysis in order to maintain stable operation in future transmission systems. newton-raphson load flow (nrlf) is widely used for power flow analysis under sinusoidal conditions of a power system. under non-sinusoidal voltage conditions and in order to find harmonic load flow solution, authors in [4] have modified the conventional nrlf method with detail nonlinear load modeling and satisfactory results were obtained with reasonable accuracy. however, it is implemented for an 8-bus system. different harmonic load flow methods have been developed in [5-7]. most use nonlinear load modeling and gave satisfactory results. authors in [5] used a unified newton’s approach to simplify the solution, while authors in [6] proposed a decoupled approach suitable for transmission systems. recently, the harmonic monitoring method [7] has been developed using pmus in the transmission system. by understanding the importance of the optimal power flow (opf) solution for economic and reliable operation under linear load conditions, traditionally, classical or deterministic engineering, technology & applied science research vol. 13, no. 1, 2023, 10093-10099 10094 www.etasr.com godbole & george: a novel algorithm for optimal harmonic load flow including harmonic … optimization techniques have been used. recently, comparatively easier to implement heuristic methods have been preferred to undertake global search [8-10]. the future transmission systems will be more and more at the risk of non-sinusoidal bus voltage conditions and under the adverse effects of harmonics. under such conditions, with the optimal placement of capacitors and with strategic placement and sizing of passive or active filters for harmonic compensation using deterministic [11] and heuristic [12-14] optimization techniques, optimal load flow solutions can be obtained. however, in most of the reviewed studies, distribution systems have been considered for harmonic analysis and associated optimization using the decoupled harmonic load flow approach, as such systems are more sensitive to harmonic distortions. looking at today’s situation of modern transmission systems with noticeable percentage of harmonics, the utilities are redirecting their focus on transmission system harmonics and their mitigation. to the best of our knowledge, there is no sufficient solution available for harmonic load flow in transmission systems with compensation. in this paper, an optimal harmonic load flow algorithm is proposed for transmission systems with reduced size of jacobean matrix which results in faster convergence. the desired amount of reactive and harmonic compensation is also addressed. ii. the proposed optimal harmonic load flow algorithm a simple and efficient optimal harmonic load flow algorithm is developed by modifying the nrlf method and employing the pso technique that helps in getting faster a global optimal solution under non-sinusoidal voltage condition. consider a � bus system with 1to m linear buses including the slack bus and (� + 1) to n nonlinear load buses out of which 2 to � buses as pv buses and (� + 1) to � buses as linear pq buses, as shown in figure 1. the specified variables and unknowns are given in table i. fig. 1. layout of a typical n-bus power system with compensators. table i. specified and unknown data of various buses bus no. (�) bus type specified variables unknown variables 1 slack ��,� , ��,� ��,� , ��,� , ��,� , ��,� 2 to � pv ��,� , ��,� ��,� , ��,�, ��,� , ��,� (� + 1) to � linear pq ��,� , ��,� ��,�, ��,� , ��,� , ��,� (� + 1) to � non-linear pq ��,� , ��,� ��,�, ��,�, ��,� , ��,� , ��,� in table i, the first subscript of a variable represents the bus number and the second represents the order of harmonics. under non-sinusoidal condition, the nrlf equation [15] can be modified as: [∆��(� !)] = [$(̅� !)]. [∆'�(� !)] (1) where ∆ represents change in the specified and calculated value of a parameter, while [∆��(� !)] is the modified mismatch vector and [∆'�(� !)] is the modified correction vector. equation (1) can be rewritten as: (∆)��(� !)∆*�̅,� + = [$�̅ ! ]. ⎣⎢ ⎢⎢ ⎡ ∆��̅,�∆ �/�,� ∆��̅,� ∆ �/�,� ⎦ ⎥⎥ ⎥⎤ (2) [∆��(� !)] includes the power mismatch vector 3∆)��(� !) 4 and the harmonic current mismatch vector 3∆*�̅,� 4, which are explained below. 1)power mismatch vector 3∆)��(� !)4 is given by: 3∆)��(� !)4 = 5 ∆�6,�, … , ∆��,�, ∆�6,�, … , ∆��,�,∆��8�,� , … , ∆�9,� , ∆��8�,� , … , ∆�9,� : ; (3) where subscript t represents the total power including fundamental and harmonic powers calculated at the <�� bus as: �� ,� = ∑ > ��,� . ∑ �?,� . @�?,� .9?a� cos>d�?,� − ��,� +�fgh�a��?,� ii (4) ��,� = ∑ > ��,� . ∑ �?,� . @�?,� .9?a� sin>d�?,� − ��,� +�fgh�a��?,� ii (5) where [@�?,�] is an element of bus admittance matrix [@lmn,� ] at the h th harmonic component with magnitude @�?,� and phase angle d�?,� . the size of 3∆)��(� !) 4 is [2(� − 1)] o 1 . however, if we consider 2 to l buses as pv buses, the corresponding ∆�/�,� = 0 reduces the size of the matrix. 2)harmonic current mismatch vector 3∆*�̅,� 4 is formed for < = 1 to n and ℎ = 2 to ℎ�rs given by: 3∆*�̅,� 4 = 3∆*�,6, … , ∆*9,6, … , ∆*�,�fgh , … , ∆*9,�fgh 4; (6) where ∆*�,� = *�,�(ntuv) − *�,�(vrw ) while xyz[ and [\� are representing the specified and calculated values of the parameters. *�,�(ntuv) at the ith bus is obtained from the engineering, technology & applied science research vol. 13, no. 1, 2023, 10093-10099 10095 www.etasr.com godbole & george: a novel algorithm for optimal harmonic load flow including harmonic … fundamental load current *�,�(ntuv) obtained using the specified powers as follows: *�,�(ntuv) = ]^_,`(abcd)8ef_,`(abcd)g_,` h ∗ (7) where ��,�(ntuv) and ��,�(ntuv) are the specified fundamental active and reactive powers at nonlinear load buses. equation (7) calculates *�,�(ntuv) for < = (� + 1) to n nonlinear load buses. ��,�(ntuv) is iteratively calculated using the ��,�(ntuv) equation that includes voltage and current distortion powers in addition to ��,�(ntuv) and ��,�(ntuv): ��,� 6 = �� ,� 6 + ��,� 6 + k�,� 6 (8) where k�,� 6 = (kl�,� 6 + kg�,� 6) with kl�,� 6 and kg�,� 6 are the squared values of total current and total voltage distortion powers respectively. the specified harmonic currents *�,�(ntuv) for ℎ = 2 to ℎ�rs are obtained using a typical harmonic spectrum for non-linear load as follows [16]: *�,�(ntuv) = *�,�(ntuv) . m� (9) d�,�(ntuv) = d�nntuv�o + ℎ. >d�,�(ntuv) − d�nntuv�o i (10) where *�,�(ntuv) and d�,�(ntuv) are the magnitude and the phase angle for *�,�(ntuv) , m� is the ratio of the h-order harmonic component to the fundamental component of the current, and d�nntuv�o is the phase angle for the h-order harmonic component. *�,�(vrw) for < = 1 tp n to form the mismatch current vectors is obtained as: *�,�(vrw) = ∑ @�?,� .9?a� �?,� . >cos>d�?,� + �?,� i +p�<�>d�?,� + �?,� ii (11) the elements of 3∆*�̅,� 4 are expressed in real and imaginary terms as: 3∆*�̅,� 4 = 3∆*�̅o,� , ∆*�̅�,� 4; (12) the harmonic current mismatch vector is updated with the desired harmonic compensation current, 3*�,�(v �t)4 as: ∆*o�,�(� !) = (*o�,�(ntuv) − *o�,�(v �t)) − *o�,�(vrw) (13) ∆*��,�(� !) = (*��,�(ntuv) − *��,�(v �t) ) − *��,�(vrw) (14) where: *o�,�(v �t) = *o�,�(vrw) . \�,� (15) *��,�(v �t) = *��,�(vrw ) . \�,� (16) where \�,� is the fractional multiplier for the harmonic current to be compensated. the desired reactive compensation current, *��,�(v �t) is obtained as: *��,�(v �t) = *��,� . \�,� (17) where \�,� is the fractional multiplier for the reactive current to be compensated. [∆'�(� !) ] includes fundamental voltage correction vectors, ∆��̅,�and ∆ �/�,� for < = 2 to n and harmonic voltage correction vectors, ∆��̅,� and ∆ �/�,� for < = 1 to n as given below: [∆'�(� !) ] = (∆�6,�, … , ∆�9,�, ∆ �6,� , … , ∆ �9,� , ∆��,� , … , ∆�9,� ,∆ ��,� , … , ∆ �9,� + ; (18) thus, the complete harmonic load flow equation with compensation can be written as: ⎣⎢ ⎢⎢ ⎡∆)��,�(� !)∆)��,� ∆*o̅�,�(� !) ∆*�̅�,�(� !) ⎦⎥ ⎥⎥ ⎤ = ⎣⎢ ⎢⎢ ⎢⎡ $q̅� _,`,r�_,` $q̅� _,`, g�_,` $q̅� _,`,r�_,s $q̅� _,`, g�_,s $q̅� _,t,r�_,` $q̅� _,t, g�_,` $q̅� _,t,r�_,s $q̅� _,t, g�_,s $l̅u̅_,s,r�_,` $l̅u̅_,s, g�_,` $l̅u̅_,s,r�_,s $l̅u̅_,s, g�_,s $l̅_̅_,s,r�_,` $l̅_̅_,s, g�_,` $l̅_̅_,s,r�_,s $l̅_̅_,s, g�_,s ⎦⎥ ⎥⎥ ⎥⎤ o ⎣⎢ ⎢⎢ ⎡ ∆��̅,�∆ �/�,� ∆��̅,� ∆ �/�,� ⎦ ⎥⎥ ⎥⎤ (19) for k order of harmonics under consideration, the size of [∆'�� ! ] is [2(� − 1) + 2v�]o1. however, for < = 2 to l as pv buses, ∆ ��,� = 0. in the proposed method, due to the use of the harmonic current spectrum, the nonlinear load parameters are not required to be included in the unknown vectors, resulting in reduction in the size of [∆'�� ! ] by 2(� − �). thus, the need of fundamental mismatch vector, [∆*�̅,� ] in 3∆��(� !)4 has been eliminated and reduced by 2(� − �) . this ultimately reduces the size of the modified jacobean matrix [$(̅� !)] . [$(̅� !)] is formed by sub-matrices represented with the notation as a partial derivative of the 3∆��(� ! )4 element given by the first subscript with respect to the 3∆'�(� !)4 element. the size of [$(̅� ! )] is [2(� − 1) +2v�] o [2(� − 1) + 2v�]. however, for the system with < = 2 to l as �� buses, the size of [$(̅� !) ] is [(2(� − 1) − (� −1)) + 2v�] o[(2(� − 1) − (� − 1)) + 2v�] . in the solution process, *�,�(ntuv ) and *�,�(ntuv) are iteratively calculated using the updated bus voltages ��,� , the specified powers �� ,�(ntuv) , and ��,�(ntuv) until the convergence set by tolerance . this є eliminates the decoupled effect to keep the solution accuracy unaffected. in the proposed algorithm, the pso technique is employed to find optimal harmonic load flow solution to achieve certain objectives keeping all inequalities within limits. two types of inequalities, i.e. control variables and functional inequalities are considered. the optimization problem is formed as follows. a. selection of control variables and formation of penalty function to handle functional inequalities the limits considered for inequalities are given in table ii. the control variables ov are system parameters like generator voltage �x,� , transformer tap ratio ti, and current multipliers \�,� and \�,� for optimal compensation. the boundaries of the search space are set by control variable limits. in modified pso, michalewicz’s non-uniform variable mutation operator, �y [17] is used to accelerate particles towards the engineering, technology & applied science research vol. 13, no. 1, 2023, 10093-10099 10096 www.etasr.com godbole & george: a novel algorithm for optimal harmonic load flow including harmonic … global best solution by adding variability into the population in each iteration. rather than generating particles with the random variables, a small differential variable yo is defined to generate new non-repeated particle positions in each iteration for enhanced search: yo = �y. >ov(�rs) − ov(��9) i (20) where ov(�rs) and ov(��9) are the maximum and minimum limits of the control variables. all the selected control variables are applied to the system to get the optimal power flow solution. the functional inequalities fp considered are the generator reactive power �x� , the bus voltage magnitudes for pq buses |�� | , %� ��!� , and the total mva capacity of lines ��w� as mentioned in table ii that are handled by selecting optimum static penalty factor |}b . the corresponding penalty function, ω}b for �t inequality is defined for < = 1 to �}b parameters with maximum and minimum limits. the total penalty function, ω}b(t�tg�) for �t inequalities is: ω}b(t�tg�) = ∑ ω}bt�b�a� (21) table ii. limits for control variables and functional inequalities system component / bus numbers inequality limits control variables xc generator bus < = 1 to �x �x (��9) ≤ �x� ≤ �x (�rs) transformer < = 1 to �; �(��9) ≤ �� ≤ �(�rs) compensator bus < = 1 to �v �t \�(��9) ≤ \�,� ≤ \�(�rs) \�(��9) ≤ \�,� ≤ \�(�rs) functional inequalities fpi generator bus < = 1 to �x �x(��9) ≤ �x� ≤ �x(�rs) pq bus < = 1 to �^f |�|(��9) ≤ |�� | ≤ |�|(�rs) %���!� ≤ %���!(�rs) transmission line < = 1 to ��w ��w� ≤ ��w(�rs) �x=no. of generators, �;=no. of transformers, �v �t = no. of compensator buses, �^f= no. of �� buses, ��w=no. of transmission lines, all minimum and maximum limits are expressed with a subscript min and max respectively b. formation of the objective function as active power loss ploss is of great concern in modern deregulated transmission systems with huge power flows over a long distance, the main objective of the proposed algorithm is considered as the minimization of ploss under non-sinusoidal voltage conditions. � = �w nn = ∑ >∑ (∑ ��?,� )9?a�,?��9�a�,��? i�fgh�a� (22) where ��?,� is the active harmonic power flow through transmission line between the i th and the k th bus. the objective function is modified using the total penalty function, ω}b(t�tg�) as: �� = � + ω}b(t�tg�) (23) this helps in getting a global solution to the power flow problem which makes the system parameters within the specified margin. the optimal harmonic power flow solution is obtained by selecting optimal control variables within the set pso iterations *�z��rs. the specialty of the algorithm is that voltage thd is allowed within the limit using harmonic compensation and voltage magnitude is controlled using fundamental reactive compensation with optimal multipliers for compensators. the flowchart for the optimal harmonic power flow is given in figure2. fig. 2. flowchart of the proposed optimal harmonic load flow algorithm. iii. simulation results a generalized program for the proposed optimization algorithm was developed in the matlab m-file platform. to verify the performance of the proposed harmonic optimization algorithm, the 30-bus ieee system [18] is modified by connecting non-linear loads in a few buses. a 6-pulse rectifier optimal harmonic load flow solution with minimum �w nn and compensator multipliers, \�,�, \�,� . initialize control variables with fundamental compensation currents, run basic nrlf. for non-linear load buses using (7) and (9), calculate specified harmonic currents, *�,�(ntuv) and *�,�(ntuv) obtain harmonic compensation currents *o�,�(v �t) & *��,�(v �t) form ∆��(� !) = 3∆)��(� !) , ∆*�̅,�(� !)4; ∆��(� !) ≤ є yes evaluate �w nn . update the best optimal solution. no *�z��rs ≥ *�z� yes no input test system line & bus data. set є and pso parameters. solve (19). update ∆'�(� !) engineering, technology & applied science research vol. 13, no. 1, 2023, 10093-10099 10097 www.etasr.com godbole & george: a novel algorithm for optimal harmonic load flow including harmonic … is taken as the non-linear load connected at buses 7, 15, 21, and 30 with load demands and total apparent power demand ��,� that includes distortion powers in addition to active and reactive powers as shown in table iii. the load at these buses is assumed such to get distorted voltage at various buses. table iii. non-linear load bus data for the modified ieee 30-bus system bus no. �� (mw) �� (mvar) ������ (mva) 7 22.8 0.9 25 15 15 2.5 17 21 22 0.2 24 30 10.6 1.9 12 the initial assumptions for the unknown variables are taken as ��,� = 1p. u. , ��,� = 0.1 p. u. , ��,� and ��,� = 0deg, and ��,� = 0 p.u. for non-linear load bus and the harmonic load flow solution is obtained without optimal control. it is observed that the rms voltages |�� | and %��,��! are exceeding the limits specified by the statutory standards of 5% at some buses. it was also found that the total active power loss including harmonic loss �w nn is 6.83mw with fundamental active power loss, �w nn,� = 6.76mw obtained from the power flows. the proposed optimization algorithm is implemented with the control variables and functional inequality limits shown in table iv. table iv. control and functional inequality limits control variable set limits a � �� �� �� �� min. limit 0.95 0.95 0.5 0.5 0.8 max. limit 1.05 1.1 1.0 1.0 1.0 functional variable set limits b ��� ��� ��� ��� ���� ���� |�| min. limit -29.8 -24 -30 -26.5 -7.5 -7.8 0.95 max. limit 59.6 48 60 53 15 15.5 1.05 a �x limits are specified in p.u. while � and multipliers \�, \  and \� are unitless. ball �x limits are specified in mvar while those for |�| are in p.u. for rigid margins of functional inequalities like |�| and voltage total harmonic distortion (thd), the high value of static penalty factor of 200 is selected. for the soft margins of �x and ��w , the comparatively smal static penalty factors of 5 and 10 are selected. the mutation ratios μ and the acceleration coefficients [� , [6 are selected as 0.1, 2.05, and 2.05, respectively. the inertia coefficient ω used to control the convergence behavior of pso is taken as 0.5 and set to gradually decrease using a damping factor of 0.7296 in each iteration. the population �t and the maximum number of pso iterations *�z��rs are set as 30 and 20. the optimal obtained values of the control variables are given in table v. it is observed that the obtained optimal values of \�,� and \�,�, \�,  are such that the required compensation will be provided depending on the fundamental reactive currents and the 5 th and 7 th harmonic components of the current, respectively, at that bus. pso with careful selection of parameters and modified with mutation operator exhibits better convergence characteristics. the optimal obtained harmonic power flow solution is given in table vi. table v. optimal control variables obtained by the modified pso system control variables �¡n¢ �¡n�£ �¤n�� ���n�� ��� 1.0011 1.05 0.9916 0.9798 1.0615 �x6 �x� �x¥ �x�� �x�¦ 1.036 0.9904 1.0166 1.0384 1.0004 compensator control variables ��,� ��£,� ��¤,� ��,� ��,� 0.942 0.846 0.8148 0.8151 1.0 ��,� ���,� ���,� ���,� ���,� 0.7633 0.9774 0.6428 0.5413 0.9209 ���,� ���,� ��£,� ��£,� ��£,� 0.6030 0.8830 0.9343 0.5 0.784 it is observed from table vi that all bus voltage magnitudes are within the limits of 0.95p.u. and 1.05p.u., showing effective reactive power compensation with optimal values of multipliers \�,� for the selected buses and system parameters. the voltage harmonic magnitudes at the buses are observed to be considerably reduced. as an effect, the values of %���! at all buses are reduced below 5%. this demonstrates the effectiveness of harmonic compensation with optimal values of multipliers \�,�, \�, . table vi. optimal harmonic load flow solution obtained by the proposed algorithm bus � ��,� (p.u.) ��,� (p.u.) ��,� (p.u.) |��| (p.u.) %��,�§� 7 0.9999 0.0002 0.0015 0.9999 0.1550 10 0.9769 0.0009 0.0072 0.9769 0.7398 15 0.9692 0.0049 0.0109 0.9693 1.2375 21 0.9643 0.0071 0.0099 0.9644 1.2668 22 0.97 0.0025 0.0078 0.9700 0.8481 23 0.9638 0.0044 0.0093 0.9639 1.0665 24 0.96 0.0041 0.0088 0.9601 1.0082 25 0.9774 0.0049 0.0059 0.9774 0.7832 26 0.9599 0.0081 0.0038 0.9600 0.9286 27 0.9963 0.0003 0.0125 0.9964 1.2590 29 0.979 0.0067 0.0113 0.9791 1.3374 30 0.9695 0.0008 0.0445 0.9705 4.5859 to validate the above results obtained by the proposed optimization algorithm, a simulink model was developed by the simpower block set of matlab as shown in figure 3. the complete system model consists of subsystems for group of buses, compensators, and nonlinear loads connected. the obtained results by the simulink model and by the proposed algorithm are matching. table vii. result comparison before and after optimization parameter before compensation after compensation �w nn 6.83 mw 5.72 mw %���! 11.4935 4.5859 |�¦¨| 0.8783 0.9705 from table vii, it is observed that �w nn is considerably reduced to 5.72mw from 6.83mw with 5 th and 7 th harmonic active power losses as 5.4037e -3 mw and 7.1817e -3 mw, respectively. the voltage magnitude at the highest affected bus 30 has been improved from 0.8783p.u. to 0.9705p.u. engineering, technology & applied science research vol. 13, no. 1, 2023, 10093-10099 10098 www.etasr.com godbole & george: a novel algorithm for optimal harmonic load flow including harmonic … fig. 3. simulation model developed for ieee 30 bus system with compensators. iv. conclusions the increased use of power electronic-based devices in various applications along with the incorporation of renewable energy sources in modern power systems result in frequent occurrence of non-sinusoidal voltages at system buses. the proposed optimal harmonic load flow algorithm gives a global solution for the transmission systems under non-sinusoidal operation conditions with optimum amount of reactive and harmonic current compensation. the objective of the algorithm is to minimize the transmission losses while maintaining the fundamental voltage magnitude and %���! within limits, while the size of the jacobean matrix is reduced, resulting in faster convergence. the specialty of the proposed method is that with the addition of a greater number of nonlinear loads, the size of the jacobean matrix remains the same, being independent of the number 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[15] w. tinney and c. hart, "power flow solution by newton&#39;s method," ieee transactions on power apparatus and systems, vol. pas-86, no. 11, pp. 1449-1460, 1967. [16] "modeling and simulation of the propagation of harmonics in electric power networks. i. concepts, models, and simulation techniques," ieee transactions on power delivery, vol. 11, no. 1, pp. 452–465, jan. 1996, https://doi.org/10.1109/61.484130. [17] p. s. andrews, "an investigation into mutation operators for particle swarm optimization," in 2006 ieee international conference on evolutionary computation, jul. 2006, pp. 1044–1051, https://doi.org/ 10.1109/cec.2006.1688424. [18] b. zhao, c. x. guo, and y. j. cao, "a multiagent-based particle swarm optimization approach for optimal reactive power dispatch," ieee transactions on power systems, vol. 20, no. 2, pp. 1070–1078, feb. 2005, https://doi.org/10.1109/tpwrs.2005.846064. authors profile prachi godbole received the be degree in electrical engineering and the me degree in electrical engineering (power systems) from the walchand college of engineering, sangli, india in 1999 and 2002, respectively. she is currently pursuing the ph.d. degree in electrical engineering at the university of mumbai, india. her research interests include power quality and renewable energy technology. sincy george received the btech and mtech degrees in electrical engineering from the government college of engineering, trivandrum-kerala in 1985 and 1989 respectively and a ph.d. degree in electrical engineering from the indian institute of technology, bombay. she worked as a professor and the head of electrical engineering department at fr. c. r. institute of technology, india for 20 years. since 2016, she is the principal at st. francis institute of technology, india,. her research interests includes power quality and power electronics. she is a senior member, ieee, a fellow of the institution of engineers india (iei), a member of the indian society for technical education (iste), and computer society of india (csi). microsoft word etasr_v13_n2_pp10249-10254 engineering, technology & applied science research vol. 13, no. 2, 2023, 10249-10254 10249 www.etasr.com boucheritte et al.: a multilevel inverter for grid-connected photovoltaic systems optimized by genetic … a multilevel inverter for grid-connected photovoltaic systems optimized by genetic algorithm wafa boucheritte electrical engineering department, larhyss laboratory, university of biskra, algeria boucherittewafa82@gmail.com (corresponding author) ammar moussi electrical engineering department, larhyss laboratory, university of biskra, algeria moussi-am@hotmail.com raihane mechgoug electrical engineering department, larhyss laboratory, university of biskra, algeria raihane.mechgoug@univ-biskra.dz hani benguesmia laboratory of electrical engineering (lge), university of m’sila, algeria hani.benguesmia@univ-msila.dz received: 12 december 2022 | revised: 15 january 2023 and 22 january 2023 | accepted: 23 january 2023 abstract this article introduces a grid-connected photovoltaic (pv) source combined with a multi-level inverter. a converter five-level neutral point (npc) can be used to integrate the pv power into the power grid with minimum harmonic distortions and high power capacity. if the output voltage of the pv generator varies significantly with solar radiation, the output voltage of the ripple must be fixed. for this reason, a regulation loop was used. in this study, we used a classical pi regulator. it is difficult to determine the pi controller transaction values, so genetic algorithm was used to optimize the pi controller parameters. the matlab/simulink simulation results show the better performance and efficiency of the pi controller optimized by the ga, in comparison to the stand-alone pi controller, regarding stability and accuracy, and the reduction of total harmonic distortions (thd) of the current injected into the grid for any difference in solar radiation. keywords-pv array; mppt; inverter npc; genetic algorithm i. introduction renewable energy is a developing sector in which many ongoing natural energy resources are utilized [1], solar energy being the most studied of them. renewable energy in the coming years must meet, by 2020 and 2050, the 20% and 50% of the total demands, respectively [2]. the inverter is the core of a photovoltaic (pv) system. it converts the continuous current produced by the pv system into alternating current [3-6]. disadvantages of the two-level pwm inverters are the high switching frequency, the many harmonics, and the large filters used [7]. the benefits of the multilevel converter are that it reduces the voltage of the apparatus, the exit wave of the staircase, and that it lowers the electromagnetic emissions. multi-level converters know many industrial uses and high voltage and high output standards are necessary [8]. the topologies for multilevel inverters are: floating capacitor, loopback diode (npc), and cascaded hbridge inverter [9]. in the npc inverter inlet, there is availability on the side of the bipolar common dc bus and it has the flexibility to add multiple pv panels in the system [10]. there is much interest in the npc inverters topologies due to their low output current and low overall total harmonic distortion (tdh) [11]. npc supports a variety of classical sinusoidal modulation methods, such as multiple triangle sinusoidal modulation, vector modulation, and selective harmonic elimination [12]. common strategies for controllers in voltage regulations include the widely used pi controllers engineering, technology & applied science research vol. 13, no. 2, 2023, 10249-10254 10250 www.etasr.com boucheritte et al.: a multilevel inverter for grid-connected photovoltaic systems optimized by genetic … due to their intrinsic simplicity and rapid dynamic response [13]. ii. multilevel inverter for a gridconnected photovoltaic system the proposed diagram shown in figure 1 [10] consists of 4 main elements: a pv array, dc/dc buck converters, npc inverter configuration, and an lc filter (filtering inductance and capacitors lf, cf are used to filter the current injected into the system). fig. 1. the five-level inverter in grid-connected pv systems. iii. the architecture of the diode-clamped multi-level inverter authors in [1] proposed the neutral point converter for a variety of applications in 1981. a multi-level inverter structure was used in high and intermediate voltage conditions. the basic architecture for this inverter was addressed in [14-15]. npc inverters are one of the most widely used pv systems. in [16], the system has significant advantages. the (n-1) capacitors required on the dc bus are part of the multilevel inverter and the required number of switches for each phase is 2(n-1). moreover, there are 2*(n-2) diodes in each phase. table i. component count of traditional mlis [24] topology components traditional mlis diode clamped mli capacitor clamped mli cascaded h bridge mli main switches 2(n-1) 2(n-1) 2(n-1) main diodes 2(n-1) 2(n-1) 2(n-1) clamping diode 2(n-2) 0 0 balancing capacitors 0 (n-2) 0 dc bus capacitors n-1 0 0 dc sources 1 1 (n-1)/2 fig. 2. the three-phase, five-level, diode-clamped inverter's schematic in simulink. iv. photovoltaic generator the power available at the terminals of a cell is very low, it is therefore necessary to combine such cells in series and in parallel to obtain satisfactory power modules. this model consists of complex equations whose solution requires many (6) parameters. another model has a single diode with 5 parameters (rs, rsh, iph, i0, a), [18]: i�� � i� �e � �� ����∗�� � 1� � ����∗���� (1) where i is the current delivered by the pv module, rsh is ths shunt resistance, iph the photoelectrical current, i0 the saturation current, rs the series resistance, k is the boltzmann's constant, and n is the coefficient of the diode ideality. fig. 3. equivalent diagram of a photovoltaic cell. the parameters of the solar array that identify (1) relate to the solar panel parameters as follows: i������� � n�i�� (2) i������ � n�i� (3) r" ����� � $% $& r" (4) r� ����� � $% $& r� (5) the photoelectric current (iph) depends on irradiation and temperature: ph ph,n i n g i =(i +k .δt). g (6) sc,n i 0 oc,n v th i +k .δt i = v +k .δt exp -1 a.v       (7) nδt=t-t (8) where iscn is the short-circuit current under nominal conditions (gn=1000w/m 2 , tn =25 o c). the cell's ambient and nominal temperatures are represented, respectively, by t and tn, where the current and nominal irradiation are g and gn, respectively. the short circuit current's temperature coefficient is ki, while the open circuit voltage's is kv. vth, given in (1) is the thermal junction constant, equal to vth=kt/q, where q is the electron charge. engineering, technology & applied science research vol. 13, no. 2, 2023, 10249-10254 10251 www.etasr.com boucheritte et al.: a multilevel inverter for grid-connected photovoltaic systems optimized by genetic … v. dc/dc buck converter a boost converter is the most widely used dc-dc converter since its input voltage is smaller than its output voltage. filters composed of inductor and capacitor combinations are regularly used together to improve the performance of a converter [20]. thus, in order to improve the solar panel's effectiveness, we use the mppt technique. there are different techniques to follow the maximum power point (mpp) [21-22]. in this paper, the perturb and observe (p&o) technique is used because it is straightforward and simple to use in real time. it is an algorithm based on perturbing and monitoring the solar panel's voltage until it reaches the optimal power level in the flowchart shown in figure 4. fig. 4. diagram of the p&o method. fig. 5. reference signal and four carrier waves. vi. commands and algorithms used a. modulation the proposed control utilizes a modulation technique that uses the sinusoidal pwm (spwm) [19]. a 5-level voltage waveform requires 4 level-shifted carrier signals as shown in figure 5. it is the sinusoidal modulation with multiple triangles which allows it. this technique requires (n-1) triangular signals with the same frequency fp and the same amplitude ap. these triangular signals are compared, for each phase, with a reference signal of amplitude aref and frequency fref. the expressions below provide the modulation rate ma and the frequency ratio mf: m� � ()*+ $,-�(. (9) m/ = /. /)*+ (10) vii. the genetic algorithm genetic algorithms (gas) are adaptive search algorithms built on the evolutionary principles of natural selection and genetics. the main goal of gas is to mimic natural system processes that are necessary for evolution. they represent a clever use of a random search inside a defined search area. the core idea of gas is to maintain a population of knowledge structures that evolve over time through a process of competition and controlled variation. each population structure represents an answer to a particular problem and a corresponding fitness function, which is used to select which structures are used to generate new ones by genetic processes like mutation and crossover. in order to address concerns with search and optimization, gas are quite prosperous. their ability to leverage information about a search space that was previously unknown in order to influence subsequent searches towards beneficial subspaces may be credited with a substantial chunk of their effectiveness. a ga starts off with solutions produced by a population chosen at random. advances made possible by chromosomes' employment of genetic operators, based on the principles of natural genetic processes. within the population, evolution via natural selection takes place. in order to finally replace the vanishing relatively bad solutions, comparatively good solutions reproduce at every generation. the environment works as a function of evaluation or fitness to distinguish between good and bad solutions. when a ga is used, a generation is the period of time between the current and the subsequent population. although the basic ga has a number of modifications, the fundamental mechanism consists of three parts:  assessment of each person's fitness.  creation of the gene pool.  mutation and recombination table ii. the structure of a simple ga [23] 1. initialization: a set of potential solutions (chromosomes or individuals) forming a population is initialized 2. evaluation: each individual is then evaluated by calculating its quality (fitness value) 3. selection: individuals with higher fitness value are selected for breeding 4. reproduction: during breeding, crossover and mutation operators are employed to selected individuals (parents) to produce new individuals (offspring) 5. termination: these steps continue over many generations or iterations until the predefined criteria are satisfied viii. optimizing the pid regulator with genetic algorithm the genetic encoding of the chromosome's pid regulator parameters defines the pid regulator parameters. there are two genes on the chromosome: ki and kp. 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 temps(s) v re f, v p engineering, technology & applied science research vol. 13, no. 2, 2023, 10249-10254 10252 www.etasr.com boucheritte et al.: a multilevel inverter for grid-connected photovoltaic systems optimized by genetic … a. generation of the initial population the chromosomes in the initial population are produced by a stochastic generation. each allele is defined in the subset: i p i p[min k min k ; max k max k ]s  (11) fig. 6. chromosome representation. b. fitness function the pid regulator is trained with a given number of alleles and is then assessed using predetermined parameters to determine an individual's fitness. the mean square error (mse) at the conclusion of training characterizes best the quality of a pid regulator. it is the output of the pid regulator.     n 2 i i i=1 y -a f x = n  (12) ix. simulation results the main objectives when transferring the pv generated energy into the utility grid are:  to track the pv's mpp.  to obtain study voltage. control of the inverter output voltage requires a closed loop. the voltage va is measured and then compared to the reference voltage vref=311v which represents the maximum value of the simple network voltage. the counter error signal is injected at the pi controller with chosen parameters: kp=0.1, ki=0.01. ga is used to select the parameters of the pid regulator by minimizing the mse. table iv shows the ga parameters used to optimize the pid parameters and table iii gives the pid regulator values. table iii. ga control parameters no of generations 20 population 70 chromosome size 2 crossover 1 mutation probability 0.08 table iv. ga parameters used to optimize the pid pid parameter value ki 0.0011 kp 0.0218 figure 7 shows that for a step change in solar radiation (from 200 to 800w/m 2 ), the controller tracks instantaneously the mpp altering thus the dc bus voltage. from figures 9-12 we can note that the conventional pi has bigger overshoot whereas the proposed pi-ga has better signal reduction of the reference signal for spwm. figures 9 and 10 show the 5-level output voltage of the inverter before the filter and after the lc low pass filter. based on the harmonic analysis, tdh is less in the filtered output voltage of the 5-level inverter. from the fft analysis shown in figure 12, it is observed that the tdh is 0.30%. after comparing the results, we notice that when using the ga, the results were improved and the thd was reduced. fig. 7. pv generator output optimal voltage. fig. 8. reference voltage with ga for spwm. fig. 9. output voltage for a step change in solar insolation. fig. 10. output voltage after filtering. x. conclusion in order to secure the dc-ac conversion stage, the current research developed a 3-phase 5-level npc multilevel gridconnected photovoltaic system. such a topology is primarily employed to meet the needs of connecting and transmitting high power between the pv system power source and the main grid. when compared to the traditional inverter topologies 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 200 400 600 800 1000 1200 times(s) v o lt a g e ( v ) vop vgpv 0.4 0.42 0.44 0.46 0.48 0.5 0.52 0.54 0.56 -1.5 -1 -0.5 0 0.5 1 1.5 times(s) v o lt a g e (v ) 0.4 0.42 0.44 0.46 0.48 0.5 0.52 0.54 0.56 0.58 0.6 -600 -400 -200 0 200 400 600 time(s) v o lt a g e (v ) 0.4 0.5 0.6 0.7 0.8 0.9 1 -400 -200 0 200 400 time(s) v o lt a g e (v ) voltage pi voltage ga engineering, technology & applied science research vol. 13, no. 2, 2023, 10249-10254 10253 www.etasr.com boucheritte et al.: a multilevel inverter for grid-connected photovoltaic systems optimized by genetic … utilized in such applications, this topology has impressively demonstrated its efficacy and adaptability and offers various advantages, including a reduction in output voltage harmonics. fig. 11. reference voltage. fig. 12. fft analysis for the 5-evel inverter. fig. 13. voltage fft analysis before filtering. fig. 14. evolution of ga. regarding future work, the behavior of various blocks can be further improved, i.e. regarding the dc/dc converter, the possibility of using a buck/boost converter can be examined and regarding the dc/ac converter new topologies can be inspected. the possibility of practical implementation using the d space card is also considered. references [1] k. arulkumar, d. vijayakumar, and k. palanisamy, "modeling and control strategy of three phase neutral point clamped multilevel pv inverter connected to the grid," journal of building engineering, vol. 3, pp. 195–202, sep. 2015, https://doi.org/10.1016/j.jobe.2015.06.001. [2] c. cecati, f. ciancetta, and p. siano, "a multilevel inverter for photovoltaic systems with fuzzy logic control," ieee transactions on industrial electronics, vol. 57, no. 12, pp. 4115–4125, sep. 2010, https://doi.org/10.1109/tie.2010.2044119. [3] j. selvaraj and n. a. rahim, "multilevel inverter for grid-connected pv system employing digital pi controller," ieee transactions on industrial electronics, vol. 56, no. 1, pp. 149–158, jan. 2009, https://doi.org/10.1109/tie.2008.928116. [4] u. b. tayab and m. a. a. humayun, "modeling and analysis of a cascaded battery-boost multilevel inverter using different switching angle arrangement techniques," engineering, technology & applied science research, vol. 7, no. 2, pp. 1450–1454, apr. 2017, https://doi.org/10.48084/etasr.1094. 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[13] p. s. rao, a. d. bhavani, and m. r. sisir, "a grid connected pv system integrated through multilevel modular cascaded h-bridge inverter by using fuzzy logic controller," international journal of multidisciplinary research and modern education, vol. 2, no. 2, pp. 486–494, sep. 2016, https://doi.org/10.5281/zenodo.215825. 0.4 0.42 0.44 0.46 0.48 0.5 0.52 0.54 0.56 -2 -1 0 1 2 times(s) r e fe re n c e v o lt a g e ref volt pi ref volt ga 0 100 200 300 400 500 600 700 800 900 1000 0 20 40 60 80 100 frequency (hz) fundamental (50hz) = 311 , thd= 0.30% m a g ( % o f f u n d a m e n ta l) 0 2 4 6 8 10 12 14 16 18 20 0 0.002 0.004 0.006 0.008 0.01 generation f it n e s s engineering, technology & applied science research vol. 13, no. 2, 2023, 10249-10254 10254 www.etasr.com boucheritte et al.: a multilevel inverter for grid-connected photovoltaic systems optimized by genetic … [14] h. chang, r. wei, q. ge, x. wang, and h. zhu, "comparison of svpwm for five level npc h-bridge inverter and traditional five level npc inverter based on line-voltage coordinate system," in 2015 18th international conference on electrical machines and systems (icems), pattaya, thailand, jul. 2015, pp. 574–577, https://doi.org/10.1109/ icems.2015.7385100. 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[21] n. hamrouni, m. jraidi, a. cherif, and a. dhouib, "measurements and simulation of a pv pumping systems parameters using mppt and pwm control strategies," in melecon 2006 2006 ieee mediterranean electrotechnical conference, malaga, spain, feb. 2006, pp. 885–888, https://doi.org/10.1109/melcon.2006.1653240. [22] b. shanthi and s. p. natarajan, "fpga based fuzzy logic control for single phase multilevel inverter," international journal of computer applications, vol. 9, no. 3, pp. 10–18, nov. 2010, https://doi.org/ 10.5120/1367-1842. [23] a. khorshidi and a. m. shahri, "ga-inspired particle filter for mitigating severe sample impoverishment," in 2016 4th international conference on control, instrumentation, and automation (iccia), qazvin, iran, jan. 2016, pp. 377–382, https://doi.org/10.1109/ icciautom.2016.7483192. [24] n. r. sulake, s. pranupa, and m. s. indira, "cross connected source based reduced switch count multilevel inverter topology with fault tolerance," in 2019 global conference for advancement in technology (gcat), bangalore, india, jul. 2019, https://doi.org/10.1109/ gcat47503.2019.8978379. microsoft word etasr_v13_n1_pp9867-9871 engineering, technology & applied science research vol. 13, no. 1, 2023, 9867-9871 9867 www.etasr.com ahmad & singh: groundwater quality assessment based on a statistical approach in gaya district, bihar groundwater quality assessment based on a statistical approach in gaya district, bihar shaz ahmad department of civil engineering, national institute of technology patna, india shaza.phd19.ce@nitp.ac.in (corresponding author) reena singh department of civil engineering, national institute of technology patna, india reena@nitp.ac.in received: 16 october 2022 | revised: 5 november 2022 | accepted: 6 november 2022 abstract india is one of the countries that face the serious problem of groundwater contamination. the current study's main objective is to evaluate the quality of the groundwater in the serghati and its surrounding region of the gaya district and its suitability for drinking purposes. to achieve this aim, 75 groundwater samples from the 15 sampling sites were collected during the period from march to may 2022. we measured and analyzed the major physicochemical characteristics of the water and compared them to the world health organization (who) standards. with the help of the water quality index (wqi), groundwater quality was assessed. according to the study results, 3 sites have a wqi value of more than 100, which is unsuitable for drinking. correlation matrices were used to assess groundwater quality and the extent of the interdependencies of the various parameters. principal component analysis (pca) reduces the number of significant variables. three principal components with a total variance of 73.53% were identified and used in the analysis. overall, the result indicates that most areas' water quality is good and safe for drinking. keywords-drinking water; physiochemical parameters; statistical analysis; pearson's correlation; principal component analysis i. introduction water resources play a critical role in the growth and development of civilization [1]. nowadays, water resources have inevitably become one of the most important factors that determine economic growth. it is necessary to assess whether water resources are sufficient and sustainable, particularly in countries like india, where water often plays a multiple-faceted role in terms of economics as well as social aspects [2]. maintaining access to safe drinking water has become an urgent requirement, even though 30% of the urban population and 90% of the rural population are still wholly dependent on contaminated surface and ground water to meet their daily needs. the availability and quality of clean drinking water are among the most important factors for promoting agricultural production and providing health care services to the general population [3]. many states, including andhra pradesh, bihar, rajasthan, west bengal, jharkhand, orissa, and punjab, are experiencing severe water scarcity, due to factors such as the lack of environmental awareness and indiscriminate waste disposal from agriculture, mining, and anthropology, resulting in one of the most dangerous situations for development in their areas [4]. the use of fertilizers and agrochemicals and the overexploitation of groundwater, result in the contamination of water resources [5]. residents of arid and semi-arid regions rely heavily on groundwater [6]. agricultural lands are also getting deteriorated due to the contamination of groundwater by excess fluoride [7, 8]. fluoride-contaminated groundwater slowly accumulates the excess fluoride and produces adverse effects [8, 9]. large quantities of fluoride are stored in various parts of the body due to the use of contaminated water [10]. crippling skeletal fluorosis has become common across the globe [2]. the immune system also gets affected by the intake of excess fluoride [11]. chronic kidney diseases may attack at a faster rate due to the intake of excess fluoride through food [12]. to remove the excess fluoride, various techniques have been developed. among them, adsorption is found to be more effective in both removal and cost. various materials have been developed as defluorination adsorbents, such as nanomaterials [13], clay [14], chitosan [15], industrial waste [16], carbonaceous [17], alumina [18], calcium [19], and metal oxides [20]. ii. materials and methods a. study area gaya district stretches over 4976km 2 and lies between 24°30' and 25°06' latitude and 84°24' and 85°30' longitude the engineering, technology & applied science research vol. 13, no. 1, 2023, 9867-9871 9868 www.etasr.com ahmad & singh: groundwater quality assessment based on a statistical approach in gaya district, bihar entire research region has a hostile environment caused by the continental monsoon. mountains surround gaya on three sides, with a river on the other side, resulting in seasonal temperature variations in the region. higher temperatures up to 45°c can be found during the summer months (may-july). the city receives about 214cm of rainfall in july and october. the winter months are known for their cold temperatures ranging from -4°c to 28°c. the study was conducted in the surrounding area of sherghati, located in the gaya district of bihar. b. water sampling and analysis a total of 75 groundwater samples, 5 from each of the 15 sites, were taken across the research region from underground sources (maximum bore wells and hand pumps). the sampling site and geo-positions (latitude and longitude) were located with global positioning system (gps). the concentrations of each individual parameter at each sampling site were determined by averaging the concentrations of each parameter. between march and may 2022, fresh groundwater samples were collected from shallow bore wells and tube wells. the water samples were collected using pre-cleaned high-density 500ml polythene bottles. the bottles were handled with gloves to prevent sample contamination. before sampling the water from a bore well, it was drained for 5 minutes. the samples were sealed tightly so contaminants were not able to enter the bottles. as soon as the samples were transported to the laboratory, they were encased in iceboxes and were preserved at 4°c for further chemical analysis. all steps were carefully monitored throughout the sampling process to ensure that the samples were not contaminated or agitated during the collection, transportation, and analysis. the fluoride concentration in the water was determined using the spadns method described in apha1994 [21]. the chemicals and distilled water used to prepare the solution (or dilution) were analytical grades and the highest purity millipore water, respectively. thermo scientific multi-parameter kit measured in situ parameters like ph immediately after sampling. the anions chloride, sulphate, and phosphate were quantified using the usual agno3 titration with a uv spectrophotometer, turbid metric, and colorimetric methods. authors in [3] used a technique to assess water samples' nitrate (no3) content. calcium and magnesium were determined using the conventional edta titration technique. all the processes used in the investigation were conventional methods for examining water and wastewater [22]. c. estimation of water quality index (wqi) wqi was estimated according to a three step process:  step-1. the weight (wn) characteristics of each specification are calculated to utilize the given equation: wn = k/sn (1) where 1 1 1 1 1 1 1 ... 1 2 3 k s s s sn sn        , where sn is the standard desirable value of the nth specification.  step-2. the sub-index (qn) is calculated to utilize the given equation: 0 100 0 vn v qn sn v     (2) where vn is the mean concentration of the nth specification, sn is the standard desirable value of the nth specification, and vo represents the real values of the specifications in pure water (generally, vo = 0, for most specifications except for ph, that has a v0 of 7).  step-3. wqi was calculated by the summation of wn and qn: ��� = ∑�� � /∑ � (3) and since ∑ � = 1, we have: ��� = ∑�� � (4) d. correlation an evaluation of the correlation between two variables can be measured by the coefficient of correlation (r), which can be defined as a measure of the degree to which the two variables are associated. as far as the range of r is concerned, it spans from -1 to +1 [23]. as a general rule, the correlation between different water quality parameters is obtained to determine their interrelationship, which helps visualizing the most effective parameters [24]. this ultimately contributes to the decisionmaking process related to monitoring water quality. however, a high or low value of r (for example, close to +1) is typically indicative of a strong correlation [25]. e. principal component analysis (pca) the pca method of multivariate statistics is usually used to reduce the dimension of a dataset [26]. pca produces eigenvalues and eigenvectors when applied to the covariance matrix of the initially correlated variables [27]. several coefficients make up the eigenvector, also referred to as the loading. to obtain the principal components (pcs) [28], one has to multiply all the loadings by the original set of variables. pca is a linear combination of initially correlated variables that forms a new set of orthogonal uncorrelated variables. in 1933, hoteling developed this method and had been widely adopted in studies regarding water quality assessment [29]. iii. results and discussion the physicochemical parameters of the groundwater samples are presented in table i. the ph of the drinking water at the 15 sites has been found to range between 6.78 and 7.20. over the study area, it is evident that the water is slightly acidic to slightly basic. there is no site where the ph values exceed the permissible limit of 8.5. as far as chloride is concerned, the minimum value is 43.23mg/l and the maximum value is 203.49mg/l and all samples are within the maximum allowable limit of 1000mg/l. sulphate concentration ranges from 15.67 to 95.18mg/l, with a mean value of 39.09mg/l and a standard deviation of 24.90mg/l. the sulphate levels do not exceed the permissible limit of 400mg/l. there is a wide range of nitrate concentrations in the samples, ranging from 3.54 to 43.23mg/l with a mean and standard deviation of 15.54 and 10.49mg/l, respectively. the nitrate levels did not exceed the permissible limit of 45mg/l. likewise, the minimum fluoride concentration was 0.37mg/l, the maximum fluoride concentration was engineering, technology & applied science research vol. 13, no. 1, 2023, 9867-9871 9869 www.etasr.com ahmad & singh: groundwater quality assessment based on a statistical approach in gaya district, bihar 2.70mg/l, with 6 locations crossing the permissible limit of 1.5mg/l. total hardness (th) ranged between 92 and 332 mg/l, with an average and standard deviation of 228.93mg/l and 58.39mg/l, respectively. no sites had th values crossing the permissible limit of 600mg/l. at some sites, the concentrations of parameters that describe the water quality were higher than those recommended by the bureau of standards (2012) for drinking water. combinations of different natural factors, such as soil salinization, mineral dissolution, prolonged residence time for water-rock interactions may be responsible. however, it should be noted that anthropogenic activities also play a significant role in the degradation of groundwater quality. there is a great concern regarding the concentration of nitrate and fluoride in groundwater since their increased value adversely affects human health. table i. statistical analysis of physicochemical parameters minimum maximum mean std. deviation ph 6.78 7.20 7.05 0.12 tds 290 426.60 331.02 33.98 f 0.37 2.70 1.378 0.7 cl 43.23 203.49 108.84 44.89 no3 3.54 43.23 15.54 10.5 so4 2 15.67 95.18 39.09 24.91 th 92 332 228.93 58.4 total alkalinity 21.40 40.50 31.36 6.59 table ii. groundwater wqi values sampling location wqi s1 81.25 s2 39.61 s3 43.6 s4 76.52 s5 90.9 s6 119.78 s7 149.15 s8 97.43 s9 20.85 s10 37.45 s11 36.26 s12 128.94 s13 47.3 s14 24.54 s15 70.32 we employed the wqi to investigate the groundwater's condition and assess whether it is suitable for drinking based on its overall quality. as wqi uses a weighted sum approach to calculate its score, it makes it easy for the data to be communicated to a broad audience because it combines all the parameters into one numerical value that can be used to convey information. table ii presents the wqi of each site. there is no doubt that 3 out of 15 sites have wqi above 100, as shown in figure 1. the groundwater at these sites is not suitable for drinking. it was found that the groundwater had the highest wqi according to this study (149.14), which indicates that the groundwater is the most polluted. however, the lowest wqi at the least polluted site is 24.53. generally, the groundwater quality in the study area is acceptable for most areas, but it is of very poor quality in some regions and shouldn't be used for drinking. we assessed the inter-dependencies among different parameters by establishing the correlations between their values. the analysis outcome is shown in table iii. fig. 1. water quality based on wqi value. table iii. pearson's correlation matrix ph tds f cl no3 so4 2 th ta ph 1.000 tds -0.351 1.000 f 0.565 -0.214 1.000 cl 0.315 0.340 0.242 1.000 no 3 -0.0022 0.361 -0.096 0.396 1.000 so4 2 -0.370 0.776 -0.192 0.527 0.584 1.000 th 0.347 -0.430 0.047 0.205 -0.094 -0.225 1.000 ta 0.126 0.150 0.097 0.376 0.331 0.111 0.592 1.000 table iv. total variance analysis componen t initial eigenvalues extraction sums of squared loadings total % of variance cumulative % total % of variance cumulative % 1 3.058 33.974 33.974 3.058 33.974 33.974 2 2.294 25.485 59.458 2.294 25.485 59.458 3 1.266 14.072 73.530 1.266 14.072 73.530 4 0.956 10.627 84.157 5 0.626 6.957 91.114 6 0.364 4.050 95.164 7 0.227 2.525 97.689 8 0.178 1.981 99.670 9 0.030 0.330 100.000 extraction method: pca. an increase in positive or negative values of r is usually indicative of a strong correlation between two variables. it can be seen that most of the parameters demonstrate a positive correlation with one another. generally, the parameters from a common origin are strong correlated and vice versa. despite this, some of these parameters show a negative correlation and some a very small correlation, indicating that these components' sources may differ. pca was also conducted on each of the water quality parameters, and the results are shown in table iv. the variances for each pc are individually and cumulatively based on the data collected. there is no doubt that pc1, pc2, pc3 are responsible for the majority of the variance (73.53%), while the rest of the pcs are responsible for a much lower percentage of the variance. most of the time, it is recommended that the pcs capable of explaining 70% of the variance are used to engineering, technology & applied science research vol. 13, no. 1, 2023, 9867-9871 9870 www.etasr.com ahmad & singh: groundwater quality assessment based on a statistical approach in gaya district, bihar reduce dimensionality while losing the least amount of information [30]. to determine the leading pcs from the original variables in the study, pca was carried out using the spss 16.0 software. the first factor accounts for about 33.974% of the variance, corresponding to the largest eigenvalue (3.058). in the total variance calculation, the second factor, which corresponds to the second eigenvalue (2.294), is responsible for approximately 25.485% of the variance. the third factor accounts for 14.072 % of the total variance with an eigenvalue of 1.266. among the remaining 9 factors, no one has an eigenvalue greater than 1. the significance of any factor is determined by its eigenvalue, which must be greater than 1. there appears to be a relatively higher loading for pc1 for the parameters tds and sulphate compared to the others, as shown in table v. meanwhile, hardness, alkalinity, chloride, and ph loadings are found to be more in pc2, and in pc3, loading is more in fluoride. table v. component matrix component 1 2 3 ph -0.589 0.564 0.359 tds 0.878 0.090 0.146 f(ppm) -0.379 0.406 0.558 cl(ppm) 0.272 0.810 0.260 no3 (mg/l) 0.595 0.453 0.006 so4 2 (mg/l) 0.849 0.283 0.149 th (mg/l) -0.467 0.568 -0.601 total alkalinity (mg/l) 0.124 0.699 -0.567 extraction method: pca iv. conclusion generally, there is a groundwater contamination issue in sherghati, gaya district. the purpose of this study is to investigate the quality of grounwater and its suitability for 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[30] n. subba rao, c. srihari, b. deepthi spandana, m. sravanthi, t. kamalesh, and v. abraham jayadeep, "comprehensive understanding of groundwater quality and hydrogeochemistry for the sustainable development of suburban area of visakhapatnam, andhra pradesh, india," human and ecological risk assessment: an international journal, vol. 25, no. 1–2, pp. 52–80, feb. 2019, https://doi.org/10.1080/ 10807039.2019.1571403. microsoft word etasr_v12_n5_pp9149-9154 engineering, technology & applied science research vol. 12, no. 5, 2022, 9149-9154 9149 www.etasr.com shah et al.: an mppt-based 31-level adc controlled micro-inverter an mppt-based 31-level adc controlled microinverter maulik j. shah department of electrical engineering, cspit, charusat charotar university of science and technology (charusat), charusat campus changa, gujarat, india maulikniki@gmail.com kartik s. pandya department of electrical engineering, cspit, charusat charotar university of science and technology (charusat), charusat campus changa, gujarat, india kartikpandya.ee@charusat.ac.in priyesh chauhan electrical and computer science engineering institute of infrastructure, technology, research and management gujarat, india priyeshchauhan@iitram.ac.in received: 12 july 2022 | revised: 22 july 2022 | accepted: 24 july 2022 abstract-this paper presents a 31-level micro-inverter with an innovative control scheme. the presented micro-inverter makes use of a single pv panel connected to an mppt converter. four half-bridge legs are connected in series to produce 31 levels at the inverter's output. at the output side of the micro-inverter, a single full-bridge power circuit is used to generate positive and negative half-cycles. a high-frequency transformer and a pushpull converter are used to generate the required isolated dc sources. the output of an analog to digital converter (adc) is used as a gate pulse for the half-bridge circuit power switching devices. psim software was used to simulate the proposed microinverter, and the results are discussed. hardware prototypes were also created and the results are displayed. keywords-analog to digital converter; micro-inverter; mppt; pv panel; perturb and observe i. introduction a solar micro-inverter, also known as a micro-inverter, is a plug-and-play photovoltaic’s component that transforms the direct current (dc) produced by a single solar module into alternating current (ac). micro-inverters stand in contrast to traditional string and central solar inverters, which connect a single inverter to several solar panels. the output of multiple micro-inverters can be pooled and often sent into the power grid. compared to normal inverters, micro-inverters provide several benefits. the key benefit is that they electrically isolate the panels from one another, so even a full module failure or minor quantities of shade, dust, or snow lines on one solar module do not significantly diminish the output of the entire array. by conducting maximum power point tracking (mppt) for the modules it is attached to, each micro-inverter collects the most power possible. since each inverter must be put next to a panel, one of the main drawbacks of a micro-inverter is that it has a greater initial equipment cost per peak watt than a central inverter of similar power (usually on a roof). due to this, they are also more difficult to maintain and expensive to take apart and replace. in this proposed mppt-based 31-level micro-inverter, the multi-level inverter is used to reduce the harmonics at the output. figure 1 shows the basic block structure of the proposed micro-inverter. fig. 1. basic block structure of the proposed system. there are many mppt techniques available. two common types are: conventional algorithms and intelligent control algorithms [1, 3]. in [1], a different comparative analysis of mppt algorithms is presented. this paper simulated a 100kw grid-connected pv system with a beta control algorithm. based on the previously known value, the accuracy of mppt can be improved [7]. in the proposed inverter, the pv panel is used for mppt with the perturb and observe (p&o) algorithm. a pushpull converter is used to separate a single source into many isolated dc sources. it employs a high-frequency transformer with a primary winding with a center tap and four different secondary windings. the isolated sources are used as asymmetric dc sources for the multi-level inverter (mli). many mli topologies are used nowadays to reduce the output voltage total harmonic distortion (thd). optimized topologies for mli are represented in [2] with asymmetric and symmetric dc sources. the home type cascaded mli with reduced power switching devices is presented in [4]. the asymmetric mli gives higher output voltage levels than symmetric mlis [5]. in the proposed topology, asymmetric power configuration is used for the generation of the 31-level output and a direct adc control scheme is developed for the corresponding author: maulik j. shah engineering, technology & applied science research vol. 12, no. 5, 2022, 9149-9154 9150 www.etasr.com shah et al.: an mppt-based 31-level adc controlled micro-inverter inverter to get a 31-level output voltage. in this scheme, the output of the adc is directly used as gate pulses of power switching devices in half-bridges. ii. modeling of the pv module the equivalent circuit model for the pv module is shown in figure 2. the equivalent circuit includes a current source in parallel with a diode and resistance. iph is the photo current, id is the diode current, rsh and rs show the shunt resistance and series resistance respectively [1, 3]. fig. 2. equivalent circuit for the pv cell. i � i�� � i� �exp��� ������� � � 1� � � � ��� ��� � (1) where i is the load current, is the diode saturation current, and t is the cell temperature. v � i��r�� � ir�� � i� �exp��� ������� � � 1� � ir� (2) by modifying (1), we get: v � i�� �i� �exp��� ������� �� 1� � � ��� � ������ (3) i � ������ � i� �exp� �� ���� ��� �� � i� � � ��� � i�� (4) from (4) we will get: ��� �������� �i � �exp� �� ����� exp� ��� ����� � 1� � ����� � ����� (5) an analytical solution for (5) is not possible. so, we ignore parameter rs and thus we get: i � � � �� ��!�� ��1 � ������� ��exp� �� ������ ��� �� (6) a. maximum power point tracking mppt is a method for maximizing energy extraction from variable power sources as conditions change. the main issue that mppt attempts to solve is the fact that the efficiency of power transmission from the solar cell is dependent on the quantity of sunlight, the amount of shade, the temperature of the solar panel, and the electrical characteristics of the load. the load characteristic (impedance) that provides the maximum power transmission changes when these variables change. the system is optimized in order to maintain the best efficiency of power transfer as the load characteristic changes. the maximum power point (mpp) refers to this ideal load property. any enhancement to the mppt's rise time will raise the system's efficiency and power extraction while also increasing system reliability. there are many algorithms developed for mppt, such as the p&o algorithm, the incremental conductance, and ripple correlation b. perturb and observe (p&o) by adjusting the voltage from the array by a little amount, the controller measures the power and, if it rises, tries more adjustments in that direction until the power stops rising. p&o is the most popular strategy because it is very simple to use, although it might lead to oscillations in the power output. because it depends on the increase of the power versus voltage curve below the mpp and the decrease above that point, it is also known as the "hill climbing" approach. if a suitable predictive and adaptive hill climbing strategy is used, p&o method may produce top-level efficiency [1]. iii. inverter with direct adc control scheme all supplied dc sources in symmetric mlis have the same magnitude, however in asymmetric mlis, the magnitude of the supplied dc sources varies. dc sources are employed in asymmetric mli binary or trinary types. dc sources in the binary pattern include vdc, 2vdc, 4vdc, etc. dc sources of the trinary kind include vdc, 3vdc, 9vdc, etc. however, the control strategy is quite complicated in trinary type power topologies and calls for a look-up table for switching power devices. using an analog to digital conversion ic or an adc channel built into a processor or microcontroller chip, the reference signal in binary-type dc sources can be converted directly. using 4 isolated dc sources, an inverter with a total of 12 power switching components and 6 half-bridge mosfet/igbt driver circuits may provide an output voltage with 31 levels. a. direct adc control scheme there is no need for a triangular carrier wave in the direct adc-controlled method. it produces n-bit controlled signals based on a look-up table for the sine wave's first half cycle. the resulting signals are immediately applied to the half-bridge of the inverter's gate pulses. as switching losses are reduced, an inverter's total efficiency also rises since the direct adc method's switching frequency is lower than that of all pwm systems. the creation of gate pulses depends on the bit resolution of the adc. the number of levels of the output voltage of the mli is determined by the bit resolution of the adc in this control system. as with 2-bit resolution, this will make only (2*2 2 )-1=7 level output, a 3-bit resolution will make (2*2 3 )-1=15 level output, and 4-bit will give (2*2 4 )-1 = 31 levels. iv. simulations and results the simulation validation of the proposed micro-inverter topology was carried out in psim software. figure 3 shows a complete simulated block diagram of the micro-inverter. a simulated block diagram contains a total of 3 subsystems and 1 pv panel. the mppt converter is developed in the first subsystem s1. subsystem s2 contains a push-pull converter with a high-frequency converter, and s3 includes a 31-level microinverter system. engineering, technology & applied science research vol. 12, no. 5, 2022, 9149-9154 9151 www.etasr.com shah et al.: an mppt-based 31-level adc controlled micro-inverter fig. 3. block diagram of the simulated system in psim. a. pv panel and mppt converter asp-7-330 (adani) pv panel was used for simulation in psim. its specifications are given in table i at 1000w/m² irradiance and 25°c cell temperature. in the simulation of the full system, the p&o algorithm is used for mppt. table i. pv panel specifications parameters value peak power (pmax) 330w maximum voltage (vmpp) 37.21v maximum current (impp) 8.87a open circuit voltage (voc) 45.87v short circuit current (isc) 9.42a module efficiency 16.84% fig. 4. i-v characteristics of the pv panel at 25°c at different irradiances. fig. 5. p-v characteristics of the pv panel at 25°c at different irradiances. figures 4 and 5 show the obtained i-v and p-v characteristics at 25°c and at different irradiances: 200w/m 2 to 1000w/m 2 irradiance is taken at 25°c for i-v and p-v characteristics of the pv panel. figure 6 represents the complete mppt buck converter connected with pv panel. in this +vin is coming from the positive terminal and gnd is coming from the negative terminal of the pv panel. in mppt block the p&o algorithm was developed in c language with the inputs the supply voltage (vin) and current (i) of the pv panel. the switching frequency of the pwm pulse is 20khz. fig. 6. simulation diagram of the mppt buck converter. b. push-pull converter with high-frequency transformer the output of the mppt converter +vout and gnd is connected to the supply of the push-pull converter. the pushpull converter is used to create isolated dc sources from a single source. it uses a high-frequency transformer with center tap primary winding and four numbers of secondary windings. secondary winding turns are chosen such that it gives binary types of supply voltages like 12, 24, 48, and 96v. each secondary winding is connected with a full-bridge diode rectifier to convert ac power into dc power. each output is used as a power supply of the inverter half-bridges. figure 8 shows the push-pull converter with a high-frequency transformer. vdc0, vdc1, vdc2, and vdc3 created the isolated dc sources in figure 7. figure 8 shows the output of the pushpull converter. fig. 7. push-pull converter to create isolated dc sources. fig. 8. simulated output of the push-pull converter. engineering, technology & applied science research vol. 12, no. 5, 2022, 9149-9154 9152 www.etasr.com shah et al.: an mppt-based 31-level adc controlled micro-inverter c. the 31-level inverter one half-bridge circuit of the power switching device is connected to each dc source that is created by the push-pull converter. to generate the negative and positive cycle, one fullbridge circuit is employed. the full-bridge circuit's gate pulse is generated by the zero-crossing logic's output. therefore, this h-switching bridge's frequency is comparable to its power frequency. the gate pulses of power switches s0 and s01 are working in inverting mode. gate driver ic is used to generate the dead band in the gate pulses of these two switches. for s1s11, s2-s21, s3-s31, and sh1-sh11, sh2-sh21, the same reasoning is used. assuming vdc0 = 12v, vdc1 = 24v, vdc2 = 48v, and vdc3 = 96v would follow. the power structure for the proposed 31-level inverter is shown in figure 9. fig. 9. simulated power circuit of the 31-level inverter. switching appears to take the form of a binary conversation. therefore, all dc sources are connected in series for the +15 vdc output level. in the 4-bit binary, it is simply (1111)2, which represents the states of power switches s3, s2, s1, and s0 respectively. similar to the +10 vdc case, the states are (1010)2 in binary, meaning that switches s3 and s1 are in the on position, while s2 and s0 are in the off position. figure 10(a) shows the simulated output voltage of the micro-inverter with a load of 65ω connected in series with a 63.7mh inductor at modulation index 1.0. figure 10(b) shows the zoomed view of the output voltage and figure 11 shows the load current of the inverter. figure 12 shows a comparison between the output voltage of the inverter and the grid voltage. (a) (b) fig. 10. (a) output voltage at r=65ω and l=63.7mh at modulation index m=1.0, (b) zoomed view of the output voltage. fig. 11. load current at r=65 ω and l=63.7mh at m=1.0. fig. 12. compared output voltage of the inverter and grid voltage. table ii. thd of the output voltage and load current at different modulation index values modulation index (m) thd (%) voltage (vout) current (iout) 1.0 3.16 0.82 0.9 3.67 1.23 0.8 3.93 1.12 0.7 4.95 1.67 0.6 5.40 1.76 0.5 6.42 1.69 table ii shows the % thd of the output voltage and load current concerning the fundamental components. it can be seen that thd will increase with the decrease in the modulation index value. as the modulation index is decreasing, the number of levels at the output side of the inverter decreases. v. hardware results for the testing of the adc control scheme, a hardware prototype of the inverter with isolated dc sources was developed. each half-bridge mosfet is driven by an ir 2104 half-bridge driver ic. so, the proposed mli uses a total of 6 ir2104 driver ics. a built-in dead-band facility exists between the top and lower mosfets of the ir2104 driver ic. therefore, a dead band between two inverted gate pulses can be generated without the need for any additional hardware or software. for the 4 half-bridge circuits, irfb4110 mosfets were used as power switching devices, and irfp460n mosfets for full h-bridge circuits. to protect the microcontroller, 817 opto-coupler ic was used to isolate the gate pulses from the microcontroller. the hardware prototype was tested on resistive and inductive loads. figure 13 shows the output of adc that is used as gate pulses for four halfbridges. figures 14 and 15 show the output voltage of an inverter at m=1.0 and m=0.8 respectively. figure 16 shows the inverter output voltage in comparison with the grid voltage. engineering, technology & applied science research vol. 12, no. 5, 2022, 9149-9154 9153 www.etasr.com shah et al.: an mppt-based 31-level adc controlled micro-inverter fig. 13. gate pulses generated using adc fig. 14. inverter output voltage at modulation index m=1.0. fig. 15. inverter output voltage at m=0.8. fig. 16. inverter output voltage in comparision with the grid voltage. (yellow color: inverter output, purple color: grid voltage). vi. conclusion in the proposed topology of the micro-inverter, the number of necessary dc power sources is reduced by using binary level dc sources. the inverter output voltage reached 31 levels utilizing only 4 isolated dc sources and direct adc control. at modulation index m=1, the thd of the inverter output voltage was reduced to 2.11%. when compared to other control methods like spwm, svpwm, etc. the direct adc control scheme utilized in this study is quite straightforward. here, there is no need to contrast any carrier (triangular) wave with the reference sine wave. the direct adc control approach makes it simple to create a grid connection for an inverter. the proposed mli's rms output voltage will fluctuate in line with variations in the grid's rms voltage. the fundamental benefit of this control strategy is that the frequency of the grid and the output voltage are constantly synchronized. references [1] f. z. kebbab, l. sabah, and h. nouri, "a comparative analysis of mppt techniques for grid connected pvs," engineering, technology & applied science research, vol. 12, no. 2, pp. 8228–8235, apr. 2022, https://doi.org/10.48084/etasr.4704. [2] b. m. manjunatha, s. n. rao, a. s. kumar, k. s. zabeen, s. lakshminarayanan, and a. v. reddy, "an optimized multilevel inverter topology with symmetrical and asymmetrical dc sources for sustainable energy applications," engineering, technology & applied science research, vol. 10, no. 3, pp. 5719–5723, jun. 2020, https://doi.org/10.48084/etasr.3509. [3] m. t. ahmed, m. r. rashel, f. faisal, and m. tlemcani, "non-iterative mppt method: a comparative study," international journal of renewable energy research, vol. 10, νο. 2, pp. 549–557, jun. 2020. [4] p. l. kamani and m. a. mulla, "a home-type (h-type) cascaded multilevel inverter with reduced device count: analysis and implementation," electric power components and systems, vol. 47, no. 19–20, pp. 1691–1704, dec. 2019, https://doi.org/10.1080/15325008. 2019.1660735. [5] m. farhadi kangarlu and e. babaei, "cross-switched multilevel inverter: an innovative topology," iet power electronics, vol. 6, no. 4, pp. 642– 651, 2013, https://doi.org/10.1049/iet-pel.2012.0265. [6] d. shunmugham vanaja and a. a. stonier, "a novel pv fed asymmetric multilevel inverter with reduced thd for a grid-connected system," international transactions on electrical energy systems, vol. 30, no. 4, 2020, αρτ. νο. e12267, https://doi.org/10.1002/2050-7038.12267. [7] m. chellal, t. f. guimarães, and v. leite, "experimental evaluation of mppt algorithms: a comparative study," international journal of renewable energy research (ijrer), vol. 11, no. 1, pp. 486–494, mar. 2021. [8] v. pakala and s. vijayan, "a new dc-ac multilevel converter with reduced device count," international journal of intelligent engineering and systems, vol. 10, no. 3, pp. 391–400, jun. 2017, https://doi.org/10.22266/ijies2017.0630.44. 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[11] d. a. tuan, p. vu, and n. v. lien, "design and control of a threephase t-type inverter using reverse-blocking igbts," engineering, technology & applied science research, vol. 11, no. 1, pp. 6614–6619, feb. 2021, https://doi.org/10.48084/etasr.3954. engineering, technology & applied science research vol. 12, no. 5, 2022, 9149-9154 9154 www.etasr.com shah et al.: an mppt-based 31-level adc controlled micro-inverter [12] j. chakravorty and g. sharma, "dvr with modified y source inverter and mcfc," engineering, technology & applied science research, vol. 9, no. 1, pp. 3803–3806, feb. 2019, https://doi.org/10.48084/etasr.2522. [13] s. paul, p. jacob, and j. jacob, "performance comparison of stand alone solar pv system with variable step size mppt," international journal of renewable energy research (ijrer), vol. 10, no. 3, pp. 1277–1286, sep. 2020, https://doi.org/10.20508/ijrer.v10i3.11212. g8002. [14] z. boumous and s. boumous, "new approach in the fault tolerant control of three-phase inverter fed induction motor," engineering, technology & applied science research, vol. 10, no. 6, pp. 6504–6509, dec. 2020, https://doi.org/10.48084/etasr.3898. [15] u. b. tayab and m. a. a. humayun, "modeling and analysis of a cascaded battery-boost multilevel inverter using different switching angle arrangement techniques," engineering, technology & applied science research, vol. 7, no. 2, pp. 1450–1454, apr. 2017, https://doi.org/10.48084/etasr.1094. microsoft word etasr_v13_n3_pp10744-10747 engineering, technology & applied science research vol. 13, no. 3, 2023, 10744-10747 10744 www.etasr.com el-gohary: a simplified energy model approach for the determination of long-term crack width in … a simplified energy model approach for the determination of long-term crack width in reinforced concrete elements hamdy a. el-gohary civil engineering department, college of engineering and islamic architecture, umm al-qura university, saudi arabia | structural engineering department, faculty of engineering, mansoura university, egypt hagohary@uqu.edu.sa (corresponding author) received: 15 march 2023 | revised: 30 march 2023 | accepted: 4 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5855 abstract the deformation of reinforced concrete elements is a main consideration during the design process due to its importance for the service life of structures. deformation (deflections and cracking) control has an effect at both the design and construction stages. the determination of crack width based on simple code provisions, leads to conservative results, due to many affecting parameters being unknown. the exact determination of the crack width is a very complicated process with significant computational load. in the current paper, a simplified procedure is proposed for the prediction of crack width at different loading stages. the procedure is based on a previously published energy model that uses the integration of the moment-curvature relationship to take into consideration the load stage and most affecting design variables. the obtained results using the simplified model are then tested against previously published experimental data and a good agreement is shown. keywords-reinforced concrete elements; deformation; state diagrams; energy model; general and residual resources i. introduction the serviceability limit state of concrete structures is one of the most important steps within the design. the determination of deflection and crack width using code provisions commonly results in conservative values due to many important variables affecting design being unknown [1-3]. the idealized stressstrain curves for both concrete and reinforcing steel as well as the equivalent stress block in concrete, represent some major causes of conservative estimations. another design approach for crack width calculation in reinforced concrete structures under short-term loading was developed in [4], based on the actual strain distribution along the spacing between two adjacent cracks. determination of the real stress-strain state of reinforced concrete elements at different stages of loading has always been a key task in reinforced concrete theory. its implementation is largely associated with the development of general models of deformation. the fulfillment of most of validity requirements in the so-called "strength" models [5] has been impractical due to the use of an idealized equivalent rectangular stress block. in "deformation" models [6-8], the methodological unity of all calculations of reinforced concrete elements according to limit states can generally be ensured with the help of complete concrete stress-strain curves (�� −�� ). however, when integrating these curves or even using simplified forms of these diagrams [7, 8], the internal static uncertainty of the cross-section of reinforced concrete elements must be calculated through numerous iterations, involving several empirical parameters and coefficients which result in a significant computational load. the concrete deformation model [9] can be considered the closest one to the generalized model of reinforced concrete elements deformation today. it shows the reason for being impossible to build a generalized model of the deformation of reinforced concrete elements with just the help of a stress-strain diagram of concrete. the calculation of concrete deformation at any stage is not controlled by the concrete deformation diagrams, but by the moment-curvature relationship of the reinforced concrete element (� − ϕ), which characterizes its stiffness. however, the concrete deformation model needs further development, especially in matters of assessing the actual technical condition of reinforced concrete elements and structures and calculating their capacity and deformations. the current paper aims to predict long-term crack width based on energy modeling. the proposed procedure is largely based on the concrete deformation model [9], modified in order to simplify the calculations and lighten the computational load. the simplified model is then applied on a previously published case study. engineering, technology & applied science research vol. 13, no. 3, 2023, 10744-10747 10745 www.etasr.com el-gohary: a simplified energy model approach for the determination of long-term crack width in … ii. moment curvature relationship for the case of short-term loading, the relation between the moment and curvature will have the form presented in [9]: � ��� ∙�����∙��/�������� ��� /�����/����∙� (1) where �� is the concrete's modulus of elasticity, ��� is the moment of inertia of the cracked section, � ! is the moment capacity at failure, and " ! is the limit value of the curvature at failure. for the case of long-term loading, the relation will follow the same curve of the short-term loading up to the value of service load (ma, "a), then it will have a constant value of moment with the increase of the curvature. the increase in curvature after applying the service load will be due to the creep of concrete. solving (1) for the curvature, the following expression is provided in [10]: " ������� #$1 − ����& ∙ �� ��� " ! ' 2� − )*$1 − ����& ∙ �� ��� " ! ' 2�+ � − 4� ∙ � ! . (2) for the case of short-term loading (figure 1), three points must be defined. for a given concrete element with defined section properties, the value of moment at the three defined points in the shown moment-curvature curve can be calculated (�/ , � , and � ! ) . the curvature at failure (" ! ) can be determined using the hypothesis of concrete plane section under bending. then the corresponding curvature at service and ultimate load ("/ and " ) can be calculated using (2). these parameters are essential for use in the energy modeling approach. iii. a simplified approach on energy modeling in general, it is known that in the deformation-force model, the main deformation and force parameters of the state of the element are interconnected by utilizing stiffness �� �/ϕ [11-13]. the mentioned parameters can be combined using another characteristic: the energy consumed on the deformation of a reinforced concrete element per unit volume 0 � ∙ " [14]. under such circumstances, the methodology for the calculation of the total energy of reinforced concrete elements can be used to determine the deformations directly. the energy modeling approach has been developed in [9, 10] and is summarized as follows: the total energy consumed at any stage of short-term loading can be determined by integrating (1) from null to the curvature value at the stage under consideration. as explained in [10], three integrations must be performed for the three defined stages on the moment curvature curve, at the service load, at the ultimate load and at the failure load. these three integration results are called 0�(0/ ), 0 and 0 ! respectively (figures 2-4). fig. 1. moment-curvature relationship for short-term and long-term loading. fig. 2. total energy consumed up to failure in case of short-term loading. fig. 3. total energy consumed up to ultimate load in case of short-term loading. fig. 4. total energy consumed up to failure in case of long-term loading. the energy consumed in both cases of the short-term and the long-term loading must be equal [9]. the following relations can be used to determine both w2 and w3: engineering, technology & applied science research vol. 13, no. 3, 2023, 10744-10747 10746 www.etasr.com el-gohary: a simplified energy model approach for the determination of long-term crack width in … 0 0� ' 0� (3) 0 ! 0� ' 0� ' 02 (4) the value of long-term loading curvature can be determined for both values of long-term ("3 ) and ultimate long-term curvature (" 3 ) using: "3 4��5 ' "/ (5) " 3 4���45�5 ' "/ (6) the application of the integrations presented in [10] for the determination of the consumed energy 0�, 0 , and 0 ! , has a significant computational load. using a rough approach for the curve line portion of long-term moment-curvature relationship from "/ to " and from " to " ! , the following equations can be derived for the calculation of w2 and w3: 0� �5���� ∙ (" − "/ ) (7) 02 �� ����� ∙ �" ! − " � (8) solving (5) with (7) and (6) with (8), the corresponding curvatures for the long-term loading case will be: "3 �� 91 ' ���5: (" − "/ ) ' "/ (9) " 3 �� 91 ' ����� : �" ! − " � ' "3 (10) following this scheme, once the moment and the corresponding curvature at the three defined stages of shortterm loading have been defined, the values of long-term curvature "3 and " 3 can be determined directly using (9) and (10). knowing the curvature, the following formula can be used to determine the crack width [15]: " ;�,<�=� />� �;�?�,<@ (11) where scr and wcr are the spacing and the normal crack width, ��,a and ��b ,a are the mean values of compression and ultimate strain in concrete at the tension side [9], respectively, and d is the effective depth of the concrete section. the corresponding curvature "3 is related to the crack width c3 and the average strain of compressed concrete ��3,a, as follows: c3 �"3 ∙ d − ��3,a − ��b ,a � ∙ e�� (12) ��3,a ��,a ∙ �1 ' f(g, gh)� (13) where f(g, gh) is the value of the creep coefficient of compressed concrete under the action of an external load with a duration of (g − gh) [7]. the value of crack width c3 can be determined from (10). the crack width at failure under long-term loading will have the form: c 3,�� �i. " 3 − ��3 ,a − ��b ,a� ∙ e�� (14) iv. comparison with experimental results the theoretical prediction of long-term crack width has been performed for the 4 beams tested in [16]. the selected beams are simply supported with spans of 3500 mm and are reinforced by two longitudinal bars of 16 mm diameter. the concrete compressive strength at 28 days was 24.8 mpa. the cross-section of the beams is shown in figure 5 and the details are given in table i. the maximum crack width measured from the tests under long-term loading at 14 and 400 days are also presented in table i along with the predicted values of crack width. the detailed results of the theoretically predicted longterm crack widths were compared with the experimental ones and the result is presented in figures 6 and 7. the theoretically predicted crack width at different ages correspond well with experimental results. from both the theoretical and experimental results, it has been observed that the crack width increases rapidly at early ages up to the first 100 days, and then slowly increases. the maximum long-term crack width has been performed at an average age of 200 days. fig. 5. cross section of the selected beams. table i. comparison of experimental and theoretical results beam cb cs s crack width (mm) experimental theoretical 14 days 400 days 14 days 400 days b1-a 40 40 150 0.13 0.38 0.14 0.37 b1-b 40 40 150 0.05 0.18 0.08 0.17 b2-a 25 25 180 0.10 0.36 0.14 0.37 b2-b 25 25 180 0.05 0.18 0.08 0.17 fig. 6. comparison of the experimental and theoretical results of the longterm crack width in reinforced concrete beam b1-a and b2-a presented in [16]. engineering, technology & applied science research vol. 13, no. 3, 2023, 10744-10747 10747 www.etasr.com el-gohary: a simplified energy model approach for the determination of long-term crack width in … fig. 7. comparison of the experimental and theoretical results of the longterm crack width in reinforced concrete beams b1-b and b2-b presented in [16]. v. conclusions in this paper, a simplified approach is proposed for the calculation of the long-term crack width in concrete elements based on an energy model earlier model published in [10]. the simplified approach is applied on experimental data previously published in [16]. as shown, the simplified model shows good agreement with the experimental results. future research should focus on testing the simplified model in other case studies. further, the exact tradeoff between computational load and achieved accuracy should be investigated. references [1] m. oad, a. h. buller, b. a. memon, and n. a. memon, "impact of long-term loading on reinforced concrete beams made with partial replacement of coarse aggregates with recycled aggregates from old concrete," engineering, technology & applied science research, vol. 9, no. 1, pp. 3818–3821, feb. 2019, https://doi.org/10.48084/etasr.2498. 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[16] r. i. gilbert and s. nejadi, an experimental study of flexural cracking in reinforced concrete members under sustained loads. sydney, nsw, australia: university of new south wales, school of civil and environmental engineering, 2004. microsoft word etasr_v13_n3_pp10680-10684 engineering, technology & applied science research vol. 13, no. 3, 2023, 10680-10684 10680 www.etasr.com hanani et al.: development of a hybrid solar and waste heat thermal energy harvesting system development of a hybrid solar and waste heat thermal energy harvesting system mohamed nadzirin hanani water & energy section, universiti kuala lumpur malaysia france institute, malaysia hanani@unikl.edu.my (corresponding author) jahariah sampe institute of microengineering and nanoelectronics (imen), universiti kebangsaan malaysia (ukm), malaysia jahariah@ukm.edu.my jasrina jaffar water & energy section, universiti kuala lumpur malaysia france institute, malaysia jasrina@unikl.edu.my noor hidayah mohd yunus electrical & electronics section, universiti kuala lumpur – british malaysian institute, malaysia noorhidayahm@unikl.edu.my received: 14 december 2022 | revised: 10 january 2023 | accepted: 15 january 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5561 abstract this research aims to develop a hybrid solar and waste heat thermal energy harvesting system that integrates thermoelectric generator (teg) with a solar pv system. the main focus is given to the development of the hybrid solar and waste heat released from the solar panel by using the teg system. this hybrid system consists of photovoltaic (pv) cells to absorb the solar energy and the teg attached to the back of the panel to absorb heat waste and convert it into usable electricity. the pv cell and the teg are integrated with each other in order to obtain maximum energy and increased system efficiency. the experimental results show that the maximum output voltage produced from the solar pv is 20.37v and the maximum output current generated is 203.72ma. the maximum output voltage obtained from the teg is 18.92v and the maximum current produced is 189.265ma. this experimental result shows that the maximum voltage and current produced from solar and waste thermal heat from pv panels can be used to charge and to power up portable electronic devices. more efficiency is accomplished by combining the teg to absorb waste heat loss from the pv cell, thus improving the performance of the pv panel system. keywords-solar and waste heat thermal energy harvesting system; thermoelectric generator (teg); photovoltaic (pv) cell; solar, thermal i. introduction energy harvesting is the process by which the energy produced from other sources is derived, collected, and sometimes stored in banks or batteries for future use. solar energy nowadays is very popular for its promising power production. however, even though its capability in producing a large amount of power is undeniable, the temperature of the panel gradually increases from time to time due to continuous hit by the solar irradiation [1]. while the solar panel is harvesting energy, the high temperature on the surface of the panel leads in performance de-escalation. many recent research projects have been conducted in renewable energy focused on increasing the chances to harvest, store, and distribute the solar energy [2]. there are several ways and types of new implementations of solar power that continue to increase as the price of harvesting solar power is reduced. the heat produced during the operation of the electrical equipment will usually be wasted and released to the environment [3]. by an energy harvesting system, a certain amount of heat can be utilized and recycled to convert the energy from the waste heat into electrical energy [4]. the thermoelectric generator (teg) has been proposed to be intergraded with photovoltaic cell (pv) in a hybrid system [5]. the purpose of this system is to analyze the output and develop a suitable design that improves energy harvesting. teg devices are widely used in studies of thermal energy development [6]. teg was designed by applying the concept of seebeck effect which was described back in 1820 engineering, technology & applied science research vol. 13, no. 3, 2023, 10680-10684 10681 www.etasr.com hanani et al.: development of a hybrid solar and waste heat thermal energy harvesting system [7]. thomas seebeck, who came with the theory, stated that thermal energy could be harvested into direct electrical energy achieved across the thermal difference between two dissimilar metals [8]. teg is a temperature-dependent device, where bigger thermal gradients possess higher capability to generate electricity [9]. to achieve the desired electrical output, the temperature gradient between the hot and cold sides of the teg are maintained by heat from pv cells and the cooling part from the flowing coolant in the heat sink [10]. this system is a hybrid system between photovoltaic (pv) and thermoelectric generator (pv/teg) [11]. when the solar panel is exposed to the sun, it will convert heat into electricity while thermal losses are produced [12]. as the temperature is getting higher, solar efficiency drops by 0.5% per degree. the purpose of applying tegs is to absorb the excess heat from the panel in conjunction with generating direct electricity [13]. the pv panel gets a source of energy from the solar radiation and the teg from the backside of the pv panel which is very hot due to heat loss [14]. the heat delivered from the bottom part of the pv module to the hot side of the teg module can be utilized in the teg module to produce electricity directly [15]. the seebeck effect concept defines that, when there is a difference in temperature from each side of the module, electrical energy can be produced. the basic teg unit consists of p-type and n-type semiconductor elements which are connected electrically in series and thermally in parallel [16]. ii. research methodology there are several methods for harvesting solar energy such as pv cells, solar thermal, combined systems, thermoelectric devices, and the recent integrated hybrid systems of pv cells and teg. this research considers developing and designing a hybrid solar and waste heat thermal energy harvesting system that integrates teg with pv cells. pv sells convert sunlight directly into electricity. when sunlight hits a cell, the energy knocks electrons free of their atoms, allowing them to flow through the material. the block diagram of the hybrid solar and waste heat thermal energy harvesting system shown in figure 1 is the basic model that defines the structure and operation of the system. fig. 1. block diagram of the hybrid solar and waste heat thermal energy harvesting system that integrates teg with solar pv cells. a. system architecture the system architecture flow consists of the main system components and the system development and implementation as shown in figure 2. the system begins with the pv panel that generates electric power by converting the incident light rays from the sun into a flow of electrons [17]. in this system, the direct current electricity produced by solar cells will be used to supply current in an electrical appliance or to recharge a battery [18]. the hot side of the teg will be placed directly under the pv panel and the cold parts will be directly placed on the heat sink [19]. the bottom part of the teg is attached with the liquid cooler radiator to create temperature gradient between the hot and cold sides of the teg [20]. the teg is connected to the boost converter to increase the output voltage to its optimum value [21]. it is then connected to a usb port charging by a direct current dc usb connector. the pv cell is connected to solar charge control and directly charges the 12v battery. the output can be delivered using a socket that is installed in the control panel. the hybrid pv/teg system can be used to charge and to power up a notebook, laptop, or any other portable electronic device [22]. fig. 2. detailed architecture flow of the hybrid solar and waste heat thermal energy harvesting system. b. design and development the design concept in this research involved a pv panel, a cooling system, and a solar control panel. the framework is designed to place the solar panel on top with an angle of 15°. the framework has 90cm height and the top and base dimensions are 60cm×40cm. the solar panel is placed on top of the framework and the teg is placed under the solar panel along with the cooling system to provide temperature difference between the hot and the cold sides. the size of the teg used is 4cm×4cm. there are 3 tegs used in this research with the same specifications. the control panel is designed to place the circuit breaker, socket outlet, inverter, terminal block, usb port charging, solar charge controller, and 12v battery. a rechargeable 12v lead-acid battery is used as a power supply which is also recharged by the pv panel. the circuit breaker is used to protect the electrical circuit from any damage caused by excess current from an overload or short circuit. the terminal block is used to connect all the wires. there are 10 terminal blocks used in this study. the solar charge controller is used to supply voltage from the pv panel to the rechargeable lead-acid battery and prevent from overcharges. figure 3 shows the block diagram of the hybrid solar and waste heat thermal energy harvesting system. the pv cells' output is directly connected to the solar charge controller to recharge the battery. it will directly be connected to the inverter to convert the direct current to alternating current so that it can be used at the socket outlet to supply power for any electrical appliance. the resulting dc (direct current) electricity is then sent to a power inverter for conversion to ac (alternating current). figure 4 shows the hardware implementation of the engineering, technology & applied science research vol. 13, no. 3, 2023, 10680-10684 10682 www.etasr.com hanani et al.: development of a hybrid solar and waste heat thermal energy harvesting system hybrid solar and waste heat thermal energy harvesting system. three tegs connected in series are attached under the pv cells to get the thermal heat and to generate electricity. that heat would be otherwise dissipated [23]. the tegs are attached by using thermal grease to avoid the presence of any air gaps and to obtain maximum heat transfer [24]. a copper plate is also attached with teg to increase the heat transfer from the liquid cooler pump. the output from teg is directly connected to the boost converter to step up the output voltage and is finally connected to the usb charging port. the type of boost converter used is xl6009 (figures 5-6). fig. 3. the overall hybrid solar and waste heat thermal energy harvesting system. fig. 4. hardware implementation of the system. the hybrid solar and waste heat thermal energy harvesting system is designed to achieve the minimum input voltage from 5v to an optimum output voltage up to 25v which is suitable for the application of small electrical appliances. the liquid cooler radiator which is placed under the solar panel is used to reduce the temperature of the cold side of the teg and increase the gradient temperature between the hot and cold sides to maximize the output [22]. the design of the liquid cooler radiator consists of a pump, two pipes, and a radiator. table i shows all the parts and pieces of equipment used in this research. fig. 5. xl6009 boost converter. fig. 6. xl6009 module circuit diagram. table i. system components no. component 1 photovoltaic cells (50w) 2 thermoelectric generator (teg) 3 liquid cooler radiator 4 boost converter 5 cooler fan 6 copper plate 7 control panel 8 battery 12v 9 inverter 10 terminal block 11 solar charge controller 12 circuit breaker 13 socket outlet 14 usb charging port iii. results and discussion figure 7 shows the data collection during experimentation. it shows that the solar panel is capable of generating higher output voltage compared to the tegs [26]. the output voltage from the tegs only depends on the temperature of the solar panel to generate electricity. as the solar panel gained higher temperature at 12.05 pm, the voltage of the tegs increased drastically. at 12.55 pm, the graph shows a decrease in solar voltage but the tegs were still generating high voltage. this event occurred as the temperature of the solar panel had exceeded the limits and performance degradation took place. the constant line for both teg and solar panel voltages in figure 7 is due to the integration of voltage during this time interval as the teg voltage is integrated with the solar panel voltage. the full line on the graph shows that this system was able to increase the teg's voltage generation by using 3 tegs engineering, technology & applied science research vol. 13, no. 3, 2023, 10680-10684 10683 www.etasr.com hanani et al.: development of a hybrid solar and waste heat thermal energy harvesting system connected in series, a voltage booster, and a cooling pump for higher thermal gradient across the tegs. fig. 7. the output voltage of tegs and pv panel. fig. 8. the output current of tegs and pv panel. fig. 9. temperature of tegs and solar panel. figure 8 shows a similar pattern with figure 7 as the current increased when the output voltage increased. as expected, the panels generate higher output than tegs. the constant line shows teg and panel having similar output current. this happened as the surface temperature of the solar panel increased contributing to the tegs' efficiency. the highest achieved voltage from the pv cells was 20.37v with current 203.72ma. the highest temperature recorded was 56.43°c as shown in figure 9 and the power generated is 4.15w. from these data, it can be concluded that the expected output voltage from pv cells of 20v is achieved. figures 7-8 show that the highest voltage from 3 tegs in series is 18.92v and the current is 189.27ma. the highest optimum temperature is 37.29°c and the output power generated is 3.58w. the highest gradient temperature between the cold and hot side of tegs is 20.87°c. from these data, it can be concluded that the voltage from tegs is expected to get 12v and the project target output voltage is finally achieved. the gradient temperature between the cold and the hot side of the tegs shows a very good result, increasing voltage and current output. iv. conclusion a hybrid solar and waste heat thermal energy harvesting system is produced in this study by integrating the thermoelectric devices into pv systems. the overall performance of the hybrid energy harvesting system and the efficiency of the thermal management in the pv solar panel have been improved. the integration of tegs with the pv panel, utilizing the waste heat, generated greater output 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licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5732 abstract in this paper, a nonlinear predictive controller is proposed for a variable-speed induction motor. the research work is directed towards improving the trajectory tracking capability, stability guarantee, robustness to parameter variations, and disturbance rejection. the generalized predictive control (gpc) without constraint and output-constrained controller to induction motor drive is illustrated. the variables to be controlled are rotor speed and flux trajectory. the load torque is considered an unknown disturbance. finally, the tuning parameter of gpc is automatically determined. the simulation results show a good performance for the nonlinear dynamic system. keywords-robust; induction motor; polynomial approach; output contraint; predictive control i. introduction generalized predictive control (gpc) is among the most popular control techniques, having many ideas in common with dynamic matrix control (dmc) [1] and model algorithm control (mac) [2]. the control algorithms differ mainly in the plant (and/or noise) models used and the cost function chosen. the gpc exhibits very good performance and robustness provided that the tuning parameters are property selected. however, the selection of these parameters is not an easy task. first there are no precise guidelines for the selection of these parameters in order to ensure closed loop stability [2, 3], although recent works have proposed modifications of the prototypical structure in order to guarantee stability. gpc algorithms have been proposed under various names by several authors [4-7] and constitute a class of powerful control algorithms that have been widely applied on industrial processes. gpc is a technique with success in industrial applications. besides its quality, gpc provides unconstrained case linear laws easy to implement in polynomial formulations [3, 4] and can further be reinforced by adding equation constraints for stability. the application to fast processes with constraints has been delayed and the optimal control action is generally provided by an on-line optimization procedure, generally a time-consuming process. the classical predictive control approach to drive applications includes several different control strategies. the various control schemes can be divided in a few main groups. the most published schemes so far belong to the families of hysteresis-based or trajectory-based predictive control. on the contrary, gpc belongs to the model-based predictive control (mbpc) group, which is founded on totally different ideas. the idea of mbpc is to calculate a control function for the future time in order to force the controlled system's response to reach the reference value. therefore, the future reference values have to be known (which is the case in many industrial applications) and the system behavior must be calculable by an appropriate model. all the gpc algorithms are very similar because they have the same general idea in common. authors in [7, 8] present an approach to the design of an rst cascade predictive structure to control rotor position, speed, and the rotor flux amplitude of an induction machine. the proposed cascaded version introduces a formulation of the reference signals in the structure of the inner and external loop which enables tracking flux and position. the purpose is to propose a new methodology to current-fed induction motor. this approach engineering, technology & applied science research vol. 13, no. 3, 2023, 10951-10956 10952 www.etasr.com bektache et al.: robust nonlinear predictive control applied to induction motors results from a combination of the differential flatness properties and the monovariable gpc with the multiple reference model (gpc/mrm) algorithm. the chosen outputs are the rotor speed and the square of the rotor flux [8]. different techniques have been proposed from the active–set methods to lmi [11]. lately, the idea of moving a part of the computational effort offline emerged and alternative techniques [9, 10] emerged based on look–up tables of linear affine controllers for regions of the sate–space. the continuous robust gpc of a permanent synchronous motor drive is explored in [14]. this work combines gpc controller with linear predictive control technology for permanent magnet synchronous model (pmsm). a continuous linear model (ctlm) is used to develop the gpc controller and determine the degree of the relative disturbance in [12-14, 18]. the svpwm (space vector pulse width modulation) gpc of linear induction motor drives was studied in [14, 15]. the authors used space vector pulse with modulation. authors in [19, 20] used the fod (field oriented control) for the robustification of explicit predictive control law [20]. the work in [21] is based on parametric programming and concentrates on control robustification. gpc strategy is introduced for the prediction of the controlled autoregressive integrated moving average (carima) plant model in [10, 21]. in this paper, an algorithm based on rst is presented. our method uses the synchronous motor as a highly nonlinear multivariable system. it deals with the development of a high performance nonlinear predictive control induction motor drive. the research work is directed towards improving the trajectory tracking capability, stability guarantee, robustness to parameter variations, and disturbance rejection. simulation results and the concluding remarks on the advantages and perspectives are also presented. ii. generalized predictive control a predictive strategy first requires the definition of a numerical prediction model. a commonly used form in gpc is the carima model [6]: ���������� = �������� − 1� + ������ ����∆ (1) where u(t), y(t) are the process input and output, a and b are polynomials in the backward shift operator, ���� is an uncorrelated random sequence and the operator ������ = 1 −��� ensures an integral control law. ������ = 1 + ����� + ⋯ ��� ���� ����� = 1 + ����� + ⋯ ��� ���� ������ = 1 �� and �� are degrees of polynomials � and respectively. a. definition of the quadratic cost funtion the performance index is a weighted sum of predicted output tracking errors and future control errors, so the cost function to be minimized is [10, 19, 20]. � = ∑ � !�� + "� + # ∑ �$!�� + " − 1�%&'(�%)'(%* (2) assuming �$�� + "� = 0 for " ≥ -$: ��� + "� = ��� + "� − �./0 �� + "� with: �$�� + "� = δu�t + j� − δ�./0 �� + "� (3) where -� and -! are the minimum and maximum costing horizons, -$ is the control horizon, and # is the control weighting factor. the gpc version with reference models imposes that the predicted output tracks a reference trajectory �./0 coupled to a reference control signal �./0 . the originality of our approach is the formulation of the reference models for the �./0 for the rotor speed and the planified trajectories which satisfy the motor’s constraints. the reference control signal �./0 will be expressed in terms of the chosen outputs [9-11, 20]. τhe linear structure rst law can be used in order to obtain access to a larger class of table controllers, by means of the youla –kucera parameterization. iii. design of the rst polynomial controller to solve the minimization problem [10], an optimal j-step ahead predictor based on the output error must be computed: δ����������� 5����� + ���6' ����� = 1 7' ����� + ���8' ����� = �����5' ����� where fj, 7' , 8' , and 5' are solutions of the diophantine equations. the optimal control law which minimizes the cost function is first deduced in a matrix form: �$ 9:� = −;<�=�> ��� + �ℎ@$ �� − 1�a (4) with: ; = <7 b 7 + #c%$ a��7 b = d ;� b⋮;%$b f (5) where: 7 = ⎣⎢ ⎢⎢ ⎡ j%*%* j%*��%* ⋯ ⋯j%*k�%*k� j%*%* k� ⋯ ⋯⋯ ⋯ ⋯ ⋯j%)%) j%)��%) ⋯ j%)�%& k�%) ⎦⎥ ⎥⎥ ⎤ the coefficients of the matrix g correspond to the step response: �= = <6%* ����� ⋯ 6%) �����ab �ℎ = <8%* ����� ⋯ 8%) �����ab �$9:� = <�$9:� ��� ⋯ �$9:� �� + -$ − 1�ab o�����∆���� = −p�������� + q�����r��� (6) with: <o�����a = stjutt< �����a p����� = ;�b �=;degree<p�����a = stjutt<������a; engineering, technology & applied science research vol. 13, no. 3, 2023, 10951-10956 10953 www.etasr.com bektache et al.: robust nonlinear predictive control applied to induction motors q�����r��� = ∆�����o������./0 ��� + p������./0 ��� (7) where p����� , o����� , and q����� compose the equivalent controller of the gpc algorithm [2, 7]. the minimization of (7) provides the determination of the polynomials' structure of the gpc controller as shown in figure 1. fig. 1. equivalent polynomial controller. iv. mathematical model of induction motor frame abc the induction motor is generally used in industrial applications because it is reliable, robust, and has a low cost. a well-founded induction motor gives good results under various operating states. to achieve this, the values of the motor are kept in mind. dynamic simulation plays a significant part in evaluating a model’s design process in order to eliminate design errors. the induction motor is modeled in a synchronously revolving rotor flux-oriented frame, which is used as a reference. for sensorless vector control and induction motor control methods, accurate knowledge of a few induction motor parameters is necessary. the presentation of the drive will degrade if the original data in the motor do not match the values utilized in the controller. various mechanisms have been developed to calculate the online and offline parameters of the induction machine for its application in highperformance drives. the aim of this paper is to present dynamic modeling and other considerable approaches used for estimating the induction motor parameters. also, some simulation examples related to dynamic modeling and parameter estimation techniques, which may be useful for specialists in the field of electric drive control systems, are considered. electrical drives based on induction motors are commonly used in industrial applications due to their simplicity and low maintenance cost. we are interested in the induction motor abc frame model. park transformation is not needed to realize the system. however, even if traditional control techniques of induction machines are adopted, e.g. scalar control, foc, direct torque control (dtc), predictive control, etc., improvements can be achieved in order to extend the operating range, improve behavior during saturations in order to reduce electrical influence and mechanical parameter variations, and improve transient performance. the reader is referred to [12-16] for the general theory of electric machine and induction motors for related control. w = pc + xyx� (7) dz[�z[�z[\ f = d p[ 0 00 p[ 00 0 p[f d c[�c[�c[\ f + xx� d ][�][�][\ f (8) the rotor voltage is described by the matrix form: dz.�z.�z.\ f = d p. 0 00 p. 00 0 p. f d c.�c.�c.\ f + xx� d ].�].�].\ f = d 000f (9) with the previous hypotheses, all the relations of induction motor are presented. the matrix of the real flux is: ^][��\].��\ _ = ` a[ ;[.;[. a. b (10) with: <a[ a = d a[ ;[ ;[;[ a[ ;[;[ ;[ a[ f (11) <a. a = d a. ;. ;.;. a. ;.;. ;. a. f (12) <;[. a = c cos �g� cos �g + 2i/3� cos �g − 2i/3�cos �g − 2i/3� cos �g� cos �g + 2i/3�cos �g + 2i/3� cos �g − 2i/3 cos �g� l (13) the dynamic equation of the system is described by: 5 xmx� = qn − qo (14) where j is the inertia of the machine, p[ and p. are the stator and rotor resistances, a[ and a. are the stator and rotor inductances, ωis the rotor speed, α is the rotor position, ;[. is the mutual inductance, p is the number of pole pairs, = is the friction coefficient, qo is the load torque, and q. is the time rotor constant. fig. 2. field oriented control of 1c by gpc. v. field orientation control the considered plan is an experimental setup of a squirrel cage induction motor. benchmark systems for the positioning control laws of asynchronous machine details regarding the general theory of electric machines and induction motors can be found in [16, 17, 21]. the machine considered is a three engineering, technology & applied science research vol. 13, no. 3, 2023, 10951-10956 10954 www.etasr.com bektache et al.: robust nonlinear predictive control applied to induction motors (squirrel) cage asynchronous motor with two pairs of poles in star power connection. the model takes into account the matrix transformations of the one phase system to a two phase representation, and the field oriented control including a torque and flux loop. the aim of the inner torque and flux control is to obtain a particular situation corresponding to the control of a dc motor. the model summarized in figure 2 will be used to test the polynomial law in speed and position. for robust control of the motor velocity (good stability margins, small overshoot of the step response according to the guaranteed stability recommendation [22]), the auto calibration procedure by a controller is designed. the compliant link where the torque is often saturated during rapid slewing is controlled. the tuning parameters have their optimal values [21, 22]. fig. 3. closed loop of poles. fig. 4. velocity of the induction motor. vi. study and test of stability the stability of the scheme can be tested by looking in the bode or black diagram (figures 6-7). 8����� = qr*stqr*uv�qr*�w�qr*�∆�qr*�x�qr*� (15) the results are shown to exhibit the stability of the external loop, considering the open loop is defined as in [10]. this is a test for both the induction machine and the polynomial algorithm. the frequency does not enter 3db, guaranteeing an overshoot less than 5. for a robust control of the motor velocity (good stability margin, small overshot of the step response) according to the guaranteed stability recommendations and the auto calibration procedure, the above described controller is designed. fig. 5. torque with pwm. fig. 6. bode plot. fig. 7. black plot. vii. simulation results to test the performance of the nonlinear predictive controller, simulations were performed on an im with nominal parameter values given in the appendix and the load torque shown in figure 8. the digital model of the motor is run with a sample time of 1μs. the space vector pwm inverter feeding the induction motor has a pwm period of 100μs. the full state vector is well known, where the stator voltage, stator current and speed are taken from the im model and the rotor is estimated by (9). at first, the machine controlled by the cascade control law is run with the nominal values of the machines parameters. the tracking performance for rotor speed -240 -210 -180 -150 -120 -15 -10 -5 0 5 10 15 20 25 30 diagramme de black phase [degré] m o d u le [ d b ] engineering, technology & applied science research vol. 13, no. 3, 2023, 10951-10956 10955 www.etasr.com bektache et al.: robust nonlinear predictive control applied to induction motors with measure is shown in figure 9, with disturbance at 0.5s in figure 10, and without disturbance in figure 11. ω��� z��� �.|}}qr*k|.~!}qr)k� ��~.�!qr*�~.~!qr) (16) fig. 8. torque with constraints. fig. 9. output reference speed. fig. 10. output speed with disturbance. the simulations were performed with a sampling period of q[ =0.05s. we chose the gpc parameters n1, n2, nu, λ, gm, qm, and bm. r�� � "� is the future set point and n1, n2, nu, and λ, are parameters that must be elaborated. 7 <1.34,5.68,0.96,14.24,18.53,22.81,24.09,31, ,96,1ab is a column vector and 77 b =2919.09 is the scalar sum of the squares of the first eight step responses. p����� 0.284 � 0.237��� � 0.0048��! o����� 1 � 0.734���1 q����� 0.0043� � 0.000182�� � 0.00319�! � 0.00319�| � 0.0045�}+0.00594 �� � 0.0731��+0.1006�� fig. 11. output speed without disturbance viii. conclusion in this paper, nonlinear predictive control is developed for speed and flux tracking of an induction motor drive. it was shown that this kind of control is effective for solving the control problem of induction machines. the computation of the predictive control law is easy and does not need online optimization. the performance of nonlinear predictive control to the induction machine drive is exhibited and the rejection of the unknown load torque is enhanced. this work presented the simulated induction motor with an abc frame, and generalized predictive control without and with constrains. rst synthesis was used for the rotor speed controller of the induction motor. simulation results were given in the case of nominal and mismatched parameters of the complete nonlinear model. this is particularly beneficial in the case of motor driven speed, as seen in the example of a computer-controlled compliant link where the torque is often saturated during rapid slewing, forming an interesting limiting case and making the performance and robustness evaluation of the designed controller a challenging engineering problem. the choice of the tuning parameters is not yet optimized, essentially dealing with the choice of the control weighting factor and the output prediction horizons. however, the resulting performances are satisfactory, and the appropriate choice of the gpc tuning knobs may improve the robustness of this controller. 0 0.5 1 1.5 -200 -150 -100 -50 0 50 100 150 200 n1=1 n2=8 nu=1 lamda=200 c o n s ig n e e t s o rt ie t[s] engineering, technology & applied science research vol. 13, no. 3, 2023, 10951-10956 10956 www.etasr.com bektache et al.: robust nonlinear predictive control applied to induction motors appendix the control law was implemented on a small 1.5kw induction motor, which corresponds to the benchmark ac machine of the lan (laboratoired’automatique de nantes), with the following features: p. 2.61ω, 5 0.0256kgm ! p[ 4.287ω, = 0.0029 a. 0.368h, p 2 a[ 0.404h, rnom 150rad/s ; 0.368h, qem 10nm, φ.�� 0.725wb the gpc chosen design parameters of the robust controller as shown in figure 1 (gain margin(db), φμ: phase margin (degree), bw : bandwidth(rad/s)) are: -� 1: is 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[21] a. bektache and b. boukhezzar, "nonlinear predictive control of a dfig-based wind turbine for power capture optimization," international journal of electrical power & energy systems, vol. 101, pp. 92–102, oct. 2018, https://doi.org/10.1016/j.ijepes.2018. 03.012. microsoft word etasr_v12_n6_pp9607-9613 engineering, technology & applied science research vol. 12, no. 6, 2022, 9607-9613 9607 www.etasr.com barhate et al.: fault detection methods suitable for automotive applications in proton exchange fuel … fault detection methods suitable for automotive applications in proton exchange fuel cells sujit sopan barhate department of technology savitribai phule pune university pune, india sujitbarhate@gmail.com rohini mudhalwadkar instrumentation and control department college of engineering pune pune, india rpm.instru@coep.ac.in swati madhe instrumentation and control department cummins college of engineering for women pune, india swati.madhe@cumminscollege.in received: 15 august 2022 | revised: 5 september 2022 | accepted: 20 september 2022 abstract-the fault conditions degrade the performance of proton exchange fuel cells and reduce their useful life. the prolonged existence of a fault condition can permanently damage the fuel cell. this paper proposes four methods for fault detection and fault type isolation. these methods were based on the coefficient of variance, ratios of change in output power to change in voltage and change in output voltage to the change in current, fuzzy membership values and euclidian distance, and wavelet transform. these methods are non-invasive to the fuel cell and involve non-destructive testing. these methods were experimentally validated. keywords-pem fuel cell; fuel cell faults; coefficient of variance; fuzzy membership values; wavelet i. introduction a proton exchange membrane fuel cell (pemfc) is the most suitable fuel cell for automotive applications [1]. pemfc performance is optimum when the operating conditions are appropriate. the fuel cell performance degrades due to poor thermal and water management [2], while prolonged water flooding can cause mechanical damage. an experiment using the energy intensity of reconstructed vibrating voltage (eiv) based on the wavelet transform was proposed in [3]. the factors affecting the performance of fuel cells in automobiles are described with the help of faults [4], using cause-and-effect chain analysis. several studies investigated fuel cell degradation [5], fault detection [6], and lifetime prediction in automobiles [7]. the degradation of the fuel cell output under various fault conditions and aging was studied in [8]. output voltage and power degradation for the expected output are modeled as ratios that can detect the fault, and their thresholds help to isolate the defect type [9]. in [10], a diagnostic survey of fuel cell stacks was compiled to summarize faults in fuel cells, their causes, and existing methods to detect them. statistically, water flooding is the largest (33%) contributing fault in fuel cell systems. modelbased and non-model-based methods were analyzed in [11] for fault diagnosis. a data-driven singular value decomposition method was applied in [12] to fuel cell parameters to detect faults. data-driven diagnostics measure parameters and estimate the potential issue in a fuel cell. an aging data test was simulated for short-term prognosis in [13]. several issues and solutions in fuel cell diagnostics were described in [14]. electrochemical impedance spectroscopy (eis) is a widely used technique in fuel cell fault diagnosis [15]. eis has proven to be an effective tool in detecting fuel cell flooding and degradation and is also able to differentiate flood and drying faults in fuel cells [16]. eis can be used to detect and isolate faults in fuel cells [17]. eis experimental data were recorded for 35 days in [18] and were analyzed using artificial neural networks (ann). eis has been used to determine the state of health of the fuel cells in electric vehicles [6] and detect catalyst degradation in fuel cells [19]. eis is an offline technique for fault diagnosis. the estimation of online parameters for eis was recently studied in [20]. the impedance obtained from eis was further analyzed as wavelet energy using wavelet and wavelet packet decomposition [21]. the data obtained using eis was converted to the frequency domain using the morlet wavelet [22]. in [18], current interruption and injection of current pulses were used to overcome issues with the eis method. other methods to detect faults in fuel cells are principle component analysis (pca) [23], fuzzy inductive reasoning [24], fuzzy logic, delta v analysis using the comsol model [25], kalman filter-based approach [26], external magnetic field-based tomography corresponding author: sujit sopan barhate engineering, technology & applied science research vol. 12, no. 6, 2022, 9607-9613 9608 www.etasr.com barhate et al.: fault detection methods suitable for automotive applications in proton exchange fuel … methods [27], takagi-sugeno interval observer approach [28], and ann-based approaches [29]. in [30], an ann model was downloaded to an fpga hardware platform to study 3 faults in a fuel cell system. a sliding mode algorithm was used for the observer design and matlab/simulink was used to implement the ann in [31]. fuel cell degradation prognosis was performed based on nonlinear autoregressive exogenous neural networks (narx) and wavelet analysis in [32]. degradation prognosis was also studied in [33] by using a degradation model based on the wavelet neural network (wnn) and cuckoo search algorithm. energy management in pemfc vehicles was studied using a matlab/simulink model in [34]. wavelet transforms were used in [35] for energy management optimization strategies on fcevs. model-based techniques have been described for offline [36] and online [37] fault detection. the online automotive fuel cell degradation was studied by modeling an electrical load in [4]. fuel cell degradation over a period causes internal changes inside the cell. these internal change behaviors were studied with the help of polarization curves and an adaptive neuro-fuzzy interference system for prognosis [38]. a fuzzy logic model was applied in [39] to common automotive stress conditions to diagnose faults. in [40], mathematical models were used to determine a fuel cell's health and predict its useful life. in [41], the useful life of the fuel cell was determined using a particle filtering framework. fuel cell state of health (soh), useful remaining life, and robustness were estimated in [42] using an extended kalman filter. in [43], artificial intelligence was used to estimate useful life and predict the degradation of a fuel cell. the echo state network is an ai tool to estimate the useful life of a fuel cell stack by considering the mean voltage of the cells [44]. a time delay nn was used along with the autoregressive moving average (arma) model for the prognosis of degradation. the arma model was used in [45] to predict the useful life of pem fuel cells along with a physical aging model and time delay nn. the arma results for the lifetime prognosis of pem fuel cell stacks were found satisfactory when compared with back propagation neural networks and least square fitting [46]. the simulation results of model predictive control (mpc) based on the arma model were found to have better control performance than mpc based on a rigorous linear model. fuel cell degradation prediction based on the arma model was found accurate in long-term forecasting [47]. a fault model based on the coefficient of variance (cv) was developed and experimentally validated in [48]. the durability of the fuel cell was analyzed by characterizing the voltage consistency [49] and consistency [50] using cv. most fault detection methods are offline, and the abovepresented studies use fixed loads. however, the load on an automotive pemfc is dynamic. this paper focuses on online fault detection and isolation methods. detecting fault conditions by merely measuring and analyzing the output voltage and current makes the models practical in automobile applications, as it enables analysis with minimum sensors and no downtime. this study compared the fault detection and isolation models, cv, and ratios of 4 novel methods developed using fuzzy membership functions and wavelets. ii. experimental observations experiments were conducted on two 25cm2 paxitech fuel cells using the pem fuel cell test setup, fct-50s, and fctlab. one cell was newly constructed and the other one was aged, having run for more than 2000 hours. the aged fuel cell had a 90% degradation in power delivery compared to the new one. faults were injected into the aged fuel cell, and the changes in polarization curves were observed. a water-flooded cell showed around a 30% decrease in performance in terms of power delivery. the reactant gas starvation fault showed around 55% degradation in the cell performance. a highoperating-temperature fault cell could not be able to deliver power. figure 1 shows the polarization curves of the experiments. fig. 1. pem fuel cell performance in operating conditions [7]. engineering, technology & applied science research vol. 12, no. 6, 2022, 9607-9613 9609 www.etasr.com barhate et al.: fault detection methods suitable for automotive applications in proton exchange fuel … iii. degradation and fault detection methods four methods were used to examine performance degradation and fault detection of the fuel cell. this section presents the methods and their results. a. coefficient of variance cv is used to measure the fuel cell output voltage dispersion and degree of asymmetry [51], and analyze its reliability using the stress-strength interference method [52]. the cv is a ratio of the standard deviation σ to the mean µ, as shown in (1). cv measures the relative variability of the parameters and can be used to compare the voltage degradation of a pemfc for a given current. �� � �µ � 100% (1) the coefficients of variance for the fuel cell output voltage cvv, the current density cvcd, and the cell power cvp were calculated for aged cells and cells operating in fault conditions [48]. the experimental results showed that the cv values could differentiate the degradation performance. b. ratio comparison experimental observations showed that fuel cell voltage drops for the current. this method compares the rate of change in the pemfc output voltage to the change in its output current, using (2). another ratio was calculated as the change in the pemfc output power to the change in output voltage, shown in (3). �� �� ����� � � � �� �������� ���� (2) ���� ����� � � �� � �������� ���� (3) ratios were calculated for the fuel cell under test and compared to the ratios of a healthy cell with the same specifications. the cell could have a fault condition if the ratio values do not match. similarly, the ratios can be compared to the threshold to isolate the fault type, as shown in (4) and (5): ���� ����� � � �� � ������ ��������� (4) �� �� ����� � � � �� ������ ��������� (5) figures 2 and 3 show, respectively, the ratios dp∕dv and dv∕di for each operating condition. the graphs show the difference in the performance of the fuel cell in a fault condition from a healthy one [9]. c. fuzzy membership values and euclidian distance method the fuzzy linear membership function of the values was used to compare the output voltage and current values of the fuel cell. the fuzzy linear membership values were obtained for the dataset. these membership values were comparable as they were unit free. the fuzzy linear membership function for the i-th observation defines a linear membership function as: !"# � ��$% �&���'����()��*��� �&���'����(� $% �&���'����( � (6) fig. 2. dp∕dv curves in different conditions [9]. fig. 3. dv∕di curve comparison between healthy and faulty operating conditions [9]. engineering, technology & applied science research vol. 12, no. 6, 2022, 9607-9613 9610 www.etasr.com barhate et al.: fault detection methods suitable for automotive applications in proton exchange fuel … the value of the membership function lies between 0 and 1. the smallest observation has a membership value of zero (m(x)=0). the membership values for the current and voltage observations can be used to calculate the euclidean distance between the standard and the observed values. let μi(x) denote the membership values for the k-th observed current value and μv(x) denote the membership value for the k-th observed voltage value. the corresponding point in the membership plane for the observed current and voltage values is given by +! � !"#, ' !"##. similarly, the point in the membership plane for benchmark values obtained from healthy cell be +′! ./ !"#, '0!"##. the euclidean distance between mm' can be calculated by: 1 � 23 � !"# 4 ./ !"#56 7 3 ' !"# 4 '0!"#56 (7) the fuel cell operation is desirable when the distance d is minimum, whereas a larger value of d indicates that the fuel cell is operating in a potential fault condition. figure 4 shows the fuzzy membership values obtained under various operating conditions. the distance between the fuzzy membership values can be calculated using the euclidean distance. fig. 4. comparison of fuzzy membership values. d. wavelet transform the wavelet transform can be used for non-destructive testing and monitoring the health of a system [54]. the time and frequency domains of a signal provide significant information. wavelet and its transform are useful to analyze the time and frequency domains of a signal [53]. equation (8) shows a "mother" wavelet or a wavelet basis function: 8�,�!9# � :√� 8 � �)� � � (8) where s is a scaling parameter that allows the dilation of the signal and u is a translational parameter that allows the translation of a signal in time. hence, it allows time-frequency spectrum generation. however, the resolution of both time and frequency is not high. the following equations calculate a continuous wavelet transform of a time-based signal: ⱳ= >?@!a, b# � ?, 8�,� !9# (a) (b) (c) (d) fig. 5. haar 3 analysis of pemfc experimental data under different operating conditions: (a) good cell, (b) old cell, (c) water flooded cell, and (d) starvation. engineering, technology & applied science research vol. 12, no. 6, 2022, 9607-9613 9611 www.etasr.com barhate et al.: fault detection methods suitable for automotive applications in proton exchange fuel … ?, 8�,� � d ?!9#8�,� !9#19 e )e !10) let the time-based signal be f(t). the time-frequency spectrum is obtained by repeating the process over the time and frequency range. however, the discrete wavelet transform can provide a sparser representation [55], as it has an advantage in analyzing signals with sudden transitions. one of the applications can be monitoring a machine failure. moreover, the computational speed is faster than the continuous transform. the haar wavelet transform was used in the analysis, as it is a discrete and the simplest wavelet. the mother wavelet function for the haar wavelet is described by: 8(9) = f 1 0 ≤ 9 < 1/2,−1 1/2 ≤ 9 < 1,0 otherwise. (11) the mother wavelet is decomposed to approximate components aj and detailed components dj. approximate components are used to analyze information at low frequencies and detailed components are used to analyze information at higher frequencies. the energy of the signal was computed using the following: tu� = ∑ w�u� (x)w6y (12) where c is the coefficient of the detailed component at level j of the k number of samples. haar 3 level decomposition was used to analyze the fuel cell experimental data. data were analyzed using the wavelet toolbox from matlab 2019b. figure 5 shows the analysis in a graphical form. the pattern of detailed decomposition levels is distinctly different from the healthy pemfc data. the oscillations in d1, d2, and d3 were observed in a healthy fuel cell when the voltage dropped as the current increased. however, the coefficients had oscillations since the beginning, and the s waveform showed a linear drop. oscillations were observed in water-flooded conditions at higher currents. high magnitude oscillations were observed at higher currents in the case of reactant gas starvation conditions. hence, the pattern in coefficients can differentiate the fuel cell performance during degradation due to the fault condition or aging. iv. results and discussion the pemfc performance was observed experimentally to degrade when the cell was aged or operated in a fault condition. the output performance of the pemfc was analyzed using methods like cv, comparing ratios, fuzzy membership values, and wavelet transform. all methods used the pemfc output voltage and current data for fault detection. cv is the simplest method to detect a fault condition. the ratios dp∕dv and dv∕di were found to be useful for fault detection and fault type identification. the results obtained from the fuzzy membership values of the pemfc output voltage and current proved to be an effective method to detect faults. however, the euclidian distance method should be used to isolate the fault type. on the other hand, the wavelet transform proved to be a better method for fault detection and fault type isolation. the simple discrete form of the haar wavelet transform was found to be effective. all these methods can be used for online and non-destructive fault detection. v. conclusion fault conditions degrading the performance of a pemfc were experimentally investigated. as the fault detection methods proposed in this paper were online, non-invasive, and non-destructive, they can be useful in automobile applications. methods, cv, ratios, and wavelet transform are useful for fault detection and fault type isolation. however, the fuzzy membership method requires further analysis of the euclidian distance to isolate the fault type. the cv and fuzzy membership value methods are more suitable for online fault detection in an automotive application. however, the wavelet transform method can be used as a self-diagnosis of the fuel cell during startup. acknowledgment this work was supported by the department of automobile engineering, psg college of technology, coimbatore, india. the authors would like to sincerely thank dr. p. karthikeyan and his research group for their guidance. references [1] m. a. biberci and m. b. celik, "dynamic modeling and simulation of a pem fuel cell (pemfc) during an automotive vehicle’s driving cycle," engineering, technology & applied science research, vol. 10, no. 3, pp. 5796–5802, jun. 2020, https://doi.org/10.48084/etasr.3352. 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[55] s. p. madhe, b. d. patil, and r. s. holambe, "on the design of arbitrary shape two-channel filter bank using eigenfilter approach," circuits, systems, and signal processing, vol. 36, no. 11, pp. 4441– 4452, nov. 2017, https://doi.org/10.1007/s00034-017-0519-4. microsoft word etasr_v13_n2_pp10306-10309 engineering, technology & applied science research vol. 13, no. 2, 2023, 10306-10309 10306 www.etasr.com merdassi et al.: gis-based selection of appropriate landfill sites: the case of communal grouping in … gis-based selection of appropriate landfill sites: the case of communal grouping in batna, algeria abdelmoumene merdassi natural hazards and territory planning laboratory (lrnat), earth sciences and universe institute, mostefa ben boulaid university of batna 2 algeria a.merdassi@univ-batna2.dz sami guellouh natural hazards and territory planning laboratory (lrnat), earth sciences and universe institute, mostefa ben boulaïd university of batna 2 algeria s.guellouh@univ-batna2.dz fatima zohra tebbi natural hazards and territory planning laboratory (lrnat), earth sciences and universe institute, mostefa ben boulaïd university of batna 2 algeria f.tebbi@univ-batna2.dz (corresponding author) khadidja boumezrag earth sciences and universe institute, mostefa ben boulaïd university of batna 2 algeria khadidjaboum2@gmail.com received: 19 december 2022 | revised: 14 january 2023 | accepted: 29 january 2023 abstract the choice of a landfill site is a complex process that includes various, social, environmental, and technical, parameters which require the processing of a large amount of spatial data. the geographic information system (gis), integrated with its functionalities, represents a powerful and well-adapted tool to solve this problem. this study uses the analytic hierarchy process (ahp) to solve the problem of quantifying qualitative features. it enables users to make intuitive judgments about the relative eight of different predetermined criteria or options in batna, northeastern algeria and its neighboring municipalities. the superposition of data related to several characteristics, such as geology, hydrology, and land use, allowed us to overcome several difficulties in evaluating the location of sites suitable for establishing landfills. results show that 88.498km 2 in total meets the specified exclusion factors, of which 34.098% represent areas of very excellent suitability and 33.741% appropriate areas. finally, low appropriateness applies to 32.161%. keywords-gis; analytical hierarchy process (ahp); landfills; communal grouping; batna i. introduction implementing an environmental management strategy requires detailed, reliable, and well-organized information on the state of the territory and the spatial distribution of socioenvironmental problems. geographic information system (gis), multi-criteria analysis (mca), and statistical methods are robust and well-adapted tools for solving the problem of illustrating the multidisciplinary approach in the selection of favorable sites for public landfills. this approach proposes, on one hand, the gis approach [1-3] which, through its spatial analysis functions, contributes to the study of a large number of potential sites according to the evaluation criteria (exclusion and appreciation), and on the other hand, the ahp approach, which is one of the most popular and widely employed mca methods, which is used to rank these alternatives. [4-6]. rapid urbanization and rapid and erratic population growth have generated huge amounts of municipal waste. several techniques and methods have been used for solid waste engineering, technology & applied science research vol. 13, no. 2, 2023, 10306-10309 10307 www.etasr.com merdassi et al.: gis-based selection of appropriate landfill sites: the case of communal grouping in … management, such as collection, transportation, recycling, physical treatment, and landfilling [6, 7]. the latter has been used for many years and is the most common method for the disposal of urban solid waste. the choice of the landfill site is a complex process that includes various social, environmental, and technical, parameters and regulations. this requires processing a massive amount of spatial data [6]. gis and mca are widely used tools and methods [8, 9]. gis specializes in capturing, storing, and analyzing databases and allows the integration of multiple layers of information with different combinations. mca is designed to produce synthetic information [10] that provides a list of candidate sites based on a combination of selection criteria. the wilaya of batna produces about 188 thousand tons of solid waste annually, including 169 thousand tons of household waste. this quantity is expected to increase due to population growth, economic development and, changing lifestyle [11]. nearly 70% of this waste is concentrated in urban areas, while managing household waste as it is currently conducted is unfavorable to the socio-economic development of wilaya due to the significant increase in demography and to the change in consumption patterns. the implementation of a gis prototype as a decision support tool in the field of environmental management is a tool that should allow managers to analyze the information necessary for the selection of appropriate sites for the storage of household waste. it will thus contribute to the protection of the environment and public health and reduce the obligations imposed on future generations by limiting the proliferation of illegal dumpsites [12]. the selection of a suitable site for a landfill consists of a compilation of data related to several disciplines, such as geomorphology, geology, hydrology, climatology, and demography. in the present study, several thematic maps were used, namely the topographic map, the geological map, and the piezometric map adding the use of the digital terrain model extracted from the srtm image. all these data have allowed the establishment of a database with a spatial reference under a gis whose purpose is the selection of appropriate sites for the establishment of landfills in batna and neighboring municipalities. fig. 1. the study area. ii. geographic location of the study area the wilaya of batna is located in northeastern algeria, 435km from the capital algiers. the study area is situated in the northeast of this wilaya, between 5°5’ and 6°2’ e longitude and 35°24’ and 35°48’ n latitude. it extends over the city of batna (capital of the wilaya of batna) and neighboring communes, namely tazoult, oued elma, seriana, ouyoun el aassafir, fesdis, and oued echaaba (figure 1). iii. methodology the proposed model for optimizing the location of waste storage sites consists of an overlay of geographic data from several disciplines in a gis that will serve as a decision support tool. each information theme used various spatialization techniques to create basic spatial documents in raster or vector format (slope, land use, hydrographic network, road networks). finally, a set of decision criteria was developed (i.e. exclusion and evaluation criteria). exclusion criteria are constraints that aim to limit the search for sites in the domain that do not tolerate competition [13]. these criteria are applied to create a constraint map. six criteria were considered in this study:  exclude areas with 500m of proximity to the hydrographic network, with the purpose to avoid the pollution of the aquatic environment.  exclude the road network with a proximity of 500m.  exclude the urban areas with a proximity of 2000m.  exclude wells, springs, reservoirs, and water towers with a proximity of 1000m  exclude the protected areas (forests, agriculture) with a proximity of 1000m.  exclude areas with a slope greater than 12%. modelbuilder is an application to create, modify and manage models. models are workflows that allow concatenating sequences of geoprocessing tools and injecting the output of one tool into another tool. modelbuilder can be compared to a visual programming language for creating workflows [14, 15]. furthermore, modelbuilder has a simple interface with drop-down menus, toolbar tools, and contextual menu options. the layout of the tools and variables connected is called the model diagram. figure 2 illustrates the sequences of geoprocessing tools used to determine suitable sites for implementing a public landfill in batna and the bordering municipalities. the next step is to examine and evaluate suitable sites for the landfill, considering geo-environmental (soil permeability) and socio-economic (proximity to the road network, slopes) factors. the results of the ahp correspond to scores that sum to 1. the construction of the hierarchy and the structuring of the priorities should ensure the consistency of the homogeneity and relevance of the groupings and the proportional relationship between the important parameters. engineering, technology & applied science research vol. 13, no. 2, 2023, 10306-10309 10308 www.etasr.com merdassi et al.: gis-based selection of appropriate landfill sites: the case of communal grouping in … fig. 2. the model determining suitable sites for landfill siting. table i. determination of the relative importance of factors by a scale of 1 to 9 [16] degree of importance definition explanation 1 equal importance two characteristics contribute equally to the goal 3 low importance of one characteristic in relation to another experience slightly favors one characteristic over another 5 strong or determining importance experience strongly favors one characteristic over another 7 very strong or proven importance a characteristic is strongly favored, and its dominance is evidenced in practice 9 absolute importance evidence favoring one characteristic over another is as convincing as possible 2, 4, 6, 8 values associated with intermediate judgments when a trade-off is necessary iv. results and discussion the results clearly show that most of the study area is excluded according to the previously established model (figure 3). the results of the ahp method show that the factor of soil permeability has an influence of 55.84% on the final result, and the factor of distance to main roads is 31.96%. finally, the factor of slope influences 12.19%. note that cr (coherence ratio) must be less than 0.10. a higher cr indicates a higher level of inconsistency. in our case, the cr is equal to 0.018. the weighted overlay scales the input data on a defined scale (graduated by default from 1 to 9), weights the input rasters and groups them. the most favorable locations for each input criterion are re-ranked based on higher values. in the weighted overlay tool, the sum of the weights assigned to the input rasters must equal 100%. the layers are multiplied by the appropriate factor, and each cell’s resulting values are grouped. weighted overlay assumes that more favorable factors result in higher values in the output raster, thus identifying these locations as the best. as with all weighted overlay analyses, we defined the problem by rendering it into submodels and then identified the input layers. in the case of our study, the input information layers are soil permeability, road proximity, and slope. in our study’s case, and after considering the problem, we explicitly focused on the permeability factor (figure 4). fig. 3. results of the implementation of the exclusion criteria. fig. 4. thematic maps representing the evaluation criteria. fig. 5. final map of suitable sites for landfills. engineering, technology & applied science research vol. 13, no. 2, 2023, 10306-10309 10309 www.etasr.com merdassi et al.: gis-based selection of appropriate landfill sites: the case of communal grouping in … the following percentages of influence were assigned to the ability cards. the values in parentheses are the percentage produced by division by 100 to normalize the values. these are assigned to each suitability map: soil permeability (50%), road proximity (30%) and slope (20%). as with the assignment of suitability scales, the assignment of weights is a subjective process that depends on the goals of our study. after the spatial analysis of suitability and appreciation, it can be noted that the total area that meets the committed exclusion factors is 88.498km², with 34.098% of that area representing areas of very good suitability, and 33.741% of the area is suitable areas. finally, 32.161% of the area falls under the low suitability class (figure 5). v. conclusion site selection is a critical issue in installing a landfill site. the objective of this work was to develop a site selection methodology that will allow the selection of the most suitable areas for installing a landfill. the core of this study is based on the processing of geospatial data related to the study area using a gis. for this purpose, a set of factors was classified and two categories (exclusion factors and appreciation factors) were defined. a siting methodology for the area is provided by the current study. it can support the decision-makers in solving the waste management problem. the selection criterion of permeability was considered as the most important in this study. references [1] m. majid and b. a. mir, "landfill site selection using gis based multi criteria evaluation technique. a case study of srinagar city, india," environmental challenges, vol. 3, apr. 2021, art. no. 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[16] t. l. saaty, "fundamentals of the analytic network process — dependence and feedback in decision-making with a single network," journal of systems science and systems engineering, vol. 13, no. 2, pp. 129–157, apr. 2004, https://doi.org/10.1007/s11518-006-0158-y. microsoft word etasr_v13_n3_pp11000-11005 engineering, technology & applied science research vol. 13, no. 3, 2023, 11000-11005 11000 www.etasr.com rashid et al.: a student learning style auto-detection model in a learning management system a student learning style auto-detection model in a learning management system amirah binti rashid department of information technology and communication, balik pulau polytechnic, malaysia amirah.rashid@pbu.edu.my raja rina raja ikram fakulti teknologi maklumat dan komunikasi, universiti teknikal malaysia melaka, malaysia raja.rina@utem.edu.my (corresponding author) yarshini thamilarasan protech digital sdn bhd, malaysia yarshinithamilarasan@gmail.com lizawati salahuddin fakulti teknologi maklumat dan komunikasi, universiti teknikal malaysia melaka, malaysia lizawati@utem.edu.my noor fazilla abd yusof fakulti teknologi maklumat dan komunikasi, universiti teknikal malaysia melaka, malaysia elle@utem.edu.my zakiah rashid department of science, penang matriculation college, malaysia zakiahzsm@gmail.com received: 3 february 2023 | revised: 14 april 2023 | accepted: 22 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5751 abstract learning style plays an important role in enabling students to have an efficient learning process. this paper proposes an auto-detection model of student learning styles in learning management systems based on student learning activities. a literature review was conducted to investigate the components of online learning activities. the search terms used were "online learning activities", "learning management systems", and "felder-silverman learning style model (fslsm)." a combination of the search terms above was also executed to enhance the search process. based on the results of the review, eleven classes of online learning activities were identified, namely forum, chat, mail, reading materials, exam delivery time, exercises, access to examples, answer changes, learning materials, exam results, and information access. the online learning activities identified were then mapped to the felder-silverman model based on four model dimensions: processing, perception, input, and understanding. the proposed model shows the attributes of the online learning activities based on the dimensions in the fslsm. the proposed model can assist educators to improve learning content according to the suitability of students and recommend appropriate learning materials to students based on their characteristics and preferences. future studies include the use of machine learning algorithms such as decision trees to auto-detect student learning styles in learning management systems. keywords-auto detection; student learning style; felder-silverman learning management system engineering, technology & applied science research vol. 13, no. 3, 2023, 11000-11005 11001 www.etasr.com rashid et al.: a student learning style auto-detection model in a learning management system i. introduction the ways that we teach and learn have changed as technology has advanced. the quick advancement of information and communication technologies has transformed conventional classrooms into cutting-edge learning spaces [1]. for instance, the ability to study whenever and wherever you want has been made possible through the internet sharing of educational information [2]. online attendance marking systems have also significantly decreased the amount of time spent by teachers verifying students' attendance, increasing the amount of time spent teaching and learning. additionally, tests or assignments can be given online along with the necessary guidance and criticism to encourage learning outside the scheduled classes [3]. there are numerous more typical amalgamations of teaching methods that are enabled or made easier by contemporary technologies. due to the growing number of smart learning elements accessible, managing these characteristics is essential for efficient and well-organized instructional processes. educational institutions now frequently run their own learning management systems (lmss) and offer a variety of online smart learning capabilities for a wide range of students [4]. an lms is a web-based system with a wide selection of instructional and course management capabilities. lms can facilitate group conversations, debates, document sharing, assignment submission, quizzes, grading, and course evaluations through these educational technologies. an lms also has the potential to serve students from a variety of backgrounds, including those related to culture, age, or gender. identification of student learning style categorizes students according to the way they view and respond to information during the teaching process [5]. there are various types of learning styles that can be adopted by students depending on the suitability of the learning environment. a study conducted between the medical students of isfahan university showed that learning style may be influenced by student gender [6]. male students are more inclined to kinesthetic learning style while female students are more inclined to aural learning style. on the other hand, there are contradicting research results stating that gender is not a key aspect in determining student learning style [7]. bizzapps software was used to study whether learning styles affect student achievement [8]. the results of the study show that learning style can contribute to the students' success if the learning process is tailored towards it. in addition, 25% of students prefer various learning styles applied during the teaching process as this encourages them to actively contribute to the classroom. identification of learning styles can assist educators to improve the learning content according to the suitability of students and recommend appropriate learning materials based on their characteristics and preferences [9]. ii. literature review there are several models that have been used to classify student learning styles. one popular model is the vark model, which categorizes students into four learning styles: visual, auditory, reading/writing, and kinesthetic/tactile [10]. the vark model has been used in various educational settings and has been found to be effective in helping students identify their preferred learning style and improving their study skills [10]. another model that has been widely used is the honey and mumford model, which classifies learners into four categories: activist, reflector, theorist, and pragmatist [11]. this model emphasizes the importance of experiential learning and encourages students to engage in various learning activities that match their preferred learning style. other notable models include the kolb learning style inventory, which categorizes students into four learning styles: converging, diverging, assimilating, and accommodating [13], and the dunn and dunn model, which emphasizes the importance of environmental factors and categorizes students into five categories: environmental, emotional, sociological, physiological, and psychological [13]. while these models have been effective in helping students identify their preferred learning styles and improving their study skills, they have some limitations. for instance, they are often criticized for oversimplifying the complex process of learning and for not accounting for the multifaceted nature of learning styles. additionally, some of these models may not be suitable for all students, as individual differences and cultural factors can play a significant role in determining learning style preferences [11]. the felder-silverman learning style model (fslsm) was defined by felder and silverman and is commonly used in engineering and computer science education studies [10–13]. fslsm learning styles have four dimensions, with each dimension consisting of two types of learning styles. the four dimensions are preprocessing, perception, input and understanding [14]. figure 1 shows the felder-silverman learning style model. fig. 1. the felder-silvermann learning style model (fslsm). the processing dimension pertains to the way students process information, with active and reflective learners as subcategories. active learners engage in discussions and group learning, while reflective learners prefer solitary learning but think deeply about the information. the perception dimension describes how students perceive information, with sensing learners focusing on facts and practical assignments and intuitive learners preferring to apply concepts in real-life engineering, technology & applied science research vol. 13, no. 3, 2023, 11000-11005 11002 www.etasr.com rashid et al.: a student learning style auto-detection model in a learning management system scenarios. the input dimension relates to the way students receive information, with visual learners understanding concepts through images and diagrams, and verbal learners preferring detailed explanations. lastly, the understanding dimension pertains to the way students organize information, with sequential learners using linear step methods to understand and solve problems, while global learners understand information in a random, non-linear fashion. the research gap in this area lies in the lack of automation in identifying student learning styles in an lms. the existing models require manual input from the student or the teacher, which can be time-consuming and may not always be accurate. therefore, there is a need for an automated system that can accurately identify student learning styles based on their behavior in the lms, e.g. navigation patterns, content access, and interaction with the learning materials. the proposed model in this paper aims to fill this gap by using machine learning algorithms to automatically detect student learning styles in the lms, which can improve the personalized learning experience and enhance student engagement and academic performance. the proposed model is based on the fslsm. iii. methodology literature review was conducted to identify the components of online learning activities used in lmss. the literature was sourced from four databases: ebsco host, ieee explore, proquest, and google scholar. the search terms used were "online learning activities", "learning management systems", and "felder-silverman learning style model (fslsm)." a combination of the search terms above was also executed to enhance the searching process. a search was also conducted in google to identify miscellaneous books, publications, and organization websites using the same terms. the purpose of the literature review was to identify online learning activities in lmss and their integration with the fslsm. the online learning components identified were then mapped to the fslsm based on the four model dimensions. the purpose of this mapping was to match the suitable online learning components in lmss with the appropriate learning dimensions. a model was then proposed from the integration of the online learning activities and the fslsm. the attributes of the proposed model are defined to support the identification of learning style using lmss. iv. results a. online learning activities based on the review, eleven components were identified as activities in online learning that can be identified in lmss. basic component requirements are important when building online activity course learning. the first basic components are forums, chat, and mail [15]. these components are used to evaluate the students' active involvement in the on-line communication. the next components are related to a student's perception. they are reading materials, whether abstract or concrete, the time taken to submit quiz questions, tests, and exams, the time taken to perform reinforcement exercises, the access to examples, the frequency of changing answers during the exams, the number of attempted exercises [16, 17]. the learning materials component categorizes a student as a visual or verbal learner. in this component, learning materials are implemented into two categories, namely through diagrams and listening. after that, a quiz can be implemented based on the given input. the obtained score can assess student tendencies. the activities involved are reading materials in the form of videos, text, diagrams, and pictures [13]. the final component is accessing information and exam results [16]. this component describes how students receive the information provided and then sort it according to their understanding. their level of understanding can be seen through the results of the examination based on the scales that have been set. table i shows the mentioned components. table i. online learning activities in lmss activities explanation references forum involves forum posts, replies, and readings [16] chat participates, listens, no participation [16] mail use, does not use [16] reading materials concrete, abstract [16, 17] exam delivery time time taken to submit the exam questions [16, 17] exercises the amount of exercises that had been done [16, 17] access to examples the number of access to examples attempted [16, 17] answer changes the numbers in the answer changes during exams [16, 17] learning materials diagrams, pictures, videos, text, presentations [17] exam results high, moderate, low [16] information access global, sequential [16] a. integration of felder-silverman learning style model and online learning activities based on the results, the components of online learning activities are mapped to the dimensions of the fslsm. table ii shows a summary of online lmss activities based on the fslsm according to the literature review. the main online activities in processing are related to forum, mail, and chat activities [16]. the main online activities for perception are related to exam revision, questions, exercises review, reading materials, and learning resource types [16, 17]. the main online activities related to input are video and visual materials, forum visits, questions, and right answers [17]. the main online activities related to understanding are information access, content visit, and exam results [16, 18]. v. the proposed model figure 2 shows the proposed model to identify student learning styles in lmss based on the felder-silverman approach. the identified attributes were mapped to the four main dimensions of the fslsm and are included in the proposed model. a definition of the attributes and its related values are displayed in table iii. engineering, technology & applied science research vol. 13, no. 3, 2023, 11000-11005 11003 www.etasr.com rashid et al.: a student learning style auto-detection model in a learning management system table ii. summary of online learning activities based on fslsm fslsm [17] [18] [16] [19] [20] processing forum_post content_visit forum format_activity question_answer self_assesment forum_post mail learning_resource_type visit_learning_content forum_view forum_stay chat interactivity_type forum_visit text_materials forum_visit interactivity_level perception concrete_materials question_graphic exam_revision format_activity right_answer examples question_text exercises learning_resource_type revised_answer abstract_materials exam_delivery_time exercises_review answer_changes access_to_examples reading_materials input visual_materials forum_visit format_activity right_answer video_materials question_graphic learning_resource_type forum_visit text_materials question_text forum_post understanding navigational_pattern content_visit information_access structure_activity option_solve_problem course_overview exam_results visit_learning_content fig. 2. the proposed model. table iii. proposed attributes and values for the learning style dimensions in the proposed model dimension in fslsm learning style attribute_name attribute_value percentage of attribute_value ref. processing active forum_post mail chat course_outline no of posting in forum use or do not use participate or not participate no of visited courses outline more than 75% more than 75% more than 75% between 25% 75%, none [16, 21] reflective forum_view mail chat course_outline no of view post in forum use or do not use participate or not participate no of visited courses outline more than 75% between 25% 75%, none between 25% 75%, none more than 75% [12, 20] perception sensing concrete_materials exercises exam_delivery_time access_to_examples answer_changes no of visits no of visits submission time in exam no of visits no of attempted answer change more than 75% more than 75% more than 75% more than 75% between 20% 50%, none [16, 21] intuitive abstract_materials exercises exam_delivery_time access_to_example answer_changes no of visits no of visits submission time in exam no of visits no of attempted answer changes more than 75% between 25% 75%, none between 50% 75%, none between 25% 75%, none more than 50% [16, 21] input visual visual_materials video_materials graphic_question_type no of visits no of visit no of correct answers more than 75% more than 75% more than 75% [19] verbal text_materials audio_materials text_question_type forum_post no of visits no of visits no of correct answers no of forum posts more than 75% more than 75% more than 75% more than 75% [17, 20] understanding sequential sequential_information_access exam_results no of visits right answers on process questions more than 75% way more than 70% [16, 20] engineering, technology & applied science research vol. 13, no. 3, 2023, 11000-11005 11004 www.etasr.com rashid et al.: a student learning style auto-detection model in a learning management system table iii shows the proposed attribute and values of online learning activities mapped to the fslsm dimensions. table iii describes in detail the mapping of each learning activity and the involvement of students in each activity. the learning style of students can be identified more accurately based on the involvement of students in each online learning activity. the attribute value for each learning style is based on previous study studies. active and reflective learning style is dependent on the number of forum posts, usage of mail, chat, and course outline visits. sensing and intuitive learning styles depend on the number of visits to course materials, exercises, exam delivery time, and number of answer changes. visual and verbal learning styles depend on the number of visits towards video, visual, text, and audio material. sequential and global learning styles depend on exam results and the number of visits. the proposed attributes and values of online learning activities mapped to the dimensions in the fslsm, as presented in table iii, provide a comprehensive guide for educators to identify students' learning styles based on their engagement with online learning activities. this approach has the potential to improve the effectiveness of online learning by enabling educators to tailor their teaching methods to the specific learning styles of their students. the proposed approach of mapping online learning activities to the dimensions of the fslsm is a novel way of identifying students' learning styles in online learning environment. this approach allows educators to use data from the lms to gain insight into the way their students engage with online activities and customize their teaching methods accordingly. for example, by analyzing a student's forum participation and email usage, educators can identify whether the student has an active or reflective learning style. similarly, by analyzing a student's usage of video and visual materials, educators can identify whether the student has a visual or verbal learning style. overall, the mapping of online learning activities to the dimensions of the fslsm is a valuable contribution to the field of online education. this approach provides a practical and data-driven method for identifying students' learning style in online learning environments and has the potential to improve the quality and effectiveness of online education. vi. conclusion knowledge of the learning style is an important element in ensuring that the teaching and learning process is well implemented. the proposed model defines the learning style attributes which can help identify the respective learning style. understanding student learning styles can help teachers to improve the learning content according to the suitability of students, recommend appropriate learning material, and improve the communication and interaction skills between humans and computers through features in the learning management system [21]. since most interactions between students and instructors occur in learning management systems, the system should be developed to cater the student specific requirements during the teaching process for a successful learning experience. furthermore, incorporating these learning style attributes into the design of learning management systems can enhance the overall learning experience. such features can include adaptive learning technologies, personalized learning pathways, and customized feedback mechanisms. by leveraging the power of technology to support and complement traditional teaching methods, educators can create a more dynamic and interactive learning environment that meets the needs of diverse learners. acknowledgment this study is supported by the fakulti teknologi maklumat dan komunikasi, universiti teknikal malaysia melaka. references [1] s. s. t. alatawi et al., "a new model for enhancing student portal usage in saudi arabia universities," engineering, technology & applied science 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[21] a. e. labib, j. h. canós, and m. c. penadés, "on the way to learning style models integration: a learner’s characteristics ontology," computers in human behavior, vol. 73, pp. 433–445, aug. 2017, https://doi.org/10.1016/j.chb.2017.03.054. microsoft word etasr_v13_n1_pp9997-10004 engineering, technology & applied science research vol. 13, no. 1, 2023, 9997-10004 9997 www.etasr.com khan & alnwihel: a brief review on cloud computing authentication frameworks a brief review on cloud computing authentication frameworks abdul raouf khan department of computer sciences, king faisal university, saudi arabia raoufkhan@kfu.edu.sa (corresponding author) latifa khalid alnwihel aljaber finance, saudi arabia latifaalnwihel@gmail.com received: 10 november 2022 | revised: 23 november 2022 | accepted: 26 november 2022 abstract cloud computing is among the most widely used technologies worldwide as it helps individual users and organizations to store and share information conveniently and cost-effectively. however, data security is a major concern in cloud computing. security involves guaranteed access to the data only to authorized users and protection against various threats and attacks. security is generally achieved through the appropriate and efficient implementation of access control, authentication, and authorization mechanisms. various frameworks have been proposed and implemented for authentication and access control in cloud computing. this paper discusses some of the main authentication frameworks in cloud computing, highlighting their methodologies, algorithms, and problems and identifying the issues that should form the focus of research in the area. keywords-cloud security; cloud computing; security framework; cloud authentication i. introduction the reliance on cloud for storage and computing makes it a prominent target for online attacks. sharing resources over the internet puts shared data at risk of being compromised or misused. thus, users are not comfortable sharing sensitive data online and it is important to ensure that they clearly understand the security-related requirements [1]. regardless of the clear risks, customers use the cloud due to its many convenient features [2]. therefore, the security of the cloud needs to be improved. many researchers have considered various security issues related to cloud computing and proposed various ways to improve it [3-4]. the following sections consider and categorize the research on security-related issues concerning the cloud. ii. authentication in cloud computing authentication is an important aspect of cloud computing in the context of data security. authentication in an information system can be achieved in multiple ways, for example, based on something the user "has" such as smartcards, something he "knows" such as passwords, and/or something the user "is" such as biometrics (fingerprint, iris scan, etc.). a. biometric authentication frameworks in [5], a biometric-based authentication scheme was proposed to offer secure user identification and authentication using elliptic curve cryptography for the generation and exchange of secure keys. an authentication scheme based on a contactless smart card was proposed for the user to improve security and avoid problems with key management. in the registration phase, the user must enter his biometric data, which are recorded in the service provider database. the user identifier was based on the username and the data associated with the server and was used to verify his identity with the cloud service provider. the latter collects the user's identifier, biometric data, and hashed password to store in the smart card during the registration phase. operation is assumed to be supervised by a monitor, and a proxy is issued at the end of each access case. the reader's sensor had a liveness detector for the data to confirm that they were not collected from an earlier scan. furthermore, the transferred data were encrypted to prevent attackers from obtaining or tracking them, and data transmission occurred only if the server and the customer met the validation criteria. the biometric scheme involved two phases: biometric verification and biometric linking. to avoid the introduction of a replay attack and guarantee the creation of a session, the nonce value is generated during the handshake message. when a user attempts to log in by inserting his biometric data, a biohash is generated and associated with their id and known password. to generate a more secure biometric pattern, the biohash is xored with the hashed password and then the smartcard compares its data with the hashed password. the authentication server matches the biometric data and the engineering, technology & applied science research vol. 13, no. 1, 2023, 9997-10004 9998 www.etasr.com khan & alnwihel: a brief review on cloud computing authentication frameworks hashed password with the relevant data in the database and checks the client identifier. following this, the authentication server generates an encrypted session key that is transferred with a hashed value. by computing the nonce value, the client can decrypt the data sent by the server and verify its origin. the client can then prove their validity by submitting a signed "hello" message with the nonce value. the authentication server then validates the message and submits proxy credentials to access the service. this scheme has low computational complexity, requires scant communication, is scalable over a large range of numbers of clients, and involves little computation on the client side, which renders it suitable for a cloud environment. however, the complexity of the used hash algorithms is high. in the context of multimodal biometric systems, a framework for biometrics-based mobile cloud computing was proposed in [6], using two-step verification based on fingerprints and iris recognition. if the user cannot be authenticated through these biometric techniques, the system supports a backup authentication code. the fingerprint recognition system takes an image of the user's fingertip through sensors. the iris recognition system scans their iris using a high-definition camera. the system converts the image of the user's fingertip to obtain a ridge structure, and their iris scan is matched with the available database. images of the fingertip and the iris of the user are recorded in each access case and compared with the saved input to authenticate them. the user's fingerprint is validated before their iris scan. backup code-based verification serves as an emergency access mode, as the user is given five to ten unique codes at registration, where each is valid for a single use to access the system. this method helps maintain data security in the cloud. the user can generate new unique codes by using the system, which notifies him of each code generation instance. however, the backup codes are at risk of attacks, and code maintenance induces complexity from the user's perspective. b. password-based authentication frameworks in [7], a model was proposed that unified the mathematical approaches to singleand two-server password-based authentication systems (pas). the reliability and availability of security services were measured to ensure secure data access through web applications. a single authentication server was involved in the single-server architecture to authenticate the client, storing a dictionary of all client passwords in its database, which must be available at the time of operation to guarantee successful client authentication. if the server fails, a single point of failure occurs that threatens the entire authentication system. to recover the system in this case, a redundant offline server with an updated database of customer passwords can be used. two servers, a frontand a back-end authentication server, were used in this architecture. the former acts as a public server, while the latter is responsible for maintaining an updated dictionary of client passwords. the client's authentication requests are sent only to the front-end authentication server. the functional behaviors of the system were represented as generalized stochastic petri nets (gspns) to visualize the impact of the authentication service, considering scaled-up/down versions of the authentication servers by exploiting a diversity of backup approaches. hot and cold standby were used to improve the reliability of the system. platform-independent petri nets (pipe) were used to generate a system reachability graph to derive the equivalent continuous-time markov chain (ctmc). the availability and reliability of the system were estimated by applying traditional markovian state-based analysis, and the performance-related attributes of the authentication framework were monitored. experimental results showed that the cold standby strategy can be used to improve the availability of the two-server pas in case of attacks to a greater extent than the single-server pas, while the reliability of the single-server pas is higher than that of the two-server. a multi-level authentication method was proposed in [8] that allowed access by authenticating the user's password at three levels. organizational authentication was first conducted by verifying that the user has the privileges to access the services provided, where a failure terminated the session. if organizational authentication succeeded, team-level authentication followed, where access was provided to specific cloud services. the third level, user authentication, was then performed, where specific permissions and privileges were granted to the user. the user can access cloud services only if the first two levels of authentication have been satisfied. this method can be used within an organization's cloud storage. c. image-based authentication frameworks a three-step data security model was proposed in [9] using cryptography and steganography during data storage and sharing in the cloud. the model was composed of three levels. the first level employed cryptography using rsa to prevent unauthorized data access. the second level used steganography, where the data were hidden in an image in the form of ciphertext using stegotools by creating a symmetric key that was sent to the receiver. in the third authentication level, the data were accessed in the image and decrypted by the rsa. the receiver decrypted the image through stegotools by specifying the symmetric key created during image steganography. the ciphertext was decrypted using the rsa algorithm to obtain the original plaintext. this model can be applied to audio, video, and text data. d. digital certificate-based authentication frameworks data anonymization was proposed in [10] to prevent the misuse of user data by the cloud provider. this study focused on the trust issue between users and cloud providers based on the anonymity of shared data in the cloud. the idea was to conserve the capability of the cloud provider to charge for the use of reliable cloud services by cutting off the semantic linkage between the data and their owners. the required operations can then be performed by the cloud service provider on an anonymized dataset, following which they can convey the outcomes to the users and charge for the use of services while keeping their identity private. cloud users can thus safely avail themselves of the services without being identified. this approach guarantees privacy in cc by using ring and group signatures. the study claimed that the anonymity of clients can be preserved using signatures. typically, this means that each client has a signature that can be verified by the cloud provider by referring to a list of users while preserving their privacy, as engineering, technology & applied science research vol. 13, no. 1, 2023, 9997-10004 9999 www.etasr.com khan & alnwihel: a brief review on cloud computing authentication frameworks it cannot identify the member of the list to whom the signature in question belongs. this approach requires preparing a set of legitimate users willing to use the cloud resources. however, it is useful only if flat-rate accounting is allowed in the relevant business model. according to it, the user has to pay in advance for access (for a fixed period) to cloud services. when group signatures are used, the group manager is an actor in addition to the verifier and signer. users can register and obtain credentials to prove that they belong to the set of registered clients. in case of a conflict, the group manager can revoke the anonymity of the group signature. in [11], a model was proposed based on elliptical curve cryptography (ecc), using a digital signature-based identification protocol for authentication. the study claimed that it does not require modular inversion, which improves its efficiency. however, the system required an algorithm to find the index by using a multiplicative group of finite fields. e. n-factor-based authentication frameworks 1) two-factor authentication an advanced encryption standard–cipher-text-identity and attribute-based encryption" (aes–cp–idabe) was proposed in [12]. this system guaranteed the secure sharing of documents for temporally confidential data using two files: the original and a metadata file. the document's time of release and its attribute were stored on the server in a separate file. the secret keys of the metadata and the original document depended on each other. if the file needed to be deleted or updated, the user can do so without having to decrypt it. furthermore, two-factor authentication was applied to prevent shoulder surfing and keylogger attacks and improve security. the first factor was a unique user id and password and the second was mobile authentication. following password authentication, a qr code was generated and sent to the user, which could be read by the built-in application in android mobile phones. then, the phone automatically sent the international mobile equipment identity (imei) number to the server and an otp was generated once the imei number was verified. the access policy file needed to be decrypted only if the data owner wished to change the data attributes, which saved time. 2) multi-factor authentication a model of a three-layer authentication mechanism was proposed in [13] to ensure data security, encrypting the data at many levels using several security-related techniques. unauthorized access was prevented in the first layer through authentication. this layer used various methods, including fast identity online alliance, multi-factor authentication, one-time password, and the short message service. the second layer was connected to the first to ensure that only legitimate customers could communicate. this layer used different cryptographic encryption techniques, such as homomorphic and proxy-based encryption. the third layer was in charge of the interactions of the second layer and ensured that users who requested access to the data were verified. the study claimed that this model can minimize data security issues in all three layers of cloud service models. this model provided login access to the end user to prevent malicious access to the stored data. to protect the user's confidential information, it ensured the fast retrieval of data while using advanced data protection security and intelligence. however, multi-factor authentication can cause a computational overhead at the user's end. in light of the drawbacks of multi-factor authentication, an architecture was proposed in [14] to improve it. this architecture used a combination of explicit and implicit authentication factors to provide users with secure access to cloud services at different levels. implicit authentication is convenient for the user but cannot deliver the required security because it considers user behavior for authentication and has a high false-positive rate [14]. explicit authentication is more secure, as the user directly provides the authentication factor, but is not user-friendly. an algorithm was proposed to reduce the perceived authentication difficulty for users at different access levels. the algorithm presented a difficult authentication factor if the user failed implicit authentication. in other words, the user needed to be validated through implicit authentication to be easily explicitly authenticated. the architecture involved sandboxing, implicit and explicit authentication, a metalearner, and component f. user access control was performed by sandboxing, whereby the user's access to different levels of the cloud service was controlled. implicit and explicit authentication mechanisms were used to authenticate the user and obtain access to different service levels in the cloud. each explicit authentication factor was assigned an authentication score. the metalearner (machine learning engine) provided the weight of the authentication based on the implicit authentication factor. the f component calculated the user authentication score and then identified a set of the best explicit authentication factors to be used by the user to obtain a higher access level. each cloud service was assigned an operational sensitivity using sandboxing, which specified its security level. if the service was highly sensitive, only highly trusted users could gain access to it. if the authentication score of the user was high, he was highly trusted. the implicit authentication factor was used to assign weights to the scores of the explicit authentication factors. the weight of an explicit factor decreased (increased) if its corresponding implicit factor was invalidated (validated). the user needed a high authentication score to gain access to sensitive services, equal to or higher than the required operational sensitivity. this method reduced the difficulty of user authentication by 29% compared to other methods and can adapt the difficulty of authentication based on the user's situation. progressive multi-factor authentication results in user fatigue if it is frequently applied because it requires user involvement, and multi-factor authentication can also excessively burden the user. in [15], a multifactor authentication framework was proposed, which was essentially an extended version of the one proposed in [12]. this framework had three phases, including registration, multi-factor authentication, and encryption phases. the multi-factor authentication, unlike [12], was implemented through captcha and otp (one time password), in addition to the traditional password authentication process. the captcha process verified if the user was a machine or a human, and otp verified if the user was genuine or not. the problem with this authentication mechanism was the redundant use of captcha, as the otp process can prove both. engineering, technology & applied science research vol. 13, no. 1, 2023, 9997-10004 10000 www.etasr.com khan & alnwihel: a brief review on cloud computing authentication frameworks f. identity-based authentication frameworks in [16], a lightweight mutual authentication system comprising three phases was proposed. in the first phase, the cloud server and the customer generate a random number and an identity request and send it to a third party known as agency. the agency verifies the identity of the customer and the server and responds with a timestamp in the second phase. in the last phase, the user and the server forward identity and timestamp, along with the random number, to each other for mutual authentication. this verification process uses three operations: string concatenation, hashing, and the logical exclusive or function. the disadvantages of this scheme are that it requires a third party as an agency and transferring computations and identities to the third party makes it vulnerable to attacks. g. location-based authentication frameworks message digest and location-based authentication (mdla) is a mutual authentication scheme proposed in [17] and involves symmetric key encryption. the goal is to authenticate a mobile user and the cloud server. the scheme consists of registration, authentication, and update phases. it starts only if the user is registered to the cloud service provider, where their credentials are stored on a server. the first phase involves the generation of a random number as a secret key and a message digest along with a primary key. the secret key is used to validate the cloud server in the authentication phase. the primary key is obtained using the user's hashed id, password, and the previous or first location of the mobile device. if the user is registered, he can send an authentication request using an authentication key, which is composed of the user's current location and timestamp, to the cloud server to access resources. when the authentication request is received on the server side, the information on the mobile user is located to obtain the associated expiration period and the primary key. if the expiry period is zero, the authentication request is rejected by the server, which asks the user to re-register or updates the notification to the mobile user. in case of successful registration, the message is decrypted by the cloud server using the primary key to obtain the current location and timestamp that form the authentication key. the encrypted message is decrypted using the authentication key to obtain the digest of the message. the user is considered legitimate if it matches the stored message digest. following the authentication of the mobile client, an authentication reply is sent to the mobile user containing the encrypted message digest through the previously shared secret key. sending this response authenticates the cloud server. a random number is selected as the new secret key by the cloud server and is sent to the mobile user for the next authentication request. if the stored message digest matches the received message digest, the cloud server is considered legitimate. there are three types of update phases: key updates, client registration or re-registration if the expiry period is zero, and updates to authentication or reauthentication in case of a connection loss. h. service model-based authentication frameworks in [18], a personal cc framework based on a service model was proposed, providing users with a conveniently exposed open api and a secure connection for accessing the cloud. the environment of "cloud orchestration and single sign-on token" was considered so that the user could have a smooth experience. the study described various details of its various components based on the service model and then presented an application of the required security technologies. optimizing customer security in an infrastructure as a service (iaas)-based cloud and the use of cloud resources were the objectives of [19], where a framework based on virtual machines (vms) was proposed for the secure usage of sensitive data. usage management (um) was applied to control the resources in the cloud and satisfy the performance and security-related requirements. um involves constantly monitoring the policies related to the resources. the study presented randomized algorithms (ras) and a policy model to specify the security policies. the ras compute the optimal distribution of cloud resources of the iaas between users to ensure security. the architecture consists of a central um framework that manages cloud resources and amazon s3 data. it ensures that the resources are moved to the vms only if the security-related requirements are met, otherwise they are rejected. the um framework also provides cloud vms. a local usage management module (umm) was developed, where any vm provided by the central um framework can be injected to enforce policies during the lifetime of the resource. if the context of the public cloud does not satisfy the policy requirements regarding the resources, the umm retracts the resources. the architecture starts when the user requests a policy-protected resource. the user submits contextual information (such as credentials) to the um framework and is authenticated and granted access based on access control policies for the relevant resources. depending on the level of security and policies, the resources are transferred to the vm. the ra then receives information on the resource utilization of the vms to calculate the cost function. following this, the umm receives the ra results and distributes the resources to multiple vms based on security parameters and performance. i. cryptography-based authentication frameworks in [20], security schemes that can guarantee the integrity, confidentiality, and authenticity of data were investigated, proposing a framework that uses symmetric and asymmetric cryptographic techniques to enhance data security, including the aes, rsa, and sha algorithms. the proposed framework used a two-step authentication process: one for user authentication based on a login password for access to data on the server, and the other used rsa to generate a fingerprint verification mechanism for enhanced authentication. the process is carried out at the sender and receiver ends to make the system invulnerable to man-in-the-middle and hijacking attacks. aes was used to encrypt the key and the message using an asymmetric key algorithm, like the rsa. the simulation results showed that the proposed strategy was scalable, efficient, and cost-effective for simple data sharing/access. in [21], a framework was proposed for secure data sharing in the cloud using hashed message authentication codes, index building, and data classification. an algorithm was developed to protect the data against several issues, e.g., malicious insiders, traffic hijacking, denial of service, and shared technology vulnerabilities, using public and private key engineering, technology & applied science research vol. 13, no. 1, 2023, 9997-10004 10001 www.etasr.com khan & alnwihel: a brief review on cloud computing authentication frameworks encryption (rsa, aes) along with a digital signature. an error localization algorithm was also proposed to specify the location of errors during an operation, such as deletion and appending while storing the data. data are classified into private, public, and restricted access modes, by the data owner, to provide access control according to the attributes of confidentiality, integrity, and availability. index-building is used to search through the encrypted data as the files are retrieved. a file index was proposed to be generated, and both the index and the files were encrypted. the index was composed of keywords that are encrypted as useless data. the encryption process involves the creation of a private/public key using rsa, and symantec's encryption desktop tool is then applied to generate the user's authentication certificate and verify his identity. this certificate is a unique identifier that can be used to prevent malicious access by attaching it to the message. the symantec tool generates the customer's private and public keys, and a request for a passphrase when they enter their username and email. the user is allowed to view the toolbar with the identifier, public key, and subkeys once they have provided the passphrase. a secure shell (ssh) is used to produce the keys, as it can be entered anywhere. a hash function is then used to generate the hash of the message, which is encrypted using the private key of the sender and joining the original message with the encrypted message. the sender and receiver share a symmetric key, which is a session key. using this shared key, the sender re-encrypts the encrypted message along with the original message. the shared key is then encrypted by the receiver's public key and sent with the re-encrypted message. on the receiver side, the message is decrypted using the private key to obtain the session key, which is checked to determine if it matches the shared key. if they match, the receiver uses the sender's public key and the session key for decryption to obtain the original message. the hmac is applied as a checksum to detect errors during data transmission. the checksum can determine if errors have occurred in the data but cannot correct them. the user can retrieve the data from the cloud by registering with the relevant organization to obtain his access credentials, and his username is stored in the cloud directory. the username is compared with the one saved in the cloud; if the user requests a segment of the data available for public access, no authentication is needed. however, if he requests access to private or restricted data, authentication is carried out by comparing the provided username with the one stored in the database. authentication is carried out as the user sends his password to the owner and answers some security questions. upon the user's request, the owner sends them using a digital signature and a keyword, and then sends the user's digital signature to the cloud along with his id for subsequent use. when the user applies the received digital signature along with the keyword, the cloud confirms whether their id is valid. the encrypted keywords help the cloud specify the user's location, which can be decrypted by the owner's sent key. the user then submits a file download request to the cloud, which sends the hmac along with the encrypted file. this is in turn decrypted using the received key. fully homomorphic encryption can be performed on the encrypted data if there are multiple subcustomers to whom the data need to be sent. the experimental study using eclipse id proved that the proposed algorithm was secure. the hybrid encryption-based scheme was faster than the rsa but suffered from memory and time limitations such that it cannot be used in the cloud. a security framework was proposed in [22] combining the processes used in kerberos and pretty good privacy (pgp). kerberos provides mutual authentication, confidentiality, and integrity, and prevents eavesdropping and reply attacks. this system used the concept of a trusted third party (ttp). kerberos has three logical components: the authentication server (as), the real server (rs), and the ticket grating serer (tgs). the authentication server acts as a key distribution center (kdc) and issues a session key after verifying the user credentials. the session key is used for communication between the as and the tgs. the tgs issues a ticket for the real server (rs) and provides a session key for communication between a user and the rs, which provides services to the user. the pgp provides cryptographic and authentication services. in this scheme, the user is registered with the kerberos kdc, which provides a ticket to communicate with the cloud service provider (sp). kdc also sends the user credentials and the ticket to the sp, which stores them and acknowledges their receipt. the user encrypts the data before transmission to the cloud. pgp authenticates the user and sends user-encrypted data to the sp. the sp in turn sends the data, as requested by the user, to pgp, which decrypts them with the user information, and sends decrypted data to the user after authentication. the problem with this framework is that kerberos does not support non-repudiation. in [23], a hybrid encryption algorithm was proposed combining rsa and aes cryptography to secure data during cloud upload and download. the algorithm uses three separate keys for encryption and decryption. the first is a public key shared between the parties, the second is a private key only on the customer side, and the third is a secret key for decryption. three keys are generated as the data are uploaded: an aes secret key, an rsa private key-d, an rsa public key-n, and an rsa public key-e. these keys are generated based on system time. the user is expected to save the aes secret key and the rsa private key, as they are needed to upload the data to the cloud (this key is unknown to the cloud administrator). upload begins through user authentication (username and password). the data are uploaded in an encrypted form to the cloud and stored in a temporary directory. the rsa and aes algorithms are then called. the user is subsequently required to provide the aes secret key, so the data are permanently kept in the cloud and their temporary directory is deleted. the user has to identify the filename to download for the download process and use the aes secret key and the rsa private key to decrypt the data. this study claimed that this hybrid mode of encryption can prevent unauthorized access to user data, as a secret private key is required for this. this access control method can protect the data even if the private key has been compromised, as the original data are not given (unreadable data are downloaded). this also applies to the cloud administrator if he tries to view the data. in [24], a mechanism based on the rsa cryptographic system was proposed, however, its key generation process is complex and unreliable for certain processes. in [25], two-layer attribute-based hybrid encryption was proposed. the first layer engineering, technology & applied science research vol. 13, no. 1, 2023, 9997-10004 10002 www.etasr.com khan & alnwihel: a brief review on cloud computing authentication frameworks used hmac on sensitive attributes. a substitution mechanism was applied in the second layer to re-encrypt the data, and access control policies were also used. the overall mechanism is inefficient as several copies of the encrypted data are stored using the same key and the computational cost is high. users are supposed to manage encryption keys, which is a significant drawback of the proposed system. to simultaneously ensure the security, authenticity, and verification of the data, a three-way mechanism was proposed in [26] using diffie–hellman key exchange merged into aes and a digital signature. the diffie–hellman algorithm is responsible for key exchange through the generation of keys. once the encryption algorithm has been executed, the digital signature is applied for user authentication. two servers are involved in this system: one for storing user data files and the other for the encryption process (it is referred to as the trusted computing platform). the flow starts when diffie–hellman key exchange is used to exchange keys once the user attempts to upload data to the cloud server. the user is authenticated through the digital signature. the aes encryption algorithm is used to encrypt user data, and the file is uploaded to the storage server. the same steps are carried out if the user wants to download data. the method proposed in [27] used the hash function, rsa, and des to ensure data security in the mobile cloud. the system consists of a data owner, a cloud service provider, and a third-party auditor. on behalf of the data owner, the third-party auditor verifies the integrity of the data stored in the mobile cloud. the data in the cloud are encrypted twice: once by the private key of the data owner and again by the third-party auditor's private key. rsa is applied for message authentication. each data owner and the third-party auditor uses rsa to generate public and private keys for each key generation phase. only the third-party auditor's public key is then exchanged with the data owner over a secure channel (key-sharing phase). the owner encrypts the data using their public key and then generates a hash message of the encrypted file. the encrypted file is then re-encrypted using the thirdparty auditor's public key, as is the hash message. the two sets are joined and sent to the third-party auditor (encryption phase). the latter stores the encrypted hash function to ensure data integrity and generates a random key to encrypt the message (using des). the received package is decrypted using the third-party auditor's private key. the produced random key is stored for later decryption. to verify the correctness of the data after performing des, the encrypted package is uploaded to the cloud and submitted to the third-party auditor. a random key generated by the third-party auditor is used to decrypt the message. the third-party auditor then produces a hash of the encrypted file and compares it with the decrypted and stored hash value. the result is used to send the appropriate file to the owner along with the requested file. the latter is encrypted by the data owner using their public key so that only they can decrypt it. in [28], a framework was proposed based on classifying the data into three segments, private, public, and limited access, and accordingly assigning sensitivity ratings to them. the owner classifies the data into segments. the framework consists of two phases. the first phase is further divided into three components: index-building, classification, and message authentication. the index builder is used to sort the encrypted data, and the index itself is encrypted to provide security. encryption is performed using the secure socket layer (ssl) with a single key. a message authentication code (mac) is generated after encryption to perform an integrity check. finally, the encrypted data are stored in the cloud based on a sensitivity rating according to the classification. in the second phase, the data retrieval process requires the registration of the user. the user credentials are stored in the cloud, and access to cloud data requires the submission of these credentials along with an access request. the cloud then takes action based on the request and the sensitivity rating of the data. authentication is not required if the data are classified as public but is needed if the requested segments are private or have limited access. a digital signature mechanism is used for authentication and verification. finally, an integrity check of the data is performed using mac. this scheme emphasizes a trade-off of key size, where a large key increases system complexity and leads to throughput problems. in the context of mobile cloud computing, an authentication scheme called message digest authentication (mda) was proposed [29]. this scheme does not involve any additional hardware infrastructure, like the imsi chip, and consists of a registration and an authentication phase. in the former, the user needs to register by creating an account consisting of a user id and password, as well as some unique identifying information. following this, the cloud stores the user's id and the hashed password along with information on the mobile device used. a message digest of the user, which consists of a user certificate and policy, is then generated by the cloud server. a message digest of the cloud, consisting of a cloud certificate and policy, is also generated. the cloud sends the registered device an encrypted message in the first phase that includes the user's message digest, the cloud's message digest, the cloud's public key, and the relevant column reference in the authentication database. a key is generated by xoring the user id and the hashed password to encrypt the message. the authentication process starts once the user's message digest, the cloud's digest, and the encryption key have been received by the user's device and consists of two operations: the authentication of the cloud by the mobile device and the authentication of the mobile device by the cloud. the key generated by xoring the user id and hashed password is used when the mobile device sends an authentication request to the cloud. this key is also used to produce an authentication key to encrypt the message digest. the encrypted message along with the column reference is sent to the cloud, which performs decryption after receiving the message. the cloud searches for the specific user id and the hashed password. if they are found, it generates a key to decrypt and obtain the message digest. the message digest is decrypted using the authentication key. the user is considered legitimate if the stored message digest matches the obtained message digest. the cloud server submits its digital signature, including the encrypted message digest, using its private key when the mobile device has been authenticated. in return, the mobile device decrypts the message by using the public key of the cloud. if the stored message digest matches the obtained engineering, technology & applied science research vol. 13, no. 1, 2023, 9997-10004 10003 www.etasr.com khan & alnwihel: a brief review on cloud computing authentication frameworks message digest, the cloud server is considered legitimate. this step establishes data transmission. however, the claimed hypothesis fails if the vulnerability of certain parameters is high. iii. conclusions and future work this study reviewed several authentication frameworks and their models in cloud computing, reported the characteristics and features of various frameworks, outlined the outstanding threats to them, and proposed solutions to counter these threats. all proposed solutions share a common problem: they are excessively geared toward the client or server side of the cloud architecture. the requirements for developing an efficient cloud computing authentication framework are outlined as follows:  client-based solutions are either based on the client's or the cloud provider's features. a common framework should be designed and implemented for both parties. such solutions should consider the requirements of the clients and the service vendors to avoid interoperability issues within the cloud environment.  greater focus is needed on data safety, confidentiality, and privacy, and less on the underlying architecture and processes running within the clients' systems.  •a low computational overhead should be a major desideratum in designing cloud-based services or devices as the scope of 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[29] s. dey, s. sampalli, and q. ye, "mda: message digest-based authentication for mobile cloud computing," journal of cloud computing, vol. 5, no. 1, nov. 2016, art. no. 18, https://doi.org/ 10.1186/s13677-016-0068-6. microsoft word etasr_v13_n2_pp10460-10465 engineering, technology & applied science research vol. 13, no. 2, 2023, 10460-10465 10460 www.etasr.com idate et al.: context-based aspect-oriented requirement engineering model context-based aspect-oriented requirement engineering model sonali r. idate department of it, college of engineering, bharati vidyapeeth (deemed to be university), india sonaliidate@gmail.com (corresponding author) t. srinivasa rao department of computer science, gitam institute of technology, gitam university, india sthamada@gitam.edu dipak j. mali tcs hinjewadi, india mali.dipak@tcs.com received: 21 january 2023 | revised: 6 february 2023 | accepted: 8 february 2023 abstract mobile applications are context-oriented systems that involve the use of context information while operating. mobile applications demand tackling context information in the early phase of software engineering. a context-aware system demands a different approach to handling the influence of the context on a system's requirements. aspect-oriented requirement engineering separates concerns throughout requirements, called crosscutting concerns, in the early phase of software development to improve the modularity of complex applications. capturing requirements embedded within context is a challenging procedure. this study aimed to identify such contextual characteristics of requirements in the early phase of software engineering, using natural language processing techniques, by proposing context-based aspect-oriented requirement engineering (cb-aore) to visualize the existence of crosscutting concerns. cb-aore performs context modeling to analyze the context dependency with base requirements and helps the analyst to visualize the correlation of functional and non-functional requirements with context. a case study analyzed the identification of context and its use to identify crosscutting concerns. keywords-context; context-aware system; crosscutting concern; aspect; aspect-oriented requirement engineering i. introduction requirement engineering is one of the important phases in software engineering, which includes a set of functional requirements specifying what functions a system should perform and a set of non-functional requirements specifying the performance characteristics of the functional features. functional requirements present the operational view to both the client and the developer and must be satisfied in terms of ease of use and less cost. due to their context-sensitive nature, mobile applications have some unique requirements that are less common in traditional software applications [1]. these requirements, including sensor handling, potential interactions with other applications from different sources, and embedded hardware devices [2], increase the complexity of mobile application development. software engineering analysis specifies what the system is currently doing, and design specifies what a new or modified system will do [3]. system design includes a top-down approach, coupling, cohesion, span of control, size, and sharing of modules. the top-down approach means understanding the problem at the top level and trying to exploit it at lower levels, which is also known as modularization. object-oriented software development (oosd) handles the complexity of an application using modularization and abstraction [4]. in [5], a formal aspectoriented requirement specification language was proposed, traced with the structural model, for complex system analysis. in [6], a role-based requirement modeling technique was proposed to facilitate analysis in the development of large and complex systems involving a large number of stakeholders. oosd aims to provide independence between modules, improve reusability, faster development, and reduced cost. however, aspect-oriented software development (aosd) does these in a much better way [7] and is possible by separating concerns. aspect-oriented programming (aop) introduces a new term called aspect, which represents crosscutting concerns as a module [8]. usually, concerns refer engineering, technology & applied science research vol. 13, no. 2, 2023, 10460-10465 10461 www.etasr.com idate et al.: context-based aspect-oriented requirement engineering model to the functionality offered by the system. aop can be used for complex cryptographic modeling and security simulation without changing legacy code [9]. aspect-oriented requirements engineering (aore) is an early phase in aosd that identifies crosscutting concerns at the level of requirements [10]. the process of separating concerns is called crosscutting concerns [11, 12], which is required in applying aosd methods. this paper proposes a requirement modeling process using additional context-specific requirements from a software requirement specification document and identifies crosscutting functional and non-functional requirements. engineering context-aware software systems, such as mobile applications, face many challenges [13]. context is any information that can be used to characterize the situation of an entity, such as a person, place, or object, necessary for the interaction between the user and the application [14]. this model was inspired by the multidimensional approach for separating concerns and identifying homogeneous crosscutting concerns [15-16]. homogeneous cross-cutting concerns are concerns that add the same behavioral variation at multiple points in the program [11]. moreover, the multi-dimensional approach treats all concerns at the same level and visualizes them from metaconcern and system spaces. a contribution matrix, developed from the compositional intersection of concerns, provides trade-off points that help to make architectural choices for the system [15]. however, the multidimensional approach lacks explicit relationship interaction [17]. the proposed context-based aspect-oriented requirement engineering (cb-aore) method provides immediate traceability at a high level of design. the future scope of cbaore specifies the articulation of the dependency relationship structure. this model contends that contextrelevant data must be gathered from the standard set of requirements. there is a need for decomposing requirements based on context to identify context-based functional and nonfunctional requirements. the aim of the paper is twofold: classify typical requirements into functional and non-functional and then apply the proposed cb-aore technique to identify crosscutting concerns in the early phase of software development. ii. methodology the proposed model used context-related requirement elements by studying requirements less commonly found in traditional software [1]. this was a two-fold activity. at first, a survey was conducted with a sample questionnaire to identify the need for a context-based model for requirement engineering. the second activity primarily focused on the extraction of mobile applications' specific requirements exhibiting special characteristics related to context. these requirements were extracted from 20 requirements documents for various mobile applications. the various contexts identified in the literature and srs documents of earlier projects were sensors context, device context, transactional context, network context, mobility context, social context, and third party software integration [18]. the special requirements for mobile applications were the use of sensors for human interactions, the use of embedded devices, and various transactions using a network. based on special requirements, the sample questions to investigate the need for context categories, relevant context elements, and activity of the mobile application are:  q1: do you find that requirement analysis based on context consideration in mobile applications will help programmers?  q.2: do you find the context-based requirement model understandable?  q3: were you able to identify individual functional requirements and their relevant context?  q4: do you agree that the implementation of mobile context-sensitive applications can be facilitated by the context-based requirement model?  q5: do you think that the development of mobile contextaware applications can be facilitated by a model that enables the automatic production of classes and methods?  q6: do you agree that exposing the context dependencies with the functional requirements makes it easier to explain to a business user of the app?  q7: how does the application adjust to the context?  q8: do you find interdependency in the context?  q9: were you able to identify non-functional requirements from context? as there is not a specific set definition for context, everyone can provide his perspective on it, which can be categorized into different classes. the proposed model was inspired by the multidimensional approach to the separation of contexts in requirement analysis, which applies uniform treatment to different types of requirements [17]. the proposed cb-aore model overcame the drawbacks of the multidimensional approach, such as exhibiting a lack of explicit relationship interaction among different requirements. seven context dimensions were identified and were embedded in the cb-aore model, as shown in table i. table i. context categories context context elements activity description device context camera, microphone, speaker, battery accessing camera, microphone, speaker, battery, device infrastucture/facilities such as time,date etc. sensor context accelerometer, proximity accessing sensors functionality/services transactional context internal storage, external storage (cloud) accessing data/information on/off mobile device, modify, add, delete data with i/o network context internet, wifi, bluetooth accessing web server through internet connection or bluetooth mobility context gprs, gps accessing map and location and provide navigation facility social context sharing, notification sharing information among users through social networks third party software integration api integrating app with third party services such a newsfeed service, payment gateways etc. engineering, technology & applied science research vol. 13, no. 2, 2023, 10460-10465 10462 www.etasr.com idate et al.: context-based aspect-oriented requirement engineering model fig. 1. engineering model of cb-aore. these dimensions are:  device context: contains mobile device features that allow users to access information about any web domain area. the features of a mobile device can be broken down into its technological, functional, and physical attributes [19-20]. physical attributes include weight, overall size, screen size, and resolution [21], functional attributes include input processes, gestures, and output mechanisms, technological attributes include cpu speed and storage capacity, and functional attributes include elements such as camera, microphone, etc. [22].  sensor context: mobile e-health apps use a variety of sensors, including an accelerometer, a low-pass filter, and a magnitude filter, to track the body's diabetes levels while the user is moving, walking, or running [23-24]. the motion, posture, and location of a mobile device can be identified by the 3d accelerometer, digital compass, etc. dedicated context-aware frameworks were developed to integrate sensor data, complex events, and data storage [25].  transactional context: it is important for taking any kind of input data and analyzing them [26]. such mechanisms transfer data to and from internal or external storage.  network context: characterizes the ability of a wireless mobile device to move from one area to another while still being able to access the data connection network facility from anywhere inside the network zone [24]. the present, growing wireless network technologies and mobile applications depend on it in fundamental ways.  mobility context: applies to the attributes and functionalities of mobile applications that use network and location elements [27].  social context: characterizes the activity that involves the exchange of information from one user to another through social media [19]. this context determines social relations through social media tools such as wikis, content hosting, social networking platforms, blogs, and podcasting.  third-party software integration (tpsi) context: captures elements of mobile apps and devices on the integration of extended functionality deployed on multiple platforms [21]. iii. the cb-aore model in software engineering, a software requirement specification document represents requirements at a higher level of abstraction [3]. context analysis is performed on user requirements with the help of a context repository. then, context interdependency analysis activities are mainly carried out by using syntactic analysis with natural language processing techniques. further dependency analysis of context with requirements is used to identify dependencies among aspects. dependency analysis is carried out by establishing dependency links among contexts and between contexts and requirements. contexts are extracted and analyzed from textual requirements. however, this requires understanding the effects of context on different requirements with reasoning [28]. therefore, the context model can be expressed as follows:  definition 1: a context model is 2-tuple cm = (c, dl), where: c is a finite set of contexts, c ≠ φ; dl ⊂ (c × c) is a set of dependency links.  definition 2: c is one context of the set c with the following properties: 1. c.dec represents the decomposition of context based on functional and non-functional requirements. 2. c.level represents the level of context. the value set of c.level is {user, system}, representing that c is user or system context, respectively. 3. c.link represents whether context c has links to fr, nfr, and other contexts. the value set of c.link is {1,0}. 4. c.type represents the type of context. the value set of c.type is {sensor context, system context, transactional context, network context, mobility context, social context, third party software integration, gui, search, misc} the potential relationship and dependency links are conceptualized using the cb-aore model. the model is represented with the help of roadmap and i* notations, as shown in tables ii and iii. table iv shows sample sets of text requirements from the inseption mobile application. this mobile application was developed to guide students who have just arrived on campus. table ii. roadmap notations notation role description nonfunctional requirement context role engineering, technology & applied science research vol. 13, no. 2, 2023, 10460-10465 10463 www.etasr.com idate et al.: context-based aspect-oriented requirement engineering model table iii. i* notations notation role description context nonfunctional requirement actor context dependency table iv. requirement text r1 the user should be able to search for a certain point of interest and navigate from a specific location to another. r2 the application should provide a map view of the campus. r3 the application shows all upcoming events regarding the university as provided in an rss feed r4 any event should be presented in a calendar form and should be searchable. r5 the application shows news items regarding the university as provided in an rss feed. r6 the application enables the student to read the student handbook r7 facebook link directs the students to the facebook page of the university/ability to view other facebook pages related to university/ furthermore uses facebook functionalities such as 'like', 'share'. r8 twitter application directs student to the twitter page of the university. r9 the user can search for personnel information available on the university server. nlp techniques were applied in stages for context realization. context repository extracted the context categories from the requirements text. in the second step, context initiation either by the system or user was identified. context dependencies with non-functional requirements are established through text processing and mapping. the mapping function of any subject clause x in non-functional requirements that matches the vocabulary of a context category is: ������� ,� � ��� � 1 (1) where m is the number of the non-functional requirement and n is the number of the context category. similarly, for functional requirements: ������ ,� � ��� � 1 (2) requirements r1 to r9 are either initiated by the user or the system. the "view map" functionality in r1 requires the network context, so the mobility context depends on it. in r9, when accessing personnel information from a server, the transactional context depends on the networking context. functional requirements are passed through nlp processes to identify contexts initiated by actors. as shown in the diagram, mobility context is captured from activity descriptions such as 'search location' or 'navigate' in r1. similarly, r2 realizes mobility context. however, context is initiated by the user in the first case and by the system in the latter. figure 2 shows context realization through context elements for the actor. r1 and r2 depend on mobility context. mobility context depends on network context, as it requires a data connection context element for map view. to provide updated news, the system depends on tpsi which is possible using an api context element and the network context's internet context element. every context element specifies a nonfunctional requirement so that realization can successfully satisfy the requirement. in this scenario, to provide a map view, network context must provide a network context element with the required speed and bandwidth, i.e. reliability and availability. likewise, all requirements are mapped with their related context element. figure 3 shows the dependency between a context element and a functional requirement. a context element related to a functional requirement exhibits the latter's dependency on the context. for example, 'r8: redirect to facebook' and 'r7: redirect to twitter' are functional requirements related to social media activity and depend on wi-fi or the internet connection context element. figure 3 visualizes the dependencies of the functional requirements r7 and r8 with the social context and the network context. thus, context elements through specific services fulfill functional requirements and also specify the needed non-functional requirements to successfully execute it. fig. 2. context and nonfunctional requirement dependencies. fig. 3. context and functional requirement dependencies. engineering, technology & applied science research vol. 13, no. 2, 2023, 10460-10465 10464 www.etasr.com idate et al.: context-based aspect-oriented requirement engineering model iv. comparative analysis of cb-aore with other aore models numerous methods have been proposed to identify early aspects using different techniques. in [29], an extensive comparative analysis on the theme/doc approach and multidimensional separation of concerns for requirements engineering (mdsocre) was performed, concluding that mdsocre focuses on the analyst's domain knowledge, and theme/doc analyses the requirements language while looking for the concern name [29]. the performance of the proposed method was verified by comparing it with goal-based aore [16], viewpoint-based aore [1], and multidimensional separation of concerns in requirements engineering [15] methods. table v shows a brief comparison. table v. cb-aore comparison with other methods parameters cb-aore gea goal based [16] preview view point based [1] multi-dimensional separation of concerns in requirements engineering [15] applicability for mobile application yes no no yes requirement modeling mobile contextbased goal and soft goal based viewpoint based multi-dimensional composability per context element and requirement per goal and softgoal per view per meta concern space and system space handling of functional and non-functional concern both functional nonfunctional both stakeholder scope mobile device, developer, system, and user analyst, developer not applicable methodology natural language analysis fuzzy logic, clustering technique fuzzy logic xml-based composition specification language to specify the composition rules a detailed comparison highlights the following:  use of requirement elicitation artifact: goal-based aore uses a case model by analyzing goal interaction, where the structure of goals considers various facets of requirements. the viewpoint-based approach divides requirements using a viewpoint to derive candidate aspects in the analysis phase. the proposed cb-aore model relies on functional and non-functional requirements from any requirement document and realizes context by mapping the requirements with the context repository.  candidate early aspect realization technique: in the goalbased approach, early aspects are identified by grouping goal interactions using a clustering algorithm. in the viewpoint approach, each candidate's early aspect is qualified with the help of concerns that are non-functional requirements. a candidate's early aspect is the concern that cuts across multiple viewpoints. in cb-aore, context is the candidate aspect that cuts across functional and nonfunctional requirements.  software application domain: the goal-based approach targets software system applications that have large concentration of only functional and nonfunctional characteristics to describe the requirements of the application. the viewpoint-based approach also relies on the functional and non-functional characteristics of any software system. so both approaches fail to accommodate context characteristics exhibited by mobile software applications. the cb-aore approach helps to envision the interactions not only between functional and non-functional requirements but also context. v. discussion many initiatives have been proposed to collect and relate aspect-oriented requirements in the early stages of software development [4, 11-12, 16, 29-30]. however, the proposed method decomposes the requirements based on contexts, which are special characteristics of a mobile application's functional and non-functional requirements. the further decomposition of contextual requirements into heterogeneous and homogeneous was not considered. furthermore, it would be interesting to focus on tracking contextual aspects in architectural decisions. vi. conclusion this paper proposed the possibility of using context in mobile applications to derive dependencies among functional and non-functional requirements in the early phase of requirement engineering. requirement engineering of mobile applications can utilize context characteristics to achieve better modularity for developing mobile software applications using an emerging aosd paradigm. a case study of the presented cb-aore gave an insight into how context dependencies of functional and non-functional requirements can identify crosscutting concerns and early aspects. future work should articulate dependency structure for describing relationships among context, functional, and non-functional requirements and also aim to strengthen the composition ability of aspects. references [1] a. i. wasserman, "software engineering issues for mobile application development," in proceedings of the fse/sdp workshop on future of software engineering research, santa fe, nm, usa, aug. 2010, pp. 397–400, https://doi.org/10.1145/1882362.1882443. 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[23] d. preuveneers, y. berbers, and w. joosen, "the future of mobile ehealth application development: exploring html5 for context-aware diabetes monitoring," procedia computer science, vol. 21, pp. 351– 359, jan. 2013, https://doi.org/10.1016/j.procs.2013.09.046. [24] a. r. lamas, j. l. filho, a. de paiva oliveira, and r. m. de almeida botelho junior, "a mobile geographic information system managing context-aware information based on ontologies," ubicc journal, vol. 4, pp. 718–727, 2009. [25] e. m. milic and d. stojanovic, "egosense: a framework for contextaware mobile applications development," engineering, technology & applied science research, vol. 7, no. 4, pp. 1791–1796, aug. 2017, https://doi.org/10.48084/etasr.1203. [26] j. floch, s. hallsteinsen, a. lie, and h. i. myrhaug, "a reference model for context-aware mobile services," sintef telecom and informatics, trondheim, norway, 2001. [27] q. h. mahmoud, "provisioning context-aware advertisements to wireless mobile users," in 2006 ieee international conference on multimedia and expo, toronto, on, canada, jul. 2006, pp. 669–672, https://doi.org/10.1109/icme.2006.262534. [28] t. yamabe and t. nakajima, "possibilities and limitations of context extraction in mobile devices: experiments with a multi-sensory personal device," international journal of multimedia and ubiquitous engineering, vol. 4, no. 4, pp. 37–52, oct. 2009. [29] a. zambrano, j. fabry, and s. gordillo, "expressing aspectual interactions in requirements engineering: experiences, problems and solutions," science of computer programming, vol. 78, no. 1, pp. 65–92, nov. 2012, https://doi.org/10.1016/j.scico.2011.12.004. [30] t. elrad, o. aldawud, and a. a. bader, "expressing aspects using uml behavioral and structural diagrams," in aspect-oriented software development with use cases (addison-wesley object technology series), boston, ma, usa: addison-wesley professional, 2004, pp. 459–478. microsoft word etasr_v12_n6_pp9665-9669 engineering, technology & applied science research vol. 12, no. 6, 2022, 9665-9669 9665 www.etasr.com maralapalle & hedge: an experimental study on the socketed pile in soft rock an experimental study on the socketed pile in soft rock vedprakash c. maralapalle civil engineering department mukesh patel school of technology management & engineering mumbai, india civilved@gmail.com r. a. hegde civil engineering department mukesh patel school of technology management & engineering mumbai, india ramachandra.hegde@nmims.edu. received: 17 september 2022 | revised: 26 september 2022 | accepted: 27 september 2022 abstract-pile foundation systems are used in india in many projects such as metro and railways, flyovers, and multi-story buildings. the pile transfers superstructure load to the substructure, i.e. to rock layers by means of skin resistance and end-bearing resistance. in this study, an attempt is made to observe the performance of socketed piles in soft rock. a series of socketed small-scale model pile load laboratory studies have been conducted using the loading frame. load tests were performed on a model steel pile to calculate its axial load-bearing capability at various socket depths. an unconfined compression test was performed on pseudo-rock variations to find out the properties of the soft rock used. the results showed the ability of the drilled pile to enhance the strength of the pseudo rock. an attempt was also made to calculate the optimum depth for the socketed pile in soft rock. keywords-pile foundation; socketed depth; settlement; axial load; model pile i. introduction utilization of socketed piles is one economical method which has been used to transfer heavy loads to the rock strata. rock socketed piles are drilled into the rock and then filled with steel and concrete. these piles are designed to carry heavy loads by base resistance and side skin resistance. broad diameter cast in situ piles are used to hold massive loads of super-structures. almost in every construction project, 1000mm to 1200mm diameter piles are used. as these piles are built for heavy loads, they are basically to be lowered to the rock surface and need to be inserted into the rock [1]. the socket in the rock layer is absolutely necessary when the piles rest just on a rock at shallow depths. boring in rock would have almost no challenge, except for occasional water pipes and boulders [2-5]. rock sockets will pose several functional issues, usually ranging from rock classification to socket depth and actual terminating standards. authors in [6] carried out a field pile load test by using osterberg-cell which measures the skin friction of the pile. authors in [7] carried out experimental investigations on the shaft friction of rock socketed piles using direct shear tests. authors in [8] conducted numerical and experimental tests on model piles with good agreement between them. the method of [9] was applied to the field loaddisplacement curve to obtain the ultimate pile load. authors in [10] presented a scale of strength and the corresponding n values for weak rock and soils. authors in [11] introduced the chiseling energy criteria applicable for rocks of the mumbai region. authors in [12] suggested that almost every load, including its subsequent settlement and the corresponding magnitude, was also drawn towards the applied load. authors in [13] investigated the case of piles in elasto-plastic rocks using finite element analysis. author in [14] strongly advocated the use of axisymmetric values of loads to define failure. authors in [15] reviewed some of the methods of socket design. in their review, they recommended a range of bond values for piles socketed in shale rock. the author in [16] applied neural network modeling to compute the maximum load for a driven pile in cohesionless soil. authors in [17] developed analytical solutions for the calculation of load-displacement response for axially loaded piles in rock. authors in [18] proposed a simple geomechanical model for calculating the settlements of foundations in soft rock masses which showed good agreement with the field data. authors in [19] carried out experimental studies for bond strength in rock socketed piers and stated that sidewall shear resistance essentially behaved in a non-brittle manner, i.e. it did not decrease even after the pile-rock bond was broken. authors in [20] presented charts for rock socket design based on finite element analysis of an elastic pile resting on the elastic socket. roughness classification and specification are shown in table i. authors in [21] proposed a design process for socketed pile in a soft rock complying with the defined settlement requirements and providing an appropriate factor of safety. authors in [22] proposed a design method, which used parameters based on a wide range of theoretical, laboratory, and field investigations. ii. pile socketing if the diameter of the pile is 1.2m, the rock socket is to be completed by breaking the hard rock for a length of 1.2m. for chiseling in hard rock, whose crushing strength is 1000kg/cm 2 , more time is required. each of these components may cause serious damage to a rock mass. the load is carried by the pile corresponding author: vedprakash c. maralapalle engineering, technology & applied science research vol. 12, no. 6, 2022, 9665-9669 9666 www.etasr.com maralapalle & hedge: an experimental study on the socketed pile in soft rock on the rock by point bearing. this makes necessary to socket the pile through the rock by breaking across the weak rock and by cutting down the hard rock for an appropriate depth generally to get the flat surface of the rock. this appropriate depth can vary between 200 and 400mm [23]. also, if the soft or medium rocks precede the hard rock, each length of the socket can be considered from the level where soft rock has an n value higher than 50. there are variations in the form of the rock almost every time. it can be weathered rock, soft rock, or hard rock. firstly, rock layer classification must be conducted. for this reason, we refer to field test reports such as rqd and spt [24, 25]. for larger constructions like flyover and highrise buildings, soil study must be conducted beneath every pier position. hence, the above-mentioned studies are crucial to be performed for every pier site. [26-28]. table i. roughness classification of rock sockets [18] roughness classification specification r1 soft socket, grooves less than 1mm deep r2 depth of grooves 1 to 4mm, spacing 50mm to 200mm, width > 2mm r3 depth of grooves 4 to 10mm, spacing 50mm to 200mm , width > 5mm r4 depth of grooves > 10mm, spacing 50mm to 200mm , width > 10mm iii. techniques for assessing socketed pile length in rock there are two different techniques used for the calculation of the socketed depth of piles in rock. a. on the basis of uniaxial compression strength method rock socketed pile is primarily executed to make use of the complete structural strength of the pile. sockets are built to hold the axial load through the side friction and the base resistance. it is important to gather all the information described above. in this regard, the elemental composition of the rock at the foundation stage should also be collected for the detection of chemical components influencing the capacity of the pile. the safe load-carrying capabilities of the socketed pile can be determined by the uniaxial compression strength of the rock. b. determination by the energy criteria method the configuration of the rock socket depth of the pile in the rock can be determined based on energy criteria. rock socketing standards have a great deal of significance in weathered/soft rock. core recovery ratio/rock content classification is the optimal measure to assess the rock type. it's hard to have the cores in the weathered/soft rock. the approach proposed in [10] is commonly used to determine the depth of the socket of the piles in soft-rock to obtain the ability of the pile and its structural strength. n values are used to describe the rock type and its shear strength. in fact, another technique uses a chisel to decide the form of the rock and the depth of the socket. the key points to be considered in the chisel energy system are the weight of the chisel, the number of blows, and the penetration into the rock for a predetermined number of blows. while this method appears to be more realistic and rational, it has many disadvantages, such as the strength of the chisel, the chisel dropping into the bentonite mixture, the mass of the chisel, and its type. chisel energy is measured based on the findings of the load test carried out in those regions. c. steps to follow during rock socketing other than drilling the rock up to the necessary depth in the rock socket, certain more important functional considerations need to be noticed. the heavy chiseling of high torque drilling can create vibrations during the rock socket operation. such vibrations can allow the soil strata to destabilize the rock base and the pile would lose the resistance component of these levels. therefore, better care must be taken to minimize disturbances. rock socketing requires a longer time and often disturbs the layers by laying the rock strata. this disruption would allow the fine particles to break down and settle down at the bottom. in order to clear these small pieces and other boulders, the borehole must be thoroughly washed with a clean bentonite solution prior to the concreting process. iv. experimental procedure rock socketed pile load testing is an experiment to be performed in the lab with the intention of providing more data on the load transfer behavior in socketed piles with varying l/d ratios. the typical sub-surface profile of soft-rock socketed pile is shown in figure 1. after the application of p downward axial load on the top of the pile, equal and opposite reaction is developed at the pile in the upward direction. q base is the base resistance. the length of the weathered stratum and the length of the soft-rock stratum represent the skin friction in different layers. fig. 1. typical sub-surface profile of the rock socketed pile. a. model pile material and tank a stainless steel hollow pipe was used, having two different diameters of 60mm and 80mm and a length 600mm. the steel tank is made up of mild steel material whose dimensions are 1000×1000×1000mm and 6mm thickness. the front side of the tank is made up of a perspex sheet to observe failure patterns during testing. the tank can be moved in the x and y directions under the load frame in order to apply centric and eccentric loading. engineering, technology & applied science research vol. 12, no. 6, 2022, 9665-9669 9667 www.etasr.com maralapalle & hedge: an experimental study on the socketed pile in soft rock b. devloping of pseudo-rock socket for pseudo-rock formation cement, sand, bentonite, and water were used. model rock specimens were developed, although their strengths varied widely. table ii provides the description of the ingredient proportions for pseudo-rock. the percentage of sand and water were kept constant and the percentage of cement and bentonite increased and decreased simultaneously. unconfined compressive strengths, as shown in figure 2, were determined by the compression testing machine (ctm) after 28 days of curing. fig. 2. testing of mortar cube and cylinder in the ctm. table ii. mortar cube test results for different bentonite percentages mix cement (%) bentonite (%) sand (%) water (%) avg. ucs (mpa) m1 17.97 4.5 67.41 10.11 19.3 m2 15.73 6.74 67.41 10.11 16.7 m3 13.48 8.98 67.41 10.11 9.5 m4 11.23 11.23 67.41 10.11 4.7 m5 8.9 13.48 67.41 10.11 3.4 m6 6.74 15.73 67.41 10.11 1.9 m7 4.5 17.97 67.41 10.11 1.2 v. experimental set-up a hydraulic jack attached to the frame's bottom allowed the gradual application of axial load to the pile head throughout the experiment. a load cell was attached between the hydraulic jack and the loading frame. therefore, two linear variable differential transformers (lvdts) were installed on the wing plates, fastened to the opposing sides of the pile cap to measure the movement of the pile head. the whole assembly, including the hydraulic jack, has a capacity of 30kn. an initial load of 0.2kn was applied before initiating any load increments. loads were applied in increments of 0.25kn up to 1kn, thereafter at 1kn increments until failure or 30kn whichever was earlier. a digital displacement monitor linked to the lvdts recorded movement readings when each load was applied. we kept increasing the load until the rate of change in the pile movement was minimal. the schematic view of the experimental setup and the actual pile load test setup are presented in figure 3 and 4 respectively. l/d ratios 1 to 7 were used for the testing program, where d is the diameter of the pile and l is the socketed length of the pile. details of the testing program for 60mm diameter pile and 80mm diameter pile are given in tables iii and iv respectively. different unconfined strengths of soft rock were used. fig. 3. schematic view of the experimental setup (1= loading frame, 2= hydraulic jack, 3= lvdt, 4= load cell, 5= model pile, 6 = metal tank, 7 = pseudo rock, 8 = pressure indicator, 9 = hydraulic pump). fig. 4. actual pile load test set-up with lvdt and load cell. vi. results and discussion the behavior of load-settlement curves is discussed in this section. based on the experimental results, the load-settlement response and the load transfer mechanism along the depth of the pile are discussed. all the piles were gradually loaded until failure to obtain their axial load-carrying capacities. two different diameter piles were used in the testing program. the load vs displacement curves for the 60mm diameter piles are shown in figure 5. a number of experimental model studies were carried out to determine the impact of the socket depth on the behavior of the in situ cast piles. seven sets of experiments with different socket lengths of 1d, 2d, 3d, 4d, 5d, 6d, and 7d, where d is the diameter of the pile in pseudo rock were used in the testing program. with the help of the load settlement curve, the ultimate pile capacity was calculated. engineering, technology & applied science research vol. 12, no. 6, 2022, 9665-9669 9668 www.etasr.com maralapalle & hedge: an experimental study on the socketed pile in soft rock table iii. details of model socketed pile load tests on soft rock for 60mm diameter pile test no. pile no l/d socket length (mm) avg. ucs (mpa) 1 p1 1 60 9.45 2 p2 2 120 9.43 3 p3 3 180 9.36 4 p4 4 240 9.40 5 p5 5 300 9.21 6 p6 6 360 9.64 7 p7 7 420 9.33 table iv. details of model socketed pile load tests on soft rock for 80mm diameter pile test no. pile no. l/d socket length (mm) avg. ucs (mpa) 1 p1 1 80 9.30 2 p2 2 160 9.45 3 p3 3 240 9.46 4 p4 4 320 9.40 5 p5 5 400 9.31 6 p6 6 480 9.54 7 p7 7 560 9.43 fig. 5. comparison of load vs. settlement curves for 1d -7d socketed piles for 60mm pile diameter. fig. 6. comparison of load vs. settlement curves for 1d -7d socketed piles for 80mm pile diameter. the load was applied incrementally up to 30kn and the corresponding vertical displacements were recorded. for 1d, 2d, 3d, 4d, 5d, 6d, and 7d socketed depths, the observed axial pile capacities by the double tangent method were 6.2kn, 9.1kn, 11.2kn, 12.8kn, 15.3kn, 16kn, and 16.6kn respectively. the load vs displacement curves for 80mm diameter piles are shown in figure 6. the loads were applied and the corresponding vertical displacements were recorded. for 1d, 2d, 3d, 4d, 5d, 6d, and 7d socketed depths, the axial pile capacities were 10.8kn, 14.1kn, 17.25kn, 21.1kn, 24.15kn, 26.1kn, and 27.9kn respectively. the compression measurements on the model piles demonstrate that the pile resistance increases as the depth of the socket increases, which is essentially due to the friction between the pile and the socketed rock. up to a length of 4d to 5d of socket depth, the capacity of the pile was observed to increase considerably, but after 5d socket length, the improvement in the pile capacity was marginal. this marginal increase in strength was caused by the decrease in strength of the material and low pile stiffness. so, it can be concluded that 5d of the length of socket is the optimum depth of the socketed pile in soft-rock. this is consistent with the observations of [7, 11]. vii. conclusions in the present study, an effort has been made to analyze the minimum depth of the socketed pile in soft rocks. the behavior of piles in the soft rock was studied through an elaborate laboratory program, with varying socket lengths. a large number of pseudo rock samples using cement and bentonite were made by changing the proportions of cement and bentonite (7 mixes, termed as m1-m7, having ucs values of up to 19.3mpa were prepared and tested). the present study demonstrated that the behavior of socketed piles can be successfully modeled in a soft rock. the results of the present model study and the reported data in the literature are in accordance. the conclusions of the experimental program are:  ucs strengths were found to decrease as the proportion of bentonite increased in the pseudo-rock.  pile capacity increases dramatically for socket length up to 5d, but this 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[28] s. rezazadeh and a. eslami, "empirical methods for determining shaft bearing capacity of semi-deep foundations socketed in rocks," journal of rock mechanics and geotechnical engineering, vol. 9, no. 6, pp. 1140– 1151, dec. 2017, https://doi.org/10.1016/j.jrmge.2017.06.003. microsoft word etasr_v13_n1_pp10140-10144 engineering, technology & applied science research vol. 13, no. 1, 2023, 10140-10144 10140 www.etasr.com vinh & ha: improved torque ripple of switched reluctance motors using sliding mode control for … improved torque ripple of switched reluctance motors using sliding mode control for electric vehicles vo quang vinh faculty of control and automation, electric power university, vietnam vinhvq@epu.edu.vn vo thanh ha faculty of electrical and electronics engineering, university of transport and communications, vietnam vothanhha.ktd@utc.edu.vn (corresponding author) received: 13 december 2022 | revised: 27 december 2022 and 5 january 2023 | accepted: 7 january 2023 abstract this study describes the direct torque control-dtc approach, based on the sliding mode control (smc) technology with chattering reduction, for reducing the torque ripple of the switched reluctance motor (srm). the srm torque control loop has been given the smc treatment to account for the low-frequency fluctuations in the torque output. to maintain a consistent motor speed, the sliding mode controller modifies the value of the reference current. the findings demonstrate that the constant sliding mode controller is superior to pi controllers at lowering the motor's torque ripple, compensating for its nonlinear torque characteristics, and rendering the drive insensitive to parameter changes. matlab/simulink simulation has been used to show how well this smc performs. the performance of the proposed smc method has been demonstrated by simulation in matlab/simulink with a threephase 8/6 pole, and a 2kw srm. keywords-switched reluctance motor; sliding mode control (smc); pi; ev; torque ripple i. introduction switched reluctance motors (srms) have become a viable electrification option for the military, civic, agricultural, mining, and transportation industries, due to their low prices, high efficiency, and ability to run in hostile settings [1-3]. however, the fact that srms are vulnerable to torque ripple, which makes noise and shortens the motor's life, has been a problem [4-6]. the primary explanation is that srms align with magnetic fields using low-reluctance materials like iron and steel. the stator of the srm features phased windings, while the rotor has low and high reluctance areas. the magnetic flux and materials' resistance creates a force that pushes the rotor pole into alignment with the closest stator pole when power is applied to the stator windings. the srm control algorithms sequentially turn the stator windings on and off to change the magnetic field, which forces the rotor to revolve. the problem is that because of structural deformations and magnetic torque harmonics that cause the stator and rotor to interact, this process also generates vibration and noise. as a result, noise is produced, and the motor's lifetime is shortened by the interactions and oscillations that alter the torque or torque ripple [7-13]. this srm torque ripple limits the possibility of their direct-drive applications in the industry. significantly, the fastness and accuracy of the torque response the engine needs to mobilize during driving are affected considerably. therefore, structure and control strategy optimization consist the primary aim of research on torque ripple reduction. in terms of structural optimization, the torque ripple was reduced by optimizing the pole shape [14-16] and stepper air gap [17] using the finite element modeling (fem) in conjunction with optimization techniques. the improvement in control is often more flexible than the optimization in construction since srms have a straightforward structure. numerous studies use sophisticated control techniques to reduce torque ripple [18], such as optimal harmonic current injection and current waveform tuning. in [19, 20], a pid fuzzy logic controller with the integration of the speed error, the sum of the speed error, and the derivative of the speed error are presented to decrease the torque ripple of srm with two inputs. a comparison of smc and fuzzy-neural network approaches was reported in [21]. smc is comparable to other popular nonlinear control techniques, including adaptive inputoutput feedback linearization [17] and adaptive back stepping engineering, technology & applied science research vol. 13, no. 1, 2023, 10140-10144 10141 www.etasr.com vinh & ha: improved torque ripple of switched reluctance motors using sliding mode control for … techniques [22]. multiple industrial control systems have been used to study the development of smc approaches [23-26]. minimization of torque ripple in switched reluctance motor based on model predictive control (mpc) and torque sharing function (tsf) was conducted in [27]. a novel continuous terminal smc technique has been devised to ensure that the system states reach the sliding surface in a finite amount of time. the suggested controller certifies robustness and continuity, making the control algorithm better suited for mechanical servo systems. in this study, the speed loop is controlled by an smc and a pi controller to enhance the performance of the dtc system by adequately determining the reference torque, further achieving accurate control, minimizing torque ripple, and improving the dynamic performance of the srm. ii. modeling of an srm motor the nonlinear, switching currents are used in the srm to drive the phases. by correctly modeling the nonlinear fluxcurrent-angle (λi-θ) characteristics of the machine, the magnetic nonlinearities of an srm may be taken into consideration [25]. the three – phase 8/6 srm is shown in figure 1. fig. 1. the three – phase 8/6 srm. ���� � �� � � � � ��,���� ���� � �� ��,��� ��� (1) the nonlinear torque dynamics are described by: ����� � � � �� (2) where: � � ������ � �� � � � ��,���� ���� � �� ��,��� ��� � ������ ���� � (3) � � ������ � �� ��,��� ��� (4) where �� is the torque srm motor, ���, � is the nonlinear function of phase flux linkage, � is the rotor position, and i is the stator current. the rate of energy change with rotor position may be used to express the srm torque. �� ��, � � �� � ���� (5) where l is the inductance at a position, �� is the rotor position, ��, ��, ��, � are the rotor positions at a phase (a, b, c, and d phases), !"�# and !"$% represent the minimum/maximum phase inductance with none aligned / aligned position. !��� � ⎩⎪⎨ ⎪⎧ !"�# * �� + �� !"�# � ��� ��� � ��� * �� + �� + �� !"$% � ��� ��� � ��� * �� + �� + �� (6) iii. sliding mode controller design for speed control the technique used in smc is intrinsically resistant to changes in parameters, nonlinear models, outside disturbances, and uncertainty. therefore, it is employed when the robustness requirement is crucial for in-vehicle applications, and there are significant uncertainties [22]. the following procedures are part of the torque controller design by the sliding mode controller.  step 1: select the sliding surface function: , � -�� �.� � /� 0 -�� �.�1. � 0�3 (7) where -�� �.� � ��∗ � �� is the error torque and /� is a positive gain coefficient.  step 2: taking the derivative of (7) and substituting from (2). the result of the sliding surface is expressed as: �5�� � ��� � ��� � /� -�� (8)  step 3: the lyapunov technique is often utilized to determine the conditions on the control rule that will cause the state to circle the equilibrium in smc. 1 0 2 tw s s  (9) then, the derivative of (8) and w is definitely negative without the sliding surface s=0. therefore, the control law is: � � ���6�� � /� -�� � 789��,�: (10) where γ is the positive gain coefficient and 89��,� is the switch function. it is selected as: 1, if ( ) , if | | 1, if s n s sgn s s n n s n         (11)  step 4: based on (5) and (10), the control law is: � � �;<= >?@� ?@ a� ?@��;<= >?@� ��� � /� ���� � � /� -�� �789��,�b (12) equation (12) has the sgn function which causes system chattering. therefore, the main disadvantage in conventional smc is chattering. chattering adversely affects the performance of system significantly. the chattering in the sliding mode controller can be reduced by modifying the engineering, technology & applied science research vol. 13, no. 1, 2023, 10140-10144 10142 www.etasr.com vinh & ha: improved torque ripple of switched reluctance motors using sliding mode control for … control law in as � � c8d.� e�� and constant factor � defines the thickness of the boundary layer around the switching surface. the 8d.�s/��is the saturation function that is defined as: 8d. � e�� � f e� * g e�g ≤ 189� � e�� * g e�g > 1 (13) iv. simulation results simulations of the dtc system were conducted to check the proposed smc controller's accuracy and efficacy. figure 2 depicts the block diagrams of the smc controller and the dtc system. matlab/simulink was used to model the srm drive's dtc system with a three-phase, 2-kw srm. simulations were run in the 2022 version of matlab/simulink. the closed-loop srm drive speed controller based on smc in figures 2, 3, and the srm motor have the parameters shown in table i. fig. 2. structure control of an improved torque ripple of an srm for electric vehicles. fig. 3. structure control reducing the torque ripple of the srm motor in matlab/simulink. table i. srm motor parameters parameters unit stator resistance (ω) 2 inertia (kg.m.n) 0.082 frication (n.m.s) 0.01 inductance lmin 11 inductance lmax 50 stator pole number 8 rotor pole number 6 maximum current (a) 120 maximum flux linkage (v.s) 0.486 the electromagnetic torque of the srm with the classical pi controller and the proposed smc for 1000 and 4000rpm are shown in figure 4. the most significant advantage of the proposed smc is its constant electromagnetic torque. figure 4 shows the simulation results of the srm at rotational speeds of 1000 and 4000rpm and a reference torque of 38nm. in addition, the srms have a significant ripple of electromagnetic torque. however, the average torque fluctuation is within 2.5%. therefore, the speed ripple of the proposed smc is smaller than that of a pi controller. furthermore, the suggested smc's electromagnetic torque is more uniform than the pi's. therefore, reducing the electromagnetic torque ripple is the essential advantage of the proposed controller. figures 5 and 6 show the change of the flux linkage which should be made as smooth as possible when designing the torque, enhancing the movement following the ability of the smc controller. engineering, technology & applied science research vol. 13, no. 1, 2023, 10140-10144 10143 www.etasr.com vinh & ha: improved torque ripple of switched reluctance motors using sliding mode control for … (a) (b) fig. 4. torque comparison, smc and pi controllers. (a) 1000rpm, (b) 4000rpm. (a) (b) fig. 5. the three-phase current response. (a) 1000rpm, (b) 4000rpm. fig. 6. the flux response. figure 7 shows that the actual speed response follows the set value. the short time is fast with t = 0.025s, and the static deviation is slight with k1%. therefore, the proposed smc method has the advantage of very small speed error of the srm motor. let's consider the case where the inductance parameter changes by 50%. the torque response is shown in figure 8 and it does not change at 1000 and 4000rpm. again, the short time is fast with t = 0.025s, and the static deviation is slight with ±1%. in contrast, the increased torque response of the pi control method is 23%, and the setting time is slower than that of the smc controller. fig. 7. simulation results of the srm control speed using smc. fig. 8. torque response when the stator resistance is increased by 50%. v. conclusions this paper proposes a torque ripple minimization of switched reluctance motors using direct torque control based on the sliding mode. the proposed torque control method combines dtc with the smc controller. the stability of the proposed system is verified through the lyapunov function. in addition, this control method has reduced the chattering of the torque response by using a saturation part in the control signal. as a result, the proposed control method performs better than the pi controller and it is robust to parameter changes. to improve the torque ripple reduction in future research, a sliding controller combined with a fuzzy logic controller or connected with a neural network or a model predictive control, will be considered to optimize the duty ratio and to minimize the torque ripple. in addition, this control method should be tested experimentally in the future to prove its correctness. acknowledgment the authors would like to acknowledge the support from the university of transport and communications. references [1] m. takeno, a. chiba, n. hoshi, s. ogasawara, m. takemoto, and m. a. rahman, "test results and torque improvement of the 50-kw switched reluctance motor designed for hybrid electric vehicles," ieee transactions on industry applications, vol. 48, no. 4, pp. 1327–1334, jul. 2012, https://doi.org/10.1109/tia.2012.2199952. 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[27] p. ren, j. zhu, z. jing, z. guo, and a. xu, "minimization of torque ripple in switched reluctance motor based on mpc and tsf," ieej transactions on electrical and electronic engineering, vol. 16, no. 11, pp. 1535–1543, 2021, https://doi.org/10.1002/tee.23458. microsoft word etasr_v13_n3_pp10646-10651 engineering, technology & applied science research vol. 13, no. 3, 2023, 10646-10651 10646 www.etasr.com hussein & ibrahim: impact of leachate recirculation on the stabilization of municipal solid waste in … impact of leachate recirculation on the stabilization of municipal solid waste in anaerobic bioreactors of different compositions omar amer hussein environmental engineering department, baghdad university, iraq o.hussein1011@coeng.uobaghdad.edu.iq (corresponding author) jathwa abd-alkareem ibrahim environmental engineering department, baghdad university, iraq jathwa58@gmail.com received: 8 march 2023 | revised: 18 march 2023 | accepted: 20 march 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5839 abstract the aim of the current study is to determine the impacts of leachate recirculation on the degradation of three compositions of municipal solid waste in anaerobic bioreactors. the study was completed by using six columns with equal volume (0.042m 3 ) containing different densities and compositions of solid waste, in order to follow waste degradation over a limited time. three compositions of waste were studied: simulated fresh waste of standard composition, simulated fresh waste of fermentable composition, and actual aged waste. measurements of the significant parameters including ph, leachate conductivity, chemical oxygen demand (cod), and waste settlement, were carried out. the quantity of oxidized organic matter was increased by the leachate recirculation, and the degradation period was reduced by using leachate recirculation. after 300, 150, and 480 days, waste stabilization seemed to be reached for fresh, aged, and fermentable waste, whereas the organic content decreased to 650, 480, and 4000mg cod/l, respectively. keywords-solid waste stabilization; leachate recirculation; bioreactor; chemical oxygen demand i. introduction the quantity of domestic waste has increased along with population density [1]. municipal solid waste (msw) generation increases gradually as the commercial and industrial activities extend [2]. the percentages of green and food waste in msw for middleand low-income countries are very high [3], whereas landfilling is the most common option of waste disposal. however, during the landfilling process, the high organics amount in msw often leads to leachate generation [4, 5]. appropriate landfill management is required globally, especially in developing countries. early landfill site stabilization and environmental pollution reduction caused by leachates are commonly recognized as important issues. in most developing countries, landfill leachates are treated in stabilization ponds [6], or are collected for further treatment [7]. the leachates are generated either from external water or from within the waste mass [8]. overflow of untreated leachates or leakage into the environment is a problem because large amounts of landfill leachates are produced by landfill sites with high seasonal rainfalls. recirculation of leachates in landfills is an attractive technology that can reduce the amount of leachates and limit the decomposition of pollutants in landfills [9, 10]. leachate recycling is a proven on-site leachate treatment method. it has been shown that leachate recirculation improves biogas production and final leachate quality and reduces waste stabilization time [11]. bioreactor landfills are designed to address the shortcomings of conventional landfills and reduce long stabilization times [12]. bioreactor landfills are categorized as aerobic, anaerobic, semi-aerobic, and hybrid, depending on their operational characteristics [13]. many researchers had applied such or similar techniques to show the impact of leachate recirculation on the stabilization of msw. authors in [14] used untreated leachates for liquid recycling and added water to investigate the effect on the anaerobic digestion of food waste. they combined batch analysis of mesophilic biochemical methane potential (bmp) with a cyclical water reuse operation. cyclic bmp assays showed that using an appropriate proportion of recycled leachates along with fresh water can stimulate the methanogenic activity and promote biogas production. authors in [15] studied the impact of different leachate recirculation strategies on the discontinuous anaerobic digestion of solid organic waste. many leachate recirculation strategies have been used in digestion systems of batch solid-phase in laboratoryengineering, technology & applied science research vol. 13, no. 3, 2023, 10646-10651 10647 www.etasr.com hussein & ibrahim: impact of leachate recirculation on the stabilization of municipal solid waste in … scales experiments. comparative studies with intermittent and continuous return of exudate showed no improvement of continuous flow. authors in [16] used landfill leachates and gases to predict the moisture distribution and the water and gas pores of typical bioreactor landfills as the leachate recirculation or injection system. the effects of the unsaturated hydraulic conductivity and the anisotropic nature and heterogeneity of msw, the geometry of vertical wells on pore water, moisture distribution, and gas pressure were tested. the unsaturated hydraulic properties of msw have significant impact on the wetted area and pore water pressure during the initial stage of leachate injection and subsequent gravity drainage. authors in [17] investigated the combination of a vertical well and a spray recirculation system simultaneously, and stated the impact of their synchronized application on landfill leachates. authors in [18] investigated the impact of aeration on leachate recycling and waste decomposition rates using leachate quality and quantity. this study investigated the stabilization of msw in different bioreactor landfills (anaerobic, semi-aerobic, aerobic, and recirculating anaerobic leachate landfills) in terms of leachate characteristics. the results noted that leachate recycling appeared to be a good solution to deliver in-situ treatment and minimize time of leachate stabilization when an aerobic landfill is not applicable. authors in [19] investigated the effect of a semi-aerobic bioreactor landfill and the cotreatment of leachate recirculation and pre-aeration on landfill stabilization. the results proved high removal rates for cod and ammonia nitrogen, reaching 97% and 88%, respectively. the current research mainly addresses the determination of the effects of leachate recirculation on solid waste stabilization and settlement at different degradation stages and for different compositions (fresh, aged, and fermentable msw) collected from different locations in baghdad, iraq to eliminate the risk of waste contamination in the long term. ii. experimental method a. waste samples the physical compositions of the msw samples adopted in this study were manually adjusted to simulate the typical msw compositions in baghdad based on the average of 12 samples (table i). table i. waste sample ingredients and collection points district type and weight of waste (kg) organic plastic paper metal glass other 1 al-shaab 41 21 17 5 6 10 2 al-ghadeer 43 21 16 4 5 11 3 new baghdad 42 22 17 4 6 8 4 al-sader1 44 19 16 4 4 13 5 al-sader2 43 20 17 4 5 11 6 al-adhamya 39 21 19 6 7 8 7 al-karada 39 21 20 5 6 9 8 al-rasafa 39 22 20 5 6 8 average 41.25 20.875 17.75 4.625 5.625 9.75 b. experimental work the experiment was conducted using 6 plastic columns of 750mm height and 300mm diameter, named c1-c6 (figures 12). each column has a cover and two perforated plastic plates, the first plate at a height of 5cm from the base of the reactor to ensure that the waste does not fall to the bottom during the decomposition process and thus clog the leachate collection valve, and the second plate at a distance of 5cm from the top of the reactor to distribute the recycled leachate and water simulating local seasonal rainfall rate. finally, an external meter containing two sensors was inserted inside the columns to measure ph and moisture content during the bioreaction processes. moisture content was maintained within the range of 40 to 60% by weight in order to prevent oxygen deficit due to void saturation from occurring. table ii shows the composition of msw compacted in each column: fresh waste generated from households without sorting, waste that have been buried for several years from an aged sanitary landfill site, and fermentable only organic waste, which are represented by food waste, tree leaves, and garden waste. fig. 1. sketch of the anaerobic bioreactor. 1-gas valve, 2-upper storage container for leachate recirculation, 3-upper perforated plate, 4-thermometer, 5-anaerobic biodegradation tank, 6-lower perforated plate, 7-leachate collection container, 8-extra leachate container, 9-pump, 10-ph and moisture content meter, 11-cover for waste feeding. fig. 2. six bioreactor columns. engineering, technology & applied science research vol. 13, no. 3, 2023, 10646-10651 10648 www.etasr.com hussein & ibrahim: impact of leachate recirculation on the stabilization of municipal solid waste in … table ii. solid waste characteristics according to columns column's code c6 c5 c4 c3 c2 c1 waste type ferment able ferment able aged aged fresh fresh waste mass (kg) 25 25 30 30 15 15 waste height (m) 0.6 0.6 0.6 0.6 0.6 0.6 waste volume (m 3 ) 0.042 0.042 0.042 0.042 0.042 0.042 waste density (kg/m 3 ) 595.24 595.24 714.29 714.29 357.14 357.14 precipitation (l/week) 0.6 0.6 0.6 0.6 0.6 0.6 leachate recirculation (flowrate) (l/day) 0.03 0 0.1 0 0.06 0 c. analysis methods leachate samples were analyzed for ph, chemical oxygen demand (cod), and electrical conductivity (ec) on a monthly basis. all the parameters were measured according to standard methods [20]. iii. results and discussion a. ph value the ph changes in the bioreactor leachates are depicted in figure 3. the waste in reactors 1, 2, 5, 6 went through aerobic decomposition and produced a greater initial co2 concentration due to the tiny amount of air in the voids of the fresh waste after loading. as a result, the ph values decreased over the first 100 days. leachate recharge has the ability to speed up the hydrolysis of organic matter [12, 21], and acidogens, which are rapidly growing bacteria, have the ability to quickly transform soluble organic waste into volatile fatty acids [22]. the ph levels of the 6 reactors gradually rose to above 8 after 100 days. the relatively lower ph level in the reactors over a longer period of time suggests that acidogenic and hydrolytic bacteria were predominant and that the accumulation of their degradation products, including small molecular organic acids and simple soluble organic matter, delayed the methanogenesis phase. acidity is the primary inhibitor of methanogenesis under anaerobic conditions. a ph range of 6.5 to 8.0 is optimal for methanogenic bacteria, while a ph range of 5.5 to 6.5 promotes the hydrolysis and acidolysis processes [23]. after this period, the ph of all the reactors rapidly increased and then was maintained at steady state levels. b. electrical conductivity monitoring ec in the leachates varied for the 3 types of msw. high values of ec indicate the presence of high dissolved inorganic materials in samples, yet conductivity values tended to decrease after the 90 th day, as shown in figure 4. it should be noted that fermentable solid waste leachates have a higher ec value. this result is in accordance with the findings of [24], where it is reported that average ec declines with increasing landfill age. the loss of some easily mobilized ions, such as sulphate, metals, and chloride, among others are possible causes of the experiment's decreased ec. these factors would tend to remove the ionic strength from the solution. (a) (b) (c) fig. 3. ph profile of (a) fresh, (b) aged, and (c) fermentable waste. c. removal of organic content the primary indication of the impact of contaminants in bioreactors is cod. all of the bioreactors' cod patterns were virtually comparable, and the cod concentration increased significantly throughout the first 100 days (figure 5). one possible reason for this could be that the generated leachates were produced in an unusually tiny amount, making it impossible for the cod to accurately reflect the concentration of organic matter in the waste leachates. afterwards, as leachates were recirculated, hydraulic loading was increased accordingly providing additional nutrients and sufficient moisture to accelerate the rates of biodegradation [25]. moreover, food waste is a component that degrades quickly [26]. because there were not enough microbes to completely break down all the soluble organic waste, the concentration of cod was likely higher [27]. in recirculation reactors, cod concentrations rose quickly to maximum levels for both fresh and aged waste after around 90 days of operation, whereas this was accomplished after 120 days for fermentable waste. these findings demonstrate that leachates might leak more organics if the amount of leachate recirculation is increased within a specific range. the cod concentrations in all the reactors rapidly dropped when the bacteria gradually adjusted to the engineering, technology & applied science research vol. 13, no. 3, 2023, 10646-10651 10649 www.etasr.com hussein & ibrahim: impact of leachate recirculation on the stabilization of municipal solid waste in … conditions in the reactor. these results are marginally better than those found in [28], despite the fact that their work involved more frequent leachate recirculation and utilized significantly more biodegradable materials. (a) (b) (c) fig. 4. profile of electrical conductivity. d. settlement of solid waste in columns one important criterion that makes anaerobic bioreactor landfills identifiable is the settlement of msw, is settlement [29]. following the end of the operation time, all bioreactors had a large settlement, as indicated in table iii, primarily as a result of the waste's gravity-induced settling. the anaerobic treatment showed a higher degree of settlement, indicating that the voids accelerated the rate and amount of subsidence. in [30] and over a 400-day testing period, the settlement in aerobic, anaerobic, and dry anaerobic reactors was 32%, 20%, and 7%, respectively, which are lower than the values acquired during the current study. this may be due to the biological decomposition of organic materials, which is influenced by humidity and the amount of organic material in the waste and partially determines the degree of settlement [31, 32]. the low aeration rates for the anaerobic reactors in this experiment could lead to high moisture content in waste, which has a visible effect on the biodegradation of organic matter. moisture content is also essential for microbial activity. (a) (b) (c) fig. 5. profile of organic content removal table iii. waste settlement information code c6 c5 c4 c3 c2 c1 total height (cm) 60 60 60 60 60 60 original colume (cm 3 ) 42412 42412 42412 42412 42412 42412 final height (cm) 5 17 44 45 29 34 final height (%) 8.33 28.3 73.3 75 48.3 56.6 remaining volume (cm 3 ) 3534 12017 31102 31809 20499 24033 removed height % 91.67 71.7 26.7 25 51.7 43.4 removal ratio difference 6c&5c c3&c4 c1&c2 percentage% 20% 1.7% 8.3% iv. conclusion the usage of different solid waste columns allowed characterizing the main stages of waste decomposition in a limited period of time and highlighting the main disadvantages and advantages of leachates recycling for waste decomposition. waste composition and degradation rate have a significant engineering, technology & applied science research vol. 13, no. 3, 2023, 10646-10651 10650 www.etasr.com hussein & ibrahim: impact of leachate recirculation on the stabilization of municipal solid waste in … impact on the duration of the degradation process. recirculating the leachate can reduce the time it takes fresh and old waste columns to reach the methanogenic stage. recirculation appeared to limit the risk of waste contamination in the long run. the amount of oxidizable substances co-released into the leachates was even more significant for columns in circulation. the quality of the recycled leachates and the quality of the leachates released from the waste appeared to be similar. after 450 days of recirculation, injecting the still-contaminated leachates appeared to mask contamination that could still be released by the waste. this study has shown interest in the application of leachate recirculation due to advantages such as the shortening of the deterioration period. the quality of the recirculating leachates and the type of waste (composition and degradation state) are the parameters that determine the impact of recirculation on emissions. the waste settlements increased the leachate recirculation up to 20, 1.7 and 8.3% for fresh, aged, and fermentable waste, respectively. acknowledgment the authors would like to thank the staff of baghdad municipality for providing fresh samples of solid waste. also, the authors highly appreciate the department of environmental engineering at university of baghdad for their technical support. references [1] m. xue, w. hu, l. huanyu, and y. fu, "beneficial reuse of municipal solid waste incineration bottom slag in civil engineering," engineering, technology & applied science research, vol. 12, no. 2, pp. 8306–8310, apr. 2022, https://doi.org/10.48084/ etasr.4693. 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[32] j. h. ko, z. ma, x. jin, and q. xu, "effects of aeration frequency on leachate quality and waste in simulated hybrid bioreactor landfills," journal of the air & waste management association, vol. 66, no. 12, pp. 1245–1256, dec. 2016, https://doi.org/10.1080/10962247. 2016.1209596. microsoft word etasr_v13_n1_pp10039-10044 engineering, technology & applied science research vol. 13, no. 1, 2023, 10039-10044 10039 www.etasr.com benbouza et al.: behavior of strip footings above voids in sandy soil behavior of strip footing/s above void in sandy soil assma benbouza lgc-roi civil engineering laboratory, department of civil engineering, faculty of technology, university of batna 2, algeria as.benbouza@univ-batna2.dz tarek mansouri lgc-roi civil engineering laboratory, department of civil engineering, faculty of technology, university of batna 2, algeria t.mansouri@univ-batna2.dz khelifa abbeche lgc-roi civil engineering laboratory, department of civil engineering, faculty of technology, university of batna 2, algeria k.abbeche@univ-batna2.dz received: 17 november 2022 | revised: 4 december 2022 | accepted: 12 december 2022 abstract this paper presents a numerical study that utilizes finite element analysis under the plain strain condition performed on sand with isolated strip footing and two closely spaced strip footings above a continuous void. the bearing capacity ratio (bcr) and the efficiency factor ζγ were introduced to determine the effect of the void on the ultimate bearing capacity of footing/s. the influence of various parameters including spacing (s/b) (i.e. edge to edge) between the two interfering footings along with the location and the shape of the void were studied. in general, the results indicate that the presence of a void reduces the bearing capacity and affects the performance of footing/s and there is a critical value of s/b beyond which the effect of the void on the bearing capacity of the interfering footings becomes negligible. keywords-bearing capacity; strip footing; finite element method; underground voids; granular soil; interfering footings i. introduction during the recent years, urban development has been one of the algerian government's top priorities, which has greatly reduced the amount of land available for the construction of projects, thus, it has become impossible to avoid constructing buildings close to each other in order to make the most of the land and reduce cost, but this type of construction can have an influence on the bearing capacity of the foundations. the calculation of the bearing capacity of shallow footings is usually done using a method similar to that developed in [1] for isolated footings. in reality, footings are rarely isolated and interfere with each other to some extent. shallow footings interference has been studied theoretically in [2] using the limit equilibrium method and the stress characteristic method. authors in [3] presented laboratory test results for two closely spaced footings on sand. they found that the interference factors are generally lower than those predicted by theory. authors in [4] studied the interaction between two closely spaced rough and smooth strip footings on dense and loose sand. authors in [5] used the method of characteristics for two different failure mechanisms. authors in [6] used the upper bound limit analysis for finding the interference effect of two nearby strip footings on sand. authors in [7] examined the closely spaced footings on geogrid-reinforced sand, and authors in [8] studied the interference effect of strip and square footings on sand reinforced with geosynthetics. authors in [9] studied numerically the bearing capacity of two interfering strip footings on sands. authors in [10] studied the failure surface in granular soil under two closely spaced strip footings and concluded that the failure patterns observed for granular soil conform to those proposed by the theory in [2]. authors in [11] experimentally studied the interference effect of two closely strip footings constructed on bi-layer soil. authors in [12] studied experimentally and numerically the interference of closely spaced square footings on sandy soil, and concluded that the maximum interference effect is observed when the spacing between the two footings is 0.5b, and was approximately negligible when the spacing between the footings was equal to 2b, where b is the footing's width. engineering, technology & applied science research vol. 13, no. 1, 2023, 10039-10044 10040 www.etasr.com benbouza et al.: behavior of strip footings above voids in sandy soil the existence of underground voids (e.g. natural or artificial caves) may be attributed to two reasons: dissolution of soluble materials (e.g. salt, dolomite, and limestone) and artificial underground activities such as tunneling, mining, subway excavations, etc. these voids could cause serious engineering problems leading to poor performance of shallow foundations, structure collapses, road settlements, etc. which need special attention in engineering practice. in many cases, footings are positioned on soil containing voids that are either not visible before construction or are formed after the construction. several studies on the subject are available and some of them deal with cavity-footing interaction, e.g. [13], while others studied experimentally, theoretically, and numerically the effect of a void on the stability of shallow footings [14-18, 19]. other studies investigated the yielding pressure of strip footings above multiple-shaped cavities using fem [20, 21]. authors in [22] adopted fe analysis to estimate the undrained bearing capacity of surface strip footings above one and two voids. authors in [23] studied with fem the behavior of shallow strip footing on twin voids and clarified the failure mechanism. authors in [24] investigated the ultimate bearing capacity and failure mechanism of strip footings subjected to vertical load placed on c-φ soil with square voids. the critical and adverse locations of voids were analyzed. authors in [25] investigated numerically the undrained stability of strip footings above voids in two-layered clays. using finite element limit analysis, the undrained bearing capacity factor ns of strip footings has been calculated and the effect of the thickness of the top layer and the effect of undrained shear stress ration on ns were studied. in case of slope, a numerical study was conducted to analyze the bearing capacity behavior of strip footings on a reinforced sand slope with a single circular void [26]. further investigations have been carried out on the effect of artificial cavities on deep foundations [27, 28]. the influence of voids on the performance of shallow interfering footings has not been well covered or is not available in the literature. for this reason, this study aims to investigate numerically the effect of interference of two closely spaced strip footings above single continuous void in sandy soil. the main purpose of this study, in order to evaluate the bearing capacity of strip footing/s above void, was to reveal the effect of various parameters, such as the spacing (s/b) (i.e. edge to edge) between two footings, the shape and the location of the void, on the ultimate bearing capacity. ii. problem definition the geometry and the key parameters of the problem analyzed in this paper are illustrated in figure 1. the geometry consists of an isolated rigid strip footing and two closely spaced rigid strip footings with b and s representing the footing width and the spacing between the two footings respectively. they are placed on the horizontal surface of an isotropic homogenous soil of friction angle φ and unit weight γ. a static vertical load is imposed. by considering the case of zero surcharge and zero soil cohesion, the bearing capacity formula reduces to: q� = � � γbn ζ (1) where ζγ is the efficiency factor which is function of s/b and φ. fig. 1. schematic view of footing/s and void. in case of voids below the footings, one square and one circular voids were adopted in this study. shape and location of the void and the spacing between voids are quantified in terms of dimensionless parameters, i.e. m, n, α. parameters m and n represent the void height and width or diameter normalized by the footing width b and they are equal to 1 in this study. parameter α designates the relative vertical distance from the centerline of the footing to the void normalized by b. the configuration of a single square or circular void is shown in figure 1. according to [20], the void continuously extends horizontally. furthermore, the ratio of void width to the width of the strip footing is equal to 1, which corresponds to the presupposition of [22]. iii. finite element model the commercially available finite element program plaxis was used to model the footings-voids system. the behavior of soil was numerically simulated as an elasticperfectly plastic material considering mohr–coulomb failure criterion in conjunction with a non-associated flow rule ( i. e. φ ≠ ᴪ ).the values of the geotechnical properties are: young's modulus e = 30mpa, poisson's ratio ν = 0.2, bulk unit weight γ = 20kn/m 3 , and friction angle φ =35°. the soil was modeled with 15-node triangular elements. furthermore, figure 1 shows two shapes of void: the continuous circular void which is considered as a tunnel without lining and the continuous square void which is introduced by excavation of the soil at the desired depth, to model a natural cavity. thus the vertical and horizontal limits of this model are chosen appropriately far to avoid any influence on the results [17]. the dimensions of the area for this analysis are 15b in vertical and 30b in horizontal taking that b=1m. figure 2 shows a engineering, technology & applied science research vol. 13, no. 1, 2023, 10039-10044 10041 www.etasr.com benbouza et al.: behavior of strip footings above voids in sandy soil schematic of the boundary conditions and the finite element mesh used in the current study. the vertical borders have been fixed in the horizontal direction and full fixities have taken place at the bottom of the model. the mesh is refined in the area adjacent to the footings and around voids to enhance the accuracy of the numerical results. the footings are considered very stiff and rough. in this study, instead of modeling the footing itself, the settlement of the footing is imposed by means of a uniform indentation at the top of the sandy layer until the ground reaches the failure state. the uniformly displacement is automatically decided with trial calculations in the program. because of the symmetrical nature of the problem and in order to reduce the time required for each run, only half of the model was taken in the numerical simulation. fig. 2. finite element mesh with boundary conditions. iv. test program a total of 98 parametric tests were performed on the loadbearing capacity of rigorous strip foundations resting on one cavity of circular or square shape, as shown in table i. table i. details of numerically model tests test series footings number shape of voids variable parameters fixed parameters α s/b a isolated footing without void / / n=m=b=1m φ=35° l/b=1 with a circular void 1 2 3 4 5 6 7 and 8 / with a square void 1 2 3 4 5 6 7 and 8 / b two interfering footings without void / 0 0,5 1 1,5 2 3 4 5 and 6 with a circular void 1 3 5 and 7 0 0,5 1 1,5 2 3 4 5 and 6 with a square void 1 3 5 and 7 0 0,5 1 1,5 2 3 4 5 and 6 the efficiency factor ζγ was introduced to determine the influence of the void on the ultimate bearing capacity. ζγ is expressed as: ζγ= �� ��� � �� ���� (2) where q� ��� � is the ultimate bearing capacity of two strip footings with or without void, and q� �� ! is the ultimate bearing capacity of an isolated strip footing without void. v. validation to validate the numerical model, the bearing capacity factor nγ of a single strip footing on sand is calculated. the obtained nγ value is compared with the results from the literature while the friction angle is equal to 35°. as shown in table ii, the result of this study is remarkably close to that given in the literature. this good accordance can be taken as a validation of the present numerical model. table ii. values of bearing capacity factor nγ reference [1] [29] [30] [31] current study nγ 45.41 37.15 48.03 33.92 45.72 vi. results and descution a. single strip footing in soil with and without void the bearing pressure-displacement curves for the strip footing in soil without void and with a circular or square void are shown in figure 3. for all cases, the footing reaches a clear limit load, which was taken as the ultimate bearing capacity. the presence of the void has a big influence on the bearing pressure. the magnitude of bearing pressure is higher for the soil without a void, therefore the presence of voids in the soil reduces bearing capacity. in addition, the magnitude of bearing pressure for a soil with circular void is slightly higher than for a square void. fig. 3. bearing pressure-displacement (α=3). 1) effect of void depth from the single footing base the influence of α on the bearing capacity is presented in figure 4 which shows the relationship between the bearing engineering, technology & applied science research vol. 13, no. 1, 2023, 10039-10044 10042 www.etasr.com benbouza et al.: behavior of strip footings above voids in sandy soil capacity ratio (bcr) as a function of the void depth α. bcr is defined as: bcr= �� ���� � �� ���� (3) where q� �� ! � is the ultimate bearing capacity of an isolated strip footing with void and q� �� ! is the ultimate bearing capacity of an isolated strip footing without void. as can be noticed in figure 4 the bearing capacity ratio increases linearly when the value of α increases from1 to 4 for circular void and from 1 to 5 for square void and remains almost constant thereafter for either circular or square void. the bcr recorded is 0.14 to 1 for α ranging from 1 to 8. this indicates that the existence of circular or square void under the foundation at a depth equal to or greater than 6 times the foundation width does not affect the bearing capacity of the footing and the void impact is eliminated. these results are in accordance with the findings of [24]. also, it is observed from figure 4 that the values of the bcr for the circular void case are larger than those of the bcr for the square void case. fig. 4. variation of bcr as a function of α. b. interfering effect of two strip footings with and without void 1) two adjacent strip footings without void the results of numerical analysis obtained by the plaxis code shown in figure 5 prove that for 0 ≤ s/b ≤ 1, the efficiency factor (ζγ) magnitude increased to its maximum value, which means that the ultimate bearing capacity of each strip footing increases almost by 60% and for 1 ≤ s/b ≤ 4, ζγ decreases with an increase in spacing ratio. finally, for s/b ≥ 4, ζγ remains constant. this means that for a spacing ratio greater than 4b, no interference effect was observed and each footing acted as an isolated footing. to verify the accuracy of the results obtained by the present study, they were compared with the obtained numerical analysis results from [8, 9], theoretical analysis [2], and experimental test [3], which are presented in figure 5. fig. 5. comparison between the literature values and present study. it appears that the general trend of interference factor variations found in this study is similar to those predicted by other studies, but there is a large variation in amplitudes between theory, the experimental, and the numerical results. from this figure, the numerical results agree very well with the experimental test results [10]. 2) two adjacent strip footings with a single, square or circular void figure 6 indicates the variation of ζγ with different spacing ratios s/b for two interfering strip footings above a single circular or square void for a variation of void depths α=1, 3, 5, and 7 at 2m intervals, for a sandy soil with a void located in the centerline of the model. it can be noted that for s/b varying from 0 to 1.5 for circular void and from 0 to 2 for square void, the value of ζγ increases with increasing α until the void is present within a certain critical depth α which is about 7 for a circular void and a little higher for a square void. the influence of the void gradually becomes insignificant so only the interference effect of the two footings remains. when the footings are located away from the centerline of the model (i.e. when the s/b value increases), the efficiency factor magnitude increases with an increase in α and reaches the maximum value when s/b = 1 for α = 1, 5, or 7 and s/b = 1.5 for α = 3. in most cases ζγ decreases until the ultimate bearing capacity remains at 100% for s/b almost equal to 4, indicating no effect of the void on footing stability while there is not much interference effect. the only exception to this observation occurs when α = 1 where ζγ values are significantly lower and keep invariant approximately for s/b varying between 1.5 and 2.5 for a circular void and between 1 and 1.5 for a square void, particularity due to the effect of the stability of the soil above the void which is more dominant than that of the effect of footings' interference. ζγ continues its increase to reach 1 at s/b=6 for a circular void and almost 1 at s/b=6 for a square void, so the void effect is neglected and there is not much interference effect. on the other hand, for the case of a circular void, the ζγ for all values of s/b and α is more than that for the case of the square void shown in figure 6. it clearly can be observed that same remark in figures 3, 5, and 6, in which the values of bearing capacity for the circular void are larger than those of the bearing capacity for the square void, due to the section of the square void which is greater than that of the engineering, technology & applied science research vol. 13, no. 1, 2023, 10039-10044 10043 www.etasr.com benbouza et al.: behavior of strip footings above voids in sandy soil circular void and not to the shape of the void, therefore the effect of the void's shape can be neglected [32]. fig. 6. variation of the efficiency factor ζγ versus spacing ratio s/b for two interfering strip footings above a single circular or square void. vii. conclusion in this paper, the behavior of strip footings above voids in sandy soil has been investigated numerically, and the bcr and ζγ factors of footings have been calculated. in addition, the critical location of the void and the spacing between footings have also been discussed. the main conclusions of the current study are:  the presence of void has a big influence on bearing pressure. the magnitude of the bearing pressure is higher for a soil without voids, therefore the presence of voids in the soil reduces bearing capacity.  with single strip footing, the existence of a circular or square void under the foundation at a depth equal to or greater than 6 times the foundation width does not affect the bearing capacity of the footing and the void impact is eliminated.  with two interfering strip footings without void the results of numerical analysis proved that for a spacing ratio greater than 4b, no interference effect was observed and each footing acted as an isolated footing.  with two interfering strip footings with a void located in the centerline of the model, it can be noted that for values of s/b varying from 0 to 1.5 for circular void and from 0 to 2 for square void, the value of ζγ increases with increasing α until the void is present within a certain critical depth α which is about 7 for a circular void and a little higher for a square void. the influence of the void becomes insignificant so only the interference effect of the two footings remains.  there is a critical value of s/b 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[32] a. al-tabbaa, "model tests of footings above shallow cavities," ground engineering, vol. 22, no. 7, pp. 39–42, oct. 1989. microsoft word etasr_v13_n1_pp9947-9954 engineering, technology & applied science research vol. 13, no. 1, 2023, 9947-9954 9947 www.etasr.com sahu et al.: implementation of crow search algorithm for achieving optimal control of a single-link … implementation of crow search algorithm for achieving optimal control of a single-link flexible manipulator venkata satya durga manohar sahu school of electrical engineering, kalinga institute of industrial technology, deemed to be university, india manohar17.me@gmail.com (corresponding author) padarbinda samal school of electrical engineering, kalinga institute of industrial technology, deemed to be university, india padarbindasamal87@gmail.com chinmoy kumar panigrahi school of electrical engineering, kalinga institute of industrial technology, deemed to be university, india panigrahichinmoy@gmail.com received: 30 september 2022 | revised: 29 october 2022 | accepted: 16 november 2022 abstract a metaheuristic optimizer based on the cognitive behavior of crows, called the crow search algorithm (csa), is suggested in this paper for the optimization of the performance of the single link flexible manipulator as a constrained optimal control problem, which comprises objective functions, constraints, and decision variables. the csa outperformed other algorithms, such as differential evolution, grey wolf optimization, and particle swarm optimization. parameter setting is another highlight of the current paper. in conclusion, csa yields more promising results than other approaches. keywords-optimal control system; crow search algorithm; single link flexible manipulator i. introduction optimization has played a critical part in a wide range of problems during the last few decades. engineers have relied on conventional search methods for decades to solve design problems. despite the fact that these approaches give promising outcomes, they may fail in more complicated design challenges. optimization problems are often complicated due to their complex objective functions, a substantial amount of decision variables, and many constraints. so, traditional optimization strategies often have limited effectiveness. the decision parameters may be too many and their influence on the objective function can be complex in real-world design challenges [1]. this means that the objective function might have multiple local optimal solutions while the design is only interested in the optimal global solution. these challenges can’t be solved by conventional methods that only discover local optima in a specific location. we need efficient optimization methods in these situations. consequently, authors in [2] developed a new field of research called swarm intelligence (si) in the late 1980s, which is still being explored today. today’s trend is to use natural metaheuristic algorithms [3, 4] to solve challenging issues, and metaheuristics have been proved to be surprisingly efficient. metaheuristic algorithms have shown promising performance in handling the most severely nonlinear and multimodal real-world optimization problems. particular randomization and local search are used by all metaheuristic algorithms [5]. these methods can find good answers to challenging optimization problems, but optimum solutions cannot be found. however, it is hoped that these methods will work in most cases. it is possible to use metaheuristic algorithms for global optimization. single-link flexible manipulators are often formulated as optimization problems [6-9] in order to optimize the performance index while meeting various constraints. as it has the potential advantage of lower cost, larger work volume, higher operational speed, greater payload-to-manipulatorengineering, technology & applied science research vol. 13, no. 1, 2023, 9947-9954 9948 www.etasr.com sahu et al.: implementation of crow search algorithm for achieving optimal control of a single-link … weight ratio, smaller actuators, lower energy consumption, better transportability, and safer operation due to reduced inertia over traditional heavy and bulky robots. the main drawback of these manipulators is the vibration problem caused by their poor rigidity [2]. the lagrangian-assumed modes technique [10] is used to create a dynamic model of a single-link flexible manipulator. controlling was conducted by various law [11] and intelligent techniques [12, 13]. an overall goal is to maximize system characteristics [14] for accessibility, which is represented by a vector. particle swarm optimization (pso) algorithm was used to model a flexible manipulator system in [15]. an optimization technique begins by creating an objective function capable of generating the problem objectives without removing any constraints in order to identify the best feasible solution. according to the glover convention, all current procedures influenced by nature are considered metaheuristics [16]. differential evolution (de) algorithm [9, 17], based on natural selection and pso which is based on bird flock and fish schooling social behavior [18], are some of the best-known metaheuristic algorithms. the crow search algorithm (csa) [19] was presented in 2016. the social intelligence and food-collecting mechanism of a crow group are included in the design. crows are a bird species that has expanded far across the globe and are considered very intelligent. they can memorize faces, utilize tools, communicate, and conceal food in various complicated ways. the main objectives of the work at hand are:  parameter setting is done with the manipulator model using the proposed approach.  performance comparison of the proposed csa with the existing de, pso, and grey wolf optimizer (gwo).  the csa's ability to identify an appropriate alternative strategy for addressing complex engineering optimization problems is investigated. ii. problem formulation an optimization problem [20] is the objective of identifying the optimal solution among all possible options. optimization problems can be classified as either unconstrained or constrained based on whether the variables are discrete or continuous. this section uses the slfm to formulate the optimal control problem [9] described in detail. a. modeling of the dynamic system regarding the modeling of the dynamic system, assume the following set of state equations: ( ( ), ( ), )z g z t v t tɺ (1) where z is a state vector, v is a manipulator control torque input vector, t is continuous-time, and g is a vector function. b. performance index an objective function or its inverse (referred to as a profit function, fitness function, utility function, or a reward function in some disciplines) is an objective function that should be maximized. it is referred to as: 0 ( ) ( ( ), ) ( ( ), ( ), ) ft f f t j v z t t l z t v t t dt    (2) l is a real-valued state function and the input vector that may or may not be explicitly time-dependent depending on the situation. the cost function is a term that is often used to describe this function. the function is a real-valued function of the vector of the final state and its time vector, with the final state vector serving as the input. when it comes to quality, a performance index should be constructed, so that it is constrained from below, and the higher the index, the poorer the controller’s performance. for example, ensuring that the first term in (2) and the integrand in the second term are positive for all values of ( ), ( )z t v t and t, may be achieved by requiring. the first term in (2) denotes a constraint on the state vector’s final or terminal value. the value of the performance index decreases as the end state vector approaches the desired value. after specifying the cost function and constraint, the objective is to find the optimal controller, that is, the value of the control signal ( )v t for the time period 0 ft t t  that yields the lowest values j under the assumption that the state vector obeys the state equation (1). c. constraints when solving an optimization problem, a constraint is a requirement that the solution must meet. there are numerous different types of constraints, the most common of which are equality constraints, inequality constraints, and integer constraints.  inequality constraints exist when a function has a border or limitations, e.g. less than equal to, less than, greater than, greater than equal to, and is expressed as: ( ( )) 0g z t  (3) where g(.) denotes the limitations imposed by inequality on the vector mapping of the state variables.  equality restrictions exist when a function is just the equal to the requirements, i.e. it perfectly matches the value of the resource, and they are expressed as: ( ( )) 0z t  (4) where (.) represents equality constraints of the state variables. it’s possible that this variable is a state or a control variable. it may alter based on the problem’s design and demand. this variable may have limits on rare occasions. it’s referred to as: min max( )v v t v  (5) where (.)v is a control variable with lower and upper limits. correspondingly, state variables may be specified based on the design and demand, but it is more complicated to identify boundary values, although a set of minimum and maximum values are used for estimations. our ultimate objective is, therefore, to achieve the best value possible. engineering, technology & applied science research vol. 13, no. 1, 2023, 9947-9954 9949 www.etasr.com sahu et al.: implementation of crow search algorithm for achieving optimal control of a single-link … d. optimal control problem (ocp) formulation consider the following description of an ocp [21] to be designed: 0 min max min ( ) ( ( ), ) ( ( ), ( ), ) su ) bjected to ( ) ( ( ) 0 ft v k f f t j z t t l z t v t t dt v v t g z t v        (6) where j is the performance index, with state constraints g(.) and control constraints ( )v t .the dynamic model of the slfm assessed the performance index as well as inequality and equality constraints. for example, in [7, 8, 21], we determine the best solution to the given issue using the csa and the constrained performance index. e. example 1) single-link flexible manipulator model assume a flexible manipulator model [6, 22, 23], as shown in figure 1. fig. 1. flexible link manipulator.   1 sin( ) sin( ) 0 h l l l s j j j mgh j j k mgh                     ɺɺ ɺɺ ɺɺ ɺɺ (7) let us assume the above equation by considering: 21 3 4 , , , z z z z      ɺ ɺ (8) and the above equation can be rewritten as follows: 1 3 2 4 2 2 3 2 3 2 2 4 2 3 1 2 2 1 1 sin( ) m g m gs h m h m h m g m gs h m h m h s z z z z k k k kk z z z v j r j r j k k k kk z z z v j r j r j kmgh z z z j j             ɺ ɺ ɺ ɺ ⋯ ⋯ (9) where m is the arm end mass, j1 is the inertia of the arm, g is the gravity acceleration, bm is the rotational friction, jh is the moment of inertia of the motor, r is the radius, z1 is the arm end position (i.e. the angular position of the motor θ), z2 is the arm axis velocity (i.e. the angular displacement of the flexible joint α), z3 is the arm position, z4 is the arm end velocity. the parameter values are taken from [6]. 2) control requirements initially, consider the manipulator was at t z=[ 0.09 0.09 0.09 0.09 ] and we wish to move it into the desired position, e.g. [0 0.4 0 0] tz  at t =0.78s with the following constraints on the velocity and control signal: 2 ( ) 0.4, [0, 0.78] 10 ( ) 10, [0, 0.78] z t t v t t       (10) 3) formulation as a constrained optimal control problem the ocp is defined and formulated as: 0 2 2 2 1 2 ft t j z z v dt   (11) subject to: 1 3 2 4 2 2 3 2 3 2 2 4 2 3 1 2 2 1 1 2 sin( ) ( ) 0.4 0 10 ( ) 10 m g m gs h m h m h m g m gs h m h m h s z z z z k k k kk z z z v j r j r j k k k kk z z z v j r j r j kmgh z z z j j z t v t                                   ɺ ɺ ɺ ɺ (12) iii. solution methodology csa [19, 22], is based on the foraging behaviors of crows. crows have various distinct characteristics that they display while hunting for food. when compared to other bird species, they have a large memory for remembering the locations of potential food stocks. crows steal their owner's food supply after following other birds to food hiding locations. the crow moves the food source from its current site to one that is more barren as it scavenges the available food in order to protect it from other crows. each point in the search space indicates a solution in the context of crow. crows have been observed to watch other birds, noting where they keep their food and then stealing it once the owner has left. if it has previously been a victim of theft, a crow will take extra precautions, such as changing hiding places, to avoid being a victim again. the previous behavior of an individual may be used to predict the future behavior of a thief and find the safest strategy to safeguard their stockpiles from theft. based on the aboveengineering, technology & applied science research vol. 13, no. 1, 2023, 9947-9954 9950 www.etasr.com sahu et al.: implementation of crow search algorithm for achieving optimal control of a single-link … mentioned intelligent behaviors, the population-based metaheuristic algorithm, csa, is implemented in this study. to attain the objectives, we must follow specific principles:  crows live in groups of individuals (flocks).  crows memorize their hiding places.  crows congregate in order to steal.  crows use measures to protect their caches against stealing. each crow is required to make a move based on 1 of the 2 fundamental csa rules: either protect its own hiding place or find the locations of other members. imagine, for instance, that a crow decides on iteration iter to steal food from a hiding spot. depending on the situation, either (1) the individual crow is not aware that it is being watched, or (2) the individual crow recognizes the presence of the plunderer and acts dishonestly. according to the first scenario, the crow may discover and pillage the hiding location. the crow can be relocated as follows: , 1 , , , , ( ) i iter i iter i iter i iter i iter iz z r fl m z       (13) where ir is a random number with an even distribution between 0 and 1 and ( , )i iter fl signifies the flight length of the crow i at iteration iter. it’s worth noting that ( , )i iter fl is a parameter of the algorithm and can affect the method’s search capabilities. assume that smaller fl values result in a local search near ( , )i iter z , whereas more significant values of fl expand the search space. in terms of optimization, smaller fl values contribute to the intensification of the results, whereas more significant fl values contribute to the diversification of the results. both high-intensification and high-diversification are desirable properties of an efficient optimization technique. alternatively, the th j crow might think a fellow flock member is chasing it (say the th i crow). the thj crow flew erroneously over a non-hideout area to guard its food source. if the th i crow is arbitrarily placed in the d-dimensional option space, the csa can repeat the operation. therefore, for the 2 conditions mentioned above, the crows' tailing motion may be explained as follows: ( , 1) , 1 , , , , rand() ( ) random crow position otherwise i iter i iter i iter i iter i iter i iter i z z ap z r fl m z               ⋯ ⋯ (14) in metaheuristic algorithms, diversity and intensity should be well-balanced. when it comes to csa, the system is essentially deepened and diversified by the awareness probability (ap) component. when a suitable solution already exists in place, csa is more likely to look locally by lowering the ap. low ap levels can be used to boost intensity. however, when knowledge grows, there may be a chance to find a workable solution, and csa often expands the search area globally (randomization). the use of high ap values enables the achievement of greater variation a. csa implementation for οptimization the step-wise procedure for the implementation of csa is given in this section. step 1: initialize parameters ap, flight length fl , randomly initialize the control variable. step 2: initialize the crows’ position and memory. step 3: estimate fitness (objective) function. step 4: generate new position using (14). step 5: inspect the possibility of new positions. step 6: update fitness of new positions step 7: update the memory step 8: verify that the end criteria has been met repeat steps 4–7 as many times as necessary until the maximum number of iterations is reached. after that, an optimal memory position in terms of the objective function’s value is provided to solve an optimization problem. b. crow search αlgorithm pseudocode initialize the parameters randomly initialize the position of n crows flows in the search space assess position, performance, and fitness state the crow memory while termination conditions not satisfied for n of the flock's crows pick a crow at random from the group state awareness probability if rand()>ap , update the position using (13) else update the position randomly end if end for assess the new performance and fitness with the new crow’s position update the crow’s memory end while iv. simulation results and discussion optimal control problems can’t be solved by a single search algorithm. another way to put it is that one algorithm may answer some problems better and others worse than other algorithms. for a fair evaluation of the proposed csa, problems are discussed and solved. csa has been run successfully on a laptop with an i5 processor and 16gb of ram in matlab environment. the flowchart of csa implementation can be seen in [24]. a. csa paramater setting for implementation optimization the csa's parameter settings have been optimized in a number of ways for 50 runs and 450 iterations. according to engineering, technology & applied science research vol. 13, no. 1, 2023, 9947-9954 9951 www.etasr.com sahu et al.: implementation of crow search algorithm for achieving optimal control of a single-link … tables i-iii, the best performance index obtained by csa is 0.001985 and 0.001982 for the single link flexible manipulator. fair ap values produce better results, nevertheless, bigger values of ap are suggested to avoid becoming trapped in local optima. if ap remains constant (ap = 0.1) and the value of fl is increased from 0.3 to 4, it is projected that the overall performance of csa will be improved on average. in table i, the impact of the ap is shown to assess the csa’s performance. ap and fl have been set to 0.1 and 2, respectively, in csa. csa is also analyzed to see how different parameter settings affect its performance. ap and fl values influence the results for the slfm, as shown in tables i and ii. table i shows that ap = 0.25 results in csa poor performance. figure 2 shows its impact. in table ii, it can be seen that when the value of ap is adjusted to 0.1, and the value of fl is increased from 0.3 to 4, the overall performance of the csa improves. as a result, fine tuning csa, like other optimization methods, is a process best accomplished by trial and error. the impact of the flight length can be observed in figure 3. table i. impact of varying ap values for fl=2 performance index (j) ap = 0.1 ap = 0.25 ap = 0.5 ap = 0.75 best value 0.00200 0.002645 0.001985 0.001998 worst value 5.1851 18.591 17.1683 8.839 mean 0.0967 0.3692 0.1079 0.038 standard deviation 0.4213 1.4912 0.8261 0.5583 table ii. the effect of fl on the performance of csa index fl = 0.3 ap = 0.1 fl = 0.5 ap = 0.1 fl = 1 ap = 0.1 fl = 1.5 ap = 0.1 fl = 1.75 ap = 0.1 fl = 2 ap = 0.1 fl = 3 ap = 0.1 fl = 4 ap = 0.1 best value 0.0073622 0.007324 0.016931 0.00496991 0.00883244 0.00200153 0.00256202 0.00250375 worst value 10.1884 11.9041 5.5145 15.0302 8.1574 5.1851 21.1613 10.3002 mean 0.9474 0.2573 0.3259 0.0733 0.1488 0.0967 0.129 0.1551 standard deviation 1.6151 1.1226 0.7193 0.6806 0.7486 0.4213 1.3639 0.7575 table iii. the effect of iteration number on the performance of csa index 500 1000 1500 2000 2500 3000 3500 4000 5000 best value 0.002002 0.001982 0.002217 0.001985 0.00198 0.001989 0.002019 0.001994 0.001988 worst value 5.1851 12.3677 16.9836 22.2053 9.3461 16.9836 8.2768 8.2161 16.9836 mean 0.0967 0.1526 0.0845 0.08 0.0196 0.0433 0.0181 0.0316 0.0268 std 0.4213 1.0856 0.8877 0.777 0.2444 0.636 0.3138 0.2933 0.493 fig. 2. the impact of varying ap values on csa performance. fig. 3. effect of fl on the performance of the csa. fig. 4. effect of iteration number on the performance of csa. from table iii we can note that by increasing the iteration number more than 2000 and by keeping the ap as 0.1 and fl as 2, the performance remains almost the same, showing poor performance which can be clearly seen in figure 4. b. comparison analysis of de, pso, gwo, and csa optimal control problem can be solved by using the csa parameters as shown in table iv. the statistical findings produced using csa are compared in table v. in comparison to the other methods on the slfm, the results suggest that csa delivers promising results. when it comes to the best index, csa surpasses de, pso, and gwo. in this example, csa’s results are roughly 45% more accurate than the other methods used in terms of performance. 0.1 0.175 0.25 0.325 0.5 0.625 0.75 1.8 2 2.2 2.4 2.6 2.8 3 x 10 -3 p e rf o rm a n c e awareness probability 0.3 0.5 1 1.5 1.75 2 3 4 0 0.005 0.01 0.015 0.02 p e rf o rm a n c e i n d e x (j ) flight length(fl) 500 1000 1500 2000 2500 3000 3500 4000 5000 1.95 2 2.05 2.1 2.15 2.2 2.25 x 10 -3 p e rf o rm a n c e iteration engineering, technology & applied science research vol. 13, no. 1, 2023, 9947-9954 9952 www.etasr.com sahu et al.: implementation of crow search algorithm for achieving optimal control of a single-link … table iv. utlizied csa parameters parameter value flight length 2 awareness probability 0.1 number of population 50 number of iteration 450 table v. slfm result comparison achieved by csa and other algorithms algorithm worst mean best std. convergence iteration de 1.3561 0.039259 0.0041536 0.15383 435 pso 1.8147 0.040232 0.003053 0.19363 363 csa 5.1851 0.0967 0.002109 0.4213 261 gwo 0.0709 0.0515 0.042707 0.0073 448 fig. 5. algorithm comparison graph. fig. 6. convergence graph of csa of slfm. fig. 7. arm axis position (z1) versus time (s) of csa. csa shows encouraging performance in terms of worst and mean indices. the std indicates the csa’s substantial flexibility. the csa's performance index value is minimum. the convergence rate of the csa for identifying the optimum slfm solution is shown in figures 5 and 6. the csa algorithm exhibits an excellent convergence rate. figure 7 explains the arm end position of the slfm which became stable 0.12 at nearly 0.7s and minimum position 0.088 at nearly 0.26s. figure 8 shows the comparison graph between the csa, de, pso, and bwo and it is clearly observed that there is more disturbance in gwo, which is unstable. table vi. comparison of de, pso, gwo, and csa for arm end position value csa de gwo pso maximum 0.1506 0.1238 1.4439 0.1239 minimum 0.0882 5.5226e-4 -0.2679 4.9009e-4 mean 0.1143 0.0293 0.5935 0.0290 fig. 8. comparison graph of arm axis position for de, pso, gwo, and csa. fig. 9. arm axis position (z2) versus time (s) of csa. table vi shows the minimum, maximum, and mean positions attained by the algorithm comparison. de, pso, and csa gave almost the same results of attained angular position, which can be observed clearly in figure 8. 0 50 100 150 200 250 300 350 400 450 0 1 2 3 4 5 6 no of iteration p e rf o rm a n c e de pso csa gwo 0 100 200 300 400 500 0 1 2 3 4 5 6 no of iteration p e rf o rm a n c e 0 0.2 0.4 0.6 0.8 0.08 0.1 0.12 0.14 0.16 a n g u la r e n d p o s it io n (r a d ) time(sec) 0 0.2 0.4 0.6 0.8 0 0.05 0.1 0.15 0.2 a n g u la r e n d p o s it io n (r a d ) tim e(se c) de 0 0.2 0.4 0.6 0.8 0 0.05 0.1 0.15 0.2 a n g u la r e n d p o s it io n (r a d ) tim e (s ec) pso 0 0.2 0.4 0.6 0.8 0.08 0.1 0.12 0.14 0.16 a n g u la r e n d p o s it io n (r a d ) tim e(se c) csa 0 0.2 0.4 0.6 0.8 -0.5 0 0.5 1 1.5 a n g u la r e n d p o s it io n (r a d ) tim e (s ec) gwo 0 0.2 0.4 0.6 0.8 -0.1 -0.05 0 0.05 0.1 a rm a x is v e lo c it y (r a d /s e c ) time(sec) engineering, technology & applied science research vol. 13, no. 1, 2023, 9947-9954 9953 www.etasr.com sahu et al.: implementation of crow search algorithm for achieving optimal control of a single-link … fig. 10. comparison graph of arm axis velocity for de, pso, gwo, and csa. figure 9 explains the arm axis velocity of the slfm. it can be seen that less velocity was required to move the slfm. figure 10 shows the comparison graph between the csa, de, pso, and gwo. table viii shows the minimum, maximum, and mean velocity attained by the algorithm comparison. table vii. comparison of de, pso, gwo, and csa for arm axis velocity value csa de gwo pso maximum 0.0900 0.0900 0.5039 0.0900 minimum -0.0644 -0.0515 -0.7292 -0.0510 mean -0.0127 -0.0018 -0.0070 -0.0017 fig. 11. applied torque versus time curve. table viii. comparsion of de, pso, gwo, and csa for the applied torque value csa de gwo pso maximum 0.1389 0.0018 10 0.0528 minimum 0.1196 -0.1874 -9.9246 -0.1862 mean 0.1295 -0.0398 0.0805 -0.0385 table viii compared the minimum, maximum, and mean torque applied to slfm by the considered algorithms. figure 11 gives an idea of how much torque is applied to slfm and we can see that for a small torque driven by slfm, it attains its position. figure 12 shows the comparison graph between the csa, de, pso, and gwo, in the presence of negative torque which leads the manipulator to brake on in order to move to the desired position. at the same time, csa has a positive torque which leads the manipulator to move to the desired position during the simulated period of time. fig. 12. comparison of de, pso, gwo, and csa for the applied torque and time. v. conclusion in this paper, crow search algorithm (csa), is proposed to solve ocp, i.e. slfm. the two regulating factors in csa are flight duration and awareness probability. csa is simpler to utilize and has fewer factors to adjust than de, pso, and gwo. the simulation results show that the csa performance is promising since it provided results that were competitive with those of the other methods. despite the reputation of the pso as a quick approach among population-based algorithms, csa's performance surpasses pso along with the other algorithms. references [1] m. i. ullah, s. a. ajwad, m. irfan, and j. iqbal, "non-linear control law for articulated serial manipulators: simulation augmented with hardware implementation," elektronika ir elektrotechnika, vol. 22, no. 1, pp. 3–7, feb. 2016, 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[24] b. zolghadr-asli, o. bozorg-haddad, and x. chu, "crow search algorithm (csa)," in advanced optimization by nature-inspired algorithms, o. bozorg-haddad, ed. singapore: springer, 2018, pp. 143– 149, https://doi.org/10.1007/978-981-10-5221-7_14. microsoft word etasr_v13_n2_pp10222-10227 engineering, technology & applied science research vol. 13, no. 2, 2023, 10222-10227 10222 www.etasr.com chew hernandez et al.: a stochastic simulator of a multi-component distillation tower built as an … a stochastic simulator of a multi-component distillation tower built as an excel macro mario luis chew hernandez technological institute of advanced studies of coacalco, mexico mario@tesco.edu.mx (corresponding author) leopoldo viveros rosas technological institute of advanced studies of coacalco, mexico leopoldo@tesco.edu.mx jose roberto perez torres technological institute of advanced studies of coacalco, mexico jose.roberto@tesco.edu.mx received: 15 december 2022 | revised: 30 december 2022 | accepted: 5 january 2023 abstract dynamic process simulation is widely used in teaching controller design, as it allows foreseeing the performance of different control configurations and controller tunings. currently, most college-level controller design exercises that are based on simulation consider deterministic perturbations (i.e. steps or ramps). in real life however, processes are more likely to face fluctuating, random disturbances, so the use of stochastic simulation in controller tuning exercises would provide students with an experience closer to their future professional practice than that provided by deterministic simulation. however, public institutions attempting to use dynamic, stochastic simulators in teaching, are hindered by the need of buying licenses of simulation packages or specialized programming languages (such as matlab), as there aren´t any dynamic, stochastic simulators available as downloadable freeware. this paper shows a dynamic, stochastic simulator with a friendly interface of a distillation tower, developed as an excel macro. this simulator has the advantage that it can be used at no cost to educational institutions since excel is almost universally known and used by college faculties. keywords-simulation; stochastic; distillation i. introduction dynamic simulators are very useful in the teaching of process control in college engineering, as they can be used to compare the performance of different control configurations (i.e. the linking of controlled and manipulated variables) and to optimize the tuning of controllers. however, almost all simulation-based learning experiences of control design use deterministic disturbances (e.g. ramp or step changes) to dynamically assess the candidate controller configurations or tunings [1]. in practice, however, process units are subjected to disturbances that are better described as stochastic, varying continuously and in an unpredictable manner. therefore, the engineering trainee would benefit from performing process control practices including stochastic disturbances. to carry out the said activities however, dynamic process simulators able to incorporate random elements (i.e. stochastic dynamic simulators) are needed. on the other hand, public institutions of higher education in developing countries are facing severe shortages of economic resources. this hinders their ability to use process simulators in their teaching activities, due to the need of purchasing user licenses. in the case of steady-state simulators, there are a few free software alternatives that have been sufficiently validated (e.g. the coco simulator [2]), however, this is not the case of dynamic simulators and certainly not of the subset of these able to handle random disturbances. this paper presents the development of a dynamic three-component distillation tower simulator with stochastic elements and a user-friendly interface (allowing user interaction via buttons and dialog boxes) created using microsoft excel macro functionalities. this allows the simulator to be run in said software, that is already being used by most developing countries college engineering faculties. a. literature review reviews of dynamic simulation applications for optimizing energy and chemical systems are shown in [3, 4], while applications of discrete event simulation to the optimization of industrial systems can be found in [4-6]. usage of simulation in engineering, technology & applied science research vol. 13, no. 2, 2023, 10222-10227 10223 www.etasr.com chew hernandez et al.: a stochastic simulator of a multi-component distillation tower built as an … specific situations are presented in [7] for sustainable plant design, in [8] for gasifier pressure modeling, and in [9] for analyzing a petrochemical process wastewater plant. additional applications include treating a desalination plant [10], optimizing the drying of phosphates [11], analyzing the benzene-toluene-xylene separation train from a sustainable point of view [12]. regarding the software used for the dynamic simulations, aspen dynamics and matlab have been used for studying separation tower trains [13], chemcad for modeling polymerization reactors [14], aspen hysis for treating energy-integrated reactors [15], and matlab and cosmol multiphysics for studying catalysts [16]. additionally, authors in [17] present a proposal for controlling combustion cycles using aspen dynamics, authors in [18] simulated a wastewater system using insel (integrated simulation environment language), and authors in [19] modeled a set of co2 absorbers for implementing a predictive control scheme, employing aspen and matlab. experiences on the didactic use of chemical process simulators are included in [20], where aspen hysis was used for training engineers in the handling of distillation trains and in [21] where honeywell unisim design was used in training operators of an isopropanol plant. regarding the reports on the development of home-grown process simulators in educational institutions for pedagogical purposes, authors in [22] describe the steady state simulator lazarus, run in uml and developed as a freeware with the option of incorporating modules from third parties, authors in [23, 24] developed programs to study the dynamics of heat exchanger networks, authors in [25] provided a web-based natural gas distribution system simulator, authors in [26] described the labvirtual learning platform which includes steady-state simulators, and authors in [27] presented a dynamic reactor simulator programmed in matlab. it can be noted that there is a growing preference for using commercial simulation software (e.g. aspen) and programming languages with pre-built routines for model construction (e.g. matlab) in reported research and pedagogical simulation applications. since both types of software require paid licenses, the reported applications are of little relevance to the teaching in public institutions which strive to optimize the spending of their limited budgets. in contrast, the simulator presented in this paper is programmed in microsoft excel. this program, even though not being freeware, is widely available to college staff as it comes with the ms office packages purchased by institutions for word processing and administrative tasks. additionally, none of the reported dynamic simulators built for teaching applications incorporates random disturbances. as in practice, process plant operation is affected by random disturbances, using stochastic dynamic simulators in teaching activities related to controller design and tuning, can better prepare the future engineer for operating real plants. ii. case study description a ten-plate distillation tower fed with a mixture of benzene, toluene and p-xylene is taken as a case study (figure 1). fig. 1. distillation tower case study. vr and vs are, respectively, the molar vapor flow in the rectifying and stripping tower sections, with lr and ls being the corresponding liquid molar flows. f, d and b are, respectively, the molar flow of feed, distillate, and bottom product, and q is the feed vapor fraction. the feed mole fraction of component i is xi,f (i=1,...,3). xi,j and yi,j denote, respectively, the mole fraction of component i in the liquid and vapor leaving the plates and the reboiler (j=1,... 10,r). the dynamic model used the following assumptions:  the molar flows of vapor and liquid in the stripping and rectifying sections are constant.  the plate (m) and the reboiler (mr) holdups are constant.  the mole fractions of the liquid and vapor in equilibrium follow raoult's law (1): pyi,j=pi 0 (tj)xi,j i=1,...,3, j=1,...,10,r (1) where p is the tower pressure and pi 0 (tj) the vapor pressure of component i at the temperature tj of stage j (j=1,...,10,r). vapor pressures follow antoine’s relation (2) with ai, bi and ci being component specific constants: ��� � ��� � � �� ����� (2)  the tower hydraulics are very fast, with the internal and external flows adjusting to changes in f, q, vs and r, which is the reflux ratio (lr/d), according to: vr=vs + qf (3) � � ������� (4) b=fd (5) engineering, technology & applied science research vol. 13, no. 2, 2023, 10222-10227 10224 www.etasr.com chew hernandez et al.: a stochastic simulator of a multi-component distillation tower built as an … ls=vs+b (6) lr=dr (7)  the mole fractions of the components in the feed xi,f (i=1,...,3), may fluctuate randomly. mole fractions add to one, so the dynamic model consists of two molar balances for each stage, resulting in 22 ordinary differential equations, i.e. (8)-(13), for i=1,2. plate 1: ���,� �� � ��� �,�!��,�"���� �,#! �,�" $ (8) plate in the rectifying section j=2,3,4: ���,� �� � �����,�%�!��,�"���� �,�&�! �,�" $ (9) feed plate: ���,' �� � (��,)��* �,+�����,,!�� �,'!�*��,' $ (10) plate in the stripping section j=6,....9: ���,� �� � �*���,�%�!��,�"��*� �,�&�! �,�" $ (11) plate 10: ���,��� � �*���,.!��,�-"��*� �,�! �,�-" $ (12) reboiler: ���,� �� � �*��,�-!���,�!�* �,� $� (13) equations (8)-(13) are integrated using an implicit euler method: defining a state vector x=[x1,1,x2,1,...,x1,r, x2,r] t , a disturbance vector d=[f,q,x1,f,x2,f] t , and a manipulated variables vector u=[r,vs] t , the value of x at time t+h, is obtained from its value at time t by solving the system of nonlinear equations (14), h being is the step size. /�0 1 ℎ� � /�0� 1 �/��3�/���4�,5���,6���" (14) fig. 2. main simulator interface. engineering, technology & applied science research vol. 13, no. 2, 2023, 10222-10227 10225 www.etasr.com chew hernandez et al.: a stochastic simulator of a multi-component distillation tower built as an … for simulating a tower with stochastic feed mole fractions, x1,f(t) and x2,f(t) are sampled from their probability distributions (using the methods described in [28]) and are substituted in (14) before solving these equations to calculate x(t+h). when running a controlled tower, an integral proportional logic (15) changes the reflux ratio r to control the temperature of a given plate in the rectifying section: 7 � 7� 1 8� 9� 1 �: ; �<0 � � = (15) where e is the deviation of the controlled plate temperature from its set-point, kc is the gain of the controller,  is its reset time, and r0 the initial value of the reflux ratio. iii. simulator description the simulator is given to the user as a macro-enabled microsoft excel file. by clicking the "begin simulation/show interface" button (figure 3) the main simulator interface is displayed (figure 4). the program works in desktop excel versions supporting visual-basic macros, i.e. those in ms office versions from 2010 onwards. fig. 3. initial screen when the excel file is opened. fig. 4. detail of the controls in the steady state interface section. fig. 5. controls for specifyng the inlet composition behavior. fig. 6. controls for defining the reflux ratio policy initially, only the controls in the "initial steady state calculation" zone appear active (figure 4). through these controls, the user specifies the steady-state condition the tower is in before the dynamic simulation starts. once the qualities of the feed, reflux ratio, and reboiler boil-up (vs) have been entered, by clicking the "calculate steady state" button the initial steady state of the system is calculated. the total error achieved in solving the steady state problem (that is formed by making the derivatives in (8)-(13) equal to zero) appears in the corresponding dialog box. the steady-state composition of the liquid in the plates and the flowrate and compositions of the outlet streams appear in the boxes placed on the plates and close to the outlets of the sketched tower (figure 2). once the steady-state solution has been achieved, the buttons associated with the dynamic simulation become active. the feed flowrate and vaporization and total simulation time are entered in the dialog boxes located to the left of the tower in figure 2. the probability distributions of the feed mole fractions, which are to be varying randomly, are defined through the controls in the section "inlet composition behavior" of the interface (figure 5). the control ratio to the left in figure 5 allows selecting how the behavior of the feed mole fractions of benzene and toluene is going to be. these mole fractions can remain constant or follow a probability distribution: uniform (specifying minimum and maximum values), normal (specifying mean and standard deviation), or triangular (specifying minimum, most likely and maximum values). the sampled feed mole fractions are standardized in case their sum exceeds unity and, as can happen when sampling from a normal distribution, if the simulated value is either negative or greater than 1, new values are produced until they lie in the required (0,1) range. figure 6 shows the interface section in which the reflux ratio management is defined. it can be set constant (by choosing "manual" and selecting its value) or used to keep the temperature of a rectifying plate close to its temperature at the initial steady state. the controller specifications are also entered here. the total absolute deviation (i.e. the absolute value of the deviation integrated along the simulated time) of the fraction mole of benzene in the distillate, with respect to its steady state value, is displayed in the relevant text box. engineering, technology & applied science research vol. 13, no. 2, 2023, 10222-10227 10226 www.etasr.com chew hernandez et al.: a stochastic simulator of a multi-component distillation tower built as an … once the simulation is complete, a dialog box asks the user if graphs of the simulation results are to be produced. if "yes" is answered, graphs of the controlled plate temperature and the mole fraction of benzene in distillate against time are displayed. these graphs are produced using the excel spreadsheet functionalities, as shown in figure 7. fig. 7. example of charts produced by the simulator. to illustrate the simulator results, the top chart of figure 8 shows the behavior of plate one temperature when the feed mole fractions of benzene and toluene are uniformly distributed between 0.1667 and 0.5. fig. 8. closed loop vs. manual operation contrast responses for a constant reflux ratio set to its steady state value, and for a manipulated reflux ratio controlling plate one temperature, with controller gain of 20 and reset time of 0.1h, are included. the bottom chart of figure 8 shows the corresponding behavior of the distillate mole fraction of benzene. the total absolute deviation of the distillate benzene mole fraction for the closed loop case is 0.0672, while that for the fixed reflux ratio case is 0.21. it is easy to visualize the usage of this simulator for training students in controller design under stochastic conditions, through exercises in which they need to tune the controller and select controlled plates so to minimize the benzene distillate composition deviation, and asking them to discuss the effect of the feed composition behavior on the results. iv. conclusions as there is a lack of freeware dynamic simulators, educational institutions seeking to use them in teaching must purchase licenses. this situation is exacerbated for dynamic simulators capable of including stochastic disturbances, as these are more specialized and have more expensive licenses than deterministic simulators. as in practice engineers need to control plants facing unpredictable, continuously varying disturbances, implementing process control exercises for engineering students using simulated stochastic disturbances can be a valuable preparation for their future practice. in this paper, a stochastic simulator intended for this purpose is presented. as the simulator runs in microsoft excel, that is already used in most engineering colleges, no specific license software is needed for its pedagogical use. a limitation of the simulator, however, is that 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[29] m. l. c. hernandez, l. v. rosas, and j. r. p. torres, "three component tower simulator.xlsm," google docs. https://drive.google.com/file/d/ 1zetawilv83lmynr2d5qzrsb2jhzvayjx/view?usp=sharing. microsoft word etasr_v12_n3_pp8723-8727 engineering, technology & applied science research vol. 12, no. 3, 2022, 8723-8727 8723 www.etasr.com saadi & yahiaoui: the effectiveness of retrofitting rc frames with a combination of different … the effectiveness of retrofitting rc frames with a combination of different techniques mohamed saadi lgc-roi, department of civil engineering faculty of technology, university of batna 2 batna, algeria m.saadi@univ-batna2.dz djarir yahiaoui lgc-roi, department of civil engineering faculty of technology, university of batna 2 batna, algeria d.yahiaoui@univ-batna2.dz received: 12 april 2022 | revised: 28 april 2022 | accepted: 28 april 2022 abstract-during the last two decades, the attention of researchers has been focused on repairing and retrofitting concrete frames to make them more earthquake-resistant. two methods have been developed to increase the seismic resistance of previously undamaged structures before they are subjected to an earthquake. the first is through the addition of new structural members, such as steel braces and the second is by selectively strengthening structural elements, for instance through steel caging. seismic response analysis results have been utilized in multi-story rc frames that were designed without seismic design criteria. this study aims to determine whether the retrofitting technique is effective based on comparisons between steel braces, steel cages, and their combinations. the seismic performance is defined by the seismic code for algeria rpa 2003 according to the latest recommendations. static nonlinear analysis was used to compare seismic responses of existing non-ductile reinforced concrete rc frames under a variety of retrofit schemes. the results show that retrofitting with steel caging gives excellent performance in terms of ductility and low shear capacity. the retrofitting with steel bracing increased the shear capacity but led to a severe ductility deficiency. the retrofitting structure combined with steel bracing and steel caging shows good performance in shear capacity and ductility. using the zipper system (steel bracing) and v system in combination with steel caging gives similar results to the rpa model. keywords-rc frame; retrofit; steel bracing; steel-cage technique i. introduction most structures before the '70s were designed to be able to resist gravity loads, and while these structures performed well under such loads, their performance under seismic loads was questionable. several recent earthquakes, such as those in taiwan (1999) and algeria (2003), have caused significant damages to buildings and many reinforced concrete structures collapsed because they did not comply with the current seismic codes and had deficiencies such as poor detailing, discontinuous load paths, and a lack of capacity design provisions. two main retrofitting approaches have been identified to improve the seismic performance of existing undamaged structures before they are exposed to an earthquake. one is the insertion of new structural elements such as structural walls or steel braces and the other is selective strengthening of deficient structural elements, for example by using concrete or steel caging and fiber reinforced polymers. for the first approach, steel bracing is typically used in the retrofitting of rc frames. this type of structure is efficient and economical for resisting lateral loads. among the first studies on retrofitting using this technique were [1, 2]. model tests have also been reported in [3]. their study indicated the effectiveness of this method in increasing the shear resistance capacity of the structure. two of the flaws of this method are architectural details and difficulties making connections between the steel bracing and the rc frames. authors in [4] performed experimental studies on the pushover response of scaled rc frames braced with both diagonal and knee bracing systems. authors in [5] investigated the seismic behavior of rc frames reinforced with various steel bracing systems, including x, inverted v, zx, and zipper systems. by adding bracing, they were able to improve deformation, strength, and ductility. it was found that x and zipper bracing systems perform better than others. authors in [6] examined the use of hysteretic dampers and column strengthening to develop the desired behavior of buildings with an open first floor. authors in [7] studied the impact of retrofitting rc frames with steel x-bracing on the global behavior of the frame, including its global displacement, performance level, and inter-story drifts. similarly, the authors in [8] analyzed the seismic response of steel x-bracing numerically and concluded that it greatly reduces the shear loads on the beam‒column joint. the maximum lateral displacement in rc frames is also reduced by retrofitting them with x-braces. in the tests conducted in [9], the joint displayed excellent self-centering properties without deteriorating in strength. the application of friction dampers to a self-centering pc frame was also studied for seismic retrofitting of reinforced concrete structures. a recent study [10] found that disk springs could provide self-centering capabilities without the drawbacks associated with post-tensioned tendons. the steel caging method is generally favored because of its high retrofitting effectiveness and economic efficiency [11-12]. authors in [13-16] first applied the steel-cage retrofitting method for bridge columns in california. authors in [17] studied the efficiency of rectangular solid steel caging and corresponding author: mohamed saadi engineering, technology & applied science research vol. 12, no. 3, 2022, 8723-8727 8724 www.etasr.com saadi & yahiaoui: the effectiveness of retrofitting rc frames with a combination of different … partial steel caging. authors in [18-19] described the effect of a partially stiffened steel caging and composite prefabricated jacket on improving the strength and ductility of rc columns. recently, authors in [20] suggested an extension of the previous works, introducing a new genetic algorithm that minimizes the cost of seismic upgrading. in the current study, a structure that was designed without seismic design criteria was retrofitted with three techniques: steel caging technique, steel bracing system, and their combination were studied and examined. the seismic performance of these frames was determined by nonlinear static pushover analysis. ii. description of different retrofitting procedures a. steel caging technique the application of metallic jackets in rc columns aims to increase shear strength and strengthen the lap-splicing region and the ductility capacity. the steel caging option involves the total encasement of the column with thin steel plates placed at a small distance from the column surface, with the ensuing gap filled with non-shrink grout. steel caging is now a common practice in many countries [21]. when the yield stress of the steel is increased, the ultimate load on the strengthened column increases [22, 23]. b. steel bracing technique steel bracing can be a very effective method for the global strengthening of buildings [24]. some of its advantages are the ability to accommodate openings, the minimal weight added to the structure, and, in the case of external steel systems, the minimum disruption to the function of the building and its occupants [25]. alternative configurations of bracing systems may be used in selected bays of a reinforced concrete frame to provide a significant increase in the horizontal capacity of the structure [26]. to improve the seismic performance of an existing reinforced concrete building, authors in [27] used steel bracing. three methods of seismic evaluation were employed in this study: the nonlinear static pushover as described in fema 356 [28] and fema 440 [29] and dynamic time history analysis. the retrofitting of an rc frame with the steel xbracing method can be seen in [30]. iii. description of the frame models a five-story rc building has been considered in this study (figure 1). the slabs were represented in the structural model of the building using their weight in the gravity load case and as concentered masses at all joints, with bay length of 4m and height of 3m. the building was designed without seismic design criteria, while it is located in a high seismicity region with a peak ground acceleration of 0.32g. table i shows the details of the design sections, where the characteristics of the original frame and the reinforcement of the beams and columns were determined according to the algerian seismic code (rpa 2003) [31]. to retrofit the structures with the bracing system, it is necessary to have studied the influence of variation in the section of the bracing element and different bracing systems (x, v, and zipper). figure 2 shows the rc frames retrofitted with different steel bracing systems. fig. 1. structural model. table i. reinforcement details columns beams orginal frame rpa frame fig. 2. bracing models. to retrofit the structures with steel caging, it is important to investigate the impact of retrofitting vertical and horizontal bays with steel caging. figures 3-4 show the retrofitting details and the models of retrofitting vertical and horizontal bays with steel caging respectively. in order to conclude the comparison between the bracing systems and to properly propose a reinforcement model close to the rpa model, a final comparison was made. a combination of the bracing systems with the steel caging was applied. 50×50×10 fig. 3. retrofitting details with steel caging. fig. 4. retrofitting with steel caging. engineering, technology & applied science research vol. 12, no. 3, 2022, 8723-8727 8725 www.etasr.com saadi & yahiaoui: the effectiveness of retrofitting rc frames with a combination of different … iv. results and discussion a. pushover results of the original and rpa frame the aim of the reinforcement of the structure is to increase the capacity of resistance to shearing, the ductility of the original frame, and to reach the capacity of new structures calculated by the rpa code. this starts with nonlinear static analysis in order to know the difference between the capacities of the two structures (original and rpa), and then the type of reinforcement is chosen. figure 5 presents a comparison between the capacity curves of the original frame and the rpa, showing that the base shear of the new structure is larger by 137.5%, and the ductility by 58%. fig. 5. curve of capacity for old and rpa structures. b. pushover results of different retrofitting systems figure 6 shows the results of the nonlinear analysis of the structure frame strengthened with different bracing systems (x, v, and zipper) and the variation in the cross-section of the bracing element. the results show that when the bracing section is increased, ductility is decreased and strength is increased, in accordance with the findings in [5]. the behavior of the different systems is much stiffer. the results show that the section of d76.1×3.2 for all the bracing systems except the x system gives a behavior close to the rpa frame with reference to the lateral load. compared to the original frame, for the retrofitting with the 76.1 tube section, the capacity of zipper, x, and v systems is increased by 2.3, 3.4, and 2.02 respectively. the highest ductility reduction factor is given by the zipper system with the 76.1 tube section which equals to almost 4.08. for the x and v systems, the ductility reduction factor is equal to 2.7 and 3.1 respectively. c. pushover results for steel caging technique figure 7 shows the lateral response of the structure frame with retrofitting with steel caging of the horizontal and vertical bays. the results show that whatever the reinforcement of the structures, whether horizontal or vertical, the ductility is almost identical to the rpa frame, but the lateral capacity is increased by 27.3% in comparison with the original frame. meanwhile, the results indicate that the lateral capacity with vertical reinforcement gives a smaller increase than the horizontal reinforcement. (a) (b) (c) fig. 6. lateral load–displacement response retrofitting with different steel bracing systems. fig. 7. lateral load–displacement response retrofitting with steel caging technique. engineering, technology & applied science research vol. 12, no. 3, 2022, 8723-8727 8726 www.etasr.com saadi & yahiaoui: the effectiveness of retrofitting rc frames with a combination of different … d. pushover results for retrofitting with steel bracing and steel caging figure 8 represents the lateral response of the structure frame with retrofitting of the vertical bays with steel caging and the different bracing systems (x, v, and zipper) at the same time. (a) (b) (c) fig. 8. lateral load–displacement response retrofitting with steel bracing system and steel caging. it is clear from figure 8 that the base shear was increased by 100% compared to the reinforcement with the steel bracing system only. the v and zipper system with the steel caging technique give almost the same curves as the rpa frame. the results show that the section of d76.1×3.2 for all the bracing systems gives a behavior close to the rpa frame with reference to the lateral load. compared to the original frame, for the retrofitting with the 76.1 tube section, the capacity of zipper, x, and v systems is increased by a factor 2.5, 3.02, and 2.4 respectively. the highest ductility reduction factor is given by the v system with the 76.1 tube section which equals almost to 8.25. for the zipper and the x systems, the ductility reduction factor is equal to 6.03 and 4.1 respectively. v. conclusion the main purpose of this research is the retrofitting of an rc frame that has been designed without seismic design criteria, and is located in a region of high seismicity. in the present work, the retrofitting of this structure was done by three techniques, namely the steel bracing system, the steel caging technique, and the combination of these two methods. the main results of the present work can be summarized as follows: • the results show that all systems have a given ductility for a small section and when there is an increase in the section of the bracing the ductility is decreased and the strength is increased. the behavior of different systems is much stiffer. • whatever the reinforcement of the structures, whether horizontal or vertical, the ductility is almost identical to the rpa frame. • retrofitting with zipper and v systems in combination with steel caging gives similar results to the rpa model. • the models with steel bracing and steel caging are good for predicting damage in the nonlinear analysis of rc structures. therefore, retrofitting for rc frames with a combination technique should take into account the two demand measures, midr and mid, particularly under nfd-hr and nffs earthquakes. references [1] i. sekiguchi, t. okada, m. murakami, f. kumazawa, f. horie, and m. seki, "seismic strengthening of an existing steel reinforced concrete city office building," in 9th world conference on earthquake engineering, tokyo, japan, aug. 1988, vol. vii, pp. 439–444. 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[31] "09 dtr b c 2 48 rpa 2003," calameo.com. https://www.calameo. com/books/000899869ad355520b3ae (accessed apr. 30, 2022). microsoft word etasr_v13_n3_pp10725-10730 engineering, technology & applied science research vol. 13, no. 3, 2023, 10725-10730 10725 www.etasr.com alnaqib & bazuhair: evaluation of hma modified with titan polymer evaluation of hma modified with titan polymer hassan m. alnaqib civil engineering department, college of engineering & islamic architecture, umm al-qura university, saudi arabia hassanalnaqib@outlook.sa rabeea w. bazuhair civil engineering department, college of engineering & islamic architecture, umm al-qura university, saudi arabia rwbazuhair@uqu.edu.sa (corresponding author) received: 16 march 2023 | revised: 29 march 2023 | accepted: 2 april 2023 licensed under a cc-by 4.0 license | copyright (c) by the authors | doi: https://doi.org/10.48084/etasr.5856 abstract improving the quality of the road pavement and ensuring the safety of the drivers on the road are issues of paramount importance. cracking and rutting are two of the most common damages that occur to asphalt pavement due to environmental effects and traffic. utilizing a modified binder is a solution for improving the pavement's resistance to these damages and enhancing pavement durability. this study investigates the performance of hot mix asphalt (hma) modified with titan7205 polymers and then compares it with that of a control mix of modified hma with styrene-butadiene-styrene (sbs) or crumb rubber (cr). two percentages of titan7205 were utilized to find out which dose provided better performance. hma was prepared by adding polymers with different percentages (3% and 5% titan7205, 4% sbs, and 8% cr). after preparing the samples, they were tested (unconditioned and aashto r30) for dynamic shear rheometer (dsr) testing, cantabro mass loss (cml), tensile strength ratio (tsr), and indirect tensile tension (idt). the results showed that the mix with 3% of titan7205 has a similar or better performance than the mixes with the other polymer additives utilized in this study. keywords-polymer; sbs; titan 7205; hot mix asphalt (hma); crumb rubber i. introduction during the last quarter of the century, road networks in the kingdom of saudi arabia are growing exponentially. it is inevitable to use durable asphalt mixtures to increase pavement quality, improve drivers' protection and comfort, decrease pavement damage, and decrease maintenance costs. one of the most common damages to asphalt pavement is fatigue cracking, which occurs as a result of the daily traffic and passing load. the use of a high-quality or modified asphalt binder is a method to improve and strengthen asphalt pavement and make it more able to resist cracking and rutting. to evaluate asphalt performance, numerous mixture tests can be used. authors in [1, 2] conducted a study on asphalt mixtures to investigate their capability to capture damage of single and combined effects of the environment (oxidation, moisture, freeze-thaw). different laboratory conditions were utilized, including single or combined environment effects of oxidation, moisture, and freeze thaw. four asphalt mixtures were utilized with nmas 12.5mm. the results showed that cml was better capture damages of environment on asphalt mixtures. asphalt additives are commonly classified as elastomers and plastomers [3-6]. titan additive is considered a plastomer asphalt binder additive, while cr and sbs additives are considered elastomer asphalt binder additives [3-11]. since the '80s, bitumen has been modified by the addition of polymers that help reduce rutting and cracking, such as sbs and cr [11-13]. also, many researchers have studied the preparation technology of bitumen using modified materials such as sbs and cr. it has been found that sbs and cr could raise high-temperature stability and possess the best aging resistance [14-16]. authors in [17] studied the performance of bitumen and asphalt mixtures modified by cr and sbs. the test results showed that it is necessary to use twice as much cr as sbs to reach the same performance as sbs. authors in [18] investigated the performance of asphalt mixtures modified with sbs polymer against low-temperature cracking. a beam rheometer (bbr) test was used with the trimmed specimens at different temperatures. the results showed that the sbs modified asphalt binder performed better in resisting low temperature cracking compared to the unmodified binder. authors in [19] stated that sbs additive is one of the most widely used bitumen modifiers because it enhances the mixture's rutting and fatigue resistance and mitigates its susceptibility to temperature variations. authors in [20] explored the experimental methods engineering, technology & applied science research vol. 13, no. 3, 2023, 10725-10730 10726 www.etasr.com alnaqib & bazuhair: evaluation of hma modified with titan polymer of polymer-modified asphalt, including sbs, with different proportions to systematically ensure the quality and requirements of construction engineering in asphalt pavement. the results showed that sbs improved the high temperature performance of asphalt and could be used to increase its compressive strength. cr is frequently used as a modifier to improve asphalt properties such as rutting and fatigue [21, 22]. the virginia department of transportation (vdot) conducted research to see the effects of cr addition on the moisture susceptibility of asphalt mixtures [23]. modified lottman and the texas boiling water test were used for the evaluation of asphalt mixtures. the results showed that cr modifiers could improve asphalt mixture stripping and moisture susceptibility. cr has been used successfully for improving the mechanical characteristics of hma mixtures, where it was observed to improve the laboratory performance of mixtures against rutting, cracking, moisture damage, and oxidation [24]. titan materials have different effects on hma depending on their type and properties. the titan additive has been shown to reduce harmful emissions from road paving by approximately 82% and the amount of fuel required in a mixture by 13% [25]. authors in [26] investigated the effect of oxidized titan7686 polymer on the rheological and performance properties of sbs modified bitumen with 0.5% by weight control binder. indirect tensile strength, resilient modulus, and dsr test were performed to investigate the binder characterization. the results of the modulus of elasticity test indicated that the addition of the titan7686 polymer enhanced the response of the modified bituminous mixtures under repeated loading, while it was observed that the mr value respectively increased by 11%, 20%, and 16% at 25°c, 35°c, and 45°c compared to the sbs bitumen mixture. also, there was an increase in the value of the tsr test compared to the sbs. on the other hand, it was observed that the complex modulus, shear modulus, and loss modulus of titan7686 are higher than that of sbs. authors in [27] investigated the negative effects of wax within bitumen from different sources to determine the wax content and the type of polymer that would be best for the needs of refineries in different countries [27]. temperature performance, fatigue cracking, and rutting were evaluated using dynamic shear tests, zero shear viscosity tests, and multiple stress creep recovery tests. titan7686 generally improved the rutting and fatigue cracking properties of waxy bitumen. depending on the asphalt mixture materials, titan can reduce the amount of additive required by around 30% and help reduce rutting issues. asphalt binders play an important role in the performance of resilient sidewalks when exposed to high traffic loads and harsh environmental conditions [28]. some tests were conducted to study the influence of the physical and rheological properties of asphalt binders using polymers, most notably sbs, polybilt, titan7686, and titan7205. the results showed that adding enhancers, especially titan7205, improved the performance of the asphalt mixtures. there is a lack of information and research on the performance of titan7205 when used with hma, and the current research fills this gap. ii. materials and methods table i shows the properties of the materials used for the asphalt mix, the gradient, the bitumen ratio, and the type of additive used. in this study, asphalt samples with a diameter of 150mm and a height of 95±5mm were prepared for mixture testing. the air void (va) range of specimens used is 7.0±0.5% according to aashto t166, and a total of 125 specimens were prepared with 3 types of polymers in various dose percentages. each polymer has been given a symbol with different percentages: neat bitumen (m0), 4% sbs (m1), 3% titan7205 (m2), 5% titan7205 (m3), and 8% cr (m4). table ii shows the physical appearance of each polymer type. table i. mixture properties mixture id m0 m1 m2 m3 m4 pb (%) 5.3 5.3 5.3 5.3 5.3 additive none 4% sbs 3% titan7205 5% titan7205 8% cr p25mm (%) 100 100 100 100 100 p19.0mm (%) 100 100 100 100 100 p12.5mm (%) 95.1 95.1 95.1 95.1 95.1 p9.5mm (%) 81.3 81.3 81.3 81.3 81.3 p4.75mm (%) 53 53 53 53 53 p2.36mm (%) 38 38 38 38 38 p1.18mm (%) 25.1 25.1 25.1 25.1 25.1 p0.60mm (%) 18.9 18.9 18.9 18.9 18.9 p0.30mm (%) 15 15 15 15 15 p1.5mm (%) 8.5 8.5 8.5 8.5 8.5 p0.075mm (%) 5.4 5.4 5.4 5.4 5.4 nmas (mm) 12.5 12.5 12.5 12.5 12.5 vma 14.4 15.3 15.4 15 14.5 vf (%) 49.4 55.3 54.2 53.1 52.5 gb 1 1 1 1 1 gsb 2.7 2.7 2.7 2.7 2.7 ps 94.7 94.7 94.7 94.7 94.7 gse 2.8 2.7 2.8 2.8 2.7 pba 1.1 0.8 0.8 0.9 0.8 pbe 4.2 4.4 4.4 4.4 4.5 dp 1.2 1.2 1.2 1.2 1.1 pb = total binder content-mix mass basis, pxxmm= percent passing a xx mm sieve, nmas = nominal maximum aggregate size, vma = voids in mineral aggregate, vf = voids filled, gb = specific gravity of the asphalt binder, gsb= bulk specific gravity of the aggregates, ps= aggregate percentage, gse = effective specific gravity of the aggregates, pba= % by mass of the absorbed asphalt binder on aggregate mass basis, pbe = % by mass of effective asphalt binder on mix mass basis, dp= dust percentage. table ii. additive properties property sbs titan 7250 cr density 0.90 g/cc 0.93 g/cc 1.32 g/cc viscosity 400 – 4320 cps 450 cps 165 237 cps product form prill prill granule size 4-6mm diameter 2-3mm 0.2-0.4mm a. laboratory conditioning aashto r30 laboratory conditioning protocol was utilized to investigate hma performance over time and simulate long-term aging effects. the specimens were cooled to room temperature before aging and then were placed in an oven at 85±3°c for 120±0.5h (figure 1). then, the oven was turn off, the oven doors were opened, and the test specimens were allowed to cool to room temperature, something that typically took about 16 hours. engineering, technology & applied science research vol. 13, no. 3, 2023, 10725-10730 10727 www.etasr.com alnaqib & bazuhair: evaluation of hma modified with titan polymer fig. 1. oven conditioning of asphalt mixtures. b. binder testing-dynamic shear rheometer testing (dsr) asphalt binder is a viscoelastic material, i.e. it behaves as both an elastic and viscous material at the same time. dsr testing was performed at high temperatures within a range of 64°c to 88°c with a 25-mm plate as per aashto m315 (figure 2). fig. 2. the dsr device. c. mixture testing 1) cantabro mass loss testing (cml) cml testing was performed on specimens with 150mm diameter and 95±5mm height. the specimens were conditioned in the air at 25 o c before testing. compacted specimens were tumbled each in turn in a los angles (la) abrasion drum (figure 3) without steel spheres for 300 rotations. the difference in the specimens mass before (m1) and after (m2) testing was determined according to (1) and referred to as mass loss (ml). ml = ����� �� × 100 (1) 2) tensile strength ratio (tsr) the tsr test was performed according to aashto t-283 to evaluate the moisture susceptibility of asphalt mixtures. the specimen size was 150mm diameter and 95±5mm height. the samples were divided into two groups: the first group was placed at environment conditions at 25°c for 2h before dry condition testing. the second group was conditioned in a water bath at 60 o c for 24h and then at 25 o c for 2h before testing. fig. 3. mixtures in the dynamic shear rheometer device (a) abrasion drum, (b) cml before testing, (c) cml after testing, (d) cml before and after testing. fig. 4. a) wet samples, (b) dry samples, (c) idt testing. 3) indirect tensile tension (idt) the idt test was used to determine the tensile strength (st) of the mixture specimens (figure 5). the idt specimens had 150mm diameter and 95 ± 5mm height. the specimens were air-conditioned at 25°c before testing. tensile strength at failure (st) was measured according to (2): �� = ��×���� �×�×� (2) fig. 5. idt instrument. iii. results and discussion table iii shows the test results for unconditioned and aashto r30-conditioned mixtures. the value for a given test (a) (b) (c) (d) (a) (b) (c) engineering, technology & applied science research vol. 13, no. 3, 2023, 10725-10730 10728 www.etasr.com alnaqib & bazuhair: evaluation of hma modified with titan polymer method represents the average of the measurement of 3 samples replicated for the mixture test. table iii. result of mixture and binder testing condition mix idt (kpa) tsr (%) cml (%) dsr ( o c) unaged m0 879.36 54.26 10.52 64 m1 877.90 80.50 18.39 88 m2 781.47 86.38 14.17 76 m3 937.97 78.03 13.98 82 m4 765.38 82.43 15.12 70 aashto r30 m0 967.29 57.44 14.82 — m1 2192.97 41.32 22.69 — m2 1566.42 55.11 21.30 — m3 2270.16 38.72 23.41 — m4 2166.28 44.47 19.14 — 1) statistical assessment of the mixtures table iv shows a statistical assessment of the obtained results that are mentioned in table iii for the 5 mixtures. the values of δ are calculated by subtracting the results of each mix (m1, m2, m3, and m4) from m0. the p-values were obtained from the statistical analysis of the t-test, which indicates the significance of the difference between the sample’s results. if the p-value is less than 0.05, there is a significant difference between the results. if it is higher than 0.05, then there is no significant difference. 2) dynamic shear rheometer (dsr) in dsr testing, it appears that with the addition of polymers, the failure temperature rises. m3 has a failure temperature of 82 o c, and m2 one of 76 o c. this concludes that the failure temperature of the binder increases with an increase in the percentage of titan7205. also, m1 has a higher failure temperature (88 o c) than m4. comparing the additives to m0, they all show an increase in the failure temperature. overall, the addition of polymers to hma can improve its rutting resistance. 3) indirect tensile strength (idt) figure 6 shows the test result of idt. comparing m0 to the other additives for unconditioned, the results show that m0 has a similar or higher st value than the other additives. subsequently, m2 and m4 have similar performance, while m3 shows a slightly higher st value. all modified hma in the study display a higher st value compared to m0 for aashto r30 conditioning. comparing the additives with each other, the st value of m2 is less than that of the other additives. in addition, there is statistical difference between m2 and the other additives (m1, m3, and m4). comparing m2 with m3, m3 had higher st value, while m2 still had higher st value than m0. overall, when comparing m0 to other additives, m0 shows similar or less crack resistance in most cases. conditioned mixtures exhibit higher st values than the unconditioned mixtures. fig. 6. comparison of the unconditioned with aashto r30 conditioned idt. table iv. statistical assessment of mixtures condition mix idt (kpa) tsr (%) cml (%) δ (mi-m0) p-value t-test significant differ δ (mi-m0) p-value t-test significant differ δ (mi-m0) p-value t-test significant differ unaged m1 -1.49 0.82 b no 26.24 0.01< ab yes 7.87 0.01< a yes m2 -97.89 0.01< c yes 32.13 0.01< b yes 3.65 0.01< c yes m3 85.62 0.01< a yes 23.77 0.01< b yes 3.46 0.01< c yes m4 -113.98 0.01< d yes 28.17 0.01< a yes 4.60 0.01< b yes aashto r30 m1 1225.67 0.01< ab yes -16.12 0.01< c yes 7.87 0.01< b yes m2 599.12 0.01< c yes -2.33 0.18 a no 6.49 0.01< c yes m3 1302.87 0.01< a yes -18.72 0.01< c yes 8.59 0.01< a yes m4 1198.99 0.01< b yes -12.97 0.01< b yes 4.33 0.01< d yes 4) tensile strength ratio (tsr) all the additives exhibit a higher value of tsr than m0, which means that they all improved the moisture resistance of the mixture. m1, m3, and m4 show similar performance, while m2 shows slightly better moisture resistance. also, m2 shows a statistically significant difference compared to the other additives. considering aashto r30 conditioning, it appears that when comparing the additives with m0, the control m0 has similar or better moisture resistance after aashto r30 conditioning. m2 has better moisture resistance after aashto r30 conditioning than the other additives. referring to table iv, m2 has a significantly higher tsr value, while its tsr value is statistically not significantly different from that of m0. overall, m0 shows similar performance before and after conditioning. all the additives show higher moisture resistance before conditioning and lower moisture resistance after conditioning. m2 has a higher tsr value than other additives in unconditioned and aashto r30 conditions. for unconditioned mixtures, m2 shows better performance than m0, while it shows similar performance after conditioning to m0. engineering, technology & applied science research vol. 13, no. 3, 2023, 10725-10730 10729 www.etasr.com alnaqib & bazuhair: evaluation of hma modified with titan polymer fig. 7. comparison of the unconditioned with aashto r30 conditioned tsr. 5) cantabro mass loos (cml) referring to figure 8 for the unconditioned case, all additives have a higher cml value than m0, which means the additives reduce mixture durability. also, there are statistically significant differences between m0 and the other additives. m1 has lower durability compared to the other additives, while m2, m3, and m4 show similar performance. all additives have a cml value higher than m0 after aashto r30 conditioning. m4 is slightly more durable than the other additives followed by m2. the cml value of m2 is statistically significant different compared to other additives. in summary, aashto r30 mass loss values increase more than the unconditioned ones, which is logical given that the durability of asphalt mixtures should decrease over time with aging. all the additives have a cml value higher than m0 either unconditioned or after aashto r30 conditioning. in most cases, m2 shows similar or better performance compared to the other additives. fig. 8. comparison of the unconditioned with aashto r30-conditioned cml. 6) cost comparison the comparison of polymer additive prices is conducted to show the economic impact of their utilization. two supplier’s prices were used, and the prices were averaged. table v shows the price per ton for each additive. crumb rubber has the lowest price, and sbs the highest. the price of the titan7205 is slightly lower than that of the sbs, which makes it a preferable choice over the sbs. comparing the performance of titan7205 to other additives with respect to price, titan7205 could be another alternative to be used with hma. table v. additive price comparison additives unit price (sr/ton) sbs 1 ton 9000 cr 1 ton 2750 titan 7205 1 ton 8000 iv. conclusions this article’s objective was to evaluate the performance of hot mix asphalt (hma) modified with titan7205 polymers. two percentages (3% and 5%) of titan 7205 were utilized in this study and showed similar or better performance compared to other mixtures (m0, m1, and m4). both percentages of titan 7205 (m2 and m3) met the required failure temperature in this study (72 o c). 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[28] k. j. al-adham, "elastic recovery evaluation of saudi asphalt modified with commercial polymers," m. s. thesis, king fahd university of petroleum and minerals, dhahran, saudi arabia, 2014. microsoft word etasr_v13_n1_pp9861-9866 engineering, technology & applied science research vol. 13, no. 1, 2023, 9861-9866 9861 www.etasr.com kara ali et al.: cutting parameter optimization based on online temperature measurements cutting parameter optimization based on online temperature measurements abdelillah djamal kara ali department of mechanical engineering, university of tlemcen, algeria dj_kara_ali@yahoo.fr (corresponding author) nasreddine benhadji serradj department of mechanical engineering, university of tlemcen, algeria kawther4499@yahoo.fr mohamed el amine ghernaout department of mechanical engineering, university of tlemcen, algeria e_amine2001@yahoo.fr received: 20 september 2022 | revised: 26 october 2022 | accepted: 27 october 2022 abstract the deformation of metallic materials during the machining operation requires a significant amount of energy. during the chip formation process and due to the plastic deformation of the metal and the friction along the tool-part interface, the thermal loads generated are strongly impacted by the cutting factors. thus, the choice of optimized cutting conditions is essential to control the quality of the work required. the aim of the present experimental study is to optimize the cutting parameters using temperature measurements. the average temperature of the cutting tool is studied using a flir a325sc type infrared camera. optimal cutting parameters for each performance metric were obtained using the taguchi techniques. keywords-machining; cutting conditions; optimization; thermography; temperature measurement i. introduction the choice of cutting conditions is a very important factor in machining. with the increasingly rapid development of machine tools and the use of new high-performance materials for the tool-part couple, cutting temperature is an essential concern in machining. to be highly competitive, the objectives sought by the mechanical manufacturing industries are to produce high quality products with low cost and time constraints. to achieve them, one of the solutions is to optimize machining parameters such as cutting speed, depth of cut and feed. the effects of cutting parameters (cutting speed, depth of cut, feed per revolution,) on surface roughness, tool wear, cutting forces related to turning operations have been studied in depth. authors in [1] used the response surface method (rsm) with a factorial design to predict surface roughness when machining high strength materials. authors in [2] studied the machinability of hard steel in turning by the response surface method. authors in [3] used a multiplicative model to predict surface roughness and tool vibration. the context of the current work is based on the use of full factorial type experimental designs based on the experimental characterization of the temperature measurement for the optimization of the cutting conditions during the turning operation. many techniques have been developed during the recent years that address this type of problem. authors in [4] propose a general classification of the different techniques for modeling and optimizing input-output relationships in metal cutting processes. they are classified into two methods, classical optimization techniques and unconventional techniques. the current work is oriented on the study of the heat flow in the zone of the cut represented by the measurement of the temperature. various techniques of temperature measurement have been studied and evaluated [58]. the optical infrared method has been used in [9-10]. fig. 1. sources of heat generation in machining. engineering, technology & applied science research vol. 13, no. 1, 2023, 9861-9866 9862 www.etasr.com kara ali et al.: cutting parameter optimization based on online temperature measurements at the heart of the process, two main phenomena are in interaction:  a very strong plastic deformation in the shear zones.  the friction of the chip on the rake face of the tool. one may also add the friction of the clearance face on the newly machined surface. the energy generated is then largely transformed into a significant heat flux which modifies and deteriorates the machined surface and the cutting tool shown in figure 1. in this paper, an experimental measurement methodology is proposed and the results are presented using an acquisition instrumentation, equipped with a single infrared camera with advantages such as contactless measurement, measurement without or with very little disturbance between the surface of the studied object and its surrounding environment, the capacity for real-time measurement, wide range of operating temperatures, the ability to adapt to any type of material, and a unit processing of the measured values. the correlation between the cutting conditions and the temperature appears on the flowchart represented in figure 2. fig. 2. correlation between cutting conditions and temperature. in industry and in order to make the best choices, very often one empirical method (taylor's law, kronenberg model, etc.) is used to calculate and optimize the cutting parameters before machining. knowing that the low cumulative gains generate significant profits, we propose an approach that allows refining the manufacturing conditions after following the experimental tests. ii. materials and methods the infrared camera used is the flir a325sc, coupled with the flir research software. the inserts are made of tungsten carbide with a beak radius r = 0.4mm (figure 3). the specimens are made of s185 steel, a material widely used in industry. for the machining we used a conventional parallel lathe made by tos trencin type (figure 4). fig. 3. thermal camera flir a325sc and tool holder with the used insert. fig. 4. machining station with tool, specimen, and camera. the conducted experimental tests and the calibration of the camera are widely discussed in [11]. before using the results, the data are retrieved from the camera software (flir quick plot) for viewing the machining sequences. figure 5 represents the acquisition chain. fig. 5. chain of acquisition and processing of thermal data. fig. 6. software interface. the recovery of the temperatures is made after tracing the curve represented by figure 7. the curve is divided into three zones:  zone 1 represents the machining initiation. engineering, technology & applied science research vol. 13, no. 1, 2023, 9861-9866 9863 www.etasr.com kara ali et al.: cutting parameter optimization based on online temperature measurements  zone 2 determines the stabilization part of the section, from the latter we recover the temperatures for analysis.  zone 3 represents the tool release and the end of the turning operation. fig. 7. software interface and curve areas studied. iii. temperature prediction model the relationship between the inputs which are the machining parameters (cutting speed, feed, depth of cut) as independent variables vary according to an n3 type design of experiments. in a 43 type experiment, each parameter has 4 levels, which gives us 64 experiments (full plan). we carried out 64 machining operations, each time using a new cutting edge. the expanded linear model of the type second-order equation is: y � b� � b�x� � b x � b x � b��x� � b x � b x � b� x�x � b� x�x � b x x (1) where y = t is the estimated response, x1, x2, x3 respectively represent the control factors (cutting speed, feed, and depth of cut), and b0, ..., b23 are the coefficients of the related factors. constants and exponents are determined by the least squares method. after careful reading of the sequences recorded by the camera, we determined the temperature of the tip of the tool according to the cutting parameters as shown in table i. table i. cutting parameters parameter code levels 1 2 3 4 cutting speed vc (m/min) x1 78 112 157 220 feed rate a (mm/rev) x2 0.08 0.11 0.14 0.20 depth of cut p (mm) x3 0.25 0.5 0.75 1 turning conditions machining without lubrication the analysis of variance in table ii shows that the interaction feed and depth of cut clearly influence the temperature (p-value =0.04). after processing, we obtain the prediction equation (2): t° tool = 89.6 + 0.054 vc 638 a 19.2 p 0.000215 vc2 + 1640 a2 + 32.3 p2 + 0.572 vc×a + 0.036 vc×p + 368 a×p (2) the residual distribution analysis is based on a powerful test for the detection of non-normality. the normal probability plot is shown in figure 8. it is clear that the residuals lie close to the reference line, which implies that the errors are normally distributed. table ii. analysis of variance source df adj ss adj ms f-value p-value regression 9 34124.1 3791.57 12.63 0.000 vc 1 8.0 7.95 0.03 0.871 a 1 677.8 677.83 2.26 0.139 p 1 38.2 38.18 0.13 0.723 vc×vc 1 14.4 14.39 0.05 0.828 a×a 1 438.5 438.46 1.46 0.232 p×p 1 260.5 260.46 0.87 0.356 vc×a 1 116.4 116.40 0.39 0.536 vc×p 1 17.9 17.85 0.06 0.808 a×p 1 1333.7 1333.65 4.44 0.040 error 54 16212.6 300.23 total 63 50336.7 table iii. coefficients of equation (2) term coef se coef t-value p-value vif constant 89.6 43.3 2.07 0.043 vc 0.054 0.335 0.16 0.871 67.55 a -638 424 -1.50 0.139 75.61 p -19.2 53.8 -0.36 0.723 48.28 vc×vc -0.000215 0.000982 -0.22 0.828 53.63 a×a 1640 1357 1.21 0.232 63.50 p×p 32.3 34.7 0.93 0.356 32.25 vc×a 0.572 0.918 0.62 0.536 17.03 vc×p 0.036 0.146 0.24 0.808 13.11 a×p 368 175 2.11 0.040 14.92 fig. 8. normality line of the distribution of residuals. iv. results and discussion the test results were divided according to the method of measurement, either in zone 2 or zone 3. the results obtained during the first method (zone 2) have been discussed in [12]. we present the results obtained in zone 3 where the temperature measurement is made just after the release of the tool. the comparison between the experimental values and the predicted values for the obtained temperature model, is represented graphically in figure 9 for the complete design of the experiment. the latter shows that the experimental and the estimated values are close with an accuracy of 88.87%. these results prove the accuracy of the model. furthermore, they confirm that the model can be effectively used to predict the machining temperature with a 95% confidence interval. 2502001 501 00500 99,9 99 95 90 80 70 60 50 40 30 20 1 0 5 1 0,1 mean 87,46 stdev 28,27 n 64 ad 1 ,029 p-value 0,01 0 t°-tool p e rc e n t normal 95% ci project: plan complé.mpj; worksheet: worksheet 2; 19/07/2022 probability plot of t°-tool engineering, technology & applied science research vol. 13, no. 1, 2023, 9861-9866 9864 www.etasr.com kara ali et al.: cutting parameter optimization based on online temperature measurements fig. 9. experimental and predicted curves. figure 10 shows the different interactions. the interaction vc×p (between the cutting speed and the depth of cut) is noticed to have an imposing effect. on the other hand, the interaction a×p (between the feed and the depth of cut) and the interaction vc×a (between cutting speed and feed) are less significant. most of the energy released is spent in deforming the chips both cutting and plastically. part of this energy is transformed into heat by friction at the two interfaces (tool-chip and tool-workpiece). the generation of heat during machining causes the temperature to rise in the process area. it turns out that the cutting speed is the imposing factor on the cutting temperature. to visualize the influence of the cutting parameters on the temperature (t°), the response surfaces (2d) are presented below. fig. 10. interactions of cutting conditions. the isotherm in figure 11 shows that the cutting temperature increases with the feed over the interval of 0.08mm/rev and 0.14mm/rev, with a drop in temperature over the interval 0.14mm/rev and 0.2mm/rev. the thermogram in figure 12 shows the concentration of heat on the tool tip and chip fragments. the isotherm in figure 13 shows that the cutting temperature increases with increasing cutting speed and depth of cut. the thermogram in figure 14 shows the heat distribution on the cut face. the isotherm in figure 15 shows that the temperature increases for the interval of the feed rate (0.14mm/rev-0.2mm/rev) and the depth of cut (0.75mm-1mm) and it remains moderate for the lower intervals. as can be seen, for a depth of cut equal to 0.25mm, the temperature decreases. the thermogram in figure 16 shows the concentration of heat on the nose of the tool. fig. 11. temperature isotherm as a function of cutting speed and feed rate. fig. 12. thermogram for vc=78m/min, a=0.08mm/rev, and p=0.25mm. fig. 13. isotherm as a function of cutting speed and depth of cut. fig. 14. thermogram for vc=157m/min, a=0.08mm/rev, and p=0.75 mm. p 0,625 hold values vc a 2201 571 1 278 0,20 0,1 4 0,1 1 0,08 > – – – – – – < 75 75 80 80 85 85 90 90 95 95 1 00 1 00 1 05 1 05 t°-outil project: minitab.mpj; worksheet: worksheet 2; 17/07/2022 contour plot of t°-tool vs a; vc a 0,1 325 hold values vc p 2201 571 1 278 1 ,00 0,75 0,50 0,25 > – – – – – – < 60 60 70 70 80 80 90 90 1 00 1 00 1 1 0 1 1 0 1 20 1 20 t°-outil project: minitab.mpj; worksheet: worksheet 2; 17/07/2022 contour plot of t°-tool vs p; vc engineering, technology & applied science research vol. 13, no. 1, 2023, 9861-9866 9865 www.etasr.com kara ali et al.: cutting parameter optimization based on online temperature measurements fig. 15. isotherm as a function of feed rate and depth of cut. fig. 16. thermogram for vc =112m/min, a=0.14 mm/rev, and p=1 mm. v. optimization of cutting conditions this goal can be achieved by intervening in the different stages of the production of the part:  design of the assembly to be manufactured.  part definition.  choice of manufacturing range.  choice of cutting conditions. cutting conditions can be optimized by setting an optimum cutting temperature obtained during experimentation. it can be given by the manufacturer depending on the technical characteristics of the pad. in this paper, a method is proposed to find the optimal cutting conditions. the choice of cutting conditions has a direct impact on the machining time of the part, therefore on the cost price of machining and on the productivity improvement. the optimization plot allows us to interactively modify the cut parameters of the input variables to perform sensitivity analysis and possibly improve the initial solution. we apply the optimization technique of the minitab software used in the current work, for the measurement just after the release of the tool and under the following machining constraints: 78 ≤ vc ≤ 220; 0.08 ≤ a ≤ 0,2 ; 025 ≤ p ≤ 1 (3) by choosing a temperature of 100° we obtained the results of the optimized input variables grouped in table iv. table iv. optimized conditions t° solution vc a p fit desirability 1 149 0.14 0.348485 99.967 0.999446 2 220 0.185560 0.256348 100.148 0.997301 3 78 0.150854 0.991703 103.348 0.939131 for desirability index equal to 0.999446, the optimal conditions are: vc=149m/min, a=0.14mm/rev, p=0.34 mm. the optimization diagram in figure 17 shows the influence of the cutting conditions with the fixed cutting temperature. fig. 17. impact of cutting conditions. vi. conclusion this work shows that a thermography technique is a useful procedure for establishing an experimental methodology for evaluating cutting temperature during the machining operations. it is therefore a method of mapping temperatures in real time, allowing the evaluation over time of surface thermal phenomena. the advances in manufacturing technology require us to estimate and predict the temperature rise at different points of the workpiece-tool interface in order to optimally adjust different parameters beforehand to improve machinability. no previous research work has used only an infrared camera. the major difficulty in taking the machining sequence by the camera is the rolling of the chip, hence the need to choose the cutting conditions well and to have good protection and fixing. the experimental results allow us to conclude that the variations of the temperatures are very weak in permanent regimes for invariant cutting parameters, that the stresses applied by the tool on the machined material lead to a rise in temperature and that the heat flow generated during machining is largely evacuated by the chip. the experiments allowed us to determine the temperatures of the machined surface of the part as well as that of the cutting edge for different cutting parameters. the fit of the model was checked and found to be adequate at an accuracy level of 88.87% for temperature measurements just after tool release. this demonstrates that the model can be used to predict the cutting temperature. the technique could be an economical and effective method for temperature prediction and optimization of the cutting parameters. the quality of the parts produced depends largely on the cutting conditions and this quality is an important parameter during the production of mechanical parts. the cutting fluid is vc 1 41 ,75 hold values a p 0,200,1 40,1 10,08 1 ,00 0,75 0,50 0,25 > – – – – – < 60 60 75 75 90 90 1 05 1 05 1 20 1 20 1 35 1 35 t°-outil project: minitab.mpj; worksheet: worksheet 2; 17/07/2022 contour plot of t°-tool vs p; a engineering, technology & applied science research vol. 13, no. 1, 2023, 9861-9866 9866 www.etasr.com kara ali et al.: cutting parameter optimization based on online temperature measurements also an important parameter since it allows to limit the rise in temperature in the cutting zones and to establish the presence of a fluid film between the different surfaces. however, in order to protect the environment and the health of the personnel, the current trend is to limit and even eliminate the use of cutting fluids. references 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[17] flir sc325. flir systems, 2010. microsoft word etasr_v13_n1_pp9919-9925 engineering, technology & applied science research vol. 13, no. 1, 2023, 9919-9925 9919 www.etasr.com kumar & roy: investigating the slope stability and factor of safety properties of soil reinforced with … investigating the slope stability and factor of safety properties of soil reinforced with natural jute fibers under different rainfall conditions saurabh kumar department of civil engineering, national institute of technology patna, india saurabhk.phd19.ce@nitp.ac.in (corresponding author) lal bahadur roy department of civil engineering, national institute of technology patna, india lbroy@nitp.ac.in received: 11 november 2022 | revised: 19 november 2022 | accepted: 21 november 2022 abstract heavy rainfall is often responsible for embankment failures. during intense rainfall, the embankment slope inclination is vital for slope stability. some failures occur in the slope due to heavy rainfall and sudden change in the matric suction. jute fiber is a reinforcing material that is added to improve soil strength. in this research, in order to explore the effects of slope inclination on soil stability, soil samples were collected and exposed to artificial rainfalls. this study presented various tests performed on the soil samples. different tests like sieve analysis, permeability test, direct shear test (dst), liquid limit, plasticity limit, and numerical modeling were conducted in the laboratory. the study's findings revealed that the failure is caused by a soil suction loss when the inclination of the slope is higher than the soil friction angle and the collapse is caused by the positive water pressure at the slope's toe when it is lower than the soil's friction angle. furthermore, when the slope angle increases, the slopes are becoming increasingly vulnerable to rapid collapse. after that, jute fibers were combined with the soil to improve its performance. samples of 2, 3, and 4 rows of jute fibers were tested. these jute fiber samples performed better than the ones without fibers under different rainfall conditions. the distribution of jute fibers had a favorable influence on both strength measurements and safety aspects. utilizing the factor of safety and matric suction, the performance of jute fiber samples is superior to those without jute fibers. consequently, by adding jute fibers the stabilization of the soil is significantly improved along with its factor of safety. keywords-soil samples; slope stability, reinforced material; jute fibers; sieve analysis; factor of safety; matric suction; deformation i. introduction every year, thousands of landslides occur around the world, causing financial losses and even deaths. soil stabilization is very important for slope embankment. to assure the ground soil’s stability during construction, embankments are usually built in several phases. in order to quantify the gain in shear strength effectively, the foundation soil’s undrained shear strength normally rises with consolidation [1]. the soil’s top layer in an embankment slope is more sensitive to erosion during rainstorms. it provides the least erosion resistance and rapidly loses strength [2]. the undrained condition of soil stability analysis was calculated by first order reliability method (form), and monte carlo simulation (mcs) method to calculate the factor of safety (fos) in [3]. ground water samples obtained from the river side embankment to check the drinking water quality and 12 parameters, namely, ph, ec, tds, ca, mg, na, f, so4, k, cl, and hco3 were used to compute the water quality based on the water quality index method [4]. the bearing capacity of a stone column is highly related to the diameter of the column, the properties of the soil, and its bearing capacity. it was found that when the diameter of the stone column increases, the bearing capacity of the soil increases exceptionally [5]. rainfall infiltration reduces the soil matric suction and shear power and increases the soil loss susceptibility [6]. displacements in the vertical and lateral planes were reduced and the bearing capacity was increased by engineering, technology & applied science research vol. 13, no. 1, 2023, 9919-9925 9920 www.etasr.com kumar & roy: investigating the slope stability and factor of safety properties of soil reinforced with … reinforced embankments [7]. to suit engineering requirements, soil stabilization is a technique of enhancing the physical, chemical, or biological qualities of natural soil. shear strength quality, cohesiveness, and friction angle are determined utilizing a laboratory direct shear test [8]. the finite difference approach was utilized to perform numerical modeling and in the numerical modeling, the model scale was used to replicate the centrifuge tests [9]. due to the high cost of creating and transporting freedraining coarse-grained materials, slope failure along highways is frequently repaired or restored using locally available soil with significant amounts of fines present (clay and silt) [10]. due to the three-dimensional nature of the reinforcement, a geocell-reinforced slope acts as a beam in the soil. furthermore, the moment of inertia is taken into consideration due to its bending features, resulting in enhanced bending strength, the reinforcement lowers slope displacement, and the slope's fos is raised [11]. jute fibers of predefined length and content are mixed extensively by hand with expansive soil until a fairly uniform distribution of jute fibers in the soil is achieved [12]. fibers improve the soil composite mechanical properties. the normal pressures acting on the soil composite mobilize tensile resistance in the fibers, giving the soil higher shear strength [13]. the reinforcing effect location on the failure and deformation behavior of soil slope and superstructure by evaluating various geogrid layers is explored in [14]. jute fiber is excellent for enhancing soil qualities since it is inexpensive, readily available, biodegradable, and environmentally friendly [15, 16]. a moisture barrier and altered recycled plastic pins were utilized to stabilize the pavement distresses and the rainfall-induced slope failure in [17]. the slopes' fos or chance of failure were displayed in ascii format in [18]. the matric suction losses caused by rainfall infiltration had only a minor impact on the reinforced sand slope's global and local fos. the tensile reinforcement strengths are necessary to sustain fos on reinforced clay and silt slopes [19]. under relatively modest stress conditions, from a geotechnical standpoint, problematic soils are those that can disperse, collapse, have an excessive settlement, expand, or even fail. there is erosion or cracking in the soil, and consequently the soil may not be stable for the embankment. due to this problem, the current paper presents various tests for testing slope soil stability. here, rainfall intensity is set up to test the soil stability, because it generates cracks and slope failure may occur and reinforcing material like jute fibers is added, to strengthen the soil and increase the slope stability. this study is based on the reinforced soil stabilization process. it investigates various researches for slope stability. authors in [20] proved the embankment slope stability for roads erected on soft terrain using prefabricated vertical drains (pvds). the slope stability was investigated using numerical analysis and modeling based on the fos with an artificial neural network. a novel approach is proposed in [21], where the soil strength follows the nonlinear yield criterion to determine the fos of soil slopes. first, the magnitude and coordinates of minor primary stress are determined using numerical simulation. the freeze-thaw cycles were investigated by the effect on the embankment slope stability of polypropylene fibers using a numerical analytic method [22]. the dst was built to measure 9 sets of specimens, shear strength metrics such as binding force and internal friction angle were considered along with 3 components (freeze-thaw cycle, fiber content, and fiber length). authors in [23] investigated the failure and deformation behaviors of reinforced slopes with various geotextile layouts utilizing a set of centrifuge model drawdown experiments. under drawdown conditions, the geotextile reinforcement was found to considerably raise the ductility and safety limit, change the slope failure feature, and minimize displacement. the injection approach was used to produce one untreated embankment and 3 small-scale bio-treated sand embankments in [24]. to investigate the embankment's slope collapse, rainfall scouring experiments were used. ii. research methodology geotextile-reinforced model slopes are investigated with tests regarding the geotextiles' mechanism and the reinforcement effect. the soil’s water content and dry density, and the slope's height and gradient, were kept constant throughout all of tests. the reinforced slopes' behavior influence is observed utilizing different geotextile layouts. different centrifuge experiments were undertaken on unreinforced and reinforced slopes. for this experiment, disturbed and undisturbed soil samples were considered. during the sampling process, the soil’s natural structure has been altered or destroyed, their structure is referred to as disturbed samples. the non-representative samples are soils from different mixed strata. the deadweight of the soil slope, which was applied to the entire slope, and the evenly distributed loading, which was applied to replicate the vehicle load are the two types of loadings that were used to the finite element model in the slope stability analysis. using the proposed slope stability analysis approach, the maximum plastic strain and the slope’s maximum horizontal displacement were respectively computed. the flow diagram of the proposed method is depicted in figure 1. fig. 1. flow diagram of the research methodology. engineering, technology & applied science research vol. 13, no. 1, 2023, 9919-9925 9921 www.etasr.com kumar & roy: investigating the slope stability and factor of safety properties of soil reinforced with … a. material collection this study studies soil samples to determine the soil embankment stability. the soil samples taken for this study have 27.17% silt and clay soil and 72.83% sand. multiple, smaller samples known as cores, compose an accurate soil sample. the majority of their nutrients are derived from plants or grasses that individual cores contain from the soil surface. in a variety of locations throughout the area, a minimum of 10 soil cores was taken. several tests were used to measure the stability of the soil slope. soil samples were powdered, sieved, and dried before being analyzed. for analysis, a homogenous mixture was ensured by grinding and sifting steps. soil samples were dried in cardboard boxes at 50°c. the soil was ground in a mechanical mortar and pestle and passed via a 12-mesh, roughly 2mm screen. mineral particles, water, air, and organic matter are present in the samples. chemistry, color, structure, porosity, and soil texture are determined by combinations of these factors. table i illustrates the plastic limit, liquid limit, plasticity index, coefficient of permeability, dry unit weight, saturated unit weight, cohesion, angle of internal friction, poisson's ratio, and young's modulus of elasticity. these are the soil properties utilized in the experiment. to test the soil stability, various soil testing methods were utilized. specified analytical equipment is utilized for the analysis. sample preparation included sample cleaning up, sample pre-concentration, alkali or acid-based chemical digestion, sample extraction, crushing and dissolution. in table i, the coefficient of permeability (ksat) was obtained by the constant head permeability test and the modulus of elasticity (e) and the coefficient of internal friction (ϕ) were obtained by direct shear test in the laboratory. table i. soil sample properties soil properties values plastic limit wp 15% liquid limit wl 21% plasticity index pi 6% soil classification sm-sc coefficient of permeability ksat 8.27×10⁻⁴cm/sec dry unit weight γdry 14.5kn/m � saturated unit weight γsat 18.67kn/m � cohesion c 5kpa the angle of internal friction ϕ 26.8° young’s modulus of elasticity e 5110kpa poisson’s ratio υ 0.25 b. reinforced slope with jute fibers for slope stability by adding a surface cover, slopes can be stabilized. the slope reinforcement and the geometry of the slope can be modified with support structures. continuous fibers are woven, stitched, braided, or knitted into the fabric from twisted and plied yarn to create multidirectional reinforcements. almost any reinforcing fiber can be utilized to make fabrics. to enhance its resiliency and strength, incorporating reinforced material into the soil is involved in the method of soil stabilization. jute fibers are widely known for their ability to be spun into coarse and strong threads. jute fibers are noted for their glossy, long, and soft nature. jute fibers can be utilized to strengthen soil to improve its engineering qualities. to endure rot and heat, jute fibers are utilized because of their high tensile strength, superior durability, and excellent drainage and filtration provided by its porous texture. jute fibers are also inexpensive, readily available, biodegradable, and environmentally beneficial. lateral deformation prevention, settlement, ductility, bearing capacity, and strength are improved by the soil reinforcement. jute fibers have the highest tensile strength among all natural fibers and can withstand rolling and heat. the fibers provide a high level of fineness and flexibility. jute fibers were utilized for the slope stability improvement (figure 2). in terms of fatigue and mechanical qualities, woven jute hybrids were found to be environmentally benign, cost-effective, and lightweight. fig. 2. jute fibers. table ii. jute fibers mechanical properties characteristics values density ρ 1.35gm/cc young’s modulus e 20gpa poisson’s ratio υ 0.38 shear modulus g 7.24gpa tensile strength t 393mpa iii. experimentation and result discussion all slope models were created in a specially designed chamber. the initial ratio of the slope is 2:1, and it contains rainfall nozzle, frame, inlet pipe, outlet pipe, rain gauge, and a digital tensiometer. initially, the soil samples are set up in slope format. here, the rainfall intensity is fixed in the experiment to test the slope soil stability. the rainfall nozzle, inlet pipe, and outlet pipe are utilized for rainfall intensity. after the rainfall intensity, cracks are appearing on the soil and slope failure occurs. fig. 3. experimental setup. for the rainfall measurement, a standard rain gauge instrument was used. this is a fundamentally 203mm diameter engineering, technology & applied science research vol. 13, no. 1, 2023, 9919-9925 9922 www.etasr.com kumar & roy: investigating the slope stability and factor of safety properties of soil reinforced with … circular funnel that collects rain into a calibrated and graduated cylinder. precipitation up to 25mm can be recorded by the measuring cylinder. the free energy shifts in a unit volume of water, known as matric suction. the digital tensiometer was used to measure the matric suction of the soil. figure 5 represents the experimental results of saturated slope deformation without utilizing jute fibers. this depicts the original slope as 2.25:1, whereas the embankment slopes are 2:1, 1.5:1, and 1.25:1. fig. 4. measurement of matric suction, rainfall, and slope failures. fig. 5. experimental results of saturated slope deformation without jute reinforcement. a. numerical modeling using the geo-studio 2021 software geo-studio software is generally used for slope analysis, seepage analysis, and deformation analysis. it is based on the finite element method. by using this, the fos of the slope can be determined at a different effective angle. by using sigma/w 2021, the maximum deformation of slope can be calculated and after that it can be compared with the experimental results. the fos of the slope can be calculated using slope/w 2021. here, initially seepage analysis was done by using seep/w 2021 and after that, it is utilized as a parent analysis in slope/w and sigma/w for calculating the deformation vector, the deformation mesh, and fos. ultimate load (strength) allowable load (stress) fos = (1) (a) (b) (c) (d) fig. 6. fos of original slope and different embankment slopes. (a) 2.25:1, (b) 1.5:1, (c) 2:1, (d) 1.25:1. table iii. fos at different embankment slopes embankment slope fos 2.25:1 1.349 2:1 0.973 1.5:1 0.826 1.25:1 0.686 engineering, technology & applied science research vol. 13, no. 1, 2023, 9919-9925 9923 www.etasr.com kumar & roy: investigating the slope stability and factor of safety properties of soil reinforced with … figure 6 exhibits the fos of original and embankment slopes. the initial figure depicts the original slopes of 2.25:1, next figure reveals the factor of safety for the embankment slopes of 2:1. then the factor of safety for the embankment slopes 1.5:1 and 1.25:1 is demonstrated in the last two figures. b. deformation analysis by using geo-studio sigma/w 2021 to perform deformation and stress analysis of earth structures, the finite element cad software sigma/w was utilized. deformation examination for mesh deformation and vectors has been completed at different embankment slopes. maximum deformation was recorded and its value was compared with the experimental data. figure 7 depicts the vector deformation of different embankment slopes of 2:1, 1.5:1, and 1.25:1. vector deformation defined the deformation pattern during slope failure of each soil particle present inside the embankment slope after heavy rainfall. (a) (b) (c) fig. 7. vector deformation of different embankment slopes. figure 8 depicts the matric suction comparison with and without 3 rows of jute for 50 mm/hr and 100 mm/hr rainfall at the middle of the slope. it shows that samples with jute perform better than the ones without jute. figure 9 represents the variation of matric suction with time for the top, middle, and bottom of the slope. it is noticed that the matric suction variation for the top layer is higher than the matric suction variation of the middle and bottom layers. (a) (b) fig. 8. matric suction comparison with and without jute fibers. (a) (b) (c) fig. 9. matric suction variation with time. engineering, technology & applied science research vol. 13, no. 1, 2023, 9919-9925 9924 www.etasr.com kumar & roy: investigating the slope stability and factor of safety properties of soil reinforced with … table iv. experimental and numerical values of using jute fibers emb. slope no jute (mm) 2 rows of jute (mm) 3 rows of jute (mm) 4 rows of jute (mm) exp. value num. value exp. value num. value exp. value num. value exp. value num. value 2:1 12.5 9.8 10.6 7.6 8.5 5.6 4.4 2.3 1.5:1 17.7 14.6 16.6 13.7 13.4 7.8 9.6 4.6 1.25:1 33.8 25.8 29.2 22.4 24.8 14.6 18.5 11.8 (a) (b) (c) (d) fig. 10. fos variation with (a) 2, (b) 3, (c) 4 rows of jute fibers and (d) without jute fibers. table iv reveals the deformation values for different embankment slopes, using 2, 3, and 4 rows of jute and without jute. it can be seen that the deformation when using jute is very lower than when not using jute. the performance of using 4 rows of jute is higher than the others. figure 10 demonstrates the fos variation with and without using jute for the rainfall intensity of 50, 100, and 150mm/hr. the figure clearly shows that the performance of 4-row jute samples is better than the others'. iv. conclusions soil stabilization is very important for embankment, but soils like clay and silt are weak for slope embankment. during heavy rainfall, these soils produce cracks and slope failures. to overcome these problems, jute fibers are combined with the soil to improve its stability. this research attempts to experimentally test slope stability. the rainfall intensity is used to assess the slope's stability and several soil tests were carried out. during the experimental and numerical analysis of the slope stability, several cracks and deformations occurred. due to this failure, the inclusion of jute fibers and its effectiveness to strengthen the soil slope under heavy rainfall condition was assessed. for the embankment slope 2, 3, and 4 rows of jute fibers were considered, and the factor of safety and matric suction were calculated. the main conclusions of the current study are:  according to the sieve analysis, the soil samples are wellgraded with 27.17% silt and clay soil and 72.83% sand.  the liquid limit of the soil is 21%, the plasticity limit is 15%, and the plasticity index is 6%.  the results from the soil permeability test gave a dry unit weight of 14.5kn/m 3 and a saturated unit weight of 18.67kn/m 3 .  regarding the direct shear test for sample test 1, the normal stress is 0.5kg/cm 2 , and the strain rate is 0.25mm/min. the predicted shear load failure is 0.093kn, the failure shear stress is 0.29588kg/cm 2 . for sample test 2, the normal stress is 78.48kn/m 2 , and the strain rate is 0.25mm/min, the shear load and shear stress failure are 0.133kn and 42.97kn/m 2 . for sample test 3, the normal stress and the strain rate are 98.1kn/m 2 and 0.25mm/min, and the shear load and shear stress failure are 0.160kn and 51.993kn/m 2 .  the experimental results for slope deformation and factor of safety were determined, and the vector deformation and mesh deformation were expressed for embankment slopes of 2:1, 1.5:1, and 1.25:1. the deformation analysis was performed in geo-studio sigma/w 2021.  the experimental results utilizing jute fibers for factor of safety, mesh deformation, and matric suction are described in the test results section above. the overall performance of 4-row jute fiber samples is better than without using jute fibers or by using less rows of fibers.  utilizing jute fibers improves the stability of the soil, the factor of safety, and matric suction performance. engineering, technology & applied science research vol. 13, no. 1, 2023, 9919-9925 9925 www.etasr.com kumar & roy: investigating the slope stability and factor of safety properties of soil reinforced with … references [1] f. kassou, j. b. bouziyane, a. ghafiri, and a. sabihi, "slope stability of embankments on soft soil improved with vertical drains," civil engineering journal, vol. 6, no. 1, pp. 164–173, jan. 2020, https://doi.org/10.28991/cej-2020-03091461. 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[24] z. wang, q. li, n. zhang, y. jin, h. qin, and j. ding, "slope failure of biotreated sand embankments under rainfall conditions: experimental investigation and numerical simulation," bulletin of engineering geology and the environment, vol. 79, no. 9, pp. 4683–4699, nov. 2020, https://doi.org/10.1007/s10064-020-01850-7. microsoft word etasr_v12_n6_pp9687-9691 engineering, technology & applied science research vol. 12, no. 6, 2022, 9687-9691 9687 www.etasr.com mouhoub et al.: performance analysis of ultrathin cu(in,ga)se2 solar cells with backwall superstrate … performance analysis of ultrathin cu(in,ga)se2 solar cells with backwall superstrate configuration using amps-1d abdelhafid mouhoub electronics department, amar teliji university and laboratory of electrochemical and materials, setif-1 university, algeria a.mouhoub@lagh-univ.dz fahima khaled electronics department mohamed el bachir el ibrahimi university bordj bou arreridj, algeria khaled_fahima@yahoo.fr abdessalem bouloufa laboratory of electrochemical and materials setif-1 university setif, algeria a_bouloufa@yahoo.fr received: 17 september 2022 | revised: 29 september 2022 | accepted: 3 october 2022 abstract-this study used amps-1d to peform numerical simulations and model the behavior of back-wall superstrate solar cells based on cu(in,ga)se2 (cigs) thin films to investigate optimal conditions and obtain maximum efficiency. the effects of absorber thickness and density of interface defects were examined along with the work function of the transparent conductive oxide (wtco) to investigate their influence on the output parameters. measurements of device performance (j-v) and quantum efficiency (qe) showed that the performance of the cell improved as the thickness of the cigs layer decreased because photons were absorbed near the junction. the device achieved an efficiency of 16.4% using an optimal thickness for the cigs layer on the order of 0.3µm, defect densities in the range of 10 13 -10 15 cm -3 , doping concentration of the n-tco back contact on the order of 10 19 cm -3 , and wtco in the range of 4.55.2ev. these results show that the generated electron-hole pairs had a high probability of separation and demonstrate the potential of this device structure. keywords-cu(in,ga)se2; thin films solar cells; backwall superstrate; transparent conductive oxide; device modeling i. introduction cu(in,ga)se2 (cigs) is regarded as one of the most promising semiconductors for use in thin-film photovoltaic applications [1, 2], due to its sizeable optical coefficient in the range of the solar spectrum and its electrical and optical properties, which vary depending on the preparation condition and the production technique [3, 4]. the production of this semiconductor using various techniques and different types of substrates was examined in [5, 6]. higher efficiency of cigs thin film solar cells was achieved recently, with values exceeding 23.4%, from devices in the typical substrate cell configuration [1, 7], wherein the first step of device fabrication, the molybdenum layer was deposited as a back contact layer on soda-lime glass (slg), followed by the deposit of the pcigs absorber layer. then, the n-type buffer layer grew on top of the cigs to form the crucial p-n junction [8] that completes the structure of the solar cell. next, a thin layer of high resistance intrinsic (i-zno) was applied to the front window, followed by a thin layer, to form the front electrode while ensuring the optimal transmission of solar spectrum photons. the device was finished by depositing the collecting grid [9] and illuminated through the tco window layer [10, 11]. the best performances were obtained by depositing 20-50nm of the cds buffer layer on top of the cigs absorber layer, whose thickness was around 2-3µ m [12-14]. the economic aspect remains critical in the industrial development of cigs technology [14], and it is necessary to reduce its production cost. one of the drawbacks of this process remains the use of rare elements, such as indium and gallium [11, 12]. in this context, this study investigated the development of low-cost and environmentally friendly photovoltaic cells. reducing the thickness of the cigs has the eventual benefit of reducing costs, while fast fabrication and limiting the use of rare elements can achieve higher manufacturing throughput [15-17]. the back-wall superstrate configuration of cigs photovoltaic devices has the potential for better light harvesting than the substrate cell structure [17-19]. in this structure, the manufacturing sequences are reversed concerning the substrate configuration. in the first step, the absorber layer is deposited onto the tco window layer and illumination comes from the back region. hence, a wide band gap transparent back contact is required in the structure [20]. in addition, the critical absorber buffer interdiffusion is restricted [1, 2]. this study focused on an original back-wall superstrate solar cell of the corresponding author: abdelhafid mouhoub engineering, technology & applied science research vol. 12, no. 6, 2022, 9687-9691 9688 www.etasr.com mouhoub et al.: performance analysis of ultrathin cu(in,ga)se2 solar cells with backwall superstrate … type slg/n-sno2:f/p-cigs/n-in2se3/i-zno/mo. the cigsbased cell eliminates the need for transparent encapsulation due to the collection grids at both the cell and the module productions and the requirement for toxic cadmium sulfide (cds) used in conventional cells [1]. developing solar cells with high conversion efficiency and based on hetero-structures requires knowledge of the effects that limit their photovoltaic performance, in particular the phenomenon of diffusion and recombination at the interfaces and in the volume of the material of the different layers of the device. the cigs-based back-wall superstrate solar cell's behavior has been the subject of considerable theoretical modeling efforts in this area. this study investigates the main parameters likely to be involved in the optimization of the photovoltaic performance of the cells studied using amps-1d [21, 22], proposing indicative design parameters for the back-wall superstrate solar cell. therefore, this study focuses on the investigation of the properties of the absorber layer with different thicknesses, densities of interface defects (nit), and the tco/absorber interface that may limit current transport in the cell, aiming to examine the limits of the device and determine the most favorable parameters. the best obtained efficiency was 16.4%, showing the prospects of this structure. the simulations results were found to be in good agreement with the values reported in [2] and allowed the verification of the proposed amps parameters. however, the main motive of this study was to examine the trends of device performance rather than predict optimum values. ii. details of the simulated solar cell the amps-1d software was used to evaluate the performance of the device as the design of the absorber layer varied. the numerical modeling of the semiconductor device was based on the simultaneous resolution of the poisson and the continuity equations for the holes and electrons [23, 24]. amps-1d solves three coupled differential equations in suitable limit conditions and then evaluates the electrostatic potential and the quasi-fermi level for holes and electrons at any point in the device [25, 26]. once these variables are identified according to the depth, it is easy to evaluate the carrier concentrations, electric fields, current density-voltage characteristics (j-v), quantum efficiency (qe) curves, and the photovoltaic output parameters open-circuit voltage (voc), short-circuit current density (jsc), fill factor (ff), and efficiency (η) [6]. these parameters describe the performance of solar cells [25, 27]. modeling solar cells has the advantage that all device and material properties are well restricted as they are input parameters of the model. therefore, trend assessment and quantified changes in j-v or qe measurements are probable. the chosen back-wall solar cell structure consists of a stack of thin layers: slg/sno2:f/p-cigs/n-in2se3/i-zno/mo. the tco layer is required to form the front electrode while ensuring the optimal transmission of the solar spectrum photons. sno2 was chosen for its excellent conductivity, as it is a wide-gap semiconductor [28]. the thin layer of in2se3 was deposited on the cigs absorber layer, which is involved in the formation of the p-n junction and also protects the surface of the cigs. figure 1 shows the proposed cigs solar cell. the interface recombination velocities were fixed at 10 7 cm/s and the light reflection of the rear and the front contacts were assumed to be 1 and 0.1 respectively. am 1.5d solar radiation was used as the illumination source, corresponding to a power of 1000w/m 2 . the electrical and optical properties of the cigs layer were incorporated using the close-spaced vapor transport technique [21]. table i shows the parameters of each semiconductor of the typical cell used in the simulation, as reported in the literature. fig. 1. basic structures of back-wall superstrate device. table i. baseline parameters used for the backwall superstrate cigs solar cells in the simulations parameters i-zno in2se3 cigs sno2:f layer thickness: d (nm) 50 50 variable 300 dielectric constant: ɛr 9 10 13.6 9 effective conduction band density: nc (cm -3 ) 2.2×10 18 2.2×10 18 2.2×10 18 2.2×10 18 effective valence band density: nv (cm -3 ) 1.8×10 19 1.8×10 19 1.8×10 19 1.8×10 19 doping concentration: (na) (cm -3 ) / / 2×10 16 / doping concentration: (nd) (cm -3 ) 1×10 14 1×10 16 / 1×10 19 band gap: eg (ev) 3.30 2.40 1.20 3.6 electron affinity: χ (ev) 4.00 3.80 4.10 4.00 electron mobility: μe (cm 2 /v.s) 100 50 50 100 hole mobility: μh (cm 2 /v.s) 25 12 12 25 defect density: ndg/nag (cm -3 ) 1.5×10 14 1.5×10 17 1×10 12 1.5×10 14 capture cross-section electrons: σe (cm 2 ) 1×10 -13 1×10 -17 1×10 -13 1×10 -13 capture cross-section holes: σh (cm 2 ) 1×10 -15 1×10 -12 1×10 -15 1×10 -15 iii. results and discussion a. effect of the cigs absorber layer thickness several studies focused on reducing the thickness of the absorber layer without affecting solar cell performance. a simulation of the j-v characteristic was obtained by varying the thickness of the p-cigs layer in the structure between 0.05 and 2µm to obtain the optimal results for the back-wall superstrate configuration cells. figure 2 shows the variation of the current density as a function of the bias voltage for different thicknesses of the absorber layer. engineering, technology & applied science research vol. 12, no. 6, 2022, 9687-9691 9689 www.etasr.com mouhoub et al.: performance analysis of ultrathin cu(in,ga)se2 solar cells with backwall superstrate … fig. 2. current-voltage characteristics of the solar cell with different thicknesses of cigs absorber. the absorber's thickness significantly influences the performance of the photovoltaic cell. the results showed that the variation and reduction of d(cigs) from 2 to 0.3µm lead to an increase of jsc from 20.19 to 36.42ma/cm 2 . this means that the power provided by the cell increases as the thickness of the cigs layer decreases and the efficiency is lost due to the parasitic losses, including higher series resistance. the thickness of the cigs layer affects the quantum efficiency of the solar cell, as shown in figure 3, and the active layer affects the short wavelength. for the thick absorber layer, the photogeneration process is produced far from the back contact region and, therefore, not near the electric field of the space charge region (zce). fig. 3. the quantum efficiency of the device with different absorber thicknesses. the generation probability in a thin absorber less than 0.5µm is very high and, therefore, produces photocarriers close to the electric field. this is partly due to a considerable absorption loss in the rear region of the cigs absorber layer. another probable explanation is that the diffusion length of the minority carrier layer in a thinner absorber layer is similar to its thickness. as a result, qe(λ) at a short wavelength is improved without a significant decrease in efficiency, and the parasitic absorption in the buffer layer is prevented, as shown in figure 3. the optimal absorber layer thickness was approximately 0.25-0.5µm in this case, which reduces the thickness of the absorber layer and has the eventual benefit of reducing the cost of manufacture due to the reduced material usage. b. effect of absorber thickness on photovoltaic parameters figure 4 illustrates the influence of the thickness of the cigs on the photovoltaic parameters of the cell (jsc, voc, ff, and η). it can be noted that the voltage voc is practically constant when reducing the thickness of the p-cigs absorber layer from 2 to 0.25µm. the current density of jsc strongly depends on the thickness of the p-cigs absorber, and it increases with decreasing thickness. the efficiency of cell structure also increases rapidly because the photons are absorbed close to the p-cigs/n-in2se3 junction and the generated photocarriers have a high probability of being separated. for absorber thickness greater than 0.5µ m, the photons are absorbed away from the electric field, so that voc and jsc decrease as the thickness of the absorber increases up to 2µm. reducing voc and jsc results in a reduction in conversion efficiency (η). this is probably due to imperfections in the thick absorber, which allowed the emergence of many defects. when the absorber thickness is reduced below 0.25µm, the performance of the device begins to deteriorate due to incomplete optical absorption. a maximum cell conversion efficiency of 16.4% was obtained for a thickness in the range of 0.25 to 0.5µm for the cigs absorber. fig. 4. the dependence of solar cell performance on cigs thickness with deferent nd(tco). c. effect of the density of defects nit of the absorber layer on the performance of the cell figure 5 shows the effect of the concentration of the absorber layer defects on the photovoltaic parameters (jsc, voc, ff, and η) with various doping concentrations of the tco layer. the results showed that high efficiency is achieved when the defect density is in the range of 10 12 to 10 15 cm -3 , because the barrier that causes the recombination is not produced at the cigs/in2se3 interface, and jsc, voc, ff, and η are practically constant. on the other hand, when the concentration of the engineering, technology & applied science research vol. 12, no. 6, 2022, 9687-9691 9690 www.etasr.com mouhoub et al.: performance analysis of ultrathin cu(in,ga)se2 solar cells with backwall superstrate … absorber layer defects is more significant than 10 15 cm -3 , the variation of voc, jsc, and ff becomes very significant, affecting the cell's performance. these parameters decrease sharply as a result of the formation of a barrier in the face of the photogenerated electrons. a strongly doped layer of tco is also preferred to shove the electrons photogenerated inward the bulk of the absorber. fig. 5. the photovoltaic parameters as a function of cigs density defect with deferent nd(tco). d. effect of the back tco/cigs contact region the development of a high-quality tco back-contact while maintaining the efficiency of light transmission throughout the top cigs layer is essential to obtain a high efficiency of the back-wall solar cells. the tco work function (wtco) of the back contact region was a means factor in affecting the backwall solar cell performance. figure 6 shows the dependence of the performance of the sno2:f/p-cigs/n-in2se3/i-zno/mo solar cell on the variation of wtco. it can be seen that voc, ff, and η increase with wtco of the back slg/sno2:f/p-cigs surface. it is necessary to use a suitable work function of the back tco to have ohmic contact in the back contact and reduce the barrier recombination. furthermore, when wtco is higher than 5.2ev, the potential barriers of the tco/p-cigs schottky contact are effectively elevated than the crucial nin2se3/p-cigs junction and the tco/p-cigs contact, and the p-cigs/n-in2se3 junction will have potential barriers on the contrary course of action. in that event, overlapping the space charge region involving the two junctions would induce a drop in the device performance. the back contact resistance depends on the barrier potential (фb) and nd(tco). a low height barrier (фb) and a high concentration of nd are needed to have low resistance and ohmic contacts and avoid the depletion zone created at the tco/cigs interface. the simulation results confirm that the nd (tco) is required to be in the range of 10 19 cm -3 , to obtain high performance and induce the increase of the qe(λ), as shown in figure 7, due to the decrease of recombination at the tco/cigs interface. fig. 6. the dependence of solar cell performance on wtco with deferent nd(tco). fig. 7. the dependence of the quantum efficiency on the nd(tco). iv. conclusions this study investigated the performance of back-wall superstrate solar cells using amps-1d software with a modified absorber layer. based on the results, the thickness of the absorber layer, the densities of interface defects (nit), and the work function of the back transparent conductive oxide on the performance of the cigs back-wall superstrate cell structure. to improve conversion efficiency, the cigs absorber thickness must be thinner as possible (0.25µm-0.5µm), because the photons will be captured in the area of the junction, and the generated electron-hole pairs will have a high probability of being split apart because there will be a gap between them. however, the results of the simulation demonstrated that even a high density of defects does not prevent a structure from achieving exceptional levels of performance. the nit of the absorber layer was in the range of 10 12 -10 15 cm -3 . the optimized conditions were the doping concentration of the n-tco back contact nd on the order of 10 19 cm -3 and wtco between 4.65.2ev. the cigs back-wall superstrate solar cell with an absorber layer thickness of 0.3µm showed the best efficiency of 16.4%. engineering, technology & applied science research vol. 12, no. 6, 2022, 9687-9691 9691 www.etasr.com mouhoub et al.: performance analysis of ultrathin cu(in,ga)se2 solar cells with backwall superstrate … acknowledgment the authors express their gratitude to dr. s.j. fonash of the pennsylvania state university for developing amps-1d, which was used in this study. references [1] m. ni, j. m. liu, z. q. li, q. shen, y. z. feng, and x. d. feng, "simulation of graded bandgap on backwall superstrate cigs solar cells with moox electron reflection layer," materials research express, vol. 6, no. 11, jul. 2019, art. no. 116441, https://doi.org/10.1088/20531591/ab4c5c. 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[28] t. b. nasrallah, d. mahboub, m. jemai, and s. belgacem, "temperature effect on al/p-cuins2/sno2(f) schottky diodes," engineering, technology & applied science research, vol. 9, no. 5, pp. 4695–4701, oct. 2019, https://doi.org/10.48084/etasr.3072. microsoft word etasr_v13_n2_pp10541-10547 engineering, technology & applied science research vol. 13, no. 2, 2023, 10541-10547 10541 www.etasr.com ly et al.: a neural network controller design for the mecanum wheel mobile robot a neural network controller design for the mecanum wheel mobile robot trinh thi khanh ly faculty of control and automation, electric power university (epu), vietnam lyttk@epu.edu.vn nguyen hong thai faculty of mechatronics, hanoi university of science and technology (hust), vietnam thai.nguyenhong@hust.edu.vn (corresponding author) hoang thien faculty of mechatronics, hanoi university of science and technology (hust), vietnam hoangthien.hust@gmail.com nguyen thi thanh hanoi university of science and technology (hust), vietnam | university of economics technology for industries (uneti), vietnam ntthanh.ddt@uneti.edu.vn received: 6 february 2023 | revised: 26 february 2023 | accepted: 4 march 2023 abstract advanced controllers are an excellent choice for the trajectory tracking problem of wheeled mobile robots (wmrs). however, these controllers pose a challenge to the hardware structure of wmrs due to the controller's complex structure and the large number of calculations needed. in that context, designing a controller with a simple structure and a small number of computations but good real-time performance is necessary in order to improve the tracking accuracy for the wmrs without requiring high hardware architecture. in this work, a neural network controller with a simple structure for the trajectory-tracking of a mecanum-wheel mobile robot (mwmr) based on a reference controller is proposed. a two-layer feedforward neural network is designed as a tracking controller for the robot. the neural network is trained with a sample input-output data set so that the error between the neural network output and the reference control signal of the supervisory controller is minimal. the neural network parameters are trained to update over time. the simulation results verified the effectiveness of the neural network controller, whose parameters are tuned adaptively to ensure a fast convergence to the desired bézier trajectory. keywords-mecanum wheel mobile robot; tracking control; neural networks; bézier trajectory i. introduction there is a considerable scientific interest in the area of wheeled mobile robots (wmrs), and especially mecanumwheeled mobile robot (mwmrs), which have been widely applied to many fields due to their maneuverability and superior motion ability [1-3]. for control engineers, the trajectory tracking control problem of mwmr has always received significant attention. trajectory tracking control is the key to realizing the autonomous movement of the mwmrs. however, the trajectory tracking control of the wmrs is a challenging study area because wmr systems are typically subjected to non-holonomic constraints, random disturbances and uncertainties. many researchers studied control design and development with different controllers to improve the tracking control performance of the mwmrs. a time-varying parameter pid controller has been proposed in [4] to control a four-mwmr along a desired trajectory with minimal error. an advanced intelligent adaptive motion controller was designed in [5] using fuzzy wavelet networks for mecanum wheeled omnidirectional robots (mwors) with parameter variations. authors in [6] presented a novel neural network adaptive sliding mode control system for an omnidirectional vehicle with four mecanum wheels. network weight adaptation was based on the analysis of the lyapunov stability. other engineering, technology & applied science research vol. 13, no. 2, 2023, 10541-10547 10542 www.etasr.com ly et al.: a neural network controller design for the mecanum wheel mobile robot controllers used for mwmr for trajectory tracking control used adaptive integral terminal sliding mode [7], robust adaptive control [8], adaptive fuzzy tracking control [9-11], pid controller with time-varying parameters [12], adaptive back stepping control using neural networks [13], predictive control [14], self-tuning fuzzy-pid control [15], and fuzzy adaptive pid control [16]. for robots to operate in a dynamic working environment and meet the required safety, accuracy, and reliability, advanced intelligent control systems are a valuable solution for the trajectory-tracking control problem [17-19]. the use of neural networks for the control of mobile robots has received attention from many researchers because they are self-learning and provide a real-time approximation of nonlinearities in a mathematical model of a robot using network weight adaptation [20-22]. artificial neural networks (anns) are increasingly used to solve trajectory tracking problems, such as the adjustment of control coefficients, the choice of the direction of motion, speed correction, and identification of information from sensors. the above discussion verified that the advanced controllers have excellent trajectory-tracking performance. even so, they have the disadvantage that the complex controller structure leads to many complex calculations requiring high hardware structure. therefore, it is necessary to design a controller with a simple structure, a small number of computations and good real-time performance to improve trajectory-tracking performance with a minor error for mwmr. therefore, this work focuses on designing a simple computational ann-based model reference controller to accommodate the trajectory tracking of the mwmr with minor errors, simultaneously significantly reducing the hardware's processing speed and capacity versus advanced controllers. ii. kinematic error model of mwmr a. kinematic model consider an mwmr moving along the bézier trajectory  with the assumption of no longitudinal and lateral slip in the global coordinate system }yxo{ ffff , as shown in figure 1. the angular velocities relationship of wheels to the linear and angular velocities of the mwmr are determined by [4]: f t qjqω ɺ)( (1) where: ttttt ])()()()([ 4321 ω                  rdlrr rdlrr rdlrr rdlrr 2/)(/1/1 2/)(/1/1 2/)(/1/1 2/)(/1/1 j             100 0)(cos)(sin 0)(sin)(cos )( tt tt   q t yx t f vvttytx ][])()()([  ɺɺɺɺq and r, l and d are the radii of the wheel, the distance in the xraxis and the yr-axis of two wheels, vx, vy, and ω are the linear and angular velocities of the mwmr in the global coordinate f , respectively. fig. 1. illustration og the kinematic error of mwmr. from (1), the forward kinematics equation of the mwmr is given by: ωjqqqq  )()(  rf ɺɺ (2) where   tt jjjj 1  is the pseudo-inverse of j. b. kinematic error model the error model describes the variation in position and orientation of the mwmr when moving along the desired trajectory , defined by the position error vector e [23]:  tyxfd eee  qqe (3)  tdddd ttytx )()()( q and  tffff ttytx )()()( q are the mwmr's desired and actual motion pose vectors in the global coordinate f . the kinematic error model of the mwmr in the local coordinate system }yx{g rrr attached to the mwmr is given by:   eqe )( ttryrxrr eee  (4) derivative (4) is obtained by: fdrr qqaeωe ɺɺɺ  ~ (5) where:              000 00)( 0)(0 ~ t t ω and             100 0cossin 0sincos   ee ee a engineering, technology & applied science research vol. 13, no. 2, 2023, 10541-10547 10543 www.etasr.com ly et al.: a neural network controller design for the mecanum wheel mobile robot iii. neural network controller design for the mecanum wheel mobile robot the proposed neural network (nn) control system to track the desired motion trajectory is described in figure 2. the control system consists of the nn controller, the kinematic model of mwmr, the reference controller and the desired trajectory . the nn's parameters are adapted online according to the reference model described in figure 2, in which the reference controller is the kinematic controller proposed in [23] to generate the reference control signals ur to determine the reference linear and angular velocities (vrr, rr) for the mwmr to follow the desired trajectory . in [23], the control gains k1, k2 and k3 of the reference controller are time-varying parameters for mwmr to achieve high tracking accuracy. the parameters for the proposed ann controller are given in table i. the inputs to the ann are the position errors of mwmr e, and the ann’s outputs are nu (the velocities of mwmr). table i. the neural network parameters parameter value number of input neurons 3 number of output neurons 3 number of hidden layers 2 number of neurons in hidden layer 1 3 number of neurons in hidden layer 2 3 n e nf   1 1 )(1 and nnf )(2 are the activation functions of the 1 st and 2 nd hidden layer, respectively. the output nu is compared with the reference control signal ru , and the error is used to adapt the weights w and bias b in order to reduce the nn’s error on the output: 0)(  nru uue (6) n e nf   1 1 )(1 and nnf )(2 are the activation functions of the 1 st and 2 nd hidden layer, respectively. the output nu is compared with the reference control signal ru , and the error is used to adapt the weights w and bias b in order to reduce the nn’s error on the output: 0)(  nru uue (6) iv. neural network controller a. the neuron network controller model it is defined by: ))(( 211122 ttttt n ff bbewwu  (7) where 2112 ,,, bbww are the weight matrix and bias vector of the nn, respectively, and e is given by (2). on the other hand, considering the mwmr's local coordinate system, we have: ndrn uqq  ɺɺ (8) where: ddr qtq ɺɺ  with t        100 001 t qd + neural network controller  fqɺ qf qf e t ρd + drqɺ un ωd vd reference model + nqɺ qd qrf eu + ur rrqɺ + qr er  rfqɺ bézier trajectory kinematic supervisory controller fig. 2. structure of neurocontrolled mwmr with supervised learning. b. neural network training the parameters of the nn, including the weight matrix w and the bias vector b, are updated as the time by the backpropagation method according to the following law:        mmm t mmmm kk kk sbb asww   )()1( )()1( 1 (9) where: -1 +1 +1( )= ( + ) t mm m m n m mks f w a b w s ,  )(,),(),(ndiag)( ,2,1, smmmmmmm nfnffn ɺ…ɺɺɺ f , )( 1 nnnnn f bawa   , engineering, technology & applied science research vol. 13, no. 2, 2023, 10541-10547 10544 www.etasr.com ly et al.: a neural network controller design for the mecanum wheel mobile robot jm imm imm n nf nf , , , )( )(   ɺ , where m = 1, 2,..n, n is the number of layers of the nn, [0,1]a  is the learning rate, fn is the activation function of the m th layer. the weights values of the nn are adjusted so that the cost function given by (10) is minimized: min 2 1  u t ue ee (10) v. simulation setup a. the mwmr dimension setup the dimensions of the mwmr are: length × width × height of 380mm × 260mm×165mm, l = 316mm, d = 270mm, and r = 30mm is the radius of wheels. b. the bézier moving trajectory of the robot the bézier curve [24] is defined by trajectory interpolation points and is given by: 10,)()( 0 ,    ttjbtp n i ini (12) where bi represents the coordinates of interpolated points, as described in figure 3, i is the ordinal number of the interpolation points, and jn,i(t) is a bernstein polynomial of degree n, given by: ini in tt i n tj        )1()(, (13) where )!(! ! ini n i n        is the the pascal coefficient, and n is the bernstein polynomial degree and the curve's degree. from the above bézier curve design method, we have the desired moving trajectory of the robot shown in figure 3 with the points ai (i = 1-14) being the interpolation points. fig. 3. the desired bézier trajectory of the mwmr. c. mwmr linear and angular velocity determination the desired velocity vd(t) of the mwmr is determined by the bézier motion trajectory d as follows: 1 2 1 2 1 )()( )(         ii iiii d tt yyxx t s tv (14) the desired angular velocity ωd of the mwmr is determined by: )(/)()( ttvt dd  (15) where ],[ maxmin  i is the radius of the desired trajectory (i= 1, 2, .), obtained by:   iiii ii i xyyx yx ɺɺɺɺɺɺ ɺɺ    2/322  (16) where:                       1 1 1 1 ii ii i ii ii i tt yy t y y tt xx t x x ɺ ɺ ,                       1 1 1 1 ii ii i ii ii i tt yy t y y tt xx t x x ɺɺɺ ɺɺ ɺɺɺ ɺɺ . clearly, from (14)-(16) and the data of the trajectory interpolation points given in figure 3, we have the desired linear velocity vd and angular velocity ωd of the mwmr described in figure 4 when the mwmr moves along the bézier trajectory  with ∆t = 0.1s and maximal allowed speed vdmax = 0.3m/s. thus, the desired dqɺ vector is defined by  tddd v qɺ . fig. 4. the desired linear and angular velocites of the mwmr. d. setting parameters of neural network training the initialization values at the input/output of the nn while training are: a0 = e, a2 = u and uk ebawfs )()( 21222  ɺ . the learning coefficient  = 1 is determined by trial and error, and is such that the jump does not exceed the optimal value. the parameter matrices are updated online to control the mwmr trajectory tracking with a minor tracking error. vi. results and discussion the installed parameters consist of (1) the size of the mwmr, (2) the parameters and the training parameters of the neural network, and (3) the motion trajectory and the engineering, technology & applied science research vol. 13, no. 2, 2023, 10541-10547 10545 www.etasr.com ly et al.: a neural network controller design for the mecanum wheel mobile robot parameters of mwmr. the motion trajectory of the mwmr, after 1072 online training updates, is depicted in figure 5, with the orange line as the desired trajectory and the blue line as the motion trajectory of the robot controlled by the proposed neural network controller. the position and posture errors of mwmr are depicted in figure 6. fig. 5. the moving trajectory of the mwmr. fig. 6. the position error of the g-point and posture error of the robot. figure 6 shows that the proposed controller has the maximum error in the x-direction (exmax) not more than 11mm, and the maximum position error in the y direction (eymax) is 17mm at position 9. the maximum posture error of the robot eφmax does not exceed 0.34 o . the points marked from 1 to 9 in figure 6 correspond to where the mwmr changes direction in figures 5 and 3. in general, significant position errors often occur at the points where the mwmr changes direction. these are the points where the mwmr changes from clockwise to counterclockwise rotation and vice versa. figures 5 and 6 clearly show that the proposed controller can track the desired trajectory with minor errors. figure 7 shows the cost function value when training the neural network to update the weight matrices w and bias vector b in real time. from figure 7, it is easy to see that at the points where the direction of the mwmr change, the control signal of the neural network has a deviation from the signal of the reference control model. still, it was trained in time to minimize the error to asymptotically reach zero. fig. 7. the cost fucntion. (a) (b) fig. 8. the network parameters of the first hidden layer: (a) the network bias b1, (b) the network weight matrix w1. figures 8 and 9 verify the online updating of the network weight matrix w and bias vector b of the proposed controller for the mwmr to follow the bézier trajectory. the nn weights from zero initial values changed during the adaptation process and stabilized at specific values. since the neural network structure is rather simple, the proposed neural network can find the optimum values of the network parameters quickly and accurately. figure 10 shows that the velocities of the mwmr are adjusted around the desired value such that the mwmr position to an asymptote value is '0'. figure 10 shows that the velocity error vxr ranges from 0 to 0.0011m/s, the velocity error vyr is adjusted around the desired value 0 to 0.0009m/s, and the maximum angular velocity error of mwmr is more than 0.00054rad/s. figure 10 shows that the proposed controller is precisely following the reference linear and angular velocities. figures 11 and 12 show that the angular velocities of the wheels always follow the desired values, and the angular velocities error varies from 0 to 0.05rad/s. the angular velocity errors were limited and had the most significant values at the beginning and at the points where the mwmr changed direction. 0 20 40 60 80 100 -5 0 5 10 w1,3,1 w1,2,1 w1,1,1 scale 200:1 scale 200:1 w1,2,3 w1,1,3 w1,3,3 scale 200:1 w1,1,2 w1,2,2 w1,3,2 w 1 t (s) 0 2 0 4 0 6 0 8 0 10 0 -10 -8 -6 -4 -2 0 2 10-6 scale 40000:1 b1,3 b1,2 b1,1 b 1 t (s) e ③ ① ② ⑥ ⑦ ④ ⑤ ⑧ ⑨ t (s) 0 20 40 60 80 100 0 1 2 3 10-6 -0.05 0 0.05 -0.02 0 0.02 -0.01 0 0.01 0 20 40 60 80 100 e φ ( ra d ) e x ( m ) 0 e y ( m ) ① t (s) t (s) t (s) ② ③ ④ ⑤ ⑥ ⑦ ⑧ ⑨ 40 100 40 100 60 60 80 80 20 20 ③ ① ② ④ ⑤ ⑥ ⑦ ⑧ ⑨ ③ ① ② ④ ⑤ ⑥ ⑦ ⑧ ⑨ 0 y f ( m ) ③ ①, ⑨ ② ⑥ ⑦ ④ ⑤ ⑧ xf (m) -1 0 1 2 3 4 5 6 -1 0 1 2 3 4 5 start point end point scale 30:1 σd σ engineering, technology & applied science research vol. 13, no. 2, 2023, 10541-10547 10546 www.etasr.com ly et al.: a neural network controller design for the mecanum wheel mobile robot (a) (b) fig. 9. the ann parameters of the second hidden layer 2: (a) the network bias b2, (b) the network weight matrix w2. fig. 10. linear and angular velocities of the mwmr. the efficacy of the proposed controller can also be proved from the velocity and error curves, which show that the control system based on the nn controller can track the desired trajectory with minimum tracking error, and the control inputs strictly follow the reference velocities. additionally, the neural network has overcome the disadvantages of our previous studies [4], where the time-varying pid controller was used to control the mwmr, such as (i) the time-varying pid controller requires the linear model of the robot and (ii) the pid controller needs to know the functions of the controller gains and the gains are often assumed as the linear function of the robot error. vii. conclusions the following conclusions can be derived from the results and discussion of the current study. an artificial neural network-based model reference controller for the bézier trajectory tracking of the mecanumwheeled mobile robot with a minor tracking error is proposed in this paper. compared to other controllers, the neural network in the proposed controller has a simple structure, but it effectively improves performance with minor error. this primarily ensures that a small number of computations increases the convergence speed to update the control gains online. the adapted gains are derived by satisfying the condition that the error between the actual and controller outputs is zero asymptotically. fig. 11. the angular velocities of the four wheels. fig. 12. the angular velocity error of four wheels. the simulation results demonstrate the effectiveness of the proposed controller. they show that the errors in the xand ydirections do not exceed 11mm and 17mm, respectively, and the direction error does not exceed 0.34 o . in addition, the position and orientation errors of the mwmr are often significant at the points where the mwmr changes direction to the desired trajectory tracking. we believe this will yield guarantees on the tracking performance of the mwmr. additionally, the proposed controller exhibited motion error, 0 20 40 60 80 100 -1.5 -1.0 -0.5 0 0.5 1.0 w2,1,1 w2,1,3 w2,1,2 w2,3,3 w2,3,2 w2,3,1 scale 5000000:1 t (s) w 2 w2,2,3 w2,2,2 w2,2,1 -3 -2 -1 0 1 2 10-3 0 20 40 60 80 100 b 2 t (s) b2,3b2,2 b2,1 scale 5000000:1 10 -3 t (s) ⑧ ⑦ ⑨ ① ③ ④ ⑤ ⑥ ⑧ ⑨ ⑦ ① ② ③ ⑤ ⑥ ⑨ ⑥ ⑧ ④ ② v xr ( m /s ) t (s) ω r ( ra d /s ) t (s) 10-4 v y r ( m /s ) ① ② ③ ⑤ ⑦ vyr vydr 0 20 40 60 80 100 0 0.1 0.2 0.3 0 20 40 60 80 100 -5 0 5 10 15 0 20 40 60 80 100 0 0.2 ④ scale 30:1 ωr ωdr scale 15:1 vxdr vxr ⑨ ⑧ ⑧ ⑨ ⑥ ⑦ ① ② ③ ④ ⑤ ⑥ ⑦ 0 e ω 2 ( ra d /s ) e ω 3 ( ra d /s ) e ω 4 (r ad /s ) e ω 1 ( ra d /s ) ① ⑨ t (s) t (s) t (s) t (s) 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 ⑨ ① ② ③ ④ ⑤ ① ② ③ ④ ⑤ ⑥ ⑦ ⑧ -0.2 0 0.2 -0.2 0 0.2 -0.2 0 0.2 -0.2 0 0.2 ② ③ ④ ⑤ ⑥ ⑦ ⑧ t (s) ω 3 ( ra d /s ) ω 1 ( ra d /s ) ⑧ ⑧ ⑨ ⑨ ⑥ ⑦ ① ② ③ ④ ⑤ ⑥ ⑦ 0 ω 2 ( ra d /s ) ω 4 ( ra d /s ) ① ② ③ ④ ⑤ ⑥ ⑦ ⑧ ⑨ t (s) t (s) t (s) 15 scale 40:1 20 40 60 80 100 0 5 10 15 0 20 40 60 80 100 0 5 10 15 0 20 40 60 80 100 0 5 10 15 0 20 40 60 80 100 0 5 10 ⑨ ① ② ③ ④ ⑤ ① ② ③ ④ ⑤ ⑥ ⑦ ⑧ ω1d ω1 scale 40:1 ω2d ω2 scale 40:1 scale 40:1 ω4d ω4 ω3d ω3 engineering, technology & applied science research vol. 13, no. 2, 2023, 10541-10547 10547 www.etasr.com ly et al.: a neural network controller design for the mecanum wheel mobile robot including the linear velocity error, limited to 0.0014m/s and angular velocity error limited to 0.00054rad/s. likewise, the proposed controller can be applied to any desired trajectory with minimal control action and perfect orientation with low hardware structure cost. nevertheless, this research does not account for the longitudinal and lateral slip, friction at the wheel-ground contact points, friction between the roller rotation and the roller's shaft on the wheels, and inertia forces. these are considered parts of our future research goals. acknowledgement this research is funded by hanoi university of science and technology (hust) under project number t2022-pc-030. master's student hoang thien was funded by the master scholarship programme of vingroup innovation foundation (vinif), code: vinif.2022.ths.128. references [1] m. szeremeta and m. szuster, "neural tracking control of a fourwheeled mobile robot with mecanum wheels," applied sciences, vol. 12, no. 11, jan. 2022, art. no. 5322, https://doi.org/10.3390/ app12115322. 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[24] l. t. k. trịnh and h. thien, "bézier trajectory tracking control of the omnidirectional mobile robot based on a linear timevarying state feedback controller," vnuhcm journal of science and technology development, vol. 25, no. 2, pp. 2444–2452, aug. 2022, https://doi.org/10.32508/stdj.v25i2.3914. microsoft word etasr_v13_n2_pp10535-10540 engineering, technology & applied science research vol. 13, no. 2, 2023, 10535-10540 10535 www.etasr.com nguyen et al.: multi-goal feature selection function in binary particle swarm optimization for power … multi-goal feature selection function in binary particle swarm optimization for power system stability classification ngoc au nguyen ho chi minh city university of technology and education, vietnam aunn@hcmute.edu.vn hoang minh vu nguyen ho chi minh city university of architecture, vietnam vu.nguyenhoangminh@uah.edu.vn trong nghia le ho chi minh city university of technology and education, vietnam trongnghia@hcmute.edu.vn (corresponding author) received: 20 february 2023 | revised: 3 march 2023 | accepted: 8 march 2023 abstract the input feature is vital for power system stability classification. feature selection can reduce the size of the input feature, making classifier training easier, and the small size of the input feature subset also reduces the cost of purchasing sensor measurement equipment. therefore, feature selection works require an efficient seeking method. binary particle swarm optimization (bpso) is a simple and easy-toimplement evolutionary calculation technique. while the classification accuracy of bpso is essential, it is also needed to drive the algorithm to minimize the number of variables. the proposed approach is to apply a multi-objective function to help the bpso algorithm identify the subset of features that can achieve the minimum number of variables and the highest classification accuracy. the k-nearest neighbor classifier is employed in the experiments to evaluate the classification performance on the ieee 39-bus dataset. keywords-feature selection; classification; power system stability; bpso; k-nearest neighbor classifier i. introduction stability analysis of electrical systems is a highly complex problem [1]. stability losses of electrical system cause widespread power outages and often significant economic damage [2]. the load growth is outpacing the investment in transmission lines and power generation. as a result, incidents can easily lead to power system instability and outages [3, 4]. therefore, rapid detection of power system instability is crucial [1], but traditional analytical methods cannot achieve it. this difficult requirement can be resolved using a recognition method [5-7]. once trained on input-output data, operating modes, and stability modes of the electrical system, the recognition system will quickly detect the instability of the electrical system [8]. however, the abundance of input data is a significant obstacle for the recognition system in learning and operation, adding a high cost of measuring sensor data and collecting data. therefore, in recognition problems, the important issue is to make the input variables accurate and straightforward. in recognition of the stability analysis of electrical systems, previous studies have proposed solutions for the primary variable selection process, mainly using ranking methods to select variables. the relief method and the divergence criterion are applied in [9]. in [9-10], the fisher criterion is applied. ranking methods are based on statistical criteria but do not consider the recognition error and are not optimal. advanced calculation techniques can help optimally expand the search space. binary particle swarm optimization (bpso) is a simple and easy-to-implement candidate computational optimization algorithm for feature selection in the stable electrical system classification problem. in this, the important objective function is the classification error. however, more than one objective functions based solely on classification error are required to guide the bpso algorithm toward selecting small and low-dimensional inputs [11]. this paper proposes the application of a multi-objective feature selection function based on the minimum classification error with minimum size of feature-subset or the highest classification accuracy with the least number of input featuresubset. the k-nearest neighbor (k-nn) algorithm is engineering, technology & applied science research vol. 13, no. 2, 2023, 10535-10540 10536 www.etasr.com nguyen et al.: multi-goal feature selection function in binary particle swarm optimization for power … recommended for assessing the classification performance in the bpso algorithm. the proposed method is tested on the ieee-39 bus power system data. ii. background a. goal function 1) correct classification in the steady-state power system classification, the correct classification is calculated according to (1): (%) 100(%) csc cc tsc  (1) where csc (correct sample classification) is the number of correctly classified samples and tsc (total sample classification) is the total number of samples in the sample set. 2) error classification error classification is calculated by: (%) 1 (%)ec cc  (2) 3) multi-objective selection function in bpso (figure 1), the total number of variables in the data set is the size of the search space. a binary string represents each candidate (a particle). the bits '1' and '0' correspond to the selected and unselected variable, respectively. fig. 1. the bpso algorithm. the single objective function (2) only contains the classification error, which can lead the bpso algorithm to converge to a solution with many variables. there are two main objectives in variable selection: the lowest classification error and the smallest number of selected variables. therefore, the variable selection objective function (3) combines these two objectives. in practice, the number of selected variables (sf) is larger than the classification error (ec). to balance these two quantities, the second quantity of the objective function is the ratio of the number of selected variables to the total number of variables, which is aimed at converting the second quantity into the sequence (0, 1]. gf sf ec tf   (3) the objective function (3) reflects the importance of the misclassification error and the minimum number of variables having equal weighting or a weighting ratio of 1:1. if we want to consider the importance of the classification error rate and the number of selected variables differently, the  weight is introduced into (3) to become: gf . (1 ). sf ec tf     (4) where [0,1]. for (0.5,1], the classification error has a higher weight than the number of selected variables, while the opposite takes place when (0,0.5) and when  = 0.5 the importance of the classification error and the number of selected variables is equal. b. bpso algorithm the pso algorithm is a nature-inspired approach proposed for solving continuous optimization problems [12]. the bpso algorithm was developed for discrete optimization problems [13]. a matrix representing the stability of an electric system is presented below. this data matrix is represented by the vector �� . the vector �� = ( ��� , ��� ,…, ��� ) used in the bpso represents the position of the ��� sample. the vector � = ( ��, ��,…, ��) is used to represent the velocity of the � �� sample. the size of the search space is designated as d. throughout the search process, the optimal position of each individual is recorded as �� � . the global best position, representing the most advantageous location for the entire herd, is referred to as ��� � . the individuals in the herd are randomly generated from the population. the objective is to find the optimal solution by iteratively updating the position and velocity of each individual based on (5) and (6). 1 1 id id id t t t x x v    (5) 1 1 1 2 2 * ( ) ( ) id id t t t i id id t i gd id v w v c r p x c r p x       (6) where t is the � �� iteration of the search process, dd is the size in the search space, �� , �� are acceleration constants, ��� , ��� are random values, valid in the range (0,1), �� and �� represent �� � and ��� � particles of size d, w is the inertial weight, v is the velocity, limited to the maximum velocity ��� , and ��� �− ��� , ��� �. the velocity in bpso represents the element that can take the value 1. equation (6) is still used to update the velocity while ��� , �� get the value 0 or 1. the sigmoid function s( �� ) engineering, technology & applied science research vol. 13, no. 2, 2023, 10535-10540 10537 www.etasr.com nguyen et al.: multi-goal feature selection function in binary particle swarm optimization for power … is used to convert the value of �� into a range of values in (0,1). the bpso updates each sample's position using (7) and (8). the rand() function is a random number generator with a uniformly distributed output between 0 and 1. 1, () ( ) 0, id id if rand s v x otherwise     (7) 1 ( ) 1 id id v s v e    (8) iii. steps to implement variable selection in the stability classification problem of the power system. the methodology for selecting variables in the stability classification of power systems involves the steps depicted in figure 2: initial variable selection analysis, data collection, the proposed variable selection method, and, lastly, the implementation and results. fig. 2. steps to implement variable selection. step 1: initial variable selection analysis. analysis for system stability assessment found that major disturbance events, such as short circuits, have a high potential to cause system instability. thus, short circuits are of particular concern. examining these input variables is crucial for the determination of their impact on the stability of the electrical system. this allows for the selection of variables that are strongly correlated with system stability, and facilitates the identification of key initial variables while eliminating unnecessary ones. the goal of variable selection is to minimize the number of variables used in the analysis, while maintaining the highest level of accuracy in the classification process. the selection of initial variables is a preliminary screening step to make the subsequent steps easier. the selected variables must have a low cost of sensor measurement. suppose all variables related to the electrical system are considered. in that case, the number of variables is very large, such as the powerful effect of branches, the power resistance of branches, the powerful effect of generators, the power resistance of generators, generator voltage current, generator speed, the relative angle deviation of the generators from the standard machine, etc. the analysis of the electrical system's stability reveals a direct correlation between the loss of stability and changes in active power and voltage. therefore, it is imperative to consider these variables. step 2: collect and organize data. the initial data collected can be historical data stored in the data collection system when operating the power system, or they can be simulated using specialized software to build the initial data set. the data consist of input and output data. the data set is stored as a matrix of data. the input data includes data columns containing information about variables, and the data matrix rows contain the variables' parameters. the output data is a matrix containing information on whether the system is stable or unstable, assigned binary labels, matrix y (bit '1' is stable, and bit '0' is unstable). figure 3 presents the organization of the input and output data matrix. fig. 3. input and output matrix. step 3: proposed variable selection method. as presented above, studies on stability recognition of electrical systems mainly apply statistical standards to rank variables. the result is that the ranking method still does not give the result of how many variables are selected and what they are. the automatic and optimal selection of variables is still a big question. the bpso algorithm is a promising candidate for variable selection in the stability classification of electrical systems and the use of one multi-objective function to guide the bpso algorithm to find the best results is proposed. the multi-objective function is introduced in section ii.a.3. when selecting recognition sets to evaluate classification accuracy, they must meet the requirements of simplicity without considering computational time. through our experiment, we found that the k-nn tool meets this criterion. step 4: implementation and results. choosing the optimal set of variables is a challenging problem as it depends on too many factors. thus, many aspects must be considered to choose the best possible set of variables. therefore, the multiobjective function (4) is suggested to be applied for variable selection in the implementation step. iv. experimental results and discussion a. results the experiment was conducted on the ieee 39 bus system, which comprises 39 buses, 10 of which are dedicated to generation. additionally, the system consists of 12 transformers, 10 generators, 34 transmission lines, and 19 loads. ten generators are connected from bus 30 to bus 39, where bus 39 is chosen as the reference bus, 9 buses are pv buses, and the remaining 29 buses are pq buses, with two different voltage levels of 345kv and 20kv. the ieee 39 bus system diagram is shown in figure 4. a hp probook laptop, intel(r) core(tm) i7 8th gen, 8gb ram was used. proposed variable selection method the initial variable selection analysis data collection implementation and results engineering, technology & applied science research vol. 13, no. 2, 2023, 10535-10540 10538 www.etasr.com nguyen et al.: multi-goal feature selection function in binary particle swarm optimization for power … initial variable selection analysis: the input variables are in the dynamic state containing information about the established operating mode and the fault mode, combined with expert opinions to select the initial variables, including voltage deviation at the buses {delvbus}, load power deviation {delpload}, and transmission line power deviation {delpflow}. the input and output variables are x and y. the survey on the diagram has 39 voltage deviation variables at the buses, 19 load power effect variables, and 46 branch power effect variables. the total number of input variables is 104 and there is only 1 output variable. fig. 4. ieee 39 bus system diagram. data collection: offline simulation was conducted using powerworld 18 software to collect data for power system stability assessment. in this experiment, the load level considered is 100% of the base load, and the fault scenario is a short circuit. in the load flow examination, the software computes the optimal power distribution and the corresponding power flow. the faults considered are three-phase short circuits, one phase to ground, and two phases at all busbars, and along all transmission lines, with each spacing of 5% of the length of the transmission line. the cutting time of the short circuit is 50ms [14]. the state of the power system is stable when the rotor angle deviation of any two generators does not exceed 180 o , and it is not stable when it does. the simulation results show that the data set contains 317 samples, 177 stable and 140 unstable. bpso algorithm and multi-objective variable selection: the k-nn (k=1, 1-nn) classifier is selected as the partitioning method. the accuracy of 1-nn classification was evaluated with the cross-validation method with k-folds=10. it involves dividing the dataset into 10 equal parts or "folds." the model is then trained on 9 of the folds and tested on the remaining 1 fold. this process is repeated 10 times, each time using a different fold for testing, while the other 9 folds are used for training. the result is the average of these 10 times. the calculation functions are supported by matlab 2018b. the bpso-1-nn algorithm is applied to execute the variable selection. the considered values to evaluate the importance of components in the multi-objective optimization variable selection function (4) are: n = {10, 20, 30, 40, 50}, w = 0.9, t = 100, �� = 2, �� = 2, while  is considered to have values in (0,1] with a step of 0.1. the convergence trajectory of the algorithm is illustrated in figure 5. the results of the variable selection, objective function value, and classification accuracy are presented in table i. b. discussion the algorithm selected 11 variables with corresponding values of  weight of 0, 0.2, 0.3, and 0.4. among them, =0.2, n=20, and sf=11 achieved 95.6% accuracy in the testing phase. fig. 5. the convergence characteristics of the algorithm. engineering, technology & applied science research vol. 13, no. 2, 2023, 10535-10540 10539 www.etasr.com nguyen et al.: multi-goal feature selection function in binary particle swarm optimization for power … v. results the accuracy when =0.8, n=30, and sf=19 was 97.1%. the accuracy when =0.9, n=50, and sf=24 was 96.8%. the accuracy when =1, n=20, and sf=46 was 97.1%. this shows that as the value of  in the objective function (4) increases, the importance of the classification error decreases and the accuracy of the classification increases, but with a larger number of variables. in the case of =1, the objective function (4) becomes a single objective, and only the single objective of the classification error remains. there, 46 variables were selected, with the number of selected variables decreasing by 55.7%, while in the case of =0.2, only 11 variables were selected, with the number of selected variables decreasing by 89.4%. in terms of classification accuracy, the case of 11 variables had accuracy only 1.5% lower than that of the case of 46 variables, while the number of selected variables decreased by 33.7%. a classification accuracy of 95.6% is considered acceptable for stable power system classification [15–17]. table i. results of the bpso algorithm implementation  n sf best gf cc (%)  n sf best gf cc (%) 0 10 17 0.1635 92.1 0.1 10 18 0.1624 93.4 20 15 0.1442 94.6 20 14 0.1265 94.6 30 11 0.1058 94.0 30 10 0.0925 94.3 40 14 0.1346 94.6 40 13 0.1166 95.9 50 11 0.1058 94.0 50 14 0.1256 95.6 0.2 10 18 0.1549 91.8 0.3 10 15 0.1208 93.4 20 11 0.0934 95.6 20 15 0.1152 95.3 30 14 0.1172 95.3 30 14 0.1026 94.9 40 11 0.1035 90.1 40 11 0.0901 94.6 50 13 0.1076 96.2 50 12 0.0997 93.7 0.4 10 15 0.1093 94.3 0.5 10 17 0.1133 93.4 20 16 0.1138 94.6 20 14 0.0910 95.3 30 12 0.0894 94.9 30 13 0.0925 94.0 40 12 0.0919 94.3 40 15 0.0942 95.6 50 11 0.0912 93.1 50 14 0.0862 96.2 0.6 10 15 0.0766 96.8 0.7 10 20 0.0842 96.2 20 17 0.0900 95.9 20 18 0.0784 96.2 30 12 0.0821 94.0 30 20 0.0820 96.5 40 16 0.0843 96.2 40 17 0.0733 96.5 50 16 0.0861 95.9 50 14 0.0691 95.9 0.8 10 25 0.0758 96.5 0.9 10 27 0.0572 96.5 20 26 0.0727 97.1 20 31 0.0582 96.8 30 19 0.0593 97.1 30 25 0.0496 97.1 40 24 0.0663 97.5 40 28 0.0553 96.8 50 24 0.0689 97.1 50 24 0.0515 96.8 1.0 10 47 0.0252 97.4 1.0 40 45 0.0284 97.1 20 46 0.0284 97.1 50 54 0.0252 97.4 30 50 0.0252 97.4 the results show that when applying the bpso algorithm for variable selection in the problem of classifying stable electrical systems, the single-objective function considering only the classification error, drives the algorithm to select a large number of variables. therefore, applying the multiobjective function (4) for the variable selection problem in the classification of stable electrical systems is appropriate when using the bpso algorithm. vi. conclusion the paper proposed the application of the multi-objective function for the bpso algorithm in selecting variables in the power system stability classification problem. the results from the experiment conducted on the ieee-39 bus system demonstrated the success of the variable reduction technique. reduction from 104 to 11 variables with the accuracy of up to 95.6% has significant economic implications, such as significantly reducing the cost of measuring devices to collect data. the proposed method opens up the direction of applying advanced computational techniques in selecting input parameters for the problem of classifying power system stability. acknowledgement this work belongs to the project t2022-45 funded by ho chi minh city university of technology and education, vietnam. references [1] k. teeparthi and d. m. v. kumar, "dynamic power system security analysis using a hybrid pso-apo algorithm," engineering, technology & 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[17] a. karami and s. z. esmaili, "transient stability assessment of power systems described with detailed models using neural networks," international journal of electrical power & energy systems, vol. 45, no. 1, pp. 279–292, feb. 2013, https://doi.org/10.1016/j.ijepes.2012. 08.071. microsoft word etasr_v13_n1_pp9906-9912 engineering, technology & applied science research vol. 13, no. 1, 2023, 9906-9912 9906 www.etasr.com abbaci & ould zmirli: cooley-tukey fft algorithm based on gdft for phasor estimation by pmu … cooley-tukey fft algorithm based on gdft for phasor estimation by pmu under power quality disturbances mohamed abbaci laboratory of advanced electronic systems (lsea), university of medea, algeria | ptapc ouargla, crapc, algeria abbaci.mohamed@crapc.dz (corresponding author) mohamed ould zmirli laboratory of advanced electronic systems (lsea), university of medea, algeria m_zmirli@yahoo.fr received: 30 september 2022 | revised: 13 november 2022 | accepted: 19 november 2022 abstract due to the high penetration of renewable energy sources, such as photovoltaic panels and wind turbines, in addition to the use of different electric power supplies in the power grid, there are major disturbances in the forms of electric waves. these variations and disturbances must be monitored and controlled for the efficient management of transmission and distribution of electrical energy, safety, and electrical protection systems. nowadays, phasor measurement unit (pmu) technology is an essential tool to develop the supervision, protection, and control of the electrical power grid. pmus measure the amplitude and angle of current and voltage waveforms on a coordinated universal time (utc) time scale and speedily measure the fundamental frequencies and their rates of change using fast and accurate estimation algorithms. this paper presents a phasor estimation using a modified cooley-tukey fast fourier transform algorithm based on the generalized discrete fourier transform (dft) used in pmus, using simulations in matlab. this algorithm was utilized to accelerate and simplify the computation of dfts. to validate the performance under waveform disturbances, several tests with different waveforms and disturbances were simulated and interpreted according to the standard and compared with dft. keywords-phasor measurement unit; rate of change of frequency; total vector error; dft; gdft; ctgdft i. introduction phasor measurement units (pmus) are widely used for many years in electrical systems for control and monitoring, with accurate and fast fundamental component measurements [1, 2]. the phasor estimation is the main component of a pmu [3], so dft is the most widely used algorithm [1, 4]. pmus were introduced in response to the need for more efficient and secure monitoring devices in power grids. since the developments in synchronized measurement technology, widearea measurement systems are suitable to follow the dynamic behavior of electrical power systems using pmus and pdc hierarchically [5, 6]. pmus precisely measure the amplitudes and phase angles of the waveforms of the electrical network (current, voltage, and frequency) at various points [7, 8] using time stamping. measured and calculated data are transmitted through a synchronized gps transmission medium to a pdc [9]. information from multiple pmus located throughout the electrical power system is analyzed and processed at the pdc to detect electrical disturbances [10] and improve the protection and control functions of an electric power system [6]. the ieee 1344-1995 was the first published standard for conventions relating to original synchrophasor measurements [11, 12]. in 2005, ieee c37.118-2005 was introduced and replaced the existing synchrophasor standard [1, 12]. in 2011, two new standards were published to address the measurement requirement (ieee c37.118.1-2011) and synchrophasor communications (ieee c37.118.2-2011 ) [11, 13, 14]. this study investigated the modified cooley-tukey fast fourier transform (fft) algorithm, based on a generalized discrete fourier transform (gdft) framework, for pmu phasor estimation. the conventional cooley-tukey algorithm accelerates and simplifies the dft calculation, but has disadvantages such as slow dynamics and sensitivity to frequency variations. the use of the cooley-tukey fft algorithm based on the gdft was proposed in [15] to overcome these drawbacks. simulations were carried out to highlight the performance of the suggested algorithm over standard dft techniques. engineering, technology & applied science research vol. 13, no. 1, 2023, 9906-9912 9907 www.etasr.com abbaci & ould zmirli: cooley-tukey fft algorithm based on gdft for phasor estimation by pmu … ii. phasor measurement architectures a. block diagram of pmu the functional diagrams of pmus may differ from one manufacturer to another. figure 1 shows a basic block diagram of a pmu [13]. a pmu generally consists of three main blocks: measurement, calculation, and communication [16]. fig. 1. phasor measurement unit components.  the measurement unit receives analog data inputs such as three-phase voltages, three-phases, and neutral currents from the secondary measurement transformers (vt and ct), which are later filtered to eliminate and prevent aliasing errors by antialiasing filters [13, 17].  the computation unit includes analog-to-digital converters (a/d), quadrature oscillator, and phasor processor [18, 20].  the computed synchrophasor and other information are transmitted to the pdc to be interchanged between other pmus for monitoring, control applications, and system protection using communication units [13, 16]. b. wide area measurement systems the wide area monitoring system (wams) collects realtime information on the status of the network at strategic points, with precise time stamping by gps satellites. wams improves network analysis, integrating pmus to detect any instability. the wams uses synchronized measurement data and modern communication systems to supervise, monitor, and analyze the current state of the wide-area power system and serves for the operation, control, and protection of the power system in real-time [18, 19]. wams systems mainly consist of three components [13]: phasor measurement unit, communication network, and phasor data concentrator. 1) phasor measurement unit (pmu) the pmu is a measuring device for electrical power systems, capable of performing phasor measurements of voltages and currents in large and distributed power system networks. the voltage and current waveforms of the power system are sinusoidal. a sinusoidal waveform is written as: ���� � �� � �2� � � �� (1) where xm is the amplitude, f is the frequency, φ is the angle, and t is the time. the representation of the phasor in the complex plane is: � � ��√� ��� (2) � � ��√� �� � � � �� �� � �� � ��� (3) where xr and xi are the real and the imaginary components of the complex form, and ��√� is the rms value. figure 2 shows the phasor representation of a sinusoidal input signal at the angular frequency in the complex plane [10, 17]. in the case of a phase current or voltage, the projection of the phase vector on the ordinate axis (imaginary axis) gives the value of the current or voltage at that instant. fig. 2. phasor representation of a sinusoidal signal. 2) communication network pmus are usually located in substations that are geographically distant from the pdc. communication networks are required to transmit information and measurements collected by pmus from the substations to the control center [18]. power grid monitoring and control require a high-speed communication framework that allows reliable, secure, and fast sharing of synchronized monitoring data between pmus and pdc. 3) phasor data concentrator figure 3 shows the implementation of pdcs in a wide area monitoring system. the pdc collects discrete events and phasor data from pmus, and probably other pdcs, and transmits them to other applications via a communications engineering, technology & applied science research vol. 13, no. 1, 2023, 9906-9912 9908 www.etasr.com abbaci & ould zmirli: cooley-tukey fft algorithm based on gdft for phasor estimation by pmu … protocol [10, 21]. depending on the location of the pmu, the communication link between the pmu and the pdc may be a wired connection, a serial or ethernet cable, or a wireless link. fig. 3. implementation of pdcs in wams. each pmu has two communication interfaces: one interface for communication of the pmus via ieee c37.118 and another to communicate with the digital control system. the central evaluation system collects the data, archives them, and displays them on a graphical user interface. this system can also be used to automatically monitor the electrical system and redistribute information to other pdcs or a numerical control system [10]. communication of pmus with pdcs, according to the ieee c37.118 standard, is a client-server communication in which the pdc works as a client and the pmu as a server [10, 22]. iii. performance indices of measurement evaluations a. total vector error (tve) c37.118.1-2011 defines the total vector error to calculate the phasor estimation error and to evaluate the performance of the phasor estimation. tve compares the theoretical value of an input signal with its estimated value at the same time [10]. tve is calculated by considering the error of estimating the amplitude and phase angle [13]. the tve at time n is defined as : ������ � � �!"�#�$�"�#�%&' �!(�#�$�(�#�%& �"�#�%&' �(�#�%& (4) where �!� ��� and �!� ��� are the real and the imaginary components of the estimated phasor, and �� ��� and �� ��� are the theoretical values at time ���. figure 4 shows the tve representation. fig. 4. calculation of tve. b. frequency error in addition to the synchrophasor, pmus also calculate the power system's frequency. frequency error (fe) is the difference between the estimated and the theoretical frequency. the sinusoidal signal of (1) may be written as [18]: ���� � �� � )���% (5) the frequency of the signal (5) is determined as: ��� � *�+ ,-.�/�-/ 0 (6) fe is defined as: 1� � 2 3 42 (7) c. rate of change of frequency error (rfe) rocof, measured by pmu at a given time instant, is determined by: 56761��� � -, 8&9:;�<�:< 0-/ � -=�/�-/ (8) rfe is the difference between the theoretical and the estimated rocof value at a particular time instant [11]: 51� � >,-=-/ 0 3 ,-=?-/ 0> (9) iv. pmu estimation algorithms most phasor estimation algorithms utilized in commercial pmus depend on the dft estimation technique. the ieee c37.118 standard does not recommend the use of a special algorithm or measurement in the pmu. consequently, various estimation methods and algorithms are used in pmus [12]. a. dft algorithm a sinusoidal waveform x(t) of kf0 frequency with a fourier series can be written as: ���� � @a � �2�b c�� � da ���2�b c�� (10) ���� � ef�@a� � da��g � �2�b c� � ∅� (11) engineering, technology & applied science research vol. 13, no. 1, 2023, 9906-9912 9909 www.etasr.com abbaci & ould zmirli: cooley-tukey fft algorithm based on gdft for phasor estimation by pmu … where ∅ � �@�$*�3da @a⁄ � . the phasor representation becomes: �j � *√� ef�@a� � da��g��∅ (12) and the complex form of the phasor becomes: �j � *√� �@a 3 �da � (13) by applying the relationship of the fourier series coefficients, the phasor formula is determined by: �j � *√� �k ∑ �#k$*#mc �$n&9opq (14) and also: �j � √�k ∑ �#k$*#mc e� ,�+a#k 0 3 � �� ,�+a#k 0g (15) where n is the number of samples, xn is the input signal, n is the sample number and k is the harmonic index. �� � √�k ∑ �#k$*#mc � ,�+a#k 0 (16) �� � √�k ∑ �#k$*#mc �� ,�+a#k 0 (17) the phasor xk becomes: �a � �� � ��� (18) the phasor magnitude of the phasor is given by: |�a | � s�� � � ��� � (19) and finally, the phase angle of the phasor is defined by: ∅ � �@�$* �(�" (20) b. proposed algorithm this study investigated the cooley-tukey fft algorithm, based on a generalized dft (ctgdft), for phasor estimation. gdft is described by: �a � ∑ tk�#'u��a'v�k$*#mc �# (21) where tk � � $&9(q , and a and b are two arbitrary complex numbers (a = b = 0 gives the ordinary dft) [23]. the second transform is presented by the cooley-tukey fft algorithm to accelerate and simplify the computation of dfts [24, 25]. this algorithm is based on the factorization of n, the length of the dft as a product of a number less than n. supposing that n is not a prime number, it is possible to write it as n = n1n2, where the two factors are greater than 1. the dft formula is: �j � ∑ �#k$*#mc �$n&9opq (22) this algorithm begins by dividing the range of integers from 0 to n-1 in two different ways. for time index n or frequency index k, the division is divided into n1 intervals of n2 length each. the variables n and k are expressed as: w� � �* � ��x*; 0 ≤ �* ≤ x* 3 1; 0 ≤ �� ≤ x� 3 1b � b*x� � b�; 0 ≤ b* ≤ x* 3 1; 0 ≤ b� ≤ x� 3 1 (23) the dft formula can be written in terms of n1, n2, k1, k2 as: �a8k&'a& � ∑ ∑ �#8'#&k8 �$n&9�p8^p&q8��o8q&^o&�qk&$*#&mck8$*#8mc (24) so, also: �a8k&'a& � ∑ tk8#8 a8k8$*#8mc tk#8a& ∑ �#8'#&k8k&$*#&mc tk&#&a& (25) where tk � � $n&9q , tk8 � � $n&9q8 , and tk& � � $n&9q& . the inner summation was reduced to a standard dft of n2 size. furthermore, the splitting of the first exponential into two factors unveils that the outer summation is also a standard dft of n1 size, of the product of the dft of n2 size multiplied by the twiddle factors. applying the composition n=n1n2, the cooley-tukey re-indexings n1+n2n1 and k1n2+k2 can be used in (21). then, the formula utilized in the modified cooleytukey fft algorithm based on gdft is given by: �a � tkau ∑ tk8#8a8k8$*#8mc tk#8a& ∑ �# tk&#&a&k&$*#&mc tk#v % (26) where k=k1n2+k2 and n=n1+n2n1. v. simulation results of disturbance faults a. simulation parameters the selected simulation parameters were:  nominal frequency: f0 = 50hz  number of samples: 400 samples/cycle  sample rate: 20khz the input signal is generated from a two-phase voltage (line voltage) of a secondary potential transformer (urms = 100v) with a cosinusoidal form, i.e. the phase ab. b. disturbance faults and evaluation performance to evaluate the operation reliability of the pmu, different disturbance faults should be examined with the application of the proposed algorithm. as the performance and evaluation of pmus are tested under disturbed power system conditions, 3 different disturbance faults were examined. for each case, voltage input signal, phasor magnitude, phasor angle, tve, estimated frequency, and rocof were simulated. this paper shows only the simulation results of the tve and the estimated frequency to evaluate the performance of the pmu. the frequency is estimated according to (6) and tracking is carried out by iterative dft with re-sampling, as presented in [26], with a modification in the first cycle of frequency calculation (3 phasors are calculated in the first cycle to obtain the measured frequency). the simulation results of the disturbance faults were as follows: 1) disturbance faults 1 the idea of this steady-state test was to examine the effect of the input signal magnitude variations and its phase angle around its nominal values while keeping the frequency constant. this test signal was then generated with a modified magnitude of ±20% of the nominal and a phase angle of 45°, as in [27], at t1= 0.2s and t2= 0.5s: engineering, technology & applied science research vol. 13, no. 1, 2023, 9906-9912 9910 www.etasr.com abbaci & ould zmirli: cooley-tukey fft algorithm based on gdft for phasor estimation by pmu … _��� � 80√2 � �2� � � 4⁄ � (27) in the first disturbance fault, a variation of amplitude and phase were introduced to the voltage input signal. figure 5 shows that the amplitude and phase values measured by the pmu were identical to the theoretical values, the evaluation parameters were in the norms, and tve was almost 0%. table i shows that the maximum value of the frequency error (fe) of the proposed algorithm was 0.0003hz. (a) (b) (c) fig. 5. simulation results under disturbance faults 1: (a) estimated phasor magnitude, (b) estimated phasor angle, (c) total vector error. table i. estimated frequency, frequency error, and rocof error under disturbance faults 1 method frequency (hz) fe (hz) rfe (hz/s) min max dft 50 50 0 0.00002 ctgdft 49.9997 50 0.0003 0.00034 2) disturbance faults 2 this test examined the variation of the magnitude of the voltage input signal when the input signal frequency is 45hz: _��� � 80√2 � �2� � � 6⁄ � (28) figure 6 shows the efficiency of the results obtained. table ii shows that the maximum fe was on the order of 0.0003hz. (a) (b) (c) fig. 6. simulation results under disturbance faults 2: (a) estimated phasor magnitude, (b) estimated phasor angle, (c) total vector error. table ii. estimated frequency, frequency error, and rocof error under disturbance faults 2 method frequency (hz) fe (hz) rfe (hz/s) min max dft 45 45 0 0.00002 ctgdft 44.9997 45 0.0003 0.00034 engineering, technology & applied science research vol. 13, no. 1, 2023, 9906-9912 9911 www.etasr.com abbaci & ould zmirli: cooley-tukey fft algorithm based on gdft for phasor estimation by pmu … 3) disturbance faults 3 standard harmonic distortion tests require signals with 10% harmonics ranging from the second to the 50th harmonic. in this last test, only test signals containing 10% of the third and fifth harmonic components were generated, and a random noise was introduced into the voltage input signal with a slight variation in amplitude (-5%) and angle (+2°) at the t= 0.2s: _��� � 95√2 � �2� � � 5.625⁄ ��10√2 � �6� � � 3⁄ ��10√2 � �10� � 5 � 6⁄ � � ���� (29) where e(t) is the random noise. when the voltage input signal is superposed on a set of the third and fifth harmonic components and random noise with amplitude and phase variations, tve was less than 0.15%, as shown in figure 7. (a) (b) (c) fig. 7. simulation results under disturbance faults 3: (a) estimated phasor magnitude, (b) estimated phasor angle, (c) total vector error. table iii shows that the maximum fe of the proposed method was again in the order of 0.0003hz. table iii. estimated frequency, frequency error, and rocof error under disturbance faults 3 method frequency (hz) fe (hz) rfe (hz/s) min max dft 49.9995 50 0.0005 0.00047 ctgdft 49.9997 50 0.0003 0.00026 the ieee c37.118.1-2011 standard specifies a tve limit of 1%, an fe limit of 0.005hz, and a limit of 0.01hz/s for the rocof error (rfe). the obtained tve and fe limits were 0.15% and 0.0003hz, respectively. vi. conclusion this study investigated the performance of the proposed cooley-tukey fft algorithm based on gdft for phasor estimation under conditions of power system disturbance. the performance of a pmu was examined and simulated by applying a voltage signal in different case studies. the performance and the evaluation of the results were analyzed according to the pmu standard (ieee c37.118.1-2011) by calculating performance indices like tve, frequency error (fe), and rocof error (rfe). the performance of the proposed algorithm was tested under static and dynamic power system conditions, which is important for protection relay applications. the results obtained by the proposed method showed that the measurement evaluation parameters and pmu performance under power system disturbance conditions, such as integer harmonics component, frequency variation, input signal variation (amplitude and phase), and noise conditions, were in the limits according to the pmu standard (ieee c37.118.1-2011). it should also be noted that the results of the pmu tests were very encouraging. future work could investigate the implementation of the proposed algorithm in an embedded system as part of a pmu architecture. references [1] r. b. sharma and g. m. dhole, "wide area measurement technology in power systems," procedia technology, vol. 25, pp. 718–725, jan. 2016, https://doi.org/10.1016/j.protcy.2016.08.165. [2] s. priyadarshini and c. k. panigrahi, "optimal allocation of synchrophasor units in the distribution network considering maximum redundancy," engineering, technology & applied science research, vol. 10, no. 6, pp. 6494–6499, dec. 2020, https://doi.org/ 10.48084/etasr.3862. [3] p. nanda, c. k. panigrahi, and a. dasgupta, "phasor estimation and modelling techniques of pmua review," energy procedia, vol. 109, pp. 64–77, mar. 2017, https://doi.org/10.1016/j.egypro.2017.03.052. [4] p. r. bedse and n. n. jangle, "review on pmu using recursive dft algorithm," in 2018 international conference on computing, power and communication technologies (gucon), sep. 2018, pp. 375–377, https://doi.org/10.1109/gucon.2018.8675049. [5] m. kiruthika and s. bindu, "classification of electrical power system conditions with convolutional neural networks," engineering, technology & applied science research, vol. 10, no. 3, pp. 5759–5768, jun. 2020, https://doi.org/10.48084/etasr.3512. [6] a. g. phadke, p. wall, l. ding, and v. terzija, "improving the performance of power system protection using wide area monitoring systems," journal of modern power systems and clean energy, vol. 4, no. 3, pp. 319–331, jul. 2016, https://doi.org/10.1007/s40565-016-0211x. engineering, technology & applied science research vol. 13, no. 1, 2023, 9906-9912 9912 www.etasr.com abbaci & ould zmirli: cooley-tukey fft algorithm based on gdft for phasor estimation by pmu … [7] t. b. costa, r. o. berriel, a. c. s. lima, and r. f. s. dias, "evaluation of a phase-locked loop phasor measurement algorithm on a harmonic polluted environment in applications such as pmu," journal of control, automation and electrical systems, vol. 30, no. 3, pp. 424–433, jun. 2019, https://doi.org/10.1007/s40313-019-00450-5. [8] r. manam and s. r. rayapudi, "sensitive constrained optimal pmu allocation with complete observability for state estimation solution," engineering, technology & applied science research, vol. 7, no. 6, pp. 2240–2250, dec. 2017, https://doi.org/10.48084/etasr.1542. [9] m. u. usman and m. o. faruque, "applications of synchrophasor technologies in power systems," journal of modern power systems and clean energy, vol. 7, no. 2, pp. 211–226, mar. 2019, https://doi.org/ 10.1007/s40565-018-0455-8. [10] "siprotec 5 application pmu functionality in siprotec 5 devices, edition 2," siemens ag, apn-037, 2021. [11] a. g. phadke and t. bi, "phasor measurement units, wams, and their applications in protection and control of power systems," journal of modern power systems and clean energy, vol. 6, no. 4, pp. 619–629, jul. 2018, https://doi.org/10.1007/s40565-018-0423-3. [12] r. p. m. silva, a. c. b. delbem, and d. v. coury, "genetic algorithms applied to phasor estimation and frequency tracking in pmu development," international journal of electrical power & energy systems, vol. 44, no. 1, pp. 921–929, jan. 2013, https://doi.org/ 10.1016/j.ijepes.2012.07.070. [13] s. das, "algorithms to improve performance of wide area measurement systems of electric power systems," ph.d. dissertation, university of western ontario, london, canada, 2014. [14] "ieee standard for synchrophasor data transfer for power systems," ieee std c37.118.2-2011 (revision of ieee std c37.118-2005), sep. 2011, https://doi.org/10.1109/ieeestd.2011.6111222. [15] h. liu, h. hu, h. chen, l. zhang, and y. xing, "fast and flexible selective harmonic extraction methods based on the generalized discrete fourier transform," ieee transactions on power electronics, vol. 33, no. 4, pp. 3484–3496, apr. 2018, https://doi.org/10.1109/ tpel.2017.2703138. [16] d. m. laverty, j. hastings, d. j. morrow, r. khan, k. mclaughlin, and s. sezer, "a modular phasor measurement unit design featuring open data exchange methods," in 2017 ieee power & energy society general meeting, chicago, il, usa, jul. 2017, pp. 1–5, https://doi.org/ 10.1109/pesgm.2017.8273986. [17] m. abbaci and m. o. zmirli, "performance evaluation of pmu using modified cooley-tukey algorithm based on gdft," in 2018 international conference on applied smart systems (icass), medea, algeria, aug. 2018, pp. 1–6, https://doi.org/10.1109/icass.2018. 8651967. [18] m. shahraeini, m. s. ghazizadeh, and m. h. javidi, "co-optimal placement of measurement devices and their related communication infrastructure in wide area measurement systems," ieee transactions on smart grid, vol. 3, no. 2, pp. 684–691, jun. 2012, https://doi.org/ 10.1109/tsg.2011.2178080. [19] x. zhao, d. m. laverty, a. mckernan, d. j. morrow, k. mclaughlin, and s. sezer, "gps-disciplined analog-to-digital converter for phasor measurement applications," ieee transactions on instrumentation and measurement, vol. 66, no. 9, pp. 2349–2357, sep. 2017, https://doi.org/ 10.1109/tim.2017.2700158. [20] a. l. kouzou, h. bentarzi, r. d. mohammedi, and m. laoumer, "optimal placement of phasor measurement unit in power system using meta-heuristic algorithms," electrotehnica, electronica, automatica, vol. 67, no. 2, pp. 98–113, 2019. [21] g. s. antonova, "phasor data concentrator definitions, functions and standards," presented at the hands on relay school, mar. 2018. [22] r. khan, k. mclaughlin, d. laverty, and s. sezer, "ieee c37.118-2 synchrophasor communication framework: overview, cyber vulnerabilities analysis and performance evaluation: 2nd international conference on information systems security and privacy," proceedings of the 2nd international conference on information systems security and privacy, pp. 159–170, feb. 2016, https://doi.org/10.5220/ 0005745001670178. [23] s. g. johnson, "modified cooley-tukey algorithms based on a generalized dft framework," 2008. [24] h. kim and s. lekcharoen, "a cooley-tukey modified algorithm in fast fourier transform," korean journal of mathematics, vol. 19, no. 3, pp. 243–253, 2011, https://doi.org/10.11568/kjm.2011.19.3.243. [25] f. qureshi, "optimization of rotations in ffts," ph.d. dissertation, linkoping university, 2012. [26] h. li, "frequency estimation and tracking by two-layered iterative dft with re-sampling in non-steady states of power system," eurasip journal on wireless communications and networking, vol. 2019, no. 1, art. no. 28, feb. 2019, https://doi.org/10.1186/s13638-018-1320-1. [27] "report of task force on testing and certification," north american synchrophasor initiative task force (naspi tf), oct. 2013. microsoft word etasr_v12_n4_pp9018-9022 engineering, technology & applied science research vol. 12, no. 4, 2022, 9018-9022 9018 www.etasr.com alghamdi: wear and indentation resistance of polyethylene nanocomposites at high temperatures wear and indentation resistance of polyethylene nanocomposites at high temperatures a. s. alghamdi mechanical engineering department college of engineering university of ha’il saudi arabia asbg945@hotmail.com received: 14 april 2022 | revised: 19 june 2022 | accepted: 22 june 2022 abstract-the presence of nanofillers in the polyethylene matrix can play an important role in changing their behavior during mechanical testing. moreover, high ambient temperature can seriously affect the properties of polyethylene and cause softening, which leads to a decrease in stiffness, strength, hardness, and wear resistance. in the current work, carbon nanotubes (cnts) and nanoclays with 0.5wt.% are embedded into polyethylene blend matrix to enhance its mechanical properties, mainly wear and indentation resistance at different ambient temperatures. the results show that the processing method used resulted in homogenous distribution and good dispersion of nanofillers. the addition of 0.5 wt.% cnt or nanoclays increased the indentation and wear resistance at both room and high temperatures. at high temperatures, the presence of nanofillers caused an increase in wear resistance by 32.2% at maximum depth. keywords-polyethylene; wear; indentation; temperature; nanotube; mechanical properies i. introduction nanoindentation testing is an alternative method that can be used to assess the near-surface properties of polymeric materials like wear and penetration resistance [1]. this type of near-surface property testing has been widely applied for polymeric materials loaded with nanoparticles to investigate the correlation between properties and volume of fraction of nanoparticles [2-8]. however, up to date, most nanoindentation experiments are limited to evaluating near-surface properties of polymeric materials at room temperature, whereas, elevated temperatures have remarkable effects on the properties of polymeric materials within their operating environments. therefore, instrumented indentation techniques have been developed to perform testing under various environmental conditions including high temperatures and moisture to meet the commercial requirements [9-15]. polyethylene-based nanocomposites are attractive to researchers due to their wide range of applications and types [16-18]. moreover, they have ease machinability, competitive cost, and various processing methods in addition to good properties like corrosion resistance, flexibility, ductility, and impact resistance. however, it is known that temperature has severe effects on the properties of polymeric materials, which cause softening and lower their properties. this work is carried out to evaluate the effects of nanoparticle addition on the penetration and wear resistance of polyethylene at different temperatures (22.8 and 40°c). a low volume of fractions of carbon nanotubes and nanoclays (0.5wt.%) were embedded separately into the blend of polymeric materials to improve their mechanical properties, mainly wear and penetration resistance. ii. experimental methods a. materials nanoclay and cnts were added separately to blended polymers of ultra-high molecular weight polyethylene and high-density polyethylene. the ultra-high molecular weight polyethylene powder has an average molecular weight of 3×106g/mol, and was provided by sabic company, saudi arabia. the high-density polyethylene pellets were purchased from exxonmobil chemical europe, belgium. nanoclay was provided by elementis specialties, usa and multi-wall nanotubes (mwnt) with an average diameter of 25nm were purchased from nanocyl, belgium. b. processing a twin-screw extruder was used to blend 75wt.% of ultrahigh molecular weight polyethylene with 25wt.% of highdensity polyethylene. then, two types of nanoparticles were embedded separately into the polymeric matrix using similar conditions. these types are cnts and nanoclay with a constant volume fraction of 0.5wt.% to form polyethylene nanocomposites. the mini twin-screw extruder consists of five controlled zones from the feeding port to the die. the processing parameters used in this work are shown in table i. the extruder produces small pellets which are then compressed using a hot press with 190ºc to form a square mould (100×100×1.65mm). various moulding pressure and holding times were applied to find the optimal one which was 309mpa moulding pressure and 15min holding time. then, water was used to cool the mould to room temperature. corresponding author: a. s. alghamdi engineering, technology & applied science research vol. 12, no. 4, 2022, 9018-9022 9019 www.etasr.com alghamdi: wear and indentation resistance of polyethylene nanocomposites at high temperatures table i. processing method parameters extruder speed (rpm) processing temperature (ºc) zone 1 zone 2 zone 3 zone 4 die cooling 400 180 190 200 210 220 water c. material testing and characterization various characterization techniques were applied to evaluate the dispersion and distribution of nanoparticles in the matrix of polyethylene nanocomposites. they were investigated using two experimental techniques, which are scanning electron microscopy (sem), and transmission electron microscopy (tem). a nanotest machine 600 from micro materials ltd (wrexham, uk) was used to perform the wear test on the specimens using a controlled chamber at temperatures of 22.8 and 40°c. a diamond rockwell tip, with a 200μm radius, 2mn load, 10µ m/s speed, and 10 scratches was applied. the surface morphology of the polymer nanocomposite was investigated using a sharp tip (in the range of 5-10nm) of an atomic force microscope manufactured by veeco instruments inc. (cambridge, uk). then, the nanoscope software was used to analyze the data. an instrumented indentation machine with a controlled chamber micro materials ltd (wrexham, uk) was used to perform the experiments under temperatures of 22.8 and 40ºc. at least 10 indents were made using a berkovich indenter, with a face angle of 65.3º with 10mn maximum load, 600s dwell period, and 2mn/s loading and unloading rates. oliver and pharr method [19] was applied to analyze the results. in this method, the initial portion of the unloading curve is described by the power low relation: p = α (h – hr)m (1) where p is the load, α and m are constants determined by curve fitting, h is penetration depth and hr is the depth of the residual impression. the contact stiffness (s) can be obtained by: � � �� �� �ℎ � ℎ � � � ∝ �ℎ � � ℎ� � �� (2) the contact depth (hc) at maximum load (pmax) can be estimated using: ℎ� � ℎ � � � ���� � (3) where ɛ is a constant related to the geometry of the indenter, which is 0.75 for the berkovich indenter and hmax is the maximum penetration depth. thus, the projected contact area (ac) is determined from hc by the following relation: ac ≈ 24.5 hc 2 (4) and hence the indentation hardness (h) is: � � ���� �� � ���� ��. �� ! (5) the reduced modulus can be calculated from stiffness (s) using the relation: � � �� �� � " � √$ %� √& (6) where a=24.5 ℎ' � , er is the reduced modulus, and β is a correction factor that depends on the type of indenter (1.034 for berkovich indenter). consequently, the elastic modulus (es) for the specimen can be calculated using the equation: � () � ���*+� ! ,+ ���*.� ! ,. (7) where es, /0 and ei, /1 are the elastic modulus and the poisson’s ratios of the specimen and the indenter respectively, (ei = 1141gpa, /1 =0.07). a dwell period of 600s was applied at maximum load to minimize the effect of viscoelastic behavior (nose). iii. results and discussion a. nanoparticle dispersion and distribution dispersion and distribution of nanoparticles into the matrix are very important factors that significantly affect the mechanical properties of the processed polymer-based nanocomposite. figures 1 and 2 show that cnts and nanoclays were dispersed very well into the polyethylene blend. figure 3 shows the surface morphology of the three materials investigated in the current paper. figure 3(a) shows the blend without any additions, whereas figures 3(b)-(c) indicate the presence of nanoclays and cnts on the surface of the tested materials. moreover, it can be seen that the nanoparticles are distributed homogeneously on the surface of polyethylene nanocomposite, which indicates the effectiveness of the applied processing technique. (a) (b) (c) fig. 1. sem images showing the dispersion of nanoparticles into the blend matrix: (a) blend, (b) blend with 0.5wt.% clay, and (c) blend with 0.5wt.% cnt. engineering, technology & applied science research vol. 12, no. 4, 2022, 9018-9022 9020 www.etasr.com alghamdi: wear and indentation resistance of polyethylene nanocomposites at high temperatures (a) (b) fig. 2. tem images showing the presence of nanoparticles in the blend: (a) blend with 0.5wt.% clay and (b) blend with 0.5wt.% cnt. (a) (b) (c) fig. 3. afm images showing the surface morphology of: (a) blend, (b) blend with 0.5wt.% clay, and (c) blend with 0.5wt.% cnt. (a) (b) fig. 4. indentation behavior of polyethylene nanocomposites at different ambient temperatures: (a) 22.8°c, (b) 40°c. b. nanoindentation behavior figure 4 shows the indentation behavior of the blend and its nanocomposites. it is clear that the addition of 0.5wt.% nanoclays enhanced the indentation resistance of the blend at both room and high temperatures. more enhancement in indentation resistance is achieved by the embedding of cnt into the blend's matrix at similar conditions. this can be attributed to the difference in geometry between cnt (onedimensional shape) and clay (two-dimensional shape). engineering, technology & applied science research vol. 12, no. 4, 2022, 9018-9022 9021 www.etasr.com alghamdi: wear and indentation resistance of polyethylene nanocomposites at high temperatures moreover, the interaction between nanoparticles and the matrix is another important factor that depends on the bond strength between the two materials and the interface thickness and properties. c. wear resistance the incorporation of nanofillers into polymeric matrix can significantly affect the tribological performance of polymer nanocomposites [20]. this is achieved by improving the load bearing capacity and reducing the crack initiation in the surface. however, it is known that nanofiller geometry has a great influence on the mechanical behavior and the mobility of polymer chains. therefore, investigating the effect of two types of nanofillers with different geometry on the wear resistance of polyethylene nanocomposites at different ambient temperatures is a novel work. it can be seen in figure 5 that the addition of cnt and nanoclays has significant influence on the wear resistance of polyethylene-based nanocomposites. (a) (b) fig. 5. wear resistance of polyethylene nanocomposites at different ambient temperatures: (a) 22.8°c, (b) 40°c. the addition of a low volume fraction of nanofillers resulted in a 25% increase in wear resistance and maximum depth at room temperature. at high temperatures, the presence of these nanofillers caused an increase in wear resistance by 32.2% at maximum depth. these results indicate that nanocomposites have higher wear resistance at different ambient temperatures. this can be attributed to the presence of nanofillers, which disrupted the movement of polymeric chains. moreover, the application of high temperature on the blended material caused a reduction in wear resistance by 15%. on the other hand, only a 5% reduction in wear resistance is observed for nanocomposites at high temperatures. this indicated that the use of polymer-based nanocomposites increases wear resistance of blends at various ambient temperatures. iv. conclusions in this study, homogeneous distribution and good dispersion of nanofillers were achieved using an in-house processing method. the addition of a low volume fraction of nanofillers caused an increase in indentation resistance of polymer-based nanocomposites at various ambient temperatures. moreover, the presence of cnts and nanoclays in the polymeric materials resulted in a significant improvement in wear resistance at both room and high temperatures, due to the chain movement mechanisms of the nanofillers, which work as obstacles for chain movements during the application of the load. references [1] j. david, r. hayes, j. hui, and r. nay, "nanoindentation as an alternative to mechanical abrasion for assessing wear of polymeric automotive coatings," journal of coatings technology and research, vol. 13, no. 4, pp. 677–690, jul. 2016, https://doi.org/10.1007/s11998016-9782-8. 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[20] j. x. chan et al., "effect of nanofillers on tribological properties of polymer nanocomposites: a review on recent development," polymers, vol. 13, no. 17, jan. 2021, art. no. 2867, https://doi.org/ 10.3390/polym13172867. microsoft word etasr_v13_n1_pp9941-9946 engineering, technology & applied science research vol. 13, no. 1, 2023, 9941-9946 9941 www.etasr.com ranjan & singh: ann and grnn-based coupled model for flood inundation mapping of the punpun … ann and grnn-based coupled model for flood inundation mapping of the punpun river basin shashi ranjan department of civil engineering, national institute of technology patna, india shashi.ce18@nitp.ac.in (corresponding author) vivekanand singh department of civil engineering, national institute of technology patna, india vsingh@nitp.ac.in received: 13 november 2022 | revised: 22 november 2022 | accepted: 25 november 2022 abstract the punpun river is primarily a rain-fed river. forecasting rainfall accurately would enable an early evaluation of drought and flooding conditions. therefore, having a flawless model for predicting rainfall is important for the hydrological analysis of any river basin. in this study, artificial neural network (ann)based models were developed to predict rainfall and discharge in the basin. during the rainy season, water is spread in and around the area of the watershed, thus a general regression neural network (grnn)based model was proposed for fast estimation of the inundation area during the flood taking as input crosssection, rainfall, and discharge. the proposed ann-grnn coupled model is the first of its kind for this study area. the assessment of the results shows that the proposed grnn-based model is capable of estimating the water-spreading area. keywords-ann; grnn; rainfall; flood plain; punpun river basin i. introduction rainfall is recognized as one of the most significant elements of the hydrological process [1]. if there is no evaporation, runoff, or infiltration, rainfall is the amount of water that falls on a flat surface over a specific period and is measured in millimeters (mm) above the horizontal surface. forecasting rainfall accurately enables the early evaluation of drought and flooding conditions. therefore, it is important to have a flawless rainfall prediction model. in a country like india, where most farmers rely on monsoons, good quality and quantity of water are very necessary for their crops. so, it is necessary to have advanced knowledge of the real amount of rainfall [2-5]. as several states in india are experiencing drought at the same time that many other states experience flooding, it is necessary to use an accurate and effective rainfall forecast model. this rainfall forecasting model could improve the handling of flood and drought problems. the ability of this model to anticipate rainfall in advance also provides sufficient time to plan transportation, lifesaving measures, and food and medication supply [6]. time-series data are provided by scientific research, meteorological stations, gps, sensor networks, etc. time-series data have high dimensions and large volumes, and are continuously updated. data analysis research is interested in the use of time series data for forecasting, pattern recognition, anomaly detection, pattern identification, clustering, classification, and segmentation [7]. artificial neural networks (anns) are a well-established method for simulating complicated nonlinear and dynamic systems. anns are useful in creating an appropriate model, especially when the physical process relationship is unclear or the nature of the event exhibits chaotic qualities. although prior knowledge of the system is necessary, anns lessen their reliance on this knowledge. as a result, there is no longer a requirement for a precise specification of the relationship's actual functional form, which the model aims to depict. several studies utilized a variety of strategies to analyze time-series data, and among them, generalized regression, pearson coefficient, fuzzy inference system, focused time daley neural network, and other neural networks (nns) were found to perform sufficiently. time series data have been analyzed in a variety of ways [8-10]. this study aimed to develop a rainfall prediction model for the punpun river basin using ann and grnn-based models for fast estimation of the inundation area, taking as input crosssection, rainfall, and discharge. the three-layer feed forward network (ffn) structure was used to construct the models and engineering, technology & applied science research vol. 13, no. 1, 2023, 9941-9946 9942 www.etasr.com ranjan & singh: ann and grnn-based coupled model for flood inundation mapping of the punpun … they were trained using back-propagation. the daily meteorological data of the punpun river basin were considered for the development of the daily rainfall prediction models. the performance of the models was evaluated using various statistical indices. ii. study area figure 1 shows a map of the punpun river basin, which originates in the highlands of the palamu district of the indian state of jharkhand at an elevation of 300 meters, 24°11' north and 84°9' east. punpun merges with the river ganga at fatuha, 25km downstream of patna. it has no flow during dry months, but it has a significant discharge during monsoons which causes floods and submerges the nearby area. the water management of the basin is affected by both high discharge and no flow. from august to october, there is a lot of rain and the humidity of the region is moderate. the average annual rainfall ranges from 99 to 134cm, the highest at the upper levels (palamu district). 80–87% of the yearly rainfall in the punpun basin falls during the monsoon. the lower portion of the basin experiences uniform precipitations that do not change frequently. the punpun river basin research area is 7,055km 2 . the region's geology is diverse, ranging from recent alluvium in the plains to granite, gneiss, and charnokites in the highlands. fig. 1. the study area of the punpun river basin. iii. methodology a. data collection the daily observed rainfall data for 39 years (1 jan 1982 to 31 december 2020) were collected from nasa’s agro climatic data (nasa power data access service (http://power.larc.nasa.gov/data-access-viewer/) for the punpun river basin in india. meteorological parameters, i.e., daily precipitation, relative humidity, wind speed, and maximum and minimum temperature, were used as input for the models to forecast daily rainfall. these data involved daily values of rainfall, temperature (min, max), relative humidity, wind speed, and solar radiation and were subjected to preanalysis and formulation of the database. 70% of the data were used for model calibration and the remaining 30% was used for validation. b. rainfall prediction modeling using ann this study used ann models to predict daily rainfall in the punpun river basin, india. the combination of meteorological parameters as input for training anns was found as the most satisfactory for forecasting [11]. therefore, the observed daily time series of temperature (tmax, tmin), relative humidity (rh), wind speed (w), and solar radiation (sr) were considered. as the rainfall process is dynamic, current-day rainfall (pij) is considered to be a function of temperature, relative humidity, wind speed, and solar radiation. the functional form of rainfall modeling can be expressed as follows: ��� � ���� , ��� , ��, �, �� � (1) anns have been widely used to model basin hydrology and develop a non-linear relationship between the variables. anns have no fixed method for determining the pairs of input and output data. to fill this void, the number of data pairs used for training should be equal to or greater than the number of parameters (weights) in the network. this study used 14244 input-output datasets, separated into training from january 1982 to december 2014 and prediction/validation from jan2015 to dec 2020. rainfall prediction was modeled using the ann tool in matlab. figure 2 shows the approach to predicting daily rainfall using an ann with lm training methods. one hidden layer was employed to mimic the rainfall in addition to the input and output layers. the model architecture used a feedforward neural network and backpropagation and was made up of several neurons dispersed across and related to each other. at first, the network was trained on a set of paired data to manage the input-output meaning. then the weights of the connections between neurons were fixed, and the network was used to determine the classification of new data. fig. 2. method for the prediction of daily rainfall in punpun river basin. engineering, technology & applied science research vol. 13, no. 1, 2023, 9941-9946 9943 www.etasr.com ranjan & singh: ann and grnn-based coupled model for flood inundation mapping of the punpun … this study used the most suitable algorithm based on the model evaluation criteria for forecasting, the feed-forward method with back-propagation [12]. the input data for the system were the daily meteorological data of the punpun river basin. the training process used 70% of the time-series data, while each of the testing and validation processes used 15%. the purpose of the training was to identify the connections, weights, and biases that allow the neural network to estimate outputs that are reasonably similar to the measured outputs. the training datasets were also used to reduce errors. by changing the weights and biases in the ann, different training methods can be used to train the input parameters to produce an output with a smaller global error [13]. the levenbergmarquardt (lm) [14] training algorithm was used in the training process of the developed anns. table i shows the training parameters. table i. details of training parameters parameters used for training ann network type feed forward neural network with backpropagation training function levenberg marquardt (lm) adoption learning function learn gdm performance function mean square error (mse); regression (r) transfer function hidden layer-tansigmoid; output layerlinear no. of neurons used in the hidden layer 5-45 c. levenberg-marquardt (lm) training algorithm the lm training algorithm is a standard and widely applied iterative method that, in most cases, deals with curve-fitting arrangements and trains anns much more quickly than the typical back-propagation algorithm. the lm method finds the base of a multivariable function and expresses it as the sum of squares of nonlinear genuine valued functions. this approach combines the advantages of two strategies by switching the parameter updates between the gauss-newton and the gradient descent update. the lm algorithm alters the conventional newton algorithm to determine the best answer to a minimization issue, as: � �� � � � ��� � � ������� (2) where x is the weight of nns, j is the jacobian matrix, e is the residual error vector, and μ represents the scaler that controls the learning process. as the lm algorithm is computationally and memory intensive, it is best suited for small networks. d. general regression neural network (grnn) the general regression neural network (grnn) model was used to estimate the river water spread by using rainfall and discharge as estimated by the ann model and river-cross section. grnn is a neural network-based function predicting algorithm, more desirable than other neural network models as it doesn't require any data for the iterative training process [15, 16]. grnn is based on nonlinear regression and can utilize the training data to approximate any arbitrary continuous nonlinear function. for grnn, a weighted average of the training dataset's outputs is used to calculate the new output. the euclidean distance between a given pattern and the training dataset is used to estimate the weight of that pattern. a smaller distance results in a higher weight for the pattern while a larger distance results in a lower. a grnn model has four fundamental layers: input, pattern, summation, and output [17]. figure 3 shows the grnn network model. the input layer contains all input data from the simulation. the pattern layer determines the relevant weight and computes the euclidean distance. the inputs' euclidean distances are used as the basis for determining how much weight to give to each pattern. equation 3 calculates the new output based on the new input and training datasets. ! ��� � ∑ $% & '( )%**+*, ∑ & '( )%**+*, (3) where di is the euclidean distance or spread between the new (x) and the training input (xi), the higher the value of, the less likely it is that the output will be close to the inputs' extreme values and vice versa. when the distance di value is small, the weight term returns a relatively large value and vice versa. if di is zero, the weight term gives a result of 1, meaning that the output of the test data will be the same as the output of the training sample. fig. 3. the basic network diagram of a grnn model. the spread value σ is the only parameter that needs to be estimated for the grnn model. the training process involves determining the ideal value of σ. the best method to determine the spread value is to use an optimization algorithm to reduce mean squared error (mse). the entire dataset is split into two parts, training and testing, to obtain the ideal value of the spread. the best value of the spread is then obtained by minimizing mse after grnn is applied to the test data based on the training data. as stated previously, the model is created to estimate the extent of water spreading, particularly during the monsoon. a possible representation of an input pattern (k) is as follows: �� ./-0 , /-0��, /-0�1, �-0 , �-0��, �-0�1, �-0 , �-0��, �-0�12 (4) where q represents the discharge, p is precipitation, and s is the river cross-section. the corresponding output pattern is given by: !� .��-0��2 (5) engineering, technology & applied science research vol. 13, no. 1, 2023, 9941-9946 9944 www.etasr.com ranjan & singh: ann and grnn-based coupled model for flood inundation mapping of the punpun … figure 4 shows the grnn model applied in this study. any arbitrary pattern k for the punpun river basin, where recorded water level data is available, is represented by the input pattern �-� . the pattern layers calculate the weight �3 � � of each individual pattern as well as the distance �4 � � between the input and training patterns. there are n different training pattern options. n neurons will therefore be present in the pattern layer. the weight of the calculated pattern is multiplied by the corresponding output in the summation layer, the result is summed at the numerator neuron, and all the weights are added up at the denominator neuron. the output neuron uses (3) to calculate the output for the arbitrary vector. the spread value σ, which is the only parameter in the model, can be calculated using an optimization algorithm. the model can now be used to estimate the extent of water spreading after it has been trained or after the optimal spread value has been determined. this model was constructed for the i th crosssection of the watershed along the punpun river line. thus, the model was named grnni. fig. 4. grnn architecture of the model. e. model performance evaluation the prediction performance of each model was determined by the statistical and hydrological indices and quantitative comparison between the observed and predicted values. 1) statistical indices a) mean square error (mse) mse is used to compare differences between observed and predicted values. mse is zero for a perfect fit, and increased values indicate a higher deviation between predicted and observed values. mse is determined using: 5�6 � � ∑ 7�89:&�;&< � �=�&<�>0&< ?1 � (6) b) correlation coefficient the correlation coefficient (r) is an indicator of the degree of closeness between the observed and predicted values and provides the level of explained variance between them [18]. the correlation coefficient is given by: @ � ∑ 7abcdefge)�abcdefge)?7ahfe)%ije)�akfe)%ije)?l%m7abcdefge)�ahfe)%ije)?*m7ahfe)%ije)�akfe)%ije)?* (7) 2) nash-sutcliffe efficiency (nse) hydrological indice the nse was developed by nash and sutcliffe in 1970. it is also called the coefficient of efficiency. it provides the proportions of variance of the observation for a model and is widely used in hydrology [19]. nse has a range between -∞ to 1, and a value of 1 indicates a perfect match. it is determined by: n�6 � 1 � ∑ 7abcdefge)� ahfe)%ije)?*l%pq∑ �abcdefge) �abcdefge)�*l%pq ∗ 100 (8) where �89:&�; &< , �=�&<�>0&< , and �89:&�;&< are observed, predicted, and mean rainfall values at the punpun river basin, and n is the number of observed datasets. iv. results and discussion the performance of the models was qualitatively and quantitatively evaluated by visual observation and various statistical and hydrological indices. a. ann-based models for rainfall prediction during training and testing the model was trained by varying the number of neurons in the hidden layer. each nn was identified by the number of input, hidden, and output nodes. table ii shows the performance evaluation indices for rainfall estimation during training and testing. the networks having lower mse and higher r and nse values were chosen as the best prediction models. table ii shows that the performance of model 5-15-1 was better during training and testing. the r values for the ann networks ranged from 0.76 to 0.93 and from 0.82 to 0.97 during training and testing, respectively. mse values ranged from 7.08 to 20.7 and from 3.35 to 16.7 during training and testing, respectively. table ii. performance of various ann models training testing network mse r nse network mse r nse 5-5-1 12.45 0.83 81 5-15-1 10.45 0.87 88 5-10-1 16.78 0.81 78 5-19-1 13.78 0.85 86 5-15-1 7.08 0.93 86 5-15-1 3.35 0.97 94 5-20-1 10.6 0.85 82 5-20-1 8.6 0.91 9 5-25-1 8.47 0.9 83 5-25-1 5.47 0.95 92 5-30-1 13.48 0.82 8 5-30-1 11.48 0.86 87 5-35-1 19.48 0.77 73 5-35-1 15.48 0.83 85 5-40-1 17.33 0.8 77 5-40-1 14.33 0.84 86 5-45-1 20.7 0.76 7 5-45-1 16.7 0.82 84 fig. 5. observed and predicted rainfall during training period. figure 5 shows the observed and predicted values of rainfall during the training period (1982-2014) using the 5-15-1 ann model, while figure 6 shows the same values for the testing period (2015-2020). these figures show that there is close or nearly close agreement between the observed and predicted rainfall, and the overall shape of the predicted rainfall engineering, technology & applied science research vol. 13, no. 1, 2023, 9941-9946 9945 www.etasr.com ranjan & singh: ann and grnn-based coupled model for flood inundation mapping of the punpun … curve is similar to the observed rainfall. the quantitative evaluation of the model, based on nse, shows a significant relationship between observed and predicted rainfall. the nse values for the 5-15-1 ann were 84% and 94% during training and testing, respectively. thus, the 5-15-1 ann was selected as the best for rainfall prediction. figure 7 shows the correlation between the observed and predicted rainfall for the 5-15-1 ann during training and testing. fig. 6. observed vs predicted rainfall for the 5-15-1 ann model during the testing period. fig. 7. correlation of observed and predicted rainfall for the 5-15-1 ann during training (left) and testing (right). the quantitative and qualitative performance during training and testing was found satisfactory, as these models predicted rainfall with acceptable accuracy. based on qualitative and quantitative performance evaluation, the ann models gave satisfactory results for the study area. b. grnn model for punpun river flood mapping a scattered plot was plotted for the surface water spread between the simulated and the actual data at different crosssections, and a map was created in arcgis for better visualization [20]. table iii and figure 8 show that the variation of the water spread in form of fluctuation is satisfactory and the r 2 value varied from 0.69 to 0.91. table iii. correlation of actual and predicted water spread cross section name r 2 value b/w actual and grnn predicted 1 0.696 2 0.769 3 0.672 4 0.619 5 0.711 6 0.699 7 0.912 8 0.811 9 0.678 10 0.745 (a) (b) (c) (d) fig. 8. scatterplots between actual and predicted spread water fluctuation by the grnn model of section 1, 2, 3, and 4 cross-sections, respectively. figure 9 shows a water spreading map, where there is not much water inundation in the punpun river basin. the map shows the width of the river to the water spread area of that river section. the main reason behind this is that punpun is a rainfed river. at some cross sections, mainly in the middle part of the river basin, the water is spreading away from the main streamline to the flood plain. engineering, technology & applied science research vol. 13, no. 1, 2023, 9941-9946 9946 www.etasr.com ranjan & singh: ann and grnn-based coupled model for flood inundation mapping of the punpun … fig. 9. actual spread water fluctuation along the river cross-sections. v. conclusions this study showed that feedforward backpropagation networks using the lm training algorithm produced better results compared to others. rainfall is more influenced by factors such as minimum and maximum temperature, relative humidity, wind speed, and solar radiation, so these characteristics cannot be ignored in predicting. instead of pre and post-monsoon months, mid-monsoon months provide more accurate results for predicting rainfall. the initial flooded area map was created using grnn, a popular machine-learning method with strong learning performance. the initial flood map projected by the grnn was subjected to easy-toimplement two-stage post-processing to further reduce missed and false water spread detections and increase the accuracy and reliability of flood mapping [20]. therefore, the proposed grnn model was capable of producing the water spread fluctuation over the cross-section. the limitation of the coupled model was that this study area is mainly a rainfed river system and the coupled model can be used in other river basin systems such as the himalayan river system to get more satisfactory results. references [1] s. rana, v. deoli, and s. r. chavan, "detection of abrupt change in trends of rainfall and rainy day’s pattern of uttarakhand," arabian journal of geosciences, vol. 15, no. 7, mar. 2022, art. no. 618, https://doi.org/10.1007/s12517-022-09883-w. 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[20] q. zhang, p. zhang, and x. hu, "unsupervised grnn flood mapping approach combined with uncertainty analysis using bi-temporal sentinel-2 msi imageries," international journal of digital earth, vol. 14, no. 11, pp. 1561–1581, nov. 2021, https://doi.org/10.1080/ 17538947.2021.1953160. microsoft word etasr_v12_n6_pp9771-9778 engineering, technology & applied science research vol. 12, no. 6, 2022, 9771-9778 9771 www.etasr.com jawad & albusoda: numerical modeling of a pile group subjected to seismic loading using the … numerical modeling of a pile group subjected to seismic loading using the hypoplasticity model ahmed salman jawad civil engineering department college of engineering university of baghdad baghdad, iraq a.jawad1901p@coeng.uobaghdad.edu.iq bushra s. albusoda civil engineering department college of engineering university of baghdad baghdad, iraq dr.bushra_albusoda@coeng.uobaghdad.edu.iq received: 21 september 2022 | revised: 14 october 2022 | accepted: 15 october 2022 abstract-various simple and complicated models have been utilized to simulate the stress-strain behavior of the soil. these models are used in finite element modeling (fem) for geotechnical engineering applications and analysis of dynamic soil-structure interaction problems. these models either can't adequately describe some features, such as the strain-softening of dense sand, or they require several parameters that are difficult to gather by conventional laboratory testing. furthermore, soils are not completely linearly elastic and perfectly plastic for the whole range of loads. soil behavior is quite difficult to comprehend and exhibits a variety of behaviors under various circumstances. as a result, a more realistic constitutive model is needed, one that can represent the key aspects of soil behavior using simple parameters. in this regard, the powerful hypoplasticity model is suggested in this paper. it is classified as a non-linear model in which the stress increment is stated in a tonsorial form as a function of strain increment, actual stress, and void ratio. eight material characteristics are needed for the hypoplastic model. the hypoplastic model has a unique way to keep the state variables and material parameters separated. because of this property, the model can implement the behavior of soil under a variety of stresses and densities while using the same set of material properties. keywords-constitutive modeling; hypoplasticity; pile; plaxis 3d; seismic loading i. introduction piles are an extensively utilized deep foundation type and are usually adopted in heavy building constructions on weak soils due to their large bearing capacity, low distortion, and high reliability [1-3]. the behavior of piles under seismic stress is a complicated soil–structure interaction phenomenon that can compromise the stability of pile-supported structures to risk. in seismically active places and during earthquakes, movements go from stiffer to softer near-surface layers, they tend to increase and pass to the superstructure via the piles. as a result, structural vibrations develop in the superstructure, imposing inertial pressure on the pile cap and pilings and if the inertial load is big enough, the piles experience substantial lateral displacement and bending moment and consequently piling foundations may be severely damaged. so, in seismically active locations, proper geotechnical and structural design techniques for pile foundations are essential. the earthquake usually creates an additional loading situation on the pile that needs special attention [4-6]. numerical modeling by fem of experimental efforts is comparatively advantageous, and is one of the preferred approaches widely utilized for the modeling of the behavior of piled foundations under earthquakes [7-8]. it has been noted that fem typically produces reliable findings that meet with the experiments. in [9], a comparison of the shaking table test and numerical model was performed to simulate the piled raft foundation in a dry bed of deposited sand. the system was subjected to a strong ground motion while the simulated model was linear visco-elastic. the authors showed that the experimental and numerical results match. the effect of pile soil interaction on resistance and stiffness of pile with sandy soil was investigated under centrifuge loading in [10]. the study adopted finite element analysis to simulate the models. the test results were compared with the analytical solution in terms of bearing capacity. it was reported that the interaction effect between raft and piles reduces the stiffness of the pile group. at the same time, the increment in vertical and horizontal stresses due to the presence of the raft on subsoil causes an enhanced pile response. a three dimensional finite element numerical analysis was performed using plaxis 3d to investigate the behavior of pile-caps under seismic and time history loading as settlement and load shearing between the piles and foundation in [11] and the results were verified with experimental work. the maximum amplitude of displacement was decreased by burying the pile cap deeper into the ground and increasing its thickness. furthermore, reducing the foundation's dynamic reaction was also accomplished by increasing the separation between the foundation and the relative density of the sand. 3d numerical finite element simulation with abaqus was conducted to predicate singlepile and pile-system behavior in soft, saturated kaolin clay during various earthquakes in [12]. the results were verified with the centrifuge results from [13]. the linear elastic model was utilized for the piles and the nonlinear kinematic hardening model with von misses failure criterion for the clay. the corresponding author: ahmed salman jawad engineering, technology & applied science research vol. 12, no. 6, 2022, 9771-9778 9772 www.etasr.com jawad & albusoda: numerical modeling of a pile group subjected to seismic loading using the … simulation results were in good agreement with the observed acceleration and bending moment. also, the distance between piles in a pile group had a significant influence on the amount of interaction, acceleration response, forces, and bending moments. in [14], numerical analysis was conducted to predicate the response of pile and soil-pile-stricture interaction with ground improvement (cement mixing method) using abaqus. a single pile model with superstructure was used to examine soil-pile-structure interaction behavior with head masses of 25, 100, and 160lbs. during the loma prieta earthquake, the piles had a maximum horizontal acceleration of 0.16g. the simulation results agreed well with the acceleration time history at the pile head of 160lbs mass. the hypoplasticity model was first proposed in [15] and has been in development since then. due to the complicated calculations of such a model, fem is used via commercially available fem software, e.g. plaxis, feat, and abaqus. some of these do not have hypoplasticity as a built-in model. this problem is solved by using the subroutine umat with plaxis 3d to provide the necessary tensor entries. plaxis 3d was used in this research due to the high capability of the software to deal with the elastic-plastic, non-linear, and contact problems [16]. this paper aims to use the hypoplasticity model in soil structure interaction problems. ii. experimental work the hypoplastic model needs eight material parameters (φ�, e��, e��, e��, n, hs, α, β). in order to obtain these model parameters, a series of physical-mechanical tests was performed on sand from baghdad city, which was utilized in this study. its physical properties are summarized in table i. table i. physical properties of sand sample test name soil property value specific gravity gs specific gravity 2.64 standard compaction test maximum dry unit weight max (kn/m 3 ) 16.55 minimum dry unit weight min (kn/m 3 ) 13.85 maximum void ratio, emax 0.87 minimum void ratio, emin 0.56 grain size analysis coefficient of uniformity, cu 3.33 coefficient of curvature, cc 0.83 unified soil classification system (uscs) sp iii. hypoplasticity model input parameters a. void ratio (e) the void ratio is an essential factor in the calculation of the parameter model. three parameters are associated with the void ratio. the relationships �� ≈ �� , �� ≈ �� , and ��� ���� = 1.2 [17] can be employed. b. critical angle of friction (c) the critical angle of friction can be determined for loosely dry sand (particle size greater than 0.1mm) by the conduction angle of repose while for finer soil (particle size less than 0.1mm), the critical angle of friction can be determined by classical mechanical soil tests [18]. c. stiffness parameters (n and hs) the soil stiffness in the hypoplasticity model relies on the hs and n parameters and is determined by the confined compression test on loose dry sandy soil [19]. cc (the compression curve slope) describes the slope of the curve derived from the confined compression test and displayed in the ln  vs. e plane: c� = ∆� ∆��� (1) the ko value along the normal consolidation line remains constant throughout the proportional loading, and ko is determined using jacky's formula [19]: k� = 1 − sin φ� (2) then, the value of ko is used to find the p by: lnσ = ln ' ()*+,� p. = ln ' ( )*+,� . + lnp (3) equation (4) used to get the value of n from the two values of cc shown in figure 1 [20] for two distinct values of (ps): n = ��'0122303221. ��'4341. (4) by applying (5), the hs can be calculated from the range of p1 and p2: ℎ6 = 38 ' �� �9 . 1 : (5) the compression curve is influenced by the stiffness parameters (hs and n), where the former governs the curve's overall slope and the latter its curvature [19]. fig. 1. confined compression test results are used to determine the hs and n parameters [20]. fig. 2. confined compression test on loosely dry sample. engineering, technology & applied science research vol. 12, no. 6, 2022, 9771-9778 9773 www.etasr.com jawad & albusoda: numerical modeling of a pile group subjected to seismic loading using the … three confined compression tests were conducted on loosely dry sand soil with an initial void ratio e of 0.82 and 800kpa maximal normal stress was applied to them. as part of the sample preparation procedure, the sand was poured down a zero-height funnel to create the loosest condition [20]. the results from the confined compression test performed on loosely sand sample are shown in figure 2. d. α and β parameters the α parameter is obtained from the triaxial consolidated drained (cd) test carried out on the dense sandy sample with initial void ratio e = 0.62, corresponding with relative density dr = 80.6% and different confining pressures of 50, 100, and 200kpa as shown in figures 3 and 4. from these tests, the α parameter was found to be equal 0.136 while the hypoplasticity model β can be set to 1 for natural [20]. the final values of the hypoplasticity model are summarized in table ii. fig. 3. deviatoric stress vs. axial strain of the triaxial cd test. fig. 4. volumetric strain vs. axial strain of the triaxial cd test. table ii. hypoplasticity model parameter values used in this research iv. validation problem in order to validate the program's capabilities in modeling the hypoplasticity problem, the findings from experimental, numerical (open sees, sani sand model), and plaxis 3d hypoplasticity analysis were compared. the problem involved a comparison between the results obtained from the experimental and numerical research performed by [22-24] and the results obtained from plaxis 3d. the problem includes conducting a number of centrifugal tests to assess the interaction between the soil and the structure of layered liquefiable soil deposits and the seismic site response. the total depth of the soil profile was 18m, consisting of a 3 layered soil of 2m coarse sand crust with a relative density dr = 90%, a 6m loose sand layer with dr = 40%, and a 10m dense sand layer with dr = 90% at the bottom. a. finite element modeling the geometry of the problem was modeled using finite elements under plaxis 3d. it is similar to that adopted in the experimental work as shown in figure 5. a scaled version of the recorded kobe earthquake was applied at the base of the model, which was referred to as the kobe-l motion. fig. 5. the finite element model adopted in plaxis 3d. b. soil modeling the material behavior of sand in this study was modeled by the hypoplasticity model and the parameters of its implementation were determined by [21] as shown in table iii. table iii. parameters of the hypoplasticity model parameter value c 30 ed0, ec0, ei0 0.53, 0.82, 0.94 hs (mpa) 2000 n 0.22  0.25  1 c. result comparison a comparison between the experimental test and plaxis 3d results is shown in figures 6 and 7. it can be seen that the results of maximum settlement are approximately compatible with the results of finite element analysis with slightly difference at 8m depth. the vertical settlement, however, is evolving considerably more quickly according to the model than what was actually seen during the experiment, even though they are still in good agreement. the results of excess pore water pressure show a good agreement between the experimental results and numerical analysis. finally, it can be concluded that the proposed (hypoplasticity) model and plaxis 3d software can manipulate the dynamic analysis with good accuracy and are considered an appropriate tool for studies of the soil pile interaction effects. parameter value critical friction angle c 30 minimum, maximum, and critical void ratio at zero pressure ed0, ec0, ei0 0.56, 0.87, 1.044 granular hardness hs (mpa) 4000 exponent relating to sensitivity of granular skeleton to changes of pressure n 0.419 exponent describing the transition between peak and critical stress  0.136 exponent representing the change of stiffness at current density  1 engineering, technology & applied science research vol. 12, no. 6, 2022, 9771-9778 9774 www.etasr.com jawad & albusoda: numerical modeling of a pile group subjected to seismic loading using the … (a) (b) (c) fig. 6. experimentally measured, numerically computed (open sees) settlement versus time after [23] and plaxis 3d results at depth (a) 0m, (b) 2m, and (c)=8m. (a) (b) (c) fig. 7. experimentally measured, numerically computed (open sees) excess pore water pressure versus time after [23] and plaxis 3d results at depth (a) 0m, (b) 2m, and (c) 8m. v. parametric study in this research, the behavior of the piled-raft system is analyzed using plaxis 3d under varying seismic loading. the analysis is focused on the pile response under seismic loading. three different elements are included in the model: volume element for the soil, plate element for the raft, and building and embedded beams for the piles as shown in figure 8. fig. 8. 3d finite element model. a. material properties the properties of the sandy soil are shown in table ii. the piles have been modeled as embedded circular massive beams with 0.3m diameter. b. earthquake data earthquake records data were utilized to study the effects of acceleration characteristics within soil and pile. two different real acceleration records, namely upland and kobe earthquakes were used (table iv and figure 9). table iv. information regarding the earthquake data [25] earthquake upland kobe region los angeles area, southern california, usa japan magnitude (mw) 5.7 6.9 date (utc) 1990-02-28 23:43:36 1995-01-16 20:24:52 shaking duration (s) 20 48 acceleration direction n-w n-s maximum acceleration (g) 0.24 0.82 epicenter depth (km) 10 7.9 station code clmcv kima station distance to the epicenter (km) 120.3 1.0 modified mercalli intensity (mmi) vii –very strong vii –very strong reference [25] engineering, technology & applied science research vol. 12, no. 6, 2022, 9771-9778 9775 www.etasr.com jawad & albusoda: numerical modeling of a pile group subjected to seismic loading using the … (a) (b) fig. 9. earthquake record. c. results and discussion 1) effect of pile length and pile spacing on vertical settlement the effect of pile spacing (2d, 3d, and 4d) on the response of the piled raft subject to earthquake excitation is studied in this section. figures 10-14 show the time history of the soil settlement measured in the middle of raft (a) and at the edge of raft point (b) for both earthquake motions. (a) (b) (c) fig. 10. variation of the vertical settlement with time at point (a) during the kobe earthquake at s/d = (a) 2, (b) 3, (c) 4. (a) (b) (c) fig. 11. variation of the vertical settlement with time at point (b) during the kobe earthquake at s/d = (a) 2, (b) 3, (c) 4. (a) (b) (c) fig. 12. variation of the vertical settlement with time at point (a) during the upland earthquake at s/d = (a) 2, (b) 3, (c) 4. engineering, technology & applied science research vol. 12, no. 6, 2022, 9771-9778 9776 www.etasr.com jawad & albusoda: numerical modeling of a pile group subjected to seismic loading using the … (a) (b) (c) fig. 13. variation of the vertical settlement with time at point (b) during the upland earthquake at s/d = (a) 2, (b) 3, (c) 4. it can be concluded that increasing the spacing among piles to 3d and 4d from the basic 2d spacing increases the total settlement. this behavior could be attributed to the decrease in spacing between piles that applied additional lateral forces between soil particles by holding them together and providing confining media. this action resists the external forces thus decreasing total settlement. this force affects the piles as well as soil particles leading more friction forces at the pile surfaces as the friction is a function of normal forces and the friction coefficient, so increasing the skin friction leads to more resistance in total settlement as a result. the decrease in spacing between piles means that the piles are concentrated at the middle of the raft which resists the dishing effect occurring in the sand. this action leads to a decrease in probable total settlement as the maximum settlement occurs in the middle of the raft in the case of sand due to the dishing phenomenon. finally, it can be concluded that total settlement increases as the pile spacing increases. similar observation was noticed in [26-27]. for increasing pile length, load transfer is affected by the pile length. this factor is considered by selection of 3 different piles lengths (l/d) equal to 35, 45, and 55. based on numerical analysis, it is found that the increase of pile length decreases the total settlement of piled foundation as shown in figures 10-14. this behavior can be attributed to the increase of the pile length which absorbs more power applied from earthquakes and dissipates the applied forces since the settlement is a function of the applied load [26-32]. earthquake excitation has a major influence on the piled raft behavior. piled raft foundation placed on loose dry soil and subjected by kobe and upland earthquake motions was modeled numerically to investigate the effect of the excitation on the total settlement (figures 10-14). from these figures, it can be concluded that the total settlement of pile raft increases as the earthquake excitation increases. higher excitation leads to higher dynamic loading, which results in higher settlement, as the settlement is a function of loading. 2) effect of pile length and pile spacing on maximum pile bending moment pile foundations can be divided into two categories based on the ratio of the effective unsupported length (l) to the average pile diameter (d), where l/d > 30 denotes a long pile and l/d  20 denotes a short pile [28]. the effect of length to pile diameter l/d (35, 45, and 55) and pile spacing s/d (2, 3, and 4) on the response of piled raft subjected to two earthquake excitations is illustrated in figures 15-17. the following points can be noted: the maximum bending moment occurred at the connection between the piles and the raft and the zero moment is located near the tip of the pile. also, it can be concluded that increasing the spacing among piles to 3d and 4d 2d increases the bending moment along the pile shaft. this behavior can be explained by the fact that higher excitation leads to higher dynamic loading which results in higher bending moment. (a) (b) fig. 14. variation of max. vertical settlement with s/d at point (a) for (a) kobe and (b) upland earthquake. the effectiveness of the constitutive models employed in the modeling of the soil-pile interaction under the influence of earthquake motion is a key factor in the precise simulation of the numerical analysis in geotechnical engineering. there are limited numerical investigations of the behavior of soil-pile interaction using various constitutive models. each of these models has its own unique features and advantages, most fall short of providing an adequate description of this behavior. due to this factor, the analysis of soil-pile-structure systems subjected to seismic stress using an efficient model (the hypoplasticity model) is the goal of this study. the hypoplasticity constitutive model is implemented using the umat subroutine, which is then incorporated as a dynamic linked library (dll) in the plaxis 3d finite element program. engineering, technology & applied science research vol. 12, no. 6, 2022, 9771-9778 9777 www.etasr.com jawad & albusoda: numerical modeling of a pile group subjected to seismic loading using the … (a) (b) (c) fig. 15. variation of bending moment along pile (p11) at peak ground acceleration during the kobe earthquake at s/d = (a) 2, (b) 3, (c) 4. (a) (b) (c) fig. 16. variation of bending moment along pile (p11) at peak ground acceleration during the upland earthquake at s/d = (a) 2, (b) 3, (c) 4. this model predicts with accuracy the soil response to various soil densities, stress levels, and loading conditions. it also requires several parameters that are easy to gather by conventional laboratory testing. the model's ability in modeling soil-pile interaction was validated with results from experimental tests and also with findings from numerical results conducted using the sanisand constitutive model. a numerical model of a 10-story building supported by pile systems (soil-pile structure) was examined in order to look into the effects of various interactional parameters. to examine the impact of the excitation frequency, two seismic motions were used. additionally, the effects of various pile lengths and spacings were examined. (a) (b) fig. 17. variation of max. bending moment with s/d at pile (p11) at peak ground acceleration for (a) kobe and (b) upland earthquake. vi. conclusion the hypoplasticity constitutive model and the finite element method were used in this study to investigate the dynamic soil pile interaction. the soil parameters for this model were obtained by laboratory tests and were calibrated according to known relationships. the main conclusions from this study are:  the hypoplasticity constitutive model is quite satisfactory in representing the behavior of the response of the pile foundation under earthquake excitation.  increasing in the length of piles decreases the settlement of the piled raft system.  increasing the spacing between piles increases the settlement of the piled raft system.  increasing the length and pile spacing increases the bending moment. references [1] r. a. rajapakse, geotechnical engineering calculations and rules of thumb, 1st ed. oxford, uk: butterworth-heinemann, 2008. 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abstract differential gene expression is an analysis of gene data, in which the rna sequence data after nextgeneration sequencing are to be visualized for any quantitative changes in the levels of the experimental data set. this work aims to derive the transcript statistics on a gene transcript file with a fold change of genes on a normalized scale, in order to identify quantitative changes in gene expression of the difference between the reference genome and non-small cell lung cancer (nsclc) samples. this insight makes a clinical impact in assessing and characterizing candidate genes. the pipeline comprises tuxedo protocol and programming language r with the standard ballgown package. the resultant data set and the plot displays depict the candidate genes in their respective location which are significant in expressing their changes in nsclc samples. the samples are compared with prominent gene labels of nsclc samples. the results explain the differential expression of particular samples across samples from both genders. keywords-differential gene expression; next-generation sequencing; rna sequence; machine learning; nonsmall cell lung cancer; classification i. introduction lung cancer is the leading type of cancer worldwide. about 1.76 million deaths were caused by lung cancer during 2019. the disease is caused by lung malignancies. there are a lot of advances in lung cancer therapies, but, despite the advancement the prognosis of the disease is unfavourable [1], because after the diagnosis the survival rate is less than 15% for the next five years. the understanding of molecular characteristics leading to identifying cancer will speed up the diagnosis. cancer is one of the most challenging diseases [2]. the recent advancement of next-generation sequencing of the human gene has created opportunities to use gene expression information for decision making [3]. lung cancer can be categorised into nsclc, which are about the 85% of the cases, and as small cell lung cancer. the study of molecular signature shows that carcinogenesis is caused by oncogenic drivers. this has led the research to oncogenic driver identification rather than clinical parameter studies [4]. the most common types of nsclc are squamous cell carcinoma, large-cell carcinoma, and adenocarcinoma, with several other types occurring less frequently. all types can occur in unusual histologic variants and as mixed cell-type combinations [5]. the lack of early detection of nsclc leads to an increased mortality rate, specifically in developing countries. cancer is globally considered as a leading cause of death [6]. it was reported that 1 in 6 deaths in 2018 happened due to cancer. the lung cancer accounts for about 2.09 million cases worldwide. in india, about 70 thousand cases of lung cancer are reported every year [7]. depending on the stage of cancer, the general condition of the person, age, reaction to chemotherapy, and other considerations, such as the possible side effects of the procedure, more than one methods of treatment are used. usually, nsclc patients are categorized as patients with early, non-metastatic disease (stages i and ii, and pick type iii tumors) and patients with locally advanced thoracic cavitybound disease (e.g. large tumors). several facets of cancer science are now being reshaped by the many implementations and uses of next generation sequencing (ngs) technologies. as a result of aberrant mutagenesis and its contribution to engineering, technology & applied science research vol. 13, no. 2, 2023, 10571-10577 10572 www.etasr.com hiremath & dayananda: differential gene expression analysis of non-small cell lung cancer … carcinogenesis, these technologies have enabled researchers to explain improvements in any degree of regulation carried out in a cell [8]. usage of rna sequencing to understand and characterize the genes involved in cancer diagnostics and therapy has become a well-used tool. the reduced cost of sequencing and its advantages over microarrays have made it accessible to everyone, which is improving the time taken to detect and treat cancer patients. rna sequencing provides a view of the transcriptome of gene incomprehensive structure [9]. it is not dependent on any prior sequence knowledge and it can detect structural variations such as alternative splicing events and gene fusion, but the data storage and the analysis are more complex and it does not use any standard protocol, while it is also an expensive process. the most significant factor in nsclc is that its identification is delayed, causing nsclcs to have the lowest survival rate. researchers have concluded that faster diagnosis happens by understanding gene expression at a molecular level, as gene sequence expression plays a very significant role in nsclcs [10]. as the latest ngs sequencing provides us with a comprehensive genome structure with high throughput, identifying the candidate genes by analyzing the rna sequence data set allows focusing on those sets of genes. the candidate genes mark a subset of biomarkers [11] or signatures of this biological condition. the present study aims to analyze and map the significant mutations in the genes responsible for nsclc, something that might help biomarker identification, leading to early detection and helping adjuvant therapies in personalised medicine which increases survival rate. the dna analysis at nucleotide level is a new research area [12], and the research on the identification of biomarkers not only supports the medication treatment, but also predicts the proteins which create and activate post gene expression [13]. ii. materials and methods a. datasets this work is based on real biological samples' data, the dataset is available on the sequence read archive database maintained by the national centre for biotechnology information (ncbi). data from the project srp117020 were selected for analyzing representative samples on both genders with age bigger than 50 years. the data consisted of rna sequences with the distribution of poor to well-differentiated adenocarcinomas and squamous cell cancers which were sequenced using illumina hiseq2500 [14]. the details of the sequence run according to the accession number are shown in table i. table i. details about sequence archive run (srr) accession, with actual sequencing data from the particular sequencing experiment [15] run average spot length bases – giga basepairs size histology date published access type gender (age > 50 years) srr6013475 199 6.3gbp 3.86gb squamous cell carcinoma 2018-08-03 public male srr6013476 199 6.16gbp 3.84gb squamous cell carcinoma 2018-08-03 public male srr6013477 199 5.46gbp 3.33gb adenocarcinoma 2018-08-03 public male srr6013479 199 6.00gbp 3.65gb adenocarcinoma 2018-08-03 public male srr6013492 199 5.56gbp 3.38gb adenocarcinoma 2018-08-03 public female srr6013502 199 6.82gbp 4.20gb adenocarcinoma 2018-08-03 public female srr6013508 199 5.56gbp 3.45gb adenocarcinoma 2018-08-03 public female srr6013509 197 7.97gbp 4.86gb adenocarcinoma 2018-08-03 public female b. data analysis the analysis of the dataset was carried out by raw sequencing data in fastq format. the reference genome was obtained from the assembly resources of the ncbi. 1) quality check the quality of the rnaseq reads was validated with the fastqc software [16]. 2) read alignment and assembly of transcripts rna-seq reads were aligned to the human reference genome using a fast and sensitive alignment programme called hisat2 [17]. the visual exploration and differences in the expressions were obtained using the ballgown r package. the experiment is carried out using a standard protocol of tuxedo suite tools which is useful in the analysis of rna-seq data. the protocol is described by different processes which are more convenient in analyzing raw sequences [18] of large data. the detailed flow chart of the processes is depicted in figure 1. the hardware environment utilized to run the tuxedo protocol was a 64-bit computer run in linux environment with 8gb ram. 3) differential gene expression and pathway analysis the transcripts and expression levels obtained from stringtie were subjected to the differentially expressed genes which were performed using the ballgown package [18]. the package uses statistical methods to get the differentially expressed genes. the obtained list of all the differentially expressed genes was subjected to pathway and gene ontology analysis. this was carried out using kobas 3.0 annotation module [19]. the annotation module accepts gene sequences in fasta format or gene id as input and presently covers 5944 different species to run the annotations. 4) enrichment analysis from the pathway analysis results, only genes involved in nsclc disease pathway were taken and functional enrichment analysis was performed using kobas 3.0 enrichment module [19]. enrichment gives gene ontologies that are significant statistically. this gives an output based on the hypergeometric distribution. 5) obtaining the candidate genes engineering, technology & applied science research vol. 13, no. 2, 2023, 10571-10577 10573 www.etasr.com hiremath & dayananda: differential gene expression analysis of non-small cell lung cancer … to obtain the main candidate genes responsible for nsclc, the mutations responsible for nsclc were obtained using the clinvar database [20]. the genes involved in mutations were taken into account and their corresponding expression values obtained from the ballgown package were evaluated to shortlist the candidate genes. fig. 1. the protocol to produce tables and plots and obtain differentially expressed genes. iii. results a. data analysis the experimental data were analyzed as shown in table ii. 1) quality check analysis of the raw reads in fastqc format gave a quick impression of the dataset with various features including sequence quality, gc content, n content, and statistics. a brief overview of the obtained results is shown in table ii. 2) read alignment and assembly of transcripts read alignment of the reference genome is a very important step. when the alignment does not occur properly, transcriptome reconstruction becomes difficult, especially for genes expressed at lower levels. the alignment of the reads to the human reference genome gave sam files whose alignment rates were above 70% which were later converted to bam, which is the compressed binary version of sam, files. when the alignment files were subjected to transcriptome reconstruction using stringtie, annotation files were obtained with all the expression levels of all genes and transcripts. 3) differential expression and pathway analysis the relevant packages under ballgown were loaded, and the phenotype data were loaded in .csv format which contained sample id and gender of the sample. ballgown gives two tables with differentially expressed genes and transcripts between genders, giving 3 types of values. one, the fold change value referring to the ratio between expression levels in male and female. the values that are <1 indicate that it is expressed at a lower level and values >1 indicate that it is expressed at a higher level. second, the p-value to get the idea of spotting data if no difference existed. third, the q-value which is the adjusted p-value obtained by applying the false discovery rate. the gene abundance, measured in terms of fpkm (fragments per kilobase of the model per million reads mapped) distribution across all samples is visualised in figure 2. fig. 2. distribution of fpkm values across 8 samples. table ii. overview of the fastqc results [15] srr6013475 srr6013476 srr6013477 srr6013479 srr6013492 srr6013502 srr6013509 srr6013508 basic stats (total sequences) 3,15,05,786 3,08,90,798 2,74,86,767 3,00,87,832 2,79,04,343 3,42,10,392 4,02,79,600 2,78,67,756 per base sequence quality average score for all bases 32-40 34-40 32-40 34-40 34-40 34-40 34-40 34-39 sequence quality score (phred mean) ave 2-32 ave 2-30 ave 2-32 ave 2-30 ave 2-30 ave 2-30 ave 2-28 ave 2-28 sequence gc content 46 48 47 45 44 45 43 45 base n content 0-2 nil nil nil nil nil nil nil engineering, technology & applied science research vol. 13, no. 2, 2023, 10571-10577 10574 www.etasr.com hiremath & dayananda: differential gene expression analysis of non-small cell lung cancer … the y-axis shows the log2 transformation of fpkm and the x-axis shows the accession numbers of the data. additionally, structure and expression levels of isoforms of kras were obtained from ballgown which is shown in figures 3-4. the kras gene belongs to a set of genes known as oncogenes. when mutated, normal cells with these oncogenes have the potential to cause cancer [21]. figure 3 shows the structure and isoforms of the kras gene in sample srr6013502. the expression levels are shown in varying colors (from yellow to red). the isoform expressed in a higher level is shown in a darker shade. the x-axis indicates the genomic position of the kras gene. figure 4 describes the expressions and structure comparison of kras gene in male and female samples. the yaxis indicates the genomic position. the darker color indicates higher expression level which means the kras gene is expressed at a higher rate in females than in males. when all the differentially expressed genes were subjected to pathway analysis setting the organism as homo sapiens and the method as gene symbol id mapping, a total of 5071 genes in different pathways were involved. the results showed different sections of output for a particular gene: the pathways the gene was involved in, the diseases the genes were involved in, and the gene ontology indicating the biological functions the genes were related to. fig. 3. structure and expression level of kras gene in srr6013502. 4) enrichment analysis out of the 5702 hits from the pathway analysis, the genes specifically related to nsclc were chosen and were again subjected to pathway analysis to see the commonality between breast cancer and small-cell lung cancer. the complete pathway analysis of these genes is provided as a supplementary document. the genes involved in nsclc and their involvement in breast and small cell lung cancer are shown in table iii. fig. 4. the structure and expression of kras in male and female samples. the genes responsible for nsclc and their involvement in breast cancer and sclc are indicated in figure 5 and table iii. figure 5 indicates that 20% of the genes are involved in both nsclc and breast cancer, 22% are involved in nsclc and sclc, and 58% are involved only in nsclc. the genes given in table iii were subjected to enrichment analysis. the detailed table of the functional enrichment is computed in the functional enrichment of the genes involved in nsclc. the enrichment analysis and the corrected p-values are conducted using a hypergeometric distribution which is used for over-representation analysis of genes. the barplot representation of functional enrichment is shown in figure 6. each row represents an enriched function, and the length of the bar represents the enrichment ratio，which is calculated as input gene number/background gene number. the indicated color codes are based on the module number which has been assigned based on the enrichment ratio. the functional annotation with the same module number is grouped and indicated by the same color. fig. 5. pie chart for genes involved in different cancers. engineering, technology & applied science research vol. 13, no. 2, 2023, 10571-10577 10575 www.etasr.com hiremath & dayananda: differential gene expression analysis of non-small cell lung cancer … table iii. genes involved in nsclc and their commonality with breast cancer and sclc. the highlighted genes are the ones involved only in nsclc gene name disease1 disease2 disease3 abcc4 breast cancer nsclc ager nsclc akt1 breast cancer nsclc akt2 nsclc araf breast cancer nsclc bad nsclc bak1 nsclc sclc bax nsclc sclc braf nsclc sclc casp9 nsclc sclc ccnd1 nsclc sclc cdk4 nsclc sclc cdk6 nsclc sclc cdkn1a nsclc sclc dcbld1 nsclc sclc ddb2 nsclc sclc dlst nsclc sclc e2f3 nsclc sclc egfr breast cancer nsclc sclc eif4e2 nsclc sclc eml4 breast cancer nsclc sclc erbb2 breast cancer nsclc sclc ets2 breast cancer nsclc sclc fhit nsclc sclc foxo3 nsclc sclc kras nsclc sclc map2k1 nsclc sclc nras nsclc sclc gadd45a nsclc sclc the circular enrich network of the functional annotation is shown in figure 7. each node represents an enriched term, and the edges represent the connections between two enriched terms that have a gene-overlapped ratio more than a specific cut-off (default > 0.5). different modules in different colors represent nodes belonging to specific topologic communities in a structured network, which were defined using the infomap algorithm. the network is in a circular layout according to the gravity of the two nodes. the color of the bar in the bar plot is the same as the color in the circular network, which represents different modules and their interactions [19]. 5) obtaining the candidate genes τhe results obtained from clinvar database considered only single nucleotide polymorphisms and the corresponding expression analysis from ballgown. it is seen that the genes braf, nras, kras, egfr, and map2k1, involved in multiple mutations, are computed in the single nucleotide polymorphisms involved in nsclc, which gives a vast idea about the snps. table iii provides detailed information about the nucleotide change and the corresponding amino acid change, chromosome number and the position in the human genome (grch38). the expression values of genes involved in mutations are highlighted in table iv. table iv. genes involved in multiple snps (amino acid changes) gene fold change p-value q-value braf 0.8108669 0.5386988 0.9979959 map2k1 1.004441 0.9728909 0.9993876 kras 0.7801372 0.2109766 0.9979959 egfr 0.4406753 0.1661845 0.9979959 nras 1.0061834 0.9705951 0.9993876 fig. 6. barplot representation of functional enrichment. engineering, technology & applied science research vol. 13, no. 2, 2023, 10571-10577 10576 www.etasr.com hiremath & dayananda: differential gene expression analysis of non-small cell lung cancer … fig. 7. circular enrichment network. iv. discussion the epidermal growth factor receptor was the first oncogenic target uncovered in nsclc (egfr). 40% of asian patients have egfr mutations, compared to 11-17% of caucasian patients. almost all egfr mutations involve exons 18 to 21. around 40-50% of egfr mutations are represented by small in-frame deletions in exon 19 (del 19), whereas p.leu858arg amino acid substitutions in exon 21 account for 30-40% [22]. braf mutations are found in 2%-8% of people with nsclc. the braf exon 15 p.val600glu activating mutation is the cause of 50% of all braf mutations. additional mutations are discovered in exons 11 and 15 and are classified as either triggering (p.gly469x, p.leu597arg, or p.lys601glu) or faulty (p.gly466val, p.asp594x, p.gly596cys). as predicted by melanoma results [23], single braf inhibitors (i.e. vemurafenib or dabrafenib) elicit cell cycle arrest and death in p.val600glu-mutated-nsclc. kras-activating mutations are detected in around 30% of the cancer population and are being employed as an exclusion biomarker. in smokers, kras-mutated tumours are more prevalent and host other drug-related drivers less frequently. the precise type of kras mutation may provide information regarding the aggressiveness of a disease or its sensitivity to certain drugs [24]. for instance, the g12d mutation in nsclc has been linked to a more favourable prognosis than the g12v or g12r variants [25]. map2k1 mutations are infrequent in nsclc and are assumed to be mutually exclusive with known driver mutations. mek1 cascade activation is believed to play a major role in the resistance to selective treatment regimens, and the map2k1 k57 n mutation has been associated with resistance in preclinical animals [26]. the fold change value for map2k1 and nras is greater than 1, indicating that these two genes are much more expressed than braf, kras, and egfr. braf and kras are also expressed with values close to 1, although egfr has a relatively low expression value. pik3ca, ros1, and fgfr1 are additional prevalent genes whose mutations are associated with nsclc, with pik3ca and fgfr1 being much more expressed than ros1. the functional enrichment employed in the research focuses on a novel classification strategy for biomarker genes across 3 major illnesses, such as breast cancer, nsclc, and sclc. v. conclusion the differential gene expression of the human genome (grch38) identifies the most frequently mutated genes as candidates. mutated genes braf, nras, kras, egfr, map2k1, pik3ca, met, ros1, and fgfr1 were found to be expressed more in the selected data of lung adenoma cancer patients. the knowledge gained from genomic profiling can be utilized to 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[26] m. scheffler et al., "co-occurrence of targetable mutations in non-small cell lung cancer (nsclc) patients harboring map2k1 mutations," lung cancer, vol. 144, pp. 40–48, jun. 2020, https://doi.org/10.1016/ j.lungcan.2020.04.020. microsoft word etasr_v12_n6_pp9767-9770 engineering, technology & applied science research vol. 12, no. 6, 2022, 9766-9770 9766 www.etasr.com nguyen et al.: reliability-based design optimization of steel-concrete composite beams using genetic … reliability-based design optimization of steelconcrete composite beams using genetic algorithm and monte carlo simulation trong-ha nguyen department of civil engineering vinh university vinh, vietnam trongha@vinhuni.edu.vn xuan-hung vu department of civil engineering vinh university vinh, vietnam xuanhungkxd@vinhuni.edu.vn viet-dong le centre for practice and experiment vinh university vinh, vietnam ledongkcn@gmail.com duy-khanh nguyen department of civil engineering vinh university vinh, vietnam duykhanhkxd@vinhuni.edu.vn received: 23 september 2022 | revised: 13 october 2022 | accepted: 15 october 2022 abstract-steel-concrete composite (scc) beams have been commonly used in civil and industrial buildings. it is the main bearing structure and accounts for 30-40% of the structural cost. therefore, the optimal design with minimum weight and safety structure of the scc beams is very important. reliability is an important part of structural safety. design according to reliability has been included in standards such as iso 2394:2012, jb50153-92, and bs 5760-0:2014. this article aims to propose and apply a design optimization algorithm for the reliabilitybased design of scc beams. the reliability-based design optimization of the scc beams combines the safety conditions of ec-4, genetic algorithm, and monte carlo simulation. the numerical results show that with safety probability constraint conditions ps=98%, the cross-section of the scc beams can be reduced from ipe 400 to ipe 300. keywords-reliability; design optimization; genetic algorithm (ga); monte carlo simulation; steel-concrete composite beams i. introduction scc beams are designed according to the american institute of steel construction (aisc360-10) [1], the european committee for standardization 2004a (ec-4) [2], and the japan society of civil engineers (jsce-2009). the calculation methods for design strengths of steel–concrete composite members can be divided into the load and resistance factor design (lrfd) method and the partial factor method (pfm) [3]. reliability assessment of steel and scc beams is an open research topic. fatigue-reliability evaluation of steel bridges according to aashto was proposed in [4]. reliability assessment of scc beams considering metal corrosion effects was published in [5]. a reliability assessment of scc beams according to ec-4 using form was proposed in [6]. seismic reliability assessment of a two-story steel-concrete composite frame designed according to eurocode 8 was conducted in [7]. some recently published studies on the reliability of steel and reinforced concrete beams and design optimization can be seen in [7-17]. however, previous studies mostly focused on the structural reliability and optimization of steel and scc structures. to the best of our knowledge, no studies have been conducted yet on the reliability-based design optimization of scc beams combined with safety conditions according to european committee for standardization 2004a (ec-4), genetic algorithm (ga), and monte carlo simulations. this study proposes an optimization algorithm for reliability-based design of scc beams. the developed algorithm combines monte carlo simulation and ga. random values of the input parameters are considered in the proposed procedure and various safety conditions according to the ec-4 are investigated. finally, numerical validation has been performed with 5 case studies. ii. materials and methods a. safety conditions of steel-reinforced concrete composite beams the steel-reinforced concrete composite beams in this study were designed according to ec-4 [2]. the safe conditions of composites steel-reinforced concrete that must be satisfied are: (i) ultimate limit state and (ii) serviceability limit state. the destructive structure of composite steel-reinforced concrete beams has three cases, as shown in figure 1. the safe conditions can be rewritten as in (1): corresponding author: trong-ha nguyen engineering, technology & applied science research vol. 12, no. 6, 2022, 9766-9770 9767 www.etasr.com nguyen et al.: reliability-based design optimization of steel-concrete composite beams using genetic … (a) (b) (c) fig. 1. plastic design of steel-reinforced concrete beams: (a) when the pna lies in concrete slab, (b) when the pna lies in steel flange, (c) when the pna lies in steel web.       0 , lim . 1.0; i 3 1.0 ultimate limit state ultimate limit state serviceability l mit st 1.0 ate ed m y pl rd saf ed f m m m w w              (1) where saf m represents the safe conditions based on ec-4. b. structural reliability the probability of failure of a structure for random strength (r) and random load (q) is calculated according to [18]:      ,f r qp i r q f r f q drdq        (2) where � � represents the load probability density functions, � � the strength probability density functions, and �(�, ) is a function indicator and defined by:   0 failure condition , 1 safety condition i r q    (3) equation (3) cannot be solved in a closed form but is instead estimated using analytical or numerical techniques. determining the reliability of the structure has been covered in detail in [18], where the reliability structure has been proposed through the first-order reliability index with the assumption that r and q have independent normal distributions. 1 2 2 ln m r q r q cov cov         (4) where �� is the mean of "true" resistance and �� the nominal resistance as determined by a specification procedure. monte carlo simulation [18] has been proposed to estimate the probability of failure and avoid the limitations of the firstorder reliability index method. the general expression (1) can be rewritten as follows:           , , , r q f xy xy i x y f x f y p k x y dxdy k x y        (5) where ��(�, �) is importance sampling density. this integral can be estimated by the sum of the discrete values as follows:      1 * ,1 n i i q i f i q i i x y f y p n f y   ⌢ (6) the variance of the sampled estimated significance is given by:         2 2 1 * ,1 1 1 n i i q i f fi q i i x y f y var p p n n f y                ⌢ ⌢ (7) c. genetic algorithm ga is based on darwinian evolution theory. the aim of gas is to search for an optimized solution to a technical problem. ga basics can be found in [19-21]. the main structure of ga is a 5-step process: step 1. randomize the first generation. step 2. evaluate the fitness of each individual. step 3. compute the probability distribution. step 4. create the next generation via crossover and mutation. step 5. repeat steps 2 to 5 for the desired number of generations. d. deterministic model and stochastic model the deterministic model is a composite steel-reinforced concrete beam design problem according to ec-4. the input parameters used include geometrical properties ( �, �, ��� ), material properties ( ��� , �� ), and total active load (�) . the input parameters can be written as � = [�, �, ���, ��� , ��, �] . the deterministic model has the following form: �� ! = �(�) (8) h a h p h c x x z pna fc1 fa b eff h a h p h c x x z fc fa2 pna fa1 b eff h a h p h c x x fc fa2 pna fa1 z w h a / 2 b eff engineering, technology & applied science research vol. 12, no. 6, 2022, 9766-9770 9768 www.etasr.com nguyen et al.: reliability-based design optimization of steel-concrete composite beams using genetic … the stochastic model was built based on the deterministic model, in which some input parameters are randomized. in this study, two input vectors have been used. the first vector consists of a deterministic inputs group �" = [�, �, ���] and the second vector consists of a stochastic inputs group �#($) = [��� ($), ��($), �($)] , where  characterizes the random value. the stochastic model has the form of: �� ! = �(�", �#($)) (9) iii. reliability-based design optimization of the steel-concrete composite beams a. schematic diagram algorithm in this study, reliability-based design optimization of scc beams has been built based on the stochastic model, monte carlo simulation, and ga. the algorithm consists of the following steps: step 1. prepare the input data (geometrical properties, material properties, and total active load) step 2. design and safety testing for cross-section of scc according to ec-4 with deterministic input parameters. step 3. randomize input parameters and build the stochastic model based on the deterministic model. step 4. reliability assessment based on the stochastic model and monte carlo simulation. step 5. reliability-based design optimization of steel-concrete composite beams.  constraint conditions: the safety probability structure.  objective function: minimum weight of steel beam. step 6. reliability-based design optimization using ga. the process diagram of the reliability-based design optimization of the scc beams using ga and monte carlo simulation is shown in figure 2. from the process diagram, a program has been built on matlab. b. optimization analysis of steel-concrete composite beams in this section, we apply reliability-based design optimization of scc beams using ga and monte carlo simulation, considering the scc beam example in [22] as shown in figure 3. the deterministic and random input parameters are shown in table i. the distribution of material properties are based on [23] and the cross-section and loading are adopted from [24]. the upper and lower bounds of the cross-section of the steel beam are shown in table ii. the safety probability constraint conditions of steel-concrete composite beams are �� = 98% and the objective function of steel beams is minimum weight. optimization analysis results of the steel beams through 5 case studies are shown in table iii, which shows that with deterministic input parameters and safety conditions according to ec-4 [22], the obtained crosssection design of the steel beams is ipe 400. meanwhile, when the reliability-based design optimization was applied to the scc beams using ga and monte carlo simulations with safety probability constraint conditions �� = 98%, the obtained optimal design of the cross-section of the steel beams is ipe 300. this proves that reliability-based design optimization of the scc beams using ga and monte carlo simulation has great economic and technical advantages. fig. 2. the schematic diagram of reliability-based design optimization of scc beams. (a) (b) fig. 3. (a) cross-section of slabs and (b) stress distribution of the crosssection. table i. statistical properties of random variables for reliability assessment of scc beams properties variables nominal mean/ nominal cov distribution ref. material (n/mm 2 ) ��� 25.0 1.10 0.06 lognormal [23] �� 450 1.10 0.06 lognormal [23] loading (kn/m) �� 9.54 1.05 0.10 normal [24] � 13.69 1.05 0.10 normal [24] crosssection ipe 400 (mm) �! 180.00 1.00 0.05 normal [24] %! 13.50 1.00 0.05 normal [24] ℎ 400 1.00 0.05 normal [24] %' 8.60 1.00 0.05 normal [24] � 21.0 1.00 0.05 normal [24] * load combinations of the overall dead load (�� ) and the service load on the floor ( � )) cross-section optimization of csc beam using ga prepare input parameter (geometrical, material, loads) end yes upper and lower bounds of the optimal parameter safe condition ec-4 cross-section design of csc beam according ec-4 stochastic model reliability assessment using monte carlo simulation randomize input parameters constraint conditions: safety probability structure objective function: minimum weight start no 3.5 m 3.5 m 0 .1 m ipe 400 h a = 4 0 0 h p b eff h c = 1 0 0 x x fc fa2 pna fa1 z w h a / 2 1 3 ,5 b f =180 ipe400 engineering, technology & applied science research vol. 12, no. 6, 2022, 9766-9770 9769 www.etasr.com nguyen et al.: reliability-based design optimization of steel-concrete composite beams using genetic … table ii. upper and lower bounds of the cross-section of beam steel no. () (mm) *+ (mm) , (mm) , (mm) weight (kg/m) area (cm 2 ) ipe 300 300 150 7.1 10.7 15 42.2 ipe 330 330 160 7.5 11.5 18 49.1 ipe 360 360 170 8.0 12.7 18 57.1 ipe 400 400 180 8.6 13.5 21 66.3 ipe 450 450 190 9.4 14.6 21 77.6 ipe 500 500 200 10.2 16.0 21 90.7 ipe 550 550 210 11.1 17.2 24 106 ipe 600 600 220 12.0 19.0 24 122 table iii. optimization analysis results through 5 case studies case study minimum weight of scc beams (kg/m) cross-section of optimization results in [22] 1 17.60 ipe 300 ipe 400 2 18.01 ipe 300 ipe 400 3 17.50 ipe 300 ipe 400 4 16.90 ipe 300 ipe 400 5 17.56 ipe 300 ipe 400 iv. conclusions this study proposes an optimization algorithm for reliability-based design of steel-concrete composite beams. the developed algorithm combined monte carlo simulations and generic algorithm. random variables for input design parameters are considered in the proposed procedure. additionally, the safety conditions according to ec-4 are investigated. finally, a numerical validation has been performed with 5 case studies. the main points of the current paper are:  a reliability-based design optimization algorithm of steelconcrete composite beams was developed.  the proposed optimization procedure was successfully built on matlab platform and it can be convenient for design practices.  a numerical validation has been performed with 5 case studies. the result shows that with safety probability constraint conditions of �� = 98%, the scc beam can reduce the cross-section from ipe 400 to ipe 300. references [1] ansi/aisc 360-10: specification for structural steel buildings. chicago, il, usa: american institute of steel construction, 2010. 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[23] b. ellingwood, j. g. macgregor, t. v. galambos, and c. a. cornell, "probability based load criteria: load factors and load combinations," journal of the structural division, vol. 108, no. 5, pp. 978–997, may 1982, https://doi.org/10.1061/jsdeag.0005959. microsoft word etasr_v13_n2_pp10511-10516 engineering, technology & applied science research vol. 13, no. 2, 2023, 10511-10516 10511 www.etasr.com maloba et al.: reutilizing single-use surgical face masks to improve the mechanical properties of … reutilizing single-use surgical face masks to improve the mechanical properties of concrete: a feasibility study julius watako maloba department of sustainable materials research & technology centre (smartec), jomo kenyatta university of agriculture and technology (jkuat), kenya juliusmlb@gmail.com (corresponding author) james maina kiambigi department of construction management, jomo kenyatta university of agriculture and technology (jkuat), kenya mkiambigi@jkuat.ac.ke charles karimi kabubo department of sustainable materials research & technology centre (smartec), jomo kenyatta university of agriculture and technology (jkuat), kenya kabcha@jkuat.ac.ke received: 10 february 2023 | revised: 27 february 2023 | accepted: 4 march 2023 abstract the coronavirus outbreak (covid-19) has caused a sharp increase in the use of single-use surgical face masks (susfms) as personal protective equipment. these eventually end up in waste disposal facilities causing environmental pollution. those that end up in the water bodies fragment into microplastics that affect marine life. since the susfm materials are made from polypropylene, a thermoplastic polymer material that takes a long time to degrade, it is important to develop sustainable mitigation measures to remove them from the environment. this study investigated the feasibility of reutilizing susfms in concrete. susfms were shredded and added to c30/37 grade concrete in various percentages, 0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0%, by mass of cement content. the specimens were cured for 28 days before being tested for compressive strength, splitting tensile strength, and ultrasonic pulse velocity. the compressive strength decreased with an increase in the length and dosage content. the least decrease of 10.4% was observed at 0.5% content of 30mm length of susfm material. the results showed that concrete improved regarding splitting tensile strength, with the highest increase of 15.2% at 0.5% content of 30mm susfm. in addition, the overall quality of concrete remains at upv values of more than 4000m/s registering good quality concrete. the results underscore the use susfm material in concrete in order to improve its quality while at the same time reducing waste. keywords-covid-19; polypropylene; surgical face masks; personal protective equipment i. introduction with the outbreak of coronavirus disease (covid-19), a sharp increase in the use of single-use surgical face masks (susfms) occurred globally [1]. the daily use of susfms in africa and asia is currently over 700 million pieces and 2.2 billion pieces, respectively [2]. in june 2020, it was estimated that the susfms that were discharged into the environment every month were 129 billion pieces [1]. with the use of the model developed in [2], 6.9 billion pieces, or 0.2 million tons of susfms are generated globally per day. these eventually end up in waste facilities or water bodies and landfills. the susfms are mainly made from polypropylene, a thermoplastic polymer, which remains in the environment for a long time (over 25 years) [1]. those that end up in water bodies fragment into microplastics causing problems to marine life [3] and probably end up in the food chain. authors in [4] deduced that the effects of this environmental pollution will continue to have an impact on human life long after the covid-19 pandemic. in kenya, the government made mandatory wearing face masks in public. so, there has been a massive use of susfms engineering, technology & applied science research vol. 13, no. 2, 2023, 10511-10516 10512 www.etasr.com maloba et al.: reutilizing single-use surgical face masks to improve the mechanical properties of … leading to a massive generation of waste. despite the government putting in place systems, especially in health facilities, to ensure the safe disposal of susfms, hand gloves, and other pieces of personal protective equipment (ppe), some are finding themselves in the environment. at the household level, there is a haphazard disposal of susfms. they are disposed of along with normal household disposables, hence they end up in landfills or are dumped directly into open fields, roadsides, and walkways and are eventually washed away into water bodies. in addition, they are often flushed through toilets into the sewer lines, blocking the sewer reticulation systems and causing overflows. to mitigate this global problem, several studies have been undertaken to examine the re-utilization of susfms in the construction of infrastructure to not only reduce pollution, but also offer green solutions [5]. concrete is strong when subjected to compressive forces and weak to tensional forces. authors in [6] deduced that adding uniformly dispersed, small, and closely spaced fibers to concrete would not only control dry shrinkage cracking, but also enhance tensile strength, fatigue resistance, and ductility. studies are active in areas of reutilizing waste materials to generate green concrete [7]. authors in [8] used susfms with recycled concrete aggregates (rca) to produce a blend material that can be used as a base and/or subbase for road construction. 1% of susfm material content mixed with rca gave the best values of unconfined compressive strength and resilient modulus. authors in [9] used shredded plastic fibers from beverage bottles in concrete. the results showed that there was an increase in compressive strength by 43.4% at 1.5% fiber content. further, there was a notable increase of 82.2% in the flexural strength at a fiber content of 1.75% and improved ultrasonic pulse velocity (upv) of concrete by 44.4% at 0.25% fiber dosage. authors in [10], while evaluating permeability and plastic shrinkage of polypropylene fiber reinforced concrete, concluded that increasing the polypropylene fiber content in concrete decreases compressive strength. the highest decrease in compressive strength of 10% was recorded at 0.3% fiber content while the least decrease of 2% was recorded at 0.1% fiber content. there was a noticeable increment in the tensile strength with the highest increase of 39% at 0.1% polypropylene fiber content. it was also concluded that plastic fibers reduce shrinkage cracking by more than half. authors in [11] used green and white recycled polypropylene fibers in concrete. it was found that with 1% green polypropylene fiber content, there was an increase of 69.7% in compression strength, 276.0% in flexural strength, and 269.4% in split tensile strength. at the same content of 1% white polypropylene fibers, an increase of 39.4% compressive strength, 162.4% flexural strength, and 254.2% split tensile strength was reported. authors in [12] used industrial waste plastic fibers in concrete. it was deduced that the highest compressive strength was registered at fiber content at 0.5% of 50mm fibers while the highest flexural strength was recorded at 1.0% fiber content of 50mm length. they concluded that the optimum dosage of 50mm waste plastic fibers was 0.75%. authors in [13] studied the influence of the length of polypropylene fibers on compression and flexural strength. it was observed that an increase in the length of polypropylene fibers increased flexural strength but decreased the compressive strength of concrete. much research has been conducted on the effect of waste plastic materials on concrete. however, there are no conclusive studies on the use of waste susfm material in new concrete. therefore, this study aims to evaluate the possibility of the use of susfm material in concrete production. the objective was to evaluate the effect of the addition of susfm material on concrete’s compressive strength, upv, and splitting tensile strength. the results can guide the concrete consumers on how to incorporate susfms in order to enhance the quality of concrete and at the same time break the landfill lifecycle of susfms. ii. materials and methods ordinary portland cement (opc) of strength class cem1/42.5n confirming to kenyan standard (ks eas 181:2001) was used in the mixes. the coarse aggregates were obtained from nzoia quarry ltd. the used coarse aggregates had granular sizes ranging from 10mm to 20mm with flakiness index of 16.5 and water absorption of 1.9%. the fine aggregates were river sand sourced from river malakisi. they had maximum size of 5mm, specific gravity of 2.7, finess modulus of 2.8, and a bulky density of 1510kg/m 3 . the particle size gradation obtained through sieve analysis showed that fine aggregate particle distribution was within the grading limits. fig. 1. a single-use surgical face mask. for commercial consumption of the recycled susfms, there must be an elaborate disinfection process to avoid crossinfection of the covid-19 virus. several methods of cleaning surgical face masks have been proposed, such as ultraviolet germicidal irradiation [14]. it was also reported that the covid19 virus can be destroyed in susfms by heating at 70 o c for 60 minutes [15]. however, with the current covid-19 restrictions, the use of recycled susfm materials in the study was not allowed, hence unused susfms were utilized. promo-kings 3ply surgical face masks (figure 1) were sourced from a local engineering, technology & applied science research vol. 13, no. 2, 2023, 10511-10516 10513 www.etasr.com maloba et al.: reutilizing single-use surgical face masks to improve the mechanical properties of … chemist in bungoma town with the properties shown in table i. the susfm fibers were produced by cutting off the nose strip and ear loops before cutting up into rectangular fibers of 5mm width and varied lengths of 20mm, 30mm, and 40mm (figure 2). sika plastiment 40 ke with a density of 1.05kg/m 3 was used as a plasticizer to achieve the desired workability in all concrete mixes where 1kg susfm fibers for every 100kg of cement dosage was adopted as per manufacturer’s specifications. ordinary drinking tap water supplied by the local water service provider was used in all mixes and specimen curing. the mix design adopted the department of environment (doe)'s concrete design to produce c30/37 concrete. the mix material proportions are shown in table ii. fig. 2. shredded single-use surgical face masks. the fine and coarse aggregates were batched in saturated dry conditions by weight. fine aggregates, coarse aggregates, and cement were weighed and mixed on a dry metallic nonabsorbent pan manually by using a spade until the mix was uniform. half of the mixing water was added and mixing continued until the mix was uniform. the remaining half of the mixing water was mixed with sika plastiment 40ke plasticizer before adding it to the concrete mixture to avoid the cement paste from reacting directly with the plasticizer. the mixing continued until a uniform mix was achieved. the shredded susfms were added slowly while mixing to allow even distribution and avoid clamping (figure 3). testing specimens from a total of 7 concrete mixes were used with cut-up susfm material in proportions of 0% as the control mix, 0.5%, 1.0%, 1.5%, 2.0%, 2.5% and, 3.0% by weight of cement in concrete for of 20mm, 30mm, and 40mm length of susfm fibers. this range is consistent with [11]. despite the increase in the scope of the study, this aggregate range enabled the determination of both optimum volume and size of the susfm fibers in concrete in agreement with [12]. using one set of aggregates (fiber) would not have yielded meaningful results for analysis. table i. properties of susfms physical properties size of susfms 172.5mm by 97.0mm width of susfm fibers 5mm length of susfm fibers 20mm, 30mm, 40mm thickness 0.35mm aspect ratio 20m – 29; 30mm – 43; 40mm – 58 density 0.166kg/m 3 weight 3.5g shape rectangular table ii. design mix proportion of concrete constituents per m3 of concrete batch no. 00 05 10 15 20 25 30 cement (kg) 404 404 404 404 404 404 404 water (kg) 210 210 210 210 210 210 210 fine aggregates (kg) 679 679 679 679 679 679 679 coarse aggregates (kg) 1107 1107 1107 1107 1107 1107 1107 susfm content (% of cement weight) % 0 0.5 1.0 1.5 2.0 2.5 3.0 susfm content (kg) 0 2.02 4.04 6.06 8.08 10.1 12.12 to prepare specimens for casting, the concrete molds were cleaned, dried, and lubricated with a thin coat of mold oil to aid in the removal of specimens. for the preparation of compressive strength and upv test specimens, 150mm cubes were adopted, while for splitting tensile strength tests, specimens were cast in 100mm diameter and 200mm height cylinders. the prepared concrete was poured into molds in 3 layers while compacting with a poker vibrator for 20s to allow the concrete to settle and fill up all the voids. the concrete in the mold was levelled with a trowel and left undisturbed for 24 hours at room temperature under shade. the specimens were then de-molded by pressure from a compressor and were then submerged in the curing tank for 28 days (figure 4). the test specimens of hardened concrete were removed from the curing tank and then were allowed to air dry before being tested. the same process was repeated for all the mixes. a. compressive strength testing compressive strength testing was conducted on a universal testing machine, basic wizard type with digital readout unit model no. 00701/a in accordance with en 12390-3:2019. the specimens were placed on the bearing surfaces of the testing machine between the platens central to the loading axle. a uniform rate of loading was applied until the tested specimen failed. the maximum load to the nearest 0.1n/mm 2 and the compressive strength were recorded. three specimens were tested for each concrete regime and the average was considered as the compressive strength of the batch with the respective susfm material dosage. b. split tensile strength testing split tensile strength testing was conducted on the same universal testing machine in accordance with en 123906:2009. the cylindrical test specimens were placed horizontally between the loading surface of the test machine and the load was gradually applied until the cylinder failed along the vertical diameter, as shown in figure 5. the split tensile strength of the concrete cylinder specimen was recorded. three specimens were tested for each concrete regime and the average was considered as the split tensile strength of the concrete batch with the susfm material. engineering, technology & applied science research vol. 13, no. 2, 2023, 10511-10516 10514 www.etasr.com maloba et al.: reutilizing single-use surgical face masks to improve the mechanical properties of … fig. 3. mixing of concrete with added susfm fibers. fig. 4. curing of concrete specimens. fig. 5. concrete split tensile strength testing. c. ultrasonic pulse velocity testing upv was conducted on the samples using matest upv testing machine model no. c372m in accordance with en 12504-4:2004 (figure 6). the ultrasonic pulse was generated by a pulse generator transmitted to the concrete surface. the time taken for the pulse to travel through the concrete and be received by the transducer on the opposite side of the concrete specimen was measured. to ensure good contact, a thin film of solid jelly was applied between the interface of the concrete specimen surface and the transducer. upv was determined to evaluate the relative quality of the concrete specimens with susfm material. three specimens were tested for each concrete regime and the average was considered as the upv of the concrete batch. fig. 6. upv testing equipment. iii. results and discussion the compressive strength results are shown in figure 7. the results indicated that the re-utilization of susfm materials in the manufacture of concrete leads to a systematic decrease in compressive strength. the compressive strength of the control specimen was 50.1n/mm 2 . the lowest decrease in compressive strength was 10.4% at 0.5% of 30mm length of susfm fibers, 11.6% at 0.5% of 20mm length, and 20.8% at 0.5% of 40mm length. the optimum dosage to yield the least negative impact on compressive strength was 0.5% content of 30mm length fibers. these results are in agreement with [10] in which it was concluded that increasing polypropylene fiber content in concrete decreases compressive strength. similarly, a decrease in compressive strength was recorded in [16] when expanded polystyrene beads were added to the concrete. the reduction in compressive strength can be attributed to the low specific gravity of susfms induced in concrete [12] and the presence of weak interfacial bonds between the binder material and susfm materials [4]. a total of 57 test cylindrical specimens were used in split tensile strength tests. the results, as represented in figure 8, have shown that at 20mm length, split tensile strength decreases progressively from 9.1% at 0.5% dosage to the highest of 24.2% at 2.0% dosage. this shows a gradual decrease in split tensile strength with an increase in susfm material content in the concrete matrix. for 30mm length, the split tensile strength increased, compared to the control specimen, by 15.2% at 0.5% dosage and 3.0% at 1.0% dosage before dropping off and starts decreasing gradually at 1.5% dosage to the lowest decrease of 27.3% at 3.0% dosage. for 40mm length, split tensile strength registered an equal value to the control specimen of 3.3n/mm 2 at 0.5% susfm material dosage before decreasing gradually from 3.0% at 1.0% dosage to the lowest of 21.2% at 3.0% dosage. engineering, technology & applied science research vol. 13, no. 2, 2023, 10511-10516 10515 www.etasr.com maloba et al.: reutilizing single-use surgical face masks to improve the mechanical properties of … fig. 7. compressive strength of concrete with different contents and lengths of susfm fibers. fig. 8. split tensile strength of concrete with different contents and lengths of susfm fibers. the specimens with susfm material of 30mm length at 0.5% and 1.0% dosage and with 40mm length at 0.5%, registered increased split tensile strength in comparison with the control specimen. these results showed that the best mix with regard to the highest split tensile strength was 0.5% dosage of 30mm length susfm fibers. the results obtained were in agreement with [10], where the split tensile strength was found to be more than the control specimen's when polypropylene fibers were added to normal concrete mix in percentages up to 0.25%. above this dosage, the split tensile strength decreased in comparison with the control specimen. this also affirms to the results obtained in [17]. the increase in split tensile strength may be a result of filling of the microcracks developed in the concrete matrix by the fibers, hence preventing their propagation. they may have caused the cracks to meander and hence demand more energy to propagate and therefore increasing the ultimate tensile load [17]. the reduced split tensile strength could be a result of insufficient binder matrix around the fibers for transfer of stresses from concrete fibers through bonding. the results of the upv test are shown in figure 9. the upv value for the control specimen was 4436m/s. for 20mm length of susfm material, upv values increased by 1.4% at 1.0% dosage, after which the values dropped off at 1.5% dosage and progressively decreased to the lowest 4011m/s at 3.0% dosage representing a 9.6% decrease. for 30mm length of susfm material, upv values increased at 0.5%, 1.0%, and 1.5% dosages by 1.2%, 2.0%, and 0.3% respectively before gradually decreasing. for 40mm length, the upv values increased by 1.7% at 0.5% dosage before starting to reduce progressively to the lowest of 4026m/s. concrete with 30mm length susfm material had higher values of upv compared to the same dosages of 20mm and 40mm lengths. the optimum dosage was 1.0% of 30mm length of susfm material. the upv values for 20mm length susfm material ranged between 4320 and 4011. for the 30mm length, the upv values ranged from 4487 to 4152 while for 40mm the values ranged from 4509 to 4026. all values were more than 4000m/s indicating that the quality of concrete is very good [9], whereas concrete that has upv values greater than 4500m/s is considered of excellent quality [18]. high upv indicates concrete with no voids and cracks as a result of fibers limiting the micro-cracks in the concrete matrix [19]. other dosages registered reduced upv values, decreasing with an increase in the susfm material content. this may be attributed to the reduced bonding of susfm materials and concrete [9]. fig. 9. upv of concrete with different contents and lengths of susfm fibers. iv. conclusion compressive strength results indicated that the re-utilization of susfm fibers in the production of concrete leads to a systematic decrease in compressive strength. among all the concrete-susfm mixes, the concrete incorporating 0.5% dosage of 30mm susfm fiber length gave the lowest reduction in compressive strength. the compressive strength of more than 40n/mm 2 can be produced with additional susfm engineering, technology & applied science research vol. 13, no. 2, 2023, 10511-10516 10516 www.etasr.com maloba et al.: reutilizing single-use surgical face masks to improve the mechanical properties of … material at a content of 0.5% by mass of cement material of 20mm or 30mm lengths. the split tensile strength of concrete with 30mm and 40mm length susfm materials at 0.5% and 30mm length at 1.0% dosage was registered higher than that of the control concrete mix, 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